Patent Description:
Manifolds for solid oxide fuel cells can be made of magnesia-magnesium aluminate spinel ceramics. The starting materials for the ceramics may be commercial grade materials that include impurities that may provide undesired colors for the manifold or potentially may contaminate other components within a solid oxide fuel cell. <CIT> is concerned with non-conductive ceramic material with a composition that is matched in such a way to a coefficient of thermal expansion predetermined by a metallic material to which it is connected in a substance-locking manner that the coefficients of thermal expansion are identical, and also to a method for its production. Improvements in manifold compositions are desired.

Embodiments are illustrated by way of example and are not limited by the accompanying figures.

Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the invention.

The following description in combination with the figures is provided to assist in understanding the teachings disclosed herein. The following discussion will focus on specific implementations and embodiments of the teachings. This focus is provided to assist in describing the teachings and should not be interpreted as a limitation on the scope or applicability of the teachings.

As used herein, color space coordinates are expressed in terms of CIE <NUM> (CIELAB) coordinates, L*, a*, and b*.

The term "dopant" is intended to mean a compound that is intentionally added to affect a property of a material to which such compound is added.

Group numbers corresponding to columns within the Periodic Table of Elements are based on the IUPAC Periodic Table of Elements, version dated January <NUM>, <NUM>.

The terms "comprises," "comprising," "includes," "including," "has," "having," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of features is not necessarily limited only to those features but may include other features not expressly listed or inherent to such process, method, article, or apparatus.

The use of "a" or "an" is employed to describe elements and components described herein. This description should be read to include one or at least one and the singular also includes the plural, or vice versa, unless it is clear that it is meant otherwise.

The materials, methods, and examples are illustrative only and not intended to be limiting. To the extent not described herein, many details regarding specific materials and processing acts are conventional and may be found in textbooks and other sources within the solid oxide fuel cell and ceramic arts.

An apparatus can include a sintered ceramic component. The apparatus can be an energy generating apparatus that includes one or solid oxide fuel cells or can be a gas-to-liquid membrane system. In an embodiment, the sintered ceramic component can be a manifold to provide a gas to or remove a gas from the apparatus or can be another component that is used in conjunction with the solid oxide fuel cell(s) or gas-to-liquid membrane system. Such other component may be used to connect a plurality of solid oxide fuel cells or systems to each other.

The sintered ceramic component may include a high purity magnesia magnesium aluminate ("MMA") that is intentionally doped with one or more impurities to provide good sintering properties, high density, a particular color, if needed or desired, and not have other impurities that could adversely affect the color or adversely interact with other components in the apparatus.

The sintered ceramic component is defined in claim <NUM>.

The desired dopant includes CaO, TiO<NUM>, or any combination thereof. In an embodiment, the desired dopant content is at least <NUM> wt. %, at least <NUM> wt. %, at least <NUM> wt. %, or at least <NUM> wt. %, and in another embodiment, the desired dopant content is no greater than <NUM> wt. %, no greater than <NUM> wt. %, no greater than <NUM> wt. %, or no greater than <NUM> wt. In a particular embodiment, the desired dopant content is in a range of <NUM> wt. % to <NUM> wt. %, <NUM> wt. % to <NUM> wt. %, <NUM> wt. % to <NUM> wt. %, or <NUM> wt. % to <NUM> wt.

