JP4044273B2 - Method for producing semi-structure SiC-ferrite ceramic composite electromagnetic wave absorber - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention fundamentally solves obstacle electromagnetic waves that cause devices to malfunction among the electromagnetic waves of 100 MHz to 10 GHz band used in various electronic devices in the advanced information communication society that has been rapidly progressing in recent years. The present invention relates to a method for manufacturing an electromagnetic wave absorber that absorbs electromagnetic waves in this band.
[0002]
[Prior art]
As the electromagnetic wave absorber material, spinel ferrite and crystalline carbon are known, and a mixed material of these and rubber or polymer resin (such as urethane) is used.
[0003]
Spinel ferrite and mixtures thereof are effective between the TV band of 100 to about 1000 MHz (1 GHz), whereas carbon and mixtures thereof exhibit absorption characteristics primarily at about 50 GHz. Moreover, SiC is used for FRP type absorbers, and it has been reported that it absorbs at 10 GHz or 55 GHz depending on the preparation method. For example, JP-A-4-275403 discloses a composite sintered material having excellent electromagnetic wave absorption characteristics in a TV frequency band in which conductor particles such as SiC short fibers and whiskers are contained in ferrite in a volume ratio of 5 to 30%. It is disclosed. Japanese Patent Application Laid-Open No. 11-335472 discloses a silicone gel molded sheet containing Mn—Zn ferrite or Ni—Zn ferrite and a thermally conductive filler. Japanese Patent Laid-Open No. 8-51292 discloses a silicon carbide radio wave absorber having a three-dimensional network structure with a porosity of 40 to 60%.
[0004]
The present inventors previously synthesized Ni—Zn ferrite and amorphous SiC composite sintered material at low temperature by performing sintering with ferrite at 1000 ° C. simultaneously with reaction from polycarbosilane (PCS) to SiC. The method and the resulting composite sintered material match frequency as PCS addition increases(The frequency at which the return loss rate is maximum and the frequency at which radio wave absorption peaks)Reported that the matching frequency increased to approximately 1 GHz with PCS 30 wt% ("Metal Powder Ind. Federation APMI Int. (New Jersey)", (1999), Vol.3, pp.12.11- 14, “Powder and Powder Metallurgy Association Abstract”, page 222, 1998 Fall Meeting, November 18 to November 20, “Powder and Powder Metallurgy Association Abstract”, page 78, 1999 Fall Conference, November 9-11, “The 1999 International Conference on Powder Metallurgy & Particulate Materials”, June 20-24, 1999, Vancouver, “Okayama Keizai”, '99 .12, Vol. 22, No. 263, ( 1999), pp. 28-35).
[0005]
[Problems to be solved by the invention]
All materials that have been used as electromagnetic wave absorbers so far are composite materials of spinel ferrite, carbon, rubber, or polymer resin, so that they are flammable and have problems with durability. Yes, it is difficult to use as building material interior materials, building wall exterior materials or tiles installed in roads and underground shopping streets, and the development of new materials with excellent fire resistance and durability has become an urgent issue worldwide. Yes. At present, there are very few electromagnetic wave absorbers effective in the 1 to 20 GHz band, which is the most urgent problem. In the spinel ferrite system, there is an upper limit in the absorption band, and the maximum is about 1 GHz.
[0006]
[Means for Solving the Problems]
In order to solve these problems, the present inventor has developed a SiC precursor and spinel ferrite MFe.₂O_Four(M: Divalent metal element) is mixed and then heated at various temperatures, and various researches are carried out to change the production conditions. As a result, we succeeded in synthesizing a ceramic composite material of quasistructured SiC and Ferai soot. ByMatching frequency is 1 GHzIn the range of about 10 GHzis thereIt has been found that it exhibits radio wave absorption characteristics, and has reached the present invention.
[0007]
That is, the present invention is a quasi-structure SiC-ferrite ceramic composite type comprising a spinel ferrite sintered material containing quasi-structure SiC and having a matching frequency with respect to electromagnetic waves between 1 GHz and 10 GHz. A manufacturing method for providing an electromagnetic wave absorber.
[0008]
The present invention relates to polycarbosilanePowderAs an infusible treatment,As powder200 ~500After heat treatment for 10 hours or more in an oxidizing atmosphere at 0 ° C., 5-30% by weight with respect to the spinel ferrite powder is mixed to obtain a mixed powder, and then the mixed powder is pressed and then non-oxidized atmosphere In1000-1100Heat treatment at ℃ to mineralize polycarbosilane to form quasistructured SiC, then in oxidizing atmosphere1000-1100In sintered materials by heat treatment and sintering at ℃QuasiA quasi-structure SiC-ferrite ceramic composite type comprising a spinel ferrite sintered material containing structured SiC, and having a thickness at which the matching frequency, which is an absorption peak of radio waves, is between 1 GHz and 10 GHz. An electromagnetic wave absorber manufacturing method characterized by obtaining an electromagnetic wave absorber.
