Preparation and characterisation of W–7Ni–3Cu alloy powder by hydrogen reduction of metal oxides

Abstract

The microstructural characteristics and hydrogen reduction behaviour of W–7Ni–3Cu heavy alloy powders synthesised from WO₃–NiO–CuO powder mixtures have been investigated. The fine and homogeneous oxide powder mixture is prepared by ball milling using stearic acid as a process control agent. The reduction behaviour of oxide powders is interpreted by thermogravimetric analysis in an N₂–10% H₂ atmosphere. After milling for 5 h and hydrogen reduction at 800 °C, the oxide powders were completely converted to W, NiCu, and Ni₄W phases without residual oxides and showed an average particle size of about 200 nm. The reduction kinetics is evaluated by the amount of peak shift in the thermogravimetric curves depending on the heating rates. The apparent activation energies for the reduction of CuO, NiO and WO₃, estimated by the slope of the Kissinger plot, are measured as 96.9 kJ/mol, 122.0 kJ/mol and 114.6–124.3 kJ/mol, respectively. The measured activation energy is considered meaningful for quantitatively analysing the reduction kinetics in the non-isothermal reduction process of oxide composite powders.