iandol on tue 25 sep 01
Dear Brant Palley,
You say <<< 2% of talc in a cone 10 body can cause it to bloat because =
of the eutectic between talc and most feldspars. Bloating is rarely =
caused by firing schedule alone.>>>
I would be pleased if you would provide me with a reference for this =
information.
It is an interesting assumption because I have always understood that =
"Bloating' was caused by gas retained within clay as it became =
pyroplastic.
Perhaps you could elaborate more on the nature of the this =
"Talc-Felspar" eutectic. Information to hand suggests that a eutectic =
may be formed in the Al2O3-K2O-MgO-SiO2 system at 960 +/-20 Celsius from =
Enstatite, Tridymite, Potash felspar and Cordierite, but I do not =
believe you are talking about a clay body made from those minerals.
Concerning the behaviour of Talc. I believe this decomposes via =
dehydroxylation to become eka-Enstatite which is much harder and durable =
at about 950 deg Celsius (a fact used by sculptors who carve Soapstone. =
They fire it !!!), . If the water vapour remained trapped then it might =
contribute to gas which caused bloating.
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