Carbon-based composite ceramic and method for manufacturing the same

Abstract

The present application relates to carbon-based composite ceramic preparation technical field, especially a kind of carbon-based composite ceramic and its preparation method, natural wood raw material is selected, and it is sequentially carried out first drying, high temperature treatment, impregnation treatment, secondary drying treatment and boron / carbon thermal reduction treatment, obtain carbon-based composite ceramic material.Natural wood and rare earth nitrate are used as raw material, and cost is low, the raw material needed is wood, shape is controllable, which greatly saves cost;Processing process is simple and easy to control, and cost is low, the size and shape of material can be accurately controlled, material synthesis and assembly integration are realized, which is suitable for industrial production.The existing problems of uneven distribution of conductive coating in the preparation method of carbon-based composite material in prior art, complicated process and expensive raw materials are solved, which makes it not suitable for large-scale industrialization.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of carbon-based composite ceramic preparation, and particularly relates to a carbon-based composite ceramic and a preparation method thereof. BACKGROUND

[0002] The wood-structured biochar is a kind of porous material, and the wood-structured biochar obtained by high-temperature carbonization treatment on natural wood has the advantages of light weight, multi-level pore structure and anisotropy. The natural three-dimensional porous conductive network of the wood-structured biochar makes it a promising candidate material for high-efficiency electromagnetic interference shielding. However, the single shielding mechanism of the wood-structured biochar limits its electromagnetic interference shielding application ability.

[0003] In the prior art, various conductive materials are integrated into the wood-structured biochar template to obtain a functional composite material with improved electromagnetic interference shielding material. Generally, the wood-structured MAX@C composite material is prepared by using a molten salt method, wherein the MXA phase is Ti2AlC, V2AlC and Cr2AlC, and a MAX phase coating is in-situ grown on the surface of the wood-structured biochar to prepare a coating with a porous structure. However, the coating prepared by using the molten salt method has uneven thickness distribution and uncontrollable shape, and the raw material M-site metal element powder, i.e. Ti, V and Cr, is expensive, and the process is complicated, which is not conducive to large-scale industrial application. SUMMARY

[0004] In view of the problems in the prior art that the preparation method of the carbon-based composite material has uneven distribution of the conductive coating, the process is complicated, and the raw material is expensive, which leads to the problem that it is not suitable for large-scale industrialization, the application provides a carbon-based composite ceramic and a preparation method thereof.

[0005] To achieve the above-mentioned purpose, the following technical solutions are adopted in the application:

[0006] The application provides a preparation method of a carbon-based composite ceramic, comprising the following steps:

[0007] The natural wood is subjected to first drying and high-temperature carbonization treatment to obtain wood-structured biochar;

[0008] An impregnation solution is prepared, and the impregnation solution is a mixed suspension of rare earth nitrate and B4C powder; wherein the rare earth nitrate is Re(NO3)3·6H2O or Re(NO3)3·5H2O, and Re is a lanthanide element;

[0009] The wood-structured biochar is immersed in the impregnation solution for impregnation and second drying to obtain wood-structured biochar containing rare earth nitrate and B4C powder;

[0010] The wood structure containing rare earth nitrate and B4C powder is subjected to boron / carbon thermal reduction treatment to obtain a carbon-based composite ceramic.

[0011] Preferably, the temperature of the first drying is 80-120 DEG C.

[0012] Preferably, the high-temperature carbonization treatment is carried out under the condition of inert gas protection at 800-1000 DEG C for 2-6 h.

[0013] Further, the method for preparing the impregnation solution is as follows: the rare earth nitrate, B4C powder, dispersant and surface modifier are dissolved in a mixed solution of deionized water and ethanol to obtain the impregnation solution; the addition amount of the dispersant is 0.2-1.0% of the mass of the B4C powder, the addition amount of the modifier is 2-5% of the mass of the B4C powder, the molar ratio of the rare earth nitrate to the B4C powder is 2:1, and the volume ratio of the deionized water to the ethanol is 9:1; the concentration of the rare earth nitrate in the impregnation solution is 0.36-2.64 mol / L, and the concentration of the B4C powder is 0.18-1.32 mol / L.

