In situ nano- to microscopic imaging and growth mechanism of electrochemical dissolution (e.g., corrosion) of a confined metal surface
In situ nano- to microscopic imaging and growth mechanism of electrochemical dissolution (e.g., corrosion) of a confined metal surface
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DOI：
10.1073/pnas.1708205114
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发表时间：
2017-09-05
影响因子：
11.1
通讯作者：
Valtiner, M.
中科院分区：
文献类型：
--
作者：
Merola, C.;Cheng, H. -W.;Valtiner, M.
限制中的反应对于广泛的应用和系统来说至关重要，但实时探测有限空间中的反应是出了名的困难。在受限金属表面上使用改进的电化学表面力装置（EC-SFA），我们在与腐蚀过程相关的环境中以明确的几何形状原位观察纳米到微米尺度的溶解和凹坑形成（与之前在非金属表面（例如二氧化硅）上的观察相似）。我们在不同 pH 值的中性 NaCl 溶液中实时跟踪“缝隙腐蚀”过程，并针对总面积类似于 0.03 mm(2) 的云母-镍限制界面施加镍表面电位（相对于溶液中的银垂直棒 AgCl 电极）。初始腐蚀以自催化点蚀的形式进行，表现为突然出现直径均匀为 6-7 μm、深度类似于 2-3 nm 的圆形凹坑。当氯化钠浓度高于 10 mM 时，点蚀在限制区域的外缘开始，而当浓度低于 10 mM 氯化钠时，点蚀在限制区域内部开始。我们将单个纳米级深坑的生长动力学和形状演变的统计分析与宏观实验的估计进行比较，以研究初始坑的生长和传播。我们的数据和实验技术揭示了一种机制，表明初始腐蚀会导致形成侵蚀性界面电解质，从而迅速加速点蚀，类似于有限区域内的裂纹萌生和扩展。这些结果支持了有限界面内多晶非贵金属、合金和无机材料的纳米级材料降解和溶解（例如缝隙腐蚀）的一般机制。
Reactivity in confinement is central to a wide range of applications and systems, yet it is notoriously difficult to probe reactions in confined spaces in real time. Using a modified electrochemical surface forces apparatus (EC-SFA) on confined metallic surfaces, we observe in situ nano- to microscale dissolution and pit formation (qualitatively similar to previous observation on nonmetallic surfaces, e.g., silica) in well-defined geometries in environments relevant to corrosion processes. We follow "crevice corrosion" processes in real time in different pH-neutral NaCl solutions and applied surface potentials of nickel (vs. Ag vertical bar AgCl electrode in solution) for the mica-nickel confined interface of total area similar to 0.03 mm(2). The initial corrosion proceeds as self-catalyzed pitting, visualized by the sudden appearance of circular pits with uniform diameters of 6-7 mu m and depth similar to 2-3 nm. At concentrations above 10 mM NaCl, pitting is initiated at the outer rim of the confined zone, while below 10 mM NaCl, pitting is initiated inside the confined zone. We compare statistical analysis of growth kinetics and shape evolution of individual nanoscale deep pits with estimates from macroscopic experiments to study initial pit growth and propagation. Our data and experimental techniques reveal a mechanism that suggests initial corrosion results in formation of an aggressive interfacial electrolyte that rapidly accelerates pitting, similar to crack initiation and propagation within the confined area. These results support a general mechanism for nanoscale material degradation and dissolution (e.g., crevice corrosion) of polycrystalline nonnoble metals, alloys, and inorganic materials within confined interfaces.