thermal radiation shields

Hi folks,
I'd appreciate any guidance I can get on the suitability of a couple of
different choices of metals in a high temp inert atmosphere furnace
application.
We are building a new series of small 1750 C furnaces for our
instruments, to be used in measuring glass and metal properties in the
molten state. The furnace, which is roughly 2.5" wide and 3 inches
working length, is based around a graphite element, and that is
surrounded by radiation shields, to insulate the core. We are using
molybdenum sheet at the moment for the shields, but as you know this is
very sensitive to oxygen, creating large volumes of MoO3 (?) "snow", and
several other oxides, like dark violet Mo2O5. We have an inert gas purge
of argon or nitrogen feeding the furnace, and we don't even switch on
until we have well under 0.5% O2 present.
Still though, we get a trace of what can only be described as a soot
formation. The soot seems to be evolved from the moly, and while iits
is more an irritant than a serious problem, we wondered whether there
was any good reason NOT to use Tungsten instead ? Are there "snowy" or
"sooty" reaction products ?
We DID wonder whether we could actually use graphite as shields too.
Does anyone have any comments on that idea ?
Thanks for any pointers.
Steve