CN113645822B - Porous hollow graphitized carbon electromagnetic wave absorbing material and preparation method thereof - Google Patents
Porous hollow graphitized carbon electromagnetic wave absorbing material and preparation method thereof Download PDFInfo
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 72
- 229910052799 carbon Inorganic materials 0.000 title claims abstract description 64
- 239000011358 absorbing material Substances 0.000 title claims abstract description 33
- 238000002360 preparation method Methods 0.000 title claims abstract description 13
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims abstract description 61
- 238000000034 method Methods 0.000 claims abstract description 20
- 238000005520 cutting process Methods 0.000 claims abstract description 4
- 239000000126 substance Substances 0.000 claims abstract description 4
- 239000003575 carbonaceous material Substances 0.000 claims description 21
- 238000010438 heat treatment Methods 0.000 claims description 20
- 238000003756 stirring Methods 0.000 claims description 16
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 14
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 12
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 9
- 238000006243 chemical reaction Methods 0.000 claims description 8
- 238000002156 mixing Methods 0.000 claims description 8
- GHMLBKRAJCXXBS-UHFFFAOYSA-N resorcinol Chemical compound OC1=CC=CC(O)=C1 GHMLBKRAJCXXBS-UHFFFAOYSA-N 0.000 claims description 8
- 239000002245 particle Substances 0.000 claims description 7
- 239000002243 precursor Substances 0.000 claims description 7
- 239000000377 silicon dioxide Substances 0.000 claims description 7
- 238000000967 suction filtration Methods 0.000 claims description 7
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims description 4
- 229910004298 SiO 2 Inorganic materials 0.000 claims description 4
- 235000011114 ammonium hydroxide Nutrition 0.000 claims description 4
- 239000008367 deionised water Substances 0.000 claims description 4
- 229910021641 deionized water Inorganic materials 0.000 claims description 4
- 235000012239 silicon dioxide Nutrition 0.000 claims description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 4
- 238000003763 carbonization Methods 0.000 claims description 3
- 238000004140 cleaning Methods 0.000 claims description 3
- WSFSSNUMVMOOMR-NJFSPNSNSA-N methanone Chemical compound O=[14CH2] WSFSSNUMVMOOMR-NJFSPNSNSA-N 0.000 claims description 3
- 238000000926 separation method Methods 0.000 claims description 2
- 239000003960 organic solvent Substances 0.000 abstract description 2
- 231100000331 toxic Toxicity 0.000 abstract description 2
- 230000002588 toxic effect Effects 0.000 abstract description 2
- 238000010521 absorption reaction Methods 0.000 description 24
- 239000000463 material Substances 0.000 description 19
- 238000005530 etching Methods 0.000 description 17
- 239000011148 porous material Substances 0.000 description 17
- 238000012360 testing method Methods 0.000 description 9
- 230000000052 comparative effect Effects 0.000 description 6
- 238000011049 filling Methods 0.000 description 6
- 239000012188 paraffin wax Substances 0.000 description 5
- 229920000642 polymer Polymers 0.000 description 5
- 230000001105 regulatory effect Effects 0.000 description 5
- 238000004364 calculation method Methods 0.000 description 4
- 238000001035 drying Methods 0.000 description 4
- 229910021389 graphene Inorganic materials 0.000 description 4
- 239000007791 liquid phase Substances 0.000 description 4
- 229910021392 nanocarbon Inorganic materials 0.000 description 4
- 238000002310 reflectometry Methods 0.000 description 4
- 238000005303 weighing Methods 0.000 description 4
- WSFSSNUMVMOOMR-UHFFFAOYSA-N Formaldehyde Chemical compound O=C WSFSSNUMVMOOMR-UHFFFAOYSA-N 0.000 description 3
- 239000011248 coating agent Substances 0.000 description 3
- 238000000576 coating method Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 230000033228 biological regulation Effects 0.000 description 2
- 229960004424 carbon dioxide Drugs 0.000 description 2
- 238000010000 carbonizing Methods 0.000 description 2
- 230000001276 controlling effect Effects 0.000 description 2
- 235000019441 ethanol Nutrition 0.000 description 2
- 230000010287 polarization Effects 0.000 description 2
- 238000001179 sorption measurement Methods 0.000 description 2
- 239000002250 absorbent Substances 0.000 description 1
