An XPS study of chromate pretreatment of aluminium

Treverton, J. A.; Davies, N. C.

doi:10.1179/030716977803292808

Cited by 58 publications

(17 citation statements)

References 5 publications

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“…The lighter appearance ͑TEM analysis͒ of the external region of CCC-wf could be attributed to the formation of a less dense layer containing both chromium mixed oxides and chromium-ferro/ferricyanide species. 19,20 The hypothesis of ferricyanide species bonded to chromium hydroxide has been recently suggested 21,22 and is in qualitative agreement with the Cr and Fe GDOES spectra of Fig. 6.…”

Section: Discussionsupporting

confidence: 84%

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Structural Analysis and Photocurrent Spectroscopy of CCCs on 99.99% Aluminum

Quarto

Santamaria

Mallandrino

et al. 2003

J. Electrochem. Soc.

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A characterization of chromate conversion coatings ͑CCCs͒ formed in the presence and in the absence of accelerator ͑ferro-ferricyanide redox couple͒ has been performed by various techniques ͑transmission electron microscopy, TEM, glow discharge optical emission spectrometry, GDOES, X-ray absorption near-end structure, XANES, and photon correlation spectroscopy͒. The results of a detailed investigation on morphological, compositional, and solid-state properties of freshly converted aluminum samples at different immersion times ͑30 s-90 min͒ are reported. The TEM and GDOES data suggest the presence of iron-cyanide species only in the external layer of CCC of nearly constant thickness. The XANES data suggest the presence of both Cr͑VI͒ and Cr͑III͒ species with a ratio Cr͑VI͒/Cr͑III͒ close to 1:2. This ratio remains constant with the conversion time and seems slightly affected by the composition of conversion solution. The photoelectrochemical study suggests an insulating or slightly p-type behavior for CCC layers. A bandgap value of about 2.55 eV has been estimated, regardless of the conversion solution, although some differences in the photocurrent spectra have been observed for coatings formed in the presence or absence of accelerator. The location of electronic energy levels of the Al/CCC/electrolyte interface has been derived which could account for the different kinetics of coating formation in the presence of accelerator. A large research effort has been devoted in the last years to the understanding of the exact nature of the chromate conversion coating ͑CCC͒ and its mechanism of protection against corrosion of aluminum metal and alloys.Surface analysis techniques have revealed that the composition of the coatings depends on the nature of the chemical conversion bath.1-3 It is now agreed that the coatings are amorphous 2,3 and that both Cr͑III͒ and Cr͑VI͒ species are incorporated into the films, with possible formation of a mixed Cr͑III͒-Cr͑VI͒ oxide as suggested by recent Raman spectroscopy analysis. 4,5 The mechanism of action of chromate in assuring the protection against pitting corrosion is still under debate. From this point of view a large interest exists in understanding the influence of aging on the protection action of CCCs. It has been shown that long-term or temperature aging acts on the mechanism of release of Cr͑VI͒ species so affecting the ''active protection'' of CCCs also called self-healing. In this frame different hypothesis have been suggested to explain the associated loss of corrosion protection.5-9 Among those, structural changes occurring into the CCC and related to dehydration were evidenced. 10As for the mechanism of formation and growth of CCCs only very few papers have addressed both the role of the redox couples, usually added to the commercial conversion bath to speed up the growth of the coating, and the mechanism of initial formation of CCCs during the conversion process. 3,4 Brown et al.3 suggested that on a very pure Al surface a uniform coating develops due to a mechanism o...

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Section: Discussionsupporting

confidence: 84%

“…Both the formation of CrFe(CN) 6 or Cr 3 ͓Fe(CN) 6 ͔ 4 are compatible with the XANES and EDX data and the presence of both species have been suggested in the literature. 19,20 Regarding the mechanism of growth of the CCC, the data of Fig. 4 and 9 are compatible with a growth controlled either by a diffusion-like or an ohmic drop mechanism.…”

Section: Discussionsupporting

confidence: 63%

Structural Analysis and Photocurrent Spectroscopy of CCCs on 99.99% Aluminum

Quarto

Santamaria

Mallandrino

et al. 2003

J. Electrochem. Soc.

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“…1 For example, Treverton and Davies used X-ray photoelectron spectroscopy (XPS) and ion-beam etching to study accelerated CCCs formed on 99.8% pure Al substrates. 4 Results indicated the presence of Fe(CN) 6 4Ϫ/3Ϫ concentrated in the near-surface regions. It was suggested that the compound was probably present as a CrFe(CN) 6 salt.…”

Section: ϫmentioning

confidence: 96%

Formation of Chromate Conversion Coatings on Al-Cu-Mg Intermetallic Compounds and Alloys

