The structures of K₂O⋅2SiO₂ and Li₂O⋅2SiO₂ glasses were investigated by the X-ray diffraction measurement. Their structures were determined by the pair function analysis of the radial distribution function and by the molecular dynamics calculation (for only K₂O⋅2SiO₂ glass). The structures of alkali disilicate glasses were shown to consist of layers of six-membered ring of SiO₄ tetrahedra with potassium or lithium ions occupying positions between them. Potassium ions and lithium ions were accomodated in the space formed by four non-bridging oxygen atoms of upper and lower layers. The layer structure of disilicate glass was recognized as a composite of chains of their corresponding metasilicate glasses. In analysis of the structure of K₂O⋅2SiO₂ glass, the molecular dynamics calculations were effective to obtain the most stable configuration. The result agreed with the previous study on Na₂O⋅2SiO₂ and Li₂O⋅K₂O⋅4SiO₂ glasses, which were determined to have the layer structures.

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Pd(Zr_0.5Ti_0.5)O₃ (PZT) was prepared by calcining the oxalates which were co-precipitated by addition of a Pb, Zr, Tiaqueous solution to oxalic acid in ethanol. Particle size and crystallinity were strongly influenced by the preparation conditions, such as reaction temperature, excess amount of oxalic acid, and addition rate of both metallic component solution and ammonia solution. The addition of an ammonia solution was necessary in order to precipitate completely the metallic componens. The PZT powders were characterized by means of X-ray diffractometry, SEM observation, and measurement of particle size distribution. Lowering the reaction temperature decreased the particle size and increased the relative amount of tetragonal perovskite phase. When the oxalation temperature was 5°C, for instance, the particle size was around 0.15μm after calcining at 800°C, and tetragonal single phase, the c/a value of which was 1.029 agreed with the reference, was obtained by calcining at 1000°C. On the other hand, the rapid addition of metallic component solution, the slow addition of ammonia solution and the use of oxalic acid in 10mol% excess had an effect to produce the finely particulated powders.

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Glass-ceramics containing tetragonal ZrO₂ (t-ZrO₂) have been prepared and their mechanical strength and fracture toughness were measured. Glasses containing up to 15mol% ZrO₂ in the ternary system SiO₂-CaO-ZrO₂ changed to glass-ceramics containing CaO⋅SiO₂, 2CaO⋅ZrO₂⋅4SiO₂ and a small amount of t-ZrO₂ by the heat-treatment at 900°-1200°C for 1-24h. These glass-ceramics, however, had large cracks inside the bodies due to the growth of fibrous CaO⋅SiO₂ and 2CaO⋅ZrO₂⋅4SiO₂ crystal from surface. On the other hand, addition of 5mol% P₂O₅ to the 50SiO₂⋅38CaO⋅12ZrO₂ composition led to bulk crystallization resulting in the formation of crack-free glass-ceramics. The crystallization mechanism was investigated by SEM, EPMA and X-ray diffraction. It was found that the glass containing 5mol% P₂O₅ formed SiO₂-rich droplets 1-2μm in diameter on cooling from melt. When the glass was heat treated above 860°C, 4CaO⋅P₂O₅ crystal 50-100nm in diameter precipitated first in the matrix of the phase separated glass, and then t-ZrO₂ crystal 30-35nm precipitated around SiO₂-rich droplets as a major crystalline phase at a temperature above 900°C. This t-ZrO₂ did not transform to monoclinic ZrO₂ by heat-treatment at 910° and 1070°C for 48h. Young's modulus, mechanical strength, fracture toughness and fracture energy of the glass and glass-ceramics were measured by sing around method, three-point bending method, indentation method and work of fracture method, respectively. Although the increase of Young's modulus was very small, the strength, fracture toughness and fracture energy increased considerably by the precipitation of t-ZrO₂.

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Spherical silica particles were prepared by the hydrolysis of orthoethyl silicate in a alcoholic solution in the presence of ammonia catalysis. The thermal behaviors of the obtained spherical particles were examined by TEM, TG-DTA, IR and XRD. Results obtained were as follows.
(1) The hydrolysis product of orthoethyl silicate was homogeneous and truly spherical. Their diameters were changed by the mol ratio H₂O/Si(OC₂H₅)₄, NH₃/Si(OC₂H₅)₄ of the solution and the reaction temperature.
(2) By heat treatment, the combustion of organic matters in silica occurred at about 400°C, and the dehydration from silanol group at nearly 450°C. The autoclave treatment removed the organic matters from silica particles and decreased silanol group. The Si-O bond became strong.
(3) By heat treatment, the density approached to that of silica glass and the specific surface area decreased. But the autoclave treatment, its density and specific surface area remained unchanged, but the autoclaved powder was highly dispersive in alcohol.

