Preparation and characterization of inorganic membranes by using sol-gel techniques

Abstract

In this research the preparation of ceramIC membranes for gas separation applications by using sol-gel techniques were investigated. The effects of water/alkoxide ratio, H+/alkoxide ratio on the catalysis of the hydrolysis-condensation reactions and the peptization process were investigated by using N2 adsorptiondesorption isotherms, thermogravimetric analysis and FfIR (Fourier Transform Infra Red). The performance and the potential use of these materials in gas separation applications depend mainly on the ability in controlling-designing the microstructurepore network in these materials.The alumina and silica sols were prepared by using aluminium isopropoxide and tetraethylorthosilicate. Sols with different H+/ AI+3 and H20 / AI+3 ratios were prepared.These peptized clear boehmite sols were used for the preparation of unsupported Ah03 membranes at 600°C. The similar ratios were varied for the preparation of clear silica sols and these sols were further dried and heat treated at 400 C.The thermogravimetric analjsis has shown that the weights of the unsupported membranes were stable at the above temperatures. The boehmite was observed to decompose to the y-Alz03 phase at about 425°C. The FfIR analysis have proved the formation of boehmite in the sols and all the organic solvent peaks disappeared upon heat treatment.The y-Alz03 membranes all displayed Type IV isothems typical of mesoporous materials. Hysteresis loops were present in all these isotherms and fast desorption took place in the 0.4-0.6 PlPo range. The BJH pore size distributions were sharp for all the samples.The desorption pore size distributions were found to become wider at an intermediate acid content membrane which also had the lowest BET surface area. The BET particle sizes of these membranes were estimated to be in the 70-100 A0 range.The throat and pore cavity sizes of monosize sphere packings for this particle size range were observed to be in close agreement with the experimentallly determined adsorptiondesorption pore sizes.The silica samples all displayed Type I isotherms with no hysteresis typical of microporous materials. The HK (Horvoath Kawazoe) pore sizes were in the 4-5 AO range. An effect of the water content of these acid-catalyzed sols on the pore size were also detected.