ALKALINE POWDER KILN FURNITURE WITH CONTROLLED-POROSITY COATING

Abstract

A kiln furniture for a powder includes an alkali, in particular Li, including a porous ceramic body forming a cavity or a container for the powder, wherein the ceramic body with open porosity of between 10 and 40% and with equivalent pore diameter between 0.5 and 25 micrometers is coated on at least part of its inner surface with a ceramic coating, the coating including a compound selected from alumina, a lithium aluminate optionally including silicon optionally silicon, aa magnesia-alumina spinel, zirconia, optionally stabilized, hafnia, yttria; having an average thickness of between 50 and 500 micrometers; a total porosity of less than 15% by volume and a volume fraction of pores of diameter greater than or equal to 2 micrometers that is less than 2.5%.

Claims

1. A kiln furniture for a powder comprising an alkali metal, comprising a porous ceramic body forming a cavity or a container for said powder, wherein said ceramic body is coated on at least part of its inner surface with a ceramic coating, wherein: a) said porous ceramic body has an open porosity of between 10 and 40%, and an equivalent pore diameter of between 0.5 and 25 micrometers, as measured by mercury and volume porosimetry; b) said coating has the following characteristics: the the coating comprises, a layer comprising a compound selected from alumina, a lithium aluminate optionally comprising silicon, a magnesia-alumina spinel, zirconia, hafnia, yttria; the coating has an average thickness that is between 50 and 500 micrometers; the coating has a total porosity that is less than 15%, by volume; the coating has a volume fraction of pores with a diameter greater than or equal to 2 micrometers that is less than 2.5%.

2. The kiln furniture according to the preceding claim 1, wherein the median pore diameter d.sub.50 of said ceramic coating is between 0.1 micrometers and 5 micrometers.

3. The kiln furniture according to claim 1, wherein the pore diameter d.sub.90 of said ceramic coating is less than 2.5 micrometers.

4. The kiln furniture according to claim 1, wherein median grain size of grains of said ceramic coating is between 5 and 100 micrometers.

5. The kiln furniture according to claim 1, wherein a mass content of alkali metal oxides except Li.sub.2O in said ceramic coating being less than 0.5%.

6. The kiln furniture according to claim 1, wherein a mass content of SiO.sub.2 in said ceramic coating is less than 0.5%.

7. The kiln furniture according to claim 1, wherein a mass content of the sum of the oxides Cr.sub.2O.sub.3+ZnO+Fe.sub.2O.sub.3+CuO in said coating is less than 0.5%.

8. The kiln furniture according to claim 1, wherein a mass content of oxides other than Al.sub.2O.sub.3, MgO, Li.sub.2O, Y.sub.2O.sub.3, ZrO.sub.2, HfO.sub.2 in said ceramic coating is less than 1%.

9. The kiln furniture according to claim 1, wherein a mass content of Al.sub.2O.sub.3 in said ceramic coating is greater than 98%.

10. The kiln furniture according to claim 1, wherein said porous ceramic body comprises alumina, zirconia, magnesia, mullite, cordierite, carbide and/or silicon oxynitride or oxynitride, boron nitride, boron carbide or molybdenum disilicide.

11. The kiln furniture according to claim 1, wherein said porous ceramic body comprises a ceramic matrix composite.

12. The kiln furniture according to claim 1, wherein a mass content of a sum of the oxides ZrO.sub.2+Al.sub.2O.sub.3+SiO.sub.2+MgO in said porous ceramic body is greater than 95%.

13. The kiln furniture according to claim 1, wherein a wall thickness of said porous ceramic body is between 3 and 30 mm.

14. A method for manufacturing a kiln furniture according to claim 1, comprising coating the porous ceramic body with said coating by thermal spraying, wherein the ceramic particles used for spraying having a mass content of the sum of the oxides Al.sub.2O.sub.3+MgO+Li.sub.2O+Y.sub.2O.sub.3+ZrO.sub.2+HfO.sub.2 greater than 99.9%.

