Investigation of the “Protection Zone” Phenomenon Established By Conducting Polymers in Coatings for Corrosion Protection

Monday, 2 October 2017: 10:40
Camellia 3 (Gaylord National Resort and Convention Center)
A. Merz and M. Rohwerder (Max-Planck-Institut für Eisenforschung GmbH)
Conducting polymers (CPs), such as polypyrrole (PPy), polyaniline (PANi) or poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS), can be employed for the corrosion protection of metals when certain design rules are followed [1, 2].

Based on the capability of a conducting polymer to work as a strong oxidant to the metallic substrate, which induces the potential to shift to a noble direction, several possible protection mechanisms based on different electrochemical effects have already been reported. However, these mechanisms often seem to work only under certain special conditions. For instance, a CP containing coating might be very effective in preventing corrosion in pin holes by passivating the metal exposed therein to the corrosive environment, while it fails disastrously in the presence of larger defects [2]. So this work focuses on the investigation of an innovative protection system which provides a long term coating stability. It was found that separated particles of conductive polymer when distributed on a zinc or iron matrix establish a “protection zone” around their boundary. The above proposed effect hinders the oxygen reduction rate at the very delamination front, establishing a region where no or only very slow delamination occurs, i.e. a degradation free zone is created. This phenomenon was investigated for the following CPs: polyaniline, polypyrrole as well as PEDOT.

Homogeneous and strongly adherent conducting polymer deposits (dots of conducting polymer) have been prepared with different thickness. Evaluation of the anticorrosion performance of the deposits covered by an organic coating was investigated with Scanning Kelvin Probe (SKP) and the role of the conducting polymer thickness and kind of metal on the corrosion performance was also examined. The experiments carried out revealed that the investigated deposit configurations are highly efficient, in fact provide a real break-through for the design of corrosion protection coatings based on conducting polymers.

Keywords: Corrosion protection; Conducting polymer; Protection zone; Scanning Kelvin Probe.

[1] Rohwerder, M.; Duc, L.; Michalik, A.: In situ investigation of corrosion localised at the buried interface between metal and conducting polymer based composite coatings. Electrochimica Acta 54 (25), pp. 6075-6081 (2009)

[2] Rohwerder, M. (2009). Conducting polymers for corrosion protection: A review. International Journal of Materials Research, 100(10), 1331-1342. doi:10.3139/146.110205.