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Author: Subject: Isolation of elemental Boron and Proof Demonstrations of Allotropes
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[*] posted on 12-11-2017 at 09:58
Isolation of elemental Boron and Proof Demonstrations of Allotropes


My primary interest is just in doing some experiments with the element Boron, but prior to that determining wether or not it would be feasible in a home lab to do so.

My current source of Boron is from Borax detergent, which I was hoping to be able to isolate and play with some of the element from there. According to multiple procedures and papers I've read, including wikipedia - it's supposedly extremely difficult to get pure elemental Boron as it is always contaminated with Carbon and other junk.

So my questions will be divided into 2 parts essentially, part 1 regarding the feasibility/necessary equipment, and part 2 detailing the actual procedure and potential demonstrations.

PART 1
----------
Can this whole process be done chemically or do you /need/ high temperatures for these reactions to work? Almost all of the procedures use things like torches and crucibles so that they pretty much only work with the oxides which are later chemically removed.

If there is a way to do it in a relatively 'cool' chemical way, what kind of materials would be necessary for that?

And finally, what is the general yield percentage of most of these procedures, im guessing somewhat low?


PART 2
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The general understanding I have of what appears to be the most commonly used method for extracting the boron from borax is:

Convert to boric acid, reduce with magnesium, heat up and drive off all contaminates until it's just boric oxides, do some washing steps, react with HCl wash/rinse/repeat.

I may have skipped some steps but those are the steps I remembered from all the papers. Is there a more efficient/easily accessible method or is this pretty much it?

And as my final query (thanks for reading this far if you have) , I was wondering apart from flame tests what potential chemical demonstrations could you do to prove that it is Boron or a specific allotrope of Boron? And are there chemical ways to alter the allotropes or do those all involve high/specific temperatures?

Really any input on this subject would be of a lot of help, thanks so much for reading this far!
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[*] posted on 12-11-2017 at 11:25


Does thermite count as "high temperatures" in your book? The most common method for amateurs to obtain boron is the reduction of boric oxide (obtained by the decomposition of boric acid at around 300 degrees C) using magnesium in the thermite reaction. You don't have to use lab grade crucibles; MrHomeScientist used a piece of pottery. Some other videos use cooking pots and a camping stove to decompose the boric acid.

I guess the "cool" chemical method would include thermite. Who doesn't love the eruption of flames and metal sparks ;)?




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[*] posted on 12-11-2017 at 11:33


Yeah, I don't exactly have a backyard and I'm not comfortable doing a redox reaction that reaches those temperatures indoors. When I said "cool" I meant temperature-wise, as in a less energetic way to reduce the oxide. If there really isn't one, then that's fine, I'll just do it with magnesium.

I know it's a messy-ish prep, and by low temperatures I meant something that a hotplate could reasonably handle without a vacuum pump. Maybe lower than 200 C if feasible.
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[*] posted on 12-11-2017 at 11:51


I tried it using boric acid and Mg thermite.

https://www.metallab.net/jwplayer/video.php?v=L2NsaXBzL0Jvcm...




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[*] posted on 12-11-2017 at 12:32


Boron tribromide can be reduced with hydrogen, but fairly high temperatures and a fume hood are required. Also, you need a source of boron tribromide.



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[*] posted on 12-11-2017 at 12:43


If you live near an open field or desert, the thermite reaction can be performed there with relative ease and safety. After the thermite reaction, cleaning the boron is simple by adding hydrochloric acid. But it has to be done slowly, due to the toxic borane gas produced from possible boride salts formed during the thermite reaction (magnesium boride, etc.).

EDIT: Added a few phrases and the warning of borane gas.

[Edited on 11-12-2017 by ninhydric1]




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[*] posted on 13-11-2017 at 07:08


Indeed, I did it originally using the thermite method. Here's the breakdown of what I did in my video: https://www.youtube.com/watch?v=0QBCyOrjR2o

1) Heat boric acid in a clay saucer until all water is driven off
2) Crush the resulting boric oxide into a powder (which is NOT easy; that stuff is hard as rocks)
3) Mix with a roughly equal weight of Mg powder & ignite thermite-style
4) Add the resulting reaction slag to dilute HCl (slowly!) to react away everything that isn't boron. Go slow and dilute to avoid incidents from the pyrophoric borane that may be produced.


I actually just did experiments on making boron last night! This time I tried replacing the thermite step with placing the reaction mixture in a small propane furnace. The goal here was to heat it to the reaction temperature in a metal crucible (stainless steel condiment cup from Walmart) to improve purity. (In the video, the clay saucer and bed of sand I did the thermite on contaminated the end product.)

This seems to have worked great, but I had a little incident while heating in the furnace. I was poking at it with a graphite rod to try mixing things around, when it suddenly reached the right temperature and I was met with a wooshing sound, a blinding white light, and very hot boron flying out of the furnace. While I was right next to it. The tabletop was scorched in several places and my shirt now has a burn mark on it. Luckily, I was doing this outside and was wearing a face shield and welding gloves. I should have also been wearing my welding jacket, apparently. That really surprised me because the reaction shouldn't produce any gas, so I don't know why it would "explode" like that.

