Method for preparing hexagonal nitride quasi-spherical particles by centrifugal stirring granulation molding-high temperature pyrolysis

Abstract

The preparation method of the hexagonal nitride quasi-spherical particle centrifugal stirring granulation forming-high temperature pyrolysis of the application, adopts boron compound or aluminum compound, nitrogen compound as the reaction precursor, is configured into the cream-like slurry with certain viscosity under the specific temperature range, is heated and dried under 80-350 DEG C, and is crushed into the ultrafine powder with particle size less than 100 mesh, is introduced into the centrifugal stirring granulation equipment, is hydrated by spraying water, is stirred and granulated to obtain the hard particles, and the hard particles are high-temperature pyrolyzed to obtain the quasi-spherical hexagonal nitride particle product. The quasi-spherical hexagonal nitride particle product has the characteristics of high strength, high density, low porosity and high crystallization, and the application has the advantages of not needing any additive, simple operation, green environmental protection, wide particle size distribution range of the obtained quasi-spherical particle product, large yield, and meeting the needs of industrial production.

Description

Technical fields:

[0001] This invention relates to the field of synthesis technology of spherical powder fillers of inorganic non-metallic materials with high insulation and high thermal conductivity, and specifically to a preparation method of hexagonal nitride quasi-spherical particles by centrifugal stirring granulation and high-temperature pyrolysis. Background technology:

[0002] Hexagonal boron nitride (h-BN) and hexagonal aluminum nitride (AlN), as high-performance nitride ceramic materials, possess high thermal conductivity, low coefficient of thermal expansion, good electrical insulation, and chemical stability, and are widely used in electronics, thermal management, optics, aerospace, and materials science. Forming hexagonal boron nitride and aluminum nitride powders into spherical structures increases their flowability. When used as fillers in composite matrices, the point-to-point contact between the particles prevents particle agglomeration and allows for a larger filling volume within the polymer. This improves the density of thermally conductive channels without affecting the fundamental properties of the polymer matrix, significantly enhancing the thermal conductivity and mechanical properties of the composite system.

[0003] Existing technologies for preparing hexagonal boron nitride spherical particles mainly include chemical vapor deposition (CVD), ball milling, spray granulation combined with sintering or pyrolysis, self-propagating high-temperature synthesis, sol-gel method, and template carbothermal in-situ reduction nitridation. While CVD produces spherical particles with high uniformity and purity, it is costly, requires strict control of equipment and processes, struggles to control particle shape, and results in a narrow particle size distribution, primarily in the nanometer to micrometer range. Ball milling relies mainly on the morphology of the milled particles, leading to uneven particle size distribution and the introduction of milling impurities. Spray granulation combined with sintering or pyrolysis makes it difficult to control particle size and shape in the same batch. Generally, the added binder needs to be removed through a debinding process. While introducing sintering aids can promote the sintering of hexagonal boron nitride spherical particles, their content is usually high, which greatly weakens the intrinsic properties of the final hexagonal boron nitride spherical particles and significantly degrades their filling thermal conductivity. The self-propagating high-temperature synthesis method has too high a requirement for raw material purity, and it is difficult to control the size of the formed particles. The sol-gel method has the disadvantages of complex process, numerous raw materials / auxiliaries, and relatively high raw material cost. The template carbothermic in-situ reduction nitridation method usually depends entirely on the carbon sphere template material for morphology, and the template spheres have a narrow particle size distribution and are at the nanoscale, so the carbon impurity content of the synthesized hexagonal boron nitride spherical particles is usually high.

[0004] Existing technologies for preparing hexagonal aluminum nitride spherical particles mainly include direct nitriding of aluminum spheres, alumina spheres, or spheres containing aluminum components, carbothermal reduction-nitriding, gas-phase synthesis, sol-gel method, spray drying method, and mechanical synthesis method. Direct nitriding is limited by the aluminum-containing spherical shape, resulting in poor control over particle shape and size. Carbothermal reduction-nitriding requires high temperatures, typically necessitating long durations at the target temperature for high-energy nitriding, leading to significant energy consumption. Gas-phase synthesis has low yields, failing to meet industrial demands. Similarly, the sol-gel method is complex and costly. Spray drying granulation can yield precursors with relatively high sphericity; however, precise control of particle size and shape is difficult, and further improvements are needed for large-scale production. Mechanical synthesis suffers from significant particle inhomogeneity, easily introducing excessive impurities, which greatly affects the further filling applications of spherical particle products.

[0005] Given the above background of synthetic technologies and their inherent limitations, developing new synthetic technologies for nitride spherical particles is crucial for promoting high-quality development in modern industry and high-tech fields. Summary of the Invention:

[0006] This invention provides a method for preparing hexagonal boron nitride quasi-spherical particles by centrifugal stirring granulation and high-temperature pyrolysis, which can efficiently prepare hexagonal boron nitride and hexagonal aluminum nitride quasi-spherical particles. The spherical particle products obtained by the technology of this invention have the advantages of controllable particle size, high strength, high density, low porosity, high crystallinity and high purity.

[0007] This invention uses ultra-dry powder generated from a universal nitrogen source and boron or aluminum source as the raw material for granulation precursor spheres. It utilizes centrifugal stirring granulation technology, which not only makes sphere formation easy to control but also results in high yield. The pyrolysis process of this invention is very simple, requiring no additional high-temperature debinding, sintering, crystallization, or decarbonization steps. It also eliminates the need for purification processes such as water washing, acid washing, and drying to remove impurities from the final pyrolysis-obtained hexagonal nitride sphere particles. This makes production more energy-efficient and economically beneficial.

[0008] The technical solution to achieve the objective of this invention is as follows:

[0009] In a first aspect, the present invention provides a method for preparing hexagonal nitride quasi-spherical particles by centrifugal stirring granulation and high-temperature pyrolysis, comprising the following steps:

[0010] (1) A mixture of a boron-containing compound or an aluminum-containing compound and a nitrogen-containing compound is added to an aqueous solution to dissolve and react, thereby obtaining a viscous paste-like slurry. The mass ratio of the mixture to the aqueous solution is 1:0.2-1.5.

[0011] (2) After the creamy slurry is dehydrated by heating and evaporation, an ultra-dry hard block is obtained. The hard block is then crushed into an ultra-fine powder that can pass through a 100-600 mesh screen.

