ON THE POSSIBILITY OF CHARACTERIZING MESOPOROUS MATERIALS BY PERMEABILITY MEASUREMENTS OF CONDENSABLE VAPORS - THEORY AND EXPERIMENTS

Transport of condensable vapours through a mesoporous medium is used f or the first time as a means for the characterization of pore structur e. For a condensable vapour, as capillary condensation occurs, the per meability of the vapour goes through a sharp maximum at a pressure bel ow its saturation pressure. In this work, experimental results are pre sented for water and pentane vapour permeabilities, on a well defined mesoporous alumina membrane. The experimental data are compared to the oretical simulation results obtained from network models. The main pro cesses involved (adsorption, mass transfer, capillary condensation) ar e simulated over the entire range of relative pressures. It is observe d that within a certain relative pressure range, a percolating cluster of capillary condensed pores is formed, resulting in a dramatic incre ase in the permeability of the vapour.the limits of this pressure rang e can be related to the percolation threshold and thus to the topology of the medium. (C) 1998 Elsevier Science B.V. All rights reserved.