High thermal conductivity hexagonal boron nitride ceramic material and preparation method thereof

Abstract

The application relates to the field and discloses a high-thermal-conductivity hexagonal boron nitride ceramic material and a preparation method thereof; the ceramic material is made of hexagonal boron nitride powder, an aluminum-boron interface precursor, a rare earth oxide additive, a fluoride fluxing agent and inevitable impurities; the hexagonal boron nitride powder comprises first flaky hexagonal boron nitride powder and second flaky hexagonal boron nitride powder, and the two are matched according to particle size gradation. During preparation, the aluminum-boron interface precursor formed by an aluminum source and a boron source is first attached to the surface of the flaky hexagonal boron nitride powder, then mixed with the additive to prepare slurry, the slurry is formed into an oriented blank through doctor blade flow casting, and the oriented blank is pressed into a ceramic blank body in a same direction through layering. Then, the ceramic blank body is subjected to pre-nitriding treatment and oscillation hot-pressing sintering, so that a nitridation bridging phase is formed in the contact area of adjacent flaky hexagonal boron nitride powder. The material can reduce interlamellar porosity and interfacial thermal resistance, improve the thermal conduction continuity between the flaky hexagonal boron nitride powder, and is suitable for insulating and heat-conducting ceramic components.

Description

Technical Field

[0001] This invention relates to the field of ceramic material preparation, specifically to a high thermal conductivity hexagonal boron nitride ceramic material and its preparation method. Background Technology

[0002] Hexagonal boron nitride ceramics possess characteristics such as high temperature resistance, electrical insulation, and good chemical stability. Furthermore, their crystal laminations exhibit high thermal conductivity, making them commonly used in electronic packaging heat dissipation, high-temperature insulation supports, and heat-resistant and conductive components. As the requirements for insulating and heat-dissipating components in power devices and high-temperature equipment increase, the thermal continuity and structural compactness of hexagonal boron nitride ceramic materials have become crucial factors influencing their application.

[0003] Existing hexagonal boron nitride ceramics are typically prepared using methods such as powder mixing, pressing, and hot pressing sintering. Other methods improve material density and thermal conductivity by adding oxide additives, rare earth additives, or employing orientation molding. While these methods can improve sintering results to some extent, lamellar hexagonal boron nitride powder is prone to forming interlamellar pores during stacking and sintering, and some oxide additives can form continuous oxygen-containing phases at grain boundaries.

[0004] Since the thermal conductivity of plate-like hexagonal boron nitride mainly depends on the continuous contact between the plates, when there are pores or oxygen-containing grain boundaries between the plates, the heat transfer path between adjacent plates is weakened, the interfacial thermal resistance increases, and the material is difficult to simultaneously achieve high thermal conductivity, high density and insulation stability. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a high thermal conductivity hexagonal boron nitride ceramic material and its preparation method, thereby solving the technical problems existing in the prior art.

[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0007] A high thermal conductivity hexagonal boron nitride ceramic material, comprising:

[0008] 90.0 to 97.5 parts of hexagonal boron nitride powder;

[0009] 1.0 to 5.0 parts of aluminum-boron interface precursor;

[0010] Rare earth oxide additives: 0.2 to 1.5 parts;

[0011] Fluoride flux, 0.1 to 0.8 parts;

[0012] Unavoidable impurities shall not exceed 0.5 parts;

[0013] The hexagonal boron nitride powder includes a first plate-shaped hexagonal boron nitride powder and a second plate-shaped hexagonal boron nitride powder. The D50 particle size of the first plate-shaped hexagonal boron nitride powder is 8 μm to 25 μm, and the D50 particle size of the second plate-shaped hexagonal boron nitride powder is 0.5 μm to 3 μm. The mass ratio of the first plate-shaped hexagonal boron nitride powder to the second plate-shaped hexagonal boron nitride powder is 65:35 to 85:15.

[0014] The aluminum-boron interface precursor is formed by the hydrolysis and condensation of aluminum and boron sources and is distributed on the surface of the first and second plate-shaped hexagonal boron nitride powders.

[0015] In the high thermal conductivity hexagonal boron nitride ceramic material, the first plate-shaped hexagonal boron nitride powder and the second plate-shaped hexagonal boron nitride powder are oriented and arranged along the forming surface of the ceramic material, and the angle between the plate-shaped hexagonal boron nitride powder and the forming surface of the ceramic material is not greater than 20°.

[0016] The contact region of adjacent plate-like hexagonal boron nitride powders forms a nitride-bridged phase. The nitride-bridged phase is detected by X-ray photoelectron spectroscopy, which shows the Al2p binding energy peak corresponding to the Al-N bond and the B1s binding energy peak corresponding to the BN bond. The Al2p binding energy peak is located between 73.5 eV and 74.8 eV, and the B1s binding energy peak is located between 190.0 eV and 191.5 eV.

[0017] A method for preparing a high thermal conductivity hexagonal boron nitride ceramic material includes the following steps:

[0018] S1: Weigh 90.0 to 97.5 parts of hexagonal boron nitride powder, 0.2 to 1.5 parts of rare earth oxide additives and 0.1 to 0.8 parts of fluoride flux according to the mass ratio, and weigh aluminum source and boron source according to the amount of 1.0 to 5.0 parts of aluminum-boron interface precursor.

[0019] The hexagonal boron nitride powder includes a first plate-shaped hexagonal boron nitride powder and a second plate-shaped hexagonal boron nitride powder. The D50 particle size of the first plate-shaped hexagonal boron nitride powder is 8 μm to 25 μm, and the D50 particle size of the second plate-shaped hexagonal boron nitride powder is 0.5 μm to 3 μm. The mass ratio of the first plate-shaped hexagonal boron nitride powder to the second plate-shaped hexagonal boron nitride powder is 65:35 to 85:15.

[0020] S2: The first and second sheet-like hexagonal boron nitride powders are dried to obtain mixed hexagonal boron nitride powders;

[0021] S3: Mix aluminum source, boron source and organic solvent to form an interface treatment liquid. Add the mixed hexagonal boron nitride powder to the interface treatment liquid for dispersion treatment, so that the aluminum-boron interface precursor formed by the hydrolysis and condensation of aluminum source and boron source is attached to the surface of the first plate-shaped hexagonal boron nitride powder and the second plate-shaped hexagonal boron nitride powder. After drying, modified hexagonal boron nitride powder is obtained.

[0022] S4: Modified hexagonal boron nitride powder, rare earth oxide additives and fluoride flux are mixed and ball-milled to obtain sintered mixed powder;

[0023] S5: The sintered mixed powder is made into a slurry and then cast into oriented blanks using a scraper, so that the first and second sheet-like hexagonal boron nitride powders are arranged along the extension direction of the oriented blanks.

