EP0363832A1 - Radiating device having a high output - Google Patents

Abstract

In a UV radiating device having a high output, the electrodes (6', 6") consist of wires, which are embedded in a glass dielectric (3). The dielectric is arranged spaced between two UV transparent plates (1, 2). The discharge chambers (8, 9) are filled with a fill-gas emitting radiation under discharge conditions. The creeping discharges (10) form on the dielectric surface between two adjacent electrode wires (6', 6") in each case. …<??>A radiating device having a high output that is constructed in this way is distinguished by a simple and economical construction and by high UV yields. …<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, with pairs of electrodes which are connected in pairs to the two poles of a high-voltage source, with at least one dielectric material lying between two electrodes at different potentials that is adjacent to the discharge space.
The invention relates to a state of the art, such as results from EP application 87109674.9 or US application 07/076926.

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 some new wavelengths for basic photochemical experiments are provided. currently for cost reasons for an industrial process 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 - November 20, 1987, a new excimer emitter 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 Existing current filaments of this discharge are excited by electron impact, noble gas atoms, which further react to excited molecular complexes (excimers), which 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.

Presentation of the invention

Starting from the prior art, the invention has for its object to provide a high-performance radiator, in particular for UV or VUV light, which is characterized in particular by higher efficiency, is economical to manufacture and also enables the construction of very large area radiators.

To solve this problem in a high-power radiator of the type mentioned at the outset, it is provided according to the invention that the electrode pairs mentioned, separated by dielectric material, are arranged directly next to one another in such a way that the silent electrical discharge is formed in the discharge space in the region of the dielectric surface.

When the voltage is applied, a large number of sliding discharges form from one electrode through the dielectric essentially along the surface of the dielectric and back into the dielectric to the adjacent electrode. These discharges emit the usable UV light, which then e.g. penetrates through the wall delimiting the discharge space. In contrast to the known configurations, the entire expansion of the discharge channels is used here to generate radiation.

The manufacture of the high-power radiator according to the invention is simplified and less expensive than in the known radiators. You can use materials that are easy to cast so that the electrodes can be cast in. This reduces problems when complying with tolerances (eg thickness of the dielectric or the distances). Also for the limiting glass / quartz material there are no very high demands, since the limiting walls only have to be transparent and are not stressed by the discharge. This leads to a longer lamp life. The gap width and its tolerances are also far less critical. In particular, because of the lower requirements with regard to tolerances, very large area radiators can be realized, which can be made very thin.

Because practically the entire length of the discharge space contributes to emission, the UV yield is very high. There are no transmission losses from an electrode grid or a partially permeable layer.

The high-power radiator according to the invention permits radiator geometries of almost any shape. In addition to surface emitters that emit on one or both flat sides, cylindrical or elliptical emitters can be created. Also, the emitters do not necessarily have to be flat or elongated, but have to be curved or curved in one or more dimensions.

Of course, in analogy to the Swiss patent application No. 152 / 88-7 dated January 15, 1988, the invention allows the applicant to provide the walls delimiting the discharge space with a luminescent layer either on the discharge space facing or on the outer wall in order to convert the UV -Light in visible light. In the first alternative, the wall no longer has to be UV-permeable because it only has to let visible light through.

Dielectrics which are not necessarily transparent to UV light can be used in the arrangement according to the invention, which means that particularly high efficiencies can be expected for special applications. In particular, UV light can be used directly for some applications without having to leave the discharge space. This applies in particular to those applications that can be carried out in the discharge space. Such applications with growing economic importance include, for example, use as a strong UV lamp for pre-ionization purposes of other discharges, for example lasers, and treatment of surfaces with UV exposure, chemical processes such as the preparation of new chemicals or surfaces and coating processes such as plasma CVD (Chemical Vapor Deposition), Photo-CVD, in which a substrate to be treated is brought as close as possible to the UV light source with a suitable filling gas. The particular advantages of such an "inner" arrangement are, among other things, the avoidance of absorption losses through windows and the exploitation of additional effects through the discharge itself.

