The effects of firing temperature and molar ratio of CaO/MgO on the formation of cubic ZrO₂ from zircon were determined. Experimental results indicate that a thermal reaction completed by firing at 1500°C for 2h using a charge of zircon and 0.4CaO/0.6MgO molar ratio is favorable for the production of mainly pure cubic ZrO₂ ss containing 1.29%MgO and 0.22%CaO after separating the silica by acid leaching. Different kinetic models have been tried, but the mechanism of the overall firing reaction obeys the diffusion model in the form of: X+(1-X) ln (1-X)=kt, where X is the extent of solubilized silica in time t and k is the rate constant. The apparent activation energy of the decomposition process is calculated and found to be 120kJ/mol.

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A new method is shown for lower temperature preparation of tungsten oxide thin film by sol-gel process without using a catalyst, but using tungsten chloride (WCl₆) as the starting material and ethanol as a solvent. When WCl₆ dissolved in ethanol, tungsten ions and ethanol formed tungsten ethoxides. Thin films prepared from the solution above 300°C did not contain organics or chloride. Tungsten oxide (WO₃) crystallized at temperatures above 350°C. The electrical and optical properties of the thin films were measured. Amorphous thin films showed electrochromism, but polycrystalline thin films did not. The relative transmittance of the amorphous thin films decreased to 45% on application of 3V for 1s.

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Reaction between α, β-Al₂O₃ ceramics (produced by fusion cast method) and Ba-Sr-alkali-silicate glass was studied on samples from glass melting tank. This tank had been used for about 6.5 years. Dendritic leucite (KAlSi₂O₆) crystals were observed at the interface between ceramics and glass. These crystals were about 120μm long at the position of the glass meniscus line. Leucite was crystallized in Al₂O₃-rich liquid due to the corrosion of α, β-Al₂O₃ ceramics. β-Al₂O₃ crystals in the ceramics showed no morphological change but chemical substitution of K, Ba and Sr for Na occurred. Leucite and β-Al₂O₃-like crystals are occasionally found as a defect in glass production. It is clear that these crystals are formed at the interface between α, β-Al₂O₃ ceramics and molten glass.

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Perovskite-type solid solutions, Sr_2-xLa_xMg_1-yTa_1+yO_z, were synthesized and cation ordering between Mg²⁺ and Ta⁵⁺ in the solid solutions was investigated. In the Sr_2-xLa_xMgTaO_z system, the (NH₄)₃FeF₆-type (1:1 order) phase was formed in the compositional range, x≥0.4. However, few degree of the cation ordering between Mg²⁺ and Ta⁵⁺ was also observed in the solid solutions, 0≤x≤0.3. These results suggest that the cation ordering between Mg²⁺ and Ta⁵⁺ in Sr_2-xLa_xMgTaO_z system is affected by the average charge of A-site cation or, in other words, by the oxygen content. The 1:2-type ordering was observed in the Sr_2-xLa_xMg_1-yTa_1+yO_z solid solutions, x=0 for y≥0.3, and x≤0.1 for y=0.1, 0.2. In particular, the disappearance of the 1:2 ordering due to small amount of La³⁺ substitution was observed in the stoichiometric Sr₂Mg_0.67Ta_1.33O₆-LaSrMgTaO₆ solid solution. However, in the case of the composition containing oxygen vacancy, the 1:2 ordered phase was formed at the composition Mg/Ta=0.8/1.2 and 0.9/1.1, although they have 20% and 35% higher Mg²⁺ content than in the case of Mg/Ta=1/2, respectively. These results suggest that the 1:2 ordered structure is stabilized by the presence of oxygen vacancy.

