Effect of additives on the crystallization of cordierite-based glass-ceramics as glazes for floor tiles

The effect of several additives such as fluxes and/or nucleants on a parent glass with composition located in the primary field of cordierite within the quaternary system CaO-MgO-Al2O3-SiO2 has been examined. Crystallization path of glasses was determined by differential thermal analysis (DTA) and X-ray powder diffraction (XRD). Pressed pellets of powdered glasses-containing different additives were submitted at thermal treatments up to 1200 degreesC. The microstructural development at several temperatures was followed by field emission scanning electron microscopy and energy-dispersive X-ray analysis. The results shown that additions of TiO2 as nucleant and/or B2O3 as flux to a chosen glass in the cordierite primary phase field of the CaO-MgO-Al2O3-SiO2 quaternary system favoured the crystallization of cordierite as only crystalline phase. However, the presence of Na2O and K2O as fluxes suppress its crystallization. Microstructural examination revealed that with TiO2 as nucleant and B2O3 as flux, crystals of cordierite with hexagonal prismatic morphology were formed after controlled thermal treatment of glass. The approach outlined in this paper to obtain cordierite-based glass-ceramic glazes from a cordieritic glass with additives could represent an useful guide to obtain new glazes with improved mechanical and optical properties. (C) 2002 Elsevier Science Ltd. All rights reserved.