US 5,552,670 A · Method of making a vacuum-tight seal between a ceramic and a metal part, sealed structure, and discharge lamp having the seal

Abstract

A vacuum-tight seal, particularly for an arc tube or discharge vessel for a metal halide or sodium high-pressure discharge lamp, is made by forming the arc tube of transparent ceramic, typically Al.sub.2 O.sub.3, having two open ends, into which connecting plugs (3), with central openings, are sealed. Open metal tubes (4) fitting into the openings of the plugs (3) are then vacuum-tightly sintered therein. An electrode system (5, 10, 10'), forming a subassembly with a current supply lead or lead-through (6, 11, 14, 15, 20, 24) is provided, having an outer diameter fitting into the metal tube. After mounting one of the electrode systems and lead-through into the metal tube (4), and welding the lead-through to the metal tube, the vessel can be evacuated through the still open tube (4) at the other end, supplied with suitable fill substances and an ignition gas, such as argon or xenon, and the second electrode system then introduced, and welded, for example by a laser, to the outer end of the other metal tube (4). The arrangement permits use of molybdenum tubes, molybdenum lead-throughs, in Al.sub.2 O.sub.3 ceramic, in spite of different thermal coefficients of expansion. Preferably, the metal tube extends beyond the end face of the vessel and/or sealing plug (3), to permit free access during the welding step and reduce heat transfer into the interior of the arc tube or discharge vessel (1).

Claims22

Dependent claims

A method of making a vacuum-tight seal between a ceramic arc discharge vessel element, the inside of which is to retain an arc discharge and to be isolated from its ambient environment, said vessel having an end portion (2) formed with an end opening,

a sealing plug (3) fitted in said end opening of the ceramic element (1) and formed with a tubular opening therethrough, and
a metallic element (6) passing through the tubular opening,
wherein the thermal coefficient of expansion of the ceramic material of the sealing plug (3) is between about 6.5.times.10.sup.-6 K.sup.-1 and 9.times.10.sup.-6 K.sup.-1,
wherein the shape of the cross section of the tubular opening of the plug (3) is similar to the shape of the cross section of the metallic element, and
wherein the thermal coefficient of expansion of the metallic element (6) is less than that of the plug (3),
said method comprising, in accordance with the invention, the steps of
(a) vacuum-tightly directly sintering an open metal tube (4), having a cross-section similar to the shape of said tubular opening in the plug (3) and a thermal coefficient of expansion less than that of the ceramic material of said plug (3), into the tubular opening of the plug;
(b) introducing the metallic element (6) into said metal tube (4), said metallic element (6) fitting into said metal tube (4) with a small clearance gap to permit said introducing step;
and
(c) vacuum-tightly connecting together said metal tube (4) and the metallic element (6) and closing said clearance gap between said metal tube (4) and said metallic element (6) to form a vacuum-tight connection.

7 more elements

Dependencies are inferred from the claim text.

Method of making a vacuum-tight seal between a ceramic and a metal part, sealed structure, and discharge lamp having the seal

Life of this patent

Method of making a vacuum-tight seal between a ceramic and a metal part, sealed structure, and discharge lamp having the seal

Life of this patent

Abstract

Claims22