REDUCTION BEHAVIOUR OF TUNGSTEN DIOXIDE BY VARIOUS CONCENTRATION OF CARBON MONOXIDE

The reduction behaviour of tungsten dioxide (WO2) under both non-isothermal and isothermal conditions in various concentrations of carbon monoxide (CO) were investigated by using temperature-programmed reduction (TPR) and X-ray diffractometry (XRD) techniques. The influences of carbon monoxide concentration (20 and 40% v/v CO in N2) on the reducibility of WO2 to tungsten metal W have been investigated in the temperature range 40 – 900 oC. The TPR profile shows that reduction using 40% CO produce higher thermal conductivity detector (TCD) signal in comparison by using 20 % CO. XRD results show that, by increasing the concentration of CO, the intensity of WO2 decreases and tungsten carbide (WC) peak appeared. Moreover, holding the reduction time for 30 min in 20 and 40% of CO resulted in the formation of new peak of tungsten hemi carbide (W2C) and WC, respectively. It can be concluded that by using CO, reduction steps comprise of WO2 → W → W2C → WC. The reduction behaviour of WO2 is strongly dependent on the concentration of CO and hold time of reaction. Furthermore, excess of CO by isothermal reduction results in the formation of WC.