Anticorrosion Performance of Sol–Gel Driven SIO 2 -Al 2 O 3 Coatings on Low Carbon Steel

Anticorrosion performance of the sol–gel coatings was investigated for their applications to carbon steels. Cracking seemed to be a major problem in achieving the corrosion protection of the sol–gel coatings. It was found that some modifications from the original coating material such as the reduced particle size and structural change of the coating layer exerts a significant effect on the crack formation, which can be understood by the concept of critical thickness. Once corrosion occurred at the steel/coating interface, the cracking of the coating became accelerated as a result of oxide formation at the interface as it generates tensile stress on the sol–gel coating for the crack propagation. From the EIS analysis, it is demonstrated that the sol–gel coating would be not an ideal barrier for corrosion protection. Even though there was no crack on the coating, the charge transfer occurred through the film (frequency shift of time constant) with time, resulting in the corrosion at the steel/sol–gel coating interface with the crack propagation of the coating.