Dr. Ikuo Yanase, Associate Professor, Graduate school of science & engineering, Saitama University, Japan

Title: Fabrication of Zr₂WP₂O₁₂ / ZrV0.6P1.4O7 composite with a nearly zero-thermal-expansion property

Abstract: Zero-thermal-expansion materials have recently received considerable attention for modern industries requiring high precision materials in a wide temperature range. Compounds exhibiting negative thermal expansion in a wide temperature range are particularly useful for fabricating composites with zero or very low thermal expansion properties. Orthorhombic Zr2WP2O12 (ZWP) with negative thermal expansion are synthesized by a solid-state method without quenching, suggesting its potential use for fabricating zero-thermal-expansion materials. Cubic P-substituted ZrV2O7 (ZVP) exhibits positive thermal expansion above room temperature although cubic ZrV2O7 exhibits negative thermal expansion. In this study, sintered bodies of Zr2WP2O12 (ZWP) and ZrV0.6P1.4O7 (ZVP) were fabricated, and their linear thermal expansion coefficients (TEC) were found to be -2.92×10-6 ℃-1 and 3.27×10-6 ℃-1, respectively, in the range of 25 to 500 ℃. For fabrication of composites with a zero-thermal-expansion property, sintered ZWP/ZVP composites with ZVP/ZWP volume ratios of 0.5/0.5, 0.53/0.47, 0.55/0.45, and 0.6/0.4 were fabricated to cancel out the negative thermal expansion of ZWP by the positive one of ZVP. Scanning electron microscopy revealed that sintering of ZVP/ZWP composites progressed well compared with ZWP. A porous ZVP/ZWP composite with a relative density of ca. 82% was fabricated at a ZVP/ZWP volume ratio of 0.53/0.47. X-ray diffraction and energy dispersive X-ray analysis spectroscopy analysis clarified that the ZVP/ZWP composite mainly consisted of ZWP and ZVP grains. Thermomechanical analysis confirmed that the ZVP/ZWP composite exhibited very low thermal expansion with a slight hysteresis with a TEC was -0.29×10-7 ℃-1 in the range of 25 to 500 ℃. Thus, we successfully fabricated ZWP/ZVP composites exhibiting zero thermal expansion in a wide temperature range of 25 to 500 ℃.

Keywords: Ceramics, Composite materials, Thermal expansion, Sintering