Charged Ice Coil Gun

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davetp425
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Charged Ice Coil Gun

Postby davetp425 » Mon Dec 15, 2008 3:36 am UTC

Is this possible (despite it being completely impractical):

Take a volume of water with salt dissolved in it. Polarize it, EDIT: apply an electric field to it so that the Na+ ions drift to one end and the Cl- ions drift to the other, then divide it in half to have two charged volumes of liquid. Each volume is water with only Na+ and Cl- dissolved, but one has more Na+ and the other has more Cl-. Freeze one. (This may be difficult because of the lowered freezing point from adding salt, but should still be possible.) Shape the charged ice into a projectile somewhere from a foot to a meter in length. Put it into a coil gun. Fire it at a speed low enough that it doesn't completely melt. Now you can shoot things and the bullet will melt and evaporate.

I remember seeing something about ice bullets on TV, might have been Mythbusters but I'm not sure. The combination of high speed and heat from the gunpowder melted it, but I think using a well cooled coil gun, a larger projectile, and possibly a lower speed could overcome this.
Last edited by davetp425 on Tue Oct 20, 2009 3:57 am UTC, edited 1 time in total.

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Durandal
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Re: Charged Ice Coil Gun

Postby Durandal » Mon Dec 15, 2008 3:52 am UTC

You don't know how polarization works, do you?

Also, completely saturated saltwater only has a freezing point of around -21 degrees Celsius. So freezing is the very least of your problems.

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Re: Charged Ice Coil Gun

Postby Charlie! » Mon Dec 15, 2008 4:51 am UTC

Durandal wrote:You don't know how polarization works, do you?

Also, completely saturated saltwater only has a freezing point of around -21 degrees Celsius. So freezing is the very least of your problems.

Maybe he just meant "stick it in a big electric field so that some of the Na separate from the Cl.
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Re: Charged Ice Coil Gun

Postby Cryopyre » Mon Dec 15, 2008 6:15 am UTC

yeah, he's talking about electrolysis.
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Re: Charged Ice Coil Gun

Postby TCL987 » Mon Dec 15, 2008 6:26 am UTC

Better yet do the exact opposite and make plasma weapons.

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Re: Charged Ice Coil Gun

Postby Carnildo » Mon Dec 15, 2008 10:05 am UTC

davetp425 wrote:Is this possible (despite it being completely impractical):

Take a volume of water with salt dissolved in it. Polarize it, then divide it in half to have two charged volumes of liquid. Freeze one.


This step doesn't work. Freezing is a good way to force all sorts of contaminants out of water -- in fact, in cold climates, you can desalinate water by sticking a bucket of saltwater outside overnight, draining off the concentrated brine that results, and melting the ice.

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Re: Charged Ice Coil Gun

Postby Cryopyre » Mon Dec 15, 2008 10:58 pm UTC

Not necessarily, if you freeze it quickly you can freeze the salt inside the water. The only reason what you're describing happens is because the salt filled water melts and freezes at different temps.
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Re: Charged Ice Coil Gun

Postby davetp425 » Tue Dec 16, 2008 3:09 am UTC

Charlie! wrote:Maybe he just meant "stick it in a big electric field so that some of the Na separate from the Cl.


Yeah, pretty much. My understanding is that since NaCl is a strong electrolyte, the vast majority of the Na+ separate from the Cl- when you dissolve them. And I thought to polarize a solution would therefore involve the charges moving around, just like the electrons in a metal gather more on one side when you stick it in a big electric field.

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Re: Charged Ice Coil Gun

Postby 4=5 » Tue Dec 16, 2008 5:07 am UTC

Perfect bullet: frozen tumor. If the shooting doesn't get them the cancer will.

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Re: Charged Ice Coil Gun

Postby Ann_on_a_mouse » Tue Dec 16, 2008 5:42 am UTC

4=5 wrote:Perfect bullet: frozen tumor. If the shooting doesn't get them the cancer will.
I think CSI might be trying this plot out. A cancer gun seems right up their alley.

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Re: Charged Ice Coil Gun

Postby Phoenix112358 » Tue Dec 16, 2008 7:44 am UTC

davetp425 wrote:
Charlie! wrote:Maybe he just meant "stick it in a big electric field so that some of the Na separate from the Cl.


