Preparation method of double-shell molybdenum carbide / carbon nanosphere composite wave-absorbing material
By preparing a double-shell hollow Mo2C/C nanosphere composite material, the problems of simple structural design, poor controllability, poor impedance matching, and narrow effective absorption bandwidth of Mo2C composite materials were solved, thereby improving the electromagnetic wave absorption performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NAT UNIV OF DEFENSE TECH
- Filing Date
- 2022-10-20
- Publication Date
- 2026-05-08
AI Technical Summary
Existing Mo2C composite materials have limited structural design, poor controllability, poor impedance matching, and narrow effective absorption bandwidth, resulting in insufficient electromagnetic wave absorption performance.
A two-step hydrothermal and pyrolysis process was used to construct a double-shell hollow Mo2C/C nanosphere composite microwave absorbing material. A uniform double-shell structure was formed by the solvothermal reaction of molybdenum glycerate nanospheres and polydopamine precursor. Combined with carbothermal reduction reactions at different pyrolysis temperatures, a double-shell carbon skeleton decorated with Mo2C nanoparticles was prepared.
The method for preparing materials with a double-shell structure that achieves the desired technical effect solves the problem of preparing Mo2C/C nanosphere composite materials in the prior art and provides better application prospects.
Smart Images
Figure CN115568199B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of microwave absorbing materials technology, and in particular to a method for preparing a double-shell molybdenum carbide / carbon nanosphere composite microwave absorbing material. Background Technology
[0002] The application of advanced electronic instruments, especially high-power electromagnetic equipment, has generated excessive electromagnetic pollution, which not only interferes with industrial production but may also endanger the health of biological systems. Electromagnetic absorption is an ideal method to mitigate electromagnetic pollution through energy conversion. Over the past few decades, extensive research has focused on achieving efficient electromagnetic absorption performance by constructing composite materials, such as magnetic metal composites, conductive polymer composites, and carbon-based composites. Among various composite materials, carbon-based magnetic composites have dominated the development of electromagnetic absorption materials. This is not only because carbon-based materials have low density, good chemical stability, and diverse types, but also because the optimized combination of magnetic and dielectric losses is beneficial to the attenuation of electromagnetic energy. However, these composite materials still suffer from drawbacks such as high density and poor corrosion resistance. Furthermore, in carbon-based magnetic composites, the presence of the carbon matrix significantly weakens the magnetic coupling interaction between magnetic particles, and the attenuation of electromagnetic energy in the composite material is mainly due to dielectric loss. Based on this, researchers have proposed using dielectric components instead of magnetic components to prepare carbon-based composites.
[0003] In recent years, carbon-based carbide composites, as potential dielectric materials, have attracted widespread attention for their electromagnetic energy attenuation due to their advantages such as tunable dielectric properties, good oxidation resistance, and good chemical stability. In particular, the emergence of Mo2C has further promoted the potential application of carbon-based carbides in the field of electromagnetic wave absorption. Compared with other carbides (such as SiC or Ti3C2MXenes), Mo2C nanoparticles can be obtained at relatively low pyrolysis temperatures, which is beneficial for suppressing crystal growth and promoting uniform distribution. However, research on the application of Mo2C composites in electromagnetic wave absorption is still scarce. The limited number of Mo2C / C composite absorbing materials available mainly focus on simple composite or single-core-shell structures, resulting in relatively narrow acceptable response bandwidths and poor impedance matching.
