CN114804041A - Hexagonal boron nitride, preparation method thereof and heat-conducting rubber - Google Patents
Hexagonal boron nitride, preparation method thereof and heat-conducting rubber Download PDFInfo
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- CN114804041A CN114804041A CN202210515165.7A CN202210515165A CN114804041A CN 114804041 A CN114804041 A CN 114804041A CN 202210515165 A CN202210515165 A CN 202210515165A CN 114804041 A CN114804041 A CN 114804041A
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- 238000002360 preparation method Methods 0.000 title claims abstract description 89
- 229910052582 BN Inorganic materials 0.000 title claims abstract description 67
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- 239000002243 precursor Substances 0.000 claims abstract description 79
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- JYEUMXHLPRZUAT-UHFFFAOYSA-N 1,2,3-triazine Chemical group C1=CN=NN=C1 JYEUMXHLPRZUAT-UHFFFAOYSA-N 0.000 description 3
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 3
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- 241000196324 Embryophyta Species 0.000 description 2
- NWGKJDSIEKMTRX-AAZCQSIUSA-N Sorbitan monooleate Chemical compound CCCCCCCC\C=C/CCCCCCCC(=O)OC[C@@H](O)[C@H]1OC[C@H](O)[C@H]1O NWGKJDSIEKMTRX-AAZCQSIUSA-N 0.000 description 2
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- JKWMSGQKBLHBQQ-UHFFFAOYSA-N diboron trioxide Chemical compound O=BOB=O JKWMSGQKBLHBQQ-UHFFFAOYSA-N 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B21/00—Nitrogen; Compounds thereof
- C01B21/06—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron
- C01B21/064—Binary compounds of nitrogen with metals, with silicon, or with boron, or with carbon, i.e. nitrides; Compounds of nitrogen with more than one metal, silicon or boron with boron
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K3/00—Use of inorganic substances as compounding ingredients
- C08K3/38—Boron-containing compounds
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
- C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/01—Particle morphology depicted by an image
- C01P2004/03—Particle morphology depicted by an image obtained by SEM
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/51—Particles with a specific particle size distribution
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/32—Thermal properties
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K3/00—Use of inorganic substances as compounding ingredients
- C08K3/38—Boron-containing compounds
- C08K2003/382—Boron-containing compounds and nitrogen
- C08K2003/385—Binary compounds of nitrogen with boron
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- Chemical & Material Sciences (AREA)
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Abstract
The invention discloses hexagonal boron nitride and a preparation method thereof and heat-conducting rubber, and relates to the technical field of heat-conducting materials, wherein the preparation method comprises the following steps: (1) dissolving a boron source and a nitrogen source in a solvent, and stirring for reaction to obtain a precursor; (2) in an oxygen-containing atmosphere, performing first roasting on the precursor to obtain an intermediate; (3) and in a nitrogen atmosphere, carrying out second roasting on the intermediate to obtain the hexagonal boron nitride. The filling amount of the hexagonal boron nitride prepared by the method in the rubber matrix can reach 65%, a heat conducting network can be effectively formed, and the heat conductivity of the rubber is improved.
Description
The technical field is as follows:
the invention relates to the technical field of heat conduction materials, in particular to hexagonal boron nitride and a preparation method thereof, and heat conduction rubber.
Background art:
the hexagonal boron nitride (h-BN) is similar to graphite in structure, is called as 'white graphite', has the advantages of acid and alkali resistance, oxidation resistance and the like, and also has outstanding thermal stability and good insulating property. The h-BN has potential application prospect in the aspects of drug delivery, pollutant adsorption, catalyst carrier, water purification and the like.
At present, a plurality of documents report the method for synthesizing h-BN in a laboratory, but few methods for realizing industrialization are available; patent CN111606311B discloses a boron nitride micro-nanorod with a vertically grown boron nitride nanosheet on the surface; the preparation method comprises the following steps: under the action of a catalyst, the mixture of boron oxide and magnesium powder is subjected to high-temperature solid-phase reaction, metal magnesium is required to be used as the catalyst in the method, and a metal mesh is required to be used for growing, so that the synthetic method is complex; meanwhile, the metal magnesium has certain potential safety hazard in the processes of storage and use, so that the industrial production is difficult to realize.
The synthesis method adopted in industry mainly takes direct nitrogen at high temperature after solid raw materials are mixed as a main material, the method is difficult to realize uniform mixing of the raw materials on the atomic layer, and when the filling amount of the prepared hexagonal boron nitride in rubber reaches 50-55%, cloud or powder hexagonal boron nitride can be separated out from the surface, namely, the floating powder phenomenon occurs, namely, the maximum filling amount of the hexagonal boron nitride in the rubber can only reach 50-55%, so that the improvement of the thermal conductivity of the rubber material is limited.
In summary, the maximum filling amount of h-BN prepared by the current industrial method in the rubber matrix can only reach 50-55%, so that the improvement of the thermal conductivity of the rubber material is limited.
The invention content is as follows:
the invention aims to overcome the technical problem that the upper limit of filling of hexagonal boron nitride in a rubber matrix is not high in the prior art, and provides hexagonal boron nitride, a preparation method thereof and heat-conducting rubber.
The technical problem to be solved by the invention is realized by adopting the following technical scheme:
one of the purposes of the invention is to provide a preparation method of hexagonal boron nitride, which comprises the following steps:
(1) dissolving a boron source and a nitrogen source in a solvent, and stirring for reaction to obtain a precursor;
(2) in an oxygen-containing atmosphere, performing first roasting on the precursor to obtain an intermediate;
(3) and in a nitrogen atmosphere, carrying out second roasting on the intermediate to obtain the hexagonal boron nitride.
