In a recent article published in the Journal of Cultural Heritage, researchers investigated the corrosion behavior of ancient iron nails from the Phoenician-Punic site of Motya in Sicily, Italy.
Using correlative microscopy techniques, they aimed to obtain detailed information about the microstructure, composition, and changes resulting from stress corrosion in these archaeological iron artifacts.
Study: Correlative microscopy and Micro-Raman spectroscopy for enhancing the evaluation of corrosion damage in archaeological objects. Image Credit: Andrey Yershov/Shutterstock.com
Background
Iron is one of the most widely used metals throughout human history, and its archaeological artifacts provide valuable information about ancient metallurgy, technology, and culture. However, iron is highly prone to corrosion, especially when exposed to moisture, oxygen, and other environmental factors.
This corrosion can significantly alter the appearance, structure, and properties of iron artifacts, and lead to their degradation and loss. Therefore, understanding the mechanisms of iron corrosion is crucial for effectively preserving and restoring cultural heritage.
About the Research
In this paper, the authors focused on two iron nails discovered from the Phoenician-Punic site of Motya, an important maritime center in the central Mediterranean region during antiquity.
These nails were made of wrought iron, a low-carbon alloy produced by hammering iron at high temperatures.
To analyze the nails, the researchers used a correlative microscopy approach, which integrates multiple complementary investigation techniques for conducting multiscale and multimodal experiments.
The study employed three primary techniques. First, X-ray microscopy (XRM), a non-destructive imaging method, was used to explore the internal structures and reconstruct the nails' three-dimensional (3D) volumes.
XRM provided highly resolved 3D images, which allowed for detailed examination of the spatial distribution of different phases, the identification of inclusions, and the detection of defects at micro- and nano-meter scales.
Second, correlative light and electron microscopy (CLEM) were employed to integrate the high-resolution capabilities of electron microscopy with the field view provided by light microscopy.
This technique allowed detailed visualization of the corrosion layers from the rim to the core of the nails. It facilitated chemical analysis, including identifying corrosion products and metallic nanostructures. The authors also employed energy-dispersive X-ray spectroscopy (EDX) to generate elemental maps of the samples.
Lastly, Micro-Raman spectroscopy provided insights into the molecular and crystalline structures, offering a "fingerprint" of the corrosion compounds.
This technique was particularly effective in differentiating between iron oxyhydroxide polymorphs, which are the primary corrosion products of iron.
Research Findings
The correlative microscopy revealed significant differences in the condition and corrosion patterns of the two iron nails, MC.14.08 and MC.03.43. Nail MC.14.08 was relatively well-preserved, with a mostly uncorroded iron core coated by a thin layer of oxyhydroxides.
The presence of lepidocrocite, goethite, and occasional magnetite indicated a slow corrosion. Nail MC.03.43 showed extensive corrosion characterized by two distinct layers: a dense outer corrosion layer and an iron corrosion phase mixed with surrounding elements.
Additionally, the Micro-Raman spectroscopy identified a complex mix of soil minerals, including microcline, calcite, and quartz.
Furthermore, 3D imaging with XRM provided additional insights into the nails' internal structures, allowing for reconstructing their original shapes.
For MC.03.43, the imaging revealed cracks and an internal cavity, suggesting it underwent repeated mechanical stress while forging, facilitating metal oxidation. In contrast, MC.14.08 displayed a well-preserved and homogeneous iron core, showing limited exposure to external environmental conditions.
This comparative analysis highlighted the varying degrees of preservation and the different corrosion mechanisms affecting these nails.
Applications
The study demonstrated the potential of correlative imaging techniques in analyzing archaeological iron artifacts. These methods provide comprehensive insights into microstructure and composition changes due to stress and corrosion.
By integrating multiple techniques, the study overcomes the limitations of individual methods, offering a more holistic understanding of the samples.
The results contribute to a deeper understanding of ancient metallurgical techniques, cultural practices, and the environmental conditions affecting iron artifacts.
Additionally, these outcomes have significant implications for developing strategies to prevent and control corrosion in modern metals and for the preservation and restoration of historical and cultural heritage.
Conclusion
In summary, correlative imaging effectively investigated the corrosion behavior of ancient iron nails. The researchers identified significant differences in the condition and corrosion patterns of the two nails, influenced by manufacturing processes, soil composition, and environmental factors.
They also gained valuable insights into the nails' internal structures, original shapes, and the types of corrosion products and soil minerals present. Moving forward, they proposed comparing corrosion mechanisms between ancient and modern metals.
Journal Reference
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