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Author: Subject: Confusion about Aluminium Powder Safety
nimgoldman
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[*] posted on 19-6-2018 at 09:48
Confusion about Aluminium Powder Safety


I wanted to add Al to my collection of metals.

Unfortunately, I realized I obtained an extremely fine powder (5-7 microns). I am now afraid of the fire hazards of the powder as it is said to self-ignite on contact with air (!).

I read the MSDS (from 2 vendors) and safety brochures, but cannot find any proper handling techniques tutorial. Can you point me on some relevant documentation?

The vendor recommends handling and storing Al powder under inert atmosphere. This is beyond capabilities of my humble lab.

The powder came in a plastic container with screw cap, nothing fancy, not even truly hermetically sealed.

I store other powders in a dark glass bottles with ground glass stopper but now I am afraid this might not be a good idea as glass can store electrostatic charge (but so does plastic) - maybe the ground glass could work as an ignition source?

I wear all the protective equipment (incl. face shield) as well as having fire extuinguisher at hand (ABC dry powder). But still this Al powder scares me...

I have a glove box, not the sealed one but I could possibly fill it with CO2 gas when handling the Al powder. Is this overkill?

Thanks for any advice and help. I have not opened the container yet so I can return it to the vendor if necessary.
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[*] posted on 19-6-2018 at 11:52


Unless you mix this powder in a ratio of 70:30 with Potassium perchlorate and hold a match to it?

You are probably not going to die in a powdered metal fire

No. It won't spontaneously combust in air under normal conditions.

I have handled a good deal of Aluminum powder, from flake and sherical Al powders rather finer than yours, on up to 10 micron propellant grade spherical on up to coarse flakes and spherical or granular of 30 microns or even larger.

All were received in packages which had air in them, and all had the usual surface layer of Aluminum oxide. Perhaps a freshly milled sample made in an airtight container would be different.

None of it was handled or stored under inert gas.

None of it ever spontaneously combusted.

I have a sample of nano Al which ALSO failed to ignite on exposure to air. It IS rather frisky when mixed with oxidizers, however.

[Edited on 6-19-2018 by Bert]

[Edited on 6-21-2018 by Bert]




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[*] posted on 19-6-2018 at 14:16


Thanks.

I thought it's not such a big deal as from the videos of people experimenting with it - it took quite a bit of agitation and flaming to ignite the stuff.

I won't mix it with anything making it more dangerous. I plan to use it as a reducing agent, for generating hydrogen, some experiments with amalgamation etc.

The atmosphere here is not super humid also.

I guess the warning label referred to an extreme case of leaving the powder in open air, letting it dust all around and waiting for ignition source as the dust-air mix is seemingly the dangerous stuff - not the powder itself.

I will therefore use the glass storage bottle, maybe put a bag of dessicant in there just to feel good and sleep well.

It will sit in secondary container far from other flammables though.
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[*] posted on 20-6-2018 at 10:39


I have 5 kilograms of fine alumminium powder (5 microns) stored at 02 glass bottles for three (03) years and nothing happened.

This story about it's pyrophoricity is just a legend, I guess. No trouble if stored at a cold and dark room. I think the related accidents may be caused by large volumes of oxidant agents impurities in it.
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[*] posted on 20-6-2018 at 11:53


If you blow it into a hot flame it'll burn nicely.

Keep it in the bottle and it won't.




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[*] posted on 20-6-2018 at 12:54


Well, it is possible for problems to arise, but usually not.

Grain silo kind-of-stuff.

The silo is used for generations, without problems.

One day, The grain and its coating are at just the perfect moisture content and temperature, the air temperature and humidity are just right. The silo is being filled, grain is falling, and the air is full of fine organic particulates.

Unexpectedly, there is a small but unfortunate static discharge, instantly followed by a resounding explosion.

The other guys present here, are much more expert regarding the actual probability of such explosions. Personally, I'd avoid scenarios where that finely powdered Aluminum is suspended in air "silo style", near a possible ignition source.

I try to know what kinds of things can happen, and I try to think things through. Seems to me, this stuff will be pretty safe, until you inadvertently create "the perfect storm".

Don't.

https://www.youtube.com/watch?v=BXjwinZEPII

https://www.youtube.com/watch?v=4hS6IGO2tdA

Oh, another point. One member suggested that in the event you are not injured by the initial Metal fire itself, you could still suffer injury. Apparently, some Metals may emit very high levels of UV during combustion. Bad "Sun burn" problems.

