EFFECT OF ALUMINA ON DENSIFICATION OF BINARY BOROSILICATE GLASS COMPOSITE

The effect of alumina on densification of the binary borosilicate glas s composite, containing low-softening borosilicate glass (BSG) and hig h-softening high silica (HSG) glass, has been investigated. It is foun d that with a small amount of alumina, 2-10 vol. %, present as a dopan t in the binary glass mixture of BSG and HSG, both densification and d ensification rate are significantly reduced, but the activation energy of densification at a given densification is dramatically increased. However, no significant change in densification behavior with increasi ng alumina content from 2 to 10 vol. % is observed. These results are attributed to a chemical reaction taking place at the interface of alu mina/BSG, forming a reaction layer adjacent to alumina. Since the comp osition of the reaction layer is known to be rich in aluminum and alka li ions and poor in silicon, the alkali ions content in BSG is continu ously decreased during sintering. Accordingly, the resultant loss of a lkali ions from BSG causes a rise in viscosity of BSG, thus slowing do wn the densification kinetics and increasing the activation energy of densification.