JP2001199764A - Conductive ceramic and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive ceramic which can easily be produced, exhibits stable conductivity at the ordinary temperature, and has high safety. SOLUTION: This conductive ceramic characterized by mixing the raw material of an alumina-based ceramic with a carbon source, molding the mixture and then sintering the molded product in a >=1,400 deg.C reducing atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive ceramic and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, ceramics having electrical insulation properties have been used for various electronic parts and electric materials.

For example, in the production of alpha-alumina ceramics, various additives are mixed with finely divided alumina raw material, pulverized, mixed with a high molecular organic compound called a binder, and spray-dried. After the granulation is performed, the granulated material is press-formed and then fired in a high-temperature oxidizing atmosphere to form a ceramic.

In some cases, extrusion molding is performed after adjusting the water content without using a spray dryer, and similarly, ceramics are formed by firing in a high-temperature oxidizing atmosphere.

[0005] Alumina-based ceramics, which has been conventionally treated as an oxide-based ceramic, naturally has a fixed concept of being heat-treated in an oxidizing atmosphere.
At present, sintering is performed in a high-temperature oxidizing atmosphere.

[0006] On the other hand, recently, research and development of ceramics having conductivity have been carried out, and examples thereof include those using rare metals which have been studied as superconducting materials,
There are research reports such as those combining gamma-alumina and sodium, or those using various metals and their oxides.

[0007]

However, in the above-mentioned conventional conductive ceramics, the temperature range in which conductivity is exhibited is limited, and development of a ceramic exhibiting conductivity at room temperature has been desired. In addition, metal oxides for which many studies have been made have a problem that their stability and harmfulness are concerned.

[0008] The present invention is to solve the above problems,
An object of the present invention is to provide conductive ceramics which are easy to manufacture, exhibit stable conductivity at room temperature, and have high safety.

[0009]

A conductive ceramic according to the present invention for achieving the above object is characterized in that a raw material of an oxide ceramic and a carbon source are mixed, molded, and fired.

According to the above construction, the raw material of the oxide ceramic having electrical insulation and the carbon source having conductivity are mixed, molded, and fired, whereby the physical and chemical characteristics of the ceramic are improved. After holding, conductivity can be imparted.

Further, the carbon source is advantageous because it can withstand a high temperature of 1400 ° C. or more when firing ceramics, and is a harmless, safe and stable substance in the air.

It is preferable that the raw material of the oxide ceramic is a raw material of alumina ceramic.

[0013] Further, since carbon is oxidized under high temperature conditions and is released as carbon dioxide gas into the atmosphere, the calcination is performed in any of a reducing atmosphere, a vacuum atmosphere, or an atmosphere in an inert gas. Oxidation of the source can be prevented.

It is preferable that the carbon source is a natural or synthetic organic substance which can exist as carbon in a high-temperature reducing atmosphere.

When the carbon source is a solid, it is preferable that the carbon source be a fine powder having a particle diameter of 10 μm or less at the time of molding.

In the method for producing a conductive ceramic according to the present invention, the raw material of an oxide ceramic and a carbon source are mixed and molded, and then the molded product is reduced to a temperature of 1400 ° C. or more in a reducing atmosphere, a vacuum atmosphere, It is characterized by being fired in any of the atmospheres in the active gas.

According to the above configuration, the conductive ceramic can be easily manufactured without oxidizing the carbon source.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a conductive ceramic according to the present invention and a method for producing the same will be specifically described with reference to the drawings. FIG. 1 is an electron micrograph showing a conductive ceramic composition obtained by mixing and molding graphite at a content of 0.5% with alumina as an example of the conductive ceramic according to the present invention, and FIG. 2 according to the present invention. As an example of conductive ceramics, alumina contains graphite 1.0%
FIG. 3 is an electron micrograph showing the composition of a conductive ceramics mixed, molded, and fired.

FIG. 3 shows an example of the conductive ceramics according to the present invention.
Fig. 4 is an electron micrograph showing the composition of the conductive ceramics mixed, molded and fired at 5%, and Fig. 4 shows a mixture of alumina and graphite at a content of 5.0% as an example of the conductive ceramics according to the present invention. Fig. 5 is an electron micrograph showing the composition of the formed and fired conductive ceramics. Fig. 5 shows an example of the conductive ceramics according to the present invention, in which graphite was mixed with alumina at a content of 10.0%, formed and fired. FIG. 3 is an electron micrograph showing the composition of a conductive ceramic.

