Influences of heat treatments on crystallization in SiO₂-Al₂O₃-MgO-K₂O-F glass-ceramics

Abstract

Five kinds of heating treatment processing were chosen according to the experiment result of differential scanning calorimeter to prepare SiO₂-Al₂O₃-MgO-K₂O-F glass ceramics samples. The effects of heat treatment processing on the crystallization of these samples were explored by X-ray diffraction and scanning electron microscopy techniques. The results indicate that phase separations can occur in the bulk regions of the glass sample when holding at 670 °C for 3 h. The phase separation can accelerate the precipitation of the crystallization phase: when the temperature directly rises to 950 °C after the phase separation, there are mainly interlocked plate-shapes mica phases; If holding at 860 °C for 3 h first after the phase separation, the star-shape cordierite phases form; Thereby, elevating temperature to 950 °C and holding for 1 h will bring plate-shapes mica phases growing at inter-phases of the star-shape cordierite and finally the homogeneously distributed micacordierite composites form. However, if heating at 950 °C directly without holding at 670 °C, there is a small quantity of phase separation appearing at 670 °C and a little crystallization phases precipitating at last.

Keywords

thermal decomposition / mechanism / kinetics / Siderite

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