Importance

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Abstract

To close off tubular ends (6a, 6b) of a metal-halide discharge vessel, a plug (11) having at least four, and preferably six or more, axially arranged layers or strata (11a-11d; 21a-21f) of a cermet, in which the metal content of the cermet of the respective layers or strata increases from the layer or stratum closest to the discharge space of the vessel to the outside. The innermost layer or stratum is directly sintered to the ceramic discharge vessel, typically of aluminum oxide, whereas the outermost layer or stratum has a metal content of such an extent that it can be welded, and is welded, to a metallic or cermet lead-through or feed-through (9, 20, 30, 35) leading through a central opening in the respective layers or strata of the plug. The outermost layer of the plug, preferably, has at least 50%, by volume, of metal, preferably of the same material as that of the lead-through in the cermet, and may even be made entirely of metal, to ensure a tight, easily made weld connection. The weld can be made, for example, by laser welding.

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First Claim