CN112292016A - Preparation method of rare earth composite wave-absorbing material - Google Patents

Abstract

The preparation method of the rare earth composite wave-absorbing material takes Nd-MOF as a precursor, and prepares Nd through a one-step pyrolysis method₂O₂S/C rare earth composite wave-absorbing material. The rare earth composite wave-absorbing material prepared by simple pyrolysis has the characteristics of high stability and light weight; by means of a semiconductor Nd₂O₂S is compounded with a porous carbon material, so that the rare earth composite wave-absorbing material shows excellent microwave absorption performance under a thinner thickness, the frequency is 12.72GHz, the matching thickness is 2.56mm, and the optimal RL value can reach-52.3 dB. The preparation method is simple, uniform in compounding, stable in material performance, low in cost and suitable for industrial production.

Description

Preparation method of rare earth composite wave-absorbing material

Technical Field

The invention relates to a preparation method of a rare earth composite wave-absorbing material, in particular to the technical field of microwave wave-absorbing materials.

Background

With the continuous progress of high-tech communication and information technology, the potential impact of electromagnetic interference or pollution on human health and electronic safety has become a problem of widespread concern. Various solutions have been adopted to overcome electromagnetic radiation contamination, with microwave absorbing materials being considered one of the most promising solutions. At present, most electromagnetic wave absorbers have poor microwave absorption performance and stability and are thick. Therefore, an electromagnetic wave absorbing material having strong absorption, a small thickness, and high stability is required. So far, a large number of dielectric loss absorbents comprising carbonaceous materials, conductive polymers and the like, and magnetic loss materials comprising ferrites, magnetic metals and the like have been reported, but their preparation methods are complicated and costly. Ni synthesized by Yaoangjun et al_0.5Zn_0.5NdxFe_2-xO₄The composite material shows better microwave absorption performance, and the maximum reflection loss value (RL) is obtained when x = 0.04 and at 4.4GHz and 8.5 mm thickness_max) Is-20.8 dB, effective absorption bandwidth (RL) at a thickness of 8.5 mm<-10 dB) at 3.2 GHz (Kun Qian, Zhengjun Yao, Haiyan Lin, et al, The influence of Nd substition in Ni-Zn transfers for The improved microwave adsorption properties, Ceramics International 2020, 46: 227-. Nd synthesized by Wang Lei et al_23.25Fe_36.75Co₄₀The composite material shows better microwave absorption performance, and the maximum reflection loss value (RL) is measured at 4.8 GHz and 1.8 mm of thickness_max) Also only-19.7 dB (Lei Wang, Peihao Lin, Shunkang Pan, et al. Microwave absorbing properties of NdFeCo magnetic powder. Journal of Rare Earth, 2012, 30: 529-. The strongest microwave absorption performance of the wave-absorbing material containing the rare earth neodymium is weaker and can only reach about-20 dB, and thicker material thickness is needed to obtain the maximum reflection loss value.

Nd₂O₃Is an important semiconductor mainly used as a colorant of glass and ceramics, a raw material for manufacturing metal neodymium and a raw material for manufacturing ferromagnetic neodymium iron boron. Further, Nd₂O₃Having unique magnetic and dielectric properties, and Nd₂O₂S and Nd₂O₃With similar properties, one sulfur atom occupies the site of an oxygen atom, and more lattice defects are obtained, enhancing the loss capability. The lower band gap is beneficial to improving the dielectric constant, the dielectric loss and the wave absorbing capacity. Thus, Nd₂O₂S is expected to be an excellent microwave absorbing material.

Disclosure of Invention

The invention provides a method for preparing a rare earth composite wave-absorbing material by taking Nd-MOF as a template, aiming at the problems of complex preparation method, strict equipment requirement, high cost and the like of the existing carbon-based microwave absorbing material.

