Pulse and direct current plating of Ni-W alloys from ammonia-citrate electrolyte

Abstract

The effect of the potential of deposition and electrode rotation rate on current efficiency and partial current density of nickel deposition from ammonia-citrate electrolyte with and without tungstate ions was investigated. In addition, the effect of pulse deposition parameters, such as frequency and ratio between pause and deposition time, t(p)/t(c), oil current efficiency and composition of Ni-W alloys was investigated. Partial current densities of tungsten and nickel deposition were calculated from experimental results and compared with those in direct current (dc) deposition at the same average current density, as well as with those calculated using theoretical equations for the pulse current (pc) deposition process controlled by mass transport. Obtained partial current densities of tungsten are in fair agreement with those predicted by theory in both cases, as a function of dimensionless pulse period and as a function of the t(p)/t(c) ratio. That confirms that the tungsten deposition process is controlled by mass transport. Dependences of the partial current densities of nickel deposition on the rotation rate as well as on the pc variables (frequency and pause to pulse ratio) were attributed to changes in surface concentration of ammonia and the pH.