上川 直文

Strontium titanate (SrTiO3) particles are expected to be applied to various catalysts, and many kinds of synthesis procedures of SrTiO3 particles with a high specific surface area have been proposed. This study investigates a synthesis procedure of preparing SrTiO3 particles with a high specific surface area by minimizing the crystallization temperature to the least possible value. The SrTiO3 particles are prepared by maintaining spherical hydrous titania particles with smooth or porous surfaces in highly concentrated strontium hydroxide solutions at <= 120 degrees C. When porous hydrous titania particles are used as the raw material and the Sr/Ti ratio in the reaction solution is set at 10, spherical protrusions of SrTiO3 develop on the surface of the original hydrous titania, even at a low temperature (25 degrees C). Single-phase SrTiO3 particles with spherical protrusions composed of very fine crystallites are obtained by treatment at 40 degrees C for 24 h. These particles have a high BET specific surface area of 237m(2) g(-1). The process developed herein is eco-friendly and effective for fabricating various perovskite-type compounds with a high specific surface area. (C) 2021 The Ceramic Society of Japan. All rights reserved.

Dialysis and peptization, which are colloid chemical solution processes, are simple and effective techniques for controlling hydrolysis of hydrated metal cations. These synthetic processes preparation of stable sol with dispersion of doped oxide nanoparticles with wide molar fraction range from metal chloride aqueous and glycol solutions. Furthermore, control and introduction of lattice defects can be possible due to low temperature synthesis below 373 K. Design of optical and electrical characteristics of oxide nanoparticles by the solutions processes can be realized by controlling the situation of doping and lattice defects.

Abstract: Gluconate modified layered titanate particles and their sol were prepared using titanium tetraisopropoxide (TIP) and gluconic acid aqueous solution. A mixture of ethylene glycol solution of TIP and gluconic acid aqueous solution was heated at 368 K for 24 h to obtain sol. The particles, which had a layered structure, were dispersed stably in the sol. Furthermore, dialysis of the sol with H2O formed sol with stable dispersion of the layered titanate particles in H2O. Fourier -Transform Infrared Spectroscopy (FT-IR) and Raman spectra of the obtained particles indicated that they were layered titanate particles with gluconic acid on the surface, that is, the particles were gluconate modified layered titanate. Drying the sol spontaneously formed plate morphology. The aggregated structure of the layered titanate particles swelled with H2O and formed gel. The addition of H2O to the aggregated structure finally lead to a stable dispersion of the layered titanate particles in H2O, when the weight ratio of H2O to the layered titanate was higher than 15. According to SEM observation of the freeze dried gels, the layered titanate particles had also plate morphology with a high aspect ratio and lamellar structure. Furthermore, when glycerol was dissolved into the sol of the layered titanate particles and the sol was heated to evaporate H2O, alternately integrated layered structures were obtained and they showed structural color, which depended on the weight ratio of the layered titanate particles and glycerol. Graphical abstract: UV–VIS transmittance spectra and photographs of the complex gel plate between the gluconate modified layered titanate particles and glycerol. The structural color depends on the weight ratio of (layered titanate sol/glycerol).

Porous titania particles were prepared by partial dissolution of hydrous titania and subsequent heat treatment. Uniform and spherical particles of hydrous titania were prepared by hydrolysis of titanium alkoxide at different hydrolysis conditions. The as-prepared hydrous titania particles were soaked in ethanol to dissolve the weakly polycondensed part of the particles. As a result, meso- and macroporous structures were formed on the surface of the hydrous titania particles that were prepared by mild hydrolysis. The porous structure was retained even after heat treatment at 400&deg;C while the particles crystallized into the anatase phase. The specific surface area of the porous titania particles prepared by heat treatment of hydrous titania at 400&deg;C for 15 min was 121 m²/g.

