Characterizing the Relaxation of the Open-Circuit Potential During an AC-DC-AC Accelerated Test

The non-conventional accelerated alternating current-direct current-alternating current (AC-DC-AC) testing method for organic coatings induces degradation by promoting cathodic reactions at the metal coating interface and ionic transport in the bulk of the coating. This cyclic method involves a test...

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Bibliographic Details
Published in:Corrosion (Houston, Tex.) Tex.), 2010-09, Vol.66 (9), p.1-11
Main Authors: Allahar, K N, Upadhyay, V, Bierwagen, G P
Format: Article
Language:English
Subjects:
Cathodic coating (process)
Charge transfer
Coating
Degradation
Direct current
Electrochemical impedance spectroscopy
Mathematical models
Transport
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Summary:The non-conventional accelerated alternating current-direct current-alternating current (AC-DC-AC) testing method for organic coatings induces degradation by promoting cathodic reactions at the metal coating interface and ionic transport in the bulk of the coating. This cyclic method involves a testing step in which the coating properties are determined using electrochemical impedance spectroscopy (EIS), a DC step in which a cathodic potential is applied for a given time period, and a relaxation step where the coating is allowed to relax back to a stable open-circuit potential (Esub OC) condition. Analysis of the relaxation Esub OC profile has been reported where characteristic times were attributed to the transport of ions through the coating, dielectric relaxation of the coating, and charge transfer at the metal/coating interface. The AC-DC-AC degradation of a standard United States Army vehicle epoxy primer on a steel substrate is reported here. The influences of applied DC potential and temperature were determined by subjecting the coating to potentials of -2 V and -8 V relative to the stable Esub OC at temperatures ranging from 25C to 65C. The relaxation Esub OC profiles were analyzed with a mathematical model to yield the characteristic times associated with the processes involved and the consistency of these processes with Arrhenius behavior was determined.
ISSN:0010-9312