A MgO-C nanochain and its preparation method and application as wave absorbing material

Abstract

The present invention discloses an MgO-C nanochain, a preparation method thereof, and an application as a microwave absorbing material. The preparation is carried out using a horizontal tube furnace, and evaporation zones and reduction zones are respectively arranged at both ends of the furnace body. Mg(acac)2 is used as a precursor and placed in the evaporation zone, and a substrate for collecting products is placed in the reduction zone. An inert gas is used as a carrier gas and reaction atmosphere, and a vacuum pump system is used to maintain the internal pressure of the system for reaction, and the MgO-C nanochains are collected on the substrate. In the MgO-C nanochains of the present invention, nano-MgO particles are connected by carbon to form a three-dimensional framework. By virtue of this unique structure, microwave absorbing effects such as enhanced interfacial polarization and multiple scattering reflections are strengthened, the microwave absorbing performance is greatly improved, and the frequency band is broadened. It has good microwave absorption performance and has very good application prospects in the fields of stealth technology and electromagnetic shielding.

Description

Technical Field

[0001] The invention belongs to the field of wave absorbing materials, and in particular relates to a MgO-C nanochain and a preparation method thereof and application thereof as a wave absorbing material. Background Art

[0002] The development background of absorbing materials is rich and diverse, and its evolution process is profoundly influenced by many factors.

[0003] In the military field, since the widespread use of radar during World War II, the demand for stealth in military equipment has increased dramatically, which has become a key driving force for the development of absorbing materials. In today's modern electronic confrontation environment, military equipment such as warships and tanks can significantly reduce the leakage of electromagnetic signals after being equipped with absorbing materials, which not only enhances the anti-interference ability, but also reduces the risk of being locked by the enemy, greatly improving the survivability on the battlefield.

[0004] In the civilian field, with the large-scale popularization of electronic devices, the problem of electromagnetic pollution has become increasingly prominent and has become an "invisible concern" that cannot be ignored. In this case, absorbing materials play the role of "protective guards" and are made into various electromagnetic shielding products to restrict electromagnetic leakage of electronic devices such as mobile phones and computers, thereby protecting human health and maintaining a good environment. At the same time, as communication technology moves towards the 5G era, the requirements for signal quality and stability continue to increase. Absorbing materials are integrated into base stations and terminal equipment, effectively optimizing signal transmission and eliminating interference during transmission.

[0005] The continuous progress of science and technology has provided strong support for the development of absorbing materials. In the field of materials science, new materials such as nano, composite, and chiral materials continue to emerge. Among them, nanomaterials have greatly broadened the frequency band range of absorbing materials due to their unique size effect. Moreover, advanced preparation processes such as chemical vapor deposition and sol-gel method are becoming more and more sophisticated, making the control of the microstructure of absorbing materials more precise and enabling "customized" production according to actual needs.

[0006] In the field of aerospace, absorbing materials have a special mission. For aircraft, the improvement of their stealth performance is highly dependent on absorbing materials. In the space environment, satellites will be interfered by electromagnetic radiation, and absorbing materials act like a "shield", protecting the electronic equipment inside the satellite and escorting the journey of space exploration.

[0007] It is the coordinated development of multiple fields such as military, civilian, science and technology, and aerospace that has jointly shaped the trajectory of the booming development of absorbing materials.

[0008] However, traditional absorbing materials have many limitations. Their absorbing performance is limited, and it is difficult to absorb waves efficiently in a wide band. The preparation process is complicated, it is difficult to mass produce, the cost is high, and the application range is limited. In terms of material structure design, there is a lack of innovation in building a microscopic three-dimensional conductive network to promote the coordination of multiple loss mechanisms of electromagnetic waves, which hinders the improvement of absorbing efficiency. Summary of the invention

[0009] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology, and provide a MgO-C nanochain and a preparation method thereof and an application thereof as an absorbing material to improve the absorbing performance.

[0010] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0011] A method for preparing MgO-C nanochains, using a horizontal tube furnace for preparation, wherein the furnace body is provided with an evaporation area and a reduction area at both ends;

[0012] Mg(acac)2 is used as a precursor and placed in an evaporation region; a substrate for collecting the product is placed in a reduction region; the temperature of the evaporation region is set to 180-200°C, and the temperature of the reduction region is set to 700-900°C;

[0013] An inert gas is used as a carrier gas and a reaction atmosphere, and a vacuum pump system is used to maintain the internal pressure of the system to carry out the reaction and collect the MgO-C nanochains on the substrate.

