Reaction control of tetraethyl orthosilicate (TEOS)/O-3 and tetramethyl orthosilicate (TMOS)/O-3 counter diffusion chemical vapour deposition for preparation of molecular-sieve membranes

Counter diffusion chemical vapour deposition (CVD) is an excellent way to p repare inorganic thin films or membranes on the surface of porous or non-po rous supports. Modification of the pore size of porous supports by this met hod to prepare molecular-sieve membranes is another interesting opportunity . However, control of the deposition profile is very difficult because of t he complex reaction kinetics. In this study, counter diffusion CVD of tetra ethyl orthosilicate (TEOS)/O-3 or tetramethyl orthosilicate (TMOS)/O-3 syst ems was investigated. To control the deposition layer profile in a thin por ous ceramic substrate, numerical simulations of the reaction sequences were performed. The reactant concentration and temperature were varied to contr ol the deposition profile, and the simulation results were compared with ex perimental results. It is shown that high quality membranes can be processe d under the optimised reaction conditions. In addition, the effect of step- coverage of the CVD reaction on final membrane performance was also investi gated by comparison of the TEOS/O-3 and TMOS/O-3 reactions.