JP5299983B2 - Porous iron powder, method for producing porous iron powder, electromagnetic wave absorber - Google Patents

Description

  The present invention relates to a porous iron powder having radio wave absorption characteristics in the 1 to 20 GHz band, a radio wave absorber using the same, and a method for producing the porous iron powder.

Japanese Patent Laid-Open No. 2005-5286 JP 7-54106 A Japanese Patent Laid-Open No. 11-354773 JP 2000-80401 A Japanese Patent Laid-Open No. 57-4288

  In recent years, the development and high functionality of small portable devices have been rapidly promoted, and the use frequency range has been expanded to the GHz band due to the necessity of transmitting high-speed and large-capacity information. Mobile devices that have been limited to special applications are generally carried as general-purpose devices due to further miniaturization and cost reduction, and the radiation of radio waves into the space is expanding more than before. This radio wave radiated to the outside causes a malfunction of an electronic circuit or the like, which is a serious problem. In order to solve the problem of malfunction due to radio waves, various radio wave absorbers have been developed to absorb radio waves flying from the outside and radio waves generated from electronic components in the device.

  For example, in a non-stop automatic toll collection system (Electronic Toll Collection System: ETC) that started operation in March 2001, 5.8 GHz band radio waves are used for information collection. In this system, there is concern about system malfunction due to multiple scattered waves of radio waves between transmitting and receiving antennas, and a radio wave absorber is adopted as one of the countermeasures.

  The present invention relates to iron powder that can be used as a magnetic material for absorbing radio waves. Currently, ferrite, pure iron, sendust, rare earth magnets, and the like are known as magnetic materials for absorbing radio waves that are effective in the band of several tens of MHz to 1 GHz. Yes. Magnetic materials are known to absorb radio waves in the high-frequency region as the aspect ratio increases, and in pure iron, sendust, etc., fine particles are manufactured by the atomizing method, and then processed by using an attritor, etc. Is commercially available.

  Patent Document 1 discloses a method of manufacturing a magnetic material for absorbing radio waves from rare earth-transition metal scrap generated with the production or disposal of rare earth magnets. Radio wave absorbing magnetic material composed of a composite of transition metal magnetic particles and rare earth oxide particles by heat treatment (so-called disproportionation reaction treatment) in a temperature range in which only rare earth elements are oxidized and other elements are not oxidized It has been shown that a powder is obtained. The electromagnetic wave absorbing magnetic powder produced by this method has a disadvantage that the content of rare earth elements is large and the proportion of α-Fe responsible for radio wave absorption is reduced. There was also a problem from the viewpoint of effective utilization of rare earths.

  As a magnet with a small amount of rare earth element added, Patent Document 2 discloses an Nd—Fe—B permanent magnet in which Nd and B each contain 1 to 10 at%. However, this document does not describe the performance as a radio wave absorbing magnetic material and the fabrication technique. These two documents do not disclose a porous magnetic material having a large specific surface area and a manufacturing method thereof.

  Patent Document 3 discloses an electromagnetic wave absorber using Fe-based flat nanocrystalline soft magnetic powder, and the magnetic powder has a thickness of 3 μm or less and an average particle size of 20 to 50 μm. It is shown that it is preferable, that a flat shape is essential, and that it is important to electrically insulate between the powder particles. Then, it is shown that an amorphous alloy powder is produced by a water atomizing method, and a nanocrystalline soft magnetic powder having a microstructure of 10 nm is produced by heat treatment. This document does not show anything about the porous powder which is the basis of the present invention and its skin effect.

  Carbonyl iron has a high magnetic permeability and is excellent as a magnetic material for absorbing radio waves, but exhibits only radio wave absorption characteristics up to around 1 GHz, has a spherical shape, has a narrow particle size distribution, and has a small particle size. There is a drawback that it is difficult to increase the density by mixing with. Recently, ultrafine pure iron powder having an average particle size of 1 μm or less has been developed and reported to exhibit excellent radio wave absorption characteristics. However, although the reflection loss exceeds -35 dB in the 9 GHz frequency band, the plate thickness at that time is as large as 3 mm, so it cannot be said that it is suitable as a radio wave absorber for small devices.

