WO2007029736A1

WO2007029736A1 - Porous iron powder, process for producing the same and radio wave absorber

Info

Publication number: WO2007029736A1
Application number: PCT/JP2006/317645
Authority: WO
Inventors: Hiroshi Ohrai; Hideo Yokoi; Akio Haruta; Kazuhiko Yamamoto; Ken-Ichi Machida; Masahiro Itoh
Original assignee: Santoku Corporation
Priority date: 2005-09-06
Filing date: 2006-09-06
Publication date: 2007-03-15
Also published as: CN102744398B; CN102744398A

Abstract

A porous iron powder that excels in the radio wave absorption performance in 1-20 GHz high-frequency region, being highly effective in reduction of radio disturbance in this region; and a process for producing the same. There is provided a porous iron powder composed mainly of iron which has a specific surface area as large as 4 m2/g or more and an average particle diameter of 2 to 90 μm and has a peak ascribed to α-Fe confirmed by X-ray diffractometry. This porous iron powder can be obtained by, for example, a method including immersing an alloy composed mainly of iron in an acid solution to thereby leach specified elements and reducing the remaining solid matter.

Description

Specification

Porous iron powder, method for producing the same, and radio wave absorber

Technical field

The present invention relates to a radio wave absorber having excellent radio wave absorption characteristics, a porous iron powder that can be used for soil improvement, a method for producing the same, and a radio wave absorber using the same.

Background art

[0002] In recent years, the development of small portable devices and the enhancement of their functions have been rapidly progressed, 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, which were limited to special applications, are now generally carried as general-purpose devices due to further downsizing and low cost, and the radiation of radio waves into the space has increased compared to conventional devices. Yes. The radio waves radiated to the outside cause malfunctions in electronic circuits, and are becoming serious problems. In order to solve this problem, various radio wave absorbers have been developed to absorb radio waves that also come from external forces and radio waves generated from electronic components in the equipment.

For example, magnetic materials such as ferrite, pure iron, sendust, and rare earth magnets are known as electromagnetic wave absorbers effective in the band of several tens of MHz to 1 GHz. In order to increase the electromagnetic wave absorption performance of the magnetic material to a higher frequency range, attempts have been made to devise the aspect ratio of the magnetic material and to add special elements. For example, pure iron, sendust, etc., which are made into fine particles by the atomizing method and then processed into a flat body using an attritor or the like, are commercially available.

[0003] Japanese Patent Application Laid-Open No. 2005-5286 discloses a method of manufacturing a rare earth-transition metal-based scrap force electromagnetic wave absorbing magnetic material generated when a rare earth magnet is manufactured or discarded. Specifically, the heat treatment in a temperature range where only the rare earth element is oxidized and the other elements are not oxidized, that is, the so-called disproportionation reaction treatment is performed, so that the transition metal magnetic particles and the rare earth oxide particles are mixed. A method for producing a magnetic powder for electromagnetic wave absorption comprising a composite is shown! The electromagnetic wave absorbing magnetic powder produced by this method has a large amount of rare earth elements, and thus has a problem related to the effective use of rare earths. That's not enough.

As a magnet with a small amount of rare earth element additive, JP-A-7-54106 discloses Nd and B Nd—Fe—B permanent magnets containing 1 to 10 at% of each are disclosed. However, this document does not describe the electromagnetic wave absorption performance and use of such a magnet material as an electromagnetic wave absorber.

Japanese Patent Application Laid-Open No. 11-354973 describes an electromagnetic wave absorber using an Fe-based flat nanocrystalline soft magnetic powder. The magnetic powder preferably has a thickness of 3 m or less and an average particle size of 20 to 50 m, a flat shape is essential, and it is important to electrically insulate the powder particles. It has been shown. In addition, it is shown that nanocrystalline soft magnetic powder can be obtained by producing amorphous alloy powder by water atomization method and generating a 10 nm microstructure by heat treatment.

In addition, it is known that carbo iron is excellent as a magnetic material for radio wave absorption with high permeability. However, the carbo iron has only a radio wave absorption characteristic up to around 1 GHz, has a spherical shape, and has a narrow particle size distribution and a small particle size. There is a drawback that it is difficult to make. Recently, ultrafine pure iron powder with an average particle size of 1 m or less was developed and reported to exhibit excellent radio wave absorption characteristics. Such powders have a reflection loss of over 35 dB in the 9 GHz frequency band, and the plate thickness at that time is as large as 3 mm.

The above-mentioned magnetic powder is blended and kneaded with an epoxy resin binder or the like at a certain ratio, formed into a sheet or board having a predetermined thickness using a metal plate or the like as a substrate, and used as a radio wave absorber. The resonance frequency at which radio waves are best absorbed depends on the thickness of the radio wave absorber, and the thickness of the radio wave absorber is adjusted according to the desired radio wave frequency. Examples of such an electromagnetic wave absorber include a bright sintered body, a bright rubber composite, a flat pure iron-containing resin, a flat sendust-containing resin, and a carbo iron rubber composite.

Incidentally, it is known that the iron powder as the magnetic powder can be used as a soil conditioner. In iron powder, Fe ions dissolve out in wet soil, react with organic halogen compounds such as tetrachloroethylene in the Fe ion force, and decompose into organic substances such as ethylene and halogens to make them harmless. be able to.

For example, Japanese Patent Application Laid-Open No. 2000-80401 proposes iron powder containing one or more of P, S, and B as iron powder for harmful substance removal treatment. The iron powder has a specific surface area of 0.01 to 1.0 m ² Zg. The particle size is preferably in the range of 1 to 1000 μm! /

In JP-A-57-4288, iron powder is added to wastewater containing phosphorus compounds, and iron ions eluted from the iron powder react with phosphate ions to drain the phosphorus compounds. It is described that it can be removed from inside.

In recent years, various materials that can be widely used for soil conditioners and radio wave absorbers have been proposed, but their performance is still not satisfactory.

Disclosure of the invention

Problems to be solved by the invention

[0005] An object of the present invention is a porous iron that has excellent radio wave absorption performance, can be used as a radio wave absorber and a soil conditioner, and is also excellent in compatibility with scabbage during production of the radio wave absorber. An object of the present invention is to provide a powder, and a magnetite powder that can be used as a raw material for the porous iron powder, and a production method that can efficiently produce these.

Another object of the present invention is to use porous iron powder that has excellent radio wave absorption performance and can be used for radio wave absorbers and soil conditioners, and is used for transmission and reception of general-purpose portable electronic devices. An object of the present invention is to provide a radio wave absorber capable of effectively absorbing radio waves in the GHz band or the like even in a thin form.

Means for solving the problem

[0006] According to the present invention, the composition is mainly composed of iron, the specific surface area is 4 m ² Zg or more, the average particle size is 2 to 90 / zm, and a peak derived from a-Fe is confirmed by X-ray diffraction. A porous iron powder is provided.

