Material for melting metal oxides

I am constructing an apparatus for high temperature, strong alkaline melts (metal melts), with extremely high oxygen rich environments.


Here what I have so far. 


Iridium is a good candidate - is it better as an alloying agent or would it suffice in an almost pure Iridium composition?


Tantalum - has good temp but from what I understand is weak against alkaline reactions. 
If nothing else gets answered, could this please. 
If I have a tantalum oxide layer coating the tantalum will that protect it from further corrosion in a high temperature, oxygen rich environment?


Tungsten seems to also have potential, I remember reading a paper from the 50's stating that under high alkaline, temperature conditions the product contained an unsuitable level of impurity from the tungsten? with the properties of tungsten would this be the case.


What I am enquiring about here does anyone know what metals or alloys off-hand that are currently used in these conditions?
Basically I am only looking at refractory metals as the temperature range is (1900 deg C - 2900 deg C)
Also there can be no carbon in the composition of the alloy.


