X‐Ray Absorption Study of Electrochemically Grown Oxide Films on AlCr Sputtered Alloys: II . In Situ Studies

Frankel, G. S.; Schrott, A. G.; Jahnes, C.; Russak,; Davenport, Alison J.; Isaacs, H.S.

doi:10.1149/1.2054714

Cited by 21 publications

(9 citation statements)

References 8 publications

(19 reference statements)

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“…[53][54][55] The valence state of atoms and their coordination numbers have been studied by using X-ray absorption near-edge structure and extended X-ray absorption fine structure analysis, but these were often limited to pure metals and binary alloys. [56][57][58][59][60][61][62][63][64][65][66][67][68][69] Synchrotron XRD measurements have been performed at grazing incidence (GIXRD) to analyze thin-surface layers with high resolution and sensitivity, showing advantages for rapid and detailed structural characterization. [70][71][72][73][74][75] Moreover, X-ray reflectivity (XRR) measurements have also been employed to study electrochemical oxide growth on pure metal and alloys.…”

Section: Introductionmentioning

confidence: 99%

Redefining passivity breakdown of super duplex stainless steel by electrochemical operando synchrotron near surface X-ray analyses

et al. 2019

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Passivity determines corrosion resistance and stability of highly-alloyed stainless steels, and passivity breakdown is commonly believed to occur at a fixed potential due to formation and dissolution of Cr(VI) species. In this work, the study of a 25Cr-7Ni super duplex stainless steel in 1 M NaCl solution revealed that the passivity breakdown is a continuous degradation progress of the passive film over a potential range, associated with enhanced Fe dissolution before rapid Cr dissolution and removal of the oxide. The breakdown involves structural and compositional changes of the passive film and the underlying alloy surface layer, as well as selective metal dissolution depending on the anodic potential. The onset of passivity breakdown occurred at 1000 mV/ Ag/AgCl , and Fe dissolved more on the ferrite than the austenite phase. With increasing potential, the passive film became thicker but less dense, while the underlying alloy surface layer became denser indicating Ni and Mo enrichment. Rapid Cr dissolution occurred at ≥1300 mV/ Ag/AgCl .

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Section: Introductionmentioning

confidence: 99%

Redefining passivity breakdown of super duplex stainless steel by electrochemical operando synchrotron near surface X-ray analyses

et al. 2019

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“…3 X-ray adsorption offers a powerful method for the in situ study of the kinetics of chemical changes taking place at surfaces, by monitoring the growth and dissolution of the films. [3][4][5][6][7][8][9][10][11][12] X-ray adsorption near-edge structure ͑XANES͒ has been used to study the products of reactions of chromate conversion coatings ͑CCC͒ adhering to Al surfaces, and the behavior of these products with time and exposure to solutions. [4][5][6][7][8][9][10][11][12][13] CCCs are made up of Cr͑III͒ and Cr͑VI͒ species such as in CrO 4…”

mentioning

confidence: 99%

“…[3][4][5][6][7][8][9][10][11][12] X-ray adsorption near-edge structure ͑XANES͒ has been used to study the products of reactions of chromate conversion coatings ͑CCC͒ adhering to Al surfaces, and the behavior of these products with time and exposure to solutions. [4][5][6][7][8][9][10][11][12][13] CCCs are made up of Cr͑III͒ and Cr͑VI͒ species such as in CrO 4…”