[0004] The purpose of this invention is to address the problems of limited structural design, poor controllability, inadequate impedance matching, and narrow effective absorption bandwidth of Mo2C composite materials by designing special double-shell hollow micro / nanostructures. Double-shell nanostructures, as an interesting type of nanostructure, offer unique advantages in electromagnetic energy attenuation due to their hollow structure, relatively low density, and abundant heterojunctions. Furthermore, the double-shell hollow structure facilitates impedance matching optimization because the encapsulated air between the shells acts as an intermediate medium, making the inherent impedance as close as possible to the impedance of the external air. In addition, the double-shell hollow structure can enhance reflection loss by extending the propagation path of incident electromagnetic waves, thereby promoting multiple reflections and refractions. The uniform dispersion of Mo2C nanoparticles within the multi-shell carbon framework not only modulates the dielectric constant of the carbon framework to a certain extent, but the tiny Mo2C nanoparticles also provide abundant polarization losses for electromagnetic energy attenuation. The synergistic effect between material losses and structural losses improves the absorption performance. To this end, a double-shell hollow Mo2C / C nanosphere composite microwave absorbing material decorated with Mo2C nanoparticles was constructed through a two-step hydrothermal and pyrolysis process, thus obtaining a method for preparing a double-shell hollow micro / nano structured Mo2C / C composite microwave absorbing material. Summary of the Invention
[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for preparing a double-shell molybdenum carbide / carbon nanosphere composite microwave absorbing material.
[0006] To achieve the above objectives, the present invention adopts the following technical solution:
[0007] A method for preparing a double-shell molybdenum carbide / carbon nanosphere composite microwave absorbing material includes the following steps:
[0008] I. Preparation of molybdenum glycerate nanospheres
[0009] (1) Mix deionized water and isopropanol solution, stir until homogeneous, then add glycerol and stir to form a homogeneous solution;
[0010] (2) Add molybdenum acetylacetonate to the mixed solution in step (1) and sonicate until the mixed solution is colorless and transparent;
[0011] (3) Transfer the transparent mixed solution obtained in step (2) to a high temperature and high pressure reactor, place it in an oven to react, and take it out after cooling in the oven. Collect the powder obtained by centrifugation, wash it several times with ethanol, and dry it at room temperature.
[0012] II. Preparation of Polydopamine Precursor Nanospheres
[0013] (4) Mix anhydrous ethanol and deionized water and stir. Take the powder from step (3) and add it to the mixed solution. Then add dopamine hydrochloride and sonicate.
[0014] (5) Place the ultrasonically treated solution from step (4) into a magnetic stirrer and stir it. Add ammonia solution during the stirring process and continue stirring.
[0015] (6) After the mixed solution in step (5) is stirred, it is transferred to a high-temperature and high-pressure reactor and reacted for 2 hours. After the reaction, it is cooled in an oven and taken out. The powder obtained is collected by centrifugation, washed several times with deionized water and anhydrous ethanol, and then placed in an oven at a temperature of 0°C to dry.
[0016] III. Preparation of Mo2C / C nanospheres with double-shell hollow structures
[0017] (7) Place the sample from step (6) into a ceramic boat, introduce argon gas into a tube furnace, raise the temperature to 700-900℃ at a heating rate of 2℃ / min, carry out carbothermic reduction reaction, and keep it at the predetermined temperature for 3h. After the reaction is completed, lower it to room temperature and collect the sample to obtain the target product Mo2C / C composite microwave absorbing material.
[0018] IV. Microwave Absorption Performance Testing of Mo2C / C Nanospheres with Double-Shell Hollow Structure
[0019] (8) Take 40mg of the composite microwave absorbing material in step (7) and 60mg of sliced paraffin wax and add it to the agate mortar. Place the mortar in a 70℃ oven and heat for 20 minutes. After the paraffin wax is completely melted, take out the mortar and grind it quickly. Mix the melted paraffin wax with the powder sample until the paraffin wax solidifies again. Then transfer the mixed sample to the sample preparation mold for pressing to obtain the concentric ring test sample.
[0020] (9) Place the concentric ring prepared in step (8) into the concentric axis transmission line fixture of the vector network analyzer, connect the fixture to the vector network analyzer, set the parameters to test the electromagnetic parameters of the material, and take out the sample after the test is completed.
[0021] Preferably, in step one, the volume ratio of isopropanol, water and glycerol in the mixed solution is (3.5-5):(0.8-1.2):1, and the volume-to-mass ratio of the mixed solution and molybdenum acetylacetonate is 1:(2-3).
[0022] Furthermore, in (2), the molar ratio of glycerol to molybdenum acetylacetonate is 0.25 to 0.40.
