Magnetic oxidized multi-walled carbon nanotubes for activating anti-corrosion phosphate coatings formation on DP steel surface

Magnetic oxidized multi-walled carbon nanotubes (magnetic o-MWCNTs) possess excellent ion adsorption properties. Since magnetic o-MWCNTs can accelerate the DP steels surface to adsorb the metal cations (Me2+) and PO43−, more nucleation sites can be formed on the surface of the steel treated with magnetic o-MWCNTs solution, which provide optimum conditions for phosphate deposition. The scanning electron microscope (SEM) has been applied to observe the coating morphology, indicating that more dense and uniform phosphate coating can be formed on the DP steel surface activated by magnetic o-MWCNTs. Potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) suggested that the adsorption of magnetic o-MWCNTs on the steel surface effectively improved the corrosion resistance of the phosphate coating. The optimal treatment time of magnetic o-MWCNTs was 40 s, which can obtain 44.1% inhibition efficiency relative to the bare steel with phosphate coating. Meanwhile, combined with the friction test, the coefficient of friction decreased from 0.556 to 0.405 for the phosphate coating with treatment by magnetic o-MWCNTs. Finally, the activation mechanism of magnetic o-MWCNTs and the growth mechanism of phosphate coatings were concluded by combining the fourier transform infrared (FT-IR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis.