Viscous sealing glass compositions for solid oxide fuel cells
A sealant for forming a seal between at least two solid oxide fuel cell components wherein the sealant comprises a glass material comprising B 2 O 3 as a principal glass former, BaO, and other components and wherein the glass material is substantially alkali-free and contains less than 30% crystalline material.
1. A sealant for forming a seal between at least two solid oxide fuel cell components wherein the sealant comprises a glass material comprising:
40-60 mol % B 2 O 3 as a principal glass former,
10-25 mol % BaO,
10-25 mol % SiO 2 ,
2-10 mol % Al 2 O 3 ,
optionally one or more alkaline earth oxides selected from CaO, SrO, and MgO, and
optionally a transition metal oxide selected from among ZnO, La 2 O 3 , and ZrO 2 ;
wherein the glass material is substantially alkali-free;
wherein the glass material contains no more than 15 vol. % crystallized material; and
wherein the sealant glass material demonstrates viscous self-healing from cracking in an SOFC operational range of 650° C. to 850° C.
2. The sealant of claim 1 wherein the glass material has a cumulative concentration of Li 2 O, Na 2 O, and K 2 O which is less than 0.5 mol %.
3. The sealant of claim 1 wherein the glass material affirmatively comprises at least two of the alkaline earth oxides selected from CaO, SrO, and MgO.
4. The sealant of claim 1 comprising between 2 and 10 mol % each of one or more of said alkaline earth oxides selected from the group consisting of CaO, SrO, and MgO.
5. The sealant of claim 1 wherein the glass material consists essentially of B 2 O 3 , BaO, SiO 2 , Al 2 O 3 , and CaO.
6. The sealant of claim 1 wherein the glass material consists essentially of B 2 O 3 , BaO, SiO 2 , Al 2 O 3 , and ZnO.
7. The sealant of claim 1 wherein the glass material consists essentially of B 2 O 3 , BaO, SiO 2 , Al 2 O 3 , CaO, and ZnO.
8. The sealant of claim 1 wherein the glass material consists essentially of B 2 O 3 , BaO, SiO 2 , Al 2 O 3 , CaO, SrO, and ZnO.
9. The sealant of claim 1 wherein the glass material consists essentially of B 2 O 3 , BaO, SiO 2 , Al 2 O 3 , CaO, and SrO.
10. The sealant of claim 1 wherein the glass material consists essentially of B 2 O 3 , BaO, SiO 2 , Al 2 O 3 , CaO, SrO, ZnO, and MgO.
11. The sealant of claim 1 affirmatively comprising the transition metal oxide selected from among ZnO, La 2 O 3 , and ZrO 2 .
12. The sealant of claim 1 wherein the glass consists essentially of 45 mol % B 2 O 3 , 20 mol % BaO, 20 mol % SiO 2 , 5 mol % Al 2 O 3 , 5 mol % CaO, and 5 mol % SrO.
13. The sealant of claim 1 wherein the glass material consists essentially of 45 mol % B 2 O 3 , 18 mol % BaO, 24 mol % SiO 2 , 6 mol % Al 2 O 3 , 3.5 mol % CaO, and 3.5 mol % SrO.
14. The sealant of claim 1 wherein the glass material has a glass transition temperature of less than 650° C.
15. The sealant of claim 1 wherein the glass material has a glass transition temperature of less than 650° C., a liquidus temperature of less than 850° C., and a coefficient of thermal expansion between about 7 and about 10×10 −6 /° C.
16. The sealant of claim 1 wherein the sealant glass material has a softening temperature below the SOFC operational range of 650° C. to 850° C.
17. The sealant of claim 1 wherein the sealant glass material has a) a liquidus temperature within the SOFC operational range of 650° C. to 850° C., b) a glass transition temperature below the SOFC operational range of 650° C. to 850° C., c) a softening temperature below the SOFC operational range of 650° C. to 850° C., and d) a viscosity at 725° C. of less than 10 6.6 Pa-s.
18. The sealant of claim 1 as a seal in a ferritic steel interconnect.
19. A ferritic steel interconnect in an SOFC comprising the sealant of claim 1 and a stainless steel component.
20. The ferritic steel interconnect of claim 19 comprising the sealant, the stainless steel component, and a yttria-stabilized zirconia component.
21. A solid oxide fuel cell comprising the sealant of claim 1 .