CN111683512A - Microwave synthesis coal-based carbon/ferromagnetic metal composite electromagnetic absorption material and method - Google Patents
Microwave synthesis coal-based carbon/ferromagnetic metal composite electromagnetic absorption material and method Download PDFInfo
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- CN111683512A CN111683512A CN202010535921.3A CN202010535921A CN111683512A CN 111683512 A CN111683512 A CN 111683512A CN 202010535921 A CN202010535921 A CN 202010535921A CN 111683512 A CN111683512 A CN 111683512A
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Abstract
The invention relates to a microwave synthetic coal-based carbon/ferromagnetic metal composite electromagnetic absorption material and a method thereof. The coal-based carbon/ferromagnetic metal composite material is formed by in-situ reaction of raw coal and chlorine salt, sulfate or nitrate of at least one metal of transition group metals of iron, cobalt and nickel under the action of microwaves, and comprises the following steps: weighing raw coal and transition metal salt according to a proportion, adding potassium hydroxide, uniformly mixing in deionized water, heating the uniformly mixed raw materials to 700 ℃ by using a microwave reaction device, cooling, washing, filtering and drying to obtain the coal-based carbon/ferromagnetic metal composite electromagnetic absorption material. The method utilizes the fact that coal has certain dielectric property and can fully respond to microwaves to synthesize the coal-based carbon/ferromagnetic metal composite electromagnetic absorption material in situ, is simple and short in synthesis time, realizes in-situ loading of ferromagnetic metal while carbonizing coal, enables the prepared multi-element composite material to have good electromagnetic absorption property, realizes high added value utilization of coal, and has wide application prospect.
Description
Technical Field
The invention belongs to the technical field of coal-based carbon composite electromagnetic absorption materials, and particularly relates to a coal-based carbon/ferromagnetic metal composite electromagnetic absorption material synthesized in situ by using coal as a carbon source through microwaves and a preparation method thereof.
Technical Field
Coal is a natural resource which people rely on for a long time to live, and is widely applied to the fields of power generation, coking, coal chemical industry and the like. The traditional coal has a single utilization mode, and wastes and waste residues generated in the conversion processes of combustion, gasification and the like easily cause environmental pollution. Therefore, a new clean and efficient utilization method of coal is urgently needed. Currently, many scholars have studied various coal-to-carbon technologies, and common techniques include: preparing porous activated carbon at high temperature by using an alkali activation method; the catalyst is used to prepare coal-based carbon nano-materials such as carbon nano-tubes, carbon nano-microspheres and the like. Chinese patent CN107376836A prepares high-performance activated carbon from coal particles and ferrocene at high temperature, and the synthesis temperature is 800-1200 ℃. The Chinese patent CN110562960A uses a catalyst to prepare the coal-based carbon nanotube under the nitrogen atmosphere, and the synthesis process is complex. Although the preparation of the coal-based carbon material improves the additional value of coal, the mass production is difficult to realize due to complex process, high synthesis temperature, long process period and the like.
In recent years, with the rapid development of science and technology, large-scale equipment and electronic products generally radiate electromagnetic waves within a certain range, which damages human health. The electromagnetic absorption material converts incident waves into heat inside the material through various loss mechanisms, and microwave pollution can be effectively reduced. The ferromagnetic metal has higher saturation magnetization intensity and is widely used in the preparation process of the wave-absorbing material, the ceramic whisker/ferromagnetic metal composite wave-absorbing material is obtained by carrying out heat treatment on the ceramic metal with the ferromagnetic metal coating plated on the surface under the condition of hydrogen or argon in Chinese patent CN101546610A, and the wave-absorbing material is obtained by sintering porous carbon spheres and ferromagnetic metal ion salts in nitrogen atmosphere in Chinese patent CN 105896099A. Moreover, although the electromagnetic absorbing material has achieved a certain success, the low frequency microwaves have a strong diffraction power and are still difficult to handle.
