Broadband wave-absorbing composite material and preparation method thereof
By utilizing the electrostatic attraction of xanthan gum molecular chains and microfluidic pre-freezing technology, combined with high-temperature pyrolysis, the problem of difficult-to-control microwave absorption performance of carbon/metal microwave absorbing composite materials was solved, achieving low reflection loss and wide-bandwidth microwave absorption effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-30
- Publication Date
- 2026-03-13
AI Technical Summary
Existing fabrication processes for carbon/metal microwave absorbing composite materials suffer from the problem of difficulty in precisely controlling their microwave absorption performance.
By utilizing the electrostatic attraction of xanthan gum molecular chains and microfluidic pre-freezing technology, combined with high-temperature pyrolysis, and controlling the microfluidic diameter, metal salt concentration, and carbonization temperature, atomic-level dispersion of metal ions and the formation of a three-dimensional porous network structure are achieved, thereby regulating the electromagnetic parameters and impedance matching of the material.
It significantly enhances the absorption performance, achieving low reflection loss and wide-bandwidth absorption effect, with a reflection loss of up to -47.0dB and an effective absorption bandwidth of 6.1GHz.
Smart Images
Figure CN121665528A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of microwave absorbing materials, and in particular to a broadband microwave absorbing composite material and its preparation method. Background Technology
[0002] Carbon / metal absorbing composites, compared to traditional absorbing materials, optimize impedance matching characteristics by combining carbon and metal, allowing electromagnetic waves to penetrate the material more easily. They also possess both electrical and magnetic loss mechanisms, enabling more efficient conversion of electromagnetic energy into heat energy, thus achieving a wide-bandwidth, strong absorption effect from low to high frequencies. Furthermore, carbon / metal composites offer a range of advantages, including high absorption performance, wide absorption bandwidth, lightweight stability, strong structural design flexibility, and adjustable performance, making them an ideal candidate material in the field of microwave absorbing materials.
[0003] Currently, the main preparation processes for carbon / metal microwave absorbing composite materials include chemical plating, solvothermal methods, and high-temperature pyrolysis. Materials prepared by chemical plating and solvothermal methods are prone to structural defects or dense agglomeration, making it difficult to obtain high-performance microwave absorbing composite materials. High-temperature pyrolysis, on the other hand, suffers from unclear control mechanisms and difficulty in precisely controlling the microwave absorption performance of the material. Summary of the Invention
[0004] The main objective of this application is to provide a broadband microwave absorbing composite material and its preparation method, aiming to solve the problem that the microwave absorption performance of carbon / metal microwave absorbing composite materials is difficult to control precisely.
[0005] To achieve the above objectives, this application provides a method for preparing a broadband microwave absorbing composite material, comprising: preparing xanthan gum powder into a gel solution; mixing lanthanum nitrate, strontium nitrate hexahydrate, cobalt nitrate hexahydrate, ferric nitrate nonahydrate, and manganese chloride tetrahydrate in a solvent to obtain a metal salt precursor solution; mixing the gel solution and the metal salt precursor solution to obtain a mixed solution; injecting the mixed solution into a pre-freezing medium for pre-freezing to obtain pre-frozen particles; freeze-drying the pre-frozen particles to obtain a freeze-dried sample; and pyrolyzing the freeze-dried sample under an Ar atmosphere to obtain the microwave absorbing composite material; wherein the pyrolysis temperature is 550~850℃ and the pyrolysis time is 2~3h.
[0006] Optionally, the mixed solution is prepared by stirring the metal salt precursor solution at a speed of 500-800 r / min for 25-35 min; adding the gel solution to the stirred metal salt precursor solution and stirring for 1-4 h to obtain the mixed solution.
[0007] Optionally, the method for preparing pre-frozen particles includes: using a syringe with a needle diameter of 0.1~5mm to draw the mixed solution and injecting it into 300~800ml of liquid nitrogen at a uniform speed for pre-freezing to obtain pre-frozen particles.
[0008] Optionally, during the freeze-drying process, the temperature is -40 to -70°C, the pressure is 1 to 3 Pa, and the time is 48 to 72 hours.
[0009] Optionally, during pyrolysis, the heating rate is 3~5℃ / min.
[0010] Optionally, the freeze-dried sample is pyrolyzed under an Ar atmosphere to obtain a microwave absorbing composite material, comprising: placing the freeze-dried sample in a reactor with a pressure of 6-10 Pa, and introducing Ar gas at a flow rate of 150-220 sccm into the reactor for 5-10 min; adjusting the flow rate of Ar gas to 180-220 sccm, and performing pyrolysis to obtain the microwave absorbing composite material.
