JPH09255408A - Radio wave absorption material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a radio wave absorbing material excellent in heat resistance and mechanical properties, consisting of a composite material composed of respective specific substances as matrix and disperse phase. SOLUTION: This radio wave absorbing material consists of a composite material composed of glass or ceramic as matrix and metallic particles as disperse phase. When the metallic particles are of flat shape and ductile, both the mechanical strength and toughness of the composite material can be improved. The volume ratio of the disperse phase is pref. 2-40%. The metal(s) is selected from Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W, Fe, Ni, Co, Cu, Al, Mg, Zn, and alloy(s) thereof, stainless steel, permalloy, and superalloy(s). The ceramic is e.g. Al2 O3 , ZrO2 , MgO, mullite, MgO/Al2 O3 , Al2 O3 /Y2 O3 .

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel electromagnetic wave absorbing material having excellent heat resistance and mechanical properties.

[0002]

2. Description of the Related Art Radio wave absorbing materials have often been conventionally attached to reflectors of ships and the like in order to suppress reflection of radio waves from ships, aircraft, vehicles, buildings, towers and the like. Further, recently, it has been used as a radio wave absorbing material for microwave ovens. As this radio wave absorbing material, a material in which carbon powder or ferrite powder is dispersed in a resin is known. However, since the matrix is a resin, its heat resistance temperature is at most about 200 ° C., and it is difficult to use it at a temperature higher than that.
Also, mechanical properties such as bending strength were inferior.

[0003]

An object of the present invention is to solve the above problems,
An electromagnetic wave absorbing material having excellent heat resistance and mechanical properties is provided.

[0004]

According to the present invention, there is provided a radio wave absorbing material comprising a composite material having glass or ceramics as a matrix and metal particles as a composite phase. The radio wave absorbing material of the present invention has excellent radio wave absorbing properties, and since the matrix is glass or ceramics, it is also excellent in heat resistance. Further, by using a granular metal as the metal particles of the composite phase, the strength of the matrix portion can be increased due to the particle dispersion effect, so that the strength of the composite can be improved. Furthermore, the mechanical properties of the composite, particularly strength and toughness, can be improved by using flattened ductile metal particles as the composite phase metal particles. Further, as the composite phase metal particles, granular metal and flat ductile metal particles may be used in combination.

The glass constituting the matrix of the composite material in the present invention is not particularly limited, and examples thereof include one or more selected from oxide-based glasses and non-oxide-based glasses such as crystallized glass and general-purpose glass. The glass of can be used. Specifically, as crystallized glass,
LAS I (Li ₂ O-Al ₂ O ₃ -SiO ₂ -MgO system), LAS II, III
(Li ₂ O-Al ₂ O ₃ -SiO ₂ -MgO-Nb ₂ O ₅ system), MAS (MgO-Al ₂ O ₃
-SiO ₂ system), BMAS (BaO-MgO-Al ₂ O ₃ -SiO ₂ system), Terna
ry mullite (BaO-Al ₂ O ₃ -SiO ₂ system), Hexacelsian (BaO-A
l ₂ O ₃ -SiO ₂ system), Li ₂ O-Al ₂ O ₃ -SiO ₂ system, Na ₂ O-Al ₂ O ₃ -SiO
₂ system, Na ₂ O-CaO-MgO-SiO ₂ system, PbO-ZnO-B ₂ O ₃ system, ZnO-B ₂ O ₃
-SiO ₂ system, ZrO ₂ -SiO ₂ system, CaO-Y ₂ O ₃ -Al ₂ O ₃ -SiO ₂ system, CaO-A
l ₂ O ₃ -SiO ₂ system, MgO-CaO-Al ₂ O ₃ -SiO ₂ system, SiO ₂ -B ₂ O ₃ -Al ₂ O ₃
-MgO-K ₂ OF system and the like. As general-purpose glass, silicate glass (SiO ₂ system), soda lime glass (Na ₂ O-CaO-S)
iO ₂ system), potassium lime glass (K ₂ O-CaO-SiO ₂ system), borosilicate glass (Na ₂ OB ₂ O ₃ -SiO ₂ system), aluminosilicate glass (Al ₂ O ₃ -MgO-CaO-SiO) ₂ series, lead glass (K ₂ O-PbO-SiO ₂
System), barium glass (BaO—SiO ₂ —B ₂ O ₃ system), and the like. Further, as the low melting point glass, lead silicate glass (PbO-SiO ₂ system, PbO-B ₂ O ₃ -SiO ₂ system, etc.), borate glass (B ₂ O ₃ system, Li ₂ OB ₂ O ₃ system, Na ₂ OB ₂ O ₃ system, etc., phosphate glass (Na ₂ OP ₂ O ₅ system, B ₂ O ₃ -P ₂ O ₅ system, etc.) and Al ₂ O ₃ -Li ₂ O-Na ₂
Examples include OK ₂ OP ₂ O ₅ series. Furthermore, Y ₂ O ₃ -Al ₂ O ₃ -SiO ₂ type glass, oxynitride glass (La-Si-ON type, Ca-Al-Si-ON type, Y-Al-type) which has been developed in recent years. Si
-ON system, Na-Si-ON system, Na-La-Si-ON system, Mg-Al-Si-ON
System, Si-ON system, Li-K-Al-Si-ON system) and small thermal expansion coefficient
Examples thereof include TiO ₂ —SiO ₂ system and Cu ₂ O—Al ₂ O ₃ —SiO ₂ system. Further, as the non-oxide glass, fluoride glass or chalcogen glass can be used.

