Patent ID: 6020685
Filing Date: 2000-02-01
Classification: H01J

Abstract:
A ceramic envelope device for a high pressure discharge lamp containing a metal halide fill comprising:a translucent ceramic tube having a first end and a second end, the tube confining a discharge volume and defining a longitudinal axis;a first electrically non-conducting cermet end plug, said first plug closing said first end of the ceramic tube;a second electrically non-conducting cermet end plug, said second plug closing said second end of the ceramic tube;at least said second plug having a multipart structure with at least three parts;a first and second metal feedthrough passing through the first and second plug respectively, each feedthrough having a inner and outer end, respectively, and at least said second feedthrough being a tube made from one of the group of the metals tungsten, molybdenum and rhenium and alloys from at least two of these metals;two electrodes located at the inner end of the first and second feedthrough respectively;the coefficient of thermal expansion of at least one part of the multipart plug being between those of the arc tube and the feedthrough;wherein said multipart plug comprises at least four radially aligned concentric parts with different coefficients of thermal expansion, including a first and a last part, the first part being innermost with respect to the second feedthrough and the last part being outermost with respect to the feedthrough;the difference between the coefficients of thermal expansion for adjacent parts including the arc tube and the related feedthrough being less than 1.0.times.10.sup.-6 /K;the multipart plug is directly sintered both to the arc tube and the feedthrough in that manner that the first part of the multipart plug is directly sintered to the related feedthrough and the last part of the multipart plug is directly sintered to the arc tube.