Hexagonal boron nitride powder and preparation method thereof

Abstract

The invention relates to the technical field of metal materials, and discloses hexagonal boron nitride powder and a preparation method thereof.The preparation method comprises the following steps that raw materials are pretreated, a boron source and a nitrogen source are selected, the boron source is boric acid or boric oxide, the nitrogen source is urea or melamine, the raw materials are smashed till the particle size is smaller than 50 micrometers, drying is conducted for 2-4 hours at the temperature of 80-100 DEG C, and the hexagonal boron nitride powder is obtained; the preparation method comprises the following steps: preparing a boron source, a nitrogen source and a functional auxiliary agent, preparing the functional auxiliary agent, and when the hexagonal boron nitride powder is synthesized and prepared, highly uniform dispersion of the boron source, the nitrogen source and the functional auxiliary agent on a micro scale is realized by adopting a double-cone mixer and cooperating with a mixing process of spraying a dispersing agent solution; and the uniformity of the mixed material in the high-temperature reaction is ensured to reach an ideal state, the problem that local reaction is incomplete or byproducts are increased due to non-uniform dispersion of the material can be solved, and a foundation is laid for obtaining a hexagonal boron nitride powder product with a complete crystal structure.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal materials, in particular to a hexagonal boron nitride powder and a preparation method thereof. BACKGROUND

[0002] Hexagonal boron nitride is the most common crystal form of boron nitride, which has a similar layered structure to graphite and is called "white graphite". The weak van der Waals force between the layers endows the material with excellent lubricity, and it can still maintain stable electrical conductivity at high temperatures.

[0003] At present, due to various influencing factors in the synthesis process of hexagonal boron nitride powder, the raw material pretreatment system equipped for the mixing of boron source and nitrogen source cannot judge in real time whether the uniformity of the mixed material during the reaction reaches the ideal state. When the material is not uniformly dispersed, it will cause incomplete local reaction or increase of by-products, which cannot guarantee the integrity of the crystal structure of the final product. At the same time, during the high-temperature reaction, the heating uniformity of the reaction material in the crucible cannot be monitored in real time, which will cause abnormal temperature gradient in the reaction area, and the reaction material cannot be adjusted in real time when it appears sintering or caking. After the synthesis of hexagonal boron nitride powder, due to the existence of unreacted raw materials or intermediate phases in the product, the step-by-step removal of different impurity components cannot be realized during the post-treatment purification, which leads to the loss of target product or the residual of impurities during the powder purification process, further affecting the crystallinity and use performance of the hexagonal boron nitride powder.

[0004] Therefore, the present application provides a hexagonal boron nitride powder and a preparation method thereof to solve the above problems. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a hexagonal boron nitride powder and a preparation method thereof, which solves the problem of being unable to judge in real time whether the uniformity of the mixed material during the reaction reaches the ideal state.

[0006] To achieve the above purpose, the present application provides the following technical solution: a hexagonal boron nitride powder and a preparation method thereof, comprising the following steps: Step 1: raw material pretreatment, selecting boron source and nitrogen source, the boron source is boric acid or boron oxide, and the nitrogen source is urea or melamine, crushing them to a particle size of less than 50 microns, and drying at 80-100℃ for 2-4 hours; Step 2: preparation of functional additives, preparing functional additives; Step 3: preparation of mixture, mixing the pretreated boron source and nitrogen source with functional additives to prepare a mixture; Step four: heat reaction treatment, the mixture is placed in a reactor, under nitrogen or argon protection, to 1000-1200℃ at 5-10℃ / min, heat preservation 1-3 hours for reaction; Step five: post-processing, the reaction product is naturally cooled to room temperature, then crushed and sieved to obtain hexagonal boron nitride powder; In step three, the mixture is made of the following raw materials by weight: boron source 50-70 parts, nitrogen source 30-50 parts, functional additives 5-10 parts.

[0007] Preferably, the raw material pretreatment of step one includes the following steps: the boron source and nitrogen source are respectively placed in a ball mill, zirconia balls are added as grinding medium, the ball-to-material ratio is 5:1, and the powder is crushed at a speed of 200-300r / min for 1-2 hours, then transferred to an oven and dried at 80-100℃ for 2-4 hours, and stirred every 30 minutes during the drying process.

