[China Aluminum Network] With the development of production and construction, science and technology and cultural progress, people's requirements for the improvement of the 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, due to its bright color, strong corrosion resistance, high insulation, no fading, 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 prospects for development. The successful application of aluminum powder pigments in water-based systems has greatly improved the weather resistance of the coatings, using the sol-gel method 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 the liquid deposition method. 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. Anodic oxidation method for preparing color aluminum powder The anodization of the aluminum powder is an electrochemical process that generates an aluminum oxide film through the anode reaction of the electrolyte. This oxide film is colored by the color of organic dyes and inorganic pigments. The aluminum powder is placed in 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 while flowing, and remains in contact with the anode, making it easy to produce 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, which 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 are present at the same time in the anodizing process. Therefore, suitable conditions must be controlled in order 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, the concentration of the electrolyte, reaction time, temperature, coloring liquid and other factors 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, and the oxidation temperature is also 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 liquid. The thicker the oxide film, the easier it is to be colored; the greater the concentration of the coloring liquid, 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 solution 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. Preparation of color aluminum powder by chemical oxidation The chemical oxidation method is to put aluminum powder in a weakly alkaline oxygen solution to form a certain thickness of 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) Aluminum powder is oxidized under the action of a weakly alkaline aqueous solution to form amorphous hydrated alumina, which is gradually converted into AlO?HO and anhydrous AlO to form an effective colored layer, which is accompanied by dissolution at the time of film formation. Membrane reaction occurs. Therefore, it is necessary to control the appropriate process conditions so that the film formation reaction rate is faster than the film reaction rate to obtain an oxide film that meets the coloring requirements. The treated aluminum powder is placed in a direct light blue GL aqueous solution (1.5g/L). This coloring process is mainly the physical process of the adsorption of dyes, but also accompanied by a certain chemical effect, the dyed aluminum powder Through the surface treatment to increase the mechanical strength, but also to carry out lipophilic treatment [3], the dyed aluminum powder is dehydrated successively with ethanol, butanol, and then the surface of the aluminum powder is protected with stearic acid, which can extend the storage period [7] . Studies have shown that the pH of the oxidizing solution has an important influence on film formation and film thickness. If the pH is low, the film forming reaction rate will slow down and the pH value will be high, which will accelerate the aluminum oxide film on the aluminum powder surface. Dissolving, at the same time will cause the surface of the aluminum powder to undergo a strong corrosion and lose its luster. Experiments have shown that the suitable pH value range is 8-12; the change of the concentration of the coloring solution has a great influence on the coloring effect, and the concentration of the coloring solution is greater. The darker the aluminum powder surface color, but when the concentration is close to a certain value and continues to increase, the color of the aluminum powder surface no longer changes significantly. 3. Preparation of color aluminum powder by surface deposition An inert silica film was coated on the surfaces of the aluminum flake particles by a sol-gel method to prepare an aluminum powder paint for waterborne paints. The surface of the aluminum powder particles coated with silica is coated with an iron oxide film by a liquid phase deposition method to color the aluminum powder, thereby obtaining an environment-friendly color aluminum powder[8]. An inert silica film is coated on the surfaces of the aluminum flake particles by the sol-gel method of hydrolysis and polycondensation of tetraethyl orthosilicate to form a surface of the aluminum powder from hydrophobic to hydrophilic, and aluminum. The powder surface will not react with water. Hydrolysis of the tetraethylorthosilicate - the polycondensation process can be divided into three steps: the previous step is the hydrolysis of ethyl orthosilicate to form silicic acid and the corresponding alcohol; the second step occurs between the silicic acid or ethyl orthosilicate The condensation reaction forms a mixture in a colloidal state; the third step is that the formed oligomer continues to polymerize to form a three-dimensional lattice structure of silicon. Under the action of the catalyst, ethyl orthosilicate undergoes a hydrolysis-condensation reaction to form a hydrated silica precipitate, which is deposited on the surface of the aluminum flake particles and dehydrated to form silica. The iron oxide film is coated by a liquid-phase deposition method to hydrolyze the iron oxide to form a precipitate of ferric hydroxide, which is deposited on the surface of the substrate and then subjected to firing to obtain an iron oxide film. The reaction principle is as follows: FeCl+3HO=Fe(OH)+3HCl 2Fe(OH)=FeO+3HO The preparation process is as follows: a certain amount of flake aluminum powder is weighed and dispersed in a certain volume of isopropyl alcohol, and after ultrasonic dispersion, it is poured into a three-necked flask and placed in a constant temperature water bath at 40° C. to stir, and a certain amount is taken. Ethyl orthosilicate was added to the flask, and the corresponding amounts of ammonia water and distilled water were measured and mixed uniformly. The mixture was placed in a dropping funnel and connected to a three-necked flask. The drip rate of the dropping funnel was adjusted to approximately 1 drop/second. Continuous stirring, the concentration of ethyl orthosilicate was controlled to be 0.05mol/L-0.1mol/L, the ratio of water to silicon R was 16, and the concentration of catalyst ammonia was 0.02mol/L-0.2mol/L. After the reaction, centrifugal washing was performed. Drying gives silica-coated aluminum flake. Weigh a certain amount of aluminum flake particles modified by silica coating, dispersed in a certain volume of distilled water, after ultrasonic dispersion into a three-necked flask, placed in a constant temperature water bath at 80 ° C stirring, said Take a certain amount of anhydrous ferric chloride, dissolve in distilled water, and put it in a dropping funnel. Connect it to a three-necked flask. Measure a certain volume of ammonia, pour into another drop, and connect it to a three-neck flask. Adjust two The drip rate of the dropping funnel was approximately 1 drop/second. Stirring was continued. After the reaction, the sample was centrifuged, washed twice, dried in an oven at 100° C., and placed in a Mafu furnace at 500° C. for 2 hours. , you can get color aluminum powder. 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Aluminum powder coloring method