JP2006156543A - Manufacture of nano complex magnetic particle by physical mixture, and electromagnetic wave absorber obtained thereby - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing nano complex powder for efficiently absorbing electromagnetic waves at a GHz band in which a utilization range tends to expand following the development of communication equipment by a magnetic medium, such as iron, taken into a matrix, such as carbon. <P>SOLUTION: The nano complex magnetic particle is obtained by mixing amorphous carbon that is a non-good conductor and a magnetic material with a transition metal or its alloy as a base by a physical method. The electromagnetic wave absorber is obtained by adding binder, such as resin, to the nano complex particles. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a composite powder in which a nanometer-sized magnetic material having electromagnetic wave absorption characteristics in the GHz band forms a fine structure with a non-good conductor such as amorphous carbon. The present invention relates to a method for producing an electromagnetic wave absorber using a slag.

  Conventionally, in the GHz band electromagnetic wave absorber, a ferrite hard magnetic material or a metal-based magnetic material imparted with shape anisotropy is used in addition to a conductor and a dielectric. The former is used as an electromagnetic wave absorber corresponding to 5 GHz to 20 GHz although the magnetization is low and the absorption ratio is small (Patent Document 1, Patent Document 1). On the other hand, the latter is manufactured and sold as an electromagnetic wave absorber having an electromagnetic wave absorbing ability in the GHz region by imparting magnetic anisotropy depending on the shape by performing processing such as flattening centering on iron (see Patent Document 2). .

On the other hand, in recent years, Sugimoto et al., After pulverizing a melt-cast rare earth-iron-based intermetallic compound, disproportionation treatment by hydrogenation and oxidation, that is, nanocomposite particles, ie, α-Fe / RO _X (X = 1 or 1 .5), it has been reported that it has a good electromagnetic wave absorbing ability in the 1 to 3 GHz band (see Paper 2 and Paper 3).

JP2000-331816

JP 11-354973

[Papers 1] S. Sugimoto, K. Okayama, S. Kondo, H. Ota, M. Kimura, Y. Yoshida, H. Nakamura, D. Book, T. Kagotani, and M. Homma, Mater. Trans. , vol. 39, 1080 (1998).

[Paper Reference 2] T. Maeda, S. Sugimoto, T. Kagotani, D. Book, M. Homma, H. Ota, and Y. Houjou, Mater. Trans., Vol. 41, 1172 (2000).

[Papers 3] S. Sugimoto, T. Maeda, D. Book, T. Kagotani, K. Inomata, M. Homma, H. Ota, Y. Houjou, and R. Sato, J. Alloys Compd., Vol. 330-332, 301 (2002).

  In the case of the ferrite hard magnetic material described in Patent Document 1 and Paper Document 1, its own conductivity is low and the loss due to eddy current is small, but the original magnetization is low and it is not suitable for producing a thin high-performance electromagnetic wave absorber. . On the other hand, in the case of the iron powder having an anisotropic shape described in Patent Document 2, although it has a high electromagnetic wave absorption ability, it is a conductor, and therefore, in addition to a magnetization loss based on eddy current, a processing process such as a flattening process This is an obstacle to cost reduction.

  On the other hand, by absorbing and oxidatively decomposing rare earth intermetallic compounds into a composite magnetic material powder of metallic iron and rare earth oxide, the electromagnetic wave absorber has the advantages of metal magnetic material and compensates for the disadvantage of eddy current loss Has been reported (see papers 2 and 3). However, since the electromagnetic wave frequency that can be absorbed is low due to the small anisotropic magnetic field of the free iron metal, and since the ingot of the intermetallic compound obtained by the usual melting method is used as a raw material for sample preparation, It is unsuitable for the production of a fusion body having a uniform structure. Furthermore, in order to obtain a fine structure of a metal magnetic body, a heterogeneous reaction by hydrogen storage is necessary, and a compound having no hydrogen storage capacity is required. On the other hand, there is a drawback that the above method cannot be applied.

  By reducing the size of metal magnetic particles by making a composite in which magnetic metals such as iron, interstitial compounds, and intermetallic compounds are highly dispersed in a matrix that is a poor conductor, the magnetization of the metal magnetic material is reduced. Improve the eddy current loss that causes the drop. Further, by making the structure of the metal and non-good conductor of the above composite fine and uniform, the insulation effect by the non-good conductor can be improved. In addition, in order to cope with electromagnetic waves in the band of several GHz to several tens of GHz, which is expected to expand in the future, magnetic anisotropy is imparted by a method other than the flattening of the magnetic particles described above, and the electromagnetic waves are highly efficient. Magnetic powder to be absorbed in Furthermore, since the composite magnetic powder of the present invention contains carbon, the composite obtained by physical mixing of the carbon powder with the surface of the carbon is previously modified before mixing with the metal magnetic powder. The affinity of the powder for the resin can be improved. As a result, it is possible to produce a radio wave absorber with high dispersibility and filling rate of the composite powder.

