High-density lanthanum hexaboride polycrystalline material and preparation method thereof

Abstract

The invention provides a high-density lanthanum hexaboride polycrystalline material and a preparation method thereof, and the preparation method comprises the following steps: (1) carrying out primary die filling on lanthanum hexaboride powder, and then carrying out hot isostatic pressing treatment to obtain a lanthanum hexaboride green body; and (2) carrying out secondary die filling on the lanthanum hexaboride green body obtained in the step (1), and then sequentially carrying out hot pressed sintering and post-treatment to obtain the high-density lanthanum hexaboride polycrystalline material. The lanthanum hexaboride polycrystalline material obtained by adopting the preparation method provided by the invention has relatively high density, and the internal organization structure and the internal grain size are uniform; and the preparation process is simple in flow, low in cost and suitable for industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of hot cathode materials, and particularly relates to a high-density lanthanum hexaboride polycrystalline material and a preparation method thereof. Background Art

[0002] In scientific research and industrial applications, the selection of cathode materials has a decisive impact on the performance of equipment. Lanthanum hexaboride (LaB6) is a lanthanide boride of a high-temperature superconducting material, which can be used as a cathode material. It is favored due to its high melting point (about 2330 °C), good thermal stability and good electrical conductivity under extreme conditions. As a cathode material, it can provide a high current density and good emission stability. Therefore, it is an indispensable material in many high-energy physics experiments and advanced electron beam technology fields.

[0003] CN 106558466A discloses a preparation method of a single-crystal lanthanum hexaboride field emission array cathode. The preparation method includes: Step A: grinding and polishing a single-crystal hexaboride substrate and then cleaning it; Step B: depositing a protective layer on the single-crystal hexaboride substrate obtained by the treatment in Step A, and forming a required pattern on the protective layer through photolithography and etching; Step C: immersing the single-crystal lanthanum hexaboride substrate with a patterned surface protective layer and a graphite rod into an electrolyte, then connecting the single-crystal lanthanum hexaboride substrate to the positive electrode of a power supply and connecting the graphite rod to the negative electrode of the power supply, and etching with an externally applied pulsed current to form a single-crystal lanthanum hexaboride cone array, and removing the remaining protective layer on the single-crystal lanthanum hexaboride cone array to finally obtain a single-crystal lanthanum hexaboride field emission cathode array.

[0004] The preparation method provided by the above patent has a complex process and high cost; moreover, the density of the obtained lanthanum hexaboride material is relatively low, and it is prone to cracking and failure, seriously affecting its service life.

[0005] In summary, it is necessary to provide a preparation method with a simple process flow and capable of obtaining a lanthanum hexaboride polycrystalline material with a relatively high density and small grains. Summary of the Invention

[0006] The purpose of the present invention is to provide a high-density lanthanum hexaboride polycrystalline material and a preparation method thereof. The preparation method has a simple process flow, and the obtained lanthanum hexaboride polycrystalline material has a relatively high density, uniform internal organizational structure and internal grain size, greatly improving the service life of the lanthanum hexaboride polycrystalline material.

[0007] To achieve the purpose of this invention, the following technical solutions are adopted:

[0008] In the first aspect, the present invention provides a preparation method of a high-density lanthanum hexaboride polycrystalline material. The preparation method includes the following steps:

[0009] (1) Load the lanthanum hexaboride powder into the mold once, and then perform hot isostatic pressing treatment to obtain a green body of lanthanum hexaboride;

[0010] (2) Load the green body of lanthanum hexaboride obtained in step (1) into the mold again, and then perform hot press sintering and post-treatment in sequence to obtain the high-density lanthanum hexaboride polycrystalline material.

[0011] The preparation method provided by the present invention has a simple process flow and extremely low preparation cost; first, the tight combination of lanthanum hexaboride powder is realized through hot isostatic pressing treatment, and then the atomic diffusion is continuously increased by using hot press sintering, thereby increasing the product density, and then the grain size of the product is regulated, and the service life of the lanthanum hexaboride polycrystalline material is improved.

