NUCLEATION AND RELATED PHENOMENA IN LITHIUM DISILICATE GLASS (CRYSTALLIZATION, RAMAN SPECTROSCOPY, NCA, VISCOSITY, PHASE DIAGRAM)

A systematic study was conducted concerning the nucleation process in lithium disilicate glass. Changes in the structure of the glass with nucleation heat treatment were studied by Raman spectroscopy. The Raman spectra of the glass were analysed based on the assignment of bands in the Raman spectrum of lithium disilicate crystal. The band assignments were determined by Normal Coordinate Analysis of the vibrational spectra of Li(,2)Si(,2)O(,5) crystal with isotopic substitution of ('7)Li and ('6)Li. The analysis of the Raman spectra of the nucleated glasses show an increase in the number of SiO(,4) units with 2 nonbridging oxygens during the initial stages of nucleation. The accuracy of the reported free energy differences between lithium disilicate crystal and glass were checked and found to be consistent with the rest of the thermodynamic and phase data for the Li(,2)O-SiO(,2) system. Rate of nucleation which was calculated with the assumptions that Li(,2)O.SiO(,2) is the mobile unit and that interfacial free energy is temperature dependent, gave the closest fit to the observed rate of nucleation. A mechanism for nucleation in lithium disilicate glass was proposed with the assumption that lithium-rich regions in the glass act as sites for nucleation. Nucleation was found to be homogeneous, and the rate of nucleation reported earlier in the literature was consistent with the results of this study. The viscosity and electrical conductivity of glasses in the Li(,2)O-SiO(,2) system were measured.