CN115180957A - Preparation method of hexagonal boron nitride ceramic with excellent thermal wave transmission performance - Google Patents

Preparation method of hexagonal boron nitride ceramic with excellent thermal wave transmission performance Download PDF

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CN115180957A
CN115180957A CN202210812537.2A CN202210812537A CN115180957A CN 115180957 A CN115180957 A CN 115180957A CN 202210812537 A CN202210812537 A CN 202210812537A CN 115180957 A CN115180957 A CN 115180957A
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boron nitride
hexagonal boron
nitride ceramic
ceramic
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贾德昌
牛波
杨治华
蔡德龙
段文九
段小明
周玉
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Harbin Institute of Technology
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Abstract

A preparation method of hexagonal boron nitride ceramics with excellent heat wave transmission performance relates to a preparation method of hexagonal boron nitride ceramics. The method aims to solve the problem that the dielectric loss of the hexagonal boron nitride ceramic is abnormally increased along with the temperature increase at high temperature. The preparation method comprises the following steps: weighing h-BN powder and a silica sol solution, uniformly mixing, then loading into a steel die, carrying out oscillation prepressing treatment, carrying out drying treatment, putting a ceramic dry blank into a graphite crucible for air pressure sintering, and obtaining the hexagonal boron nitride ceramic with the texture index of 2000-8000, wherein the hexagonal boron nitride ceramic is used as a thermal wave-transparent material. The hexagonal boron nitride ceramic has the texture index of 2000-8000 and low defect concentration, can prevent the abnormal attenuation of the wave transmission performance of the hexagonal boron nitride ceramic at high temperature, and has excellent heat wave transmission performance.

Description

Preparation method of hexagonal boron nitride ceramic with excellent thermal wave transmission performance
Technical Field
The invention relates to a preparation method of hexagonal boron nitride ceramic with excellent heat wave transmission performance.
Background
The aircraft antenna housing is positioned at the head of an aircraft and is an important device for protecting an aircraft guidance system from normally working in an extreme high-temperature environment. The radome material needs to have excellent dielectric loss with less change with temperature rise so as to ensure the heat wave-transmitting performance of the radome and the accurate guidance of the aircraft. The hexagonal boron nitride (h-BN) ceramic has the advantages of low normal-temperature dielectric constant and dielectric loss, excellent thermal shock resistance, good chemical stability, high thermal stability, excellent processability and the like, and is a main candidate material of a new-generation aircraft radome. However, the dielectric loss of the hexagonal boron nitride ceramic at high temperature can be sharply increased along with the temperature rise, so that the thermal wave transmission performance of the hexagonal boron nitride ceramic is seriously influenced, and the practical application requirement of the antenna housing of the aircraft is difficult to meet.
Disclosure of Invention
The invention provides a preparation method of hexagonal boron nitride ceramic with excellent thermal wave transmission performance, aiming at solving the problem that dielectric loss of the hexagonal boron nitride ceramic is abnormally increased along with temperature increase at high temperature.
The preparation method of the hexagonal boron nitride ceramic with excellent heat wave transmission performance comprises the following steps:
selecting h-BN powder with the graphitization index of 1.6-2.5, the purity of 99.0-99.999 percent, the grain size of 10-50 mu m, high crystallinity, high purity and high lamellar shape as a raw material; the h-BN powder with the low graphitization index has high crystallinity, contains less intrinsic defect ions, has low conductivity of the intrinsic defect ions excited at high temperature, and can generate low dielectric loss, thereby improving the thermal wave transmission performance of the hexagonal boron nitride ceramic; the h-BN powder with higher purity contains fewer impurity defect ions, and can generate lower dielectric loss; the h-BN powder with larger grain size has a typical lamellar structure, the directional arrangement of crystal grains is easier to occur under the action of oscillation prepressing treatment, and the electrical conductivity of the h-BN crystal in the direction vertical to the lamellar direction is obviously lower than that in the direction parallel to the lamellar direction, so that the electrical conductivity of the hexagonal boron nitride ceramic is favorably reduced after the directional arrangement, the dielectric loss of the hexagonal boron nitride ceramic is reduced, and the heat wave-transmitting performance of the hexagonal boron nitride ceramic is improved.
