Lanthanum orthoferrites were prepared by firing co-precipitated hydroxides of La³⁺ and Fe³⁺ at various temperatures. The materials fired below 700°C apparently had a cubic perovskite-type structure imperfectly crystallized, and the firing temperature elevation changed it to the orthorhombic phase of the GdFeO₃-type structure. The chemical analysis and the density measurements showed that the thermally metastable crystals fired below 1100°C more or less contain such lattice vacancies that the vacancy concentration ratio of V_La:V_Fe:V_o is always equal to that of the constituent atoms of LaFeO₃. To clarify the origin of the remarkable line broadening of the X-ray diffraction peaks, the effect of crystallite size on half-height width, β, was separated by plotting β cos θ vs. sin θ. A fairly large fluctuation of interplaner spacing, Δd/d, decreased with increasing firing temperature. Lanthanum orthoferrites containing lattice vacancies were also characterized by a large magnetic susceptibility, a low Néel temperature, a small spontaneous magnetization, and moreover, “diffuse magnetic anomaly” in the vicinity of antiferromagnetic-paramagnetic transition compared with lanthanum orthoferrites without vacancies. Essentially, these characteristics were interpreted in terms of a local decrease in anisotropic superexchange interaction at vacant sites.

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The effect of calcium oxide on the sintering, the crystallite growth and grain growth of magnesia were studied.
Magnesium hydroxide, the starting materials for magnesia, was precipitated by treating magnesium chloride solution with milk of lime. Calcium oxide was added to the magnesium hydroxide as a form of calcium hydroxide in two ways. The one was precipitated by mixing magnesium chloride solution with stoichiometric excess of lime.
The other was prepared by adding milk of lime to conventional high purity magnesium hydroxide slurry.
The calcium oxide retarded remarkably the crystallite growth of magnesia in the temperature range of 900 to 1200°C.
The abrupt growth of the magnesia grains in the sintering process below 1400°C was found both in the calcium oxide added compacts and in the conventional high purity magnesia compacts. The relative density of the former was 92% at 1400°C for 240min. While that of the latter was 78%. It was concluded that the uniformly distributed calcium oxide in magnesia improved the sinterability of magnesia below 1400°C.

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Prismatic single crystals of α-Si₃N₄ were prepared on a graphite susceptors by vapor phase reaction from SiCl₄, N₂ and H₂ gaseous mixture. Growth conditions were chosen as follows; SiCl₄=2.7×10^-4mol/min, H₂=1000cc/min, N₂=1000cc/min, total pressure=1atm, susceptor temperature=1600°C, duration=3-6h.
1) Oxygen and water in a gaseous mixture were analysed from electromotive force of an oxygen concentration cell and dew point. The amounts of oxygen and water supplied in the reaction vessel were 8.9×10^-7mol per min and 4.46×10^-8mol per min at room temperature, respectively.
2) Equilibrium oxygen partial pressure at elevated temperature was calculated using the data of raw gas analysis, growth condition and JANAF thermochemical data. The results calculated in the system were as follows;
Po₂=3.5×10^-26atm at 1300°K
Po₂=6.7×10^-20atm at 1900°K
The values were very much lower than those of equilibrium state governed by the reduction of H₂ or CO which had been used in the conventional processes.
3) Calculation of equilibrium oxygen partial pressure in the system indicated the following results;
1. The effect of hydrogen-nitrogen mole ratio were very small.
2. Oxygen as an impurity in raw gas mixture affected Po₂ distinctly at low temperature.
3. Water as an impurity in raw gas mixture affected Po₂ distinctly at high temperature.
4) Oxygen content and structural data of α-Si₃N₄ crystals prepared by this method under the above mentioned conditions were compared with those already reported. It contained less oxygen (0.05-0.09wt%) than any other α-Si₃N₄ crystals ever prepared.

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Paying attention to both the thermal fractures taking place in glass tempering process and the fracture densities of tempered glass, the experiments of oil tempering of glass were performed. From these experimental data, the following results have been obtained.
1) Critical thermal conditions on which the fracture takes place in tempering are depended on both the preheating temperature of glass and Biot's number. Furthermore, stress relaxation of glass surface in visco-elastic region can be determined on the basis of the conditions mentioned above.
2) There exists the linear relationship between the fracture densities and the residual surface stresses determined by the procedure of extrapolation on the basis of the curve obtained by experiments.

