I'm interested in building a forge, mainly for playing around with flux crystallization of corundum (ruby/sapphire), but I want it to be versatile for other things I might want to do in the future.
Withstand temperatures up to 1400 C (2550 F) for months at a time (crystallization can have very slow kinetics)
Walls with a thermal resistance of at least 1 m2
*K/W (otherwise I'd be spending tens of thousands of dollars to keep the furnace at temperature)
Electrical resistance heaters (MoSi2 or other)
Somewhat air-tight to allow for manipulation of furnace atmosphere through gas injection
Interior volume of ~8 cubic feet
Aerogel is pretty much the only suitable material I've found that will give my furnace walls an acceptable thermal resistance without having to have walls that are 4+ feet thick. I'm concerned that at high temperatures the aerogel might sinter and after several duty cycles, might degrade as thermal insulation. My concerns come from this paper: https://e-reports-ext.llnl.gov/pdf/242911.pdf
Any thoughts on the suitability of aerogel as forge insulation, or on my plans in general?