Ⅰ: what is anodic oxidation?
The anodic oxidation of aluminum is an electrolytic oxidation process. In this process, the surface of aluminum and aluminum alloy is usually transformed into a layer of oxide film, with protective, decorative, and other functional characteristics. According to this definition, anodic oxidation of aluminum consists only of the process of forming the anodic oxide film.
Anodic oxidation is the electrochemical oxidation of metals or alloys. Aluminum and its alloy in the corresponding electrolyte and specific process conditions, under the action of the external current, aluminum products (anode) formed oxide film. Anodizing, if not specified, is usually referred to as anodizing sulfuric acid.
In order to overcome the defects of surface hardness and wear resistance of aluminum alloy, expand the scope of application and prolong the service life, surface treatment technology has become an indispensable part of the use of aluminum alloy, anodic oxidation technology is the most widely used, the most successful.
Ⅱ: Parameters of anodizing
Principle: The principle of hydroelectricity solution
Cathode reaction: H2:2H + + 2e → H2
Anodic reaction: 4OH-4E → 2H2O + O2
Ⅲ: The closed process of anodizing
The aluminum oxide film is a porous film, regardless of whether there is a coloring treatment before it is put into use, it should be closed, so as to improve its corrosion resistance and weather resistance. There are three treatment methods: high-temperature hydration reaction seal, inorganic salt seal, and organic seal.
(1) high temperature water closure
This method uses the hydration reaction of aluminum oxide film and water to turn the amorphous plasma film into hydrated crystalline film:
Hydration reaction can be carried out at room temperature and high temperature, but at high temperature, especially at the boiling point, the generated hydrated crystalline film is very stable and irreversible crystalline film, therefore, the most commonly used sealing treatment of aluminum oxide film is boiling water or steam treatment.
(2) inorganic salt seal
Inorganic salt method can improve the fastness of organic coloring dyes, so it is commonly used in chemical coloring methods.
① Acetate method
② Silicate method
(3) Organic sealing method
This is to dip the aluminum oxide film in oil, paint or coating, due to the high cost and increase the process, so it is not used, more or the aforementioned two methods, and the first high temperature water method as the mainstream.