In situ nano- to microscopic imaging and growth mechanism of electrochemical dissolution (e.g., corrosion) of a confined metal surface

Abstract

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|AgCl electrode in solution) for the mica-nickel confined interface of total area ∼0.03 mm The initial corrosion proceeds as self-catalyzed pitting, visualized by the sudden appearance of circular pits with uniform diameters of 6-7 μm and depth ∼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.

Surface Forces Apparatus Measurements of Interactions between Rough and Reactive Calcite Surfaces

“…Any 4 substantial roughening of calcite led to a significant increase of the repulsive mechanical force contribution.Even though the AFM is an extremely powerful tool in force measurements, it usually provides no information about the instantaneous changes in contact surface topography. In this work, we used the Surface Forces Apparatus (SFA), a force measuring technique that enables in situ observations of surface alteration processes by multiple beam interferometry (MBI) 42,[48][49] . We follow how the growth, dissolution and related changes in surface roughness in µm-sized contact areas affect the magnitude and range of forces between dynamic and rough, polycrystalline calcite surfaces.…”

Steel corrosion inhibition by calcium nitrate in halide-enriched completion fluid environments

“…In unpassivated alloys, this forebodes the fast expansion of the pit mouth due to an electrostatically induced change in interfacial tension at the steel-solution interface. 45 At later times, however, such lateral expansion is expected to hinder pit deepening due to attenuation of the local concentration gradients of ions in the pit. This suggests that in simply oxidized, that is, non-passivated systems, the pit morphology shown in Fig.…”

Theory and experiments join forces to characterize the electrocatalytic interface

“…Similarly, organic electronics could be better described if the influence of the applied voltage and the surrounding electrolyte were included. On a more industrial level, these methods would also be ideally suited to study electroplating and corrosion (25), which is very poorly understood and, despite its economic importance (corrosion generates costs of ∼3% of the gross domestic product) (26), underrepresented in fundamental research. Lastly, the characterization of relevant reaction intermediates during electrocatalytic reactions might accelerate catalyst design in diverse areas of electrolysis and fuel cells, including the production of hydrogen over (nonnoble) metals from water reduction and biomass oxidation; the improvement in the still incompletely understood oxygen reduction and evolution reaction; the development of efficient nitrogen reduction catalysts that would allow the decentralization of ammonia production; and, of course, the CO 2 electroreduction investigated by Cheng et al (3) that has the potential to sustainably close the carbon cycle by converting the greenhouse gas CO 2 into carbon building blocks that, one day, could replace fossil resources as the basis of chemical industry.…”