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tyro
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The documentation on the manufacturer's site (Dernord, in this case) rates these pieces at a max of 250 PSI at ambient temp.
I had shelved the project due to safety and noise concerns. I'm still trying to suss out the likelihood of encountering catastrophic results. The
vibrating platform approach, to me, introduced a lot of variables around stress for the apparatus; not to mention it was egregiously loud.
One of my projects during the hiatus from this was to investigate electrochemical approaches to borohydride. Unfortunately, it seems that most of the
literature is misleading. There was some mention of a continuous voltage differential impeding borohydride formation due to electrostatic repulsion of
the material at the cathode. Some references indicate that reverse pulse processes might bear fruit - i.e. forward voltage with differential to drive
borohydride formation, reverse voltage below breakdown to offset the electrostatic repulsion, along with some neutral refectory period. Alas, there
seems to be no clear signal of reproducibility from what I've seen in any of these. Additionally, none of the trials I ran were conclusive (though my
methods, materials, and analytical capabilities in this regard are rather limited).
I've recently acquired a tank of argon and am picking up tinkering on the tri clamp bits to try a go at a rotating mill approach. I'm not sure if the
necessary conditions for borohydride formation can be had outside of high energy milling, but I may be up for some trials if I can gain enough
confidence in the setup.
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Texium
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Thread Moved
30-11-2023 at 10:52 |
chempyre235
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I had been mulling over some ideas for possible substitutes that would make this reaction safer, and work at least in theory. Here are the preliminary
calculations I've done so far. I have included the enthalpies of the compounds in (kJ/mol).
Potassium borohydride:
3KOH (-425.8) + 8 Al (0) + 3B(OH)3 (-1094.9) ---> 3KBH4 (-228.86) + 4Al2O3 (-1675.7) (Δh
= -2827.28 kJ/mol.)
This could potentially work for sodium too, and would not produce any gas, provided the hydroxide is fresh (i.e., free of carbonate). Boric acid is
OTC for use as a pesticide, but could also be made from borax.
Potassium cyanoborohydride.
2K3Fe(CN)6 (-173.2) + B2O3 (-1254) ---> 2KB(CN)4 (-770.36) +
Fe2O3 (-824.2) + 4KCN (-131.5) (Δh = -1290.12 kJ/mol.)
KB(CN)4 (-770.36) + 3KOH (-425.8) +2Al (0) ---> KBH3CN (-354.06) + Al2O3 (-1675.7) + 3KCN
(-131.5) (Δh = -376.5 kJ/mol.)
Notes: Potassium ferricyanide isn't necessarily OTC, but is readily available from photography chemical suppliers. Obviously, boric acid will react
with cyanide to form HCN, but by keeping the ball mill pressurized with inert gas, HCN formation should be disfavored. The reason I have this synth
divided into two steps is to prevent a thermite reaction between the aluminum and the iron (II) oxide. The main drawback to this synthesis is that
there are five moles of KCN formed for every mole of KBH4.
"However beautiful the strategy, you should occasionally look at the results." -Winston Churchill
"I weep at the sight of flaming acetic anhydride." -@Madscientist
"...the elements shall melt with fervent heat..." -2 Peter 3:10
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MrDoctor
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i saw a paper that pressurized a ball mill with a balloon via a silicone hose.
It was one of those shaker style ones not limited by gravity to make the media fall.
the paper itself i dont remember details of well, but it was about how under mild conditions sodium oxide absorbs hydrogen and dissociates into NaH +
NaOH, and because its intimately mixed with oxide and hydroxide, it does this thing where, under vacuum and very mild heating, it releases the
hydrogen well below NaH decomposition temp, and does so on demand like a chemical demand-flow-regulator, dropping the temp a little and returning the
hydrogen then causes it to eventually re-absorb, it was being researched as a sort of phase-change hydrogen storage technology, or, idk the proper
word for it. at balloon pressure i think it got to like 10-15%, and ultimately at 30-50PSI, it goes as far as it can go, whatever the pressure was, i
recall taking note of the fact that cheap plastic pumps could reach those pressures, including a heavy duty peristaltic pump.
in this instance the purpose of the ball mill was to establish and maintain a slurry that hydrogen was mixed intimately through, on a porous substrate
i believe it inhales and exhales hydrogen relatively freely.
the core mechanic at play is that, NaH decomposes at an increasingly lower temperature as Na2O and NaOH content rises, but it turned out that this was
a reversible equilibrium, and by converting to a fine disperson, it no longer becomes neccesary to provide such extreme hydrogen pressure to diffuse
through the protective layer of hydride that forms. actually now that i say it, im pretty sure that another paper i read, if it wasnt just a footnote
in this one, was that the same mechanism applies to hydrogenating sodium metal, where ultrasound or milling keeps the hydride stripped away, allowing
for atmospheric pressure reaction, or, whatever PSI a balloon provides.
shaker type ball mills ive also seen can run so fast, what takes days can be accomplished within hours, i know one mention in a paper somewhere had it
only mill for like 20 minutes or so, after i began paying attention to when they pop up.
one of the merits of the style is that the density of the media is no longer important, just its relative hardness, the grinding action is no longer
limited by how quickly a pile of it can tumble down over itself. the few ive seen photos of pretty much just look like beefy crucibles or hydrothermal
reactors, really, just a very short, very thick walled, threaded pipe not unlike plumbing pipe with one end welded shut already.
