Hi everyone,

A few years ago I tried to melt aluminium using an old steel fire extinguisher as crucible.
This was done in a homemade foundry using coke as fuel.

Me having no patience, I tried getting the temperature up as fast as possible and a hole was melted in the crucible, producing a very bright light.

Could the molten aluminum have reacted with the rusty steel fire extinguisher to produce thermite?

Thermite needs a very high temperate to start its reaction, I’ve seen it done with a magnesium strip, which is easy to light but burns VERY hot.

Probably not in any meaningful capacity. You would not have produced nearly enough iron oxide with enough of a surface area to react with the aluminum fast enough to accomplish anything noticeable. It's likely you just flat out melted your steel "crucible" by getting it too hot on the bottom. Steel is going to go white hot before it melts.

It's no enough for aluminum to be in contact with iron, they must be powdered and mixed. Also you need extreme temperatures to start the reaction.

Steel has surprisingly very poor thermal conductivity compared to many other metals and alloys, stainless steel especially, not sure what alloy they use for fire extinguishers, but the geometry of relatively thin-walled tanks like that means there is very little neighboring metal at any point for heat to transfer through. This means it heats particularly unevenly, wherever you're applying heat is where all the heat is going to be heavily concentrated, and takes a long time for applied heat to even out as it "soaks" through to the rest of the material. This also means it is relatively poor at transferring the heat into your target metal you're trying to melt, too. So that's even more of the heat being concentrated into the area of steel that's being directly heated, not where you're hoping for it to go. Your impatience probably just melted a hole in it.

What about the bright light? Everything else makes sense though?

He said at the end steel goes white hot when it melts, probably that?

Thanks, it makes alot of sense.
What about the super bright light coming off though, is it normal for melting steel?
Now that I'm writing this I realize that I could just go check videos of steel melting to compare...
But the question remains: would it be possible for thermite to have formed just from the presence of aluminium, iron oxyde and heat?

Edit: My bad, the question has been answered!
I didn't see the other comments when I wrote this...

Yeah that makes sense.
It was my original thought at the time but there I was the other day remembering about this after seeing something about thermite and I started wondering if magic had happened... But no it was just a "learning experience".
Thanks for taking the time!

Yeah it has to have been that