[0024] S6: Multiple oriented blanks are stacked in the same extension direction and pressed into a ceramic blank;

[0025] S7: The ceramic green body is pre-nitrided in a nitrogen-containing atmosphere. After the pre-nitriding treatment, the initial nitrided interface layer formed by the aluminum-boron interface precursor is located on the surface of the first plate-shaped hexagonal boron nitride powder and the second plate-shaped hexagonal boron nitride powder.

[0026] S8: The pre-nitrided ceramic blank is subjected to oscillating hot pressing sintering. After oscillating hot pressing sintering, the initial nitrided interface layer is transformed into a nitrided bridging phase located in the contact area of ​​adjacent plate-like hexagonal boron nitride powder, thus obtaining a high thermal conductivity hexagonal boron nitride ceramic material.

[0027] Preferably, the D50 particle size of the first plate-shaped hexagonal boron nitride powder is 10 μm to 18 μm, the D50 particle size of the second plate-shaped hexagonal boron nitride powder is 0.8 μm to 2.0 μm, and the mass ratio of the first plate-shaped hexagonal boron nitride powder to the second plate-shaped hexagonal boron nitride powder is 70:30 to 80:20.

[0028] Preferably, the aluminum source is aluminum isopropoxide, the boron source is triethyl borate, and the molar ratio of aluminum in the aluminum source to boron in the boron source is 1:1.5 to 1:3.5.

[0029] Preferably, the rare earth oxide additive is yttrium oxide, the fluoride flux is calcium fluoride, and the mass ratio of yttrium oxide to calcium fluoride is 2:1 to 6:1.

[0030] Preferably, in step S2, the first sheet-like hexagonal boron nitride powder and the second sheet-like hexagonal boron nitride powder are dried at 80°C to 120°C for 2 hours to 6 hours, and the moisture content of the dried mixed hexagonal boron nitride powder is 0.05% to 0.20%.

[0031] Preferably, in step S3, the interface treatment solution is made of aluminum isopropoxide, triethyl borate, anhydrous ethanol and deionized water, and the mass ratio of aluminum isopropoxide, triethyl borate, anhydrous ethanol and deionized water is from 1:1.2:20:0.3 to 1:2.8:45:0.8.

[0032] After mixing hexagonal boron nitride powder and adding it to the interface treatment solution, the mixture is stirred at 30℃ to 55℃ for 1h to 4h and then vacuum dried at 40℃ to 70℃ for 4h to 10h to obtain modified hexagonal boron nitride powder.

[0033] Preferably, in step S4, the modified hexagonal boron nitride powder, rare earth oxide additives, and fluoride flux are ball-milled in anhydrous ethanol. The ball milling media is silicon nitride balls, the ball-to-material mass ratio is 2:1 to 5:1, the ball milling speed is 120 r / min to 250 r / min, and the ball milling time is 4 h to 8 h. After ball milling, the powder is dried and sieved to obtain sintered mixed powder.

[0034] Preferably, in steps S5 and S6, the sintered mixed powder is mixed with polyvinyl butyral, dibutyl phthalate and anhydrous ethanol to form a slurry, and the slurry is cast by a scraper to form an oriented blank, with the scraper gap being 100 μm to 500 μm.

[0035] After drying, the oriented blanks are stacked in the same extension direction and pre-pressed at 10MPa to 30MPa to obtain a ceramic blank.

[0036] Preferably, in steps S7 and S8, the ceramic green body is pre-nitrided in a nitrogen atmosphere by heating to 900°C to 1200°C at a rate of 2°C / min to 5°C / min and holding for 1h to 3h.

[0037] After pre-nitriding treatment, the ceramic green body is subjected to oscillating hot pressing sintering in a nitrogen atmosphere or an argon-nitrogen mixed atmosphere. The sintering temperature is 1750℃ to 1900℃, the base pressure is 20MPa to 35MPa, and an oscillation pressure of 2MPa to 8MPa is superimposed on the base pressure. The oscillation frequency is 0.1Hz to 2Hz, and the holding time is 1h to 3h. After sintering, it is annealed in a nitrogen atmosphere at 1400℃ to 1600℃ for 2h to 6h.

[0038] In summary, the present invention has the following main beneficial effects:

[0039] This application combines first and second plate-shaped hexagonal boron nitride powders according to particle size distribution, and aligns the plate-shaped hexagonal boron nitride powders along the forming surface during the doctor blade casting and co-directional stacking process. This allows the large-particle-size plate-shaped powders to form a continuous plate skeleton, while the small-particle-size plate-shaped powders enter the gaps between the plates and the contact transition area. This achieves the effect of reducing the voids between the plates and improving the contact continuity of the plate-shaped hexagonal boron nitride powders, avoiding the problem of large pores and insufficient local contact that is easily formed when single-particle-size powders are piled up.

[0040] This application achieves improved bonding stability and reduced interlayer thermal resistance by forming aluminum-boron interface precursors on the surfaces of first and second lamellar hexagonal boron nitride powders, and transforming these precursors into an initial nitrided interface layer during pre-nitriding treatment. Then, during oscillating hot-pressing sintering, the initial nitrided interface layer concentrates in the contact region of adjacent lamellar hexagonal boron nitride powders, forming a nitrided bridging phase. This method differs from simply relying on oxide additives to promote densification and avoids the adverse effects of continuous oxide grain boundaries on the heat transfer path between hexagonal boron nitride lamellars.

[0041] This application combines pre-nitriding treatment with oscillating hot pressing sintering to allow the organic components in the green body to be expelled first, while the lamellar hexagonal boron nitride powder undergoes re-bonding and orientation retention during hot pressing. This achieves the simultaneous effects of green body degassing, lamellar bonding, interfacial bridging phase formation, and material densification. As a result, the prepared hexagonal boron nitride ceramic material, while maintaining the insulating and heat-resistant properties of hexagonal boron nitride, forms a relatively continuous in-plane thermal conductivity path, making it suitable for applications requiring insulation and thermal conductivity, such as electronic packaging heat sinks and high-temperature insulating heat dissipation components. Attached Figure Description

[0042] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Example 1

[0045] refer to Figure 1 A high thermal conductivity hexagonal boron nitride ceramic material, comprising:

[0046] 90.0 to 97.5 parts of hexagonal boron nitride powder;

[0047] 1.0 to 5.0 parts of aluminum-boron interface precursor;

[0048] Rare earth oxide additives: 0.2 to 1.5 parts;

[0049] Fluoride flux, 0.1 to 0.8 parts;

[0050] Unavoidable impurities shall not exceed 0.5 parts;

[0051] The hexagonal boron nitride powder includes a first plate-shaped hexagonal boron nitride powder and a second plate-shaped hexagonal boron nitride powder. The D50 particle size of the first plate-shaped hexagonal boron nitride powder is 8 μm to 25 μm, and the D50 particle size of the second plate-shaped hexagonal boron nitride powder is 0.5 μm to 3 μm. The mass ratio of the first plate-shaped hexagonal boron nitride powder to the second plate-shaped hexagonal boron nitride powder is 65:35 to 85:15.

