On thermodynamics of first-phase formation during interfacial reactions

The use of heat or free energy of compound formation as a value expressing the effect of thermodynamics on phase formation at interfaces is discussed. Applying the effective heat of formation (EHF) model, it is shown that this implies that the intermixed interfacial layer is an ideal solution of the reacting elements. An expression is derived for the parameter F0 that replaces the effective heat of formation, ΔH′, when non-ideality of the intermixed layer is taken into account. It is shown that F0 may differ significantly from ΔH′ for a strongly non-ideal intermixed layer. However, the EHF approximation remains valid for the majority of binary systems. Application of the proposed approach to multicomponent systems is discussed. It is demonstrated for ternary systems that the choice of the thermodynamic functions of the interface layer can affect the predictions of the model.