Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
  • C03C3/095—Glass compositions containing silica with 40% to 90% silica, by weight containing rare earths
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C10/00—Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition
  • C03C10/0036—Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition containing SiO2, Al2O3 and a divalent metal oxide as main constituents
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B19/00—Other methods of shaping glass
  • C03B19/06—Other methods of shaping glass by sintering, e.g. by cold isostatic pressing of powders and subsequent sintering, by hot pressing of powders, by sintering slurries or dispersions not undergoing a liquid phase reaction
  • C03B19/063—Other methods of shaping glass by sintering, e.g. by cold isostatic pressing of powders and subsequent sintering, by hot pressing of powders, by sintering slurries or dispersions not undergoing a liquid phase reaction by hot-pressing powders
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C10/00—Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition
  • C03C10/0009—Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition containing silica as main constituent
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C10/00—Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition
  • C03C10/0054—Devitrified glass ceramics, i.e. glass ceramics having a crystalline phase dispersed in a glassy phase and constituting at least 50% by weight of the total composition containing PbO, SnO2, B2O3
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/062—Glass compositions containing silica with less than 40% silica by weight
  • C03C3/064—Glass compositions containing silica with less than 40% silica by weight containing boron
  • C03C3/068—Glass compositions containing silica with less than 40% silica by weight containing boron containing rare earths
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
  • C03C3/089—Glass compositions containing silica with 40% to 90% silica, by weight containing boron
  • C03C3/091—Glass compositions containing silica with 40% to 90% silica, by weight containing boron containing aluminium
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C8/00—Enamels; Glazes; Fusion seal compositions being frit compositions having non-frit additions
  • C03C8/02—Frit compositions, i.e. in a powdered or comminuted form
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C8/00—Enamels; Glazes; Fusion seal compositions being frit compositions having non-frit additions
  • C03C8/14—Glass frit mixtures having non-frit additions, e.g. opacifiers, colorants, mill-additions
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C8/00—Enamels; Glazes; Fusion seal compositions being frit compositions having non-frit additions
  • C03C8/14—Glass frit mixtures having non-frit additions, e.g. opacifiers, colorants, mill-additions
  • C03C8/20—Glass frit mixtures having non-frit additions, e.g. opacifiers, colorants, mill-additions containing titanium compounds; containing zirconium compounds
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C8/00—Enamels; Glazes; Fusion seal compositions being frit compositions having non-frit additions
  • C03C8/24—Fusion seal compositions being frit compositions having non-frit additions, i.e. for use as seals between dissimilar materials, e.g. glass and metal; Glass solders
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/02—Hydrogen or oxygen
  • C25B1/04—Hydrogen or oxygen by electrolysis of water
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/02—Hydrogen or oxygen
  • C25B1/04—Hydrogen or oxygen by electrolysis of water
  • C25B1/042—Hydrogen or oxygen by electrolysis of water by electrolysis of steam
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/60—Constructional parts of cells
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/70—Assemblies comprising two or more cells
  • C25B9/73—Assemblies comprising two or more cells of the filter-press type
  • C25B9/75—Assemblies comprising two or more cells of the filter-press type having bipolar electrodes
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
  • C25B9/70—Assemblies comprising two or more cells
  • C25B9/73—Assemblies comprising two or more cells of the filter-press type
  • C25B9/77—Assemblies comprising two or more cells of the filter-press type having diaphragms
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
  • H01M8/0271—Sealing or supporting means around electrodes, matrices or membranes
  • H01M8/028—Sealing means characterised by their material
  • H01M8/0282—Inorganic material
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
  • H01M8/0271—Sealing or supporting means around electrodes, matrices or membranes
  • H01M8/0286—Processes for forming seals
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes
  • H01M8/12—Fuel cells with solid electrolytes operating at high temperature, e.g. with stabilised ZrO2 electrolyte
  • H01M8/124—Fuel cells with solid electrolytes operating at high temperature, e.g. with stabilised ZrO2 electrolyte characterised by the process of manufacturing or by the material of the electrolyte