Moreover, according to this invention, the electromagnetic wave absorber containing the said porous iron powder is provided. Further, according to the present invention, the step (1A) of preparing an Fe—M-containing alloy containing iron containing any M element as a main component, and eluting the M element from the Fe—M-containing alloy, A step (1B) of immersing the Fe—M-containing alloy in an acid solution and a step (1C) of reducing the Fe-containing solid matter to obtain an Fe-containing solid matter comprising, as a main component, an X-ray Provided is a method for producing porous iron powder (hereinafter referred to as method (1)) in which a peak derived from oc Fe can be confirmed by diffraction.

[0007] Furthermore, according to the present invention, a step (2A) of preparing an Fe-M-containing alloy containing iron as a main component containing an arbitrary M element, and the M-element from the Fe-M-containing alloy are prepared. The Fe hydroxide A step (2B-1) of immersing the Fe-M-containing alloy in an acid solution to obtain a Fe hydroxide-containing solid as a main component, and a Fe hydroxide-containing solid to obtain a magnetite powder Of porous iron powder in which a peak derived from oc-Fe can be confirmed by X-ray diffraction, comprising a step of immersing an object in an alkaline solution (2B-2) and a step of reducing the magnetite powder (2C) A method (hereinafter referred to as method (2)) is provided.

Further, according to the present invention, in order to obtain a step (3A) of preparing an Fe-M-containing alloy mainly containing iron containing any M element, and an intermediate magnetite solid matter mainly containing magnetite, A step of immersing the Fe-M containing alloy in an alkaline solution (3B-1) and a step of immersing the intermediate magnetite solid in an acid solution to elute M element and obtain a magnetite powder (3B-2) And a step (3C) of reducing the magnetite powder, a method for producing a porous iron powder (hereinafter referred to as method (3)) in which a peak derived from a Fe can be confirmed by X-ray diffraction is provided. The

[0008] Furthermore, according to the present invention, use of the porous iron powder for producing a radio wave absorber is provided.

Furthermore, according to the present invention, a magnetite powder having a specific surface area of 4 m ² Zg or more and an average particle size of 2 to 90 / ζ πι is provided.

Further, according to the present invention, the above step (2 (), the step (2Β-1), the step (2Β-2), the above step (3Α), the step (3Β-1), There is provided a method for producing a magnetite powder, comprising the step (3-2).

Brief Description of Drawings

[0009] FIG. 1 is a copy of the SEM image of the surface of the porous iron powder prepared in Example 1-1.

FIG. 2 is a graph showing the radio wave absorption characteristics of a radio wave absorber manufactured using the porous iron powder prepared in Example 11 1.

FIG. 3 is a diagram showing the radio wave absorption characteristics of a radio wave absorber manufactured using the flattened atomized iron powder prepared in Comparative Example 11.

FIG. 4 is a view showing an X-ray diffraction spectrum of magnetite powder obtained by heating to 300 ° C. in Production Example 2.

[Fig. 5] X-ray diffraction spectrum of magnetite powder obtained by heating to 400 ° C in Production Example 2. FIG.

FIG. 6 is a graph showing the relationship between the specific surface area of the magnetite powder prepared in Production Example 2 and the heating temperature, and the relationship between the average particle size and the heating temperature.

BEST MODE FOR CARRYING OUT THE INVENTION

[0010] Hereinafter, the present invention will be described in more detail.

The porous iron powder of the present invention has a plurality of pores and a large specific surface area. Therefore, 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 specific surface area of the porous iron powder of the present invention is 4 m ² Zg or more, preferably 5 m ² Zg or more, more preferably 8 m ² / g or more, and the upper limit is not particularly limited, but is usually about 30 m ² / g. It is. The specific surface area is a value measured by a BET method using nitrogen gas. If the specific surface area is less than 4 m ² Zg, the eddy current increases and the desired radio wave absorption performance cannot be obtained.

[0011] The porous iron powder of the present invention has an average particle size of 2 to 90 μm, preferably 5 to 15 μm. The average particle diameter is a value of D50 measured by a laser diffraction method. If the D50 force is less than ^ / zm, it becomes difficult to mix with the resin when preparing the radio wave absorber. On the other hand, if the D50 is greater than 90 m, the filling rate of the radio wave absorber decreases and the radio wave absorber Performance decreases.

[0012] The porous iron powder of the present invention has specific characteristics such as the above-mentioned specific surface area and average particle diameter, and the composition contains iron as a main component, preferably 85 at% or more. Contains components other than Fe for the purpose of improving various properties in each application of porous iron powder and, regardless of whether or not there is a purpose, the use of porous iron powder in each application is not hindered. It can be done.

As components other than Fe, when the rare earth-iron alloy scrap described later is used as a raw material for producing the porous iron powder of the present invention, it is derived from the raw material, for example, a rare earth element including Y, B, It can contain at least one element of C, N, Co, Al, Cu, Ga, Ti, Zr, Nb, V, Cr, Mo, Mn, Ni, Si, Mg, and Ca. The content of elements other than iron is usually 15 at% or less, preferably 0.01 to 15 at%. If the content is less than 0.01 at%, the effect of inclusion is insufficient. If the content is more than 15 at%, the radio wave absorption characteristics may be deteriorated and the economy may be further deteriorated when a radio wave absorber is formed. [0013] When the porous iron powder of the present invention is used for a radio wave absorber, the iron particles in the surface layer portion may generate eddy currents, which may reduce radio wave absorption performance. In order to suppress the occurrence and make it difficult to ignite and facilitate handling, it is preferable that a part or all of the porous surface layer is oxidized and an oxide exists in the surface layer.

In the composition of the porous iron powder of the present invention, among the elements other than Fe, rare earth elements including Y, Al, Ti, Si, V, Cr, Nb, Zr, Mg or Mn have an affinity for oxygen of Fe. Therefore, the inclusion of these is preferable because an oxide layer is easily formed on the surface layer portion of the porous iron powder. In particular, the inclusion of 5 at% of a rare earth element is preferable from the viewpoint of easy formation of the oxide layer. The rare earth element preferably contains Nd, Pr, Tb, Dy. In addition, pure iron has a high magnetic permeability and is excellent as a magnetic material for electromagnetic wave absorption. By adding at least one element such as Co, Al, Si, Ni, etc., high permeability can be achieved. Therefore, the porous iron powder of the present invention preferably contains at least one of these elements.

[0014] The porous iron powder of the present invention is porous having a plurality of pores, and the average pore diameter of the porous iron powder is usually lOOnm or less, preferably from the viewpoint of further increasing the skin effect. 50 nm or less, most preferably 20 or less. The lower limit is not particularly limited, but is usually about 5 nm.

The pore volume of the porous iron powder of the present invention is usually greater than or equal to O.OlmlZg, preferably in order to allow a large amount of air to be contained inside the particles and to enable light weight when used as a radio wave absorber. It is 0.02mlZg or more. The upper limit of the pore volume is not particularly limited, but is usually about O.lOmlZg.