Further, as the ceramics constituting the matrix of the composite material, Al ₂ O ₃ , ZrO ₂ , MgO,
Mullite, MgO / Al ₂ O ₃ , Al ₂ O ₃ / Y ₂ O _{3 and the} like can be mentioned. On the other hand, as the metal of the composite phase, Ti, V, C
r, Zr, Nb, Mo, Hf, Ta, W, Fe, Ni,
At least one metal selected from Co, Cu, Al, Mg, Zn and alloys thereof, stainless steel, permalloy and super heat resistant alloy is used. As a composite phase metal,
When the granular metal and the flattened ductile metal are used together, these may be the same or different.

In the present invention, ceramic particles, ceramic whiskers, inorganic short fibers and the like may be used together with the metal particles as the composite phase. By using these together, the strength and toughness of the composite can be further improved. As ceramic particles, Ti,
V, Cr, Zr, Nb, Mo, Hf, Ta, W, Fe,
Oxides and nitrides of Ni, Co, Al, Y, Si and B,
At least one ceramic particle selected from carbides, borides, silicides and carbonitrides can be mentioned. Ceramic whiskers include Si ₃ N ₄ , SiC, Ti
C, graphite, potassium titanate, aluminum borate, ZnO, MgO, magnesium borate, Ti
At least one selected from ceramic whiskers such as B ₂ and mullite. As the inorganic short fibers, short fibers such as alumina, alumina-silica, silica, zirconia, alumina, Si ₃ N ₄ , SiC, Si, Ti, C and O typified by Japanese Patent Publication No. 58-5286 can be used. At least one kind selected from chopped long fibers such as inorganic fibers as the main component can be used.
It is important to select those which do not react with the metal particles used at the sintering temperature to form a brittle compound.

As for the combination of the matrix and the metal, it is necessary to select a combination in which the melting point of the metal is higher than the sinterable temperature of the matrix. When glass is used as the matrix, for example, if the matrix is silicate glass-based or
In the case of the TiO ₂ —SiO ₂ system, the sintering temperature is 1600 ° C. or higher, and therefore, the metals V and C having a melting point higher than that are used.
It is preferable to use r, Zr, Nb, Mo, Hf, Ta, W and alloys thereof. Also, the sintering temperature and the crystallization temperature of the crystallized glass except the sintering temperature, and PbO-ZnO-B ₂ O ₃ based oxynitride glass is approximately 700 to 130
Since the temperature is 0 ° C., Ti, Fe, Ni, Co and alloys thereof, stainless steel, permalloy, and super heat resistant alloy can be used. Further, since general-purpose glass has a sintering temperature of approximately 600 to 1000 ° C., Cu can be used in addition to the above, and PbO-ZnO-B ₂ O ₃ -based crystallized glass and low-melting glass have a sintering temperature of Is about 200-600
Since the temperature is ° C, Al, Mg, Zn and alloys thereof can be used.

