| The influence of Thiobacillus ferrooxidans bacteria on corrosion of iron was studied by using electrochemical techniques combined with Atomic Force Microscopy (AFM). The interaction reactions of iron with bacteria were examined as a function of the pH, electrolyte, oxygen bubbling, and immersion time. The corrosion parameters (especially, corrosion current density), determined by linear polarization measurements were drastically changed after two days of immersion of iron in inoculated solutions. The AFM study revealed that bacteria were present on the iron surface at high density levels.; Significant changes in the morphology of iron specimens after longer immersion times (2–3 days) were attributed to the bacterial activity. Tapping Mode AFM images revealed the dimensions of rod shapes pits of .0.75–1.1μm in length. Since these dimensions corresponded to the length of a single Thiobacillus ferrooxidans bacterium, this result was evidence of bacterial involvement in the corrosion of iron in both deionized water and medium salt. The effect of the bacteria on corrosion behavior of iron depended on the pH range.; Tafel polarization measurements showed the inhibition effect of Thiobacillus ferrooxidans on the iron corrosion for a short time of immersion (t = 15 min) in stagnant solutions. This decrease in corrosion of iron is explained by the depletion in oxygen due to the respiration of bacteria, and by small amount of ferrous ions initially produced by spontaneous dissolution of iron.; Tafel polarization and AFM studies on iron immersed in deionized water, medium salt, and sulfate solutions with constant ionic strength ( I = 1. 5 M) revealed that the iron corrosion mediated by T. ferrooxidans bacteria was influenced by the type of electrolyte. Sulfate solutions with constant ionic strength were more corrosive than those of pure DIW or medium salt. In deionized water and medium salt, the bacterial effect on the iron corrosion is not as clear as it was in constant ionic strength solutions. This implies that bacteria activity increases with the increasing of ionic strength, which can be responsible for bacteria adhesion, and thus, mobility. (Abstract shortened by UMI.)... |
