Craig Martell on mon 24 jul 00
Hello again:
>your choice of clay is critical - preferably it should be a highly plastic=
=20
>(high percentage of colloidal clay particles) with a nice high carbon=20
>content (show=B4s up in the analysis as loi - loss on ignition)
I guess I have another nit to pick. LOI will not necessarily give you a=20
true idea of carbon content. Some kaolins have higher LOIs than ball clay=20
and they don't have much carbonaceous material to burn off. When ball=20
clays are given a test of differential thermal analysis they show=20
exothermic peaks when the carbonaceous material is burned off between 300=20
to 500 degrees C. Kaolins show exothermic peaks at higher temps when the=20
hydroxyls(water) are driven off, resulting in the approximate 13%LOI for=20
most kaolins. There's another later exothermic peak for kaolin when=20
primary mullite begins to form. But these have nothing to do with=20
carbon. My point is that a high LOI does not signify high carbon content=20
in clays.
later, Craig Martell in Oregon
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