Microfabrication Methods Applied to the Development of Rigorously Defined Occluded Region Corrosion Samples

9811412裂纹腐蚀是由于金属表面的小封闭区域内的侵蚀性条件造成的。在缝隙腐蚀的模拟和实验结果的比较中，主要的绊脚石之一是在实验中产生直接相当于可用于计算建模的几何图形的缝隙样本所涉及的异常困难。在这项工作中，缝隙的两侧都构建在硅片衬底上。在金属沉积之前，通过对硅进行图案化、蚀刻和氧化来形成缝隙的金属侧。产生了高度平坦的表面。金属表面被分割，以允许测量缝隙内的电流分布。缝隙的缝隙形成侧(通过图案化和沉积二氧化硅形成)包含精确生长的间隔物，它将缝隙形成表面和金属电极之间的间隙控制到统一的、预先选定的水平。缝隙形成器包含pH、氯浓度和电化学势的微型传感器。利用这些样品进行了测量，测量结果与最近发展的二维遮挡区域质量传输模型的计算结果直接相关。探讨了控制缝隙腐蚀萌生和扩展的现象。%这项工作调查了阻碍开发有效的缝隙腐蚀缓解战略以及寿命预测方法的问题。这项研究对其他形式的腐蚀也有影响，因为控制许多类型腐蚀的关键结构和工艺在微米到亚毫米尺度上运行。例如，由于不锈钢中的夹杂物、铝合金中的成分颗粒、大气腐蚀中的液滴和有机涂层中的缺陷而引起的腐蚀的化学和电化学发生在1微米到几毫米的尺度上。控制结构的大小、规模和维度使得实验和计算研究非常具有挑战性，需要妥协和近似才能使问题易于处理。这种新方法可以改进量化评估。*

9811412KellyCrevice corrosion occurs as a result of aggressive conditions inside small occluded regions on metal surfaces. One of the primary stumbling blocks to the comparison of modeling and experimental results in crevice corrosion has been the extraordinary difficulty involved in experimentally producing a crevice sample that is directly equivalent to a geometry that is amenable to computational modeling. In this work, both sides of the crevice are constructed on silicon wafer substrates. The metal side of the crevice is formed by patterning, etching, and oxidizing the silicon before deposition of the metal. A highly planar surface is produced. The metal surface is segmented to allow measurement of current distribution within the crevice. The crevice-former side of the crevice (formed by patterning and depositing SiO2) contains precisely grown spacers that control the gap between the crevice-former surface and the metal electrode to a uniform, preselected level. The crevice former contains microsensors for pH, chloride concentration, and electrochemical potential. Using these samples, measurements are made that directly relate to computational results from a recently developed two dimensional occluded region mass transport model. In this way, the phenomena controlling crevice corrosion initiation and propagation are probed. %%%The work investigates issues that have prevented the development of effective crevice corrosion mitigation strategies as well as life prediction methodologies. The research has impact on other forms of corrosion because the critical structures and processes that control many types of corrosion operate on the micron to sub-mm size scale. For example, the chemistry and electrochemistry associated with corrosion due to inclusions in stainless steel, constituent particles in aluminum alloys, droplets in atmospheric corrosion, and defects in organic coatings occur on the 1-micron to several mm size scales. The size scale and dimensionality of the controlling structures make experimental and computational studies very challenging, requiring compromises and approximations in order to make the problem tractable. This new approach permits improved quantitative assessments.***