CN103193473A - Preparation method of microwave absorbing material with three-dimensional ordered macroporous structure - Google Patents

Abstract

The invention discloses a preparation method of a microwave absorbing material with a three-dimensional ordered macroporous structure. The preparation method comprises the following steps of: adding nickel nitrate (or cobalt nitrate) and ferric nitrate according to a molar ratio of 1:2 into a mixed solution of ethylene glycol and methanol and uniformly dissolving; then adding polymethyl methacrylate (PMMA) serving as a hard template and soaking for a period of time; and finally calcining to remove a template so as to acquire the microwave absorbing material with the three-dimensional ordered macroporous structure. The material has good degree of crystallization and shape; and electromagnetic waves are mainly absorbed by the material in high-frequency regions, and the absorption effect is good.

Description

A preparation method of a microwave absorbing material with a three-dimensional ordered macroporous structure

technical field

The invention belongs to the field of synthesis of inorganic chemicals, in particular to a structure and a preparation method of a microwave absorbing material, more specifically to a material structure and a preparation method for absorbing electromagnetic waves

Background technique

In recent years, with the rapid development of electromagnetic wave technology, the pollution caused by electromagnetic radiation has become an important culprit that endangers the environment and human health, so it has begun to attract extensive attention. At the same time, in the military field, microwave absorbing materials can effectively reduce the radar wave emission cross section of weapons and equipment, realize radar stealth, and improve the survivability and penetration capabilities of weapons and equipment. The main mechanism of action of the absorbing material is to enable the incident electromagnetic wave to enter into the material to the greatest extent after it touches the material, and rapidly attenuate and lose it through energy conversion. the

Ferrite is a traditional magnetic material. It has high resistivity and good magnetic loss characteristics, so it is widely used as an electromagnetic wave absorber, but limited by the snoek effect, spinel ferrite absorbs The magnetic loss of the material drops dramatically in the gigahertz frequency range. Therefore, the current research on microwave absorbing materials focuses on the high frequency range. For example, patent CN101914821A discloses a method for preparing a composite nanofiber material of Ni-Zn ferrite and SiO ₂ , which realizes the controllable electromagnetic properties by controlling the microstructure and morphology of the product, and its influence on electromagnetic waves The absorption performance overcomes the shortcomings of traditional ferrite powder such as too low resonance frequency and low snoek limit; patent CN102214509A discloses a preparation method of a new type of (FeCo)N microwave absorbing material, which combines carbonyl iron powder and cobalt powder by The mass percentage is 50%-95% for mechanical alloying, and then the alloyed material is subjected to nitriding treatment to obtain a (FeCo)N microwave absorbing material with a nitrogen content of 0.08%-2.10% by mass. High saturation magnetization and low remanence and coercive force, so it has better absorbing performance; Patent CN1240659C discloses a chemical formula of _{SmMexFe1 - xO3} , where Me is Mn, Co or Ni element One or two of them, the value range of x is 0.05-0.75. When the material has a thickness of 1mm, the minimum value of electromagnetic wave reflection attenuation in the frequency range of 2-18GHz reaches -15dB, and has the advantages of wide absorption frequency, simple synthesis method, and low production cost.

Contents of the invention

The purpose of the present invention is to synthesize a ferrite with a three-dimensional ordered macroporous structure, and exhibit good microwave absorption effect. the

The technical scheme adopted in the present invention: adopting the hard template impregnation method, comprising the following steps: dissolving soluble iron salt and nickel salt (or cobalt salt) in the solvent, adding the template agent and impregnating for a period of time, and then suction filtering to obtain the solid into the horse After furnace calcination, the product is obtained. the

The part of the templating agent used polymethyl methacrylate (PMMA) microspheres. PMMA is synthesized according to literature reports, and the particle size is very uniform. Through the method of centrifugation and sedimentation, the PMMA microspheres are closely arranged and packed to form a colloidal crystal template. the

What the soluble metal salt of described part adopts is ferric nitrate and nickel nitrate (or cobalt nitrate). the

The solvent of said part is a mixed solvent of ethylene glycol and methanol. the

Preparation includes the following steps

(a) according to bibliographical reports, prepare polymethyl methacrylate (PMMA) microsphere templating agent with uniform particle size;

(b) nickel nitrate (or cobalt nitrate) and ferric nitrate are dissolved in the mixed solution of ethylene glycol and methanol as precursor solution;

(c) A certain amount of PMMA microsphere templates are immersed in the precursor solution, soaked for a period of time, and then suction filtered to obtain a solid;

(d) calcining the dried solid under air to remove the template, and finally obtain a spinel-type ferrite with a three-dimensional ordered macroporous structure. the

Beneficial effects of the present invention: adopting this technical route to prepare ferrite wave-absorbing materials has the advantages of wide source of raw materials, simple reaction process, convenient operation and the like. In addition, the invention overcomes the disadvantage of poor absorption effect in the high frequency range of traditional ferrite absorbing materials. The template agent PMMA microspheres adopted in the present invention are easy to synthesize and have controllable particle size. The ferrite synthesized by the invention is a traditional spinel crystal type and has a macroporous structure. The ferrite wave-absorbing material in the present invention is arranged in three-dimensional order, thus improving the absorption performance of electromagnetic waves. the

