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Topic: "Thermite" reaction with hydroxides?  (Read 13333 times)

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Offline silenceisgod

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"Thermite" reaction with hydroxides?
« on: December 23, 2009, 05:38:57 PM »
Hello, new user here asking if it's possible to replace the oxide of a metal with the hydroxide in a thermite reaction. The general thermite reaction uses iron oxide and aluminum powder, basically switching the oxides around (assuming the two metals are the same oxidation number). (Fe2O3 + 2Al to 2Fe + Al2O3)

I was wondering if it's possible to do the same thing with a metal hydroxide and a powdered metal, and if it would work at all and if it would release the hydrogen or turn the other metal into a hydroxide as well. I remember seeing on youtube once a demonstration (I can't find it now) of magnesium powder mixed with sodium hydroxide and when lit, created elemental sodium and magnesium oxide. Has anyone else heard of this, and can they help me with it if it's possible?

Offline 408

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Re: "Thermite" reaction with hydroxides?
« Reply #1 on: December 23, 2009, 06:03:35 PM »
Metal hydroxides dehydrate to their oxides at high temperatures.  The energy you input into your reaction would be partly used up in this process, making it harder to ignite. Reaction propagation through the bulk material will use up more energy than in an oxide thermite due to the energy needed for dehydration.  Net effect: less energetic/fun thermite.  The hydrogen will be released as water.

It is only technically thermite reaction when it is a metal oxide and aluminum, but many other solid-state oxidation-reduction processes can be energetic including halides with any number of electropositive metals.


Offline silenceisgod

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Re: "Thermite" reaction with hydroxides?
« Reply #2 on: December 23, 2009, 08:08:16 PM »
Would the ending products, not caring about the fireworks, actually be produce? I've never heard of hydroxides degrading under heat.

The water thing doesn't make sense to me, though. If I were going to be doing this I would do it with all the oxygen surrounding the mixture removed, so if water was formed, the oxygen would have to come from the hydroxide (and there would be nothing to oxidize the other metal, magnesium or otherwise).

Isn't a thermite reaction a general term, though? according to Wiki, "Thermite is a pyrotechnic composition of a metal powder and a metal oxide." It doesn't say it has to be aluminum. and technically, a hydroxide is still an oxide. ;D

Thanks for the reply, though!

Edit: I think I realized my mistake about the water, 4OH to 2H2O +O2, not 2OH to H2O.

Offline 408

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Re: "Thermite" reaction with hydroxides?
« Reply #3 on: December 23, 2009, 08:21:17 PM »
 Metal hydroxides do dehydrate, the transition metal hydroxides easily, alkaline earth with some work, and alkali metals only under rather hardcore conditions.

2Fe(OH)3 --(heat)--> Fe2O3 + 3H2O

The phrase 'thermite' was originally used to describe the reduction of Fe2O3 by Al as in the Goldschmidt process.  Then it was extended to the aluminothermic reduction of other metal oxides.   Recently again it was expanded to include other metals as the reducing agent, and even more recently some call the reduction of non-oxides by Mg or Al a thermite reaction.  It all depends on where you choose to draw the line in terms of how the term has evolved.  I tend to call 'the rest' thermite-type reactions.

And yes, NaOH and Mg can produce sodium.   :)

Offline silenceisgod

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Re: "Thermite" reaction with hydroxides?
« Reply #4 on: December 24, 2009, 11:19:36 AM »
Interesting. By "hardcore conditions", how much energy are you talking about? The original video I saw started the reaction with a simple magnesium fuse, the way you would light regular thermite using a transition metal. My question then is, if it's annoying already to light thermite using the easiest of metals, is it even possible to do the same thing with an alkali metal under normal conditions, like they allegedly did?

Unless the energy needed for a dehydration and a thermite reaction are vastly different, wouldn't it require masses of energy?

Thanks, and I bask in your greater chemical knowledge.

Offline billnotgatez

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Re: "Thermite" reaction with hydroxides?
« Reply #5 on: December 24, 2009, 11:56:05 AM »
silenceisgod -

Do you understand the safety issues with these reactions.

408 -

do you have anything to add about safety

One that has been suggested to me is do it small
remember that some of these reactions start and will not stop until all the reagents are used up.

Offline silenceisgod

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Re: "Thermite" reaction with hydroxides?
« Reply #6 on: December 24, 2009, 04:34:28 PM »
Yes, I know the safety issues involved. I have done general thermite reactions before, I understand the risks and have the necessary equipment to keep myself safe. If I were to actually try this experiment, I would probably only use a few grams of hydroxide and magnesium.

Offline 408

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Re: "Thermite" reaction with hydroxides?
« Reply #7 on: December 24, 2009, 06:03:10 PM »
Nothing really to add about safety, other than hot NaOH burns pretty bad.  If you can not get injured from regular thermite you should be fine with this.

  Are you trying to isolate Na or just do an unusual thermite-type reaction?

see: https://www.sciencemadness.org/whisper/viewthread.php?tid=2105&page=7

Members have had success using sealed reactors, only allowing hydrogen to escape.
More info in that thread regarding making sodium than I want to write out...

Oh and I made a incorrect statement inadvertently, alkali metal hydroxides will not dehydrate forming water under these conditions.  For the transition metals this still stands.

Offline skyjumper

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Re: "Thermite" reaction with hydroxides?
« Reply #8 on: January 09, 2010, 03:33:14 PM »
I saw this in a Youtube video...

From the looks a very energetic reaction:
http://www.youtube.com/watch?v=908rjHQ5mmc

Offline silenceisgod

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Re: "Thermite" reaction with hydroxides?
« Reply #9 on: January 11, 2010, 07:01:59 PM »
I did this experiment yesterday, it worked very well; I managed not to injure myself and ended up with a sodium-magnesium oxide crust. I used a regular fireworks fuse, not magnesium ribbon. I did not see steam leave the sides of the pot, and there was a collected sodium layer on the lid too, so steam couldn't have gone there either. So was it H2 being released, not water?

Moving down the periodic table, is it possible to do this same basic idea but with more reactive elements (a more reactive reducing agent, calcium, and a more active hydroxide, potassium)? I just so "happen" to have both of those lying around, and was going to try this tomorrow. Any specific safety issues involving mixing these elements together before I try it?

Thanks

Offline silenceisgod

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Re: "Thermite" reaction with hydroxides?
« Reply #10 on: January 17, 2010, 07:11:42 PM »
I did this experiment again today using snow to cool the pot I was doing it, and I guess it's not as effective as water. When I opened the lid I got a whiff of what I assume to be sodium vapor. Man, that stuff is nasty. I didn't get much of it, and as of five hours later I'm not dead (yet!). Is the stuff *that* dangerous though that I should wear, say a gas mask when I do this? (that's an option, but wondering if it would be safe enough to just wait a little longer than before).

Offline billnotgatez

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Re: "Thermite" reaction with hydroxides?
« Reply #11 on: January 17, 2010, 08:00:27 PM »
Think fume hood

the reaction is not stopped by water

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