[0012] (3) The ultrafine powder is loaded into the granulation tank of a centrifugal stirring granulation equipment equipped with a stirring rod and a rotating drum with adjustable clockwise and counterclockwise rotation directions. Liquid reagent is sprayed during the stirring process. After the centrifugal stirring granulation process, fluffy white granular powder is obtained. After drying, hard granular powder with good dispersibility is obtained. This granular powder is the hard quasi-spherical precursor powder for the preparation of hexagonal nitride quasi-spherical particles by pyrolysis.

[0013] (4) The precursor powder of the hard quasi-spherical particles obtained is subjected to a constant temperature reaction of 0.5-24 hours in a protective gas atmosphere within the target temperature range of 1100℃-1500℃ to obtain a white or grayish-white granular product. The granular product after pyrolysis retains the quasi-spherical particle characteristics of the precursor.

[0014] At least one powder obtained after centrifugal mixing granulation, drying, or pyrolysis reaction is subjected to balling treatment.

[0015] The molar ratio of the boron-containing compound or aluminum-containing compound to the nitrogen-containing compound is in the range of 0.1-8; the mixture is stirred and dissolved in an aqueous solution at a temperature range of 45℃-99℃ for 2-48 hours to obtain a viscous cream-like slurry.

[0016] The boron-containing compound in step (1) is at least one of boric acid, borax, or boron trioxide;

[0017] The nitrogen-containing compound is at least one of dicyandiamide, guanidine, guanidine carbonate, 3-amino-1,2,4-triazole, or melamine;

[0018] The aluminum-containing compound is at least one of anhydrous aluminum chloride, aluminum chloride hexahydrate, aluminum nitrate nonahydrate, or aluminic acid.

[0019] The aqueous solution in step (1) and the liquid reagent sprayed in step (3) are water, which is pure water without any added binder, flux, accelerant or dispersant, including deionized water, purified water, distilled water or tap water;

[0020] The mass of the sprayed liquid reagent is 10 wt.%-50 wt.% of the mass of the ultrafine powder added to the granulation tank, preferably 15 wt.%-40 wt.%.

[0021] During the centrifugal granulation process, there is a certain matching relationship between the clockwise and counterclockwise rotation of the stirring rod and the barrel, namely:

[0022] The first stage is the mixing process. The ultrafine powder is transferred into the centrifugal mixing tank. The stirring rod is rotated counterclockwise at a speed of 10r / min-500r / min, and the tank is rotated clockwise at a speed of 10r / min-50r / min. The centrifugal mixing time ranges from 10 to 30 minutes in this mode.

[0023] The second stage is the granulation process. The stirring rod is rotated clockwise at a speed of 500r / min-2000r / min, and the barrel is rotated clockwise at a speed of 50r / min-100r / min. During this operation, liquid reagent is sprayed evenly and the process continues for 30-90 minutes.

[0024] The third stage is the pellet drying process. The stirring rod is rotated counterclockwise at a speed of 2000r / min-5000r / min, and the barrel is rotated clockwise at a speed of 100r / min-200r / min. No liquid reagent water is sprayed during this process. This process takes 15-60 minutes.

[0025] The specific process of granulation is as follows: an abrasive surface with a mesh size range of 600-10000 is created on the inner wall and bottom of the granulation tank. The stirring rod is rotated clockwise at a speed of 500-5000 r / min, and the tank is rotated counterclockwise at a speed of 50-200 r / min. No liquid reagents are sprayed during this process. The running time of this process is 60-1000 minutes.

[0026] There are two types of barrels used in the spheroidizing process: one type consists of a barrel structure with an upright barrel wall and a bottom surface perpendicular to the upright barrel wall, with the angle between the rotation axis and the horizontal plane varying from 30 to 60 degrees. The inner wall and bottom of the barrel are made into abrasive surfaces with a mesh size range of 600 to 10,000. The other type is a spherical barrel structure, with the angle between the rotation axis and the horizontal plane varying from 20 to 45 degrees. The inner wall of the spherical barrel is made into abrasive surfaces with a mesh size range of 600 to 10,000.

[0027] The protective gas flow atmosphere in step (4) is an inert atmosphere or an atmosphere containing a certain reducing gas component;

[0028] The inert atmosphere is at least one of nitrogen or argon;

[0029] The atmosphere containing a certain reducing gas component is applied during the high-temperature pyrolysis process when the aluminum-containing compound is aluminic acid or aluminum nitrate.

[0030] The reducing gas component is at least one of ammonia or hydrogen, wherein the volume proportion of ammonia is not less than 10% and the volume proportion of hydrogen is not more than 10%.

[0031] An atmosphere containing a certain reducing gas component is: nitrogen + ammonia, argon + ammonia, or hydrogen + nitrogen.

[0032] The hexagonal boron nitride or hexagonal aluminum nitride quasi-spherical particle powder products obtained in step (4) have the characteristic of achieving a wide range of particle size distribution from 37μm to 800μm in the same batch. After vibrating and filtering through filter screens of different mesh sizes, nitride quasi-spherical particle products with different particle size specifications are obtained. The vibration screening process of filter screens of different mesh sizes can be carried out before or after high-temperature pyrolysis.

[0033] Secondly, the present invention provides a hexagonal nitride quasi-spherical particle, which is obtained by the above-mentioned preparation method. The sphericity of the quasi-spherical particle is 0.8-1.0, preferably 0.9-1.0. The quasi-spherical particle has quasi-spherical morphology characteristics, high strength, high density, low porosity and high crystallinity.

[0034] The centrifugal mixing granulation equipment used in this invention includes a control panel, a cooling device, a stirring rod, and a barrel. The dried material is poured into the barrel, and under the rotation of the stirring rod and the barrel, the material undergoes a hydration reaction with water, gradually crystallizing and forming granular substances. As these crystalline substances gradually increase, the material exhibits hardening characteristics.

[0035] Compared with the prior art, the beneficial effects of the present invention are:

[0036] This invention provides a universal method for preparing quasi-spherical particles of hexagonal boron nitride and aluminum nitride. By reacting boron sources and these nitrogen sources, as well as aluminum sources and these nitrogen sources, in water to form a slurry and subsequently an ultra-dry powder, the slurry is further granulated by centrifugal stirring to form quasi-spheres. In this granulation process, no additional non-nitrogen, non-aluminum, or non-boron source binders, fluxes, solvents, sintering aids, surfactants, or other components are required. Simply spraying water is enough to allow the raw materials to form high-density quasi-spherical precursor particles during centrifugal stirring granulation.

[0037] The process provided by this invention, from precursor to final hexagonal nitride quasi-spherical particles, is a very convenient high-temperature pyrolysis process. It does not require any additional high-temperature or purification processes such as debinding, sintering, crystallization, decarbonization, and cleaning, and can obtain quasi-spherical hexagonal boron nitride and aluminum nitride particles with high strength, high density, low porosity, and high crystallinity.

