Preparation of Phosphate Coating Solution to Increase the Corrosion Resistance of Carbon Steel in Ambient Conditions

Abstract

In this work, different zinc phosphating solutions were prepared using sodium phosphate (Na₃PO₄), sodium nitrate (NaNO₃), and nickel carbonate (NiCO₃) as accelerators. NaNO₃ concentration was ranged from 20 to 80 g/L. While the NiCO₃ concentration ranged from 1 to 15 g/L. To identify the interactions between the NaNO₃and NiCO₃, mixed accelerators were also investigated. Corrosion inspection of the metal surface was tested using potentiostatic experiments. Portable camera microscope was used to capture the surface images of coated samples.  The experimental investigations revealed that the immersion time of 10 min significantly enhanced the corrosion tendency of all accelerators. It was noticed that the corrosion resistance was enhanced with more concentration of NaNO₃in the phosphate solution and reached their maximum protection at 80 g/L. While 1 g/L of NiCO₃ in solution (which represents the lower value), exhibited higher protection against corrosion. Mixed accelerators resulted in smaller grain size with lower corrosion current (1.83 mA) at 80 g/L and 5 g/L of NaNO₃ and NiCO₃, respectively. It was also found that chromic acid concentration significantly affected the corrosion resistance.