Fuel cell interconnect heat treatment method

1. A method of fabricating an interconnect for a fuel cell stack, comprising:

placing a compressed metal powder interconnect on a porous support;

sintering the compressed metal powder interconnect in the presence of a non-oxidizing gas;

placing the sintered interconnect on a dense, non-porous support; and

oxidizing the sintered interconnect in an environment that is substantially nitrogen-free to fill pores throughout the thickness of the sintered interconnect prior to using the oxidized interconnect to separate fuel and oxidant gas flows in a solid oxide fuel cell stack.

2. The method of claim 1 , wherein the interconnect comprises chromium and iron having an iron content of greater than 3% by weight.

3. The method of claim 1 , wherein the porous support comprises at least one of a porous ceramic mesh or grid.

4. The method of claim 1 , wherein the non-oxidizing gas comprises at least one of hydrogen and forming gas.

5. A method of fabricating an interconnect for a fuel cell stack, comprising:

placing a compressed metal powder interconnect on a porous support;

sintering the compressed metal powder interconnect in the presence of a non-oxidizing gas, wherein sintering the compressed metal powder interconnect comprises at least one of partially sintering and fully sintering the compressed metal powder interconnect;

providing the partially sintered or fully sintered interconnect on a porous support in flowing air; and

oxidizing the sintered interconnect such that the flowing air permeates into the sintered interconnect through the porous support to purge out nitrogen and form oxides to fill pores throughout the thickness of the sintered interconnect prior to using the sintered interconnect to separate fuel and oxidant gas flows in a solid oxide fuel cell stack.

6. The method of claim 1 , wherein sintering the compressed metal powder interconnect comprises at least one of partially sintering and fully sintering the compressed metal powder interconnect, and oxidizing the sintered interconnect further comprises:

oxidizing the sintered interconnect in a gas comprising pure oxygen and that is substantially nitrogen-free.

7. The method of claim 1 , wherein sintering the interconnect comprises at least one of partially sintering and fully sintering the compressed metal powder interconnect, and oxidizing the sintered interconnect further comprises:

oxidizing the sintered interconnect in a gas comprising an oxygen/inert gas mixture that is substantially nitrogen-free.

8. The method of claim 1 , wherein the interconnect comprises chromium and iron having an iron content of greater than 7% by weight, and wherein sintering the compressed metal powder interconnect comprises:

partially-sintering the compressed metal powder interconnect at an elevated temperature of at least about 1100° C.; and

stopping the sintering before the compressed metal powder interconnect is fully sintered and while the compressed metal powder interconnect has a coefficient of thermal expansion that is within 5% of the coefficient of thermal expansion (CTE) of an electrolyte material for a solid oxide fuel cell.

9. The method of claim 1 , further comprising:

pressing a metal powder in a single pressing step to near net shape or to net shape to form the compressed metal powder interconnect.

10. The method of claim 1 , wherein the compressed metal powder interconnect is sintered at a temperature between approximately 1100° C. and 1520° C.

11. The method of claim 10 , wherein the compressed metal powder interconnect is sintered at a temperature between approximately 1250° C. and 1350° C.

12. The method of claim 1 , further comprising:

placing a metal powder containing chromium in a vacuum at an elevated temperature of at least about 1200° C. for a period sufficient to remove gas impurities; and

pressing the metal powder to provide the compressed metal powder interconnect.

13. The method of claim 12 , wherein the powder is placed in the vacuum at a temperature between about 1200° C. and 1600° C. for a period of between about 2 and 3 days.

14. The method of claim 13 , wherein the powder is placed in the vacuum atmosphere at a temperature of about 1400° C. for a period of about 2.5 days.

15. A method of fabricating an interconnect for a fuel cell stack, comprising:

removing alumina from a chromium metal powder;

adding aluminum to the chromium metal powder;

pressing the chromium metal powder with the aluminum powder to provide a compressed metal powder interconnect;

placing the compressed metal powder interconnect on a porous support;

sintering the compressed metal powder interconnect in the presence of a non-oxidizing gas; and

following the sintering, oxidizing the sintered interconnect to convert at least a portion of the aluminum to alumina.

16. The method of claim 15 , wherein the adding aluminum comprises adding approximately 200-500 ppm of aluminum.

17. The method of claim 15 , wherein the oxidizing further comprises:

oxidizing the sintered interconnect in the presence of air on the porous support.

18. The method of claim 15 , wherein the oxidizing further comprises:

placing the sintered interconnect on a dense, non-porous support; and

oxidizing the sintered interconnect in the presence of a gas comprising pure oxygen that is substantially nitrogen-free.

19. The method of claim 15 , wherein the oxidizing further comprises:

placing then sintered interconnect on a dense, non-porous support; and

oxidizing the sintered interconnect in the presence of a gas comprising an oxygen/inert gas mixture that is substantially nitrogen-free.

20. The method of claim 1 , further comprising incorporating the interconnect into the solid oxide fuel cell stack such that when fuel and oxidant are provided to opposite fuel and oxidant sides of the interconnect in the solid oxide fuel cell stack, the interconnect separates the fuel and the oxidant gas flows and prevents air or another oxidant gas from reaching an anode electrode of a fuel cell located in contact with the fuel side of the interconnect.