CN116161962A - Silicon carbide pressure-sensitive ceramic with anisotropic electrical property and preparation method thereof - Google Patents
Silicon carbide pressure-sensitive ceramic with anisotropic electrical property and preparation method thereof Download PDFInfo
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- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 title claims abstract description 91
- 229910010271 silicon carbide Inorganic materials 0.000 title claims abstract description 91
- 239000000919 ceramic Substances 0.000 title claims abstract description 56
- 238000002360 preparation method Methods 0.000 title claims abstract description 6
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 57
- 239000002041 carbon nanotube Substances 0.000 claims abstract description 56
- 229910021393 carbon nanotube Inorganic materials 0.000 claims abstract description 56
- 238000005245 sintering Methods 0.000 claims abstract description 24
- 239000011159 matrix material Substances 0.000 claims abstract description 16
- 239000000463 material Substances 0.000 claims abstract description 10
- 239000000945 filler Substances 0.000 claims abstract description 8
- 239000012752 auxiliary agent Substances 0.000 claims abstract description 4
- 238000000280 densification Methods 0.000 claims abstract description 4
- 230000001737 promoting effect Effects 0.000 claims abstract description 4
- 238000000498 ball milling Methods 0.000 claims description 17
- 238000000034 method Methods 0.000 claims description 15
- 239000006185 dispersion Substances 0.000 claims description 13
- 239000002270 dispersing agent Substances 0.000 claims description 12
- 239000011812 mixed powder Substances 0.000 claims description 12
- 239000000843 powder Substances 0.000 claims description 12
- 238000005303 weighing Methods 0.000 claims description 12
- 239000007788 liquid Substances 0.000 claims description 11
- 235000013855 polyvinylpyrrolidone Nutrition 0.000 claims description 8
- 229920000036 polyvinylpyrrolidone Polymers 0.000 claims description 8
- 239000001267 polyvinylpyrrolidone Substances 0.000 claims description 8
- 238000009210 therapy by ultrasound Methods 0.000 claims description 7
- 238000002490 spark plasma sintering Methods 0.000 claims description 6
- LZZYPRNAOMGNLH-UHFFFAOYSA-M Cetrimonium bromide Chemical compound [Br-].CCCCCCCCCCCCCCCC[N+](C)(C)C LZZYPRNAOMGNLH-UHFFFAOYSA-M 0.000 claims description 5
- DBMJMQXJHONAFJ-UHFFFAOYSA-M Sodium laurylsulphate Chemical compound [Na+].CCCCCCCCCCCCOS([O-])(=O)=O DBMJMQXJHONAFJ-UHFFFAOYSA-M 0.000 claims description 5
- 238000001035 drying Methods 0.000 claims description 5
- 239000011268 mixed slurry Substances 0.000 claims description 5
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 4
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- 238000010438 heat treatment Methods 0.000 claims description 4
- 238000007873 sieving Methods 0.000 claims description 4
- KXGFMDJXCMQABM-UHFFFAOYSA-N 2-methoxy-6-methylphenol Chemical compound [CH]OC1=CC=CC([CH])=C1O KXGFMDJXCMQABM-UHFFFAOYSA-N 0.000 claims description 3
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims description 3
- 229930091371 Fructose Natural products 0.000 claims description 3
- RFSUNEUAIZKAJO-ARQDHWQXSA-N Fructose Chemical compound OC[C@H]1O[C@](O)(CO)[C@@H](O)[C@@H]1O RFSUNEUAIZKAJO-ARQDHWQXSA-N 0.000 claims description 3
- 239000005715 Fructose Substances 0.000 claims description 3
- 229910003481 amorphous carbon Inorganic materials 0.000 claims description 3
- KGBXLFKZBHKPEV-UHFFFAOYSA-N boric acid Chemical compound OB(O)O KGBXLFKZBHKPEV-UHFFFAOYSA-N 0.000 claims description 3
- 239000004327 boric acid Substances 0.000 claims description 3
- 239000005011 phenolic resin Substances 0.000 claims description 3
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- 238000005469 granulation Methods 0.000 claims description 2
- 230000003179 granulation Effects 0.000 claims description 2
- 239000007921 spray Substances 0.000 claims description 2
- 229910052799 carbon Inorganic materials 0.000 claims 1
- 238000004519 manufacturing process Methods 0.000 claims 1
- 229910010293 ceramic material Inorganic materials 0.000 description 5
- 238000004321 preservation Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 2
- 239000002048 multi walled nanotube Substances 0.000 description 2
- 239000002109 single walled nanotube Substances 0.000 description 2
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Abstract
The invention relates to a silicon carbide pressure-sensitive ceramic with anisotropic electrical properties and a preparation method thereof, wherein the silicon carbide pressure-sensitive ceramic with anisotropic electrical properties comprises the following components: the SiC matrix, conductive phase filler carbon nano tubes dispersed in the SiC matrix, and sintering auxiliary agent B sources and C sources for promoting densification of materials; the sum of the components is calculated according to the mass fraction of 100wt%, the mass fraction of the SiC matrix is 96.4-97.9 wt%, the mass fraction of the carbon nano tube is 0.5-2 wt%, the mass fraction of the B source is 0.2-1 wt%, and the mass fraction of the C source is 0.6-1.4 wt%.
