A Low-Specific-Gravity Composite Absorbing Material and Its Preparation Method

Abstract

The present invention provides a low-specific-gravity composite microwave absorbing material and a preparation method thereof. The preparation method includes the following steps: (1) Preparation of hollow microsphere@MnO2: The surface of the hollow microsphere is etched, and then a flower-shaped MnO2 layer is formed on the surface of the hollow microsphere using a KMnO4 solution as the manganese source to obtain a hollow microsphere@MnO2 composite material; (2) Deposition of nano-carbonyl iron powder: Vaporized Fe(CO)5 and preheated nitrogen are introduced into a pyrolysis furnace containing hollow microsphere@MnO2. After thermal decomposition, the carbonyl iron powder is deposited on the surface of the flower-shaped hollow microsphere@MnO2, and thus a low-specific-gravity composite microwave absorbing material of hollow microsphere@MnO2@carbonyl iron powder is obtained. By coating a flower-shaped MnO2 layer and a nano-carbonyl iron powder layer on the surface of the hollow microsphere, the present invention not only effectively reduces the specific gravity of the composite material, but also greatly increases the number of reflections and scatterings of incident electromagnetic waves in the material, effectively improving the absorption intensity and solving the problems of high specific gravity of traditional microwave absorbing agents and low absorption intensity of single absorbing agents.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave absorbing materials, and particularly relates to a preparation method of a low specific gravity microwave absorbing material. Background Art

[0002] With the rapid development of electronic devices, local area networks and communication facilities, electromagnetic wave pollution has become an increasingly serious problem. It not only interferes with the operation of various commercial and industrial equipment, but also threatens human health and national defense security. To prevent the harm caused by electromagnetic radiation, the development of electromagnetic wave absorbing materials is considered an effective method. Currently, the commonly used microwave absorbing materials in the market mainly include carbonyl iron powder, metal micro-powder and barium titanate, etc. These materials have a relatively high specific gravity and are difficult to meet the requirements of ideal microwave absorbing materials for wide absorption bandwidth, light weight, thin thickness and strong absorption ability. In order to develop ideal microwave absorbing materials with light weight, strong absorption and chemical stability, the preparation and performance research of composite materials have attracted extensive attention. For example, Patent No. CN 109207123 A discloses a double-shell structure carbonyl iron powder composite microwave absorbing material and its preparation method, but this method uses carbonyl iron powder as the core and is still difficult to meet the requirements of ideal microwave absorbing materials for light weight. Patent No. CN 109943018 A provides a three-dimensional structure microwave absorbing agent formed by ferrite-coated hollow glass microspheres and graphene. The hollow glass microspheres have the characteristics of light weight and chemical stability. Coating the surface with nano-ferrite can enhance the microwave absorption effect. However, the raw material graphene oxide used has the disadvantage of complex process operation. At the same time, the dielectric constant of graphene material is relatively large and the impedance matching is poor, making it difficult to increase its content in the composite system. As the main microwave absorbing agent, ferrite is difficult to improve the absorption intensity, and the maximum reflection constant of the material in the embodiment is only -15 dB. In order to improve the high specific gravity of traditional microwave absorbing materials and further improve the microwave absorption performance, this patent has developed a novel lightweight and high-absorbing composite microwave absorbing material. Summary of the Invention

[0003] To solve the above technical problems, the present invention provides a hollow microsphere@MnO2@carbonyl iron powder low specific gravity composite microwave absorbing material, and its action mechanism is as follows:

[0004] (1) Core layer: The core layer is a hollow glass microsphere, which has a relatively low density and effectively reduces the specific gravity of the overall composite material. On the other hand, when electromagnetic waves enter the core layer, they will enter the hollow structure inside the core layer, and the electromagnetic waves will undergo multiple reflections inside to absorb the electromagnetic waves, increasing the propagation path of the electromagnetic waves.

[0005] (2) Intermediate layer: The intermediate layer is a flower-shaped MnO₂ layer assembled from square sheet structures. The numerous folds in the flower-shaped structure have abundant cavities, enhancing the multiple reflections and scattering of electromagnetic waves. Meanwhile, the dielectric loss type of MnO₂ can promote the migration and hopping of electrons, accelerating the formation of a conductive network, thereby increasing the conductive loss.

