A preparation method of spherical boron nitride

Abstract

The invention relates to a method for preparing spherical boron nitride. The method comprises the following steps: preparing a precursor, adopting a double-furnace reaction, and chemical vapor deposition to prepare the spherical boron nitride; and subsequently subjecting the spherical boron nitride to a high-temperature, pickling treatment to obtain a smooth, dense spherical boron nitride free of defects such as obvious cracks and having high sphericity.

Description

Technical Field

[0001] The invention belongs to the technical field of material preparation, and particularly relates to a preparation method of spherical boron nitride. Background Art

[0002] Boron nitride (BN) exhibits excellent high-temperature resistance, high thermal conductivity, strong insulation, and wave-transmitting properties. Furthermore, spherical BN exhibits excellent particle flowability and high filler loading, making it an indispensable filler in polymer-based composites. However, conventional BN granulation techniques primarily produce BN flake particles, which are difficult to precisely control and improve the packing density of BN, limiting its application in advanced composites.

[0003] As a member of the BN family, boron nitride spheres offer advantages such as improved stability and wear resistance compared to BN sheets and tubes. Boron nitride spheres have a layered structure similar to graphite, allowing for easy interlayer sliding, resulting in excellent lubricity and potential use as an additive in solid lubricants. Their unique spherical shape allows for a high filler density, significantly enhancing the thermal conductivity of polymer composites when used as a thermally conductive filler.

[0004] Research has found that the particle size of spherical products synthesized under different conditions is non-uniform. To address the problem of non-uniform particle size of boron nitride spheres, the present invention focuses on improving the synthesis process of boron nitride spheres and improving their uniformity by controlling the temperature and atmosphere.

[0005] Boron nitride spheres also have certain drawbacks. They easily aggregate and have poor compatibility with most polymers. Their dispersibility is a common problem for nanomaterials. Their hydrophobicity prevents them from dispersing evenly in water, hindering their applications in aqueous solutions. To enhance the diverse applications of boron nitride, this paper focuses on functional modification to improve the surface structure and properties of the spheres. Summary of the Invention

[0006] The object of the present invention is to provide a method for preparing spherical boron nitride.

[0007] In order to solve the above technical problems, the specific process of the present invention is as follows:

[0008] A method for preparing spherical boron nitride, characterized by:

[0009] Take 10 parts of boron oxide, 35-40 parts of methanol, and 10 parts of water respectively, heat at a constant temperature of 70-80°C using an intelligent heating device, stir magnetically at 200-300 rpm, and continue the reaction for 30 minutes. The entire reaction is completed under dry conditions to obtain 12-18 parts of the mixture as a boron source precursor for boron nitride;

[0010] The container containing the boron source precursor is placed in a room temperature environment. A high-temperature tube furnace provides the energy required for the reaction. The high-temperature steel tube is used as the reaction chamber. A double-furnace reaction is adopted. First, pure nitrogen is introduced to clean the pipeline to remove impurity gases. Then, the temperature is increased at a rate of 5°C / min. A mixed ammonia gas is introduced at a rate of 400ml / min, and a carrier gas is introduced into the reaction zone containing the boron source precursor. The reaction is carried out for 1 hour. The white substance deposited on the tube wall at the outlet end is collected to obtain the product.

[0011] Among them, the double-furnace reaction includes two stages, the front is a high-temperature furnace and the back is a low-temperature furnace, which is raised to the preset temperature at 5°C / min. The high-temperature furnace is 900-1000°C and the low-temperature furnace is 200-300°C. The ammonia mixture is an argon-ammonia mixture with an argon:ammonia mass ratio of 1:3.

[0012] Among them, the deposited white substance also includes subsequent processing: the collected sediment is placed in an alumina crucible, 8-12% of a flux is added thereto, the crucible is placed in the central temperature zone of a high-temperature furnace, the nitrogen gas flow rate is set to 150 mL / min, and the temperature is started after 30 minutes of pre-opening, and is increased to the set temperature of 1100°C at a rate of 5°C / min and maintained for 4 hours, and then decreased to 800°C at a rate of 5°C / min, naturally cooled to room temperature, sent to a jaw crusher, broken into small pieces, and passed through a 10-mesh sieve to obtain spherical boron nitride.

[0013] Wherein, the flux is rubidium bromide.