The desired dopant concentrations may be tailored more closely to particular dopants. For CaO, the CaO content can be at least <NUM> wt. %, at least <NUM> wt. %, at least <NUM> wt. %, or at least <NUM> wt. %, or may be no greater than <NUM> wt. %, no greater than <NUM> wt. %, no greater than <NUM> wt. %, or no greater than <NUM> wt. In a particular embodiment having CaO, the CaO content is in a range of <NUM> wt. % to <NUM> wt. %, <NUM> wt. % to <NUM> wt. %, <NUM> wt. % to <NUM> wt. %, <NUM> wt. % to <NUM> wt. %, or <NUM> wt. % to <NUM> wt. For Y<NUM>O<NUM>, the Y<NUM>O<NUM> content can be at least <NUM> wt. %, at least <NUM> wt. %, at least <NUM> wt. %, or at least <NUM> wt. %, or may be no greater than <NUM> wt. %, no greater than <NUM> wt. %, no greater than <NUM> wt. %, or no greater than <NUM> wt. In a particular embodiment having Y<NUM>O<NUM>, the Y<NUM>O<NUM> content is in a range of <NUM> wt. % to <NUM> wt. %, <NUM> wt. % to <NUM> wt. %, <NUM> wt. % to <NUM> wt. %, or <NUM> wt. % to <NUM> wt. For TiO<NUM>, the TiO<NUM> content can be at least <NUM> wt. %, at least <NUM> wt. %, at least <NUM> wt. %, or at least <NUM> wt. %, or may be no greater than <NUM> wt. %, no greater than <NUM> wt. %, no greater than <NUM> wt. %, or no greater than <NUM> wt. In a particular embodiment having TiO<NUM>, the TiO<NUM> content is in a range of <NUM> wt. % to <NUM> wt. %, <NUM> wt. % to <NUM> wt. %, <NUM> wt. % to <NUM> wt. %, or <NUM> wt. % to <NUM> wt.

In a particular embodiment, some compounds may not be desired dopants. For example, the desired dopant may not include Cr<NUM>O<NUM>, NiO, CuO, or any combination thereof. Such compounds may react with MgO or Al<NUM>O<NUM> to form a different compound.

The ceramic material may be co-doped with a first dopant and a second dopant that is different from the first dopant. The first dopant can include CaO, Y<NUM>O<NUM>, or TiO<NUM>, and the second dopant includes CaO, Y<NUM>O<NUM>, TiO<NUM>, Fe<NUM>O<NUM>, SrO, BaO, Sc<NUM>O<NUM>, La<NUM>O<NUM>, ZrO<NUM>, HfO<NUM>, V<NUM>O<NUM>, Nb<NUM>O<NUM>, Ta<NUM>O<NUM>, Mo<NUM>O<NUM>, W<NUM>O<NUM>, Co<NUM>O<NUM>, or any combination thereof. In an embodiment, the first dopant is present in the final composition at a higher concentration than the second dopant, and in another embodiment, the first dopant is present in the final composition at a lower concentration than the second dopant. In a particular embodiment, a combination of the first and second dopants is in a range of <NUM> wt. % to <NUM> wt. % of the final composition.

Most of the sintered ceramic component may include magnesia and alumina. In an embodiment, the composition of the sintered ceramic component can be selected to achieve a coefficient of thermal expansion (CTE) to match another component to which the sintered ceramic component may be coupled. CTEs as described herein are the CTEs as measured from <NUM> to <NUM>. In conjunction with the annealing conditions disclosed above, the CTE can be at least <NUM> ppm/°C, such as at least <NUM> ppm/°C or at least <NUM> ppm/°C. In another embodiment, the sintered ceramic component may have a CTE of no greater than <NUM> ppm/°C, such as no greater than <NUM> ppm/°C, or no greater than <NUM> ppm/°C. In yet another embodiment, the sintered ceramic component can have a CTE in a range of <NUM> ppm/°C to <NUM> ppm/°C, <NUM> ppm/°C to <NUM> ppm/°C, or <NUM> ppm/°C to <NUM> ppm/°C. Depending on the applications of the sintered ceramic component, the CTE of the sintered ceramic component can match closely to that of the material to be coupled. For example, the sintered having a CTE in a range of <NUM> ppm/°C to <NUM> ppm/°C is well suited for use with an SOFC. In another embodiment, the sintered ceramic component having a CTE of <NUM> ppm/°C to <NUM> ppm/°C can be suitable for use with a gas-to-liquid membrane system.

In another embodiment, the content may be expressed as an amount of MgO and another amount of Al<NUM>O<NUM>. In an embodiment, the MgO has a content that is at least <NUM> wt. %, at least <NUM> wt. %, or at least <NUM> wt. %, and the MgO has a content that is no greater than <NUM> wt. %, no greater than <NUM> wt. %, or no greater than <NUM> wt. In a particular embodiment, the MgO has a content that is in a range of <NUM> wt. % to <NUM> wt. %, <NUM> wt. % to <NUM> wt. %, <NUM> wt. % to <NUM> wt. In an embodiment the Al<NUM>O<NUM> has a content that is at least <NUM> wt. %, at least <NUM> wt. %, or at least <NUM> wt. %, and in another embodiment, the Al<NUM>O<NUM> has a content that is no greater than <NUM> wt. %, no greater than <NUM> wt. %, or no greater than <NUM> wt. In a particular embodiment, the Al<NUM>O<NUM> has a content that is in a range of <NUM> wt. % to <NUM> wt. %, <NUM> wt. % to <NUM> wt. %, <NUM> wt. % to <NUM> wt.

