The Effect Of Chloride Ion And Sulfate-reducing Bacteria On Dissolved Oxygen Reduction Reaction On The Surface Of Q235 Steel

The dissolved oxygen reduction reaction (ORR) is one of the main factors influenced steel corrosion in seawater environment. The chloride ion (Cl?) and sulfate-reducing bacteria (SRB) in seawater may affect on the ORR and the behavior of steel corrosion. In this thesis, the effect of Cl? and SRB on the ORR on the surface of the offshore engineering Q235 steel was investigated by cyclic voltammetry, electrochemical impedance spectroscopy and rotating ring/disk electrode electrochemical methods.The results show that the reductions of dissolved oxygen and iron oxide on the surface of Q235 steel in simulated concrete pore solutions (0.02 M Ca(OH)2) occurred simultaneously. The ORR was a two-electron reaction which was controlled by mass-transfer and electron-transfer processes at the beginning of the reaction potentials. It was a four-electron reaction controlled by mass-transfer process at the more negative potentials. The peak potentials of ORR shifted to more positive direction and the rate of ORR decreased with increasing the concentration of chloride ions in 0.02 M Ca(OH)₂ solutions.The ORR was inhibited, because the dissolved oxygen diffusion was hindered by the biofilm formed on the surface of Q235 steel in simulated seawater (3.5% NaCl) containing SRB. At the same time, the rate of ORR decreased and the mechanism was changed. ORR was a four-electron reaction in simulated seawater without SRB and a two-electron reaction with a small number SRB and a one-electron reaction with a large number SRB.