EP2130414B1 - Device and method for generating a plasma beam - Google Patents

Description

The invention relates to a device for generating a plasma jet or multiple plasma jets. Moreover, the invention relates to a method for generating a plasma jet or multiple plasma jets.

Devices for generating a plasma jet are already known from the prior art. For example, the DE 195 32 412 C2 a plasma jet generator with a nozzle. At the nozzle opening is an annular electrode. Coaxially reset from the nozzle opening into the nozzle, a pin electrode is arranged. By means of a high-frequency voltage generator, an arc discharge between the pin electrode and ring electrode is ignited. In operation, the plasma nozzle is flowed through by a working gas. The working gas is fluidized in the plasma nozzle by means of a twisting device. The swirling of the working gas in the nozzle causes the arc discharge along the vortex core coaxially in the nozzle from the pin electrode in the direction of the nozzle opening, where it then branches radially to the annular electrode. As a result of the arc discharge, the working gas is excited to a plasma jet separated from the arc discharge, which discharges from the nozzle opening with the remaining working gas.

Another example can be found in DE 10145131 A1 , US 5753886 discloses two electrodes transverse to the flow direction of a working gas for a capacitive discharge.

Plasma nozzles of this type are used, for example, in the plasma pre-treatment of workpieces. If workpieces are to be coated, painted or glued, pretreatment is often required to To remove impurities from the surface and, especially for plastic workpieces to change the molecular structure so that the treated surface with liquids such as adhesives, paints and the like can be wetted. Furthermore, with a plasma pretreatment, the weldability of electrically conductive workpieces tending to form a surface layer hindering the welding process can be improved. It is particularly preferred if the plasma pretreatment can be carried out at low temperatures. Such a pretreatment at low temperature is advantageously feasible with a plasma jet generated by a plasma nozzle.

In addition, plasma nozzles of the type described above can be used in the plasma coating of workpieces. In plasma coating, it is necessary to supply a coating material or a precursor material to the plasma. However, additive materials with advantageous effects can also be used in the plasma pretreatment of workpieces. These materials are supplied with the plasma jet of the surface to be processed and unfold there, the desired effect caused by the plasma energy, for example, they are deposited on the surface in the form of a layer.

The coaxial arrangement of a pin electrode in the nozzle and a ring electrode at the nozzle opening is disadvantageous, because usually the plasma-forming working gas flowing through the nozzle is swirled to provide a defined channel in the vortex core in which the discharge from the pin electrode to the ring electrode is performed , Due to the swirling is a big part of kinetic energy of the working gas bound in the rotary motion. In order to increase the flow rate of the plasma jet emerging from the nozzle opening, the flow rate of the working gas into the nozzle needs to be disproportionately increased because a certain part of the kinetic energy is converted into the rotational movement of the working gas.

The manufacture of a plasma nozzle of the type described above is facilitated if the ring electrode is integrally formed on the nozzle opening from the nozzle housing. In this case, the nozzle body is made of a conductive material and functions as an electrode as a whole. A disadvantage of this embodiment, however, is that the interior of the nozzle to receive the pin electrode and thus must have a certain cross-sectional size.

To generate the plasma, a high-frequency high voltage is applied to the electrodes, which must be so high that a discharge from the pin electrode to the ring electrode can penetrate through the working gas and thereby ionize the working gas along the discharge path. As a rule, such a length of the discharge path is selected that a working gas flowing at a certain speed is ionized by the discharge for a sufficiently long time in order to achieve a desired plasma intensity. To produce a very plasma-intensive beam, the electrodes are thus far apart. However, the farther the electrodes are spaced apart, the greater must be the voltage differential, ie the voltage amplitude, between the electrodes to allow discharge by the working gas. This places high demands on the Supply unit, with which the voltage is generated, as well as to all electrical connections of the plasma nozzle.

A plasma jet is understood to mean a beam of a reactive medium which, in addition to neutral, excited atoms or molecules, also has ionized atoms or molecules. The excited or ionized particles cause a strong interaction on the surface to be treated, which leads to a surface pretreatment. In this case, the plasma jet is preferably transmitted to the surface without transfer of discharge sparks, that is, floating. However, plasma jet applications are also conceivable in which both the plasma jet and discharge sparks are interacting with the surface.

By high-frequency high voltage is meant, for example, an alternating voltage with polarization changes or a pulsed direct voltage with voltage values of only one polarity in which the voltage values change between two extreme values. Ultimately, a pulsed DC voltage is an alternating voltage superimposed with a constant DC component. The frequency is preferably in a range of 10 kHz to 100 kHz. Deviations from this range of values are possible. The amplitude of the voltage, measured peak-to-peak, is approximately 1 kV to 50 kV. But even with these values, there may be deviations up or down.

The invention is therefore based on the technical problem of providing a device for generating a plasma jet or multiple plasma jets, which at least partially eliminates the aforementioned disadvantages. Furthermore, the invention is based on the technical problem of specifying a method for producing a plasma jet or multiple plasma jets, with which the device according to the invention for generating a plasma jet or multiple plasma jets can be used efficiently.

