The Naked Scientists

The Naked Scientists Forum

Author Topic: Thermite with sand and extraction of silicon metalloid  (Read 9810 times)

Offline SorryDnoodle

  • Sr. Member
  • ****
  • Posts: 125
    • View Profile
Hello, I come with a experiment for everyone to try if you haven't already, a Thermite with sand from your regular beach to get Silicon in the end, I also come with a question regarding this.

I saw this video on YouTube and, and as I am starting to collect Elements, I thought this would be a good start.

And the thought of just going to the beach and scooping up a bit of sand and then grinding it your self was a very cool thought, so I gave it a go, and it worked, though not as well in the video.

The reaction was very slow and didn't ignite everything, so I had about 2/5th's left of my experiment, and my Parking space smells like rotten eggs, though that was to be expected (:

When it had reacted it formed one nice large lump of "metal" I then put that along with some smaller remains in water- If you do this, do not breathe this, it's hydrogen sulfide from what I have read, but I am unsure.-  and waited until all the bubbling had stopped, which took a good hour or so, which I filtered out and I got some pieces of Silicon which is sitting right now in Acid to get more of a look like in the video.

Now to my question: Is there any way I can make the reaction a bit, better?

It seems it's not getting enough heat, even with that much Sulfur in it, I still want to be able to get all of the impurities out by adding water & acid.

Any advice?
« Last Edit: 21/08/2012 17:06:44 by SorryDnoodle »


 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
Re: Thermite with sand and extraction of silicon metalloid
« Reply #1 on: 21/08/2012 19:06:03 »
I certainly wouldn't say "everyone" should try thermite reactions.
Presumably the reason sulfur was chosen instead of something like iron oxide is that the sulfur is relatively easy to clean from the final product.  Iron might be more problematic.

Did you wash and dry your sand before using it?  I would imagine the purer the products, and the finer the powder the better.  Does the aluminum have to be "fresh"?
 

Offline SorryDnoodle

  • Sr. Member
  • ****
  • Posts: 125
    • View Profile
Re: Thermite with sand and extraction of silicon metalloid
« Reply #2 on: 21/08/2012 19:18:42 »
I certainly wouldn't say "everyone" should try thermite reactions.
Presumably the reason sulfur was chosen instead of something like iron oxide is that the sulfur is relatively easy to clean from the final product.  Iron might be more problematic.

Did you wash and dry your sand before using it?  I would imagine the purer the products, and the finer the powder the better.  Does the aluminum have to be "fresh"?

Hmm, no I didn't bathe my sand, perhaps putting it in acid before using it? and washing it off with water?

The Silicon Dioxide would't be affected right?

And, what do you mean by "Does the aluminum have to be "fresh"?"

Thanks for the reply!
 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
Re: Thermite with sand and extraction of silicon metalloid
« Reply #3 on: 21/08/2012 19:34:24 »
Your beach sand (from the ocean) would have salt, maybe other dirt, and other organics. 
I think I'd just rinse it a few times with plain water, perhaps first tap water, followed with a final rinse with distilled water.

Aluminum will oxidize in air.  I assume even aluminum powder will oxidize quickly to some extent.  Although perhaps surface oxidation is just expected.

I'm not sure how you acquire the reagents.  If you are filing the aluminum off of a block or something, then I'd do it just before you're ready to use it.  Heat from a grinding stone might make it worse.

If you are getting an incomplete reaction, perhaps a touch more aluminum will help, or try changing other reagents.
 

Offline SorryDnoodle

  • Sr. Member
  • ****
  • Posts: 125
    • View Profile
Re: Thermite with sand and extraction of silicon metalloid
« Reply #4 on: 21/08/2012 20:11:28 »
Your beach sand (from the ocean) would have salt, maybe other dirt, and other organics. 
I think I'd just rinse it a few times with plain water, perhaps first tap water, followed with a final rinse with distilled water.

Aluminum will oxidize in air.  I assume even aluminum powder will oxidize quickly to some extent.  Although perhaps surface oxidation is just expected.

I'm not sure how you acquire the reagents.  If you are filing the aluminum off of a block or something, then I'd do it just before you're ready to use it.  Heat from a grinding stone might make it worse.

If you are getting an incomplete reaction, perhaps a touch more aluminum will help, or try changing other reagents.

I'll try washing the sand and i will also try with pure silicon dioxide when I get it, and the aluminium I am using is stored in a air-tight plastic container, I only open it when I am going to use it, so it's not open to air very long, and I haven't seen any signs of oxidization so far on my stock of aluminum kept in the container.

I'll try some varying ratios tomorrow and I'll come back to anyone who is interested in the results.
 

Offline CliffordK

  • Neilep Level Member
  • ******
  • Posts: 6321
  • Thanked: 3 times
  • Site Moderator
    • View Profile
Re: Thermite with sand and extraction of silicon metalloid
« Reply #5 on: 21/08/2012 20:53:29 »
Quartz, of course, is almost pure SIO2.  So, perhaps looking for white sand?