[0006] (3) Outermost layer: The outermost layer of carbonyl iron powder itself has strong absorption, effectively improving the absorption intensity of a single MnO₂ layer. The dual loss characteristics of magnetic loss and dielectric loss are far superior to a single loss mechanism. At the same time, there is interfacial polarization between the carbonyl iron powder and MnO₂, and a certain loss will be generated during the polarization process, enhancing the dissipation of electromagnetic wave energy in the composite absorbing material.

[0007] The technical solution adopted in the present invention is as follows:

[0008] A low-specific gravity composite absorbing material and its preparation method, and the specific preparation steps are as follows:

[0009] (1) Preparation of hollow microsphere@MnO₂: Etch the hollow microspheres; add a certain amount of KMnO₄ solution to the etched hollow microspheres, ultrasonically disperse to form a suspension, drop a certain amount of hydrochloric acid into it and stir at room temperature for 20 - 60 min. Transfer the mixture to a stainless steel autoclave, keep it warm at 100 - 150 °C for 6 - 12 h. After the autoclave naturally cools to room temperature, filter the product and continuously rinse it with ethanol and deionized water for 3 - 6 times. Finally, place it at 80 °C and vacuum dry it for 12 h to obtain flower-shaped hollow microsphere@MnO₂.

[0010] (2) Deposition of nano-carbonyl iron powder:

[0011] Place the hollow microsphere@MnO₂ prepared in step (1) in a pyrolysis furnace with a mixing device, while stirring, introduce vaporized Fe(CO)₅ and preheated nitrogen. After pyrolyzing at 250 - 350 °C for 0.5 - 5 h, the carbonyl iron powder is deposited on the surface of the flower-shaped hollow microsphere@MnO₂, and the low-specific gravity composite absorbing material of hollow microsphere@MnO₂@carbonyl iron powder is obtained.

[0012] In the said step (1), the particle size of the hollow microspheres is 1 - 10 μm, and the density is 1.1 - 2.8 g / cm 3 .

[0013] In the said step (1), the solution used for the etching treatment is HF with a mass fraction of 5% - 15%; the specific etching step is to mix HF and the hollow microspheres according to a mass ratio of 5 - 10:1, and place them in a water bath at 50 °C and stir for 15 - 40 min.

[0014] In the step (1), the mass fraction of the KMnO4 solution is 0.6%-1.8%, the mass fraction of the hydrochloric acid solution is 25-37%, and the mass ratio of the hollow microspheres, the KMnO4 solution to the hydrochloric acid is 1:100-250:2.0-7.5.

[0015] In the step (2), the vaporized Fe(CO)5 is obtained by vaporizing the liquid pentacarbonyl iron in a vaporizer at 140-160°C, the preheating temperature of the nitrogen gas is 250-350°C, and the volume ratio of the preheated nitrogen gas to the vaporized Fe(CO)5 is 100-150:1.

[0016] In the step (2), the stirring speed is 5-50 r / min.

[0017] Advantages of the technology of the present invention:

[0018] The hollow microsphere@MnO2@carbonyl iron powder of the present invention is a three-layer composite wave-absorbing material with a hollow microsphere as the core, a flower-like structure manganese dioxide as the shell, and a layer of carbonyl iron powder particles coated on the outermost layer. The hollow cavity of the hollow microsphere and the flower-like structure of the MnO2 layer not only effectively reduce the specific gravity of the composite material, but also greatly increase the number of reflections / scatterings of the incident electromagnetic wave in the material. The carbonyl iron powder deposited on the outermost layer solves the problem of low reflection constant of the single MnO2 absorber, effectively improves the absorption intensity, and the prepared composite material has an efficient electromagnetic wave absorption effect.

[0019] Description of the drawings

[0020] Figure 1 It is a schematic structural diagram of the flower-like hollow microsphere@MnO2 material.

[0021] Figure 2 It is a schematic diagram of the wave-absorbing mechanism of the hollow microsphere@MnO2@carbonyl iron powder composite wave-absorbing material. Detailed implementation manners

[0022] In order to better understand the present invention, the content of the present invention patent will be further clarified below in combination with the implementation examples. However, the content of the present invention patent is not limited to the following implementation examples. Other implementation examples obtained by those skilled in the art based on the embodiments of the present invention without creative efforts all fall within the scope of protection of the present invention.