The technical problem is solved according to the invention by a device for generating a plasma jet, with a housing and with at least two electrodes, wherein the housing has a gas inlet and a gas outlet, characterized in that the at least two electrodes are integrated in the side wall of the housing.

During operation of the device, the housing is flowed through by a working gas from the gas inlet to the gas outlet.

Due to the integral arrangement of at least two electrodes in the side wall of the housing, a turbulence of the working gas when flowing through the housing is no longer necessary. The requirement to provide a defined discharge channel between the electrodes is eliminated. As a result of this configuration of the device, the working gas can flow through the housing from the gas inlet to the gas outlet in a translatory motion essentially without eddy, so that the kinetic energy with which the working gas is introduced into the housing as it flows through the gas inlet is the translational movement of the working gas through the housing and out of the housing through the gas outlet is maintained.

Furthermore, within the housing no pin electrode must be arranged coaxially with the flow direction of the working gas. In contrast, the at least two electrodes are integrated to save space in the side wall of the housing in the inventive device. This has the advantage that the housing of the device according to the invention for generating a plasma jet requires a smaller flow cross-section than comparable plasma nozzles with coaxially arranged inside the nozzle pin electrode. The device according to the invention can thus be made more efficient material. In addition, a device with small external dimensions allows use in environments where only a limited working space is available.

A further advantage of the integral electrode arrangement in the side wall of the housing of the device according to the invention for producing a plasma jet and the resulting small flow cross section of the housing is that the distance of the electrodes from each other can be kept small. As a result, the amplitude of the electrical voltage which has to be applied to the electrodes in order to generate a discharge channel and thus an arc discharge between the electrodes can be chosen smaller. The requirements for the power supply and the associated electrical connections are thus reduced.

The term arc discharge is understood in the context of the present application phenomenologically as an arc. This means that the voltage applied to the electrodes for plasma generation is not a continuous DC voltage. Rather, the plasma, as mentioned in the introduction, with a high-frequency Voltage, in particular with a high-frequency AC voltage generated. However, since the frequency of the applied voltage is selected to be so high that an observer can not visually detect any difference to discharges generated by continuous discharges on the basis of the luminous phenomena of the discharge, in the present application a simplification is referred to as an arc discharge.

Preferably, the at least two electrodes are spaced apart transversely to the flow direction of the working gas in the side wall of the housing integrated. This arrangement ensures that the distance between the at least two electrodes is kept as low as possible. Thus, the amplitude of the voltage for generating the discharge is kept as low as possible.

In a preferred embodiment, the surfaces of the at least two electrodes facing the interior of the housing are arranged in alignment with the surface of the side wall of the housing facing the interior of the housing. The aligned arrangement of the electrodes avoids sources of gas turbulence. If the electrodes protrude into the interior of the housing or if the surface of the electrodes facing the interior of the housing is set back from the surrounding side wall, turbulence vortices may form in the transition region from side wall to electrode, at least partially converting the translational energy of the working gas into rotational energy and ultimately convert into heat and thus reduce the flow rate of the working gas perpendicular to the flow cross-section from the gas outlet out.

In the context of the present application, the term working gas for plasma generation comprises suitable one-component gases, for example nitrogen, as well as multicomponent gas mixtures, for example air, forming gas, CO ₂ , acetylene / N ₂ mixture or any other gas mixtures suitable for plasma generation.

The housing having a gas inlet and a gas outlet as well as at least two electrodes of the device according to the invention for generating a plasma jet is preferably designed substantially in the form of a hollow cylinder. In this embodiment, the at least two electrodes can be integrated transversely to the flow direction of the working gas diametrically spaced from each other in the side wall of the housing. Furthermore, the gas inlet and the gas outlet can be arranged at a distance from one another at the mutually opposite end faces of the hollow cylinder.

It is also possible to form the housing in the shape of a hollow cuboid. The design of the housing as a hollow cuboid is advantageous packaging technology, when several devices according to the invention for generating a plurality of plasma jets are arranged close to each other.

However, the above-mentioned embodiments of the housing are exemplary and should not be construed as limiting.

In the context of the present invention, the term sidewall of the housing comprises all parts of the housing between the gas inlet and the gas outlet, which extend essentially along the flow direction of the working gas, and is used only in the singular, even if the shape of the housing suggests the presence of several sidewalls, for example four sidewalls in a case in the shape of a hollow cuboid.

In a further preferred embodiment of the device, the side wall of the housing is curved or bent in a cross-sectional plane lying in the flow direction of the working gas in the region of the gas outlet. In particular, the side wall of the housing is formed so that the flow cross section of the housing tapers in the direction of the gas outlet. This embodiment is particularly advantageous if the flow rate of the working gas is to be increased by the gas outlet from the housing relative to the flow rate of the working gas in the housing.

Preferably, the side wall of the housing is at least partially formed of an insulating material. This insulating material may be a ceramic material or a glass, preferably a quartz glass. However, any other insulating materials may be used.

It is particularly preferred if the region of the side wall of the housing surrounding the at least two electrodes is formed from an insulating material, for example a ceramic material or a glass, in particular a quartz glass.