[0012] As a preferred technical solution of the present invention, the average particle size of the lanthanum hexaboride powder in step (1) is 10 - 30 μm, for example, it can be 10 μm, 14 μm, 18 μm, 22 μm, 26 μm or 30 μm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0013] Preferably, the purity of the lanthanum hexaboride powder in step (1) is 99 - 99.9%, for example, it can be 99%, 99.2%, 99.4%, 99.6%, 99.8% or 99.9%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0014] As a preferred technical solution of the present invention, the packing density of the first mold loading in step (1) is 45 - 55%, for example, it can be 45%, 47%, 49%, 51%, 53% or 55%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0015] As a preferred technical solution of the present invention, the temperature of the hot isostatic pressing treatment in step (1) is 450 - 750 °C, for example, it can be 450 °C, 500 °C, 550 °C, 600 °C, 650 °C, 700 °C or 750 °C, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0016] Preferably, the pressure of the hot isostatic pressing treatment in step (1) is 100 - 110 MPa, for example, it can be 100 MPa, 102 MPa, 104 MPa, 106 MPa, 108 MPa or 110 MPa, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0017] Preferably, the time of the hot isostatic pressing treatment in step (1) is 40 to 120 min. For example, it can be 40 min, 60 min, 80 min, 100 min, or 120 min, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0018] In the present invention, the purpose of the hot isostatic pressing treatment is as follows: Through hot isostatic pressing (pre-sintering), the lanthanum hexaboride powder is initially formed after being loaded into the mold once; if the temperature of the hot isostatic pressing treatment is too high, it will cause the density of the subsequent hot-pressed material not to be improved, and if the temperature is too low, it will cause phenomena such as cracking and slagging of the material during processing under high pressure, making it impossible to process; when the pressure of the hot isostatic pressing treatment is too high, it will cause the material to crack and severely deform, and if the pressure is too low, the density cannot be well improved, and the obtained material has a low density.

[0019] As a preferred technical solution of the present invention, the packing density of the secondary mold loading in step (2) is 70 to 85%. For example, it can be 70%, 73%, 76%, 79%, 82%, or 85%, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0020] As a preferred technical solution of the present invention, the temperature of the hot pressing sintering in step (2) is 1600 to 2000 °C. For example, it can be 1600 °C, 1700 °C, 1800 °C, 1900 °C, or 2000 °C, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0021] Preferably, the pressure of the hot pressing sintering in step (2) is 25 to 35 MPa. For example, it can be 25 MPa, 27 MPa, 29 MPa, 31 MPa, 33 MPa, or 35 MPa, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0022] Preferably, the time of the hot pressing sintering in step (2) is 120 to 240 min. For example, it can be 120 min, 150 min, 180 min, 210 min, or 240 min, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0023] In the present invention, the purpose of the hot pressing sintering is as follows: Through high-temperature treatment, the density of the material is well improved, and grain growth begins to form polycrystalline material; if the temperature of the hot pressing sintering is too high, it will cause abnormal grain growth and a significant reduction in the strength of the material, and if the temperature is too low, the density of the material cannot be well improved; when the pressure of the hot pressing sintering is too high, it will cause the material to crack, and if the pressure is too low, the material requires a very high reaction driving force and cannot form polycrystalline material.

[0024] As a preferred technical solution of the present invention, the post-treatment in step (2) includes grinding and polishing treatments carried out in sequence.