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High silica porous glasses were prepared by varying acid treatment of phase-separated soda borosilicate glass and one of them was impregnated by sodium nitrate solutions. The porous glasses were heat treated to form nonporous glasses and the end point of their thermal shrinkage (sintering temperature) was determined. The glass transition temperature was determined for NaNO₃-impregnated and sintered glasses. The glass transition temperature was linearly related to the sintering temperature and decreased linearly with increasing logarithm of sodium oxide content. ΔT_g/ΔlogC, where T_g is the glass transition temperature and C is the content of water (-0.1wt%) or sodium oxide (0.1-3wt%) of nonporous glasses, was determined. Sodium oxide lowered the glass transition temperature more strongly than water. ΔT_g/ΔlogC was calculated for pure silica glass and some silicate glasses from the data available in the literatures and compared with the results of the present work. ΔT_g/ΔlogC for water decreased and that for sodium oxide increased with decreasing glass transition temperature.

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The hexagonal ice formation on the surfaces of several substrates which have different crystallographic configuration of oxygen atoms from that on the preferentially crystallized surface of ice was studied by taking rate and direction of cooling into consideration. It was found that the cooling direction is the dominating factor for the preferential orientation of crystal axis of ice formed on a substrate. That is, the hexagonal ice grows preferentially along c-axis for thin layer ice and along c-axis or a-axis for fine columnar ice parallel to the cooling direction, regardless of the degree of epitaxy of oxygen atoms on surfaces between substrate and ice, or of the degree of wettability between substrate and water. But it has been also found that the freezing temperature lowering and the temperature range for single crystal formation of ice in the whole capillary space of glass tubing on substrates were significantly influenced by the epitaxy, i.e. the degree of misfit of interatomic spacing of oxygen on crystallographic surfaces of substrate and ice (00l).

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The thermal shock behavior of 3mol% Y₂O₃-partially stabilized zirconia with average grain size of 0.4μm (Z3Y-I) and 1.0μm (Z3Y-II) has been studied by the water quench method. Twenty three specimens of rectangular cross-section bar (3 by 3 by 45mm) were quenched at 300°, 350° and 400deg;C temperature differentials (ΔT) and their retained strength (σ_f) were plotted using the Weibull distribution function and doubly exponential distribution function. The retained strength distribution at ΔT=350°C are similar to the original strength distribution. On the other hand, the distribution at ΔT=350° and 400°C showed a shoulder at F=0.458 and 0.875, respectively, They are the initiation points of thermal shock damage, Assumming the surface heat transfer coefficient (h) of 0.19 and 0.4cal/cm²·°C·s, calculated stress intensity factors K_I's for crack initiation by water quench were 73-75% and 91-92% of the critical stress intensity factor K_IC for Z3 Y-I, and 69-70% and 86-88% for Z3 Y-II, respectively. A σ_f-δT curve for a certain failure probability level F showed instantaneous decline at a critical temperature differential δT_c. High failure probability level F resulted in a high critical temperature diffrential δT_c. Estimated δT_c's are 310°, 360° and 400°C for F=0.2, 0.5 and 0.9, respectively.

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Sol mixtures with mullite composition were prepared from aluminum sulfate and ethyl silicate and freeze- or spray-dried. The process of mullite formation from the dried materials and the microstructure of specimens fired at 1760°C were investigated Anhydrous aluminum sulfate in the freeze-dried specimen fired at 600°C had a slightly large apparent crystallite size, and the decomposition temperature of aluminum sulfate on DTA curve was about 10°C higher in the freeze-dried specimen. The lattice parameter of the spinel phase forming in the temperature range of 900° to 1100°C was somewhat larger in the freeze-dried specimen. Mullite formed above 1150°C in both specimens, but the amount of mullite in the freeze-dried specimen increased rapidly at lower temperatures. The lattice parameter of mullite, b₀, increased a little in the temperature range form 1300° to 1500°C and decreased above 1500°C, and a₀ decreased considerably in the temperature range from 1300° to 1500°C or 1600°C and increased at higher temperatures. The freeze-dried specimen had a larger value of a₀ above 1600°C than the spray-dried specimen. The glass phase in the specimens fired at 1760°C increased with soaking time and the tendency was striking in the spray-dried specimen.