[0023] Preferably, the reaction conditions for (3) are: place the 150mL high-temperature and high-pressure reactor into an oven at 160℃ and react for 5 hours, and then remove the reactor after cooling in the oven.
[0024] Preferably, in step two, the volume ratio of anhydrous ethanol to deionized water in the mixed solution is (1.5-1):1, the weight ratio of molybdenum glycerate nanosphere powder to dopamine hydrochloride is (0.95-1.05):1, and the molar ratio of dopamine hydrochloride to ammonia in the ammonia solution is (9.5-10.5):1.
[0025] Preferably, the specific steps of the thermal reaction in step (6) are as follows: after the mixed solution in step (5) is stirred for 10 minutes, it is transferred to a 100 mL high-temperature and high-pressure reactor and reacted at 140°C for 2 hours. After the reaction, it is cooled and taken out in an oven, and the powder obtained is collected by centrifugation. It is washed several times with deionized water and anhydrous ethanol, and then placed in an oven at 60°C for 10 hours.
[0026] Preferably, the temperature of the thermal reduction reaction in step (7) is 700℃, and the temperature is kept at 700℃ for 3 hours. After the reaction is completed, the temperature is lowered to room temperature, and the collected sample is the target product Mo2C / C composite microwave absorbing material, denoted as DS-Mo2C / C-700, and its electromagnetic absorption performance is tested.
[0027] Preferably, the temperature of the thermal reduction reaction in step (7) is 800℃, and the temperature is kept at 800℃ for 3 hours. After the reaction is completed, the temperature is lowered to room temperature, and the collected sample is the target product Mo2C / C composite microwave absorbing material, denoted as DS-Mo2C / C-800, and its electromagnetic absorption performance is tested.
[0028] Preferably, the temperature of the thermal reduction reaction in step (7) is 900℃, and the temperature is kept at 900℃ for 3 hours. After the reaction is completed, the temperature is lowered to room temperature, and the collected sample is the target product Mo2C / C composite microwave absorbing material, denoted as DS-Mo2C / C-900, and its electromagnetic absorption performance is tested.
[0029] Preferably, in step (9), the specifications of the concentric annular test sample are: inner diameter 3mm, outer diameter 7mm, and thickness 2mm.
[0030] Compared with the prior art, the beneficial effects of the present invention are:
[0031] This invention provides a simple method for preparing a double-shell hollow micro / nanostructured Mo2C / C composite microwave absorbing material. The method uses molybdenum acetylacetonate (MoO2), an organic salt containing molybdenum, as the molybdenum source, and glycerol, deionized water, and isopropanol as solvents. The mixture is ultrasonically dissolved and subjected to a solvothermal reaction to generate uniform molybdenum glycerate nanospheres. Dopamine hydrochloride is used as the polymerization surface layer, exhibiting the characteristics of uniform polymerization, rapid polymerization, and high efficiency. The MoO2 glycerate nanospheres are mixed with dopamine hydrochloride under alkaline conditions, and a polymer precursor is obtained through a solvothermal process. Controlling the alkaline conditions can regulate the degree and efficiency of dopamine polymerization. The polymer precursor is then pyrolyzed. During this process, the polymer transforms into a carbon skeleton and reacts with molybdenum atoms to obtain molybdenum carbide nanoparticles. During the transformation of the inner layer of MoO2 glycerate nanospheres into molybdenum carbide, molybdenum atoms transfer to the shell layer, ultimately forming a double-shell hollow structured Mo2C / C nanosphere. Its innovative points are as follows:
[0032] (1) Dopamine hydrochloride, as a polymer shell, has the characteristics of fast polymerization reaction, high degree of polymerization, and regular polymerization morphology. By adjusting the amount of ammonia added during the experiment, the polymerization time of dopamine hydrochloride can be increased, the degree of polymerization of dopamine hydrochloride can be reduced, and multilayer polymerization of dopamine can be avoided. During the carbothermic reduction process, the polymerized dopamine hydrochloride undergoes a reduction reaction with molybdenum glycerate nanospheres while being converted into a carbon skeleton, forming a distinct double-shell structure while being converted into molybdenum carbide and carbon skeleton.