[0014] As a further improvement, the distance between the evaporation area and the reduction area is 25-35 cm.

[0015] As a further improvement, the inner diameter of the furnace body is 40-80 mm and the length is 100-150 cm.

[0016] As a further improvement, the purity of the Mg(acac)2 is ≥97%.

[0017] As a further improvement, the substrate is a SiO2 wafer.

[0018] As a further improvement, the flow rate of the inert gas is 150-250 standard cubic centimeters per minute.

[0019] As a further improvement, a vacuum pump system is used to maintain the internal pressure of the system at 80~120Pa.

[0020] As a further improvement, the reaction time is 2.5 to 3.5 hours.

[0021] The present invention also provides a MgO-C nanochain, which is prepared by the method described above. In the MgO-C nanochain, MgO is in granular form, and the MgO particles are connected by carbon to form a three-dimensional structure through weaving.

[0022] The present invention also provides an application of the MgO-C nanochain as a wave absorbing material.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] In the MgO-C nanochain of the present invention, nano-MgO particles are connected by carbon to form a three-dimensional structure. With the help of this unique structure, the absorption effects such as interface polarization and multiple scattering reflection are strengthened, which greatly improves the absorption performance and broadens the frequency band. It has good microwave absorption performance and has very good application prospects in the fields of stealth technology and electromagnetic shielding.

[0025] The present invention uses an organic chemical vapor deposition method to prepare MgO-C nanochains in large quantities at one time, with a simple process, low cost and high efficiency, and can make up for the shortcomings of the existing absorbing material structure and preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 is the TEM image of MgO-C nanochain;

[0028] Figure 2 is the particle size distribution diagram of MgO-C nanochains;

[0029] Figure 3 is the SEM image of MgO-C nanochain;

[0030] Figure 4 is the three-dimensional and corresponding two-dimensional reflection loss diagram of MgO-C nanochain;

[0031] Figure 5 This is a diagram of the formation mechanism of MgO-C nanochains. DETAILED DESCRIPTION

[0032] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the present invention, but the protection scope of the present invention is not limited to the following specific embodiments.

[0033] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0034] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0035] In some specific embodiments of the present invention, the MgO-C nanochains of the present invention are prepared using a horizontal steel tube furnace with a vacuum pump system (ie, an existing horizontal tube furnace, the furnace body of which is made of steel tubes).

[0036] In some embodiments, the inner diameter of the furnace body (steel tube) of the horizontal steel tube furnace is 40-80 mm, preferably 50 mm, and the length is 100-150 cm, preferably 120 cm. Figure 5 The furnace body is provided with an evaporation area (located at the left end) and a reduction area (located at the right end) at both ends. In some embodiments, the evaporation area is 25-35 cm away from the left end of the steel pipe, preferably 30 cm, the reduction area is 55-65 cm away from the left end, preferably 60 cm, and the distance between the evaporation area and the reduction area is 25-35 cm, preferably 30 cm.

[0037] The horizontal steel tube furnace with a specific structural size ensures the thermal field distribution and material transport conditions during the synthesis process to achieve the effective synthesis of MgO-C nanochains.

[0038] The distance between the evaporation zone and the reduction zone is about 30 cm, and there is a temperature gradient in the middle, which is conducive to the pre-decomposition of the raw materials, thereby increasing the yield of MgO-C nanochains; and the distance between the evaporation zone and the reduction zone will affect the size of the MgO particles in the MgO-C nanochains. Generally, the reduction zone is close to the evaporation zone, and the obtained MgO particle size is larger; if the distance between the evaporation zone and the reduction zone is less than 25 cm, it will cause temperature crossover between the two zones, the temperature of the evaporation zone is much higher than the set temperature, and the raw materials will decompose prematurely in the evaporation zone, resulting in too low a yield of MgO-C nanochains.

[0039] In some specific embodiments of the present invention, the method for preparing the MgO-C nanochains of the present invention comprises the following steps:

[0040] S1. Use Mg(acac)2 (magnesium acetylacetonate) as a precursor and place it in the evaporation area; use a SiO2 wafer (Al2O3, iron plate, etc. can also be used) as a substrate for collecting the product and place it in the reduction area.

[0041] In some embodiments, the temperature of the evaporation zone is set to 180-200° C., preferably 190° C. The temperature of the reduction zone is set to 700-900° C., preferably 800° C.

[0042] In some embodiments, the purity of the Mg(acac)2 precursor is ≥97%. The precursor with this purity level, at the set evaporation temperature, cooperates with the subsequent process conditions to promote the formation of the target MgO-C nanochain structure. If the purity is too low, it will affect the yield and purity of the MgO-C nanochain.

