A Comparative Study of the Electrochemical and Microstructural Characteristics of Optimized Electroless Ni-P-SiO2 Nanocomposite Coatings Using a Sulphamate Bath on Brass Alloy

In this study, the anti-corrosion behaviour of coated samples from nickel sulphamate bath with different amounts of SiO 2 nanoparticles (NPs) was investigated using potentiodynamic (DC) polarization and electrochemical impedance spectroscopy (EIS) test in a 3.5 wt.% NaCl solution. Next, the coating morphology and distribution of SiO 2 NPs were evaluated using field emission scanning electron microscopy (FESEM). Also, the coatings’ structure and chemical composition were obtained using x-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS), respectively. Finally, the microhardness of the nanocomposite coatings was measured using the Vickers microhardness test, and the topography of optimum Ni-P and Ni-P-SiO 2 coatings was evaluated by atomic force microscopy (AFM). According to results, the microhardness of the nanocomposite coatings was increased compared to the bare sample. In contrast, the roughness of the optimized Ni-P-SiO 2 (1 g/L) nanocomposite coating was decreased compared to optimized Ni-P coating. The SiO 2 NPs amount affected the phosphorus content (9–15 wt.% P) and created coatings with semi-crystalline and fully amorphous structures. Overall, the best anti-corrosion behaviour was obtained in optimized Ni-P-SiO 2 (1 g/L) nanocomposite coating (Rp = 50,709 Ω cm 2 and i corr = 0.45 μA/cm 2 ), which significantly improved compared to the bare sample (Rp = 3687 Ω cm 2 and i corr = 2.72 μA/cm 2 ).