Enhanced properties of ZrSiO4/ZrO2 composites produced by colloidal processing and spark plasma sintering

Zirconium oxide and silicate are well-known reference materials in ceramics. However, the performance of zircon/zirconia composites has not received the required attention considering the interesting properties and capabilities. Zircon and zircon/zirconia suspensions were optimised by colloidal processing routes. These suspensions were either slip cast to obtain pieces that were conventionally sintered or freeze-dried to obtain homogeneous powder mixtures for consolidation by non-conventional Spark Plasma Sintering (SPS). Pure zircon materials with densities up to 97.0 % and a hardness of 10.1 GPa were obtained by conventional sintering (1550 degrees C/120 min) whereas densities higher than 99.5 % and hardness up to 12.7 GPa were achieved by SPS (1500 degrees C/ 5 min). By introducing 20 vol.% zirconia as a sintering additive, densities up to 99.3 % and a hardness of 11.1 GPa were achieved by conventional sintering (1500 degrees C/120 min) whereas densities of 99.9 % and a hardness of 13.5 GPa were obtained by SPS (1400 degrees C/5 min).