Mullite porous bodies were produced by means of simultaneous induction of a foaming reaction between aluminum powder and sodium hydroxide and a gel-set reaction between sodium aluminate, a binding agent, and sodium silicate The effects of aluminum lactate on the porosity and pore size of the porous bodies were investigated. The effects of the amount of aluminum lactate powder were most pronounced at 0.5mass%, at which the maximum porosity was 50% and the mean pore size was 200μm. In addition, the pore size of the porous bodies increased to 100-800μm by the addition of aluminum lactate powder.

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Reduction behavior of α-Fe₂O₃ containing SnO₂, Al₂O₃ or Cr₂O₃ under low oxygen pressure (nitrogen atmosphere) was investigated by the thermogravimetry. α-Fe₂O₃ powders mixed with 1-10mol% SnO₂, 5mol% Al₂O₃ or 5mol% Cr₂O₃ were pressed, sintered at 1250°C for 10h, and then crushed. 5mol% Al₂O₃ and 5mol% Cr₂O₃ made solid solutions with α-Fe₂O₃, and SnO₂ was estimated to dissolve up to about 9mol% at 1250°C for 10h. Pure α-Fe₂O₃ was reduced between 1150 and 1300°C. The reduction behavior of α-Fe₂O₃ with 5mol% Al₂O₃ or 5mol% Cr₂O₃ was similar to that of pure α-Fe₂O₃, and there was no effect of Al₂O₃ or Cr₂O₃ addition on the reduction inhibition of α-Fe₂O₃. On the other hand, the onset temperature and the offset temperature of weight loss for α-Fe₂O₃ with SnO₂ increased with increasing SnO₂ content. The activation energy for the reduction reaction of α-Fe₂O₃ was calculated to be about 633kJ/mol by Ozawa method, and this value coincides with the activation energy for oxygen diffusion in α-Fe₂O₃. Therefore, it is considered that the reduction reaction of α-Fe₂O₃ was controlled by the oxygen diffusion. The reduction inhibition of α-Fe₂O₃ by SnO₂ addition has been explained by the suppressed creation of oxygen ion defects responsible for oxygen ion diffusion.

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Clear second harmonic generation (SHG) was observed from xPbO⋅(100-x)SiO₂ glasses after electrical poling. PbO can be considered to be responsible for the SHG center since no SHG was detected from electrically poled PbO-free SiO₂ glass. SHG was seen from the glasses poled above 100°C, and the intensity increased as the poling temperature increased. The minimum dc voltage necessary for SHG was 1kV. SHG intensity increased first and then decreased with the increase of PbO content, showing a maximum at 34.8 mol% PbO. This dependence of SHG seems to relate the microstructure associated with Pb²⁺, probably Si-O^-Pb²⁺ units.

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Alumina-based ceramic composites prepared by particulate dispersion using SiC and Y₂O₃ as additives were studied under hot-pressing at 1400 to 1600°C for 0 to 20h. An yttrium aluminum garnet (YAG, Y₃Al₅O₁₂) phase was formed by the reaction between Al₂O₃ and Y₂O₃ above at 1400°C after 10min of hot-pressing, and dense Al₂O₃/5vol% SiC/20vol% YAG composites resulted. The YAG phase was dispersed at the grain boundary of the Al₂O₃ matrix with equiaxed grains. Fine SiC was dispersed uniformly within the Al₂O₃ matrix, whereas coarse SiC particulates, which showed stacking faults, were located in the grain boundaries between the Al₂O₃ and YAG. The YAG phase was bonded directly to the Al₂O₃. An impurity phase, which apparently was amorphous, could be detected at the interface between the Al₂O₃ and SiC. The grain size of the monolithic Al₂O₃ increased remarkably with increases in hot-pressing temperature and time; grain growth in the Al₂O₃/SiC/YAG composites were effectively restrained, and those samples exhibited a narrower grain size distribution. This uniformly fine microstructure could be attributed to the incorporation of the YAG and SiC particulates, because of grain boundary pinning by the particulates.

