Corrosion Inhibition Of Metals By Marine Aerobic Microorganisms

In this paper, the influence of the marine aerobic biofilms on the corrosion of5083aluminum alloy （5083AA） was investigated using electrochemical techniques （the open circuitpotential, electrochemical impedance spectroscopy （EIS）, and pothentiodynamic polarizationcurves） and surface analysis （epifluorescence microscopy, scanning electron microscopy （SEM）,and energy dispersive X-ray spectroscopy （EDS））. The electrochemical results showed that theOCP （open circuit potential） of5083AA shifted about150mV vs. SCE negatively in naturalseawater than in sterile seawater, and the marine aerobic biofilms prompted the increase of thecharge transfer resistance （Rct） and the pitting potential of5083AA, which indicated that themarine aerobic biofilms inhibited the corrosion of5083AA. In addition, the surface analyticalresults showed that the marine aerobic biofilms consolidated the passive layer and prompted thedecrease of content of magnesium and silicon elements on the surface of5083AA, indicatingthat the marine aerobic biofilms inhibited the dissolved reaction of intermetallic phases in themetallic matrix, which contributed to the corrosion inhibition of5083AA ultimately.To investigated the microbiologically influenced corrosion inhibition （MICI） in-depth, theinfluence of biofilms comprising iron-reducing bacteria （IRB） on the corrosion of Q235carbonsteel and316L stainless steel was studied, and the results showed that:1)The OCP （open circuit potential） of Q235carbon steel shifted about20mV vs. SCEnegatively with bacteria than without bacteria, and IRB biofilms prompted the increase of thecharge transfer resistance （Rct） and the decrease of the corrosion current density (I_corr) of Q235carbon steel, which indicated that the corrosion of Q235carbon steel was inhibited by IRBbiofilms. The SEM showed that a thin and dense protective film was formed on the surface ofcarbon steel with bacteria, which may be due to the reduction of Fe³⁺to Fe²⁺by IRB biofilmscontributing to the oxygen depletion. And the EDS showed that the content of phosphorus element on the surface of Q235carbon steel was increased by IRB biofilm indicating that theformation of iron phosphate products that contributed to the corrosion inhibition of Q235carbonsteel. Otherwise, the EIS showed the charge transfer resistance （Rct） of carbon steel was alsoincreased in sterile LB medium, which indicated the corrosion inhibition of carbon steel alsohappened in sterile LB medium. And the EDS showed that the content of phosphorus element onthe surface of Q235carbon steel was also increased in sterile medium indicating that theformation of iron phosphate products which contributed to the corrosion inhibition of Q235carbon steel.2) The OCP （open circuit potential） of316L stainless steel shifted about300mV vs. SCEnegatively in IRB pure culture than in sterile PGC medium. The EIS showed that the the chargetransfer resistance （Rct） of316L stainless steel was increased in IRB pure culture, whichindicated that IRB biofilms inhibited the corrosion of316L stainless steel, and the corrosioninhibition was enhanced firstly but then weakened at the end. The cyclic polarization curesshowed that the area of hysteresis loop （A） and the characteristic potential range （Eb-Ep, Eb:breakdown potential, and Ep: protection potential） of316L stainless steel was decreased from1day to5days of immersion, and then increased from5days to11days of immersion in IRB pureculture, which indicated that IRB biofilms inhibited the pit initiation and propagation of316Lstainless steel.