In the present invention, the average pore diameter and pore volume are values obtained by a nitrogen adsorption method.

In the porous iron powder of the present invention, a peak derived from ex Fe having a radio wave absorption action can be confirmed by X-ray diffraction.

[0015] The porous iron powder of the present invention can be obtained, for example, by the method (13) of the present invention, or a hydroxide or carbonate obtained by precipitation using a solution containing Fe ions as a raw material. It can also be obtained by oxidation and reduction of Fe salts such as

[0016] In the method (1) of the present invention, an Fe-M-containing alloy mainly containing iron containing any M element Including the step (1A) of preparing

The element M in the Fe—M-containing alloy must be capable of eluting into the acid solution in the process described below. Examples of the M element include at least one element of rare earth elements including Y, alkaline earth metals, P, C, S, Al, Ti, Si, Mn, Co, B, Cu, and Ga. It is done.

The Fe-M-containing alloy can contain various elements other than the above M element and Fe within the range of improving the various characteristics of the porous iron powder to be finally obtained, or without impairing the characteristics. Also good.

In Fe-M containing alloys, the content of each element is not particularly limited, but the content of Fe is usually about 50 to 99 at%, and the content of M element is usually 1 to 50 at%

[0017] The Fe-M-containing alloy is obtained by, for example, dissolving M element, Fe prepared as a raw material so as to have a predetermined composition, a single metal of other elements if necessary, and a raw material alloy, and then solidifying. It is done.

The melting can be performed by, for example, a high frequency melting method, an arc melting method, or the like. The solidification can be performed by, for example, a molding method, an atomizing method, a strip casting method, or the like.

Fe-M-containing alloys are several mm or less in advance and preferably about 0.1 mm or less in advance for the purpose of improving the work efficiency in the subsequent steps and adjusting the particle diameter of the finally obtained porous iron powder. It is effective to pulverize it.

[0018] Examples of the Fe-M-containing alloy include rare earth-iron-boron-based permanent magnet alloys, rare-earth-iron-iron-based permanent magnet alloys, rare-earth-iron-iron alloys widely used in industry. Alloys for magnetic refrigeration materials include, but are not limited to, alloy scrap generated by cutting, grinding and polishing of unnecessary parts when processing into magnets, magnetic refrigeration materials, etc. (hereinafter referred to as rare earth-iron) Alloy scrap). In these cases, the rare earth element mainly corresponds to the M element.

In the method (1) of the present invention, the Fe—M-containing alloy force prepared in the step (1A) is eluted to obtain an Fe-containing solid material containing Fe as a main component. A step (1B) of immersing the alloy containing in an acid solution. Examples of the acid solution used in step (IB) include hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, and mixed acids thereof. The concentration of the acid solution is usually 0.1 to 10 molZl, preferably 1 to 5 molZl. The amount of the acid solution used is, for example, 0.1 to 10 times the number of moles of the M element in the Fe—M containing alloy. The reaction temperature is usually 30 ° C or higher, preferably 40 ° C or higher, more preferably 60 ° C or higher. The reaction time is usually 1 to 100 hours, preferably 10 to 24 hours.

[0020] In the step (1B), an Fe-containing solid material having a large specific surface area can be obtained by selectively eluting the element M. Part or all of Fe in the Fe-containing solid is in the form of an oxide and Z or hydroxide. In addition, by appropriately controlling the above immersion conditions and the like, a part of the M element can remain and a part of the Fe element can be eluted. The Fe-containing solid can be filtered off from the acid solution and washed if necessary.

[0021] The resulting Fe-containing solid is mainly composed of Fe hydroxide and oxide, partially remaining M element and other element oxide and hydroxide, Fe, partially remaining M element and It contains compounds such as other elements and acid anions used, and water such as hydration water and adhesion water. The porous iron powder finally obtained when the Fe-M-containing alloy prepared in the step (1A) is, for example, a rare earth-iron-boron based permanent magnet alloy and hydrochloric acid is used as the acid solution. May contain rare earth oxysalts. Rare earth oxysalts have the property of lack of hygroscopicity and therefore low solubility in water. Unlike the rare earth oxides disclosed in JP-A-2005-5286, such rare earth oxysalts do not exhibit the drawback of forming hydroxides due to moisture absorption.

[0022] When the Fe-M-containing alloy is immersed in an acid solution, the element M is selectively eluted by oxidizing the immersed Fe-M-containing alloy and oxidizing Fe in an acid solution. It is preferable to use a product or a hydroxide. The oxidation is performed by, for example, a method in which an Fe—M-containing alloy is fired in the air in advance, or a method in which a Fe-M-containing alloy is dispersed in water or the like and a gas containing oxygen such as air is blown in. be able to.

[0023] The method (1) of the present invention comprises a porous iron powder, preferably a peak derived from ex-Fe, which can be confirmed by X-ray diffraction by performing the step (1C) of reducing the Fe-containing solid. The porous iron powder of the present invention is obtained.

In step (1C), the reduction can be performed, for example, in an atmosphere containing 3 vol% or more of hydrogen. Preferably, it can be carried out by heat treatment at a temperature of 300 ° C. or higher for 1 minute to 100 hours in a reducing atmosphere containing 5 vol% or more of hydrogen.

After the reduction, if necessary, an oxide layer may be formed on the surface layer of the porous iron powder. As described above, when it has a high affinity for oxygen and contains rare earth elements, etc., the disproportionation reaction treatment is performed under the conditions that only the rare earth elements are oxidized and the other elements are not oxidized. It can also be done.

[0024] The method (1) of the present invention preferably includes a step of heating to dry or oxidize the Fe-containing solid after step (1B) and before step (1C) U, . The above-mentioned Fe-containing solid contains water such as hydration water and adhesion water. Since the specific surface area may be reduced in the reduction of the step (1C) when the moisture content is too much, it is preferable to perform the heating step. The heating step can be performed by appropriately setting the temperature and time according to the properties of the Fe-containing solid material.

Also, when the Fe-containing solid contains a hydroxide, it can be heated and oxidized by setting the temperature and time appropriately. Heating and acidification can be performed in the atmosphere by a known method.

[0025] The element M eluted in step (1B) of the method (1) of the present invention can be recovered and reused by a known precipitation fractionation method, solvent extraction method, etc., and in particular, Fe-M When rare earth ferrous alloy scrap is used as the alloy, effective metals such as rare earth elements can be recovered.

[0026] The method (2) of the present invention includes a step (2A) of preparing an Fe-M-containing alloy mainly composed of iron containing any M element. The step (2A) can be performed in the same manner as the step (1A) in the method (1) described above. However, in the method (2), since it is necessary to obtain an Fe hydroxide-containing solid in the next step, it is preferable to perform the above oxidation treatment after the step (2A) and before the next step. It ’s not good.

