Corrosion-sensing behavior of an acrylic-based coating system

Paint systems containing color-change or fluorescing compounds were found t o be sensitive to underlying corrosion processes by reacting to the pH incr ease associated with the cathodic reaction that accompanies corrosion. The sensitivity of acrylic-based coating systems Sor detection of cathodic reac tions associated with corrosion was determined by applying constant cathodi c current and measuring the charge at which color change or fluorescence wa s detected. Unaided visual observation of coated samples detected changes r esulting from a charge corresponding to a hemispherical pit with a depth of 10 mu m Characteristics of modified acrylic coating systems were studied b y titration tests. Electrochemical impedance spectroscopy also was performe d to test the influence of the indicating compound addition on the coating corrosion protectiveness. The time for color change was determined to be co ntrolled by the sensitivity of the coating to pH increase, and not by the c oating protectiveness.