Due to the at least partial formation of the housing made of an insulating material ensures that by a voltage difference between the at least two electrodes caused discharge in a channel between the electrodes runs.

In further preferred embodiments of the device, the flow cross sections of the gas inlet and / or the gas outlet are smaller than the flow cross section of the housing. The flow cross-section of the gas inlet or gas outlet is understood, for example, to mean the circular area of a circular gas inlet or gas outlet. As a flow cross-section of the housing, for example, the surface of the inner circle of a hollow cylindrical housing is understood. In the case of a hollow-cuboid configuration of the housing, the flow cross-section of the housing means the area of a rectangle, in particular of a square.

A narrowing of the flow cross-section of the gas inlet in comparison to the flow cross-section of the housing is advantageous, since thus the working gas can be supplied to the interior of the housing with a defined directed flow. As a result, the occurrence of vortices that would bind part of the kinetic energy of the working gas in a rotary motion, largely avoided.

A narrowing of the flow cross section of the gas outlet in comparison to the flow cross section of the housing is advantageous, since thus the working gas and the plasma formed therein can be focused and directed for targeted application jet-shaped example, on the surface of a workpiece to be machined.

The gas outlet may be slit-shaped. It is particularly preferred if the longitudinal axis of the slot is parallel to the connecting line between the extends at least two electrodes. Due to this configuration of the gas outlet, the plasma jet can be widened in the longitudinal direction of the slot. This makes it possible to produce a large-area, yet uniform plasma jet, which is particularly suitable, for example, for the plasma treatment of workpiece surfaces.

In a cross-sectional plane lying in the flow direction of the working gas, the gas outlet may also have the shape of a Laval nozzle. This means that the flow cross-section of the gas outlet tapers in the flow direction of the working gas, starting from a region facing the interior of the housing, before the flow cross-section of the gas outlet then widens again from the narrowest region to an area facing the environment. This configuration of the gas outlet, the flow rate of the working gas and the plasma can be increased out of the housing.

Furthermore, it is preferred that the dimension of the surfaces of the at least two electrodes facing the interior of the housing is smaller than the inner dimension of the flow cross section of the housing. For example, the diameter of a circular electrode is smaller than the inner diameter of a hollow cylindrical housing in the flow cross-section. This means that the electrodes have a small extent in the direction of the circumference of the housing. The circumference of the housing at the level of the electrodes is, for example, a circle in a hollow cylinder, while in the case of a hollow cuboid, for example, it is a rectangle, in particular a square. The small extent of the electrodes serves to maximize the path of the discharge as possible and set. at Larger dimensions, the arc discharge would tend to start only from a portion of the electrode surface, since discharges always take the shortest path.

In a further preferred embodiment of the device, the at least two electrodes are rod-shaped, with the longitudinal axes of the electrodes in the side wall extending parallel to the flow direction of the working gas. By a longitudinal extension of the rod-shaped electrodes in the flow direction of the working gas, the surface of the electrodes facing the interior of the housing is enlarged, so that the working gas can flow over a larger area of the electrodes. This enhances an advantageous cooling effect of the working gas on the electrodes, which may be desirable due to the heating occurring at the electrodes during a gas discharge. Because the discharge and thus the heating takes place downstream.

Preferably, the gas inlet and the housing and / or the gas outlet and the housing are integrally formed. For example, a gas inlet and / or gas outlet can be formed on a hollow cylinder closed on all sides in that a bore with the desired diameter is made at the two end faces. This type of integral formation of gas inlet and / or outlet facilitates in particular the manufacture of the device for generating a plasma jet.

However, it is also possible to form the gas inlet and / or the gas outlet with the housing in several pieces. For example, since the gas outlet, in contrast to the plasma nozzles described in the prior art not more than It must be possible to form the gas outlet in each case from a component with which the flow cross section of the gas outlet can be changed in the manner of an iris diaphragm. Of course, it is also possible to design the gas inlet in such a way that the flow cross-section of the gas inlet can be changed in the manner of an iris diaphragm. This embodiment would thus allow a change in the flow rate and the flow cross-section of the working gas or plasma jet during operation of the device for generating a plasma jet.

In another exemplary multi-piece embodiment of the housing and the gas outlet, the gas outlet may be formed on the housing so that the flow direction of the working gas through the gas outlet out of the housing is arranged obliquely against the flow direction of the working gas in the housing. Such an arrangement is in the prior art, for example in the EP 1 067 829 B1 , already known for plasma jets.

If then the gas outlet is rotatably formed on the rotationally fixed housing, can be applied by rotation of the gas outlet during plasma generation with a single device for generating a plasma jet, a large area, for example, a workpiece to be machined with a plasma jet. The rotation can be active, for example, by providing a rotating device on the rotatable gas outlet, or passively, for example, by the force exerted by the effluent from the gas outlet working gas recoil.

In a further alternative embodiment, the device for generating a plasma jet is provided with at least one supply device with which at least one material can be supplied to the working gas and / or the plasma jet. The supply can be active, for example by injection, or passively, for example by using a capillary effect and evaporation done. The at least one material may be in the supply in the solid, liquid and / or gaseous state. Suitable materials may be those suitable for coating or plasma polymerization. It can also be, for example, a precursor material, ie a multicomponent material, in which the several components only join together in the plasma jet to form the actually desired material, for example a product of a chemical reaction. As another application, it can be stated that water vapor is added to the plasma nozzle, wherein the water of the steam is converted to oxygen and hydrogen in the plasma jet.

