Diffusion of SF6 in 13X zeolite

Abstract

Experimental diffusivities for SF₆ and 13X zeolite show the same from of concentration dependence as has been recently reported for small molecules in 5A zeolite. The data can be explained by the same type of collisional diffusion mechanism, which is based on the assumption that the flux arises mainly from a small fraction of rapidly moving molecules with mean free paths spanning several cages. The diffusivities derived from the sorption measurements are very much smaller than those previously estimated from n.m.r. experiments but the jump frequency, estimated from the Henry's law constants, agrees well with the n.m.r. correlation time. This suggests that the adsorbed molecules may have a high degree of mobility on a localized scale (possibly within a cage) but that over larger distances (several cages) the mobility is very much smaller.