JP5270499B2 - Radio wave absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio wave absorber which has processability capable of thinning and has enough radio wave absorption characteristic even if being thin. <P>SOLUTION: A porous silicon carbide radio wave absorber uses a silicon carbide material powder having a mean particle size of 2 &mu;m or less and a particle size distribution of D90/D10&le;10, and contains 300 to 1,000 ppm of the total of ratios of elements, wherein the elements are one or more elements among Al, Fe, Ca, Mg, and Na. Furthermore, the porous silicon carbide radio wave absorber contains 100 to 500 ppm of Al and Fe respectively and 100 ppm or less of one or more elements among Ca, Mg, and Na respectively. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

The present invention relates to a thin and light porous ceramic radio wave absorber.

Radio wave absorbers are used in various devices to prevent noise and radio wave interference between various devices. Conventionally, a composite of magnetic powder such as ferrite and dielectric powder or short metal fiber with a resin or the like is often used.

However, when a resin is used as the radio wave absorber, there is a problem that the absorbed radio wave generates heat and deteriorates or deforms due to heat conversion.

Therefore, the applicant has a radio wave absorber that is made of porous silicon carbide ceramics that does not contain resin and has excellent heat resistance and durability, and that can efficiently absorb radio waves in a wide frequency range of about 25 to 45 GHz. Proposed.

JP 2003-226579 A

However, in recent years, various devices have been made lighter, smaller, and thinner as seen in mobile phones and notebook computers. In the case of a radio wave absorber made of only porous ceramics as in Patent Document 1, the thickness is reduced. However, workability is insufficient, and sufficient radio wave absorption characteristics may not be obtained even if the thickness is reduced.

Further, in recent years, automobiles have been digitized, and the in-vehicle radio wave absorber is required to have durability and reliability that can be used even in harsh environments. Therefore, if the device is thin when it is thinned or the radio wave absorption property is not sufficient, a device such as an in-vehicle radar that enables automatic operation may malfunction, leading to a serious accident.

The present invention has been made in view of these problems, and provides a radio wave absorber having a workability that can be reduced in thickness and having sufficient radio wave absorption characteristics even when the thickness is low.

The present invention provides the following (1) to (4) in order to solve such problems.
(1) A silicon carbide raw material powder having an average particle size of 2 μm or less and a particle size distribution of D90 / D10 ≦ 10 is used, and at least one of Al, Fe, Ca, Mg, or Na is used in a total element ratio of 300 A porous silicon carbide radio wave absorber comprising -1000 ppm.
(2) The porous silicon carbide radio wave absorber according to (1), which contains 100 to 500 ppm of Al and Fe, respectively.
(3) The porous silicon carbide radio wave absorber according to (1) or (2), which contains 100 ppm or less of at least one of Ca, Mg, and Na.
(4) The porous silicon carbide radio wave absorber according to (1) to (3), which is a thin plate having a thickness of 0.5 mm or less.

It is possible to provide a radio wave absorber that has sufficient strength for thinning and has sufficient radio wave absorption characteristics even if it is thin.

Hereinafter, the radio wave absorber of the present invention will be described in detail.

The radio wave absorber of the present invention is made of porous silicon carbide. When microwave to millimeter wave radio waves are incident on a porous silicon carbide radio wave absorber, the incident waves are absorbed by scattering, reflection and attenuation inside the silicon carbide having a porous structure. Can be efficiently absorbed. Especially, the electromagnetic wave absorber of the present invention is effective for attenuation of a frequency of 15 to 30 GHz.

Porous silicon carbide contains one or more of Al, Fe, Ca, Mg, or Na in a total element ratio of 300 to 1000 ppm. By including these, in the solid phase sintering, there is an effect of lowering the necking start temperature of the particles. Thereby, it is possible to perform strong particle bonding and maintain workability while maintaining a desired porosity by low-temperature sintering.

In particular, by including both Al and Fe, the particle binding force in low-temperature sintering can be increased. When these are not included, the workability is lowered, and thin plate processing becomes difficult. Moreover, sintering at a high temperature is required, and it becomes difficult to control the porosity.

It is preferable to contain 100 to 500 ppm of Al and Fe. By including a predetermined amount, a porous body having a desired porosity and particle binding force can be obtained by low-temperature sintering. Moreover, by making these amounts into the above ranges, the workability in processing the porous body into a thin plate can be enhanced. Furthermore, even when the porous body is processed into a thin plate, sufficient radio wave absorption can be maintained.

As described above, in addition to containing 100 to 500 ppm of Al and Fe, it is preferable to contain 100 ppm or less of one or more of Ca, Mg, or Na. By including these, the necking start temperature of particles in solid phase sintering can be lowered. A more preferable range of these contents is 0.1 to 100 ppm, and a more preferable range is 1 to 100 ppm.

The average particle diameter of the silicon carbide raw material powder is preferably 2 μm or less. Further, in addition to the average particle size, the particle size distribution is more preferably D90 / D10 ≦ 10. Low-temperature sintering is facilitated by setting the average particle size to 2 μm or less. The reason why the particle size distribution is determined as described above is to improve workability when processing into a thin plate. By having a sharp particle size distribution, the particle binding force can be increased. In addition, there is an effect of making the load applied to the porous body uniform during processing and making it difficult to break. In the present invention, the median diameter (D50) determined by laser diffraction particle size distribution measurement is used as the average particle diameter of the ceramic powder molded particles. D90 and D10 are also values obtained by laser diffraction particle size distribution measurement.

