Abstract
The membrane formation mechanism of silica
membranes prepared by chemical vapor deposition
method for gas separation was investigated. The initial
diffusion of carrier gases was measured to estimate the
deposition rate of the silica. The effects of the organic
substituent of the silica precursors on the pore sizes of
the deposited membranes were investigated by using
this in-situ analysis. The effects of the organic group of
the silica precursors were discussed. The TMOS
(tetramethoxysilane) deposited membrane showed high
H2 permselectivity. TMOS consists of 4 alkoxy groups
without organic groups. Both Ar (0.34 nm) and SF6
(0.55 nm) diffusion through the membrane during the
deposition decreased with increasing deposition time.
On the other hand, Ar diffusion decreased through the
MTMOS (methyltrimethoxysilane) membrane after
increasing the diffusion of SF6. The methyl group of
MTMOS must be decomposed during the deposition of
MTMOS. The pore size of the MTMOS deposited
membrane was estimated to be approximately 0.39 nm,
which is larger than that of the TMOS membrane.
Smaller pores were obtained from the silica precursors
with the smaller substituent, while the silica precursor
with larger substituent do not diffuse into the deposited
pores. As a results, Ar diffusion during the deposition
for the silica precursor with larger substituent increased
with increasing the deposition periods.
