In order to investigate the mechanical properties of Si₃N₄-SiC composites with various microstructures fabricated by a newly developed technique, compression and bend tests were conducted at temperatures from room temperature to 2000K. The following results have been obtained; (1) the Young's modulus is low in low stress range and increases with stress at room temperature, which shows that the materials have a higher flexibility, (2) the stress dependence of the modulus decreases with increasing temperature, and above about 1370K it is reversed, (3) the fracture stress is correlated roughly with the largest pore diameter observed on the polished surface, (4) the strength in vacuum decreases above about 1300K, while the strength in 1 atm. N₂ does not decrease up to about 2000K, and (5) there exists a special grain boundary connecting two grains by continuous lattice distortion. The present results show that the composite material, if the microstructure is well controlled, is very promising as high-temperature material.

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Compatibility relationships of the system ZrO₂-CaO-SiO₂ have been studied at 1400°-1500°C by a clarifying cross method (Klärkreuzverfahren) and synthesis of binary and ternary compounds. Two ternary compounds 3CaO⋅2SiO₂⋅ZrO₂(C₃S₂Z) and 2CaO⋅4SiO₂⋅ZrO₂(C₂S₄Z) were prepared by solid state reactions from the mixture of ZrO₂, SiO₂ and CaCO₃. C₃S₂Z was also formed from CS+CZ₄, C₂S+ZrO₂, C₂S+CZ₄ and C₃S₂+CZ at 1500°C. These reveal that C₃S₂Z is compatible with ZrO₂, CZ₄, CZ, C₂S, C₃S₂ and CS at 1400°-1500°C and that C₂S₄Z is compatible with ZrO₂, ZS, SiO₂ and CS at 1400°C. In addition, the conjugation lines CZ-C₈S and CZ-C₂S have been confirmed but the line ZS-CS was excluded from the conjugation lines. These results indicate that the system ZrO₂-CaO-SiO₂ consists of 12 compatible triangles; CaO-CZ-C₃S, C₃S-CZ-C₂S, C₂S-C₃S₂Z-CZ, CZ-C₃S₂Z-CZ₄, CZ₄-C₃S₂Z-ZrO₂, ZrO₂-C₃S₂Z-CS, C₂S-C₃S₂-C₃S₂Z, C₃S₂-CS-C₃S₂Z, ZrO₂-CS-C₂S₄Z, ZrO₂-ZS-C₂S₄Z, ZS-SiO₂-C₂S₄Z and SiO₂-CS-C₂S₄Z.

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Subcritical crack growth and crack-tip blunting in sintered silicon nitride with controlled surface flaws were studied at high temperatures under static load. A semicircular crack was introduced on the surface of sintered silicon nitride by Knoop indentation. The residual stress introduced during indentation was removed by surface grinding. After heated at high temperatures under the constant bending stress, the sample was removed from the furnace and the fracture stress was measured to calculate apparent fracture toughness. An initial stress intensity factor was calculated from the dimension of the Knoop flaw and the stress applied at high temperatures. The relation between apparent K_IC values and the initial stress intensity factor at 1200°C in a nitrogen atmosphere suggests the presence of the threshold stress intensity factor of crack-tip blunting. When heated at 1200°C with the initial stress intensity factor more than 0.1MPa·m^1/2, values of apparent K_IC were about 4.7MPa·m^1/2, which agreed with fracture toughness of sintered silicon nitride. Intergranular crack growth stemming from the Knoop flaw was observed at the higher initial stress intensity factor. But, when the initial stress intensity factor was below 0.1MPa·m^1/2, apparent K_IC value was about 12MPa·m^1/2, which was evaluated as an extraordinary high value. This phenomenon was attributed to crack-tip blunting, and the threshold stress intensity factor of crack-tip blunting agreed with the theoretically calculated value.

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Densities, elastic moduli, Vickers hardnesses, fracture toughnesses and fracture energies of Ca₃(PO₄)₂-Al₂O₃-SiO₂ glasses have been studied. Bulk, Young's and shear moduli were 55.26-62.19, 79.92-86.24 and 31.74-33.94GPa, respectively. If Ca₃(PO₄)₂ and Al₂O₃ contents were kept constant, elastic moduli of these glasses decreased with increasing mean atomic volumes. On the other hand, if SiO₂ contents were kept constant, there was an abnormal tendency that bulk modulus increased with increasing mean atomic volumes. If Ca₃(PO₄)₂ contents were kept constant, Young's modulus decreased with increasing mean atomic volumes. Furthermore, if SiO₂ or Al₂O₃ contents were kept constant, Young's elastic moduli increased with increasing mean atomic volumes. The elastic moduli of Ca₃(PO₄)₂-Al₂O₃-SiO₂ glasses (50-60% SiO₂, 20-30% Al₂O₃) were higher than those of CaO-P₂O₅-SiO₂ (0-15% SiO₂) and CaO-P₂O₅-Al₂O₃ (0-7% Al₂O₃) which have been reported in the previous papers, and close to those of silicate glasses containing 50-60% SiO₂. Vickers hardness was 510-580kg/mm² and larger than that of CaO-P₂O₅-SiO₂ and CaO-P₂O₅-Al₂O₃ glasses. The hardness increased with substitution of Al₂O₃ or SiO₂ for Ca₃(PO₄)₂. Al₂O₃ was the most effective component for increasing the hardness of these glasses. Fracture toughness and fracture energy were 0.99-1.47MPa·m^1/2 and 5.6-12.2J/m², respectively, and decreased with increasing Ca₃(PO₄)₂ contents. It is estimated that fracture toughness and fracture energy of glasses related to the number of weak bonds. The weak bonds in Ca₃(PO₄)₂-Al₂O₃-SiO₂ glasses are Ca-O bond, and Si-O bond in P-O-Si bond. Because the number of these weak bonds increase with increasing Ca₃(PO₄)₂ contents, fracture toughness and fracture energy decreased with increasing Ca₃(PO₄)₂ contents.

