CN106520071A - Rice husk based C/magnetic Co particle composite wave absorber and preparation method thereof - Google Patents

Abstract

A rice husk-based carbon/magnetic Co particle composite wave absorbing agent and a preparation method thereof belong to the technical field of wave absorbing materials. In the rice husk-based carbon/magnetic Co particle composite absorber material provided by the invention, the size of the magnetic Co particles is 1.3 μm, and the rice husk-based carbon has a porous structure. The preparation process of the composite absorber material is divided into the following three steps: pretreatment, washing the rice husk with pure water, and then treating it with hydrofluoric acid (HF), etching to remove the silicon-containing compound in the rice husk, and drying Obtain HF-treated rice husks; modify, place HF-treated rice husks in an aqueous solution of CoCl ₂ , soak, and remove water by distillation under reduced pressure to obtain CoCl ₂ modified rice husks; carbonize, place CoCl ₂ modified rice husks Placed in a tube furnace, carbonized at high temperature in an inert gas atmosphere, and the carbonized material is further ground to obtain a rice husk-based/magnetic Co particle composite wave absorber material. The prepared wave-absorbing agent has excellent wave-absorbing properties, and exhibits strong absorbing properties for electromagnetic waves.

Description

Rice husk-based carbon/magnetic Co particle composite wave absorber and preparation method thereof

technical field

The invention belongs to the technical field of wave-absorbing materials, in particular to a rice husk-based carbon/magnetic Co particle composite wave-absorbing agent and a preparation method thereof.

Background technique

The rapid development of the electronics industry has made electromagnetic pollution more and more serious in recent years, and absorbing materials have played a vital role in the fields of electromagnetic pollution protection and electromagnetic attenuation. At the same time, in the field of stealth of military targets, wave-absorbing materials also play a vital role, which can effectively ensure the safety of military targets such as target aircraft. Absorbing materials, also known as microwave absorbing materials or electromagnetic wave attenuating materials, can effectively reduce the reflection of incident electromagnetic waves on the surface of objects, so that electromagnetic waves can effectively enter the interior of the material, thereby passing through the dielectric loss of the absorbing material itself And the magnetic loss characteristics are rapidly attenuated to achieve the purpose of absorbing electromagnetic waves. The absorbing material can be divided into two parts according to its composition: one part is the matrix that plays a bonding role, generally some resin materials with good wave transmission and thermal stability; the other part is the absorbing agent, which is used as the absorbing material The main body mainly plays the role of electromagnetic loss. Therefore, the preparation of a wave absorbing agent with excellent performance is the prerequisite for the preparation of a wave absorbing material. Excellent absorber materials should have the characteristics of light weight, high absorption strength, strong loss capacity, simple preparation process and low price.

According to the transmission line theory in the field of electromagnetic waves (Qin, F.; Brosseau, C., J.Appl.Phys.2012, 111, 061301), a single-component absorber material, such as a single dielectric loss material or magnetic loss Materials, because it is often difficult to achieve better electromagnetic matching characteristics, it is difficult for electromagnetic waves to effectively enter the interior of the material and be lost, and the wave-absorbing performance is often limited, which has been difficult to meet the characteristics of high efficiency, light weight, and broadband. Therefore, the preparation of composite absorbers with both electric and magnetic losses is a research hotspot in the field of absorbing materials. The effective combination of dielectric loss components and magnetic loss components can solve the problem of electromagnetic matching on the one hand, so that electromagnetic waves can effectively enter the interior of the wave-absorbing material; The electromagnetic wave is quickly lost, so as to achieve the characteristics of low reflection and strong absorption. Carbon materials have good chemical stability, high mechanical strength and excellent electrical conductivity, while having excellent thermal stability and low material density. Therefore, carbon materials have great potential in the field of preparing excellent microwave absorbers. At the same time, using certain methods to combine magnetic particles with magnetic loss capability with carbon materials to prepare carbon/magnetic particle composite absorbers is expected to achieve rapid loss of electromagnetic waves and obtain excellent absorbing properties.

Rice husks are rich in carbon elements, and as a waste of the agricultural industry, they are often directly incinerated. The price is relatively low, and it is a cheap carbon source material. However, the further modification of magnetic components of rice husk carbon materials is often more complicated, so the research on rice husk-based carbon absorbers is relatively lacking. Therefore, designing a certain modification method to effectively combine magnetic particles with rice husk-based carbon is expected to obtain a rice husk-based absorber material with excellent performance.

Contents of the invention

The technical problem mainly solved by the invention is to provide a rice husk-based carbon/magnetic Co particle composite wave absorbing agent with excellent wave absorbing performance and a preparation method thereof. The invention makes full use of the structural characteristics of rice husk components, designs a method for pretreatment and modification of magnetic particles, and prepares rice husk-based carbon/magnetic Co particle composite wave absorbing agent materials. The preparation process of the composite wave absorbing agent is simple, convenient for practical operation and easy for industrialized production. At the same time, the prepared material has strong absorbing performance, wide absorbing frequency band, small matching thickness and other characteristics, and has great application potential in the field of absorbing materials in the future.

In the present invention, rice husks are used as raw materials, and the rice husk-based carbon/magnetic particle composite wave absorber is obtained through successive processes of etching, modification, carbonization and grinding. The prepared wave-absorbing agent has excellent wave-absorbing properties, and exhibits strong absorbing properties for electromagnetic waves. When the thickness of the absorbing material is 1.8mm, its maximum reflection loss reaches -40.1dB (more than 99.99% absorption). At the same time, by adjusting the thickness of the absorbing material, the absorption of electromagnetic waves in the _3.9-18GHz frequency band (C band, X band and Ku band) exceeding -10dB can be realized.

In the rice husk-based carbon/magnetic Co particle composite absorber material provided by the invention, the size of the magnetic Co particles is 1.3 μm, and the rice husk-based carbon has a porous structure. The preparation process of the composite absorber material is divided into the following three steps: pretreatment, washing the rice husk with pure water, and then treating it with hydrofluoric acid (HF), etching to remove the silicon-containing compound in the rice husk, and drying Obtain HF-treated rice husks; modify, place HF-treated rice husks in an aqueous solution of CoCl ₂ , soak, and remove water by distillation under reduced pressure to obtain CoCl ₂ modified rice husks; carbonize, place CoCl ₂ modified rice husks Placed in a tube furnace, carbonized at a high temperature in an inert gas atmosphere, and the carbonized material is further ground to obtain a rice husk-based/magnetic Co particle composite wave absorber material.

The preparation method of the rice husk-based carbon/magnetic Co particle composite absorber material of the present invention, its specific synthesis steps are as follows:

(1) Wash the rice husk with distilled water 3 to 5 times to remove dust and other impurities on the surface of the rice husk; after drying, place the rice husk in a hydrofluoric acid aqueous solution with a mass fraction of 20 to 40%, and stir and etch for 8 to 12 hours , centrifuged (1000～3000rpm) to remove the supernatant; then the centrifuged product was washed 2 to 4 times with a hydrofluoric acid aqueous solution with a mass fraction of 20～40%, and centrifuged; then the centrifuged product was washed 2 to 4 times with distilled water, centrifuged Separation; finally, drying the centrifuged product at 60-100°C for 8-12 hours to obtain hydrofluoric acid-treated rice hulls;

(2) Add 2.5 to 3.5 g of hydrofluoric acid-treated rice husks obtained in step (1) and 12.5 to 17.5 mmol of cobalt chloride hexahydrate CoCl ₂ 6H ₂ O into 40 to 80 mL of distilled water, stir until chlorine hexahydrate The cobalt chloride is dissolved and then left to soak for 8-12 hours, then the distilled water is removed by distillation under reduced pressure, and finally dried at 100-140°C for 8-12 hours to obtain cobalt chloride-modified rice husk;

(3) Carbonize the cobalt chloride-modified rice husk obtained in step (2) at 900-1100° C. for 1-3 hours, and finally grind the carbonized product to obtain the rice-husk-based carbon/magnetic Co particles of the present invention Composite absorber material.

Using the rice husk-based carbon/magnetic Co particle composite wave-absorbing agent material prepared by the present invention, and further using paraffin as a matrix, wave-absorbing materials with different wave-absorbing agent fillings can be prepared, and the preparation method is as follows:

(1) mixing paraffin and rice husk-based carbon/magnetic Co particle composite wave absorbing agent, wherein the mass percentage of the composite wave absorbing agent/(composite wave absorbing agent+paraffin wax) is 15% to 35%;

(2) Press the mixture of the wave absorbing agent and paraffin in the previous step into a test ring with an outer diameter of 7 mm and an inner diameter of 3 mm through a mold using a hydraulic press;

(3) Use Agilent N5244A PNA-X to test the electromagnetic parameters (ε', ε", μ', μ") of the above-mentioned samples in the range of 2-18GHz, and use the following formula to calculate the reflection loss of the composite absorber RL (Lu Shaowei, Li Qian, Xiong Xuhai, Ma Keming, Xu Weikai, Jia Caixia, Journal of Inorganic Materials, 2015, 30, 23-28).

In the formula: Z ₀ is free space impedance; μ ₀ and ε ₀ are vacuum permeability and permittivity, ε ₀ =8.854187817×10 ^-12 F/m, μ ₀ =4π×10 ^-7 H/m; Z _in is the input impedance of the absorbing material (calculated using ε', ε", μ', μ"data); f is the frequency of electromagnetic waves (ranging from 2 to 18 GHz); d is the thickness of the absorbing material; c is The propagation speed of electromagnetic waves in free space is equal to the speed of light 3×10 ⁸ m/s; ε _r (ε _r ＝ε'-jε″) and μ _r (μ _r ＝μ'-jμ″) are the equivalent Relative to complex permittivity and complex permeability, j is the unit of the imaginary part of complex permittivity and complex permeability, which has no practical significance. The experiment can measure the ε', ε", μ', μ" of the material at different electromagnetic wave frequencies f.

Description of drawings

Figure 1: Schematic diagram of the molecular structure of lignin and cellulose, the main components of rice husk;

Figure 2: The XRD spectrum of the rice husk-based carbon/magnetic Co particle composite absorber material prepared in Example 1.

Figure 3: Scanning electron micrograph of the rice husk-based carbon/magnetic Co particle composite absorber material prepared in Example 1.

Figure 4: Scanning electron micrograph of the rice husk-based carbon/magnetic Co particle composite absorber material prepared in Example 2.

Figure 5: Scanning electron micrograph of the rice husk-based carbon/magnetic Co particle composite absorber material prepared in Example 3.

Fig. 6: The scanning electron micrograph of the rice husk-based carbon/magnetic Co particle composite absorber prepared in Example 1 after grinding.

Figure 7: Transmission electron micrograph of the rice husk-based carbon/magnetic Co particle composite absorber material prepared in Example 1.

Fig. 8: The electromagnetic parameter curve of the rice husk-based carbon/magnetic Co particle composite absorber material prepared in Example 1.

Fig. 9: The reflection loss RL data diagram calculated by using the electromagnetic parameters of the rice husk-based carbon/magnetic Co particle composite absorber material tested in Example 2.

Figure 1 shows a schematic diagram of the molecular structure of lignin and cellulose, the main components in rice husk. It can be seen from the figure that there are a large number of hydroxyl groups in the structure of lignin and cellulose, and the existence of these hydroxyl groups makes the rice husk have strong water absorption characteristics. The present invention utilizes this characteristic, etches the rice husk with hydrofluoric acid to remove silicon-containing compounds, and then further uses an aqueous solution of cobalt chloride for treatment. Due to the water absorption characteristics of rice husk, the aqueous solution of cobalt chloride can enter the interior of rice husk, and in the subsequent carbonization process, cobalt chloride is reduced to metal cobalt, which is filled in the interior of rice husk-based carbon, thus obtaining the rice husk. Shell-based carbon/magnetic Co particle composite absorber material.

Figure 2 shows the XRD spectrum of the rice husk-based carbon/magnetic Co particle composite absorber material prepared in Example 1. It can be seen from the XRD characterization that after high-temperature carbonization treatment, cobalt chloride is reduced to cobalt simple substance, which brings magnetic loss components to rice husk-based carbon.

Figure 3 shows the scanning electron micrographs of the rice husk-based carbon/magnetic Co particle composite absorber material prepared in Example 1. From the scanning electron microscope photos, it can be seen that the magnetic cobalt particles are more uniformly dispersed in the rice husk charcoal. In addition, the magnetic cobalt particles have a size of about 1.3 μm and are embedded in the rice husk carbon. In addition, rice husk carbon has a certain porous structure, which can effectively reduce the quality of the material, and at the same time, the porous structure can enhance the reflection of electromagnetic waves inside the absorbing material, thereby increasing the contact probability between electromagnetic waves and absorbing agents, so that electromagnetic waves can is rapidly depleted.

Figure 4 shows the scanning electron micrograph of the rice husk-based carbon/magnetic Co particle composite absorber material prepared in Example 2.

FIG. 5 shows the scanning electron micrograph of the rice husk-based carbon/magnetic Co particle composite absorber material prepared in Example 3.

FIG. 6 shows the scanning electron micrographs of the rice husk-based carbon/magnetic Co particle composite absorber prepared in Example 1 after grinding. It can be seen from the figure that after the prepared wave absorber is ground, the particle size is below 150 μm.

FIG. 7 shows the transmission electron micrograph of the rice husk-based carbon/magnetic Co particle composite absorber material prepared in Example 1. The characterization of the transmission electron microscope further proved the size and dispersion characteristics of the magnetic cobalt particles.

Figure 8 shows the electromagnetic parameters of the test sample prepared by mixing the rice husk-based carbon/magnetic Co particle composite absorber prepared in Example 1 with paraffin. Since the real part and imaginary part of the dielectric constant and magnetic permeability in the electromagnetic parameters represent the energy storage capacity and loss capacity of the material to the electromagnetic field, respectively, the prepared rice husk-based carbon/magnetic Co particle composite absorber material has a relatively high performance. Strong dielectric loss capability and magnetic loss capability. It has a strong dielectric loss capability for low-frequency electromagnetic waves, and a strong magnetic loss capability for high-frequency electromagnetic waves.

Figure 9 shows the reflection loss data of the rice husk-based carbon/magnetic Co particle composite absorber material prepared in Example 1. The rice husk base carbon/magnetic Co particle composite wave absorber material has shown excellent loss characteristics to electromagnetic waves, when the thickness of the wave absorber is 1.8mm (thickness here is not a concept with the thickness in embodiment 4. Embodiment The thickness in 4 is the thickness of the sample prepared when testing the electromagnetic parameters of the material. This thickness is the assignment of d when calculating the reflection loss of the material using the electromagnetic parameters combined with the formula), which realizes the maximum loss of electromagnetic waves, and the reflection loss reaches - 40.1dB. At the same time, by adjusting the thickness of the absorbing material, when the thickness varies from 1.1 to 4.0mm, the material can exhibit a strong absorption capacity for electromagnetic waves of 3.9 to 18GHz (reflection loss RL≤-10dB). Therefore, the prepared rice husk-based carbon/magnetic Co particle composite absorber material has strong electromagnetic loss capability. In the present invention, the structural characteristics of rice husk components are utilized, and the method of preparing rice husk-based carbon/magnetic Co particle composite wave absorbing agent material by pretreatment modification can improve the wave-absorbing performance of rice husk-based carbon materials, and provide high-performance absorbing materials. Wave materials provide certain technical means and have potential application value.

detailed description

Example 1

The synthetic method of the rice husk-based carbon/magnetic Co particle composite absorber material provided by the invention can be realized through the following reaction steps:

(1) Rice husk (10.0 g) was washed 3 times with distilled water to remove impurities such as dust on the surface of the rice husk. After drying, the rice husk is placed in a plastic container containing hydrofluoric acid aqueous solution (mass fraction 30%), stirred and etched for 10h, centrifuged (2000rpm) to remove the supernatant, and then the centrifuged product is used hydrofluoric acid aqueous solution (mass fraction 20%), washed 3 times, and centrifuged; then the centrifuged product was washed 3 times with distilled water, centrifuged; finally, the centrifuged product was placed in an oven and dried at 80° C. for 10 h to obtain 7.6 g of hydrofluoric acid-treated rice husk.

(2) Add 3.0 g of hydrofluoric acid-treated rice husk to a 250 mL single-necked round bottom flask, add 15 mmol of cobalt chloride hexahydrate CoCl ₂ 6H ₂ O, add 50 mL of distilled water, and stir until after the dissolution of cobalt chloride hexahydrate , let stand to soak for 10h, distilled off the distilled water under reduced pressure. The cobalt chloride-modified rice husk was placed in an oven and dried at 120° C. for 10 h to obtain 4.6 g of the product.

(3) Put the cobalt chloride-treated rice husk in a porcelain crucible, transfer it to a high-temperature tube furnace, and treat it at 1000°C for 2h (programmed temperature rise: 20-1000°C, 5°C/min, 196min; 1000°C, 120min; 1000～100°C, 5°C/min, 180min). The product after carbonization was further mechanically ground (the specific mesh number has not been tested, but the particle size is below 150 μm) to obtain a rice husk-based carbon/magnetic Co particle composite wave absorber material, and the product was 2.4g.

Example 2

The synthetic method of the rice husk-based carbon/magnetic Co particle composite absorber material provided by the invention can be realized through the following reaction steps:

(1) Add 2.5 g of rice husks treated with hydrofluoric acid in step (1) of Example 1 in a 250 mL single-necked round bottom flask, add 15 mmol of cobalt chloride hexahydrate CoCl ₂ 6H ₂ O, add 50 mL of distilled water, and stir After the cobalt chloride hexahydrate is dissolved, let it stand and soak for 10 hours, and distill off the distilled water under reduced pressure. The cobalt chloride-modified rice husk was placed in an oven and dried at 120° C. for 10 h to obtain 4.0 g of the product.

(2) Place the cobalt chloride-treated rice husk in a porcelain crucible, transfer it to a high-temperature tube furnace, and treat it at 1000°C for 2h (programmed temperature rise: 20-1000°C, 5°C/min, 196min; 1000°C, 120min; 1000～100°C, 5°C/min, 180min). The carbonized product was further mechanically ground to obtain a rice husk-based carbon/magnetic Co particle composite wave absorber material, and 1.8 g of the product was obtained.

Example 3

The synthetic method of the rice husk-based carbon/magnetic Co particle composite absorber material provided by the invention can be realized through the following reaction steps:

(1) Add 3.2 g of rice husks treated with hydrofluoric acid in step (1) of Example 1 in a 250 mL single-necked round bottom flask, add 17 mmol of cobalt chloride hexahydrate CoCl ₂ 6H ₂ O, add 50 mL of distilled water, and stir After the cobalt chloride hexahydrate is dissolved, let it stand and soak for 10 hours, and distill off the distilled water under reduced pressure. The cobalt chloride-modified rice husk was placed in an oven and dried at 120° C. for 10 h to obtain 5.1 g of the product.

(2) Place the cobalt chloride-treated rice husk in a porcelain crucible, transfer it to a high-temperature tube furnace, and treat it at 1000°C for 2h (programmed temperature rise: 20-1000°C, 5°C/min, 196min; 1000°C, 120min; 1000～100°C, 5°C/min, 180min). The carbonized product was further mechanically ground to obtain a rice husk-based carbon/magnetic Co particle composite absorber material, and 2.6 g of the product was obtained.

Example 4:

As an application of the rice husk-based carbon/magnetic Co particle composite absorber material prepared in the present invention, paraffin is used as a matrix, and the rice husk-based carbon/magnetic Co particle composite material prepared in Example 1 is used as a wave absorber to prepare the absorber The test sample with wave agent filling amount of 25% can be realized through the following steps:

(1) mixing paraffin wax and rice husk-based carbon/magnetic Co particle composite wave absorbing agent material according to a certain mass ratio; wherein the mass percentage of wave absorbing agent/(wave absorbing agent+paraffin wax) is 25%;

(2) Press the mixture of the wave absorbing agent and paraffin in the previous step through a mold and use a hydraulic press to form a test ring with an outer diameter of 7mm, an inner diameter of 3.04mm, and a thickness of 2mm;

(3) Use Agilent N5244A PNA-X to test the electromagnetic parameters (ε', ε", μ', μ") of the above-mentioned samples in the range of 2-18 GHz, and use the formula to calculate the reflection loss RL of the composite absorber.

Claims (3)

1. the preparation method of a kind of rice husk base carbon/magnetic Co particle composite wave-absorbing agent material, its step are as follows：

(1) rice husk is removed into the impurity on rice husk surface using distilled water wash 3～5 times；After drying, rice husk is placed in into quality point In the hydrofluoric acid aqueous solution of number 20～40%, stirring 8～12h of etching is centrifuged off supernatant；Then by centrifugation product quality The hydrofluoric acid aqueous solution of fraction 20～40% is washed 2～4 times, centrifugation；Again will centrifugation product distilled water wash 2～4 times, Centrifugation；Centrifugation product is dried into 8～12h at 60～100 DEG C finally, the rice husk of hydrofluoric acid treatment is obtained；

(2) rice husk and 12.5～17.5mmol cobalt chloride hexahydrates of the hydrofluoric acid treatment that 2.5～3.5g steps (1) are obtained CoCl₂·6H₂O is added in 40～80mL distilled water, is stirred and is standing and soak for 8～12h again after cobalt chloride hexahydrate dissolving, so Vacuum distillation afterwards removes distilled water, is finally dried 8～12h at 100～140 DEG C, obtains the rice husk of cobaltous chloride modification；

(3) rice husk of the cobaltous chloride modification for obtaining step (2) be carbonized under the conditions of 900～1100 DEG C 1～3h, will finally be carbonized Product grinds, so as to obtain rice husk base carbon/magnetic Co particle composite wave-absorbing agent material.

2. a kind of rice husk base carbon/magnetic Co particle composite wave-absorbing agent material, it is characterised in that：It is by the side described in claim 1 Method is prepared.

3. a kind of absorbing material of different wave absorbing agent loadings, it is characterised in that：It is by the rice husk described in paraffin and claim 2 Base carbon/magnetic Co particle composite wave-absorbing agent mixes, and the mass percent of wherein composite wave-absorbing agent/(composite wave-absorbing agent+paraffin) is 15%～35%.