JPH0147405B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat-treated carbon material having high electrical conductivity. More specifically, the present invention relates to a highly conductive carbon-based heat-treated product characterized in that a pyrolyzed product obtained by vapor-phase pyrolysis of a halogen-substituted organic compound is heat-treated at a temperature higher than that of the pyrolysis.

In recent years, it has been discovered that complex compounds of natural or artificial high-purity graphite and electron acceptors or electron donors (hereinafter referred to as dopants) exhibit high electrical conductivity comparable to that of metals, and have attracted attention as highly conductive materials. It's starting to feel like this.

As this type of highly conductive carbon material, highly oriented high purity pyrolyzed graphite obtained by vapor phase pyrolysis of a hydrocarbon compound and further heat treatment at an ultra-high temperature is known. For example, it is produced by heat-treating the product of high-temperature pyrolysis of hydrocarbons such as methane at an ultra-high temperature of 2800°C or higher while applying uniaxial pressure.

Also, hydrocarbons such as methane and benzene,
At 950℃~1300℃, using iron fine particles as a catalyst,
It is known that fibrous pyrolytic carbon is produced, and it is also known that conductivity can be improved by heat treatment.

Carbon materials obtained by gas-phase pyrolysis of hydrocarbon compounds containing only carbon and hydrogen can be heated to 2800℃.
A graphite structure is obtained only by performing the above heat treatment.

It was also known that it forms an intercalation compound with a dopant and becomes a highly conductive material. That is,
Conventionally, carbon materials known as highly conductive materials comparable to metals are limited to those with a highly developed graphite structure made from hydrocarbon compounds as starting materials. It was something that gave rise to sexuality.

However, it is known that heat treating a carbon raw material at high temperatures does not necessarily result in a graphite structure, and that the type of starting carbon material has a great influence on the subsequent heat treatment effect.

For example, even if carbon fibers obtained by heat-treating organic fibers such as polyacrylonitrile, pitch, and rayon are heat-treated at higher temperatures, the conductivity hardly improves; It only shows an electrical conductivity of 10 ³ S/cm or less, and there is almost no effect of improving electrical conductivity due to the formation of a complex compound of the dopant. Carbon fiber is lightweight and widely used as an industrial material with excellent strength and elasticity, but its electrical conductivity is inferior to metal materials, so its use is limited to heating elements and antistatic materials that do not require high conductivity. This is the current situation.

On the other hand, regarding the thermal decomposition of compounds containing halogens, 1,2-dichloroethylene was thermally decomposed on a graphite substrate at a low temperature of 700℃ to 1100℃, and carbon Methods of manufacturing coatings are known. However, the pyrolytic carbonized product obtained by this method exhibits a maximum electrical conductivity of about 350 S/cm, which cannot be said to be highly electrically conductive.

The present inventors extensively studied compounds containing halogen, and as a result, discovered a new fact and arrived at the present invention.

In other words, when using not only 1,2 dichloroethylene but also halogen-containing compounds, especially organic compounds that have saturated or carbon-carbon double bonds and also contain halogens, it is possible to heat them at lower temperatures than hydrocarbons. It has been found that a uniformly glossy pyrolytic carbon deposit can be formed on a heat-resistant molded substrate that is susceptible to decomposition at temperatures below 950°C. This indicates that the conductivity hardly changes even when a dopant is applied. Moreover, it was surprisingly discovered that conductivity was significantly improved when heat treatment was performed at a temperature higher than the thermal decomposition temperature.

Furthermore, the inventors have discovered that such a secondary heat-treated pyrolytic carbonized product can be easily complexed with a dopant, thereby further improving the electrical conductivity, thereby achieving the present invention.

It has not been previously known that heat treatment of such a thermally decomposed product of a halogen compound significantly improves the conductivity, and that the conductivity is further improved by the action of a dopant.

That is, the purpose of the present invention is to thermally decompose an organic compound having a saturated or carbon-carbon double bond and containing a halogen atom at a temperature of 500°C or higher in an inert atmosphere, and then heat-treating it at a higher temperature. An object of the present invention is to provide a highly conductive carbon-based heat-treated product and a highly conductive composition containing the carbon-based heat-treated product and a dopant as essential components.