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Powders containing perovskite type double oxides of the series Pb(Mg_1/3Nb_2/3)O₃-Pb(Zn_1/3Nb_2/3)O₃ as a main constituent have been prepared by firing the batch mixture according to the chemical formulae. It is interesting to know the substitutional solid solubility of ZnO for MgO in this series because the latter end member Pb(Zn_1/3Nb_2/3)O₃ is known not to be prepared under ordinary firing conditions. The substituted ratio was estimated by the precise determination of lattice constant and its comparison with the Vegard's line. It was shown that MgO in the Pb(Mg_1/3Nb_2/3)O₃ was able to be substituted by ZnO up to 35 or 40mol% depending on the firing temperature (950° or 1100°C). Peak temperature of capacitance (corresponding to Curie point) of the fired disc varied from 0° to 40°C depending on the substitutional ratio of this series. Parallelism between the observed data and the predicted line connecting the Curie points of the end members suggested that the substitution of ZnO for MgO proceeded up to 30-35mol% in this series. However, a certain unbiguity still remained as the observed data at the higher substitutional ratios of the batch mixture were shown to be considerably high. Single crystals of this series were prepared by the “PbO-flux method”. According to the variation of the lattice constant of perovskite type crystal along with the feed composition, it was judged that the homogeneous substitution of ZnO for MgO went up to 30-35mol% in this series. Summarizing the above-mentioned results it has been concluded that the solid solubility of ZnO for MgO in this series is 35±5mol%.

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To investigate the effect of α- and β-Si₃N₄ content on the thermal conductivity of silicon nitride ceramics, six samples containing various quantities of α-Si₃N₄ were prepared by the reaction bonding process and the thermal conductivity of the reaction bonded Si₃N₄ (RBSN) was measured by the transient hot wire method at various temperatures from room temperature to 1000°C. The RBSN samples containing 1, 25, 33, 45, 55 and 66% α-Si₃N₄ were produced by nitriding the compacts of pure silicon powder in a nitrogen atmosphere at 1480°C for prescribed periods. Bulk density, true density and total porosity of samples were 2.51±0.02g/cm³, 3.08±0.03g/cm³ and 18.6±1.0%, respectively, regardless of the α-content. No significant change in microstructure of RBSN samples was observed by scanning electron microscopy With an increase in the content of α-Si₃N₄, the thermal conductivity (λ) of BRSN samples decreased from λ=17.4Wm^-1K^-1 for the sample with α-Si₃N₄ of 1% (viz. consisted mainly of β-Si₃N₄) to λ=9.3Wm^-1K^-1 for that of 66%. It was considered that the α-Si₃N₄ solid solutions by which the thermo-elastic wave carrying the heat energy in the non-electro-conductive solid materials such as Si₃N₄ ceramics is scattered, might be formed with the impurities included in silicon powder as a starting material. The thermal conductivity of all RBSN samples decreased simply with increasing temperature due to the increase of the mutual scattering of the thermo-elastic wave, and the decreasing rate of thermal conductivity for the RBSN with lower α-contents was found to be larger than that for those with higher α-contents.

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Alumina hydrate gel was synthesized by the homogeneous precipitation method using aluminum sulfate and urea. The effects of concentration of aluminum sulfate and of (NH₂)₂CO/Al₂(SO₄)₃ ratio on the average particle size and the particle size distribution of the alumina hydrate gel were investigated using grading analysis. When the (NH₂)₂CO/Al₂(SO₄)₃ ratio was 9 and the concentration of aluminum sulfate was high, the average particle size of the alumina hydrate gel particle was large and the particle size distribution was wide. When the (NH₂)₂CO/Al₂(SO₄)₃ ratio was 30 and 90, and the concentration of aluminum sulfate was higher than 0.05mol/l, the average particle size of the alumina hydrate gel particle was large.

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The Si₃N₄-SiC composite (0 to 0.25wt fraction of SiC) system was investigated to understand the effect of addition of one metal oxide (e.g. MgO, Al₂O₃, Y₂O₃ or CeO₂) and two metal oxides (e.g. Y₂O₃-Al₂O₃, CeO₂-Al₂O₃ etc.) on the sintering and Vickers hardness. The composites were hot-pressed at 1700°C under 400kg·mm^-2 or pressureless-sintered at 1700° and 1800°C. The results are as follows: The relative density of the composite decreased with the increasing of SiC content. The hot-pressed composites with 5wt% Y₂O₃+10wt% Al₂O₃ and 5wt% CeO₂+10wt% Al₂O₃ had 96 to 98% relative density and 1800 to 2000kg·mm^-2 Vickers hardness (at 5kg load), and pressureless-sintered composites with 5wt% Y₂O₃+10wt% Al₂O₃ fired at 1700°C far 4h had 87% relative density and 1200kg·mm^-2 Vickers hardness.

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