Microstructural Evolution in Fast-Heated Cordierite-Based Glass-Ceramic Glazes for Ceramic Tile

The crystallization mechanism of α-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 μ-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 α-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 α-cordierite crystals was fast, and the crystals seemed to grow by consuming glass directly from the growing interphase. The estimated amount of α-cordierite in the glass heated at 1160°C 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 μm, immersed in a residual glassy phase. The feasibility to develop new glass-ceramic glazes using the present and previous works is considered.