Preparation method of high-density nano lithium metatitanate ceramic

Abstract

The invention provides a preparation method of high-density nano lithium metatitanate ceramic, and belongs to the technical field of preparation of ceramic materials. According to the method, continuous ball milling is carried out by replacing a ball milling solvent and controlling the size of a ball milling ball, target powder is obtained, and lithium metatitanate ceramic is directly obtained after forming and sintering. The preparation method disclosed by the invention has the advantages of simple process, low cost and good ceramic performance. In the continuous ball-milling process, multiple times of sintering are not needed, only the solvent needs to be replaced, the sintering process in the multiple times of ball-milling process is greatly saved, meanwhile, the density of the obtained lithium metatitanate ceramic is remarkably improved and reaches 99% T.D., the grain size of the lithium metatitanate ceramic can be nanoscale (within 100 nm), and the lithium metatitanate ceramic has the advantages of being simple in preparation process, low in cost and good in application prospect. The problem that the nanoscale grain size and the high density cannot be considered at the same time in existing tritium breeding agent ceramic preparation is well solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of ceramic materials, and particularly relates to a method for preparing highly dense nano-lithium metatitanate ceramics. Background Art

[0002] Nuclear fusion is the most promising new energy in the future. Among them, deuterium-tritium fusion is the easiest to occur, and it is urgent to create a new type of energy for this kind of nuclear fusion reaction. Tritium breeder is a key material in the tritium breeding blanket of a nuclear fusion reactor. Its function is to undergo a nuclear reaction with neutrons to provide the necessary tritium for the fuel cycle. Based on the fact that tritium can be produced by the reaction of tritium breeder with neutrons, tritium breeder has been applied to deuterium-tritium nuclear fusion.

[0003] The design criteria for tritium breeder materials should have a high density (>80% T.D.) to maintain the structural integrity during service. At the same time, increasing the density is also beneficial to increasing the number of lithium atoms per unit volume, thereby contributing to the improvement of tritium release efficiency. Among them, lithium orthosilicate (Li4SiO4) is recognized as the preferred tritium breeder by the China Fusion Engineering Test Reactor (CFETR) due to its high lithium atom density, low neutron activation characteristics, and outstanding low-temperature tritium release rate. However, Li4SiO4 has a strong tendency to absorb water and easily reacts with H2O to form decomposition products such as Li2SiO3 and LiOH, making it difficult to maintain the phase and structural stability in a humid environment, which poses challenges to the storage, transfer, and loading of this material. Therefore, it is urgent to develop new tritium breeder materials.

[0004] Lithium metatitanate (Li2TiO3) ceramics are another candidate material for tritium breeders. However, there are the following problems in the process of preparing Li2TiO3 ceramics: It is a great challenge in the ceramic sintering process to further increase the density while ensuring the nanocrystallization of grain size. Currently, the main method to increase the density of Li2TiO3 ceramics is to increase the sintering temperature, but this method will cause grain growth. There is a contradiction between the two and they cannot be taken into account simultaneously. For example, currently, the density of lithium ceramics can be increased to 96% T.D. by the melting method, but its grain size will grow to hundreds of nanometers; while the grain size of the ceramics obtained from the powder by the hydrothermal method can be controlled within 100 nanometers, but its density only reaches 90% T.D.

[0005] Therefore, how to provide a preparation method for Li2TiO3 ceramics that can take into account the requirements of high density and nanoscale size at the same time, so that it can be better used as a tritium breeder in deuterium-tritium nuclear fusion, has become a technical problem to be solved urgently. Summary of the Invention

[0006] The present invention is to solve the above technical problems, thereby providing a method for preparing high-density nano-lithium metatitanate ceramics. The technical purpose of the present invention is to provide a method for preparing lithium metatitanate ceramics with both high density and nano-scale size using a simple process, while achieving high density of ceramics and nano-scale grain size under low energy consumption conditions.

[0007] In order to achieve the above technical objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing high-density nano-lithium metatitanate ceramics comprises the following steps:

[0009] (1) Deionized water ball milling: LiOH·H2O, H2TiO3 and Zr(OH)4 powders are mixed as raw materials, ZrO2 balls with a diameter of 2 mm are used as ball milling media, and deionized water is used as solvent. Ball milling is performed in a ball milling jar to obtain a ball milling slurry with deionized water as solvent; the obtained ball milling slurry is dried to remove the solvent to obtain a primary ground powder;

[0010] (2) ball milling with anhydrous ethanol: placing the primary ground powder obtained in step (1) in the ball milling tank of step (1) and continuously ball milling with anhydrous ethanol as solvent to obtain a ball milling slurry with anhydrous ethanol as solvent; drying the obtained ball milling slurry to remove the solvent to obtain a final ground powder;

[0011] (3) forming: pressing the final ground powder obtained in step (2) into a green billet;

[0012] (4) Sintering: Sintering the green blank obtained in step (3) to prepare the high-density nano-lithium titanate ceramic.

