Abstract
Successful measurement of electrochemical noise (EN) signals requires that a number of pre-conditions be fulfilled. In particular, fundamental understanding of the dynamics of the corrosion system concerned must be combined with an appreciation of the way in which the measurements are being made. Broader acceptance of the technique requires a joint effort by the various corrosion investigators and laboratories concerned and this, in turn, requires that a common basis for discussion be established.
With this in mind, the Institute of Materials Technology and Testing (IWW) of the University of Magdeburg organised a Round Robin experiment on the measurement of EN and obtained the participation of 17 organisations (universities, commercial firms, R&D laboratories) from 5 countries. The experiment involved the investigation of EN signals from aluminium and stainless steel exposed under conditions in which pitting corrosion can occur.
The data provided by the participants were analysed at IWW according to various criteria. Evaluation methods included visual inspection of the noise in the curves of potential or current versus time, calculation of the standard deviation, counting of transients and transformation of the meaurements into the frequency domain. Almost all of the participants were able to detect differences in EN behaviour during different stages of the experiment qualitatively. Quantitative evaluation, however, revealed a more complex situation. At times, differences in measured EN signal intensity of two orders of magnitude were obtained as a result of the different apparatus used (sensitivity, frequency range, etc.). Nonetheless, the fact that more than half of the participants reported data within a relatively narrow scatterband is a positive result.
Additional analysis of the results at IWW showed that uniform, numerical treatment of the measured data is of decisive importance in order to obtain comparable results. Furthermore, it became clear that the complex interactions between the way in which EN data are recorded (sampling rate, filtering, on-line data manipulation, baseline noise level) and the subsequent data evaluation should receive increased attention.
Critical evaluation of the results from the Round Robin experiment has clearly shown that comparable EN measurements can be made if suitable equipment is used and correct procedures are adhered to. The experience gained provides a sound basis for further development of EN as a tool both for the fundamental understanding of various aspects of corrosion and for the solution of practical problems of corrosion protection, in particular in the area of corrosion monitoring.
