Electroless Nickel Coating for Corrosion Protection of Carbon Steel rebars in cement mortar exposed to Chloride environment

Abstract

Corrosion is one of the common and natural processes that occur mainly in metals and low-carbon steel is one of the most susceptible to corrosion it is one of the main materials used in the construction industry in coastal areas where deicing of salt used this low-carbon steel gets affected because of occurrence of localized corrosion of chloride ions. To protect such sort of corrosion coatings is one of the method and electroless deposition method of Nickel Phosphorus and Nickel Phosphorus Tungsten alloy is considered one of the viable solutions for industrialists and researchers in comparison with hard chromium coating, the electroless deposition method applied on the rebars in cement mortar by developing a coating bath. 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 coating's phase, morphology, and topography. Potentiodynamic Polarization and Linear Polarization Resistance were performed by applying a voltage window of ± 0.25 Volts versus Open Circuit Potential both Polarization curve results and Linear polarization resistance results were consistent with each other, with 95% + corrosion rate improvement observed for Ni-P and Ni-P-W coated rebar in comparison with a bare sample of rebar for potentiodynamic polarization curves and for Linear polarization resistance at an optimized temperature of 85°C and X-ray diffraction confirmed the presence of Ni3P phase and NiW3P4 for Ni-P and Ni-P-W coating, SEM micrographs confirm the uniform deposition of a coating with the presence of small nodules and also EDX weight percentage of Ni-P and Ni-P-W coating lies within 4 % - 7% Phosphorus element range that gives medium phosphorus range that given better corrosion resistant properties, optical profilometry gives surface roughness of 0.7µm for Ni-P coating and 3.11 µm for Ni-P-W at an optimized temperature of 85°C that got reduced in comparison with surface roughness of bare sample.