Glass compositions for protective coatings

Abstract

The present invention relates to glass compositions and coating materials comprising the glass compositions that are suitable for coating metal components for use in high temperature and corrosive environments, such as electrochemical devices, particularly solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) stacks.

Description

[Technical Field]

[0001] The present invention relates to glass compositions for forming protective coatings on metal components exposed to high-temperature corrosive environments, including electrochemical devices or cells, such as solid oxide fuel cell stacks and similar devices, such as solid oxide electrolysis cell stacks, etc. The invention also extends to uses of the glass compositions, coating materials comprising the glass compositions, and methods of forming coatings on metal substrates. [Background technology]

[0002] An electrochemical device or electrochemical cell is a device that can generate electrical energy from a chemical reaction or use electrical energy to drive a chemical reaction. An example of an electrochemical device is a solid oxide fuel cell (SOFC) device, which is used to convert chemical energy, such as that of a gaseous fuel, such as hydrogen, into electrical energy through electrochemical oxidation. A typical SOFC stack consists of multiple interconnected cells, each having a porous ceramic cathode and a porous ceramic anode separated by a dense, ion-conducting solid oxide electrolyte. The stack typically includes a support structure made of one or more supports made of a suitable material, such as a suitable metal. During operation of the SOFC stack, a fuel, such as natural gas, is supplied to the anode of each cell, and an oxidant, such as air, is supplied to the cathode of each cell. The cell components are assembled to allow the fuel and oxidant to be supplied to the anode and cathode of each cell, respectively. Another example of an electrochemical device is a solid oxide electrolysis cell (SOEC) device, which is essentially a SOFC that operates in a regenerative (reverse) mode and achieves the electrolysis of water to produce hydrogen and oxygen gases.

[0003] The internal operating environment of electrochemical devices can be a high temperature, corrosive environment. The lifespan of metal components within these devices, such as fuel cells, and thus the lifespan of the device or fuel cell itself, can be extended by providing protective coatings for the metal components.

[0004] During operation, SOFC and SOEC stacks reach high temperatures, typically in the range of about 500°C to about 1000°C, and are subjected to intentional and unintentional temperature fluctuations (thermal cycling), ranging from as low as ambient to operating temperatures, with different heating and cooling rates. To ensure the commercial viability of SOFC and SOEC stacks, one or more protective coatings on the metal components must maintain their integrity and meet all of the above requirements under thermal cycling conditions and under constant-temperature operation for thousands of hours. For example, the thermal expansion and contraction mismatch between the coating material and the metal components of the SOFC or SOEC stack must be small enough so that thermal stresses generated during thermal cycling do not cause the coating to crack or spall. Furthermore, the coating must not adversely affect other SOFC or SOEC stack components by releasing undesirable volatiles that change their chemical or physical properties or by reacting with other components with which it comes into contact.

[0005] Various types of ceramic coatings have been developed as coatings in SOFC and SOEC stacks.

[0006] These protective coatings can be divided into two categories: electrically conductive and electrically blocking (electrically insulating). Electrically conductive coatings are typically applied over areas of the metal that come into contact with the cell electrodes. They protect the electrodes while facilitating the passage of electrical current by reducing the release of harmful substances from the metal. Such coatings are typically made of either reactive metal oxides or spinels. However, these coatings are generally not suitable for areas where glass seals are applied because they can react with the glass seals, potentially destroying them.

[0007] YSZ and alumina coatings are examples of electrical barrier coatings (electrically insulating coatings). Alumina coatings can be prone to spalling due to their large difference in coefficient of thermal expansion (CTE) from metals. Dense YSZ coatings can be difficult to fabricate, especially using simple, low-cost methods. If the coating is too thin or porous, it provides relatively little protection against harmful emissions from the metal substrate, such as Cr. Summary of the Invention [Problem to be solved by the invention]

[0008] The above drawbacks can degrade the protective coatings on the metal components and, consequently, the performance of the SOFC and SOEC stacks. Therefore, there is a need for alternative coatings suitable for use in electrochemical devices that protect the metal components from corrosion and reduce the risk of possible harmful emissions in high-temperature, corrosive environments, such as SOFC and SOEC stacks. [Means for solving the problem]

[0009] The reference to prior art in the specification is not an admission or suggestion that this prior art forms part of the common general knowledge in any jurisdiction, or that this prior art could reasonably be expected to be understood, considered relevant, and / or combined with other pieces of prior art by a person skilled in the art.

[0010] The present inventors have developed glass compositions capable of forming protective coatings on metal components for use in high-temperature corrosive environments. When applied, the glass coating advantageously has one or more crystalline phases and a glassy phase.

