Accelerated formation of zinc phosphate coatings with enhanced corrosion resistance on carbon steel by introducing α-zirconium phosphate

Abstract In this study, α-zirconium phosphate (α-ZrP) is used as an accelerator for phosphate coatings on carbon steel. A more compact phosphate coating with enhanced corrosion resistance is obtained with the incorporation of α-ZrP. Scanning electron microscopy (SEM) was used to observe the growth of phosphate crystals and the surface morphology of phosphate coatings during the phosphating process. The phosphate crystals composition was analyzed by X-ray diffraction (XRD) spectra. Coating weight and surface roughness tests were also performed. Results of all these characterizations reveal that the incorporation of α-ZrP reduces the phosphate crystals size, coating weight and decreases coating roughness. The potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests demonstrate that the incorporation of α-ZrP effectively improves corrosion resistance of phosphate coatings (i.e. the corrosion rate is decreased by one order of magnitude). Optimally when the concentration of α-ZrP in the phosphating solution is 0.8 g/L, the minimum corrosion rate (0.17 mpy) is obtained.