Preparation and Properties of Zirconium Tungstate with Isotropic Negative Thermal Expansion

概要

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We investigated two aspects of zirconium tungstate (ZrW2O8). First, we investigated the formation of ZrW2O8 in a sol-gel process that used tungsten (VI) chloride and zirconium chloride oxide 8-hydrate as raw materials, and ethanol and 2-butyl alcohol as solvents. Crystalline ZrW2O8 powder was obtained by heat treated between 600 and 777°C in air for one hour. ZrW2O8 ceramics could not be made using a conventional sintering process because the ZrW2O8 decomposition to WO3 and ZrO2 when it was heated to over 777°C. However, we made dense ZrW2O8 ceramics by heating ZrW2O8 amorphous powder at 600°C for 10 minutes by using spark plasma sintering. Second, we used X-ray diffraction analysis and DSC to clarify how humidity affects the thermal expansion properties of ZrW208. Low density ZrW2O8 ceramics showed positive thermal expansion between room temperature and 120°C. On the other hand, high density ceramics showed negative thermal expansion between room temperature and 400°C. Both ZrW2O8 powder and lower density ceramic have H2O either on or in their particles. The H2O prevented any other influence besides that of the thermal expansion property of ZrW2O8.
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