Influence of firing parameters on phase composition of raw glazes

Raw glazes are well suited for glazes fired traditionally at high top temperatures. Final phase composition of these glazes is assumed to be controlled by nucleation and growth of crystals in the melt. At shorter firing cycles the phase composition of glazes is likely to be restricted by the limited reaction time. In this work the influence of firing cycle and glaze composition on final glaze phase composition was studied. Fifteen experimental raw glazes were fired at short, intermediate and long cycles. Crystalline phases developed in the surfaces were identified with X-ray diffraction and SEM/EDXA. Sintering behaviour of the glazes was studied with hot stage microscopy. Compositional dependence for two typical temperatures from sintering curves was established. The results indicate that the phase composition strongly depends on the firing cycle. Crystalline phases in fast-fired glazes were intermediate products of first raw material reactions, diopside, wollastonite and pseudowollastonite. Traditional firing favours feldspar formation.