Source: https://patents.google.com/patent/US7794170
Timestamp: 2018-04-25 17:08:27
Document Index: 51737593

Matched Legal Cases: ['art 1', 'art 2', 'art 1', 'art 2', 'art 2', 'art 1', 'art 2', 'art 1', 'art 2', 'art 1', 'art 2', 'art 1']

US7794170B2 - Joint with application in electrochemical devices - Google Patents
Joint with application in electrochemical devices Download PDF
US7794170B2
US7794170B2 US11112122 US11212205A US7794170B2 US 7794170 B2 US7794170 B2 US 7794170B2 US 11112122 US11112122 US 11112122 US 11212205 A US11212205 A US 11212205A US 7794170 B2 US7794170 B2 US 7794170B2
US11112122
US20060239765A1 (en )
Those skilled in the art of electrochemical devices, including without limitation, solid oxide fuel cells, oxygen separators, and hydrogen separators, recognize a need for improved seals at the interface between ceramic and metal parts utilized in these devices. For example, among solid oxide fuel cell designs, the planar stack (pSOFC) has received growing attention because its compact nature affords high volumetric power density—a design feature of particular importance in transportation applications. With the advent of anode-supported cells that employ thin YSZ electrolytes, these devices can be operated at reduced temperature (700-800° C.) and still achieve the same current densities exhibited by their high-temperature, thick electrolyte-supported counterparts, as described in B. C. H. Steele, A. Heinzel (2001) Materials for fuel-cell technologies, Nature, 414(X) 345-52. The entire contents of this, and each and every other patent, paper or other publication referenced herein is hereby incorporated into this disclosure in its entirety by this reference. The lower operating temperature not only makes it possible to consider inexpensive, commercially available high temperature alloys for use in the stack and balance of plant, but also expands the range of materials that can be considered for device sealing.
Because SOFCs function under an oxygen ion gradient that develops across the electrolyte, hermiticity across this membrane is paramount. In a planar design, this means that the YSZ layer must be dense, must not contain interconnected porosity, and must be connected to the rest of the device with a high temperature, gas-tight seal of the type shown in FIG. 1. One of the fundamental challenges in fabricating pSOFCs is how to effectively seal the thin electrochemically active YSZ membrane against the metallic body of the device creating a hermetic, rugged and stable stack. Typical conditions under which these devices are expected to operate and to which the accompanying YSZ-to-metal seal will be exposed include: (1) an average operating temperature of 750° C.; (2) continuous exposure to an oxidizing atmosphere on the cathode side and a wet reducing gas on the anode side; and (3) an anticipated device lifetime of 10,000+ hours.
The inventors of the present disclosure recently developed an alternative method of ceramic-to-metal brazing specifically for fabricating high temperature solid-state devices such as oxygen generators described in J. S. Hardy, J. Y. Kim, K. S. Weil (in press) Joining mixed conducting oxides using an air-fired electrically conductive braze, J. Electrochem. Soc. Vol. 151, No. 8, pp. j43-j49 and U.S. patent application Ser. No. 10/334,346. Referred to as air brazing, the technique differs from traditional active metal brazing in two important ways: (1) it utilizes a liquid-phase oxide-noble metal melt as the basis for joining and therefore exhibits high-temperature oxidation resistance and (2) the process is conducted directly in air without the use of fluxes and/or inert cover gases. In fact, the strength of the bond formed during air brazing relies on the formation of a thin, adherent oxide scale on the metal substrate. The technique employs a molten oxide that is at least partially soluble in a noble metal solvent to pre-wet the oxide faying surfaces, forming a new surface that the remaining molten filler material easily wets. A number of metal oxide-noble metal systems are suitable, including Ag—CuO, Ag—V2O5, and Pt—Nb2O5 as described in Z. B. Shao, K. R. Liu, L. Q. Liu, H. K. Liu, S. Dou (1993) Equilibrium phase diagrams in the systems PbO—Ag and CuO—Ag, J. Am. Cer. Soc., 76 (10) 2663-4, A. M. Meier, P. R. Chidambaram, G. R. Edwards (1995) A comparison of the wettability of copper-copper oxide and silver-copper oxide on polycrystalline alumina, J. Mater. Sci., 30 (19) 4781-6, and R. S. Roth, J. R. Dennis, H. F. McMurdie, eds. (1987) Phase Diagrams for Ceramists, Volume VI, The American Ceramic Society, Westerville, Ohio.