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The mixture of silica powder, a by-product of metalic silicon, and milk of lime, prepared from quick lime of fine grain, was stirred in an autoclave and treated hydrothermally under the following conditions; molar ratio of CaO/SiO₂ 0.975, weight ratio of water/total-solid 24, pressure 12kg/cm², temperature 191°C, reaction time 8h. Thus milky slurry consisting of xonotlite was prepared.
Xonotlite aggregate grain prepared by this method was fairly different from that by the previous method in which silica sand was used as raw material. As it is shown in the figures, the grain is hollow and has finer size, and xonotlite single crystals constituting the aggregate grain are relatively longer and thinner.
The molded material from this slurry is more excellent than the previous one; bulk density is 0.1, bending strength is 6kg/cm² and shrinkage at 1000°C is about 1%. Bending strength of a material having bulk density of 0.2 becomes over 20kg/cm².

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Phases obtained from the glass of the system K₂O-TiO₂ under hydrothermal conditions depended on the presence of potassium hydroxide in water. Using aqueous solution of potassium hydroxide, potassium hexatitanate and non-crystalline potassium titanate fibers were obtained. And using water without potassium hydroxide as starting liquid, potassium hexatitanate, potassium tetratitanate and non-crystalline potassium titanate fibers were formed, even though potassium hydroxide was formed by the dissolution of glass into water during the process.

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The oxidation resistance of α-Si₃N₄ was lower than that of β-Si₃N₄. But the difference was smaller than that suggested by the results in the powder mixture of α and β phase. The values of activation energy for oxidation reaction were 62 and 68 kcal/mol for α and β phase respectively and showed agreement with each other within experimental error. The result fitted a parabolic rate law and the diffusion of oxygen in cristobalite was inferred to be rate determining process.

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To make nitrided materials from volcanic ash, a mixture of Shirasu (chemical composition in wt% SiO₂:63.7, Al₂O₃:19.6, FeO+Fe₂O₃:3.8, CaO:5.4, MgO:1.2, Na₂O:5.0, K₂O:1.0, ignition loss: 0.5) and Al powder was pressed under a pressure of 400kg/cm², and heated at 1400°C in N₂.
The products were mainly composed of α-Al₂O₃ and β-Si₃N₄*. When 35% Al was present in the starting mixture, unknown phase with d values (Å) of 2.795, 2.605, 2.493, 2.396, 2.331 and 2.154 was found. Each β-Si₃N₄* peaks in the X-ray patterns was shifted to lower angle than those of pure β-Si₃N₄, and the magnitude of the peak shift was nearly proportional to Al content. It may indicate the formation of solid solution. Some properties of the sintered bodies are as follows; compressive strength of 1000 to 1200kg/cm², apparent specific gravity of 2.8, bulk specific gravity of 1.8, apparent porosity of about 33%.

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Mixtures of Ca(OH)₂, Al₂O₃ and ZnO corresponding to 100-80 (3CaO+Al₂O₃)+0-20 (ZnO) in composition were treated hydrothermally at temperatures between 120°C and 300°C in saturated steam condition. The treated specimens were examined with an X-ray diffractometer and a polarizing or electron microscope.
The results obtained were as follows.
1) The mixture of 3CaO+Al₂O₃ gave Ca₃Al₂(OH)₁₂ at temperatures between 120°C and 220°C and a mixture of Ca₃Al₂(OH)₁₂+Ca₄Al₆O₁₀(OH)₆+Ca(OH)₂ at temperatures between 230°C and 300°C.
2) The mixtures of 98-80 (3CaO+Al₂O₃)+2-20 (ZnO) gave mixtures of Ca₃Al₂(OH)₁₂+ZnO at temperatures between 120°C and 170°C, Ca₃Al₂(OH)₁₂+Ca(OH)₂+ZnAl₂O₄ at temperatures between 180°C and 220°C and Ca₃Al₂(OH)₁₂+Ca₄Al₆O₁₀(OH)₆+Ca(OH)₂+ZnAl₂O₄ at temperatures between 230°C and 300°C.
3) The crystals of Ca₃Al₂(OH)₁₂ were appeared as characteristic dodecahedrons ranging from 4μm to 10μm in diameter. ZnAl₂O₄ were appeared as granular crystals ranging from 1μm to 5μm in diameter.

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[in Japanese]

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