Capability of oxygen store and release of ceria-zirconia solid solution made by attrition mill process was measured by thermo-gravimeter with 1mass% of Pt. Ceria-zirconia solid solution made by conventional heating method of ceria powder with zirconium salt was also characterized for comparison. Capability of oxygen store and release of ceria-zirconia solid solution made by attrition mill process is about three times larger than that of conventionally made samples. And, the point, where zirconium content is 100% on the relation between capability of oxygen store and release and zirconia content in the ceria-zirconia solid solution, corresponds to the state in which the valence of all the cerium ion being contained in the solid solution is 3. This fact suggests that the mechanism, that the increase of capability of oxygen store and release by dissolving zirconia into ceria, is that zirconium ions, which are smaller than cerium ions of the valence 4, release the strain caused by the expansion due to a reduction of cerium ions.

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Hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂, doped with 0.3 to 5.0mass% Na₃PO₄ as external sintering aid was studied by transmission electron microscopy. Densification of the powder blend was performed by hot-pressing at 1200°C for 30min. The overall microstructure of the material was composed of homogenous, equiaxed hydroxyapatite grains with an average size of about 1.5μm. Apart from the matrix grains, a sodium-plus calcium-containing secondary phase, β-NaCaPO₄, precipitated at triple pockets of few hundred nanometer scale. The occurrence of this precipitated phase was typically accompanied by microcrack formation. Microcrack opening typically occurred at one edge of the three or four visible phase boundaries. It should be emphasized that nearly all of the secondary phase pockets revealed such a microcrack. The microcrack formation process is likely to be governed by two interacting material characteristics the thermal expansion mismatch of the adjacent phases and the interface bonding strength.

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We report a new sealant material for solid oxide fuel cells (SOFCs) using glass-ceramic. A glass-ceramic based on the CaO-Al₂O₃-SiO₂ system was selected as a sealant because it can be easily molded to give a gastight seal and remains in a solid-like state under typical fuel cell operating conditions. Calcium alumina silicate glass powder is placed in the gas-sealing area before crystallization. During heating, the glass softens and bonds with the SOFC components. At higher temperatures, bulk crystallization occurs in the glass and the viscosity of the glass-ceramic sealant increases. We show that this sealing material which is able to seal at higher viscosities compared with the melt sealing method produces a good gas-tight seal and is chemically stable in contact with SOFC components, e.g., yttria-stabilized zirconia electrolytes and lanthanum chromite separators.

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Densification behavior and micro structural characteristics were examined for BaTiO₃ containing 0.25-2.00mass% Li₂Si₂O₅. Li₂Si₂O₅ lowered the sintering temperature of BaTiO₃. The optimum concentration to obtain high density was 1mass%. A concentration smaller than the optimum value did not effectively lower the sintering temperature, while a larger concentration resulted in the formation of inhomogeneous microstructure. There was an optimum sintering temperature to obtain compacts with maximum density. Extensive grain growth occurred above the optimum temperature. The grain boundary phase, which was a liquid phase at the sintering temperature, contained TiO₂-rich particles, whose distribution was non-uniform. The formation mechanisms of such microstructure were discussed.

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The effect of partial substitution of magnesium on the electrochemical property of LiMn₂O₄ has been investigated. As a result of magnesium doping, the specific surface area decreased. In addition the lattice constant decreased along with the polarization at a high discharge rate and an excellent cycle performance was realized in exchange for somewhat of reduction of the capacity. The voltage jump of 4.1V for the discharge curve of LiMn₂O₄ became indistinct with the magnesium doping. The reaction of LiMn_1.8SMg_0.2O₄ during lithium insertion and desertion was a homogeneous phase reaction. Electrochemical measurements revealed that LiMn_1-xMg_xO₄ is a cathode active material appropriate for use at high rates. The optimum x value in LiMn_1-x Mg_xO₄ was found to be in the range of about 0.1 to 0.2.

