Anodized alumina is the end product of exposing alumina, or rather aluminum, products to a special surface treatment known as anodizing. This treatment imparts a tough, robust surface layer on the product that resists wear and corrosion and presents a receptive base for decorative finishes. Anodizing may be used on several non-ferrous metals, but is most commonly applied to aluminum. The treatment consists of a electrolytic passivation process which acts at an atomic level to build a controlled and beneficial layer of natural oxide on the metal surface. The fact that the finish is part of the metal structure and not a separate adhesive layer is what lends anodized alumina products their outstanding surface wear characteristics and aesthetic longevity.
Metal items are generally seen as being extremely tough and long-lived. The truth is, however, that regular use with its associated wear and tear very quickly degrades metal products, particularly the exposed surfaces. Prolonged exposure to the elements takes an especially heavy toll on metals in the form of fading of decorative finishes and corrosion. Conventional surface finishes such as paints are applied to metal surfaces to protect them from the ravages of wear and corrosion, but are often of marginal value as they only form a thin adhesive skin that is prone to scratching and chipping. An deep finish such as that applied to anodized alumina products solves this problem by forming an integral part of the metal surface.
Ironically, anodized alumina harnesses one of the scourges of metal products, oxidation, to affect its long-lasting and robust protective coating. Oxidation is chemical reaction on exposed metal surfaces between oxygen in the air and moisture. Left unchecked, it can lead to the eventual destruction of the metal. This is particularly true of ferrous, or iron-based, metals where the oxidization, also known as rust, causes the metal surface to flake. In the case of anodized alumina, however, the natural oxide layer on the aluminum surface is enhanced to form a deep, long-lasting protective layer that also constitutes a receptive base for decorative finishes such as paints and dyes.
Prevention of galling, which is a process where like metals tend to aggressively abrade each other where they meet under pressure, is also avoided in anodized alumina items. This is a highly desirable benefit in all aluminum items which include screw on elements where galling occurs when the metal is not treated. Aluminum films used in electrolytic capacitors are also anodized to extend the life and efficiency of the components.