In addition, the Fe-M-containing alloy is previously several mm or less, preferably 0.1 mm, for the purpose of increasing the working efficiency in the subsequent steps and adjusting the particle diameter of the finally obtained porous iron powder. It is effective to grind to the following extent. Prior to the pulverization step, a heat treatment step can be performed in consideration of the characteristics of the finally obtained porous iron powder. The heat treatment conditions are, for example, the power that can be implemented in the range of heating temperature 500 to 1200 ° C, heating time 1 minute to 24 hours Depending on the case, heat treatment outside this range can be performed.

[0027] In the method (2) of the present invention, the Fe—M-containing alloying force M prepared in the step (2A) is eluted to obtain an Fe hydroxide-containing solid material mainly composed of Fe hydroxide. The step (2B-1) of immersing the Fe—M-containing alloy in an acid solution is included.

Examples of the acid solution used in the step (2B-1) include hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, or a mixed acid thereof. The concentration of the acid solution is usually 0.1 to 10 molZl, preferably 1 to 5 molZ1. The amount of the acid solution used is, for example, 0.1 to 10 times the number of moles of M element in the Fe—M containing alloy. The reaction temperature is usually 30 ° C or higher, preferably 40 ° C or higher, more preferably 60 ° C or higher. The reaction time is usually 1 to 100 hours, preferably 10 to 24 hours.

[0028] The reaction by immersion in the step (2B-1) is effectively promoted by blowing a gas containing oxygen into the acid solution.

In the step (2B-1), by selectively eluting the element M, an Fe hydroxide-containing solid having a large specific surface area and containing Fe hydroxide as a main component can be obtained.

“Fe hydroxide as a main component” means that when an X-ray diffraction spectrum is measured, a diffraction peak derived from Fe hydroxide is observed as a main peak.

[0029] In the Fe hydroxide-containing solid, by appropriately controlling the above immersion conditions and the like, a part of the M element can remain and a part of the Fe element can be eluted. The Fe-containing solid can be filtered off from the acid solution and washed as necessary.

[0030] The method (2) of the present invention includes a step (2B-2) of immersing the Fe hydroxide-containing solid in an alkaline solution in order to obtain magnetite powder.

Examples of the alkali solution used in the step (2B-2) include an aqueous solution of an alkali metal salt, an aqueous ammonia solution or an aqueous ammonium salt solution.

Examples of the alkali metal salt include hydroxides or carbonates of alkali metals such as sodium, potassium, and lithium. From the viewpoint of reactivity, lithium hydroxide, potassium hydroxide, and hydroxide Hydroxide such as sodium is desirable.

Examples of the ammonium salt include ammonium carbonate, sodium carbonate, and sodium hydrogen carbonate.

[0031] Conditions for immersing in an alkaline solution to obtain magnetite powder in step (2B-2) Varies depending on the composition of the Fe hydroxide-containing solid, the shape of the Fe hydroxide-containing solid, etc.Type of alkali solution used, concentration of alkali solution, amount of alkali solution used, reaction temperature, reaction time, etc. Can be appropriately determined so that a magnetite powder can be obtained by a reaction by immersion in an alkaline solution.

The concentration of the alkaline solution is, for example, 0.1 to 10 molZl, preferably 1 to 5 molZl. The amount of the alkaline solution used is, for example, 0.1 to 10 times the number of moles of Fe element in the Fe—M-containing alloy. The reaction temperature is, for example, 30 ° C or higher, preferably 40 ° C or higher, more preferably 60 ° C or higher. The reaction time is 1 to 100 hours, preferably 10 to 24 hours.

The reaction by immersion in an alkaline solution is efficiently promoted by carrying out the reaction under pressure using a reaction vessel that can be pressurized to atmospheric pressure or higher. The reaction can also be accelerated by blowing oxygen-containing gas into the alkaline solution.

[0032] The magnetite powder obtained in the step (2B-2) is filtered off from the reaction solution, and can be washed if necessary. Magnetite powder is mainly composed of Fe oxides, some remaining M elements, other elements, oxides and hydroxides, and some remaining M elements and other elements. And water such as hydration water and adhesion water

[0033] The method (2) of the present invention includes a step (2C) of reducing the magnetite powder prepared in the step (2B-2).

The target porous iron powder can be obtained by performing the reduction in the step (2C) in the same manner as in the step (1C) in the above-described method (1) of the present invention.

[0034] In carrying out the step (2C), if necessary, a drying step of heating the magnetite powder prepared in the step (2B-2) to a temperature of 400 ° C or lower can be performed.

The drying step can be performed in an atmosphere containing oxygen or an inert gas atmosphere. When the drying temperature exceeds 400 ° C, part of the magnetite becomes hematite.

The magnetite powder used in the step (2C) may contain hematite, but hematite generates a large amount of water vapor by the reduction treatment in the step (2C), and the treatment requires extra cost. Therefore, it is better to produce less hematite. The drying temperature is preferably 400 ° C or less. [0035] The method (3) of the present invention includes a step (3A) of preparing an Fe-M-containing alloy mainly containing iron containing any M element. The step (3A) can be performed in the same manner as the step (1A) in the method (1) described above. However, in the method (3), since it is necessary to obtain an intermediate magnetite solid in the next step, it is not preferable to perform the above oxidation treatment after the step (3A) and before the next step.

In addition, the Fe-M-containing alloy is previously several mm or less, preferably 0.1 mm, for the purpose of increasing the working efficiency in the subsequent steps and adjusting the particle diameter of the finally obtained porous iron powder. It is effective to grind to the following extent. Prior to the pulverization step, a heat treatment step can be performed in consideration of the characteristics of the finally obtained porous iron powder. The heat treatment conditions are, for example, a force that can be carried out within a heating temperature range of 500 to 1200 ° C. and a heating time range of 1 minute to 24 hours.

[0036] The method (3) of the present invention includes a step of immersing the Fe-M-containing alloy prepared in step (3A) in an alkaline solution in order to obtain an intermediate magnetite solid containing magnetite as a main component. Includes (3 B— 1).

Here, having magnetite as the main component means that when an X-ray diffraction spectrum is measured, a diffraction peak derived from magnetite is observed as a main peak.

[0037] Examples of the alkali solution used in the step (3B-1) include an aqueous solution of an alkali metal salt, an aqueous ammonia solution, or an aqueous ammonium salt solution.

Examples of the ammonium salt include ammonium carbonate, sodium carbonate, sodium hydrogen carbonate and the like.

