Isoperibolic calorimetry was employed for the first time to study the mixing enthalpies of Al–Lu–Cu melts along four radial sections with xAl/xLu = 0.42/0.58 and 0.76/0.24 and with xCu/xLu = 0.35/0.65 and 0.7/0.3 at 1780 ± 3 K. When aluminum was added to the CuxLu1–x melts, the thermal effect of its dissolution increased. This was due to the formation of strong bonds between aluminum and lutetium. In the other two sections, on the contrary, when copper was added to the AlxLu1–x melts, the strong bonds between aluminum and lutetium were broken. Therefore, the integral mixing enthalpies of these melts hardly changed up to xCu = 0.4. Using the formation enthalpies for liquid alloys and compounds in the Cu–Lu system known from the literature, all thermodynamic properties of melts, associates in melts, and intermetallics were optimized and calculated with the ideal associated solution (IAS) model. The calculated activities of components in melts of this system exhibited moderate negative deviations from ideal solutions. The IAS model was also used to calculate temperature–composition dependences of the Gibbs energies, enthalpies, and entropies of formation for melts and temperature dependences for intermetallics to further determine the liquidus curve of the system phase diagram. As a result, complete information was obtained on the thermodynamic properties of all phases and the liquidus curve of the Cu–Lu phase diagram, which agrees with the one known from the literature. The reliable thermochemical properties of melts in the boundary binary Al(Cu)–Lu and Al–Cu–Lu subsystems were presented as Redlich–Kister polynomials to calculate the same data for the studied ternary melts with the analytical Redlich–Kister–Muggianu model. Comparison of the measured and calculated mixing enthalpies for these melts showed that our data and those found with the analytical Redlich–Kister–Muggianu model without the ternary contribution were consistent within the experimental error. The extreme value of the integral molar enthalpy of melts in the ternary Al–Cu–Lu system was –37 ± 4 kJ/mol and corresponded to the Al0.6Lu0.4 melt, i.e., the boundary Al–Lu subsystem provided the main contribution to the interaction energy between dissimilar atoms in these ternary melts.

Thermodynamic Properties of Cu–Lu and Al–Cu–Lu Melts

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发表日期：

2026年7月21日

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L. O. Romanova,
V. G. Kudin,
M. I. Ivanov,
N. V. Podoprigora,
V. S. Sudavtsova

摘要

Isoperibolic calorimetry was employed for the first time to study the mixing enthalpies of Al–Lu–Cu melts along four radial sections with x_Al/x_Lu = 0.42/0.58 and 0.76/0.24 and with x_Cu/x_Lu = 0.35/0.65 and 0.7/0.3 at 1780 ± 3 K. When aluminum was added to the Cu_xLu_1–x melts, the thermal effect of its dissolution increased. This was due to the formation of strong bonds between aluminum and lutetium. In the other two sections, on the contrary, when copper was added to the Al_xLu_1–x melts, the strong bonds between aluminum and lutetium were broken. Therefore, the integral mixing enthalpies of these melts hardly changed up to x_Cu = 0.4. Using the formation enthalpies for liquid alloys and compounds in the Cu–Lu system known from the literature, all thermodynamic properties of melts, associates in melts, and intermetallics were optimized and calculated with the ideal associated solution (IAS) model. The calculated activities of components in melts of this system exhibited moderate negative deviations from ideal solutions. The IAS model was also used to calculate temperature–composition dependences of the Gibbs energies, enthalpies, and entropies of formation for melts and temperature dependences for intermetallics to further determine the liquidus curve of the system phase diagram. As a result, complete information was obtained on the thermodynamic properties of all phases and the liquidus curve of the Cu–Lu phase diagram, which agrees with the one known from the literature. The reliable thermochemical properties of melts in the boundary binary Al(Cu)–Lu and Al–Cu–Lu subsystems were presented as Redlich–Kister polynomials to calculate the same data for the studied ternary melts with the analytical Redlich–Kister–Muggianu model. Comparison of the measured and calculated mixing enthalpies for these melts showed that our data and those found with the analytical Redlich–Kister–Muggianu model without the ternary contribution were consistent within the experimental error. The extreme value of the integral molar enthalpy of melts in the ternary Al–Cu–Lu system was –37 ± 4 kJ/mol and corresponded to the Al_0.6Lu_0.4 melt, i.e., the boundary Al–Lu subsystem provided the main contribution to the interaction energy between dissimilar atoms in these ternary melts.