Characterisation of five coins from the archaeological heritage of Portugal |
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Authors: | Ana L Mata André Carneiro M Manuel M Neto Luís A Proença M Manuela L Salta M Helena Mendonça Inês Teodora Elias Fonseca |
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Institution: | 1. Centro de Ciências Moleculares e Materiais (CCMM), Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, Ed. C8, 1749-016, Lisbon, Portugal 2. Departamento de História, Universidade de évora, Largo Marquês do Marialva, 8, 7000-554, évora, Portugal 3. Departamento de Química Agrícola e Ambiental, Instituto Superior de Agronomia, Tapada da Ajuda, TU Lisbon, 1349-017, Lisbon, Portugal 4. Instituto Superior de Ciências da Saúde Egas Moniz (ISCSEM), Quinta da Granja, Monte de Caparica, 2829-511, Caparica, Portugal 5. Laboratório Nacional de Engenharia Civil, Avenida do Brasil 101, Lisbon, Portugal
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Abstract: | This paper reports a study carried out on three Roman and two Portuguese coins found in the archaeological site of São Pedro, in Fronteira (Alentejo, Portugal). The three Roman coins have been identified as a Follis, an AE 2 and an AE 3 (bronze alloys), while the Portuguese coins have been identified as a Ceitil (copper) and the “6 vinténs” (Ag–Cu alloy). Scanning electron microscopy (SEM) coupled to energy dispersive spectroscopy (EDS) has allowed the semi-quantitative determination of the elemental composition of both the corrosion products and the alloy used in the manufacture of the coins. The crystalline corrosion products constituents of the patinas were identified by X-ray powder diffraction spectroscopy (XRD). The more deteriorated coin, the AE 3, was submitted to electrochemical studies in Na2SO4 aqueous solution and the corresponding data analysed. After 3 weeks, the E OCP was still quite stable, ranging between ?0.050 and ?0.070 V vs. SCE; the corrosion resistance, R p, was of the order of 5 to 3?×?103 Ω. Chemical treatment of the sample by 1-h immersion in 0.1 M NaOH produced a more active surface, with R p showing a decrease of a factor of about ten. On the other hand, it was concluded from voltammetric data that polarisations of E a?≥?0.050 V vs. SCE led to copper oxidation, with no reduction of the other corrosion products. |
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