[0038] In the step (3B-1), conditions for immersing in an alkaline solution for obtaining an intermediate magnetite solid vary depending on the composition of the Fe-M-containing alloy, the shape of the Fe-M-containing alloy, etc. The type of the alkali solution, the concentration of the alkali solution, the amount of the alkali solution used, the reaction temperature, the reaction time, and the like can be appropriately determined so that an intermediate magnetite solid can be obtained by the reaction by immersion in the alkali solution. The concentration of the alkaline solution is, for example, 0.1 to 10 molZl, preferably 1 to 5 molZl. The amount of the alkaline solution used is, for example, 0.1 to 10 times the number of moles of Fe element in the Fe—M-containing alloy. The reaction temperature is, for example, 30 ° C or higher, preferably 40 ° C or higher, more preferably 60 ° C or higher. The reaction time is 1 to 100 hours, preferably 10 to 24 hours. The reaction by immersion in an alkaline solution is efficiently promoted by carrying out the reaction under pressure using a reaction vessel that can be pressurized to atmospheric pressure or higher. The reaction can also be accelerated by blowing oxygen-containing gas into the alkaline solution.

[0039] The intermediate magnetite solid obtained in the step (3B-1) is separated from the reaction solution by filtration and can be washed if necessary. In the step (3B-1), part of the M element in the Fe-M containing alloy and contained elements other than Fe may be dissolved depending on the immersion conditions in the alkaline solution.

[0040] The method (3) of the present invention comprises a step (3B—) for eluting M element and obtaining magnetite powder.

A step (3B-2) of immersing the intermediate magnetite solid material prepared in 1) in an acid solution.

Examples of the acid solution used in the step (3B-2) include hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, or a mixed acid thereof. The concentration of the acid solution is usually 0.1 to 10 molZl, preferably 1 to 5 molZ1. The amount of the acid solution used is, for example, 0.1 to 10 times the number of moles of M element in the Fe—M containing alloy. The reaction temperature is usually 30 ° C or higher, preferably 40 ° C or higher, more preferably 60 ° C or higher. The reaction time is usually 1 to 100 hours, preferably 10 to 24 hours.

[0041] The reaction by dipping in the step (3B-2) is effectively promoted by blowing a gas containing oxygen into the acid solution.

In the step (3B-2), the conditions for immersing in the acid solution for obtaining the magnetite powder vary depending on the yarn of the intermediate magnetite solid, the shape of the intermediate magnetite solid, etc. The type, acid concentration, amount of acid solution used, reaction temperature, reaction time, and the like can be appropriately determined so as to obtain a magnetite powder.

In order to selectively elute M element, it can be controlled in the pH range where only M element elutes. By selectively eluting the element M, a magnetite powder mainly composed of Fe having a large specific surface area can be obtained. By appropriately controlling the conditions, a part of the M element may remain or a part of the Fe element may be eluted. [0042] The magnetite powder obtained in the step (3B-2) is filtered off from the reaction solution, and can be washed if necessary. The obtained magnetite powder is mainly composed of Fe oxide, oxides or hydroxides of partially remaining M elements and other elements, and partially used M elements and other elements. Contains a compound with an anion, and water such as hydration water and adhesion water.

[0043] The method (3) of the present invention includes a step (3C) of reducing the magnetite powder prepared in the step (3B-2).

The target porous iron powder can be obtained by performing the reduction in the step (3C) in the same manner as in the step (1C) in the above-described method (1) of the present invention.

[0044] In carrying out the step (3C), a drying step of heating the magnetite powder prepared in the step (3B-2) to a temperature of 400 ° C or lower can be performed as necessary.

The magnetite powder used in the step (3C) may contain hematite, but hematite generates a large amount of water vapor by the reduction treatment in the step (3C), and the treatment requires extra cost. Therefore, it is better to produce less hematite. The drying temperature is preferably 400 ° C or less.

[0045] The element M eluted in the step (2B-1) in the method (2) of the present invention or the step (3B-2) in the method (3) of the present invention is a known precipitation fractionation method, solvent extraction method, etc. It is possible to effectively use effective metals such as rare earth elements by collecting and reusing at

When a rare earth-iron-boron based permanent magnet alloy is used as the Fe-M-containing alloy, the magnetite powder or porous iron powder obtained can contain a rare earth element. Such porous iron powder does not easily ignite even when it comes into contact with air, because rare earth oxides are present on the surface layer.

[0046] The magnetite powder obtained by the step (2B-2) in the method (2) of the present invention or the step (3B-2) in the method (3) of the present invention has a plurality of pores and has a large ratio. Has a surface area. Therefore, it is extremely effective for decomposing organic halogen compounds in a wet state, and is useful as a purification agent for contaminated soil and wastewater. The specific surface area of the magnetite powder is 4 m ² / g or more, preferably 5 m ² / g or more, more preferably 8 m ² / g or more. The upper limit is not particularly limited, but is usually about 50 m ² / g. is there. The specific surface area is a value measured by a BET method using nitrogen gas. If the specific surface area is less than 4 m ² Z g, the eddy current increases and the desired radio wave absorption performance may not be obtained.

[0047] The magnetite powder has an average particle size of 2 to 90 µm, preferably 5 to 15 µm. The average particle diameter is a value of D50 measured by a laser diffraction method. If it is less than D50 force ^ / z m, the finally obtained porous iron powder may be easily ignited. On the other hand, if the D50 force is greater than ^ O / zm, the filling rate of the finally obtained porous iron powder in the radio wave absorber may be reduced, and the radio wave absorption performance may be reduced.

[0048] The magnetite powder has characteristics of a shape typified by the above-mentioned specific surface area and average particle diameter, and the composition is such that the remaining components excluding oxygen are mainly composed of iron, preferably 85at. It contains more than% and can contain components other than Fe.

As components other than Fe, when rare earth-iron alloy scrap is used as a raw material, for example, rare earth elements including Y, B, C, N, Co, Al, Cu, Ga, Ti, Zr, Nb , V, Cr, Mo, Mn, Ni, Si, Mg and Ca can be contained. The content of elements other than iron is usually 15 at% or less, preferably 0.01 to 15 at%. If the content is less than 0.01 at%, the effect of inclusion is insufficient, and if the content is more than 15 at%, the radio wave absorption characteristics of the radio wave absorber may be lowered, and further, the economic efficiency may be lowered.

[0049] Among the elements of the magnetite powder, among the elements other than Fe, rare earth elements including Y, Al, Ti, Si, V, Cr, Nb, Zr, Mg, or Mn have an affinity for oxygen. Is larger than Fe, and inclusion of these is preferable because an oxide layer can be easily formed on the surface layer portion of the finally obtained porous iron powder. In particular, it is preferable to contain 1 to 5 at% of a rare earth element from the viewpoint of easy formation of the oxide layer. The rare earth element preferably contains Nd, Pr, Tb, Dy. In addition, pure iron has a high magnetic permeability and is excellent as a magnetic substance for electromagnetic wave absorption. By including at least one element such as Co, Al, Si, Ni, etc., a higher magnetic permeability can be achieved.

[0050] The radio wave absorber of the present invention contains the above-described porous iron powder of the present invention. The radio wave absorber can be produced by mixing and kneading and heating the resin and the porous iron powder of the present invention. Manufacturing conditions The conditions can be appropriately selected according to a known method.

