The preparation of WSi₂ powder by a carbothermal reduction process was investigated using ammonium paratungstate, quartz and active carbon in Ar+H₂ atmosphere. Excess silica and carbon were required for producing WSi₂ without W₅Si₃, WC and SiC. Increase only in the amount of carbon led to increase in WC and SiC contents. WSi₂ single phase was obtained by adjusting the amounts of silica and carbon at W:Si:C=1:4:8. The formation of WSi₂ became rapid at 1400°C. It was found that WSi₂ was formed via WC, and SiO vapor took part in the reaction. Wet-mixing of tungsten source by using ammonium salt solutions was effective to produce fine WSi₂ powder with a particle size of about 1μm.

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As a model experiment, the grain growth of aluminum nitride (AlN) was studied at different fractions of yttrium aluminate (7-31%) to compare to the results of computer simulation using Monte Carlo method (MC simulation) of grain growth in presence of a liquid phase. In the model experiment, the time dependence of mean grain size for sintered AlN ceramics was measured from scanning electron photomicrographs. At 2123K, yttrium aluminate appears to be a liquid. The liquid fraction remained relatively constant over the time intervals studied. The cube of mean grain size was observed to be proportional to heat treatment time. The mean AlN grain size decreased as the yttrium aluminate fraction increased. Results of these observations indicated that the solution-reprecipitation process is the dominant growth mechanism in this system and that the rate of grain growth is controlled by AlN diffusion in the liquid phase. On the other hand, microstructures obtained by MC simulation were isotropic and the dependence of grain size in simulated microstructures on fraction of liquid phase and Monte Carlo steps showed similar ones in the model experiment. As a result, it was concluded that MC simulation could express isotropic grain growth and the mechanism that was observed in AlN grain growth.

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Magnesium silicon nitride (MgSiN₂) was synthesized by the nitridation of powders in the magnesium (Mg)-silicon (Si) system. Although an Mg and Si powder with an Mg/Si ratio of 1.0 (=stoichiometric ratio of MgSiN₂) was heated up to 1400°C in nitrogen (N₂), a single phase of MgSiN₂ could not be obtained, due to evaporation of Mg during heating. On the basis of the information that Mg₂Si formed as an intermediate phase during the synthesis of MgSiN₂, an Mg₂Si powder was heated at a temperature between 600 and 1600°C for 1h in N₂. Although MgSiN₂ and other phases such as Si and amorphous Mg₃N₂ were present in the temperature range of 900°C to 1300°C, the powder heated at 1400°C consisted of only MgSiN₂ phase. The chemical composition of the powder heated at 1400°C for 1h was almost stoichiometric; the content of the oxygen was as low as 0.76mol%. The powder consisted of agglomerates with sizes of -5μm; these agglomerates were furthermore composed of primary particles with an average size of 0.54μm. The oxidation resistant temperature of MgSiN₂ was estimated to be -830°C. The MgSiN₂ powder had good resistivity to hydration.

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Gels were prepared in the SiO₂-TiO₂-ZrO₂ system (SiO₂, TiO₂ and ZrO₂=0-100mol%) from Si(OC₂H₅)₄, Ti(O-isoC₃H₇)₄ and Zr(O-nC₃H₇)₄ solutions with or without H₂O and CH₃COOH. Without H₂O and CH₃COOH transparent bulk gels were formed in the range 30-100mol% SiO₂, 0-70mol% TiO₂ and 0-50mol% ZrO₂ and opaque bulk gels in the rest compositions. X-ray diffraction measurement indicated that all the gels were non-crystalline even after drying at 50°C for 3 days. Crystallization peak temperatures T_c were determined by DTA on the dried gels preliminarily heat-treated at 200°C for 1h. T_c was low in the TiO₂-ZrO₂ rich compositions (T_c=366°C for TiO₂ and 419°C for ZrO₂). T_c increased up to 1258°C with increasing SiO₂ content. From T_c and liquidus temperature T_L, T_c/T_L ratio was calculated. T_c/T_L ratio means the thermal stability of the amorphous solids. It was discovered that TiO₂ and ZrO₂ alone are thermally unstable (T_c/T_L=0.3 for TiO₂ and 0.23 for ZrO₂) but mixing TiO₂ with ZrO₂ enhances the thermal stability (for example, T_c/T_L=0.45 for 50TiO₂⋅50ZrO₂) with increased ability of forming amorphous phase (amorphous-forming ability). This is true in the SiO₂-TiO₂-ZrO₂ system for fixed SiO₂ concentrations. T_c/T_L increased with SiO₂ content and reached the highest value of 0.86 at 90SiO₂⋅10TiO₂ composition, which is higher than that of SiO₂ (0.77). Yet it seems likely that there are more stable compositions centering around the 80SiO₂⋅10TiO₂⋅10ZrO₂ in the SiO₂-TiO₂-ZrO₂ system. It is expected that compositions of high T_c/T_L value have a high amorphous-forming ability.