FIG. 6 is a view showing the electric resistance of a conductive ceramic obtained by mixing and molding alumina with graphite at different contents as an example of the conductive ceramic according to the present invention, and FIG. FIG. 3 is a view showing voltage-current characteristics of a conductive ceramic obtained by mixing and molding graphite with alumina at different contents as an example of the conductive ceramic according to the present invention, and firing.

FIG. 1 to FIG. 5 show that an alumina raw material, which is a raw material of an alumina-based ceramic which is an example of an oxide ceramic as a conductive ceramic according to the present invention, contains graphite as a carbon source in a content of 0.5% and 1.0. 0%, 2.5
%, 5.0% and 10.0%, mixed, and molded. The molded product was used as a reducing atmosphere in an electric furnace in which nitrogen gas was constantly introduced at a heating rate of 1000 ° C./60 minutes for 160 minutes.
The composition of the conductive ceramic obtained by firing at a constant temperature of 0 ° C. for 2 hours and lowering the temperature to room temperature in the same reducing atmosphere is shown.

Each of FIGS. 1 to 5 is an electron microscope photograph at a magnification of 200 times, and the index length shown at the bottom of each figure is 100 μm. In each figure, the black portions indicate carbon grains 1 and the other portions such as white other than black indicate crystal grains 2 of alumina.

As shown in FIGS. 1 to 5, the graphite content was 0.5%, 1.0%, 2.5%, 5.0%, 1%.
As the amount increases to 0.0%, carbon particles per unit area 1
Are increasing.

In addition, as shown in FIGS. 4 and 5, it can be observed that in the region where the amount of added graphite is large, the crystal grains 2 of alumina formed are large and the carbon particles 1 are accumulated around the periphery.

Further, no product obtained by reaction between alumina and graphite could be confirmed by X-ray diffraction. That is, it is considered that there is no chemical reaction between both alumina and graphite, and the physical and chemical properties of each of them are not hindered even after firing in a reducing atmosphere at a high temperature of 1600 ° C.

Therefore, in a conductive ceramics composed of alumina having electrical insulation and graphite having conductivity, it is considered that electricity flows only through graphite, and when electricity is passed through, the closest carbon is used. Grain 1
It is thought that the exchange of electrons takes place between the two.

In the region where the amount of graphite is large as shown in FIGS. 4 and 5, it is considered that the current is supplied while bypassing the periphery of the large alumina crystal grains 2.

FIG. 6 shows that the contents of graphite were 3.0%, 4.0%, 5.0%, 7.0%, and 1% in the alumina raw material, respectively.
After adding and mixing at 0.0% and molding, the molded product is fired at a constant temperature of 1600 ° C. for 2 hours at a heating rate of 1000 ° C./60 minutes in an electric furnace in which nitrogen gas is constantly introduced as a reducing atmosphere. Then, the electric resistance value of the conductive ceramic obtained by lowering the temperature to room temperature in the reducing atmosphere was measured.

The measured conductive ceramics were 10 mm wide,
Using a plurality of strip-shaped test pieces A to I having a height of 4 mm (cross-sectional area of 40 mm ² ) and a length of 50 mm, a probe of a tester to which a DC voltage is applied is connected to each test piece A to I in length It was measured at room temperature in contact with both ends (interval of 50 mm) in the direction.

In FIG. 6, test pieces A and B have a graphite content of 3.0%, test pieces C and D have a graphite content of 4.0%, and test pieces E and F have a graphite content of 5.0. %, The test pieces G and H are set to a graphite content of 7.0%, and the test piece I is set to a graphite content of 10.0%.

Here, the graphite content is 3.0%,
For 4.0%, 5.0%, and 7.0% conductive ceramics, two test pieces were measured, and for the conductive ceramics with 10.0% graphite content, one test piece was measured. .

As shown in FIG. 6, the test pieces having the same graphite content have substantially the same electric resistance value, and the test pieces E to I having the graphite content of about 3.0% or more have conductive ceramics. It was found that the electrical resistance of the sample was substantially constant.

By controlling the graphite content, the electric resistance of the conductive ceramics can be changed to a desired value, and the electric resistance is stable when the graphite content is equal. It turned out to show a substantially constant value.

