SEALING MATERIAL

Abstract

The present invention relates to composite sealing materials for a gasket. The gaskets are useful in solid oxide fuel/electrolyser cells (SOFC and SOEC). The fuel cell gaskets contain sealing material based upon chemically exfoliated vermiculite that has improved corrosion resistance. The sealing material comprises chemically exfoliated vermiculite; filler; and insoluble carbonate.

Claims

1. A composite sealing material for a gasket comprising: (a) a chemically exfoliated vermiculite (CEV); (b) a filler; and (c) an insoluble carbonate, wherein the insoluble carbonate has a solubility in water of less than 0.1 g/ml at 25 C.

2. The composite sealing material according to claim 1, wherein the composite sealing material is in the form of a sheet or foil.

3. The composite sealing material according to claim 1, wherein the composite sealing material comprises 1-15% w/w insoluble carbonate.

4. The composite sealing material according to claim 1, wherein the CEV provides up to 100% w/w of a total exfoliated vermiculite in the composite sealing material.

5. The composite sealing material according to claim 1, wherein a level of the CEV in the composite sealing material is at least 25% w/w.

6. (canceled)

7. The composite sealing material according to claim 1, wherein the filler is one or more inert fillers.

8. (canceled)

9. The composite sealing material according to claim 1 wherein a level of the filler in the composite sealing material is at least 25% w/w.

10. (canceled)

11. The composite sealing material according to claim 1, wherein the CEV, filler, and insoluble carbonate are intimately mixed in the composite sealing material and evenly distributed throughout the composite sealing material so that they form a generally homogenous mixture.

12. The composite sealing material according to claim 1, wherein the composite sealing material has a density prior to use of 1.5-2.2 g/cm.sup.3.

13. (canceled)

14. The composite sealing material according to claim 1, wherein the composite sealing material is compressible; and wherein an uncompressed thickness of the sealing material is in the range of 10-2000 m.

15. (canceled)

16. The composite sealing material according to claim 1, wherein the insoluble carbonate is selected from a group II carbonate.

17. The composite sealing material according to claim 1, wherein the filler does not comprise an insoluble carbonate.

18. (canceled)

19. The composite sealing material according to claim 1, wherein the CEV is not modified CEV comprising water resistance enhancing monovalent cations.

20. A gasket for sealing two mating surfaces of a solid oxide cell, the gasket comprising the composite sealing material according to claim 1.

21. The gasket according to claim 20, further comprising a core layer comprising the composite sealing material, wherein the core layer is interposed between a first and a second coating layer, the coating layers each comprising glass, glass-ceramic, and/or ceramic material.

22. A solid oxide cell or a solid oxide cell component comprising one or more gaskets according to claim 20.

23. A composition for use in forming a composite sealing material for a gasket comprising: (a) a chemically exfoliated vermiculite (CEV); (b) a filler; (c) an insoluble carbonate; and (d) a liquid carrier, wherein the insoluble carbonate has a solubility in water of less than 0.1 g/ml at 25 C.

24. A process for the production of the composite sealing material according to claim 1 comprising the steps of: a. mixing the CEV with the filler, the insoluble carbonate, and a liquid carrier to form an intimate mixture thereof; b. optionally, forming a sheet or foil from the mixture; c. optionally, drying the said sheet or foil; d. optionally, forming a gasket or core layer from the sheet or foil, wherein the insoluble carbonate has a solubility in water of less than 0.1 g/ml at 25 C.

25. A process for sealing a solid oxide cell component comprising incorporating at least one gasket according to claim 20 into the solid oxide cell component.

26-27. (canceled)

28. The composite sealing material according to claim 16, wherein the group II carbonate is selected from at least one of calcium carbonate or strontium carbonate.

Description

EXAMPLES

[0129] Example gaskets 1 to 4 were prepared according to the compositions of Table 1 using the following method.

Mixing Method.

[0130] In examples 1-3 and comparative examples 1 and 2, ingredients are added in a controlled manner by using a dedicated mixer. The mixer has a blender (propeller) and an agitator (paddles) which operate independently. Both these have different speed settings during the mixing cycle. Add small volumes of the dry powders to HTS over a period time, with the mixer at medium speed. After all the powders have been added, increase mixer speed to maximum until all the powders are well dispersed.

Casting Method

[0131] Using a tape caster line, the material is passed under a doctor blade to allow a thin film of wet material to be formed to the required thickness. Once formed, the material is left to dry.

TABLE-US-00001 TABLE 1 Compositions used to prepare Examples 1 to 3 and Comparative Example 1 and 2 Compar- Compar- ative ative Exam- Exam- Exam- Exam- Exam- ple 1 ple 2 ple 3 ple 1 ple 2 HTS*, kg 5 5 5 5 5 D200**, kg 0.747 0.814 0.840 0.960 0 CaCO.sub.3***, kg 0.212 0.193 0.097 0.957 Water 0.75 1.26 CaCO.sub.3 dry wt % 12.2 10.8 5.6 0 55 *water and CEV mixture containing 15.7 wt % CEV **steatite/talc ***precipitated grade with an average particle size of 2-10 microns

[0132] Comparative Example 2 produces a sheet that cracked badly during drying. No useable material was obtained due to excessive curling and cracking. Accordingly, no gaskets could be cut for testing from Comparative Example 2.

[0133] Thermal and compression cycling was carried out to test the leakage rate of dried Example gaskets 1 to 3 and comparative example 1 in SOFCs. All leakage rates were found to be within acceptable limits for SOFCs both under compression cycling and thermal cycling.

Testing Corrosion Resistance

[0134] Corrosion resistance was tested under the following conditions on the dried gasket sealing elements. Two gasket sealing elements of comparative example 1 were located on either side of a steel plate (Crofer 22 APU) about a central aperture and the arrangement was sealed between mating end plates (Crofer 22 APU) of a SOFC. The shape of the gasket is endless and defines a generally dumbbell shaped recess which includes the central aperture of the central plate and extends beyond this to additionally include a circular outlet of the first end plate and the corresponding circular inlet of the 2.sup.nd end plate so that fuel can pass between the end plates and through an aperture in the central steel plate without escaping between the end plates. The radially outermost extent of the gasket is within the outer edges of the central steel plate in use so that after use any corrosion of the outwardly overlapping surfaces of the central steel plate can be inspected for corrosion damage.

[0135] Comparative example 1 showed extensive corrosion damage to the central steel plate beyond the outer edges of the gaskets. The test was repeated for examples 1-3. The presence of CaCO.sub.3 in example 1 reduced the level of corrosion and together with the results of examples 2 and 3, a clear inverse correlation of concentration of CaCO.sub.3and extent of corrosion could be observed.

[0136] The outer edges of the steel plates were scored from 0-5 as follows:

TABLE-US-00002 Substantially all outer area affected by corrosion 5 More than of the outer area affected by corrosion 4 More than half of the outer are affected by corrosion 3 More than of the outer area affected by corrosion 2 Corrosion of the outer area slight but observable 1 No clear corrosion of the outer area 0

[0137] The results are shown in table 2.

TABLE-US-00003 TABLE 2 Corrosion Testing Results Comparative Example 1 Example 2 Example 3 Example 1 Test Score* 0 1 3 5

[0138] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0139] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[0140] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0141] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.