Effect of zinc oxide on corrosion resistance of magnesium ammonium phosphate cement-based coating

In order to improve the anticorrosive performance of magnesium ammonium phosphate cement (MAPC) coating, a small amount of zinc oxide was added to the MAPC coating to modify and coat the surface of Q235 steel. The anti-corrosion resistance and mechanism of MAPC coating modified by zinc oxide were analyzed based on electrochemical test results, and the morphology and composition changes of the coating before and after immersion were observed and tested using X-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), and a thermogravimetric analyzer (TG-DTG). Low field nuclear magnetic resonance testing was used to determine the porosity of the coating and the corrosion resistance of the modified coating was tested by a neutral salt spray test. The results show that after immersion in a 3.5% NaCl solution for 28 days, the MAPC coating with 3% (mass fraction) zinc oxide exhibited a corrosion current density of 2.96 x 10-4 & mu;A/cm2 at a corrosion potential of -0.870 V, demonstrating a favorable outcome with a positive shift.; Meanwhile, the 28 days polarization resistance of the modified coating was 97436 & omega;& BULL;cm2, which was 78% higher than that of the blank. The shielding performance of the coating was enhanced, and the charge transfer resistance was also significantly improved. The porosity of the modified coating before and after immersion was lower than that of the blank group. After 1440 h of neutral salt spray testing, there was no swelling or peeling on the coating surface, and there was no trace of corrosion on the internal substrate.