Negative thermal expansion ceramic material as well as preparation method and application thereof

Abstract

The invention provides a negative thermal expansion ceramic material as well as a preparation method and application thereof, the chemical formula of the negative thermal expansion ceramic material is ScaYbW3O12, 0 lt, 0 lt, 0 lt, 0 lt, 0 lt, 0 lt, 0 lt, 0 lt, 0 lt, 0 lt, 0 lt, 0 lt, a < lt >; 2, 0lt; blt; according to the negative thermal expansion ceramic material, through the synergistic effect of the rare earth elements Sc and Y and the tungsten-oxygen network, the negative thermal expansion effect with the wide temperature range and the high stability is achieved; and the fuel cell stack fastening part can continuously provide higher fastening force in a high-temperature environment without being influenced by operating temperature, so that the problems of looseness, sealing failure or overlarge structural stress of fasteners such as bolts and the like are solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ceramic materials, and relates to a negative thermal expansion ceramic material and a preparation method and application thereof. BACKGROUND

[0002] Solid oxide fuel cell (SOFC) is a new type of power generation technology with high efficiency and low pollution, which has the advantages of wide fuel adaptability, high electrical efficiency, flexible system integration, etc., and is widely used in distributed power generation, vehicle-mounted power supply, aerospace and military equipment, etc. The working temperature of SOFC is usually between 700-1000℃, and the basic unit is composed of a cathode, an electrolyte and an anode. Multiple units are stacked through interconnects to form a stack to output higher voltage and power.

[0003] During the operation of the SOFC system, the high-temperature environment requires that the electrical contact and the sealing between the cell units must be maintained well, which puts higher requirements on the structural design and loading mode of the stack. The common SOFC stack compression methods currently include mechanical spring loading, bolt pre-tightening, external gas pressure loading, etc. Although these methods can achieve a certain degree of compression effect, they each have disadvantages.

[0004] The mechanical spring loading system is prone to elastic failure, creep and deformation at high temperatures, resulting in attenuation of the compression force during the operation of the stack, thereby causing poor electrical contact, gas leakage and even damage to the sealing material, etc. The bolt pre-tightening scheme is relatively stable, but it is difficult to compensate for the dimensional changes caused by thermal expansion, and the assembly is complex, which poses a challenge to the consistency and reliability of the stack. The external gas pressurization system needs to be matched with a gas source, a pipeline and a control system, and has a complex structure and high power consumption, which makes it difficult to apply to compact systems.

[0005] The SOFC stack will undergo frequent thermal cycles during start-up, steady-state operation and cold stop, and the thermal expansion mismatch problem is particularly prominent. Due to the large difference in the thermal expansion coefficients of different components (such as metals, ceramics, sealing materials, etc.) in the stack, if the compression system responds late or cannot be dynamically adjusted, the sealing performance, electrical contact stability and long-term reliability of the stack will be significantly reduced.

[0006] In recent years, negative thermal expansion materials (NTE) have been widely studied due to their abnormal thermodynamic behavior of size contraction when heated.

[0007] CN115763926A discloses a fuel cell stack which uses ZrW2O8, HfV2O7, ZrV2O7, etc. as the negative thermal expansion material for the fixing piece material of the anti-loose structure.

[0008] CN120004318A discloses a wide temperature range inorganic negative thermal expansion material and a synthesis method thereof, and the Mn2V2O7 inorganic negative thermal expansion material is prepared based on a solid phase reaction method. The negative thermal expansion temperature interval of the Mn2V2O7 inorganic negative thermal expansion material is 69-497 DEG C.

[0009] The negative thermal expansion materials used in the above scheme have the problems of low negative thermal expansion coefficient or small negative thermal expansion temperature interval, and it is difficult to meet the high temperature requirement of 1000 DEG C of the solid oxide fuel cell. SUMMARY

[0010] The purpose of the present application is to provide a negative thermal expansion ceramic material and its preparation method and application. The negative thermal expansion ceramic material disclosed in the present application realizes wide temperature range and high stability of negative thermal expansion effect through the synergistic effect of rare earth elements Sc and Y and tungsten oxygen network. The negative thermal expansion ceramic material can be used in the fastening part of the fuel cell stack to continuously provide high fastening force under high temperature environment, avoid the problems of loosening of fasteners such as bolts, sealing failure or excessive structural stress.

