Plasma

Rather than hijack the thread that started me wondering, I am starting a new one.

When we talk about the other three states of matter, we can state what they are made from i.e. water, stone, air etc. Can we do the same with plasma?

Just wondering

David

Well yes actually I think you can. Essentially if you strip electrons from atoms in a gas you get a plasma. The atomic neuclii and whatever electrons remain associated with them retain the characteristic identity of the particular element you started with in terms of atomic number.

regards Martin

I don't know. I worked with ionised gases, flames, for more than half my working life and never thought of combustion in terms of a plasma.

Before the really bright members of the forum answer this, flames are ionised gases (free radicals) and conduct electricity. The temperatures we reached at work lead to the gases dissociating and start behaving strangely.

JA

edit - I suspect that the mean free molecular path in a plasma is far larger than in a normal ionised gas.

Edited By JA on 17/02/2022 18:29:03

Edited By JA on 17/02/2022 18:30:58

It's all about boundaries, I think.

If you look at an ice cube, then you're going to say "It's a solid".

If you look really closely then it has a little puddle of water on top. Obviously that isn't a solid.

They say that a flame isn't a plasma because it isn't hot enough. If you get the flame hot enough it can be a plasma.

If you lower the pressure, then the flame doesn't have to be as hot to become a plasma.

It still has unburned reactants and combustion products in it, even at reduced pressure.

If you took the wet ice cube and crushed it into a Slush Puppy, no-one is going to call it solid any more.

I don't know about anyone else, but that makes sense to me.

Many thanks for the replies

I can imagine that the gas that is being used to form the plasma ( if that's what it is ) in a fluorescent tube is the gas that it is filled with but what about the plasma in a plasma cutter? Is that the surrounding air?

If it doesn't show, I'm at the limits of my knowledge here

David

It's the air that is pumped through the arc to heat it up. There is no effect on the nuclei of the gas forming the plasma, unless you get it really REALLY hot!

Thank you John, I'm a little, but only a little, nearer understanding.

David

Every element is characterised by its nucleus - the protons it contains, to be specific. Different isotopes of the same element have different numbers of neutrons in the nucleus - but always the same number of protons.

It is only the tearing free of electrons which occurs in a plasma, which allow these charged nuclei/atoms to impart cutting energy to the sub-strait. Hot and charged means high energy (with a good potential gradient between the plasma source and the earth potential metal).

Only at sufficient temperature and pressure can nuclei be changed. Currently tritium and deuterium being converted to helium - think here of the temperatures and pressures in the fusion experiments. A good deal hotter than our little plasma cutters!🙂

Solid, liquid, gas and plasma are the four classical states of matter and at GCSE level only the first three are really taught, however that online encyclopedia which is often derided for inaccuracies suggest this is a more complete list:-

• Solid
• Liquid
• Gas
• Plasma
• Glass
• Crystals with some degree of disorder
• Liquid crystal states
• Magnetically ordered
• Microphase-separated
• Superconductor
• Superfluid
• Bose–Einstein condensate
• Fermionic condensate
• Rydberg molecule
• Quantum Hall state
• Photonic matter
• Dropleton
• Degenerate matter
• Quark matter
• Color-glass condensate
• Supersolid
• String-net liquid
• Superglass (and if you think of this 'Even in the quietest moments' you listened to too much music in the 1970s and your memory is, like mine, now getting unreliable! )

Edited By Nick Clarke 3 on 18/02/2022 15:50:36

I am surprised that Polywater does not feature in the list. (Don't look for this in Wikipedia, try www.sciencehistory.org).

JA

Looking at the list there are some very obvious double entries

Edited By JA on 18/02/2022 16:37:23

My Physics isn't really up to this, but I still imagine atoms as the model we were taught at school - of a nucleus of protons-neutrons surrounded by shells of electrons. As energy is supplied, then the electron shell expends and pushes the atoms/molecules apart and allows greater individual activity - water being one of the oddities that contracts in the change from solid to liquid. The set activity barriers of latent heat apply to the fundamental state changes solid-liquid-gas but after that is just a case of the electron shells moving further away until they strip off and leave what we call plasma.
Presumably there has been detailed analysis of whet is happening during those jump states with glass being an intermittent 'stable' form?.
Since the neutron/proton/electron have been subdivided then the real meaning of 'matter' becomes blurred and doubtless there will be states of matter where some subatomic particle is absent from the atom - exotic matter with a zero or negative mass?

pgk