Lightweight Ceramic Thermal Insulation Materials

BACKGROUND OF THE INVENTION

(1 ) Field of the Invention

[0001] The present invention relates in general to ceramic high temperature insulation materials for high temperature applications and to methods for their production, and more particularly multi-layer, multi-functional insulation assemblies and components for high temperature fuel cells.

(2) Description of Related Art including information disclosed under 37 CFR 1 .97 and 1 .98.

[0002] High temperature fuel cells include solid oxide fuel cells (SOFC) and molten carbonate fuel cells (MCFC). Compared with other fuel cells, SOFC/MCFC have advantages such as high efficiency, no expensive precious metal content, fuel flexibility, and simple system architecture, all of which contribute to an economic advantage over other types of fuel cell.

[0003] Operating temperatures of the fuel cells are 700 - 1 ,000°C for SOFC and 500 - 700°C for MCFC respectively, which means that high efficiency thermal insulation of the fuel cell "hot box" that includes the cell stack and all necessary accessories at operating temperature is needed for thermal management that functions within designed size constraints. The atmosphere inside the "hot box" usually has high humidity up to the saturation level. During continuous operation and maintenance, the outside of the "hot box", i.e., the cold or ambient face of the insulation material, must be "cool-to-touch" for short durations to eliminate risk of personal injury.

[0004] Known insulation materials for fuel cell insulation include fibrous and so-called microporous particulate based insulation, as they have the required combination of insulation performance and chemical stability in SOFC and MCFC for long term continuous operation at operating temperature and pressure. Such insulation materials, however, typically have disadvantages such as low mechanical strength, lack of sufficient structural rigidity, permeability to gas and moisture, high machining scrap rate, friability and dust production which makes it necessary to use special tooling and HEPA grade dust collection in machining and assembly. Often the insulation material assembly must be encased in a rigid metal (usually stainless steel) box to keep dust and volatile materials from spreading inside the fuel cell.

[0005] Therefore, there exists a need, in SOFC, MCFC and other applications, for a net shape or near net shape high performance insulation material that is free from surface dust and is impermeable to gas or moisture. There is also a need for an insulation material that can maintain "cool-to-touch" cold face temperature under normal high temperature fuel cell operating conditions. Further, there is a need in the art for an insulation that has sufficient mechanical strength and rigidity for use as either a load- bearing structural component or a non-load bearing component in small to large fuel cells.

BRIEF SUMMARY OF THE INVENTION

[0006] The present invention relates in in general to ceramic high temperature insulation materials for high temperature applications and methods for their production, and more particularly multi-layer, multi-functional composite insulation assemblies and components for high temperature fuel cells.

[0007] In one aspect, there is disclosed a high temperature composite insulation board or panel for fuel cells that includes a rigid shell and a core. The light weight rigid shell is made from porous fused silica or other porous silica based ceramic materials that have sufficient strength for use as either load-bearing structural and non-load bearing components in small to large fuel cells. The composite insulation board consists of side walls and cold face panel formed as one piece and a separate hot face panel securely attached to the side walls. In the case that the composite insulation board is used for small fuel cells, ceramic fiber or other flexible gaskets can be used between hot face panel and side walls and between cold face panel and side walls to minimize heat transfer through side walls.

[0008] In another aspect, there is disclosed a high temperature composite insulation board or panel for fuel cells that includes a shell and a core, and the "hot face" panel of the rigid shell facing the fuel cell "hot box" contains an IR opacifier to reduce infra-red radiate heat transfer through the panel.

[0009] In another aspect, there is disclosed a high temperature composite insulation board for fuel cells that includes a shell and a core, and the surfaces of the "hot face" panel facing the fuel cell "hot box" can have an optional ceramic high emissivity or insulating coating to further reduce radiate heat through the panel.

[0010] In another aspect, there is disclosed a high temperature composite insulation board for fuel cells that includes a shell and a core, and the inside surface of the "hot face" panel of the shell is lined with a thin stainless steel foil that has high infra-red radiation heat reflectance. Also multiple thin stainless steel foils can be placed such that they are separated by spacers to form multiple radiate heat reflecting sheets in parallel to the "hot face" panel to further improve radiate heat blocking by multiple reflection.

[0011] In another aspect, there is disclosed a high temperature composite insulation board for fuel cells that includes a shell and a core, and the core can be wholly or partially filled with loose ceramic powders that have very low thermal conductivities. In the case of partial filling with ceramic powder, an air gap is formed between the filled core and the "cold face" panel of the rigid shell.