[0011] To achieve the purpose of the present application, the following technical scheme is adopted:

[0012] In a first aspect, the present application provides a negative thermal expansion ceramic material, the chemical formula of the negative thermal expansion ceramic material is Sc a Y b W3O 12 , wherein 0

[0013] The negative thermal expansion ceramic material disclosed in the present application contains scandium elements, yttrium elements and tungsten acid roots. The tungsten acid root has a rigid tetrahedral structure, as a rare earth metal ion, Sc 3+ and Y 3+ occupy the sites in the tungsten acid root lattice, Sc 3+ has a small ionic radius, Y 3+ has a large ionic radius, realizing the gradient distribution of lattice stress, Sc 3+ fills the lattice gap, inhibits the overall expansion, Y 3+ induces local distortion, promotes bridge oxygen vibration, and the two together improve the negative thermal expansion performance of the material.

[0014] In the negative thermal expansion ceramic material disclosed in the present application, the addition of Sc can inhibit the high temperature phase transition, and Y can help to widen the temperature range of the material. The synergistic effect of the two makes the negative thermal expansion ceramic material disclosed in the present application still maintain stable negative thermal expansion performance at high temperature of 1000 DEG C.

[0015] Preferably, the chemical formula of the negative thermal expansion ceramic material is Sc a Y b W3O12 wherein 0.1 < a < 1.9, 0.1 < b < 1.9, and a + b = 2.

[0016] Preferably, the coefficient of thermal expansion of the negative thermal expansion ceramic material is -4 x 10 -6 / K to -4.5 x 10 -6 / K, for example, -4 x 10 -6 / K, -4.1 x 10 -6 / K, -4.2 x 10 -6 / K, -4.3 x 10 -6 / K, -4.4 x 10 -6 / K, or -4.5 x 10 -6 / K, and the like, and other values within the range of values listed are also applicable.

[0017] The negative thermal expansion ceramic material of the present application can maintain excellent negative thermal expansion performance in the range of 100°C to 1000°C, has a wide temperature range of use, and has good effects, and can be combined with other oxides to form a zero-expansion or low-expansion composite material, thereby widening the application field thereof.

[0018] Preferably, the median particle size D50 of the negative thermal expansion ceramic material is 0.1 μm to 100 μm, for example, 0.1 μm, 1 μm, 5 μm, 50 μm, or 100 μm, and the like, and other values within the range of values listed are also applicable.

[0019] In a second aspect, the present application provides a preparation method of the negative thermal expansion ceramic material according to the first aspect, and the preparation method comprises the following steps:

[0020] The yttrium source, the scandium source, and the tungstic acid source are mixed with an acidic solution, and then a complexing agent is added to obtain a mixed solution, and the mixed solution is subjected to a self-propagating combustion treatment to obtain a precursor;

[0021] The precursor is subjected to a calcination treatment to obtain the negative thermal expansion ceramic material.

[0022] In the method of the present application, the yttrium source, the scandium source, and the tungstic acid source are highly dispersed in a solution, and then a complexing agent is added to chelate metal ions, thereby further ensuring uniform distribution of the elements, avoiding precipitation or segregation caused by excessively high local concentration, and ensuring mixing of the three ions at a molecular scale. This uniformity is retained in the precursor after the self-propagating combustion, thereby ensuring consistency of the negative thermal expansion performance. The self-propagating combustion can volatilize organic residues, and finally, the crystal form is optimized through calcination to obtain a negative thermal expansion ceramic material with high-purity single phase, stable negative thermal expansion performance, and high mechanical strength.

[0023] Preferably, the yttrium source comprises yttrium nitrate.

[0024] Preferably, the scandium source comprises scandium nitrate.

[0025] Preferably, the tungsten source comprises ammonium metatungstate.

[0026] Preferably, the molar ratio of yttrium element in the yttrium source, scandium element in the scandium source and tungsten element in the tungsten source is a:b:3, wherein 0

[0027] Preferably, the acidic solution comprises dilute nitric acid aqueous solution.

[0028] Preferably, the complexing agent comprises citric acid and / or EDTA, preferably citric acid and EDTA.

[0029] Preferably, the molar ratio of total amount of metal elements in the mixed solution to citric acid and EDTA is 1:(0.8-1.2):(0.5-1), for example, 1:0.8:0.1, 1:1:0.8, 1:1:1, 1:1.2:0.8 or 1:1.2:1, etc., not limited to the listed values, other values not listed in the range are also applicable.

[0030] Preferably, the pH of the mixed solution is adjusted before the self-propagating combustion process.

[0031] Preferably, the pH adjusting agent of the adjusting solution comprises ammonia water.

