Method for producing a cerium-gadolinium oxide powder, in particular intended for the production of an electrolyte

Abstract

The invention relates to a method for producing a gadolinium-doped cerium oxide powder comprising a cobalt oxide, the method comprising the following successive steps of: 1) preparing a wet product comprising a mixture of: - particles of gadolinium-doped cerium oxide; - water containing a cobalt complex; d) optionally, removing at least some of the water; e) calcining the product obtained in step d), or, in the absence of step d), the product obtained in step 1), in an oxygenated fluid, so as to obtain the powder.

Description

[0001] PROCESS FOR PRODUCING A CERIUM GADOLINIUM OXIDE POWDER, IN PARTICULAR INTENDED FOR THE PRODUCTION OF AN ELECTROLYTE

[0002] Technical field

[0003] The invention relates to a method for manufacturing a powder based on gadolinium-doped cerium oxide. It also relates to a method for manufacturing a sintered product, in particular an electrolyte, as well as a solid oxide fuel cell and a solid oxide electrolysis cell comprising such an electrolyte. Finally, it relates to the powder based on gadolinium-doped cerium oxide obtained or capable of being obtained according to the method of the invention.

[0004] State of the art

[0005] In the field of solid oxide fuel cells (or "SOFCs") and solid oxide electrolysis cells (or "SOECs"), gadolinium-doped cerium oxide (or "CGO"), used as an electrolyte, represents an interesting alternative to yttrium-stabilized zirconia due to its higher ionic conductivity for lower operating temperatures (500°C-700°C).

[0006] During electrolyte manufacturing, a high sintering temperature, greater than or equal to 1500°C, is necessary to obtain significant densification of the CGO. This typically results in a reduction in mechanical properties linked to a coarsening of the microstructure.

[0007] In order to achieve high densification at lower temperatures, it is known to use nanometric CGO powders and / or to use as sintering agent a small amount of transition metal oxides, such as cobalt, copper, nickel, manganese, or iron.

[0008] The addition of cobalt oxide to CGO powder is conventionally carried out by suspending CGO powder in ethanol, followed by the addition of cobalt dinitrate dissolved in ethanol, drying and calcination, for example at 400°C, the calcination transforming the cobalt dinitrate into cobalt oxide.

[0009] There is a continuing need to improve the manufacturing process of a sintered electrolyte.

[0010] One aim of the invention is to meet, at least partially, this need.

[0011] Summary of the invention

[0012] The invention provides a method for manufacturing a gadolinium-doped cerium oxide powder comprising a cobalt oxide, or "Co-CGO powder", said method comprising the following successive steps:

[0013] 1) preparation of a wet product comprising, preferably consisting of a mixture:

[0014] - gadolinium-doped cerium oxide particles;

[0015] - water containing a cobalt complex; the wet product preferably having a Qc ratio o ' / QCGO' such that 0.005 < Qco' / QCGO' < 0.15, QCGO' designating the sum of the molar quantities of cerium and gadolinium in the wet product, and Qco' designating the molar quantity of cobalt in the wet product, d) optionally, elimination of at least part of the water; e) calcination of the product resulting from step d), or, in the absence of step d), resulting from step 1), in an oxygenated fluid, so as to obtain said Co-CGO powder.

[0016] Surprisingly and unexplainedly, the inventors discovered that the sintering of the powder according to the invention is improved.

[0017] Co-CGO particles have the shape of gadolinium-doped cerium oxide particles coated with cobalt oxide particles. The coating is particularly homogeneous.

[0018] In a preferred embodiment, the method comprises a step d) and step 1) comprises the following steps: a) suspending a gadolinium-doped cerium oxide powder in water; b) adding, to the suspension, at least one water-soluble cobalt compound, or "first reactant", so as to form cobalt cations, the amount of first reactant preferably being determined so that 0.005 < Qco / QCGO < 0.15, QCGO denoting the sum of the molar amounts of cerium and gadolinium added in step a) and Qc odesignating the molar quantity of cobalt brought by the first reagent; c) adding, to the suspension, at least one water-soluble cobalt ligand and / or at least one precursor of a said ligand, or “second reagent”, so as to form a cobalt complex.

[0019] A method according to the invention may also comprise one or more of the following optional and preferred features:

[0020] - the Qc report o ' / QCGO' is greater than or equal to 0.01, preferably greater than or equal to 0.02, and less than or equal to 0.10, preferably less than or equal to 0.05 and / or wherein in step b), the ratio Qc o / QCGO is greater than or equal to 0.01, preferably greater than or equal to 0.02 and less than or equal to 0.10, preferably less than or equal to 0.05;

[0021] - the molar content of gadolinium in the gadolinium-doped cerium oxide powder of said wet product and / or of the powder suspended in step a), expressed as a percentage based on the sum of the molar contents of cerium and gadolinium, is greater than or equal to 10% and less than or equal to 20%;

[0022] - in step a), the median size of the gadolinium-doped cerium oxide powder is greater than 20 nm and less than 0.8 pm;

[0023] - the gadolinium-doped cerium oxide powder of said wet product and / or the powder suspended in step a) is obtained by a fusion process;