[0014] Preferably, the dispersant is tetramethylammonium hydroxide or polyethylene imine, and the surface modifier is 3-aminopropyl triethoxysilane.

[0015] Preferably, the particle size of the B4C powder is 45-55 nm.

[0016] Preferably, the impregnation is carried out under the condition of vacuum impregnation for 4-8 h, and the second drying is carried out at 40-60 DEG C.

[0017] Preferably, the boron / carbon thermal reduction treatment is carried out under the condition of argon atmosphere at 1800-2000 DEG C for 1-6 h.

[0018] Preferably, the natural wood is one or more of Chinese fir, poplar, pine, catalpa, fragrant wood, sycamore and basswood.

[0019] The application further provides a carbon-based composite ceramic prepared by the above method, which has a porosity of 63-82%, an electrical conductivity of 80.1-250.4 S / cm, a thermal conductivity of 4.38-23.14 W·m-1·K-1, an electromagnetic interference shielding effectiveness of 27-65 dB, and a bending strength of 6-38 MPa. 1 ·K -1

[0020] Compared with the prior art, the application has the following beneficial effects:

[0021] ​The application discloses a preparation method of carbon-based composite ceramics, which comprises the following steps: selecting natural wood as raw material, and sequentially performing first drying, high-temperature treatment, impregnation treatment, secondary drying treatment and boron / carbon thermal reduction treatment on the wood to obtain carbon-based composite ceramics with a honeycomb structure.

[0022] The application further provides the carbon-based composite ceramics prepared by the method, which has high electric conductivity and high thermal conductivity, the electric conductivity is 80.1-350.4 S / cm, the thermal conductivity is 4.38-23.14 W·m -1 ·K -1 The electromagnetic interference shielding effectiveness is 27-65 dB, and the bending strength is 6-38 Mpa, which overcomes the defects that general porous ceramic composite materials cannot have high porosity, good electric conductivity, thermal conductivity, electromagnetic interference shielding effectiveness and bending strength. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 FIG. 1 is a schematic diagram of a preparation process of the carbon-based composite ceramics.

[0024] Figure 2 FIG. 5 is an XRD diagram of a sample after the boron / carbon thermal reduction reaction in the embodiment of the application.

[0025] Figure 3 FIG. 6 is an SEM diagram of the sample after the boron / carbon thermal reduction reaction in the embodiment of the application. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the embodiments of the application clearer, the technical scheme in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments of the application. The components of the embodiments of the application described and shown in the drawings can be arranged and designed in various different configurations.

[0027] Therefore, the following detailed description of the embodiments of the application provided in the drawings is not intended to limit the scope of the claimed application, but only represents selected embodiments of the application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the application without creative efforts fall within the scope of the protection of the application.

[0028] It should be noted that like reference numerals and characters refer to like elements throughout the several views of the drawings, and that, unless otherwise indicated, like elements in two or more figures are of like design and function for which no further discussion is needed in the interest of brevity.

[0029] In the description of the embodiments of the present application, it should be noted that the orientation or position relationship indicated by the terms "upper", "lower", "horizontal", "inner" and the like is based on the orientation or position relationship shown in the drawings or the orientation or position relationship in which the product of the present application is usually placed, and is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" and the like are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0030] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly inclined. For example, "horizontal" only means that its direction is relatively more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly inclined.

[0031] In the description of the embodiments of the present application, it should be noted that, unless otherwise specified and limited, if the terms "arrangement", "installation", "connection", "connection" appear, they should be understood in a broad sense, for example, they can be fixedly connected, or can be detachably connected, or integrally connected; can be mechanically connected, or can be electrically connected; can be directly connected, or can be indirectly connected through an intermediate medium; can be connected inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0032] The present application will be further described in detail below in conjunction with specific embodiments, which are an explanation of the present application rather than a limitation.

