Method for preparing nanoscale spherical boron nitride powder

Abstract

The invention provides a method for preparing nanoscale spherical boron nitride powder, and relates to the field of boron nitride powder. The method for preparing the nanoscale spherical boron nitride powder comprises the following steps of surface pretreatment, liquid-phase ultrasonic stripping, slurry preparation and spray granulation. The invention discloses a method for preparing nanoscale spherical boron nitride powder. The problems that an existing preparation method of the nanoscale spherical boron nitride powder is long in preparation period, high in preparation cost, poor in controllability of the preparation process, poor in morphology controllability of the nanoscale spherical boron nitride powder, poor in size stability of the nanoscale spherical boron nitride powder and not suitable for industrial large-scale production can be solved. Based on a large-size hexagonal boron nitride powder raw material, the shape controllable preparation of the nanoscale spherical boron nitride powder on an industrial scale is realized.

Description

Technical Field

[0001] The invention relates to the field of boron nitride powders, and in particular to a method for preparing nano-scale spherical boron nitride powders. Background Art

[0002] Nano hexagonal boron nitride is a two-dimensional graphene-like material, and also a new type of ceramic material with excellent performance and development potential. It has a wide range of applications in metallurgy, aerospace, electronics, and nuclear industries due to its high-temperature oxidation resistance, radiation resistance, high thermal conductivity, high-temperature lubricity, good dielectric properties, and insulation properties. Hexagonal boron nitride powder materials are generally three-dimensional network structure materials formed by spatial crosslinking of two-dimensional boron nitride nanosheets; in addition to the properties of two-dimensional boron nitride nanosheets, three-dimensional boron nitride nanomaterials have greater advantages in spatial thermal conductivity, catalyst carriers, and sound absorption and shockproofing; at the same time, hexagonal boron nitride can still remain stable in an inert atmosphere at 2500°C, and can maintain good stability in an oxidizing atmosphere at 850°C, with excellent thermal stability and broad application prospects.

[0003] At present, the existing preparation methods of boron nitride materials mainly include: two synthesis methods of precursor synthesis and ammonia nitridation two-step method, high temperature solid phase reaction method, and exfoliation methods for preparing boron nitride nanosheets such as chemical exfoliation, liquid phase exfoliation, dielectric enhanced liquid phase exfoliation, supercritical exfoliation and mechanical exfoliation. Among them, the two-step method of precursor synthesis and ammonia nitridation and high temperature solid phase reaction method are mainly used to synthesize hexagonal boron nitride nanosheets; chemical exfoliation, dielectric enhanced liquid phase exfoliation, supercritical exfoliation, mechanical exfoliation and other methods are mainly used for the exfoliation of multilayer boron nitride, which realizes the preparation of single-layer or few-layer boron nitride nanosheets (BNNS) by exfoliating the layered structure of boron nitride.

[0004] However, the products obtained by the above process are all boron nitride nanosheets, and nano-scale spherical boron nitride powder cannot be directly obtained. Sphericity and nanometer size are indicators that need to be strictly controlled in the preparation of nano-scale spherical boron nitride powder. Although the ball milling process can be used to modify the shape of single-layer or few-layer boron nitride nanosheets, it is impossible to achieve controllable preparation of the microscopic morphology of nano-scale powders; specifically, it is difficult to accurately control the particle size and morphology of boron nitride powder during ball milling, the product size distribution is uneven, and the batch stability of boron nitride powder is poor, which cannot meet the requirements of large-scale preparation; at the same time, as the ball milling treatment time increases, powder particles are very likely to agglomerate, the preparation controllability is poor, the preparation cycle is long, and the yield is low.

