MICROSTRUCTURAL PROPERTIES OF NON-SUPPORTED MICROPOROUS CERAMIC MEMBRANE TOP-LAYERS OBTAINED BY THE SOL-GEL PROCESS

Dried and calcined non-supported membrane top-layers of SiO2, SiO2/TiO 2, SiO2/ZrO2 (10, 20 and 30 mol% TiO2 and ZrO2, respectively) and SiO2 /Al2O3 (10 mol% AlO1.5) were prepared using acid catalyzed hydrolysis and condensation of alkoxides in ethanol. The microstructure was deter mined using nitrogen physisorption. The modified Horvath-Kawazoe model for nitrogen adsorption in cylindrical pores was used for pore size a ssessment. SiO2 non-supported membrane top layers were 100% microporou s with an average porosity of 30-37%, depending on drying conditions. The bimodal pore size distribution shows a maximum at an effective por e diameter of 0.5 nm, and a broader tail with a weaker maximum around 0.75 nm. Microporous non-supported binary systems can be prepared with porosities between 15 and 40%. The high reactivity of the Ti, Zr, Al- alkoxides requires carefully chosen conditions. Too much water results in dense materials. The pore size distributions (PSDs) of the binary systems resemble the PSDs for silica.