Preparation and characterization of sol-gel-derived unsupported Al2O3-SiO2composite membranes

The synthesis of unsupported Al2O3-SiO2 composite membranes has been achiev ed by controlling hydrolysis and condensation of aluminium iso-propoxide an d tetraethyl silicate under acidic conditions. The phase transformation and pore structural evolution of composite membranes are investigated by X-ray diffraction and nitrogen adsorption measurement, respectively. After sinte ring at 600 degreesC for 10 h, the composite membranes consist of only amor phous phase as SiO2 concentration ranges from 25 to 100 mol% and crystallin e gamma -Al2O3 appears at lower SiO2 content. Both micropores and mesopores contribute to the total pore volume and BET surface area, and mesopores be come dominant. At high SiO2 content (50 mol%), the composite materials exhi bit a I-nm pore diameter decrease and about 100 m(2) g(-1) surface area inc rease, as well as only a negligible pore volume drop of 0.0164 cm(3) g(-1), compared with the single Al2O3 membrane. For the composite membrane with 4 0 mol% SiO2 concentration, sintering at higher temperature leads to phase t ransformation and grain growth, and both densification and phase transforma tion result in a decrease in both total pore volume and surface area, as we ll as an increase in mean pore diameter and finally the collapse of pores. Further study is required to improve the thermal stability of the composite membrane. (C) 2001 Elsevier Science B.V. All rights reserved.