The at least one supply device can be arranged on the device for generating a plasma jet so that the supply of the at least one material takes place in the region of the gas inlet. However, the supply can also take place in the region in which the arc discharge manifests. It is also possible to make the supply in the area of the gas outlet or outside of the housing. It is crucial that the at least one material comes into contact with the plasma jet.

Furthermore, the supply device may consist of a burn-off material. By acting at the Plasma generation occurring electrical discharge and the heat generated thereby, a material can be sputtered from a combustion material and thus supplied to the plasma jet. In this case, the burn-off material would have to be arranged in the region in which the arc discharge manifests. In particular, the burn-up material can be integrated into the material of the electrodes. The vaporized material may also be supplied through a secondary source in the flow direction.

In a further preferred embodiment of the device for generating a plasma jet, the device has at least one voltage supply which is connected to the at least two electrodes. Power supplies with which a high-frequency voltage, in particular a high-frequency AC voltage, can be generated are particularly preferred.

High-frequency voltages, in particular high-frequency alternating voltages, are preferably used in the production of a non-thermal plasma. Since the amount of the voltage amplitude at a high-frequency voltage at regular intervals below a certain value necessary for the discharge generation, the discharge is extinguished, until then the amount of the voltage amplitude exceeds the certain value necessary for the discharge generation again and thus again forms a discharge. This periodic firing and extinguishing of the discharge causes only a small portion of the energy bound in the discharge to be converted into heat. Thus, the temperature rise of the working gas and also of the plasma is limited. The high-frequency voltage can thus also be considered as having a constant DC voltage superimposed AC voltage can be formed up to a pulsed DC voltage. An essential aspect of the high-frequency voltage is nevertheless the high frequency, but not the polarity of the voltage values.

In a further preferred embodiment, four electrodes are integrated in the side wall of the housing of the device for generating a plasma jet. Preferably, the four electrodes are spaced transversely to the flow direction of the working gas in the side wall of the housing integrated.

In particular, the four electrodes form two pairs of electrodes, so that a first connecting line between the first pair of electrodes intersects with a second connecting line between the second pair of electrodes, preferably at a right angle. It is particularly preferred that the device for generating a plasma jet comprises two independent, in particular equal-clocked, power supplies, each one power supply is connected to one pair of electrodes. Preferably, the two power supplies are connected to a clock.

The technical problem is further solved by a device for generating a plurality of plasma jets with a plurality of devices arranged in series for generating a plasma jet, characterized in that the plurality of devices arranged in series for generating a plasma jet are electrically connected in series with at least one voltage supply.

Characteristic of the device according to the invention for generating a plasma jet is that at least two Electrodes are integrated in the side wall of the housing. From this, several devices for generating a plasma jet can be arranged in series and thus form an apparatus for generating a plurality of plasma jets.

It has been recognized that this series arrangement of the plasma jet generation devices makes it possible to electrically connect the multiple devices in series with at least one power supply. As already explained above, the spacing of the electrodes within a housing in the device according to the invention for generating a plasma jet can be smaller than in the case of plasma nozzles with a coaxial electrode known from the prior art. Therefore, it is possible to operate with the voltage generated by the power supply a plurality of series-connected devices for generating a plasma jet. In this way one can produce a series of similar plasma jets advantageously with a single power supply.

In a preferred embodiment of the device for generating a plurality of plasma jets, the gas outlets of all of the devices arranged in series for generating a plasma jet lie in one plane. In this embodiment, the series connection is particularly simple, since the facing electrodes of the adjoining devices are immediately adjacent and thus can be electrically connected by a short path. It is further preferred that the electrodes of all the devices arranged in series lie on a straight line. At least one plasma jet generating device or multiple plasma jet generating device as described above may be further arranged eccentrically on a rotary head. Such an arrangement is in the prior art, for example in the EP 0 986 939 B1 , already known. With this arrangement can be realized with appropriate adjustment of the rotation and translation of the rotary head, a time-saving, yet efficient plasma treatment of larger surfaces.

Furthermore, the technical problem is solved by a method for generating a plasma jet, in which a housing is traversed by a working gas from a gas inlet to a gas outlet, in particular substantially eddy-free, in which by applying a high-frequency voltage, in particular a high-frequency AC voltage, an arc discharge is generated in the working gas between the at least two electrodes on at least two electrodes integrated in the side wall of the housing, and in which the working gas is at least partially excited by the arc discharge to form a plasma jet.

In the method, the housing is particularly preferably flowed through by the working gas from the gas inlet to the gas outlet in a substantially eddy-free manner. As a result, the kinetic energy with which the working gas is supplied into the housing as it flows through the gas inlet, the translational movement of the working gas through the housing and out of the housing through the gas outlet and is not bound in a rotational movement of the working gas. This embodiment of the method in particular simplifies the setting of a specific flow rate of the plasma jet, which in this case is directly above the flow rate of the gas flowing into the housing through the gas inlet working gas can be controlled.

