Preparation method of apatite-type lanthanum silicate solid electrolyte

Abstract

The application discloses a preparation method of an apatite-type lanthanum silicate solid electrolyte, and comprises the following steps: step (1), mixing LaCrO3 powder and Ti3SiC2 powder to obtain mixed powder A; step (2), grinding the mixed powder A in anhydrous ethanol as a medium; step (3), drying the ground mixed powder A, and obtaining mixed powder B after the drying; step (4), secondly grinding the mixed powder B to obtain mixed powder C; and step (5), sintering the mixed powder C by using a discharge plasma technology, and obtaining the apatite-type lanthanum silicate bulk material after cooling to room temperature. Compared with a traditional preparation method, the method has the advantages of low sintering temperature, simple process, high efficiency, low cost, energy saving and environmental protection, and the prepared product is dense and has excellent mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of lanthanum silicate solid electrolyte technology. Specifically, it relates to a method for preparing an apatite-type lanthanum silicate solid electrolyte. Background Technology

[0002] Solid oxide fuel cells (SOFCs) are widely used solid-state power generation devices with advantages such as high efficiency, all-solid-state structure, and no pollution. The electrolyte is an important component, serving to separate the electrodes and transfer oxygen. 2- The role of ions. The spatial structures of SOFC electrolytes are mainly fluorite, perovskite, and apatite; among them, apatite-type electrolyte materials solve the problems of poor compatibility between traditional electrolytes and electrode materials, and poor stability under specific atmospheres. Apatite-type lanthanum silicate (molecular formula La) 9.33 Si6O 26 Lanthanum silicate has advantages such as low activation energy, thermal expansion coefficient matching with electrode materials, and high ionic conductivity at medium and low temperatures, making it a suitable material for medium and low temperature SOFC electrolytes. However, current synthesis methods and sintering processes limit the development of lanthanum silicate of the apatite type.

[0003] Currently, the main methods for preparing apatite-type lanthanum silicate include solid-state methods, sol-gel methods, and co-precipitation methods. Traditional solid-state methods often use SiO2 and La2O3 as raw materials, resulting in products with poor purity and containing high levels of La2O3 and La2SiO5. Sol-gel and co-precipitation methods use C8H... 20 Using O4Si and La(NO3)3 as raw materials, auxiliary raw materials such as organosilicon and ethanol are used in the preparation process. Sol gel or precipitated powder must be obtained first, and then ground and calcined to obtain apatite-type lanthanum silicate powder. Although the purity is high, the process is complicated and the production cost is high. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to provide a method for preparing apatite-type lanthanum silicate solid electrolyte, so as to solve the problems of cumbersome production process and high production cost of existing apatite-type lanthanum silicate.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] A method for preparing an apatite-type lanthanum silicate solid electrolyte includes the following steps:

[0007] Step (1): Thoroughly mix LaCrO3 powder and Ti3SiC2 powder to obtain mixed powder A;

[0008] Step (2): Grind the mixed powder A thoroughly using anhydrous ethanol as the medium;

[0009] Step (3): Dry the ground mixed powder A to obtain mixed powder B after drying.

[0010] Step (4): Grind the mixed powder B a second time to obtain mixed powder C;

[0011] Step (5): The mixed powder C is sintered using spark plasma technology. After sintering, it is cooled to room temperature to obtain apatite-type lanthanum silicate bulk material.

[0012] In the preparation method of the above-mentioned apatite-type lanthanum silicate solid electrolyte, in step (1), the molar ratio of LaCrO3 powder to Ti3SiC2 powder is 1:1. After the two substances are mixed, Ti3SiC2 acts as a reducing agent, and LaCrO3 acts as a calcination aid. Mixing the two in an equimolar ratio may lead to more reaction pathways, thereby generating appropriate reaction conditions and reaction intermediates to promote the reaction of LaCrO3. 9.33 Si6O 26 The formation of.

