JP2005306698A - Ceramic composition and wave absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a ceramic composition and a wave absorber where a superior wave absorbing effect is obtained and which can alter a frequency band capable of absorbing electric waves. <P>SOLUTION: The ceramic composition is obtained by baking a material containing barium titanate and 0.006 pt.wt. or more and 1.1 pts.wt. or less of lithium oxide per barium titanate of 100 pts.wt. The wave absorber comprises a material involving the ceramic composition. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a porcelain composition and a radio wave absorber. More specifically, the present invention relates to a porcelain composition and a dielectric wave absorber that have a large dielectric loss tangent (tan δ) in a specific frequency band and can provide an excellent wave absorption effect.

  A radio wave absorber is a material that is used to convert the energy of incident radio waves (electromagnetic waves) into heat energy and absorb unnecessary radio waves that cause malfunctions and performance degradation of devices. Today, such electromagnetic wave absorbers are used in the interior of precision electronic equipment, ETC peripheral parts, indoor walls using wireless LAN, exterior wall materials such as buildings, roads, and tunnels, peripheral parts of medical equipment, etc. It is used for various purposes.

The types of materials used for the radio wave absorber can be roughly classified into three types: a resistive radio wave absorption material, a magnetic radio wave absorption material, and a dielectric radio wave absorption material.
Resistive electromagnetic wave absorbing material is made by depositing a conductive thin film such as tin oxide or indium oxide on a protective film such as polyethylene terephthalate and sticking it to an insulating spacer such as a glass plate or resin. A structure with a metal film attached is typically used to accelerate the electrons inside the material by the electric field of the radio wave and convert the energy of the radio wave into thermal energy generated when the electrons collide. It is.
The magnetic wave absorbing material is typically made of a magnetic material such as ferrite, and utilizes the fact that the followability of the magnetic moment in the magnetic material to the external AC magnetic field depends on the frequency of the external AC magnetic field. It is.
Dielectric electromagnetic wave absorbing materials are typically made by blending conductive materials such as carbon and silicon carbide into insulating materials such as resin and rubber, which converts radio wave energy into thermal energy by dielectric loss. is there. Recently, attention has been focused on dielectric radio wave absorption materials using a ceramic composition (ceramics) as a material for radio wave absorbers having heat resistance and weather resistance that can be applied even in harsh external environments. As an example of such a dielectric wave absorbing material, a dielectric ceramic composition disclosed in Patent Document 1 is known.

JP 2003-335576 A

When making electromagnetic wave absorbers such as the inner and outer walls of buildings using dielectric electromagnetic wave absorbing materials, there is an “antireflection curve” that shows the correspondence between the real and imaginary parts of the complex permittivity obtained by solving Maxwell's equations. Design guide (for theoretical explanation, see, for example, Osamu Hashimoto, published by Nikkan Kogyo Shimbun [June 29, 2001], “None of radio wave absorbers”). Therefore, if a radio wave absorber is produced using a dielectric loss material having a complex dielectric constant on the line of the non-reflection curve and further above the non-reflection curve, a radio wave absorber having an excellent radio wave absorption effect can be realized. It can be said that it is possible.
However, even though the conventional dielectric loss material has a large dielectric loss tangent, it has a complex dielectric constant that is located below the non-reflection curve, so that a sufficient radio wave absorption effect cannot be obtained. In addition, since the frequency band in which the dielectric loss tangent (tan δ) varies greatly cannot be changed, it is practically impossible to design a radio wave absorber that can absorb radio waves in the target frequency band (that is, has a large dielectric loss). I had a problem.

  Then, this invention makes it a subject to provide the porcelain composition and electromagnetic wave absorber which can obtain the outstanding electromagnetic wave absorption effect. It is another object of the present invention to provide a porcelain composition and a radio wave absorber that can change the frequency band of radio waves that can be absorbed.