  • H01M8/1246—Fuel cells with solid electrolytes operating at high temperature, e.g. with stabilised ZrO2 electrolyte characterised by the process of manufacturing or by the material of the electrolyte the electrolyte consisting of oxides
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23D—ENAMELLING OF, OR APPLYING A VITREOUS LAYER TO, METALS
  • C23D1/00—Melting or fritting the enamels; Apparatus or furnaces therefor
  • C23D1/02—Granulating the melt; Drying the granules
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23D—ENAMELLING OF, OR APPLYING A VITREOUS LAYER TO, METALS
  • C23D5/00—Coating with enamels or vitreous layers
  • C23D5/02—Coating with enamels or vitreous layers by wet methods
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes
  • H01M8/12—Fuel cells with solid electrolytes operating at high temperature, e.g. with stabilised ZrO2 electrolyte
  • H01M2008/1293—Fuel cells with solid oxide electrolytes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/24—Grouping of fuel cells, e.g. stacking of fuel cells
  • H01M8/241—Grouping of fuel cells, e.g. stacking of fuel cells with solid or matrix-supported electrolytes
  • H01M8/2425—High-temperature cells with solid electrolytes
  • H01M8/2432—Grouping of unit cells of planar configuration
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/24—Grouping of fuel cells, e.g. stacking of fuel cells
  • H01M8/2465—Details of groupings of fuel cells
  • H01M8/2483—Details of groupings of fuel cells characterised by internal manifolds
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/50—Fuel cells

Definitions

• the present invention relates to glass compositions and sealing materials comprising same which are suitable for use in electrochemical devices requiring a hermetic seal, including solid oxide fuel cell stacks and similar apparatus, such as solid oxide electrolyser cell stacks.
• Electrochemical devices or electrochemical cells are devices capable of either generating electrical energy from chemical reactions or using electrical energy to cause chemical reactions.
• An example of an electrochemical device is a solid oxide fuel cell (SOFC) device, which is used to convert chemical energy of a gaseous fuel such as hydrogen into electrical energy by electrochemical oxidation.
• SOFC solid oxide fuel cell
• a typical SOFC stack consists of a number of cells connected to each other, where each cell has a porous ceramic cathode and a porous ceramic anode separated by a dense, ionically conducting solid oxide electrolyte.
• the stacks typically include a support structure made up of one or more supports made of a suitable material, for example made of suitable metals.
• a fuel such as natural gas is supplied to the anode and an oxidant such as air is supplied to the cathode of each cell.
• the cell components are assembled in such a way the fuel and the oxidant can be supplied to the anode and the cathode of each cell respectively.
• SOEC solid oxide electrolyser cell
• SOEC solid oxide electrolyser cell
• the cells of SOFC and SOEC devices require gas tight (hermetic) seals which prevent mixing of the fuel and the oxidant and are therefore important for the performance, durability and safe operation of a SOFC or SOEC stack.
• the seals are commonly used to separate the anode and cathode cavities of SOFC or SOEC stacks from each other and from the surrounding environment as required by the stack design.
• the seals also allow for mechanical bonding of the components of a SOFC or SOEC stack and electrical insulation between bonded components.
• SOFC and SOEC stacks During operation SOFC and SOEC stacks reach elevated temperatures, usually in the range of about 500°C to about 1000°C, and are subjected to both intentional and unintentional temperature fluctuations (thermal cycles) ranging from as low as ambient temperature to the operating temperature with varying heating and cooling rates.
• thermal cycles intentional and unintentional temperature fluctuations
• the seals must maintain their integrity and fulfil all the above requirements under the thermal cycling conditions as well as under the constant temperature operation for many thousands of hours.
• the mismatch between the thermal expansion and contraction of each seal and the other components of the SOFC or SOEC stack should be sufficiently low to prevent the failure of the seal or any of the other components under the thermal stresses developed during thermal cycling.
• the seal should not have adverse interactions with other components of the SOFC or SOEC stack, either by way of emitting undesirable volatile species that alter the chemical or physical nature of the other components or by reacting with the other components that the seal is in contact with.
• Various types of glasses have been developed for use as seals in SOFC and SOEC stacks.
• One type of glass has been designed to retain a large fraction of liquidlike glassy phase. This provides the glass with the ability to flow (exhibit viscous relaxation) under the thermal stresses generated as the main means of reducing the magnitude of the stresses imparted on the other components and the interfaces with the other components at temperatures above the glass transition temperature (T g ).
