海洋微生物附着腐蚀铁铝金属间化合物的机制研究

【作者】 常雪婷；

【导师】 尹衍升；

【作者基本信息】 山东大学 ， 材料学， 2007， 硕士

【摘要】 海水中金属材料普遍受表面生物膜的腐蚀。因此，研究海洋材料表面微生物膜的形成规律、结构特点以及微生物膜与金属电化学之间的关系等，对于从材料微观结构上提高耐海水及海洋微生物腐蚀能力至关重要。Fe₃Al金属间化合物具有高硬度、高强度、低密度、强耐腐蚀性等独特的性能，作为海洋材料具有广泛的应用前景。但是，在海洋微生物环境下的腐蚀规律及机理至今没人涉及。本文将实海腐蚀、实验室培养基腐蚀以及模拟微生物膜腐蚀技术相结合，利用电化学、SEM、TEM等先进研究手段，对Fe₃Al材料表面附着微生物膜的形成规律、微生物膜对金属电化学性质的影响进行了研究。将Fe₃Al材料暴露在实际海水和灭菌海水中进行比较，发现微生物的存在会阻止钝化膜形成，使真实海水环境中材料的腐蚀速率接近无菌海水中的2倍；Fe₃Al材料暴露在海水中大概10天开始出现腐蚀，至180天，发生SRB的显著影响，出现剥蚀现象；在灭菌海水中浸泡只出现黄色的疏松絮状锈层；在实验室微生物培养基介质中，考察了有微生物和无微生物两种情况下Fe₃Al材料的开路电位、动电位极化曲线和交流阻抗谱等电化学特征，研究了在海洋微生物作用下Fe₃Al材料的腐蚀行为和腐蚀机制的变化。在浸泡初期，在有菌介质中的开路电位高于无菌介质，但是在短暂延滞期结束后电位快速负移；在有菌培养基中，随着浸泡时间的延长，SRB的阴极极化作用和氧元素的扩散同时使Fe₃Al电极的阴极极化过程加快，电流密度增加，腐蚀电位严重负移；同时由于钝化膜孔蚀及破裂，使得阳极极化曲线出现明显电流峰；无菌环境的极化电流较小，腐蚀电位稍负，钝化区正移。通过模拟微生物膜方法研究了不同种菌类对Fe₃Al材料腐蚀的行为和机理。结果表明，没有微生物膜覆盖的金属表面遇到模拟海水后立即在表面进行具有钝态特征的成膜反应；而有模拟微生物膜的Fe₃Al材料在浸泡初期，由于生物膜的不均匀性及透过机制使得钝化膜并不完整，Fe₃Al材料处于钝化膜孔蚀诱导状态；Fe₃Al电极在锰沉积菌环境中的腐蚀过程属于典型的氧扩散控制机制；在模拟醋酸菌环境下，由于介质被酸化，H⁺通过膜扩散至电极表面，使Fe₃Al电极的阴极极化反应变为析氢反应，同时处于钝化态的Fe₃Al电极表面孔蚀击穿电位随氯离子浓度的增加及pH之降低而负移；模拟SRB通过把SO₄^2-还原成S^2-促进材料表面的阴极极化过程，同时电极的腐蚀电位急剧下降，表面氧化膜在极化电压为-0.5V时破裂。另外，选用碳钢和304不锈钢进行对比实验。发现在有菌环境中，碳钢材料表面出现大量的腐蚀坑，且微生物的存在使氧的扩散速率降低，阳极过程加剧而阴极过程减弱。不锈钢材料表面并未出现明显锈蚀；微生物的存在使不锈钢电极的极化电流密度略有增加，阴极极化性质未发生变化，阳极极化区的钝化电流密度始终保持稳定，未出现峰值。更多还原

【Abstract】 MIC （Microbiologically Influence Corrosion） on metal is of universality in the seawater. Accordingly, studying the formation rules, structural characteristics of microbial film on the surface and the correlation between the film and electrochemical behavior of oceanic materials will be extremely important to improve the corrosion resistance of oceanic materials to seawater and oceanic microbe.The intermetallic compounds Fe₃Al possesses excellent performance of high hardness, high strength, low density and high corrosion resistance and can be applied in seawater for surface protection. However, few literatures can be traced on the corrosion rules and mechanism of Fe₃Al with the existence of marine microbe.In this paper, the corrosion behavior of Fe₃Al in seawater and in culture medium and the influence of simulated microbial film adhering on the surface of Fe₃Al were investigated by Electrochemistry, SEM, TEM etc. Some conclusions of the formation rules of microbial films attached to Fe₃Al surface and its influence on electrochemistry property of Fe₃Al have been achieved.It can be concluded that microbe can prohibit the formation of passivating film and accelerate the corrosion of Fe₃Al in real seawater as two times fast as in aseptic seawater. After having been exposed in real seawater for about 10 days, the surface of Fe₃Al began to be eroded and after 180 days denudation phenomenon can be observed owing to the prominent influence of SRB.Open circuit potential, polarization curves and impedance spectra curves of Fe₃Al in culture medium with and without microbe were studied in lab, and the corrosion behavior and mechanism of Fe₃Al influenced by oceanic microbe were also investigated. The open circuit potential of Fe₃Al exposed in culture medium with bacteria was higher than without bacteria but moved towards negative quickly after transient arrearage. In culture medium with bacteria, the cathodic polarization related to SRB and the diffusion of oxygen element simultaneously accelerated the cathodic polarization process of Fe₃Al electrode, increased the current density and moved the corrosion potential negative severely. At the same time, an evident current peak of anodic polarization curve emerged due to the pitting corrosion and the cracking of the passivating film. In the culture medium without bacteria, polarization current was lower, the corrosion potential moved negative slightly and the passivation section towards positive.Simulating microbe film method was used to investigate the corrosion behavior and mechanism of Fe₃Al influenced by different kinds of bacteria. The results indicated that the passivating film formed immediately when Fe₃Al electrodes without biofilm covered was exposed in simulated seawater, yet due to the inhomogeneity of the biomembrane and the permeation mechanism Fe₃Al with microbe film covered was under the condition of inducement pitting corrosion of passivating film. The corrosion process of Fe₃Al in the medium with manganic sediment was representative dominated by oxygen-diffusion. In the simulated environment with acetic acid, owing to the acidification of the medium hydrogen ion （H⁺） diffused to the surface of the electrodes through the film and converted the polarization reaction of cathode to hydrogen evolution reaction, and the pitting corrosion potential on the surface of Fe₃Al move towards negative in company with the increasing concentration of chlorine ion and the decreasing value of pH. Simulated SRB accelerated cathodic polarization process of Fe₃Al surface by reducing SO₄^2- to S^2-, corrosion potential dropped sharply and the surface oxidative membrane broken when polarization potential was at -0.5V.In addition, contrast test was done between stainless steel 304, carbon steel and Fe₃Al. Experimental results showed that there was abundant corrosive pittings on the surface of carbon steel when immersed in natural seawater. The existence of microbe decreased the diffusion velocity of oxygen and enhanced the corrosion process of anode of carbon steel but weakens that of cathode. As for stainless steel, there was no outstanding rust on the surface. The density of polarization current increased slightly and character of cathodic polarization didn’t change, density of passivation current in the region of anodic polarization remained stable all the time and didn’t reach any peak value when there was microbe.更多还原