JP2007247036A - Iron-based nanofine wire and its production method, iron-based carbon-compounded fine wire and its production method, and wave absorber using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an iron-based nanofine wire which can easily be produced, is high in aspect ratio, is excellent in wave absorbing characteristics, and has a surface shape advantageous even for the securance of reactivity when surface coating is performed. <P>SOLUTION: The iron-based nanofine wire has a wire diameter of 50 to 300 nm, and also has a fine wire shape where iron-based granular crystals stand in a line or a shape where the fine wire parts standing in a line are connected so as to be a dendritic shape in such a manner that its wire aspect ratio is controlled to ≥20. Further, the shape of the surface part constituting the outer circumferential face of the wire in each iron-based metal granular crystal in the longitudinal direction of the wire is the rosary-like one so as to be a projecting curved face where the minimum value of the cross-sectional area of the wire is formed at the position of the connection face with the adjoining grain, and also, the maximum value of the cross-sectional area of the wire is formed at the middle position of the connection face on both the sides. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an iron-based nanowire and a manufacturing method thereof, an iron-based carbon composite wire and a manufacturing method thereof, and a radio wave absorber using the same.

JP 11-354773 A JP 2002-93607 A JP 2001-342014 A JP 2004-269987 A

A magnetic loss type wave absorber represented by ferrite has good wave absorption characteristics in the region of several GHz to several tens GHz, but its electrical length [d × (εμ) ^0.5 : D is the sample physical length], and the absorber must be thick. Since metal magnetic materials such as iron have a large saturation magnetization, it is possible to increase the magnetic permeability compared to an oxide magnetic material. However, a dielectric binder is required for the production of the absorber, and a large permeability is required. When the filling rate of the magnetic particles is increased in order to obtain magnetic permeability, a large electric capacity is generated between the magnetic particles. Therefore, even in a commercially available magnetic sheet having a high magnetic permeability, a slight magnetic permeability (1 GHz) Thus, the dielectric material (μ ′ = ˜8) is obtained (ε ′> 40). As a result, as can be understood from the following equation, the impedance decreases due to the increase of the dielectric constant, and an effective radio wave absorption characteristic cannot be obtained.

  In radio wave absorption by metallic magnetic materials, when the filling rate of metallic magnetic powder to the binder is increased, the eddy current induced by the electric field component of the radio wave causes a reduction in magnetization due to the good conductivity of the metal, resulting in a complex ratio. The value of the real part of the magnetic permeability decreases and good radio wave absorption cannot be obtained. In order to suppress this, it is necessary to reduce the metal particle size (to increase the resistance by reducing the cross-sectional area of the particle) and to electrically insulate the metal particles. Further, from the phenomenon that radio waves enter only the surface layer of the metal surface (skin effect), the electrical resistance can be increased by lengthening the propagation path of the radio waves by making the particle surface uneven. Patent Document 1 shows a radio wave absorber using an Fe-based flat nanocrystalline soft magnetic powder, and the magnetic powder has a thickness of 3 μm or less and an average dragon diameter of 20 to 50 μm. In addition, it has been shown that a flat shape is essential and that it is important to insulate between powder particles, but there is no mention that the eddy current loss can be reduced by lengthening the propagation path .

  A material combining a magnetic material and a dielectric material having a form similar to that of the present invention is also reported in Patent Document 2. It has been shown that magnetic multilayer fine particles having a high complex permeability and a high complex permittivity can be obtained by coating a ferrite having a high magnetic permeability on a particle having ferroelectricity as a central core. Further, it has been stated that the dielectric constant is preferably 100 or more and more preferably 500 or more in order to obtain the effect of a high dielectric constant, but here it can be easily inferred from the above-described formula (1). In addition, when a material having such a large dielectric constant is used, it is difficult to obtain good radio wave absorption characteristics. In fact, for this high dielectric / magnetic composite, measured values of magnetic permeability are described in the examples, but the results of the absorption characteristics are not introduced.

