FR2980190A1 - MOLTEN PRODUCT FOR ELECTRODE. - Google Patents

Abstract

A molten product comprising, for more than 50% of its mass, a material having a eutectic structure and a composition such that: - (ZrO + dopant of the optional zirconia): 42.5% - 46.5%, - Mn 0: 53.5% -57.5%.

Description

TECHNICAL FIELD The present invention relates to a molten eutectic product, in particular for producing an element of a solid oxide fuel cell (SOFC), and in particular a cathode of such a cell. The invention also relates to processes for manufacturing said molten eutectic product. STATE OF THE ART FIG. 1 is a diagrammatic sectional view of an example of a solid oxide fuel cell (SOFC) manufactured by a hot pressing process. The stack 10 comprises first and second elementary cells, 12 and 14 respectively, separated by an interconnector layer 16. The first and second elementary cells being of similar structure, only the first elementary cell 12 is described. The first elementary cell 12 successively comprises an anode 18, an electrolyte layer 20 and a cathode 22. The anode 18 consists of an active anode layer 24 (in English "anode functional layer", or AFL), in contact with the electrolyte layer 20, and a support anode layer 26. The anode 18 is generally manufactured by a method of depositing on the support anode layer 26, an anode active layer 24, for example by screen printing (in English "screen printing"). At this stage, the layers 24 and 26 may be precursor-based of the final anode material. Consolidation by sintering is then performed. The cathode 22 consists of a cathode functional layer (or CFL) 28, in contact with the electrolyte layer 20, and a support cathode layer 30. Fuel cells or materials Suitable for use in the manufacture of fuel cells are, for example, described in WO2004 / 093235, EP 1 796 191, US Pat. No. 2007/0082254, EP 1,598,892 or EP 0 568 281. Among fuel cells, there is a distinction between fuel cells and fuel cells. capable of operating at "low" temperatures, that is, at temperatures of 850 ° C or lower. In such fuel cells, the electrolyte used, generally in the form of a thin film, is generally a doped cerium oxide, for example gadolinium, or stabilized zirconia, for example yttrium or scandium.

The cathode is generally made from "LSCF" materials, that is, materials of the formula Lao (x) Sr, C00-yTe103-8, which are mixed conductors, i.e. both ionic and electronic conductors. However, the "LSCF" can react with the zirconia doped with the electrolyte or with the active cathode layer to form new phases at their interface, in particular a SrZrO 3 phase, as described in "Time-dependent performance of mixed- SOFC cathodes ", Solid State Ionics, Volume 177, Issues 19-25, p 1965-1968, especially in Figure 6, for the product La0.58Sr0.4Co0.2Fe0.803_8. The presence of these phases can reduce the performance of the battery.

In addition, it is preferable that the cathode material has a coefficient of thermal expansion close to that of the electrolyte material, so as not to generate stresses that can lead to the creation of cracks and the decommissioning of the fuel cell. In order to increase the performance of SOFC batteries operating at low temperatures, there is therefore a need for a mixed conductive product, capable of forming only a small amount of new phases when in contact with a doped zirconia powder, in particular the SrZrO3 phase and having a coefficient of thermal expansion close to that of the electrolyte material, in particular when the latter is a doped zirconia. An object of the invention is to respond, at least partially, to this need.

SUMMARY OF THE INVENTION According to the invention, this object is achieved by means of a melted product consisting, for more than 50% of its mass, of a material having a eutectic structure and a composition such that: - (ZrO 2 + dopant of the optional zirconia): 42.5% - 46.5%, - Mn304: 53.5% - 57.5%, in molar percentages based on the sum of the ZrO 2, dopant and Mn 3 O 4 contents. This material is hereinafter referred to as "eutectic material".