The second object of the present invention is to provide a hexagonal boron nitride prepared according to the aforementioned method.
The invention also aims to provide a heat-conducting rubber, which comprises 35-95 wt% of rubber matrix and 5-65 wt% of heat-conducting filler; the heat-conducting filler is the hexagonal boron nitride.
The invention has the beneficial effects that:
1. the filling amount of the hexagonal boron nitride prepared by the method in the rubber matrix can reach 65%, a heat conducting network can be effectively formed, and the heat conductivity of the rubber is improved;
2. the preparation method of hexagonal boron nitride provided by the invention has the characteristics of cheap raw materials and wide sources, is simple and convenient in process and low in energy consumption, and can realize large-scale production of hexagonal boron nitride.
Description of the drawings:
FIG. 1 is an SEM photograph of precursors prepared in preparation examples 1 to 4;
FIG. 2 is an SEM photograph of hexagonal boron nitride obtained in preparation examples 1 to 4;
FIG. 3 is an SEM photograph of precursors prepared in preparation examples 5 to 8;
FIG. 4 is a particle size distribution diagram of hexagonal boron nitride obtained in production example 5;
FIG. 5 is a microscopic view of intermediates obtained in preparation examples 5 and 6;
FIG. 6 is an SEM photograph of hexagonal boron nitride prepared in preparation examples 5 to 8 at different magnifications;
FIG. 7 is an infrared spectrum of a precursor, an intermediate and hexagonal boron nitride obtained in preparation example 6;
FIG. 8 is an XRD pattern of hexagonal boron nitride obtained in preparation 3 and preparation 7;
FIG. 9 is an XRD pattern of hexagonal boron nitride obtained in preparation example 7 and preparation examples 9 to 13;
fig. 10 is an XRD pattern of hexagonal boron nitride prepared in preparation example 17.
The specific implementation mode is as follows:
in order to make the technical means, the creation characteristics, the achievement purposes and the effects of the invention easy to understand, the invention is further explained by combining the specific embodiments and the drawings.
As described above, the present invention provides a method for preparing hexagonal boron nitride, comprising the steps of:
(1) dissolving a boron source and a nitrogen source in a solvent, and stirring for reaction to obtain a precursor;
(2) in an oxygen-containing atmosphere, performing first roasting on the precursor to obtain an intermediate;
(3) and in a nitrogen atmosphere, carrying out second roasting on the intermediate to obtain the hexagonal boron nitride.
In a preferred embodiment of the invention, the boron source is calculated by boron element, the nitrogen source is calculated by nitrogen element, and the molar ratio of the boron source to the nitrogen source is (2.5-3.5): 1; for example, it may be 2.5:1, 3:1, 3.5:1, or any value in the range consisting of any two of the ratios described above.
In the invention, the boron source is selected from boric acid and/or borax; the nitrogen source is at least one selected from melamine, amine chloride and urea.
In the present invention, in the step (1), the nitrogen source and the boron source are stirred in the solvent to react to obtain the composition C 3 N 6 H 6 ·H 3 BO 3 The precursor of (2). Preferably, the temperature of the stirred reaction is from 70 to 110 deg.C, preferably from 85 to 105 deg.C, more preferably from 90 to 100 deg.C. The longer the stirring reaction time is, the larger the size of the obtained precursor is, and the more uniform the morphology is, and under the preferable conditions, the stirring reaction time is 4-24h, for example, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h or any value in the range of any two values, preferably 8-16 h; further preferably, in order to obtain the precursor with uniform size, the rotation speed of the stirring reaction is 200-800 r/min; preferably 250-500r/min, and more preferably 300-400 r/min.
In the present invention, the solvent may be water or a mixture of oil and water. The oil-water mixed solution is a mixture of water and oil, and comprises 20-80 Vol% of water and 20-80 Vol% of an oily solvent; preferably, the oil-water mixture comprises 30-70 Vol% of water and 30-70 Vol% of oily solvent; further preferably, the oil-water mixture comprises 40-60 Vol% of water and 40-60 Vol% of an oily solvent; more preferably, the oil-water mixture comprises 45-55 Vol% of water and 45-55 Vol% of an oily solvent. Wherein Vol% is volume percentage.
In the present invention, the oily solvent is a water-insoluble solvent, and the kind thereof may be known to those skilled in the art, and includes, but is not limited to, at least one of liquid paraffin, oleic acid, alkane solvents, silicone oil, and petroleum ether.
According to the present invention, when an oil-water mixture is used as a reaction solvent, in order to improve the uniformity of the mixing of water and oil and to bring the oil-water mixture to an equilibrium state, it is preferable that the oil-water mixture further contains an emulsifier; the type of emulsifier may be known to those skilled in the art and includes anionic emulsifiers and/or nonionic emulsifiers; the anionic emulsifiers include, but are not limited to, alkyl sulfates, alkyl benzene sulfonates, fatty acid salts, and phosphates; the nonionic emulsifiers include, but are not limited to, sorbitol esters, polyoxyethylene ethers, and polyoxypropylene ethers.
According to the invention, the precursor is sequentially roasted in two steps in an oxygen-containing atmosphere and a nitrogen atmosphere, so that the high-crystallinity hexagonal boron nitride can be obtained. The oxygen-containing atmosphere refers to a gas atmosphere containing oxygen, such as an air atmosphere.
