NON-ANOMALOUS NI-ZN COATINGS FOR THE CORROSION PROTECTION OF STEEL - AS A REPLACEMENT FOR CADMIUM COATINGS

摘要

A novel technique for obtaining non-anomalous Ni-Zn coatings with high Ni content (72-wt percent as compared to 15-20 wt percent in conventional Zn-Ni deposition) has been developed. Ni-Zn coatings were cathodically deposited from alkaline sulfate electrolytes in the presence of complexing agents and additives. The Zn content in the coating was optimized based on the corrosion resistance and corrosion potential of the final deposit. The higher amount of nickel content in the deposit induces barrier properties and the presence of zinc helps to maintain the sacrificial nature of the coating. Corrosion potential of the optimized Ni-Zn alloy was -0.678 V vs. SCE. This low potential is a result of the decreased Zn content in the deposit. Deposition parameters such as applied potential and pH have been optimized based on composition of the coating and the surface morphology. Corrosion studies show that Ni-Zn coatings obtained using this method show a higher barrier resistance and better stability as compared to Cadmium coatings.