[0033] The present application discloses a preparation method of carbon-based composite ceramic, referring to Figure 1 , comprising the following steps:

[0034] S1: first drying and high-temperature carbonization treatment of natural wood to obtain a wood structure biochar; the temperature of the first drying is 80-120℃, and the drying time is 48-96h; the high-temperature carbonization treatment conditions are: 800-1000℃ for 2-6h under inert gas protection; the natural wood is one or more of Chinese fir, poplar, pine, catalpa, fragrant wood, sycamore and basha wood.

[0035] S2: preparing the impregnation solution; the specific operation is as follows: dissolving the rare earth nitrate, B4C powder, dispersant and surface modifier in the mixed solution of deionized water and ethanol to obtain the mixed suspension of the rare earth nitrate and B4C powder, i.e. the impregnation solution; the addition amount of the dispersant is 0.2-1.0% of the mass of the B4C powder, the addition amount of the modifier is 2-5% of the mass of the B4C powder, the molar ratio of the rare earth nitrate to the B4C powder is 2:1, and the volume ratio of the deionized water to the ethanol is 9:1; the concentration of the rare earth nitrate in the impregnation solution is 0.36-2.64 mol / L, and the concentration of the B4C powder is 0.18-1.32 mol / L; the dispersant is tetramethylammonium hydroxide or polyethyleneimine; the surface modifier is 3-aminopropyltriethoxysilane; the particle size of the B4C powder is 45-55 nm; and the rare earth nitrate is Re(NO3)3·6H2O or Re(NO3)3·5H2O, wherein Re is a lanthanide element, and Re is preferably Y, Gd, Lu or Yb.

[0036] S3: impregnating the wood-structured bio-carbon in the impregnation solution and secondarily drying to obtain the wood-structured bio-carbon containing the rare earth nitrate and B4C powder; the impregnation condition is vacuum impregnation for 4-8 h; and the secondary drying condition is 40-60°C for 48-96 h.

[0037] S4: subjecting the wood-structured bio-carbon containing the rare earth nitrate and B4C powder to boron / carbon thermal reduction treatment to obtain the carbon-based composite ceramic; the boron / carbon thermal reduction treatment condition is 1800-2000°C for 1-6 h under an argon atmosphere.

[0038] Example 1

[0039] Taking natural Chinese fir as the raw material, the natural wood was cut into small pieces for easy polishing, and was placed in a blast drying oven for drying at 100°C for 24 h. The dried wood was placed in a tube furnace, and was heated to 500°C at a heating rate of 0.5°C / min, and then heated to 1000°C at a heating rate of 1°C / min, and was kept at 1000°C for 4 h, and was cooled to room temperature with the furnace, to obtain the wood-structured bio-carbon.

[0040] A 200 mL beaker was prepared, 90 mL of deionized water and 10 mL of absolute ethanol were measured, 0.036 mol of yttrium nitrate was weighed, and a yttrium nitrate solution with a concentration of 0.36 mol / L was prepared; 0.018 mol of B4C powder was weighed, 0.2% of the mass of the B4C powder of tetramethylammonium hydroxide was added, 2.0% of the mass of the B4C powder of 3-aminopropyl triethoxysilane was added, a magnetic stirring rotor was added, and electromagnetic stirring was performed at room temperature for 24 h, after which electromagnetic stirring was performed in an 80°C oil bath for 3 h, and after cooling to room temperature, the impregnating solution and the wood-structured biochar were placed in a 250 mL suction filter bottle, a vacuum state was achieved using a vacuum water pump, and ultrasonic dispersion was performed using an ultrasonic instrument for 6 h. Finally, mechanical vacuum pumping was performed for 20 min under ultrasonic dispersion conditions to ensure that the suspension was fully and uniformly infiltrated into the wood-structured biochar. The wood-structured biochar after impregnation was placed in a 100 ml beaker and placed in a forced air drying oven, and dried at 40°C for 48 h.

[0041] The dried sample was placed in a BN crucible, the BN crucible was placed in a multifunctional furnace, argon was introduced, and the temperature was raised from room temperature to 1200°C at a rate of 10°C / min, then raised from 1200°C to 1850°C at a rate of 5°C / min, and held for 2 h. The obtained honeycomb-like structure carbon-based composite ceramic was denoted as C@YB2C2, and the test results showed that the porosity of the composite ceramic was 73.7%, the electrical conductivity was 80.1 S / cm, the thermal conductivity was 4.38 W·m -1 ·K -1 , the electromagnetic interference shielding effectiveness was 27 dB, and the bending strength was 6.1 Mpa.

