Sciencemadness Discussion Board - Transparent Sodium?

Transparent Sodium?

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MrHomeScientist - 27-2-2015 at 08:01

Today I came across this extremely interesting video by Thoisoi2 on an observation he made of sodium in water:
<iframe sandbox width="560" height="315" src="https://www.youtube.com/embed/DJGVZNth68k" frameborder="0" allowfullscreen></iframe>

After placing sodium metal on a wet filter paper floating in a bowl of water, the sodium doesn't explode right away - instead it stops burning completely and goes <I>transparent</I>. Really crazy, and I've never noticed this before. I will definitely try this at some point.

I think he covers all the points I was going to make here, in his narration already. My first hypothesis is that this is a blob of NaOH, or concentrated NaOH solution, floating on a cushion of gas (hydrogen from the sodium reaction, or water vapor from the heat of dissolution <I>ala</I> the leidenfrost effect). I think it still explodes in the end from the NaOH falling off the cushion and rapidly boiling the water around it. But that's awfully fast for the whole blob of Na to get converted completely to NaOH. I think the clip at 4:00 supports the hypothesis that it is a solution, as you can see a lot of bubbling in the droplet that (I think) wouldn't happen if it were some sort of transparent metal instead.

What's everyone think? Very cool video if nothing else.

[Edited on 2-27-2015 by MrHomeScientist]

deltaH - 27-2-2015 at 08:40

The Leidenfrost effect is often touted as an explanation, but has anyone ever dropped a drop/blob of molten sodium hydroxide from a spatula into some water and seen if it indeed behaves similarly and gives a similar pop explosion at the end?

It's been mentioned on another thread somewhere that there is now increasing evidence that the sodium explosion is, in fact, a 'coulombic explosion' resulting from the build-up of unbalanced charges. Perhaps the transparent bead phase is molten sodium hydroxide with a slight excess of Na+ causing a pop.

If testing with ordinary molten sodium hydroxide does not give similar behaviour (which I doubt it would), then I think there's the beginning of some support for such a charge imbalance hypothesis.

[Edited on 27-2-2015 by deltaH]

Zyklon-A - 27-2-2015 at 08:57

Thunderf00t did a lot of research on this and there's is indeed much evidence that's its a coulombic explosion. He also has a lot of footage of the transparent sodium.

deltaH - 27-2-2015 at 09:05

I don't like this term 'transparent sodium' which I think is just sensationalism. Even if it is charge imbalanced, is is still probably almost entirely sodium hydroxide or a hydrate thereof, not just sodium.

MrHomeScientist - 27-2-2015 at 09:15

I agree that molten NaOH would almost certainly sink if dropped in water, as its density is greater (as mentioned in the video). Perhaps the sodium reaction generates the cushion of gas the droplet can float on, which a blob dropped in water would not have in place. It still seems extremely quick to react the chunk of sodium completely into transparent molten NaOH. I think a blob of primarily NaOH with some dissolved sodium is a good candidate.

Edit:
Possibly obscure reference: I wonder what this guy would think about "transparent sodium"?

[Edited on 2-27-2015 by MrHomeScientist]

deltaH - 27-2-2015 at 11:06

MrHomeScientist, I remember that :cool:

blogfast25 - 27-2-2015 at 11:09

Quote: Originally posted by deltaH

I don't like this term 'transparent sodium' which I think is just sensationalism. Even if it is charge imbalanced, is is still probably almost entirely sodium hydroxide or a hydrate thereof, not just sodium.

Of course. No need to look any further.

morganbw - 27-2-2015 at 15:59

Nothing to add, (too dumb to offer insight), but the video was pretty thought provoking.

aga - 27-2-2015 at 16:05

For the stupid amongst us (ok, just me then) can anyone say exactly Why sodium cannot exist in any state in which it is transparent ?

phlogiston - 27-2-2015 at 16:25

On the contrary, seems like a pretty good question to me.

I was going to argue that metals are reflective/not transparent to light because they are conductive.
Light, being an oscillating electromagnetic field, should not pass through electrically conductive materials.
However, I just realised a solution of a salt by that mechanism should appear reflective as well, and it obviously doesn't. Perhaps it has to do with the number and mobility of charge carriers being much higher in metals?

[Edited on 28-2-2015 by phlogiston]

aga - 27-2-2015 at 16:34

I guess the key would be how photons travel, and how they interact with matrices of matter.

Research time !

blogfast25 - 27-2-2015 at 16:37

Quote: Originally posted by aga

For the stupid amongst us (ok, just me then) can anyone say exactly Why sodium cannot exist in any state in which it is transparent ?

According to the paper cited in the video it can be transparent in specific conditions.

At RT Na isn't transparent because the conduction electrons also reflect photons (light).

My guess is that this is molten sodium oxide. Heat from the initial reaction with water and combustion of the evolved hydrogen sets the sodium on fire. The filter paper limits access to water, causing the sodium oxide to stay 'intact'. Only later does it get to react almost explosively with water.

aga - 27-2-2015 at 16:51

Conduction electrons ?

Please elaborate.

Photon interacts with some electron(s) and gets absorbed/repelled/ejected in a way that it retains it's speed, yet it's trajectory is altered.

Edit:

As Work is done, i.e. the trajectory is altered, then Energy must be consumed, somewhere ...

[Edited on 28-2-2015 by aga]

j_sum1 - 27-2-2015 at 17:41

This is intriguing if only because the old classic of sodium and water has had its mechanism challenged twice in the last few months. The thing we thought we understood is now shown to be mechanistically more complex than imagined.

I agree, the most likely candidate for the transparent substance is molten Na2O. Fascinating to see it in this form.
The next question that arises (for me anyway) is, if this is indeed Na2O or NaOH, then by what mechanism does it explode? We have learned that the explosion of Na is from coulombic repulsion. But I can't see that a molten salt would behave in the same way. I am going to have to try this.

As an aside, metals do transmit light if thin enough. I have some gold leaf that appears blue when you hold it up to the light.

As another aside, I have seldom seen the characteristic explosion of sodium on water. This is because I am usually using very small pieces when I do this experiment. Less than half a gram and explosions are rare. The video specifies a "medium-sized piece". I guess the observations are dependent on the size of the piece as well as other factors.

Molecular Manipulations - 27-2-2015 at 18:05

Blogfast, you sure it's sodium oxide? Melting point 1,132 °C, seems unlikely but at that temperature the Leidenfrost effect would certainly occur, but at that temperature it would certainly be visibly bright red hot at least, although it would probably appear yellow due to sodium's spectrum.
Perhaps there's another reason why it doesn't seem to be glowing.
If it was molten sodium oxide, could the explosion be because of the temps required for the Leidenfrost effect to keep it above the water, lessen enough and it sinks, instantly vaporizing a lot of water? I think not. Coulombic explosion seems more probable, like the blob is not molten sodium oxide but mostly sodium ions, perhaps a little oxide but not much.

m1tanker78 - 27-2-2015 at 18:23

Quote: Originally posted by j_sum1

This is intriguing if only because the old classic of sodium and water has had its mechanism challenged twice in the last few months. The thing we thought we understood is now shown to be mechanistically more complex than imagined.

I agree, the most likely candidate for the transparent substance is molten Na2O. Fascinating to see it in this form.
The next question that arises (for me anyway) is, if this is indeed Na2O or NaOH, then by what mechanism does it explode? We have learned that the explosion of Na is from coulombic repulsion. But I can't see that a molten salt would behave in the same way. I am going to have to try this.

As an aside, metals do transmit light if thin enough. I have some gold leaf that appears blue when you hold it up to the light.

