Molybdenum–phosphorus compounds based passivator to control corrosion of hot dip galvanized coated rebars exposed in simulated concrete pore solution

Hot dip galvanized (HDG) coating passivated with molybdenum–phosphorus compounds based passivator exhibits high degree of corrosion protection exposed in chloride contaminated simulated concrete pore solution (SPS). The coating develops very stable corrosion products and its corrosion potential gets greatly ennobled due to the formation of a complex passive layer. This composite layer has been identified as hydrozincite (HZ) embedded with several other compounds. The studies reveal that the presence of passive films on HDG makes the HZ layer more impervious and less soluble in the test electrolyte. The layer also helps in faster development of hydrozincite film on HDG surface. A faster healing of defects in hydrozincite layer takes place for passivated than the unpassivated surface. Electrochemical impedance spectroscopy (EIS), Raman Spectroscopy, Scanning Electron Microscopy (SEM), energy dispersive X-ray analysis (EDXA), and X-ray diffraction (XRD) studies etc. have been performed to study the kinetics and understand the mechanism of formation of hydrozincite at the corroding interface. These studies are expected to provide a new area in development of lesser polluting protective passive layer on galvanized coatings.