Plasma to Solid Change
Name: Shannon S.
In chemistry class we are learning about different states of matter. A few of us
asked our teacher what the name is for the physical change from plasma to a solid, but she did
not know. What is it?
I am not familiar with any experiment which has ever observed a plasma condensing directly into a
solid. Consequently, I do not think there is a name for it!
Best, Prof. Topper
Historically, things were simple. Everything was either a solid, a liquid, or a gas. Now however
the concept of a "state of matter" needs to be more general. Many, if not most, solids have more
than one crystal structure depending upon the temperature (some solids even have multiple melting
points). If the pressure is increased most solids have multiple solid phases. Ice for example, has
at least 9 and possibly 11 solid phases. A few liquids, liquid helium is the classic case, have
more than one liquid phase. In the case of helium the "normal" liquid and the superfluid liquid
below a temperature of about 2.2 Kelvins. A plasma is a (usually gas-like phase composed of ions
of the material. I don't know of a special name given to the condensation of a plasma into a
condensed phase. Certain molecules (called liquid crystals) are ordered in 1 or 2 directions
but not the other 2 or 1 respectively, so that makes up another "state of matter" for those
Like many definitions that were "easy" when introduced the definition of a "state of matter"
becomes more complicated and less clear cut as knowledge advances.
At low temperatures, matter exists in the form of atoms. A positive nucleus
is surrounded by electrons. Each atom as a whole is neutral.
In some gases and liquids (air, nitrogen, pure water for example) the atoms
move around but hang onto their electrons. If a voltage difference is
applied, no electric current can flow because there are no free charges to
move. The neutral atoms do not move in an electric field. In some solids
too, no current can flow because there are also no free charges to move
(glass, wood, plastic for example.)
If a gas is heated to a high temperature, some of the electrons come off the
atom, resulting in a mixture of free electrons and a positive ions. That is
called the process of ionization, and the resulting mixture is called a
plasma. ( Going from a plasma to a gas would be called recombination of the
electrons and ions to become neutral atoms.) If a voltage difference is
applied to the plasma, the electrons can move, and an electric current can
flow. If the electric current is very large, it can further heat the gas
and ionization becomes self sustaining. That is how a plasma torch works.
Metals consist of positive atoms that are surrounded by a gas of free
electrons. Metals conduct electricity because these electrons can move.
The positive atoms or ions cannot move. Metals are sort of a solid plasma.
The difference between a gas plasma and metal is that even if a metal is
cooled to near absolute zero, the electrons stay free, so a metal is not a
Making a real solid plasma would be difficult. White dwarf stars contain
solid plasmas. The extreme high pressure forces the materials (carbon and
oxygen atoms) into a rigid solid. But the pressure and temperature are so
high that the atoms remain ionized.
I am not aware of a name for the change from plasma to solid because it is
not something that can easily be made to happen.
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Update: June 2012