  In addition, Patent Document 3 and Patent Document 4 report a material in which an iron fine wire similar to the present invention is coated with carbon nanotubes. However, the former invention uses a highly linear iron needle as a catalyst and template. The carbon nanotubes are excellent in linearity by heating them at 510-550 ° C. to precipitate carbon on the outer periphery, and then removing the iron-based components by acid dissolution. It is about the technique to do. However, the particle surface of the iron wire / carbon nanotube composite serving as the precursor of the carbon nanotube is flat, which is greatly different from the composite fine wire of the present invention having a complicated surface structure coated with granular particles. In the latter invention, carbon nanotubes are synthesized by heating a substrate in an organic liquid in which an organometallic complex is dissolved, and at the same time, metal nanowires are synthesized by depositing metal of the organometallic complex inside the carbon nanotubes. However, it has a flat surface similar to the former complex on the surface of this complex, its particle surface structure is different, and its synthesis temperature is as high as 800 ° C. or higher.

  As described above, in order to improve the radio wave absorption characteristics (high reflection loss and thinning) in the absorber in which the metal magnetic powder is fixed with resin, it is necessary to increase the magnetic permeability. Since it is performed by increasing the rate, the electrical insulation between the magnetic particles is deteriorated, and eddy current loss occurs, which causes a problem in radio wave absorption in the high frequency range (> 10 GHz). Further, since the capacitance between the magnetic particles is reduced and the dielectric constant becomes very large (ε ′> 40), the absorption characteristics are not generally good.

  The present invention is an iron-based nanowire having a surface form that is easy to manufacture, has a high aspect ratio, is excellent in radio wave absorption characteristics, and is advantageous for ensuring reactivity when performing surface coating, and a method for manufacturing the same, and further An object of the present invention is to provide an iron-based carbon composite thin wire whose surface insulation is enhanced by coating the surface of the nanowire with an aggregate of carbon-based fine particles, a method for producing the same, and a radio wave absorber using them.

Means for Solving the Problems and Effects of the Invention

  In order to solve the above problems, the iron-based nanowire of the present invention has a wire shape in which iron-based granular crystals are arranged in a row so that the wire diameter is 50 nm or more and 300 nm or less and the line aspect ratio is 20 or more. Alternatively, the thin wire portions connected in a row form a dendritic shape, and the shape of the surface portion constituting the wire outer peripheral surface of each iron-based metal granular crystal in the wire longitudinal direction is a connection surface with adjacent particles. A minimum value of the line cross-sectional area is formed at the position, and a bead shape is formed that becomes a convex curved surface having a maximum value of the line cross-sectional area at the midpoint of the connecting surfaces on both sides.

  In the magnetic metal electromagnetic wave absorber, the specific surface area is increased by reducing the particle size of the magnetic material, and the magnetic material volume that can generate magnetic permeability even with a very thin skin depth (skin effect) in the GHz band, for example. It is possible to absorb radio waves due to magnetic loss. Usually, the particle size is about 1 μm even if it is small, and when it is a spherical particle or smaller, a large magnetic permeability cannot be obtained due to the influence of the demagnetizing field. On the other hand, in the present invention, even if the wire diameter is as thin as 50 nm or more and 300 nm or less, the effect of the demagnetizing field can be almost ignored by having a very high aspect ratio (> 20). It becomes possible. Moreover, since the specific surface area is increased as compared with a thin wire with a flat surface by being a structure in which the above-described bead-like thin wire form or a structure in which this is connected in a dendritic shape, it is possible to supplement more electromagnetic fields. In addition, since the propagation path of electromagnetic waves becomes longer, eddy current loss that causes a decrease in magnetization can be suppressed, and excellent characteristics are exhibited when used in a radio wave absorber. This effect is particularly prominent when the dendritic bond form is obtained.

  Further, in order to make the above effect more remarkable, it is desirable that the line length is 1 μm or more and 10 μm or less. In the case of a dendritic joined body, the length of each thin line portion connecting the joining points is defined as a line length. The wire diameter is represented by an average value in the wire length direction of the thin wire portion.

  In addition, the method for producing the iron-based nanowire of the present invention is a method for producing the iron-based nanowire of the present invention, in which a volatile iron carbonyl is converted into a carrier gas comprising an inert gas in a heated state of room temperature to 150 ° C. And a step of thermally decomposing the volatile iron carbonyl by supplying it to the reaction section maintained at 250 ° C. or more and 400 ° C. or less at a concentration of 150 ppm or more and 450 ppm or less.