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La(Fe, Al)₁₂O₁₉ powder was synthesized by the two-step solid-state reaction of La(Fe, Al)O₃ with α-Fe₂O₃ and α-Al₂O₃ powders. The stability and the formation rate of LaFe₁₂O₁₉-based magnetoplumbite compounds are greatly improved by the formation of a solid solution with La_xAl₁₂O₁₉. The highest value of the saturation magnetization (52.9emu/g) was obtained at the composition of 95mol% LaFe₁₂O₁₉ (LaM95) in La(Fe, Al)₁₂O₁₉. In Ce-TZP (ceria-stabilized tetragonal zirconia polycrystal) ceramic matrix, 90mol% LaFe₁₂O₁₉ in La(Fe, Al)₁₂O₁₉ (LaM90) was stable in a wider temperature range than LaM95. Platelike LaM90 crystals were successfully grown in situ in Ce-TZP matrix at temperatures ranging from 1350 to 1375°C. The formation of anisotropic La(Fe, Al)₁₂O₁₉ crystals was found to depend upon the preferential diffusion of La³⁺ ions through the initially formed magnetoplumbite lattice.

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The effect of cobalt on enamel reaction was studied using Co-vitreous enamel. Observation and analysis of Co-vitreous enamel interface were performed with scanning electron microscope, X-ray photoelectron spectrometer and X-ray diffractometer. The following results were obtained. (1) The sunken parts of Co-vitreous enamel interface were formed by erosion of the base iron. Cobalt and iron deposited on the base iron and formed convex parts. Further, the convex parts grew by firing from the initial interface towards the glass (enamel layer) side. (2) Interface layer of Co-vitreous enamel was consisted of two layers. The first interface layer was very thin and consisted of CoFe₂O₄ or FeFe₂O₄. The second interface layer was the iron solid solution containing cobalt. The thickness of Co-vitreous enamel reaction layer was thicker than the rough parts. (3) The Co-vitreous enamel reaction was a galvanic cell reaction between base iron and cobalt ion in glass. Cobalt circulate by reaction as deposition, oxidation and dissolution.

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The sintering behavior of La_1-xSr_xMnO₃ (LSM) was studied using porous electrodes of various compositions. Radii of particles at the surface, radii of imprints at the interface, and number of imprints per unit area were determined by SEM after heat treatment. Grain growth occurred mainly in the initial stage, and was suppressed by slow mass transfer in the successive stage. The activation energy of grain growth was calculated to be approximately 400kJ/mol. The relationship between the particle radii of the bulk electrode and the length of three-phase-boundary (TPB) at the interface was clarified. The overpotential change due to sintering over time was estimated using this relationship. It was suggested that porous LSM electrode can be operated over 100000h at 800°C without detectable decrease of TPB length.

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The relationships between the formation fraction and boiling time of monoclinic hydrous-zirconia fine particles produced by the hydrolysis of ZrOCl₂ solutions with and without an addition of HCl were measured to investigate the effects of added HCl on the formation rate. The chemical kinetics analyses revealed that the formation-rate constant (k) of hydrous-zirconia particles, under a constant ZrOCl₂ concentration, decreased with increasing HCl concentration. The decrease in the k-value can be explained by the decrease of the k(I)-term in the ionic strength function contained in k.

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Hard amorphous carbon thin films containing small amounts of oxygen were deposited by the radio frequency (13.56MHz) self-bias method, using isopropanol as a starting material. The effect of the deposition temperature and the behavior of oxygen atoms during the film depositions were investigated in detail with controlling the deposition temperature by the plasma pulsed deposition technique. As a result, the deposition rates decreased by about 50% as compared with the diamond-like carbon film depositions from isobutane, because deoxygenation reactions from the films actively progressed. The effect of the deposition temperature was almost similar to that found in the diamond-like carbon film depositions but, an increase in the film density and a decrease of the film surface micro-roughness were recognized. The deposited films were considered to consist of a three-dimensional network structure of carbon chains, within which carbonyl structures and graphite-like carbon clusters were intermixed. Furthermore, as the film formation ability of the applied deposition method in this study was exceedingly high, C=C=O structures in the deposited films were observed by FT-IR spectroscopy, which was considered to be the precursors for the deoxygenation reactions from the films.

