Abstract
Molecular-sieve materials contain isolated macropore regions connected to the open macropore network by micropores which inhibit gaseous diffusion. We model the macroporosity as the allowed region of an uncorrelated site-percolation problem on a lattice. The scaling theory of percolation clusters above the percolation threshold is used to predict the long-time rate of gaseous desorption from molecular sieves. The analysis also predicts the transient electrical discharge from a random superconducting network.