Description
Technical Field
The invention belongs to the field of silicon carbide ceramics, and particularly relates to silicon carbide pressure-sensitive ceramics with anisotropic electrical properties and a preparation method thereof.
Background
The silicon carbide ceramic has the advantages of high strength, high modulus, corrosion resistance, oxidation resistance, high heat conduction, low thermal expansion coefficient, low neutron absorption section and the like, is an excellent structural material, and is widely applied to various fields. In fact, silicon carbide ceramics also exhibit nonlinear volt-ampere characteristics, which rapidly decrease in resistivity as the applied voltage increases. The piezoresistor characteristics of the silicon carbide ceramic combine with the structural performance advantages of the silicon carbide ceramic to enable the silicon carbide ceramic to be used as a voltage limiting protection device in a bad environment. In particular, silicon carbide ceramic piezoresistors can be used in various applications such as power transmission circuit protection, power control systems, surge suppression elements, automotive electronics, household appliance protection, motor protection, and the like.
The rapid development of the industry has placed more innovative demands on materials. For example, in the field of microelectronics, various circuit switches, sensing elements, etc. have different requirements on the electrical properties (resistivity, volt-ampere characteristics, etc.) of materials in different directions. The conductive phase filler is introduced into the main phase material, and the anisotropy of the electrical property of the material can be realized through proper process control. The silicon carbide ceramic with anisotropic electrical properties is developed, the comprehensive performance advantages of the silicon carbide ceramic can be fully exerted, and the application field of the silicon carbide ceramic is greatly widened.
Disclosure of Invention
The invention provides silicon carbide pressure-sensitive ceramic with anisotropic electrical properties and a preparation method thereof, and aims to fully exert the comprehensive performance advantages of a silicon carbide ceramic material and expand the application field of the silicon carbide ceramic material.
In a first aspect, the present invention provides a silicon carbide pressure sensitive ceramic having anisotropic electrical properties, the silicon carbide pressure sensitive ceramic having anisotropic electrical properties comprising: the SiC matrix, conductive phase filler carbon nano tubes dispersed in the SiC matrix, and sintering auxiliary agent B sources and C sources for promoting densification of materials; the sum of the components is calculated according to the mass fraction of 100wt%, the mass fraction of the SiC matrix is 96.4-97.9 wt%, the mass fraction of the carbon nano tube is 0.5-2 wt%, the mass fraction of the B source is 0.2-1 wt%, and the mass fraction of the C source is 0.6-1.4 wt%.
Preferably, the carbon nanotubes are single-walled carbon nanotubes or multi-walled carbon nanotubes; the diameter of the carbon nanotube is 5-25 nm, preferably 5-15 nm, and the length is 5-30 μm, preferably 10-30 μm. When the content of the carbon nano tube is changed within the range of 0.5 to 2 weight percent, the density of the silicon carbide ceramic is 3.00 to 3.05 g.cm -3 The relative density is 94.90-95.56%; the silicon carbide ceramic has obvious anisotropy in electrical property and axial resistivity of 136-4.10X10 3 Omega cm, axial nonlinear coefficient of 1.016-1.331, radial resistivity of 55.1-1.65X10 3 Omega cm, radial nonlinear coefficient is 1.029-1.292, and ratio of radial resistivity to axial resistivity is 0.34-0.41.
Preferably, the B source is B 4 C. At least one of boron powder and boric acid, wherein the C source is at least one of amorphous carbon, carbon black, phenolic resin and fructose.
In a second aspect, the present invention also provides a method for preparing the silicon carbide pressure sensitive ceramic with anisotropic electrical properties, comprising the steps of:
(1) And (3) preparing a carbon nano tube dispersion liquid. Respectively weighing carbon nanotubes and a dispersing agent, adding the carbon nanotubes and the dispersing agent into absolute ethyl alcohol, and preparing a carbon nanotube dispersion liquid through high-power ultrasonic treatment;
(2) And (3) preparing mixed powder. Weighing SiC powder, a source B and a source C according to a designed proportion, placing the SiC powder, the source B and the source C in a ball milling tank, adding the carbon nanotube dispersion liquid prepared in the step (1), and performing ball milling treatment by taking SiC balls as media to obtain mixed slurry; then drying and sieving to obtain mixed powder;
(3) Weighing the mixed powder prepared in the step (2), and sintering at high temperature to prepare the silicon carbide pressure-sensitive ceramic with anisotropic electrical property.
Preferably, the dispersing agent is at least one of polyvinylpyrrolidone (PVP), sodium Dodecyl Sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), and the adding amount of the dispersing agent is 5-25 wt% of the adding amount of the carbon nano tube, preferably 10-20 wt%.
Preferably, the high-power ultrasonic treatment conditions are as follows: the power is 800-1000W, preferably 900-1000W; the ultrasonic time is 0.5-2 h, preferably 0.5-1 h.
Preferably, the ball milling treatment conditions are as follows: the ball milling rotating speed is 200-400 r.min -1 Preferably 200 to 300 r.min -1 The method comprises the steps of carrying out a first treatment on the surface of the The ball milling time is 2 to 6 hours, preferably 2 to 4 hours.
Preferably, the high-temperature sintering is selected from hot-pressed sintering (HP) or Spark Plasma Sintering (SPS), preferably spark plasma sintering, the sintering temperature is 1900-2000 ℃, and the heating rate is 50-100 ℃ min -1 The heat preservation time is 5-10 min, the axial pressure is 30-50 MPa, and the sintering atmosphere is vacuum atmosphere.
According to the invention, the conductive phase filler carbon nano tube is introduced into the silicon carbide matrix, and the carbon nano tube with a larger length-diameter ratio is preferentially distributed on a plane perpendicular to the axial pressure direction by virtue of axial pressure in the sintering process. This preferential distribution distinguishes between impeded electron transfer of the material when energized. In particular, when energized perpendicular to the axial compressive direction (radial), the carbon nanotubes may occupy a longer distance on the conductive path; and when energized parallel to the axial compressive direction (axial direction), the carbon nanotubes occupy a smaller proportion of the conductive path. Clearly, electrons are less resistive when conducted inside the carbon nanotubes than when passing through silicon carbide grains and silicon carbide grain boundaries, which results in less resistance when electrons pass radially through the sample. Therefore, the anisotropy of the electrical properties of the silicon carbide ceramic can be realized through the selection of the conductive phase filler and the control of the sintering process.
Advantageous effects
The silicon carbide pressure-sensitive ceramic with anisotropic electrical properties is obtained through the selection of the conductive phase filler and the control of the sintering process, so that the comprehensive performance advantages of the silicon carbide pressure-sensitive ceramic are fully exerted, the application fields of the silicon carbide pressure-sensitive ceramic are greatly widened, and the silicon carbide pressure-sensitive ceramic has wide application prospects in the aspects of circuit switches, power supply control systems, surge suppression elements, automobile electronic systems, household appliance protection, motor protection, sensing elements, electronic control systems and the like.
Drawings
FIG. 1 is a graph showing the voltammetric characteristics of a silicon carbide ceramic in different directions at a carbon nanotube content of 0.5 wt%;
FIG. 2 is a graph showing the voltammetric characteristics of silicon carbide ceramics in different directions at a carbon nanotube content of 1 wt%;
FIG. 3 shows the voltammetric characteristics of silicon carbide ceramics at a carbon nanotube content of 2wt% in different directions.
Detailed Description
The present invention will be described in detail with reference to examples below in order to further explain the summary, features and practical effects of the present invention. It should be noted that the modification method of the design of the present invention is not limited to these specific embodiments. Equivalent substitutions and modifications will occur to those skilled in the art upon reading the teachings of the present invention without departing from the spirit and scope of the present invention, and are also within the scope of the present invention as hereinafter claimed.
The invention provides a silicon carbide pressure sensitive ceramic with anisotropic electrical properties, comprising: the SiC matrix, conductive phase filler carbon nano tubes dispersed in the SiC matrix, and sintering auxiliary agent B sources and C sources for promoting densification of materials; the sum of the components is calculated according to the mass fraction of 100wt%, the mass fraction of the SiC matrix is 96.4-97.9 wt%, the mass fraction of the carbon nano tube is 0.5-2 wt%, the mass fraction of the B source is 0.2-1 wt%, and the mass fraction of the C source is 0.6-1.4 wt%.
The carbon nanotubes are single-wall carbon nanotubes or multi-wall carbon nanotubes; the diameter of the carbon nanotube is 5-25 nm, preferably 5-15 nm, and the length is 5-30 μm, preferably 10-30 μm. When the content of the carbon nano tube is changed within the range of 0.5 to 2 weight percent, the density of the silicon carbide ceramic is 3.00 to 3.05 g.cm -3 The relative density is 94.90-95.56%. The silicon carbide ceramic has obvious anisotropy in electrical property and axial resistivity of 136-4.10X10 3 Omega cm, axial nonlinear coefficient of 1.016-1.331, radial resistivity of 55.1-1.65X10 3 Omega cm, radial nonlinear coefficient is 1.029-1.292, and ratio of radial resistivity to axial resistivity is 0.34-0.41.
The source B is B 4 C. At least one of boron powder and boric acid, wherein the C source is at least one of amorphous carbon, carbon black, phenolic resin and fructose.
The following illustrates a method for preparing the silicon carbide pressure sensitive ceramic material with anisotropic electrical properties, which may include the steps of:
(1) And (3) preparing a carbon nano tube dispersion liquid. Respectively weighing carbon nanotubes and a dispersing agent, adding the carbon nanotubes and the dispersing agent into absolute ethyl alcohol, and preparing a carbon nanotube dispersion liquid through high-power ultrasonic treatment;
the dispersing agent is at least one of polyvinylpyrrolidone (PVP), sodium Dodecyl Sulfate (SDS) and Cetyl Trimethyl Ammonium Bromide (CTAB), and the adding amount of the dispersing agent is 5-25 wt% of the adding amount of the carbon nano tube, preferably 10-20 wt%.
The high-power ultrasonic treatment conditions are as follows: the power is 800-1000W, preferably 900-1000W; the ultrasonic time is 0.5-2 h, preferably 0.5-1 h.
(2) And (3) preparing mixed powder. Weighing SiC powder, a source B and a source C according to a designed proportion, placing the SiC powder, the source B and the source C in a ball milling tank, adding the carbon nanotube dispersion liquid prepared in the step (1), taking SiC balls as media, and performing planetary ball milling treatment to obtain mixed slurry; then the mixed powder is prepared through a drying, sieving or spray granulation process;
to obtain a uniformly mixed slurry and maintain the structural integrity of the carbon nanotubes, the ball milling process conditions are: the ball milling rotating speed is 200-400 r.min -1 Preferably 200 to 300 r.min -1 The method comprises the steps of carrying out a first treatment on the surface of the The ball milling time is 2 to 6 hours, preferably 2 to 4 hours.
The drying temperature is 70-100 ℃, the time is 12-24 hours, and the fineness of the powder is required to be sieved by a 100-mesh sieve.
(3) Weighing a proper amount of the mixed powder prepared in the step (2), and preparing the silicon carbide pressure-sensitive ceramic with anisotropic electrical property through high-temperature sintering.
In order to obtain a ceramic material which is sintered compactly, maintain the integrity of the carbon nanotubes in the silicon carbide matrix and enable the carbon nanotubes to exhibit anisotropic arrangement in the silicon carbide matrix, the high-temperature sintering can be selected from hot press sintering (HP) or Spark Plasma Sintering (SPS), preferably spark plasma sintering, the sintering temperature is 1900-2000 ℃, and the heating rate is 50-100 ℃ and min -1 The heat preservation time is 5-10 min, the axial pressure is 30-50 MPa, and the sintering atmosphere is vacuum atmosphere.
Example 1
(1) And (3) preparing a carbon nano tube dispersion liquid. Respectively weighing 0.5g of carbon nano tube and 0.05g of polyvinylpyrrolidone, adding into 100g of absolute ethyl alcohol, stirring and mixing, and performing ultrasonic treatment with power of 1000W for 1h by using a high-power ultrasonic instrument to obtain a carbon nano tube dispersion;
(2) And (3) preparing mixed powder. Respectively weighing 97.9g of SiC powder and 0.6. 0.6g B 4 Placing the C powder and 1g of carbon black into a ball milling tank, adding the carbon nanotube dispersion liquid prepared in the step (1), taking SiC balls as a medium, and using a planetary ball mill to obtain a dispersion liquid with the particle size of 300 r.min -1 Ball milling for 4 hours at the rotating speed to obtain mixed slurry; and then placing the obtained slurry into a 70 ℃ oven for drying for 12 hours, and sieving the dried powder with a 100-mesh sieve to obtain mixed powder.
(3) Weighing a proper amount of the mixed powder prepared in the step (2), and sintering by discharge plasma to obtain the silicon carbide pressure-sensitive ceramic material with anisotropic electrical property; wherein the sintering temperature is 2000 ℃, the heat preservation time is 10min, and the heating rate is 100 ℃ and min -1 The axial pressure is 40MPa, and the sintering atmosphere is vacuum.
The density was measured by an Archimedes drainage method, and the density of the silicon carbide ceramic was 3.02g cm -3 The relative density was 94.90%; electrical properties were measured using a Keithley2450 multichannel tester, and the voltammetric characteristic curves of the silicon carbide ceramic in different directions at a carbon nanotube content of 0.5wt% were as shown in FIG. 1, with an axial resistivity of 4.1X10 3 Omega cm, axial nonlinear coefficient of 1.331, radial resistivity of 1.65X10 3 Omega cm, radial nonlinear coefficient 1.292, radial to axial resistivity ratio of 0.40.
Example 2
The silicon carbide pressure sensitive ceramic having anisotropic electrical properties in this example 2 was prepared by referring to example 1, and the only difference was that: 1g of carbon nano tube weighed in the step (1), 0.1g of polyvinylpyrrolidone and 97.4g of SiC powder weighed in the step (2). The density of the silicon carbide ceramic was measured to be 3.02g cm -3 The relative density was 95.16%; the voltammetric characteristic curves of the silicon carbide ceramic in different directions at the carbon nanotube content of 1wt% are shown in fig. 2, the axial resistivity is 337 Ω·cm, the axial nonlinear coefficient is 1.095, the radial resistivity is 114 Ω·cm, the radial nonlinear coefficient is 1.061, and the ratio of the radial to axial resistivity is 0.34.
Example 3
The silicon carbide pressure sensitive ceramic having anisotropic electrical properties in this example 3 was prepared by referring to example 1, and the only difference was that: 2g of carbon nano tube weighed in the step (1), 0.2g of polyvinylpyrrolidone and 96.4g of SiC powder weighed in the step (2). The density of the silicon carbide ceramic was measured to be 3.02g cm -3 The relative density was 95.56%; the voltammetric characteristic curves of the silicon carbide ceramic in different directions when the carbon nano tube content is 2wt% are shown in fig. 3, the axial resistivity is 136 Ω & cm, the axial nonlinear coefficient is 1.016, the radial resistivity is 55.1 Ω & cm, the radial nonlinear coefficient is 1.029, and the ratio of the radial to the axial resistivity is 0.41.
With the increase of the introduced amount of the carbon nanotubes, the carbon nanotubes form more conductive paths in the SiC matrix, so that the resistivity of the SiC pressure-sensitive ceramic in the axial direction and the radial direction is reduced, and the nonlinear coefficient is also reduced. The carbon nanotubes are uniformly distributed, so that the resistivity ratio of the SiC ceramics with different carbon nanotube contents in the axial direction and the radial direction is kept stable.
