Atmospheric corrosion of metals is the most common type of corrosion which has a significant impact on the environment and operational safety in various situations of everyday life. Some of the common examples can be observed in land, water and air transportation systems, electronic circuit boards, urban and offshore infrastructures. The dew drops formed on metal surface due to condensation of atmospheric moisture facilitates corrosion as an electrolyte. The corrosion mechanisms under these droplets are different from classically known bulk electrolyte corrosion. Due to thin and non-uniform geometric thickness of the droplet electrolyte, the atmospheric oxygen requires a shorter diffusion path to reach the metal surface. The corrosion under a droplet is driven by the depletion of oxygen in the center of the droplet compared to the edge, known as differential aeration. In case of a larger droplet, differential aeration leads to preferential cathodic activity at the edge and is controlled by the droplet geometry. Whereas, for a smaller droplet, the oxygen concentration remains uniform and hence cathodic activity is not controlled by droplet geometry. The geometry of condensed droplets varies dynamically with changing environmental parameters, influencing corrosion mechanisms as the droplets evolve in size. In this review, various modelling approaches used to simulate the corrosion under droplet electrolytes are presented. In the efforts of developing a comprehensive model to estimate corrosion rates, it has been noted from this review that the influence of geometric evolution of the droplet due to condensation/evaporation processes on corrosion mechanisms are yet to be modelled. Dynamically varying external factors like environmental temperature, relative humidity, presence of hygroscopic salts and pollutants influence the evolution of droplet electrolyte, making it a complex phenomenon to investigate. Therefore, an overview of available dropwise condensation and evaporation models which describes the formation and the evolution of droplet geometry are also presented from an atmospheric corrosion viewpoint.

通过对碳钢和不锈钢紧固件在海洋环境中的腐蚀特征、腐蚀产物和电偶极化等内容的比较性研究，提出了两种不同的腐蚀机制。对于碳钢紧固件，锈层增加了额外的IR降，削弱了阴极区对阳极缝隙区的极化作用，供氧的差异导致螺纹曝露部位的腐蚀更为严重，腐蚀形式以均匀腐蚀为主。对于不锈钢紧固件，缺氧的环境导致螺纹缝隙部位的钝化膜性能劣化，螺杆曝露区对螺纹缝隙区的电偶极化作用促使缝隙区腐蚀更为严重，腐蚀形式以点蚀为主。针对碳钢和不锈钢紧固件在海洋环境中的不同腐蚀机制，提出了差异化的腐蚀防护技术思路。

为研究海洋浪溅区Q690高强钢材腐蚀行为和表面形貌分布特征，通过盐水周浸-湿热循环试验得到不同周期锈蚀试件，利用激光共聚焦显微镜 (LSCM) 采集表面的坐标参数，分析了微观形貌尺寸随着腐蚀周期的变化规律。结果表明：在腐蚀初始阶段，表面产生少量针状点蚀产物，金属色泽逐渐丧失，随着腐蚀损伤程度增加，材料表面点蚀形貌逐渐向坑蚀发展，处于腐蚀后期时，分布有大量层状产物，局部区域存在剥落现象。此外，根据微观扫描分析可知，表面堆积产物对基体内部具有较好保护作用，腐蚀行为沿着水平方向快速延伸，最终完全包裹试件表面，当腐蚀周期为100 d时，体积损失率和表面腐蚀高度分别为1.38%和840 μm。

This communication provides an overview of the literature on the biocorrosion of steel in marine media, influenced by the presence of sulphate-reducing bacteria (SRB). Electrochemical aspects, microbial interactions within biofilms, the significance of medium composition and the role of iron sulphides, and hydrogen effects are discussed. A brief description of recent experiments involving the use of electrochemical techniques for corrosion assessment, surface studies employing energy dispersive X-ray analysis (EDAX), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and electron microprobe complemented with electron microscopy observations, as well as the application of novel techniques, such as micro sensors and atomic force microscopy, is given. The growth of SRB in marine environments causes significant modifications of many physicochemical parameters at the steel/seawater interface, including local changes in pH and redox potential values, variations in anion and cation concentrations and alteration of the composition and structure of corrosion products. Complex chemical and biological reactions and equilibria are also markedly altered during bacterial proliferation. These effects, which are absent in abiotic media, often lead to significant changes in the corrosion behaviour of steel. The complicated nature of the local environment at the steel/seawater interface is enhanced in the presence of microorganisms and their extracellular polymeric substances (EPS). As a consequence of biofilm heterogeneity, areas with different ion concentrations are formed and the development of corrosion product layers of dissimilar protective characteristics occurs.

To determine the signal recognition particle (SRP)-SRP receptor (Srb) system in Bacillus subtilis (Bs), we cloned the Bs srb gene, which encodes a homologue of the mammalian SRP receptor alpha-subunit [Oguro et al., DNA Res. 2 (1995) 95-100]. We sequenced a 6098-bp DNA containing srb and analyzed the gene organization. Primer extension experiment and Northern blot analysis revealed that srb constitutes an operon with two additional ORFs. A database search of known proteins revealed that one encodes a homologue of Escherichia coli RNase III [36.0% identical amino acids (aa)] and the other encodes a homologue of yeast Smc1 (26.6% identical aa). We then constructed a Bs mutant in which srb expression was induced by IPTG. The depletion of Srb caused a defect in the cell growth and the cells became filamentous and twisted. Furthermore, pulse-chase experiments using this mutant revealed that the 17% of the beta-lactamase precursor accumulated in the cell after a 4-min chase in the absence of IPTG, although almost all of the precursors were converted into the mature from after a 1-min chase in the presence of IPTG.

In this study, the corrosion behavior of X60 was investigated in the presence of a mixed culture of sulfate-reducing bacteria (SRB) and iron-reducing bacteria (IRB) via weight loss, electrochemical impedance spectroscopy (EIS), and Tafel polarization techniques. Moreover, field emission scanning electron microscope (FESEM) images and X-ray diffraction spectrometry (XRD) were used to study the morphological changes of the surface of X60 and the composition of corrosion products after exposing X60 to the abiotic and biotic systems. EIS result confirmed the occurrence of microbial corrosion in the presence of SRB and IRB. In the exposed coupon to the mixture of bacteria, the result illustrated that the existence of IRB promoted the SRB growth, so corrosion rate increased compared to the exposed coupon to SRB and IRB, respectively. The mixture of SRB and IRB showed a synergistic effect and enhanced the pitting corrosion on the surface of X60.

采用不同含量的Na₂S来模拟不同的含硫环境，利用挂片浸泡实验研究P110S钢级油套管在含硫体系中的腐蚀行为；利用电化学测试研究了其在不同含硫浓度中电化学特征；利用扫描电镜、激光共聚焦、XRD以及拉曼光谱对样品表面的腐蚀产物和形貌进行了表征。结果表明，P110S钢级油套管钢在含硫体系中发生严重的腐蚀，腐蚀速率和腐蚀电流密度均随含硫浓度增大而增大，腐蚀类型由均匀腐蚀转变为点蚀，腐蚀产物疏松。