Time-Dependent Solution to Interstitial Diffusion in A Temperature Gradient

An equilibrium thermodynamical model is developed for the time-dependent interstitial diffusion process in a temperature gradient in binary compounds. A new analytical solution is obtained from a linearization of the model. The linearized solution is in agreement (1 to 3%) with an accurate numerical solution of the nonlinear model and is significantly faster in evaluation. The sensitivity of this solution to parameter variations permits its use in detailed experimental comparisons. This new time-dependent solution makes possible, for the first time, an accurate, simultaneous determination of the chemical interdiffusion coefficients and the effective heat of transport of interstitial compounds, such as refractory carbides and hydrides, from a concentration measurement for short diffusion times.