THE POTENTIAL FOR UNANTICIPATED BIODEGRADATION DURING EIS ANALYSIS OFPOLYMER-COATED METALLIC SUBSTRATES

During a recent long-term electrochemical test in aqueous NaCl produce d from deionized water, microscopic inspection revealed that the surfa ce of the polymer was heavily colonized by micro-organisms, which had developed naturally. The deionized water was considered as a possible source and, to establish the extent of contamination, samples were pro cured from universities in Italy, the U.S.A. and England. In all cases , when aliquots were cultured to test for the presence of biological c ontaminants, both bacterial and fungal growth ensued, thus reflecting the widespread contamination of deionized water systems. Many electroc hemical experiments currently employ electrolytes produced from deioni zed water, and there is a body of evidence suggesting both that biodeg radation may be partially responsible for early failure of inoculated samples and that the technique of EIS is sensitive enough to reveal su ch failures when they occur. There is, however, no conclusive evidence showing that EIS is capable of distinguishing between classical and b iologically induced degradation. Thus, unanticipated biological contam ination of long-term electrochemical tests may seriously affect the in tegrity of an experiment and subsequent interpretation of results. How ever, even if a source of non-contaminated water is available, a probl em may still exist due to the ubiquitous nature of contaminants. Thus, assuming the absence of extraordinary measures to destroy biological contaminants, samples associated with longer term electrochemical expe riments may suffer from inadvertent inoculation and subsequent growth. In addition, it seems likely that where this is followed by undetecte d and unanticipated biodegradation of a coating, a metal or the combin ed system, subsequent EIS analysis may produce spurious data. (C) 1997 Elsevier Science Ltd.