Ceramic laminate material

Abstract: Ceramic laminate material comprising at least one dense layer of a perovskite material and at least one layer of a dense non-perovskite material and/or at least one layer of a dense superstructural perovskite material.

Description: The present invention relates to a ceramic laminate material or compositional graded ceramic for use in the production of ion and/or electron conducting ceramic products. Perovskite ceramic material in oxygen separation membranes, have the general formula: A x A' x' A" x" By B' y' B" y" O 3-ä , wherein x + x' + x" = 1, and y + y' + y" = 1, and δ is a number, which renders the composition charge neutral. Those materials are known from U.S. Patent No. 5,240,473. Dense ceramic membranes comprising a non-perovskite material represented by the formula: (Sr 1-y M y ) α (Fe 1-x Co x ) α+β O δ having electron conductivity and oxygen ion conductivity are known from US Patent No. 5,580,497. High oxygen ion conductivity of ceramic materials comprising a superstructural form of the cubic perovskite structure, with the general chemical formula: A x A' x' B y B' y' O 2.5 has been reported in the scientific literature. In the Proceedings of the Electrochemical Society, Vol. 93, No. 4, 1993, pages 598-612, Chen et al. have studied cathode/electrolyte interactions and their expected impact on SOFC parameters. Herein are described perovskite materials combined with materials considered to represent non-perovskite materials. These materials YSZ and CSO consist of combined sintered oxides of the individual metals. Sahibzada et al. have described in Catalysis Today, Vol. 38, No 4, 1997, pages 459-466, a dense film.of non-perovskite material. This material, Ce 0.9 Gd 0.1 O 1.95 , consists solely of lanthanide metals. It has been observed that perovskite materials with high oxygen conductivity exhibit poor structural stability and high thermal expansion at low oxygen partial pressures leading to limitations when these materials are used in separation of oxygen. In practice a compromise between high oxygen conductivity or high stability must be accepted (cf. "Dimensional Instability of Doped Lanthanum Chromites in an Oxygen Pressure Gradient", P.V. Hendriksen, J.D. Carter and M. Mogensen, in Proceedings of the fourth international Symposium on Solid Oxide Fuel Cells, Ed. by M. Dokiya, O. Yamamoto, H. Tagawa and S.C. Singhal, The Electrochemical Society Proc. Vol. 95-1, (1995) 934; "Dimensional Instability and effect chemistry of doped lanthanum chromites", P.H. Larsen, P.V. Hendriksen and M. Mogensen, Journal of Thermal Analysis, Vol. 49, (1997), 1263; and "Lattice Expansion induced strains in solid oxide fuel cell stacks and their significance for stack integrity", P.V. Hendriksen and O. Joergensen, in "High Temperature Electrochemistry: Ceramics and Metals". Proceedings of the 17th Risoe International Symposium on Materials Science (1996), 263). Pursuant to these observations and findings this invention provides a dense ceramic laminate material comprising at least one dense layer of a perovskite material and at least one layer of a dense non-perovskite material and at least one layer of a dense superstructural perovskite material. The perovskite material for use in the invention is represented by the chemical formula: A x A' x' A" x" B y B' y' B'' y'' O 3-δ wherein: x + x' + x" ≤ 1 and y + y' + y" ≤ 1, and δ is a number which renders the composition charge neutral. A, A' and A" each is one or more metals selected from the group of lanthanide metals and/or a divalent metal, preferably from the group IIA of the Periodic Table. B, B' and B" each is a metal selected from the group of transition metals, group IIIA and noble metals of group VIII of the Periodic Table. The non-perovskite material is represented by the chemical formula: (A x A' x' A" x" ) a (B y B' y' B" y" ) b O 3-δ wherein x + x' + x" ≤ 1 and y + y' + y" ≤ 1 and a is a number in a range from 1 to 4 b is a number in a range from 1-10 and δ is a number, which renders the composition charge neutral, and . A, A', A", B, B' and B" are as previously defined. The superstructural perovskite material has a Brownmillerite structure with the general chemical formula: A x A' x' A" x" By B' y' B" y" O 2,5 or with pyroclore structure having the general chemical formula: A x A' x' A" x" By B' y' B" y" O 3.5 wherein x + x' + x" ≤ 1 and y + y' + y" ≤ 1 Each layer in the ceramic laminate is selected in such a way that an improved structural and chemical stability is obtained in comparison with each single layer when exposed to an oxygen rich gas on one side and an oxygen poor gas on the other side. Brownmillerite material contains a large number of ordered intrinsic oxygen vacancies, which become disordered above a certain transition temperature depending on the chemical composition, leading ultimately to intrinsic fast oxygen ion conductivity. Correspondingly, pyroclore materials can be substituted on the A site and on the B site in the chemical formula leading to intrinsic fast oxygen ion conductivity. Contrary to the classical oxygen ion conducting perovskites, Brownmillerite material can be classified as a superstructural cubic perovskite with a fixed high concentration of oxygen ion vacancies. Therefore, the Brownmillerite material exhibits a higher dimensional and mechanical stability than the perovskite materials during reduction at low partial pressures. In a configuration in accordance with the invention a thin dense brownmillerite layer with a thickness from 0.5 µm to 5000 µm is coated on a thin dense perovskite layer with a thickness of 0.5 µm to 5000 µm and placed on the oxygen-poor side of the membrane to protect the perovskite layer from the reducing environment. Both layers possess a high oxygen ion conductivity or a high mixed electronic and oxygen ionic conductivity. In another configuration in accordance with the present invention, the dense Brownmillerite is coated on the dense perovskite on the oxygen rich side of the membrane to ensure a high flux of oxygen ions through the membrane when the perovskite is selected to possess maximal dimensional and mechanical stability. In accordance with specific embodiments of the invention, the membrane consists of Brownmillerite and pyroclore, and non-perovskite coated or laminated layers on one or both sides of a perovskite layer or multilayers of different composition belonging to the types of perovskites, Brownmillerite and pyroclores or non-perovskites mentioned above. Example 1 This example is a comparative example useful for understanding the invention. Using drip pyrolysis procedure a ceramic powder was produced. Aqueous solutions of metal nitrates, acetates or carbonates were mixed in the required proportions according to the proposed chemical formula. Then combustion fuel such a glucose or glycine was added to the above solution in order to get fuel-rich mixtures. The stock solutions as prepared were drip pyrolysed in a rotary kiln. From XRD analysis the powders were found to have a perovskite structure. The material has the chemical formula: (La 0.7 Sr 0.3 ) 0.9 Fe 0.8 Co 0.2 O 3-δ or (La 0,7 Sr 0,3 ) 0,9 Ga 0,8 Mn 0,2 O 3-δ and may be used for applications such as: SOFC cathode, mixed electronic/ionic conductive membranes, oxidation catalyst and sensor. The A-site deficient perovskite compound has an improved chemical stability towards other ceramic materials such as yttria stabilised zirconia in comparison with perovskite with A/B = 1. After mixing the fine-grained perovskite powder with water and a suitable binder such as methylcellulose, the mixture may be shaped as tubes by extrusion followed by drying and sintering based on well known ceramic production methods. The sintered tubes may be coated on the inside or on the outside and on both sides by a ceramic slurry consisting of a ceramic powder with Brownmillerite structure synthesised by the technique analogously to the above mentioned. The Brownmillerite material employed in this example has the chemical formula: Sr 2 Fe 1.6 Co 0.4 O 5 or Sr 2 Ga 1,6 Mn 0,4 O 5 . After sintering of the Brownmillerite coated perovskite tube, a dense mixed electronic and oxygen ionic conducting tubular multilayer membrane is obtained. As many related structures may exist between the perovskites and the Brownmillerite structures depending on the sintering conditions, a functionally graded membrane, which may be used for oxygen separation and membrane reactors, is obtained.

