LONG-RANGE WATER TRANSPORT AND SELF-DIFFUSION IN ZEOLITE 4A POWDER BEDS

The diffusion of water in industrial-grade sodium zeolite 4A powder be ds has been visualized using broad-line gradient-echo magnetic-resonan ce imaging, Profiles of the equilibration of hydrated beds contacting dehydrated beds have been compared with hydrated beds contacting beds hydrated with D2O in order to compare hydration-gradient-driven water- transport diffusion with self-diffusion, Although the equilibration ra tes are very different in the two cases, they are both in agreement wi th a model of coupled intraparticle liquid and interparticle vapor dif fusion extended to incorporate the tracer experiments, The extended mo del is further tested by studies at elevated temperature, reduced hydr ation levels, and in ammonium-substituted material. (C) 1996 Academic Press, Inc.