Preparation and corrosion resistance study of a pH-responsive plasma electrolytic oxidation coating modified by halloysite nanotubes

In this research work, pH-responsive halloysite nanotubes (HNTs) microcontainers were utilized to load 2-mercaptobenzothiazole (MBT) corrosion inhibitors by adopting the layer-by-layer assembly method (LbL). Additionally, a pH-responsive composite self-healing coating was fabricated utilizing plasma electrolytic oxidation combined with micro/nano-container loadings in organic coating technology. To study the evolution of the structure and repair performance of the composite self-healing layer under various pH values, and understand the release behavior of the corrosion inhibitor, SEM, TEM, DTA, infrared absorption spectroscopy, and electrochemical testing techniques were employed. The results of the study indicated that poly allylamine hydrochloride (PAH) and poly sodium 4-styrenesulfonate (PSS) displayed efficient encapsulation of HNTs, and the release rate revealed an increase in acidic and alkaline solutions, while it showed a decrease in neutral solutions. Furthermore, scratch tests were conducted on the coated samples, demonstrating that the HNTs-loaded corrosion inhibitors significantly improved the corrosion resistance and repair performance of the coating. Besides, the protonation of the polyelectrolyte coating layer enabled the corrosion inhibitor MBT to gradually release and diffuse into the defects, leading to the formation of an adsorption film, thus inhibiting corrosion and achieving a self-healing effect.