Dave Finkelnburg on sun 28 apr 02
John,
What Craig is saying is the mineral apatite is the source of
manufactured bone ash.
The process works like this. The apatite you mention is reacted with
sulfuric acid to form solid calcium sulfate and liquid phosphoric acid. In
the process flourine is evolved as a gas. The phosphoric acid is then
reacted with limestone to form calcium phosphate, either dical or trical.
Thus the fluorine is gone by the time the phosphorous and calcium become
a commercial product.
By the way, I don't think a glaze can tell whether the phosphorous or
the calcium in it came from the skeletons of sea creatures layed down on the
ocean floor millions of years ago and turned into apatite or whether the Ca
and P came from the bones of animals that lived in our time.
I do think one should get an accurate analysis of the particular
phosphorous product one is going to use in a glaze. There is a lot of
variation among products sold as "bone ash," both in the percent calcium,
percent phosphorous, and the ratio of calcium to phosphorous.
Good glazing,
Dave Finkelnburg
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From: John Hesselberth
>Now I'm confused. Help me please. My handbook says Apatite is
>CaF2.3Ca3P2O8. That would certainly have F in unity or an LOI depending on
>how you treat the fluorine. I didn't calculate the molecular weight, but it
>would be way over 126--it has 400 just of calcium. My handbook also says
>dicalcium phosphate is CaHPO4.2H2O with a molecular weight of 172.1
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