Gas permeation of PECVD membranes inside alumina substrate tubes

The purpose of this work is the gas permeation study of silicon carbide mem branes inside asymmetric porous alumina tube. Membranes have been synthesiz ed by the Plasma Enhanced Chemical Vapor Deposition (PECVD). The reactor we have set lip allows the deposition of amorphous hydrogenated inorganic thi n films on the inner surface of tubular substrates and involves the reactio n between an organosilicon vapor (Diethylsilane: SiH2(C2H5)(2)) and a trans ported glow discharge of argon. In a previous study, the composition and mo rphology of a:SixCyHz layers have been investigated as a function of differ ent plasma conditions (electric power applied to the plasma, gases flow rat es, substrate temperature). It appears that the well controlled homogeneity and composition of the layers result in a good control of the substrate te mperature induced by the glow discharge heating during the deposition. The good mechanical properties and thermal stability of the amorphous hydrogena ted silicon carbide layers, and the alumina substrate allow an important he ating without any damage. In this work the permeation and separation experi ments are performed using a laboratory made gas permeation cell by testing H-2, CO2, and N-2 gases through thin films synthesized with different condi tions on two kind of alumina tubes whose average pore size is 5 or 200 mn. The nitrogen permeance at room temperature is in the range of 10(-6)-10(-7) mol m(-2) s(-1) Pa-1 for membranes with a thickness above I mum. This perm eability remains quite constant regardless pressure, which means that our m embranes permeate gases principally according the Knudsen diffusion mechani sm. (C) 2001 Elsevier Science B.V. All rights reserved.