Specifically, the metal powder, which is a magnetic material, is physically pulverized and mixed with carbon, which is a non-good conductor, using a planetary ball mill or the like to obtain a composite magnetic material powder having a fine and uniform structure. In addition, as an electromagnetic wave absorber corresponding to several GHz to several tens GHz, an interstitial compound magnetic material such as iron boride having magnetic anisotropy derived from a crystal structure or an intermetallic compound magnetic material is similarly combined with a non-good conductor. Therefore, it is possible to cope with the problem by shifting the resonance frequency to a high frequency region compared to a cubic magnetic material such as iron. In addition, before mixing with magnetic powder, surface modification is performed by treating carbon with an acid such as nitric acid in advance, and resin such as epoxy of composite powder obtained by mixing this with magnetic powder By improving the affinity for the radio wave absorber, it is possible to produce a radio wave absorber with improved dispersibility and filling rate of the composite powder. In addition to the carbon surface modification described above, the surface of the obtained composite magnetic powder is modified with a silane coupling agent to improve the affinity (familiarity) with the resin and provide durability. be able to.

  According to the present invention, an electromagnetic wave absorber capable of supporting the GHz band can be manufactured by a simple process and at a low cost. In particular, compared to conventional magnetic powders for electromagnetic wave absorbers due to the introduction of boron and carbon between Fe lattices or the application of an anisotropic magnetic field by alloying iron and cobalt to the transition to the high frequency region of the electromagnetic wave absorption region. Electromagnetic waves in a high frequency range can be effectively absorbed.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows a cross-sectional view of an electromagnetic wave absorber according to the present invention. As shown in FIG. 1, when electromagnetic waves are incident on the absorber perpendicularly, the normalized input impedance Z for expecting a metal plate from the surface of the absorber is expressed by the following equation (1). Using this Z, the reflection loss R is (2 ) And (3). Thus, although the reflection loss is determined by Z, as is clear from the equation (1), Z is a function of ε, μ, wavelength λ of electromagnetic wave, and specimen thickness d, and calculation of a region satisfying 20 dB. The law is complex. Therefore, the frequency characteristics of ε and μ are measured by the S-parameter method using a network analyzer, and the reflection loss when the thickness of the specimen is changed is calculated from the measurement results using the equations (1) to (3). The electromagnetic wave absorber can be designed and manufactured based on this value.
That is, a resin binder such as an epoxy resin is kneaded with the electromagnetic wave absorbing magnetic powder described above, and a metal plate is used as a substrate to form a sheet or board having a predetermined thickness, which is used as an electromagnetic wave absorber. In this case, the resonance frequency at which electromagnetic waves are best absorbed depends on the thickness of the electromagnetic wave absorber, and the thickness can be adjusted to correspond to the frequency of the desired electromagnetic wave. Further, in addition to the form shown in FIG. 1, it is also possible to form an electromagnetic wave absorber in the form of a thin sheet or tape.

  Hereinafter, the results of experiments conducted to confirm the effects of the present invention will be described.

Example 1
Iron-amorphous carbon composite powder is added by adding 10% by weight of amorphous carbon from which moisture has been removed by heating deaeration to metallic iron, and mixing in an argon atmosphere at a rotational speed of 200 rpm for 30 hours using a planetary ball mill. Was made. Here, the mixing time by the ball mill is 30 hours in the present invention, but the time can be shortened by changing the number of rotations, the type and size of the balls used.

The XRD pattern of the powder before and after the treatment is shown in FIG. A sharp peak attributed to iron was observed before mixing, whereas a broad peak was observed after mixing, although the diffraction position did not change. From this, it was confirmed that the primary particles of iron were refined by physical combination with amorphous carbon. On the other hand, since the carbon used for complexing with iron was amorphous, no diffraction peak was found in the XRD pattern. In direct observation with a scanning electron microscope, the particle size of iron before pulverization was several tens of μm, and that after pulverization was several tens to several hundreds of nm. Moreover, since there is no shift in the XRD peak before and after pulverization, it can be seen that under the current physical mixing conditions, carbon does not enter between the iron lattices and iron carbide is not generated.

