Determination of Binary Diffusion Coefficients of Gases Using Holographic Interferometry in a Loschmidt Cell

A measuring system for the determination of binary diffusion coefficients of gases has been developed. The lower and upper half cells of the Loschmidt diffusion cell are fixed, one upon the other, contrary to the usual shearing cells. A sliding component between the half cells is moved to connect them and to start the diffusion. The concentration changes due to diffusion are determined by the optical method of real-time holographic interferometry. In this way the concentration is obtained as a function of time and location resulting from the analysis of the interference pattern. The data are evaluated by using the integrated diffusion equation for the closed-tube technique. First, measurements on the system argon-propane have been successfully performed at 1 bar and at room temperature. The results show an uncertainty of 1 per cent and are in good agreement with data by Wakeham and Slater (1974). Furthermore, refractive index measurements on the pure gases, argon and propane, as a function of gas density have been performed and evaluated to derive values of the first refractivity virial coefficient.