sara goldman suli summer internship august 12, 2010
TRANSCRIPT
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Degradation of marine archaeological wood through
acidification
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
SpectrumTall 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 reducedRight 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
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80
1
2
3
4
5
6
7
8
9
10
sulfate/reduced sulfur vs total amount
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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 SarangiSULI & SLAC