Sciencemadness Discussion Board - SiO2 + Na thermite reaction?

SiO2 + Na thermite reaction?

NickBlackDIN - 11-7-2023 at 05:40

I was curious, the typical amateur synthesis of making elemental silicon is via the thermite process using aluminum. But then you have to remove the aluminum products, so typically people add sulfur to make that easier, but end up making some nasty fumes.

I was thinking, could I just melt some sodium metal, mix in the SiO2 to make the thermite mix (that way I don't have to deal with milling sodium and have to fuss around with argon atmospheres and such)

That way all the products I don't want should be water soluble.

How many issues do you see with this before I start investing any time on it?

j_sum1 - 11-7-2023 at 14:41

You will probably have a problem with the Na boiling away.
I have not checked the thermodynamics either. But I think it will be energetically favourable.
Nothing wrong with trying though.

I have used Mg powder to make Si. It gets around the problem of boiling. The products are soluble in water. And use of Mg has a better delta H than Na. Not to mention that it is cheaper and more accessible. You might want to consider that option.

Rainwater - 11-7-2023 at 14:54

Not sure sodium metal will work for silicon. Its the primary component of glass and does not get attacked it by sodium in anhydrous conditions.

Code:

SiO2 + 4 Na = 2 Na2O + Si
T = 0C
ΔH  69.5381  kJ/mol 
ΔS  -108.8677  J mol/K 
ΔG  99.2753  kJ/mol  

T=1000c
ΔG  208.1430  kJ/mol

Admagistr - 11-7-2023 at 15:13

I would try it,but I see a problem in that the sodium would ignite in the air before attacking the SiO2.Therefore I would cover the reaction mixture with a layer of NaCl.

NickBlackDIN - 11-7-2023 at 17:24

J_sum1:
I did think about Mg, but I didn't think MgO was water soluble.

the Na boiling away is a good point, I personally thought the bigger problem would be it just not getting hot enough for it to start taking the Oxygen from the silicon. (Which I guess is the same problem)

Rainwater;
Ohh, good point, I didn't think about it that way. Though in glassmaking, isn't it usually sodium ions that are added? Not the metal?

Admagistr:
Ohh, that's not a bad idea to try and increase yield (assuming it even works in the first place)

We'll see how busy I am next long weekend whether or not I have the time to try it

-----

Thank you folks for all the replies!

BromicAcid - 11-7-2023 at 18:57

Lithium will undergo a sustained reaction with glass.

B(a)P - 11-7-2023 at 20:52

Quote: Originally posted by NickBlackDIN

J_sum1:
I did think about Mg, but I didn't think MgO was water soluble.

It converts to hydroxide with the addition of water. You could wash your silicon with an appropriate acid to get rid of the magnesium hydroxide/oxide.

Edit
Typo

[Edited on 12-7-2023 by B(a)P]

Admagistr - 11-7-2023 at 21:09

Quote: Originally posted by B(a)P

Quote: Originally posted by NickBlackDIN

J_sum1:
I did think about Mg, but I didn't think MgO was water soluble.

It converts to hydroxide with the addition of water. You could wash your silicon with an appropriate acid to get ride of it.

Magnesium works very well, but the purity of the silicon obtained this way will not be high, some of the Si will certainly form some silicide with Mg, which will be very difficult to clean from silicon with acid.Sodium would probably provide a purer product.

[Edited on 12-7-2023 by Admagistr]

[Edited on 12-7-2023 by Admagistr]

B(a)P - 11-7-2023 at 21:24

Quote: Originally posted by Admagistr

Quote: Originally posted by B(a)P

Quote: Originally posted by NickBlackDIN

J_sum1:
I did think about Mg, but I didn't think MgO was water soluble.

It converts to hydroxide with the addition of water. You could wash your silicon with an appropriate acid to get ride of it.

Won't magnesium silicide react rapidly with a mineral acid to form silane? Making sure you do not have an excess of magnesium should reduce the magnesium silicide.

Admagistr - 11-7-2023 at 21:49

Won't magnesium silicide react rapidly with a mineral acid to form silane? Making sure you do not have an excess of magnesium should reduce the magnesium silicide.
[/rquote]

If the Mg silicide is dispersed in the silicon, the reaction will probably not be very fast...But the silicon could be finely pulverized...Another impurity in Si will be unreacted SiO2.

averageaussie - 15-8-2023 at 17:54

[/rquote]
Another impurity in Si will be unreacted SiO2.[/rquote]

Could melting the bulk silicon in an inert atmosphere make the silica sink in the liquid silicon? silica has a density of 2.65 g/cm3, and liquid silicon has a density of 2.57 g/cm3.
I know that melting the silicon might be a pain, but I see no other way to remove SiO2 impurities without turning your silicon to dust and picking it out.

even then, SiO2 impurities aren't even that visible I think, nor do they interfere with a reaction.

metalresearcher - 16-8-2023 at 07:10

I tried reacting SiO2 with Mg powder, it is a (rather slow) sustainable reaction, it gets very hot and then I dump it into HCl solution to dissolve MgO.
But indeed, melting the reaction result is a pain, not particularly because of the required 1410 C temperature (can be reached in a propane / air furnace or with a carbon arc of a welder), but the air. It oxidizes very quickly, hence the chip manufacturers use vacuum or inert gas (Ar) furnaces to handle liquid Si in the Czochralski process to purify it.

averageaussie - 16-8-2023 at 15:24

Quote: Originally posted by metalresearcher

I tried reacting SiO2 with Mg powder, it is a (rather slow) sustainable reaction, it gets very hot and then I dump it into HCl solution to dissolve MgO.
But indeed, melting the reaction result is a pain, not particularly because of the required 1410 C temperature (can be reached in a propane / air furnace or with a carbon arc of a welder), but the air. It oxidizes very quickly, hence the chip manufacturers use vacuum or inert gas (Ar) furnaces to handle liquid Si in the Czochralski process to purify it.

what setup do you have to melt the silicon? do you have access to an air free method of melting it?

also, can you post an image of the silicon obtained? I am quite curious about what it looks like.

Admagistr - 16-8-2023 at 16:15

Quote: Originally posted by averageaussie

[/rquote]
Another impurity in Si will be unreacted SiO2.[/rquote]

Could melting the bulk silicon in an inert atmosphere make the silica sink in the liquid silicon? silica has a density of 2.65 g/cm3, and liquid silicon has a density of 2.57 g/cm3.
I know that melting the silicon might be a pain, but I see no other way to remove SiO2 impurities without turning your silicon to dust and picking it out.

even then, SiO2 impurities aren't even that visible I think, nor do they interfere with a reaction.

An interesting aspect of fusing Si with SiO2 is the formation of SiO,which is volatile,hence one could probably remove SiO2 from silicon in this way!

metalresearcher - 17-8-2023 at 12:15

Quote: Originally posted by averageaussie

what setup do you have to melt the silicon? do you have access to an air free method of melting it?

also, can you post an image of the silicon obtained? I am quite curious about what it looks like.

No, I don't have access to it, but here a video of the reaction of Mg powder with silica sand. Afterwards I dumped it into HCl solution to dissolve the MgO.

https://www.metallab.net/jwplayer/video.php?f=/forums/MgO-Si...

averageaussie - 17-8-2023 at 18:43

[/rquote]

No, I don't have access to it, but here a video of the reaction of Mg powder with silica sand. Afterwards I dumped it into HCl solution to dissolve the MgO.

https://www.metallab.net/jwplayer/video.php?f=/forums/MgO-Silicon-20230817.mp4[/rquote]
with all those sparks, that would make quite the sparkler, no?