Alkaline powder kiln articles having controlled porosity coatings - Patents.com

Abstract

1. A kiln article for an alkali, particularly Li-containing powder, comprising a porous ceramic body forming a cavity or container for said powder, said porous ceramic body having an open porosity of 10-40% and an equivalent pore size of 0.5-25 μm, coated on at least a part of its inner surface with a ceramic coating, said coating comprising a compound selected from alumina, lithium aluminate, optionally containing silicon, magnesia-alumina spinel, zirconia, preferably stabilized, hafnia, yttria; having an average thickness of 50-500 μm; and having a total porosity of less than 15 vol. % and a volume fraction of pores with a diameter of 2 μm or more of less than 2.5%.

Description

[Technical field]

[0001] The present invention relates to the field of kiln articles, in particular containers, crucibles or saggers, for the heat treatment of alkaline powders for the manufacture of batteries, in particular lithium-based powders used in the manufacture of the positive electrodes that make up the latest generation of batteries. [Background technology]

[0002] The need for lithium-ion batteries is constantly increasing. Most of them include a part, typically the cathode, made of an oxide containing lithium, in particular an oxide of a metal or of several lithiated transition metals, in particular LiFePO4 (or LPF), LiMn2O4 (or LMO), or Lithium-Nickel-Cobalt-Manganese (or NMC) oxide.

[0003] The cathode is generally prepared by forming a powder of the oxide of a metal or of several alkali transition metals, particularly the lithiated ones.

[0004] Among the conventional methods for producing said powders, the production of a mixture of oxides and / or a mixture of various oxide precursors, followed by a heat treatment at temperatures above 800° C., makes it possible to carry out a solid-phase synthesis of the oxides of a metal or of several lithiated transition metals.

[0005] During the heat treatment, the mixture is placed in a kiln article, particularly a sagger. The conditions for synthesizing the powders and the mixture, particularly the lithium-containing elements, are particularly demanding for kiln articles containing lithiated powders.

[0006] Known solutions of monolithic crucibles, such as those described in US Patent Application Publication No. 2021 / 269365, remain deficient in terms of their service life.

[0007] Solutions of kiln articles formed by assembling various plates, such as those disclosed, for example, by WO 2021 / 151917, make it possible to adapt and replace certain parts of the vessel that are most stressed, but remain complex to implement.

[0008] Other solutions, especially repair solutions, are proposed in CN112537967, which consist, for example, of depositing a layer by cold spraying a suspension of a composition containing alumina, quartz, titanium oxide, tungsten carbide, sintering agents, and molding agents. CN111233482 also proposes a sagger with a sintered coating from a composition of deposited minerals containing silicon carbide, magnesia, talc, and graphite. However, the corrosion resistance of this coating is insufficient.

[0009] Korean Patent Publication No. 2002-0050390 proposes an alumina sagger that is coated with a 30-500 μm deposit of zirconia and then sintered at 400-1500° C., thereby improving the chemical resistance of the coating to ferrite or barium titanate powder.

[0010] Korean Patent Publication No. 2001-0045759 provides an alumina sagger that is provided with a rough layer of 30-1000 μm zirconia deposited at a specific angle by thermal spraying, thereby reducing deposition costs and improving the mechanical properties of the coating.

[0011] Thus, although the corrosion resistance is improved in these latter coating solutions obtained by plasma spraying, the performance of these solutions remains inadequate against the most aggressive alkali metal powders.

[0012] There is therefore a need for a kiln article for alkali metal powder, and in particular lithium powder, that has a relatively good compromise between the various requirements: - Stability of the coating of the kiln articles during operation to eliminate the possibility of contamination of the powder being fired; - ease of cleaning the heat-treated powder after discharge and before reuse for calcining new alkaline powder; - Resistance to thermal stresses during operation (especially cracks due to thermal shock and thermal cycling). Summary of the Invention [Problem to be solved by the invention]

[0013] The object of the present invention is to propose a kiln article that makes it possible to at least partially address this need, and in particular a container in the form of a crucible or in the form of a sagger, which can be easily reused, is highly resistant to corrosion by alkali metals, in particular by lithium, and is highly resistant to thermal shocks and cycling. [Means for solving the problem]

