The distribution of hydroxyl ions at the surface of anodic alumina

Alexander, Morgan R.; Beamson, G.; Bailey, Paul; Noakes, T.C.Q.; Skeldon, P.; Thompson, G.E.

doi:10.1002/sia.1585

Cited by 66 publications

(65 citation statements)

References 32 publications

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“…• C) showed a reduction of coating defects (R coat ) compared to the specimens after treatment II (20 • C). Furthermore, the post-treatment of immersion in the warm water can also produce an improved inner coating layer, especially in the coating formed for 600 s, as evidenced by the two times increase in the charge-transfer resistances than that after cold water post-treatment.…”

Section: Resultsmentioning

confidence: 93%

Influence of Water Immersion Post-Treatment Parameters on Trivalent Chromium Conversion Coatings Formed on AA2024-T351 Alloy

Hashimoto

Thompson

et al. 2016

J. Electrochem. Soc.

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In this work, the influence of water immersion post-treatment, with consideration of temperature and pH values, on trivalent chromium conversion coating morphologies, compositions and corrosion protection has been investigated, using high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy and electrochemical impedance spectroscopy. Compared to the coating formed without the water immersion post-treatment, the post-treatment in the deionized water bath at 40 • C evidently reduced the concentrations of fluorine-containing constituents and increased the extent of oxides/hydroxides across the coating. Consequently, the enhanced corrosion protection property was investigated in the post-treated coatings during full immersion in naturally-aerated NaCl solution with mass fraction of 3.5%. In terms of water pH effects, the coatings displayed comparable thicknesses after post-treatment in the as-prepared deionized water bath (pH 5) and neutral water bath (pH 7); However, a considerable shrinkage was observed in the caustic water bath (pH 9). It was found that the resultant corrosion resistance of the coatings was greatest after post-coating treatment in the water bath of pH 5 and the least for pH 9. Inductively coupled plasma-atomic emission spectroscopy was used to trace small amounts of Zr and Cr elements in the used water baths. A robust chemical titration, adding 1, 5-diaminonaphthalene into the used water baths, revealed that Cr species were only in trivalent form. For AA2024 aluminum alloy, the presence of copper and magnesium elements increases the alloy susceptibility to localized corrosion.1 Therefore, chromate conversion coatings were used to improve the surface resistance against corrosion by a dipping process. However, the toxic hexavalent chromate species in chromate conversion coatings are an ecological concern and, hence, the chromate conversion coating process has been highly regulated by legislation such as the Restriction of Hazardous Substances (RoHS). 3In this regard, trivalent chromium conversion (TCC) coatings are a promising alternative due to the low toxicity of trivalent chromium species.4 Such coating process on AA2024 alloy, driven by the increased pH, consists of surface activation by fluorine attack and coating initiation around second-phase particle and lateral growth on the macroscopic alloy surface. [5][6][7] The freshly-formed coatings have many hydrated channels and the post-treatment in air for 24h can reduce the coating porosity to enhance the corrosion protection while maintaining the hydrated structure. 8 In terms of coating structure, Zr-and Cr-rich oxides comprise the outer layer above a fluoroaluminate layer. 9,10 Notably, a significant amount of fluoride constituent at the coating base was found and it correlated with the locally enhanced corrosion of aluminum substrate, 6 which was assigned with the fluorine attack. 11Fluoride accumulation, especially after prolonged conversion treatment, is a composition challenge for the optimal coating process t...

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Section: Resultsmentioning

confidence: 93%

Influence of Water Immersion Post-Treatment Parameters on Trivalent Chromium Conversion Coatings Formed on AA2024-T351 Alloy

Hashimoto

Thompson

et al. 2016

J. Electrochem. Soc.

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“…The explanation for that structure relies on the unavoidable presence of oxidized aluminum species formed at both sides of the Al metalic layer, exposed to moisture and oxygen present in the capacitor's atmosphere, [6] as suggested by the ion yield enhancement produced at the topmost layers (at 1-2 min) and the interface region (at 8-10 min). The structure of the capacitors is sketched in Fig.…”

Section: Resultsmentioning

confidence: 99%

Development of an energy‐resolved method for SIMS in‐depth analysis of metal–polymer interfaces

Téllez

Vadillo

Laserna

2011

Surface & Interface Analysis

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Energy-resolved SIMS depth profiling has been succesfully applied in the analysis of Al-metalized polypropylene films used in the capacitor industry. The accurate identification of the metal-polymer interface was not straightforward due to the simultaneous contribution of isobaric ions coming from each layer ( 27 Al + / 43 AlO + ions from the aluminium layer and 27 C 2 H 3 + / 43 C 3 H 7 + from the polymer substrate). Kinetic energy filtering by means of a 45• electrostatic analyzer (ESA) has allowed the resolution of the metal-polymer interface by selecting a suitable kinetic energy corresponding to the ions generated in the metallized layer but not on the polymer. Owing to the dielectric polymeric substrate, charge effects might be produced during depth profiling. These charge buildup effects are minimized by flooding the surface with low-energy electrons (500 eV) and a specific sample-mounting procedure assuring grounded conditions. The excellent repeatability and sensibility of the technique allows studying the degradative process in the capacitor films and the accurate location of the metal-polymer interface, and therefore, the nanometric metal thickness variations. These factors drastically affect the capacitor's performance and they will determine the potential failures that could be developed during the capacitor's life cycle.

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“…This structure was postulated to be more stable in comparison with the structure (c) by Alexander et al 19 and Deacon et al 33 It has been postulated that VOCs are likely to adsorb on the Al oxide/hydroxide surface and form structures similar to carboxylic acid reaction in solution, namely, bidentate-bound carboxylates. 34 Following this argument, the peak situated at 4.2 eV shift was assigned to a bidentate carboxylate in the C 1s core level for Al. Here, we assign the peak at 4.2 eV shift to a bidentate carboxylate compound with the magnesium.…”

Section: Assignment For the Carboxylate Peaks In C 1s Core Levelmentioning

confidence: 99%

Characterisation of the surface chemistry of magnesium exposed to the ambient atmosphere

Fotea

Callaway

Alexander

2006

Surf. Interface Anal.

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The changes in the surface chemistry of the oxidised surface of evaporated magnesium metal stored in the ambient atmosphere are studied with water contact angle (WCA) measurement, polarisation-modulation infrared reflection-absorption spectroscopy (PM-IRRAS) and X-ray photoelectron spectroscopy (XPS). Upon exposure to the ambient atmosphere, the surface picks up volatile organic compounds (VOC), which cause a significant increase in the WCA values. The PM-IRRAS and XPS analyses indicate that the adsorbates contain hydrocarbons, carboxylates and carbonate functionalities. After long ambient storage times, the composition of the carbon-containing functionalities on the surface changes significantly. This change could be caused by the build-up and/or surface-catalysed oxidation of adsorbed organic species. Thickening of the air-formed oxide/hydroxide layer was also noted, ascribed to the reaction of adsorbed atmospheric moisture with the magnesium surface.

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The distribution of hydroxyl ions at the surface of anodic alumina

Cited by 66 publications

References 32 publications

Influence of Water Immersion Post-Treatment Parameters on Trivalent Chromium Conversion Coatings Formed on AA2024-T351 Alloy

Influence of Water Immersion Post-Treatment Parameters on Trivalent Chromium Conversion Coatings Formed on AA2024-T351 Alloy

Development of an energy‐resolved method for SIMS in‐depth analysis of metal–polymer interfaces

Characterisation of the surface chemistry of magnesium exposed to the ambient atmosphere

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