[0052] The aluminum-boron interface precursor is formed by the hydrolysis and condensation of aluminum and boron sources and is distributed on the surface of the first and second plate-shaped hexagonal boron nitride powders.

[0053] In the high thermal conductivity hexagonal boron nitride ceramic material, the first plate-shaped hexagonal boron nitride powder and the second plate-shaped hexagonal boron nitride powder are oriented and arranged along the forming surface of the ceramic material, and the angle between the plate-shaped hexagonal boron nitride powder and the forming surface of the ceramic material is not greater than 20°.

[0054] The contact region of adjacent plate-like hexagonal boron nitride powders forms a nitride-bridged phase. The nitride-bridged phase is detected by X-ray photoelectron spectroscopy, which shows the Al2p binding energy peak corresponding to the Al-N bond and the B1s binding energy peak corresponding to the BN bond. The Al2p binding energy peak is located between 73.5 eV and 74.8 eV, and the B1s binding energy peak is located between 190.0 eV and 191.5 eV.

[0055] A method for preparing a high thermal conductivity hexagonal boron nitride ceramic material includes the following steps:

[0056] S1: Weigh 90.0 to 97.5 parts of hexagonal boron nitride powder, 0.2 to 1.5 parts of rare earth oxide additives and 0.1 to 0.8 parts of fluoride flux according to the mass ratio, and weigh aluminum source and boron source according to the amount of 1.0 to 5.0 parts of aluminum-boron interface precursor.

[0057] The hexagonal boron nitride powder includes a first plate-shaped hexagonal boron nitride powder and a second plate-shaped hexagonal boron nitride powder. The D50 particle size of the first plate-shaped hexagonal boron nitride powder is 8 μm to 25 μm, and the D50 particle size of the second plate-shaped hexagonal boron nitride powder is 0.5 μm to 3 μm. The mass ratio of the first plate-shaped hexagonal boron nitride powder to the second plate-shaped hexagonal boron nitride powder is 65:35 to 85:15.

[0058] S2: The first and second sheet-like hexagonal boron nitride powders are dried to obtain mixed hexagonal boron nitride powders;

[0059] S3: Mix aluminum source, boron source and organic solvent to form an interface treatment liquid. Add the mixed hexagonal boron nitride powder to the interface treatment liquid for dispersion treatment, so that the aluminum-boron interface precursor formed by the hydrolysis and condensation of aluminum source and boron source is attached to the surface of the first plate-shaped hexagonal boron nitride powder and the second plate-shaped hexagonal boron nitride powder. After drying, modified hexagonal boron nitride powder is obtained.

[0060] S4: Modified hexagonal boron nitride powder, rare earth oxide additives and fluoride flux are mixed and ball-milled to obtain sintered mixed powder;

[0061] S5: The sintered mixed powder is made into a slurry and then cast into oriented blanks using a scraper, so that the first and second sheet-like hexagonal boron nitride powders are arranged along the extension direction of the oriented blanks.

[0062] S6: Multiple oriented blanks are stacked in the same extension direction and pressed into a ceramic blank;

[0063] S7: The ceramic green body is pre-nitrided in a nitrogen-containing atmosphere. After the pre-nitriding treatment, the initial nitrided interface layer formed by the aluminum-boron interface precursor is located on the surface of the first plate-shaped hexagonal boron nitride powder and the second plate-shaped hexagonal boron nitride powder.

[0064] S8: The pre-nitrided ceramic blank is subjected to oscillating hot pressing sintering. After oscillating hot pressing sintering, the initial nitrided interface layer is transformed into a nitrided bridging phase located in the contact area of ​​adjacent plate-like hexagonal boron nitride powder, thus obtaining a high thermal conductivity hexagonal boron nitride ceramic material.

[0065] This ceramic material is primarily composed of lamellar hexagonal boron nitride powder. A particle size distribution is achieved through first and second lamellar boron nitride powders, and an aluminum-boron interface precursor is formed on the surface of the lamellar boron nitride powder. During subsequent pre-nitriding treatment and oscillating hot-pressing sintering, the aluminum-boron interface precursor transforms into a nitrided bridging phase located in the contact region of adjacent lamellar boron nitride powders. This structure differs from solutions that simply use oxide additives to increase density, and also from solutions that rely solely on 3D printing or hot-pressing rearrangement to form an oriented structure. The focus of this application is to enable the lamellar hexagonal boron nitride powder to form an oriented arrangement while simultaneously creating an interface connection structure containing Al-N and BN bonds in the lamellar contact region.

[0066] In this application, the first lamellar boron nitride powder refers to lamellar boron nitride powder with a D50 particle size of 8 μm to 25 μm, and the second lamellar boron nitride powder refers to lamellar boron nitride powder with a D50 particle size of 0.5 μm to 3 μm. The D50 particle size can be determined using a laser particle size analyzer. During the determination, the powder is dispersed in anhydrous ethanol and ultrasonically dispersed for 3 to 10 minutes before testing. The first lamellar boron nitride powder is mainly used to form a continuous lamellar skeleton, and the second lamellar boron nitride powder fills the spaces between the first lamellar boron nitride powder. Here, "filling" does not mean completely filling all pores, but rather that the second lamellar boron nitride powder is distributed in the interlamellar gaps and contact transition areas between the first lamellar boron nitride powder.

[0067] In this application, the aluminum-boron interface precursor is formed by the hydrolysis and condensation of an aluminum source and a boron source. The aluminum source can be aluminum isopropoxide, and the boron source can be triethyl borate. Anhydrous ethanol can be used as the organic solvent. Deionized water is used to provide the moisture required for the hydrolysis and condensation. The aluminum-boron interface precursor adheres to the surfaces of the first and second lamellar hexagonal boron nitride powders. This adhesion can be achieved through stirring dispersion, ultrasonic dispersion, vacuum drying, and subsequent powder mixing processes; a continuous coating layer is not required, nor is complete coverage of the entire surface of the lamellar hexagonal boron nitride powder required.

[0068] In this application, the nitride bridging phase refers to the interfacial phase containing aluminum, boron, and nitrogen elements formed in the contact region of adjacent lamellar hexagonal boron nitride powders after sintering. This nitride bridging phase is not dispersed in the ceramic material as a large number of independent particles, but is located at the contact sites of the lamellar hexagonal boron nitride powders. The nitride bridging phase can be confirmed by X-ray photoelectron spectroscopy. During detection, the sintered ceramic material can be cut and polished along its thickness direction, and the test surface exposing the lamellar contact region can be selected for detection; energy calibration is performed using the C1s peak at 284.8 eV, or correction is performed using the instrument's standard calibration method. In the detection results, an Al2p binding energy peak between 73.5 eV and 74.8 eV can be used as a criterion for determining the presence of Al-N bonds; a B1s binding energy peak between 190.0 eV and 191.5 eV can be used as a criterion for determining the presence of BN bonds. To further confirm the interface location, scanning electron microscopy (SEM) can be used to observe the distribution of aluminum elements in the contact region of the lamellar hexagonal boron nitride powders.

