Bimetallic lattice doped fillers with durable oxygen vacancies for corrosion resistance of coated steel in hostile environments

A series of Ca-doped Co3O4 nano-sheets (Ca-Co3O4) rich in oxygen vacancies were prepared using the alkali precipitation method at different pH values and added to the coating. Scanning electron microscopy and X-ray diffraction were performed to confirm the successful synthesis of the nano-fillers. The electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) spectroscopy determined that the nano-filler has abundant oxygen vacancies. The corrosion resistance test results showed that the epoxy coating containing the Ca-Co3O4 (pH = 12.5) filler exhibited the best corrosion resistance. After 48 h of corrosion in a high-temperature and high-pressure oxygen-rich (HTHP-O2) environment, the |Z|0.01 Hz is 5 orders of magnitude higher than that of the pure Co3O4 coating. Furthermore, the scanning vibrating electrode technique and O2-adsorption-desorption test indicated that Ca-Co3O4 with durable and stable oxygen vacancies could provide a complete, stable and dense passive film for the substrate (Q235B steel). Because oxygen vacancies can selectively transport O2 to the coating-substrate interface ahead of other corrosive media.