Grain-oriented Bi₄Ti₃O₁₂ ceramics with 80%-orientation and the density of more than 95% of theoretical are fabricated by combining molten salt synthesis of plate-like powder particles, tapecasting forming of green compacts with aligned particles, and normal sintering. The effects of processing parameters such as preparation and firing conditions of cast sheets on the density and grain orientation of sintered sheets have been studied. A large powder content in the slurry is favorable to obtain cast sheets with a high degree of particle orientation. The density increases with increasing firing temperature, whereas the grain orientation increases above 1050°C. The grain growth is found to increase the grain orientation. Uniformity of the particle orientation in the cast sheets can be improved by narrowing the blade opening.

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By use of the colloidal solution of synthetic fluorine mica (Na-TSM), the three methods of forming mica film were investigated. The results obtained are summarized as follows:
(1) It is necessary to obtain the film that the flaky particles are stacked closely with high orientation.
(2) In order to obtain the thicker film, it is necessary to form the concentrated colloidal layer on the base, however, its layer tends to become non-orientated and highly viscous with increasing concentration.
(3) The films obtained by the doctor blade method have the highest strength for tension. The suction method offers the uniform and slightly lower strength film. The films obtained by the electrophoresis method have low strength and non-layer structure.

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The Nd-Al co-doping into SiO₂ glass was realized by plasma torch CVD using high purity SiCl₄, AlCl₃ and NdCl₃ as starting materials. The key point of this method was the development of a new AlCl₃ saturation apparatus supplying impurity free AlCl₃ vapour constantly. To prepare clear Nd-Al co-doped SiO₂ glasses at a high deposition rate, various plasma torch CVD operation parameters were investigated. It was found that co-doping of a small amount of Al₂O₃ makes effectively the undesirable fluorscence properties of Nd doped SiO₂ glass suitable for laser applications:
The clustering Nd³⁺ ions were dissolved in the host glass homogeneously and the intensity of laser transition became larger. The Nd-Al co-doped SiO₂ glass was evaluated to have radiative properties similar to those of the silicate laser glasses without little degradation in the excellent properties of SiO₂ glass as a host glass.

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Preparation of ZrN powders from ZrO₂ by reduction with Mg was investigated from 500°C to 1100°C at Mg/ZrO₂ molar ratio from 2 to 5 under N₂ stream (150-200ml/min). ZrN was formed above 600°C. γ-Zr₂ON₂ was formed as an intermediate product at Mg/ZrO₂ molar ratio from 2 to 4. In order to remove by-products such as MgO and Mg₃N₂, the products were washed with 1N HNO₃ and ethanol, followed by vacuum drying (-10^-3Torr). The products obtained in the temperature range from 600°C to 1000°C for 1h at the Mg/ZrO₂ molar ratio of 5 were purified by the treatment to prepare ZrN of single phase. The crystallite size and the specific surface area of ZrN powder obtained below 1000°C were 16-18nm and 30-33m²/g, respectively. However, the ZrN powder obtained at 1100°C had the crystallite size of 23.0nm and the specific surface area of 17.6m²/g. According to SEM observation, the particle size of ZrN powder obtained at 700°C ranged from 30 to 100nm, and the state of dispersion and homogeneity were sufficiently good. Although the ZrN powder obtained at 1000°C was homogeneous and fine, the particles were apt to agglomerate. The contents of N, O and Mg in the ZrN powder obtained at 1000°C were 12.0, 3.1 and 0.9wt%, respectively. The apparent activation energy for the formation of ZrN was approximately 3.7kcal/mol (750°-900°C).

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Ultrafine powders of silicon carbide were prepared by an r.f. plasma-CVD method using a chemical system of Ar-SiH₄-CH₄ under a reduced pressure of 2.13×10⁴Pa. Since these reactant gases were passing through the center of thermal plasma, the gases reacted completely to form SiC powders. The polytype of the powder was β-SiC only. The gaseous pressure and r.f. power were kept constant in the experiments while the growing parameters such as flow rate, reactant concentration and molar ratio of C/Si being changes. The particle radii of SiC are changed from 7nm to 4nm not by super saturation of reactant gases but by range of molar ratio in reactant gases between 1.0 and 7.6. The color of ultrafine SiC powder under 10nm was black as well as that of metal powder. The yield of the powder was between 70% and 90% under the experimental conditions. Pure silicon carbide powders were obtained under the molar ratio of reactants between 2.3 and 4.9.