[0024] - the first reagent has a solubility in water, measured at 20°C, greater than 300 g / l;

[0025] - the first reagent is chosen from a cobalt dinitrate, a cobalt acetate, a cobalt acetylacetonate, a cobalt dichloride, a cobalt difluoride, a cobalt sulfate, a cobalt tartrate, a cobalt bromide, a cobalt iodide, a cobalt thiocyanate, a cobalt phosphate, and mixtures thereof, and / or the second reagent is chosen from molecules comprising an amino group (-NH2) and / or a carboxylate group (-COO) and / or a thiol group (-SH);

[0026] - the first reagent is chosen from a cobalt dinitrate, a cobalt acetate, and their mixtures, and / or the second reagent is chosen from urea and its derivatives, citric acid, oxalic acid, ethylenediamine, salen, ethylenediaminetetraacetic acid, and their mixtures;

[0027] - the first reagent is a cobalt dinitrate and / or the second reagent is chosen from urea and its derivatives;

[0028] - in step c), the quantity of the second reagent is adapted so that more than 99% of the quantity of cobalt cations in the suspension are complexed;

[0029] - in step c), the second reactant contains only carbon, hydrogen, and oxygen atoms, and optionally nitrogen and / or chlorine atoms;

[0030] - in step d), more than 80% by mass of the water is removed;

[0031] - in step e), the calcination temperature is greater than 300°C and less than 800°C, the holding time at said temperature preferably being greater than 1 hour and less than 10 hours.

[0032] The invention also relates to a gadolinium-doped cerium oxide powder comprising a cobalt oxide, said powder having the following chemical analysis, in mass percentage based on the oxides:

[0033] - more than 9.60% and less than 20.79% of Gd2O3, and

[0034] - more than 72.55% and less than 89.32% of CeCL, and

[0035] - more than 0.23% and less than 6.51% of cobalt oxide expressed as CO3O4, and

[0036] - less than 2% of oxides other than Gd2C>3, CeO2, and cobalt oxide expressed as CO3O4, the powder of gadolinium-doped cerium oxide particles being at least partially coated with cobalt oxide particles, such that the N90-N10 difference, or “E value”, is greater than 110,

[0037] N10 and N90 being, on a cobalt map

[0038] - consisting of pixels, each pixel having a shade of a color, said shade being between 0 and 255, and

[0039] - carried out by energy spectrometry on a pellet consisting of a compression of the powder at a pressure of 125 MPa, the shades corresponding to the percentages in number of said pixels of 10% and 90% respectively, on the cumulative distribution curve of the pixels, according to the shades, without taking into account the pixels having shade 0, the shades being classified in ascending order, a shade being all the higher as the cobalt content is high.

[0040] Preferably, the E value is greater than 125 and / or the powder has an S value of less than 2.20, preferably less than 2.00, the S value being the ratio (Ngo-Niol / Nso, where N50 is the shade corresponding to the percentage by number of said pixels of 50% on said cumulative distribution curve.

[0041] The color may be, for example, green. Preferably, the powder is manufactured using a process according to the invention.

[0042] The invention also relates to a method for manufacturing a sintered part comprising a step f) of manufacturing a preform from a powder according to the invention, preferably manufactured or capable of having been manufactured by a method for manufacturing a powder according to the invention, then a step g) of sintering the preform so as to obtain a sintered part.

[0043] The sintering of the preform is preferably carried out at a temperature below 1500°C, preferably below 1490°C.

[0044] The invention also relates to a method for manufacturing a device chosen from a solid oxide fuel cell and a solid oxide electrolysis cell, comprising the manufacture of a sintered part from a powder manufactured or capable of having been manufactured by a method for manufacturing a powder according to the invention, said sintered part being found after manufacture between electrodes of said battery or of said electrolysis cell so as to constitute an electrolyte.

[0045] Said method preferably comprises the manufacture of a sintered part manufactured according to a method according to the invention, said sintered part being found after manufacture between electrodes of said battery or said electrolysis cell so as to constitute an electrolyte.

[0046] The invention also relates to a wet product comprising particles of gadolinium-doped cerium oxide in water containing a cobalt complex. It also relates to the Co-CGO powder obtained or capable of being obtained according to a process of the invention.

[0047] The invention finally relates to the sintered part, in particular the electrolyte, and the device obtained according to a method of the invention.

[0048] Brief description of the figures

[0049] Other characteristics and advantages of the invention will become apparent upon examination of the description which follows and with regard to the appended drawing in which:

[0050] - figure 1 [Fig 1] represents a photograph taken using a scanning electron microscope of particles of the powder of example 1, outside the invention;

[0051] - Figure 2 [Fig 2] represents a cobalt map produced by energy dispersive spectroscopy (or “EDS”) of the same particles as those present in Figure 1;

[0052] - figure 3 [Fig 3] represents a photograph taken using a scanning electron microscope of particles of the powder of example 2, according to the invention;

[0053] - Figure 4 [Fig 4] represents a cobalt mapping carried out by EDS of the same particles as those present in Figure 2;

[0054] - Figure 5 [Fig 5] represents the cumulative distribution of pixels, as a function of shades, for the maps of examples 1, 2 and 3, in solid lines for example 1 (the percentiles Nio, Nso and N90 being identified), in dotted lines for example 2 and in mixed lines for example 3. Figures 1 to 4 were all produced with the same magnification.

