sounds like a turbo/gas turbine to me
1200 deg F
100000 rpm
couple of bar of pressure difference on each side
get an old turbo, seal one half in a box, suck out the air and check for leaks. this will prove/disprove the concept
centrifugal blowers are geared up heaps
chesterton do seals for this kind of thing for industry
your going to need to balance this flywheel at a MIN to turbo specs. an engine balancer wont cut it.
as shaft dia increases surface speed will increase too

graphite?
http://www.roccarbon.com/cgcompressor ... Iz9iJiVip0CFR0SagodlhGX_w