Weighing 10-50% of h-BN powder and the balance of silica sol solution according to mass fraction;
step three, uniformly mixing the raw materials by a vacuum stirrer to obtain ceramic material viscous slurry;
step four, the ceramic material viscous slurry is loaded into a steel mould and placed on a press to be subjected to oscillation prepressing treatment, so that a ceramic blank body is obtained; the oscillation prepressing treatment is carried out on the basis of a preset pressure value, the pressure value is changed up and down under the action of certain amplitude and frequency, the phenomenon of directional arrangement of h-BN powder can be more easily caused, and the hexagonal boron nitride ceramic with high texture index is prepared, so that the dielectric loss is reduced, and the heat wave transmission performance is improved.
Putting the ceramic blank into an oven for drying treatment to obtain a ceramic dried blank;
and sixthly, placing the ceramic dry blank into a graphite crucible, covering h-BN powder on the periphery of the graphite crucible, and placing the graphite crucible into an atmosphere sintering furnace for air pressure sintering to obtain the hexagonal boron nitride ceramic with the texture index of 2000-8000, wherein the hexagonal boron nitride ceramic is used as a heat wave transmission material.
The principle and the beneficial effects of the invention are as follows:
in order to solve the problem of abnormal increase of dielectric loss of the hexagonal boron nitride ceramic at high temperature, the invention adopts h-BN powder with low graphitization index (high crystallinity), high purity and large particle size as a raw material and adopts silica sol solution as a sintering aid, and the hexagonal boron nitride ceramic with the texture index of 2000-8000 and low defect concentration is obtained through raw material slurry preparation, oscillation prepressing treatment, drying treatment and air pressure sintering, so that abnormal attenuation of the wave permeability of the hexagonal boron nitride ceramic at high temperature is prevented. The method comprises the following specific steps:
1. the method adopts the h-BN powder with low graphitization index, high purity and large particle size as the raw material, so that h-BN crystal grains can be more easily textured in the prepressing process, and the dielectric loss of the h-BN crystal grains is reduced by reducing the conductivity in the direction vertical to the lamella. Meanwhile, the h-BN powder with low graphitization index and high purity contains less defects and impurity ions, and can reduce dielectric loss of the hexagonal boron nitride ceramic caused by defect conductivity to a certain extent, so that the heat wave-transmitting performance of the hexagonal boron nitride ceramic is improved.
2. According to the invention, h-BN grains can be highly directionally arranged through vacuum stirring mixing and oscillation pre-pressing treatment of h-BN powder and a silica sol solution, and fused quartz ceramics with low melting point and excellent wave-transmitting performance can be generated in situ through subsequent drying treatment and air pressure sintering, so that the densification process of hexagonal boron nitride ceramics is promoted, and then the hexagonal boron nitride ceramics with high densification degree and high texturing degree are obtained, thereby improving the heat wave-transmitting performance of the hexagonal boron nitride ceramics.
Drawings
FIG. 1 is a scanning electron micrograph of hexagonal boron nitride ceramic prepared in example 1;
FIG. 2 is a scanning electron micrograph of hexagonal boron nitride ceramic prepared in example 2;
FIG. 3 is a graph of dielectric loss tangent versus temperature for hexagonal boron nitride ceramics.
Detailed Description
The technical scheme of the invention is not limited to the specific embodiments listed below, and any reasonable combination of the specific embodiments is included.