In order to solve the above problems, the inventions described in the following (1) to (6) are configured.
(1) A porcelain composition obtained by firing a material containing barium titanate and lithium oxide.
(2) A porcelain composition obtained by firing a material containing barium titanate and 0.006 parts by weight or more and 1.1 parts by weight or less of lithium oxide with respect to 100 parts by weight of the barium titanate.
(3) The porcelain composition according to (1) or (2), wherein the porcelain composition is processed into powder, fiber, flake, film, or granule.
(4) A radio wave absorber made of a material containing the porcelain composition according to any one of (1) to (3) above.
(5) A radio wave formed by laminating a matching layer made of a material having a dielectric constant smaller than the dielectric constant of the radio wave absorber on the surface of the radio wave absorber described in (4) formed in a predetermined shape. Absorber.
(6) A method for producing a porcelain composition comprising a step of firing a material containing barium titanate and 0.006 parts by weight or more and 1.1 parts by weight or less of lithium oxide with respect to 100 parts by weight of the barium titanate. .

  ADVANTAGE OF THE INVENTION According to this invention, the porcelain composition and electromagnetic wave absorber which have a big dielectric loss tangent (tan-delta) can be provided. Moreover, the porcelain composition and electromagnetic wave absorber which can change the frequency band of the electromagnetic wave which can be absorbed can be provided.

Hereinafter, embodiments of the present invention will be described in detail.
The porcelain composition of the present invention is a porcelain composition obtained by firing a material containing barium titanate (BaTiO ₃ ) and lithium oxide (Li ₂ O). More preferably, a material containing barium titanate (BaTiO ₃ ) and 0.006 parts by weight or more and 1.1 parts by weight or less of lithium oxide (Li ₂ O) with respect to 100 parts by weight of the barium titanate is fired. It is a porcelain composition obtained. That is, a preferable blending ratio of these two kinds of raw materials is 0.006 parts by weight or more and 1.1 parts by weight or less of lithium oxide (Li ₂ O) with respect to 100 parts by weight of barium titanate (BaTiO ₃ ). . When this is expressed in terms of mole, it is 0.05 mol% or more and 8 mol% or less of lithium oxide with respect to 100 mol% of barium titanate.

The barium titanate used as a raw material of the porcelain composition of the present invention may be any barium titanate obtained by a conventionally known method, and the origin and production method of barium titanate are not particularly limited. For example, barium titanate obtained by mixing and heating titanium oxide and barium carbonate can be used as a raw material for the porcelain composition of the present invention. Barium titanate used as a raw material may contain inevitable impurities that could not be excluded in the purification process. For example, metal oxides such as Al ₂ O ₃ , CaO, Fe ₂ O ₃ , and ZrO ₂ may be contained as impurities. In addition, SrO or the like may be added in advance for a multilayer capacitor or the like.

The lithium oxide (Li ₂ O) used as a raw material for the porcelain composition of the present invention may be lithium oxide obtained by a conventionally known method, and the origin and production method of lithium oxide are not particularly limited. For example, lithium oxide obtained by oxidizing lithium carbonate (Li ₂ CO ₃ ) by heating, lithium oxide obtained by heating metallic lithium, or the like can be used as a firing material for the ceramic composition of the present invention. .
Note that lithium oxide used as a raw material may contain inevitable impurities that could not be excluded in the purification process. For example, inevitable impurities such as Al ₂ O ₃ , metal oxides exemplified by CaO, Fe ₂ O ₃ , ZrO ₂ , Na ₂ O, MgO, K ₂ O and the like may be contained. .

  The lithium oxide used as a raw material of the porcelain composition of the present invention may be added to the material before firing in other modes such as lithium carbonate. That is, after being added in the form of lithium carbonate in the material before firing, the lithium carbonate is oxidized during the firing to change into lithium oxide, whereby a firing material containing barium titanate and lithium oxide is obtained. You may make it obtain. In this case, since the material containing barium titanate and lithium oxide is fired from the middle of firing, as a result, the porcelain composition of the present invention can be similarly obtained. The amount of lithium carbonate added to barium titanate is such that the lithium oxide after oxidation of lithium carbonate is 0.006 to 1.1 parts by weight with respect to 100 parts by weight of barium titanate. Adjust it.

By firing a material containing barium titanate and lithium oxide, the porcelain composition of the present invention can be obtained. In addition to barium titanate and lithium oxide, other substances may be added to the material before firing.
For example, in order to adjust the dielectric constant or tan δ of the ceramic composition after firing, other substances such as metal oxides and nitrides may be added. In addition, water serving as a dispersion medium for uniformly mixing the raw materials, or an organic binder (such as polyvinyl alcohol) for forming and baking the material into a predetermined shape may be added. Thus, even a porcelain composition obtained by firing a raw material containing a substance other than barium titanate and lithium oxide can be included in the scope of the present invention.

The porcelain composition of the present invention can be processed into various shapes such as powder, fiber, flake, film, or granular. For example, the porcelain composition of the present invention can be processed into a powder form by pulverization in an alumina porcelain mortar. The porcelain composition thus processed into a powder form is convenient for producing a radio wave absorber molded into a predetermined shape. For example, a radio wave absorber molded into a predetermined shape can be produced by adding a binder to a porcelain composition processed into a powder, forming the powder into a predetermined shape with a molding die, and then sintering. Moreover, when the porcelain composition processed into powder is actually used as a radio wave absorber on the inner and outer walls of a building, it can be easily mixed with other materials such as resin and paint.
When molding the porcelain composition of the present invention into a predetermined shape, various known ceramic molding methods can be used. For example, various ceramic forming methods such as hot isostatic pressing can be used.

The porcelain composition of the present invention is excellent in heat resistance and corrosion resistance, and is suitably used for outdoor exposure use. For example, it can be suitably used in an environment exposed to sunlight including ultraviolet rays or an environment exposed to moisture such as rainwater. In addition, since changes with time of various characteristics including electrical characteristics are small, it can be used as a dielectric wave absorbing material having excellent long-term reliability. Moreover, it can mix with resin, rubber | gum, etc., and can be used as a sheet-like and film-like electromagnetic wave absorber. For example, it can be used in a state where it is laminated with a metal reflector for reflecting radio waves from outside.
The ceramic composition of the present invention has a very high dielectric constant because the main component of the raw material is barium titanate. Therefore, it is very advantageous to realize a thin wave absorber. For example, it has a characteristic that it is very advantageous for producing a thin and flat wave absorber or a thin and sheet wave absorber.

  The porcelain composition of the present invention can be applied as a material for a radio wave absorber used for various purposes. Fields that can be applied include, for example, electronic circuit boards, packages, communication equipment, electromagnetic environment preservation members, medical equipment, microwave transceiver equipment peripheral members, microwave heating equipment peripheral members, automobiles, ships, aircraft, radar peripheral members, These include toll gate peripheral members, building materials, bridges, building outer walls, towers, tunnel inner walls, roads, paints, indoor wireless LAN inner walls, and the like.

  In Example 1, the porcelain composition of the present invention was produced, and the dielectric constant and dielectric loss tangent (tan δ) of the produced porcelain composition were measured.

[Base adjustment]
The following three types of materials were prepared as materials for the porcelain composition of the present invention.

(1) Barium titanate (BaTiO ₃ , commercially available product): 50 g
(2) Additive A: predetermined amount (3) Water (tap water): 60 ml

In order to compare the case of firing a material containing lithium oxide (Li ₂ O) with respect to barium titanate and the case of firing a material containing other substances, the above additives As A, the following three types of substances were prepared.

(1) Li ₂ CO ₃ : reagent special grade (manufactured by Kishida Chemical Co., Ltd.)
(2) B ₂ O ₃ : Reagent grade 1 (Wako Pure Chemical Industries, Ltd.)
(3) Trisodium citrate: food additive (manufactured by Kanto Chemical Co., Inc.)

Of the above three types of substances, Li ₂ CO ₃ is a substance that changes to lithium oxide (Li ₂ O) during firing. Trisodium citrate is a substance that changes to sodium oxide (Na ₂ O) during firing. That is, in this example, a material containing three kinds of substances of Li ₂ O, B ₂ O ₃ , and Na ₂ O, which are relatively light element oxides, is fired against barium titanate. The porcelain compositions obtained were compared. Each content, referred to 100 parts by weight of barium titanate, Li ₂ O is 0.40 parts by _weight, B 2 _{O 3} is 0.92 parts by weight, Na ₂ O is 0.82 parts by weight. When these amounts are expressed in terms of mole, barium titanate is about 3 mol% with respect to 100 mol%.

