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[*] posted on 8-10-2015 at 15:07


Er, I just added the lithium citrate solution to the calcium nitrate solution, and I got absolutely no precipitate. What the heck happened? Is calcium citrate actually appreciably soluble unlike Wikipedia says?
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[*] posted on 8-10-2015 at 15:31


Quote: Originally posted by Upsilon  
Er, I just added the lithium citrate solution to the calcium nitrate solution, and I got absolutely no precipitate. What the heck happened? Is calcium citrate actually appreciably soluble unlike Wikipedia says?


It really is NOT a good idea to try and carry out these displacement reactions between compounds that have some solubility, like calcium citrate.

Citrates are the salts of a weak triprotic acid and their solubility is likely to be very pH dependent. Represent citric acid by H<sub>3</sub>Ct, so Ca citrate would be the Ca<sup>2+</sup> salt of Ct<sup>3-</sup>. As the conjugated base of a weak acid, Ct<sup>3-</sup> is a weak base:

Ct<sup>3-</sup>(aq) + H<sub>2</sub>O(l) < === > HCt<sup>2+(aq)</sup> + OH<sup>-</sup>(aq)

pH affects the form of the citrate ions present, thus also citrate solubility. Check the pH of your mixed solution.



[Edited on 8-10-2015 by blogfast25]




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[*] posted on 8-10-2015 at 15:42


A much simpler way is to take advantage of the modest solubility of LiCO3 and the high insolubility of CaCO3:

Ca(NO3)2(aq) + 2 LiCO3(s,aq) === > CaCO3(s) + 2 LiNO3(aq)

Simply simmer a slurry of LiCO3(s,aq) with a Ca(NO)2 solution (stoichiometric amounts) and the slurry will precipitate the Ca as carbonate, leaving the Li in solution as the highly soluble nitrate. Filter and recrystallise the LiNO3.

[Edited on 8-10-2015 by blogfast25]




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[*] posted on 8-10-2015 at 15:45


Well that's an issue, I don't have any pH indicators. Even if I did, I don't know how I would adjust it without screwing with the contents of the final product. Luckily I did this in small scale to test it so it's not a big deal at all. I think I can make the direct reaction between lithium carbonate and calcium nitrate work.

EDIT: Just ordered a pH meter, don't know why I waited so long to get one. I'll save the solution so I can test it when it gets here, but I'm still going to use the other method to make lithium nitrate.

[Edited on 8-10-2015 by Upsilon]
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[*] posted on 11-10-2015 at 16:31


Today I did a quick silicon dioxide thermite since I was frustrated with the fact that I have been making almost no progress on any of this. I found some extra time today, so I used the method entailed here:
http://thehomescientist.blogspot.com/2010/03/experiment-sili...

I didn't use very much (4.5g SiO2, 6g S, and 5g Al). I put it in a small aluminum foil boat and then put the whole thing into my makeshift thermite reactor made of bricks. It burned spectacularly and calmly for at least 30 seconds. I was left with a single mass of slag that I chiseled apart when it cooled. I put the pieces in water to get rid of the majority of the slag (Al2S3), and then moved them to conc. HCl for a brief time. I got some decent lumps which I was initially sure were silicon metal, but I have a hunch that they are just more pieces of slag. They don't really split apart like the other slag but they degrade easily - small bits are falling off even from being knocked around the vial I'm storing them in. The lumps are dark gray and quite rough, yet they shimmer in light. They certainly don't look at all like the image on that website. The material I saved weighs 0.35g. Not sure what to make of all this, anyone have any thoughts?
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[*] posted on 11-10-2015 at 17:19


Sounds like alumina slag to me - are they a cohesive mass, or sort of sintered in appearance? At any rate, your reaction went forward - there's got to be some silicon in there...

Don't worry about losing your silicon - if any formed, it won't be too badly attacked by the HCl. You might get an unappealing gray powder, but it'll still be pure silicon.

I bought some fumed silica as part of a failed shear-thickening fluid experiment last month - I'm tempted to take it home and try out this reaction on it.





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[*] posted on 11-10-2015 at 17:38


@Upsilon:

These very small amounts don't work well. Minimum 100 g of mix (approx.). Small amounts of mix don't allow enough time for metal/slag separation and also lose far too much heat. 'Go large' with this one!

