Composite body useful in gas discharge lamp

Claim 1

A composite body comprising two parts formed of a material selected from the group consisting of (1) densely sintered aluminum oxide, (2) sapphire, (3) one of the metals tantalum, niobium, tungsten, molybdenum, (4) an alloy having as the main component a metal selected from the group consisting of tantalum, niobium, tungsten, iron, nickel and cobalt and (5) a material consisting of a mixture of a metal oxide and a metal, said parts being joined together in gas and vacuum-tight relationship by means of sealing material which results in a joint which is resistant to the action of iodide, bromide and chloride vapours and liquid at temperatures up to approximately 1350° C, said sealing material including aluminum oxide and an oxide of a rare earth metal, wherein said joint comprises at least two of the oxides SiO 2 , Al 2 O 3 and B 2 O 3 and at least one of the trivalent oxides La 2 O 3 and Y 2 O 3 in quantities which in mole % have at the utmost the following value: SiO 2 66.6, La 2 O 3 50, B 2 O 3 50, Y 2 O 3 50 and Al 2 O 3 70, the sealing material for obtaining the joint being applied at a temperature of not more than 1700° C and the material of the joint obtained therewith being located in a composition range within a tetrahedron formed by the components Al 2 O 3 -La 2 O 3 -SiO 2 -B 2 O 3 , whose limits in the side planes of the tetrahedron are shown in the accompanying FIGS. 1, area a, 2, area a and 3, area a and which are further defined by the cross-sections in FIG. 8, area a, FIGS. 9, area a and FIG. 10, area a, or in a composition range located within a tetrahedron formed by the components Al 2 O 3 -La 2 O 3 -SiO 2 -Y 2 O 3 , whose limits in the side planes of the tetrahedron are shown in the FIGS. 1, area a and 4, area a, 6 area a and 7, area a.