15. The method for manufacturing a kiln furniture according to claim 14, wherein a median diameter of the population of said ceramic particles is between 10 and 50 micrometers.

16. A method comprising providing the kiln furniture according to claim 1 for the heat treatment of the powders of an alkali metal intended for the manufacture of batteries.

17. The kiln furniture according to claim 1, wherein the alkali metal is Li.

18. The kiln furniture according to claim 1, wherein the coating consists of said layer.

19. The kiln furniture according to claim 1, wherein the lithium aluminate optionally comprising silicon is LiAlO.sub.2, LiAlSi.sub.2O.sub.6, Li.sub.3AlSiO.sub.5, LiAlSi.sub.4O.sub.10, LiAlSiO.sub.4.

20. The kiln furniture according to claim 1, wherein the zirconia is stabilized.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0070] The invention will be better understood in light of the following non-limiting examples, shown by FIGS. 1 to 3.

[0071] FIGS. 1 to 3 show a cross-section of a porous ceramic body 1 with its coating 2, respectively for examples 1 to 3.

DEFINITION

[0072] For the sake of clarity, the chemical formulae of the corresponding simple oxides are used, even if they are not actually present, to designate the content levels of these oxides in a composition. For example, SiO.sub.2 or Al.sub.2O.sub.3 refers to the contents of these oxides in said composition and the expressions silica and alumina are used to denote phases of these oxides actually present and consisting of SiO.sub.2 and Al.sub.2O.sub.3, respectively.

[0073] The oxides are typically determined by X-ray or ICP fluorescence analysis according to the measured contents. [0074] Unless otherwise mentioned, all the contents of oxides are mass percentages on the basis of the oxides. A mass content of an oxide of a metal element relates to the total content of this element expressed in the form of the most stable oxide, according to the usual convention of the industry. [0075] HfO.sub.2 is not chemically dissociable from ZrO.sub.2 when HfO.sub.2 is not intentionally added. That is because this oxide is always naturally present in zirconia sources at mass contents generally less than 5%, generally less than 2%. Symmetrically, during a deliberate addition of HfO.sub.2, there may be inevitable impurities of zirconium oxide. For the sake of clarity, the total content of zirconium oxide and of traces of hafnium oxide can be denoted interchangeably as ZrO.sub.2 or as ZrO.sub.2+HfO.sub.2 and vice versa for HfO.sub.2. [0076] The sum of contents of oxides does not imply the presence of all these oxides. [0077] A sialon, SiAlON, is a compound of oxynitride of at least the elements Si, Al and N, in particular a compound complying with one of the following formulas: [0078] Si.sub.xAl.sub.yO.sub.uN.sub.v, wherein: [0079] x is greater than or equal to 0 [0080] y is greater than or equal to 0 [0081] u is greater than 0 [0082] v is greater than 0

