Metal aluminum was once used to make cooking utensils and was very popular, because aluminum pots and the like are not easy to rust. Aluminum will react with oxygen in the air to form a dense aluminum oxide film. However, it has been scientifically proved that aluminum tableware is not suitable for use. Cooking or storing acidic, alkaline and salty foods for a long time, because acid and alkali salts can directly corrode the protective film on the metal aluminum surface and the aluminum product itself.
Artificial methods are used to form an oxide film (AlO) on the surface of aluminum and its alloy products and apply different colors to improve the wear resistance of aluminum materials, prolong the service life and increase the appearance of color. The basic process of oxidation coloring is aluminum surface treatment, oxidation, coloring and subsequent hydration sealing, organic coating and other treatment processes.
The surface of aluminum maintains a layer of oxide film of 10-100 angstroms under natural conditions, and the artificial oxide film is controlled to a thickness of 0.5-250 microns according to different purposes. The methods of artificial membrane generation include chemical oxidation and electrochemical oxidation (ie, anodic aluminum).
The aluminum or aluminum alloy after surface purification treatment is chemically reacted in an oxidizing solution containing an oxidant and an activator to form an oxide film. The function of the activator is to partially dissolve the oxide film during the formation process, resulting in pores, so that the oxidation can continue and the oxide film can be thickened. There are many types of oxidizing solutions, often with chromate as the oxidant and carbonate as the active agent.
It is usually carried out in an electrolyte solution such as sulfuric acid, oxalic acid or chromic acid. With aluminum as the anode, lead and other metals as the cathode, under the action of the DC electric field, the anion (OH) moves to the anode, and the new oxygen is generated at the anode to interact with the aluminum as the anode to form an oxide film. The acid in the electrolyte can locally dissolve the oxide film and generate pores, so that the oxidation reaction can develop in depth. This method forms a porous structure on the surface of aluminum, which can be used for various coloring treatments and can be used as the bottom layer of spray paint. The coloring and coloring methods of the oxide film include chemical coloring, electrolytic coloring and natural coloring.
The oxidized aluminum material is immersed in an organic or inorganic dye solution, and the dye penetrates into the pores of the oxide film and is colored by chemical or physical action. The chemical coloring equipment is simple, the cost is low, and there are many kinds of colors, but the light resistance and corrosion resistance are poor, and it is only suitable for interior decoration.
The oxidized aluminum material is subjected to secondary electrolysis in a single metal salt or a variety of metal salt aqueous solutions. Under the action of an electric field, metal cations penetrate into the pores of the oxide film and deposit on the bottom of the pores, so that the oxide film produces bronze Color, brown, gray and red, cyan, blue and other tones.
A method of coloring aluminum while anodizing. There are alloy coloring method and solution coloring method. The alloy color development method is to control the composition of the aluminum alloy to obtain different hues; the solution color development method, also known as the electrolytic color development method, is to control the composition of the electrolyte and the electrolysis conditions to control the hue. In actual production, organic acid is generally used as the electrolyte for natural coloring, and a small amount of sulfuric acid is added to adjust the pH.