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Observation of the enameles interface with SEM, EPMA and ESCA, and measurement of adhesive strength of the enameles were done. Simultaneously, cobalt and nickel in the enamel layer examined a given influence at the interface and the adhesive strength. As a result, the relationship between iron-oxygen, cobalt-oxygen and nickel-oxygen, at the reaction of enamel process was explained by the interface thermodynamics. Furthermore, characteristics and differences of reaction of cobalt and nickel were clarified. (1) The adhesive ability of Co-enamel was larger than that of Ni-enamel. (2) The adhesive behavior of cobalt changes at about 730°C, but that of nickel remains unchanges. Consequently, cobalt has an adhesion with the high temperature (over 730°C) but nickel does not have an influence on the temperature. (3) At high firing temperature, the Co-enamel can create FeO easily compared with Ni-enamel, and dissolve Fe₂O₃ of steel surface into glass. (4) Cobalt spreads for a vertical direction of interface, but nickel tends deposition on the interface surface. And the diffusion capability of cobalt into the steel was considerably greater than that of nickel.

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The structure and electronic states of Na₂S-SiO₂ oxysulfide glasses were investigated and the role of sulfur in the glasses is discussed. Na₂S formed stable glass with SiO₂ at an alkali concentration range similar to that of Na₂O-SiO₂ systems by the conventional melt-quench method. The obtained glasses were reddish brown in color and a remaining of sulfur was confirmed. X-ray photoelectron spectroscopy (XPS) was used to study the chemical bonding state of bridging and nonbridging anionic species in Na₂S-SiO₂ glass. The S2p binding energy of the glass was observed to be approximately 161eV. This value is lower than that of orthorhombic crystalline sulfur and almost the same as the value of Na₂S. From the results, the electron density around sulfur was near to that of S^2-. Furthermore, by ²⁹Si magic angle spinning (MAS) and nuclear magnetic resonance (NMR) measurement, three clear-cut peaks were detected between 0 and -120ppm. It was assumed that a sulfur atom was joined to silicon via substitution for an oxygen atom, and was present as nonbridging sulfur in Na₂S-SiO₂ glass with low alkali ion concentration. On the other hand, it was revealed that a portion of the sulfur ions existed in an isolated state from the glass-network structure at high alkali content. The glass composition changed to a chemical composition that was more silica rich than predicted. The sulfur ions made sulfide clusters with the sodium ions isolated from the glass-network.

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Alumina-zirconia powder (AZ) was prepared by thermal decomposition of organic precursors synthesized from ethyl acetoacetate aluminium diisopropoxide and zirconium tetra-n-butoxide. The specific surface area of AZ was higher than that of alumina-zirconia powder (ALK) prepared from aluminium tri-sec-butoxide and zirconium tetra-n-butoxide in the range of 0-40mol% ZrO₂. The pore radius for AZ containing 0-40mol% ZrO₂ distributed from 1 to 3nm. The true density of AZ was lower than that of ALK in the range of 0-40mol% ZrO₂. Four- and 6-coordinated Al atoms existed in ZrO₂-free AZ, while 5-coordinated Al atoms in addition to 4- and 6-coordinated Al atoms existed in AZ containing 20-80mol% ZrO₂. These results indicate that alumina component and zirconia component in AZ were mixed homogeneously at the atomic level.

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Crystalline layered silica hydrates were prepared from a natural apophyllite pretreated with 0.1mol⋅dm^-3 hydrochloric acid at 5° or 25°C. In these treatments, a product with higher crystallinity was obtained by acidic treatment at a lower temperature. The two silica hydrates had the different local silica structure, and were found to correspond to the silicas reported as an H-apophyllite and a Silica-AP, respectively. The silica hydrates have a fundamental silica sheet structure of apophyllite, and the structure is destroyed by heating above 200°C due to condensation of silanol groups in the interlayer spaces. On the other hand, a crystalline layered alumino-silica hydrate was also obtained from a natural apophyllite pretreated with an aluminum chloride solution. Formation of four different hydrate phases depended mainly upon pH of the reacting solution and/or temperature in the drying process. The introduced aluminum ion was coordinated tetrahedrally and occupied mainly at the interlayer of the silica sheets. On heating, these alumino-silicates maintained their crystal structures up to ca. 400°C. These results suggested that the introduced aluminum ion should prevent the basal silica sheet distance from narrowing and the silanol groups from condensing. In consequence, the sheet structure of these alumino-silicates were more stabilized thermally than that of the silica hydrate.

