A flaky Al2O3@SiC high thermal conductivity composite wave absorbing material and preparation method thereof

Abstract

The present invention provides a flaky Al2O3@SiC high thermal conductivity composite wave absorbing material and a preparation method thereof, the preparation method comprising the following steps: (1) Preparation of flaky Al2O3@SiO2: using tetraethyl orthosilicate as a silicon source to coat a layer of SiO2 on the surface of flaky Al2O3 to obtain a composite material of Al2O3@SiO2 having a flaky structure; (2) Preparation of flaky Al2O3@SiC: using sucrose as a carbon source, introducing Ar gas into a high temperature furnace containing flaky Al2O3@SiO2 for reaction, and reducing SiO2 by carbon to obtain a flaky Al2O3@SiC high thermal conductivity composite wave absorbing material. The present invention not only effectively improves the thermal conductivity of the composite material by coating a layer of SiC on the surface of flaky Al2O3, but also greatly increases the number of reflections and scatterings of incident electromagnetic waves in the material, effectively improves the absorption intensity, and improves the problem of low thermal conductivity of traditional wave absorbing agents.

Description

Technical Field

[0001] The invention belongs to the technical field of absorbing materials, and in particular relates to a flaky Al2O3@SiC high thermal conductivity composite absorbing material. Background Art

[0002] As a traditional absorbing material, silicon carbide also has the characteristics of high thermal conductivity, and can be used to develop multifunctional thermal conductive absorbing materials with strong attenuation absorption and good heat dissipation characteristics for electromagnetic signals. Compared with other absorbing materials, silicon carbide has low density and high thermal conductivity, good chemical stability and high temperature resistance, and can adjust its dielectric properties by doping and modification to absorb electromagnetic waves, and can achieve light weight, thin layer, and broadband absorption. It is a high temperature resistant absorbing material with broad application prospects. Therefore, in recent years, there have been increasing reports on research on silicon carbide-based composite materials. For example, patent number CN 112694661 A provides an electromagnetic shielding polypropylene composite material prepared by doping ultrafine nickel powder and coupling modified silicon carbide powder as functional fillers. The electromagnetic shielding polypropylene composite material prepared by doping ultrafine nickel powder and coupling modified silicon carbide powder as functional fillers has good thermal conductivity and absorbing properties, but due to the addition of metal nickel powder in the patent, the cost and specific gravity of the material are greatly increased. Patent No. CN 109811429 B discloses a silicon carbide fiber containing nano-aluminum nitride and metallic nickel and a preparation method thereof, which converts aluminum oxide into aluminum nitride and uses its high thermal conductivity to make the material stable under high temperature conditions. The patent does not explore the thermal conductivity of silicon carbide fibers, and the performance of aluminum nitride is not stable and is easily hydrolyzed at room temperature, thus affecting its thermal conductivity.

[0003] In summary, current research mainly uses spherical and fibrous silicon carbide as absorbing materials. However, due to the high price of silicon carbide fibers and the complex preparation and purification grading processes, the manufacturing cost of the absorbing materials is high, and from a practical point of view, it is difficult to obtain widespread application. Conventional spherical silicon carbide has limited absorption performance, so it is necessary to research and develop new structures of silicon carbide-based composite materials.

[0004] In view of the above situation, the problem can be solved by flaking spherical particles. The flaky absorber has a larger surface, which produces a larger dipole moment, increases its natural resonance frequency, and thus breaks through the Snoek limit, increasing the absorption and scattering capabilities of the absorber. Therefore, the flaky absorber has better absorbing performance than spherical particles. However, due to the high hardness of silicon carbide, it is difficult to directly flaky spherical silicon carbide. In order to better improve the comprehensive performance of thermal conductivity and wave absorption of silicon carbide-based composite materials, this patent has developed a novel flaky Al2O3@SiC high thermal conductivity composite absorbing material. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a flaky Al2O3@SiC high thermal conductivity composite absorbing material, the mechanism of which is as follows:

[0006] (1) Core layer: The core layer is flaky aluminum oxide. On the one hand, flaky aluminum oxide has high chemical stability and high thermal conductivity; on the other hand, the special two-dimensional flaky structure has a significant shielding effect. The dense flaky structure can make the electromagnetic waves gradually attenuate after multiple reflections between the flaks, and it is difficult for them to diffract and escape from the "flak array", so that the electromagnetic waves are finally completely attenuated and absorbed.

