Crystallite Size on Micromechanical Characteristics of WO3 Microparticles

This study evaluated the correlation between crystallite size and micromechanical characteristics of micrometer-sized monoclinic WO3 particles. To avoid the existence of other parameters in the measurement (such as impurities and porous structure in the particle), micrometer WO3 particles were prepared using a direct heat treatment of ultrapure micrometer-sized ammonium tungstate powders. The crystallite size was controlled independently in a constant WO3 particle outer diameters to obtain a precise measurement result. The mechanical properties, i.e., hardness and Young’s modulus, were measured by load-controlled nanoindentation test on the singular WO3 particles. The force and displacement relationship data was plotted and analyzed to obtain the correlation between crystallite size and mechanical properties. The results revealed that the micro-mechanical properties of WO3 particles were strongly dependent on the crystallite size. The hardness and Young’s modulus values increased more than 40 and 15 times, respectively, when increasing the crystallite size to about 40 nm. The study was completed with a proposed mechanism of crack propagation inside the particle due to static load. The study demonstrates the important role of crystallite size in determining the micro-mechanical characteristics of WO3 particles. The result is useful especially when utilizing WO3 microparticles for various processes involving extreme conditions, such as high pressure reaction.