Calorimetric and magnetic determination of the interfacial enthalpy and heat of mixing in Ag(Ni) alloys

Abstract

A new method for the determination of the interfacial enthalpy between unlike phases is presented. A differential scanning calorimeter was used to measure the heat released during precipitation of a superparamagnetic phase from a supersaturated solid solution. The volume distribution of the precipitated phase was determined by maximum entropy modeling of the magnetization, measured to ultra-high fields, as a linear superposition of Langevin functions. Transmission electron microscopy was used to determine the aspect ratios of the precipitates, which were combined with the volume distributions to calculate the total interfacial area in each specimen. The saturation magnetization was used to determine the total amount of the precipitated phase in each sample. The changes in enthalpy, interfacial area, and amount precipitated were used in a thermodynamic and kinetic model to calculate the interfacial enthalpy and heat of mixing. This method was applied to Ag–(5–10) at.% Ni alloys, produced in thin-film form by electron-beam co-evaporation. The average interfacial enthalpy between Ag and Ni, and the heat of mixing were found to be, respectively, 779±76 mJ/m 2 and 3.59±0.03 kJ/mol for the average alloy composition of 6.89 at.% Ni.