[0007] (2) Shell: The silicon carbide in the shell not only has a strong electromagnetic wave absorption effect, but also has a low specific gravity. SiC has a high dielectric constant and will generate a large amount of electric dipole moment on the Al2O3 surface with excellent electrical insulation and low dielectric loss, enhancing the interface polarization ability, thereby improving the impedance matching performance and wave absorption performance of SiC, and achieving a strong absorption loss effect on electromagnetic waves.

[0008] The technical solution adopted by the present invention is:

[0009] A high thermal conductivity composite absorbing material and a preparation method thereof, the specific preparation steps are as follows:

[0010] (1) Preparation of flaky Al2O3@SiO2: Weigh a certain amount of flaky Al2O3 and disperse it in a mixed solution of anhydrous ethanol and deionized water, add ammonia water, and transfer the mixed solution into a three-necked flask after ultrasonic dispersion for 30 min. Use an electric stirrer to add ethyl orthosilicate while stirring and react for 3-6 h. After washing the product with anhydrous ethanol for 4 times, the product is dispersed in anhydrous ethanol to form a flaky Al2O3@SiO2 suspension.

[0011] (2) Preparation of flaky Al2O3@SiC: The flaky Al2O3@SiO2 prepared in step (1) was added to a sucrose solution, stirred thoroughly, allowed to stand for 24 h, and then dried to obtain a solid product. The solid product was ground into powder using a planetary ball mill at a low speed and then placed in a high-temperature furnace for high-temperature reaction under an Ar atmosphere for 1-3 h. Finally, the remaining carbon was removed in air at 800°C to obtain a flaky Al2O3@SiC product.

[0012] In step (1), the particle size of the flaky Al2O3 is 1-20 μm and the density is 3.5 g / cm 3 .

[0013] In the step (1), the mass ratios of flaky Al2O3, anhydrous ethanol and deionized water are 1:80-150:30-60 respectively.

[0014] In the step (1), the mass ratios of flaky Al2O3, ammonia water and tetraethyl orthosilicate are 1:15-20:5-10 respectively.

[0015] In the step (1), the stirring speed of the electric stirrer is 300-500 r / min.

[0016] In the step (1), the mass ratio of anhydrous ethanol to flaky Al2O3 required for product dispersion is 30-50:1.

[0017] In the step (2), the mass fraction of the sucrose solution is 40-60%.

[0018] In the step (2), the mass ratio of the flaky Al2O3@SiO2 to the sucrose solution is 1:10-30.

[0019] In the step (2), the rotation speed of the planetary ball mill is 100-200 r / min.

[0020] In the step (2), the temperature of the high temperature furnace is set to 1400-2100°C.

[0021] Beneficial effects of the technology of the present invention:

[0022] The flaky Al2O3@SiC of the present invention is a composite absorbing material with flaky aluminum oxide as a core and silicon carbide as a shell. The flaky aluminum oxide can form a dense "sheet array" to greatly increase the number of reflection / scattering times of the incident electromagnetic wave in the material, and the contact area between the flaky aluminum oxide is large, and the heat transfer effect is better; the shell silicon carbide can solve the problem of poor absorption performance of aluminum oxide, effectively improve the absorption intensity and greatly enhance the thermal conductivity of the composite material. The prepared composite material has the effects of high thermal conductivity and strong electromagnetic wave absorption. DETAILED DESCRIPTION

[0023] In order to better understand the invention, the content of the patent of the present invention is further explained below in conjunction with the implementation examples. However, the content of the patent of the present invention is not limited to the following implementation examples. Based on the embodiments of the present invention, other embodiments obtained by technicians in this field without creative work all fall within the scope of protection of the present invention.