Zinc oxide (ZnO) nanowires (NWs) are grown on fluorine-doped tin oxide (FTO) glass substrates via a simple reactive evaporation method without the presence of any catalysts or additives. The ZnO NWs show high crystallinity and preferential elongation along the c-axis of the hexagonal wurtzite crystal structure. The highly crystalline NWs as electron transporting layer have been used to fabricate the CH3NH3PbI3 perovskite solar cells and their photovoltaic performance were investigated. In this report, we studied the effect of filtration of PbI2-solution on surface morphology of CH3NH3PbI3 layer. Spin-coating of the filtered PbI2-solution leads to a better crystallization and relatively homogenous coverage of the CH3NH3PbI3 film, resulting in an enhancement of the solar cell efficiency compared to the cell fabricated using non-filtrated PbI2-solution. By synthesizing the CH3NH3PbI3 film using filtrated PbI2-solution, we achieved the best power conversion efficiency of 4.8% with a current density of 7.6 mA cm(-2), the open circuit voltage of 0.79V and fill factor of 0.63. (C) 2016 The Japan Society of Applied Physics

A layered titanate sol was prepared at room temperature (298 K) using dialysis of a mixed solution of ethylene glycol solution of TiCl3, ammonium carbonate aqueous solution, and hydrogen peroxide. A sol with dispersion of plate-shaped layered titanate nanoparticles was obtained. A stable sol with dispersion of spindle-shaped anatase TiO2 nanoparticles was obtained by heating the sol with dispersion of layered titanate at 368K for 24 h in a closed vessel. The optical transmittance spectrum of the TiO2 thin film obtained by coating the sol with dispersion of anatase nanoparticles and firing at 773 K for 1 h showed no interference of an incident light beam into the TiO2 thin film. Optical characteristics on interference originated from pores among TiO2 primary nanoparticles in the thin film, which caused incoherent scattering of incident light into the thin film. When the sols containing both of the plate-shaped layered titanate nanoparticles and the spindle-shaped anatase nanoparticles were used as the coating solution, the interparticle pore volume was controlled by the volume ratio of the anatase sol in the coating solution. The effects of interference on the optical transmittance spectra of the thin films depended on the interparticle pore volume. (C) 2016 The Ceramic Society of Japan. All rights reserved.

Zinc oxide (ZnO) nanowires (NWs) are grown on fluorine-doped tin oxide (FTO) glass substrates via a simple reactive evaporation method without the presence of any catalysts or additives. The ZnO NWs show high crystallinity and preferential elongation along the c-axis of the hexagonal wurtzite crystal structure. The highly crystalline NWs as electron transporting layer have been used to fabricate the CH<inf>3</inf>NH<inf>3</inf>PbI<inf>3</inf>perovskite solar cells and their photovoltaic performance were investigated. In this report, we studied the effect of filtration of PbI<inf>2</inf>-solution on surface morphology of CH<inf>3</inf>NH<inf>3</inf>PbI<inf>3</inf>layer. Spin-coating of the filtered PbI<inf>2</inf>-solution leads to a better crystallization and relatively homogenous coverage of the CH<inf>3</inf>NH<inf>3</inf>PbI<inf>3</inf>film, resulting in an enhancement of the solar cell efficiency compared to the cell fabricated using non-filtrated PbI<inf>2</inf>-solution. By synthesizing the CH<inf>3</inf>NH<inf>3</inf>PbI<inf>3</inf>film using filtrated PbI<inf>2</inf>-solution, we achieved the best power conversion efficiency of 4.8% with a current density of 7.6 mA cm⁻², the open circuit voltage of 0.79 V and fill factor of 0.63.

Optically transparent and stable sols of copper ion doped zinc sulfide (ZnS:Cu) nanoparticles were obtained by heating a mixture of ethylene glycol aqueous solution and sulfide precipitate at 348K for 24 h. The sulfide precipitates containing zinc ions, copper ions and citrate ions were peptized in an aqueous solution of ethylene glycol having a 0.5 molar fraction of [Ethylene glycol]/([H2O]+[Ethylene glycol]). Photoluminescence characteristics and stability of the sols depended on the amount of citrate ions in the aqueous solution which was used for preparing sulfide precipitates. The citrate ions strongly affected the characteristics of the obtained sols with dispersion of the copper ion doped-ZnS nanoparticles. According to TG-DTA curves and N-2 adsorption isotherms of the precipitated sulfides, the citrate ions in the aqueous solution containing zinc ions, copper ions coprecipitated in the sulfide precipitates formed by adding the sodium sulfide aq. The citrate ions played an important role for the peptization and the formation of stable sols. (C) 2015 The Ceramic Society of Japan. All rights reserved.