@EC1:

Si isn't attacked by HCl at all. It's not a metal (it's a metalloid) and doesn't have any 'loose' electrons in it's valence shell.

[Edited on 12-10-2015 by blogfast25]




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[*] posted on 11-10-2015 at 17:48


Quote: Originally posted by blogfast25  
@Upsilon:

These very small amounts don't work well. Minimum 100 g of mix (approx.). Small amounts of mix don't allow enough time for metal/slag separation and also lose far too much heat. 'Go large' with this one!


I figured as much. I guess the small mixtures just don't have enough mass to retain heat long enough to allow the molten metal to join together? (EDIT: Duh, I didn't even see that this is exactly what yiu said) I did notice a couple of tiny (2mm diameter max) perfect silvery spheres - I suppose these are the nice pure silicon samples I'm after. It seems wasteful to use so much chemical to make a lot of silicon when I only need a gram or two at most, but if that's what must be done then so be it. At any rate, I guess all I managed to do was stink up the property with H2S.

I'll be redoing this experiment as well as the titanium dioxide thermite this weekend (first days off in weeks!). I may also get to the lithium nitrate electrolysis, the design of which I still need confirmation on (scroll up).

[Edited on 12-10-2015 by Upsilon]
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[*] posted on 11-10-2015 at 17:53


Quote: Originally posted by Upsilon  


I figured as much. I guess the small mixtures just don't have enough mass to retain heat long enough to allow the molten metal to join together? I did notice a couple of tiny (2mm diameter max) perfect silvery spheres - I suppose these are the nice pure silicon samples I'm after. It seems wasteful to use so much chemical to make a lot of silicon when I only need a gram or two at most, but if that's what must be done then so be it. At any rate, I guess all I managed to do was stink up the property with H2S.



H2S is the reason I stopped preparing Si this way. Try and use large scrubbers with thin bleach to capture it, it oxidises the H2S to sulphur very effectively.

Si thermites are quite hard, also because the density of molten Si is actually lower than the density of molten alumina!




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[*] posted on 11-10-2015 at 18:09


Quote: Originally posted by blogfast25  

H2S is the reason I stopped preparing Si this way. Try and use large scrubbers with thin bleach to capture it, it oxidises the H2S to sulphur very effectively.


The H2S isn't really an issue until you try to dissolve the slag with either acid or water; dissolving the slag can easily be done in a controlled lab environment where it can be easily neutralized (I just didn't for the sake of time). Some sulfur dioxide is produced when the thermite burns, but that's not a big deal. H2S can be produced by the Al2S3 hydrolyzing with the moisture in air, but this doesn't happen at a fast enough rate to warrant a scrubber setup over the thermite reactor itself.

Other methods of producing silicon metal may have advantages, but I'm trying to work strictly with SiO2 and don't really want to buy another silicon compound. SiO2 is obviously quite difficult to work with chemically.
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[*] posted on 12-10-2015 at 03:19


Quote: Originally posted by blogfast25  
A much simpler way is to take advantage of the modest solubility of LiCO3 and the high insolubility of CaCO3:

Ca(NO3)2(aq) + 2 LiCO3(s,aq) === > CaCO3(s) + 2 LiNO3(aq)

Simply simmer a slurry of LiCO3(s,aq) with a Ca(NO)2 solution (stoichiometric amounts) and the slurry will precipitate the Ca as carbonate, leaving the Li in solution as the highly soluble nitrate. Filter and recrystallise the LiNO3.

[Edited on 8-10-2015 by blogfast25]

I do not want to nitpick, but I see a disturbing error in your post. From blogfast I expect better :P

LiCO3 is a very special salt, which only exists in a parallel universe, yet to be discovered. In our universe we do have Li2CO3.




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[*] posted on 12-10-2015 at 06:17


Quote: Originally posted by woelen  


LiCO3 is a very special salt, which only exists in a parallel universe, yet to be discovered. In our universe we do have Li2CO3.


I never get those memos, woelen!

Oooopsie, Li<sub>2</sub>CO<sub>3</sub>, my very bad :mad:. Thank you.




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[*] posted on 12-10-2015 at 07:03


Even the best sometimes has a slip of the brain ;)



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[*] posted on 12-10-2015 at 19:58


I attempted the thermite again today - much better results with the larger amounts (I used roughly 100g of mixture). I got similar pieces to what I had before, though (definitely more of them however). I think I didn't allow them enough time in the HCl last time. I'll let them soak overnight and whatnot and report back tomorrow.