In some preferred embodiments of the present invention, the precursor C can be made by performing the first firing in an oxygen-containing atmosphere 3 N 6 H 6 ·H 3 BO 3 The triazine ring and the B-O bond in the intermediate are gradually broken to form an intermediate containing B, N, C elements. Preferably, in the step (2), the conditions of the first firing include: the temperature is 600 ℃ and 800 ℃, and the time is 2-6 h.
The inventors have also found that too fast a temperature rise rate of the first calcination may result in incomplete sintering of the precursor, resulting in poor crystallinity of the obtained intermediate product; further preferably, the conditions of the first firing further include: heating the precursor from room temperature to 600-800 ℃ at a heating rate of not higher than 1-4 ℃/min, wherein the room temperature is 25 +/-5 ℃.
In the invention, the intermediate is roasted in a nitrogen atmosphere, so that redundant groups in the intermediate can be removed, and high-purity and high-crystallinity hexagonal boron nitride is obtained; the inventor also finds that the higher the temperature of the second roasting is, the higher the crystallinity of the obtained h-BN, and in the step (3), the temperature of the second roasting is 1100-1800 ℃, more preferably 1300-1700 ℃, and still more preferably 1500-1600 ℃; the time of the second roasting is 2 to 10 hours, and is further preferably 4 to 8 hours.
In the present invention, in order to sufficiently nitridize the intermediate product and obtain hexagonal boron nitride (h-BN) having high crystallinity, it is preferable that the conditions of the second firing further include: the intermediate is heated from 800 ℃ to 1000 ℃ at a heating rate of 5-8 ℃/min, and then heated from 1000 ℃ to 1100 ℃ at a heating rate of 1-4 ℃/min.
In a particularly preferred embodiment of the present invention, when water is used as the solvent, the hexagonal boron nitride is prepared by the following steps:
(1) dissolving a boron source and a nitrogen source in water, stirring and reacting for 4-16h at 70-110 ℃, then cooling to room temperature to obtain white precipitate, and centrifuging, washing and drying the white precipitate to obtain a precursor;
(2) in the air atmosphere, heating the precursor from room temperature to 600-800 ℃ at the heating rate of 1-4 ℃/min, and preserving the heat for 2-6h to obtain an intermediate;
(3) in the nitrogen atmosphere, the temperature of the intermediate is raised from 800 ℃ to 900 ℃ at the heating rate of 2-8 ℃/min, then raised to 1800 ℃ at the heating rate of 1-4 ℃/min, and kept for 4-8h, so as to obtain the hexagonal boron nitride.
The particle-shaped precursor with good dispersibility is prepared by the preferred embodiment, and the particle size range is 3-10 mu m; the particle precursor is roasted to obtain rod-shaped hexagonal boron nitride with smooth surface, the diameter of the hexagonal boron nitride is 2-16 mu m, the length of the hexagonal boron nitride is 20-100 mu m, and the length-diameter ratio of the hexagonal boron nitride is 6:1-12: 1.
In another preferred embodiment of the present invention, when the oil-water mixture is used as the solvent, the hexagonal boron nitride is prepared by the following steps:
(1) dissolving a boron source and a nitrogen source in water to obtain a clarified liquid; dropwise adding the clear liquid into an oily solvent containing an emulsifier, stirring and reacting for 4-16h at 70-110 ℃, then cooling to room temperature to obtain a white precipitate, and centrifuging, washing and drying the white precipitate to obtain a precursor;
(2) in the air atmosphere, heating the precursor from room temperature to 600-800 ℃ at the heating rate of 1-4 ℃/min, and preserving the heat for 2-6h to obtain an intermediate;
(3) in the nitrogen atmosphere, the temperature of the intermediate is raised from 800 ℃ to 900 ℃ at the heating rate of 2-8 ℃/min, then raised to 1800 ℃ at the heating rate of 1-4 ℃/min, and kept for 4-8h, so as to obtain the hexagonal boron nitride.
The precursor in a rod shape is prepared by the preferred embodiment, the diameter is 2-20 μm, and the length is 50-120 μm; roasting the rod-shaped precursor to obtain flaky boron nitride or rod-shaped hexagonal boron nitride with rough surface; the particle size of the flaky hexagonal boron nitride is 800-900nm, and the thickness of the flaky hexagonal boron nitride is 20-80 nm; the rod-shaped hexagonal boron nitride with the rough surface has the diameter of 4-20 mu m, the length of 20-100 mu m and the length-diameter ratio of 6:1-12: 1.
In the invention, the shapes of the precursors prepared by taking water as a solvent and taking an oil-water mixed solution as a solvent are completely different, and the possible reasons are as follows: when the oil-water mixed solution is used as a solvent, when an aqueous solution is dispersed into an oil phase incompatible with the aqueous solution, the aqueous phase tends to form small droplets so as to reduce the contact area with the oil phase as much as possible, so that the solution reaches an equilibrium state to form an emulsion, at the moment, precursor crystals (spherulites) undergo agglomeration and fracture conversion reactions, so precursors with different shapes are generated, and the precursors with different shapes are calcined at high temperature to finally obtain h-BN products with different shapes.
The invention also aims to provide a heat-conducting rubber, which comprises 35-95 wt% of rubber matrix and 5-65 wt% of heat-conducting filler; the heat-conducting filler is the hexagonal boron nitride; preferably, the heat conductive rubber comprises 35 to 60 wt% of a rubber matrix and 40 to 65 wt% of a heat conductive filler.
In the present invention, the rubber matrix includes, but is not limited to, at least one of silicon rubber, styrene-butadiene rubber, ethylene-propylene rubber, nitrile rubber, ethylene-propylene-diene rubber, butadiene rubber and natural rubber.