[0055] Definitions

[0056] A "cobalt complex" is a compound classically formed by the association of at least one cobalt cation with molecules or ions capable of providing an electronic pair to the said cobalt cation(s). These pair donors are classically called "ligands".

[0057] The 50th (D50) and 90th (D90) percentiles or "percentiles" of a powder are the particle sizes corresponding to the 50% and 90% percentages, by volume, respectively, on the cumulative particle size distribution curve of the powder particles, with the particle sizes listed in ascending order. For example, 90%, by volume, of the particles in the powder are smaller than D90 and 10% of the particles by volume are larger than D90. The percentiles can be determined using a particle size distribution performed with a laser particle size analyzer.

[0058] The fifty percentile of a powder is called the "median size" of that powder.

[0059] By "impurities" is meant unavoidable constituents, introduced unintentionally and necessarily with the raw materials or resulting from reactions with these constituents. Impurities are not necessary constituents, but only tolerated. Preferably the mass quantity of impurities is less than 2%, less than 1%, less than 0.5%, or even substantially zero.

[0060] The verbs "to understand" or "to behave" or "to present" should be interpreted in a non-restrictive manner, unless otherwise indicated.

[0061] Detailed description

[0062] Other features and advantages of the present invention will become apparent upon reading the detailed description of a preferred embodiment which follows, provided for illustrative and non-limiting purposes.

[0063] In particular, step 1) described in detail comprises steps a) to c). However, those skilled in the art may consider other known techniques for manufacturing the wet product.

[0064] All the preferred characteristics for the CGO powder used in step a), and in particular the characteristics relating to the particle size distribution and the gadolinium content, are also preferred characteristics for the CGO powder of step 1).

[0065] Similarly, the Qc report o ' / QCGO' is preferably such that 0.005 < Qco' / QCGO' < 0.15, QCGO' denoting the sum of the molar quantities of cerium and gadolinium in the wet product, and Qc o ' denoting the molar quantity of cobalt in the wet product. Preferably, the ratio Qc o' / QCGO' is greater than or equal to 0.01, preferably greater than or equal to 0.02 and less than or equal to 0.10, preferably less than or equal to 0.05. Method of a according to the invention

[0066] In step a), a CGO powder is suspended in water.

[0067] The CGO powder can be manufactured by any conventional method. In a preferred embodiment, the CGO powder is obtained by a melting process, preferably an arc furnace melting process.

[0068] The molar content of gadolinium in the CGO powder, expressed as a percentage based on the sum of the molar contents of cerium and gadolinium, is preferably greater than or equal to 10%, and preferably less than or equal to 20%. In one embodiment, this content is equal to 10%. In one embodiment, this content is equal to 20%.

[0069] Preferably, the median size of the gadolinium-doped cerium oxide powder is greater than 20 nm, preferably greater than 30 nm, preferably greater than 50 nm, preferably greater than 0.1 pm, and preferably less than 0.8 pm, preferably less than 0.6 pm, preferably less than 0.4 pm.

[0070] Preferably, the D90 of the gadolinium-doped cerium oxide powder is less than 2.5 pm, preferably less than 2 pm.

[0071] Water is preferred, but other equivalent solvents are possible.

[0072] Water preferably represents more than 30%, preferably more than 40%, preferably more than 45% and / or less than 90%, preferably less than 80%, preferably less than 70%, preferably less than 60%, preferably less than 55% of the mass of the suspension.

[0073] The CGO powder and water together preferably represent more than 95%, more than 98%, preferably more than 99% of the mass of the suspension, the remainder to 100% preferably consisting of impurities.

[0074] Preferably, the suspension contains only water and CGO powder.

[0075] The suspension is traditionally made by simple mixing.

[0076] In step b), the first reagent, chosen from water-soluble cobalt compounds and their mixtures, is added to the suspension. The objective of step b) is to form cationic cobalt in the suspension.

[0077] The sum of the molar quantities of cerium and gadolinium, QCGO, brought in step a) and the molar quantity of cobalt brought by the first reactant, Qc o , in step b) are such that 0.005 < Qco / QCGO < 0.15.

[0078] Preferably, the Qc report o / QCGO is greater than or equal to 0.01, preferably greater than or equal to 0.02 and / or preferably less than or equal to 0.10, preferably less than or equal to 0.05.

[0079] Any water-soluble cobalt compound is suitable, with water-soluble cobalt compounds with high solubility being preferred.