[0038] Compared with spray drying granulation, the method of this invention has the following advantages: the particle size range of the granules obtained by this invention is wider, and the output on a large scale is higher; the surface of the obtained quasi-spherical particles is denser, and the spherical structure is more stable; this invention does not involve excessive consumption and waste of raw materials, the production process is more energy-efficient, and the economic benefits are obvious.

[0039] A key advantage of this invention is that, unlike the precursors used in spray drying granulation, sol-gel formation, or high-temperature self-propagating methods, the pyrolysis precursor and the final pyrolysis hexagonal nitride spherical particles in this invention maintain a high degree of consistency in their quasi-spherical structure. This provides a feasible way to achieve precise control over the shape of hexagonal nitride particles by flexibly adjusting the centrifugal stirring granulation process. Attached image description:

[0040] To more clearly illustrate the technical solutions and product types of the present invention, the accompanying drawings used in the description of the embodiments are briefly described below. It should be emphasized that these accompanying drawings are only some embodiments of the present invention. For those skilled in the art, there is a possibility that other similar and related accompanying drawings may be extended and derived without creative effort. In the case of similar and related drawings as new creative embodiments, it shall be regarded as an infringement of the present invention.

[0041] Figure 1 The XRD diffraction patterns of quasi-spherical boron nitride particle products obtained by pyrolysis at different temperatures in Example 1 of the present invention are shown below.

[0042] Figure 2 The Fourier transform infrared spectra of quasi-spherical boron nitride particles obtained by pyrolysis at different temperatures in Example 1 of the present invention are shown.

[0043] Figure 3 This is a SEM image of the unscreened powder from the 1100℃ pyrolysis product of Example 1 of the present invention without the balling process, and a statistical distribution data diagram of its particle size.

[0044] Figure 4 This is a graph showing the weight distribution of pyrolysis products with different particle sizes at 1100℃ without the balling process in Example 1 of the present invention.

[0045] Figure 5 This is a scanning electron microscope (SEM) image of the pyrolysis product at 1100℃ after the balling process in Example 1 of the present invention.

[0046] Figure 6 This is a scanning electron microscope (SEM) image of the pyrolysis product at 1500℃ after the balling process in Example 1 of the present invention.

[0047] Figure 7This is a scanning electron microscope (SEM) image showing the surface microstructure of the pyrolysis product at 1500℃ after the balling process in Example 1 of the present invention.

[0048] Figure 8 The nitrogen adsorption-desorption curve and BET specific surface area data of the pyrolysis product at 1500℃ after the balling process in Example 1 of this invention are shown.

[0049] Figure 9 The XRD diffraction patterns of quasi-spherical boron nitride particle products obtained by pyrolysis at different temperatures in Example 2 of the present invention are shown below.

[0050] Figure 10 The Fourier transform infrared spectra of quasi-spherical boron nitride particles obtained by pyrolysis at different temperatures in Example 2 of the present invention are shown.

[0051] Figure 11 These are scanning electron microscope (SEM) images of the pyrolysis products at 1500°C with and without the balling process in Example 2 of this invention.

[0052] Figure 12 This is a schematic diagram of the barrel used in the balling process of the present invention;

[0053] Figure 13 This is a scanning electron microscope (SEM) image of the pyrolysis product at 1500℃ that has undergone the balling process but has not been screened by a mesh screen in Example 2 of the present invention.

[0054] Figure 14 This is a scanning electron microscope (SEM) image of the 1500℃ pyrolysis product of Embodiment 2 of the present invention, which has undergone a balling process and has been sieved through screens of different mesh sizes.

[0055] Figure 15 This is a scanning electron microscope (SEM) image showing the surface microstructure of the pyrolysis product at 1500℃ after the grinding and balling process in Example 2 of the present invention.

[0056] Figure 16 The nitrogen adsorption-desorption curve and BET specific surface area data of the pyrolysis product at 1500℃ after the balling process in Example 2 of this invention are shown.

[0057] Figure 17 The XRD diffraction patterns of quasi-spherical boron nitride particle products obtained by pyrolysis at different temperatures in Example 3 of the present invention are shown below.

[0058] Figure 18 The Fourier transform infrared spectra of quasi-spherical boron nitride particles obtained by pyrolysis at different temperatures in Example 3 of the present invention are shown.

[0059] Figure 19 This is a scanning electron microscope (SEM) image of the pyrolysis product at 1100℃ after the balling process in Example 3 of the present invention.

[0060] Figure 20 This is a scanning electron microscope (SEM) image of the pyrolysis product at 1500℃ after the balling process in Example 3 of the present invention.

[0061] Figure 21 This is a scanning electron microscope (SEM) image showing the surface microstructure of the pyrolysis product at 1500℃ after the balling process in Example 3 of the present invention.

[0062] Figure 22 The XRD diffraction pattern of the quasi-spherical boron nitride particle product obtained by pyrolysis at 1500℃ in Example 4 of the present invention is shown.

[0063] Figure 23 This is a scanning electron microscope (SEM) image of the pyrolysis product at 1500°C in Example 4 of the present invention.

[0064] Figure 24 This is a scanning electron microscope (SEM) image showing the surface microstructure of the pyrolysis product at 1500℃ in Example 4 of the present invention.

[0065] Figure 25 The XRD diffraction pattern of the quasi-spherical hexagonal aluminum nitride particle product obtained by pyrolysis at 1100℃ in Example 5 of the present invention is shown below.

[0066] Figure 26 The Fourier transform infrared spectrum of the quasi-spherical hexagonal aluminum nitride particle product obtained by pyrolysis at 1100℃ in Example 5 of the present invention is shown.

[0067] Figure 27 This is a scanning electron microscope (SEM) image of the pyrolysis product at 1100°C in Example 5 of the present invention.

[0068] Figure 28 This is a scanning electron microscope (SEM) image showing the surface microstructure of the pyrolysis product at 1100℃ in Embodiment 5 of the present invention. Detailed implementation method:

[0069] The present invention will be further described below with reference to the embodiments.