[0025] As a preferred technical solution of the present invention, the method for preparing a high-density lanthanum hexaboride polycrystalline material provided in the first aspect of the present invention includes the following steps:

[0026] (1) Loading lanthanum hexaboride powder with an average particle size of 10 - 30 μm and a purity of 99 - 99.9% into a mold at one time, and then performing hot isostatic pressing treatment to obtain a lanthanum hexaboride green body;

[0027] Among them, the filling density of the one-time mold loading is 45 - 55%;

[0028] The temperature of the hot isostatic pressing treatment is 450 - 750 °C, the pressure is 100 - 110 MPa, and the time is 40 - 120 min;

[0029] (2) Loading the lanthanum hexaboride green body obtained in step (1) into a mold for the second time, and then performing hot press sintering, grinding and polishing treatments in sequence to obtain the high-density lanthanum hexaboride polycrystalline material;

[0030] Among them, the filling density of the second mold loading is 70 - 85%;

[0031] The temperature of the hot press sintering is 1600 - 2000 °C, the pressure is 25 - 35 MPa, and the time is 120 - 240 min.

[0032] In the second aspect, the present invention provides a high-density lanthanum hexaboride polycrystalline material, and the high-density lanthanum hexaboride polycrystalline material is obtained by using the preparation method provided in the second aspect.

[0033] As a preferred technical solution of the present invention, the density of the high-density lanthanum hexaboride polycrystalline material is ≥ 90%, for example, it can be 90%, 91%, 92%, 93%, 94% or 95%, etc., but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0034] The numerical range described in the present invention not only includes the above-listed point values, but also includes any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The preparation method of the high-density lanthanum hexaboride polycrystalline material provided by the present invention has a simple process flow, low cost, and is applicable to industrial production;

[0037] (2) The lanthanum hexaboride polycrystalline material obtained by using the preparation method provided by the present invention has a high relative density, and the internal organizational structure and internal grain size are uniform. Detailed implementation manners

[0038] The technical solution of the present invention will be further described below through specific implementation manners. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0039] Example 1

[0040] This example provides a lanthanum hexaboride polycrystalline material with high relative density. The preparation method of the lanthanum hexaboride polycrystalline material with high relative density includes the following steps:

[0041] (1) Loading the lanthanum hexaboride powder with an average particle size of 20 μm and a purity of 99.5% into a mold for the first time, and then performing hot isostatic pressing treatment to obtain a lanthanum hexaboride green body;

[0042] Among them, the packing density of the first loading is 50%;

[0043] The temperature of the hot isostatic pressing treatment is 750 °C, the pressure is 105 MPa, and the time is 80 min;

[0044] (2) Loading the lanthanum hexaboride green body obtained in step (1) into a mold for the second time, and then successively performing hot press sintering, grinding and polishing treatments to obtain the lanthanum hexaboride polycrystalline material with high relative density;

[0045] Among them, the packing density of the second loading is 78.5%;

[0046] The temperature of the hot press sintering is 1800 °C, the pressure is 30 MPa, and the time is 180 min.

[0047] Example 2

[0048] This example provides a lanthanum hexaboride polycrystalline material with high relative density. The preparation method of the lanthanum hexaboride polycrystalline material with high relative density includes the following steps:

[0049] (1) Loading the lanthanum hexaboride powder with an average particle size of 10 μm and a purity of 99.9% into a mold for the first time, and then performing hot isostatic pressing treatment to obtain a lanthanum hexaboride green body;

[0050] Among them, the packing density of the first loading is 45%;

[0051] The temperature of the hot isostatic pressing treatment is 450 °C, the pressure is 110 MPa, and the time is 120 min;

[0052] (2) Subject the lanthanum hexaboride green body obtained in step (1) to secondary die filling, and then successively perform hot press sintering, grinding, and polishing treatments to obtain the high-density lanthanum hexaboride polycrystalline material;

[0053] Among them, the filling density of the secondary die filling is 70%;

[0054] The temperature of the hot press sintering is 1600 °C, the pressure is 35 MPa, and the time is 240 min.

