Highly optically transparent polycrystalline fluorapatite ceramics with hexagonal crystal structures were fabricated via a liquid-phase synthesis of fluorapatite powder, followed by spark plasma sintering (SPS). The effect of sintering temperature, as observed using a thermopile, on the optical transmittance and microstructure of the ceramics was investigated in order to determine suitable sintering conditions. As a result, high optical transmittance was obtained in the SPS temperature range of 950–1100 °C. The highest optical transmittance was obtained for the ceramic sample sintered at 1000 °C, and its average grain size was evaluated at only 134 nm. The grain size dramatically increased with temperature, and the ceramics became translucent at SPS temperatures above 1200 °C. The mechanical and thermal properties of the ceramics were measured to evaluate the thermal shock parameter, which was found to be comparable to or slightly smaller than that of single-crystal fluorapatite. This transparent polycrystalline fluorapatite ceramic material should prove useful in a wide range of applications, for example as a biomaterial or optical/laser material, in the future. Furthermore, the knowledge obtained in this study should help to promote the application of this ceramic material.

This paper describes the synthesis of B4C/carbon nanotube (CNT) composite by hot-pressing and shows the details for the effectiveness of CNT addition, additive amount and its orientation on the thermal shock resistance. CNTs tend to array perpendicular to the hot-pressing direction, which caused anisotropic mechanical and thermal properties of B4C/CNT composite. We investigated the residual bending strength of thermally shocked B4C/CNT composites and determined the critical temperature Delta T-C that causes precipitous strength drop. In the case of B4C/15 vol% CNT composite, the residual bending strength almost unchanged at similar to 450 degrees C; Delta T-C increased by 150 degrees C or more than that of monolithic B4C. Based on the thermal stress fracture-resistance parameter R' of the composites, it was clarified that the excellent R' is mainly due to the higher thermal conductivity and lower elastic modulus. The numerical results showed that CNT addition has a pronounced effect on the thermal shock residual bending strength and thermal stress fracture-resistance of B4C/CNT composite.

The temperature dependence of the flexural strength of sintered boron carbide was studied. At temperatures above 2000 °C, B4C showed an ultrahigh flexural strength exceeding 1 GPa which was accompanied by a change in the deformation mechanism from brittle fracture to plastic deformation. Scanning transmission electron microscopy (STEM) observations revealed that the amorphization can be of microstructural origin for the observed plasticity in B4C at temperatures above 2000 °C and a strain rate of 3•10−3 s−1. The amorphization occurs inside of the severely deformed grains. Flexural tests below 2000 °C provided evidence for the formation of stacking faults or dislocations, which are ordinary defects after the flexural tests. The results at 2000 °C suggest that the magnitude of the tensile stresses imposed on the B4C grains during deformation in flexure and the total strain transferred to a ceramic during the deformation process play the dominant role in the crystalline-amorphous transformation.

Transition metal silicides constitute a promising class of inexpensive and nontoxic thermoelectric materials showing competitive properties. This article reports an efficient process to synthesize highly textured polycrystalline CrSi2 by performing slip casting under a strong magnetic field. The crystallographic texture of spark plasma sintered samples, characterized by electron backscattered and X-ray diffraction techniques, showed a fiber texture symmetry with the c-axis of hexagonal CrSi2 aligning preferentially along the magnetic field direction. The thermoelectric properties measured both parallel and perpendicular to the c-axis texture direction showed a large anisotropy. In particular, a significantly higher Seebeck coefficient was measured,.c, reaching a maximum value of 200 mu V K-1 at 650 K, inducing a power factor.c twice higher than.c with an average value of 2.2 mW m(-1) K-2. Density functional theory and transport property calculations revealed that an anisotropic two-band model can explain the higher thermoelectric property along the c-axis direction, which can be traced to Cr-Cr bonding interactions along this direction. The estimated thermoelectric figure of merit ZT. c was improved to 0.20 at 773 K. This is 50% higher than that measured for randomly oriented samples and comparable to that observed for single crystals. Such a performance boost can certainly be reiterated for other types of thermoelectric materials using the efficient magnetic slip-casting process reported in this article.

The elastic properties of a single-crystalline Ti SiC MAX phase with a nanolayered crystal structure, comprising Ti-Si and two distinct Ti-C bonding layers, that had remained unclear because of the difficulty in growing large single crystals, were studied. Rather than unavailable large single crystals, polycrystalline samples with a crystallographic texture were prepared. By analyzing the polycrystalline elastic constants on the basis of an inverse Voigt–Reuss–Hill approximation, the elastic properties of a single crystal Ti SiC with a hexagonal symmetry were determined. This revealed that the single-crystalline Young's modulus was almost isotropic despite its highly anisotropic layered structure. The shear modulus for (0001)〈112¯0〉 was higher than that for {112¯0}[0001] in contrast to the basal slip-dominated plastic deformation reflecting the layered structure. Furthermore, first-principles calculations revealed that heterogeneous interlayer elastic deformation caused by the stabilization of Ti-Si bonding is the origin of the elastic isotropy in a Ti SiC MAX phase. 3 2 3 2 3 2

The effect of Y2O3:MgO ratio on the microstructures, optical and mechanical properties of the Y2O3:MgO composites were investigated. Although the dense Y2O3:MgO composites were successfully fabricated in various Y2O3:MgO ratios using the spark-plasma-sintering (SPS) technique, the Y2O3:MgO ratio significantly influenced the microstructures and the optical/mechanical properties of the composites. Fine grain size was obtained in the composite with Y2O3:MgO = 50:50 owing to the effective pinning force caused by the homogenous two phase microstructure. The SPSed dense composites showed good transmittance in the wide wavelength range from visible to infrared (IR). The monolithic Y2O3 polycrystal, that is Y2O3:MgO = 100:0, showed the highest transmittance of 62.3 % at 600 nm and 84.3 % at 5 mu m. Although the IR transmittance is independent of the Y2O3:MgO ratio, the visible transmittance decreased with the MgO particle dispersion. Among the Y2O3:MgO composites, the higher visible transmittance was obtained in the composite with Y2O3:MgO = 50:50 than those of the other two composites with Y2O3:MgO = 30:70 and 70:30 due to its smallest grain size. In contrast to the transmittance, the hardness H-v and toughness K-IC tend to increase with increasing the MgO fraction irrespective of the grain size; both H v and K ic increased from 9.6 GPa and 1.1 MPa m(1/2) for the monolithic Y2O3 to 12.7 GPa and 2.5 MPa m(1/2) for the composite with Y2O3:MgO = 30:70, respectively. The enhanced hardness and toughness of the composite can be interpreted dominantly by the mixture rule as a function of the volume fraction of the MgO phase.

High strength transparent Y2 O3 ceramics were fabricated from commercial powders using spark plasma sintering (SPS) technique by optimizing the heating rate. The heating rate significantly influenced the microstructures and the optical/mechanical properties of the Y2 O3 ceramics. Grain growth was limited accordingly with increasing the heating rate. The ball milling process of the commercial Y2 O3 powders is likely to further enhance the sinterability during the SPS processing. The dense Y2 O3 ceramics, which were sintered by SPS with 100◦ C/min, showed good transmittance range from visible to near infrared (IR). For a high heating rate of 100◦ C/min, the in-line transmittance at a visible wavelength of 700 nm was 66%, whereas for a slow heating rate of 10◦ C/min, it reduced to 46%. The hardness Hv tends to increase with increasing the heating rate and rigorously followed the Hall–Petch relationship; that is, it is enhanced with a reduction of the grain size. The toughness KIC, on the other hand, is less sensitive to both the heating rate and the grain size, and takes a similar value. This research highlighted that the high heating rate SPS processing can fabricate fully dense fine-grained Y2 O3 ceramics with the excellent optical and mechanical properties.

In order to improve IR transparency of the Y2O3-MgO composite, the effect of powder calcination conditions was investigated. The absorption intensity of carbonate peaks sensitively changes with the powder calcination conditions, such as temperature and time, before the pulsed electric current sintering (PECS). The calcination at 1150°C for 8 h can eliminate the contamination of the carbonate groups pre-existing in the starting Y2O3 and MgO powders. The composites fabricated from the powders, which were calcinated at the optimum conditions, can attain high IR transparency with maintaining the fine and dense microstructures. This indicates that the pre-calcination of the powders is an effect method to remove the carbonate contamination without causing significant powder coarsening and agglomeration in the Y2O3-MgO composites. During the PECS processing, however, a small amount of carbon contaminations occurs additionally from the graphite die/paper and remains even in the post-annealed Y2O3-MgO composite. It can be concluded that for the Y2O3-MgO composites, although the carbonate related contaminations are succeeded to remove from the starting power mixture, the carbon contamination occurs additionally from the graphite die/paper during the PECS processing and degrades the IR transparency.

The crystal structure of Nowotny chimney-ladder phase FeGe gamma with gamma approximate to 1.52 was studied by X-ray diffractometry from 300 K to 850 K. The diffraction patterns were fitted by Rietveld refinement considering an incommensurate composite crystal structure. The refined crystal structure of FeGe gamma is described in details and compared to MnSi gamma, a thermoelectric material with gamma = 1.74. The lattice parameters a, c(Fe) and c(Ge) were found to increase with the temperature following a polynomial law, while the modulation vector component gamma remained constant up to the peritectoid decomposition into FeGe and FeGe2. Within the temperature range considered, the linear and volumetric thermal expansion parameters increased from about 3 x 10(-6) K-1 to 10 x 10(-6) K-1 and from 9.6 x 10(-6) K-1 to 31.5 x 10(-6) K-1, respectively. (C) 2020 Elsevier B.V. All rights reserved.

In order to clarify plastic deformation behavior and mechanism of fracture energy absorption of Ti3SiC2, Vickers indentation tests were conducted for Ti3SiC2 sintered bodies with various textured orientations. Textured Ti3SiC2 sintered bodies were fabricated by slip casting in a strong magnetic field and spark plasma sintering (SPS), and their orientation distribution were analyzed by SEM/EBSD. It was found that for the textured Ti3SiC2, the plastic deformation behavior around Vickers indents such as an indent shape and a grain pile-up were strongly affected by basal slip and kink deformation. Furthermore, the fracture energy absorption mechanism around the indents also depended on the texture orientations. From our results, it is concluded that the most effective factor for suppressing the crack propagation was the grain pile-up, and the second one was crack deflections.

In this study, we introduce a simple and effective method for producing a ternary solid-solution of diborides, a medium-entropy Zr1/3Hf1/3Ta1/3B2. Using commercially available diboride powders with equimolar ratio and performing spark plasma consolidation at 1927°C we demonstrate that single-phase medium-entropy ceramic can be consolidated using an hour-long procedure. The flexural strength and fracture toughness at room temperature were 318 ?14MPa and 2.9MPam1/2, respectively. ?020 The Ceramic Society of Japan.

A high-pressure spark plasma sintering (SPS) process was applied for consolidating Y2O3-MgO nanocomposites. This approach enabled to fabricate a fully dense infrared (IR) transparent nanocomposites, which possess an average grain size of similar to 70 nm and high hardness, at a relatively low sintering temperature of 1130 degrees C under a high pressure of 300 MPa. The light transmittance was improved with increasing pressure and reached to the maximum transmittance of 64.5% at a wavelength of 0.2-1.6 mu m owing to the fine-grained microstructure. The Vickers hardness exhibited 16.6 +/- 0.7 GPa for the grain size of 74 nm, which is significantly higher than that of the sub-micro grains obtained at a conventional sintering pressure of 70 MPa (11.9 +/- 0.8 GPa). The hardness rigorously followed the Hall-Petch relationship, that is, it is enhanced with a reduction of the grain size. Successful fabrication of the high-performance Y2O3-MgO nanocomposites indicates that the nanopowder processing followed by the high-pressure sintering process can be applied for fabricating fully dense fine-grained nanocomposites with excellent optical and mechanical properties.

In this study, we explore a simple and effective method for producing a quaternary solid-solution of carbides, a medium-entropy (Ti1/4Ta1/4Zr1/4Nb1/4)C. Using commercially-available carbide powders with an equimolar ratio and performing spark plasma consolidation at 1927 ​°C and 1977 ​°C, we demonstrated that the phase formation and high-temperature flexural strength can be controlled using the processing conditions. The flexural strength and fracture toughness at room temperature were reached an average of 560 ​MPa and 3.2 ​MPa ​m1/2, respectively. The high-temperature performance of these ceramics was analyzed and compared with the available data for the group IV and V transition metal carbide monoliths.

Infrared (IR) transparent Y2O3-MgO nanocomposites with a volume ratio of 50:50 were synthesized by combining colloidal and spark-plasma-sintering (SPS) techniques. In order to attain well-dispersed and homogeneous starting Y2O3-MgO nanopowder mixture, the effects of the pH value and the amount of polyetherimide (PEI) dispersant on the suspension stability were studied. Rheological measurement reveals that highly-dispersed and stable suspension was obtained at 7 wt% of PEI dispersant under pH = 10.6. The obtained nanopowders with particle size of 20-30 nm were densified using SPS at several sintering temperatures. The sintered composites show fine grains, narrow grain size distribution and uniform microstructure. The nanocomposite sintered at 1250 degrees C showed the maximum IR transmittance of 84% at a wavelength range of 2.5-6 mu m. The Vickers hardness of the nanocomposite was about 11.9 +/- 0.3 GPa, which is significantly higher than those of single phase MgO or Y2O3. Successful fabrication of the high-performance Y2O3-MgO nanocomposite indicates that i) the colloidal technique is an effect method to obtain highly dispersed and homogeneous nanopowders and ii) the SPS technique is a powerful tool to fabricate fine-grained dense transparent ceramics, which are suitable for fabricating IR transparent Y2O3-MgO composite ceramics from commercial starting powders.

© 2020, Springer-Verlag GmbH Germany, part of Springer Nature. We conducted Vickers indentation tests on Fe-free (Mg2SiO4) and Fe-bearing (Mg1.8Fe0.2SiO4) olivine single crystals and high-density polycrystalline material with average grain sizes ranging from 170 to 890 nm. The Vickers microhardness (Hv) of the Fe-free polycrystalline material with the finest grain size is ~ 17 GPa at a load of 0.1 N, while that of the Fe-bearing single crystal is ~ 8 GPa at the largest load applied. Overall, Hv decreases with increasing grain size, load (indentation depth), and the presence of Fe. For each grain size, Hv is well characterized by a power law of the form Hv/Hv0∝l-x, where Hv0 is the depth-independent value of Hv, l represents either grain size or indentation depth, and x is 0.09. Despite the small exponent value for each size effect, the nonlinear interaction of the two size effects results in large variations of Hv in our samples. We show that our semi-empirically derived relationship as a function of grain size and indentation depth explains the Hv of both polycrystalline and single-crystal olivine at any indentation conditions. Indentation fracture toughness of the finest-grained material is 0.8 MPam1/2, which increases slightly to 1.1 MPam1/2 with increasing grain size, while the toughness of the single crystals varies from 0.5 to 0.8 MPam1/2 depending on the crystallographic orientation of the fracture planes.

We report for the first time the effect of temperature on the mechanical properties of (Ta1/3Ti1/3Zr1/3)C carbide. Flexural strength and fracture toughness were investigated using the three-point bending technique in argon. Using commercially available carbide powders with an equimolar ratio and performing spark plasma consolidation at 1973°C, we obtained a bulk single-phase medium-entropy carbide ceramic with the lattice parameter a= 4.458 Å. The flexural strength and fracture toughness at room temperature reached on average 700 MPa and 3.2 MPa m1/2, respectively. At 1800°C, local decomposition of the medium-entropy carbide took place as a structure with a local chemical gradient was observed after high-temperature tests, which increased fracture toughness by 30% (to 4.4 MPa m1/2).

Mixtures of B4C, α-AlB12 and B powders were reactively spark plasma sintered at 1800 °C. Crystalline and amorphous boron powders were used. Samples were tested for their impact behavior by the Split Hopkinson Pressure Bar method. When the ratio R = B4C/α-AlB12 ≥ 1.3 for a constant B-amount, the major phase in the samples was the orthorhombic AlB24C4, and when R < 1 the amount of AlB24C4 significantly decreased. Predictions that AlB24C4 has the best mechanical impact properties since it is the most compact and close to the ideal cubic packing among the Al-B-C phases containing B12-type icosahedra were partially confirmed. Namely, the highest values of the Vickers hardness (32.4 GPa), dynamic strength (1323 MPa), strain and toughness were determined for the samples with R = 1.3, i.e., for the samples with a high amount of AlB24C4. However, the existence of a maximum, detectable especially in the dynamic strength vs. R, indicated the additional influence of the phases and the composite’s microstructure in the samples. The type of boron does not influence the dependencies of the indicated mechanical parameters with R, but the curves are shifted to slightly higher values for the samples in which amorphous boron was used.

The properties of ceramics can be improved by controlling the microstructure through texturing ceramics in a strong magnetic field. Fabricating dense boron carbide (B4C) requires high temperature sintering, therefore sintering additives are often used in order to densify B4C ceramics at lower temperatures. However, combined effect of texturing and sintering additives on densification of B4C has not been made clear yet. Here we report the effect of alumina (Al2O3) sintering additive on texturing in a strong magnetic field and densification of B4C. Texturing was performed by rotating superconducting magnet at 12 T during slip casting process. Electron backscatter diffraction (EBSD) was used to observed the texturing projection. {0001} plane is clearly oriented in the plane parallel to rotating magnetic field. In addition, Lotgering factor was also calculated as quantitatively evaluation of texturing degree. Results on densification showed that addition of Al2O3 successfully increased density of B4C sintered by spark plasma sintering (SPS) at 1800 degrees C to 97.8%. Formation of aluminum borate (Al5BO9) as secondary phase was detected by X-Ray diffraction (XRD). It is considered that the generation of Al5BO9 assisted finer densification of B4C ceramic. Textured B4C sintered at 1700 degrees C by SPS without alumina addition exhibited the highest orientation of c-axis. Addition of alumina caused decrease in degree of orientation of c-axis.

The problem regarding the distribution of relaxation times (DRT) is revisited and discussed from the point of view of mathematics and computing algorithms. Although the algorithm in conventional DRT analysis software involves an implicit hypothesis that DRT is a continuous real function with continuous relaxation time, this hypothesis is not a principle of nature but a demand by a mathematical equation used for analysis. It is to be noted that the DRT calculated using the conventional algorithm is a continuous distribution of relaxation times (CDRT). As per the CDRT hypothesis, DRT is a set of discrete values. On the other hand, there is a model that involves the discrete distribution of relaxation times (DDRT). Thus, the fundamental difference between the CDRT and DDRT models originates f

Oxidation resistance of textured Ti3AlC2 ceramics was measured in the temperature range 1273–1573 K. It was found that the oxidation was markedly anisotropic and the samples exhibited a better oxidation resistance when tested along a direction transverse to the c-axis. This behavior was attributed to the rapid diffusion of Al within its basal planes to form a passivating Al2O3 scale and it respected Ellingham diagrams. The scales formed had different compositions depending on the testing direction
this response was clearly resulting from the crystallographic orientation. Even at 1473 K after 20 h exposure, the samples tested in a direction transverse to the c-axis showed a reduced weight gain which was 45 times lower than one seen on a basal plane.

Transparent polycrystalline alumina was developed over many years because its attractive properties are expected to find applications in many fields. Crystallographic orientation is one of the effective ways to improve transparency in birefringent ceramics such as alumina, because birefringence at grain boundaries can be suppressed by the alignment of optical axis. Fabrication of high-transparency alumina with an oriented c-axis and fine microstructure can be attained by slip casting in a strong magnetic field, followed by spark plasma sintering at 1150 °C for 20 min. The real in-line transmittance of the textured alumina with a thickness of 0.80 mm was 70% at λ = 640 nm, which was higher than that of randomly-oriented alumina. The c-axis orientation reduced the actual difference of the refractive index and suppressed remarkably the birefringence.

Conventional ceramic processing techniques do not produce ultrafine-grained materials. However, since the mechanical and optical properties are highly dependent on the grain size, advanced processing techniques are needed to obtain ceramics with a grain size smaller than the wavelength of visible light for new laser sources. As an empirical study for lasing from an ultrafine-grained ceramics, transparent Yb3+:Y2O3 ceramics with several doping concentrations were fabricated by spark plasma sintering (SPS) and their microstructures were analyzed, along with optical and spectroscopic properties. Laser oscillation was verified for 10at.% Yb3+:Y2O3 ceramics. The laser ceramics in our study were sintered without sintering additives, and the SPS produced an ultrafine microstructure with an average grain size of 261nm, which is about one order of magnitude smaller than that of ceramics sintered by conventional techniques. A load was applied during heating to enhance densification, and an in-line transmittance near the theoretical value was obtained. An analysis of the crystal structure confirmed that the Yb3+:Y2O3 ceramics were in a solid solution. To the best of our knowledge, this study is the first report verifying the lasing properties of not only ultrafine-grained but also Yb-doped ceramics obtained by SPS.

Electrophoretic deposition (EPD) process has certain advantages such as it can be applied for a mass production and also can be combined with magnetic crystal alignment technique. In this work, we prepared lead-free 85(Bi0.5Na0.5)TiO3-15BaTiO(3) (85BNT-15BT) piezoelectric ceramics by conventional uniaxial pressing and EPD process. Various conditions were optimized such as suspension media, applied electrical field, and deposition time in order to yield dense green ceramics of 85BNT-15BT composition using EPD process. 85BNT-15BT ceramics prepared using EPD process revealed the Curie temperature of about 250 A degrees C, coercive field of about 30 kV/cm, and piezoelectric constant (d (33)) of 75 pC/N. The EPD-processed samples exhibited structural and electrical properties similar to that of the conventionally processed one suggesting the successful fabrication of 85BNT-15BT piezoelectric ceramics by EPD method without composition deviation. This study lays a foundation on the fabrication of Bi-based lead-free piezoelectric ceramics by an alternative route other than the conventionally practiced solid-state reaction method maintaining the similar chemical composition, moreover, leaving a large space to explore more in the future.

The high-temperature phase of lanthanum germanate is useful due to its high oxide ion conductivity. While the transition from the high- to low-temperature phase could be suppressed by yttrium substitution in lanthanum sites, full stabilization of the high-temperature phase was difficult to achieve by yttrium substitution under conditions of different lanthanum-deficient compositions, as some X-ray diffraction (XRD) peaks were broadened after annealing at 873 K. With lattice constant analysis using the XRD peaks, the degree of lattice asymmetry for the low-temperature phase with triclinic lattice was found to decrease with increases in the deficiency of the lanthanum site and yttrium concentration. Formation of the low-temperature phase was difficult to detect even from Raman shift spectra. On the other hand, Raman shift spectra showed high sensitivity to detection of the La2GeO5 impurity phase. The influence of the total conductivity on the phase transition showed different trends with increases in the lanthanum deficiency and yttrium concentration. With tuning of the composition, the highest conductivity was observed in La8.51Y0.96(GeO4)6O2.205. This conductivity (6.12 © 1011 S/m11 at 873 K) is higher than that of yttria-stabilized zirconia at the same temperature.

