Crystallization behavior of CaO-Al₂O₃-SiO₂ glass-ceramics prepared from wastes of glass and clay raw materials (Kira)

Very large amounts of wastes (called Kira) are produced by the purification of raw materials for sheet glass and porcelain manufacture in Japan; it is highly desirable to develop effective usage of this waste. To this end, the crystallization behavior of CaO-Al₂O₃-SiO₂ glass prepared from mixtures of Kira and CaCO₃ was investigated to obtain fundamental data about these glass-ceramic materials. The glass powders obtained by melting at 1400°C were water-quenched and ground, then re-heated at 900-1250°C for 2-240 min. Wollastonite (Wo), the low temperature phase of CaSiO₃, crystallized at ∼900°C. The amount of Wo increased very steeply with higher heating temperature to a maximum content of 55 vol%. Anorthite was formed only as a minor phase under restricted conditions. The Wo transformed into the high temperature phase pseudowollastonite (PW) above 1150°C but the transformation is relatively slow, requiring heating times >60 min. The activation energies for nucleation and nucleation-growth of Wo were 223 and 259 kJ/mol, respectively, significantly smaller than other reported values. The crystallization and phase transformation of Wo showed complicated behavior related to the particle size.