On the Heat of Mixing of Liquid Copper Alloys

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The heat of mixing of liquid copper alloys is measured in terms of the temperature change of liquid alloys on mixing. In the liquid Cu-Bi alloy, a heat absorption depending parabolically upon alloying composition is observed. In the liquid alloys of Cu-Sb, Cu-Ge, Cu-Sn and Cu-In, on the other hand, the heat of mixing curve shows a deep minimum of heat evolution in the range of 75% to 80% of Cu. The results indicate that Cu and Bi atoms are randomly mixed in the Cu-Bi alloy, but in the other alloys such as Cu-Sn and Cu-In, not every constituent atom can always be randomly distributed. It may be expected from the above results and other physical properties that in these liquid alloys some atoms are randomly distributed, but others associate into clusters of small groups of atoms, which are like molecules of the type A_mB bound by a sort of covalent bond and having a flexible structure different from a rigid molecule. These will be referred to as pseduo-molecules. The heat evolved on mixing may be mainly due to the formation of these pseudo-molecules. Under the above assumption free energy of an assembly consisting of the pseudo-molecules and free atoms is calculated, and from the condition of the minimum free energy the distribution of the pseudo-molecules n_R is determined as a function of alloy composition. The heat of mixing curves for the liquid Cu-Sn and Cu-In alloys calculated with the above n_R functions are in good agreement with the observations. Considering the large difference between atomic volumes of Cu and Bi the heat of mixing of the liquid Cu-Bi alloy is estimated. The calculated results give a parabolic curve with a maximum at 40% Bi, which is in good agreement with the experiment.
東北大学の論文

On the Heat of Mixing of Liquid Copper Alloys

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