Glasses also have varying purity of SIO2, usually doped with other elements.
I wonder what would happen if you added a little carbon.

SiO2(s) + 2 C(s) → Si(s) + 2 CO(g)
 

Offline damocles

  • Hero Member
  • *****
  • Posts: 756
  • Thanked: 1 times
    • View Profile
Re: Thermite with sand and extraction of silicon metalloid
« Reply #6 on: 21/08/2012 22:51:56 »
Quartz, of course, is almost pure SIO2.  So, perhaps looking for white sand?

Glasses also have varying purity of SIO2, usually doped with other elements.
I wonder what would happen if you added a little carbon.

SiO2(s) + 2 C(s) → Si(s) + 2 CO(g)

The last reaction here is the first step in production of silicon "metal" for the modern electronic technologies. The crucial thing about it is that it requires an extremely high temperature. In the industrial process this reaction is usually done in an electric furnace. The thermite reaction does produce extremely high temperatures, but only just high enough for this sort of transformation. Aluminium can replace carbon as the reductant.

Carbon reduction does offer a significant advantage, though: unlike aluminium oxide, the carbon monoxide by-product is a gas, and so there is no need for an extra separation step at the end of the reaction.

So I am wondering whether talking to a welder might provide a better, cleaner option than the thermite process for your crude silicon metal. I would expect that with a welding flame you could get temperatures higher than those in a thermite reaction and similar to those in the industrial process. There are other aspects to be explored as well -- what sort of container to use for the reaction, whether an inert atmosphere is required to prevent reaction between hot silicon metal and atmospheric oxygen and/or nitrogen, and probably one or two others. They are the sorts of issues where you could get good practical advice from the experience of a welder.
 

Offline SorryDnoodle

  • Sr. Member
  • ****
  • Posts: 125
    • View Profile
Re: Thermite with sand and extraction of silicon metalloid
« Reply #7 on: 23/08/2012 04:50:31 »
There are other aspects to be explored as well -- what sort of container to use for the reaction, whether an inert atmosphere is required to prevent reaction between hot silicon metal and atmospheric oxygen and/or nitrogen, and probably one or two others. They are the sorts of issues where you could get good practical advice from the experience of a welder.

What reaction takes place?
What reaction would take place between hot silicon "metal" and Nitrogen?

Any, since I bathe it in water first, and is still sitting in HCL at 30% concentration, 2 day's at the moment and counting, would't that get rid of just about everything except the Silicon?

Also, It was raining pretty hard yesterday so I could't do my second test burn, I'll do it today instead, though I have gotten my silicon Dioxide today, but it's discolored kinda lightly towards brown, so it's not really pure I guess, anyhow, i'll get back to you later today.
 

Offline damocles

  • Hero Member
  • *****
  • Posts: 756
  • Thanked: 1 times
    • View Profile
Re: Thermite with sand and extraction of silicon metalloid
« Reply #8 on: 23/08/2012 06:15:46 »
Sliicon at 1300-1400C will react directly with atmospheric nitrogen to produce silicon nitride -- an intractable ceramic substance.

http://en.wikipedia.org/wiki/Silicon_nitride

That particular reaction is slow but not insignificant.

Silicon will also react with oxygen much faster and down to a lower temperature to revert to silica. Depending on the conditions this silica might put a protective layer over the elemental silicon to prevent further reaction.
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Re: Thermite with sand and extraction of silicon metalloid
« Reply #9 on: 23/08/2012 10:17:29 »
I certainly wouldn't say "everyone" should try thermite reactions.
Certainly  :)

Quote
Presumably the reason sulfur was chosen instead of something like iron oxide is that the sulfur is relatively easy to clean from the final product.  Iron might be more problematic.
I think the main reason is that you have to avoid oxygen, because silicon cobines reacts extremely easily with it; you can use excess aluminum as reducing agent, but if you use it only, it would absorb heat of reaction, so you use sulfur to combine with Al with a bit of excess heat; the Al sulfide is still a reducing agent and sulfur doesn't combine react with silicon. However the percent of Al and sulfur in excess shouldn't be high or the heat of reaction is not enough.

Certainly the sand shoud be well dried, but I imagine it should also be grind in fine powder with a mortar or like: the grains of sand are too big for that kind of reaction, IMHO.
« Last Edit: 23/08/2012 20:13:48 by lightarrow »
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Re: Thermite with sand and extraction of silicon metalloid
« Reply #10 on: 23/08/2012 10:25:07 »

When it had reacted it formed one nice large lump of "metal" I then put that along with some smaller remains in water- If you do this, do not breathe this, it's hydrogen sulfide from what I have read, but I am unsure.
It's the aluminum sulfide with water.

Quote

-  and waited until all the bubbling had stopped, which took a good hour or so, which I filtered out and I got some pieces of Silicon which is sitting right now in Acid to get more of a look like in the video.
This is the reason for which "not everyone" should try these reactions :)
If water reacts with Al sulfide to give the extremely toxic H2S, you can imagine an acid...
 

