EP0861575B1 - Four-nozzle plasma generator for forming an activated jet - Google Patents

Description

The invention relates to a plasma generator with four nozzles for the formation of an activated jet, according to the preamble of claim 1.

This generator can be used in particular in surface treatment process (sterilization, cleaning, stripping, modification, deposit of recovery and films), of dispersed materials and monoliths, as well as for obtaining chemicals in electronics, automotive, food, medicine, chemistry, manufacture of machines and tools, etc.

We know plasma generators with four nozzles containing two chambers with anode and cathode electrodes, connected to direct current sources and which generate four plasma jets whose shape and trajectory create using an external magnetic field so that the plasma jets, by converging, form a unique flow of plasma whose temperature in the central area, in which chemicals and / or materials to be treated, is lowered compared to the zones peripheral devices. Such devices are described in the document "Basics of the realization of the dynamic processing method by plasma from the surface of a solid body "P. P. Koulik and others, "Plasmochimie 87", Moscow 1987, part 2, pp. 58 to 96, as well as in patent applications FR 2 678 467 and GB 2 271 044.

The construction of the electrode chambers (anode and cathode) is described in the document "Plasmatron with two jets Frounze ", I.I. Lenbayev, V.S. Enguelsht," Ilim ", 1983.

The advantage of such generators according to the prior art is due on the one hand to the specific configuration of plasma flows which is shaped like a plasma funnel, which allows to introduce and effectively treat different products. On the other hand, the electric current flowing through the plasma jet heating and activating it with losses minimal, given the absence of cooled walls, implies that the performance of this device is high.

1. La génération des jets et du flux de plasma s'accompagne de la formation de tourbillons toroïdes. Les flux de gaz chauds qui en résultent viennent échauffer les pièces des chambres à électrodes des éléments de fixation et d'alimentation, d'une part, et occasionnent des pertes sensibles de chaleur diminuant ainsi le rendement du générateur. D'autre part, dans certains cas le degré de turbulence du flux de plasma est augmenté et il apparaít des pertes des produits introduits dans la partie centrale du flux, donnant naissance à des effets secondaires néfastes pour le temps de vie du générateur, puisque ces produits se déposent sur la surface des chambres à électrodes, des pièces de fixation et d'alimentation. La radiation du plasma, qui est spécialement élevée lors de l'introduction dans le flux de plasma de produits chimiques, est aussi une source d'échauffement superflue des diverses pièces du générateur exposées à cette radiation. Le résultat de l'effet simultané des flux de convection et de radiation est, en fin de compte, que le temps de vie du générateur est diminué à cause de l'échauffement superflu de ses pièces et de la formation de couches de dépôts de faible conduction thermique, rendant difficile le refroidissement de ces pièces.En plus, de temps à autres, les couches de dépôt se détruisent et, emportées par les tourbillons de gaz, viennent souiller les surfaces traitées et le flux de plasma lui-même, rendant ce dernier de composition pratiquement incontrôlable.

2. Le flux de plasma ayant accompli son action d'échauffement et d'activation des produits qui y sont introduits, son rôle est terminé et sa présence à la périphérie du flux de produit activé n'est plus nécessaire. Quand le produit activé est un gaz (cas de beaucoup d'applications, notamment nettoyage, décapage, dépôt de films, modification de surface) la présence du plasma original à la périphérie du flux activé devient un obstacle à l'efficacité du traitement de surface. En effet, le plasma, toujours chaud, chauffe la surface traitée ce qui, en général, est à éviter. En outre, le plasma, à la surface n'est plus qu'une composante passive qui n'entre pas en action avec la surface, les seules particules agissantes étant celles que le plasma a activées et qui atteignent la surface par diffusion. Le plasma résiduel est un obstacle à cette diffusion, obstacle d'autant plus signifiant que la section efficace des particules corrigées composant le plasma est, en moyenne, d'un ordre de grandeur supérieur à celle des particules neutres (activées) et donc la présence de ces particules réduit très sensiblement le coefficient de diffusion des particules activées, donc le flux de diffusion, et en fin de compte l'efficacité du traitement.

Such a device can be used effectively for the sterilization of surfaces, their cleaning, modification, pickling and depositing of covers and films. However, its exploitation made it possible to observe the following disadvantages:

1. The generation of jets and plasma flow is accompanied by the formation of toroid vortices. The resulting hot gas flows heat the parts of the electrode chambers of the fastening and supply elements, on the one hand, and cause appreciable heat losses, thereby reducing the efficiency of the generator. On the other hand, in some cases the degree of turbulence of the plasma flow is increased and it appears losses of the products introduced into the central part of the flow, giving rise to harmful side effects for the lifetime of the generator, since these products are deposited on the surface of the electrode chambers, fixing and supply parts. Plasma radiation, which is especially high when chemicals are introduced into the plasma stream, is also an unnecessary source of heat for the various parts of the generator exposed to this radiation. The result of the simultaneous effect of convection and radiation fluxes is, ultimately, that the life of the generator is reduced due to the superheat heating of its parts and the formation of low deposit layers heat conduction, making it difficult to cool these parts. In addition, from time to time, the deposit layers are destroyed and, carried away by the gas vortices, contaminate the treated surfaces and the plasma flow itself, making this last of almost uncontrollable composition.

