engleski

Applicability of the paste electrolyte cell for in situ electrochemical testing the surface protection of bronze

Various electrochemical techniques can be used to obtain information about the condition of bronze artefacts as well as other metallic cultural artefacts exposed to the atmospheric corrosion condition in situ. In particular, electrochemical impedance spectroscopy (EIS) has proven to be a suitable method to generate valid data. A major challenge in performing EIS measurements in situ is the placement of a liquid electrolyte cell on an irregular, uneven and thin surface of the artefact. One approach to solve this problem is based on the use of a paste electrolyte cell instead of a liquid electrolyte cell. In this study, the applicability of the paste electrolyte cell for EIS testing of non-patinated copper and bronze as well as patinated bronze without and with the protective coating is investigated. Comparative measurements were made with three- electrode and two-electrode electrochemical cells and in three different types of electrolytes, an aqueous solution of sodium chloride, tap water, and electrolyte paste in the solid state. The aim of this work was to compare the measurements in the two types of electrochemical cells previously mentioned, to evaluate the repeatability and reproducibility of the measurements and to determine the influence of the different electrolytes. The EIS spectra were measured and the numerical values of impedance at 0.1 Hz were used as an indicator of the degree of surface protection by patina or coating. By comparing the impedance for different electrolytes, it was found that the aqueous solution of sodium chloride did not provide a reasonable indication of the degree of surface protection. By comparing the corrosion potential of samples in different electrolytes, an aqueous solution of sodium chloride and tap water was found to be a more aggressive electrolyte than electrolyte paste in the solid state. The surface of non-patinated bronze was changed after measurement in an aqueous solution of sodium chloride and tap water, while the plate remained unchanged after measurement with electrolyte paste. Electrolyte paste in the solid state proved to be a promising candidate for in situ measurements by determining the impedance in the following order: copper> bronze> patinated bronze> patinated bronze with a protective coating. It was also investigated whether the paste electrolyte cell detects any insulating layer as well as surface damage.

bronze, EIS, artificially patina

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