I don't think I'll be doing this again though. The sulfur dioxide produced this time was much more significant, as was the H2S involved (it quickly overpowered the bleach I used to neutralize it, I should have used a more concentrated oxidizer). I'm surprised I didn't incite any reaction from the neighbors with the billowing SO2 cloud and rotten egg smell. I didn't even dissolve most of the slag; I picked out what I wanted and left the rest alone. I bagged it up and I may use it as a crude H2S source in the future.
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[*] posted on 12-10-2015 at 21:32


Thanks for reminding me how smelly this one gets. I am due for another attempt on a larger scale but have put it aside because, of all things, my lab has lacked... sand. I now have some nice silica sand and so am ready for silicon extraction. I might want to choose a windy day.
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[*] posted on 13-10-2015 at 08:06


Quote: Originally posted by j_sum1  
Thanks for reminding me how smelly this one gets. I am due for another attempt on a larger scale but have put it aside because, of all things, my lab has lacked... sand. I now have some nice silica sand and so am ready for silicon extraction. I might want to choose a windy day.


In the quest to eliminate sulphur (and thus H2S) from the SiO2 thermite I tried replacing the S+Al booster system with a KClO3 + Al booster system several times (years ago). Although that worked well unfortunately the silicon got caught into extremely hard alumina from which it was impossible to remove it. Very frustrating.

But I wonder if it's worth trying this with the CaSO4 + Al booster method. That would simply mean taking the TiO2/CaSO4/Al/CaF2 formulation and substituting the TiO2 with SiO2, mol for mol. Worth a shot, methinks!

[Edited on 13-10-2015 by blogfast25]




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[*] posted on 13-10-2015 at 15:55


So I recovered the pieces a little while ago. Upon applying even slight pressure they crumbled into a bunch of tiny useless shiny flakes (it is literally glitter). I dumped this in frustration and have since tried again with a couple more pieces I pulled out of the slag I saved. It's strange; these pieces that I pulled out looked exactly like what's in the picture on the website I used, and that was before HCl treatment. I put them in HCl and I'll let them simmer a while.
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[*] posted on 13-10-2015 at 17:33


Quote: Originally posted by Upsilon  
So I recovered the pieces a little while ago. Upon applying even slight pressure they crumbled into a bunch of tiny useless shiny flakes (it is literally glitter). I dumped this in frustration and have since tried again with a couple more pieces I pulled out of the slag I saved. It's strange; these pieces that I pulled out looked exactly like what's in the picture on the website I used, and that was before HCl treatment. I put them in HCl and I'll let them simmer a while.


Please bear in mind that silicon prepared this way is not particularly pure: apart from alloyed aluminium it probably also contains micro-occlusions of slag, which would explain the poor mechanical properties.

To increase size of globules obtained, you might want to 'stoke up the heat' by increasing both S and Al content. A higher end-temperature allows more cooling time and thus more longer time for the molten Si metal to coalesce into larger units.




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[*] posted on 13-10-2015 at 18:02


Quote: Originally posted by blogfast25  

Please bear in mind that silicon prepared this way is not particularly pure: apart from alloyed aluminium it probably also contains micro-occlusions of slag, which would explain the poor mechanical properties.

To increase size of globules obtained, you might want to 'stoke up the heat' by increasing both S and Al content. A higher end-temperature allows more cooling time and thus more longer time for the molten Si metal to coalesce into larger units.


That's probably it, then. I don't mind impurities so much, but if I can't even get a cohesive sample then I don't really want it. Like I said I don't think I'll be doing this again just because of the nasty sulfur-based gas byproducts. Perhaps the calcium sulfate booster you mentioned would work, but after using so much aluminum powder on this already I'm not really too keen on using some more unless I know it'll work.

That being said, I honestly have no idea what else I would do to prepare elemental silicon. Perhaps the most promising compound is silicon tetraiodide (which I could melt down and electrolyze) but I don't know how I would get here from silicon dioxide. Maybe I could dissolve it in molten phosphoric acid, then react this silicon phosphate (which I cannot find information on surprisingly) with hydroiodic acid?

