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Water and plasma

by The legend
Tags: plasma, water
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The legend
#1
Mar30-10, 12:48 AM
P: 423
Hello,
Recently i was into chem books and read about this plasma matter. So now i know plasma matter is in the sun and all stars and also in the humble candle flame.

What i wanna know is whether only a few kinds of elements can form plasma or is it that all compounds,(eg water) and elements (or molecules or atoms ....) can exist in plasma state.

If yes, where is the plasma form of water found?

If no, why cant all elements exist in plasma?

(Look i might be making a mistake or might be overlooking something. If anything as such, please correct me.)
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Borek
#2
Mar30-10, 02:43 AM
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Any substance - regardless of what is its composition - becomes plasma if heated high enough. However, once it is heated it doesn't contain molecules, as all chemical bonds are broken.

There are some differences in plasma properties depending on what has been converted into plasma, but they don't depend on the substance, but just on the composition - that is, it doesn't matter if you heated metallic copper and elemental sulfur in equimolar proportions, or copper sulfide - resulting plasma will be identical, but slightly different from plasma made by heating water. But my guess is that you are at the very beginning of learning science - at this stage you don't have to worry about these differences.

Note, that there are also very important differences based on the plasma temperature - while plasma can be found both in stars and flame, their temperature differs by orders of magnitude.

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The legend
#3
Mar31-10, 02:39 AM
P: 423
Thanks Borek!!!
Thats one doubt out of my mind.
Another question. Has any form of water plasma ever been made by humans and at what temperature does it change into plasma and back?
And when it changes back(hopefully it does) does it then exist in molecular or broken(atomic) form???

Borek
#4
Mar31-10, 03:02 AM
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Water and plasma



This is in German so I don't understand a word, but it is about making plasmoids over water, so my bet is these plasmoids contain ionized hydrogen and oxygen from water.

What you get after plasma cools down... depends. In the case of water I think recombination of hydrogen and oxygen to make water back seems the most obvious path. In the case of other substances final result will depend on combination of thermodynamic stability and kinetics, just like in case of any other chemical reactions. So - especially when you start with more complicated compounds - don't expect to get them back.

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The legend
#5
Mar31-10, 04:27 AM
P: 423
Yup!!!
got it!!!
(though even I dont understand German.......)
DrDu
#6
Mar31-10, 09:48 AM
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As far as I know, a (relatively) cold plasma can contain even molecules and molecular ions. E.g. in the spectra of rather cold stars (red giants), there are lines of molecular ions present.
mgb_phys
#7
Mar31-10, 10:38 AM
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Quote Quote by DrDu View Post
As far as I know, a (relatively) cold plasma can contain even molecules and molecular ions. E.g. in the spectra of rather cold stars (red giants), there are lines of molecular ions present.
Then that isn't a plasma, it's just a gas.
The outer envelope of cool stars is cool enough that the gas isn't ionized
mgb_phys
#8
Mar31-10, 10:42 AM
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Quote Quote by The legend View Post
Another question. Has any form of water plasma ever been made by humans and at what temperature does it change into plasma and back?
And when it changes back(hopefully it does) does it then exist in molecular or broken(atomic) form???
Yes, everytime you get a water leak in a high voltage circuit - you have to be careful designing high voltage power lines that rain water can't form a path between a live wire and ground.

The water will be split into hydrogen and oxygen and then be ionized into H and O ions.
When they move away from the power source the ions will quickly recombine just as they normally would - that they were once a plasma doesn't matter.
What proportion of water (H2O) free hydrogen and Oxygen or Ozone (O3) you form depends on the conditions
The legend
#9
Apr2-10, 04:47 AM
P: 423
I got all of what you have written & I really liked your example of the high voltage circuit. Though too bad that the water quickly recombines back. Does the water undergo this process continuously till it's leaking in the high voltage circuit???? Why doesnt it continue to stay in its plasma state????

And...Still I didn't get to know the temperature ( at STP) at which the water turns into plasma!!

