Abstract
The surface oxidation of tungsten powder has been studied in the temperature range 150∼400° and at the oxygen pressure ranging from 10 to 400 mmHg, using a vacuum microbalance technique. Tungsten powders are pyropholic above the temperature which is dependent on the particle size, doping, heat treatment and oxygen pressure, etc. Below this temperature, two oxide layers are formed during the oxidation process. The outer layer is porous WO3 and the inner one is a dense, thin oxide film of a certain composition similar to that of the outer. The oxidation rate eventually comes to comply with linear law after a initial stage of film growth which is governed by a parabolic law. The mechanism of this oxidation kinetics is explained by the use of a model of a barrier scale layer.