The desired dopants may help to achieve good density without having to sinter the ceramic component at too high of a temperature or having relatively high levels of undesired impurities. The sintered ceramic component has a density that is at least <NUM>% of theoretical density, at least <NUM>% of theoretical density, or at least <NUM>% of theoretical density, and in another embodiment, no greater than <NUM>% of theoretical density, no greater than <NUM>% of theoretical density, or no greater than <NUM> % of theoretical density. In a particular embodiment, the sintered ceramic component has a density in a range of <NUM>% to <NUM>% of theoretical density, <NUM>% to <NUM>% of theoretical density, or <NUM>% to <NUM>% of theoretical density.

Density may also be expressed on a relative basis. The relative densities can be expressed as a difference in percentages of theoretical density. As an example, two different components have different compositions and are sintered under the same conditions. One of the components may have a density that is <NUM>% of theoretical density, and the other component may have a density that is <NUM>% of theoretical density. The density of the one component is <NUM>% higher than the density of the other component. In an embodiment, when sintered under the same conditions, the sintered ceramic component has a density that is at least <NUM>%, at least <NUM>%, at least <NUM>%, or at least <NUM>% higher than a density of a different sintered ceramic component that includes at least <NUM> wt. % MgO, all impurities are present at a combined impurity content of less than <NUM> wt. %, a remainder comprising Al<NUM>O<NUM>, and other than MgO and Al<NUM>O<NUM>, no other metal oxide is present at a content of at least <NUM> wt. In another embodiment, when sintered under the same conditions, the sintered ceramic component has a density that is no greater that <NUM>%, no greater than <NUM>%, no greater than <NUM>%, or no greater than <NUM>% higher than a density of a different sintered ceramic component that includes at least <NUM> wt. % MgO, all impurities are present at a combined impurity content of less than <NUM> wt. %, a remainder comprising Al<NUM>O<NUM>, and other than MgO and Al<NUM>O<NUM>, no other metal oxide is present at a content of at least <NUM> wt. In a particular embodiment, when sintered under the same conditions, the sintered ceramic component has a density that is in a range of <NUM>% to <NUM>%, <NUM>% to <NUM>%, <NUM>% to <NUM>% higher than a density of a different sintered ceramic component that includes at least <NUM> wt. % MgO, all impurities are present at a combined impurity content of less than <NUM> wt. %, a remainder comprising Al<NUM>O<NUM>, and, other than MgO and Al<NUM>O<NUM>, other metal oxide is present at a content of at least <NUM> wt.

The color of the sintered ceramic component can be expressed in CIELAB coordinates. In an embodiment, the sintered ceramic component has L* is at least <NUM>, at least <NUM>, or at least <NUM>; a* is in a range of -<NUM> to +<NUM>, -<NUM> to +<NUM>, or -<NUM> to +<NUM>; and b* is in a range of +<NUM> to +<NUM>, +<NUM> to +<NUM>, or +<NUM> to +<NUM>. A user of the sintered ceramic component may desire that the sintered ceramic component have a relatively white appearance. In an embodiment, the sintered ceramic component has L* is at least <NUM>, at least <NUM>, or at least <NUM>; a* is in a range of -<NUM> to +<NUM>, -<NUM> to +<NUM>, or -<NUM> to +<NUM>; and b* is in a range of +<NUM> to +<NUM> +<NUM> to +<NUM>, or +<NUM> to +<NUM>. Contamination, rather than color, may more of a concern. Alternatively, a user may desire that the sintered ceramic component have a yellow or dark yellow appearance. In a particular embodiment, the sintered ceramic component has L* is at least <NUM>, at least <NUM>, or at least <NUM>; a* is in a range of <NUM> to +<NUM> +<NUM> to +<NUM> or +<NUM> to +<NUM>; and b* is in a range of +<NUM> to +<NUM>, +<NUM> to +<NUM>, or +<NUM> to +<NUM>.

