Patent Application
20070001612
The invention relates generally to the field of lighting systems and, more particularly, to high-intensity discharge lamps.
High-intensity discharge lamps generally include an arc tube, end plugs sealed against and into opposite ends of the arc tube, lead wires extending through the opposite end plugs, arc electrode tips coupled to the respective lead wires inside the arc tube, and one or more seal materials between the various components. These lamp components are typically made of different materials to enable the lamps to withstand certain operational conditions, such as high temperature (e.g., 900° C. to 1200° C.), high-pressure (e.g., 15 psi to 6000 psi), and corrosive dosing materials (e.g., halides) inside the lamps. Unfortunately, these different materials have different coefficients of thermal expansion (CTE), which can lead to thermal stress and cracks during operation of the lamp. For example, the joint between a lead wire and the end plugs and/or the arc tube can be susceptible to thermal stress and cracks due to different CTEs of the lead wire, the end plugs and/or the arc tubes, and the seal material.
Accordingly, a need exists for a conductive and corrosion resistant lead system having a relatively close CTE match with the arc tube and/or end plugs.
In certain embodiment, the present technique provides a lamp having a ceramic arc envelope, an end structure coupled to the ceramic arc envelope and extending across an opening in the ceramic arc envelope, where the end structure includes a passageway communicative with an interior chamber of the ceramic arc envelope. The lamp further includes a molybdenum-rhenium electrode lead extending through and sealed with the passageway, where the molybdenum-rhenium electrode lead includes a molybdenum-rhenium alloy. Furthermore, the lamp includes an arc electrode tip coupled to the electrode lead inside the interior chamber.
In another embodiment, the present technique provides a system having a lighting device. The lighting device includes a ceramic arc envelope having an interior, a dosing material disposed within the ceramic arc envelope, where the dosing material includes a corrosive material. The lighting device further includes an end structure coupled to the ceramic arc envelope and extending across an open end of the ceramic arc envelope, where the end structure includes a hollow leg communicative with the interior, an electrode lead extending at least partially through the hollow leg, where the electrode lead includes a molybdenum-rhenium alloy, and an arc electrode tip coupled to the coil assembly.
In yet another embodiment, the present technique provides a method of making a lamp. The method includes coupling an end structure to the ceramic arc envelope and extending across an open end of a ceramic arc envelope, disposing a molybdenum-rhenium electrode lead in a passageway that extends through the end structure, wherein the molybdenum-rhenium electrode lead comprises a molybdenum-rhenium alloy. The method further comprises sealing the molybdenum-rhenium electrode lead to the passageway.
In further embodiment, the present technique provides a method of operating a lamp. The method includes reducing halide attack and thermo-mechanical stress via a molybdenum-rhenium electrode lead coupled to an electrode tip within a ceramic arc envelope, wherein the molybdenum-rhenium electrode lead comprises a molybdenum-rhenium alloy.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
Embodiments of the present technique provide lamps employing molybdenum-rhenium electrode leads, which improve performance and mechanical stability of the lamps. Advantageously, the molybdenum-rhenium electrode leads provide reduced thermo-mechanical stress in the ceramic arc envelope at least partly due to an improved match between the coefficients of thermal expansion of the molybdenum-rhenium electrode leads and the ceramic arc envelope. Also, the molybdenum-rhenium electrode leads provide reduced halide attack due to their general chemical resistance towards the dosing materials (e.g., metal halides) employed in the ceramic arc envelope. Moreover, the lamps of the present technique facilitate the sealing process by employing shorter seal glass lengths to bond the electrode leads to the end structures. These features introduced above are described in detail below with reference to figures of several exemplary embodiments of the present technique. However, various combinations and variations of the disclosed features are also within the scope of the present technique.