The present invention will be described in detail below with reference to examples. In the examples, room temperature means 25. + -. 5 ℃.
Thermal conductivity: the test temperature is 20 ℃, the depth of a sample to be tested is 2mm, the thickness of the sample is 3mm, the length and the width of the sample are respectively 4cm, each sample is tested for 5 times, and the average value is taken.
The formula for the Thermal Conductivity Enhancement (TCE) is: TCE ═ K (K-K) 1 )/K 1 Wherein K is the thermal conductivity of the composite material, K 1 Is the intrinsic thermal conductivity of the matrix.
The viscosity was measured by a digital viscometer (Shanghai model Xin scientific instrument) of model NDJ-8S.
In the following examples, liquid paraffin was obtained commercially and had a density of 0.84 to 0.86g/cm 3 (ii) a Room temperature vulcanized silicone rubber (hereinafter referred to simply as silicone rubber) is commercially available and has a viscosity (25 ℃ C.) of 1.509X 10 3 mPa.s, volatile matter (150 ℃, 3h) is less than or equal to 2 percent, and surface drying time is less than or equal to 2 h; the curing agent is commercially available.
Preparation example: preparation of hexagonal boron nitride (h-BN)
1. Pure water is used as solvent
Preparation example 1
Preparing a precursor:
dissolving 0.06mol of boric acid and 0.02mol of melamine in 100mL of pure water, stirring and heating to 95 ℃ by using a magnetic stirrer, assisting with the rotation speed of 350r/min, continuing stirring and reacting for 4h after the solution is transparent and clear, and cooling. And cooling the reaction liquid to room temperature to obtain a white precipitate, centrifugally washing the white precipitate by using absolute ethyl alcohol, and drying the white precipitate for 24 hours in a vacuum drying oven at the temperature of 60 ℃ to obtain the BN precursor.
BN synthesis:
and (3) placing the BN precursor in a corundum crucible, then transferring the corundum precursor to a muffle furnace, heating to 700 ℃ at a speed of 3 ℃/min, preserving heat for 4h, and cooling along with the furnace to obtain an intermediate. And transferring the intermediate into a nitrogen atmosphere tube furnace, heating to 1000 ℃ at the speed of 5 ℃/min, heating to 1600 ℃ at the speed of 3 ℃/min, preserving heat for 6h, and cooling along with the furnace to obtain the hexagonal boron nitride (h-BN).
Preparation examples 2 to 4
The procedure of preparation 1 was followed except that: the reaction time was stirred as shown in Table 1.
TABLE 1
| Product of | Solvent(s) | Time of stirring | |
| Preparation example 1 | h-BN-A1 | Water (W) | 4h |
| Preparation example 2 | h-BN-A2 | Water (W) | 8h |
| Preparation example 3 | h-BN-A3 | Water (W) | 12h |
| Preparation example 4 | h-BN-A4 | Water (W) | 16h |
FIG. 1 is an SEM photograph of the precursors obtained in preparation examples 1 to 4, wherein FIG. 1a is an SEM photograph of the precursor in preparation example 1; FIG. 1b is an SEM image of the precursor in preparation example 2; FIG. 1c is an SEM photograph of the precursor of preparation 3; FIG. 1d is an SEM image of the precursor of preparation 4. As can be seen from fig. 1a to 1 d: precursor particles with good dispersibility are obtained under different reaction times.
In FIGS. 1a and 1b, the particle size of the precursor particles was about 5 μm when reacted for 4h and 8h (preparative example 1 and preparative example 2); in FIG. 1c, at reaction time 12h (preparation 3), the particle size of the precursor particles increased to 8 μm; in FIG. 1d, the size of the precursor particles was further increased to 9 μm when the reaction time was 16h (preparation 4). This can result in: in the synthesis stage of the precursor, the size of the precursor can be increased by prolonging the stirring reaction time, but the overall appearance of the precursor is not changed.
FIG. 2 is an SEM photograph of hexagonal boron nitride obtained in production examples 1 to 4, wherein FIG. 2a is an SEM photograph of h-BN in production example 1; FIG. 2b is an SEM picture of h-BN in preparation example 2; FIG. 2c is an SEM picture of h-BN in preparation 3; FIG. 2d is an SEM picture of h-BN in preparation 4. As can be seen from FIG. 2, the h-BN synthesized in the presence of the water solvent has smooth surface and length-diameter ratio of 6-12:1 long rod-like morphology.
In FIG. 2a, when the stirring reaction time was 4 hours (preparation example 1), the synthesized rod-like h-BN had a diameter of about 2 to 8 μm and an overall length of about 20 to 85 μm, but the uniformity of the length and diameter of the rod-like h-BN was poor; in FIG. 2b, when the stirring reaction time was 8 hours (preparation example 2), the length of the rod-shaped h-BN and the uniformity of the diameter were improved, the diameter was increased to 2 to 10 μm, and the length was increased to about 80 μm; in FIG. 2c, when the reaction time was 12 hours (preparation example 3), the length of the rod-shaped h-BN was further improved as well as the uniformity of the diameter, increasing the diameter to 2 to 16 μm and the length to 100 μm; in FIG. 2d, when the reaction time is 16 hours (preparation example 4), the rod-shaped BN has a diameter of 2 to 14 μm and a length of about 100. mu.m.
In conclusion, in the water solvent, h-BN obtained by calcining the precursor synthesized at different times is in a long rod shape with a smooth surface, and the diameter, the length and the uniformity of the rod-shaped h-BN are increased along with the increase of the time of stirring reaction; however, when the stirring reaction time reached 12 hours, the diameter and length of the obtained rod-like h-BN did not increase any more.
