The mechanism of corrosion inhibition by chromate conversion coatings from x-ray absorption near edge spectroscopy (Xanes)

Kendig, M.; Davenport, Alison J.; Isaacs, H.S.

doi:10.1016/0010-938x(93)90257-h

Cited by 221 publications

(138 citation statements)

References 12 publications

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“…Chromate is retained in the CCC [3,4]. Indirect evidence from, for instance, salt spray tests indicates that it is possible for the chromate in the CCC to promote self-healing of damaged areas by dissolving into a local defect and altering the local environment and dissolution kinetics.…”

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confidence: 99%

“…Other evidence that chromate retained in CCCs is an important part of the mechanism of corrosion protection also exists. For instance, exposure of CCC-treated samples to NaCl [4] or salt spray [5] resulted in a decrease in the Cr(VI) content of the film and an increase in the Cr(III) content. Any comparison of a substitute for CCCs must take this unique property into consideration.…”

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confidence: 99%

“…In summary, the mechanism for chromate inhibition of Al alloy dissolution is that chromate is a very soluble, higher-valent, oxidizing ion (CrO 4 2-or Cr 2 O 7…”

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confidence: 99%

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Effects of chromate and chromate conversion coatings on corrosion of aluminum alloy 2024-T3

Zhao

Xiao

Sehgal

et al. 2001

Surface and Coatings Technology

239

129

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Various effects of chromate conversion coatings (CCCs) and chromate in solution on the corrosion of AA2024-T3 and pure Al are studied in this work. Raman spectroscopy was used to investigate the nature of chromate in CCCs through a comparison with the spectra of known standards and artificial Cr(III)/Cr(VI) mixed oxides. Chromate was shown to be released from CCCs and to migrate to and protect a nearby, uncoated area in the artificial scratch cell. However, experiments investigating the effect of chromate in solution on anodic dissolution kinetics under potentiostatic control indicated that large chromate concentrations were needed to have an effect.

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confidence: 99%

mentioning

confidence: 99%

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Effects of chromate and chromate conversion coatings on corrosion of aluminum alloy 2024-T3

Zhao

Xiao

Sehgal

et al. 2001

Surface and Coatings Technology

239

129

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“…37,38 Formation of the Cr(III) species can block electron transfer and consequently decrease the oxygen reduction reaction kinetics. 39 A small shoulder on the high binding energy side the Cr(III) peak is tentatively assigned to Cr(VI). As shown in Figure 7, a higher polarization resistance was measured on the solutionized AA5083 without an ASL than with an ASL in the chromate solution.…”

