Micro and Nanoscale Structures and Corrosion Patterns in Brass: The Case Study of Ancient Roman Orichalcum Coins
Abstract
:1. Introduction
2. Materials and Methods
2.1. Materials
2.2. Methods
3. Results
4. Discussion
5. Conclusions
- The investigation of the patinas revealed the occurrence of selective trans-granular corrosion, due to the Cu-Zn ratio and to the presence of exogenous elements, such as chlorine;
- Two different degrees of corrosion were observed, i.e. F13 and F14 samples were protected by the presence of exogenous Si in the patinas, while the silicon-free coins, A3 and F1, showed a severe condition of degradation;
- X-ray maps of the main elements and high magnification investigation showed there was also the presence of corrosion inside the slipped crystal planes, due to plastic deformation induced by hammering. The related strain lines were heterogeneous in composition and Zn depleted;
- Sub-micro scale images indicated an early stage of corrosive processes, despite the presence of the noble patina (Type I) that usually protects the sample from corrosion (Figure 6). This consideration suggested that the structures produced by mechanical stress could be the trigger of corrosion and degradation processes in orichalcum.
- The use of SEM-EDS and HR-FESEM-EDS confirmed the use of cold-working by hammering to mint coins.
- Laboratory simulation could be a useful guide to understand the dezincification process, but cannot completely describe the long-term corrosive mechanism influenced by several random factors, such as mechanical stress or environmental events.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Sample | Cu % wt. | Zn% wt. | Sn % wt. | ||||||
---|---|---|---|---|---|---|---|---|---|
Max. | Min. | Avg. | Max. | Min. | Avg. | Max. | Min. | Avg | |
A3 | 82.12 | 81.14 | 81.52 | 17.82 | 16.73 | 17.32 | 0.84 | 0.61 | 0.72 |
F1 | 81.62 | 81.34 | 81.48 | 18.10 | 17.89 | 18.02 | 0.12 | 0.05 | 0.10 |
F13 | 90.75 | 89.55 | 90.18 | 9.97 | 8.80 | 9.34 | 0.16 | b.l.d | 0.05 |
F14 | 93.07 | 91.36 | 91.99 | 8.30 | 6.70 | 7.66 | 0.14 | b.l.d | 0.09 |
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Di Fazio, M.; Felici, A.C.; Catalli, F.; Medeghini, L.; De Vito, C. Micro and Nanoscale Structures and Corrosion Patterns in Brass: The Case Study of Ancient Roman Orichalcum Coins. Minerals 2022, 12, 827. https://doi.org/10.3390/min12070827
Di Fazio M, Felici AC, Catalli F, Medeghini L, De Vito C. Micro and Nanoscale Structures and Corrosion Patterns in Brass: The Case Study of Ancient Roman Orichalcum Coins. Minerals. 2022; 12(7):827. https://doi.org/10.3390/min12070827
Chicago/Turabian StyleDi Fazio, Melania, Anna Candida Felici, Fiorenzo Catalli, Laura Medeghini, and Caterina De Vito. 2022. "Micro and Nanoscale Structures and Corrosion Patterns in Brass: The Case Study of Ancient Roman Orichalcum Coins" Minerals 12, no. 7: 827. https://doi.org/10.3390/min12070827