The reduction of tungsten-VI-oxide to tungsten: A thermogravimetric microscale study with focus on the intermediates

• Investigation of the tungsten-VI-oxide reduction under thermodynamic reaction control. • Proof that the reduction path is less complex than the kinetics of large-scale processes suggest. • Resolution of the intermediate steps / phases run through. The purpose of this work is to add further details to the course of the hydrogen reduction reaction from tungsten-VI-oxide to tungsten powder. The investigations have been carried out under conditions far away from technical processes. The reduction has been studied by thermogravimetry forcing a thermodynamic reaction control by the use of tiny sample amounts and the application of non-isothermal conditions. Thereby the dominance of the kinetics (diffusion control of the reaction pathway) is minimized and the product ratio is determined by the relative stability of the products. The resulting reduction intermediates have been analysed by X-ray diffraction and scanning electron microscopy. It can be demonstrated that the reduction of WO 3 to tungsten exhibits a 3-step process in which well crystalline and pure phase intermediate stages are run through.