Copper ion is one of the more common impurities in bright nickel plating. The plating solution is contaminated by Cu2+, which will cause poor brightness in the low current density area of the plated parts. Excessive Cu2+ will also cause the brittleness of the coating to increase and the disadvantages of poor bonding. In bright nickel plating bath, ρ(Cu2+) should be less than 0.01g/L. There are several ways to remove Cu2+ in the plating solution.
1) Electrolysis method. That is, the method of depositing Cu2+ in the plating solution on the cathode plate with low current density. The cathode plate used for processing has three types: corrugated plate, sawtooth plate and flat plate. When the corrugated plate is electrolyzed with a certain current, the Jκ range on the cathode plate is wider, the Jκ at the peak is larger, and the Jκ at the trough is smaller, so Cu2+ and other metal impurities can be deposited at the same time to achieve the purpose of removing multiple impurities. The zigzag cathode plate is affected by the tip effect. During the electrolysis process, Ni2+ and Cu2+ are deposited at the same time, resulting in an increase in the loss of nickel salt in the plating solution. Different Jκ can be used with flat cathode to achieve the purpose of selectively removing metal impurities. According to experience, when Jκ is 0.5A/dm2, it is beneficial to the precipitation of Cu2+ at the cathode.
Regardless of which type of cathode is used for electrolysis treatment, several issues should be paid attention to: a. During long-term electrolysis treatment, the electrolytic plate should be cleaned regularly to prevent the loose coating on the electrolytic plate from falling off and re-contaminating the plating solution; b. Using cathode movement or air Stirring can improve the treatment effect; c. The anode plate used in the electrolysis treatment must be a high-quality nickel anode plate, otherwise it will affect the treatment effect and cause unnecessary waste.
2) Chemical precipitation agent method. Commonly used QT copper removal agent, the main component of the precipitation agent is ferrocyanide, which forms copper ferrocyanide precipitate with Cu2+ in the plating solution, and then filters the precipitate to achieve the purpose of removing copper impurities. The disadvantage of this method is the need for precision filtration, which is time-consuming.
3) Chelating agent method. The chelating agent is generally an organic substance with aromatic ring or heterocyclic structure. It forms a chelate with Cu2+ in the plating solution. Because the chelate and Ni2+ co-deposit during electrolysis, the ρ(Cu2+) in the plating solution will not rise too much. high. This method is simple and easy to implement, and is currently a better and effective method for treating impurities in the nickel plating solution. High-quality chelating agents must be selected during application, especially to ensure that they do not adversely affect the coating.