[Edited on 20-6-2018 by zed]

[Edited on 20-6-2018 by zed]

[Edited on 20-6-2018 by zed]
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[*] posted on 21-6-2018 at 02:07


I would store it in a glass bottle with good seal. Do not add anything else, just use a well-dried bottle, no desiccant or other stuff in there. I store my Al-powder that way already for many years. No problem at all. Even my LiAlH4 and LiH are stored in that way and they are still as good as when I purchased them.



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[*] posted on 21-6-2018 at 04:23


I don't think the fire catching story is a complete legend, metal powders can catch fire in a semi-explosive manner when ball-milled in a very fine state in an airtight container upon opening. But if the container is slightly not airtight or a bit of oil is added this should occur.
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[*] posted on 21-6-2018 at 05:18



Quote:

Oh, another point. One member suggested that in the event you are not injured by the initial Metal fire itself, you could still suffer injury. Apparently, some Metals may emit very high levels of UV during combustion. Bad "Sun burn" problems.


This is more of a hazard to your vision, if thermal dammage from IR isn't happening as well.

From personal experience, I would worry more about the IR emission.

Another do as I say, not as I did Bert story: Wearing shorts about 3' feet from a good ammount of burning Ti powder once gave me second degree burns on the side of my leg towards that fire, with NO fireball/hot gas contacting my skin. Just the flash of heat. Really sucked, that. No scars, but very painful for a couple of days, about a month for new skin to cover the blistered area.

Oh, and I learned the valuable lesson that if one has any option, ALLWAYS ignite anything you can remotely. In a hurry to dispose of a failed effect, I didn't care to dig out an electric match and an electrical firing rig already packed away at the end of the day, so I got out 3' of black match. Should have given me over 20 seconds of time. But a spark almost immediately jumped to the other end while I was still turning to walk away from the burn. FWOOSH.




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3. Mention anything you have learned from your target.
4. Only then are you permitted to say so much as a word of rebuttal or criticism.

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hissingnoise
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[*] posted on 21-6-2018 at 05:39


Quote: Originally posted by Tsjerk  
I don't think the fire catching story is a complete legend, metal powders can catch fire in a semi-explosive manner when ball-milled in a very fine state in an airtight container upon opening.

Within a running mill, the newly exposed metal surfaces are oxidised as they are formed and the oxygen inside is quickly used up so that on opening, a large amount of unoxidised Al is present in finely divided form ─ this oxidises on contact with air and the powder inflames with great vigour...

Al with its protective oxide layer cannot spontaneously ignite.



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21-6-2018 at 06:20
hissingnoise
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[*] posted on 21-6-2018 at 06:24


Quote: Originally posted by D.Orthp  

That wound would heal in about a week had you reduced other activities, especially eating. Wounds and pains dissapear much faster when we do not eat or drink or do anything.

My current cat who adopted me and my SO many years ago likes to treat my hand as a live toy and I'm always pleasantly surprised at how quickly my scratches heal...

This, of course, is down to my "chronic" cannabis smoking!

I kid you not...



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[*] posted on 21-6-2018 at 06:57


Quote: Originally posted by hissingnoise  

My current cat who adopted me and my SO many years ago likes to treat my hand as a live toy and I'm always pleasantly surprised at how quickly my scratches heal...

This, of course, is down to my "chronic" cannabis smoking!

I kid you not...



lol - it is because you are a human being. They heal fast.

Love cats and kittens. A lady I knew in her 80s scratched her arm on a thorn... it was still bleeding a week later. I think we heal less fast as we get older.

Whoops - just realised this is off topic and was split. Sorry.

Couldn't let that go though - humans heal fast anyway. It's natural.




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[*] posted on 21-6-2018 at 07:11


I remember some female swimmer attempting some long distance swim in the ocean and the photos of sores after days in the saltwater. But it was remarked how quickly the affected skin healed, whereupon she attributed it to being in top physical condition.
It comes to mind that the older you get, the longer it can take to heal from an injury. And if you were low on vitamin C, maybe fasting wouldn't be the best option or rather there may not be absolute truths for healing in all cases. That said, fasting could very well be the best option for many ills or heightening the senses.
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AJKOER
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[*] posted on 23-6-2018 at 16:16


I suspect aluminum alloys present a greater risk of explosion in air than pure Al.

Logic: an aluminum alloy powder may invite a higher potential for electrostatic discharge, which could trigger an explosion of metal dust in air. This is due to different metals forming corresponding regions of positive and negative charges, with an excess charge buildup leading to a possible problematic discharge.

The presence of an electrolyte (like water vapor from increased humidity) is a factor.

