High aspect ratio hexagonal boron nitride and method of making same

Abstract

The application provides a high aspect ratio hexagonal boron nitride powder and a preparation method thereof. The method comprises the following steps: taking a boron source, a nitrogen source and water to prepare a solid-liquid mixed slurry; performing heating and heat preservation and heating and drying treatment on the slurry to obtain a nitrogen-boron intermediate product; briquetting the nitrogen-boron intermediate product, performing low-temperature sintering, crushing and screening the product to obtain a hexagonal boron nitride intermediate product; mixing the hexagonal boron nitride intermediate product with carbon powder, briquetting and then performing high-temperature sintering, crushing the product to obtain a carbon powder and boron nitride mixture; placing the mixture in air to perform heating and oxidation decarburization, and then performing acid pickling, filtration, drying, dispersion and screening to obtain the hexagonal boron nitride powder. The aspect ratio of the hexagonal boron nitride powder is greater than 30, and the particle size D50 is 4.5-7.5 μm. The method can effectively reduce the thickening degree of boron nitride sheet crystals, improve the aspect ratio, ensure the obtained boron nitride powder with a high aspect ratio, and improve the thermal conductivity of the boron nitride powder by first performing low-temperature sintering and then adding carbon powder for high-temperature sintering.

Description

Technical Field

[0001] This invention relates to the field of boron nitride technology, specifically to a high aspect ratio hexagonal boron nitride and its preparation method. Background Technology

[0002] Hexagonal boron nitride (BON) is an inorganic non-metallic material with a hexagonal crystal structure, exhibiting layered slip properties similar to graphite, and is commonly known as white graphite. BON is resistant to common acids, alkalis, and organic solvents at room temperature and shows good stability in air below 900°C. As a wide-bandgap insulator, hexagonal BON can prevent short circuits, making it suitable for high-voltage, high-frequency devices. BON has a higher thermal conductivity than most insulating ceramic materials such as alumina, and is widely used in chip heat dissipation, CPU interface heat dissipation, and electronic packaging.

[0003] The thermal conductivity of hexagonal boron nitride (BON) lamellars is closely related to the ratio of their lamellar diameter to thickness (aspect-to-thickness ratio). When the diameter and crystallinity of the BON lamellars are similar, thinner lamellars and a higher aspect ratio result in better thermal conductivity. Currently, methods for improving the aspect ratio of hexagonal BON include exfoliation, which uses physical processes such as ball milling and solvothermal treatment, along with the addition of acids, alkalis, or metal compounds, to effectively exfoliate the BON lamellars and thin them. However, exfoliation is inefficient and costly; the chemical reagents used pose environmental problems, and post-processing costs are high. Furthermore, exfoliation introduces numerous surface defects into the BON material and inevitably reduces the lamellar size of the BON product. This reduction in BON size due to exfoliation leads to a significant decrease in its tap density and filling performance. In addition, methods for improving the aspect ratio of hexagonal BON by synthesizing BON at lower synthesis temperatures have also been disclosed. However, when the calcination temperature is lowered, the hexagonal boron nitride produced by this method can usually only reach the submicron level. Moreover, compared with boron nitride obtained by high-temperature calcination, its crystallinity will decrease and its oxygen content will increase significantly. These factors are not conducive to improving the thermal conductivity and filling performance of hexagonal boron nitride.

[0004] Therefore, developing a preparation process that can effectively produce micron-sized hexagonal boron nitride powder with a high aspect ratio remains a key focus and challenge in this field. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a high aspect ratio hexagonal boron nitride powder and its preparation method. This method employs a two-step sintering process. First, low-temperature sintering allows for more thorough nitriding of the boron source in the presence of a nitrogen source, removing most of the oxygen atoms from the boron source from the reaction system. This significantly reduces the amount of water generated during the second-step high-temperature sintering, mitigating the adverse effects of released water vapor on the product and equipment. The second step involves high-temperature sintering, with carbon powder added to the boron nitride intermediate for a high-temperature reaction. This effectively controls and ensures that the boron nitride flake size reaches the micrometer level. Simultaneously, the carbon powder physically separates the boron nitride in this high-temperature reaction system, effectively reducing the thickness of the boron nitride flakes and thus significantly improving the aspect ratio. This ensures the acquisition of hexagonal boron nitride powder with a high aspect ratio, ultimately enhancing the thermal conductivity of the hexagonal boron nitride powder.

[0006] The technical solution of the present invention is as follows:

[0007] A high aspect ratio hexagonal boron nitride powder, wherein the aspect ratio of the hexagonal boron nitride powder is >30 and the particle size D50 is 4.5~7.5μm.

[0008] Furthermore, the aspect ratio of the hexagonal boron nitride powder is 31~60.

[0009] Furthermore, the hexagonal boron nitride powder also satisfies one or more of the following conditions:

[0010] The tap density is 0.15~0.4 g / cm³. 3 ;

[0011] Specific surface area is 3~12m² 2 / g;

[0012] Boron oxide content ≤0.1%;

[0013] D99≤35μm;

[0014] Graphitization index ≤ 2.

[0015] A method for preparing high aspect ratio hexagonal boron nitride powder includes the following steps:

[0016] S1, take boron source, nitrogen source and water to make solid-liquid mixed slurry;

[0017] S2, the solid-liquid mixture is subjected to heating and heat preservation treatment and heating and drying treatment in sequence to obtain nitrogen-boron intermediate product;

[0018] S3, the nitrogen-boron intermediate product is compressed into blocks and then sintered at low temperature. The low-temperature sintered product is crushed and sieved to obtain hexagonal boron nitride intermediate product.

[0019] S4, the hexagonal boron nitride intermediate product is mixed with carbon powder, pressed into blocks and sintered at high temperature, and the high-temperature sintered product is crushed to obtain a mixture of carbon powder and boron nitride.

[0020] S5, the mixture of carbon powder and boron nitride is heated in air for oxidation and decarburization, and then acid washed, filtered, dried, dispersed and sieved to obtain hexagonal boron nitride powder.

[0021] Furthermore, the boron source is one or more of orthoboric acid, metaboric acid, and borax;

[0022] The nitrogen source is melamine and / or morpholine guanidine hydrochloride.

[0023] Furthermore, the total weight ratio of the boron source and nitrogen source to the weight of water is 1:0.5~2;

[0024] The weight ratio of the boron source to the nitrogen source is 1.5 to 2:1.