[0042] Example 2

[0043] Natural camphor wood was used as the raw material, and the natural wood was cut into small pieces for easy polishing and placed in a forced air drying oven and dried at 120°C for 36 h. The dried wood was placed in a tube-type atmosphere furnace, a flowing nitrogen atmosphere was introduced for protection, and the temperature was raised to 500°C at a rate of 0.5°C / min, then raised to 800°C at a rate of 1°C / min, and held for 4 h, and the furnace was cooled to room temperature, and wood-structured biochar was obtained.

[0044] A 200 mL beaker was prepared, 90 mL of deionized water and 10 mL of absolute ethanol were measured, 0.12 mol of yttrium nitrate was weighed, and a yttrium nitrate solution with a concentration of 1.2 mol / L was prepared. Then 0.06 mol of B4C powder was weighed, 1.0% of the mass of the B4C powder of polyethyleneimine was added, 5.0% of the mass of the B4C powder of 3-aminopropyltriethoxysilane was added, a magnetic stirring rotor was added, and electromagnetic stirring was performed at room temperature for 24 h. Then the modified B4C powder was placed in a 250 mL filter flask together with the wood structure biochar, a vacuum state was achieved using a vacuum water pump, and ultrasonic dispersion was used for impregnation for 4 h. Finally, the mechanical vacuum pump was used for 20 min under the condition of ultrasonic dispersion to ensure that the suspension was fully and uniformly infiltrated into the sample.

[0045] The impregnated sample was placed in a 100 mL beaker and placed in a forced air drying oven and dried at 50°C for 72 h.

[0046] The dried sample was placed in a BN crucible, the BN crucible was placed in a multifunctional furnace, argon was introduced, the temperature was increased from room temperature to 1200°C at a rate of 10°C / min, then increased from 1200°C to 1900°C at a rate of 5°C / min, and held for 1 h. The resulting honeycomb-like structure carbon-based composite ceramic C@YB2C2 was obtained. The porosity of the composite ceramic was 69.9%, the electrical conductivity was 165.4 S / cm, the thermal conductivity was 4.98 W·m -1 ·K -1 , the electromagnetic interference shielding effectiveness was 34 dB, and the bending strength was 16.6 Mpa.

[0047] Example 3

[0048] Natural fragrant wood was used as the raw material, and the natural wood was cut into small pieces for easy polishing and placed in a forced air drying oven and dried at 80°C for 72 h. The dried wood was placed in a tube-type atmosphere furnace, a flowing argon atmosphere was introduced for protection, and the temperature was increased to 500°C at a rate of 0.5°C / min, then increased to 900°C at a rate of 1°C / min, and held for 6 h. The furnace was cooled to room temperature, and wood structure biochar material was obtained.

[0049] A 200 mL beaker was prepared, 90 mL of deionized water and 10 mL of anhydrous ethanol were measured, 0.10 mol of lutetium nitrate was weighed, and a yttrium nitrate solution with a concentration of 1.0 mol / L was prepared. Then 0.05 mol of B4C powder was weighed, 0.5% of the B4C powder mass of dispersant tetramethylammonium hydroxide was added, 3.0% of the B4C powder mass of 3-aminopropyl triethoxysilane was added, a magnetic stirring rotor was added, and electromagnetic stirring was performed at room temperature for 24 h. Then the modified B4C powder was cooled and placed in a 250 mL suction filter bottle together with the wood-structured biochar. A vacuum state was achieved using a vacuum water pump, and ultrasonic dispersion was used for impregnation for 6 h. Finally, mechanical vacuum pumping was used for 20 min under ultrasonic dispersion conditions to ensure that the suspension was fully and uniformly infiltrated into the wood-structured biochar.

[0050] The impregnated sample was placed in a 100 mL beaker and placed in a forced air drying oven and dried at 60°C for 48 h.