[0070] The present invention provides a method for preparing hexagonal nitride quasi-spherical particles by centrifugal stirring granulation and high-temperature pyrolysis, comprising the following steps (1)-(4):

[0071] (1) When the ratio of the total mass (in grams) of a mixture formed by a boron-containing compound or an aluminum-containing compound and a nitrogen-containing compound to the total mass (in grams) of water as a solvent is in the range of 0.2-1.5, the mixture is completely dissolved in an aqueous solution at a temperature range of 45℃-99℃ under uniform stirring. After continuous stirring and reaction within this temperature range for 2-48 hours, a viscous cream-like slurry is obtained; wherein the molar ratio of the boron-containing compound or the aluminum-containing compound to the nitrogen-containing compound is in the range of 0.1-8.

[0072] (2) After heating the creamy slurry at a temperature range of 80-350℃ for 3-192 hours to evaporate the water, the water solvent molecules of the crystalline structure of the reaction products in the slurry are removed, forming an ultra-dry hard block material without water solvent molecules of crystalline structure. The hard block material is then crushed into ultra-fine powder that can completely pass through a 100-600 mesh screen using industrial crushing equipment.

[0073] (3) A suitable amount of ultrafine powder is loaded into the granulation tank of a centrifugal mixing granulation device equipped with a stirring rod and a rotating drum with adjustable clockwise and counterclockwise rotation directions. During the mixing process, a suitable amount of liquid reagent is sprayed. After centrifugal mixing granulation and balling process for 150-1200 minutes, a fluffy white granular powder is obtained. The white granular powder is dried at a temperature range of 90-300℃ for 1-96 hours to obtain a well-dispersed white hard granular powder. This granular powder is the hard granular quasi-spherical particle prepared by pyrolysis. The spherical precursor powder; wherein, the stirring rod speed of the centrifugal granulator is in the range of 10 r / min-5000 r / min, preferably 500 r / min-4000 r / min, and the barrel rotation speed is in the range of 10 r / min-200 r / min; a higher stirring speed will lead to an increase in the collision energy between particles, which may increase particle wear and reduce particle quality and performance; a lower stirring speed will lead to an increase in the gaps between particles, making the particles not densely packed, and too low a stirring speed will also result in a larger particle size, which cannot achieve the required degree of fineness.

[0074] (4) The precursor powder of the hard quasi-spherical particles obtained is subjected to pyrolysis reaction at a constant temperature for 0.5-24 hours in a protective gas flow atmosphere with a flow rate of 1-2000 mL / min and a heating rate of 1℃ / min-200℃ / min, respectively, to a target temperature range of 1100℃-1500℃. White or grayish-white granular products are obtained. The pyrolyzed granular products retain the quasi-spherical particle characteristics of the precursor, that is, hexagonal boron nitride or hexagonal aluminum nitride quasi-spherical particle powder products.

[0075] The boron-containing compound in step (1) is, but is not limited to, at least one of boric acid, borax, or boron trioxide;

[0076] The nitrogen-containing compound in step (1) is, but is not limited to, at least one of dicyandiamide, guanidine, guanidine carbonate, 3-amino-1,2,4-triazole or melamine;

[0077] The aluminum-containing compound in step (1) is, but is not limited to, at least one of anhydrous aluminum chloride, aluminum chloride hexahydrate, aluminum nitrate nonahydrate, or aluminic acid.

[0078] The aqueous solution in step (1) and the liquid reagent sprayed in step (3) are water. The water is a pure aqueous solution that has not been artificially treated with any binders, fluxes, accelerants or dispersants. It includes, but is not limited to, all water solvents that can completely dissolve the compound in step (1), such as deionized water, purified water, distilled water or tap water.

[0079] The mass of the sprayed liquid reagent is 10wt.%-50wt.% of the mass of the ultrafine powder added to the granulation tank;

[0080] The centrifugal mixing granulation and grinding balling processes are matched with the clockwise and counterclockwise rotation of the stirring rod and the barrel, and are divided into four stages:

[0081] The first stage is the mixing process. The ultrafine dry powder is transferred into the centrifuge drum, and the stirring rod is rotated counterclockwise at a speed of 10r / min-500r / min, and the drum is rotated clockwise at a speed of 10r / min-50r / min. The centrifugal mixing time in this mode is 10-30 minutes. This stage can make the material fully mixed, with uniform particle size distribution, and the particles are small and round.

[0082] The second stage is the granulation process. The stirring rod is rotated clockwise at a speed of 500r / min-2000r / min, and the barrel is rotated clockwise at a speed of 50r / min-100r / min. During this operation, liquid reagent water is sprayed evenly. This centrifugal granulation process is continued for 30-90 minutes. In this stage, the particle size and sphericity can be controlled by adjusting the time and speed.

[0083] The third stage is the pellet drying process. The stirring rod is rotated counterclockwise at a speed of 2000-5000 rpm, and the barrel is rotated clockwise at a speed of 100-200 rpm. No liquid reagent water is sprayed during this process. The running time ranges from 15 to 60 minutes. By controlling the running time and the coupling effect of centrifugal force, the edges of the particles can be further tapped, which can increase the collision probability, improve the sphericity, and shorten the drying time.

[0084] The fourth stage is the balling process. Select a barrel with a frosted surface, rotate the stirring rod clockwise at a speed of 500r / min-5000r / min, and rotate the barrel counterclockwise at a speed of 50r / min-200r / min. Do not spray liquid reagent water during this process. The running time of this process is 60-1000 minutes.

[0085] In the fourth stage of the grinding process, the angle between the rotation axis of the barrel and the horizontal plane varies from 20° to 60°. The inner wall of the barrel is made into an abrasive surface with different abrasive particle size characteristics. The equivalent mesh number of the abrasive particle size used to form the abrasive surface ranges from 600 to 10000 mesh. The abrasive surface can be formed by embedding sandpaper or by casting a rough sand surface, etc.

[0086] The fourth stage of balling process can be carried out after the third stage of balling and granulation in direct centrifugal stirring granulation, or it can be carried out after obtaining well-dispersed white hard granular powder in step (3), or after obtaining white or grayish-white granular hexagonal boron nitride or hexagonal aluminum nitride products by high-temperature pyrolysis in step (4).

[0087] The ball milling process in the fourth stage uses two types of barrels: one type consists of a vertical barrel wall and a bottom surface perpendicular to the vertical barrel wall, with the angle between its rotation axis and the horizontal plane varying from 30 to 60 degrees. Both the inner wall and bottom of the barrel are made with an abrasive surface featuring a mesh size of 600-10000. The other type is a spherical barrel structure, with the angle between its rotation axis and the horizontal plane varying from 20 to 45 degrees. The inner wall of the spherical barrel is also made with an abrasive surface featuring a mesh size of 600-10000. Using different barrel types with appropriate tilt angles is beneficial for obtaining smoothly milled particles.