The possible use of SiC as a Spark Plasma Sintering (SPS) die was examined. Although SiC has good strength even at high temperatures, electrical conductivity is generally too low for use as the SPS die. Maximum output voltage of a typical SPS machine is 10 V. Joule heating of SiC by application of 10 V is too small to increase its temperature. One approach to this problem is to apply a higher voltage to the SiC die. Using prototype high voltage SPS equipment, the temperature of a SiC die was successfully elevated. Another approach is to heat the SiC die in advance. SiC has a semiconducting behavior, so that the electrical conductivity at high temperatures becomes sufficient for the ordinary SPS equipment. Using an SPS machine that has a "hot-wall" (heaters surrounding the die), the temperature of the SiC die was successfully increased by application of low voltage. This SPS had similar sintering results compared to traditional ones. As an example, partly transparent alumina was successfully prepared. Also, the initial compositional fluctuation of Pb(Zr,Ti)O3 was maintained after it was densified by this SiC-SPS. © (2014) Trans Tech Publications, Switzerland.

An aqueous solution of aluminum nitrate and yttrium nitrate was prepared and ethylenediamine molecules were added into the aqueous solution. The obtained precipitated precursor particles were fired and oxide particles were obtained. When ethylenediamine was used for the precipitation, the single phase of YAG was obtained by firing the precursor particles at more than 1073 K. On the other hand, when hexamethylenediamine was used for the precipitation, the YAG phase was not able to obtained by firing the precursor at 1373 K. Formation behavior of YAG phase greatly depended on the used diamine molecules. Furthermore, Ce³⁺-doped YAG particles were prepared by firing precipitated particles from the aqueous solution in which the nitrates of Al³⁺, Y³⁺, and Ce³⁺ were dissolved with ethylenediamine as precipitating agent. The PL spectra of the obtained particles had the photoluminescence (PL) peak at 535 nm even though the firing temperature was 1073 K.

ZnO nanoparticles and their stable sols were prepared by heating an ethylene glycol solution of Zn(NO₃)₂·6H₂O (0.1 mol/L, 50 mL) with 2 mL of NH₃ aq at 328 K for 24 h. The obtained sol contained ZnO nanoparticles with average diameter of around 20 nm. The particle size decreased with increased the concentration of NH₃. Furthermore, the ZnO nanoparticles dispersed in the sols showed a green photoluminescence peak around 550 nm. The heating procedure of the ethylene glycol solution at 328 K yielded stable sols of ZnO nanoparticles with photoluminescence characteristics. In order to control the photoluminescence characteristics of the ZnO nanoparticles, the ethylene glycol solution which contained zinc nitrate hydrate, glucose, and 1 mol/L of NH₃ aq was heated at 328 K for 24 h. The obtained ZnO nanoparticles dispersed in the sols showed a blue photoluminescence peak at around 420 nm. The glucose reacted with Zn²⁺ ions as a reduction agent. Accordingly, the simple one-pot synthesis process using the heating of the ethylene glycol solution containing zinc nitrate hydrate, NH₃, and glucose achieved control of photoluminescence spectra and enabled the stable dispersion of ZnO nanoparticles.

Ce-TZP/BaAl₁₂O₁₉ composites were prepared using an amorphous precursor powder as the starting material of the second phase BaAl₁₂O₁₉. With increase of the weight ratio of the second phase, the average grain size of matrix zirconia decreased markedly from 2.5 µm of the monolithic zirconia to 0.62 µm of the Ce-TZP/20 wt % BaAl₁₂O₁₉ composite. Three-point bending strength of the composites was increased by incorporation of second-phase particles. The Ce-TZP/15 wt % BaAl₁₂O₁₉ composite showed a maximum value of 769 MPa. Although fracture toughness of the composites decreased concomitantly with an increase in the weight ratio of the second phase, the degree of the toughness degradation was suppressed by crack deflection effects arising from the incorporated anisotropic second-phase particles.

Transparent and stable sols of titanium oxide nanoparticles were obtained by heating a mixture of ethylene glycol solution of titanium tetraisopropoxide (TIP) and a NH3 aqueous solution at 368K for 24h. The concentration of NH3 aqueous solution affected the structure of the obtained titanium oxide nanoparticles. For NH3 aqueous solution concentrations higher than 0.2mol/L, a mixture of anatase TiO 2 nanoparticles and layered titanic acid nanoparticles was obtained. The obtained sol was very stable without formation of aggregated precipitates and gels. Coordination of ethylene glycol to Ti 4+ ions inhibited the rapid hydrolysis reaction and aggregation of the obtained nanoparticles. The obtained titanium oxide nanoparticles had a large specific surface area: larger than 350m 2/g. The obtained titanium oxide nanoparticles showed an enhanced adsorption towards the cationic dye molecules. The selective adsorption corresponded to presence of layered titanic acid on the obtained anatase TiO 2 nanoparticles. © 2012 Naofumi Uekawa et al.

