銅合金液体の混合熱について

抄録

The heats of mixing of liquid copper alloys were measured from temperature changes of liquid alloys on mixing.
In the liquid Cu-Bi alloy, a heat absorption which depends parabolically upon composition was observed. On the other hand, heat of mixing curves with a deep valley of heat evolution in the range of 80% to 75% Cu were obtained for the liquid Cu-Sb, Cu-Ge, Cu-Sn and Cu-In alloys.
It is supposed 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, all the constituent atoms cannot 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 form clusters of small groups of atoms. These clusters appears to be molecules of the type A_mB bound by a sort of covalent bond and have a flexible structure different from a rigid molecule. They have been named as pseudo-molecules. The heat evolved on mixing may be mainly due to the formation of the pseudo-molecules.
Under the above assumption, the partition function of an assembly consisting of the pseudo-molecules and free atoms and then the free energy of such an assembly were calculated. From the condition of the minimum free energy, the distribution of the pseudo-molecules n_R was also determined as a function of alloy composition. In the case of the liquid Cu-Sn and Cu-In alloys the values for the heat of mixing calculated from the above n_R function are in good agreement with the observed values. Considering the large difference between atomic volumes of Cu and Bi, the heat of mixing of the liquid Cu-Bi alloy was estimated. The calculated results give a parabolic curve with a maximum at 40% Bi, which is in good agreement with the experiment.