[0009]
The present invention also provides polycarbosilane.PowderAs an infusible treatment,As powder200 ~500After heat treatment for 10 hours or more in an oxidizing atmosphere at 0 ° C., 5-30% by weight with respect to the spinel ferrite powder is mixed to obtain a mixed powder, and then the mixed powder is pressure-molded and then an oxidizing gas Under a partial pressure control of oxygen using a mixture of oxygen and non-oxidizing gas1000-1100It consists of a spinel ferrite sintered material containing quasi-structured SiC by forming quasi-structured SiC in the sintered material by mineralizing polycarbosilane by heat treatment at ℃ to form quasi-structured SiC and sintering at the same time And obtaining a quasi-structure SiC-ferrite ceramic composite electromagnetic wave absorber in which the thickness of the sintered material is set to a thickness in which the matching frequency, which is an absorption peak of radio waves, is between 1 GHz and 10 GHz. It is a manufacturing method of a body.
[0010]
Moreover, this invention mixes what melt | dissolved 3-10% of polycarbosilane by weight ratio with respect to a spinel ferrite powder in a solvent to make a mixed powder, and volatilizes a solvent. After the powder is infusibilized, the mixed powder is subjected to pressure molding, and then heat treated at 900 to 1200 ° C. in a non-oxidizing atmosphere to mineralize the polycarbosilane to form a quasi-structure SiC, and then in an oxidizing atmosphere. In sintered material by heat treatment at 900-1200 ° C and sinteringQuasiA quasi-structure SiC-ferrite ceramic composite type comprising a spinel ferrite sintered material containing structured SiC, and having a thickness at which the matching frequency, which is an absorption peak of radio waves, is between 1 GHz and 10 GHz. An electromagnetic wave absorber manufacturing method characterized by obtaining an electromagnetic wave absorber.
[0011]
The present invention also provides: A solution of 3-10% polycarbosilane in a weight ratio with respect to the spinel ferrite powder was mixed with the spinel ferrite powder to form a mixed powder, and the mixed powder after the solvent was volatilized was infusibilized. Thereafter, the mixed powder is subjected to pressure forming, heat-treated at 900 to 1200 ° C. under oxygen partial pressure control using a mixed gas of an oxidizing gas and a non-oxidizing gas, and the polycarbosilane is mineralized to form a semi-structure SiC. Is formed of a spinel ferrite sintered material containing a quasistructured SiC by forming a quasistructured SiC in the sintered material by sintering at the same time, and the thickness of the sintered material is a radio wave absorption peak A quasi-structure SiC-ferrite ceramic composite type electromagnetic wave absorber having a matching frequency between 1 GHz and 10 GHz is obtained. Production method is,.
[0012]
Ferrite is Fe₂O_ThreeThe chemical composition and crystal form are fundamental elements that govern magnetic properties. The crystal type is Me²⁺O ・ Fe₂O_ThreeA spinel structure represented by M²⁺O · 6Fe₂O_ThreeMagnetoplumbite (hexagonal) type crystal represented by R_ThreeFe_FiveO₁₂It is classified into the garnet type crystal represented by. Where Me²⁺Is a divalent metal element, M²⁺Represents an alkaline earth metal, and R represents a trivalent rare earth ion. Spinel ferrite has an absorption characteristic at about 200 MHz and is of a magnetic loss mechanism type, and product powders having sufficiently high performance and various absorption characteristics are readily available.
[0013]
Crystalline SiC is a dielectric loss mechanism type having absorption characteristics at 50 to 70 GHz, and is lightweight. However, the absorption characteristic of the crystalline SiC-ferrite composite material is 1 GHz or less.
[0014]
The electromagnetic wave absorber made of the composite sintered material obtained by the production method of the present invention is an electromagnetic wave absorber in a band of 1 to 10 GHz which is a region that cannot be achieved by only spinel ferrite, only crystalline SiC, or these composite sintered materials. Was able to provide. By combining spinel ferrite and quasistructured SiC, the matching frequency of the radio wave absorption characteristics mainly due to magnetic loss can be arbitrarily changed between 100 MHz and 1 GHz. Also,compositeSinteringMaterialBy reducing the thickness of the antenna, another matching condition is satisfied, and radio wave absorption characteristics mainly due to dielectric loss appear around 8 GHz. Therefore,In composite sintered materialsMixing proportion of quasistructured SiC andComposite sintered materialBy changing the matching thickness, it is possible to produce a radio wave absorber that continuously exhibits absorption characteristics in the range of 100 MHz to 10 GHz.The “matching thickness” refers to a thickness at which the absorption of radio waves increases specifically and reaches a peak as the thickness of the electromagnetic wave absorber is changed.