[0014] To this end, the invention relates to a kiln article for powders containing an alkali metal, in particular Li, which can be used for the heat treatment of a filler containing an alkali powder intended for the manufacture of a battery, having a porous ceramic body forming a cavity or container for said powder, said ceramic body being coated, on at least a portion of its inner surface, with a ceramic coating, in which: (a) the porous body has an open porosity, as measured by mercury and volume porosimetry, of 10 to 40%, and an equivalent or median diameter of the pores of 0.1 to 25 μm, preferably 0.5 to 25 μm; preferably the open porosity of the porous body is 10 to 30%, more preferably 10 to 20%; (b) said coating has the following characteristics: - It is a lithium aluminate, in particular LiAlO2, LiAlSi2O6, Li3AlSiO5, LiAlSi4O, optionally containing alumina and silicon. 10The present invention comprises, or preferably consists of, a layer comprising a compound selected from the group consisting of alumina, lithium aluminate, optionally containing silicon, in particular LiAlO2, LiAlSi2O6, Li3AlSiO5, LiAlSi4O, LiAlSiO4, magnesia-alumina spinel, zirconia, preferably stabilized, hafnia, yttria. 10 , LiAlSiO4, and magnesia-alumina spinel. its average thickness is between 50 and 500 μm; preferably between 100 and 300 μm; its total porosity is less than 15% by volume, preferably less than 12% by volume, preferably less than 10% by volume; its volume fraction of pores with a diameter of 2 μm or more is less than 2.5%; preferably less than 2.2%, preferably less than 2%.

[0015] According to preferred embodiments of the invention, which may be combined with one another where appropriate, there are: - the median pore size of the ceramic coating, d 50 is 0.1 to 1.5 μm. Preferably, the median pore size d of the ceramic coating is 50 is greater than 0.5 μm and / or less than 1 μm; - pore size d of the material 90 is less than 2.5 μm. - the median grain size of said ceramic coating is between 5 and 100 μm. Preferably, said size is greater than 10 μm and / or less than 70 μm, preferably less than 50 μm, preferably less than 30 μm; the mass content of alkali metal oxides, excluding Li2O, in the ceramic coating is less than 0.5%, in particular the mass content of Na2O and / or K2O in the ceramic coating is preferably less than 0.5%, more preferably less than 0.2%, preferably less than 0.1%; the mass content of SiO2 in said ceramic coating is less than 0.5%, preferably less than 0.2%; more preferably less than 0.1%; - the chemical composition of the ceramic coating with metal oxides Cr2O3, Fe2O3, ZnO or CuO capable of reacting with the alkaline powder is such that the mass content of the coating in total of the oxides Cr2O3+ZnO+Fe2O3+CuO is less than 0.5%. In particular, the mass content of Fe2O3 in the ceramic coating is less than 0.5%, preferably less than 0.2%; the mass content of oxides other than Al2O3, MgO, Li2O, Y2O3, ZrO2, HfO2 in said ceramic coating is less than 1%, preferably less than 0.5%, even more preferably less than 0.2%; the mass content of Al2O3 in said ceramic coating is greater than 98%, preferably greater than 98.5%, more preferably greater than 99.0%, even more preferably greater than 99.5%; - the porous ceramic body comprises alumina, zirconia, magnesia, mullite, cordierite, carbides, and / or silicon oxynitride or silicon oxynitride, boron nitride, boron carbide, or molybdenum disilicide. Preferably, the porous ceramic body comprises alumina, zirconia, magnesia, mullite, cordierite, carbides, and / or silicon oxynitride or silicon oxynitride; - the porous ceramic body comprises, preferably consists of, a ceramic matrix composite. Preferably, the ceramic matrix comprises alumina, zirconia, magnesia, mullite, cordierite, carbides and / or silicon nitride or silicon oxynitride, including SiAlON and Si2ON2, boron nitride (BN), boron carbide (B4C) or molybdenum disilicide (MoSi2). Preferably, the matrix comprises alumina, zirconia, magnesia, mullite, cordierite, carbides and / or silicon oxynitride or silicon oxynitride; the ceramic matrix composite preferably comprises fibres of alumina and / or mullite and / or SiC and / or carbon; the total mass content of the oxides ZrO2+Al2O3+SiO2+MgO ​​in said porous ceramic body is greater than 95%, preferably greater than 98%, more preferably greater than 99%; The wall thickness of the porous ceramic body is preferably between 3 and 30 mm, more preferably between 5 and 15 mm.