As another aside, I have seldom seen the characteristic explosion of sodium on water. This is because I am usually using very small pieces when I do this experiment. Less than half a gram and explosions are rare. The video specifies a "medium-sized piece". I guess the observations are dependent on the size of the piece as well as other factors.

I third this assertion. Back when I did a lot of experiments with sodium, I was also puzzled by this. This can be somewhat unreliably reproduced by placing a piece of sodium in a dish with just enough water to float the molten sodium. I've always thought that the water became saturated with base and slowed the reaction enough that the sodium could burn (in air) faster than it reacts with the water. The 'explosion' ensues when the glass bead cools enough that it can contact the (relatively) cool lye solution.

So what happens if you drop a piece of sodium in a saturated NaOH solution??

j_sum1 - 27-2-2015 at 18:27

Good points on temp glow etc MM.
I'm still not convinced on coulombic explosion if it is a non-metal at this stage. However, it looks the same as normal Na. It could be the same mechanism. But that's going to require another rethink on what happens with sodium.

Molecular Manipulations - 27-2-2015 at 18:49

It makes more sense to me if the coulombic explosion takes place with a transparent substance. The lusterous, reflective sodium comes from only the outer valance electron, once removed it becomes a colorless, non-reflective ion. It seems likely that ionized sodium, be itself would be colorless. I just can't figure out what takes it so long to explode? Without something holding it together they would fly apart as soon as they're ionized, not wait until most of them are ionized and then explode. So what's holding them together?

blogfast25 - 27-2-2015 at 19:29

Quote: Originally posted by Molecular Manipulations

Blogfast, you sure it's sodium oxide? Melting point 1,132 °C, .

Where did I say I was sure? It wouldn't have to molten sodium oxide either, come to think of it.

Coulombic explosion would be very superficial.

It's certainly intriguing, assuming it's not a hoax of course. And no, before y'll start getting myopic, I'm not saying it is, just that the possibility should not be dismissed a priori. Weirder science hoaxes have been committed.

[Edited on 28-2-2015 by blogfast25]

blogfast25 - 27-2-2015 at 19:37

Quote: Originally posted by m1tanker78

So what happens if you drop a piece of sodium in a saturated NaOH solution??

Work out the mol fraction water in a saturated NaOH solution. That should put things into perspective.

Molecular Manipulations - 27-2-2015 at 20:08

I'm sure sodium would also react with pure sodium hydroxide to make sodium oxide and isolate hydrogen.
What do you mean by the "Coulombic explosion would be very superficial"?
My question is why does it take so long to explode? It appears not to be very superficial, else it would probably be more steady. Unless nothing happens for a few seconds and the a lot of the sodium suddenly gets ionized in milliseconds?

[Edited on 28-2-2015 by Molecular Manipulations]

deltaH - 27-2-2015 at 21:46

Quote: Originally posted by Molecular Manipulations

I'm sure sodium would also react with pure sodium hydroxide to make sodium oxide and isolate hydrogen.
What do you mean by the "Coulombic explosion would be very superficial"?
My question is why does it take so long to explode? It appears not to be very superficial, else it would probably be more steady. Unless nothing happens for a few seconds and the a lot of the sodium suddenly gets ionized in milliseconds?

[Edited on 28-2-2015 by Molecular Manipulations]

Key to the coulomb explosion hypothesis is probably sodium's tendency to form electrides (solvated electrons). I presume the electrons diffuse out of the drop and that the drop accumulates net Na[+].

My hypothetical explanation as to what then causes the delay is this:

Water has a very strong dielectric constant and would immediately pack around the 'naked' sodium ions so that their dipoles partially cancel out that field. In effect, they decrease the field strength at a certain distance away from the Na+ that would otherwise have been there.

Water also strongly hydrogen bonds with itself with the net result that the cohesion between water molecules is unusually strong.

But as the charge builds up and more and more water shield Na+, an internal strain between the water molecules also start to build up and at some point, the forces start to exceed water's ability to hold itself together.

At this point, just as in a solid, fracturing occurs, i.e. it starts out as a small breaking apart, but this seeds new 'tears' and quickly everything goes flying apart from the stored potential energy of the coulombic strain.

******

Oh, some more speculative points:

The drop being liquid means that the unbalanced Na+ can diffuse around and would probably make their way to the surface of the drop, just as charges on an insulator accumulate on the surface, so the 'strain' I was previously talking about could be nothing else than surface strain.

It pops when the strain caused by coulombic repulsion (partially shielded by water) exceeds the surface strain of the solution.

The amount of unbalanced sodium cations must surely be quite small or the forces and stored potential energy would be enormous and a much larger explosion would have ensued.

[Edited on 28-2-2015 by deltaH]

deltaH - 27-2-2015 at 22:16

The naughty in me wonders how one could carry this out so as to favour the accumulation of a very large amount of strain and unbalanced charge, trapped in a solid matrix like ice, for example, and not just on its surface.

Charge explosive :cool:

[sciencemadness=ON] Mill a slurry of ice and sodium in liquid nitrogen for a long time. Allow to warm up slowly... at some point BOOM!

Perhaps this can be done in a mortar and pestle by first pouring in some liquid nitrogen to cool down the M&P wearing face shield and gloves, then to a decent pool of liquid nitrogen, add a tiny piece of ice and a tiny piece of sodium, mill under liquid nitrogen until very fine, place blast shield in place, step back and wait for remaining liquid nitrogen to boil off and everything to heat up, make awesome video

[sciencemadness=OFF]

[Edited on 28-2-2015 by deltaH]

blogfast25 - 28-2-2015 at 07:43

Quote: Originally posted by Molecular Manipulations

What do you mean by the "Coulombic explosion would be very superficial"?

This phenomenon works (if we're to believe the video) if contact between the sodium and water is quite small (hence the filter paper).

Even at 50 w% NaOH the mole fraction of water is nearly 70 %, plenty of water to react with the sodium.

m1tanker78 - 1-3-2015 at 11:24

Fair enough blogfast. Let me unpack my question. What purpose does the filter paper serve?

blogfast25 - 1-3-2015 at 13:08

Quote: Originally posted by m1tanker78

Fair enough blogfast. Let me unpack my question. What purpose does the filter paper serve?

From what I understand: to limit the sodium's access to the water.

j_sum1 - 1-3-2015 at 14:51

I intend to try this today. I will let you know how it goes.

j_sum1 - 1-3-2015 at 20:08

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.)

MrHomeScientist - 2-3-2015 at 06:06

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).

blogfast25 - 2-3-2015 at 06:16

Excellent. Good write up too. Corroboration is everything.

Molecular Manipulations - 2-3-2015 at 06:53

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...

deltaH - 2-3-2015 at 09:00

+1, very nice reporting indeed!

j_sum1 - 2-3-2015 at 11:20

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...

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]

aga - 2-3-2015 at 11:26

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]

Molecular Manipulations - 2-3-2015 at 11:34

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...

Morgan - 2-3-2015 at 12:12

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

j_sum1 - 2-3-2015 at 12:49

I haven't come across Recalescence before, but it seems plausible.

Endo - 2-3-2015 at 13:17

I wonder if a conductive metal screen on top of the filter paper would make a difference.

aga - 2-3-2015 at 13:30

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.

j_sum1 - 2-3-2015 at 15:49

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.

m1tanker78 - 2-3-2015 at 18:08

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.

woelen - 2-3-2015 at 23:49

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]

deltaH - 3-3-2015 at 00:46

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]

j_sum1 - 3-3-2015 at 00:51

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]

deltaH - 3-3-2015 at 01:01

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]

Sulaiman - 5-3-2015 at 10:51

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?

deltaH - 5-3-2015 at 22:33

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]

j_sum1 - 5-3-2015 at 23:27

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.