[0015]
In normal sintering using ferrite powder, SiC powder, and fibers as starting materials, the reaction is intense and a sintered material cannot be produced. As a method for producing an electromagnetic wave absorber comprising the composite sintered material of the present invention, a low temperature synthesis method previously developed by the present inventor is preferable. This methodSolution mixing method,Using polycarbosilane (PCS), which is a precursor of SiC, which is made liquid with a solvent such as diethyl ether, mixed with ferrite powder, gelled, and then subjected to heat treatment to react from PCS to SiC. This is a method for producing a composite sintered material by simultaneously sintering with ferrite.
[0016]
In order to have a semi-structured SiC-spinel ferrite ceramic composite sintered material obtained by the production method of the present invention and to have absorption characteristics at 1 to 10 GHz, the melting point of PCS is as low as 242 and the semi-structure SiC It is necessary to prevent melting and retain the shape during mineralization to produce PCS powder and spinel ferrite as raw materials.PowderMixed powder withIn the case of the powder mixing method used, the PCS powderIt turns out that it must be infusible. For this infusibilization process, PCSPowderSurface is oxidized and SiO₂Thermal oxidation infusibilization method to form oxide film and PCSPowderThere is an electron beam infusibility method in which an electron beam or γ-ray is applied to the surface to form a Si—Si bond to form a film. The formation of an oxide film and the formation of Si-Si bonds during the infusibilization treatment are important for the development of dielectric properties due to the formation of quasistructured SiC.
[0017]
In the case of the thermal oxidation infusibilization method, spinel ferrite powder is obtained by an infusibilization treatment for 10 hours or more at a low temperature of 200 to 600 ° C. in an oxidizing atmosphere, for example, in the air.InmixturedidAfter high temperatureMineralization heat treatmentPrevents the complete reaction of polycarbosilane and spinel ferrite at temperature, polycarbosilane as quasistructured SiCIn composite sintered materialThe rest of the inventionAimAn electromagnetic wave absorber having both magnetic loss and dielectric loss can be obtained.
[0018]
An inert atmosphere is required when mineralizing PCS, which changes the properties of the ferrite. Inorganic under inert atmosphere such as argon gas to obtain stable characteristicsConversionLater in an oxidizing atmosphereSinteringIn one step in an atmosphere with controlled oxygen partial pressureMineralizationSinter.
[0019]
In order to make the semi-structured SiC-spinel ferrite ceramic composite sintered material obtained by the production method of the present invention to have an absorption characteristic at 1 to 10 GHz, it is heated at 900 to 1200 ° C.And mineralizationMust. The heating time is 6 hours or more. When synthesized under this condition, SiC is neither crystalline nor amorphous (amorphous), and SiC showing partially crystalline in the middle is generated. “Partially showing crystallinity” means, for example, a structure that is not regular in three dimensions but has regularity in two dimensions. In this specification, SiC having such a structure is referred to as “quasi-structure SiC”.
[0020]
MineralizedWhen the heating temperature is less than 900 ° C. and less than 6 hours, SiC is in an amorphous state, and the composite sintered body exhibits the characteristics of an equivalent electromagnetic wave absorber obtained by magnetically diluting the case of ferrite alone. If you want to obtain a composite sintered material of SiC and ferrite,For sinteringWhen the heating temperature exceeds 1200 ° C., ferrite reacts with SiC to react with a low melting point compound such as Fe₂SiO_Four(Melting point 1205 ° C.) is generated, so that the decomposition of ferrite starts, and when the ferrite decomposes, the composite sintered body collapses and does not show the characteristics of the radio wave absorber at all. When a liquid phase appears during sintering, grain growth is accelerated, which adversely affects electromagnetic wave absorption characteristics. On the other hand, however, the sintering temperature is as high as possible.Is goodSintering improves durability. A more preferable heating / sintering temperature is 1000 to 100 ° C.
[0021]
Ceramics with an intermediate crystal structure in which the arrangement of atoms and ions in ceramics is partially (for example, two-dimensional) regular but mostly irregular (three-dimensional) is usually semi-structured ceramics. That's it.