Yeah, pretty much. My understanding is that since NaCl is a strong electrolyte, the vast majority of the Na+ separate from the Cl- when you dissolve them. And I thought to polarize a solution would therefore involve the charges moving around, just like the electrons in a metal gather more on one side when you stick it in a big electric field.


I don't see how this can work.

If you're planning on electrolysing a NaCl solution, it doesn't work, as far as I know. The Na+ ion is too weak of an oxidant to be reduced by electrolysis in water, instead the water electrolyses and makes H2 and OH-. So you'll still have the Na+, yes. However, the Cl- oxidises and forms Cl2, which doesn't carry a charge. So you'll end up with Na+ ions gathering at one end but the other end Chlorine gas forms and then exits the system.

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Re: Charged Ice Coil Gun

Postby Carnildo » Tue Dec 16, 2008 8:54 am UTC

Phoenix112358 wrote:
davetp425 wrote:
Charlie! wrote:Maybe he just meant "stick it in a big electric field so that some of the Na separate from the Cl.


Yeah, pretty much. My understanding is that since NaCl is a strong electrolyte, the vast majority of the Na+ separate from the Cl- when you dissolve them. And I thought to polarize a solution would therefore involve the charges moving around, just like the electrons in a metal gather more on one side when you stick it in a big electric field.


I don't see how this can work.

If you're planning on electrolysing a NaCl solution, it doesn't work, as far as I know. The Na+ ion is too weak of an oxidant to be reduced by electrolysis in water, instead the water electrolyses and makes H2 and OH-. So you'll still have the Na+, yes. However, the Cl- oxidises and forms Cl2, which doesn't carry a charge. So you'll end up with Na+ ions gathering at one end but the other end Chlorine gas forms and then exits the system.


That's only if you run a current through the water. If you put a pair of charged plates outside the bucket, you should get a charge separation: the Cl- tending to move to one side, and the Na+ tending to move to the other.

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Re: Charged Ice Coil Gun

Postby Tass » Tue Dec 16, 2008 9:10 am UTC

But the charge separation is very small, and quickly neutralized by stray ions from the air anyway.

Just charge the ice.

But in any case an electrostatic coil gun is very impractical exept when shooting individual ions.

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Re: Charged Ice Coil Gun

Postby Phoenix112358 » Tue Dec 16, 2008 11:15 am UTC

Carnildo wrote:That's only if you run a current through the water. If you put a pair of charged plates outside the bucket, you should get a charge separation: the Cl- tending to move to one side, and the Na+ tending to move to the other.


Ah, I see. I stand corrected! Didn't even occur to me that you could do that. xD

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Re: Charged Ice Coil Gun

Postby davetp425 » Tue Oct 20, 2009 3:53 am UTC

So I'm just remembering that I posted this almost a year ago and kind of abandoned it...

but I wanted to clarify what I meant:

You have a tub of NaCl(aq), which is really Na+(aq) and Cl-(aq) because NaCl is an electrolyte.
If you apply an electric field to the tub somehow...
Will the concentration of each ion be a gradient across the field?
That is, would there be more Na+ on one side and more Cl- on the other because the field applies a force to the charged particles?

Then, couldn't you extract a volume of water that contains only Na+ and Cl-, but which has a higher concentration of one ion than the other (giving the sample a net charge)?

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Re: Charged Ice Coil Gun

Postby rflrob » Tue Oct 20, 2009 4:19 am UTC

Tass wrote:But the charge separation is very small, and quickly neutralized by stray ions from the air anyway.

Just charge the ice.

But in any case an electrostatic coil gun is very impractical exept when shooting individual ions.


What if you had two bullet shaped glass (or your favorite insulator) containers, filled with salt water, connected by a severable tube, then applied an electric field to the outside? Once you had your salt-ice bullets, it seems to me that they wouldn't conduct very well...

Actually, that is an interesting question... how conductive is ice? My sense of things that most of water's conductivity was actually ions flowing around (distilled water is actually insulative), so if you blocked that movement by freezing, it'd be an insulator again.
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Re: Charged Ice Coil Gun

Postby sikyon » Tue Oct 20, 2009 4:44 am UTC

How exactly were you planning on shooting this?

You realize that coilguns rely on magnetic bullets.