[0014] Among them, the spherical boron nitride also includes an acid washing treatment: add 3 times the mass fraction of 95-98% strong acid to the container of sieved boron nitride, place the container in an oil bath at 120°C, keep warm and stir at 200 rpm for 12 hours, centrifuge the solution until neutral, and place the obtained powder in an oven at 80°C to fully dry.

[0015] Among them, the strong acid is octanesulfonic acid.

[0016] The beneficial effects of the present invention are:

[0017] 1. The present invention uses a high-low temperature dual furnace process combined with an argon-nitrogen atmosphere reaction, subsequent flux calcination, and pickling treatment to obtain spherical boron nitride with a smooth and dense surface, high sphericity, stable structure, and uniform particle size.

[0018] 2. High-temperature treatment first significantly reduces the activation energy of the reactants, accelerates the reaction rate, and facilitates the initial formation of crystals. By conducting the reaction under high-temperature conditions, the synthesis of boron nitride can be promoted and the nitridation reaction can be quickly initiated. This facilitates the rapid conversion of the reactants, making the synthesis process of boron nitride more efficient. Subsequently, the reactants are transferred to a low-temperature environment, which helps slow the reaction rate and make the reaction more stable. Low temperature helps control the crystal growth of the synthesized product, preventing uneven particles or excessive particle size caused by excessively rapid reactions, thereby obtaining boron nitride spheres with more uniform particle size. This change in temperature gradient makes the crystals more regular, reduces the generation of defects and impurities, and improves the purity and performance of the product.

[0019] 3. The hydrogen-nitrogen mixed gas environment helps improve the crystalline surface and amorphous nuclei of the boron nitride spheres. At high temperatures, the presence of nitrogen promotes the synthesis reaction of boron nitride, while argon maintains an inert atmosphere, preventing the introduction of impurities and ensuring that crystals grow under ideal conditions, thereby enhancing the crystallinity of the product. This optimized treatment helps reduce defects in boron nitride, improve its lattice integrity, and thus improve its thermal stability.

[0020] 4. The rubidium ion has a larger radius than other alkali metal ions, which means it plays a more significant role in the reaction. The ion pair formed by the combination of rubidium ions and bromide ions has a weaker lattice energy, which results in a lower melting point and allows it to participate in the reaction at lower temperatures. Rubidium bromide has a lower lattice energy, so it can melt at lower temperatures. During the boron nitride synthesis process, rubidium bromide melts to form a liquid phase environment, lowering the melting temperature of the reactants and promoting high-temperature reactions.

[0021] 5. Rubidium bromide flux reduces resistance during crystal growth, facilitating the nucleation and growth of boron nitride crystals. Because rubidium bromide has a low melting point, it can provide a uniform chemical environment in the molten state, promoting the crystallization of boron nitride in a more regular and spherical form. Rubidium bromide also provides additional vacancies and charge compensation, thereby improving reaction efficiency and product quality. It also increases the specific surface area of spherical boron nitride to a certain extent, improving thermal conductivity, and effectively preventing excessive increase in specific surface area and the occurrence of aggregation. The resulting spherical boron nitride has a smooth, dense surface, free of obvious cracks and other defects, and has a high degree of sphericity.

[0022] 6. Octanesulfonic acid has strong acidity and can react with unstable, poorly crystalline areas on the surface of boron nitride nanospheres. The surface of boron nitride materials often contains some weak chemical bonds or unstable functional groups, which may lead to uneven structural integrity. Octanesulfonic acid pickling removes unstable chemical bond areas, such as incompletely cross-linked BN bonds or defect sites containing hydroxyl / amino groups, amorphous boron-nitrogen fragments, and incompletely reacted boron / nitrogen precursor residues. This removes loose structural components, making the boron nitride surface more uniform and reducing surface defects. This helps improve the structural stability and consistency of the material.

[0023] 7. The sulfonic acid groups of octanesulfonic acid can react with oxides, defects, or other unstable moieties on the surface of boron nitride, promoting the introduction of surface groups. These reactions can form new functional groups, particularly hydroxyl groups, on the surface of boron nitride nanospheres. Because octanesulfonic acid has a long alkyl chain, this hydrophobic moiety can reduce the likelihood of boron nitride particles agglomerating, thereby increasing their dispersibility in solution. This is crucial for the application of boron nitride, especially in applications requiring uniform dispersion, such as catalysis, composite materials, and drug delivery.

