Author Topic: High speed camera reveals why sodium explodes! (5 billion amps)  (Read 30071 times)

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Offline EEVblog

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #25 on: January 31, 2015, 01:33:57 pm »
Yes, his channel looks positively loony.

His channel might look loony because it's mostly about using science and reason to debunk and challenge loony stuff.
If you don't like that stuff then there is plenty of just straight science stuff.
 

Offline hamdi.tn

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #26 on: January 31, 2015, 02:40:13 pm »
saw that yesterday and it's amazing , what i mostly like is how he explain the way science work from observation to experience to analysis to conclusion , and how challenging to look behind the obvious, all that with so much enthusiasm.  :clap: walking this path is as valuable as the discovery it self.
 

Offline tom66

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #27 on: January 31, 2015, 03:32:31 pm »
Maybe if you could find some way to make it directional - for example place it in a minature tube and wrap a separate coil around each end, you could induce a brief pulse of current. Not sure how useful it would be though.
 

Offline G7PSK

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #28 on: January 31, 2015, 03:34:36 pm »
Maybe if you could find some way to make it directional - for example place it in a minature tube and wrap a separate coil around each end, you could induce a brief pulse of current. Not sure how useful it would be though.
Some form of ultra powerful battery that produces a pulse of power, Star wars type laser weapons comes to mind.
 

Offline Marco

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #29 on: January 31, 2015, 04:08:47 pm »
The current is obviously traveling only a very short distance, and it's not very coherently directed, so the vector sum of all the currents is going to be small.  It would be hard to measure, and much harder to harness.

The initial escape of the electrons happens before the drop deforms into spikes and on the side hitting the water it's straight away from the surface of the drop (current from the back will be coherent too, just mostly cancelling out EM wise).

That said, I have my doubts about the current. The current on the initial surge away from the surface is limited by the speed at which the surface of the drop enters the water, the current on the second surge is limited by the chaotic nature of chemical reactions. I'd have to see the actual calculations to buy it.

You could wet the tip of a small wire with NAK and drop it in the water to get a better radiator BTW. Equipotential and all.
 

Offline hamdi.tn

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #30 on: January 31, 2015, 04:22:18 pm »
i watched the video 3 times and am not sure how he jumped to the 5 billion amps conclusion ... i guess it's the number of positive charge accelerating in the point where everything goes boom going through the total spherical surface around the point where the reaction take place, and since this reaction happen layer by layer until all the sodium decompose allowing more particulars to accelerate and to be taking in count of this current calculation he made. ... i can be talking rubbish right now  :-DD

The current is obviously traveling only a very short distance, and it's not very coherently directed, so the vector sum of all the currents is going to be small.  It would be hard to measure, and much harder to harness.
 
since a current is the quantity of charge going through a surface and if you suppose all the material go through that surface in the same time it will be easy to consider that as a current. yes he vector sum of all the currents is going to be small.
 

Offline Zero999

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #31 on: January 31, 2015, 06:19:26 pm »
I don't see how one could measure the current and if it does radiate, most of the radiation will be absorbed by the water. The timescale of the current pulse is in the ps range so any resulting radiation will be in the upper microwave/low IR band, which doesn't pass through water and is attenuated by even short pieces of cable by the skin effect.
« Last Edit: January 31, 2015, 07:02:46 pm by Hero999 »
 

Offline IanB

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #32 on: January 31, 2015, 06:53:43 pm »
One thing about the current that nobody seems to be noticing is that it must be balanced by an equal and opposite current. Consider: the system starts out neutral. So if a large amount of negative charge accumulates in one place, an equal and opposite amount of positive charge must accumulate nearby at the same time. Since these two bodies of charge are now going to move apart and spread out simultaneously, the net movement of charge in the system will remain balanced and close to zero overall on a macroscopic scale. It is highly unlikely that an unbalanced current flows sufficient to produce EM or magnetically detectable effects.
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Offline lapm

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #33 on: January 31, 2015, 06:59:59 pm »
Now thats some impresive amps... maybe they could try calculate total power to ;)
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Offline devanno

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #34 on: January 31, 2015, 07:03:48 pm »
Rather than trying to capture the current, why not capture the energy of the pressure wave from the explosion? 
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Offline tom66

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #35 on: January 31, 2015, 07:04:46 pm »
Hang on. Even if the net charge balances out over the whole system, what would happen if you isolated one portion... for example, a coil of wire on only one half of the test tube. Would you be able to measure a change in charge there?

