JP4707380B2 - Conductive material - Google Patents

Description

  The present invention relates to a conductive ceramic suitable for a structural material or a component such as an antistatic component, a heater, or a current-carrying component.

  Conductive ceramics are used as structural materials or constituent parts such as antistatic parts, heaters, and current-carrying parts. As conductive ceramics using silicon carbide, for example, those comprising silicon carbide and a metal material capable of imparting conductivity are known (see, for example, Patent Document 1 and Patent Document 2). In addition, in the conductive ceramic of patent document 2, a part of carbon is contained as a sintering aid for the silicon carbide substrate and a resistance value adjusting agent for the ceramic.

Thus, conventionally, when silicon carbide is used as the material for the conductive ceramic, the metal material has been considered to be an essential component because of insufficient conductivity.
Japanese Patent Laid-Open No. 4-6156 Japanese Patent Laid-Open No. 9-221367

  An object of the present invention is to provide a silicon carbide carbon composite-based conductive ceramic having excellent conductivity.

  That is, the gist of the present invention relates to a conductive ceramic containing 10 to 50 parts by weight of carbon with respect to 100 parts by weight of silicon carbide and having a relative density of 92% or more.

  ADVANTAGE OF THE INVENTION According to this invention, the conductive ceramic of the silicon carbide carbon composite type | system | group excellent in electroconductivity used suitably for structural materials or structural components, such as an antistatic component, a heater, and an electricity supply component, can be provided.

  In the conventional conductive ceramics using silicon carbide as a material, the present inventors thought that a metal material was an indispensable component. However, even if a metal material is not included, silicon carbide carbon is used under a certain carbon content. Surprisingly, the present inventors have found that the ceramics can exhibit sufficient conductivity by increasing the relative density of the composite ceramics, thereby completing the present invention. According to the conductive ceramics of the present invention, there is an advantage that there is no oxidative deterioration and high steel properties compared to conventional conductive ceramics containing a metal material as an essential component.

  The conductive ceramic of the present invention contains 10 to 50 parts by weight of carbon with respect to 100 parts by weight of silicon carbide, and the relative density is 92% or more. If the carbon content is less than 10 parts by weight, the electrical conductivity is small, whereas if it exceeds 50 parts by weight, the strength of the structure is insufficient. Further, if the relative density is less than 92%, it is difficult to ensure sufficient conductivity. The carbon content is preferably 12 to 36 parts by weight, more preferably 16 to 26 parts by weight with respect to 100 parts by weight of silicon carbide. The relative density is preferably 95% or more.

  In this specification, the relative density means a value obtained by dividing the bulk density by the theoretical density, and the bulk density is measured according to JIS R1634. When the conductive ceramic is composed of a plurality of components, the theoretical density of each component x the content of each component (% by weight) ÷ 100 is calculated, and the sum of the values for each component thus obtained is calculated. The theoretical density of the entire ceramic.

  The conductive ceramic of the present invention can be produced according to a known method for producing silicon carbide carbon composite ceramics (for example, see JP-A-3-1991164). In addition, the material used for the ceramic of this invention can be used suitably individually or in mixture of 2 or more types, respectively.

  Silicon carbide serves as a ceramic matrix, and may be either α or β crystal form. Further, the purity is not particularly limited, but is preferably 90% by weight or more, more preferably 95% by weight or more because of excellent dispersibility and sinterability. The form of silicon carbide is preferably a powder having an average particle diameter of 5 μm or less because of its good sinterability. In addition, the average particle diameter described in the present specification is measured by, for example, a laser diffraction / scattered light type particle size distribution measuring apparatus (LA700, manufactured by Horiba, Ltd.).

  The conductive ceramic is preferably composed only of silicon carbide having a purity within the above-described preferred range and a carbon source, but may contain an optional component such as a carbide within a range not impairing the effects of the present invention.

The carbon in the conductive ceramic of the present invention is a simple substance of carbon and mainly exists in two phases of a crystalline phase and an amorphous phase. Specifically, amorphous carbon, graphite, etc. are mentioned as a simple substance of carbon. These single crystal phases have a peak from 1450 to 1700 cm ⁻¹ centered around 1580 cm ⁻¹ in the spectrum obtained by measurement by laser Raman spectroscopy. The crystal structure is, for example, a graphite type Although a plane hexagonal structure, a rhombohedral structure, etc. are mentioned, there is no limitation in particular. Further, an amorphous phase has a peak of over the 1300～1450Cm ^-1 centered around 1360 cm ^-1. The peak area ratio (crystal phase / amorphous phase) of the laser Raman spectral intensity between the crystalline phase and the amorphous phase of carbon in the conductive ceramic of the present invention is not particularly limited, but excellent mechanical strength (strength, From the viewpoint of ensuring fracture toughness and the like, it is preferably 1 to 10, more preferably 1 to 5. The peak area ratio is considered to correspond to the degree of graphitization of carbon, and when this value is in the preferred range, good strength and fracture toughness can be achieved. In the measurement of the spectrum, for example, an argon laser spectroscope manufactured by NEC is used.