  The magnetic powder described above is mixed and kneaded with a resin binder such as epoxy at a certain ratio. For example, a metal plate or the like is used as a substrate to form a sheet or board having a predetermined thickness, and this is used as a radio wave absorber. . The resonance frequency at which the radio wave is best absorbed depends on the thickness of the radio wave absorber, and the thickness of the radio wave absorber is adjusted in accordance with the desired radio wave frequency. Examples of such wave absorbers include ferrite sintered bodies, ferrite rubber composites, flat pure iron-containing resins, flat sendust-containing resins, and carbonyl iron rubber composites.

  It is known that pure iron dissolves in a wet soil, Fe ions dissolve, reacts with organic halogen compounds such as tetrachloroethylene in the soil, decomposes into organic substances such as ethylene and halogen, and is rendered harmless.

Patent Document 4 introduces iron powder containing at least one of P, S, and B as iron powder for harmful substance removal treatment. This iron powder has a specific surface area of 0.01 to 1.0 m ² / g and a particle diameter of 1 to 1000 μm.

  Patent Document 5 describes that P compound can be removed from waste water by adding iron powder to waste water containing a phosphorus compound and reacting iron ions eluted from the iron powder with phosphate ions.

  These documents show that it is effective to decompose and detoxify harmful substances with eluted Fe ions, and to add special elements to increase the amount of elution, but to increase the surface area of iron powder. There is no attempt to increase the amount of elution due to the accompanying increase in reaction area.

  Since radio waves in the 1 to 20 GHz band are used for transmission and reception of general-purpose portable electronic devices, the electromagnetic wave absorbing magnetic material absorbs radio waves in this frequency band and is as small and thin as possible for use in portable devices. It ’s important to be light. Conventional magnetic materials do not have sufficient radio wave absorption characteristics in a high frequency band, particularly in a band of 10 GHz or more. In addition, because it is processed into a flat body for high performance, the surface is smooth, so it does not fit well with the resin, and after forming into a radio wave absorber, cracks occur after a little processing, etc. There was a problem. Further, when the particle diameter is reduced in order to solve the above problem, a new problem that mixing with the resin becomes difficult occurs.

  In the present invention, if the magnetic material is made porous, the surface roughness increases, and coupled with the skin effect of the magnetic material itself, the path length of the current flowing on the surface increases, so that eddy current loss can be suppressed, and adhesion to the resin It has been newly found that the resistance is improved and the resistance to compression deformation is small.

The porous iron powder of the present invention has a large specific surface area. Since the surface roughness cannot be measured directly because the particles are small, when the specific surface area is used as a surrogate index, it is porous of 4 m ² / g or more and has an average particle diameter of 1 to 90 μm. It is a porous iron powder. A specific surface area of less than 4 m ² / g is not preferable because eddy current increases. The specific surface area is preferably 5 m ² / g or more, more preferably 8 m ² / g or more. In the present invention, the specific surface area is a value measured by a BET method using nitrogen gas, and the average particle diameter is a value of D50 measured by a laser diffraction method. When the average particle size is smaller than 1 μm, mixing with the resin becomes difficult. On the other hand, when the average particle size is larger than 90 μm, the filling rate is lowered, so that the radio wave absorption performance is lowered. The average particle size is preferably 5 to 15 μm.

  The porous iron powder of the present invention preferably has an oxide in the surface layer. If the iron particles are in contact with each other and there is continuity, eddy currents are generated and the radio wave absorption performance decreases. Due to the porous nature and the oxide formed on the surface, generation of eddy current can be suppressed. Moreover, it becomes difficult to ignite and handling becomes easy.

