Research On Preparing Nanostructured Tungsten Carbide Powders By Hydrogen Plasma

In this paper, The C-H equilibrium diagram at the high plasma temperature has been studied. At the temperature range of 2000-3500K, the main product of C-H equilibrium is acetylene. When hydro-carbon gas is used to prepare tungsten carbides by plasma, it can change into acetylene. The reaction took in plasma reactor is that the raw materials react with acetylene, and not with hydrocarbon itself. So the cheaper acetylene has been selected instead of the normally used and expensive high purified methane and makes the cost of preparing tungsten carbides decrease greatly. The mechanisms of reduction and carburization at plasma temperature have been studied. Low boiling point tungsten-cobalt compounds(CoWO4) are selected as raw materialsinstead of WO3 to prepare nanostructured WC-Co powders directly. The optimum condition is at the temperature range of 2700-3100K, when C0W04 and acetylene areselected to prepare nano structured WC-Co powders directly by hydrogen plasma.In this paper, The numerical investigation has been applied to design and optimize the parameters of the plasma reactor structure and processing, with the view that the reactor has the highest volume efficiency. The flow and heat transfer in plasma reactor have been studied. The optimum parameters that the plasma reactor of heating wallhas the highest volume efficiency have been obtained: P'=1.323-1.467 x 10⁷ J/kg, G_j/G_p=0.6⁰.8.The regularity of preparation nano structured tungsten carbide has also been studied. The influence of the arc current, the flow rate of hydrogen and acetylene to the WC content in the final powders has been obtained respectively. The better processing parameters have been obtained by experiments. The nano structured WC-Co composite powders with the average particle size of 40nm and the shape of sphere, including a little amount of W₂C and W, have been prepared. The cobalt content in powders isabout 11%. The post processing for improving the quality of nanostructured tungsten carbide powders has been studied. The nanostructured powders prepared by plasma can be carburized completely by traditional carburization processing at the low temperature and short time, comparing to carburize the other powders at the same condition. The average particle size after processing is about 80nm.The method to prepare nano structured WC-Co composite powders with C0W04and acetylene at the hydrogen plasma temperature of 2700-3100K is feasible, and can be applied widely. There is no report to prepare nano structured WC-Co powders directly by use of hydrogen plasma, no matter with C0W04 or with acetylene. Thework of this paper belongs to the National Advanced High Technology 863 Project— Metal-Nonmetal Nanostructured Materials. It has been appraised and supported continuously by the high technology experts committee.