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DocX
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Sodium Borohydride synthesis at room temp
So there's a paper on the synthesis of Sodium Borohydride by ball milling Mg, borax and sodium carbonate at room temperature.
Yongyang Zhu et al: "Efficient Synthesis of Sodium Borohydride: Balancing Reducing Agents with Intrinsic Hydrogen Source in Hydrated Borax",
https://doi.org/10.1021/acssuschemeng.0c04354.
In the paper it's also mentioned that Al might substitute for Mg, which would be very appealing for me since I have a buttload of Al powder and borax
lying around, and since this seems to be an interesting synth.
So now the practical issues: I have a small ball mill, and I can make the drum airtight. An inert atmosphere is said to be needed for the use of Mg
powder, and I may be able to provide that. Not as yet sure where I'll get the N2 though, any tips on that?
Also, I expect there wil be some build-up of vapor presssure in the container during the reaction, so I'll need to install a safety valve.
Other than that, what needs to be adressed?
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crow6283
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Some welding supply shops have Nitrogen as well. Comes in a variety of sized tanks. Basically you ‘rent’ the tank and then can bring it back to
‘fill it’ (swap it out for a full one) as often as you like. The rental on a K tank (large size, up to your waist) might be as much as 200 USD,
refilling could vary might be ~40 USD. You’ll need a regulator as well. Different tanks have different fittings and require different regulators
depending on what they are for. Nitrogen and CO2 regulators are interchangeable and should be available from the shop.
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Fery
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DocX interesting route! They used NaH + MgH2 initially and managed to replace MgH2 with Mg finally, but they still use NaH
Na2B4O7·5H2O, Na2B4O7·10H2O, NaH, Mg in molar ratio 0.6:0.4:2:17.5
https://sci-hub.ee/10.1021/acssuschemeng.0c04354
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tyro
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Hi all!
DocX, you beat me to posting this! Exciting to see others are looking to try out this method 
I recently come across another publication by these authors, where they were able to generate NaBH4 in a ball mill at ambient temperature using only
borax (the decahydrate), sodium carbonate, and magnesium.
The overall reaction scheme looks like this:
Na2B4O7*10H2O + Na2CO3 + 20Mg -> 4NaBH4 + 20MgO + CH4
They report that using an excess of magnesium pushes the yield up to a max of 75.7% when using a molar ratio of 24.75:1:1 (Mg, Na2B4O7*10H20, Na2CO3).
https://onlinelibrary.wiley.com/doi/10.1002/anie.201915988
A couple weeks ago, I bought a hobby rock tumbler to give this a shot. The rubber jar was loaded with magnesium turnings made from fire starters,
borax (re-crystalized to get the decahydrate since it was sold as the pentahydrate), sodium carbonate made from baking soda, and some 14mm glass
marbles. The jar was flushed with nitrogen and tumbled for about a week. On the last day, the bottom of the jar was bulging out, indicating gas
production (assuming this is the methane). Interestingly, when the jar was opened, there was a strong and uniquely sweet smell which could be noticed.
At the end of a week of milling, the contents of this first run were incompletely reacted, and I was ill equipped to extract any produced borohydride.
The rock tumbler likely needs to be run for quite a bit longer. The author's mentioned a mill time/speed of 20H @ 1000CPM, and this rock tumbler does
somewhere under 60CPM. If we go by total number of cycles, this would put the mill time needed closer to 2-4 weeks, not accounting for other factors
like milling media or energy put into the system by running at higher speeds.
I started a second run using magnesium turnings which were purchased. Unfortunately, these came coated with some sort of machine oil which, aside from
smelling awful, seems to hinder the reaction.
Currently I'm modifying the drive shaft size on the rock tumbler to increase CPMs (should be able to get up to 60-90CPM) and also have some 0.5 inch
stainless steel ball bearings on the way. In the coming weeks I'll perform a third run using magnesium from the fire starters and the modified ball
mill with stainless steel media. In regard to gas build up, I'll likely "burp" and flush the jar with nitrogen from time to time. Additionally I'm
extracting isopropylamine from weed killer to extract any produced borohydride. As far as I can tell, The isopropylamine shouldn't dissolve or
interact with the reactants or the produced MgO (though my research is only cursory at this point).
