Physical and mechanical properties of ultrapure copper obtained by zone melting

Abstract

This paper presents the results of studies on the electrical conductivity, macro- and microstructure of ultrapure copper (5N3) obtained after zone melting of refined copper (99.96% Cu). The effect of residual concentrations of impurity metals on the electrical conductivity of ultrapure copper has been established. To assess the effect of low concentration impurities on the electrical conductivity of copper, the authors used a linear dependence of the increase in resistivity on the concentration of impurities (Ci), which was determined by the Mathyssen-Fleming rule. It is shown that low residual concentrations of impurity metals obtained in copper after its zone melting refining, ppm (ppm = 10–4 %): 0.2As; 0.06Sb; 0.006Ag; 0.07Bi; 0.006Sn; 0.02Pb; 1,1Ni have practically no effect on the electrical conductivity of ultrapure copper. The maximum electrical conductivity of M00K industrial grade copper (99.99% Cu) is 59 MSm/m, while zonerefined copper with a copper content of 99.999% has the electrical conductivity of 60.2 MSm/m. The values of the electrical conductivity of the obtained samples can serve to control the quality of obtained copper. It is shown that, in contrast to the microstructure of the initial copper sample, the ultrapure copper microstructure is a densely packed structure consisting of fine grains. On the microstructure map of ultrapure copper, the presence of individual impurity metals in the form of rounded small balls was established. Elongated filaments in the form of continuous lines, which are associated with the formation of chemical compounds of impurity metals with each other, are also found. This phenomenon is clearly observed on the microstructure map of ultrapure copper, captured at a magnification of 1000x under conditions of etching of the sample under study. The values of macro- and microhardness of the initial copper sample and ultrapure copper sample are established. The hardness of the initial copper sample is 84.42 HB (according to Brinell). After zone melting refining of copper from impurities, the hardness of the resulting ultrapure copper was 59.85 HB. Measurements of the microhardness of samples of the initial copper sample and ultrapure copper obtained by zone melting showed the microhardness of 103.0 and 70.42, respectively.