Roles of CaO, MgO and SiO2 on crystallization and microstructure development in diopside-based glass-ceramic glazes under industrial fast-firing condition

The research objective of the study was to increase the current understanding about how oxide compositions (CaO, MgO and SiO2 ratios) influence the (1) crystallization behaviour of starting frits, and subsequently (2) morphological features of diopside crystals, formed after wall tile industrial firing. It has been shown that the replacement of CaO and MgO at the expense of SiO2 causes a decrease in the crystallization temperature. The increase of CaO content also results in lower softening temperature and faster densification. SEM results of the glazes showed that spherical and needle-shape diopside crystals were formed during heating. While increase of MgO content results in finer needle-shape crystals, increase of CaO results in coarser spherical-shape crystals. Although all the glaze formulations showed a high whiteness index, lower densification and higher crystallization in the glazes caused an unfired matt appearance.