Description of drawings

Figure 1 is the X-ray diffraction pattern of three-dimensional ordered macroporous ferrite

Figure 2 is a scanning electron microscope image of a three-dimensional ordered macroporous ferrite

Figure 3 is the _N2 adsorption-desorption isotherm of three-dimensional ordered macroporous ferrite

Figure 4 is the microwave absorption diagram of three-dimensional ordered macroporous ferrite

Detailed ways

The embodiment of three-dimensional ordered macroporous ferrite synthesized by hard template method:

(1) Dissolve nickel nitrate (or cobalt nitrate) and iron nitrate with a molar ratio of 1:2 in 10 mL of a mixed solvent of ethylene glycol and methanol, and stir until uniform to obtain a precursor solution;

(2) 2g polymethyl methacrylate (PMMA) microsphere templating agent is added in the precursor solution and soaked for several hours;

(3) After the impregnation, remove excess solution, and dry the resulting solid at room temperature for 24 hours;

Calcining the solid obtained above in a muffle furnace to remove the template agent, the specific steps are: rise from room temperature to 550°C or 600°C in an air atmosphere, keep it for several hours, and after the template agent is completely removed, drop to At room temperature, a ferrite absorbing material with a three-dimensional ordered macroporous structure can be obtained. Referring to the XRD characterization of accompanying drawing 1, at 2θ=30.31 °, 35.42 °, 43.66 °, 53.8 °, 57.51 °, 63.15 ° respectively correspond to (220), (311), (400), (422 ), (511) and (440) crystal planes, fully consistent with the structure of nickel (or cobalt) iron spinel (JCPDS No.10-325). the

Referring to the accompanying drawing 2, the ferrite synthesized by the hard template method has a very complete three-dimensional ordered macroporous structure. It can be seen that the pore diameter of the macroporous structure is also very uniform, which is consistent with the particle size of the templating agent we selected. uniform diameter. The pore size of our material shrinks slightly after calcination of the detemplating agent. the

It can be seen from Figure 3 that the nitrogen adsorption-desorption isotherm of the ferrite synthesized by the hard template method is a typical type III isotherm with an H3 hysteresis loop, and the isotherm has a very obvious section after p/p0 > 0.8 Uplift, which indicates the presence of large pores in our material. The pore wall of the ferrite wave absorbing agent with three-dimensional ordered macropore structure is formed by the accumulation of many small particles, so the thickness of the pore wall and the size of the pore size can be controlled. We prepare polymethacrylic acid with different particle sizes Ferrite absorbing materials with different pore wall thicknesses and pore sizes can be prepared by using methyl ester (PMMA) template or selecting different microsphere templates. the

It can be seen from Figure 4 that the absorption bandwidth of the ferrite wave absorbing agent with three-dimensional ordered macroporous structure is relatively narrow, and when the thickness is 3.5mm, the maximum reflection loss value of the material of the present invention can reach less than -20dB. Moreover, the ferrite absorber concentrates on the absorption of electromagnetic waves in the high-frequency region, and the absorption peak is located between 11GHz-18GHz. Compared with other ferrite type microwave absorbing materials, the invention has narrow-band and high-efficiency wave-absorbing characteristics. the

The above content is only a basic description of the concept of the present invention, and any equivalent transformation made according to the technical solution of the present invention shall fall within the scope of protection of the present invention. the

Claims (4)

1. A preparation method of a ferrite type microwave absorbing material with a three-dimensional ordered macroporous structure, comprising the following steps: dissolving nickel nitrate (or cobalt nitrate) and ferric nitrate in ethylene glycol and methanol mixed solvent to form a precursor body solution, then add a template agent for impregnation, and finally remove the template agent to obtain a ferrite wave absorber. 2. A ferrite wave-absorbing material with a three-dimensional ordered macroporous structure according to claim 1, characterized in that: polymethyl methacrylate (PMMA) microspheres are used as a template, and the template is based on the document report synthesis. 3. A nickel ferrite absorbing material with a three-dimensional ordered macroporous structure according to claim 1, characterized in that: the ferrite absorbing agent is nickel (or cobalt) iron spinel type, At the same time, it has a three-dimensional ordered macroporous structure, uniform pore size, and a certain specific surface area. 4. A nickel ferrite wave-absorbing material with a three-dimensional ordered macroporous structure according to claim 3, characterized in that: the absorption of electromagnetic waves by the wave-absorbing material is concentrated in the high-frequency region, making up for the traditional ferrite Insufficient oxygen absorber. When the thickness is 3.5mm, the absorbing material has a very large reflection loss value (<-20dB) at the high frequency, which means that the electromagnetic wave has >99% loss in this frequency.

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