Corrosion Protection of Steel Using Nonanomalous Ni-Zn-P Coatings

A novel technique for obtaining nonanomalous Ni-Zn-P coatings with high Ni content ~74 wt % as compared to 15-20 wt % in the conventional plating method! has been developed. These coatings show promise as a replacement for Cd in sacrificially protecting steel. Ni-Zn-P coatings were deposited using an electroless method from a solution containing NiSO4 , complexing agent and ammonium chloride. Varying the concentration of ZnSO4 in the bath controls the final amount of Zn in the deposit. The Zn content in the coating was optimized based on the corrosion resistance of the final deposit. Coatings with 16.2 wt % Zn were found to display a potential of 20.652 V vs. SCE that is more electronegative to steel and hence can be used as a sacrificial coating for the protection of steel. Deposition parameters like pH and temperature have been optimized based on composition of the coating and the surface morphology. Corrosion studies in corroding media show that Ni-Zn-P coatings obtained using the electroless method show a higher barrier resistance and better stability as compared to cadmium coatings. © 2003 The Electrochemical Society. @DOI: 10.1149/1.1556015# All rights reserved.