[0032] Preferably, the pH is 7-8, for example, 7, 7.2, 7.5, 7.8 or 8, etc., not limited to the listed values, other values not listed in the range are also applicable.

[0033] Preferably, the temperature of the self-propagating combustion process is 250-300℃, for example, 250℃, 260℃, 270℃, 280℃, 290℃ or 300℃, etc., not limited to the listed values, other values not listed in the range are also applicable.

[0034] In the self-propagating combustion process, the mixed solution is first placed in a ceramic crucible and heated in an electric hot plate or a box furnace, and the self-propagating combustion reaction occurs during slow evaporation, and finally a fluffy precursor ash is formed.

[0035] Preferably, the temperature of the calcination process is 900-1100℃, for example, 900℃, 950℃, 1000℃, 1050℃ or 1100℃, etc., not limited to the listed values, other values not listed in the range are also applicable.

[0036] Preferably, the calcination treatment time is 2h-4h, for example: 2h, 2.5h, 3h, 3.5h or 4h, etc., not only limited to the listed values, other values not listed in the range of values are also applicable.

[0037] The negative thermal expansion ceramic material obtained after the calcination treatment needs to be further treated to improve uniformity and pressing performance, and the ball milling method is used for treatment, usually using zirconia balls and ethanol medium wet milling for 12 hours to obtain fine powder with narrow particle size distribution and good compressibility, and then dried at 60℃ and sieved with a 200 mesh sieve for molding use.

[0038] In a third aspect, the present application provides a negative thermal expansion ceramic solid, which comprises the negative thermal expansion ceramic material according to the first aspect.

[0039] Preferably, the negative thermal expansion ceramic solid further comprises a binder.

[0040] Preferably, the binder comprises PVA and / or PEG.

[0041] Preferably, the mass fraction of the binder in the negative thermal expansion ceramic solid is 3%-5%, for example: 3%, 3.5%, 4%, 4.5% or 5%, etc., not only limited to the listed values, other values not listed in the range of values are also applicable.

[0042] The shape of the negative thermal expansion ceramic solid according to the present application includes a rod shape, and the negative thermal expansion ceramic solid can be made by the following method:

[0043] After the green body of the negative thermal expansion ceramic material is prepared by dry pressing, gel injection or extrusion process, it is dried and then pre-fired at 400℃-600℃ for 1h-3h, and then calcined at 1400℃-1500℃ for 30h-40h. Alumina support plate is recommended during calcination to maintain the integrity of the rod shape. After calcination, it is cooled to room temperature.

[0044] If dry pressing method is used, 3-5% PVA or PEG solution by mass fraction can be added to the powder as a binder and stirred uniformly to prepare granulated powder with good compressibility. If gel injection or extrusion molding process is used, the powder can be made into high concentration slurry or ceramic paste for extrusion to meet the requirements of fluidity and plasticity for molding.

[0045] The forming process of the ceramic green body can be dry pressing, isostatic pressing or extrusion according to the needs. For conventional experimental research, dry pressing is usually adopted, that is, the treated ceramic powder is loaded into a metal mold and pressed into a columnar green body with a diameter of about 610 mm and a length of 40-100 mm under a pressure of 100-200 MPa. In order to improve the density, an initial green body can also be prepared, and then cold isostatic pressing is performed under a pressure of 20-30 MPa. If a long-size or continuous structure ceramic rod is needed, a uniform and dense extruded rod can be prepared through a screw extruder.

[0046] After calcination, the ceramic can be subjected to necessary end face grinding or cutting to meet the size accuracy requirements, and the prepared ceramic rod body can be used for high-temperature thermal expansion regulation, negative thermal expansion support structure and other applications. The process path can realize complete conversion from the raw material solution to the high-density ceramic product, and has good controllability and repeatability.

[0047] In a fourth aspect, the present application provides a fuel cell stack comprising the negative thermal expansion ceramic fastener according to the third aspect.

[0048] Compared with the prior art, the present application has the following beneficial effects:

[0049] (1) The negative thermal expansion ceramic material according to the present application realizes wide temperature range and high stability of negative thermal expansion effect through the synergistic effect of rare earth elements Sc and Y and tungsten oxygen network, which can continuously provide high fastening force in a high temperature environment for the fastening part of the fuel cell stack, is not affected by the operating temperature, avoids the problems of loosening of the fastener such as bolt, sealing failure or excessive structural stress.

