Anorthite-based transparent glass-ceramic glaze for ceramic tiles: Preparation and crystallization mechanism

Abstract A series of high hardness anorthite-based transparent glass-ceramic glaze was successfully developed for ceramic tiles. These glazes were prepared by mixing a high-calcium frit (denoted as HCa) that can crystallize anorthite with other fluxes. The effect of HCa content on the crystalline phase, microstructure and properties of the glaze was studied. In addition, the phase transformation, microstructure evolution and crystallization kinetics of anorthite from frit glaze were investigated in detail. The results revealed that when the HCa content was 45 - 55 wt%, the glazes had excellent transparency with a hardness of 6.4 - 7.3 GPa, which was higher than conventional glazes. The XRD and SEM tests showed the crystallization of single-phase lamellar-shaped anorthite crystals up to 20 - 40 μm in length. Anorthite was found to crystallize directly from the frit glaze at 850 °C. The laminated anorthite was composed of thinner lamellae, and cracks were observed inside the large crystals. The activation energy of anorthite crystallization was about 420 kJ/mol, and the Avrami index (n) was 2.03 - 2.36. The n value indicates that the crystal is grown in two dimensions, which explains the formation of lamellar-shaped anorthite in SEM.