[0022]
For example, when wood waste is fired at 700-800 ° C., it shows a regular honeycomb arrangement in a honeycomb shape in two dimensions, but in three dimensions, the carbon arrangement has no regularity, and this is non-oriented. Called Turbulent Carbon. This partially irregular structure is called a quasistructure. When the same waste material is fired at a high temperature, crystalline carbon in which carbon is regularly arranged three-dimensionally is obtained. The quasistructured SiC formed in the composite sintered material of the present invention is also an intermediate crystal structure that is regular in two dimensions but irregular in three dimensions, similar to non-oriented turbostratic carbon. Say something like that. In SiC alone, no quasistructure has been found so far.
[0023]
The characteristics of the manufacturing method of the present invention are that the degree of freedom of the ratio of the mixing amount of the semi-structure SiC and ferrite is widened, the control of the distribution of the semi-structure SiC is easy, and if it is molded and processed in a gel form, a sheet form, a fiber Products in various forms, such asCompared to the case where a composite sintered material is synthesized using SiC powder or fiber.low temperatureheatingCan be synthesized. In addition, the cost is much lower than the use of SiC powder and fiber, which is extremely advantageous when considering practical use.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
PCS is the first method for compounding raw material powders.PowderAfter infusibility treatment at low temperature, the powder mixing method is mixed in a ferrite powder powder in a weight ratio of 5-30%, and secondly, 3-10% PCS in a weight ratio with respect to the ferrite powder is diethyl. Ferrite dissolved in etherPowderAnd a solution mixing method in which the mixture after volatilizing diethyl ether is infusibilized.
[0025]
As the infusible treatment, heat treatment is performed at 200 to 600 ° C. in an oxidizing atmosphere, for example, in the air for 10 hours or more. The infusibilization treatment temperature and the electromagnetic wave absorption characteristics are significantly affected by the infusibilization treatment temperature.ofOptimize heat treatment. Below 200 ° C. or less than 10 hours, a sufficient thickness of SiO on the polycarbosilane surface₂A film is not formed. If the temperature exceeds 600 ° C. or exceeds 24 hours, the entire polycarbosilane is oxidized and SiO 2₂become. A more preferable infusibilization temperature is 200 to 500 ° C, and further preferably 200 to 300 ° C.
[0026]
After the infusibilization treatment, the mixed powder is pressed and molded at 900-1200 ° C for over 6 hoursHeat treatmentTo do. This heat treatment at a high temperature is, for example, a two-stage process. That is, first, PCS is mineralized in a non-oxidizing atmosphere such as argon or nitrogen (99.99%).Heat treatmentAfter that, heat treatment is performed for sintering in an oxidizing atmosphere. A more preferable heat treatment temperature is 1000 to 100 ° C. in both stages.
[0027]
The quasistructured SiC in the composite sintered material has a particle shape with a diameter of about 30 μm and is relatively uniformly dispersed in the ferrite matrix. The density of the sintered material decreases as the amount of PCS increases. The matching frequency of the radio wave absorption characteristics of the composite sintered material shifts to the high frequency side as the PCS amount increases. In particular, when the infusibilization process is performed at a low temperature, the matching frequency moves to the high frequency side and increases to about 8 GHz. This result is a value exceeding the snake limit of the conventional spinel ferrite, and is a great effect by the hybridization of SiC.
[0028]
Instead of two-stage heat treatment at high temperature, a mixed gas of oxidizing gas and non-oxidizing gas is used for simultaneous progress of mineralization and sintering reaction of PCS by one-stage heat treatment with controlled oxygen partial pressure. It can also be made. For example, oxygen partial pressure is changed by mixing oxygen and argon. For a sample with 5 wt% PCS, O₂A composite sintered electromagnetic wave absorber free from an impurity phase can be produced by one-step heat treatment by heat treatment in an atmosphere with an oxygen ratio of: Ar = 1: 9. This oxygen partial pressure controlled single-stage heat treatment composite sintered material exhibits two types of electromagnetic wave absorption characteristics with matching frequencies of about 900 MHz and about 9 GHz depending on the thickness of the composite sintered material.
[0029]
ManufacturingExample 1
An example of producing a composite sintered material using a powder mixing method is shown below. The raw material is Ni-Zn ferrite (G1: Ni manufactured by Toda Kogyo)_0.20Zn_0.70Cu_0.18Fe₂O_y, Compression density 3.18 g / cm^Three, Average particle size 1.33 mm) and commercial polycarbosilane which is a precursor polymer used as a precursor for the production of silicon ceramics (Nippon Carbon, density 1.10, melting point 242 ° C., number average molecular weight; GPC suggested refractive index / Polystyrene conversion 1370, GPC ultraviolet absorption / polystyrene conversion 2330).
[0030]
PCS is used as an infusibilized PCS as a powder, and after heat treatment in the air at 500 ° C. for 10 hours, the ferrite powder has a weight ratio of 5-30.wt%mixtureAnd mixedAfter pressing the powder mixture, it is 6 hours at 1000 ° C. in an argon atmosphere.Heat treatment to mineralize PCSdid.
