Effect of electroless bath composition on the mechanical, chemical, and electrochemical properties of new NiP–C3N4 nanocomposite coatings

Abstract

C3N4 nanosheets, which have high hardness and excellent thermal and chemical stability, were used in the electroless nickel-phosphorous (NiP) bath to deposit the NiP–C3N4 nanocomposite coatings (NCCs) on API X100 carbon steel (CS). The effect of plating time, pH, surfactant type and C3N4 concentration on the mechanical, chemical, and electrochemical properties of the electroless NiP–C3N4 NCC were thoroughly stated. The morphology and structure of the NiP–C3N4 NCC were investigated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The results indicated that the alkaline electroless bath produced a NiP–C3N4 NCC with a microhardness 250 HV200 higher than that produced from the acidic one. A small addition of polyvinyl pyrrolidone (PVP) as a surfactant was sufficient for increasing the homogeneity of the nanocomposite coating and, consequently, its microhardness. The corrosion performance of the NiP–C3N4 NCC prepared at the optimum conditions was studied in a 3.5 wt% NaCl solution through electrochemical impedance spectroscopy (EIS) and Tafel analysis techniques. An electroless bath of 0.5 g L−1 C3N4 offered a nanocomposite coating with the highest microhardness and superior corrosion resistance. It has an efficiency of approximately 96% that decreased gradually, losing about only 2% after one week and 20% after one month of immersion time in the aforementioned chloride solution.