【作者】 郑莹莹；

【导师】 王佳；

【作者基本信息】 中国海洋大学 ， 应用化学， 2010， 硕士

【摘要】 腐蚀产物覆盖下金属的腐蚀行为是一个复杂的电化学过程,金属表面电化学不均一性是影响金属腐蚀行为及腐蚀速度的重要因素。经典电化学方法在金属腐蚀研究中仅能获得金属表面平均电化学信息,很难得到腐蚀界面微区的阴极和阳极电化学分布特征。而表面电位及电流分布是研究腐蚀电化学微区特征的重要参数,因此本论文采用扫描微电极技术及新型阵列电极技术研究了海水中碳钢腐蚀过程的电位及电流分布,结果表明虽然海水全浸环境中碳钢表面电化学状态分布不均匀,但是其表面电位及电流呈现一定的时空分布特征：当水平浸泡时,阳极区主要分布在中间,而阴极区分布在电极边缘,呈现包围分布的特征；垂直浸泡初期,阴极区主要分布在电极上端,随着时间增长表面电位逐渐正移,5周后电极底端成为主要的阴极区。本文还探讨了形成这种分布特征的原因：当水平浸泡时,海水中的溶解氧较容易扩散到电极边缘,使得电极周边溶解氧浓度远远大于中间部位,发生溶解氧还原反应,形成阴极区,从而导致了阴阳极包围分布的特征；当竖直浸泡时,初期由于氧浓差的存在使得电极顶端形成阴极区,但是为何阴极区随时间增长转移到电极底端,研究仍在进行之中。由于电极表面电位差是腐蚀过程的驱动力,本文在测试表面电位分布的同时发现碳钢表面电位随浸泡时间增长趋于正移并逐渐稳定,而阴阳极电位差也呈现逐渐减小的趋势,表明金属腐蚀速度逐渐稳定。腐蚀产物的存在严重地影响金属的腐蚀速率,因此本文研究了腐蚀产物在金属表面的分布特征和结构特征,研究表明碳钢在海水中浸泡一段时间(约8周)后锈层开始分为外锈层和内锈层：外锈层棕黄色,疏松多孔,主要由γ-FeOOH构成,并且随着时间增长锈层成分变化不大；内锈层为黑色,较致密,紧密附着于金属表面,其成分随时间增长变化很大,其中γ-FeOOH的量开始减少甚至消失,而β-FeOOH, Fe3O4的含量逐渐超过了γ-FeOOH,并且随着时间增长而增多。随着浸泡时间增长,内锈层逐渐增厚,而外锈层逐渐减薄。文章还探讨了腐蚀产物分布与电位分布的相关性,证实了腐蚀产物分布与表面电位分布特征存在着必然的联系：阴极区的腐蚀产物主要为β-FeOOH和Fe304,阳极区的腐蚀产物主要为γ-FeOOH和α-FeOOH。通过对碳钢电极表面的电化学不均匀性进行研究发现其阴阳极分布呈现一定的规律性,并且这种规律影响了表面腐蚀产物的形成,导致表面锈层成分产生差异,研究结果还证实了整体电极的电化学性质及表面腐蚀产物的形成与电位分布特征存在相关性,对于金属电化学腐蚀机理的研究有着重要的意义。更多还原

【Abstract】 Corrosion behavior of the metal covered with rust is a complex electrochemical system. The heterogeneous electrochemical characteristics of solution/metal interface can influence the corrosion behavior and corrosion rate which has drawn increasing attentions. Conventional electrochemical techniques, which have been successfully used in metal corrosion for many years can only obtain average data on metals surface. Therefore, it is very difficult to perform them in heterogeneous electrochemical research, but local electrochemical techniques can overcome these limitations. The current and potential distributions of metal surface are important parameters to study the micro-electrochemical characteristics. In order to study the current and potential distributions of the metal, scanning micro-electrode technique and wire beam electrode technique were used. The result showed that the current and potential had temporal and spatial distribution characteristics during the corrosion process though the metal surface was not uniform. When the samples were immersed into seawater horizontally, the cathodic region was chiefly distributed around the metal surface, while the middle area was the anode; when immersed vertically for only a few days, cathode was mainly located at the top of the electrode, with the immersion time increasing, potential on the surface shifted to positive direction and the bottom area with black products became the main cathodic region.The reasons for these distribution characteristics were explored. When immersed horizontally, dissolved oxygen could reach the edge of the electrode more easily than the middle area, so regions around the electrode had higher dissolved oxygen concentration, the dissolved oxygen reduced into OH-1 which made the edges became the cathode and the middle area was the main anode. When immersed vertically, the top of the strip electrode was closer to the surface of seawater and free oxygen from the atmosphere entered the water easily to form higher concentration of dissolved oxygen which resulted in the oxygen concentration cell. But then why the bottom of the electrode became the main cathode was not clear.A large number of experimental data have showed that the impetus for galvanic cell came from the potential difference between the cathode and anode. The potential difference on the surface was tested and the result indicated that the surface potential difference diminished with time, by which indicated that the corrosion rate was steadier than the early immersion.The composition and distribution characteristics of corrosion products which can influence the corrosion rate were tested by IR spectroscopy and ESEM. Studies indicated that after a period of time (about 8 weeks), rust layers were divided into two layers:the outer layer and the inner layer. The outer layer was loose and porous which was mainly composed ofγ-FeOOH and the rust composition changed little with time. The inner layer was black, more compact and closely attached to the metal surface and which components changed with time:theγ-FeOOH reduced or even disappeared while theβ-FeOOH and Fe3O4 gradually accumulated. With the increase of immersion time, the inner rust layer gradually thickened and the outer rust layer thinning. The result also indicated that there was a certain correlation between the corrosion products and potential distribution. Rust layer in the anode region was composed of (3-FeOOH and Fe3O4, in the meanwhile cathodic area was mainlyγ-FeOOH andα-FeOOH.All in all, the distribution of anode/cathode regions had certain regular by study the heterogeneous electrochemical characteristics on metal surface. These distribution features influenced the generation of the corrosion products as well as the composition of the rust. It was concluded that the potential distribution on metal surface was closely related to the corrosion products which have great significance for the further research on the corrosion electrochemical properties and mechanism of metal covered with rust.更多还原