Reduction of tungsten oxides with carbon. Part 2. Tube furnace experiments

Abstract

Further information on the kinetics and mechanism of the reduction of WO 3 with carbon (in the form of graphite and of lamp black), complementing the results obtained in Part 1 using isothermal thermogravimetry in the temperature range 935–1100°C, was obtained using larger sample masses (up to 5 g) heated isothermally in flowing argon in a tube furnace (935–1060°C). The amounts of CO and CO 2 in the evolved gas were determined using infrared gas detectors. Results obtained supported the proposed two-stage reduction to W metal, via WO 2. The rate of reduction was influenced by the flow rate of argon, the CO CO 2 ratio in the product gases, the form of the carbon used, and the WO 3 carbon ratio. From kinetic data obtained from tube furnace experiments, an activation energy of 374 ± 2 kJ mol −1 was calculated for the diffusion-controlled first stage of the reduction with graphite. Lamp black was less reactive than graphite at the temperatures studied. Activation energies of 386 ± 9 kJ mol −1 and 465 kJ mol −1 were calculated from TG experiments for the reduction with graphite and lamp black, respectively. The gravimetric measurements from the tube furnace experiments were insufficient to analyse the kinetics of the second stage of reaction.