The mechanism of spontaneous dissolution of the air-formed oxide film on iron in a deaerated neutral phosphate solution

Konno, Hidetaka; Kawai, Masato; Nagayama, Masaichi

doi:10.1016/0376-4583(85)90076-7

Cited by 11 publications

(10 citation statements)

References 14 publications

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“…It is found that a critical thickness of 0.71 nm at t ) t c is required before passivity with more protection is established. Similar results were observed in conferring the stability of air-formed oxide film 41 and passive film 31,32,42 against open-circuit breakdown in borate buffer solutions. The critical thickness presented here is much less than those reported for air-formed oxide film (1.7 nm) 41 and passive film (1.3 nm).…”

Section: Resultssupporting

confidence: 76%

Reconstruction in Air of an Iron Passive Film Formed at −0.4 V in a Borate Buffer Solution

et al. 2004

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The reconstruction in air of passive films on iron formed at −0.4 V in a borate buffer solution was investigated by STM and galvanostatic cathodic reduction. With exposure to air (<30% RH), the apparent thickness rapidly increased in initial stages until a critical exposure duration of about 130 min, and after a transition between 130 and 360 min, slowly increased in the following stages, and the changes of surface structures from the amorphous state to short-range order and then to long-range order and further to crystal structures with a wide terrace were observed. These processes are suggested to be attributed to rapid dehydration of Fe3+ and Fe2+ hydroxides and partial rapid oxidation upon removal from electrolytic solution after passivation, steady oxidation in air until the attainment of a passive state to be more protective one at t = t c, and reconstruction in air, respectively. The reconstruction process remarkably improved the resistance of the passive films against open-circuit breakdown. The behavior of passive films formed at −0.4 V observed during air exposure is actually self-protective.

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Section: Resultssupporting

confidence: 76%

Reconstruction in Air of an Iron Passive Film Formed at −0.4 V in a Borate Buffer Solution

et al. 2004

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“…They found that the breakdown characteristics were dependent on the solution anion, and Karma et al (15) also noted that the arrest time was strongly dependent on the age of the air-formed film, and thus on its thickness. Gilroy and Mayne (14) suggested the following mechanism of reductive dissolution Fe~*(solid) + e--* FeZ+(solid) -* Fe2+(aq) with the electrons again being supplied by anodic oxidation of metallic Fe.…”

Section: Resultsmentioning

confidence: 95%

“…Konno et al (15) argued against this mechanism on thermodynamic grounds. Instead, they proposed that the film was reductively dissolved according to ~-FeOOH + H2L + 3H + + e---* FeH2L + + 2H20 or FeaO4 + 3H2L-+ 8H + 4-2e --* 3FeH2L* + 4H20 where L was the PO43-anion.…”

Section: Resultsmentioning

confidence: 97%

Use of 18O/SIMS and Electrochemical Techniques to Study the Reduction and Breakdown of Passive Oxide Films on Iron