[0055] Example 3

[0056] This example provides a high-density lanthanum hexaboride polycrystalline material. The preparation method of the high-density lanthanum hexaboride polycrystalline material includes the following steps:

[0057] (1) Subject lanthanum hexaboride powder with an average particle size of 30 μm and a purity of 99% to primary die filling, and then perform hot isostatic pressing treatment to obtain a lanthanum hexaboride green body;

[0058] Among them, the filling density of the primary die filling is 55%;

[0059] The temperature of the hot isostatic pressing treatment is 550 °C, the pressure is 100 MPa, and the time is 40 min;

[0060] (2) Subject the lanthanum hexaboride green body obtained in step (1) to secondary die filling, and then successively perform hot press sintering, grinding, and polishing treatments to obtain the high-density lanthanum hexaboride polycrystalline material;

[0061] Among them, the filling density of the secondary die filling is 85%;

[0062] The temperature of the hot press sintering is 2000 °C, the pressure is 25 MPa, and the time is 120 min.

[0063] Example 4

[0064] This example provides a high-density lanthanum hexaboride polycrystalline material. The preparation method of the high-density lanthanum hexaboride polycrystalline material includes the following steps:

[0065] (1) Subject lanthanum hexaboride powder with an average particle size of 25 μm and a purity of 99.6% to primary die filling, and then perform hot isostatic pressing treatment to obtain a lanthanum hexaboride green body;

[0066] Among them, the filling density of the primary die filling is 52%;

[0067] The temperature of the hot isostatic pressing treatment is 600 °C, the pressure is 105 MPa, and the time is 100 min;

[0068] (2) The lanthanum hexaboride green compact obtained in step (1) is remolded, and then hot press sintering, grinding and polishing treatments are carried out in sequence to obtain the high-density lanthanum hexaboride polycrystalline material;

[0069] Among them, the packing density of the remolding is 74%;

[0070] The temperature of the hot press sintering is 1700 °C, the pressure is 30 MPa, and the time is 150 min.

[0071] Example 5

[0072] This example provides a high-density lanthanum hexaboride polycrystalline material. The difference between the preparation method of the high-density lanthanum hexaboride polycrystalline material and that of Example 1 is only that:

[0073] In this example, the temperature of the hot isostatic pressing treatment in step (1) is adjusted to 400 °C.

[0074] Example 6

[0075] This example provides a high-density lanthanum hexaboride polycrystalline material. The difference between the preparation method of the high-density lanthanum hexaboride polycrystalline material and that of Example 1 is only that:

[0076] In this example, the temperature of the hot isostatic pressing treatment in step (1) is adjusted to 900 °C.

[0077] Example 7

[0078] This example provides a high-density lanthanum hexaboride polycrystalline material. The difference between the preparation method of the high-density lanthanum hexaboride polycrystalline material and that of Example 1 is only that:

[0079] In this example, the pressure of the hot isostatic pressing treatment in step (1) is adjusted to 90 MPa.

[0080] Example 8

[0081] This example provides a high-density lanthanum hexaboride polycrystalline material. The difference between the preparation method of the high-density lanthanum hexaboride polycrystalline material and that of Example 1 is only that:

[0082] In this example, the pressure of the hot isostatic pressing treatment in step (1) is adjusted to 120 MPa.

[0083] Example 9

[0084] This example provides a high-density lanthanum hexaboride polycrystalline material. The difference between the preparation method of the high-density lanthanum hexaboride polycrystalline material and that of Example 1 is only that:

[0085] In this example, the temperature of the hot press sintering in step (2) is adjusted to 1500 °C.

[0086] Example 10

[0087] This example provides a high-density lanthanum hexaboride polycrystalline material. The difference between the preparation method of this high-density lanthanum hexaboride polycrystalline material and that of Example 1 is only that:

[0088] In this example, the temperature of the hot pressing sintering described in step (2) is adjusted to 2200 °C.

[0089] Example 11

[0090] This example provides a high-density lanthanum hexaboride polycrystalline material. The difference between the preparation method of this high-density lanthanum hexaboride polycrystalline material and that of Example 1 is only that:

[0091] In this example, the pressure of the hot pressing sintering described in step (2) is adjusted to 20 MPa.

