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July 1995

By: Luz Calle & Louis MacDowell

Abstract

Electrochemical Impedance Spectroscopy (EIS) was used to evaluate the performance of two doped polyanilines (PAN's) in the emeraldine base form (EB) as protective coatings for carbon steel under immersion in 3.55% NaCl.  Coatings A and B consisted of EB doped with tetracyanoethylene (TCE) and with p-toluenesulfonic acid (PTSA) respectively.  Corrosion potential as well as Bode and Nyquist plots of the data were obtained for each coating after various immersion times.  The equivalent circuit R_e(C_c [R_c(QR_a)]) provided a satisfactory fit for the EIS data.  The variation with immersion time of the equivalent circuit parameters R_c and C_c was recorded and analyzed.  Both coatings exhibited similar behavior except for the initial decrease in C_c observed for coating B.  The results showed that EIS can be used as a technique to evaluate the progress in the development and optimization of conductive polymers as protective coatings for carbon steel.

For additional information, a complete copy of this study is available as NASA-KSC Report 95-1M0070.  Send requests for copies to corrosion@ksc.nasa.gov.

To download a full copy of this report in Adobe's pdf format for local printing, click 95-1m0070.pdf.  (2.1MB)

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