Reducing Residue In Nickel Electroplating Operations

Abstract

Most commercial nickel electroplating cells use soluble nickel anodes that generate some amount of residue, typically nickel fines and impurities that detach from the bulk during normal operation. Build-up of residue over time leads to failure of the anode and necessitates shutdown and cleaning of the anode assembly before plating can resume. Of specific concern is the increase in plating residue from anode current densities less than 1 A dm-2 because as a consequence of cell design, the anode will often operate at a much lower current density than the cathode. The electrodissolution of carbonyl nickel pellet, a commercial product for the electroplating market has been examined using electrochemical methods, coupled with in situ and ex situ microscopy to better understand the formation of anode residue. Applied potentials above the pitting potential resulted in current densities greater than 3 A dm-2 and pit interiors that were markedly different than those of galvanostatic pits at 0.4 A dm-2. Current transients for potentiostatic pulses above the pitting potential were analyzed and the transition times for stages of pit growth were identified. A potential pulse sequence was then used to execute highly controlled cycles of pit nucleation, growth and repassivation that resulted in anode surface morphologies different than those treated galvanostatically. Potential pulse dissolution with a pulse time of 50 ms and 45% duty cycle gave a current density of 0.33 A dm-2 and resulted in more than a six-fold decrease in anode residue when compared to galvanostatic dissolution.