[0012] In another aspect, there is disclosed a high temperature composite insulation board for fuel cells that includes a shell and a core, and the loose ceramic powders for core filling can be doped with an IR opacifier to reduce infra-red radiate heat transfer through the board. [0013] In another aspect, there is disclosed a high temperature composite insulation board for fuel cells that includes a shell and a core, and the core that is wholly or partially filled with loose ceramic microporous powders and the filling consists of multiple layers of different IR opacifier levels.

[0014] In another aspect, there is disclosed a high temperature composite insulation board for fuel cells that includes a one-piece rigid fused silica shell without IR dopant that forms the cold face panel and side walls. A fiber glass cloth is placed inside the cold face panel that creates an air gap between the filled layers of loose ceramic microporous powders and the cold face panel.

[0015] In another aspect, there is disclosed a high temperature composite insulation panel for fuel cells that includes a shell and a core, and the hot face layer of the rigid shell facing the device to be insulated, or fuel cell "hot box", contains an IR opacifier to reduce infra-red radiated heat transfer through the layer.

[0016] In another aspect, there is disclosed an insulating layer comprised of silica, (such as porous fused silica), alumina, or alumina-silica ceramic containing an IR opacifier to reduce infra-red radiated heat transfer through the layer. This layer may be incorporated into a high temperature composite insulation board. The insulating layer may contain porosity in fluid noncommunication with a major surface, porosity oriented in a direction other than the minor dimension of the layer (where the minor dimension is the smallest of the three dimension of the layer), or porosity oriented parallel to a surface of the layer.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0017] Fig. 1 is a cross-section schematic view, in a vertical plane, of a panel assembly according to the present invention; and

[0018] Fig. 2 is a cross-section view, in a vertical plane, of a panel assembly according to the present invention; [0019] Fig. 3 is a cross-section schematic view, in a vertical plane, of a panel assembly according to the present invention;

[0019] Fig. 4 is a cross-section schematic view, in a vertical plane, of a panel assembly according to the present invention;

[0019] Fig. 5 is a cross-section schematic view, in a vertical plane, of a panel assembly according to the present invention; and

[0019] Fig. 6 is a cross-section schematic view, in a vertical plane, of a panel assembly according to the present invention;

[0020] The drawings are not intended to be limiting in any way, and it is contemplated that various embodiments of the invention may be carried out in a variety of other ways, including those not necessarily depicted in the drawings. The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention; it being understood, however, that this invention is not limited to the precise arrangements shown.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The following description of certain examples should not be used to limit the scope of the present invention. Other features, aspects, and advantages of the versions disclosed herein will become apparent to those skilled in the art from the following description. As will be realized, the versions described herein are capable of other different and obvious aspects, all without departing from the invention. Accordingly, the drawings and descriptions should be regarded as illustrative in nature and not restrictive.

[0022] The term "microporous" is used herein to define porous or cellular materials in which the ultimate size of the cells or voids is less than the mean free path of an air molecule at standard temperature and pressure, e.g., of the order of 100 nm or smaller. A material which is microporous in this sense will exhibit very low transfer of heat by air conduction (that is, collisions between air molecules). Such microporous materials can be obtained by controlled precipitation from solution, the temperature and pH being controlled during precipitation to obtain an open lattice precipitate. Other equivalent open lattice structures include pyrogenic (fumed) and electro-thermal types in which a substantial proportion of the particles have an ultimate particle size less than 100 nm. Any of these materials, based for example on silica, alumina or other metal oxides, may be used to prepare a composition which is microporous as defined above.

[0023] Figure 1 depicts an embodiment of an insulating panel 10 according to the invention. In this embodiment, a device face layer or hot face layer 12 is disposed in proximity to, or in contact with, a surface of intermediate layer 14. An opposite surface of intermediate layer 14 is disposed in proximity to, or in contact with, an ambient face layer or cold face layer 16.

[0024] Figure 2 depicts an embodiment of an insulating panel 20 according to the invention. Device face layer or hot face layer 12 contains hot face layer refractory material 22. Hot face layer refractory material 22 has a hot face layer refractory material device side surface or front surface 24 and, on an opposite surface, a hot face layer refractory material ambient side surface or back surface 26. The hot face layer refractory material device side surface may be covered, partially or completely, by a hot face layer device side coating 28. The hot face layer refractory material ambient side surface or back surface 26 may be covered by a hot face layer ambient side metal foil covering 30. Device face layer 12 may incorporate a porous structure, wherein the porosity is not in fluid communication with hot face layer refractory material device side surface or front surface 24.