[0088] The protective gas flow atmosphere in step (4) is an inert atmosphere or an atmosphere containing a certain reducing gas component:

[0089] Among them, the inert atmosphere environment is applied to the high-temperature pyrolysis process of quasi-spherical particle precursors formed by boron-containing compounds and nitrogen-containing compounds or to the high-temperature pyrolysis process of quasi-spherical particle precursors formed by aluminum-containing compounds and nitrogen-containing compounds. These inert protective atmosphere environments are, but are not limited to, nitrogen, argon or a mixture of the two gases in any proportion.

[0090] Among them, an environment with a certain reducing atmosphere is used in the high-temperature pyrolysis process of quasi-spherical particle precursors formed by aluminum-containing compounds such as aluminic acid or aluminum nitrate and nitrogen-containing compounds. These reducing atmosphere environments include, but are not limited to, any one or a combination of nitrogen + ammonia (ammonia volume ratio not less than 10%), argon + ammonia (ammonia volume ratio not less than 10%), or hydrogen + nitrogen (hydrogen volume ratio not higher than 10%).

[0091] The hexagonal boron nitride or hexagonal aluminum nitride quasi-spherical particle powder products obtained in step (4) have the characteristic that the same batch can achieve a wide range of particle size distribution from 37μm to 800μm. After vibrating and filtering through filter screens of different mesh sizes, nitride quasi-spherical particle products with different particle size specifications can be obtained. The vibration screening process of filter screens of different mesh sizes can be carried out before or after high-temperature pyrolysis. It can be carried out after the process of obtaining well-dispersed hard particle powder in step (3), or after the process of obtaining white or grayish-white granular products - hexagonal boron nitride or hexagonal aluminum nitride - through high-temperature pyrolysis in step (4). The particle size classification and screening products of the quasi-spherical particle powder obtained in the end are the same.

[0092] The particles obtained by pyrolysis in step (4) have the characteristics of high strength, high density, low porosity and high crystallinity, and have quasi-spherical morphology. The sphericity of the particles formed by centrifugal stirring granulation is increased from the range of 0.8-1.0 to the range of 0.9-1.0.

[0093] The required water volume for the hydration reaction in this invention is 10wt.%-50wt.%, preferably 15wt.%-40wt.%. Excessive water volume will result in overly large granules, while insufficient water volume will lead to poor sphericity and density. The amount of liquid reagent added is calculated based on the total mass of the ultrafine powder added to the granulation tank, and the specific water volume is set according to the different water absorption rates of the ultrafine powder itself.

[0094] Example 1

[0095] Boric acid and 3-amino-1,2,4-triazole in a molar ratio of 3:1 were dissolved in deionized water at 95°C with constant stirring until the solution became clear (oil bath temperature was 98°C). The oil bath temperature was then adjusted to 120°C and stirred continuously for 16 hours to obtain a viscous paste-like slurry.

[0096] The viscous creamy slurry was placed in an oven at 120°C for 72 hours to dehydrate and solvent-treat, resulting in an ultra-dry, hard, blocky precursor free of crystalline water-soluble molecules. The blocky precursor was then fed into a baghouse pulverizer to be pulverized, yielding an ultrafine powder with a particle size of less than 300 mesh.

[0097] At room temperature, the ultrafine powder is fed into the rotary granulation chamber of the centrifugal mixer through the feeding port. The stirring rod of the centrifugal mixer is adjusted to rotate counterclockwise at 500 r / min, and the chamber rotates clockwise at 50 r / min. The mixture is stirred for 15 minutes. The stirring rod speed is then adjusted to rotate clockwise at 1500 r / min, and the chamber continues to rotate clockwise at 100 r / min. 30% pure water (by weight of the ultrafine powder) is sprayed in, and the mixture is stirred and granulated for 45 minutes. The stirring rod speed is then adjusted to rotate counterclockwise at 2500 r / min, and the chamber continues to rotate clockwise at 200 r / min. The pellet drying process is carried out for 30 minutes.

[0098] After the pellet drying process is completed, adjust the stirring rod speed to 500 r / min clockwise and the barrel speed to 100 r / min counterclockwise to carry out the grinding process. When the barrel is upright during the grinding process, attach 1000 and 3000 grit sandpaper to the bottom and inner wall of the barrel respectively, tilt the barrel so that the angle between its rotation axis and the horizontal plane is 30° to ensure that the pellets can be fully ground by the sandpaper at the bottom of the barrel. Change the angle between the barrel's rotation axis and the horizontal plane to 60° so that the pellets can be further ground by the sandpaper on the inner wall of the barrel. The grinding process lasts for 16 hours. When the barrel is spherical, attach 1000 grit sandpaper to the entire inner wall of the barrel, change the angle between the rotation axis and the horizontal plane to 45°, and grind for 8 hours. Then change the sandpaper to 3000 grit and grind for 8 hours.

[0099] After centrifugal mixing, granulation, and spheroidization processes, the resulting precursor powder of hard quasi-spherical particles is discharged and dried at 120°C for 4 hours to remove excess moisture, yielding relatively dense precursor particles of hard quasi-spherical particles. These precursor particles are then fed into a vibrating screen for classification, obtaining different grades of quasi-spherical precursors with particle sizes ranging from 20 to 400 mesh (37 to 800 μm). The sieved precursor particles are placed in a boron nitride crucible and then into a tube furnace. Under a nitrogen atmosphere, the temperature is raised to 1100°C or 1500°C and held for 240 minutes to sinter and form BN material with a morphology of uniformly dispersed micron-sized quasi-spherical particles.

[0100] The prepared quasi-spherical hexagonal boron nitride particle product was characterized by XRD diffraction and infrared spectroscopy (as shown in the figure). Figure 1 , Figure 2In the XRD diffraction pattern, due to the observation of diffraction peaks on the 002, 100, 101, and 110 planes, it was identified as h-BN. The pyrolysis product at 1500℃ showed a significant improvement in crystallinity compared to the 1100℃ product, with the 1500℃ sample exhibiting higher crystallinity characteristics. In the infrared spectrum, the pyrolysis products at 1100℃ and 1500℃ showed peaks in the 1300-1400 cm⁻¹ range. -1 and 770-810cm -1 The presence of two typical vibration zones within the range indicates that the h-BN phase has essentially formed within this temperature range, and the pyrolysis product at 1100℃ exhibits a vibration pattern at 3300 cm⁻¹. -1 Vibrations of -OH and -NH2 groups were observed nearby, which were caused by residual boron oxides from sintering.