Sulaiman - 6-3-2015 at 03:52

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]

deltaH - 6-3-2015 at 05:23

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.

Why don't you think Na2O formation is not feasible?

[Edited on 6-3-2015 by deltaH]

Molecular Manipulations - 6-3-2015 at 05:55

Inert gas is easy. You can even use a helium balloon if you can't get nitrogen.
To generate nitrogen, drop a hot solution of sodium nitrite in pressure equalized addition funnel onto warm ammonium chloride, nitrate, sulfate or any common salt. It's best to dry the gas by bubbling it through concentrated sulfuric acid, which will also get rid of ammonia impurities.

deltaH - 6-3-2015 at 06:03

Also, this flame that burns briefly on the sodium, it just occurred to me that it might be a small amount of residual paraffin used to shield the sodium from oxidising. Simply dabbing the sodium on some filter paper is not going to remove the film of oil clinging to it.

To test this hypothesis, I suggest dipping the tiny piece of sodium in some ethanol with tongs, then waiting for the ethanol to evaporate when pulled out before putting the sodium bead on water.

blogfast25 - 6-3-2015 at 06:48

Quote: Originally posted by deltaH

Also, this flame that burns briefly on the sodium, it just occurred to me that it might be a small amount of residual paraffin used to shield the sodium from oxidising. Simply dabbing the sodium on some filter paper is not going to remove the film of oil clinging to it.

To test this hypothesis, I suggest dipping the tiny piece of sodium in some ethanol with tongs, then waiting for the ethanol to evaporate when pulled out before putting the sodium bead on water.

If you clean up the outside of your piece of sodium, then cut out a cubic (e.g.) piece from that, then you are working essentially oil free.

Morgan - 6-3-2015 at 09:11

One time I put about 50 grams of sodium in a jar with rocks to weight it down and a few holes punched in the lid. The jar sank to the bottom of the backwater slough I had previously been exploding sodium on the surface of the water. The jar bubbled for a seemingly long time but didn't crack or do anything fun like I thought it would because of the lack of oxygen. I was only 15 at the time and didn't quite grasp what would happen.
The pieces that I threw on the surface however exploded in such a way as to propagate a machine gun jungle warfare sound when a tossed single hunk of metal became molten and subdivided into several pieces after the first explosion. My friend who was with me couldn't stop talking about it to his friends later. It was fun I have to admit.
Anyway would a piece of sodium held underwater in some sort of quartz glass chamber be anything to study as it melted but didn't explode? It could bubble away but not take fire. Of course this would upset the conditions that occur in air but maybe it would provide some insight of how the byproducts behave if enough heat were generated. I guess it would be about the same as using an inert atmosphere except the "air" or "inert gas" would be hydrogen.
The electrostatic properties would be fun to harness if you could use sodium in this way to generate a very large spark somehow for a demonstration.

[Edited on 7-3-2015 by Morgan]

Sulaiman - 6-3-2015 at 11:09

I suspect that a hydrogen atmosphere would cause NaH to be produced,
even nitrogen can form Na3N but as it decomposes above 87C I'm unsure of the result.
Sodium is really reactive!

I've been looking for a denser-than-air gas, or a liquid less dense than sodium
that is easily available and doesn't react with molten sodium or NaOH .
argon is the best so far but I'm still looking

meanwhile found a few relevant YouTube videos.
I like this one https://www.youtube.com/watch?v=BIGMfai_ICg

Also, been doing a few sums;
1g of sodium has about 4197 Coulombs available
maybe enough to form a plasma or sparks beneath the sodium?
the sodium ball is obviously above it's melting point of 97.8C
and below it's boiling point of 883C
hydrogen spontaneously ignites in air above 500C so it could be that simple
or it could be electrical ignition?

Molecular Manipulations - 6-3-2015 at 11:21

Quote: Originally posted by Sulaiman

even nitrogen can form Na3N but as it decomposes above 87C I'm unsure of the result.

No it can't. Just because it doesn't decompose readily at STP doesn't mean it can form at STP.

Quote:

Originally posted on Wikipedia
Sodium nitrite can be generated by combining atomic beams of sodium and nitrogen deposited onto a low-temperature sapphire substrate.

Doesn't sound like something that's going to form anywhere near water or at high temperatures.

Sulaiman - 6-3-2015 at 12:12

OK, thanks for clarifying that, my mistake.

Regarding the first YouTube video on transparent sodium that I watched
https://www.youtube.com/watch?v=DJGVZNth68k

there is an interesting similarity to part of the Wikipedia article on sodium
"Sodium at standard temperature and pressure is a soft silvery metal, that oxidizes to grayish white unless immersed in oil or inert gas. Sodium can be readily cut with a knife, and is a good conductor of electricity. These properties change dramatically at elevated pressures: at 1.5 Mbar, the color changes from silvery metallic to black; at 1.9 Mbar the material becomes transparent, with a red color; and at 3 Mbar sodium is a clear and transparent solid"

just coincidence?

P.S. can anyone suggest a transparent liquid less dense than and un-reactive with sodium?
GOT IT ... simple hydrocarbons like kerosene.

P.P.S. checked with my son, no high speed video capture available.

[Edited on 6-3-2015 by Sulaiman]

420MLGnOhEADsCOPEpro - 6-3-2015 at 14:19

i agree with deltaH about the transparent end product being NaOH with Na2O dissolved in it

judging by the color of radiated light it never gets much hotter than 500C so we can rule out boiling Na 883C NaOH 1388C Na2O 1950C or molten Na2O 1132C
thus i conclude that the explosion of the transparent droplet must be caused by water
i assume it's something like this
water is pulled into the droplet where it reacts with Na2O
water that rushes into the droplet increases the temperature, decreases the boiling point of dissolved water, decreasing the surface tension and increasing the mass of the droplet
after some amount of time one of two things happens
some of the water boils causing the droplet to break
or the increased temperature and water content reduces the surface tension enough that the droplet breaks
then the hot NaOH solution hits the water causing it to boil
thus explosion

i think that in an inert atmosphere the Na would react with NaOH to form Na2O and H2 thus producing a similar result to when in air

the droplet can't be sodium because it's not reflective
as far as i'm aware a transparent metal is effectively a contradiction as a metallic bond is reflective by nature
metals can be transparent if they are thin enough though but that's confusing quantum mechanics stuff that can't be scaled up
so it can't be transparent metal (as the droplet is more than a few hundred nanometers thick)
sodium can be transparent however this is in one of it's electride states and requires a pressure of 3 Mbar
so it can't be an electride because the droplet surely wasn't under that kind of pressure (however there may have been small amounts of electride sodium produced by internal voltage gradients while the was still metallic sodium but this more resembles sodium ions stuck to an electrode in an electrolytic capacitor than electride ions and there lots of weird properties of such ions so it's hardly anything like an electride)

also for anybody wondering about reflection
metals are reflective because metallic bonds are basically pools of free floating electrons
when that pool of electrons is struck by a photon it matches the oscillations of the electric field and thus absorbs and re-emits it
molten salts can't do this because all the electrons are bound to an atom
though i think molten salts can reflect radiowaves and microwaves because
this is because radiowaves and microwaves are huge compared to visible light and thus the ions can match the field enough to absorb and re-emit them however there are some big differences between reflection of visible light and microwaves and radiowaves

Molecular Manipulations - 6-3-2015 at 14:26

Quote: Originally posted by 420MLGnOhEADsCOPEpro

[...]the droplet can't be sodium because it's not reflective
as far as i'm aware a transparent metal is effectively a contradiction as a metallic bond is reflective by nature

That's where coulombic explosion comes in:

Quote: Originally posted by Molecular Manipulations

reflective sodium comes from only the outer valance electron, once removed it becomes a colorless, non-reflective ion. It seems likely that ionized sodium, by itself would be colorless.

m1tanker78 - 6-3-2015 at 18:01

The strange thing is that when sodium burns in air, it forms a white coral-like structure that turns yellowish (sodium peroxide) when it cools sufficiently. There is a period when it turns black, before it goes white IIRC. In the video, I didn't see any such formation. I still say steam plays a major role.