In a further preferred embodiment of the method for producing a plasma jet, the arc discharge is deformed by the flow of the working gas in the direction of the region of the gas outlet. In particular, the arc discharge may be at least partially slidably deformed by the flow of the working gas on the inner side wall of the housing towards the region of the gas outlet.

In a substantially vortex-free flow of the working gas, that is, in an approximately laminar flow of the working gas in the housing, the arc is deformed by the flow of the working gas toward the region of the gas outlet substantially into a parabolic-like arc. In the extreme case, the arc discharge at least partially slides along the inner side wall of the housing. Furthermore, the tip of the arc of the arc discharge may even protrude from the plasma jet generating device through the gas outlet. However, it is preferable that the tip of the arc of the arc discharge does not protrude through the gas outlet from the plasma jet generating device so as not to form discharge channels between the arc and the workpiece to be processed, which may adversely affect the workpiece. Thus, in certain applications of the method, an arc-free, that is potential-free, plasma jet is to be generated.

The deformation of the arc is caused by the fact that the molecules ionized by the discharge undergo Working gas to be moved by the flow of the working gas in the flow direction to the gas outlet. Since the electrical resistance in the ionized region of the working gas is lower than in the non-ionized region of the working gas, the high-frequency successive discharges preferably form in the region which has already been at least partially ionized during a preceding discharge.

In the housing, no ideal laminar flow of the working gas is formed, since heat is released in the working gas through the at least partial ionization of the working gas, which leads to at least small-scale turbulence and also at least small-scale pressure differences in the working gas. Consequently, the deformed arc does not assume an ideal parabolic shape, but is subject to irregular shape changes, which are caused by the small-scale vortex and pressure differences and by the given by the geometry of the housing flow conditions. Another effect can lead to the deformation of the arc. The arc containing portion of the working gas is heated and thereby expands. This results in the production of an arc advantageous lower pressures. As a result, the arc has the tendency to evade areas of low pressure, ie areas of higher temperature. This happens then in the direction of the side wall.

It is also possible that the arc discharge is at least partially slidably deformed by the flow of the working gas on the inner side wall of the housing in the direction of the region of the gas outlet, because the applied between the electrodes electric field through the different dielectric properties of the working gas and the housing material is distorted. It is not necessary that the housing is formed as a whole of an insulating material. Rather, it is sufficient if the electrodes are surrounded by an insulating material. The other areas can then also be made of conductive materials, such as metals. In this case, it should be noted that, for example, the metallic part of the housing is not connected to ground or grounded, so that no charge carriers can be discharged via the metallic part of the housing.

In a further preferred embodiment of the method, at least one material, in particular a coating material or precursor material, is supplied to the working gas and / or the plasma jet by means of at least one feed device.

In a further preferred embodiment of the method, two independent high-frequency voltages are applied to two pairs of electrodes integrated in the side wall of the housing. Preferably, these two independent high-frequency voltages are equal-clocked and in particular provided with a phase difference. The phase difference is preferably substantially 90 °.

By providing two pairs of electrodes arranged so that their connecting lines are perpendicular to each other, a high plasma intensity can be achieved while maintaining the non-thermal property of the plasma. The preferred phase difference of substantially 90 ° between the two high-frequency voltages is chosen so that that, when the arc between the first pair of electrodes goes out, because the voltage amplitude of the first voltage supply falls below a certain amount, the arc is generated between the second pair of electrodes, because the voltage amplitude of the second voltage supply exceeds a certain amount. This ensures that the two power supplies independently of one another alternately generate an arc discharge and thus a plasma in the working gas. This embodiment of the method can also be extended with more than two pairs of electrodes.

The technical problem is also solved by a method for generating a plurality of plasma jets, in which the plurality of housings of the devices for generating a plasma jet of a working gas from the respective gas inlet to the respective gas outlet, in particular substantially vortex-free flows through, in which by means of application a high-frequency voltage, in particular a high-frequency AC voltage, to the electrodes arranged in series, an arc discharge in the working gas between the at least two electrodes of each housing is generated, and wherein the working gas is at least partially excited by the arc discharges to a plasma.

In an alternative embodiment of the method, the plurality of arc discharges are deformed by the flow of the working gas, in particular at least partially slidingly on the inner side walls of the plurality of housings, toward the region of the respective gas outlets.

In a preferred embodiment of the method, at least one material, in particular a coating material or precursor material, is supplied to the working gas and / or the plasma jets by means of at least one feed device.

For example, a plasma jet produced by the above-described apparatuses and methods can be used in the stripping of surfaces of a workpiece. For example, with such a plasma jet, a layer of organic material, for example a lacquer layer, can be removed from a surface of a workpiece. In this case, the organic material, preferably at low temperatures, pyrolyzed and / or sublimated. But it is also possible to remove inorganic layers with such a plasma jet.

