Fluorescence based corrosion detecting epoxy coating

Abstract

Corrosion at metal-coating interface remains unseen and undetected which may result into catastrophic failure of the structure. Therefore, to detect the onset of corrosion, a chemical method for modification of epoxy resin with 2-amino-N[2-{3′,6′-bis(diethylamino)-3-oxospiro(isoindoline-1,9′-xanthen)-2-yl}ethyl] propanamide at various concentrations is described. These resins were characterized by various techniques (FTIR, NMR, TGA and DSC). UV–vis spectroscopy was used to study the resin-Fe(II) complex formation. Unmodified and modified resins were individually mixed with a hardener and applied as a coating on steel specimens. Coated specimens were immersed in 3.5% NaCl solution and evaluated for corrosion resistance by electrochemical impedance spectroscopy (EIS). Modified coatings exhibit fluorescence upon interaction with ferrous ions releasing during the early stage of corrosion. The fluorescence response of modified coating was studied by using fluorescence spectrophotometer and confocal laser scanning microscope (CLSM). Corrosion resistance of coated specimens and fluorescent spots are correlated with respect to immersion time. Scanning electron microscopy (SEM) was used to reconfirm that onset of corrosion was took place at metal-coating interface. Resin modification does not have any adverse effect on mechanical properties as well as chemical resistance of the coating. Modified epoxy coating possessing 10% w/w modifier has shown large number of fluorescent spots at the corroded regions as an early warning for the onset of corrosion.