What are the Functions and Uses of Caustic Soda Flakes NaOH in the Electroplating Industry?
Sodium hydroxide (caustic soda flakes) has multiple functions in electroplating, and its main uses include degreasing and rust removal, adjusting the pH value of the plating solution, and passivation treatment. Details are as follows:
1. Pretreatment: oil removal and rust removal
①Chemical degreasing
Sodium hydroxide is a strongly alkaline substance that plays a key role in chemical oil removal. It can saponify oils and fats, breaking them down into water-soluble fatty acid salts and glycerol. For example, in the case of oil on the steel surface, sodium hydroxide will react with animal and vegetable oils to form soap-like substances, which can be dissolved in alkaline solutions, to remove oil effectively. In general, in alkaline degreasing fluid, the concentration of sodium hydroxide can be about 20-50g/L according to the severity of oil pollution and other factors.
②Electrochemical degreasing
In electrochemical degreasing, sodium hydroxide is used as one of the main components of the electrolyte. When the workpiece is used as the cathode, under the action of current, hydrogen ions get electrons on the cathode surface to produce hydrogen. The hydrogen production process will produce mechanical stripping of oil, and hydroxide ions in sodium hydroxide solution will also promote the saponification reaction of oil. Moreover, sodium hydroxide can ensure the strong alkalinity of the electrolyte, maintain a suitable electrochemical oil removal environment, and usually the pH value of the electrolyte is maintained between 12-14.
③Rust removal auxiliary
In some rust removal solutions, sodium hydroxide can be used as an auxiliary component. It can react with the iron oxide and other components in the rust, such as reacting with ferric oxide to produce substances such as sodium ferrate, which can be dissolved in the solution to help remove rust, and can regulate the pH value of the descaling solution to prevent excessive corrosion of the metal substrate caused by too strong an acidity.
2. Electroplating process: adjust the pH value of the plating solution
Many plating solutions require a specific pH range for plating to be effective. Sodium hydroxide is a commonly used pH regulator. For example, in alkaline copper plating baths, in order to maintain stable deposition of copper ions on the surface of the plated parts, the pH of the plating bath needs to be kept within a suitable alkaline range, usually around 12-13. When the pH value of the plating solution decreases, sodium hydroxide solution can be added to raise the pH value to ensure that the copper ion deposition reaction can be carried out smoothly. Meanwhile, in other plating processes such as nickel plating and galvanizing, sodium hydroxide can also be used to a certain extent to regulate the pH value of the plating solution, but care needs to be taken to avoid the introduction of impurities that affect the quality of plating.
3. Post-plating treatment: passivation treatment
Sodium hydroxide can be used as one of the components of the passivate solution during the passivation process after plating. For example, in the passivation treatment of zinc coatings, the alkaline passivation solution contains sodium hydroxide. This passivation solution can form a passivation film on the surface of the zinc coating and improve the corrosion resistance of the zinc coating. The passivation film is formed by the chemical reaction between the zinc and the components in the passivation solution, in which sodium hydroxide can regulate the pH value of the passivation solution and participate in the reaction process, so that the passivation film is more uniform and dense, which strengthens the zinc coating's resistance to the environment and prolongs the service life of the coating.