I still don't see a strong case for using an inert atmosphere. I still see a case for burning a piece of sodium in steam... Unless I'm missing something?

If the events in the video line up with my observations from when I started messing around with a Downs cell design then the reaction can be quenched with mineral oil at any stage. I pulled some translucent beads as well as some red beads. The explanation for the red beads at the time was that the oxide layer was creating an interference pattern or something like that. I don't buy it.

I'm giving some thought to how NOT to destroy my camera and still get the shot before I roll up my sleeves and play ball.

j_sum1 - 6-3-2015 at 19:36

The reason for the inert atmosphere is to try to eliminate any reaction between Na and air. This simplifies things a bit and enables one to observe the reaction with water without a flame getting in the way.
Argon is available at welders' supplies. You can also buy a can at a wine shop. Helium might be your cheapest inert gas if you onky want a small amount but you will need to contain it since it is so light. A bell jar or glass bowl might work.

I expressed doubt on Na2O being produced because its MP is sohigh and we clearly have a melt. It is possible that it is a solution of some Na2O in NaOH. But I haven't checked a phase diagram and I am not sure what temps we are talking about here. I doubt there is a sphere of molten NaOH reacting on the inside with its metallic skin. Where would the H2 go?
I also thought the bead might contain some water. This would mean that it doesn't contain the oxide.

Eddygp - 7-3-2015 at 04:30

Maybe some sort of molten sodium + molten sodium oxide + molten sodium hydroxide... think about how the filter paper does not allow water to join the blob immediately. The explosion suggests that it has not reacted completely, so it cannot be pure sodium hydroxide. My guess would be either a Coulombic explosion or some sort of solution of sodium and sodium oxide in molten something.

Morgan - 7-3-2015 at 07:44

Maybe it would be interesting to try some coin shaped disks to offer more surface area if a coulombic effect is taking place. Although the smaller sodium pieces once melted take on a somewhat spherical shape, there might be something to elicit in the first second or so when initial contact with the water is made, dumping more charge more suddenly with intimate contact. Or maybe not.

[Edited on 7-3-2015 by Morgan]

Molecular Manipulations - 7-3-2015 at 08:47

Eddygp, that's not a bad theory. But theres one problem. I know molten sodium hydroxide about 60 deg. above it's melting point will dissolve sodium, per experience with a caster cell. But I always thought it was an irreversible reaction, not just a regular solvent-solute solution, but rather the hydroxide ion oxidized the sodium and reduced hydrogen to elemental. I highly doubt sodium wouldn't reduce hydroxide in such a situation.

m1tanker78 - 7-3-2015 at 09:31

Morgan - sodium 'tortillas' tend to break up into multiple spheres.

j_sum - Might be worth a try if nothing else, to have a reference. There shouldn't be a flame but there will be steam.

eddy - Did you ever observe the hydride salt in the leftovers of the Castner cell? I would regularly encounter it when dissecting the cooled salt block of a Downs cell when sodium bicarbonate was added to the melt.

Could we make a spreadsheet with all possible elements, molecules and transitional species in this scheme on X and Y and figure the HOF of each for reference?

How about a RBF 1/3 filled with water, Ar purge and gentle flow, film from below and hope to have a little magnification and clear sight up through the apparatus? There shouldn't be any explosion or other RBF-destroying events.....right?? The phone/camera should survive too...??

Anybody have an underwater camera or one of those water proof cell phones?

Sulaiman - 10-3-2015 at 05:53

My five individually sealed 28g sodium ingots arrived today
but I have not made all of the safety preparations for experimenting yet

meanwhile, could someone check these calculations for me as the results are surprising;

1 mole = 23g = 6.022 x 10^23 atoms/ions = (6.022 x 10^23) / (6.241 x 10^18) = 96500 Coulomb

So 1g of sodium reacting in 10 seconds = 96500 / (28 x 10) = about 420 Amps average !

This would mean;

phenomenal I^2 x R heating
and
if the molten bead is at times supported by the Leidenfrost effect then
there could be a huge voltage difference between the sodium and the water due to
dV = dQ/C where C (capacitance) would be very small. (V=voltage, Q=charge)

This is why I want to try to view the voltage difference on my oscilloscope.
I have a high voltage, high frequency probe that will add 100 MOhm plus 3pF to 5 pF 'load'
so results may be affected by the probe but I should get an indication of the effect.
I still have no idea how to attach the probe,
I have no platinum wire so I will first try very thin copper wire and (hopefully) progress from there.

I also want to 'collect' the transparent bead for analysis,
I suspect (for no scientifically researched reason, just a guess) that there is massive surface tension on the bead,
so touching it may cause instant detonation (to be determined)
so i'm thinking of using a puff of air to blow the transparent bead on to a ceramic tile.
Any better/other ideas welcome.

Sulaiman - 11-3-2015 at 10:20

Couldn't edit my last post, hope double post is ok.

Unpacked one of the 28g sodium ingots today,
only a fraction of a millimeter surface corrosion found.
I cut it up to fit under (Johnsons baby) oil in a small container.

Good news;
I found it very easy to repeatedly produce 'transparent sodium' spheres in a quick test.

Bad news;
whilst setting up I broke the head off of my camera tripod

and I did not want to try cutting up the sodium or experimenting with one hand holding the camera.
so no video yet.
Safety procedures for collecting the spheres and electronic measurements not ready yet.

Kitsune1 - 11-3-2015 at 14:17

Very interesting Sulaiman, I look forward to hearing more about your experimentations with this.

I have a thought on this subject that I don't think anyone has yet touched on yet, how would an identical reaction take place with Li or K in place of Na? would a similar reaction be possible? How would the rate of reaction vary between the group 1 metals?

As has been pointed out previously, the leidenfrost effect certainly seems plausible to be at least one part of what is going on here.

morganbw - 11-3-2015 at 14:28

Quote: Originally posted by Sulaiman

Couldn't edit my last post, hope double post is ok.

Unpacked one of the 28g sodium ingots today,
only a fraction of a millimeter surface corrosion found.
I cut it up to fit under (Johnsons baby) oil in a small container.

Good news;
I found it very easy to repeatedly produce 'transparent sodium' spheres in a quick test.

Bad news;
whilst setting up I broke the head off of my camera tripod

That it is repeatable is great.
It actually made me smile.
Collecting the spheres may be a serious task.

[Edited on 11-3-2015 by morganbw]

j_sum1 - 11-3-2015 at 14:45

Quote: Originally posted by Kitsune1

I have a thought on this subject that I don't think anyone has yet touched on yet, how would an identical reaction take place with Li or K in place of Na? would a similar reaction be possible?

I reported on an experiment with K upthread. No Li done yet.
I have given considerable thought to a mechanism nd can account for most observations. However, reporting this will take some time that I don't have at the moment. Watch this space.

Sulaiman - 11-3-2015 at 14:55

Quote: Originally posted by Kitsune1

Very interesting Sulaiman, I look forward to hearing more about your experimentations with this.

