Effect of Floating Zone Refining under Reduced Hydrogen Pressure on Copper Purification

Abstract

Floating zone refining of copper under a reduced hydrogen pressure of 0.7 Pa has been carried out. Commercial 99.9999% pure 8-mm-diameter Cu rod was used as a starting material. The purification effect has been examined by the bulk residual resistivity ratio (RRR_B) and glow discharge mass spectrometry (GDMS). The RRR_B of the starting material is 3200, and that of refined copper is 22000. Almost all impurities were effectively reduced to near or below their detection limits of GDMS . The removal of S and Se is attributable to the reaction with hydrogen. The marked decrease of Al and Si is ascribed to a convective transportation of alumina and silica inclusions to the surface of the molten zone, and these inclusions are concluded to come from the starting material. This result suggests that trace amounts of Al and Si present as solid solution in starting material can be removed in the same manner by zone melting in a slight oxidizing atmosphere for the first few passes.