That is another data point for my favorite saying: No matter how many times you've done a reaction before, it's a new experiment every time. Be prepared for anything!
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[*] posted on 13-11-2017 at 17:25


Huh, so upon closer inspection I'm not sure that reaction worked at all. I started with 4g of boric oxide, so theoretically I should have about 1g of boron at the end. After acid digestion I actually have 5g of black material, and when I sprinkle this on a propane flame it's only barely green. The majority is orange sparks. It looks a lot like what carbon powder would do in a flame, but where would the C have come from? I only used the boric oxide and magnesium powders, in a metal crucible. Certainly MgB<sub>2</sub> was a side product, but that should have been reacted away with the acid step. And over 4g of unknown products? Any ideas what happened?

Reactions:
2H<sub>3</sub>BO<sub>3</sub> --> B<sub>2</sub>O<sub>3</sub> + 3H<sub>2</sub>O (boric acid dehydration)
B<sub>2</sub>O<sub>3</sub> + 3Mg --> 2B + 3MgO (thermal synthesis)
Mg + 2B --> MgB<sub>2</sub> (side rxn)
Mg<sub>3</sub>B<sub>2</sub> + 6HCl ---> B<sub>2</sub>H<sub>6</sub> + 3MgCl<sub>2</sub> (acid digestion)
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[*] posted on 13-11-2017 at 18:34


I don't know how elemental boron shows in a flame test. You get the brilliant green when it is bonded to something. Ethylborate or methylborate being the most obvious. You should be able to work out a reaction with something that will display the green if boron is present.

400% additional material seems a bit strange. MgO should have digested pretty well. Bit like you, I can't think of what else might be there.

I would try a larger scale if possible.
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[*] posted on 13-11-2017 at 18:50


You did poke it with a graphite rod. Maybe pieces of the rod broke off without you knowing?



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[*] posted on 13-11-2017 at 19:38


Definitely not 4g of rod, I would have noticed! No, the rod is perfectly intact.

Far as I know elemental B is pretty inert to lots of things. I've seen references that it reacts with hot concentrated nitric or sulfuric acids; presumably forming boric acid again? It's also supposed to burn in air to boron trioxide, which is why I'd expect a green color. Maybe it's too quick to form a lot of it and the color gets washed out easily. I'll have to try acid treatments and see where that gets me.

In any case, I clearly have a lot of excess material of some sort. Theoretical yield is 1.26g, and I'd expect a good deal less than that due to the boride-forming side reaction.

Also I'm somewhat reluctant to try larger scale based on the near-explosive suddenness of the reaction! Maybe thermite-style really is the way to go.

[Edited on 11-14-2017 by MrHomeScientist]
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[*] posted on 13-11-2017 at 22:35


Quote: Originally posted by MrHomeScientist  

Also I'm somewhat reluctant to try larger scale based on the near-explosive suddenness of the reaction

I am looking forward to the YT video. :)


As an aside, your boron thermite was one of the first chem YT videos I watched and one of the first experiments I tried in my home lab. It was a pretty cool place to start. I still have my ampoule of boron but I won't vouch for its purity. I do want to do a bigger one some day. Maybe I should crack open what I have and do a flame test.
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[*] posted on 14-11-2017 at 05:07


I can confirm B reacts with hot acids, though I haven't confirmed the product is boric acid. I just had to deal with such yesterday as part of my senior project - you would not believe how hard it is to dissolve a magnet when boric acid coats the entire reaction area. Good thing it's water-soluble...



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[*] posted on 20-11-2017 at 08:10


Thanks a lot, j_sum! It's great to hear from people that liked my videos, and replicated them successfully! I'm proud of that one because as far as I know, it was the first on YouTube on making elemental boron.


I did some more experimenting this weekend and I figured out the excess product problem. It turns out it just takes a long while for the acid to do its work on the magnesium boride side products. I took a 0.25g sample of the black products, put it in a test tube, and covered it with HCl diluted a bit with water. I left this to sit for two days, and upon filtering and drying it had been reduced to 0.05g, precisely 1/5 of the starting mass. I'm reasonably confident that all of this is elemental B. I repeated this with the remainder of the products (5g) and ended up with 1.7g, which is still above the theoretical 1.2g. I'll put this back in the acid for a few more days and that should hopefully take care of the rest. With that, it's time to start recording!
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[*] posted on 20-11-2017 at 08:58


I too followed your procedure MrHomeScientist to make my boron sample. One improvement I found is to use a metal rod like a coat hanger to pull the boron trioxide into long fibers while it is still hot. These fibers are easier to break up and are less prone to pulling pieces of the pot out with them. I used a clay pot like you and I had no visible contamination from it in my final product.
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[*] posted on 21-11-2017 at 20:55


I like to heat Boric acid on steel cans because after it freezes you can smash the bottom of the can and get pretty much all of the B2O3 without much contamination(i.e. ceramic powder)
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