Further, in the illustrated embodiment, the end structures 16 and 18 are coupled to, and extend across, the openings in opposite ends 20 and 22 of the ceramic arc envelope 14. In other words, the end structures 16 and 18 generally cover and close the opposite ends 20 and 22 of the ceramic arc envelope 14. Further, as illustrated, the end structures 16 and 18 may be sealed to the ceramic arc envelope 14 by employing seal materials or sealants 21 and 23. In some embodiments, these seal materials may include a sealing glass, such as calcium aluminate, dysprosia-alumina-silica, magnesia-alumina-silica, and yttria-calcia-alumina. Other potential non-glass seal materials include niobium-based brazes. As will be appreciated, the seal materials 21 and 23 used for the foregoing bonds have characteristics at least partially based on the type of materials used for the various lamp components, e.g., the arc envelope 14 and end structures 16 and 18. For example, some embodiments of the lamp 10 are formed from a sapphire tubular arc envelope 14 bonded with polycrystalline alumina (PCA) end structures 16 and 18. By further example, some embodiments of the lamp 10 are formed from a YAG tubular arc envelope 14 bonded with cermet end structures 16 and 18, which have a similar coefficient of thermal expansion (CTE) as alumina (PCA). The seal materials 21 and 23 generally have a CTE to control stresses at each interface between the arc envelope 14 and the end structures 16 and 18, e.g., each PCA/sapphire seal interface. For example, the seal materials 21 and 23 may include a niobium braze or a seal glass that minimizes tensile stresses developed upon cooling, e.g., a seal glass with a CTE value that is the average value of PCA and the a-axis or radial value of edge-defined-grown sapphire. In certain embodiments, localized heating is applied to the seal materials 21 and 23 to control the local microstructural development of the seal material, e.g., the seal glass.
In other embodiments, the end structures 16 and 18 may be diffusion bonded to opposite ends 20 and 22 of the arc envelope 14 via material diffusion without using any seal material. For example, localized heating (e.g., a laser) may be applied to the interface between the end structures 16 and 18 and the opposite ends 20 and 22 to bond the materials together, thereby forming a hermetical seal. Further, in certain embodiments where the end structures 16 and 18 include ceramic parts, the end structures 16 and 18 and the arc envelope 14 may be co-sintered together.
Further, in certain embodiments, the end structures 16 and 18 include flat structures 24 and 26 having an opening into protruding passageways, such as hollow legs or passageways 28 and 30 communicative with an interior chamber 32 of the ceramic arc envelope 14. Further, in certain embodiments, the dosing material is disposed within the interior chamber 32. In the illustrated embodiment, the hollow legs 28 and 30 may also be used as dosing tubes to introduce dosing material in the interior chamber 32 of the ceramic arc envelope 14. In certain embodiments, the dosing material is mercury-free, in other words, the dosing material includes one or more materials without any mercury. In certain embodiments, the dosing material includes a rare gas, or a metal, or a metal halide, or combinations thereof. In these embodiments, the rare gas may include argon, or xenon, or krypton, or combinations thereof. Further, in these embodiments, the metal may include mercury, or zirconium, or titanium, or hafnium, or gallium, or aluminum, or antimony, or indium, or germanium, or tin, or nickel, or magnesium, or iron, or cobalt, or chromium, or indium, or copper, or calcium, or lithium, or cesium, or potassium, or yttrium, or tantalum, or thallium, or lanthanum, or cerium, or praseodymium, or neodymium, or samarium, or europium, or yttrium, or gadolinium, or terbium, or dysprosium, or holmium, or erbium, or thulium, or lutetium, or scandium, or ytterbium, or combinations thereof. In some embodiments, the dosing material includes rare gas and mercury. In other embodiments, the dosing material includes halide, such as bromide, or a rare earth metal halide. In these embodiments, the dosing material includes a halide, or a metal halide, or mercury, or sodium, or sodium iodide, or thallium iodide, or dysprosium iodide, or holmium iodide, or thulium iodide, or a noble gas, or argon, or krypton, or xenon, or combinations thereof. In some embodiments, the dosing material is corrosive. Accordingly, in these embodiments, it is desirable to have an end structure made of a material, which is resistant to the corrosive dosing material. In some of these embodiments, the end structures 16 and 18 are formed from a variety of ceramics and other suitable materials, such as zirconia stabilized cermet, alumina-tungsten, or other conductive or non-conductive materials depending on the application.
