Mechanical properties of porcelain stoneware tiles: the effect of glass-ceramic systems

The influence of the glass-ceramic addition on mechanical properties and microstructural characteristics of porcelain stoneware tiles has been studied. Mechanical characterisation has been carried out on industrial and laboratory porcelain stoneware tiles obtained by mixing glass-ceramic systems to current industrial bodies. Moreover, microstructure and texture have been studied and bulk density, open and close porosity and phase composition determined. Industrial bodies contain very low open porosity (0.2-0.3 vol%) and closed porosity (1.6-4.1%), flexural strength ranging from 30 to 40 MPa, Young modulus from 63 to 71 GPa and Poisson coefficient 0.18. The addition of NAS and KCMAS glass-ceramics precursors led to 3.7-4.3% of residual porosity, flexural strength of 39-43 MPa and Young modulus of 69-73 GPa, equal or higher than the industrial product ones. In standard conditions bodies added with BAS and ZCS glass-ceramics did not come to complete sintering leaving significant residual porosity (12-14%). Flexural strength and Young modulus were rather low (26-29 MPa and 51 GPa, respectively). However, an appropriate mixture of BAS and ZCS systems allowed to achieve excellent mechanical performances (flexural strength 40 MPa, Young modulus 74 GPa, Poisson coefficient 0.26) notwithstanding the remarkable residual porosity (7.3%).