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A glass of the composition Fe₂O₃ 40, CaO 32, SiO₂ 31, P₂O₅ 3 in weight ratio is converted into a bioactive and ferrimagnetic glass-ceramic which is chemically stable in the body environment for a long period by a heat treatment. This type of galss-ceramic is believed to be useful as thermoseeds for hyperthermia treatment of cancers.

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Epitaxially grown PZT films with crack- and void-free smooth surfaces were successfully prepared on MgO (100) by DP process using a constituent metal naphthenate solution. Epitaxial PZT was considered to crystallize directly from the amorphous precursor, not via pyrochlore, and the orientation relationship between PZT films and MgO substrates was: PZT (100)//MgO (100) and PZT [001]//MgO [010], [001].
Epitaxy and surface morphology of the films were found to depend chiefly on their crystallinity. The crystallinity and epitaxy of the films increased with increasing final heat treatment temperature in the range 650-750°C. However, optimum surface morphology, i.e., a smooth and homogeneous texture, was obtained at lower crystallinity, for example, with a film pyrolyzed at 500°C and finally heat-treated at 650°C. On the other hand, low-temperature prefiring lowered the crystallinity of the product films if the final heat treatment temperature was the same. Namely, a film prefired at 200°C and finally heat-treated at 750°C showed similar crystallinity and morphology with the above 500°C-pyrolyzed and 650°C-annealed film.

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Effect of preformed silica protective film on the oxidation behavior of porous SiC ceramics at 1700K in Ar-O₂ atmosphere with P_O2 in the active oxidation range was investigated and following results were obtained.
(1) when the inner pore surface of the ceramics was incompletely covered by the silica layer, CO evolution rate exhibited a peak indicative of the occurrence of the active oxidation soon after the dropping operation for P_O2 from 2 or 10kPa to 0.02kPa. This active oxidation accompanied the silica reduction.
(2) The sample oxidized for 10h at P_O2=10kPa showed no peaking in the CO evolution rate after the P_O2 dropping operation. Thickness of the silica layer of this oxidized sample was about 0.2μm. This sample showed no weight change during the successive soaking for 10h at P_O2=0.02kPa.
(3) As the scheme without the weight change during the soaking in the oxygen-deficient atmosphere, the following reaction was assumed, SiC+4/3O₂→2/3SiO₂+1/3SiO(g)+CO
This reaction forcing the volume increase in the reacting zone, was assumed to contribute to the preservation of the silica protective film.
(4) It was pointed out that, in the case of the well-passivated SiC ceramics, at least minor correction should be done in Gulbransen's theory which is known to be valid for the fresh ceramics.

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Heteronuclear complexes of Ln[Fe_xCo_1-x(CN)₆]⋅4H₂O (Ln=Pr-Yb) were synthesized and their thermal decomposition products were investigated. Thermal decomposition of the complexes results in the formation of perovskite-type oxides for Ln=Pr-Gd even at 800°C. The lattice parameters, a-, b- and c-lattice constants (crystal system: orthorhombic) increase linearly with the ratio of Fe/Co for the perovskite-type oxide. For Ln=Dy through Yb, the Ln₂O₃ phase is observed as the major product for x=0, but its content decreased with an increase in the Fe content; however, a single phase of the perovskite-type oxide was not formed for x=1. The perovskite-type structure for the Fe systems is easier to form compared with the Co systems. We clarified that the formation of the perovskite-type oxide is mainly affected by the ionic radius of the Ln³⁺ ion and the T³⁺ ion (T=Fe or Co).

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Alumina-ceramic materials have been used instead of metals as structural components for aircraft, space craft and automotives. These materials are highly brittle, superhard and difficult to machine. Therefore, the cost of machining alumina-ceramic materials is considerably higher than that of metals. As a result a new cutting method has been developed to achieve lower-cost processing of the alumina-ceramic materials. In this cutting process, the corner of single-crystal octahedral diamonds in native state is used as the cutting edge. The applicability of this method to practical uses was evaluated by measuring the finished surface roughness and the tool life, and the strength characteristics of the materials, cut using this method, were investigated by the bending test. The cutting tool life is longer in the wet cutting method as compared with that in the dry cutting process. Moreover, when the abrasion side position of the diamond crystal edge corresponded to (100) of the crystallographic orientation, the cutting tool life tended to be longer. The maximum roughness of the finished surface was about 18μm and the material strength after cutting was decreased by about 15% compared to that before cutting.