[0033] (2) Using nanospheres polymerized with dopamine hydrochloride as precursors, carbothermic reduction reaction was carried out at 700, 800 and 900 °C. The higher carbothermic reduction temperature improved the graphitization degree of the carbon skeleton, which is beneficial to enhancing the dielectric loss capability of the composite material. On the other hand, the higher carbothermic reduction temperature improved the reduction characteristics of the carbon skeleton, which is beneficial to the full reaction of molybdenum and carbon to obtain molybdenum carbide particles.
[0034] (3) Compared with solid materials, the air trapped inside the double-shell hollow structure improves the inherent impedance of the material, making the inherent impedance of the material closer to the air impedance, which is conducive to the entry of incident electromagnetic waves into the material. At the same time, the double-shell hollow structure forms a network structure that binds the incident electromagnetic waves, effectively changing and prolonging the transmission path of the incident electromagnetic waves inside the material, enhancing the interaction time between the incident electromagnetic waves and the internal components of the material, and achieving high efficiency and repeated attenuation of the incident electromagnetic waves.
[0035] (4) The interior of the carbon shell forms the main region for electromagnetic energy consumption. The molybdenum carbide particles dispersed within the carbon skeleton disrupt the electron transport balance of the carbon skeleton, prolonging the electron transport path and increasing the energy consumption of the electric branch of the incident electromagnetic wave. In addition, the resistive loss characteristics of molybdenum carbide itself further enhance the energy consumption of the electric branch of the electromagnetic wave. At the same time, the addition of molybdenum carbide particles introduces more defects into the carbon skeleton. These introduced defects, together with some residual groups in the carbon skeleton, form dipole centers, enhancing the dipole polarization loss characteristics. The combined effect of electrical loss and polarization loss increases electromagnetic energy loss and enhances the absorption performance. Attached Figure Description
[0036] Figure 1 This is a SEM image of the polydopamine precursor nanospheres prepared in this invention.
[0037] Figure 2 XRD patterns of DS-Mo2C / C nanospheres at different pyrolysis temperatures;
[0038] Figure 3 SEM images of DS-Mo2C / C nanospheres at different pyrolysis temperatures, where a is the SEM image of DS-Mo2C / C-700 prepared in Example 1, b is the SEM image of DS-Mo2C / C-800 prepared in Example 2, and c is the SEM image of DS-Mo2C / C-900 prepared in Example 3.
[0039] Figure 4 TEM images of DS-Mo2C / C nanospheres at different pyrolysis temperatures are shown. Among them, a is the TEM image of DS-Mo2C / C-700 prepared in Example 1, b is the TEM image of DS-Mo2C / C-800 prepared in Example 2, c is the TEM image of DS-Mo2C / C-900 prepared in Example 3, and d is the HR-TEM image of DS-Mo2C / C-800 prepared in Example 3.
[0040] Figure 5 These are the Raman spectra of DS-Mo2C / C nanospheres at different pyrolysis temperatures;
[0041] Figure 6 These are the dielectric constant curves of DS-Mo2C / C at different pyrolysis temperatures, where a is the real part curve of the dielectric constant of DS-Mo2C / C-700, DS-Mo2C / C-800 and DS-Mo2C / C-900, and b is the imaginary part curve of the dielectric constant of DS-Mo2C / C-700, DS-Mo2C / C-800 and DS-Mo2C / C-900.
[0042] Figure 7These are three-dimensional reflection loss diagrams of DS-Mo2C / C at different pyrolysis temperatures, where a is the three-dimensional reflection loss diagram of DS-Mo2C / C-700 prepared in Example 1, b is the three-dimensional reflection loss diagram of DS-Mo2C / C-800 prepared in Example 2, and c is the three-dimensional reflection loss diagram of DS-Mo2C / C-900 prepared in Example 3. Detailed Implementation
[0043] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.