The first specific implementation way is as follows: the preparation method of the hexagonal boron nitride ceramic with excellent heat wave transmission performance comprises the following steps:
selecting h-BN powder with the graphitization index of 1.6-2.5, the purity of 99.0-99.999 percent, the grain size of 10-50 mu m, high crystallinity, high purity and high lamellar shape as a raw material; the h-BN powder with the low graphitization index has high crystallinity, contains fewer intrinsic defect ions, has low conductivity of the intrinsic defect ions excited at high temperature, and can generate low dielectric loss, so that the heat transmission performance of the hexagonal boron nitride ceramic is improved; the h-BN powder with higher purity contains fewer impurity defect ions, and can also generate lower dielectric loss; the h-BN powder with larger grain size has a typical lamellar structure, the directional arrangement of crystal grains is easier to occur under the action of oscillation prepressing treatment, and the electrical conductivity of the h-BN crystal in the direction vertical to the lamellar direction is obviously lower than that in the direction parallel to the lamellar direction, so that the electrical conductivity of the hexagonal boron nitride ceramic is favorably reduced after the directional arrangement, the dielectric loss of the hexagonal boron nitride ceramic is reduced, and the heat wave-transmitting performance of the hexagonal boron nitride ceramic is improved.
Step two, weighing 10-50% of h-BN powder and the balance of silica sol solution according to mass fraction;
step three, uniformly mixing the raw materials by a vacuum stirrer to obtain ceramic material viscous slurry;
step four, the ceramic material viscous slurry is loaded into a steel mould and placed on a press to be subjected to oscillation prepressing treatment, so that a ceramic blank body is obtained; the oscillation prepressing treatment is carried out on the basis of a preset pressure value, the pressure value is changed up and down under the action of certain amplitude and frequency, the phenomenon of directional arrangement of h-BN powder can be more easily caused, and the hexagonal boron nitride ceramic with high texture index is prepared, so that the dielectric loss is reduced, and the heat wave transmission performance is improved.
Putting the ceramic blank into an oven for drying treatment to obtain a ceramic dried blank;
and step six, placing the ceramic dry blank into a graphite crucible, covering h-BN powder on the periphery, placing the graphite crucible into an atmosphere sintering furnace for air pressure sintering to obtain the hexagonal boron nitride ceramic with the texture index of 2000-8000, and using the hexagonal boron nitride ceramic as a heat wave transmission material.
In order to solve the problem of abnormal increase of dielectric loss of the hexagonal boron nitride ceramic at a high temperature, the embodiment adopts h-BN powder with low graphitization index (high crystallinity), high purity and large particle size as a raw material, adopts a silica sol solution as a sintering aid, and obtains the hexagonal boron nitride ceramic with a texture index of 2000-8000 and low defect concentration through raw material slurry preparation, oscillation prepressing treatment, drying treatment and air pressure sintering, thereby preventing abnormal attenuation of the wave permeability of the hexagonal boron nitride ceramic at the high temperature. The method comprises the following specific steps:
1. the embodiment adopts the h-BN powder with low graphitization index, high purity and large particle size as the raw material, so that h-BN crystal grains can be more easily textured in the prepressing process, and the dielectric loss of the h-BN crystal grains is reduced by reducing the conductivity in the direction vertical to the lamella. Meanwhile, the h-BN powder with low graphitization index and high purity contains less defects and impurity ions, and can reduce the dielectric loss of the hexagonal boron nitride ceramic caused by defect conductance to a certain extent, so that the heat wave-transmitting performance of the hexagonal boron nitride ceramic is improved.
2. According to the embodiment, h-BN grains can be highly directionally arranged through vacuum stirring mixing and oscillation pre-pressing treatment of h-BN powder and a silica sol solution, and fused quartz ceramics with low melting point and excellent wave-transmitting performance can be generated in situ through subsequent drying treatment and air pressure sintering, so that the densification process of hexagonal boron nitride ceramics is promoted, the hexagonal boron nitride ceramics with high densification degree and high texturing degree are further obtained, and the heat wave-transmitting performance of the hexagonal boron nitride ceramics is improved.
The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: step two nanometer SiO in the silica sol solution 2 The content of the particles is 20-60 wt.%.
The third concrete implementation mode: the present embodiment differs from the first or second embodiment in that: and step three, mixing the materials by using the vacuum mixer for 12 to 36 hours.
