Electroless Nickel Coating for Corrosion Protection of Carbon Steel Rebars in Cement Mortar in Chloride Environment.

Corrosion protection of metallic structures is essential in aggressive environments, especially for reinforced concrete exposed to chlorides, which significantly accelerates deterioration of embedded steel. This study investigates electroless Nickel coatings on carbon steel rebars as a protective strategy to enhance corrosion resistance in such conditions. Plain carbon steel rebars were coated with nickel and its alloys, using an electroless deposition process. X-ray diffraction, scanning electron microscopy, optical profilometry, and atomic force microscopy were performed to analyze the presence of the Ni-P and Ni-P-W coatings’ phases, their morphologies, and topographies. X-ray diffraction confirmed the presence of Ni and Ni₃P phases for Ni-P and Ni-P-W coatings, whereas Scanning electron microscopy revealed uniform coatings and small island-like features. Energy dispersive spectroscopy analysis confirmed the elemental compositions of Ni-P and Ni-P-W in the respective coatings. Optical profilometry determined a surface roughness of ~0.7µm for Ni-P coating and ~3.1 µm for Ni-P-W coatings deposited at an optimized temperature of 85°C. To analyze the efficacy of the coatings, potentiodynamic polarizations were performed using a 3-electrode system, demonstrating improved corrosion resistance and indicating their potential application in marine infrastructure, coastal buildings, and chloride-contaminated construction sites. The results suggest that electroless Ni-based coatings can significantly improve the service life of steel-reinforced concrete structures in harsh environments.