Under the action of weak alkaline aqueous solution, the surface of chemical raw material aluminum powder is oxidized to form amorphous hydrated alumina, which forms an effective coloring layer. At the same time of film formation, film dissolution reaction occurs. Therefore, it is necessary to control the appropriate process conditions, so that the film-forming reaction rate is faster than the film-dissolving reaction rate, in order to obtain an oxide film that meets the coloring requirements.
The treated aluminum powder is placed in a direct lightfast turquoise blue GL aqueous solution for coloring. This coloring process is mainly a physical process of adsorbing dyes, and it is also accompanied by a certain chemical action. The dyed aluminum powder increases its mechanical strength through surface treatment. At the same time, lipophilic treatment is also required, the dyed aluminum powder is dehydrated with ethanol and butanol successively, and then stearic acid is used to protect the surface of the aluminum powder, which can prolong the storage period. Studies have shown that the pH value of the oxidizing solution has an important influence on whether the film can be formed and the thickness of the film. If the pH value is low, the film forming reaction speed will slow down, and the pH value will be high, which will accelerate the dissolving of aluminum oxide film on the surface of the aluminum powder, at the same time, the surface of the aluminum powder will suffer from strong corrosion and lose its luster. The experiment shows that the suitable pH value range is 8~12; the change of the coloring solution concentration has a great influence on the coloring effect. The darker the color of the surface of the aluminum powder, but when the concentration approaches a certain value and continues to increase, the color of the surface of the aluminum powder no longer changes significantly.
The anodic oxidation of chemical raw material aluminum powder (7429 90 5) is an electrochemical process in which an aluminum oxide film is formed through the anodic reaction of the electrolyte. This oxide film is colored by adsorbing the color of organic dyes and inorganic pigments. The aluminum powder is placed in the sulfuric acid electrolyte and stirred continuously, so that the aluminum powder is in a floating and semi-floating state, and the anode is in contact with the anode at any time while flowing, and the state of being kept out of contact with the anode is maintained, so that an aluminum oxide film that is easy to be colored is formed on the surface of the aluminum powder. The anode reaction is the reaction of the nascent oxygen precipitated by the anode and the aluminum atoms on the surface of the aluminum powder to synthesize alumina, and part of the alumina is immediately hydrated to synthesize hydrated alumina, which is the formation process of the alumina film. At the same time, the aluminum oxide film can be dissolved by the sulfuric acid electrolyte, so there are both film-forming reaction and film-dissolving reaction in the anodic oxidation process. Therefore, appropriate conditions must be controlled to form an aluminum oxide film with a certain thickness. Hydrogen is generated in the cathode reaction, so the formed alumina film has the characteristics of porous and loose, which is beneficial to the enhancement of adsorption capacity.
Aluminum powder coloring is a physical and chemical process. The anodized aluminum powder is soaked in an organic dyeing solution, so that the oxide film on the surface of the aluminum powder adsorbs organic dye molecules, and the aluminum oxide molecules in the aluminum oxide film can interact with organic dyes. Molecules combine in the form of covalent bonds, coordination bonds or hydrogen bonds to form complexes, thereby coloring the oxide film.
A layer of inert silica film is coated on the surface of flake aluminum powder particles by sol-gel method to prepare aluminum powder pigments for water-based coatings. A layer of iron oxide film is coated on the surface of the silica-coated aluminum powder particles by a liquid deposition method, so that the chemical raw material aluminum powder is colored, and an environment-friendly colored aluminum powder is obtained. The surface of flake aluminum powder particles is coated with an inert silica film by the sol-gel method of hydrolyzed polycondensation of ethyl orthosilicate to form a film, so that the surface of the aluminum powder changes from hydrophobicity to hydrophilicity. The powder surface will not react with water.