[0023] Example 1

[0024] Preparation of hollow microspheres@MnO2: Take 3 g of hollow microspheres and mix them with 15 g of 10% HF by mass. Place the mixture in a water bath at 40 °C and stir for 25 min. Then filter the product and rinse it three times with deionized water. Finally, place it at 80 °C and vacuum dry for 6 h to obtain etched hollow microspheres. Mix the etched hollow microspheres with 300 g of a 1.2% KMnO4 solution by mass, place the mixture in an ultrasonic device for ultrasonic dispersion to form a suspension, and then add 1.2 g of a 37% hydrochloric acid solution by mass. After stirring at room temperature for 20 min, transfer the mixture to a stainless-steel autoclave and keep it at 100 °C for 6 h. After the autoclave cools naturally to room temperature, filter the product and rinse it three times with ethanol and deionized water. Finally, place it at 80 °C and vacuum dry for 12 h to obtain flower-like hollow microspheres@MnO2.

[0025] Deposition of nano-carbonyl iron powder: Place the hollow microspheres@MnO2 composite microwave-absorbing material in a pyrolysis furnace equipped with a mixing device. While stirring at a speed of 20 r / min, introduce vaporized Fe(CO)5 and nitrogen preheated to 250 °C. The volume ratio of nitrogen to Fe(CO)5 is 100:1. After thermal decomposition at 250 °C for 1 h, obtain the hollow microspheres@MnO2@carbonyl iron powder composite microwave-absorbing material.

[0026] Example 2

[0027] Change the temperature used in the preparation of the hollow microspheres@MnO2 composite material in Example 1 to 120 °C, and keep other steps and dosages the same as those in Example 1.

[0028] Example 3

[0029] Change the addition amount of the 37% hydrochloric acid solution used in the preparation of the hollow microspheres@MnO2 composite material in Example 1 to 0.8 g, and keep other steps and dosages the same as those in Example 1.

[0030] Comparative Example 1

[0031] The preparation method of Comparative Example 1 is similar to that of Example 1, except that carbonyl iron powder is not deposited on the hollow microspheres@MnO2 material, and other steps and dosages are the same as those in Example 1.

[0032] Comparative Example 2

[0033] The preparation method of Comparative Example 2 is similar to that of Example 1, except that the flower-like MnO2 intermediate layer is not prepared, and only nano-carbonyl iron powder is deposited on the hollow microspheres, and other steps and dosages are the same as those in Example 1.

[0034] Comparative Example 3

[0035] Comparative Example 3 is a wave-absorbing and heat-conducting material prepared by uniformly mixing carbonyl iron powder, hollow microspheres, and MnO₂ in a mass ratio of 5:2:3 while maintaining the same proportion as in Example 1. The specific preparation method is as follows: Weigh 500 g of carbonyl iron powder, 200 g of hollow microspheres, and 300 g of MnO₂ respectively and place them in a 10 L mixer for uniform mixing. The mixing speed is 250 r / min, and the mixing time is 10 min.

[0036] Blank Example

[0037] The blank example is carbonyl iron powder with a particle size of 1 μm.

[0038] The test methods and standards for each property are as follows:

[0039] Wave-absorbing performance test: The wave-absorbing performance is tested by the coaxial method using a vector network analyzer. The dielectric constant and magnetic permeability are measured to calculate the reflection loss (RL). The formula is as follows, and the equipment model used is N5222B;

[0040]

[0041] Specific gravity test: An organosilicon gasket is prepared according to a mass ratio of 1:2 of mixed silicone oil to wave-absorbing powder, and it is tested using a direct-reading electronic specific gravity meter, model DH-300.

[0042] The preparation process of the wave-absorbing performance test sample is as follows: 12 g of the composite wave-absorbing material and 8 g of paraffin are placed in a beaker. After preliminary dispersion, it is put into an oven at 80 °C. After keeping warm for 30 min, it is stirred evenly with a glass rod and then put into a mold to make a sample with an inner diameter of 3.04 mm, an outer diameter of 7.00 mm, and a thickness of 3 mm.

[0043] The preparation process of the specific gravity test sample is as follows: 80 g of the composite wave-absorbing material and 40 g of mixed silicone oil are preliminarily dispersed, and then dispersed evenly using a vacuum stirring and degassing machine. The rotation speed is set to 900 r / min, and the dispersion time is 120 s; the mixed silicone oil system is 100 parts of 500 cP vinyl silicone oil + 4.0 parts of side hydrogen-containing silicone oil + 0.33 parts of ethynylcyclohexanol inhibitor + 0.33 parts of platinum catalyst.