This is the first comprehensive review on inherent anisotropic features of transition metal diboride (MB2) and their implementation for tailoring the microstructure and properties of MB2-based Ultra-high temperature Ceramics (UHTCs). The emphasis is on the processing approaches, microstructures, and properties of self-reinforced and/or textured MB2-based composites with elongated MB2 grains. The crystal structure characteristics and grain growth behaviour of MB2 are also critically reviewed. Benefiting from the tailored microstructure, the MB2-based ceramics exhibit some improved properties. Considering the success of Si3N4 ceramics in the field of structural ceramics, it is expected that the potential MB2-based ceramic composites with abundant elongated MB2 grains, textured structures, and controlled grain boundaries would possess improved fracture toughness, thermal shock resistance, and reliable high-temperature properties, which are desired for their practical applications. Accordingly, microstructure designing and tailoring provide an important perspective for the future development of UHTCs.

Lanthanum silicate oxyapatite (LSO) has superior features for application of solid electrolyte in solid oxide fuel cells. Because LSO has a higher oxygen-ion conductivity compared with yttria stabilized zirconia at temperatures below 600°C. Textured LSO bulk ceramics were fabricated by using a magnetic field-assisted colloidal processing technique. The c-axis of LSO was aligned parallel to the applied magnetic field. The anisotropic electric conductivity of the textured bulk ceramics was evaluated by the complex impedance method. It was demonstrated that the conductivity was very high along the c-axis. Battery performance was higher in the textured LSO compared with the random LSO.

セラミックスの創製において、成形過程で強磁場を印加することにより常磁性、反磁性セラミックスであっても結晶配向制御を可能とするプロセスと、さらに積層構造を造り込むことを可能にする電気泳動堆積法の二つのプロセスを重畳させることで配向積層セラミックスの創製を可能とした。このセラミックスの配向積層構造を造り込むための装置を紹介する。

A new algorithm for the automatic estimation of an equivalent circuit and the subsequent parameter optimization is developed by combining the data-mining concept and complex least-squares method. In this algorithm, the program generates an initial equivalent-circuit model based on the sampling data and then attempts to optimize the parameters. The basic hypothesis is that the measured impedance spectrum can be reproduced by the sum of the partial-impedance spectra presented by the resistor, inductor, resistor connected in parallel to a capacitor, and resistor connected in parallel to an inductor. The adequacy of the model is determined by using a simple artificial-intelligence function, which is applied to the output function of the Levenberg-Marquardt module. From the iteration of model modifications, the program finds an adequate equivalent-circuit model without any user input to the equivalent-circuit model.

Ti3SiC2 is a typical Mn+1AXn (MAX) phase ceramic and exhibits both metal-like and ceramic-like properties. To improve these properties, texturing and Al2O3 addition were performed. The commercial Ti3SiC2 powder used contained approximately 10 mass% TiC phase. Textured Ti3SiC2 was prepared by slip casting in a strong magnetic field (MF) followed by spark plasma sintering (SPS) at 1623 K under a pressure of 40 MPa for 5 min. The Lotgering orientation factor of the (00l) peaks of Ti3SiC2 prepared under an MF was 0.96, and the relative density of samples exceeded 99%. The bending strength and fracture toughness of Ti3SiC2 were improved by texturing. The textured Ti3SiC2 exhibited an excellent bending strength of 978 MPa, but Al2O3 addition, reduced the bending strength and fracture toughness. The textured Ti3SiC2 showed the plastic deformation at a temperature of approximately 1173 K.

NIMSでは毎年4月中旬の科学技術週間に合わせて研究所一般公開を行い、土曜日には小学生、中学生向けに青少年企画を実施している。この時にミネラルファンデーション作製体験を実施しており、小学生から主婦まで幅広い層から人気を得ている。また、日本全国からの高校生の研究所見学、体験学習も随時受け付けており、その受け入れ人数は年に2000人を超えている。NIMSでは3〜4箇所の実験施設を20分〜30分程度ずつで見学するコースと、一つのテーマで2時間程度の体験実験をしながら学習を行うコースとで種々のテーマを用意している。その中でも、著者らが中心となって行っている強磁場の見学、ファンデーションの作製、CIPを用いた実験による圧力の体験学習を行っており、本記事ではこれらについて紹介する。

&lt; 110 &gt; grain-oriented ceramics with the composition of 0.15BaTiO(3)-0.85(Bi0.5Na0.5)TiO3 with a high Curie temperature of similar to 300 degrees C were successfully fabricated by reactive templated grain growth of layered hydrogen titanate platelets with (Bi0.5Na0.5)TiO3 and BaCO3 matrix powders. A large degree of &lt; 110 &gt; orientation F-110 = 84% was achieved by decreasing green sheet thickness and application of pressure on a compact during sintering. As a consequence, improved remanent polarization was observed in these ceramics compared with randomly oriented ceramics, owing to easier polarization switching. A piezoelectric constant d(33) of 103 pC/N and an electromechanical coupling factor k(33) of 0.44 were obtained for the &lt; 110 &gt; grain-oriented ceramics. (C) 2017 The Japan Society of Applied Physics

T3SiC2 is a typical Mn+1AXn (MAX) phase ceramics and shows unique metallic-like and ceramic-like properties. To improve these properties, texturing and Al2O3 addition have been conducted. The commercial T3SiC2 powder used contains approximately 10 wt% TiC phase. Textured T3SiC2 was prepared by slip cast in strong magnetic fields followed by spark plasma sintering (SPS) at 1350°C under 40 MPa for 5 min. The Lotgering orientation factor of (00l) peaks of T3SiC2 with magnetic field (MF) was 0.96, and relative density of samples was beyond 99%. The bending strength and fracture toughness of T3SiC2 were improved by texturing. T3SiC2 with magnetic field showed excellent value of bending strength of 978 MPa, but Al2O3 addition caused deterioration of bending strength and fracture toughness. T3SiC2 with MF showed the plastic deformation at temperature at around 900°C.

The Li1+x-yNb1-x-3yTix+4yO3(0.06 &lt;= x &lt;= 0.33, 0 &lt;= y &lt;= 0.09) (hereafter LNT), forms a unique and periodical structure in the Li2O-Nb2O5-TiO2 ternary system. In this work, toward application of the unique qualities of an electro-ceramic, we fabricated oriented LNT balk ceramics by slip casting in a strong magnetic field of 12 T using various sizes of particles. The c-axis of the LNT powders was aligned parallel to the magnetic field. As a result, we found anisotropic- and unique- electric properties which were caused by a superstructure with intergrowth layers of corundum-type [Ti2O3](2+). The Qf value parallel to the c-axis was about five times greater than that of perpendicular to the c-axis. We first clarified the mechanism showing that the anisotropic Of value was caused by the anisotropic electron conductivity and the anisotropic bonding strength in the superstructure. (C) 2017 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

Tribological property of c-axis textured shell-like Ti3AlC2 ceramic was investigated using reciprocating sliding balls (SUS304) under loads of 1, 5, and 9 N. It was found that the textured top surface (TTS), corresponding to the (000l) plane, shows the lowest mean coefficient of friction in comparison with those measured on the textured side surface (TSS), where the sliding directions are parallel (TSS-1) and perpendicular (TSS-2) to c axis, under the same load. Among all the tested orientations, the TSS-2 exhibited the lowest wear rate of 1.51x10(-3) mm(3)/(N.m) under the load of 9 N. The worn mechanisms on the TTS and TSS-1 were delamination, grain fracture, and grain spalling-off. On the TSS-2, plowing effect against balls was the dominating mechanism. This work suggests the criteria to maximize the wear resistance in the load range of 1-9 N.

The densification behavior during the isothermal sintering of 7.8 mol% Y2O3-stabilized zirconia was examined in the intermediate and final stages of sintering. In the intermediate stage, it is shown that the relationship between the grain size and the relative density is not invariant, but is temperature dependent. The relationship is combined with the measured densification rate to evaluate the grain size exponent, the activation energy and an unspecified function of density. The evaluation of the characteristic parameters indicates that the densification and the grain growth are related to a mechanism of grain-boundary diffusion and sliding. The densification rate predicted with the evaluated parameters shows a good consistence to the measured rate. In the final stage, the densification rate is inversely proportional to the grain size, and the kinetics is well explained by using the diffusive model modified with a gas pressure in closed pores. (C) 2017 The Ceramic Society of Japan. All rights reserved.

我々は、セラミックス粒子の配向を高度に制御できる方法として、強磁場を利用した配向プロセスに着目してきた。これまでの知見を基に、個々のゼオライトの結晶磁気異方性に基づき、種結晶の配向挙動を制御できれば、それぞれのゼオライトに適した配向状態が実現できると考えた。しかしながら、ゼオライトの磁気的性質を調査した報告例は無く、強磁場を用いたゼオライト配向膜の作製はまさに未踏の分野である。本報では、結晶磁気異方性に基づく種結晶の磁場配向制御を検討し、磁場配向制御で製膜された種結晶配向層の水熱固化からゼオライトの緻密配向膜を得る手法について紹介した。

Tailoring the crystallographic orientation in ceramics is very useful for improving their properties. A magnetic field is shown to be very effective in controlling the crystallographic orientation in bulk ceramics. The particles were rotated to an angle minimizing the system energy by a magnetic torque generated from the interaction between the magnetic anisotropy and the applied magnetic field. This processing was applied to control the microstructure in lanthanum silicate oxyapatite (LSO) for SOFC and LiCoO2 for Li ion secondary battery. Electric conductivity parallel to the c-axis in the c-axis oriented LSO was higher than that perpendicular to the c-axis. The battery performance of the ideal textured cell fabricated using a rotating magnetic field has a significantly higher performance than a oriented cell prepared by a static magnetic field.

An oriented La2NiO4 cathode was successfully fabricated on a dense Gd2O3-doped CeO2 electrolyte pre-coated with conducting polypyrrole by electrophoretic deposition in a static magnetic field of 12 T for use in low-temperature operating solid oxide fuel cell. The orientation of La2NiO4 was based on an anisotropic magnetic property in its crystal structure. Firm adhesion of the La2NiO4 cathode to an electrolyte was made by the co-deposition of starch added as a pore former. The La2NiO4 cathode with the preferential orientation of the a-b plane perpendicular to the surface of the electrolyte showed a polarization loss lower than that with a random orientation, leading to an enhancement in the cell performance at 500 degrees C. (C) 2016 Elsevier Ltd. All rights reserved.

A new program for electrochemical impedance analysis has been developed based on the expanded measurement model. The main feature of this program is that it allows the user to easily estimate the equivalent circuit, as well as an initial guess of the fitting parameters, through a graphic user interface (GUI). The function to illustrate the partial impedance spectra is implemented in the graphs of log f-Z(real) and log f-Z(imag). In this context, f represents the alternating current frequency applied to the sample; Z(real) and Z(imag) represent the real and imaginary components of the impedance, respectively. By employing the GUI supporting function, the impedance spectrum can be analyzed without the use of a pseudo-element such as a constant phase element and with an empirical parameter in the Warburg and Gerischer impedance. Based on the results, it is possible to calculate a discrete distribution of the relaxation times from the optimized parameters. (C) 2016 The Ceramic Society of Japan. All rights reserved.

Tailoring the crystallographic orientation in ceramics is very useful for improving their properties. We reported that the colloidal processing in a strong magnetic field was able to control the crystallographic orientation even in diamagnetic ceramics. In this process, a strong magnetic field is applied to the particles in a stable suspension. The orientation of the crystal depends on the axis having easy magnetization and one-dimensional orientation can be controlled. In this study, our concept is that control of multiaxial crystalline orientation in ceramics by using both anisometric particles and a magnetic field. The control of the triaxial orientation was achieved by tape casting of rod-like MgTi2O5 particle in a magnetic field. The b-axis was aligned by the magnetic field, and the a-axis was aligned by the geometric effect and shear stress during tape casting.

The densification behavior during the isothermal sintering of 8YSZ was examined in the initial and intermediate stages of sintering. In the initial stage, a difficulty in evaluating the densification behavior arises from the transition of the stable pore structure and the limitation of the theoretical two-sphere model. In the intermediate stage, a linear relationship with a slope of -1/2 is observed between the densification rate and the time. An empirical equation of the densification kinetics is proposed and found to be valid in a wide density range. At a relative density of 0.6-0.73, the activation energy is 688 kJ/mol. Rapid grain growth is observed at a relative density of 0.73-0.8 and &gt;0.9 for the isothermal sintering at 1200-1300 degrees C and 1400-1500 degrees C, respectively. The rapid grain growth reduced significantly the densification rate. The densification mechanism and grain growth behavior are also discussed. (C) 2015 Elsevier Ltd. All rights reserved.

The aim of the current paper is to present the development of the method used for fabricating highly textured a-alumina elements. The experimental procedure described is based on a combination of two techniques: gelcasting is used in tandem with high magnetic field exposure. In the element shaping process, a new, low-toxic and environmentally friendly gelating system was implemented that is based on in situ polymerisation of an acryloyl derivative of galactose. Here, care was taken to achieve a highly textured structure of elements gelcast from the ceramic slurries of high solid contents (45-50 vol%), which have not been processed successfully for magnetic field alignment before. A secondary aim of the study was to investigate the combined effect of magnetic field exposure duration and the idle time of polymerisation on the effectiveness of the alignment. In the course of the experiment, high degrees of crystalline orientation of the gelcast samples were obtained ranging from 0.92 to 0.96, developed after the subsequent sintering at 1600 degrees C (the parameters were calculated on the basis of XRD pattern of the surface perpendicular to the magnetic field direction). The microstructures of the obtained elements are described in detail at the end of the paper, in a stereological analysis. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

This study develops a fabrication technique to obtain Fe-free and Fe-bearing (Fe:Mg = 1:9) olivine aggregates not only with high density and fine grain size but with crystallographic preferred orientation (CPO). A magnetic field is applied to synthetic, fine-grained, olivine particles dispersed in solvent. We find that (1) preparation of fully reacted olivine particles, with less propensity to coalesce; (2) preparation of a suspension with highly dispersed particles; and (3) application of a certain strength of the magnetic field are essential to obtain well sintered and well-aligned aggregates. High density and fine grain size Fe-free and Fe-bearing olivine aggregates were successfully synthesized with uniaxially aligned a- and c-axes, respectively.

金属材料だけでなくセラミックスにおいても，その材料特性を改善させるためには，微構造制御が有効で有り，その中でも結晶配向制御は有望な方法として挙げられる．金属では集合組織の制御が精緻に行われているが，セラミックスにおいては，その制御手法も限られる．しかしながら，強磁場を用いることで反磁性セラミックスであっても結晶配向制御することが可能になり，近年ではさらに反応焼結や，相変態，形状異方性粒子などの他のプロセス技術を組み合わせることにより，さらにその展開が広がっている．ここでは，最近での強磁場によるセラミックスの配向制御の展開について紹介する．

Despite of good oxidation resistance and ablation resistance, challenge to densify and tendency to loss high temperature (H.T.) strength have limited its potential applications in aerospace for HfB2-SiC ceramic. In this work, dense HfB2-SiC ceramic with improved H.T. flexural strength was prepared using WC as sintering aid. Pure HfB2-SiC ceramic exhibited creep deformation at 1600 degrees C with measured strength value of 389 +/- 82 MPa, whereas WC doped sample showed much higher flexural strength of 658 +/- 69 MPa with linear elastic behavior prior to fracture. In addition to clean grain boundary, the addition of 5 vol.%WC into HfB2-SiC ceramic promoted the formation of fine (Hf,W)B-2, (Hf,W)C and WB precipitates. This combinative effect is responsible for its excellent H.T. mechanical property of WC doped HfB2-SiC ceramic. (C) 2015 Elsevier Ltd. All rights reserved.

(111)-oriented tetragonal barium titante (BaTiO3, BT) ceramics with the degree of (111) orientation of 100 % were fabricated by sintering (001)-oriented hexagonal BT accumulations prepared by a magnetic field assisted electrophoretic deposition (EPD) method. Apparent piezoelectric constant d33* value calculated from the slope of a unipolar strain vs. electric field curve of the (111)-oriented tetragonal BT ceramics was 597 pm/V, which was larger than that of randomly oriented ceramics (d33* = 460 pm/V). This enhancement was associated with an electric field induced phase transition.

Highly transparent (Y0.95-xGdxEu0.05)(2)O-3 (x=0.15-0.55) ceramics have been fabricated by vacuum sintering at the relatively low temperature of 1700 degrees C for 4h with the in-line transmittances of 73.6%-79.5% at the Eu3+ emission wavelength of 613nm (similar to 91.9%-99.3% of the theoretical transmittance of Y1.34Gd0.6Eu0.06O3 single crystal), whereas the x=0.65 ceramic undergoes a phase transformation at 1650 degrees C and has a transparency of 53.4% at the lower sintering temperature of 1625 degrees C. The effects of Gd3+ substitution for Y3+ on the particle characteristics, sintering kinetics, and optical performances of the materials were systematically studied. The results show that (1) calcining the layered rare-earth hydroxide precursors of the ternary Y-Gd-Eu system yielded rounded oxide particles with greatly reduced hard agglomeration and the particle/crystallite size slightly decreases along with increasing Gd3+ incorporation; (2) in the temperature range 1100 degrees C-1480 degrees C, the sintering kinetics of (Y0.95-xGdxEu0.05)(2)O-3 is mainly controlled by grain-boundary diffusion with similar activation energies of similar to 230kJ/mol; (3) Gd3+ addition promotes grain growth and densification in the temperature range 1100 degrees C-1400 degrees C; (4) the bandgap energies of the (Y0.95-xGdxEu0.05)(2)O-3 ceramics generally decrease with increasing x; however, they are much lower than those of the oxide powders; (5) both the oxide powders and the transparent ceramics exhibit the typical red emission of Eu3+ at similar to 613nm (the (D0F2)-D-5-F-7 transition) under charge transfer (CT) excitation. Gd3+ incorporation enhances the photoluminescence and shortens the fluorescence lifetime of Eu3+.

Highly anisotropic single crystal-like ceramic of La2Ti2O7 was successfully prepared by an effective 2-D grain alignment using both seed crystals and magnetic field alignment during slip casting followed by templated grain growth (TGG). It was found that the highest magnetic susceptibility is in the [0 0 l] direction of LTO. The grain orientation factors of the three directions for the textured ceramic were calculated as 0.76, 0.71, and 0.73, respectively. The dielectric and ferroelectric properties of the textured ceramic were found to be single crystal like. The dielectric permittivity of the aligned ceramic in the different directions is higher than for single crystal due to contributions from domain walls and grain boundaries. Crown Copyright (C) 2014 Published by Elsevier Ltd. All rights reserved.

Chemical precipitation at the freezing temperature of similar to 4 degrees C has directly yielded layered rare-earth hydroxide [LRH, Ln(2)(OH)(5)-NO3 center dot nH(2)O, Ln = Y0.95Eu0.05] nanosheets (up to 7 nm thick) for the Y/Eu binary system, with the interlayer NO3- exchangeable with SO42-. Calcining the sulfate derivative at 1100 degrees C for 4 h produces well-dispersed and readily sinterable Ln(2)O(3) red phosphor powders (similar to 14.8 m(2)/g) that can be densified into highly transparent ceramics via optimized vacuum sintering at the relatively low temperature of 1700 degrees C for 4 h (average grain size similar to 14 mu m; in-line transmittance similar to 80% at the 613 nm Eu3+ emission or similar to 99% of the theoretical transmittance of Y2O3 single crystal). Our systematic studies also found that (1) the extent of SO42 - exchange and the interlayer distance of LRH are both affected by the SO42-/Ln(3)(+) molar ratio (R), and an almost complete exchange is achievable at R = 0.25 as expected from the chemical formula (one SO42- replaces two NO3- for charge balance). The optimal R value for sintering, however, was found to be 0.03; (2) The Ln(3+) concentration for LRH synthesis substantially affects properties of the resultant oxides, and hard agglomeration has been significantly reduced at the optimized Ln(3+) concentration of 0.05-0.075 mol/L; (3) Sulfate exchange significantly alters the thermal decomposition pathway of LRH, and was found essential to produce well-dispersed and highly sinterable oxide powders; (4) Both the oxide powders and transparent ceramics exhibit the typical red emission of Eu3+ at similar to 613 nm (the D-5(0) -&gt; F-7(2) transition) under charge-transfer (CT) excitation. Red-shifted CT band center, stronger excitation/emission, and shorter fluorescence lifetime were, however, observed for the transparent ceramics.

Highly oriented compositionally modified Pb(Zr, Ti)O-3 (PZT) ceramics were successfully obtained by slip casting in a high magnetic field. PZT is a well-known superior ceramic with the highest piezoelectric properties, and these properties have been expected to be further improved through crystalline orientation. However, highly oriented PZT ceramics fabricated by slip casting in a high magnetic field have never been reported. We obtained oriented ceramics using compositionally modified PZT with Pb(Ni, Nb)O-3, and their Lotgering factor was 0.77. The electromechanical coupling coefficient (k(31)) increased by 30%, and an extremely high value of 0.44 was achieved for the oriented ceramics. (C) 2015 The Japan Society of Applied Physics

Sinterable lanthanum silicate oxyapatite (LSO) powders were prepared by the combination of solid-state reaction synthesis and particle size control via planetary ball-milling. We successfully fabricated the LSO ceramics with relative densities exceeding 94% at 1773K even though it was suggested that the densified LSO ceramics could not be obtained below 1923K using a powder synthesized by a solid-state reaction. Impurity phases resulting from contamination due to the ball and pod during the planetary ball milling were, in some cases, detected by the X-ray diffraction analysis of the sintered ceramics. The planetary ball-milling conditions were deemed important for the successful fabrication of the sinterable LSO powder. (C) 2015 The Ceramic Society of Japan. All rights reserved.