[0025] Device face layer or hot face layer 12 is disposed in proximity to, or in contact with, a surface of intermediate layer 14. Intermediate layer 14 may be homogeneous, or may consist of a plurality of compositions. In the embodiment depicted in Figure 2, intermediate layer 14 contains an intermediate layer device-side composition 34, disposed on the side of intermediate layer 14 proximal to device face layer or hot face layer 12. The side of intermediate layer device-side composition proximal to device face layer or hot face layer 12 is designated as the intermediate layer device-side composition device-side surface 36. The side of intermediate layer device-side composition distal to device face layer or hot face layer 12 is designated as the intermediate layer device-side composition ambient-side surface 38. Device face layer or hot face layer 12 may be in direct contact with intermediate layer 14, or layers 12 and 14 may be separated from each other by a low conduction volume 42. Low conduction volume 42 may be an air gap. In embodiments in which intermediate layer 14 is homogeneous, intermediate layer device side surface or front surface 36 faces device face layer or hot face layer 12, and intermediate layer ambient side surface or back surface 48 faces away from device face layer or hot face layer 12.

[0026] In the embodiment depicted in Figure 2, intermediate layer 14 contains an intermediate layer ambient-side composition 44, disposed on the side of intermediate layer 14 distal to device face layer or hot face layer 12. The side of intermediate layer ambient-side composition proximal to device face layer or hot face layer 12 is

designated as the intermediate layer ambient-side composition device-side surface 46. The side of intermediate layer device-side composition distal to device face layer or hot face layer 12 is designated as the intermediate layer ambient-side composition ambient- side surface 48. In particular embodiments of the invention, surfaces 46 and 48 may be partially or completely covered with a glass fiber cloth 50.

[0027] In the embodiment depicted in Figure 2, the intermediate layer ambient-side composition ambient-side surface 48 is disposed in proximity to ambient face layer or cold face layer 16. The side of ambient face layer or cold face layer 16 proximal to intermediate layer 14 is designated as ambient-face layer device side surface or front surface 52. The side of ambient face layer or cold face layer 16 distal to intermediate layer 14 is designated as ambient-face layer ambient side surface or back surface 54. Intermediate layer 14 may be in direct contact with ambient face layer or cold face layer 16, or layers 14 and 16 may be separated from each other by a low conduction volume 58. Low conduction volume 58 may be an air gap. [0028] Ambient face layer or cold face layer 16 may be planar, or may be configured with a circumferential lip extending in the direction of intermediate layer 14. Ambient face layer or cold face layer 16 may be configured to receive a portion of, or the entirety of, the thickness of intermediate layer 14. Insulating panel 20 may be provided with a peripheral shell 60 extending from ambient face layer or cold face layer 16 to

intermediate layer 14 and enclosing at least a portion of the periphery of intermediate layer 14. Peripheral shell 60 may be integral with ambient face layer or cold face layer 16, or may represent a discrete piece. Gasket 62 seals the periphery of low conduction volume 42 is disposed between hot face layer refractory material ambient side surface or back surface 26 and the device side or front side of intermediate layer 14 (or, in the embodiment shown, intermediate layer device-side composition device-side surface 36).

[0029] Figure 3 depicts an embodiment of an insulating panel 80 according to the invention. In this embodiment, a device face layer or hot face layer 12 is disposed in proximity to, or in contact with, a surface of intermediate layer 14. An opposite surface of intermediate layer 14 is disposed in proximity to, or in contact with, an ambient face layer or cold face layer 16. A lip 82 extends from the periphery of hot face layer 12 in the direction of cold face layer 16. The extension of lip 82 from the back surface or ambient-side surface of hot face layer 12 forms a recess to accommodate intermediate layer 14. In this embodiment, device face layer or hot face layer 12 and cold face layer or ambient face layer 16 combine to enclose intermediate layer 14.

[0030] Figure 4 depicts an embodiment of an insulating panel 90 according to the invention. In this embodiment, a device face layer or hot face layer 12 is disposed in proximity to, or in contact with, a surface of intermediate layer 14. An opposite surface of intermediate layer 14 is disposed in proximity to, or in contact with, an ambient face layer or cold face layer 16. A lip 92 extends from the periphery of cold face layer 16 in the direction of hot face layer 12. The extension of lip 92 from the device-side surface of hot face layer 16 forms a recess to accommodate intermediate layer 14. In this embodiment, device face layer or hot face layer 12 and cold face layer or ambient face layer 16 combine to enclose intermediate layer 14.

