MadSci Network: Chemistry

Re: please explain the 4th state of matter, plasma.

Date: Sat Feb 20 09:47:51 1999
Posted By: Richard Bersin, Other (pls. specify below), Senior Technical Staff Member, Emergent Technologies
Area of science: Chemistry
ID: 918893301.Ch

The fourth state of matter, plasma, in its most common form consists of a gas volume in which a large fraction of the atoms or molecules are ionized. This means that they are electrically charged positively, and that there are also equal numbers of free electrons moving within the plamsa.

Normally, electrical energy is pumped into the plasma to keep it going by attaching electrodes and putting a high voltage across the electrodes. A current then flows continuously through the plasma through motion of the ions and electrons. A simple example of a plasma a neon sign. The gas inside the glass tube is glowing because the electrons in the plasma collide with the molecules and cause them to give off light from the energy of the collision. In general if you turn off the electric power the plasma will quickly disappear. It is generally a very unstable environmant and the active molecules and electrons recombine and cease to exist there when no more energy is put in.

Plasmas can be made at atmospheric pressure, when they become very hot-several thousand degrees in temperature. Plasmas are also made under vaccum in a glass or metal chamber; under vacuum you can have a plasma which is very cool, essentially at room temperature. However, the sun is also really a great big plasma. In the case of the sun the mass is so large that the gravity keeps the molecules together and the thermonuclear reactions within the sun keep going and generating plasma continuously without any external source pumping in energy.

So for a plasma you need:

Many of the molecules which exist in the plasma state never exist in any other environment because they would immediately decompose when the plasma turns off.

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