Inspired by seeing some nifty pictures of molten steel, I asked my friend what kind of container the molten steel is held in and he said iron. Hmmm then what is the molten iron held in? Some kind of ceramic, he guessed. But eventually this has got to lead to some kind of turtles all the way down kind of situation. What’s the chain of molten goodies, each with a higher melting point, and where does it all end?
Ceramic should be a good stopping point, since you never need to hold molten ceramic in a container. It turns from its malleable state to its rigid state through a chemical process, not a mere physical one like freezing.
REALLY hot stuff is contained within magnetic fields.
When I was in high school we did the obligatory tour of the steel mills in Hamilton. I still remember seeing railcars loaded with molten steel sitting on a siding*… you could see in their shadowed parts that they were glowing dull red. And a wave of heat came through the windows of the bus. So evidently there are enough things that are strong at red heat that they can handle the stuff.
[sub]*Of course they aren’t the sort of thing that you’d want to leave out too long, or the steel inside would harden. And cleaning it out would be somewhat inconvenient.[/sub]
A google search reveals that the hot-metal railcar is used to carry molten iron from the blast furnace to the ‘steel making units’. It’s called a ‘torpedo car’ or ‘ladle car’. Here’s an overview of steelmaking. It appears that the interior of the blast furnace gets to around 2600K, and the molten iron comes out the bottom at around 1800K (around 1530C). So evidently they can build a solid container that can withstand those temperatures.
The ladles in the railcars used to transport pig iron and/or steel are lined with firebrick.
Molten metal might not be the worst case to consider – molten glass is not only hot, it’s incredibly corrosive, as well. In one of my courses they showed us the effect molten glass had on a ceramic basin it was contained in – it ate it away.
When I was doing some research at a glass manufacturer we used platinum crucibles to contain the glass - platinum could resist both high temperatures and the corrosivity. But it’s extremely valuable, of course. I didn’t get to touch the crucibles, which were locked in a safe every night.
I live in an area with steelworkers, and one of my neighbors was a mason specializing in high-temperature brick work. He was one of the guys who would line the rail cars and anything else that would hold molten steel with the high-temperature brick developed to withstand the conditions involved. He kept pretty busy, as apparently the brick didn’t have a great deal of longevity and needed to be replaced fairly often.
I was gonna say refractory brick, and yes, it erodes away in use.
The firebrick used to line the smelter itself is chosen for its chemical properties (alkaline, such as silica and dolomite/limestone, if the ore is acidic) to remove impurities. It’s a consumable, obviously.
For ladles, remember too that the molten steel isn’t in the ladle all that long. Anything will hold something really really hot for a short enough period of time.
The lances that introduce oxygen into the interior of the molten iron mass in a modern furnace are generally made from copper, with high-flow-rate water cooling jackets in their walls. That’s a quick in-and-out operation too.