[0016] As will be explained in more detail in the remainder of the text, a kiln article having a porous ceramic body provided with a coating of controlled porosity according to the invention solves the above mentioned technical problem in that the coating has excellent corrosion resistance, very low adhesion to alkali metals, in particular lithium, whilst remaining adherent to the article despite thermomechanical stresses, thereby improving its service life.

[0017] According to other optional and advantageous additional features of said kiln articles, in particular of their ceramic coatings, which can be combined with one another if necessary, are: - The maximum pore size of the ceramic coating (D 100 ) is less than 7 μm. - Median pore size D of the ceramic coating 50 is 0.1 to 5 μm, particularly 0.5 to 5 μm, more preferably 0.5 to 1.5 μm; - the median grain size of said ceramic coating, determined by image analysis on a polished cross-section observed under a scanning electron microscope, is between 10 and 100 μm, preferably between 20 μm and / or less than 70 μm, more preferably between 20 μm and 50 μm; - the thickness of said ceramic coating is less than 500 μm, preferably less than 400 μm, preferably less than 300 μm, and / or more than 50 μm, preferably more than 100 μm; - the material constituting said ceramic coating is preferably essentially alumina; said coating being obtained by thermal spraying; - said coating consists of two layers, preferably of similar chemical composition, i.e. the difference in chemical composition is less than 5% with respect to their constituent elements;

[0018] According to other optional and advantageous additional features of the porous ceramic body of the kiln article, which may be combined where appropriate, are: - the porous ceramic body in monolithic form is particularly well suited for use in automated loading and unloading processes before and after the heat treatment of the alkaline powder, respectively; - the porous ceramic body is preferably coated over at least 50% or 60%, in particular 80% or 90%, or even over the entire inner surface thereof with a coating as defined above; - the ceramic body typically has a base and a wall; - the ceramic body contains little or no free silica, i.e., silica (SiO2) that is not combined with other oxides, e.g., in the form of mullite or cordierite; the mass content of alkali metal oxides in the porous ceramic body is less than 1%, in particular the content of Na2O is less than 0.5%; the mass content of alkaline earth oxides in said porous ceramic body is less than 1%, in particular the content of K2O or CaO is less than 0.5%; - the chemical composition of said porous ceramic body made of metal oxides capable of reacting with an alkali powder is such that the mass content of each of the following oxides Cr2O3, Fe2O3, ZnO or CuO is less than 1%. In order to improve the performance of the material constituting the ceramic body, the content of each of these oxides in the ceramic body is preferably less than 0.5% by mass; - the median pore size of said porous ceramic body is between 0.1 and 10 μm as measured by mercury porosimetry; - the porous ceramic body preferably has a diameter of at least 1 dm 3 , especially 2dm 3 Volume or 3dm3 It has a volume of over .

[0019] The invention also relates to a method for the manufacture of a kiln article according to the invention, in which the coating is formed by thermal spraying by depositing a number of superimposed layers of molten particles, which are subsequently solidified by cooling. Among the techniques known to those skilled in the art, flame spraying and plasma spraying are preferred.

[0020] In particular, according to the above-mentioned method for manufacturing the article of the invention, a porous ceramic body is coated with said coating by thermal spraying, the ceramic particles used for spraying having a total mass content of the oxides Al2O3+MgO+Li2O+Y2O3+ZrO2+HfO2 greater than 99.9%.

[0021] According to one possible embodiment, the median diameter of the population of particles is between 10 and 50 μm, preferably greater than 10 μm and / or less than or equal to 40 μm. Preferably, the ratio of particle diameters (D 90 -D 10 ) / D 10 is less than 3, preferably less than 2.

[0022] The porous ceramic body, preferably a sagger or a crucible, is obtained by conventional techniques known to those skilled in the art.

[0023] According to one possible embodiment, the porous ceramic body is made of material Alundum® AN199B, sold by Saint-Gobain Performance Ceramics & Refractories, for example. According to another embodiment, the material of the porous ceramic body is Si3N4-bonded SiC, typically obtained by reactive sintering, for example made of N-durance® material, sold by Saint-Gobain Performance Ceramics & Refractories. The porous ceramic body can be obtained, for example, by reactive sintering of a preform made of a mixture or suspension containing silicon and / or silicon nitride powder, and in particular by the techniques described in WO 2007 / 148986, WO 2004 / 016835 or WO 2012 / 084832.

