A CONTRIBUTION TO EVALUATION METHOD OF DIFFUTION COEFFICIENT

Abstract

In order to estimate the diffusion coefficient D_c depending on the concentration, the graphical method proposed by Matano¹⁾ has been widely used, but the accuracy is not always satisfactory.
In this paper, a method is presented to evaluate D_c more accurately using an empirical formula (a) and equation (b).
The procedure to calculate D_c from concentration distributions is as follows:
1. Approximate values of β, γ and C₀ in formula (a) are caldulated using concentration distributions.
2. Most probable values of β, γ and C₀ are determined by a least squares method using the approximate values of β, γ and C₀ obtained in procedure 1. and concentration distributions. And then the empirical formula (a) is determined.
3. Differential and integral numericals of formula (a) are calculated.
4. D_c's are calculated by substituting the differentials and integrals obtained in procedure 3. into equation (b).
The application of this method to some theoretical Fickian, non-Fickian distributions and some experimental distributions shows that D_c calculated by this method are more accurate compared to that obtained by the graphical method.