인산망간 피막의 아질산나트륨 첨가가 내식성에 미치는 영향에 대한 연구

Effect of Sodium Nitrite Addition on the Corrosion Resistance of Manganese Phosphate Coating

This paper describes an effective metal finishing technology for obtaining manganese phosphate coatings on steel. In this study, the effect of sodium nitrite addition on the corrosion resistance of a manganese phosphate coating was investigated. The microstructure, surface morphology, and chemical composition were analyzed by FE-SEM, EDS, and XRD, while the cross-sectional images and thickness of the coating layer were analyzed by FIB. According to the results of the EDS analysis, the main components of the manganese phosphate coating were C, O, P, Mn, and Fe. The XRD results showed that (Mn,Fe)5H2(PO4)4 4H2O in the manganese phosphate coating layer was formed by a chemical reaction between manganese phosphate and elements in the underlying carbon steel. Additionally, electrochemical polarization testing was carried out in order to evaluate the corrosion protection properties of the manganese phosphate coating in a 3.5 wt.% NaCl solution. The corrosion resistance of the phosphate coating was remarkably improved by adding sodium nitrite.