[0092] Example 12

[0093] This example provides a high-density lanthanum hexaboride polycrystalline material. The difference between the preparation method of this high-density lanthanum hexaboride polycrystalline material and that of Example 1 is only that:

[0094] In this example, the pressure of the hot pressing sintering described in step (2) is adjusted to 40 MPa.

[0095] Example 13

[0096] This example provides a high-density lanthanum hexaboride polycrystalline material. The difference between the preparation method of this high-density lanthanum hexaboride polycrystalline material and that of Example 1 is only that:

[0097] In this example, the average particle size of the lanthanum hexaboride powder described in step (1) is adjusted to 5 μm.

[0098] Example 14

[0099] This example provides a high-density lanthanum hexaboride polycrystalline material. The difference between the preparation method of this high-density lanthanum hexaboride polycrystalline material and that of Example 1 is only that:

[0100] In this example, the average particle size of the lanthanum hexaboride powder described in step (1) is adjusted to 40 μm.

[0101] Comparative Example 1

[0102] This comparative example provides a high-density lanthanum hexaboride polycrystalline material. The difference between the preparation method of this high-density lanthanum hexaboride polycrystalline material and that of Example 1 is only that:

[0103] In this comparative example, the hot isostatic pressing treatment described in step (1) is adjusted to cold isostatic pressing treatment; the temperature of the cold isostatic pressing treatment is 25 °C and the pressure is 105 MPa.

[0104] The high-density lanthanum hexaboride polycrystalline materials provided in the above-mentioned examples and comparative examples were subjected to density detection, and the results are shown in Table 1.

[0105] Table 1

[0106] Density Example 1 97％ Example 2 95％ Example 3 96％ Example 4 95％ Example 5 92％ Example 6 91％ Example 7 89％ Example 8 90％ Example 9 89％ Example 10 91％ Example 11 90％ Example 12 92％ Example 13 91％ Example 14 90％ Comparative Example 1 87％

[0107] It can be seen from Table 1 that:

[0108] (1) Through comprehensive analysis of Examples 1-4, it can be seen that the lanthanum hexaboride polycrystalline materials obtained by using the preparation method provided by the present invention have a relatively high density and good control effect on crystal grains;

[0109] (2) Through comprehensive analysis of Example 1 and Examples 5-8, it can be seen that both the temperature and pressure of the hot isostatic pressing treatment described in step (1) will affect the density of the obtained lanthanum hexaboride polycrystalline materials;

[0110] When the temperature is on the high side, it will cause the crystal grains of the material to be coarse, which will hinder the improvement of density during subsequent hot pressing sintering. At the same time, a high temperature will affect the service life of the equipment and cause unnecessary waste; when the temperature is on the low side, it will lead to a low degree of densification of the material, and it will be difficult for atoms to diffuse during subsequent sintering, thus affecting the performance improvement of the material;

[0111] When the pressure is on the high side, it will cause the material to crack and severely deform; when the pressure is on the low side, it will lead to the density not being well improved, and the obtained material has a low density;

[0112] (3) Through comprehensive analysis of Example 1 and Examples 9-12, it can be seen that both the temperature and pressure of the hot pressing sintering described in step (1) will affect the density of the obtained lanthanum hexaboride polycrystalline materials;

[0113] When the temperature is on the high side, it will cause the phenomenon of overburning and abnormal crystal grain growth of the product, greatly reducing the various performances of the material; when the temperature is on the low side, it will lead to the occurrence of material cracking and low density;

[0114] When the pressure is on the high side, it will cause the occurrence of material cracking and equipment die cracking; when the pressure is on the low side, it will lead to the occurrence of too long sintering time and low density;

[0115] (4) Through comprehensive analysis of Example 1 and Examples 13-14, it can be seen that the average particle size of the lanthanum hexaboride powder described in the preparation process will affect the density of the obtained products;

[0116] When the average particle size of the lanthanum hexaboride powder is too small, it will lead to difficult die loading, and fine powders are prone to "bridging" and adhesion, hindering the mutual movement of particles, resulting in a decrease in the loose packing density and poor fluidity, and making agglomeration more likely to occur; when the average particle size of the lanthanum hexaboride powder is too large, it will be more difficult to improve the density, and many small pores are likely to be generated, causing cracking of the material.