I have a thought on this subject that I don't think anyone has yet touched on yet, how would an identical reaction take place with Li or K in place of Na? would a similar reaction be possible? How would the rate of reaction vary between the group 1 metals?

As has been pointed out previously, the leidenfrost effect certainly seems plausible to be at least one part of what is going on here.

A similar effect has been observed using sodium/potassium amalgam (liquid at room temperature)
during research into the mechanism proposed for the sudden violent explosions ... 'coulombic explosion'
excellent video
https://www.youtube.com/watch?v=LmlAYnFF_s8

420MLGnOhEADsCOPEpro - 11-3-2015 at 18:09

i just noticed something after watching https://www.youtube.com/watch?v=BIGMfai_ICg
he says that the droplet is a dark blue not black in this video (which seems to show the same reaction as is in question here)
i was wondering why the droplet was so dark before becoming transparent and then i remembered that alkali metals dissolved in ammonia are blue
https://en.wikipedia.org/wiki/Electride
this video shows that it's about the same dark blue we're seeing
https://www.youtube.com/watch?v=JefumJFatsw

i think this is strong evidence that an electride state is present at least while it's blue
is it possible this is [Na(H2O)x]+ e- (i don't know what x would be)
i find it unlikely that [Na(H2O)x]+ e- is the electride though when i heard about electrides i though it was odd that the ammonia doesn't react into Na+ NH2- (wikipedia says that this happens slowly but i don't get why)

this is definitely relevant to the composition and it gives me an idea as to how it might explode

consider that it's sodium with some amount of hydroxide OH-, some amount of hydride H- and some amount of oxide O-2 dissolved in it that allows it to take on an electride structure
i theorize this is possible considering if there are sodium ions Na+ in the sodium metal then they would often trade places and at some concentration would be more stable in the electride phase where no electron swapping is required to switch places relative to the anions
this should prevent a columbic explosion by allowing some flow of electrons to the Na+ that is reacting with the water
if for whatever reason the sodium was no longer an electride it would explode as it usually does
this may be occurring at the surface of the sodium that is reacting with the water due to a change in ion concentration or temperature

edit i think you could test if it's an electride by holding a strong magnet next to it
so if anybody is going to test it and has a rare earth magnet lying around i'd suggest taping it to a stick and waving it by the drop at various points during the experiment

[Edited on 12-3-2015 by 420MLGnOhEADsCOPEpro]

morganbw - 12-3-2015 at 04:17

Quote: Originally posted by Sulaiman

Quote: Originally posted by Kitsune1

I was reluctant to watch the video because of its length but I am glad that I did.
Thank you for the link

Kitsune1 - 12-3-2015 at 13:34

Quote: Originally posted by j_sum1

I happen to have some Lithium left over from a few months back which should be ideal for trying this out with. Hopefully I'll be able to find some time tomorrow to do a few runs, will report back once done.

Really interesting video, a bit on the long side but the content does justify it.

Wizzard - 12-3-2015 at 17:53

Perhaps a light source with a special spectral characteristic to differentiate molten NaOH, molten NaO and molten Na?

j_sum1 - 12-3-2015 at 19:04

Quote: Originally posted by Wizzard

Perhaps a light source with a special spectral characteristic to differentiate molten NaOH, molten NaO and molten Na?

Care to elaborate?
What wavelength are we talking about here? How would this be set up? Are there sufficient differences at play here that you could use a regular light with a gel filter? (We are talking home science here.)
Interested in what 420mLetc says on electrides and blueness observed.
There are a few videos I need to watch too.

I don't know when my next chance will be to get into the lab. Frustrating.

Sulaiman - 12-3-2015 at 22:43

When I did my quick test with sodium one of the transparent spheres 'jumped' off the filter paper onto the wooden table.
I didn't collect it because it was contaminated with wood / lacquer and was brown.

Assuming that I will 'catch' uncontaminated transparent spheres, e.g under oil.

What can I do to analyse the sphere?

even weighing it will be a challenge,

I could do a titration against very dilute acid (0.1 mL divisions on my burettes)

if I put the sample in water bubbles may indicate hydrogen due to unreacted sodium,
but I don't know how I'd analyse such a small quantity of hydrogen.

How would I look for other sodium/oxygen/hydrogen compounds?

I am clearly out of my depth here, HELP !

j_sum1 - 12-3-2015 at 23:21

I am of the opinion that there is no sodium present at the stage when the sphere is transparent. Of course I might be wrong (which would make the whole thing exceedingly interesting!) I think it is likely to be NaOH with possibly some Na2O. My analysis would be based on that assumption.

If you can catch it in a weighing dish (pre weighed) then you can get its mass. You could correlate this with the initial mass of the sodium. This is another thing to be said for attempting a reaction in an inert atmosphere. If you can avoid burning off the sodium in air and avoid losses as fumes and if you can capture the entire lump, then you could do some stiochiometric calculations based on having no losses. That could inform you on whether there is Just NaOH or also some Na2O present. It will be a bit rough because there are a variety of other avenues for losses including splattering into the air, and concentrated NaOH solution in the filter paper. The latter can be collected and analysed too if desired.

The next thing I would do is drop it into a conical flask containing some water and try to avoid splashes. Then you can titrate with an acid and that should tell you how much NaOH/Na2O is in the lump.

Morgan - 13-3-2015 at 09:08

Have any attempts of a direct measurement been taken of this coulombic effect or is it even possible to measure it without destroying the effect?
Would saltwater work better or worse?
I was wondering if you put a needle or pincushion of needles on the surface of the water and ran a connecting wire through the bottom of the vessel whereupon someone holds the wire to see if they detect any electricity in their fingers when a piece of NaK or Na is set or dropped upon the surface? If it was saltwater I guess you could forgo the needles and just have some contact with the water or if it perchance was very high voltage tap water might conduct well enough. Or is this a high amperage low voltage discharge? So many things to consider or facts to be aware of which would negate this half-baked idea of test. Maybe there wouldn't be any current flow at all to the outside wire.

Tidbit on ohms.
"A Kelvin waterdrop generator might produce 20,000volts at 1/2 microamp. Dividing this voltage by this current gives 40,000,000,000 ohms, forty gigohms. That's the line between insulator and conductor. Quite different than three ohms! So, if an object is to act as an insulator, its resistance must be MUCH greater than forty billion ohms! For a Kelvin generator, a ten-megohm piece of wood will act like a dead short, a very good conductor. Is it any wonder that a bit of surface moisture can convert an insulating object into a conductor? The highest value of resistor commonly available in catalogs is 33 megohms, and most electrostatic devices will see this device not as an insulator or even as a resistor, but as a dead short."
http://amasci.com/emotor/stathint.html

Kitsune1 - 13-3-2015 at 15:30

Quote: Originally posted by Kitsune1

Just conducted the Lithium experiment multiple times; following the "Transparent Sodium" video as closely as I could.

All ten reactions were not dissimilar to the control (Li in water). It seems that this transparency effect might be limited to metals of a greater reactivity than Lithium. It would be interesting to see this effect in slow motion with K and potentially Rb and Cs though arguably much more control would be required to record any following effects.

A note, I also tried this with molten lithium but a thick passivation layer of oxide and hydroxide formed very quickly after coming in contact with the water, thus obscuring the reaction.

Kit

zed - 13-3-2015 at 16:09

http://phys.org/news156104532.html

Might be transparent Sodium. Time will tell.

Pure transparent aluminum was created as a new state of matter by a team of scientists in 2009. A laser pulse removed an electron from every atom without disrupting the crystalline structure.[3] However, the transparent state lasted for only 40 femtoseconds, until electrons returned to the material.

