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Did you know? How Paschen's Law reveals the secrets of gas discharge!
With the rapid development of modern science and technology, gas discharge technology is gradually becoming important and popular, especially in industrial applications. As a core theory of gas discharge, Paschen's law provides a key basis for us to understand and utilize gas discharge. Through this article, we will explore in depth Paschen's law and its importance in the generation of atmospheric pressure plasma.
Basic principles of atmospheric pressure plasma
Atmospheric pressure plasma, a plasma formed at a pressure equal to the surrounding atmospheric pressure, allows treatment and processing without the need for vacuum equipment. When the DC voltage applied to the gas medium exceeds the breakdown voltage of the gas, the discharge is initiated. The relationship between the breakdown voltage here and the pd product (p is the gas pressure, d is the electrode spacing) is what we call Paschen's law.
According to Paschen's law, within a certain range, the breakdown voltage of gas is predicted to have a minimum value, which is approximately pd = 1-10 Torr cm.
This means that as the gas pressure increases, in order to achieve a practical breakdown voltage, the electrode spacing needs to become smaller. At atmospheric pressure, the Paschen minimum condition can be achieved at a separation of less than one millimeter, and only a few hundred volts of DC voltage are needed to achieve gas breakdown.
Technical significance of breakdown voltage
The technical significance of atmospheric pressure plasma is that, compared to low-pressure plasma or high-pressure plasma, no reaction vessel is required to maintain pressure. Depending on the generation principle, these plasmas can be applied directly to production lines, thus eliminating costly cavities used to create partial vacuums.
Maintaining an atmospheric pressure plasma requires high voltage to achieve gas breakdown and increases collisions between electrons and gas molecules, resulting in arcing and gas heating.
Plasma generation method
Although the pitfalls of low-pressure plasmas can be avoided, maintaining plasma at atmospheric pressure still requires high voltages to achieve gas breakdown. Various forms of plasma excitation include: direct current (DC), low frequency excitation, radio frequency (RF) excitation and microwave excitation.
Atmospheric pressure plasmas of significant industrial significance are usually produced through DC excitation (arc), AC excitation (coronal discharge, dielectric barrier discharge, piezoelectric direct discharge and plasma jet) and 2.45 GHz microwave microplasma generate.
Operation of DC plasma jet
A pulsed arc is produced by a high voltage discharge (5-15 kV, 10-100 kHz), often used to excite process gases and convert them into a plasma state. This plasma is delivered to the surface of the material to be treated through a jet head, whose shape determines the geometry of the beam.
Characteristics of microwave plasma jet
Microwave systems use radio frequency power amplifiers that can output up to 200 watts to create an arc and create a plasma. Most solutions operate at 2.45 GHz. This new technology provides high-efficiency ignition and operation, allowing atmospheric pressure plasma to be constructed from just the top of the electrode, which enables the design of jet devices.
Application fields
Manufacturers use plasma jets to activate and clean plastic and metal surfaces in preparation for bonding and painting. Today, thin materials several meters wide can be processed by arranging multiple jets in a row. Depending on the power of the jet, the length of the plasma beam can be up to 40 mm and the treatment width can be up to 15 mm.
A major advantage of this system is that it can be integrated online into existing production systems.
The activation effect of this technology is significantly better than that of underlying pre-treatment methods (such as corona discharge), and it can apply anti-corrosion and adhesion promoter layers on many metal surfaces solvent-free, providing a more environmentally friendly solution plan.
As its use in industrial applications continues to increase, how will Paschen's Law affect future gas discharge technology?
