Crystallization of the Glasses in the Li2O-SiO2 System

Heterogeneity of the Li2O—SiO2 glass and the process of crystallization through heating were investigated by using the electron- and ordinary microscopic techniques. Under the electron microscope the separated droplet phases of about 100 Å in diameter were observed comprised in the matrix of the opales-cent glass composed of lithium trisilicate, while the parts of the colorless and transparent glass of lithium disilicate were also found to be slightly heterogeneous. In addition to above, the fact that the interfacial boundaries between two separated phases are not favorable for nucleation of the crystals was also confirmed. As a result of the differential thermal analysis, a small-scaled endothermic phenomenon assumed to be necessary for the atomic rearrangement was recognized just before the remarkable exothermic reaction ascribed to crystallization. Moreover, it is to be noted that devitrification of the glass rod accompanied with crystallization of lithium silicate and lithium metasilicate was markedly promoted in a short period of about two months.