2. The plasma flow having accomplished its heating and activating action of the products introduced into it, its role is ended and its presence at the periphery of the flow of activated product is no longer necessary. When the activated product is a gas (in the case of many applications, in particular cleaning, pickling, film deposition, surface modification) the presence of the original plasma at the periphery of the activated flux becomes an obstacle to the effectiveness of the surface treatment . Indeed, the plasma, always hot, heats the treated surface which, in general, is to be avoided. In addition, the plasma on the surface is only a passive component which does not come into action with the surface, the only active particles being those which the plasma has activated and which reach the surface by diffusion. Residual plasma is an obstacle to this diffusion, an obstacle all the more signifying that the cross-section of the corrected particles composing the plasma is, on average, of an order of magnitude greater than that of neutral (activated) particles and therefore the presence of these particles very significantly reduces the diffusion coefficient of the activated particles, therefore the diffusion flow, and ultimately the effectiveness of the treatment.

The object of the invention is to propose a generator for plasma with four nozzles to obtain a gas jet activated of controllable composition, stable form, long resource for continuous work and optimal action on objects to be treated.

To this end, the invention relates to a plasma generator with four nozzles comprising two chambers with anode electrodes and two cathode electrode chambers, connected to sources of direct current and generating four plasma jets, the shape and trajectory are created using a system of external magnetic fields, so that the jets plasma form a single plasma flow with an area lowered temperature control unit in which is introduced the chemical component and / or the materials to treat, the electrode chambers of this generator being arranged in an enclosure into which a gas is introduced, this enclosure being composed of a concave flange to which are fixed the electrode chambers and a first flat diaphragm, water-cooled and provided with an orifice circular central arranged at the junction of the jets of plasma from the electrode chambers and crossed by the current.

According to one embodiment, the generator comprises, in downstream of the first diaphragm, a second diaphragm, cooled to water, whose orifice with a variable diameter, less than that of the plasma flow, this diaphragm being fixed to the enclosure through a circular wall, allowing the evacuation of part of the plasma and gases introduced into the enclosure.

The solution proposed by the present invention consists in modify the four nozzle plasma generator of art anterior, so as to create an activated composition flow controlled and effective action on the treated surface, while increasing the lifetime of the generator. Is equivalent to eliminate the disadvantages of the known four-nozzle generator described above, i.e. to suppress the flows of convection and reduce the radiation flux acting on the electrode chambers, their fasteners and while intensifying the action on the surface treated activated components of the flow created by the generator, reducing the amount of plasma reaching the surface to be treated.

• les figures 1a et 1b illustrent un premier exemple de générateur selon l'invention, respectivement selon une vue du côté du diaphragme (le diaphragme étant montré en traitillés) et en section latérale; les repères relatifs à ces deux figures sont les suivants:
• 1. Chambres à électrodes
• 2. Bride concave de l'enceinte, refroidie à l'eau
• 3. Buse d'introduction des composantes chimiques et/ou des matériaux à traiter.
• 4. Jets de plasma
• 5. Diaphragme plat refroidi à l'eau
• 6. Flux résultant de plasma
• 7. Système magnétique
• 8. Orifice circulaire du diaphragme
• 9. Tuyères d'introduction du gaz.
• les figures 2a et 2b illustrent un second exemple de générateur selon l'invention, respectivement selon une vue du côté des diaphragmes (les diaphragmes étant montrés en traitillés) et en section latérale; les repères relatifs à ces deux figures sont les suivants:
• 1. Chambres à électrodes
• 2. Bride concave de l'enceinte, refroidie à l'eau
• 3. Buse d'introduction des composantes chimiques et/ou des matériaux à traiter
• 4. Jets de plasma
• 5. Diaphragme plat refroidi à l'eau
• 6. Flux résultant de plasma
• 7. Système magnétique
• 8. Orifice circulaire du diaphragme
• 9. Tuyères d'introduction du gaz
• 10. Deuxième diaphragme, ajustable, refroidi à l'eau
• 11. Paroi circulaire
• 12. Orifice d'évacuation du plasma et du gaz introduit dans l'enceinte
• 13. Jet résultant de gaz activé
• la figure 3 est un schéma illustrant la fonction des diaphragmes d'après la distribution de la température (T) et de la composition (C) du flux issu du générateur, à différentes distances des chambres à électrodes.

