The rhombohedral, monoclinic and triclinic tricalcium silicate solid solutions were synthesized and then hydrated in paste with water solid ratio of 0.3 and 0.4 for 91 days at 20°C. The initial hydration rate obtained from quantitaive X-ray diffraction analysis was in the order: monoclinic<triclinic<rhombohedral. The hydration degree of all the polymorphs, decreasing the difference with the progress of hydration, came up similarly to 70% at 91 days, Ultra high voltage transmission electron microscopy revealed that there are apparent differences in the morphology of the calcium silicate hydrate formed on the surfaces of the grains. Thin sheet and fibrous hydrate were the results of the hydration of rhombohedral and monoclinic form of tricalcium silicate respectively, whereas the calcium silicate hydrate produced from the triclinic form was amorphous. The crystallinity of the calcium silicate hydrate was fo undto depend greatly upon the initial rate of hydration. The specific surface area assessed from nitrogen adsorption and the pore size distribution obtained with a high pressure mercury porosimeter suggested that there took place appreciable changes in the microstructures of the hardened tricalcium silicate during hydration. The results confirm that the increase and decrease in the specific surface area elucidates the hydration process can be classified into four stages. The first rise in the specific surface area indicates the beginning of dissolution of Ca and Si ions from the tricalcium silicate grains. The following fall attributed to the remarkable increase of the microstructure of diameter less than the size of a nitrogen molecule represents the formation of the calcium silicate hydrate formed on the grain surfaces. The third increase in the specific surface area shows the further dissolution from the inner part of grains. The final decrease is ascribed to the formation of the inner hydrate due to the diffusion of the water into the deep part of the grains. It is not easy to show the relationship between the structure and strength characteristic at present, owing mainly to the difficulty in numerizing the microstructures of the hydrate products. The set of studies demonstrate, however, that there are remarkable influences of the polymorphism of tricalcium silicate both on the structure and strength of hardened paste.

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High pressure synthesis of cubic BN was carried out by employing urea as a catalyst. By examining the synthesized cubic BN under an electron microscope, the relation between the synthesis condition and the crystal shape and size is investigated.
It is found that cubic BN can be synthesized at a pressure and temperature region of at least 43kbar and 900°C. The synthesized cubic BN is a white powder. The primary particles have a morphology of a tetrahedron with crystal habits. However, when the synthesis takes place either at a high temperature, 1800°C, or a long time, 60 minutes, the crystal edges are rounded off, which indicates a melting process. The crystal size ranges from 0.02 to 0.7μm. The size tends to increase with the synthesis temperature and/or the amount of urea, and to decrease with increasing pressure and/or the synthesis time.

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Repeated glost-firing can often eliminate slight crazing in vitreous chinaware. The cause of the disappearance of crazing was investigated. It was found that the tensile stress in the glaze of an originally crazed specimen (A-I) decreased to around zero after the first refiring in a glost-firing kiln and changed to compressive stress with the second and the third refiring. It was also found that the compressive stress in the glare of an originally noncrazed specimen (A-II) increased with repeated firings in a glast-firing kiln. The rate of increase of the compressive stress in A-series specimens was -200--400kg/cm² with each refiring. The refractive index of the glaze layer decreased with repeated firings, and the index of the surface layer and that adjacent to the body was always lower than that of the middle part of the layer. This may be caused by the reaction. of the glaze layer with the body and the loss of volatile components from the glaze surface. The change in the composition of glaze may given rise to the change in the thermal expansion coefficient of the glaze layer. In the case of biscuited body specimens (B-series) which were refired in a glost-firing kiln one to three times, then glazed and glost-fired, the stress in the glaze was found to increase by -150--200kg/cm² with each refiring.
It was revealed by the X-ray diffraction technique that the amount of cristobalite in the body of specimens increased considerably with repeated firings in a glost-firing kiln, while the amount of mullite and quartz remained unchanged.
In the diagram which shows the relationship between the stress in the glaze and the crystal content [I_Q(100)+1/6⋅I_Cr(101)] of the body of standard vitreous chinaware, the compressive stress in the glaze of refired specimens originally glazed (Series A) is shown to be substantially higher than that of standard vitreous china with the same crystal content.
The change in the thermal expansion coefficient of the glaze was calculated taking into account the correction terms for the change in the glaze composition and the revised maturing point of the glaze. The thermal expansion coefficient of the original glaze glass, 6.7×10^-6, was estimated to change to about 5.2×10^-6 by the glost firing on the body and to about 4.4-3.7×10^-6 by repeated firings in a glost-firing kiln.
It was concluded that the disappearance of crazing in vitreous chinaware by refiring in a glost-firing kiln was caused by a change in stress in the glaze. The refiring gave rise to
1) a change in the composition of the glaze layer, which subsequently decreased the thermal expansion coefficient of the layer,
2) the deposition of cristobalite from the glass phase in the body and the subsequent increase in the thermal expansion coefficient of the body.
These two effects make the stress in the glaze more compressive and eliminate crazing.

