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In situ studies of conversion coated zinc/polymer surfaces during exposure to corrosive conditions
KIMAB.
KIMAB.
KIMAB.
2010 (English)In: Progress in organic coatings, ISSN 0300-9440, E-ISSN 1873-331XArticle in journal (Refereed) Published
Abstract [en]

This work investigates the hidden interface between a conversion-coated zinc surface and a polymer coating upon exposure to an electrolyte by simultaneous in situ ATR-FTIR and EIS. Various system properties were distinguished, such as the ingress of electrolyte constituents, and an active process of water-induced alterations of the conversion layer. The interface between a polymer film and a surface treated metal surface is of considerable fundamental and technical interest in many areas of application, and the results obtained open up the use of this method for a wide range of important applications.

Place, publisher, year, edition, pages
2010.
Keyword [en]
ATR-FTIR, Spectro-electrochemistry, Interface, Conversion coating, Zinc
Identifiers
URN: urn:nbn:se:kth:diva-26328DOI: 10.1016/j.porgcoat.2010.09.012ISI: 000285904000003Scopus ID: 2-s2.0-78649631493OAI: oai:DiVA.org:kth-26328DiVA: diva2:371773
Note
QC 20101122Available from: 2010-11-22 Created: 2010-11-22 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Development of ATR-FTIR Kretschmann Spectroscopy for In situ Studies of Metal / Polymer Interfaces: and its Intergration with EIS for Exposure to Corrosive Conditions
Open this publication in new window or tab >>Development of ATR-FTIR Kretschmann Spectroscopy for In situ Studies of Metal / Polymer Interfaces: and its Intergration with EIS for Exposure to Corrosive Conditions
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The environmental stability of a metal / polymer interface is essential for the durability and mechanical stability of constructions in several important areas such as the automotive, offshore, building and aerospace industries. The protective capability of a polymer film is strongly connected to its barrier properties, but the transport of water and corrosive constituents through the polymer and the subsequent processes at the metal surface are complicated to analyse in detail. The surface to be analysed is confined between two media that are impermeable to most probing particles used in conventional analytical techniques. Several methods exist to describe separate parts of the system, but few techniques work atambient pressure and have the capacity to conduct real-time analysis at relevant exposure conditions. In this work, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) in the Kretschmann geometry was successfully employed for systematic studies of metal / polymer interfaces. This technique requires the use of thin metal films deposited on an internal reflection element (IRE). Most studies were performed on aluminium, which is an important structural light-weight material, but also zinc was analysed, being frequently used for corrosion protection of steel. Upon exposure to water and electrolytes, the ATR-FTIR Kretschmann technique was found capable to monitor and to separate early deterioration related processes at the aluminium / polymer interface, including water sorption and transport of ionic species through the polymer film. Other main processes identified were the formation of corrosion products and swelling of the surface-near polymer network. To perform more comprehensive interpretations, a spectro-electrochemical method was further developed for in situ studies of the hidden metal / polymer interfaces. The ATR-FTIR Kretschmann technique was here combined with the complementary acting technique, Electrical Impedance Spectroscopy (EIS). The integrated set-up was able to provide complementary information, with ATR-FTIR Kretschmann being sensitive to the surface-near region and EIS to the whole system. For instance, metal oxidation and delamination processes can be difficult to distinguish by EIS, while on the other hand oxidation and hydration reactions on aluminiumcan be confirmed as IR bands at distinct positions. Delamination and swelling of a polymer both result in negative bands in an IR spectrum, but these processes may be distinguished by EIS as alterations in different frequency regions. While traditional chemical pre-treatments for enhanced hydrolytic stability perform excellent, they are being phased out from industrial applications due to environmental concerns and work health issues. Today there is an intense ongoing research regarding the mechanisms and performance of environmentally friendly pretreatments to develop systems of similar performance, and the analysis of the confined metal / polymer interface is crucial for this development. The capability of the integrated in situ ATR-FTIR Kretschmann and EIS set-up was therefore further applied to systems where a surface pre-treatment had been applied to the metal prior to the organic coating. Studies were first performed on vacuum-evaporated films of zinc treated with a titanium-based conversion coating and further coated with a UV-curing polymer. Alterations of the conversion layer could be detected upon exposure to the electrolyte. Also alkaline-cleaned aluminium coated with an amino-functional silane film and a thermo-curing epoxy top-coat was thoroughlycharacterized by both ATR-FTIR and IRRAS and further investigated upon exposure toelectrolyte and humid air. Changes at the hidden interface were detected upon thermal curingof the epoxy film and during exposure in electrolyte, and the in situ ATR-FTIR Kretschm annanalysis showed a high sensitivity towards alterations in the interfacial region. Complementary studies in the absence of metal could confirm a water uptake within the silane film and water-induced alterations of the siloxane network.

Place, publisher, year, edition, pages
Stockholm: KTH, 2010. vi, 60 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2010:47
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-26996 (URN)978-91-7415-782-6 (ISBN)
Public defence
2010-12-03, F3, Lindstedtsvägen 26, entréplan, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20101222Available from: 2010-12-02 Created: 2010-12-02 Last updated: 2011-02-03Bibliographically approved

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