[0024] 8. Octanesulfonic acid pickling has little effect on the crystal phase stability of boron nitride. It does not destroy the structure of boron nitride. On the contrary, it can further enhance the phase stability of boron nitride by removing unstable surface areas. The structure of boron nitride is optimized by octanesulfonic acid treatment, avoiding phase transitions or degradation that may occur under high temperature or strong acid conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a SEM schematic diagram of the present invention Figure 1 .

[0026] Figure 2 This is a SEM schematic diagram of the present invention Figure 2 .

[0027] Figure 3 This is a SEM schematic diagram of the present invention Figure 3 . DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below with reference to the embodiments.

[0029] Example 1

[0030] Take 10 parts of boron oxide, 38 parts of methanol, and 10 parts of water respectively, heat at 75°C using an intelligent heating device, stir magnetically at 250 rpm, and continue the reaction for 30 minutes. The entire reaction is completed under dry conditions to obtain 15 parts of the mixture as a boron source precursor for boron nitride;

[0031] The container containing the boron source precursor is placed in a room temperature environment, and the energy required for the reaction is provided by a high-temperature tube furnace. The high-temperature steel tube is used as the reaction chamber, and a double-furnace reaction is adopted. First, pure nitrogen is introduced to clean the pipeline to remove impurity gases, and then the temperature is increased at a rate of 5°C / min. The high-temperature furnace is 950°C and the low-temperature furnace is 250°C. Argon and ammonia mixed gas are introduced at a rate of 400ml / min, with an argon:ammonia mass ratio of 1:3. The carrier gas is introduced into the reaction zone containing the boron source precursor and reacted for 1 hour. The white substance deposited on the tube wall at the outlet end is collected to obtain;

[0032] Example 2

[0033] Take 10 parts of boron oxide, 35 parts of methanol, and 10 parts of water respectively, heat at 80°C with an intelligent heating device, stir magnetically at 200 rpm, and continue the reaction for 30 minutes. The entire reaction is completed under dry conditions to obtain 12 parts of the mixture as a boron source precursor for boron nitride;

[0034] The container containing the boron source precursor is placed in a room temperature environment. The energy required for the reaction is provided by a high-temperature tubular furnace. The high-temperature steel tube is used as the reaction chamber. A double-furnace reaction is adopted. First, pure nitrogen is introduced to clean the pipeline and remove impurity gases. Then the temperature is increased at a rate of 5°C / min. The high-temperature furnace is 1000°C and the low-temperature furnace is 300°C. An argon-ammonia mixture is introduced at a rate of 400ml / min. The mass ratio of argon:ammonia is 1:3. The carrier gas is introduced into the reaction zone containing the boron source precursor. The reaction is carried out for 1 hour. The white substance deposited on the tube wall at the outlet end is collected to obtain the product.

[0035] Example 3

[0036] Take 10 parts of boron oxide, 40 parts of methanol, and 10 parts of water respectively, heat at 70°C with an intelligent heating device, stir magnetically at 300 rpm, and continue the reaction for 30 minutes. The entire reaction is completed under dry conditions to obtain 18 parts of the mixture as a boron source precursor for boron nitride;

[0037] The container containing the boron source precursor is placed in a room temperature environment. The energy required for the reaction is provided by a high-temperature tubular furnace. The high-temperature steel tube is used as the reaction chamber. A double-furnace reaction is adopted. First, pure nitrogen is introduced to clean the pipeline and remove impurity gases. Then the temperature is increased at a rate of 5°C / min. The high-temperature furnace is 900°C and the low-temperature furnace is 200°C. An argon-ammonia mixture is introduced at a rate of 400ml / min. The mass ratio of argon:ammonia is 1:3. The carrier gas is introduced into the reaction zone containing the boron source precursor. The reaction is carried out for 1 hour. The white substance deposited on the tube wall at the outlet end is collected to obtain the product.

[0038] Comparative Example 1

[0039] The difference between this comparative example and Example 1 is that the gas used in this comparative example is pure ammonia, and the rest is the same as Example 1.

[0040] Comparative Example 2

[0041] The difference between this comparative example and Example 1 is that in this comparative example, an argon-ammonia mixed gas is introduced, wherein the mass ratio of argon to ammonia is 1:1, and the rest is the same as in Example 1.

[0042] Comparative Example 3

[0043] The difference between this comparative example and Example 1 is that in this comparative example, an argon-ammonia mixed gas is introduced, wherein the mass ratio of argon to ammonia is 1:2, and the rest is the same as in Example 1.