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Pressureless-sintering process of translucent AlN ceramic has been investigated. Density, Ca content and thermal conductivity were measured and SEM observations were made with 8 samples of each stage in 1800°C-3h sintering. It was found that the sintering is a typical liquid phase sintering, and the following steps were observed: (1) Rearrangement of AlN particles (1300°-1600°C). (2) Solution of AlN particles and precipitation of AlN grains (1600°-1800°C). (3) Growth of AlN grains (1800°C). After sintering at 1800°-3h, only 120ppm of Ca was detected in the translucent sample, which was caused by the evaporation of calcium aluminate phase during sintering. Furthermore, the effects of oxygen and metallic impurity content on the thermal conductivity of sintered AlN have been investigated. It was observed that the thermal conductivity is inversely proportional to the logarithm of the oxygen content in thesintered AlN ranging from 0.26 to 7.3wt%. The maximum thermal conductivity, 131W/mK, was obtained with the pressureless-sintered AlN containing a minimum oxygen, 0.26wt%. Addition of metallic impurities in the range of ≤200ppm such as Si, Fe and Mg resulted in the drastic decrease in the thermal conductirity. For example, the initial value with undoped AlN, 140W/mK, decreased to 105W/mK, 114W/mK and 122W/mK by the addition of about 200ppm of Si, Fe, and Mg, respectively. These results prove that both low oxygen content and low metallic impurity content are required to attain high thermal conductivity in AlN ceramics.

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Tin oxide films were prepared on quartz substrates by glow discharge from tetramethyltin (TMT) in O₂. Crystalline and electro-conductive films were deposited on the substrates located near the cathode while amorphous and nonconducting films were obtained near the anode and also outside of the electrodes. A reason for the results was the more rise in the temperature of the substrates near the cathode (220°-290°C) than at the other positions (110°-170°C). The conductivity of the films deposited near the cathode was 2-20S·cm^-1. The carrier concentration was 10¹⁹-10²⁰cm^-3. The mobility was about 1cm²·V^-1·s^-1. The polarity of the electrodes and the position of the substrates affected also the appearance of the films. The films were contaminated with about 10wt% of saturated and unsaturated hydrocarbons of various chain lengths, which resulted from the decomposition and oxidation of TMT. The hydrocarbons also comprised oxygen atoms. The electron temperature (2-4eV) and the degree of ionization (10^-9-10^-7) in plasmas were measured. Their effects on the films properties, however, remained obscure. It seemed that electrons did not take part in the deposition of the films directly but neutral species (overwhelming majorities in plasmas) or ionic species played an important role in the process.

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The effects of pyrolysis pressure and supercritical water on the formation and morphology of formed carbon were studied by the pressure carbonization of p-terphenyl in the presence of supercritical water up to 1500kg/cm² and 700°C. The p-terphenyl is a compound of which carbonization was difficult at normal pressure, and the morphological control of the formed carbon was impossible even by the pressure pyrolysis of p-terphenyl itself without additives because of the lack of liquid phase separation during the pyrolysis. The p-terphenyl reacted with supercritical water to form CO₂, while of carbon-carbon bonds and carbon-hydrogen bonds in pyrolysis products were not influenced by the coexistence of supercritical water. However, the morphological change of formed carbon was found to be controllable by the phase separation between the highly viscous, pyrolized carboneous component and the supercritical fluid of very low viscosity. The carbon yield by this process was 70% in the system where water was added to p-terphenyl by 10 times in molar ratio. The pressure level for the pyrolysis with supercritical water was also an important factor to control the morphology of the formed nongraphitizable carbon from p-terphenyl.

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Growth of SiC whiskers by thermal decomposition of Si(CH₃)₄ and reaction of silicon powder and propylene was examined in the presence of hydrogen sulfide at 1100°-1350°C. If hydrogen sulfide was absent, both reactions gave no SiC whiskers but only carbonaceous deposits such as soot and carbon film. When hydrogen sulfide was mixed in the two reaction systems, however, a number of SiC whiskers were produced. The products were white and woolly whiskers of high aspect ratios; 0.1-0.5μm in diameter and several mm in length. The yield was maximum in the reaction of silicon and propylene at 1300°C for 60min. The whisker axis was the ‹111› direction of β-SiC. Electron microscopic observation revealed that the whiskers had the tapered or curved shape of the tips and that they carried no particles on the tips. From this observation and also from thermodynamic consideration, it was suggested that the present β-SiC whiskers grew by a VS mechanism via volatile SiS or SiS₂ intermediates.

