I'd like to melt alumina in a slow, controlled manner. So I thought a graphite crucible with a tungsten wire wrapped around it for heating would be a good start. To reduce heat losses, I put that crucible inside an outer crucible. Question 1 - can I get away with Al2O3 for the outer one, given that the radial temp profile will be something like 1/r . If not Al2O3 then what - Al2O3 would be nice as it has the lowest thermal conductivity that I can find of the refractory materials I looked at (W,SiC, C, BN) . And should I fill the annular space with e.g. YSZ powder (the quartz fiber I used to use for this kind of thing wont handle 2000C - is there some other fiber or 'wool' that can be used?) Finally, can I zets the melt from above with microwaves conducted thru a waveguide - will the electrical conductivity of the graphite be trouble or maybe help matters due to eddy currents?