  In the production of the conductive ceramic of the present invention, the simple substance of carbon is simple, and thus it is preferable to produce it from an appropriate carbon source during the production process. For example, the above silicon carbide, a carbon source described later, and, as desired, commonly used additives and the like (for example, known boron compounds, titanium compounds, aluminum compounds, yttria compounds and other sintering aids) are wet-mixed, Calcinate. By this calcining step, the carbon source is converted into simple carbon. What is necessary is just to adjust suitably the mixing ratio of each raw material in the case of wet mixing so that a composition of electroconductive ceramics may become as above-mentioned.

  The wet mixing may be performed using a ball mill, a vibration mill, a planetary mill, or the like. In addition to water, the solvent used is preferably an organic solvent, for example, an aromatic solvent such as benzene, toluene or xylene, an alcohol solvent such as methanol or ethanol, or a ketone solvent such as methyl ethyl ketone.

  The mixture after wet mixing may be calcined according to a known method if desired, but the viewpoint of maintaining good dispersibility by preventing free sintering of particles while sufficiently converting the carbon source to be used to carbon alone. Preferably, the heat treatment is performed at 400 to 800 ° C. in an inert atmosphere (for example, in an atmosphere of nitrogen gas, argon gas, or the like).

  The carbon source is preferably one that is soluble or dispersible in the organic solvent used for wet mixing and is converted to carbon under the calcining conditions, but is not particularly limited. The properties are preferably spherical and have good crystallinity, and the average particle size is preferably about 5 to 200 μm. The carbon source is preferably an aromatic hydrocarbon since it has a high conversion rate to carbon after calcination, and examples thereof include furan resin, phenol resin, coal tar pitch, and the like, among which phenol resin, coal tar pitch. Are more preferably used.

  Finally, the desired conductive ceramics can be obtained by firing after granulation molding.

  In granulation molding, granulation may be performed by spray drying or the like. On the other hand, the molding may be performed by a mold molding method, a CIP (COLD ISOSTATIC PRESS) method, a slip casting method, or the like.

  Firing may be performed according to a known method, but it is preferably performed at 1800 to 2300 ° C. in an inert atmosphere or under vacuum. Examples of the firing method include a hot press and a HIP (HOT ISOSTATIC PRESS) method. By firing in such a manner, the conductive ceramic of the present invention can be obtained as a sintered body having a desired relative density.

  As described above, desired conductive ceramics can be obtained, but conductive ceramics having sufficient characteristics can be obtained by manufacturing according to the method described above. The volume resistivity of the ceramic is not particularly limited, but is preferably 10 Ω · cm or less, more preferably 1 Ω · cm or less, more preferably 0.1 Ω · cm, from the viewpoint of imparting sufficient conductivity. cm or less. Volume resistivity (also simply referred to as resistivity) is an electrical resistance having a unit cross-sectional area and unit length, and the conductivity can be obtained by calculating the reciprocal thereof. Therefore, the lower the volume resistivity, the higher the conductivity. The volume resistivity can be measured, for example, according to “(1) Insulation Resistance Test” on page 222 of “Ceramics Measurement” (author: Ceramics Readers Editorial Board, Issuer: Ceramic Industry Association).

  The conductive ceramic of the present invention is suitably used as a structural material or a component such as, for example, an antistatic component, a heater, or a current-carrying component.

Examples 1-5 and Comparative Examples 1-2 (However, Examples 1-3 are reference examples.)
The carbon source shown in Table 1, β-silicon carbide having an average particle diameter of 0.5 μm (purity 98 wt%), and B ₄ C 2 wt% as a sintering aid were wet-mixed in ethanol using a vibration mill, and argon gas (Ar ) Calcined at 600 ° C. in an atmosphere. After granulation by spray drying, it was molded by a mold molding method, and then fired for 1 hour in the firing atmosphere and firing temperature shown in Table 1. In Table 1, the carbon content indicates the carbon content relative to 100 parts by weight of silicon carbide. The coal tar pitch has a residual carbon ratio of 53%.

  The obtained conductive ceramic was evaluated for the following characteristics. The evaluation results are also shown in Table 1.

(1) Laser Raman ratio The laser Raman ratio, that is, the peak area ratio (crystalline phase / amorphous phase) of the laser Raman spectral intensity between the crystalline phase and the amorphous phase of carbon is obtained with an argon laser Raman spectrometer manufactured by NEC. It was.

(2) Relative density Relative density was determined by calculating the bulk density according to JIS R1634 and dividing it by the theoretical density.

(3) Volume resistivity Volume resistivity was determined according to “(1) Insulation resistance test” on page 222 of “Ceramic industry measurement” (author: Ceramic Industry Readers Editorial Board, publisher: Ceramic Industry Association).

  From Table 1, it can be seen that if the carbon content is 10 to 50 parts by weight with respect to 100 parts by weight of silicon carbide and the ceramic has a high relative density, the ceramic can obtain excellent conductivity even if it does not contain a metal material.

  The present invention provides a silicon carbide carbon composite-based conductive ceramic having excellent conductivity.

Claims (2)

To silicon carbide 100 parts by weight, 25 to 50 and a weight portion conductive ceramic comprising a carbon of state, and are relative density of 92% or more, and a volume resistivity of 5 × 10 ^-3 Ω · cm conductive material consisting of der Ru ceramics or less. 2. The conductive material according to claim 1, wherein the peak area ratio (crystalline phase / amorphous phase) of the laser Raman spectral intensity between the carbon crystalline phase and the amorphous phase of the conductive ceramic is 1.3 to 1.4 .