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Al₂O₃-ZrO₂ composite precursor was synthesized by introducing ammonia into a liquid mixture of ZrO₂ sol and Al(NO₃)₃ aqueous solution. Precipitation of bayerite suggested a degradation in the dispersion of ZrO₂ nanoparticles in the Al₂O₃ matrix during heat treatment. In order to avoid the formation of bayerite, it was preferred to produce a precipitation with a diluted NH₃ water solution with NH₃+N₂ gas by controlling the hydration temperature and the NH₃-adding methods. After suitable calcination and hot pressing, we successfully synthesized a uniform Al₂O₃-ZrO₂ microstructure in which tetragonal zirconia particles of 30nm were finely dispersed within the alumina grains.

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In Situ processing and microstructure of calcium dialuminate (CaAl₄O₇)-based porous materials have been investigated. Powder mixtures of CaCO₃ and α-Al₂O₃ (1:2 in molar ratio, doped with 0.5mass% LiF), and CaCO₃, α-Al₂O₃, and ZrO₂ (2:2:1 with 0.5mass% LiF) were prepared by a high-energy ball-mill process. Reactions of the powder mixtures during heating processes were revealed by high-temperature X-ray diffraction (HT-XRD), and by thermogravimetry and differential thermal analysis (TG-DTA). Porous CaAl₄O₇ monolith and its CaAl₄O₇/50mol% CaZrO₃ composite have been successfully synthesized using reactive pressureless sintering (at 1100-1200°C, for 2h in air) of powder mixtures. Both porous monolith and composite had homogeneous microstructure and very narrow pore-size distribution with mean pore size of -1μm. These porous materials, which are expected to have good thermal shock resistance, can be applied to high-temperature gas filters and lightweight structural components.

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Al chelate compounds with different carbon chain lengths were synthesized through reactions of aluminum sec-butoxide with acetoacetic acid ethyl ester (n=2), acetoacetic acid pentyl ester (n=5), acetoacetic acid octyl ester (n=8) and acetoacetic acid oleyl ester (n=18). Silica powder was modified with aluminum sec-butoxide (ALK) and its Al chelate compounds abbreviated as C2, C5, C8 and C18 according to chain length. The effects of carbon chain length on the tap density, specific surface area, compaction and sintering behavior of modified silica were investigated. The tap density of modified silica decreased with an increase in the length of the carbon chain. In ALK, porous Al₂O₃ was formed by hydrolysis of aluminum sec-butoxide upon drying at 100°C. In contrast, in C2, C5, C8 and C18, porous Al₂O₃ was formed by thermal decomposition of Al chelate compounds above 200°C. The green density of the pressed bodies increased with an increase in the length of the carbon chain, resulting in the decrease in the porosity of sintered bodies fired at 1400-1500°C.

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A new type of continuous SiC-based, Si-M-C-O fiber, containing zirconium instead of titanium, has been developed. This new Si-Zr-C-O fiber exhibits improved thermal stability compared to a Si-Ti-C-O fiber. In this study, oxidation resistance of Si-Zr-C-O fiber was investigated in order to clarify the role of zirconium in the fiber. It was cleared that the oxidation resistance of Si-Zr-C-O fiber was better than that of Si-Ti-C-O fiber. Zirconium plays an important role in inhibiting of crystallization of the oxide material which forms on the surface of the fiber during oxidation.

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The effect of the surface force on subcritical crack growth in glass was investigated in various aqueous solutions. Microcracks were induced on the glass surface by indentation method, which enabled to determine the fatigue limit, K_scc, with good precision. K_scc values obtained in solutions containing K⁺ or Na⁺ ions showed that a different factor other than the surface force dominates the crack growth. For solutions containing Li⁺ or Cs⁺ ions, a trend opposite to that predicted by the surface force theory was observed, which also suggests that the surface force does not affect the crack growth. For solutions containing n-alkyl-trimethyl-ammonium ions the effect of the surface force on subcritical crack growth was almost negligible, namely in the range 0.010-0.027MPa·m^1/2 in the region of an applied stress intensity factor >0.25MPa·m^1/2.

