Preparation of ZrW₂O₈ / ZrO₂ composites with controllable thermal expansion

ZrW₂O₈ which exhibit s excellent isot ropic negative thermal expansion was synthesized using the step bystep solid state reaction. The ZrW₂O₈ / ZrO₂ composites with cont rollable thermal expansion coefficient were prepared by mixing ZrW₂O₈ and ZrO₂ at different volume ratios and sintered at 1200 ℃for 24 h. The thermal expansioncoefficient of ZrW₂O₈ / ZrO₂ composites can be cont rolled , being negative , positive or even zero , by adjusting the volume fraction of ZrW₂O₈ . The ZrW₂O₈ / ZrO₂ composites show almost zero thermal expansion when the volume f rac2tion of ZrW₂O₈ is 37 %. In order to obtain dense and tough ZrW₂O₈ / ZrO₂ ceramic , Al₂O₃ was adopted as an additive. The result s reveal that it is effective to improve the density of the composites. 0. 35 wt % Al₂O₃ additive canincrease the density of the composites rapidly with slight effect s on the thermal expansion property.