Injection of Vacancy-Type Defects and Hydrogen by Metallic Corrosion

技术：PI实验室最近的工作揭示了铝上凹坑引发的潜在重要方面。特别是，正电子湮没研究已经在氧化物/金属界面附近发现了纳米级的空洞，因为它们的金属表面是无氧化物的，可以作为局部腐蚀开始的高活性部位。通过常温腐蚀过程观察到界面空洞的形成，导致了空洞是由空位-氢缺陷注入造成的假设。该项目将结合显微镜和表面分析探针，使用正电子方法来确定空洞形核和生长的机制。使用高纯度铝的研究将表征简单腐蚀过程中亚表面缺陷的行为，包括由于金属溶质原子捕获缺陷的影响。与实验相结合，将开发一个原子水平的空穴形成模拟，基于从严格的理论方法得出的控制缺陷形成、结合和迁移率的计算能量。实验和理论相结合的方法将为理解金属相组成影响的腐蚀相关缺陷的形成提供基本的基础。这一结果有望阐明氢在腐蚀过程中进入铝的机理，以及氢在近表面区域的扩散和反应。非技术性：点蚀，即金属溶解被限制在受氧化膜保护的表面的一小块区域内，在结构金属中普遍存在。由于凹坑形成的固有表面缺陷的性质不能很好地理解，因此不能有效地预测由凹坑引起的损伤。这些结果对于理解环境辅助裂化也是至关重要的，因此所获得的基本理解应该会影响这一领域。通过这项工作，学生将接受由化学工程、物理、材料科学和化学方面的教员组成的跨学科团队的培训。他们将学习将凝聚态物理建模方法引入工程科学领域，以应对一个具有重大经济意义的问题。即使在当今跨学科研究的氛围下，这样的教育经历也是不寻常的。学生培训将利用爱荷华州研究生和本科生课程的强大影响力，在系级和大学层面促进代表性不足的群体。

TECHNICAL: Recent work in the PI's laboratory has revealed potentially important aspects of pit initiation on aluminum. In particular, positron annihilation studies have detected nanometer-scale voids near the oxide/metal interface, which because their metal surface is oxide-free, can function as highly reactive sites at which localized corrosion initiates. The observation of interfacial void formation by ambient-temperature corrosion processes has led to the hypothesis that voids result from the injection of vacancy-hydrogen defects. The project will determine the mechanism of void nucleation and growth using positron methods in combination with microscopy and surface analytical probes. Studies using high-purity Al will characterize the behavior of subsurface defects during a simple corrosion process, including effects due to trapping of defects by metal solute atoms. In tandem with the experiments, an atomistic-level simulation of void formation will be developed, based on calculated energies governing defect formation, binding, and mobility, derived from rigorous theoretical approaches. The combined experimental-theoretical approach will provide a fundamental basis of understanding for formation of corrosion-relevant defects, as affected by metal-phase composition. The results are expected to elucidate the mechanism of hydrogen entry into aluminum during corrosion, and its diffusion and reactions in the near-surface region. NON-TECHNICAL: Pitting corrosion, in which metal dissolution is confined to a small area on an otherwise oxide film-protected surface, is widespread among structural metals. Since the nature of inherent surface defects where pits form is not well understood, damage due to pitting cannot be effectively predicted. Results are also of critical interest for understanding of environment assisted cracking, and so the fundamental understanding obtained should impact this field. Through this work, students will be trained by an interdisciplinary team assembled from faculty in chemical engineering, physics, materials science and chemistry. They will learn to bring condensed matter physics modeling approaches into the realm of engineering science, in order to confront a problem of significant economic relevance. Even in today's atmosphere of interdisciplinary research, such educational experiences are unusual. Student training will take advantage of the strong presence at Iowa State of graduate and undergraduate programs promoting under-represented groups, both at the Departmental and University levels.