Abstract
Preparation method for large amount of negative thermal expansion oxide, ZrW2O8, with high purity has been developed. From TG-DTA data of ZrO2 and WO3 mixture, it was revealed that heat-treatment at 1200°C and successive rapid quenching to room temperature is necessary for preparation of ZrW2O8 by solid state reaction of ZrO2 and WO3. Employing Pt crucible covered with Pt plate, large ZrW2O8 ceramic with high density could be synthesized although press process using mold was not employed. Using quenching process of melt prepared with heating ZrW2O8 powder above melting point determined by TG-DTA measurement, the specimen with high density and negative thermal expansion could be prepared. The specimen was composed of ZrW2O8 grains with 10∼25μm diameter and ZrO2 or WO3 ones with ∼1μm diameter, to which smaller negative thermal expansion of the specimen than that of ZrW2O8 ceramic could be ascribed. Materials with tailored thermal expansion coefficient have been prepared by intentional hybridization at optimum ratio of ZrO2 and ZrW2O8 with cosintering. Using Al2O3 as sintering aid, density of the cosintered specimen increased due to generation of liquid phase of Al2(WO4)3 during sintering.