[0044] Comparative Example 4

[0045] The difference between this comparative example and Example 1 is that a high-temperature furnace with a single heating process and a temperature of 950° C. is used in this comparative example, and the rest is the same as Example 1.

[0046] Test 1: Boron Nitride Particle Size Distribution

[0047] The instrument used in this paper is an X-ray diffraction analyzer, a D8DISCOVER model produced by Bruker AXS GmbH, Germany. The target material used in the test is a copper target, the operating voltage is 40kV, and the operating current is 150mA. The wavelength of the Kα monochromatic radiation source is The test speed is 12° / min and the test range is 20°-80°.

[0048] Specific testing method: First, grind the samples obtained in Examples 1-3 and Comparative Examples 1-4 into powder. Then, place the samples in the groove of a glass slide, compact them with a glass sheet, and clean the area around the groove. The prepared glass slide was placed in a test chamber for testing and analysis. The results are shown in Table 1.

[0049] Table 1

[0050]

[0051] The following examples and comparative examples were all performed on the basis of Example 1.

[0052] Example 4

[0053] The collected sediment was placed in an alumina crucible, 10% rubidium bromide was added thereto, the crucible was placed in the central temperature zone of a high-temperature furnace, the nitrogen gas flow rate was set to 150 mL / min, and the temperature was started to rise after 30 minutes of pre-opening, and the temperature was increased to the set temperature of 1100°C at a rate of 5°C / min and maintained for 4 hours, then decreased to 800°C at a rate of 5°C / min, naturally cooled to room temperature, sent to a jaw crusher, broken into small pieces, and passed through a 10-mesh sieve to obtain spherical boron nitride.

[0054] Acid washing treatment: add 3 times the mass fraction of 97% octanesulfonic acid to the container of sieved boron nitride, place the container in an oil bath at 120°C, keep warm and stir at 200 rpm for 12 hours, centrifuge the solution until neutral, and place the obtained powder in an oven at 80°C to fully dry.

[0055] Example 5

[0056] The collected sediment was placed in an alumina crucible, 12% rubidium bromide was added thereto, the crucible was placed in the central temperature zone of a high-temperature furnace, the nitrogen gas flow rate was set to 150 mL / min, and the temperature was started to rise after 30 minutes of pre-opening, and the temperature was increased to the set temperature of 1100°C at a rate of 5°C / min and maintained for 4 hours, then decreased to 800°C at a rate of 5°C / min, naturally cooled to room temperature, sent to a jaw crusher, broken into small pieces, and passed through a 10-mesh sieve to obtain spherical boron nitride.

[0057] Acid washing treatment: add 3 times the mass fraction of 95% octanesulfonic acid to the container of sieved boron nitride, place the container in an oil bath at 120°C, keep warm and stir at 200 rpm for 12 hours, centrifuge the solution until neutral, and place the obtained powder in an oven at 80°C to fully dry.

[0058] Example 6

[0059] The collected sediment was placed in an alumina crucible, into which 8% rubidium bromide was added, and the crucible was placed in the central temperature zone of a high-temperature furnace. The nitrogen gas flow rate was set to 150 mL / min. After 30 minutes of pre-opening, the temperature began to rise and was increased to the set temperature of 1100°C at a rate of 5°C / min and maintained for 4 hours. Then, the temperature was decreased to 800°C at a rate of 5°C / min, and naturally cooled to room temperature. The crucible was sent to a jaw crusher, broken into small pieces, and passed through a 10-mesh sieve to obtain spherical boron nitride.

[0060] Acid washing treatment: add 3 times the mass fraction of 98% octanesulfonic acid to the container of sieved boron nitride, place the container in an oil bath at 120°C, keep warm and stir at 200 rpm for 12 hours, centrifuge the solution until neutral, and place the obtained powder in an oven at 80°C to fully dry.

[0061] Comparative Example 5

[0062] The difference between this comparative example and Example 4 is that rubidium bromide is not added in this comparative example, and the rest is the same as Example 4.

[0063] Comparative Example 6

[0064] The difference between this comparative example and Example 4 is that rubidium bromide is replaced by sodium fluoride; the rest is the same as Example 4.

[0065] Comparative Example 7

[0066] The difference between this comparative example and Example 4 is that octanesulfonic acid in this comparative example is replaced by sulfuric acid; the rest is the same as Example 4.