Dense SiC having strongly aligned plate-like grains was prepared by slip casting under strong magnetic field and subsequent densification using Al3BC3 additive. Irregular-shaped 6H-SiC powders in the green body were strongly aligned by the magnetic treatment. Subsequently, Al3BC3 additive induced the formation of aligned plate-like SiC grains during densification. The hardness of SiC could be tailored up to 11% by the strong alignment of the grains. Crack deflection was also strongly affected by the direction of the aligned plate-like grains. As a result, the length of the cracks which propagated parallel to the elongated grains was 18.6% shorter compared to that formed perpendicular to the grains. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Textured Ti3AlC2 ceramic was successfully fabricated by a strong magnetic field alignment (SMFA) technique followed by spark plasma sintering (SPS). About 15 vol.% Al2O3 particles were formed in situ during the process. The unique combination of excellent bending strength of 1261 MPa (//c axis) and fracture toughness of 14.6 MPa m(1/2) (perpendicular to c axis) was achieved. Also, the high electrical and thermal conductivities were determined as 1.0 x 10(6) Omega(-1) m(-1) (//c axis) and 25.3 W (mK)(-1) (perpendicular to c axis), respectively. (C) 2014 Elsevier Ltd. All rights reserved.

Orientation technique based on the magneto-scientific crystal alignment phenomenon combined with electrophoretic deposition (EPD) technique was applied for the seeding process of zeolite L particles. Well-dispersed, ethanol-based zeolite L suspension was prepared and then consolidated on porous zirconia substrates by EPD. Conducting polypyrrole film synthesized on the zirconia substrate was used as an anodic substrate for the EPD process. The EPD was performed in a superconducting magnet with applying 12 T strong magnetic field to the suspension. The degree of orientation was characterized by XRD and compared with that of the zeolite L layer prepared by slip casting in a 12 T strong magnetic field using the same suspension.

The surface modification of Gd doped ceria (GDC) and Sr- and Mg-codoped lanthanum gallate (LSGM) powders with cationic and anionic polyelectrolytes, Poly(diallyldimethylammonium chloride) (PDDA) and poly(2 -acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS), respevtively, was performed by the Layer by Layer (LbL) adsorption method to improve the surface-charging uniformity. The tri-layer of GDC/LSGM/GDC was deposited on a polypyrrole coated porous NiO-YSZ substrate by sequential EPD using the ethanol-based suspensions of the surface-modified powders. The topcoating of hydroxyl-propyl cellulose (HPC) on the deposited layers was conducted to control the drying rate with suppressing the cracking and peeling-off of the deposits. The advantage of the use of those polymers for the EPD process including the drying technique was demonstrated.

The controlled development of texture in ceramics allows to improve some electrical, piezoelectric and mechanical properties of advanced ceramics materials by tailoring the microstructure. A highly textured microstructure of undoped dense alumina was attained by applying a novel combination of gelcasting techniques with magnetic alignment followed by sintering. A newly synthesized low-toxic acrylic monomer based on galactose was introduced to the gelcasting procedure. Thermal analysis of the gelcast has been performed to examine decomposition process of the new binder and match appropriate sintering rate. The effectiveness of the proposed procedure has been related to rheological properties of the suspension by clarifying the influence of the powder and the dispersant content. It has been also related to the idle time of polymerization by clarifying the influence of the initiator content. The new method is compared to slip casting in high magnetic field that has been used widely so far. (C) 2014 Elsevier Ltd. All rights reserved.

MAX phase materials are known to show unique properties with the combination of metallic and ceramic properties. Recently textured MAX phase materials have been expected to show excellent properties. Here Ti2AlN powders were synthesized from Ti, Al and TiN powders, or Ti and A1N powders heating at 1573 K-1773 K. Then highly textured Ti2AlN was fabricated by slip casting in a strong magnetic field and spark plasma sintering at 1473 K - 1773 K and the relative density was nearly 91%. The c-axis of the Ti2AlN grains were oriented parallel direction of the magnetic field, the lotgering orientation factor was determined 0.96. The nacre like structure was observed in the side surface of the textured sample.

Sinterable Ti3SiC2 powder was synthesized from a powder mixture with a molar ratio of 1.0Ti:0.3Al:1.2Si:2.0TiC by heating at 1200 degrees C in Ar flow. Almost single-phase peaks of Ti3SiC2 were observed in X-ray diffraction patterns. The powder was dispersed in ethanol using polyethylenimine (PEI) as the polymer dispersant. Textured dense Ti3SiC2 ceramics were successfully fabricated by slip casting in a strong magnetic field followed by pressureless sintering at 1400 degrees C for 2 h. The relative density of these Ti3SiC2 ceramics was 99.4%, and the bending strength, fracture toughness and electrical resistivity were 623 +/- 9 MPa, 5.9 +/- 0.1 MPa.m(1/2) and 0.31 mu Omega.mu, respectively. Compared with those of nontextured pressureless sintered samples of almost full density, the bending strength and fracture toughness of the textured Ti3SiC2 ceramics were increased by factors of 1.6 and 1.4, respectively. (C) 2014 The Ceramic Society of Japan. All rights reserved.

Highly transparent zinc aluminate ceramics were fabricated by the solid-state reaction using a spark plasma sintering machine. The sintered body exhibited a microstructure consisting of submicron-sized grains and extremely low porosities. Annealing of the sintered body in air improved the transmission close to the theoretical limit in a wavelength range of 1-5 mu m. The band gap energy estimated from the absorption coefficient was 4.3 eV. The Young's modulus and the bulk modulus measured for the fully dense zinc aluminates were 282 and 211 GPa, respectively. (C) 2014 The Ceramic Society of Japan. All rights reserved.

(111)-oriented Mn and Nb-doped barium titanate (BaTiO3, BT) ceramics with fine grains were fabricated with an electrophoretic deposition (EPD) method in a high magnetic field and a topotactic phase transition. Initially, accumulations of (0001)-oriented hexagonal Ba(Ti0.95Mn0.05)O3 particles added with 2.5 mol%-Nb2O5 powder were prepared by the EPD method in the high magnetic field of 12 T. Then, the (111)-oriented, Mn and Nb-doped pseudo-cubic BT ceramics with fine grains of ~0.4 μm in diameter were obtained via the topotactic phase transition, with the degree of the (111) orientation being as high as 79 %. The piezoelectric properties of the oriented ceramics were also studied.

直径が10-7〜10-9 m程度の大きさの粒子が気体や液体に分散している状態をコロイドという。サブミクロン〜ナノサイズのセラミックスの粒子も、水や非水溶媒などの液体に分散すると、通常のコロイド粒子と全く同じ性質を示す。コロイド粒子のサスペンションから、粒子を適当な方法で凝集させると、緻密な固化成形体を得ることができる。スラリーを経由する粉体成形法はコロイドプロセスと呼ばれ、複雑形状のセラミックス製品を製造する方法として注目されている。本稿では、セラミックスを中心にコロイド粒子の分散、凝集についてまず概説し、次いでコロイドプロセスにおけるサスペンション調製の注意点について、例をあげて紹介する。

In the Li2O-Nb2O5-TiO2 system, Li1+x-yNb1-x-3yTix+4yO3 (0.06 &amp;#61603; x &amp;#61603; 0.33, 0 &amp;#61603; y &amp;#61603; 0.09) (LNT) forms with a superstructure, and this is so-called M-phase. The superstructure of the M-phase is formed by periodical insertion of an intergrowth layer in a matrix having a trigonal structure. As an application of the unique qualities of an electro-ceramic with an anisotropy structure, we prepared an oriented LNT ceramic by slip casting in a high magnetic field (12 T). Consequently, c-axis of the LNT powder was aligned parallel to the magnetic field. The orientation degree was determined using a Lotgering factor and high orientation degrees (over 90 %) were achieved.

The distribution of magnesium ions at the lanthanum and silicon sites in MgO-doped lanthanum silicate oxyapatite as well as the concentration of neutral lanthanum vacancies were determined using densities and chemical compositions of the doped samples. On the basis of the density data, it was found that magnesium ions are substituted at the silicon site as well as the lanthanum sites in the oxyapatite phase. Owing to the existence of neutral lanthanum vacancies, it was difficult to evaluate the number of the oxygen ions present, Which are related to the oxygen ion conductivity of the compound, from the chemical compositions of the samples alone. Further, it was found that the fact that the total conductivity of MgO-doped lanthanum silicate oxyapatite depends on the MgO concentration as well as that of other defects could not be explained on the basis of conventional defect chemistry. (c) 2014 Elsevier B.V. All rights reserved.

La(OH)3，SiO2粉末を出発原料とした固相反応により，ランタンシリケートオキシアパタイトセラミックスの緻密体を作製した．水溶媒中で正に帯電したLa(OH)3粒子と，負に帯電したSiO2粒子をヘテロ凝集させることで両粉末の均一混合凝集粉を得た。このとき，La(OH)3については，ポリカチオン(poly-diallyldimethylammonium chloride)とポリアニオン(poly-sodium 4-styrenesulfonate)をLayer-by-Layer法を適用して，交互に吸着させることにより，正のゼータ電位を向上させた．得られたヘテロ凝集粉は，スリップキャストにより成形し，大気中で1600 ℃，10 時間焼成した．この焼成体がランタンシリケートオキシアパタイトの単相よりなることがXRDにより確かめられた．また，焼成体の相対密度は97 ％であった．

本研究では、MAX相セラミックスの中で、最も検討されているTi3SiC2を用いて、薄くて大きな板状粒子どうしの結合力を低くして、破壊される際の粒子引き抜く効果を高め、高強度でありながら、高靱性で、壊れにくい材料の創製を目的とした。

Dense, highly textured ZrB2 and ZrB2-MoSi2 ceramics were fabricated via a strong magnetic field alignment method followed by spark plasma sintering. Unlike with the previous studies, which only focused on the alignment of single-phase particles, both ZrB2 and MoSi2, which exhibited a magnetic anisotropy, have been aligned in this study. The alignment of MoSi2 in the same direction of ZrB2 enhanced the degree of orientation of ZrB2, decreased the grain size, but increased the aspect ratio of the platelet ZrB2 grains. The microstructure and anisotropic mechanical properties as well as the oxidation resistance in different directions were discussed.

Binderless WC ceramics were prepared by reactive spark plasma sintering, using tungsten trioxide, tungsten and carbon black as the starting materials. Phase assemblages and microstructure of the as-sintered ceramics were investigated. It was found that graphite existed as an impurity phase due to the volatilization of WO3, and W could compensate for the WO3 loss to form WC with a single phase. Benefiting from the enhanced sinterability, WC ceramics with high relative density and good hardness could be obtained at temperature as low as 1500 degrees C. (C) 2013 Elsevier Ltd. All rights reserved.

Silicon carbide is one of the most important ceramics used as structural and functional materials in a wide variety of applications. Many studies have reported the densification of SiC using oxide and nonoxide additives such as the Al2O3, B4C and Al-B-C system. However, it is difficult to densify SiC at temperatures below 2000 degrees C without sintering additives even if spark plasma sintering (SPS) is used. The authors attempted to densify SiC using colloidal processing and SPS without sintering additives. A commercially available SiC powder with the average particle size of 0.55 mm was used as the starting material. The densities of the green body prepared by slip casting and the sintered body by SPS were 65.5 and 98.7% respectively.

Zirconium diboride (ZrB2) ceramic possesses a unique combination of nice mechanical performance, high melting point (&gt; 3000 degrees C) and great high-temperature oxidation resistance (up to 1600 degrees C), which makes it a promising material system for ever-increasing ultra-high temperature (UHT) applications. However, ZrB2 suffers from poor mechanical performance at UHTs, which could strongly limit its applications at UHT. Here, we successfully demonstrate that texturing is an effective strategy to greatly enhance the flexural strength of monolithic ZrB2, reaching a high value of 810 +/- 60 MPa at 1600 degrees C when loaded in c-axis direction. We thoroughly discuss the strengthening mechanism by in-depth microstructural observations and analysis. Our discovery has technological and scientific implications for other UHT ceramic systems, especially those using ZrB2 as a matrix.

Barium titanate (BaTiO3) nanoparticles were prepared by a 2-step thermal decomposition method using nano oxalate particles. BaTiO3 nanoparticles were characterized using various methods. Accumulations were prepared by electrophoresis deposition method using the obtained BaTiO3 nanoparticles. They were performed necking structure by a solvothermal method. Polymer was infiltrated into the accumulations in vacuum to prepare a polymer film capacitor.

Barium titanate (BaTiO3, BT) gain-oriented ceramics were prepared by electrophoresis deposition (EPD) method under high magnetic field (HM-EPD) of 12 T. For this objective, the BT single-domain nanoparticles with high c/a ratio of 1.008 and size of 103 nm were prepared by two-step thermal decomposition method. Using the BT nanoparticle slurry, BT nanoparticle accumulations were prepared by EPD or slipcasting (SC) methods with/without high magnetic field. After binder burnout, these accumulations were sintered at 1350 degrees C and it was revealed that only the BT ceramics prepared by the HM-EPD method was assigned to grain-oriented ceramics with weak preferential crystallographic orientation along [110] direction.

The relationship between the development of the crystallographic orientation and the grain growth behavior were studied. The degree of orientations of the green compacts and sintered samples were evaluated by the Lotgering factor. The f(0 0 l) of all the samples were drastically increased with the increasing applied magnetic field strength. The f(0 0 l) of the samples sintered at 1223 K were improved in comparison to those of the green compacts. However, the f(0 0 l) value of the samples sintered at 1273 K were not increased at 4 T or lower. To characterize the grain growth process, these samples were analyzed using electron backscatter diffraction (EBSD). The sintered samples prepared in the magnetic field at 4 T or lower showed abnormal grain growth. The samples with an applied magnetic field of 8 T or higher had no abnormal grain growth. It was revealed that the orientation angle of the particles has an effect on the grain growth. (C) 2013 Elsevier Ltd. All rights reserved.

Anodic aluminum oxide (AAO)-template method is a synthesis process that AAO film with uniform pores is used as a template for 1-D nanostructure. In this study, we have synthesized well-defined TiO2 nanorods or nanowires using AAO-template method. As for the first method, AAO template was immersed for 1 min in the Ti precursor solution with slightly decompressed atmosphere (Immersion setting, IS). As for the second method, AAO template was put on the filtering flask as a cover plate. Precursor solution was dropped on the AAO template for 1 min with vacuuming from the bottom part of AAO template (Vacuum and drop setting, VDS). With the calcination and HCl treatment to remove AAO, polycrystalline TiO2 anatase nanorods and nanowires were successfully fabricated, just by changing the sample setting, viz., IS and VDS, respectively. (C) 2013 The Ceramic Society of Japan. All rights reserved.

Randomly-oriented and b-axis oriented mordenite seed layers, which were pre-fabricated out of and in a strong 12T magnetic field, were hydrothermally treated in clear reaction solutions with molar ratios of 6Na(2)O:Al2O3:30SiO(2):xH(2)O ( x = 1500, 3500 and 10000). Crystal growth of the seed particles only slightly occurred in the solution of x = 10000, but occurred in the solutions of x = 1500 and 3500, giving rise to densified films. However, the films treated with x = 1500 were composed of two layers with different morphologies; i.e., the precipitation of crystals from the solution was considered to induce the upper layer in the bi-layered films. Homogenized films were formed in the solutions of x = 3500. The initial orientation of the seed layer was retained in the continuous films treated at x = 3500. Thus, dense, continuous mordenite films with random and b-axis orientations were successfully fabricated from random and b-axis oriented seed layers by hydrothermal treatment in the clear reaction solutions at the molar ratio of 6Na(2)O:Al2O3:30SiO(2):3500H(2)O. (C)2013 The Ceramic Society of Japan. All rights reserved.

Zirconium carbide and hafnium carbide ceramics were prepared by reactive spark plasma sintering, using oxides and carbon black as the raw materials. The phase and microstructure evolution during the sintering process was investigated. It was found that ZrC and HfC powder intermediates were formed at 1750 and 1800 °C, respectively. Due to the high sinterability of the in situ formed carbide particles, samples with a fine microstructure could be densified at a relatively low temperature. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The anisotropic initial sintering of oriented LiCoO2 green compacts prepared by slip casting in a strong magnetic field was studied. The activation energy and the mechanism of the initial stage of sintering were analyzed in order to understand the effect of the orientation. The analysis was carried out using constant rate heating (CRH). The activation energy of the initial stages of sintering for random, a, b-axes and c-axis direction was evaluated from the Arrhenius plots of the dilatometric measurements. It was confirmed that the activation energy of the c-axis direction was larger than that of the a, b-axes direction at the initial stage of sintering. The anisotropic shrinkage was attributed to the differences in the surface energies. (C) 2012 Elsevier Ltd. All rights reserved.

Tailoring the crystallographic orientation in piezoelectric ceramics is very useful for improving their properties. Orientation in ceramics can be controlled by templated grain growth, hot forging, etc. We have focused on using a strong magnetic field for the crystallographic orientation even in diamagnetic ceramics. In a previous study, although only a one-directional orientation could be controlled by these methods, it was difficult to control the multi-axis orientation in the ceramics. In this study, we demonstrated that alignments of the c-axis and the &lt
100&gt
axis in Bi4Ti 3O12 piezoelectric ceramics were controlled by using a strong magnetic field as well as platelet particles. We also estimated the degree of orientation by an electron back scattering diffraction analysis. When the magnetic field was applied to the platelet particles, appropriately 80% of the grains were aligned with the tilt angle made by the c-axis and the vertical direction less than 10° and 73% of grains were oriented with the angle between the &lt
100&gt
axis and the magnetic field less than 10°. © 2013 The American Ceramic Society.

Magneto-scientific technique combined with colloidal processing was applied to obtain crystalline-oriented zeolite L seed layers. Well-dispersed non-aqueous suspensions of the zeolite L were prepared for the fabrication of thin seed layers on porous substrates by electrophoretic deposition (EPD) in a superconducting magnet. The c-axis oriented seed layers of the zeolite L was successfully obtained on porous YSZ substrates by EPD under the magnetic field. (C)2013 The Ceramic Society of Japan. All rights reserved.

Textured ceramic materials arouse recently great interest due to the effective improvement of their physical and mechanical properties compared to those not crystalline oriented. Feeble magnetic ceramics, such as alumina can be textured under high magnetic field of 12T during shaping process. The connection between shaping by gelcasting method and crystalline orientation of alpha-alumina in high magnetic field is reported in this paper. Gelcasting allows obtaining high-quality complex-shaped elements with small quantities of organic binders. A new environmentally friendly compound on the basis of glucose (3-O-acryloyl-D-glucose) was synthesized and applied as a monomer in gelcasting process. The ceramic slurries of solid loading 30-50 vol % have been exposed to high magnetic field at the time of consolidation through an in situ polymerization of used monomer. The degree of crystalline orientation of sintered at 1600 degrees C bodies was evaluated by X-ray diffraction (XRD). (C)2013 The Ceramic Society of Japan. All rights reserved.

Preferentially oriented thick and thin compacts of zeolite L with a large anisotropy in their crystal structures were successfully prepared by colloidal processes in a strong 12 T magnetic field. The orientation along the direction of the applied magnetic field was characterized by XRD using slip-cast compacts. In the present experiments, it was revealed that the c-axis of zeolite L was an easy-magnetization axis. The c-axis oriented zeolite L layer with a thickness of ca. 3 μm was formed on a porous ceramics substrate via electrophoretic deposition in a strong magnetic field applied perpendicular to the surface of the substrate. © 2012 Elsevier B.V.

Textured, dense, polycrystalline Ti3AlC2 ceramics was fabricated by spark plasma sintering (SPS) of plate-like Ti3AlC 2 powder nsynthesized by a reactive SPS-heat treatment of elemental Ti, Al and carbon black powders. The relative density was found to nexceed 99% for samples sintered at 1573 K. The Lotgering orientation factor was determined to be f(00l) = 0.69. The crack npropagation behavior near the indentation marks formed by a force of 49N was observed. On the surface parallel to the SPSloading ndirection, the toughening mechanism of crack deflection was observed. n©2013 The Ceramic Society of Japan. All rights reserved.

Porous potassium niobate (KNbO3, KN) system ceramics were prepared by spark plasma sintering (SPS) method using carbon black (CB, 5 mu m). First, the powders of raw materials were mixed in ethanol by ball milling, and then calcined. Obtained KN powders with CB were sintered by SPS in argon atmosphere. Their piezoelectric properties were measured and a relationship between porosity, pore size, and sensor properties was studied. It was found that d(33) increased as pore size decreased. Thus, pore size was important for the improvement of value of g(33)/rho.

Barium titanate (BaTiO3, BT) nanoparticle accumulations were prepared by an electrophoresis deposition (EPD) method, and their dielectric properties were measured. The BTKK accumulation exhibited high dielectric constant of 100. To prepare the BT ceramic/polymer film capacitors, the polymer was injected into the accumulations in vacuum. Finally, dielectric properties were measured, and it was clarified that the dielectric constant of the ceramic/polymer film capacitors became smaller than those of the accumulation because of surfactant used as particle dispersion.

The piezoelectric response of [110]-oriented, fine-grained BaTiO3 ceramics was investigated. It was found that an exposure of the BaTiO3 compacts to high-pressure, high-temperature steam in an autoclave promoted the orientation of the sintered ceramics. As temperature in the autoclave increased, the orientation increased. A large small-field piezoelectric constant of d3(3) = 517 pC/N was observed for the oriented BaTiO3 ceramics with the grain size of 1.76 and the Lotgering factor of 85.3 %.

To improve the energy density and practical realization of the all-solid-state Li-ion secondary battery, the principal requirement is a high electric conductivity in the densely sintered positive electrode. To accomplish this task, we focused on the anisotropic Li-ion and electron conductivities of the LiCoO2. As a result of our work, the ideal design of the texturing, perpendicular alignment of the c-plane and horizontal but random orientation of the c-axis on the electrode, was proposed. The battery performance of the ideal textured cell fabricated using a rotating strong magnetic field has a significantly higher performance than a randomly oriented cell. © 2013 Author(s).

Aiming at designing a high performance cathode for solid oxide fuel cells (SOFC), orientation of the La2NiO4 (LNO) with layered structure was controlled by slip casing in a strong magnetic field. The oriented LNO compact along a, b-axes was successfully fabricated in a static magnetic field. The c-axis oriented one was managed by applying a rotating magnetic field perpendicular to the slip casting direction. Enhanced conductivities were valid along a,b-axes orientation which resulted in the accelerated mobility of conducive carriers. From those results, it is clearly expected that the orientation control of LNO brings about high performance in the cathode of SOFC.

Porous MgTi2O5 ceramics with pseudobrookite-type structure have been prepared by in situ processing (viz. reactive sintering). In this communication, further studies have been carried out in order to evolve the porous MgTi2O5, viz., (1) X-ray absorption fine structure (XAFS) study of porous MgTi2O5, (2) improved in situ synthesis (i.e., more precise stoichiometric control), and (3) new in situ surface coating, which enables in situ MgTi2O5 synthesis, in situ uniform pore formation, and in situ surface coating in only one-step heating.

