With the advancement of production, construction, and scientific and technological development, people's demand for the aesthetic appeal of products has also increased. Color aluminum powder is widely used in various industries such as gas, coatings, printing, and dyeing due to its bright colors, strong corrosion resistance, high insulation properties, fade resistance, metallic luster, and low cost. Its application has expanded the color range of metallic pigments significantly. For decorative purposes, colored aluminum powder has been applied in different fields. Research on coloring aluminum powders started overseas in the 1930s [1], and some successful experiences have been gained. In recent years, domestic reports [2] have also shown that anodizing can be used to prepare colored aluminum powder with a particle size of 320 mesh, although it is still at the experimental stage. In the 21st century, environmental awareness has grown, and water-based paints are showing promising development. The successful use of aluminum powder pigments in water-based systems has greatly improved the weather resistance of coatings. Using sol-gel methods, an inert silica film is coated on the surface of aluminum powder particles, and then an iron oxide film is deposited on the SiO₂/Al composite particles through liquid deposition. This has led to the successful development of colored aluminum powder, promoting the development of eco-friendly water-based coatings. Below, I will review three common methods for coloring aluminum powder. 1. **Anodizing to Prepare Colored Aluminum Powder** Anodizing is an electrochemical process where an aluminum oxide film is formed on the surface of aluminum powder through the anode reaction in an electrolyte. This oxide film is then colored using organic dyes or inorganic pigments. The aluminum powder is placed in a sulfuric acid electrolyte and continuously stirred so that it floats and semi-flows [5]. As the powder moves, it maintains contact with the anode, enabling the formation of a colored aluminum oxide film. During the anode reaction, oxygen from the anode reacts with aluminum atoms on the surface to form alumina, some of which is immediately hydrated to create hydrated alumina. This is how the aluminum oxide film forms. At the same time, the oxide film can dissolve in the sulfuric acid electrolyte, meaning both film formation and dissolution occur simultaneously during anodizing. Therefore, careful control of conditions is necessary to achieve a specific thickness of the oxide film. Hydrogen is produced during the cathode reaction, resulting in a porous structure of the oxide film, which enhances its adsorption capacity. The coloring of aluminum powder is a physical-chemical process. After anodizing, the aluminum powder is soaked in an organic dye solution, allowing the surface of the aluminum oxide film to absorb organic dye molecules. These molecules can bond with the aluminum oxide through covalent, coordination, or hydrogen bonds, leading to coloration of the oxide film. Several factors influence the formation of the oxide film during anodizing, and different coloring solutions produce varying results. Key factors include electrolyte concentration, reaction time, temperature, and the type of coloring solution. Experimental results show: - A sulfuric acid concentration of 5–10% is optimal for oxide film formation. - Anode current density affects the rate of film formation; higher current density leads to faster oxidation and looser films, which are more favorable for coloring. - Oxidation time should be between 60–90 minutes, with a temperature range of 25–35°C. - Thicker oxide films and higher concentrations of coloring solutions result in deeper colors. Coloring is typically done at 50–60°C for 20–40 minutes, with a pH of 4.5–6.0. 2. **Chemical Oxidation Method to Prepare Colored Aluminum Powder** This method involves placing aluminum powder in a weakly alkaline oxygen solution to form a thin oxide layer on its surface. The main chemical reactions during this process include: - 2Al + (3+x)H₂O → Al₂O₃·xH₂O + 3H₂ - Al₂O₃·xH₂O → Al₂O₃·xH₂O + (x−1)H₂O - Al₂O₃·H₂O → Al₂O₃ + H₂O - Al₂O₃·xH₂O + 2OH⁻ → 2[Al(OH)₄]⁻ + (x−3)H₂O - 2Al₂O₃ + 4OH⁻ + 6H₂O → 4[Al(OH)₄]⁻ These reactions help in forming a stable oxide layer that can be further colored.

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