Disclosure of Invention
The invention provides a coal-based carbon/ferromagnetic metal composite electromagnetic absorption material synthesized by microwave and a method thereof, aiming at realizing high added value utilization of coal and treating the problem of low-frequency microwave pollution.
The invention adopts the following technical scheme:
a microwave synthesis coal-based carbon/ferromagnetic metal composite electromagnetic absorption material is formed by in-situ reaction of raw coal and chlorine salt or sulfate or nitrate of at least one metal of transition group metals of iron, cobalt and nickel under the action of microwaves; the magnetic medium of the coal-based carbon/ferromagnetic metal composite material comprises a metal oxide formed by chloride salt or sulfate or nitrate of the transition group metal iron, cobalt and nickel or a metal alloy coexistence form of the metal oxide and at least two metals of the transition group metal iron, cobalt and nickel.
Preferably, the preparation method of the microwave synthetic coal-based carbon/ferromagnetic metal composite electromagnetic absorption material comprises the following steps:
s1, crushing and screening raw coal to a particle size of 2-5mm in dry air;
s2, weighing raw coal, transition metal salt and potassium hydroxide according to a proportion, adding deionized water, and stirring and mixing the raw coal, the transition metal salt and the potassium hydroxide uniformly to obtain a mixed raw material; the transition metal salt is any one of chloride, sulfate or nitrate of at least one of transition metals of iron, cobalt and nickel;
s3, placing the mixed raw materials in a microwave reaction device, reacting to 700 ℃, cooling to room temperature after the reaction is finished, and taking out to obtain a product after the reaction;
and S4, washing the product after the filtering reaction with deionized water, and drying to obtain the coal-based carbon/ferromagnetic metal composite electromagnetic absorption material.
Preferably, the raw coal is unlimited kind of coal having a fixed carbon content of 75 wt% or more after washing.
Preferably, in step S2, a mixture of raw coal and a transition metal salt is weighed, and when the mass of the raw coal is X, the mass of the transition metal salt is (1-X), potassium hydroxide is weighed, and the mass of the potassium hydroxide is 2X; wherein X is more than 0 and less than 1.
Preferably, in the step S2, the volume of the deionized water is 10-25ml per 10g of the mixture of the raw coal and the transition metal salt.
Preferably, in step S3, the frequency of the microwave reaction device is 915MHz or 2.45 GHz.
Preferably, in step S3, the microwave reaction device heats the uniformly mixed raw materials with a fixed power to a temperature of 700 ℃, and closes the microwave reaction device to stop heating after the uniformly mixed raw materials reach the reaction temperature. .
Preferably, in step S3, the uniformly mixed raw materials are contacted with air in a microwave reaction device for reaction, and after the reaction is completed, the raw materials are cooled in the air.
The invention has the beneficial effects that:
1) according to statistics, the coal reserves in China are huge, the third place in the world is that the traditional coal utilization mode is low in yield value and easy to damage the environment. The method utilizes the characteristics of the raw materials of the coal, which are rich in the carbon source, so that the coal can be fully utilized, no pollutant is generated, and the high added value utilization of the coal is realized.
2) The invention adopts the microwave in-situ synthesis technology, utilizes the coupling heat effect generated by the material absorbing the microwave and has the advantages of homogeneity and rapidness. In the synthesis process, the microwave generates heat inside the material, so that the heat is expanded from inside to outside, the material is uniformly heated, the microwave replaces the heat to be transferred through a medium, the energy is effectively prevented from being dissipated in the transfer process, and a better heating effect can be achieved. The coal-based carbon/ferromagnetic metal composite electromagnetic absorption material is synthesized in situ by using a microwave reaction device with the microwave frequency range of 915MHz and 2.45GHz, the traditional composite process is simplified, the raw materials are naturally cooled after being heated and reacted to the required temperature, heat preservation is not needed, the synthesis time is effectively shortened, the synthesis cost is reduced, and the purpose of industrial popularization is facilitated; the microwave frequency ranges of 915MHz and 2.45GHz are also used in civil microwave devices, so that the application range of the method is further expanded;
3) because microwave synthesis has selectivity, heat with different degrees can be generated according to different dielectric losses of materials, coal is used as a carbon source, the coal has certain dielectric property and can fully respond to microwaves, and the prepared composite material has a rough surface with a latticed pore structure and a larger specific surface area due to the homogeneity of coal heating.