Bardwell

MacDougall

Graham

1988

J. Electrochem. Soc.

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Secondary ion mass spectrometry (SIMS) has been used to study the cathodic removal and open-circuit breakdown of passive oxide films formed on Fe in ~SO-enriched borate buffer solution. For film removal by galvanostatic cathodic reduction, the initial stage of reduction resulted in a layer by layer thinning of the film. The rates of film removal with cathodic charge passed were determined to be 1.56 and 0.30 nm/mC cm -2 during the two distinct stages of reduction. These results are analyzed in terms of the various models for the passive film on Fe. Immersion of the passivated Fe electrodes in acidic sulfate solutions on open circuit resulted in a distinct potential arrest followed by a very rapid potential decrease. The length of this arrest is strongly dependent on the oxide film thickness and on the solution pH. '80 SIMS and electrochemical results are discussed in terms of mechanisms of reductive and chemical dissolution on open circuit.Despite over a century of scientific research, there is still no consensus as to the true nature of the passive oxide film on Fe. There is general agreement that the film is compact and contains Fe, O (and maybe protons), and is less than 5.5 nm thick, but there is little agreement as to its exact composition. Some confusion has certainly arisen from attempting to describe such thin layers in terms of bulk materials and some fundamental questions remain hotly contested. (i) Does the film contain H? (ii) Is the film best described as a single layer, a duplex layer, or as a single layer with concentration gradients?The technique of cathodic reduction has been used extensively to investigate the nature of the passive film and to provide support for the various proposed models. In this paper cathodic reduction is also used in conjunction with ~80 SIMS experiments to shed light on the nature, formation, and breakdown of the passive film on Fe. Passive oxide films undergo breakdown on open circuit in acidic sulfate solutions, and the mechanism of this breakdown is investigated using both '80 SIMS and cathodic reduction techniques. The results are compared with those found for galvanostatJc cathodic reduction of the film. ExperimentalFe samples were cut from a zone-refined ingot obtained from Battelle Memorial Institute. An analysis of this 99.99+% material has been published previously (1). The samples were polished with 600 grit SiC and then down to 1 ~m diamond and electropolished immediately before use. In electrochemical experiments, samples were reduced galvanostatically before stepping the potential to the required value in the passive region.Borate buffer solutions of pH 8.4, 0.15N Na2SO4 of pH 3 or 5, and pH 0.27 H2SO4 solutions were thermostated at 24~ and deaerated before use. Potentials were measured relative to a 0.15N Hg/Hg2SO4/Na2SO4 reference electrode (0.421V vs. SCE, 0.661V vs. SHE). A PAR Model 173 Potentiostat with a Model 276 interface, connected to an IBM compatible computer was used. This enabled currents to be measured as early as a few milliseconds after the p...

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“…Results are presented for two takeoff angles, 0 ∘ and 50 ∘ , with respect to the normal. detail by Gilroy and Mayne [19] and Konno et al [20] for airformed oxide films on iron. Both research groups carried out open circuit potential measurements in corrosive solutions and observed that, due to dissolution of the oxide film, oc initially decreases gradually with immersion time and then it drops rapidly to −0.76 V (Ag/AgCl), the free corrosion potential of Fe.…”

Section: Xps Analysis X-ray Photoelectron Spectroscopy (Xps)mentioning

confidence: 90%

The Inhibition Effect of Sodium Glutarate towards Carbon Steel Corrosion in Neutral Aqueous Solutions

Chan-Rosado

Pech‐Canul

2016

International Journal of Corrosion

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The inhibition effect of sodium glutarate towards corrosion of carbon steel in neutral 0.02 M NaCl solution was investigated with potentiodynamic polarization and electrochemical impedance measurements. Results of electrochemical measurements revealed a poor inhibitive action for low concentrations (1 mM and 5 mM) and a significant improvement in efficiency for concentrations of 32 mM or higher. The protective film exhibited excellent stability in the temperature range 22°C–55°C. Full chemical passivation was accomplished and analysis of the impedance spectra for the high concentrations of glutarate was consistent with the inhibition mechanism which assumes that the carboxylates support the passivation of carbon steel in aerated solutions by plugging the defect sites and that the passivation process is enhanced by adsorption of the carboxylates on the oxide-covered surface. Such mechanism was confirmed by the XPS analysis.

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The mechanism of spontaneous dissolution of the air-formed oxide film on iron in a deaerated neutral phosphate solution

Cited by 11 publications

References 14 publications

Reconstruction in Air of an Iron Passive Film Formed at −0.4 V in a Borate Buffer Solution

Reconstruction in Air of an Iron Passive Film Formed at −0.4 V in a Borate Buffer Solution

Use of 18O/SIMS and Electrochemical Techniques to Study the Reduction and Breakdown of Passive Oxide Films on Iron

The Inhibition Effect of Sodium Glutarate towards Carbon Steel Corrosion in Neutral Aqueous Solutions

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