Structure of anodic aluminum oxidation anodic oxidation film is composed of two layers, the outer layer is called porous layer, thick, loose porous, low resistance. The inner layer is called the barrier layer (also known as the active layer), which is thin, dense and has high resistance. The porous outer layer grows on a dense inner layer with dielectric properties. In general, the anodized film is a hexagonal column array, each column has a star-shaped hole filled with solution, shaped like a honeycomb structure, the thickness of the hole wall is twice the diameter of the pore.
(1) The barrier layer is composed of anhydrous AI2O3, thin and compact, with high hardness and prevent the current through the role.
(2) The outer layer of the porous oxide film is mainly composed of amorphous AI2O3 and a small amount of R-Ai2O3.H2O, as well as anions of the electrolyte.
The pore size of the anodic aluminum oxide film is between 100nm~200nm, the thickness of the oxide film is about 10 microns, the porosity is about 20%, and the pore distance is between 300 nm and 500nm. The cross section of the oxide film shows that the pore of the oxide film is basically tubular structure and the dissolution reaction of the oxide film occurs at the bottom of the pore. And the general sulfuric acid DC anodic oxidation film aperture is about 20nm, if it is 12 microns of the oxide film, how deep is the thin tubular structure ah! If this is a 1m diameter well, it 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 these two are closely related to the anodizing conditions, so the film can be obtained by changing the anodizing conditions to meet different requirements. Film thickness is a very important indicator of the performance of anodized products, and its value directly affects the corrosion resistance, wear resistance, insulation and chemical coloring ability of the film. In the conventional anodizing process, the film thickens with time. After rounding to the limit thickness, it gradually becomes thinner with the extension of treatment time. Some alloys, such as AI-Mg and AI-MG-Zn alloys, are particularly obvious. Therefore, the oxidation time is generally controlled within the internal limiting film thickness time.
Anodic aluminum oxidation properties and applications Anodic oxidation film has high hardness and wear resistance, strong adhesion ability, strong adsorption ability, good corrosion resistance and electrical insulation and high thermal insulation. Because of these special properties, it has been widely used in various aspects.
The main uses of anodic aluminum oxidation are:
(1) improve the wear resistance, corrosion resistance and climate corrosion resistance of parts.
(2) the transparent film generated by oxidation can be colored into a variety of color films.
(3) as capacitor dielectric film.
(4) improve the binding force with organic coating. For coating bottom layer.
(5) as the bottom layer of plating and enamel.
(6) Other applications under development, solar absorption panels, ultra-hard film, dry lubrication film, catalyst film, nanowires, deposition of magnetic alloys in porous film as memory elements.