In the case of using ceramics as a matrix, for example, in the case of Al ₂ O ₃ , since the sintering temperature is 1600 ° C. in general powder, metals such as V, Cr, which have melting points higher than that, Zr, Nb, Mo, Hf, T
It is preferable to use a and W. Further, in the low temperature sintering type (for example, Taimicron TM-DAR; manufactured by Daimei Chemical Industry Co., Ltd.), the sintering temperature is 1200 ° C.,
Further, Ti, Fe, Ni, Co, stainless steel, and super heat resistant alloy can also be used. Furthermore, since the sintering temperature can be lowered to about 900 ° C. by adding a glass phase to Al ₂ O ₃ , Cu can be used in addition to the above. In addition, ZrO ₂ (sintering temperature> 1800 ° C.) and MgO
In case of (sintering temperature> 1400 ° C), Ti, V, C
r, Zr, Nb, Mo, Hf, Ta, W, Fe, Ni,
Co, stainless steel, and super heat resistant alloy can be used. In the case of mullite (sintering temperature> 1500 ° C),
V, Cr, Zr, Nb, Mo, Hf, Ta, W, Fe can be used.

In the present invention, by adding metal particles as a composite phase to a glass or ceramic matrix matrix, the mechanism is not yet well understood, but the volume resistivity of the composite can be controlled and the excellent electromagnetic wave absorption effect can be obtained. Is expressed. Further, by making the shape of the metal of the composite phase flat, the plastic deformation of the metal acts more, so that the strength and toughness of the composite material can be improved.
In particular, when the minimum diameter of the flat surface is d and the thickness is t, d /
It is desirable that t ≧ 3. When d / t is less than 3, it is not preferable because cracks easily progress at the interface between the metal particles and the matrix and the plastic deformation of the metal phase cannot be fully utilized. The range of d and t is not particularly limited, but it is preferable that the relationship of d / t ≧ 3 is satisfied. Further, by using the particulate metal and the flattened ductile metal together as the composite phase, the strength of the matrix portion can be increased due to the particle dispersion effect of the particulate metal, so that the strength of the composite can be further improved.

Further, ceramic particles as a composite phase,
By using ceramic whiskers, inorganic short fibers and the like together, the strength of the glass matrix portion can be increased, so that the strength and toughness of the composite can be further improved. It is desirable that the particle size of the ceramic particles be 2 μm or less, preferably 1 μm or less. If the particle size is larger than 2 μm, the particle dispersion effect cannot be obtained, which is not preferable. The shape of the ceramic whisker is not particularly limited, and the inorganic short fiber has a length of 5 m due to dispersibility.
m or less is preferable.

The volume ratio of the composite phase in the composite material of the present invention is preferably 2 to 40%, particularly 5 to 30%.
When the volume ratio of the composite phase is less than 2%, the plastic deformation amount of the metal is too small, so the effect of improving the mechanical properties is not sufficient, and the volume ratio of the composite phase is less than 40%. When it also increases, the volume resistivity of the composite becomes too small and the effect of the invention is not exhibited. When ceramic particles, ceramic whiskers, inorganic short fibers, etc. are used in combination as the composite phase, the volume ratio thereof is 2 to 40.
%, Particularly preferably 3 to 30%. Volume ratio is 2
If it is less than%, the effect of addition does not appear. Further, even if the volume ratio exceeds 40%, the mechanical properties are not further improved.

