Thermodynamic simulation of systems with refractory metals melted by Ar-H₂ plasma

Thermodynamic calculations were carried out to simulate impurity removal from refractory metals by Ar-H₂ plasma arc melting. The calculations enable us to estimate the impurity removal degree. Numerical agreement between the experimental and calculated results for the base metals Ti, V, Zr, Nb to Ta improve in that order. Addition of H₂ to the plasma gas results in faster transfer of the system toward equilibrium-like state, while the equilibrium composition of the metal does not depend on the plasma gas, but on temperature. The examined impurities transfer to the gas phase in the form of atoms while hydride formation makes a minor contribution; thus, the major factor for better metal purification with Ar-H₂ plasma is considered to be an increase in the molten-metal temperature.