Mechanism of crystallization of pyroxene-based glass-ceramic glazes

The mechanism of crystallization of a powdered glass with composition in the pyroxene crystallization primary field within the CaO–MgO–Al2O3–SiO2 quaternary system and containing some additives was studied. The crystallization sequence was compared with that from the same base glass without additives. After a short thermal anneal both powdered glasses showed phase separation. Further thermal treatment gave rise to the crystallization of pyroxene. Anorthite as secondary crystalline phase was also detected in the quaternary glass (without additives). The starting crystallization in the glass with additives took place in the outer surface of glass particles probably in the immiscibility region and extended progressively to the whole particle by a spherulitic growth mechanism. The standard and fast heated glass containing additives developed at temperatures between 1100 °C and 1190 °C well-shaped, non-stoichiometric pyroxene crystals with compositions close to (Ca,Mg,K,Na)0.84(Mg,Al,Ti)(Si,Al)2O6. Fast heated glass-ceramic glazes with improved mechanical properties have been developed.