Mechanism of crystallization of fast fired mullite-based glass-ceramic glazes for floor-tiles

The mechanism of crystallization from a B2O3-containing glass, with composition based in the CaO-MgO-Al2O3-SiO2 system, to a glass-ceramic glaze was studied by different techniques. Glass powder pellets were fast heated, simulating current industrial tile processing methods, at several temperatures from 700 to 1200 degrees C with a 5 min hold. Microstructural study by field emission scanning electron microscopy revealed that a phase separation phenomenon occurred in the glass, which promoted the onset of mullite crystallization at 900 degrees C. The amount of mullite in the glass heated between 1100 and 1200 degrees C was around 20 wt%, as determined by Rietveld refinement. The microstructure of the glass-ceramic glaze heated at 1160 degrees C consisted of interlocked, well-shaped, acicular mullite crystals longer than 4 mu m, immersed in a residual glassy phase. (c) 2006 Elsevier B.V. All rights reserved.