The generator according to the invention is described below, with reference to the drawing in which:

• FIGS. 1a and 1b illustrate a first example of a generator according to the invention, respectively according to a view from the side of the diaphragm (the diaphragm being shown in dashed lines) and in lateral section; the references relating to these two figures are as follows:
• 1. Electrode chambers
• 2. Concave flange of the enclosure, water cooled
• 3. Nozzle for introducing the chemical components and / or the materials to be treated.
• 4. Plasma jets
• 5. Water-cooled flat diaphragm
• 6. Flux resulting from plasma
• 7. Magnetic system
• 8. Circular diaphragm opening
• 9. Nozzles for introducing gas.
• FIGS. 2a and 2b illustrate a second example of a generator according to the invention, respectively according to a view from the side of the diaphragms (the diaphragms being shown in dashed lines) and in lateral section; the references relating to these two figures are as follows:
• 1. Electrode chambers
• 2. Concave flange of the enclosure, water cooled
• 3. Nozzle for introducing the chemical components and / or the materials to be treated
• 4. Plasma jets
• 5. Water-cooled flat diaphragm
• 6. Flux resulting from plasma
• 7. Magnetic system
• 8. Circular diaphragm opening
• 9. Gas introduction nozzles
• 10. Second diaphragm, adjustable, water cooled
• 11. Circular wall
• 12. Plasma and gas discharge opening introduced into the enclosure
• 13. Jet resulting from activated gas
• FIG. 3 is a diagram illustrating the function of the diaphragms according to the distribution of the temperature (T) and of the composition (C) of the flux coming from the generator, at different distances from the electrode chambers.

The four nozzle generators shown in the Figures 1 and 2 include, like the known prototype described above, four electrode chambers 1, a system magnetic for shape and trajectory control plasma jets 7, a tube for the introduction of chemical components and / or products to be activated in the plasma funnel. The new element of the construction of the generator is the enclosure, ventilated by a gas introduced by the nozzles 9, to which the chambers are fixed electrodes 1.

The enclosure consists of a cooled concave flange 2 with water and the water-cooled diaphragm system.

Figures 1a and 1b illustrate the case where the diaphragm includes a diaphragm in the form of a flange annular cooled 5, whose internal diameter is such that it allows the passage of the plasma flow inside which the products to be activated are introduced via the nozzle 3, and the peripheral flow of gas introduced into the enclosure by the nozzles 9.

This gas stabilizes the plasma flow and prevents formation of vortices and their contact with the electrodes, their fixing and supply parts. The plasma jets from the converging electrode chambers and join in the plane of the diaphragm 8. The accompanying flow of gas, passing peripherally through the orifice of the diaphragm 5 stabilizes plasma flow, decreases mixing plasma with surrounding gases, decreases the transfer of radical heat of the plasma flow, which lengthens the jet resulting from plasma. The diaphragm 5 whose opening 8 is relatively small, greatly reduces radiation from plasma 6 directed towards the electrode chambers.

Figures 2a and 2b illustrate the case where the diaphragms includes, in addition to diaphragm 5 whose functions are exposed above, a diaphragm 10 cooled with water, adjustable hole, the diameter of which is smaller than that of the plasma flow and which only allows the flow of gas activated.

The diaphragm 10 is fixed to the enclosure by through a circular wall 11. The gas from nozzles (9) as well as the activating plasma are evacuated by through orifices 12. This diaphragm eliminates peripheral plasma gases and accompanying gases which are an obstacle to the diffusion of activated particles towards the surface to be treated. As shown in the diagram of the FIG. 3, the diaphragm 10 also makes it possible to obtain a uniform distribution of temperature and composition of the activated stream from the proposed generator.

Claims (2)

1. A four-nozzle plasma generator comprising two anode electrode chambers and two cathode electrode chambers connected to DC power sources and generating four plasma jets of which the shape and the trajectory are determined by an external magnetic field system, such that the plasma jets form a single plasma stream with a central zone of lowered temperature into which the chemical component and/or materials to be treated are introduced,
   characterised in that the electrode chambers are arranged in an enclosure into which a gas is introduced, this enclosure consisting of a concave flange to which the electrode chambers are fixed and a first flat water-cooled diaphragm provided with a central circular aperture positioned at the point of convergence of the plasma jets from the electrode chambers and through which the current passes.
2. Generator according to claim 1, characterised in that it comprises, downstream of the first diaphragm, a second water-cooled diaphragm, with an aperture of variable diameter, smaller than that of the plasma stream, this diaphragm being fixed to the enclosure by means of a circular wall, enabling evacuation of a part of the plasma and gases introduced into the enclosure.

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