Stability of Porous Ceramic Membranes

Abstract

Publisher Summary This chapter discusses the stability of porous ceramic membranes. These membranes with pores of ∼1 nm, and below, are suitable for nanofiltration, pervaporation, and gas separation. Besides the porous ceramic membranes, dense ion-conducting membranes have also been developed during the last decades. These materials are used as electrolytes in fuel cells, or as hydrogen- and oxygen-selective membranes. The majority of the porous membranes, including almost all commercially available membranes, are made up of metal oxides. The oxides preferably used are aluminum oxide or alumina (Al2O3), zirconium oxide or zirconia (ZrO2), titanium oxide or titania (TiO2), and silicium oxide or silica (SiO2). Mixtures of these metal oxides are also frequently used. Membrane supports are mainly produced by slip casting or extrusion. The main method for the preparation of metal oxide intermediate and top layers is the sol–gel technique. In this technique, mesoporous intermediate layers are made by colloidal sols and microporous top layers by polymeric sols. The sols are prepared from metal salts or metal organic precursors. The layers are deposited on the supports or on the previous multilayer structure by dip coating. The porosity of the supports or of the previous multilayer structure leads to the gelling of the sols. These gel layers are further dried and thermally treated to form the final membrane layers. This final thermal treatment—called “calcination” or “sintering”—stabilizes the crystallographic and morphological structure of the dried layer.