[0011] Optionally, the mass ratio of lanthanum nitrate, strontium nitrate hexahydrate, cobalt nitrate hexahydrate, ferric nitrate nonahydrate and manganese chloride tetrahydrate is 4: (15~21): (5~10): (8~13): (3~6).
[0012] Optionally, the mass ratio of xanthan gum to metal salt is 6 to 10:1.
[0013] Optionally, the preparation method of the gel solution includes: placing xanthan gum powder in deionized water to obtain a precursor solution with a concentration of 20~50 g / L; and alternately stirring the precursor solution at temperatures of 60~80℃ and 20~30℃ for 4~6 h to obtain a homogeneous, semi-transparent gel solution.
[0014] To achieve the above objectives, this application also provides a broadband absorbing composite material, which is obtained by the above preparation method.
[0015] Compared with the prior art, the beneficial effects of this application are as follows: The preparation method of the broadband microwave absorbing composite material of the present invention utilizes the electrostatic attraction of metal cations by the polyanionic electrolyte formed by the large number of hydroxyl and carboxyl groups contained in the xanthan gum molecular chain. Through vigorous stirring, metal ions are atomically dispersed in the gel, effectively preventing metal particle agglomeration during carbonization and promoting the formation of fine nano-metal particles. This significantly improves the impedance matching characteristics of the material and overcomes the insufficient microwave absorption performance of traditional metal materials due to severe electromagnetic wave reflection. Microfluidic pre-freezing treatment is employed to inhibit the crystallization and precipitation of metal salts and the excessive growth of metal grains during carbonization, promoting the formation of extremely fine metal nanocrystalline particles. Controlling the microfluidic diameter can effectively regulate the electromagnetic parameters and impedance matching of the material, significantly enhancing its microwave absorption performance. Through the synergistic effect of microfluidic pre-freezing and freeze-drying, a three-dimensional porous network structure is naturally formed while suppressing metal precipitation, effectively extending the electromagnetic wave propagation path and enhancing absorption efficiency. Controlling the high-temperature pyrolysis temperature to regulate the ratio of amorphous carbon to graphite carbon in the carbonization products allows for precise regulation of the material's magnetic and dielectric properties, thereby achieving effective control over its microwave absorption performance. Through the synergistic regulation of multiple parameters such as microfluidic diameter, carbonization temperature, and metal salt concentration, a microwave absorption composite material with low reflection loss and a wide bandwidth was obtained. Attached Figure Description
[0016] Figure 1 This is a photograph of the microwave absorbing composite material prepared in Example 1 of this application; Figure 2 Here is a physical image of the microwave absorbing composite material prepared in Example 4 of this application; Figure 3 This is a scanning electron microscope image of the microwave absorbing composite material prepared in Example 1 of this application; Figure 4 The energy spectrum of the microwave absorbing composite material prepared in Example 1 of this application; Figure 5 The X-ray diffraction patterns are of the microwave absorbing composite materials prepared in Examples 1-3 of this application; Figure 6 The X-ray diffraction patterns are of the microwave absorbing composite materials prepared in Examples 3 and 4 of this application; Figure 7 The Raman spectrum of the microwave absorbing composite material prepared in Example 3 of this application; Figure 8 The Raman spectrum of the microwave absorbing composite material prepared in Example 4 of this application; Figure 9 The Raman spectrum of the microwave absorbing composite material prepared in Comparative Example 3 of this application is shown. Figure 10 The three-dimensional reflection loss spectrum of the microwave absorbing composite material prepared in Example 3 of this application; Figure 11 The three-dimensional reflection loss spectrum of the microwave absorbing composite material prepared in Example 4 of this application; Figure 12 The three-dimensional reflection loss spectrum of the microwave absorbing composite material prepared in Comparative Example 1 of this application is shown. Figure 13 The three-dimensional reflection loss spectrum of the microwave absorbing composite material prepared in Comparative Example 2 of this application. Figure 14 The three-dimensional reflection loss spectrum of the microwave absorbing composite material prepared in Comparative Example 3 of this application. Figure 15 The two-dimensional reflection loss spectrum of the microwave absorbing composite material prepared in Example 3 of this application; Figure 16 The two-dimensional reflection loss spectrum of the microwave absorbing composite material prepared in Example 4 of this application; Figure 17 This is a two-dimensional reflection loss spectrum of the microwave absorbing composite material prepared in Comparative Example 1 of this application.