McGovern¹,

Schmutz

Buchheit

et al. 2000

J. Electrochem. Soc.

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"Accelerated" chromate conversion coating (CCC) formulations are distinguished among all CCC types by the fact that they utilize a special chemical additive to increase coating weight, 1 or increase the rate of the film forming Cr VI to Cr III reduction reaction. 2 Ostensibly, accelerated CCCs are used on corrosion-prone Al-Cu-Mg and AlZn-Mg-Cu alloys to ensure maximum protection. 3 Ferricyanide [Fe(CN) 6 3Ϫ ] has been used as an accelerant in commercial CCC formulations since the 1960s. 1 Despite the long history, its role in coating formation has not been precisely established. Both Fe(CN) 6 3Ϫ and Fe(CN) 6 4Ϫ are readily detected in CCCs by various surface-sensitive techniques, supporting the notion that it contributes to coating weight by becoming part of the CCC film. 1 For example, Treverton and Davies used X-ray photoelectron spectroscopy (XPS) and ion-beam etching to study accelerated CCCs formed on 99.8% pure Al substrates. 4 Results indicated the presence of Fe(CN) 6 4Ϫ/3Ϫ concentrated in the near-surface regions. It was suggested that the compound was probably present as a CrFe(CN) 6 salt. However, the findings were insufficient to establish a clear role for Fe(CN) 6 3Ϫ in coating formation. In subsequent studies aimed at clarifying their earlier work, these workers prepared accelerated CCCs on 99.8% Al from a bath formulation based on commercial chemistries. 5 XPS results indicated that Fe(CN) 6 3Ϫ/4Ϫ was present throughout the coating but was concentrated in the near-surface region. Mixed metal cyanides identified in the earlier study were now not present. Additionally, evidence of ferrocyanide [Fe(CN) 6 4Ϫ ] was found. The authors equivocated on the significance of ferrocyanide determination since ferri-to ferrocyanide reduction in X-ray beams was known to occur. Despite these complications, it was proposed that the primary film growth reaction, chromate reduction, was stifled by adsorption of ferricyanide on the nascent CCC, thereby increasing the availability of free chromate for reaction with uncoated metal.Hagans and Haas specifically considered film formation on Cu and Fe intermetallic compounds (IMCs) in studies of accelerated CCC formation on 2024-T3. 6 Auger electron spectroscopy (AES), XPS, and ion-beam depth profiling were used to show that for coating formation times up to 3 min, the film formation rate on various phases in 2024-T3 decreased in the order: matrix phase > Cu IMC > Fe IMC. After 5 min of immersion time, coating thickness appeared to be similar on the different phases. These workers proposed that ferrocyanide interacted with Cu-rich IMCs to form Cu 4 Fe(CN) 6 or Cu 2 Fe(CN) 6 and that these compounds promoted corrosion resistance by eliminating the galvanic couples that would otherwise form between the noble particles and the matrix phase.Lytle et al. used a variety of surface analytical techniques, including X-ray absorption spectroscopy (XAS), X-ray absorption near edge spectroscopy (XANES), extended X-ray absorption fine structure (EXAFS), and Fourier transform infrared s...

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“…The material of substrates used pure aluminum sheets (1:2 Â 10 À3 m thick A1100-O). The substrate was degreased with a mild alkaline degreasing agent and treated with chromium phosphate treatment, 1) a typical conversion coating for aluminum. The chromium deposit per unit area was 2 Â 10 À5 kg/m 2 in terms of metallic chromium.…”

Section: Preparation Of Pre-coated Aluminum Sheetsmentioning

confidence: 99%

Effects of Glass Transition Temperatures of Films on the Corrosion Resistance after Forming of Pre-Coated Aluminum Sheets

2008

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Aluminum sheets with superior surface functions have been increasingly used in electrical fields. In this paper, the effects of the glass transition temperatures of the films on the corrosion resistance of pre-coated aluminum sheets before and after forming were investigated. The corrosion resistance after forming of polyester type pre-coated aluminum sheets with three different glass transition temperatures were investigated by salt spray test. It was found that corrosion resistances of the film with glass transition temperatures higher than the forming temperature were low. In the cups with low corrosion resistance after forming, whitening phenomena were observed. This whitening behavior was also investigated by the stretching test. Results showed that whitening was only caused in areas where lubricants were applied, and microcracks were only observed in the areas where whitening occurred. In addition, whitening was observed only in films with high glass transition temperatures. As films with high glass transition temperatures are hard, excessive internal stress (cause of cracks) tend to concentrate on local area. It is considered that the adsorbed lubricant on the polyester films acts to decrease the mechanical strength of the films. As a result of the lubricant adsorption, the film can not withstand internal stress in stress-concentrated regions, which in turn causes micro-cracks to develop. It can be thought that the corrosion resistance was deteriorated by the sodium chloride solution that penetrated into these micro-cracks.

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An XPS study of chromate pretreatment of aluminium

Cited by 58 publications

References 5 publications

Structural Analysis and Photocurrent Spectroscopy of CCCs on 99.99% Aluminum

Structural Analysis and Photocurrent Spectroscopy of CCCs on 99.99% Aluminum

Formation of Chromate Conversion Coatings on Al-Cu-Mg Intermetallic Compounds and Alloys

Effects of Glass Transition Temperatures of Films on the Corrosion Resistance after Forming of Pre-Coated Aluminum Sheets

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