  The iron-amorphous carbon composite powder obtained above is mixed with 25% by weight of an epoxy resin to produce a molded body, and cured at 130 ° C. for 30 minutes and then at 180 ° C. for 30 minutes. By doing so, an electromagnetic wave absorber was created. The absorber was evaluated for electromagnetic wave absorption characteristics by a network analyzer. The results are shown in FIG. In a sample having a thickness of 1.9 to 3.4 mm, a reflection loss of −20 dB or less, which is required as a performance of the radio wave absorber, was observed in the region of 4.5 to 9.0 GHz. The good radio wave absorption characteristics obtained here are obtained by a nanocomposite having a uniform microstructure by compounding with carbon, which is a non-good conductor, and induced by an electromagnetic field by miniaturization of magnetic metal particles. It is thought that eddy current loss was suppressed. In addition, the electric resistance value of the iron-amorphous carbon composite powder (no resin mixing, green compact) was 200 Ωm. Further, in the process of producing the above iron-amorphous carbon composite powder, the amorphous carbon is treated with hot nitric acid for 1 hour in advance for surface modification, and the iron-amorphous carbon is physically mixed with this. (Surface modification) Composite powder was obtained. When this powder was subjected to FT-IR measurement, a peak peculiar to the stretching vibration of the carbon-oxygen double bond of the carbonyl group was observed. With respect to this composite powder, the amount of epoxy resin used was reduced to produce a molded product. As a result of evaluating the characteristics of the obtained radio wave absorber, it showed almost the same tendency with respect to the radio wave absorption range compared to the absorber not subjected to the modification treatment, but the dispersibility and filling rate of the composite powder were improved. As a result, the reflection loss was improved.

(Example 2)
A predetermined amount of metallic iron and boron were weighed and arc-melted to prepare an Fe ₂ B ingot. A Fe ₂ B metal ribbon was prepared from this ingot using an ultra-quenching device, and this was pulverized to obtain a Fe ₂ B powder having a particle size of about 3 μm or less. From this and the above-mentioned amorphous carbon, an Fe ₂ B-amorphous carbon composite powder was prepared by the same physical mixing method as in Example 1.

FIG. 4 shows the results of X-ray diffraction of the produced Fe ₂ B powder and Fe ₂ B-amorphous carbon composite powder. It was confirmed from the diffraction pattern (a) of the sample obtained by ultra rapid cooling that single-phase Fe ₂ B was obtained. In sample (b) after complexing with amorphous carbon, the diffraction pattern coincided with the peak of Fe ₂ B which is the starting material. Again, the peak half-width of the sample after mixing was increased, confirming that the crystallite size was decreasing due to physical mixing. The crystallite size of Fe ₂ B in the composite estimated from the peak half width was about 30 nm.

The result of transmission electron microscope observation of the Fe ₂ B-amorphous carbon composite powder is shown in FIG. It was confirmed that acicular Fe ₂ B of several nm to several tens of nm was highly dispersed in the composite. This result is consistent with the result obtained by XRD.

Similarly, Fe ₂ B-amorphous carbon / epoxy resin (25% by weight) was prepared by the method described in Example 1, and electromagnetic wave absorption characteristics were evaluated using a network analyzer. The results are shown in FIG. In the absorber having a thickness of 1.2 to 2.2 mm, a good reflection loss of −20 db or less was observed in the region of 6 to 16 GHz. Also here, it was confirmed that by combining Fe ₂ B and amorphous carbon having a relatively large electric resistance value, eddy current loss was suppressed and good electromagnetic wave absorption characteristics were obtained even in a high frequency range. Furthermore, the absorption frequency in the Fe ₂ B-amorphous carbon composite shifted to the high frequency side as compared with the iron-amorphous carbon composite. This is because the interstitial compound Fe ₂ B is tetragonal and has magnetic anisotropy associated with the crystal structure, so that the resonance frequency is shifted to the high frequency side compared to cubic iron. In addition to providing magnetic anisotropy by flattening conventional spherical particles, it was confirmed that electromagnetic waves in a high frequency region can be absorbed by changing the crystal structure.

(Example 3)
It was prepared an ingot of Y ₂ Fe ₁₇ by weighing predetermined amounts of arc melting the metal yttrium and metallic iron. A Y ₂ Fe ₁₇ metal ribbon was prepared from this ingot using an ultra-quenching apparatus and pulverized to obtain a Y ₂ Fe ₁₇ powder having a particle size of about 3 μm or less. A Y ₂ Fe ₁₇ -amorphous carbon composite powder was prepared from this magnetic powder in the same manner as described above.