Furthermore, a plasma jet produced by the above-described apparatuses and methods can also be used to pretreat the surfaces of workpieces. For example, the adhesive properties and / or the wettability of the surface of a workpiece can be improved, in particular the surface can be activated. The pretreatment with such a plasma jet may also be used to improve the weldability of a workpiece, particularly an oxide / hydroxide layered metal piece or piece of metal alloy.

Another possible application of a plasma jet generated by the devices and methods described above is the cleaning, disinfection or even sterilization of surfaces. The application of such a plasma jet is a reactive medium with the Surface brought into contact. The plasma as a reactive medium has a high reactivity due to high electron excitation, but may nevertheless have a non-thermal property. The high reactivity can be used, for example, for cleaning or for disinfecting the surface. In the treatment with a plasma jet, the germs present on the surface to be processed are at least partially, preferably predominantly, killed due to the electron reactivity. At a non-thermal property of the plasma while the thermal stress of the surface is kept low. This opens up applications for the plasma jet, for example in the medical or food technology sector.

Fig. 1

ein erstes Ausführungsbeispiel der Vorrichtung zur Erzeugung eines Plasmastrahls im Seitenquerschnitt,

Fig. 2a-d

vier beispielhafte Ansichten des Strömungsquerschnitts einer Vorrichtung zur Erzeugung eines Plasmastrahls,

Fig. 3

ein zweites Ausführungsbeispiel der Vorrichtung zur Erzeugung eines Plasmastrahls mit einer Zuführungsvorrichtung im Seitenquerschnitt,

Fig. 4

ein drittes Ausführungsbeispiel der Vorrichtung zur Erzeugung eines Plasmastrahls mit einer Zuführungsvorrichtung im Seitenquerschnitt, und

Fig. 5

ein Ausführungsbeispiel einer Vorrichtung zur Erzeugung mehrerer Plasmastrahlen mit vier in Reihe angeordneten Vorrichtungen zur Erzeugung eines Plasmastrahls im Seitenquerschnitt.

Further features and advantages of the present invention will become apparent in the description of embodiments, reference being made to the accompanying drawings. In the drawings show:

Fig. 1

A first embodiment of the device for generating a plasma jet in the lateral cross-section,

Fig. 2a-d

four exemplary views of the flow cross section of a device for generating a plasma jet,

Fig. 3

A second embodiment of the device for generating a plasma jet with a supply device in the side cross-section,

Fig. 4

a third embodiment of the apparatus for generating a plasma jet with a feeding device in the side cross-section, and

Fig. 5

An embodiment of an apparatus for generating a plurality of plasma jets with four arranged in series devices for generating a plasma jet in the lateral cross section.

Fig. 1 shows the side cross-section of a first embodiment of the inventive device for generating a plasma jet. The device comprises a substantially hollow cylindrical housing 2, which is formed of a ceramic material. On this housing 2, a gas inlet 6 and a gas outlet 8 are arranged. The gas inlet 6 is formed in this example in multiple pieces with the housing 2, and has, for example, an annular disc made of ceramic, which is arranged flush with the inner side wall of the housing 2, and the inner annular opening is dimensioned so that it the flow cross-section of the gas inlet. 6 narrows in comparison to the flow cross-section of the housing 2. The gas outlet 8 is formed in this example in one piece with the housing 2 through a central circular bore in the end facing away from the gas inlet 6 of the housing 2. The bore may for example have a diameter of 2.5 mm to 4 mm. In the region of the side wall of the housing 2 between the gas inlet 6 and the gas outlet 8, two electrodes 4 are integrated diametrically spaced apart in the side wall of the housing 2. The electrodes preferably consist of a copper alloy. The interior 22 of the housing 2 facing surfaces of the two electrodes 4 are arranged in alignment with the surrounding inner side wall of the housing 2, so that on the inner side wall of the housing 2 forms a substantially planar surface. The two electrodes 4 are electrically connected to a power supply 12, with which a high-frequency voltage, in particular a high-frequency alternating voltage, can be generated. The flow cross-section of the housing 2 tapers from the region in which the two electrodes 4 are arranged to the region of the gas outlet 8 in that the side wall of the housing 2 is bent in this section.

In operation of the device for generating a plasma jet according to the Fig. 1 If a working gas 10, for example air, is introduced into the housing 2 through the gas inlet 6, the housing 2 flows largely parallel to the axis of the hollow cylinder and then exits the housing 2 in a focused manner through the gas outlet 8. A high-frequency electrical voltage is applied between the two electrodes 4 by means of the voltage supply 12, the frequency in particular comprising approximately values of the order of 1 kHz to 100 kHz, while the voltage values measured by the peak-to-peak are of the order of magnitude of approximately 0.5 kV to 30 kV. The voltage ensures that an arc 16 is formed in the working gas 10 between the electrodes 4, along which the working gas 10 is at least partially ionized and thus excited to a plasma 14. As a result of the flow of the working gas 10 through the housing 2, the ionized part of the working gas 10, which has the lowest electrical resistance in the working gas 10, is deformed in the direction of the gas outlet 8, so that a correspondingly shaped arc 16 is formed. Since the flow of the working gas 10 through the housing 2 is not ideally homogeneously distributed, it is possible that in addition to a Main arc also form several smaller arcs, along which run at least smaller partial discharges. These smaller arcs will be in the Fig. 1 represented by two smaller arcs adjacent to the main arc. The plasma 14 formed along the arc 16 is then guided out of the gas outlet 8 by the flow of the working gas 10 in the form of a jet, that is to say as a directed and focused plasma jet. As can be seen from this illustration, therefore, a separation of the current-carrying arc and the potential-free plasma jet takes place. Thus, in a surface treatment direct exposure of the surface can be avoided by the arc.

