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Anodizing

Anodic oxidation, the electrochemical oxidation of metals or alloys. Aluminum and its alloys form a layer of oxide film on aluminum products (anode) under the action of applied current under corresponding electrolyte and specific process conditions. If an


The so-called aluminum anodic oxidation is an electrolytic oxidation process in which the surface of aluminum and aluminum alloys is usually transformed into an oxide film, which has protective, decorative and other functional properties. The anodization of aluminum starting from this definition includes only the part of the process of generating anodized film.

A metal or alloy product is used as an anode, and an oxide film is formed on the surface by electrolysis. The metal oxide film changes the surface state and properties, such as surface coloring, improving corrosion resistance, enhancing wear resistance and hardness, and protecting metal surfaces. For example, aluminum anodic oxidation, aluminum and its alloys are placed in corresponding electrolytes (such as sulfuric acid, chromic acid, oxalic acid, etc.) as anodes, and electrolysis is carried out under specific conditions and applied current. The anode aluminum or its alloy is oxidized to form a thin layer of aluminum oxide on the surface, the thickness of which is 5-30 microns, and the hard anodized film can reach 25-150 microns. The anodized aluminum or its alloy improves its hardness and wear resistance to 250~500kg/mm2, good heat resistance, the melting point of hard anodized film is as high as 2320K, excellent insulation, shock resistance The breakdown voltage is as high as 2000V, which enhances the corrosion resistance and does not corrode in ω=0.03NaCl salt spray for thousands of hours. There are a large number of micropores in the thin oxide film, which can adsorb various lubricants, which is suitable for manufacturing engine cylinders or other wear-resistant parts; the film micropores have strong adsorption capacity and can be colored into various beautiful and gorgeous colors. Non-ferrous metals or their alloys (such as aluminum, magnesium and their alloys, etc.) can be anodized. This method is widely used in mechanical parts, aircraft and automobile parts, precision instruments and radio equipment, daily necessities and architectural decoration. [1] 
Generally speaking, aluminum or aluminum alloy is used as the anode for the anode, and the lead plate is selected for the cathode. The aluminum and lead plate are placed together in the aqueous solution, which contains sulfuric acid, oxalic acid, chromic acid, etc., for electrolysis. An oxide film is formed on the surface. Among these acids, the most widespread is anodic oxidation with sulfuric acid.

Other typesedit

In addition to metals, the oxidation caused by other substances as anodes is also called "anodic oxidation".
In the actual process, there are more anodic oxidation of aluminum alloys, which can be applied in daily life. The characteristics of this process can produce a hard protective layer on the surface of aluminum parts, which can be used to produce kitchen utensils and other daily necessities. However, the anodizing effect of cast aluminum is not good, and the surface is not shiny, it can only be black. The aluminum alloy profile is better.

effect
Protective
Decorative
Insulation
Improve the bonding force with organic coating
Improve the bonding force with the inorganic covering layer
Other functions in development

the difference
The difference between anodic oxidation and conductive oxidation
1) Anodizing is carried out under the condition of high voltage electricity. It is an electrochemical reaction process; while conductive oxidation (also called chemical oxidation) does not need to be energized, it only needs to be immersed in liquid medicine. It is a kind of electrochemical reaction. Kind of pure chemical reaction.
2) Anodizing requires a long time, often tens of minutes, while conductive oxidation only requires a few tens of seconds.
3) The film produced by anodic oxidation is several micrometers to tens of micrometers, and is hard and wear-resistant; the film produced by conductive oxidation is only 0.01-0.15 micrometers, and the wear resistance is not very good, but it can conduct electricity and resist atmospheric corrosion. That is its advantage.
4) The oxide film is originally non-conductive, but because the film formed by conductive oxidation is really thin, it is conductive.

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