- 230000002745 absorbent Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 238000006555 catalytic reaction Methods 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 231100000481 chemical toxicant Toxicity 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000000945 filler Substances 0.000 description 1
- 238000001000 micrograph Methods 0.000 description 1
- 239000002057 nanoflower Substances 0.000 description 1
- 239000002086 nanomaterial Substances 0.000 description 1
- 239000002105 nanoparticle Substances 0.000 description 1
- 238000012856 packing Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000004729 solvothermal method Methods 0.000 description 1
- 230000007847 structural defect Effects 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
- 239000003440 toxic substance Substances 0.000 description 1
- 238000004627 transmission electron microscopy Methods 0.000 description 1
Classifications
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K9/00—Screening of apparatus or components against electric or magnetic fields
- H05K9/0073—Shielding materials
- H05K9/0081—Electromagnetic shielding materials, e.g. EMI, RFI shielding
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/20—Graphite
- C01B32/205—Preparation
Abstract
The electromagnetic wave absorbing material is in a regular sphere shape, the diameter of the sphere is 200-400 nm, the surface of the electromagnetic wave absorbing material is randomly distributed with nano holes with the size of 5-20 nm, and the electromagnetic wave absorbing material is etched by hydrogen peroxide on the surface of the hollow graphitized carbon through a chemical bond cutting means. The electromagnetic wave absorbing material can effectively absorb electromagnetic waves with wider frequency band width, does not use extremely toxic organic solvents in the preparation process, and has low cost and simple process.
Description
Technical Field
The invention relates to the technical field of electromagnetic wave absorbing materials, in particular to a porous hollow graphitized carbon electromagnetic wave absorbing material and a preparation method thereof.
Background
The electromagnetic technology is increasingly widely applied to the fields of modern military and industry, the demand for electromagnetic stealth materials is continuously increased, and graphene has high conductivity and ultralow density due to the special hexagonal carbon network structure and is widely focused in the field of electromagnetic stealth material research. However, the raw materials of the graphene are expensive, the application cost is high, the graphitized hollow carbon spheres are products obtained by high-temperature carbonization of the polymer, the graphitized hollow carbon spheres have electromagnetic loss performance similar to that of the graphene, and the graphene substitutes with low cost because of the hollow structure and relatively low density.
Heretofore, various graphitized carbon spheres have been successfully prepared and applied to the fields like energy storage, catalysis and the like, and patent CN 106861618A discloses a nitrogen-doped porous hollow carbon sphere carbon dioxide adsorption material, a preparation method and application thereof, wherein the porous hollow carbon sphere uses a solvothermal method, uses silica nanoflower as a template, and the synthesized porous carbon has higher adsorption rate, but the pore structure is difficult to regulate and control, so that the further improvement of the performance of the porous hollow carbon sphere is limited.
At present, the graphitized carbon spheres are synthesized by a main template method, the process is relatively mature, but the method for introducing the pore structure into the carbon material is still studied, and the method has two main difficulties for exploring: 1. the method of introducing the hole structure needs to be relatively mild, controllable and low in cost; 2. the original structure cannot be damaged greatly by the structure of the introduction hole. The proper controllable pore structure can balance the impedance matching and dielectric attenuation capability of the carbon material, enhance the electromagnetic wave absorption performance of the material, and meanwhile, the nanoparticle with the special structure can be applied to various other fields. Therefore, the preparation and development of the porous hollow graphitized carbon electromagnetic wave absorbing material with regular morphology and uniform size of the prepared product are very necessary.
