Effect of Hydrothermal Synthesis Conditions on the Morphology and Negative Thermal Expansivity of Zirconium Tungstate Nanoparticles

摘要

Zirconium tungstate (ZrW_2O_8) is a unique ceramic material that exhibits isotropic negative thermal expansion behavior, which can be produced at relatively low temperatures using hydrothermal synthesis and subsequent heat treatment. In this work, the effect of reaction conditions on morphology and crystallite size of ZrW_2O_8 nanoparticles is characterized through careful selection of initial reactants, acid types and concentration, reaction time, and temperature. Three types of ZrW_2O_8 nanoparticles with distinct morphologies and crystallite size scales were chosen to characterize and compare thermal and physical properties. Nano-sized ZrW_2O_8 particles for two of the morphologies exhibit a negative coefficient of thermal expansion (CTE) that is about 30% larger than the CTE of bulk ZrW_2O_8 in the a-phase (ca. -11.4 vs.-8.8 ppm/℃). A dependence of CTE on crystallite size and crystalline structure is demonstrated. It is also found that the morphology of the zirconium tungstate has a significant effect on the pore structure and level of hydration in the nanoparticles.