Activities of bismuth and antimony in liquid copper base binary alloys have been determined in the range up to N_Bi=0.1 and N_Sb=0.3 by using the Knudsen effusion method with Electro-balance.
At first, the vapor pressure of each gaseous species such as Bi, Bi₂, Sb, Sb₂ and Sb₄ and the total pressures were calculated for pure bismuth and antimony from the data obtained in the present work and the available equilibrium data among these gaseous species. The results shown below agreed well with the values so far reported:
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\ oindentThe standard enthalpy of vaporization for Bi, Bi₂, Sb, Sb₂ and Sb₄ calculated by the second- and the third-law methods agreed well with published data.
The activity of bismuth in binary dilute solutions shows positive deviation from Raoult’s law, and the activity coefficient of bismuth at infinite dilution, γ⁰_Bi, is estimated at 2.6 at 1373 K. The activity of antimony in binary dilute solutions shows considerable negative deviation from Raoult’s law, and the values of γ⁰_Sb are estimated at 2.0×10⁻² at 1373 K, 1.0×10⁻² at 1273 K and 4.9×10⁻³ at 1173 K. Activity curves of antimony at various temperatures show a crossover point at about N_Sb=0.3, near the composition corresponding to the intermetallic compounds, for the Cu-Sb system.
These γ⁰ values suggest that the removal of Bi and Sb from liquid copper by oxidation or vaporization is not easy as compared with the case of other elements.