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blogfast25
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From what I understand: to limit the sodium's access to the water.
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j_sum1
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I intend to try this today. I will let you know how it goes.
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j_sum1
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Ok. Done. It works. It aint no hoax.
I used a 9cm plastic petri dish filled with water and an 11cm filter paper on top. Surface formed a shallow dish-like shape. Lumps of Na were around
0.3 cm3.
Similar observations on three runs:
Reaction slow at first. Fizzing at the lower surface. Gradual melting.
puddle of yellowish liquid appeared under the metal. Presumably high concentration NaOH.
Na melted and formed a sphere which skated around the surface a bit. Not the same mobility as normal Na on water.
Na burst into flames. 2-3cm yellow/orange flame. Copious clouds of white fumes. Continued to skate around the surface.
Flame extinguished. Na was still spherical and appeared grey, almost black. This lasted less than two seconds.
black colour faded and material appeared to get hotter, glowing red before clarifying into a transparent droplet. Still some movement on the
surface of the paper.
sudden pop / explosion and the material broke up into small pieces / disappeared. Observations varied at this point. The smallest piece stayed
in the transparent stage longest and when it exploded, none was visible. One of the pieces popped into numerous smaller pieces, some of which landed
on the filter paper and then popped again. One piece had a more violent explosion and left a large number of smaller pieces scattered over the floor
of the fume cupboard.
These smaller pieces were stuck fast to the tiles. I tried to dislodge them with tweezers but couldn't move them quickly enough. After a
matter of 20 seconds or so, all but the largest had (presumably) absorbed water from the atmosphere / splashes on the tiles and formed a slurry
reminiscent of deliquescent NaOH.
Here is my tentative assessment of the situation.
The reaction is slower than normal due to the limited access to water.
Heat of the reaction is sufficient to melt the Na.
Once the Na reaches a temperature where it can ignite in air it does so.
At this point, there are two simultaneous reactions occurring.
(1) Na burns in air leaving particulate Na2O fumes
(2) Na continues to react with water at its lower surface. Critically, the reaction product has nowhere to go. There is insufficient available water
to dissolve the products and insufficient movement of the water to transport the sodium hydroxide away. Temperature is high enough for the sodium
hydroxide to be molten, so above 318°C It may also contain some water. (Likely on reflection.)
This is where I will get hazy and throw wild conjectures around.
Due to a combination of density, surface interaction between the two molten species, and temperature gradients the globule
forms into two concentric spheres: the inner sphere containing NaOH melt and an outer skin of metallic sodium. (Nice hand-waving there. Did you
notice? I would conjecture that the surface tension property is the critical one here.)
At some stage the kinetics do not favour further combustion of sodium in air. Whether this is because of impurities (oil?) the thin-ness of the
layer, some kind of interaction with the NaOH or what, I don't know. The flame extinguishes.
The remaining sodium continues to react at the surface between the two phases -- either reacting with trapped water or perhaps forming some
Na2O. The temperature rises and the globule changes appearance from black to glowing red to transparent when all of the sodium is gone.
At this stage there is a Leidenfrost effect. There is a hot droplet of NaOH and any water at the interface with the paper is turned to steam.
Then, the droplet cools and or encounters some water that it has insufficient energy to vaporise. The Leidenfrost effect disappears and this
leads to a runaway increase in contact between the NaOH and the water.
At this point, the hot NaOH begins to hydrolyse exothermically. This results in a steam explosion that shatters the droplet and scatters it in
all directions.
The scattered droplets of NaOH solidify when they strike a cool surface and dissolve quickly when they encounter water -- which is pretty
abundant in the air by this time.
Lots of fun. Definitely worth a try. See how much your observations correlate with mine. And see if we can come up with some feasible mechanism
here.
[Edited]
Potassium works well too. Maybe even better. Lovely skating ball of pink/lilac flame and then a tiny clear mass that shoots all over the place
before it crackles and splatters.
No Lithium on hand at present.
I am going to check out access to a high speed video camera.
Anyone got some rubidium?
