CN113912400A - Method for preparing isotropic high-thermal-conductivity composite material based on boron nitride - Google Patents
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Abstract
The invention discloses a method for preparing an isotropic high-thermal-conductivity composite material based on boron nitride, which comprises the following steps: s1, weighing 100 parts of raw materials of aluminum nitride powder and boron nitride powder according to mass fraction, wherein the mass ratio of aluminum nitride to boron nitride is 85: 15, weighing a sintering aid calcium difluoride, wherein the mass fraction of the calcium difluoride is 1-4%; s2, putting the aluminum nitride powder and the boron nitride powder into a stirrer to be fully stirred and mixed for 50 min; s3, adding the mixed powder of aluminum nitride and boron nitride and calcium difluoride into a ball mill to be ground into powder, adding zirconium dioxide into the ball mill as a grinding body during grinding, adding absolute ethyl alcohol as a grinding medium, and wet mixing for 20-24 h.
Description
Technical Field
The invention belongs to the technical field of boron nitride composite materials, and particularly relates to a method for preparing an isotropic high-thermal-conductivity composite material based on boron nitride.
Background
The composite material is a material with new performance formed by two or more than two materials with different properties by a physical or chemical method on a macroscopic (microscopic) scale; the composite material has the characteristics of light weight, high strength, convenient processing and forming, excellent elasticity, chemical corrosion resistance, good weather resistance and the like, gradually replaces wood and metal alloy, and is widely applied to the fields of aerospace, automobiles, electronics and electrical, buildings, body-building equipment and the like; the materials make up for each other's deficiencies in performance to produce a synergistic effect, so that the composite material has comprehensive performance superior to that of the original material and meets various requirements. The matrix materials of the composite materials are divided into two main categories of metal and nonmetal. Commonly used metal substrates are aluminum, magnesium, copper, titanium and alloys thereof. The nonmetal substrate mainly comprises synthetic resin, rubber, ceramics, graphite, carbon and the like. The reinforced material mainly comprises glass fiber, carbon fiber, boron fiber, aramid fiber, silicon carbide fiber, asbestos fiber, crystal whisker, metal wire, hard fine particles and the like. The boron nitride is introduced into the composite material, so that the advantages of the boron nitride ceramic can be fully exerted, the defects that the single-phase boron nitride ceramic material is low in mechanical property, poor in rain erosion resistance, difficult to manufacture into a large-shaped component and the like can be overcome, the composite material with excellent comprehensive performance is obtained, and the boron nitride composite material is widely applied to the fields of thermal protection materials, high-temperature wave-transmitting materials, high-performance aviation friction materials, anti-oxidation coating materials and the like.
However, the boron nitride high thermal conductivity composite material in the prior art has low thermal conductivity and insufficient surface stress, so that the thermal shock resistance is poor, and the bending strength and hardness of the existing boron nitride high thermal conductivity composite material are low, so that the machinability of the existing boron nitride high thermal conductivity composite material is poor.
Disclosure of Invention
The invention aims to provide a method for preparing an isotropic high-thermal-conductivity composite material based on boron nitride, which improves the thermal conductivity of aluminum nitride/boron nitride composite ceramic to a certain extent, and ensures that the bending strength and the hardness of the aluminum nitride/boron nitride composite ceramic are high enough and the aluminum nitride/boron nitride composite ceramic has better machinability, so as to solve the problems that the boron nitride high-thermal-conductivity composite material in the prior art is low in thermal conductivity and insufficient in surface stress pressure, and further the thermal shock resistance of the boron nitride high-thermal-conductivity composite material is poor, and the bending strength and the hardness of the boron nitride high-thermal-conductivity composite material in the prior art are not high, so that the machinability of the boron nitride high-thermal-conductivity composite material is poor.