[0008] Preferably, the boron source uses boric acid with a purity of more than 99.5%, the nitrogen source uses urea with a purity of more than 98%, and the particle size after crushing is controlled within the range of 10-50 microns, and the moisture content after drying is less than 1%.

[0009] Preferably, the preparation of functional additives in step two includes the following steps: collecting alumina or silicon carbide ceramic waste from industrial waste, removing impurities after sorting, placing in a drum cleaning machine and cleaning with deionized water for 30-60 minutes, then drying at 100-120℃ for 3-5 hours, after drying, preliminary crushing with a jaw crusher, then grinding in a planetary ball mill for 2-4 hours, sieving to obtain ceramic microparticles, the particle size of the ceramic microparticles is 80-100 microns, the ceramic microparticles are laid flat in a plasma reaction chamber, vacuumized to a vacuum degree of 1×10 -1 -1×10 -3 Pa, nitrogen gas is injected at a flow rate of 10-50sccm, the plasma generator is started, the power is set to 300-700W, and the ceramic microparticles are taken out after 10-20 minutes of treatment to obtain functional additives.

[0010] Preferably, in the preparation of functional additives, the particle size distribution of the ceramic microparticles is 80-100 microns, the nitrogen gas purity is greater than 99.99% during plasma treatment, the chamber temperature is controlled at 50-100℃ during the treatment process, and the surface oxygen content of the ceramic microparticles after treatment increases by less than 5%, and the specific surface area increases to 1.5-2 times of the original.

[0011] Preferably, the mixture preparation of step three comprises the following steps: the pretreated boron source and nitrogen source are added into a double-cone mixer in a proportion by weight, the rotation speed of the mixer is controlled at 30-60 r / min, the mixing time is 30-60 minutes, then the functional additives are added, and the mixing is continued for 20-40 minutes, and the temperature is kept at 20-30℃ and the relative humidity is less than 40% during the mixing.

[0012] Preferably, a dispersant can be added in the mixture preparation, the dispersant is polyvinylpyrrolidone or polyethylene glycol, and the addition amount is 0.1-0.5% of the total weight of the mixture; the dispersant is first dissolved in ethanol with a concentration of 5-10%, and then is sprayed into the mixer.

[0013] Preferably, the heat reaction treatment of step four comprises the following steps: the mixture is loaded into a graphite crucible, the compaction density is 1.5-2.0 g / cm 3 , then the crucible is placed in a tube-type reaction furnace, high-purity nitrogen or argon is used as the protective gas after sealing, the gas flow is 100-200 mL / min, the temperature is first raised to 500-600℃ at a rate of 5-10℃ / min to remove the volatile components, the temperature is kept for 30 minutes, then the temperature is raised to 1000-1200℃ at a rate of 3-5℃ / min, and the temperature is kept for 1-3 hours, and the pressure is kept at normal pressure during the reaction.

[0014] Preferably, the post-treatment of step five comprises the following steps: the product after the heat reaction is cooled to room temperature, is first coarsely crushed by a jaw crusher to a particle size of less than 5 mm, then is transferred into an air flow pulverizer, compressed air is used as the medium, the pressure is 0.5-0.8 MPa, the crushed product is sieved through a 400-mesh sieve to obtain a preliminary powder, the powder is washed with a 5-10% hydrochloric acid solution for 2-3 times, each time the washing is stirred for 30 minutes, then the powder is washed with deionized water until neutral, and finally the powder is dried at 100-120℃ for 4-6 hours to obtain the hexagonal boron nitride powder.

[0015] Preferably, the hexagonal boron nitride powder is white or off-white powder, has a hexagonal crystal structure, the average particle size is 0.5-2 microns, the specific surface area is 10-50 m 2 / g, and contains uniformly dispersed ceramic microparticles, the ceramic microparticles are alumina or silicon carbide, the particle size is 80-100 microns, and the content is 5-10% of the total weight of the powder.