[0024] The coating according to the invention can be obtained by thermal spraying consisting of at least partial melting of the particles sprayed onto the porous ceramic body. The mixture of particles is preferably very low in impurities, whereby the content of SiO2, Na2O, KO, Cr2O3, ZnO, CuO and Fe2O3 is particularly low. In particular, a total mass content of the oxides Al2O3+MgO+Li2O+YO3+ZrO2+HfO2 of more than 99.9% is particularly advantageous in order to relatively well control the solidification-recrystallization phase after spraying the molten particles onto the porous ceramic body.

[0025] The mass content of the spray particles is such that the total mass content of SiO2+Na2O+Fe2O3 oxides is preferably less than 0.05%, which advantageously makes it possible to control the grain boundaries and ensure perfect cohesion of the coating.

[0026] Preferably, the median diameter of the sprayed particle mass is 20-40 μm, such range being particularly suited to obtain the grain size of the coating according to the invention with the best performance.

[0027] According to one possible embodiment, the method for depositing the coating consists of flame spraying, consisting of spraying the particles from the cord passing in front of a flame from a spray gun in which a gaseous mixture of acetylene and oxygen is generated, thereby at least partially melting the ceramic particles of the cord. Typically, Alumina Supra Flexicord type cords supplied by Saint-Gobain Coating Solutions are particularly suitable due to the diameter of the alumina particles of the cord (median diameter of the population of particles is 10-15 μm) and the very high purity of the alumina particles (more than 99.9% Al2O3). Flame guns of the Master Jet® type are particularly suitable for this type of spraying.

[0028] According to another possible embodiment, the deposition of the coating consists of plasma spraying, such as with a professional plasma torch similar to that shown in FIG. 1 of EP 2407012, supplied with a ceramic powder, such as an alumina powder having a purity of more than 99% and a median diameter of 10-100 μm.

[0029] Regardless of the spraying method used, the substrate formed by the porous ceramic body is preheated, preferably in air and at atmospheric pressure, to a temperature of 200-400° C. Spraying is performed with the axis of the spray tool perpendicular to the surface, with overlapping movements and crenellations.

[0030] The coated porous ceramic body is then placed in an oven at 200-400° C., preferably in air, and subjected to a controlled temperature ramp of less than 200° C. / h.

[0031] According to one possible embodiment, several depositions can be carried out, but preferably the porous ceramic body after the deposition of the first layer is temperature stabilized in a furnace at 200-400° C. before the deposition of the second layer.

[0032] The invention also relates to the use of a kiln article according to the invention as described above for the heat treatment of powders of alkali metals, in particular powders containing lithium, intended for the manufacture of batteries.

[0033] The present invention will be better understood in light of the following non-limiting examples, illustrated by FIGS. 1-3. [Brief description of the drawings]

[0034] [Figure 1] FIG. 1 shows a cross section of a porous ceramic body 1 with a coating 2 for Example 1. [Figure 1] FIG. 2 shows a cross section of a porous ceramic body 1 with a coating 2 for Example 2. [Figure 1] FIG. 3 shows a cross section of a porous ceramic body 1 with a coating 2 for Example 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] definition

[0036] - For the sake of clarity, the chemical formulas of the corresponding simple oxides are used to designate the inclusion levels of these oxides in the compositions, even if they are not actually present. For example, "SiO2" or "Al2O3" indicate the content of these oxides in the composition, and the expressions "silica" and "alumina" are used to indicate that these oxide phases are actually present and consist of SiO2 and Al2O3, respectively.