For example, Fe (CO) ₅ can be used as the volatile iron carbonyl. The inert gas may be nitrogen gas or a rare gas (for example, argon).

  In order to obtain the iron-based nanowire of the present invention having a high aspect ratio as described above, as a result of screening of various reaction conditions by the present inventors, volatile iron carbonyl (carbonyl iron complex) in an inert gas is obtained. It was found that the concentration of is preferably 150 ppm or more and 450 ppm or less. When the concentration is less than the lower limit, the concentration of the complex gas is too low so that the growth base of the iron-based nanowire (for example, the wall of the reaction vessel (for example, reaction tube) or the substrate disposed in the reaction vessel) No deposition occurs. On the other hand, when the density exceeds the upper limit, only a line having an excessive wire diameter or a small aspect ratio can be obtained.

  On the other hand, when the reaction temperature exceeds 400 ° C., it becomes impossible to obtain an iron carbonyl decomposition active site for producing fine flaky iron that becomes a growth nucleus of the iron-based granular crystal constituting the fine wire. The yield of iron-based nanowires is extremely low and the production efficiency is poor. On the other hand, when the reaction temperature is less than 250 ° C., the iron carbonyl complex is hardly decomposed, resulting in a similar yield reduction.

  Further, when the warmed state of volatile iron carbonyl is less than room temperature (20 ° C.), it remains in a liquid state, and when it exceeds 150 ° C., it decomposes into iron and carbon monoxide.

Depending on the set values of the reaction temperature and the concentration of iron carbonyl, the iron-based granular crystal can be an iron-based metal granular crystal containing various types of metallic iron as a main component (50% by mass or more: the balance is, for example, iron carbide), It is also possible to use iron carbide-based granular crystals (50% by mass or more: the balance is, for example, metallic iron) containing iron carbide (for example, Fe ₃ C) as a main component. In addition, the iron-based metal granular crystal may have a composition substantially close to that of pure iron (for example, metallic iron is 95% by mass or more). Further, all of the iron carbide-based granular crystals can be iron carbide. In particular, by making the structure in which iron carbide is precipitated in an iron matrix, an effect of improving radio wave absorption characteristics due to a distortion effect can be expected.

  Next, in the iron-based carbon composite fine wire of the present invention, the surface of the iron-based nanowire (core) of the present invention is covered with an aggregate layer of carbon-based fine particles having a thickness of 50 nm or more and 500 nm or less, and the wire diameter is 100 nm or more. It is characterized by being 2 μm or less. The surface of the iron-based nanowires is coated with aggregates of carbon-based fine particles, which improves the electrical insulation between the iron-based nanowire cores, which are magnetic materials, due to the carbon-based fine particles, which are non-good conductors, and eddy current loss. Is further reduced. As a result, compared with a single iron-based nanowire, radio wave absorption at a lower frequency is possible with the same absorber thickness. If the thickness of the carbon-based fine particle aggregate layer is less than 50 nm, an effective insulating effect cannot be obtained. If the thickness of the carbon-based fine particle aggregate layer exceeds 500 nm, the amount of carbon that is a non-magnetic material increases per volume. Leads to a decrease in the magnetic permeability. Further, if the wire diameter is less than 200 nm, the thickness of the carbon coating layer is insufficient and is susceptible to oxidation.

  The present invention also provides a method for producing the iron-based carbon composite fine wire. The first is that the volatile carbonaceous compound is supplied alone or together with a carrier gas composed of an inert gas (nitrogen or a rare gas) to the reaction section held at 300 ° C. or more and 500 ° C. or less to supply the volatile carbon compound. A carbon component generated on the surface of or inside the iron-based nanowire by depositing a carbon component generated by the thermal decomposition on the surface of the iron-based nanowire of the present invention. And

  The second is that the volatile carbonaceous compound is volatilized while being supplied alone or together with a carrier gas composed of an inert gas (nitrogen or a rare gas) to a reaction section maintained at 100 ° C. or higher and 300 ° C. or lower. A carbon component is plasma-decomposed, and a carbon component generated by the plasma decomposition is deposited on the surface of the iron-based nanowire of the present invention, thereby imparting a carbon component to the surface or inside of the iron-based nanowire. It is characterized by.