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This paper describes experimental results of 200hours running and high heat fluxes over 300W/cm² durability tests for a 96% purity BeO ceramic cold type insulator.
By the operation with an ETL Mark III and VI, the electrical and thermophysical characteristics of the wall were obtained, and failure of the ceramic elements was analyzed. The maximum heat fluxes were 180W/cm² in Mark III and 120W/cm² in Mark VI and heat fluxes distribution along the channel axis agreed approximately with a theoretical values, and a time elaps characteristics of the open circuit voltage was stabilized after about 4 hours from the starting of the power generation. This transient phenomena coresponded with the decay time of Si-Al₂O₃ system clearance filler.
A surface deterioration of the ceramic elements near the cathodes was examined with a SEI figures and XMA analysis, and evidence of chemical reaction with potassium and some impurities diffused in it was obtained.
By the use of high heat fluxes testing apparatus, the limitation of heat fluxes for the wall was determined. The experiments showed that good durability against the heat flux around 400W/cm² was promised with the use of high heat fluxes structure wall and element thickness under 5mm.

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Effects of the condition to prepare Zr(OH)₄, the grain size and the heating atmosphere on the crystallization of tetragonal and monoclinic ZrO₂ were studied. The conditions to precipitate Zr(OH)₄ had little influence on the results. Prolonged drying increased the content of monoclinic ZrO₂ because of the structure change in the hydroxide by aging in the process of drying. The coarser grains of the hydroxide or the lower heating rate increased the content of monoclinic ZrO₂. The crystal structure of ZrO₂ obtained from Zr(OH)₄ was related to the atmosphere in which Zr(OH)₄ was heat-treated: monoclinic ZrO₂ was crystallized in water vapor and tetragonal ZrO₂ under reduced pressure. The effect of water vapor on the crystallization of ZrO₂ was remarkable rather than in the formation of amorphous ZrO₂. These results suggest that water vapor decreases the difference of surface energies of tetragonal and monoclinic ZrO₂.

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The chemical corrosion of an optical glass by organic acid solutions has been examined using the surface of a heavy crown, barium borosilicate glass (SK-16) with weak chemical durability. pH 4 solutions of acetic, oxalic, tartaric, citric and nitric acids were employed as corrosion solutions. In order that only a definite surface area is subjected to corrosion, the residual surface was coated with an organic paint (Vinylose). The glasses were then immersed in the solutions at 50°C. After a given corrosion period the depth of corrosion was measured by multiple-beam interferometry and, at the same time, the quantities of the dissolved SiO₂ and Ba were determined by calorimetry using ammonium phosphomolybdate and photometric EDTA titration, respectively.
In spite of the same pH values of the solutions, the magnitude of corrosion was found to depend on the kind of acid. The ability of corrosion decreases in the order acetic, citric, nitric, tartaric and oxalic acids. The order is closely related to (1) the dissociation constant of acid and (2) the solubility of the resulting Ba salt.
In the corrosion process Ba ions in the glass diffuse out into the acid solution, leaving SiO₂ skeleton layer, and then the SiO₂ skeleton layer breaks and dissolves in the solution. The stability of the SiO₂ skeleton layer is supposed to be associated with the chemical property of acid.

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The leucite crystal growth was investigated with an optical microscope, X-ray diffractometer and electron probe microanalyser for glasses in the system SiO₂-Al₂O₃-K₂O-Na₂O. The investigation was focused on the 6SiO₂⋅0.7 Al₂O₃⋅K₂O⋅Na₂O glass showing both clear glass formation and easy crystallization. Leucite dendrite crystals were grown as cubic pyramidal hillocks with the edge angle 90° on the glass surface at temperatures from 650° to 1020°C under atmospheric gas. The maximum height of the hillocks was about 1/25 of the trunk length of dendrites. The growth rate perpendicular to the glass surface was slightly smaller than that parallel to the surface. The direction of the leucite crystal growth was along c-axis. A linear relationship was found between the growth of crystal trunks and the time of heat-treatment. The activation energy for the crystal growth is given to be about 40kcal/mol, which is a little smaller than the yalue for the parent glass flow, from the observed relationship of the growth rate and the reciprocal absolute temperature up to about 1070K. The sodium ion concentration in the surface crystals was lower than that in the parent glass, and contrary to this for the potassium ion concentration. The crystals were leucite solid solutions containing a different amount of SiO₂ component and about 0.9wt% of Na₂O component. These results lead to the conclusion that the crystal growth is initiated through the process of diminishing the surface free energy after the formation of a highly viscos medium on the crystalline surface at elevated temperature; this process is connected with decreasing the sodium ion component together with the SiO₄ group and increasing the potassium ion component in the viscous medium.

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Formation of solid solution of calcium sulfite hemihydrate and calcium sulfate and the solid solubility limit thereof were investigated. In the products prepared by coprecipitation of calcium sulfite hemihydrate and calcium sulfate from aqueous solutions containing sulfate and sulfite ions in different ratios, presence of sulfate which can not be removed by washing with water and is assumed to be incorporated into CaSO₃⋅1/2H₂O crystal lattice was confirmed. The products were verified to be solid solution of calcium sulfite hemihydrate and calcium sulfate by means of differential thermal analysis, thermogravimetry, IR spectroscopy and X-ray diffraction analysis. Solid solubility of sulfate in CaSO₃⋅1/2H₂O was indicated to be dependent on reaction temperature, and it was, in the present investigations, about 9mol% at 15°C, increasing with temperature to the maximum value of about 19.5mol% at 83°C and higher. It was found that sulfate ions up to about 9mol% substituted in good order for sulfite ions of CaSO₃⋅1/2H₂O to form solid solution accompanying small changes in lattice parameters, and that sulfate ions of more than 9mol% caused disorder of sulfite crystal. In addition, from the results of examination of thermal properties and content of combined water of this solid solution, it was considered that the state of forming solid solution changed at the solid solubility of about 9mol%.

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