Mass transfer in the gas phase during top-blowing with plasma jets

Abstract

Deoxidation of copper melts by hydrogen has been investigated experimentally by top-blowing with argon-hydrogen plasma jets. The course of the deoxidation process has been described mathematically using kinetic laws. The overall divided course of the process can be examined in live partial steps, which are hydrogen transport within the gas phase, hydrogen transport within the melt, oxygen transport within the melt, reaction between hydrogen and oxygen, and H2O transport within the gas phase. Based on these five elementary processes, an equation for the velocity of deoxidation has been derived. The values of the rate of deoxidation resulting from this equation, in combination with the mass-transter coefficients valid for this process, have been compared to the experimental data. The results of this study verify those of former investigations on vaporization of elements out of copper melts. The mass-transfer coefficients are the same, when the local activity differences are used as the driving force for mass transport in a system. This means that the surface-renewal theory is valid, when mass-transfer coefficients are defined in this way. This is the case, at least, when metallic melts are subjected to top-blowing by plasma jets.