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bnull
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| Quote: | Potassium borohydride:
3KOH (-425.8) + 8 Al (0) + 3B(OH)3 (-1094.9) ---> 3KBH4 (-228.86) + 4Al2O3 (-1675.7) (Δh
= -2827.28 kJ/mol.)
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I see a problem here. There is the reaction between KOH and boric acid:
$$3KOH + B(OH)_3 \rightarrow K_3BO_3 + 3H_2O.$$ The result is a sludge of potassium borate, boric acid and aluminum. Heat that and water evaporates.
Keep on heating and aluminum borates appear. All hydrogen is lost as water and elemental hydrogen. It may be thermodynamically feasible but in
practice neutralization wins.
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MrDoctor
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would the solution then not be to use either potassium oxide, and/or boric anhydride? boric anhydride at very least is easy to produce and most of the
issues it has, because its basically molten glass that barely reacts with water, are resolved in the mill.
I just now recalled another synthesis of sodium hydride using methane as a hydrogen source, is the methane that formed perhaps participating in the
OP's reaction?
excessive gas burping could be that.
lastly, have any methods been determined where magnesium could be supplemented by aluminum or what happens? because a lot of reactions that occur
under extreme heat and pressure also occur when grinding media collide, i could imagine the instantaneous formation of aluminum hydride that transfers
to the magnesium unless there is no reason for it to not just go right back.
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bnull
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| Quote: | | would the solution then not be to use either potassium oxide, and/or boric anhydride? |
Where would hydrogen come from?
There is too much oxygen involved and all the hydrogen is bonded to oxygen. It is not easy, otherwise industry would have solved that long ago.
Edit: Perhaps urea could be used in a modified process. But then there is the possibility of the formation of boron nitride in place
of borane, which is the main goal here. Not much wriggle room here.
[Edited on 17-10-2025 by bnull]
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MrDoctor
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no just, reducing the amount or physical state of the water that is present to reduce the excess without changing the potassium:boron balance. in one
of the papers provided, the reaction goes from taking 3.5 hours to 30, still with significant yield loss too, in what to my understanding was because
too much water existed decreasing the milling efficiency. the powdered reaction mixture needs to be at a certain level of dryness to progress smoothly
without say, getting too soft or whatever it is that happens with water that is in a solid adsorbed / crystaline state. In that paper they used
magnesium and sodium hydrides to make sure there was enough hydrogen without it being present in the form of water. Aluminum was able to replace the
magnesium hydride, but not the sodium. One can only hope that a bit of borohydride starter from a previous run, and/or adding 5-10/15PSI of hydrogen
in the argon can remedy the situation and get conversion back in the upper 90s
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bnull
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What about aluminum boride, AlB2, in place of aluminum? Or maybe a mixture of aluminum and aluminum boride?
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chempyre235
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I think that would help to reduce the oxygen sources, but the problem is still the lack of OTC sources of hydrogen. Using pressurized gaseous hydrogen
would warrant special alloys for the mill (and severe risk), and other sources seem to either result in water or (in the case with amines/amides)
boron nitrides of borazines. I think we're on the right track, though, and I'm thankful that more minds are on this.
"However beautiful the strategy, you should occasionally look at the results." -Winston Churchill
"I weep at the sight of flaming acetic anhydride." -@Madscientist
"...the elements shall melt with fervent heat..." -2 Peter 3:10
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clearly_not_atara
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Quote: Originally posted by bnull  | | What about aluminum boride, AlB2, in place of aluminum? Or maybe a mixture of aluminum and aluminum boride? |
The production of borides is nontrivial and usually does not occur at room temperature. There are some Indian papers claiming that MgB2 can be
electrodeposited from DMSO, but the route is not attested outside India and "I'll believe it when I see it"  . Thermite rxns are discussed far more often than they are performed.
MgB2 is well-known as a precursor to borohydride by rxn with NaOH and it is plausible that other borides will be as well. However, the production of
the borides remains difficult. It may however be possible to obtain MgB2 commercially, since there is substantial interest in this compound. At the
very least, it is basically nonflammable and should be easy to ship, unlike borohydride.