Many aluminum applications appear to involve aluminum alloys, so known your Al source!
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hissingnoise
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[*] posted on 24-6-2018 at 11:38


Quote: Originally posted by AJKOER  

Logic: an aluminum alloy powder may invite a higher potential for electrostatic discharge, which could trigger an explosion of metal dust in air.

Any machinery which could generate metal powders must be very well earthed as a safety measure ─ and dry air is much more prone to static-buildup as moist air normally dissipates static charge to earth.



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[*] posted on 25-6-2018 at 14:29


Yes Hissingnoise, there is an opinion at this source confirming your thoughts (see https://www.quora.com/Why-does-static-electricity-occur-more... ).

However, also mentioned is:

'When it is humid, static discharges more often and at lower voltages because the moist environment is more conductive."

which is in line with my thoughts. So, a critical assumption is a higher voltage electrostatic discharge (ESD), in general, required to initiate an explosive mixture? Perhaps yes, but note ESD in terms of volts are generally high to start (see https://www.esda.org/about-esd/esd-fundamentals/part-1-an-in... ). Further, on the topic of the effect of humidity and possibility of significantly lowering (or not) of the voltage and associated effects on explosive initiation, I did come across an actual report of a sugar dust factory explosion in Georgia, USA (see http://www.slate.com/articles/news_and_politics/explainer/20... ) in February (the 4th highest month in average rainfall, see https://www.google.com/imgres?imgurl=http://dssni5kiwicxb.cl... ).

My perception of Georgia is one of usually higher average humidity (in fact, based on morning relative humidity, second only to Florida, see https://www.currentresults.com/Weather/US/annual-average-hum...). So perhaps caution is probably advisable, in general, even in more humid conditions :(
--------------------------------------------

Interestingly, the same article references a grain elevator explosion in June in Kansas (also surprisingly high on the relative morning humidity rankings by state), which is a warmer month with higher humidity than winter months (one source puts average rainfall highest for Kansas in June, see https://www.google.com/imgres?imgurl=http://dssni5kiwicxb.cl... ).
--------------------------------------------

An examination of a likely ESD N2O gas explosion suggested, to quote:

"Electrostatic discharge (ESD) has surfaced as a probable hazard for oxidizer flows over polymeric seals infused with high concentrations of N2O"

Source: http://www.dtic.mil/dtic/tr/fulltext/u2/a489459.pdf

The N2O study, in the particular case of Laughing gas, suggests voltage associated with an ESD (which actually has more volts than a light switch, see https://www.esda.org/about-esd/esd-fundamentals/part-1-an-in...) was sufficient!

[Edited on 26-6-2018 by AJKOER]
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[*] posted on 25-6-2018 at 16:00


In North Florida you can get low humidity days if the wind is out of the north. February 8th for an example humidity was 27% at one point during the day.
68 °F Sunny. 9 mph ↑ 27% 30.31 "Hg 10 mi

April 11 2018 it was 25%.
78 °F Sunny. 7 mph ↑ 25% 30.13 "Hg 10 mi

[Edited on 26-6-2018 by Morgan]
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[*] posted on 26-6-2018 at 00:27


Electrostatic charges don't have anything to do with this. Oxide covered aluminium doesn't burn, and oxygen is enough to make non-oxidized aluminium burn. So the lack of oxygen during milling is enough to make the aluminium burn. You don't need an electrostatic charge.
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[*] posted on 28-6-2018 at 14:49


Quote: Originally posted by Tsjerk  
Electrostatic charges don't have anything to do with this. Oxide covered aluminium doesn't burn, and oxygen is enough to make non-oxidized aluminium burn. So the lack of oxygen during milling is enough to make the aluminium burn. You don't need an electrostatic charge.


See 'Dust Explosion during transfer of Aluminum Powder (Static Electricity)' at http://www.safteng.net/index.php/free-section/safety-info-po... , and more generally, comments at www.dtic.mil/get-tr-doc/pdf?AD=ADA507249 .

Note, I do believe that there are likely several paths to initiation of an explosive dust/air mixture (per the last reference, resulting from very low initiation energies due to either low ignition temperature or low electrostatic discharge initiation energies, or possibly high chemical reactivity with, I suspect, the likes of water vapor resulting in solvated electrons and H2 gas products, as in the case of Mg and Al dust), consisting of, for example, sugar, metals, saw dust, or also generally solid powders which on heating or sunlight exposure or due to chemical reactivity release combustible gases or initiate an explosive chain reaction.