The radio wave absorbing material of the present invention is manufactured by the following method. First, a composite powder in which glass powder or ceramic powder is attached to the surface of metal powder is manufactured. Such composite powder can be produced by mixing metal powder and glass powder or ceramic powder. The flat metal particles can be produced by plastically deforming the ductile metal powder during mixing to flatten it. The particle size of the glass powder is not particularly limited, but is preferably 50 μm or less. The particle size of the ceramic powder is not particularly limited, but an average particle size of 1 μm or less with good sinterability is desirable. When the particle size of the metal powder is spherical, it is 150 μm or less, particularly 100 μm, from the viewpoint of maintaining mechanical properties.
The following are desirable: When it is made flat, it is 1 to 200 μm, particularly 3 to 10 in order to easily promote flattening.
A range of 0 μm is preferred. Particle size of ductile metal powder is 1μ
If it is smaller than m, it cannot be flattened because it is fine. On the other hand, if it is larger than 200 μm, it becomes difficult to sinter because of coarse particles and violently separates from the glass powder, which makes uniform mixing difficult. As for the mixing ratio of the metal powder and the glass powder or the ceramic powder, the volume ratio of the metal powder in the mixed powder is preferably 2 to 60%, particularly preferably 10 to 50%.

When ceramic particles, ceramic whiskers, inorganic short fibers and the like are used as the composite phase, they are added when the metal powder and the glass powder or the ceramic powder are mixed. The particle size of the ceramic powder is preferably 2 μm or less, and particularly preferably 1 μm or less. If the particle size of the ceramic powder is larger than 2 μm, the particle dispersion effect cannot be obtained. The shape of the ceramic whiskers is not particularly limited, and the types available in the market can be used as they are. When the inorganic short fibers or long fibers are cut and used, it is preferable to use those having a length of 5 mm or less in view of easy handling and dispersibility. The mixing ratio of these is preferably 2 to 40%, particularly 3 to 30% by volume.

There are no particular restrictions on the method of mixing the metal powder with the glass powder or the ceramic powder, and both wet and dry methods can be adopted. As a solvent in the case of wet mixing, ethanol, methanol and the like are generally used. For mixing equipment, ball mill, vibration mill, attritor,
A planetary ball mill or the like can be used. The ductile metal powder is deformed from a spherical shape to a flat shape by mechanical mixing with a mixing medium such as a ball at the time of mixing. Therefore, the degree of flattening can be controlled by controlling the mixing conditions,
A spherical or flat shape can be selected. In general, the amount of deformation changes depending on the conditions such as mixing time and rotation speed, so when flat particles are used, these conditions should be controlled.
It is desirable to flatten the flattened shape so that d / t ≧ 3 is satisfied. Furthermore, since glass powder or ceramic powder adheres to the surface of the metal powder during this mixing process, it is possible to prevent the metals from contacting and granulating during the sintering process. Needless to say, depending on the mixing ratio of the metal powder and the glass powder or the ceramic powder, the glass powder or the ceramic powder that does not adhere to the metal surface may coexist. Further, depending on the particle size of the metal powder used, undeformed particles remain after mixing, but if the flattened particles are in an appropriate amount, the effect of improving mechanical properties can be obtained. Further, the composite powder in which the glass powder or the ceramic powder is adhered to the surface of the flat ductile metal powder is flattened by a rolling process or the like in advance of the ductile metal powder, and by mixing this with the glass powder or the ceramic powder. However, the above-mentioned method in which mixing and flattening are performed simultaneously is advantageous in terms of process simplification and uniform mixing.