[00001]$x+y>0$ [0083] Me.sub.xSi.sub.12(m+n) Al.sub.(m+n) O.sub.nN.sub.16-n, where 0x2, Me is a cation selected from lanthanide, Fe, Y, Ca, Li cations and mixtures thereof, 0m12, 0n12 and 0<n+m12, generally called -SiAlON or SiAlON-. [0084] Ceramic Matrix Composite or CMC is conventionally understood to mean a product composed of ceramic fibers rigidly linked together by a ceramic matrix. [0085] Ceramic is understood to mean a product which is neither metallic nor organic. In the context of the present invention, an oxide glass and carbon are considered to be ceramic products. [0086] Coating is understood to mean one or more layers of material(s). At least one of said layers, in particular the layer comprising a compound selected from alumina, lithium aluminate, magnesia-alumina spinel, zirconia, preferably stabilized for example by yttrium, hafnia, yttria. This layer may be the result of the reaction of the ceramic body and of the deposition by thermal spraying of the particles on the surface of said ceramic body. [0087] Unless otherwise indicated, the term pores refers to all pores. [0088] The porosity and the size of the pores of the ceramic body can be determined using a mercury porosimeter in application of the Washburn law mentioned in standard ISO 15901-1.2005 part 1. From a cube-shaped sample of about 1 cm.sup.3, a mercury porosimeter makes it possible to establish a volume distribution of the pores by volume, that is to say to determine, for each pore size, a volume occupied by the pores having this size. It is thus possible to determine an equivalent diameter (also called median pore diameter D.sub.50) corresponding to the 50th percentile of the median size of the population of pores of the ceramic body. This size splits said 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 greater than or equal to said median size. [0089] The size or diameter of the pores or grains of the coating or the size of the grains of the porous ceramic body are determined by analyzing images of cross-sections 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 are obtained from images by conventional image analysis techniques, optionally after a binarization or segmentation of the image that aims to increase the contrast thereof. A distribution of grain diameters by percentage (by number) or of pores in percentage (by volume) is thus deduced, from which the median diameter of grains or pores corresponding to the percentile D.sub.50 is extracted. It is also possible to determine from this distribution the percentiles D.sub.10 and D.sub.90 or D.sub.100 of the grain (or pore) population diameter which are the grain (or pore) diameters corresponding respectively to the percentages of 10% and 90% or 100% on the cumulative distribution curve of the diameter of grains by number (or of pores by volume) classified in increasing order obtained by image analysis of said coating cross-section or porous ceramic body. By integrating the volume pore distribution curve, it is possible to deduce the volume of pores or total porosity of the coating or of the porous ceramic body. From such a cumulative pore volume distribution, it is also possible to calculate a volume fraction of pores greater than or equal to a predetermined pore size, in particular the volume fraction of pores with a diameter greater than or equal to 2 micrometers in said coating.

[0090] Comprise should be interpreted non-limitingly, in the sense that elements other than those indicated may be present.

EXAMPLES

[0091] The following examples are provided for purposes of illustration and do not limit the scope of the invention.

[0092] Saggars with an overall square cross-section of dimensions 200*200*100 mm.sup.3 and wall thickness 10 mm made of an Alundum AN199B material (chemical composition Al.sub.2O.sub.3: 99.5%; SiO.sub.2: 0.07%; Fe.sub.2O.sub.3: 0.03%; K.sub.2O+Na.sub.2O: 0.1%; other oxides: 0.3%) sold by Saint-Gobain Performance Ceramics & Refractories were supplied. The open porosity of the material, measured according to the mercury porosimetry techniques described above, is about 16% (by volume) and its median pore diameter is on the order of 5 micrometers.

[0093] According to a first example (comparative example 1), a first series of ten saggars was preheated to a temperature of 300 C. in a furnace before being coated on its interior surface (side and bottom) with an alumina coating by thermal spraying using a flame gun of the Master Jet type fed by a cord of Flexicord Pure Alumina with reference code 982101147000 provided by Saint-Gobain Coating Solutions. The saggars are placed in an oven at 300 C., subjected to a controlled 100 C./h decrease in temperature.

[0094] According to a second example (example 2 according to the invention), unlike the previous example, on a second series of ten saggars, the layer is deposited using a flame gun of the Master Jet type fed by a Flexicord Alumina Supra cord with reference 98210 1347000 provided by Saint-Gobain Coating Solutions. The saggars are placed in an oven at 300 C., subjected to a controlled 100 C./h decrease in temperature.

[0095] According to a third example (example 3 according to the invention), a series of ten saggars is coated on its inner surface (side and bottom) with an alumina coating by thermal spraying using a Proplasma torch similar to that shown in FIG. 1 of EP2407012B1 of WO2014/083544 fed with an alumina powder. The substrate formed by the saggar has been preheated to a temperature of 300 C. The plasma spraying is done with the axis of the thermal spraying tool normal to the surface, performing translations and crenellations with overlap. The cooling of the coated gases after plasma spraying of the coating is free.