[0044] The performance tests of the hollow microsphere@MnO₂@carbonyl iron powder composite wave-absorbing materials prepared in each example are shown in Table 1.

[0045] Table 1:

[0046]

[0047] As can be seen from Table 1, the microwave absorption performance of the microwave absorption material is greatly affected by material composite and its structure. 1) Compared with the hollow microsphere@MnO2 composite microwave absorption material without deposited carbonyl iron powder in Comparative Example 1, after depositing carbonyl iron powder in Example 1, the microwave absorption frequency band of the composite material shifts to lower frequency, and the peak value of reflection loss decreases from -12 dB to -36 dB, and the microwave absorption effect is improved by about 200%, indicating that there is a synergistic enhancement effect between carbonyl iron powder and MnO2. 2) Compared with Comparative Example 2 and Comparative Example 3, the reflection loss peaks of the hollow microsphere@MnO2@carbonyl iron powder composite material in Example 1 are reduced by 100% and 300% respectively, indicating that the flower-like MnO2 intermediate layer structure plays a significant role in the composite microwave absorption material. 3) Compared with the blank example, the specific gravity of the hollow microsphere@MnO2@carbonyl iron powder in Example 1 is reduced by about 34%, and the reflection loss peak is reduced by about 157%, indicating that the lightweight hollow microspheres and flower-like structure of the present invention can effectively reduce the specific gravity of the material and enhance the multiple reflection / scattering effect of electromagnetic waves.

Claims

1. Preparation method of a low-specific-gravity composite wave-absorbing material, and the specific preparation steps are as follows: (1) Preparation of hollow microspheres@MnO₂: Etch the hollow microspheres; add a certain amount of KMnO₄ solution to the etched hollow microspheres, ultrasonically disperse to form a suspension, drop a certain amount of hydrochloric acid into it and stir at room temperature for 20 - 60 min, transfer the mixture to a stainless-steel autoclave, keep it warm at 100 - 150 °C for 6 - 12 h, after the autoclave naturally cools to room temperature, filter the product and continuously rinse it with ethanol and deionized water for 3 - 6 times, and finally place it at 80 °C and vacuum-dry for 12 h to obtain hollow microspheres@MnO₂ with a flower-like structure; (2) Deposition of nano carbonyl iron powder: Place the hollow microspheres@MnO₂ prepared in step (1) in a pyrolysis furnace with a mixing device, while stirring, introduce vaporized Fe(CO)₅ and preheated nitrogen, after thermal decomposition at 250 - 350 °C for 0.5 - 5 h, carbonyl iron powder is deposited on the surface of the flower-like hollow microspheres@MnO₂, thus obtaining a low-specific-gravity composite wave-absorbing material of hollow microspheres@MnO₂@carbonyl iron powder; In the said step (1), the mass fraction of the KMnO₄ solution is 0.6% - 1.8%, the mass fraction of the hydrochloric acid solution is 25 - 37%, and the mass ratio of the hollow microspheres, KMnO₄ solution and hydrochloric acid is 1:100 - 250:2.0 - 7.

5.

2. The preparation method of a low specific gravity composite absorbing material according to claim 1, characterized in that, In the step (1), the hollow microspheres have a particle size of 1-10 μm and a density of 1.1-2.8 g / cm 3 .

3. The preparation method of a low specific gravity composite wave absorbing material according to claim 1, characterized in that, In the said step (1), the solution used for the etching treatment is HF with a mass fraction of 5% - 15%. The specific etching step is to mix HF and the hollow microspheres in a mass ratio of 5 - 10:1, and place them under a water bath condition of 50 °C and stir for 15 - 40 min.

4. The preparation method of a low specific gravity composite wave-absorbing material according to claim 1, characterized in that, In the said step (2), the vaporized Fe(CO)₅ is obtained by vaporizing liquid iron pentacarbonyl in a vaporizer at 140 - 160 °C, the preheating temperature of the nitrogen is 250 - 350 °C, and the volume ratio of the preheated nitrogen and the vaporized Fe(CO)₅ is 100 - 150:

1.

5. The preparation method of a low specific gravity composite absorbing material according to claim 1, characterized in that In the said step (2), the stirring speed is 5 - 50 r / min.

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