[0011] Broadly speaking, the present invention provides a glass composition comprising, as mole percent of the glass composition: - about 40 to about 50 mol% SiO2; - about 5 to about 8 mol% B2O3; - about 2 to about 5 mol% Al2O3; - about 0.5 to about 7 mol% TiO2; - 0 to about 3 mol% CeO2; and - about 30 to about 45 mole % SrO; and Here, the mole % of SiO2 is greater than the mole % of SrO.

[0012] In particular, the present invention provides a glass composition comprising, as mole % of the glass composition: - 42-48 mol% SiO2; - 5-7 mol% B2O3; - 2.5-4.5 mol% Al2O3; - 2-6 mol% TiO2; - 1-2.5 mol% CeO2; - 35 to 42 mol% SrO, Here, the mole % of SiO2 is greater than the mole % of SrO.

[0013] In a preferred form, the glass composition consists essentially of the components listed above.

[0014] In some embodiments, the glass composition is substantially free of alkali metal oxides.

[0015] In some embodiments, the glass composition is substantially free of BaO.

[0016] Advantageously, devices having metal components coated with the substantially BaO-free glass compositions described herein have improved operational life.

[0017] In some embodiments, the glass composition is substantially free of MgO and CaO. Advantageously, coatings formed from this composition are substantially free of undesirable crystalline phases, such as 2MgO.2Al2O3.5SiO2 and CaO.Al2O3.2SiO2. These crystalline phases, which have very low CTEs, are preferably avoided.

[0018] In some embodiments, the glass composition comprises, as mole % of the glass composition: - about 42 to about 48 mol % SiO2, preferably about 44.5 to about 45.5 mol % SiO2, - about 5 to about 7 mol% B2O3, preferably about 5.8 to about 6.2 mol% B2O3, - about 2.5 to about 4.5 mol% Al2O3; preferably about 3.2 to about 3.8 mol% Al2O3; - about 2 to about 6 mol % TiO2; preferably about 4.2 to about 4.8 mol % TiO2; - about 1 to about 2.5 mol% CeO2; preferably about 2 to about 2.5 mol% CeO2; - about 35 to about 42 mole % SrO; preferably about 37 to about 39 mole % SrO.

[0019] In particular, the glass composition may include, as mole % of the glass composition: - 43.5-46.5 mol% SiO2; - 5.5-6.6 mol% B2O3; - 2.8-4.2 mol% Al2O3; - 3.5-5.2 mol% TiO2; - 1.5-2.5 mol% CeO2; - 36-40.5 mol% SrO.

[0020] In a preferred form, the glass composition consists essentially of the components listed above.

[0021] In another aspect, the present disclosure provides a glass composition for coating a metal component.

[0022] In some embodiments, the metal component is in an electrochemical device.

[0023] In another aspect, the present invention provides a coating material for use in an electrochemical device, comprising the glass composition described herein. The electrochemical device can be any electrochemical device having metal components exposed to high temperatures and / or oxidizing environments. In a preferred embodiment, the electrochemical device is a SOFC or SOEC stack.

[0024] In some embodiments, the coating material comprises one or more crystalline phases and a glass phase, hi some embodiments, the one or more crystalline phases of the glass coating each comprise crystals having a structure selected from 2SrO.SiO2, SrO.SiO2, 3SrO.B2O3, 2SrO.TiO2.2SiO, SrO.3B2O3, and SrO.B2O3, and combinations thereof.

[0025] In some embodiments, the coating materials described herein comprise about 40 to about 60 volume percent of one or more crystalline phases and about 40 to about 60 volume percent of a glass phase, based on the total amount of glass coating material.

[0026] In some embodiments, the coating materials described herein have a thermal expansion and contraction mismatch with the metal they are coated on, which is defined as follows:

number

[0027] This is the glass transition temperature (T g ) at any temperature (T) up to about -0.02 to about 0.18. In an embodiment, the coating material has a -6 / ℃ ~ approx. 13×10 -6 / °C coefficient of thermal expansion (CTE).

[0028] In another aspect, 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 having one or more supports; and a glass coating composition described herein. Optionally, the electrochemical device comprises a seal, such as a glass seal covering the glass coating of the present invention. In a preferred embodiment, the electrochemical device is a SOFC or SOEC stack.

[0029] In another aspect, the present invention provides a method of forming a coating on a metal substrate for use in an electrochemical device, the method comprising: - applying a coating material described herein onto a metal substrate; and - subjecting the metal substrate and coating material to a heat treatment in which the glass composition of the coating material softens to provide a sintered glass while minimizing interconnected pores, and then undergoes controlled crystallization to provide a glass-ceramic comprising one or more crystalline phases and a glass phase; This forms a coating on the metal substrate.

[0030] In some embodiments, the heat treatment comprises a soaking step in which the glass composition is heated to a minimum temperature of the glass transition temperature of the composition or at least 50°C above the intended operating temperature of the metal component, whichever is higher. Preferably, the glass composition is heated to a temperature of about 550°C to about 1050°C.

[0031] In some embodiments, the soaking step has a duration of about 2 hours to about 5 hours.