[0005] Furthermore, the existing methods for preparing boron nitride powder mainly include: hexagonal boron nitride spray granulation method, precursor spray granulation method, plasma melting method, and chemical vapor deposition method. Among them, the hexagonal boron nitride spray granulation method generally comprises the following steps: after the hexagonal boron nitride raw material powder and raw materials such as solvent are configured into a slurry, the hexagonal boron nitride raw material powder is bonded into balls through a spray granulation device; however, the particle size of the spherical boron nitride powder prepared by this method is several times or dozens of times that of the hexagonal boron nitride raw material powder, and the particle size of the hexagonal boron nitride raw material powder is mostly in the micron level, which has a large size characteristic compared to the required nano-level boron nitride powder, and thus the nano-level boron nitride powder cannot be balled. The precursor spray granulation method has a high overall preparation cost due to the high price of the monomer for synthesizing boron nitride precursor (more than 1,000 yuan / kg), which is not conducive to industrial-scale production; the plasma melting method has strict requirements on equipment and high energy consumption, which is also not conducive to the promotion of industrial-scale production; although the chemical vapor deposition method can achieve the preparation of spherical boron nitride, the spherical boron nitride prepared by it has a high oxygen content (greater than 5wt%), and the product quality is poor, which seriously limits its subsequent application performance; at the same time, the addition of nano-size requirements makes the disadvantages of the aforementioned boron nitride powder preparation methods more prominent.

[0006] It can be seen that the existing preparation methods of nano-scale spherical boron nitride powders have the problems of long preparation cycle, high preparation cost, poor controllability of the preparation process, poor controllability of the morphology of nano-scale spherical boron nitride powders, poor dimensional stability of nano-scale spherical boron nitride powders, and unsuitability for industrial-scale production, and it is impossible to achieve industrial-scale preparation of nano-scale spherical boron nitride powders. Summary of the invention

[0007] In order to solve the technical problems existing in the prior art, the present invention provides a method for preparing nano-scale spherical boron nitride powder, which can overcome the problems of the existing method for preparing nano-scale spherical boron nitride powder, such as long preparation cycle, high preparation cost, poor controllability of the preparation process, poor controllability of the morphology of the nano-scale spherical boron nitride powder, poor dimensional stability of the nano-scale spherical boron nitride powder, and unsuitability for industrial-scale production; based on large-size hexagonal boron nitride powder raw materials, industrial-scale morphology controllable preparation of nano-scale spherical boron nitride powder is achieved.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for preparing nano-scale spherical boron nitride powder, comprising the following steps: surface pretreatment, liquid phase ultrasonic peeling, slurry preparation, and spray granulation; The surface pretreatment method comprises adding large-sized hexagonal boron nitride powder to a sodium hydroxide solution, stirring and reacting at a temperature of 80-120° C.; cooling and separating to obtain a solid, and washing and drying the solid to obtain a modified boron nitride powder; The liquid-phase ultrasonic exfoliation method comprises selecting one or more of methanol, ethanol, isopropanol, and tert-butyl alcohol, mixing with water to form an ultrasonic exfoliation solvent, adding the modified boron nitride powder into the ultrasonic exfoliation solvent, and controlling the solid content to be 30-60wt%; after liquid-phase ultrasonic exfoliation treatment, separating and obtaining solid matter, washing and drying the solid matter, and obtaining quasi-nanoscale boron nitride nanosheets; The method for preparing the slurry is to grind and mix anhydrous ethanol, acrylic acid, dispersant KOS-110, and quasi-nano-sized boron nitride nanosheets uniformly to prepare a nano-sized boron nitride nanosheet slurry with a viscosity of 100-1000 Pa·s; The spray granulation method comprises the following steps: using nano-sized boron nitride nanosheet slurry as a raw material, and performing spray granulation treatment to obtain nano-sized spherical boron nitride powder.

[0009] Preferably, in the surface pretreatment, the liquid-to-solid mass ratio of the sodium hydroxide solution to the large-sized hexagonal boron nitride powder is 5-10:1; The concentration of the sodium hydroxide solution is at least 4 mol / L.

[0010] Preferably, in the surface pretreatment, the stirring reaction speed is 200-500 rpm, and the stirring reaction time is 12-48 h; The average particle size of the large-size hexagonal boron nitride powder is 3-5 μm.

[0011] Preferably, in the liquid-phase ultrasonic stripping, one or more of methanol, ethanol, isopropanol and tert-butanol are selected and mixed with water in a mass ratio of 1-5:1 to form an ultrasonic stripping solvent.