• T g glass transition temperature
• This type of glass has a number of deficiencies. For example, it is typically prone to cracking at temperatures below the T g where the viscous relaxation is absent.
• the glass usually contains high amounts of constituents such as alkali oxides and B2O3 which can (a) make the seal a poor electrical insulator, (b) either volatilise or get leached out in the humidified gaseous environment within the fuel cell stack, resulting in continuous changes in the chemical and physical properties of the seal, and (c) lead to adverse reactions with the other components.
• Another type of glass has been designed to turn into highly crystalline rigid glass-ceramics at the SOFC and SOEC operating temperatures. Whilst this type of highly crystalline glass mitigates the disadvantages relating to the reactivity of the less crystalline glass seals described above, to densify a seal made from this type of glass and eliminate large intrinsic flaws can be extremely difficult. The presence of large intrinsic flaws and the absence of a substantial amount of glassy phase sufficient to reduce stress concentration at the tips of the existing flaws can make this type of glass vulnerable to cracking by the propagation of existing intrinsic flaws under severe thermal cycling.
• the present inventors have developed a glass composition which is capable of forming a glass seal suitable for use in a SOFC device.
• the formed glass seal advantageously comprises one or more crystalline phases and a glassy phase.
• the present invention provides a glass composition comprising, as mol% of the glass composition: about 50 to about 60 mol% SiO2; about 2 to about 10 mol% B2O3; about 0.5 to about 3 mol% AI2O3; about 4 to about 6 mol% TiC>2; about 1 to about 4 mol% CeC>2; about 2 to about 30 mol% SrO; and about 2 to about 25 mol% BaO.
• the glass composition is substantially free of alkali metal oxides.
• the present invention provides a sealing material for use in an electrochemical device comprising the glass composition described herein.
• the electrochemical device may be any electrochemical device that requires a hermetic seal.
• the electrochemical device is an SOFC or SOEC stack.
• the present invention provides an electrochemical device comprising one or more cells, each cell comprising a cathode, an anode and a solid electrolyte; a support structure comprising one or more supports; and the sealing material described herein.
• the electrochemical device may be any electrochemical device that requires a hermetic seal.
• the electrochemical device is an SOFC or SOEC stack.
• the present invention provides the use of the glass composition described herein or the sealing material described herein for forming a seal in an electrochemical device.
• the electrochemical device may be any electrochemical device that requires a hermetic seal.
• the electrochemical device is an SOFC or SOEC stack.
• the present invention provides a method of forming a seal in an electrochemical device which is a SOFC or SOEC stack, the method comprising: applying the sealing material described herein on one or both of a cell and a support structure of a SOFC or SOEC stack; and subjecting the sealing material to a sintering thermal cycle, wherein the glass composition of the sealing material softens to provide a sintered glass and subsequently undergoes controlled crystallisation to provide a glass-ceramic comprising one or more crystalline phases and a glassy phase; thereby forming a seal in the SOFC or SOEC stack.
• Figure 1 is a schematic diagram of a portion of a solid oxide fuel cell stack with cell components shown in an exploded view.
• Figure 2 is a graph of the typical particle size distribution of a glass powder prepared from the glass composition of the invention.
• Figure 3 shows scanning electron microscope images at two different magnifications of a sintered glass sample prepared from a glass composition of the invention.
• Figure 4 is a graph of the expansion difference between the metal used for the support structure of a SOFC stack and the sintered glass bars prepared from glass compositions of the invention.
• Figure 5 is a graph of the expansion difference between the metal used for the support structure of a SOFC stack and the sintered glass bars prepared from a glass composition of the invention which has been subjected to an atmospheric air environment at 850°C for 0, 1000, 2000, 4000 and 6000 hours.
• Figure 6 shows scanning electron microscope images of sintered glass bars prepared from a glass composition of the invention which have been air aged at 850°C at 0, 1000, 2000 and 6000 hours.
• Figure 7 is a graph of the expansion difference between the metal used for the support structure of a SOFC stack and sintered glass bars prepared from a glass composition of the invention which has been subjected to a fuel environment at 850°C for 0, 1000, 2000, 4000 and 6000 hours.
• Figure 8 shows scanning electron microscope images of sintered glass bars prepared from a glass composition of the invention which have been fuel aged at 850°C at 0 hours (top left), 500 hours (top right), 1000 hours (bottom left) and 2000 hours (bottom right).
