Influence of composition on mechanical behaviour of porcelain tile. Part I: Microstructural characterization and developed phases after firing

The porcelain tile is a ceramic product with high technical and aesthetic performance, whose composition is formulated from a mixture of clay or kaolin, quartz and feldspar. This paper is the first part of a study focusing on determining the influence of the porcelain tile composition on mechanical behaviour of sintered bodies. Seven compositions were prepared according to a simplex-centroid mixture design for a triaxial mixture, comprised of kaolinite, quartz and albite. The mixtures were processed reproducing industrial conditions: wet mixing followed by spray-drying, forming by pressing and fast firing with maximum temperatures ranged from 1210 to 1260 °C. The presence of kaolinite increases the dry apparent density in a significant way up to 30 wt%. Because of the fast firing, the microstructure is directly influenced by particle packing after forming. The internal porosity presented little change as a function of starting composition in the tested intervals. The surface porosity of the polished product increased with higher amounts of quartz. The results obtained in this first part of the study showed how the starting and end composition could generate the microstructure and suggest its influence on the mechanical properties of the porcelain tile, which will be later analysed in the second part of this paper.