4) The electromagnetic absorption material mainly has two loss mechanisms, namely dielectric loss and magnetic loss; the transition metal iron, cobalt and nickel have ferromagnetism, under the action of microwave, the reducing gas released in the carbonization process of coal can make the salt compounds of iron, cobalt and nickel form metal oxides, and when the salt compounds of various ferromagnetic metals exist simultaneously, the metal alloys of the metals in the various ferromagnetic metals and the metal oxides can coexist in two forms. The metal oxides of iron, cobalt and nickel and the metal alloy among the metal oxides can be used as a magnetic medium of the composite material, so that the magnetic loss of the composite material is increased, and the electromagnetic absorption performance is enhanced.
5) The potassium hydroxide used in the method plays a role in alkali activation and catalysis in a reaction system, and the deionized water dissolves the potassium hydroxide and the transition metal salt, so that the potassium hydroxide and the transition metal salt are fully and uniformly mixed with the raw coal to form a bonded mixture reaction system; the potassium hydroxide is dissolved in the deionized water to release heat, partial redundant deionized water can be evaporated, so that a mixture reaction system is not excessively humid, and the microwave heating accelerates the reaction time, so that the mixture reaction system using the method does not need an additional drying step, the raw materials can be directly subjected to subsequent experimental operation after being mixed, and the method is efficient and safe.
Drawings
Fig. 1 is an SEM image of the coal-based carbon/ferromagnetic metal composite electromagnetic absorption material prepared by the present invention: the surface of the coal-based carbon has abundant micron-sized pores, and most of metal particles are embedded in the pores.
FIG. 2 is an XRD pattern of the coal-based carbon/ferromagnetic metal composite electromagnetic absorption material prepared by examples 1, 2 and 3 of the present invention; and comparative example 1 XRD patterns of the coal-based carbon/ferromagnetic metal composite synthesized in a nitrogen atmosphere at 700 deg.c in a tube furnace using a conventional synthesis method, in which the horizontal axis represents diffraction angle and the vertical axis represents intensity. As can be seen from the figure: the coal-based carbon/ferromagnetic metal composite material synthesized in situ by microwave has more obvious characteristic peak of carbon at 15-25 degrees, which shows that the carbonization effect is better.
FIGS. 3, 4 and 5 are graphs of reflection loss measured at 2-18GHz using an AV3672B-S vector network analyzer in a 1:1 mass ratio of the coal-based carbon/ferromagnetic metal composite electromagnetic absorbing material prepared using anthracite and metal chloride in different proportions in examples 1, 2 and 3, respectively, according to the present invention, and a molten paraffin, wherein the horizontal axis represents frequency and the vertical axis represents reflection loss.
FIG. 6 is a graph showing a comparison of reflection loss of comparative example 1, in which the horizontal axis represents frequency and the vertical axis represents reflection loss, which was synthesized in a tube furnace by a conventional synthesis method at 800 ℃ in a nitrogen atmosphere, and a molten paraffin were mixed at a mass ratio of 1:1 and measured at 218GHz using an AV3672B-S vector network analyzer.
Detailed Description
The technical scheme of the invention is more specifically explained by combining the following embodiments and comparative examples:
example 1:
weighing 10g of anthracite, analytically pure nickel chloride hexahydrate and analytically pure ferric chloride hexahydrate in a mass ratio of 10:7:3, and weighing potassium hydroxide by taking the anthracite and potassium hydroxide in a mass ratio of 1:2 as a standard theoretical formula; under the condition of air drying, crushing and screening anthracite to 2-5mm of particle size, and uniformly stirring and mixing the processed anthracite, analytically pure nickel chloride hexahydrate, analytically pure ferric chloride hexahydrate and potassium hydroxide in 15ml of deionized water to obtain a mixed raw material; heating the mixed raw materials to 700 ℃ by using a WY3L type microwave reactor (actual power of 2700W) with the frequency of 915MHz, cooling to room temperature and taking out; washing the product after the filtering reaction with deionized water, and drying to obtain the coal-based carbon/ferromagnetic metal composite electromagnetic absorption material.