[0032] In some embodiments, the glass composition is applied to the metal substrate as a slurry of glass powder.

[0033] In some embodiments, the coated metal component is in an electrochemical device, preferably in an SOEC or SOFC stack.

[0034] In some embodiments, the metal components are coated before being placed in an electrochemical device, preferably an SOEC or SOFC stack.

[0035] In another aspect, the present invention provides a use of a glass composition as described herein or a coating material as described herein to form a protective coating on a metal component, in an embodiment, the metal component is in an electrochemical device, preferably a SOFC or SOEC stack.

[0036] Further aspects of the invention and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description, by way of example only, and with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0037] [Figure 1] FIG. 1 is a schematic diagram of a portion of a solid oxide fuel cell stack showing the cell components exploded.

[0038] [Figure 2]FIG. 2 is a scanning electron microscope image of a metal substrate coated with a glass coating and having a glass seal on top of the glass coating.

[0039] [Figure 3] FIG. 3 is a schematic representation of a repeat unit of a fuel cell stack showing the metal components coated with a glass coating. DETAILED DESCRIPTION OF THE INVENTION

[0040] definition

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, preferred methods and materials are described. For purposes of the present invention, the following terms are defined below.

[0042] As used herein, the term "about" refers to a quantity, value, dimension, size, or amount that varies by 30%, 25%, 20%, 15%, or 10% relative to the reference quantity, value, dimension, size, or amount.

[0043] In this specification, unless the context requires otherwise, the term "comprises" and variations of this term, such as "comprising," "comprises (third person singular present tense)," and "included," are not intended to exclude further additives, components, integers, or steps.

[0044] Glass composition

[0045] In a broad sense, the present invention relates to a glass composition comprising, as mole percent of the glass composition: - about 40 to about 50 mol% SiO2; - about 5 to about 8 mol% B2O3; - about 2 to about 5 mol% Al2O3; - about 0.5 to about 7 mol% TiO2; - 0 to about 3 mol% CeO2; and - about 30 to about 45 mole % SrO; and Here, the mole % of SiO2 is greater than the mole % of SrO.

[0046] As used herein, the term "substantially free" in the context of a glass composition is intended to mean that the glass composition is free of the specified oxide(s), or that it contains only an amount of the specified oxide(s) that does not measurably affect the properties and / or performance of a glass coating formed from the glass composition. Accordingly, the term "substantially free of BaO" is understood to mean that the glass composition is completely free of BaO, or that it contains an amount of BaO that does not measurably affect the properties and / or performance of a glass coating formed from the glass composition. Thus, a glass coating may contain a small amount of BaO, provided that the amount does not substantially affect the properties and / or performance of a glass coating formed from the composition.

[0047] Without being bound by theory, the inventors hypothesize that the presence of BaO in the glass coating may shorten the service life of the protective coating on the metal component, and consequently, the service life of the electrochemical device having the metal component. BaO may readily react with Cr present in the metal to form BaCrO4 at the interface. BaCrO4 has a much higher CTE (coefficient of thermal expansion) than that of the metal component. Therefore, the large difference in CTE between BaCrO4 and the metal component onto which the glass composition is coated may cause the coating to separate from the metal component under thermal stress.

[0048] As can be seen, the combination of CeO2 and TiO2 is essential in the compositions of the present invention. Extensive testing by the inventors surprisingly revealed that the microstructure of similar compositions without CeO2 is characterized by the formation of undesirably large crystals, resulting in a less uniform structure. In thin coatings (approximately 5-10 μm), the presence of crystals of this size can create significant internal stresses at the crystal / matrix interface and, therefore, a relatively high risk of failure, especially when subjected to thermal cycling. At the same time, similar compositions without TiO2 resulted in excessively high crystallinity in the product. Thus, the inventors' research has revealed that a specific combination of TiO2 and CeO2 is essential for controlling both the level of crystallization and the size of individual crystals in the resulting material, i.e., for producing a crystallized glass-ceramic product with the desired ratio of glass and crystalline phases and with crystals small enough to ensure adequate coating uniformity.

[0049] Known compositions have not been able to evaluate this point. For example, U.S. Patent Application Publication No. 2013 / 0108946 discloses a glass-ceramic glass composition for gaskets used in electrochemical devices. However, this document does not consider the need for the combination of TiO2 and CeO2. Furthermore, this document does not consider forming a thin protective coating for metals from a composition that does not contain CaO and / or La2O3. As can be understood, the high Al2O3 content of the composition disclosed in U.S. Patent Application Publication No. 2013 / 0108946 may potentially be suitable for compositions containing CaO, MgO, La2O3, etc. Such a high concentration of Al2O3 in a composition that does not contain these oxides (such as the composition of the present invention) would result in a material with an unacceptably low coefficient of thermal expansion (CTE). In summary, the compositions of the present invention rely on a combination of crystalline phases different from those proposed or used in conventional materials, thereby obtaining a seal with properties suitable for use as a coating on metals used in SOFC / SOEC articles.

