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.