A process of forming the sintered ceramic compound can include obtaining appropriate powders that make up the sintered ceramic compound. Sources for the MgO and Al<NUM>O<NUM> may include those particular compounds or can include other sources. In an embodiment, powders of MgO and spinel (MgAl<NUM>O<NUM>) may be used. In another embodiment, a powder including a fused MgO-containing MgAl<NUM>O<NUM> may be used. Thus, the relative amounts of MgO and Al<NUM>O<NUM> may be controlled in a variety of ways. One or more desired dopants can be added. Any of the dopants previously described may be added at the amounts previously described. In another embodiment, the dopants may be added using a different compound. For example, CaCO<NUM> may be used instead of or in conjunction with CaO. During the formation sequence, CaCO<NUM> decomposes into CaO and CO<NUM>, thus, leaving CaO in the sintered ceramic component. The amount of CaCO<NUM> in the starting material may be adjusted to account for a higher molecular weight as compared to CaO. The powders may be agglomerated, milled, subjected to another particle size changing operation, or the like, if needed or desired. In an embodiment, the powders may have different particle sizes for the same material or different materials. The powders for the ceramic component can be combined before, during or after the powders have an appropriate particle size. The powders can include at least <NUM> wt. % MgO; at least one desired dopant, wherein each dopant of the at least one desired dopant has a desired dopant content of at least <NUM> wt. %; all impurities are present at a combined impurity content of less than <NUM> wt. %; and a remainder comprising Al<NUM>O<NUM>.

The process can further include combining the powders and a binder, another material, or a combination thereof to form a green mixture. The binder or other material can include a polyacrylate, a polyvinyl alcohol, a polyethylene glycol, another suitable material to aid in mixing or binding the powders, or any combination thereof. A solvent can be used if needed or desired. The solvent can include water, alcohol, glycol, another suitable liquid that can aid in allow for better mixing of the powders and the binder, or any combination thereof. One or more additional materials can be added if needed or desire. Such additional materials can include a surfactant, a polyvinyl alcohol, a polyvinyl butyral, a butyl benzyl phthalate, a fish oil, or any combination thereof.

The method can further include shaping the green mixture having a shape corresponding to the sintered ceramic component. The shape can be larger than the final sintered ceramic component due to densification during a subsequent sintering operation.

The object can be heated during one or more operations to form the sintered ceramic component. The object may be heated to a first temperature to drive out volatile components, such as the solvent. The temperature can be in a range of <NUM> to <NUM> for a time in a range of <NUM> hour to <NUM> hours. The pressure during volatile component drive off can be at atmospheric pressure or under vacuum pressure. If vacuum pressure is used, the pressure should not be so low as to cause any cracks, fractures, or other defects to form in the object. The temperature can be increased to burn out the binder and any other carbon-containing material. The temperature for the burn out operation can be in a range of <NUM> to <NUM> for a time in a range of <NUM> to <NUM> hours. The pressure for the burn out can be performed at atmospheric pressure, at a higher pressure than atmospheric pressure, or under vacuum. Gas evolved during burn out may be difficult to remove if the pressure is too higher. In an embodiment, the pressure may not be greater than <NUM> kPa. If the pressure is too low, cracks, fractures, or other defects may form in the object. In an embodiment, the pressure may be at least <NUM> kPa-abs. In another embodiment, pressures higher or lower than recited may be used. The burn out can be performed using an oxygen-containing gas, such as O<NUM>, ozone, N<NUM>O, NO, or the like. O<NUM> may be in the form of air (<NUM> vol. % O<NUM>) or may be provided at a concentration different from air. Air may be flown into the furnace during the burn out of the binder or other carbon-containing material.

