Metal surface chemical oxidation technology
Chemical oxidation of metal surfaces is a treatment process that improves the surface properties of metals by immersing the metal workpiece in a specific chemical solution and using a chemical reaction to form a dense oxide film on its surface. Unlike electrochemical oxidation, this technology does not require an external power source and relies solely on the spontaneous reaction between the chemical solution and the metal surface to form the oxide film, making it easy to operate and low-cost. The main components of the oxide film are metal oxides or hydroxides, and its thickness is usually between 0.5 and 10 microns. Although thin, it can effectively isolate the metal substrate from contact with external corrosive media and improve corrosion resistance. At the same time, the oxide film can also enhance the bonding strength between the metal surface and coatings and adhesives, and is often used in the pretreatment stage of processes such as painting and bonding. In addition, some oxide films are also decorative. For example, the chemical oxide film of aluminum can appear in different colors to meet appearance requirements.
The core of metal surface chemical oxidation technology is to select appropriate chemical solutions and process parameters to control the formation speed, thickness and performance of the oxide film. Commonly used chemical oxidation solutions vary depending on the type of metal, mainly including alkaline oxidation solutions, acidic oxidation solutions and neutral oxidation solutions. Alkaline oxidizing solutions are mostly composed of sodium hydroxide, sodium carbonate, sodium nitrite, etc., and are suitable for oxidation treatment of metals such as steel and copper; acidic oxidizing solutions contain chromic acid, phosphoric acid, sulfuric acid and other ingredients, and are often used for oxidation of amphoteric metals such as aluminum and zinc; neutral oxidizing solutions are mainly composed of phosphates, silicates, etc., and are suitable for surface treatment of various metals. In terms of process parameters, solution temperature, treatment time, and pH value have a significant impact on the quality of the oxide film. For example, increasing the temperature will accelerate the reaction rate, but too high a temperature may cause the oxide film to become loose; if the treatment time is too short, the film layer will be too thin, and if the treatment time is too long, the film layer may fall off.
The chemical oxidation process for metal surfaces typically consists of three stages: pretreatment, chemical oxidation, and post-treatment. Pretreatment is crucial for ensuring the quality of the oxide film. It involves removing impurities such as oil, rust, and scale from the workpiece surface. Common methods include chemical degreasing, pickling, and mechanical polishing. Workpieces with significant oil contamination require degreasing, which can be done by soaking in an alkaline solution or wiping with an organic solvent. Rusted metals require pickling to remove the rust and reveal a clean metal surface. The chemical oxidation stage involves immersing the pre-treated workpiece in an oxidizing solution, which reacts at a specific temperature for a period of time to form an oxide film on the surface. Post-treatment includes cleaning, drying, and sealing. Cleaning removes residual chemical solution from the surface, preventing subsequent corrosion. Drying requires low temperatures to prevent cracking of the oxide film. Sealing treatments (such as oiling or painting) further enhance the corrosion resistance of the oxide film.
Chemical oxidation technology for metal surfaces has many advantages, making it widely used in industrial production. First, the process is simple and does not require complex equipment, making it suitable for small and medium-sized enterprises. Second, it has low energy consumption and is independent of electricity, meeting energy-saving requirements. Third, it has a wide range of applications and can process workpieces of various shapes, especially complex structural parts. Finally, the oxide film forms quickly, usually within a few minutes to tens of minutes, with high production efficiency. However, this technology also has certain limitations. For example, the oxide film is thin and has limited corrosion resistance, making it difficult to meet the requirements of long-term outdoor use or in harsh environments. The oxide film also has low hardness and poor wear resistance, making it unsuitable for friction conditions. In addition, some chemical oxidation solutions contain toxic substances such as chromates, which pollute the environment and need to be properly handled.
With the increasing awareness of environmental protection and the advancement of technology, metal surface chemical oxidation technology has made significant progress in environmental protection and functionalization. The development of new environmentally friendly oxidation solutions has reduced the use of toxic substances, such as chromium-free oxidation solutions and low-toxic phosphate oxidation solutions, thereby reducing harm to operators and the environment. At the same time, the development of functional oxide films has expanded their application areas. For example, by adding nanoparticles, the hardness and wear resistance of the oxide film can be improved; by adjusting the oxidation process parameters, the oxide film can have special functions such as conductivity and thermal insulation. In addition, the combined application of chemical oxidation and other surface treatment technologies (such as electroplating and coating after chemical oxidation) can give full play to their respective advantages and further improve the performance of the metal surface. In the future, metal surface chemical oxidation technology will continue to develop in the direction of environmental protection, high efficiency and multifunctionality, and play a more important role in the fields of automobiles, electronics, construction and so on.