A group of scientists led by Ralf Röhlsberger at Deutsches Elektronen-Synchrotron (DESY), Hamburg, Germany, succeeded in turning iron transparent during research in 2012 to create quantum computers.[4][5]

[Edited on 14-3-2015 by zed]

Morgan - 18-3-2015 at 06:56

It just seems like when the charged spikes are forming you could get a wire in there on the metal and directly measure some sort of voltage spike on the mass of metal when the reaction takes place with water. And if there is a high voltage discharge, maybe you could do something fun with it other than watching an explosion. Would it be possible to bleed off the charge to create bolt of electricity?

http://www.nature.com/articles/nchem.2161.epdf?referrer_acce...

Sulaiman - 20-3-2015 at 12:14

my experiments with transparent sodium were delayed due to re-starting work after a long absence but I hope to have a go tomorrow or Sunday, so

assuming that I can collect say 1g of the transparent spheres, e.g. in oil
how can I determine Na, Na2O, NaOH etc. content ?
all dissolve exothermically in water to NaOH solution so I guess aqueous analysis is pointless,
suggestions please ......

Morgan - 20-3-2015 at 13:36

I wonder how well plain sodium would work compared to the NaK alloy if you preheated clean sodium in an inert atmosphere and then let it fall on some water, so that it would be liquid and hopefully more "coulombic"?

j_sum1 - 20-3-2015 at 18:08

Ok. I have been back through the videos cited. There are certainly some interesting observations there.
Thunderf00t has been really busy on this and what he has presented looks very sound: although his attention has been on the coulombic explosion of Na and water without filter paper added. If you haven't seen his videos (cited by several others above -- the long one is best) then I refer to them several times in what follows, so they may be worth a look.
Another thing I noted is that the original video has the transparent pellet sitting in a fairly deep puddle. When I did the experiment I had the filter paper dry by comparison. Water was basically wicking through the filter paper to feed the reaction and there was very little liquid visible. Similar observations however.

Here is a list of open questions. In no particular order.

What exactly is the composition of the transparent pellet?
By what mechanism does this pellet explode?
What is the reaction producing the visible flame?
What causes that flame to be extinguished?
What is occurring that causes the appearance of the pellet to go from dark (blue?) to glowing red to transparent?
Why does the pellet continue to float on water (in Thunderf00t's videos)?

I am both intrigued and convinced by Thunderf00t's observation of gaseous metal -- green in the case of potassium and blue for sodium. He also claims that the burning is a reaction between the gaseous metal and steam -- which makes sense: especially if the flame has been observed in an inert atmosphere. I have never seen gaseous metal before. It does seem strongly attracted to the lump of material. That would put the temperature above 760C for potassium, 883C for sodium and my guess is some lower temperature for NaK -- perhaps a kind of azeotrope. There might be a reason why the gaseous material was observed more easily with NaK.

My guess is that the flame extinguishes when the amount of steam decreases and there just isn't the availability of reactants to sustain a flame. That and the fact that the pellet cools a bit and there is not the same amount of gaseous metal present. At this point there is a thin film of liquid metal coating a transparent pellet. This continues to react without a flame and eventually the transparent pellet is fully exposed. Possible reactions for this include:

liquid sodium reacting with steam to produce NaOH / Na2O fumes and H2 gas
liquid sodium reacting with steam to produce NaOH / Na2O liquid that forms part of the pellet and H2gas that is expelled outwards
liquid sodium reacting with H2 to form a hydride
liquid sodium dissolving into the pellet
liquid sodium dissolving into the pellet and forming an electride solution (which would also account for the dark bluish appearance on the surface)

Of these options My hunch is towards the first even if it is the most boring option.

The glowing red phenomenon might be due to Recalescence but I think it is just normal radiation due to the temperature. As it cools the spectrum given off drops to the infra side of visible and the droplet is transparent in appearance.

As for what the pellet actually is, there are a number of possibilities.
I think it is basically molten NaOH. This is consistent with the temperatures assumed. Molten Na2O seems like too high of a temperature. Apart from anything else, there would be a lot more gaseous metal if the temperature reached 1132C necessary to melt Na2O. I don't think there is sufficient evidence to propose something exotic like transparent metal: however exciting that might be. In my experiment, splattered fragments of the pellet had exactly the same appearance as NaOH once cooled.
There may be something dissolved in the NaOH however. Proposals in this thread include:
Na2O
H2O
Na
Na+ and e- (an electride solution)

Now we are talking about the reaction at the interface between the sodium and the liquid water on the filter paper. The critical element here appears to be the inavailability of the water to react with the sodium. This is what distinguishes this experiment from the standard Na in water experiment. I think there is cause for caution in making assumptions here. Thunderf00t observed the same transparent pellet without filter paper (and so water more accessible) and noted that (a) atmospheric oxygen was not a factor. The reaction in the ampoule would have quickly used up all available oxygen. (b) The pellet appears to be less dense than water since it floats. This might give cause to question some proposed compositions of the pellet.
H2O and Na2O are incompatible. deltaH has pointed out the incredibly high energy content of Na2O that is released on dissolution with water. This might be useful for accounting for the later explosion. I see a continuum:
NaOH+H2O ----- NaOH ---- NaOH+Na2O
I had originally favoured the left side of this continuum: discounting the ability of Na2O to dissolve in NaOH, recognising the affinity that NaOH has for water and noting that the stuff was sitting in a puddle of water. I am now more inclined to favour the right side of the continuum. There are no observations that require H2O to be present and the Na2O has more explanatory power.
Which then leaves open what other species may be present.
The possibility of an electride solution is intriguing. (Nice video [url=http://www.periodicvideos.com/videos/liquid_electrons.htm]]here[/url.) I just don't see the same observations however. I am on thin ground as far as my understanding of such things and I know little abut the required conditions to form such species. My instinct is to dismiss such an idea for now.
Dissolved Na atoms is also an intriguing idea. I think both this and the electride idea are proposed to explain the explosion of the transparent pellet at the end: by the mechanism of coulombic explosion. I think they fail in this regard.
The coulombic explosion described ably by Thunderf00t to explain the explosion of Na and water involved the build up of positive ions close together on the surface of the liquid sodium and a corresponding build up of OH-ions in the water underneath it. When the repulsion force between these ions of like charge exceeds the surface tension of the liquids present then there is a runaway acceleration that exposes new surface to the reaction. Thunderf00t considers the rate of reaction to increase exponentially. I would propose that it is governed by a quadratic since the reaction is occurring on a planar surface. Butt in either case it is not steady state.
The coulombic explosion is dependent on a number of factors. Unclean surfaces, and in particular oxide on the surface seems to inhibit this behaviour. Addition of a surfactant also suppressed these explosions. And logically, there is a critical density of ions that must be present to initiate the explosion. This density is unlikely to be reached if the free sodium atoms or ions are at a lower concentration dissolved in liquid NaOH. I just don't see that coulombic explosion adequately explains the explosion of the pellet. Therefore I see little reason to propose Na or Na+/e- dissolved in the pellet.

So the next question is what causes the transparent pellet to eventually explode? And, perhaps more critically, what prevents that mechanism from occurring earlier?
To get an explosion there must be some kind of runaway mechanism where the reaction accelerates.
Na2O + H2O --> 2NaOH certainly releases a significant quantity of energy. However, I don't see how this can cause a runaway reaction. And I don't see what might prevent this reaction from occurring until a critical point is reached.
Maybe the following occurs...
O2- + H2O --> 2OH-
These OH- ions would then repel and the Na+ ions in the transparent pellet would also repel. This could potentially cause the phenomenon observed. And just like the coulombic explosion observed with regular sodium, this reaction needs for the repulsion forces to exceed the surface tension forces for a runaway to occur. Wild speculation here of course.

