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Process method and principle of hard oxidation of aluminum

August 17, 2023
There are many hard anodic oxidation electrolytic methods, such as: sulfuric acid, oxalic acid, propylene glycol, sulfosalicylic acid and other inorganic salts and organic acids. The power supply used can be divided into DC, AC, AC-DC superposition, pulse and superposition pulse power supply, etc. At present, the following kinds of hard anodizing are widely used:
(1) sulfuric acid hard anodizing method;
(2) oxalic acid hard anodizing method.
(3) mixed acid type hard anodizing
Among them, sulfuric acid process is a kind of hard oxidation method which is widely used at present.
Principle: Hard anodizing principle
There is no essential difference between simple sulfuric acid type aluminum alloy hard anodizing principle and ordinary anodizing, if it is mixed acid type hard oxidation, there are some side reactions. Reaction nature
1. Cathode reaction :4H+ +4e=2H2↑
2. Anode reaction :4OH--4e=2H2O+O2↑
3. Aluminum oxidation: The oxygen precipitated on the anode is in an atomic state, which is more active than the oxygen in the molecular state and easier to react with aluminum :2A1+3O→A12O3
4. The dynamic balance of oxidation in the anodic film dissolution: the oxide film thickens with the increase of energizing time and the increase of current. At the same time, due to the duality of the chemical properties of (Al2O3), that is, it is an alkaline oxide in an acidic solution, and an acidic oxide in an alkaline solution. There is no doubt that the oxide film liquid dissolves in the sulfuric acid solution. Only when the formation rate of the oxide film is greater than its dissolution rate, the oxide film is likely to thicken. When the dissolution rate is equal to the formation rate, the oxide film will no longer thicken. When the oxidation rate is too much greater than the dissolution rate, the surface of aluminum and aluminum alloy is easy to form a powdery oxide film.
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