Assisting an experimental investigation by assessment and use of a thermodynamic description for the Cd-Ge system

Certain disagreement is observed in the binary Cd-Ge system; in our opinion this is due to the fact that cadmium presents a high vapour pressure and a low temperature of vaporisation. In this case, if experiments are performed at constant volume, variation of pressure must be taken into account with the variation of temperature. The Cd-Ge binary system was experimentally investigated by differential thermal analysis (DTA), differential scanning calorimetry (DSC), and X-ray diffractometry. As it is difficult to realise a good measurement of the pressure in a sealed ampoule of silica, we chose to estimate the pressure by using thermodynamic data. The optimised model parameters for the Gibbs energy functions of the system were obtained by using the optimisation/calculation programs [1, 2]. The experimental results were reproduced correctly by calculation using the thermodynamic description established in this work. In order to explain the disagreement, a calculation of the phase diagram at different pressures has been made by using the Thermo-Calc program [3].