[0012] Preferably, in the liquid phase ultrasonic stripping, the ultrasonic frequency is controlled to be 20-40kHz, the ultrasonic power is 1000-2000W, and the liquid phase ultrasonic stripping treatment time is 1-2h; The number of layers of the quasi-nanoscale boron nitride nanosheets is 1-5.

[0013] Preferably, in the preparation of the slurry, the weight ratio of quasi-nanoscale boron nitride nanosheets, anhydrous ethanol, acrylic acid, and dispersant KOS-110 is 100:150-300:5-15:0.1-1.

[0014] Preferably, in the preparation of the slurry, the ball mass ratio is controlled to be 1:10-20 during the grinding and mixing process, the grinding and mixing speed is 150-300 rpm, and the grinding and mixing time is 5-10 h.

[0015] Preferably, in the spray granulation, the inlet temperature of the spray granulation device is controlled to be 120-135°C, the outlet temperature is 110-130°C, the atomizer speed is 50-200Hz, and the feed rate is 2-5L / h.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The method for preparing nano-scale spherical boron nitride powder of the present invention uses large-sized hexagonal boron nitride powder as raw material, prepares a predetermined number of quasi-nano-scale boron nitride nanosheets by surface pretreatment and liquid-phase ultrasonic exfoliation, and then prepares a boron nitride nanosheet slurry with a predetermined viscosity, and then cooperates with a spray drying process to prepare nano-scale spherical boron nitride powder with controllable morphology; wherein, by hydroxylating the surface of the large-sized hexagonal boron nitride powder, the exfoliation efficiency and exfoliation effect can be effectively improved; the single boron nitride nanosheet prepared by liquid-phase ultrasonic exfoliation is prepared by a spray granulation process. The above-mentioned technical means cooperate with each other and work synergistically to overcome the problems of the existing preparation method of nano-scale spherical boron nitride powder, such as long preparation cycle, high preparation cost, poor controllability of the preparation process, poor controllability of the morphology of nano-scale spherical boron nitride powder, poor dimensional stability of nano-scale spherical boron nitride powder, and unsuitability for industrial-scale production. The method has the characteristics of high preparation efficiency, low preparation cost, easy controllability of the preparation process and product specifications, and is conducive to industrial-scale production.

[0017] (2) The method for preparing nano-scale spherical boron nitride powder of the present invention has a controllable preparation process, and the nano-scale spherical boron nitride powder has good controllable morphology and dimensional stability. The prepared nano-scale spherical boron nitride powder has an average particle size (D50) of 900nm, a particle size distribution range of 500-1500nm, a sphericity of ≥90%, and a bulk density of 0.2-0.3g / cm 3 , specific surface area (BET) is 5-15m 2 / g; the particle size distribution of nano-scale spherical boron nitride powder is uniform and the batch stability is good, which is conducive to industrial-scale production.

[0018] (3) The method for preparing nano-scale spherical boron nitride powder of the present invention has high activity and good thermal conductivity. The thermal conductivity of the prepared nano-scale spherical boron nitride powder is 50-80 W / m·K, which can be effectively applied to emerging fields such as thermal management, further expanding the application scope of boron nitride powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The figure is a schematic diagram of the process of preparing nano-scale spherical boron nitride powder according to the present invention.

[0020] Figure 2 This is the particle size distribution diagram of the nano-scale spherical boron nitride powder prepared in Example 1. DETAILED DESCRIPTION

[0021] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific embodiments of the present invention are now described. It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those of ordinary skill in the art to which the present invention belongs.

[0022] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, "first", "second", etc. are used to distinguish similar objects, and are not used to describe a specific order or sequence. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0023] like Figure 1 As shown, an embodiment of the present invention provides a method for preparing nano-scale spherical boron nitride powder, comprising the following steps: surface pretreatment, liquid phase ultrasonic peeling, slurry preparation, and spray granulation.