2. Using water-paraffin as solvent
Preparation example 5
Preparing a precursor:
dissolving 0.06mol of boric acid and 0.02mol of melamine in 100mL of pure water, stirring and heating to 95 ℃ by using a magnetic stirrer, and cooling after the solution is transparent and clear with the rotation speed of 350 r/min. The clear solution was then added dropwise to 100mL of liquid paraffin (95 ℃ C.) containing span-80 (in an amount of 0.05 wt% based on the weight of the liquid paraffin), and the reaction was continued for 4h, followed by cooling. And cooling the reaction liquid to room temperature to obtain a white precipitate, centrifugally washing the white precipitate with toluene, and drying in a vacuum drying oven at 60 ℃ for 24 hours to obtain the BN precursor.
BN synthesis:
and (3) placing the BN precursor in a corundum crucible, then transferring the corundum precursor to a muffle furnace, heating to 700 ℃ at a speed of 3 ℃/min, preserving heat for 4h, and cooling along with the furnace to obtain an intermediate. And transferring the intermediate into a nitrogen atmosphere tube furnace, heating to 1000 ℃ at the speed of 5 ℃/min, heating to 1600 ℃ at the speed of 3 ℃/min, preserving heat for 6h, and cooling along with the furnace to obtain the hexagonal boron nitride (h-BN).
Preparation examples 6 to 8
The procedure of preparation 5 was followed: the difference is that: the reaction time with stirring is shown in Table 2.
TABLE 2
FIG. 3 is an SEM photograph of the precursors obtained in preparation examples 5-8, wherein FIG. 3a is an SEM photograph of the precursor in preparation example 5; FIG. 3b is an SEM photograph of the precursor of preparation 6; FIG. 3c is an SEM photograph of the precursor of preparation 7; fig. 3d is an SEM image of the precursor in preparation 8.
As can be seen from FIG. 3a, when the stirring reaction time was 4 hours (preparation example 5), the precursor obtained contained both small-sized plate-like particles having an average particle size of 5 μm and elongated rods (about 2 μm in diameter and 100 μm in length) having a regular morphology and good uniformity; as can be seen from FIG. 3b, when the stirring reaction time was 8 hours (preparation example 6), the flaky precursor particles were significantly reduced, and the precursor was mostly long rods with a diameter of about 10 μm; as can be seen from fig. 3c, when the stirring reaction time was 12 hours (preparation example 7), the diameter of the rod-shaped precursor was further increased to 10 μm or more, and a phenomenon in which crystals grew together occurred; as can be seen from FIG. 3d, when the stirring reaction time was 16h (preparation example 8), the rod-like morphology was substantially disappeared with no clear profile and the crystals were completely agglomerated.
FIG. 5a is a microscopic image of an intermediate obtained in preparation example 5; FIG. 5b is a microscopic image of an intermediate obtained in preparation example 6;
FIG. 6 is an SEM photograph of hexagonal boron nitride obtained in production examples 5 to 8 at different magnifications, wherein FIGS. 6(a-1) to 6(a-3) are SEM photographs of h-BN obtained in production example 5 at different magnifications; FIGS. 6(b-1) to 6(b-3) are SEM images of h-BN in production example 6 at different magnifications; FIGS. 6(c-1) to 6(c-3) are SEM images of h-BN in preparation example 7 at different magnifications; FIGS. 6(d-1) to 6(d-3) are SEM images of h-BN in production example 8 at different magnifications.
As can be seen from FIGS. 6(a-1) to 6(a-3), after the precursor is calcined by nitrogen, flaky h-BN with the size of 800nm-1 μm is formed, and the flaky h-BN has good dispersibility and no obvious agglomeration phenomenon. As can be seen from the comparison of fig. 3a, 5a and 6a, when the stirring reaction time is 4h (preparation example 5), a mixture of a flake precursor and a rod precursor is obtained, the precursor forms a spherical intermediate after air calcination (fig. 5a), and the spherical intermediate forms flake h-BN after nitrogen atmosphere (fig. 6 a); indicating that there was agglomeration of crystals and fracture transformation reactions during calcination in a nitrogen atmosphere.
FIG. 4 is a distribution diagram of the particle size of the flake h-BN obtained in preparation example 5, and as shown in FIG. 4, the particle size of the flake h-BN obtained in example 5 is intensively distributed at 800-900 nm.
As can be seen from FIGS. 6(b-1) to 6(b-3), when the stirring reaction time was 8 hours (preparation example 6), rod-like h-BN having a diameter of 6 to 20 μm and a length of 20 to 80 μm was obtained, the aspect ratio thereof was 6 to 12:1, but the uniformity of the rod-like h-BN was poor and the surface of the rod-like h-BN was porous and loose. As can be seen from the comparison of FIGS. 3b, 5b and 6b, when the stirring reaction time is 8h (preparation example 6), the morphologies of the prepared precursor, intermediate and product h-BN are basically consistent and are rod-shaped.
As can be seen from FIGS. 6(c-1) to 6(c-3), when the reaction time was 12 hours under stirring (preparation example 7), the uniformity of the obtained rod-like h-BN was remarkably improved as compared with preparation example 6, the rod-like h-BN had a diameter of 4 to 12 μm, a length of 40 to 80 μm and an aspect ratio of 6 to 12: 1;
as can be seen from FIGS. 6(d-1) to 6(d-3), when the stirring reaction time was 16 hours (preparation example 8), the obtained rod-like h-BN was further increased in size, had a diameter of 4 to 10 μm and a length of 100 μm; however, the compactness of the rod-like h-BN is lowered, and a large number of cracks appear on the surface.
