Patent Application
20140028183
This application claims priority to German Patent Application Serial No. 10 2012 213 191.4, which was filed Jul. 26, 2012, and is incorporated herein by reference in its entirety.
Various embodiments relate generally to a high-pressure discharge lamp.
WO 2010/069678 discloses a ceramic electrode, which is designed as a series of layers and is made from LaB6 or CeB6. Such a layered electrode is laboriously produced by means of dry pressing, an injection-molding process or multi-layer technology.
In WO 2011/085839, the basic use of ceramic electrodes for high-pressure lamps is described. For this, the head, or a region of the head, is produced from ceramic material of the boride type. So far there has not been any suitable technical implementation of ceramic electrodes in high-pressure discharge lamps.
Various embodiments provide a high-pressure discharge lamp. The high-pressure discharge lamp may include a discharge vessel; and an electrode, which is secured in one end of the discharge vessel, the electrode having a stem designed as an elongated pin-shaped body, the electrode being part of an electrode system that also comprises a lead-through, with the aid of which the end of the discharge vessel is sealed in a gas-tight manner; wherein at least the stem comprises an electrically conductive ceramic boride of a metal that comprises at least lanthanum, cerium, yttrium or ytterbium, alone or in combination.
In the drawings, like reference characters generally refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the invention are described with reference to the following drawings, in which:
The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced.
The word “exemplary” is used herein to mean “serving as an example, instance, or illustration”. Any embodiment or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or designs.
The word “over” used with regards to a deposited material formed “over” a side or surface, may be used herein to mean that the deposited material may be formed “directly on”, e.g. in direct contact with, the implied side or surface. The word “over” used with regards to a deposited material formed “over” a side or surface, may be used herein to mean that the deposited material may be formed “indirectly on” the implied side or surface with one or more additional layers being arranged between the implied side or surface and the deposited material.
Various embodiments provide a high-pressure discharge lamp which makes it possible to achieve a long service life for such lamps by using a ceramic body, which has a high resistance to corrosive filling and to erosion and in which the ceramic body e.g. has a coefficient of thermal expansion that is adapted well to a ceramic discharge vessel, and consequently improves the sealing.
Various embodiments of the high-pressure discharge lamp have an electrode, which is designed as a pin-shaped ceramic body which includes a boride of a rare earth metal, selected from lanthanum, cerium, yttrium and ytterbium. In various embodiments, the electrode and the lead-through may be designed as an integral combined part.
Various embodiments of the electrode have at least one stem of ceramic, which is designed as a pin. Used as the ceramic material is a boride of lanthanum, cerium, yttrium or ytterbium, alone or as a mixture. Such compounds have the chemical formula MB6, where M is at least one of the rare earth metals mentioned.
The electrode is generally simply a pin of a constant diameter. However, it may also be of a different form, for example flattened. A head may also be mounted in the front region of the electrode that is facing the discharge. In various embodiments, such a head may also be produced on such a ceramic material. In various embodiments, LaB6 may be used for this.
In various embodiments, the pin is made sufficiently long for a front portion to be able to perform the task of the stem and a rear portion to be able at the same time to perform the task of a lead-through.
Such elongated pins combine the advantages pertaining to electrodes and a lead-through as a single component that is ceramic throughout. The two main advantages of such materials are favorable, well-adapted thermal expansion characteristics and the low electron work function of such materials, which can consequently be used simultaneously.
Used e.g. as a novel material for the stem or the combined stem/lead-through part is a ceramic composite on the basis of LaB6. LaB6 has a work function of 2.14 eV and an electrical resistance of 15 μohm-cm. The coefficient of thermal expansion α is 6.2*10−6K−1. It is consequently less than the coefficient of expansion of pure PCA, which is α=8.3*10−6K−1. The most important properties of LaB6 are compared with those of tungsten, see Table 1.
The particular advantage of the aforementioned ceramic materials is the combination of:
1) the favorable thermal expansion, which may make it possible for the electrode system to be embedded in the discharge vessel in a largely stress-free and gas-tight manner, and
2) the low electron work function, with resultant low electrode temperatures.
This may make a much simpler electrode design possible than the solutions conventionally used, in that the typically different materials for the electrode and the lead-through can now be replaced by a one-part component of the same material.
However, the ceramic materials that are used differ considerably in their processability from the materials that are otherwise used.
Thus, in various embodiments, the conventional methods for contacting the electrode/electrode system to the electrical supply lead or the lamp frame cannot be used. Used instead are novel connection techniques, which ensure a suitable electrical, thermal and mechanical contact between the ceramic electrode system and the metallic power supply lead/lamp frame.
Advantages of this are, in various embodiments:
The described technical embodiments of electrode systems on the basis of ceramic components may allow the large-scale production of high-pressure discharge lamps with the advantages of a low electron work function and favorable thermal expansion.
The about 2 eV lower work function of materials such as LaB6 as compared with tungsten leads to an experimentally determined lowering of the temperature at the tip of the electrode of approximately 1300 K as compared with tungsten, for which the typical value is 3100 K.
On account of the lower thermal conductivity and the lower operating temperature, this may lead to much lower thermal losses, which is synonymous with higher efficiency. This in turn may have the consequence that the energy input into the lead-through is reduced.
The lower working temperature or operating temperature and the fact that LaB6 has a much higher coefficient of thermal expansion than tungsten, which is much closer to that of Al2O3, e.g. PCA, gives rise to the possibility of a much shorter overall length of the lamp, because the capillaries can be reduced in their length. A further associated positive effect may result in a reduced volume of dead space.
