Diffusion of gases in porous silica gel

Gas diffusion in porous silica gels prepared by the sol-gel process is studied at room temperature. It is shown from the measurement of helium or oxygen gas diffusion in the gels that the gas diffusion is limited by the average pore diameter of the gel, R_a; that is, the mean free path of gas in a porous gel can be regarded as equal to R_a. The results also indicate that the gas diffusing length is about three times larger than the geometrical thickness of the sample gel. Some adsorption of oxygen gas appears to take place on the silica surface of the gel at room temperature.