A method for preparing single metal Ni nanosphere electromagnetic absorbing material

Abstract

The invention discloses a method for preparing a single metal Ni nanosphere electromagnetic wave absorbing material, comprising the following steps: (1) placing NiCl2 in ethylene glycol and mechanically stirring the mixture in a constant temperature water bath to obtain an ethylene glycol solution of NiCl2; (2) adding hydrazine hydrate dropwise into the solution of step (1) to change the color of the solution to blue; (3) adding NaOH solution dropwise into the blue solution of step (2) to make the pH value of the mixed solution alkaline, stirring the mixture until the color of the solution turns black and then continuing to stir the mixture to ensure that the reaction is complete; (4) after the reaction, centrifuging the obtained reaction solution, washing the product and vacuum drying the product to obtain the single metal Ni nanosphere electromagnetic wave absorbing material.

Description

Technical Field

[0001] The invention relates to a method for preparing a single metal Ni nanosphere electromagnetic wave absorbing material. Background Art

[0002] Electromagnetic wave absorbing material refers to a material that can convert electromagnetic energy into heat energy or eliminate electromagnetic waves fundamentally through interference, and has a high electromagnetic wave energy loss efficiency. Magnetic metal materials have good electrical conductivity and magnetism, so they have both electrical loss and magnetic loss capabilities and can be used as electromagnetic wave absorbing materials. Commonly used magnetic metal materials are mainly iron, cobalt, and nickel. However, the use of magnetic metal Ni in the field of wave absorption is often limited by the following shortcomings: the magnetic metal Ni particles obtained by traditional preparation methods are large in size, small in specific surface area, and have a small number of surface atoms, resulting in poor interface polarization and multiple scattering capabilities; at the same time, the material has poor structural stability, is easy to agglomerate, and has different sizes. Summary of the invention

[0003] Purpose of the invention: The purpose of the present invention is to provide a method for preparing a single metal Ni nanosphere electromagnetic absorbing material. The Ni nanospheres prepared by the method are single metal and do not contain Ni-based oxides, so they have high saturation magnetization intensity; at the same time, the structure is stable, not easy to agglomerate and the size is uniform. The particle size of the Ni nanospheres is 300-400nm. The smaller size makes the material have a large specific surface area. The large specific surface area effectively enriches the dielectric resonance behavior and interface polarization ability of the material, thereby promoting the dielectric loss of the material and improving the absorbing performance.

[0004] Technical solution: The method for preparing the single metal Ni nanosphere electromagnetic absorbing material of the present invention comprises the following steps:

[0005] (1) NiCl2 is placed in ethylene glycol and mechanically stirred in a constant temperature water bath to obtain an ethylene glycol solution of NiCl2, which is clear, transparent and green;

[0006] (2) adding hydrazine hydrate dropwise to the solution of step (1), and the color of the solution changes to blue;

[0007] (3) adding NaOH solution dropwise to the blue solution of step (2) to make the pH of the mixed solution alkaline, stirring until the solution turns black, and then continuing to stir to ensure complete reaction;

[0008] (4) After the reaction, the obtained reaction solution is centrifuged, and the product is washed and vacuum dried to obtain a single metal Ni nanosphere electromagnetic absorbing material.

[0009] Wherein, in step (1), the mass volume ratio of NiCl2 to ethylene glycol is: 23.75-23.8 mg:1 mL.

[0010] Wherein, in step (1), the temperature of the constant temperature water bath is 60-65°C.

[0011] Wherein, in step (2), the mass volume ratio of NiCl2 to hydrazine hydrate is: 190-192 mg: 1 mL.

[0012] Wherein, the mass fraction of hydrazine hydrate is not less than 80%.

[0013] Wherein, in step (3), the mass volume ratio of NiCl2 to NaOH solution is: 19-20 mg: 1 mL.

[0014] Wherein, the concentration of NaOH solution is 1-1.5 mol / L.

[0015] Wherein, in step (3), the pH of the mixed solution is not less than 11.

[0016] Wherein, in step (3), after the NaOH solution is added dropwise, stirring is continued for not less than 40 minutes to make the solution turn black, and stirring is continued for not less than 10 minutes to ensure complete reaction.

[0017] Wherein, in step (4), the rotation speed of centrifugal separation is 8000-8500 r / min, and the time of vacuum drying is 10-12 h.

[0018] Wherein, in step (4), the particle size of the Ni nanospheres is 300 to 400 nm.