As will be seen in more detail in the following description, a product according to the invention advantageously has properties that make it suitable for application to batteries of the SOFC type, in particular in a cathode and / or an active layer. cathode. Preferably, said eutectic material represents more than 60%, more than 70%, more than 90%, more than 95%, more than 98%, even substantially 100% of the mass of a melted product according to the invention. The 100% complement is preferably constituted by impurities and / or optionally doped zirconia and / or MnO manganese oxide and / or Mn203 manganese oxide and / or Mn304 manganese oxide. In regions that are not in said eutectic material, the molten product may have different chemical compositions and / or different structures (for example with a fibrous structure or a regular structure) than that of said eutectic material. Said eutectic material may also comprise one or more of the following optional characteristics (to the extent that they are not incompatible): - For a total of 100%, in molar percentages based on the sum of the ZrO 2 contents, dopant and in Mn 3 O 4, - (ZrO 2 + dopant): 43% - 46% - Mn 3 O 4: 54% - 57%, - Preferably - (ZrO 2 + dopant): 43.5% - 45.5% - Mn 3 O 4 54.5% - 56.5%, - Preferably - (ZrO 2 + dopant): 44% - 45% Mn 3 O 4 55% - 56%, - Preferably - (ZrO 2 + dopant): 44.5% - Mn 3 O 4 55.5%, - In the eutectic material, the constituents other than ZrO 2, the dopant and Mn 3 O 4 represent less than 5%, less than 3%, less than 2%, less than 1% by weight; The zirconia is not doped or is doped with an element chosen from cerium, yttrium, magnesium, calcium, scandium, aluminum and their mixtures, preferably chosen from cerium; a mixture of scandium and aluminum, a mixture of scandium and cerium, and yttrium. More preferably, the dopant is yttrium; More than 90%, more than 95%, or even substantially 100%, in mole percentage, of ZrO 2 zirconia is doped; The molar dopant content of the ZrO 2 zirconia, based on the sum of the zirconium cation and dopant cation contents, is greater than 5% and / or less than 25%; ZrO 2 zirconia is preferably doped only with yttrium; The molar content of yttrium, based on the sum of the molar contents of zirconium cations and yttrium cations, is preferably greater than 5%, preferably greater than 10%, preferably greater than 15%, and or less than 22%, preferably less than 21%, preferably substantially equal to 16% or substantially equal to 20%; ZrO2 zirconia is doped only with scandium; The molar content of scandium, based on the sum of the molar contents of zirconium cations and scandium cations, is preferably greater than 14% and / or less than 22%, preferably substantially equal to 20%; ZrO 2 zirconia is doped only with a mixture of scandium on the one hand and aluminum and / or cerium on the other hand; In this embodiment: the molar content of scandium, on the basis of the sum of the molar contents of zirconium, scandium, aluminum and cerium cations, is preferably greater than 14% and / or less than 22%, preferably substantially equal to 20%; and / or the molar content of aluminum on the basis of the sum of the molar contents of zirconium, scandium, aluminum and cerium cations is preferably greater than 1% and / or less than 3%, preferably substantially equal to 2% ; and / or the molar content of cerium on the basis of the sum of the molar concentrations of zirconium, scandium, aluminum and cerium cations is preferably greater than 0.5% and / or less than 1.5%, preferably substantially equal to at 1%; Zirconia, manganese oxide Mn304 and dopant together preferably represent more than 90%, more than 95%, more than 98%, more than 99%, or even substantially 100% of said melted material, or even of the eutectic product according to the invention, in percent by weight; Preferably, the 100% complement is constituted by impurities; The eutectic material has an impurity content of less than 5%, less than 3%, preferably less than 2%, more preferably less than 1% by mass percentage; - The eutectic material preferably has a fibrous structure; At least a part of the manganese of the eutectic material, preferably more than 5 atom%, more than 10 atom%, or even more than 15 atom%, is solubilized in the zirconia. The solubility of manganese in zirconia can be in particular equal to 16 atom%. A melted product according to the invention may be in the form of a melted ball, a melted plate, a melted block, or a particle or powder resulting from a grinding of a such melted plate or such a melted block. The present invention also relates to a powder of melted product particles according to the invention. A powder according to the invention may also comprise one or more of the following optional characteristics: the median size D 