CN101914722A - An electromagnetic wave absorbing material - Google Patents

Abstract

The invention relates to a material which can absorb electromagnetic waves more effectively within the range of 1G to 100G. The material has a general formula of R2Fe14B, wherein R is a composition of rare earth elements of Sm and Nd according to the proportion of Nd<1-x>Sm<x>, wherein x is not less than 0.3 and not more than 1. The easily magnetized direction of the electromagnetic wave absorption material is not parallel to the C-axis. The invention also relates to a method for preparing the electromagnetic composite material with better performance. The preparation method of the composite material comprises the following steps of: putting the material in an uncured bonding material, fully and evenly mixing, then putting the mixture into a die made of a nonmagnetic material, and putting the die in the magnetic field for oriented treatment.

Description

An electromagnetic wave absorbing material

technical field

The invention relates to a material capable of absorbing electromagnetic waves and a composite material capable of absorbing electromagnetic waves prepared from the material. The invention also provides a preparation method of these materials. More precisely, the present invention is a material that can absorb electromagnetic waves with a frequency higher than 1G. The material of the present invention is a 2:14:1 phase rare earth iron boron alloy; the composite material of the present invention refers to a composite material with higher electromagnetic wave absorption performance made by the orientation of the aforementioned electromagnetic wave absorbing material and bonding material.

Background technique

With the development of science and technology and communication technology, computers, mobile phones, disks, etc. have been widely used in the process of information generation and transmission, but the wide application of this electromagnetic wave material has brought increasingly serious problems of electromagnetic radiation and electromagnetic interference. An effective way to overcome electromagnetic wave interference is to use electromagnetic wave absorbing materials.

Chinese invention patent application 200710049468.X discloses a rare-earth-doped rare-earth iron-based wave-absorbing material mainly composed of α-Fe. In addition, "Broadband and thin microwave absorber of nickel-zinc ferrite/carbonyl iron" (Journal of Alloys and Compounds 487 (2009) 708-711) (hereinafter referred to as Document 1) discloses a microwave-absorbing composite material of ferrite and metal particles ; "Dependence of Microwave Absorbing Property on Ferrite Volume Fraction in MnZn Ferrite-Rubber Composites" (D.Y.Kim, Y.C.Chung, T.W.Kang, and H.C.Kim IEEETRANSACTIONS ONMAGNETICS, VOL 32, NO 2, MARCH 1996) (hereinafter referred to as iron literature) Oxygen electromagnetic wave absorbing materials; Gigahertz range electromagnetic wave absorbers made of amorphous-carbon-based magnetic nanocomposites (Jiu Rong Liu, Masahiro Itoh, Takashi Horikawa, and Ken-ichi Machida JOURNAL OF APPLIEDPHYSICS 98, 054 for short) The microwave-absorbing properties of composite materials composed of iron and carbon are disclosed.

A common deficiency in the prior art is that the matching thickness of the material is relatively large. For example, the matching thickness of the material disclosed in Chinese patent application 200710049468. The content of the accompanying drawings); while the material in Document 1 has a corresponding thickness of 3.5-4 mm when the frequency is 3 GHz; the corresponding thickness of the material in Document 2 exceeds 4 mm when the frequency is less than 8 GHz; the material in Document 3 has a corresponding thickness when the frequency is 3 GHz The corresponding thickness is 4mm, and when the frequency is 2GHz, its thickness will reach about 6mm. Due to the large matching thickness of the material in the prior art, its application is limited, and it is even completely unusable in some special application fields.

NdFeB material has been widely used since its appearance in the last century, but in the disclosed technical field, this kind of material belongs to hard magnetic material, such as the material disclosed in Chinese patent 02132613.4.

Contents of the invention

The present invention is to provide an electromagnetic wave absorbing material which can overcome the deficiencies of the prior art, is superior to the prior art, has a suitable frequency of 1G to 100G, and has stronger electromagnetic wave absorption performance under the thinner thickness than the prior art, especially It is a material that has a stronger absorption effect on electromagnetic waves with a frequency above 1G when the thickness of the material is thinner; the invention also provides the preparation process of this material, and prepares a composite material with better wave absorption effect by using this material. material method.

The general formula of the electromagnetic wave absorbing material of the present invention is R ₂ Fe ₁₄ B. In the general formula, R is a combination of two rare earth elements, Sm and Nd, in the ratio of Nd _1-x Sm _x (0.3≤x≤1), and R ₂ Fe ₁₄ B The easy magnetization direction of the material is not parallel to the C-axis. It should be noted that if the composition satisfies the above general formula, but its easy magnetization direction is parallel to the C-axis, this type of material is a typical hard magnetic material, and this type of material is not suitable for absorbing electromagnetic waves.

