Fabrication of Tungsten powder mixtures with nano and micro size by reduction of Tungsten oxides

An optimum route to fabricate a hybrid-structured W powder composed of nano and micro size powders was investigated. The mixture of nano and micro W powders was prepared by a ball milling and hydrogen reduction process for WO₃ and W powders. Microstructural observation for the ball-milled powder mixtures revealed that the nano-sized WO₃ particles were homogeneously distributed on the surface of large W powders. The reduction behavior of WO₃ powder was analyzed by a temperature programmed reduction method with different heating rates in Ar-10% H₂ atmosphere. The activation energies for the reduction of WO₃, estimated by the slope of the Kissinger plot from the amount of reaction peak shift with heating rates, were measured as 117.4 kJ/mol and 94.6 kJ/mol depending on reduction steps from WO₃ to WO₂ and from WO₂ to W, respectively. SEM and XRD analysis for the hydrogen-reduced powder mixture showed that the nano-sized W particles were well distributed on the surface of the micro-sized W powders.