50 is greater than 0.3 μm, even greater than 0.5 μm, or even greater than 1 μm, or even greater than 2 μm; 1m, and / or less than 80μm, or even less than 50μm, or even less than 4011111; In a first particular embodiment, the powder has a median size greater than 0.3 μm, even greater than 0.5 μm, even greater than 1 μm, and less than 10 μm, or even less than 4 μm. The characteristics of an active cathode layer of the SOFC stack obtained from such a powder are advantageously improved; In a second particular embodiment, the powder has a median size greater than 10 μm, even greater than 20 microns, even greater than 30 μm, and even greater than 40 μm, and / or less than 80 μm, or even less than at 50 microns; Preferably, the median size is about 45 microns; The characteristics of a cathode layer supporting the SOFC stack obtained from such a powder are advantageously improved; The maximum size of the powder is less than 200 μm, or even less than 150 or even less than 110 μm; - The distribution of the form factor R of the powder is such that: o less than 90%, or even less than 80% of the particles of the powder have a form factor R greater than 1.5, and / or o more than 10 %, or even more than 20%, and / or less than 60% or even less than 40% of the particles of the powder have a form factor R greater than 2, and / or more than 5%, or even more than 10%, and / or less than 40% or even less than 20% of the particles of the powder have a form factor R greater than 2.5, and / or o more than 2% or even more than 5%, and / or less than 20% or even less than 10% of the particles of the powder have a form factor R greater than 3, the percentages being percentages by number, the factor of form of a particle being the ratio L / W between the length L and the width W of said particle; The particles of the powder are ground particles, that is to say resulting from a grinding operation of a molten product, for example in the form of larger particles or blocks. Such grinding gives a particular shape to the ground particles. The invention also relates to a preform or "green part" obtained by shaping a powder according to the invention, a sintered product obtained from such a preform, in particular a sintered part or a sintered layer. The preform or the sintered product may in particular be in the form of a layer of thickness less than 2 mm, less than 1 mm or less than 500 pin. The sintered product may in particular have a total porosity greater than 20%, preferably between 25% and 50% by volume, preferably between 25% and 45% by volume. The present invention also relates to an electrode, in particular at a cathode, comprising a region, in particular a functional cathode, said electrode, in particular said functional cathode being constituted from a powder according to the invention. The invention also relates to an elementary cell of a solid oxide fuel cell comprising an electrode, preferably a cathode according to the invention, and such a fuel cell. The invention finally relates to a manufacturing method, called "general manufacturing process", comprising the following successive steps: a) preparation, by mixing particulate raw materials, of a feedstock comprising ZrO 2, a manganese oxide, optionally a dopant of zirconia, and / or a precursor of one or more of these constituents; b) melting of the feedstock until a molten material is obtained, c) cooling to complete solidification of said molten material so as to obtain a molten product comprising a eutectic material, d) optionally, grinding said melted product, e) optionally, shaping, or even sintering, of the melted and optionally ground product, the raw materials being chosen so that at the end of step c), the melted product obtained is in accordance with cooling in step c) comprising contacting the molten material and / or the molten product with a fluid comprising oxygen. Preferably, the oven used in step b) is selected from an induction furnace, a plasma torch, an arc furnace or a laser. Definitions A product is conventionally called "molten" when it is obtained by a process involving a melting of raw materials in the form of a liquid mass (or "molten material"), then a solidification of this liquid mass. by cooling. A liquid mass may comprise solid particles, but insufficient to stiffen said mass. Conventionally referred to as "eutectic" is a structure or morphology obtained by melting a eutectic composition and then curing the melt by cooling. The chapter "Solidification microstructure: Eutectic and peritectic" of the document "Fundamentals of Solidification", third edition, W. KURZ and D. J. FISHER, Trans. Tech. Publication Ltd, Switzerland (1989), describes eutectic structures. A eutectic structure can be of two types: regular (normal) or irregular (abnormal).