[0031] Insulating panel 10 or 20 may be constructed to have a total thickness in the range from and including 50 mm to and including 250 mm, from and including 75 mm to and including 150 mm, from and including 1 10 mm to and including 135 mm, or from and including 1 10 mm to and including 125 mm.

[0032] Insulating panel 10 or 20 may be constructed from a rigid shell made of two parts, and having a partially-filled or entirely-filled inner volume. The rigid shell is composed of front hot face layer 12 and a one-piece back cold face side with side walls 16.

[0033] The portion of insulating panel 10 or 20 containing hot face layer refractory material 22 may be formed from a base material that may be combined with at least one dopant, and may have a thickness in the range from and including 15 mm to and including 40 mm, or from and including 25 mm to and including 35 mm. The base material may be a porous lightweight silica, alumina, or alumina-silica based ceramic material, and may specifically be a fused silica based porous rigid material, and may have a density, expressed exclusive of porosity, in the range from and including 0.7 g per cubic centimeter to and including 4.0 g per cubic centimeter, a density in the range from and including 1 .0 g/cm ³ to and including 1 .6 g/cm ³ , a density in the range from and including 0.9 g/cm ³ to and including 1 .6 g/cm ³ , a density in the range from and including 0.8 g/cm ³ to and including 1 .6 g/cm ³ , a density in the range from and including 0.6 g/cm ³ to and including 1 .6 g/cm ³ , a density in the range from and including 0.5 g/cm ³ to and including 1 .6 g/cm ³ , or a density in the range from and including 0.4 g/cm ³ to and including 1 .6 g/cm ³ . The silica may be a fused silica, and may be a form of silica having a porosity equal to or greater than 45 volume percent, and less than 100 volume percent. The base material may also include magnesia, and phosphate materials, and may incorporate calcium-based components as a bonding phase. The at least one dopant may be a material or IR opacifier dopant selected from the group consisting of Ζ1 2, SiC, rutile, ΤΊΟ2, MnO, iron oxides, C1 2, ZrSi02, AI2O3 and mixtures thereof, or may be selected from the group consisting of Zr02 or SiC. The hot face layer refractory material 22 may contain from and including 4 wt% IR opacifier dopant to and including 30 wt% IR opacifier dopant, 8 wt% IR opacifier dopant to and including 25 wt% IR opacifier dopant, or from and including 12 wt% IR opacifier dopant to and including 20 wt% IR opacifier dopant. The portion of insulating panel 10 or 20 containing hot face layer refractory material 22 may have a density in the range from and including 0.9 g per cubic centimeter to and including 1.8 g per cubic centimeter, or a density in the range from and including 1 .2 g per cubic centimeter to and including 1 .6 g per cubic centimeter. The portion of insulating panel 10 or 20 containing hot face layer refractory material 22 may have a flexural strength equal to or greater than 4 MPa, and may have a thermal conductivity k less than 0.5 W/m-K at 700 degrees C.

[0034] The base material for the portion of insulating panel 10 or 20 containing hot face layer refractory material 22 may be a slip cast dense form comprising silica and presenting a low heat conductivity. The dense form may also be obtained by laminating, rolling, pressing and other techniques capable of producing a thin heat resistant structure.

[0035] The base material for the portion of insulating panel 10 or 20 containing hot face layer refractory material 22 may be formed by a gel casting method, and may incorporate an IR opacifier.

[0036] Hot face layer device side coating 28 may be applied to hot face layer refractory material ambient side surface or back surface 26. The coating 28 may be a ceramic coating, such as a high-emissivity nanoparticle ceramic coating, and may have an emissivity value in the range from and including 0.85 to and including 0.95, measured as a value of the ratio of re-radiated energy to absorbed energy, and may contain nanosilica materials. The ceramic coating may be rated 1900 degrees C and may be applied with a spray gun. In certain embodiments, the hot face layer device side coating may be infused or infiltrated into hot face layer refractory material ambient side surface or back surface 26. High temperature high emissivity coatings include ceramic- based, black-pigmented coatings and silicone-ceramic, black-pigmented coatings. High temperature high emissivity coatings may contain an inorganic adhesive such as an alkali/alkaline earth metal silicate such as sodium silicate, potassium silicate, calcium silicate, and magnesium silicate; a filler such as a metal oxide for example silicon dioxide, aluminum oxide, titanium dioxide, magnesium oxide, calcium oxide and boron oxide; and one or more emissivity agents such as silicon hexaboride, carbon

tetraboride, silicon tetraboride, silicon carbide, molybdenum disilicide, tungsten disilicide, zirconium diboride, cupric chromite, or metallic oxides such as iron oxides, magnesium oxides, manganese oxides, chromium oxides and copper chromium oxides, and derivatives thereof.