[0069] In this application, the orientation of the flake-shaped hexagonal boron nitride powder along the forming surface of the ceramic material means that the angle between the flake-shaped boron nitride powder and the forming surface of the ceramic material is no greater than 20°. This angle can be determined statistically by scanning electron microscopy images of the polished section. Specifically, no fewer than five fields of view can be randomly selected on the cross-section along the thickness direction of the ceramic material, and no fewer than twenty identifiable flake-shaped boron nitride particles can be counted in each field of view. The angle between the extension direction of the flake-shaped boron nitride powder and the forming surface direction is used as the statistical angle. When at least 80% of the flake-shaped boron nitride powder particles have an angle no greater than 20°, it can be considered that the flake-shaped boron nitride powder is oriented along the forming surface direction.

[0070] Example 2

[0071] This embodiment provides a method for preparing a high thermal conductivity hexagonal boron nitride ceramic material.

[0072] Weigh out 95.0 parts by weight of hexagonal boron nitride powder, 0.8 parts by weight of yttrium oxide, and 0.3 parts by weight of calcium fluoride. Weigh out aluminum isopropoxide and triethyl borate in an amount of 3.0 parts to generate an aluminum-boron interface precursor. The hexagonal boron nitride powder consists of a first plate-shaped hexagonal boron nitride powder and a second plate-shaped hexagonal boron nitride powder. The D50 particle size of the first plate-shaped hexagonal boron nitride powder is 15 μm, and the D50 particle size of the second plate-shaped hexagonal boron nitride powder is 1.5 μm. The mass ratio of the first plate-shaped hexagonal boron nitride powder to the second plate-shaped hexagonal boron nitride powder is 75:25.

[0073] The target amount of aluminum-boron interface precursor generated is determined by the following formula:

[0074] ;

[0075] In the formula, The target mass of the aluminum-boron interface precursor is expressed in grams. The mass of hexagonal boron nitride powder is expressed in grams. This refers to the target mass ratio of the aluminum-boron interface precursor to the hexagonal boron nitride powder. In this embodiment, the target amount of the aluminum-boron interface precursor is calculated to be 3.0 parts by mass according to the defined mass ratio.

[0076] The amounts of aluminum isopropoxide and triethyl borate are determined according to the molar ratio of aluminum to boron, and the calculation formula is as follows:

[0077] ;

[0078] In the formula, This represents the amount of substance of aluminum, expressed in moles (mol). This represents the amount of substance of boron, expressed in mol. The value represents the mass of aluminum in aluminum isopropoxide, in grams. This represents the mass of boron in triethyl borate, in grams. The molar mass of aluminum is taken as 26.98 g / mol; The molar mass of boron is taken as 10.81 g / mol. In this embodiment, the molar ratio of aluminum to boron is controlled at 1:2.5.

[0079] First and second sheet-like hexagonal boron nitride powders were placed in a vacuum drying oven and dried at 100°C for 4 hours to obtain mixed hexagonal boron nitride powder. The moisture content of the powder was measured after drying, and was controlled within the range of 0.05% to 0.20%. The moisture content could be determined using a halogen moisture analyzer or the Karl Fischer moisture method. The purpose of drying the powder is to reduce the free water on the surface of the sheet-like hexagonal boron nitride powder, thus preventing the hydrolysis and condensation reaction in the subsequent interface treatment solution from being too rapid and forming large particle precipitates.

[0080] An interface treatment solution was prepared using aluminum isopropoxide, triethyl borate, anhydrous ethanol, and deionized water. The mass ratio of aluminum isopropoxide, triethyl borate, anhydrous ethanol, and deionized water was 1:2.0:32:0.5. During preparation, aluminum isopropoxide was first dissolved in anhydrous ethanol by stirring, followed by the addition of triethyl borate, and finally, deionized water was added dropwise. Stirring was maintained during the dropwise addition of deionized water to allow the aluminum and boron sources to undergo hydrolysis and condensation, forming an aluminum-boron interface precursor sol.

[0081] The dried mixed hexagonal boron nitride powder was added to the interface treatment solution and stirred at 45°C for 3 hours, allowing the aluminum-boron interface precursor to adhere to the surfaces of the first and second lamellar hexagonal boron nitride powders. After stirring, it was vacuum dried at 60°C for 6 hours to obtain modified hexagonal boron nitride powder. During the drying process, the organic solvent evaporated, and the aluminum-boron interface precursor remained on the surface of the lamellar hexagonal boron nitride powder. In this step, tetraethyl orthosilicate was not used to form a silica coating layer, nor was the formation of a continuous oxide coating layer intended.

[0082] Modified hexagonal boron nitride powder, yttrium oxide, and calcium fluoride were ball-milled in anhydrous ethanol. Silicon nitride balls were used as the milling media, with a ball-to-powder mass ratio of 3:1. The milling speed was 180 r / min, and the milling time was 6 h. After milling, the slurry was dried at 70℃ and then passed through a 100-mesh sieve to obtain a sintered mixed powder. The milling time was controlled within the range of 4 h to 8 h to ensure that yttrium oxide and calcium fluoride were dispersed among the modified hexagonal boron nitride powder, while avoiding excessive breakage of the first layer of flake-like hexagonal boron nitride powder.

[0083] A slurry was prepared by mixing sintered mixed powder, polyvinyl butyral, dibutyl phthalate, and anhydrous ethanol. Based on 100 parts by weight of the sintered mixed powder, 3 parts of polyvinyl butyral, 1.5 parts of dibutyl phthalate, and 55 parts of anhydrous ethanol were added. After degassing, the slurry was cast using a doctor blade with a gap of 300 μm to form oriented preforms. During the casting process, the slurry extended along the casting direction under the shearing action of the doctor blade. The surfaces of the first and second lamellar hexagonal boron nitride powders aligned with the slurry flow direction, causing the lamellar hexagonal boron nitride powders to align along the extension direction of the oriented preforms.

[0084] The oriented blanks are dried at 50℃ and then cut into blank units of the same size. Multiple blank units are stacked in the same extension direction and pre-pressed at 20MPa to obtain a ceramic green body. During stacking, the flow direction of each blank unit is kept consistent, and adjacent blanks are not stacked crosswise. This treatment is to ensure that the orientation direction of each layer of lamellar hexagonal boron nitride powder is consistent, avoiding the cancellation of orientation directions between different blanks.