A regular structure can be in particular fibrous (Figure 5A) or lamellar (Figure 5B). The regular structure of the eutectic material of a product according to the invention preferably has a fibrous morphology, in which there is a marked crystallographic relationship between the phases of the eutectic. Indeed, the fibrous morphology corresponds to a morphology in which one of the phases, in the form of fibers, is embedded in a continuous matrix formed by the second phase. The axis of the fibers is then parallel to the direction of propagation of the growth front Df (FIG. 5A). A fibrous structure may in particular result from a process for the manufacture by melting of an eutectic mixture comprising a solidification step at a speed greater than 0.17 K / s, preferably greater than 1.7 K / s, greater than 8 , 5 Kls, greater than 17 K / s, greater than 34 K / s, greater than 50 K / s, or even greater than 85 K / s. An irregular eutectic structure has no relationship between the orientation of the two phases, although fibers generally grow along the direction of propagation of the eutectic growth front (Figures 5C and 5D).

A "dopant" of zirconia is a metal cation other than the zirconium cation, integrated within the crystalline ZrO2 lattice, most often in solid solution. The dopant may be present as an insertion and / or substitution cation within the zirconia. When ZrO 2 zirconia is said to be "doped at x% with a dopant", this conventionally means that in said doped zirconia, the amount of dopant is the molar percentage of dopant cations on the basis of the total amount of dopant and zirconium cations. For example, in a zirconia doped with 20 mol% yttrium (Y), 20% of the zirconium cations are replaced by yttrium cations. Similarly, in a zirconia doped with 20% of scandium (Sc) and 1% of cerium, 21% of the zirconium cations are replaced by 20% of scandium cations and 1% of cerium cations. "ZrO2", "zirconia" and "zirconium oxide" are synonymous. By (ZrO 2 + dopant) is meant the sum of the molar contents of zirconium cations and dopant.

A precursor of ZrO 2, Mn 3 O 4 or dopant is a compound capable of leading to the formation of these oxides or dopant, respectively, by a process involving melting and then cooling solidification. Zirconia doped with a dopant or with an oxide of said dopant is a particular example of a precursor of said dopant.

By "particle size" is meant the size of a particle conventionally given by a particle size distribution characterization performed with a laser granulometer. The laser granulometer used here is a Partica LA-950 from the company HORIBA. The percentiles or "percentiles" (D10), 50 (D50), 90 (D90) and 99.5 (D99.5) of a powder are the particle sizes corresponding to the percentages, by mass, of 10%, 50 %, 90% and 99.5%, respectively, on the cumulative particle size distribution curve of the powder particles, the particle sizes being ranked in ascending order. For example, 10% by weight of the particles of the powder are smaller than D10 and 90% of the bulk particles are larger than D10. Percentiles can be determined using a particle size distribution using a laser granulometer. The "maximum size" is the 99.5 percentile (D99.5) of said powder. The so-called "median size" is the percentile D50, that is to say the size dividing the particles into first and second populations equal in mass, these first and second populations comprising only particles having a larger size, or smaller respectively, at the median size. The "ratio of shape" R is the ratio between the largest apparent dimension, or "length" L, and the smallest apparent dimension, or "width" W, of a particle. The length and the width of a particle are classically evaluated by the following method. After taking a representative sample of the particles of the powder, these particles are partially embedded in the resin and undergo polishing capable of making possible a polished surface observation. The shape factor measurements are made from images of these polished surfaces, these images being acquired with an electron scanning microscope (SEM), in secondary electrons, with an acceleration voltage of 10 kV and a magnification of x100. (This represents 1 μm per pixel on the SEM used). These images are of preference acquired in areas where the particles are best separated, in order to subsequently facilitate the determination of the form factor. On each particle of each image are measured the largest apparent dimension, called length L, and the smallest apparent dimension, called W. Preferably, these dimensions are measured using an image processing software, such as for example VISILOG sold by the company NOESIS. For each particle, the form factor R = L / W is calculated.

By "impurities" is meant the inevitable constituents introduced involuntarily and necessarily with the raw materials or resulting from reactions with these constituents. Impurities are not necessary constituents, but only tolerated. For example, the compounds forming part of the group of oxides, nitrides, oxynitrides, carbides, oxycarbides, carbonitrides and metallic species of sodium and other alkalis, iron, vanadium and chromium are impurities if their presence is not desired. Unless otherwise indicated, all percentages are molar percentages. "With one" means "at least one" or "with one or more" unless otherwise indicated.