To create a magnetic coilgun you would... have to make a double inductor system (each coil is a coil, methinks) but that seems both needlessly complex and rather large.

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Re: Charged Ice Coil Gun

Postby Kow » Tue Oct 20, 2009 5:17 am UTC

sikyon wrote:How exactly were you planning on shooting this?

You realize that coilguns rely on magnetic bullets.

To create a magnetic coilgun you would... have to make a double inductor system (each coil is a coil, methinks) but that seems both needlessly complex and rather large.

The OP realizes this. Which is why he's trying to charge the water to make charged ice to shoot in place of a magnetic object.
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Re: Charged Ice Coil Gun

Postby BlackSails » Tue Oct 20, 2009 5:29 am UTC

I remember thinking of somethiing similar to this once.

It wont work. You cant possibly induce enough charge seperation.

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Re: Charged Ice Coil Gun

Postby skeptical scientist » Tue Oct 20, 2009 5:31 am UTC

There's a much easier way to shoot an ice bullet: use an air cannon. Expanding air won't create any heat, and there's probably no more friction than with the coil gun.

As for the effectiveness of an ice bullet, I have no idea. The Mythbusters tested ice bullets on Magic Bullet and again on Myths Revisited, and busted the idea both times because the exploding gunpowder vaporized the bullets rather than propelling them when fired from a rifle. However, they didn't test any firing methods other than rifles, so they never managed to test the damage they would inflict; just whether they could be fired from a rifle.
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Re: Charged Ice Coil Gun

Postby sikyon » Tue Oct 20, 2009 12:19 pm UTC

Kow wrote:
sikyon wrote:How exactly were you planning on shooting this?

You realize that coilguns rely on magnetic bullets.

To create a magnetic coilgun you would... have to make a double inductor system (each coil is a coil, methinks) but that seems both needlessly complex and rather large.

The OP realizes this. Which is why he's trying to charge the water to make charged ice to shoot in place of a magnetic object.


What would your gun setup be.

Electric Charge =/= magnetic dipole.

You can't just replace the magnetic bullet in a coilgun with a charged bullet...

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Re: Charged Ice Coil Gun

Postby skeptical scientist » Tue Oct 20, 2009 9:57 pm UTC

The principles are quite similar, it's simply a matter of setting up an electric field rather than a magnetic field.
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Re: Charged Ice Coil Gun

Postby Goemon » Wed Oct 21, 2009 5:36 am UTC

Ever seen Kelvin's Thunderstorm? You can put a charge on a bucket of water without needing any salt or external fields...

A "capacitor gun" or whatever you want to call it - to shoot a charged object using electric fields - probably couldn't match a real coil gun or other device using magnetic fields. In practice, electric fields have much lower energy density than magnetic fields. That's why your vacuum cleaner uses a magnetic motor and not an electrostatic one. Ion drives are efficient for spacecraft, but generate REALLY low thrust.
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Re: Charged Ice Coil Gun

Postby sikyon » Wed Oct 21, 2009 8:44 pm UTC

skeptical scientist wrote:The principles are quite similar, it's simply a matter of setting up an electric field rather than a magnetic field.


It's not the science in question, it's the engineering of the system that is difficult. Good luck getting enough voltage in a handheld device to drive this using a capacitor around the barrel.

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Re: Charged Ice Coil Gun

Postby Tass » Wed Oct 21, 2009 8:52 pm UTC

rflrob wrote:What if you had two bullet shaped glass (or your favorite insulator) containers, filled with salt water, connected by a severable tube, then applied an electric field to the outside? Once you had your salt-ice bullets, it seems to me that they wouldn't conduct very well...

Actually, that is an interesting question... how conductive is ice? My sense of things that most of water's conductivity was actually ions flowing around (distilled water is actually insulative), so if you blocked that movement by freezing, it'd be an insulator again.


Sure you probably could charge ice that way, but they wont stay charged for very long regardless of whether they are conducting. If there are positive charge trapped inside then negative charges from the air are going to build up on the surface until it is neutral.

You are better off freezing a projectile and then charging it with an electron gun afterwards (or just a Van de Graaf). In the short term what will limit the amount of charge you can put on it will be the breakdown voltage of the air, or electron tunneling voltage in vacuum.