[0050] In a preferred embodiment, the glass composition is substantially free of alkali metal oxides.

[0051] The presence of substantial amounts of highly reactive alkali metal oxides can cause rapid corrosion of metals coated with the glass composition. Furthermore, alkali metals can interact with components in contact with the glass coating. For example, glass seals in SOFC / SOEC stacks that are in contact with the glass coating can be altered by interdiffusion of alkali metal oxides. Therefore, advantageously, coatings formed from glass compositions that are free of alkali metal oxides have relatively good protective properties and can be suitable for use in combination with glass seals.

[0052] In a preferred embodiment, the glass composition does not contain any further metal oxides, i.e., other metal oxides, in addition to SiO, BO, AlO, TiO, CeO, and SrO. In particular, the glass composition is substantially free of CaO, and / or MgO, and / or ZnO, and / or iron oxide.

[0053] In particular, as noted above, the glass composition is preferably substantially free of MgO and CaO, which, in the presence of Al2O3 and SiO2, can form undesirable crystalline phases with low coefficients of thermal expansion (CTE), such as 2MgO.2Al2O3.5SiO2 and CaO.Al2O3.2SiO2. The presence of low CTE crystalline phases in a glass coating can create thermal stresses that can cause the coating to delaminate from the metal substrate.

[0054] In this context, the terms "consisting essentially of" and "consisting of" are understood to mean that the composition does not contain any significant amount of any further oxides, i.e., the composition is substantially free of any oxides other than those specified in the composition.

[0055] The glass composition may contain any suitable range of oxide components within the broadest range specified for each oxide. The amount of each metal oxide in the composition may be appropriately selected depending on the desired properties of the glass coating formed from the glass composition.

[0056] Preferably, the glass composition comprises or consists essentially of, in mole % of the glass composition: 42 to 48 mol % SiO2, in particular about 43.5 to about 46.5 mol % SiO2, in particular 44.5 to 45.5 mol % SiO2; - 5 to 7 mol% B2O3, in particular about 5.5 to about 6.6 mol% B2O3, in particular 5.8 to 6.2 mol% B2O3; - 2.5 to 4.5 mol% Al2O3; in particular from about 2.8 to about 4.2 mol% Al2O3, in particular from 3.2 to 3.8 mol% Al2O3; - 2 to 6 mol % TiO2, in particular about 3.5 to about 5.2 mol % TiO2, more in particular 4.2 to 4.8 mol % TiO2; - 1 to 2.5 mol % CeO2, in particular about 1.5 to about 2.5 mol % CeO2, more in particular 2 to 2.5 mol % CeO2; 35 to 42 mol % SrO; in particular about 36 to about 40.5 mol % SrO, especially 37 to 39 mol % SrO.

[0057] The glass compositions of the present invention can be produced by methods known in the art. Glass compositions are typically provided in the form of glass powder. Glass may also be provided in the form of a frit, in which the glass frit is ground into a powder with a desired particle size distribution for use in a coating material. Briefly, the oxide components of the glass composition or their precursors are weighed out in the correct proportions to produce the desired glass composition. The weighed powders are mixed to produce a homogeneous mixture and then melted. The melt is poured onto a suitable surface, such as a marble or mold, and then rapidly cooled to provide a molten glass frit. The molten glass frit may be ground, for example, using a ball mill, to produce a glass powder. The ground glass powder can be appropriately sieved to provide a glass powder with a desired particle size or particle size distribution (PSD). The desired PSD can be selected, for example, depending on the technique used to apply the glass composition to a component.

[0058] The glass compositions of the present invention can be used as coatings for metal substrates in electrochemical devices. Accordingly, the present invention also provides the use of the glass compositions of the present invention for forming coatings on metal components used in electrochemical devices, in particular in SOFC or SOEC stacks. Advantageously, as shown in the examples and explained in more detail below, the glass compositions of the present invention are capable of forming protective glass coatings having properties that make them suitable for use in SOFC (and SOEC) stacks.

[0059] Glass Coating

[0060] The glass compositions of the present invention can be used to form glass coatings on metal substrates. In embodiments, the glass coatings are for metal components used in electrochemical devices, such as SOFC or SOEC stacks. Accordingly, the present invention provides coating materials formed from the glass compositions described herein.

[0061] Having a protective layer on the metal components in an electrochemical device can help extend the life of the device in two ways: first, by protecting the metal components from high temperature corrosion, and second, by preventing any harmful emissions (e.g., Cr) from the metal components. For example, if the electrochemical device is a SOFC or SOEC stack, harmful emissions such as Cr can degrade the fuel cells in the device over time.