The temperature can be further increased to form the sintered ceramic component. The one or more dopants in the object can help to lower the sintering temperature of the material. Thus, the sintering can be performed lower than the magnesia-alumina material by itself. The sintering can be performed at a temperature less than <NUM>. Without dopant, the magnesia-alumina material will not properly sintered until the material is well above <NUM>, such as closer to <NUM>. In an embodiment, sintering is performed at a temperature of at least <NUM>, at least <NUM>, or at least <NUM>, and in another embodiment, sintering is performed at a temperature no greater than <NUM>, no greater than <NUM>, or no greater than <NUM>. In a particular embodiment, sintering is performed at a temperature in a range of <NUM> to <NUM>, <NUM> to <NUM>, or <NUM> to <NUM>. The sintering may be performed for a time to allow sufficient sintering and densification to occur. In an embodiment, the time is at least <NUM> hour, at least <NUM> hours, or at least <NUM> hours, and in another embodiment, the time may be no greater than <NUM> hours, no greater than <NUM> hours, or no greater than <NUM> hours. In a particular embodiment, the time is in a range of <NUM> hour to <NUM> hours, <NUM> hours to <NUM> hours, or <NUM> hours to <NUM> hours. Sintering can be performed at a pressure of at least atmospheric pressure (also referred to as pressureless sintering) to a relatively high pressure. The pressure can be applied in the form of pressurized gas, hot pressing or hot isostatic pressing. Sintering can be performed using an oxygen-containing gas, such as O<NUM>, ozone, N<NUM>O, NO, or the like. O<NUM> may be in the form of air (<NUM> vol. % O<NUM>) or may be provided at a concentration different from air.

Although many values of sintering parameters are described, after reading this specification, skilled artisans will appreciate that values outside those disclosed may be used without deviating from the concepts herein. The operations described above may be performed during a single heating cycle or during different heating cycles. Additional operations may be performed during heating. For example, during cooling after sintering, the sintered ceramic component may be allowed to soak at a temperature to reduce the likelihood of building up too much strain within the component. Controlling the heating rate and cooling rate may also be used to reduce the likelihood of building up too much strain and cracking within the component.

The sintered ceramic component is well suited for use as a gas manifold or another component used in conjunction with a solid oxide fuel cell, a gas-to-liquid membrane system, or for another application where the sintered ceramic component configured such that it withstand exposure to a relatively high (i.e., greater than <NUM>) during normal operating conditions of an apparatus.

Many different aspects and embodiments are possible. Some of those aspects and embodiments are described herein. After reading this specification, skilled artisans will appreciate that those aspects and embodiments are only illustrative. Additionally, those skilled in the art will understand that some embodiments that include analog circuits can be similarly implemented using digital circuits, and vice versa.

The examples presented below demonstrate that sintered ceramic components having compositions as described above may be formed at sintering temperatures that are less than <NUM> and achieve desired densities and visible appearances. The sintered ceramic components may have different colors depending on the dopants and dopant concentrations selected. Samples were generated for analysis of sintering temperatures, densities when sintered at <NUM> for <NUM> hours, and color information of the sintered materials.

Samples were generated with different compositions. One sample was made using conventional commercial-grade starting materials that were relatively high in impurities and is referred to as the Impure Sample. Samples were made with starting materials that had relatively low impurity levels and are referred to the Pure <NUM> Sample and the Pure <NUM> Sample. Tables <NUM> and <NUM> below include particle size distributions and the compositions of the Impure and Pure <NUM> and <NUM> Samples. For particle size distributions, d<NUM>, d<NUM>, and d<NUM> represent the <NUM>th percentile, <NUM>th percentile, and the <NUM>th percentile of the Impure and Pure Samples.

Other samples were generated using the starting materials with the relatively low impurity levels and had dopants at different concentrations added to such starting materials. In particular, doped samples below were generated using the material used to form the Pure <NUM> Sample, except for samples doped or co-doped with TiO<NUM> and the Y1-Ca0. <NUM> Sample, each of which were generated using the material used to form the Pure <NUM> Sample. Below are tables with samples and the doping concentrations.

After preparing the samples, samples were heated to <NUM> at a rate of <NUM>/minute to obtain data for dilatometry curves. Other samples were heated to <NUM> for <NUM> hours in air to obtain densification data.

Dilatometry curves were generated for the samples and are included in <FIG>, which have %dL/dT as a function of temperature during the heating to <NUM>. <FIG> includes a dilatometry curve of the Impure Sample. <FIG> and <FIG> include dilatometry curves of the Pure <NUM> and Pure <NUM> Samples. <FIG> include the dilatometry curves for selected doped and co-doped samples.