[0025] Furthermore, the nitrogen source is melamine and morpholine guanidine hydrochloride, and the weight ratio of melamine to morpholine guanidine hydrochloride is 3~9:1.

[0026] Further, in step S4, the mass ratio of the hexagonal boron nitride intermediate to the carbon powder is 1:0.05~0.1.

[0027] Furthermore, in step S2, a heating and heat preservation treatment is performed under sealed conditions. The temperature of the heating and heat preservation treatment is 95~140℃, and the heat preservation time is 6~24h.

[0028] Under the conditions of a hot-drying process, the temperature of the hot-drying process is 100~200℃, and the drying time is 6~24h.

[0029] Further, in step S3, the low-temperature sintering is carried out in a non-oxidizing atmosphere, the low-temperature sintering temperature is 900~1200℃, and the sintering time is 6~12h;

[0030] And / or,

[0031] In step S4, the high-temperature sintering is carried out in a non-oxidizing atmosphere at a temperature of 1800~2100℃ for 4~10h.

[0032] Furthermore, in step S5, the temperature of the oxidation decarburization is 600~800℃, and the decarburization time is 3~12h.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] 1. The method for preparing high aspect ratio hexagonal boron nitride powder of the present invention adopts a two-step sintering method. First, low-temperature sintering allows the boron source to be fully nitrided in the presence of a nitrogen source, and most of the oxygen atoms in the boron source are discharged from the reaction system, thereby significantly reducing the amount of water generated during the second high-temperature sintering process and reducing the adverse effects of the water vapor released during the reaction on the product and equipment. The second step adopts high-temperature sintering, and carbon powder is added to the boron nitride intermediate product for high-temperature reaction. This can effectively control and ensure that the boron nitride flake size reaches the micron level. At the same time, the carbon powder plays a physical separation role for boron nitride in this high-temperature reaction system, which can effectively reduce the degree of thickening of the hexagonal boron nitride powder flakes, thereby effectively improving the aspect ratio of the hexagonal boron nitride powder flakes and ensuring that a high aspect ratio hexagonal boron nitride powder is obtained. Ultimately, this effectively improves the thermal conductivity of the hexagonal boron nitride powder. Moreover, the hexagonal boron nitride powder obtained by this method has excellent surface morphology, which is conducive to filling and making thermally conductive fillers.

[0035] 2. By controlling the temperature and time of low-temperature sintering and high-temperature sintering, the proportion and timing of carbon powder addition, as well as the selection and amount of raw materials, it is possible to effectively ensure that the boron nitride flake size reaches 4.5 micrometers or more and the aspect ratio reaches 30 or more, thereby obtaining hexagonal boron nitride powder with excellent filling performance and thermal conductivity.

[0036] 3. The high aspect ratio hexagonal boron nitride powder provided by this invention has a particle size D50 of 4.5~7.5μm and D99≤35μm; a high aspect ratio, >30, concentrated in the range of 31~60; and a tap density of 0.15~0.4g / cm³. 3 The lamellar crystals have a clean and smooth surface with a specific surface area of ​​3~12m². 2 / g; high purity, boron oxide content ≤0.1%; high crystallinity, graphitization index ≤2, this hexagonal boron nitride powder has good surface morphology and excellent filling and thermal conductivity. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of the process for preparing high aspect ratio hexagonal boron nitride powder.

[0039] Figure 2 SEM image (200x) of the hexagonal boron nitride powder prepared in Example 1.

[0040] Figure 3 The image shows a SEM image (5000x magnification) of the hexagonal boron nitride powder prepared in Example 1.

[0041] Figure 4 The image shows the XRD pattern of the hexagonal boron nitride powder prepared in Example 1.

[0042] Figure 5 SEM image (5000x) of the hexagonal boron nitride powder prepared in Comparative Example 1, Example 1.

[0043] Figure 6 The aspect ratio distribution of the hexagonal boron nitride powder prepared in Example 1 is shown.

[0044] Figure 7 The aspect ratio distribution of the hexagonal boron nitride powder prepared in Comparative Example 1 is shown.

[0045] Figure 8 SEM image (200x) of the hexagonal boron nitride powder prepared in Comparative Example 2. Detailed Implementation

[0046] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0047] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0048] like Figure 1 As shown, a method for preparing high aspect ratio hexagonal boron nitride powder includes the following steps:

[0049] S1, take the raw materials boron source, nitrogen source and water in proportion, mix them, and then grind them in a ball mill to make a solid-liquid mixture slurry.

[0050] S2, the prepared solid-liquid mixture is subjected to heating and heat preservation treatment and heating and drying treatment in sequence to obtain nitrogen-boron intermediate product.

[0051] Preferably, the solid-liquid mixture is placed in a sealed container and heated and kept at a constant temperature under sealed conditions. After the heat preservation treatment, the sealed container is opened, and the mixture is heated and dried under open conditions. Heating and keeping the mixture in a sealed state effectively ensures that the reaction proceeds fully in a hydrothermal environment and prevents moisture loss from adversely affecting the reaction.

[0052] S3, the obtained nitrogen-boron intermediate product is briquetting, then sintered at low temperature, and then the sintered product is crushed and sieved to obtain hexagonal boron nitride intermediate product.

[0053] S4. The hexagonal boron nitride intermediate product obtained by low-temperature sintering is mixed with carbon powder in a certain proportion and then pressed into briquettes. After pressing, it is sintered at high temperature. Then, the high-temperature sintered product is crushed to obtain a mixture of carbon powder and boron nitride. Adding carbon powder to the hexagonal boron nitride intermediate product and sintering it at high temperature can physically separate the boron nitride during the high-temperature sintering process, effectively reducing the thickness of the boron nitride lamellars, improving the aspect ratio of the boron nitride lamellars, and thus improving the thermal conductivity of the boron nitride lamellars.

[0054] S5. The prepared carbon powder and boron nitride mixture are heated in air for oxidation and decarburization. After decarburization, the mixture is acid washed, filtered, dried, dispersed, and sieved to obtain the desired hexagonal boron nitride powder.

[0055] The preferred boron source is one or more of orthoboric acid, metaboric acid, and borax.

[0056] The nitrogen source is preferably melamine and / or morpholine guanidine hydrochloride; more preferably, the nitrogen source is melamine and morpholine guanidine hydrochloride.

[0057] Preferably, the ratio of the total weight of the boron source and nitrogen source to the weight of water is controlled to be 1:0.5~2.