[0062] The coating material may include one or more fillers. Preferably, the fillers are substantially chemically inert to the coating formed from the glass composition, allowing the fillers to be used without affecting the performance of the coating. The fillers also preferably have a thermal expansion coefficient similar to that of the glass and / or high strength. Examples of suitable fillers include, but are not limited to, powdered or fibrous ZrO, ceria, and strontium silicate.

[0063] In some embodiments, the coating material comprises about 80 to about 100 volume percent of a glass composition and 0 to about 20 volume percent of one or more fillers, based on the total amount of coating material.

[0064] The glass composition of the coating material may be subjected to a suitable sintering thermal cycle to provide a glass coating on a metal substrate suitable for use in an electrochemical device, particularly a SOFC or SOEC stack. The suitable thermal cycle may include a first step to allow the glass powder particles of the glass composition to soften and sinter to provide a sintered glass of relatively low viscosity, and a second step to allow the sintered glass to transform into a stable glass coating having a relatively high viscosity by forming crystals of many different compositions.

[0065] In some embodiments, the glass coating, which can then be formed from the sintered glass, comprises one or more crystalline phases and a glass phase. In some embodiments, the glass coating comprises about 40 to about 60 volume %, particularly about 45 to about 55 volume %, of one or more crystalline phases and about 40 to about 60 volume %, particularly about 45 to about 55 volume %, of the glass phase, based on the total amount of the glass coating.

[0066] In some embodiments, one or more crystalline phases of the glass coating comprise crystals having a structure selected from 2SrO.SiO2, SrO.SiO2, 3SrO.B2O3, 2SrO.TiO2.2SiO, SrO.3B2O3, and SrO.B2O3, and combinations thereof.

[0067] Without being bound by theory, it is proposed that the presence of B2O3 in a specified amount in the glass phase before crystallization improves the wetting of the metal component by the glass coating during the first heating step, resulting in a good bond between the glass coating and the metal component.

[0068] Eliminating BaO from glass coatings can advantageously extend the service life of devices having coated metal components. BaO can react with Cr in the metal components to form BaCrO4, which has a significantly different CTE than the metal components. Without being bound by theory, the inventors hypothesize that the presence of BaCrO4 at the interface can cause the coating to separate from the metal components during thermal cycling.

[0069] It has also been proposed that the presence of specified amounts of TiO2 may facilitate the completion of the formation of desired crystals in the glass coating during the immersion process, thereby helping to obtain a stable glass coating. Furthermore, the presence of some TiO2 in the residual glass phase may improve the barrier properties of the coating against undesirable interactions between Cr-containing metal components and Ba-containing components of electrochemical devices. For example, glass seals that may come into contact with the glass coating are a potential source of Ba ions. The presence of TiO2 in the glass phase of the coating may help to form a stable crystalline phase with the Ba ions at the seal-coating interface.

[0070] The presence of CeO2 promotes the formation of relatively fine and relatively uniformly distributed crystals within the resulting glass coating, thereby improving its homogeneity.

[0071] In embodiments, if the electrochemical device also has a glass seal, the glass seal can be a source of BaO. By minimizing the amount of BaO in the glass coating, the glass coating can act as a protective barrier from other sources of BaO within the electrochemical device.

[0072] Advantageously, SOEC / SOFC stacks having metal components coated with the glass coatings of the present invention may reduce Cr release from the metal components, thereby extending the useful life of the SOEC / SOFC stack. Cr release from SOEC / SOFC stacks having metal components coated as described herein may be about 100- to about 1000-fold lower than SOEC / SOFC stacks having uncoated metal components. For example, Cr release tests performed on metal samples coated with the compositions of the present invention have shown that Cr release from the coated metal surface is about 900- to about 1000-fold lower than that of uncoated metal samples. In this regard, the present inventors have confirmed that the presence of SrO in the compositions of the present invention functions to capture Cr released by the metal substrate.

[0073] The glass coating preferably has thermal expansion and contraction properties that closely match those of other components of the electrochemical device, particularly an SOFC or SOEC stack, within the temperature range in which the glass is rigid, i.e., below the glass transition temperature. This advantageously prevents thermal stresses generated during operation of the electrochemical device from exceeding the mechanical strength of the components of the electrochemical device. Thus, in some embodiments, the glass coating has a thermal expansion and contraction mismatch with the metal components it coats of about −0.02 (negative 0.02) to about 0.18 (positive 0.18) at any temperature up to the glass transition temperature of the glass phase, where the thermal expansion and contraction mismatch is defined as follows:

number

[0074] Here, "Glass" refers to the glass coating, and "Other" refers to the metal component. The glass transition temperature of the glass phase depends on its composition and can be determined by methods known in the art, for example, by performing dilatometry tests. Advantageously, glass samples produced from the glass compositions of the present invention exhibit stable dilatometry even when subjected to high-temperature air or fuel environments for extended periods of time.

