Showing papers by "Sumio Sakka published in 1962"

Studies on the Dielectric Loss of Polycrystalline Material Produced from the Glass of the System Li₂O-MgO-Al₂O₃-SiO₂

Abstract: S showed that, during its heat treatment, ,8-eucryptite was first precipitated at about 850°C and then ,8-spodLlmene at about 1000uC. Microscopic examination showed that ,8-spodumene, after its precipitation, decreased its grain size by fission, by still unknown reason, with increasing temperature. Above 1000°C the marked increase in specific density of the specimen with increasing temperature was also observed. ( il) Effects of heat treatments on streng-tho The conditions of heat treatment such as the heating rate and the maximum holding temperature were varied and their effects on the modulus of rupture of the resultant polyerystalline materials were determined. The slow heating with the rate at least below 5\"Cj min. in the temperature interval of 800 to 900°C, in which ,8-eucryptite was first precipitated in the specimen, was found to be necessary increasing the strength. The specimen which missed this heat treatment had poor strength. The strength was also found to increase with incresing the maximum holding temperature. This change was attributed to the decrease in grain size of ,8-spodumene and also to the compacting of microstructure. Studies on the Dielectric Loss of PolycrystalIine Material Produced from the Glass of the System LizO-MgO-AhOa-SiOe Sumio SAKKA and Megumi TASHIRO Yogyo Kyolwishi (Journal of the Ceramic Association, japan), 69, 393 (1961) In the previous paper (J. Ceram. Assoc. japan, 60 [10J 223 (1960» the authors have given the method of converting the glasses of the system LLO-MgO-ALO,,SiOz into a polycrystalline material with or without the addition of platinum nucleus, the amount of which was limited to a very small value. The results of the measurement of the mechanical and thermal properties of the material produced were also published (J. Ceram. Assoc., japan, 69 [2J 35 (1961». The present paper concerns the dielectric loss of the same material which was expected to show the effect of chemical composition and heat treatment. ( 1) Effect of heat treatment. The glass of the composition, MgO 15, AleO\" 23, Si02 62, Li20 x, I\",here x 4, 6, 8, 12 by weight ratio, were melted, and reheated with the constant rate of 5°Cjmin. to a temperature from 750°C to 1200°C. The tan 0 at 1 Me of the crystallized specimens showed that, in general, it became higher than the base glass by the heat treatment at a temperature between 750°C and 950°C, whereas the heating at a temperature higher than 1000°C brought about a great deCl-ese in tan o. The increase of tan 0 may be attributed to the formation of ,8-eucriptite which usually occurs in the low temperature range, while the sudden decrease in tan 0 may be attributed to the formation of ,8-spodumen which appears with the cost of vanishing ,8-eucryptite. ( 2) Effect of the chemical composition of the base glass. It is likely that