Silicium
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Silicon from Quartz
Hello, I'm new here (yep a noob  ) so don't be to harsh (I scar easily). Ok so
here we go...I was doing a google search on a electorchemical series table and found a good one from CRC (I'll post it for you guys).
Anyways I found this half reaction:
SiO2 (quartz) + 4H+ + 4e- ---> Si + 2H 2O
E=0.857
Looking at the E value I am hopefully correct in assuming this can be done in an aqueous solution. But something in the back of my mind says that
this isnt possible under normal conditions, perhaps high temperatures are required... So what do you guys think?
P.S. I also tried searching google on something like this but I found nothing.
Attachment: Echem_series.pdf (122kB)
This file has been downloaded 1986 times
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guy
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Why don't you try it out and see if it works. I would but I don't have any strong acids. Try using Fe2+ and see if it forms Fe3+ and some Si.
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Chris The Great
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SiO2 is insoluble so that might cause problems for the reaction. If you could get it to dissolve then you could have something going. Then again,
metal replacement reactions work even though the metal is insoluble...
I know you can dissolve SiO2 somehow but I don't remember. I think it might have been with NaOH to form sodium silicate.
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Silicium
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Yeah, I remeber reading that SiO2 is attacked by hot NaOH to form sodium silicate. But the reduction half reaction calls for SiO2, not sodium
silicate. It also had quartz in parthensis. After so further reading glass (SiO2) has a very irregular structure while quartz makes a nice lattice
work of SiO4 -4, like this:
O O O
\ / \ /
Si Si etc....
/ \ / \
O O O
err...that didnt come out right but i hope u get the idea....
[Edited on 1-3-2006 by Silicium]
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guy
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Just use sodium silicate, since it also has the SiO4 4- structure. It can still be reduced even in this form, could possibly be even easier.
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woelen
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I doubt whether it will be possible to make silicon from aqueous solution, in fact, I'm very sure it is not possible.
I have some powdered Si and when this is added to a solution of NaOH, then it dissolves fairly easily, giving hydrogen and silcate ion. So, making Si
in an alkaline environment will be impossible (or at least very hard). Using very electropositive metals in such cases just results in formation of
hydrogen.
On the other hand, in acidic solutions, the SiO3(2-) ion cannot exist. Solid SiO2 is formed, which is VERY insoluble. If you take waterglass (which
can best be described as a solution of Na2SiO3 in water), and you add acid, then hard pieces of impure SiO2 are formed.
Commercially, silicon is made by heating SiO2 (or some silicate) with a strongly reducing metal at a very high temperature. I'm not sure whether this
can be done at home, but I guess it will be hard at least.
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BromicAcid
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I too see silicon as being neigh impossible with conventional electrolysis, however I bet there are methods involving molten electrolysis, however the
energy requirements for such an endevor would be monsterously high. Hence the prefered method being chemical reduction of either the oxide or the
chloride. Additionally if aqueous electrolysis were feasible people in the electronics industry would have a much simpler alternative to purification
then the ever cumbersome zone refining. But then again I have been shocked before.
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IrC
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Powdered Si in HCl is going to make trichlorosilane, I was thinking silane would be a danger in playing around here but it seems you also need AlCl3
or similar catalysts. Interesting chemicals though, I have 600 mesh Si so maybe here is something new to play with? Below is wiki link:
http://en.wikipedia.org/wiki/Silane
Also interesting:
http://energiparken.hia.no/silisiumdoktor.htm
[Edited on 1-3-2006 by IrC]
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Fleaker
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As bromic mentioned, it is simple to reduce the oxide with magnesium powder at a dull red heat. I have done this reaction before, it is fairly
straightforward. Unfortunately, magnesium silicide also results, and gradually reacts with any moisture to yield SiH4, which explodes on contact with
oxygen. Electrochemically speaking, I see it as being an impossibility in aqueous media.
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Silicium
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Hey...I was looking through my chem book when a thought occured to me. What if I did the following:
SiO3 2- + 3 H2O + 4e- ----> Si + 6 OH- E=-1.697
(the SiO3 2- ion could be from Sodium silicate)
and
Mg ---> Mg 2+ + 2e- E=2.37
overall: SiO3 2- + 3 H2O + 2Mg ----> Si + 6 OH- + 2 Mg 2+ E=0.673
Do you guys think that this is possible?
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guy
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That might work theoretically, but then theres the problem of Mg reacting with water, and then Si reacting with water and base.
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Cyrus
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It is fairly simple to make something silicon-ish with just silica powder and Mg, although the product I made was extremely impure, and I never tested
for Si vs magnesium silicide. If you baked the thing at high temperatures for a while with flux, it might help... perhaps.
Chemoleo has posted great results with a reaction mixture consisting of Al powder, SiO2 (sand), and sulfur, to start things off. See the "Boron (and
silicon)" thread, IIRC.
I think your only possible hope for making silicon in solution from SiO2 would be if you used colloidal silica. I have a bit, but I'm not sure I just
want to dump it in concentrated acids or similar and waste it, as it's reasonably expensive.
Waterglass will just make SiO2 as others have said, and IME.
Really, the higher-temperature versions of the reaction work and are much more fun. I've tried chemoleo's mixture with great success, just not on as
large of a scale.
Cy
[Edited on 2-3-2006 by Cyrus]
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