I don't think there will be significant power available but it would be interesting to see what the discharge looks like on a scope which could have 1ns resolution.

I might just have to get me some sodium...
 

Offline Marco

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #36 on: January 31, 2015, 07:14:44 pm »
One thing about the current that nobody seems to be noticing is that it must be balanced by an equal and opposite current.
Only on larger time scales, initially the flow of electrons to the water preceding and during the mechanical deformation happens faster than the chemical reaction which brings everything back to electrical equilibrium. You could not get a Coulomb explosion if the NAK wasn't at a non-zero potential.
 

Offline Zero999

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #37 on: January 31, 2015, 07:22:11 pm »
Hang on. Even if the net charge balances out over the whole system, what would happen if you isolated one portion... for example, a coil of wire on only one half of the test tube. Would you be able to measure a change in charge there?

I don't think there will be significant power available but it would be interesting to see what the discharge looks like on a scope which could have 1ns resolution.

I might just have to get me some sodium...
There's no way this could be used to generate useful energy because it takes more energy to isolate alkali metals from their salts than is released during the violent reaction with water.

How would an oscilloscope with 1ns resolution help when we're talking about ps timescales here and that coil of wire is huge compared to the wavelengths generated?
 

Offline Marco

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #38 on: January 31, 2015, 07:22:55 pm »
If you earth a piece of Natrium and drop it in water (salt and earth the water as well while you're at it). Will it still explode?
 

Offline tom66

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #39 on: January 31, 2015, 07:24:33 pm »
Well, I was talking about faster than the high speed camera which captures in 100us intervals. It would be interesting to see the field change there. And, you could use a single turn to minimise any wavelength effects (transmission line?) or tune it to the right length, although you'd need a much higher sensitivity setting.

I'm probably not a chemist for a very good reason.
 

Offline IanB

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #40 on: January 31, 2015, 07:41:41 pm »
Only on larger time scales, initially the flow of electrons to the water preceding and during the mechanical deformation happens faster than the chemical reaction which brings everything back to electrical equilibrium. You could not get a Coulomb explosion if the NAK wasn't at a non-zero potential.

But the flow of electrons into the water leaves behind a positive charge on the sodium, producing a sea of negative charge surrounding a sea of positive charge. The system remains balanced at that scale.

After this happens the sodium disperses, the metal particles expanding rapidly into the surrounding water due to charge repulsion. This movement of positively charged sodium particles does represent a current flow. But there is at the same time a movement of negatively charged water molecules away from each other due to their own charge repulsion. Because water molecules are transparent the camera doesn't pick this up. But the two simultaneous movements of charged particles will tend to cancel each other out.

When fresh sodium atoms contact water molecules an electron is transferred producing a positive ion adjacent to a negative ion. In each one of these transactions the system is electrically balanced.

So it is not really correct to say the chemical reaction brings everything back to equilibrium. The transfer of an electron from a sodium atom into the surrounding water is the chemical reaction. All that happens after that is that the electron attached to a water molecule displaces a hydrogen atom (this hydrogen atom was previously donating an electron of its own which is no longer needed--the electron coming from the sodium atom gives back the donated electron to the hydrogen atom allowing the hydrogen to float free leaving an OH- ion behind). This latter reaction (H2O + e- = OH- + ½H2) is charge balanced.
« Last Edit: January 31, 2015, 08:10:44 pm by IanB »
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Offline Zero999

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #41 on: January 31, 2015, 08:01:23 pm »
And, you could use a single turn to minimise any wavelength effects (transmission line?) or tune it to the right length, although you'd need a much higher sensitivity setting.
You'd need a very small coil. A period of 1ps, is a frequency of 1THz and a wavelength of 300um.

Only on larger time scales, initially the flow of electrons to the water preceding and during the mechanical deformation happens faster than the chemical reaction which brings everything back to electrical equilibrium. You could not get a Coulomb explosion if the NAK wasn't at a non-zero potential.