The radio wave absorber of the present invention preferably contains as much of the porous iron powder of the present invention as possible in order to improve the absorption performance of electromagnetic waves and the like in the lGHz to 20 GHz band. Preferably, it is 50% by weight or more. If the content of porous iron powder is too high, it will be difficult to form a radio wave absorber, so it is usually 95% by weight or less. Further, in order to obtain a desired radio wave absorption characteristic, other magnetic powder can be contained.

Further, a flattened porous iron powder can be contained in the radio wave absorber in accordance with the desired radio wave absorption characteristics.

The porous iron powder of the present invention can easily increase the aspect ratio when the processing pressure in the flat wrinkle treatment is small.

[0051] The porous iron powder of the present invention, combined with the skin effect of the magnetic material itself, increases the path length of the current flowing on the surface, so that eddy current loss can be suppressed, and the adhesion to the resin is improved. Compression deformation resistance can be reduced. Therefore, for example, it has excellent 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.

In addition, the above-described magnetite powder obtained in the method (2) or method (3) of the present invention contains M element, so that it can be used as a raw material for porous iron powder having low ignitability even after reduction treatment. It is effective as a soil conditioner.

Example

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

Example 1-1

Ingredients with a composition of l l.INd—3.03Dy—0.56Co— 6.20B—79.07Fe were melted in an argon atmosphere in a high-frequency melting furnace, and an alloy thin film with a thickness of about 0.5 mm was obtained by strip casting. I got a belt. Next, the alloy ribbon was pulverized to obtain an alloy powder having an average particle size of about 10 m. 500 g of the powder was mixed with 1000 ml of pure water to obtain an alloy slurry. The slurry was stirred and 1500 ml of 5 mol Zl nitric acid solution was added while publishing 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 is filtered with a Nuts filter, and the resulting solid matter is washed by a decantation method. Purified. Next, after this solid was heated in the atmosphere at 400 ° C. for 5 hours, it was confirmed by an X-ray diffractometer (XRD) that it also mainly became acidic. Thereafter, a porous iron powder was prepared by heating at 600 ° C. for 4 hours in an atmosphere of 100% hydrogen.

About the obtained porous iron powder, the presence or absence of iron oxide by XRD and the presence or absence of acid oxide on the surface layer by EPMA (Electron Probe Micro Analyzer) are determined, the specific surface area by BET method, and the laser diffraction method. Average particle diameter (D50), average pore diameter and pore volume were measured by nitrogen adsorption method. The results are shown in Table 1.

As a result of analyzing the obtained porous iron powder by XRD, peaks of a Fe and oxysalt / neodymium were confirmed. As a result of analysis by ICPOnductively coupled plasma), the composition of the porous iron powder was 2.32 at% for the total amount of Nd and Dy, 1.06 at% for Co, 0.1 at% for B, and Fe for the rest. Fig. 1 shows a copy of the SEM image of the surface of the obtained porous iron powder.

[0053] Next, the obtained porous iron powder and epoxy resin were mixed at a weight ratio of 65:35, and then formed into a disk shape. The obtained molded product was heated at 130 ° C. for 30 minutes, and further cured at 180 ° C. to prepare a sample for measuring radio wave absorption characteristics. The sample was formed into a donut shape with an outer diameter of 7.00πιπι Φ and an inner diameter of 3.04πιπι Φ using an ultrasonic machine, and then attached to a measurement probe. Using a commercially available network analyzer, S 11 in the sample thickness direction (reflection coefficient) The frequency dependence of was measured. The result is shown in figure 2.

[0054] Comparative Example 1 1

The same measurement as in Example 1-1 was performed on a commercially available flattened atomized iron powder having a particle size of 5 μm. The results are shown in Table 1. The radio wave absorption characteristics were also prepared and measured in the same manner as in Example 1-1. The results are shown in Figure 3.

As is clear from Figs. 2 and 3, the sample of Comparative Example 1-1 was strong enough to show no absorption characteristics exceeding -20dB above 10GHz. In the sample of Example 1-1, radio wave absorption exceeding 20 dB was observed even in the region exceeding 10 GHz, and characteristics exceeding 20 dB were observed near 13 GHz, and the plate thickness at that time was as small as 1.5 mm. .

[0055] Example 1 2

Porous iron powder was obtained in the same manner as in Example 1-1 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 is The total amount of iron was l.7at%, and the balance was Fe. A peak derived from a-Fe was confirmed by X-ray diffraction. Further, the same measurements as in Example 1-1 were performed. The results are shown in Table 1.

Regarding the radio wave absorption characteristics, a sample was prepared and measured in the same manner as in Example 1-1, and radio wave absorption characteristics exceeding -20 dB were obtained in the region of 1 to 20 GHz. Furthermore, when the sample after measurement of the radio wave absorption characteristics was exposed for 1 hour in an environment of 80% humidity and 40 ° C, and the state of igniting was examined, no soot was found.

[0056] Example 1 3

Porous iron powder was obtained in the same manner as in Example 12 except that the conditions were changed so as to reduce the elution of misch metal. As a result of analysis by ICP, the composition of the obtained porous iron powder was a total amount of 1.5% by weight of the misty metal, and the balance was Fe. Peaks derived from a-Fe were confirmed by X-ray diffraction. Further, the same measurements as in Example 1-1 were performed. The results are shown in Table 1.

Regarding the radio wave absorption characteristics, a sample was prepared and measured in the same manner as in Example 1-1. The force with which a radio wave absorption characteristic exceeding 20 dB was obtained in the region of 1 to 20 GHz was slightly compared with Example 1-2. Absorption was small. Further, when an exposure test was conducted in the same manner as in Example 2, soot was confirmed. Thus, it was found that when the porous iron powder has a high rare earth content, the radio wave absorption characteristics and corrosion resistance may be slightly inferior.

[0057] [Table 1]

[0058] Production Example 1

The raw materials blended so as to have a composition of 12.9Nd-0.5Co-6.0B-80.6Fe were melted in a high-frequency melting furnace in an argon atmosphere, and an alloy ribbon having a thickness of about 0.6 mm was obtained by strip casting. The ribbon was pulverized to obtain an alloy powder having an average particle size of about 15 m. 500 g of the powder was mixed with 1000 ml of pure water to obtain an alloy slurry. Stir the slurry, add 5 molZl of nitric acid solution while blowing 300 ml of air per minute, and control the amount of air blown and the rate of charging nitric acid solution so that it does not exceed 60 ° C, and pH 5. When 5 is reached, throw the nitric acid solution. After that, the mixture was stirred while blowing air for 2 hours. The total amount of nitric acid solution was 1600 ml. The obtained solution was filtered with a Nucci filter, and the precipitate and the solution were separated. As a result of measuring the X-ray diffraction spectrum of the precipitate, it was mainly composed of ferric hydroxide.