In the experiment, the deionized water is used for dissolving the potassium hydroxide, the nickel chloride hexahydrate and the ferric chloride hexahydrate, so that the potassium hydroxide, the nickel chloride hexahydrate and the ferric chloride hexahydrate are fully and uniformly mixed with the raw coal to form a bonded mixture reaction system; the potassium hydroxide is dissolved in the deionized water to release heat, redundant deionized water is evaporated, a reaction system of the mixture is not too wet, and the raw materials can be directly subjected to subsequent experimental operation after being mixed.
And (3) performance detection results: fig. 3 shows the reflection loss in the range of 2 to 18GHz measured in this example as a coal-based carbon/ferromagnetic metal composite electromagnetic absorber material paraffin wax 1:1 (mass ratio). From the figure, it can be seen that: the prepared coal-based carbon/ferromagnetic metal composite electromagnetic absorption material has the minimum reflection loss lower than-10 dB (the absorption rate is more than 90%) in different thicknesses, and has the maximum effective absorption bandwidth of 3.34GHz and the minimum reflection loss of-43.36 dB in 5.20 GHz.
Example 2:
weighing 10g of anthracite, analytically pure nickel chloride hexahydrate and analytically pure ferric chloride hexahydrate in a mass ratio of 10:5:5, and weighing potassium hydroxide by taking the anthracite and potassium hydroxide in a mass ratio of 1:2 as a standard theoretical formula; under the condition of air drying, crushing and screening anthracite to 2-5mm of particle size, and uniformly stirring and mixing the processed anthracite, analytically pure nickel chloride hexahydrate, analytically pure ferric chloride hexahydrate and potassium hydroxide in 15ml of deionized water to obtain a mixed raw material; heating the mixed raw materials to 700 ℃ by using a WY3L type microwave reactor (actual power of 2700W) with the frequency of 915MHz, cooling to room temperature and taking out; washing the product after the filtering reaction with deionized water, and drying to obtain the coal-based carbon/ferromagnetic metal composite electromagnetic absorption material.
And (3) performance detection results: fig. 4 shows the reflection loss in the range of 2 to 18GHz measured in this example with a coal-based carbon/ferromagnetic metal composite electromagnetic absorber material paraffin wax of 1:1 (mass ratio). From the figure, it can be seen that: the prepared coal-based carbon/ferromagnetic metal composite electromagnetic absorption material has the minimum reflection loss lower than-10 dB (the absorption rate is larger than 90%) in different thicknesses, has the maximum effective absorption bandwidth of 3.03GHz, has the reflection loss value lower than-20 dB in the thickness range of 3-5mm, and has the minimum reflection loss of-51.66 dB at 5.52 GHz.
Example 3:
weighing 10g of anthracite, analytically pure nickel chloride hexahydrate and analytically pure ferric chloride hexahydrate in a mass ratio of 10:3:7, and weighing potassium hydroxide by taking the anthracite and potassium hydroxide in a mass ratio of 1:2 as a standard theoretical formula; under the condition of air drying, crushing and screening anthracite to 2-5mm of particle size, and uniformly stirring and mixing the processed anthracite, analytically pure nickel chloride hexahydrate, analytically pure ferric chloride hexahydrate and potassium hydroxide in 15ml of deionized water to obtain a mixed raw material; heating the mixed raw materials to 700 ℃ by using a WY3L type microwave reactor (actual power of 2700W) with the frequency of 915MHz, cooling to room temperature and taking out; washing the product after the filtering reaction with deionized water, and drying to obtain the coal-based carbon/ferromagnetic metal composite electromagnetic absorption material.