[0058] Furthermore, the weight ratio of boron source to nitrogen source is controlled to be 1.5 to 2:1.

[0059] The preferred nitrogen sources are melamine and morpholine guanidine hydrochloride, with the weight ratio of melamine to morpholine guanidine hydrochloride controlled at 3~9:1. This effectively ensures the acquisition of the desired hexagonal boron nitride powder, with high utilization of raw materials and reagents and low loss.

[0060] Further, in step S2, the solid-liquid mixture is placed in a sealed container and heated and kept warm under sealed conditions, with the holding temperature controlled at 95~140℃ and the holding time at 6~24h; then it is heated and dried under open conditions, with the heating and drying temperature controlled at 100~200℃ and the drying time at 6~24h, to obtain the desired nitrogen-boron intermediate product.

[0061] In step S3, low-temperature sintering is preferably performed in a non-oxidizing atmosphere, with the sintering temperature controlled within the range of 900~1200℃ and the sintering time within the range of 6~12h. After sintering, the low-temperature sintered product is crushed and sieved to obtain hexagonal boron nitride intermediate product.

[0062] In step S4, a high-temperature sintering treatment is performed in a non-oxidizing atmosphere, with the temperature controlled within the range of 1800~2100℃ and the sintering time within the range of 4~10h.

[0063] The first step employs low-temperature sintering, controlling the temperature and time within the aforementioned range. This allows for thorough nitriding of the boron source in the presence of a nitrogen source, and removes most of the oxygen atoms from the boron source from the reaction system. This significantly reduces the amount of water generated during the second step's high-temperature sintering in the graphite crucible, thereby minimizing the adverse effects of water vapor released during high-temperature sintering on the product and the graphite crucible. Controlling the temperature and time during the second step's high-temperature sintering within the aforementioned range effectively ensures that the obtained boron nitride crystals reach a size of 4.5 micrometers or larger.

[0064] Furthermore, in step S4, the amount of carbon powder added needs to be controlled, preferably with the mass ratio of hexagonal boron nitride intermediate product to carbon powder in the range of 1:0.05~0.1. This allows for better control of the thickness of the boron nitride, ensuring that boron nitride wafers with an aspect ratio of 30 or higher are subsequently obtained. If too little carbon powder is added, the aspect ratio of the boron nitride wafers cannot be guaranteed to be above 30; if too much carbon powder is added, it will reduce the density of the reaction powder, leading to a reduction in the furnace charge and an increase in production costs.

[0065] In step S5, the mixture of carbon powder and boron nitride is heated in air for oxidative decarburization. Preferably, the heating temperature is controlled within the range of 600~800℃, and the decarburization time is within the range of 3~12h. Within this temperature and time range, complete decarburization / carbon removal can be effectively ensured, avoiding carbon residue from affecting the quality of the hexagonal boron nitride powder product.

[0066] After decarburization, the product undergoes sequential acid washing, filtration, drying, dispersion, and sieving to obtain the desired hexagonal boron nitride powder. The acid washing process preferably uses sulfuric acid, hydrochloric acid, or nitric acid solution under heating conditions. The acid washing temperature is controlled at 60–95°C, and the acid washing time is controlled at 1–3 hours. This effectively removes oxides (such as boron oxide) and impurities from the hexagonal boron nitride product, ensuring the subsequent acquisition of a powder with high purity and a clean surface.

[0067] Testing revealed that the hexagonal boron nitride powder prepared by this method had a particle size D50 of 4.5–7.5 μm and a particle size D99 ≤ 35 μm; the aspect ratio was greater than 30, concentrated in the range of 31–60; and the tap density was 0.15–0.4 g / cm³. 3 Within the range; specific surface area is 3~12m² 2 Within the range of / g; boron oxide content ≤0.1%; graphitization index ≤2.

[0068] Example 1

[0069] Weigh orthoboric acid, melamine, morpholine guanidine hydrochloride and pure water according to a mass ratio of 2:0.9:0.1:1.5, and mix them by ball milling until uniform to obtain a solid-liquid mixture slurry.

[0070] The solid-liquid mixture was transferred to a sealed container and heated to 95°C under sealed conditions, and then kept at 95°C for 24 hours. After the heat treatment, the lid of the sealed container was opened, and the mixture was heated to 100°C under open conditions and then dried for 24 hours to obtain the nitrogen-boron intermediate.

[0071] The nitrogen-boron intermediate product was briquetting, and then subjected to a first sintering (i.e., low-temperature sintering) in a nitrogen atmosphere. The first sintering was controlled at 900℃ for 12 hours. The sintered product was crushed and sieved to obtain hexagonal boron nitride intermediate product.

[0072] The hexagonal boron nitride intermediate product and carbon powder were mixed evenly at a mass ratio of 1:0.1 and then briquetting. The briquetting carbon powder and the hexagonal boron nitride intermediate product were then subjected to a second sintering treatment (i.e., high-temperature sintering) in a nitrogen atmosphere. The second sintering was controlled at 2100℃ for 4 hours. After the second sintering, a mixture of carbon powder and boron nitride was obtained.

[0073] The carbon powder and boron nitride mixture obtained from the second sintering were crushed and sieved, and then placed in air and heated at 700℃ for 10 hours for decarburization / carbon removal.

[0074] The decarbonized product was acid-washed with sulfuric acid solution at 70°C for 2 hours, and then subjected to filtration, drying, dispersion and sieving to obtain hexagonal boron nitride powder.

[0075] The particle size, aspect ratio, tap density, specific surface area, graphitization index, boron oxide content, viscosity, and thermal conductivity of the prepared hexagonal boron nitride powder are shown in Table 1. The hexagonal boron nitride powder was examined by scanning electron microscopy, and the resulting SEM images are shown below. Figure 2 and Figure 3 As shown; the XRD pattern obtained by X-ray diffraction testing is as follows. Figure 4 As shown; the diameter-to-thickness ratio distribution diagram is as follows. Figure 6 As shown.

[0076] Example 2

[0077] Weigh boric acid, melamine, morpholine guanidine hydrochloride and pure water in a mass ratio of 1.9:0.9:0.2:1.8, and mix them by ball milling until homogeneous to obtain a solid-liquid mixture slurry.

