Chinese aluminium plant blows up when floodwater hits molten aluminium

So a few days ago, an aluminium refinery flooded and the electricity was shut off and the place evacuated. The floodwaters eventually reached the furnace full of molten aluminium with the result you see on this video. I would imagine such a large scale operation would be electric rather than natural gas, so this might be the rare explosive aluminium-water chemical reaction. You can see multiple shockwaves condense atmospheric moisture so these were quite strong explosions rather than just a big fire.

 

Yikes!! So what is the actual mechanism for an explosion like that? Does the molten aluminum strip the oxygen from steam creating free hydrogen which then fuels the explosion?

 

Aluminium is very chemically reactive and just like potassium, sodium and certain other metals explode when thrown in water, aluminium can do the same in theory. The video below has some discussion of it from a chemical viewpoint and also tries to create such an explosion. There's more discussion elsewhere on this forum too.

 

That's what made me suggest the mechanism that I did. The explosion you see with a sodium and water reaction is in fact a hydrogen explosion. The sodium strips the oxygen from the water in a reaction that forms sodium hydroxide and hydrogen gas, the hydroxide goes into solution with the excess water, the overall reaction is exothermic and if the conditions are appropriate, that heat will ignite the hydrogen gas causing an explosion.

 

There's definitely hydrogen being burnt in the reaction but there appears to be electrons also being released in great quantity which makes the donor atoms positive and fiercely repulsive generating a coulombic explosion as well. Thunderfoot, the guy who made the aluminium explosion video has written a scientific paper based on one of his Youtube videos of alkali metals in water.

https://en.wikipedia.org/wiki/Coulomb_explosion

 

It seems funny that at smaller scales (home foundry) we don't see this reaction? We just see steam explosions?
Robert

 

That safety film showing an explosion at the 12:35 minute mark in post number 3 is well within the realms of the home foundry.

 

I am not sure what is happening there (12:35)? It looks like aluminum dripping into water and then a steam explosion? There is no flash or flame to suggest a chemical detonation? I wonder if the coulomb explosion only occurs with really hot aluminum and we just don't get to those temps. There are plenty of videos of people pouring melted aluminum into water. I suspect aluminum at 2500 deg F is a different animal.
Robert

 

Ok I'll restate what the man in the video said: aluminium readily forms an oxide layer which prevents the explosive reaction, this oxide layer is easily disturbed in molten aluminium. The explosion shown in the foundry safety video didn't occur when the pouring height was one metre into the steel box full of water. This allowed an oxide skin to form over the molten aluminium, when they lowered the crucible much closer to the water the explosion then occurred. The degreed chemistry researcher in the video also pointed out that it was dumb luck that the multitude of people pouring molten aluminium into water didn't get a coulombic explosion.

 

Thanks Mark. Not trying to be argumentative. I am just trying to understand some real world observations. Clearly something other than a steam explosion was happening at that Chinese plant!
Robert

 

It's a hard concept to wrap your head around as much physics as chemistry: bulk ionize a group of atoms and they explosively repel each other. You can chemically do this with aluminium in water or you can do it with physic by hitting an atom of uranium 235 with a slow neutron to form two charged atoms of barium and krypton and 200 mega electron volts of energy. Nuclear fission is another example of a coulombic explosion just done with atomic physics instead of chemically.

 

https://youtube.com/shorts/5T8jamtBhJA?feature=share

 

Great video! That explains a lot.

 

Bigstack D (Edit: Some other youtuber's video) has an interesting accident while pouring copper into ice water, it's some sort of steam explosion and I wonder if the ice somehow helped the explosion or if it would occur at all without the ice water. Does the ice chunks help confine the steam?.

 

I wasn't paying attention and didn't realize it was some other person with the explosion. There's what looks like a pool of molten metal on the bucket floor after the explosion. He started with a bucket full of ice and topped it off with water so it would result in a semi solid chunk of slurry.

 

I am sure glad the guy used PPE —-sort of! And wore shorts, picked up the crucible with a plier, stood right over the crucible as he poured molten metal onto ice and then had the good sense to hose off the burns on his shins post eruption. That was an impressive kerpow! Scary. Could have been so much worse.

Like the old saying says “you can put water on molten metal but not molten metal on water.” Good demo.

Denis

 

Yes, had the seam on that bucket been oriented at 180° from where it was it could easily have sliced him severely. That was one of the dumbest stunts I’ve seen in a long long time.

Denis

 

Regarding the PPE, I would hope the leather apron extension and maybe the welding spats I wear would have stopped the sheetmetal fragments. The shin injury looked like it was caused by bucket fragments rather than a burn, he also stepped on the remains of the molten copper as he ran off in panic. Obviously if you do random things with incandescent molten metal you'll get random results. Reference.com says the water to steam expansion is 1:1700 so you'd only need a spoonful of water to convert to steam to get the result in the video.