Effect of surfactants on the coating properties and corrosion behaviour of Ni–P–nano-TiO2 coatings

• Ni–P–nano-TiO2 composite was deposited on mild steel by the electroless method.
• Effects of anionic and cationic surfactants in the deposits were analysed.
• In the presence of DTAB, uniform distribution of TiO2 particles was obtained.
• At CMC value, DTAB had higher deposition rate and TiO2 content than SDS.
• Corrosion protective ability of Ni–P–nano-TiO2 reached almost four times than Ni–P deposit.

In this paper, the effects of two different types of surfactants on the properties of Ni–P–TiO2 coating on low carbon steel substrate were investigated. Sodium dodecyl sulphate (SDS) — anionic surfactant and dodecyl trimethyl ammonium bromide (DTAB) — cationic surfactant were used for the deposition. Deposits were characterized by a high resolution scanning electron microscope (HR-SEM), an energy dispersive X-ray spectrometer (EDS), and X-ray diffraction (XRD) to study the surface morphology, composition and crystal structure of the coatings respectively. In addition, the influence of surfactants on the corrosion behaviour of Ni–P–TiO2 coatings was also examined using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% sodium chloride solution. The results showed that at an optimum concentration of cationic surfactant DTAB, uniform distribution of TiO2 particles with no defects was observed. The corrosion properties were improved by the incorporation of TiO2 particles in the Ni–P matrix. The increase in corrosion resistance of the Ni–P-TiO2 coatings significantly depends on the surfactant and its concentration.