Formation and electrochemical behaviour of poly(pyrrole) coatings on steel substrates
article
This paper focuses on the deposition process and the semi-conductive properties of PPy layers on steel. The polymerisation of PPy was performed galvanostatically on steel in an aqueous solution of 0.1 M pyrrole and 0.1 M oxalic acid (H2C2O4) using a current density of 1 mA/cm2. The build-up of a ferrous oxalate (FeC2O 4) layer, which seals the seel substrate surface, is initially observed. PPy layers made by this method are always doped with oxalate anions. A mechanism is proposed in which PPy deposits at sites where ferrous oxalate is dissolved. PPy is a semiconductor, just like oxide films formed naturally on some metals. Mott-Schottky diagrams for 9.0, 11.6 and 15.0 kHz suggests a frequency dependence of the dielectric constant of polypyrrole (εppy The flatband potential EFB was about -0.39 V vs. NHE and the charge carrier density was estimated to be about 5.1020 m-3. Also, in earlier work by Rammelt et al. and by Miller and Bockris (using different electrolytes and substrate materials) a frequency dependence has been found for a constant phase element that was used to describe the space charge capacitance Csc. The frequency dependence observed can partly be ascribed to surface roughness, which seems experimentally supported by SEM-research.
Topics
TNO Identifier
237979
ISSN
09475117
Source
Materials and Corrosion, 55(9), pp. 653-658.
Publisher
Wiley
Place of publication
Weinheim, Germany
Pages
653-658
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