[0016] Compared with the prior art, the hexagonal boron nitride powder and the preparation method thereof provided by the present application have the following beneficial effects: 1. In the present application, when synthesizing hexagonal boron nitride powder, by using a double-cone mixer and a mixing process of spraying a dispersant solution, the boron source, nitrogen source and functional additives are highly uniformly dispersed on a microscale, ensuring the uniformity of the mixture during high-temperature reaction to reach an ideal state, solving the problem of incomplete local reaction or increased by-products caused by uneven material dispersion, and laying a foundation for obtaining hexagonal boron nitride powder products with complete crystal structure.

[0017] 2. In the present application, when performing high-temperature reaction of hexagonal boron nitride powder, by setting a segmented temperature rising program including volatile matter removal and final reaction stage, and strictly controlling the compaction density of the material and the flow of protective gas, the uniformity of the reaction material heated in the crucible is controlled, so that the system can reduce the abnormal temperature gradient in the reaction area, and through the optimized process parameters in the reaction process, the sintering or caking of the material is reduced, ensuring that the hexagonal boron nitride crystal grows smoothly in a stable and uniform thermal field.

[0018] 3. In the present application, after the synthesis reaction of hexagonal boron nitride powder is completed, by using a staged post-processing process including mechanical crushing, air flow crushing, acid washing, water washing and drying, the different impurity components in the reaction product are removed in stages and targeted, so that the preparation method can efficiently purify hexagonal boron nitride powder, reduce the situation that the product purity does not meet the standard due to unreacted raw materials or intermediate phase residues, and improve the crystallization quality and use reliability of hexagonal boron nitride powder. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0020] Embodiment 1: The hexagonal boron nitride powder and the preparation method thereof, comprising the following steps: Step one: raw material pretreatment, selecting boron source and nitrogen source, the boron source is boric acid or boron oxide, the nitrogen source is urea or melamine, crushing to a particle size of less than 50 microns, and drying at 80°C for 2 hours; Step two: functional additive preparation, preparing the functional additive; Step three: mixture preparation, mixing the pretreated boron source and nitrogen source with the functional additive to prepare the mixture; Step four: heat reaction treatment, placing the mixture in a reactor, heating to 1000°C at 5°C / min under nitrogen or argon protection, and reacting for 1 hour; Step five: post-processing, the reaction product is naturally cooled to room temperature, then crushed and sieved to obtain hexagonal boron nitride powder; In step three, the mixture is made from the following raw materials by weight: boron source 50 parts, nitrogen source 30 parts, functional additive 5 parts.

[0021] The raw material pretreatment of step one includes the following steps: the boron source and nitrogen source are placed in a ball mill respectively, zirconia balls are added as grinding medium, the ball-to-material ratio is 5:1, the crushing is carried out at a speed of 200 r / min for 1 hour, then it is transferred to an oven and dried at 80℃ for 2 hours, and it is turned over every 30 minutes during the drying process.

[0022] The boron source is boric acid with a purity of more than 99.5%, and the nitrogen source is urea with a purity of more than 98%, the particle size after crushing is controlled within 10 microns, and the water content after drying is less than 1%.

[0023] The functional additive preparation of step two includes the following steps: collecting alumina or silicon carbide ceramic waste from industrial waste, removing impurities after sorting, placing it in a drum cleaning machine and cleaning it with deionized water for 30 minutes, then drying it at 100℃ for 3 hours, after drying, it is preliminarily crushed with a jaw crusher, then it is ground in a planetary ball mill for 2 hours, and sieved to obtain ceramic particles, the particle size of the ceramic particles is 80 microns, the ceramic particles are laid flat in a plasma reaction chamber, vacuumed to a vacuum degree of 1×10 -1 Pa, nitrogen gas is injected at a flow rate of 10 sccm, the plasma generator is started, the power is set to 300 W, it is taken out after 10 minutes of treatment, and the functional additive is obtained.

[0024] In the preparation of the functional additive, the particle size distribution of the ceramic particles is 80 microns, the nitrogen gas purity is more than 99.99% during plasma treatment, the chamber temperature is controlled at 50℃ during the treatment process, and the surface oxygen content of the ceramic particles after treatment increases by less than 5%, and the specific surface area increases to 1.5 times of the original.

[0025] The mixture preparation of step three includes the following steps: the pretreated boron source and nitrogen source are added to a double-cone mixer according to the weight ratio, the mixer speed is controlled at 30 r / min, the mixing time is 30 minutes, then the functional additive is added and mixed for another 20 minutes, the temperature is maintained at 20℃ during the mixing process, and the relative humidity is less than 40%.

