Pyroplasticity in porcelain tiles

Clay bodies exhibit pyroplasticity when they are fired. Basically they get soft again in the heat of the kiln and can deform under their own weight. This property is especially important when firing products with very low porosity like porcelain tiles, due their content in melting materials. In this way, five raw materials, a kaolin, a talc, an albite, a phyllite and a clay were used in a study to form porcelain tile pastes resistant to pyroplasticity. After raw materials analysis (XRF and XRD), a mixture design with constraint limits was used to compose the pastes, resulting in 13 compositions (five factors and one centroid). All compositions were mixed, wet grounded (<44 μm), dried and pressed (450 kgf/cm2) in rectangular plates (10 cm × 5 cm). The pyroplasticity was determined by the measure of the plate bending caused by temperature variation in an industrial roller kiln. All results were analyzed using response surfaces with data obtained by analysis of variance (ANOVA).