Corrosion behavior of Ni-P-nano-Al2O3 composite coating in the presence of anionic and cationic surfactants

Ni-P-nano-Al 2 O 3 composite coatings on the mild steel were obtained by adding Al 2 O 3 nanoparticles into the traditional electroless Ni-P bath. Cationic and anionic surfactants were used to prevent the agglomeration of the incorporated nano-Al 2 O 3 . Surface morphology , compositions and microstructures of the coating were studied using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD) as well. Corrosion resistances of the modified mild steel samples were evaluated in 3.5   wt.% NaCl solution by electrochemical impedance spectroscopy (EIS). The results showed that compared to the pure Ni-P coating on the mild steel, the coating formed in the bath with 6   g/L nano-Al 2 O 3 performed the highest resistance. Under the optimal conditions, the adding of anionic surfactant (SDBS) improved the anti-corrosion performance of the samples further, while the addition of cationic surfactant led to a worse corrosion resistance. The potential mechanism was that anionic surfactant molecules would contact with active sites of Ni-P composite coating and nano-Al 2 O 3 in the bath, which would improve the dispersion of nano-Al 2 O 3 , thus leading to a homogeneous coating with better corrosion resistance.