  The raw materials prepared as described above were placed in a polyethylene bottle having a capacity of 1000 ml together with 1000 g of porcelain stone (made of zirconia, 10 mmφ), and mixed at a rotational speed of 36 rpm for 24 hours. Next, 0.5 g of polyvinyl alcohol (degree of polymerization: 500) was added to the bottle and mixed at a rotational speed of 36 rpm for 0.5 hour. The obtained mixed slurry was passed through a 60-mesh sieve to remove impurities, and the slurry was vacuum-lyophilized and then passed through a 60-mesh sieve to obtain a base material for firing.

[Molding]
The substrate obtained in the above-described process was molded into a columnar shape having a height of about 9 mm at a pressure of 30 MPa using a metal mold having a diameter of 15 mm. Next, a hydrostatic pressure of 250 MPa was applied to the molded substrate to form a firing sample.

[Baking]
A sample for firing was fired in an electric furnace. At this time, while changing the temperature at the time of baking, the size and weight of the sample were measured, and the baking temperature at which the density of the fired product was maximized was determined.

〔processing〕
In order to measure dielectric properties in a relatively low frequency band of the porcelain composition obtained by firing, a test piece having a size of 11 mmφ × 6 mm was prepared by subjecting both end faces to surface grinding. In addition, in order to measure dielectric properties in a relatively high frequency band of the porcelain composition obtained by firing, an 11 mmφ fired product was processed to a thickness of 1 mm, gold was deposited on both end faces, and then cut into a size of 1 mm × 1 mm. A test specimen was prepared. Furthermore, in order to measure the dielectric characteristics in the high frequency band, a test piece cut out to a size of 57 mm × 57 mm × 0.2 mm was prepared.

[Measurement]
Using the prepared test piece, the dielectric constant (ε ′) and the dielectric loss tangent (tan δ) when the frequency of the radio wave was changed were measured.
The measurement method used impedance analyzer HP419A (made by Agilent Technologies) based on the principle of the impedance method (capacitor method) about the range of frequencies from 100 MHz to 1 MHz. For a frequency range of 1 MHz to 1.8 GHz, an impedance material analyzer 4291B (manufactured by Agilent Technologies) was used based on the principle of the impedance method (capacitor method). For frequencies ranging from 18 GHz to 26.5 GHz, 26.5 GHz to 40 GHz, 50 GHz to 75 GHz, and 75 GHz to 110 GHz, based on the principle of the free space method, a network analyzer 8510C (manufactured by Agilent Technologies) and a dielectric lens are used. An attached horn antenna (HVS, USA) was used.
The measurement results are shown in Table 1 below. Moreover, the graph of a measurement result is shown in FIG. 1, FIG.

As shown in Table 1, FIG. 1 and FIG. 2, only when Li ₂ O is added to the raw material for firing, a sudden decrease in dielectric constant ε ′ and a sudden increase and decrease in tan δ in a band near a frequency of 0.52 MHz. It was confirmed that the dielectric dispersion phenomenon occurred.
That is, for a porcelain composition obtained by firing a material containing barium titanate and lithium oxide, radio waves in a specific frequency band can be absorbed by adjusting the amount of lithium oxide added and the like. It was possible to confirm that it could be applied as a material for radio wave absorbers.

In order to further confirm the above conclusion, an experiment was performed under the same conditions as in the above example except that the amount of lithium oxide added was changed. That is, a porcelain composition was produced by firing a material containing 0.039 parts by weight of lithium oxide with respect to 100 parts by weight of barium titanate, and the dielectric constant ε ′ and tan δ of the produced porcelain composition were measured. . In addition, when content of lithium oxide is expressed in terms of mole, it is about 0.3 mol% lithium oxide with respect to 100 mol% barium titanate.
The measurement results of the dielectric constant ε ′ and tan δ are shown in Table 2 below.