[0101] The prepared quasi-spherical hexagonal boron nitride particles were analyzed by scanning electron microscopy, and their particle size and weight distribution were statistically analyzed (as shown in Figure 1). Figure 3 , 4 SEM images of the unscreened powder from the 1100℃ pyrolysis product of Example 1 without the spheroidizing process were analyzed using Nano Measurer software. The analysis revealed that the quasi-spherical hexagonal boron nitride particles were mainly concentrated in the 80-150 micrometer range, with an average particle size of approximately 97.6 micrometers. The unscreened powder from the 1100℃ pyrolysis product of Example 1 without the spheroidizing process was sieved using different mesh sizes, and the weight distribution of the particles was statistically analyzed. The particles with a size distribution of 178-350 micrometers accounted for the largest proportion (27.4%). SEM images of the 1100℃ and 1500℃ particles sieved using a 100-mesh spheroidizing process showed that they were quasi-spherical particles with good and uniform sphericity. Localized, progressively magnified SEM images of a single 1500℃ particle revealed that its surface was formed by stacked lamellar h-BN particles in different directions. Figure 8 The adsorption-desorption curves illustrate the low porosity of the quasi-spherical hexagonal boron nitride particles. The specific surface area of ​​the material, calculated using BET surface area analysis, is 10.59 m². 2 / g.

[0102] Example 2

[0103] Using boric acid and guanidine carbonate in a molar ratio of 5:1 as raw materials, the mixture was stirred in deionized water at 45°C until the slurry was homogeneous, and then stirred at 95°C for 8 hours to obtain a viscous cream-like slurry. The viscous cream-like slurry was white.

[0104] A viscous, creamy slurry was dried in an oven at 105°C for 96 hours to obtain a hard, blocky precursor that does not contain water molecules with a crystalline structure. The blocky precursor was then pulverized in a baghouse pulverizer to obtain an ultrafine powder with a particle size of less than 300 mesh.

[0105] At room temperature, the ultrafine powder is fed into the rotary granulation chamber of the centrifugal mixer through the feeding port. The stirring rod of the centrifugal mixer is adjusted to rotate counterclockwise at 500 r / min, and the chamber rotates clockwise at 50 r / min. The mixture is stirred for 15 minutes. The stirring rod speed is then adjusted to rotate clockwise at 1800 r / min, and the chamber continues to rotate clockwise at 100 r / min. 35% pure water (by weight of the ultrafine powder) is sprayed in, and the mixture is stirred and granulated for 45 minutes. The stirring rod speed is then adjusted to rotate counterclockwise at 3000 r / min, and the chamber continues to rotate clockwise at 200 r / min. The pellet drying process is carried out for 30 minutes.

[0106] After the pellet drying process is completed, adjust the stirring rod speed to 500 r / min clockwise and the barrel speed to 100 r / min counterclockwise to carry out the grinding process. When the barrel is upright during the grinding process, attach 1000 and 3000 grit sandpaper to the bottom and inner wall of the barrel respectively, tilt the barrel so that the angle between its rotation axis and the horizontal plane is 30° to ensure that the pellets can be fully ground by the sandpaper at the bottom of the barrel. Change the angle between the barrel's rotation axis and the horizontal plane to 60° so that the pellets can be further ground by the sandpaper on the inner wall of the barrel. The grinding process lasts for 16 hours. When the barrel is spherical, attach 1000 grit sandpaper to the entire inner wall of the barrel, change the angle between the rotation axis and the horizontal plane to 45°, and grind for 8 hours. Then change the sandpaper to 3000 grit and grind for 8 hours.

[0107] After centrifugal mixing, granulation, and spheroidization processes, the resulting precursor powder of hard quasi-spherical particles is discharged and dried at 105°C for 4 hours to remove excess moisture, yielding relatively dense precursor particles of hard quasi-spherical particles. These precursor particles are then fed into a vibrating screen for classification, obtaining spherical precursors of different sizes ranging from 20 to 400 mesh (37 to 800 μm). The sieved spherical precursor particles are placed in a boron nitride crucible and then into a tube furnace. Under a nitrogen atmosphere, the temperature is raised to 1100°C and held at 1500°C for 240 minutes to sinter and form BN material with a morphology of uniformly dispersed micron-sized quasi-spherical particles.

[0108] Through Example 2 Figure 9 XRD analysis of the granular products at 1100℃ and 1500℃ revealed a characteristic peak of boron oxide at 1100℃. This is because the low sintering temperature and short holding time resulted in incomplete volatilization of residual boron oxides, which is related to... Figure 10 The corresponding infrared spectrum. Figure 11 The images show the SEM images of the unscreened pyrolysis products at 1500℃ in Example 2, before and after the balling process. The comparison reveals significant differences between the two, demonstrating the effect of the balling process of the present invention on improving the sphericity of the granulated particles. Figure 12The diagram shows the grinding and balling process barrels, namely a barrel-type grinding and ball-type grinding and balling barrels. These two types of grinding barrels have almost the same grinding and balling effect. Figure 13 , Figure 14 Examples 2 show the 1500℃ pyrolysis products after the balling process, both without and after sieving through screens of different mesh sizes. Gradual magnified scanning electron microscope images (e.g.) Figure 15 As shown, this also demonstrates the significant surface characteristic of higher crystallinity obtained by pyrolysis at 1500℃. Similarly, from... Figure 16 Data analysis and combination Figure 15 The photograph also indicates that the quasi-spherical powder particles have low porosity, with a specific surface area of ​​only 3.075 m². 2 / g.

[0109] Example 3

[0110] The difference from Example 2 is that the nitrogen source was replaced with melamine, and the molar ratio of boric acid to melamine was 5:1. From Figure 17 and Figure 18 As can be seen, although the XRD and infrared spectroscopy results did not significantly differentiate the differences after changing to melamine nitrogen source, the sphericity of the particles obtained by the same granulation and balling process was worse than that of Examples 1 and 2. This is because the adduct crystals formed by melamine and boric acid are very prone to water absorption and oriented growth during the spray-mixing granulation process, resulting in a very rough particle surface after drying. Although the balling process can smooth and even out the surface edges and irregular protrusions to a certain extent, the effect is not as significant as that of Examples 1 and 2. Figure 19 and Figure 20 Although the sphericity of the particles is poor, their microstructure is good. Figure 21 These quasi-spherical particles still have a high degree of crystallinity, which is consistent with... Figure 17 The XRD pattern of the pyrolysis sample at 1500℃ corresponds to that of the sample.