And (3) performance detection results: fig. 5 shows the reflection loss in the range of 2 to 18GHz measured in this example with a coal-based carbon/ferromagnetic metal composite electromagnetic absorber material paraffin wax of 1:1 (mass ratio). From the figure, it can be seen that: the prepared coal-based carbon/ferromagnetic metal composite electromagnetic absorption material has the minimum reflection loss lower than-10 dB (the absorption rate is more than 90%) in different thicknesses, and has the maximum effective absorption bandwidth of 2.89GHz and the minimum reflection loss of-40.10 dB at 5.68 GHz.
Comparative example 1:
weighing 10g of anthracite and analytically pure nickel chloride hexahydrate in a mass ratio of 1:1, and weighing potassium hydroxide by taking the anthracite and potassium hydroxide in a mass ratio of 1:2 as a standard theoretical formula; under the condition of air drying, crushing and screening anthracite to 2-5mm of particle size, uniformly stirring and mixing the processed anthracite, analytically pure nickel chloride hexahydrate, analytically pure ferric chloride hexahydrate and potassium hydroxide in 15ml deionized water, and drying in a vacuum oven at 100 ℃ for 24 hours to obtain a mixed raw material; and (3) heating the mixed raw materials to 550 ℃ at the speed of 5 ℃/min by using a tubular furnace in a nitrogen atmosphere, preserving heat for 2h, heating to 800 ℃ at the speed of 2 ℃/min, preserving heat for 2h, cooling to room temperature, and taking out. Washing the reaction product with deionized water, and drying to obtain the coal-based carbon/nickel composite electromagnetic absorption material.
In the above experiment, the effect of potassium hydroxide was the same as in examples 1, 2 and 3; in order to obtain a proper carbonized structure by using a conventional method, the final reaction temperature needs to be 800 ℃; because the heat preservation time of the tube furnace is long, the mixed reactants need to be dried in advance for the safety and the sufficient reaction of the system, and then the subsequent test operation is carried out.
And (3) performance detection results: fig. 6 shows the reflection loss in 2 to 18GHz in the present comparative example measured by a coal-based carbon/nickel composite electromagnetic absorbing material paraffin wax 1:1 (mass ratio). From the figure, it can be seen that: the coal-based carbon/nickel composite electromagnetic absorption material prepared by the comparative example has the minimum reflection loss lower than-10 dB (the absorption rate is more than 90%) in different thicknesses, has the maximum effective absorption bandwidth of 3.53GHz, and has the minimum reflection loss of-42.49 dB at 13 GHz and 68 GHz.
The microwaves in the range of 2-18GHz are divided into a plurality of wave bands according to the frequencies, and as can be seen from the analysis of the experimental results of the examples 1, 2, 3 and 1, the coal-based carbon/ferromagnetic metal composite absorbing material prepared in the examples of the present application has good microwave absorbing performance in the C-band (4-8GHz), and the absorbing frequency is far lower than the Ku-band (12-18GHz) where the best microwave absorbing performance of the coal-based carbon/nickel composite electromagnetic absorbing material prepared in the comparative examples is located, so that the invention has good absorbing capability for low-frequency microwaves.
The above embodiments are only used to illustrate the technical solutions of the present invention, and do not limit the present invention; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those skilled in the art that: any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (8)
1. A coal-based carbon/ferromagnetic metal composite electromagnetic absorption material is characterized in that: the coal-based carbon/ferromagnetic metal composite material is formed by in-situ reaction of raw coal and any one of chloride, sulfate or nitrate of at least one of transition group metals of iron, cobalt and nickel under the action of microwaves; the magnetic medium of the coal-based carbon/ferromagnetic metal composite material comprises a metal oxide formed by chloride, sulfate or nitrate of the transition group metal iron, cobalt and nickel or a metal alloy coexistence form of the metal oxide and at least two metals of the transition group metal iron, cobalt and nickel.