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The suitability of MgO as a densification additive for SiC was investigated. Dense and fine-grained SiC ceramics could be obtained by hot-pressing at 1900°C with addition >1mass% (and up to 29mass%) of MgO. X-ray diffraction (XRD) analysis of the SiC ceramics showed little reaction between SiC and MgO except for formation of small amount of Mg₂SiO₄, which indicated the presence of a liquid phase at high temperature. XRD analysis also showed the transformation from 3C-SiC to 4H-SiC during hot-pressing. The grain sizes of the SiC sintered with 2-29mass% MgO were almost the same and in the range of 100-300nm. Mechanical properties, thermal conductivity and electrical properties of these ceramics were measured and discussed in relation to their microstructure.

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Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HAp) whisker was synthesized by hydrothermal crystallization of amorphous calcium phosphate (Ca₃(PO₄)₂⋅nH₂O, ACP) with 0-5.0mol·dm^-3 of different carboxylic acid solutions such as acetic acid, malic acid, and citric acid at 140-220°C, in autoclave. The products were characterized by X-ray diffractometry, Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The shape of the products changed by kinds of carboxylic acid used, and the largest HAp whisker was obtained under conditions such as acetic acid of concentration 1.0mol·dm^-3, hydrothermal temperature of 200°C, and holding time of 3h; the resulting whisker was hexagonal prismatic with 100μm in length and 4μm in diameter, and had Ca/P atomic ratio of 1.56±0.02. The formation of HAp whisker is ascribed to adsorption of dimer-carboxylic acid on the a-plane of HAp. Accordingly, carboxylic acid promoted growth toward the c-axis. The existence of dimer-carboxylic acid was also influenced by the acid dissociation constant of carboxylic acid. Synthesis conditions for HAp whisker was calculated from the dissociation constant.

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Effect of Si₃N₄/SiO₂/BN packing powder and Si₃N₄/SiO₂ powder compacts, which produce SiO gas atmosphere upon heating were investigated for suppressing mass loss in Si₃N₄ ceramics during sintering in 0.1MPa N₂ atmosphere. As a result, packing powder with larger SiO₂ particles effectively suppressed the generation of SiO gas according to mass loss reaction from the samples. Upon sintering with Si₃N₄/SiO₂/BN packing powder and Si₃N₄/SiO₂ powder compacts, a surface porous layer with several hundreds micrometer thick which generated under the condition of Si₃N₄/BN mixed powder bed or without powder bed at long soaking time in 0.1MPa N₂, was not observed at all. The cross-sectional morphologies under this experimental condition were comparable to those under 1MPa N₂.

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An oxidation model for carbon interface in ceramic matrix composites was developed to evaluate the parameters that affect the oxidation rate of the carbon interface. The model considers geometrical changes of pores resulting from both consumption by oxidation of the carbon interface and oxygen consumption due to oxidation of the pore walls. The lengths of oxidized carbon interface were calculated for various cases using the oxygen concentration profile in the pore. Oxidation temperatures, interface thickness, oxygen concentration in the atmosphere, oxidation parameters on the pore walls were found to be the main parameters that control the oxidation behavior of carbon interfaces. By the present treatment, the results of interfacial shear tests could be quantitatively understood. The lengths of oxidized carbon interfaces increased with increasing temperature, interface thickness, and oxygen concentration in atmosphere. Furthermore, oxidation simulations were conducted in various ceramic matrix composites. In case of fibers and matrices with high volume expansion coefficients during oxidation reaction, the oxidation of the carbon interface was drastically inhibited.

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Slips of alumina powders with various particle sizes (0.2-0.54μm) were put into a glass tube and mounted in a high-speed centrifuge with a rotor radius of 120mm. The centrifuge were operated at 3000-5000rpm for 1-3ks. The falling velocity of particles increased in proportion to centrifugal force and to the square of particles size, as predicted by the Stokes' sedimentation law. On the other hand, the velocity decreased dramatically as the concentration of the slip increased. The velocity V of particles in varied concentration φ of slip can be expressed by V=V₀ (1-φ/φ_max)^φ_max×k as proposed by Buscall et al. V₀ and k were empirically derived by assuming φ_max=0.63 (the closest packing density for green compact). The compacting velocity was estimated by Kynch's theory. The falling flux of particles in the slip can be calculated using the Buscall equation, and the relation between slip concentration and flux (Kynch-plot) drawn. The gradient of Kynch-plot at the slip concentration of 50vol% showed roughly the compacting velocity.