[0078] The solid-liquid mixture was transferred to a sealed container and heated to 140°C under sealed conditions, and then kept at 140°C for 6 hours. After the heat treatment, the lid of the sealed container was opened, and the mixture was heated to 200°C under open conditions and then dried for 6 hours to obtain the nitrogen-boron intermediate.

[0079] The nitrogen-boron intermediate product was briquetting, and then subjected to a first sintering (i.e., low-temperature sintering) in a nitrogen atmosphere. The first sintering was controlled at 1000℃ for 10 hours. The sintered product was crushed and sieved to obtain hexagonal boron nitride intermediate product.

[0080] The hexagonal boron nitride intermediate product and carbon powder were mixed evenly at a mass ratio of 1:0.095 and then briquetting. The briquetting carbon powder and the hexagonal boron nitride intermediate product were then subjected to a second sintering treatment (i.e., high-temperature sintering) in a nitrogen atmosphere. The second sintering was controlled at 2000℃ for 6 hours. After the second sintering, a mixture of carbon powder and boron nitride was obtained.

[0081] The carbon powder and boron nitride mixture obtained from the second sintering were crushed and sieved, and then placed in air and heated at 600℃ for 12 hours for decarburization / carbon removal.

[0082] The decarbonized product was acid-washed with nitric acid solution at 60°C for 3 hours, and then subjected to filtration, drying, dispersion and sieving to obtain hexagonal boron nitride powder.

[0083] The particle size, aspect ratio, tap density, specific surface area, graphitization index, boron oxide content, viscosity and thermal conductivity of the prepared hexagonal boron nitride powder are shown in Table 1.

[0084] Example 3

[0085] Weigh boric acid, melamine, morpholine guanidine hydrochloride and pure water according to the mass ratio of 1.9:0.87:0.23:2, and mix them by ball milling until uniform to obtain a solid-liquid mixture slurry.

[0086] The solid-liquid mixture was transferred to a sealed container and heated to 120°C under sealed conditions, and then kept at 120°C for 7 hours. After the heat treatment, the lid of the sealed container was opened, and the mixture was heated to 120°C under open conditions and then dried for 12 hours to obtain the nitrogen-boron intermediate product.

[0087] The nitrogen-boron intermediate product was briquetting, and then subjected to a first sintering (i.e., low-temperature sintering) in a nitrogen atmosphere. The first sintering was controlled at 1000℃ for 10 hours. The sintered product was crushed and sieved to obtain hexagonal boron nitride intermediate product.

[0088] The hexagonal boron nitride intermediate product and carbon powder were mixed evenly at a mass ratio of 1:0.09 and then briquetting. The briquetting carbon powder and the hexagonal boron nitride intermediate product were then subjected to a second sintering treatment (i.e., high-temperature sintering) in a nitrogen atmosphere. The second sintering was controlled at 2000℃ for 6 hours. After the second sintering, a mixture of carbon powder and boron nitride was obtained.

[0089] The carbon powder and boron nitride mixture obtained from the second sintering were crushed and sieved, and then placed in air and heated at 800℃ for 3 hours for decarburization / carbon removal.

[0090] The decarbonized product was acid-washed with hydrochloric acid solution at 95°C for 1 hour, and then subjected to filtration, drying, dispersion and sieving to obtain hexagonal boron nitride powder.

[0091] The particle size, aspect ratio, tap density, specific surface area, graphitization index, boron oxide content, viscosity and thermal conductivity of the prepared hexagonal boron nitride powder are shown in Table 1.

[0092] Example 4

[0093] Weigh boric acid, borax, melamine, morpholine guanidine hydrochloride and pure water according to the mass ratio of 1.78:0.02:0.9:0.3:1.8, and mix them by ball milling until uniform to obtain a solid-liquid mixture slurry.

[0094] The solid-liquid mixture was transferred to a sealed container and heated to 120°C under sealed conditions, and then kept at 120°C for 7 hours. After the heat treatment, the lid of the sealed container was opened, and the mixture was heated to 120°C under open conditions and then dried for 12 hours to obtain the nitrogen-boron intermediate product.

[0095] The nitrogen-boron intermediate product was briquetting, and then subjected to a first sintering (i.e., low-temperature sintering) in a nitrogen atmosphere. The first sintering was controlled at 1000℃ for 10 hours. The sintered product was crushed and sieved to obtain hexagonal boron nitride intermediate product.

[0096] Hexagonal boron nitride intermediate and carbon powder were mixed evenly at a mass ratio of 1:0.085 and then briquetting. The briquetting carbon powder and hexagonal boron nitride intermediate were then subjected to a second sintering (i.e., high-temperature sintering) in a nitrogen atmosphere. The second sintering was controlled at 2000℃ for 6 hours. After the second sintering, a mixture of carbon powder and boron nitride was obtained.

[0097] The carbon powder and boron nitride mixture obtained from the second sintering were crushed and sieved, and then placed in air and heated at 700℃ for 10 hours for decarburization / carbon removal.

[0098] The decarbonized product was acid-washed with hydrochloric acid solution at 70°C for 2 hours, and then subjected to filtration, drying, dispersion and sieving to obtain hexagonal boron nitride powder.

[0099] The particle size, aspect ratio, tap density, specific surface area, graphitization index, boron oxide content, viscosity and thermal conductivity of the prepared hexagonal boron nitride powder are shown in Table 1.

[0100] Example 5

[0101] Weigh out metaboric acid, melamine, morpholine guanidine hydrochloride and pure water in a mass ratio of 1.8:0.9:0.3:6, and mix them by ball milling until homogeneous to obtain a solid-liquid mixture slurry.

[0102] The solid-liquid mixture was transferred to a sealed container and heated to 120°C under sealed conditions, and then kept at 120°C for 7 hours. After the heat treatment, the lid of the sealed container was opened, and the mixture was heated to 120°C under open conditions and then dried for 12 hours to obtain the nitrogen-boron intermediate product.

[0103] The nitrogen-boron intermediate product was briquetting, and then subjected to a first sintering (i.e., low-temperature sintering) in a nitrogen atmosphere. The first sintering was controlled at 1000℃ for 10 hours. The sintered product was crushed and sieved to obtain hexagonal boron nitride intermediate product.

[0104] The hexagonal boron nitride intermediate product and carbon powder were mixed evenly at a mass ratio of 1:0.08 and then briquetting. The briquetting carbon powder and the hexagonal boron nitride intermediate product were then subjected to a second sintering treatment (i.e., high-temperature sintering) in a nitrogen atmosphere. The second sintering was controlled at 2000℃ for 6 hours. After the second sintering, a mixture of carbon powder and boron nitride was obtained.