[0085] The ceramic green body is placed in a tube furnace and pre-nitrided in a nitrogen-containing atmosphere. The nitrogen-containing atmosphere can be a pure nitrogen atmosphere or a mixture of nitrogen and ammonia. Preferably, the pre-nitriding process uses a nitrogen atmosphere for heating in the initial stage and a nitrogen-ammonia atmosphere for holding in the subsequent stage. The heating rate is 3℃ / min, and the temperature is raised to 1050℃ and held for 2 hours. During the pre-nitriding process, polyvinyl butyral and dibutyl phthalate decompose and are released. The aluminum-boron interface precursor undergoes deorganization, dehydroxylation, and nitrogen-containing transformation, forming an initial nitrided interface layer on the surfaces of the first and second lamellar hexagonal boron nitride powders. This initial nitrided interface layer refers to an interface layer containing aluminum, boron, and nitrogen elements, which is located on the surface of the lamellar hexagonal boron nitride powder after the pre-nitriding process and continues to react and rearrange during subsequent oscillating hot pressing sintering.

[0086] The pre-nitrided ceramic green body was placed in a hot-press sintering furnace for oscillating hot-press sintering. The sintering atmosphere was either nitrogen or an argon-nitrogen mixture, the sintering temperature was 1820℃, the base pressure was 28MPa, and an oscillating pressure of 5MPa was superimposed on the base pressure. The oscillation frequency was 0.5Hz, and the holding time was 2h. The oscillation pressure was applied by periodically varying between the base pressure and the base pressure plus the oscillation pressure while maintaining the base pressure. During sintering, the lamellar hexagonal boron nitride powder continued to adhere under the combined action of pressure and temperature. The initial nitrided interface layer enriched in the contact area of ​​adjacent lamellar hexagonal boron nitride powders and transformed into a nitrided bridging phase located in the contact area. After sintering, it was annealed at 1500℃ for 4h in a nitrogen atmosphere, followed by furnace cooling, to obtain a high thermal conductivity hexagonal boron nitride ceramic material.

[0087] After sintering, the ceramic material was cut along its thickness and polished before being observed using a scanning electron microscope. The angle between the flake-like hexagonal boron nitride powder and the formed surface of the ceramic material was statistically analyzed using cross-sectional images. The method for calculating the angle was as follows: five fields of view were randomly selected on the cross-section, and at least twenty flake-like hexagonal boron nitride particles were counted in each field of view. The angle between the extension direction of the flake-like powder and the direction of the formed surface was calculated. The statistical results were used to confirm whether the flake-like hexagonal boron nitride powder met the requirement that the angle between the flake-like powder and the formed surface should not exceed 20°.

[0088] The sintered ceramic material was also subjected to X-ray photoelectron spectroscopy (XPS). Before testing, the test surface underwent a light ion beam cleaning to remove surface adsorbates. During testing, the Al2p, B1s, N1s, and O1s spectral regions were measured, and peak fitting was performed on the Al2p and B1s peaks. If the Al2p binding energy peak was in the range of 73.5 eV to 74.8 eV, and the B1s binding energy peak was in the range of 190.0 eV to 191.5 eV, then the presence of Al-N and BN bonds in the nitride bridging phase was confirmed. To avoid confusion between the BN bonds of the plate-like hexagonal boron nitride powder itself and the interfacial bridging phase, the distribution of aluminum could be used for judgment. When aluminum was distributed in the plate-contact region, and the Al2p binding energy peak corresponding to the Al-N bond was detected in this region, this region could be identified as the location of the nitride bridging phase.

[0089] This embodiment does not use photocurable resin systems such as HDDA, THFA, and PUA, and does not require 3D printing to form the green body. This embodiment also does not use tetraethyl orthosilicate to form a silica coating layer on the surface of hexagonal boron nitride powder. Yttrium oxide and calcium fluoride are used as sintering aids in this embodiment, while the aluminum-boron interface precursor is used to form the nitride bridging phase; their roles and formation stages differ. Therefore, this embodiment differs from boron nitride ceramic preparation methods that solely rely on oxide additives to promote densification.

[0090] Example 3

[0091] The difference between this embodiment and Embodiment 2 is that the D50 particle size of the first plate-shaped hexagonal boron nitride powder is 10 μm, the D50 particle size of the second plate-shaped hexagonal boron nitride powder is 0.8 μm, and the mass ratio of the first plate-shaped hexagonal boron nitride powder to the second plate-shaped hexagonal boron nitride powder is 70:30.

[0092] In this embodiment, the amount of hexagonal boron nitride powder is 94.0 parts, the amount of aluminum-boron interface precursor is 4.0 parts, the amount of yttrium oxide is 1.2 parts, and the amount of calcium fluoride is 0.4 parts. Aluminum isopropoxide is used as the aluminum source, and triethyl borate is used as the boron source, with a molar ratio of aluminum to boron of 1:2.0. In the interface treatment solution, the mass ratio of aluminum isopropoxide, triethyl borate, anhydrous ethanol, and deionized water is 1:1.6:28:0.4.

[0093] In this embodiment, the first sheet-like hexagonal boron nitride powder has a smaller particle size, while the second sheet-like hexagonal boron nitride powder has a higher proportion, making it suitable for preparing thinner ceramic sheets. During the preparation process, the scraper gap is set to 150 μm. After drying, the oriented blanks are stacked in the same extension direction, with a pre-compression pressure of 15 MPa. The pre-nitriding temperature is 1000℃, and the holding time is 2 hours. The oscillating hot-pressing sintering temperature is 1780℃, the base pressure is 25 MPa, the oscillation pressure is 4 MPa, the oscillation frequency is 1 Hz, and the holding time is 2 hours. After sintering, the sheet is annealed at 1450℃ for 4 hours.

[0094] The remaining steps of this embodiment are the same as in Embodiment 2. This embodiment demonstrates that, within a defined particle size range and mass ratio range, the specific ratio of the first plate-shaped hexagonal boron nitride powder and the second plate-shaped hexagonal boron nitride powder can be adjusted according to the thickness of the blank and the molding fluidity.

[0095] Example 4

[0096] The difference between this embodiment and Embodiment 2 is that the D50 particle size of the first plate-shaped hexagonal boron nitride powder is 18 μm, the D50 particle size of the second plate-shaped hexagonal boron nitride powder is 2.0 μm, and the mass ratio of the first plate-shaped hexagonal boron nitride powder to the second plate-shaped hexagonal boron nitride powder is 80:20.

[0097] In this embodiment, the amount of hexagonal boron nitride powder is 96.5 parts, the amount of aluminum-boron interface precursor is 2.0 parts, the amount of yttrium oxide is 0.5 parts, and the amount of calcium fluoride is 0.2 parts. The molar ratio of aluminum to boron is 1:3.0. In the interface treatment solution, the mass ratio of aluminum isopropoxide, triethyl borate, anhydrous ethanol, and deionized water is 1:2.4:40:0.7.