The chemical formula of the best electromagnetic wave absorbing material in the present invention is: (Nd _0.66 Sm _0.34 ) ₂ Fe ₁₄ B, or (Nd _0.54 Sm _0.46 ) ₂ Fe ₁₄ B.

The preparation method of the electromagnetic wave absorbing material of the present invention is to smelt rare earth elements, iron and ferroboron into an alloy, then fully homogenize the alloy at high temperature, pulverize and grind the alloy into fine particles, and then perform ball milling to obtain metal powder.

In the preparation of the material of the present invention, 1% to 5% of the alloy mass phthalate coupling agent and isopropanol solvent for diluting the coupling agent can be added during ball milling, and the coupling agent can be fully contacted with the alloy surface. By adopting this measure, the coupling agent can be coated on the surface of the material to reduce the oxidation of the material and keep it in a 2:14:1 phase.

A composite material with better electromagnetic wave absorption performance can be prepared by using the aforementioned electromagnetic wave absorbing material of the present invention. The preparation method of this composite material is to put the described material into an uncured bonding material, mix it thoroughly and then Put it into a mold made of non-magnetic material, place the mold in a magnetic field, and rotate the mold in the magnetic field at the same time, so that the material is oriented until the bonding material is cured. The bonding material described here is resin or paraffin. Or polyethylene, or polypropylene and other polymer materials.

In the preparation of the aforementioned composite material, the magnetic field during the orientation treatment is 10 ^-4 ~ 10T, and the rotation speed of the mold is 1 ~ 200 rpm.

The present invention recommends that the adhesive material used in the preparation of the composite material be heat-cured epoxy resin.

Relevant experimental studies have shown that the electromagnetic wave absorbing material of the present invention and the composite material prepared from the material have better electromagnetic wave performance than the prior art under thin material thickness conditions, such as 2 to 3mm, and can meet the requirements of strong absorption. Requirements, the material of the present invention is a new type of wave-absorbing material with excellent performance, which can be used to shield electromagnetic radiation and eliminate electromagnetic interference, and can also meet the requirements of modern instruments for miniaturization, integration and high efficiency.

Description of drawings

Accompanying drawing 1 is the XRD diffraction pattern before and after orientation of the material of example 1 of the present invention.

Accompanying drawing 2 is the electromagnetic wave absorption spectrogram of the composite material that the material of example 1 of the present invention uses paraffin as binder preparation, wherein ● curve is the absorption curve of composite material without orientation treatment, and curve is the composite material after orientation treatment The absorption curve of the material. 2mm and 2.5mm in the figure refer to the thickness values of the material corresponding to the reflection loss of the measured sample being 2mm and 2.5mm respectively.

Accompanying drawing 3 is the electromagnetic wave absorption spectrogram of the composite material that heat-cured epoxy resin is prepared as binder in example 1 material of the present invention, and 2 and 2.5 in the figure mean respectively that the thickness value of the material corresponding to the reflection loss of the tested sample is 2mm and 2.5mm.

Accompanying drawing 4 is the XRD diffraction pattern before and after orientation of the material of example 2 of the present invention.

Accompanying drawing 5 is the electromagnetic wave absorption spectrogram of the composite material that the material of example 2 of the present invention uses paraffin as binder preparation, wherein ● curve is the absorption curve of composite material without orientation treatment, and curve is the composite material after orientation treatment The absorption curve of the material. 2mm and 2.5mm in the figure refer to the thickness values of the material corresponding to the reflection loss being 2mm and 2.5mm respectively.

Accompanying drawing 6 is the electromagnetic wave absorption spectrogram of the composite material that the material of example 2 of the present invention uses thermosetting epoxy resin as binder preparation, and 2mm and 2.5mm in the figure mean respectively the thickness of the material corresponding to the reflection loss of the tested sample Values are 2mm and 2.5mm.

Detailed ways

The specific embodiment of the present invention is:

a. First smelt the rare earth element, iron, and ferroboron into an alloy under the protection of an inert gas, then anneal the alloy for a week under vacuum, and then pulverize it into powder under the protection of a protective agent.

b. Mix the prepared rare earth transition group intermetallic compound powder with the uncured bonding material with a volume ratio of 1 to 9:9 to 1, put it into a mold made of non-magnetic material, and place it at 10 ^-4 to 10T (Tesla) magnetic field, and the mold is rotated at a speed of 1 to 200 rpm in the magnetic field at the same time until the bonding material is solidified.

