EFFECT OF GALLIUM OXIDE IN PREVENTING CRISTOBALITE FORMATION IN BINARY BOROSILICATE GLASS COMPOSITE

When an appropriate mixture of low-softening borosilicate (BSG) and hi gh-softening high silica (HSG) glasses is sintered at temperatures ran ging from 800 to 1000-degrees-C, a crystalline phase, identified as cr istobalite by XRD, is known to precipitate out of the initial amorphou s binary mixture of glasses as the sintering continues. The precipitat ion of cristobalite is found to originate in HSG and is controlled by the transport of alkali ions (e.g., K, Na, and Li) from BSG to HSG.1 I n this paper we report that when a small amount of gallium oxide is pr esent as a dopant in the above binary mixture of BSG and HSG, the cris tobalite formation is completely prevented at the sintering temperatur es investigated. The above result is attributed to a strong affinity b etween Ga+3 from gallium oxide particle and alkali ions from BSG, whic h diverts the diffusion of alkali ions from HSG to gallium oxide, thus forming a K+ and Ga+3-rich reaction layer adjacent to gallium oxide p articles far too rapidly compared with that of cristobalite formation.