[0013] In the preparation method of the above-mentioned apatite-type lanthanum silicate solid electrolyte, in step (2), the mass ratio of mixed powder A to anhydrous ethanol is 1:1.2. If too much anhydrous ethanol is used, it will increase the loss of raw materials and grinding time, and may also cause particle aggregation, which will reduce the grinding effect. If too little anhydrous ethanol is used, it will cause increased friction between particles during the grinding process, damage the particles, and also cause particles to stick together, making it difficult to grind fully.

[0014] In the above-mentioned method for preparing lanthanum silicate solid electrolyte of apatite type, the grinding time in step (2) is 1.5 h. If the grinding time is too short, it will lead to insufficient grinding and uneven particle distribution; if the grinding time is too long, it will not only increase energy consumption, but also cause ethanol to evaporate, thereby affecting the uniformity of particle dispersion and reaction effect.

[0015] In the above-mentioned preparation method of lanthanum silicate solid electrolyte of apatite type, in step (3), the medium particle size of mixed powder B is 18.09 μm; the drying temperature is 90℃ and the drying time is 12h.

[0016] In the above-mentioned method for preparing apatite-type lanthanum silicate solid electrolyte, the secondary grinding time in step (4) is 1 hour; the medium particle size of the mixed powder C is 10.01 μm. If the secondary grinding time is too long, the particles may become too fine, thereby affecting the performance of the product.

[0017] In the preparation method of the above-mentioned apatite-type lanthanum silicate solid electrolyte, the sintering method using discharge plasma technology in step (5) is as follows:

[0018] Step (5-1): Pour the mixed powder C into the graphite mold. Separate the top and bottom of the mixed powder C from the graphite mold with carbon paper to prevent it from sticking to the mold.

[0019] Step (5-2): Place the graphite mold in a spark plasma hot pressing sintering furnace for sintering; during the sintering process, a vacuum is drawn and the graphite mold is axially pressurized by a hydraulic pump to ensure that the sintered body is dense; after sintering, apatite-type lanthanum silicate bulk material is obtained.

[0020] In the preparation method of the above-mentioned apatite-type lanthanum silicate solid electrolyte, in step (5-2), during sintering, if the heating rate is too fast, it will cause a temperature gradient inside the material, resulting in stress concentration and uneven sintering. If the heating rate is too slow, it will increase production costs and cycle time. In this invention, during sintering, the temperature is first raised from room temperature to 1000℃ at a heating rate of 100℃ / min to completely burn or volatilize the volatile residues in the raw materials in advance, reducing the generation of pores and defects in the subsequent sintering process. Then, the temperature is raised to 1300-1500℃ at a heating rate of 50℃ / min (continuous rapid heating may cause a large temperature gradient inside the material, resulting in uneven sintering and reduced sintering quality), and held at 1300-1500℃ for 5-10 min. Then, to inhibit further particle growth, the temperature is rapidly cooled to 1000℃ at a cooling rate of 100℃ / min, and finally naturally cooled to room temperature to prevent rapid shrinkage that could cause product cracking.

[0021] In the above-mentioned method for preparing apatite-type lanthanum silicate solid electrolyte, in step (5-2), the axial pressure of the graphite mold is 45 MPa.

[0022] In the above-mentioned preparation method of lanthanum silicate solid electrolyte of apatite type, in step (1), the molar ratio of LaCrO3 powder and Ti3SiC2 powder is 1:1; in step (2), the mass ratio of mixed powder A to anhydrous ethanol is 1:1.2, and the grinding time is 1.5h; in step (3), the medium particle size of mixed powder B is 18.09μm; the drying temperature is 90℃, and the drying time is 12h (too low a drying temperature or too long a drying time will prolong the production cycle, and conversely, it will easily cause powder agglomeration, which is not conducive to subsequent work); in step (4), the second grinding time is 1h; the medium particle size of mixed powder C is 10.01μm; in step (5), the sintering method of discharge plasma technology is as follows: step (5- 1) Pour the mixed powder C into a graphite mold, separating the top and bottom of the mixed powder C from the graphite mold with carbon paper; Step (5-2) Place the graphite mold in a spark plasma hot pressing sintering furnace for sintering; Vacuum is drawn during sintering, and axial pressure is applied to the graphite mold by a hydraulic pump to ensure the sintered body is dense; After sintering, apatite-type lanthanum silicate bulk material is obtained; During sintering, the temperature is first raised from room temperature to 1000℃ at a heating rate of 100℃ / min, then raised to 1300-1500℃ at a heating rate of 50℃ / min, and held at this temperature for 5-10 minutes; Then, the temperature is rapidly cooled to 1000℃ at a cooling rate of 100℃ / min, and finally cooled naturally to room temperature; The axial pressure of the graphite mold is 45MPa.

