Design, construction, and validation for in-situ water layer thickness determination during accelerated corrosion testing

Katona, Ryan; Tokuda, Setsuko; Perry, Jane; Kelly, Robert G.

doi:10.1016/j.corsci.2020.108849

Cited by 18 publications

(9 citation statements)

References 34 publications

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“…51 At atmospheric conditions, the number of water layers residing on the outer surface of the oxide film depends on the humidity but usually exceed a few nanometer in thickness. 52,53 We focus on charge-neutral interfaces with no electric double layers in the electrolyte, and assume that ∼12-18 Å thick pure water films suffice. A system size convergence check is conducted for the lower energy cut of the (110) oxide surface.…”

Section: A Dft Detailsmentioning

confidence: 99%

First Principles Determination of the Potential-of-Zero-Charge in an Alumina-coated Aluminum/Water Interface Model for Corrosion Applications

Leung

2022

Preprint

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The surfaces of most metals immersed in aqueous electrolytes have a several-nanometer-thick oxide/hydroxide surface layer. This gives rise to the existence of both metal|oxide and oxide|liquid electrotlyte interfaces, and makes it challenging to correlate atomic length-scale structures with electrochemical properties such the potential-of-zero-charge (PZC). The PZC has been shown to be correlated the pitting onset potential for corrosion. In this work, we conduct large-scale Density Functional Theory and ab initio molecular dynamics to calculate the PZC of a Al(111)|γ-Al 2 O 3 (110)|water double-interface model within the context of aluminum corrosion. By partitioning the multiple interfaces involved into binary components with additive contributions to the overall work function and voltage, we predict the PZC to be -1.53 V vs. SHE for this model. We also calculate the orbital energy levels of defects like oxygen vacancies in the oxide, which are critical parameters in theories associated with pitting corrosion. We predict that the Fermi level at the PZC lies above the impurity defect levels of the oxygen vacancies, which are therefore uncharged at the PZC. From the PZC estimate, we predict the voltage needed to create oxygen vacancies with net positive charges within a flat-band approximation.

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Section: A Dft Detailsmentioning

confidence: 99%

First Principles Determination of the Potential-of-Zero-Charge in an Alumina-coated Aluminum/Water Interface Model for Corrosion Applications

Leung

2022

Preprint

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“…Control of the WL thickness is important in these tests, although none of the standard test methods address it. Tokuda, et al, 34 developed a means of measuring WL thickness in conditions where the electrolyte composition is known, such as B117 testing. The principle is simple: measure the resistance of the WL using electrochemical impedance then, knowing the solution composition (and hence the conductivity), the WL thickness can be calculated as long as the cell constant is known.…”

Section: Measurement Of Water Layer Thicknessmentioning

confidence: 99%

“…Some standard test methods allow angles from 6°to 45°. 34 This phenomenon not only could be part of the explanation for the well-known variability in B117 testing but also creates concerns about the lack of tight control of WL in the lab and the connection to service conditions.…”

Section: Measurement Of Water Layer Thicknessmentioning

confidence: 99%

“…For AA5XXX alloys, the rate of IGC is strongly dependent on potential, increasing as the potential becomes more positive. 34 To investigate how this may occur, Lim, et al, 35 described the use of electrodes made with the same chemistry as the main solid solution (α) and the β phase. During IGC, the majority of the surface of the grain boundary fissure itself is α, so it would be expected that the fissure solution chemistry would reflect the α composition.…”

Section: Modeling Of Intergranular Corrosion In Aa5xxxmentioning

confidence: 99%

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2021 W.R. Whitney Award: The Importance of Local Chemistry and Potential in Localized Corrosion and Stress Corrosion Cracking

Kelly¹

2021

Corrosion

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The nature and rates of the chemical and electrochemical reactions that occur within the occluded regions of a given alloy are controlled by the local electrochemical potential and the local solution composition. The very small physical dimensions of these regions lead to challenges in both measurement and modeling. When performed in a coordinated and complementary way, measurements and modeling provide insights into the controlling processes of a range of localized corrosion phenomena, including crevice corrosion, pitting, intergranular corrosion, and stress-corrosion cracking. Examples of attempts to overcome the measurement challenges are described for a range of corrosion scenarios, including identification of the critical ionic species in stainless steel crevice corrosion and in the corrosion of aircraft lap joints, operando measurement of chemistry and potential simultaneously within stress-corrosion cracks, and monitoring of water layer thickness in salt spray testing. Examples of work addressing the challenges in modeling localized corrosion including intergranular corrosion of AA5XXX alloys, scaling laws in crevice corrosion, the extent to which the Laplace Equation can be used and applied to geometrically complex galvanic structures, and an approach to modeling localized corrosion for extraordinarily long service times. Finally, suggestions regarding future avenues of research are provided.

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“…However, the convection caused by density gradients has to be considered in electrochemical measurements, especially at high redox concentrations and long time durations . Intriguingly, spontaneous convection, in which the local microscopic chaotic motion in stagnant solution was regarded as the cause for this convection, has been adopted in many aqueous systems. − However, this spontaneous convection model was built based on a turbulent flow case; therefore, we will not consider this spontaneous convection in the present study . Instead, Andrieux et al described the natural convection effects on electrochemical reactions with a convection–diffusion layer (CDL) model .…”

Section: Introductionmentioning

confidence: 99%

Natural Convection in Molten Salt Electrochemistry

Ge,

Cai,

Zhu

et al. 2023

J. Phys. Chem. B

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Molten salt electrochemistry has been widely used in many fields, especially for metal extraction/refinement. The understanding of mass transfer in molten salts under harsh operation conditions is of great importance to reveal reaction mechanisms and advance fine technologies. It has been generally assumed that natural convection is negligible in stagnant molten salt electrochemistry. Herein, we report an abnormal natural convection in molten LiCl−KCl, with the arising time from 2.37 s at 873 K to 10.13 s at 673 K. Using the concentration correction factor, the derived thickness of the natural convection−diffusion layer (δ conv. ) was found to be ranging from 128 to 163 μm, much thinner than those in aqueous solutions (∼200 μm). The simulations showed that the notable natural convection resulted from convection−diffusion layer (CDL) convection dominated over the density-driven convection even at high redox concentrations, implying the severe vibration of molten salt systems. To suppress the intense natural convection, we predicted that the use of microelectrodes (with radii less than 23.2 μm for δ conv. = 150 μm) would be a promising tool, regardless of their inferior stabilities in high-temperature molten salts at this stage. These innovative findings offer insights into the impact of natural convection on mass transfer in molten salts that have not been previously revealed.

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Design, construction, and validation for in-situ water layer thickness determination during accelerated corrosion testing

Cited by 18 publications

References 34 publications

First Principles Determination of the Potential-of-Zero-Charge in an Alumina-coated Aluminum/Water Interface Model for Corrosion Applications

First Principles Determination of the Potential-of-Zero-Charge in an Alumina-coated Aluminum/Water Interface Model for Corrosion Applications

2021 W.R. Whitney Award: The Importance of Local Chemistry and Potential in Localized Corrosion and Stress Corrosion Cracking

Natural Convection in Molten Salt Electrochemistry

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