Thus, it is an object of the present invention to provide a joint between a metal and a ceramic part that will maintain a hermetic seal at operating temperatures of greater than 600° C. It is a further object of the present invention to provide a joint between a metal and a ceramic part that will maintain a hermetic seal despite repeated thermal cycling in excess of 600° C. It is a further object of the present invention to provide a joint between a metal and a ceramic part that will maintain a hermetic seal in a hostile operating environment, such as an opeting environment where one side of the joint is continuously exposed to an oxidizing atmosphere and the other side is continuously exposed to a wet reducing gas. It is a further object of the present invention to provide a joint between a metal and a ceramic part that will maintain a hermetic seal for a lifetime of 10,000+ hours of operation.
These and other objects of the present invention are accomplished by providing a joint as shown in FIG. 2. The joint of the present invention is formed of a metal part 1, a ceramic part 2, and a flexible gasket 3. One side of the flexible gasket 3 is attached to the metal part 1 to form a hermetic seal between the two. The other side of the flexible gasket 3 is bonded to the ceramic part 2 to form a separate hermetic seal between the flexible gasket 3 and the ceramic part 2. The flexible gasket 3 is made of metal, preferably the a high temperature oxidation resistant metal with a coefficient of thermal expansion between that of metal part 1 and ceramic part 2. However, the flexible gasket 3 is thinner and more flexible than the metal part 1. As the joint is heated and cooled, differences in the material's coefficient of thermal expansion cause the ceramic part 2 and metal part 1 to expand and contract at different rates. The flexible gasket 3 is thus configured to flex in response to these changes in temperature, up to and including changes in temperature in excess of 600° C. while maintaining a hermetic seal between the ceramic part 2 and the flexible gasket 3, and between the metal part 1 and the flexible gasket 3.
A number of high temperature alloys were considered for use as the metal gasket in experiments conducted to demonstrate joints of the present invention. As part of this proof-of-concept study, the initial materials screening analysis focused on four key properties: high oxidation resistance, low stiffness, high ductility, and low cost. Based on these factors, a commercial alumina-forming ferritic steel was selected as the foil membrane: DuraFoil (22% Cr, 7% Al, 0.1% La+Ce, bal. Fe, manufactured by Engineered Materials Solutions, Inc. Attleboro, Mass.). The DuraFoil was supplied as 50 μm thick sheet. It was then sheared into 3 cm×3 cm samples, annealed in vacuum at 900° C. for 2 hrs, and stamped into cap-shaped washers using a die designed specifically for this purpose. The stamped foils were ultrasonically cleaned in soap and water, and then flushed with acetone to remove the lubricant from the stamping operation.
Each foil washer was bonded to a 6.2 mm thick Haynes 214 washer, with an outside diameter of 4.4 cm and an inside diameter of 1.5 cm, using BNi-2 braze tape purchased from Wall Colmonoy, Inc. Madison Heights, Mich. An alumina-scale forming nickel-based superalloy, Haynes 214 displays excellent oxidation resistance at temperatures in excess of 1000° C., but also exhibits an average CTE of 15.7 m/m·K, which is almost 50% higher than that of the anode-supported bilayer, which consists of a thick porous layer of Ni chemically bonded to a dense, nonporous YSZ membrane. (CTE=10.6 μm/m·K).