[0075] The glass coating may have a coefficient of thermal expansion (CTE) that makes the glass coating suitable for use in electrochemical devices, particularly SOFC or SOEC stacks. The CTE may be substantially the same as the CTE of the coated metal components in the SOFC or SOEC stack or other electrochemical device. In some embodiments, the glass coating has a coefficient of thermal expansion (CTE) of about 10×10 -6 / ℃ ~ approx. 13×10 -6 / °C CTE.

[0076] The coating materials of the present invention can be useful for forming glass coatings on metal substrates for use in electrochemical devices, particularly SOFC or SOEC stacks. Accordingly, the present invention provides an electrochemical device, preferably an SOFC or SOEC stack, comprising one or more cells, each cell comprising a cathode, an anode, and a solid electrolyte; a support structure having one or more supports; and a coating material as described herein. The present invention also provides an electrochemical device, preferably an SOFC or SOEC stack, comprising one or more cells, each cell comprising a cathode, an anode, and a solid electrolyte; a support structure having one or more supports; a glass coating material; and a glass seal, wherein the glass coating material is as described herein and the glass seal is as described in WO 2022 / 165554, the entire contents of which are hereby incorporated by reference. The glass coating can be formed using a suitable sintering thermal cycle as described herein. The support structure is an interconnected support structure having one or more supports made of a suitable material, for example a suitable metal such as steel. In some embodiments, the support structure is a series of interconnected plates. It should be understood that each plate may be interpreted as a support for the support structure, and each cell may have one or more plates.

[0077] The present invention also provides a method of forming a coating on a metal substrate for use in an electrochemical device that is a SOFC or SOEC stack, the method comprising: - applying a coating material described herein onto a metal substrate; and - subjecting the metal substrate and coating material to a heat treatment in which the glass composition of the coating material softens to provide a sintered glass while minimizing interconnected pores, and then undergoes controlled crystallization to provide a glass-ceramic comprising one or more crystalline phases and a glass phase; This forms a coating on the metal substrate.

[0078] During the immersion process, the coating material transforms into a stable glass coating by forming crystals of many different compositions, such as 2SrO.SiO2, SrO.SiO2, 3SrO.B2O3, 2SrO.TiO2.2SiO, SrO.3B2O3, and SrO.B2O3, etc. These crystals preferably impart high mechanical strength and thermal expansion and contraction properties that closely match those of the other components of the SOFC / SOEC stack.

[0079] The constituent oxides are consumed during the immersion process to form stable crystalline phases, leaving behind a less reactive silicate glass matrix.

[0080] Preferably, the heat treatment comprises a soaking step in which the glass composition is heated to the glass transition temperature of the composition or to a temperature at least 50°C above the intended operating temperature of the metal component, whichever is greater. For example, if the metal component is for use in a SOFC or SOEC stack, the intended operating temperature may be from about 500°C to about 1000°C, and the soaking step comprises heating the glass composition to a temperature of at least about 550°C to about 1050°C.

[0081] Preferably, the soaking step has a duration of about 2 hours to about 5 hours.

[0082] In some embodiments, the glass composition is applied to the metal substrate as a glass powder slurry, which is made using a suitable vehicle, such as alcohol.

[0083] During heat treatment, the glass powder particles soften and sinter together to minimize interconnecting pores and form a glass coating on the metal surface.

[0084] In embodiments, the metal substrate comprises a metal component for an electrochemical device.

[0085] In embodiments, the metal components are coated before being placed in an electrochemical device or in an SOEC or SOFC stack, i.e., the glass composition is applied to the metal components and subjected to a heat treatment step before the metal components are assembled in the electrochemical device.

[0086] In some embodiments, the glass composition is applied to the metal component prior to placement in the electrochemical device, and the heat treatment step is performed in situ within the electrochemical device.

[0087] An example of a SOFC stack is shown in Figure 1, which is a schematic diagram of a portion of a SOFC stack (1) showing the cell components, namely, the cathode (2), anode (3), electrolyte (4), support structure (5), and glass seal (6), in an exploded view.

[0088] The diagram in Figure 3 showing multiple units stacked in a fuel cell stack shows the support structure for the metal interconnect plates, to each of which a glass coating according to the present invention is applied, and the glass seal that provides a seal between the electrolyte layer and the coated support layer.

[0089] Advantageously, SOFC stacks having metal components coated with the coating material of the present invention operated for extended periods at standard operating temperatures experience less degradation than SOFC stacks having uncoated components. Thus, in some embodiments, SOFC (or SOEC) stacks of the present invention, when operated for about 2,000 hours or about 5,000 hours and subjected to multiple thermal cycles from room temperature (about 20° C. to about 25° C.) to the intended operating temperature of the SOFC (or SOEC) stack, experience an overall performance degradation of less than 10%, particularly less than 6%, more particularly less than about 3%, and even more particularly less than 2%.