As described above, the characteristic of the porous iron powder of the present invention is the specificity of the shape represented by the specific surface area and the average particle diameter. The porous iron powder contains one or more elements selected from rare earth elements including Y. Further, the rare earth be described later as a raw material if e Example - iron alloy scrap used as a raw material, a rare earth element containing component (e.g. Y other than Fe derived from raw materials, B, C, Co, Al , Cu, Ga, Ti, Zr, Nb, V, Cr, Mo, Mn, Ni, Si, Mg, Ca, and the like). The content of components other than iron is preferably 15 at% or less.

  The porous iron powder of the present invention contains 0.01 to 15 at% of one or more elements selected from rare earth elements including Y, Al, Ti, Si, Mn, Co, Ni, B, C, and N It is preferable to do. The affinity of rare earth elements including Y, Al, Ti, Si, and Mn with oxygen is larger than that of Fe, and an oxide layer is easily formed on the surface of iron particles. In particular, it is preferable to contain 1 to 5 at% of a rare earth element. Pure iron has a high magnetic permeability and is excellent as a magnetic material for absorbing radio waves. However, it is preferable to contain elements such as Co, Al, Si, and Ni in order to further increase the magnetic permeability. If the amount of these elements added is 0.01 at% or less, the effect is not sufficient, and if it exceeds 15 at%, the radio wave absorption characteristics are deteriorated or the cost is lower than that of Fe, which is the main component, and the economic efficiency is impaired. .

  The average pore diameter of the porous iron powder of the present invention is preferably 100 nm or less, and more preferably 50 nm or less. Most preferably, it is 20 nm or less. In the present invention, the average pore diameter and pore volume were determined by a nitrogen adsorption method. When the average pore diameter is 100 nm or less, the skin effect is further increased.

  The pore volume of the porous iron powder of the present invention is preferably 0.01 ml / g or more, more preferably 0.02 ml / g or more. When the pore volume is 0.01 ml / g or more, a large amount of air is contained inside the particles, so that the weight of the radio wave absorber can be reduced.

  Since the porous iron powder of the present invention has a large specific surface area, it is extremely effective for decomposing organic halogen compounds in a wet state, and is useful as a purification agent for contaminated soil and waste water.

  The radio wave absorber of the present invention contains the porous iron powder described above. The radio wave absorber is prepared by mixing, kneading and heating a resin and porous iron powder. In order to improve the absorption performance of electromagnetic waves in the 1 GHz to 20 GHz band, it is preferable to contain the porous iron powder of the present invention as much as possible. Preferably it contains 50 volume% or more. When the content of the porous iron powder is too large, it is difficult to form the radio wave absorber, and therefore, the content is usually 95% by volume or less. Further, in order to obtain a desired radio wave absorption characteristic, other magnetic powder can be contained. According to the desired radio wave absorption characteristics, the flattened porous iron powder can be contained in the radio wave absorber. The porous iron powder of the present invention has a low processing pressure in the flattening treatment, and can easily increase the aspect ratio.

  As the method for producing the porous iron powder described above, it can be industrially carried out using a metal or a raw material alloy as a raw material. In addition to the production method of the present invention described below, a solution containing Fe ions is used as a raw material by a precipitation method. It can also carry out by the manufacturing method which oxidizes and reduces Fe salt, such as obtained hydroxide and carbonate.

The method for producing porous iron powder of the present invention includes the following steps 1 to 3.
(Step 1) 0.01 to 15 at% of one or more M elements selected from rare earth elements including Y , or one or more elements selected from rare earth elements , Al, Ti, Si, Mn, Co, An alloy (Fe-M alloy) containing as a main component iron containing M element containing M element consisting of at least one element selected from Ni, B, C, and N in a total amount of 0.01 to 15 at%. Step of preparing (Step 2) Step of immersing the Fe-M alloy in an aqueous acid solution to elute M element to obtain a solid containing Fe as a main component (Fe solid) (Step 3) Reduction to obtain porous iron powder