We attempted to fabricate the oriented bulk LiCoO2 using slip casting in a strong magnetic field. The shrinkage of the oriented green compact was measured using a dilatometer. It was confirmed that the oriented green compact undergoes anisotropic shrinkage. The shrinkage in the c-plane direction of the oriented LiCoO2 was greater than that in the c-axis direction. The degree of orientation in the bulk LiCoO2 was analyzed using XRD and electron backscatter diffraction; the c-axis of LiCoO2 was oriented parallel to the magnetic field. Moreover, the orientation parameter, r, was 0.234, indicating that 92% of the grains was aligned with a tilt angle less than 10 degrees between the c-axis and the magnetic field direction. The texturing led LiCoO2 to anisotropy in the electric conductivity between the c-plane and c-axis directions. It was concluded that the magneto-scientific technique is a powerful method to fabricate highly oriented bulk LiCoO2.

We present a novel application of gelcasting in a strong magnetic field for texture development in the ternary MAX phase carbide-Ti3SiC2. The applicability of a low-toxic and water soluble monomer-glycerol monoacrylate for gelcasting Ti3SiC2 has been shown. Textured green bodies of Ti3SiC2 with a,b-axis oriented along the direction parallel to the applied magnetic field could be fabricated. The relative green density was found to increase from 34 to 58% with increasing solid-loading (30 to 55 vol %) of the suspension but at the cost of the degree of orientation. The Lotgering's orientation factor- f(L(001)) - on the textured top surfaces varied from 0.81 to 0.2 as the solid-loading increased from 30 to 55 vol %. (C)2012 The Ceramic Society of Japan. All rights reserved.

最近、我々は、水系スラリーのEPDにおいて、通常の連続通電場ではなくDCパルス電場（矩形波）を印加すると、気泡発生のない良好な膜質の堆積層が形成される場合があることを見出し、粒子堆積速度や気泡生成・抑止に及ぼす条件を系統的に検討してきた。この方法は、印加する電場のパルス電圧・電流やON/OFF時間の制御だけで、電極基板の材質によらず、また、カソードでポジション、アノードでポジションのいずれのケースにおいても適用できる。本稿では、直流パルス電場を用いたEPDプロセスとその特徴について、最近のデータを紹介して解説する。

現在のセラミックスにおける磁場配向技術では、そのほとんどが結晶軸の一軸のみの配向制御にとどまっているが、組織制御としては配向の多軸化へとその高度化が望まれる。上記のように様々な材料への展開が可能なTGGプロセスおよび磁場プロセスを組み合わせたセラミックスプロセスを新規に提案することで、より精緻な配向構造を制御できると期待できる。そこで、本報においては、この配向方位の多軸化の取り組みとして、板状粒子と強磁場を組み合わせた組織制御による2軸配向を試みたので紹介する。

The microstructure control of NiO-YSZ for SOFC anode was performed using rice starch as pore former. Positively-charged NiO-YSZ slurry and negatively-charge rice starch slurry were heterocoaglated and then filtrated to prepare green plates. The rice starch was burnt out by sintering in air and porous NiO-YSZ electrode was obtained. The surface of NiO-YSZ substrate was coated with conductive polypyrrole to give electric conduction that is essential for EPD processing. The GDC/LSGM/GDC laminar coating was conducted by sequential deposition on the same substrate. The electrolyte layers were easily sintered together on the anode without cracking and peering-off at the interfaces.

We attempted to fabricate the oriented bulk LiCoO2 using slip casting in a strong magnetic field. The degree of orientation in the bulk LiCoO2 was analyzed using electron backscatter diffraction; the c-axis of LiCoO2 was oriented parallel to the magnetic field. Moreover, the orientation parameter, r, was 0.234, indicating that 92% of the grains was aligned with a tilt angle less than 10° between the c-axis and the magnetic field direction. The texturing led LiCoO2 to anisotropy in the electric conductivity between the c-plane and c-axis directions. It was concluded that the magneto-scientific technique is a powerful method to fabricate highly oriented bulk LiCoO2.

In this study,we have shown the applicability of electrophoretic deposition (EPD) for shape-forming in Ti3SiC2-a representative MAX phase; and viability of texture development thereof by application of a strong magnetic field (12 T). The dispersion characteristics of Ti3SiC2 suspension were investigated in terms of surface charge, rheological measurement, and adsorption study. Polyethyleneimine has been used as dispersant to stabilize the suspension. It was found that the iso-electric point (IEP) of Ti3SiC2 powder was pHIEP 4. The surface charge of powder changed in presence of the Polyethyleneimine dispersant and IEP shifted significantly towards basic pH 10. The shift in IEP has been quantified in terms of ?G0SP, the specific free energy of adsorption between the surface sites and the adsorbing polyelectrolyte (PEI) (The value of ?G0SP obtained is -9.521 RT units). The optimized suspension parameters for EPD were determined as 10 vol% Ti3SiC2 and 1 dwb PEI in 50% ethanolic water at pH similar to 7. X-ray diffraction analysis of the textured samples developed, revealed that the preferred orientation of Ti3SiC2 grains parallel to the magnetic field direction was along the a, b-axis (The Lotgering orientation factors on the textured top surface and textured side surface were determined as fL(hk0) = 0.35 and fL(00l) = 0.75, respectively).

異方性工学研究会では、「新しい有用人工物を生み出すために、物質や材料の持つ異方的な性質を解明する、または創造する、または積極的に利用する科学と技術」を「異方性工学」と定義している。これらの定義から言えば、形状や異方的な特性をもつ物質と材料そのものについてと、その異方的な特性を付与することと微構造を制御するプロセスとについても異方性工学として扱うことになる。異方性というキーワードで俯瞰した場合には、気体と液体を除くほぼすべての材料が当てはまり広範にわたるため、ここでは形状や結晶方位などの異方性を揃える、また、異方性を組み合わせるデザインをすることで特性を引き出された材料とそれらの材料を創製するプロセスについてバルクセラミックスを中心として総説を述べる。

We report that hydrogen gas can be easily produced from water at room temperature using a Mg nanopowder (30-1000 nm particles, average diameter 265 nm). The Mg nanopowder was produced by dc arc melting of a Mg ingot in a chamber with mixed-gas atmosphere (20% N-2-80% Ar) at 0.1MPa using custom-built nanopowder production equipment. The Mg nanopowder was passivated with a gas mixture of 1% O-2 in Ar for 12 h in the final step of the synthesis, after which the nanopowder could be safely handled in ambient air. The nanopowder vigorously reacted with water at room temperature, producing 110 ml of hydrogen gas per 1 g of powder in 600 s. This amount corresponds to 11% of the hydrogen that could be generated by the stoichiometric reaction between Mg and water. Mg(OH)(2) flakes formed on the surface of the Mg particles as a result of this reaction. They easily peeled off, and the generation of hydrogen continued until all the Mg was consumed.

Oriented compacts of mordenite zeolite with an orthorhombic structure were successfully fabricated in a strong magnetic field up to 12 T by a slip casting process. The magnetic orientation was achieved by removing the large agglomerated particles from the suspensions prior to the slip casting. The b-axis oriented compacts of mordenite were fabricated in a static magnetic field. On the other hand, the c-axis orientation was made in a rotating magnetic field which was artificially produced by rotating a vessel put on a turntable in a horizontally-placed magnet. The c-axis was preferentially aligned perpendicular to the plane on which the magnetic field was rotated. The controlled orientation of mordenite was based on the anisotropic magnetic properties in the orthorhombic mordenite crystals. (c) 2011 Elsevier Inc. All rights reserved.

ゼオライトはアルミノケイ酸塩のなかで結晶構造中に比較的大きな空隙を持つものの総称であり、ナノサイズの細孔や取り込まれたカチオンの種類がゼオライトの様々な機能性を発現させる要因となり、分子ふるい、触媒、吸着材として利用されている。ランダムに配列した細孔を用いた場合には、これらの機能が相殺されてしまったり、十分にその特性を引き出すことが出来ないこともある。その場合、細孔を一方向に配列させることで、光学、電気機能だけでなく分子ふるい等の機能においても、その特性を効果的に利用することが期待できる。例えば、モルデナイトは、b軸とc軸に径が異なる細孔を持つため、それぞれの細孔の向きを揃えることで、精緻に細孔を使用することができるようになると期待される。ここでは、それぞれの細孔を使い分けするために結晶磁気異方性を用いて直径1nm以下の細孔の方向制御を行うことを試みた結果を紹介する。

Fabrication of textured hematite was achieved from paramagnetic goethite by electrophoretic deposition in a strong magnetic field followed by thermal treatment via topotactic phase transformation. The textured microstructure of the hematite was characterized by XRD and SEM observations. It was confirmed that the a,b-axes of the goethite were taken over the c-axis of the hematite through the topotactic phase transformation The magnetization vs magnetic field measurement using a VSM revealed that the textured hematite showed an anisotropic magnetic property depending on the direction of the crystalline orientation.

We present a method for fabrication of textured MAX phase ceramics, particularly, Ti3SiC2; by EPD in a strong magnetic field (12T). Ti3SiC2 was dispersed in cationic polyelectrolyte-Polyethylenimine (PEI). Addition of 0.3-1dwb PEI resulted in high zeta potential values and suspension was found to be stable and of good fluidity. The optimized suspension parameters for EPD were determined as 10vol% Ti3SiC2 and 1dwb PEI in 50 % ethanolic water at pH similar to 7. X-ray diffraction analysis of the textured samples revealed that the preferred orientation of Ti3SiC2 grains parallel to the magnetic field direction was along the a,b-axis. The Lotgering orientation factors on the textured top surface and textured side surface were determined as f ((hk0)) = 0.35 and f ((001)) = 0.75, respectively.

Low-temperature formation routes of lanthanum silicate and neodymium silicate oxyapatites were analyzed by a combination of powder X-ray diffraction and thermogravimetric/differential thermal analysis by using precursors prepared from the water-based sol-gel method. Oxyapatite phase was found to form at about 1073 K in the case of lanthanum silicate and at about 1273 K in the case of neodymium silicate - temperatures much lower than those for a conventional solid-state reaction method. In each system, the oxyapatite phase was formed after decomposition of the lanthanoid oxycarbonate or metastable lanthanoid oxide. In particular, decomposition of lanthanum oxycarbonate was found to play an important role in lanthanum silicate oxyapatite formation. In addition to proposing a crystal structure for the lanthanoid oxycarbonate, we hypothesize an in-situ chemical pulverization process due to the delamination of lanthanoid oxide by carbon dioxide dissociation. (C) 2011 Elsevier B.V. All rights reserved.

LiCoO2 is a popular positive electrode material for Li-ion secondary batteries. The perpendicular alignment of the interlayer of the LiCoO2 lattice on the electrode contributes to easy access of Li-ions. In this study, we report the preparation of an oriented LiCoO2 sheet using the conventional coating method followed by drying in a maximum 12 T strong magnetic field. We discuss the effect of the particle shape and viscosity of the paste on the degree of orientation. As a result, when the sheets are dried in a strong horizontal magnetic field, the electrochemical active planes of the LiCoO2 are aligned perpendicular to the sheet surface. (C) 2011 The Ceramic Society of Japan. All rights reserved.

Silicon carbide is a very important material for various applications and its properties are expected to be improved by controlling the crystallographic orientation. It was difficult to simultaneously consolidate SiC powder and sintering additives by electrophoretic deposition (EPD) because of the Afferent electrophoretic mobility. When using the alumina-coated SiC by the sol-gel method, it is possible to deposit SiC and sintering additives by EPD at the same time.
In this study, we demonstrated that the c-axis alignment of SiC was controlled by EPD and a strong magnetic field, and we investigated the effect of the surface-modification on the microstructure and the degree of orientation. The dilute solution and the large number of repeated coating times prevent the oxide phase from precipitating at the multiple grain junctions and enhance grain growth. The grain growth promoted the degree of orientation in the textured SiC prepared by EPD in a strong magnetic field. (C) 2011 The Ceramic Society of Japan. All rights reserved.

アーク溶解法によるNb精錬過程で表面清浄なNb(Zr)‐Fe 系合金は，室温，大気圧下で水素と接触させることにより，合金が粉化することが判明した．この事実を基に各種Nb-Zr-Fe 合金の粉化を試みるとともにその領域を探索した．合金が粉化する様子をビデオカメラで観察し，粉化時に生ずる気流の駆動力の成因について考察した． 各種組成のNb, Zr, Fe 三元合金（35種類）を作製して水素による粉化する領域を探索し．極めて広範囲の組成域が粉化することが判明した．合金組成により粉化の特性は異なるが，微細粉を作るとの観点よりすればFe 濃度を15 〜 30at% に固定してNbとZr 割合が同量付近の組成が最適であった．一例として45Nb40Zr15Fe合金の微細粉の粒径は0.6ミクロン（比表面積測定）で，その水素吸収濃度は1.8wt%, 水素放出の最大ピーク温度は473K〜503Kであった．Nb-Zr-Fe三元合金が微粉化する条件は，適量のFe が合金中に含有されることであると考えられる．

Titania is a very important material for various applications and its properties are expected to be improved by controlling the crystallographic orientation. In this study, we demonstrated that the c-axes of both rutile and anatase were aligned parallel to a magnetic field and we investigated the effect of the orientation on the microstructure development and the effect of the transformation from anatase to ruffle on the orientation during heating. When using rutile as the starting material, the c-axis was aligned and the elongated grains were aligned after sintering. When using anatase as the starting material, the c-axis of anatase was aligned parallel to the magnetic field. However, after transformation, the rutile had a tilt and the anisotropic grain growth was suppressed. (C) 2011 The Ceramic Society of Japan. All rights reserved

Highly textured Ti3SiC2 ceramic was successfully fabricated by slip casting in a 12 T strong magnetic field followed by spark plasma sintering. The optimized suspension parameters for slip casting were determined as 20 vol% Ti3SiC2 and 1.5 wt% polyethyleneimine dispersant of powder in deionized water. After texturing in the 12 T strong magnetic field and then cold isostatic pressing, the relative densities of green bodies were 51.4% and 63.8%, respectively. X-ray diffraction analysis revealed that the preferred orientation of Ti3SiC2 grains perpendicular to the magnetic field direction was along the c-axis. After sintering at 1100 degrees and 1000 degrees C under the pressure of 120 and 500 MPa, respectively, the relative density of Ti3SiC2 reached 88.2% and 98.6%. The Lotgering orientation factors on the textured top surface and textured side surface were determined as f((00l))=0.95 and f((hk0))=0.31, respectively. The textured microstructure contributed to the anisotropic mechanical property tested by Vickers indentation.

ナノセラミックスセンターでは，光，電磁機能，耐熱性や高強度といった基本的特性の先鋭化に加えて，これらの特性を意図的に重畳あるいは洗練させた多機能性のイノベイティブセラミックスを創製すること目指している。本総説では，外場を作用させたコロイドプロセスを中心とした研究を紹介する。

High-hardness B4C was prepared by sintering samples textured by a strong magnetic field alignment technique (12 T). The c-axis was highly oriented perpendicular to the applied magnetic field. The hardnesses measured on the surface perpendicular and parallel to c-axis were 38.86 +/- 2.13 and 31.31 +/- 0.79 GPa, respectively. The high values of hardness and elastic modulus were in agreement with those reported for B4.38C monocrystal. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Grain-oriented Barium titanate (BaTiO3) ceramics were prepared using an electrophoresis deposition (EPD) method under high magnetic field of 12 T and sintering at 1350 degrees C. It was found that BT03 and BTKK nanoparticles were necessary to synthesize the grain-oriented BT ceramics. The grain orientation was correlated with particles size and c/a ratio of lattice constants. The reason why the grain-oriented BT ceramics using the BT03 and BTKK were prepared was having the large values of the particles size and the c/a ration of lattice constants.

Effect of the microstructural homogeneity of 0.5 BaTiO3 - 0.5 KNbO3 (0.5BT-0.5KN) solid solution ceramics on the dielectric and piezoelectric properties was investigated. Microstructure of a sample prepared by a conventional sintering method was homogenous, and the room temperature crystal structure was assigned to cubic Pm3m symmetry and therefore the sample was paraelectric. On the other hand, microstructure of samples prepared by a two-step sintering method was inhomogeneous, that is, it was made of BT and KN grains. The large electric field piezoelectric constant d(33)* increased with increasing interface area.

Oriented PbTiO3 ceramics were obtained by slip casting under a high magnetic field, and the orientation factor was 90%. Such highly oriented perovskite ceramics by slip casting under a high magnetic field have never been reported as far as we know. It was thought that dispersibility and crystallinity of the powder were important for orientation by slip casting under a high magnetic field. In this study, we controlled the dispersibility and crystallinity of powder by calcination temperature. As a result, the sample obtained from the powder calcined at 1100 degrees C was oriented, but the one obtained from the powder calcined at 900 degrees C was not. The powder calcined at 900 degrees C is more aggregated than that at 1100 degrees C and the crystallinity of the powder calcined at 1100 degrees C is higher than that of the powder calcined at 900 degrees C. It became clear that highly oriented PbTiO3 ceramics can be fabricated from the powder with high dispersibility and high crystallinity by slip casting under a high magnetic field. (c) 2011 The Ceramic Society of Japan. All rights reserved.

KBaTiNbO6, i.e., 0.5BT-0.5KN complete solid solution ceramics and barium titanate (BaTiO3, BT) - potassium niobate (KNbO3, KN) system (0.5BT-0.5KN) ceramics with various microstructures were prepared by conventional sintering method and two-step sintering method. The 0.5BT-0.5KN with diffusion of BT and KN completely were paraelectrics. Their microstructures were investigated using X-ray diffraction (XRD) measurement and scanning electron microscopy (SEM). KBaTiNbO6 at room temperature was assigned to cubic Pm3m symmetry. For the 0.5BT-0.5KN patially solid solution system ceramics, the control of the interface area between two phases was important to enhance piezoelectric property. Their piezoelectric property was measured, and the apparent piezoelectric constant d(33)* increased with increasing interface area.

Dense barium titanate (BaTiO3, BT) nanoparticle accumulations were prepared by an electrophoresis deposition (EPD) method using three kinds of BT nanoparticles with different particles sizes and tetragonality. First, the BT particles were dispersed into ethanol using ball-milling technique, and an optimum milling condition was investigated. As the results, it was confirmed that ball-milling led to a formation of mixture between single-dispersed nanoparticles and aggregated particles. Thus, the aggregated particles in the slurry were removed by a centrifuge in order to obtain narrow the size distribution. Using well-dispersed slurry, BT nanoparticle accumulations were deposited on paradigm electrode by the EPD method. Despite various BT nanoparticles, the dense BT nanoparticle accumulations were obtained at relative densities of around 60%. Mier gold electrode deposition on the both surfaces of the accumulations by spattering method, dielectric properties were measured at 20 degrees C, the highest dielectric constants of around 160 was measured at 10 MHz.

Barium titanate (BaTiO3) grain-oriented ceramics were prepared using electrophoresis deposition (EPD) method under high magnetic field of 12 T. First, BaTiO3 nanoparticles with high c/a ratio of 1.008 and size of 84 nm were prepared by two-step thermal decomposition method with barium titanyl oxalate nanoparticles. Using the BaTiO3 slurry, BaTiO3 nanoparticle accumulations were prepared by EPD method under high magnetic field. After binder burnout, the accumulations were sintered and BaTiO3 grain-oriented ceramics were prepared. Moreover, dielectric properties of their ceramics were investigated

KBaTiNbO6, i.e., 0.5BT-0.5KN complete solid solution ceramics and barium titanate (BaTiO3, BT) - potassium niobate (KNbO3, KN) system (0.5BT-0.5KN) ceramics with various microstructures were prepared by conventional sintering method and two-step sintering method. The 0.5BT-0.5KN with diffusion of BT and KN completely were paraelectrics. Their microstructures were investigated using X-ray diffraction (XRD) measurement and scanning electron microscopy (SEM). KBaTiNbO6 at room temperature was assigned to cubic Pm3m symmetry. For the 0.5BT-0.5KN patially solid solution system ceramics, the control of the interface area between two phases was important to enhance piezoelectric property. Their piezoelectric property was measured, and the apparent piezoelectric constant d(33)* increased with increasing interface area.

ANbO(3) - BaTiO3 (A=K, Na, or K0.5Na0.5) system ceramics were prepared using a conventional sintering method, and their dielectric properties were investigated. It was found that the dielectric constant of KNbO3-BaTiO3 system ceramics did not strongly depend on temperature between 20 and 400 degrees C, making them useful for capacitor application. However, the dielectric constant of KNbO3-BaTiO3 system ceramics was low. The high dielectric constant is attributable to a large area of interfaces between KN and BT grains. Ceramics sintered by spark plasma sintering (SPS) are expected to suppress a grain growth, increasing area of the interfacial layer. In this study, SPS method was employed to achieve a large area of the interfaces and to see how the dielectric properties change with the interfacial structure. The structure was controlled by changing sintering temperatures and time of the spark plasma sintering. As a result, X-ray diffraction patterns showed that perovskite single phase and their relative densities were greater than 97%. By contrast, the dielectric constant was decreased.

We have studied the combined effects of the templated grain growth and magnetic alignment processes on sintering, anisotropic sintering shrinkage, microstructure development and texture in ZnO ceramics. Suspensions of 0-10 vol % ZnO template particles were slip cast in a 12 T rotating magnetic field. Sintering and texture characteristics were investigated via thermomechanical analysis and electron backscatter diffraction, respectively. Sintering as well as texture characteristics depend on template concentration. For the studied ZnO system, there is a critical template concentration (2 vol % in this study) above which densification is limited by the templates owing to constrained sintering. Below this limit, the densification is enhanced and the anisotropic shrinkage is reduced, which is attributed to densifying characteristics of the templates.

In general, the mechanical and physical properties of a crystal depend on the direction of the crystal axis. The controlled development of the crystallographic texture in ceramics is very useful for improvement of their properties. The preparation of the textured SiC polycrystal was achieved by slip casting in a strong magnetic field. The effects of the sintering conditions and sintering additives on the degree of orientation in the SiC were investigated. The pressing during the liquid phase sintering prevented the development of a texture in the SiC prepared by slip casting in a strong magnetic field. (C) 2010 Elsevier Ltd. All rights reserved.