(too bad that my doubts are never ending!! but I still need to clear them. If you feel that I have gone crazy, well maybe I have. But even then please tell me the answer!!!)
The legend
#10
Apr5-10, 02:07 AM
P: 423
I am waiting!! Please reply!!!!!
Borek
#11
Apr5-10, 04:47 AM
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There is no one simple answer to that question, as there is no "sharp" definition of plasma that would let you tell "this is plasma, this is not". Flames have several hundred deg C and that's enough to ionize some of the molecules - this can be enough to classify it as plasma. But someone may argue that plasma starts when everything is ionized and all molecules are destroyed, that means several thousands deg range up.

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Absconder
#12
Feb16-12, 12:50 AM
P: 4
"Though too bad that the water quickly recombines back. Does the water undergo this process continuously till it's leaking in the high voltage circuit???? Why doesnt it continue to stay in its plasma state???? "

Any matter would radiate energy until at equilibrium with it's environment.
If you freeze water and place it on the counter, it melts because it will absorb energy from the air to try and balance with it. If you boil water it will release energy even while you add heat to it.
If you wanted to superheat water into plasma state, you would want to decrease the pressure in a sealed chamber with a very high density heat exchanger.

Water releases energy in a predictable manner relative to it's environment's ability to absorb it.

A plasma cutter uses electricity to cut metal by changing the state of the solid material into ionized gas that gets blown away.

I suspect that if you could "insulate the water" by containing it in something that has a very high melting point, is a poor conductor of heat, and layer something else on top of it that reflects the particular frequency range of infrared radiation (heat) you could significantly slow the cooling to lengthen it's time spent as plasma.

I don't yet know the temp at which water changes to plasma. I am currently looking for that answer and came across this. I'll try to remember to come back here and update when I find the answer.
Absconder
#13
Feb16-12, 12:58 AM
P: 4
http://www.madsci.org/posts/archives...3860.Ph.r.html
This person gave a decent answer.

FYI 12000 K = 21140.33 F (http://www.easysurf.cc/cnver14.htm#kf2)
Borek
#14
Feb16-12, 02:12 AM
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Quote Quote by Absconder View Post
I don't yet know the temp at which water changes to plasma.
As I wrote earlier - there is no simple answer to the question, as there is no single universal definition of plasma. You have to decide on the definition first, answer will follow.
Absconder
#15
Feb17-12, 12:51 AM
P: 4
Let's just say for the sake of this thread that Plasma state is the point at which a gaseous composition begins to break down and ionize. As in to say, when there is enough energy to break the molecular bonds in water and it becomes ionized hydrogen and oxygen, excited to a point beyond the ability for it to be water anymore.
The person who asked this question surely doesn't require a more complicated definition... Plasma would be H20 with less electrons making H+ and O+ plasmoids.

It is not that difficult to say: "In defined pressure, there will be a specific thermal point at which ionization occurs. Chances are, we do not have the technology or physical understanding to achieve this in experiment to determine a definitive answer.
However we can speculate using measurable electrical energy and calculate the relative temperature in theory. This is somewhat unreliable though, given that electrical energy has additional influences on material due to induction caused by directional flow of current which behaves much differently from thermal absorption...

But if our asker is still around, here's a video he/she might like to watch:
http://www.youtube.com/watch?v=LZI8nfA_zsA
Borek
#16
Feb17-12, 03:37 AM
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Quote Quote by Absconder View Post
Let's just say for the sake of this thread that Plasma state is the point at which a gaseous composition begins to break down and ionize.
It happens already in a match flame, just in a very low degree. So you need to be more precise, otherwise the answer you get is meaningless.
Absconder
#17
Feb17-12, 04:25 AM
P: 4
Again, we're talking about the thermal degree at which it occurs without the use of chemical reaction or other forms of energy transfer. Water boils at 212 degrees Fahrenheit and yet ice sublimates to a very small degree, so water can "become gas" at a range of temperature far below it's boiling point. But at 212 degrees it basically has no other choice but to vaporize.
Similarly, in theory, there is a definitive temperature at which water vapor will have no choice but to enter a plasma state.
Borek
#18
Feb17-12, 04:31 AM
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Quote Quote by Absconder View Post
Similarly, in theory, there is a definitive temperature at which water vapor will have no choice but to enter a plasma state.
No, phase transitions occur at well defined temperatures, ionization degree changes gradually with temperature. These are completely different and unrelated situations.


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