[0017] Figure 18 This is a two-dimensional reflection loss spectrum of the microwave absorbing composite material prepared in Comparative Example 2 of this application.
[0018] Figure 19 This is a two-dimensional reflection loss spectrum of the microwave absorbing composite material prepared in Comparative Example 3 of this application.
[0019] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation
[0020] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0021] The first embodiment of the present invention provides a method for preparing a broadband microwave absorbing composite material, specifically including the following steps: Step S1: Prepare a gel solution from xanthan gum powder; Specifically, 3-7g of xanthan gum powder is placed in 120-180ml of deionized water to obtain a precursor solution with a concentration of 20-50g / L; the precursor solution is then stirred alternately at 60-80℃ and 20-30℃ (room temperature) for 4-6 hours, i.e., first stirred at 60-80℃, then stirred at 20-30℃, and so on for 4-6 hours to obtain a homogeneous, semi-transparent gel solution.
[0022] Step S2: Lanthanum nitrate, strontium nitrate hexahydrate, cobalt nitrate hexahydrate, ferric nitrate nonahydrate, and manganese chloride tetrahydrate are mixed in a solvent to obtain a metal salt precursor solution. The mass ratio of lanthanum nitrate, strontium nitrate hexahydrate, cobalt nitrate hexahydrate, ferric nitrate nonahydrate, and manganese chloride tetrahydrate is 4:(15~21):(5~10):(8~13):(3~6). For example, 0.0529~0.1058g of lanthanum nitrate, 0.2165~0.4330g of strontium nitrate hexahydrate, 0.073~0.146g of cobalt nitrate hexahydrate, 0.101~0.202g of ferric nitrate nonahydrate, and 0.0495~0.099g of manganese chloride tetrahydrate metal salt powder are mixed in 30~80ml of deionized water to obtain a metal salt precursor solution.
[0023] Step S3: Mix the gel solution and the metal salt precursor solution to obtain a mixed solution; The mass ratio of xanthan gum to metal salt is 6-10:1. Specifically, the metal salt precursor solution is stirred at 500-800 r / min for 25-35 min; the gel solution is added to the stirred metal salt precursor solution and stirred for 1-4 h to obtain a mixed solution.
[0024] In this embodiment, the gel solution and the metal salt precursor solution are mixed. The polyanionic electrolyte formed by the large number of hydroxyl and carboxyl groups contained in the xanthan gum molecular chain has an electrostatic attraction effect on the metal cations. Through vigorous stirring, the metal ions are dispersed at the atomic level in the gel, which helps to form fine nanoparticles in the subsequent carbonization process and effectively enhances the dielectric loss and magnetic loss of the material.
[0025] Step S4: Inject the mixed solution into a pre-freezing medium for pre-freezing to obtain pre-frozen particles; Specifically, the mixed solution is drawn using a syringe with a needle diameter of 0.1-5 mm and injected at a uniform rate into 300-800 ml of liquid nitrogen for pre-freezing, while being gently stirred, to obtain pre-frozen particles with uniform particle size. Microfluidic pre-freezing treatment can further disperse metal ions, inhibit excessive growth and aggregation of metal grains during metal salt crystallization and carbonization, promote the subsequent formation of extremely fine metal nanocrystalline particles, and, by controlling the microfluidic diameter, effectively regulate the electromagnetic parameters and impedance matching of the material, significantly enhancing its microwave absorption performance.
[0026] Step S5: Freeze-dry the pre-frozen particles to obtain a freeze-dried sample; during the freeze-drying process, the temperature is -40~-70℃, the pressure is 1~3Pa, and the time is 48~72h.
[0027] In this embodiment, the pre-frozen particles are freeze-dried in a freeze dryer. Through the synergistic effect of microfluidic pre-freezing and freeze-drying, the network skeleton of xanthan gum is completely preserved, thereby naturally forming a three-dimensional porous network structure while inhibiting metal precipitation, effectively extending the electromagnetic wave propagation path and enhancing absorption efficiency.
[0028] Step S6: Pyrolyze the freeze-dried sample under an Ar atmosphere to obtain a microwave absorbing composite material; The pyrolysis temperature is 550~850℃, and the pyrolysis time is 2~3h. During the pyrolysis process, the heating rate is 3~5℃ / min.
