THE ELECTROCHEMICAL BEHAVIOR OF Zn–Mn ALLOY COATING IN CARBONATED CONCRETE SOLUTION

Abstract

In order to improve the protective performance of Zn coating on reinforcing steel in concrete, the electrochemical deposition of Zn–Mn coatings was conducted on steel surface. The morphology, chemical and phase compositions of Zn–Mn coatings obtained from sulfate–citrate bath were investigated in the first part of paper. In the second part, the obtained deposits were tested in solution simulating carbonated concrete, consisting of NaHCO3 and Na2CO3. Data obtained from Tafel analysis showed higher corrosion resistance for Zn–Mn alloy deposits obtained at –1700 and –1800[Formula: see text]mV versus SCE, when compared to pure Zn deposit. Impedance spectroscopy investigations revealed that the total impedance of Zn–Mn coatings increased steadily with time, and was significantly higher as compared to pure Zn after 24[Formula: see text]h in corrosion solution. On the contrary, for pure Zn, the impedance increased in the first 12[Formula: see text]h, and then decreased during prolonged exposure time, which can be explained by rapid growth of nonprotective white rust and the degradation of zinc coating, as was confirmed by optical microscope after 24[Formula: see text]h of immersion in carbonated concrete pore solution.