Dear Amalia,
As mentioned before, the conventional way to estimate carbon content is to cut and polish an opaque sample and look at it with a reflected light microscope. If you are in a materials science department, they should have a set of steel standards that go from ferrite to cast iron that you can visually compare with your archaeological samples.
There is a completely non-destructive method for direct measurement of bulk carbon content in steel, and that is neutron diffraction. You would need to bring or send the samples to a neutron facility such as ISIS in Harwell (UK) in order to do this. I'm an archaeomellurgist specialising in early ironworking, and for the past 5 years I've been doing neutron diffraction experiments specifically because there was no other way to measure carbon directly in intact iron artefacts non-destructively.
The neutron beam passes right through the object (can be up to 10 cm thick), and you get a diffraction signal from the whole volume that the beam goes through. This is different from for example X-ray diffraction, which is very dependent on the geometry and matrix of the sample, really just gets a signal from the surface (hence it is best to powder and homogenise XRD samples first), and has quite poor detection limits for the compound that you are looking for - cementite (Fe3C). It's not pure carbon (e.g. graphite) that you see in steels in the range 0.1wt%C to 1.8wt%C, but cementite. I've run a lot of standards now on the diffractometers at ISIS as well as archaeological objects, and cementite can be measured quantitatively down to 0.05wt%C. That equates to just about the lowest level of carbon that one can estimate visually in a metallography sample, so it is all you need. I wrote a short paper on measuring carbon content and martensite in archaeological iron for the 2008 Archaeometry Symposium proceedings (Siena), which must be out by now.
I've sent occasional notices to this list about upcoming deadlines to submit neutron diffraction proposals to ISIS.... if your proposal is accepted, experiments are done free of charge to users from anywhere in the world, provided you agree to publish the results. UK users of the facility get their travel and accommodation costs paid to bring their samples to the facility, and some EU countries will pay researchers to come from their country to analyse things at ISIS as well (e.g. the Italian research council CNR does).
You would need to be able to either process your own diffraction data (the software is freely available, but not so easy to understand), or submit the proposal in collaboration with someone who can process the data for you, which I am willing to do, or at least help people get started with the software.
Cheers,
Evelyne
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Dr Evelyne Godfrey
Visiting Research Associate,
Materials Engineering Group,
Faculty of Mathematics
Computing and Technology,
The Open University, Walton Hall,
Milton Keynes, MK7 6AA, England
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From: Amalia Siatou [[log in to unmask]]
Sent: 27 May 2010 10:27
To: [log in to unmask]
Subject: requesting information on iron analysis
dear all,
I'm a metals conservator from Greece doing a master in materials science. Part of my thesis is the study of archaeological iron and bronze. I came across some difficutlies in measuring the carbon content of archaeological iron (roman nails). Using SEM-EDS the percentage measured was particularly high (almost 10%) which doesn't follow the dating of the objects. Furthermore, I was anable to find adequate equipment to perform chemical analysis.
Do you know of a different method of estimating the carbon percentage in iron?
thank you in advance
sincerely
Amalia Siatou
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