  Volatile carbonaceous compounds include volatile oxygenates such as methanol, ethanol, propanol, butanol, dimethyl ether, diethyl ether, and acetone, and saturated or unsaturated such as methane, ethane, propane, butane, ethylene, propylene, and acetylene. One kind or two or more kinds of hydrocarbons can be used.

  Since the surface of the iron-based nanowire of the present invention has a bead-like shape rich in undulations as described above, it is rich in reaction activity, and as described above, the agglomeration of carbon-based fine particles by thermal decomposition or plasma decomposition of volatile carbonaceous compounds. Aggregates can be efficiently deposited. In the case of thermal decomposition, if the reaction temperature is less than 300 ° C., the decomposition of the volatile carbonaceous compound is not easy, and if it exceeds 500 ° C., remarkable aggregation of the iron nanowires is observed. In the case of plasma decomposition, the temperature is not particularly set. However, when the reaction temperature is less than 100 ° C., atomic interdiffusion at the interface between the iron nanowire and the carbon hardly occurs, and the adhesion is deteriorated. In order to suppress aggregation of nanowires, it is desirable that the temperature is 300 ° C. or lower.

  The radio wave absorber of the present invention is characterized in that the iron-based nanowires or the iron-based carbon composite wires of the present invention are bonded with a resin binder. By using the iron-based nanowire or the iron-based carbon composite wire of the present invention, a radio wave absorber having excellent radio wave absorption characteristics can be realized. Moreover, since it is the form which couple | bonded with the resin binder, shaping | molding into a board, a sheet | seat, a tape, or a code | cord | cover code | cord | cover is easy.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows a cross-sectional view of an electromagnetic wave absorber according to the present invention. As shown in FIG. 1, when electromagnetic waves are incident on the absorber perpendicularly, the normalized input impedance Z for expecting a metal plate from the surface of the absorber is expressed by the following equation (1). Using this Z, the reflection loss R is (2 ) And (3). Thus, although the reflection loss is determined by Z, as is apparent from the equation (1), Z is a function of ε, μ, wavelength λ of electromagnetic wave, and specimen thickness d, and is a region satisfying −20 dB. The calculation method is complicated. Therefore, the frequency characteristics of ε and μ are measured by the S-parameter method using a network analyzer, and the reflection loss when the thickness of the specimen is changed is calculated from the measurement results using equations (1) to (3). The electromagnetic wave absorber can be designed and manufactured based on this value.

  That is, a resin binder such as an epoxy resin is kneaded with the electromagnetic wave absorbing magnetic powder described above, and a metal plate is used as a substrate to form a sheet or board having a predetermined thickness, which is used as an electromagnetic wave absorber. In this case, the resonance frequency at which electromagnetic waves are best absorbed depends on the thickness of the electromagnetic wave absorber, and the thickness can be adjusted to correspond to the frequency of the desired electromagnetic wave. Further, in addition to the form shown in FIG. 1, it is also possible to form an electromagnetic wave absorber in the form of a thin sheet or tape.

  Hereinafter, the results of experiments conducted to confirm the effects of the present invention will be described. The production of nanowires related to this case is not limited to the following.

Example 1
The fine metal wire was synthesized using the reaction line shown in FIG. A Pyrex glass tube (reaction tube a) having an inner diameter of 8 mm, a length of 50 mm, a central portion of an inner diameter of 15 mm, and a length of 300 mm is used as the reaction tube. And filled with quartz wool near the outlet of the reaction tube. Iron carbonyl was introduced into the reaction tube heating section together with argon gas by filling the bubbler shown in FIG.

  As a result of carrying out the reaction at a heating section temperature of 300 ° C. and an argon gas flow rate of 150 mL / min, iron flakes adhere to the inner wall of the reaction tube at the inlet A of the reaction tube shown in FIG. 1, and the reaction tube is packed thereon. Thus, iron micro fine wires (diameter 1 to 50 μm) were produced. Further, at the exit B, iron-based nanowires (diameter: 100 to 200 nm) were generated.

  The results of morphological observations of iron microwires and iron-based nanowires using a scanning electron microscope are shown in FIGS. 3 and 4, respectively. From FIG. 2, the shape of the iron microwire is a series of iron fine particles in a rosary shape, the particle diameter is 1-50 μm, which is larger than the iron-based nanowire, and each one is branched rather than linear, and they are entangled It was confirmed to have a structure. On the other hand, from FIG. 3, it was confirmed that the iron-based nanowire is similar in shape to the iron microwire, but the wire diameter is 100 to 200 nm and the total length is several tens to several hundreds μm. .

