Production of tungsten powder by plasma reduction of WO3 : Structure and morphology

Plasma reduction is a new and promising technology for the production of tungsten powder from its trioxide (WO 3 ). Three plasma configurations were evaluated: a hollow cathode with the powder immersed in the plasma: a hollow cathode with no direct contact between the plasma and the powder; and a fluidized bed reactor. Experiments were performed in dry hydrogen at a pressure of 700 Pa, at temperatures ranging from 800°C-1,000°C using a DC-generated plasma. Rapid reduction of the WO 3 was observed when the powder was immersed in the plasma. In the absence of direct contact between the powder and the plasma, long reduction times were required. Full reduction by the plasma was accompanied by structural transformation of the original WO 3 powder into particles of similar size and shape, but with a skeletal structure of interconnected submicron size a tungsten crystals. Fluidized bed plasma experiments with short treatment times (< 1 s) resulted in particles exhibiting varying levels of reduction.