Mechanistic approach for evaluation of the corrosion inhibition of potassium zinc phosphate pigment on the steel surface: Application of surface analysis and electrochemical techniques

Abstract

Potassium zinc phosphate pigment was synthesized through a co-precipitation method. Then, the steel panels were immersed in 3.5% NaCl solution containing potassium zinc phosphate pigment extract and in the blank 3.5% NaCl solution (containing no pigment) at different immersion times. X-ray diffraction and scanning electron microscope were employed in order to characterize the composition and morphology of the pigment. Corrosion inhibition of the pigment in the extract solution was studied by linear polarization test. The morphology and composition of the film precipitated on the surface of steel panels were investigated by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy techniques. Solubility of pigment in the extract solution and the rate of ions consumption were studied by employing an inductively coupled plasma-optical emission spectrometer.Results showed that potassium zinc phosphate has sufficient water solubility to provide corrosion inhibition on the steel surface. The inhibitive spices like Zn2+ and PO43− ions could form protective layer over the anodic and cathodic regions of the metal surface, restricting the aggressive species access to the metal surface. It was found that the inhibition mechanism of potassium zinc phosphate pigment changed during the immersion. Zn2+ ions precipitated on the anodic sites of metal surface at short immersion times affecting the anodic reaction rate but PO43− ions formed protective layer over the cathodic regions at longer immersion times affecting the cathodic reaction rate.