BRIEF DESCRIPTION OF THE FIGURES Other features and advantages of the invention will become apparent on reading the following description and on examining the appended drawing in which FIG. 1 is a diagrammatic sectional view of a solid oxide fuel cell. (SOFC); FIGS. 2, 3 and 4 represent photographs of molten eutectic products of ZrO 2 doped with 8 mol% Y 2 O 3 - Mn 3 O 4 of Examples 2, 3 and 4, respectively, according to the invention, taken with the aid of a microscope. scanning electronics (SEM); Figure 5 shows diagrams illustrating regular (Figure 5A and 5B) and irregular (Figure 5C and 5D) eutectic morphologies.

In the photographs, the zirconia doped with 16 mol% of Y appears white and the manganese oxide Mn304 appears gray in color. DETAILED DESCRIPTION Conventional melting methods, adapted to obtain the desired composition and microstructure, make it possible to manufacture molten products according to the invention, of different sizes, for example in the form of particles or blocks. A melted product according to the invention may in particular be manufactured according to steps a) to e).

In step a), the feedstock is conventionally adapted so that the manufacturing process leads, at the end of step c), to a molten product according to the invention optionally having one or more optional features described above.

The dopant can be added separately from the zirconia in the feedstock. It is also possible to add, in the starting charge, the doped zirconia. The oxides ZrO 2, Mn 3 O 4, Mn 2 O 3, MnO, the zirconium dopants and their precursors preferably constitute, with the impurities, 100% of the oxides of the feedstock. Preferably, the impurities are such that, in molar percentages based on the oxides of the feedstock: CeO.sub.2 <0.5%, when the dopant is not a mixture of scandium and aluminum and / or cerium; and / or Na2O4 <0.5%; and / or Fe2O3 <1%; and / or - Al 2 O 3 <0.3%, when the dopant is not a mixture of scandium and aluminum and / or cerium; and / or TiO2 <0.3%; and / or CaO <0.2%, when the dopant does not contain calcium; and / or MgO 4 <0.2%, when the dopant does not contain magnesium.

In step b), it is possible in particular to use an induction furnace, a plasma torch, an arc furnace or a laser. Preferably, an arc or induction furnace is used. Advantageously, it is thus possible to obtain large quantities of product, industrially. In step b), the melting is preferably carried out under oxidizing conditions. The oxidizing conditions in step b) can be maintained in step c). Step c) preferably comprises bringing the molten material into contact with a fluid comprising oxygen. Preferably, the fluid comprises more than 10% oxygen, more than 20% oxygen, by volume. Preferably, the fluid is air. The molten product obtained at the end of step c) can also be brought into contact with such a fluid comprising oxygen. In step c), the cooling rate is preferably greater than 0.17 K / s, preferably greater than 1.7 K / s, or even greater than 8.5 K / s, or even greater than 17 K / s, or even above 34 K / s, or even above 50 K / s, or even above 85 K / s. Such a cooling rate, coupled with bringing the molten material and / or the molten product into contact with a fluid comprising oxygen, advantageously makes it possible to keep the content of manganese oxide in the form Mn304 substantially constant (no or little conversion to Mn203). In step d), optional, the melt product from step c) can be milled to facilitate the effectiveness of subsequent steps. The granulometry of the crushed product is adapted according to its destination. If necessary, the ground particles undergo a granulometric selection operation, for example by sieving.

The crushed particles, and optionally sieved, can in particular have a size greater than 0.1 μm, or even greater than 1 μm, or even greater than 0.3 μm, or even greater than 0.5 μm, or even greater than 1 μm, or even greater at 15 μm, or even greater than 20 μm, and / or less than 6 mm, even less than 4 mm, even less than 3 mm, even less than 70 μm, or even less than 50 μm.

In step e), optional, the product is shaped, in particular to be sintered. All conventional shaping and sintering techniques can be used. In a particular embodiment, the sintering is carried out in situ, that is to say after the melted product, possibly ground, has been placed in its service position, for example in the form of a cathode layer. .

A product according to the invention may have a high total porosity, typically greater than 20% and / or less than 60%. The porosity of said product is of great importance because the pores are the seat of part of the catalysis reactions necessary for the operation of the fuel cell. Pores are also the means of conveying a gas, usually air, within the cathode.

The invention also relates to a first particular manufacturing method comprising the steps a), b) described above, and a step c) comprising the following steps: ci ') dispersion of the melt in the form of liquid droplets, cl ") solidification of these liquid droplets by contact with a fluid comprising oxygen, so as to obtain melt particles according to the invention.

