Abstract

The reduction mechanism of the composite powders mixed with WO_3 and CuO has been studied by using thermogravimetry (TG), X-ray diffraction, and microstructure analyses. The composite powders were made by simple Turbula mixing, spray drying, and ball-milling in a stainless steel jar with the ball to powder ratio of 32 to 1 at 80 rpm for 1 h without process controlling agents. It is observed that all the oxide composite powders are converted to W-coated Cu composite powder after reducing treatment under hydrogen atmosphere. For the formation mechanism of W-coated Cu composite powder, the sequential reduction steps are proposed as follows: CuO contained in the ball-milled composite powder is initially reduced to Cu at the temperature range from 200°C to 300°C. Then, WO_3 powder is reduced to W O_2 via W O_2.9 and W O_2.72 at higher temperature region. Finally, the gaseous phase of WO_3(OH)_2 formed by reaction of WO_2 with water vapour migrates to previously reduced Cu and deposits on it as W reduced by hydrogen. The proposed mechanism has been proved through the model experiment which was performed by using Cu plate and WO_3 powder.

• Keywords: W and Cu oxide composite powders;W-Cu composite powder;Reduction mechanism;Ball-milling;