In certain embodiments, the arc envelope 14 may include a variety of different geometrically shaped structures, such as a hollow cylinder, or a hollow oval shape, or a hollow sphere, or a bulb shape, or a rectangular shaped tube, or another suitable hollow transparent body. Moreover, as described in detail below, the end structures 16 and 18 may have a variety of geometries, such as a plug-shaped geometry that at least partially extends into the ceramic arc envelope 14 or a cap-shaped geometry that at least partially overwraps around the edges of the opposite ends 20 and 22 of the arc envelope 14. In other embodiments, the end structures 16 and 18 may have a substantially flat mating surface, which is butt-sealed against the opposite ends 20 and 22 without extending into an interior or wrapping around an exterior of the arc envelope assembly 12 (e.g., arc tube).
Further, the illustrated arc envelope assembly 12 includes molybdenum-rhenium electrode leads 34 and 36 extending through and sealed with the passageways 24 and 26 by using seal glasses 38 and 40. During operation, the electrode leads facilitate power supply from a power source to the electrode tips 42 and 44 to create an arc between the electrode tips 42 and 44. As will be appreciated, it is desirable to have a thermal match between the seal glass 38 and 40 and the materials employed in the hollow legs 28 and 30 and the electrode leads 34 and 36. In some embodiments, the seal glasses 38 and 40 may include materials, such as calcium-aluminate, dysprosia-alumina-silica, magnesia-alumina-silica, and yttria-calcia-alumina. Advantageously, the lengths 39 and 41 of the seal materials 38 and 40, as illustrated in
Further, in certain embodiments, the molybdenum-rhenium alloy employed in the electrode leads 34 and 36 includes about 35 weight percent to about 55 weight percent of rhenium. In some embodiments, the molybdenum-rhenium alloy includes about 40 weight percent to about 48 weight percent of rhenium. As will be appreciated, because of the operational limitations caused by high temperature and high-pressure operations of these lamps, various parts of these lamps are made of different types of materials. In view of the potential for thermal stresses and cracks resulting from substantially mismatched (coefficient of thermal expansions) CTEs, it is desirable to provide the electrode leads 34 and 36 and the arc envelope 14 with comparable CTEs to reduce the likelihood of thermal stresses and cracks. Accordingly, in some of these embodiments, the molybdenum-rhenium alloy has a CTE varying in a range from about 5.5×10−6/K to about 7×10−6/K. In these embodiments, the ceramic arc envelope 14 has a CTE varying in a range from about 7.5×10−6/K to about 9×10−6/K. In an exemplary embodiment, the molybdenum-rhenium alloy has a CTE in a range from about 6×10−6/K to about 7×10−6/K. Moreover, the molybdenum-rhenium alloy employed in the electrode leads 34 and 36 is generally resistant to the corrosive dosing material (e.g., metal halides). Further, in these embodiments, the electrode leads 34 and 36 have a ductility in a range from about 0.1 percent to about 3.0 percent. As will be appreciated, a high value of ductility in the lead system reduces the likelihood of breakage or cracking, e.g., during bending, of the electrode leads 34 and 36. Furthermore, it is desirable to have a substantially close CTE match between the seal materials 34 and 36 and both the electrode leads 34 and 36 and the ceramic arc envelope 14 to minimize the thermal stresses that may be generated during sealing of the lamp and subsequent operation.
Furthermore, the electrode tips 42 and 44 may include overwraps, such as overwraps 46 and 48. As will be appreciated, these overwraps 46 and 48 sometimes act as heat sinks and absorb the heat from the electrode tips 42 and 44 and dissipate the heat into the surroundings. In some embodiments, the electrode tips 42 and 44 and/or the overwraps 46 and 48 may include tungsten, or tungsten alloys, or rhenium, or rhenium alloys, or tantalum, or tantalum alloys, or combinations thereof.