[0080] Preferably, the first reagent has a solubility in water, measured at 20°C, greater than 50 g / l, preferably greater than 100 g / l, preferably greater than 150 g / l, preferably greater than 200 g / l, preferably greater than 250 g / l, preferably greater than 300 g / l, and / or less than 1000 g / l. Preferably, the first reagent is selected from a cobalt dinitrate, in particular a hydrated cobalt dinitrate, a cobalt acetate, a cobalt acetylacetonate, a cobalt dichloride, in particular a hydrated cobalt dichloride, a cobalt difluoride, a cobalt sulfate, in particular a hydrated cobalt sulfate, a cobalt tartrate, a cobalt bromide, a cobalt iodide, a cobalt thiocyanate, a cobalt phosphate, and mixtures thereof.Preferably, the first reagent is selected from a cobalt dinitrate, in particular a hydrated cobalt dinitrate, a cobalt acetate, a cobalt dichloride, in particular a hydrated cobalt dichloride, a cobalt sulfate, in particular a hydrated cobalt sulfate, a cobalt bromide, a cobalt iodide, a cobalt thiocyanate, and mixtures thereof. Preferably, the first reagent is selected from a cobalt dinitrate, in particular a hydrated cobalt dinitrate, a cobalt acetate, and mixtures thereof. More preferably, the first reagent is a cobalt dinitrate, in particular a hydrated cobalt dinitrate, preferably a hexahydrated cobalt dinitrate.

[0081] Preferably, the first reactant is introduced with water, in the form of an aqueous solution.

[0082] Preferably, step b) is carried out with stirring.

[0083] In step c), the second reagent is added to the suspension from step b). Preferably, the second reagent consists of a water-soluble cobalt ligand. Alternatively, or in addition, a precursor of a said ligand may be added, i.e. a compound which, after being added to the suspension, produces said ligand, for example a precursor which decomposes in water to release the cobalt ligand.

[0084] The ligand's function is to react with the cobalt cations resulting from the addition of the first reagent, in order to form cobalt complexes.

[0085] Preferably, the cobalt ligand is a cobalt chelating ligand.

[0086] Preferably, the ligand is a strong field ligand.

[0087] The amount of said second reagent is preferably adapted so that more than 99%, preferably all of the cobalt cations in the suspension are complexed. Preferably, the second reagent contains only carbon, hydrogen, and oxygen atoms, and optionally nitrogen and / or chlorine atoms.

[0088] Preferably, the second reagent is chosen from molecules comprising an amino group (-NH2) and / or a carboxylate group (-COO) and / or a thiol group (-SH). Preferably, the second reagent is chosen from molecules comprising an amino group (-NH2) and / or a carboxylate group (-COO).

[0089] Preferably, the second reagent is selected from urea and its derivatives, citric acid, oxalic acid, ethylenediamine, salen, ethylenediaminetetraacetic acid (or “EDTA”), and mixtures thereof.

[0090] Preferably, the second reagent is chosen from urea and its derivatives, ethylenediamine, and mixtures thereof.

[0091] More preferably, the second reagent is chosen from urea and its derivatives. Preferably, the second reagent is introduced with water, in the form of an aqueous solution.

[0092] Preferably, step c) is carried out with stirring. In one embodiment, the suspension is preferably maintained at a temperature above 40°C, preferably above 50°C and below 90°C, preferably below 80°C.

[0093] The order of steps a) to c) may be any: a) + b) + c) or a) + c) + b) or b) + a) + c) or b) + c) + a) or c) + b) + a) or c) + a) + b). In one embodiment, these steps are simultaneous.

[0094] The solution obtained after these steps can be called a “complexed suspension”.

[0095] The amount of water in the complexed solution is not limited, except to limit the duration and / or cost of step d).

[0096] In step d), all or part of the water is extracted from the complexed suspension, preferably until a product having the consistency of a wet sand cake or a powder is obtained. This extraction is preferably continued until more than 70% by mass of the water is removed from the complexed suspension. Preferably, in step d), more than 80%, preferably more than 85%, preferably more than 90%, preferably more than 95% by mass of the water from the complexed suspension is removed.

[0097] In one embodiment, substantially all of the water from the complexed suspension is removed.

[0098] Any technique known to those skilled in the art for at least partially removing water from the complexed suspension may be used, for example drying or freeze-drying.

[0099] When drying is carried out in step d), it is preferably accompanied by stirring of the complexed suspension. Preferably, the drying temperature is above 50°C and below 90°C, and the drying is preferably in air.

[0100] In step e), the product from step d) is calcined.

[0101] Preferably, the calcination temperature is greater than 300°C, preferably greater than 400°C, and less than 800°C. The holding time at this temperature is preferably greater than 1 hour, preferably greater than 2 hours and preferably less than 10 hours.

[0102] Calcination is carried out in an oxygenated fluid, preferably in air.

[0103] In a non-preferred embodiment, steps d) and e) are performed simultaneously.

[0104] The Co-CGO powder according to the invention obtained has proven to be particularly suitable for manufacturing a sintered product, in particular an electrolyte.

[0105] The inventors found that the surface of the gadolinium-doped cerium oxide particles is covered with cobalt oxide particles, the latter being distributed in a remarkably homogeneous manner, as shown in Figures 2 and 4.