[0037] The oxides are typically determined by X-ray fluorescence analysis or ICP fluorescence analysis depending on the measured content. - Unless otherwise stated, all oxide contents are mass percentages based on the oxide. The mass content of the oxide of a metallic element relates to the total content of this element expressed in its most stable oxide form, according to industry practice. - When HfO₂ is not intentionally added, HfO₂ is not chemically separable from ZrO₂. This is because this oxide is always naturally present in zirconia sources, generally with a mass content of less than 5%, generally less than 2%. Symmetrically, when HfO₂ is intentionally added, unavoidable impurities of zirconium oxide may exist. For clarity, the total content of zirconium oxide and the total content of trace hafnium oxide may be equivalently denoted as "ZrO₂" or "ZrO₂ + HfO₂", and vice versa in the case of "HfO₂". - The total content of the oxides does not imply the presence of all these oxides. - "Sialon", SiAlON, is a compound of oxynitride of at least the elements Si, Al, and N, and in particular is a compound conforming to one of the following formulas: - Si x Al y O u N v , where: - x is 0 or more, - y is 0 or more, - u is greater than 0, - v is greater than 0, - x + y > 0, - Me x Si 12-(m+n) Al (m+n) O n N 16-n , where 0 ≤ x ≤ 2, Me is a cation selected from lanthanides, Fe, Y, Ca, Li cations, and mixtures thereof, 0 ≤ m ≤ 12, 0 ≤ n ≤ 12, and 0 < n + m ≤ 12, and is generally called "α'-SiAlON" or "SiAlON-α'. - "Ceramic Matrix Composite" or "CMC" has conventionally been understood to mean an article composed of ceramic fibers firmly bonded together by a ceramic matrix. "Ceramic" is understood to mean an article that is neither metallic nor organic. In the context of the present invention, oxide glasses and carbon are considered as ceramic articles. - "coating" is understood to mean one or more layers of one or more materials. At least one of said layers, in particular the layer comprising a compound selected from alumina, lithium aluminate, magnesia-alumina spinel, zirconia, is preferably stabilized, for example by yttrium, hafnia, yttria, etc. This layer can be the result of a reaction of a ceramic body and the deposition by thermal spraying of particles on the surface of said ceramic body. -Unless otherwise specified, the term "pore" refers to all pores. - The porosity and pore size of a ceramic body can be determined using a mercury porosimeter, applying Washburn's law as described in standard ISO 15901-1.2005 part 1. 3 From a cubic shaped sample, the mercury porosimeter makes it possible to establish the pore volume distribution by volume, i.e. to determine for each pore size the volume occupied by pores having this size. In this way, it is possible to determine the equivalent diameter (median pore diameter D), which corresponds to the 50th percentile of the median size of the population of pores in the ceramic body. 50 This size can be used to separate the population into two groups by volume: one group representing 50% of the pore volume whose pores have a size smaller than the median size, and another group representing 50% of the pore volume whose pores have a size equal to or larger than the median size. - the size or diameter of the pores or grains of the coating or the size of the grains of the porous ceramic body is determined by analyzing an image of the cross section observed under a scanning electron microscope, with a magnification of at least 1000, preferably equal to 2000. The area and diameter of each of the grains or pores is obtained from the image by conventional image analysis techniques, optionally after binarization or segmentation of the image with the aim of increasing the contrast of the image. In this way, the percentage distribution (by number) of grains or the percentage distribution (by volume) of pores is estimated, from which the percentile D 50 Also, from this distribution, percentiles D of the particle population diameter (or pore population diameter) are extracted, which are the particle diameters (or pore diameters) corresponding to 10%, 90% and 100% percentages, respectively, on a cumulative distribution curve of the particle diameters (or pore diameters) classified by number in ascending order (or pore diameters classified by volume) obtained by image analysis of the coating cross section or the porous ceramic body. 10 and D. 90 Or D 100 By integrating this volumetric pore distribution curve, the pore volume or total porosity of the coating or porous ceramic body can be inferred. From such cumulative pore volume distribution, the volume fraction of pores equal to or larger than a given pore size, particularly the volume fraction of pores equal to or larger than 2 μm in diameter in the coating, can be calculated.

[0038] - "Comprising" is to be interpreted in an open-ended manner, in that other elements than those indicated may be present. EXAMPLES

[0039] The following examples are offered for illustrative purposes and are not intended to limit the scope of the invention.

[0040] Sold by Saint-Gobain Performance Ceramics & Refractories, made of Alundum® AN199B material (chemical composition Al2O3: 99.5%; SiO2: 0.07%; Fe2O3: 0.03%; K2O + Na2O: 0.1%; other oxides: 0.3%), dimensions 200 x 200 x 100 mm 3 A sagger was supplied having a generally square cross section, and a wall thickness of 10 mm. The open porosity of the material, measured according to the mercury porosimetry technique described above, is about 16% (by volume) and its median pore size is about 5 μm.

[0041] According to a first example (Comparative Example 1), a first series of 10 saggers are preheated in a furnace to a temperature of 300° C. and then coated on their internal surfaces (sides and bottom) with an alumina coating by thermal spraying using a flame gun of the Master Jet® type supplied by Saint-Gobain Coating Solutions under the code Flexicord Pure Alumina® with reference 982101147000. The saggers are placed in an oven at 300° C. and subjected to a controlled temperature drop of 100° C. / h.

