High-performance boron nitride nanoceramics and methods of making

Abstract

The application discloses high-performance boron nitride nanoceramics and a preparation method thereof, and relates to the technical field of ceramics. The preparation method comprises the following steps: S1, mixing trimethyl borate, urea and ethanol according to a molar ratio of 1:(1.2-1.5):(5-8) to obtain a mixed solution, adding nano carbon powder, stirring and reacting to obtain a transparent boron nitride precursor sol; S2, freeze-drying the boron nitride precursor sol to obtain fluffy boron nitride precursor powder; S3, heating the boron nitride precursor powder to 800-1000 DEG C under an ammonia atmosphere, and keeping the temperature for 2-3 h to obtain boron nitride nano powder; and S4, carrying out spark plasma sintering on the boron nitride nano powder to obtain high-performance boron nitride nanoceramics. Through synergistic effect of multiple steps and precise control of process parameters, the boron nitride ceramic with a grain size of 20-50 nm, high density and high thermal conductivity and excellent comprehensive performance is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ceramics, in particular to a high-performance boron nitride nanoceramic and a preparation method thereof. BACKGROUND

[0002] Boron nitride (BN) ceramics have excellent thermal conductivity, electrical insulation, high-temperature resistance and chemical stability, and are key materials in the fields of high-power electronic device heat dissipation and high-temperature insulation structure. Among them, nano-structured boron nitride ceramics can significantly improve mechanical properties while maintaining high thermal conductivity due to the enhanced interface scattering caused by grain refinement, and have become a research hotspot in recent years. The traditional preparation methods of boron nitride ceramics mainly include hot-pressing sintering, pressureless sintering and chemical vapor deposition (CVD).

[0003] The existing technology has the following defects in the preparation of boron nitride ceramics:

[0004] 1. Coarse grains: Hot-pressing sintering needs to be carried out at high temperature (1800-2000℃) and high pressure (20-50MPa), and the powder is easy to agglomerate, which leads to uneven nitriding. The powder agglomeration leads to difficulty in removing pores during sintering, resulting in low density of the ceramic, and high-temperature long-time sintering easily leads to grain coarsening (usually >100nm), affecting the performance of the material.

[0005] 2. Low density: Due to the difficulty in removing pores during sintering caused by powder agglomeration, and the addition of a large amount of sintering aids in pressureless sintering, impurities are introduced to form defects, etc., resulting in low density of the ceramic (usually <95%).

[0006] 3. Insufficient thermal conductivity: Due to pore scattering (thermal flow obstruction), impurity scattering (such as B2O3, free carbon), and grain boundary defects caused by coarse grains, the thermal conductivity is insufficient (usually 200-300W / (m・K).

[0007] Therefore, it is of great technical value and application prospect to develop a boron nitride ceramic preparation method that can realize nanoscale grain control, high density and high performance. SUMMARY

[0008] The present application is to solve the technical problems of coarse grains, low density and insufficient thermal conductivity of existing boron nitride ceramics, and aims to provide a high-performance boron nitride nanoceramic and a preparation method thereof. By using specific precursor raw materials such as trimethyl borate, urea and ethanol as the basis for uniform nitriding, and adding nano-carbon powder to avoid abnormal grain growth and ensure ceramic densification, combined with freeze-drying to improve dispersibility and low-temperature nitriding treatment, a boron nitride ceramic with grain size of 20-50nm, high density and thermal conductivity, and excellent comprehensive performance is obtained under the synergistic effect of multiple steps and precise control of process parameters.

[0009] The application is achieved by the following technical solutions.

[0010] The first aspect of the application is to provide a preparation method of high-performance boron nitride nanoceramics, comprising the following steps:

[0011] S1, trimethyl borate, urea and ethanol are mixed according to a molar ratio of 1: (1.2-1.5): (5-8) to obtain a mixed solution, and then nano-carbon powder is added and stirred to obtain a transparent boron nitride precursor sol;

[0012] S2, the boron nitride precursor sol is freeze-dried to obtain fluffy boron nitride precursor powder;

[0013] S3, the boron nitride precursor powder is heated to 800-1000℃ under an ammonia atmosphere, and kept for 2-3h to obtain boron nitride nano-powder;

[0014] S4, the boron nitride nano-powder is subjected to spark plasma sintering (SPS) to obtain high-performance boron nitride nanoceramics.