[0031]
At this stage, a part of the sample was molded into a hollow cylindrical shape having an outer diameter of 7 mm and an inner diameter of 3 mm with an ultrasonic machine for measuring the radio wave absorption characteristics. Then, heat treatment at 1000 ° C for 6 hours in airSinteringWent.
[0032]
In the obtained sample, the product phase was identified by powder X-ray diffraction measurement (Cu-Kα ray). Moreover, the structure | tissue was observed using the scanning electron microscope and the elemental analysis was performed by EPMA. The complex relative permeability (μ ′, μ ″) and the complex relative permittivity (ε ′, ε ″) at 50 MHz to 10 GHz were measured with a vector network analyzer (HP 8720D manufactured by HP). Using the obtained material constants, the absorption characteristics of the samples with different thicknesses were determined by theoretical calculation.
[0033]
As a result of X-ray diffraction measurement confirming the product phase after the non-oxygen heat treatment in the argon atmosphere and after the heat treatment in the air,Heat treatmentLater, in addition to ferrite, SiO₂, Zn₂SiO_FourAnd ZnO peaks were observed.
[0034]
Later in the atmosphereHeat treatmentAs a result, the ZnO peak almost disappeared, and ZnO₂SiO_FourThe peak intensity of the steel also decreases, and ferrite and SiO₂The peak was observed. SiO₂The intensity of the peak due to is relatively increased as the amount of PCS added is increased. In addition, the peak due to crystalline SiC is in an argon atmosphere.Heat treatmentAfter, in the atmosphereHeat treatmentIt was not recognized later.
[0035]
This is because ordinary SiC fiber is PCS in an inert atmosphere at 1400-1600 ° C.Heat treatmentIn contrast to crystalline SiC,ManufacturingIn the exampleHeat treatmentSince the temperature is 1000 ° C., it is considered that crystallization has not been achieved.
[0036]
SEM observation of these samples was performed. FIG. 1 is a photograph showing a cross section of a composite sintered material in which 5 wt% of PCS is mixed. Since it can be confirmed by analysis by EPMA that Si is contained in a region that appears white, it can be determined that the particles are caused by PCS. This particle has a two-layer structure of a central portion and an outer shell portion surrounding it. Furthermore, it has been clarified that oxygen is present in the outer shell portion and carbon is present in the central portion. Combining this result with the result of X-ray diffraction measurement, the central part is quasistructured SiC and the outer shell part is SiO.₂It can be estimated that it is an oxide film.
[0037]
In an argon atmosphereHeat treatmentZn later observed by X-ray diffraction₂SiO_FourIs produced at the interface between the outer shell and the ferrite, which is an oxide film of PCS.Heat treatmentAgain with ferrite and SiO₂It is thought that it returned to.
[0038]
FIG. 2 shows the results of measuring the material constants (complex permeability, complex permittivity) of these samples and calculating the amount of absorption (dB) in comparison with the conventional Ni—Zn ferrite. From this, it became clear that the matching frequency changes to the high frequency side as the mixing amount of PCS increases. Moreover, it turns out that the width | variety of the frequency region which shows absorption below -20dB has hardly changed.
[0039]
thisManufacturingRelationship between the PCS mixing ratio and the frequency dependence of the complex permittivity (real part), the relation between the complex dielectric constant (imaginary part) and the frequency dependence of the complex permeability (real part) FIG. 3 to FIG. 6 show the relationship between the complex magnetic permeability (imaginary part) and the frequency dependence, as compared with the conventional Ni—Zn ferrite. In fact, looking at the frequency dependence of the dielectric constant, no dispersion is observed in the frequency region where absorption is observed, and it is assumed that the absorption is due to magnetic loss.
[0040]
ManufacturingExample 2
An example of producing a composite sintered material using the solution mixing method is shown below. 3-10% by weight of PCS with respect to the ferrite powder was dissolved in diethyl ether and mixed with ferrite, and the mixture after volatilizing diethyl ether was infusibilized. The infusibilization conditions and the processes after press molding areManufacturingSame as Example 1.
[0041]
In the composite sintered material in which 5 wt% of PCS was mixed, clear particles as seen in FIG. 1 could not be observed. As a result of the analysis by EPMA, it can be confirmed that Si is contained in the vicinity of the grain boundary, so that it is presumed that the compound resulting from PCS is very finely dispersed.
[0042]
Next, in FIG.ManufacturingExample 1 andManufacturingThe relationship between the PCS mixing ratio of Example 2 and bulk density is shown. The raw material PCS is CH in the process of mineralization._FourAnd H₂In view of the fact that the weight ratio of the semi-structured SiC becomes small and the density of the β-SiC sintered material is 3.1, this result can be said to be very small. From this, it is presumed that the produced composite sintered material is not dense and contains pores and voids. Actually, in the structure photograph of FIG. 1, it is observed that voids are formed around the white particles, and ferrite and SiO 2 are observed.₂It can be confirmed that pores and voids are generated at the interface of the oxide film.
[0043]
ManufacturingExample 1 andManufacturingAlthough the state of density reduction varies depending on the mixing method of Example 2, it is presumed that in the case of the solution mixing method, it is dispersed at the grain boundary and the surface area of the interface is wider than the sample of the particle mixing method. In the case of the solution mixing method, the sintered material can be produced only up to 10% by weight of PCS to ferrite, and the shape cannot be maintained at 10% or more.
[0044]
FIG. 8 shows the relationship between the PCS mixing amount and the matching frequency. From this, it can be seen that as the PCS mixing amount increases, the matching frequency changes almost linearly to the high frequency side up to about 30 wt% of the PCS mixing amount.ManufacturingIn the sample by the powder mixing method of Example 1, the matching frequency was increased to approximately 1 GHz at a PCS mixing ratio of 30 wt%. When the PCS mixing ratio exceeds 30 wt%, sintering becomes extremely difficult.
[0045]
further,ManufacturingExample 1 andManufacturingIt became clear that the magnitude of the change in the matching frequency differs depending on the mixing method in Example 2. For example, the sample by the powder mixing method changes to about 800 MHz at a PCS mixing ratio of 25 wt%, whereas the sample by the solution mixing method changes to 800 MHz at 7 wt%. For this reason, the electromagnetic wave absorption characteristics differ depending on the dispersion state of the semi-structured SiC particles due to the difference in the mixing method.
[0046]
FIG. 9 shows a graph in which matching frequencies are arranged by bulk density. This shows a good correlation between bulk density and matching frequency. It is considered that not only the dielectric property of the dispersed quasistructure SiC is essentially effective, but also the difference in pore density and void density caused by the difference in dispersion state.
[0047]
Next, PCS mixingratioThe relationship between quantity and alignment thickness is shown in FIG. It has been clarified that the matching thickness increases linearly up to the addition of 20 wt% of PCS and takes a substantially constant value beyond that. There is no significant difference in the matching thickness depending on the mixing method.
[0048]
Example1
ManufacturingA sintered material was produced in the same manner as in Example 2. However, PCS 5 wt% was mixed in solution and subjected to infusibilization treatment at 200 ° C. for 24 hours. The electromagnetic wave absorption characteristics, complex relative permittivity, and complex relative permeability of the obtained sintered material are shown in FIGS. Around 840MHz when the thickness is 7.9mmRadio waveabsorptionPeak ofAround 8.4 GHz when the thickness is 3.0 mmRadio waveabsorptionPeak ofWas recognized. From the frequency dependence of the complex relative permittivity and complex relative permeability,Matching frequencyAbsorption near 840MHz is due to magnetic loss,Matching frequencyAbsorption near 8.4 GHz is considered to be due to dielectric loss.
[0049]
Example2
ManufacturingRaw material powders were mixed in the same manner as in Example 1. However, as the infusibilization treatment, heat treatment was performed at 240 ° C. in the atmosphere for 12 hours. After the infusibilized mixed powder is pressed, it is used for 6 hours at 1000 ° C. under oxygen partial pressure control using a mixed gas of argon and oxygen (each 99.99%).Simultaneously with heating and PCS mineralizationSintered. As the oxygen partial pressure, the respective flow rates of argon and oxygen were controlled, and the flow rate ratio was assumed to be the partial pressure ratio. Measurement of radio wave absorption characteristicsManufacturingPerformed as in Example 1.
[0050]
The result of X-ray diffraction measurement confirming the formed phase after heat treatment under oxygen partial pressure control is as follows:Heat treatmentLater, in addition to ferrite, Zn₂SiO_Four, SiO₂And the peak of ZnO is recognized. However, when the oxygen partial pressure is 0.1 atm, almost no peak is recognized except for ferrite. Even if the oxygen partial pressure is increased to 0.5 atm, the X-ray diffraction pattern is basically unchanged, and only a peak that is considered to be caused by a very small amount of impurities is observed. Zn again at 1 atm of oxygen₂SiO_FourThe peak of₂O_ThreeThe peak also appeared.
