Smart Corrosion Sensing Coatings Based on Color Change or Fluorescence

Polymer coatings have found various applications for corrosion protection of metallic substrates. Detection of corrosion beneath the coatings is of great importance, and corrosion sensing coatings can provide early detection of occurrence of corrosion before it would otherwise be visible. So, application of corrosion sensing coatings is expected to reduce costs by detecting corrosion in the early stages, reducing the cost of repairing and structural metal replacement. Generally, corrosion indicators are incorporated into the coatings directly, or via encapsulation. Localized corrosion is often associated with pH and electrochemical changes. Coating systems containing color-change or fluorescing corrosion indicators are found to be sensitive to underlying corrosion processes by reacting to the increase of pH associated with the cathodic reaction. Moreover, in some cases corrosion indicating compounds can make a complex with metallic cations from anodic reaction, resulting in color change and detection of corrosion. This review emphasizes the recent advances in corrosion sensing coatings based on color change or fluorescence, and different mechanisms associated with corrosion sensing are categorized and discussed precisely.