EP0515711A1 - High power radiator - Google Patents

Abstract

In the case of UV high-power radiators, in order to protect the electrodes (5, 3) facing the process and/or coolant against environmental influences, said electrodes are coated with a protective layer (8a). <IMAGE>

Description

Technical field

The invention relates to a high-power radiator, in particular for ultraviolet light, with a discharge space filled with filling gas emitting radiation under discharge conditions, the walls of which are formed by a first and a second dielectric, which have metallic grid-like or mesh-like first ones on their surfaces facing away from the discharge space and second electrodes is provided with an AC power source connected to the first and second electrodes for supplying the discharge.

The invention relates to a state of the art, as can be seen for example from EP-A 0254 111.

Technological background and state of the art

The industrial use of photochemical processes depends heavily on the availability of suitable UV sources. The classic UV lamps deliver low to medium UV intensities at some discrete wavelengths, such as the low-pressure mercury lamps at 185 nm and especially at 254 nm. Really high UV powers can only be obtained from high-pressure lamps (Xe, Hg), which then but distribute their radiation over a larger wavelength range. The new excimer lasers have provided some new wavelengths for basic photochemical experiments. for cost reasons for an industrial process is probably only suitable in exceptional cases.

In the EP patent application mentioned at the beginning or in the conference paper "New UV and VUV excimer emitters" by U. Kogelschatz and B. Eliasson, distributed at the 10th lecture conference of the Society of German Chemists, Photochemistry Group, in Würzburg (FRG) 18. -20. November 1987, a new excimer radiator is described. This new type of emitter is based on the fact that excimer radiation can also be generated in silent electrical discharges, a type of discharge that is used on a large scale in ozone generation. In the current filaments of this discharge, which exist only for a short time (<1 microsecond), noble gas atoms are excited by electron impact, which react further to excited molecular complexes (excimers). These excimers only live for a few 100 nanoseconds and release their binding energy in the form of UV radiation when they decay.

The construction of such an excimer radiator, up to the power supply, largely corresponds to that of a conventional ozone generator, with the essential difference that at least one of the electrodes and / or dielectric layers delimiting the discharge space is transparent to the radiation generated. In addition to the high UV transmission, these electrodes must also have the following properties: good conductivity of the electrical current, low costs, good flexibility for producing the closest possible contact with the dielectric and long service life. The long service life in particular requires a low chemical reactivity with the environment of the lamp. If you want to use the emitter as a light source in chemical reactors, chemical inertness to some substances is absolutely necessary for many applications.

Brief description of the invention

Starting from the prior art, the object of the invention is to create a high-power radiator, in particular for UV or VUV radiation, the electrodes of which are optimally protected against environmental influences in addition to high UV transmission.

To achieve this object, it is provided according to the invention that at least the first electrodes are provided with a protective layer or are embedded in one.

• Die der Umgebung ausgesetzten Elektroden sind vor chemischen Angriffen geschützt (Verlängerung der Lebensdauer);
• Die Elektroden sind darüber hinaus auch gegenüber physikalischen Angriffen geschützt: Enladungen verursachen Erosion; Erosion trägt Elektrodenmaterial ab, das sich auf den transparenten Stellen des Dielektrikums niederschlägt und dort die Transparenz vermindert;
• Ist die Umgebung selbst ein mit UV-Strahlung zu behandelndes Gas oder Flüssigkeit, so wird ein metallischer Kontakt dieser Substanz vermieden, um keine zusätzlichen chemischen Reaktionen auszulösen, bei denen Metalle beteiligt sind (chemische Inertheit);
• Eventuelle Entladungen (z.B. Korona) in der Umgebung von Elektroden auf das Dielektrikum oder zu in der Nähe befindlichen spannungsführenden Teilen oder Oberflächenentladungen längs des Dielektrikums werden vermieden durch den besseren Kontakt zum Dielektrikum; durch die bessere elektrische Isolation der Elektrodem werden darüber hinaus unerwünschte energiekostende Entladungen verhindert.

