4-dimensional digital inline holography of pitting corrosion of metal alloys

许多环境和经济上重要的化学反应发生在固体和气体或液体之间的界面上。其中一些反应具有负面后果，例如材料腐蚀。该研究计划将专注于金属合金，特别是不锈钢和铝合金的破坏性点蚀。这些合金被设计成耐腐蚀的，并且通常由氧化物层保护。然而，在某些情况下，它们会受到局部点蚀的影响，这可能会导致问题。大约30%的化工厂故障与这种形式的腐蚀直接相关，代价巨大。 为了研究点蚀的初始步骤，我采用了椭圆显微镜表面成像（EMSI），这是我的团队早期开发的一种技术，能够监测液相。我们现在可以测量不锈钢和其他合金上亚稳态点蚀事件周围保护性氧化层的厚度变化。与理论家合作，将进一步开发和分析这种腐蚀现象的新数学模型。 在这个项目中，我们提出了一种新的方法，数字同轴全息（DIH），同时与EMSI和对比度增强的光学显微镜图像粒子从腐蚀表面喷射。DIH将样品前面的整个体积表示为一个单一的图像，即全息图。数学算法可以重建成像体积内的颗粒的三维呈现。这将有助于理解点蚀过程中发生的初始过程。 这些研究的长期目标将是找到表面活性剂，即使是少量的表面活性剂也能够抑制点蚀的发生。减少腐蚀可能会产生巨大的经济和环境后果。

Many environmentally and economically important chemical reactions take place on surfaces at the interface between solids and gases or liquids. Some of these reactions have negative consequences, e.g. corrosion of materials. This research program will be focusing on the devastating pitting corrosion of metal alloys, specifically stainless steels and aluminum alloys. These alloys are designed to be corrosion resistant and are normally protected by an oxide layer. Nevertheless under some conditions they are affected by localized pitting corrosion, which can cause problems. About 30% of chemical plant failures are directly correlated to this form of corrosion at tremendous costs.           To study the initial steps of pitting corrosion, I adapted Ellipso-Microscopy for Surface Imaging (EMSI), a technique my group had developed earlier, to be able to monitor liquid phases. We can now measure thickness changes of the protective oxide layer surrounding metastable pitting events on stainless steels and other alloys. In collaboration with theoreticians, a new mathematical model of such corrosion phenomena will be further developed and analyzed.           In this project, we propose to apply a new method, Digital Inline Holography (DIH), simultaneously with EMSI and contrast enhanced optical microscopy to image particles ejected from a corroding surface. DIH represents the complete volume in front of the sample into one single image, the hologram. Mathematical algorithms can reconstruct a 3-dimentional presentation of particles within the imaged volume. This will help to understand the initial processes occurring during pitting corrosion.           The long-term aim of these studies will be to find surfactants, which, even in diminutive quantities are capable of suppressing the onset of pitting corrosion. Reducing corrosion could have enormous economical and environmental consequences.