  FIG. 5 shows a powder X-ray diffraction pattern of the iron-based nanowire obtained. These peaks were all attributed to the α-Fe phase, and it was found from the intensity ratio of the respective diffraction peaks that there was no anisotropy in crystal growth. This result coincides with the result of FIG. 4, and although the appearance of the nanowire has a form with a high aspect ratio, the fine structure reflects a structure in which spherical particles are connected. Moreover, as a result of performing powder X-ray diffraction similarly about an iron micro fine wire and an iron thin piece, it confirmed that the alpha-Fe phase was obtained similarly.

The effects of the amount of iron carbonyl charged to the bubbler, the argon gas flow rate, the reaction temperature, and the inner diameter of the reaction tube on the yield of the iron-based nanowires were investigated. Here, the yield of the iron-based nanowires was determined by the following calculation. The used iron carbonyl has a molecular weight of 195.9, a purity of 95%, and a density of 1.5 g / mL, and the weight of iron metal (atomic weight 55.8) contained in the iron carbonyl XmL is represented by the following formula.
1.5 × X × 0.95 × (55.8 / 195.9) = 0.41 × X (g) (4)
Taking this calculated value as 100%, the yield was determined from the weight of the obtained iron-based nanowires. When the amount of iron carbonyl charged is 2 mL, the reaction temperature is 300 ° C., and the reaction tube a is used, the iron-based nanometer when the argon gas flow rate is changed to 100, 120, 150, 160, 170, 180, and 200 mL / min. The yield of thin wires is shown in FIG. In addition, iron was used when the reaction was carried out at 200, 250, 270, 280, 300, 320, and 350 ° C. using a reaction tube a with an iron carbonyl charge of 2 mL and an argon gas flow rate of 180 mL / min. The yield of the system nanowire is shown in FIG. In the case of using 2 liters of iron carbonyl and the reaction tube a, the optimum reaction conditions with the highest yield of iron-based nanowires are an argon gas flow rate of 180 mL / min and a reaction temperature of 300 ° C. The yield at this time is About 35%. It was found that even when the amount of iron carbonyl charged was changed, the amount of iron-based nanowires did not change so much, and iron-based nanowires were formed only in the initial stage of the reaction. In addition, a decrease in yield was observed in the reaction tube b (Table 1).

  About 30 wt% epoxy resin was added to the produced iron-based nanowires, iron microwires, and iron flakes and mixed uniformly using an agate mortar, followed by using a die for an outer diameter of 10 mm, a thickness of 1 to Molded into a 2 mm disk. This was heated and cured at 120 ° C. for 40 minutes, and cut into a donut shape having an outer diameter of 7 mm and an inner diameter of 3 mm using an ultrasonic cutter. The produced resin molding was placed in a 7 mm coaxial waveguide, and each material constant was measured by an S parameter method using a network analyzer. The results of relative permittivity (real part: ε ′, imaginary part: ε ″) and relative permeability (real part: μ ′, imaginary part; μ ″) are shown in FIG. 8, and the radio wave absorption characteristics calculated therefrom are shown. 9 shows. For comparison, FIG. 10 shows the radio wave absorption characteristics of a sample prepared in the same manner from commercially available carbonyl iron fine particles (Wako Pure Chemical Industries, particle size 6 μm).

  Compared with iron-based nanowires, the electromagnetic wave absorption characteristics of iron microwires and iron flakes are low. This is because the particle diameter of iron microwires and iron flakes is large, as can be seen from the frequency dependence of the imaginary part of relative permeability. Therefore, it corresponds to the fact that the value of the real part of the relative permeability is rapidly decreased as the frequency is increased due to the eddy current loss. In the iron-based nanowire, in the absorber having a thickness of 4.0 to 1.3 mm, a favorable reflection loss of −20 dB or less was observed in the region of 5 to 17 GHz. Nanowires have very fine particle size, so the electrical resistance value of the particles themselves increases, eddy current loss is suppressed, and good electromagnetic wave absorption characteristics are obtained by low loss in the high frequency range. . For comparison, a radio wave absorber made from commercially available iron carbonyl iron powder shows a reflection loss of -20 dB or less around 2 to 4 GHz in a sample having a thickness of 4.0 to 2.0 mm, and an iron-based material in a sample having the same thickness. In the radio wave absorber produced from the nanowire, the absorption region shifted to the high frequency side. This is because the resonance frequency shifts to the high frequency side from the magnetic anisotropy associated with the shape of the iron-based nanowire.

