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Principle of Anodic Oxidation
Principle of Anodic Oxidation
An oxide film is formed on the surface of a metal or alloy as an anode. Metal oxide film has changed the surface state and performance, such as surface coloring, improve the corrosion resistance, enhance the wear resistance and hardness, protection of metal surface, etc.. For example, aluminum anodizing of aluminum and its alloy is placed in the corresponding electrolyte (such as sulfuric acid, chromic acid, oxalic acid, etc.) as the anode, in particular conditions and external current under, electrolysis was carried out. The aluminum or its alloy is oxidized to form a thin layer of aluminum oxide on the surface. The thickness is 5 to 30 microns, and the hard anodic oxide film can reach 25 to 150 microns. Improves the hardness and wear resistance of the anodic oxidation of aluminum and its alloy, up to 250 to 500 kg / mm2, good heat resistance, hard anodic oxidation film melting point up 2320K, excellent insulation, resistance to breakdown voltage high of 2000V, enhances the performance in corrosion resistance, in w = 0.03NaCl salt fog by thousands of hours without corrosion. In the thin film, it has a large number of micro pores, which can absorb all kinds of lubricant, which is suitable for the manufacture of engine cylinder or other wear-resistant parts. Non ferrous metals or their alloys (such as aluminum, magnesium and its alloys, etc.) can be anodized, this method is widely used in mechanical parts, aircraft parts, precision instruments and radio equipment, daily necessities and architectural decoration and other aspects.
Generally speaking, the anode is made of aluminum or aluminum alloy as anode, cathode, select the stereotype, together the aluminum and stereotype in aqueous solution, there is sulfuric acid, oxalic acid, chromic acid and so on, electrolysis, let aluminum and grids formed on the surface of an oxide film. In these acids, the most widely used is the anodic oxidation of sulfuric acid.