The fourth concrete implementation mode is as follows: the difference between this embodiment mode and one of the first to third embodiment modes is: and step three, the vacuum degree of the vacuum stirrer is 0.09-0.1 MPa when the vacuum stirrer is used for mixing.
The fifth concrete implementation mode is as follows: the difference between this embodiment and one of the first to fourth embodiments is: the oscillation prepressing treatment process comprises the following steps: the prepressing pressure is 5-50 MPa, the pressure oscillation amplitude is 5-15% of the set pressure value, the oscillation frequency is 0.5-2.5 Hz, and the pressure maintaining time is 1-10 min.
The sixth specific implementation mode: the fifth embodiment is different from the fifth embodiment in that: the oscillation prepressing treatment process comprises the following steps: the prepressing pressure is 20MPa, the pressure oscillation amplitude is 10% of a set pressure value, the oscillation frequency is 1.5Hz, and the pressure maintaining time is 5min.
The seventh embodiment: the difference between this embodiment and one of the first to sixth embodiments is: the drying process comprises the following steps: the drying treatment temperature is 50-75 ℃, and the drying treatment time is 3-10 hours.
The specific implementation mode is eight: the seventh embodiment is different from the seventh embodiment in that: the drying process comprises the following steps: the drying temperature was 60 ℃ and the time was 6 hours.
The specific implementation method nine: the present embodiment differs from the first to eighth embodiments in that: the process of the air pressure sintering comprises the following steps: the sintering temperature is 1650-2200 ℃, the pressure is 5-50 MPa, the sintering atmosphere is nitrogen, and the time is 60-120 minutes.
The specific implementation mode is ten: the present embodiment differs from the ninth embodiment in that: the process of the air pressure sintering comprises the following steps: the sintering temperature is 1900 ℃, the pressure is 15MPa, the sintering atmosphere is nitrogen, and the sintering time is 90 minutes.
Example 1
The preparation method of the hexagonal boron nitride ceramic with excellent thermal wave-transparent performance of the embodiment is carried out according to the following steps:
step 1, selecting h-BN powder with graphitization index of 2.1, purity of 99.5% and particle size of 15 mu m as raw material;
step 2, weighing 50% of h-BN powder according to mass fraction, and then weighing the rest of silica sol solution; nano SiO in silica sol solution 2 The content of the particles was 40wt.%;
step 3, fully and uniformly mixing the raw materials by a vacuum stirrer, wherein the mixing time is 24 hours, and the vacuum degree is 0.09MPa, so as to obtain ceramic material viscous slurry;
step 4, filling the mixed viscous slurry into a steel mold, placing the steel mold on a press for oscillation prepressing treatment, setting the prepressing pressure to be 10MPa, setting the pressure oscillation amplitude to be 5% of a set pressure value, setting the oscillation frequency to be 1Hz, and keeping the pressure for 3min to obtain a ceramic forming blank body;
and 5, putting the ceramic blank into an oven for drying treatment at the temperature of 50 ℃ for 3 hours to obtain a ceramic dried blank.
Step 6, carrying out powder embedding treatment on the ceramic dry blank, wherein the embedded powder is h-BN powder, putting the h-BN powder into an atmosphere sintering furnace for carrying out air pressure sintering, the sintering temperature is 2000 ℃, the pressure is 20MPa, the sintering atmosphere is nitrogen, the time is 60 minutes, and after cooling along with the furnace, the ceramic dry blank can obtain the ceramic with the texture index of 2300 and the dielectric loss of 8 multiplied by 10 at the temperature of 1000 DEG C -3 The hexagonal boron nitride ceramic of (2) is used as a thermal wave-transmitting material. FIG. 1 is a scanning electron micrograph of hexagonal boron nitride ceramic prepared according to example 1; the h-BN crystal grains of the hexagonal boron nitride ceramic have certain directional arrangement characteristics, and the texture index is 2300.