[0051] The dried sample was placed in a BN crucible, the BN crucible was placed in a multifunctional furnace, argon was introduced, and the temperature was raised from room temperature to 1200°C at a rate of 10°C / min, then raised from 1200°C to 1950°C at a rate of 5°C / min, and held for 2 h. The resulting honeycomb-like structure carbon-based composite material was denoted as C@LuB2C2, and the porosity was 82.1%, the electrical conductivity was 215.6 S / cm, the thermal conductivity was 23.14 W·m -1 ·K -1 , the electromagnetic interference shielding effectiveness was 48 dB, and the bending strength was 28.1 Mpa.

[0052] Example 4

[0053] Natural fir wood was used as the raw material, and the natural wood was cut into small pieces for easy polishing and placed in a forced air drying oven and dried at 90°C for 96 h. The dried wood was placed in a tube-type atmosphere furnace, a flowing nitrogen atmosphere was introduced for protection, and the temperature was raised to 500°C at a rate of 0.5°C / min, then raised to 1000°C at a rate of 1°C / min, and held for 2 h. The furnace was cooled to room temperature, and wood-structured biochar material was obtained.

[0054] A 200 mL beaker was prepared, 90 mL of deionized water and 10 mL of absolute ethanol were measured, 0.264 mol of yttrium nitrate was weighed, and a yttrium nitrate solution with a concentration of 2.64 mol / L was prepared. Then 0.132 mol of B4C powder was weighed, 0.5% of the mass of the B4C powder of tetramethylammonium hydroxide was added, 3.5% of the mass of the B4C powder of 3-aminopropyl triethoxysilane was added, a magnetic stirring rotor was added, and the mixture was stirred at room temperature for 24 h under electromagnetic stirring. Then the mixture was stirred at 80°C in an oil bath for 3 h under electromagnetic stirring. After cooling, the mixture was placed in a 250 mL filter flask together with the wood-structured bio-carbon material, vacuum was applied using a vacuum water pump, and ultrasonic dispersion was used for 8 h. Finally, the suspension was uniformly infiltrated into the sample by using a mechanical vacuum pump for 20 min under ultrasonic dispersion.

[0055] The impregnated sample was placed in a 100 mL beaker and placed in a forced air drying oven and dried at 55°C for 72 h.

[0056] The dried sample was placed in a BN crucible, the BN crucible was placed in a multifunctional furnace, argon was introduced, the temperature was increased from room temperature to 1200°C at a rate of 10°C / min, then increased from 1200°C to 1900°C at a rate of 5°C / min, and held for 4 h. The obtained honeycomb-like structure C@YB2C2 composite ceramic had a porosity of 77.3%, a conductivity of 186.9 S / cm, a thermal conductivity of 5.34 W·m -1 ·K -1 , an electromagnetic interference shielding effectiveness of 39 dB, and a bending strength of 18.1 Mpa.

[0057] Example 5

[0058] Natural poplar wood was used as the raw material, the natural wood was cut into small pieces for easy polishing, and the small pieces were placed in an oven and dried for 72 h. The dried wood was placed in a tube furnace and protected by a flowing argon atmosphere, heated to 500°C at a rate of 0.5°C / min, then heated to 1000°C at a rate of 1°C / min, and held for 6 h. The furnace was cooled to room temperature, and wood-structured bio-carbon material was obtained.

[0059] A 200 mL beaker was prepared, 90 mL of deionized water and 10 mL of anhydrous ethanol were measured, 0.15 mol of gadolinium nitrate was weighed, and a gadolinium nitrate solution with a concentration of 1.5 mol / L was prepared. Then 0.075 mol of B4C powder was weighed, 0.4% of the B4C powder mass of dispersant polyethyleneimine was added, 3.5% of the B4C powder mass of 3-aminopropyltriethoxysilane was added, a magnetic stirring rotor was added, and the mixture was stirred at room temperature for 24 h under electromagnetic stirring. Then the mixture was modified at 80°C in an oil bath for 3 h. After cooling, the mixture was placed in a 250 mL filter flask together with the wood-structured biochar material, vacuum was applied using a vacuum water pump, and ultrasonic dispersion was used for 4 h. Finally, the mechanical vacuum pump was used for 20 min under ultrasonic dispersion to ensure that the suspension was fully and uniformly infiltrated into the sample.

