Microstructural evolution in fast-heated cordierite-based glass-ceramic glazes for ceramic tile

The crystallization mechanism of alpha-cordierite from a B2O3 and TiO2-containing glass submitted to fast heating in the cordierite primary phase field of the CaO-MgO-Al2O3-SiO2 quaternary system was investigated. Addition of B2O3 to a SiO2-rich glass suppressed the formation of mu-cordierite. This suppression facilitated densification- by viscous flow before crystallization. Powder X-ray diffractometry, field-emission electron scanning microscopy, and energy-dispersive X-ray analysis revealed that alpha-cordierite nucleated directly from glass on the boundaries of original particles and was probably favored by TiO2, which acted as a nucleant. The growth kinetics of alpha-cordierite crystals was fast, and the crystals seemed to grow by consuming glass directly from the growing interphase. The estimated amount of at-cordierite in the glass heated at 1160degreesC was 69.5 wt%, as determined using the Alegre method. The final microstructure consisted of an arrangement of well-shaped hexagonal prisms, with sizes <3 mum, immersed in a residual glassy phase. The feasibility to develop new glass-ceramic glazes using the present and previous works is considered.