Vapor pressures of zinc and cadmium in liquid copper-zinc and copper-cadmium alloys have been measured by means of the transportation method.
Activities calculated for copper-zinc alloy show considerable negative deviations from Raoult's law. The following equation derived from activities determined is well realized in the measured temperature range from 850°Cto 1200°C.
RTlnγ_Zn=-6400N²Cu±90
From this relation, both of the activity coefficients of copper and zinc atinfinite dilution are estimated to be 0.11 at 1200°C. Heats of mixing are exothermic and show a parabolic curve having a maximum of about -1.6kcal/mole at N_zn=0.5. From the above equation and the uniformity of a-function, it is considered that the liquid copper-zinc alloy shows the behavior of regular solution in the range of N_zn=0 to 0.6.
Owing to the high vapor pressure of cadmium, the measurements were limited in the ranges of composition from 0.40 to 0.85 in N_Cd and of temperature from 600°Cto 650°C for copper-cadmium system. Calculations of activities were extended to total range of Cu-Cd binary system by extraporation. Activities thus obtained agreed well with the values reported by previous investigators and also agreed well with the values estimated from liquidus. Free energies of mixing and excess free energies were also in good agreement with the other data, but not the heats of mixing.