From: Bob Higgins
* CoorsTek is the major supplier of such alumina forms - they have been
around forever in this market. The choice is AD998 (99.8% alumina) or mullite
( http://css.coorstek.com/scripts/css512.wsc/op/op_indexB2C.html ).
Yes - CoorsTek is no doubt the major US supplier, but on the World market, they
are one of many. Their prices are typically significantly higher than ceramics
from Asia and 998 is a pricey specialty material.
* Alumina ceramics, in general, come in different grades varying from 96%
to 99.8% but the tubes are not available in 96%,
Yes they are. They come in grades as low as 92% ... maybe not from CoorsTek but
that is apparently as far as you have looked. Plus - 96% is porous. What makes
you say it is not?
* None of these substrates are porous.
That may not be true for even the specialty material CoorsTek 998, but clearly
96% is porous and in fact anything less than 100% will be slightly porous by
definition. If they do not supply 96%, then you really should look at what
other suppliers have to offer. What I am calling porous alumina is sometimes
sold by density… such as 3.65 g/cc.
* In both the successful experiments, there was porous alumina
BH: You have absolutely no basis for saying this. Based on available
alumina tube materials, there is no "porous alumina".
I would be just as easy for me to say that all alumina is porous, since
even from Coors, the 100% grade is not available and 998 is ever so slightly
porous. Perhaps there is no 96% from CoorsTek, but have you actually looked at
anything beyond the one supplier? In fact, I suspect that most alumina is
porous, in the sense of having density around 3.65.
The 998 you have is a specialty material which is not commonly called
“sintered alumina” as was both successful experiments.