[0044] Example 1:
[0045] A method for preparing a double-shell molybdenum carbide / carbon nanosphere composite microwave absorbing material includes the following steps:
[0046] (1) Mix 15 mL of deionized water and 65 mL of isopropanol solution, stir well, then add 16 mL of glycerol solution, stir and mix to form a uniform mixed solution;
[0047] (2) Take 245 mg of molybdenum acetylacetonate and add it to the mixed solution in step (1), and sonicate until the mixed solution is colorless and transparent.
[0048] (3) Transfer the transparent mixed solution obtained in step (2) to a 150 mL high temperature and high pressure reactor, place it in an oven at 160 °C and react for 5 h. After the reaction, remove it from the oven and cool it down. Collect the powder obtained by centrifugation, wash it several times with ethanol, and dry it at room temperature.
[0049] (4) Mix 8 mL of anhydrous ethanol and 6 mL of deionized water and stir for 10 min. Take 20 mg of the powder from step (3) and add it to the mixed solution. Then add 20 mg of dopamine hydrochloride and sonicate for 20 min.
[0050] (5) Place the ultrasonically treated solution from step (4) into a magnetic stirrer and stir. Add 0.02 mL of 0.5 mol / L ammonia solution during stirring and continue stirring.
[0051] (6) After stirring the mixed solution in step (5) for 10 min, transfer it to a 100 mL high temperature and high pressure reactor and react at 140 °C for 2 h. After the reaction, take it out with the oven to cool and collect the powder by centrifugation. Wash it several times with deionized water and anhydrous ethanol, and then put it into an oven at 60 °C for 10 h.
[0052] (7) Place the sample from step (6) into a ceramic boat, introduce argon gas into a tube furnace, raise the temperature to 700°C at a heating rate of 2°C / min, carry out a carbothermic reduction reaction, and keep it at the predetermined temperature for 3 hours. After the reaction is completed, lower the temperature to room temperature and collect the sample, which is the target product Mo2C / C composite microwave absorbing material, denoted as DS-Mo2C / C-700.
[0053] (8) Take 40 mg of the composite microwave absorbing material from step (7) and 60 mg of sliced paraffin wax and add them to an agate mortar. Place the mortar in a 70°C oven and heat for 20 minutes. After the paraffin wax has completely melted, remove the mortar and grind quickly. Mix the melted paraffin wax with the powder sample thoroughly until the paraffin wax solidifies again. Then transfer the mixed sample to a sample preparation mold for pressing to obtain a concentric ring test sample. The ring specifications are: inner diameter 3 mm, outer diameter 7 mm, and thickness 2 mm.
[0054] (9) Place the concentric ring prepared in step (8) into the concentric axis transmission line fixture of the vector network analyzer, connect the fixture to the vector network analyzer, set the parameters to test the electromagnetic parameters of the material, and take out the sample after the test is completed.
[0055] Example 2
[0056] Using the same conditions as in Example 1, except that the carbothermic reduction reaction temperature in step (7) is 800℃, DS-Mo2C / C-800 composite microwave absorbing material is obtained.
[0057] Example 3
[0058] Using the same conditions as in Example 1, except that the carbothermic reduction reaction temperature in step (7) is 900℃, DS-Mo2C / C-900 composite microwave absorbing material is obtained.
[0059] The structural composition and performance testing are as follows:
[0060] Figure 1 The nanospheres are polydopamine precursors. As can be seen from the figure, the nanospheres obtained after dopamine polymerization and coating exhibit a regular spherical morphology, are uniformly dispersed, and have a uniform size with a particle size of approximately 800 nm.
[0061] Figure 2The XRD patterns of DS-Mo2C / C at different temperatures are shown. The figures show characteristic diffraction peaks at θ = 34.4°, 38°, 39.4°, 52.1°, 61.5°, 69.6°, and 75° for the samples at the three temperatures. These peaks correspond to the (100), (002), (101), (102), (110), and (103) crystal planes of hexagonal Mo2C, respectively, and the corresponding X-ray diffraction standard card is JCPDS35-0787. The figures also show that as the temperature increases, the peak shape of the Mo2C diffraction peaks gradually becomes sharper and the intensity gradually increases, indicating that higher temperatures are beneficial for the growth of Mo2C nanoparticles.