[0096] According to a fourth example (example 4 according to the invention) on a series of ten saggars, an intermediate layer is deposited in a manner similar to example 1 and then a second layer is deposited by plasma spraying in a similar manner to example 3. The cooling of the coated gases after plasma spraying of the coating is free.

Characterization methods and performance tests:

[0097] The average thickness of the whole coating was determined by observation with a scanning electron microscope.

[0098] The size of the grains and of the pores constituting the coating comprises the succession of the following steps, which is conventional in the field:

[0099] A series of five SEM images is taken from the furniture in a cross-section (that is to say throughout the thickness of a wall). For more clarity, the images are made on a polished section of the material. The image acquisition is carried out over a cumulative length of the coating at least equal to 1.5 cm, in order to obtain values representative of the whole sample. [0100] The images are subjected to binarization techniques, well known in image processing techniques, to increase the contrast of the contour of the grains or of the pores. [0101] For each grain or each pore, a measurement of its area is carried out. A pore or grain diameter is determined, corresponding to the diameter of a perfect disc of the same area as that measured for said grain or for said pore (this operation possibly being carried out using dedicated software, in particular Visilog sold by Noesis).

[0102] A distribution of particle or grain size or of pore diameter is thus obtained according to a conventional distribution curve and a median size of the grains or pores constituting the coating is thus determined, this median size respectively corresponding to the diameter dividing said distribution into a first population comprising only grains with a diameter greater than or equal to this median size and a second population comprising only grains or pores with a diameter lower than this median size or this median diameter. Likewise, it is possible to calculate the volume fraction of pores with a size of less than or equal to 2 micrometers.

[0103] In example 4, the measurements (median grain size, porosity, pore diameter) were carried out by analyzing images of both the two layers constituting the coating.

[0104] The corrosion resistance of the coating by lithium was evaluated for each example by the following method: A lithium hydroxide powder of purity >99.9% by mass of LiOH was placed in a saggar provided with the coating. The assembly is then placed in an electric furnace under vacuum at a temperature of 900 C. maintained for 8 hours (rise to 900 C. at a speed equal to 500 C./h, natural descent to room temperature by thermal inertia of the furnace. After five cycles, the presence of lithium penetration is observed by image analysis according to the same method as for the average coating thickness: [0105] the resistance is excellent if there is no trace of lithium penetration beyond micrometers deep in the thickness of the coating; [0106] the resistance is considered to be good for a penetration depth between 20 and less than 30 micrometers; [0107] the resistance is considered to be average for a penetration depth greater than 30 and less than 50 micrometers; [0108] the resistance is considered to be mediocre for a penetration depth greater than 50 micrometers;

[0109] The thermal shock resistance of the saggar was determined according to the following method: a sample of five saggars previously dried at 110 C. is placed in a furnace then heated up to 900 C., ramping by 250 C./h. The furnace is then maintained at this temperature for one hour. Each saggar is then quickly removed from the furnace to undergo tempering in ambient air (20 C.) for 20 minutes. The operation thus continues until ten cycles are carried out. Each saggar is then analyzed for external and internal observation of the microstructure, in particular of the coating. Observation with the naked eye makes it easy to identify the appearance of external cracks. In particular, very good thermal shock resistance corresponds to an absence of cracks in the coating or at the interface between the coating and the ceramic body. Good thermal shock resistance corresponds to a localized presence of one or more microcracks, which however do not threaten the integrity of the coating.

[0110] The deposition conditions are specified in table 1 which follows.

