Protective properties of multilayer coatings containing inhibitive primer

Abstract

The protective properties of multilayer coatings on mild steel substrate were evaluated in 3% NaCl solution at ambient temperature (21oC) and 50oC using the electrochemical impedance spectroscopy technique. In this work the investigation was performed on coated panels mostly at 50oC with data also taken at elevated temperature to understand better in terms of protection mechanism given by multilayer coatings with inhibitive primer to the metal substrate. Result obtained from this work show those multilayer coatings at 21oC exhibit excellent protective properties even after prolonged immersion in sodium chloride solution up to ten months duration. At elevated temperatures, impedance changes with temperature whereby at 50oC low impedance was observed. However, upon cooling to ambient temperature the impedance value increases by about two orders of magnitude which indicates that low impedance at 50oC is not really a good indicator of coating condition. Elevated temperature test was also unable to distinguish this multilayer coating resistance from charge transfer resistance but there is a high possibility that the high resistance is related to the charge transfer resistance.