[0024] Example 1

[0025] Preparation of flaky Al2O3@SiO2: Take 5g of 5μm flaky Al2O3 and disperse it in a mixed solution of 400g anhydrous ethanol and 150g deionized water, drop 75g of ammonia water, and ultrasonically disperse for 30min. Transfer the mixed solution to a 1000ml three-necked flask, use an electric stirrer at 300r / min and drop 25g of ethyl orthosilicate while stirring, and react for 3h. After washing the product with anhydrous ethanol 4 times, finally disperse the product in 150g of anhydrous ethanol to form a flaky Al2O3@SiO2 suspension.

[0026] Preparation of flaky Al2O3@SiC: Take 3g of flaky Al2O3@SiO2 prepared in step (1), add 30g of 40% sucrose solution, stir thoroughly, let stand for 24 hours and then dry to obtain a solid product. The solid product is ball-milled into powder using a planetary ball mill set to a speed of 100r / min and placed in a high-temperature furnace. After reacting for 1h at 1400℃ under Ar atmosphere, air is introduced and calcined at 800℃ for 2h to remove remaining carbon to obtain a flaky Al2O3@SiC product.

[0027] Example 2

[0028] The temperature used in the preparation of flaky Al2O3@SiC in Example 1 was changed to 1900°C, and the other steps and amounts were the same as in Example 1.

[0029] Example 3

[0030] The reaction time for preparing the flaky Al2O3@SiC in Example 1 was changed to 3 h, and the other steps and amounts were the same as in Example 1.

[0031] Comparative Example 1

[0032] The preparation method of Comparative Example 1 is similar to that of Example 1, except that spherical Al2O3 is used as the core, and the 5μm flake Al2O3 in step (1) is replaced with 5μm flake Al2O3, and the other steps and amounts are the same as those in Example 1.

[0033] Comparative Example 2

[0034] Comparative Example 1 is a physically mixed product of Al2O3 and SiC powders with the same specific gravity as the flaky Al2O3@SiC product of Example 1; Comparative Example 1 is a wave absorbing and thermally conductive material formed by mixing 5μm flaky Al2O3 and 2μm spherical SiC in a mass ratio of 6:1. The specific preparation method is as follows: 600g of flaky Al2O3 and 100g of SiC are weighed respectively and placed in a 10L mixer and mixed evenly, wherein the mixing speed is 250r / min and the mixing time is 10min.

[0035] Blank example 1

[0036] Blank Example 1 is 5μm flake Al2O3.

[0037] Blank example 2

[0038] Blank Example 2 is 2 μm spherical SiC.

[0039] The performance test methods and standards are as follows:

[0040] Wave absorption performance test: The wave absorption performance was tested by the coaxial method of the vector network analyzer, and the dielectric constant and magnetic permeability were tested to calculate the reflection loss (RL) of 2mm thickness. The formula is as follows. The equipment model used is N5222B;

[0041]

[0042] Thermal conductivity test: a silicone gasket was prepared with a mass ratio of 1:3 between the mixed silicone oil and the absorbing powder. A heat flow thermal conductivity tester was used according to the ASTME D5470-6 standard. The sample size was 26mm*26mm and the thickness was 2mm.

[0043] The sample preparation process for the absorbing performance test is as follows: 12g of the composite absorbing material and 8g of paraffin are placed in a beaker, and after preliminary dispersion, they are placed in an oven at 80°C. After keeping warm for 30 minutes, they are stirred evenly with a glass rod and placed in a mold to produce a sample with an inner diameter of 3.04mm, an outer diameter of 7.00mm, and a thickness of 3mm.

[0044] The preparation process of the thermal conductivity test sample is as follows: after 60g of the composite absorbing material and 20g of the mixed silicone oil are initially dispersed, a vacuum stirring degassing machine is used to disperse them evenly, the speed is set to 900r / min, and the dispersion time is 120s; the mixed silicone oil system is 100 parts of 500cP vinyl silicone oil + 4.2 parts of side hydrogenated silicone oil + 0.33 parts of acetylene cyclohexanol inhibitor + 0.33 parts of platinum catalyst.

[0045] The performance tests of the prepared Al2O3@SiC composite absorber are shown in Table 1.