[0098] In this embodiment, the proportion of the first sheet-like hexagonal boron nitride powder is relatively high, making it suitable for preparing ceramic sheets with high thermal conductivity requirements along the forming surface. The casting blade gap is 500 μm, and the pre-compression pressure is 30 MPa. The pre-nitriding temperature is 1150℃, and the holding time is 3 h. The oscillating hot pressing sintering temperature is 1880℃, the base pressure is 32 MPa, the oscillation pressure is 6 MPa, the oscillation frequency is 0.2 Hz, and the holding time is 3 h. After sintering, it is annealed at 1550℃ for 5 h.

[0099] The remaining steps of this embodiment are the same as in Embodiment 2. This embodiment demonstrates that even when the proportion of the first plate-shaped hexagonal boron nitride powder is high, the second plate-shaped hexagonal boron nitride powder and the aluminum-boron interface precursor still participate in the construction of the interlayer contact region, avoiding the formation of large interlayer gaps in the ceramic green body solely from the stacking of large-sized plate-shaped powders.

[0100] Example 5

[0101] This embodiment illustrates the formation method of the aluminum-boron interface precursor.

[0102] Aluminum isopropoxide is added to anhydrous ethanol and stirred until it is fully dissolved or forms a uniform dispersion. Triethyl borate is then added and stirring continues. Deionized water is then added dropwise to the mixture, with the stirring speed controlled during the addition to ensure the hydrolysis-condensation reaction proceeds uniformly in the liquid phase. The mass ratio of aluminum isopropoxide, triethyl borate, anhydrous ethanol, and deionized water can be adjusted within the range of 1:1.2:20:0.3 to 1:2.8:45:0.8.

[0103] When the amount of deionized water added is too low, the hydrolysis and condensation of the aluminum and boron sources are insufficient, making it difficult to form a stable adhesion layer on the surface of the plate-like hexagonal boron nitride powder after drying. When the amount of deionized water added is too high, the aluminum and boron sources easily form large colloidal particles in the solution, resulting in the aluminum-boron interfacial precursor not being uniformly adhered to the surface of the plate-like hexagonal boron nitride powder. Therefore, this embodiment uses the above-mentioned mass ratio range to ensure that the aluminum-boron interfacial precursor forms a dispersed adhesion state on the powder surface.

[0104] After the mixed hexagonal boron nitride powder is added to the interface treatment solution, aluminum-boron interface precursors are adsorbed on the surface of the plate-like hexagonal boron nitride powder. During the subsequent vacuum drying process, anhydrous ethanol evaporates, and the aluminum-boron interface precursors remain on the surfaces of the first and second plate-like hexagonal boron nitride powders. Because this application uses an interface precursor formed by both aluminum and boron sources, rather than a single silica coating layer, the interface phase formed after subsequent pre-nitriding and hot-pressing sintering has a structural feature involving aluminum, boron, and nitrogen.

[0105] Example 6

[0106] This example illustrates the compatibility between pre-nitriding treatment and oscillating hot pressing sintering.

[0107] The prepared ceramic green body is placed in a nitrogen-containing atmosphere for pre-nitriding treatment. The pre-nitriding treatment includes a heating stage and a holding stage. The heating stage involves increasing the temperature at a rate of 2°C to 5°C per minute to 900°C to 1200°C. The holding stage lasts for 1 to 3 hours. The nitrogen-containing atmosphere can be a pure nitrogen atmosphere or a mixture of nitrogen and ammonia. When using a mixture of nitrogen and ammonia, the ammonia component can be controlled to be between 5% and 15%, with the remainder being nitrogen.

[0108] After the pre-nitriding treatment, the organic groups in the aluminum-boron interface precursor have been largely decomposed and removed, and the aluminum and boron components form a nitrogen-containing interface layer on the surface of the plate-like hexagonal boron nitride powder. This nitrogen-containing interface layer is referred to as the initial nitriding interface layer in this application. The initial nitriding interface layer is still located on the surface of the plate-like hexagonal boron nitride powder, and it is not required that the final nitrided bridging phase be completely formed during the pre-nitriding stage.

[0109] After pre-nitriding, the ceramic green body enters the oscillating hot pressing sintering stage. During oscillating hot pressing sintering, the ceramic green body is compacted under the base pressure, and under the oscillating pressure, periodic micro-displacement and interlaminar re-adhesion occur. Since the initial nitriding interface layer is located on the surface of the lamellar hexagonal boron nitride powder, when adjacent lamellar hexagonal boron nitride powders approach and form contact during hot pressing, the initial nitriding interface layer concentrates in the contact area and continues to react to form a nitrided bridging phase.

[0110] Therefore, the oscillating hot pressing sintering in this application is not a conventional pressure sintering step used alone to improve density, but rather works in conjunction with the initial nitrided interface layer formed by pre-nitriding to create a nitrided bridging phase in the contact region between adjacent lamellar hexagonal boron nitride powders. This formation path differs from ordinary powder mixing followed by direct hot pressing sintering, and also from processes that rely solely on oscillating pressure to induce boron nitride grain orientation.

[0111] Example 7

[0112] This embodiment illustrates the detection and confirmation method for nitride-bridged phases.

[0113] The sintered high thermal conductivity hexagonal boron nitride ceramic material was cut along a direction perpendicular to the molding surface to obtain a cross-sectional sample. The cross-sectional sample was then subjected to coarse grinding, fine grinding, and polishing to expose the cross-section of the flake-shaped hexagonal boron nitride powder and the contact area between adjacent flakes. The polished cross-sectional sample was then placed in an X-ray photoelectron spectroscopy (XPS) instrument for analysis.

[0114] During detection, a full-spectrum scan was first performed to confirm the presence of B, N, Al, and O elements on the sample surface. Then, a high-resolution scan was performed, acquiring the Al2p, B1s, N1s, and O1s spectral regions respectively. Calibration was performed using the C1s peak at 284.8 eV. After calibration, peak fitting was performed on the Al2p and B1s spectral peaks. If the Al2p binding energy peak is within the range of 73.5 eV to 74.8 eV, it indicates the presence of aluminum bound to nitrogen in the tested region; if the B1s binding energy peak is within the range of 190.0 eV to 191.5 eV, it indicates the presence of a BN bond structure in the tested region.

[0115] To further confirm that the bridging phase is located in the contact region of adjacent plate-like hexagonal boron nitride powders, an energy dispersive spectroscopy (EDS) scan can be performed on a selected area with obvious plate-like contact under a scanning electron microscope. If aluminum is mainly distributed in the contact region of adjacent plate-like hexagonal boron nitride powders, rather than forming a large number of isolated particles, this area can be combined with the X-ray photoelectron spectroscopy (XPS) results to confirm the location of the bridging phase.