優れた特性を発現させる手法として，組織の配向制御が注目されている．従来，反磁性体や常磁性体は，非磁性体として扱われてきたが，10Tを超える強磁場では結晶磁気異方性を利用した配向制御が可能になった．ここでは，アルミナを例として，コロイドプロセスによる配向制御の概要と配向制御に必要なプロセス因子の要件，またその適用例を紹介する．

先端科学技術としてのファインセラミックス分野，また，伝統工芸を含む広義のセラミックス産業を今後発展させていくためには，若手人材の育成がますます重要な課題となっている．本稿では，日本セラミックス協会年会などに毎回優れた作品を出展している，大阪市立泉尾工業高校，愛知県立瀬戸窯業高校，佐賀県立有田工業高校，愛知県立常滑高校，岐阜県立多治見工業高校を訪問し，高校におけるセラミックス教育の現場をレポートした。

The easy-magnetization axis of mordenite zeolite was determined using commercially available mordenite powder. The well-dispersed suspension of the powder was consolidated by slip casting in a 12-T static magnetic field. The thick bulk deposit was cut into a dice in order to investigate the XRD patterns from the mutually orthogonal surfaces of the consolidated mordenite compacts, the normal lines of which surfaces were parallel and perpendicular to the applied magnetic field. The easy-magnetization axis of mordenite was determined to be the b axis based on the XRD measurements.

Experimental measurement and verification of the pH localization at the electrode/solution interface was conducted during continuous and pulsed DC electrophoretic deposition (EPD) from aqueous solution. Application of pulsed DC enabled controlling bubble incorporation and obtaining bubble-free deposits during electrophoretic deposition (EPD) from aqueous suspension. The pH localization at the electrode/solution interface on application of electric field was attributed as the underlying mechanism of particle consolidation during continuous as well as Pulsed EPD. The Suspension pH tends to shift towards isoelectric point (i.e.p.) leading to spontaneous coagulation of particles at the electrode. Application of continuous DC tends to attain the i.e.p. faster and closer compared to pulse DC leading to maximum deposit yield. The kinetics and closeness of attainment of pH towards i.e.p. decreased progressively with decreasing Pulse size resulting in a corresponding decrease in deposit yield. (C) 2009 Elsevier Ltd. All rights reserved.

The fabrication of c-axis oriented zinc oxide was attempted by electrophoretic deposition (EPD) in a rotating magnetic field. The EPD was conducted in a small container which was placed on a turntable arranged in a Superconducting magnet. The suspension was rotated at 0-90 rpm in a 12 T magnetic field during the deposition. The deposits were dried and then sintered at 1400 degrees C for 2 h. The degree of the c-axis orientation was evaluated by the Lotgering factor calculated from the X-ray diffraction data. (C) 2009 Elsevier Lid. All rights reserved.

The dehydrogenation kinetics of Ti600, TC21 and Ti40 alloys has been studied using a tubular thermohydrogen processing furnace and simultaneous DTA-TG apparatus. The results show that the initial dehydrogenation temperatures in Ti600, TC21 and Ti40 alloys were 580 degrees C, 600 degrees C and 540 degrees C, respectively. At the initial stage of dehydrogenation, the passive layer on the alloy surface was the barrier to enhance the diffusion activation energy. Therefore, activation energy decreased with the increase of reacted fraction. At the initial stage, values of activation energy for the three alloys were 255 kJ/mol, 322 kJ/mol and 177 kJ/mol, respectively. After incubation period, the dehydrogenation average values of activation energy were 200 +/- 5 kJ/mol, 240 +/- 5 kJ/mol and 155 +/- 5 kJ/mol, respectively. (C) 2009 Elsevier B.V. All rights reserved.

Electrophoretic Deposition（EPD）法は、セラミックスなどの粒子を液中で帯電、分散させ、そのサスペンションに電場を印加し粒子をその表面電荷と正負の異なる電極方向に電気泳動させて、基材上に粒子堆積層を形成させる固化成形法である。電気泳動堆積法、泳動電着法または単に電気泳動法などとも呼ばれ、比較的均一な粒子堆積膜が低コストかつ短時間で得られる簡便な方法として注目されている。本稿では、電気泳動プロセスの概略を解説し、ナノ粒子集積技術としての電気泳動プロセスの利点について紹介する。

Textured PbTiO3 (PT) ceramics were fabricated by slip casting in a high magnetic field of 12 T. The sample obtained from the powder calcined at 1100 degrees C was (100), (010), and (001)-oriented, and the orientation factor was 90 %. On the other hand, the sample obtained from the powder calcined at 900 degrees C was not oriented. Aggregability and crystallinity of powder are an important factor when textured ceramics are fabricated by slip casting in a high magnetic field.

Dense bulk ZrB(2) ceramic was synthesized by mechanical alloying (MA) and followed spark plasma sintering (SPS) using zirconium and boron as initial materials. It was found that MA process was effective to fragment the coarse metal zirconium particles from 45 mu m to less than 1 mu m within 20 hours. In comparison with the commercial ZrB(2) powder, the as-obtained zirconium and boron mixture powders showed higher sinterability. When the sintering was carried out at 1800 degrees C, the relative density of synthesized ZrB(2) samples using mixture powder was above 95%, higher than that of ZrB(2) sample prepared using commercial powder (73%). Vickers hardness of those ZrB(2) samples was at the same level of 15 GPa. However, the fracture toughness of ZrB(2) samples seemed to depend on the heating rate of the SPS process. Corresponding to the heating rates of 10, 50, and 100 degrees C/min, the fracture toughness of as-prepared ZrB(2) samples were 3.83, 3.19, and 2.74 MPa.m(1/2), respectively.

The c-axis texture development in seeded Si3N4 with beta-Si3N4 whiskers by slip casting in a rotating magnetic field was investigated by powder X-ray diffraction, scanning electron microscopy and thermal anisotropy evaluation, including the effects of magnetic flux density, suspension rheological properties and rotational speed. By increasing the magnetic flux density from 1 to 12 T, the c-axis orientation of beta-Si3N4 whiskers is achieved in the well-dispersed 30 vol.% suspension but hindered in the flocculated 40 vol.% suspension. The degree of orientation tends to decrease with increasing rotational speed from 5 to 30 rpm. The green body shows no density gradient but nonuniform orientation of beta-Si3N4 whiskers regardless of the rotational speed, resulting in the similar nonuniform texture in the sintered body. The nonuniform texture is featured in three major layers: lower surface, inner region and upper surface, corresponding to the lower, higher and lower e-axis orientation, respectively. The resultant c-axis textured Si3N4 exhibits thermal anisotropy as high as 55%, slightly lower than the intrinsic thermal anisotropy (62%) of beta-Si3N4. A theoretical analysis is performed to help understand the key factors affecting the orientation of beta-Si3N4 whiskers by slip casting in the rotating magnetic field. The formation mechanisms of the nonuniform texture were discussed. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Barium titanate (BaTiO3, BT) - potassium niobate (KNbO3, KN) solid solution system (0.5BT-0.5KN) ceramics with various microstructures were prepared by conventional sintering method and two-step sintering method using BT and KN nanoparticles. Their microstructures were investigated using X-ray diffraction (XRD) measurement and scanning electron microscopy (SEM), and it was confirmed that two ferroelectric phases, i.e., BT-rich tetragonal and KN-rich orthorhombic phases, always coexisted for all ceramics, which suggested that 0.5BT-0.5KN ceramics had "pseudo-morphotropic phase boundary (MPB)" structure. Thus, the control of the interface area between two phases was important to enhance piezoelectric property. Finally, their piezoelectric property was measured, and the apparent piezoelectric constant d(33)* increased with increasing interface area.

Barium titanate (BaTiO3, BT) grain-oriented ceramics along [110] direction were prepared by a templated grain growth (TGG) method. The [110] oriented BT platelike particles (t-BT) were used as template particles. BT grain-oriented ceramics with higher relative density (D-rel) over 95 %, high degree of orientation along [110] direction (F-110) over 80% and grain sizes around 30 mu m were successfully prepared using only the template particles. The relationship between microstructures and piezoelectric constant (d(33)) was investigated. The higher F-110 was, the higher D-rel and the smaller grain size were required for enhancement of the piezoelectric properties.

The formation of thin tri-layers of Sr- and Mg-doped lanthanum gallate (LSGM) and Gd-doped ceria (GDC) solid electrolytes was performed by electrophoretic deposition (EPD) on a Ni-YSZ anode for use in solid oxide fuel cell (SOFC) applications. The surface of the NiO-YSZ substrate was coated with a conductive polypyrrole to provide electric conduction, which is essential for the EPD processing. The GDC/LSGM8282/GDC laminar coating was performed by sequential deposition on the same substrate. The electrolyte layers were easily sintered together on the anode without cracking and peering-off at the interfaces. (C) 2009 The Ceramic Society of Japan. All rights reserved.

配向（集合）組織制御は、多結晶材料の諸特性を最大限まで高める有効手段として研究されている。金属材料では、加工・再結晶等の手法により比較的容易にその形成・制御が可能であるのに対し、脆性なセラミックスでは高機能化に向けた配向制御手法の開発が課題となっていた。近年、著者により磁場（外場）を用いた新規配向制御プロセスが開発され、種々のセラミックスに応用可能であること、また、特性向上が期待できることが確認されれてきている。そこで、磁場配向プロセスの原理からセラミックスの高・多機能化の例について紹介し、セラミックスにおける配向制御の有効性について解説した。

The preparation of oriented AlN bulk ceramics with and without additives was achieved by slip casting in a high magnetic field. The a and b axes of the AlN were aligned parallel to the direction of the magnetic field. The degree of crystallographic orientation was controlled by the viscosity of the slurry and the grain growth during sintering attributed to the sintering additives. The mechanical properties of the textured AlN depended on the direction of the crystallographic orientation. (C) 2009 Elsevier Ltd. All rights reserved.

We have developed a method of forming textured tetragonal zirconia. A suspension containing 10 vol% solid loading of monoclinic ZrO(2) mixed with 3 mol% Y(2)O(3) was prepared, and then a bead-milling process was performed using 50 mu m diameter zirconia beads resulting in a well-dispersed suspension. The mixture suspension of monoclinic zirconia and yttria nanoparticles was slip cast under a magnetic field of 12 T to produce oriented monoclinic zirconia with yttria. The reaction sintering between yttria and the oriented monoclinic zirconia produces a final 3 mol% Y(2)O(3) doped tetragonal zirconia that remains oriented. (C) 2009 Elsevier Ltd. All rights reserved.

Electrophoretic deposition (EPD) from aqueous suspension generally forms deposits containing enormous pores because of evolution of hydrogen gas at cathode and oxygen at anode due to electrolysis of water on application of DC electric field. We have demonstrated through this investigation on aqueous EPD of alumina suspension as an example that application of pulsed DC instead of the conventionally used continuous DC is a convenient and effective way to control and suppress the amount of bubble incorporation in the deposit. Bubble-free deposits of reasonable yield were obtained at suitable pulse widths and/or duty cycle. The deposit yield and bubble incorporation decreased progressively with decrease in the pulse width and duty cycle of the applied pulse current. A characteristic deposition window was found in the current vs. pulse width plot within which smooth and bubble-free deposits are obtained. The window is wider at low-applied currents compared to that at higher currents implying that it is easier to control the pulsed EPD at lower applied currents. No deposition occurred below the window whereas deposits with incorporated bubbles formed above the window. Possible mechanisms involved in pulsed EPD have been advocated on the basis of amount of hydrogen evolved/pulse due to the electrolysis of water. The discrete amount of H(2) evolved/pulse was higher for larger pulse widths leading to incorporation of more bubbles and vice versa. This was verified by monitoring the gain in weight of palladium (Pd) electrode used as cathode for electrolysis experiment since it is known to absorb hydrogen. (C) 2009 Published by Elsevier Ltd.

配向（集合）組織制御は、多結晶材料の諸特性を最大限まで高める有効手段として研究されています。金属材料では、加工・再結晶等の手法により比較的容易にその形成・制御が可能であるのに対し、脆性なセラミックスでは高機能化に向けた配向制御手法の開発が課題となっていました。 近年、著者により磁場（外場）を用いた新規配向制御プロセスが開発され、種々のセラミックスに応用可能であること、また、特性向上が期待できることが確認されました。そこで、磁場配向プロセスの原理からセラミックスの高・多機能化の例について紹介し、セラミックスにおける配向制御の有効性について解説します。

We have performed neutron diffraction experiments on highly oriented alpha-Al2O3, obtained by slip casting under a magnetic field and sintering. In order to investigate the magnetic field, B, and sintering temperature, T-sint, dependence of the degree of alignment of the orientation, we used samples treated with systematically varied B up to 12 T and T-sint up to 1600 degrees C. The degree of alignment of the magnetic easy axis (the hexagonal c-axis) is rapidly enhanced by sintering above 1200 degrees C, which is coincident with the temperature at which crystal grains start to grow. The angular distribution of the c-axis for the sample sintered at 1600 degrees C, obtained by omega-scan neutron diffraction profiles, is almost coincident with the probability distribution calculated for the particle size two times larger than that in the starting material. We discuss the orientation process mechanism with sintering in light of the results of this analysis.

The advantages of a good colloidal processing of tetragonal zirconia for achieving a full densification and a small grain size were determined in this study. The optimization of slurry preparation was studied to obtain well-dispersed suspensions. A deagglomeration technique was applied by bead-milling using grinding media of 50 mu m diameter and initial particle size and green density were improved. Colloidal processing was considered responsible for the improvements of particle packing that increase the green density. A conventional sintering at low temperatures and two-step sintering were observed to be more effective with the final bead-milling treatment. (C) 2009 The Ceramic Society of Japan. All rights reserved.

The effect of starting powders on the sintering of nanostructured tetragonal zirconia was evaluated. Suspensions were prepared with a concentration of 10 vol.% by mixing a bicomponent mixture of commercial powders (97 mol.% monoclinic zirconia with 3 mol.% yttria) and by dispersing commercially available tetragonal zirconia (3YTZ, Tosoh). The preparation of the slurry by bead-milling was optimized. Colloidal processing using 50 mu m zirconia beads at 4000 rpm generated a fully deagglomerated suspension leading to the formation of high-density consolidated compacts (62% of the theoretical density (TD) for the bicomponent suspension). Optimum colloidal processing of the bicomponent suspension followed by the sintering of yttria and zirconia allowed us to obtain nanostructured tetragonal zirconia. Three different sintering techniques were investigated: normal sintering, two-step sintering and spark plasma sintering. The inhibition of grain growth in the bicomponent mixed powders in comparison with 3YTZ was demonstrated. The inhibition of the grain growth may have been caused by inter-diffusion of cations during the sintering.

The magnetic anisotropies and easy axes of magnetization at room temperature were determined, and the effects of rare-earth (RE) ions were clarified for RE-based cuprates, RE-doped bismuth-based cuprates and RE-doped Bi-based cobaltite regarding the grain orientation by magnetic field. The easy axis, determined from the powder orientation in a static field of 10 T, depended qualitatively on the type of RE ion for all three systems. On the other hand, the magnetization measurement of the c-axis oriented powders, aligned in static or rotating fields, revealed that the type of RE ion strongly affected not only the directions of the easy axis but also the absolute value of magnetic anisotropy, and an appropriate choice of RE ion is required to minimize the magnetic field used for grain orientation. We also studied the possibility of triaxial grain orientation in high-critical-temperature superconductors by a modulated oval magnetic field. In particular, triaxial orientation was attempted in a high-oxygen-pressure phase of orthorhombic RE-based cuprates Y2Ba4Cu7Oy. Although the experiment was performed in epoxy resin, which is not practical, in-plane alignment within 3 degrees was achieved.

Highly oriented transparent (Sr,Ba)Nb2O6 (SBN) ceramics were prepared to obtain excellent electrooptic properties and a high spontaneous polarization, such as those observed in a Sr0.75Ba0.25Nb2O6 (SBN75) single crystal. As a result of slip casting at a high magnetic field of 12T and firing at 1460 degrees C for 48 h in an oxygen atmosphere, highly oriented ceramics and strong ferroelectric properties were observed. The spontaneous polarization of highly oriented SBN ceramics was above 15 mu C/cm(2), which was close to that of the SBN75 single crystal (17 mu C/cm(2)). (C) 2009 The Japan Society of Applied Physics

Electrophoretic deposition (EPD) from aqueous suspension generally forms deposit containing incorporated bubbles because of evolution of gases at electrodes due to electrolysis of water. We have demonstrated here that application of pulsed voltage /current instead of continuous DC enables controlling the amount of bubble incorporation and obtain bubble-free deposits during EPD of aqueous suspension. The yield and bubble incorporation decreased progressively with decrease in size of the applied pulse. A characteristic band of deposition window was found in the plot of voltage/current vs. pulse width within which smooth and bubble-free deposits are obtained. The window is wider at low applied voltages/currents than at higher voltages/currents implying that it is more easier to control the pulsed EPD at lower applied voltages and/currents. No deposition occurred below the window whereas deposits with incorporated bubbles formed above the window. Suppression of bubbles with decreasing pulse size was attributed to decrease in the amount of hydrogen evolved per pulse and verified by monitoring the gain in weight of palladium (Pd) electrode used as cathode during electrolysis of water.

Crystal-oriented and crack-free thin TiO2 films with a good interfacial adhesion on indium-tin oxide (ITO) glass substrates for photoelectrodes were fabricated by the electrophoretic, deposition (EPD) method in a 12 T strong magnetic field. A binder-free suspension for the EPD was prepared by dispersing TiO2 in the mixture of 2-propanol and 2,4-pentanedione. The electrophoretic mobility and the sedimentation rate were measured at various ratios of the mixed solution. The optimized state of the suspension exhibiting the highest surface charge potential and producing deposits with the highest green density was obtained at the 50:50 mixing ratio. The TiO2 films were characterized by XRD and SEM analyses. The photo-current measurement was also conducted to investigate the relation between the photo-anode characteristics of a dye-sensitized solar cell and the plane orientation of the TiO2 films.

The mechanical properties of ceramics materials can be tailored by designing their micro structures. Residual stress is one of the important factors for controlling the crack propagation and consequently improving the mechanical properties. On the other hand, development of the crystallographic orientation even in a diamagnetic ceramic can be controlled by colloidal processing in a strong magnetic field. In this study, alumina/alumina laminar composites with different crystalline-oriented layers were fabricated by EPD in a strong magnetic field in order to control the residual stress using the difference in the thermal expansion of each layer.

We report the fabrication of p- and n-type thermoelectric oxide thick films laminated by insulating alumina using electrophoretic deposition and their thermoelectric performance. From the experimental studies performed for optimization of the thermoelectric performance in the p- and n-type mono-layers, the control of sintering temperature for densification and the usage of fine powder were effective for reducing the electrical resistivity of thermoelectric layers. These findings could be applicable also to the triple-layered thick films. When one assumes that two triple-layered films of p- and n-type thermoelectric materials are combined as unicouple of thermoelectric module, an estimated maximum output power was 20 times higher than a measured maximum output power of a previously reported multi-layered thermoelectric module. It was found that precise control of the microstructure in the thermoelectric layers is indispensable for development of the thermoelectric modules based on the electrophoretic deposition.

This report describes a simple strategy for preparing dispersion of multi-walled carbon nanotubes (MWCNTs) in water. Zirconium acetate (ZrAc3) was used as a dispersant for the MWCNTs in water. Interestingly, an aqueous dispersion of MWCNTs was stabilized by adding an extremely small amount of ZrAc3, followed by ultrasonic agitation. The resultant MWCNT dispersion was durably retained even after storing at room temperature over 6 months. The dispersion state of MWCNTs on a substrate was observed by means of reflection optical and scanning electron microscopes. Furthermore, we demonstrated the effect of external high magnetic field on the orientation of MWCNTs on the substrate surface from the aqueous dispersion.

This paper has clarified the anelasticity of 8Y-FSZ/alpha-alumina composites wherein the 8Y-FSZ phases are dispersed like islands. The amount of anelastic strain generated and the manner of anelastic deformation were compared to those of monolithic 8Y-FSZ. The anelastic strains of six kinds of 8Y-FSZ/alpha-alumina, as well as of monolithic 8Y-FSZ and monolithic alpha-alumina, were measured. The results showed that the anelastic strain was produced even in the composite where 8Y-FSZ phases existed as islands, and that the more the anelastic strain produced, the higher the volume fraction of 8Y-FSZ. In addition, the composition with a fully densified alumina phase had the effect of inhibiting anelastic strain in the 8Y-FSZ phase.

Tri-axial orientation of orthorhombic and twin-free Y2Ba4Cu7Oy (Y247) powders was attempted using a rotating magnetic field with modulated rate. Although magnetic anisotropy of paramagnetic Y247 originated only from the two-dimensional CuO2 and one-dimensional Cu-O chain structures are small, strong tri-axial grain orientation with misorientation angles below 1.5 degrees was successfully achieved during the solidification process of epoxy resin. Our present results indicate the possibility of fabrication of tri- or bi-axial grain-orierited bulk and thick films without applying epitaxial methods, such as melt-solidification or thin film deposition, and that the modulated-rotation magnetic field is applicable not only to RE247 compounds but also to orthorhombic high critical temperature cuprate superconductors, including practical REBa2Cu3Oy, in principle. (C) 2008 The Japan Society of Applied Physics

A novel method based on the application of a square-wave pulse potential of 50% duty cycle has been demonstrated to obtain dense bubble-free deposits of alumina by constant voltage electrophoretic deposition (EPD) from an aqueous suspension. Application of continuous dc voltage invariably resulted in the incorporation of bubbles in the deposits. Bubbles in the deposit decreased progressively with decrease in the size of pulse width during the pulse potential EPD. A unique and narrow band of pulse width exists for each voltage within which a bubble-free deposit is obtained. The band is wider at low applied voltages than at higher voltages. Such bands of pulse width were found to be independent of substrate material and occurred at the same range for stainless steel and nickel substrates, suggesting that the process may be generic and applicable to any conductive substrate. The green density of deposits obtained by pulse EPD has been found to be the same as those obtained by continuous dc voltage EPD. The cathodic pulse EPD produced uniform and homogeneous deposits and was more convenient and amenable to better control than anodic pulse EPD.

Uniform coating and line patterning of a conductive polypyrrole (Ppy) film on nonconductive ceramic materials were performed for use as substrates in the electrophoretic deposition (EPD) process. The Ppy was synthesized by chemical oxidation in the pyrrole solution. Direct shaping or line patterning of alumina or zirconia particles by EPD was carried out using the Ppy films as cathodes.

