RogueRose
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Al catching fire in a cast iron crucible in a kiln?
I was reading on another forum that deals with casting metals and one of the members reported that he almost burnt down his shop by heating aluminum
in a cast iron pipe/crucible b/c it got "too hot". I really can't imagine how this could happen and he said it was b/c of a "thermite reaction"
happened, lighting the Al on fire. What seems odd was this guy had thousands of posts in this forum and not one person called him out on it. I can't
see how over a lb of Al could catch fire, no matter how hot, by heating it in a cast iron crucible, even if there was a little rust on the crucible.
Is this even remotely possible?
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Ubya
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i also thought it to be impossible, but he's not the only one to comment this event. years ago i followed a YT channel called "the art of weapons" now
he is called TAOW, he makes cast aluminium slingshots and at the beginning used an old fire extinguisher as crucible, and reported that once this
crucible got really hot in the furnace, blindly hot, and melted through the bottom. i don't know if at those temperatures iron and aluminium can react
somehow, to make a thermite reaction you need iron oxide, and i don't think there would be much on the inside of a crucible. any way, take a look at
his video https://youtu.be/F21SKWKJJL4
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Tsjerk
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Doesn't aluminium burn on its own at very high temperatures?
I believe I once saw an aluminum rod burning in air after it was dipped in liquid oxygen. It kept burning after the liquid oxygen was gone.
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RogueRose
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Quote: Originally posted by Tsjerk  | Doesn't aluminium burn on its own at very high temperatures?
I believe I once saw an aluminum rod burning in air after it was dipped in liquid oxygen. It kept burning after the liquid oxygen was gone.
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Hmm. I'm thinking the crucible failed and the forge/kiln was made with CaSO4 and/or SiO2 and those two provided the O2 necessary for a reaction.
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DraconicAcid
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Many years ago, I worked at a plant that used the Hall process, and we were warned about the dangers of aluminum fires. Once it starts burning, it is
almost impossible to put out.
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Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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RogueRose
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| Quote: Originally posted by DraconicAcid | | Many years ago, I worked at a plant that used the Hall process, and we were warned about the dangers of aluminum fires. Once it starts burning, it is
almost impossible to put out. |
But did you deal with powdered aluminum there or just hot/melted Al? I know a lot of places that machine Al have to be super careful with the
dust/swarf so that no sparks or lite things being thrown into them.
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Herr Haber
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Iron melting point vs Aluminium boiling point I cant see a fire happening before the crucible melts.
I dont know about this guys kiln but mine is closed so no oxygen and uses graphite crucibles.
The spirit of adventure was upon me. Having nitric acid and copper, I had only to learn what the words 'act upon' meant. - Ira Remsen
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RedDwarf
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At one time I used a home made crucible (made of 4mm wall steel pipe with a plate welded onto the end) for melting aluminium in my barbeque/patio
heater (an old washing machine drum fueled with wood). The first time i used it I was surprised to see how much scrap aluminium I could ram into it
while hot, until I took it out to pour the molten aluminium and discovered a hole in the side (not near my weld, before anyone starts dissing my
welding  ). As I struggle to get much over 650C in the barbeque I could only
assume that some rust in the pipe had created a thermite reaction sufficient to melt a hole.
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wg48temp9
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It not easy igniting aluminium as it readily forms a high melting temperature oxide that protects the metal from further oxidation.
I am wg48 but not on my usual pc hence the temp handle.
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MrHomeScientist
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Thermite seems unlikely. Even if there were rust, there wouldn't be very much of it.
Iron crucibles are known to fail frequently with aluminum. The iron is slightly soluble in molten Al, so every time you use it it gets a bit thinner
until you get a hole. Clay graphite crucibles are the way to go, IMO.
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Junk_Enginerd
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I have melted lots of aluminium in steel containers. The only time something close to what you describe has happened is when I used a particularly
rusty steel rod to stir my molten aluminum. The aluminum was a bit unnecessarily heated, I'd guess 900°C based on glow. It wasn't very dramatic, but
some aluminum clearly reacted with the rust with a few intensely white flashes and pops. I guess if you had an extremely cruddy and rusty crucible
something bad could happen.
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