[0116] Example 8

[0117] This embodiment is used to illustrate the method for confirming the orientation structure.

[0118] The sintered high thermal conductivity hexagonal boron nitride ceramic material was cut and polished along a direction perpendicular to the molding surface to obtain a cross-sectional sample. The cross-sectional sample was observed using a scanning electron microscope, and images were acquired from areas where the flaky hexagonal boron nitride powder flakes could be clearly identified. At least five fields of view were selected for each sample, and at least twenty flaky hexagonal boron nitride particles were counted in each field of view.

[0119] During the statistical analysis, the extension direction of the ceramic material's molded surface is used as the reference direction, and the extension direction of the flake-shaped hexagonal boron nitride powder is used as the measurement direction. The angle between the two is measured. If at least 80% of the flake-shaped hexagonal boron nitride powder flakes have an angle of no more than 20° with the ceramic material's molded surface, then the ceramic material is considered to meet the structural requirement of the flake-shaped hexagonal boron nitride powder being oriented along the molded surface direction.

[0120] Example 9

[0121] This embodiment is used to illustrate the differences from existing preparation methods.

[0122] In existing methods for preparing hexagonal boron nitride ceramics, one approach typically involves directly mixing hexagonal boron nitride powder with oxide additives and then hot-pressing and sintering, with the focus on promoting densification through the additives. Another approach involves forming a silica coating layer on the surface of the hexagonal boron nitride powder before sintering. Yet another approach involves forming an oriented structure through 3D printing or other molding methods, followed by hot-pressing and sintering to further rearrange the grains.

[0123] The implementation method of this application differs from the above-described scheme. This application first forms a dual-particle-size plate-shaped powder gradation using first and second plate-shaped hexagonal boron nitride powders. Then, an aluminum-boron interface precursor is formed on the surface of the plate-shaped hexagonal boron nitride powders using an aluminum source and a boron source. Subsequently, an oriented blank is formed by doctor blade casting, and the aluminum-boron interface precursor is transformed into an initial nitrided interface layer during pre-nitriding treatment. Finally, oscillating hot pressing sintering is used to form a nitrided bridging phase in the contact region between adjacent plate-shaped hexagonal boron nitride powders.

[0124] In this application, yttrium oxide and calcium fluoride are present as sintering auxiliary components, but this is not the only means by which this application differs from the prior art. Even though the prior art has disclosed rare earth oxide sintering or oscillating pressure sintering, it is still not possible to directly obtain the preparation path of this application, which consists of dual-particle-size lamellar hexagonal boron nitride powder, aluminum-boron interface precursor, oriented blank, pre-nitrided initial nitrided interface layer, and nitrided bridging phase.

[0125] Optional verification example

[0126] To verify the fit between the features in the technical solution of this application, the following verification example can be set up. The verification example is not a necessary limitation of this application, but is only used to illustrate that the technical solution of this application can be verified by conventional material testing methods.

[0127] Verification Example 1 uses a single-size lamellar hexagonal boron nitride powder, but does not use the particle size distribution of the first and second lamellar hexagonal boron nitride powders. The remaining steps are the same as in Example 1. This verification example allows observation of the interlayer gaps formed by the single-size powder in the green body.

[0128] In Verification Example 2, no aluminum-boron interface precursor was added; only yttrium oxide and calcium fluoride were added, and the remaining steps were the same as in Example 1. This verification example allows observation of whether an interface structure containing Al-N bonds is formed in the contact region of adjacent plate-like hexagonal boron nitride powders.

[0129] In Verification Example 3, no pre-nitriding treatment was performed. The ceramic green body was degreased and then directly subjected to hot pressing and sintering, with the remaining steps being the same as in Example 1. This verification example allows observation of the retention and transformation of the aluminum-boron interface precursor on the surface of the lamellar hexagonal boron nitride powder without pre-nitriding treatment.

[0130] Verification Example 4 employs constant-pressure hot-pressing sintering without superimposed oscillation pressure; the remaining steps are the same as in Example 1. This verification example allows observation of the adhesion degree of the plate-like hexagonal boron nitride powder in the contact area and the distribution of the nitride bridging phase.

[0131] In the above verification examples, the same SEM cross-sectional observation, XPS detection, relative density test, and thermal conductivity test methods can be used for comparison. Thermal conductivity can be tested by determining the thermal diffusivity using the laser flare method, and then calculating the thermal conductivity by combining specific heat capacity and density. The calculation formula is as follows:

[0132] ;

[0133] In the formula, Thermal conductivity, expressed in W / (m·K); The thermal diffusivity is expressed in m² / s. Specific heat capacity, expressed in J / (kg·K); Density is expressed in kg / m³. The direction of thermal conductivity testing should be clearly defined: thermal conductivity measured along the molded surface of the ceramic material is in-plane thermal conductivity, while thermal conductivity measured perpendicular to the molded surface is thickness-direction thermal conductivity.

[0134] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high thermal conductivity hexagonal boron nitride ceramic material, characterized in that, include: 90.0 to 97.5 parts of hexagonal boron nitride powder; 1.0 to 5.0 parts of aluminum-boron interface precursor; Rare earth oxide additives: 0.2 to 1.5 parts; Fluoride flux, 0.1 to 0.8 parts; Unavoidable impurities shall not exceed 0.5 parts; The hexagonal boron nitride powder includes a first plate-shaped hexagonal boron nitride powder and a second plate-shaped hexagonal boron nitride powder. The D50 particle size of the first plate-shaped hexagonal boron nitride powder is 8 μm to 25 μm, and the D50 particle size of the second plate-shaped hexagonal boron nitride powder is 0.5 μm to 3 μm. The mass ratio of the first plate-shaped hexagonal boron nitride powder to the second plate-shaped hexagonal boron nitride powder is 65:35 to 85:

15. The aluminum-boron interface precursor is formed by the hydrolysis and condensation of aluminum and boron sources and is distributed on the surface of the first and second plate-shaped hexagonal boron nitride powders. In the high thermal conductivity hexagonal boron nitride ceramic material, the first plate-shaped hexagonal boron nitride powder and the second plate-shaped hexagonal boron nitride powder are oriented and arranged along the forming surface of the ceramic material, and the angle between the plate-shaped hexagonal boron nitride powder and the forming surface of the ceramic material is not greater than 20°. The contact region of adjacent plate-like hexagonal boron nitride powders forms a nitride-bridged phase. The nitride-bridged phase is detected by X-ray photoelectron spectroscopy, which shows the Al2p binding energy peak corresponding to the Al-N bond and the B1s binding energy peak corresponding to the BN bond. The Al2p binding energy peak is located between 73.5 eV and 74.8 eV, and the B1s binding energy peak is located between 190.0 eV and 191.5 eV.

