Is plasma and fire similar??

[Newbies_Kid]

Is that really plasma?

[swansont]

As far as I can tell, yes (i.e. the video doesn't look faked). Combustion can ionize some of the gases, and then the microwaves interact with the charged particles.

[Newbies_Kid]

urm.. so you agree plasma is a fire?? then, should the temperature in that glass increased?

[John Cuthber]

It's probably better to say that fire is a kind of (weak) plasma.

Some of the gases in a flame are ionised but most are not. The glowing blob in the microwave is probably much more strongly ionised than any flame.

[Sisyphus]

urm.. so you agree plasma is a fire?? then, should the temperature in that glass increased?

 

Plasma is just ionized gas. It isn't necessarily hot, though the most straightforward way of producing it is making gas very hot. Fire is a particular chemical reaction - fuel combining with oxidizer and releasing heat, which in turn can ionize some of the gas around it, producing plasma. So no, plasma is not a fire. The entire surface of the sun is plasma (because it's so hot), but there is no fire there.

[Newbies_Kid]

urm.. so fire is a kind of plasma but plasma definitely is not a fire??. About ionized gas, how much energy needed to ionized a gas for example... an argon? what types of energy sources we need to produce plasma? last but not least, what is the minimum temperature does a plasma have? I can't find any below 10^2 Kelvin. Can someone give me an example?

[Sisyphus]

urm.. so fire is a kind of plasma but plasma definitely is not a fire??. About ionized gas, how much energy needed to ionized a gas for example... an argon? what types of energy sources we need to produce plasma? last but not least, what is the minimum temperature does a plasma have? I can't find any below 10^2 Kelvin. Can someone give me an example?

 

Fire is not a plasma. Plasma is often the result of a fire, but the fire itself is just a chemical reaction. Another common place you'll see plasma is in fluorescent lights, which shows that you don't actually need all that much energy. The electric current (flow of electrons) knocks electrons off the gas atoms, which in turn knock electrons off other atoms, and so on.

 

Incidentally, argon is one of the gases they use in fluorescent lights. It's the blue parts of "neon" signs. (The tubes that are actually filled with neon only glow orange.)

 

As for making plasma just by getting something really hot, I don't think there's a minimum temperature. It's not a phase change like melting or boiling that happens at a specific temperature. Just, the hotter you get it, the more atoms will be ionized.

[Newbies_Kid]

ok, that's clear enough for me to understand the basic. But i still don't understand why a gas become visible when got ionized? how they emit light? where the photon comes from?

[Red Hypergiant]

I believe you can get plasma if you do a similar setup with a grape.

[CharonY]

Or you can create plasma with an RF oscillating electric field. You may want to google ionized air glow.

Edited November 3, 2010 by CharonY

[CaptainPanic]

ok, that's clear enough for me to understand the basic. But i still don't understand why a gas become visible when got ionized? how they emit light? where the photon comes from?

the microwave sends radiation (also photons, but not visible light) to the material (the gas in this case). Electrons on the gas molecules get extra energy. Some get so much extra energy that they leave the atom altogether (so we get a plasma), and some just get a different orbital. If an electron falls back to a lower orbital, it will send out a photon. And those photons can be in the visible spectrum.

[swansont]

the microwave sends radiation (also photons, but not visible light) to the material (the gas in this case). Electrons on the gas molecules get extra energy. Some get so much extra energy that they leave the atom altogether (so we get a plasma), and some just get a different orbital. If an electron falls back to a lower orbital, it will send out a photon. And those photons can be in the visible spectrum.

 

A single RF or microwave photon isn't usually going to ionize an atom or molecule unless it's already in a highly excited state. What happens here is more classical — you get a bunch of photons in the same place, and their electric fields add, and you get field ionization of the molecules. There are a lot of photons when you have several hundred Watts of the radiation bouncing around.

[Newbies_Kid]

For comparison, can you simply explain to me what is the correlation between wave frequency and the behavior of the plasma. Why they use RF generator instead of microwave to produce plasma in rocket thruster? also, what we need if we want to produce plasma from something not gas, may be from water or solid matter perhaps?

[swansont]

In general, the generating radiation in a useful way is more difficult as the frequency increases, and if you look at the history of devices, the earliest ones had a lower frequency than later ones. I know from experience that more headaches exist in dealing with piping microwaves around than in doing similar things with RF, and many aspects get harder still as you approach the visible and go beyond. So it's possible that using RF is simply because it's easier and more efficient.

 

If you want to generate a plasma from a solid, I think you're going to have to vaporize it first. Unless what you really want is an electron cloud, rather than a neutral plasma. Boiling off electrons from a filament (thermionic emission) is fairly easy.

[Newbies_Kid]

 

I'm little bit confused on stage 3 & 5, how a stream of RF can turn the gas into plasma? I understand the concept of generating plasma using electrodes, but for such this VASIMR engine, what happen to the atom of the gas when flowing through those RF antennas? With the same principle, is it can be true that a human body can instantly exploded in RF oven?

[lemur]

I believe that microwaves affect water and water is a by-product of combustion. What would the effect of microwave agitation on newly formed water particles at flame-temperature? Could the microwaves just be scattering the reaction as it occurs?

Edited November 19, 2010 by lemur

[Newbies_Kid]

Microwave heating is very different with combustion because microwave don't cause fire. But, if you talking about the video i attached above i think because of the distance between the water molecules in air is too far, its got no chance to bump into each other to generate heat.