The preparation method of the rare earth composite wave-absorbing material takes Nd-MOF as a template to prepare Nd₂O₂The S/C rare earth composite wave-absorbing material comprises the following specific steps:

step 1: dissolving neodymium nitrate hexahydrate, thiophenic diacid and ammonium acetate in a mixed solution of deionized water and ethanol, transferring the mixed solution to a high-pressure reaction kettle, preserving heat for 2-4 days at 100 ℃, alternately centrifuging and washing the obtained product for three times by using the deionized water and absolute ethyl alcohol, and finally drying the product in vacuum at 50-60 ℃ to obtain a blocky Nd-MOF crystal;

wherein: the molar ratio of neodymium nitrate hexahydrate, thiophenic diacid and ammonium acetate is 0.3-0.5: 0.7-1.0: 3-5, the dosage ratio of thiophenic diacid and deionized water is 0.8-1.2 mmol: 8-12 mL, and the volume ratio of deionized water and ethanol is 1.0: 1.0-1.2;

step 2: heating the bulk Nd-MOF crystal from room temperature to 600-900 ℃ in a nitrogen atmosphere, roasting for 2-4 h, and naturally cooling to room temperature in the nitrogen atmosphere to obtain the rare earth composite wave-absorbing material; the temperature rising/reducing rate in the process is 2-5 ℃/min.

The rare earth composite microwave absorbing material is mixed with paraffin serving as a substrate material to obtain the microwave absorbent, and the mixing mass ratio of the microwave absorbent to the paraffin is 1: 0.8-1.2.

The invention has the beneficial effects that:

1. the invention is a semiconductor Nd₂O₂S is compounded with porous carbon material, and graphitization of the composite material is changed by changing the heating rate, the calcining temperature and the timeAnd the degree, and thus the impedance matching. After the rare earth composite wave-absorbing material is matched with paraffin, excellent microwave absorption performance can be ensured to be displayed under the condition of a low coating thickness, the frequency is 12.72GHz, the matching thickness is 2.56mm, and the optimal RL value can reach-52.3 dB.

2. Compared with the existing preparation method of the carbon-based microwave absorbing material, the preparation method disclosed by the invention is simple, uniform in compounding, stable in material performance, low in production cost and suitable for industrial production.

Drawings

FIG. 1 shows Nd according to the invention₂O₂An X-ray diffraction pattern of S/C-800;

FIG. 2 shows Nd prepared in example 1 of the present invention₂O₂The reflection loss spectrum of the S/C-800 composite wave-absorbing material;

FIG. 3 shows Nd prepared in example 2 of the present invention₂O₂Reflection loss spectrum of the S/C-900 composite wave-absorbing material;

Nd₂O₂S/C-800 and Nd₂O₂S/C-900 is a calcined product of Nd-MOFs at 800 and 900 degrees, respectively.

Detailed Description

Example 1

Step 1: 0.1752g of neodymium nitrate hexahydrate, 0.136g of thiophenedioic acid and 0.308g of ammonium acetate are dissolved in a mixed solution of 8mL of deionized water and 8mL of ethanol, then the mixed solution is transferred into a high-pressure reaction kettle, the temperature is kept at 100 ℃ for 3 days, and the obtained product is respectively and alternately centrifugally washed by the deionized water and the absolute ethanol for three times; finally, placing the Nd-MOF crystal in a vacuum oven, and drying the Nd-MOF crystal under the vacuum condition of 50 ℃ to obtain a blocky Nd-MOF crystal;

step 2: heating the blocky Nd-MOF crystal from room temperature to 800 ℃ under the conditions of nitrogen atmosphere and 5 ℃/min of temperature rising/reducing rate, roasting for 2h, and naturally cooling to room temperature under the nitrogen atmosphere to obtain Nd₂O₂S/C-800 composite wave-absorbing material.

And step 3: the prepared hollow Nd₂O₂The S/C-800 composite material and the paraffin base are uniformly mixed to prepare a circular ring, and the mass of the composite material and the mass of the paraffin are 0.05g and 0.05g respectively.