[0050] (2) The thermal expansion coefficient of the negative thermal expansion ceramic material according to the present application can reach -4.15x10 -6 / K or below within 100℃-1000℃, which can quickly offset the positive expansion of the fastening part of the fuel cell stack at high temperature. BRIEF DESCRIPTION OF DRAWINGS

[0051] Figure 1 is a negative thermal expansion curve diagram of the negative thermal expansion ceramic material provided in Example 1 of the present application. DETAILED DESCRIPTION

[0052] The technical solutions of the present application will be further described through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations on the present application.

[0053] Example 1

[0054] The present embodiment provides a negative thermal expansion ceramic material, the chemical formula of which is ScYW3O 12, the negative thermal expansion ceramic material is prepared by the following method:

[0055] (1) First, ammonium metatungstate, yttrium nitrate and scandium nitrate are weighed and dissolved in a small amount of mixed solution of dilute nitric acid and deionized water according to the molar ratio of Sc:Y:W = 1:1:6, ensuring complete dissolution of the three metal ions. Then, the complexing agents citric acid and EDTA are added to the mixed solution in sequence, and the molar ratio of the total number of metal ions to citric acid and EDTA is 1:1:0.8, respectively. The mixed solution is continuously heated under the condition of thermal magnetic stirring until the citric acid and EDTA are completely dissolved to form a clear solution. In order to neutralize the excess acid and promote the complexation reaction of metal ions, ammonia water is slowly added to adjust the solution pH to 7.5. After adjustment, the mixture is continuously heated and stirred until uniform and transparent, then it is poured into a ceramic crucible and placed on an electric hot plate or box furnace to heat to 270℃, and a self-propagating combustion reaction occurs during slow evaporation, finally forming a fluffy precursor;

[0056] (2) The obtained precursor is ground and transferred to a muffle furnace, calcined at 1000℃ for 3h under air atmosphere, to obtain the negative thermal expansion ceramic material. The negative thermal expansion ceramic material is treated by ball milling method, wet milling for 12h to obtain fine powder with narrow particle size distribution and good compressibility, then dried at 60℃ to obtain the negative thermal expansion ceramic material with a median particle size D50 of 5μm.

[0057] The negative thermal expansion curve of the negative thermal expansion ceramic material is shown in Figure 1 .

[0058] Example 2

[0059] This example provides a negative thermal expansion ceramic material, the chemical formula of the negative thermal expansion ceramic material is Sc 0.5 Y 1.5 W3O 12 , the negative thermal expansion ceramic material is prepared by the following method:

[0060] (1) First, the ammonium metatungstate, yttrium nitrate and scandium nitrate are weighed and dissolved in a mixed solution of a small amount of dilute nitric acid and deionized water according to the molar ratio of Sc:Y:W = 0.5:1.5:6, ensuring that the three metal ions are completely dissolved. Then, the complexing agents citric acid and EDTA are sequentially added to the mixed solution, and the molar ratio of the total number of metal ions to citric acid and EDTA is 1:0.8:1, respectively. The mixed solution is continuously heated under the condition of thermal magnetic stirring until the citric acid and EDTA are completely dissolved to form a clear solution. In order to neutralize the excess acidity and promote the complexation reaction of metal ions, ammonia water is slowly added to adjust the solution pH to 7. After adjustment, the mixture is continuously heated and stirred until it is uniform and transparent, then it is poured into a ceramic crucible and placed on an electric hot plate or box furnace to heat to 250°C. During the slow evaporation process, a self-propagating combustion reaction occurs, and finally a fluffy precursor is formed;

[0061] (2) The obtained precursor is ground and transferred to a muffle furnace, calcined at 900°C for 4h in an air atmosphere to obtain the negative thermal expansion ceramic material. The negative thermal expansion ceramic material is treated by ball milling for 12h to obtain a fine powder with narrow particle size distribution and good compressibility. Then it is dried at 60°C to obtain a negative thermal expansion ceramic material with a median particle size D50 of 10μm.