[0090] It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more individual features mentioned or apparent from the specification or drawings, all of which different combinations constitute various alternative aspects of the invention. [Example]

[0091] The present invention will be further described by one or more non-limiting examples. Those skilled in the art will understand that many modifications may be made without departing from the spirit and scope of the invention.

[0092] Example 1. Glass composition

[0093] Eight glass compositions were evaluated to identify glass compositions that may be suitable for coating metal components in electrochemical devices. The glass compositions are shown in Table 1. Values ​​within the required range are shown in bold. Only compositions 1 through 5 were able to form satisfactory coatings on metal substrates.

[0094] Table 1. Glass composition

[0095] [Table 1]

[0096] Condition (a): The mole percent of SiO2 is greater than the mole percent of SrO.

[0097] Glass coatings formed from compositions satisfying condition (a) form crystals such as 2SrO.SiO2, SrO.SiO2, 3SrO.B2O3, 2SrO.TiO2.2SiO, SrO.3B2O3, and SrO.B2O3 during the coating process. These crystals impart high mechanical strength to the coating. When present in the appropriate proportions, these crystals also contribute to the thermal expansion and contraction properties of the coating, thereby allowing the thermal expansion and contraction properties of the coating to be well matched to those of the other components.

[0098] Condition (b): The thermal expansion and contraction differential ratio of the glass coating relative to the metal component to which it is applied, expressed as % expansion differential as defined herein, is between −0.02 and 0.18 for temperatures below the glass transition temperature of the retained glass phase.

[0099] Glass coatings having a % differential expansion within a predetermined range have a relatively low risk of developing tensile thermal stresses within the coating when the coated metal components are exposed to relatively high temperatures and corrosive operating environments, such as during operation of a SOFC / SOEC stack.

[0100] Glass coatings with a % differential expansion within a given range have a low enough compressive stress to prevent delamination of the coating from the metal.

[0101] Condition (c): The glass coating must be continuous and have good adhesion to the metal substrate.

[0102] Furthermore, compositions 1 to 5, in which the various components of the composition were within the required ranges, met all the conditions for a glass coating that would exhibit good performance.

[0103] Compositions 6 to 9 have at least one component whose concentration is outside the required range. Compositions 6 to 9 do not satisfy at least one of the conditions required for a glass coating that exhibits good performance.

[0104] Example 2. Characterization of glass coatings by SEM

[0105] Scanning electron microscopy (SEM) was performed to determine the microstructure of the glass coating. An example SEM image is shown in FIG. 2, showing a thin glass composition coating and an overlying glass seal. The glass composition forms a continuous, highly adherent coating on the metal substrate. Both multiple crystalline and glass phases are present in the coating. The percentages of the glass and crystalline phases were estimated from the SEM images using image analysis, with the crystalline phase being about 40 to about 60% by volume and the glass phase being about 40 to about 60% by volume, based on the total amount of glass coating.

[0106] As will be appreciated, an overlying glass seal is not essential to the use of the glass composition coating of the present invention, and in many applications the glass coating may be used without such a cover.

[0107] Example 3. Results of Cr release tests on metal surfaces with and without glass coating

[0108] The effectiveness of glass coatings in preventing chromium release from metals was investigated by capturing chromium from the metal using a getter material (strontium carbonate coated on a yttria-stabilized zirconia sheet) in contact with the coated metal. This mechanism was examined by measuring the trapped chromium content of the SrCO3 coating by inductively coupled plasma spectroscopy (ICP) after 350 hours in a furnace at 800°C. This test was repeated for uncoated metal and for metals coated with three different coatings, and the results are shown in Table 2.

[0109] Table 2. Cr release test

[0110] [Table 2]

[0111] As shown in Table 2, the Cr release from metal plates coated according to the present invention is more than 1000 times lower than the Cr release from uncoated metal. Metals coated with the glass coatings described herein have shown improvements in Cr release of 5% or more, or even 10% or more, compared to alternative coatings.

[0112] The reduction in Cr release indicates the protective properties of the coating and the ability of the glass coating to protect metal components in high temperature and highly corrosive environments.

[0113] By reducing the amount of Cr released from the metal components by approximately 1 / 1000, the rate of cell performance degradation can be slowed, thereby extending the useful life of the SOFC / SOEC stack.

[0114] Example 4. Extending the service life of SOFC / SOEC stacks with glass coating

[0115] When a SOFC / SOEC stack with multiple fuel cells and interconnects having metal components coated with the glass coating of the present invention and sealed with a suitable glass is operated for up to 5,000 hours and subjected to multiple thermal cycles from room temperature to normal operating temperature, the fuel cells are expected to experience less than a 10% overall performance degradation.