Next, the obtained mixed powder is molded into a desired shape and then sintered at 200 to 1800 ° C. in an atmosphere of an inert gas such as nitrogen or argon or in a vacuum. As a sintering method, a known sintering method can be used. For example, in the process of densifying a CIP-molded or injection-molded body by pressureless sintering, vacuum sintering, and HIP, isotropic because spherical particles or flattened particles are randomly oriented in three dimensions. However, when flattened particles are molded by a uniaxial pressing method such as hot pressing, the flattened particles are two-dimensionally oriented in the direction perpendicular to the pressing direction, so that the strength especially in the thickness direction is obtained. improves. Further, in the case of a glass matrix, it can be formed into a long shape by an extrusion method or roll forming. Further, it is possible to directly form a complicated shape by a forging method or a casting method, preferably a pressure casting method. Also, the sintering is 200 to 1
Although it can be performed in a temperature range of 800 ° C., when flat particles are used, the ductility of the glass powder and the ductility of the above-mentioned glass powder is set so that the flat ductile metal can be maintained at a temperature lower than the melting point of the ductile metal. It is necessary to choose a metal.

[0017]

According to the present invention, by adding metal particles as a composite phase to a glass or ceramic matrix, the mechanism is not yet well understood, but the volume resistivity of the composite can be controlled and an excellent electromagnetic wave absorption effect can be obtained. Is expressed. Furthermore, by making the shape of the metal of the composite phase flat, the plastic deformation of the flat particles can also be fully utilized, which can contribute to high toughness and further improve the strength, resulting in excellent mechanical properties. A radio wave absorbing material can be provided. In addition, by combining ceramic particles, ceramic whiskers, inorganic short fibers, etc. as the composite phase,
Since the strength of the glass matrix portion can be increased, the strength and toughness of the composite can be further improved. Further, by selecting particles having a coefficient of thermal expansion greatly different from that of glass or ceramics, the residual stress due to the thermal stress generated in the sintering process can further increase the strength, and the glass can be applied to a structural member having high strength and high toughness. Composite materials can be provided. Further, as described above, if the composite phase is two-dimensionally oriented, the strength in the orientation direction and the vertical direction can be further improved. Furthermore, since the morphology of the composite phase can be flattened by utilizing the deformation during mixing of the ductile metal powder as the raw material powder and the glass powder or the ceramic powder, it is easy to control the shape of the composite phase and The manufacturing process is not required, and the cost increase due to compounding can be suppressed.

[0018]

The present invention will be described more specifically with reference to the following Examples and Comparative Examples. Example 1 MAS (MgO-Al ₂ O ₃ -SiO ₂ system) powder (particle size 20 μm or less)
And 45 μm under stainless powder (SUS316
L; made by Sanyo Special Steel Co., Ltd., has a volume ratio of stainless steel of 10, 1
Weighed to be 5, 20, 30. These mixed powders were subjected to ball mill mixing using silicon nitride balls in an ethanol solvent. 1 and 2 show a scanning electron microscope image and an optical microscope image of a cross-sectional structure of the appearance of the mixed powder after ball milling when the volume ratio of the stainless powder is 15%.
From these, it can be seen that the added 45 μm-under stainless powder is flattened by the ball mill mixing and further the glass powder is attached to the surface. Similar results were obtained for other volume ratios of stainless powder. This mixed powder is placed in a graphite mold, and
Sintering was carried out at 000 ° C. and a pressure of 100 kg / cm ² in argon for 1 hour. Figure 3 shows that the volume ratio of stainless steel is 1
The optical microscope image of the cross-section structure of the composite material in the direction parallel to the press direction in the case of 5% is shown. It can be seen that the 45 μm-under stainless powder is two-dimensionally oriented and satisfies d / t ≧ 3 to be flattened.

A disk-shaped test piece of φ3 × 1 mm was processed from this composite material, and the relative permittivity (εr ′) and the dielectric loss ta at 10 MHz were measured using an impedance analyzer.
nδ is calculated, and from these, the complex relative permittivity (εr ″ = εr ′)
× tan δ; εr ′: real part, εr ″: imaginary part) were obtained.
Table 1 shows the results. For comparison, a composite material obtained by adding 50% by volume of MAS glass single phase and stainless powder was manufactured by the same method as in Example 1, and the measurement results are also shown. From this, in the present invention, in any case, high tan δ and ε
r ”, and has excellent electromagnetic wave absorption characteristics. Especially, the composite material containing 15% by volume of stainless powder has a very high ta.
It is shown that n δ and ε r ″ are shown, and an excellent electromagnetic wave absorbing material is obtained by the present invention. In addition, since the composite material containing 50% by volume of stainless steel powder has a too low volume resistivity, In addition, the results of measuring the bending strength by the three-point bending test and the fracture toughness by the SEVNB method are also shown in Table 2 together with the results of the MAS glass single phase. , Both strength and toughness are improved compared to MAS glass single phase,
It can be seen that the present invention can provide an excellent electromagnetic wave absorber having high mechanical properties.

