| With the development of marine industry, the corrosion of metal structures in marine sediment has gradually been considered. Marine sediment can be seen as a kind of special soil, which is covered and saturated by seawater. Corrosion in marine sediment is a complex phenomenon and many environmental factors such as physical factors, chemical factors and microbiological factors have important influences on the corrosion of materials in the environment. Therefore, the equipments worked in marine sediment for a long time may be serious damaged by those corrosion factors, sometimes can lead to environmental pollution and huge economic losses. Sacrificial anodes are widely used for protection of steel structures in marine environment due to no need to impress current, could not interfere with the neighbouring metal facilities, easy to manage and maintain and low cost. In marine environment, these sacrificial anodes may be attacked by microbial activity and the microbial fouling may result in serious failure and loss of energy. Some researchers have investigated the biocidal activity of sacrificial anodes, but the influence of microbes on the performance of sacrificial anodes in marine sediment has not been reported.At first, the sulphate reducing bacteria (SRB) were enriched and purified cultivated from muddy sediment in Jiaozhou Bay of Qingdao. After that, the influence of SRB on corrosion behaviour of Al-Zn-In-Sn, Al-Zn-In-Mg-Ti, Zn and Zn-Al-Cd sacrificial anodes have been studied using weight loss, galvanic corrosion test, electrochemical methods, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) during a growth cycle of SRB in marine sediment.The results of weight loss experiments indicate that localized corrosion occurs for the two Al base sacrificial anodes in the sterile marine sediment as well as the SRB-containing marine sediment, and uniform corrosion occurs for the two Zn base sacrificial anodes in the two kinds of marine sediment. The corrosion rates of the four kinds of sacrificial anodes in both the sterile and SRB-containing medium decrease with exposure time, while the corrosion rates of the sacrificial anodes in the SRB-containing medium are obviously higher than that in the sterile medium.The galvanic corrosion tests reveal that all of the four kinds of samples in biotic system act as anodes, while those in abiotic system act as cathodes, and the corrosion rate of the anodes increased with time, which was possibly due to the increasing of active SRB during the preliminary stage. During the whole experiment, for Al-Zn-In-Mg-Ti and Zn-Al-Cd, the reversion of polarity happened, for Al-Zn-In-Sn and Zn, the reversion didn't occur.Electrochemical studies suggest that pitting corrosion occurs for Al-Zn-In-Sn immersed in the marine sediment without and with SRB during exposure time, while the growth rates of pits can be further enhanced by SRB in the biotic marine sediment. At first, the corrosion rate of Al-Zn-In-Mg-Ti immersed in the SRB-containing medium is higher than that immersed in the sterile medium, whereas, the situation is reversed when both samples have been immersed for several days. Finally, the corrosion rate of the sample immersed in the biotic medium becomes much higher than that immersed in the abiotic medium. The corrosion rates of Zn and Zn-Al-Cd are enhanced sharply in the presence of SRB at the beginning, while the corrosion performance of the sample in marine sediment without and with SRB gradually become similar with each other due to the decreasing SRB populations.Surface analyses reveal that the damage of the four kinds of sacrificial anodes immersed in the biotic medium was more severe than that immersed in the abiotic medium as the exposure time goes on, and the concentration of matrix metal in the surface film for the samples with SRB is lower than that for samples without SRB, which suggest that the corrosion rates of the sacrificial anodes are accelerated by SRB. |
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