[0037] Hot face layer refractory material ambient side surface or back surface 26 may be obscured to energy transfer by the use of infrared blockers incorporated into, or onto, surface 26. Infrared blockers may include highly insulative surfaces or coatings, such as mica, fibers and cenospheres, high emissivity materials such as metals or high E glass, reflective materials such as metal dispersions or cermets, or high porosity structures provided by introducing foams, large size particles, or roughness onto hot face layer refractory material ambient side surface or back surface 26. Hot face layer refractory material ambient side surface or back surface 26 may also be made retro- diffusive to prevent migration, by conduction, of heat into the body of hot face layer refractory material 22. For this purpose, fibers, a structure with high rugosity, or sprayed particles with high heat conductivity may be applied to hot face layer refractory material ambient side surface or back surface 26.

[0038] Hot face layer ambient side metal foil covering 30 may comprise stainless steel foil. Metal foil covering 30 may have a thickness in the range from and including 0.2 mm to and including 0.45 mm. Metal foil covering may utilized in a single layer, two layers or a plurality of layers. If two layers are used, one foil covering 30 may be disposed on the ambient side of the hot face layer, and one foil covering 40 may be disposed on the device side of intermediate layer 14. A gap or reduced conductivity volume 42 may be formed by the separation between foil covering 30 and foil covering 40. If two layers are used, they may be separated by a gap having a separation dimension in the range from including 2 mm to and including 5 mm. In a specific embodiment, two layers of metal foil covering are formed from 0.3 mm polished foil and are separated by a gap having a separation dimension in the range from and including 2 mm to and including 5 mm.

[0039] Intermediate layer 14 may be formed from fumed silica, alumina,

aluminosilicate, oxide compounds, carbide compounds, vermiculite, mica, natural diatom materials, synthetic diatom materials, insulating fiber, hollow ceramic

microspheres, a microporous material, a microporous material based on silica alumina or another metal oxide, or aerogel. Intermediate layer 14 may incorporate a binder such as a magnesia material or a phosphate material, or may contain a calcium-based bonding phase. Intermediate layer 14 may also be formed from other rigid materials, including high-temperature polymers. In certain embodiments of the invention, intermediate layer 14 may consist essentially of air, gas or a fluid insulator so that these materials are in communication with device face layer 12 and with ambient face layer 16. Materials in intermediate layer may be in amorphous, fiber or crystalline form. The entire intermediate layer may be doped with an IR opacifier comprising Zr02, SiC, rutile, ΤΊΟ2, MnO, iron oxides, Cr02, ZrSi02, AI2O3 and mixtures thereof, or may be selected from the group consisting of Zr02 or SiC.

[0040] In particular embodiments of the invention, intermediate layer 14 contains an intermediate layer device-side composition 34, disposed on the side of intermediate layer 14 proximal to device face layer or hot face layer 12, and an intermediate layer ambient-side composition 44, disposed on the side of intermediate layer 14 distal to device face layer or hot face layer 12. In particular embodiments of the invention containing an intermediate layer device-side composition 34 differing from intermediate layer ambient-side composition 44, composition 34 is doped with an IR opacifier. In particular embodiments of the invention containing an intermediate layer device-side composition 34 differing from intermediate layer ambient-side composition 44, either or both of compositions 34 and 44 may comprise an IR opacifier, may consist essentially of an IR opacifier, or may consist entirely of an IR opacifier. In particular embodiments of the invention containing an intermediate layer device-side composition 34 differing from intermediate layer ambient-side composition 44, composition 34 has a greater IR opacifier content than does composition 44. The IR opacifier of composition 34 may comprise Zr02, SiC, rutile, ΤΊΟ2, MnO, iron oxides, Cr02, ZrSi02, AI2O3 and mixtures or combinations thereof, or may be selected from the group consisting of Zr02 or SiC. The cross-section thickness, or transverse thickness from face 36 to face 38, of the sublayer of composition 34 may have a dimension in the range from and including 15 mm to and including 40 mm, or from and including 35 mm to and including 40 mm. In certain embodiments, the IR opacifier content of the sublayer of composition 34 may range from and including 5 wt% to and including 500 wt% of the weight of the remaining components of the sublayer of composition 34, may range from and including 50 wt% to and including 200 wt% of the weight of the remaining components of the sublayer of composition 34, may range from and including 100 wt% to and including 200 wt% of the weight of the remaining components of the sublayer of composition 34, or may range from and including 60 wt% to and including 120 wt% of the weight of the remaining components of the sublayer of composition 34. In particular embodiments of the invention containing an intermediate layer device-side composition 34 differing from intermediate layer ambient-side composition 44, composition 34 may have an IR opacifier content in the range from and including 10 wt% to and including 100 wt% of the total composition of the layer. Composition 34 may have a thermal conductivity k less than 0.5 W/m-K at 700 degrees C, and may have a stability up to 1000 degrees C.

