The permeation of H and He through vitreous glass and silica membranes was modelled using ab initio density functional calculations. The total energy of the system was obtained as the permeating species approach and pass through H2nSinOn (n = 4 to 8) cyclosiloxane n-membered rings of different size to give activation energies of permeation. Comparison of the calculated activation energies to those reported for vitreous glass (20–40kJ/mol) indicate the presence of 5- and 6-membered siloxane rings, consistent with the accepted structure of glass as a disordered form of β-cristobalite. Similar comparison to activation energies measured for silica membranes (10–20kJ/mol) indicate the presence of 6- and 7-membered rings, and suggest that the structure of the membranes was more open than that of the vitreous glass.

Activation Energies for Permeation of He and H2 Through Silica Membranes - an Ab Initio Calculation Study. P.Hacarlioglu, D.Lee, G.V.Gibbs, S.T.Oyama: Journal of Membrane Science, 2008, 313[1-2], 277-83