The crystallization behaviour of borosilicate glass (Pyrex) with and without a continuous SiC fibre reinforcement has been investigated as a function of heat treating time (10 min to 20h), temperatures (800 to 1050°C) and particle sizes. The tendency to crystallize into cristobalite was found to be very sensitive to the particle size of Pyrex glass. Finer particles exhibited a higher amount of cristobalite than coarse particles for the same heat treating conditions, indicating that crystallization of Pyrex resulted from heterogeneous nucleation and growth on the surface of each particle. For the SiC fibre/Pyrex composite, the presence of fibres appeared not to contribute significantly to the devitrification of matrix, since (1) nearly same degree of devitrification occurred in the Pyrex powder compact alone compared with the degree of crystallization in the SiC fibre/Pyrex composite with same size of Pyrex particle, and (2) devitrification occurred randomly rather than occurring preferentially at the matrix-fibre interfaces. The devitrification of Pyrex matrix to cristobalite under processing conditions used for composites gave rise to extensive microcracking. The thermal mismatch stress originating from both a higher coefficient of thermal expansion of devitrified cristobalite and -3.9% volume change at the phase transition temperature (-250°C) of cristobalite was calculated using the particle sphere model. The magnitude of stress calculated was high enough to cause cracking in and around a cristobalite particle surrounded by a Pyrex matrix.

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Different alumina characteristics of a raw material were tested in the glaze composition with a view toward overcoming difficulties in forming the intermediate layer during the fast firing process of porcelain tiles. The alumina samples, obtained by dehydrating aluminum trihydrate and grinding for various periods, had different particle size distributions. An outstanding improvement in the the quality was observed for the fine grained alumina, which was expected to dissolve rapidly in the glaze melt. Differences in the internal tensions between glaze and body were also observed. The acquired characteristics and effects of the intermediate layer formed between body and glaze in relation to the alumina grain size are discussed.

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Structure and magnetic properties of the Sc₂Cu_2-x Co_xO₅ system were investigated up to the solid solution limits x=0.4 and x=0.6. Undoped Sc₂Cu₂O₅ has, like isostructural Y₂Cu₂O₅, a magnetic structure with weak ferromagnetic coupling along the b-axis and strongly coupled Cu²⁺ chains parallel to the a-axis which were antiferromagnetically coupled below the Néel temperature of 16K. Doping with Co²⁺ caused the paramagnetic Curie temperature (θ_p) to decrease from the x=0 value of 40K, making (θ_p) negative for x>0.2, and caused the Néel temperature to increase to about 35K for x=0.4. Thus the interchain weak ferromagnetic coupling along the b-axis was weakened and the interchain antiferromagnetic coupling was strengthened, while the intrrchain strong ferromagnetic coupling, which displays the one-dimensional spin-spin interaction, was not influenced by the Co doping. Room-temperature structure refinement for Sc₂Cu_1.6Co_0.4O₅ from neutron powder diffraction data indicated that random substitution of Co²⁺ for Cu²⁺ occurred and that the Cu-O-O-Cu interchain superexchange pathway was enhanced by geometric changes as x increased from x=0 to 0.4.

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The strength degradation of silicon nitride ceramics up-cut surface ground under different conditions were studied by specific grinding energy and maximum grain depth of cut statistically analyzed by new direct evaluation method of successive cutting point spacing. Main results are summarized as follows; (1) Strength decreases with increase in wheel depth of cut and with decrease in specific grinding energy, and dose not depend on the change of table speed under the grinding conditions with a wheel including large grain size (#100; grain diameter=125-150μm). (2) Strength degradation is much large by 70-80% compared to inherent strength of the work at the range of more than 0.5-1.0μm in mean value of maximum grain depth of cut.

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The effects of composition on refractive index, density, glass transition temperature, and ultaviolet-visible and infrared transmissions were studied for gallate glasses containing a large amount (80mol%) of PbO, Bi₂O₃ and Tl₂O. The resonance wavelengths of Pb²⁺, Bi³⁺ and Tl⁺ were determined from the reflection spectra of gallate glasses. The refractive indexes of gallate glasses were measured down to the fourth decimal in the wavelength range of 480nm to 1710nm using the minimum deviation method. Refractive index in the system Bi₂O₃-PbO-Ga₂O₃ increases as PbO is substituted for Bi₂O₃. Refractive index in the systems Tl₂O-PbO-Ga₂O₃ and Tl₂O-Bi₂O₃-Ga₂O₃ increases as Tl₂O content increases. Factors affecting the refractive index of heavy metal gallate glasses are discussed by using the single-oscillator Drude-Voigt equation.