In an alternative embodiment shown in
Further, in some embodiments, the mandrels 62 and 66 are formed from a first molybdenum-rhenium alloy and the coils overwraps 64 and 68 are formed from a second molybdenum rhenium alloy, which may be same or different than the first molybdenum rhenium alloy of the mandrel. Accordingly, in some of these embodiments, the molybdenum-rhenium alloy includes about 35 weight percent to about 55 weight percent of rhenium. Further, in these embodiments, the overwraps 64 and 68 may be made of molybdenum, or a molybdenum alloy, or a second molybdenum-rhenium alloy, or tungsten, or combinations thereof. In some embodiments, the mandrel and the overwrap may be made of substantially similar molybdenum-rhenium alloys. As will be appreciated, the overwraps 64 and 68 facilitate distribution of stress experienced by the mandrels 62 and 66 at points where the seal glasses 58 and 60 are in contact with the electrode leads 54 and 56, thereby substantially reducing the likelihood of any cracks or structural defects in the mandrel caused by the stress. Further, the seal glasses 58 and 60 may have lengths 59 and 61, which may vary depending on the composition of the mandrel or coil overwrap. Further, as illustrated, the ends of the two electrode leads 54 and 56 disposed inside the interior chamber 32 are coupled to the electrode tips 70 and 72. As described above with reference to
Referring to
In certain embodiments, the shanks 86 and 94 and the coil assemblies 88 and 96 may include a molybdenum-rhenium alloy. In these embodiments, the molybdenum-rhenium alloy includes about 35 weight percent to about 55 weight percent of rhenium. In alternate embodiments, the coil overwraps 92 and 100 may be made of molybdenum, or a molybdenum alloy, or a second molybdenum-rhenium alloy, or tungsten, or combinations thereof.
Furthermore, the lamp 78 includes electrode tips 99 and 101 coupled to the electrode leads 82 and 84. In the illustrated embodiment, the electrode tips 99 and 101 may include overwraps, such as overwraps 103 and 105. As will be appreciated, these overwraps 103 and 105 sometimes act as heat sinks to absorb the heat from the electrode tip and dissipate the heat into the surroundings. In some embodiments, the electrode tips 99 and 101 and/or the overwraps 103 and 105 may include tungsten, or tungsten alloys, or rhenium, or rhenium alloys, or tantalum, or tantalum alloys, or combinations thereof.
Further, in the presently contemplated embodiment, the seal glasses 102 and 104 join the electrode leads 82 and 84 to the hollow legs 28 and 30. Although in the illustrated embodiment, the seal glasses 102 and 104 are located on the shanks 86 and 94, as will be appreciated, alternatively, the seal glasses 102 and 104 may be located on the coil assemblies 88 and 96. As will be appreciated, in embodiments where the seal glasses 102 and 104 are located on the coil assemblies 88 and 96, stress otherwise experienced by the mandrels 90 and 98 may be re-distributed due to the presence of coil overwrap on the mandrel, thereby substantially reducing the likelihood of any cracks or structural defects in the mandrel caused by the stress. Further, the seal glasses 102 and 104 may have lengths 106 and 108, which may vary depending on the composition of the mandrel, coil overwrap, or shank.
Further,
In another alternative embodiment illustrated in
In another alternate embodiment,
Further, the lamp 154 includes a plug member 178 exploded from a dosing passageway 180 in the end structure 166 in accordance with embodiments of the present technique. As will be appreciated, the lamp 154 is filled with a dosing material through the dosing passageway 180. As described above with reference to
As illustrated, the end structures 164 and 166 are hermetically sealed to the ceramic arc envelope 158 by seal materials 182 and 184. As mentioned above, the seal materials 182 and 184 used for the foregoing bonds have characteristics at least partially based on the type of materials used for the various lamp components, e.g., the arc envelope 158 and end structures 164 and 166. In an alternative embodiment, the end structures 164 and 166 may be butt-sealed to the ceramic arc envelope 158 with or without a seal material.
Although the illustrated embodiment of
In the illustrated embodiment of
Furthermore, the dosing material 190 may be injected into the arc envelope 14 in the form of a gas, a liquid, or a solid, such as a dosing pill. After the desired dosing material 190 has been injected into the arc envelope 14, the present technique proceeds to close the passageway 28, as illustrated in
Turning now to
In certain embodiments, the reflective lamp assembly 204 may be incorporated or adapted to a variety of applications, such as transportation systems, video systems, general purpose lighting applications (e.g., outdoor lighting systems), and so forth. For example,
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