[0105] The carbon powder and boron nitride mixture obtained from the second sintering were crushed and sieved, and then placed in air and heated at 700℃ for 10 hours for decarburization / carbon removal.

[0106] The decarbonized product was acid-washed with hydrochloric acid solution at 70°C for 2 hours, and then subjected to filtration, drying, dispersion and sieving to obtain hexagonal boron nitride powder.

[0107] The particle size, aspect ratio, tap density, specific surface area, graphitization index, boron oxide content, viscosity and thermal conductivity of the prepared hexagonal boron nitride powder are shown in Table 1.

[0108] Example 6

[0109] Weigh orthoboric acid, melamine, morpholine guanidine hydrochloride and pure water according to a mass ratio of 2:0.8:0.2:4, and mix them by ball milling until homogeneous to obtain a solid-liquid mixture slurry.

[0110] The solid-liquid mixture was transferred to a sealed container and heated to 120°C under sealed conditions, and then kept at 120°C for 7 hours. After the heat treatment, the lid of the sealed container was opened, and the mixture was heated to 120°C under open conditions and then dried for 12 hours to obtain the nitrogen-boron intermediate product.

[0111] The nitrogen-boron intermediate product was briquetting, and then subjected to a first sintering (i.e., low-temperature sintering) in a nitrogen atmosphere. The first sintering was controlled at 1000℃ for 10 hours. The sintered product was crushed and sieved to obtain hexagonal boron nitride intermediate product.

[0112] Hexagonal boron nitride intermediate and carbon powder were mixed evenly at a mass ratio of 1:0.07 and then briquetting. The briquetting carbon powder and hexagonal boron nitride intermediate were then subjected to a second sintering (i.e., high-temperature sintering) in a nitrogen atmosphere. The second sintering was controlled at 2000℃ for 6 hours. After the second sintering, a mixture of carbon powder and boron nitride was obtained.

[0113] The carbon powder and boron nitride mixture obtained from the second sintering were crushed and sieved, and then placed in air and heated at 700℃ for 10 hours for decarburization / carbon removal.

[0114] The decarbonized product was acid-washed with hydrochloric acid solution at 70°C for 2 hours, and then subjected to filtration, drying, dispersion and sieving to obtain hexagonal boron nitride powder.

[0115] The particle size, aspect ratio, tap density, specific surface area, graphitization index, boron oxide content, viscosity and thermal conductivity of the prepared hexagonal boron nitride powder are shown in Table 1.

[0116] Example 7

[0117] Weigh orthoboric acid, melamine, morpholine guanidine hydrochloride and pure water according to a mass ratio of 2:0.8:0.2:4, and mix them by ball milling until homogeneous to obtain a solid-liquid mixture slurry.

[0118] The solid-liquid mixture was transferred to a sealed container and heated to 120°C under sealed conditions, and then kept at 120°C for 7 hours. After the heat treatment, the lid of the sealed container was opened, and the mixture was heated to 120°C under open conditions and then dried for 12 hours to obtain the nitrogen-boron intermediate product.

[0119] The nitrogen-boron intermediate product was briquetting, and then subjected to a first sintering (i.e., low-temperature sintering) in a nitrogen atmosphere. The first sintering was controlled at 1000℃ for 10 hours. The sintered product was crushed and sieved to obtain hexagonal boron nitride intermediate product.

[0120] The hexagonal boron nitride intermediate product and carbon powder were mixed evenly at a mass ratio of 1:0.06 and then briquetting. The briquetting carbon powder and the hexagonal boron nitride intermediate product were then subjected to a second sintering treatment (i.e., high-temperature sintering) in a nitrogen atmosphere. The second sintering was controlled at 1900℃ for 8 hours. After the second sintering, a mixture of carbon powder and boron nitride was obtained.

[0121] The carbon powder and boron nitride mixture obtained from the second sintering were crushed and sieved, and then placed in air and heated at 700℃ for 10 hours for decarburization / carbon removal.

[0122] The decarbonized product was acid-washed with hydrochloric acid solution at 70°C for 2 hours, and then subjected to filtration, drying, dispersion and sieving to obtain hexagonal boron nitride powder.

[0123] The particle size, aspect ratio, tap density, specific surface area, graphitization index, boron oxide content, viscosity and thermal conductivity of the prepared hexagonal boron nitride powder are shown in Table 1.

[0124] Example 8

[0125] Weigh orthoboric acid, melamine, morpholine guanidine hydrochloride and pure water according to a mass ratio of 2:0.8:0.2:4, and mix them by ball milling until homogeneous to obtain a solid-liquid mixture slurry.

[0126] The solid-liquid mixture was transferred to a sealed container and heated to 120°C under sealed conditions, and then kept at 120°C for 7 hours. After the heat treatment, the lid of the sealed container was opened, and the mixture was heated to 120°C under open conditions and then dried for 12 hours to obtain the nitrogen-boron intermediate product.

[0127] The nitrogen-boron intermediate product was briquetting, and then subjected to a first sintering (i.e., low-temperature sintering) in a nitrogen atmosphere. The first sintering was controlled at 1200℃ for 6 hours. The sintered product was crushed and sieved to obtain hexagonal boron nitride intermediate product.

[0128] The hexagonal boron nitride intermediate product and carbon powder were mixed evenly at a mass ratio of 1:0.05 and then briquetting. The briquetting carbon powder and the hexagonal boron nitride intermediate product were then subjected to a second sintering treatment (i.e., high-temperature sintering) in a nitrogen atmosphere. The second sintering was controlled at 1800℃ for 10 hours. After the second sintering, a mixture of carbon powder and boron nitride was obtained.

[0129] The carbon powder and boron nitride mixture obtained from the second sintering were crushed and sieved, and then placed in air and heated at 700℃ for 10 hours for decarburization / carbon removal.

[0130] The decarbonized product was acid-washed with hydrochloric acid solution at 70°C for 2 hours, and then subjected to filtration, drying, dispersion and sieving to obtain hexagonal boron nitride powder.

[0131] The particle size, aspect ratio, tap density, specific surface area, graphitization index, boron oxide content, viscosity and thermal conductivity of the prepared hexagonal boron nitride powder are shown in Table 1.