[0111] Example 4

[0112] The difference from Example 1 is that the nitrogen source was replaced with dicyandiamide, and the molar ratio of boric acid to dicyandiamide was 3:1. From Figure 22 The results showed that the crystallinity of the sample obtained at 1500℃ after changing to dicyandiamide as the nitrogen source was also very high. However, the sphericity of the particles obtained by the same granulation and spheroidizing process was the worst compared to Examples 1, 2, and 3. This is because dicyandiamide is more reactive than the nitrogen sources mentioned above, and it is easier to decompose its nitrogen source components first during pyrolysis, leading to non-spherical deformation of the particles during high-temperature pyrolysis. Figure 23 and Figure 24 .

[0113] Example 5

[0114] Using melamine and aluminum chloride hexahydrate in a molar ratio of 1:3 as raw materials, the mixture was stirred in deionized water at 45°C until a homogeneous slurry was obtained, followed by stirring at 95°C for 8 hours to obtain a viscous, creamy slurry.

[0115] After filtration, the slurry was placed in an oven at 80°C for dehydration and solvent treatment for 48 hours to obtain a hard, blocky precursor that does not contain water molecules with crystalline structure. The blocky precursor was then fed into a baghouse pulverizer to be pulverized to obtain ultrafine powder with a particle size of less than 400 mesh.

[0116] At room temperature, the ultrafine powder is fed into the rotary granulation chamber of the centrifugal mixer through the feeding port. The stirring rod of the centrifugal mixer is adjusted to rotate counterclockwise at 500 r / min, and the chamber rotates clockwise at 50 r / min. The mixture is stirred for 15 minutes. The stirring rod speed is then adjusted to rotate clockwise at 2000 r / min, and the chamber continues to rotate clockwise at 100 r / min. 15% pure water (by weight of the ultrafine powder) is sprayed in, and the mixture is stirred and granulated for 45 minutes. The stirring rod speed is then adjusted to rotate counterclockwise at 3500 r / min, and the chamber continues to rotate clockwise at 200 r / min. The pellet drying process is carried out for 30 minutes.

[0117] After the pellet drying process is completed, adjust the stirring rod speed to 500 r / min clockwise and the barrel speed to 100 r / min counterclockwise to carry out the grinding process. When the barrel is upright during the grinding process, attach 3000 and 5000 grit sandpaper to the bottom and inner wall of the barrel respectively, tilt the barrel so that the angle between its rotation axis and the horizontal plane is 30° to ensure that the pellets can be fully ground by the sandpaper at the bottom of the barrel. Change the angle between the barrel's rotation axis and the horizontal plane to 60° so that the pellets can be further ground by the sandpaper on the inner wall of the barrel. The grinding process lasts for 16 hours. When the barrel is spherical, attach 3000 grit sandpaper to the entire inner wall of the barrel, change the angle between the rotation axis and the horizontal plane to 45°, and grind for 8 hours. Then change the sandpaper to 5000 grit and grind for 8 hours.

[0118] After centrifugal mixing, granulation, and spheroidization processes, the resulting precursor powder of hard quasi-spherical particles was discharged and dried at 80°C for 4 hours to remove excess moisture, yielding relatively dense precursor particles of hard quasi-spherical particles. These precursor particles were then fed into a vibrating screen for classification, obtaining spherical precursors of different sizes ranging from 20 to 400 mesh (37 to 800 μm). The sieved spherical precursor particles were placed in a boron nitride crucible and then into a tube furnace. Under a nitrogen atmosphere, the temperature was raised to 1100°C and held for 240 minutes to sinter and form AlN material with a morphology of uniformly dispersed micron-sized quasi-spherical particles.

[0119] The prepared quasi-spherical hexagonal aluminum nitride particles were characterized by XRD diffraction and infrared spectroscopy (as shown in the figure). Figure 25 , Figure 26 In the XRD diffraction pattern, due to the observed diffraction peaks on the 100, 002, 101, 102, 110, 103, and 112 planes, it was identified as hexagonal aluminum nitride; in the infrared spectrum, the 500-750 cm⁻¹... -1 The presence of N-Al group vibrations indicates that the hexagonal aluminum nitride phase has essentially formed at this temperature. Figure 27 It can be seen that although this method can granulate aluminum nitride precursor particles, and although the sphericity is poor, the proportion of quasi-spherical particles is not less than 50%. The surface microstructure of the quasi-spherical aluminum nitride particles ( Figure 28 It can be seen that the microstructure surface of these aluminum nitride quasi-spherical particles has high roughness characteristics.

[0120] Example 6

[0121] The aluminum source in Example 5 was replaced with aluminum nitrate nonahydrate, and all other operations were the same as in Example 5, resulting in aluminum nitride particles with the same quasi-spherical morphology as in Example 5.

[0122] Examples 7, 8, and 9

[0123] The nitrogen source in Example 5 was replaced with guanidine carbonate, dicyandiamide, and 3-amino-1,2,4-triazole. All other operations were the same as in Example 5, and the product was aluminum nitride particles with the same quasi-spherical morphology as in Example 5.

[0124] Examples 10, 11, and 12

[0125] The aluminum source and nitrogen source in Example 5 were replaced with aluminum nitrate nonahydrate, guanidine carbonate, or dicyandiamide and 3-amino-1,2,4-triazole, respectively. All other operations were the same as in Example 5, and the product was aluminum nitride particles with the same quasi-spherical morphology as in Example 5.

[0126] The synthesis method of any one or more of the four processes in the centrifugal stirring granulation of high-crystallinity quasi-spherical particles prepared by centrifugal stirring at high temperature to produce hexagonal boron nitride or aluminum nitride quasi-spherical particles, whether indirectly or directly using the technical route and basic principles of this invention, to synthesize and prepare hexagonal boron nitride or aluminum nitride spherical particles and their corresponding product types, as well as the technology and means of applying the hexagonal boron nitride and aluminum nitride quasi-spherical particles obtained by this preparation method to other related fields, are equivalent to the protection scope of this invention.

[0127] Any non-inventive techniques and processes that, without departing from the basic principles, basic raw materials, and basic route of this invention, involve at least one or more substitutions, simplifications, replacements, modifications, improvements, alterations, and additions to experimental steps and raw materials to synthesize boron nitride spherical particles or aluminum nitride spherical particles similar to those produced by this invention, shall be deemed to infringe upon the scope of protection of this invention.

[0128] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A method for preparing hexagonal nitride quasi-spherical particles by centrifugal stirring granulation-high-temperature pyrolysis, characterized in that, Includes the following steps: (1) A mixture of a boron-containing compound or an aluminum-containing compound and a nitrogen-containing compound is added to an aqueous solution to dissolve and react, thereby obtaining a viscous paste-like slurry. The mass ratio of the mixture to the aqueous solution is 1:0.2-1.

