Improvement of Phase Transformation and Densification of SiO2-ZrO2 Ceramics by Using Desert Sand as a SiO2 Source

Desert sand was introduced to improve the transformation of zircon (ZrSiO4) and densification of SiO2-ZrO2 ceramics. The effect of desert-sand addition on the phase transformation, densification, microstructure, and properties were investigated using X-ray diffractometer (XRD), differential scanning calorimeter (DSC). scanning electronic microscope with an energy disperse spectroscope (SEM/EDS), and mechanical and thermal expansion test machines. Results show that use of desert sand made the transformation temperature decrease to 1100 °C for samples with 10.0–61.5 wt% ZrO2 additions; the densification temperature can also be decreased to 1100 °C by an addition of 10.0 wt% ZrO2. ZrSiO4 was firstly occurred in the outer layer of m-ZrO2 particles by its solid reaction to β-tridymite and then grew into the ZrO2 particles to form structures of “core–shell” (ZrO2-ZrSiO4) and ZrO2 particles dispersively embedding in ZrSiO4 matrix. The ceramics were mainly composed of α-quartz, ZrSiO4, and glass phase; their relative contents depended on the ZrO2 addition and sintering temperature. A 50 wt% ZrO2 addition and sintering at 1500 °C for 2 h produced the highest flexural strength and hardness; while 10 wt% ZrO2 addition and sintering at 1100 °C for 2 h produced the highest efficiency and the lowest cost for improving the mechanical properties. This indicates success in preparation of the dense SiO2-ZrO2 composite ceramics at relatively low temperatures merely by a replacement of desert sand to pure SiO2.