By simple adaptation of the composition of the feedstock, conventional dispersion processes, in particular by blowing, centrifugation or atomization, thus make it possible to manufacture, from a molten material, particles into a molten product according to the invention. invention.

A first particular manufacturing method may further include one or more of the optional features of the general manufacturing method listed above. At the end of step c), beads according to the invention are obtained in a melted product according to the invention. In another variant, the dispersion stages ci ') and the solidification stages ci ") are substantially simultaneous, the means used for the dispersion causing the melt to cool, for example, the dispersion results from a blowing of a gas comprising oxygen, for example air, through the melting material, the temperature of said gas being adapted to the desired rate of solidification, the contact between the droplets and the oxygen-containing fluid may be However, preferably a contact between the droplets and this fluid is maintained until complete solidification of said droplets. In step c1 "), the solidification rate of the liquid droplets is preferably greater than 8, 5 K / s, or even higher than 17 K / s, or even higher than 25.5 K / s.

The invention also relates to a second particular manufacturing method comprising the steps a) and b) described above as part of the general manufacturing process, and a step c) comprising the following steps: c2 ') pouring said molten material in a mold; c2 ") solidification, by cooling with a fluid comprising oxygen, of the material cast in the mold until a block at least partially, or completely, solidified; c2" ') demolding the block. This second particular manufacturing method may further include one or more of the optional features of the general manufacturing method listed above. In a particular embodiment, in step c2 '), a mold is used which allows rapid cooling. In particular, it is advantageous to use a mold capable of forming a block in the form of a plate, and preferably a mold as described in US 3,993,119. In step c2 ') and / or in step c2 ") and / or in step c2'") and / or after step c2 "), said material is brought into contact with an oxidizing fluid. melting and / or the cast material being solidified in the mold and / or the demolded block, the fluid comprising oxygen used in step c2 ') and / or in step c2 ") and / or in step c2 '") and / or after step c2"), preferably gaseous, preferably air, may be the same. Preferably, said contact with the oxygen-containing fluid is initiated as soon as the molten material is poured into the mold and until the block is demolded. More preferably, maintaining said contact until complete solidification of the block. In step c2 "), the solidification rate of the liquid droplets is preferably greater than 8.5 Kis, or even greater than 17 K / s, or even greater than 25.5 Kis. is preferably demolding before complete solidification of the block. Preferably, the block is demolded as soon as it has sufficient rigidity to substantially retain its shape. The effect of the contact with the fluid comprising oxygen is then increased. The first and second particular methods are industrial processes for manufacturing large quantities of products, with good yields. Of course, other methods than those described above could be envisaged for making a molten product according to the invention. A powder of a molten product according to the invention may in particular be used to manufacture a porous product according to the invention, in particular a porous cathode layer and / or a porous cathode active layer, for example by following a method comprising the following successive stages: A) preparation of a powder of a melted product according to the invention; B) shaping the powder prepared in step A); C) sintering of said powder thus shaped. The product powder according to the invention used in step A) may in particular be manufactured according to steps a) to f) described above. In step B), the powder may be deposited in the form of a layer.

In step C), the shaped powder is sintered according to conventional sintering techniques, preferably by hot pressing. Examples The following nonlimiting examples are given for the purpose of illustrating the invention. The products of the examples according to the invention 2, 3 and 4 were obtained by melting in floating zone under laser heating ("Laser floating zone" in English), using a CO2 laser power 600 Watts. The raw materials used are as follows: a zirconia powder doped with 16 mol% of yttrium, sold by the company TOSOH under the name 8YSZ, with a median size equal to 0.25 μm and a purity equal to 99.9%; an MnO manganese oxide powder, marketed by Sigma Aldrich under the name MnO Manganese (II) oxide powder-60 Mesh, with a purity equal to 99%. The raw materials in powder are chosen and their quantities adapted according to the product to be manufactured. In the present case, the raw material mixture consists of 73% MnO and 27% 8YSZ, in percentages by weight. These raw materials are intimately mixed in a ball mill. When mixing in the ball mill, a solution of 5% PVA and 95% water is added in proportions of 1 ml per 1.5 to 2 g of powder mixture. The mixture thus obtained is put in the form of rods by cold isostatic pressing ("Cold Isostatic pressing" or "CEP" in English) at 200 Mbar for 3 to 4 minutes. The rods obtained are then sintered in air as follows: Increase of the ambient temperature to 400 ° C. to 2 ° C./min; Bearing 30 minutes at 400 ° C; Rise from 400 ° C to 1300 ° C at 5 ° C / min; Bearing 120 minutes at 1300 ° C; Descent at room temperature to 10 ° C / min.