We report magnetic anisotropies (Delta chi) depending on rare earth (RE) element in the paramagnetic REBa2CU3Oy (RE123) system as an important finding of magneto-scientific grain-orientation. The c-axis-oriented RE123 powder samples using static or rotating magnetic fields were fabricated at room temperature to clarify Delta chi. Their easy axes of magnetization were mainly dominated by second-order Stevens factors, whereas vertical bar Delta chi vertical bar largely depended on y and RE elements. Especially for heavy RE elements, vertical bar Delta chi vertical bar reached the order of 10(-4), indicating that appropriate choice of RE directly leads to a drastic reduction of required magnetic fields for grain-orientation of RE123. (C) 2008 The Japan Society of Applied Physics.

We have first studied the orientation process of alpha-Al(2)O(3) fine particles, using in situ neutron diffraction measurements on the particles in a liquid solvent under magnetic fields. The neutron diffraction intensity of 006 and 116 reflections is significantly reduced by the vertical magnetic field up to 100 kOe, while the 113 and 204 reflections remain unchanged within the experimental accuracy. The energy balance between the magnetic anisotropic energy and the thermal fluctuation following the Boltzmann distribution is important for the crystal orientation of the alpha-Al(2)O(3) particles in suspension. Comparing the experimental data with the theoretical equation, we find that the magnetic field, where the particles are fully oriented, is above 200 kOe. Our obtained data prove that the in situ neutron diffraction measurement is a powerful tool for investigating the alignment of the crystal orientation under magnetic fields. (c) 2008 American Institute of Physics.

This paper reports the texturing behavior of beta-sialon by strong magnetic field alignment (SMFA) during slip casting, followed by reaction pressureless sintering, using either alpha or beta-Si3N4, Al2O3, and AlN as the starting materials. It is found that the beta-Si3N4 crystal exhibits a substantially stronger orientation ability than the alpha-Si3N4 crystal regardless of the Si3N4 raw powders in the magnetic field of 12 T. The beta-raw powder produces a highly a, b-axis-oriented beta-Si3N4 green body with a Lotgering orientation factor of up to 0.97. During sintering, the beta-raw powder allows the a, b-axis-oriented beta-sialon to retain the Lotgering orientation factor similar to and even higher than that of beta-Si3N4 in the green body. In contrast, the alpha-raw powder leads to a faster transformation rate of alpha/beta-Si3N4 to beta-sialon but a substantially lower texture in beta-sialon. The results indicate that the use of the beta-raw powder is more efficient for producing highly textured beta-sialon via SMFA than that of the alpha-raw powder as well as the prolonged sintering.

Hydroxyapatite (HAP, Ca-10(PO4)(6)(OH)(2)) is a main component in the human body and teeth, and a specific crystal orientation is required because of the different properties for each crystal plane. In this study, two types of hydroxyapatite powders were used for the fabrication of a textured HAP. The effects of the processing parameters on the orientation, such as de-agglomeration by ultrasonication and milling procedures, applied magnetic field and sintering temperatures, were examined. Using the de-agglomerated particle by a milling procedure, it is possible to control the particle orientation, but when using heavily agglomerated particles, it was impossible to control the particle orientation by applying a high magnetic field. Highly textured HAP can be fabricated by slip casting using a well-dispersed suspension in a high magnetic field followed by sintering above 1373 K. (C) 2007 Elsevier B.V. All rights reserved.

This paper reports the texture development in Si3N4 by strong magnetic field alignment (SMFA), using slip casting of alpha-Si3N4 raw powder (SN-E10) and pressureless sintering. The texture of beta-Si3N4 in the green and sintered bodies was characterized by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The a, b-axis and c-axis aligned beta-Si3N4 has been obtained by the static and rotating magnetic field of 12 T, respectively. The beta-seed addition and prolonged sintering both enhance the texture, but the former is more efficient. This work suggests an efficient SMFA strategy of producing highly textured beta-Si3N4, particularly the unidirectionally c-axis aligned beta-Si3N4 by seeding the alpha-raw powder using the less-agglomerated beta-phase particles.

An attempt has been made to study the texture behavior in sintered reaction-bonded silicon nitride by strong magnetic field alignment, using slip casting of Si-powder without and with beta-Si3N4 Particle addition. It is shown that the a, b-axis aligned texture, parallel to the magnetic field, develop in the resultant SRBSN with P-seed addition, whereas no texture develops in those SRBSN without beta-seed addition. The degree of orientation of beta-Si3N4 is found to decrease with the formation of new beta-phase during the nitridation, regardless of the nitriding conditions, suggesting that the initially oriented beta-seed dose not promote the formation of newly oriented beta-Si3N4. Compared to the nitridation, the degree of texture is enhanced by the post-sintering, but the nitridation condition has little effect on the texture development during the post-sintering. The present work implies that the texture development in SRBSN is governed by the initial orientation Of beta-Si3N4 seed and the post-sintering. (c) 2007 Elsevier Ltd. All rights reserved.

Recently to improve properties, highly microstructure controlled ceramics such as fine-grained, textured and laminated structures are required. We have demonstrated a new processing of textured ceramics with a feeble magnetic susceptibility by colloidal processing in a high-magnetic field and subsequent heating. As colloidal processing, slip casting and electrophoretic deposition (EPD) have been conducted successfully. Colloidal processing is known to be a powerful method for consolidating fine particles with a high density and homogeneous microstructure. Crystalline-textured controlled laminated alumina can be fabricated using EPD by varying the angle between the vectors of electric field and magnetic field. Also textured ceramics with complicated structure such as P-alumina and alumina-based nanocomposite can be fabricated by reaction sintering. The textured alumina-related compounds showed anisotropic properties depending on the crystal plane. The colloidal processing in a high-magnetic field confers several advantages and can be applied to many non-cubic ceramics. (c) 2007 Elsevier Ltd. All rights reserved.

We report the development of a new high oxygen pressure synthesis method of orthorhombic and twin-free RE2Ba4Cu7Oy (RE247, RE = rare earth elements) superconductors and their tri-axial orientation using by a modulated rotation magnetic field. By the new synthesis method using quartz ampoule and a chemical reaction generating additional source of oxygen pressure in it, we have successfully fabricated RE247 (RE=Y, Er) polycrystals in the almost same synthesis conditions with those using a high oxygen pressure furnace. Furthermore, tri-axial orientation of these RE247 powders has been successfully accomplished using a modulated rotation magnetic field. Although our experimental studies on the magnetic orientation were performed in epoxy resin, high degrees of in-plane orientation less than 6 degrees were achieved. Especially for RE=Y, the degree of in-plane orientation was found to be less than 1.5, and high effectiveness of this tri-axial orientation technique was shown in principle.

We report magnetic properties of [Ca2CoO3-delta](0.62)COO2 (Ca349) powders with various average size and the Bi- and Sr-doping effects on thermoelectric properties for the magnetically grain-aligned and densified Ca349 thick films. Magnetic anisotropy at 300 K depended on the initial average size of Ca349 powders and decreased with the decrease in the size. This presumably suggests that distortion of crystal structure was induced by a ball-milling process and led to the change of magnetic anisotropy. On the Bi- and Sr-doping effects, an obvious enhancement of thermoelectric properties did not emerge in the case of the Sr-doping, whereas the enhancement was observed for the Bi-doped Ca349 thick films. However, a drastic decrease of magnetic anisotropy was caused by the Bi-doping. For usage of the p-type layer in multilayered thermoelectric module, tuning of the Bi-doping levels in which both enhancement of thermoelectric properties and a certain level of magnetic anisotropy are achieved is required.

We report thermoelectric (TE) properties of mono-layer thick films of p-type [Ca2CoO3-delta](0.62)CoO2 (Ca349) and n-type compounds of Ca0.9La0.1MnO3 (Mn113) and LaNi0.98MO0.02O3 (Ni113) for the improvement of TE performance in multi-layered TE modules. In the case of magnetically aligned Ca349 film, the improvement of TE properties due to the reduction of resistivity (p) was achieved by optimization of hot-pressing temperature and rho was sensitive to relative density of the Ca349 layer. For the decrease in rho of the n-type layers, two different approaches, the choice of Ni113 as a n-type compound and usage of fine powders of Mn113, were attempted. Both approaches were effective for reducing p even in the sintering at similar to 900 degrees C.

Hydroxyapatite (HAP, Ca-10(PO4)(6)(OH)(2)) is a main component of bones and teeth, and a specific crystal orientation is required for biomaterial application. In this study, the effects of the processing parameters on the orientation, such as de-agglomeration by milling procedure, applied magnetic field and sintering temperatures, were examined. Using the de-agglomerated particle by a milling procedure, it is possible to control the particle orientation, but when using heavily agglomerated particles, it was impossible to control the particle orientation by applying a high magnetic field. Highly-textured HAP can be fabricated by slip casting using a well-dispersed suspension in a high magnetic field (above 4 T) followed by sintering above 1373 K.

In general, the mechanical and physical properties of a crystal depend on the direction of the crystal axis. The controlled development of the crystallographic texture in ceramics is very useful for improvement of their properties. The preparation of the textured SiC polycrystal was achieved by colloidal processing in a strong magnetic field. The c-axis of the SiC was parallel to the direction of the applied magnetic field. The bending strength of the textured SiC depends on the crack-growth direction.

This paper reports a dense textured single Ca-alpha-sialon fabricated by strong magnetic field alignment (SMFA) during non-aqueous slip casting of alpha-Si3N4, CaCO3, Al2O3 and AIN starting powders, followed by reaction pressureless sintering at 1800 degrees C. XRD analysis reveals that the orientation of the alpha-Si3N4 crystals occurs with the c-axis perpendicular to the magnetic field during slip casting. It is shown that the formation of the single Ca-alpha-sialon is complete within 5 min and nearly complete densification is achieved within 60 min. SEM observation reveals that the textured Ca-alpha-sialon is featured by the long-axis (c-axis) of large elongated grains perpendicular to the magnetic field. The texturing mechanism is attributed to the heterogeneous nucleation and epitaxially elongated growth on the initially oriented alpha-Si3N4 seeds. The prolonged sintering leads to a higher orientation as a result of the promoted grain growth.

Factors limiting the strain rate of superplastic deformation in ceramic materials are discussed on the basis of existing models and experimental results concerning high-temperature plastic deformation, intergranular cavitation and dynamic grain growth. From the discussion, it is indicated that simultaneously fulfilling the following conditions is essential for attaining high-strain-rate superplasticity (HSRS) in ceramic materials: reduction in the initial grain size, enhanced diffusivity, suppressed dynamic grain growth, a homogeneous microstructure and a reduced number of residual defects. In the light of these conditions, explanations are given for HSRS attained in earlier studies on some oxide materials. It is also shown that HSRS can be intentionally attained in doped yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) and composites synthesized from ZrO2, Al2O3 and MgO2; the tensile ductility of these composites reached 300-2500% at a strain rate of 0.01-1.0 s(-1). The postdeformation microstructure indicates that some secondary phases may suppress cavitation damage and thereby enhance HSRS. (C) 2007 NIMS and Elsevier Ltd. All rights reserved.

Fabrication of thermoelectric Bi-based cobaltites with large magnetic anisotropy (Delta chi = chi c - chi ab) and relatively low resistivity using a crystallochernical process is reported. Doping of various rare earth (RE) ions into the Ca site in [(Bi0.5Pb0.5)(2)Ca2O4](y)CoO2 [(Bi,Pb)Ca222] enhanced Delta chi comparable to that of [Ca2CoO3-delta](0.62)CoO2. Tailoring of the Sr-doping level in Dy-doped (Bi,Pb)Ca222 enabled the resistivity to be reduced without decreasing Ay. The magnetically c-axis-oriented (Sr,Dy)-doped (Bi,Pb)Ca222 bulk exhibited improved thermoelectric performance compared with the Sr-free RE-doped BiCa222 and a-axis grain-oriented [(Bi0.5Pb0.5)(2)Sr2O4](similar to 0.55) CoO2. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

強磁場中での成形によるセラミックスの配向制御と電気泳動堆積法について概説し、電場と強磁場を重畳作用する強磁場中電気泳動堆積法についての解説を行なう。さらに磁場と電場のなす角を制御することにより多層セラミックスにおいて各層での結晶方位制御が可能であることを述べ、実際にアルミナについて適用した例を紹介する。

Textured CaBi4Ti4O15 (CBT) ceramics were fabricated by slip casting in a high magnetic field of 12 T, and a layer structure was obtained by co-firing with the textured CBT ceramics and a metal internal electrode. The crystalline a(b)-axis of CBT was aligned parallel to the magnetic field, and highly a(b)-axis textured ceramics were obtained. The orientation degree of the textured ceramics was 0.82, and the electromechanical coupling coefficient of thickness extensional (TE) vibration was about 1.5 times larger than that of the randomly oriented ceramics. The second harmonic TE vibration was successfully generated in the layer structure specimens, which contained two layers of the textured ceramics and an internal electrode. Therefore, it was recognized that the layer structure was satisfactorily fabricated.

The roles of polyethylenimine (PEI) in the hydrolysis and dispersion properties of aqueous Si3N4 suspensions were studied in terms of the hydrolysis, adsorption, electrokinetic, and rheological measurements. It was found that the pH change of the suspensions in the acidic environment could be minimized in the presence of &gt;= 0.5 dwb% PEI. The ammonia and oxygen measurements suggest that this phenomenon is primarily attributed to the buffer mechanism generated by the ionized PEI, instead of the protection mechanism. The constant pH enables the suspensions to retain a better stability with time at acidic pH. The adsorption of PEI on Si3N4 is a high-affinity type at highly basic pH, but is a low-affinity type at acidic pH. As the PEI amount increases, the adsorption shifts the isoelectric point (IEP) of Si3N4 from pH 5.9 to pH similar to 11 until complete coverage is attained. The stability of Si3N4 suspensions is found to depend strongly on the saturated adsorption of PEI, which is as a function of the pH and PEI amount. Once the saturated adsorption limit is reached, the excess free PEI molecules become more detrimental to the stability with increased solid loading. The stabilization mechanisms of Si3N4 suspensions by PEI were discussed in detail.

電気泳動プロセスでは、蒸着やスパッタリングなどの製膜法と異なり、帯電した粒子は電極間の最短距離を直線的に泳動するわけではなく、溶媒で満たされた空間を電位勾配に従って泳動、堆積する。電極間を電気力線に沿って泳動した粒子は電極の裏側にも回り込むため、曲面や凹凸を持つ基材表面にも比較的均一な粒子堆積膜の形成が容易にできる。この特徴を積極的に利用すると、電極の極性と空間的配置を工夫し、電場のポテンシャルを3次元的に制御することにより、粒子を基材上のある特定の場所に優先的に導き堆積させることも可能である。このことは、電場の精密制御による粒子アセンブリングの可能性を示しており、電気泳動プロセスの大きなメリットの１つとも言える。本稿では、電気泳動プロセスの概略を解説し、３次元的複雑形状部材の作製に電気泳動プロセスを応用した例を紹介する。

著者らの研究に基づいて、酸化物多結晶体で高速超塑性を実現するための微視構造、組成、プロセシング上の必要条件を解説する。また、これらの条件を満たすことによって得られた超塑性特性について述べる。

Highly structure controlled ceramics were required for improving their properties. Colloidal processing using fine particles provides this required control mechanism through well-dispersed suspension or hetero-coagulate suspension. We demonstrate highly structure controlled ceramics fabricated by novel colloidal processing; (i) dense nano-sized zirconia without pressure sintering, (ii) porous ceramics with controlled pore size by hetero-coagulated suspension of ceramics and polymer, (iii) nanocomposite by reaction sintering, and (iv) textured ceramics with feeble magnetic susceptibility by colloidal processing in a high magnetic field.

We have demonstrated that textured Al2O3-mullite-SiC nanocomposites can be fabricated by slip casting followed by partial oxidation - reaction sintering of mixed suspensions of Al2O3 and SiC powders in a high magnetic field. The sintered density was changed by the degree of oxidation at 1200 degrees C and 1300 degrees C. The degree of orientation of alumina in the nanocomposite was examined on the basis of the X-ray diffraction patterns and scanning electron micrographs. It is confirmed that alumina-oriented nanocomposites were fabricated. The three-point bending strength at room temperature was observed for the nanocomposites.

The disintegration of 6 different Nb-Zr-Fe alloys and their hydrogen storage properties due to hydrogenation have been investigated. The hydrogenation was performed in a 0.1MPa hydrogen pressure held at room temperature in are melting chamber without exposure to air atmosphere. The thermal stability of hydrogen dissolved in disintegrated powder was measured in the temperature range from room temperature to 600 degrees C by using the thermal analysis equipment. Hydrogen contents in alloys were evaluated from the mass difference of TG curve and chemical determinations for hydrogen gas analysis. The values of hydrogen content are in accordance with both chemical and mass difference methods. The hydrogen contents of disintegrated alloys synthesized were in the range of 1.2-2.0 wt% which depend on the composition of alloys.

The controlled development of microstructure such as nanocomposite or texture is a way for effectively improving physical and mechanical properties. Al(2)O(3)-mullite-SiC nanocomposites were prepared by partial oxidation of the Al(2)O(3)-SiC green body followed by reaction sintering. Recently, we reported that the crystal orientation of alumina can be controlled in a high magnetic field due to its crystal magnetic anisotropy. By the combination of both techniques we have demonstrated that textured Al(2)O(3)-mullite-SiC nanocomposites can be fabricated by slip casting of mixed suspensions of Al(2)O(3) and SiC powders in a high magnetic field followed by partial oxidation and reaction sintering of the Al(2)O(3) and SiC. The sintered density depended on the degree of dispersion and oxidation of SiC. Dense nanocomposites were prepared by suitable oxidation and reaction sintering at 1600 without pressure. The three-point bend strength was observed approximately 800 MPa for the nanocomposites. The strength depended on the textured plane and amount of mullite phase, and increased using the suspension treated by beads-milling due to the de-agglomeration of SiC powders.

Cathodic electrophoretic deposition of bimodal alumina suspension was performed using conductive polypyrrole (Ppy) film as an electrode. The coating of the Ppy on nonconductive ceramic substrates was performed by polymerization of pyrrole (Py) in an aqueous solution. The relative green density of the deposits measured by Archimedes' method was 68 %. Alumina ceramics were obtained by sintering the deposits together with the Ppy coated ceramic substrates in air.

Highly structure controlled ceramics were required for improving their properties. Here, we demonstrate such ceramics fabricated by novel colloidal processing; (i) dense nano-sized zirconia without pressure sintering, (ii) porous ceramics with controlled pore size by hetero-coagulated suspension of ceramics and polymer, and (iii) textured ceramics with feeble magnetic susceptibility by electrophoretic deposition in a high magnetic field.

Recently to improve properties, highly microstructure controlled ceramics such as fine-grained, textured and laminated structures are required. We have demonstrated a new processing of textured ceramics with a feeble magnetic susceptibility by colloidal processing in a high magnetic field and subsequent heating. As colloidal processing, slip casting and electrophoretic deposition (EPD) have been conducted successfully. Colloidal processing is known to be a powerful method for consolidating fine particles with a high density and homogeneous microstructure. The degree of orientation strongly depends on the particle dispersion and some processing factors, such as particle size, applied magnetic field, concentration of the suspension, sintering temperature, etc. Crystalline-textured controlled laminated composites can be fabricated using EPD by varying the angle between the vectors of electric field and magnetic field. Also textured ceramics with complicated structure can be fabricated by reaction sintering. The colloidal processing in a high magnetic field confers several advantages and it is possible for this type of processing to be applied to non-cubic ceramics, such as alumina, titania, zinc oxide, tin oxide, hydroxy apatite, aluminium nitride, silicon carbide, silicon nitride, etc. The textured ceramics showed anisotropic properties depending on the crystal plane.

Electrophoretic deposition (EPD) of alumina in a superconducting magnet was performed at various magnetic field strengths. A stable colloidal suspension of alumina appropriate for magnetic alignment was prepared in an ethanol medium by using a phosphate ester (PE) as a dispersant. The amount of PE appropriate for the stability of the alumina suspension was investigated by measuring the pH, zeta-potential and the relative density of the green compacts. The consolidation of alumina powder was performed by EPD under a magnetic field of 0-12 T. The degree of crystalline orientation of the sintered bodies was evaluated by X-ray diffraction (XRD) as a function of the applied magnetic field during deposition and the sintering temperature.

The effects Of alpha-Si3N4 powder, beta-Si3N4 seed particles and sintering conditions on the texture development in Si3N4 ceramics, which were prepared by slip casting in a strong field of 12 T, followed by pressureless sintering. In the case of the replacement of the fine powder (UBE SN-E10) with the coarse powder (UBE SN-EO5), no alignment Of alpha-Si3N4 crystals was observed, but the alignment Of beta-Si3N4 crystals was observed in the green body, despite the low amount Of beta-Si3N4 (similar to 1 wt%). This suggests that the grain alignment during slip casting is predominant by the grain alignment of the minor beta-Si3N4 phase present in the alpha-Si3N4 raw powder, which is featured by the rod-like shape and less-agglomerated form. The alignment of both alpha-Si3N4 and beta-Si3N4 crystals occurs by the c-axis of the crystals perpendicular to the magnetic field. The addition of 5 wt% beta-Si3N4 particles leads to the enhanced grain orientation of the beta-Si3O4 particles in the green body for both raw alpha-Si3N4 powders. It is shown that the crystallographic orientation Of beta-Si3N4 is enhanced by the substitution of SN-E10 for SN-E05 powder, the addition Of beta-Si3N4 particles and prolonged sintering, but the phase transformation of alpha to P may play a dominant role in the texture development in Si3N4 during sintering, compared to the grain growth after the complete phase transformation. Owing to the crystallographic orientation, the samples exhibited anisotropic shrinkage behavior during sintering and the anisotropy becomes strong with enhanced grain orientation. The present study suggests that the control of the alignment Of beta-Si3N4 is crucial for the texture development in Si3N4 by the magnetic field alignment.

ファインセラミックスの原料に用いるサブミクロン以下の微粒子は凝集しやすく、この凝集は成形体の高密度化、均質化を妨げる要因となる。微粒子の分散状態を制御して均一で高充填の成形体を作ることは、低温焼結と欠陥サイズの低減を目指すセラミックス製造技術の基本となる。セラミックス微粒子のサスペンション中における分散制御が、その後の成形、焼結における組織制御に重要であることを示し、超塑性セラミックスや配向セラミックスの作製への適用について紹介する。

セラミックスにおける高速超塑性現象を高速度下で発現させるために必要な材料科学的な諸条件、そのための材料創製手法、将来の応用化を見据えた今後の課題について、NIMSの最新成果を含めて論じた。

微粒子の分散制御とコロイドプロセスについて概説し，強磁場中でのコロイドプロセスを用いた配向セラミックスの作成について筆者らの実験結果を紹介する。特に、アルミナ微粒子分散系において、プロセスパラメーターと配向の関係を明確にし、多様な系に適用できることを示した。

The texture of feeble magnetic ceramics can be controlled by a strong magnetic field. When the magnetic susceptibility of the c axis is smaller than that of the other axes, the c axis aligns perpendicular to the magnetic field; however, the direction is randomly oriented on the plane perpendicular to the magnetic field. The authors demonstrate in this letter that a highly controlled texture in bismuth titanate, which has a c-axis susceptibility smaller than the other axes, can be achieved using a two-step magnetic field procedure. This highly controlled orientation is effective for improving the electromechanical coupling coefficient. (c) 2006 American Institute of Physics.