[0023] The technical solution of the present invention achieves the following beneficial technical effects:

[0024] 1. This invention uses a mixture of LaCrO3 and Ti3SiC2 powders with excellent conductivity as raw materials, and directly prepares apatite-type solid electrolytes through spark plasma sintering technology. Compared with traditional preparation methods, the method of this invention not only reduces the types and amounts of raw materials, but also has advantages such as low sintering temperature, simple process, high efficiency, low cost, energy saving and environmental protection. The prepared product is dense and has excellent mechanical properties.

[0025] 2. In this invention, LaCrO3 is a compound of lanthanum oxide and chromium oxide, exhibiting high-temperature stability and good electrical conductivity. In the mixed reaction, LaCrO3 acts as a calcination aid. As the reaction temperature increases, LaCrO3 can provide oxygen ions, promoting the conversion of reactants, and the reaction kinetics can be controlled by adjusting the reaction temperature and pressure. Ti3SiC2 acts as a reducing agent in the mixed reaction; at high temperatures, Ti3SiC2 is oxidized, while Si and C react with LaCrO3 to form stable La... 9.33 Si6O 26 .

[0026] 3. The apatite-type lanthanum silicate prepared by this invention exhibits good high-temperature phase stability and a certain degree of anisotropy. Its radial strength is slightly higher than its axial strength, and its density is 86.08%–91.95%. Its radial microhardness is 5.71–8.27 GPa, and its axial microhardness is 4.35–8.23 GPa. Its radial fracture toughness is 2.07–2.33 MPa. 1 / 2 The axial fracture toughness is 1.37–1.93 MPa.m. 1 / 2 . Attached Figure Description

[0027] Figure 1 Microscopic morphology of the apatite-type lanthanum silicate solid electrolyte prepared in Example 1 of this invention;

[0028] Figure 2 The XRD pattern and related standard diffraction pattern of the apatite-type lanthanum silicate prepared in Example 1 of this invention;

[0029] Figure 3 XRD patterns of apatite-type lanthanum silicate prepared in Examples 1-3 of this invention;

[0030] Figure 4 The packing density of the apatite-type lanthanum silicate prepared in Examples 1-3 of this invention;

[0031] Figure 5 Axial and radial microhardness diagrams of the apatite-type lanthanum silicate prepared in Examples 1-3 of this invention;

[0032] Figure 6 Axial and radial fracture toughness diagrams of the apatite-type lanthanum silicate prepared in Examples 1-3 of this invention. Detailed Implementation

[0033] Example 1

[0034] In this embodiment, the preparation method of the apatite-type lanthanum silicate solid electrolyte includes the following steps:

[0035] Step (1): Mix LaCrO3 powder and Ti3SiC2 powder thoroughly in a molar ratio of 1:1 to obtain mixed powder A;

[0036] Step (2): Mix powder A with anhydrous ethanol at a mass ratio of 1:1.2 and grind it thoroughly in an agate mill for 1.5 hours. Anhydrous ethanol is used as the grinding medium here. Grinding for 1.5 hours will make the two powders mix evenly and further reduce the particle size.

[0037] Step (3): Place the ground mixed powder A into a forced-air drying oven and dry it at 90°C for 12 hours. After drying, mixed powder B is obtained. The medium particle size of mixed powder B is 18.09 μm.