Next, the precipitate was mixed with 1000 ml of pure water to form a slurry. Using an auto-turve as a reaction vessel, 1600 ml of a 5 molZl sodium hydroxide aqueous solution was added while stirring, and the reaction was stirred at 150 ° C. for 10 hours. The solid matter remaining in the slurry was filtered with a Nutsche filter to obtain a magnetite powder. The obtained magnetite powder was washed by a decantation method. ICP analysis of the magnetite powder revealed that the composition was 1.62Nd—0.70CO—0.84 B—96.84Fe. The magnetite was heated at 300 ° C. in the atmosphere for 5 hours. The magnetite powder after heating was measured for specific surface area by BET method and D50 by laser diffraction method. As a result, the BET value was 20.5 m ² / g and the average particle size was 17.5 m.

Production example 2

The raw material with a composition of 10.9Nd— 3.10Dy— 0.50Co— 6.10B— 79.4Fe was melted in an argon atmosphere in a high-frequency melting furnace, and an alloy ribbon with a thickness of approximately 0.4 mm was formed by strip casting. Obtained. The alloy ribbon was pulverized to obtain an alloy powder having an average particle size of about 10 m. 500 g of the powder was mixed with 1000 ml of pure water to obtain an alloy slurry. The slurry was stirred, and 2500 ml of a 2 mol Zl aqueous sodium hydroxide solution was added while blowing 300 ml of air per minute, and the temperature was raised to 60 ° C., followed by stirring for 24 hours. The obtained solution was filtered with a Nutsche filter to separate the precipitate from the solution. Next, the precipitate was mixed with 1000 ml of pure water to form a slurry. 1500 ml of 5 mol / l hydrochloric acid solution was added to the slurry. The slurry temperature was kept at 60 ° C. After sufficiently proceeding with the reaction, the solid matter remaining in the slurry was filtered with a Nutsche filter to obtain magnetite powder. The obtained magnetite powder was washed by a decantation method. ICP analysis of the magnetite powder revealed that the composition was 1.41Nd—0.45Dy-0.72Co—0.70B—96.7Fe.

Next, the magnetite powder was divided into seven equal parts and heated in air at 100, 200, 300, 400, 500, 600, and 700 ° C. for 5 hours, respectively. The magnetite powder after heating was measured for specific surface area by BET method and D50 by laser diffraction method. Figures 4 and 5 show 300 ° C and 400 ° C respectively. An X-ray diffraction spectrum of magnetite powder obtained by heating is shown. When heated below 400 ° C, the only oxide is magnetite, but when heated above 400 ° C, hematite is precipitated. In addition, from the relationship between the specific surface area and heating temperature shown in Fig. 6, the specific surface area is significantly reduced by heating at 300 ° C or higher, and at 600 ° C it is 4m ² Zg or lower. Therefore, it can be seen that heating at 600 ° C or lower is necessary to obtain a specific surface area of 4 m ² Zg or higher. From the relationship between the average particle size and the heating temperature shown in Fig. 6, the average particle size tends to be slightly smaller as the heating temperature increases.

[0060] Production Example 3

Magnetite was produced in the same manner as in Production Example 1 except that the alloy composition was 10.8 at%, the balance was Fe, and the particle size after grinding was 24.2 m. As a result of analyzing the composition by ICP, the total amount of misty metal was 1.3at% and the balance was Fe. When the specific surface area and D50 were measured in the same manner as in Production Example 1, the specific surface area was 25.5 m ² / g and the average particle size was 15.8 m. The X-ray diffraction revealed that hematite peaks could not be confirmed.

[0061] Production Example 4

Magnetite was produced in the same manner as in Production Example 3, except that the alloy composition was 8.5 at%, the remaining Fe, and the particle size after grinding was 23.8 m. As a result of analyzing the composition by ICP, the total amount of misty metal was 1.1 atomic% and the balance was Fe. When the specific surface area and D50 were measured in the same manner as in Production Example 1, the specific surface area was 24.5 m ² Zg and the average particle size was 16.8 m. The X-ray diffraction showed that hematite peaks could not be confirmed.

[0062] Production Example 5

Magnetite was produced in the same manner as in Production Example 1 except that 1600 ml of 5 mol Zl aqueous sodium hydroxide solution was changed to 4000 ml of 3 mol Zl ammonium bicarbonate aqueous solution. The composition was analyzed by ICP. As a result, it was 1.54Nd—0.65Co—1.45B—96.36Fe. When the specific surface area and D50 were measured in the same manner as in Production Example 1, the specific surface area was 19.3 m ² / g and the average particle size was 18.3 m. Hematite peaks were not confirmed by X-ray diffraction.

[0063] Production Example 6

Magnetite was produced in the same manner as in Production Example 1 except that 1600 ml of 5 molZl sodium hydroxide aqueous solution was changed to 4000 ml of 3 molZl potassium hydroxide aqueous solution. Analyzing composition by ICP As a result, it was 1.38Nd—0.70Co—0.43B—97.49Fe. When the specific surface area and D50 were measured in the same manner as in Production Example 1, the specific surface area was 15.3 m ² / g and the average particle size was 14.1 m. The X-ray diffraction showed that hematite peaks could not be confirmed.

[0064] Production Example 7

Magnetite was produced in the same manner as in Production Example 2 except that 2500 ml of 2 molZl aqueous sodium hydroxide solution was changed to 4000 ml of 3 molZl aqueous ammonium hydrogen carbonate solution. The obtained magnetite powder was heated at 300 ° C for 5 hours. The composition was analyzed by ICP and found to be 1.22Nd-0.3 IDy- 0.99Co- 2.8B- 94.68Fe. When the specific surface area and D50 were measured in the same manner as in Production Example 1, the specific surface area was 18.3 m ² / g and the average particle size was 20.1 m. The X-ray diffraction revealed that hematite peaks could not be confirmed.

[0065] Production Example 8

Magnetite was produced in the same manner as in Production Example 2, except that 2500 ml of a 2 mol Zl aqueous sodium hydroxide solution was changed to 4000 ml of a 3 mol Zl aqueous potassium hydroxide solution. The obtained magnetite powder was heated at 300 ° C for 5 hours. As a result of analyzing the composition by ICP, the composition of the obtained magnetite powder was 1.33Nd—0.50Dy—0.67Co—0.50B—97.00Fe. When the specific surface area and D50 were measured in the same manner as in Production Example 1, the specific surface area was 24.6 m ² Zg and the average particle size was 16.5 m. The X-ray diffraction showed that hematite peaks could not be confirmed.

