Porous films and method of forming them
AssigneeAlcan International Limited
InventorsRobin C. Furneaux, William R. Rigby, Alexander P. Davidson
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Abstract
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.
Claims19
An anodic aluminium oxide film (12) having pores extending from one face of the film to the other,
- including a system of larger pores (14) extending in from one face (16) a distance h into the film, the larger pores having a diameter d near their inner ends, and a system of smaller pores (22, 24) extending in from the other face (26) a distance s into the film, the smaller pores having a substantially uniform minimum diameter p,
- the system of larger pores interconnecting with the system of smaller pores, such that the inner ends of one or more smaller pores are joined to the inner end of a larger pore and there are substantially no blind larger pores,
- wherein
- d=10 nm-2 microns,
- p is at least 2 nm but less than 0.5 d, and
- s=10 nm-1.0 micron.
A method of forming a porous anodic aluminium oxide film which method comprises
- subjecting an aluminium metal substrate to the action of electric current in an electrolyte so as to form a porous anodic oxide film thereon,
- subjecting the substrate with the porous anodic oxide film thereon to the action of an electric current in an electrolyte and reducing the applied voltage at a rate sufficiently slow that partial or complete recovery of the current keeps step with the voltage reduction, the voltage reduction being effected either continuously or incrementally in steps of not more than the greater of 5 V and 50% of the existing voltage down to a level of not more than 15 V,
- the electric current used being either DC, or alternatively AC with the extent of cathodic polarization of the metal substrate being limited such that gas evolution does not significantly take place thereon during the cathodic part of the cycle,
- and separating from the metal substrate and recovering the anodic oxide film.
An aluminum oxide sheet having two substantially parallel major faces with pores extending from one face of the sheet to the other,
- including a system of larger pores extending from one face into the sheet and a system of smaller pores extending in from the other face,
- the system of larger pores interconnecting with the system of smaller pores such that the inner ends of one or more smaller pores are joined to the inner end of a larger pore and there are substantially no blind larger pores.
Dependencies are inferred from the claim text.