Conduction mechanism of the anodic film on chromium in acidic sulphate solutions

Bojinov, Martin; Fabricius, Gunilla; Laitinen, Timo; Saario, Timo; Sundholm, G.

doi:10.1016/s0013-4686(98)00169-8

Cited by 59 publications

(38 citation statements)

References 28 publications

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“…When the potential was stepped in the negative direction after forming the film in this region, an exponentially increasing negative photocurrent was observed for pure Cr (see also Ref. 13) and the Fe-25% Cr alloy, whereas no stable photocurrent was observed for the Fe-12% Cr alloy and for pure Fe.…”

Section: Methodsmentioning

confidence: 91%

“…The spectra are qualitatively analogous to those published by other authors [20][21][22] and to the spectra reported earlier for pure Cr by us. 13 In the potential region corresponding to the high and almost stable resistance ( Fig. 3a and b), the impedance spectra are independent of potential, showing a predominantly capacitive response, and the impedance magnitude at low frequencies is very high.…”

Section: Methodsmentioning

confidence: 94%

“…This model has been found to describe the anodic layer on pure Cr in a highly satisfactory way. 13 It is based on the idea that as a result of defect formation at one interface the conductivity of the film is exponentially dependent on the distance from that interface.…”

Section: Discussionmentioning

confidence: 99%

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Conduction Mechanism of the Anodic Film on Fe‐Cr Alloys in Sulfate Solutions

Bojinov

Fabricius²,

Laitinen

et al. 1999

J. Electrochem. Soc.

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The relationship between the structure, electric, and electrochemical properties of anodic passive films on stainless steels and their ability to protect the underlying metal from different types of corrosion is still a matter of considerable debate.In recent years, advanced in situ surface analytical techniques such as X-ray absorption near-edge spectroscopy (XANES), X-ray diffraction, and X-ray scattering techniques as well as scanning tunneling microscopy (STM) have made possible a much deeper insight into the structure of the anodic film on iron and iron-chromium alloys. 1-7 Using these techniques it has been shown that anodic films have nanocrystalline structure, which is to a certain extent analogous to that of the corresponding bulk oxides of iron and chromium.Concerning pure iron, it has been demonstrated that the passive film has a spinel structure which is intermediate between magnetite (Fe 3 O 4 ) and maghemite (␥-Fe 2 O 3 ). The concentration of interstitial Fe 2ϩ species in the octahedral positions of this spinel was suggested to vary from ca. 20% at low potentials to below 10% at high potentials, while in Fe 3 O 4 it is 33%. 2,3,8 It was considered likely that there is a coupling between the motion of tetrahedral vacancies and octahedral interstitials, because the interstitial cations have a high probability of occupying sites near tetrahedral vacancies. 3 It was also proposed 3 that metal interstitials are the predominating defects close to the metal/film interface, while metal vacancies predominate closer to the oxide/solution interface, since iron species are probably in a higher oxidation state closer to the electrolyte.Concerning iron-based alloys and stainless steels in particular, the strong enrichment of the passive films in Cr with respect to the base material has been recently quantified with XANES. 2 It was also demonstrated that the higher the potential is, the smaller is the enrichment in Cr of the overall passive film. The high content of Cr in the films formed on Fe-Cr alloys suggests that the structure of these films should be to some extent similar to that of the films formed on pure Cr. A supplementary view has been lent by ex situ and in situ STM studies on the structure of the crystalline oxide films on Fe-Cr alloys. They pointed to a slightly distorted triangular lattice with symmetry close to the rhombohedral (111) plane of Cr 2 O 3 , which suggests the presence of oxygen vacancies in the oxide structure. [5][6][7] In addition, sputtered thin iron and chromium oxide films on inert substrates as model systems have proven to be an important tool to assess the structure and to characterize the oxidative/reductive dissolution of passive films. 8-11 Using these synthetic oxide films, it has been demonstrated that the dissolution of the film on iron in the passive state is essentially a chemical process. The rate of which is almost independent of potential. 10 On the other hand, reductive dissolution of iron oxide and mixed iron-chromium oxides during the passive-to-active transition...

