lahthffire
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Arsenic decontamination
If you had some aluminum, stainless steel, and ceramic (probably alumina) that had a very thin layer of arsenic containing contaminant, such as might
be left on parts used in an ion implanter doping silicon wafers with arsenic, what would be your preferred method of removing and containing that
arsenic? There's plenty of information on precipitating As from solutions, but what would be the best way to dissolve it into solution in the first
place? (without harming the substrates)
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unionised
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I probably wouldn't try with the aluminium. Any acid or base will produce nascent hydrogen and turn the arsenic to arsine.
Depending on the total quantity of As and where I was living, I might consider a bonfire as the easy way, particularly for the ceramic. (I know you
said containing, but if the quantity is small, it isn't worth it.)
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The_Davster
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Aqua regia, followed by extended heating at high temp.
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not_important
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HNO3,medium strength I believe, boiling point for the ceramics. Avoid halides, as they can form somewhat volatile arsenic halides.
After that soak the pieces in several M NaOH, which will grab on to any arsenic oxides left on the surface. Combine the NaOH aq and the rinse water
used to remove it with the HNO3 from the first step, carefully to avoid splattering from heat of reaction. Use standard methods to ppt the arsenic,
adjust pH as needed.
There's some other ways, but I need to dig in books to check details.
[Edited on 2-8-2006 by not_important]
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unionised
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I have a feeling that aqua regia doesn't quite meet the description of "without harming the substrates"
Bleach is use to dissolve the arsenic mirror produced by Marsh's test- might work here as it won't attack stainless or alumina very quickly.
Destroy the excess hypochlorite (alcohol, perhaps) then ppt the As as the sulphide (or better, don't, because if you need to ask this sort of thing
you might be better off not working with arsenic).
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12AX7
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I would tune the ion beam so it doesn't strike anything besides the intended silicon wafer...yup...less wasted beam besides...
Tim
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The_Davster
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Alumina(at least the crucibles we use in the lab) are completly unharmed by aqua regia. I missed the Al and SS though, those definatly would react.
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lahthffire
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Yeah, the Al and SS are the hard part. What about nitric acid? The stainless can handle that. Won't the Al2O3 layer on the Al protect it from the
HNO3? I think pure Al would be OK, but I'm talking about 6061 Al. Here's a list of the alloy composition:
http://www.aircraftmaterialsuk.com/data/aluminium/6061.html
Would HNO3 dissolve arsenic?
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not_important
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It takes pretty strong HNO3, reactions starts with the 50% acid.
Better might be alkaline hydrogen peroxide, maybe 0.5 molar on the base, or persulfate solution. If you have time, soaking in ammonium nitrate
solution for days to several weeks should do it.
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cranium
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The best way to remove the arsenic is to wipe it up with a cloth with distilled water only on it.
[Edited on 10-8-2006 by cranium]
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