[0026] A dispersant can also be added during the mixture preparation, the dispersant is polyvinylpyrrolidone or polyethylene glycol, the addition amount is 0.1% of the total weight of the mixture, the dispersant is first dissolved in ethanol with a concentration of 5%, and then sprayed into the mixer.

[0027] The thermal reaction treatment of step four includes the following steps: the mixture is loaded into a graphite crucible, the compaction density is 1.5 g / cm3 The crucible is then placed in a tube-type reaction furnace, and after sealing, high-purity nitrogen or argon is used as the protective gas at a flow rate of 100 mL / min. The temperature is first raised to 500°C at a rate of 5°C / min to remove volatile components, and the temperature is maintained for 30 min. Then, the temperature is raised to 1000°C at a rate of 3°C / min, and the temperature is maintained for 1 h. During the reaction, the pressure is maintained at normal pressure.

[0028] The post-treatment of step five includes the following steps: cooling the product after the heat reaction to room temperature, first coarsely crushing to a particle size of less than 5 mm with a jaw crusher, then transferring to an air jet pulverizer, using compressed air as the medium, and the pressure is 0.5 MPa. After crushing, the powder is sieved through a 400-mesh sieve to obtain the preliminary powder. The powder is then washed twice with a 5% dilute hydrochloric acid solution, each time stirring for 30 min. Then, the powder is washed with deionized water until it is neutral. Finally, the powder is dried at 100°C for 4 h to obtain the hexagonal boron nitride powder.

[0029] The hexagonal boron nitride powder is white or off-white powder, has a hexagonal crystal structure, an average particle size of 0.5 microns, a specific surface area of 10 m 2 / g, and contains uniformly dispersed ceramic microparticles, which are alumina or silicon carbide, with a particle size of 80 microns, accounting for 5% of the total weight of the powder.

[0030] Example 2: The hexagonal boron nitride powder and the method for preparing the same, including the following steps: Step one: raw material pretreatment, selecting a boron source and a nitrogen source, the boron source being boric acid or boron oxide, and the nitrogen source being urea or melamine, and crushing the same to a particle size of less than 50 microns, and drying at 90°C for 3 h; Step two: functional additive preparation, preparing the functional additive; Step three: mixture preparation, mixing the pretreated boron source and nitrogen source with the functional additive to prepare a mixture; Step four: heat reaction treatment, placing the mixture in a reactor, and under the protection of nitrogen or argon, raising the temperature to 1100°C at a rate of 7°C / min, and maintaining the temperature for 2 h for reaction; Step five: post-treatment, naturally cooling the reaction product to room temperature, then crushing and sieving to obtain the hexagonal boron nitride powder; In step three, the mixture is prepared from the following raw materials by weight: 60 parts of the boron source, 40 parts of the nitrogen source, and 7 parts of the functional additive.

[0031] The raw material pretreatment of step one includes the following steps: placing the boron source and the nitrogen source in a ball mill, respectively, adding zirconia balls as grinding media, the ball-to-material ratio being 5:1, and crushing at a speed of 250 r / min for 1.5 h. Then, the mixture is transferred to an oven and dried at 90°C for 3 h, and the mixture is turned over every 30 min during the drying process.

[0032] The boron source is boric acid with purity greater than 99.5%, and the nitrogen source is urea with purity greater than 98%, and the particle size is controlled within 30 microns after crushing, and the moisture content is less than 1% after drying.

[0033] The functional aid preparation of step two includes the following steps: collecting alumina or silicon carbide ceramic waste from industrial waste, removing impurities after sorting, placing in a drum cleaning machine for cleaning with deionized water for 40 minutes, then drying at 110°C for 4 hours, after drying, preliminary crushing with a jaw crusher, then transferring to a planetary ball mill for grinding for 3 hours, sieving to obtain ceramic microparticles, the particle size of the ceramic microparticles is 90 microns, the ceramic microparticles are laid flat in a plasma reaction chamber, vacuumed to a vacuum degree of 1x10 -2 Pa, nitrogen gas is injected at a flow rate of 30 sccm, the plasma generator is started, the power is set to 500W, and after 15 minutes of treatment, the functional aid is obtained.

