Relation between excess volume, excess free energy and isothermal compressibility in liquid alloys

Excess volume data of 32 liquid alloys were reviewed and plotted versus their excess free energies. It is hereby found that all combinations of the signs of ^EV and ^EG are possible. The excess volume data split into two different curves which are monotonous in ^EG. For one of these curves the signs of ^EV and ^EG are equal and they are opposite for the other. We improved our previously developed model and found that there is an unspecified sign which can be chosen either + or -, depending on the system. This explains why there are two curves corresponding to the experimental finding. The model relates excess volume, excess free energy and isothermal compressibility with each other whereby the concept of internal pressure is used. The model can also predict the excess volume as function of the excess free energy, when the correct sign, either + or -, is known and a reasonable assumption is made for the effective isothermal compressibility. In the present work, the latter has been estimated as an average from the isothermal compressibility values over the involved pure elements. Good qualitative and quantitative agreement with the experimental data is obtained for the systems investigated. The model is valid at least for -3RT < ^EG < +1RT.