Continuing work to enable electrochemical methods to be used to monitor the performance of organic coatings in the field

Abstract

Although the most commonly used electrochemical method to assess anti-corrosive coatings in the laboratory is Electrochemical Impedance Spectroscopy (EIS), the Electrochemical Noise Method (ENM) is finding increasing use. EIS has also been used occasionally to assess coatings on metals in the field. However despite ENM's advantages (non-intrusive, quickness in gathering data, etc., ease of interpretation) rarely has ENM been used for the latter application even though Resistance Noise ( R n) has been shown to quantifiably relate to DC resistance and hence to protection afforded. However to obtain R n requires two contemporaneous measurements, one of the current noise and one of the voltage noise and hence two separate working electrodes are required. This is difficult to achieve in most practical situations. To overcome this in previous work there were validated two novel experimental arrangements of ENM, viz. single substrate (SS) and no connection to the substrate (NOCS). The current paper builds on this work. It describes methods of dealing with the practical considerations involved in making a measurement in the field, for example, dismountable non-marking cells acting as temporary “connectors” to the substrate, light battery operated equipment and experiments designed to minimize the length of time that the measurement takes to make. The “time to settle” experiments indicate that for most coatings a time of about 30–45 min is likely to be needed. The results obtained from changing the noise gathering parameter suggest that a frequency of 10 Hz may be suitable, enabling measurements to be made in one fifth of the time.