Aluminum plate anodized
1, the general principle of anodized aluminum plate oxide film generation:
Aluminum plate as the anode placed in the electrolyte solution, the use of electrolytic action, so that the surface of the formation of aluminum oxide film process, called the anodizing of aluminum plate. The cathode of the device is a material with high chemical stability in the electrolytic solution, such as lead, stainless steel, aluminum, etc. The principle of anodizing aluminum is essentially the principle of water electrolysis. When an electric current passes through, hydrogen gas is released on the cathode; On the anode, the oxygen precipitated is not only molecular oxygen, but also atomic oxygen (O) and ionic oxygen, usually expressed as molecular oxygen in the reaction. The aluminum as the anode is oxidized by the oxygen precipitated on it to form an anhydrous alumina film, and the generated oxygen is not all of the action with aluminum, and some of it is precipitated in the form of a gaseous state.
2, anodized aluminum plate oxidation electrolytic solution selection:
A prerequisite for the growth of anodic oxide film is that the electrolyte should dissolve the oxide film. However, this does not mean that anodizing can generate oxide films or the resulting oxide films are the same in all dissolved electrolytes.
3, anodized aluminum plate oxidation types:
Anodizing is divided into direct current anodizing, alternating current anodizing and pulse current anodizing according to current form. According to the electrolyte, it can be divided into sulfuric acid, oxalic acid, chromic acid, mixed acid and natural colored anodizing with sulfonic organic acid as the main solution. According to the film layer, it can be divided into: ordinary film, hard film (thick film), porcelain film, bright modification layer, semiconductor barrier layer and other anodizing. Common anodizing methods and process conditions for aluminum and aluminum alloys are shown in Table -5. The application of direct current sulfuric acid anodizing is the most common.
4, anodized aluminum plate oxide film structure, properties:
The anodic oxide film consists of two layers, a porous, thick outer layer that grows on top of a dense inner layer with dielectric properties, which is called the barrier layer (also known as the active layer). By electron microscopy, the vertical and horizontal surfaces of the film almost all show tubular holes perpendicular to the metal surface, which penetrate through the outer layer of the film until the barrier layer between the oxide film and the metal interface. Around each pore as the main axis is dense alumina to form a honeycomb hexagonal body, called the cell, the entire film layer is composed of countless such cells. The barrier layer is composed of anhydrous aluminum oxide, thin and dense, with high hardness and prevents the passage of current. The thickness of the barrier layer is about 0.03-0.05μm, which is 0.5% to 2.0% of the total membrane. The porous outer layer of the oxide film is mainly composed of amorphous alumina and a small amount of hydrated alumina, in addition to containing electrolyte cations. When the electrolyte is sulfuric acid, the sulfate content in the film layer is 13%-17% under normal circumstances. Most of the excellent properties of the oxide film are determined by the thickness and porosity of the porous outer layer, which are closely related to the anodized strip.