TABLE-US-00001 TABLE 1 flame gun flame gun plasma torch Examples deposition deposition deposition Supply cord Pure Alumina Alumina Supra Mass mineral Al.sub.2O.sub.3: 99.7% Al.sub.2O.sub.3: 99.9% composition (%) other: 0.3% Fe.sub.2O.sub.3: 0.02%. of the cord SiO.sub.2: 0.02% Na.sub.2O: 0.01% other: 0.05% FEPA standard size F320 F500 (D50 = 30 m) (D50 = 13 m) Cord feed speed 40 40 (cm/min) Cord diameter 4.75 4.75 (mm) Flow rate of HB75 at 1.2 bar HB75 at 1.2 bar acetylene (bead height/bar) Flow rate of oxygen HB65 at 4 bar HB65 at 4 bar (bead height/bar) Air pressure (bars) 4.5 4.0 Masterjet gun 3769/2941 3769/2952 gas/air nozzles Spraying distance 120 80 (mm) Linear speed of 300 300 gun movement (mm/s) increment of 3 3 advance (mm) # of passes 5 25 Cathode features ProPlasma, lanthanum-doped tungsten Anode features ProPlasma Std Copper material with tungsten insert Diameter: 6.5 mm Median alumina 40 m powder diameter (m) Mass chemical Al.sub.2O.sub.3: 99.9% composition (%) Fe.sub.2O.sub.3: 0.02%. of the injected SiO.sub.2: 0.02% Na.sub.2O: powder 0.01% other: 0.05% Injection rate of the 30 powder (g/min) Injection angle % 90 the X-axis of the torch Injector radial 7 distance - gun axis (mm) Injector diameter 1.8 (mm) Flow rate of the Argon/4.5 carrier gas (L/min) Voltage (V) 69 Plasma arc 600 intensity (A) Flow rate of the 40 (Argon) primary gas (L/min) Flow rate of the 13 (Hydrogen) plasmagen gas (L/min)

[0111] The final composition and morphology as well as the coating properties are reported in table 2 below.

TABLE-US-00002 TABLE 2 Example 1 Example 2 Example 3 Example 4 comparative invention invention invention Characteristics of the method for obtaining the coating 1st deposition flame flame plasma flame deposition deposition deposition deposition Pure Alumina Pure Alumina Supra Alumina 2nd deposition No No No plasma deposition Chemical composition of the coating Al.sub.2O.sub.3 (% wt) >99 >99 >99 >99 SiO.sub.2 (% wt) <0.01 <0.01 <0.02 <0.01 NaO.sub.2 (% wt) <0.01 <0.01 <0.01 <0.01 MgO (% wt) <0.1 <0.1 <0.01 <0.1 Li.sub.2O (% wt) <0.1 <0.1 <0.01 <0.1 Fe.sub.2O.sub.3 (% wt) <0.01 <0.01 <0.02 <0.01 ZrO.sub.2 (% wt) <0.01 <0.01 <0.01 <0.01 HfO.sub.2 (% wt) <0.1 <0.1 <0.01 <0.1 Y.sub.2O.sub.3 (% wt) <0.1 <0.1 <0.1 <0.1 Cr.sub.2O.sub.3 + ZnO + <0.5 <0.5 <0.5 <0.5 Fe.sub.2O.sub.3 + CuO(% wt) Na.sub.2O + K.sub.2O <0.5 <0.5 <0.5 <0.5 Coating features by image analysis Mean thickness 150 230 130 280 (m) Median grain size 23 10 25 24 Total porosity (%) 8.3 14.3 8.1 8.2 Volume fraction 2.7 1.4 1.4 2.0 of pores 2 m in % D.sub.50: median 1.0 0.8 0.7 Not diameter (m) measured D.sub.90 (m) of pores 4.3 2.0 2.3 Not measured D.sub.100: maximum 8.0 5.1 3.0 5.5 pore diameter (m) Saggar performance tests with its coating Appearance after No cracks No cracks No cracks No cracks deposition Thermal shock very good good good very good resistance LiOH corrosion mediocre good excellent excellent resistance

[0112] The examples according to the invention, the coating of which has a volume fraction of pores greater than or equal to 2 micrometers that is less than 2.5%, as measured by image analysis, show 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 little adhesion after firing, although the saggars are easily cleaned by blowing or scraping without significant deterioration of the coating after 5 lithium corrosion tests. Example 4 shows that in case of superimposition of deposits, the performance of the coated final furniture is also dependent on the distinctive criterion cited above.

[0113] Of course, the invention is not limited to the embodiments described and shown.