Multicomponent diffusion in the system 85Kr-He-Kr

Abstract

The diffusion coefficients of 85 Kr in trace quantities in mixtures of helium and normal krypton, as well as in pure helium and pure krypton, have been determined by using an all-metal apparatus. The apparatus consists of two diffusion chambers joined by a diffusion capillary of special design so that the chambers can be connected or disconnected by a bellows operated piston valve. For analysis one of the chambers has a thin cellophane window with a scintillation counter placed close to it. First both the chambers were filled with the desired gas mixture and then a small amount of 85 Kr was added to one chamber and the pressures equalized. Diffusion was then started and the counting rate determined at regular intervals, from which the relaxation time and the diffusion coefficient were calculated. The diffusion coefficient D 1→23 of 85 Kr in the mixture of Krypton and helium is found to be accurately given by the theoretically predicted formula: 1 D 1→23 = ( C 2 D 12 )+( C 3 D 13 ) where C 2 C 3 are the concentrations of normal krypton and helium, and D 12 and D 13 are the binary diffusion coefficients. As expected, a plot of the experimental values of 1/ D 1→23 against C 3 is found to be a straight line from which D 12 and D 13 are calculated.