Precision of diffusion coefficients by the isotope exchange technique

摘要

The precision of diffusion coefficients determined by the gasndash;solid isotope exchange technique was analyzed for planar sheet diffusion, rate controlled by the isotope exhange reaction. An objective function was employed to estimate the degree of fit of a theoretical calculation to the experimental diffusion profile as a function of the sample size (l), the diffusion coefficient (D), the surface exchange coefficient (K), and the atomic ratio in the gas and solid phases. The results indicate that the diffusion coefficient can be determined to a high degree of precision when (Kl/D) is greater than 1 and furthermore that when this condition is satisfied, the precision of the determined diffusion coefficient increases with longer diffusion times.