[0060] The impregnated sample was placed in a 100 ml beaker and placed in a forced air drying oven at 50°C for 96 h.

[0061] The dried sample was placed in a BN crucible, which was placed in a multifunctional furnace, and argon was introduced. The temperature was increased from room temperature to 1200°C at a rate of 10°C / min, then increased from 1200°C to 2000°C at a rate of 5°C / min, and held for 1 h. The resulting honeycomb-like structure C@GdB2C2 composite ceramic had a porosity of 77.3%, a conductivity of 178.9 S / cm, a thermal conductivity of 10.51 W·m -1 ·K -1 , an electromagnetic interference shielding effectiveness of 42 dB, and a bending strength of 26.6 Mpa.

[0062] Example 6

[0063] Natural catalpa wood was used as the raw material, and the natural wood was cut into small pieces for easy polishing and placed in a forced air drying oven at 100°C for 48 h. The dried wood was placed in a tube-type atmosphere furnace and protected by flowing argon atmosphere. The temperature was increased to 500°C at a rate of 0.5°C / min, then increased to 900°C at a rate of 1°C / min, and held for 3 h. The furnace was cooled to room temperature, and a porous carbon material was obtained.

[0064] A 200 mL beaker was prepared, 90 mL of deionized water and 10 mL of absolute ethanol were measured, 0.18 mol of ytterium nitrate was weighed, and a ytterium nitrate solution with a concentration of 1.80 mol / L was prepared. Then 0.09 mol of B4C powder was weighed, 0.7% of the mass of the B4C powder of tetramethylammonium hydroxide was added, 2.5% of the mass of the B4C powder of 3-aminopropyl triethoxysilane was added, a magnetic stirring rotor was added, and electromagnetic stirring was performed at room temperature for 24 h. Then the modified B4C powder was placed in a 250 mL filter flask together with the wood-structured biochar, a vacuum state was achieved using a vacuum water pump, and ultrasonic dispersion was performed for 8 h using an ultrasonic instrument. Finally, the suspension was uniformly infiltrated into the sample by performing ultrasonic dispersion and using a mechanical vacuum pump for 20 min.

[0065] The impregnated sample was placed in a 100 mL beaker and placed in a forced air drying oven and dried at 40°C for 72 h.

[0066] The dried sample was placed in a BN crucible, the BN crucible was placed in a multifunctional furnace, argon was introduced, the temperature was increased from room temperature to 1200°C at a rate of 10°C / min, then increased from 1200°C to 2000°C at a rate of 5°C / min, and held for 2 h. The obtained honeycomb-like structure C@YbB2C2 composite ceramic had a porosity of 82.1%, a conductivity of 143.9 S / cm, a thermal conductivity of 11.69 W·m -1 ·K -1 , an electromagnetic interference shielding effectiveness of 58 dB, and a bending strength of 38.1 Mpa.

[0067] Example 7

[0068] Natural pine wood was used as the raw material, the natural wood was cut into small pieces for easy polishing, and the small pieces were placed in a forced air drying oven and dried at 120°C for 48 h. The dried wood was placed in a tube-type atmosphere furnace, a flowing argon atmosphere was introduced for protection, the temperature was increased to 500°C at a rate of 0.5°C / min, then increased to 1000°C at a rate of 1°C / min, and held for 2 h. The furnace was cooled to room temperature, and wood-structured biochar material was obtained.

[0069] A 200 mL beaker was prepared, 90 mL of deionized water and 10 mL of absolute ethanol were measured, 0.24 mol of ytterium nitrate was weighed, and a ytterium nitrate solution with a concentration of 2.40 mol / L was prepared. Then 0.12 mol of B4C powder was weighed, 0.6% of the mass of the B4C powder of polyethyleneimine was added, 3.5% of the mass of the B4C powder of 3-aminopropyltriethoxysilane was added, a magnetic stirring rotor was added, and electromagnetic stirring was performed at room temperature for 24 h. Then the modified B4C powder was placed in a 250 mL filter flask together with the wood-structured biochar, a vacuum state was achieved using a vacuum water pump, and ultrasonic dispersion was performed for 8 h using an ultrasonic instrument. Finally, the suspension was fully and uniformly infiltrated into the sample by performing mechanical vacuum pumping for 20 min under ultrasonic dispersion.