コロイド分散系に２つの外部場である強磁場と電場を重畳作用させることにより、結晶方位と高次構造が高度に制御された配向セラミックスを作製するNIMS独自の試みについて、我々の最近の研究成果を紹介する。

The authors report the fabrication of grain-aligned [Ca2CoO3-delta](0.62)CoO2 (Ca349) thick films and a multilayered thermoelectric unicouple of Ca349 and Ca0.9La0.1MnO3-delta (Mn113) using electrophoretic deposition (EPD) and magnetic alignment methods. Strongly c-axis-oriented Ca349 thick films were obtained by EPD performed under magnetic fields. In addition, the c axis of grains was found to always align parallel to the direction of field, independently of the EPD cell configuration. The required conditions for magnetic grain alignment of fine Ca349 powders were quantitatively discussed based on magnetization anisotropy. An alpha-Al2O3/Mn113/alpha-Al2O3/Ca349/alpha-Al2O3 multilayered thick film was successfully developed.

The controlled development of texture has recently become a topic of interest in ceramic processing, since it allows improved tailoring of the properties of a material. Anisotropic susceptibilities of feeble magnetic ceramics such as A12O3 and ZnO are quite small. It is generally difficult to apply a magnetic field effectively in order to rotate fine feeble magnetic particles, since fine particles tend to spontaneously agglomerate due to strong attractive interactions (van der Waals forces). It is necessary to disperse the particles in a suspension in order to effectively utilize a magnetic field to rotate the particles. Colloidal processing is a powerful technique for controlling the stability of particles in a suspension. This processing can be used for production of textured ceramics with complex shapes by near-net-shape slip casting. In addition, the direction of textured polycrystalline can be controlled by the direction of the applied magnetic field.

Electrical, mechanical and other properties of ceramic materials can be controlled by designing their microstructures. It had generally been difficult to utilize a magnetic field for tailoring the microstructure, in feeble magnetic ceramics, such as Al2O3; however, the possibility of controlling the microstructure by a magnetic field occurred with the development of superconducting magnets. In this review paper, we introduce a novel processing for the microstructual design in ceramics by colloidal processing in a strong magnetic field and an electric field. We demonstrate that the textured alumina can be fabricated by slip casting in a strong magnetic field and the production of alumina/alumina laminar composites with different crystalline-oriented layers can be achieved by electrophoretic deposition in a strong magnetic field. In order to control the texture using a magnetic field, a good dispersion of powder in a suspension is necessary because a strong attractive force between the agglomerated particles prevents each particle in a suspension from rotating in the magnetic field. The degree of orientation depends on the processing factors, such as heating temperature, viscosity of suspension, etc. And the grain growth in Al2O3 matrix enhances crystallographic texture development. The bending strength of the laminar composite depended on the direction of the multilayered microstructure with alternate crystalline-oriented layers. Crack propagation and fracture mode depend on the direction of microstructure in the laminar composite with controlled crystalline orientation. (c) 2006 NIMS and Elsevier Ltd. All rights reserved.

2005年9月に行われた6th Pacific Rim Conference on Ceramics and Glass Technology (PAC RIM 6)について報告し、最近のセラミックスの研究、開発動向の情報を提供する。

The effects of α-Si3N4 powder, β-Si 3N4 seed particles and sintering conditions on the texture development in Si3N4 ceramics, which were prepared by slip casting in a strong field of 12 T, followed by pressureless sintering. In the case of the replacement of the fine powder (UBE SN-E10) with the coarse powder (UBE SN-E05), no alignment of α-Si3N4 crystals was observed, but the alignment of β-Si3N4 crystals was observed in the green body, despite the low amount of β-Si3N4 (∼1 wt%). This suggests that the grain alignment during slip casting is predominant by the grain alignment of the minor β-Si3N4 phase present in the α-Si 3N4 raw powder, which is featured by the rod-like shape and less-agglomerated form. The alignment of both α-Si3N 4 and β-Si3N4 crystals occurs by the c-axis of the crystals perpendicular to the magnetic field. The addition of 5 wt% β-Si3N4 particles leads to the enhanced grain orientation of the β-Si3N4 particles in the green body for both raw α-Si3N4 powders. It is shown that the crystallographic orientation of β-Si3N4 is enhanced by the substitution of SN-E10 for SN-E05 powder, the addition of β-Si3N4 particles and prolonged sintering, but the phase transformation of α to β may play a dominant role in the texture development in Si3N4 during sintering, compared to the grain growth after the complete phase transformation. Owing to the crystallographic orientation, the samples exhibited anisotropic shrinkage behavior during sintering and the anisotropy becomes strong with enhanced grain orientation. The present study suggests that the control of the alignment of β-Si3N4 is crucial for the texture development in Si3N4 by the magnetic field alignment.

The coating of conductive polypyrrole (Ppy) on nonconductive ceramic substrates was performed by polymerization of pyrrole (Py) in an aqueous solution. The Ppy film was characterized by scanning electron microscopy and conductivity measurements. Electrophoretic deposition of bimodal alumina suspension prepared with a phosphate ester was performed using Ppy film as a cathode. Fabrication of alumina ceramics with irregular shapes or complicated patterns were also attempted by sintering the deposits together with the Ppy coated substrates in air.

Highly crystalline-textured alumina ceramics were fabricated by electrophoretic deposition (EPD) in a strong magnetic field of 12 T. Preferred orientation of the bulk was controlled by changing the direction of the applied electric field E relative to the magnetic field B during the EPD. Average orientation angle of the prepared monoliths as a function of the angle between the vectors E and B, phi B-E was estimated from the X-ray diffraction analysis. Alumina/alumina laminar composites with crystalline-oriented layers were also fabricated by alternately changing the phi B-E layer by layer during EPD in a magnetic field of 12 T.

Crystalline oriented titania (anatase) thick films have been fabricated by electrophoretic deposition in a strong 12T magnetic field. Anatase particles in an aqueous suspension are rotated due to their magnetic anisotropy and then deposited on a substrate in a dc electric field. The angle between the directions of the magnetic and electric fields phi(B-E) is fixed at specified angles (phi(B-E) = 0, M 60 and 90 degrees) during the deposition to control the dominant crystalline orientation of the deposits. The crystalline orientation characterized by the X-ray diffraction for the anatase films proves the orientation dependence of anatase upon the phi(B-E) angle during the EPD. The crystalline orientation of the anatase films can be controlled by varying the angle of E versus B. (c) 2005 Elsevier Ltd. All rights reserved.

The coating of conductive polypyrrole (Ppy) on nonconductive ceramic substrates was performed by polymerization of pyrrole (Py) in an aqueous solution. The Ppy film was characterized by scanning electron microscopy and conductivity measurements. Electrophoretic deposition of bimodal alumina suspension prepared with a phosphate ester was performed using Ppy film as a cathode. Fabrication of alumina ceramics with irregular shapes or complicated patterns were also attempted by sintering the deposits together with the Ppy coated substrates in air.

Magnetic susceptibility is very small in feeble magnetic ceramics; consequently, it had been very difficult to develop a textured microstructure in these ceramics by using a magnetic field. We have demonstrated, however, that textured microstructures in alumina can be prepared by colloidal processing in a high magnetic field. We applied this processing technique to alumina based composites. The degree of crystallographic texture was small in specimen sintered at the low temperature. The degree of orientation increased rapidly with increasing sintering temperature and depended on the grain size of alumina matrix. The grain size can be controlled by the content of YTZ particle as a second phase, the kind of dopant, sintering temperature, annealing temperature and annealing time.

コロイドプロセスにおける電場を用いた積層制御および強磁場を用いた配向制御を概説した。さらに電場と強磁場を重畳作用することによる配向積層させた構造制御についての解説を行った。アルミナについて、配向方向が層毎に90度づつ異なる積層体を実際に作製し、このプロセスの応用の一例として示した。

Fabrication conditions for high-density and fine-grained hydroxyapatite (Ca-10 (PO4)(6) (OH)(2): HAp) ceramic were examined; the tensile elongation of HAp ceramic during heating was measured in order to evaluate its possible superplastic behavior. The HAp compact was fired in air at a temperature between 1100 and 1200 degrees C for 5 h. The relative density of HAp compact fired at 1100 degrees C for 5 h showed a maximum (99.2%), whereas the average grain size was as small as 0.56 mu m. The tensile elongation of this HAp specimen was tested at a temperature between 940 and 1100 degrees C. The tensile elongations tested at 1050 and 1100 degrees C attained 156 and 157%, respectively; the specimen tested at 1050 degrees C contained a limited number of cavities, whereas the specimen tested at 1100 degrees C was observed to have a large number of cavities.

コロイド分散系に2つの外部場である強磁場と電場を重畳作用させることにより、結晶方位と高次構造が高度に制御された新しい配向セラミックスを作製する試みについて紹介する。

当グループでは反磁性セラミックスでさえも配向を可能とする強磁場プロセスを既に開発してきており、さらに、配向と積層を組み合わせることで高次な構造の創製を目指している。そのために、強磁場中での電気泳動堆積を試みており、任意の方向に配向させた層を堆積させることにより、配向と積層を組み合わせた高度な異方性制御が可能であることを見出した。磁場と電場の重畳印加による配向積層制御プロセスについて紹介する。

The orientation distributions of alpha-alumina textured ceramics are determined from neutron di9ffraction spe3ctra. A curved position-sensitive detector coupled to a tilt angle scan allowed treatment of the whole diffraction pattern in a Rietvelt-WIMV-Popa algorithm. With increasing the sintering temperature of alumina, the texture strength is enhanced and the c-axis distribution is sharper. We se

アルミナ等の反磁性・常磁性セラミックスであっても強磁場とコロイドプロセスを用いれば結晶配向が可能であり、この手法が適用物質と成形法の選択の広さから汎用性が高く、高次な構造をデザインすることが可能となるプロセスでることを紹介する。

溶媒中におけるセラミックス粒子の表面帯電現象と粒子間の相互作用を利用して固化成形体の微構造制御を行う「コロイドプロセス」を、電場や磁場などの外場が印加された環境下で行うことで、より高次な組織微構造の制御が行える「外場印加コロイドプロセス」という新しい手法・概念に発展させた。本報は、I. 電気泳動堆積法における粒子堆積挙動に及ぼす諸因子の影響の解明II．強磁場中鋳込み成形法による粒子配向技術の確立と適応系の拡大III．強磁場電気泳動堆積法による結晶方位制御と積層コンポジットの作製について、ホソカワ粉体工学振興財団による助成研究の成果報告書として寄稿されたものであるが、内容・スタイルは、オリジナルな研究論文となっている。

Preparation of oriented AIN bulk ceramics was achieved by slip casting in a high magnetic field. The c-axis of AIN was perpendicular to the direction of a magnetic field. The mechanical properties and the thermal conductivity of the textured AIN depend oil the direction of the crystallographic orientation. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Factors limiting the strain rate available to superplastic deformation in oxide ceramics are discussed from existing knowledge about high-temperature plastic deformation and cavitation mechanisms. Simultaneously controlling these factors is essential for attaining high-strain-rate superplasticity (HSRS). This is shown in monolithic tetragonal zirconia and composite materials consisting of zirconia, alpha-alumina and a spinel phase: at strain rates higher than 10(-2)s(-1), tensile ductility reached 300-600% in the monolithic material and 600-2500% in the composite materials. Post-deformation microstructure indicates that certain secondary phases should be effective in suppressing cavitation damage and thereby enhancing HSRS.

従来は磁場の影響を受けないと考えられてきたアルミナのような弱磁性セラミックスでもコロイドプロセスと強磁場を用いることで、その結晶方位を制御できることを見出した。ここでは、弱磁性セラミックスの結晶磁気異方性を利用した磁場配向と、電気泳動法の高次成形プロセスを組み合わせた強磁場電気泳動法による結晶配向積層コンポジットの創製について解説する。

コロイドプロセスの高度化を図ることにより、優れた特性を有する原子力用構造材料を作成することを目的とした。今年度は、SiCナノ粒子にポリエチレンを添加することによる水系サスペンションの安定性チタニアナノ粒子の電気泳動堆積挙動とサスペンションの安定性、およびスリップキャストによる高速超塑性の作成について報告した。

The controlled development of texture is one of the ways for effective in improving the physical and mechanical properties. We'll demonstrate new processing of textured ceramics as an example of alumina by slip casting in a high magnetic field and subsequent heating. Susceptibility of diamagnetic alpha-alumina is very small, but the orientation energy of alumina particle by a high magnetic field becomes larger than the thermal energy. alpha-alumina of a rhombohedral structure shows anisotropic susceptibility, but this anisotropy has up to now been more or less ignored due to its very low value. However, in a high magnetic field the energy of crystal anisotropy becomes comparable to or larger than the energy of thermal motion. The degree of orientation depends on processing factors such as heating temperature, particle size, magnetic field and concentration of suspension, etc. This process technique confers several advantages and it is possible for this type of processing to be applied to other non-cubic ceramics, such as TiO2, ZnO, SnO, HAP, AlN, SiC, etc.

The orientation distributions of alpha-Al2O3 textured ceramics are determined from neutron diffraction and SEM-EBSD. A curved position-sensitive detector coupled to a tilt angle (chi) scan allowed the whole neutron diffraction pattern treatment in the combined Rietveld-WIMV-Popa algorithm. Analyses from neutron and electron diffraction data gave similar results if EBSD data are smoothed to account for grain statistics. Four textured alumina ceramics were prepared by slip-casting under a high magnetic field and sintered at 800 degrees C, 1300 degrees C, 1400 degrees C and 1600 degrees C. The inverse pole figures and EBSD-mapping highlights the influence of the magnetic field and sintering temperature on the texture development. The inverse pole figures calculated for the fiber direction show a major (001) component for all the samples. With the increasing sintering temperature, the texture strength is enhanced and the c-axis distribution is sharper. The effectiveness of the combined approach for determining the crystallite size is also evident. As a global trend, the calculated crystallite size and observed grain size are similar and increase with the increasing sintering temperature. The mechanism of the texture development in the sintered specimens is certainly initiated from the preferred orientation of the green body after slip-casting under a high magnetic field. The basal texture is enhanced during sintering by selective anisotropic grain growth. We evidenced here the powerfulness of the Rietveld texture analysis correlated to SEM-EBSD calculation to provide a basis for the correlation of texture, microstructural parameters and anisotropic properties.

The controlled development of texture is one of the ways for effectively improving physical and mechanical properties. In this review paper, we introduce a new processing of textured ceramics with a feeble magnetic susceptibility by slip casting in a high magnetic field and subsequent heating. As an example of feeble magnetic ceramics, we demonstrate the fabrication of textured alumina in details. The susceptibility of diamagnetic alpha-alumina is very small, but the orientation energy of the alumina particle by a high magnetic field becomes greater than the thermal energy. alpha-Alumina with a rhombohedral structure shows anisotropic susceptibility, but this anisotropy has up to now been more or less ignored due to its very low value. However, in a high magnetic field, the energy of crystal anisotropy becomes comparable to or greater than the energy of thermal motion. The degree of orientation depends on the processing factors, such as heating temperature, particle size, applied magnetic field, concentration of the suspension, etc. This process technique confers several advantages and it is possible for this type of processing to be applied to other non-cubic ceramics, such as TiO2, ZnO, SnO, hydrooxy apatite (HAP), AIN, SiC, Si3N4, etc.

The orientation distributions of alpha-Al2O3 textured ceramics are determined from neutron diffraction spectra. A curved position-sensitive detector coupled to a tilt angle (chi) scan allowed the whole diffraction pattern treatment in the combined Rietveld-WIMV-Popa algorithm. Four textured alumina ceramics were prepared by slip-casting under a high magnetic field and sintered at 800, 1300, 1400, and 1600 degreesC. The calculation of the distribution density, correlated to the representation of the normal and inverse pole figures, highlights the influence of the magnetic field and sintering temperature on the texture development. The principal pole figures show a pronounced (00l) texture: (001) pole parallel to the direction of slip-casting, and (110) pole with higher distribution density for the directions perpendicular to the expected fiber axis. The inverse pole figures calculated for the fiber direction show a major (001) component for all the samples. With the increasing sintering temperature, the texture strength is enhanced and the c-axis distribution is sharper. The effectiveness of the approach for determining the crystallite size is also evident. As a global trend, the calculated crystallite size and observed grain size are similar and increase with the increasing sintering temperature. The mechanism of the texture development in the sintered specimens is certainly initiated from the preferred orientation of the green body after slip-casting under a high magnetic field. The basal texture is enhanced during sintering by selective anisotropic grain growth. We evidenced here the powerfulness of the Rietveld texture analysis to provide a basis for the correlation of texture, microstructural parameters, and anisotropic properties.

We report the conversion of the easy axis of magnetization from the a-axis to the c-axis in thermoelectric misfit-layered Bismuth-based cobaltites for a magnetic grain-alignment process. The conversion was accomplished by the substitution of Ca for Sr in the block layer of [(Bi0.5Pb0.5)(2)Sr2O4](0.55)CoO2. Moreover, magnetic anisotropy along the c-axis was enhanced by partial substitution of Pr for Ca in [(Bi0.5Pb0.5)(2)Ca2O4](z)CoO2. From the analysis of their crystal structures, we concluded that the doping of Pr and Ca played a role in distortion of the block layer, indirectly leading to changes in the local structure of the CoO2 layers and magnetic anisotropy. The c-axis grain-aligned bulk has been successfully fabricated by a magnetic grain-alignment method in 10T, and a drastic reduction in the resistivity perpendicular to the applied field and the grain-oriented microstructure were observed.

High magnetic field is well known to have the function of crystal orientation, which is largely influenced by crystal size and shape to some extent. For crystals with large rod shape, the gravity force functions and affects the crystal orientation. In our experiment, different results were got when a high magnetic field was applied perpendicular and parallel to the gravity force. In this paper, the effect of the gravity force for crystal orientation under the high magnetic field is summarized and compared with the experiment result.

Abstract: Superplastic tensile ductility in Al2O3-10 vol% ZrO2 (3 mol% Y2O3) exhibits processing-dependence when the grain size is reduced to 0.45 um for a given relative density of ~99.5%. The reduced grain size leads to largely enhanced ductility in a material prepared by colloidal processing, but does not in a material prepared by conventional dry processing. This result is explained from cavity-damage accumulation sensitive to rather a small variation in a few processing-dependent factors: the numerical densities of residual defects and ZrO2 particles. The rate of damage accumulation is shown to depend mainly on the former and additionally on the latter.

Electrophoretic Deposition process was used to deposit titania particles on an electrode to form the thick films from an aqueous suspension, while a high magnetic field was used to align the particles at the same time. X-ray diffraction pattern and scanning electron microscope revealed that textured titania thick films were fabricated successfully, the grains in the c-axis direction were orientated along the high magnetic field even though the anisotropic susceptibility of titania is quite feeble. The suspension condition and heating temperature play important role on the alignment of the particles. The degree of crystalline texture increased with sintering temperature, and a highly dispersed suspension was also favorable for the alignment of particle direction in the high magnetic field t

Textured titania thick films were fabricated by applying external electrical and magnetic fields. X-ray diffraction (XRD) results and scanning electron microscopy (SEM) images revealed that the titania grains in the c-axis direction were orientated along the high magnetic field (10 T) even though the anisotropic susceptibility of titania ceramic is quite weak. (C) 2004 Elsevier Ltd. All rights reserved.

Designing texture is one possible way for improving the electrical, chemical, mechanical and other properties of ceramics. We have reported that oriented alpha-alumina was obtained by slip casting in a high magnetic field followed by sintering. beta-Alumina is well known as sodium ion conductor used in a sodium-sulfur battery. beta-Alumina consists of spinel blocks and ion conductive planes. Since the direction of the ion conductive plane of polycrystalline beta-alumina is random, the ionic conductivity of the polycrystal is lower than that of the single crystal. The purpose of this study is to prepare oriented beta-alumina to enhance the sodium ion conductivity. Oriented beta-alumina was prepared by the following method: (1) oriented alpha-alumina green bodies were prepared by colloidal processing in a high magnetic field, (2) the oriented alpha-alumina green bodies were infiltrated with Na2O and MgO, and (3) the oriented beta-alumina bodies were synthesized by reaction sintering at 1600 and 1700 degreesC. The reaction product and orientation of the beta-alumina were confirmed by XRD. (C) 2004 Elsevier B.V. All rights reserved.

The 3 mol% yttria doped tetragonal zirconia (3YTZ) is known to show ionic conductivity and superplastic property. However, the application of superplasticity to the manufacturing process is limited because the strain rate is low. The purpose of this study is to fabricate high-strain rate superplastic zirconias by adding titania and magnesia to 3YTZ. Effect of titania and magnesia addition to 3YTZ on diffusion related phenomena such as sintering, grain growth, superplastic properties and ionic conductivity was investigated. Dense and fine-grained zirconia polycrystals were obtained by colloidal processing, where aqueous suspensions were prepared by dispersing 3YTZ, magnesia and titania powders by ultrasonication and adding the appropriate amount of polyelectrolyte. The grain growth was controlled by cation lattice diffusion and the grain growth rate was enhanced by adding titania and magnesia. The tensile ductility of about 216% was established for the titania and magnesia added 3YTZ at the low temperature of 1350 degreesC and high strain rate of 1.2 x 10(-2)s(-1). The ionic conductivity of 3YTZ was decreased with titania addition. (C) 2004 Elsevier B.V All rights reserved.

Many trials have been reported for the production of textured ceramics. Recently, such processing using a high magnetic field has been developed. After the suspension was compacted in a high magnetic field, a green body with a slight degree of crystallographic orientation was obtained. The degree of texture increased with increasing temperature. After densification, grains grew to produce ceramics with a higher degree of crystallographic orientation. We were able to produce a highly textured microstructure. In this paper, we discuss the relationship between the microstructure and the crystalline orientation, and demonstrate that the crystalline orientation depends on the grain size.