The rods thus sintered are then moved in translation (without rotation of the rods) through the beam of a laser set to 60W. They thus undergo a floating zone melting under laser heating, in air, with a constant growth rate of between 50 and 500 mm / h, which corresponds to a cooling rate of between 8.5 and 85 K / s. After directional solidification, the product of the rods is a melted product according to the invention. The product La0.58Sro, 4Coo, 2Fe0, 803_8 of Comparative Example 1 is the product described in "Time-dependent performance of mixed-conduct SOFC cathodes," Solid State Ionics, Volume 177, Issues 19-25, 1965- 1968. In the various examples according to the invention, the content of impurities was less than 2%. The nature of the manganese oxide is evidenced by X-ray diffraction. In the products of the examples according to the invention 2, 3 and 4, the X-ray diffracted manganese oxide is Mn 3 O 4. All the products of the examples according to the invention are made up of more. 99%, in a eutectic material. The results are summarized in Table 1 below: Ex Material Zr02 doped with Mn304 (% mol Vr Structure New Fig 16 mol% of) (K / s) Eutectiqu phase created Y e in contact with (% mol) the zirconia doped 1 * La0.58Sr0.4C00.2Feo, 803-8 - - - SrZr03 - 2 Zr02 doped Y203: 44.5 55.5 8.5 fibrous - 2 Mn304 3 Zr02 doped Y203: 44.5 55.5 17 fibrous - 3 Mn304 4 Zr02 doped Y203: 44.5 55.5 85 fibrous - 4 Mn304 15: comparative example Vr: cooling rate during manufacture of the melted product Table 1 The products according to examples 2, 3 and 4 have a coefficient of thermal expansion at a temperature below 1000 ° C of the order of 1.10-6 ICI, which is of the same order of magnitude as that of the doped zirconia.

Moreover, the products according to the invention do not form an undesirable phase of SrZrO3 when they are used in SOFC cell electrodes, as is the case for the product according to Comparative Example 1. More generally, they exhibit a low reactivity vis-à-vis the doped zirconia which can constitute the electrolyte of a SOFC stack.

As it is now clear, the invention provides a new molten product comprising an optionally doped ZrO2 eutectic material: Mn304 perfectly adapted to the manufacture of SOFC batteries. Of course, the present invention is not limited to the embodiments described, provided for illustrative purposes.

Claims (23)