[0029] Specifically, the freeze-dried sample is placed in a reactor with a pressure of 6-10 Pa, and Ar gas with a flow rate of 150-220 sccm is introduced into the reactor for 5-10 min. Under normal pressure, the flow rate of Ar gas is adjusted to 180-220 sccm, and the temperature is increased to 550-850℃ at a heating rate of 3-5℃ / min. The temperature is then maintained for 2-3 h for carbonization to obtain the microwave absorbing composite material.
[0030] In this embodiment, while controlling the microfluidic diameter of the precursor, the ratio of amorphous carbon to graphite carbon in the carbonization products is controlled by controlling the high-temperature pyrolysis temperature. This allows for precise control of the magnetic and dielectric properties of the material, thereby achieving effective control of the microwave absorption performance of the material and successfully preparing a microwave absorbing material with adjustable performance.
[0031] The second embodiment of the present invention provides a broadband absorbing composite material, prepared by the above-described method, achieving optimal performance with a reflection loss of -47.0 dB and an effective absorption bandwidth of 6.1 GHz at a thickness of 2.0 mm. Furthermore, the absorption performance can be adjusted within the range of 2-18 GHz by modifying the metal salt concentration, microfluidic diameter, and carbonization temperature, achieving a performance of less than or equal to -40 dB.
[0032] Example 1 Step S10: Place 5g xanthan gum powder in 180ml of deionized water to obtain a precursor solution; stir the precursor solution at 80℃ and then cool it to room temperature and continue stirring. Repeat this alternating cycle for 5 hours to obtain a homogeneous, semi-transparent gel solution. In step S20, 0.1058g of lanthanum nitrate, 0.433g of strontium nitrate hexahydrate, 0.146g of cobalt nitrate hexahydrate, 0.202g of ferric nitrate nonahydrate, and 0.099g of manganese chloride tetrahydrate metal salt powder are mixed in 50ml of deionized water to obtain a metal salt precursor solution. Step S30: Stir the metal salt precursor solution at 600 r / min for 30 min; add the gel solution to the stirred metal salt precursor solution and stir at room temperature for 1 h to obtain a mixed solution. Step S40: Use a syringe with a needle diameter of 0.1 mm to draw the mixed solution and slowly inject it into 500 ml of liquid nitrogen for pre-freezing while gently stirring to obtain pre-frozen particles; Step S50: Transfer the pre-frozen particles to a mold and place them in a freeze dryer. Freeze-dry the pre-frozen particles at a temperature of -70°C and a pressure of 1 Pa for 48 hours to obtain a freeze-dried sample. Step S60: Place the freeze-dried sample in a quartz tube with a pressure of 6 Pa, place the quartz tube in a single-temperature zone tube furnace, and introduce Ar gas at a flow rate of 220 sccm into the quartz tube for 10 min; under normal pressure, adjust the flow rate of Ar gas to 200 sccm, raise the temperature to 550°C at a heating rate of 3°C / min, hold for 2 h for carbonization, turn off the heating device, and cool to room temperature with the furnace to obtain an amorphous carbon / graphite carbon / magnetic metal salt microwave absorbing composite material in a quartz boat.
[0033] Example 2 Step S10: Place 4g xanthan gum powder in 150ml deionized water to obtain a precursor solution; stir the precursor solution at 80℃ and then cool it to room temperature and continue stirring. Repeat this alternating cycle for 4 hours to obtain a homogeneous, semi-transparent gel solution. In step S20, 0.1058g of lanthanum nitrate, 0.433g of strontium nitrate hexahydrate, 0.146g of cobalt nitrate hexahydrate, 0.202g of ferric nitrate nonahydrate, and 0.099g of manganese chloride tetrahydrate metal salt powder are mixed in 50ml of deionized water to obtain a metal salt precursor solution. Step S30: Stir the metal salt precursor solution at 800 r / min for 30 min; add the gel solution to the stirred metal salt precursor solution and stir at room temperature for 1 h to obtain a mixed solution; Step S40: Use a syringe with a needle diameter of 0.1 mm to draw the mixed solution and slowly inject it into 500 ml of liquid nitrogen for pre-freezing while gently stirring to obtain pre-frozen particles; Step S50: Transfer the pre-frozen particles to a mold and place them in a freeze dryer. Freeze-dry the pre-frozen particles at a temperature of -65°C and a pressure of 3 Pa for 60 hours to obtain a freeze-dried sample. Step S60: Place the freeze-dried sample in a quartz tube with a pressure of 10 Pa, place the quartz tube in a single-temperature zone tube furnace, and introduce Ar gas at a flow rate of 200 sccm into the quartz tube for 5 min; under normal pressure, adjust the flow rate of Ar gas to 180 sccm, raise the temperature to 650°C at a heating rate of 3°C / min, hold for 2 h for carbonization, turn off the heating device, and cool to room temperature with the furnace to obtain an amorphous carbon / graphite carbon / magnetic metal salt microwave absorbing composite material in a quartz boat.
