Strengthened porous alumina membrane tube prepared by means of internal anodic oxidation

A method for preparing an anodic aluminum oxide tube with a much higher mechanical strength than before was developed, where anodic oxidation was carried out from the inside of an aluminum tube (internal anodizing method). It was considered that the internal stress remaining in the alumina layer, which was formed in the course of the internal anodizing, resulted in a considerable improvement of compressive strength against external pressure. As a matter of fact, the tube could withstand at least up to 0.98 MPa of transmembrane pressure, which corresponded to 32.6 MPa in terms of breaking pressure. The tubular alumina membrane obtained had straight mesopores of 20–25 nm in diameter and, therefore, showed the Knudsen permselectivity for inorganic gases. Such a strengthened alumina tube is expected to be used as a porous membrane or as a support for composite membranes.