Wherein, the texture Index (IOP) is calculated as follows:
Figure BDA0003739793520000051
I 100 and I 002 Respectively represent diffraction intensities, I 'of corresponding crystal planes on the surface of the hexagonal boron nitride ceramic' 100 And l' 002 Respectively represents the diffraction intensity of corresponding crystal faces on the side surface of the hexagonal boron nitride ceramic, and the larger the texture index is, the more obvious the directional arrangement phenomenon of the hexagonal boron nitride ceramic is.
Example 2
The preparation method of the hexagonal boron nitride ceramic with excellent thermal wave transmission performance of the embodiment comprises the following steps:
step 1, selecting h-BN powder with the graphitization index of 1.8, the purity of 99.9 percent and the particle size of 20 mu m as a raw material;
step 2, weighing 45% of h-BN powder according to mass fraction, and then weighing the rest of silica sol solution; nano SiO in silica sol solution 2 Content of particles was 50wt.%;
step 3, fully and uniformly mixing the raw materials by a vacuum mixer for 36 hours under the vacuum degree of 0.1MPa to obtain ceramic material viscous slurry;
step 4, the mixed viscous slurry is loaded into a steel die and placed on a press for oscillation prepressing treatment, the prepressing pressure is set to be 20MPa, the pressure oscillation amplitude is 10 percent, the oscillation frequency is 1.5Hz, and the pressure maintaining time is 5min, so that a ceramic forming blank body is obtained;
and 5, putting the ceramic blank into an oven for drying treatment at the temperature of 70 ℃ for 5 hours to obtain a ceramic dried blank.
Step 6, carrying out powder embedding treatment on the ceramic dry blank, wherein the embedded powder is h-BN powder, putting the h-BN powder into an atmosphere sintering furnace for carrying out air pressure sintering, the sintering temperature is 1900 ℃, the pressure is 15MPa, the sintering atmosphere is nitrogen, the time is 90 minutes, and after cooling along with the furnace, the ceramic dry blank can obtain a texture index of 6500 and dielectric loss of 5.6 multiplied by 10 at 1000 DEG C -3 The hexagonal boron nitride ceramic of (2) is used as a thermal wave-transmitting material. FIG. 2 is a scanning electron micrograph of hexagonal boron nitride ceramic prepared in example 2; the h-BN crystal grains of the hexagonal boron nitride ceramic have a strong directional arrangement characteristic, and the texture index is 6500.
Comparative example 1:
the preparation method of the hexagonal boron nitride ceramic of the embodiment is carried out according to the following steps:
step 1, selecting h-BN powder with the graphitization index of 3, the purity of 95.5 percent and the particle size of 5 mu m as a raw material;
step 2, weighing 45% of h-BN powder according to mass fraction, and then weighing the rest of silica sol solution; nano SiO in silica sol solution 2 Content of particles was 50wt.%;
step 3, fully and uniformly mixing the raw materials by a vacuum stirrer, wherein the mixing time is 30 hours, and the vacuum degree is 0.1MPa, so as to obtain ceramic material viscous slurry;
step 4, the mixed viscous slurry is loaded into a steel die and placed on a press for prepressing treatment, the constant prepressing pressure is set to be 20MPa, and the pressure maintaining time is set to be 10min, so that a ceramic forming blank body is obtained;
and 5, putting the ceramic blank into an oven for drying treatment at the temperature of 70 ℃ for 5 hours to obtain a ceramic dried blank.
Step 6, carrying out powder embedding treatment on the ceramic dry blank, wherein the embedded powder is h-BN powder, putting the h-BN powder into an atmosphere sintering furnace for carrying out air pressure sintering, the sintering temperature is 2000 ℃, the pressure is 15MPa, the sintering atmosphere is nitrogen, the time is 90 minutes, and after cooling along with the furnace, the ceramic dry blank with the texture index of 120 and the dielectric loss of 1.4 multiplied by 10 at the temperature of 1000 ℃ can be obtained -2 Hexagonal boron nitride ceramics.
FIG. 3 is a graph of dielectric loss tangent versus temperature for hexagonal boron nitride ceramics; in the figure, 1 is a conventional hexagonal boron nitride ceramic prepared by a comparative example, 2 is a hexagonal boron nitride ceramic prepared by example 1, and 3 is a hexagonal boron nitride ceramic prepared by example 5. The hexagonal boron nitride ceramics prepared in examples 1 and 2 have low dielectric loss tangent values at high temperatures and show excellent heat wave-transmitting properties.