[0034] Example 3 Step S10: Place 7g xanthan gum powder in 180ml of deionized water to obtain a precursor solution; stir the precursor solution at 80℃ and then cool it to room temperature and continue stirring. Repeat this alternating cycle for 5 hours to obtain a homogeneous, semi-transparent gel solution. In step S20, 0.1058g of lanthanum nitrate, 0.433g of strontium nitrate hexahydrate, 0.146g of cobalt nitrate hexahydrate, 0.202g of ferric nitrate nonahydrate, and 0.099g of manganese chloride tetrahydrate metal salt powder are mixed in 50ml of deionized water to obtain a metal salt precursor solution. Step S30: Stir the metal salt precursor solution at 800 r / min for 30 min; add the gel solution to the stirred metal salt precursor solution and stir at room temperature for 1 h to obtain a mixed solution; Step S40: Use a syringe with a needle diameter of 0.1 mm to draw the mixed solution and slowly inject it into 800 ml of liquid nitrogen for pre-freezing while gently stirring to obtain pre-frozen particles; Step S50: Transfer the pre-frozen particles to a mold and place them in a freeze dryer. Freeze-dry the pre-frozen particles at a temperature of -70°C and a pressure of 1 Pa for 72 hours to obtain a freeze-dried sample. Step S60: Place the freeze-dried sample in a quartz tube with a pressure of 6 Pa, place the quartz tube in a single-temperature zone tube furnace, and introduce Ar gas at a flow rate of 220 sccm into the quartz tube for 5 min; under normal pressure, heat to 850°C at a heating rate of 3°C / min, hold for 2 h for carbonization, turn off the heating device, and cool to room temperature with the furnace to obtain an amorphous carbon / graphite carbon / magnetic metal salt microwave absorbing composite material in a quartz boat.
[0035] Example 4 Step S10: Place 7g xanthan gum powder in 180ml of deionized water to obtain a precursor solution; stir the precursor solution at 80℃ and then cool it to room temperature and continue stirring. Repeat this alternating cycle for 5 hours to obtain a homogeneous, semi-transparent gel solution. In step S20, 0.1058g of lanthanum nitrate, 0.433g of strontium nitrate hexahydrate, 0.146g of cobalt nitrate hexahydrate, 0.202g of ferric nitrate nonahydrate, and 0.099g of manganese chloride tetrahydrate metal salt powder are mixed in 50ml of deionized water to obtain a metal salt precursor solution. Step S30: Stir the metal salt precursor solution at 800 r / min for 30 min; add the gel solution to the stirred metal salt precursor solution and stir at room temperature for 1 h to obtain a mixed solution; Step S40: Use a syringe with a needle diameter of 2 mm to draw the mixed solution and slowly inject it into 800 ml of liquid nitrogen for pre-freezing while gently stirring to obtain pre-frozen particles. Step S50: Transfer the pre-frozen particles to a mold and place them in a freeze dryer. Freeze-dry the pre-frozen particles at a temperature of -70°C and a pressure of 1 Pa for 72 hours to obtain a freeze-dried sample. Step S60: Place the freeze-dried sample in a quartz tube with a pressure of 6 Pa, place the quartz tube in a single-temperature zone tube furnace, and introduce Ar gas at a flow rate of 220 sccm into the quartz tube for 5 min; under normal pressure, heat to 850°C at a heating rate of 3°C / min, hold for 2 h for carbonization, turn off the heating device, and cool to room temperature with the furnace to obtain an amorphous carbon / graphite carbon / magnetic metal salt microwave absorbing composite material in a quartz boat.