The preferred material preparation method of the present invention is that the mold is placed in a magnetic field of 10 ^-4 ~ 10T (Tesla), and the rotation speed of the mold is 1 ~ 200 rpm.

Below are two preferred embodiments of the present invention:

Example 1

Weigh 1.837g of neodymium, 1.128g of samarium, 6.789g of iron, and 0.510g of ferroboron, and melt them into ingots under the protection of argon. Annealed in a vacuum quartz tube at 1000 °C for one week. Grind the annealed ingot into particles of about 70 microns with an agate mortar, then wet-mill the particles with a planetary ball mill by adding 100ml of isopropanol and 0.2ml of phthalate coupling agent, the ball-to-material ratio is 20:1, and ball mill The speed is 200 rpm, the forward and reverse ball milling method is adopted, the time interval is 1 hour, the total time of ball milling is set to 8 hours, and finally the sample is dried to obtain (Nd _0.66 Sm _0.34 ) ₂ Fe ₁₄ B material. Then the samples were compounded in three situations: (1) mixed evenly with the paraffin wax diluted with n-hexane at a volume ratio of 35:65, and put it into a mold (with an inner diameter of 3.04mm and an outer diameter of 7.00mm) after drying , Pressed and molded under 1Mpa pressure, and then taken out for testing. (2) Mix the paraffin wax diluted with n-hexane at a volume ratio of 35:65, put it into a mold (with an inner diameter of 3.04mm and an outer diameter of 7.00mm) prepared by a non-magnetic material after drying, and place the mold Heat it in an oven at 90°C for 15 minutes to melt the paraffin, then put the mold into a magnetic field for rotation orientation, the size of the magnetic field is 0.8-1.2T (Tesla), and the rotation speed is about 120 rpm for 20 minutes Allow the sample to completely solidify, then remove for testing. (3) Mix the epoxy diluted with acetone at a volume ratio of 35:65, and after drying, press it into a ring-shaped sample with an inner diameter of 3.04mm, an outer diameter of 7.00mm, and a thickness of 2-3mm, and then put the sample into Cured in a vacuum oven at 140°C for 1 hour, and then tested. Its X-ray diffraction spectrum is shown in Figure 1, and its electromagnetic wave absorption performance is shown in Figures 2 and 3.

It can be seen from Fig. 1 that the material obtained in Example 1 is a pure 2:14:1 phase sample. After multiple orientations, the result is the same, and there are obvious (214), (105), (410), (314), (006) diffraction peaks, and other diffraction peaks disappear substantially. It can be seen that the material obtained in Example 1 is in the At room temperature, it has the characteristics of non-plane anisotropy and non-axial anisotropy. We think it is a kind of cone anisotropy between the axis and the plane.

It can be seen from Figure 2 that after the material is compounded with paraffin, without orientation, at 2-4GHz, the thickness is 2-2.5mm, and the reflection loss can reach about -5dB; after orientation, at 4-5GHz, the thickness is 2 -2.5mm, the minimum reflection absorption value can reach -30dB. It can be seen that under the condition that the thickness of the tested sample remains basically unchanged, the maximum reflection loss value can be greatly improved after orientation treatment.

It can be seen from Figure 3 that the composite material obtained by compounding the material and the heat-cured epoxy resin can reach -25dB in the minimum reflection absorption at 2-2.5 mm. Therefore, the present invention recommends using heat-cured epoxy resin as the adhesive, which can greatly increase the reflection loss value under the condition that the thickness of the tested sample remains basically unchanged. On the other hand, if the material is further oriented, a composite material with better absorbing properties can be obtained.

