Mike, I have designed and assembled furnaces for combustion of sulfate and
sulfides. The heating element was wound on a piece of hollow ceramic pipe
(both purchased from Pottery Supply House, Oakville, Ontario - for a few
bucks), which was secured in a steel housing (insulated), made from steel 
pipes of different diameters (another few bucks). For 550 degrees,
aluminium pipes may be fine - they are much easier to machine and probably
cheaper. The entire assembly rests on a lab jack for vertical positioning.
Please feel free to contact me directly by e-mail for more details. Good
luck. Jerry Pulchan.