Tables 8.3a and 8.3b list the activity coefficients along the two liquidus curves calculated from the above equations. The activity coefficients approach unity as the mole fraction of the component approaches unity, which is expected behavior. At lower concentrations, the activity coefficients are less than unity, indicating attractive Au-Si molecular interactions in the liquid phase. This behavior contrasts with the strong repulsive Au-Si interactions in the solid phase, as indicated by the complete immiscibility of the two components.
The last column in the tables constitutes a test of whether the system obeys regular solution theory. If it did, according to Eq (7.42), the combination of variables in the last column should be a constant. However, the data show substantial variation of this group of parameters, indicating that nonideality in liquid solutions of gold and silicon cannot be described by regular solution theory.
Table 8.3a Activity coefficients of gold along the Au-rich liquidus in the Au-Si System
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