[0106] Figures 1 and 3 represent the particles of the gadolinium-doped cerium oxide powder comprising a cobalt oxide of Example 1 and Example 2, respectively. Figures 2 and 4 are superimposable on Figures 1 and 3, respectively, but show the cobalt concentrations. Cobalt appears gray in color, and the higher its concentration, the lighter the gray color. Figure 2, produced on the powder of Example 1 outside the invention, shows a non-homogeneous distribution of the gray color, with numerous light-colored areas. On the contrary, in Figure 4, produced on the powder of Example 2 according to the invention, the gray color is distributed more homogeneously, representative of a more homogeneous distribution of the cobalt on the surface of the CGO particles.

[0107] Cobalt oxide is cobalt(II,III) oxide expressed as CO3O4.

[0108] In Co-CGO powder, not all of the cobalt oxide is necessarily located on the surface of the CGO particles.

[0109] The invention also relates to said Co-CGO powder manufactured or capable of being manufactured according to a method of manufacturing a powder of the invention.

[0110] The percentiles N10, N50 and N90 are called, on a cobalt map, in 256 shades of a color, produced, on a pellet consisting of a compression of the powder at a pressure of 125 MPa, by energy spectrometry (or "EDS" in English), the shades corresponding to the percentages, in number of pixels of the map, of 10%, 50% and 90% respectively, on the cumulative distribution curve of the pixels, according to the shades, the shades being classified in ascending order, a shade being all the higher as the cobalt content is high.

[0111] In other words, 90% of the pixels in the map (percentage in number) have a shade lower than N90 and 10% of the pixels have a shade lower than Nio-

[0112] The more pixels there are in the map, the more accurate the percentile assessment will be. To increase the number of pixels, it is best to map multiple areas of the map.

[0113] The color whose shades are used can be chosen arbitrarily, for example the shades in the examples are shades of bright green for cobalt.

[0114] The mapping can be carried out in particular as described for the examples.

[0115] The value E defines the difference N90-N10, and the value S defines the ratio (N9O-NIO) / N5O = E / N50.

[0116] The inventors consider that the manufacturing process according to the invention results, on the Co-CGO powder, in a particularly homogeneous covering of the particles by cobalt in oxide form. In addition, they observed an E value greater than 110.

[0117] Preferably, the E value is greater than 115, preferably greater than 120, preferably greater than 125, preferably greater than 130, preferably greater than 135.

[0118] More preferably, a powder according to the invention has an S value of less than 2.20, preferably less than 2.10, preferably less than 2.00, preferably less than 1.90, preferably less than 1.80, preferably less than 1.70, preferably less than 1.60. This powder preferably comprises, as a mass percentage based on the oxides,

[0119] - more than 9.60% and / or less than 20.79% of Gd2O3; and / or

[0120] - more than 72.55% and / or less than 89.32% of CeCh; and / or

[0121] - more than 0.23%, preferably more than 0.50%, preferably more than 1.00%, preferably more than 1.50%, and / or less than 6.51%, preferably less than 5.50%, preferably less than 4.50%, preferably less than 3.50%, preferably less than 2.50% of cobalt oxide expressed as CO3O4; and / or

[0122] - less than 2%, preferably less than 1% of oxides, preferably less than 0.5% of oxides other than Gd2C>3, CeO2, and cobalt oxide expressed as CO3O4.

[0123] The oxides represent more than 95%, preferably more than 98%, preferably more than 99%, preferably 100% of the mass of the Co-CGO powder.

[0124] Preferably, the median size of the Co-CGO powder is greater than 0.1 pm, and preferably less than 0.8 pm.

[0125] Preferably, the D90 of the Co-CGO powder is less than 2.5 pm, preferably less than 2 pm.

[0126] Method for manufacturing a sintered part according to the invention

[0127] In step f), the Co-CGO powder is shaped, in the form of a “preform”, according to any conventional technique, then, in step g), the preform is sintered.

[0128] Cooling leads to the sintered part.

[0129] When the sintered part is intended to constitute an electrolyte, the shaping can be carried out by tape casting or by screen printing a slip generally containing Co-CGO powder, a solvent, often water, a binder, generally a polymer, and a dispersant.

[0130] Remarkably, whatever the embodiment, the sintering temperature may be less than 1600°C, preferably less than 1500°C, preferably less than 1490°C.

[0131] In one embodiment, the sintering of the preform may be carried out at the same time as that of other components of a solid oxide fuel cell or a solid oxide electrolysis cell, for example the electrodes. This is called co-sintering.

[0132] The sintered part obtained preferably constitutes an electrolyte.

[0133] Examples

[0134] The invention is not limited to the embodiments provided as examples and described below.

[0135] To determine the chemical composition of a powder, a bead is made by melting the powder. The content of the various elements is measured on this bead by X-ray fluorescence, with oxygen being considered as the 100% mass balance.

[0136] The median size of a powder is conventionally measured using a laser granulometer model LA950V2 marketed by Horiba. In the examples, the following raw materials were used:

[0137] - a gadolinium-doped cerium oxide powder, manufactured by arc furnace fusion and having a molar gadolinium content, expressed as a percentage on the basis of the sum of the molar cerium and gadolinium contents, equal to 20% and having a median size equal to 0.6 pm;

[0138] - cobalt dinitrate hexahydrate, with a purity greater than 99% by mass;

[0139] - for example 1, ethanol with a mass purity greater than 99.9%;

[0140] - for example 2, urea with a mass purity greater than 99%.