Composites consisting of Ce-TZP matrix and in-situ grown particles of barium hexaaluminate (BaAl₁₂O₁₉) as the second phase were prepared. To lower the sintering temperature and improve the microstructure of the composites, starting materials of two types of the second phase were used: mixed powders of BaCO₃ and α-Al₂O₃, and amorphous precursor powder. When the composites were prepared using the mixed powder of BaCO₃ and larger α-Al₂O₃ (3.0 µm) particles, aggregations of in-situ formed BaAl₁₂O₁₉ particles were observed in the Ce-TZP matrix. Although the formation temperature of BaAl₁₂O₁₉ decreased with decreasing average size of α-Al₂O₃ particles, full dense composites were unobtainable, even at the sintering temperature of 1400°C. To lower the formation temperature of the second phase further, amorphous precursor powder of BaAl₁₂O₁₉ was prepared using coprecipitation method. The composite prepared using the amorphous precursor powder was sufficiently densified at 1400°C. The BaAl₁₂O₁₉ particles formed in the composite were finer than those prepared using the mixed powder of BaCO₃ and α-Al₂O₃.

A sol of Mn2+-doped ZnS nanoparticles was prepared by heating a ZnS precipitate with Mn2+ ions in ethylene glycol at 348 K for 24h. The precipitate was prepared by mixing the aqueous solution of Zn(NO3)(2)center dot 6H(2)O and Mn(NO3)(2)center dot 6H(2)O with an aqueous solution of Na2S According to the UV-VIS absorption spectra, when the wavelength was more than 400 nm, the optical absorptions of the obtained sols with the molar fraction of Mn2+ ions in the solution (X-solution: the molar fraction of Mn2+/(Mn2+ + Zn2+) in the aqueous solution) less than 0.02 were less than 0.12 and the obtained sols were clear and transparent for the visible light. The sol of Mn2+-doped ZnS nanoparticles showed PL characteristics when irradiated with an excitation light with a wavelength of 345 nm. Accordingly, a simple process to heat the mixture of the sulfide precipitate and ethylene glycol at 348 K enabled us to obtain a homogeneous transparent sol of Mn2+-doped ZnS nanoparticles with PL characteristics. According to the results of the chemical analysis of the molar fraction of Mn2+ in the obtained precipitate (X-Precipitate) and the nanoparticles in the sols (X-Nano), the X-Nano was less than that the X-Precipitate as compared with the same X-solution. The Mn2+ ions in the nanoparticles were dissolved in the solvent during the heat treatment since the solubility product of MnS was much larger than that of ZnS. As such, the dissolution-precipitate process played an important role in the formation of the sol. (C) 2011 The Ceramic Society of Japan. All rights reserved.

硫化亜鉛(ZnS)は代表的な蛍光体材料であり、金属イオンのドープによりその蛍光発光特性の制御が可能である。本研究では、エチレングリコール(EG)が遷移金属イオンに強く配位し、粒子の成長や凝集を抑制しナノ粒子の分散の安定性を向上させる機能に着目した。そこで、水溶液中で調製したZnS沈殿をEG中にて解膠し再分散させる非常に簡便な方法により、Mn&lt;SUP&gt;2+&lt;/SUP&gt;およびCu&lt;SUP&gt;2+&lt;/SUP&gt;ドープZnSナノ粒子分散ゾルが得られた。特に、Mn&lt;SUP&gt;2+&lt;/SUP&gt;ドープZnSゾルの場合は特有のオレンジ色の蛍光発光を示した。Cu&lt;SUP&gt;2+&lt;/SUP&gt;ドープの場合は沈殿生成用水溶液にカルボン酸イオンを添加することで蛍光発光特性を改善することができた。

Composites consisting of Ce-TZP matrix and in situ-grown particles of barium ferrite (BaM) were prepared using various starting materials. For the starting material for the second phase, an amorphous precursor powder of BaM was prepared by coprecipitation and calcination. Uniform hematite particles were also prepared using liquid-phase synthesis under hydrothermal conditions. The Ce-TZP/20 wt % BaM composites were prepared by sintering the mixed powders of Ce-TZP, barium carbonate, hematite, and amorphous precursor of BaM. The aspect ratio of the in situ-grown BaM particles increased concomitantly with an increase in the mixing ratio of the amorphous precursor powder. The exaggerated grain growth of the BaM in the Ce-TZP matrix was efficiently suppressed by the addition of a small amount of barium carbonate and hematite to the amorphous precursor of BaM.