Disclosure of Invention
In order to solve the technical problems, the invention provides the porous hollow graphitized carbon electromagnetic wave absorbing material and the preparation method thereof, and the electromagnetic wave absorbing material can effectively absorb electromagnetic waves with wider frequency band width, does not use extremely toxic organic solvents in the preparation process, and has low cost and simple process.
In order to achieve the technical purpose, the adopted technical scheme is as follows: the porous hollow graphitized carbon electromagnetic wave absorbing material is in a regular sphere shape, the diameter of the sphere is 200-400 nm, the surface of the electromagnetic wave absorbing material is randomly distributed with nano holes with the size of 5-20 nm, and the nano holes are etched on the surface of the hollow graphitized carbon by hydrogen peroxide through a chemical bond cutting means.
The preparation method of the porous hollow graphitized carbon electromagnetic wave absorbing material comprises the following steps:
step 1, preparing a polymer-coated template precursor by using a silica template method, converting the polymer-coated template precursor into a carbon material by heat treatment, and removing the silica template to obtain hollow graphitized carbon;
step 2, mixing the hollow graphitized carbon obtained in the step 1 with hydrogen peroxide according to the following ratio of 1: and 0.8-1.5, maintaining the common heating temperature for stirring for a certain time, and performing suction filtration and deionized water cleaning to obtain the porous hollow graphitized carbon electromagnetic wave absorbing material.
Further, the specific implementation method of the step 1 is as follows: 3-8 g of nano SiO with particle diameter of 200-300 nm is adopted 2 Respectively adding 1000-2000 ml of ethanol, 40-100 m of formaldehyde, 4-8 g of resorcinol and 50-100 ml of ammonia water as templates, uniformly stirring and reacting for 18-24h, centrifugally separating, carbonizing at a high temperature of 700-900 ℃, completely immersing a sample by using a sodium hydroxide solution with a concentration of 2mol/L, performing co-heat treatment at 80-100 ℃ for at least 8 hours, and etching and completely removing nano SiO 2 Hollow graphitized carbon is obtained.
Further, in the step 1, the diameter of the hollow graphitized carbon material is 200-300 nm.
Further, the mass fraction of hydrogen peroxide in the step 2 is 30wt%.
Further, the common heating temperature of the hydrogen peroxide and the hollow graphitized carbon in the step 2 is 60-90 ℃.
Further, the common heating time of the hydrogen peroxide and the hollow graphitized carbon in the step 2 is 1-3 hours.
The invention has the beneficial effects that: the porous hollow graphitized carbon electromagnetic wave absorbing material has the advantages that firstly, the method for introducing the pore structure into the carbon material is mild and controllable, the integrity of the original structure can be maintained while the nano-scale pore structure is introduced, and compared with the traditional microwave absorbent, the porous hollow graphitized carbon electromagnetic wave absorbing material has the characteristics of wide effective absorption bandwidth and high electromagnetic absorption intensity under the conditions of low filling ratio (10wt%) and low thickness (2 mm), and has better microwave absorption performance; the co-heating time is controlled to be 2-3 hours, wider electromagnetic waves can be absorbed, meanwhile, no extremely toxic chemical reagent is used in the production process, complex and expensive synthesis equipment is not needed in the preparation method, the process is simple, the cost is low, the yield can be improved by amplifying the reaction multiple, and the method can be used as a functional coating filler for production and application.
Drawings
FIG. 1 is a transmission electron microscope image of porous hollow graphitized carbon-0;
FIG. 2 is a transmission electron microscopy image of porous hollow graphitized carbon-3;
FIG. 3 is a graph of the specific surface area and pore distribution of porous hollow graphitized carbon;
FIG. 4 is a graph of electromagnetic parameters of porous hollow graphitized carbon;
FIG. 5 is a graph of reflection loss for porous hollow graphitized carbon-0;
FIG. 6 is a graph of reflection loss for porous hollow graphitized carbon-3;
FIG. 7 is a graph of reflection loss for porous hollow graphitized carbon-5.
