A corona discharge is the plasma curtain that is created when air around a conductor gets ionized.
Corona discharges are usually a glowing purple veil that is used to alter the adhesion properties of surfaces. They are created by applying a high voltage to small electrode tips. When a surface undergoes corona treatment, it passes under a
corona discharge. This causes
surface activation of the material by bombarding it with plasma ions. Surfaces that go through corona adhesion treatments enhance their adhesion capabilities.
Corona discharges are also used to reduce drag on a flat surfaces, sanitize pool water, remove unwanted volatile organics including pesticides and chemical agents from the air.
The Properties of Corona Discharges
The bluish-purple glow that
corona discharges produce is a side effect of electrons recombining with positive ions to reform neutral atoms. When atoms reform they release a photon of light. These photons ionize more atoms maintaining the corona discharge. Corona discharges are a non-thermal, non-equilibrium product. They are created through an electric arc and this process does not release enough energy to heat the plasma.
Corona discharges come in two forms: positive and negative. This is determined by the polarity of the electrode used to produce the corona. Positive and negative coronas are similar but there are some key differentiations. Positive corona discharges have a much lower free electron density, than negative coronas. However, the electrons in a positive corona discharge are concentrated and contain more energy. Negative
corona discharges appear larger than positive ones. This is due to the free electrons being more spread out and more abundant.