In order to achieve the purpose, the invention adopts the following technical scheme: the method for preparing the isotropic high-thermal-conductivity composite material based on the boron nitride comprises the following steps:
s1, weighing 100 parts of raw materials of aluminum nitride powder and boron nitride powder according to mass fraction, wherein the mass ratio of aluminum nitride to boron nitride is 85: 15, weighing a sintering aid calcium difluoride, wherein the mass fraction of the calcium difluoride is 1-4%;
s2, putting the aluminum nitride powder and the boron nitride powder into a stirrer to be fully stirred and mixed for 50 min;
s3, adding the mixed powder of aluminum nitride and boron nitride and calcium difluoride into a ball mill, grinding into powder, adding zirconium dioxide into the ball mill as a grinding body during grinding, adding absolute ethyl alcohol as a grinding medium, and wet mixing for 20-24 hours;
s4, placing the ground mixture into a vacuum barrel, and heating to 80 ℃ to carry out rotary evaporation on the mixture;
s5, drying the mixture, placing the mixture into a graphite die for cold press molding, and sintering the mixture at 1750-2000 ℃;
s6, putting the sintered composite material into a forming die, and pressing for 3-5 min under the pressure of 500-700 MPa;
and S7, naturally cooling for 1-3 h under the condition of normal temperature and normal pressure to obtain the sample of the aluminum nitride/boron nitride composite ceramic.
Preferably, in S1, the aluminum nitride powder has a specific surface area of 3.3m2The particle size of the boron nitride powder particles is 0.3-0.4 micrometer, the average particle size of the calcium difluoride powder particles is less than 1 micrometer, and the purity of the aluminum nitride powder and the purity of the boron nitride powder are both greater than 98.5%.
Preferably, in S2, the inside of the stirrer is kept in a sealed state during stirring and mixing, the rotation speed of the stirrer is controlled to be 60 to 100r/min, and nitrogen gas is filled into the stirrer as inert gas.
Preferably, in S3, the ball mill is a high-speed mill, the rotation speed of the ball mill is 150 to 350r/min, and the particle diameter of the composite material powder after grinding is 30 to 60 nm.
Preferably, in S4, the vacuum barrel is internally provided with a disperser, and when the composite material powder is subjected to rotary evaporation, the disperser can continuously turn up the composite material powder, so as to increase the contact area between the composite material powder and hot air and accelerate drying, and the rotation speed of the composite material powder is 20-30 r/min.
Preferably, in S5, the pressure during sintering is 30MPa, the temperature during sintering is gradually increased, and the rate of temperature increase is 10 ℃/min.
Preferably, in S6, the pressing is performed for 5min at a pressure of 500MPa, for 4min at a pressure of 600MPa, and for 3min at a pressure of 700 MPa.
Preferably, in S6, the size of the cavity of the forming die is 1cm × 1cm, i.e., the size of the obtained aluminum nitride/boron nitride composite ceramic sample is 1cm × 1 cm.
The invention has the technical effects and advantages that: compared with the prior art, the method for preparing the isotropic high-thermal-conductivity composite material based on the boron nitride has the following advantages:
according to the invention, 3% of calcium difluoride is introduced to react with aluminum oxide attached to the surfaces of aluminum nitride powder particles in a high-temperature sintering process to generate a liquid phase, so that the sintering compactness of the aluminum nitride/boron nitride composite ceramic is promoted, therefore, when the calcium difluoride is introduced into the aluminum nitride/boron nitride composite ceramic, the sintering temperature is increased to obtain a pure aluminum nitride/boron nitride composite ceramic sintered body, and the comparison of multiple groups of test data shows that when the sintering temperature is 1850 ℃, the thermal conductivity of the aluminum nitride/boron nitride composite ceramic is 109W/(mK), the thermal conductivity of the aluminum nitride/boron nitride composite ceramic is improved to a certain extent, and the bending strength and the hardness of the aluminum nitride/boron nitride composite ceramic are high enough, so that the aluminum nitride/boron nitride composite ceramic has good machinability.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
FIG. 1 is a flow chart of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The specific embodiments described herein are merely illustrative of the invention and are not intended to be limiting. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making an invasive task, are within the scope of the present invention.