Brief description of the drawings

• Fig. 1 Ein erstes Ausführungsbeispiel eines Flächen­strahlers mit beidseitiger Abstrahlung im Quer­schnitt;
• Fig. 2 der Flächenstrahler nach Fig.1 im Längsschnitt mit einer schematischen Darstellung der elek­trischen Anspeisung;
• Fig. 3 eine eines erste Abwandlung des Flächenstrahlers nach Fig.1 und 2 mit einseitiger Abstrahlung und Elektroden, die auf ein Substrat aufgebracht und mit einer dielektrischen Schicht überzogen sind;
• Fig. 4 eine zweite Abwandlung des Flächenstrahlers nach Fig.1 und 2 mit inhomogenem Dielektrikum;
• Fig. 5 eine dritte Abwandlung des Flächenstrahlers nach Fig.1 und 2 mit von dielektrische nMaterial ummantelten Einzelelektroden;
• Fig. 6 ein Ausführungsbeispiel der Erfindung in Form eines Zylinderstrahlers im Querschnitt;

In the drawing, embodiments of the invention are shown schematically; in it shows

• Fig. 1 A first embodiment of a panel radiator with radiation on both sides in cross section;
• 2 shows the surface radiator according to FIG. 1 in longitudinal section with a schematic illustration of the electrical feed;
• 3 shows a first modification of the surface radiator according to FIGS. 1 and 2 with one-sided radiation and electrodes which are applied to a substrate and are coated with a dielectric layer;
• 4 shows a second modification of the surface radiator according to FIGS. 1 and 2 with an inhomogeneous dielectric;
• 5 shows a third modification of the surface radiator according to FIGS. 1 and 2 with individual electrodes coated with dielectric material;
• Fig. 6 shows an embodiment of the invention in the form of a cylinder radiator in cross section;

Detailed description of the invention

1 and 2 consists of two spaced UV-transparent plates 1, 2 made of quartz glass, between which a further plate 3 made of dielectric material, e.g. Glass or ceramic or a plastic dielectric is arranged. Spacers 4, 5 distributed over the surface secure the spacing of the plates 1, 2 and 3 and at the same time serve to hold them together. In the plate 3 metal electrodes, 6 ', 6' are embedded at regular intervals and spaced apart. As can be seen in Fig.2, the electrodes 6'6˝ are alternately connected to one and the other pole of an alternating current source 7. The alternating current source 7 basically corresponds to those used for supplying ozone generators. Typically, it supplies 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 kHz - depending on the electrode geometry, pressure in the discharge space and composition of the filling gas.

The discharge spaces 8 and 9 between the plates 1 and 3 or 3 and 2 are filled with a filling gas which emits radiation under discharge conditions, for example 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, 320-360, 390-420 nm selenium 196, 204, 206 nm deuterium 150-250 nm Xenon + fluorine 400 - 550 nm Xenon + chlorine 300-320 nm

In addition, a whole series of other filling gases are possible:
- An inert 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 forming electrical discharge (surface discharge) the electron energy distribution can be optimally adjusted by the thickness of the dielectric plate 3 and its properties, distance between the electrodes 6 ', 6˝, pressure and / or temperature.

When a voltage is applied between two adjacent electrodes 6 ', 6˝, a plurality of discharge channels 10 form from one electrode 6' through the dielectric 3 along the surface of the dielectric 3 and back into the dielectric 3 into the adjacent electrode 6˝. These sliding discharges 10 running along the surface emit the UV light, which then penetrates through the transparent plates 1, 2 in the example. If different filling gases are used in rooms 8 and 9, two different radiations can be generated with one and the same radiator if the electrode arrangement and distribution are selected accordingly. By applying a coating 11, 12 to the two surfaces of the dielectric 3, lower ignition voltages for the discharge can be achieved, so that the costs for the supply can be reduced. The primary coating materials are the oxides of magnesium, ytterbium, lanthanum and cerium (MgO, Yb₂O₃, La₂O₃, CeO₂).