2. A method for preparing a high thermal conductivity hexagonal boron nitride ceramic material is applicable to the high thermal conductivity hexagonal boron nitride ceramic material according to claim 1, characterized in that, Includes the following steps: S1: Weigh 90.0 to 97.5 parts of hexagonal boron nitride powder, 0.2 to 1.5 parts of rare earth oxide additives and 0.1 to 0.8 parts of fluoride flux according to the mass ratio, and weigh aluminum source and boron source according to the amount of 1.0 to 5.0 parts of aluminum-boron interface precursor. The hexagonal boron nitride powder includes a first plate-shaped hexagonal boron nitride powder and a second plate-shaped hexagonal boron nitride powder. The D50 particle size of the first plate-shaped hexagonal boron nitride powder is 8 μm to 25 μm, and the D50 particle size of the second plate-shaped hexagonal boron nitride powder is 0.5 μm to 3 μm. The mass ratio of the first plate-shaped hexagonal boron nitride powder to the second plate-shaped hexagonal boron nitride powder is 65:35 to 85:

15. S2: The first and second sheet-like hexagonal boron nitride powders are dried to obtain mixed hexagonal boron nitride powders; S3: Mix aluminum source, boron source and organic solvent to form an interface treatment liquid. Add the mixed hexagonal boron nitride powder to the interface treatment liquid for dispersion treatment, so that the aluminum-boron interface precursor formed by the hydrolysis and condensation of aluminum source and boron source is attached to the surface of the first plate-shaped hexagonal boron nitride powder and the second plate-shaped hexagonal boron nitride powder. After drying, modified hexagonal boron nitride powder is obtained. S4: Modified hexagonal boron nitride powder, rare earth oxide additives and fluoride flux are mixed and ball-milled to obtain sintered mixed powder; S5: The sintered mixed powder is made into a slurry and then cast into oriented blanks using a scraper, so that the first and second sheet-like hexagonal boron nitride powders are arranged along the extension direction of the oriented blanks. S6: Multiple oriented blanks are stacked in the same extension direction and pressed into a ceramic blank; S7: The ceramic green body is pre-nitrided in a nitrogen-containing atmosphere. After the pre-nitriding treatment, the initial nitrided interface layer formed by the aluminum-boron interface precursor is located on the surface of the first plate-shaped hexagonal boron nitride powder and the second plate-shaped hexagonal boron nitride powder. S8: The pre-nitrided ceramic blank is subjected to oscillating hot pressing sintering. After oscillating hot pressing sintering, the initial nitrided interface layer is transformed into a nitrided bridging phase located in the contact area of ​​adjacent plate-like hexagonal boron nitride powder, thus obtaining a high thermal conductivity hexagonal boron nitride ceramic material.

3. The method for preparing a high thermal conductivity hexagonal boron nitride ceramic material according to claim 2, characterized in that, The first plate-shaped hexagonal boron nitride powder has a D50 particle size of 10 μm to 18 μm, the second plate-shaped hexagonal boron nitride powder has a D50 particle size of 0.8 μm to 2.0 μm, and the mass ratio of the first plate-shaped hexagonal boron nitride powder to the second plate-shaped hexagonal boron nitride powder is 70:30 to 80:

20.

4. The method for preparing a high thermal conductivity hexagonal boron nitride ceramic material according to claim 3, characterized in that, The aluminum source is aluminum isopropoxide, and the boron source is triethyl borate. The molar ratio of aluminum in the aluminum source to boron in the boron source is 1:1.5 to 1:3.

5.

5. The method for preparing a high thermal conductivity hexagonal boron nitride ceramic material according to claim 4, characterized in that, The rare earth oxide additive is yttrium oxide, and the fluoride flux is calcium fluoride, with a mass ratio of yttrium oxide to calcium fluoride of 2:1 to 6:

1.

6. The method for preparing a high thermal conductivity hexagonal boron nitride ceramic material according to claim 5, characterized in that, In step S2, the first sheet-like hexagonal boron nitride powder and the second sheet-like hexagonal boron nitride powder are dried at 80°C to 120°C for 2 hours to 6 hours, and the moisture content of the dried mixed hexagonal boron nitride powder is 0.05% to 0.20%.

7. The method for preparing a high thermal conductivity hexagonal boron nitride ceramic material according to claim 6, characterized in that, In step S3, the interface treatment solution is made of aluminum isopropoxide, triethyl borate, anhydrous ethanol and deionized water, and the mass ratio of aluminum isopropoxide, triethyl borate, anhydrous ethanol and deionized water is 1:1.2:20:0.3 to 1:2.8:45:0.

8. After mixing hexagonal boron nitride powder and adding it to the interface treatment solution, the mixture is stirred at 30℃ to 55℃ for 1h to 4h and then vacuum dried at 40℃ to 70℃ for 4h to 10h to obtain modified hexagonal boron nitride powder.

8. The method for preparing a high thermal conductivity hexagonal boron nitride ceramic material according to claim 7, characterized in that, In step S4, the modified hexagonal boron nitride powder, rare earth oxide additives, and fluoride flux are ball-milled in anhydrous ethanol. The ball milling media is silicon nitride balls, the ball-to-material mass ratio is 2:1 to 5:1, the ball milling speed is 120 r / min to 250 r / min, and the ball milling time is 4 h to 8 h. After ball milling, the powder is dried and sieved to obtain sintered mixed powder.

9. The method for preparing a high thermal conductivity hexagonal boron nitride ceramic material according to claim 8, characterized in that, In steps S5 and S6, the sintered mixed powder is mixed with polyvinyl butyral, dibutyl phthalate and anhydrous ethanol to form a slurry. The slurry is then cast by a scraper to form an oriented blank, with a scraper gap of 100 μm to 500 μm. After drying, the oriented blanks are stacked in the same extension direction and pre-pressed at 10MPa to 30MPa to obtain a ceramic blank.

10. The method for preparing a high thermal conductivity hexagonal boron nitride ceramic material according to claim 9, characterized in that, In steps S7 and S8, the ceramic green body is pre-nitrided in a nitrogen atmosphere by heating to 900°C to 1200°C at a rate of 2°C / min to 5°C / min and holding for 1h to 3h. After pre-nitriding treatment, the ceramic green body is subjected to oscillating hot pressing sintering in a nitrogen atmosphere or an argon-nitrogen mixed atmosphere. The sintering temperature is 1750℃ to 1900℃, the base pressure is 20MPa to 35MPa, and an oscillation pressure of 2MPa to 8MPa is superimposed on the base pressure. The oscillation frequency is 0.1Hz to 2Hz, and the holding time is 1h to 3h. After sintering, it is annealed in a nitrogen atmosphere at 1400℃ to 1600℃ for 2h to 6h.

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