The invention provides a method for preparing an isotropic high-thermal-conductivity composite material based on boron nitride, which comprises the following steps of:
s1, weighing 100 parts of raw materials of aluminum nitride powder and boron nitride powder according to mass fraction, wherein the mass ratio of aluminum nitride to boron nitride is 85: weighing a sintering aid calcium difluoride with a mass fraction of 1-4%, specifically, when the mass fraction of the calcium difluoride is 3%, the obtained aluminum nitride/boron nitride composite ceramic has more excellent comprehensive performance, and in S1, the specific surface area of the aluminum nitride powder is 3.3m2The particle size of the boron nitride powder particles is 0.3-0.4 micrometer, the average particle size of the calcium difluoride powder particles is less than 1 micrometer, specifically, the average particle size of the calcium difluoride powder particles is 0.8 micrometer, and the purities of the aluminum nitride powder and the boron nitride powder are both more than 98.5%;
s2, placing the aluminum nitride powder and the boron nitride powder into a stirrer to be fully stirred and mixed for 50min, in S2, keeping the inside of the stirrer in a sealed state in the stirring and mixing process, keeping the air pressure inside the stirrer at 10MPa, controlling the rotating speed of the stirrer at 60-100 r/min, fully mixing the aluminum nitride powder and the boron nitride powder, and filling nitrogen into the stirrer as inert gas to prevent the aluminum nitride powder, the boron nitride powder and oxygen in the air from reacting in the stirring process;
s3, adding the mixed powder of aluminum nitride and boron nitride and calcium difluoride into a ball mill to be ground into powder, adding spherical zirconium dioxide into the ball mill as a grinding body during grinding, adding absolute ethyl alcohol as a grinding medium, grinding the mixed powder of aluminum nitride and boron nitride into powder with a fine particle size, wet mixing for 20-24 h, setting the ball mill as a high-speed grinding machine in S3, wherein the rotating speed of the ball mill is 150-350 r/min, and the particle size of the ground composite material powder is 30-60 nm;
s4, placing the ground mixture into a vacuum barrel, wherein the air pressure in the vacuum barrel is 10MPa, heating the mixture to 80 ℃ to carry out rotary evaporation on the mixture, in S4, a disperser is arranged in the vacuum barrel, a motor for driving the disperser to rotate is arranged at the bottom of the vacuum barrel, the motor is set as a servo motor, the disperser can continuously turn up the composite powder when the composite powder is subjected to rotary evaporation, so that the composite powder can be continuously rolled in the vacuum barrel, the contact area between the composite powder and hot air is increased, a liquid phase mixed in the composite powder can be contacted with the hot air to generate friction, drying is accelerated, and the rotating speed of the composite powder is 20-30 r/min;
s5, adding 3% of calcium difluoride, and sintering at different temperatures, wherein the thermal conductivity of the aluminum nitride/boron nitride composite ceramic is different:
example 1
After the mixture is dried, placing the mixture in a graphite mold for cold press molding, and then sintering the mixture, wherein the sintering temperature is 1750-2000 ℃, in S5, the pressure during sintering is 30MPa, the temperature during sintering gradually rises, the temperature rising rate is 10 ℃/min, specifically, when the sintering temperature is 1750 ℃, the introduced trace calcium difluoride can react with aluminum oxide attached to the surfaces of aluminum nitride powder particles during high-temperature sintering to generate a liquid phase, so that the sintering compactness of the aluminum nitride/boron nitride composite ceramic is promoted, and the thermal conductivity of the aluminum nitride/boron nitride composite ceramic is 87W/(mK), so that when calcium difluoride is introduced into the aluminum nitride/boron nitride composite ceramic, the sintering temperature is raised to obtain a pure aluminum nitride/boron nitride composite ceramic sintered body;
example 2
After the mixture is dried, placing the mixture in a graphite mold for cold press molding, and then sintering the mixture, wherein the sintering temperature is 1750-2000 ℃, in S5, the pressure during sintering is 30MPa, the temperature during sintering gradually rises, the temperature rising rate is 10 ℃/min, specifically, when the sintering temperature is 1800 ℃, the introduced trace calcium difluoride can react with aluminum oxide attached to the surfaces of aluminum nitride powder particles during high-temperature sintering to generate a liquid phase, so that the sintering compactness of the aluminum nitride/boron nitride composite ceramic is promoted, and the thermal conductivity of the aluminum nitride/boron nitride composite ceramic is 98W/(mK), so that when calcium difluoride is introduced into the aluminum nitride/boron nitride composite ceramic, the sintering temperature is raised to obtain a pure aluminum nitride/boron nitride composite ceramic sintered body;