Example 2

Weigh 1.393 g of neodymium, 1.659 g of samarium, 6.781 g of iron, and 0.509 g of ferroboron, and melt them into ingots under the protection of argon. Annealed in a vacuum quartz tube at 1000 °C for one week. The annealed ingot was ground into particles of about 70 microns with an agate mortar, and then the particles were wet-milled with a planetary ball mill by adding 100 ml of isopropanol and 0.2 ml of phthalate coupling agent, with a ball-to-material ratio of 20:1. The ball milling speed was 200 rpm, and the forward and reverse ball milling method was adopted. The time interval was 1 hour. The total milling time was set at 8 hours. Finally, the sample was dried to obtain (Nd _0.54 Sm _0.46 ) ₂ Fe ₁₄ B material. Then the samples were compounded in three situations: (1) mixed with paraffin wax diluted with n-hexane at a volume ratio of 35:65, dried and placed into a mold (with an inner diameter of 3.04 mm and an outer diameter of 7.00 mm) , pressed into shape under a pressure of 1 Mpa, and then taken out for testing. (2) Mix the paraffin wax diluted with n-hexane at a volume ratio of 35:65. After drying, put it into a mold made of non-magnetic material (the inner diameter is 3.04 mm and the outer diameter is 7.00 mm). Heat it in an oven at 90°C for 15 minutes to melt the paraffin, then put the mold into a magnetic field for rotation orientation, the size of the magnetic field is 0.8-1.2T (Tesla), and the rotation speed is about 120 rpm for 20 minutes Allow the sample to completely solidify, then remove for testing. (3) Mix the epoxy diluted with acetone at a volume ratio of 35:65, and after drying, press it into a ring-shaped sample with an inner diameter of 3.04 mm, an outer diameter of 7.00 mm, and a thickness of 2-3mm, and then put the sample into Cured in a vacuum oven at 140°C for 1 hour, and then tested. Its X-ray diffraction spectrum is shown in Figure 4, and its electromagnetic wave absorption performance is shown in Figures 5 and 6.

As can be seen from Fig. 4, this material obtained in the present embodiment 1 is a pure 2: 1 4: 1 phase sample. After orientation, obvious (004), (105), (006), (008), (0010) diffraction peaks appeared, and other diffraction peaks basically disappeared. It can be seen that the material obtained in Example 2 has a planar shape at room temperature. Anisotropic characteristics.

It can be seen from Figure 5 that after the material is compounded with paraffin, without orientation, the frequency is 1-2GHz, the thickness is 2-2.5mm, and the reflection loss is about -3dB; after orientation, the thickness is 5-7GHz. 2-2.5 mm, the minimum reflection absorption value can reach -25dB. It can be seen that orientation can increase the maximum reflection loss value while the thickness remains substantially constant.

It can be seen from Figure 6 that the composite material obtained by compounding the material and the heat-cured epoxy resin has a minimum reflection absorption of -30dB at 2 to 2.5 mm. Therefore, the present invention recommends using heat-cured epoxy resin as the adhesive, which can greatly increase the reflection loss value under the condition that the thickness of the tested sample remains basically unchanged. On the other hand, if the material is further oriented, a composite material with better absorbing properties can be obtained.

Claims (8)

1. electromagnetic wave absorbent material, the general formula that it is characterized in that material is R ₂Fe ₁₄B, R is that Sm and two kinds of rare earth elements of Nd are with Nd in the general formula _1-xSm _xThe ratio combination, wherein 0.3≤x≤1, and R ₂Fe ₁₄The easy magnetization axis of B material and C axle are not parallel.

2. the described electromagnetic wave absorbent material of claim 1, its chemical formula is: (Nd _0.66Sm _0.34) ₂Fe ₁₄B.

3. the described electromagnetic wave absorbent material of claim 1, its chemical formula is: (Nd _0.54Sm _0.46) ₂Fe ₁₄B.

4. according to the preparation method of the described arbitrary electromagnetic wave absorbent material of claim 1 to 3, it is characterized in that rare earth element, iron and ferro-boron are smelted into alloy, alloy high-temp fully being carried out homogenizing handles again, carry out ball-milling processing after again the alloy powder breakdown mill being become tiny particle, obtain metal-powder.

5. according to claim 4 preparation method, it is characterized in that when ball milling, adding the phthalate ester coupling agent of alloy mass 1%～5% and being used to dilute the solvent Virahol of coupling agent, and coupling agent is fully contacted with alloy surface.

6. the method for preparing matrix material with the described electromagnetic wave absorbent material of claim 1, it is characterized in that described material is put into uncured matrix material, after thorough mixing is even, put into the mould that nonmagnetic substance is made again, mould is placed magnetic field, mould is rotated in magnetic field, so material is carried out orientation process and solidify up to matrix material, matrix material described here is resin or paraffin wax, or polyethylene, or macromolecular material such as polypropylene.

7. the described method of claim 6, magnetic field is 10 when it is characterized in that orientation process ^-4～10T, the mould speed of rotation is 1～200 rev/min.

8. claim 6 or 7 described composite material and preparation method thereofs is characterized in that used matrix material is a heat-curable epoxy resin.

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