Research and modeling of thermodynamical properties of melts of Bi—Cu—Eu and Cu—Eu systems

Abstract

The partial and integral enthalpies of mixing of the melts of the Bi—Cu—Eu system were determined for the first time by the method of calorimetry on three radial sections with a constant ratio of two components: xCu/xEu = 0,3/0,7, xEu/xBi = 0,23/0,77, xEu/xBi = = 0,8/0,2 at T = 1400 ± 1 K. It is shown that the partial and integral enthalpies of mixing of the studied melts are mainly exothermic. Moreover, when adding bismuth to CuхEu1-х melt, the thermal effect of dissolution of the latter increases. This is due to the formation of strong bonds between Bi and Eu. In the other two sections, the opposite happens. Using the literature enthalpies of mixing of melts of the Cu—Eu system, investigated by the method of calorimetry at 1313—1480 K in the entire range of compositions, Gibbs energies, enthalpies and entropies of the formation of melts and intermetallics, their temperature-concentration dependences, and from them — the liquidus curve of the state diagram were calculated of the studied system according to the model of the ideal associated solution. It is shown that the activities of the components in these melts exhibit small negative deviations from ideal solutions and a small amount of associates, especially Eu5Cu, is formed in them. The maximum mole fraction of the EuCu associate reaches a value of 0,09, and the other two (Eu2Cu, EuCu5) — 0,05 and 0,02. From the critically analyzed thermodynamic properties of melts of the Cu—Eu, Bi—Cu and Bi—Eu systems, their reliable data were derived, from which similar parameters for liquid alloys of the ternary system Bi—Cu—Eu were calculated according to various known models. It is shown that the experimental mixing enthalpies of melts of the Bi—Cu—Eu system best agree with those calculated according to the Redlich—Kister—Mujianu model. It was established that ΔHmin = = −61,5 kJ/mol at xBi = 0,5. According to the same model, G, S of these melts were calculated. It was established that Gmin = –40 kJ/mol, and Smin = –18 J/mol•K, the minima of which also fall on the boundary subsystem Bi—Eu, i.e., the main contribution to the interaction energy between different-named atoms of melts of the Bi—Cu—Eu system contribute to the components of this subsystem. Keywords: calorimetry, melts, intermetallics, thermodynamic properties, systems, Bi—Cu—Eu, Cu—Eu, ideal associated solution model, phase equilibria.