[0034] In the preparation of the functional aid, the particle size distribution of the ceramic microparticles is 90 microns, the nitrogen gas purity is greater than 99.99% during plasma treatment, the chamber temperature is controlled at 70°C during the treatment process, and the surface oxygen content of the ceramic microparticles after treatment increases by less than 5%, and the specific surface area increases to 1.7 times of the original.

[0035] The mixture preparation of step three includes the following steps: adding the pretreated boron source and nitrogen source into a double-cone mixer according to the weight ratio, controlling the mixer speed to 50 r / min, mixing for 40 minutes, then adding the functional aid, continuing to mix for 30 minutes, and the temperature is maintained at 25°C and the relative humidity is less than 40% during the mixing process.

[0036] In the mixture preparation, a dispersant can also be added, the dispersant is polyvinylpyrrolidone or polyethylene glycol, and the addition amount is 0.3% of the total weight of the mixture. The dispersant is first dissolved in ethanol with a concentration of 7%, and then sprayed into the mixer.

[0037] The thermal reaction treatment of step four includes the following steps: loading the mixture into a graphite crucible, the compaction density is 1.7 g / cm 3 , then placing the crucible in a tube-type reaction furnace, sealing it with high-purity nitrogen or argon as the protective gas, the gas flow rate is 150 mL / min, first heating at 7°C / min to 550°C to remove volatile matter, holding for 30 minutes, then heating at 4°C / min to 1100°C, holding for 2 hours, and the pressure is maintained at atmospheric pressure during the reaction process.

[0038] The post-treatment of step five includes the following steps: cooling the product after the heat reaction to room temperature, first coarsely crushing to a particle size of less than 5 mm with a jaw crusher, then transferring to an air flow pulverizer, using compressed air as the medium, a pressure of 0.6 MPa, after pulverizing, passing through a 400 mesh sieve to obtain the preliminary powder, then washing the powder with a 7% concentrated hydrochloric acid solution for 2 times, each time stirring for 30 minutes, then washing with deionized water until neutral, and finally drying at 110°C for 5 hours to obtain the hexagonal boron nitride powder.

[0039] The hexagonal boron nitride powder is white or off-white powder, has a hexagonal crystal structure, an average particle size of 1 micron, a specific surface area of 30 m 2 / g, and contains uniformly dispersed ceramic microparticles, the ceramic microparticles are alumina or silicon carbide, the particle size is 90 microns, and the ceramic microparticles account for 7% of the total weight of the powder.

[0040] Example 3: The hexagonal boron nitride powder and the preparation method thereof, including the following steps: Step one: raw material pretreatment, selecting a boron source and a nitrogen source, the boron source is boric acid or boron oxide, the nitrogen source is urea or melamine, crushing to a particle size of less than 50 microns, and drying at 100°C for 4 hours; Step two: functional additive preparation, preparing the functional additive; Step three: mixture preparation, mixing the pretreated boron source and nitrogen source with the functional additive to prepare a mixture; Step four: heat reaction treatment, placing the mixture in a reactor, heating to 1200°C at a rate of 10°C / min under nitrogen or argon protection, and reacting for 3 hours; Step five: post-treatment, naturally cooling the reaction product to room temperature, then crushing and sieving to obtain the hexagonal boron nitride powder; In step three, the mixture is prepared from the following raw materials by weight: 70 parts of boron source, 50 parts of nitrogen source, and 10 parts of functional additive.

[0041] The raw material pretreatment of step one includes the following steps: placing the boron source and the nitrogen source in a ball mill respectively, adding zirconia balls as grinding medium, the ball-to-material ratio is 5:1, crushing for 2 hours at a speed of 300 r / min, then transferring to an oven and drying at 100°C for 4 hours, and turning over every 30 minutes during the drying process.

[0042] The boron source is boric acid with a purity of more than 99.5%, and the nitrogen source is urea with a purity of more than 98%, the particle size after crushing is controlled within 50 microns, and the water content after drying is less than 1%.