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In our previous report on hot-pressed Si₃N₄ monolith and SiC whisker (SiC (w))/Si₃N₄ composite compacts, it was clarifed that the fracture tougness (K_IC) measured by CSF method (the shape of pre-crack is semi-ellipse) were nearly the same for VV and PV specimens (VV specimen; the tensile surface and longitudinal direction of the specimen are both vertical to hot-press direction (HD), PV specimen; the tensile surface and longitudinal direction are parallel and vertical to HD, respectively); anisotropy of K_IC was not observed. This phenomenon was considered to be due to the fact that the average angle (θ) of the intersection or cutting direction of propagating crack to the longer axes of acicular Si₃N₄ grains and/or SiC (w) around the precrack is nearly the same (about 68°) for both specimens. Therefore, when SEPB method is used as a K_IC evaluating method where the shape of the pre-crack in the specimen is rectangle, VV and PV specimens are presumed to show different K_IC values, because the θ is different for both specimens (about 90° and 45°, respectively). In this study, this presumption was experimentally investigated. The result was in accordance with the presumption, and the fracture morphology (intergranular or transgranular fracture of acicular Si₃N₄ grain and/or SiC (w)) near the pre-crack supported the experimental results.

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Effect of Me²⁺(Me²⁺=Ni²⁺, Zn²⁺) on the formation of precipitation in the Fe(NO₃)₃-Me(NO₃)₂-HNO₃ solutions was determined on the basis of the potentiometric titration curve. By comparison of the titration curves obtained from Fe(NO₃)₃-Me(NO₃)₂ solutions with those of Me(NO₃)₂ solutions, it was found that the pH values of the plateau in the titration curve and its variation against the amount of added alkali depended on the nature of the respective cation. In the Fe(NO₃)₃-Ni(NO₃)₂ solution system, Ni²⁺ only reacted with Fe³⁺ untill the molar ratio of Ni²⁺ to Fe³⁺ in the precipitates becomes 2:1, but the reaction between Ni²⁺ and Ni²⁺ preferentially proceeded to produce Ni(OH)₂ when the amount of Ni²⁺ in the precipitates increased further. In the Fe(NO₃)₃-Zn(NO₃)₂ solution system, Zn²⁺ reacted with Fe³⁺ to produce amorphous precipitate but the reaction between Zn²⁺ and Zn²⁺ simultaneously occurred to produce Zn₅(NO₃)₂(OH)₈⋅2H₂O irrespective to the amount of Zn²⁺ in the precipitates. These precipitates were aged at 25 and 75°C. The precipitates obtained at 25°C were heat-treated at 500°C for 2h. The amount of crystalline McFe₂O₄ in these samples varied between the Fe(NO₃)₃-Ni(NO₃)₂ and the Fe(NO₃)₃-Zn(NO₃)₂ solution systems. By the aging and heating treatments, only Ni(OH)₂ or NiO crystallized in the former system, whereas both ZnFe₂O₄ and ZnO crystallized in the latter system when the amounts of Me²⁺ in the precipitates increased.

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Influence of fracture surface interactions on fracture toughness measured by chevron notched beam (CN) method was investigated with a fracture mechanical model. The fracture surface interaction was assumed to be elastic bridging and pull out, respectively. Load/displacement curves during chevron notched beam testing were calculated in consideration of the decrease in compliance caused by elastic bridging and the increase in dissipated energy caused by pull out. The apparent fracture toughness measured by chevron notched beam method was calculated by a maximum load in the load/displacement curve. Analytical results showed that there was a little influence of elastic bridging and pull out on the apparent fracture toughness measured by chevron notched beam method, when a CN specimen with a section of 3mm×4mm (JIS type specimen) was used.

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To develop a tempered glass under 3mm in thickness, boiling heat transfer characteristics of mineral oil and molten salt were studied experimentally. Heat flux and heat transfer coefficient with temperature and kinematics viscosity were measured using a copper disk of 40mm in diameter and 3mm in thickness. As a result, silicone oil showed no burn out point in this experimental condition and this tendency is different from another type of oils.

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The color of the alumina grains in the Al₂O₃-C refractories changes from white to dark-gray and the metals such as Si and Fe precipitate in alumina grain during using. In this paper, the mechanism of color changing and metal precipitating was studied. When the alumina grains containing many pores are heated in carbon powder, since the partial pressure of Al(g) in the pores is higher than that near the surface of the grain, Al diffuses from the surface of the grain to the pore, the Al reduces the impurities such as SiO₂ and FeO to form Si, Fe etc. As a result, the color of grains changes to dark-gray. When the dark-gray alumina grains are reheated in air, its color changes to white again because of the contrary diffusion to that stated above.

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In order to obtain pressureless-sintered SiC ceramics with high thermal conductivity, effect of BeO addition on sintering properties boron-doped β-SiC powder was investigated. The β-SiC powder was produced by the plasma arc method from SiH₄, B₂H₆ and CH₄ gases. Pressureless-sintered boron-doped β-SiC ceramics showed high thermal conductivity of 180 W·m^-1·K^-1 and electrical resistivity of 1100Ω·m (10mV). On the other hand, pressureless-sintered boron-doped β-SiC ceramics containing BeO showed varistor characteristics with electrical resistivity of 10¹¹Ω·m at 10V, and thermal conductivity of 230 W·m^-1·K^-1. These ceramics consisted of net-like elongated β-SiC grains. Thus, addition of BeO increased the thermal conductivity and electrical resistivity.

