Press-free preparation method of dense negative-thermal-expansion oxide, Zr1-xYxW2O8-δ (x=0.00-0.02) ceramic using reactive sintering

By performing reactive sintering of a powder mixture of ZrO2, Y2O3 and WO3 (whose particle size distribution was 10-50 mu and of submicron-order), large pieces of dense Zr1-xY2O8-delta oxide with a negative thermal expansion coefficient were prepared. The density of the sintered specimens prepared by such a press-free process was comparable with that of similar materials prepared by processes that include molding/pressing. It was found that the partial substitution of Y3+ for Zr4+ was effective for promoting grain growth, resulting in an increase of density. Zr0.98Y0.02W2O8-delta sintered bodies with density of similar to96% of a truncated cone shape with upper diameter, lower diameter and height of similar to40 mm, similar to45 rum and 20-25 rum, respectively, were obtained. Negative thermal expansion was observed in all Zr1-xYxW2O8-delta specimens (x=0.00-0.02), this coefficient being hardly affected by the Y3+ content. It was also found that only porous and fragile specimens could be prepared by using a mixture with particle size distribution of submicron order as the raw material. This was ascribed to the formation of second-order particles that tended not to sinter within larger particles.