Microbial Membrane And Metal Electrochemical State Of The Marine Environment Correlation

There are lots of microorganisms in seawater. When immersed in seawater, surfaces of metals will soon be covered by a layer of biofilm. Marine boifilms are typically composed of bacteria, microalgae, protozoa and other materials, including silt and corrosion products. All these organisms and inorganisms are embedded in the extracellular polymeric substance (EPS) excreted by bacteria. For their metabolism, factors that vary little in the open ocean (such as pH, dissolved oxygen, metals ions and other chemicals) can vary dramatically at the metal-biofilm interface and these factors can change electrochemical conditions of metals surfaces. The consequence of electrochemical changes is microbiologically influenced corrosion (MIC). MIC was often neglected by people who studied corrosion and now are investigated by more groups. On the other hand the formation of biofilms are important for subsequent attachment, development and metamorphosis of invertebrate larvae. Unwanted adsorption of macroorganisms on materials surfaces is called biofouling. Biofouling can decrease the velocity of ships, increase the heat transfer resistance, clog some porous media and impart technical damage for structures in ocean. Now the most common countermeasure is the application of biocides. For the complicated structure, biofilm can decrease the effectiveness of the biocides. Although can be killed by the biocides, unviable microorganisms and biofilm still attach on metal surfaces and this can also cause corrosion. So study the law of biofilm formation, biofilm structure characteristics and interactions between biofilm formation and metal electrochemical parameters will be beneficial to find countermeasures to control MIC and biofouling.In order to find theoretic knowledge for controlling MIC and biofouling. This paper used electrochemical technology and epifluoresence microscopy to study biofilm formation and interactions between biofilm formation and electrochemical conditions of metals. The main results and conclusions are summarized as follows:(1) Six kinds of metals electrochemical parameters influenced by marine biofilm were studied. The results showed that: Corrosion of carbon steel and aluminium werethe main processes. In natural seawater, surfaces of them changed quickly and corrosion was serious. Electrochemical conditions influenced by the activities of microorganisms were faint compared with corrosion processes. But we can also see influence of boifilm, for example the changes of their polarization curves with and without biofilm. Corrosion of copper and titanium was faint in seawater for oxide film formed on their surfaces and the activities of microorganisms influenced little on their corrosion. For that both corrosion processes and microorganisms activities on their surfaces were very faint, their electrochemical processes changed little. Copper is a kind of heavy metal which ion is poisonous to most microorganisms. So biofilm is hard to form on copper surface. Stainless steel and high Mo steel are typical passive metals and electrochemical characteristics of them were greatly influenced by biofilm attached on their surfaces. These two kinds of passive metals were hard to corrode. Then through measuring their electrochemical characteristics can detect biofilm attachment. Passive metals can be used to study the law of biofilm formation and the influence caused by metal electrochemical condition changes.(2) The ennoblement of two kinds of passive metals and the law of bioflm formation on their surfaces were studied with electrochemical technology and epifluoresence microscopy. The results showed that in natural seawater, passive metals corrosion potential can shift in noble direction for about two hundred microvolts. Microorganisms attached on metal surface according to negative exponential law which was similar to passive metal corrosion potential shift. Contrasted to test result measured in sterile seawater we can concluded that microorganisms adsorption was the reason for ennoblement.(3) Bacteria attac...