When aluminum is anodized, an oxide film is formed on its surface, generally characterized by anticorrosive properties and abrasive mechanical resistance. The oxide film also has good dielectric properties. These properties strongly depend on the operating parameters of the anodizing process, such as electrolyte type, component concentrations, pH value, current density, current form, applied voltage, and temperature, as well as pretreatment conditions. Anodizing electrolytes may be based on inorganic acids or organic acids, as well as combinations with or without other additives. For many applications, it is necessary to obtain a more compact anodic film having a barrier-type structure. When aluminum foil is too thin, even a little dissolution of oxide is a great disadvantage such as when it has to be used as an electrical insulator. In these cases, certain electrolytes are involved, usually based on boric acid and ammonium tartrate or others, at a neutral, sometimes basic pH value.
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