A spotlight constructed in this way fulfills all practical requirements:

• The electrodes exposed to the environment are protected against chemical attacks (prolongation of the service life);
• The electrodes are also protected against physical attacks: discharges cause erosion; Erosion removes electrode material, which is deposited on the transparent areas of the dielectric and reduces transparency there;
• If the environment itself is a gas or liquid to be treated with UV radiation, metallic contact with this substance is avoided in order not to trigger additional chemical reactions in which metals are involved (chemical inertness);
• Any discharges (eg corona) in the vicinity of electrodes on the dielectric or to nearby live parts or surface discharges along the dielectric are avoided by the better contact with the dielectric; the better electrical insulation of the electrodes also prevents unwanted energy-costing discharges.

The practical implementation of the invention can be done in different ways. In addition to the mere coating of the metallic wires, for example by immersing the electrodes in a corresponding one Bathroom, it is advantageous to immerse the fully assembled spotlight in a bathroom. Coatings with so-called thick-layer potting compounds are also possible, which have the advantage of an easy-to-clean outer surface of the radiator.

Particularly suitable as coating or embedding material are dielectric materials which make good contact with the dielectric of the radiator and at the same time are easy to apply. If materials are used that are UV-curing, they can be cured extremely quickly by the emitter itself.

Particular embodiments of the invention and the further advantages which can be achieved thereby are explained in more detail below with reference to the drawings.

Brief description of the drawings

Fig.1

einen UV-Zylinderstrahler bekannter Bauart;

Fig.2

einen Ausschnitt aus dem äusseren Dielektrikumsrohr eines UV-Strahlers mit darauf angeordneter Aussenelektrode aus mit Dielektrikumsmaterial beschichtetem Runddraht;

Fig.3

einen Ausschnitt aus dem äusseren Dielektrikumsrohr eines UV-Strahlers mit darauf angeordneter Aussenelektrode aus Runddraht, wobei die gesamte Aussenfläche mit einem Beschichtungsmaterial versehen ist;

Fig.4

einen Ausschnitt aus dem äusseren Dielektrikumsrohr eines UV-Strahlers mit darauf angeordneter Aussenelektrode aus Runddraht, der in Vertiefungen des äusseren Dielektrikumsrohrs liegt, die ihrerseits mit Beschichtungsmaterial ausgefüllt sind;

Fig.5

einen Ausschnitt aus dem äusseren Dielektrikumsrohr eines UV-Strahlers mit darauf angeordneter Aussenelektrode aus Runddraht mit einem glatten äusseren Dielektrikumsrohr und einer Dickschichtvergussmasse, in welcher die Elektroden eingebettet sind;

Fig.6

einen Auschnitt aus einem UV-Strahler, der Strahlung sowohl nach aussen als auch nach innen aussendet.

In the drawing, embodiments of high-power radiators are shown in a highly simplified form; shows

Fig. 1

a UV cylinder lamp of known design;

Fig. 2

a section of the outer dielectric tube of a UV lamp with an outer electrode arranged thereon made of round wire coated with dielectric material;

Fig. 3

a section of the outer dielectric tube of a UV lamp with an outer electrode made of round wire arranged thereon, the entire outer surface being provided with a coating material;

Fig. 4

a section of the outer dielectric tube of a UV lamp with an outer electrode arranged thereon from round wire, which lies in depressions of the outer dielectric tube, which in turn are filled with coating material;

Fig. 5

a section of the outer dielectric tube of a UV lamp with an outer electrode made of round wire arranged thereon with a smooth outer dielectric tube and a thick-layer potting compound in which the electrodes are embedded;

Fig. 6

a section of a UV lamp that emits radiation both outwards and inwards.

Detailed description of the invention

The UV high-power radiator shown schematically in FIG. 1 consists of an outer dielectric tube 1, for example made of quartz glass, and an inner dielectric tube 2 arranged concentrically therewith, the inner wall of which is provided with an inner electrode 3. The annular space between the two tubes 1 and 2 forms the discharge space 4 of the radiator. The inner tube 2 is inserted gas-tight in the outer tube 1, which was previously filled with a gas or gas mixture which emits UV or VUV radiation under the influence of silent electrical discharges.
A metal net or metal grid, which extends over the entire circumference of the outer tube 1, serves as the outer electrode 5. Both the outer electrode 5 and the outer dielectric tube 1 are transparent to the UV radiation generated.
The electrodes 3 and 5 are led to the two poles of an AC power source 6. The AC power source basically corresponds to those used to feed ozone generators. It typically delivers an adjustable AC voltage in the order of magnitude of several 100 volts to 20,000 volts at frequencies in the range of technical alternating current up to a few 1000 kHz - depending on the electrode geometry, pressure in the discharge space 4 and the composition of the filling gas.