Detailed Description
The invention is realized by the following technical scheme:
(1) In particular, the invention relates to a porous hollow graphitized carbon electromagnetic wave absorbing material which is in a regular sphere shape, the diameter of the sphere is 200-400 nm, and the surface of the electromagnetic wave absorbing material is randomly distributed with nano holes with the size of 5-20 nm. The hydrogen peroxide is used as a pore-forming agent, nano holes can be etched on the surface of graphitized carbon by a chemical bond cutting means, as shown in fig. 1 and 2, the edges of the hollow porous graphitized carbon-0 obtained in the comparative example 1 before etching are obvious, the structure is complete, the hollow porous graphitized carbon-3 etched by the hydrogen peroxide for a certain period of time can basically keep uniform spheres, the edges of the sample which is not treated by the hydrogen peroxide are lighter, a large number of white light spots appear on the surfaces of single sphere particles, the light spots are nano holes which are etched under the action of the hydrogen peroxide, the existence of the nano holes does not influence the spherical structure, and the particles can still keep the spheres basically without collapsing.
(2) In addition, the etching of hydrogen peroxide further improves the specific surface area of the hollow porous graphitized carbon, so that the density of the material is further reduced. FIG. 3 is a graph showing BET specific surface area and average pore diameter of the hollow porous graphitized carbon obtained in examples 2 and 3 of comparative example 1. According to the image, after the hydrogen peroxide is treated, the specific surface area of the material is increased, the average pore diameter is suddenly increased from 2nm to 8nm, and the specific surface area and the average pore diameter are further improved along with the extension of the treatment time.
(3) The electromagnetic parameters of the material are regulated and controlled by introducing the pore structure, so that the impedance matching can be effectively regulated, and the dielectric attenuation capability can be enhanced to a certain extent. Fig. 4 shows electromagnetic parameter patterns of the hollow porous graphitized carbon obtained in examples 2 and 3 of comparative example 1. Wherein the filling ratio of the sample to the paraffin wax is 1:9 in the test, and the corresponding sample filling ratio is 10wt%. According to the image display, after hydrogen peroxide treatment, the dielectric real part and the dielectric imaginary part of the material are reduced, and the dielectric real part and the dielectric imaginary part are further reduced along with the extension of the treatment time, which symbolizes the optimal regulation and control of the impedance matching performance of the material.
(4) The porous hollow graphitized carbon electromagnetic wave absorbing material is prepared by using a silicon dioxide template method to prepare a precursor, coating a polymer on the silicon dioxide template to prepare the precursor, converting the precursor into a carbon material by heat treatment, removing the template to obtain hollow graphitized carbon spheres, forming holes on the surfaces of the hollow carbon spheres by utilizing the etching action of hydrogen peroxide on the carbon material, controlling the etching time to control the degree of hole forming, preparing the porous hollow graphitized carbon, reducing the density of the carbon material by introducing a hole structure, optimizing impedance matching, and improving the electromagnetic absorption performance.
(5) According to the porous hollow graphitized carbon electromagnetic wave absorbing material, the nano carbon is synthesized by a conventional template method, the effect of hydrogen peroxide and hollow graphitized carbon is utilized to introduce a pore structure, the reaction condition and the degree are mild and controllable, the introduction of the pore structure not only reduces the density of the material, but also regulates and controls the impedance matching characteristic of the material, the electromagnetic absorption performance of the material is optimized, the effective absorption bandwidth of the synthesized hollow graphitized carbon material-3 can reach 6.3GHz when the thickness of a sample is 2mm, the electromagnetic performance of the material mainly derives from dielectric loss of the carbon material and dipole polarization caused by structural defects generated by pore-forming, the shape of the material can be regulated and controlled by regulating and controlling the etching time, the electromagnetic parameters of the material can be regulated and controlled, the purpose of attenuating electromagnetic waves is achieved, the low density and the environmental friendliness of the porous material can be ensured, the pollution to the environment in the production and application process is reduced, and the application of the porous material to the functional coating is possible.
