Preparation of Silica Membranes by CVD Method

Amorphous silica is paid attention as a material for H ₂ separation membranes because it shows diffusion selectivity of H ₂ . Usually, the silica membrane is formed on a porous ceramic support in order to maintain the mechanical strength of the thin membrane. There are a sol-gel method and a chemical vapor deposition (CVD) method as a typical membrane preparation method. A silica sol is prepared by hydrolyzing a silica source such as a silicon alkoxide for the sol-gel method, and a porous ceramic substrate is coated with the solution to form a membrane. Here, we have paid attention to the CVD methods that the silica source is supplied by a vapor phase. A silica source is vaporized to deposit on a porous ceramic substrate. Silica membranes can be deposited on modules with complicated shape such as a multimembrane module because of the higher diffusivity of the vapor silica sources. The CVD method can be classified into two types, a one side geometry method and a counter-diffusion method.