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

9811412 KellyCrevice腐蚀是由于金属表面上小闭塞区域内的侵蚀性条件而发生的。 在缝隙腐蚀的建模和实验结果的比较的主要障碍之一是非常困难的实验产生的缝隙样品，是直接相当于一个几何形状，是服从计算建模。 在这项工作中，裂缝的两侧都被构造在硅晶片衬底上。 在沉积金属之前，通过图案化、蚀刻和氧化硅来形成缝隙的金属侧。 产生高度平坦的表面。 金属表面被分段以允许测量缝隙内的电流分布。 缝隙的缝隙形成器侧（通过图案化和沉积SiO2形成）包含精确生长的间隔物，其将缝隙形成器表面和金属电极之间的差距控制到均匀的预选水平。 缝隙形成器包含用于pH、氯化物浓度和电化学电势的微传感器。 使用这些样品，测量直接涉及到最近开发的二维闭塞区质量输运模型的计算结果。 通过这种方法，探讨了控制缝隙腐蚀起始和扩展的现象。 这项工作调查的问题，阻碍了有效的缝隙腐蚀缓解战略的发展，以及寿命预测方法。 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都是在微米到亚毫米的尺度上进行的。 例如，由于不锈钢中的夹杂物、铝合金中的成分颗粒、大气腐蚀中的液滴以及有机涂层中的缺陷，与腐蚀相关的化学和电化学发生在1微米到几毫米的尺寸尺度上。 控制结构的尺寸尺度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，以便使问题易于处理。 这一新办法有助于改进定量评估。

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.***