Pyroplastic deformation of porcelain stoneware tiles: Wet vs. dry processing

Several batches of porcelain stoneware were formulated by partial replacement of coarse Na and Na-K feldspars (standard batch) with quartz in two different grain sizes, micronized K-feldspar or a mixture of these components. Everyone was processed (laboratory scale) by wet and dry routes to compare: sintering curve, microstructure, phase composition and viscosity of the liquid phase at high temperature. Pyroplasticity index was determined by 3-point bending test. Results indicate that finer the quartz particles, more they dissolved in liquid phase, increasing viscosity and reducing deformation. Micronized K-feldspar increased the sintering kinetics (causing deformation). However, when K-feldspar was combined with quartz, densification rate was improved without compromising integrity of tile. About dry route, microstructural heterogeneity turned as fundamental to prevent Pyroplastic deformation. As conclusion, pyroplastic deformation occurs by different mechanisms in samples prepared by the two processing routes and bodies prepared via dry route are less likely to undergo pyroplastic deformation.