Diffusion Coefficients of Sodium Vapors in Argon and Helium

Diffusion coefficients of sodium vapors in argon and helium gases were measured from 380 to 560°C by the Stefan method under atmospheric pressure. Careful considerations were made in the design of the apparatus to obtain data within a ±10% error, which arises from several sources inherent in the Stefan method. The experimental errors inherent in such sources were theoretically evaluated. The experimental diffusion coefficients were compared with those predicted by the majority of previous theoretical expressions. The comparisons revealed that the expressions proposed by Moulaert for the sodium-argon mixture and by Aref'yev et al. for the sodium-helium mixture predicted values that were in excellent agreement with the measurements.