(6) The invention relates to a porous hollow nano carbon electromagnetic wave absorbing material and a preparation method thereof, comprising the following steps:
step 1, preparing a nano carbon material by using a template etching method: 3-8 g of nano SiO with particle diameter of 200-300 nm is added into a container 2 As a template, the particle size of the synthesized nano carbon can be controlled by using the template, 1000-2000 ml of ethanol, 40-100 m of formaldehyde, 4-8 g of resorcinol and 50-100 ml of ammonia water are respectively added, the uniform stirring reaction is carried out for 18-24h, centrifugal separation is carried out, the sample is completely immersed by using 2mol/L sodium hydroxide solution after high-temperature carbonization at 700-900 ℃, and the nano SiO is completely removed by etching and complete removal under the condition of 80-100 ℃ for at least 8 hours 2 Obtaining hollow graphitized carbon;
different polymer components can be selected in the range, and the etching effect of the prepared hollow graphitized carbon and hydrogen peroxide material is consistent and does not fluctuate greatly.
And 2, mixing the hollow graphitized carbon material in the step 1 with 500ml of hydrogen peroxide, maintaining a certain temperature, continuously stirring for a certain time, performing suction filtration, and cleaning with deionized water to obtain the porous hollow graphitized carbon electromagnetic wave absorbing material.
In the step 1, the diameter of the hollow graphitized carbon material is 200-300 nm.
The mass fraction of the hydrogen peroxide in the step 2 is 30wt%.
In the step 2, the co-heating temperature of the hydrogen peroxide and the hollow graphitized carbon is 60-90 ℃, the etching effect of the hydrogen peroxide on the carbon material is consistent within the temperature range, and the temperature is fixed at 80 ℃ in the embodiment as the co-heating temperature. .
And (2) the total heating time of the hydrogen peroxide and the hollow graphitized carbon in the step (2) is 2-3 hours.
Embodiments of the present invention are further described below with reference to the accompanying drawings.
Example 1
The porous hollow graphitized carbon electromagnetic wave absorbing material and the preparation method thereof comprise the following steps:
step 1, preparing a hollow graphitized carbon material by using a template etching method: 5g of SiO with the particle size of 200-300 nm is added into a container 2 And 1000ml of absolute ethyl alcohol, adding 40ml of formaldehyde and 4g of resorcinol after stirring and dispersing uniformly, then adding 50ml of ammonia water to adjust the solution to be alkaline, stirring at a constant speed for reacting for 18-24 hours, centrifuging, carbonizing at a high temperature of 700 ℃ and then carrying out heat treatment at 90 ℃ for at least 8 hours by using 2mol/L sodium hydroxide solution to obtain nano SiO 2 Completely removed to obtain the hollow graphitized carbon material.
And 2, weighing 500mg of the hollow graphitized carbon material obtained in the step 1, adding 400-750 ml of hydrogen peroxide solution with the mass fraction of 30wt%, mixing and stirring until the hollow graphitized carbon powder is uniformly dispersed in a liquid phase, continuously stirring, heating the reaction environment to 80 ℃, maintaining the temperature for 1h, and extracting and drying the obtained product by a suction filtration mode to obtain the porous hollow graphitized carbon material-1.
The sample is mixed with paraffin wax in the proportion of 1:9 and pressed into a sample ring with the inner diameter of 3.04mm and the outer diameter of 7.00mm, a vector network analyzer is used for carrying out electromagnetic parameter test of 2-18 GHz, the reflectivity of the sample is obtained through test and calculation, and the effective absorption bandwidth is 4.2GHz when the thickness of the sample is 2 mm.