  In step 1, an alloy containing Fe element as a main component (Fe-M alloy) is prepared. As the M element, rare earth elements including Y, alkaline earth metals, P, C, S, Al, Ti, Si, Mn, Co, B, Cu, Ga, and the like can be used. The element M is eluted in the acid aqueous solution in step 2, but it does not elute or does not elute depending on various conditions for performing step 2. Therefore, the above element is not always the element M. You may contain elements other than M element and Fe in the objective which improves the various characteristics of the porous iron powder finally obtained, or the range which does not inhibit a characteristic. An alloy (Fe-M) containing iron containing M element as a main component by melting M element, Fe, single metal of other elements and raw material alloy prepared as raw materials so as to have a predetermined composition and then solidifying Alloy) can be obtained.

  The raw material single metal and the raw material alloy may be melted by any method such as a high frequency melting method or an arc melting method, and the solidification method may be any of a molding method, an atomizing method, and a strip casting method. In addition, it is pulverized to several mm or less in advance for the purpose of increasing the working efficiency of the immersion treatment and reduction treatment in the acid solution performed in the subsequent steps and adjusting the particle diameter of the finally obtained porous iron powder. It is effective to keep it.

  As an Fe-M alloy, a rare earth-iron-boron-based alloy, a rare-earth-iron-nitrogen-based alloy for permanent magnets, a rare-earth-iron-silicon-based alloy for magnetic refrigerating materials, or the like is used. Can do. When these are used, the rare earth element mainly corresponds to the M element. These are not limited to those produced for the porous iron powder of the present invention, but when processing into magnets, magnetic refrigeration materials, etc., scraps of alloy, etc. (hereinafter referred to as rare earth-iron) generated by cutting away, grinding and polishing unnecessary portions. Alloy scrap).

  In step 2, the Fe-M alloy is immersed in an acid aqueous solution to elute the M element to obtain a solid (Fe solid) containing Fe as a main component. Hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, or a mixed acid thereof can be used for the acid aqueous solution in which the Fe-M alloy is immersed. In order to selectively elute the M element, the Fe-M alloy can be oxidized to form Fe as an oxide or hydroxide that is hardly soluble in an acid aqueous solution. Oxidation may be performed by firing in the air in advance or by blowing air into a slurry in which an Fe-M alloy is dispersed in water or the like. Thus, by eluting M element, the solid (Fe solid) which has Fe with a large specific surface area as a main component can be obtained. Part or all of Fe in the Fe solid is in an oxide and / or hydroxide state. By appropriately controlling the conditions, 1 part of the M element may remain or 1 part of the Fe element may be eluted. Thereafter, the Fe solid is filtered off from the acid aqueous solution and can be washed if necessary. Fe solids mainly consist of Fe, 1 part remaining M element and other element oxides, hydroxide and Fe, 1 part remaining M element and other elements and compounds of anions of acids used, Contains water such as hydration water and adhesion water. For example, when a rare earth-iron-boron based permanent magnet alloy is used as the RM alloy and hydrochloric acid is used as the acid aqueous solution, the finally obtained porous iron powder can contain a rare earth oxychloride. The rare earth oxychloride has a property of not being hygroscopic and therefore has a low solubility in water, and unlike the rare earth oxide disclosed in Patent Document 1, does not exhibit the disadvantage of forming a hydroxide due to moisture absorption.

  In step 3, the Fe solid is reduced to obtain porous iron powder. The reduction is preferably performed in an atmosphere containing 3% or more of hydrogen. More preferably, a porous iron powder can be obtained by performing heat treatment for 1 minute to 100 hours at a temperature of 300 ° C. or more in a reducing atmosphere containing 5% or more of hydrogen to reduce most of the Fe solid matter. . Thereafter, if necessary, an oxide layer may be formed on the surface of the particles. As described above, when a rare earth element having a high affinity with oxygen is contained, the disproportionation reaction treatment can be performed under the condition that only the rare earth element is oxidized and other elements are not oxidized.

