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It is desirable to use certain oxides of rare-earth metals for obtaining highly refractory heat resistant materials.

This communication is a brief account of the results of a study of phase separation in aluminosilicate glasses containing oxides of Li, Na, Ca, Ba, Cd, Sn, and Zn. The need for such an investigation became obvious in studies of formation of glass-ceramics in these systems. A total of about 200 glass compositions were studied in the course of the investigation by electron microscopy and other methods both with and without addition of TiO2 as a catalyst of volume crystallization.

Titanium dioxide is widely used as a catalyst in production of glass-ceramics from a number of aluminosilicate systems. Most investigators consider that the influence of TiO2 is manifested primarily in separation of the melt into two glassy phases, and that the metastable phase separation which occurs ensures fine-grained volume crystallization. However, the structural changes occurring during the period preceding volume crystallization have not been studied or fully explained.

Glass 13 was investigated. Titanium dioxide, in amounts from 1 to 11% TiO2 by weight, was added as the catalyst.All the glasses were made in a semiproduction furnace. A series of the glasses was then subjected to heat treatment under laboratory conditions in special thermostatic furnaces.