• Figure 9 shows scanning electron microscope images of samples before and after fuel aging of a glass composition of the invention.
• Figure 10 is a graph showing percent voltage degradation against the number of thermal cycles of a SOFC stack with a glass composition of the invention subjected to about 100 thermal cycles over about 9000 hours.
• Figure 11 shows optical microscopy images of glass seals prepared from a glass composition of the invention after a SOFC stack test.
• the term “about” refers to a quantity, value, dimension, size, or amount that varies by as much as 30%, 25%, 20%, 15% or 10% to a reference quantity, value, dimension, size, or amount.
• the present invention provides a glass composition which comprises, as mol% of the glass composition: about 50 to about 60 mol% SiC>2; about 2 to about 10 mol% B2O3; about 0.5 to about 3 mol% AI2O3; about 4 to about 6 mol% TiC>2; about 1 to about 4 mol% CeC>2; about 2 to about 30 mol% SrO; and about 2 to about 25 mol% BaO.
• condition (a) and one or both of conditions (b) and (c) are satisfied:
• satisfying condition (a) and one or both of conditions (b) and (c) may allow the glass composition to form a glass seal having a glassy phase which is substantially free of BaO and B2O3, respectively.
• the term “substantially free” in the context of the glassy phase is intended to mean that the glassy phase does not comprise the specified metal oxide(s) or only comprises the metal oxide(s) in amounts that do not have a measureable effect on the properties and/or performance of the glass seal formed from the glass composition.
• the term “substantially free of BaO and B2O3” will be understood to mean that the glassy phase does not comprise BaO or B2O3 or comprises BaO and B2O3 in amounts that do not have a measureable effect on the properties and/or performance of the glass seal formed from the glass composition.
• the glassy phase may comprise small amounts of BaO and/or B2O3 provided that these amounts do not have a measureable effect on the properties and/or performance of the glass seal formed from the composition.
• condition (a) and one or more of conditions (b) and (c) allow substantially all of the BaO and Ba2Os, respectively, to be in crystalline form in the glass seal.
• the glass composition is substantially free of alkali metal oxides.
• Glass seals containing alkali metal oxides can be contaminating, electrochemically unstable and lack robustness, which may lead to degraded performance of a SOFC or SOEC stack, or other electrochemical device requiring a hermetic seal.
• the glass composition may optionally comprise no further metal oxides, i.e. , no other metal oxides in addition to SiC>2, B2O3, AI2O3, TiC>2, CeC>2, SrO and BaO.
• the glass composition does not comprise CaO.
• the glass composition does not comprise ZrO2.
• the glass composition consists essentially of, or consists of, as mol% of the glass composition: about 50 to about 60 mol% SiC>2; about 2 to about 10 mol% B2O3; about 0.5 to about 3 mol% AI2O3; about 4 to about 6 mol% TiC>2; about 1 to about 4 mol% CeC>2; about 2 to about 30 mol% SrO; and about 2 to about 25 mol% BaO.
• condition (a) and one or both of conditions (b) and (c) are satisfied:
• the glass composition may contain any suitable range of metal oxide component within the broadest range specified for each metal oxide.
• the amounts of each metal oxide in the composition may be suitably selected depending on the desired properties of the glass seal to be formed by the glass composition.
• the glass composition comprises, or consists of, one or more of the following, as mol% of the glass composition: about 52 to about 59 mol% SiC>2, especially about 54 to about 58 mol% SiC>2; about 3 to about 10 mol% B2O3, especially about 5 to about 7 mol% B2O3; about 0.5 to about 2 mol% AI2O3, especially about 1 to about 2 mol% AI2O3; about 4 to about 5.5 mol% TiC>2; about 2 to about 3 mol% CeC>2, especially about 2 to about 2.5 mol% CeC>2; about 9 to about 20 mol% SrO, especially about 9 to about 12 mol% SrO, more especially about 10 to about 12 mol% SrO, even more especially about 10 to about 11 mol% SrO; about 15 to about 25 mol% BaO, especially about 16 to about 21 mol% BaO, more especially about 17 to about 20 mol% BaO, even more especially about 17 to about 19 mol% SrO; about 15
• the glass composition of the invention may be prepared by methods known in the art.
