Estimation of thermodynamic properties of Cu–La binary alloy with modified Miedema’s theory

Resumo

According to modified Miedema’s theory, mixing enthalpies (ΔH), excess entropies (S^E), excess Gibbs free energy (G^E), and component activities (a) of Cu–La binary alloy were estimated using the basic thermodynamic principles and some simple physical parameters of Cu and La, such as electronegativity, atomic volume and electron density. Based on the Cu–La binary alloy phase diagram, the Gibbs free energy of the phase precipitation reactions of Cu₆La and Cu₅La was deduced. The results showed that the values of ΔH, S^E, and G^E of Cu–La binary alloy were all negative. Compared to the ideal solution, the activities of the components presented a large negative deviation from Raoult’s law, which indicated that there was a strong interaction between Cu and La. The calculated data are well consistent with the experimental data. The Gibbs free energies of the phase precipitation reactions of Cu₆La are lower than those for Cu₅La, which means that Cu₆La is thermodynamically more stable than Cu₅La. Furthermore, the experimental results show that rareearth rich Cu₆La phase particles in copper matrix are formed after La microalloying.