Pulse plating of Ni-W alloys from model electrolytes

Pulse plating of nickel-tungsten alloys has been studied from two citrate ammonia based model electrolytes containing either an excess of nickel or an excess of tungsten. The alloy composition and current efficiency were determined for pulse periods ranging from 1 ms to 50 s at a constant duty cycle of 0.4. Deposits were analysed by X-ray fluorescence and by gravimetry. In the nickel rich electrolyte the rate of co-deposition of tungsten was found to be controlled by mass transport as previously observed with Ni-Mo alloys. In the tungsten rich electrolyte the tungsten concentration in the deposited alloys was the highest at short pulse periods. This suggests that the deposition rate of tungsten was affected by the rate of transport of nickel which is the highest at short times. As the pulse on time exceeded the transition time for nickel the current efficiency for alloy deposition dropped owing to hydrogen formation.