Permeation of gases through poly (ethylene terephthalate) membranes metallized with palladium

Abstract

The permeation of He, H 2, CO 2, Ar and N 2 at 50°C through poly(ethylene terephthalate) (PET) membranes metallized with Pd layers ranging from 125 to 1000 Å in thickness was studied. It was found that the Pd layers act as gas barriers which reduce the rate of gas transfer through the polymer with up to more than one order of magnitude. The fact that the Pd layers failed to be perfect gas barriers was attributed to the presence of defects in the structure of the Pd layers and to additional gas diffusion through preferential diffusion paths along grain boundaries. A particular case is represented by the permeation of H 2. Since H 2 is able to dissolve into the Pd layers it permeates not only through the defects of the layers but also through the layers themselves. The experimental results show that catalytic activity of Pd in dissociating H 2 molecules determines the permeation rate of H 2 through the metallized PET membranes.