Alumina As A Devitrification Inhibitor During Sintering Of Borosilicate Glass Powders

Cristobalite is formed when borosilicate glass is sintered at temperatures ranging from 700C to 1000C. The precipitation kinetics determined by XRD analysis exhibit a characteristic incubation period which decreases with increasing sintering temperature, from 60-120 min at 700C to 3-5 min at 1000C. Activation analysis of precipitation shows an activation energy of 75kJ/mol, which is close to that for the diffusion of Na+ in borosilicate glass, suggesting mass-transport kinetics. With added alumina content greater than a critical value, however, the cristobalite formation is completely prevented at the sintering tempertures investigated.