Porous alumina with uniform microstructure was prepared using needle-like boehmite particles. A procedure for improving its thermal stability was examined. Uniform, needle-like boehmite particles were synthesized using a hydrothermal procedure. Porous boehmite was prepared using vacuum filtration of boehmite aqueous suspension. Porous alumina was prepared by heat treatment of the porous boehmite. During heat treatment at 1200°C for 2 h, the specific surface area of the porous boehmite decreased to about one-twentieth (8 m²/g) of the as-prepared porous boehmite. To improve the thermal stability of the porous alumina, La addition to the porous boehmite surface was conducted merely by filtrating La aqueous solution using the porous boehmite itself. The porous alumina with 1.1 mol % of La showed specific surface area of 46 m²/g, even after heat treatment at 1200°C for 2 h.

Several eutectic-like microstructures were prepared from amorphous phases in the authors&apos; previous works. In this research, the formation process of the microstructure from amorphous phase was investigated for GdAlO3-Al2O3 eutectic system. Amorphous films were prepared by rapid quenching of melt having the eutectic composition. The films were heated at temperatures between 1000 and 1600 degrees C for 30 min to form eutectic phases (GdAlO3 and Al2O3). The films were also heated at 1500 degrees C for various periods between 0.5 and 30 min. GdAlO3 and Al2O3 crystal phases formed from the amorphous phases were identified by XRD. Both components began to crystallise and grow from the amorphous phase separately at different temperatures. This formation process was different from that of the ordinary eutectic microstructure. The microstructures formed from the amorphous phases at sufficiently high temperatures were similar to the ordinary eutectic microstructures.

Stable sols with a homogeneous dispersion of ZnO nanoparticles were prepared by heating zinc hydroxide (Zn(OH)₂) precipitate in an ethylene glycol solution of zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O) at 308 K. The formation of ZnO nanoparticles occurred within 1 h when the mixed solution of Zn(OH)₂ precipitate and 0.05 mol/L of the ethylene glycol solution of zinc nitrate hydrate was heated at 308 K. The obtained sol was homogeneous, and no aggregation of the ZnO nanoparticles was observed. The formation process of ZnO nanoparticles in the mixed solution of Zn(OH)₂ and the 0.05 mol/L ethylene glycol solution of zinc nitrate hexahydrate was examined by measuring changes in the UV-VIS spectra of the obtained sol and the XRD patterns of the particles separated from the sol. Strong absorption due to the electron transition between the band gap of ZnO appeared during heating at 308 K for 1 h. When the heating time decreased, the shift in the absorption edge to a shorter wavelength was observed. This shift in the absorption edge would be related to changes in the particle size during the formation process of ZnO nanoparticles. Furthermore, the photoluminescence spectra of the obtained ZnO nanoparticles were examined. The intensity of photoluminescence increased with increases in the concentrations of zinc nitrate hydrate in the ethylene glycol solution.

Microstructure control of BaTiO₃/Ag composite was examined from the preparation stage of Ag-deposited BaTiO₃ particles. Uniform BaTiO₃ particles were prepared by hydrothermal treatment of a hydroxide gel. Then Ag nanoparticles were deposited uniformly on the BaTiO₃ particle surface by the reduction of diamminesilver (I) ions using glucose. Dense BaTiO₃/Ag composites were obtained respectively via pressureless sintering and spark plasma sintering of the Ag-deposited BaTiO₃ particles. Although the BaTiO₃ and Ag particles grew well after pressureless sintering, their grain growth was suppressed by spark plasma sintering. The Vickers hardness and dielectric constant of the composites were much higher than those of the monolithic BaTiO₃ sintered body.

Off-eutectic microstructures generally have both coarse crystals of rich component and ordinary eutectic microstructures. This paper shows a new method to form a dense bulk material having homogeneous eutectic-like microstructure with off-eutectic compositions. Mixture of Gd2O3 and Al2O3 powders with the off-eutectic composition was melted and quenched rapidly to form the amorphous phase. The amorphous film was pulverized. The dense bulk material could be fabricated by the consolidation of the amorphous powder using spark plasma sintering method. Field emission scanning electron microscope (FE-SEM) observation of the material showed homogeneous fine eutectic-like microstructure without coarse crystals. This is the first case that such material was successfully prepared. (C) 2009 Elsevier Ltd. All fights reserved.