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Coprecipitated gels were prepared by hydrolysis of mixed chloride solutions containing Sn⁴⁺ and Nb⁵⁺. The form of the precipitates, phase and structure changes during thermal dehydration process have been investigated. X-ray powder diffraction patterns of as-precipitated gels were the same as those of hydrous SnO₂ gel, and no additional pattern to crystalline SnO₂ was observed for co-precipitated gel with Nb:Sn atomic ratios below about 0.5:1 even after calcination at 1073K for 6h. The results of X-ray studies and the similarity of the chemical and physical properties of individual precipitate (i.e. hydrous SnO₂ gel and hydrous Nb₂O₅ gel) suggest that Nb⁵⁺ ions are incorporated in the SnO₂-like lattice of coprecipitated gel. Soluble Nb⁵⁺ ions affect the polymerization caused by dehydration of structural water between primary particles. Detailed examination of the broadening of SnO₂ diffraction profiles for coprecipitated gels heat-treated at 1173K for 6h indicated that dehydrated coprecipitates having higher Nb contents (0.23<Nb/Sn<0.5) consisted of a mixture of highly and poorly crystallized particles which correspond to Nb-poor and Nb-rich phases, respectively. Heat-treatment above 1223K (depending on Nb content) yielded free Nb₂O₅ in X-ray diffraction patterns of the heated coprecipitates, which shows the exsolution of Nb⁵⁺ ions out of metastable (Sn, Nb)O₂ solid solution. It is possible to synthesize homogeneous polyphase-ceramics by controlling the exsolution phenomenon of the second component out of a meta-stable solid solution system.

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The crystallization of HfO₂-Eu₂O₃ amorphous co-precipitates was studied under hydrothermal conditions. The precipitates with the weight ratios of HfO₂:Eu₂O₃=80:20 and 70:30, coprecipitated by NH₄OH from the solution of HfOCl₂ and EuCl₃, and dried at 90°C for 100h yielded a single phase cubic solid solution Hf_1-xEu_xO_2-x/2 (x=0.230 and 0.339) with a fluorite lattice by hydrothermal treatment at 300°C under 10MPa for 3h. These products consist of non-aggregated, ultrafine, narrow-sized and single-crystalline particles of about 10nm and 8nm in size for 20wt% and 30wt% Eu₂O₃ samples, respectively. It was comfirmed by the TEM observation, X-ray diffraction and specific surface area measurement by BET method which gave almost the same particle size. The maximum compositional fluctuation in the products was less than 2wt% by energy dispersive spectroscopy for each particle and by precise X-ray profile analysis of all the diffraction lines of the cubic phase using a Williamson-Hall plotting (β cosθ/λ vs sinθ/λ).

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Homogeneous gels of the system TiO₂-V₂O₅ containing up to 18mol% TiO₂ were obtained by hydrolysis of a mixture of Ti- and V-alkoxides in ethanol solution. The dried gel was characterized by TG-DTA, IR absorption spectra and X-ray diffraction. The fraction of reduced V ion in dark green gel was determined to be about 0.2 by wet chemical analysis. The crystallization temperature, which was determined by DTA, was higher than 310°C and increased with increasing TiO₂ content. The heat treatment of the gels at 260°C for 2 hours, yielded amorphous solid containing H₂O. The molar ratio [H₂O]/[V₂O₅] was about 0.3 to 0.6. Amorphous films of thickness from 0.3 to 10μm were made from the gels by dip-coating on glass substates. Several micro metre thick film containing 18mol% TiO₂ was yellowish green and transparent. The adhesion of the film containing TiO₂ was better than V₂O₅ film without TiO₂ addition. The dc conductivity of the coating film was about 10^-1 to 10^-3ohm^-1·cm^-1 at room temperature, and decreased with increasing TiO₂ content. In the amorphous solids, both V⁴⁺ and V⁵⁺ ions were considered to be 6-coordinated as in crystalline VO₂ and V₂O₅. The coordination state of V ions was affected little by TiO₂ addition. The conduction mechanism was assigned to be electronic.

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The various characteristics of silicon carbide powders mechano-chemically modified by vibration ball milling were investigated by surface area measurement, X-ray diffractometry, calorimetry and temperature-programmed desorption method. From the annealing treatment in the temperature range of 1300°-1700°C, the powder properties were considered.
The results obtained are as follows:
(1) The specfic surface area increased remarkably with grinding time and the surface activity was heightened. The elevation of surface activity was caused by the increase in the number of high active sites. The lattfce strain, was increased with grinding time.
(2) The surface diffusion was enhanced by milling, which suggests that the surface layer of powder was activated remarkably. However, a large gain of lattice strain was relaxed by annealing treatment.