• the glass compositions are typically provided in the form of glass powders.
• the glass can also be provided in frit form, where the glass frit is milled to a powder with desired particle size distribution for use in a sealing material.
• the metal oxide components of the glass composition or their precursors are each weighed in correct proportions that would result in the desired glass composition.
• the weighed powders are mixed to produce a homogeneous mixture and then smelted.
• the melt is poured onto a suitable surface, such as a marver or a mould, and then rapidly cooled to provide a smelted glass frit.
• the smelted glass frits may be milled, for example using a ball mill, to produce glass powders.
• the milled glass powder may be suitably sieved to provide glass powders having the desired particle size or particle size distribution (PSD).
• PSD particle size or particle size distribution
• the glass composition of the invention may be used for providing a seal in an electrochemical device requiring a hermetic seal. Accordingly, the present invention also provides the use of the glass composition of the invention for forming a seal in an electrochemical device, especially a SOFC or SOEC stack.
• the glass compositions of the invention are capable of forming glass seals which have properties that make them suitable for use in SOFC (and SOEC) stacks.
• the glass composition of the invention may be used in a sealing material for an electrochemical device requiring a hermetic seal, including a SOFC or SOEC stack. Accordingly, the present invention provides a sealing material comprising the glass composition described herein. The present invention also provides use of the sealing material for forming a seal in an electrochemical device, especially a SOFC or SOEC stack.
• the sealing material may comprise one or more fillers.
• the fillers are substantially chemically inert toward the seal formed from the glass composition, which allows the fillers to be used without affecting the performance of the seal.
• the fillers may also preferably have a CTE similar to that of glass, and/or have high strength. Examples of suitable fillers include, but are not limited to, ZrO2 in powder or fibre form, ceria and barium silicates.
• the sealing material comprises about 80 to about 100 vol% of the glass composition and about 0 to about 20 vol% of the one or more fillers, based on the total amount of sealing material.
• the glass composition of the sealing material may be subjected to a suitable sintering thermal cycle to provide a glass seal for an electrochemical device, especially a SOFC or SOEC stack.
• a suitable thermal cycle may include a first step which allows the glass powder particles of the glass composition to soften and sinter together to provide a sintered glass having a relatively low viscosity, and a second step which allows the sintered glass to turn into a stable glass-ceramic having a relatively high viscosity by forming crystals of many different compositions.
• the glass seal formed from the glass composition of the invention may provide the beneficial properties of the both highly glassy seals and highly crystalline seals currently used in SOFC and SOEC stacks.
• the glass composition of the sealing material of the invention after being subjected to a sintering thermal cycle, softens to provide a sintered glass and subsequently undergoes controlled partial crystallisation to provide a glass-ceramic which comprises one or more crystalline phases and a glassy phase.
• a suitable sintering thermal cycle comprises: a first step conducted over a period of about 30 to about 120 minutes, especially about 30 to about 60 minutes, and at a temperature which is above the glass transition temperature and is about 10 to about 30 °C below the commencement of the crystallisation of the glass; and a second step conducted over a period of about 2 to about 5 hours and at a temperature which is at least 50 °C above the intended operating temperature of the electrochemical device, which is especially a SOFC or SOEC stack, and at least 50 °C above the commencement of the crystallisation of the glass.
• the glass powder particles of the composition soften and sinter together to eliminate interconnected pores and readily flow into the gap(s) between the components of the electrochemical device to be sealed, for example either or both of a cell and an interconnecting support structure of a SOFC/SOEC stack.
• the sintered glass may establish a hermetic seal between the components of the electrochemical device.
• the sintered glass may also advantageously provide a strong mechanical bond between the components on either side of the seal.
• the presence of B2O3 in the specified amounts in the glassy phase prior to crystallisation may improve wetting of the electrochemical device components by the glass during the first step, which may advantageously result in strong bonding between the seal and the components.
• the first step may be conducted over a longer period of time, although this would increase the cost of production.
• conducting the first step for a shorter period of time may result in a poor seal, for example a seal which poorly adheres to other stack components or a seal which is poorly sintered leaving a high level of porosity resulting in a mechanically weak and partially permeable seal.
• the temperature of the commencement of the crystallisation of the glass may be determined by methods known in the art, for example differential thermal analysis (DTA) and differential scanning calorimetry (DSC).