[0015] In the application, trimethyl borate is used as a high-activity boron source, and the B-O-C bond in the molecular structure of trimethyl borate is easy to undergo controllable hydrolysis to generate B(OH)3 in an ethanol solvent. + The amino group of urea contains lone pair electrons, which can form a B←N coordination bond with B3

[0016] In addition, nano-carbon powder is added to the boron nitride precursor, which can be adsorbed on the surface of BN grains and hinder atomic diffusion and combination between grains during the nitriding stage.

[0017] In addition, the freeze-drying process can obtain boron nitride nano-powder with good dispersity, compared with traditional hot air drying, spray drying, etc., can avoid powder agglomeration, control the powder particle size through pre-freezing temperature, sublimate without solvent flow, so that the boron source and nano-carbon powder do not migrate, can keep uniform distribution in the powder, and improve the uniformity of subsequent nitriding reaction.

[0018] In addition, the low-temperature nitriding treatment can avoid excessive carbonization of nano-carbon powder to form graphite phase to cause thermal conductivity loss while ensuring complete nitriding, and the low-temperature nitriding treatment and nano-carbon powder inhibit abnormal grain growth and freeze-drying dispersion play a synergistic role, so that the boron nitride nano-powder particle size is controlled in 20-50nm, which has high activity (beneficial to SPS rapid densification) and low interface scattering.

[0019] In summary, the application uses specific precursor raw materials such as trimethyl borate, urea and ethanol to lay the foundation for uniform nitriding, adds nano-carbon powder to avoid abnormal grain growth and ensure ceramic densification, combines freeze-drying to improve dispersity and low-temperature nitriding treatment, and finally controls the grain size of boron nitride nano-ceramic to 20-50nm, the density is ≥99%, the room temperature thermal conductivity is 300-400W / (m·K), the bending strength is ≥300MPa, the dielectric constant is ≤4.0(1MHz), the comprehensive performance is excellent, the sintering time is short, the energy consumption is low, the process is efficient, and the controllability is strong. The boron nitride ceramic prepared by the application can be used in 5G base station radio frequency module heat dissipation, new energy automobile power device substrate, aerospace high temperature insulation structural parts and other high-end fields.

[0020] Further, the nano-carbon powder addition amount is 0.5-2% of the mass of the mixed solution. A large number of experiments have proved that when the nano-carbon powder addition amount is less than 0.5%, the grain inhibition and conductivity effect are insufficient, and when the nano-carbon powder addition amount is more than 2%, the residual carbon will reduce the ceramic insulation (dielectric constant>4.0), which violates the application requirements of "high temperature insulation structural parts".

[0021] Further, the nano-carbon powder is single-walled carbon nanotubes or graphene quantum dots, with a purity of 99.9% or above and a particle size of 5-20 nm. The nano-carbon powder is prepared by a gas phase method, which is the only mature technology for preparing high-purity nano-carbon materials. Compared with traditional solid phase methods (such as mechanical grinding and laser stripping), the gas phase method has the advantages of extremely low impurity content and high structural integrity. Compared with multi-walled carbon nanotubes or carbon black, single-walled carbon nanotubes have better dispersibility and are more suitable for transparent sol systems and can be directionally adsorbed and inhibited to precisely control the grain size. As a zero-dimensional carbon material, graphene quantum dots (with a particle size of 5-20 nm) have the advantages of zero-dimensional dispersion, avoiding short circuits of the conductive network caused by carbon powder agglomeration, and interface modification, thereby improving the compatibility of BN powder with the SPS mold.

[0022] Further, the reaction temperature in step S1 is 60-80℃.

[0023] Further, the freeze-drying specifically includes: pre-freezing the boron nitride precursor sol at -40 to -60℃ for 2-3h, and then freeze-drying at a vacuum degree of ≤10Pa and a temperature of -40 to -50℃ for 12-24h.

[0024] Further, the flow rate of the ammonia gas is 200-500mL / min, and the gas purity is ≥99.99%.

[0025] Further, the boron nitride nano-powder has a particle size of 20-50nm.