Fabrication of the specimen was completed by joining the stamped Durafoil component to the Haynes 214 using BNi-2 braze tape. A second brazing operation was conducted by air brazing the top side of the stamped foil to the YSZ side of a 25 mm diameter bilayer disc using a Ag-4 mol % CuO paste. Joining was conducted by applying a concentric 24 mm ring of braze paste to the Durafoil washer using an automated pressure-driven dispenser. After allowing the paste to dry, the bilayer was placed YSZ-side down onto the washer and dead-loaded with 25 g of weight. The assembly was heated in air at 20° C./min to 1050° C. and held at temperature for 15 min before furnace cooling to room temperature.
Thermal cycle testing was conducted by heating the specimens in air at a rate of 75° C./min to 750° C., holding at temperature for ten minutes, and cooling to ≦70° C. in forty minutes before re-heating under the same conditions. A minimum of six specimens was tested for each test condition. Microstructural analysis was conducted on polished cross-sectioned samples using a JEOL JSM-5900LV scanning electron microscope (SEM) equipped with an Oxford energy dispersive X-ray analysis (EDX) system.
The specimens were characterized via rupture and thermal cycle testing and subsequently analyzed by SEM and EDS. Shown in FIG. 3 is a composite cross-sectional micrograph of a joint according to the present invention. The joint was well sealed, as determined by hermeticity testing conducted prior to metallographic analysis. The entire seal between the metal gasket and the metal part is approximately 1.1 mm thick, although it is expected that this can be readily reduced simply by altering the geometry of the DuraFoil stamping. On the ceramic side of the seal, the CuO—Ag braze forms a robust joint between the YSZ and the alumina scale of the DuraFoil. Note that the braze is thicker toward the center of the specimen. No reaction zone is observed at the YSZ/braze interface, however a 10-15 μm thick zone forms on the DuraFoil due to reaction between the Al2O3 scale and the CuO in the braze. The dominant product is the mixed oxide phase 2CuO.Al2O3.
US11112122 2005-04-22 2005-04-22 Joint with application in electrochemical devices Active 2027-11-27 US7794170B2 (en)
US11112122 US7794170B2 (en) 2005-04-22 2005-04-22 Joint with application in electrochemical devices
PCT/US2005/014344 WO2005106999A1 (en) 2004-04-27 2005-04-26 Improved joint with application in electrochemical devices
US20060239765A1 true US20060239765A1 (en) 2006-10-26
US7794170B2 true US7794170B2 (en) 2010-09-14
ID=37187075
US11112122 Active 2027-11-27 US7794170B2 (en) 2005-04-22 2005-04-22 Joint with application in electrochemical devices
US (1) US7794170B2 (en)
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WO2015199775A3 (en) * 2014-03-28 2016-04-21 Mako Frederick M Method for joining ceramics to ceramics or ceramics to metals, and apparatus
JPH0967672A (en) 1995-08-29 1997-03-11 Tokyo Gas Co Ltd Ferritic stainless steel, solid electrolytic fuel cell and production of the same ferritic stainless steel
US20030132270A1 (en) 2002-01-11 2003-07-17 Weil K. Scott Oxidation ceramic to metal braze seals for applications in high temperature electrochemical devices and method of making
US20060239765A1 (en) 2006-10-26 application
US20100193104A1 (en) 2010-08-05 Method of manufacturing transition metal oxide having spinel structure
Geng et al. 2006 Evaluation of Haynes 242 alloy as SOFC interconnect material
Chou et al. 2003 Mid-term stability of novel mica-based compressive seals for solid oxide fuel cells
US20070003811A1 (en) 2007-01-04 Sealing arrangement for a fuel cell stack and process for the production of such a sealing arrangement
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:WEIL, K. SCOTT;HARDY, JOHN S.;REEL/FRAME:016518/0919
Free format text: CONFIRMATORY LICENSE;ASSIGNOR:BATTELLE MEMORIAL INSTITUTE, PACIFIC NORTHWEST DIVISION;REEL/FRAME:016573/0652