[0062] Example 3

[0063] This example provides a negative thermal expansion ceramic material, the chemical formula of which is Sc 1.5 Y 0.5 W3O 12 , which is prepared by the following method:

[0064] (1) First, the ammonium metatungstate, yttrium nitrate and scandium nitrate are weighed and dissolved in a mixed solution of a small amount of dilute nitric acid and deionized water according to the molar ratio of Sc:Y:W = 1.5:0.5:6, ensuring that the three metal ions are completely dissolved. Then, the complexing agents citric acid and EDTA are sequentially added to the mixed solution, and the molar ratio of the total number of metal ions to citric acid and EDTA is 1:1.2:1, respectively. The mixed solution is continuously heated under the condition of thermal magnetic stirring until the citric acid and EDTA are completely dissolved to form a clear solution. In order to neutralize the excess acidity and promote the complexation reaction of metal ions, ammonia water is slowly added to adjust the solution pH to 8. After adjustment, the mixture is continuously heated and stirred until it is uniform and transparent, then it is poured into a ceramic crucible and placed on an electric hot plate or box furnace to heat to 300°C. During the slow evaporation process, a self-propagating combustion reaction occurs, and finally a fluffy precursor is formed;

[0065] (2) The obtained precursor is ground and transferred to a muffle furnace, calcined at 1100°C for 2h under air atmosphere to obtain the negative thermal expansion ceramic material, the negative thermal expansion ceramic material is treated by ball milling method, wet grinding for 12h to obtain fine powder with narrow particle size distribution and good compressibility, and then dried at 60°C to obtain the negative thermal expansion ceramic material with a median particle size D50 of 1μm.

[0066] Example 4

[0067] The difference between this example and Example 1 is that the chemical formula of the negative thermal expansion ceramic material is Sc 0.1 Y 1.9 W3O 12 , and other conditions and parameters are exactly the same as those in Example 1.

[0068] Example 5

[0069] The difference between this example and Example 1 is that the chemical formula of the negative thermal expansion ceramic material is Sc 1.9 Y 0.1 W3O 12 , and other conditions and parameters are exactly the same as those in Example 1.

[0070] Example 6

[0071] The difference between this example and Example 1 is that the temperature of the self-propagating combustion process is 200°C, and other conditions and parameters are exactly the same as those in Example 1.

[0072] Example 7

[0073] The difference between this example and Example 1 is that the temperature of the self-propagating combustion process is 350°C, and other conditions and parameters are exactly the same as those in Example 1.

[0074] Example 8

[0075] The difference between this example and Example 1 is that the calcination temperature is 800°C, and other conditions and parameters are exactly the same as those in Example 1.

[0076] Example 9

[0077] The difference between this example and Example 1 is that the calcination temperature is 1200°C, and other conditions and parameters are exactly the same as those in Example 1.

[0078] Comparative Example 1

[0079] The difference between this comparative example and Example 1 is that no Sc element is added, and the chemical formula of the negative thermal expansion ceramic material prepared is Y2W3O 12 , and other conditions and parameters are exactly the same as those in Example 1.

[0080] Comparative Example 2

[0081] The comparative example is different from example 1 only in that no Y element is added, and the chemical formula of the negative thermal expansion ceramic material prepared is Sc2W3O 12 The other conditions and parameters are completely same as example 1.

[0082] Comparative example 3

[0083] The chemical formula of the negative thermal expansion ceramic material provided by the comparative example is ZrW2O8.

[0084] Performance test:

[0085] The negative thermal expansion ceramic materials described in the examples and comparative examples are tested, and the test results are shown in Table 1:

[0086] Table 1

[0087]

[0088]

[0089] As can be seen from Table 1, according to examples 1-9, the coefficient of thermal expansion of the negative thermal expansion ceramic material described in the application can reach -4.15x10 -6 / K or below within 100℃-1000℃, which can quickly offset the positive expansion of the high-temperature part of the battery stack fastening part.

[0090] As can be seen from the comparison of example 1 and examples 4-5, in the negative thermal expansion ceramic material described in the application, the molar ratio of the elements of scandium and yttrium will affect its performance, the molar ratio of the elements of scandium and yttrium, i.e. a, is controlled in 0.1

[0091] As can be seen from the comparison of example 1 and examples 6-7, in the preparation process of the negative thermal expansion ceramic material described in the application, the temperature of self-propagating combustion will affect its performance, the temperature of self-propagating combustion is controlled in 250℃-300℃, and the performance of the negative thermal expansion ceramic material prepared is better, if the temperature of self-propagating combustion is too low, the fuel is not fully burned, and there are residual organic carbon or unreacted nitrate, which will generate impurities after calcination, if the temperature of self-propagating combustion is too high, the rapid high temperature will cause the abnormal growth of the precursor grains, which will weaken the negative thermal expansion performance of the material.