Fig. 2a shows a flow cross section of the substantially hollow cylindrical housing 2 in the region in which the two electrodes 4 are integrated in the side wall of the housing 2. The electrodes 4 are arranged diametrically spaced apart in the side wall of the housing 2. It is particularly preferred that the extent of the electrodes 4 along the circumference of the housing 2, here along a circumference, is small against the circumference itself. In this way, the base area of the arc 16 at the electrodes 4 can be kept small.

Fig. 2b shows a flow cross section of a housing 2 in the region of the electrodes 4, wherein the housing 2 is formed in this example substantially hollow cuboid.

Fig. 2c shows a flow cross-section of a hollow cylindrical housing 2 in the region of the electrodes 4, in which a total of four electrodes in the side wall of the housing 2 are integrated. Two diametrically opposed spaced electrodes 4a, b each form a pair of electrodes. The pairs of electrodes are arranged such that a first connecting line 18a extends between the first pair of electrodes perpendicular to a second connecting line 18b between the second pair of electrodes. Furthermore, two independent, in particular equal-clocked, voltage supplies 12a-b are provided on the device, which are electrically connected to one pair of electrodes each.

Fig. 2d shows one of the Fig. 2c comparable arrangement with a substantially hollow cuboid housing 2. The electrodes 4 are arranged centrally on the opposite side walls of the housing 2. However, this central arrangement is to be understood as an example.

Fig. 3 shows an embodiment of the apparatus for generating a plasma jet similar to that Fig. 1 , The difference is that the device is provided with a supply device 20, with which a material can be supplied to the working gas 10 and / or the plasma jet 14. In this example, the feeding device 20 comprises an angled pipe, one of whose angled pipe end protrudes coaxially in the flow direction of the working gas 10 into the housing 2.

By means of this angled pipe, for example, a material in the gaseous state can be supplied to the working gas 10 and / or the plasma jet 14. In this example, the angled pipe on the pipe end facing away from the housing 2, for example, with a pressure regulator, not shown, and a desired material in the gaseous state containing, not shown compressed gas cylinder connected.

It is also possible to supply a material in the liquid state by means of the angled tube. In this example, the pipe end facing away from the housing 2, for example, connected to a pump, not shown, and a reservoir containing the desired material in the liquid state, not shown. With the pump then the material can be supplied to the working gas 10 or the plasma jet 14. Furthermore, in this case, the angled tube preferably has a sputtering device (not shown) on its angled pipe end arranged in the housing 2, for example a close-meshed grating so that the material can be atomized in the liquid state when it is fed into the working gas 10 or the plasma jet 14.

In the in Fig. 3 As shown, the material in the housing 2 is supplied in the area immediately before the gas outlet 8. However, it is also possible to arrange the feeding device 20 in the region of the gas inlet 6. Furthermore, it is possible to arrange the feeding device 20 entirely outside the housing 2 in the region in which the plasma jet 14 emerges.

Fig. 4 shows a device for generating a plasma jet with a delivery device 20 similar to the Fig. 3 , The difference is in the design of the delivery device 20. In this example, the delivery device 20 comprises a capillary system, for example a wick, which is connected to its one end is connected to a reservoir 24. The reservoir 24 contains a material in the liquid state, which is to be supplied to the working gas 10 and / or the plasma jet 14. The end of the capillary system facing away from the reservoir 24 is integrated in an opening in the side wall of the housing 2 and protrudes at least partially into the interior 22 of the housing 2. With this supply device 20, it is possible to supply a material in the liquid state from the reservoir 24 via the capillary with the help of capillary forces the end of the reservoir 24 remote from the capillary system, where it can then evaporate into the interior 22 of the housing 2 inside.

Again, the supply device 20 is arranged so that the material in the liquid state in the region of the gas outlet 8 to the working gas 10 and / or the plasma jet 14 is supplied. Again, that the delivery device 20 can be arranged in other areas within or outside of the housing 2.

Fig. 5 shows four in Fig. 1 described, arranged in series devices for generating a plasma jet. The four housings 2a-d are arranged so that the respective gas outlets 8a-d lie in a plane and the respective electrodes 4a-d lie on a straight line. The electrodes 4a-4b, 4b-4c and 4c-4d integrated in different housings 2a-d form three electrode pairs and are immediately adjacent. The surroundings of the device facing two electrodes 4a and 4d are electrically connected to a power supply 12. In addition, the mutually facing electrode pairs are electrically connected to each other, so that a series circuit of the four Devices is effected. By applying a voltage to the two outer electrodes 4a and 4d, arc discharges 16a-d are generated in each case 2a-d. Due to the voltage drop between the electrodes 4 integrated in a housing 2, the voltage amplitude in this example must be selected to be substantially four times as large as in the case of a single example in FIG Fig. 1 described housing 2 to meet the discharge condition in each housing 2a-d. The gas inlets 6a-d having ends of the housing 2a-d are connected to a gas channel 26 having the gas inlets 6a-d corresponding openings. Via this gas channel 26, a working gas 10a-d is supplied to the devices arranged in series.