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The sand erosion of alumina ceramics by the impingement of alumina abrasives with an average diameter of 363μm at a velocity of 65m/s has been investigated for temperatures ranging between room temperature and 919°C. Erosion rate, defined as the volume of the alumina ceramics removed by the unit mass of the impingement particles, increased both with an increase in temperature, and with the impact angle from 30 to 90°. Scanning electron microscopy (SEM) studies showed that intergranular microfracture was present on all of the eroded surfaces. Plastic cutting features were also observed in the specimens tested at the lower impact angles. At elevated temperatures, flow-like layers were observed together with features showing brittle fracture. From estimation of the ratios of brittle and ductile fracture, the amount of brittle fracture increased with an increase in temperature, while ductile damage was independent of temperature. A relationship between erosion rate and the mechanical properties of the alumina ceramics has been determined. It suggests that the temperature dependence of the erosion rate is related to both the hardness and the fracture toughness up to temperatures around 800°C. Above 800°C, and especially at the highest temperatures studied (919°C), the significant increase in the erosion rate may be due to grain boundary softening.

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Highly oriented diamond films can play an important role in replacing single crystal diamond for their use as substrates in electronic devices. However, for practical application, homogeneous films with low defect densities are required. The focus of our study is on the formation of highly oriented diamond on Si(100) substrate via differed multi-step processes. Highly oriented diamond films of -14μm thickness have been successfully synthesized on Si(100) at the experimental conditions followed by the multi-step growth processes: bias enhanced nucleation treatment, selective etching treatment and smooth growth. The diamond films has an epitaxial relationship of (100) diamond//(100)Si and [110]diamond//[110]Si with respect to the Si substrate.

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Optimum sintering and annealing conditions for iron-disilicide thermoelectric material were determined. The chemical compositions of the starting material were Fe_0.91Mn_0.09Si₂ and Fe_0.98Co_0.02Si₂. The mean particle diameter of both powders was about 6μm. The powder concentration was 77mass%, and the hydrogen exponents (=pH) of Fe_0.91Mn_0.09Si₂ and Fe_0.98Co_0.02Si₂ were 8.5 and 7, respectively. The green body was demolded in 1 h, and then was dried at 353K for 8h in air. Sintering was performed in the temperature range from 1423 to 1453K for 3h, and annealing, in the temperature range from 973 to 1143K for 14h. Vacuum was used for both sintering and annealing. The relative density increased with increasing sintering temperature. The relative density of the Fe_0.91Mn_0.09Si₂ specimen was higher than that of the Fe_0.98Co_0.02Si₂ specimen, because the solidus temperature of Fe_0.91Mn_0.09Si₂ is lower than that of Fe_0.98Co_0.02Si₂. The grain size of the ε-phase in the specimen sintered at 1453K was much larger than that in the specimen sintered at 1443K, and is covered with a thick β-phase layer, which restrains the reaction of ε+Si→β. The optimum annealing temperature was at 1123K, at which the eutectoid reaction, α→β+Si, and the subsequent reaction, ε+Si→β, mainly occurred. Some compacts were formed by cold isostatic pressing (CIP) or uniaxial pressing. Density and thermoelectric properties of the specimen formed by slip casting were better than those prepared by uniaxial pressing and almost the same as those prepared by CIP. Thus, slip casting is regarded as a superior forming method to conventional methods such as CIP and uniaxial pressing.

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Al₂O₃-coated graphite powder was prepared by a sol-gel method using ethyl acetoacetate aluminium diisopropoxide. An Al₂O₃-C castable refractory was prepared from the Al₂O₃-coated graphite powder. The flowability of this castable refractory was higher than that prepared from a graphite powder. The apparent porosity of the present Al₂O₃-C castable refractory was lower than that prepared from a graphite powder.

