It is generally mentioned that quartz is stable up to 867°C, that tridymite is the stable polymorph from 867°C to 1470°C, and that cristobalite is the stable phase of silica between 1470°C and the melting point in silica refractories. However it was sometimes found that cristobalite appeared in silica refractories used at the stable temperature region of tridymite in hot blast stove or some other furnaces. The cause of this phenomenon and its transformation mechanism were, therefore, studied.
The transformation temperature of tridymite-cristobalite is also 1470°C in sample used in this research. But when the dust of hot blast stove was added to the sample, an amount of cristobalite increased at 1400°C. It was found that the transformation temperature of tridymite-cristobalite dropped gradually with addition of aluminium oxide. The transformation temperature, however, approached to 1470°C with the increase of calcium oxide in silica refractories.

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The corrosion of refractories is considered as a process by which refractories come to equilibrium with the condition of environment where they are used. The state of corroded refractories was studied in order to explain the feature of the process.
Surface layers of the refractories used in the superstructure of the glass-melting furnaces for sheet glass were chemically analyzed. Their Na₂O contents were approximately constant and their Na₂O levels (chemical potential) were considered to be equal to those of the environment where the refractories were used. Na₂O increase was essentially the only change in the composition of the surface layers of the refractories under service.
Therefore the surface layer of the refractories could be considered as one system, which was opened for alkali but closed for the other components and alkali content in the system was affected by the alkali level in the environment. The state of the corroded refractories could be estimated from the equilibrium state of the system with Na₂O level equal to that of the environment.
The refractories corroded by molten glass at temperatures from 1300°C to 1500°C were investigated by electron beam microanalysis and analytical data were obtained about the interface. zones between the refractories and glass. Na₂O level for each data was approximately constant and seemed to be close to that of the glass. Therefore in this case also Na₂O content in the surface of the refractories was considered to be equilibrium with the Na₂O level of the environment (glass). The content of CaO in the interface zones, however, increased also at higher temperatures and the influence of CaO could not be ignored. (CaO+Na₂O)/Al₂O₃ mole ratios of the zones were nearly constant at any temperatures. Therefore at higher temperatures Ca²⁺ ions were considered to enter into the interface zone partially instead of Na⁺ ions.

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Silica powders were obtained by decomposing tetraethoxysilane vapor thermally in an oxygen-containing gas at several stages of temperature between 400° and 1000°C, and mesurements of particle diameter, surface area, density, infrared spectrum, X-ray diffraction pattern and dispersibility in water, ethanol or n-hexane were carried out on them. The particle diameters, 0.07-1.9μm, of the silica powders decreased, and the BET surface area of them increased to 70m²/g at 733°C, with the rise of decomposing temperature. The powders obtained in the range from 544°C to 820°C exhibited densities of 2.18-2.07g/cm³. The surface areas estimated from the particle diameters and densities were about one third the BET surface areas. The internal hydroxyl group was contained in the powders obtained at temperatures below 650°C, and its concentration decreased with the rise of decomposing temperature. The powders were hydrophilic at decomposing temperature below 650°C, and the dispersibility of powders in water lowered with the rise of temperature above 650°C. The powders were amorphous. Silica was also obtained in a fibrous form, with diameters of 0.12-1.6μm, on the quartz plate surface on which a small amount of BaCl₂, NiCl₂ or SrCl₂ was deposited from an aqueous solution.

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Infrared radiation characteristics of alumino-silicate ceramics were investigated by using instrument which is infrared spectrophtometer with black body furnace as reference beam source.
It was found that the infrared radiation power of almost all ceramic radiants are better than the infrared radiation of metal radiants from present experimental results. The infrared radiation spectra of sintered silica and alumina showed characteristics as called far-infrared radiants, because they had maximum of infrared radiation at 5-7μm wavelength. When alkali or transitional elements are added to aluminosilicate ceramics, the infrared emissivity of them became higher. The infrared emissivity of such ceramics was estimated in comparision with the black body emissivity which is calculated from Planck's distribution of emissive power.

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Reactions of the compounds of the system CaO-Al₂O₃ in phosphoric acid solutions were studied by hydrothermal techniques at 100°C under the pressure of 10MPa. C₃A, C₁₂A₇, CA and CA₂ hydrated in pure water or phosphoric acid solutions to form C₃AH₆ and AH₃ (gibbsite). The hydration reactivity of Calucium aluminates decreased with the decrease of its CaO/Al₂O₃ ratio and the hydration of CA and CA₂ could not proceed even after 30 days by the addition of a phosphoric acid. It seemed that phosphoric acid formed AlPO₄-like insoluble materials on the surface of CA and CA₂ to retard the hydration. CA₆ and α-A hydrated neither in water nor in phosphoric acid solutions.
H₃PO₄ preferentially reacted with CaO components to form Ca₁₀(PO₄)₆(OH)₂ or CaHPO₄. The formation region of C₃AH₆ appeared to extend to the line from CaHPO₄ to Al₂O₃ in the system CaO-Al₂O₃-H₃PO₄(H₂O). AH₃ was formed together with AlPO₄⋅2H₂O below the line of H₃PO₄/CaO+Al₂O₃+H₃PO₄=50mol%.
The formation of various phosphates were strongly dependent on the pH of solutions. The products were Ca₁₀(PO₄)₆(OH)₂ in alkaline solutions, Ca₁₀(PO₄)₆(OH)₂, CaHPO₄, AlPO₄⋅2H₂O (Messbach-type) or AlPO₄⋅2H₂O (Lucin-type) in neutral or weak acid solutions, CaHPO₄, AlPO₄⋅2H₂O (Messbach-type), AlPO₄⋅2H₂O (Lucin-type) or weak AlPO₄⋅2H₂O (Metavariscite) in acid solutions and Ca(H₂PO₄)₂⋅H₂O or AlPO₄⋅2H₂O (Metavariscite) in strongly acidic solutions.

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The effect of preparatory conditions on the properties of vitrified bonded silicon carbide abrasive sintered specimens was studied. The conditions considered were bond fraction, molding pressure, firing temperature, time and atmosphere. The properties studied included apparent density, bending strength and Young's modulus. The effect of those conditions on properties and the effect of developed micro-structure during firing on the properties of abrasive article were discussed. Close correlations were found between apparent density, bending strength and Young's modulus.

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