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Microstructure and electrical properties of ZnO-Nb₂O₅-MnO ceramics depend on the cooling condition after the liquid-phase sintering. Zinc oxide specimens containing 1mol% Nb₂O₅ and 0.5mol% MnO were prepared by varying cooling schedules from their firing temperature, 1305°C at which some eutectic melt was formed in the bodies. In the specimens quenched to various temperatures, T_q (after the temperature reached T_q, the specimens were cooled in the furnace), the resistivity and non-linear coefficient of voltage-current relation increased with decreasing T_q.
The specimen cooled slowly from the firing temperature to the room temperature had a high electrical resistivity and showed no varistor characteristics. Although the second phase wetted ZnO grains well in the specimens quenched to lower T_q, the increase of their electrical resistivity and non-linear coefficient could not be sufficiently explained by the wettability of the second phase to ZnO grains alone. Since a part of ZnO precipitated epitaxially on the ZnO host grain surface from the melt during cooling, it was suggested that the grain boundary region or very thin surface layer of the ZnO grains became to have electrical properties different from those in their inner part, and that such a difference caused high resistivity and non-linearity of voltage-current relation.

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Absorption spectra of Ni²⁺ ions in PbO-B₂O₃-R₂O (R=Na or/and K) glasses containing NiO and their IR absorption spectra and refractive indices were measured. The ligand field strength and the Racah's B parameter were calculated from the absorption wavenumbers of Ni²⁺ ions. The effect of alkali metal oxide contents and of the ratio of PbO/B₂O₃ on the state of Ni²⁺ ions and glass structure was discussed on the basis of these results. Intensity of IR absorption spectra around 900cm^-1 of these glasses was decreased with increasing alkali content, suggesting that a part of BO₄ units was transformed to BO₃ units with increasing alkali content. The refractive indices of those glasses decreased with increasing alkali content. This was ascribed to the decrease of the ratio of Pb²⁺ with increasing alkali content. The variation of refractive indices of mixed alkali glasses with alkali ratio showed no clear mixed effect. The ligand field strength calculated from the absorption spectra of Ni²⁺ shifted toward high wavenumber with increasing alkali content in single alkali glasses, and the variation became small with increasing PbO content. In mixed alkali glasses the variation of refractivity with that of alkali content indicated 1:1. Racah's B parameter in 84 (PbO⋅2B₂O₃)+xK₂O+(16-x)Na₂O glasses and 76 (PbO⋅2B₂O₃)+xK₂O+(24-x)Na₂O glasses shifted toward low wavenumber with increasing K₂O content.

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The thermal shock fracture resistance of reused cylindrical glass bottles subjected to hydraulic internal pressure was measured by quenching at outer surfaces. Next, on the basis of a linear fracture mechanics, fracture toughness of a glass cylinder with straight-front crack at its outer surface, under both thermal shock and internal pressure was theoretically calculated using Bueckner's solution (Weight Function). Further, the theory was extended to reused glass bottles with semi-elliptical cracks at their outer surface. As a result, the experimental results on the glass bottles coincided well with those of the theoretical ones of glass cylinders.

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The effect of calcium hydroxide and aluminate on the setting and hardening of the system of paper sludge-sulfuric acid-slag-calcium hydroxide was investigated. The results obtained were as follows.
(1) In the system of paper sludge-sulfuric acid-slag, the CaO and MgO components in the slag reacted with free sulfuric acid. This reaction caused the formation of calcium sulfate dihydrate and the increase of the reactivity of SiO₂ and Al₂O₃ components in the reacted slag.
(2) The addition of calcium hydroxide into this system resulted in the formation of ettringite. When the amount of calcium hydroxide added was less than 3 in the molar ratio of CaO/Al₂O₃, it was difficult to form ettringite. On the other hand, when the molar ratio was more than 3, the formation of ettringite was observed in the system, and the paste of the system set and hardened.
(3) Setting of the paste of the system was accelerated markedly with the addition of aluminate. When Ca (OH)₂ and CaSO₄⋅2H₂O were present more than 3/3/1 in the molar ratio of CaO/CaSO₄⋅2H₂O/Al₂O₃, the addition of NaAlO₂ caused the formation of ettringite and the increase of the strength of hardened bodies. When there was no Ca(OH)₂ or CaSO₄⋅2H₂O, ettringite did not form and the strength of the hardened bodies decreased by the addition of NaAlO₂.

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