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A procedure for the quantitative phase analysis (QPA) using the whole-powder-pattern fitting methods was applied to eight- to ten-component mixtures of ceramic materials. Accuracy in the QPA using the whole-powder-pattern decomposition (WPPD) method and the Rietveld method was examined. Average deviations of the calculated weight fractions of respective phases using the WPPD method from those prepared by mixing were within 0.5 mass%, and they were smaller than those obtained by using the Rietveld refinement. Minor phases (-1 mass%) in ten-component samples were analyzed, and their weight fractions could be measured within the error of less than 0.1 mass% by using the WPPD method. Rapid QPA using the WPPD method was also tested.

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Single-phase cubic spinel structure MgCr_2-xO₄ compounds with a controlled Mg/Cr ratio were obtained in stoichiometric composition and Mg excessive region. All of those single phase samples were p-type semiconductor and their electrical resistivity decreased with increasing the Cr vacancy concentration. This result supports our former conclusion that electrical conduction mechanism of this system is based on the p-type semiconductor conduction due to electrical hole by Cr⁴⁺.

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To improve the high-temperature stability, Si-C-O fibers (Nicalon) were oxidized at temperatures of 1073-1773K under an oxygen partial pressures of 2.53×10⁴-1.01×10⁵Pa and then were exposed to 1773K in argon. X-ray diffraction, resistivity measurement and tensile test were conducted for both the oxidized and the exposed fibers. At an early stage of oxidation, the characteristics of oxidized fibers abruptly changed. This was because an incomplete SiO₂ coating caused pyrolysis of the fibers. High levels of tensile strength was retained in the as-oxidized state at elevated oxidation temperatures and under high oxygen partial pressure. The strength of the oxidized fiber could be controlled by the imperfections of the SiO₂ film. After exposure in argon, the highest strength was retained in the fiber oxidized at 1373K under an oxygen partial pressure of 2.53×10⁴Pa, that is, in the fiber having SiO²-film thickness of 0.2μm.

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Addition of calcium, strontium or barium nitrates to alumina powders promotes the crystallization “in situ” of calcium, strontium and barium hexaluminates during the sintering of green compacts. Calcium and strontium hexaluminates develop platelike structures randomly dispersed in the alumina matrix whereas barium hexaluminate does not. The strength and toughness of as-fired samples containing calcium or strontium hexaluminates are greater than those of the matrix. Materials containing barium hexaluminate have lower values. These composites maintain the same properties after aging for 30d at 35°C in aqueous or physiological solution and no chemical reaction between the ageing media and the hexaluminates was observed on examination by scanning electron microscope.

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CeO₂ thin films were prepared on Si(100) and Si(111) substrates from cerium acetate monohydrate via sol-gel process. The thin films were crystallized at approximately 700°C and had polycrystalline microstructure. Scanning electron microscopy (SEM) observation showed that those films consisted of small grains of 60-70nm in diameter and had even surfaces. SrTiO₃ films with a platinum top electrode were formed on Pt/Si and Pt/CeO₂/Si substrates. Current voltage (I-V) characteristics of the SrTiO₃ films were measured on Pt/SrTiO₃/Pt/Si and Pt/SrTiO₃/Pt/CeO₂/Si structures. The leakage current density for the former sample was approximately 6.6×10^-6A/cm² under the applied electric field of 9.4×10⁴V/cm. An increase in the applied electric field above 9.4×10⁴V/cm resulted in a marked increase in the leakage current. The leakage current for the latter sample was 4.1×10^-6A/cm² under 2.5×10⁵V/cm. The I-V characteristics of the SrTiO₃ films were improved by the use of the CeO₂ film as an intermediate layer.

