Influence of low magnesia content on the CaO-Al2O3-SiO2 glass-ceramics: Its crystallization behaviour, microstructure and physical properties

This study illuminates the role of low amounts of magnesia (<= 3 wt%) on the crystallization behaviour of CaO-Al2O3-SiO2 glass-ceramics. Differential thermal analysis demonstrates that the peak temperature and activation energy for crystallization decrease with the addition of MgO. The crystallization pattern changes from one-dimensional crystallization to two-dimensional growth, as indicated by higher values of the Avrami parameter (n) with increasing MgO contents. Analyses of the Rietveld refinement of XRD data, FTIR, Raman spectra and scanning electron microscopy reveal that MgO causes a simple change in CaO-Al2O3-SiO2 glass-ceramics, which form an Mg-containing solid solution (Ca(1-)xMg(x)SiO(3); 0 <= x <= 1) by replacement of some of the CaO with small amounts of MgO. When the MgO content increases to 1.8 wt%, diopside is primarily formed at the interfaces of sintered glass frits, acting as nucleation sites for the inward growth of wollastonite. The density of glass-ceramics increases with magnesia addition. Their hardness is strongly influenced by the phase species present, and can be enhanced by the crystallization of diopside.