Offline SorryDnoodle

  • Sr. Member
  • ****
  • Posts: 125
    • View Profile
Re: Thermite with sand and extraction of silicon metalloid
« Reply #11 on: 23/08/2012 15:09:18 »
This is the reason for which "not everyone" should try these reactions :)
If water reacts with Al sulfide to give the extremely toxic H2S, you can imagine an acid...

Hehe, yes you do make a valid case for why everyone probably should't do them, but still, if you venture away from civilization and just put it in a field and wait a few hours from a safe distance it should be fine, and when putting the silicon in the acid, would't the acid remove any left over Sulfur until only "pure" silicon "metal" remains, which reacts very very slowly with Hcl, so it would't produce any toxic gasses after the sulfur is gone, which would't take very long?

I am just guessing that, I have no idea in reality, but I am keeping it away, blockaded by "stuff" so no animals or people can go near it by accident.

Either way, here's an update on my little experiments:

I got my "pure" silicon Dioxide today and I replaced the sand with it, I used:

55 grams of aluminum powder
60 grams of sulfur powder
45 grams of silicon dioxide.

It was supposed to only be 50 grams of aluminum but I added 5 grams to try make it a bit fiercer reaction.

I put the mix in a hole I had made with sand, so it made a nice lump of metal once it was finished, which it did nicely, the reaction was perfect, looked like mostly everything reacted, and it had a very nice blue color flame from the sulfur.

Anyway, I just got back from it right now, and my remains are laying outside in a bucket, which I will proceed to put in water, but It's quite a lot so I need to go away from where I live this time to avoid any unnecessary risks.

I also filmed the firing which I will upload along with pictures later if anyone is interested, pretty bad video but it shows the reaction

Thanks for all the responses and advice.
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Re: Thermite with sand and extraction of silicon metalloid
« Reply #12 on: 23/08/2012 20:23:09 »

Hehe, yes you do make a valid case for why everyone probably should't do them, but still, if you venture away from civilization and just put it in a field and wait a few hours from a safe distance it should be fine, and when putting the silicon in the acid, would't the acid remove any left over Sulfur until only "pure" silicon "metal" remains, which reacts very very slowly with Hcl, so it would't produce any toxic gasses after the sulfur is gone, which would't take very long?
I don't think you can remove sulfur in that way, you intended Al2S3? This one, yes.
However I wonder how you can separate silicon from Al2O3.
Yes, aluminum oxide is soluble in a water solution of NaOH (hot, if the oxide is thick, compact) but if I remember well, that solution would dissolve silicon too...
Or in this reaction silicon separates from the oxide as a real metal, like iron, does?
« Last Edit: 23/08/2012 20:25:02 by lightarrow »
 

Offline SorryDnoodle

  • Sr. Member
  • ****
  • Posts: 125
    • View Profile
Re: Thermite with sand and extraction of silicon metalloid
« Reply #13 on: 23/08/2012 20:44:47 »
I don't think you can remove sulfur in that way, you intended Al2S3? This one, yes.
However I wonder how you can separate silicon from Al2O3.
Yes, aluminum oxide is soluble in a water solution of NaOH (hot, if the oxide is thick, compact) but if I remember well, that solution would dissolve silicon too...
Or in this reaction silicon separates from the oxide as a real metal, like iron, does?
[/quote]

Yeah sorry, I meant Al2S3, I think. it's all a bit fuzzy in my head, tired ^^

And yes, this reaction makes a solid metalloid form of silicon, putting it in Hcl will crystallize if from what I can tell, it's been in for a few days now and it's really starting to look a lot more crystalline than it was at the beginning, though it seems to be breaking up in to smaller pieces as well gradually, so for best results you want a really big piece to start with.

The Al reacts with the sulfur, creating a lot of heat which will then melt the Silicon dioxide, and the Al will "take" the oxygen from it I believe which leaves the metalloid left, then just put it in water, and everything (almost) but the silicon will dissolve, decant that and just put it in hcl for a few days for best results, I had a lump of solid metal, then I put it in water a few day's ago and all that was left was just a few pellets of silicon, quite amazing, just from putting it in water.

The only downside is that putting it in water will create really nasty gasses, so need to be careful with it, but going to an empty area and just sitting down for an hour or two while it does it's thing is easy, but you should keep an eye on it so no one goes near it by accident.
 

Offline SorryDnoodle

  • Sr. Member
  • ****
  • Posts: 125
    • View Profile
Re: Thermite with sand and extraction of silicon metalloid
« Reply #14 on: 06/09/2012 06:43:47 »
And, done!

I put the remains after having it all in water in HCL, 30%  But it looks nothing like in the video, it's very grey blueish, is it  forming an oxide layer perhaps?

I also put it under a microscope, it looks crystalline, but the crystals are very, very small.

Anyway, i am going to put it back in to HCL later today to give it a little bit more time.

Any suggestions to keep it from oxidizing?

I do not have access to inert gasses and ampules though^^
 

The Naked Scientists Forum

Re: Thermite with sand and extraction of silicon metalloid
« Reply #14 on: 06/09/2012 06:43:47 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums