Method for preparing porous SiC wave-absorbing material from balsa wood and phenolic resin

Abstract

The invention discloses a method for preparing a porous SiC wave-absorbing material from balsa wood and phenolic resin, and relates to a preparation method of a wave-absorbing material. The invention aims to solve the problems of high cost, poor heat insulation performance, poor thermal stability, narrow absorption frequency band and difficulty in realizing large-scale production of the existing porous SiC wave-absorbing material. The method comprises: 1, preparing a boric acid solution; 2, preparing a phenolic resin solution; 3, mixing the boric acid solution with the phenolic resin solution, then adding zirconium oxychloride powder, and heating and dissolving; fourthly, the blocky balsa wood is placed in the mixed solution to be soaked; 5, carbonizing; and 6, carbon thermal reduction. The method is used for preparing the porous SiC wave-absorbing material from the balsa wood and the phenolic resin.

Description

Technical Field

[0001] The invention relates to a method for preparing a wave absorbing material. Background Art

[0002] The rapid development of electronic information and military detection technology has led to an increase in electromagnetic interference caused by communication equipment, which not only has a negative impact on military applications, but also poses a major threat to human health. In recent years, there has been increasing interest in biomass-derived absorbing materials. Biomass materials are not only abundant and widely available, but also conducive to the absorption of electromagnetic waves due to their unique microstructure and high porosity.

[0003] However, existing porous SiC absorbing materials have the problems of high cost, poor thermal insulation performance, poor thermal stability, narrow absorption band, and difficulty in large-scale production. Summary of the invention

[0004] The present invention aims to solve the problems of existing porous SiC absorbing materials, such as high cost, poor thermal insulation performance, poor thermal stability, narrow absorption band and difficulty in large-scale production, and further provides a method for preparing porous SiC absorbing materials using balsa wood and phenolic resin.

[0005] A method for preparing a porous SiC absorbing material using balsa wood and phenolic resin is carried out according to the following steps:

[0006] 1. Add boric acid into anhydrous ethanol and heat to dissolve to obtain a boric acid solution;

[0007] 2. adding phenolic resin into anhydrous ethanol and heating to dissolve, to obtain a phenolic resin solution;

[0008] 3. mixing the boric acid solution with the phenolic resin solution, and then adding zirconium oxychloride powder and heating to dissolve to obtain a mixed solution;

[0009] Fourth, placing the block of balsa wood in the mixed solution, performing vacuum impregnation at room temperature, and then taking it out to obtain a balsa wood mixture;

[0010] 5. Drying the balsa wood mixture, then heating it under an argon atmosphere, and carbonizing it under the conditions of an argon atmosphere and a temperature of 600° C. to 800° C. for 2 h to 4 h, and finally cooling it under an argon atmosphere to obtain porous carbon;

[0011] 6. Using porous carbon as the carbon source and a mixture of silicon and silicon dioxide as the silicon source, the silicon source is laid on the bottom of a graphite crucible, and then the carbon source is placed on the silicon source, the temperature is increased under an argon atmosphere, and a carbon thermal reduction reaction is carried out under an argon atmosphere and a temperature of 1250°C to 1600°C for 2h to 4h, and finally the temperature is reduced under an argon atmosphere to obtain a porous SiC absorbing material.

[0012] The beneficial effects of the present invention are as follows:

[0013] 1. Balsa wood is one of the lightest woods in the world. Its low density gives it significant advantages in weight-sensitive application scenarios. For example, in the protection of internal equipment of aircraft in the aerospace field or the protection of the enclosures of some weight-demanding electronic devices, compared with traditional metal electromagnetic shielding materials such as copper (density 8.96 g / cm3) or aluminum (density 2.7 g / cm 3 ), balsa wood is much lighter and will not impose too much burden on the overall weight of the equipment, which is helpful for the lightweight design of the equipment. The porous structure of balsa wood can not only provide a large specific surface area but also improve the impedance matching of the absorbing material, which is beneficial to the absorption of electromagnetic waves.

[0014] 2. Phenolic resin, boric acid, and zirconium oxychloride all have certain dielectric constants. Adding them to the absorbing material can adjust the dielectric properties of the overall material, enabling it to interact better with the incident electromagnetic waves and achieve effective absorption and attenuation of electromagnetic waves. Moreover, phenolic resin has high strength and hardness. Adding it to the absorbing material can significantly improve the overall mechanical properties of the material. In addition, phenolic resin, boric acid, and zirconium oxychloride have good high-temperature resistance, which can improve the thermal stability of the absorbing material. In some high-temperature environments, such as in the aerospace and electronic equipment fields, the absorbing material needs to maintain good absorbing performance and physical properties at high temperatures. Their addition can prevent the absorbing material from decomposing, deforming, etc. at high temperatures and ensure its normal use in high-temperature environments.

[0015] 3. The porous SiC absorbing material prepared by the present invention has the advantages of light weight, low cost, environmental friendliness, easy preparation, good absorbing performance, and wide absorption bandwidth. The main crystal phase of the prepared porous SiC absorbing material is 3C-SiC. When the thickness is 2.78 mm, it has a minimum reflection loss of -26.7941 dB. When the thickness is 3 mm, it has the widest absorption bandwidth of 7.1 GHz (10.6 GHz - 17.7 GHz).

[0016] 4. The porous SiC absorbing material prepared by the present invention has good heat insulation performance. The thermal conductivity of this porous SiC absorbing material is 0.033 W / (m·K).

[0017] 5. The porous SiC absorbing material prepared by the present invention has good thermal stability, and its weight hardly changes from room temperature to 600 °C. Description of the Drawings

[0018] Figure 1 SEM cross-sectional view of the porous SiC absorbing material prepared in Example 1;

[0019] Figure 2Cross-sectional scanning electron microscopy image of the porous SiC microwave absorbing material prepared in Example 1;

[0020] Figure 3 Longitudinal-sectional scanning electron microscopy image and Mapping image of the porous SiC microwave absorbing material prepared in Example 1;

[0021] Figure 4 XRD pattern of the porous SiC microwave absorbing material prepared in Example 1;

[0022] Figure 5 Microwave absorption performance graph of the porous SiC microwave absorbing material prepared in Example 1;

[0023] Figure 6 Reflection loss graph of the porous SiC microwave absorbing material prepared in Example 1;

[0024] Figure 7 Thermogravimetric graph of the porous SiC microwave absorbing material prepared in Example 1. Detailed implementation method

[0025] Detailed implementation method 1: A method for preparing a porous SiC microwave absorbing material using balsa wood and phenolic resin, which is carried out according to the following steps:

[0026] 1. Add boric acid to absolute ethanol and heat to dissolve to obtain a boric acid solution;

[0027] 2. Add phenolic resin to absolute ethanol and heat to dissolve to obtain a phenolic resin solution;

[0028] 3. Mix the boric acid solution and the phenolic resin solution, then add zirconium oxychloride powder and heat to dissolve to obtain a mixed solution;

[0029] 4. Place the block of balsa wood in the mixed solution, perform vacuum impregnation at room temperature, and then take it out to obtain a balsa wood mixture;

[0030] 5. Dry the balsa wood mixture, then heat it up in an argon atmosphere, and carry out carbonization for 2 h to 4 h under the conditions of an argon atmosphere and a temperature of 600 °C to 800 °C, and finally cool it down in an argon atmosphere to obtain porous carbon;

[0031] 6. Using the porous carbon as a carbon source and a mixture of silicon and silicon dioxide as a silicon source, lay the silicon source at the bottom of a graphite crucible, then place the carbon source on the silicon source, heat it up in an argon atmosphere, and carry out a carbothermal reduction reaction for 2 h to 4 h under the conditions of an argon atmosphere and a temperature of 1250 °C to 1600 °C, and finally cool it down in an argon atmosphere to obtain a porous SiC microwave absorbing material.

[0032] Principle:

[0033] In this specific embodiment, light wood and phenolic resin are used as dual carbon sources, silicon and silicon dioxide are used as silicon sources, and zirconium and boron elements are introduced. Through steps such as carbonization and carbothermal reduction, a carbon, silicon, boron, zirconium quaternary composite porous SiC microwave absorbing material is prepared under high-temperature conditions.

[0034] The beneficial effects of this embodiment are as follows:

[0035] I. Light wood is one of the lightest woods in the world. Its low density gives it significant advantages in weight-sensitive application scenarios. For example, in the protection of internal equipment of aircraft in the aerospace field or the protection of the enclosures of some electronic devices with strict weight requirements, compared with traditional metal electromagnetic shielding materials such as copper (density 8.96 g / cm 3 ³) or aluminum (density 2.7 g / cm³), light wood is much lighter and will not impose too much burden on the overall weight of the equipment, which is conducive to the lightweight design of the equipment. The porous structure of light wood can not only provide a large specific surface area but also improve the impedance matching of the microwave absorbing material, which is beneficial to the absorption of electromagnetic waves.

[0036] II. Phenolic resin, boric acid, and zirconium oxychloride all have certain dielectric constants. Adding them to the microwave absorbing material can adjust the dielectric properties of the overall material, enabling it to better interact with incident electromagnetic waves and achieve effective absorption and attenuation of electromagnetic waves. Moreover, phenolic resin has high strength and hardness. Adding it to the microwave absorbing material can significantly improve the overall mechanical properties of the material. In addition, phenolic resin, boric acid, and zirconium oxychloride have good high-temperature resistance, which can improve the thermal stability of the microwave absorbing material. In some high-temperature environments, such as in the aerospace and electronic equipment fields, the microwave absorbing material needs to maintain good microwave absorbing performance and physical properties under high-temperature conditions. Their addition can prevent the microwave absorbing material from decomposing, deforming, etc. at high temperatures, ensuring its normal use in high-temperature environments.

[0037] III. The porous SiC microwave absorbing material prepared in this embodiment has the advantages of light weight, low cost, environmental friendliness, convenient preparation, good microwave absorbing performance, and wide absorption bandwidth. The main crystal phase of the prepared porous SiC microwave absorbing material is 3C-SiC. When the thickness is 2.78 mm, it has a minimum reflection loss of -26.7941 dB. When the thickness is 3 mm, it has the widest absorption bandwidth of 7.1 GHz (10.6 GHz - 17.7 GHz).

[0038] IV. The porous SiC microwave absorbing material prepared in this embodiment has good heat insulation performance. The thermal conductivity of this porous SiC microwave absorbing material is 0.033 W / (m·K).

[0039] V. The porous SiC microwave absorbing material prepared in this embodiment has very good thermal stability, and its weight hardly changes from room temperature to 600 °C.

[0040] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that: in Step 1, the mass ratio of boric acid to absolute ethanol is 1:(5 - 10). Others are the same as Specific Embodiment 1.

[0041] Specific Embodiment 3: The difference between this embodiment and either Specific Embodiment 1 or 2 is that: in Step 2, the mass ratio of phenolic resin to absolute ethanol is 1:(1 - 5). Others are the same as Specific Embodiment 1 or 2.

[0042] Specific Embodiment 4: The difference between this embodiment and any one of Specific Embodiments 1 to 3 is that: in Step 3, the mass ratio of phenolic resin to boric acid in the mixed solution is 1:(5 - 10), and the mass ratio of zirconium oxychloride powder to boric acid is 1:(1 - 2). Others are the same as Specific Embodiment 3.

[0043] Specific Embodiment 5: The difference between this embodiment and any one of Specific Embodiments 1 to 4 is that: the heating and dissolution in Steps 1 to 3 are all carried out under the condition of a temperature of 50°C to 80°C for 5h to 10h. Others are the same as Specific Embodiments 1 to 4.

[0044] Specific Embodiment 6: The difference between this embodiment and any one of Specific Embodiments 1 to 5 is that: the vacuum impregnation in Step 4 is specifically carried out at room temperature and a pressure of -0.1MPa to -0.5MPa for 8h to 12h. Others are the same as Specific Embodiments 1 to 5.

[0045] Specific Embodiment 7: The difference between this embodiment and any one of Specific Embodiments 1 to 6 is that: the block of balsa wood in Step 4 is balsa wood; the mass ratio of the block of balsa wood to the mixed solution in Step 4 is 1:(10 - 30). Others are the same as Specific Embodiments 1 to 6.

[0046] Specific Embodiment 8: The difference between this embodiment and any one of Specific Embodiments 1 to 7 is that: the temperature increase in Step 5 is specifically carried out in an argon atmosphere, first increasing the temperature at a rate of 3°C / min to 5°C / min to 300°C to 500°C, and then increasing the temperature at a rate of 1°C / min to 3.5°C / min to 600°C to 800°C; the temperature decrease in Step 5 is specifically carried out in an argon atmosphere, decreasing the temperature at a rate of 5°C / min to 10°C / min to room temperature. Others are the same as Specific Embodiments 1 to 7.

[0047] Specific Embodiment 9: The difference between this embodiment and any one of Specific Embodiments 1 to 8 is that: the molar ratio of the carbon source to the silicon source in Step 6 is 1:(4 - 8); the molar ratio of silicon to silicon dioxide in the mixture of silicon and silicon dioxide in Step 6 is (1 - 10):1. Others are the same as Specific Embodiments 1 to 8.

[0048] Embodiment 10 in detail: The difference between this embodiment and any one of Embodiments 1 to 9 is that: in Step 6, the temperature increase is specifically carried out in an argon atmosphere. First, the temperature is increased to 800 °C to 1000 °C at a heating rate of 8 °C / min to 10 °C / min, then the temperature is increased to 1000 °C to 1200 °C at a heating rate of 3 °C / min to 5 °C / min, and then the temperature is increased to 1250 °C to 1600 °C at a heating rate of 2 °C / min to 5 °C / min; in Step 6, the temperature decrease is specifically carried out in an argon atmosphere. First, the temperature is decreased to 1000 °C to 1200 °C at a cooling rate of 2 °C / min to 5 °C / min, then the temperature is decreased to 800 °C to 1000 °C at a cooling rate of 3 °C / min to 5 °C / min, and finally the temperature is decreased to room temperature at a cooling rate of 8 °C / min to 10 °C / min. Others are the same as those in Embodiments 1 to 9.

[0049] The following examples are used to verify the beneficial effects of the present invention:

[0050] Example 1:

[0051] A method for preparing a porous SiC wave-absorbing material using balsa wood and phenolic resin is carried out according to the following steps:

[0052] I. Under the condition of a temperature of 60 °C, boric acid is added to absolute ethanol and heated and dissolved for 5 h to obtain a boric acid solution;

[0053] The mass ratio of the boric acid to the absolute ethanol is 1:6;

[0054] II. Under the condition of a temperature of 60 °C, phenolic resin is added to absolute ethanol and heated and dissolved for 5 h to obtain a phenolic resin solution;

[0055] The mass ratio of the phenolic resin to the absolute ethanol is 1:1; the phenolic resin is hard phenolic resin PF131;

[0056] III. The boric acid solution and the phenolic resin solution are mixed, and then zirconium oxychloride powder is added. Under the condition of a temperature of 60 °C, it is heated and dissolved for 5 h to obtain a mixed solution;

[0057] In the mixed solution, the mass ratio of the phenolic resin to the boric acid is 1:6, and the mass ratio of the zirconium oxychloride powder to the boric acid is 1:1;

[0058] IV. The blocky balsa wood is placed in the mixed solution, and under the conditions of normal temperature and a pressure of -0.1 MPa, it is vacuum-impregnated for 12 h, and then taken out to obtain a balsa wood mixture;

[0059] The blocky balsa wood is balsa wood; the mass ratio of the blocky balsa wood to the mixed solution is 1:20;

[0060] V. Under the condition that the temperature is 60 °C, dry the balsa wood mixture for 12 h, then heat it up under an argon atmosphere, and carry out carbonization for 2 h under an argon atmosphere and at a temperature of 600 °C. Finally, cool it down under an argon atmosphere to obtain porous carbon;

[0061] VI. Using the porous carbon as the carbon source and the mixture of silicon and silicon dioxide as the silicon source, lay the silicon source at the bottom of the graphite crucible, then place the carbon source on the silicon source, heat it up under an argon atmosphere, and carry out carbothermal reduction reaction for 2 h under an argon atmosphere and at a temperature of 1500 °C. Finally, cool it down under an argon atmosphere to obtain a porous SiC wave-absorbing material;

[0062] The molar ratio of the carbon source to the silicon source is 1:4; the molar ratio of silicon to silicon dioxide in the mixture of silicon and silicon dioxide is 1:1.

[0063] The heating up in Step V specifically means that under an argon atmosphere, first heat it up to 300 °C at a heating rate of 5 °C / min, and then heat it up to 600 °C at a heating rate of 1 °C / min; the cooling down in Step V specifically means that under an argon atmosphere, cool it down to room temperature at a cooling rate of 5 °C / min.

[0064] The heating up in Step VI specifically means that under an argon atmosphere, first heat it up to 800 °C at a heating rate of 10 °C / min, then heat it up to 1000 °C at a heating rate of 5 °C / min, and then heat it up to 1500 °C at a heating rate of 2.5 °C / min; the cooling down in Step VI specifically means that under an argon atmosphere, first cool it down to 1000 °C at a cooling rate of 2.5 °C / min, then cool it down to 800 °C at a cooling rate of 5 °C / min, and finally cool it down to room temperature at a cooling rate of 10 °C / min.

[0065] Figure 1 is the SEM cross-sectional view of the porous SiC wave-absorbing material prepared in Example 1; Figure 2 is the SEM cross-sectional view of the porous SiC wave-absorbing material prepared in Example 1; It can be seen from the figure that the porous SiC obtained by carbonization and carbothermal reduction retains the well-developed three-dimensional interconnected porous structure of balsa wood. The pore diameters are concentrated in the range of about 20 μm to 50 μm. Many obvious granular substances can be seen on the surface of the pore walls.

[0066] Figure 3 is the SEM cross-sectional view and its Mapping image of the porous SiC wave-absorbing material prepared in Example 1; It shows that a carbon, silicon, boron, zirconium quaternary composite porous SiC wave-absorbing material is synthesized.

[0067] Figure 4 is the XRD pattern of the porous SiC wave-absorbing material prepared in Example 1. It can be seen from the figure that the main crystal phase of SiC in the porous SiC is 3C-SiC.

[0068] Weigh the porous SiC absorbing material prepared in Example 1 and paraffin according to a mass ratio of 3:7. Then place the paraffin on the porous SiC absorbing material. In a vacuum drying and heating oven, evacuate the air and heat to melt the paraffin. The paraffin is vacuum-impregnated into the porous SiC absorbing material, and finally a coaxial ring shape is formed.

[0069] Figure 5 It is the absorbing performance graph of the porous SiC absorbing material prepared in Example 1. As can be seen from the figure, the porous SiC exhibits excellent absorbing performance. When the thickness is 2.78 mm, it has a minimum reflection loss of -26.7941 dB.

[0070] Figure 6 It is the reflection loss graph of the porous SiC absorbing material prepared in Example 1. As can be seen from the figure, when the thickness is 3 mm, it has the widest absorption bandwidth of 7.1 GHz (10.6 GHz to 17.7 GHz).

[0071] The thermal conductivity of the SiC-based porous material prepared in Example 1 was measured to be 0.033 W / (m·K).

[0072] Figure 7 It is the thermogravimetric graph of the porous SiC absorbing material prepared in Example 1. As can be seen from the figure, the weight of this porous SiC hardly changes from room temperature to 600 °C, that is, it has good thermal stability.

