We report calorimetric data for the size-dependence of the melting temperature as well as the enthalpy and entropy of melting for nanoscale Pb particles in an Al matrix, prepared by high energy ball-milling. The results are discussed with respect to various models for the melting of small confined systems. We can rule out models based on a temperature-independent Gibbs excess free energy of the particle-matrix interface, and a model based on an increased mean-square displacement of the interfacial layer. The best agreement to the data is provided by modeling the interface as an inert layer of finite thickness, which does not participate in the phase transition.
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