Multiple-scan voltammetry of immobilized particles of ancient copper/bronze coins

Evaluation of the corrosion resistance of bronze patina or/and protective coating on the surface of the archaeological coins

Archaeological coins are considered essential sources of historical documentation. Over time, they are subjected to corrosion processes that gradually alter their appearance, shape, and composition. This study aims to evaluate the effects of the patina and/or protective coating on the corrosion process. Protection of the original coin surface was crucial following the completion of the cleaning protocol. Various finishes of coin fragments (uncoated, aged, and freshly coated) were investigated to determine their chemical composition, nature of the patina, and corrosion products on their surface using stereo microscopy(SM), X-ray diffraction (XRD), and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDX). The analysis revealed that the coins were composed of a Cu-Sn- and Pb bronze alloy. Furthermore, the efficiency of the patina and/or protective coatings on the coin fragments was evaluated using potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) techniques. The highest protection was achieved for patinated-freshly protective coated fragments, while the most corrosive fragments were those affected by bronze diseases.

Correlation Between Voltammetry of Immobilized Particles and Mott-Schottky Analysis of Metal Corrosion Patinas

The conjoint application of the voltammetry of immobilized particles (VIMP) methodology and the Mott-Schottky analysis (MS) of impedance data to studying metal corrosion patinas is described. The study is applied to copper and bronze objects exploiting the semiconducting character of cuprite and other copper corrosion products. A simplified theoretical modeling of MS analysis at microparticulate deposits extracted from metal corrosion layers attached to graphite electrodes is provided. The proposed model compensates for the disturbing effect of the regions of the basal electrode directly exposed to the electrolyte. Alternative models accounting for the variation of the density of charge carriers with depth are tested as well as the correlation between VIMP and MS data with reasonably satisfactory results.

Electrochemical Approximation to Bronze Age Chronology via Multiple Scan Voltammetry

Insert A multiple-scan voltammetry strategy is described and applied to a set of 107 Bronze Age and later copper/bronze objects, mainly from sites in Central Europe. This methodology allows the study of the compositional and textural properties (compactness, crystallinity, degree of hydration) of the patina to be studied from the accumulated peak current values for the characteristic signals corresponding to the reduction of cuprite and tenorite to metallic copper. A new model for the relationship between peak current and the depth reached in successive scans is presented and used to discriminate samples of different provenance and manufacturing technique, as well as their ascription to different Bronze Age periods.

Can Electrochemical Sensors Be Used for Identification and Phylogenetic Studies in Lamiaceae?

Electrochemical sensors have shown potential in recent years for plant species identification and phylogenetic studies. These works have been used to investigate the affinities of different species in many genera. However, the ability of electrochemical sensors to study relationships between different genera within a family has not been investigated. In this work, we selected 31 species in the Labiatae and 5 exotaxa as subjects to investigate the feasibility of electrochemical sensors at the genus level. The results show that electrochemical sensors are still very effective for the identification of these plants. Different pattern recognition techniques can make the identification more efficient. Also, the fingerprint profiles collected by the sensors can be used for phylogenetic studies of Labiatae. The phylogram divides all the species into five clusters, where the exotaxa are in one cluster. Species in the Labiatae are mainly distributed in four other clusters. Importantly, the different genera of species all showed close affinities, representing that electrochemical fingerprinting can well distinguish the affinities between the different genera. The results of this work demonstrate the great potential of electrochemical sensors in the study of plant phylogeny. Its application is not limited to the study at the species level, but can be extended to the genus level.

An Electrochemical and Spectroscopic Study of Surfaces on Bronze Sculptures Exposed to Urban Environment

Polluted urban environment enhances dissolution of patina and underlying bronze material of recent and historical bronze sculptures exposed outdoors. In this work, two bronze statues, situated in one of the most polluted Croatian cities, were examined in order to characterize composition of patina and its electrochemical stability. The composition of patina on several positions on each sculpture was determined by EDS, Raman spectroscopy, and FTIR measurements. Electrochemical impedance spectroscopy measurements were conducted in order to evaluate the corrosion stability of both patina and underlying bronze. Results obtained in this work show that the two examined bronze sculptures were covered with patina layer that was mainly composed of copper sulfides and sulphates, which is in accordance with the high concentrations of H₂S and SO₂ in the atmosphere. However, the variations in the appearance of FTIR and Raman spectra revealed that the amount of each species differed from spot to spot, as well as the fact that other compounds, such as carbonates, were present at some areas. This difference in patina composition was reflected in electrochemical behavior as observed by electrochemical impedance spectroscopy.