[0026] Further, the spark plasma sintering method is as follows: the boron nitride nano-powder is loaded into a graphite mold, and a spark plasma sintering furnace is used to heat the boron nitride nano-powder to 1600-1800℃ under a vacuum degree of ≤5Pa and an axial pressure of 50-80MPa, and then the temperature is maintained for 5-15min before the furnace is cooled to room temperature. The inner wall of the graphite mold is coated with a boron nitride coating with a thickness of 5-10μm, and the coating is prepared by a magnetron sputtering method. The 5-10μm BN coating is the core component that simultaneously performs the functions of "anti-adhesion, diffusion resistance, and uniform heat pressing". Without the coating, even if the SPS parameters (temperature, pressure, and time) fully meet the requirements, the ceramic performance will not meet the standards (such as a density of <95%, a thermal conductivity of <300W / (m·K), and insulation failure) due to "adhesion damage, carbon contamination, and uneven sintering". The thickness limitation of 5-10μm ensures the optimal balance between "protection effectiveness" and "process economy", which is one of the keys to realizing the "high-performance boron nitride nano-ceramic" of the present application.

[0027] Further, during the sintering process, the pulse current parameters are as follows: pulse width 10-20ms, pulse interval 5-10ms, and current density 50-100A / mm 2 .

[0028] The second aspect of the present application is to provide a high-performance boron nitride nanoceramics prepared by the above method.

[0029] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0030] The present application lays the foundation for uniform nitriding by using specific precursor raw materials trimethyl borate, urea and ethanol, adds nano carbon powder to avoid abnormal grain growth, ensures ceramic densification, improves dispersibility by freeze-drying, and performs low-temperature nitriding treatment, finally controls the grain size of boron nitride nanoceramics to 20-50 nm, the density is ≥99%, the room temperature thermal conductivity is 300-400 W / (m·K), the bending strength is ≥300 MPa, the dielectric constant is ≤4.0 (1 MHz), the comprehensive performance is excellent, the sintering time is short, the energy consumption is low, the process is efficient, the controllability is strong, and the boron nitride ceramic prepared by the present application can be used in 5G base station radio frequency module heat dissipation, new energy automobile power device substrate, aerospace high-temperature insulation structural parts and other high-end fields. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the example embodiments of the present application, the following will briefly introduce the drawings needed to be used in the examples. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor. In the drawings:

[0032] Figure 1 SEM image of the fluffy precursor powder after freeze-drying for Example 3;

[0033] Figure 2 SEM image of boron nitride nanometer powder after nitriding for Example 3;

[0034] Figure 3 SEM image of boron nitride nanoceramics prepared for Example 3. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the present application more clear, the following will clearly and completely describe the technical solutions in the example embodiments of the present application with reference to the examples and drawings. Obviously, the illustrative embodiments of the present application and the description thereof are only used to explain the present application, and should not be regarded as a limitation on the present application.

[0036] The embodiments of the high-performance boron nitride nanoceramics and the preparation method of the present application will be described in detail below with appropriate reference to the accompanying drawings. However, unnecessary detailed description will be omitted. For example, detailed description of matters known well and repeated description will be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art.

[0037] The ranges disclosed herein are made on a basis of the lower limit and the upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of the particular range. The ranges defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range.

[0038] If not particularly stated, all the embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0039] If not particularly stated, all the technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0040] If not particularly stated, the "comprising" and "including" mentioned in the present application means open or closed. For example, the "comprising" and "including" can mean that other substances not listed can also be included or contained, or only the listed substances can be included or contained.

[0041] If not particularly stated, all the steps of the present application can be performed in sequence or randomly, and preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, the method can further comprise step (c), which means that step (c) can be added to the method in any order. For example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0042] The technical solutions of the present application will be further described in detail below in combination with the embodiments.

[0043] It should be noted that the experimental methods used in the embodiments are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained by commercial channels by those skilled in the art.

[0044] Example 1

[0045] A method for preparing high-performance boron nitride nanoceramics, comprising the following steps:

[0046] (1) Precursor preparation: weigh trimethyl borate, urea and ethanol according to a molar ratio of 1:1.2:5, mix them, and then add single-walled carbon nanotubes (particle size 5 nm, purity 99.9%) accounting for 0.5% of the mass of the mixed solution; place the mixed system in a 60°C constant-temperature water bath, and stir at a speed of 300 r / min for 4 h; during the process, it is observed that the system gradually clarifies, and finally a transparent boron nitride precursor sol is obtained (transmittance > 85% at a wavelength of 600 nm).

[0047] (2) Freeze-drying: transfer the above-mentioned precursor sol into a polytetrafluoroethylene freeze-drying mold, and place it into a freeze-drying machine; first, pre-freeze at -40°C for 3 h (to ensure that the sol is completely frozen into a solid state); then, reduce the vacuum degree of the freeze-drying machine to 10 Pa, and maintain the temperature at -50°C for continuous drying for 24 h; after the freeze-drying is completed, take out the fluffy boron nitride precursor powder (bulk density 0.12 g / cm 3 ).