[0013] The above method provided by the present invention is to obtain the target powder by changing the ball milling solvent for continuous ball milling (first using deionized water as the solvent, and then using anhydrous ethanol as the solvent), and directly obtain lithium titanate ceramics after molding and sintering. The preparation method is simple in process, and multiple sintering is not required during the continuous ball milling process. It only needs to replace the solvent, which greatly saves the sintering process during multiple ball milling processes. At the same time, the density of the obtained lithium titanate ceramic is significantly improved, and its density is as high as 99% TD, and its grain size can be achieved at the nano level (within 100nm), which solves the problem that the existing tritium breeding agent ceramic preparation cannot take into account the nano-level grain size and high density. The existing ceramic preparation process either often reaches hundreds of nanometers under the premise of obtaining a higher density; or when the grain size reaches within one hundred nanometers, the density of the ceramic is not high; in addition, the existing ceramic preparation process often requires multiple sintering of the ceramic powder during multiple ball milling, and the preparation process is relatively complicated, and the processing cost is increased.

[0014] In addition, as shown in the comparative example of the present invention, the solvent replacement and selection during the continuous ball milling process of the present invention are crucial for obtaining lithium metatitanate ceramics with high density. When the solvent is not replaced or other solvent combinations are selected, the density of the obtained lithium metatitanate ceramics decreases significantly.

[0015] Furthermore, the molar ratio of LiOH·H2O, H2TiO3, and Zr(OH)4 in step (1) is 0.55:0.2:0.02.

[0016] Furthermore, the rotation speed of the ball milling in step (1) is 200 r / min, and the ball milling time is 4 - 16 h.

[0017] Furthermore, the amount of ZrO2 ball milling balls used in step (1) accounts for 1 / 3 of the volume of the ball milling tank.

[0018] Furthermore, the amount of deionized water used in step (1) accounts for 1 / 3 of the volume of the ball milling tank.

[0019] Furthermore, the rotation speed of the ball milling in step (2) is 200 r / min, and the ball milling time is 60 h.

[0020] Furthermore, the amount of absolute ethanol used in step (2) accounts for 1 / 3 of the volume of the ball milling tank.

[0021] Furthermore, the drying in steps (1) and (2) is to pour out the ball milling slurry and dry it in an oven at 70°C for 10 h.

[0022] Furthermore, the pressure of the pressing forming in step (3) is 10 - 15 MPa.

[0023] Furthermore, the sintering in step (4) is to sinter in a muffle furnace at 700°C for 2 h in an air atmosphere.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) The existing traditional ceramic preparation methods generally obtain powders through ball milling, either using one solvent for one - time ball milling; or using the same solvent for two - time ball milling, and a powder calcination process at several hundred degrees or several thousand degrees must be carried out between the two ball millings. The method of the present invention uses the method of replacing the solvent for continuous ball milling, no longer requiring the multi - step powder calcination process in the intermediate steps. Using the method of the present invention, lithium metatitanate ceramics with 99% theoretical density and nanocrystalline grain size can be prepared.

[0026] (2) The preparation method of the present invention has the advantages of simple process, low cost, and good ceramic performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 XRD patterns of the corresponding powders and ceramics in steps (2), (4), and (6) of Example 1.

[0028] Figure 2 Grain size distribution map of the ceramic sintered at 700 °C in Example 1.

[0029] Figure 3 Effect of different diameters of ball milling balls on the density of the ceramic in Comparative Example 1. The diameters of the corresponding ball milling balls are: (a) 2 mm, (b) 5 mm, (c) 10 mm, (d) 18 mm.

[0030] Figure 4 Effect of different solvents on the density of the ceramic in Comparative Example 2. The corresponding solvent combinations are: (a) deionized water + absolute ethanol; (b) absolute ethanol + deionized water; (c) absolute ethanol + absolute ethanol; (d) deionized water + deionized water. Detailed implementation manners

[0031] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be specifically described below in conjunction with embodiments. It should be noted that the following embodiments are only used to explain and illustrate the present invention, and are not used to limit the present invention. Some non-essential improvements and adjustments made by those skilled in the art according to the above invention content still fall within the protection scope of the present invention.

[0032] Example 1

[0033] The Li2TiO3 ceramics prepared in the following examples are non-stoichiometric Li2TiO3 ceramics. Therefore, in the composition of the finally obtained 99% dense Li2TiO3 ceramics, in addition to containing α-Li2TiO3, there is also a very small amount of Li2CO3 generated.