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Amorphous calcium phosphate (ACP), which generally forms as an unstable precursor during the initial stage of hydroxyapatite (HAp) synthesis, was synthesized by rapid dropwise addition of aqueous ammonia into calcium dihydrogenphosphate monohydrate (MCP) solution. ACP was crystallized easily to various calcium phosphates such as dicalcium phosphate dihydrate (DCPD), octacalcium phosphate (OCP) and HAp by dipping ACP (Ca/P atomic ratio 1.25-1.55) in various solutions. The present work was undertaken in order to elucidate the crystallizing conditions, composition and crystallographic data of a new phase formed by crystallizing ACP. The new phase was characterized by means of X-ray diffraction, thermal analysis (TG-DTA), infrared spectroscopy and scanning electron microscopy. The new phase was formed only by dipping ACP with a Ca/P atomic ratio above 1.40 in aqueous solution at 0°C for 24h. The results of chemical analysis and thermal analysis (TG-DTA) determined the chemical formula of the new phase to be Ca₃(PO₄)₂⋅8H₂O. Powder X-ray diffraction data did not correspond to those of already known calcium phosphates. Also, it was proved that crystallographic data of the new phase belongs to the monoclinic system with a=1.312nm, b=1.111nm, c=1.264nm, β=109.0°. Its crystal shape was plate-like 4-6μm across.

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Composites of silica aerogel and porous alumina were prepared by the supercritical drying method on autoclave of mixed solution of TMOS-MeOH-H₂O. Attempts to pack silica aerogels homogeneously in the pores of alumina and to increase the mechanical strength were successful. A linear relationship was found between the permeation rate of gas in composites and the inverse root of molecular weights from 298 to 523K. That is, the gas flow mechanism showed Knudsen flow rule. The mean pore diameters of composites were calculated to be 0.90-1.36nm by analysis of a linear relationship between permeation rate and mean pressure.

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ZrO₂-CaO thin films have been prepared by thermal decomposition of 2-ethylhexanoate. Butanol solutions of Zr and Ca 2-ethylhexanoate containing 0 to 80mol% CaO were coated on Al₂O₃ ceramic substrates, dried at room temperature and 110°C, and then thermally decomposed at 550°C. The above operation was repeated eleven times, and then the specimens were finally heated at various temperatures from 550 to 1400°C. Results of X-ray diffraction and electric conductivity measurements showed that the thin films prepared from the coating solutions with compositions of 13 and 17mol% CaO by final heating at 1200°C had the highest X-ray diffraction intensity and electric conductivity, respectively. Activation energies for conduction were 0.78 to 1.36eV, and a maximum value of 1.36eV was obtained when CaO content in the coating solution was 20mol%.

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Sintered aluminum titanate has a very low thermal expansion and an infrared radiative property selectively emitting large amounts of far infrared rays. However, it is weak in mechanical strength. Spectral infrared emittance, thermal expansion coefficient, and mechanical strength of aluminum titanate-clay composites were studied to develop a material for infrared radiators. The composites containing 10 to 50mass% clay has low spectral emittance in the range of 5000 to 2500cm^-1 and high emittance in the range of 1500 to 360cm^-1. The bending strength of the composite increased with increasing clay content. The composite with a clay content of 30mass% formed by hand pressing using a plaster mold and fired at 1500°C had a large strength for infrared radiators; 80MPa. The average linear thermal expansion coefficient from room temperature to 800°C of the 30mass% clay-containing composite fired at 1500°C was lower than 2.5×10^-6/°C.

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As a plasma facing material of nuclear fusion reactors, B₄C-high thermal conductivity carbon fiber (CF) composite ceramics have been fabricated through hot-pressing. Effect of sintering temperature on the thermal conductivity of the composites was investigated in a 1600-2100°C range. The mean density of substitutional solute B in the CF, estimated from shifts in (110) Bragg diffraction angle, was found to increase from 0.26 to 0.90atom%, as the hot-pressing temperature was increased from 1600 to 2100°C. The reciprocal phonon mean free path in the CF's of the composite, 1/l_L, was estimated from sound velocity in graphite in the in-plane directions divided by thermal diffusivity in the fiber axis direction of the composite, v_L/α. Thus, the phonon scattering probability due to structural defects, including substitutional B solution into CF's of B₄C-CF's of different sintering temperatures, was estimated from vertical axis intersection in 1/l_L-T plot. The mean substitutional B density was found to change proportionally to the vertical axis intersection in the 1/l_L-T plot. The decrease in thermal conductivity due to substitutional B solution into the CF's was found to be remarkable only below 400°C, but the decrease was insignificant above 400°C. Thus, hot-pressing at 2100°C is recommendable from total material designing aspects.

