Research On The Vacuum Purification Of High-purity Copper

With social development, application of copper has broad prospects. High-purity copper (5N-7N purity) because of its excellent thermal conductivity, low impurity content, good ductility can be widely used in semiconductor, bonding wire, sputtering targets and other industry fields.Traditional methods to produce high purity copper conclude electrolysis, zone melting, ion exchange and vacuum refining. And electrolysis is the most widely used method but with some defects, such as high energy consumption, complex process and instable quality. Zone melting need repeated heating and it is difficult to remove the element which the value of ko is near 1. Anion exchange is complex, quality inconsistent and not environmentally friendly. The latest study have found that P, Ag, As, Se, Te which vapor pressure is higher than that of copper's can be effectively removed by electron beam(EB) melting and most other impurities can be removed by directional solidification technique.In this paper, all the efforts are devoted to producing large-sized high purity copper.4N purity cathode copper was used as the start material, and F 67mm, lengths greater than 90mm, 5N high purity copper ingots have been prepared by vacuum melting and directional solidification.Impurities with high vapor pressure can be effectively removed by vacuum melting. Because of the strong affinity of Cu for some of the impurities, the segregation effect does occur when the ko value is in the range from 0.72 to 1.3. Vacuum 30～90Pa, induction melting temperature of 1573K, after 30min refining, the content of impurities decreased from 11ppmw to 5.06ppmw, and the main gas elements(O, H) decreased 69.47%, the content of hydrogen is lower than 1 ppmw.Impurities can be removed effective by EB pool melting, and the removal efficiency of Na, Mg, Al, P, Zn, Ga, Pd, Ag,In, W, U is up to 60% separately. The content of main impurities decreased from 1 lppmw to 3.1ppmw after vacuum induction melting directional solidification and two times of EB pool refining; the removal effeciency of gas and other impurities in the secondary EB pool melting was not significant.In the EB drip melting and directional solidification experiment, the content of impurities was 28.2% lower than that of the raw materials. EB drip melting experiments show that reaction between crucible and molten copper was the limiting factor. Using more high purity graphite crucible will be able to minimize melt contamination. Comparing the results of EB pool melting with EB drip melting, a reasonable purification process is the vacuum induction melting and directional solidification-electron beam drip melting and directional solidification.