[0038] Step (4): The mixed powder B is ground twice for 1 hour to obtain mixed powder C; the medium particle size of mixed powder C is 10.01 μm.

[0039] Step (5): The mixed powder C is sintered using spark plasma technology. The method for sintering using spark plasma technology is as follows:

[0040] Step (5-1): Pour the mixed powder C into the graphite mold, and separate the top and bottom of the mixed powder C from the graphite mold with carbon paper.

[0041] Step (5-2): Place the graphite mold in a spark plasma hot pressing sintering furnace for sintering; during sintering, a vacuum is drawn, and a hydraulic pump applies an axial pressure of 45 MPa to the graphite mold to ensure the sintered body is dense; after sintering, apatite-type lanthanum silicate bulk material is obtained; during sintering, the temperature is first raised from room temperature to 1000℃ at a heating rate of 100℃ / min, then raised to 1300℃ at a heating rate of 50℃ / min, and held at 1300℃ for 5 min; finally, with the assistance of a water cooling device, the temperature is lowered to 1000℃ at a cooling rate of 100℃ / min, and then naturally cooled to room temperature. The sample is then polished with sandpaper until it becomes glossy, thus obtaining the apatite-type lanthanum silicate solid electrolyte, whose molecular formula is La. 9.33 Si6O 26 .

[0042] Figure 1 The image shows the microstructure of the apatite-type lanthanum silicate solid electrolyte prepared in this embodiment. As can be seen from the image, it has a porous structure, which is due to the volatilization of Cr and Si elements.

[0043] Figure 2 The XRD pattern and related standard diffraction pattern of the apatite-type lanthanum silicate solid electrolyte prepared in this embodiment show that the apatite-type lanthanum silicate solid electrolyte prepared in this embodiment contains a small amount of reaction byproducts TiC and Cr3Si. However, these two products are also good conductive materials and will not affect the conductivity of the apatite-type lanthanum silicate solid electrolyte; in fact, they may enhance its conductivity.

[0044] Testing revealed that the apatite-type lanthanum silicate solid electrolyte prepared in this embodiment had a density of 91.95%, an axial microhardness of 8.23 ​​GPa, a radial microhardness of 8.27 GPa, and an axial fracture toughness of 1.93 MPa. 1 / 2 The radial fracture toughness is 2.07 MPa.m. 1 / 2 .

[0045] Example 2

[0046] In this embodiment, the preparation method of the apatite-type lanthanum silicate solid electrolyte includes the following steps:

[0047] Step (1): Mix LaCrO3 powder and Ti3SiC2 powder thoroughly in a molar ratio of 1:1 to obtain mixed powder A;

[0048] Step (2): Mix powder A with anhydrous ethanol at a mass ratio of 1:1.2 and grind it thoroughly in an agate mill for 1.5 hours. Anhydrous ethanol is used as the grinding medium here. Grinding for 1.5 hours will make the two powders mix evenly and further reduce the particle size.

[0049] Step (3): Place the ground mixed powder A into a forced-air drying oven and dry it at 90°C for 12 hours. After drying, mixed powder B is obtained. The medium particle size of mixed powder B is 18.09 μm.

[0050] Step (4): The mixed powder B is ground twice for 1 hour to obtain mixed powder C; the medium particle size of mixed powder C is 10.01 μm.

[0051] Step (5): The mixed powder C is sintered using spark plasma technology. The method for sintering using spark plasma technology is as follows:

[0052] Step (5-1): Pour the mixed powder C into the graphite mold, and separate the top and bottom of the mixed powder C from the graphite mold with carbon paper.