• the sintered glass seal partially crystallises to form a stable glass-ceramic comprising one or more crystalline phases and a glassy phase.
• the crystals of each of the crystalline phases may advantageously increase the mechanical strength of the glass-ceramic.
• the crystalline phases may also advantageously impart the glass-ceramic with thermal expansion and contraction characteristics that closely match with those of other components of the SOFC or SOEC stack, or other electrochemical device requiring a hermetic seal.
• the time period for the second step may be suitably selected depending on one or more factors. One factor may be the temperature for the second step, where typically the higher the temperature the lesser the time required.
• the temperature of the second step is about 50°C above the commencement of the crystallisation temperature of the SOFC or SOEC stack, a time period of 2 hours may be sufficient to stabilise the glass by crystallisation. It will be appreciated that a longer time period at a temperature much higher than the intended operating temperature of the SOFC or SOEC stack may cause undesirable and irreversible changes in other components of the stack. It will also be appreciated that a longer time period would increase cost of production.
• the intended operating temperature of the SOFC or SOEC stack may be suitably selected depending on the design of the SOFC or SOEC stack and the characteristics of the other functional components in the stack such as the anode, cathode, electrolyte and metal supports.
• the intended operating temperature of the SOFC or SOEC stack is from about 500 to about 1000°C, especially from about 500 to about 900 °C.
• the temperature of the commencement of the crystallisation of the glass may be determined by methods known in the art, for example differential thermal analysis (DTA) and differential scanning calorimetry (DSC).
• the sintering cycle may optionally include binder burn out step prior to the first and second steps of the sintering thermal cycle.
• the binder burn out step may be suitably conducted to burn out organic materials present in the seal paste and/or cell coatings.
• An example of a suitable binder burn out step comprises heating to a temperature of about 445 °C to about 455 °C, especially a temperature of about 450 °C, over a period of about 0.5 hours.
• the sintered glass which may be formed from the glass composition of the invention when subjected to a suitable sintering thermal cycle, forms a hermetic seal within the SOFC or SOEC stack, or other electrochemical device requiring a hermetic seal.
• the glass-ceramic which may be subsequently formed from the sintered glass, comprises one or more crystalline phases and a glassy phase.
• the glass-ceramic comprises about 45 to about 80 vol%, especially about 50 to about 70 vol%, of the one or more crystalline phases and about 20 to about 55 vol%, especially about 30 to about 50%, of the glassy phase, based on the total amount of glass-ceramic.
• the one or more crystalline phases of the glassceramic comprise crystals having a structure selected from 2BaO.TiO2.2SiC>2, 2SrO.TiO2.2SiC>2, 3BaO.3B2C>3.2SiO2, BaO.2SiC>2, BaO.B2O3, and combinations thereof.
• the BaO of the glass composition may be consumed during crystallisation of the sintered glass to the glass-ceramic such that substantially all of the BaO is in crystalline form in the glass-ceramic.
• the B2O3 of the glass composition may be consumed during crystallisation such that substantially all of the B2O3 is in crystalline form in the glass-ceramic.
• the glassy phase of the glass-ceramic is substantially free of BaO.
• the glassy phase of the glass-ceramic is substantially free of B2O3.
• this may provide a highly viscous silicate glass matrix of low reactivity.
• BaO and B2O3 in the glassy phase may have adverse interactions with other components of the SOFC or SOEC, or other electrochemical device requiring a hermetic seal, but may become essentially inert when crystallised.
• “essentially inert” is intended to mean that the BaO and/or B2O3 when crystallised do not react with other components of the electrochemical device or only react in such a way that does not have a measureable effect on the properties and/or performance of the glass seal formed from the glass composition.
• the glass-ceramic may preferably have thermal expansion and contraction characteristics that closely match with those of other components of the electrochemical device, which is especially a SOFC or SOEC stack, in the range of temperatures where the glass is rigid, i.e. , below the glass transition temperature. This may advantageously allow the thermal stresses generated during the operation of the electrochemical device to not exceed the mechanical strengths of the components of the electrochemical device. Accordingly, in some embodiments, the glass-ceramic has a thermal expansion and contraction mismatch with any other stack component it is bonded to of about -0.04 (negative 0.04) to about 0.10 (positive 0.10) at any temperature up to the glass transition temperature of the glassy phase, where the thermal expansion and contraction mismatch is defined as:
• Expansion 100 where Glass refers to the glass-ceramic and Other refers to the other electrochemical device component the glass is bonded to (for example, in the case of a SOFC or SOEC stack, either or both of a cell and an interconnecting support structure).