Section: Resultsmentioning

confidence: 98%

Corrosion Inhibition of Sensitized and Solutionized AA5083

Seong

Frankel

Sridhar³

2015

J. Electrochem. Soc.

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Al-Mg alloys can precipitate β phase, Mg 2 Al 3 , along grain boundaries during long-term exposure to moderate temperatures, resulting in susceptibility to intergranular corrosion. It is of interest to investigate the corrosion inhibition of this alloy in this sensitized condition. Furthermore, recent work has shown that the presence of an altered surface layer (ASL) affects the corrosion behavior of polished AA5083, making it difficult to determine the effectiveness of corrosion inhibitors. The combined effects of the presence of the ASL and inhibitors are not well understood. In this work, the effects of adding potassium chromate (K 2 CrO 4 ), sodium silicate (Na 2 SiO 3 ), and sodium vanadate (NaVO 3 ) to NaCl solution were examined using electrochemical methods on sensitized and solutionized AA5083 with and without the ASL present on the surface. The ASL alone may protect the alloy depending on whether or not the alloy was sensitized. All of the tested inhibitors exhibited a suppression of the cathodic reaction, with chromate causing mixed inhibition on sensitized AA5083 without the ASL present. The composition and surface morphology of samples exposed to inhibitors were also investigated. When β phase (Mg 2 Al 3 ) precipitates on the grain boundaries of AA5xxx (Al-Mg alloys), which can happen even at moderate temperatures over long periods of time, they become sensitized and susceptible to intergranular corrosion (IGC).1,2 Investigations into improving the corrosion properties of AA5xxx have focused on suppressing precipitation by alloying addition or changing the microstructure, 3-6 or on application of corrosion inhibitors. 7-15Aballe et al. studied the corrosion mechanism of the Al-Mg alloys in 3.5 wt% NaCl and concluded that localized corrosion results from the alkalinization around the cathodic sites, such as Fe-rich intermetallic particles in the metal matrix.7 Based upon this idea, inhibiting the cathodic reaction is expected to be a promising method to mitigate the corrosion on Al-Mg alloys. Chromates are cathodic inhibitors that have been widely used as pre-treatments of all aluminum alloys. 16 However, because chromates are toxic and carcinogenic, other inhibitors have been investigated. 17,18 Much research has been performed on the corrosion inhibition provided by rare earth element ions, which have been shown to provide good corrosion resistance by cathodic inhibition and to prevent localized corrosion of Al-Mg alloys. Aballe et al. and Bethencourt et al. showed that weight loss measurement results in 3.5 wt% NaCl solution decreased significantly with the addition of rare earth inhibitors. 9,10,14 Electrochemical impedance spectroscopy (EIS) was utilized to confirm the effect of CeCl 3 , by observing that the thickness of cerium in the compact film increased with exposure time. 8,19 Yasakau et al. used scanning Kelvin probe force microscopy (SKPFM) to investigate the dependence of the surface potential on the presence of cerium and lanthanide inhibitors. 20 The cathodic sites were preferent...

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“…In traditional methods, chromates are widely adopted due to their low cost, good performance and simple operations. [5][6][7][8][9] Nonetheless, as hexavalent chromium is both toxic and carcinogen, strict restrictions on the use of chromate have been imposed by new regulations. As to this, it is urgent to develop the replacement of chromates.…”

Section: Introductionmentioning

confidence: 99%

Preparation and Corrosion Behaviour of Cerium Based Sol-gel Composite Coatings on AA2024-T4 Aluminum Alloy

Peng

Chang

et al. 2016

Electrochemistry

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A serial of composite coatings produced by combination of cerium sol-gel coatings and cerium conversion layers has been developed in this work: (1) sol-gel coating sealed by conversion coating; (2) sol-gel coating sealed by lowdensity sol; (3) conversion coating thickened by sol-gel coating. For both sol-gel coatings and conversion coatings, cerium chloride heptahydrate (CeCl 3 ·7H 2 O) was used as cerium source. In order to evaluate the anti-corrosion properties of these composite coatings, Electrochemical Impedance Spectroscopy (EIS) and salt spray test (SST) were employed as the assessing method. Furthermore, the surface morphology of these composite coatings was characterized by SEM observation. The EIS and SST results thus obtained showed that the anti-corrosion properties of the composite coating (1) had been remarkably improved compared to the any single layer of sol-gel coating or conversion coating. Furthermore, the SEM observation revealed that the morphology of that composite coating was uniform and homogeneous, which may explicate the superior corrosion-resistant performance obtained by the composite coating (1). By contrast, other composite coatings including composite coating (2) and (3) were not as good as composite coating (1) in corrosion resistance, which could be attributed to cracks and heterogeneous microstructure existing on the surface of these composite coatings.

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The mechanism of corrosion inhibition by chromate conversion coatings from x-ray absorption near edge spectroscopy (Xanes)

Cited by 221 publications

References 12 publications

Effects of chromate and chromate conversion coatings on corrosion of aluminum alloy 2024-T3

Effects of chromate and chromate conversion coatings on corrosion of aluminum alloy 2024-T3

Corrosion Inhibition of Sensitized and Solutionized AA5083

Preparation and Corrosion Behaviour of Cerium Based Sol-gel Composite Coatings on AA2024-T4 Aluminum Alloy

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