Study On Corrosion Resistance of Magnesium Phosphate Cement-based Coating Modified by Metakaolin

Magnesium ammonium phosphate cement (MAPC) with a ceramic-like structure has good anti-corrosion properties. As an anti-corrosion coating, it can resist steel corrosion and reduces economic losses caused by steel corrosion. To further improve the anticorrosive properties of the coating, this study modified MAPC by partially replacing MgO with metakaolin (MK). Electrochemical tests analyzed the effect of MK on the anticorrosive properties of the coating. The results showed that the incorporation of MK significantly improved the anticorrosive properties of the coating, and the maximum improvement was obtained when the substitution amount was 15%. The compositions and microscopic morphology of the coatings were analyzed by X-ray diffraction (XRD), thermogravimetric analysis (TG-DTG), and scanning electron microscopy (SEM). According to the results, MK addition did not significantly alter the main composition of the coating, but the MK promoted the formation of MgNH4PO4 center dot 6H2O(MAP) to some extent. The microscopic morphology of the coating surface showed that the crystals were stacked together in flower-like layers before soaking, and the crystals grew more entirely after soaking. The internal microstructure of the coating is very dense, which helps to resist the erosion of corrosive media. In addition, the changes in coating pores before and after the incorporation of MK were tested by low-field nuclear magnetic resonance (LF-NMR). Based on the results, the doping of MK can optimize the pores of the coating and reduce its porosity. It is feasible to replace part of the MgO with MK to improve the corrosion resistance of magnesium phosphate cement-based coating, and the optimal dosage of MK is 15%. This research is helpful to improve the anti-corrosion performance of the coating and reduce corrosion costs.