Effects of Li2O on structure of CaO-SiO2-CaF2-Na2O glasses and origin of crystallization delay

Abstract

The structure and kinetics in the glass system with increasing Li2O contents were characterized to determine how Li2O interrupts melt crystallization of cuspidine in CaO-SiO2-CaF2-Na2O glasses, despite the observations that Li2O reduces the polymerization degree of silicate and the viscosity, and that these reductions generally accelerate crystallization. 19F MAS NMR and molecular dynamic simulation showed that Li2O formed LiF bonds and distributed tetrahedral environment of fluorine, thereby disrupting the interaction of fluorine, one of the major components that compose cuspidine. Most of the displaced calcium from fluorine interacted with NBO of silicate, resulting in the decreased self-diffusion coefficients of Ca2+ ions. Therefore, these results show that Li2O delays crystallization by interfering with the Ca-F interaction and lowering the activity of fluorine despite depolymerizing the silicate network.