Sciencemadness Discussion Board

Aluminum Factory Explosion

Metallophile - 23-7-2021 at 06:08

I recently saw some videos of an aluminum plant in China, which exploded due to flooding. The blasts are huge, some with visible shockwaves. Any guesses what chemistry would cause this? Could molten Al + H2O actually detonate like that?

Herr Haber - 23-7-2021 at 06:42

Very hot metal and water... No chemistry, just physics.

Metallophile - 23-7-2021 at 07:22

"Very hot metal and water... No chemistry, just physics."

Are you sure about that? I have a friend who works at Alcoa, and he said they need to be very careful with any tools used in liquid aluminum. Any bit of moisture on a tool, will make a big *POP* that blows molten aluminum everywhere. He told me this is not a steam explosion, but actually forms Al2O3. (and H2 I guess?). The video from China sure did not look like a steam explosion. More like military HE.

Fyndium - 23-7-2021 at 09:09

https://www.youtube.com/watch?v=4Kg94QP4m-w

The blast waves do appear. Aluminum is very sensitive to water, issue reckoned in aluminum casting, and any moisture will cause the metal to splash around, and if it is caused by this, it must be a chain reaction where the surface area and reaction speed grows exponentially, resulting in an explosive event.

I'm not sure what will happen if you'd dump 10 tons of molten, almost boiling sodium metal into water. But I'm sure that at least acid and base will react almost explosively, as some user or a Tuber demonstrated here by mixing H2SO4 and NaOH and other stuff.

Johnny Cappone - 23-7-2021 at 09:22

Well, maybe it's possible.
I know that explosive emulsions exist exclusively based on nanometric aluminum particles and water. Aluminum is a very reactive metal. When solid, the oxide layer protects it, but in molten aluminum this oxide would float in the slag leaving only the pure metal below. So maybe water plus aluminum at 700 degrees Celsius will be able to make it a little "energetic". Not to mention that the impact of water on a large crucible of molten aluminum would hurl glowing metal particles into the air that would surely burn violently. Whether it would be violent enough to create shock waves I don't know. Do you have the video? Was there nothing else at the factory capable of detonating besides aluminum and water?

Oxy - 23-7-2021 at 09:30

Quote: Originally posted by Metallophile  
"Very hot metal and water... No chemistry, just physics."

Are you sure about that? I have a friend who works at Alcoa, and he said they need to be very careful with any tools used in liquid aluminum. Any bit of moisture on a tool, will make a big *POP* that blows molten aluminum everywhere. He told me this is not a steam explosion, but actually forms Al2O3. (and H2 I guess?). The video from China sure did not look like a steam explosion. More like military HE.


You're right. Besides Al2O3 there can form also Al(OH)3 and aluminium oxhydroxide. Also a huge amount of hydrogen is produced which likes to explode when mixed with oxygen, especially when heated. Molten aluminium is hot, the reactions are exothermic... boooom

Johnny Cappone - 23-7-2021 at 09:41

Quote: Originally posted by Fyndium  
https://www.youtube.com/watch?v=4Kg94QP4m-w


[...]"Later, the floodwater washed into an alloy tank with a high-temperature solution and caused the explosion, according to an official article posted by the Publicity Department of the CPC Dengfeng City Committee."

Does anyone have any idea what kind of "alloy tank" this could be? Maybe they were mixing aluminum and magnesium to produce light alloys like those used in car wheels? Of course, it's not magnalium, but I suppose it would be more energetic than pure aluminum. And such a "high temperature solution", what could it be? I've read a lot about industrial aluminum production, but I don't remember the details.

[Edited on 23-7-2021 by Johnny Cappone]

unionised - 23-7-2021 at 10:40

Here's an interesting experiment.
Get a tin can with a push-fit lid and put some gravel in it- flint (silica) for example and punch a small hole in the top .
Then heat it to red hot.
And then drop it, lid first into a shallow container of water.
The water cools the tin a little. The air contracts and draws in some water.
The water hits the red hot rock and boils.
The steam takes up a lot more space than the water did.

The steam explosion blows the lid off with a loud bang.


Now imagine scaling that up...

There may be chemistry happening in the factory explosion, but we don't need any.

j_sum1 - 23-7-2021 at 14:00

Don't forget tonnes of molten cryolite. And the huge currents that result when a pot line is shorted out.
I am not the slightest bit surprised if the result is a bit bangy. There's lots to go wrong here.

unionised - 23-7-2021 at 16:05

And white hot molten alumina,the graphite cell...
The question is why don't they blow up more often?

Herr Haber - 29-7-2021 at 07:37

Quote: Originally posted by Oxy  
Quote: Originally posted by Metallophile  
"Very hot metal and water... No chemistry, just physics."

Are you sure about that? I have a friend who works at Alcoa, and he said they need to be very careful with any tools used in liquid aluminum. Any bit of moisture on a tool, will make a big *POP* that blows molten aluminum everywhere. He told me this is not a steam explosion, but actually forms Al2O3. (and H2 I guess?). The video from China sure did not look like a steam explosion. More like military HE.


You're right. Besides Al2O3 there can form also Al(OH)3 and aluminium oxhydroxide. Also a huge amount of hydrogen is produced which likes to explode when mixed with oxygen, especially when heated. Molten aluminium is hot, the reactions are exothermic... boooom


Well, then other processes than thermal decomposition of water are at work since this occurs at temperatures above 2200 degrees and Al boils slightly above 2400.
I first assumed a steam explosion but you are right to mention that molten Al doesnt have a protective layer.

Metallophile - 30-7-2021 at 07:21

I did find a good video on this subject, and it looks like molten Al + H2O really can explode like this. This was just on an incredibly huge scale, due to the overabundance of water.

https://youtu.be/Rt-dtjYORok

Peaches - 11-8-2021 at 12:35

2Al + 6H20 --> Al2O3 + 2 H2.
If you think about it as a redox reaction, it makes sense. I'm pretty sure all metals react violently with water, but the alkili metals are the ones that react violently at STP. In any case, the evolved hydrogen is probably mostly responsible for the concussive blasts seen in the video.

Fyndium - 12-8-2021 at 08:05

Considering that aluminum metal has twice the energy content of gasoline per volume, something like this could be very possible, if the surface area is large enough for the reaction to occur sudden enough, and what would be a better way to do it than expose a lot of liquid, hot metal to water that instantly turns to steam and causes it to turn into aerosol and microparticulates?

rockyit98 - 12-8-2021 at 22:06

don't forget when electrolyzing it makes CO and very little H2 from the carbon electrodes along with CF4 which can react with Al melt.