Microstructure and technological properties of porcelain stoneware tiles moulded at different pressures and thicknesses

Moulding pressure and thickness are pre-fixed variables in the porcelain stoneware tile industry. This paper examines the effect of both parameters on technological and microstructure properties of unfired and fired porcelain stoneware bodies. The moulding pressure in unfired tiles has a noticeable effect on bending strength and load borne. Common technological properties such as water absorption, porosity, bulk density and bending strength were obtained from the fired tiles. The results indicate that the variation in properties is independent of the thicknesses of the tiles. Moulding pressure affects at lower values, whereas higher moulding pressure produces tiles with similar technological properties. The microstructure exhibits a constant amount of mullite and quartz in all pieces after the firing process. Observations from scanning electron microscopy show that mullite crystals enlarge as moulding pressure increases, but the shape of the crystals are unaffected by the individual thicknesses. Furthermore, the aspect ratio of the mullite needles increases with the moulding pressure, which is invariable to the thicknesses of the tiles. Although the total porosity remains constant, the number of pores is influenced by the thickness. The moulding pressure also influences pore size. The results show a strong relationship between the number of closed pores and the thickness of the ceramic tile.