Effect of Phosphorus on Anodic Dissolution and Passivation of Nickel in Near-Neutral Solutions

Abstract

Anodic dissolution of nickel, electroless nickel deposits with 2.9 and 12.3 wt% P, and amorphous Ni₈₁P₁₉ alloy was examined in sodium hydroxide, sulfate, borate, and chloride solutions at 25 C. Phosphorus enhanced the anodic dissolution of nickel; however, the dissolution decreased as the phosphorus content rose from 2.9 to 12.3%. Auger electron spectroscopy (AES) analysis indicated that oxide-passivating films on the NiP materials were thinner than those on nickel, while scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDXA) examinations revealed the precipitation of phosphorus-containing corrosion products at the surface of the NiP materials. It is suggested that the detrimental effect of phosphorus on corrosion resistance of nickel is associated with lower protectiveness of the oxide film, whereas the inhibitive effect at the higher phosphorus contents can be associated with the formation of phosphates.