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Zirconia thin films were prepared by thermal decomposition of the painted film of zirconium 2-ethylhexonate, and stabilized zirconia thin films were also prepared from mixture of zirconium 2-ethylhexonate and yittrium 2-ethylhexonate. The formation processes of the films were examined by TG-DSC, DTA, X-ray diffration and scanning electron microscopy. The zirconia thin films consisted of both tetragonal and monoclinic polycrystals, whose proportions depend on temperature and time of the thermal decomposition. Similarly, stabilized films on RF sputtered stabilized zirconia films were prepared by thermal decomposition of the painted films. The overcoated films were characterized for the application to solid electrolyte. The EMF measured with an oxygen concentration cell was five times higher than that of the RF sputtered films. These results suggest that this process is applicable to fuel cell and sensors as thin solid electrolyte film technique.

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The PBMA (polybutyl-methacrylate)-EVA (etylene-vinyl acetate copolymer)-PS (polystyrene) binder system was applied to injection molding of alumina. It was clarified that the relatively small and thin alumina product has good molding and binder removal characteristics with considerably smooth surface. A few problems of injection molding of ceramics were discussed on the basis of the present study.

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Mixtures of Al(OC₃H₇ⁱ)₃ and Si(OC₂H₅)₄ corresponding to xAl₂O₃⋅2SiO₂(x=1, 2, 3, 4) were dissolved in benzene and refluxed (81°-83°C) under a dried N₂ flow. Hydrolysis with equivalent amount of distilled water to formation of SiO₂ and Al(OH)₃ gave amorphous powders showing an exothermic peak at 980°C in DTA connected with crystallization to Al-Si spinel and mullite. Phases produced in the powders and disks heated at 800°-1620°C were compared with a phase diagram of the SiO₂-Al₂O₃ system. Compositions of mullite formed at 1400°C and 1550°C were estimated from the lattice constant a₀. Average particle size of the SiO₂-Al₂O₃ powders heat-treated at 1400°C for 3h, which showed narrow size distributions, were ≈0.15μm for x=1 and 2, and 0.082-0.089μm for x=3 and 4, respectively.

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The rapid-quenching technique extended the glass-forming region in the system Li₂O-SiO₂ toward the composition with high Li₂O content. The ratio of the glass transition temperature T_g to the liquidus one T₁ deviates largely from the so-called “two thirds rule” (T_g/T₁=2/3) in the glasses containing large amounts of Li₂O. The deviation was observed only in the glasses prepared by rapid quenching and it can be attributed to their high liquidus viscosity or small temperature variation of viscosity. The relation between the deviation from the “two thirds rule” and the glass-forming ability was discussed on the basis of the temperature and time variation curves of viscosity.

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1) Submicron monodispersed ZrO₂ fine particles were synthesized by the hydrolysis of Zr(ⁿOBu)₄ in n-propanol.
2) The particles were uniform spheroids ranging in size from 0.4 to 0.8μm and free from agglomeration. X-ray and DTA-TG analysis showed particles were amorphous and hydrated.

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Newly developed engineering ceramics are very difficult to be ground using conventional diamond grinding wheel because of their poor dressability and low cutting ability. In this study, a rigid and porous vitrified diamond grinding wheel was made so that a diamond grain might not deteriorate and it might be tightly bonded to the bond bridge using proper frit bond at lower firing temperature. According to the grinding test results, the grinding force was very low and dimensional accuracy of ground ceramics was very excellent.

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Geometry of quenched V₂O₅ was examined under 32 quenching conditions using a single-roller apparatus. It was observed that amorphous ribbons of relatively uniform geometry can be prepared in a variety of conditions, e.g. at the melting temperature of 890°-990°C, 2000-4000rpm of the stainless steel roller (20cm in diameter) and the ejection pressure of 1.5atm. Geometrical considerations of samples combined with the roller speed showed that these amorphous ribbons were made through an unstable puddle beneath the melt jet.

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A disorder phase with a cubic pyrochlore lattice (space group Fa3m) was obtained by rapid quenching of a Gd₃TaO₇ (3Gd₂O₃⋅Ta₂O₅) melt. A fluorite-related phase with orthorhombic weberite lattice (C222₁) was formed both by firing at 1350°C for 96h or at 1700°C for 4h, and by melting of the 3Gd₂O₃+Ta₂O₅ mixture. Annealing at 1350°C for 96h or at 1700°C for 4h of the rapidly quenched pyrochlore also produced the weberite phase. Order-disorder transition may occur above 1700°C in this compound.

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