[0024] The surface pretreatment method comprises the following steps: adding large-sized hexagonal boron nitride powder (h-BN) to a sodium hydroxide solution with a concentration of at least 4 mol / L at a liquid-solid mass ratio of 5-10:1, and then stirring the solution at a temperature of 80-120°C and a rotation speed of 200-500 rpm for reaction for 12-48 hours; filtering the solution after cooling to obtain a solid, and washing and drying the solid to obtain a modified boron nitride powder (hBN-OH) with a neutral pH and hydroxyl (-OH) groups grafted on the surface.

[0025] In the surface pretreatment, the liquid-to-solid mass ratio of the sodium hydroxide solution to the large-sized hexagonal boron nitride powder is preferably 4.5-5.5:1.

[0026] In the surface pretreatment, the temperature is preferably 80-100° C., the rotation speed is preferably 200-300 rpm, and the stirring reaction time is preferably 12-24 h.

[0027] In the surface pretreatment, the average particle size of the large-size hexagonal boron nitride powder h-BN is preferably 3-5 μm.

[0028] The liquid-phase ultrasonic stripping method comprises the following steps: selecting one or more of methanol, ethanol, isopropanol and tert-butyl alcohol, and preparing the mixture with water in a mass ratio of 1-5:1 to form an ultrasonic stripping solvent; then adding the modified boron nitride powder into the ultrasonic stripping solvent, and controlling the solid content to be 30-60wt%; then performing liquid-phase ultrasonic stripping treatment, controlling the ultrasonic frequency to be 20-40kHz, the ultrasonic power to be 1000-2000W, and the liquid-phase ultrasonic stripping treatment time to be 1-2h; after the liquid-phase ultrasonic stripping treatment is completed, filtering to obtain a solid, and washing and drying the solid to obtain a quasi-nanoscale boron nitride nanosheet (BNNS) having 1-5 layers.

[0029] In the liquid-phase ultrasonic stripping, ethanol and / or isopropanol are preferably used to prepare the ultrasonic stripping solvent with water; Preferably, the ethanol and / or isopropanol is mixed with water in a mass ratio of 1-2:1 to form an ultrasonic stripping solvent.

[0030] In the liquid-phase ultrasonic stripping, the solid content is preferably controlled to be 40-45wt%; the ultrasonic frequency is preferably 30-35kHz, the ultrasonic power is preferably 1500-2000W, and the ultrasonic time is preferably 1.5-2h.

[0031] Preferably, in the liquid phase ultrasonic exfoliation, the number of layers of quasi-nanoscale boron nitride nanosheets (BNNS) is preferably a single layer or a few layers.

[0032] The slurry preparation method comprises the following steps: using anhydrous ethanol as a solvent, acrylic acid as a binder, KOS-110 as a dispersant, and putting the quasi-nanoscale boron nitride nanosheets (BNNS) into a stirring grinder, controlling the material ball mass ratio to be 1:10-20, and the grinding speed to be 150-300 rpm. After stirring and grinding for 5-10 hours, a nano-sized boron nitride nanosheet slurry with a viscosity of 100-1000 Pa·s is obtained.

[0033] Preferably, the weight ratio of quasi-nanoscale boron nitride nanosheets, anhydrous ethanol, acrylic acid, and KOS-110 is 100:150-300:5-15:0.1-1; more preferably, the weight ratio of quasi-nanoscale boron nitride nanosheets, anhydrous ethanol, acrylic acid, and KOS-110 is 100:150-200:5-10:0.7-1.

[0034] Preferably, the viscosity of the nano-sized boron nitride nanosheet slurry is 200-300 Pa·s.

[0035] The spray granulation method comprises the following steps: using nanometer-sized boron nitride nanosheet slurry as raw material, carrying out spray granulation treatment, controlling the inlet temperature of the spray granulation device to be 120-135°C, the outlet temperature to be 110-130°C, the atomizer speed to be 50-200Hz, and the feed rate to be 2-5L / h; the nanometer-sized boron nitride nanosheet slurry is atomized into tiny particles by the atomizer, and is quickly dried in the process of spray descent, so as to obtain nanometer-sized spherical boron nitride powder with uniform particle size distribution.

