Impurity removal from Fe, Cr, Ti, and V metals by hydrogen plasma arc melting and thermodynamic estimation of hydride and sulfide formation

Experimental data of Fe, Cr, Ti, and V metals purified by Ar and Ar-30 vol% H-2 plasma arc melting was compared with results of thermodynamic estimations. The Fe metal refined by Ar and Ar-30 vol% H-2 plasma gas at 101.3 and 5.3 kPa had approximate 45% removal degree of the total impurities. On the other hand, Co, Ni, Zr, Nb, and Mo were not reduced from the Fe metal due to their lower vapor pressures than that of Fe. At 5.3 kPa, hydrogen plasma arc melting of Ti and V, which have lower initial impurity contents than that of Fe, resulted in a removal degree of near 40% of impurities, while the average removal degree of impurities in the Cr metal close to 30%. Thermodynamic estimation could explain qualitatively a tendency of each impurity behavior. It was shown by the thermodynamic calculations that several impurities, namely Mn, S and P, form hydrides with relatively high pressures compared with pressures of atomic species. Furthermore, It was also confirmed that the formation of some sulfides in the gas phase including FeS, SiS and GeS affects the behavior of S and sulfide forming elements. (c) 2005 Elsevier B.V. All rights reserved.