[0062] Figure 3 Images a and c represent SEM images of DS-Mo2C / C obtained at 700, 800, and 900 °C, respectively. The images clearly show that all three samples maintain a complete spherical morphology, are uniformly dispersed, and have a uniform size, with a particle size of approximately 800 nm. Further comparison reveals that at 700 °C, small aggregated particles appear on the surface of the DS-Mo2C / C-700 spheres. However, at 800 and 900 °C, the sphere surface is smooth and the particles are uniform in size. This is mainly because higher temperatures are more conducive to the reaction between the organic polymer and molybdenum, resulting in Mo2C nanoparticles uniformly dispersed within the spherical shell. Furthermore, higher temperatures enhance the graphitization of the carbon shell, increasing the orderliness of the carbon layer and making the carbon layer distribution on the spherical shell surface more uniform.
[0063] Figure 4 Images a and c are TEM images of DS-Mo2C / C obtained at 700, 800, and 900 °C, respectively. Clearly, the Mo2C / C nanospheres exhibit a distinct hollow shell structure. At 700 °C, the Mo2C / C nanospheres only show a clear hollow structure and do not exhibit a distinct double shell. This is mainly because at lower temperatures, the polymer is less likely to undergo sufficient reduction with molybdenum during carbonization to obtain a double shell structure. With increasing temperature, both DS-Mo2C / C-800 and DS-Mo2C / C-900 exhibit double shell structures. (HR-TEM image) Figure 4 d) Further confirmation shows that the lattice fringe spacing of Mo2C nanoparticles is 0.23 nm, corresponding to the (101) plane of Mo2C, indicating that the reaction of molybdenum with the carbon skeleton during high-temperature pyrolysis produces Mo2C particles dispersed in the carbon skeleton, which is consistent with the XRD analysis results.
[0064] Figure 5 These are the Raman spectra of DS-Mo2C / C-700, DS-Mo2C / C-800, and DS-Mo2C / C-900. The figures show that all three samples have two distinct Raman shift peaks, located at 1350 and 1590 cm⁻¹, respectively. -1The left and right bands correspond to the D and G bands of the carbon framework. It is clearly visible in the figure that the full width at half maximum (FWHM) of the Raman shift peak gradually narrows from 700 to 900 °C, indicating an increase in the degree of graphitization of carbon. I D / I G The ratio also gradually increases, indicating that the degree of graphitization of the carbon skeleton gradually increases, mainly because for amorphous carbon skeletons, I D / I G A higher ratio indicates a higher degree of graphitization. This is mainly because the formation of graphitized carbon involves a process of graphite crystallization, during which the degree of graphitization is enhanced. I D / I G The ratio increases. Increased graphitization enhances the conductivity of the composite material. Raman spectroscopy results show that as temperature increases, the degree of graphitization in the composite material increases, leading to increased conductivity and enhanced dielectric loss capacity.
[0065] Figure 6 Figure a shows the real part curves of the dielectric constant of DS-Mo2C / C-700, DS-Mo2C / C-800, and DS-Mo2C / C-900. It can be seen that at 700℃, the real part of the dielectric constant is less than 8, and remains essentially unchanged throughout the entire test frequency range (2.0-18.0GHz), indicating its weak dielectric loss capability. With increasing pyrolysis temperature, the real part of the dielectric constant of both DS-Mo2C / C-800 and DS-Mo2C / C-900 shows a significant increase, mainly because the increased temperature enhances the graphitization of the carbon skeleton, leading to improved conductivity. Figure 6 b shows the imaginary part curves of the dielectric constant for DS-Mo2C / C-700, DS-Mo2C / C-800, and DS-Mo2C / C-900. Clearly, the imaginary and real parts of the dielectric constant maintain the same trend, indicating that increasing temperature is beneficial to enhancing dielectric loss.
