Fundamental interfacial chemical processes, structures, and compositions underlying corrosion reactions

我们用来建造各种物品的许多金属，如核反应堆、硬币、飞机、整形外科植入物和POP罐，都是如此不稳定，以至于如果没有3-5纳米厚的氧化层(“钝化膜”)的保护，它们会迅速与周围环境反应，恢复到我们开采和提炼它们之前的化学形式。*这个项目使用先进的表面分析和电化学技术，能够探测到这样的薄层，以研究钛、锆和镍基高温合金上钝化膜的形成、它们的物理结构、它们的组成(从金属到金属)、以及它们如何降解或对周围环境做出反应。我们的目标是学习如何形成抵抗降解的被动氧化膜，以及如何使被动氧化膜在受损时自我修复。*金属面临的另一个重大挑战是局部腐蚀，即损害不是分布在金属表面，而是集中在一个小区域，导致深度渗透。局部腐蚀的一种隐蔽形式是缝隙腐蚀，它发生在接头和涂层下的裂缝和隐藏区域，其中狭窄的几何形状限制了化学物质进入或流出缝隙。*这个项目开发了创新的电化学方法来分析和绘制裂缝内腐蚀物种的分布和由此产生的腐蚀损害，我们将与裂缝的几何形状和形成它的材料的成分有关。我们还将使用X射线成像技术，在裂缝腐蚀时“看到”裂缝内部的结构。所学知识将用于帮助理解、避免和减轻缝隙腐蚀的影响，并设计更耐腐蚀的合金。*最后，我们将探讨氢在腐蚀反应中的作用。氢在腐蚀中大量存在，因为它是由金属与水或酸反应产生的，但在不破坏被分析的金属的情况下，很难在金属表面或金属表面检测到氢。我们将使用中子束或电子束来确定腐蚀反应期间或之后金属表面上的氢浓度，以调查表面氢是否可能导致腐蚀中的两种奇怪现象，即“负差效应”(加速镁合金的腐蚀)和“阴极修饰”(保护钛合金免受腐蚀)。我们还将测量隐藏在裂缝内的氢驱动腐蚀的量，仅基于裂缝外发生的氧驱动腐蚀，在损害预测中没有考虑到这一点。对钛和镍基合金的初步测量表明，氢反应会使腐蚀损害增加60%-500%或更多。

Many of the metals that we use to construct such diverse items as nuclear reactors, coins, aircraft, orthopaedic implants, and pop cans are so unstable that, without the protection of a 3-5 nanometres-thick layer of oxide (a “passive film”), they would quickly react with their surroundings and revert to the chemical forms in which they existed before we mined and refined them.***This project uses advanced surface analysis and electrochemical techniques capable of probing such thin layers to investigate how passive films form on titanium, zirconium, and nickel-based superalloys, their physical structure, their composition (which varies from metal to metal), and how they degrade or react with their surroundings. The goals are to learn how to form passive oxide films that resist degradation and how to make passive films that repair themselves if they become damaged.****Another significant challenge for metals is localized corrosion, in which the damage, rather than being distributed across the metal surface, is focused in a small area, resulting in deep penetration. An insidious form of localized corrosion is crevice corrosion, which occurs largely unseen in cracks and hidden areas in joints and under coatings where the narrow geometry restricts movement of chemical species into or out of the crevice. A build-up of corrosive chemical species occurs within the crevice, leading to accelerated attack.****This project develops innovative electrochemical methods to analyze and map the distribution of corrosive species and resultant corrosion damage inside crevices, which we will relate to the geometry of the crevice and the composition of the materials from which it is formed. We will also use X-ray imaging to “see” the internal structure inside a crevice as it corrodes. The knowledge gained will be used to help understand, avoid, and mitigate the effects of crevice corrosion and to design more resistant alloys.****Finally, we will explore the role of hydrogen in corrosion reactions. Hydrogen is abundant in corrosion, as it is produced by the reaction of a metal with water or acid, but difficult to detect in or on metal surfaces without destroying the metal being analyzed. We will use beams of neutrons or electrons to determine concentration of hydrogen on metal surfaces during or following corrosion reactions to investigate the possibility that surface hydrogen is responsible for two curious phenomena in corrosion called the “negative difference effect” (which accelerates corrosion of magnesium alloys) and “cathodic modification” (which protects titanium alloys from corrosion). We will also measure amounts of hydrogen-driven corrosion occurring hidden within crevices, unaccounted for in damage predictions based only on oxygen-driven corrosion occurring outside the crevice. Preliminary measurements on titanium and nickel-based alloys suggest that hydrogen reactions multiply corrosion damage by 60-500% or more.***