Composite body for gas discharge lamp

Claim 1

A composite body formed from two or more parts, at least one of which consists of an oxidic material, which which oxidic material is bonded to one or more parts of e metallic material or a mixture thereof with a metal oxide (cermet), the oxidic material being chosen from densely sintered aluminum oxide (dga), rare earth perowskites of the types ABO 3 wherein A represents La, Ce, Pr, Nd, or a mixture thereof and B represents: Al, Sc, Lu or a mixture thereof, garnets of the type A 3 Al 5 O 12 , wherein A is Mg, Li or Y, or sapphire, and the metallic part being chosen from tantalum, niobium, tungsten, molybdenum, alloys having one of these metals as the main component and alloys having iron, nickel or cobalt as the main component, molybdenum-silicon alloys, titanium boride and titanium nitride, which parts are bonded together in a gas and vacuum-tight manner with a bonding material, the bonding material containing aluminum oxide and at least one oxide of a rare earth metal, characterized in that the bonding material consists of a finely dispersed polycrystalline product comprising at least three oxidic components and whose composition is within the following limits in mole % Al 2 O 3 --5-70 at least one oxide chosen from Sc 2 O 3 and Ti 2 O x , wherein 2<x<4--2-70 at least one oxide chosen from Y 2 O 3 , Gd 2 O 3 , Tb 2 O 3 , Dy 2 O 3 , Ho 2 O 3 , Er 2 O 3 , Eu 2 O 3 , Pr 2 O 3 , Ce 2 O 3 , Sm 2 O 3 , Tm 2 O 3 , Yb 2 O 3 , Lu 2 O 3 , La 2 O 3 and Nd 2 O 3 --7-80 and one or more oxides chosen from ZrO 2 , B 2 O 3 , SiO 2 , P 2 O 5 , MgO, SrO, BaO and CaO--0-20.