Claims: Ceramic laminate material comprising at least one dense layer of a perovskite material, at least one layer of a dense non-perovskite material and at least one layer of a dense superstructural perovskite material, wherein the perovskite material is represented by the chemical formula: A x A' x' A" x" B y B' y' B" y" O 3-δ where: x + x' + x" ≤ 1 y + y' + y" ≤ 1 δ is a number, which renders the composition charge neutral, A, A' and A" each is one or more metals selected from the group of lanthanide metals and/or a divalent metal, preferably from group IIA of the Periodic Table, B, B' and B" each is a metal selected from the group of transition metals, group IIIA and noble metals of group VIII of the Periodic Table, and the non-perovskite material is represented by the chemical formula: (A x A' x' A" x" ) a (B y B' y' B" y" ) b O 3-δ where: x + x' + x" ≤ 1 y + y' + y" ≤ 1 1 < a ≤ 4 1 < b ≤ 10 δ is a number, which renders the composition charge neutral and A, A', A", B, B' and B" are as previously defined, and the superstructural perovskite material is represented by the Brownmillerite structure having the general chemical formula: A x A' x' A" x" B y B' y' B" y" O 2,5 or by the pyroclore structure having the general chemical formula: A x A' x' A" x" B y B' y' B" y" O 3.5 Where: x + x' + x" ≤ 1 y + y' + y" ≤ 1 and A, A', A", B, B' and B" are as previously defined.

Inventors: CHRISTIANSEN NIELS, CHRISTIANSEN, NIELS
Applicants: TOPSOE HALDOR AS, HALDOR TOPSOE A/S
Application year: 1999
Main classification: C04B35
IPC codes: H01M8, C04B41, B32B9, C04B35, B01D71, C01B13