  Step 2 'can be included between Step 2 and Step 3 as necessary. In step 2 ', the Fe solid is heated to dry or oxidize. As described above, the Fe solid contains water such as hydration water and adhesion water. If there is too much water to be contained, the specific surface area may be reduced when reduced in Step 3, so it is preferable to set the temperature and time appropriately and heat and dry according to the properties of the Fe solid. . Also, when the Fe solid contains a hydroxide, it can be appropriately heated and oxidized by setting the temperature and time. Heating and oxidation can be performed in the atmosphere by a known method.

  When rare earth-iron alloy scrap is used as the Fe-M alloy, the M element eluted in step 2 can be recovered and reused by known precipitation fractionation methods, solvent extraction methods, etc., enabling effective use of resources. It is.

  The magnetic body of the present invention is excellent in radio wave absorption characteristics in a high frequency region of 1 to 20 GHz, particularly in a band of 10 GHz or more, and is extremely effective in reducing radio wave interference in this region. In addition, it is extremely effective for decomposing organic halogen compounds.

Next, the present invention will be described in detail by way of examples.

Example 1
The raw materials blended so as to have a composition of 11.1Nd-3.03Dy-0.56Co-6.20B-79.07Fe were melted in a high-frequency melting furnace in an argon atmosphere, and the thickness was about 0.00 by strip casting. A 5 mm alloy ribbon was obtained. Next, the alloy ribbon was pulverized to obtain an alloy powder having an average particle size of about 10 μm. 500 g of this powder was mixed with 1000 ml of pure water to obtain an alloy slurry. The slurry was stirred and 1500 ml of 5N nitric acid aqueous solution was added while bubbling 300 ml of air per minute. The temperature of the slurry was kept at 50 ° C. After allowing the reaction to proceed sufficiently, the solid matter remaining in the slurry was filtered with a Nutsche filter, and the resulting solid matter was washed by a decantation method. The solid was then heated in the atmosphere at 400 ° C. for 5 hours. It was confirmed by X-ray diffraction that it was mainly composed of iron oxide. Then, it heated at the temperature of 600 degreeC in the atmosphere of 100% of hydrogen for 4 hours. About the obtained porous iron powder, the presence or absence of iron oxide is determined by XRD, the presence or absence of an oxide in the surface layer is determined by EPMA, the specific surface area is determined by the BET method, the average particle diameter (D50) is determined by the laser diffraction method, and the nitrogen adsorption method is determined. The average pore diameter and pore volume were measured. The results are shown in Table 1. The peak of neodymium oxychloride was confirmed by XRD. As a result of analysis by ICP, the composition of the obtained porous iron powder was such that the total amount of Nd and Dy was 2.32 at%, Co was 1.06 at%, and B was 0.1 at%. Moreover, the SEM image of the obtained porous iron powder surface was shown in FIG.

  Next, the obtained porous iron powder and epoxy resin 35% by mass are mixed, formed into a disk shape, heated at 130 ° C. for 30 minutes, further cured at 180 ° C., and a sample for measuring radio wave absorption characteristics It was. This sample is formed into a donut shape having an outer diameter of 7.00 mmΦ and an inner diameter of 3.04 mmΦ with an ultrasonic processing machine, and is attached to a measurement probe, and a commercially available network analyzer is used to measure S11 (reflection coefficient) in the sample thickness direction. Frequency dependence was measured. The measurement results are shown in FIG.

(Comparative Example 1)
For a flattened atomized iron powder having a particle size of 5 μm that is generally used, the same measurement as in Example 1 was performed, and the results are shown in Table 1. Radio wave absorption characteristics were also performed in the same manner as in Example 1, and the results are shown in FIG.

  As is clear from comparison between FIG. 2 and FIG. 3, the sample of Comparative Example 1 did not show absorption characteristics exceeding −20 dB above 10 GHz. In the sample of Example 1, radio wave absorption exceeding −20 dB was observed even in a region exceeding 10 GHz, and characteristics exceeding −20 dB were observed in the vicinity of 13 GHz, and the plate thickness at that time was as small as 1.5 mm.