I'll post information/pictures about this third run when I get it started.
[Edited on 1-1-2022 by tyro]
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DocX
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Wow, great to hear and good work!
I was actually not aware of the RPM and media used in the ball milling, and was also just looking to use a regular tumbler. However, reading this (and
the really badly written article) I'm thinking about possibly making a ball mill from a washing machine motor I have lying around waiting for a
project. That should be able to produce the 1000 RPMs needed.
But I never ball milled at those speeds, I have a hard time seeing how any tumbling whatsoever will occur inside the drum? Won't the balls just be
smeared onto the barrel wall from the centrifugal force?
My guess is the pressure build up is foremost from H2 gas. This concerns me somehow, since I would basically be tumbling a pressurized H2 bomb. What
are your thoughts on this?
Also, I would probably use magnesium powder when/if I give this a run. Any reason you opted for turnings? Powder is readily available as a
pyrotechnic supply here in the EU (so far, at least ... If you're in this part of the world, do check out Polish PyroGarage). They always deliver on time, have good communication and an impressive product list ). Like I wrote, I'd love to use aluminum powder
since I'm already stocked on this, but I'm not comfortable with trying things outside of the box at my first run.
And then there's the question of purifying and identifying. Not much use with an unidentified mixture of salts after the run, is it? I would probably
use absolute ethanol treated with an appropriate amount of NaOH. This would eliminate all the unreacted borax and carbonate, and the borohydride would
be stabilized by the alkalinity and hopefully not hydrolize. I haven't checked out all the possible intermediates yet, but as a first washing i'm
thinking that would probably be optimal.
When it comes to identifying i'm unsure. Possibly just try and ignite it or dump some in slightly acidic water to see if it reacts violently?
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tyro
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The authors did not mention the type of mill being used. For 1000RPM... I have a feeling this might be a planetary or some other specialty mill. I
would imagine, as you do, that those speeds to be problematic in a simple rotating mill, though a lot of this is new to me.
H2 does sounds right after re-reading the article and doing some thinking. The question here is, what are the kinetics of adsorption of hydrogen on
the magnesium surfaces in this system? All the papers I've read where MgH2 is prepared in a ball mill seem to indicate something like 10 bar required
for the H2 pressure. But these are using Mg and an externally provided atmosphere of hydrogen, and not generating the H2 in situ. It's not clear to me
if the H2 produced from Mg + Mg(OH)2 -> MgO + 2MgO + H2 needs to reach some critical pressure in the mill for the MgH to form, or if it would be
consumed relatively quickly. Safety concerns aside, this makes me question if the jar "burping" will be detrimental to reaction progress.
The turnings were chosen since I had a bunch of those camping fire starters lying around and it was easy enough to get turnings off with a drill. I
certainly could go for powder though. Perhaps some part of me was also thinking that it would prevent the reaction from proceeding too quickly
initially, and perhaps add some safety to the fact that this is being done with crude tools.
For purifying - Aren't carbonate salts slightly soluble in EtOH? Perhaps the small amount which would come over would be a non-issue or able to be
removed later. Additionally, might magnesium ethoxide form from any unreacted Mg? Perhaps the kinetics are slow enough that this isn't too much of an
issue either.
Were you thinking of just testing out the ethanolic solution as is, or trying to crash out the borohydride, say with cold isopropyl alcohol?
I was trying to think of ways for purification using easily acquired solvents. Initially I was considering isopropyl alcohol in a soxhlet, but this
seems too reactive. I noticed on the wiki here for NaBH4, that toluene is listed under the solubility section, but I failed to find any info to
confirm this. Isopropylamine was chosen since it seems to be the industry standard and is not terribly difficult to produce OTC.
I do have some borohydride on hand as a reference in this endeavor, so perhaps some can be spared to investigate purification strategies. Open to any
suggestions.
With regard to identification - Observing reactivity was along the lines of what I was thinking too. Perhaps also measuring the volume of gas produced
when hydrolyzing the borohydride?
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DocX
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I found an account of materials used in the much better written original article that has a detailed experimental section:
The mechanochemical reaction
was conducted by ball milling mixtures in a shaker mill (QM-3C, Nanjing, China) at 1000 or 1200
cycles per min (cpm) under Ar and ambient temperature.
