Nickel Plating Formulation Additives and Processes
The Watt-type formula has only three basic components: nickel sulfate, nickel chloride, and boric acid. This is because the main salt concentration of the Watt-type nickel plating solution is relatively high, the bath temperature is also relatively high, the main salt concentration is high, and the conductivity of the plating solution is improved. , The temperature of the bath is increased, the moving speed of various ions in the plating solution is accelerated, the resistance is reduced, and the conductivity is also increased, so it has better covering ability and dispersion ability.
1) Nickel Sulfate Nickel sulfate is the main salt in the electrolyte and supplies Nr. The content of nickel sulfate in production ranges from 100 to 3509/L. Under normal circumstances, the electrolyte with low nickel sulfate content has better dispersibility, and the coating has fine crystals and is easy to polish. However, its cathode current efficiency is low, allowing a lower cathode current density to be used, and thus a slower deposition rate. The electrolyte with higher nickel sulfate content can use a higher cathode current density, the deposition rate is accelerated, and the color of the coating is uniform, but the dispersing ability of the electrolyte is reduced, the coating is glossy, and the amount of electrolyte carried out is large. Therefore, electrolytes with high nickel sulfate content are generally only suitable for rapid nickel plating and bright nickel plating.
2) Chloride Nickel chloride or sodium chloride is a conductive salt and an anode activator and also has the effect of improving the dispersing ability of the electrolyte. Because sodium chloride is widely available and inexpensive, it is a commonly used anode activator in common nickel-plating electrolytes. In general bright nickel plating, in order to reduce the adverse effects of sodium ions (reduce the upper limit of cathode current density), nickel chloride is often used as an anode activator. Nickel chloride can also supplement the consumption of metallic nickel ions in the electrolyte. The content of chloride should be controlled between 7209/L (calculated as sodium chloride). When the content is too low, the anode is easily passivated, so that the content of nickel in the electrolyte decreases, and the current efficiency and deposition rate decrease accordingly. If the content is too high, it will cause the anode to dissolve too quickly, which will easily cause the coating to have coarse crystals and burrs, and at the same time, the internal stress of the coating will increase, thereby reducing the quality of the coating, and it is easy to corrode the electroplating tank and its auxiliary equipment.
3) Boric acid is a buffering agent in the nickel plating electrolyte of the electroplating solution formula, which plays a role in stabilizing the pH of the electrolyte. Boric acid has a good buffering effect in weakly acidic solutions, so boric acid is an important component in common nickel plating electrolytes (pH is 4-6). The strength of the buffering effect of boric acid is related to its content. When its content is higher than 319/L, its buffering effect is more significant. If its content continues to increase, a part of boric acid will be converted into tetraboric acid.
4) Sulfate sodium sulfate and magnesium sulfate can improve the conductivity of the plating solution and reduce the resistance, thereby improving the covering ability and dispersion ability of the plating solution. When sodium sulfate is used as a conductive salt, the content of sodium ions in the electrolyte is higher, although the cathode polarization is increased, which is conducive to the discharge of hydrogen ions, and the pH of the cathode region rises faster, resulting in the formation of hydroxide or basic salt. The precipitation deteriorates the quality of the coating. Therefore, sodium sulfate or other sodium salts should be added as little as possible to the electrolyte, and not in the electrolyte for rapid nickel plating. When magnesium sulfate is added, the coating can be naturally soft. These inorganic salts function as auxiliary additives.
5) Sodium dodecyl sulfate is an anionic surfactant, and its molecular structure contains a hydrophilic group (sulfate) and a hydrophobic group (long-chain alkyl), which reduces The liquid-gas and liquid-solid interfacial tension can be added to the nickel plating solution of the electroplating solution to reduce the surface tension of the plating solution so that the hydrogen bubbles are easily precipitated and will not stay on the surface of the cathode and cause pinhole pitting in the plating layer. So-called anti-pinhole agent (or wetting agent).
