抄録
The plasma-arc melting process has reacently been noted for the refining and degassing of several metals, by applying hydrogen to the plasma-generating gas.
In this work, deoxidation and decarburization of crude tantalum, prepared by carbon-reduction smelting of Ta2O5 with Ar plasma-arc heating, has been investigated by using H2–Ar plasma-arc melting under 0.1 MPa. Also, the possibilities and conditions for winning high purity and ductile tantalum metal has been examined.
The oxygen and carbon contents in tantalum by carbon-reduction smelting were dependent on the carbon mixing-mole ratio to Ta2O5, the product of (%O) and (%C) being nearly constant. Therefore, the ratio of carbon/oxygen in tantalum is able to be adjusted by the selection of a suitable C/Ta2O5 ratio, for the following refining process.
At the subsequent stage of H2–Ar plasma-arc melting, oxygen in tantalum was quickly liberated but carbon was scarcely removed. As a result, ductile tantalum whose sum of oxygen and carbon was less than 100 mass ppm could be produced by the excellent deoxidation effect of H2–Ar plasma-arc melting for a high oxygen- and low carbon-bearing tantalum. Since the deoxidation rate increased in proportion to the about 1/2th power of hydrogen composition of the plasma gas, deoxidation may be caused by dissociated and activated hydrogen atoms. Consequently. the evaporation of tantalum suboxide and tantalum, known in high vacuum melting, was so small in this stage that it was made possible to considerably reduce the loss of tantalum.
