Abstract
The models of Wagner and of Blander et al. for dilute solutions of a nonmetal X in binary melts A–B have been improved in the following way. In the PCC model (preferential coordination cluster model), the number of solvent atoms, n, bonded to a solute X is assumed to be smaller than that of solvent atoms, Z, which surround it. In the PBB model (preferential break bond model), it is assumed that Z=n, and strong solvent-solute interactions reduce the strength of the solvent-solvent bonds formed by m of the Z solvent atoms bonded to the solute X by a fractional extent. When the solvent A–B exhibits regular solution behavior, the resulting equations for the activity coefficient of X, γx, yield results comparable with those obtained by the previous models. If the interaction between solvents A and B is very strong, the present equations lead exclusively to an abrupt change in γx around a particular composition, as demonstrated by the experimental data.
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