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

Abstract

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–Al 2 O 3 –SiO 2 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 °C. 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 TiO 2 as nucleant and/or B 2 O 3 as flux to a chosen glass in the cordierite primary phase field of the CaO–MgO–Al 2 O 3 –SiO 2 quaternary system favoured the crystallization of cordierite as only crystalline phase. However, the presence of Na 2 O and K 2 O as fluxes suppress its crystallization. Microstructural examination revealed that with TiO 2 as nucleant and B 2 O 3 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.