• the glass transition temperature of the glassy phase is dependent on its composition and may be determined by methods known in the art, for example by conducting a dilatometry test.
• glass samples prepared from the glass compositions of the invention showed stable expansion mismatch when subjected to an air environment or a fuel environment at elevated temperatures for extended periods of time.
• the glass-ceramic may have a coefficient of thermal expansion (CTE) which allows the glass-ceramic (and therefore the sealing material) to be suitable for use in an electrochemical device requiring a hermetic seal, especially a SOFC or SOEC stack.
• the CTE may be substantially the same as the CTE of any of the other components in the SOFC or SOEC stack, or other electrochemical device requiring a hermetic seal.
• the glass-ceramic (or the sealing material) has a CTE of about 10 x 10 -6 /°C to about 13 x 10 -6 /°C.
• the sealing material of the invention may be useful for forming a glass seal in an electrochemical device requiring a hermetic seal, especially a SOFC or SOEC stack.
• the present invention provides an electrochemical device, preferably a SOFC or SOEC stack, comprising one or more cells, each cell comprising a cathode, an anode and a solid electrolyte; a support structure comprising one or more supports; and the sealing material described herein.
• the present invention also provides an electrochemical device, preferably a SOFC or SOEC stack, comprising one or more cells, each cell comprising a cathode, an anode and a solid electrolyte, a support structure comprising one or more supports, and a glass seal, wherein the glass seal is formed from the sealing material described herein.
• the glass seal may be formed using a suitable sintering thermal cycle as described herein.
• the support structure is an interconnected support structure which comprises one or more supports made of a suitable material, for example made of a suitable metal such as steel.
• the support structure is a set of interconnected plates. It will be understood that each plate may be interpreted as a support of the support structure, and each cell may comprise one or more of the plates.
• the present invention also provide a method of forming a seal in an electrochemical device which is a SOFC or SOEC stack, the method comprising: applying the sealing material described herein on either or both of a cell and a support structure of an SOFC or SOEC stack; and subjecting the sealing material to a sintering thermal cycle, wherein the glass composition of the sealing material softens to provide a sintered glass and subsequently undergoes controlled crystallisation to provide a glass-ceramic comprising one or more crystalline phases and a glassy phase; thereby forming a seal in the SOFC or SOEC stack.
• Suitable sintering thermal cycles which may be used in the method of the invention and features and properties of the sealing material (or sintered glass, glassceramic or glass seal formed therefrom) are as described herein.
• FIG. 1 is a schematic diagram of a portion of a SOFC stack (1) with cell components, namely the cathode (2), anode (3) and electrolyte (4), support structure (5) and glass seal (6) shown in an exploded view.
• SOFC stacks operated at standard operating temperatures over extended periods of time which were sealed with the glass composition of the invention degraded less than those sealed from a comparative glass currently used in the production of SOFC stacks. Accordingly, in some embodiments, the SOFC (or SOEC) stacks of the invention undergo a total performance degradation of less than 10%, especially less than 6%, more especially less than about 3%, even more especially less than about 2%, when operated for about 10,000 hours and subjected to about 100 thermal cycles from room temperature (about 20°C to about 25°C) to the intended operating temperature of the SOFC (or SOEC) stack.
• Example 1 Glass compositions and powders.
• glass seals which may be suitable for electrochemical devices such as SOFC and SOEC stacks
• 19 different glass compositions were assessed.
• the glass compositions are provided in Table 1. Table 1. Glass compositions
• Glass powders corresponding to glass compositions 1-19 were prepared by the following method. Oxides of each metal component or their precursors were weighed in correct proportion that would result in the desired glass composition. The weighed powders were thoroughly mixed to produce a homogeneous mixture and smelted at 1450°C for 2 h. Once the raw materials were converted to a melt, it was poured onto a marver and then rapidly cooled in water to produce a glass frit.
• the smelted glass frits were dried and ball milled and sieved to provide glass powders with the desired particle size distribution (PSD).