(Example 2)
Porous iron powder was obtained in the same manner as in Example 1 except that the alloy composition was changed to 10 at% Misch metal and the remaining Fe. As a result of analysis by ICP, the composition of the obtained porous iron powder was 1.7 at% of the total amount of misch metal and the balance was Fe. The same measurement as in Example 1 was performed and the results are shown in Table 1. Regarding the radio wave absorption characteristics, the same radio wave absorption characteristics as in Example 1 were obtained, and radio wave absorption characteristics exceeding -20 dB were obtained in the region of 1 to 20 GHz. Further, when the sample after the radio wave absorption characteristic measurement was exposed for 1 hour in an environment at a temperature of 80% and 40 ° C. and the rusting state was examined, no rust was confirmed.

(Example 3)
Porous iron powder was obtained in the same manner as in Example 2 except that the conditions were changed so that the elution of misch metal was reduced. As a result of analysis by ICP, the composition of the obtained porous iron powder was 5.5 at% in the total amount of misch metal, and the balance was Fe. Measurements similar to those of Example 1 were performed, and the results are shown in Table 1. The radio wave absorption characteristics were the same as in Example 1. As a result, a radio wave absorption characteristic exceeding −20 dB was obtained in the region of 1 to 20 GHz, but the absorption was slightly smaller than that in Example 2. Moreover, when the exposure test was done like Example 2, rust was confirmed. Thus, when there are many rare earth contents of porous iron powder, a radio wave absorption characteristic and corrosion resistance may be a little inferior.

3 is a SEM image of the surface of the porous iron powder of Example 1. It is a figure which shows the electromagnetic wave absorption characteristic of the electromagnetic wave absorber manufactured using the porous iron powder of Example 1. FIG. It is a figure which shows the electromagnetic wave absorption characteristic of the electromagnetic wave absorber manufactured using the flattened atomized iron powder of the comparative example 1.

Claims (10)

0.01 to 15 at% of one or more elements selected from rare earth elements including Y , or one or more elements selected from rare earth elements including Y, and Al, Ti, Si, Mn, Co, Ni, One or more elements selected from B, C, and N are included in a total of 0.01 to 15 at%, a specific surface area is 4 m ² / g or more, and an average particle diameter is 1 to 90 μm. Porous iron powder.   The porous iron powder according to claim 1, wherein an oxide is present in the surface layer portion.   The porous iron powder according to claim 2, containing 1 to 5 at% of one or more elements selected from rare earth elements including Y.   The porous iron powder according to any one of claims 1 to 3, wherein an average pore diameter is 100 nm or less.   The porous iron powder according to any one of claims 1 to 4, wherein a pore volume is 0.01 ml / g or more.   The electromagnetic wave absorber containing the porous iron powder in any one of Claims 1-5. The manufacturing method of the porous iron powder characterized by including the following processes 1-3.
(Step 1) 0.01 to 15 at% of one or more M elements selected from rare earth elements including Y , or one or more elements selected from rare earth elements , Al, Ti, Si, Mn, Co, An alloy (Fe-M alloy) containing as a main component iron containing M element containing M element consisting of at least one element selected from Ni, B, C, and N in a total amount of 0.01 to 15 at%. Step of preparing (Step 2) Step of immersing the Fe-M alloy in an aqueous acid solution to elute M element to obtain a solid containing Fe as a main component (Fe solid) (Step 3) Reduction to obtain porous iron powder The method for producing porous iron powder according to claim 7, comprising the following step 2 ′ between step 2 and step 3.
(Step 2 ′) A step of heating the Fe solid to dry or oxidize it   The method for producing porous iron powder according to claim 7 or 8, wherein, as step 3, heat treatment is performed in a reducing atmosphere containing 3% or more of hydrogen at a temperature of 300 ° C or more for 1 minute to 100 hours. .   The method for producing porous iron powder according to any one of claims 7 to 9, wherein rare earth-iron alloy scrap is contained as the Fe-M alloy.

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