[0036] Comparative Example 1 Step S10: Place 6g xanthan gum powder in 150ml deionized water to obtain a precursor solution; stir the precursor solution at 70℃ and then cool it to room temperature and continue stirring. Repeat this alternating cycle for 4 hours to obtain a homogeneous, semi-transparent gel solution. In step S20, 0.0529g of lanthanum nitrate, 0.2165g of strontium nitrate hexahydrate, 0.073g of cobalt nitrate hexahydrate, 0.101g of ferric nitrate nonahydrate, and 0.00495g of manganese chloride tetrahydrate metal salt powder are mixed in 50ml of deionized water to obtain a metal salt precursor solution. Step S30: Stir the metal salt precursor solution at 700 r / min for 30 min; add the gel solution to the stirred metal salt precursor solution and stir at room temperature for 1 h to obtain a mixed solution; Step S40: Use a syringe with a needle diameter of 0.1 mm to draw the mixed solution and slowly inject it into 700 ml of liquid nitrogen for pre-freezing while gently stirring to obtain pre-frozen particles; Step S50: Transfer the pre-frozen particles to a mold and place them in a freeze dryer. Freeze-dry the pre-frozen particles at a temperature of -50°C and a pressure of 1 Pa for 72 hours to obtain a freeze-dried sample. Step S60: Place the freeze-dried sample in a quartz tube with a pressure of 6 Pa, place the quartz tube in a single-temperature zone tube furnace, and introduce Ar gas at a flow rate of 200 sccm into the quartz tube for 8 min; under normal pressure, adjust the flow rate of Ar gas to 200 sccm, raise the temperature to 900℃ at a heating rate of 5℃ / min, hold for 3 h for carbonization, turn off the heating device, and cool to room temperature with the furnace to obtain an amorphous carbon / graphite carbon / magnetic metal salt microwave absorbing composite material in a quartz boat.
[0037] Comparative Example 2 Step S10: Place 5g xanthan gum powder in 150ml of deionized water to obtain a precursor solution; stir the precursor solution at 60℃ and then cool it to room temperature and continue stirring. Repeat this alternating cycle for 6 hours to obtain a homogeneous, semi-transparent gel solution. Step S20: Use a syringe with a needle diameter of 0.1 mm to draw the gel solution and inject it slowly and uniformly into 300 ml of liquid nitrogen for pre-freezing, while gently stirring to obtain pre-frozen particles; Step S30: Transfer the pre-frozen particles to a mold and place them in a freeze dryer. Freeze-dry the pre-frozen particles at a temperature of -70°C and a pressure of 1 Pa for 48 hours to obtain a freeze-dried sample. Step S40: Place the freeze-dried sample in a quartz tube with a pressure of 6 Pa, place the quartz tube in a single-temperature zone tube furnace, and introduce Ar gas at a flow rate of 150 sccm into the quartz tube for 10 min; under normal pressure, adjust the flow rate of Ar gas to 220 sccm, raise the temperature to 850°C at a heating rate of 5°C / min, hold for 2 h for carbonization, turn off the heating device, and cool to room temperature with the furnace to obtain an amorphous carbon / graphite carbon microwave absorbing composite material in a quartz boat.
[0038] Comparative Example 3 Step S10: Place 7g xanthan gum powder in 180ml of deionized water to obtain a precursor solution; stir the precursor solution at 80℃ and then cool it to room temperature and continue stirring. Repeat this alternating cycle for 5 hours to obtain a homogeneous, semi-transparent gel solution. In step S20, 0.1058g of lanthanum nitrate, 0.433g of strontium nitrate hexahydrate, 0.146g of cobalt nitrate hexahydrate, 0.202g of ferric nitrate nonahydrate, and 0.099g of manganese chloride tetrahydrate metal salt powder are mixed in 50ml of deionized water to obtain a metal salt precursor solution. Step S30: Stir the metal salt precursor solution at 800 r / min for 30 min; add the gel solution to the stirred metal salt precursor solution and stir at room temperature for 1 h to obtain a mixed solution; Step S40: Slowly pour the above mixed solution into 800ml of liquid nitrogen for pre-freezing while gently stirring to obtain pre-frozen particles; Step S50: Transfer the pre-frozen particles to a mold and place them in a freeze dryer. Freeze-dry the pre-frozen particles at a temperature of -70°C and a pressure of 1 Pa for 72 hours to obtain a freeze-dried sample. Step S60: Place the freeze-dried sample in a quartz tube with a pressure of 6 Pa, place the quartz tube in a single-temperature zone tube furnace, and introduce Ar gas at a flow rate of 220 sccm into the quartz tube for 5 min; under normal pressure, heat to 850°C at a heating rate of 3°C / min, hold for 2 h for carbonization, turn off the heating device, and cool to room temperature with the furnace to obtain an amorphous carbon / graphite carbon / magnetic metal salt microwave absorbing composite material in a quartz boat.
[0039] To illustrate the performance of the adjustable carbon metal microwave absorbing powder provided by the present invention, the following description is provided in conjunction with the accompanying drawings.