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When magnesium oxalate hydrates were precipitated by mixing ethanolic solutions of the metal nitrates and oxalic acid with addition of water, particular attention was paid to the age of the starting solutions, which had drastically influenced the precipitation behavior. For instance, the aging time of several days exponentially delayed the occurrence of the clouds in the solution, in other words, elongated the incubation period of the precipitation. Although the structural features in the aged solution have not yet been clarified by NMR, we believe that a visibly transparent solution is not always homogeneous, even if it looks stable for a long period.

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ESR spectra of V⁴⁺ were studied in sols and dried gels prepared from tetramethoxysilane. It is confirmed that V⁴⁺ ions are present as [VO(H₂O)₅]²⁺ in the sols and gels. The tumbling motion of the complexes in the sols and the gels dried in the ambient atmosphere for 2 months was as fast as that in aqueous solutions. This motion ceased when the gels were dehydrated in vacuum and started again after the dehydrated gels were left in the ambient atmosphere for a day or so. Spectral changes between dehydrated and hydrated gels were reversibly observed.

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Carbon-silica hybrid precursors for SiC with different carbon contents were prepared by firing hybrid gels consisting of crosslinked phenol resin and silica gel. The SiC precipitation processes in these precursors at 1873K were traced in terms of X-ray diffraction and scanning electron microscope (SEM) observation. Excess carbon in the system reduces the size of the formed SiC crystallite during the heat treatment. The precursor with high carbon content yielded aggregated grains consisting of small SiC crystallite, while the precursor with low carbon content yielded coarse isolated grains of 100-200nm after a long-term of heat treatment.

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Semiconducting donor (La)-doped barium titanate (BaTiO₃) ceramics were synthesized at 1100°C in air by firing fine-grained crystalline gel powders of Ba-, La-, and Ti-alkoxides prepared by the sol-gel method. The ceramics showed resistivity of <10³Ω·cm at room temperature with an average grain size of 0.2-0.5μm, which was one order of magnitude smaller than that sintered from conventional powder oxides. Moreover, in the La-doping concentration range of 0.2-0.7at%, BaTiO₃ ceramics showed room temperature resistivity of <10³Ω·cm, though the value of PTCR jump was small (about one order) because no acceptor-type element was added. Early incorporation of La atoms in the BaTiO₃ lattice during the sol-gel processes may contribute to these results.

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Silica thin films containing organic polymers, such as poly (vinyl alcohol), poly (vinylpyrrolidone) or poly (vinyl acetate), were prepared on PET substrates by the sol-gel method. Poly (vinyl alcohol) was found to be most effective to suppress the water permeability of PET substrates coated with the organic-inorganic composite films among the three. Under the optimal condition, the water permeability coefficient was about 40% of that of PET substrates. The oxygen permeability coefficient was decreased with an increase in the poly (vinyl alcohol) content in the composites and was about 10% of that of PET substrates when a large amount of poly (vinyl alcohol) was included in the composites.

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Thin flakes of yttrium hydroxide coagulate in a manner similar to the houses of cards at an aging temperature lower than room temperature. Increasing the temperature results in an increase in the thickness of the flakes together with collapse of the structure of the house of cards. Relatively thick tablets of yttrium hydroxide appear at temperatures above approximately 50°C. Sulfate ions enhance the sinterability of yttria irrespective of the aging temperature of yttrium hydroxide, and have an influence on the transparency of yttria ceramics. Both the aging of yttrium hydroxide at temperatures lower than room temperature and the doping of sulfate ions are essential to the fabrication of transparent yttria ceramics using the present method.

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Vickers indentation in the silicon nitride, which was produced by superplastic compressive deformation, was conducted. The specimen had a highly anisotropic microstructure, where rod-shaped grains oriented almost two-dimensionally. The Vickers crack introduced in such microstructure exhibited an unusual crack system with a Cone-Vickers complex shape. Three dimensional crack system was estimated on the basis of the observation, and the crack evolution process was discussed.

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