Example 2
Step 1, same as in example 1.
And 2, weighing 500mg of the hollow graphitized carbon material obtained in the step 1, adding into 500ml of 30% hydrogen peroxide solution, mixing and stirring until the hollow graphitized carbon powder is uniformly dispersed in a liquid phase, continuously stirring, heating the reaction environment to 80 ℃, maintaining the temperature for 3 hours, extracting and drying the obtained product by a suction filtration mode, and obtaining the porous hollow graphitized carbon material-3.
The sample is mixed with paraffin wax in the proportion of 1:9 and pressed into a sample ring with the inner diameter of 3.04mm and the outer diameter of 7.00mm, a vector network analyzer is used for carrying out electromagnetic parameter test of 2-18 GHz, the reflectivity of the sample is obtained through test and calculation, and the result is shown in figure 6, and the effective absorption bandwidth is 6.3GHz when the thickness of the sample is 2 mm.
Example 3
Step 1, same as in example 1.
And 2, weighing 500mg of the hollow graphitized carbon material obtained in the step 1, adding into 500ml of 30% hydrogen peroxide solution, mixing and stirring until the hollow graphitized carbon powder is uniformly dispersed in a liquid phase, continuously stirring, heating the reaction environment to 80 ℃, maintaining the temperature for 5 hours, extracting and drying the obtained product by a suction filtration mode, and obtaining the porous hollow graphitized carbon material-5.
The sample is mixed with paraffin wax in the proportion of 1:9 and pressed into a sample ring with the inner diameter of 3.04mm and the outer diameter of 7.00mm, a vector network analyzer is used for carrying out electromagnetic parameter test of 2-18 GHz, the reflectivity of the sample is obtained through test and calculation, and the result is shown in figure 7, and the effective absorption bandwidth is 1.0GHz when the thickness of the sample is 2 mm.
Comparative example 1
Step 1, same as in example 1.
And 2, weighing 500mg of the hollow graphitized carbon material obtained in the step 1, adding 500ml of deionized water, mixing and stirring until the hollow graphitized carbon powder is uniformly dispersed in a liquid phase, continuously stirring, heating the reaction environment to 80 ℃, maintaining the temperature for 3 hours, extracting and drying the obtained product by a suction filtration mode, and thus obtaining the porous hollow graphitized carbon material-0.
The sample is mixed with paraffin wax in the proportion of 1:9 and pressed into a sample ring with the inner diameter of 3.04mm and the outer diameter of 7.00mm, a vector network analyzer is used for carrying out electromagnetic parameter test of 2-18 GHz, the reflectivity of the sample is obtained through test and calculation, and the effective absorption bandwidth is 3.9GHz when the thickness of the sample is 2mm as shown in a result figure 7.
Through the regulation and control of electromagnetic parameters, the performance of the sample is improved to a certain extent. Fig. 5, 6 and 7 are reflection loss patterns of the samples obtained in comparative example 1, examples 2 and 3, respectively. As can be seen from fig. 5, the hollow porous graphitized carbon-0 has a certain performance at a packing ratio of 10wt%, but its effective absorption bandwidth is narrow, and at a sample thickness of 2mm, the effective absorption bandwidth is 3.9GHz.
Under the condition that the filling ratio is 10wt%, the effective absorption bandwidth of the hollow porous graphitized carbon-1 can be increased to 4.2GHz when the thickness of a sample is 2mm, the absorption frequency range covers the frequency range of 13.8-18 GHz, and the performance is slightly better than that of a sample which is not treated by hydrogen peroxide.
