HIGH TEMPERATURE THERMOCOUPLE DESIGN AND FABRICATION

• US 20080205483A1
• Filed: 02/26/2007
• Published: 08/28/2008
• Est. Priority Date: 02/26/2007
• Status: Active Grant

• Current Assignee: Battelle Energy Alliance LLC (Battelle Memorial Institute)
• Original Assignee: Battelle Energy Alliance LLC (Battelle Memorial Institute)
• Inventors: Knudson, Darrell L., Wilkins, S. Curt, Condie, Keith G., Rempe, Joy L.
• Granted Patent: US 7,871,198 B2
• Time in Patent Office: Days
• US Class Current: 374/179
• CPC Class Codes: G01K 7/02 using thermoelectric elements, e.g. thermocouples
• CPC Class Codes: H10N 10/01 Manufacture or treatment
• CPC Class Codes: Y10T 29/49085 Thermally variable

Abstract

A method for fabricating a thermocouple capable of long-term operation in high temperature, hostile environments without significant signal degradation or shortened thermocouple lifetime due to heat induced brittleness.

Claims

1. A method of manufacturing a thermocouple, comprising:

(a) providing first and second thermoelement wires of thermoelectrically dissimilar materials, each thermoelement wire have opposing first and second ends;

(b) forming a thermocouple junction between the thermoelement wires by swaging a metallic tube onto the first ends of the thermoelement wires;

(c) providing a first electrical insulating material having first and second longitudinal passageways and a void for receiving a portion of the thermocouple junction, and a second electrical insulating material having a void for receiving a portion of the thermocouple junction;

(d) providing a third electrical insulating material having a different density than the first and second insulating materials;

(e) threading the first thermoelement wire through the first passageway and the second thermoelement wire through the second passageway;

(f) providing a sheath having a longitudinal interior and a diameter sufficient to receive the first and second electrical insulating materials containing the thermoelement wires and thermoelement junction;

(g) loading the sheath with the electrical insulating materials, the third electrical insulating material interfacing with the second electrical insulating material, the thermocouple junction being positioned within the voids of the first and second insulating material;

(h) swaging the sheath so that the first and second electrical insulating materials intimately contact the thermoelement wires and thermocouple junction;

(i) determining a junction between the second electrical insulating material and the third electrical insulating material;

(j) cutting the thermocouple between the thermoelement junction and the interface between the second and third electrical insulating materials to form a sheath end;

(k) capping the sheath end with an end plug to form a thermocouple.

2. The method of claim 1 further comprising after step (b) the step of heating said first, second and third electrical insulating materials at a sufficient temperature and time to remove moisture contained therein.

3. The method of claim 1 further comprising after step (g) the step of heating the thermoelement wires and insulation at a sufficient temperature and time to removed moisture contained therein.

4. The method of claim 3 further comprising after step (k) heating the thermocouple at least 100°

C. above a planned service temperature for at least three hours to stabilize grain structure.

5. The method of claim 1 wherein the first and second electrical insulating materials are comprised of hafnia.

6. The method of claim 1 wherein the third electrical insulating material is comprised of alumina.

7. The method of claim 1 wherein the first thermoelement wire is comprised of molybdenum doped with elements selected from the group consisting of tungsten, potassium, and silicon.

8. The method of claim 7 wherein the doped elements are present in the amounts ranging from between 100 parts per million to 300 parts per million.

9. The method of claim 1 wherein the second thermoelement is comprised of a niobium and zirconium alloy.

10. The method of claim 9 wherein the niobium and zirconium alloy is 99% by weight niobium and 1% by weight zirconium.

11. The method of claim 1 wherein the junction between said second and third insulating materials is determined by an x-ray imaging system.

12. The method of claim 1 wherein the capping of the sheath end is by laser welding a niobium plug onto the sheath end.

13. The method of claim 1 wherein the sheath is comprised of a niobium and zirconium alloy.

14. The method of claim 13 wherein the niobium and zirconium alloy is 99% by weigh niobium and 1% by weigh zirconium.

15. A method of fabricating a thermocouple, comprising the steps of:

(a) providing first and second thermoelement wires of thermoelectrically dissimilar materials, each thermoelement wire having opposing first and second ends, the first ends of each thermoelement wires being swaged together with a metallic tube thereon to form a thermocouple junction;

(b) providing first, second and third insulating materials, the first and second insulating materials having voids therein for receiving the thermocouple junction, the first insulating material further having first and second passageways for receiving the first and second thermoelement wires;

(c) heating the first, second and third insulating materials at a sufficient temperature and time to remove moisture and impurities contained therein;

(d) threading the first thermoelement wire through the first passageway and the second thermoelement wire through the second passageway;

(e) providing a metallic sheath having a longitudinal interior and diameter sufficient to receive the first, second and third insulating materials, thermoelement wires and thermocouple junction;

(f) loading the sheath with the insulating materials, the second and third insulating materials being in contact with each other to form an interface, the thermocouple junction being positioned within the voids of the first and second insulating materials;

(g) swaging the sheath so that the first and second insulating materials intimately contact the thermoelement wires and thermocouple junction;

(h) cutting the thermocouple at a location between the junction and the interface between the second and third insulating material to form a sheath end;

(i) capping the sheath end with an end plug to form a thermocouple.

16. The method of claim 15 further comprising after step (i) heating the capped thermocouple at a sufficient temperature and time to stabilize grain structure.

17. The method of claim 15 wherein the first and second insulating materials are comprised of hafnia.

18. The method of claim 15 wherein the third insulating material is comprised of alumina.

19. The method of claim 15 wherein the first thermoelement wire is comprised of molybdenum doped with elements selected from the group consisting of tungsten, potassium and silicon.

20. The method of claim 15 wherein the doped elements are present in amounts ranging from between 100 to 300 parts per million.

21. The method of claim 15 wherein the second thermoelement is comprised of a niobium and zirconium alloy.

22. The method of claim 21 wherein the niobium and zirconium alloy is 99% by weight niobium and 1% by weight zirconium.

23. The method of claim 15 wherein the location of the junction and said interface between the second and third insulating materials is determined by x-ray imaging.

24. The method of claim 15 wherein the capping of the sheath end is by laser welding a niobium plug onto the sheath end.

25. The method of claim 15 wherein the sheath is comprised of a niobium and zirconium alloy.

26. The method of claim 25 wherein the niobium and zirconium alloy is 99% by weigh niobium and 1% by weigh zirconium.

27. A thermocouple produced by the method of claim 15.