Dave Finkelnburg on fri 23 mar 07
Thomas,
You are absolutely right, of course, that fired
clay is composed of glass and may contain crystals
that have never melted. Good point! I do have to
ask, what are the, "...other more appropriate
methods..." you refer to? Thanks in advance for
elaborating on this.
Dave Finkelnburg in Idaho, USA
From: Thomas Malone
It is not that calculations can not be used for clay
bodies, far from it. It is just that it is invalid to
apply glass theory to bodies. These assume the
complete melting of all components to form a glass,
where as bodies are composed of glass and crystalline
phases that never melted. You are fortunate to have
achieved success by using unity formulae for bodies,
but why use this method when other more appropriate
methods are available?
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Thomas Malone on fri 23 mar 07
Hello David. Yes I should have expanded more on that comment. Calculations
based on the chemical analysis, or even better combined with the mineral
content, is the most appropriate method. These are not difficult, although
obtaining the necessary analyses maybe, but these would be needed to
attempt a unity formula calculation anyway. (Responsible suppliers
generally provide this information, albeit often typical values rather the
actual of each batch.)
And to clarify: a chemical analysis would be the percentage of
the =91classical=92 oxides of SiO2, Al2O3, Fe2O3, TiO2, CaO, MgO, K2O, Na2O =
and
the Loss on Ignition. The mineral content would be the percentage of the
minerals present, such as kaolinite, montmorillionite, various feldspars,
various micas, quartz.
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