Plasma?

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Rasputin
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Postby Rasputin » Mon Aug 20, 2007 3:54 am UTC

Plasma is not necessarily a particle becoming excited, but rather the particle gaining or losing electrons.

However, given our atmospheric gasses, ionizing the air won't do. When lightning forms, it ionizes the surrounding air, creating a stream of plasma (that we _usually_ can't see) that allows for the free flow of electrons (since the plasma acts like a conductor due to the free electrons floating around inside it). In lightning, the plasma stream is known as a stepped leader, and exists just before the visible strikes.

On a side note, lightning DOES start from the cloud as a stepped leader, but the return stroke back up to the cloud is (usually) the first visible sign of lightning.

Back on topic. The colors of the fire depends on the chemical being burned, and how pure that chemical is. The heated particles could (in my mind) become ionized as they're burning off the chemical, then quickly revert back to their natural gas state once they've cooled in the atmosphere.

In other words, it is POSSIBLE for fire to be plasma, but I have not looked for or come across valid statements justifying that fire IS plasma. Someone want to hook this thread up with some authentic, factual articles?
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bbctol
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Postby bbctol » Mon Aug 20, 2007 4:00 am UTC

I believe that incredibly hot fire, the kind that just sort of glows and doesn't flicker, can be classified as plasma, but the rest is... something else.

Notice the complete lack of factual articles and facts in general in this post.

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evilbeanfiend
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Postby evilbeanfiend » Mon Aug 20, 2007 8:32 am UTC

there is another thread on this iirc.

a brief summation:

1) a plasma is an ionised gas with electorns that are close enough together that they all effect each other (rather than just their nearest neighbours)

2) temperature has nothing to do with the definition of a plasma (although it is one good way to ionise a gas)

3) flames actually can get reasonably hot e.g. 1000-2000 K

4) not all of a flame is necessarily a plasma

5) some of it is hence flames react with electro-magnetic fields
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Postby po2141 » Mon Aug 20, 2007 9:10 am UTC

I think in your run-of-the-mill, everday flames, the orange light is given off by soot particles that are literally orange-hot. Heat something up to around 500-800 degrees (or something) and it will glow orange, like a hot poker. Just like the soot in flames. The blue flame you get from a bunsen burner contains no soot (all carbon to CO2) so dosnt glow much, even though it is hotter (around 1200 degrees).

The light is indeed electrons falling down energy levels, but the gas dosn't need to be ionised for this to occur, the electron don't usually escape their atoms. Mind you there will be a certain proporsion of plasma in the flames. But then theres plasma in most places if you want to get pedantic.

PS: I've always wondered, those "air ioniosers" you get for, like, your living room or office. WTF do they do? Cos they don't seem to do much.

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Postby Rasputin » Mon Aug 20, 2007 4:58 pm UTC

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Nosforit
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Postby Nosforit » Mon Aug 20, 2007 5:15 pm UTC

What qualifies a plasma as such seems to be the speed at which the charged particles are moving at. If in a gas the electrons are so energized that they escape their proton, then it's a plasma.

Fire is mostly hot gas, and a rather small portion of that is in a state of plasma. The plasma state is mostly due to the chemical reactions taking place, namely nuclei and electrons switching molecular configurations. During the time this switch takes place, some of the particles are in a state of plasma.

Plasma forms more easily at lower pressure too, meaning it could 'feel' a lot colder than the particles actually are.
Last edited by Nosforit on Mon Aug 20, 2007 5:20 pm UTC, edited 1 time in total.

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Postby evilbeanfiend » Mon Aug 20, 2007 5:19 pm UTC

http://www.grc.nasa.gov/WWW/RT2002/6000/6711yuan.html

pretty much shows you have ions, not enough to prove its a plasma though
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