But the flow of electrons into the water leaves behind a positive charge on the sodium, producing a sea of negative charge surrounding a sea of positive charge. The system remains balanced at that scale.
Does that really mean it won't radiate?

The random motion of electrons in any substance causes EM radiation to be emitted (thermal radiation) even though the average momentum is zero.

The emitted spectrum would be interesting but unfortunately water blocks most of it so it would be difficult to measure.
 

Offline T3sl4co1l

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #42 on: January 31, 2015, 08:02:39 pm »
The current flow is due to the reduction potential of the metal: around 3V.  It truly is a massive current.  Perhaps not as massive as claimed -- a liter won't react instantaneously, as only the surface is doing anything, as noted.  But also, the surface area might be fantastically wider than is apparent from the one frame of evidence provided...and the event itself might be taking place in fantastically smaller time scales than these cameras can measure!

It might produce unbalanced E&M, sensible as radiation.  The peak frequencies will probably be on the order of dimensional features of the system (wavelength around the width of the droplet, or length of the spikes), or frequencies on the order of physical activity of the system (milliseconds, microseconds, nanoseconds -- femtoseconds??).

Chemical reactions generally proceed quickly, on the atomic level, because atoms are small; but there may not be much amount of reaction taking place, because of the limitations of surface area.  So, maybe not femtoseconds (hell, if the instant of the explosion was going *that* fast, I'd expect to see gamma and neutron radiation resulting from hydrogen fusion!), but microseconds are absolutely on the table.

There are also frequencies due to energy levels rather than time constants, which are quantum in origin.  This is actually easy to anticipate and disregard: sodium's reduction potential is around 3V, as are other molecular and atomic orbital interactions.  So you'd expect visible light from the reaction; which you don't observe, except as secondary byproducts (primarily the subsequent hydrogen flare-off).  That's simply because some reactions do result in emission (the colors of a candle flame are due to blue and green spectral lines of CH2 and CH radicals, and the broad yellow emission of diatomic C2), some simply don't.  You could perhaps liken it to the difference between direct and indirect bandgap semiconductors, which are good and bad for LEDs, respectively.

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Offline T3sl4co1l

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #43 on: January 31, 2015, 08:19:46 pm »
If you earth a piece of Natrium and drop it in water (salt and earth the water as well while you're at it). Will it still explode?

Yes.

You can perform this experiment yourself, on a much safer scale:

Obtain a piece of aluminum (any kind will do, as long as it's uncoated), and an alkaline solution (preferably NaOH or KOH in H2O; others won't be corrosive enough).  For cathode, use something generic like steel or copper.

Insert the metals in solution (not touching), and observe the aluminum begins to bubble (hydrogen).  Measure the voltage between the electrodes; should be something like 0.8V.

The [ideal] reduction potential of aluminum is actually something like 2V.

Short the electrodes together, and you should see some hydrogen from the cathode as well (this is due to the electrolysis current).  Measure the current and you'll probably see something in the mA range -- it's a bad battery, but it does produce some power.

Now apply more than 2V (in the same polarity as measured).  Ideally... this should stop, in fact reverse the reaction.  But at most, you will simply cause more hydrogen to be produced (at the cathode), and not be able to prevent hydrogen production at the anode.

The reason is this: aluminum is so reactive that it is attacked by water, even when polarized with plenty of voltage.  It is impossible to apply sufficient polarization to prevent attack, because the water itself will decompose above 1.2V or so.  You simply can't get the necessary 2V at the metal-to-water interface -- try, and it tears itself apart.  It doesn't matter whether this is applied to inert electrodes (like graphite or platinum) or by the force of a metal.  It looks the same: the metal gives up electrons, with such force (electromotive force -- voltage) that the water is broken down in the process.

So, you might have an ideally 2V battery, but it only measures 1.2V (or less), and the remaining 0.8V is simply lost to heat, whether you're discharging the cell or not.  So, the self-discharge is terrible, too.  This is basically part of the reason why aluminum batteries aren't a thing, by the way...

