Role of tannic acid based rust converter on formation of passive film on zinc rich coating exposed in simulated concrete pore solution

Pretreatment of reinforcement steel surface with tannic acid based rust converter (RC) prior to the application of zinc rich coating (ZRC) is observed to improve its corrosion resistance appreciably. This improvement is caused due to decrease of pH of the corroding interface as a result of outward diffusion of acidic components of RC from the converted rust layer. The decrease in pH of corroding interface brings the ZRC in the protective pH range of Zinc and accelerates the formation of passive layer. This layer is identified as Hydrozincite (HZ). Electrochemical Impedance Spectroscopy (EIS), Potential-time studies, Raman Spectroscopy, Scanning electron Microscopy (SEM), energy dispersive X-ray analysis (EDXA) and X-ray diffraction studies have been performed to understand the mechanism and kinetics of the film formation.