FIG. 7 is an infrared spectrum of the precursor, intermediate and rod-shaped h-BN prepared in preparation example 6, as can be seen from FIG. 7: in the absorption peak of the precursor, 3523cm -1 Is a stretching vibration of-OH; 3496cm -1 And 3416cm -1 is-NH 2 The antisymmetric stretching vibration of (2) indicates the presence of hydrogen bonds between molecules. 3196cm -1 is-NH in melamine 2 The stretching vibration peak is overlapped with the characteristic peak of B-OH in boric acid; 1577cm -1 And 1455cm -1 Is caused by triazine ring characteristic peak and B-O stretching vibration; 803cm -1 Is BO 3 The stretching vibration peak of (1); from this, the precursor was C 3 N 6 H 6 ·H 3 BO 3 A compound is provided.
The precursor is treated at 700 ℃ to obtain an intermediate, and the intermediate can be seen by comparing the infrared spectrogram of the precursor: part of absorption peaks in the intermediate disappear, which indicates that triazine ring and B-O bond in the precursor are gradually broken and combined to form an intermediate containing B, N, C elements;
the intermediate calcined at 1600 ℃ under nitrogen to give a 1381cm product -1 And 812cm -1 Two absorption peaks, which also correspond to the stretching vibration peaks of B-N and B-N-B, indicate that the final product synthesized under these conditions is h-BN.
FIG. 8 is an XRD pattern of h-BN produced in preparation example 3 and preparation example 7; as can be seen from FIG. 8, the crystallinity of h-BN synthesized in a water-paraffin solvent (preparation example 7) is higher as compared with that of h-BN synthesized in water (preparation example 3).
Preparation examples 9 to 13
The process of preparation 5 was followed, except that: the final temperature of the second calcination is specifically shown in Table 3.
TABLE 3
FIG. 9 is an XRD pattern of h-BN produced in preparation example 7 and preparation examples 9 to 13; in the range of 1100-1600 ℃, the crystallinity of the obtained h-BN is gradually improved along with the increase of the second roasting temperature.
Preparation example 14
The process of preparation 5 was followed, except that: the preparation method of the precursor comprises the following steps:
dissolving 0.06mol of boric acid and 0.02mol of melamine in 100mL of pure water, stirring and heating to 95 ℃ by using a magnetic stirrer, and cooling after the solution is transparent and clear with the rotation speed of 350 r/min. The clear solution was then added dropwise to 200mL of liquid paraffin (95 ℃ C.) containing span-80 (in an amount of 0.05% by weight based on the weight of the liquid paraffin), and the reaction was continued for 4 hours and then cooled. Cooling the reaction liquid to room temperature to obtain white precipitate, centrifugally washing the white precipitate with toluene, and drying in a vacuum drying oven at 60 ℃ for 24 hours to obtain a BN precursor;
the BN precursor is roasted in two steps to obtain h-BN-B9, wherein the method of roasting in two steps is the same as that of preparation example 5.
Preparation example 15
The process of preparation 5 was followed, except that: the temperature of the first roasting is 600 ℃ and the time is 4 hours, so that h-BN-B10 is obtained.
Preparation example 16
The process of preparation 5 was followed, except that: the temperature of the first roasting is 800 ℃ and the time is 4 hours, so that h-BN-B11 is obtained.
Preparation example 17
The process of preparation 5 was followed except that: directly roasting the precursor in a nitrogen atmosphere, specifically as follows:
the BN precursor is placed in a nitrogen atmosphere tube furnace, the temperature is increased from room temperature to 1600 ℃ at the speed of 5 ℃/min, the temperature is kept for 6h, the furnace cooling is carried out, the XRD pattern of the obtained product is shown in figure 10, and as can be seen from figure 10, the product obtained by directly calcining in the nitrogen atmosphere is not hexagonal boron nitride, and the crystallization property is poor.
Preparation example 18
Hexagonal boron nitride BN-D, with a particle size of 16.2 μm, was prepared according to CN111453706A, example 2.
Examples 1 to 18
The BN powder prepared in preparation examples 3, 5 and 7, silicone rubber and a curing agent (the amount is 4% of the amount of the silicone rubber) were mixed in a homogenizer at a rotation speed of 3000r/min for 2min, and after the mixture was uniform, the mixture was placed in a vacuum chamber to be defoamed at room temperature and exhausted for 10min to obtain a slurry, and the viscosity of the slurry is shown in Table 4. The slurry was filled into a stainless steel mold, hot-pressed at 150 ℃ for 10min on a flat plate vulcanizing machine (Henan Shangqiu rubber machinery plant, model XBL-D400), and then cold-pressed for 10 min. Finally, the mixture is continuously cured for 12 hours at room temperature, and demolding is carried out, so that the BN/SR composite material can be obtained, and the results are shown in Table 4.
TABLE 4
Note: judging the maximum filling amount of the h-BN by the existence of floating powder, and when the floating powder appears, indicating that the h-BN achieves the maximum filling in the rubber matrix; the floating powder is heat-conducting powder precipitated on the surface of the rubber.
As can be seen from table 4: as can be seen by comparing example 1, example 7 and example 14, at a loading level of 10 wt%, the viscosities of the slurries obtained by filling h-BN-A3, h-BN-C and h-BN-B2 are relatively close, and the slurries all have good fluidity.
As can be seen by comparing example 3, example 9 and example 16, the viscosity of the sample obtained in example 9 was the smallest when the filling amount was increased to 30%, indicating that the viscosity of the BN/SR composite filled with h-BN-B2 had the smallest increase in viscosity.