[0043] The functional aid of step two is prepared by the following steps: collecting alumina or silicon carbide ceramic waste from industrial waste, removing impurities by sorting, washing in a drum washing machine with deionized water for 60 minutes, then drying at 120℃ for 5 hours, after drying, primary crushing with a jaw crusher, then grinding in a planetary ball mill for 4 hours, sieving to obtain ceramic microparticles, the particle size of the ceramic microparticles is 100 microns, laying the ceramic microparticles in a plasma reaction chamber, vacuumizing to a vacuum degree of 1×10 -3 Pa, injecting nitrogen at a flow rate of 50sccm, starting the plasma generator, setting the power to 700W, taking out after 20 minutes of treatment, to obtain the functional aid.

[0044] In the preparation of the functional aid, the particle size distribution of the ceramic microparticles is 100 microns, the purity of nitrogen is greater than 99.99% during plasma treatment, the chamber temperature is controlled at 100℃ during the treatment, and the surface oxygen content of the ceramic microparticles increases by less than 5% after treatment, and the specific surface area increases to twice the original.

[0045] The mixture of step three is prepared by the following steps: adding the pretreated boron source and nitrogen source into a double-cone mixer according to the weight ratio, controlling the mixer speed to 60r / min, mixing for 60 minutes, then adding the functional aid, continuing to mix for 40 minutes, the temperature is maintained at 30℃ during the mixing process, and the relative humidity is less than 40%.

[0046] In the mixture preparation, a dispersing agent can also be added, the dispersing agent is polyvinylpyrrolidone or polyethylene glycol, the addition amount is 0.5% of the total weight of the mixture, the dispersing agent is first dissolved in ethanol with a concentration of 10%, and then sprayed into the mixer.

[0047] The thermal reaction treatment of step four includes the following steps: loading the mixture into a graphite crucible, the compaction density is 2.0g / cm 3 , then placing the crucible in a tube-type reaction furnace, sealing it with high-purity nitrogen or argon as the protective gas, the gas flow rate is 200mL / min, first heating to 600℃ at a rate of 10℃ / min to remove volatile matter, holding for 30 minutes, then heating to 1200℃ at a rate of 5℃ / min, holding for 3 hours, the pressure is maintained at atmospheric pressure during the reaction.

[0048] The post-treatment of step five includes the following steps: cooling the product after thermal reaction to room temperature, first coarsely crushing to a particle size of less than 5mm with a jaw crusher, then transferring it into an air jet mill, using compressed air as the medium, the pressure is 0.8MPa, after crushing, sieving through a 400 mesh sieve to obtain the primary powder, then washing the powder with a 10% concentrated hydrochloric acid solution for 3 times, each time stirring for 30 minutes, then washing with deionized water until neutral, finally drying at 120℃ for 6 hours to obtain the hexagonal boron nitride powder.

[0049] The hexagonal boron nitride powder is white or off-white powder, has a hexagonal crystal structure, an average particle size of 2 microns, a specific surface area of 50 m 2 / g, and contains uniformly dispersed ceramic microparticles, the ceramic microparticles being alumina or silicon carbide, having a particle size of 100 microns, and accounting for 10% of the total weight of the powder.

[0050] Comparative Example 1, the difference between this comparative example and Example 1 is that no functional additives are added when preparing the mixture in this comparative example.

[0051] Comparative Example 2, the difference between this comparative example and Example 2 is that no double-cone mixer and dispersant are used when mixing the raw materials in this comparative example, but manual stirring is used for mixing for 30 minutes.

[0052] Comparative Example 3, the difference between this comparative example and Example 3 is that no staged temperature rising procedure is used when performing the heat reaction treatment in this comparative example, but the reactor is directly heated from room temperature to the final reaction temperature at a rate of 10°C / min.

[0053] Comparative Example 4, the difference between this comparative example and Example 3 is that no acid pickling and staged purification steps are performed when post-treating in this comparative example, and the reaction product is directly crushed as the final product.

[0054] The hexagonal boron nitride powders prepared in Examples 1-3 and Comparative Examples 1-4 are subjected to performance testing, and the testing items and testing methods are as follows: Crystallinity testing, an X-ray diffractometer is used to calculate the crystallinity of the product; Purity testing, an inductively coupled plasma atomic emission spectrometry method is used to test the total content of metal impurities other than boron elements; Particle size distribution testing, a laser particle size analyzer is used for testing, and the D50 value is recorded; Specific surface area testing, a nitrogen adsorption specific surface area analyzer is used for testing.