(Example 2)
From the iron-based nanowires produced in Example 1, iron carbide / carbon composite fine wires were produced by the following method. Here again, the reaction line having the structure shown in FIG. 2 was used. Similarly, a reaction tube of type a is used, and after production of the iron-based nanowire, the iron-based nanowire collected in the site B is made to react with the site A of the reaction site via the glass wall surface using the attractive force of the magnet. Moved to. Since iron-based nanowires are easily oxidized, it is desirable to carry out such a series of processes. After completion of the reaction, 3.0 mL of ethanol was injected into a bubbler that had been emptied due to vaporization of iron carbonyl. Alcohols other than ethanol, alcohols such as isopropyl alcohol and butanol, and linear or cyclic hydrocarbons such as hexane, cyclohexane, ethylene and acetylene may be used as the carbon source. However, since the toxicity and the gas concentration of the carbon-containing vapor component introduced into the reaction heating part are important for obtaining fine granular particles, the best results are obtained by using ethanol under these reaction conditions. Obtained. The ethanol in the bubbler was bubbled with argon gas (flow rate 60 mL / min), vaporized and introduced into the reaction tube, and the reaction tube was heated from 300 ° C. to 500 ° C. in an electric furnace over 1 hour, thereby iron-based nanowires. And reacted. In the reaction at 300 ° C. or lower, no ethanol decomposition reaction was observed, and at 500 ° C. or higher, the aggregation of the obtained composite fine wire particles was confirmed by observation with a scanning electron microscope.

  FIG. 11 shows a surface observation image of the obtained iron carbide / carbon composite fine wire particles by a scanning electron microscope. It was confirmed that the synthesized iron carbide / carbon composite fine wire particles had a linear form with a diameter of 1 to 2 μm. The wire diameter is thicker than the starting iron nanowire (wire diameter: 100-200 nm), but the surface of the starting iron nanowire is flat, but the surface is granular. A fine structure was obtained because it was covered with an object. As a result of measuring the weight of the sample before and after the reaction, an increase in weight was observed after the reaction, and as a result of dissolving and removing the metal component with hydrochloric acid, a black powder was obtained (the powder X-ray diffraction of the black powder). Confirm that the result is amorphous). Furthermore, from observation with an electron microscope of the obtained black powder, both the particle form and size are similar to the granular product on the surface shown in FIG. 11, and the radio wave absorber produced from the black powder is The behavior was similar to that of the carbon ohmic loss wave absorber we fabricated. FIG. 12 shows the characteristics of a radio wave absorber manufactured from the residual black powder, and FIG. 13 shows that of a radio wave absorber manufactured from commercially available carbon.

Furthermore, as a result of the powder X-ray diffraction measurement of the above sample (FIG. 14), all the observed peaks are attributed to Fe ₃ C, and as described above, since the carbon component is amorphous, peaks derived from it are observed. There wasn't. From the above, the composite thin wire obtained by the reaction of the iron-based nanowire and ethanol was identified as an iron carbide / amorphous carbon composite thin wire. Here, the aforementioned iron-based nanowires are very susceptible to oxidation, and were ignited by exposure to air. However, the above iron carbide / carbon composite wires have improved oxidation resistance due to surface coating with carbon, and air There was no ignition inside.

  On the other hand, as a result of conducting the reaction under the same conditions using the above-mentioned commercially available carbonyl iron powder, no increase in weight was observed before and after the reaction, and the iron-based nanowire prepared in the present invention has high catalytic activity (ethanol cracking). It has been shown that it can react with ethanol even at low temperatures, resulting in an iron carbide / carbon composite wire having a very complicated surface structure as seen in an electron microscope.

  About 30 wt% of an epoxy resin was added to the obtained iron carbide / carbon composite fine wire, and a radio wave absorber was prepared in the same manner as the iron-based nanowire, and the radio wave absorption characteristics were evaluated. FIG. 15 shows the measurement results of the relative permittivity and the relative permeability, and FIG. 16 shows the radio wave absorption characteristics calculated therefrom.

  The magnetic permeability characteristics of the iron carbide / carbon composite fine wire resin molded body obtained by the present invention are as follows. The iron carbide / carbon composite (JR Liu, M. Itoh, T. Horikawa, E. Taguchi, H. Mori, K. Machida, Appl. Phys. A, Vol. 82, 2006, p. 509-513.). Like the surface structure seen with a scanning electron microscope, some of the granular particles produced on the surface of the composite fine wire by reaction with ethanol are iron carbide, and the propagation surface of electromagnetic waves is increased by increasing the specific surface area. It was found that the eddy current loss was suppressed by the increase in electrical resistance due to the increase in length.

  The electromagnetic wave absorber produced from the iron carbide / carbon composite fine wire was an absorber having a thickness of 6.0 to 1.0 mm, and a good reflection loss of −20 dB or less was obtained in the region of 3 to 16 GHz. In the iron-based nanowires described above, eddy current loss was suppressed by reducing the particle size, and good electromagnetic wave absorption characteristics were obtained even in the high frequency range. In addition, iron carbide with high electrical resistance was generated, and because the surface has a complicated shape, considering the skin effect, the propagation length of electromagnetic waves in the particles increased, and it was covered with carbon, which is a non-good conductor It can be seen that the eddy current loss is further reduced. In addition, due to the addition of dielectric properties derived from carbon in the composite wire, the electrical length is increased, so that the iron carbide / carbon composite wire has a lower thickness at the same absorber thickness than the iron-based nanowire. Absorption at frequency is possible (synonymous with thinning of wave absorber). Also, in the frequency range where absorption of -20 dB or less was obtained, the band that can be absorbed by changing the thickness of the sample to 3 to 16 GHz with respect to 5 to 17 GHz seen in the iron-based nanowires is on the low frequency side. Spread. Moreover, since the corresponding | compatible band of the electromagnetic wave absorber produced from commercially available carbonyl iron powder (general-purpose magnetic powder for electromagnetic wave absorption) is about 2-4 GHz, it is produced from the iron carbide / carbon composite thin wire by this invention. The electromagnetic wave absorber is characterized by its very wide absorption response range.

  At the carbonization temperature (300 to 500 ° C.) using ethanol described above, the formation of a carbon film progressed on the surface of the iron-based nanowire, and the iron-based nanowire itself shifted to iron carbide. On the other hand, by generating plasma using an induction coil from the outside, it is possible to synthesize iron / carbon composite nanowires (diameter 500 nm or less) in which iron-based nanowires are only covered with carbon.

  In general, when a radio wave absorbing sheet is produced, it is necessary to increase the magnetic material / resin mixing ratio in order to improve the absorption characteristics. The iron / carbon nanowires obtained above have a lower electrical conductivity (high contact resistance) than the iron nanowires alone, so it is possible to introduce the magnetic substance more densely into the resin. It is possible to produce an absorber sheet that is thinner and can absorb even lower frequencies.

  As described above, the nanowire produced by the present invention exhibits high catalytic activity, and it becomes possible to easily obtain an iron carbide / carbon composite fine wire by reaction with ethanol. The surface structure of the iron carbide / carbon composite fine wire is very fine, which can effectively suppress eddy current loss. Furthermore, this composite fine wire is composed of a magnetic material (magnetic field component) and a dielectric material (electric field component). Therefore, compared to the case of the above-mentioned iron-based nanowire alone, the radio wave absorber produced from this can broaden the absorption range to a low frequency. Furthermore, the width of the absorption region can be greatly increased as compared with the conventional magnetic powder for electromagnetic wave absorber (carbonyl iron powder).