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A C-SiC-TiC composite fiber was obtained by heating a C-SiO₂-TiO₂ precursor, which was prepared from the carbon fiber (Kynol) impregnated with a mixed solution of ethylsilicate and titanium tetraisopropoxide. The reduction mechanism of the precursor has been investigated. The reduction rate was determined by means of a thermobalance in an atmosphere of Ar at temperatures from 1673 to 1973 K. The reaction products were examined by X-ray diffraction, SEM observation and chemical analysis. The precursor hydrolyzed in air was uniform and smooth in appearance, and had a microstructure of intermixed amorphous silica, anatase and carbon. The reduction of TiO₂ preceded that of SiO₂. Ti₃O₅ and Ti₂O₃ were transiently formed until TiO₂ was fully reduced to TiC. The atomic ratio of Ti to C in titanium carbide was smaller than unity. The reduction products of SiO₂ were SiC and SiO. The carbon core was surrounded by the reduction layer, in which the crystals of SiC and TiC were finely mixed. The reaction mechanism of the precursor changed with reduction time.

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The distribution in the tetragonal-monoclinic (t-m) phase transition temperature was investigated by the thermal expansion measurements for the arc-melted ZrO₂-YO_1.5 specimens. The peak temperature on heating A_p where the apparent thermal expansion coefficient has a minimum value, is higher than that on cooling M_p. The distribution of the transition temperatures increases with an increase of YO_1.5 content. Therefore, the difference between the starting points of m→t transition on heating and of t→m transformation on cooling, A_s-M_s decreases with increasing YO_1.5 content, and the M_s is higher than A_s in the 4mol%YO_1.5 sample.

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To measure the particle size distribution of fine ceramics powders, many models based on various measuring principles have been developed. Although sample is the same, the particle size distributions which are obtained by these various models do not always agree. This scatter may be caused by the difference of the equipment or sample preparation condition, but the details have been yet unknown. So the particle size distributions which are obtained with different commercial analysers must be compared systematically by optimizing and standardizing the condition of sample preparation. In this study, alumina, barium titanate and granulated zirconia powders were used as samples, and the features of these measuring principles were clarified by analyzing the obtained data for each sample, and the following results were obtained. (1) In spherical powders having narrow distribution, a good dispersibility and micron meter size, the obtained data are independent of the measuring principles and models if the sample preparation conditions are standardized. (2) In granulated powders having wide distribution, a remarkable scatter is indicated by the measuring principle. The effect of the ultrasonication condition can not be disregarded for the dispersion of granulated powder. The importance of the quantitative evaluation method of dispersion state is suggested.

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Viscosities and thermal properties of glasses in the Na₂O-B₂O₃ system were investigated in the temperature region of glass transformation. The values of ΔC_p and Eη/T_g, where ΔC_p is the heat capacity change during glass transition and Eη is the activation energy for viscous flow at around the glass transition temperature T_g, were maximum at 30mol% Na₂O, indicating that the fragility of liquid was maximized at the composition where the BO₄ tetrahedral unit was maximum in the corresponding glass. The relationship between the measures of liquid fragility and the average coordination number ‹r› of the elements comprising the glasses was discussed on the basis of Phillips' idea concerning the degree of bond constraint and glass-forming ability.

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Addition of polysilastyrene and minimizing the grain size of silicon powder with a ball mill improved the flexural strength of the carbon fiber reinforced SiC composites produced by reaction-bonding. The flexural strength of these composites with a bulk density of as low as about 1.85Mg·m^-3 was about 530 MPa. This improvement is attributed to the increase in the volume fraction of carbon fiber and the elastic modulus of the composites.

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Twentey vol% titanium carbide whisker/alumina composites added with 0.5 mass% yttria or 0.5 mass% magnesia were fabricated by hot-pressing at 1400-1700°C under 30MPa for 30 min. Their densification and mechanical properies were compared to those with no addition. Little effect of these addition on the densification was observed, and each composite had the highest density at a sintering temperature of 1600°C. The addition of yttria increased the room temperature and the high temperature bending strength, due to the existence of yttrium aluminum garnet (Y₃Al₅O₁₂). The magnesia addition also improved the room temperature strength although the effect was less than that in the case of yttria addition. These addition was ineffective for improvement of hardness and fracture toughness of the composites.

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Silicon nitride sintered bodies composed of finegrained α-Si₃N₄ and β′-sialon were fabricated by the gas-pressing sintering method. The silicon nitride sintered body showed a very high strength of about 2.0 GPa at room temperature, shock resistance of about 20kJ·m^-2 (Charpy impact value) and 3-point bending fatigue limit of about 1.3 GPa.

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