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Anode small classroom | Structural characteristics of aluminum anodizing

Release time:

2023-04-28 13:39

The structure of the anodic oxide film The anodic oxide film consists of two layers. The outer layer is called the porous layer, which is thicker, loose and porous, and has low resistance. The inner layer is called the barrier layer (also known as the active layer), which is thin, dense and high resistance. The porous outer layer is grown on a dense inner layer having dielectric properties. In general, the anodic oxide film is an array of hexagonal columns, each of which requires a star-shaped hole filled with solution, resembling a honeycomb structure, and the thickness of the hole wall is twice the diameter of the hole.

(1) barrier layer barrier layer is composed of anhydrous AI203, thin and compact, with high hardness and prevent the current through the role.
(2) Porous outer layer The porous outer layer of the oxide film is mainly composed of amorphous AI203 and a small amount of r-AI203.H20 also contains anions of the electrolyte.
The pore size of the oxide film is between 100nm and 200nm, the thickness of the oxide film is about 10 microns, the porosity is about 20%, and the pore distance is between 300 and 500nm. The cross-sectional diagram of the oxide film shows that the oxide film hole is basically a tubular structure, and the oxide film dissolution reaction occurs basically at the bottom of the hole. However, the aperture of the general sulfuric acid DC anodic oxide film is about 20nm. If it is a 12 micron oxide film, how deep is it! Assuming that this is a well with a diameter of 1m, its well depth will be 600m deep.

Most of the excellent characteristics of the oxide film, such as corrosion resistance, wear resistance, adsorption, insulation and other properties are determined by the thickness and porosity of the porous outer layer, but the two are closely related to the anodic oxidation conditions, so the film can be obtained by changing the anodic conditions to meet the different requirements of the use of the film. Film thickness is a very important performance indicator of anodic oxidation products. Its value directly affects the corrosion resistance, wear resistance, insulation and chemical coloring ability of the film. In a conventional anodizing process, the film layer is thickened with time. After reading the maximum thickness, it gradually becomes thinner with the extension of processing time, and some alloys such as AI-Mg and AI-Mg-Zn alloys are particularly obvious. Therefore, the time of oxidation is generally controlled within the maximum film thickness time.

The anodic oxide film has high hardness and wear resistance, strong adhesion, strong adsorption capacity, good corrosion resistance and electrical insulation and high thermal insulation. Because of these specific properties, it has been widely used in various aspects.

The main uses of aluminum anodizing are:

(1) Improve the wear resistance, corrosion resistance and weather corrosion resistance of the parts.

(2) The transparent film generated by oxidation can be colored into various color films.

(3) as a capacitor dielectric film.

(4) The bonding force with the organic coating is improved. For coating the bottom layer.

(5) the bottom layer of electroplating and enamel.

(6) Other uses under development, solar absorption panels, ultra-high hard films, etc.