Abstract:
A solid-oxide fuel cell system comprising a plurality of components having mating ports therebetween, the port interfaces being sealed by gaskets that include fluorophlogopite mica (F-mica).

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to fuel cells; more particularly, solid-oxide fuel cell assemblies which operate at elevated temperatures; and most particularly, to gasket material for sealing joints between components of such fuel cell assemblies.  
         BACKGROUND OF THE INVENTION  
         [0002]    Fuel cells for combining hydrogen and oxygen to produce electricity are well known. A known class of fuel cells includes a solid oxide electrolyte layer through which oxygen anions migrate; such fuel cells are referred to in the art as “solid-oxide” fuel cells (SOFCs).  
           [0003]    In some applications, for example, as an auxiliary power unit (APU) for an automotive vehicle, an SOFC is preferably fueled by “reformate” gas, which is the effluent from a catalytic gasoline oxidizing reformer. Reformate typically includes amounts of carbon monoxide (CO) as fuel in addition to molecular hydrogen. The reforming operation and the fuel cell operation may be considered as first and second oxidative steps of the liquid hydrocarbon, resulting ultimately in water and carbon dioxide. Both reactions are exothermic, and both are preferably carried out at relatively high temperatures, for example, in the range of 700° C. to 1000° C.  
           [0004]    A complete fuel cell assembly comprises a plurality of components and sub-assemblies joined together mechanically to provide the desired flow paths and control pathways for the liquid hydrocarbon, reactive gases, spent gases, and cooling gases. It is essential that the joints or interfaces between the components and sub-assemblies be durably leak-free at temperatures from below 0° C. to as high as 1000° C., at pressures from subatmospheric to up to several atmospheres. Such conditions place very high demands on materials selected for gaskets at these joints and interfaces.  
           [0005]    It is known to use various glass and ceramic compositions as sealants. However, a drawback is that such sealants, though effective, tend to be quite brittle and are easily fractured in assembly or in use. Further, typically they require high-temperature sintering during manufacture of a fuel cell system, which adds difficulty and cost.  
           [0006]    What is needed is a material for gasketing in an SOFC system which is thermally stable over the range between shutdown and operating temperatures for both the reformer and the fuel cell assembly; which is chemically stable in oxidizing and reducing environments; which is more robust during assembly and during operation of the system; which is compatible with other materials of the system; and which is relatively inexpensive.  
           [0007]    It is a principle object of the present invention to provide an improved material for gasketing joints and seals in a fuel cell assembly.  
         SUMMARY OF THE INVENTION  
         [0008]    Briefly described, in a solid-oxide fuel cell assembly comprising a plurality of components having mating ports therebetween, the port interfaces are sealed by gaskets that include fluorophlogopite mica (F-mica). 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    These and other features and advantages of the invention will be more fully understood and appreciated from the following description of certain exemplary embodiments of the invention taken together with the accompanying drawings, in which:  
         [0010]    [0010]FIG. 1 is an isometric view from above of a fuel cell assembly having gasketing in accordance with the invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0011]    The advantage and benefit of gasketing in accordance with the invention may be best illustrated by considering the exemplary gasketing requirements of an integrated SOFC fuel cell assembly.  
         [0012]    Referring to FIG. 1, fuel cell assembly  10  includes a plurality of sub-assemblies and components assembled together generally by bolts. An integrated base manifold  12  comprises a bottom plate  14 , and lower section  16 , an intermediate plate  18 , an upper section  20 , and a top plate  22 . The plates  14 ,  18 ,  22  have patterns of apertures (not visible) formed therein which mate with other patterns of chambers (also not visible) formed in sections  16 ,  20  such that manifold  12  is a three-dimensional structure of interwoven flow paths for various gases. Patterned sheet gaskets  24 ,  26 ,  28 ,  30  in accordance with the invention are provided between the sections and plates to seal the port interfaces against leakage of gases flowing through the manifold.  
         [0013]    Fuel cell sub-assembly  32  is mounted on manifold  12 , ports (not visible) in the sub-assembly being mateable with ports (not visible) in the manifold to provide reformate from the manifold into the sub-assembly, to exhaust spent reformate from the sub-assembly, and to provide cooling air to and from the assembly. A patterned sheet gasket  34  is disposed therebetween to seal the port interfaces against gas leakage. Manifold  12  and sub-assembly  32  are bolted together by bolts  36 .  
         [0014]    Fuel cell sub-assembly  32  also contains passage joints (not visible) which are gasketed (not shown) between adjacent plates and fuel cell modules.  
         [0015]    A hydrocarbon fuel reformer  38  is mounted to manifold  12  via bolts  40 , having a patterned sheet gasket (not visible) therebetween. A fuel pre-heater and vaporization sub-assembly  42  is attached to reformer  38  for supplying heated and vaporized hydrocarbon fuel to the reformer. A patterned sheet gasket  44  is provided therebetween, and sub-assembly  42  is secured to reformer  38  via throughbolts  46 .  
         [0016]    A cover plate  48  for sub-assembly  42  supports a fuel injector  50  for the reformer. A patterned sheet gasket  52  is provided under the cover plate.  
         [0017]    Heat exchangers  54   a ,  54   b  are mounted to manifold  12  via bolts  56 , having a patterned sheet gasket  58  therebetween.  
         [0018]    Air inlet fittings  60   a ,  60   b ,  62  are received, as for example by a threaded connection, into bores in manifold  12 , the threads  64  preferably being sealed with gasket material.  
         [0019]    The various patterned sheet gaskets and the thread-sealing material include, and preferably are formed from, fluorophlogopite mica (F-mica). F-mica, a synthetic fluorine mica believed to have the formula KMg 3 (AlSi 3 O 10 )F 2  contains no (OH) −  of natural phlogopite KMg 3 (AlSi 3 O 10 )(OH) 2 . The (OH) −  is fully substituted with F − . The fluorine mica has the following unique characteristics which are much superior to those of natural mica: high chemical stability, excellent transmittance, outgassing-free at high temperature in vacuum, excellent electrical insulation, high heat endurance (up to 1100° C.), non-radioactive background, and highly flexible and cleavable. F-mica sheets may be made by the processes of, as for example, screening, paper making, inorganic binder impregnating and hot pressing etc. F-mica sheets are known in the prior art for a variety of uses, such as substrates of thin film, windows and monochromater for x-ray, neutron diffraction, microwave and optics, spacers of electrical vacuum devices, scanning electron microscopes, and water gauges of high pressure boilers, which uses are important in industry and science. F-mica has not heretofore been used for gasketing in high-temperature fuel cells, as disclosed herein. Both sheet and tape forms of F-mica are commercially available from, for example, G.B. Group, Inc., New York, N.Y., USA, in thicknesses from 0.05 mm to 5 mm.  
         [0020]    While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.