As can be seen by comparing example 4, example 10 and example 17, when the loading was increased to 40%, the resulting slurry had almost no fluidity; the slurry obtained in example 4 had a viscosity of 8.662X 10 5 mPas, viscosity of the slurry obtained in example 10 was 8.825X 10 5 mPas, viscosity of the slurry obtained in example 12 was 9.657X 10 5 mPa · s. In conclusion: the flaky h-BN-C thickening effect is the most serious under the same filling amount.
When the filling amount of the h-BN-A3, h-BN-C or h-BN-B2 reaches more than 50 percent, the viscosity of the slurry exceeds the range of a digital viscometer, and the viscosity is difficult to measure.
As can be seen by comparing examples 1 to 6, the thermal conductivity of the BN/SR composite material is increased along with the increase of the filling amount of the rod-shaped h-BN-A3, because the probability of mutual contact among the heat-conducting fillers (the rod-shaped h-BN-A3) is increased along with the gradual increase of the content of the rod-shaped h-BN-A3, and a complete heat-conducting network is easier to form. When the filling amount is between 10% and 30%, the increase rate of heat conduction is smooth because at a low filling amount, the rod-shaped h-BN-A3 particles are surrounded by the rubber matrix without contacting each other, and an effective heat conduction path cannot be formed. When the filling amount of the heat conductive filler (rod-shaped h-BN-A3) is increased to 40%, the heat conductive growth rate starts to increase sharply, and when the filling amount reaches 40%, the phenomenon of "percolation" starts to occur.
As can be seen by comparing examples 1-6 with examples 7-13, the thermal conductivity of the BN/SR composite obtained in examples 7-12 is better than that of the BN/SR composite obtained in examples 1-6 under the same filling amount. The reason is that: the rod-shaped h-BN-B2 has a rough surface, can increase the probability of mutual contact among particles, can form a perfect heat conducting network in a rubber matrix more easily, provides more channels for phonon transportation, and has better heat conducting effect.
In the invention, the maximum filling amount of h-BN is judged by the existence of floating powder, and when the floating powder appears, the h-BN reaches the maximum filling in the rubber matrix; the floating powder is heat-conducting powder precipitated on the surface of the rubber. As can be seen from examples 6, 13 and 19, when the filling amount of the rod-like h-BN-B2 was 65%, no floating powder appeared on the surface of the silicone rubber, indicating that the filling amount of h-BN-B2 in the silicone rubber was as high as 65%; when the filling amount of the rod-shaped h-BN-A3 and the flake-shaped h-BN-C is 60 percent, no floating powder appears on the surface of the silicon rubber, which indicates that the filling amount of the rod-shaped h-BN-A3 and the flake-shaped h-BN-C in the silicon rubber can reach 60 percent.
As can be seen by comparing examples 1-6 with examples 14-19, the BN/SR composites obtained in examples 14-19 have inferior thermal conductivity to the BN/SR composites obtained in examples 1-6 at equivalent loading levels.
Preparation examples 20 to 32 and comparative examples 1 to 2
According to the method of preparation example 5, the filling amounts of the heat conductive fillers were all 40 wt%, except that: the kind of the heat conductive filler is shown in table 5.
TABLE 5
Comparative example 3
Spherical BN (s-BN) with a particle size of 100 μm, which is commercially available from Baituohai Co Ltd, was used 100 ) As a thermally conductive filler.
Reacting s-BN 100 Mixing the silicon rubber and a curing agent (the dosage is 4 percent of the dosage of the silicon rubber) in a homogenizer at the rotating speed of 3000r/min for 2min, placing the mixture into a vacuum box after the mixture is uniform, defoaming and exhausting air at room temperature for 10min to obtain the slurry. The slurry was filled into a stainless steel mold, hot-pressed at 150 ℃ for 10min on a flat plate vulcanizing machine (Henan Shanghai rubber machinery plant, model XBL-D400), and then cold-pressed for 10 min. And finally, continuously curing for 12 hours at room temperature, and demolding to obtain the BN/SR composite material.
It was found that, when the loading was 55%, the surface of the BN/SR composite appeared to be dusty. Illustrating the s-BN 100 The maximum loading in the rubber was 55%.
The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (10)
1. A preparation method of hexagonal boron nitride is characterized by comprising the following steps:
(1) dissolving a boron source and a nitrogen source in a solvent, and stirring for reaction to obtain a precursor;
(2) in an oxygen-containing atmosphere, performing first roasting on the precursor to obtain an intermediate;
(3) and in a nitrogen atmosphere, carrying out second roasting on the intermediate to obtain the hexagonal boron nitride.
2. The method of claim 1, wherein: the boron source is selected from boric acid and/or borax;
preferably, the nitrogen source is selected from at least one of melamine, amine chloride and urea;
preferably, the molar ratio of the boron source to the nitrogen source is (2.5-3.5):1, wherein the boron source is calculated by the element of boron and the nitrogen source is calculated by the element of nitrogen.
3. The method of claim 1, wherein: the solvent is water or oil-water mixed solution;
preferably, the oil-water mixture comprises 20-80 Vol% of water and 20-80 Vol% of oily solvent;
preferably, the oil-water mixture comprises 30-70 Vol% of water and 30-70 Vol% of oily solvent;
preferably, the oily solvent is selected from at least one of liquid paraffin, oleic acid, alkane solvents, silicone oil and petroleum ether.