[0055] The test data of the hexagonal boron nitride powders prepared in Examples 1-3 and Comparative Examples 1-4 are recorded in the following table:

[0056] By comparing and analyzing the data in the table, it can be seen that the hexagonal boron nitride powder prepared by the process in Examples 1-3 has more excellent performance in crystallinity, purity, particle size distribution uniformity and specific surface area than the hexagonal boron nitride powder prepared by the process in Comparative Examples 1-4. This shows that by using the double-cone mixer and the mixing process of spraying the dispersant solution, the boron source, nitrogen source and functional additives are highly uniformly dispersed on a microscale, ensuring the uniformity of the mixed materials during high-temperature reaction to reach an ideal state, which can solve the problem of incomplete local reaction or increased by-products caused by uneven dispersion of materials, lay a foundation for obtaining hexagonal boron nitride powder products with complete crystal structure, and by setting a segmented temperature rising program including the removal of volatile components and the final reaction stage, and strictly controlling the compaction density of the materials and the flow rate of the protective gas, the uniformity of the reaction materials in the crucible is controlled, so that the system can reduce the abnormal temperature gradient in the reaction area, and by optimizing the process parameters during the reaction, the sintering or caking of the materials is reduced, ensuring that the hexagonal boron nitride crystals can grow smoothly in a stable and uniform thermal field. By using a staged post-processing process including mechanical crushing, airflow crushing, acid washing, water washing and drying, the staged and targeted removal of different impurities in the reaction products is realized, so that the preparation method can efficiently purify the hexagonal boron nitride powder, reduce the situation that the product purity does not meet the standard due to unreacted raw materials or intermediate phase residues, and improve the crystallization quality and use reliability of the hexagonal boron nitride powder.

[0057] By comparing and analyzing the related data in the table, it can be seen that the hexagonal boron nitride powder prepared by the preparation process has the characteristics of high crystallinity, high purity, uniform particle size distribution and large specific surface area, which shows that the hexagonal boron nitride powder preparation process provided by the present application has more excellent comprehensive performance.

[0058] It should be noted that in this text, relational terms such as first and second are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between the entities or operations. Moreover, the terms "include", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or equipment. Without more limitations, the element defined by the statement "includes a" does not exclude the presence of another identical element in the process, method, article or equipment including the element.

[0059] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely exemplary of the principles and application of the present application. Numerous modifications and adaptions can be effected without departing from the spirit and scope of the present application, which is not limited to the exact construction and arrangement described. It is intended, therefore, to cover all modifications and adaptions that fall within the scope of the claims and their equivalents.

Claims

1. A method for producing a hexagonal boron nitride powder, characterized by, The method comprises the following steps: Step 1: raw material pretreatment, selecting boron source and nitrogen source, the boron source is boric acid or boron oxide, the nitrogen source is urea or melamine, crushing them to a particle size of less than 50 microns, and drying at 80-100℃ for 2-4 hours; Step 2: functional additive preparation, preparing the functional additive; Step 3: mixture preparation, mixing the pretreated boron source and nitrogen source with the functional additive to prepare a mixture; Step 4: heat reaction treatment, placing the mixture in a reactor, under nitrogen or argon protection, heating to 1000-1200℃ at a rate of 5-10℃ / min, and keeping the temperature for 1-3 hours for reaction; Step 5: post-treatment, naturally cooling the reaction product to room temperature, then crushing and sieving to obtain hexagonal boron nitride powder; In step 3, the mixture is prepared from the following raw materials by weight: boron source 50-70 parts, nitrogen source 30-50 parts, and functional additive 5-10 parts.

2. The method of claim 1, wherein the hexagonal boron nitride powder is prepared by the steps of: The raw material pretreatment of step 1 comprises the following steps: placing the boron source and nitrogen source in a ball mill respectively, adding zirconia balls as grinding medium, ball-to-material ratio of 5:1, crushing at a speed of 200-300 r / min for 1-2 hours, then transferring to an oven and drying at 80-100℃ for 2-4 hours, and turning over every 30 minutes during the drying process.