[0066] Figure 7Figures ac show the three-dimensional reflection loss diagrams of DS-Mo2C / C-700, DS-Mo2C / C-800, and DS-Mo2C / C-900, respectively. DS-Mo2C / C-700 exhibits poor absorption performance, not only in terms of weak reflection loss but also in its narrow effective absorption bandwidth. This is mainly due to its weak dielectric loss capability, making it difficult to attenuate incident electromagnetic waves. DS-Mo2C / C-900 exhibits the highest dielectric constant and the strongest dielectric loss capability. However, its high dielectric constant leads to poor impedance matching, making it difficult for incident electromagnetic waves to penetrate more deeply into the material. DS-Mo2C / C-800 exhibits the best absorption performance, not only due to its strong dielectric loss capability but also because its impedance matching is superior to DS-Mo2C / C-900. DS-Mo2C / C-800 achieves a maximum effective absorption bandwidth of 4.5 GHz with a thickness of only 1.5 mm.
[0067] Based on the above charts and data analysis, this invention constructs a double-shell hollow Mo2C / C composite microwave absorbing material through a two-step solvothermal process, achieving uniform morphology, clear structure, and uniform dispersion of molybdenum carbide particles within the carbon framework. The air trapped inside the double-shell structure helps improve impedance matching, making the material impedance closer to air impedance. Furthermore, the double-shell structure helps extend the transmission path of incident electromagnetic waves, enhancing multiple reflections. The introduction of Mo2C nanoparticles brings abundant heterogeneous interfaces, enhancing interfacial polarization loss. Simultaneously, Mo2C nanoparticles also provide abundant resistive loss and dipole polarization loss. The synergistic effect of multiple loss mechanisms and the structure improves the microwave absorption performance of the composite material, providing valuable inspiration and reference for the design of other structural carbide microwave absorbing materials. The prepared composite microwave absorbing material has promising application prospects.
[0068] The synthesized DS-Mo2C / C-800 composite absorbing material exhibits significantly improved absorbing performance, with a maximum effective absorption bandwidth (frequency range corresponding to a reflection loss value <-10dB) of 4.5GHz and a corresponding thickness of only 1.5mm.
[0069] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A method for preparing a double-shell molybdenum carbide / carbon nanosphere composite microwave absorbing material, characterized in that, Includes the following steps: I. Preparation of molybdenum glycerate nanospheres (1) Mix deionized water and isopropanol solution, stir until homogeneous, then add glycerol and stir to form a homogeneous solution; (2) Add molybdenum acetylacetonate to the mixed solution in step (1) and sonicate until the mixed solution is colorless and transparent; (3) Transfer the transparent mixed solution obtained in step (2) to a high temperature and high pressure reactor, place it in an oven to react, and take it out after cooling in the oven. Collect the powder obtained by centrifugation, wash it several times with ethanol, and dry it at room temperature. II. Preparation of Polydopamine Precursor Nanospheres (4) Mix anhydrous ethanol and deionized water and stir. Take the powder from step (3) and add it to the mixed solution. Then add dopamine hydrochloride and sonicate. (5) Place the ultrasonically treated solution from step (4) into a magnetic stirrer and stir it. Add ammonia solution during the stirring process and continue stirring. (6) After the mixed solution in step (5) is stirred, it is transferred to a high-temperature and high-pressure reactor and reacted for 2 hours. After the reaction, it is cooled in an oven and taken out. The powder obtained is collected by centrifugation, washed several times with deionized water and anhydrous ethanol, and then put into an oven to dry. III. Preparation of Mo2C / C nanospheres with double-shell hollow structures (7) Place the sample from step (6) into a ceramic boat, introduce argon gas into a tube furnace, raise the temperature to 700-900℃ at a heating rate of 2℃ / min, carry out carbothermic reduction reaction, and keep it at the predetermined temperature for 3h. After the reaction is completed, lower it to room temperature and collect the sample to obtain the target product Mo2C / C composite microwave absorbing material. IV. Microwave Absorption Performance Testing of Mo2C / C Nanospheres with Double-Shell Hollow Structure (8) Take 40mg of the composite microwave absorbing material in step (7) and 60mg of sliced paraffin wax and add it to the agate mortar. Place the mortar in a 70℃ oven and heat for 20 minutes. After the paraffin wax is completely melted, take out the mortar and grind it quickly. Mix the melted paraffin wax with the powder sample until the paraffin wax solidifies again. Then transfer the mixed sample to the sample preparation mold for pressing to obtain the concentric ring test sample. (9) Place the concentric ring prepared in step (8) into the concentric axis transmission line fixture of the vector network analyzer, connect the fixture to the vector network analyzer, set the parameters to test the electromagnetic parameters of the material, and take out the sample after the test is completed.
