The Electrochemical Behavior of Electroless Plated Ni‐P Alloys in Concentrated NaOH Solution

Electroless Ni‐P deposits with phosphorus content ranging from 4.8 to 12.8 weight percent were examined using potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) techniques to characterize the effect of phosphorus on the corrosion behavior of electroless nickel‐plated mild steel in deaerated 40 solution. Anodic polarization of the electroless Ni‐P alloys in caustic solution shows that the passive current density decreases with increasing phosphorus content in the deposits. At an applied potential of −1.2 V vs. saturated calomel electrode (VSCE) (close to their Ecorr), EIS data indicate that the for Ni‐P alloys in solution increases with increasing phosphorus content. X‐ray photoelectron spectroscopy (XPS) results suggest that the primary constituent formed on the Ni‐P surface after EIS measurement in 40 solution at an applied potential of −0.4 VSCE (in the passive region) is , which is responsible for the passivity of the Ni‐P alloys. The polarization resistance of Ni‐P alloys in solution at −0.4 VSCE also increases with increasing phosphorus content.