[0048] (3) Nitriding treatment: put the precursor powder into a corundum boat, and place it in a tube furnace; introduce ammonia gas with a purity of 99.99%, control the ammonia gas flow to be 200 mL / min (precisely adjusted through a gas flow meter), and heat it to 800°C at a rate of 5°C / min, and maintain the temperature for 3 h; after the heat preservation is completed, cool the furnace to room temperature, and collect the boron nitride nano-powder (the average particle size is 20 nm, and the purity is 99.92% through a laser particle size instrument).

[0049] (4) Spark plasma sintering: put the boron nitride nano-powder into a graphite mold (inner diameter 20 mm) coated with a 5 μm boron nitride coating (prepared by a magnetron sputtering method) on the inner wall; place the mold into a spark plasma sintering furnace, and vacuumize it to 5 Pa; apply an axial pressure of 50 MPa; set the pulse current parameters: pulse width 10 ms, pulse interval 10 ms, and current density 50 A / mm 2 ; heat it to 1600°C at a rate of 100°C / min, and maintain the temperature for 15 min; after the heat preservation is completed, turn off the power, cool the furnace to room temperature, and demold to obtain the boron nitride nanoceramic sample.

[0050] Example 2

[0051] A method for preparing high-performance boron nitride nanoceramics, comprising the following steps:

[0052] (1) Preparation of precursor: trimethyl borate, urea and ethanol were weighed according to the molar ratio of 1:1.5:8, and then graphene quantum dots (particle size 20 nm, purity 99.9%) accounting for 2% of the mass of the mixed solution were added. The mixture was stirred at 400 r / min in a 80℃ constant temperature water bath for 2h to obtain a transparent precursor sol (transmittance > 82%).

[0053] (2) Freeze-drying: the sol was placed in a freeze-drying mold, pre-frozen at -60℃ for 2h, and then freeze-dried at a vacuum degree of 5Pa and a temperature of -40℃ for 12h to obtain fluffy precursor powder (bulk density 0.10g / cm 3 ).

[0054] (3) Nitriding treatment: 500mL / min of ammonia gas with a purity of 99.99% was introduced into a tube furnace, which was heated to 1000℃ at a rate of 10℃ / min and kept for 2h to obtain boron nitride nano-powder with an average particle size of 40nm (purity 99.95%).

[0055] (4) Spark plasma sintering: a graphite mold coated with a 10μm boron nitride coating on the inner wall was used, and a vacuum degree of 3Pa and an axial pressure of 80MPa were applied. The pulse current parameters were width 20ms, interval 5ms, and current density 100A / mm 2 . The temperature was raised to 1800℃ at a rate of 200℃ / min, and the sample was kept for 5min. After cooling and demolding, boron nitride nano-ceramic samples were obtained.

[0056] Example 3

[0057] A method for preparing high-performance boron nitride nano-ceramics, comprising the following steps:

[0058] (1) Preparation of precursor: trimethyl borate, urea and ethanol were weighed according to the molar ratio of 1:1.3:6, and then single-walled carbon nanotubes (particle size 10nm, purity 99.9%) accounting for 1% of the mass of the mixed solution were added. The mixture was stirred at 350r / min in a 70℃ constant temperature water bath for 3h to obtain a transparent precursor sol (transmittance > 84%).

[0059] (2) Freeze-drying: pre-frozen at -50℃ for 2.5h, freeze-dried at a vacuum degree of 8Pa and a temperature of -45℃ for 18h to obtain fluffy precursor powder (bulk density 0.11g / cm 3 ), as shown in Figure 1 .

[0060] (3) Nitriding treatment: ammonia flow 300 mL / min (purity 99.99%), heated to 900°C at a rate of 8°C / min, and kept for 2.5 h to obtain boron nitride nano-powder with an average particle size of 25 nm (purity 99.93%), as shown in FIG. 3. Figure 2

[0061] (4) Spark plasma sintering: the inner wall of the graphite mold was coated with a boron nitride coating of 8 μm, the vacuum degree was 4 Pa, an axial pressure of 60 MPa was applied, the pulse current parameters were width 15 ms, interval 8 ms, and current density 80 A / mm 2 , heated to 1700°C at a rate of 150°C / min, kept for 10 min, and cooled and demolded to obtain a boron nitride nano-ceramic sample, as shown in FIG. 4. Figure 3

[0062] Comparative Example 1

[0063] The difference between this comparative example and Example 3 is that, during preparation of the precursor, the molar ratio of trimethyl borate, urea, and ethanol was adjusted to 1:1:4, and the other conditions remained unchanged.

