MEMBRANE MATERIALS BASED ON POROUS ANODIC ALUMINIUM OXIDE

Abstract

Anodized aluminum oxide (AOA) is applied in many technological areas such as formation of decorative or anticorrosive coating, hydrophobic and hydrophilic surfaces, development of functional micro- and nanomaterials. Due to unique properties of porous structure (most direct, regular and through pores with size in a narrow range) AOA films can be used for membrane separation. The morphological features of such films mainly depend on synthesis conditions. This review consists of the models of pore formation on the aluminum surface and the correlation parameters of films with anodizing conditions. Particular attention is paid to the influence of synthesis factors (electrolyte composition, voltage, temperature conditions, etc) on the porous structure of AOA and the film thickness that determines the mechanical strength of membranes. The optimal voltage values for the porous structure arraingment of anodized aluminum oxide were indicated for each electrolyte. It is noted formation of cylindrical shaped pores with controllable pore diameters, periodicity and density distribution can be produced during two-stage anodizing. The pre-treatment of the metal surface and stage of separation of the formed film from its surface are also considered. Modern research are mainly aimed to synthesis of porous AOA membranes in new anodizing electrolytes and determining pore formation factors on the aluminum surface. The new anodizing conditions in most popular electrolytes (oxalic, sulfuric, phosphoric acids) for obtaining of porous AOA with the required morphological features is also under investigation. Such conditions include, for example, a lower voltage or higher temperature in case for a particular electrolyte. To avoid of local heating the electrolytes with additional components, for example, organic additives is also studied. Some practical aspects of AOA membrane utilization obtained under certain conditions are considered.