The electromagnetic parameters of the material are measured by a vector network analyzer, and according to the transmission line theory, the reflection loss of the material to electromagnetic waves is calculated by the complex dielectric constant and the complex permeability under given frequency and the thickness of the wave-absorbing material through the following equation.

Example 2

Step 1: 0.1752g of neodymium nitrate hexahydrate, 0.136g of thiophenedioic acid and 0.308g of ammonium acetate are dissolved in a mixed solution of 8mL of deionized water and 8mL of ethanol, then the mixed solution is transferred into a high-pressure reaction kettle, the temperature is kept at 100 ℃ for 3 days, and the obtained product is respectively and alternately centrifugally washed by the deionized water and the absolute ethanol for three times; finally, placing the Nd-MOF crystal in a vacuum oven, and drying the Nd-MOF crystal under the vacuum condition of 50 ℃ to obtain a blocky Nd-MOF crystal;

step 2: heating the blocky Nd-MOF crystal from room temperature to 900 ℃ under the conditions of nitrogen atmosphere and 5 ℃/min of temperature rising/reducing rate, roasting for 2h, and naturally cooling to room temperature under the nitrogen atmosphere to obtain Nd₂O₂S/C-900 composite wave-absorbing material.

And step 3: the prepared hollow Nd₂O₂The S/C-900 composite material and the paraffin base are uniformly mixed to form a circular ring, and the mass of the composite material and the mass of the paraffin are 0.05g and 0.05g respectively.

The present embodiment differs from embodiment 1 in that: the calcination temperature of the bulk Nd-MOF crystals was 900 ℃.

Nd of FIG. 1 of the invention₂O₂X-ray diffraction pattern of S/C-800, by XRD analysis, the synthesized Nd was investigated₂O₂Crystal structure and phase composition of the S/C-800 sample. In general, 12 peaks corresponding to Nd were shown at 26.11, 29.16, 37.30, 45.96, 48.13, 53.99, 55.37, 60.76, 62.35, 69.11, 74.75 and 75.23, respectively₂O₂The (100), (101), (102), (110), (103), (004), (201), (104), (113), (005), (211) and (105) cubic crystal planes of S.

From FIG. 2It can be seen that the product Nd₂O₂The strongest reflection loss of S/C-800 at a frequency of 12.7GHz and a matching thickness of 2.56mm is-52.3 dB. As can be seen from FIG. 3, the product Nd₂O₂The strongest reflection loss of the S/C-900 is-66.4 dB when the frequency is 7.24GHz and the matching thickness is 4.47mm, the effective bandwidth is 3.32GHz, and the maximum effective bandwidth is 4.92GHz when the matching thickness is 3.0 mm.

Claims (1)

1. A preparation method of a rare earth composite wave-absorbing material is characterized by comprising the following steps: the method takes Nd-MOF as a template to prepare Nd₂O₂The S/C rare earth composite wave-absorbing material comprises the following specific steps:

step 1: dissolving neodymium nitrate hexahydrate, thiophenic diacid and ammonium acetate in a mixed solution of deionized water and ethanol, transferring the mixed solution to a high-pressure reaction kettle, preserving heat for 2-4 days at 100 ℃, alternately centrifuging and washing the obtained product for three times by using the deionized water and absolute ethyl alcohol, and finally drying the product in vacuum at 50-60 ℃ to obtain a blocky Nd-MOF crystal;

wherein: the molar ratio of neodymium nitrate hexahydrate, thiophenic diacid and ammonium acetate is 0.3-0.5: 0.7-1.0: 3-5, the dosage ratio of thiophenic diacid and deionized water is 0.8-1.2 mmol: 8-12 mL, and the volume ratio of deionized water and ethanol is 1.0: 1.0-1.2;

step 2: heating the bulk Nd-MOF crystal from room temperature to 600-900 ℃ in a nitrogen atmosphere, roasting for 2-4 h, and naturally cooling to room temperature in the nitrogen atmosphere to obtain the rare earth composite wave-absorbing material; the temperature rising/reducing rate in the process is 2-5 ℃/min.

Images