What is Cold Plasma?

Plasma is the fourth state of matter, and has properties that differentiate it from solids, liquids, and gases. The figure below illustrates graphically the transition of water through the different states of matter. Each of the phase changes, starting from a solid, occurs through the addition of energy. Add energy, such as through heating, to ice and the ice melts into water. Add more heat energy to water and you will get steam. Add additional heat energy to steam and you will get water in the plasma state.

Plasma composes 99% of the visible universe—stars are plasma and there are tenuous plasmas throughout “empty” outer space as well as in the near-Earth space environment, from the ionosphere on out. On Earth we see plasma as the spark in static electricity, the spark when you pull an electric plug from the wall, in lightning and in the aurorae. Plasma is all around us in lights—fluorescent lights, mercury vapor, sodium vapor streetlights and plasma TVs. Plasma is used to clean and etch computer and cell phone microprocessors.

Plasma compared to other states of matter

The phrase “electrified gas” is commonly used to describe a plasma state. What makes a plasma is that electrons are knocked out of orbit of an atom and the atom becomes charged, i.e., it becomes an “ion.” The process of creating the charged atom from a ground state atom is called “ionization.” Ordinarily, the number of protons, positively charged particles, and electrons, negatively charged particles, are equal in an atom and its charge is neutral. Such a balanced charge atom or molecule is called a “neutral” atom/molecule. When one or more electrons are removed by ionization then the charge balance is no longer neutral. In the case of a positive ion the charges of the number protons are greater than the number of electrons resulting in a net positive charge.

How Atmospheric Plasma Works to Remove Coatings

Because an ion is electrically unbalanced, it wants to quickly find another electron to return to a neutral state. A lightning flash illustrates the transient nature of this process. The ionized air molecules that constitute the flash quickly restore the charge imbalance and hence the lightning flash goes away quickly. Because plasmas are so unstable, maintaining a plasma, so that it becomes a useful tool, is quite difficult, especially at atmospheric pressure. This is why most plasma applications, to date, take place in low pressure vacuum chambers. Atmospheric plasma is a plasma produced at one atmosphere of pressure—in other words the same pressure as the atmosphere we live in every day.
Atmospheric-pressure plasmas have prominent technical significance because, in contrast with low-pressure plasma or high-pressure plasma, no reaction vessel is needed to ensure the maintenance of a pressure level differing from atmospheric pressure. Accordingly, depending on the method of generation, atmospheric plasmas can be employed directly in portable systems, laboratory platforms and commercial production lines. The need for cost-intensive chambers for producing a partial vacuum as used in low-pressure plasma technology is eliminated.

Atmospheric Plasma Coating Removal Development

The atmospheric plasma coating removal system originated from research in plasma related deposition, etching and surface modification of materials at the Center for Advanced Manufacturing Processes and Materials at North Carolina State University. The Center focused on numerous vacuum plasma processes such as reactive magnetron sputtering, plasma enhanced chemical vapor deposition, vacuum ion plating and hollow cathode enhanced plasma sources. Research in creating stable and controllable atmospheric pressure plasma discharges using air as well as mixed gas environments lead to the development of the necessary power supply technology and reactor design knowledge to support each process. Atmospheric Plasma Solutions (APS) was founded in February 2005 to commercialize the technology and create customized atmospheric plasma systems for a wide variety of coating removal and surface treatment applications.