[Edited on 2-3-2015 by j_sum1]
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MrHomeScientist
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Awesome work j_sum1! I'm really glad this topic has generated so much discussion and a new experiment. I'm definitely going to try this out myself
when I get a chance. I can try lithium too. I suspect it won't have the same effect, though - much less vigorous reaction with water, which never
leads to explosion no matter how large the piece (in my experience).
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blogfast25
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Excellent. Good write up too. Corroboration is everything.
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Molecular Manipulations
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I wonder if it would be possible to pick up the sphere of whatever it is before it explodes and see if it explodes later without the water. This would
be more proof that it indeed is coulombic explosion and not the result of water being heated rapidly.
I'll give this a go with lithium if time permits, sadly I have only one ampule with a couple grams, and since that my element sample, I'll have to go
through that dreaded process of extracting it from a lithium battery, which I hate.
Anyway I doubt it it'll work with lithium, but who knows? Also only have an ampule of both sodium and potassium, which I won't be breaking...
-The manipulator
We are all here on earth to help others; what on earth the others are here for I don't know. -W. H. Auden
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deltaH
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+1, very nice reporting indeed!
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j_sum1
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Quote: Originally posted by Molecular Manipulations  | I wonder if it would be possible to pick up the sphere of whatever it is before it explodes and see if it explodes later without the water. This would
be more proof that it indeed is coulombic explosion and not the result of water being heated rapidly.
I'll give this a go with lithium if time permits, sadly I have only one ampule with a couple grams, and since that my element sample, I'll have to go
through that dreaded process of extracting it from a lithium battery, which I hate.
Anyway I doubt it it'll work with lithium, but who knows? Also only have an ampule of both sodium and potassium, which I won't be breaking...
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With the set up that I used you could probably flick it into an adjacent container with a glass rod. I would wear good gloves. A premature splat and
300°C molten hydroxide flying around would not be much fun on the skin.
[edit]
Does anyone have the ability to attempt this in an argon or nitrogen atmosphere?
[Edited on 2-3-2015 by j_sum1]
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aga
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Use a filter paper, and maybe just lift it up when the blob starts going transparent ?
Edit :
If that works, set it down on a stack of Dry absorbent paper ..
[Edited on 2-3-2015 by aga]
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Molecular Manipulations
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Yeah I can get nitrogen but I have no sodium. And lithium reacts with nitrogen, but not oxygen. Perhaps I can borrow an argon cylinder from a friend.
I should buy some sodium...
-The manipulator
We are all here on earth to help others; what on earth the others are here for I don't know. -W. H. Auden
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Morgan
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I wonder if any of this could be coming into play? Just an out of the blue thought.
https://www.youtube.com/watch?v=aUt2iYGNnlU
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j_sum1
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I haven't come across Recalescence before, but it seems plausible.
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Endo
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I wonder if a conductive metal screen on top of the filter paper would make a difference.
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aga
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My favourite chem website is offline at the moment, otherwise i'd order a few Kg of Na and find out what this is all about.
Looks like a very interesting area to explore.
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j_sum1
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I am rethinking the mechanisms I proposed. I probably need to look up some numbers, but I think I have something that accounts for most of the
observations and makes sense. More details to come -- realistically over the next few days rather than today.
I am pretty convinced that the transparent material is molten NaOH and not some other product. Na2O doesn't seem feasible.
I am reasonably confident of the concentric spheres idea but now doubt that there is any reaction at the interface between the two materials.
Otherwise, where would the H2 go?
I believe there are a couple of different instances of the leidenfrost effect which are critical to the way the reaction proceeds.
I don't see a case for coulombic explosion of a liquid salt.
The one detail I cannot account for is the flame and more specifically why it extinguishes. I think this is incidental to the transparency anyway
which is why I suggested an inert atmosphere experiment. Better brains than mine might help here.
Anyway, very much looking forward to a few more observations and ideas about what might be happening.
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m1tanker78
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| Quote: Originally posted by j_sum1 | | I think this is incidental to the transparency anyway which is why I suggested an inert atmosphere experiment. |
I can run an experiment with argon but I think that air oxidation is essential to the formation of the molten salt (or whatever it is). I believe the
inert blanket would defeat the purpose here, would it not?