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Trace amounts of impurities in alumina powder are known to cause platelike alumina grains to generate in sintered bodies. In many studies of platelike alumina grain growth in sintered bodies, fine and high pure alumina powders built-up by the sol-gel method have been examined by addition of SiO₂, CaO and so on. The authors reported in a previous paper that the platelike grains were formed in sintered compacts of a fine alumina powder ground by wet rotation ball milling. In this study, sintering properties were investigated for two kinds of alumina powders: ground powder, built-up powder with similarities in average particle size, particle mass-size distribution and amounts of impurities. The platelike grains were generated in both of powder compacts. However, platelike grains of ground powder compacts were formed at low sintering temperatures and short sintering time compared to other compacts, which can be explained by the fact that the ground powder contained ultra-fine particle of less than or equal to 0.1μm. The grinding processes proceeded with micro-decay of particle surface on the powder. When platelike grain growth isotherms in logarithmic plot were compared, the slopes were nearly equivalent. Therefore, it was suggested that the platelike grain growth mechanism of two kinds of powders compacts was similar.

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The thermodynamic stabilities (i.e., bound strength from the solid surface) of water on the surface of three kinds (alumina, silica and titania) of ultrafine oxide particles were evaluated using the cooling DSC by changing the statistical thickness of water layers t and the crystalline state through heat treatment at high temperature. The water layers on the surface of amorphous particles showed two exothermic peaks on the thermograms. Judging from the relation of peaks and t, one peak P_L at lower temperature resulted from the structural change of the most stable water layer on the surface. Another peak P_H at higher temperature resulted from freezing of quasi-stable water layers, stabilities of which decrease with the distance from the surface of particles towards the bulk state of water. The water layers on the surface of the particles crystallized by heat treatment showed only P_H without peak of P_L. The difference in enthalpy changes Ht on the P_H of the surface water between amorphous and crystalline states of the particles was the most remarkable in silica powder among three kinds of ultrafine powders used in the present experiment.

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A series of tungsten bronze-type solid solutions Ba_6-3xR_8+2xTi₁₈O₅₄ (R=La, Pr, Nd and Sm) has good microwave dielectric properties. Though the dielectric constant ε_r and the temperature coefficient τ_f of resonant frequency change linearly as a function of composition x, the quality factor Q⋅f shows nonlinear behavior of steep increase around x=0.5. The highest gradient was found in the Sm system in which the difference in ionic radius from Ba is largest. Increasing of ionic radii of R, the gradient gradually decreases. Release of inner stress which will be caused by the distribution of large ions with different sizes might bring the increase in Q⋅f. When Ba ions remain in the 2×2 perovskite blocks which is mainly occupied by R ions in the tungsten bronze structure, the inner stress might become large. Vacancies created by the substitution also bring decrease of the stress. It is also discussed that the deviation of the composition from the solid solutions decreases the sintering temperature without influence of the dielectric properties.

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The effects of acetophenone and benzophenone on the photosensitivity of Al₂O₃ gel films chemically modified with benzoylacetone have been studied. Benzophenone was found to accelerate the dissociation of remaining chelate rings and densification of the gel films on UV-irradiation, whereas acetophenone was little effective. To get insight on the mechanism of sensitization by benzophenone, the effects of excitation wavelength were studied using two different excimer lasers: KrF (249nm) and XeF (351nm), nearly corresponding to the π-π* (252nm) and n-π* (335nm) transitions of benzophenone, respectively. The photolysis rate of the chelate rings in the benzophenone-containing gel films was the same as that of the undoped films for KrF (249nm) laser irradiation, while it was higher than the latter for XeF (351nm) laser irradiation. It was also found that the photolysis rate of the chelate rings was decreased by drying the gel films for a given amount of benzophenone. These findings indicate that the sensitization by benzophenone is associated with the excitation of n-π* transition of benzophenone and the abstraction of H atom from residual i-PrOH solvent in the gel films. Furthermore, the fine-patterning characteristics of modified Al₂O₃ gel films containing benzophenone were examined.

