Effect of B2O3 on crystallization behavior and microstructure of MgO–SiO2–Al2O3–K2O–F glass–ceramics

The crystallization behavior of fluorphlogopite, a glass–ceramic located in MgO–SiO2–Al2O3–K2O–F system was studied by varying the B2O3 content in the glass composition. DTA, XRD and scanning electron microscopy (SEM) were used for the study of crystallization behavior and microstructure of resulting glass–ceramics. Heat treatment of glass specimens in the form of pressed powders in 600–950 °C range led to the formation of MgF2 and fluorphologopite. DTA analysis revealed that the first peak crystallization temperatures (Tc1) and glass transition temperature (Tg) decreased by increasing B2O3 content, while the crystallization temperature increased with increasing the particle size of each composition. DTA and XRD results indicated that the phlogopite crystallites probably transform from monoclinic to trigonal (3t) polytype at a temperature in the range of 950–1000 °C. It was also shown that the higher the B2O3 content, the higher the aspect ratio of the phlogopite crystals.