2. The method for preparing a double-shell molybdenum carbide / carbon nanosphere composite microwave absorbing material according to claim 1, characterized in that, In step one, the volume ratio of isopropanol, water and glycerol in the mixed solution is (3.5-5):(0.8-1.2):1, and the volume-to-mass ratio of the mixed solution and molybdenum acetylacetonate is 1:(2-3).
3. The method for preparing a double-shell molybdenum carbide / carbon nanosphere composite microwave absorbing material according to claim 2, characterized in that, In (2), the molar ratio of glycerol to molybdenum acetylacetonate is 0.25 to 0.
40.
4. The method for preparing a double-shell molybdenum carbide / carbon nanosphere composite microwave absorbing material according to claim 1, characterized in that, The reaction conditions for (3) are as follows: the reaction is carried out in a 150 mL high-temperature and high-pressure reactor and placed in an oven at 160 °C for 5 h. After the reaction, the reactor is cooled and removed from the oven.
5. The method for preparing a double-shell molybdenum carbide / carbon nanosphere composite microwave absorbing material according to claim 1, characterized in that, In step two, the volume ratio of anhydrous ethanol to deionized water in the mixed solution is (1.5-1):1, the weight ratio of molybdenum glycerate nanosphere powder to dopamine hydrochloride is (0.95-1.05):1, and the molar ratio of dopamine hydrochloride to ammonia in the ammonia solution is (9.5-10.5):
1.
6. The method for preparing a double-shell molybdenum carbide / carbon nanosphere composite microwave absorbing material according to claim 1, characterized in that, The specific steps of the thermal reaction in step (6) are as follows: After the mixed solution in step (5) is stirred for 10 minutes, it is transferred to a 100 mL high-temperature and high-pressure reactor and reacted at 140°C for 2 hours. After the reaction, it is taken out by cooling in an oven, and the powder obtained is collected by centrifugation. It is washed several times with deionized water and anhydrous ethanol, and then placed in an oven at 60°C for 10 hours.
7. The method for preparing a double-shell molybdenum carbide / carbon nanosphere composite microwave absorbing material according to claim 1, characterized in that, The temperature of the thermal reduction reaction in step (7) is 700℃, and the temperature is kept at 700℃ for 3 hours. After the reaction is completed, the temperature is lowered to room temperature, and the collected sample is the target product Mo2C / C composite microwave absorbing material, denoted as DS-Mo2C / C-700, and its electromagnetic absorption performance is tested.
8. The method for preparing a double-shell molybdenum carbide / carbon nanosphere composite microwave absorbing material according to claim 1, characterized in that, The temperature of the thermal reduction reaction in step (7) is 800℃, and the temperature is kept at 800℃ for 3 hours. After the reaction is completed, the temperature is lowered to room temperature, and the collected sample is the target product Mo2C / C composite microwave absorbing material, denoted as DS-Mo2C / C-800, and its electromagnetic absorption performance is tested.
9. The method for preparing a double-shell molybdenum carbide / carbon nanosphere composite microwave absorbing material according to claim 1, characterized in that, The temperature of the thermal reduction reaction in step (7) is 900℃, and the temperature is kept at 900℃ for 3 hours. After the reaction is completed, the temperature is lowered to room temperature, and the collected sample is the target product Mo2C / C composite microwave absorbing material, denoted as DS-Mo2C / C-900, and its electromagnetic absorption performance is tested.
10. The method for preparing a double-shell molybdenum carbide / carbon nanosphere composite microwave absorbing material according to claim 1, characterized in that, In step (9), the specifications of the concentric annular test sample are: inner diameter 3mm, outer diameter 7mm, and thickness 2mm.