1 is a basic structure of an electromagnetic wave absorber according to the present invention. It is the figure which showed the outline of the reaction line. It is a scanning electron microscope observation image of an iron micro fine wire. It is a scanning electron microscope image of an iron-based nanowire. It is an X-ray diffraction pattern of an iron-based nanowire. It is the figure which showed the yield of the iron-type nano fine wire at the time of changing argon gas flow rate. It is the figure which showed the yield of the iron-type nanowire at the time of changing reaction temperature. It is the figure which showed the frequency dependence of the dielectric constant and the relative magnetic permeability of the absorber produced from the iron-type nanowire, the iron microwire, and the iron thin piece. It is the reflection loss characteristic of the absorber produced from the iron-type nanowire, the iron microwire, and the iron flake. It is the reflection loss characteristic of the absorber produced from commercially available carbonyl iron fine particles. It is the surface observation image by a scanning electron microscope of an iron carbide / carbon composite fine wire. It is the figure which showed the reflection loss of the electromagnetic wave absorber produced from the black powder which remained after the acid etching of the iron carbide / carbon composite fine wire. It is the figure which showed the reflection loss of the electromagnetic wave absorber produced from the commercially available amorphous carbon. It is an X-ray diffraction pattern of the obtained iron carbide / carbon composite fine wire. It is the figure which showed the frequency dependence of the dielectric constant and the relative magnetic permeability of the electromagnetic wave absorber produced from the iron carbide / carbon composite fine wire. It is the reflection loss characteristic of the electromagnetic wave absorber produced from the iron carbide / carbon composite fine wire.

Claims (11)

  A thin wire form in which iron-based granular crystals are connected in a row such that the wire diameter is 50 nm or more and 300 nm or less and the line aspect ratio is 20 or more, or a form in which the thin wire portions connected in a row are connected in a dendritic shape And the shape of the surface portion constituting the line outer peripheral surface of each iron-based metal granular crystal in the line longitudinal direction forms a minimum value of the line cross-sectional area at the connection surface position with the adjacent particles, and An iron-based nanowire characterized by forming a bead-like shape that forms a convex curved surface having a maximum value of a line cross-sectional area at a midpoint of a connecting surface.   The iron-based nanowire according to claim 1, wherein the wire length is 1 μm or more and 10 μm or less.   The iron-based nanowire according to claim 1, wherein the iron-based granular crystal is an iron-based metal granular crystal containing metallic iron as a main component.   The iron-based nanowire according to claim 3, wherein the iron-based metal granular crystal has a structure in which a part of the iron-based component is iron carbide.   The iron-based nanowire according to claim 1 or 2, wherein the iron-based granular crystal is an iron carbide-based granular crystal containing iron carbide as a main component.   The surface of the iron-based nanowire according to any one of claims 1 to 5 is covered with an aggregate layer of carbon-based fine particles having a thickness of 50 nm or more and less than 500 nm, and the wire diameter is 200 nm or more and 2 μm or less. Featuring iron-based carbon composite thin wires. A method for producing an iron-based nanowire according to any one of claims 1 to 5,
By supplying volatile iron carbonyl in a heated state of room temperature to 150 ° C. together with a carrier gas composed of an inert gas at a concentration of 150 ppm to 450 ppm to a reaction section maintained at 250 ° C. to 400 ° C. A method for producing an iron-based nanowire comprising the step of thermally decomposing the volatile iron carbonyl. A method for producing an iron-based carbon composite fine wire according to claim 6,
A volatile carbonaceous compound is supplied alone or together with a carrier gas composed of an inert gas to a reaction section held at 300 ° C. or more and 500 ° C. or less to thermally decompose the volatile carbonaceous compound, and A carbon component is imparted to the surface or inside of the iron-based nanowire by depositing the generated carbon component on the surface of the iron-based nanowire according to any one of claims 1 to 5. A method for producing an iron-based carbon composite fine wire. A method for producing an iron-based carbon composite fine wire according to claim 6,
While supplying the volatile carbonaceous compound alone or together with a carrier gas such as nitrogen or argon to the reaction section held at 100 ° C. or higher and 300 ° C. or lower, the volatile carbonaceous compound is plasma-decomposed, A carbon component is imparted to the surface or inside of the iron-based nanowire by depositing the generated carbon component on the surface of the iron-based nanowire according to any one of claims 1 to 5. A method for producing an iron-based carbon composite fine wire.   A radio wave absorber comprising the iron-based nanowire according to any one of claims 1 to 5 or the iron-based carbon composite wire according to claim 6 bonded together by a resin binder.   9. The radio wave absorber according to claim 8, wherein the radio wave absorber is formed into a board, a sheet, a tape, or a cord cover.