PDF(Pubmed)
Abstract：
Corrosion processes at cut edges of galvanized steels proceed as highly localized electrochemical reactions between the exposed bulk steel matrix and the protective thin metallic coating of a more electrochemically active material. Scanning microelectrochemical techniques can thus provide the spatially resolved information needed to assess the corrosion initiation and propagation phenomena, yet most methods scan cut edge sections as embedded in insulating resin to achieve a flat surface for scanning purposes. In this work, the galvanized coatings on both sides of the material were concomitantly exposed to simulated acid rain while characterizing the cut edge response using SECM and SVET techniques, thereby maintaining the coupled effects through the exposure of the whole system as rather realistic operation conditions. The cut edges were shown to strongly promote oxygen consumption and subsequent alkalization to pH 10-11 over the iron, while diffusion phenomena eventually yielded the complete depletion of oxygen and pH neutralization of the nearby electrolyte. In addition, the cathodic activation of the exposed iron was intensified with a thinner coating despite the lower presence of sacrificial anode, and preferential sites of the attack in the corners revealed highly localized acidification below pH 4, which sustained hydrogen evolution at spots of the steel-coating interface.
摘要：
镀锌钢的切割边缘处的腐蚀过程随着暴露的块状钢基体与电化学活性更强的材料的保护性薄金属涂层之间的高度局部化的电化学反应而进行。因此，扫描微电化学技术可以提供评估腐蚀引发和传播现象所需的空间分辨信息。然而，大多数方法扫描切割边缘部分嵌入绝缘树脂，以实现扫描目的的平面。在这项工作中,材料两侧的镀锌涂层同时暴露于模拟酸雨中，同时使用SECM和SVET技术表征切割边缘响应，从而保持耦合效应通过曝光的整个系统相当现实的操作条件。切割边缘显示出强烈促进氧气消耗和随后在铁上碱化至pH10-11，而扩散现象最终导致氧气的完全耗尽和附近电解质的pH中和。此外,尽管存在较低的牺牲阳极，但较薄的涂层增强了暴露的铁的阴极活化，并且在角落的优先攻击位置显示出低于pH4的高度局部化酸化，从而在钢-涂层界面的斑点处持续析氢。