[0043] S2. Using inert gas as carrier gas and reaction atmosphere, using a vacuum pump system to maintain the internal pressure of the system, reacting, and collecting MgO-C nanochains on a substrate.

[0044] In some embodiments, Ar is used as a carrier gas and reaction atmosphere, and the flow rate is 150 to 250 standard cubic centimeters per minute, preferably 200 standard cubic centimeters per minute. This flow setting is combined with the reaction system pressure, temperature and other conditions to regulate the reaction material transmission and energy exchange process, which is conducive to building a chemical environment suitable for the growth of MgO-C nanochains in the reaction system. If the flow rate is too large, the particle size of MgO in the product will be too large, and too much raw material will be taken away by the gas before it can decompose, resulting in a relatively low yield.

[0045] In some embodiments, a vacuum pump system is used to maintain the internal pressure of the system at 80-120 Pa, preferably 100 Pa, during the reaction.

[0046] In some embodiments, the reaction time is 2.5 to 3.5 hours, preferably 3 hours.

[0047] Figure 5 The mechanism diagram of the present invention adopts vapor deposition technology. The main process is as follows: First, Mg(acac)2 becomes gaseous in the evaporation area and then transported to the reaction area by Ar gas flow. The gaseous Mg(acac)2 decomposes in the reaction area, and the reaction process can be expressed as (where ads represents the adsorption state):

[0048] Mg(acac)2(g)→Mg(acac)·(ads)+(acac)·(ads)

[0049] Mg(acac)·(ads)→Mg(g)+(acac)·(ads)

[0050] The generated magnesium atoms float in the reaction zone for further reaction. At the same time, (acac)· further decomposes to provide a large number of carbon atoms and oxygen-containing gases, including H2O, CO2, CH2OH, etc. Due to the high chemical activity of magnesium atoms, magnesium atoms can react with these oxygen-containing gases to form MgO molecules, which polymerize to form MgO nanoclusters and further nanochains. Third, MgO nanoclusters and further nanochains are deposited on the surface of the SiO2 wafer to construct the basic spatial framework of the MgO-C nanochains, and then the carbon atoms reach the surface of the MgO nanoparticles. These carbon atoms are more likely to stay in the gaps of the MgO nanoparticles. This is because in the high-temperature deposition reaction, carbon atoms can migrate on the surface of the MgO nanoparticles due to thermal motion, and the gaps between the nanochains usually have lower potential energy. Fourth, carbon atoms condense in the gaps to combine with MgO nanoparticles. As this process proceeds, more and more MgO combines to form nanochain microstructures, thereby obtaining MgO-C nanochains.

[0051] The MgO-C nanochain of the present invention has a unique microstructure, wherein the MgO inside is in granular form with a particle size of about 40 nanometers, and each MgO particle is connected by carbon to form a three-dimensional structure. Figure 1 (d) This special structure lays a solid foundation for efficient wave absorption.

[0052] Embodiment 1:

[0053] First, prepare a horizontal steel tube furnace with a vacuum pump system, whose inner diameter is precisely 50 mm and length is 120 cm. The evaporation area is 30 cm away from the left end of the steel tube, and the reduction area is 60 cm away from the left end. The Mg(acac)2 precursor purchased from Aldrich Chemical Company and with a purity of 97% is carefully placed in the evaporation area with a temperature set to 190°C. In the reduction area of ​​the horizontal steel tube furnace with a temperature of 700°C, a SiO2 wafer is placed steadily, which will serve as a substrate for collecting subsequent synthetic products. Turn on the gas supply device to allow Ar gas to be stably introduced into the horizontal steel tube furnace at a flow rate of 200 standard cubic centimeters per minute as a carrier gas and reaction atmosphere. At the same time, start the vacuum pump system, and keep the internal pressure of the system stable at 100 Pa throughout the 3-hour process of the reaction. After the reaction is completed, the product collected on the SiO2 wafer is marked as S700, which is the MgO-C nanochain sample synthesized at a reaction temperature of 700°C.

[0054] Embodiment 2:

[0055] Parallel experiments were performed according to Example 1. In a set of parallel experiments, only the reaction temperature was changed to 800°C, and other conditions remained unchanged, that is, the same horizontal steel tube furnace, Mg(acac)2 precursor (purity 97%, placed in the 190°C evaporation area), SiO2 wafer substrate (located in the 800°C reduction area), Ar carrier gas (flow rate 200 standard cubic centimeters per minute) and the system pressure was maintained at 100 Pa and reacted for 3 hours. After the reaction was completed, the collected product was marked as S800.