[0051]
From the result of X-ray diffraction, it is considered that the reaction at the interface is suppressed when the oxygen partial pressure is in the range of 0.1 to 0.5 atm. In addition, no peak due to crystalline SiC was observed regardless of the oxygen partial pressure. this is,Heat treatmentThis is probably because crystallization was not achieved because the temperature was 1000 ° C.
[0052]
This example214 and 15 show the complex relative permeability and complex relative permittivity, respectively, and FIG. 16 shows the result of calculating the amount of absorption (dB) using them. The data shown in the figure is for a sample heat treated at 1000 ° C. for 6 hours in an atmosphere with an oxygen partial pressure of 0.1 atm. From FIG. 16, when the thickness is 9.9 mm, around 830 MHz.Radio waveabsorptionPeak ofCan be seen, thickness1.8around 8.4 GHz when mmRadio waveabsorptionPeak ofIt was accepted. From the frequency dispersion of FIG. 14 and FIG.Matching frequencyAround 830MHzMatching frequencyAbsorption near 8.4 GHz can be determined as absorption due to magnetic loss and dielectric loss, respectively.
[0053]
With one-step heat treatmentManufacturingSuccessful production of a composite sintered material exhibiting electromagnetic wave absorption characteristics substantially equivalent to those of Examples 1 and 2. The results of X-ray diffraction suggested that the reaction at the interface was suppressed, but the results of the absorption characteristics revealed that PCS exhibited dielectric properties without being oxidized to the inside. It was.
[0054]
FIG. 17 shows the relationship between the oxygen partial pressure and the matching frequency. ○ represents a matching frequency mainly derived from magnetic loss, and ● represents a matching frequency mainly derived from dielectric loss. In the case of argon only, as has been clarified so farRadio waveabsorptionPeak ofWas not recognized. In the range of the oxygen partial pressure of 0.05 to 0.5 atm, the low frequency side near 800 MHz and the high frequency side near 8 GHzRadio waveabsorptionPeak ofWas recognized. Also, it is about 850 MHz in 1 atmosphere of oxygen.Radio waveabsorptionPeak ofOnly was observed. In the range of the oxygen partial pressure of 0.05 to 0.5 atm, the matching frequency has almost no oxygen partial pressure dependency on the low frequency side and the high frequency side. From this, it is clear that the infusibilization processing condition is very important for the control of the matching frequency. In this way, an electromagnetic wave absorber having both magnetic loss and dielectric loss almost equivalent to those of the two-stage heat treatment was obtained by the one-stage heat treatment under the oxygen partial pressure control.
[0055]
【The invention's effect】
As described above, the electromagnetic wave absorber made of the novel composite sintered material obtained by the production method of the present invention has been difficult to realize with the conventional electromagnetic wave absorber.1 GHzTo electromagnetic waves between 10 GHz and 10 GHzDue to dielectric lossIt is an epoch-making material with matching frequency, and has excellent fire resistance and weather resistance. Adaptable.
[Brief description of the drawings]
[Figure 1]Manufacturing5 is a drawing-substituting photograph showing an SEM image of a cross-section of a sintered body in which 5 wt% of PCS is mixed in the electromagnetic wave absorber of Example 1.
[Figure 2]ManufacturingIn the electromagnetic wave absorber of Example 1, it is a graph which shows the electromagnetic wave absorption characteristic at the time of changing PCS mixing ratio.
[Fig. 3]ManufacturingIn the electromagnetic wave absorber of Example 1, it is a graph which shows the relationship between the frequency dependence of a complex dielectric constant (real part), and PCS mixing ratio.
[Fig. 4]ManufacturingIn the electromagnetic wave absorber of Example 1, it is a graph which shows the relationship between the frequency dependence of a complex dielectric constant (imaginary part), and PCS mixing ratio.
[Figure 5]ManufacturingIn the electromagnetic wave absorber of Example 1, it is a graph which shows the relationship between the frequency dependence of a complex magnetic permeability (real part), and PCS mixing ratio.
[Fig. 6]ManufacturingIn the electromagnetic wave absorber of Example 1, it is a graph which shows the relationship between the frequency dependence of complex permeability (imaginary part), and PCS mixing ratio.
[Fig. 7]ManufacturingIn the electromagnetic wave absorber of Examples 1 and 2, it is a graph which shows the relationship between the bulk density of a composite sintered compact, and PCS mixing ratio.
[Fig. 8]ManufacturingIn the electromagnetic wave absorber of Examples 1 and 2, it is a graph which shows the relationship between a matching frequency and PCS mixing ratio.
FIG. 9ManufacturingIn the electromagnetic wave absorber of Examples 1 and 2, it is a graph which shows the relationship between a matching frequency and a bulk density.
FIG. 10Manufacturing4 is a graph showing the relationship between the matching thickness and the PCS mixing ratio in the electromagnetic wave absorbers of Examples 1 and 2.
