Study Of Corrosion Inhibition Of Vibrio Neocaledonicus Sp. For Copper、 Aluminum And Aluminum Bronze

In our previous research, the corrosion inhibitory effect of marine Vibrioneocaledonicus sp. bacterium was introduced for first time. EIS results showedthat the corrosion resistance of carbon steel increased by more than sixty fold inthe presence of this bacterium. This is the highest corrosion inhibitory effectreported for bacteria and is comparable with some industrial coating such aselectroless Ni. The aim of this project is examination of the corrosion inhibitoryefficiency of this bacterium for some other marine alloys such as copper、aluminum and aluminum bronze. Different electrochemical (open circuitpotential, electrochemical impedance spectroscopy (EIS), and potentiodynamicpolarization measurements)and surface analysis techniques ((field emissionscanning electron microscopy (FESEM), confocal laser scanning microscopy(CLSM) and Fourier Transform infrared spectroscopy(FTIR)) were used.Theresult showed that: (1) In the presence of bacterium, EOCP(open circuit potential) of coppershifted to negative direction about500mv/SCE; while the charge transferresistance (Rct) and the corrosion current density (Icorr) increased and decreasedrespectively in the presence of bacterium. These results confirmed that theVibrio neocaledonicus sp. could control the corrosion process of pure copper.FESEM images showed biofilm didn’t cover the surface entirely maybe becauseof the toxicity of Cu2O passivation film.(2)For pure aluminum (Al), the corrosion current density didn’t changeuniform by exposure time. At the initial stage of bacterial attachment, Icorrdecreased significantly because of the adsorption of bacteria on the metalsurface and decrease in oxygen reduction rate (up to10days). But after10daysexposure, the Icorrincreased and FESEM images also showed some cracks on thesurfaces which confirm the localized attacks.(3)For aluminum bronze, EIS results showed the charge transfer resistance(Rct) increased at first and then decreased. It means the bacterium has theinhibitory effect for the Aluminum bronze at first exposure time (up to10days).It is suggested that this bacterium improved the anticorrosive properties ofaluminum bronze via retarding the cathodic reaction rate of Aluminum bronze.FESEM images showed a small amount of biofilm on the Al-Cu surfaces whichcan be because of toxicity of copper.(4)To improve the inhibitory effect of bacterium for pure Al and Al-Cu,some medium parameters such as culture media and pH were changed and optimized. It is found that bacterium could control the corrosion of Al at pH=9.However, the addition of carbon sources decreased the inhibitory effect ofVibrio neocaledonicus sp. and adding other nitrogen sources such as yeastextract didn’t affect the corrosion inhibitory effect of bacteria, considerably. So,the optimized media for this bacterium is artificial seawater containing3g/L ofpeptone with the range of pH=7.5to9for different alloys.