Densification of nearly-zero-thermal-expansion ZrW₂O₈/ZrO₂ ceramics synthesized by chemical co-precipitation method

A kind of nearly-zero-thermal-expansion 26 wt% ZrW₂O₈/ZrO₂ ceramics was prepared by calcining the precursors synthesized by the chemical co-precipitation method at 1150℃ for 3.5 h. The effects of Al(NO₃)₃·9H₂O addition on the phase composition，density and thermal expansion properties of the 26 wt% ZrW₂O₈/ZrO₂ composites were investigated by X-ray diffraction，scanning electron microscopy and dilatometry. The results indicate that the composites with Al(NO₃)₃·9H₂O added in the precursor contain only α-ZrW₂O₈ and m-ZrO₂ phases，and a small amount of Al(NO₃)₃·9H₂O additive can increase the density of the 26 wt% ZrW₂O₈/ZrO₂ composites with slight effects on the thermal expansion properties. The relative density of the 26 wt% ZrW₂O₈/ZrO₂ composites doped 2.21 wt% Al(NO₃)₃·9H₂O can reach 98.67% of the theoretical density. The densification mechanism can be at tributed to the formation of the Al₂(WO₄)₃ liquid phase，which accelerates the diffusion and promotes the sintering process and leads to the increasing of the density of the composites to some extent.