The radio wave absorber of the present invention is a thin plate having a thickness of 0.5 mm or less. In the case of a conventional porous body, in order to obtain such a thin plate, the pores of the porous body had to be filled with resin to increase the strength. However, when a resin is used as a radio wave absorber as described above, heat is generated to convert the absorbed radio wave into heat, and it deteriorates or deforms. It is not preferable. In addition, since the radio wave vibrates inside the pores of the porous body and exhibits a great attenuation effect, the attenuation effect is also reduced when it is filled with resin. The present invention has been found that by containing a predetermined amount of Al and Fe and Ca, Mg or Na, an extremely thin radio wave absorber can be obtained without filling pores with resin. Furthermore, in addition to these contents, workability can be further improved by specifying the average particle size and particle size distribution of the raw material powder. In the present invention, it is possible to produce a thin plate having a thickness of 0.3 mm or less.

The porosity of the porous body is preferably 10 to 40%. Within such a range, both radio wave absorptivity and workability can be achieved, so that a thin radio wave absorber can be obtained.

Next, the manufacturing method of the electromagnetic wave absorber of this invention is demonstrated.

The silicon carbide powder preferably has an average particle size and particle size distribution as described above, and an oxygen content of 3.0% by mass or less. This is because if the oxygen content is high, even if B or C is added by solid phase sintering, the oxygen content cannot be removed, particle bonding becomes insufficient, and the workability deteriorates. Further, impurities other than Al, Fe, Ca, Mg, and Na are preferably 0.01% or less.

Al and Fe can be added in the form of various compounds in addition to oxides. Ca, Mg or Na can be added in various forms such as carbonates and hydroxides in addition to oxides. Moreover, these content can be made into the quantity containing the impurity contained in the raw material powder of silicon carbide.

These raw material powders are mixed and then molded. For forming, various methods such as uniaxial pressing, press forming such as CIP, and casting using slurry can be used. In the case of press molding, granules obtained by adding a binder, a plasticizer or the like to the raw material powder and granulated by a spray drying method may be used.

After molding, firing is performed. Firing can be performed in a temperature range of 1600 to 2000 ° C. in an inert atmosphere such as argon, helium, and nitrogen.

The obtained sintered body is processed into a thin plate shape having a thickness of 0.5 mm or less. For processing, a commonly used method such as surface grinding can be employed.

Hereinafter, the present invention will be described in more detail with reference to test examples.

[Test Example 1]
As a sintering aid, 2% carbon and 0.6% boron carbide were added to a silicon carbide powder having an average particle size of 0.7 μm and a particle size distribution D90 / D10 = 5.5. Fe and Al, and Ca, Mg and Na were added and mixed so as to have the contents shown in Table 1, and then press molded at a molding pressure of 50 MPa to produce a molded body. The obtained molded body was fired in Ar at a temperature of 1700 ° C. to produce a silicon carbide sintered body. The obtained silicon carbide sintered body was processed into a shape of 5 × 20 × 0.3 mm by surface grinding. The average particle size and particle size distribution were determined by laser diffraction particle size distribution measurement.

A silicon carbide sintered body is inserted into a sample holder, and a radio wave absorption characteristic when a 20 GHz radio wave is irradiated to each sample using a linear waveguide (apparatus: WRJ220) by a waveguide method is measured with a network analyzer. It measured using. The results are shown in Table 1.

As a result, no. In 3-7, 9 and 10, the attenuation amount exceeding 10 dB was shown, and it was confirmed that excellent radio wave absorption ability was exhibited.
On the other hand, No. which is outside the scope of the present invention. Nos. 1 and 2 were damaged during processing. In 8, 11, and 12, the radio wave absorptivity decreased.

[Test Example 2]
Next, tests were performed using different silicon carbide powders having different average particle sizes and particle size distributions. The average particle size and particle size distribution were determined by laser diffraction particle size distribution measurement.

2% carbon and 0.6% boron carbide are added to silicon carbide powder with an average particle size of 0.4 to 2.5 μm as a sintering aid, and Fe and Al are added to each contain 300 ppm and mixed. After that, press molding was performed at a molding pressure of 50 MPa to produce a molded body. The obtained molded body was fired in Ar at a temperature of 1800 ° C. to produce a silicon carbide sintered body. The obtained silicon carbide sintered body was processed into a shape of 5 × 20 × 0.3 mm by surface grinding.

A silicon carbide sintered body is inserted into a sample holder, and a radio wave absorption characteristic when a 20 GHz radio wave is irradiated to each sample using a linear waveguide (apparatus: WRJ220) by a waveguide method is measured with a network analyzer. It measured using. The results are shown in Table 2.

As a result, no. In 21-24, the attenuation amount exceeding 10 dB was shown, and it was confirmed that excellent radio wave absorption ability was exhibited. On the other hand, No. which is outside the scope of the present invention. In 25-27, workability was bad and a radio wave absorber could not be obtained.

Claims (4)

Silicon carbide raw material powder having an average particle size of 2 μm or less and a particle size distribution of D90 / D10 ≦ 10 is used, and contains at least one of Al, Fe, Ca, Mg, or Na in a total element ratio of 300 to 1000 ppm A porous silicon carbide radio wave absorber characterized by comprising: 2. The porous silicon carbide radio wave absorber according to claim 1, which contains 100 to 500 ppm of Al and Fe, respectively. 3. The porous silicon carbide radio wave absorber according to claim 1, comprising at least 100 ppm of at least one of Ca, Mg, and Na. 4. 4. The porous silicon carbide wave absorber according to claim 1, wherein the porous silicon carbide wave absorber is a thin plate having a thickness of 0.5 mm or less.