The fill gas is e.g. Mercury, noble gas, noble gas-metal vapor mixture, noble gas-halogen mixture, optionally using an additional further noble gas, preferably Ar, He, Ne, as a buffer gas.

Depending on the desired spectral composition of the radiation, a substance / substance mixture according to the following table can be used: Filling gas radiation helium 60-100 nm neon 80 - 90 nm argon 107 - 165 nm Argon + fluorine 180-200 nm Argon + chlorine 165-190 nm Argon + krypton + chlorine 165-190, 200-240 nm xenon 160-190 nm nitrogen 337 - 415 nm krypton 124, 140-160 nm Krypton + fluorine 240 - 255 nm Krypton + chlorine 200-240 nm mercury 185, 254, 320-370, 390-420 nm selenium 196, 204, 206 nm deuterium 150-250 nm Xenon + fluorine 340 - 360 nm, 400 - 550 nm Xenon + chlorine 300-320 nm

• Ein Edelgas (Ar, He, Kr, Ne, Xe) oder Hg mit einem Gas bzw. Dampf aus F₂, J₂, Br₂, Cl₂ oder eine Verbindung, die in der Entladung ein oder mehrere Atome F, J, Br oder Cl abspaltet;
• ein Edelgas (Ar, He, Kr, Ne, Xe) oder Hg mit O₂ oder einer Verbindung, die in der Entladung ein oder mehrere O-Atome abspaltet;
• ein Edelgas (Ar, He, Kr, Ne, Xe) mit Hg.

In addition, a whole series of other filling gases are possible:

• A noble gas (Ar, He, Kr, Ne, Xe) or Hg with a gas or vapor from F₂, J₂, Br₂, Cl₂ or a compound that splits off one or more atoms F, J, Br or Cl in the discharge;
• a noble gas (Ar, He, Kr, Ne, Xe) or Hg with O₂ or a compound that releases one or more O atoms in the discharge;
• an inert gas (Ar, He, Kr, Ne, Xe) with Hg.

In the silent discharge that forms, the electron energy distribution can be optimally adjusted by the thickness of the dielectrics and their properties, pressure and / or temperature in the discharge space.

When an alternating voltage is applied between the electrodes 3, 5, a large number of discharge channels (partial discharges) form in the discharge space 4. These interact with the atoms / molecules of the filling gas, which ultimately leads to UV or VUV radiation.

In the cutout according to FIG. 2, the individual wires 7 of the outer electrode are provided with a coating 8. In the simplest case, this can consist of wire enamel. Such insulated wires with burned-in lacquer are common in transformer construction. Depending on the thickness and type of paint, the additional voltage increase caused by the paint can be optimized to tension the discharge.

In the detail according to FIG. 3, not only the wire but also the entire radiator surface is provided with a coating 8a made of clear lacquer. Although this arrangement reduces the UV lamp output for some wavelengths, it can be manufactured particularly easily by immersing the completely assembled lamp in a lacquer bath, or spraying or painting a lacquer and then curing it. With 308 nm radiation and a typical layer thickness of 1 to 2 µm, the transmission is more than 80%. UV-curing clear lacquers are preferably used, which can be cured extremely quickly by the emitter itself and in which the transmission improves after the curing due to the chemical conversion.

In the arrangement shown in FIG. 4, the individual wires 7 of the outer electrode 5 lie in recesses in the outer dielectric tube 1 and are completely in the coating 8b, e.g. a clear coat, embedded. The lacquer layer 8b then alternately has different thicknesses along the radiator surface. Since thin layers of lacquer allow the UV radiation to pass through better than thick ones, a corresponding intensity pattern results. This is advantageous for applications in which an object which is to be irradiated with UV is moved along the surface and should have well-defined exposure pauses.

