Corrosion-Sensing Behavior of an Acrylic-Based Coating System

Paint systems containing color-change or fluorescing compounds were found to be sensitive to underlying corrosion processes by reacting to the pH increase associated with the cathodic reaction that accompanies corrosion. The sensitivity of acrylic-based coating systems for detection of cathodic reactions associated with corrosion was determined by applying constant cathodic current and measuring the charge at which color change or fluorescence was detected. Unaided visual observation of coated samples detected changes resulting from a charge corresponding to a hemispherical pit with a depth of 10 μm. Characteristics of modified acrylic coating systems were studied by titration tests. Electrochemical impedance spectroscopy also was performed to test the influence of the indicating compound addition on the coating corrosion protectiveness. The time for color change was determined to be controlled by the sensitivity of the coating to pH increase, and not by the coating protectiveness.