In any case it probably bears repeating that this is not a coil gun, but an electrostatic gun, which will be terribly inefficient for macroscopic objects, although they work great on ions.

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Re: Charged Ice Coil Gun

Postby sikyon » Wed Oct 21, 2009 9:23 pm UTC

Meteorswarm wrote:I don't actually know how this would work, so the following is a conjecture:

If you need a dipole to launch, could you apply a VERY strong electric field to your ice in the container you want to freeze it, and then freeze it with the field still active? That way, the ice itself would be a big dipole.


Theoretically it's definitely possible.

However, the primary reason that I could think of for an ice gun would be an untraceable bullet.
In this event, you'd obviously want it to be capable of being held in your hands. Furthermore you'd probably want it as small as possible, so that you can get closer to your target.

With these design constraints, it is extremely unlikely that you could actually implement the idea and meet them.

Remember, anyone can have an idea. But ideas are only valuable if they can be put to use.

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Re: Charged Ice Coil Gun

Postby sikyon » Thu Oct 22, 2009 4:04 am UTC

Meteorswarm wrote:
sikyon wrote:
Meteorswarm wrote:How conductive is ice, anyway?


Good question. I can't pretend to be an expert but I will give it a shot. It has been awhile though so my fundamentals may infact be wrong.

Electrical conductivity from the ions is not because the ions actually move. It is from the movement of the free electrons from the ions.

If you were to use an electric field to separate ice, then you would have a bunch of positive p-type sodium and negative n-type clorine on each side. This would basically form a p-n junction in your water.

If you then froze these ions in place, you would have a p-n junction. These are addressed typically by semiconductor considerations. That is, it should act like a diode.

Without an electric field, if you freeze ice then most of the ions will probably come together (poorer solivation) and become non-conducting, but if they did infact stay in solution then the ice should be fine as a conductor, if not better than before due to the rigidity of the crystaline structure.

Again, I am not that familiar with ice.

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Re: Charged Ice Coil Gun

Postby skeptical scientist » Thu Oct 22, 2009 10:28 am UTC

sikyon wrote:
skeptical scientist wrote:The principles are quite similar, it's simply a matter of setting up an electric field rather than a magnetic field.


It's not the science in question, it's the engineering of the system that is difficult. Good luck getting enough voltage in a handheld device to drive this using a capacitor around the barrel.

Very true, but the entire thread is way too speculative to be worrying about how hard the engineering would be, imo. The question was what is possible in principle, not what is practical.
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Re: Charged Ice Coil Gun

Postby Technical Ben » Thu Oct 22, 2009 5:04 pm UTC

They have been able to levitate a frog using really powerful magnets to pull on the water molecules in it's body (in a similar way that microwaves effect water in a microwave oven).
So, why not just have a massive magnetic rail gun and use that to fire a ice bullet? However, if you have a handheld device capable of producing that big a magnetic field, you could just point it at the target and neatly vapourise it. :P
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Re: Charged Ice Coil Gun

Postby skeptical scientist » Thu Oct 22, 2009 7:19 pm UTC

Technical Ben wrote:So, why not just have a massive magnetic rail gun and use that to fire a ice bullet?

Because ice doesn't conduct electricity.
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Re: Charged Ice Coil Gun

Postby Heisenberg » Thu Oct 22, 2009 8:59 pm UTC

skeptical scientist wrote:
Technical Ben wrote:So, why not just have a massive magnetic rail gun and use that to fire a ice bullet?

Because ice doesn't conduct electricity.

No problem. Build a gun that accelerates a metal piece but doesn't release it. Put the ice bullet in front of the metal piece.

It works with a coil and a piece of plastic. Can't imagine why it wouldn't work for ice.

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Re: Charged Ice Coil Gun

Postby Technical Ben » Thu Oct 22, 2009 9:33 pm UTC

skeptical scientist wrote:
Technical Ben wrote:So, why not just have a massive magnetic rail gun and use that to fire a ice bullet?

Because ice doesn't conduct electricity.


Sorry, I got rail gun, and coil gun back to front! :facepalm:
Ok, I missed the point that ice looses all the conductivity that water has through ionisation. How about shooting a jelly mold? At a high enough speed, it will be equivalent to a bullet...
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