For the past two decades, there has been a tremendous amount of research focused on smart coatings for structural applications; coatings that can sense certain conditions and then respond. These are coatings that typically contain one or more indicators that can sense conditions such as corrosion and respond by means of changes in pH, color, fluorescence or a combination thereof. Many of the coating systems that have initially shown promise have been hindered by factors such as an overall reduction in the performance of the coating due to the presence of the indicator; limitations in the ability of the corrosion condition to be seen through the primer and/or topcoat; limitations in the sensitivity of the indicator; and the presence of competing reactions associated with the indicator and the corrosion products. Recently, however, indicators that reveal dramatic changes as a result of changes in corrosion conditions/products and indicators that respond to changes in the production of specific ions due to corrosion processes have been reported. In this paper, recent progress that has been made on the topic of smart coatings for corrosion detection will be described. The focus will be on coatings that reveal corrosion conditions and products before they can be observed with the naked eye
Since the 1990s, a large body of work has been developed based on smart coatings. In general, these are coatings that can sense certain conditions and reveal and/or respond to these conditions; conditions such as corrosion. In a detailed review article by Agarwala and Ahmad in 2000 (Agarwala and Ahmad, 2000), many methods of corrosion detection and monitoring were described. The techniques included ultrasonic and acoustic methods; radiographic methods; thermal imaging; electromagnetic methods; electrical resistance measurements; electrochemical methods, including noise, and electrochemical impedance spectroscopy (EIS); visual and miscellaneous methods; and chemical sensors.