Contribution a l'etude thermodynamique de l'alliage Cd-Zn. Pressions partielles et proprietes: Thermodynamiques des solutions solides et liquides riches en zinc

Abstract

The system Cd-Zn has been studied for a number of compositions from 79.8 to 99.9 at.% Zn between 526 and 758 K by the optical absorption method. The logarithm of the optical density is a linear function of reciprocal temperature, log D Cd = f( 1 T ), for both liquid and solid solutions. The phase boundaries have been determined from intersections of such straight lines with the three-phase loop for the temperatures and compositions under consideration. The partial pressures of Cd over the Cd-Zn alloys have been obtained from cadmium optical density values by using the literature data on the vapour pressure of pure Cd. It is shown that Henry's law holds for the partial pressure of Cd in the range of solid solutions. The partial molar enthalpy (Δ mix H̄ Cd) and entropy (Δ min S̄ Cd) are obtained from the log P Cd = f ( 1 T ) equations for solid and liquid solutions. A uniform decrease of Δ mix H̄ Cd and Δ mix S̄ Cd with x Cd increasing was observed. The partial enthalpies Δ mix H Cd for different solid solution compositions are not distinguishable within experimental error. The average value Δ mix H̄ Cd = 25.6 ± 1.4 kJ mol −1 for x Zn = 0.994 was obtained.