[0036] The method for preparing nano-scale spherical boron nitride powder uses large-sized hexagonal boron nitride powder as raw material, prepares quasi-nano-scale boron nitride nanosheets with a predetermined number of layers by surface pretreatment and liquid-phase ultrasonic exfoliation, prepares boron nitride nanosheet slurry with a predetermined viscosity, and then prepares nano-scale spherical boron nitride powder with controllable morphology by using a spray drying process; wherein the hydroxylation surface pretreatment of the large-sized hexagonal boron nitride powder surface can effectively improve the exfoliation efficiency and exfoliation effect; the single layer or A few layers of BNNS are converted into nano-sized spherical boron nitride powder with uniform particle size distribution; the aforementioned technical means cooperate and work synergistically with each other, which can overcome the problems of the existing preparation method of nano-scale spherical boron nitride powder, such as long preparation cycle, high preparation cost, poor controllability of the preparation process, poor controllability of the morphology of nano-scale spherical boron nitride powder, poor dimensional stability of nano-scale spherical boron nitride powder, and unsuitability for industrial-scale production. The method has the characteristics of high preparation efficiency, low preparation cost, easy control of the preparation process and product specifications, and is conducive to industrial-scale production.

[0037] The nano-scale spherical boron nitride powder prepared by the above method has an average particle size (D50) of 900nm, a particle size distribution range of 500-1500nm, a sphericity of ≥90%, and a bulk density of 0.2-0.3g / cm 3 , specific surface area (BET) is 5-15m 2 / g, thermal conductivity is 50-80W / m·K.

[0038] The specific implementation methods of the present invention are further described below in conjunction with some specific embodiments.

[0039] Example 1 This embodiment provides a method for preparing nano-scale spherical boron nitride powder, specifically: 1. Surface pretreatment Large-sized hexagonal boron nitride powder (h-BN) was added to a 5 mol / L sodium hydroxide solution at a liquid-to-solid mass ratio of 5:1, and then the reaction was stirred at 80°C and 200 rpm for 12 hours. After cooling, the solid was filtered to obtain a solid. The solid was washed and dried to obtain a modified boron nitride powder (hBN-OH) with a neutral pH and hydroxyl (-OH) groups grafted on the surface.

[0040] Among them, the average particle size of large-size hexagonal boron nitride powder h-BN is 5μm.

[0041] 2. Liquid phase ultrasonic peeling After ethanol and water are prepared into an ultrasonic exfoliation solvent in a mass ratio of 1:1, the modified boron nitride powder is put into the ultrasonic exfoliation solvent and the solid content is controlled to be 40wt%; then liquid phase ultrasonic exfoliation treatment is carried out, the ultrasonic frequency is controlled to be 30kHz, the ultrasonic power is controlled to be 2000W, and the liquid phase ultrasonic exfoliation treatment time is 2h; after the liquid phase ultrasonic exfoliation treatment is completed, the solid is filtered to obtain the solid, and the solid is washed and dried to obtain quasi-nanoscale boron nitride nanosheets (BNNS) with 1-3 layers.

[0042] 3. Slurry preparation Anhydrous ethanol was used as solvent, acrylic acid as binder, KOS-110 as dispersant, and quasi-nanoscale boron nitride nanosheets (BNNS) were put into a stirring mill. The mass ratio of the material and the ball was controlled to be 1:10, and the grinding speed was 150 rpm. After stirring and grinding for 10 hours, a nano-sized boron nitride nanosheet slurry with a viscosity of 200 Pa·s was obtained.

[0043] Among them, the weight ratio of quasi-nanoscale boron nitride nanosheets, anhydrous ethanol, acrylic acid, and KOS-110 is 100:150:5:1.

[0044] 4. Spray granulation Nano-sized boron nitride nanosheet slurry is used as raw material for spray granulation treatment. The inlet temperature of the spray granulation device is controlled to be 135°C, the outlet temperature is 125°C, the atomizer speed is 200Hz, and the feed rate is 2L / h. The nano-sized boron nitride nanosheet slurry is atomized into tiny particles by the atomizer and quickly dried during the spray descent process to obtain nano-scale spherical boron nitride powder with uniform particle size distribution.