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Section: Methodsmentioning

confidence: 91%

Section: Methodsmentioning

confidence: 94%

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Conduction Mechanism of the Anodic Film on Fe‐Cr Alloys in Sulfate Solutions

Bojinov

Fabricius²,

Laitinen

et al. 1999

J. Electrochem. Soc.

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“…The polarization behaviour of pure Cr coating in the solution studied was discussed elsewhere [14,15]. The passive film formed on the Cr surface upon anodic oxidation in H 2 SO 4 solution was identified in [16][17][18]. According to [17] the passive film is a thin hydrated chromic oxide (5-25 Å ) that may be considered as a dielectric with a dielectric constant of 25.…”

Section: Resultsmentioning

confidence: 99%

“…CrOOH(film) + H + + e ) . Taking into account the data cited in [19], it may be suggested that during the negative potential sweep the reverse reaction Cr(III) ! -Cr(II) occurs in the oxide film at the potential below +0.2 V. Analysis of the PCs obtained leads to the conclusion that the higher WC concentration in the Cr(VI) bath is the lower current density is observed in the region of active dissolution.…”

Section: Resultsmentioning

confidence: 99%

Effect of WC on electrodeposition and corrosion behaviour of chromium coatings

Surviliene¹,

Jasulaitienė²,

Lisowska-Oleksiak

et al. 2005

J Appl Electrochem

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To study the effect of WC particles on corrosion behaviour of chromium coating steel samples were plated in Cr(VI) baths with various concentrations of WC. XPS, EPM and XRD were used to study the chemical composition, morphology and texture of the coatings. The corrosion behaviour was studied at different exposure times in solution containing 0.01 mol L )1 H 2 SO 4 + 0.5 mol L )1 Na 2 SO 4 using cyclic voltammetry and impedance spectroscopy. Cyclic polarization measurements suggest that WC particles slow down the processes of passive film dissolution and penetration of aggressive ions to the substrate. Electrochemical impedance spectroscopy (EIS) was used to reveal the details of the corrosion process at the solution/electrode interface. The simulation of EIS data with a proposed equivalent circuit model made it possible to obtain quantitative valuation of the Y 0 (Q c ), Y 0 (Q s ) and R pore parameters, reflecting corrosion behaviour of samples at the solution/electrode interface. Samples plated in a Cr(VI) bath with WC provided better resistance to corrosion than those plated in a bath without WC. Analysis of the data obtained suggests that WC particles enhance corrosion resistance due to the microstructural features of the coatings.

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Passivity of Metals and Alloys

Marcus

Maurice

2013

Materials Science and Technology

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The sections in this article are Introduction Electrochemical Characteristics of Passive Systems Current–Potential Curves Thermodynamic Aspects of Passivity Potential Drops at the Passivated Surface Chemical Composition and Thickness of Passive Films on Metals Iron Nickel Chromium Copper Anodic Films on Aluminum Electronic Properties of Passive Films Structure of Passive Films Growth Mechanisms Effects of Alloying Elements Chromium Enrichment in Passivated Iron‐Based and Nickel‐Based Alloys Structural Aspects of Chromium Enrichment in Passive Films on Stainless Steels in Aqueous Solution: Aging Effects The Effects of Molybdenum The Effects of Nitrogen The Effect of Tungsten Passivity of Aluminum Alloys Alloying Elements as Passivity Promoters and Dissolution Moderators Detrimental Effects of Material Impurities: Sulfur‐Induced Corrosion Passivity Breakdown and Initial Stages of Pitting Phenomenology of Pitting Mechanisms of Pit Initiation Conclusions

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Conduction mechanism of the anodic film on chromium in acidic sulphate solutions

Cited by 59 publications

References 28 publications

Conduction Mechanism of the Anodic Film on Fe‐Cr Alloys in Sulfate Solutions

Conduction Mechanism of the Anodic Film on Fe‐Cr Alloys in Sulfate Solutions

Effect of WC on electrodeposition and corrosion behaviour of chromium coatings

Passivity of Metals and Alloys

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