[0040] Figure 1 The image shows the physical specimens of amorphous carbon / graphite carbon / magnetic metal salt obtained in Example 1. Figure 2 The images shown are of the amorphous carbon / graphite carbon / magnetic metal salt obtained in Example 4. A comparison clearly shows that adjusting the microfluidic diameter can effectively control the macroscopic morphology of the material. The scanning electron microscope (SEM) image and EDS spectrum of the amorphous carbon / graphite carbon / magnetic metal salt microwave absorbing composite material prepared in Example 1 are shown below. Figures 3-4 ,from Figure 3 The microstructure of the composite material is plate-like, indicating that the propagation path of electromagnetic waves within the absorbing material can be lengthened by altering its microstructure, thereby enhancing the material's absorption performance. Figure 4 As can be seen from the energy spectrum, the microwave absorbing composite material prepared in Example 1 has its metal uniformly dispersed at the atomic or nanoscale scale, rather than forming a macroscopic continuous phase. This avoids excessive growth of metal grains during the subsequent carbonization process and effectively enhances the impedance matching of the material. This makes it easier for electromagnetic waves to enter the interior of the material instead of being reflected, thus achieving highly efficient microwave absorption. Figure 5 The images show the X-ray diffraction patterns of the microwave absorbing materials obtained after carbonization at different temperature fields in Examples 1, 2, and 3. Figure 5It can be seen that all samples show two similar diffraction characteristic peaks at 26° and 45°, corresponding to the (002) and (101) crystal planes of the carbon material, respectively. When the carbonization temperature increases, the two diffraction peaks (002) and (101) are the strongest and sharpest at 850°C, which corresponds to the high degree of graphitization of the material at this temperature, that is, the sample exhibits the characteristics of graphitic carbon. At 550°C, the (002) and (101) diffraction peaks of the material are weak and wide, which corresponds to the low degree of graphitization of the material at this temperature, and the sample exhibits the characteristics of amorphous carbon, with most of the foamed carbon material not yet graphitized. At 650°C, the intensity of the (002) and (101) diffraction peaks of the material is between the peak intensities at 550°C and 850°C, indicating that the carbonization temperature can significantly affect the degree of graphitization of the foamed carbon material, demonstrating the influence of the temperature field on its degree of graphitization, and thus proving the feasibility of the present invention to control the content ratio of amorphous carbon and graphitic carbon in the microwave absorbing composite material by controlling the high-temperature pyrolysis temperature. Figure 6 Examples 3 and 4 show the X-ray diffraction patterns of the microwave absorbing materials obtained after quenching and carbonization in different microfluidic fields at the same temperature. Figure 6 It can be seen that, in Example 3, the carbon material obtained by quenching under a smaller diameter microfluidic exhibits stronger (002) and (101) diffraction peaks, indicating a higher degree of graphitization. This further demonstrates the feasibility of controlling the ratio of amorphous carbon to graphite carbon in the microwave absorbing composite material by controlling the precursor microfluidic diameter. The Raman spectra of the microwave absorbing composite materials prepared in Examples 3, 4, and Comparative Example 3 are shown below. Figure 7 , Figure 8 and Figure 9 As can be seen from the figure, under the same temperature field control, the microwave absorbing material I obtained by small-diameter microfluidic injection quenching... D / I G Smaller; when the microfluidic diameter is 0.1 mm, its I D / I G It is 0.82; when the microfluidic diameter changes by 5 mm, its I D / I G The value increased to 0.976. This indicates that as the microfluidic diameter increases, the graphitization degree of the resulting carbon / metal microwave absorbing composite material weakens. For Comparative Example 3, which did not employ microfluidic pre-freezing, its I... D / I G The value is 1.05, indicating the weakest degree of graphitization at the same temperature. This further illustrates that the microfluidic pre-freezing method of this invention can improve and control the content ratio of amorphous carbon and graphite carbon in the microwave absorbing composite material. Its Raman data is consistent with the test results of the above X-ray diffraction pattern. Figure 10 , Figure 11 , Figure 12 , Figure 13 and Figure 14The images show three-dimensional reflection loss diagrams of the microwave absorbing composite materials prepared in Examples 3, 4, 1, 2, and 3, respectively. Analysis... Figure 10 , Figure 11 , Figure 12 and Figure 14 It can be seen that, with the addition of metal salts, the microwave absorbing composite material obtained by pre-freezing and quenching with the minimum microfluidic diameter in Example 3 exhibits higher reflection loss for electromagnetic waves compared to materials pre-freezing with a large microfluidic diameter or those without microfluidic pre-freezing treatment. The lowest reflection loss of the prepared microwave absorbing composite material can reach -47.0 dB, indicating that the microwave absorption performance of the material can be controlled by microfluidic pre-freezing and adjusting the microfluidic diameter. Analysis Figure 10 and Figure 12 It is known that excessively high carbonization temperatures reduce its ability to absorb electromagnetic waves. Analysis Figure 10 and Figure 13 It can be seen that, compared to pure xanthan gum, the effective absorption band of the metal salt-doped composite material shifts from high frequency to low frequency, indicating that adjusting the metal salt concentration can control the absorption band of the composite material. Figure 15 , Figure 16 , Figure 17 , Figure 18 and Figure 19 Two-dimensional reflection loss diagrams of the wave composite materials prepared in Examples 3, 4, 1, 2, and 3. Analysis Figures 15-19 It can be seen that the microwave absorbing composite material obtained by pre-freezing and quenching with the minimum microfluidic diameter can achieve an effective absorption bandwidth of 6.1 GHz. This indicates that a broadband high-performance microwave absorbing composite material can be obtained by controlling the precursor microfluidic diameter and the high-temperature pyrolysis temperature.
