Ceramics-Silikáty 53 (3) 161-164 (2009)

TRANSFORMATION OF GLASS TO GLASS-CERAMICS IN LiO₂–SiO₂ SYSTEM

M. Palou, E. Kuzielová, M. Vitkokič, G. Lutišanová, M. S. M. Noaman

The mechanism and kinetics of crystallization of Li₂O–SiO₂ glass as function of grain size and fluorapatite content were investigated using non-isothermal DTA method. Two samples of glass based on lithium disilicate (LS₂) without and with fluorapatite (FA) were synthesised. Then, glass-ceramics were obtained by thermal treatment of parent glasses. Activation energy of glass transformation calculated according to Kissinger (299 ± 1 kJ mo^l-1 for pure LS₂ glass and 288 ± 7 kJ mol^-1 kJ for glass containing FA) or according to Ozawa (313 ± 1 kJ mol^-1 for pure LS₂ glass and 303 ± 8 kJ mol^-1 for glass containing FA) indicates that the presence of FA in glass reduces its stability against crystallization. It was found that grain size determines the mechanism of crystallization. The smaller particles crystallize preferably through surface mechanism, while the coarser ones undergo the crystallization via internal volume process. The onset point of internal crystallization, which substitutes the surface one is found at about 0.3 mm for pure LS₂ glass, while this change occurs at size of 0.9 mm approximately in glass containing FA. The addition of FA into LS₂ glass-parent supports the crystallization by surface mechanism.

Keywords: Glass, Glass-ceramics, Crystallization kinetics, Glass stability