Atmospheric-pressure plasma
Than atmospheric pressure plasma ( Ad- plasma or atmospheric pressure plasma ) refers to the specific case of plasma, in which the pressure of the ambient atmosphere about the - the so-called normal pressure - corresponds.
Below is essentially about the procedure with a nozzle and a gas discharge low current density. Other forms of plasma generation in normal atmosphere See also:
- Corona treatment
- Ionizer
- Electrostatic precipitator
- Silent electric discharge
Technical significance
Nuclear pressure plasmas require, in contrast to low pressure plasma or high-pressure plasma is no reaction vessel which will maintain a different pressure to the atmospheric pressure level or differing gas atmospheres. Such plasmas are used at low current densities for activation of surfaces or to ionize and ozone generation. The production of nitrogen oxides, however, has lost its meaning and is rather undesirable. When also working without vascular plasma cutter working with significantly increased pressure and higher current densities.
Equally important is the plasma spraying (thermal coating process ). DC arc plasmas for this purpose may be used at atmospheric pressure.
The splicing of optical fibers is also working at atmospheric pressure in normal atmosphere, but does not require any nozzle but there is a fire, a gas-discharge small current density between the electrodes compared to the cold arc welding.
Generating the plasma
There are different types of excitation:
- AC (alternating current ) excitation low-frequency alternating currents
- Stimulation with alternating currents in the radio wave range
- Microwave excitation
A notable industrial importance but have gained only atmospheric pressure plasmas generated by AC excitation ( corona discharge and plasma jets). The following section discusses in more detail on the plasma nozzle. Another important embodiment of the plasma source is a dielectric barrier discharge ( DBD ), which is used for producing ozone or processing of plastics. Other plasma generator can be found in tendero et. al, see literature.
Operating principle of a plasma nozzle
A pulsed arc generated in the plasma by means of high-voltage discharge (100 kHz 5 - - 15 kV, 10). A process gas, typically oil-free compressed air is used, which flows past the discharge path is activated and transferred into the plasma state. This plasma then passes through a die head to the surface of the material to be treated. The nozzle head is at ground potential, thus keeping potential- carrying parts of the plasma stream largely alleviated. In addition, it determines the geometry of the exiting beam.
Applications
Industrial application finds the plasma nozzle, among others to enable and cleaning of plastic and metal surfaces prior to splicing and painting processes. Also broadloom treatment with widths of several meters can be treated by lining up many nozzles. The plasma jet generated by the modification of the surface may well be compared with the effects obtained in the low pressure plasma.
The plasma jet can be long depending on the performance of the nozzle up to 40 mm, and width to achieve a treatment of 15 mm. Specific rotation systems allow treatment width per nozzle tool of up to 13 cm.
The plasma source according to the required processing power at a distance of 10 - 400 m / min is moved to the surface of the material to be treated relative to - 40 mm at a rate of 5.
A major advantage of these systems is the so-called in-line capability, i.e., an installation in existing production equipment is usually no problem. The costs, however, are comparatively low. In addition, the achievable activation is significantly higher than for non-floating pretreatment methods ( corona discharge).
With this, or similar systems, a wide variety of surfaces can be coated. For corrosion protection coatings and adhesive layers can be applied solvent free and therefore environmentally friendly to various metals.