Claims

1. 1. A glass composition comprising, in mole percent of said glass composition: 42 to 48 mol% SiO ２ ; 5 to 7 mol% B ２ O ３ ; 2.5 to 4.5 mol% Al ２ O ３ ; 2 to 6 mol% TiO ２ ; 1 to 2.5 mol% CeO ２ ; 35 to 42 mol% SrO, Including, Here, SiO ２ The glass composition of claim 1, wherein the mole percent of SrO is greater than the mole percent of SrO.

2. The glass composition of claim 1 , wherein the glass is substantially free of BaO.

3. The glass composition according to claim 1 or 2, wherein the glass composition is substantially free of alkali metal oxides.

4. The glass composition according to any one of claims 1 to 3, wherein the glass composition is substantially free of MgO and CaO.

5. The glass composition of claim 1 consisting essentially of the components specified.

6. The composition comprises, as mole percent of the glass composition: 43.5 to 46.5 mol% SiO ２ ; 5.5 to 6.6 mol% B ２ O ３ ; 2.8 to 4.2 mol% Al ２ O ３ ; 3.5 to 5.2 mol% TiO ２ ; 1.5 to 2.5 mol% CeO ２ ; 36 to 40.5 mol% SrO, The glass composition according to any one of claims 1 to 5, comprising:

7. The composition comprises, as mole percent of the glass composition: 44.5 to 45.5 mol% SiO ２ , 5.8 to 6.2 mol% B ２ O ３ , 3.2 to 3.8 mol% Al ２ O ３ ; 4.2 to 4.8 mol% TiO ２ ; 2 to 2.5 mol% CeO ２ ; 37 to 39 mol% SrO, The glass composition according to any one of claims 1 to 6, comprising:

8. 8. The glass composition according to claim 6 or claim 7, consisting essentially of the specified components.

9. 9. A coating material for coating a metal component, said metal component being for use in an electrochemical device, said coating material comprising the glass composition of any one of claims 1 to 8.

10. The one or more crystalline phases of the glass coating are each selected from the group consisting of 2SrO, 2SiO, ... ２ , SrO.SiO ２ , 3SrO.B ２ O ３ , 2SrO.TiO ２ .. 2SiO, SrO. 3B ２ O ３ , SrO.B ２ O ３ 10. The coating material of claim 9, comprising crystals having a structure selected from:

11. 11. The coating material of claim 9 or 10, wherein the glass coating comprises about 40 to about 60 volume % of one or more crystalline phases and about 40 to about 60 volume % of a glass phase, based on the total amount of the glass coating.

12. The glass coating has a thermal expansion and contraction mismatch with the metal being coated, the mismatch being determined by the following formula: [Equation 1] and is defined as about −0.02 to about 0.18 at any temperature up to the glass transition temperature of the glass phase.

13. The glass coating is about 10×10 －６ / ℃ ~ approx. 13×10 －６ 12. The coating material according to any one of claims 8 to 11, having a coefficient of thermal expansion (CTE) of 1 / °C.

14. Electrochemical device having a coated metal component, said metal component being coated with a coating material according to any one of claims 9 to 13.

15. 1. An electrochemical device comprising: - one or more cells, each cell comprising a cathode, an anode, and a solid electrolyte; a support structure having one or more supports; and - a coating material according to any one of claims 9 to 13, An electrochemical device comprising:

16. 16. The electrochemical device of claim 15, wherein the electrochemical device is an SOFC or SOEC stack.

17. 1. A method of forming a coating on a metal substrate for use in an electrochemical device, the method comprising: - applying a coating material according to any one of claims 9 to 13 onto a metal substrate; and - subjecting the metal substrate and coating material to a heat treatment in which the glass composition of the coating material softens to provide a sintered glass while minimizing interconnected pores, and then undergoes controlled crystallization to provide a glass-ceramic comprising one or more crystalline and glass phases; thereby forming a coated metal component; A method comprising:

18. 18. The method of claim 17, wherein the heat treatment comprises a soaking step in which the glass composition is heated to a minimum temperature of the glass transition temperature of the composition or at least 50°C above the intended operating temperature of the metal component, whichever is higher.

19. The method of claim 17, wherein the glass composition is heated to a temperature of about 550°C to about 1050°C.

20. 20. The method of any one of claims 17 to 19, wherein the soaking step has a duration of about 2 hours to about 5 hours.

21. The method of any one of claims 17 to 20, wherein the glass composition is applied to the metal substrate as a slurry of glass powder.

22. 22. The method of any one of claims 17 to 21, wherein the coated metal component is part of the electrochemical device and the heat treatment step is carried out before the metal component is assembled into the electrochemical device.

23. A method according to any one of claims 17 to 21, wherein the coated metal component is part of the electrochemical device and the heat treatment step is carried out in situ within the electrochemical device.

24. The method of any one of claims 17 to 23, wherein the electrochemical device is an SOEC or SOFC stack.

25. Use of a glass composition according to any one of claims 1 to 8 or a coating material according to any one of claims 9 to 13 for forming a protective coating on a metal component in an electrochemical device.

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