[0041] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.
Claims
1. A method for preparing a broadband microwave absorbing composite material, characterized in that, include: Xanthan gum powder was prepared into a gel solution; Lanthanum nitrate, strontium nitrate hexahydrate, cobalt nitrate hexahydrate, ferric nitrate nonahydrate, and manganese chloride tetrahydrate were mixed in a solvent to obtain a metal salt precursor solution. The gel solution and the metal salt precursor solution are mixed to obtain a mixed solution; The mixed solution is injected into a pre-freezing medium for pre-freezing to obtain pre-frozen particles; The pre-frozen particles were freeze-dried to obtain freeze-dried samples; The freeze-dried sample was pyrolyzed under an Ar atmosphere to obtain a microwave absorbing composite material. The pyrolysis temperature is 550~850℃, and the pyrolysis time is 2~3h.
2. The method for preparing the broadband absorbing composite material according to claim 1, characterized in that, The method for preparing the mixed solution is as follows: The metal salt precursor solution was stirred at a speed of 500-800 r / min for 25-35 min; The gel solution was added to the stirred metal salt precursor solution and stirred for 1-4 hours to obtain a mixed solution.
3. The method for preparing the broadband absorbing composite material according to claim 1, characterized in that, The method for preparing the pre-frozen particles includes: The mixed solution was drawn using a syringe with a needle diameter of 0.1-5 mm and injected at a constant rate into 300-800 ml of liquid nitrogen for pre-freezing to obtain pre-frozen particles.
4. The method for preparing the broadband absorbing composite material according to claim 1, characterized in that, During the freeze-drying process, the temperature is -40 to -70°C, the pressure is 1 to 3 Pa, and the time is 48 to 72 hours.
5. The method for preparing the broadband absorbing composite material according to claim 1, characterized in that, During the pyrolysis process, the heating rate is 3~5℃ / min.
6. The method for preparing the broadband absorbing composite material according to claim 1, characterized in that, The process of pyrolyzing the freeze-dried sample under an Ar atmosphere to obtain a microwave absorbing composite material includes: The freeze-dried sample was placed in a reactor with a pressure of 6-10 Pa, and Ar gas with a flow rate of 150-220 sccm was introduced into the reactor for 5-10 min. The flow rate of Ar gas was adjusted to 180~220 sccm, and pyrolysis was carried out to obtain a microwave absorbing composite material.
7. The method for preparing the broadband absorbing composite material according to claim 1, characterized in that, The mass ratio of lanthanum nitrate, strontium nitrate hexahydrate, cobalt nitrate hexahydrate, ferric nitrate nonahydrate and manganese chloride tetrahydrate is 4: (15~21): (5~10): (8~13): (3~6).
8. The method for preparing the broadband absorbing composite material according to claim 1, characterized in that, The mass ratio of xanthan gum to metal salt is 6~10:
1.
9. The method for preparing the broadband absorbing composite material according to claim 1, characterized in that, The method for preparing the gel solution includes: Xanthan gum powder was placed in deionized water to obtain a precursor solution with a concentration of 20-50 g / L. The precursor solution was alternately stirred at 60-80℃ and 20-30℃ for 4-6 hours to obtain a homogeneous, semi-transparent gel solution.
10. A broadband microwave absorbing composite material, characterized in that, It is obtained by the preparation method according to any one of claims 1 to 9.