[0064] Comparative Example 2

[0065] The difference between this comparative example and Example 3 is that, during preparation of the precursor, the molar ratio of trimethyl borate, urea, and ethanol was adjusted to 1:1.3:10, and the other conditions remained unchanged.

[0066] Comparative Example 3

[0067] The difference between this comparative example and Example 3 is that, during preparation of the precursor, the amount of added nano-carbon powder was adjusted to 0.3% of the mass of the mixed solution, and the other conditions remained unchanged.

[0068] Comparative Example 4

[0069] The difference between this comparative example and Example 3 is that, during preparation of the precursor, the amount of added nano-carbon powder was adjusted to 2.5% of the mass of the mixed solution, and the other conditions remained unchanged.

[0070] Comparative Example 5

[0071] The difference between this comparative example and Example 3 is that, during drying, hot air drying was used, the precursor sol was placed in a 80°C air drying oven, and dried at normal pressure for 6 h (traditional hot air drying), to obtain a block-shaped precursor (which needs to be crushed before nitriding).

[0072] Comparative Example 6

[0073] The difference between this comparative example and Example 3 is that, during nitriding treatment, the temperature was raised to 1600°C (at a rate of 8°C / min), and kept for 2.5 h.

[0074] ​​The boron nitride nanoceramics samples prepared in the above examples and comparative examples were subjected to performance detection. The density was measured by Archimedes drainage method, the average grain size was obtained by field emission scanning electron microscopy (FE-SEM) observation, the thermal conductivity at room temperature was measured by laser flash method, the bending strength was measured by three-point bending method, and the dielectric constant was measured by impedance analyzer (1 MHz). The results are shown in Table 1.

[0075] Table 1, test results of example and comparative example samples

[0076]

[0077] From the data in Table 1, it can be seen that:

[0078] (1) The patent examples 1-3 achieve the performance target of "density ≥ 99%, average grain size 20-50 nm, thermal conductivity 300-400 W / (m·K), bending strength ≥ 300 MPa, and dielectric constant ≤ 4.0" of boron nitride nanoceramics by strictly controlling the molar ratio of precursor raw materials at 1:(1.2-1.5):(5-8), the amount of nano-carbon powder at 0.5-2%, using freeze-drying process, and controlling the nitriding temperature at 800-1000°C. The comprehensive performance is excellent.

[0079] (2) Comparing the data of comparative examples 1 and 2 and example 3, it can be seen that:

[0080] Comparative example 1 (urea and ethanol are insufficient): The amount of urea is too low to form B←N coordination bond with B(OH)3 generated by hydrolysis of trimethyl borate, resulting in the polymerization of B(OH)3 to form micron-sized particles; the insufficient ethanol makes the viscosity of the sol rise to 150 mPa·s, the nano-carbon powder is not uniformly dispersed, and the ammonia gas penetration is blocked during nitriding, resulting in a 2.2% decrease in density, a 22.9% loss in thermal conductivity, and an 18.75% decrease in bending strength after sintering.

[0081] Comparative example 2 (excess ethanol): The high amount of ethanol reduces the solid content of the sol from 18% to 10%, and the powder porosity after freeze-drying is too high (>70%), resulting in insufficient contact between particles during SPS sintering, a 2.5% decrease in density, a 25.7% loss in thermal conductivity, and a 21.9% decrease in bending strength.

[0082] (3) Comparing the data of comparative examples 3 and 4 and example 3, it can be seen that:

[0083] Comparative example 3 (insufficient carbon powder): The low amount of carbon powder cannot form a continuous grain growth inhibition layer, and the incomplete conductive network during SPS sintering results in uneven current distribution and a 100% increase in grain size, a 22.9% decrease in bending strength.

[0084] Comparative Example 4 (carbon powder excess): The amount of carbon powder added is too high, and the excess carbon powder cannot completely react with ammonia gas during the nitriding stage. The residual free carbon forms a conductive channel, although the grain size is further reduced, the thermal conductivity is lost by 18.6%, the dielectric constant is increased by 56.8%, and the insulation performance advantage is lost.