[0045] The nano-scale spherical boron nitride powder prepared in this embodiment has an average particle size D50 of 900 nm, D10 of 500 nm, D90 of 1500 nm, a sphericity of 93%, and a bulk density of 0.3 g / cm 3 , specific surface area (BET) is 15m 2 / g, and the thermal conductivity is 76W / m·K. The particle size distribution of the nano-scale spherical boron nitride powder prepared in this embodiment is shown in FIG. Figure 2 shown.

[0046] Example 2 This embodiment provides a method for preparing nano-scale spherical boron nitride powder, specifically: 1. Surface pretreatment Large-sized hexagonal boron nitride powder (h-BN) was added to a 5 mol / L sodium hydroxide solution at a liquid-to-solid mass ratio of 5:1, and then the reaction was stirred at 100°C and 200 rpm for 24 hours. After cooling, the solid was filtered to obtain a solid. The solid was washed and dried to obtain a modified boron nitride powder (hBN-OH) with a neutral pH and hydroxyl (-OH) groups grafted on the surface.

[0047] Among them, the average particle size of large-size hexagonal boron nitride powder h-BN is 5μm.

[0048] 2. Liquid phase ultrasonic peeling After isopropanol and water are prepared into an ultrasonic stripping solvent in a mass ratio of 1:1, the modified boron nitride powder is put into the ultrasonic stripping solvent and the solid content is controlled to be 40wt%; then liquid phase ultrasonic stripping treatment is carried out, the ultrasonic frequency is controlled to be 32kHz, the ultrasonic power is controlled to be 2000W, and the liquid phase ultrasonic stripping treatment time is 2h; after the liquid phase ultrasonic stripping treatment is completed, the solid is filtered to obtain the solid, and the solid is washed and dried to obtain quasi-nanoscale boron nitride nanosheets (BNNS) with 3-5 layers.

[0049] 3. Slurry preparation Anhydrous ethanol was used as solvent, acrylic acid as binder, KOS-110 as dispersant, and quasi-nanoscale boron nitride nanosheets (BNNS) were put into a stirring mill. The mass ratio of the material and the ball was controlled to be 1:10, and the grinding speed was 150 rpm. After stirring and grinding for 10 hours, a nano-sized boron nitride nanosheet slurry with a viscosity of 200 Pa·s was obtained.

[0050] Among them, the weight ratio of quasi-nanoscale boron nitride nanosheets, anhydrous ethanol, acrylic acid, and KOS-110 is 100:200:10:1.

[0051] 4. Spray granulation Nano-sized boron nitride nanosheet slurry is used as raw material for spray granulation treatment. The inlet temperature of the spray granulation device is controlled to be 135°C, the outlet temperature is 125°C, the atomizer speed is 200Hz, and the feed rate is 2L / h. The nano-sized boron nitride nanosheet slurry is atomized into tiny particles by the atomizer and quickly dried during the spray descent process to obtain nano-scale spherical boron nitride powder with uniform particle size distribution.

[0052] The nano-scale spherical boron nitride powder prepared in this embodiment has an average particle size D50 of 1200nm, D10 of 600nm, D90 of 2000nm, sphericity of 90%, and a bulk density of 0.25g / cm 3 , the specific surface area (BET) is 13m 2 / g, thermal conductivity is 53W / m·K.

[0053] Example 3 This embodiment provides a method for preparing nano-scale spherical boron nitride powder, specifically: 1. Surface pretreatment Large-sized hexagonal boron nitride powder (h-BN) was added to a 5 mol / L sodium hydroxide solution at a liquid-to-solid mass ratio of 5:1, and then the reaction was stirred at 80°C and 300 rpm for 12 hours. After cooling, the solid was filtered to obtain a solid. The solid was washed and dried to obtain a modified boron nitride powder (hBN-OH) with a neutral pH and hydroxyl (-OH) groups grafted on the surface.

