Sinterability, crystallization and properties of glass-ceramic tiles belonging to CaF2 -CaO -MgO -Al2O3 -SiO2 system

The effect of substituting different amounts of MgO for CaO on crystallisation and various properties of the CaF2-CaO-Al2O3-SiO2 glass system were investigated. It was shown that the properties of the obtained glass-ceramics are greatly influenced by the MgO content. The Avrami exponent and activation energy for crystallisation of the most promising and the MgO-free specimens were determined. Results suggest that surface crystallisation was the main precipitation mechanism for both samples and, while the activation energy for crystallisation of the MgO-containing sample was less than the MgO-free one, its ability to crystallise was diminished. SEM results confirm the occurrence of surface crystallisation of samples, and reveals microstructure coarsening with increasing MgO content as well as reduced densification of specimens with MgO content > 9 wt%. 16 refs.