In all examples and comparative examples, the electromagnetic absorption performance of the porous hollow graphitized carbon-3 corresponding to fig. 6 is optimal, the effective absorption bandwidth can reach 6.3GHz at a sample thickness of 2mm, the absorption frequency range covers the frequency range of 11.7 to 18GHz, and the minimum reflection loss value can be lower than-30 dB. Under the condition that the filling ratio is 10wt%, the hollow porous graphitized carbon-3 has relatively better performance than a sample which is not treated by hydrogen peroxide, because the introduction of the pore structure improves impedance matching on the basis of not damaging the original spherical structure, simultaneously enhances polarization and effectively improves the electromagnetic wave absorption performance of the material.
The hollow porous graphitized carbon-5 has reduced performance compared with a sample with the treatment time of 3 hours under the condition that the filling ratio is 10wt%, because the hydrogen peroxide etching treatment time is too long, the spherical structure is destroyed, the electromagnetic absorption performance is reduced, and the effective absorption bandwidth of the sample is 1GHz under the condition that the thickness of the sample is 2 mm.
Therefore, the electromagnetic absorption frequency bandwidth of the hollow graphitized carbon can be effectively widened by introducing the pore structure, but proper etching degree is required to be controlled, the original nano material structure is damaged by too deep etching process, the performance is reduced, the electromagnetic wave material with the electromagnetic wave absorption function can be prepared within 0-5 hours of etching, the optimal etching time period for exploration is 2-3 hours, the optimal time is 3 hours, and the pore structure can be introduced while the structural integrity is maintained within the etching range, so that the electromagnetic absorption bandwidth of the material is effectively widened.
Claims (5)
1. A porous hollow graphitized carbon electromagnetic wave absorbing material, characterized in that: the electromagnetic wave absorbing material is in a regular sphere shape, the diameter of the sphere is 200-400 nm, nanopores with the size of 5-20 nm are randomly distributed on the surface of the electromagnetic wave absorbing material, the nanopores are etched on the surface of the hollow graphitized carbon by hydrogen peroxide through a chemical bond cutting means, and the preparation method of the porous hollow graphitized carbon electromagnetic wave absorbing material comprises the following steps:
step 1, preparing a precursor by using a silicon dioxide template method, converting the precursor into a carbon material by heat treatment, and removing the silicon dioxide template to obtain hollow graphitized carbon;
step 2, mixing the hollow graphitized carbon obtained in the step 1 with hydrogen peroxide according to the following ratio of 1: mixing 0.8-1.5, maintaining the common heating temperature and continuously stirring for a certain time, and performing suction filtration and deionized water cleaning to obtain the porous hollow graphitized carbon electromagnetic wave absorbing material;
the specific implementation method of the step 1 is as follows: 3-8 g of nano SiO 2 with the particle diameter of 200-300 nm is adopted as a template, 1000-2000 ml of ethanol, 40-100 m of formaldehyde, 4-8 g of resorcinol and 50-100 ml of ammonia water are respectively added, the uniform stirring reaction is carried out for 18-24 hours, centrifugal separation is carried out, after high-temperature carbonization at 700-900 ℃, a sample is completely immersed by using a sodium hydroxide solution with the concentration of 2mol/L, and the nano SiO 2 is etched and completely removed by co-heat treatment at 80-100 ℃ for at least 8 hours, so that the hollow graphitized carbon is obtained.
2. A porous hollow graphitized carbon electromagnetic wave absorbing material as set forth in claim 1, wherein: in the step 1, the diameter of the hollow graphitized carbon material is 200-300 nm.
3. A porous hollow graphitized carbon electromagnetic wave absorbing material as set forth in claim 1, wherein: the mass fraction of the hydrogen peroxide in the step 2 is 30wt%.
4. A porous hollow graphitized carbon electromagnetic wave absorbing material as set forth in claim 1, wherein: and in the step 2, the common heating temperature of the hydrogen peroxide and the hollow graphitized carbon is 60-90 ℃.
5. A porous hollow graphitized carbon electromagnetic wave absorbing material as set forth in claim 1, wherein: and (2) the common heating time of the hydrogen peroxide and the hollow graphitized carbon in the step (2) is 1-3 h.
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