Kouji Mimura1 and Michio Nanjo1
1Research Institute of Mineral Dressing and Metallurgy, Tohoku University, Sendai
Recently H2-Ar plasma arc melting, using a gas mixture of hydrogen and argon as a plasma generating gas, has been recognized to be available for refining of various metals.
In this work, deoxidation and decarburization of crude tantalum, prepared by carbon reduction of Ta2O5 with Ar plasma arc heating, has been investigated by using H2-Ar plasma arc melting. Also the possibilities and conditions for winning high-purity and ductile tantalum metal has been examined.
The oxygen and carbon contents in tantalum obtained by carbon reduction smelting are dependent on the carbon to Ta2O5 mixing mole ratio, and the product of (%O) and (%C) in each tantalum is found to be almost constant. Therefore, The carbon/oxygen ratio in tantalum can be adjusted by changing the C/Ta2O5 ratio for the refining process that follows.
At the subsequent stage of H2-Ar plasma arc melting, oxygen in tantalum can be quickly liberated but carbon is scarcely removed. As a result, ductile tantalum whose sum of oxygen and carbon is less than 100 mass ppm can be produced by the excellent deoxidation effect of H2-Ar plasma arc melting for a high oxygen- and low carbon-bearing tantalum. Deoxidation is considered to be mainly caused by dissociated and activated hydrogen atoms in the H2-Ar plasma gas. The evaporation of tantalum suboxide and tantalum, known in electron beam melting, is very small in this stage so that the loss of tantalum can be reduced.
tantalum, plasma metallurgy, plasma arc melting, hydrogen plasma, carbon reduction smelting, deoxidation, decarburization, purification
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