[0070] The impregnated sample was placed in a 100 mL beaker and placed in a forced air drying oven and dried at 40°C for 72 h.

[0071] The dried sample was placed in a BN crucible, the BN crucible was placed in a multifunctional furnace, argon was introduced, the temperature was increased from room temperature to 1200°C at a rate of 10°C / min, then increased from 1200°C to 2000°C at a rate of 5°C / min, and held for 1 h. The obtained honeycomb-like structure C@YbB2C2 composite ceramic had a porosity of 74.6%, a conductivity of 165.6 S / cm, a thermal conductivity of 16.32 W·m -1 ·K -1 , an electromagnetic interference shielding effectiveness of 65 dB, and a bending strength of 30.6 Mpa.

[0072] Example 8

[0073] Natural Bashan wood was used as the raw material, the natural wood was cut into small pieces for easy polishing, and the small pieces were placed in a forced air drying oven and dried at 100°C for 96 h. The dried wood was placed in a tube-type atmosphere furnace, a flowing argon atmosphere was introduced for protection, the temperature was increased to 500°C at a rate of 0.5°C / min, then increased to 1000°C at a rate of 1°C / min, and held for 4 h. The furnace was cooled to room temperature, and wood-structured biochar material was obtained.

[0074] A 200 mL beaker was prepared, 90 mL of deionized water and 10 mL of anhydrous ethanol were measured, 0.16 mol of lutetium nitrate was weighed, and a lutetium nitrate solution with a concentration of 1.60 mol / L was prepared. Then 0.08 mol of B4C powder was weighed, 0.5% of the B4C powder mass of dispersant tetramethylammonium hydroxide was added, 4.0% of the B4C powder mass of modifier 3-aminopropyl triethoxysilane was added, a magnetic stirring rotor was added, and electromagnetic stirring was carried out at room temperature for 24 h. Then the sample was placed in a 250 mL filter flask, vacuum was applied using a vacuum water pump, and ultrasonic dispersion was used for impregnation for 6 h. Finally, the mechanical vacuum pump was used for 20 min under the condition of ultrasonic dispersion, so that the suspension was fully and uniformly infiltrated into the sample.

[0075] The impregnated sample was placed in a 100 ml beaker and placed in a forced air drying oven and dried at 55℃ for 96h.

[0076] The dried sample was placed in a BN crucible, the BN crucible was placed in a multifunctional furnace, argon was introduced, and the temperature was raised from room temperature to 1200℃ at a rate of 10℃ / min, then raised from 1200℃ to 1950℃ at a rate of 5℃ / min, and kept for 3h. The porosity of the honeycomb-like structure C@LuB2C2 composite ceramic obtained was 69.9%, the electrical conductivity was 250.4S / cm, the thermal conductivity was 22.86W·m -1 ·K -1 , the electromagnetic interference shielding effectiveness was 46dB, and the bending strength was 18.2Mpa.

[0077] Referring to Figure 2 The honeycomb-like structure C@YB2C2 composite ceramic obtained in Example 1 was subjected to XRD test, and the results showed that after the boron / carbon thermal reduction reaction, the obtained phase was single YB2C2. Referring to Figure 3 The SEM results of the honeycomb-like structure C@YB2C2 composite ceramic obtained in Example 4 can be seen that the YB2C2 lamellar crystals are stacked with each other to form the honeycomb-like structure C@YB2C2 composite ceramic.

