[Twigg]

I'm writing a batch design to produce HNO3 as a learning exercise, and I got stumped picking a suitable material for the interior of a furnace. This furnace is roasting hydrated sulfate and nitrate salts, so there will be acid gas at around 380 degrees celsius. I've ruled out every pure metal except platinum (and I don't even know if that would work), and all the alloys I know off-hand. Stainless would react at high temperatures, brass is a question mark but I doubt it would resist the acid gases, and the only other ones I'm at all familiar with are aluminum alloys in general, which would be the least apt to resist acid gas.

What about lead? I know it's resistant to sulfuric acid but not nitric. Still, it has to have some resistance against nitric acid; it was used in to make sulfuric acid in the presence of nitric acid in the lead chamber process. The situation I am designing is quite analogous to the lead chamber process, except that I want to go from SO3 to NO2 and not SO2 to SO3. Any help on this one?

[Stepan]

As far as I remember, industry uses ceramic lined furnaces

[Enthalpy]

In a big plant one would go to cheap ceramic.
In a lab, you have a wide choice. Includes technical ceramics, probably graphite...

Even some rather common alloys may fit - I'd search in the direction of cobalt-base or nickel-base alloys, and even the best among stainless steel. Oxidizing conditions, without chlorine, aren't difficult to metals. They use to work at over 700°C in air at gas turbines.

Metals are easier to assemble into big gas-tight vessels, but ceramic must be better and cheaper.