[0042] According to a second example (example 2 according to the invention), different from the previous example, on a second series of 10 saggers, the layers are deposited using a flame gun of the Master Jet type supplied by Saint-Gobain Coating Solutions with the Flexicord Alumina Supra code reference 98210 1347000. The saggers are placed in an oven at 300° C. and subjected to a controlled temperature drop of 100° C. / h.

[0043] According to a third example (example 3 according to the invention), a series of 10 saggers are coated on their inner surface (sides and bottom) with an alumina coating by thermal spraying using a Proplasma™ torch similar to that shown in FIG. 1 of EP 2407012 of WO 2014 / 083544, supplied with alumina powder. The substrate formed by the saggers is preheated to a temperature of 300° C. The plasma spraying is carried out with the axis of the spraying tool perpendicular to the surface, with movements and crenellations with overlap. Cooling of the coated saggers after plasma spraying is free.

[0044] According to a fourth example (Example 4 according to the invention), on a series of 10 saggers, an intermediate layer is deposited in the same way as in Comparative Example 1, then a second layer is deposited by plasma spraying in the same way as in Example 3. Cooling of the coated saggers after plasma spraying of the coating is free.

[0045] Characterization methods and performance tests:

[0046] The average thickness of the entire coating was determined by observation with a scanning electron microscope.

[0047] The size of the grains and the size of the pores that compose the coating comprises the following sequence of steps, which are conventional in the art:

[0048] A series of 5 SEM images are taken from the cross-section of the article (i.e. throughout the thickness of the wall). For better clarity, the images are made on polished cross-sections of the material. The image acquisition is carried out over a cumulative length of the coating equal to at least 1.5 cm, thereby obtaining values ​​representative of the entire sample. The image is subjected to a binarization technique, well known in image processing technology, to enhance the contrast of the grain or pore contours. - for each grain or each pore, a measurement of its area is made, and the diameter of the pore or grain is determined corresponding to the diameter of a complete disk of the same area as that measured for said grain or said pore (this operation can be carried out using dedicated software, in particular Visilog™ sold by Noesis).

[0049] In this way, a distribution of the particle or grain size or pore diameter is obtained according to a conventional distribution curve, thus determining the median size of the grains or pores constituting the coating, said median size corresponding to a diameter that divides said distribution into a first population containing only grains with a diameter equal to or greater than this median size, and a second population containing only grains or pores with a diameter smaller than this median size or this median diameter. Similarly, the volume fraction of pores with a size of 2 μm or less can be calculated.

[0050] In Example 4, measurements (median grain size, porosity, pore size) were performed by analyzing images of both of the two layers that make up the coating.

[0051] For each example, the corrosion resistance of the coating with lithium is evaluated in the following way: Lithium hydroxide powder with a purity of more than 99.9% by weight is placed in the sagger provided with the coating. The assembly is then placed in an electric furnace maintained at a temperature of 900° C. under vacuum for 8 hours (ramp up to 900° C. at a rate equal to 500° C. / h, natural fall to room temperature due to the thermal inertia of the furnace). After 5 cycles, the presence of lithium penetration is observed by image analysis according to the same method as for the average coating thickness: - The resistance is excellent if there are no traces of lithium penetration beyond a depth of 20 μm in the coating thickness; - resistance is considered good if the penetration depth is ≥ 20 μm and < 30 μm; - If the penetration depth is greater than 30 μm and less than 50 μm, the resistance is considered average; - If the penetration depth is more than 50 μm, the resistance is considered to be mediocre;

[0052] The thermal shock resistance of the saggers was determined according to the following method: 5 samples of saggers, previously dried at 110°C, are placed in a furnace and then heated to 900°C with an increase of 250°C / h. The furnace is then maintained at this temperature for 1 hour. Each sagger is then quickly removed from the furnace and subjected to tempering in air (20°C) for 20 minutes. This operation continues in this way until 10 cycles have been performed. Each sagger is then analyzed and the microstructure, especially the microstructure of the coating, is observed externally and internally. Observation with the naked eye makes it easy to see the occurrence of external cracks. In particular, a very good thermal shock resistance corresponds to the absence of cracks in the coating or at the interface between the coating and the ceramic body. A good thermal shock resistance corresponds to the local presence of one or more microcracks (which, however, do not threaten the integrity of the coating).

