Effect of MgO/CaO ratio on the microstructure of cordierite-based glass-ceramic glazes for floor tiles

The effect of the MgO/CaO ratio on the microstructure and microhardness of cordierite-based glass-ceramic glazes was studied. For this purpose glasses, with compositions in the cordierite primary phase field of the CaO-MgO-Al2O3-SiO2 quaternary system and, with different MgO/CaO ratios, were prepared by melting. Glass powder pellets pressed under low pressure were fast heated at several temperatures simulating industrial floor-tile processing, and characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray emission spectroscopy (EDX). The studied glasses crystallized α-cordierite as the only crystalline phase in the range of temperatures between 1160 and 1190 °C. The glass with intermediate MgO/CaO ratio yielded on heating the relative highest amount of α-cordierite as well as the best well-shaped hexagonal prism crystals. These features were coupled with the highest microhardness value obtained for the glass-ceramic glaze on the tile support.