Facile Tuning of Black Nickel Electroplating Bath for Optimal Performance

Black nickel plating is a decorative coating typically electrodeposited from an electroplating bath containing nickel and zinc cations. To ensure coating quality, chemical composition and pH value of plating bath should be closely monitored and maintained within the working ranges, especially when an inert anode is used. With plating by using an inert anode, both pH and bath composition will change and eventually drift out of the working range, leading to coating defects. In this paper, we propose a new methodology to tune the black nickel plating bath back to its usable range, by identifying the critical parameters and their limits, and give a recommended sequence for facile tuning to obtain optimal performance in terms of uniform black appearance. The recommended sequence of tuning is to first adjust the pH value, then the zinc concentration, and finally the nickel concentration when they reach their critical limits. The deposited black nickel coatings are characterized using sphere spectrophotometer and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy where the ratio of deposited zinc to nickel is found to be critical for obtaining a uniform and consistent black appearance.