[0067] Comparative Example 8

[0068] This comparative example differs from Example 1 in that the amount of octane sulfonic acid added is different. The acid wash treatment is as follows: 5 times the mass fraction of 97% octane sulfonic acid is dropwise added to a container of sieved boron nitride. The container is placed in an oil bath at 120°C, kept warm, and stirred at 200 rpm for 12 hours. The solution is centrifuged and washed until neutral. The resulting powder is placed in an oven at 80°C and thoroughly dried. The remaining steps are the same as in Example 4.

[0069] Comparative Example 9

[0070] This comparative example differs from Example 1 in that the amount of octane sulfonic acid added is different. The acid wash treatment is as follows: 1 mass fraction of 97% octane sulfonic acid is added dropwise to a container of sieved boron nitride. The container is placed in an oil bath at 120°C, kept warm, and stirred at 200 rpm for 12 hours. The solution is centrifuged and washed until neutral. The resulting powder is placed in an oven at 80°C and thoroughly dried. The remaining steps are the same as in Example 4.

[0071] Experiment 2: Performance Testing

[0072] The samples obtained in the Examples and Comparative Examples were subjected to BET tests to measure specific surface area and weight loss ratio. The weight loss ratio was analyzed using a differential thermal-thermogravimetric analyzer (SDTQ-600, manufactured by TA Instruments-Water LLC, USA) over a temperature range of room temperature to 1200°C. The results are shown in Table 2.

[0073] Table 2

[0074] sample Specific surface area (m2 / g) Weight loss ratio (%) Example 4 36.58 0.22 Example 5 34.92 0.31 Example 6 35.61 0.29 Comparative Example 5 13.85 6.54 Comparative Example 6 19.64 5.87 Comparative Example 7 17.59 8.20 Comparative Example 8 16.47 6.98 Comparative Example 9 18.72 4.53

Claims

1. A method for preparing spherical boron nitride, characterized in that: Take 10 parts of boron oxide, 35-40 parts of methanol, and 10 parts of water respectively, heat at a constant temperature of 70-80°C using an intelligent heating device, stir magnetically at 200-300 rpm, and continue the reaction for 30 minutes. The entire reaction is completed under dry conditions to obtain 12-18 parts of the mixture as a boron source precursor for boron nitride; The container containing the boron source precursor is placed in a room temperature environment. A high-temperature tube furnace provides the energy required for the reaction. The high-temperature steel tube is used as the reaction chamber. A double-furnace reaction is adopted. First, pure nitrogen is introduced to clean the pipeline to remove impurity gases. Then, the temperature is increased at a rate of 5°C / min. A mixed ammonia gas is introduced at a rate of 400ml / min, and a carrier gas is introduced into the reaction zone containing the boron source precursor. The reaction is carried out for 1 hour. The white substance deposited on the tube wall at the outlet end is collected to obtain the product. The dual-furnace reaction includes two stages, a high-temperature furnace in the front and a low-temperature furnace in the back, which are raised to a preset temperature at 5°C / min. The high-temperature furnace is 900-1000°C and the low-temperature furnace is 200-300°C. The ammonia mixture is an argon-ammonia mixture with an argon:ammonia mass ratio of 1:

3.

2. The method for preparing spherical boron nitride according to claim 1, wherein: The obtained deposited white substance also includes subsequent processing: the collected sediment is placed in an alumina crucible, 8-12% flux is added thereto, the crucible is placed in the central temperature zone of a high-temperature furnace, the nitrogen gas flow rate is set to 150 mL / min, and the temperature is started after 30 minutes of pre-opening, and is increased to the set temperature of 1100°C at a rate of 5°C / min and maintained for 4 hours, and then decreased to 800°C at a rate of 5°C / min, naturally cooled to room temperature, sent to a jaw crusher, broken into small pieces, and passed through a 10-mesh sieve to obtain spherical boron nitride.

3. The method for preparing spherical boron nitride according to claim 2, wherein: The flux is rubidium bromide.

4. The method for preparing spherical boron nitride according to claim 2, wherein: The spherical boron nitride also includes an acid washing treatment: 3 times the mass fraction of 95-98% strong acid is added dropwise to the container of sieved boron nitride, the container is placed in an oil bath at 120°C, kept warm and stirred at 200 rpm for 12 hours, the solution is centrifuged and washed until neutral, and the obtained powder is placed in an oven at 80°C and fully dried.

5. The method for preparing spherical boron nitride according to claim 4, wherein: The strong acid is octanesulfonic acid.

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