Preparation of thin Li4SiO4 membranes by using a CVD method

CVD (chemical vapor deposition) procedures were investigated by using a counter diffusion CVD method. The effects of silica precursors on the hydrogen permeation properties of the silica membranes were discussed. 5 types of silica alkoxides (tetramethylorthosilicate (TMOS), methyltrimethoxysilane (MTMOS), propyltrimethoxysilane (PTMOS), dimethyldimethoxysilane (DMDMOS), and trimethylmethoxysilane (TMMOS)) were employed as the silica precursors; they have different numbers of methyl groups. Hydrogen permeance through the DMDMOS membrane prepared at 500 degrees C was 9.0 x 10(-7) mol m(-2) s(-1) Pa-1, and H-2/N-2 selectivity was 920. Activation energy of H-2 permeation through the silica membrane prepared from TMOS was 10.5 kJ mol(-1) that was the maximum among the 5 types of the silica precursor. This indicates dense silica layer can be obtained from TMOS. Thus, TMOS was employed for the further Li4SiO4 preparation. High temperature CO2 permselective membranes were successfully prepared by using Li4SiO4 as a CO2 selective layer. Pinholes of the Li4SiO4 layer was filled by the CVD post treatment at 600 degrees C. CO2/N-2 permselectivity was 1.2 at the 600 degrees C permeation test. The CO2 permeance ratio is higher than the Knudsen diffusion difference. Thus, this selectivity was explained by the CO2 selective adsorption on the Li4SiO4 layer. (C) 2013 The Authors. Published by Elsevier Ltd. Open access under CC BY-NC-ND license. Selection and/or peer-review under responsibility of GHGT