Steamboy
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Obtain boron via electrolysis
Hi. I am new on these forums.
I'm trying to get boron without using magnesium, so I thought electrolysis could be applied to molten boron trioxide.
2 B2O3 -> 4 B + 3 O2
To melt it I need to reach temperatures of ~ 450 celsius (~ 823 kelvin or ~ 842 farhenheit), which is not a problem for me. However I have several
doubts:
*. The main and most obvious is, if this really will work, and its viability.
*. Can graphite be used as anode and cathode material?
*. What is the minimum voltage required?
*. Will the temperature and air affect the newly formed metal boron (reversing the process or worsening it)? How can it be avoided?
*. Others. What others problems will I find?
Edit: electrolysis of molten boron trioxide will be done having salts in this, for increase the conductivity.
[Edited on 24-1-2017 by Steamboy]
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elementcollector1
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This might belong in Beginnings.
Here's an important question: Is molten B2O3 conductive?
The answer is no, it's an insulator. It has an fairly wide bandgap of about 6.2 electron volts, so good luck with getting that to conduct.
Now, by combining it with other salts, it's reported that electrolysis can be performed. A cursory search brought up patents US3030284 and
US20100294670.
https://www.google.com/patents/US3030284
https://www.google.com/patents/US20100294670
I'll take a stab at some of your other questions.
2) Graphite probably could be used, but your boron would be horribly contaminated with carbon. Not even close to worth it. The methods above are
obtained with platinum and tantalum electrodes, both of which are available as foil on EBay.
3) The minimum voltage is a bit confusing when it comes to electrolysis. From a glance at some other half-reactions of boron, it's probably somewhere
around a volt. However, water electrolysis requires much the same, and most good results are obtained between 5 and 12 volts for that reaction. Best
to shoot for low voltage, high current - the higher the current density, the faster the deposition (and the more dangerous your cell). Care may have
to be taken to avoid reducing any of the other salts in the melt, though I'm unsure how. Just follow the patents as best you can.
4) The temperature and air will not affect the boron. Its MP (shorthand for melting point) is 2,076 degrees Celsius, which your cell is not even close
to, and although it burns in air at higher temperatures, the boron should be protected by the melt. Interestingly, boron is also self-passivating at
high temperatures, because the oxide (MP 450 C) is a liquid coating the solid boron (MP 2076 C). Any air that penetrates the viscous liquid barrier
just creates more liquid, and this is just split apart again immediately by the electrolytic current.
Other stuff:
-The slower you grow the boron, the better it looks. Fast electrolysis creates a boron powder that will likely flake off the electrode and collect at
the bottom of the cell, while slow electrolysis allows time for harder, more crystalline deposits to form.
-Why even avoid Mg in the first place? It's not exactly hard to find or work with. You're only creating more work for yourself, unless you enjoy a
challenge.
Elements Collected:52/87
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NitratedKittens
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I'm afraid that boron trioxide is covalent not ionic, because it's atoms are not charged electrolysis will not be effective.
Basket of kittens for you ........BOOM
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Steamboy
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What salts can I use for increase the conductivity of boric trioxide without increase too the melting point or impurities?
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elementcollector1
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Read the patents.
Elements Collected:52/87
Latest Acquired: Cl
Next in Line: Nd
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j_sum1
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As to doing it without magnesium, you can perform a thermite successfully with aluminium. The problem is the workup. The advantage with Mg is that
MgO dissolves nicely in acid whereas Al2O3 does not. But there might be other workup options.
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MrHomeScientist
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The other problem with aluminum is that it forms aluminum dodecaboride (AlB<sub>12</sub> , which is very difficult to separate out. Magnesium boride (MgB<sub>2</sub> is easily reacted with HCl and
escapes as diborane gas, leaving your boron product much more pure.
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Steamboy
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About the use of aluminium for isolate boron:
What is the usual quantity of impurities (borides) by mass percentage that I will obtain?
Is it possible to avoid such impurities?
What if was the aluminium powder used in low quantities stoichiometricly speaking (ie, if the aluminium is the limiting reactant)?
What substance or methode can I use for separate the aluminium oxide and boron oxide with the elemental boron?
Can I use separation by density using some fluid without create a reaction?
[Edited on 25-1-2017 by Steamboy]
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Steamboy
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Specially, about the density separation, I read that elemental boron has a density of 2.08 g/cm3; while boron trioxide and aluminium borides have
densities of 2.4~3, and aluminium trioxide has a density of 3~4.
I only need to find a liquid with a density similar but slightly bigger than elemental boron, and inert with this; for separate such from aluminium
trioxide and reduce a little impurities.
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