[0117] (5) Through comprehensive analysis of Example 1 and Comparative Example 1, it can be seen that compared with hot isostatic pressing treatment, cold isostatic pressing treatment will lead to insufficient bonding degree of the material, resulting in edge and corner chipping, and it is impossible to provide a billet with better quality for subsequent hot pressing.

[0118] In summary, the lanthanum hexaboride polycrystalline material obtained by using the preparation method provided by the present invention has a high density, uniform internal organizational structure and internal grain size; and the preparation process flow is simple, the cost is low, and it is applicable to industrial production.

[0119] The applicant declares that the specific embodiments described above further elaborate on the purpose, technical solution and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a high-density lanthanum hexaboride polycrystalline material, characterized in that, The preparation method comprises the following steps: (1) Loading lanthanum hexaboride powder into a mold for the first time, and then performing hot isostatic pressing treatment to obtain a green body of lanthanum hexaboride; (2) Loading the green body of lanthanum hexaboride obtained in step (1) into a mold for the second time, and then performing hot pressing sintering and post-treatment in sequence to obtain the high-density lanthanum hexaboride polycrystalline material.

2. The preparation method according to claim 1, characterized in that, The average particle size of the lanthanum hexaboride powder in step (1) is 10 - 30 μm; Preferably, the purity of the lanthanum hexaboride powder in step (1) is 99 - 99.9%.

3. The preparation method according to claim 1 or 2, characterized in that, The filling density of the first mold loading in step (1) is 45 - 55%.

4. The preparation method according to any one of claims 1-3, characterized in that, The temperature of the hot isostatic pressing treatment in step (1) is 450 - 750 °C; Preferably, the pressure of the hot isostatic pressing treatment in step (1) is 100 - 110 MPa; Preferably, the time of the hot isostatic pressing treatment in step (1) is 40 - 120 min.

5. The preparation method according to any one of claims 1-4, characterized in that, The filling density of the second mold loading in step (2) is 70 - 85%.

6. The preparation method according to any one of claims 1-5, characterized in that, The temperature of the hot pressing sintering in step (2) is 1600 - 2000 °C; Preferably, the pressure of the hot pressing sintering in step (2) is 25 - 35 MPa; Preferably, the time of the hot pressing sintering in step (2) is 120 - 240 min.

7. The preparation method according to any one of claims 1-6, characterized in that, The post-treatment in step (2) includes grinding and polishing treatments performed in sequence.

8. The preparation method according to any one of claims 1-7, characterized in that, The preparation method comprises the following steps: (1) Loading lanthanum hexaboride powder with an average particle size of 10 - 30 μm and a purity of 99 - 99.9% into a mold for the first time, and then performing hot isostatic pressing treatment to obtain a green body of lanthanum hexaboride; Wherein, the filling density of the first mold loading is 45 - 55%; The temperature of the hot isostatic pressing treatment is 450 - 750 °C, the pressure is 100 - 110 MPa, and the time is 40 - 120 min; (2) Loading the green body of lanthanum hexaboride obtained in step (1) into a mold for the second time, and then performing hot pressing sintering, grinding and polishing treatments in sequence to obtain the high-density lanthanum hexaboride polycrystalline material; Wherein, the filling density of the second mold loading is 70 - 85%; The temperature of the hot pressing sintering is 1600 - 2000 °C, the pressure is 25 - 35 MPa, and the time is 120 - 240 min.

9. A lanthanum hexaboride polycrystalline material with high density, characterized in that, The high-density lanthanum hexaboride polycrystalline material is obtained by using the preparation method according to any one of claims 1 - 8.

10. The high-density lanthanum hexaboride polycrystalline material according to claim 9, wherein, The density of the high-density lanthanum hexaboride polycrystalline material is ≥ 90%.