Phase evolution during reactive sintering by viscous flow: Disclosing the inner workings in porcelain stoneware firing

Porcelain stoneware is sintered by partial vitrification through viscous flow of a liquid phase formed at high temperature. This sintering process involves a complex evolution of both phase composition and chemistry of the liquid phase, according to the dynamic equilibrium established with the residual minerals and the new crystalline phases formed during firing. The present contribution overviews the evolution of phase composition and microstructure of seven body formulations during firing at different temperatures and dwell times. Each mixture was characterized from the chemical point of view and, once fired, by XRPD (quantitative phase composition), SEM and optical microscopy (microstructure). Moreover, the sintering behavior of the batches was investigated in isothermal conditions by optical thermo-dilatometric analysis. The results indicate that the continuous variation of the phase composition during the heating treatment affects the chemical composition of the liquid phase reflected on the densification kinetics and pyroplastic deformation of tiles.