The UV light can also be used directly for some applications without it having to penetrate through the cover plates 1, 2. This applies to those applications that can be carried out in the discharge spaces 8, 9 themselves. Such applications with growing economic importance include, for example, the treatment of surfaces with UV exposure, chemical processes such as the preparation of new chemicals or surface coating such as plasma CVD, photo CVD, that is to say processes in which a treatment is carried out

With a suitable filling gas, the substrate is brought as close as possible to the dielectric surface, i.e. where the radiation is generated.
The particular advantages of such an “interior” arrangement include the avoidance of absorption losses (through the plates 1, 2) and the use of additional effects through the discharge itself, the electrical properties of the substrate to be treated being relatively insignificant.

The production of the dielectric 3 together with the electrodes 6 ', 6' embedded in it is simplified compared to the known high-power radiators and thus less expensive. You can use materials that can be cast relatively easily, so that the electrodes 6 ', 6˝ can be cast in at the same time. This eliminates problems with compliance with tolerances, e.g. the thickness of the dielectric 3 or the distances between the plates 1 and 3 or 3 and 2 is reduced. Also for the material of the UV-permeable plates - if they have to be UV-permeable at all - there are no very high demands, since they are not stressed by the discharge. This in turn leads to an increase in the total life of the lamp.

For an inexpensive production of the electrodes 6, 6˝ embedded in the dielectric 3, techniques can also be used which are used in the production of plasma display cells (cf. "AC Plasma Display" by TNCriscimagna & P.Pleshko in "Display Devices"", JIPamkove (Ed.), Springer-Verlag Berlin, Heidelberg, New York 1980, pp. 92-150).
Instead of metallic wires 6 ′, 6˝ according to FIG. 1, the electrodes according to FIG. 3 are applied as discrete conductor tracks 6a, 6b to a substrate 13 made of glass, quartz or ceramic using thin-film or thick-film techniques. Here vaporization and sputtering processes are used for metallization on the one hand, and conductive pastes on the other. Fine conductor tracks can be produced by photo-lithographic processes, wider ones (> 25 micrometers) can be created by metal deposition through a mask. The conductor tracks (electrodes) thus applied are then covered by a dielectric layer 14. For example, layers of lead oxide glass can be applied as a spray or paste and then heated, forming a continuous layer of glass. Layers of borosilicate glass can be made using evaporation techniques. It is also possible to deposit other dielectric layers using methods that are common in semiconductor technology, for example by means of plasma CVD or photo CVD.

Without departing from the scope of the invention, a multitude of modifications of the UV high-power lamp described above are possible, which will be dealt with below.

Instead of two discharge spaces 8, 9, only one discharge space can be provided. Appropriate insulation, e.g. sulfur hexafluoride or water, in which a space or another geometry of the dielectric and / or the electrodes, e.g. one according to FIG. 3, to ensure that the sliding discharges only form in the other room.

Instead of round electrodes 6 ′, 6˝ according to FIG. 1, electrodes with an almost constant cross section can also be used. The electrodes also do not have to run in a straight line, but can also be arranged, for example, in a meandering shape or in a zigzag pattern next to one another.

To improve the heat dissipation from the dielectric, it is possible to design the electrodes 6 ′, 6˝ as hollow electrodes, or in the dielectric 3 in FIG. 1 or in the substrate 13 in FIG. 3, additional channels running in the longitudinal direction of the electrode (item 15 in FIG. 3) to provide through which channels a liquid or gaseous coolant is passed.

In addition to individual electrodes embedded in a flat dielectric 3 or 14, it is also possible, according to FIGS. 4 and 5, to use individual wires 16 ′, 16˝, each with a dielectric sheath 17, which are either close to close (FIG. 5) , loosely spaced apart or spaced from one another by intermediate layers 18 or spacers, are arranged between the two plates 1 and 2.