It is also possible in a series arrangement of the devices to provide them with at least one of the above description resulting feeding device 20. In particular, multiple feeders 20 may be used to supply different materials to the working gas 10a-d or the plasma jet 14a-d.

Claims (15)

1. Device for generating a directed and focussed plasma beam,

   - with a housing (2), and

   - with at least two electrodes (4) and

   - with at least one voltage supply (12),

   - wherein the voltage supply (12) is connected to the at least two electrodes (4),

   - wherein the housing (2) has a gas inlet (6) and a gas outlet (8),

   - wherein the at least one voltage supply (12) can be used to generate a high-frequency voltage, in particular a high-frequency alternating voltage, for generating an arc discharge between the electrodes (4), and

   - wherein the flow cross-section of the gas outlet (8) is smaller than the flow cross-section of the housing (2),
   characterized in that

   - the at least two electrodes (4) are spaced apart from each other in a direction transverse to the flow direction of a working gas (10) and integrated into the side wall of the housing (2).
2. The device according to claim 1,
   characterized in that
   the surfaces of the at least two electrodes (4) facing towards the interior (22) of the housing (2) are aligned flush with the surface of the side wall of the housing (2) facing towards the interior (22) of the housing (2).
3. The device according to claim 1 or 2,
   characterized in that
   the flow cross-section of the gas inlet (6) is smaller than the flow cross-section of the housing (2).
4. The device according to any one of claims 1 to 3,
   characterized in that
   the gas outlet (8) is slot-shaped and that the longitudinal axis of the slot extends parallel to the connecting line between the at least two electrodes (4).
5. The device according to any one of claims 1 to 4,
   characterized in that
   the at least two electrodes (4) are rod-shaped, wherein the longitudinal axes of the electrodes (4) extend in the side wall parallel to the flow direction of the working gas (10).
6. The device according to any one of claims 1 to 5,
   characterized in that
   at least one supply device (20) is provided, with which at least one material, in particular a coating material or precursor material, can be supplied to the working gas (10) and/or the plasma beam (14).
7. The device according to any one of claims 1 to 6,
   characterized in that
   four electrodes (4) are integrated into the side wall of the housing (2), that the four electrodes (4) form two electrode pairs, so that a first connecting line (18a), between the first pair of electrodes intersects with a second connecting line (18b) between the second pair of electrodes, preferably at a right angle, and that the device comprises two independent, in particular synchronized, voltage supplies (12), wherein each voltage supply (12) is connected in each case to one pair of electrodes.
8. The device according to claim 7,
   characterized in that
   the four electrodes (4) are spaced apart from each other in a direction transverse to the flow direction of a working gas (10) and are integrated into the side wall of the housing (2).
9. Device for generating multiple plasma beams,

   - with a plurality of devices according to any one of claims 1 to 8 arranged in series,
   characterized in that

   - the plurality of devices arranged in series are electrically connected in series to at least one voltage supply (12).
10. A method for generating a plasma beam using a device according to one of claims 1 to 8,

    - in which a working gas (10) flows through a housing (2) from a gas inlet (6) to a gas outlet (8),

    - in which by applying a high-frequency voltage to at least two electrodes (4) being integrated into the side wall of the housing (2) an arc discharge (16) is generated in the working gas (10) between the at least two electrodes (4),

    - in which the working gas (10) is excited by the arc discharge (16) at least partially to form a plasma beam (14) and

    - in which the arc discharge (16) is deformed by the flow of the working gas (10) in the direction of the area of the gas outlet (8).
11. The method according to claim 10,
    in which the working gas (10) flows through the housing (2) from a gas inlet (6) to a gas outlet (8) in a substantially non-vortical manner.
12. The method according to claim 10 or 11,
    in which at least one material, in particular a coating material or precursor material, is supplied to the working gas (10) and/or the plasma beam (14) by means of at least one supply device (20).
13. The method according to any one of claims 10 to 12,
    in which two independent, in particular synchronized, high-frequency voltages are applied to two electrode pairs being integrated into the side wall of the housing (2).
14. The method according to claim 13,
    in which a phase difference, in particular substantially of 90°, is provided between the two high-frequency voltages.
15. Method for generating a plurality of plasma beams by means of a device according to claim 9,

    - in which a working gas (10a-d) flows through the plurality of housings (2a-d) from the respective gas inlet (6a-d) to the respective gas outlet (8a-d),

    - in which by application of a high-frequency voltage to the electrodes (4a-d) arranged in series, an arc discharge (16a-d) is generated in the respective working gas (10a-d) between the at least two electrodes (4a-d) of each housing (2a-d), and

    - in which the working gas (10a-d) is excited by the arc discharges (16a-d) at least partially to form plasma beams (14a-d).

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