Delamination of Poylmer Coatings from Metal Substrates: Submicroscopic and Molecular Aspects
- PDF / 153,865 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 17 Downloads / 162 Views
B2.8.1
Delamination of Poylmer Coatings from Metal Substrates: Submicroscopic and Molecular Aspects M. Rohwerder, E. Hornung and Xing-Wen Yu Max-Planck-Institut für Eisenforschung Max-Planck-Str.1, D-40237 Düsseldorf Germany INTRODUCTION Delamination of organic coatings from metal surfaces can occur in a number of different ways, e.g. as pure cathodic delamination, as Filiform corrosion or a mixture of these. In fact, in most technical systems the pure cases are the exception and, of course, delamination is usually very slow. It has been shown that in fast delaminating systems the length scales may range between several 100 µm and several millimetres, while in systems which show slow delamination the reaction zones can be confined to submicroscopic distances [1]. This underlines the importance of investigation methods with submicroscopic resolution. As a very promising new technique Scanning Kelvin Probe Force Microscopy (SKPFM) was applied for the investigation of cathodic delamination and filiform corrosion on a submicroscopic scale [1 , 2]. Indeed, these first investigations have shown that SKPFM gives basically the same information as the standard Scanning Kelvin Probe (SKP), but with a much improved resolution. It could be shown, for instance, that the extension of the reaction zone seems to be much narrower than would have to be assumed from the SKP measurements. Based on the knowledge about the different delamination types that was obtained from investigations with the standard SKP [3-12] the SKPFM should be the ideal tool to get information on the submicroscopic scale. However, SKPFM alone is not sufficient for revealing the underlying fundamental mechanisms; of even higher importance is the knowledge of the molecular and mesoscopic structure at the buried interface. In this paper a design for suitable model samples is proposed and first results are presented. EXPERIMENTAL DETAILS The in situ use of the SKPFM set-up for delamination experiments requires the use of a humidity cell to keep the delamination active. Therefore a custom-made glass cell for the Dimension 3100 (Veeco, Digital Instruments) was built. This cell can be purged with humid air. Depending on flow rate and washing flask parameters, relative humidities of up to 100% can be reached. Since the KPM works with low scan frequencies around 0.5Hz, only slow delamination systems can be investigated. In order to achieve a high topographic and potential resolution, ultrathin coatings on model substrates have been chosen. For the cathodic delamination experiments discussed in this paper, gold evaporated on glass substrates served as a model surface. The defect was prepared on a part of the gold surface not covered by the polymer coating. The potential at the defect site was adjusted potentiostatically. The electrolyte was 0.1M NaCl in agar applied onto the surface. The gold surface, which allows electron transfer but no ion transfer reactions, behaves similar to a passive iron electrode below the organic coating and served as the local cathode during
Data Loading...