Finally, FIG. 5 shows the arrangement of wires completely embedded in a UV-transparent thick-layer potting compound 8c on a smooth outer dielectric tube 1. The modern development of UV-curing products has made it possible to produce such casting compounds from clear lacquer and even pigmented systems. Examples of UV-curing epoxy resins and UV-curing acrylates are described, for example, in the lecture manuscript by Panacol-Elosol GmbH "UV-EPOXIES - New Possibilities with Radiation-Curing Adhesives and Potting Compounds", Haus der Technik eV Essen, on November 20, 1990. With such an arrangement, the "carrier" of the potting compound 8c, the outer dielectric tube 1 can be made thinner, in the borderline case even dispensed with if the dielectric properties of the potting compound are adapted to the discharge process.

In addition to cylindrical emitters, the displacement of the electrodes according to the invention can also be used successfully with area emitters. The outer electrode itself can also be designed differently, for example not in the form of a mesh or lattice, but only consist of parallel strips, which is particularly suitable for an arrangement according to FIG. 3.
Instead of separate or discrete electrode arrangements, those which are in the form of strips or grids can also be used Metallizations are applied to the outer surface of the dielectric tube 1 and are then provided with a coating using the method described in connection with FIG.

The invention was explained above on the basis of exemplary embodiments which relate to so-called outdoor radiators. The measures presented here for protecting the electrodes naturally also apply to what is known as an internal radiator. Apart from the position of the transparent electrodes 5, such an internal radiator corresponds to the external radiator shown in FIG.

Furthermore, emitter configurations are also possible in which the UV radiation is emitted both outwards and inwards. Fig. 6 illustrates a section of such a radiator. In such arrangements, both dielectric tubes 1, 2 and also the respective electrodes 3, 5 must be transparent to the radiation generated. In this case, both the first electrodes 5 and the second electrodes 3 can be optimally protected from chemical and physical attacks in the manner described above.

Outdoor and indoor radiators are regularly cooled with a liquid coolant. In the case of external emitters, this is passed through the inner dielectric tube 2; in the case of internal emitters, the coolant flows around the outer dielectric tube 1. Here too, protective layers made of the materials described help to prevent or at least reduce the erosion attack by the coolant. If these are electrodes that do not have to transmit UV radiation, other protective layers can also be used, for example those that are applied by anodizing, enamelling, etc. In the case of aluminum electrodes that are vapor-deposited or sputtered onto the dielectric, it makes sense to anodize the free surface. In the case of mesh-shaped or grid-shaped electrodes, It is important to ensure that no (external) discharges occur between the electrode and the dielectric surface, which do not have to transmit UV radiation, which can be done by filling the space with a varnish or other fillers such as adhesive or non-conductive conductive or pastes, e.g. conductive silver .

Claims (6)

High-power radiator, in particular for ultraviolet light, with a discharge space (4) filled with filling gas emitting radiation under discharge conditions, the walls of which are formed by a first and a second dielectric (1, 2) which has a surface on its surfaces facing away from the discharge space (4) metallic grid or mesh-shaped first (5) and a second electrode (3) is provided with an alternating current source (6) connected to the first and second electrodes for supplying the discharge, characterized in that at least the first electrodes (5) are provided with a Protective layer (8; 8a; 8b; 8c) provided or embedded in such. High-power radiator according to claim 1, characterized in that only the material from which the electrode (5,3) is made is provided with a protective layer (8), preferably made of wire enamel (Fig.2). High-power radiator according to Claim 1, characterized in that at least the first electrode (5) and at least the surface of the first dielectric (1) are provided with a UV-permeable protective layer (8a) in the region of this electrode (FIG. 3). High-power radiator according to claim 1 or 3, characterized in that the outer surface of the first dielectric (1) and / or the inner surface of the second dielectric (2) is provided with regular depressions in which the electrodes (5,3) are at least partially embedded and the depressions are filled with a UV-permeable mass (8b) which completely covers the electrodes (5,3). High-power radiator according to claim 1 or 3, characterized in that at least the first electrode (5) is embedded in a protective layer (8c) made of a UV-permeable potting compound. High-power radiator according to one of Claims 1 to 5, characterized in that the protective layer is a UV-curing lacquer, adhesive or potting compound which is hardened by the radiator itself.

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