[0141] The manufacturing process of gadolinium-doped cerium oxide powder manufactured by arc furnace fusion is now described in more detail.

[0142] A starting charge consisting of a cerium oxide powder and a gadolinium oxide powder is produced by mixing. Then said starting charge is melted in a single-phase electric arc furnace of the Héroult type with graphite electrodes, with a furnace tank of 0.8 m in diameter, a voltage of 195 V, an intensity of 1300 A and a specific electrical energy supplied of 3 kWh / kg charged. The molten material is then poured in the form of a net, then dispersed into balls by blowing with compressed air. After complete cooling, the balls are then heat-treated in air at 1200°C for a holding time at this temperature equal to 4 hours. After heat treatment, the balls are ground, first in a jar mill, then in a humid environment in a micro-ball mill so as to obtain, after drying, the gadolinium-doped cerium oxide powder.

[0143] For Example 1, the following prior art method was implemented.

[0144] 6 g of gadolinium-doped cerium oxide powder are suspended in 100 ml of ethanol in a beaker at room temperature. Then 0.491 g of cobalt dinitrate hexahydrate, suspended in ethanol, are added, with stirring. Then this suspension is dried with stirring on a hot plate at 60°C for 1 hour, then calcined in air in the following thermal cycle:

[0145] - rise to 400°C at a speed equal to 100°C / hour;

[0146] - maintain at 400°C for 3 hours;

[0147] - descent to 250°C at a speed equal to 100°C / hour, then natural descent to room temperature.

[0148] For example 2, the method according to the invention was implemented.

[0149] In step a), 150 g of the gadolinium-doped cerium oxide powder are suspended in 400 ml of water, in a beaker at room temperature. In step b), 12.3 g of cobalt dinitrate hexahydrate are added to the suspension, with stirring. In step c), 7.59 g of urea are added to the suspension, while maintaining stirring for 1 minute after introduction of said urea. In step d), the complexed suspension obtained at the end of step c) is dried with stirring on a hot plate at 80°C for 6 hours, then calcined in step e), in air in the following thermal cycle:

[0150] - rise to 400°C at a speed equal to 100°C / hour;

[0151] - maintain at 400°C for 3 hours; - lower to 250°C at a speed equal to 100°C / hour then natural lowering to room temperature.

[0152] For example 3, the method according to the invention was implemented.

[0153] In step a), 150 g of the gadolinium-doped cerium oxide powder are suspended in 400 ml of water, in a beaker at room temperature. In step b), 10.5 g of cobalt dinitrate hexahydrate are added to the suspension, with stirring. In step c), 6.5 g of urea are added to the suspension, while maintaining stirring for 1 minute after introduction of said urea. In step d), the complexed suspension obtained at the end of step c) is dried with stirring on a hot plate at 80°C for 6 hours, then calcined in step e), in air, in the following thermal cycle:

[0154] - rise to 400°C at a speed equal to 100°C / hour;

[0155] - maintain at 400°C for 3 hours;

[0156] - descent to 250°C at a speed equal to 100°C / hour then natural descent to room temperature.

[0157] The cumulative distribution curve of pixels, as a function of shades, with shades ranked in ascending order, was prepared as follows:

[0158] 2 g of powder of each example are pressed at a pressure of 125 MPa in a 10 mm diameter die so as to obtain, for each example, a pellet. Each pellet is then metallized using a Sputter Coater 208HR metallizer marketed by the company CRESSINGTON, equipped with a Platinum target, the pellet being placed 10 cm from the target during the metallization operation, the intensity of the sputtering current being equal to 40 mA.

[0159] Each pellet is then observed, in a mode using secondary electrons, using a GeminiSEM 560 scanning electron microscope (SEM) marketed by ZEISS, equipped with an energy dispersive spectroscopy (or “EDS” in English) probe model X Flash 6 / 60 marketed by BRUKER, under the following conditions:

[0160] - Working Distance (WD): 10 mm,

[0161] - High Voltage (HV): 20 keV,

[0162] - Gun Mode: Analytic,

[0163] - VP mode: 30 Pa,

[0164] - Diaphragm.: 120 pm,

[0165] - Magnification: x 10000.

[0166] To carry out cobalt mapping on a pellet, 5 zones each representing 11.4 x 8.6 pm 2, are mapped by energy spectrometry (or “EDS” in English), using the EDS probe and the Esprit software, version 2.3.1.1019, developed by the company BRUKER, the scanning configuration being defined with the following parameters:

[0167] - image size [i.e. number of pixels]: 600,

[0168] - Image inputs: signal A; None, - maps:

[0169] - time / points [ps]: 2048,

[0170] - line averaging: 1.

[0171] The images obtained represent the location and local content of cobalt: the more intense the color, the higher the local cobalt content, the color used being bright green.