FIG. 7 shows the results of X-ray diffraction of the produced Y ₂ Fe ₁₇ powder and Y ₂ Fe ₁₇ -amorphous carbon composite powder. Mixing from XRD measurement of the sample before and after, Y ₂ while maintaining the crystal structure of Fe ₁₇ uniform and fine Y ₂ Fe 17 _- it was confirmed that the amorphous carbon composite is obtained. The crystallite size of Y ₂ Fe ₁₇ in the composite estimated from Scherrer's formula was about 20 nm.

An electromagnetic wave absorber was prepared from the Y ₂ Fe ₁₇ -amorphous carbon composite powder by the same method as described above, and the electromagnetic wave absorption characteristics were evaluated. The results are shown in FIG. In the absorber having a thickness of 1.3 to 2.2 mm, a good reflection loss of −20 db or less was observed in the 9 to 18 GHz region. Also in this composite, it was confirmed that Y ₂ Fe ₁₇ was combined with amorphous carbon having a relatively large electrical resistance value to reduce the electrical resistance value and suppress eddy current loss. In addition, the electrical resistance value of Y ₂ Fe ₁₇ -amorphous carbon composite powder (green compact) prepared without adding an epoxy resin is 200 Ωm, that of a typical intermetallic compound (˜10 ⁻⁶ Ωm ) Also showed a large value. Further, the composite powder was subjected to a surface modification treatment using diphenylsilane to produce a radio wave absorber in which the amount of epoxy resin used was reduced as compared with the above radio wave absorber. As a result of evaluating the characteristics of the obtained radio wave absorber, an increase in reflection loss was observed due to improvement in dispersibility and filling rate as compared with the untreated absorber. In addition, as a result of an endurance test in the atmosphere at 80 ° C. for the surface-modified powder and the untreated powder, the untreated powder showed an increase in oxygen content due to oxidation. Since the surface of the powder was modified with a functional group having hydrophobicity, no significant increase in oxygen content was observed.

Example 4
Metallic iron and amorphous carbon were weighed 3: 1 (atomic ratio) and mixed with a planetary ball mill at 500 rpm for 100 hours to prepare Fe ₃ C source powder. As a result of XRD measurement on the sample before and after mixing (FIG. 9), the diffraction pattern (a) of amorphous carbon and iron before mixing showed a sharp peak, but the sample (b) after mixing was amorphous. It showed a broad peak. Therefore, the amorphous-like sample was crystallized by heating in a helium atmosphere at 400 ° C. for 1 hour. The XRD pattern (c) of the sample after crystallization showed an XRD pattern attributed to orthorhombic Fe ₃ C although being broad. From this, by optimizing the mixing process conditions, it is possible to avoid inter-starting materials (iron and amorphous carbon in the above example) in the composite mixing process without using a compound such as Fe ₂ B as the starting material. It can be seen that the compound can be prepared by reaction.

Fe ₃ C-amorphous carbon composite powder was prepared from the Fe ₃ C powder obtained above and amorphous carbon by the same method as in Example 1, and X-ray diffraction measurement was performed. The result is shown in FIG. Although the obtained diffraction pattern coincides with the peak of Fe ₃ C as a starting material, the half width of the diffraction peak is increased, and the crystallite size of Fe ₃ C is decreased by physical mixing. Was also confirmed. The crystallite size of Fe ₃ C in the composite estimated from the half width of the diffraction peak was about 10 nm.

An electromagnetic wave absorber was produced from Fe ₃ C-amorphous carbon in the same manner as in Example 1, and its characteristics were evaluated. The results are shown in FIG. In the absorber having a thickness of 1.0 to 1.3 mm, a good reflection loss of −20 db or less was observed in the region of 18 to 26 GHz. It was confirmed that good electromagnetic wave absorption characteristics can be obtained by combining the composite powder with amorphous carbon.

(Example 5)
A predetermined amount of metallic iron, metallic cobalt and boron were weighed and mixed with a planetary ball mill, and the obtained amorphous-like powder was annealed to obtain Fe _1.4 Co _0.6 B powder. From this and amorphous carbon, Fe _1.4 Co _0.6 B-amorphous carbon composite powder was prepared by the method of Example 1.

FIG. 11 shows the results of X-ray diffraction of the prepared Fe _1.4 Co _0.6 B powder and Fe _1.4 Co _0.6 B-amorphous carbon composite powder. It was confirmed from the diffraction pattern (a) of the sample obtained by ultra rapid cooling that single-phase Fe _1.4 Co _0.6 B was obtained. Moreover, the diffraction pattern of Fe _1.4 Co _0.6 B-amorphous carbon composite powder showed a broad diffraction peak attributed to Fe _1.4 Co _0.6 B. The crystallite size of Fe _1.4 Co _0.6 B in the composite estimated from the half width was about 20 to 30 nm.