[0046] Table 1:

[0047]

[0048] As can be seen from Table 1, the absorbing performance of the absorbing material is greatly affected by the material composition and its structure. 1) Compared with Comparative Example 1, Comparative Example 2 and Blank Example 2, the reflection loss peak of the flaky Al2O3@SiC composite absorbing material in Example 1 is reduced from -19dB, -13dB and -15dB to -29dB, respectively, and the absorbing effect is improved by about 52.6%, 123% and 93%, indicating that the Al2O3 flaky structure provides an attachment surface for SiC, and the "flake array" formed greatly increases the reflection / scattering effect of the incident electromagnetic wave in the material. 2) Compared with Blank Example 1, the flaky Al2O3@SiC composite absorbing material in Example 3 has an absorbing performance improved by 150%, and a thermal conductivity improved by about 75%. The SiC coating improves the absorbing performance of the flaky Al2O3, and the good heat dissipation characteristics of SiC improve the thermal conductivity of the flaky Al2O3.

Claims

1. A method for preparing a flaky Al2O3@SiC high thermal conductivity composite absorbing material, the specific preparation steps are as follows: (1) Preparation of flaky Al2O3@SiO2: Weigh a certain amount of flaky Al2O3 and disperse it in a mixed solution of anhydrous ethanol and deionized water, add ammonia water, and transfer the mixed solution into a three-necked flask after ultrasonic dispersion for 30 min. Use an electric stirrer to add ethyl orthosilicate while stirring and react for 3-6 h. After washing the product with anhydrous ethanol for 4 times, the product is dispersed in anhydrous ethanol to form a flaky Al2O3@SiO2 suspension. (2) Preparation of flaky Al2O3@SiC: The flaky Al2O3@SiO2 prepared in step (1) was added to a sucrose solution, stirred thoroughly, allowed to stand for 24 h, and then dried to obtain a solid product. The solid product was ground into powder using a planetary ball mill at a low speed and then placed in a high-temperature furnace for high-temperature reaction under an Ar atmosphere for 1-3 h. Finally, the remaining carbon was removed in air at 800°C to obtain a flaky Al2O3@SiC product.

2. The method for preparing a flaky Al2O3@SiC high thermal conductivity composite absorbing material according to claim 1, characterized in that: In step (1), the particle size of the flaky Al2O3 is 1-20 μm and the density is 3.5 g / cm 3 .

3. The method for preparing a flaky Al2O3@SiC high thermal conductivity composite absorbing material according to claim 1, characterized in that: In the step (1), the mass ratios of flaky Al2O3, anhydrous ethanol and deionized water are 1:80-150:30-60 respectively.

4. The method for preparing a flaky Al2O3@SiC high thermal conductivity composite absorbing material according to claim 1, characterized in that: In the step (1), the mass ratios of flaky Al2O3, ammonia water and tetraethyl orthosilicate are 1:15-20:5-10 respectively.

5. The method for preparing a flaky Al2O3@SiC high thermal conductivity composite absorbing material according to claim 1, characterized in that: In the step (1), the stirring speed of the electric stirrer is 300-500 r / min.

6. The method for preparing a flaky Al2O3@SiC high thermal conductivity composite absorbing material according to claim 1, characterized in that: In the step (1), the mass ratio of anhydrous ethanol to flaky Al2O3 required for product dispersion is 30-50:

1.

7. The method for preparing a flaky Al2O3@SiC high thermal conductivity composite absorbing material according to claim 1, characterized in that: In the step (2), the mass fraction of the sucrose solution is 40-60%.

8. The method for preparing a flaky Al2O3@SiC high thermal conductivity composite absorbing material according to claim 1, characterized in that: In the step (2), the mass ratio of the flaky Al2O3@SiO2 to the sucrose solution is 1:10-30.

9. The method for preparing a flaky Al2O3@SiC high thermal conductivity composite absorbing material according to claim 1, characterized in that: In the step (2), the rotation speed of the planetary ball mill is 100-200 r / min.

10. The method for preparing a flaky Al2O3@SiC high thermal conductivity composite absorbing material according to claim 1, It is characterized in that In the step (2), the temperature of the high temperature furnace is set to 1400-2100°C.

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