The effect of fired scrap addition on the sintering behaviour of hard porcelain

The effect of the addition of porcelain fired scraps on the sintering, phase composition and properties of a hard porcelain was studied. Two ceramics were compared: a commercial triaxial porcelain labelled C-0 and one, where 15% of the mass of C-0 was substituted by scraps yielding a composition labelled C-15. The sintering was evaluated by the linear shrinkage, the water absorption and the variation of closed and total porosity, while the phase transformations were investigated by DTA-TG, dilatometry and XRD. Samples, sintered at 1350 and 1400 °C, were used for the evaluation of the Young modulus and the bending strength. The addition of the fired scrap had a positive effect on the quartz dissolution and on the formation of the liquid phase during the sintering. The sintering and the mechanical properties were improved by heat treatment in the 1300–1350 °C range. Above this temperature, a significant over-firing with a decrease of the mechanical properties was observed.