This leaves the question of why the pellet does not sink in the ampoule that Thunderf00t experimented with. I have nothing to propose except the leidenfrost effect and maybe some additional surface effects. Hot liquid NaOH in contact with water will produce some steam -- just because of its temperature but also because the dissolution of NaOH when it occurs is exothermic and may also boil some water. I am not sure this is an entirely satisfactory explanation. But it does explain limited contact between the pellet and the water and hence the delay in explosion and also the observed buoyancy.

A couple more lines of investigation.
1.
It has been proposed (by me) that the chief difference that the filter paper makes is that the water is less available to the reaction. This causes the reaction to proceed differently from the standard Na/water scenario. I think that this is a simplification. One of the things that I think happens is that the sodium metal is now sitting in a very concentrated solution of NaOH in water. In the standard Na/water experiment the reaction is Na + H2O --> NaOH + ½H2. I think that in a concentrated solution, some of the sodium may react with the sodium hydroxide:
Na(l) + NaOH(aq) --> Na2O(l) + ½H2(g)
I think this goes a long way to explaining why the same Na/water explosions are not seen. Remembering of course that unclean Na surface has been shown to inhibit or delay the explosion of sodium in water.
I propose an experiment where a lump of sodium is dropped into a very concentrated solution of NaOH without filter paper present. My hypothesis is that it will behave much the same way as the filter paper experiment.
(Concerning the experiment where Thunderf00t dropped NaK into an ampoule of water, I think that the reaction proceeded at a faster rate than the water could diffuse the reaction products and therefore the metal was sitting in rather concentrated NaHO/KOH solution.)

2.
I think it is worth investigating the behaviour of liquid NaOH when it is dropped into (a) water, (b) a concentrated NaOH solution and (c) wet filter paper. this will give some insight into what the transparent pellet is comprised of.

3.
Anyone equipped to observe the reaction between gaseous sodium or potassium and steam? I don't think it would be that helpful to describe what is happening here but it sure would be cool to watch.

That's my thoughts for now. I don't know when I will get a chance to try this stuff.

deltaH - 21-3-2015 at 04:31

A test for the Na2O + NaOH hypothesis is simply to melt a mixture of those in a spatula and drop them onto water. This will also help to see if a solution can be formed in the first place and to what concentration.

As for the presence of electride, the blue colour is indicative of that, but that is still a rather dilute electride (concentrated electrides are gold in colour). It also appears to be transient, so to be honest, I don't think it's very important.

As for the coulombic explosion hypothesis, while very sexy, I'm not that convinced yet, especially after seeing the numbers for the heat of Na2O hydration.

The safe money is on Occam's razor

[Edited on 21-3-2015 by deltaH]

Morgan - 21-3-2015 at 07:35

First the transparent sodium coming into question and now the coulombic explosion possibly falling by the wayside. Maybe it's nuclear. ha

This morning before getting out of bed and not fully awake, I wondered if the NaK that was dropped into water forming the spikes, what else might be causing the alloy to do that. Are there other examples of spikes forming in such a manner or something similar to draw upon for insight? Could you suddenly put a high voltage charge on a drop of NaK and make it behave/spike similarly using a high voltage source?

When you look at this https://www.youtube.com/watch?v=LmlAYnFF_s8#t=15m58s it seems the metal is as flat as a pancake and even causing a concavity in the water at T=0.3ms (right frame). So could it be at least entertained that some separation of the drop allowed water to break through the layer of metal and then become superheated, jetting away in a needle/spike manner?

For some reason I thought of these examples of electrical discharge, just some left field associations
Making Electron Trees with a Linear Accelerator
https://www.youtube.com/watch?v=xoKloJwmLjI

2.5 million volts at 3,500 amps with a piece of acrylic
"Some specimens spontaneously self-discharge while being irradiated by the beam, causing bright flashes and bangs ..."
https://www.youtube.com/watch?v=9Po35g23fYI

j_sum1 - 23-3-2015 at 02:25

There's something about the paper.
I am not totally unserious here. There are some very confusing things going on.

I have just spent an hour finishing off a bottle of sodium fragments and did about 30 or 40 trials with highly oxidised slivers of sodium ranging in size from about 0.02 to 0.1 grams.
I have largely ignored the phenomenon of the transparent bead exploding. That is highly reproducible when the conditions are right. I have been focussing on certain observations that always proceed the explosion. Namely:

The liquid metal sphere turning dark bluish almost black.
The sphere bursting into bright yellow flame
The flame extinguishing leaving a bead that may still appear black but quickly turns to glowing red and then to transparent

Here are some observations.
Filter Paper below the sodium
All above effects were observed consistently on wet filter paper.
The effects were observed when there was a puddle of liquid on the paper -- depth sometimes greater than radius of the sphere.
The effects were observed on damp paper without any additional water.
The effects were observed when the sodium was pushed through a perforation in the paper but was somewhat constrained by the paper edge.

Reaction with NaOH solution without paper
The effects were not observed on a glass petri dish containing concentrated NaOH solution. Several depths and concentrations were attempted ranging from barely wet through to a deep dish. Concentration was in excess of 50% NaOH with some fresh prills of NaOH thrown in for good measure.
I think that is the end of that hypothesis.

Effect of plastic
The effects were observed with a plastic petri dish and moderately concentrated NaOH (maybe 25%) to a depth of 1.5mm. The sodium burst into flame and burnt a hole in the plastic which prompted a change to glass.

Paper on top of sodium
The effects were not observed when wet filter paper was placed on top of the sodium. Again the amount of water was varied. On a couple of occasions the sodium remained in the centre of the dish and fizzed mildly. This occurred both with just a damp paper and also with up to 5mm of water poured over the top. Generally however the sodium skated around below the paper. The paper tended to balloon up with the H2 evolved. When the sodium made it to the edge of the paper it did suddenly go dark and burst into flames. I did not see it go transparent the couple of times I saw this. (I did crack a petri dish though.) The flame extinguished and left some unreacted sodium.

Submerged sodium
The effects were not observed when the sodium was submerged in a wide test tube of water and held there with a wad of steel wool.
The effects were not observed when the sodium was submerged in a test tube of water and held there by a wad of tissue paper. Instead, a bubble of H2 built up under the tissue paper and the appearance of the whole reaction was exactly the same as the standard Na on water.

The effects were observed when the sodium was sandwiched between a disc of filter paper and a wad of tissue paper and the whole thing submerged in a test tube full of water. First a quantity of H2 built up separating the papers somewhat. Then I saw the pellet turn dark blue and burst into flame. The fumes produced prevented me from seeing if the sphere had gone transparent. There was a bit of a pop but it was hard to say whether this was the same as a small pellet explosion.

Add to this the intriguing observations made by Thunderf00t with his NaK in an ampoule. There were some obvious differences to the set-up:
NaK not sodium
No paper at all
Very small volumes
Very clean metal
Ampoule open to air but limited oxygen available in top of ampoule.

The additional observations from his experiment
Obvious green metallic gas
Blue seen after the flame extinguished. (I have observed this on occasions too.)
Transparent pellet floats on water.