Fe _1.4 Co _0.6 B-Amorphous carbon / epoxy resin (25% by weight) was prepared in the same manner as in Example 1, and the electromagnetic wave absorption characteristics were evaluated using a network analyzer. The results are shown in FIG. In the absorber thickness of 0.6 to 0.8 mm, good reflection loss of −20 db or less was observed in the 27 to 40 GHz region. Here, electromagnetic wave absorption in a high frequency band was obtained with Fe _1.4 Co _0.6 B as compared with Fe ₂ B produced in Example 2. As described above, it is possible to shift the electromagnetic wave absorption region to a high frequency region by imparting magnetic anisotropy by making the crystal structure anisotropic, but here, one of the Fe sites of Fe ₂ B The magnetic anisotropy was increased by replacing the portion with Co to form a solid solution, and the electromagnetic wave absorption frequency was successfully increased.

The electromagnetic wave absorber according to the present invention has a basic structure. It is an X-ray diffraction pattern before and after physical mixing of iron and amorphous carbon. (a) Before mixing, (b) After mixing. It is the absorption characteristic of the electromagnetic wave absorber obtained by mixing resin with iron-amorphous carbon composite powder. It is an X-ray diffraction pattern before and after physical mixing with amorphous carbon of Fe ₂ B. (a) Before mixing, (b) After mixing. Fe ₂ B- is a TEM observation image of amorphous carbon composite powder. Fe 2 _B- is the absorption properties of the obtained electromagnetic wave absorber by mixing the resin into amorphous carbon composite powder. It is an X-ray diffraction pattern before and after physical mixing with amorphous carbon of Y ₂ Fe ₁₇ . (a) Before mixing, (b) After mixing. Y 2 _Fe 17 _- the absorption properties of the obtained electromagnetic wave absorber by mixing the resin into amorphous carbon composite powder. It is an X-ray diffraction pattern before and after physical mixing of Fe and amorphous carbon. (a) Before mixing, (b) After mixing, (c) After annealing the sample of b in helium at 400 ° C. for 1 hour, (d) After physical mixing of the sample of c and amorphous carbon. Fe 3 _C-to amorphous carbon composite powder is the absorption characteristic of the electromagnetic wave absorber obtained by mixing resin. It is an X-ray diffraction pattern before and after physical mixing with amorphous carbon of Fe _1.4 Co _0.6 B. (a) Before mixing, (b) After mixing. The absorption properties of the obtained electromagnetic wave absorber by mixing the resin into Fe _1.4 Co _0.6 B- amorphous carbon composite powder.

Claims (7)

  A composite for electromagnetic wave absorption comprising a nanocomposite structure in which a magnetic metal phase of several tens to several hundreds of nanometers is dispersed by physically mixing a transition metal magnetic material such as iron and a non-good conductor such as amorphous carbon. A method for producing magnetic powder. Dispersion of magnetic metal phase from several nm to several hundred nm obtained by physically mixing magnetic powder such as interstitial metal boride, carbide, nitride, or intermetallic compound with amorphous carbon Of producing a composite magnetic powder for electromagnetic wave absorption comprising a nanocomposite structure. The starting material of the magnetic powder according to claim 1, wherein a single magnetic metal and a typical element such as carbon or boron are combined by physical mixing, and then mixed with carbon to obtain a composite magnetic material for electromagnetic wave absorption. How to make powder. As a starting material of the magnetic metal material in the composite magnetic powder according to claim 3, at least two kinds of metal powders are selected, and alloy elements enter by physically mixing these with typical elements such as carbon and boron. A method for producing a composite magnetic powder for absorbing electromagnetic waves obtained by mixing a carbon compound with a carbon compound. 5. The composite magnetic powder according to claim 1, wherein an amorphous carbon to be used is reacted with nitric acid in advance before being combined with the magnetic powder to introduce an aldehyde group or a carboxy group on the carbon surface, and the magnetic substance. A magnetic powder for electromagnetic wave absorption having improved affinity with a resin such as epoxy obtained by physically mixing the powder.   5. The magnetic powder for electromagnetic wave absorption according to claim 1, wherein the powder surface is modified by silane coupling treatment to improve the affinity to a resin such as epoxy and to provide durability. . 7. An electromagnetic wave absorbing material obtained by molding the composite particle type magnetic substance powder produced in claim 1 into a board, sheet, tape, or cord cover using a binder such as an organic resin and imparting electromagnetic wave absorption characteristics.