The optimum calcination for the Sb₂O₃-doped SnO₂ ceramics was obtained at 1000°C for 2 to 4hrs. The solubility of Sb₂O₃ in SnO₂ was 20 to 25wt% under the calcinating conditions. Lattice constants of the Sb-doped SnO₂ ceramic specimens were decreased up to 15% Sb₂O₃ and increased above 15% Sb₂O₃. Their density was increased up to 10 to 15% Sb₂O₃ and decreasd above 15% Sb₂O₃. Sintering of the ceramic specimens was markedly promoted by the addition of ZnO, MnO₂, or CuO with the best. It is assumed that the addition of ZnO or MnO₂ produces a substitution of Sn⁴⁺ ions in the SnO₂ lattice. These substitutions give a charge unbalance creating oxygen vacancies. The CuO addition causes a liquid phase sintering. It is conjectured that both of the oxyen vacancies and the liquid phase promote sintering. High density of the ceramic specimens gives high flexural strength. Electrical resistivities of the Sb₂O₃-doped specimens with ZnO were 5 to 50Ω-cm and those of the Sb₂O₃-doped ones with CuO, 1 to 10⁴Ω-cm at room temperature. Those of the Sb₂O₃-doped ones with MnO₂ were extremely high.

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Viscosity of casting slips, casting rate and thickness of remaining slip layer on draining were investigated to obtain equations expressed as functions of fundamental parameters, i.e. solid fraction (F₃), specific surface area (S_a) and hydration degree of solid (d_s). The results were summarized as follows.
(1) Viscosity of slips could be given by the equation η=I(AF₃^2/3)S_af(d/d_s), where (AF₃^2/3)S_a and f(d/d_s) related to the contact area of particles and the binding force at contact points depending on water film thickness d, respectively. Viscosity coefficient (I) was found to be rather constant except slips with different type of flow curves.
(2) Casting rate could be calculated from the viscosity and the fundamental parameters. The reliability depended largely upon accuracy of the measured viscosity.
(3) The thickness of remaining slip layer on draining could be expressed by the equation Δl=θ/(ρ_sgsinα), where ρ_s, θ and α denoted slip density, yield value and draining angle, respectively.

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Fibrous magnesia crystals were grown via vapor phase, by means of oxidation of magnesium vapor with moisture. Magnesium vapor was made from the reduction of MgO with CaC₂. The results obtained were as follows:
1) The morphology of crystals obtained mainly depends on the quantity of water diffusing into the crystal growth region. The crystal changes its form from fibrous polycrystal to whisker-like crystal, and finally to bulk crystal with increase of water vapor.
2) The growth axis of whisker-like crystal has mainly ‹100› direction. The axial growth is restricted by the two-dimensional nucleation on the prism faces of the crystal. Tensile strength of whisker-like crystals increases with decreasing cross section. A value of 100kg/mm² was measured from a crystal of 5μ in diameter.

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The self-diffusion coefficient of oxygen ion in a single crystal of MgAl₂O₄ has been measured in the temperature range of 1420° to 1630°C by a gas solid exchange technique utilizing O¹⁸ as a tracer. The temperature dependence of the self-diffusion coefficient was expressed by the equation:
D=1.5×10³ exp(-36×10³/RT) cm²/sec,
which was interpreted to be due to intrinsic diffusion. The determined self-diffusion coefficient of oxygen ion was smaller by several orders of magnitude than that of magnesium ion in MgAl₂O₄ and was close to the apparent diffusion coefficients calculated from the sintering rate of MgAl₂O₄.

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Sintering by hot-pressing of the system, Si₃N₄-Al₂O₃, was investigated.
The purities of the raw materials were about 98.5% for Si₃N₄ and 99.99% for Al₂O₃. Their grain sizes were, both, about 1μ in diameter. Temperature, time and pressure in the hot-pressing were 1650°-1850°C, 6-60min and 250kg/cm², respectively.
The following results were obtained. The quantity of Al₂O₃ necessary for full densification of the mixture Si₃N₄-Al₂O₃ was more than 20mol%, which agreed with that given by Deeley et al. Grain-growth in the sintered body was observed to be remarkable when Al₂O₃-concentration exceeds 40mol%. The activation energies for sintering under the pressure of 250kg/cm² were determined to be 100kcal/mol for 80mol% Si₃N₄-20mol%Al₂O₃ and 67kcal/mol for 60mol% Si₃N₄-40mol% Al₂O₃. Oxidation resistance of sintered Si₃N₄-Al₂O₃, evaluated by the weight gain, increased with Al₂O₃-concentration, reaching the maximum at 65mol% of Al₂O₃, followed by decreasing when Al₂O₃-concentration exceeds 65mol%. At the Al₂O₃-concentration of 65mol%, the oxidation resistance was more than 10 times as high as that of the system, Si₃N₄-MgO. Abrasive resistance of the sintered body, evaluated by the weight-loss during a abrasive test with abrasive powder, SiC #800, increased with Al₂O₃-concentration, reaching the maximum at the Al₂O₃-concentration of 50mol%, followed by decreasing when Al₂O₃ concentration exceeds 50mol%. The maximum abrasive resistance was about 4 times as high as that of sintered 85mol% Si₃N₄-15mol% MgO, which is in practical use.
By hot-pressing, the solid solution of Si₃N₄ and Al₂O₃, Si₃N₄ss, was found to be formed, which was already pointed out by the present authors. The solubility limit of Al₂O₃ in Si₃N₄s.s. was estimated to be about 67mol% at 1750°C and 78mol% at 1850°C. From the observation of specific gravity of Si₃N₄ss, the solid solution is thought to be of a substitutional type. A new compound was also found, whose composition was estimated to be 2Si₃N₄⋅3Al₂O₃. The new compound was stable under slightly oxidizing atmosphere and unstable under neutral or slightly reducing atmosphere. The eutectic point in the system was estimated to be 1870°±30°C. An approximate phase diagram was given for Si₃N₄-Al₂O₃.

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Anhydrous magnesium sulfate exists in two monotropic forms and its transition point 595°±5°C. The data of the lowtemperature form correspond to that reported by P. J. Rentzeperis et al.
The high-temperature form is orthorhombic and its lattice constants 4.75₀, 8.58₉ and 6.70₃Å.

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