The electric resistance of the conductive ceramics is 100Ω to 100kΩ at room temperature, so that it can be widely used as an electric resistor incorporated in various electric circuits and electronic circuits.

Other possible applications include fixed or variable electrical resistors, electrical wiring components,
The present invention can be applied to bearings and bearing parts utilizing characteristics of carbon, in addition to electric fields such as sensing units of various sensors, antistatic materials, and anti-microbial materials.

FIG. 7 shows each test piece A shown in FIG.
To I, a DC constant voltage is applied to both ends of the DC ammeter by a constant voltage DC power supply, and the current value flowing through each test piece A to I at room temperature is measured. -Measured current characteristics.

In FIG. 7, the horizontal axis represents voltage (V), and the vertical axis represents current (m).
A) is shown. The voltage applied to each of the test pieces A to I by the constant voltage DC power supply is 5V, 10V, 20V, 30V.
V, 40V, 50V, each test piece A ~ I
The value of an ammeter connected in series to was measured.

As shown in FIG. 7, the voltage-current characteristics of each of the test pieces A to I of the conductive ceramic change substantially linearly with a substantially constant gradient in the range of DC voltage 5V to 50V. It turned out to be. As a result, the electric resistance value of the conductive ceramic is determined by the applied voltage (current flowing).
It was found that the value showed a stable and almost constant value irrespective of the value of.

Therefore, when the conductive ceramic is incorporated as an electric resistor in various electric circuits, electronic circuits, and the like, it can function as an electric resistor showing a stable electric resistance value in a voltage range generally applied. It has been found.

The raw materials for the oxide ceramics include, in addition to the above-mentioned raw materials for the alumina ceramics, silica ceramics, zirconia ceramics, alumina / silica ceramics, cerium oxide ceramics, magnesia ceramics, titania ceramics. Raw materials such as ceramics, mullite ceramics, spinel ceramics, and cordierite ceramics can be applied, and the firing temperature at that time depends on the characteristics of each raw material.

After the oxide ceramic material and the carbon source are mixed and molded, firing is performed in an atmosphere in which oxygen and air are shut off in order to prevent oxidation of the carbon source. The firing may be performed in a reducing atmosphere such as a hydrogen gas or a hydrocarbon gas at 1400 ° C. or higher, may be performed in a vacuum atmosphere at 1400 ° C. or higher, or may be performed in a nitrogen gas at 1400 ° C. or higher. The sintering may be performed in an atmosphere of an inert gas such as a gas or an argon gas.

The carbon source is preferably any of various organic substances, natural or synthetic, which can be present as carbon in a high-temperature reducing atmosphere in addition to the above-mentioned graphite. It is preferable that the fine powder has a particle diameter of 10 μm or less at the time of molding the base ceramics.

The reason why the fine powder having a particle diameter of 10 μm or less during molding is that the fine powder having a particle diameter of more than 10 μm (for example,
After adding a carbon source (fine powder of about 50 μm), the mixture is pulverized with a mill or the like at the time of mixing, so that the carbon source becomes a fine powder having a particle diameter of 10 μm or less at the time of molding.

That is, when the particle size of the carbon source is several μm or more, it can be used in the pulverizing step of mixing the raw material of the oxide ceramic with the carbon source in the same manner as other additives in the pulverizing process.
When the particle size of carbon itself is sufficiently small, such as carbon black, it can be used simultaneously with mixing of the binder.
Moreover, it can also mix after granulation.

As the carbon source, powder of charcoal, coke or the like, carbon black or the like can be applied in addition to the above-mentioned graphite.

When a raw material of alumina-based ceramics is used as a raw material of oxide-based ceramics, additives such as silica or kaolin having a content of 30% or less may be appropriately added in order to adjust the specific gravity.

According to the above configuration, it is possible to provide a conductive ceramic which is easy to manufacture, exhibits stable conductivity at room temperature, and has high safety.

That is, a raw material of an electrically insulating oxide-based ceramic and a conductive carbon source are mixed, molded, and fired to maintain the physical and chemical properties of the ceramic. Conductivity can be imparted.

Further, the carbon source is advantageous because it can withstand a high temperature of 1400 ° C. or more when firing ceramics, is a harmless and safe substance in the air.

