Study on corrosion resistance of passive sealant to Fe-based amorphous coating at atomic-scale

Pore defect elimination is the most effective way to prolong the service life of Fe-based amorphous coating. In this study, the passive sealant (PSG) was successfully prepared by the sol-gel method, and the sealing and passive film continuous repair were completed in one-step. Three-dimensional X-ray tomography (3D-XRT) was used to reveal the PSG penetration depths, which was more than 180 mu m and resulted in a significant rising of the coating density. The ferric phosphate film formed on the interface of the sealant/coating changed the semiconductor properties of the passive film. The results of Mott-Shottky test showed that the donor density (Nd) decreased by 5 orders of magnitude, which slowed down the diffusion rate of the point defect of the passive film, and the thickness of the passive film increased from 2.37 nm to 12.04 nm. With the extension of immersion time, the concentration of Fe2O3 and Cr2O3 increased by 183.5 % and 93.5 %, respectively. In addition, the increasing concentrations of Fe3+/Fe2+ and Cr3+/Cr0 also demonstrated the improvement of the coating's passive ability. This study provides a low-cost and a simple strategy for one-step completion of coating sealing and passive film repair to extending the service life of Fe-based amorphous coating.