[0056] In another set of parallel experiments, the reaction temperature was set to 900°C, and the above experimental process was repeated. The corresponding collected product was marked as S900.

[0057] A series of characterization analyses were performed on the products synthesized at three different temperatures, S700, S800 and S900, such as observing their microscopic morphology through scanning electron microscopy (SEM); the MgO-C nanochains were fully mixed with paraffin, in which the content of MgO-C nanochains was 16%, and the resulting mixture was pressed into coaxial rings, and its electromagnetic parameters were tested using a vector network analyzer. The reflection loss (RL) value was calculated based on the electromagnetic parameters (as listed in the attached table). The results showed that the samples synthesized at different temperatures had differences in microwave absorption performance, which provided a valuable data basis for further research on the performance optimization and application of MgO-C nanochains.

[0058] Figure 1 TEM images of MgO-C nanochains. (a), (b) and (c) are TEM images of S700, S800 and S900 samples respectively. (d) and (e) are typical TEM high-resolution images of S800. These images show the microstructure of MgO-C nanochains, where MgO is granular and multiple particles are linked by carbon to form a three-dimensional network structure.

[0059] Figure 2 The particle size distribution diagram of MgO-C nanochain S700, S800 and S900 samples shows that the particle size of the MgO-C nanochain microstructure is approximately 40 nanometers, and the synthesis temperature has little effect on the particle size.

[0060] Figure 3 The SEM images of MgO-C nanochains are (a) low magnification and (b) high magnification SEM images of S700. It can be observed that the MgO-C nanochains have a three-dimensional network structure.

[0061] Figure 4 The three-dimensional and corresponding two-dimensional reflection loss (RL) diagrams of MgO-C nanochains, where (a) and (a1) are S700; (b) and (b1) are S800; (c) and (c1) are S900.

[0062] from Figure 4 The wave absorbing performance data shown in Table 1 below can be obtained.

[0063] Table 1 Minimum reflection loss of MgO-C nanochains ( ) and effective bandwidth ( ) corresponds to the thickness

[0064]

[0065] from Figure 4 It can be seen from Table 1 that MgO-C nanochain has excellent microwave absorption performance, with the lowest reflection loss reaching -49.4dB, and the thickness is only 1.4mm, the optimal temperature is 800℃, and compared with the same type of microwave absorption materials, the reflection loss of the same thickness is obviously superior. For example, the thickness of chain-structured carbon nanotubes (carbon nanotubes NCONC-400) is 1.4mm, the effective bandwidth is 4.71GHz, and the lowest reflection loss is -35.47dB.

[0066] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Therefore, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing MgO-C nanochains, characterized in that: A horizontal tube furnace is used for preparation, and an evaporation area and a reduction area are respectively arranged at both ends of the furnace body; the distance between the evaporation area and the reduction area is 25-35 cm; Mg(acac)2 is used as a precursor and placed in an evaporation region; a substrate for collecting the product is placed in a reduction region; the temperature of the evaporation region is set to 180-200°C, and the temperature of the reduction region is set to 700-900°C; An inert gas is used as a carrier gas and a reaction atmosphere, and a vacuum pump system is used to maintain the internal pressure of the system to carry out the reaction and collect the MgO-C nanochains on the substrate.

2. The preparation method according to claim 1, characterized in that: The furnace body has an inner diameter of 40 to 80 mm and a length of 100 to 150 cm.

3. The preparation method according to any one of claims 1 to 2, characterized in that The purity of the Mg(acac)2 is ≥97%.

4. The preparation method according to any one of claims 1 to 2, characterized in that The substrate is a SiO2 wafer.

5. The preparation method according to any one of claims 1 to 2, characterized in that The flow rate of the inert gas is 150-250 standard cubic centimeters per minute.

6. The preparation method according to any one of claims 1 to 2, characterized in that The vacuum pump system is used to maintain the internal pressure of the system at 80~120Pa.

7. The preparation method according to any one of claims 1 to 2, characterized in that The reaction time is 2.5~3.5 hours.

8. A MgO-C nanochain, characterized in that: It is prepared by the method described in any one of claims 1 to 7, wherein the MgO in the MgO-C nanochain is in granular form, and the MgO particles are connected by carbon to form a three-dimensional structure through weaving.

9. Use of the MgO-C nanochain according to claim 8 as a wave absorbing material.

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