Microscopy & Microtechniques
How the world’s most advanced analytical techniques are saving ‘doomed’ shipwrecks
Dr Claudia Mondelli, Research Scientist, Institut Laue-Langevin (ILL)
When wooden objects sink to the bottom of the sea, they are generally served an extended lifespan. On land, wooden artefacts such as shipwrecks may be destroyed through rotting, animals, or human action, but marine environments can prevent the biological, chemical, and mechanical changes that would cause an object to decay – preserving a rare time capsule to our past.
Further, the solution could be a transformative step in archaeology due to the considerable safety, sustainability and cost-effectiveness of the new nanoparticle approach. The solution uses water in the production and suspension of the nanoparticles, instead of alcohol. Given the size of many waterlogged wooden objects such as shipwrecks, immersing entire structures in a massive pool of alcohol represents a huge health and safety risk to archaeological researchers, as well as being an extremely expensive method. By proving that water is an effective way to deliver the nanoparticles to the artefact, the team has opened the doors to more affordable and sustainable restoration techniques that will not impact the health and working practices of cultural heritage professionals.
Exploration with neutrons
The study and characterisation of a new nanoparticle suspension, especially one where the materials being treated are so delicate, rare, and precious to human history, is an essential step before any solution is applied. Ahead of testing the new solution on any archaeological wood samples, the treatment underwent extensive analysis, including small angle neutron scattering (SANS), to examine and compare the suspension of calcium- and magnesium-hydroxide nanoparticles in water.
Drying process carried out inside the apparatus for large-scale lyophilisation procedure (Credit ARC-Nucleart) somewhere near top of page
However, when an ancient shipwreck is pulled from the water, the process of acidifi cation can start and they can begin to crumble. In addition to structural changes from the drying of the wood – causing shrinking and cracking – iron present in features such as nails, combined with sulphur from bacteria, creates the compound ‘iron sulphide’. This material, dormant under water, can develop into destructive sulphuric acid when met with oxygen above ground. This acidifi cation ‘infection’ of the wood can spread and make the entire structure crumble within days, risking the loss of thousands of years of human history. One of the world’s most famous shipwrecks, the 400-year old Vasa ship in Stockholm, was partially eaten by sulphuric acid in the early 2000s due to the ferociousness of the process.
Tackling the disease
New research from a consortium of scientists based at Institut Laue-Langevin (ILL), Grenoble (France) and University of L’Aquila (Italy) has explored the potential of an innovative new solution that uses nanoparticles in aqueous suspensions to tackle this ‘disease’ of archaeological wood.
Using neutron scattering to reveal the atomic structure deep inside materials alongside a variety of imaging techniques including microscopy and X-ray probing, the group showed how the nanoparticle suspension can be highly effective at neutralising the acid in the pores of the wood before it can cause further damage. Used in combination with a common technique of submerging the objects in polyethylene glycol (PEG) to replace the water in the structure, this approach has the potential to save precious relics from turning to dust.
SANS measurements were carried out at Institut Laue-Langevin (ILL), the world’s fl agship centre for neutron science, to study the particles directly in suspension in their solvent. To demonstrate the effectiveness of the nanoparticles in water, rather than alcohol, this technique was essential – it is uniquely capable of revealing the form of the nanoparticles without drying them, a process which may impact the shape or function of the active factors.
Using D11, an instrument designed for the study of chemistry, biology, solid state physics and materials science, a powerful beam of neutrons was directed at the suspension. The subsequent scattering of neutrons as a result of the atomic structure or magnetic properties in the material indicate the size and shape of the nanoparticles. This confi rmed that the particles would be free to move into the wood and successfully deacidify.
EPN campus MONFRONT
co-author Ralf Schweins and Sylvain Prevost with D11
INTERNATIONAL LABMATE - FEBRUARY 2021
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