The nitrogen-doped ZnO particles were prepared by heating a mixture of an ammonium salt and the aqueous sol of zinc peroxide nanoparticles. In the case that the sol of zinc peroxide nanoparticles were mixed with ammonium nitrate in the sol, nitrogen-doped ZnO particles were obtained by heating the mixture at 573K for 1h in the air. The obtained particles showed characteristic Raman peaks that can be assigned to the nitrogen-related local vibrational mode. The strength of the UV-VIS absorption peak, which corresponds to the nitrogen-related impurity state, also increased with increases in the mixed amount of ammonium nitrate (NH_4NO_3). The results of iodometric titration also showed the formation of acceptor states in the obtained nitrogen-doped ZnO particles. The nitrogen-doping successively occurred when the peroxo ions (O_2^<2->) in the zinc peroxide did not react with the anions in the ammonium salts as an oxidizing agent.

Homogeneous and ultrafine eutectic like microstructures without coarse primary crystals were formed by a crystallisation of amorphous phases for several rare earth (RE) oxide-Al2O3 eutectic systems with the off eutectic compositions. Mixtures of RE oxide and Al2O3 powders with the off eutectic compositions were melted and quenched rapidly to form the amorphous phases. A heat treatment of the amorphous phases at 1000 and 1300 degrees C for 30 min formed RE3Al5O12/Al2O3 (or REAlO3/Al2O3) phases. This method utilises a low migration rate in the amorphous phases. SEM observation of these materials heat treated at 1300 degrees C showed homogeneous eutectic like microstructures. Formation of primary crystals, which are always formed in the ordinal off eutectic microstructure, was absolutely suppressed. Furthermore, the microstructures were much finer than those of materials ordinarily prepared from eutectic melts.

Ultrafine eutectic-like microstructures of various rare earth (RE) oxide-Al(2)O(3) systems were formed by use of amorphous phases. This new method uses a low migration rate in the amorphous phases. Mixtures of RE oxide (RE: Yb, Dy, Er, Ho, Gd, Sm, Eu) and Al(2)O(3) powders with the eutectic compositions were melted and quenched rapidly to form the amorphous phases. A heat treatment of the amorphous phases of various eutectic systems at 1000 and 1300 degrees C, for 30 min, formed RE aluminium garnet (RE(3)Al(5)O(12))/Al(2)O(3) phases or RE aluminium perovskite (REAlO(3))/Al(2)O(3) phases. Scanning electron microscopy observation of these materials heat-treated at 1300 degrees C showed eutectic-like microstructures, in which crystals of eutectic component were entangled with each other. Furthermore, the microstructures were much finer than those of materials generally prepared from eutectic melts. In this study, it was confirmed that this method is useful for the formation of ultrafine eutectic-like microstructures for many eutectic systems.

Porous materials were prepared by stacking needle-like boehmite particles using a vacuum filtration. Uniform size of needle-like boehmite particles was prepared via hydrothermal treatment of a precursor gel. Boehmite aqueous suspensions with various pH values were prepared and vacuum-filtered to form porous bulk. Porous materials with uniform microstructures were obtained when the pH value of the suspension was adjusted to 9. The mechanical property of the porous boehmite was improved by heat treatment at 1000℃-1100℃ with a slight change of the pore structure. Porous α-alumina was also prepared by heat treatment at higher temperatures. The porous α-alumina prepared from boehmite porous materials with uniform microstructure had a finer microstructure than that prepared from the as-prepared boehmite powder.

GdAlO3 and Al2O3 powders were mixed and pulverized using ball mills. The prepared powder was sintered by SPS at 1450 degrees C without holding time. SEM observation of the sintered specimen showed a eutectic-like microstructure. This is called 'pseudo-eutectic' in this research. The microstructure formed from a powder pulverized by a tumbling ball milt for one week was much finer than that by a planetary ball mill for 5 and 10h. The fine homogeneous eutectic-like (pseudo-eutectic) microstructures could be formed at both eutectic and off-eutectic compositions. In case of crystallization from a melt of eutectic components, homogeneous eutectic microstructures can be formed only at restricted compositions very close to the eutectic one. Coarse primary crystals generally exist in the eutectic microstructure at off-eutectic compositions. The pseudo-eutectic microstructures can be formed at any compositions because a mixing ratio of the starting powders can be varied. (c) 2008 Elsevier Ltd. All rights reserved.