As shown in Table 2, for the porcelain composition obtained by firing a material containing 0.039 parts by weight of lithium oxide with respect to 100 parts by weight of barium titanate, the dielectric constant ε in a band near a frequency of 6.3 GHz. It was confirmed that the dielectric dispersion phenomenon of 'sudden decrease and tan δ sudden increase and decrease occurred.
That is, the porcelain composition obtained by firing a material containing barium titanate and lithium oxide can absorb radio waves in a specific frequency band by adjusting the amount of lithium oxide added and the like. It was confirmed that it could be a material for the absorber.

  In Example 2, a radio wave absorber was produced using the porcelain composition obtained in Example 1, and the radio wave absorption characteristics of the radio wave absorber were measured. The used porcelain composition is a porcelain composition obtained by firing a material containing barium titanate and 0.039 parts by weight of lithium oxide with respect to 100 parts by weight of the barium titanate.

[Production of radio wave absorber]
The porcelain composition obtained in Example 1 was ground to form a plate-like piece having a size of 55 mm × 55 mm × 0.2 mm. A matching layer (also called a matching layer) having a thickness of 0.5 mm was laminated on one surface of both sides of the plate-like piece. This matching layer is a layer formed of a material having a dielectric constant relatively smaller than that of the main body of the radio wave absorber. For example, ceramic, glass (including glaze), resin, a mixture of resin and ceramics, etc. It is a layer to be formed. In this embodiment, ceramics having a dielectric constant ε ′ = 21 is used as the matching layer. By laminating such matching layers, radio waves incident on the radio wave absorber can enter the interior without being reflected by the surface.

[Measurement of radio wave absorption characteristics]
The radio wave absorption characteristics of the radio wave absorber produced as described above were measured by the free space method. This free space method is a well-known method described in Osamu Hashimoto, “Introduction to Wave Absorber” [Morikita Publishing Co., Ltd. (1997)]. Specifically, a plane wave or a focused wave is focused on a plate specimen. This method is capable of measuring the dielectric loss tangent, dielectric constant, radio wave absorption characteristic, etc. in the high frequency band by entering the reflected beam and obtaining the reflection / transmission characteristics.
In this example, each of the radio wave reflected on the surface of the radio wave absorber and the radio wave transmitted through the back surface of the radio wave absorber was absorbed by the radio wave attenuation [dB], that is, the radio wave absorber. The amount of radio waves was measured. These measurement results are shown graphically in FIG.

  As shown in FIG. 3, the radio wave absorber manufactured in this example has an absorption amount of reflected radio waves in a band near a frequency of 32 GHz of about −44 dB, and an absorption amount of reflected radio waves in a band near a frequency of 95 GHz. The result was about -31 dB. In addition, the result was that the amount of transmitted radio waves absorbed was approximately −20 dB or less. From these results, it was confirmed that the radio wave absorber produced in this example sufficiently satisfied the level of radio wave absorption of −20 dB to −30 dB which is considered to be a practical level.

Li 2 _O, is a graph showing the results of measurement of dielectric constant and dielectric loss tangent of the B ₂ O ₃ ceramic composition obtained by firing a material containing. It is a graph showing the results of measurement of dielectric constant and dielectric loss tangent of the ceramic composition obtained by firing a material containing Na 2 _O. It is a graph which shows the measurement result of the radio wave absorption amount of a radio wave absorber.

Claims (6)

A porcelain composition obtained by firing a material containing barium titanate and lithium oxide. A porcelain composition obtained by firing a material containing barium titanate and 0.006 to 1.1 parts by weight of lithium oxide with respect to 100 parts by weight of the barium titanate. The porcelain composition according to claim 1 or 2, wherein the porcelain composition is processed into powder, fiber, flake, film, or granule. An electromagnetic wave absorber made of a material containing the porcelain composition according to any one of claims 1 to 3. A radio wave absorber formed by laminating a matching layer made of a material having a dielectric constant smaller than that of the radio wave absorber on the surface of the radio wave absorber according to claim 4 formed in a predetermined shape. A method for producing a porcelain composition comprising a step of firing a material containing barium titanate and 0.006 parts by weight or more and 1.1 parts by weight or less of lithium oxide with respect to 100 parts by weight of the barium titanate.

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