[0034] The preparation process of Li2TiO3 ceramics in this example includes: ball milling with deionized water, drying, ball milling with absolute ethanol, drying, forming, and sintering; specifically as follows:

[0035] (1) Ball milling with deionized water: Weigh the required powder raw materials: LiOH·H2O, H2TiO3, Zr(OH)4, weighing 23.31 g, 18.87 g, and 3.28 g respectively. Pour the above raw material powders into a ball milling tank with a volume of 500 ml, add 1 / 3 of the ZrO2 ball milling balls with a diameter of 2 mm, add deionized water to 2 / 3 of the volume, and place it in a planetary ball mill. Ball mill at a speed of 200 r / min for 16 h to obtain a ball milling slurry with deionized water as the medium;

[0036] (2) Drying treatment: Pour the above ball milling slurry into a drying dish and place it in an oven at 70 °C for 10 h. After drying to remove the solvent water completely, the obtained powder, and the XRD pattern of the powder is asFigure 1 as shown

[0037] (3) Ball milling with absolute ethanol: The powder after completely removing water in step (2) is placed in the above ball milling tank again and continuously ball milled with absolute ethanol. The planetary ball mill mills at 200 r / min for 60 h to obtain a ball mill slurry with absolute ethanol as the medium;

[0038] (4) Drying treatment: Similar to step (2), after fully drying to remove the solvent absolute ethanol, it is ground and sieved to obtain the final powder. The XRD pattern of the powder is as Figure 1 shown;

[0039] (5) Forming: Take 0.25 g of the final powder and place it in a bench-top powder press to press it into a cylindrical green body with a diameter of 10 mm and a thickness of 1.1 mm under a pressure of 10 - 15 MPa;

[0040] (6) Sintering: Place the cylindrical green body in a muffle furnace and sinter it at 700 °C in air for 2 h to obtain Li2TiO3 ceramic with a relative density of 99% T.D. Its XRD pattern is shown in Figure 1 . It can be seen that the main phase of the ceramic after sintering at 700 °C is α-Li2TiO3, and there is also a very small amount of Li2CO3. According to the measured SEM, it can be seen that the cross-section of the ceramic is very dense; and according to the SEM image, the grain size after sintering at 700 °C for 2 h is only 89 nm measured by Nano Measurer software.

[0041] Comparative Example 1

[0042] The present invention has studied the influence of ball milling balls with different diameters on the density of ceramics, as Figure 3 shown. Ball milling balls with diameters of 5 mm, 10 mm, and 18 mm are processed through steps (1)-(6) in Example 1. A large number of pores exist inside the obtained ceramics. Only ball milling balls with a diameter of 2 mm can obtain highly dense ceramics.

[0043] Comparative Example 2

[0044] The present invention has adjusted the solvent to explore its influence on the density of ceramics, as Figure 4 shown. Figure 4 In (b) and (d) in, the order of solvents is absolute ethanol + deionized water, deionized water + deionized water respectively. It can be seen that its cross-section is very rough and the pores are very large. Figure 4 In (c) in, the order of the solvent is absolute ethanol + absolute ethanol, and a large number of pores are distributed on its cross-section. Only Figure 4 in the scheme (a) where the order of the solvent is deionized water + absolute ethanol in can highly dense ceramics be obtained.

Claims

1. A preparation method of a highly dense lithium metatitanate nanoceramics, characterized in that, It includes the following steps: (1) Deionized water ball milling: Using a mixture of LiOH·H2O, H2TiO3, and Zr(OH)4 powders as raw materials, ZrO2 ball milling balls with a diameter of 2 mm as the ball milling medium, and deionized water as the solvent, perform ball milling in a ball milling tank to obtain a ball milling slurry with deionized water as the solvent; dry the obtained ball milling slurry to remove the solvent to obtain a preliminarily milled powder; (2) Absolute ethanol ball milling: Place the preliminarily milled powder obtained in step (1) in the ball milling tank of step (1) and perform continuous ball milling with absolute ethanol as the solvent to obtain a ball milling slurry with absolute ethanol as the solvent; dry the obtained ball milling slurry to remove the solvent to obtain a finally milled powder; (3) Shaping: Press the finally milled powder obtained in step (2) into a green body; (4) Sintering: Sinter the green body obtained in step (3) to prepare the high-density nano-lithium metatitanate ceramic.

2. The preparation method according to claim 1, wherein In step (1), the molar ratio of LiOH·H2O, H2TiO3, and Zr(OH)4 is 0.55:0.20:0.

02.

3. The preparation method according to claim 1, characterized in that, In step (1), the rotation speed of the ball milling is 200 r / min, and the ball milling time is 4 - 16 h.

4. The preparation method according to claim 1, characterized in that, In step (1), the dosage of the ZrO2 ball milling balls accounts for 1 / 3 of the volume of the ball milling tank.

5. The preparation method according to claim 1, wherein In step (1), the dosage of the deionized water accounts for 1 / 3 of the volume of the ball milling tank.

6. The preparation method according to claim 1, characterized in that, In step (2), the rotation speed of the ball milling is 200 r / min, and the ball milling time is 60 h.

7. The preparation method according to claim 1, characterized in that, In step (2), the dosage of the absolute ethanol accounts for 1 / 3 of the volume of the ball milling tank.

8. The preparation method according to claim 1, wherein In steps (1) and (2), the drying is to pour out the ball milling slurry and dry it in an oven at 70°C for 10 h.

9. The preparation method according to claim 1, wherein, In step (3), the pressure for pressing and shaping is 10 - 15 MPa.

10. The preparation method according to claim 1, wherein In step (4), the sintering is to sinter in a muffle furnace in an air atmosphere at 700°C for 2 h.

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