Sciencemadness Discussion Board - Si + NaOH

Si + NaOH

hodges - 12-10-2009 at 14:20

Pretty energetic reaction:

http://www.youtube.com/watch?v=TinQ3iV403s

I'm certainly not agreeing with the guy's claims for this being a cheap source of hydrogen (uhm, how much energy is required to produce the Si anyway....), but this is an energetic reaction that I had not read of before.

I'm guessing

Si + 2NaOH + H2O --> Na2SiO3 + 2H2

This might make a neat and relatively safe demo for energetic materials. I have Si powder - don't think it is too hard to get.

Hodges

chemoleo - 12-10-2009 at 15:07

Reminds me a bit of the reaction with Mg and NaOH - which practically is a flash powder when heated (dry solids) - I'd imagine, with water it'd behave as here with the Si. The water of course only serves to get the reaction going - hence the self-ignition with a smaller amount of water.

That dude is a dork though - he annoys me! And as you say, it's everything but a cheap H2 source!

Professional lab? With dixie cups, and metal cans? ...right!

DougTheMapper - 12-10-2009 at 20:59

I'll venture to guess that a lot of the gas released was steam.

Jor - 13-10-2009 at 08:18

The splashing of all the droplets in the first reaction makes a mess... Wouldn't want to be in that caustic rain.

vulture - 13-10-2009 at 11:40

This idiot pisses me off. Silicon can be mined? Right. People like this make you consider approving the death penalty.

hodges - 13-10-2009 at 16:03

I tried this reaction. I used 0.6g of powdered Si, 2.0g of NaOH (used excess since it it likely not pure), and a moderate excess of water.

The reaction is fast, but only when the silicon is a fine powder. I tried putting little lumps of black silicon in a fairly concentrated NaOH solution, and it reacts about as fast as iron does in HCl (i.e. not very fast). With finely powdered silicon the reaction is about as energetic as adding a ball of Al foil to NaOH - besides the hydrogen, it definitely vaporizes some of the NaOH, resulting in irritating fumes if done indoors without a fume hood.

Hodges

ChrisWhewell - 22-12-2009 at 07:11

Quote: Originally posted by hodges

Pretty energetic reaction:

http://www.youtube.com/watch?v=TinQ3iV403s

I'm certainly not agreeing with the guy's claims for this being a cheap source of hydrogen (uhm, how much energy is required to produce the Si anyway....), but this is an energetic reaction that I had not read of before.

I'm guessing

Si + 2NaOH + H2O --> Na2SiO3 + 2H2

This might make a neat and relatively safe demo for energetic materials. I have Si powder - don't think it is too hard to get.

Hodges

What I would like most for Christmas, is to be able to go the other way, a reagent which when applied to a glass surface causes a layer of the SiO2 to be reduced to Si.

[Edited on 22-12-2009 by ChrisWhewell]

12AX7 - 23-12-2009 at 01:36

Hydrogen/methane plasma???

Easier to deposit poly-Si with SiCl4 and heat (and maybe some plasma too).

Tim

ChrisWhewell - 23-12-2009 at 19:14

there's got to be a way to do it via magnetron.....

not_important - 29-12-2009 at 00:36

It's fairly tough to get from SiO2 to Si, the best route uses carbon. Really hard to do on glass because of the alkali and alkaline earth metals content and the stability of their oxides and silicates.

Appears that in the SiO2-H2-H2O-Si system it is SiO2-H2 that are the stable states below around 1.500 K, SiO becoming increasingly important above that until around 3.000 K while Si(g) arrives on the scene and becomes dominate in the upper 4.000s K.

See Fig 1 in the attached PDF

Attachment: phpEyrd2s (430kB)
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Also see

http://adsabs.harvard.edu/abs/1993JJAPL..32L1273K

and DOI 10.1111/j.1551-2916.2005.00144.x

A plasma in acetylene might work, but the SiO2 substrate would have to be pretty toasty.

One more PDF : Low-temperature fabrication of silicon films by large-area microwave plasma enhanced chemical vapor deposition

Attachment: 01.09_jian-de_gu_pei-li_c_english.pdf (751kB)
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The WiZard is In - 8-4-2010 at 10:32

Quote: Originally posted by hodges

The Silicol process "plants are made in sizes varying from
1500 to 80 000 cubic feet per hour production" used (me
thinks for economic reasons) ferro-silicon.

Details in :—
P. Litherland Teed
The Chemistry and Manufacture of Hydrogen
Longmans Green 1919

I ran down an original copy, you can DL yours from Google.com/books.

By da in long gone youth it was possible to buy lithium hydride
WW II surplus hydrogen weather balloon hydrogen generators.
Li hydride is some interesting stuff.

buy?

michaeljayclark - 14-3-2011 at 07:14

where can Si and NaOH be purchased?

interested in trying out this experiment

Bot0nist - 15-3-2011 at 08:30

Sodium hydroxide can be bought at most DIY stores even if you can't buy reagents online. Lye drain cleaner is what your looking for, though it often contains potassium hydroxide as well. Powdered silicon can be bought all over the net. I use skylighter.com personally.

[Edited on 15-3-2011 by Bot0nist]

kingkool - 23-3-2011 at 13:36

Quote:

What I would like most for Christmas, is to be able to go the other way, a reagent which when applied to a glass surface causes a layer of the SiO2 to be reduced to Si.

Seal a microscope slide with magnesium. Heat it to ~600C for a couple of hours or with a bulk flame ( http://www.youtube.com/watch?v=MJ3oCT_HMoE ). You will have microscope slide with a blue layer. Heat this in air or under argon at 600-800C for a few hours then dip in HCl.

See this patent: http://www.faqs.org/patents/app/20100092141

[Edited on 23-3-2011 by kingkool]