Microstructure and non-isothermal reduction behavior of ball-milled WO₃-CuO powders in pure hydrogen atmosphere

The microstructural characteristics and hydrogen reduction behavior of W and W-10 wt% Cu powders have been investigated. These powders are synthesized by ball milling and hydrogen reduction of WO₃ and WO₃–CuO. The reduction behavior of oxide powders under non-isothermal condition is examined using thermogravimetric analysis at varing heating rates in pure hydrogen atmosphere. After milling for 5 h and hydrogen reduction at 800 °C, the oxide powders were completely converted to W and W-Cu with an average particle size of about 300 nm. TEM analysis for the reduced W-Cu powder revealed that nano-sized Cu particles were located on the surface of the coarse W particles. The activation energies for the reduction of pure WO₃ and WO₃–CuO, estimated by the slope of the Kissinger plot, were measured as 58.9–123.3 kJ/mol depending on reduction steps. In the reduction process of WO₂ to W, the WO₃-CuO powder mixture exhibited lower activation energy compared to pure WO₃ powder. The decrease in activation energy is attributed to the role of pre-reduced Cu particles as nucleation sites for W during the reduction process via chemical vapor transport of WO₂(OH)₂.