[0054] The average particle size of the hexagonal boron nitride powder h-BN is 5 μm.

[0055] 2. Liquid phase ultrasonic peeling After ethanol, isopropanol and water are prepared into an ultrasonic stripping solvent in a mass ratio of 1:1:1, the modified boron nitride powder is put into the ultrasonic stripping solvent and the solid content is controlled to be 45wt%; then a liquid phase ultrasonic stripping treatment is performed, the ultrasonic frequency is controlled to be 35kHz, the ultrasonic power is controlled to be 2000W, and the liquid phase ultrasonic stripping treatment time is 2h; after the liquid phase ultrasonic stripping treatment is completed, the solid is filtered to obtain the solid, and the solid is washed and dried to obtain quasi-nanoscale boron nitride nanosheets (BNNS) with 2-4 layers.

[0056] 3. Slurry preparation Anhydrous ethanol was used as solvent, acrylic acid as binder, KOS-110 as dispersant, and quasi-nanoscale boron nitride nanosheets (BNNS) were put into a stirring mill. The mass ratio of the material and the ball was controlled to be 1:10, and the grinding speed was 150 rpm. After stirring and grinding for 10 hours, a nano-sized boron nitride nanosheet slurry with a viscosity of 200 Pa·s was obtained.

[0057] Among them, the weight ratio of quasi-nanoscale boron nitride nanosheets, anhydrous ethanol, acrylic acid, and KOS-110 is 100:150:10:1.

[0058] 4. Spray granulation Nano-sized boron nitride nanosheet slurry is used as raw material for spray granulation treatment. The inlet temperature of the spray granulation device is controlled to be 135°C, the outlet temperature is 125°C, the atomizer speed is 200Hz, and the feed rate is 2L / h. The nano-sized boron nitride nanosheet slurry is atomized into tiny particles by the atomizer and quickly dried during the spray descent process to obtain nano-scale spherical boron nitride powder with uniform particle size distribution.

[0059] The nano-scale spherical boron nitride powder prepared in this embodiment has an average particle size D50 of 1000 nm, D10 of 600 nm, D90 of 1800 nm, sphericity of 910%, and a bulk density of 0.27 g / cm 3 , specific surface area (BET) is 15m 2 / g, thermal conductivity is 67W / m·K.

[0060] Comparative Example 1 Comparative Example 1 adopts the scheme of Example 1, except that the surface pretreatment is omitted and the large-sized hexagonal boron nitride powder (h-BN) is directly subjected to liquid phase ultrasonic exfoliation.

[0061] In the preparation of the boron nitride powder of Comparative Example 1, after liquid phase ultrasonic exfoliation, the amount of quasi-nanoscale boron nitride nanosheets (BNNS) exfoliated from the large-sized hexagonal boron nitride powder was less than 30wt%, and the exfoliation effect was poor and the exfoliation efficiency was low. After spray granulation, the average particle size D50 of the spherical boron nitride powder prepared in Comparative Example 1 was 7000nm, D10 was 3000nm, D90 was 15000nm, the sphericity was 88%, and the bulk density was 0.16g / cm 3 , specific surface area (BET) is 10m 2 / g, thermal conductivity is 34W / m·K.

[0062] In the preparation of the spherical boron nitride powder of Comparative Example 1, there are defects such as low preparation efficiency, poor controllability of the preparation process, and poor dimensional stability of the spherical boron nitride powder, and it is impossible to prepare nano-scale spherical boron nitride powder that meets the requirements.

[0063] Comparative Example 2 Comparative Example 2 adopts the scheme of Example 1, except that the liquid phase ultrasonic stripping step is omitted; and the modified boron nitride powder obtained in the surface pretreatment step is directly used in the slurry preparation.

[0064] The average particle size D50 of the spherical boron nitride powder prepared in Comparative Example 2 is 20000nm, D10 is 10000nm, D90 is 50000nm, the sphericity is 89%, and the bulk density is 0.10g / cm 3 , specific surface area (BET) is 8m 2 / g, thermal conductivity is 19W / m·K.

