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Exploring the hidden chemical depths of the Mary Rose

To develop conservation strategies for Henry VIII s warship Mary Rose, detailed knowledge of the compounds residing in the wood is required. Advanced X-ray methods, combining X-ray total scattering and computed tomography have now revealed the presence of zinc-containing sulfide nanoparticles, which are potential precursors for acid attacks.

On a summer day in 1545, the Mary Rose, one of the principal warships in Henry VIII s Royal Navy, was manoeuvring to confront the invading French fleet outside Portsmouth on the English coast. Whilst engaging in battle, the Mary Rose tragically sank, and for the next 437 years, she was submerged in marine clay sediments. After being salvaged in 1982, she now resides in a purpose-built, state-of-the-art museum in Portsmouth (Figure 128), where efforts to preserve the remaining hull have been ongoing for over 30 years.

However, major threats to the integrity of the hull remain due to the presence of harmful sulfur species that reside within the wood [1,2]. These reduced sulfur compounds originate from the activities of anaerobic sulfur-reducing bacteria, and whilst stable under the seabed, they can oxidise in air to form potentially harmful acids. There are potentially several tons of sulfur-containing species residing in the Mary Rose hull.

Effective conservation requires detailed knowledge of the distribution and chemical nature of these species. Previous

Fig. 128: The Mary Rose on display at the Mary Rose Museum in Portsmouth, UK. Photo: Hufton + Crow.

X-ray spectroscopy studies have revealed the presence of iron- and sulfur-containing species [3,4]. However, determination of the atomic structure of these inclusions has so far not been possible. In this study, by using a new approach to cultural heritage studies, combining computed tomography (CT) and X-ray pair distribution function (PDF) analysis in the newly developed ctPDF method [5] at beamline ID15A, it has now been possible to identify nanostructured sulfides residing in the wood.

Figure 129 shows maps of the wood obtained using the ctPDF method. Figure 129a represents a map of the electron density of the wood, and clearly shows the expected structural heterogeneity. However, the ctPDF data provide much more information. Each voxel contains a total scattering pattern from which a PDF can be obtained. For example, Figure 129c shows the PDF obtained for a representative voxel in the keelson wood. The PDF is typical for organic polymers as present in wood and can be modelled with the structure of cellulose.

Further analysis of the data showed that several other compounds resided in the wood. Most importantly, significant amounts of sphalerite nanoparticles were identified and mapped. A PDF obtained from a voxel containing such particles is seen in Figure 129d, and the distribution is seen in Figure 129b. By modelling the PDFs, it was possible to extract quantitative information, which showed nanoparticles in the size range 2-6 nm, with unit cell parameters corresponding to zinc sulfide with different degrees of iron substitution. In addition to identifying the presence of sphalerite nanoparticles, the ctPDF analysis revealed the presence of other polycrystalline phases,