Either way this is certainly not the quick and easy lunch-break experiment I was hoping for! :P Goes to show that things are so much easier on paper in chemistry.

EDIT: You know, I might as well try carbothermic reduction since I'm planning on building an arc furnace anyway. This silicon can then be purified using a silicon tetrachloride method. I suppose I could have done this already but I didn't really want to try and scrape together a bunch of this fine silicon powder.

[Edited on 14-10-2015 by Upsilon]
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[*] posted on 13-10-2015 at 18:37


Quote: Originally posted by Upsilon  


That being said, I honestly have no idea what else I would do to prepare elemental silicon. Perhaps the most promising compound is silicon tetraiodide (which I could melt down and electrolyze) but I don't know how I would get here from silicon dioxide. Maybe I could dissolve it in molten phosphoric acid, then react this silicon phosphate (which I cannot find information on surprisingly) with hydroiodic acid?



Nah, SiI<sub>4</sub> is a purely covalent compound and can't be electrolysed. It's also hard to prepare at hobby level. Silicon phosphate doesn't even exist: Si is not a real metal, remember?

Industrially, reduction of SiCl<sub>4</sub> with Mg metal is used but forget about trying that in your garage or potting shed lab! :(




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[*] posted on 13-10-2015 at 19:07


Quote: Originally posted by blogfast25  

Industrially, reduction of SiCl<sub>4</sub> with Mg metal is used but forget about trying that in your garage or potting shed lab! :(


Does it occur with explosive force or something? What exactly makes it impractical for the home lab?

Also like I said I may try the carbothermic reduction method for producing silicon when I get around to building my arc furnace.

...hell, with an arc furnace, I could probably just run the SiO2 + All thermite on its own, right? And avoid toxic gases altogether? Since the problem with this reaction normally is just not enough heat to sustain the reaction? In an arc furnace this would be no issue, plus I could keep the heat going as long as I want to allow the silicon metal to coalesce as much as I want it to.

[Edited on 14-10-2015 by Upsilon]
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[*] posted on 13-10-2015 at 21:12


Hmm. Sorry it didn't work out for you, Upsilon.
Last time I did this reaction was over a year ago. From memory it was somewhere between 50 and 80 grams of mix in total. IO used the same ratios as you. I got a few pebbles of silicon -- the largest of which would have been 8mm diameter. It seemed to have pretty good mechanical properties.
I can't remember how fine my aluminium was. That might make a difference. I am definitely looking forward to doing it again. I was thinking of perhaps a half kilo batch.
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[*] posted on 14-10-2015 at 07:03


Quote: Originally posted by Upsilon  

Does it occur with explosive force or something? What exactly makes it impractical for the home lab?

Also like I said I may try the carbothermic reduction method for producing silicon when I get around to building my arc furnace.

...hell, with an arc furnace, I could probably just run the SiO2 + All thermite on its own, right? And avoid toxic gases altogether? Since the problem with this reaction normally is just not enough heat to sustain the reaction? In an arc furnace this would be no issue, plus I could keep the heat going as long as I want to allow the silicon metal to coalesce as much as I want it to.


It's highly exothermic and with a volatile reactant (SiCl<sub>4</sub>;) that means pressurised reactors.

Arc furnace for carbothermic or aluminothemic reduction of sand should work. The carbothermic version is of course used industrially.

[Edited on 14-10-2015 by blogfast25]




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[*] posted on 14-10-2015 at 07:06


Quote: Originally posted by j_sum1  
I was thinking of perhaps a half kilo batch.


Why not try a small batch with CaSO<sub>4</sub> + Al, instead of sulphur?




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[*] posted on 14-10-2015 at 08:54


Quote: Originally posted by blogfast25  


Arc furnace for carbothermic or aluminothemic reduction of sand should work. The carbothermic version is of course used industrially.

[Edited on 14-10-2015 by blogfast25]


Honestly I think I'll go with the carbothermic. I was worried about carbon monoxide but then I remembered that it would simply burn immediately after being produced to form carbon dioxide. Besides, the alumina would probably be too hard to melt in the arc furnace (especially since I'll probably be using alumina brick), plus the carbothermic reduction should leave nothing but Si metal behind so I don't have to deal with slag (in reality though, I expect there to be a noticeable amount of carbon left over).
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