2. The preparation method of the coal-based carbon/ferromagnetic metal composite electromagnetic absorption material according to claim 1, characterized by comprising the following steps:
s1, crushing and screening raw coal to a particle size of 2-5mm in dry air;
s2, weighing raw coal, transition metal salt and potassium hydroxide according to a proportion, adding deionized water, and stirring and mixing the raw coal, the transition metal salt and the potassium hydroxide uniformly to obtain a mixed raw material; the transition metal salt is any one of chloride, sulfate or nitrate of at least one of transition metals of iron, cobalt and nickel;
s3, placing the mixed raw materials in a microwave reaction device, reacting to 700 ℃, cooling to room temperature after the reaction is finished, and taking out to obtain a product after the reaction;
and S4, washing the product after the filtering reaction with deionized water, and drying to obtain the coal-based carbon/ferromagnetic metal composite electromagnetic absorption material.
3. The method for preparing the coal-based carbon/ferromagnetic metal composite electromagnetic absorption material as claimed in claim 2, wherein: the raw coal is coal of unlimited types with fixed carbon content of more than 75 wt% after washing and selecting.
4. The method for preparing the coal-based carbon/ferromagnetic metal composite material synthesized by the microwave by using the coal as the carbon source according to claim 2, wherein the method comprises the following steps: in the step S2, weighing a mixture of raw coal and transition metal salt, wherein if the mass of the raw coal is X, the mass of the transition metal salt is (1-X), and weighing potassium hydroxide, the mass of the potassium hydroxide is 2X; wherein X is more than 0 and less than 1.
5. The method for preparing the coal-based carbon/ferromagnetic metal composite material synthesized by the microwave by using the coal as the carbon source according to claim 4, wherein the method comprises the following steps: in the step S2, the volume of the deionized water is 10-25ml per 10g of the mixture of the raw coal and the transition metal salt.
6. The method for preparing the coal-based carbon/ferromagnetic metal composite electromagnetic absorption material as claimed in claim 2, wherein: in the step S3, the frequency of the microwave reaction device is 915MHz or 2.45 GHz.
7. The preparation method of the coal-based carbon/ferromagnetic metal composite electromagnetic absorption material according to claim 2, characterized by comprising the following steps: in the step S3, the microwave reaction device heats the uniformly mixed raw materials with a fixed power to a temperature of 700 ℃, and closes the microwave reaction device to stop heating after the uniformly mixed raw materials reach the reaction temperature.
8. The preparation method of the coal-based carbon/ferromagnetic metal composite electromagnetic absorption material according to claim 2, characterized by comprising the following steps: in the step S3, the uniformly mixed raw materials are contacted with air in a microwave reaction device for reaction, and after the reaction is completed, the raw materials are cooled in the air.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113621345A (en) * | 2021-08-23 | 2021-11-09 | 安徽理工大学 | Method for preparing electromagnetic wave absorbing material |
| CN113747777A (en) * | 2021-09-08 | 2021-12-03 | 济南市中恒光机电技术中心 | Electromagnetic wave shielding material |
| CN114613967A (en) * | 2022-03-24 | 2022-06-10 | 大连理工大学 | FeS @ C composite material prepared rapidly by microwave method, and method and application thereof |
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2020
- 2020-06-12 CN CN202010535921.3A patent/CN111683512A/en active Pending
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113621345A (en) * | 2021-08-23 | 2021-11-09 | 安徽理工大学 | Method for preparing electromagnetic wave absorbing material |
| CN113747777A (en) * | 2021-09-08 | 2021-12-03 | 济南市中恒光机电技术中心 | Electromagnetic wave shielding material |
| CN113747777B (en) * | 2021-09-08 | 2022-04-08 | 北京伊斯普电子技术有限公司 | Electromagnetic wave shielding material |
| CN114613967A (en) * | 2022-03-24 | 2022-06-10 | 大连理工大学 | FeS @ C composite material prepared rapidly by microwave method, and method and application thereof |
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