So a shaker type Ball Mill ... I never heard of it before, but from the name and google implies that it's a rocking motion produced rather than a
rotational. This is something else altogether.
Also:
"After ball milling, the product mixture was first extracted by 20 mL ethylenediamine (C2H8N2,
purity: ≥99%, Sigma-Aldrich) and filtered through a polytetrafluoroethylene (PTFE) membrane
(0.25 μm) in a glove box (MIKROUNA, China) with the oxygen and water concentrations below
0.1 ppm"
So ethylenediamine.
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tyro
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Nice find!
These high energy/planetary mills are not cheap! I'd like to continue pursuing the rock tumbler, as it would be interesting if it's possible to use
off the shelf components, even if it takes a good while longer. These jars cannot hold any substantial pressure, so venting is a must. I imagine
there'd be a substantial effect on yield if the gas buildup is mostly hydrogen. I'll continue reading to see if I can understand the hydrogen
absorption mechanics better; but in the end experimentation is needed.
One concern I've been wrestling with is the risk associated with milling magnesium. From several accounts, it seems that this can be really dangerous
if the particle size gets too small and there isn't controlled oxidation to form a passivation layer. Initially I've been thinking that the borax and
carbonate would help to provide a controlled oxidation, but I can't help to wonder if this would become problematic in the later stages of milling as
particle size gets smaller. There was an account described where milling magnesium and carbosil (SiO2) resulted in a nasty accident in another thread:
https://www.sciencemadness.org/whisper/viewthread.php?tid=14...
Perhaps someone can chime in with thoughts with regard to this specific mixture?
Ethylenediamine does look like a good solvent. Though it seems most amine solvents should work to varying degrees. Page 9 on this brochure has a table
of solvent solubilities: https://ecochem.com.co/pdf/Hydrifin%20Brochure.pdf
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monolithic
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Quote: Originally posted by DocX  | | When it comes to identifying i'm unsure. Possibly just try and ignite it or dump some in slightly acidic water to see if it reacts violently?
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https://sci-hubtw.hkvisa.net/10.1021/ac60071a041
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DocX
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Yes. This worries me too. I have been fooling around quite a bit with pyrotechnics, and Mg powder is one of those things you always treat with the
utmost respect. It's a very potent fuel. I would normally never ball mill anything with a metal powder.
so even if the jar doesn't contain any oxidizers, not even oxygen, I would be very weary as long as it was running, or when I was about to open it ...
It also contains any number of projectiles in the form of ceramic or steel balls.
So let's review: we have a tightly sealed container full of very flammable gas, steel balls and a really potent explosive fuel, that has been running
for something like two weeks with possible side products being produced through shedding of the milling media or the container reacting with Mg, or
intermediates, or something ... and then I'm supposed to bend over it, pick it up and *pssshhht open it to let oxygen in?
I am Jacks growing state of concern.
My hat off once more to you sir for already doing this. You have balls the size of very large milling medias.
[Edited on 20222222/1/2 by DocX]
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DocX
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Thank you! Yes, the potassium iodide titration is actually accounted for in the original article. It was the authors choice of quantifying
NaBH4.
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crow6283
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| Quote: Originally posted by DocX |
Yes. This worries me too. I have been fooling around quite a bit with pyrotechnics, and Mg powder is one of those things you always treat with the
utmost respect. It's a very potent fuel. I would normally never ball mill anything with a metal powder.
so even if the jar doesn't contain any oxidizers, not even oxygen, I would be very weary as long as it was running, or when I was about to open it ...
It also contains any number of projectiles in the form of ceramic or steel balls.
So let's review: we have a tightly sealed container full of very flammable gas, steel balls and a really potent explosive fuel, that has been running
for something like two weeks with possible side products being produced through shedding of the milling media or the container reacting with Mg, or
intermediates, or something ... and then I'm supposed to bend over it, pick it up and *pssshhht open it to let oxygen in?
I am Jacks growing state of concern.
My hat off once more to you sir for already doing this. You have balls the size of very large milling medias.
[Edited on 20222222/1/2 by DocX] |
I think this could be mitigated by instead of just flushing the tumbler with Nitrogen, to evacuate it with a vacuum pump, fill with nitrogen, spin it
a couple of times, evacuate again and then fill it with nitrogen. This should probably be repeated a couple of times actually.
