Powders of CaTi1−xFexO3−δ (x = 0.15, 0.20) were obtained by ceramic route and used to prepare dense membranes covered with porous layers of the same material. The catalytic properties of some of these layers were enhanced by dispersed small particles of metallic Ag or a mixture of Pt and Pr oxide. Comparison of the O permeability for membranes with different thickness indicated the existence of surface limitations to O permeation. The increase of the membrane surface area with porous layers leads to an increase of the measured O permeability. Maximum enhancements were attained with both sides modified (70%) and with the permeate side modified with Ag (86%). Smaller values were obtained when only the feed (13%) or the permeate (55%) sides were modified with porous layers. Results suggested that the effective electrochemically active area of the porous layer was restricted to the vicinity of the dense part of the membrane. Oxygen diffusion (DO) and surface exchange (Kex) coefficients in air were estimated to be DO = 8.8 x 10−7cm2/s and Kex = 6.7 x 10−6cm/s at 950C.

Surface Enhanced Oxygen Permeation in CaTi1-xFexO3-δ Ceramic Membranes. F.M.Figueiredo, V.V.Kharton, A.P.Viskup, J.R.Frade: Journal of Membrane Science, 2004, 236[1-2], 73-80