Thermal diffusion of vacancies in aluminum

Abstract

Thermal diffusion of vacancies in pure aluminum has been studied by use of the technique employed in our earlier paper. In this approach, the entire sample is held at an elevated temperature (between 480°C and 630°C) with a linear temperature gradient of 150°/cm. A contraction of a 1-cm long specimen of about 70 μ is observed in an interval of 46 days. From the data a value of ( Q∗ − ΔHν) equal to −1.5 ± 0.3 kcal/g-atom is obtained where Q∗ and ΔH ν are the heat of transport and vacancy formation energy respectively. Substitution of the data for ΔH ν available in the literature leads to a value for Q∗ of 16 kcal/g-atom. This value corresponds to the value of ΔH m , the enthalpy of motion of an atom into a vacancy which on the basis of a large number of measurements is found to lie between 14.3 and 16.5 kcal/g-atom. This agreement is in quantitative agreement with the predictions of simple kinetic theories. The observation may also be rationalized qualitatively in terms of a discussion involving an analysis of localized vibrational modes.