4. The production method according to claim 3, characterized in that: the oil-water mixed solution also contains an emulsifier;
preferably, the emulsifier is an anionic emulsifier and/or a nonionic emulsifier;
preferably, the anionic emulsifier is selected from at least one of alkyl sulfate, alkyl benzene sulfonate, fatty acid salt and phosphate;
preferably, the nonionic emulsifier is selected from at least one of sorbitol ester, polyoxyethylene ether and polyoxypropylene ether.
5. The method of claim 1, wherein: the conditions of the stirring reaction comprise: the temperature is 70-110 ℃, the time is 4-24h, and the rotating speed is 200-;
preferably, the conditions of the stirring reaction include: the temperature is 85-105 ℃, the time is 8-16h, and the rotating speed is 250-500 r/min.
6. The production method according to any one of claims 1 to 5, wherein the step (1) comprises:
dissolving a boron source and a nitrogen source in water, and carrying out stirring reaction for 8-16h at 85-105 ℃ to obtain the precursor;
or
Dissolving a boron source and a nitrogen source in water to obtain a clarified liquid; and then dropwise adding the clarified liquid into an oily solvent containing an emulsifier, and carrying out stirring reaction for 8-16h at 85-105 ℃ to obtain the precursor.
7. The production method according to any one of claims 1 to 6, characterized in that: the conditions of the first firing include: the temperature is 600 ℃ and 800 ℃, and the time is 2-6 h;
preferably, the conditions of the first firing further include: and heating the precursor from room temperature to 600-800 ℃ at a heating rate of not higher than 1-4 ℃/min.
8. The production method according to any one of claims 1 to 6, characterized in that: the temperature of the second roasting is 1100-1800 ℃, and the time is 2-10 h; preferably: the temperature is 1300-1700 ℃, and the time is 4-8 h;
preferably, the second firing conditions further include: the intermediate is heated from 800 ℃ to 1000 ℃ at a heating rate of 5-8 ℃/min, and then heated from 1000 ℃ to 1100 ℃ at a heating rate of 1-4 ℃/min.
9. A hexagonal boron nitride produced by the production method according to any one of claims 1 to 8;
preferably, the hexagonal boron nitride is platelet hexagonal boron nitride or rod-shaped hexagonal boron nitride;
preferably, the particle size of the flaky hexagonal boron nitride is 800-900nm, and the thickness is 20-80 nm;
preferably, the rod-shaped hexagonal boron nitride is rod-shaped hexagonal boron nitride with a smooth surface or rod-shaped hexagonal boron nitride with a rough surface;
preferably, the rod-shaped hexagonal boron nitride with smooth surface has the diameter of 2-16 μm, the length of 20-100 μm and the length-diameter ratio of 6:1-12: 1;
preferably, the rod-shaped hexagonal boron nitride with rough surface has the diameter of 4-20 μm, the length of 20-100 μm and the length-diameter ratio of 6:1-12: 1.
10. A heat conductive rubber characterized in that: the heat-conducting rubber comprises 35-95 wt% of a rubber matrix and 5-65 wt% of a heat-conducting filler; the thermally conductive filler is the hexagonal boron nitride of claim 9;
preferably, the heat conductive rubber comprises 35 to 60 wt% of a rubber matrix and 40 to 65 wt% of a heat conductive filler;
preferably, the rubber matrix is selected from at least one of silicone rubber, styrene-butadiene rubber, ethylene-propylene rubber, nitrile rubber, ethylene-propylene-diene rubber, butadiene rubber and natural rubber.
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| CN114988375A (en) * | 2022-06-06 | 2022-09-02 | 安徽壹石通材料科技股份有限公司 | Heat-conducting microsphere, preparation method thereof and polymer composite material |
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| CN107376825A (en) * | 2017-08-22 | 2017-11-24 | 中国科学院过程工程研究所 | A kind of hexagonal boron nitride material and its production and use |
| CN111285337A (en) * | 2020-04-28 | 2020-06-16 | 中国科学院兰州化学物理研究所 | Preparation method and application of porous hexagonal boron nitride with high specific surface area |
| CN111453706A (en) * | 2020-04-27 | 2020-07-28 | 信阳市德福鹏新材料有限公司 | Synthesis method of hexagonal boron nitride |
| US20200307998A1 (en) * | 2019-03-28 | 2020-10-01 | Nichia Corporation | Hexagonal boron nitride fibers and method of manufacturing same |
| CN112520714A (en) * | 2020-03-20 | 2021-03-19 | 山东晶亿新材料有限公司 | Hexagonal boron nitride and preparation method and application thereof |
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| CN107376825A (en) * | 2017-08-22 | 2017-11-24 | 中国科学院过程工程研究所 | A kind of hexagonal boron nitride material and its production and use |
| US20200307998A1 (en) * | 2019-03-28 | 2020-10-01 | Nichia Corporation | Hexagonal boron nitride fibers and method of manufacturing same |
| CN112520714A (en) * | 2020-03-20 | 2021-03-19 | 山东晶亿新材料有限公司 | Hexagonal boron nitride and preparation method and application thereof |
| CN111453706A (en) * | 2020-04-27 | 2020-07-28 | 信阳市德福鹏新材料有限公司 | Synthesis method of hexagonal boron nitride |
| CN111285337A (en) * | 2020-04-28 | 2020-06-16 | 中国科学院兰州化学物理研究所 | Preparation method and application of porous hexagonal boron nitride with high specific surface area |
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| CN114988375A (en) * | 2022-06-06 | 2022-09-02 | 安徽壹石通材料科技股份有限公司 | Heat-conducting microsphere, preparation method thereof and polymer composite material |
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