The effects of pH and temperature on Ni-Fe-P alloy electrodeposition from a sulfamate bath and the material properties of the deposits

The effects of pH and temperature on Ni-Fe-P alloy electrodeposition from a Ni sulfamate bath and the material properties of the deposits were investigated. Electrochemical behavior was evaluated by potentiostat and impedance spectroscopy and the material properties of the deposits were determined using Inductively Coupled Plasma, Scanning Electron Microscope, X-Ray Diffractometer. Nyquist plots of the impedance spectra of Ni-Fe-P deposition were characterized by a capacitive loop and an inductive loop similar to those obtained for Ni-Fe deposition, while the mechanism of Ni-Fe-P deposition was normally controlled by the introduction of P unlike abnormal Ni-Fe deposition. Sulfur content of the deposits from the Ni sulfamate bath increased with the pH of the electrolyte and decreased at an elevated temperature of electrolyte up to 60 °C. As the pH of the electrolytes increased from 1 to 3.5, current efficiency, grain size and stresses in the deposits increased. It seems to be related to the decrease of the hydrogen evolution reaction and hydrogen absorption, and the increase of NH4 added into the bath in order to control the pH. When the temperature of the electrolyte increased from 60 to 70 °C, the increase of the value of Re and a rapid decrease in the crystallinity appeared due to the transformation of sulfamate into impurities, fairly consistent with the results of the sulfur contents of the deposits.