Ceramic discharge vessel having a sealing composition

1. A ceramic discharge vessel, comprising: a ceramic body, at least one electrode assembly, and at least one seal, the ceramic body enclosing a discharge chamber, the seal containing a sealing composition having a melting point of less than about 1800° C. and consisting of about 20 to about 40 mole percent MgO, about 20 to about 45 mole percent Y 2 O 3 , about 20 to about 60 mole percent Al 2 O 3 and less than about 5 weight percent silica.

2. The ceramic discharge vessel of claim 1 wherein the melting point of the sealing composition is greater than about 1700° C. and less than about 1800° C.

3. The ceramic discharge vessel of claim 1 wherein the sealing composition comprises about 38 mole percent MgO, about 31 mole percent about Y 2 O 3 , and about 31 mole percent Al 2 O 3 and has a melting point of about 1740° C.

4. The ceramic discharge vessel of claim 1 wherein the ceramic body is comprised of polycrystalline alumina and the discharge chamber contains a metal halide fill.

5. The ceramic discharge vessel of claim 4 wherein the sealing composition comprises about 38 mole percent MgO, about 31 mole percent about Y 2 O 3 , and about 31 mole percent Al 2 O 3 and has a melting point at about 1740° C.

6. The ceramic discharge vessel of claim 1 wherein the sealing composition joins at least two ceramic parts of the discharge vessel.

7. The ceramic discharge vessel of claim 1 wherein the discharge vessel has at least one capillary tube extending outwardly from the ceramic body and the at least one seal is between the at least one capillary tube and a portion of the at least one electrode assembly.

8. The ceramic discharge vessel of claim 7 wherein the capillary tube is comprised of polycrystalline alumina and the portion of the electrode assembly is comprised of molybdenum or niobium.

9. The ceramic discharge vessel of claim 8 wherein the sealing composition comprises about 38 mole percent MgO, about 31 mole percent about Y 2 O 3 , and about 31 mole percent Al 2 O 3 and has a melting point at about 1740° C.

10. The ceramic discharge vessel of claim 1 wherein the sealing composition is selected from the group consisting of eutectic compositions A, B, C, and D, wherein:

Composition (mol %)

Eutectic Composition

MgO

Y 2 O 3

Al 2 O 3

A

38

31

31

B

37

42

21

C

27.5

22.5

50

D

21

21

 58.

11. The ceramic discharge vessel of claim 1 wherein the sealing composition has a melting point in a range from 1740° C. to 1790° C.

12. The ceramic discharge vessel of claim 1 wherein the sealing composition joins two polycrystalline alumina parts of the discharge vessel.

13. The ceramic discharge vessel of claim 1 wherein the sealing composition joins a polycrystalline alumina part of the discharge vessel to a sapphire part of the discharge vessel.

14. A sealed ceramic article, comprising a first part comprised of a first ceramic material and a second part comprised of either a second ceramic material or a metal, a sealing composition joining the first and second parts to form the seal, the sealing composition having a melting point of less than about 1800° C. and consisting of about 20 to about 40 mole percent MgO, about 20 to about 45 mole percent Y 2 O 3 , about 20 to about 60 mole percent Al 2 O 3 and less than about 5 weight percent silica.

15. The sealed ceramic article of claim 14 wherein the melting point of the sealing composition is greater than about 1700° C. and less than about 1800° C.

16. The sealed ceramic article of claim 14 wherein the sealing composition comprises about 38 mole percent MgO, about 31 mole percent about Y 2 O 3 , and about 31 mole percent Al 2 O 3 and has a melting point of about 1740° C.

17. The sealed ceramic article of claim 14 wherein the first and second ceramic materials are polycrystalline alumina.

18. The sealed ceramic article of claim 14 wherein the sealing composition has a melting point in a range from 1740° C. to 1790° C.