[0053] Step (5-2): Place the graphite mold in a spark plasma hot pressing sintering furnace for sintering; during sintering, a vacuum is drawn, and a hydraulic pump applies an axial pressure of 45 MPa to the graphite mold to ensure the sintered body is dense; after sintering, apatite-type lanthanum silicate bulk material is obtained; during sintering, the temperature is first raised from room temperature to 1000℃ at a heating rate of 100℃ / min, then raised to 1400℃ at a heating rate of 50℃ / min, and held at 1400℃ for 5 min. Finally, with the assistance of a water cooling device, the temperature is lowered to 1000℃ at a cooling rate of 100℃ / min, and then naturally cooled to room temperature. The sample is then polished with sandpaper until it becomes glossy, thus obtaining the apatite-type lanthanum silicate solid electrolyte, whose molecular formula is La. 9.33 Si6O 26 .

[0054] Testing revealed that the apatite-type lanthanum silicate solid electrolyte prepared in this embodiment had a density of 88.40%, an axial microhardness of 5.94 GPa, a radial microhardness of 7.51 GPa, and an axial fracture toughness of 1.30 MPa. 1 / 2 The radial fracture toughness is 2.37 MPa·m. 1 / 2 .

[0055] Example 3

[0056] In this embodiment, the preparation method of the apatite-type lanthanum silicate solid electrolyte includes the following steps:

[0057] Step (1): Mix LaCrO3 powder and Ti3SiC2 powder thoroughly in a molar ratio of 1:1 to obtain mixed powder A;

[0058] Step (2): Mix powder A with anhydrous ethanol at a mass ratio of 1:1.2 and grind it thoroughly in an agate mill for 1.5 hours. Anhydrous ethanol is used as the grinding medium here. Grinding for 1.5 hours will make the two powders mix evenly and further reduce the particle size.

[0059] Step (3): Place the ground mixed powder A into a forced-air drying oven and dry it at 90°C for 12 hours. After drying, mixed powder B is obtained. The medium particle size of mixed powder B is 18.09 μm.

[0060] Step (4): The mixed powder B is ground twice for 1 hour to obtain mixed powder C; the medium particle size of mixed powder C is 10.01 μm.

[0061] Step (5): The mixed powder C is sintered using spark plasma technology. The method for sintering using spark plasma technology is as follows:

[0062] Step (5-1): Pour the mixed powder C into the graphite mold, and separate the top and bottom of the mixed powder C from the graphite mold with carbon paper.

[0063] Step (5-2): Place the graphite mold in a spark plasma hot pressing sintering furnace for sintering; during sintering, a vacuum is drawn, and a hydraulic pump applies an axial pressure of 45 MPa to the graphite mold to ensure the sintered body is dense; after sintering, an apatite-type lanthanum silicate bulk material is obtained; during sintering, the temperature is first raised from room temperature to 1000℃ at a heating rate of 100℃ / min, then raised to 1500℃ at a heating rate of 50℃ / min, and held at 1500℃ for 5 min. Finally, with the assistance of a water cooling device, the temperature is lowered to 1000℃ at a cooling rate of 100℃ / min, and then naturally cooled to room temperature. The sample is then polished with sandpaper until it becomes glossy, thus obtaining the apatite-type lanthanum silicate solid electrolyte, whose molecular formula is La. 9.33 Si6O 26 .

[0064] Testing revealed that the apatite-type lanthanum silicate solid electrolyte prepared in this embodiment exhibits good high-temperature phase stability, with a density of 86.08%, an axial microhardness of 4.35 GPa, a radial microhardness of 5.71 GPa, and an axial fracture toughness of 1.37 MPa.1 / 2 The radial fracture toughness is 2.12 MPa·m. 1 / 2 .

[0065] from Figure 3 As can be seen from the present invention, the apatite-type lanthanum silicate solid electrolyte has good high-temperature phase stability. As the sintering temperature increases, the phase composition does not change, which also means that it has good thermal shock stability and can be used in high-temperature environments.

[0066] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A method for preparing an apatite-type lanthanum silicate solid electrolyte, characterized in that, Includes the following steps: Step (1): Thoroughly mix LaCrO3 powder and Ti3SiC2 powder to obtain mixed powder A; Step (2): Grind the mixed powder A thoroughly using anhydrous ethanol as the medium; Step (3): Dry the ground mixed powder A to obtain mixed powder B after drying. Step (4): Grind the mixed powder B a second time to obtain mixed powder C; Step (5): The mixed powder C is sintered using spark plasma technology. After sintering, it is cooled to room temperature to obtain apatite-type lanthanum silicate bulk material.