Claims (10)

1. A preparation method of hexagonal boron nitride ceramics with excellent heat wave transmission performance is characterized by comprising the following steps: the preparation method of the hexagonal boron nitride ceramic with excellent thermal wave transmission performance comprises the following steps:
selecting h-BN powder with graphitization index of 1.6-2.5, purity of 99.0-99.999% and particle size of 10-50 mu m;
weighing 10-50% of h-BN powder and the balance of silica sol solution as raw materials according to mass fraction;
step three, uniformly mixing the raw materials by a vacuum stirrer to obtain ceramic material viscous slurry;
step four, the ceramic material viscous slurry is loaded into a steel mould and placed on a press to be subjected to oscillation prepressing treatment, and a ceramic blank body is obtained;
putting the ceramic blank body into an oven for drying treatment to obtain a ceramic dried blank body;
and sixthly, placing the ceramic dry blank into a graphite crucible, covering h-BN powder on the periphery of the graphite crucible, and placing the graphite crucible into an atmosphere sintering furnace for air pressure sintering to obtain the hexagonal boron nitride ceramic with the texture index of 2000-8000, wherein the hexagonal boron nitride ceramic is used as a heat wave transmission material.
2. The method for producing a hexagonal boron nitride ceramic having excellent heat wave-transmitting properties according to claim 1, characterized in that: step two nanometer SiO in the silica sol solution 2 The content of the particles is 20-60 wt.%.
3. The method for producing a hexagonal boron nitride ceramic having excellent heat wave-transmitting properties according to claim 1, characterized in that: and step three, mixing the materials by using the vacuum mixer for 12 to 36 hours.
4. The method for producing a hexagonal boron nitride ceramic having excellent heat wave-transmitting properties according to claim 1, characterized in that: and step three, the vacuum degree of the vacuum stirrer is 0.09-0.1 MPa when the vacuum stirrer is used for mixing.
5. The method for producing a hexagonal boron nitride ceramic having excellent heat wave-transmitting properties according to claim 1, characterized in that: the oscillation prepressing treatment process comprises the following steps: the prepressing pressure is 5-50 MPa, the pressure oscillation amplitude is 5-15% of the set pressure value, the oscillation frequency is 0.5-2.5 Hz, and the pressure maintaining time is 1-10 min.
6. The method for producing a hexagonal boron nitride ceramic having excellent heat wave-transmitting properties according to claim 5, characterized in that: the oscillation prepressing treatment process comprises the following steps: the prepressing pressure is 20MPa, the pressure oscillation amplitude is 10% of a set pressure value, the oscillation frequency is 1.5Hz, and the pressure maintaining time is 5min.
7. The method for producing a hexagonal boron nitride ceramic having excellent heat wave-transmitting properties according to claim 1, characterized in that: the drying process comprises the following steps: the drying temperature is 50-75 ℃ and the drying time is 3-10 hours.
8. The method for producing a hexagonal boron nitride ceramic having excellent heat wave-transmitting properties according to claim 7, characterized in that: the drying process comprises the following steps: the drying treatment temperature was 60 ℃ and the drying treatment time was 6 hours.
9. The method for producing a hexagonal boron nitride ceramic having excellent heat wave-transmitting properties according to claim 1, characterized in that: the process of the air pressure sintering comprises the following steps: the sintering temperature is 1650-2200 ℃, the pressure is 5-50 MPa, the sintering atmosphere is nitrogen, and the sintering time is 60-120 minutes.
10. The method for producing a hexagonal boron nitride ceramic having excellent thermal wave-transmitting properties according to claim 9, characterized in that: the process of the air pressure sintering comprises the following steps: the sintering temperature is 1900 ℃, the pressure is 15MPa, the sintering atmosphere is nitrogen, and the time is 90 minutes.
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