X-ray technique finds zinc nanoparticles ‘eating’ Mary Rose
Image credit: Dreamstime
An international team of researchers have applied a new X-ray technique to discover potentially harmful zinc-containing nanoparticles within the remains of Henry VIII’s famous warship, the Mary Rose.
The technique, computed tomography ctPDF (ctPDF), was developed by researchers at Columbia Engineering and the European Synchrotron Radiation Facility (ESRF) with the intention of using it to study catalysts and batteries.
One of the researchers, Professor Simon Billinge, was approached by nanoscientists from the University of Sheffield, and the idea arose to use ctPDF to examine what was happening inside the remains of the Mary Rose non-destructively.
The Mary Rose sank during the Battle of the Solent in 1545. The shipwreck was excavated and raised in 1982 through an extremely complex procedure. It is displayed and carefully conserved, along with the thousands of artefacts found onboard, at the Mary Rose Museum in Portsmouth.
Continuing to conserve the unique ship requires detailed knowledge of the distribution and chemistry of destructive materials in the historic timber. This is a challenge given the heterogenous nature of waterlogged wood, which cannot be characterised with traditional examination techniques. For instance, X-ray spectroscopy performed on the shipwreck extracted much information about the iron and sulphur chemistries in the wood, but did not allow for phase composition to be determined.
Applying ctPDF, Billinge’s group observed how X-rays scattered through sample cross sections at the nanoscale and used these data to characterise the nature of the materials hidden deep within the wood of the shipwreck. Comparing the images pixel by pixel revealed that, over the centuries on the seabed, the timber of the hull had become riddled with 5nm zinc sulphide nanoparticles.
“It was especially exciting to get a glimpse into the history of the Mary Rose in the years since it sank,” said Billinge. “The zinc sulphide deposits come from anaerobic bacteria living in the wood as it sat sunk in the seabed; they are essentially bacteria poop. Our results were like a microscale archaeological dig, where, by studying the location and composition of the deposits, we could see how the bacteria colonised the wood and what they ate.”
The nanoparticles became embedded in the wood under the anaerobic conditions on the seabed; the researchers identified them as precursors to acid attack on the wood upon its removal to an aerobic environment.
They also discovered deposits of a polymer (polyethylene glycol) within the wood. The polymer was sprayed on the ship in an effort to preserve it after being raised, with the idea being that the polymer could provide some mechanical stability. However, recent evidence suggests that this polymer could degrade and act as a source of degrading acids to surrounding materials.
Billinge and colleagues will be able to track the polymer within the timber using ctPDF. They hope this could inform future strategies to conserve the Mary Rose and other important archaeological discoveries.
Marco Di Michiel, scientist in charge of the ESRF’s beamline ID15A (which is dedicated to high-energy X-ray imaging), commented: “This is the first time that we have used the technique of X-ray total scattering with computed tomography to successfully study cultural heritage samples at the nanoscale. This work opens doors to new experiments in the domain of conservation.”
According to the Matter paper describing the investigation, there are potentially tonnes of sulphur-containing species and polymer breakdown products in the Mary Rose hull. Efforts are now under way to understand in detail the degradation effects these zinc-based particles may have had on the Mary Rose, and how they might be neutralised.
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