Superplastic-like flow in a fine-grained MgAl2O4 polycrystal exhibits strain softening and hardening, which cannot be ascribed to cavity damage and grain growth during deformation, respectively. The softening and hardening can be related to a change in the internal stress, which depends on a decrease and an increase in the density of the intragranular dislocations, respectively, whose motion contributes to the relaxation of stress concentrations exerted through the predominant deformation mechanism of grain-boundary sliding. In these two regions, the rate of deformation is controlled by the continuous recovery of the dislocations limited by lattice diffusion of the oxygen ions.

従来は磁場の影響を受けないと考えられてきた弱磁性セラミックスでもコロイドプロセスと強磁場を用いることで、その配向を制御できることを見出した。ここでは、アルミナを例にとり、強磁場を用いて配向制御するためのプロセス因子を解説し、その応用として酸化チタン、酸化亜鉛なども配向制御した例を示した。

Highly crystalline-textured pure dense alumina ceramics were fabricated from spherical alumina powder without any seed particles and sintering additives by electrophoretic deposition (EPD) in a strong magnetic field of 10 T. The crystalline texture was confirmed by x-ray diffraction (XRD) for alumina ceramics deposited at 10 T followed by sintering at 1873 K. The angle between the directions of the magnetic and electric fields (phi(B-E)) was altered to control the dominant crystal faces of the alpha-alumina monoliths. The average orientation angles estimated from the XRD diagram of the samples prepared at phi(B-E) = 0degrees, 45degrees, and 90degrees were 16.52degrees, 45.15degrees, and 84.90degrees, respectively. Alumina/alumina laminar composites with different crystalline-oriented layers were also fabricated by alternately changing the phi(B-E) layer by layer during EPD in a 10 T magnetic field. It was demonstrated that by using this technique, it is possible to control the crystalline orientation by changing the angle of E versus B during the EPD.

コロイドプロセスは、溶液中の微粒子の分散・凝集を制御し成形する手法で、緻密で微細粒焼結体の作製手段として注目されてきた．さらに，外界から電界・磁界を印加することにより，高度に微構造を制御するプロセスとして期待されいる．ここでは、我々の行っている超塑性微細粒セラミックスの作製と特性、電気泳動堆積法による積層体の作製、および強磁場印加コロイドプロセス―粒成長による高配向構造体の作製、について紹介する．

Textured alumina ceramics were fabricated by electrophoretic deposition in a strong magnetic field of 10 T (Tesla) followed by sintering. Single crystalline alpha-alumina particles dispersed in aqueous media were aligned due to their anisotropic diamagnetic susceptibility and then deposited on a cathodic substrate. The degree of crystalline orientation of the as-deposited specimen characterized by X-ray diffraction was small but highly improved by sintering in the temperature range of 1273-1873 K. Microstructural observations showed the absence of any anisotropic grain growth. (C) 2004 Kluwer Academic Publishers.

Textured monolithic alumina ceramics were synthesized by electrophoretic deposition (EPD) in strong magnetic field of 10 T. Single crystalline, granular a-alumina particles in aqueous suspensions were rotated due to their anisotropic diamagnetic susceptibility and then deposited on substrate. A multilayered alumina composite of oriented and randomly oriented layers was also synthesized by the alternate EPD of alumina suspensions which were placed in and out of a superconducting magnet. It was demonstrated that the EPD in a strong magnetic field is a promising ceramic processing technique for fabricating sophisticated ceramic composites. (C) 2003 Elsevier Ltd. All rights reserved.

Two types of tailored ceramics were prepared by colloidal processing. First, colloidal processing was applied to obtain dense and homogeneous alumina- and zirconia-based ceramics with fine-grained microstructure. Large tensile elongation exceeding 550% was achieved for 10 vol.% zirconia-dispersed Al2O3 at 1773 K and high-strain-rate (above 10(-2) s(-1)) superplastic zirconia-based ceramics were achieved by adding TiO2 and MgO. In the second process, a high magnetic field was applied during slip casting of alumina suspension to produce textured microstructure. A green body with a slight degree of crystallographic orientation was obtained and the degree of texture increased as temperature was increased. After densification, alumina grains grow to yield ceramics with textured grains and high degrees of crystallographic orientation. This processing can be applied to other ceramics having asymmetric unit cell, such as SiC, Si3N4, etc.

The purpose of this study is to fabricate high-strain fate above 10(-2) s(-1) superplastic zirconia systems. Dense, homogeneous and fine-grained zirconia systems of MgO and TiO2 added 3YTZ (3mol%Y2O3 doped tetragonal zirconia), and Al2O3 and/or Mn3O4 added 3YTZ were obtained by colloidal processing. The grain growth was controlled by cation lattice diffusion and the grain growth rate was enhanced by adding TiO2, Al2O3 and/or Mn3O4. High-strain rate superplasticity was established for the systems of 3(Y2O3, MgO) (.) 97(Zr0.95Ti0.05)O-2 and small amounts of Al2O3 and/or Mn3O4 added 3YTZ,. Such excellent superplasticity is due to the homogeneous, fine grained microstructure and enhancement of cation lattice diffusion in 3YTZ by addition of TiO2, Al2O3 and/or Mn3O4.

Electrophoretic deposition of titania (anatase) suspension was conducted in a strong magnetic field of 10 T. The direction of the electric field E relative to the magnetic field B was altered (phi(B-E) = 0, 30, 60 and 90degrees) to control the dominant crystal faces of the deposit surfaces. The crystalline orientation was investigated by the X-ray diffraction for the titania films of as-deposited, sintered at 650, 750 and 1200 degreesC as a function of the angle between the directions of B and E (phi(B-E)). It was found that changing the angle phi(B-E) during the EPD could control the crystalline orientation of the titania films. (C) 2004 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Conventional superplastic ceramics have been established at temperatures over 1400 degreesC with a slower deformation velocity of about 10(-4) (s(-1)). For the application of superplasticity to the manufacturing process, however, high-strain rate deformation velocity of around 10(-2)/s(-1) is necessary. We have reported that alumina addition to 3YTZ (3 mol.%Y2O3 doped ZrO2) is effective in the enhanced ductility. The purpose of this study is to fabricate high-strain rate superplastic 3YTZ by adding manganese and aluminium oxides. Dense and fine-grained 3YTZ systems were obtained by slip casting and low temperature sintering. Manganese and alminium oxides added 3YTZ showed a maximum tensile ductility of about 600% at 1450 degreesC at a strain rate of 1.2 x 10(-2)s(-1). (C) 2003 Elsevier Ltd. All rights reserved.

The electrophoretic deposition of single-crystalline a-alumina particles dispersed in aqueous media was performed in a strong magnetic field of 10 T. The a-alumina particles in the stable suspension were aligned due to their anisotropic diamagnetic susceptibility and then deposited on a cathodic substrate. The orientation of the a-alumina crystallites was confirmed by x-ray diffraction of the sintered specimen.

In order to find a new energy-saving-powder manufacturing process, the pulverization due to hydrogenation of Nb-Zr-Fe alloys with 35 different compositions has been studied. The hydrogenation was performed under the hydrogen atmosphere of 0.1 MPa and room temperature in an arc melting chamber without exposure to air after arc-melting. Nb-Zr-Fe alloys absorb a large amount of hydrogen from 0.1 to 1.8wt%H and pulverize into powders. This pulverization is closely related to the composition of alloys. The composition which is easy to pulverize is concentrated to the ranges of 15 at%Fe in Nb-Zr-Fe alloys and 15-30 at% Fe with fixed to Nb/Zr ≒ 1/1 in Nb-Zr-Fe alloys. For an example, hydrogen absorbed powder of 45Nb-40Zr-15Fe alloy has wide size distribution from 5 to 200 micron with flake figure and with many fine cracks. The hydrogen in powder of 45Nb-40Zr-15Fe alloy is stably stable until 473 K and dehydrogenation temperature is from 473 K to 773 K. It is estimated that hydrogenation is induced by proper amount of iron element in Nb-Zr-Fe alloys and a hydrogen rich phase and a hydrogen poor phase are formed in an alloy ingot. Forming of two phases by absorbing hydrogen causes to pulverization of Nb-Zr-Fe alloys.

The role of the initial degree of ionization (alpha(i)) of polyethylenimine (PEI) in the dispersion of SiC nanopartilces in water was investigated by sedimentation and rheological measurements. The ionization of PEI was characterized by potentiometric titration, which indicated a pH-dependent conformational transition. The dispersion of SiC particles in the presence of PEI was found to strongly depend on the alpha(i). In the presence of 0.4% by weight PEI, the 23.8% SiC by volume (Phi(SiC) = 23.8) slurries showed a Newtonian behavior for alpha(i) = 0.12-0.4 values, whereas a shear-thinning behavior was observed for alpha(i) &gt; 0.4 in the optimal pH range of around pH 4. The rheological behavior of the slurries exhibited a strong dependence on the concentration of PEI of alpha(i) = 0.12-0.4 and the slurry showed a Newtonian behavior at an optimal concentration of 0.4% by weight. The stabilization may be dominated by an electrosteric effect arising from the adsorbed PEI of alpha(i) = 0.12-0.4. The flocculation mechanism of the slurries with PEI of alpha(i) 0.4 is also discussed.

The control of texture in ceramics is one of the ways for effectively improving their properties. Anisotropic susceptibility is very small in ZnO and TiO2; therefore, it had been very difficult to developing the textured microstructure using a magnetic field. But we demonstrate in this paper that the textured ZnO and TiO2 can be prepared by a colloidal processing in a high magnetic field followed by heating. A green solid with a slight degree of crystallographic orientation was obtained before sintering. The degree of texture increased with increasing temperature, and crystallographic texture development accompanies the densification and grain growth in the specimens.

Anisotropic susceptibilities of feeble magnetic ceramics such as zinc oxide are quite small; therefore, it had been difficult to control the textured microstructures of these ceramics using a magnetic field. However, fabrication of the textured ZnO is achieved by slip casting in a strong magnetic field followed by heating. After the stable suspension of ZnO fine particles was compacted by slip casting in a strong magnetic field, a green body with a slight degree of crystalline texture was obtained. Densification and the grain growth enhanced the degree of texture during the sintering.

Whisker alignment is one possible way in order to improve the properties of whisker reinforced materials. Susceptibility is very small in diamagnetic ceramics such as titania and alumina, etc.; therefore, the effects of a high-magnetic field on these ceramics had been generally neglected. Recently, superconducting magnet technologies have been developed and used for applications for such feeble magnetic materials. We demonstrate that the alignment of titania whiskers can be controlled by colloidal filtration of a well-dispersed suspension of the whiskers in a high magnetic field (10T) when the direction of the magnetic field was perpendicular to the direction of the fluid.

Anisotropic susceptibility is very small in feeble magnetic ceramics such as titania; therefore, it had been very difficult to develop a textured microstructure using a magnetic field. However, we demonstrate in this paper, that textured titania can be prepared by slip casting in a high magnetic field and heating. After the suspension was compacted by slip casting in a high magnetic field, a green solid with a slight degree of crystallographic orientation was obtained. The degree of texture increased with increasing temperature, and crystallographic texture development accompanied grain growth in the specimens.

High-temperature tensile ductility in alumina-based ceramics is usually limited due to dynamic grain growth. In this study, superplasticity in zirconia-dispersed alumina has been achieved by colloidal processing using monoclinic, tetragonal and cubic zirconia powders. The densities and microstructures depend on the zirconia particles used as a second phase. Differences in the static alumina grain growth in various zirconia-dispersed alumina composites were caused by differences in distribution of the zirconia particles. The tensile ductility of these materials was found to depend on the type of zirconia used. Limited superplasticity seems to be caused by the density and dynamic alumina grain growth during deformation.

High-temperature tensile ductility in alumina-based ceramics is usually limited due to dynamic grain growth. In this study, superplasticity in zirconia-dispersed alumina has been achieved by colloidal processing using monoclinic, tetragonal and cubic zirconia powders. The densities and microstructures depend on the zirconia particles used as a second phase. Differences in the static alumina grain growth in various zirconia-dispersed alumina composites were caused by differences in distribution of the zirconia particles. The tensile ductility of these materials was found to depend on the type of zirconia used. Limited superplasticity seems to be caused by the density and dynamic alumina grain growth during deformation.

Super-plastic zirconia-dispersed alumina ceramics with fine-grained microstructure and the other is highly textured alumina were prepared. Colloidal processing was applied to obtain dense and homogeneous zirconia-dispersed alumina ceramics with mean grain size of 0.45 mum. Large tensile elongation exceeding 550% was achieved for 10 vol% zirconia-dispersed Al2O3 at 1773K, High magnetic field (10T) was applied during slip casting of alumina suspension to produce textured microstructure. Green body with slight degree of crystallographic orientation was obtained and the degree of texture increased with increasing temperature. After densification, alumina grains grow to yield cerarnics with textured grains and high degrees of crystallographic orientation. This processing can be applied to other ceramics with asymmetric unit cell.

Colloidal processing was applied to obtain dense and homogeneous yttria-doped tetragonal zirconia (YTZ), alumina-dispersed YTZ, and magnesia- and titania-doped YTZ. Their slurries were prepared by adding appropriate amounts of polyelectrolyte, and their fine-grained bodies were obtained through slip casting, cold isostatic pressing and low-temperature sintering. The obtained bodies show excellent superplastic properties. In particular alumina addition was found to (1) decrease the limit temperature of superplasticity in YTZ to 1573 K or lower, (2) increase the limit strain rate for large elongation exceeding 300% up to 1.2x10(-2) s(-1) at 1573 K and (3) large tensile elongation exceeding 1000% at 1.7x10(-4) s(-1). The effects of microstructure such as grain size, grain-boundary stracture and cavity density on the superplastic properties are discussed by comparison with the conventionally prepared samples. The creep parameters prepared by the colloidal processing were similar to those prepared by conventional dry processing. Their excellent superplasticities are due to the reduction of residual defects, fine-grained and homogeneous microstructures.

We achieved to produce the highly textured microstructure of undoped dense alumina prepared by slip casting in a high magnetic field and subsequent heating. Well-dispersed alumina aqueous suspensions were prepared by adding appropriate amount of polyelectrolyte. After the suspension was consolidated by slip casting in high magnetic field, the green body with slight degrees of crystallographic orientation was obtained. The degree of texture increased with increasing temperature. After densification, alumina grains grow to yield ceramics with textured grains and high degrees of crystallographic orientation. This processing can be applied to other ceramics with asymmetric unit cell.

Electrophoretic deposition of single crystalline a-alumina particles dispersed in aqueous media was performed in a strong magnetic field of 10 T. The a-alumina particles in the stable suspension were aligned due to their anisotropic diamagnetic susceptibility. and then deposited. on a cathodic substrate. The orientation of the a-alumina crystallites was confirmed by X-ray diffraction of the sintered specimen.

Developing texture is one possible way for improving the properties of ceramics. Texture in ferromagnetic materials can be tailored by a magnetic field, but it had been difficult to produce texture in diamagnetic and paramagnetic materials, such as silicon carbide and alumina, because their susceptibility is very small. A well-dispersed suspension of SiC (w) -Al2O3 was prepared and consolidated by slip casting in a high magnetic field. The Al2O3 matrix with a slight degree of orientation was observed in the green body and the degree of texture increased by annealing.

Developing texture is one possible way for improving the properties of ceramics. Texture in ferromagnetic materials can be tailored by a magnetic field, but it had been difficult to produce texture in diamagnetic and paramagnetic materials, such as silicon carbide and alumina, because their susceptibility is very small. A well-dispersed suspension of SiC (w)-Al2O3 was prepared and consolidated by slip casting in a high magnetic field. The Al2O3 matrix with a slight degree of orientation was observed in the green body and the degree of texture increased by annealing.

The present study on a tensile-deformed superplastic alumina reveals that the growth of cavities finer than the current grain size (fine cavities) into larger ones (large cavities) is constrained from the surrounding matrix. As a result of the constraint, the density of the large cavities becomes noticeably lower than that of the finer ones and shows non-linear dependence on strain, although the total cavity density, i.e., the sum of the fine and large cavity densities depends linearly on strain. Analysis of cavity size distributions also reveals the formation and growth laws of the large cavities.

Surface coating of Si3N4, powder with an alumina precursor was achieved by a sol-gel method using aluminum isopropoxide. Electrophoretic data showed the surface-coated Si3N4 powder behaved like alumina. Consolidation of the surface-coated powder was attempted by an electrophoretic deposition (EPD) technique. EPD rate was improved for the surface-coated powder. Sintering characteristics and fracture toughness were investigated for EPDed compacts. It was demonstrated that the surface coating of Si3N4 powder with alumina precursor had the advantage of not only the improvement of suspension stability, but also the addition of sintering aid.

High temperature tensile failure in a fine-grained alumina with zirconia particle dispersion is found to relate closely to the separation distance among micrometer-sized cavities Bowing from preexistent defects and from newly formed ones during deformation. As the separation distance is decreased to a certain level with an increase in both density and size of such cavities, extensive cavity interlinkage starts to cause microcracking, and the microcracking leads to the occurrence of macroscopic cracks propagating in a direction perpendicular to the tensile axis toward the final failure. The dependence of the onset strain of microcracking on temperature and grain size is also found to relate closely to the dependence of cavity formation and growth rates on these factors.

Creep tests of base metal. weld metal and welded joint of Hastelloy XR, which had the same chemical composition as Hastelloy XR produced for an intermediate heat exchanger of the High-Temperature Engineering Test Reactor, were conducted in simulated primary coolant helium. The weld metal and welded joint showed almost equal to or longer rupture time than the base metal of Hastelloy XR at 850 and 900 degrees C, although they gave shorter rupture time at 950 degrees C under low stress and at 1,000 degrees C. The welded joint of Hastelloy SR ruptured at the base metal region at 850 and 900 degrees C. On the other hand, it ruptured at the weld metal region at 950 and 1,000 degrees C. The steady-state creep rate of weld metal of Hastelloy SR was lower than that of base metal at 850, 900 and 950 degrees C. The creep rupture strengths of base metal, weld metal and welded joint of Hastelloy XR obtained in this study were confirmed to be much higher than the design allowable creep-rupture stress (S-R) of. the Design Allowable Limits below 950 degrees C.

Al2O3-dispersed ZrO2-3mol%Y2O3 composites have been prepared by slip casting and electrophoretic deposition to compare the sinterability and microstructure, using three commercially-available Al2O3 powders. Composites were prepared by pressureless sintering at 1300 °C. The consolidated (green) density, sintered density, grain size and dispersion are compared for both colloidal techniques with the aim of improving the homogeneity and reducing the necessary temperature for sintering.

Substantial superplasticity, where total tensile elongation to failure exceeds 500% at 1773 K, is attained in a zirconia-dispersed alumina by grain size refinement to less than 0.5 mu m through colloidal processing. The material shows gradual strain hardening persisting up to large strains owing to gradual grain growth and damage accumulation. In contrast, the grain size refinement to 0.45 mu m through conventional dry processing is not effective in enhancing tensile ductility. From the microstructural data of these materials, the prerequisites are discussed for obtaining large tensile ductility in zirconia-dispersed alumina.

Substantial superplasticity, where total tensile elongation to failure reaches 550 % at 1773 K, can be attained in a 10-vol%-ZrO2-dispersed alumina when the alumina grain size is reduced to 0.45 mu m by colloidal processing. Although the same grain size is attainable by conventional dry processing, the resultant tensile elongation stays about 260%. The examination of undeformed and deformed microstructures revealed that both homogeneous particle dispersion and reduction in the size and density of residual defects in the sintered bodies are the prerequisites for obtaining large superplastic tensile ductility in zirconia dispersed alumina.

For an initial grain size of 1.0 mu m, the accumulation of damage volume in a ZrO2-dispersed alumina is shown to proceed more slowly than that in a MgO-doped alumina under a given loading condition, irrespective of higher tensile flow stress in the former than in the latter. The slower damage accumulation in the ZrO2-dispersed alumina is caused from the slower formation and growth of cavities larger than the initial grain size. Such slower cavitation is also shown to delay the onset of microcracking. The delayed microcracking leads to higher tensile ductility in the ZrO2-doped material than in the MgO-doped one.

Colloidal processing is well known to be an effective method to avoid the agglomeration of particles in powder processing. In this method, particles are dispersed by the electrostatic repulsion arising from their surface charge which can be controlled by the pH-value of the suspension. Since fine particles tend to agglomerate, however, additional redispersion treatment is necessary to obtain dispersed suspension of submicrometer-sized particles. In this study was used ultrasonication such as additional re-dispersion treatment for the dispersion of fine powders. Al2O3 and ZrO2 used in this study were high-purity fine powders and their particle sizes were 0.2 and 0.07 mu m, respectively. Three types of suspensions were prepared under different conditions of mixing with ultrasonication for various treatment periods. With increasing degree of ultrasonication, the apparent viscosity of suspension decreased, the dispersion of the particles in the suspensions was promoted and the relative densities of the compacts and the sintered specimens increased, because of a decrease in both total pore volume and the pore size. The microstructure of the sintered specimen prepared from the sufficiently ultrasonicated suspension was very fine, which resulted in high superplasticity.

Slurries of monoclinic zirconia and CuO adsorbed tetragonal zirconia (3mol% Y2O3 doped tetragonal ZrO2: 3Y-TZ) were prepared. Their dense compacts were obtained by pressure filtration follwed by CIP treatment. The compacts were densified by pressureless sintering in air to &gt; 98%. Dense bodies of the undoped monoclinic zirconia and CuO doped tetragonal 3Y-TZ with average grain size under 100 nm are obtained.

Composites of gamma-TiAl intermetallic compound and a complex carbide (Ti2AlC) have been formed by mechanical alloying of Ti-Al-heptane system followed by hot consolidation. The amount of the carbide can be controlled by the milling parameters. The composites have fine microstructures of an average grain size of a few hundreds nm. Mechanical properties at elevated temperatures have been investigated by tensile tests. At 1073K, different deformation behaviors depending on the carbon content are distinct, while the total elongation is still small. The total elongation of specimen tested at 1273K and at a strain rate of 1x10(-3) s(-1) exceeds 300%.

The reaction process during milling of Zr and Ti with n-heptane has been investigated. Formation of a metastable intermediate phase characterized by fee-like structure has been revealed at a certain milling time. It disappears upon heating with reversible appearance of the original hcp structure. The amounts of H and C in the metal powders increase with milling time to a constant level at which stabilization of the intermediate phase takes place. The intermediate phase is presumably the stacking fault of hcp structure stabilized by H and C atoms as the precursor of the stable carbides. Dissociation of H from heptane precedes that of C. Site occupation is competitive between H and C, and stabilization of the intermediate phase during milling takes place by the increase of C content excluding H to sites with lower binding energy with H.