Early Detection of Steel Corrosion via “Turn-On” Fluorescence in Smart Epoxy Coatings

Abstract

In the present work, we describe the successful application of spiro[1H-isoindole-1,9'-[9H]xanthen]-3(2H)-one, 3',6'-bis(diethylamino)-2-[(1-methylethylidene)amino] ("FD1") as a smart indicator in epoxy-based coatings for the early detection of steel corrosion. The FD1 indicator was used for epoxy-based coatings on steel for its desirable property of "turn-on" fluorescence upon forming a complex with ferric ions produced at the anodic site during steel corrosion and because it does not prematurely fluoresce when mixed with the coating precursors (i.e., epoxy resin and amine). This indicator, after incorporation into a filled epoxy coating at a concentration as low as 0.5 wt %, was observed to become fluorescent in areas where corrosion started before any obvious sign of metal damage was observable. FD1 fluorescence was apparent both in areas around a scribed portion of the coating where the metal was exposed and in undercoating corrosion, where the coating surface was intact. This nondestructive method of early corrosion detection can help signal when maintenance is needed before the metal suffers serious damage.

Microencapsulated indicators and inhibitors for corrosion detection and control

“…[4][5][6][7] Among these, corrosion sensing coatings are highly desired for corrosion detection, especially if the signal can be detected during visual inspections by the naked eye at a stage that occurs signifi cantly earlier than the appearance of the observable corrosion products. [8][9][10][11][12][13] Theoretically, corrosion sensing coatings can be formulated by incorporating a corrosion indicator directly into the coating. Since corrosion is an electrochemical process, there are at least three types of color or fl uorescent indicators that can be used as corrosion indicators to detect the changes that are associated with this process: redox indicators to detect the electron transfer, pH indicators to detect the pH changes, and ion indicators for metal ions detection.…”

“…77 Subsequently, attempts were made to develop corrosion sensing coatings by incorporating corrosion indicators directly into commercially relevant coating formulas, with some success. 8,13 Recently, a pH-responsive polymer was synthesized from a fl uorescent pH indicator and a thermal plastic epoxy resin for early corrosion detection and mechanism study of corrosion initiation. 78,79 Considering the wide range of pH, redox and ion indicators that can potentially be used as corrosion indicators, the success of corrosion sensing coatings has been very limited.…”

Designing green, self-healing coatings for metal protection

“…Th e ability to obtain signals from a coating that indicate the presence of corrosive species, the condition of the coating, or the presence of corrosion products is therefore desirable. Th is could be achieved, for example, by addition of a fl uorophore that fl uoresces in the presence of metal ions [76] or dye indicators [58,64]. Other approaches involved the introduction of quantum dot materials into a coating to act as environmental indicators based on changes in fl uorescence [77].…”

Smart corrosion sensing phenanthroline modified alkyd coatings

“…Color changing chemicals (phenolphthalein and bromothymol blue) and fluorescing chemicals (fluorescein, coumarin, morin, hydroxyquinolines, oxines and Schiff's bases) have been blended individually in primers/paints to sense corrosion on aluminum surfaces. Recently Augustyniak et al [16,17] have reported the use of chelation enhanced fluorescence indicator, spiro [1H-isoindole-1,9 -[9H] xanthen]-3(2H)-one,3 ,6 -bis (diethylamino)-2-[(1-methylethylidene)-amino] in paint composition for detection of corrosion on steel and aluminum.…”