Developing electrochemical measurements in order to assess anti-corrosive coatings more effectively

The aim of this project was to check reproducibility of results obtained using NOCS (no connection to the substrate) arrangement of the electrochemical noise method (ENM). NOCS involves taking measurements from three nominally identical areas on the coated surface. Thus, no electrical connection to substrate is required. In practice the areas are not identical and various arrangements for connection of the three cells were tried to see if the individual areas could be separated out and whether the individual resistances could be computed. Also different ways of calculating the Rn (noise resistance) and Rsn (spectral noise resistance) parameters were attempted to see which one gave the best comparison with the more standard EIS measurements. The maximum entropy method was recognized to be the most useful for comparison with EIS, as well as for graphic evaluation of results. Regarding distinguishing three areas using different connection arrangements, it was possible to identify the situation when one of the three values was different to the other two. However further experiments are needed before it will be possible to confidently assign an Rn value to each individual area.

► In general value at 0.1 Hz from an MEM plot would probably be the most accurate for comparison with EIS.
► Averaging of MEM data from multiple configurations gives excellent correlation with Bode plots for high resistance coatings.
► Heterogeneity of the coating can be seen on the MEM spectrum graphs assuming a number of different combinations are used.