3. The method of claim 1, wherein the hexagonal boron nitride powder is prepared by the steps of: The boron source is boric acid with a purity of more than 99.5%, and the nitrogen source is urea with a purity of more than 98%, the particle size after crushing is controlled within the range of 10-50 microns, and the water content after drying is less than 1%.

4. The method of claim 1, wherein the hexagonal boron nitride powder is prepared by the steps of: The functional additive preparation of step 2 comprises the following steps: Alumina or silicon carbide ceramic waste is collected from industrial waste, sorted to remove impurities, washed in a drum washing machine with deionized water for 30-60 minutes, then dried at 100-120°C for 3-5 hours, after drying, the ceramic particles are obtained by primary crushing with a jaw crusher and then grinding in a planetary ball mill for 2-4 hours, and sieving. The particle size of the ceramic microparticles is 80-100 microns. The ceramic microparticles are laid flat in a plasma reaction chamber, vacuumed to a vacuum degree of 1×10 -1 -1×10 -3 Pa, nitrogen gas is injected at a flow rate of 10-50 sccm, the plasma generator is started, the power is set to 300-700 W, and after 10-20 minutes of processing, the functional adjuvant is obtained.

5. The method of claim 1, wherein the hexagonal boron nitride powder is prepared by the steps of: preparing a mixture of a boron source and a nitrogen source; and heating the mixture to a temperature of 1,000°C to 1,500°C in a non-oxidizing atmosphere. In the functional additive preparation, the particle size distribution of the ceramic microparticles is 80-100 microns, the nitrogen gas purity during plasma treatment is more than 99.99%, the chamber temperature during the treatment process is controlled at 50-100℃, the surface oxygen content of the ceramic microparticles after treatment increases by less than 5%, and the specific surface area increases to 1.5-2 times of the original.

6. The method of claim 1, wherein the hexagonal boron nitride powder is prepared by the steps of: The mixture preparation of step 3 comprises the following steps: adding the pretreated boron source and nitrogen source into a double-cone mixer according to the weight ratio, controlling the mixer speed at 30-60 r / min, mixing for 30-60 minutes, then adding the functional additive and continuing to mix for 20-40 minutes, and keeping the temperature at 20-30℃ and the relative humidity below 40% during the mixing process.

7. The method for preparing hexagonal boron nitride powder according to claim 1, characterized in that, In the mixture preparation, a dispersant can also be added, the dispersant is polyvinylpyrrolidone or polyethylene glycol, the addition amount is 0.1-0.5% of the total weight of the mixture, the dispersant is first dissolved in ethanol with a concentration of 5-10%, and then sprayed into the mixer.

8. The method for preparing hexagonal boron nitride powder according to claim 1, characterized in that, The heat reaction treatment of step four includes the following steps: loading the mixture into a graphite crucible, compacting the density to 1.5-2.0 g / cm 3 Then, the crucible is placed in a tube-type reaction furnace, sealed with high-purity nitrogen or argon as the protective gas, the gas flow is 100-200 mL / min, first heated to 500-600 ℃ at a rate of 5-10 ℃ / min to remove volatile matter, and then heated to 1000-1200 ℃ at a rate of 3-5 ℃ / min, and the pressure is maintained at atmospheric pressure during the reaction.

9. The method for preparing hexagonal boron nitride powder according to claim 1, characterized in that, The post-treatment of step 5 comprises the following steps: cooling the heat-treated product to room temperature, coarsely crushing with a jaw crusher to a particle size of less than 5 mm, then transferring to an air jet pulverizer, using compressed air as medium with a pressure of 0.5-0.8 MPa, sieving the crushed product through a 400-mesh sieve to obtain preliminary powder, washing the powder with 5-10% dilute hydrochloric acid solution for 2-3 times, stirring for 30 minutes each time, then washing with deionized water until neutral, and finally drying at 100-120℃ for 4-6 hours to obtain hexagonal boron nitride powder.

10. A hexagonal boron nitride powder obtainable by the process according to any one of claims 1 to 9, characterized in that The hexagonal boron nitride powder is white or off-white powder, has a hexagonal crystal structure, an average particle size of 0.5-2 microns, a specific surface area of 10-50 m 2 / g, and contains uniformly dispersed ceramic microparticles, which are alumina or silicon carbide, have a particle size of 80-100 microns, and account for 5-10% of the total weight of the powder.

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