[0172] The settings used, which can be found in the Combined Maps section, are as follows:

[0173] - image filter: none

[0174] - map filter: smooth, indicated value: 3

[0175] - combined image: raw signal

[0176] - color control: the 3 parameters are not modified, the cursor of each parameter being located in the middle of the range, the Co-Ka value being kept at 1.

[0177] The resulting images do not contain a scale bar or other such information.

[0178] For each pellet, each of the 5 images is analyzed using the imageJ software, available on the site https: / / imagej.net / ij / download.html, in order to assign to each pixel of the said image a shade of the green color, the shades being between a value of 0 (black color representing the absence of cobalt, or even an absence of material) and 255 (the most intense color noted on the image, in other words the highest cobalt content).

[0179] Before analysis using imageJ software, the images do not undergo any processing, particularly aimed at modifying their contrast.

[0180] The analysis of each image using imageJ software is carried out according to the following method:

[0181] - open the image in imageJ;

[0182] - select Analyze, then Histogram: ImageJ represents in the form of a graph the distribution of the pixels of the analyzed image according to the nuances;

[0183] - select List to access the numeric data and copy it to a spreadsheet.

[0184] For each pellet, we determine, for each shade, the sum of the pixels presenting said shade for all five images (i.e. for the cobalt mapping), shade 0 not being taken into account.

[0185] We then plot the curve representing the cumulative number of pixels, as a percentage, by shade value, the shades being arranged in ascending order from 1 to 255. Figure 5 represents, for examples 1, 2 and 3, the cumulative distribution curve of pixels, as a function of the shades, the shades being classified in ascending order.

[0186] The E value defines the difference N90-N10, N90 being the shade reached by 90% of the pixels in total, and N10 being the shade reached by 10% of the pixels in total. The S value defines the ratio (Ngo-Nioj / Nso = E / N50, N50 being the shade reached by 50% of the pixels in total.

[0187] The following Table 1 presents the characteristics of the Co-CGO powders obtained.

[0188] [Table 1]

[0189] The inventor surprisingly found that the sintering behavior of the powder of Example 2 according to the invention was better than that of the powder of Example 1, outside the invention.

[0190] In particular, after having carried out a thermal expansion test on a dry cylindrical sample of examples 1 and 2, with a diameter equal to 10 mm and a height equal to 6 mm, on a TMA SETSYS EVO 1750 differential dilatometer marketed by the company SETARAM KEP TECHNOLOGIES, equipped with a dense alumina probe, with a rise rate equal to 1.6°C / min up to 1450°C, a hold at 1450°C for 1 hour and a descent at a rate of 5°C / min, the curve of the derivative of the thermal expansion (in % / min) as a function of the temperature shows a minimum value equal to 1362°C for example 1, outside the invention, and equal to 1250°C for example 2 according to the invention. The powder of example 2 according to the invention therefore has a maximum shrinkage speed reached at a lower temperature (1250°C) than for the powder of example 1, outside the invention (1362°C).

[0191] The invention thus makes it possible to improve the process for manufacturing an electrolyte.

[0192] Without being bound by this theory, the inventor explains this result by a remarkably more homogeneous dispersion of the cobalt oxide particles on the surface of the gadolinium-doped cerium oxide particles for the powder according to example 2 according to the invention compared to the powder of example 1, outside the invention, as illustrated in figures 2 and 4: the value of E is equal to 147 for the powder of example 2 according to the invention, and greater than the value of E, equal to 105, for the powder of example 1.

[0193] Of course, the present invention is not limited to the embodiments described, provided as illustrative and non-limiting examples.

[0194] In particular, the products according to the invention are not limited to particular shapes or dimensions.

Claims

CLAIMS 1. Method for manufacturing a gadolinium-doped cerium oxide powder comprising a cobalt oxide, said method comprising the following successive steps: 1) preparation of a wet product comprising a mixture: - gadolinium-doped cerium oxide particles; - water containing a cobalt complex; the wet product preferably having a Qc ratio o ' / QCGO' such that 0.005 < Qco' / QCGO' < 0.15, QCGO' denoting the sum of the molar quantities of cerium and gadolinium in the wet product, and Qc o ' designating the molar quantity of cobalt in the wet product, d) optionally, elimination of at least part of the water; e) calcination of the product resulting from step d), or, in the absence of step d), resulting from step 1), in an oxygenated fluid, so as to obtain said powder.

2. Method according to the preceding claim, comprising a step d) and in which step 1) comprises the following steps: a) suspending a gadolinium-doped cerium oxide powder in water; b) adding, to the suspension, at least one water-soluble cobalt compound, or "first reactant", so as to form cobalt cations, the quantity of first reactant preferably being determined so that 0.005 < Qco / QCGO < 0.15, QCGO designating the sum of the molar quantities of cerium and gadolinium added in step a) and Qc o designating the molar quantity of cobalt brought by the first reagent; c) adding, to the suspension, at least one water-soluble cobalt ligand and / or at least one precursor of a said ligand, or “second reagent”, so as to form a cobalt complex.

