Optimisation of the setup of LPR and EIS measurements for the onsite, non-invasive study of metallic artefacts

Abstract

Electrochemical techniques have been successfully applied in the past as non-destructive techniques to the cultural heritage field. In particular, linear polarisation resistance (LPR) and electrochemical impedance spectroscopy (EIS) have been employed for the onsite monitoring of corrosion on metallic works of art, providing valuable results. Such techniques have been successfully adapted from the industrial field for this particular kind of application, but a systematic evaluation of the influence of all experimental settings on the obtained results is still lacking: several factors and parameters can affect the results, and it is important to properly consider their influence for a reliable interpretation of data. Therefore, in this work, the influence of a series of experimental parameters was evaluated in order to obtain a reliable and time-effective setup by performing a series of tests on a bronze artefact. Several variables were considered, with particular attention to those affecting the reproducibility and reliability of the measurements, as well as the duration of each single acquisition. It was demonstrated, in fact, that an optimised experimental setup from the point of view of the duration could improve also reproducibility and reliability of the measurements. The optimised protocol was then adopted in the framework of a diagnostic campaign of the Monumento ai Caduti (War Memorial) of Lecco (IT)

Electrochemical impedance spectroscopy evaluation of nonthermal plasma restoration for ductile metals in cultural heritage artifacts

“…In that case, the formation of a compact oxide layer on copper resulted in a large impedance value. [56] It can also be seen in the data fitting (see Supporting Information: Tables S1 and S2) that the equivalent circuit used for modeling the data was composed of a parallel combination of Rf1 and CPE1, representing the sulfate layer, in series with another parallel Rf2 and CPE2 combination, because of the presence of PbO in the corrosion layer. It is worth mentioning that large Rf1 and Rf2 values were obtained (25.8 and 4.9 kΩcm 2 , respectively).…”

The Effect of Exposure Condition on the Composition of the Corrosion Layers of the San Carlone of Arona

“…Thus, to obtain a more reliable measurement, a longer waiting time before the measurement may be considered. However, this may lead to a measurement duration that is not sustainable for on-site characterizations and a reduction of the reproducibility of results [36]. Consequently, a precise estimation of the corrosion rate could hardly be obtained and Rp should then be considered as an indicator of the surface's corrosion resistance and used mainly for comparative purposes.…”

Artistic and Laboratory Patinas on Copper and Bronze Surfaces

“…Moreover, such Rp values are lower also with respect to those measured on natural corrosion layers formed upon atmospheric corrosion in non-marine outdoor environment. In such cases, in fact, Rp values that normally range between 2 and 20 Ω•m 2 [75,[109][110][111][112][113][114]. In particular, patina black 605, constituted by Cu2S and SnO2 resulted the most stable from the corrosion point of view, showing the highest Rp values while all the nitrate-based patinas showed Rp lower than 1 Ω•m 2 .…”

“…Rp values calculated for all kind of laboratory patinas are summarised in Figure 17. As it can be observed, when cuprite patinas are considered, the one obtained by "boiling solution" procedure shows a significantly lower Rp value with respect to the one of not patinated copper and to those typically measured on natural patinas that normally range between 2 and 20 Ω•m 2 [75,[109][110][111][112][113][114]. Cuprite patinas realised by means of wet and dry cycles in deionised water or artificial seawater allowed instead the development of less reactive surface layers.…”