[0132] Comparative Example 1

[0133] Weigh orthoboric acid, melamine, morpholine guanidine hydrochloride and pure water according to a mass ratio of 2:0.8:0.2:4, and mix them by ball milling until homogeneous to obtain a solid-liquid mixture slurry.

[0134] The solid-liquid mixture was transferred to a sealed container and heated to 120°C under sealed conditions, and then kept at 120°C for 7 hours. After the heat treatment, the lid of the sealed container was opened, and the mixture was heated to 120°C under open conditions and then dried for 12 hours to obtain the nitrogen-boron intermediate product.

[0135] The nitrogen-boron intermediate was briquetting, and then subjected to a first sintering treatment in a nitrogen atmosphere. The first sintering was controlled at 1200℃ for 6 hours. The sintered product was crushed and sieved to obtain hexagonal boron nitride intermediate.

[0136] The hexagonal boron nitride intermediate was briquetting, and the briquetting intermediate was then subjected to a second sintering treatment in a nitrogen atmosphere. The second sintering was controlled at 1800℃ for 10 hours, and the sintered boron nitride product was obtained after the second sintering.

[0137] The boron nitride sintered product obtained from the second sintering was crushed and sieved, then placed in air and heated at 700℃ for 10 hours.

[0138] The treated product was acid-washed with hydrochloric acid solution at 70°C for 2 hours, and then successively filtered, dried, dispersed and sieved to obtain hexagonal boron nitride powder.

[0139] The only difference between Comparative Example 1 and Example 8 is that no carbon powder was added for mixing before the second sintering (i.e., high-temperature sintering). The rest of the operation is basically the same as in Example 8.

[0140] The particle size, aspect ratio, tap density, specific surface area, graphitization index, boron oxide content, viscosity, and thermal conductivity of the prepared hexagonal boron nitride powder are shown in Table 1. The hexagonal boron nitride powder was examined by scanning electron microscopy, and the resulting SEM images are shown below. Figure 5 As shown; the diameter-to-thickness ratio distribution diagram is as follows. Figure 7 As shown.

[0141] Comparative Example 2

[0142] Orthoboric acid, melamine, morpholine guanidine hydrochloride, and pure water were weighed according to a mass ratio of 2:0.8:0.2:4, and a certain amount of carbon powder was added. The mixture was ball-milled until homogeneous to obtain a solid-liquid slurry. Given that the yield of the product after the first sintering of the three raw materials (orthoboric acid, melamine, and morpholine guanidine hydrochloride) was 25%, carbon powder was added at a mass ratio of 1:0.0125 between the total mass of the three raw materials and the carbon powder.

[0143] The solid-liquid mixture was transferred to a sealed container and heated to 120°C under sealed conditions, and then kept at 120°C for 7 hours. After the heat treatment, the lid of the sealed container was opened, and the mixture was heated to 120°C under open conditions and then dried for 12 hours to obtain the nitrogen-boron intermediate product.

[0144] The nitrogen-boron intermediate product was briquetting, and then sintered at high temperature in a nitrogen atmosphere. The sintering was controlled at 1800℃ for 10 hours, and a mixture of carbon powder and boron nitride was obtained after sintering.

[0145] The carbon powder and boron nitride mixture obtained by sintering were crushed and sieved, and then placed in air and heated at 700℃ for 10 hours for decarburization / carbon removal.

[0146] The decarbonized product was acid-washed with hydrochloric acid solution at 70°C for 2 hours, and then subjected to filtration, drying, dispersion and sieving to obtain hexagonal boron nitride powder.

[0147] The difference between Comparative Example 2 and Example 8 is that the two sintering processes of Example 8 were changed to a single high-temperature sintering process, the carbon powder addition steps were adjusted, and the rest of the operations were basically the same as those of Example 8.

[0148] The particle size, aspect ratio, tap density, specific surface area, graphitization index, boron oxide content, viscosity, and thermal conductivity of the prepared hexagonal boron nitride powder are shown in Table 1. The hexagonal boron nitride powder was examined by scanning electron microscopy, and the resulting SEM images are shown below. Figure 8 As shown.

[0149] Comparative Example 3

[0150] Orthoboric acid, melamine, morpholine guanidine hydrochloride, and pure water were weighed according to a mass ratio of 2:0.8:0.2:4, and a certain amount of carbon powder was added. The mixture was ball-milled until homogeneous to obtain a solid-liquid slurry. Given that the yield of the product after the first sintering of the three raw materials (orthoboric acid, melamine, and morpholine guanidine hydrochloride) was 25%, carbon powder was added at a mass ratio of 1:0.0125 between the total mass of the three raw materials and the carbon powder.

[0151] The solid-liquid mixture was transferred to a sealed container and heated to 120°C under sealed conditions, and then kept at 120°C for 7 hours. After the heat treatment, the lid of the sealed container was opened, and the mixture was heated to 120°C under open conditions and then dried for 12 hours to obtain the nitrogen-boron intermediate product.

[0152] The nitrogen-boron intermediate was briquetting, and then subjected to a first sintering treatment in a nitrogen atmosphere. The first sintering was controlled at 1200℃ for 6 hours. The sintered product was crushed and sieved to obtain hexagonal boron nitride intermediate.

[0153] The hexagonal boron nitride intermediate was briquetting, and the briquetting intermediate was then subjected to a second sintering treatment in a nitrogen atmosphere. The second sintering was controlled at 1800℃ for 10 hours, and a mixture of carbon powder and boron nitride was obtained after the second sintering.

[0154] The carbon powder and boron nitride mixture obtained from the second sintering were crushed and sieved, and then placed in air and heated at 700℃ for 10 hours for decarburization / carbon removal.

[0155] The decarbonized product was acid-washed with hydrochloric acid solution at 70°C for 2 hours, and then subjected to filtration, drying, dispersion and sieving to obtain hexagonal boron nitride powder.

[0156] The main difference between Comparative Example 3 and Example 8 is that carbon powder is added during the raw material mixing process, but no carbon powder is added after the first sintering (i.e., low-temperature sintering). The remaining operations are basically the same as in Example 8.

[0157] The particle size, aspect ratio, tap density, specific surface area, graphitization index, boron oxide content, viscosity and thermal conductivity of the prepared hexagonal boron nitride powder are shown in Table 1.

[0158] Detection and Analysis

[0159] Hexagonal boron nitride powders from Examples 1-8 were collected and tested for particle size D50, D99, aspect ratio, tap density, specific surface area, graphitization index, boron oxide content, viscosity, and thermal conductivity. The test results are shown in Table 1.

