Patent Application
20080067939
The single FIGURE is a diagrammatic, sectional view of a lamp employing an aspect of the invention.
For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims taken in conjunction with the above-described drawing.
Referring now to the FIGURE with greater particularity, there is shown a lamp 10 having an hermetically sealed envelope 12 made of a high-temperature glass, preferably fused quartz, fused silica or a high-silica content glass (>95% by weight SiO2) such as Vycor®. As shown in this particular embodiment, the light source 14 is a tungsten filament 15 situated within the volume 16 of the glass envelope 12. However, the choice of the light source is not limited. For example, the light source may comprise an arc discharge such as is present in metal halide and high-pressure mercury lamps. In such cases, the inner electrical leads may comprise tungsten electrodes which serve as the attachment points for the arc discharge. Depending on the type of lamp, the volume 16 may contain a fill gas, such as a halogen-containing gas as in a tungsten-halogen lamp, small amounts of various metal halide salts, or mercury. Moreover, the light source 14 may be further contained within an inner envelope such as a ceramic or quartz arc tube or the lamp envelope 14 may be enclosed in an outer jacket. Thus, the term “envelope” as used herein is not restricted to comprising the outermost enclosure of a lamp and may instead comprise an inner containment vessel such as an arc tube.
Referring again to the FIGURE, a pair of inner electrical leads, 18, 20, are attached to the light source 14, and a pair of outer electrical leads, 22. 24, are provided for conducting electrical energy from an outside source (not shown) to the light source 14. An intermediate connector 25 electrically joins the inner and outer pairs of electrical leads and is sealed in a seal area 26 of the envelope 12. The combination of an inner electrical lead, an intermediate connector and an outer electrical lead together comprising a feedthrough assembly.
The intermediate connector 25 is resistant to oxidation up 1200° C. and has a thermal expansion coefficient in the range of 0-2 ppm/° C. A preferred material is a carbon/silicon carbide (C/SiC) composite. Materials of this type are available from Hyper-Therm of Huntington Beach, Calif.
Preferably, the composite material comprises a uni-directional carbon fiber mat having silicon carbide infiltrated therein. This material is electrically conductive and extremely resistant to oxidation even at temperatures well in excess of 1200° C. The electrical leads can be brazed or soldered to the intermediate connector and, because its thermal expansion coefficient matches that of the high-temperature glass even better than molybdenum, the seal should be more resistant to cracking caused by thermal expansion mismatches. Further, seals including the C/SiC material exhibit superior resistance to cold, having been emerged in liquid nitrogen without showing any evidence of cracking.
While there have been shown and described what are at present considered to be the preferred embodiments of the invention, it will be apparent to those skilled in the art that various changes and modifications can be made herein without departing from the scope of the invention as defined by the appended claims.