Further, as compared with the conventional conductive ceramics in which the temperature range showing the conductivity is limited, it is possible to obtain stable conductivity at room temperature and in a wide temperature range. Preferred without instability or harm.

Further, since carbon is oxidized under high temperature conditions and released as carbon dioxide gas into the atmosphere, calcination is performed in any of a reducing atmosphere, a vacuum atmosphere, or an atmosphere in an inert gas, so that the carbon source is reduced. Can be prevented from being oxidized.

[0052]

Since the present invention has the above-described structure and operation, it is easy to manufacture and exhibits stable conductivity at room temperature.
A highly safe conductive ceramic can be provided.

That is, a raw material of an electrically insulating oxide-based ceramic and a conductive carbon source are mixed, molded, and fired to maintain the physical and chemical properties of the ceramic. Conductivity can be imparted.

Further, the carbon source is advantageous because it can withstand a high temperature of 1400 ° C. or more when firing ceramics, is a harmless substance, is safe and stable in the air.

Further, as compared with the conventional conductive ceramics in which the temperature range showing the conductivity is limited, it is possible to obtain stable conductivity at room temperature and in a wide temperature range. Preferred without instability or harm.

Further, since carbon is oxidized under high temperature conditions and released as carbon dioxide gas into the atmosphere, calcination is performed in any of a reducing atmosphere, a vacuum atmosphere, or an atmosphere in an inert gas, so that the carbon source is reduced. Can be prevented from being oxidized.

[Brief description of the drawings]

FIG. 1 is an electron micrograph showing a conductive ceramic composition obtained by mixing and molding alumina at a content of 0.5% with alumina as an example of a conductive ceramic according to the present invention, followed by firing.

FIG. 2 is an electron micrograph showing the composition of a conductive ceramic obtained by mixing and molding graphite at a content of 1.0% with alumina as an example of the conductive ceramic according to the present invention, and firing the mixture.

FIG. 3 is an electron micrograph showing the composition of a conductive ceramic obtained by mixing and molding alumina with graphite at a content of 2.5% as an example of the conductive ceramic according to the present invention, and then firing.

FIG. 4 is an electron micrograph showing the composition of a conductive ceramic obtained by mixing, shaping, and sintering alumina with graphite at a content of 5.0% as an example of the conductive ceramic according to the present invention.

FIG. 5 is an electron micrograph showing the composition of a conductive ceramic obtained by mixing and molding alumina at a content of 10.0% with alumina as an example of the conductive ceramic according to the present invention, followed by firing.

FIG. 6 is a view showing an electric resistance value of a conductive ceramic obtained by mixing and molding graphite with alumina at a different content as an example of the conductive ceramic according to the present invention, and firing.

FIG. 7 is a diagram showing voltage-current characteristics of a conductive ceramic obtained by mixing and molding graphite at different contents with alumina as an example of the conductive ceramic according to the present invention, and then firing.

[Explanation of symbols]

 1. Carbon particles 2. Alumina crystal particles A to I: Test pieces

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tateo Ogaya 1-56, Miyamae-cho, Mizunami-shi, Gifu Wing Hi-Cera Co., Ltd. No. Haneda Hume Tube Co., Ltd. F-term (reference) 4G030 AA36 AA60 BA02 GA11 GA24 GA26 5G301 CA02 CA12 CA30 CD04 CE02

Claims (6)

[Claims] 1. A conductive ceramic obtained by mixing a raw material of an oxide-based ceramic and a carbon source, molding and firing the mixture. 2. The conductive ceramic according to claim 1, wherein the raw material of the oxide-based ceramic is a raw material of an alumina-based ceramic. 3. The conductive ceramic according to claim 1, wherein the firing is performed in any of a reducing atmosphere, a vacuum atmosphere, and an atmosphere in an inert gas. 4. The conductive ceramic according to claim 1, wherein the carbon source is a natural or synthetic organic substance that can exist as carbon in a high-temperature reducing atmosphere. 5. The carbon source has a particle size of 10 μm during molding.
The conductive ceramic according to any one of claims 1 to 4, wherein the conductive ceramic is the following fine powder. 6. An oxide ceramic material and a carbon source are mixed and molded, and then the molded product is fired in a reducing atmosphere at 1400 ° C. or higher, a vacuum atmosphere, or an atmosphere in an inert gas. A method for producing a conductive ceramic, comprising: