CN112608163B - Barium titanate doped modified carbon-based composite material and preparation method thereof - Google Patents

Barium titanate doped modified carbon-based composite material and preparation method thereof Download PDF

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CN112608163B
CN112608163B CN202011493122.0A CN202011493122A CN112608163B CN 112608163 B CN112608163 B CN 112608163B CN 202011493122 A CN202011493122 A CN 202011493122A CN 112608163 B CN112608163 B CN 112608163B
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barium titanate
composite material
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based composite
carbon
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CN112608163A (en
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张福勤
王化中
吕波
杨宇
夏莉红
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Central South University
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Abstract

The invention discloses a barium titanate doped modified carbon-based composite material and a preparation method thereof. The prepared barium titanate doped modified carbon-based composite material is a cylinder with a hole in the center. The invention can achieve the aim that barium titanate is uniformly dispersed on the prefabricated body in the early stage of the preparation of the prefabricated body in an innovative way. The method is simple and controllable, barium titanate particles in the composite material are uniformly distributed, and the composite material has the characteristics of low cost, easily obtained raw materials, no damage to fibers and the like, and is suitable for large-scale production and application.

Description

Barium titanate doped modified carbon-based composite material and preparation method thereof
Technical Field
The invention belongs to the technical field of preparation methods of carbon-based composite materials, and particularly relates to a barium titanate doped modified carbon-based composite material and a preparation method thereof.
Background
From the current research situation of carbon/carbon materials, the carbon/carbon material is mainly applied to the fields of aerospace high-strength materials, friction materials and ablation-resistant materials, and the application of the carbon/carbon material in the field of electronic functional materials needs to be explored. In the application of carbon/carbon materials, it is common to modify them, for example by adding a second phase medium, which can serve two functions: the second phase medium is added to improve the organization structure of the carbon/carbon composite material, improve the performances of the carbon/carbon composite material such as mechanics, ablation resistance, frictional wear resistance and the like, and better meet the requirements of the original field on the material. And secondly, a second phase medium is added to modify the carbon/carbon composite material to endow the carbon/carbon composite material with new functionality, and the application value of the carbon/carbon composite material in a new field is explored and researched.
When the material is used in the field of electron emission, the material needs to have the properties of high temperature resistance, ablation resistance and uniform distribution of micro-points on the surface of the material, while the carbon-carbon material has the properties of high temperature resistance, ablation resistance and excellent mechanical properties, but the material needs to realize uniform high-density emission by means of the micro-points on the surface of the material when the material is used for electron emission.
The barium titanate is suitable for serving as a reinforcement to improve the organization structure of the carbon/carbon composite material and improve the physical and mechanical properties of the carbon/carbon composite material, and meanwhile, the barium titanate also has excellent high dielectric property and low dielectric loss; the carbon/carbon material has better functional characteristics, so that the modified carbon-carbon composite material can emit stably and has good uniformity when being applied to an emission process.
The conventional doping methods mainly comprise an in-situ growth method and an electrophoresis method, and although the uniform dispersion of barium titanate can be realized, the method has the advantages of complex process, higher equipment requirement, less introduction amount and certain damage to fibers.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a barium titanate doped modified carbon-based composite material and a preparation method thereof. The method is simple and controllable, barium titanate particles in the composite material are uniformly distributed, and the barium titanate composite material has the characteristics of low cost, easily obtained raw materials, no damage to fibers and the like, and is suitable for large-scale production and application.
In order to achieve the above purpose, the invention provides the following technical scheme:
the invention relates to a preparation method of a barium titanate doped modified carbon-based composite material, which comprises the following steps:
spraying the mixed solution dispersed with the barium titanate powder on the double surfaces of the single-layer full-mesh-based fiber, then carrying out laminated needling on the single-layer full-mesh-based fiber containing the barium titanate powder to obtain a barium titanate-doped carbon fiber preform, and then carrying out chemical vapor deposition densification on the barium titanate-doped carbon fiber preform to obtain the barium titanate-doped modified carbon-based composite material.
According to the preparation method, the mixed liquid with the barium titanate powder dispersed is sprayed on the surface of the single-layer full-mesh-based fiber, then the barium titanate-doped carbon fiber preform is obtained through a needle punching method, the barium titanate can be brought into the mesh-based layer through the needle punching fiber, and meanwhile, the interlayer binding force is increased. According to the invention, barium titanate is introduced in the weaving process, the process is simple, the barium titanate is uniformly dispersed in the preparation process of the preform, the doping amount of the barium titanate is increased, the function of protecting the structural integrity of the fiber is also realized, and finally the barium titanate doped modified carbon-based composite material is prepared by using a chemical vapor deposition method.
The invention relates to a preparation method of a barium titanate doped modified carbon-based composite material, wherein the particle size of barium titanate powder is 100-500 nm; preferably 300 to 500 nm.
In the present invention, the particle size of the barium titanate powder has a certain influence on the properties of the final material, and if the particle size is too small, the barium titanate powder is completely coated with pyrolytic carbon formed by deposition, and the emission performance effect is weak in electron emission, while if the particle size of the barium titanate is too large, the dispersibility attached to the fiber is not good.
The invention relates to a preparation method of a barium titanate doped modified carbon-based composite material, which comprises the following steps of: adding barium titanate powder into absolute ethyl alcohol, and dispersing under the action of ultrasound, wherein the power of the ultrasound is 300-500 w, and the time of the ultrasound is 1-2 hours.
In the actual operation process, under the action of ultrasonic waves, a mixed solution in which barium titanate powder is fully dispersed is obtained and is immediately sprayed on the full-mesh fiber layer.
Preferably, the solid-liquid mass volume ratio of the barium titanate powder to the absolute ethyl alcohol is 1g: 10-30 mL.
The invention relates to a preparation method of a barium titanate doped modified carbon-based composite material, wherein the surface density of a single-layer full-mesh tire fiber is 20-30 g/m2。
Controlling the area density of the single-layer full-mesh tire fiber within the range can ensure that the finally obtained barium titanate doped modified carbon-based composite material has the best performance, and if the density of the single-layer full-mesh tire is too high, the density of a finally woven and formed preform is too high, the content of relative pyrolytic carbon is low, and the stability and uniformity of electron emission are not ideal.
The invention relates to a preparation method of a barium titanate doped modified carbon-based composite material, wherein fibers used in full-mesh fibers are T700-grade carbon fibers.
The invention relates to a preparation method of a barium titanate doped modified carbon-based composite material, which comprises the steps of wetting and loosening chopped fibers with water, laying a net-shaped tire, and needling long fibers arranged on the net-shaped tire into radial fibers to form single-layer full-net-shaped tire fibers.
The invention relates to a preparation method of a barium titanate doped modified carbon-based composite material, wherein a single-layer full-mesh-fabric fiber containing barium titanate powder is dried at 100-200 ℃ and then laminated and needled; the time is 1-2 h.
The invention relates to a preparation method of a barium titanate doped modified carbon-based composite material, wherein a barium titanate doped carbon fiber prefabricated body is a cylinder with a hole in the center, and the diameter of the hole is 20-30 mm.
Preferably, the barium titanate doped carbon fiber preform has an outer diameter of 50-60 mm and a height of 40-50 mm.
In the invention, the barium titanate doped carbon fiber preform is made into a structure with a hole in the center, so that gas can diffuse outwards through the inside of the cylinder under the action of pressure difference in the vapor deposition process, and the densification and the uniformity can be accelerated.
The invention relates to a preparation method of a barium titanate doped modified carbon-based composite material, wherein the density of a barium titanate doped carbon fiber preform is 0.2-0.3 g/cm3。
The invention relates to a preparation method of a barium titanate doped modified carbon-based composite material, wherein in a barium titanate doped carbon fiber preform, the mass fraction of barium titanate is 5-25%; preferably 15% to 25%.
In the invention, the doping amount of barium titanate is controlled within the range, the comprehensive performance of the barium titanate doped modified carbon-based composite material is optimal, and if the doping amount of barium titanate is too small, the electron emission performance of the material is not obviously improved, and the uniformity of deposited carbon is influenced by too large doping amount.
The invention relates to a preparation method of a barium titanate doped modified carbon-based composite material, which comprises the following steps: with N2Using propylene as carbon source gas for diluting gas, the propylene and N2The flow ratio of (A) to (B) is 4-120: 1; preferably 60-100: 1.
The invention relates to a preparation method of a barium titanate doped modified carbon-based composite material, wherein the temperature is 1000-1100 ℃ during chemical vapor deposition; the pressure in the furnace is 1-8 kpa.
The invention relates to a preparation method of a barium titanate doped modified carbon-based composite material, wherein the density of the barium titanate doped modified carbon-based composite material is more than or equal to 1.8g/cm3。
According to the invention, the barium titanate doped modified carbon-based composite material is subjected to multiple CVD depositions until the barium titanate doped modified carbon-based composite material is compact, the mass of the carbon fiber preform is respectively weighed by a balance before and after each CVD, the weight gain and the density after each deposition are calculated, meanwhile, machining is carried out after each deposition is finished, a channel of which the surface layer obstructs the diffusion of carbon source gas is removed, and the carbon fiber preform is cleaned.
The invention also provides the barium titanate doped modified carbon-based composite material prepared by the preparation method.
The invention also provides application of the barium titanate doped modified carbon-based composite material prepared by the preparation method, and the barium titanate doped modified carbon-based composite material is applied to the field of electron emission.
Advantageous effects
The preparation method can introduce barium titanate in the weaving process so as to prepare the barium titanate modified carbon-based composite material preform, has simple process, not only realizes the uniform dispersion of barium titanate in the preparation process of the preform, but also plays a role in protecting the structural integrity of fibers, and prepares the barium titanate doped modified carbon-based composite material by utilizing a chemical vapor deposition method.
The invention aims to provide a preparation method of a barium titanate doped modified carbon-based composite material, which has the characteristics of simplicity, controllability, low cost, easiness in obtaining raw materials, no damage to fibers and the like, and is suitable for large-scale production and application. Meanwhile, in the prepared barium titanate doped modified carbon-based composite material, barium titanate particles are uniformly distributed, the doping amount of barium titanate is high, and the barium titanate doped modified carbon-based composite material not only has excellent mechanical properties, but also greatly improves the electron emission performance, so that the emission stability, uniformity, current density and the like are greatly improved.
Drawings
FIG. 1 is a scanning electron micrograph of doped barium titanate prepared according to example 1;
FIG. 2 is a scanning electron microscope image of a barium titanate doped modified carbon-based composite preform prepared in example 1;
FIG. 3 is a diagram of a barium titanate-doped modified carbon-based composite preform prepared in example 1.
Detailed Description
Example 1
Mixing 20.59g of barium titanate powder with the particle size of 500nm with 300ml of absolute ethyl alcohol, oscillating and stirring the mixture in an ultrasonic instrument for dispersing for 1.5 hours, and immediately spraying the prepared barium titanate dispersion liquid on the surface of a full-mesh-tire single-layer fiber with the mass of 391.11g after the barium titanate powder is fully mixed, dispersed and not agglomerated, wherein the surface density of the full-mesh-tire single-layer fiber is 20g/cm3Drying single-layer fibers, laminating and needling the single-layer fibers to obtain a barium titanate doped carbon fiber preform, wherein the prepared barium titanate doped carbon fiber preform is provided with a hole in the middle, the inner diameter of the hole is 30mm, the outer diameter of the hole is 60mm, and the height of the hole is 50 mm; barium titanate dopingThe density of the carbon fiber preform was 0.2g/cm3The mass fraction of barium titanate in the barium titanate-doped carbon fiber preform is 5%.
Then the barium titanate doped carbon fiber preform is placed in a chemical vapor deposition furnace for deposition, propylene is used as gas required for depositing pyrolytic carbon, and N2For diluting the gas, N2The flow rate was 0.5L/min and the flow rate of propylene was 40L/min. The deposition conditions were: the temperature in the furnace is 1000 ℃, the pressure in the furnace is 1kpa, the deposition time is 168h as one deposition period, the barium titanate doped modified carbon-based composite material is prepared after deposition for 4 periods, and the density of the obtained composite material is 1.8g/cm3。
The obtained barium titanate doped modified carbon-based composite material is used for electron emission, the emission stability is good, and the current density reaches 12KA/cm3。
FIG. 1 is a scanning electron micrograph of the barium titanate-doped carbon fiber preform of example 1, in which the barium titanate particles are relatively uniform and are uniformly dispersed in the carbon fiber preform of FIG. 2.
Fig. 2 is a scanning electron microscope image of the morphology of the barium titanate doped modified carbon-based composite preform prepared in example 1, and it can be seen from the image that the internal morphology of the preform structure is short fibers and barium titanate small particles uniformly attached thereon.
FIG. 3 is a physical diagram of the morphology of a preform of the barium titanate-doped modified carbon-based composite material prepared in example 1, which is a cylinder with a hole in the center, and has an inner diameter of 30mm, an outer diameter of 60mm and a height of 50 mm.
Example 2
Taking barium titanate powder with the particle size of 500nm and absolute ethyl alcohol, controlling the mass ratio of the barium titanate powder to the absolute ethyl alcohol to be 1g:20mL, oscillating and stirring the barium titanate powder and the absolute ethyl alcohol in an ultrasonic instrument for dispersing for 1.5h, immediately spraying the prepared barium titanate dispersion liquid on the surface of the full-mesh-based single-layer fiber after fully mixing and dispersing and no agglomeration, wherein the surface density of the full-mesh-based single-layer fiber is 0.2g/cm3And drying the single-layer fiber, laminating and needling to obtain a barium titanate doped carbon fiber preform, wherein the inner diameter of the prepared barium titanate doped carbon fiber preform is 30mm, the outer diameter is 60mm, and the height is 50 mm. The obtained titaniumThe density of the acid barium doped carbon fiber preform is 0.2g/cm3The mass fraction of the barium titanate powder in the barium titanate-doped carbon fiber preform is 15%.
Then the barium titanate doped carbon fiber preform is placed in a chemical vapor deposition furnace for deposition, propylene is used as gas required for depositing pyrolytic carbon, and N2For diluting the gas, N2The flow rate was 0.5L/min and the flow rate of propylene was 40L/min. The deposition conditions were: the temperature in the furnace is 1050 ℃, the pressure in the furnace is 3kpa, the deposition time is 150h as one deposition period, and the barium titanate doped modified carbon-based composite material is prepared after 3 deposition periods, wherein the density of the composite material is 1.80g/cm3。
The obtained barium titanate doped modified carbon-based composite material is used for electron emission, and the current density reaches 14KA/cm3。
Example 3
Taking barium titanate powder with the particle size of 500nm and absolute ethyl alcohol, controlling the mass ratio of the barium titanate powder to the absolute ethyl alcohol to be 1g:30mL, oscillating and stirring the barium titanate powder and the absolute ethyl alcohol in an ultrasonic instrument for dispersing for 1.5h, immediately spraying the prepared barium titanate dispersion liquid on the surface of the full-mesh-based single-layer fiber after fully mixing and dispersing and no agglomeration, wherein the surface density of the full-mesh-based single-layer fiber is 20g/cm3And drying the single-layer fiber, laminating and needling to obtain the barium titanate doped carbon fiber preform, wherein the prepared barium titanate doped carbon fiber preform is provided with a hole in the middle, the inner diameter of the hole is 30mm, the outer diameter of the hole is 60mm, and the height of the hole is 50 mm. The density of the obtained barium titanate doped carbon fiber preform is 0.2g/cm3, and the mass fraction of barium titanate powder in the barium titanate doped carbon fiber preform is 25%.
Using propene as the gas, N, required for the deposition of pyrolytic carbon2For diluting the gas, N2The flow rate was 0.5L/min and the flow rate of propylene was 40L/min. The deposition conditions were: the temperature in the furnace is 1100 ℃, the pressure in the furnace is 8kpa, the deposition time is 150h as one deposition period, and the barium titanate doped modified carbon-based composite material is prepared after 4 deposition periods, wherein the density of the composite material is 1.81g/cm3。
The obtained barium titanate doped modified carbon-based composite material is used for electron emissionThe current density reaches 16KA/cm3。
Comparative example 1
The other conditions were the same as in example 1 except that the particle size of barium titanate powder was 50 nm.
The properties of the obtained product were as follows: barium titanate powder is completely coated with pyrolytic carbon formed by deposition, and the emission performance effect in electron emission is very weak and is basically not the same as that of undoped barium titanate powder.
Comparative example 2
The other conditions were the same as in example 2 except that the mass fraction of barium titanate powder in the barium titanate-doped carbon fiber preform exceeded 40%. The excessive addition of the barium titanate powder can slow down the densification effect of the barium titanate doped carbon fiber preform in the deposition process, reduce the efficiency, increase the time and the economic cost, and can not reach 1.8/cm3The density requirement of (2).

Claims (5)

1. A preparation method of a barium titanate doped modified carbon-based composite material is characterized by comprising the following steps: the method comprises the following steps:
spraying the mixed solution dispersed with the barium titanate powder on the double surfaces of the single-layer full-mesh-based fiber, then carrying out laminated needling on the single-layer full-mesh-based fiber containing the barium titanate powder to obtain a barium titanate-doped carbon fiber preform, and then carrying out chemical vapor deposition densification on the barium titanate-doped carbon fiber preform to obtain a barium titanate-doped modified carbon-based composite material;
the particle size of the barium titanate powder is 100-500 nm;
the surface density of the single-layer full-mesh tire fiber is 20-30 g/m2；
In the barium titanate-doped carbon fiber preform, the mass fraction of barium titanate is 5-25%;
the barium titanate doped carbon fiber preform is a cylinder with a hole in the center, and the diameter of the hole is 20-30 mm; the barium titanate doped carbon fiber preform has an outer diameter of 50-60 mm and a height of 40-50 mm;
the chemical vapor deposition process comprises the following steps: with N2Using propylene as carbon source gas for diluting gas, the propylene and N2Flow rate ratio ofIs 4-120: 1; the temperature is 1000-1100 ℃; the pressure in the furnace is 1-8 KPa.
2. The preparation method of the barium titanate doped modified carbon-based composite material according to claim 1, wherein the preparation method comprises the following steps: the method for obtaining the mixed liquid dispersed with the barium titanate powder comprises the following steps: adding barium titanate powder into absolute ethyl alcohol, and dispersing under the action of ultrasonic waves, wherein the power of the ultrasonic waves is 300-500W, and the time of the ultrasonic waves is 1-2 h; the solid-liquid mass volume ratio of the barium titanate powder to the absolute ethyl alcohol is 1g: 10-30 mL.
3. The preparation method of the barium titanate doped modified carbon-based composite material according to claim 1, wherein the preparation method comprises the following steps: the density of the barium titanate doped carbon fiber preform is 0.2-0.3 g/cm3。
4. The preparation method of the barium titanate doped modified carbon-based composite material according to claim 1, wherein the preparation method comprises the following steps: the density of the barium titanate doped modified carbon-based composite material is more than or equal to 1.8g/cm3。
5. The barium titanate doped modified carbon-based composite material prepared by the preparation method according to any one of claims 1 to 4.
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