[0019] NiCl2 can be evenly dispersed in weakly alkaline ethylene glycol without inert gas protection, and then Ni 2+ The solution is reduced by the slowly added hydrazine hydrate solution. The slowly added NaOH solution can not only adjust the pH value of the solution but also help to catalyze the formation of Ni nanoparticles. During the whole reaction process, the color of the solution changes from green to blue and finally to black. The obtained product is a single metal Ni nanosphere with uniform particle size, and no side reaction products such as Ni-based oxides are generated.

[0020] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the present invention uses hydrazine hydrate as a reducing agent to prepare magnetic metal Ni nanospheres under alkaline conditions, and prepares a single metal Ni nanosphere electromagnetic absorbing material with a zero-dimensional nanosphere structure, no obvious agglomeration and uniform size distribution; the Ni nanosphere has a large specific surface area and is a single metal, thereby giving the material multiple interface polarization effects and extremely strong magnetic loss capabilities, and the magnetic nanoparticles are coupled to form a magnetic network, which can enhance the material's eddy current loss, natural resonance, exchange resonance and other multiple magnetic loss capabilities, thereby making the material have good absorbing performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1The X-ray diffraction pattern of the single metal Ni nanospheres prepared in Example 1;

[0022] Figure 2 This is a low-magnification SEM photograph of the single metal Ni nanospheres prepared in Example 1;

[0023] Figure 3 This is a high-magnification SEM photo of the single metal Ni nanospheres prepared in Example 1;

[0024] Figure 4 This is a particle size distribution diagram of the single metal Ni nanospheres prepared in Example 1;

[0025] Figure 5 : is the hysteresis loop diagram of the single metal Ni nanosphere prepared in Example 1;

[0026] Figure 6 This is a reflection loss diagram of the single metal Ni nanospheres prepared in Example 1 at different thicknesses. DETAILED DESCRIPTION

[0027] Example 1

[0028] The preparation method of the single metal Ni nanosphere electromagnetic wave absorbing material of the present invention comprises the following steps:

[0029] Step 1, 4.75 g NiCl2 was placed in a 500 mL three-necked flask filled with 200 mL ethylene glycol, and mechanically stirred in a 60°C constant temperature water bath, and the solution was clear and transparent green;

[0030] Step 2, slowly adding (drop by drop) 25 mL of 80% by mass hydrazine hydrate to the transparent green solution of step 1, and the color of the solution changes from green to blue;

[0031] Step 3: Add 250 mL of 1 mol·L -1 The pH of the mixed solution was adjusted to 11 by adding NaOH solution, and the solution was stirred for 40 minutes until the solution turned black, and then stirred for another 10 minutes to ensure complete reaction;

[0032] Step 4: The solution after the reaction in step 3 was heated at 8000 r / min. -1 The product was centrifuged at a speed of , and the separated product was washed three times with deionized water and three times with anhydrous ethanol in sequence. After washing, it was vacuum dried for 12 hours to obtain a single metal magnetic Ni nanosphere electromagnetic absorbing material.

[0033] The present invention first disperses the nanoparticles in a weakly alkaline environment of ethylene glycol, so that the monometallic Ni nanoparticles can be prepared by reduction with hydrazine hydrate without the need for inert gas protection. Since NiCl2 is added to ethylene glycol, the solution is green and no black substance is generated, it can be inferred that Ni 2+ It is reduced by hydrazine hydrate instead of ethylene glycol. The addition of NaOH not only adjusts the pH value of the solution but also catalyzes the formation of Ni nanoparticles. The entire reaction process is placed in an air atmosphere, but no Ni oxide is generated, indicating that protective gas (inert gas) is generated during the reaction. The reaction equation is: 2Ni 2+ +N2H4+4OH - =2Ni+N2+4H2O.

[0034] Figure 1 The X-ray diffraction pattern of the single metal Ni nanosphere electromagnetic absorbing material prepared in Example 1 is as follows: Figure 1 It can be seen that the product prepared in Example 1 has three significant sharp diffraction peaks at 2Theta angles of 44.8°, 52.2° and 76.8°, representing the (111) plane, (200) plane and (220) plane of Ni, respectively, proving that the prepared material is a single metal Ni material.

[0035] Figure 2 This is a low-magnification SEM photo of the single metal Ni nanosphere electromagnetic absorbing material prepared in Example 1. Figure 2 It can be seen that the product obtained in Example 1 has a nanosphere morphology with uniformly distributed particles, indicating that a single metal Ni nanosphere electromagnetic absorbing material is successfully prepared after hydrazine hydrate reduction, and the single metal magnetic Ni material has high crystallinity and purity. The single metal Ni nanosphere electromagnetic absorbing material has uniform particle size, so that a magnetic network with a large specific surface area can be constructed, which can not only introduce multiple interface polarization behaviors and free electron absorbing ability, but also increase the magnetic loss capacity such as eddy current loss, natural resonance and exchange resonance, so that the material has good absorbing performance.