REVENDICATIONS1. A molten product comprising, for more than 50% of its mass, a eutectic material having a eutectic structure and a composition such that: (ZrO 2 + dopant of the optional zirconia): 42.5% - 46.5%, - Mn304 : 53.5% - 57.5%, in molar percentages based on the sum of the ZrO 2, dopant and Mn 3 O 4 contents. 2. Product according to the preceding claim, wherein said eutectic material represents more than 70% of the mass. 3. Product according to the preceding claim, wherein said eutectic material represents more than 90% of the mass. A product according to any one of the preceding claims, wherein the composition of said eutectic material is such that, for a total of 100%, in molar percentages based on the sum of ZrO 2, dopant and Mn 3 O 4 contents; (ZrO 2 + dopant): 43% - 46%, - Mn 3 O 4: 54% - 57%. - 5. The product according to the immediately preceding claim, wherein the composition of said eutectic material is such that for a total of 100%, in molar percentages or the base of the sum of the contents of Zr02, dopant and Mn304; (ZrO 2 + dopant): 43.5% - 45.5%, - Mn 3 O 4: 54.5% - 56.5%. 6. The product according to the immediately preceding claim, wherein the composition of said eutectic material is such that for a total of 100%, in molar percentages or the base of the sum of the contents of Zr02, dopant and Mn304; - (ZrO 2 + dopant): 44% - 45%, - Mn 3 O 4 55% - 56%. The product according to any of the preceding claims, wherein in said eutectic material ZrO 2 is not doped or doped with a selected element among cerium, yttrium, magnesium, calcium, scandium, aluminum and their mixtures. 8. Product according to the preceding claim, wherein in said eutectic material, zirconia Zr02 is doped with yttrium. The product according to any of the preceding claims, wherein in said eutectic material, the molar dopant content, based on the sum of the molar contents of zirconium cations and dopant cations, is greater than 5%. and less than 25%. A product according to any one of the preceding claims, wherein in said eutectic material zirconia ZrO 2 is doped only with yttrium, the molar content of yttrium cations, based on the sum of the contents. molar zirconium cation and yttrium cation, being greater than 5% and less than 22%, or zirconia Zr02 is doped only with scandium, the molar content of scandium cations, on the basis of the sum of the molar contents of zirconium cations and scandium cations being greater than 14% and less than 22%, or ZrO 2 zirconia is doped only with a mixture of scandium and cerium, the molar content of scandium cations, on the base of the sum of the molar contents of zirconium cations, scandium cations and cerium cations being greater than 14% and less than 22%, and the molar content of cerium cations, on the basis of the molar contents of zircon cations in the case of scandium and cerium cation cations, being greater than 0.5% and less than 1.5%, or ZrO 2 zirconia is doped only with a mixture of scandium and aluminum, the molar content of cations of scandium, on the basis of the sum of the molar contents of zirconium cations, scandium cations and aluminum cations, being greater than 14% and less than 22%, and the molar content of aluminum cations, on the basis of the molar content of zirconium, scandium cation and aluminum cation, being greater than 1% and less than 3%. 11. Product according to the preceding claim, wherein, in said eutectic material, the molar content of yttrium cations, on the basis of the sum of the molar contents of zirconium cations and yttrium cations, is greater than 15%. and less than 21%. 12. A product according to any one of the preceding claims, wherein said eutectic material has a fibrous structure. 13. The powder of molten product particles as claimed in any one of the preceding claims. 14. Electrode comprising a region formed from a particle powder according to the preceding claim. 15. Manufacturing process comprising the following successive steps: a) Preparation, by mixing of particulate raw materials, of a feedstock comprising ZrO 2, a manganese oxide, optionally a zirconia dopant, and / or a precursor of one or more of these constituents, b) melting of the feedstock to obtain a melt, c) cooling to complete solidification of said melt to obtain a molten product comprising a eutectic material d) optionally, grinding said melted product, e) optionally forming, or even sintering, the melted product, optionally ground, the raw materials being chosen so that, after step c), the molten product obtained according to any one of claims 1 to 12, the cooling in step c) comprising contacting the molten material and / or the molten product with a fluid comprising oxygen. 16. The method according to the preceding claim, wherein the oven used in step b) is selected from an induction furnace, a plasma torch, an arc furnace and a laser. 17. A method according to any one of the two immediately preceding claims, wherein in step c) the cooling rate is greater than 0.17 K / s. 18. The method according to the preceding claim, wherein in step c), the cooling rate is greater than 1.7 K / s. 19. Method according to the preceding claim, wherein in step c), the cooling rate is greater than 8.5 K / s. 20. A method according to any one of the three immediately preceding claims, wherein in step c), the fluid comprising oxygen has more than 10% oxygen by volume. 21. Method according to the preceding claim, wherein the fluid comprising oxygen is air. 22. A process according to any one of claims 15 to 21, wherein step c) comprises the following steps: cl ') dispersing the molten material in the form of liquid droplets, ci ") solidification of these liquid droplets by contact with a fluid comprising oxygen, so as to obtain melted particles. 23. A process according to any one of claims 15 to 21, wherein step c) comprises the following steps: c2 ') pouring said molten material into a mold; c2 ") solidification, by cooling with a fluid comprising oxygen, of the material cast in the mold until a block at least partially, or completely, solidified; c2" ') demolding the block.