[China Aluminum Industry Net] With the development of production and construction, scientific and technological and cultural progress, people's requirements for the beautification of goods have also been correspondingly increased. The color aluminum powder is widely used in various departments such as gas, coating, printing and dyeing and other industrial productions for its bright colors, strong corrosion resistance, high insulation, not fade, strong metallic luster and low price. The application opens up a wide range of ways to broaden the color range of metallic pigments.

For decoration purposes, colored aluminum powder has been applied. Research on the coloring of aluminum powders has been started overseas since the 1930s [1] and some successful experiences have been obtained. In recent years, there are also reports in the country [2] that anodizing can be used to prepare colored aluminum powder with a particle size of 320 mesh, but it is still in the experimental stage. In the 21st century, people’s awareness of environmental protection has been continuously enhanced, and water-based paints have shown good development prospects. The successful application of aluminum powder pigments in water-based systems has greatly improved the weatherability of coatings, using sol-gel methods in sheet aluminum. An inert silica film is coated on the surface of the powder particles, and a layer of iron oxide film is deposited on the surface of the SiO/Al composite particles by liquid deposition. The aluminum powder is successfully developed into a colored aluminum powder, and the water-based environmental protection coating is promoted. development of.

Below I will review the three methods of coloring.

1. Anodizing to prepare colored aluminum powder Anodizing of aluminum powder is an electrochemical process that generates an aluminum oxide film through the anode reaction of an electrolyte. This oxide film is colored by the color of organic dyes and inorganic pigments. The aluminum powder is placed in a sulfuric acid electrolyte and continuously stirred to make the aluminum powder float and semi-floating[5]. The aluminum powder is in contact with the anode at any time while flowing, and remains in contact with the anode, making it easy to form on the surface of the aluminum powder. Colored aluminum oxide film. The anode reaction is the reaction between the initial oxygen precipitated from the anode and the aluminum atoms on the surface of the aluminum powder to synthesize alumina, and part of the alumina is instantly hydrated to form hydrated alumina. This is the formation process of the aluminum oxide film. At the same time, the aluminum oxide film can be dissolved by the sulfuric acid electrolyte, so the film forming reaction and the film-dissolving reaction occur simultaneously in the anodizing process. Therefore, appropriate conditions must be controlled to form a certain thickness of the aluminum oxide film. Hydrogen is generated in the cathode reaction, so that the formed aluminum oxide film has a porous feature, which is advantageous to the enhancement of the adsorption capacity.

The coloring of aluminum powder is a physical chemical process. The anodized aluminum powder is soaked in an organic dyeing liquid to make the surface of the aluminum oxide film adsorb an organic dye molecule, and the aluminum oxide molecule in the aluminum oxide film can be combined with an organic dye. The molecule forms a complex in the form of a covalent bond, a coordination bond, or a hydrogen bond, thereby coloring the oxide film.

Anodic oxidation In the process of forming aluminum oxide film on the surface of aluminum powder particles, there are many factors affecting the film formation, and different coloring liquids lead to different coloring effects. Therefore, factors such as electrolyte concentration, reaction time, temperature, and coloring liquid should be considered. Impact. The results show that: (1) the concentration of sulfuric acid electrolyte has a significant impact on the formation of oxide film. The sulfuric acid concentration is too low, the conductivity of the electrolyte is not strong, the film formation rate of alumina is slow, the concentration of sulfuric acid is too high, and the resulting oxide film is dissolved. The preferred experimental conditions: the concentration of sulfuric acid electrolyte should be 5-10% . (2) The anode current density is proportional to the alumina film formation rate. Since the aluminum powder contacts the anode at a certain moment, the anode current density is greater, which is more conducive to aluminum powder discharge at the anode, and the larger the anode current density, the more oxidation occurs. The looser the aluminum film, is conducive to coloring. Experiments have shown that anodic oxidation is carried out in 7% sulfuric acid electrolyte, and the general control current density is 5 A/dm 2 or more, and the voltage should not be less than 40 V. (3) In the anodizing process, only after a certain period of time can the aluminum powder be fully contacted with the anode. Experiments have shown that the oxidation time is suitable for 60-90 minutes while the oxidation temperature is maintained at 25-35°. C is appropriate. (4) Coloring on the aluminum oxide film is related to the degree of difficulty in coloring and the thickness of the oxide film and the concentration of the coloring solution. The thicker the oxide film, the easier it is to be colored; the greater the concentration of the coloring solution, the easier it is to color and the color The deeper [4]. Therefore, in the coloring process, a thicker coloring liquid is generally used. Experiments show that the concentration of the coloring liquid is adjusted according to the depth of the desired color. At the same time, the coloring liquid temperature is 50-60°C, the coloring time is 20-40 minutes, and the pH is 4.5-6.0.

2. Chemical oxidation method to prepare color aluminum powder chemical oxidation method is to put aluminum powder in a weak alkaline oxygen solution, the formation of a certain thickness of the oxide film on the surface. During the oxidation of aluminum powder, the following main reactions occur:

2Al+(3+x)HO=AlO•xHO+3HO(1)

AlO•xHO=AlO•xHO+(x-1)HO(2)

AlO•HO=AlO+HO(3)

AlO•xHO+2OH=2(Al(OH))+(x-3)HO(4)

2AlO+4OH+6HO=4(Al(OH))(5),

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