Densification was performed at <NUM> for <NUM> hours in air except as explicitly noted. <FIG> includes a plot of densification, expressed as percentage of theoretical density as a function of doping concentration for particular dopants. The material for the Impure Sample has typically has a densification in a range of <NUM>% to <NUM>%. Table <NUM> includes the densification data.

Samples were checked for their visible appearance to the human eye. Samples were inspected after densification, and after annealing the densified samples were annealed at <NUM> for <NUM> hours in air. Table <NUM> includes the visual appearance information.

Samples after densification were analyzed for their color in terms of color space coordinates L*, a* and b*. YI E313 [D65/<NUM>] is yellowness as measured using ASTM standard E313 using the version in effect as of the filing date of this specification. D65 is the standard illuminant, and <NUM> refers to the angle of insert light. Table <NUM> includes color space coordinate and yellowness information.

The Impure Sample has good sintering and densification properties; however, the Impure Sample has a high level of impurities due to commercial-grade starting materials being used. The Pure <NUM> Sample has a white appearance, but the density is <NUM>% when exposed to <NUM> for <NUM> hours. In some applications, a densification of at least <NUM>% may be needed or desired. Thus, sintering would need to be performed at a temperature greater than <NUM> or the exposure at <NUM> or lower would be long, both of which are undesired. The Pure <NUM> and <NUM> Samples have very low levels of impurities and have a white appearance. As compared to Pure <NUM> Sample, the Pure <NUM> Sample has a significantly higher ZrO<NUM> content; however, even at such a ZrO<NUM> content, the Pure <NUM> Sample still does not have sufficiently good sintering and density properties.

The CaO-doped samples have a white appearance and good sintering characteristics. After sintering at <NUM> for <NUM> hours in air, the density is over <NUM>% of theoretical density at a CaO content of <NUM> wt. % and higher. Overall, the density is the highest in a range of <NUM> wt. % to <NUM> wt. % CaO content. Higher CaO can be used; however, the higher content levels increase manufacturing costs and does not further improve density.

The Y<NUM>O<NUM> <NUM> sample has a white appearance. As the Y<NUM>O<NUM> content increases the sample becomes more yellow. At <NUM> vol. % and higher, the Y<NUM>O<NUM>-doped samples have a dark yellow appearance that can change to yellow when exposed at <NUM> for <NUM> hours in air. The sintering characteristics are good, but not as good as the CaO-doped samples. Based on the data, the density increases until the Y<NUM>O<NUM> content reaches <NUM> wt. % and then decreases.

The TiO<NUM>-doped samples have a white appearance. The sintering characteristics are good, and between the sintering characteristics of the CaO-doped samples and the Y<NUM>O<NUM>-doped samples. Based on the data, the density increases until the TiO<NUM> content reaches <NUM> wt. % and then decreases.

<NUM>-co-doped samples have a white appearance and with a density of <NUM>%, the same as CaO <NUM> singly doped samples both in density and in appearance while higher than Y <NUM> (<NUM> Vol%. Y<NUM>O<NUM>) singly doped samples (<NUM>%). <NUM> has a higher density (<NUM>%) than the density of Y or Ca samples, regardless of Y or Ca content in their corresponding singly doped samples, and the Y2. <NUM> co-doped samples have dark yellow appearance, the same as Y<NUM>O<NUM> doped samples with a Y<NUM>O<NUM> content of <NUM> wt% and higher. The data indicates that a certain amount of Y<NUM>O<NUM> and CaO doping can be used if both color and density are important in some applications. <NUM> and Ti1. <NUM> co-doped samples have similar results in the both density and appearance as the CaO <NUM> singly doped samples but higher than Ti <NUM> and Ti <NUM> singly doped samples for the density.

Claim 1:
A sintered ceramic component having a composition consisting of:
MgO in a content of <NUM> wt% to <NUM> wt%;
at least one desired dopant including CaO, TiO<NUM>, or a combination thereof, wherein each dopant of the at least one desired dopant has a dopant content of at least <NUM> wt.%;
impurities, wherein all impurities are present at a combined impurity content of less than <NUM> wt.%; and
a remainder comprising Al<NUM>O<NUM>,
wherein the sintered ceramic component has a density that is at least <NUM>% of theoretical density.