Nanoscale Corrosion Mechanisms in Carbon Steel

How can liquid cell TEM reveal nanoscale corrosion mechanisms in carbon steel?

Zhiheng Lyu, Qian Chen, and colleagues at the University of Illinois Urbana–Champaign, in collaboration with BP Technology, utilized a Hummingbird Scientific liquid flow TEM holder to capture real-time nanoscale corrosion initiation and progression in carbon steel lamellae immersed in pentanoic acid, a representative degradation product of triglyceride-based biofeedstocks. By correlating in-situ liquid-phase TEM imaging with ex-situ transmission Kikuchi diffraction (TKD), energy dispersive X-Ray spectroscopy (EDX), and thickness mapping, they identified key structural factors governing corrosion behavior: strain accelerates corrosion, lattice orientation directs propagation, and grain boundaries surprisingly exhibit minimal influence.

Liquid-phase TEM setup and observation of corrosion initiation. (A) Schematic illustration showing the setup of a liquid-phase TEM, where a carbon steel lamella is positioned parallel to the chip and immersed in pentanoic acid, both sealed between two SiNx chips. (B) SEM image of the coarse-grain lamella lying on the SiNx chip. The black box highlights the corrosion initiation area shown in (C,D). The blue and light blue boxes highlight the random perforation areas shown in Figures 4 and 5. (C) Grain orientation (inverse pole figure colored with respect to the z-axis orientation), KAM, and EDX maps of the area where corrosion initiates. The white dashed lines in the liquid-phase TEM image label the boundary of the crevice. (D) Time-lapse TEM images showing the corrosion propagation across the lamella. The orange boxes highlight the areas where perforation occurs. The two voids are labeled C1 and C2, respectively. The black dashed lines in (C,D) highlight the GBs. The light gray circles in (D) highlight species that are likely carbonaceous, potentially generated during corrosion. (E) Conductivity of pentanoic acid compared to typical conductivity ranges for different applications. Scale bars: 0.5 μm. Copyright © 2025 American Chemical Society. ACS Nano.

Using atomic-scale imaging and multimodal characterization techniques, the study reveals that corrosion in pentanoic acid behaves differently from corrosion in water. The results show that strain plays a major role, accelerating localized corrosion and often surpassing galvanic effects. Crystal orientation also influences the process, as corrosion tends to spread faster along the ⟨100⟩ direction. Grain boundaries appear to have minimal impact on corrosion rates, challenging the long-held belief that they are key drivers of localized corrosion.
Together, these insights suggest practical strategies for protecting petroleum infrastructure when using biofeedstocks, including reducing internal strain through heat treatments, applying protective coatings, and designing steel microstructures with improved resistance.

Zhiheng Lyu, Samyukta Shrivastav, Jiahui Li, Chang Qian, Lehan Yao, Nachi Shah, Maryam Eslami, Chang Liu, Sheila Ismail, John Shabaker, Eric Doskocil, Daniel V. Krogstad, Jessica A. Krogstad, Qian Chen. ACS Nano 2025, DOI: https://doi.org/10.1021/acsnano.5c06142.

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