Effect of lead alloying on corrosion characteristics of galvanized coatings exposed in atmosphere, simulated laboratory and a service environment

Abstract

Role of alloying of lead in hot dip galvanized coating deposited on mild steel wire on their corrosion characteristics are studied exposing them in industrial, coastal urban environments and laboratory simulated electrolytes. Various corrosion evaluation techniques namely mass loss, electrochemical impedance spectroscopy and direct current polarization methods are used to assess corrosion characteristics of the wires. Corrosion products formed on the exposed samples and cross section of the coatings are analyzed by X-Ray Diffraction, Raman Spectroscope and Scanning Electron Microscope. Lead is observed to change the corrosion characteristics of the coatings with change in constituents of the environments. In saline electrolytes, alloying of lead is found to accelerate the corrosion rate. This metal deposits as cluster on top layer of the galvanized coatings and acts as strong cathodes with respect to the zinc and accelerates the corrosion rate. In sulfurous environments, a stifling effect on rate of corrosion is noted which is attributed to the formation of stable and moisture insoluble sulfate compounds of lead on the surface of the coating.