[0066] Production Example 9

Magnetite was produced in the same manner as in Production Example 2, except that 1500 ml of 5 mol Zl hydrochloric acid solution was changed to 3000 ml of 2 mol Zl nitric acid solution. The obtained magnetite powder was heated at 300 ° C for 5 hours. As a result of analyzing the composition by ICP, it was 1.53Nd—0.50Dy—0.88Co—0.70B—96.6Fe. When the specific surface area and D50 were measured in the same manner as in Production Example 1, the specific surface area was 22.6 m ² / g and the average particle diameter was 17.2 m. Hematite peak could not be confirmed by X-ray diffraction o

[0067] Production Example 10

Magnetite was produced in the same manner as in Production Example 2 except that 2500 ml of 2 molZl sodium hydroxide aqueous solution was changed to 4000 ml of 3 molZl potassium hydroxide aqueous solution and 1500 ml of 5 molZl hydrochloric acid solution was changed to 2000 ml of nitric acid solution of ImolZl. The obtained magnetite powder is heated at 300 ° C for 5 Heated for hours. As a result of analyzing the composition by ICP, it was 1.56Nd—0.53Dy—0.69Co—0.47B—96.75Fe. When the specific surface area and D50 were measured in the same manner as in Production Example 1, the specific surface area was 24.6 m ² Zg and the average particle size was 15.4 m. Hematite peaks were also confirmed by X-ray diffraction.

[0068] Comparative Production Example 1

A commercially available magnetite powder for toner having an average particle size of 0.30 m and a specific surface area of 8.5 m ² / g was heated in a 100% hydrogen atmosphere at a temperature of 600 ° C. for 4 hours. When reduced iron powder was taken out into the atmosphere, it ignited.

[0069] Production Example 11

The same procedure as in Production Example 2 was used, except that an alloy slurry was used that was prepared by mixing 500 ml of grinding scraps with an average particle size of 10 μm generated in the process of manufacturing rare earth-iron-boron-based sintered magnets with 1000 ml. Magnetite was manufactured. As a result of analyzing the composition by ICP, it was 1.40 Nd—0.36Pr—0.65Co—0.35B—97.24Fe. When the specific surface area and D50 were measured in the same manner as in Production Example 1, the specific surface area was 18.6 m ² Zg and the average particle diameter was 7.5 m. X-ray diffraction revealed a hematite peak that could not be confirmed.

Further, after adding the hydrochloric acid solution and reacting, the filtrate obtained when the magnetite was filtered was stirred, and an acidic ammonium fluoride 200 g ZL solution was added to precipitate the rare earth fluoride. The precipitate was filtered and washed to obtain a rare earth fluoride. Further, the filtrate obtained by filtering the precipitate of the rare earth fluoride was stirred, and 5 mol Zl of aqueous sodium hydroxide solution was added to precipitate cobalt hydroxide. The precipitate was filtered and washed to obtain cobalt hydroxide.

From the above, when rare earth-iron-iron alloy scrap is used as a raw material, it is possible to recover useful metals such as rare earth elements and cobalt other than iron.

[0070] Examples 2-1 to 2-10

The magnetite powders obtained in Production Examples 1 and 3 to 11 were heated in the atmosphere of 100% hydrogen at a temperature of 600 ° C. for 4 hours in the same manner as in Example 11. The resulting porous iron powder is checked for the presence of iron oxide by XRD and the presence or absence of acid oxides on the surface by EPMA, specific surface area by BET method, D50 by laser diffraction method, and average fineness by nitrogen adsorption method. The pore diameter and pore volume were measured. The results are shown in Table 2. In addition, it was confirmed by XRD that all samples showed a diffraction pattern derived from X-Fe. The radio wave absorption characteristics were also the same as in Example 1-1. An electromagnetic wave absorption characteristic exceeding 1-20 dB was obtained in the above region.

[Table 2] Specific surface area average particle size average pore size average pore size pore volume of iron oxide surface layer

Oxide / g) (β m) (nm) (ml / g)

Example 2-1 No Yes 12.1 8.9 10.3 0.033 Example 2-2 Yes 15.3 8.0 13.4 0.032 Example 2-3 No Yes 17.5 8.7 16.5 0.047 Example 2-4 Yes 16.4 9.2 13.4 0.054 Example 2-5 Yes 9.7 7.1 14.6 0.035 Example 2—6 Yes 10.8 10.3 11.3 0.024 Example 2—7 Yes 14.4 8.3 15.2 0.027 Example 2—8 Yes 13.2 9.1 20.7 0.031 Example 2 — 9 Yes 18.3 7.9 12.2 0.056 Example 2 — 10 No Yes 11.5 4.7 15.5 0.042

Claims

The scope of the claims

[I] A porous iron powder whose composition is mainly composed of iron, has a specific surface area of 4 m ² Zg or more, an average particle diameter of 2 to 90 μm, and a peak derived from ex Fe can be confirmed by X-ray diffraction.

[2] The porous iron powder according to claim 1, wherein at least a part of the surface layer portion is oxidized.

[3] The porous iron powder according to claim 1, wherein the composition contains 0.01 to 15 at% of at least one element selected from the group consisting of rare earth elements including Y, Al, Ti, Si, Mn, Co, Ni, B, C and N.

[4] The porous iron powder according to claim 1, wherein the composition contains 1 to 5 at% of at least one element of rare earth elements including Y.

5. The porous iron powder according to claim 1, wherein the average pore diameter of the pores is lOOnm or less.

6. The porous iron powder according to claim 1, wherein the pore volume is O.OlmlZg or more.

[7] A radio wave absorber comprising the porous iron powder according to claim 1.

[8] Step (1A) of preparing an Fe—M containing alloy containing iron as a main component containing any M element, and eluting M element from the Fe—M containing alloy, and containing Fe containing Fe as a main component A step (1B) of immersing the Fe-M-containing alloy in an acid solution to obtain a solid;

Reducing the Fe-containing solid (1C),

A method for producing porous iron powder in which a peak derived from ex-Fe can be confirmed by X-ray diffraction.

[9] The production method according to claim 8, comprising a step of heating the Fe-containing solid material for drying or oxidation after the step (1B) and before the step (1C).

[10] A step (2A) of preparing an Fe—M-containing alloy containing iron containing any M element as a main component, and eluting M element from the Fe—M-containing alloy; In order to obtain an Fe hydroxide-containing solid, a step (2B-1) of immersing the Fe-M-containing alloy in an acid solution; and to obtain a magnetite powder, the Fe hydroxide-containing solid A step of immersing in an alkaline solution (2B-2);

Reducing the magnetite powder (2C),

[II] A step (3A) of preparing an Fe-M-containing alloy mainly containing iron containing any M element A step of immersing the Fe-M-containing alloy in an alkaline solution (3B-1) to obtain an intermediate magnetite solid containing magnetite as a main component;

A step (3B-2) of immersing the intermediate magnetite solid in an acid solution to elute element M and obtain magnetite powder;

Reducing the magnetite powder (3C),

[12] The method according to claim 8, 10, or 11, wherein the element is at least one rare earth element including elemental force Y.

[13] The reduction in step (1C), step (2C) and step (3C) is performed in a reducing atmosphere containing 3% by volume or more of hydrogen at a temperature of 300 ° C or higher for 1 minute to 100 hours. The method according to claim 8, 10 or 11.

[14] The method according to claim 8, 10 or 11, wherein the Fe—M-containing alloy contains rare earth-iron alloy scrap.