|
چکیده
|
In order to produce tungsten carbide from its oxide through mechanochemical process, a mixture of tungsten oxide, carbon and aluminum powders was subjected to high energy milling. Excess carbon addition was made in expense of aluminum, so that carbon acts not only as a carbide former agent but also as a reductant. Aluminum and carbon contents of the mixture were altered according to the following reaction: WO3 + (4 − 1.5x)C + xAl = WC + (x/2)Al2O3 + (3 − 1.5x)CO(g). The value of x varied from 0.5 to 1.9 and the effect of Al content on the mechanism of tungsten carbide formation was investigated. Thermodynamic calculations revealed that the amount of Al in the mixture plays a key role. Experimental results showed that at lower Al content in the WO3–Al–C mixture (x = 0.5–1.2), reactions proceed through a gradual mode. By increasing Al content (x = 1.3–1.6), type of reactions changed to mechanically induced self-propagating reaction (MSR) with no carbothermic reduction reaction of WO3. Further increase of Al content (x = 1.7–1.9) resulted in MSR mode reactions consisting of both aluminothermic and carbothermic reactions. Optimum value of x which yields maximum amount of WC was found to be around 1.7. Discussion has been made to elucidate the phase formation types in accordance with the above three reaction modes.
|