2. The method for preparing the apatite-type lanthanum silicate solid electrolyte according to claim 1, characterized in that, In step (1), the molar ratio of LaCrO3 powder to Ti3SiC2 powder is 1:

1.

3. The method for preparing the apatite-type lanthanum silicate solid electrolyte according to claim 1, characterized in that, In step (2), the mass ratio of mixed powder A to anhydrous ethanol is 1:1.

2.

4. The method for preparing the apatite-type lanthanum silicate solid electrolyte according to claim 1, characterized in that, In step (2), the grinding time is 1.5 hours.

5. The method for preparing the apatite-type lanthanum silicate solid electrolyte according to claim 1, characterized in that, In step (3), the medium particle size of the mixed powder B is 18.09 μm; the drying temperature is 90℃ and the drying time is 12h.

6. The method for preparing the apatite-type lanthanum silicate solid electrolyte according to claim 1, characterized in that, In step (4), the second grinding time is 1 hour; the medium particle size of the mixed powder C is 10.01 μm.

7. The method for preparing the apatite-type lanthanum silicate solid electrolyte according to claim 1, characterized in that, In step (5), the sintering method using spark plasma technology is as follows: Step (5-1): Pour the mixed powder C into the graphite mold, and separate the top and bottom of the mixed powder C from the graphite mold with carbon paper. Step (5-2): Place the graphite mold in a spark plasma hot pressing sintering furnace for sintering; during the sintering process, a vacuum is drawn and the graphite mold is axially pressurized by a hydraulic pump to ensure that the sintered body is dense; after sintering, apatite-type lanthanum silicate bulk material is obtained.

8. The method for preparing the apatite-type lanthanum silicate solid electrolyte according to claim 7, characterized in that, In step (5-2), during sintering, the temperature is first raised from room temperature to 1000℃ at a heating rate of 100℃ / min, then raised to 1300-1500℃ at a heating rate of 50℃ / min, and held at 1300-1500℃ for 5-10 minutes; then it is rapidly cooled to 1000℃ at a cooling rate of 100℃ / min, and finally cooled naturally to room temperature.

9. The method for preparing the apatite-type lanthanum silicate solid electrolyte according to claim 1, characterized in that, In step (5-2), the axial pressure of the graphite mold is 45 MPa.

10. The method for preparing the apatite-type lanthanum silicate solid electrolyte according to claim 1, characterized in that, In step (1), the molar ratio of LaCrO3 powder to Ti3SiC2 powder is 1:1; In step (2), the mass ratio of mixed powder A to anhydrous ethanol is 1:1.2, and the grinding time is 1.5h; In step (3), the medium particle size of the mixed powder B is 18.09 μm; the drying temperature is 90℃ and the drying time is 12h; In step (4), the secondary grinding time is 1 hour; the medium particle size of the mixed powder C is 10.01 μm; In step (5), the sintering method using spark plasma technology is as follows: Step (5-1): Pour the mixed powder C into the graphite mold, and separate the top and bottom of the mixed powder C from the graphite mold with carbon paper. Step (5-2): Place the graphite mold in a spark plasma hot pressing sintering furnace for sintering; during the sintering process, a vacuum is drawn and the graphite mold is axially pressurized by a hydraulic pump to ensure that the sintered body is dense; after sintering, apatite-type lanthanum silicate bulk material is obtained. During sintering, the temperature is first raised from room temperature to 1000℃ at a heating rate of 100℃ / min, then raised to 1300-1500℃ at a heating rate of 50℃ / min, and held at the target temperature for 5-10 minutes; then it is rapidly cooled to 1000℃ at a cooling rate of 100℃ / min, and finally cooled naturally to room temperature; the axial pressure of the graphite mold is 45MPa.

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