What Is Clear Anodizing?

The process of using aluminum or aluminum alloy as the anode and placing it in an electrolyte solution to conduct electricity treatment and forming an aluminum oxide film on its surface by electrolysis is called anodization of aluminum and aluminum alloy. After anodizing, the surface of aluminum can form a few micrometers-hundreds of micrometers of oxide film. Compared with the natural oxide film of aluminum alloy, its corrosion resistance, abrasion resistance and decorative properties are significantly improved.

Anodized aluminum

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The principle of aluminum anodizing is essentially the principle of water electrolysis. When the current passes, the following reactions occur:

On the cathode, H2 is emitted according to the following reaction: 2H + + 2e H2

On the anode, 4OH-4e 2H2O + O2, the precipitated oxygen is not only molecular oxygen (O2), but also atomic oxygen (O), and ionic oxygen (O-2), usually expressed as molecular oxygen in the reaction .

The aluminum as the anode is oxidized by the oxygen precipitated thereon to form an anhydrous Al2O3 film: 2AI + 3 [O] = AI2O3 + 1675.7KJ It should be noted that not all of the generated oxygen interacts with aluminum, and part of it is precipitated in the gaseous form .

Types of anodizing Anodizing has long been widely used in industry. There are many ways of naming different names, and they are summarized in the following categories:

According to the current type, there are: direct current anodization, alternating current anodization, and pulse current anodization that can shorten the production time to reach the required thickness, the film layer is thick and uniform and dense, and the corrosion resistance is significantly improved.

According to the electrolytic solution: sulfuric acid, oxalic acid, chromic acid, mixed acid, and natural color anodizing with organic sulfonic acid solution.

According to the properties of the film layer, there are: anodization of ordinary films, hard films (thick films), porcelain films, bright modified layers, and barrier layers for semiconductors.

The application of the direct current sulfuric acid anodizing method is the most common, because it has anodizing treatment suitable for aluminum and most aluminum alloys; the film layer is thick, hard and wear-resistant, and better corrosion resistance can be obtained after sealing; The film is colorless and transparent, with strong adsorption ability and easy to be colored. The processing voltage is low and the power consumption is low. The processing process does not need to change the voltage cycle, which is conducive to continuous production and practical operation automation. , Low price and other advantages.

In the past ten years, China's construction industry has gradually used aluminum doors and windows and other decorative aluminum materials, and their surface treatment production lines have adopted this method.

1) Structure of anodized film Anodized film is composed of two layers. The outer layer is called porous layer, which is thick, loose and porous, and has low resistance. The inner layer is called a barrier layer (also known as an active layer), which is thin, dense and has high electrical resistance. The porous outer layer is grown on a dense inner layer with dielectric properties. In general, the anodized film is an array of hexagonal cylinders, each of which requires a star-shaped hole filled with a solution, resembling a honeycomb structure, and the thickness of the hole wall is twice the diameter of the hole.

(1) Barrier layer The barrier layer is composed of anhydrous AI2O3, which is thin and dense, has high hardness and prevents the current from passing. (2) porous outer layer

The aluminum oxide film is a porous film. Regardless of whether it is colored or not, it must be sealed before being put into use, so as to improve its corrosion resistance and weather resistance. There are three types of treatment methods, namely high temperature

Aluminum alloy sacrificial anode is suitable for cathodic protection of metal in ships, machinery and equipment, marine engineering and harbour facilities in seawater medium, as well as pipelines and cables in sea mud.