TIME-DEPENDENT THERMOMIGRATION - ANALYTIC SOLUTIONS AND EXPERIMENT DESIGN

An approximate but highly accurate analytic solution, valid for short- time nonisothermal diffusion of an interstitial solute in a linear gra dient of temperature, has been derived, by a perturbation method, for the initial and boundary conditions of a semi-infinite source, a thin film source and a finite source, respectively. The solution indicates that a normal isothermal diffusion profile is perturbed by two effects ; the temperature dependence of the isothermal (ordinary) diffusivity and thermomigration. The magnitudes of the perturbations are determine d, respectively, by the activation energy for diffusion and the heat o f transport of the solute, and both terms are proportional to the magn itude of the temperature gradient. On the basis of the present analyti c solution, non-stationary experiments for the measurement of the heat of transport have been proposed, as promising alternatives to the con ventional stationary state technique, that can be carried out using an nealing times that are several orders of magnitude shorter than in the usual steady-state experiment.