Degradation of marine archaeological wood through acidification
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Transcript of Degradation of marine archaeological wood through acidification
Degradation of marine archaeological wood through
acidificationSara Goldman
SULI Summer InternshipAugust 12, 2010
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
The sample
Sample from the stem post timber
Mary Rose, warship of King Henry VIII
Sank in 1545, excavated 1981
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?
X-ray Absorption Spectroscopy
Bohr model of the atom
X-ray bombardment
Each electron shell requires a very specific energy
XAS graphical results
SpectrumTall peak,
“edge”Additional
structure, “near edge”
Edge jump
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
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
The spectra
Previous studies have shown uniform sulfur content
Our 15 positions on the same piece differ wildly
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
Oxidized sulfur
The flatter lines indicate aqueous sulfate
The distinct features indicate an ordered molecule
Fitting the data
A library of sulfur standards was created to fit our sample spectra
Left is most reducedRight is most oxidized
Sample fit
All 15 spectra were fit to the sulfur standards
This sample contains at least 5 sulfur types
Missing information on additional structure.
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
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2
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sulfate/reduced sulfur vs total amount
How does elemental sulfur get into the wood?
Anaerobic bacteria
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
Acknowledgements
Mentor Apurva Mehta
Riti SarangiSULI & SLAC