There has been substantial research interest in the production of MgB2, but the vast majority of papers are concerned with producing
superconductor-grade boride, which is much more complicated than what we need. It is difficult to search for "crude" methods that may be more easily
adopted by, uh, me.
EDIT: maybe someone can access the paper:
https://pubs.acs.org/doi/10.1021/acsaem.2c02946
[Edited on 20-10-2025 by clearly_not_atara]
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bnull
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I suggested aluminum boride because I was reading about it in a book of inorganic preparations. Brauer has both AlB2 and AlB12,
but I think it was somewhere else.
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davidfetter
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| Quote: Originally posted by clearly_not_atara | | Quote: Originally posted by bnull | | What about aluminum boride, AlB2, in place of aluminum? Or maybe a mixture of aluminum and aluminum boride? |
The production of borides is nontrivial and usually does not occur at room temperature. There are some Indian papers claiming that MgB2 can be
electrodeposited from DMSO, but the route is not attested outside India and "I'll believe it when I see it" . Thermite rxns are discussed far more often than they are performed.
MgB2 is well-known as a precursor to borohydride by rxn with NaOH and it is plausible that other borides will be as well. However, the production of
the borides remains difficult. It may however be possible to obtain MgB2 commercially, since there is substantial interest in this compound. At the
very least, it is basically nonflammable and should be easy to ship, unlike borohydride.
There has been substantial research interest in the production of MgB2, but the vast majority of papers are concerned with producing
superconductor-grade boride, which is much more complicated than what we need. It is difficult to search for "crude" methods that may be more easily
adopted by, uh, me.
EDIT: maybe someone can access the paper:
https://pubs.acs.org/doi/10.1021/acsaem.2c02946
[Edited on 20-10-2025 by clearly_not_atara] |
I accessed it. Here's the meat, as I see it:
| Quote: | 2. MATERIALS AND METHODS
Mg particles (800 nm, 99.9%, US Research Nanomaterials) and boric
acid powder (99.5%, Sigma Aldrich) were used in the synthesis.
Commercial MgB2 (−100 mesh, 99%, Sigma Aldrich) was purchased
to serve as a standard against which to compare the amount of energy
released. The synthesis method involves annealing the physical
mixture of the Mg and boric acid powders by a process similar to that
used to produce Mg/B solid solutions from Mg and B.10 Briefly, Mg
and boric acid were mixed in the weight ratio of 1:1 (excess Mg) by
dry powder-based magnetic mixing, and the mixture was spread on
the surface of the glass slide (Dot Scientific Inc.). After forming a layer
on the glass slide, the powder was compressed with another glass slide
from the top to maximize contact between particles in the powder and
minimize contact with air. Glass slides were packed using aluminum
foil and placed into a muffle furnace (model: FB1415M, Thermolyne)
for annealing. The temperature was increased to 550 °C at a rate of 30
°C/min and was maintained at 550 °C for 2 h. After processing, the
furnace was turned off, and the particles were left to cool inside for 3
h. Time and temperature conditions for the synthesis were optimized
by measuring the energy released from the oxidation of synthesized MgB2.
X-ray diffraction (XRD) was performed using Cu Kα X-rays on a
Malvern Panalytical XPert Pro MPD theta−theta diffractometer. X-
ray photoelectron spectroscopy (XPS) was carried out using a
Physical Electronics VersaProbe II instrument equipped with a
monochromatic Al Kα X-ray source. Scanning transmission electron
microscopy (STEM) with energy-dispersive spectroscopy (EDS) was
executed on a Talos F200X at 200 kV with an XFEG source and high-
angle annular dark-field (HAADF) imaging. Particle size analysis was
carried out using dynamic light scattering (DLS) on a Malvern
Zetasizer Nano ZS. Intensity fluctuations were analyzed, which gives
the velocity of the Brownian motion of the particles from which we
can measure the particle size using the Stokes−Einstein equation.
Thermal analysis was performed on a TA Instruments Model Q600
SDT, which provided simultaneous measurements of heat flow
(differential scanning calorimetry (DSC)) and weight change (TGA)
on the sample from ∼20 to 1000 °C. Analyses were conducted in air
at a volumetric flow rate of 100 mL/min. Alumina sample cups (90
μL, TA Instruments) were used in the analysis to hold the sample. A
heating rate of 20 °C/min was used till 1000 °C after maintaining
isothermal conditions for the first 10 min. To determine the storage
stability of the synthesized MgB2 and compare it with the stability of
Mg, accelerated aging tests were conducted. The Mg and MgB2
samples were placed in an oven for 120 min with temperature and
relative humidity of 100 °C and 70%, respectively. After this, both
samples were taken for DSC analysis to measure their oxidation
energy release. The changes in the energy release were noted and
compared before and after the aging tests to quantify the effect of
synthesizing MgB2 on Mg.
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