[0065] In the preparation of the spherical boron nitride powder of Comparative Example 1, there are problems such as poor controllability of the preparation process, poor controllability of the morphology of the nano-scale spherical boron nitride powder, and poor dimensional stability of the nano-scale spherical boron nitride powder, and it is impossible to prepare nano-scale spherical boron nitride powder that meets the requirements.

[0066] Unless otherwise specified, all percentages used in the present invention are by mass.

[0067] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing nano-scale spherical boron nitride powder, characterized in that: The method consists of the following steps: surface pretreatment, liquid phase ultrasonic stripping, slurry preparation, and spray granulation; The surface pretreatment method comprises adding large-sized hexagonal boron nitride powder to a sodium hydroxide solution, stirring and reacting at a temperature of 80-120° C.; cooling and separating to obtain a solid, and washing and drying the solid to obtain a modified boron nitride powder; The liquid-phase ultrasonic exfoliation method comprises selecting one or more of methanol, ethanol, isopropanol, and tert-butyl alcohol, mixing with water to form an ultrasonic exfoliation solvent, adding the modified boron nitride powder into the ultrasonic exfoliation solvent, and controlling the solid content to be 30-60wt%; after liquid-phase ultrasonic exfoliation treatment, separating and obtaining solid matter, washing and drying the solid matter, and obtaining quasi-nanoscale boron nitride nanosheets; The method for preparing the slurry is to grind and mix anhydrous ethanol, acrylic acid, dispersant KOS-110, and quasi-nano-sized boron nitride nanosheets uniformly to prepare a nano-sized boron nitride nanosheet slurry with a viscosity of 100-1000 Pa·s; The spray granulation method comprises the following steps: using nano-sized boron nitride nanosheet slurry as a raw material, and performing spray granulation treatment to obtain nano-sized spherical boron nitride powder.

2. The method for preparing nano-scale spherical boron nitride powder according to claim 1, characterized in that: In the surface pretreatment, the liquid-to-solid mass ratio of the sodium hydroxide solution to the large-sized hexagonal boron nitride powder is 5-10:1; The concentration of the sodium hydroxide solution is at least 4 mol / L.

3. The method for preparing nano-scale spherical boron nitride powder according to claim 1, characterized in that: In the surface pretreatment, the stirring reaction speed is 200-500 rpm, and the stirring reaction time is 12-48 hours; The average particle size of the large-size hexagonal boron nitride powder is 3-5 μm.

4. The method for preparing nano-scale spherical boron nitride powder according to claim 1, characterized in that: In the liquid-phase ultrasonic stripping, one or more of methanol, ethanol, isopropanol and tert-butanol are selected and mixed with water in a mass ratio of 1-5:1 to form an ultrasonic stripping solvent.

5. The method for preparing nano-scale spherical boron nitride powder according to claim 1, characterized in that: In the liquid phase ultrasonic stripping, the ultrasonic frequency is controlled to be 20-40kHz, the ultrasonic power is 1000-2000W, and the liquid phase ultrasonic stripping treatment time is 1-2h; The number of layers of the quasi-nanoscale boron nitride nanosheets is 1-5.

6. The method for preparing nano-scale spherical boron nitride powder according to claim 1, characterized in that: In the preparation of the slurry, the weight ratio of the quasi-nanoscale boron nitride nanosheets, anhydrous ethanol, acrylic acid, and dispersant KOS-110 is 100:150-300:5-15:0.1-1.

7. The method for preparing nano-scale spherical boron nitride powder according to claim 1, characterized in that: In the preparation of the slurry, the ball mass ratio is controlled to be 1:10-20 during the grinding and mixing process, the grinding and mixing speed is 150-300 rpm, and the grinding and mixing time is 5-10 hours.

8. The method for preparing nano-scale spherical boron nitride powder according to claim 1, characterized in that: In the spray granulation, the inlet temperature of the spray granulation device is controlled to be 120-135° C., the outlet temperature is controlled to be 110-130° C., the atomizer speed is controlled to be 50-200 Hz, and the feed rate is controlled to be 2-5 L / h.

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