[0053] The deposition conditions are shown in Table 1 below.

[0054] [Table 1]

[0055] The final composition and morphology, as well as the coating properties, are reported in Table 2 below.

[0056] [Table 2]

[0057] The examples according to the invention show that the coatings, which have a volume fraction of pores of 2 μm or more of less than 2.5%, as determined by image analysis, have a satisfactory appearance after deposition, good or even very good resistance to thermal shock, and good or excellent corrosion resistance, unlike Comparative Example 1. The examples according to the invention have almost no adhesion after firing after 5 lithium corrosion tests, so that they can be easily cleaned by sagger spraying or scraping without significant degradation of the coating. Example 4 shows that when deposits are superimposed, the performance of the coated final article also depends on the characteristic criteria cited above.

[0058] Of course, the invention is not limited to the embodiments described and shown.

Claims

1. 1. A kiln article for a powder comprising an alkali metal, particularly Li, having a porous ceramic body forming a cavity or container for said powder, said ceramic body being coated on at least a portion of its interior surface with a ceramic coating, wherein: (a) the porous ceramic body has an open porosity of 10 to 40% and an equivalent pore diameter of 0.5 to 25 μm, as measured by mercury and volume porosimetry; (b) the coating has the following characteristics: alumina, optionally containing silicon, lithium aluminate, in particular LiAlO ２ , LiAlSi ２ O ６ , Li ３ AlSiO ５ , LiAlSi ４ O １０ , LiAlSiO ４ , magnesia-alumina spinel, zirconia, preferably stabilized, hafnia, yttria; its average thickness is between 50 and 500 μm; its total porosity is less than 15% by volume; the volume fraction of pores with a diameter of 2 μm or more is less than 2.5%; A kiln article having

2. The median pore size d of the ceramic coating ５０ The kiln article of claim 1, wherein is 0.1 μm to 5 μm.

3. The pore diameter d of the ceramic coating ９０ 3. The kiln article of claim 1 or 2, wherein the average particle size is less than 2.5 μm.

4. 3. The kiln article of claim 1 or 2, wherein the grains of the ceramic coating have a median grain size of 5 to 100 μm.

5. Li in the ceramic coating ２ 3. The kiln article of claim 1 or 2, wherein the mass content of alkali metal oxides excluding O is less than 0.5%.

6. SiO in the ceramic coating ２ 3. The kiln product of claim 1, wherein the mass content of is less than 0.5%.

7. Cr oxide in the coating ２ O ３ +ZnO +Fe ２ O ３ 3. A kiln product according to claim 1 or 2, wherein the total mass content of CuO is less than 0.5%.

8. Al in the ceramic coating ２ O ３ , MgO, Li ２ O, Y ２ O ３ , ZrO ２ , HfO ２ 3. The kiln article of claim 1 or 2, wherein the mass content of oxides other than is less than 1%.

9. Al in the ceramic coating ２ O ３ 3. The kiln article of claim 1, wherein the mass content of is greater than 98%.

10. 3. The kiln article of claim 1 or 2, wherein the porous ceramic body comprises alumina, zirconia, magnesia, mullite, cordierite, carbide, and / or silicon oxynitride or silicon oxynitride, boron nitride, boron carbide, or molybdenum disilicide.

11. 3. The kiln article of claim 1 or 2, wherein the porous ceramic body comprises, preferably consists of, a ceramic matrix composite.

12. The oxide ZrO in the porous ceramic body ２ +Al ２ O ３ +SiO ２ 3. A kiln product according to claim 1 or 2, wherein the total mass content of MgO is greater than 95%.

13. 3. The kiln article of claim 1 or 2, wherein the wall thickness of the porous ceramic body is 3 to 30 mm.

14. A method for manufacturing a kiln article according to claim 1 or 2, wherein the porous ceramic body is coated with the coating by thermal spraying, and the ceramic particles used for thermal spraying are more than 99.9% Al ２ O ３ + MgO + Li ２ O+Y ２ O ３ + ZrO ２ +HfO ２ The method of claim 1, wherein the total mass content of the oxides is

15. The method of claim 14, wherein the median diameter of the population of particles is between 10 and 50 μm.

16. 3. Use of a kiln article according to claim 1 or 2 for the heat treatment of powders of alkali metals, in particular alkali metals containing lithium, intended for the manufacture of batteries.

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