Corrosion Behaviour of Polyurethane Coating Containing Flurocarbon on Carbon Steel in Tropical Marine Atmospheric Environment
Junhang Chen, Jialiang Song, Wei Hu, Taiyang Zhu, Jin Gao, Kui Xiao
Abstract
To study the corrosion behaviour of carbon steel/fluorocarbon epoxy composite coating materials in a tropical marine atmosphere, outdoor exposure tests of intact and damaged coatings were conducted in Wenchang, Hainan, China. Macroscopic corrosion morphology, glossiness tests, adhesion tests, electrochemical impedance spectrometry (EIS) and scanning Kelvin probes (SKPs) were used to study the performance changes of the intact and damaged coatings after outdoor exposure for 3, 6, 9 and 12 months. The results show that the intact coatings have good protective properties in the tropical marine atmosphere, while the coatings with defects undergo subsurface corrosion. The results show that the carbon steel substrate exposed at the initial stage of corrosion dissolves as the anode and the interface between the metal and the coating is the cathode, which results in the formation of a large amount of OH - in the alkaline environment, which reduces the adhesion of the epoxy primer to the carbon steel substrate. As the corrosion progresses, a large number of corrosion products are generated at the defects, which makes the potential at the defects move to a new cathode area in a positive direction, and the potential at the adjacent areas moves to a negative direction and becomes a new anode area. The potential difference between the two provides a driving force for the corrosion of the metal under the film. With the accumulation of corrosion products under the film, the adhesion between the epoxy primer and the carbon steel substrate decreases further and finally leads to blistering and peeling failure of the adjacent coating.