Modified Epoxy Coatings for Corrosion Detection

An epoxy resin based corrosion sensing coating was prepared by modifying epoxy resin with varying amounts of 1,10-phenanthroline-5-amine. The modified epoxy resins were characterized by spectroscopic methods (Fourier transform infrared, nuclear magnetic resonance, and UV-visible spectroscopy) and epoxide content. Thermal analysis of unmodified and modified resins was also performed using thermogravimetric analyzer and differential scanning calorimeter. These resins were mixed with a hardener and applied on steel specimens. The corrosion sensing property of these resins was studied by immersing the steel specimen coated with modified resins in 3.5% NaCl solution. Electrochemical impedance spectroscopy was used to study the corrosion resistance of the coated specimens. The modified epoxy coatings immersed in 3.5% NaCl solution showed red colored spots at metal/coating interface at an early stage of corrosion. Color change and polarization resistance of coating was correlated to describe the mechanism of corrosion detection. Coating from the point of color change was removed and bare metal was analyzed by scanning electron microscopy to reconfirm that the point of color change was the corrosion site. Modified epoxy coating has shown potential to detect the onset of corrosion at an early stage.