Along those lines, surely there must be a more elegant way to carry this out. Without really thinking it through, I'd impulsively be inclined to try
steam and maybe a water/glycol(?) mixture. There'd be a side reaction with the glycol but, aghh. Something to initiate the burning but moderate the
runaway, I guess.
Chemical CURIOSITY KILLED THE CATalyst.
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woelen
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This is a very interesting observation. The video is good and really shows what happens. I myself am inclined to explain it as follows:
- sodium reacts with water, heat is produced and it melts
- at a certain point in time, the temperature becomes so high that the sodium (and hydrogen form in the reaction with water) ignite
- the sodium burns for some time, becoming red hot
- while the sodium is burning, it also reacts with water at the bottom, forming NaOH
- the NaoH and Na both remain molten, the Na on top, the NaOH at the bottom
- at a certain point in time, the Na is used up, buring stops and what remains is a red hot glowing glass-like blob, which emits red light
- the glass-like blob cools down and becomes transparent
- when the glass-like blob cools down sufficiently, it does not float anymore on the water, but disintegrates and falls into the water. It still is so
hot, that this event leads to a steam explosion.
I could try this myself next weekend, but filming it is more problematic. I need to put my camera quite close to this stuff to get a decent macro
image and I do not want to risk my $400 camera on this. Maybe I can contrive something with a glass window in front of the camera. This is something I
have to work out, before I do any recording. The explosions do not look very powerful, so more than splattering water and NaOH against the glass will
not happen.
[Edited on 3-3-15 by woelen]
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deltaH
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I've got some interesting thermodynamics for you guys:
If sodium is burning in air at least in part, it is not unreasonable to assume that some sodium oxide is formed in the molten drop. It may well be a
solution of sodium oxide and sodium hydroxide. That would certainly add a significant kick of hydration energy when the blob does eventually decide to
mix with water. The deltaH for the reaction:
Na2O(l) + H2O(l) => 2Na+(aq) + 2OH-(aq) at 25°C (T is standard for the heats I used)
is... (drumroll please)... 4586kJ/kg Na2O(l)
That's a little higher than TNT! 
[Edited on 3-3-2015 by deltaH]
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j_sum1
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I generally concur. [with woelen] Except that there seems to be some Na left after the flame goes out and it appears to become hotter at that point.
I am more nervous of the explosion with this than with straight sodium on water even though it seems less vigorous. There are some decent sized (mm)
lumps of molten NaOH that would make a mess of a lens or an eyeball or skin.
[Edited on 3-3-2015 by j_sum1]
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deltaH
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The flame goes out perhaps because when the glob is too hot, the reaction at the interface with water that produces hydrogen slows too much because of
the leidenfrost effect 'lifts' the blob. The sodium on the outside still continues to oxidise with air (flamelessly), forming sodium oxide, which is
why the blob then glows red and the sodium is consumed, aided by the fact that it no longer is physically in contact with water and so partially
insulated (this is perhaps why it doesn't glow before that stage).
I also think the sodium is on top and partially curved, which allows it to react nicely with air.
The final explosion is more severe than a simply NaOH dissolution because it's a Na2O hydration explosion which is much more powerful.... in fact,
similar in energy to TNT, but not a detonation, of course.
******************************************************
If anyone ever conducts this in an inert atmosphere, if my hypothesis is correct, then the sodium cannot oxidise to form sodium oxide and so one is
left only with the reaction of sodium with water. This should be far less energetic and might simply fizz for some time until the sodium is consumed.
Another comparative test might be to try it in oxygen gas, that should proceed very rapidly and would be dangerous, so please take care. In oxygen,
some yellow sodium peroxide might even form in the bead.
[Edited on 3-3-2015 by deltaH]
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Sulaiman
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I just ordered 5x 28g Sodium metal ingots to investigate this phenomenon,
they should arrive in one to two weeks so
hopefully I can do some (limited) analyses,
video and put on YouTube for inspection
Any specific suggestions for experiments so that I can get prepared?
