Effects of Oxygen and Sulfate Concentrations on the Corrosion Behavior of Zinc in NaCl Solutions

Galvanized steel is one of the most common materials used in the construction industry for its relatively low cost paired with an acceptable corrosion resistance. Nevertheless, the early failure of a number of structures around the world that use galvanized steel as reinforcement has raised some controversy on the understanding of the corrosion behavior of zinc. The purpose of this paper was to study the effect of variable oxygen concentration on the corrosion performance of zinc. High-purity zinc was immersed in solutions with varied concentrations of sodium sulfate (Na₂SO₄, 1 wt% to 4 wt%), a fixed concentration of sodium chloride (NaCl, 3.5 wt%), and different concentrations of oxygen to simulate the conditions found in soils and groundwater. Differential oxygen access can promote corrosion macrocells that will compromise the performance of the protected structure. The electrochemical corrosion behavior of zinc was studied using potentiodynamic polarization testing and electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) and x-ray diffraction (XRD) were used to characterize the corroded samples. Results indicate an increase on the corrosion rate with an increasing amount of Na₂SO₄, as well as a potential difference between samples in oxygen saturated, aerated, and deaerated conditions, indicating the possibility for macrocell formation under the studied conditions.