You can react aluminum with an oxidant in an alternate solvent, and observe its reduction potential correctly; such solvents peak around 2.5 or 3V (something like propyl carbonate with a dissolved ionic salt), which is also necessary for lithium ion batteries, and also why ultracapacitors are rated for exactly 2.5V and little more: above this, the solvent breaks down, just as water breaks down beyond 1.2V.  (You can build your own ultracapacitor, at home, using activated charcoal pads and salt water; it will have extremely high ESR because it's not optimized, and once again, 1.2V maximum before it stops working much like a capacitor.  But the extreme capacity -- 10s to 1000s of farads -- is nonetheless sensible, as long as you take your time measuring it.)

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Offline Dave Turner

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #44 on: January 31, 2015, 08:35:58 pm »
To me whether or not it takes more energy to refine the metals than is released in the reaction is almost irrelevant. After all the same could be said of the use of batteries yet their value is undeniable.

Of more interest is whether or not it is possible to utilise the undeniable energy released in a controllable/directable manner. With greater understanding of the mechanism of the reaction comes the possibility of further innovation.

I don't pretend to know how such a result could be accomplished but am reluctant to accept that it would be impossible without detailed research.
 

Offline XynxNet

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #45 on: January 31, 2015, 08:49:00 pm »
Well, it's a cool discovery and also how it came to be is a great story.

What i really don't like are the parts of the video, where he drones on how everybody else was wrong and didn't see the obvious.
Even going as far as cutting in some scenes of the periodic table guys.

That's just cheap in my opinion.
It's inherent to the process of scientific discovery that you look at an former overlooked aspect. It's also inherent to scientific progress to confirm, disprouf or add to older theories.
 

Offline T3sl4co1l

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #46 on: January 31, 2015, 09:35:26 pm »
To me whether or not it takes more energy to refine the metals than is released in the reaction is almost irrelevant. After all the same could be said of the use of batteries yet their value is undeniable.

Of more interest is whether or not it is possible to utilise the undeniable energy released in a controllable/directable manner. With greater understanding of the mechanism of the reaction comes the possibility of further innovation.

I don't pretend to know how such a result could be accomplished but am reluctant to accept that it would be impossible without detailed research.

http://en.wikipedia.org/wiki/Sodium%E2%80%93sulfur_battery ?

Tim
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Offline EEVblog

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #47 on: January 31, 2015, 10:00:46 pm »
What i really don't like are the parts of the video, where he drones on how everybody else was wrong and didn't see the obvious.
Even going as far as cutting in some scenes of the periodic table guys.
That's just cheap in my opinion.
It's inherent to the process of scientific discovery that you look at an former overlooked aspect. It's also inherent to scientific progress to confirm, disprouf or add to older theories.

I bet if you discovered a major thing like this you'd be crowing about that no one else found it either.
If the periodic table guys did a video on this and got it wrong, then that's fair enough to point that out.
 

Offline IanB

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #48 on: January 31, 2015, 10:56:39 pm »
If the periodic table guys did a video on this and got it wrong, then that's fair enough to point that out.

If you watch the video ( http://youtu.be/7IT2I3LtlNE ), it's not like they got it wrong. They simply observed the explosions and said "Ooh! Cool!". They did not attempt to give any deeper explanation of why the explosions happened.

Someone perhaps should have asked, "Why does the reaction proceed smoothly for a while and then suddenly go bang? Why doesn't it go bang the instant you drop the sodium in the water?" We cannot know why that question wasn't asked. But perhaps the periodic videos team will do a follow up video given the recent publication.
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Offline Marco

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Re: High speed camera reveals why sodium explodes! (5 billion amps)
« Reply #49 on: January 31, 2015, 11:13:25 pm »
The reason is this: aluminum is so reactive that it is attacked by water, even when polarized with plenty of voltage.  It is impossible to apply sufficient polarization to prevent attack

But I was not suggesting stopping the reaction in the first place, so the experiment safe as it may be doesn't really prove much ... it's not reaction which causes the explosion, it's the surface of the metal repelling itself. If the aluminium is grounded can the surface of the aluminium still maintain a potential?
« Last Edit: January 31, 2015, 11:20:26 pm by Marco »
 


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