5. The aluminum-containing compound is at least one of anhydrous aluminum chloride, aluminum chloride hexahydrate, aluminum nitrate nonahydrate, or aluminic acid. The boron-containing compound in step (1) is at least one of boric acid, borax, or boron trioxide; The nitrogen-containing compound is at least one of dicyandiamide, guanidine, guanidine carbonate, 3-amino-1,2,4-triazole, or melamine; (2) After the creamy slurry is dehydrated by heating and evaporation, an ultra-dry hard block is obtained. The hard block is then crushed into an ultra-fine powder that can pass through a 100-600 mesh screen. (3) The ultrafine powder is loaded into the granulation barrel of a centrifugal stirring granulation equipment equipped with a stirring rod and a rotating barrel with adjustable clockwise and counterclockwise rotation. During the stirring process, liquid reagent is sprayed. Under the rotation of the stirring rod and the barrel, the material and water undergo a hydration reaction, gradually crystallize and form granular substances. As these crystalline substances gradually increase, the material exhibits hardening characteristics. After the centrifugal stirring granulation process, fluffy white granular powder is obtained. After drying, hard granular powder with good dispersibility is obtained. This granular powder is the hard granular quasi-spherical precursor powder for the preparation of hexagonal nitride quasi-spherical particles by pyrolysis. (4) The precursor powder of the obtained hard quasi-sphere particles is subjected to a constant temperature reaction of 0.5-24 hours in a protective gas atmosphere within a target temperature range of 1100℃-1500℃ to obtain a white or grayish-white granular product. The granular product after pyrolysis retains the quasi-sphere particle characteristics of the precursor. The granular product after pyrolysis is a micron-sized quasi-sphere. At least one powder obtained after centrifugal stirring granulation, drying, or pyrolysis reaction is subjected to balling treatment. The aqueous solution in step (1) and the liquid reagent sprayed in step (3) are water, which is pure water without any added binder, flux, accelerant or dispersant, including deionized water, purified water, distilled water or tap water; During the stirring process, there is a certain matching relationship between the clockwise and counterclockwise rotation of the stirring rod and the barrel body, namely: The first stage is the mixing process. The ultrafine powder is transferred into the centrifugal mixing tank. The stirring rod is rotated counterclockwise at a speed of 10 r / min-500 r / min, and the tank body is rotated clockwise at a speed of 10 r / min-50 r / min. The centrifugal mixing time ranges from 10 to 30 minutes in this mode. The second stage is the granulation process. The stirring rod is rotated clockwise at a speed of 500 r / min-2000 r / min, and the barrel is rotated clockwise at a speed of 50 r / min-100 r / min. During this operation, liquid reagent is sprayed evenly and the process continues for 30-90 minutes. The third stage is the pellet drying process. The stirring rod is rotated counterclockwise at a speed of 2000 r / min-5000 r / min, and the barrel is rotated clockwise at a speed of 100 r / min-200 r / min. No liquid reagent water is sprayed during this process. This process takes 15-60 minutes.

2. The preparation method according to claim 1, characterized in that, The molar ratio of the boron-containing compound or aluminum-containing compound to the nitrogen-containing compound is in the range of 0.1-8; the mixture is stirred and dissolved in an aqueous solution at a temperature range of 45℃-99℃ for 2-48 hours to obtain a viscous cream-like slurry.

3. The preparation method according to claim 1, characterized in that, The mass of the sprayed liquid reagent is 10 wt.%-50 wt.% of the mass of the ultrafine powder added to the granulation tank.

4. The preparation method according to claim 3, characterized in that, The mass of the sprayed liquid reagent is 15 wt.%-40 wt.% of the mass of the ultrafine powder added to the granulation tank.

5. The preparation method according to claim 1, characterized in that, The specific process of spheroidization is as follows: an abrasive surface with a mesh size range of 600-10000 mesh is created on the inner wall and bottom of the granulation tank. The stirring rod is rotated clockwise at a speed of 500 r / min-5000 r / min, and the tank is rotated counterclockwise at a speed of 50 r / min-200 r / min. No liquid reagents are sprayed during this process. The running time of this process is 60-1000 minutes.

6. The preparation method according to claim 1, characterized in that, There are two types of barrels used in the spheroidizing process: one type consists of a barrel structure with an upright barrel wall and a bottom surface perpendicular to the upright barrel wall, with the angle between its rotation axis and the horizontal plane varying from 30° to 60°, and the inner wall and bottom of the barrel being made into an abrasive surface with a mesh size ranging from 600 to 10,000; the other type is a spherical barrel structure, with the angle between its rotation axis and the horizontal plane varying from 20° to 45°, and the inner wall of the spherical barrel being made into an abrasive surface with a mesh size ranging from 600 to 10,000.

7. The preparation method according to claim 1, characterized in that, The protective gas flow atmosphere in step (4) is an inert atmosphere or an atmosphere containing a certain reducing gas component; The inert atmosphere is at least one of nitrogen or argon; The atmosphere containing a certain reducing gas component is applied during the high-temperature pyrolysis process when the aluminum-containing compound is aluminic acid or aluminum nitrate. The reducing gas component is at least one of ammonia or hydrogen, wherein the volume proportion of ammonia is not less than 10% and the volume proportion of hydrogen is not more than 10%. An atmosphere containing a certain reducing gas component is: nitrogen + ammonia, argon + ammonia, or hydrogen + nitrogen.

8. The preparation method according to claim 1, characterized in that, The hexagonal boron nitride or hexagonal aluminum nitride quasi-spherical particle powder obtained in step (4) has the characteristic of achieving a wide range of particle size distribution from 37 μm to 800 μm in the same batch. After vibrating and filtering through filter screens of different mesh sizes, nitride quasi-spherical particles with different particle size specifications are obtained. The vibration screening process of filter screens of different mesh sizes is carried out before or after high-temperature pyrolysis.

9. A hexagonal nitride quasi-spherical particle, characterized in that, The quasi-spherical particles are obtained by any one of the preparation methods described in claims 1-8, and the sphericity of the quasi-spherical particles is 0.8-1.0; the quasi-spherical particles have quasi-spherical morphological characteristics, high strength, high density, low porosity and high crystallinity.

10. The hexagonal nitride quasi-spherical particles according to claim 9, characterized in that, The sphericity of the quasi-spherical particles is 0.9-1.0.

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