example 3
After the mixture is dried, placing the mixture in a graphite mold for cold press molding, and then sintering the mixture, wherein the sintering temperature is 1750-2000 ℃, in S5, the pressure during sintering is 30MPa, the temperature during sintering gradually rises, the temperature rising rate is 10 ℃/min, specifically, when the sintering temperature is 1850 ℃, the introduced trace calcium difluoride can react with aluminum oxide attached to the surfaces of aluminum nitride powder particles during the high-temperature sintering process to generate a liquid phase, so that the sintering compactness of the aluminum nitride/boron nitride composite ceramic is promoted, and the thermal conductivity of the aluminum nitride/boron nitride composite ceramic is 109W/(mK), so when calcium difluoride is introduced into the aluminum nitride/boron nitride composite ceramic, the sintering temperature is raised to obtain a pure aluminum nitride/boron nitride composite ceramic sintered body;
example 4
After the mixture is dried, placing the mixture in a graphite mold for cold press molding, and then sintering the mixture, wherein the sintering temperature is 1750-2000 ℃, in S5, the pressure during sintering is 30MPa, the temperature during sintering gradually rises, the temperature rising rate is 10 ℃/min, specifically, when the sintering temperature is 1900 ℃, the introduced trace calcium difluoride can react with aluminum oxide attached to the surfaces of aluminum nitride powder particles during high-temperature sintering to generate a liquid phase, so that the sintering compactness of the aluminum nitride/boron nitride composite ceramic is promoted, and the thermal conductivity of the aluminum nitride/boron nitride composite ceramic is 108W/(mK), so that when calcium difluoride is introduced into the aluminum nitride/boron nitride composite ceramic, the sintering temperature is raised to obtain a pure aluminum nitride/boron nitride composite ceramic sintered body;
example 5
After the mixture is dried, placing the mixture in a graphite mold for cold press molding, and then sintering the mixture, wherein the sintering temperature is 1750-2000 ℃, in S5, the pressure during sintering is 30MPa, the temperature during sintering gradually rises, the temperature rising rate is 10 ℃/min, specifically, when the sintering temperature is 1950 ℃, the introduced trace calcium difluoride can react with aluminum oxide attached to the surfaces of aluminum nitride powder particles during high-temperature sintering to generate a liquid phase, so that the sintering compactness of the aluminum nitride/boron nitride composite ceramic is promoted, and the thermal conductivity of the aluminum nitride/boron nitride composite ceramic is 107W/(mK), so that when calcium difluoride is introduced into the aluminum nitride/boron nitride composite ceramic, the sintering temperature is raised to obtain a pure aluminum nitride/boron nitride composite ceramic sintered body;
example 6
After the mixture is dried, placing the mixture in a graphite mold for cold press molding, and then sintering the mixture, wherein the sintering temperature is 1750-2000 ℃, in S5, the pressure during sintering is 30MPa, the temperature during sintering gradually rises, the temperature rising rate is 10 ℃/min, specifically, when the sintering temperature is 2000 ℃, introduced trace calcium difluoride can react with aluminum oxide attached to the surfaces of aluminum nitride powder particles during high-temperature sintering to generate a liquid phase, so that the sintering compactness of the aluminum nitride/boron nitride composite ceramic is promoted, and the thermal conductivity of the aluminum nitride/boron nitride composite ceramic is 106W/(mK), so that when calcium difluoride is introduced into the aluminum nitride/boron nitride composite ceramic, the sintering temperature is raised to obtain a pure aluminum nitride/boron nitride composite ceramic sintered body;
from this result, it is found that the thermal conductivity of the aluminum nitride/boron nitride composite ceramic is best at 1850 ℃;
when the sintering temperature is 1850 ℃, the bending strength of the aluminum nitride/boron nitride composite ceramic is 266MPa, the hardness is 57.5, the bending strength and the hardness are both sufficiently high, and the aluminum nitride/boron nitride composite ceramic in the state has better machinability;
s6, putting the sintered composite material into a forming die, applying 500-700 MPa pressure to press for 3-5 min, in S6, pressing for 5min when applying 500MPa pressure, pressing for 4min when applying 600MPa pressure, pressing for 3min when applying 700MPa pressure,
and S7, naturally cooling for 1-3 h at normal temperature and pressure to obtain the aluminum nitride/boron nitride composite ceramic sample, wherein in S6, the size of the inner cavity of the forming die is 1cm x 1cm, and the size of the obtained aluminum nitride/boron nitride composite ceramic sample is 1cm x 1 cm.
Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that modifications may be made to the embodiments described above, or equivalent substitutions and modifications may be made to some features of the embodiments described above, and any modifications, equivalents, improvements, etc. within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (8)
1. The method for preparing the isotropic high-thermal-conductivity composite material based on boron nitride is characterized by comprising the following steps of: the method comprises the following steps:
s1, weighing 100 parts of raw materials of aluminum nitride powder and boron nitride powder according to mass fraction, wherein the mass ratio of aluminum nitride to boron nitride is 85: 15, weighing a sintering aid calcium difluoride, wherein the mass fraction of the calcium difluoride is 1-4%;
s2, putting the aluminum nitride powder and the boron nitride powder into a stirrer to be fully stirred and mixed for 50 min;
s3, adding the mixed powder of aluminum nitride and boron nitride and calcium difluoride into a ball mill, grinding into powder, adding zirconium dioxide into the ball mill as a grinding body during grinding, adding absolute ethyl alcohol as a grinding medium, and wet mixing for 20-24 hours;
s4, placing the ground mixture into a vacuum barrel, and heating to 80 ℃ to carry out rotary evaporation on the mixture;
s5, drying the mixture, placing the mixture into a graphite die for cold press molding, and then sintering the mixture at 1750-2000 ℃;
s6, putting the sintered composite material into a forming die, and pressing for 3-5 min under the pressure of 500-700 MPa;
and S7, naturally cooling for 1-3 h under the condition of normal temperature and normal pressure to obtain the sample of the aluminum nitride/boron nitride composite ceramic.
2. The method for preparing the isotropic high thermal conductive composite material based on boron nitride as claimed in claim 1, wherein: in S1, the aluminum nitride powder had a specific surface area of 3.3m2The particle size of the boron nitride powder particles is 0.3-0.4 micrometer, the average particle size of the calcium difluoride powder particles is less than 1 micrometer, and the purity of the aluminum nitride powder and the purity of the boron nitride powder are both greater than 98.5%.
3. The method for preparing the isotropic high thermal conductive composite material based on boron nitride as claimed in claim 1, wherein: in S2, the inside of the stirrer is kept in a sealed state during stirring and mixing, the rotating speed of the stirrer is controlled to be 60-100 r/min, and nitrogen is filled into the stirrer to be used as inert gas.
4. The method for preparing the isotropic high thermal conductive composite material based on boron nitride as claimed in claim 1, wherein: in S3, the ball mill is set to be a high-speed grinding mill, the rotating speed of the ball mill is 150-350 r/min, and the particle diameter of the ground composite material powder is 30-60 nm.
5. The method for preparing the isotropic high thermal conductive composite material based on boron nitride as claimed in claim 1, wherein: in S4, a disperser is arranged in the vacuum barrel, when the composite material powder is subjected to rotary evaporation, the disperser can continuously turn up the composite material powder, so that the contact area between the composite material powder and hot air is increased, the drying is accelerated, and the rotating speed of the composite material powder is 20-30 r/min.
6. The method for preparing the isotropic high thermal conductive composite material based on boron nitride as claimed in claim 1, wherein: in S5, the pressure during sintering was 30MPa, the temperature during sintering was gradually increased, and the rate of temperature increase was 10 ℃/min.
7. The method for preparing the isotropic high thermal conductive composite material based on boron nitride as claimed in claim 1, wherein: in S6, the pressing is required to be performed for 5min when a pressure of 500MPa is applied, for 4min when a pressure of 600MPa is applied, and for 3min when a pressure of 700MPa is applied.
8. The method for preparing the isotropic high thermal conductive composite material based on boron nitride as claimed in claim 1, wherein: in S6, the size of the cavity of the molding die was 1cm × 1cm, i.e., the size of the obtained aluminum nitride/boron nitride composite ceramic sample was 1cm × 1 cm.
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| CN116004115A (en) * | 2022-12-13 | 2023-04-25 | 苏州鸿钜金属制品有限公司 | Heat-conducting insulating coating for power battery and preparation method thereof |
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| CN116004115A (en) * | 2022-12-13 | 2023-04-25 | 苏州鸿钜金属制品有限公司 | Heat-conducting insulating coating for power battery and preparation method thereof |
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