[0041] The intermediate layer ambient-side composition 44 may comprise undoped fumed silica, aerogel, hollow ceramic microspheres, or other lightweight low thermal conductivity ceramic powders. The cross-section thickness, or transverse thickness from face 46 to face 48, of the sublayer of composition 44 may have a dimension in the range from and including 15 mm to and including 65 mm, in the range from and including 15 mm to and including 40 mm, in the range from and including 25 mm to and including 40 mm, or in the range from and including 15 mm to and including 33 mm. [0042] In another embodiment of the invention, the intermediate layer ambient-side composition can be composed of refractory ceramic fibers. The refractory fibers may be in the form of bulk, blanket or preformed module, and may have a thermal conductivity of k < 0.5 W/m-K at 700 degrees C.

[0043] Intermediate layer 14 may be separated from ambient face layer or cold face layer 16 by a low conduction volume 58. Low conduction volume 58 may be filled with air.

[0044] Intermediate layer 14 may also comprise a volume occupied by a fluid, such as a substance in the gaseous state, such as air. In certain embodiments in which intermediate layer 14 comprises a volume, it may be partially evacuated.

[0045] Ambient face layer or cold face layer 16 may be planar, or may be configured with a sidewall extending around the periphery of a planar structure and extending in the direction of device face layer or hot face layer 12. The thickness of layer 16 may range from and including 10 mm to and including 40 mm, or may range from and including 12 mm to and including 18 mm. Ambient face layer or cold face layer 16 may be formed form fused silica based porous rigid material or other silica based light weight rigid material, a circumferential lip extending in the direction of intermediate layer 14. The thickness of the sidewall in the plane of ambient face layer or cold face layer 16 may range from and including 10 mm to and including 25 mm, or from and including 12 mm to and including 18 mm.

[0046] For large insulating panels 10 and 20 according to the invention, support columns may be attached to both device face layer 12 extending in the direction of ambient face layer 16, and to ambient face layer 16 extending in the direction of device face layer 12, to provide compression and bending strength across the area of entire panels. [0047] Figure 5 depicts an insulating panel 100 according to the invention. Device layer or hot face layer 12 is in communication with intermediate layer 14. Intermediate layer 14 is in communication with ambient face layer or cold face layer 16. Device face layer or hot face layer 12 contains at least one pore structure 102 in fluid noncommunication with hot face layer refractory material device side surface or front surface 24. This embodiment of device layer or hot face layer 12 may be formed by the extrusion of tubes or rods into a slab. The pore structure 102 may be in fluid

communication with the exterior of device layer or hot face layer 12, or may be isolated from the exterior of device layer or hot face layer 12. The pore structure 102 may take the form of channels oriented in a plane parallel to hot face layer refractory material device side surface or front surface 24. Hot face layer refractory material device side surface or front surface 24 is a major surface of device layer or hot face layer 12, a major surface being a surface having the two largest dimensions of the three

dimensions of the layer. An embodiment of device layer or hot face layer 12 may contain porosity that is oriented parallel to one of the dimensions of the major surface of the layer.

[0048] Figure 6 depicts an insulating panel 1 10 according to the invention. In this embodiment, a device face layer or hot face layer 12 is disposed in contact with intermediate layer 14. An opposite surface of intermediate layer 14 is disposed in contact with, an ambient face layer or cold face layer 16.

[0049] In the embodiment shown in Figure 6, device face layer or hot face layer 12 contains hot face layer refractory material 22. Hot face layer refractory material 22 has a hot face layer refractory material device side surface or front surface 24 and, on an opposite surface, a hot face layer refractory material ambient side surface or back surface 26. The hot face layer refractory material device side surface may be covered, partially or completely, by a hot face layer device side coating 28. The hot face layer refractory material ambient side surface or back surface 26 may be covered by a hot face layer ambient side metal foil covering 30. Device face layer 12 may incorporate a porous structure, wherein the porosity is not in fluid communication with hot face layer refractory material device side surface or front surface 24.