It would not be that difficult to rig up a three way valve for this including pressure gauge or combination vacuum + pressure gauge. This would allow
an easy way to bleed off excess pressure as well without having to fully open the apparatus. Stick it behind a blast shield if you’re that worried
about it.
[Edited on 2-1-2022 by crow6283]
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tyro
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crow6283 - Those are good ideas.
I think the concern is around how reactive magnesium is when it's super fine. In the above mentioned incident, it was speculated that the magnesium
was reactive enough to take oxygen from the SiO2; though I don't recall if the mill was purged or not; perhaps the reaction was initiated by
atmospheric oxygen and then further fueled by the oxygen in the silicon dioxide.
In any case, the stainless steel media I received today loads my cheap-o rock tumbler down too much to be of use. At the moment I'm considering
building a custom rotary tumbler with pressure relief, pressure gauge, gas inlet, and possibly some sort of temperature monitoring. Jar material might
be PVC (clear to see what's going on?), though I have my doubts on if this material makes sense. Schedule 40 PVC should be able to take max pressure
of ~140 PSI which, depending on vessel and batch size, the end methane pressure should be well below; however, I'm unsure of what the H2 pressures
might reach at any given point. Most DIY tumbler projects I've come across are rotary style, but I did see one DIY vibrational tumbler setup on
YouTube. All these start looking pretty loud too, perhaps a blast shield and soundproofing together would be in order.
So much for a super off-the-shelf approach! I was hoping to adapt this procedure in an economical way; but the cost and perceived risk are seeming to
climb. In working to test out the method in this paper, do other care to see economy? I know borohydride is relatively easy to acquire, so maybe this
isn't a huge consideration.
Anyone here have experience with or built a high-energy vibrational or planetary ball mill?
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DocX
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| Quote: Originally posted by tyro | | crow6283 Jar material might be PVC (clear to see what's going on?), though I have my doubts on if this material makes sense. |
I don't know ... that was the material used in the incident you linked. And in the comments, some people speculated that powdered PVC had a part in
the bada-boom.
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tyro
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| Quote: Originally posted by DocX | | Quote: Originally posted by tyro | | crow6283 Jar material might be PVC (clear to see what's going on?), though I have my doubts on if this material makes sense. |
I don't know ... that was the material used in the incident you linked. And in the comments, some people speculated that powdered PVC had a part in
the bada-boom. |
Hmm.. scratch that then.
I came across a video, without much other information, where someone built a vibratory ball mill. The design doesn't seem too complicated, but
definitely need more research.
https://www.youtube.com/watch?v=yV6UHPeNco8&t=6s
Probably won't get around to actually doing anything substantial this month as I'll be traveling.
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Nitrous2000
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| Quote: Originally posted by crow6283 | | Some welding supply shops have Nitrogen as well. Comes in a variety of sized tanks. Basically you ‘rent’ the tank and then can bring it back to
‘fill it’ (swap it out for a full one) as often as you like. The rental on a K tank (large size, up to your waist) might be as much as 200 USD,
refilling could vary might be ~40 USD. You’ll need a regulator as well. Different tanks have different fittings and require different regulators
depending on what they are for. Nitrogen and CO2 regulators are interchangeable and should be available from the shop. |
keep an eye out on eBAY for a nitrogen membrane separator. They sell out fast and are either ridiculously expensive or gone quickly. The other is
the Nitrogen Fill gun that you just attach to compressed air and get ~95+ nitrogen gas out.
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crow6283
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| Quote: Originally posted by Nitrous2000 | | Quote: Originally posted by crow6283 | | Some welding supply shops have Nitrogen as well. Comes in a variety of sized tanks. Basically you ‘rent’ the tank and then can bring it back to
‘fill it’ (swap it out for a full one) as often as you like. The rental on a K tank (large size, up to your waist) might be as much as 200 USD,
refilling could vary might be ~40 USD. You’ll need a regulator as well. Different tanks have different fittings and require different regulators
depending on what they are for. Nitrogen and CO2 regulators are interchangeable and should be available from the shop. |
keep an eye out on eBAY for a nitrogen membrane separator. They sell out fast and are either ridiculously expensive or gone quickly. The other is
the Nitrogen Fill gun that you just attach to compressed air and get ~95+ nitrogen gas out.
