Effects of Microorganism on Corrosion of Zn-Al-Cd Sacrificial Anode in Natural Seawater

The effects of the sterile seawater and natural seawater on corrosion of Zn-Al-Cd sacrificial anode were investigated by using electrochemical impedance spectroscopy(EIS),scanning electron microscopy(SEM) and fluorescence microscopy.The results show that the corrosion potential of sample in the sterile seawater is lower than that in the natural seawater at the beginning of experiment,but at the late of experiment,the result is opposite.The EIS results show that the Rct value in the sterile seawater is much smaller than that of anode in natural seawater,which is because in the natural seawater,a layer of biofilm through the metabolic activities of bacteria is formed on the sample surface.The biofilm could prevent the sample from contacting with seawater directly and slow down the corrosion rate.SEM images reveal the presence of localized corrosion morphologies on the sample in the sterile seawater,while in natural seawater,the corrosion is much uniform.Fluorescence microscopy results show that the bacteria uniformly attach to the sample first,and then reunite uneven.About fourteen days later,the local biofilm forms,and it detaches from the sample finally because of the exhaustion of nutrients.