This in turn may lead to lower color dispersion and a longer service life.
A construction that is almost completely without any capillary dead space is also possible, which for the first time allows an unsaturated filling to be used for the discharge vessel, with all its advantages, such as for example dimmability.
Added to this is that a material such as LaB6 is corrosion-resistant to rare-earth iodides as a constituent of the filling. As a result, the service life is increased further.
Overall, there are therefore advantages as a result of the lower operating temperature, reduced thermal losses, higher efficiency, saving of electrical energy, low color dispersion, greater reliability, high resistance to corrosion.
In various embodiments, a filling that is free from mercury may be used.
Various features of various embodiments in the form of an enumeration are:
1. A high-pressure discharge lamp with a discharge vessel and an electrode, which is secured in one end of the discharge vessel, the electrode having a stem designed as an elongated pin-shaped body, the electrode being part of an electrode system that also comprises a lead-through, with the aid of which the end of the discharge vessel is sealed in a gas-tight manner, wherein at least the stem includes an electrically conductive ceramic boride of a metal that comprises at least lanthanum, cerium, yttrium or ytterbium, alone or in combination.
2. The high-pressure discharge lamp as described unter item 1, wherein the pin-shaped stem is cylindrical or flattened.
3. The high-pressure discharge lamp as described unter item 1, wherein a front portion of the pin-shaped body acts as a stem and a rear portion attached integrally thereto acts as a lead-through.
4. The high-pressure discharge lamp as described unter item 3, wherein the lead-through is sealed off by means of glass solder in the end.
5. The high-pressure discharge lamp as described unter item 1 or 3, wherein the pin-shaped body is connected to an electrically conducting connection part by means of butt welding and/or by way of a connecting sleeve.
6. The high-pressure discharge lamp as described unter item 5, wherein the connection part is a power supply lead, a frame part or a sleeve with a bush.
7. The high-pressure discharge lamp as described unter item 1 or 3, wherein the discharge vessel is produced from ceramic material, e.g. Al2O3 or Y2Al5O12 or AlN.
8. The high-pressure discharge lamp as described unter item 1 or 3, wherein the discharge vessel is produced from PCA.
9. The high-pressure discharge lamp as described unter item 1 or 3, wherein the discharge vessel is produced from quartz glass.
10. The high-pressure discharge lamp as described unter item 9, wherein the discharge vessel is closed by means of a pinch seal, there being embedded in the end of the discharge vessel a connecting sleeve or a connecting coil, which ensures the connection of the body to a connection part.
The pin 20 may in this case be understood as an elongated component with a geometry that is not defined any more specifically; it may in various embodiments be a cylindrical pin or else a flattened pin.
The rear portion of the ceramic electrode is connected to a metallic outer power supply lead 21 or a component of the lamp frame. To ensure the electrical, thermal and mechanical contact, the connection takes place by inserting or else press-fitting the rear portion into a bore 22, as already known in principle from DE 102 56 389 and German utility model DE 20 2004 013 922, or by laser welding. For press-fitting, the rear portion may possibly have a projecting stub with a reduced diameter.
In various embodiments, a laser welding connects the rear portion of the ceramic pin to the metallic power supply lead, the cross sections of the pin and the power supply lead not having to be uniform. The laser welding is performed with preference as butt welding. The reliable connection of the materials of the pin and the power supply lead is based in this case on the melting and penetration of the molten metal of the power supply lead in the layers near the surface of the ceramic of the pin.
If a bore 22 for receiving the ceramic electrode is incorporated in a correspondingly larger cross section of the power supply lead, as represented in
The resultant region of a connection between the pin and the power supply lead may be both positioned outside the ceramic discharge vessel and arranged within a capillary at the end of the discharge vessel of ceramic (as represented in
The embedding and sealing of the electrode system in the capillary of the ceramic discharge vessel takes place by means of glass solder, the glass solder being used in various embodiments level with the ceramic electrode. The region of the embedding may, however, likewise include the connecting point between the ceramic pin and the power supply lead or lamp frame.
Here, too, the largely stress-free and gas-tight embedding and sealing also takes place by a glass solder 19 within the ceramic capillary. Again, the connecting point in the region of the sleeve 25 may also be positioned outside the capillary, and be embedded there in glass solder.
In this embodiment it is not important that the coefficient of thermal expansion of the pin and the discharge vessel, mostly PCA, are made to match each other.
Alternatively, the connection techniques according to
The occurrence of critical thermal stresses between the electrode system and the quartz glass burner is avoided in a known way by use of a molybdenum foil 35. With respect to the connecting point 45 to the electrode, this foil is located behind the latter, and is therefore further away from the discharge volume. Attached to the foil 35 on the outside in a known way is a supply lead 36, which protrudes from the pinch seal 37.
The occurrence of critical thermal stresses between the electrode system and the quartz glass burner is again avoided in a known way by using a molybdenum foil 35. With respect to the connecting point 45, this foil is located behind the latter, and is therefore away from the discharge volume.
The electrode system represented here is well suited both for discharge vessels of Al2O3, specifically PCA, and for those of quartz glass. The electrode in accordance with various embodiments may also be used for discharge vessels of other materials, such as e.g. AlN, AlON or Y2O3. The use of mixtures of LaB6/AlN, LaB6/AlON or LaB6/Y2O3 is recommendable here for the electrode. In various embodiments, the proportion of the conductive LaB6 should in each case lie above the percolation limit.
While the invention has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2012 213 191.4 | Jul 2012 | DE | national |
