I.Lewis on sun 7 nov 99
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To Subscribers clayart=40lsv.uky.edu
Fumes.
There are often interesting postings about fumes and fume extraction and =
recent
dialogues about those issuing from electric kilns attracted my attention =
even
though I do not have an electric kiln. However, when teaching I always =
noticed
that the metal casings of electric kilns around the spy holes were often
corroded. I always attributed this to the effects of hot steam on steel.
I would like to know if the following notions are tenable.
Given that the original rocks were granite intrusions they would have been =
in
contact with crustal rocks which metamorphosed. Volatiles in the rising =
magma
would react with such things as limestone producing gypsum and fluorite.
Weathering and further metamorphism change the rocks, forming clays. =
Transport
would degrade the size of the particles.
Hence, it is reasonable to suppose that ball clays and other sedimentary
deposits also have a percentage of sulphate, sulphide and fluoride minerals.
When heated to a high enough temperature these minerals break down releasing
fluorine, sulphur and chlorine (NaCl get everywhere) as elements or through
reaction with water vapour, Hydrofluoric acid, Sulphuric acid and =
Hydrochloric
acid.
Should this be possible, it might be that emanations from kilns may be a =
greater
hazard than we might believe.
Can some one satisfy my curiosity and confirm that firing out of doors is a =
safe
thing to do.
Ivor.
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