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That’s very interesting is never seen those before. I’m not really sure what the use would be though. I’ve used nitrogen from cylinders in the
past for running reactions under or for storage of air sensitive compounds.
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macckone
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Another name for a planetary ball grinder is vibratory tumbler.
The difference in nomenclature accounts for price but not for effectiveness.
The vibratory tumblers usually use a 1750 rpm motor.
https://www.harborfreight.com/5-lb-metal-vibrator-tumbler-67...
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Mateo_swe
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I looked into making Sodium Borohydride using a DIY electrochemical cell some years ago but i dont know if it would actually work.
The project never made it into actual experiments but it was a very intresting idea, maybe i can find my notes and papers about it.
It used a electrochemical divided cell with a (correction: not anion it was a cation membrane) cation-exchange membrane and borax was in the
electrolyte if i remember correctly.
I remember this project because i searched for a cation exchange membrane that could withstand very high pH and i actually ordered such a
cation-exchange membrane from Fumatech online store and i still have it laying around somewhere unused.
The goal of the idea was not only to make NaBH4, but also to make it very cheap so it could be used as a hydrogen storage medium.
I post info if i can find it on my old computer.
Maybe someone with knowledge of similar things can comment if such an idea could be a possible way to make NaBH4.
[Edited on 2022-3-8 by Mateo_swe]
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tyro
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| Quote: Originally posted by Mateo_swe | I looked into making Sodium Borohydride using a DIY electrochemical cell some years ago but i dont know if it would actually work.
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Interesting! Was this your reference // inspiration?
https://doi.org/10.1016/j.ijhydene.2010.01.129
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Mateo_swe
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These PDFs and similar inspired me.
Attachment: US3734842 - Electrolytic process for the production of alkali metal borohydrates.pdf (893kB)
This file has been downloaded 432 times
Attachment: Review of Chemical Processes for the Synthesis of Sodium Borohydride.pdf (404kB)
This file has been downloaded 1031 times
Attachment: US20050224365A1 One-step electrosynthesis of Borohydride.pdf (481kB)
This file has been downloaded 491 times
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Texium
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Thread Moved
17-3-2022 at 07:06 |
clearly_not_atara
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This high speed ball milling tek came up on some other forum years ago. Turns out fast ball milling is hard.
But IIRC you can make borohydride by milling with magnesium silicide, Mg2Si. This is a reasonably accessible precursor methinks.
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mysteriusbhoice
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you know this is gonna sound wild but if you are producing borohydride in situ why not just shove in your reactant to be reduced in with this
concoction of borax and magnesium and you can potentiallly have a setup where this reduction occurs as the borohydride is formed in small amounts and
you can simply extract your product at the end.
say you wanna reduce a nitro group compound just shove it in there and see if you have an amine at the end.
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tyro
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I'm in the process of prototyping a vibrating ball mill using (relatively) readily available parts, which will have the ability to charge an inert
atmosphere and monitor pressure buildup.
The milling container is constructed out of a 3"W x 4"L stainless steel tri-clamp tube (this is used for brewing equipment). The tube is sealed with
PTFE seals and two stainless steel end caps with 1/4" NPT fittings. The end caps are held in place with purportedly high-pressure clamps. To each of
the NPT fittings on the end caps, there will be pressure snubber adaptors (stainless steel mesh), which will serve to keep the milling media and
material out of the inlets. One side will have a pressure gauge, and the other an overpressure relief.
The milling jar sits on a spring-supported platform which has a vibrating motor intended for concrete work on one side, and a counterweight on the
other.
Currently I'm working to optimize placement of components for optimal motion of milling media inside the jar. Afterwards, I'll move on to running
tests to verify the vessel can hold pressure in operation, and also that the overpressure works as expected.
This thing is *extremely* loud. It definitely will need to have some sort of noise-reducing enclosure built for it.
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Mateo_swe
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How much pressure could such an stainless steel tri-clamp tube with the high-pressure clamps and PTFE seals take before failing?
The PTFE seals should be able to withstand quite high temps as well.
Very interesting, such a tube could be used in many DIY ideas.
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