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To control the hetero-coagulation structure of ultra-fine γ-Al₂O₃ and SiO₂ powders for mullite ceramics, hetero-coagulation structures under different pH conditions were investigated by focusing on electrophoretic mobility and aggregate size distribution in suspensions. A bimodal electrophoretic mobility distribution was observed when precursor powders were prepared by colloidal mixing processes at pH=9.5. Since each peak almost corresponded to the electrophoretic mobility of γ-Al₂O₃ and SiO₂ particles, heterocoagulates were not formed in the suspension. In the case of pH=6.0, weak hetero-coagulates were generated in suspension. However, uniform mixing could not be attained and large coagulates were formed. On the other hand, narrow and single mode electrophoretic mobility distribution was observed after colloidal mixing at pH=4.4. It is concluded that the uniform hetero-coagulates for mullite precursor with the stoiciometric composition can be obtained. The change in structures of hetero-coagulates with pH conditions was analyzed by DLVO theory. Uniform and fine grained mullite ceramics were prepared from uniformly hetero-coagulated precursor powders mixed at pH=4.4.

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B-C-Si system composites were prepared by arc melting in argon atmosphere using B₄C, B and Si powders. The composites contained three phases: B₄C, SiB_n (n≥14) and free Si. The electrical conductivity (σ) of the composites in which the main phase was B₄C decreased with increasing SiB_n content, but slightly increased with increasing the solid solution of silicon. The Seebeck coefficient (α) of almost all the composites increased with increasing temperature, but B₄C containing a small amount of Si showed a maximum at 800K. The composites in which the main phase was SiB_n containing free Si and B₄C had greater α values than B₄C. The thermal conductivity (κ) of the composites decreased with increasing temperature. The κ of the composites in which the main phase was B₄C increased and decreased by forming solid solutions of Si and B, respectively. The dimensionless figure-of-merit (ZT) increased with increasing temperature. The composites in which the main phase was SiB_n containing B₄C and several tens mol% Si had the greatest ZT value of 0.4 at 1100K. This value is the largest level among high performance boron-rich borides.

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Plasma sprayed zirconia applying to the thermal barrier coating in gas turbine has been developing for protecting the hot parts such as blades and nozzles from high-temperature enviroments. In this paper, four point bending tests under various temperature conditions are conducted on plasma sprayed zirconia and its mechanical properties are examined. Results show that the bending strength at room temperature for plasma sprayed zirconia is much lower than that of sintered zirconia and is decreased with the increase in temperature. However, Weibull modulus at each temperature is relatively large and the dispersion of bending strength is very small in comparison with that of sintered zirconia. It is also clarified by the SEM observations of fracture surface that many defects such as debonding and microcrack are responsible for the lower bending strength.

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Mechanical properties and microstructures of both fine-grained β-silicon nitride ceramics and annealed materials were examined. The microstructure of fine-grained β-silicon nitride ceramics has fine and uniform grains. After annealing, fine and rod-like grains have been developed. Fracture toughness and bending strength of fine-grained β-silicon nitride ceramics increased by the annealing. The increased mechanical properties are related to the microstructural change during the annealing. Further, SEM and EDS analyses made clear that the size of flaw in samples were over 10 times of average diameters of the grains. The fracture origin changed from large silicide particles to smaller pores by annealing under high nitrogen pressure.

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The firing behavior of β-Si₃N₄ powder corroded under hydrothermal conditions was investigated by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX). TEM and EDX analyses suggested that the hydrothermal treatment enhanced the formation of transient growth bands in β-Si₃N₄ ceramics containing Y₂O₃-Nd₂O₃ additive during firing at high temperature. Also, EDX analysis indicated that the grain boundary regions around the grown β-Si₃N₄ grains contained a Y-Nd-Si-O-N phase.

