Electrochemical stability, physical, and electronic properties of thermally pre-formed oxide compared to artificially sputtered oxide on Fe thin films in aqueous chloride

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Atomic emission spectroelectrochemistry (AESEC) combined with linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) provided insights on both active and passive dissolution of a Ni-Fe-Cr-Mn-Co multi-principal element alloy. Elemental dissolution rates measured by AESEC during open-circuit experiment were in agreement with those extrapolated from AESEC-LSV and indicated element-specific dissolution tendencies. AESEC-EIS at open-circuit potential showed nearly in-phase elemental dissolution during potential modulation which suggests a direct dissolution from the alloy surface to the electrolyte. In the passive potential domain, no oscillation of the elemental dissolution rate was detected by AESEC-EIS, suggesting non-oxidative chemical dissolution of the outer layer of the passive film. In this case, dissolution at the passive film/electrolyte interface was equal to the metal oxidation rate (passive current density) at the metal/passive film interface and the passive current density was independent of potential.

“…At 0.60 V vs SCE (Fig. 8b), a porous passive film model circuit 35,67 is suggested, probably due to the selective dissolution of Mn, Cr and Fe as previously shown in Fig. 7.…”

Section: ′ and Jsupporting

confidence: 70%

Elementally Resolved Dissolution Kinetics of a Ni-Fe-Cr-Mn-Co Multi-Principal Element Alloy in Sulfuric Acid Using AESEC-EIS

Han¹,

Gerard²,

Lü³

et al. 2022

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“…Oxide-based passivation was not likely in FLiNaK salts. 7 Instead, the E-i behavior resembled the behavior of salt film precipitation on a corroding metal surface as seen in some aqueous corrosion studies (e.g., chloride salt films on Ni-Cr alloy and stainless steel surfaces [32][33][34][35][36] ). The formation of a salt film on the Cr corroding surface may also occur in this case especially due to the low solubility limit of CrF 3 in FLiNaK salts (0.3 wt% or 5.51*10 −2 mol l −1 calculated by Yin et al 28,37 ).…”

Section: ( ) + ↔ ( ) [ ] + −mentioning

confidence: 52%

“…The smooth morphology may serve as another piece of evidence that the Cr was dissolving beneath a salt film. [32][33][34][35][36] The current density remained positive during the 50 h potentiostatic holding, indicating that the salt film formed did not retard Cr dissolution. Using Faraday's Law, it was calculated that up to 4 mm of Cr would have been dissolved assuming uniform attack (Fig.…”

Section: Hf Ms E H G F Ms 13mentioning

confidence: 99%

Corrosion Electrochemistry of Chromium in Molten FLiNaK Salt at 600 °C

Chan

Romanovskaia

Hong

et al. 2023

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The paper revisits the corrosion behavior of pure Cr in molten FLiNaK salt at 600°C from the perspective of corrosion electrochemistry. In this work, the potential-dependent, rate-limiting charge-transfer, and salt film-mediated mass-transport controlled regimes of Cr corrosion in FLiNaK at 600°C are investigated. The kinetic and thermodynamic parameters that limit electrodissolution and the consideration of grain orientation on these regimes are elucidated. At low Cr(III) concentrations, the corrosion process is governed by charge transfer control at low overpotentials and is crystal orientation dependent. However, when Cr(III) concentrations are high or when there is a high overpotential, the formation of a metal fluoride salt film on the Cr surface shifts the kinetic behavior to be governed by mass transport control at all anodic potentials with a surface morphology controlled by salt film deposition location and identity. Evan's diagrams were developed to consolidate and elucidate these observations. These findings were supported by an examination of the post-corrosion microstructure, X-ray diffraction of solidified salts, and thermo-kinetics analysis in each corrosion regime.

“…44,45 Suitability of sputtered thin films as surrogates is often a question in corrosion research as far as how accurately they represent a bulk alloy produced conventionally. 54 This is the subject of our separate studies and is beyond the scope of the current manuscript.…”

Section: Alloymentioning

confidence: 95%

A High Throughput Aqueous Passivation Testing Methodology for Compositionally Complex Alloys Using a Scanning Droplet Cell

Sur,

Joress,

Hattrick-Simpers

et al. 2023

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Compositionally complex alloys containing five or more principal elements provide an opportunity to explore a wide range of compositions, processing, and microstructural variables to find new materials with unique properties. In particular, the discovery of novel alloys that form self-healing protective passivating films is of substantial interest. Probing experimentally a robust landscape of such alloys requires the utilization of high-throughput electrochemical methods to uncover key differences, ideally captured by discriminating metrics, indicative of superior properties. Herein, a methodology is demonstrated using a scanning droplet cell for a rapid passivation behavior evaluation of Al0.7-x-yCoxCryFe0.15Ni0.15 combinatorial alloy library in 0.1 mol/L H2SO4(aq).