The plasmas under consideration here are part of a class called thermal plasmas or plasma arcs. The graph shows the transitions in state as plasma current increases. Thermal plasmas begin at approximately 10 A.
Plasma, often called the fourth state of matter, normally consists of neutral atoms, positive ions, and free electrons. Plasma is produced by transferring energy into a gas until the energy level is sufficient to ionize the gas, allowing the electrons and ions to act independently of one another. The plasma state is achieved when, under an electric field, currents can be sustained as the free electrons move through the ionized gas. After the energy input is removed, the electrons and ions recombine, releasing energy in the form of heat and light.
It has been estimated that 98% of the visible universe exists in the form of plasma. Plasmas occur naturally on Earth as the aurora borealis, aurora Australis, St. Elmo’s fire, and lightning. Common man-made plasmas include neon and fluorescent tubes and bulbs.
Volume 5A, Thermal Spray Technology ⇒ Thermal Spray Processes and Coatings ⇒ Thermal Spray Processes ⇒ Thermal Spray Processes
