Preparation and properties of CaO-MgO-Al₂O₃-SiO ₂ glass-ceramics from kaolin clay refining waste (Kira) and dolomite

CaO-MgO-Al₂O₃-SiO₂ glass-ceramics were prepared from mixtures of waste generated from refining of kaolin clay (called Kira) and dolomite (CaMg(CO₃)₂). Kira was mixed with dolomite in mass ratios of 65/35 (sample 1) and 75/25 (sample 2). They were melted at 1350°C and quenched in water to obtain glasses. The quenched glasses were ground to < 100mesh and used to prepare glass-ceramics. Crystallization of the parent glass occurred above 900°C, producing diopside (CaMgSi₂O₆) and anorthite (CaAl₂Si ₂O₈) as major crystalline phases; diopside > anorthite in sample 1 and anorthite > diopside in sample 2. The macroscopic appearance of the samples changed from transparent pale green glass to smooth-textured shiny white upon crystallization. The four point bending strengths of the as-fired glass-ceramics were 130MPa in sample 1 and 73 MPa in sample 2, which was approximately half of the value for sample 1. Vickers microhardness values were found to be 7.4 and 7.6 GPa in samples 1 and 2, respectively. The thermal expansion coefficients of the glass-ceramics prepared at 1000°C for 1h were 6.7 × 10^-6°C^-1 (30-380°C) in sample 1 and 4.7 × 10^-6°C^-1 in sample 2. Since the chemical durability for acid and alkali was excellent in these glass-ceramics, they are considered to be candidates for applications such as building materials, ceramic tiles, etc.