• PSD particle size distribution
• the particle sizes fall within the ranges shown in Table 2.
• the measurement was performed using a laser diffraction method and the typical particle size distribution of the glass powder is shown in Figure 2.
• Example 2 Characterisation of sintered glass by SEM and XRD.
• Figure 4 shows the expansion mismatch of sintered glass bar samples 9, 10, 11 , 14 and 19 against the stainless steel metal support material given by the following equation:
• Expansion 100 where Glass is the sintered glass bar sample and Other is the stainless steel material.
• the two dotted lines in Figure 4 encapsulate the preferred region where expansion mismatch is to be between room temperature and the glass transition temperature for the stresses within the stack to be minimized for its safe operation and thermal cycling.
• the results show that glass compositions 9, 10, 11 , 14 and 19 exhibited expansion differences with the metal support which fall within the two dotted lines and therefore fall within the defined range. Accordingly, the results may indicate that glass compositions 9, 10, 11 , 14 and 19 provide a glass having thermal expansion and contraction characteristics that closely match with those of other components of an SOFC (or SOEC) stack in the range of temperatures where the glass is rigid, i.e. , below the glass transition temperature.
• Figure 5 shows the expansion mismatch of sintered bars prepared from glass composition 11 subjected to an atmospheric air environment at 850°C for 0, 1000, 2000, 4000 and 6000 hours.
• the air aged samples of glass composition 11 showed relatively stable expansion mismatch with the metal over the extended time period.
• Figure 6 shows SEM micrographs of the air aged samples of glass composition 11. SEM analysis showed that the crystals of the initially formed crystalline phases had coarsened while small amounts of some new crystal types had grown over the exposure time but generally the glass remained pore free where formation of pores could contribute to seal failure.
• Figure 7 shows the expansion mismatch of sintered bars prepared from glass composition 11 subjected to a fuel environment at 850°C for 0, 1000, 2000, 4000 and 6000 hours. Although the fuel environment is more reactive towards glass compared to air, the expansion mismatch of the fuel aged samples of glass composition 11 remained relatively stable over the extended time period.
• Figure 8 shows SEM micrographs of the fuel aged samples of glass composition 11. SEM analysis indicated some growth of crystals, but not as much as in the air aged samples. It was observed that there was some level of porosity growth in the glass, although this was minimal as shown in Figure 9.
• Example 6 Validation of glass as a seal for SOFC stacks.
• Glass compositions 11 , 14 and 18 of Table 1 were selected for validation as a seal for SOFC stacks.
• Glass powder from each composition was converted to a paste with a suitable binder/solvent system, applied onto stack parts where a seal is required (either on the cell and/or interconnecting support structure), stacked to build a stack and then sintered with a suitable sintering temperature program as described in paragraph [0048] above to provide a SOFC stack with a hermetic seal.
• the stack sintering cycle included a binder burnout step as described in paragraph [0051] above in addition to the two steps required for glass sealing, to burn out organic materials present in the seal paste and the cell coatings.
• the stacks were operated at standard stack operating temperature of 750°C and subjected to about 100 thermal cycles over about 9000 hours.
• the summary of percent voltage degradation results for the stacks is provided in Table 3 and the percent voltage degradation of the stack with glass composition 18 with each thermal cycle is shown in Figure 10.
• the degradation% per thermal cycle includes both intrinsic degradation of the stack and the degradation purely due to thermal cycling, that is, degradation of the stack under normal operation as well as degradation due to thermal cycling combined together and normalised to number of thermal cycles the stack was subjected to. It is noted that if no thermal cycles had been conducted, the percent degradation would be expected to be less.
• the glass seals from the tested stacks were examined for porosity growth. Glass seals near the fuel exhaust in the stack were selected for the analysis as they were subjected to most reactive environment. Level of porosity can be determined by image analysis. An acceptable level of porosity can depend on many factors including the strength of the seal, level of thermal stresses generated which in turn depends on the CTE mismatch between glass and other components. Continuous porosity growth in a glass eventually leads to seal failure. Therefore, the useful life of a stack typically increases with the decrease in the rate of pore formation and growth.
• Figure 11 shows an optical microscopy image of the glass seal taken from the stack with glass composition 18 tested for 9200 hours. The image indicates that the glass seal exhibited minimal porosity growth.

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