[China Aluminum Network] When oxidizing from a sulfuric acid solution, it can be seen that in the solution area near the anode, the content of aluminum ions is added, oxygen is separated out, and there is an oxide film, while hydrogen is separated from the cathode, and the oxide film is formed. Reflect the two processes together. That is, the electrochemical film formation process and the chemical dissolution process of the oxide film. Of course, only the film formation rate is greater than the film dissolution rate, then the thickening of the oxide film can be achieved because the resistance of the aluminum oxide film is great when it's When the thickness reaches a certain limit, resistance will hinder the continued reaction of the anode, and the current will not pass. At this time, the film formation rate is equal to zero and the dissolution process is not suspended. Therefore, the thickness of the oxide film that has been formed tends to decrease.
The nature of the anodic oxidation process is the discharge of H+ and OH- and the subsequent oxidation of aluminum by the new eco-oxygen to form AlzO3. At the beginning of the oxidation, a thin, fine oxide film (ie, a non-porous inner layer that is close to the metal surface) is quickly formed on the anode. The resistance is also large, and the voltage rises sharply in the first few seconds. The increase in voltage causes local thinning of the oxide film to "break down." The breakdown of the breakdown of the local film accelerates, presents holes, and then extends, providing the conditions for further thickening of the film, and forming a hexagonal outer layer of the oxide film with the holes as the middle.
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