mentioning

confidence: 99%

Formation of Chromate Conversion Coatings on Aluminum and Its Alloys

Isaacs

Sasaki

Jeffcoate

et al. 2005

J. Electrochem. Soc.

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In situ X-ray adsorption near-edge structure ͑XANES͒ has been used to investigate the formation of chromate conversion coatings on pure Al, commercial Al alloys ͑AA 1100, AA2024, and AA7075͒, and a series of binary Al-Cu alloys. The method employed cells designed to determine the growth of the total chromium ͓Cr͑total͔͒ and hexavalent chromate ͓Cr͑VI͔͒ in the chromate conversion coating ͑CCC͒ as a function of exposure time to a chromate solution. Three sets of data were obtained, where ͑i͒ the Al was exposed to only a limited amount of solution; ͑ii͒ the chromate solution was excluded after short periods of repeated exposures to the solution; and ͑iii͒ the Al was exposed continuously to the chromate solution. All the results showed a very rapid initial growth within the first seconds, followed by a continued increase in thickness for exposures up to 1 h. Measurements with Al-Cu binary alloys demonstrated that the difference observed in AA2024 and AA1100 may not be due to Cu alloying. used electrochemical reduction of chromate on graphite electrodes to monitor chromate that did not react at the Al surface. The former investigators used a rotating ring-disk method with an Al alloy as the disk and graphite ring.2 The latter investigators employed a flow system with a graphite electrode downstream to an Al alloy to study CCC growth following laser removal of a thin mask that initially protected the Al. They also employed a quartz crystal microbalance on which the alloy film was sputtered, and coupled the mass variations with chromate consumption. 3 X-ray adsorption offers a powerful method for the in situ study of the kinetics of chemical changes taking place at surfaces, by monitoring the growth and dissolution of the films.3-12 X-ray adsorption near-edge structure ͑XANES͒ has been used to study the products of reactions of chromate conversion coatings ͑CCC͒ adhering to Al surfaces, and the behavior of these products with time and exposure to solutions. [4][5][6][7][8][9][10][11][12][13] CCCs are made up of Cr͑III͒ and Cr͑VI͒ species such as in CrO 4 2− ; the latter is believed to be responsible for CCC's ability to protect scratches on a metal surface from undergoing further electrochemical degradation. A factor that assists in the determination of Cr speciation is a distinct pre-edge peak at 5993 eV in the XANES spectrum when hexavalent chromium Cr͑VI͒ is present. In addition, the ratio of height above the edge arising from all chromium species present ͓Cr͑total͔͒ to the pre-edge height ͓only Cr͑VI͔͒ provides a quantitative measure of Cr͑VI͒ content in the CCC. However, XANES measurements of CCC have generally been made ex situ.In this study, we introduce designs of cells that allow monitoring of a specimen surface exposed to a chromate solution without being removed from the aqueous environment. We present data on aluminum and its alloys ͑i͒ when exposed to a limited volume of solution; ͑ii͒ when subjected to repeated exposure to the chromate solution; and ͑iii͒ when continuously exposed to the CCC solution. Fro...

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“…The depth distribution and valence of ion species in artificial crevices have been investigated by Isaacs et al using X-ray fluorescence techniques. [9][10][11] For instance, an in situ study of anodic dissolution of stainless steel in chloride solution found that the salt layer formed on nickel/chromium steels was rich in iron and contained little nickel and a very small amount of chromium. 9 In an attempt to understand the dissolution kinetics for pits and crevices in aluminum and to determine if dichromate inhibits localized corrosion by reducing the dissolution kinetics, the electrochemical behavior of aluminum artificial crevice electrodes in chloridecontaining solutions with and without dichromate ions was investigated in the present work.…”

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confidence: 99%

The Influence of Dichromate Ions on Aluminum Dissolution Kinetics in Artificial Crevice Electrode Cells

Akiyama

Frankel

1999

J. Electrochem. Soc.

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*Electrochemical Society Active Member.Dissolution kinetics for pits and crevices in aluminum and the effect of dichromate ions on the dissolution kinetics were investigated by using artificial crevice electrodes. The aluminum artificial crevice electrodes were potentiostatically polarized over a range of potential in 0.1 M NaCl solution with and without dichromate ions. The anodic dissolution charge, and cathodic charges for the hydrogen and dichromate reduction reactions, were measured. The addition of dichromate ions did not suppress the active dissolution. This indicates that the mechanism of localized corrosion inhibition by dichromates is something other than anodic inhibition of Al dissolution in the pit or crevice environment. The relative amount of local cathodic reactions on Al was increased by the addition of dichromate because of the dichromate reduction. The initial dissolution of aluminum in a crevice was ohmic controlled. From the change in the dissolution current with time, the conductivity of the crevice and potential at the bottom of crevice were estimated. The conductivity and the bottom potential decreased with the ratio of cathodic charge of hydrogen evolution to anodic dissolution charge. The conductivity in the crevice and thus the dissolution current seem to be controlled by hydrogen evolution and only indirectly by dichromate concentration.The influence of chromate on pitting of aluminum and aluminum alloys is well-known, and chromate-based corrosion inhibitors and coatings are widely used for the protection of Al and its alloys. However, the mechanism of the inhibition effect of chromates is still unclear. One possible explanation for the inhibition of localized corrosion of aluminum by chromates is that they reduce the local dissolution kinetics, effectively preventing pitting from occurring.In order to study various aspects of the kinetics of pit growth, artificial pit or crevice electrodes have been used by researchers previously.

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X‐Ray Absorption Study of Electrochemically Grown Oxide Films on AlCr Sputtered Alloys: II . In Situ Studies

Cited by 21 publications

References 8 publications

Redefining passivity breakdown of super duplex stainless steel by electrochemical operando synchrotron near surface X-ray analyses

Redefining passivity breakdown of super duplex stainless steel by electrochemical operando synchrotron near surface X-ray analyses

Formation of Chromate Conversion Coatings on Aluminum and Its Alloys

The Influence of Dichromate Ions on Aluminum Dissolution Kinetics in Artificial Crevice Electrode Cells

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