[0036] Figure 3 This is a high-magnification SEM photo of the single metal Ni nanosphere electromagnetic absorbing material prepared in Example 1. Figure 3It can be seen that the weakly alkaline dispersion environment provided by ethylene glycol makes it possible to use hydrazine hydrate reduction without the protection of inert gas to obtain a product having a zero-dimensional nano-spherical structure. The use of NaOH can not only adjust the solution to an alkaline environment but also catalyze the formation of Ni nanoparticles. The particle size of the product is 300 to 400 nm, which can enrich the dielectric resonance behavior and interface polarization of the material, thereby enhancing the dielectric loss of the material and improving the wave absorption performance of the material. Therefore, the present invention can give the magnetic metal material a larger specific surface area, more contact interfaces, abundant multiple scattering channels and high saturation magnetization by preparing small-sized zero-dimensional single metal Ni nanospheres, thereby greatly improving the wave absorption performance of the material.

[0037] Figure 4 The particle size distribution diagram of the single metal Ni nanospheres prepared in Example 1 is shown in FIG. Figure 4 It can be seen that the particle size of the single metal Ni nanosphere is mainly distributed between 300nm and 400nm, among which the distribution of particle size between 325-350nm accounts for 42%, the distribution of particle size between 325-375nm accounts for 35%, and the particle size between 300-325nm and 375-400nm accounts for a minority of 23%. The average particle size of the single metal Ni nanosphere is 358nm after statistical analysis and calculation. Therefore, the above results show that the particle size of the Ni nanosphere prepared by the method of the present invention has good uniformity.

[0038] Figure 5 The hysteresis loop diagram of the single metal Ni nanosphere electromagnetic absorbing material prepared in Example 1 is shown in FIG. Figure 5 It can be seen that the saturation magnetization intensity of the product prepared in Example 1 is as high as 45.58emu·g -1 , indicating that the single metal Ni nanosphere material can provide magnetic loss characteristics of multiple magnetic loss mechanisms such as eddy current loss, natural resonance and exchange resonance for efficient electromagnetic wave absorption performance, thus giving the material good wave absorption performance.

[0039] Figure 6 The figure is a reflection loss diagram of the single metal Ni nanosphere electromagnetic wave absorbing material prepared in Example 1 at different thicknesses. Figure 6 It can be seen that the product prepared in Example 1 exhibits excellent electromagnetic absorbing performance; when the filling degree is 50%, the product achieves the strongest reflection loss value of -31.48 dB at 17.04 GHz when the matching thickness is only 1.35 mm, and the effective absorption bandwidth at this thin thickness starts from 15.72 GHz and ends at 18.00 GHz, occupying a total bandwidth of 2.28 GHz, indicating that the single metal Ni nanosphere electromagnetic absorbing material has strong magnetic loss attenuation ability and dielectric loss ability, which helps to enhance the absorption intensity.

Claims

1. A method for preparing a single metal Ni nanosphere electromagnetic absorbing material, characterized in that: The steps include: Step 1, 4.75 g NiCl2 was placed in a 500 mL three-necked flask filled with 200 mL ethylene glycol, and mechanically stirred in a 60°C constant temperature water bath, and the solution became clear and transparent green; Step 2, adding 25 mL of 80% by mass hydrazine hydrate dropwise to the transparent green solution of step 1, and the color of the solution changes from green to blue; Step 3: Add 250 mL of 1 mol·L -1 The pH of the mixed solution was adjusted to 11 by adding NaOH solution, and the solution was stirred for 40 minutes until the solution turned black, and then stirred for another 10 minutes to ensure complete reaction; Step 4: The solution after the reaction in step 3 was heated at 8000 r / min. -1 The separated product was centrifuged at a speed of , and washed with deionized water for 3 times, and with anhydrous ethanol for 3 times, and then vacuum dried for 12 hours to obtain a single metal magnetic Ni nanosphere electromagnetic wave absorbing material; the particle size of the Ni nanosphere was 300-400nm; The saturation magnetization intensity of the above-mentioned single metal magnetic Ni nanospheres is as high as 45.58emu•g-1; when it is used as an electromagnetic absorbing material, when the filling degree is 50%, the product achieves the strongest reflection loss value of -31.48dB at 17.04GHz when the matching thickness is only 1.35mm. The effective absorption bandwidth at this thickness starts from 15.72GHz and ends at 18.00GHz, occupying a total bandwidth of 2.28GHz.

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