[0050] In the embodiment shown in Figure 6, device face layer or hot face layer 12 is disposed in contact with intermediate layer 14. In this embodiment, intermediate layer 14 is a volume configured to be occupied by a fluid, such as a substance in the gaseous state, such as air.

[0051] The side of ambient face layer or cold face layer 16 proximal to intermediate layer 14 is designated as ambient-face layer device side surface or front surface 52. The side of ambient face layer or cold face layer 16 distal to intermediate layer 14 is designated as ambient-face layer ambient side surface or back surface 54. Ambient- face layer device side surface or front surface 52 may be covered by an ambient layer device side metal foil covering 1 12.

[0052] Ambient face layer or cold face layer 16 may be planar, or may be configured with a circumferential lip extending in the direction of intermediate layer 14. Device face layer or hot face layer 12 may be planar, or may be configured with a circumferential lip extending in the direction of intermediate layer 14. Insulating panel 1 10 may be provided with a peripheral shell 60 extending from ambient face layer or cold face layer 16 to intermediate layer 14 and enclosing at least a portion of the periphery of intermediate layer 14. Peripheral shell 60 may be integral with device face layer or hot face layer 12, may be integral with ambient face layer or cold face layer 16, or may represent a discrete piece.

[0053] A hot face layer may be prepared by adding dispersant to water to form a dispersant in water solution, adding a dopant to the dispersant in water solution under stirring to form a combination, mixing starch with water to produce a starch in water solution, adding the starch in water solution to a slip to form a slip mixture, adding the combination to the slip mixture to form a dopant-slip combination, adding foaming agent, water and acid to the dopant-slip combination to form an acidified, foamed, dopant-slip combination, and casting and curing the acidified, foamed, dopant-slip combination to form a cast shape constituting the hot face layer. A coating may be applied to a surface of the cast shape to constitute the hot face layer. A metal foil may be attached to a surface of the cast shape to constitute the hot face layer. In an embodiment of the invention in which a coating is applied to a surface of the cast shape and a metal foil is attached to a surface of the cast shape, the coating and the metal foil are applied to distal surfaces of the cast shape.

[0054] EXAMPLE I

[0055] Preparation of 15% SiC doped fused silica by a slip casting method

[0056] A dispersant in water solution is prepared by adding a dispersant to water (for example, 125 g of dispersant to 375 g of water stepwise to a total of 35 percent by weight to form a 25% dispersant in water solution). A high shear mixer may be used until the dispersant is thoroughly mixed in water.

[0057] A dopant is then added to the dispersant in water solution (for example, 468 g of water is added to 168 g of the 25% dispersant in water solution under stirring. Using a high shear mixer, SiC powder (for example, 1400 g) is added to the above solution stepwise under stirring. The combination is mixed until the SiC powder is fully dispersed in the solution. A smooth flowable semi-solid mix is produced.

[0058] Doped fused silica slip is prepared by mixing starch (for example, 57 g) in water (for example, 500 g) under stirring to produce a starch in water solution. The starch in water solution is added to fused silica slip (for example, to an 8700 g quantity) to form a slip mixture. The SiC dopant dispersed in water solution (for example, a 1650 g quantity) prepared previously is added to the slip mixture to form a dopant-slip combination. A low shear mixer is used to mix the dopant-slip combination. A separate combination of foaming agent (for example, 16 g) is added to water (for example, 82 g) under high shear mixing. The combination of foaming agent and water is added to the dopant-slip combination previously produced under stirring. Acid is added (for example, 1 1 drops of 30% HCI) to the dopant-slip combination. The acidified, foamed, dopant-slip combination is then cast into a steel mold that is coated with a mold release agent and the mold is covered with a plastic wrap. Optionally a plaster mold can be used instead of a steel mold. The filled mold is loaded in an oven for curing (for example, stepwise curing at 54, 73, 93 and 1 10 degrees C). The cured piece is demolded after cooling to ambient temperature. The piece is then loaded into a high fire furnace for complete final firing (to a temperature of, for example, 1 150 degrees C).

[0059] EXAMPLE II

[0060] Preparation of 15% ZrO2 doped fused silica by a slip casting method

[0061] A solution of dopant in water is prepared by addition of an IR dopant (for example, 1400g ZrO2 powder, to water (for example, 600g) under stirring and then mixed.

[0062] Separately, starch (for example 57 g) is mixed in 500g water. The starch in water solution is added to fused silica slip (for example, 8700 g) to form a mixed slip. The IR dopant solution in water previously prepared is added to the mixed slip.

