THE FREEZING POINTS OF HIGH PURITY METALS AS PRECISION TEMPERATURE STANDARDS: III. THERMAL ANALYSES ON EIGHT GRADES OF ZINC WITH PURITIES GREATER THAN 99.99 + %

Abstract

Extensive thermal analyses have been carried out on eight grades of high purity zinc with the suppliers' analyzed impurity contents in the range < 0.5 to <70 p.p.m. The liquidus points have been intercompared with a precision of about 0.0002 °C. and the alloy melting ranges have been examined following different rates of freezing. A melting range parameter may provide a more sensitive index of the purity than the liquidus temperature since the shape of the melting curve is strongly influenced by segregation of impurities due to coring on freezing. Two grades of Russian high purity zinc have liquidus points and melting ranges so close to those of New Jersey S.P. zinc that it is difficult to discriminate among them using precision resistance thermometry. This shows that a reported discrepancy of about 0.1 °C. in the freezing points of zinc between the Russian and Canadian laboratories is not due to different impurity contents of the zincs that were used.