Claims

1. A method for preparing a porous SiC wave-absorbing material using balsa wood and phenolic resin, characterized in that It is carried out according to the following steps: First, boric acid is added to absolute ethanol and heated for dissolution to obtain a boric acid solution; Second, phenolic resin is added to absolute ethanol and heated for dissolution to obtain a phenolic resin solution; Third, the boric acid solution and the phenolic resin solution are mixed, and then zirconium oxychloride powder is added and heated for dissolution to obtain a mixed solution; Fourth, block balsa wood is placed in the mixed solution, and vacuum impregnation is carried out at room temperature, and then taken out to obtain a balsa wood mixture; Fifth, the balsa wood mixture is dried, then heated up in an argon atmosphere, and carbonized for 2 h to 4 h under the conditions of an argon atmosphere and a temperature of 600 °C to 800 °C, and finally cooled down in an argon atmosphere to obtain porous carbon; Sixth, using the porous carbon as a carbon source and the mixture of silicon and silicon dioxide as a silicon source, the silicon source is laid on the bottom of a graphite crucible, and then the carbon source is placed on the silicon source, heated up in an argon atmosphere, and subjected to a carbothermal reduction reaction for 2 h to 4 h under the conditions of an argon atmosphere and a temperature of 1250 °C to 1600 °C, and finally cooled down in an argon atmosphere to obtain a porous SiC wave-absorbing material.

2. The method for preparing a porous SiC wave-absorbing material using balsa wood and phenolic resin according to claim 1, characterized in that In step one, the mass ratio of the boric acid to the absolute ethanol is 1:(5 - 10).

3. The method for preparing a porous SiC wave-absorbing material using balsa wood and phenolic resin according to claim 1, characterized in that In step two, the mass ratio of the phenolic resin to the absolute ethanol is 1:(1 - 5).

4. A method for preparing a porous SiC wave-absorbing material using balsa wood and phenolic resin according to claim 1, characterized in that In step three, in the mixed solution, the mass ratio of the phenolic resin to the boric acid is 1:(5 - 10), and the mass ratio of the zirconium oxychloride powder to the boric acid is 1:(1 - 2).

5. A method for preparing a porous SiC wave-absorbing material using balsa wood and phenolic resin according to claim 1, characterized in that In steps one to three, the heating and dissolution are all carried out at a temperature of 50 °C to 80 °C for 5 h to 10 h.

6. A method for preparing a porous SiC wave-absorbing material using balsa wood and phenolic resin according to claim 1, characterized in that In step four, the specific vacuum impregnation is carried out at room temperature and a pressure of -0.1 MPa to -0.5 MPa for 8 h to 12 h.

7. A method for preparing a porous SiC microwave absorption material using balsa wood and phenolic resin according to claim 1, characterized in that The block balsa wood described in step four is balsa wood; the mass ratio of the block balsa wood to the mixed solution described in step four is 1:(10 - 30).

8. A method for preparing a porous SiC microwave absorption material using balsa wood and phenolic resin according to claim 1, characterized in that In step five, the specific heating up is carried out in an argon atmosphere. First, it is heated up to 300 °C to 500 °C at a heating rate of 3 °C / min to 5 °C / min, and then heated up to 600 °C to 800 °C at a heating rate of 1 °C / min to 3.5 °C / min; the specific cooling down in step five is carried out in an argon atmosphere at a cooling rate of 5 °C / min to 10 °C / min to room temperature.

9. A method for preparing a porous SiC wave-absorbing material using balsa wood and phenolic resin according to claim 1, characterized in that In step six, the molar ratio of the carbon source to the silicon source is 1:(4 - 8); in the mixture of silicon and silicon dioxide described in step six, the molar ratio of silicon to silicon dioxide is (1 - 10):

1.

10. A method for preparing a porous SiC wave-absorbing material using balsa wood and phenolic resin according to claim 1, characterized in that The temperature increase described in Step 6 is specifically carried out in an argon atmosphere. First, it is heated from room temperature to 800 °C - 1000 °C at a heating rate of 8 °C / min - 10 °C / min, then to 1000 °C - 1200 °C at a heating rate of 3 °C / min - 5 °C / min, and then to 1250 °C - 1600 °C at a heating rate of 2 °C / min - 5 °C / min. The temperature decrease described in Step 6 is specifically carried out in an argon atmosphere. First, it is cooled from 1250 °C - 1600 °C to 1000 °C - 1200 °C at a cooling rate of 2 °C / min - 5 °C / min, then to 800 °C - 1000 °C at a cooling rate of 3 °C / min - 5 °C / min, and finally to room temperature at a cooling rate of 8 °C / min - 10 °C / min.

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