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Mullite of stoichiometric composition (3Al₂O₃⋅2SiO₂) is a highly attractive candidate material for structural applications. In this study, the effect of Mo addition to mullite matrix has been investigated. Mullite/Mo composites have been densified at 1600°C for 2h by pressureless sintering. Conditions have been made to sinter the samples in a non-oxidizing atmosphere. No traces of oxides have been identified by XRD analysis after polishing the specimens. Young's modulus increases with increase in Mo content and hardness decreases with the Mo content by obeying the rule of mixtures. Fracture toughness has been increased from 1.7 to 3.5MPa·m^1/2 for the 30vol%. Mo containing composites, which is twice that of monolithic mullite. Microstructures of the sintered samples were analyzed using SEM.

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We synthesized single crystals of perovskite-type new compounds in the system Li_x(W_1-yNb_y)O (x-0.4, 0≤y<0.15) by electrolysis of fused salt. Their lithium ion conductivity was measured by a dc method using electron-blocking electrodes. A sample (x=0.4, y=0.06) showed conductivity of 1.0(1)×10^-7S/cm along [100] at room temperature.

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Si₃N₄ ceramics with Y₂O₃ and Al₂O₃ additives set in an Al₂O₃ sagger with a Si₃N₄ powder bed were successfully sintered in air atmosphere furnace at 1600-1700°C. Bulk densities of the sintered Si₃N₄ ceramics were 3.10-3.16g/cm³ which were similar to the densities of those sintered in a nitrogen gas furnace of 0.1MPa. No heterogeneous surface layer was observed. When the sagger and powder bed are structured so that SiO gas continuously generated during the sintering, Si₃N₄ ceramics can be sintered in air without serious oxidation.

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The oxidation of the carbide single crystals (ZrC, HfC, TiC) was carried out at temperatures of 500 to 1500°C and oxygen pressures of 0.02 to 80kPa. X-ray diffraction showed the preferred {200} or {220} orientation of cubic-, tetragonal-, or monoclinic ZrO₂, monoclinic HfO₂ and tetragonal TiO₂ on the oxidized surface of the crystals. The oxide scale consisted of inner dense dark scale (zone 1) and outer porous white/gray scale (zone 2). Zones 1 and 2 contained as much as 23 to 25 at.% carbon and 5 to 11 at.% carbon, respectively. Zone 1 grew parabolically to finally attain a constant thickness, in contrast to zone 2 which increased linearly. From HRTEM at the ZrC/zone 1 interface, it was observed that c-ZrO₂ crystallites of 2 to 10nm sizes are formed with the above preferred orientation. It was found from TEM-EDX analysis that a considerable amount of carbon is concentrated at the interface and that oxygen exhibits the concentration gradient both in the ZrC and zone 1 over a distance of 300nm. Zone 1 was separated as carbon films from the oxidized carbides by HF or HF/H₂SO₄ treatment and characterized by Raman spectroscopy and TEM, which showed the formation of amorphous carbon. The mechanism on oxidation of the carbides with the formation of carbon was elucidated from the above results as well as from the kinetic and thermodynamic considerations. The perspectives for the oxidation of the carbides with formation of carbon is mentioned.

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The microtextures of belite induced by a remelting reaction and other transformations (e.g., the polymorphic phase transitions of α→α′→β) have been reviewed. The remelting reaction, in which the α-phase belite decomposes into a liquid and the α′-phase during cooling, is necessarily preceded by the phase transition of α→α′; the α′-phase nucleates as lamellae within the parent α-phase so that there is good lattice matching across the interface. The resulting lamella boundaries provide heterogeneous nucleation sites for the exsolving liquid by the remelting reaction. A variety of microtextures results depending on the wettability of the belite lamellae by the exsolved liquid as well as on the cooling rate. The belite in which the remelting reaction occurred to a large extent showed higher hydration reactivity and better grindability than the quenched material. Recent years have seen developments in a new application for the remelting reaction that involves modifying belite-rich cement.

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