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The adsorption behavior of various water soluble polymers with different ionicities on ceramic particle surfaces was investigated in order to control the flocculation from an electrokinetic and rheological point of view. The results are summarized as follows: (1) Various water soluble polymers with different ionicities adsorb on high affinity sites in ceramic particles containing SiO and/or Al (O, OH). The cationic polymer mainly adsorbs on negatively charged SiO sites (adsorbs on Al (O, OH) sites above the isoelectric point of alumina). The anionic polymer adsorbs on positively charged Al (O, OH) sites. And the nonionic polymer adsorbs on Al (O, OH) sites (adsorbs on SiO sites at low pH). (2) In many polymer-powder systems showing both affinity and low yield stress of polymer solution at low pH, the amount of polymer adsorption increases with decreasing pH, and vice versa. There are two systems at high pH which show attraction such as alumino-silicate/cationic polymer or repulsion such as alumina/anionic polymer.

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We have discussed the effect of comb macromolecule adsorbed on fused silica particles to the dispersion of the particle. The effect of the amount and thickness of the polymers adsorbed on the fused silica particles on the total interparticle potential energy was investigated. The evaluation of dispersed property of the particles in solvent was considered by magnitude of interparticle potential energy. The total interparticle potential energy was calculated by summing up the steric hindrance effect and London-van der Waals interaction. The amount of polymers adsorbed were not influenced by the minimum of the total potential energy. The maximum radius of the particles that can be dispersed in polymer solution was in proportion to the thickness of the adsorbed layer.

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Silica films with various surface morphologies, such as flatness, mesoporosity, uneveness, convexity, were prepared by hydrolysis and polymerization of tetraethoxysilane, Si(OC₂H₅)₄(TEOS) and methyltrietoxysilane, CH₃Si(OC₂H₅)₃(MTES) under acid-catalyzed conditions. The morphology of coatings could be changed by changing the molar ratio (denoted as f, f=KITES/TEOS) in TEOS-MTES mixture, as well as the conditions of drying process and heat treatment temperature. Especially, in the case of 5<f≤7.5, the surface of coatings was uneven, when films were prepared at humidities higher than 45RH%. Water repellent glasses obtained by coating hydrolyzed heptadecafluorodecyltrimethoxysilane, CF₃(CF₂)₇CH₂CH₂Si(OCH₃)₃ on to this uneven surface showed an excellent abrasion resistance and UV-light stability for windows of automobiles and buildings.

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The purpose of this paper is to present the relationship between mechanical properties and thermoelectric properties of p-type Bi-Te polycrystalline materials. Semiconducting ceramics of p-type bismuth telluride were prepared by a hot press method. Their bending strength was over 40MPa and decreased with increasing particle size. The Seebeck coefficient and resistivity were dependent upon the particle size, those thermoelectric properties decreased with increasing particle size. The results suggest that the carrier density varies with concentration of oxygen which adsorbed at the surface of the powders. Thermoelectric properties were nonisotropic. Especially, the resistivity was different for the hot press directions. The ratio of the resistivity increased with increasing the particle diameter. The bending strength, Seebeck coefficient and resistivity decreased with increasing a hot press temperature. A sample with a bending strength of more than 50MPa and a power factor of 40×10^-3W/cm·K² was obtained by controlling the particle size and the hot press temperature.

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CaTiO₃ porous substrates required for spin-coating of mixed conductor Ca(Ti, Fe)O₃ films were prepared by a foam-burning method. Mixtures of calcined CaTiO₃ powder and foaming agents such as corn starch, wheat starch D(+)-glucose and carbon black were heated gradually up to 500°C, then kept at 500°C for 2h and finally sintered at 1350°C. Relatively large pores above 15μm in diameter were formed when 15-35mass% corn starch was used as a foaming agent. Pore diameter distribution broadened with wheat starch. Sintered compacts with pore diameters as small as 5-10μm were prepared by using 15-25mass% carbon black or D(+)-glucose. The addition increased the mechanical properties of the spin-coated substrate. Gas permeability was found to increase according to the order; corn starch>wheat starch>D(+)-glucose≥carbon black for a fixed amount of addition. An accelerated increase in the gaseous permeability was ascertained with increasing amount of foaming agent. A CaTiO₃ porous substrate prepared with 20mass% carbon black or 40mass% wheat starch exhibited sufficiently high mechanical strength for the thermal cyclic process of spin-coating and subsequent sintering.

