Alcan International Limited

William R Rigby

Robin C Furneaux

Alexander P Davidson

Anthony T Thomas

A porous anodic aluminum oxide membrane, at least one surface of which is profiled on a scale of 0.01 to 50 mm, may be made by profiling a surface of an aluminium metal substrate anodizing the substrate to form a porous membrane on the surface and separating the membrane from the substrate. The profiling may consist of a system of parallel ribs and troughs. Structure having an interesting properties as filters can be built up by the use of several such membranes bonded to one another along the crests of the ribs.

Anodic aluminium oxide membranes

The invention provides porous anodic aluminium oxide film having a major face with an area of at least 50 cm.sup.2, the film material containing phosphorus derived from the anodizing electrolyte, preferably at least 5 microns thick and preferably having pores spaced 0.1-0.5 microns apart. The film may be made by anodizing one or more aluminium metal anodes of suitable area in an electrolyte based on phosphoric acid at a concentration of 5-150 g/l maintained at a temperature in the range 5.degree.-50.degree. C. using an anodizing voltage of 40-200 V. After separation from the metal substrate, the films have intersecting properties for use in filters.

Porous anodic aluminum oxide films

An anodic aluminum oxide film (12) has a system of larger pores (14) extending in from one face (16) and interconnecting with a system of smaller pores (24) extending in from the other face (26). The film is made by anodizing an aluminum metal substrate, then reducing the applied voltage at a rate to permit partial or complete recovery of the oxide film, either continuously or incrementally in small steps down to a level preferably below 3 V, and separating the oxide film from the substrate.

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Banbury, United Kingdom

William R Rigby