Also, I don't have a sheet of polycarbonate to use as a shield for me and the camera,
does anyone know a reason not to use toughened soda-lime glass?
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deltaH
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I would use safety glass with at least two layers, that way if the glass does shatter for some reason, it stays in one piece held in place by the
laminate and so less likely to cause injury.
As far as my hypothesis of sodium oxide goes, you could also simply burn a tiny piece of sodium on a spatula, then when red hot, drop a drop of molten
liquid into water from close to the surface. This can be compared to doing the same with molten sodium hydroxide.
Please wear thick welding gloves when doing this and behind a screen, even the tiniest spec of molten sodium/sodium oxide/sodium hydroxide would burn
through flesh in a second if it landed there.
EDIT: forgot you need some NaOH if you're burning sodium in a spatula so that you can have a liquid phase for the sodium oxide to dissolve in
(possibly)
[Edited on 6-3-2015 by deltaH]
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j_sum1
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Weigh and video every run. Replace your filter paper with a new piece every time. Try as much as possible to keep the geometry of the reaction
identical each time. Then you can produce some graphs that detail the duration of each phase of the reaction.
Use a pyrometer to get the temperature at various stages of the reaction.
See if you can collect the transparent bead before it explodes and analyse it.
For at least a few runs, collect the NaOH solution from your dish and also extract it from the filter paper (repeated rinsings). Then analyse it to
find out how much NaOH has entered into solution versus how much has gone in other directions.
If you can, attempt a few runs in an inert atmosphere so that you can observe what happens without the flame -- simplifying the situation by reducing
the number of elements in play.
Use a high-speed video camera and see if you can capture exactly what happens during the explosion.
get good at reading phase diagrams and calculating and interpreting the thermodynamics of the situation.
Draw diagrams of what you think is happening. See if you can work out what the exact mechanism is and compare your hypothesis with the data
collected.
At least that is what I would do. I am toying with the idea of suggesting this as a project for my students.
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Sulaiman
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Weigh and video every run. Replace your filter paper with a new piece every time. Try as much as possible to keep the geometry of the reaction
identical each time. Then you can produce some graphs that detail the duration of each phase of the reaction.
........
OK
===
Use a pyrometer to get the temperature at various stages of the reaction.
......
this could be difficult, I'll consider it, probably needs the inert atmosphere,
do you think that a hand held IR thermometer would suffice?
===
See if you can collect the transparent bead before it explodes and analyse it.
.....
no problem
===
For at least a few runs, collect the NaOH solution from your dish and also extract it from the filter paper (repeated rinsings). Then analyse it to
find out how much NaOH has entered into solution versus how much has gone in other directions.
.....
OK
===
If you can, attempt a few runs in an inert atmosphere so that you can observe what happens without the flame -- simplifying the situation by reducing
the number of elements in play.
.....
can you suggest an inert gas that I can (cheaply) buy or prepare?
===
Use a high-speed video camera and see if you can capture exactly what happens during the explosion.
.....
I only have normal video rate cameras but my son is in the video business, I'll see if I can persuade him to help
===
get good at reading phase diagrams and calculating and interpreting the thermodynamics of the situation.
Draw diagrams of what you think is happening. See if you can work out what the exact mechanism is and compare your hypothesis with the data
collected.
.....
OK, learning required.
===
At least that is what I would do. I am toying with the idea of suggesting this as a project for my students.
.....
I'm also considering attaching a fine wire to the sodium to monitor voltage or current relative to the water on my oscilloscope, loking for a
'coulombic explosion'.
how to maintain contact with an energetic liquid ball I don't know yet !
Yay! just got a notification that the sodium has been shipped......
[Edited on 6-3-2015 by Sulaiman]
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deltaH
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| Quote: Originally posted by j_sum1 |
I am pretty convinced that the transparent material is molten NaOH and not some other product. Na2O doesn't seem feasible.
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Why don't you think Na2O formation is not feasible?
[Edited on 6-3-2015 by deltaH]
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