Using novel electrochemical test methods to aid in the development of low volatile organic compound (VOC) coatings

Electrochemical Methods have proved useful for assessing coated systems intended for anti-corrosive applications. Three areas of application are to assist new product formulation, quality control and to monitor in service. The Electrochemical Noise Method (ENM) has particular attractions because of its non-intrusive nature, quickness in gathering data and ease of interpretation. It has recently been successfully employed to help the development of new coating systems with reduced level of Volatile Organic Compounds (VOCs). In that work intact organic coatings were monitored using the standard bridge method in the laboratory under immersion conditions on steel substrates. The most common parameter derived was Rn and for the better systems the value started and stayed high throughout the period of the test including after higher temperature excursions in some cases. Comparison with outdoor exposure and salt spray testing confirmed the ability of ENM to predict subsequent behaviour from short term tests. The electrode arrangement for the standard ("Bridge") method of conducting ENM requires two separate working electrodes e.g. two painted Q-panels™ and a reference electrode. Although fine for laboratory use, e.g. the work described above, it is not so satisfactory for monitoring or quality control applications. The technique has been further developed to allow an electrode configuration which requires No Connection to Substrate (NOCS). Such an arrangement would provide a real advantage when attempting to monitor anti-corrosive systems in service. This paper presents the first results obtained using the NOCS method. So far, using the ENM NOCS arrangement with immersion testing has given a good indication of the anti-corrosive properties in comparison with the standard method. Also results have been compared with DC resistance and with the single substrate method.