[0085] (4) Comparing the data of Comparative Example 5 and Example 3, it can be seen that:

[0086] Comparative Example 5 uses traditional hot air drying, and the capillary force generated during solvent evaporation causes the precursor to form hard agglomeration (agglomerate particle size > 500 nm). During nitriding, ammonia gas cannot penetrate into the interior of the agglomerate, resulting in residual B2O3 impurities inside. During SPS sintering, the agglomerate is difficult to densify, and the density drops by 7%, the grain size increases by 200%, the thermal conductivity is lost by 34.3%, and the bending strength decreases by 34.4%. This fully proves the irreplaceability of freeze-drying in "avoiding agglomeration and retaining nano structure".

[0087] (5) Comparing the data of Comparative Example 6 and Example 3, it can be seen that:

[0088] Comparative Example 6 has a high nitriding temperature, which accelerates the atomic diffusion of BN grains at high temperature, resulting in a 300% increase in grain size. At the same time, the excessive carbonization of nano-carbon powder forms a graphite phase, which scatters phonons and results in a 14.3% loss in thermal conductivity. This verifies that 800-1000°C is the optimal temperature range for "complete nitriding" and "grain control".

[0089] As can be seen, any deviation of a single process parameter will cause significant degradation of ceramic performance, further proving that only through the precise control of multiple steps and process parameters in the present application can the technical pain points of traditional boron nitride ceramics, such as "coarse grains, low density, and insufficient thermal conductivity", be effectively solved, and the present application is suitable for high-end fields such as high-power electronic device heat dissipation substrates and high-temperature insulation structural parts.

[0090] Finally, it should be noted that: the above specific examples are only used to explain the purpose, technical solutions and beneficial effects of the present application in detail. It should be understood that the above description is only a specific embodiment of the present application and does not limit the protection scope of the present application; although the present application has been described in detail with reference to the foregoing specific embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions, improvements, etc. to some or all of the technical features; and these modifications, equivalent substitutions, improvements do not make the essence of the corresponding technical solution deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and description of the present application.

Claims

1. A method for preparing high-performance boron nitride nanoceramics, characterized in that, Includes the following steps: S1. Mix trimethyl borate, urea, and ethanol in a molar ratio of 1:(1.2-1.5):(5-8) to obtain a mixture. Then add 0.5-2% of nano carbon powder by mass of the mixture and stir to react, to obtain a transparent boron nitride precursor sol. S2. Freeze-dry the boron nitride precursor sol to obtain a fluffy boron nitride precursor powder; S3. The boron nitride precursor powder is heated to 800-1000℃ under an ammonia atmosphere and kept at that temperature for 2-3 hours to obtain boron nitride nanopowder. S4. Boron nitride nanoparticles are subjected to spark plasma sintering to obtain high-performance boron nitride nanoceramics.

2. The method for preparing high-performance boron nitride nanoceramics according to claim 1, characterized in that, The nano-carbon powder is single-walled carbon nanotubes or graphene quantum dots with a purity ≥99.9% and a particle size of 5-20 nm.

3. The method for preparing high-performance boron nitride nanoceramics according to claim 1, characterized in that, The reaction temperature in step S1 is 60-80℃.

4. The method for preparing high-performance boron nitride nanoceramics according to claim 1, characterized in that, The freeze-drying process specifically includes: pre-freezing the boron nitride precursor sol at -40 to -60°C for 2-3 hours, followed by freeze-drying at a vacuum of ≤10Pa and a temperature of -40 to -50°C for 12-24 hours.

5. The method for preparing high-performance boron nitride nanoceramics according to claim 1, characterized in that, The ammonia flow rate is 200-500 mL / min, and the gas purity is ≥99.99%.

6. The method for preparing high-performance boron nitride nanoceramics according to claim 1, characterized in that, The boron nitride nanoparticles have a particle size of 20-50 nm.

7. The method for preparing high-performance boron nitride nanoceramics according to claim 1, characterized in that, The spark plasma sintering method is as follows: Boron nitride nanoparticles were loaded into a graphite mold and heated to 1600-1800℃ in a spark plasma sintering furnace under conditions of vacuum degree ≤5Pa and axial pressure 50-80MPa. After holding at this temperature for 5-15 minutes, the mixture was cooled to room temperature in the furnace.

8. The method for preparing high-performance boron nitride nanoceramics according to claim 7, characterized in that, During sintering, the pulse current parameters are: pulse width 10-20ms, pulse interval 5-10ms, and current density 50-100A / mm². 2 .

9. A high-performance boron nitride nanoceramic, prepared by the method described in any one of claims 1-8.

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