engleski

In the field application of electrochemical impedance spectroscopy for quality and durability quantification of paint coatings

Long-term corrosion protection may be achieved by a coating system that requires little or no maintenance, or by a system that requires several major maintenance operations during the structure’s design lifetime. Exposing the coating in the real-life exposure condition is the best way of evaluating its performance. Since the corrosion process is electrochemical in nature, electrochemical characterization techniques are more appropriate and are widely used in understanding the corrosion behavior of structures and protective performance of organic coatings. These techniques also circumvent the disadvantage of subjective and qualitative evaluation of coatings performed with the exposure testing methods. The electrochemical impedance spectroscopy (EIS) has been widely used in the investigation of the performance and degradation degree of coatings because of its good ability to provide abundant information. Each circuit element obtained by fitting the EIS data correlates to the corrosion properties of the system and the extracted values of the circuit elements provide quantitative information of the processes involved. EIS is equally successfully applied in the field for a performance rating of new coatings and coatings that have spent time in service. Coating resistance, capacitance, water uptake and dielectric constant may be recorded as functions of time and indicate probable premature coating failure before it can be visually observed. When used, on reference samples and at multiple positions on a structure, the technique can also discriminate between the low-quality coating and improper workmanship. Early detection of corrosion under coating is observed as a significant drop in coating impedance and the appearance of additional time constant representing steel/coating pores interface. Recent technical advances originating from the Research Laboratory for Corrosion Engineering and Surface Protection of FKIT, Zagreb, that led towards EIS method simplification for use in laboratory and in the field, will be presented, alongside with the examples of successful application. Reference will be made to state-of- the-art and prospects of wide-spreading the use of electrochemical methods for paint coating QA and QC.

EIS ; coatings ; quantification ; quality

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