There are a lot of things I cannot explain here.
Thunderf00t's claim that the flame is gaseous metal reacting with steam cannot be sustained. It seems that some oxygen availability is required. (I am going to guess that some air was trapped in the test tube experiment I conducted.)
[edit]Maybe I should retract that. It appears that it is possible to get underwater flames with no access to oxygen at all. See below. Which leaves me wondering why I did not observe the flame and the colour changes when the sodiumwas covered in a sheet of filter paper.[/edit]
It seems that some kind of interaction with the paper is a contributing factor -- one that is not duplicated by glass.
A certain degree of contact with the paper seems to be needed -- something that does not occur when the paper is on the sodium but does occur when the sodium is on the paper. Of course the NaK experiment puts paid to that generalisation.
So I am unsure exactly what reaction is taking place in the flame.

Then there is the blue which could be explained either by Na gas or by an electride. Both are intriguing. I am not sure how you would determine which (if either) is correct.

And all this is before considering the transparent pellet, its composition and what makes it explode,

There is a whole lot going on here.

[Edited on 23-3-2015 by j_sum1]

[Edited on 24-3-2015 by j_sum1]

j_sum1 - 23-3-2015 at 20:53

Just for fun.
Wrap a small clean piece of sodium in a tissue paper and twist it tightly. Submerge it in water. I used a wide test tube. Allow the bulk of the paper to get wet before fully submersing to minimise the amount of air in the tissue.
Step back and watch the excitement. Underwater flames are always cool to watch.

(And it seems that I might have to modify some of my earlier thoughts.)

deltaH - 25-3-2015 at 00:53

I once did an experiment where I poked a wooden kebab stick into a small pool of very hot molten sodium hydroxide. A vigorous reaction occurs producing a carbonaceous char and gas that is flammable with a yellow flame, if memory serves correctly? The wood is probably hydrolysing, but to what exactly? Perhaps a retro aldol reaction is chopping up the cellulosic material into small flamable volatiles.

Perhaps something similar is going on here between the filter paper and hot molten bead.

j_sum1 - 25-3-2015 at 01:31

Quote: Originally posted by deltaH

I once did an experiment where I poked a wooden kebab stick into a small pool of very hot molten sodium hydroxide. A vigorous reaction occurs producing a carbonaceous char and gas that is flammable with a yellow flame, if memory serves correctly? The wood is probably hydrolysing, but to what exactly? Perhaps a retro aldol reaction is chopping up the cellulosic material into small flamable volatiles.

Perhaps something similar is going on here between the filter paper and hot molten bead.

It's a thought. But the paper seems to be relatively unscathed. I am drawing blanks whenever I think about it. Nothing I have come up with fits all the observations.

deltaH - 25-3-2015 at 08:26

Quote: Originally posted by j_sum1

... But the paper seems to be relatively unscathed. ...

No, then that doesn't sound right, the wood definitely formed a lot of black char, so you would expect the paper also to blacken if this happened. The water is probably cooling it sufficiently. Must be something else then.

[Edited on 25-3-2015 by deltaH]

deltaH - 10-3-2016 at 23:16

The plot thickens:

https://www.youtube.com/watch?v=PDRWQUUUCF0

Sodium chloride, WTF? Look at that shockwave, OMG!

What makes sodium chloride so special and not the other salts? I'm sad he didn't try molten sodium hydroxide, but I'm guessing that goes boom too.

I have a speculative hypothesis... the anion needs to be strong hard bases (HSAB theory). But, why does that matter?

While I think water is entering, mixing and superheating, I think there is more at play than just a physical process. Some kind of fast water conduction (like fast ion conduction)? I wish this would be studied more because I think there is unusual phenomenon at play here.

[Edited on 11-3-2016 by deltaH]

j_sum1 - 11-3-2016 at 04:26

Interesting.
Agree that NaOH would be a sensible salt to try. As would KCl.

Pok - 11-3-2016 at 07:07

I made a similar observation during the reaction of potassium with water a few years ago. I also thought of "transparent metal" but very soon I found the explanation in the literature (Leidenfrost effect of molten KOH):

with photoflash only the smoke and the purple flame is visible:

When the flame extinguishes, the smoke formation also stops and a transparent little ball is visible which is running over the water:

detail of the ball:

another ball:

j_sum1 - 11-3-2016 at 17:06

I get that Pok, but there are still a bunch of unanswered questions.
I am confident that the transparent bead is either molten NaOH or Na2O or a mix of the two. And I am pretty sure that some leidenfrost effect prevents it from reacting immediately. I think the transparent bead explosion occurs when the bead cools somewhat and the leidenfrost effect diminishes. And I think the "explosion" is driven by heat of dissolution when the bead contacts the water.

But still unanswered...

Why does this transparency phenomenon only happen when the paper is present?
Why does the sodium burst into flame with the paper present but this does not happen with water only?
What is the blue-black skin that appears?
And now, thanks to deltaH, what is going on that molten NaCl and perhaps some other salts interact with water in an explosive way that is not observed with borax, sodium bicarbonate and other salts? I don't think thebackyardscientist's explanation is complete enough to account for the observations or adequately describe a mechanism.

deltaH - 11-3-2016 at 22:39

Previously in this thread I had calculated that the heat released by a molten Na2O combined with hydration gives similar energy outputs as a TNT explosion, so I thought this was enough to explain the bang, BUT

we observe a bang with even just molten NaCl, which leads me to believe that the explosion DOESN'T have hydration occurring, that happens slowly in the prior step resulting in strong heating (the stage when the bead turns red?)

The explosion seems to be due pure to a later stage portion where the product is in very hot molten form. NaOH for the case of sodium, probably. The chemical reaction stage doesn't seem too important, it might 'merely' be the engine that get's the final salt bead to a high enough temperature, i.e. it's not that very high initial reaction heats that causes the explosion

The main question, why the sudden detonation-like explosion at the end and why with certain molten salts only?

One very important observation thebackyardscientist makes is that 'just' molten salt isn't enough, it has to be very hot molten salt.

Pok - 12-3-2016 at 06:00

Quote: Originally posted by j_sum1

Why does this transparency phenomenon only happen when the paper is present?

I don't think that this is true. With potassium no paper is needed. The same for sodium (probably, haven't tried it).

Quote: Originally posted by j_sum1

Why does the sodium burst into flame with the paper present but this does not happen with water only?

The paper prevents the sodium from running away. The heat can build up locally so that the hydrogen (not the sodium) inflames. Maybe some sodium vapour (which ignites) starts this reaction. This could be the reason why in the case of potassium there is always a flame visible (lower boiling point).

@delta-H: why at the end? Because the Leidenfrost effect stops.

And concerning the NaCl/H2O explosion: the youtube video shows reference where possible explanations are given for the molten salt explosion. There is alot of literature, e.g. here. It doesn't have anything to do with strong bases or so. Molten metals can show the same behaviour.

[Edited on 12-3-2016 by Pok]

deltaH - 12-3-2016 at 06:16

Thanks for that literature Pok. It is very extensive, I think the answers I seek are probably there.

MeshPL - 12-3-2016 at 07:49

Has anybody tried to poke that sodium with a glass rod? Or in any other way? Or to pick it up using coffe grater? Or to dump liquid N2 on it? Or to use ethanol or any other solvent with varying amounts of water? Or to drop sodium into an acid or something simmilar? (I realised I've never seen dumping sodium into actual acid, only water and ammonia and alcohols. Reaction of Na with >90% HNO3 could be fun

)

Edit: reactions of acids with sodium are not much more fun than reaction of water. There are some videos on youtube. Well, in one of them I've seen slightly simmilar behaviour of sodium to the transparent sodium in Thoisoi2 video:

https://youtu.be/X_vMr-3P0KQ

But only with Na in 4M H2SO4. The sodium blob ignites and fizzes, than stops burning, goes dark gray and than pops, it kinda omits transparent stage.

[Edited on 12-3-2016 by MeshPL]

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