Electrochemical impedance spectroscopy and dielectric properties of polymer: application to PEEK thermally sprayed coating

Poly(ether ether ketone) (PEEK) thermally sprayed coatings find more and more applications, and ensure often the protective effect of substrate metals when the coated material is exposed to an aggressive medium. This coating exhibits extremely high impedance, and the impedance measurements of coated specimen were impossible to perform several years ago. Therefore, it was unable to evaluate quantitatively the coating protective performance by an electrochemical impedance method. Such measurements were realized, in this paper, with a recent device, and the impedance behaviour observed was interpreted in terms of dielectric relaxation after extracting the frequency dependent capacitance from the impedance spectra. It was found that the water uptake in PEEK coating is particularly low, ca. 1% and no interaction with absorbed water molecules and polymer matrix was detected. This result verifies therefore exceptionally high performance behaviour of PEEK thermally sprayed coating in an aqueous medium. The impedance measurements may therefore be used to evaluate accurately the corrosion protective effect of such a coating during development for new applications, and also to optimize the deposition conditions. (C) 2004 Elsevier Ltd. All rights reserved.