[Edited on 28-6-2018 by AJKOER]
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Tsjerk
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[*] posted on 28-6-2018 at 20:13


I know I shouldn't reply to you... But where did you pull solvated electrons from?
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[*] posted on 29-6-2018 at 03:00


Quote:
But where did you pull solvated electrons from?

Is that a serious question, Tsjerk?


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[*] posted on 29-6-2018 at 10:15


Highly anodic metals (like Mg, Al, Zn, Fe,..) can create a metal-air battery. The generated current can likely form some partially solvated electrons to varying degrees depending on the medium.

Interestingly, it is claimed that a mix of H2 and N2O is prone to chain reaction initiated explosion from a hydrogen radical (.H). The latter is easy formed, for example, by the action of solvated electrons acting on any H+ (from say water). An illustrative reaction sequence:

e- + n H2O = e-(aq)

H2O = H+ + OH-

e-(aq) + H+ = .H (see https://pubs.acs.org/doi/abs/10.1021/ba-1965-0050.ch017)

.H + .H = H2

Interestingly, I suspect that Laughing Gas can also react indirectly with solvated electrons that have been converted to .H and surface adsorbed on a select metal (see https://patents.google.com/patent/US6296754B1/en and Eq 5 at https://books.google.com/books?id=1etfSdk55SYC&pg=PA818&...):

.H (surface adsorbed) + N2O = N2 + .OH

H2 + .OH --> .H + H2O

Sources claim that an explosive chain reaction could follow in the presence of .H (for details, see, for example, https://www.osti.gov/biblio/6523721 and historic work at https://www.jstor.org/stable/2935494?seq=1#page_scan_tab_con... ).

The solvated electrons above can be produced by the action of, for example, Aluminum on OH- where the Al is also known to surface adsorb the hydrogen radical. Also, the action of light on select metal oxides present as impurities (like TiO2, MgO, ZnO,...) can also release electrons.

Bottom line, what appears to occur is that the mix of H2/N2O in the presence of impurities may explode unexpectedly producing a dangerously high temperature.

I further suspect, in addition to ESD, the mixing of H2 (or CH4 or other known explosive gas formed by the action of heat or light) with O2 can also be made more likely to explode without an apparent ignition source by a radical chain reaction process, but this capricious behavior is more subdued with O2 than with N2O. Now, sources (see for example, https://www.iitk.ac.in/tkic/workshop/gian/2/content/GIAN-Lec... including discussion with methane and also Table 1 where radical formation were induced by thermally shocking a Ar/H2/O2 mixture at https://www3.nd.edu/~powers/ame.60636/maas1988.pdf ) discuss high temperature .OH induced formation, but I would argue per my discussion above, anodic metals, photo-active metal oxides,..., may supplant the high temperature radical formation paths.

[Edited on 30-6-2018 by AJKOER]
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Tsjerk
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[*] posted on 30-6-2018 at 00:00


Ok, but where are the hydrogen and the N2O coming from? I thought we were talking about oxidation of metal powders in oxygen...
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[*] posted on 30-6-2018 at 13:15


The discussion touched on the possible influence of humidity, in general, leading to dust/air explosions.

The level of water vapor appears to inversely impact the magnitude of ESD.

However, while high levels of moisture may lower the likelihood of a high electrostatic discharge, this may be offset, I suspect, by the chemical reactivity factor, especially in the presence of anodic metals (like Mg, Al, Zn,...) and water. The latter metals can produce hydrogen from water, which increases with the anodic index of the metal and also with a reduction in particle size. Oxygen and anodic metals with an electrolyte (like water, CO2 and any dissolved metal salts) formed the basis of electrochemical cells (metal air batteries). The latter can create electrons, partially solvated electrons, and possibly therefrom radicals. The latter can lead to chain reaction explosions as study in the case of H2/N2O (and H2/Cl2 in UV light), and with methane, CH4/N2O (and CH4/Cl2/UV). Interestingly, the reference on the sugar factory explosion suggested that the volatile agent was a product formed from heating of the sugar.

The study of N2O/H2 mixtures appears to demonstrate more sensitivity to the creation of radical chain reaction explosions than corresponding H2/O2 mixtures. However, this does not imply, in my opinion, the complete lack of risk for this path in dust air explosions.

Here is a source that briefly on p. 41 explores the topic "A radical chemistry explosion?" occurring with photolysis at http://acmg.seas.harvard.edu/education/eps133/Jacob_atmchem_... where the role of light may be underestimated given its ability to introduce radicals.

[Edited on 30-6-2018 by AJKOER]
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