Instead of surface emitters according to FIGS. 1 to 5, cylindrical emitters are also possible, as is illustrated in FIG. 6. There, a tube 21 made of dielectric material is arranged coaxially between two quartz tubes 19, 20. Spacers, not shown, secure the mutual position of the three tubes. Analogously to FIG. 1, metal electrodes 22 ′, 22˝ are embedded in the dielectric tube 21, which are alternately connected to one and the other pole of an AC power source (not shown) analogously to FIG.

In the example, the cylinder emitter according to FIG. 6 emits both inwards (into the interior of the tube 20) and outwards. If different filling gases are used in rooms 8 and 9, two different radiations can be generated with the same radiator if the electrode arrangement and distribution are selected accordingly. Of course, this also applies to a radiator according to Fig. 4.

As already described in connection with FIG. 1, the desired reactions can also take place in the discharge space (s) 8 or 9 itself in the case of cylindrical radiators according to FIG. 6.

The above description of exemplary embodiments of the invention concentrated on the generation of UV or VUV radiation. By coating the plates 1, 2 or the tubes 19, 20 with a luminescent layer 23, 24 (FIG. 1), visible light of high power can also be generated based on the technology known for luminescent tubes for lighting purposes. Such layers are known and can also be applied to the inner surfaces of the plates 1, 2 or the tubes 19, 20 adjacent to the discharge space 8 or 9. In the latter case, these plates or tubes no longer need to be UV-transparent but only transparent to visible light.

Claims (10)

1. high-power radiator, in particular for ultraviolet light, with a filling gas (8, 9), which is filled with discharge gas and emits radiation emitting under discharge conditions, with pairs of electrodes which are connected in pairs to the two poles of a high-voltage source (7), wherein at least one dielectric material lies between two electrodes lying at different potential and adjoins the discharge space, characterized in that said electrode pairs (6 ′, 6˝; 6a, 6b; 16 ′, 16˝; 22 ′, 22˝) spatially separated from said walls (1, 2) and separated from one another by dielectric material (3; 14; 21), such that the electrical discharge in the discharge space (8, 9) essentially only develops in the region of the dielectric surface. 2. High power radiator according to claim 1, characterized in that the electrodes (6 ', 6˝; 6a, 6b; 16', 16˝; 22 ', 22˝) are embedded in the dielectric material (3; 14; 21) and Adjacent electrodes (6 ', 6˝; 6a, 6b; 16', 16˝; 22 ', 22˝) are each connected to different poles of the high voltage source (7). 3. High-power radiator according to claim 2, characterized in that all electrodes (6 ', 6˝; 22', 22˝) are embedded in a common carrier made of dielectric material. 4. High-power radiator according to claim 2, characterized in that the electrodes (16 ', 16˝) are each individually surrounded by a dielectric sheath (17). 5. High-power radiator according to claim 1, characterized in that the electrodes (6a, 6b) are arranged on a substrate (13) made of insulating material and are covered with a dielectric layer (14). 6. High-power radiator according to one of claims 1 to 5, characterized in that cooling channels (15) extending in the longitudinal direction of the electrodes are provided in the electrodes or in the material in which they are embedded or arranged thereon. 7. High-power radiator according to one of claims 1 to 6, characterized in that on the discharge space (8,9) facing surface of the dielectric an additional layer (11,12) to reduce the ignition voltage of the electrical discharge, preferably a layer of magnesium , Ytterbium, lanthanum or cerium oxide is provided. 8. High-power radiator according to one of claims 1 to 7, characterized in that a filling gas with at least two noble gases and at least one non-noble gas is provided for generating radiation with several different wavelengths in a discharge space (8; 9). 9. High-power radiator according to one of claims 1 to 8, characterized in that filling gases of different compositions are provided in the two discharge spaces (8, 9). 10. High-power radiator according to one of claims 1 to 9, characterized in that the plates (1, 2) or tubes (19, 20) delimiting the discharge space (8, 9) are provided with a luminescent layer (24, 25).

Images