[0020]

[Table 1]

[0021]

[Table 2]

Example 2 An alumina powder (AK of 99.99% purity) (AK
P-30; manufactured by Sumitomo Chemical Co., Ltd. and Mo powder (MA-60; manufactured by Showa Denko) having a particle size of 53 to 10 μm in a volume ratio of 85:15 to manufacture a composite material in the same manner as in Example 2. did. The hot press temperature is 1600 ° C and the pressure is 3
It was set to 00 kg / cm ² . In the same manner as in Example 1, 10M
The relative permittivity (εr ′) at Hz and the dielectric loss tan δ are obtained, and from these, the complex relative permittivity (εr ″ = εr ′ × tan)
δ; εr ′: real part, εr ″: imaginary part), and high tan δ of 100.5, 11.5, and 1156, respectively.
And εr ”are shown, indicating that the electromagnetic wave absorption characteristics are excellent. In addition, the bending strength was determined by a 3-point bending test to determine the SEVNB.
Bending strength of 40kg /
High values of mm ² and fracture toughness of 9.7 MPam ^1/2 were obtained.

Example 3 ZrO ₂ powder (3Y; manufactured by Tosoh) and Co (300 mesh under; manufactured by Kojundo Chemical Laboratory Co., Ltd.) in a volume ratio of 80: 2.
A composite material was produced in the same manner as in Example 2 so that the value was 0. The hot press temperature was 1400 ° C. and the pressure was 300 kg / cm ² . In the same manner as in Example 1, 1
Relative permittivity (εr ') and dielectric loss tan at 0MHz
δ is calculated from these and the complex relative permittivity (εr ″ = εr ′ × t
An δ; εr ′: real part, εr ″: imaginary part) are obtained, and tan δ and ε are high as 90, 3.5 and 315, respectively.
r ”, indicating that the electromagnetic wave absorption characteristics are excellent.
The bending strength was measured by a 3-point bending test and the fracture toughness was measured by the SEVNB method. The bending strength was 88 kg / m.
High values of m ² and fracture toughness of 13.5 MPam ^1/2 were obtained.

[Brief description of drawings]

FIG. 1 is a scanning electron microscope photograph instead of a drawing showing a particle structure of a mixed powder after ball milling in Example 1 of the present invention.

FIG. 2 is an optical microscope photograph instead of a drawing showing a particle structure of a mixed powder after ball milling in Example 1 of the present invention.

FIG. 3 is an optical microscope photograph instead of a drawing showing the structure of the composite material obtained in Example 1 of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiko Shintoku 5 Ube, Ube City, Yamaguchi Prefecture 5 1978, Kobe, Ube Ube Laboratory Ltd.

Claims (4)

[Claims] 1. A radio wave absorbing material comprising a composite material comprising glass or ceramics as a matrix and metal particles as a composite phase. 2. The electromagnetic wave absorbing material according to claim 1, wherein the metal particles of the composite phase are flat and ductile metal particles. 3. The electromagnetic wave absorbing material according to claim 1, wherein the volume ratio of the composite phase is 2 to 40%. 4. The composite phase metal is Ti, V, Cr, Z.
r, Nb, Mo, Hf, Ta, W, Fe, Ni, Co,
The electromagnetic wave absorbing material according to claim 1 or 2, which is at least one selected from Cu, Al, Mg, Zn and alloys thereof, stainless steel, permalloy and super heat resistant alloy.