Claims (8)
1. A silicon carbide pressure sensitive ceramic having anisotropic electrical properties, the silicon carbide pressure sensitive ceramic having anisotropic electrical properties comprising: the SiC matrix, conductive phase filler carbon nano tubes dispersed in the SiC matrix, and sintering auxiliary agent B sources and C sources for promoting densification of materials; the sum of the components is calculated according to the mass fraction of 100wt%, the mass fraction of the SiC matrix is 96.4-97.9 wt%, the mass fraction of the carbon nano tube is 0.5-2 wt%, the mass fraction of the B source is 0.2-1 wt%, and the mass fraction of the C source is 0.6-1.4 wt%.
2. The silicon carbide pressure sensitive ceramic having anisotropic electrical properties according to claim 1, wherein the density of the silicon carbide ceramic is 3.00 to 3.05 g-cm when the content of the carbon nanotubes is varied in the range of 0.5 to 2wt% -3 The relative density is 94.90-95.56%; the silicon carbide ceramic has obvious anisotropy in electrical property and axial resistivity of 136-4.10X10 3 Omega cm, axial nonlinear coefficient of 1.016-1.331, radial resistivity of 55.1-1.65X10 3 Omega cm, radial nonlinear coefficient is 1.029-1.292, and ratio of radial resistivity to axial resistivity is 0.34-0.41.
3. The silicon carbide pressure sensitive ceramic having anisotropic electrical properties according to claim 1 or 2, wherein the B source is B 4 C. At least one of boron powder and boric acid, wherein the C source is at least one of amorphous carbon, carbon black, phenolic resin and fructose.
4. A method for preparing a silicon carbide pressure sensitive ceramic having anisotropic electrical properties according to any of claims 1 to 3, comprising the steps of:
(1) Preparation of carbon nanotube dispersion: respectively weighing carbon nanotubes and a dispersing agent, adding the carbon nanotubes and the dispersing agent into absolute ethyl alcohol, and preparing a carbon nanotube dispersion liquid through high-power ultrasonic treatment;
(2) Preparing mixed powder: weighing SiC powder, a source B and a source C according to a designed proportion, placing the SiC powder, the source B and the source C in a ball milling tank, adding the carbon nanotube dispersion liquid prepared in the step (1), and performing ball milling treatment by taking SiC balls as media to obtain mixed slurry; then the mixed powder is prepared through a drying, sieving or spray granulation process;
(3) Weighing the mixed powder prepared in the step (2), and sintering at high temperature to prepare the silicon carbide pressure-sensitive ceramic with anisotropic electrical property.
5. The method for preparing silicon carbide pressure sensitive ceramic with anisotropic electrical properties according to claim 4, wherein the dispersant is at least one of polyvinylpyrrolidone, sodium dodecyl sulfate and cetyltrimethylammonium bromide, and the addition amount of the dispersant is 5-25 wt%, preferably 10-20 wt% of the addition amount of the carbon nanotubes.
6. The method for preparing a silicon carbide pressure sensitive ceramic having anisotropic electrical properties according to claim 4 or 5, wherein the high power ultrasonic treatment conditions are: the power is 800-1000W, preferably 900-1000W; the ultrasonic time is 0.5 to 2 hours, preferably 0.5 to 1 hour.
7. The method for producing a silicon carbide pressure sensitive ceramic having anisotropic electrical properties according to any of claims 4 to 6, wherein the ball milling treatment conditions are: the ball milling rotating speed is 200-400 r/min, preferably 200-300 r/min;
the ball milling time is 2 to 6 hours, preferably 2 to 4 hours.
8. The method for preparing a silicon carbide pressure sensitive ceramic having anisotropic electrical properties according to any of claims 4 to 7, wherein the high temperature sintering is hot press sintering or spark plasma sintering, preferably spark plasma sintering, at a sintering temperature of 1900 to 2000 ℃, at a heating rate of 50 to 100 ℃/min, for a holding time of 5 to 10min, at an axial pressure of 30 to 50MPa, and in a vacuum atmosphere.
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