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Published byJane Bennett Modified over 9 years ago
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Sara Goldman SULI Summer Internship August 12, 2010
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The sulfur problem Sulfuric acid is appearing on museum artifacts These pieces have already been extensively treated to preserve them Widespread issue in the archaeological community
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The sample Sample from the stem post timber Mary Rose, warship of King Henry VIII Sank in 1545, excavated 1981
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What are we looking for? What types (species) of sulfur are in the wood? Which species are becoming acidic? Where is it coming from? Can we stop it?
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X-ray Absorption Spectroscopy Bohr model of the atom X-ray bombardment Each electron shell requires a very specific energy
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XAS graphical results Spectrum Tall peak, “edge” Additional structure, “near edge” Edge jump
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Advantages of XAS XAS is a very sensitive detector, it can find small amounts of specific items It can detect differences in oxidation state and structure
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Identifying species with XAS Your unknown contents are like a finger print You must compare them to prints that are already on file to identify what you have
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The spectra Previous studies have shown uniform sulfur content Our 15 positions on the same piece differ wildly
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Observing total sulfur and sulfate content Edge jumps indicated some locations had up to x3 as much total sulfur as their neighbors The amount of oxidized sulfur differed dramatically
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Oxidized sulfur The flatter lines indicate aqueous sulfate The distinct features indicate an ordered molecule
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Fitting the data A library of sulfur standards was created to fit our sample spectra Left is most reduced Right is most oxidized
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Sample fit All 15 spectra were fit to the sulfur standards This sample contains at least 5 sulfur types Missing information on additional structure.
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Information from the fits There is a correlation between the amount of total sulfur, and the amount of oxidized sulfur
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How does elemental sulfur get into the wood? Anaerobic bacteria
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Focus for future efforts Acknowledge the wide variation in sulfur content for treatment purposes Focus on the species that have the potential to become acidic
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Acknowledgements Mentor Apurva Mehta Riti Sarangi SULI & SLAC
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