[0063] Separately, foaming agent (for example, 16 g) is added to water (for example, 82 g) under high shear mixing and continued mixing to produce foam. Under stirring the foam is added to the mixed slip produced previously and the combination is mixed. Acid (for example, 1 1 drops of 30% HCI) is added to the combined mixed slip.

[0064] The combined mixed slip is cast into a steel mold that is coated with a mold release agent and the mold is covered with a stretchable plastic wrap. Optionally a plaster mold can be used instead of steel mold. The filled mold is loaded in an oven for curing (for example, stepwise curing at 54, 74, 93 and 100 degrees C) to produce a cured piece. The cured piece is demolded after cooling to ambient temperature. The cured piece is then subjected to final firing (for example, by loading it into a high fire furnace and completing final firing to 1 150°C.

[0065] A multilayer panel may be prepared by assembling a layer according to

Example I, Example II or the composition provided for device face layer or hot face layer 12 so that a major surface of device face layer or hot face layer 12 is disposed adjacent to or in contact with a major surface of a cold face layer or ambient face layer 16. An intermediate layer 14 may be interposed between device face layer or hot face layer 12 and cold face layer or ambient face layer 16 so that a major surface of layer 14 is disposed adjacent to or in contact with a major surface of device face layer or hot face layer 12, and so that a major surface of layer 14 is disposed adjacent to or in contact with a major surface of cold face layer or ambient face layer 16. Peripheral spacers may be used to connect a major surface of device face layer or hot face later 12 to a major surface of cold face layer or ambient face layer 16, or may be used to connect a major surface of device face layer or hot face later 12 to a major surface of intermediate layer 14, and a major surface of intermediate layer 14 to a major surface of cold face layer or ambient face layer 16. Cements or other bonding agents may be used to adhere the respective surfaces.

[0066] The invention is also directed to use of the multilayer panels in insulating applications. In such applications, one or more multilayer panels are disposed around a device to be insulated and oriented with the front surfaces or hot side surfaces of the panel or panels facing towards a heat-producing device to be insulated. The device to be insulated is then operated. The multilayer panels may have, in their major plane, polygonal geometries such as triangular, rectangular, pentagonal or hexagonal geometries. The multilayer panels may be curved or bent in one or two dimensions, and may be assembled to form insulating enclosures with various geometries, such as polygonal-prism-shaped enclosures (e.g., rectangular-prism-shaped enclosures, triangular-prism-shaped enclosures, or hexagonal-prism-shaped enclosures), cylindrical enclosures or hemispherical enclosures. [0067] Also within the scope of the invention is the use of an insulating panel as described herein to provide insulation between a fuel cell and its surroundings.

[0068] Having shown and described various versions in the present disclosure, further adaptations of the methods and systems described herein may be accomplished by appropriate modifications by one of ordinary skill in the art without departing from the scope of the present invention. Several of such potential modifications have been mentioned, and others will be apparent to those skilled in the art. For instance, the examples, versions, geometries, materials, dimensions, ratios, steps, and the like discussed above are illustrative and are not required. Accordingly, the scope of the present invention should be considered in terms of the following claims and is understood not to be limited to the details of structure and operation shown and described in the specification and drawings.

[0069] Elements of the invention:

10. Insulating panel

12. Device face layer (or hot face layer)

14. Intermediate layer

16. Ambient face layer (or cold face layer)

20. Insulating panel

22. Hot face layer refractory material

24. Hot face layer refractory material device side surface or front surface

26. Hot face layer refractory material ambient side surface or back surface

28. Hot face layer device side coating

30. Hot face layer ambient side metal foil covering

34. Intermediate layer device-side composition

36. Intermediate layer device-side composition device-side surface or

Intermediate layer device-side surface or front surface

38. Intermediate layer device-side composition ambient-side surface

40. Intermediate layer device-side metal foil covering

42. Device-side low conduction volume 44. Intermediate layer ambient-side composition

46. Intermediate layer ambient-side composition device-side surface

48. Intermediate layer ambient-side composition ambient-side surface or

Intermediate layer ambient-side surface or back surface

50. Glass fiber cloth

52. Ambient-face layer device-side surface or front surface

54. Ambient-face layer ambient-side surface or back surface

58. Ambient-side low-conduction volume

60. Peripheral shell

62. Gasket

80. Insulating panel

82. Hot face layer peripheral lip

90. Insulating panel

92. Ambient-face layer peripheral lip

100. Insulating panel

102. Pore structure

1 10. Insulating panel

1 12. Ambient layer device side metal foil covering