New body mixes for porcelain stoneware tiles with improved mechanical characteristics

Starting from an industrial body mix for porcelain stoneware tiles, part of its fluxing agent, a sodium feldspar, was replaced by the stronger fluxing agent spodumene. In addition, two alumina powders as reinforcing agents were considered: (i) a high purity alumina and, (ii) a calcined bauxite. The high purity alumina was added at 15 wt.% to the body mix, whereas the calcined bauxite (a mixture of alumina, mullite and quartz) was added at 20.5 wt.%. The resulting composite materials showed a significant microstructural improvement, with a decrease of both bulk porosity and average pores size and an increase of hardness and fracture toughness. The higher microstructural homogeneity of the systems decreased the likelihood of mechanical failure. In addition, the temperature over which sintering of the material occurs was extended and the dimensional stability of the material improved. Several of the results obtained can be attributed to the presence of spodumene which, during sintering, allows the development of a low viscosity liquid phase and favours strong links being formed between the added oxides (alumina and mullite) and the glassy phase.