[0160] Particle size detection (D50, D99):

[0161] In this application, a laser particle size analyzer (e.g., Bettersize2600 from Dandong Bettersize Instruments Co., Ltd.) was used to determine the average particle size of the hexagonal boron nitride powder. During the measurement, the refractive index of water was set to 1.33 and the refractive index of the boron nitride powder was set to 1.728.

[0162] Calculation of diameter-to-thickness ratio:

[0163] Scanning electron microscopy (SEM) was used to measure the major diameter and thickness of hexagonal boron nitride (BN) lamellar crystals. One hundred different BN lamellar crystals were randomly selected from 5000x SEM images, and their major diameter and thickness were measured. The aspect ratio (ratio of major diameter to thickness) of each lamellar crystal was calculated, and the average value was taken as the aspect ratio of the BN sample.

[0164] Graphitization Index (GI) Calculation:

[0165] The crystallinity of boron nitride powder is correlated with its graphitization index, which reflects the degree of crystallinity. A lower graphitization index indicates higher crystallinity. The graphitization index (GI) is calculated from X-ray diffraction results using the following formula:

[0166] GI = [S(100) + S(101)] / [S(102)]

[0167] Wherein, S(100), S(101), and S(102) are the integrated intensities (i.e., peak areas) of the (100), (101), and (101) planes with 2θ values ​​of approximately 41°, 43°, and 50° in the XRD spectrum of the boron nitride product.

[0168] The X-ray diffraction test results (i.e., graphitization index) of the hexagonal boron nitride powder in Example 1 are as follows: Figure 4 As shown.

[0169] Viscosity and thermal conductivity testing:

[0170] 3.9 parts by mass of benzyl alcohol and 14 parts by mass of hexagonal boron nitride powder were added to 22.1 parts by mass of bisphenol A epoxy resin (E-128). After uniform mixing and degassing using a degassing machine, the viscosity was tested using a rheometer (Anton Paar MCR 302e) and the thermal conductivity was tested using a thermal constant analyzer (HOT Disk).

[0171] Table 1. Detection results of hexagonal boron nitride powders prepared in the examples and comparative examples.

[0172] sample D50 D99 Aspect Ratio Tap density Specific surface area Graphitization Index Boron oxide content 10 / s viscosity thermal conductivity unit μm μm —— g / cm³ m² / g —— % 10,000 mPa·s W / (m·K) Example 1 6.04 30.24 56.62 0.180 10.44 1.06 0.032 73.50 1.535 Example 2 4.84 33.46 50.68 0.203 9.71 1.22 0.046 70.82 1.431 Example 3 6.57 34.21 58.87 0.228 8.62 1.35 0.074 47.13 1.421 Example 4 6.18 32.12 42.80 0.293 7.29 1.29 0.081 55.73 1.340 Example 5 6.64 33.56 39.24 0.316 7.36 1.31 0.081 43.46 1.321 Example 6 5.87 26.25 37.51 0.259 6.86 1.44 0.078 46.74 1.307 Example 7 6.08 25.12 32.17 0.356 6.76 1.58 0.066 43.92 1.221 Example 8 6.19 22.54 32.44 0.364 4.69 1.60 0.055 38.64 1.200 Comparative Example 1 5.02 25.38 21.36 0.418 3.85 1.63 0.074 27.18 1.024 Comparative Example 2 5.63 138.1 29.65 0.337 3.90 1.66 0.046 33.81 1.145 Comparative Example 3 5.41 26.76 26.19 0.402 4.22 1.57 0.055 29.69 1.061

[0173] As shown in Table 1, the particle size D50 of the hexagonal boron nitride powder prepared by the method of this application in each embodiment is in the range of 4.5~7.5μm, the particle size D99 is less than 35μm, the aspect ratio is between 32 and 60, and the tap density is between 0.18 and 0.37 g / cm³. 3 Within this range, the specific surface area is 4.5~11m². 2 Within the range of / g, the boron nitride content is less than 0.1%, and the graphitization index is less than 2 (see [reference]). Figure 4 This indicates that the hexagonal boron nitride powder prepared by this method has micron-sized lamellar crystals and a high aspect ratio, exhibiting good filling performance and thermal conductivity.

[0174] According to Table 1, the detection results of Example 8 and Comparative Example 1 are compared; according to Figure 2 , Figure 3 and Figure 5 As shown, SEM images of the powders from Comparative Example 1 and Comparative Example 1 are displayed; and according to... Figure 6 and Figure 7 As shown, the aspect ratios of the hexagonal boron nitride powders prepared in Example 1 and Comparative Example 1 are compared. It is evident that by mixing carbon powder with the intermediate product of hexagonal boron nitride (i.e., the product from the first sintering) and then performing a second sintering (i.e., high-temperature sintering), the lamellar thickness of the resulting hexagonal boron nitride powder is significantly reduced, and the aspect ratio is significantly increased from 21.36 to 32.44. This indicates that adding carbon powder can promote the thinning of hexagonal boron nitride lamellars / or inhibit lamellar thickening, effectively improving the aspect ratio of the hexagonal boron nitride powder.

[0175] according to Figure 2 , Figure 3 and Figure 5 As shown in the SEM images, the lamellar thickness of the hexagonal boron nitride powder prepared in Example 1 is between 80 and 140 nm, which is much lower than the lamellar thickness of the hexagonal boron nitride powder prepared in Comparative Example 1, which is 180 to 580 nm. This variation in lamellar thickness can be attributed to the introduction of carbon powder into the reaction system, which hinders the lamellar thickening process.

[0176] As shown in Table 1, compared with the hexagonal boron nitride powder lamellars of Comparative Example 1, the thickness of the hexagonal boron nitride powder lamellars in Examples 1-8 was reduced. Simultaneously, the tap density and specific surface area of ​​the hexagonal boron nitride powder lamellars also changed. Specifically, as the hexagonal boron nitride powder lamellars became thinner, the specific surface area increased from 3.85 m² / g to 4.69-10.44 m² / g. As the hexagonal boron nitride powder lamellars became thinner, the tap density decreased from 0.418 g / cm³ to 0.36-0.18 g / cm³. The increased specific surface area and decreased tap density of these hexagonal boron nitride powder lamellars indicate that the powder became more porous. Tap density and specific surface area are correlated with the aspect ratio and thermal conductivity of hexagonal boron nitride lamellars. When the specific surface area is higher and the tap density is lower, the hexagonal boron nitride powder is more fluffy and the lamellars are thinner, which means that the aspect ratio of the lamellars may increase and the thermal conductivity may improve.