FIG. 11 Example1It is a graph which shows the electromagnetic wave absorption characteristic of a composite sintered compact (PCS5 wt%).
FIG. 12 Example1It is a graph which shows the frequency dependence of the complex dielectric constant of a composite sintered compact (PCS5 wt%).
FIG. 13 Example1It is a graph which shows the frequency dependence of the complex magnetic permeability of the composite sintered compact (PCS5 wt%).
FIG. 14 Example2It is a graph which shows the frequency dependence of the complex magnetic permeability of the composite sintered compact (PCS5 wt%).
FIG. 15 shows an example.2It is a graph which shows the frequency dependence of the complex dielectric constant of a composite sintered compact (PCS5 wt%).
FIG. 16 Example2It is a graph which shows the electromagnetic wave absorption characteristic of a composite sintered compact (PCS5 wt%).
FIG. 17 Example2It is a graph which shows the relationship between the matching frequency of the compound sintered compact (PCS5 wt%), and the oxygen partial pressure at the time of heat processing.

Claims (4)

As an infusibilizing treatment for polycarbosilane powder , after heat-treating at 200 to 500 ° C. in an oxidizing atmosphere for 10 hours or longer as a powder , 5 to 30% by weight with respect to spinel ferrite powder is mixed and mixed powder Thereafter, the mixed powder is subjected to pressure forming , and then heat-treated at 1000 to 1100 ° C. in a non-oxidizing atmosphere to mineralize polycarbosilane to form a quasi-structure SiC, and then in an oxidizing atmosphere at 1000 to 1100 ° C. It consists of a spinel ferrite sintered material containing quasi- structure SiC in the sintered material by heat treatment and sintering, and the thickness of the sintered material is a matching frequency that is an absorption peak of radio waves between 1 GHz and 10 GHz. A method for producing an electromagnetic wave absorber comprising obtaining a quasi-structure SiC-ferrite ceramic composite type electromagnetic wave absorber having a thickness of As an infusibilizing treatment for polycarbosilane powder , after heat-treating at 200 to 500 ° C. in an oxidizing atmosphere for 10 hours or longer as a powder , 5 to 30% by weight with respect to spinel ferrite powder is mixed and mixed powder Then, the mixed powder is subjected to pressure molding, and then heat-treated at 1000 to 1100 ° C. under oxygen partial pressure control using a mixed gas of an oxidizing gas and a non-oxidizing gas to mineralize the polycarbosilane to form a semi-structure. It is composed of a spinel ferrite sintered material containing quasistructured SiC by forming quasistructured SiC in the sintered material by sintering at the same time as forming SiC, and the thickness of the sintered material is expressed by the absorption peak of radio waves. A quasi-structure SiC-ferrite ceramic composite electromagnetic wave absorber having a thickness with a matching frequency between 1 GHz and 10 GHz is obtained. Method for producing a wave absorber. A solution of 3-10% polycarbosilane in a weight ratio with respect to the spinel ferrite powder was mixed with the spinel ferrite powder to form a mixed powder, and the mixed powder after the solvent was volatilized was infusibilized. Thereafter, the mixed powder is subjected to pressure forming, and then heat treated at 900 to 1200 ° C. in a non-oxidizing atmosphere to mineralize polycarbosilane to form a quasi-structure SiC, and then heat treated at 900 to 1200 ° C. in an oxidizing atmosphere. to become a spinel ferrite sintered material containing semi-structured SiC in the sintered material by sintering, and during the radio wave absorption peak thickness of matching frequency of the sintered material is from 1GHz to 10GHz A method for producing an electromagnetic wave absorber, comprising obtaining a quasi-structure SiC-ferrite ceramic composite type electromagnetic wave absorber having a thickness. A solution of 3-10% polycarbosilane in a weight ratio with respect to the spinel ferrite powder was mixed with the spinel ferrite powder to form a mixed powder, and the mixed powder after the solvent was volatilized was infusibilized. Thereafter, the mixed powder is subjected to pressure forming, heat-treated at 900 to 1200 ° C. under oxygen partial pressure control using a mixed gas of an oxidizing gas and a non-oxidizing gas, and the polycarbosilane is mineralized to form a semi-structure SiC. Is formed of a spinel ferrite sintered material containing quasistructured SiC by forming quasistructured SiC in the sintered material by sintering simultaneously, and the matching frequency which is the absorption peak of radio waves is from 1 GHz to 10 GHz. A method for producing an electromagnetic wave absorber, comprising obtaining a semi-structure SiC-ferrite ceramic composite type electromagnetic wave absorber having a thickness in between.

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