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The effects of the particle size of SnO₂ and glass on the densification behavior, the microstructure and the electrical properties of SnO₂-glass composites were examined. Moreover, the relationship between the electrical properties of the glass composites and the particle dispersion of SnO₂ in a glass matrix was discussed following quantitative analysis of SnO₂ particle dispersion by computer-assisted image analysis on SEM photographs. The results are summarized as follows: (1) when coarse grained SnO₂ particles were used, the densification of the glass composites proceeded at low firing temperatures. Therefore, the use of coarse SnO₂ particles was useful to get the glass composite having a high electrical conductivity and a small negative temperature coefficient of resistance (TCR) at low firing temperatures. However, after the completion of densification, the glass composite prepared using fine SnO₂ particles showed a higher electrical conductivity and a smaller negative TCR because SnO₂ particles were more highly crowded in a glass matrix and thus the SnO₂ interparticle spacings were smaller than those of the sample dispersed with coarse SnO₂ particles. (2) when fine glass particles were used, the densification of the glass composites proceeded at low firing temperatures and the particle dispersion of SnO₂ in a glass matrix was homogeneous. Besides, the glass composite prepared using fine glass particles showed a high electrical conductivity and a small negative TCR at low firing temperatures. On the other hand, at high firing temperature, the glass composite having a higher conductivity and a smaller negative TCR was obtained when coarse glass particles were used, because the densely aggregated SnO₂ particles formed highly conductive networks in a glass matrix.

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Viscous solutions of polymethylsilane (PMS) and polycarbosilane (PCS) mixed at various ratios were prepared and shaped into fiber form by the dry-spinning method using benzene as solvent. The addition of PMS to PCS lowered onset temperature of the precursor fiber oxidation, and slightly increased the residual mass after pyrolysis. The fibers from the precursors containing PMS yielded the ceramic fibers after heat treatment at 1273K without degradation and fusing, but they changed into crystalline fibers having thin amorphous layer on the surface after the heat treatment at 1673K.

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{(1-x)Pb(Sc_1/2Ta_1/2)O₃-xPb(Sc_1/2Nb_1/2)O₃+0.5 mass% MnO₂} (PST-PSN) solid-solution ceramics, where x=0.1-0.9, were prepared by normal sintering in a PbO atmosphere. The physical, dielectric and pyroelectric properties were evaluated using PST-PSN ceramics with x=0.1-0.9, respectively. All the obtained samples were high density sintered bodies with the low apparent porosities of less than 0.2%, ranging in bulk densities from 7.67×10³ to 8.55×10³kg/m³. The temperature dependence of the relative dielectric constant, ε_r for PST-PSN ceramics apparently exhibited the diffuse phase transition in all the compositions. Assuming that the volume specific heat, C_v of the present samples with x=0.4-0.9 are 2.5×10⁶J/m³⋅K, x=0.4 PST-PSN sample exhibited the highest figures of merit, F. M. for voltage responsivity, R_v of around 8.5×10^-14C⋅m/J and F. M. D* for specific detectivity, D* of around 5.9×10^-11C⋅m/J, among the six samples studied here.

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Chalcogenide glasses of As₂₀S₈₀, Ge₂₀As₂₀S₆₀, As₄₀S₆₀ and As₄₀S₅₇Se₃ were prepared. The wavelength dispersions of the Faraday effect for these glasses were examined. The Verdet constants of the glasses decreased at wavelengths longer than the absorption edge of the glasses. The values of the Verdet constants of the glasses were in the order of As₂₀S₈₀<Ge₂₀As₂₀S₆₀<As₄₀S₆₀<As₄₀S₅₇Se₃, which were successfully confirmed on the basis of the Becquerel theory.

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ZnO films were prepared by anodic-oxidation of Zn metal plates at various anodic-oxidation conditions. Pr-Co-O thin films having various Co contents were deposited on the ZnO films by radio-frequency (RF) magnetron sputtering for the formation of heterojunctions. Nonlinear properties were observed in voltagecurrent (V-I) characteristics of the heterojunctions, and the threshold voltage shifted to the lower voltage side with increasing Co contents in the Pr-Co-O thin films. The nonlinearity coefficients α in the V-I characteristics became large as about 30 when transparent ZnO films were used.

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Three mol% Y₂O₃-doped tetragonal ZrO₂ compacts with a small amount of SiO₂ were prepared by the hydrolysis of Si(OC₂H₅)₄ suspended with ZrO₂ particles and using a pressure filtration technique. The SiO₂ content of the compacts was successfully controlled within the range of about 0.1-1mass% by treating the ZrO₂ powder with an aqueous H₂SO₄ solution prior to the hydrolysis of Si(OC₂H₅)₄. The compacts doped with 0.36 and 1.22mass% SiO₂ showed a high relative density of above 98% when sintered at 1300°C for 2h.

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