High-Temperature Determination of Surface Free Energy of Copper Nanoparticles

The experimental study of the thermodynamic properties of nanoparticles at high temperatures is still a challenge. In this work we report the experimental determination of the surface free energy, gamma, of copper nanoparticles in the temperature range from 750 to 950 K. The solid electrolyte galvanic cell technique makes it possible to study the system under strict equilibrium conditions. The experiment was designed to avoid nanoparticle coalescence, which is one of most severe obstacles to the attainment of reliable results. The surface free energy (in J m(-2)) of 20 nm Cu nanoparticles changes with temperature according to the equation gamma = 60.97 - 0.234T + 3.09 x 10(-4) T-2 - 1.37 x 10(-7) T-3. At the lowest explored temperature, i.e., 750 K, a surface free energy of 1.70 +/- 0.03 J m(-2) was found. This value is in good agreement with numerical simulation data for copper nanoparticles previously reported in literature. A theoretical model is also proposed that accounts for the behavior of the surface energy on temperature.