Use of Electrochemical Noise Method and ElectrochemicalImpedance Spectroscopy for Investigation of a set of OrganicCoatings on steel

摘要

Both Electrochemical Noise Method (ENM) and Electrochemical ImpedancernSpectroscopy (EIS) are used to assess organic coatings both for assisting selection ofrncoatings, for quality control and for monitoring in the field and in accelerated testing.rnBoth methods have their advantages. ENM is less intrusive, quicker to perform, easierrnto interpret and is arguably better for continuous monitoring. EIS has the potential tornobtain mechanism information and is less prone to interference from extraneousrnsources. EIS is the more commonly employed method but the authors have conductedrnconsiderable work with ENM. A set of industrial coatings (acrylic, epoxy,rnpolyurethanes) were investigated in the laboratory over a period of several months inrnboth ammonium sulphate and sodium chloride solutions. Regular measurements werernmade using both the standard ENM (bridge arrangement) and EIS on the samernsamples at the same time. With one set of samples the solution concentration wasrnchanged after six weeks and both methods picked up changes in the resistance as arnresult of this change. These results will be presented along with observations of therncoatings/substrate at the end of the test. The conclusion of this work is that using thern0.1 Hz value from the EIS measurement compares very well with the Rn valuernobtained from analysis of the noise data. This was true for all the coatings examinedrnalong the time line. As the coatings systems had a range of resistance, it would appearrnto be a reasonable conclusion that ENM, using the bridge arrangement, and EIS arernboth essentially measuring the same parameter and either can be used satisfactorily tornassess organic coatings on steel substrates in the laboratory. Further work is in hand torninvestigate whether data obtained using other, more practical configurations of thernElectrochemical Noise Method (Single Substrate and NOCS) can be directlyrncompared with EIS.