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The results of systematic study on compositional variations within Sr₂CuO₃-(Bi_1.7Pb_0.3)CuO_y-Ca₂CuO₃ pseudo-ternary systems are reported. In this system, the solid solution range of superconducting 110K (H: 2223) and 80K (L1: 4425) phase was defined. Besides these phases a new 65K (L2) phase with composition Sr₇(Bi₅Pb)Ca₇Cu₁₀O_y (76710) was found. Superconductive properties (δT_c) are influenced by the composition ratio of Sr:Bi (A), and ideally they require the stoichiometric composition of A=1. The introduction of PbO is effective not only in promoting the formation reaction of H-phase, but also in compensating the Sr-deficient composition and in the improving the superconducting properties.

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A dynamic durability test system was constructed and checked which can change the preload, temperature and driving voltage for piezoelectric pellets of lead zirconate titanate (PZT) ceramics. Durability tests on samples with various initial properties revealed that decrease in electromechanical coupling factor was less for samples which have lagre coercive fields. In addition, the same tendency was observed for the samples which have higher Curie temperatures, indicating that the improvement of coercive field and Curie temperature prevents property degradation.

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Preparation of coated particles by an injection method was presented. The raw material of a coating layer is injected into a core particle suspension in which a precipitant is dissolved. By this method, some coated particles including titania hydrate-coated calcium carbonate powders and alumina hydrate-coated SiC whiskers were prepared. It was noticeable that CaCO₃, which is soluble in the raw material of titania hydrate, could be coated with titania hydrate. Furthermore, it was shown that aluminum nitrate and aluminum chloride as well as aluminum sulfate were useful as the raw material salts. Homogeneous nucleation and coalescence of the homogeneous nuclei onto the coating layers were expected to be included in the coating process.

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TiN whiskers were synthesized using K₂TiF₆ as a starting material and B₂O₃ as an additive. The largest amount of TiN whiskers was deposited when 1mmol of B₂O₃ was placed in a graphite boat (1), a mixed powder containing K₂TiF₆ and B₂O₃ was placed in another boat (2), and then they were both heated at 1400°C for 10h. B₂O₃ evaporated was considered to accelerate the thermal decomposition of alumina tube, investigating the effect of addition of B₂O₃. Scanning electron microscopy and transmission electron microscopy of the obtained whiskers revealed that most of the whiskers were square prismoidal shaped and some were hexagonal or octagonal prismoidal shaped. The square and octagonal prismoidal whiskers grew in the ‹100› direction and the hexagonal prismoidal whiskers grew in the ‹111› direction. As in the case of whiskers synthesized from other materials, the tensile strength of the whiskers increased with decreasing cross-sectional area of the whiskers, indicating the size effect.

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Deflection of a main crack along an artificially formed weak plane consisting of a group of preexisting cracks in a sillicon nitride ceramic, was studied experimentally. The weak planes inside the ceramics were formed by diffusion joining of the ceramics. Main cracks were produced by indentation. Deflection of a main crack was related to the strength of a joining interface. A weak joining interface could cause deflection of a main crack, and strengthen a specimen with an initial main crack. A main crack passed across a strong interface and caused catastrophic failure.

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Electrical properties of W-doped KNbO₃ ceramics were studied by combining their diffuse reflectance measurements. In the case of samples sintered in a reducing atmosphere, CH₄/Ar=1/99, they were conductive and two step of positive temperature coefficient of resistivity (PTCR) effects were observed at temperatures where ferroelectric phase transitions from orthorhombic to tetragonal (Tr) and successively to cubic (Tc) occurred, while the resistivities higher than 10⁶Ωcm were observed for those sintered in air. The 0.2mol% W-doped sample sintered in the reducing atmosphere showed room-temperature resistivity of 10¹-10²Ωcm, with PTCR jump (Log R_max/R_min) of about 1.4 order of magnitude. Diffuse reflectance measurements for the samples sintered in the reducing atmosphere also indicated an increase of the conduction electron concentration with increasing doped amount of W.

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