[0092] From the comparison of Example 1 and Examples 8-9, it can be seen that the temperature of calcination affects the performance of the negative thermal expansion ceramic material. If the temperature of calcination is controlled at 250-300℃, the performance of the negative thermal expansion ceramic material is better. If the temperature of calcination is too low, the precursor is not completely converted into ScYW3O 12 , and amorphous or intermediate phases such as Sc2W3O6 are left, resulting in unstable negative thermal expansion performance. If the temperature of calcination is too high, the negative thermal expansion ceramic material is decomposed into Sc2O3, Y2O3 and WO3 and other materials at high temperature, weakening the negative thermal expansion performance of the material.

[0093] From the comparison of Example 1 and Comparative Examples 1-2, it can be seen that the negative thermal expansion ceramic material contains scandium, yttrium and tungstate. The tungstate has a rigid tetrahedral structure, and as a rare earth metal ion, Sc 3+ and Y 3+ occupy the sites in the tungstate lattice. The ionic radius of Sc 3+ is small, and the ionic radius of Y 3+ is large, achieving a gradient distribution of lattice stress. Sc 3+ fills the lattice gap, inhibiting overall expansion, and Y 3+ induces local distortion, promotes bridge oxygen vibration, and the two work together to improve the negative thermal expansion coefficient of the material.

[0094] From the comparison of Example 1 and Comparative Example 3, it can be seen that the zirconium tungstate negative thermal expansion ceramic material is prone to phase transition at high temperature, resulting in a significant decrease in its high-temperature stability and unstable negative thermal expansion performance. The high-temperature stability of the negative thermal expansion ceramic material of the present application is greatly improved compared with conventional zirconium tungstate negative thermal expansion ceramic materials.

[0095] The applicant declares that the above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. It should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the present application can be easily thought of by those skilled in the art, and all fall within the protection scope and disclosure scope of the present application.

Claims

1. A negative thermal expansion ceramic material, characterized in that, The chemical formula of the negative thermal expansion ceramic material is Sc. a Y b W3O 12 , of which 0 <a<2,0<b<2,a+b=2。 2. The negative thermal expansion ceramic material as described in claim 1, characterized in that, The chemical formula of the negative thermal expansion ceramic material is Sc. a Y b W3O 12 , of which 0.1 <a<1.9,0.1<b<1.9,a+b=2; Preferably, the coefficient of thermal expansion of the negative thermal expansion ceramic material is -4 × 10⁻⁴ in the temperature range of 100℃ to 1000℃. -6 / K~-4.5×10 -6 / K.

3. The negative thermal expansion ceramic material as described in claim 1 or 2, characterized in that, The median particle size D50 of the negative thermal expansion ceramic material is 0.1 μm to 100 μm.

4. A method for preparing a negative thermal expansion ceramic material as described in any one of claims 1-3, characterized in that, The preparation method includes the following steps: Yttrium source, scandium source, tungstate source and acidic solution are mixed evenly and then a complexing agent is added to obtain a mixed solution. The mixed solution is subjected to self-propagating combustion treatment to obtain the precursor. The negative thermal expansion ceramic material is obtained by calcining the precursor.

5. The preparation method according to claim 4, characterized in that, The yttrium source includes yttrium nitrate; Preferably, the scandium source includes scandium nitrate; Preferably, the tungstate source includes ammonium metatungstate; Preferably, the molar ratio of yttrium in the yttrium source, scandium in the scandium source, and tungsten in the tungstate source is a:b:3, wherein 0 <a<2,0<b<2,a+b=2; Preferably, the acidic solution comprises a dilute aqueous nitric acid solution.

6. The preparation method according to claim 4 or 5, characterized in that, The complexing agent includes citric acid and / or EDTA, preferably citric acid and EDTA; Preferably, the total molar amount of metal elements in the mixed solution is in a molar ratio of citric acid to EDTA of 1:(0.8-1.2):(0.5-1); Preferably, the pH of the mixed solution is adjusted before the self-propagating combustion treatment; Preferably, the pH adjuster for the solution includes ammonia. Preferably, the pH is 7 to 8.

7. The preparation method according to any one of claims 4-6, characterized in that, The temperature for self-propagating combustion treatment is 250℃~300℃.

8. The preparation method according to any one of claims 4-7, characterized in that, The calcination temperature is 900℃~1100℃; Preferably, the calcination treatment time is 2h to 4h.

9. A negative thermal expansion ceramic fastener, characterized in that, The negative thermal expansion ceramic fastener comprises the negative thermal expansion ceramic material as described in any one of claims 1-3.

10. A fuel cell stack, characterized in that, The fuel cell stack includes the negative thermal expansion ceramic fastener as described in claim 9.

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