[0078] In summary, the preparation method of the carbon-based composite ceramic provided by the application selects natural wood as raw material, and sequentially performs first drying, high-temperature treatment, impregnation treatment, second drying treatment and boron / carbon thermal reduction treatment to obtain honeycomb-like structure carbon and rare earth diboron dicarbon composite ceramic. The natural wood and rare earth nitrate are used as raw materials, the cost is low, the original material is wood, the shape is controllable, the cost is greatly saved, the processing process of the honeycomb-like structure carbon and rare earth diboron dicarbon composite ceramic is simple, the size and shape of the material can be accurately controlled, the material synthesis and assembly integration are realized, the control of the thickness in the preparation process by the molten salt method is avoided, the method is suitable for industrialized production, and can be widely applied in the field of electromagnetic interference shielding.

[0079] The present application also provides a carbon-based composite ceramic prepared by the above preparation method, which has a porosity of 63-82%, an electrical conductivity of 80.1-250.4 S / cm, a thermal conductivity of 4.38-23.14 W·m -1 ·K- 1 , an electromagnetic interference shielding effectiveness of 27-65 dB, and a bending strength of 6-38 MPa.

[0080] The above merely describes the preferred embodiments of the present application and is not intended to limit the technical solutions of the present application in any way. Those skilled in the art should understand that the technical solutions can be modified or replaced in several simple ways without departing from the spirit and principle of the present application, and these modifications and replacements also fall within the protection scope of the claims.

Claims

1. A method for preparing carbon-based composite ceramics, characterized in that, Includes the following steps: Natural wood is first dried and then carbonized at high temperature to obtain biocarbon from the wood structure. An impregnation solution is prepared, wherein the impregnation solution is a mixed suspension of rare earth nitrate and B4C powder; wherein the rare earth nitrate is Re(NO3)3·6H2O or Re(NO3)3·5H2O, and Re is a lanthanide element; the method for preparing the impregnation solution is as follows: the rare earth nitrate, B4C powder, dispersant and surface modifier are dissolved in a mixed solution of deionized water and ethanol to obtain the impregnation solution; the amount of dispersant added is 0.2-1.0% of the mass of B4C powder, the amount of modifier added is 2-5% of the mass of B4C powder, the molar ratio of rare earth nitrate to B4C powder is 2:1, and the volume ratio of deionized water to ethanol is 9:1; the concentration of rare earth nitrate in the impregnation solution is 0.36-2.64 mol / L, and the concentration of B4C powder is 0.18-1.32 mol / L; The biochar of the wood structure was impregnated in an impregnation solution and then dried twice to obtain biochar of the wood structure containing rare earth nitrates and B4C powder. Biochar containing rare earth nitrates and B4C powder from wood structures was subjected to boron / carbothermic reduction treatment to obtain carbon-based composite ceramics; wherein the boron / carbothermic reduction treatment conditions were: holding at 1800-2000℃ for 1-6 h under an argon atmosphere.

2. The method for preparing carbon-based composite ceramics according to claim 1, characterized in that, The initial drying temperature is 80–120℃.

3. The method for preparing carbon-based composite ceramics according to claim 1, characterized in that, The conditions for high-temperature carbonization treatment are: holding at 800–1000℃ for 2–6 hours under inert gas protection.

4. The method for preparing carbon-based composite ceramics according to claim 1, characterized in that, The dispersant is tetramethylammonium hydroxide or polyethyleneimine; the surface modifier is 3-aminopropyltriethoxysilane.

5. The method for preparing carbon-based composite ceramics according to claim 1, characterized in that, The particle size of B4C powder is 45–55 nm.

6. The method for preparing carbon-based composite ceramics according to claim 1, characterized in that, The impregnation conditions are vacuum impregnation for 4–8 hours; the secondary drying conditions are 40–60℃.

7. The method for preparing carbon-based composite ceramics according to any one of claims 1-6, characterized in that, The natural wood is one or more of the following: fir, poplar, pine, catalpa, fragrant wood, paulownia, and balsa wood.

8. A carbon-based composite ceramic prepared by the preparation method according to any one of claims 1-7, characterized in that, The composite ceramic has a porosity of 63%–82%, an electrical conductivity of 80.1–250.4 S / cm, and a thermal conductivity of 4.38–23.14 W·m. -1 ·K -1 The electromagnetic interference shielding effectiveness is 27–65 dB, and the bending strength is 6–38 MPa.

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