[0177] According to Table 1, the test results of Comparative Example 2 were compared with those of Example 8 and Comparative Example 3. Unlike the two-step sintering method in Example 8 and Comparative Example 3, Comparative Example 2 used a one-step sintering method. The aspect ratio of the product obtained in Comparative Example 2 was close to that of the product in Example 8 (aspect ratio 32.44), at 29.65. However, a large number of agglomerates appeared in the product of Comparative Example 2. Figure 8 The presence of these agglomerates significantly increased the D99 of the product from 22.54 μm in Example 8 and 26.76 μm in Comparative Example 3 to 138.1 μm, which is detrimental to the application of the product in ultrathin thermally conductive coatings (e.g., coating thickness requirements ≤150 μm). Therefore, a two-step sintering method combining low and high temperatures to prepare hexagonal lamellar boron nitride can reduce the number of agglomerates in the boron nitride product more effectively than a one-step high-temperature sintering method, thereby improving the dispersibility of the boron nitride product.

[0178] Table 1 compares the test results of Example 8 and Comparative Example 3. Unlike Example 8, where carbon powder was added to the product after a single sintering, Comparative Example 2 added carbon powder during raw material mixing. Compared to the product of Example 8 (aspect ratio 32.44), the aspect ratio of the product obtained in Comparative Example 3 was 26.19, which was significantly lower. This may be because after the carbon powder is mixed with the raw materials, some of the carbon powder is consumed during the nitriding process of boron oxide, resulting in a reduction in the amount of carbon powder participating in the high-temperature growth process of boron nitride wafers, thereby weakening the influence of carbon powder on the aspect ratio of boron nitride. Therefore, by adopting the process scheme of Example 8 and adding carbon powder after a single sintering, a more effective improvement in the aspect ratio of hexagonal boron nitride wafers can be achieved with less carbon powder.

[0179] As shown in Table 1, when hexagonal boron nitride powder lamellars are used in thermally conductive composite materials, compared with Comparative Examples 1-3, the thermal conductivity of the thermally conductive composite materials made using the hexagonal boron nitride powder lamellars in Examples 1-8 increased from 1.02-1.15 W / (m•K) in Comparative Examples 1-3 to 1.2-1.5 W / (m•K). This indicates that the reduction in the thickness of the hexagonal boron nitride powder lamellars and the increase in the aspect ratio are beneficial to improving the thermal conductivity of boron nitride powder.

Claims

1. A method for preparing high aspect ratio hexagonal boron nitride powder, characterized in that, Includes the following steps: S1, take boron source, nitrogen source and water to make solid-liquid mixed slurry; S2, the solid-liquid mixture is subjected to heating and heat preservation treatment and heating and drying treatment in sequence to obtain nitrogen-boron intermediate product; S3, the nitrogen-boron intermediate product is compressed into blocks and then sintered at low temperature. The low-temperature sintered product is crushed and sieved to obtain hexagonal boron nitride intermediate product. S4, the hexagonal boron nitride intermediate product is mixed with carbon powder, pressed into blocks and sintered at high temperature, and the high-temperature sintered product is crushed to obtain a mixture of carbon powder and boron nitride. S5, the mixture of carbon powder and boron nitride is heated in air for oxidation and decarburization, and then acid washed, filtered, dried, dispersed and sieved to obtain hexagonal boron nitride powder.

2. The method for preparing high aspect ratio hexagonal boron nitride powder according to claim 1, characterized in that, The boron source is one or more of orthoboric acid, metaboric acid, and borax; The nitrogen source is melamine and / or morpholine guanidine hydrochloride.

3. The method for preparing high aspect ratio hexagonal boron nitride powder according to claim 1 or 2, characterized in that, The total weight ratio of the boron source and nitrogen source to the weight of water is 1:0.5~2; The weight ratio of the boron source to the nitrogen source is 1.5 to 2:

1.

4. The method for preparing high aspect ratio hexagonal boron nitride powder according to claim 3, characterized in that, The nitrogen source is melamine and morpholine guanidine hydrochloride, and the weight ratio of melamine to morpholine guanidine hydrochloride is 3~9:

1.

5. The method for preparing high aspect ratio hexagonal boron nitride powder according to claim 1, characterized in that, In step S4, the mass ratio of the hexagonal boron nitride intermediate to the carbon powder is 1:0.05~0.

1.

6. The method for preparing high aspect ratio hexagonal boron nitride powder according to claim 1, characterized in that, In step S2, a heating and heat preservation treatment is carried out under sealed conditions. The temperature of the heating and heat preservation treatment is 95~140℃, and the heat preservation time is 6~24h. Under the conditions of a hot-drying process, the temperature of the hot-drying process is 100~200℃, and the drying time is 6~24h.

7. The method for preparing high aspect ratio hexagonal boron nitride powder according to claim 1 or 5, characterized in that, In step S3, the low-temperature sintering is carried out in a non-oxidizing atmosphere. The low-temperature sintering temperature is 900~1200℃ and the sintering time is 6~12h. And / or, In step S4, the high-temperature sintering is carried out in a non-oxidizing atmosphere at a temperature of 1800~2100℃ for 4~10h.

8. The method for preparing high aspect ratio hexagonal boron nitride powder according to claim 7, characterized in that, In step S5, the temperature for oxidative decarburization is 600~800℃, and the decarburization time is 3~12h.

9. A high aspect ratio hexagonal boron nitride powder, characterized in that, The hexagonal boron nitride powder is prepared by the preparation method according to any one of claims 1 to 8; the aspect ratio of the hexagonal boron nitride powder is >30, and the particle size D50 is 4.5~7.5μm.

10. The high aspect ratio hexagonal boron nitride powder according to claim 9, characterized in that, The aspect ratio of the hexagonal boron nitride powder is 31~60.

11. The high aspect ratio hexagonal boron nitride powder according to claim 9 or 10, characterized in that, The hexagonal boron nitride powder also meets one or more of the following conditions: The tap density is 0.15~0.4 g / cm³. 3 ; Specific surface area is 3~12m² 2 / g; Boron oxide content ≤0.1%; D99≤35μm; Graphitization index ≤ 2.

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