3. Method according to any one of the preceding claims, in which the ratio Qc o' / QCGO' is greater than or equal to 0.01 and less than or equal to 0.10, and / or wherein in step b), the ratio Qc o / QCGO is greater than or equal to 0.01 and less than or equal to 0.

10.

4. Method according to the immediately preceding claim, in which the ratio Qc o ' / QCGO' is greater than or equal to 0.02 and less than or equal to 0.05, and / or wherein, in step b), the ratio Qc o / QCGO is greater than or equal to 0.02 and less than or equal to 0.

05.

5. A method according to any one of the preceding claims, wherein the molar content of gadolinium in the gadolinium-doped cerium oxide powder of said wet product and / or of the powder suspended in step a), expressed as a percentage based on the sum of the molar contents of cerium and gadolinium, is greater than or equal to 10% and less than or equal to 6. Method according to any one of the preceding claims, wherein the median size of the gadolinium-doped cerium oxide powder of said wet product and / or of the powder suspended in step a) is greater than 20 nm and less than 0.8 pm.

7. A method according to any one of the preceding claims, wherein the gadolinium-doped cerium oxide powder of said wet product and / or the powder suspended in step a) is obtained by a fusion process.

8. Method according to any one of claims 2 to 7, in which the first reagent has a solubility in water, measured at 20°C, greater than 300 g / l.

9. Method according to any one of claims 2 to 7, in which: - the first reagent is chosen from a cobalt dinitrate, a cobalt acetate, a cobalt acetylacetonate, a cobalt dichloride, a cobalt difluoride, a cobalt sulfate, a cobalt tartrate, a cobalt bromide, a cobalt iodide, a cobalt thiocyanate, a cobalt phosphate, and mixtures thereof, and / or - the second reagent is chosen from molecules comprising an amino group -NH2 and / or a carboxylate group -COO and / or a thiol group -SH.

10. Method according to the immediately preceding claim, in which: - the first reagent is chosen from a cobalt dinitrate, a cobalt acetate, and their mixtures, and / or - the second reagent is chosen from urea and its derivatives, citric acid, oxalic acid, ethylenediamine, salen, ethylenediaminetetraacetic acid, and their mixtures.

11. Method according to the immediately preceding claim, in which the first reagent is a cobalt dinitrate and / or the second reagent is chosen from urea and its derivatives.

12. Method according to any one of claims 2 to 11, in which, in step c), the quantity of the second reagent is adapted so that more than 99% of the quantity of cobalt cations in the suspension are complexed.

13. A method according to any one of claims 2 to 12, wherein, in step c), the second reactant contains only carbon, hydrogen, and oxygen atoms, and optionally nitrogen and / or chlorine atoms.

14. A method according to any preceding claim, wherein in step d), more than 80% by mass of the water is removed.

15. Method according to any one of the preceding claims, wherein in step e), the calcination temperature is greater than 300°C and less than 800°C, the holding time at said temperature being greater than 1 hour and less than 10 hours.

16. Cerium oxide powder doped with gadolinium and comprising a cobalt oxide, said powder having the following chemical analysis, in mass percentage based on the oxides: - more than 9.60% and less than 20.79% of Gd2O3, and - more than 72.55% and less than 89.32% of CeC, and - more than 0.23% and less than 6.51% of cobalt oxide expressed as CO3O4, and - less than 2% of oxides other than Gd2C>3, CeO2, and cobalt oxide expressed as CO3O4, the powder of gadolinium-doped cerium oxide particles being at least partially coated with cobalt oxide particles, such that the difference N90-N10, or "E value", is greater than 110, N10 and N90 being, on a cobalt map - consisting of pixels, each pixel having a shade of a color, said shade being between 0 and 255, and - carried out by energy spectrometry on a pellet consisting of a compression of the powder at a pressure of 125 MPa, the shades corresponding to the percentages in number of said pixels of 10% and 90% respectively, on the cumulative distribution curve of the pixels, according to the shades, without taking into account the pixels having shade 0, the shades being classified in ascending order, a shade being all the higher as the cobalt content is high.

17. Powder according to the immediately preceding claim, having an E value greater than 125.

18. Powder according to any one of the two immediately preceding claims, having an S value of less than 2.20, the S value being the ratio (Ngo-Niol / Nso, where N50 is the shade corresponding to the percentage by number of said pixels of 50% on said cumulative distribution curve.

19. Powder according to the immediately preceding claim, the value S being less than 2.

00.

20. Method for manufacturing a sintered part comprising a step f) of manufacturing a preform from a powder according to any one of the four immediately preceding claims, or from a powder manufactured according to a method according to any one of claims 1 to 15, then a step g) of sintering the preform so as to obtain a sintered part.

21. Method according to the immediately preceding claim, in which the sintering temperature is less than 1500°C.

22. A method of manufacturing a device selected from a solid oxide fuel cell and a solid oxide electrolysis cell, said method comprising manufacturing a sintered part manufactured according to any one of the two immediately preceding claims, said sintered part found after manufacture between electrodes of said battery or said electrolysis cell so as to constitute an electrolyte.

Images