Impurity behavior in Cu refined by Ar plasma-arc zone melting

Purification of a 4N grade Cu rod by argon plasma-arc zone melting (APZM) was carried out. Detailed impurity analysis of the Cu rod was performed using glow discharge mass spectrometry (GDMS). Three impurity behavior groups based on segregation and evaporation during APZM were discussed using the GDMS analysis. Although the impurities with segregation coefficient k₀ < 1 were theoretically expected to be segregated towards the end of the Cu rod, it was found that the segregation effect by APZM can occur when the equilibrium distribution coefficient (k₀) is less than 0.4 due to the strong affinity of Cu for some metallic and non-metallic impurities. On the other hand, the impurities for which k₀ > 1 had no significant reduction in their impurity concentrations. Some impurities, like Mg, S, Cd and Zn, were reduced much faster than the others in Cu. This was ascribed to the removal by zone refining coupled with the evaporation of impurities for P _imp/P_Cu > 10² .