As the halogen compound of the present invention, an organic compound having at least one halogen atom can be used. The halogen atom is preferably chlorine or bromine-iodine.

In the present invention, saturated or unsaturated organic halogen compounds having a carbon-carbon double bond are widely used. Examples of the saturated organic halogen compound include ethyl iodide and propyl iodide.
Halogen-substituted unsaturated compounds have a particularly large heat treatment effect on conductivity. That is, halogen-substituted aromatics in which a halogen atom is directly substituted on the aromatic ring; for example, chlorobenzene, bromobenzene, iodobenzene, p-dibromobenzene, p-diiodobenzene, O-diiodobenzene, etc. adjacent to the aromatic ring. Compounds in which a halogen atom is substituted on the carbon; for example, benzyl chloride, benzyl bromide,
Benzyl iodide, benzylidene dibromide, benzylidene trichloride, p-xylylene dichloride, p-xylylene dibromide, O-xylylene chloride, O-xylylene dibromide, p-
Xylidene tetrabromide, halogen-substituted aliphatics with a halogen atom directly substituted on the double bond; e.g. vinyl chloride, vinyl bromide, 1,2-dichloroethylene, 1,2-dibromoethylene, Aliphatic compounds in which halogen atoms are substituted on adjacent carbons; for example, allyl chloride, allyl bromide, allyl iodide, 1,4-dibromo-2-butene,
It may be 1,4-dichloro-2-butene, or an alicyclic or heterocyclic compound, and examples thereof include 3,6-dichloro-1-cyclohexene, 1-chloromethylcyclopentene, and 1-chloromethylnorbornadiene.

Among these, halogen-substituted unsaturated compounds easily produce homogeneous, glossy pyrolytic carbon deposited at a pyrolysis temperature of 1000°C or less, and the effect of heat treatment is remarkable. Particularly preferred are compounds having a halogen on a carbon adjacent to a double bond, such as a compound having a halogen atom substituted on a carbon adjacent to an aromatic ring, or a compound having a halogen atom substituted on a carbon adjacent to an aliphatic double bond. That is, it is a group of compounds typified by aryl halides, benzyl halides, and the like.

When carrying out thermal decomposition, for example, when a decomposition product is obtained in the form of a powder, the target product can be obtained independently even without the presence of a base material. In the case of forming a carbon-coated molded article, the shape and type of the base material can be selected arbitrarily. For example, molded body base materials include powder, spherical, irregularly shaped, fibrous, sheet-like,
It is possible to use a shape such as a tape shape, a tube shape, or any other irregularly shaped shape.

In the present invention, a base material having heat resistance is preferable,
Examples include molded bodies made of heat-resistant resin, quartz glass, alumina, silicon nitride, silicon carbide, boron nitride, carbon, etc., which retain the shape of the base material during the subsequent heat treatment step.

Thermal decomposition temperature varies depending on each compound, but generally 500°C or higher is used. In particular, if the thermal decomposition is carried out at as low a temperature as possible, the generation of soot can be suppressed and shiny carbon deposits can be produced. This phenomenon is in contrast to the tendency of hydrocarbon compounds to turn into soot, and is one of the characteristics of halogen compounds. The heat treatment for imparting high conductivity is carried out at a temperature higher than the thermal decomposition of the halogen compound, in the temperature range of 8500° C. or lower. External indirect heating is preferred in order to uniformly deposit the carbon-based coating.

Pyrolysis and heat treatment must be carried out in an inert atmosphere.

In thermal decomposition, the halogen-substituted compound may be used as it is or in an inert atmosphere gas such as argon,
It may be introduced into the heating section along with nitrogen or the like, or it may be introduced into the heating section under reduced pressure.

The pyrolysis product obtained in this way is 10 to ^{10 3} S/
It shows conductivity of cm. What should be noted is that even if doping is performed by a conventional method, the conductivity will hardly improve.

In other words, high conductivity is achieved only after the next heat treatment step, and the effect of improving conductivity due to doping appears.

The heat treatment temperature is limited by the temperature at which the shape of the base material is maintained; for example, for quartz glass molded base materials,
It can be carried out at 1200°C or lower, 2000°C or lower for ceramic molded base materials, and 3500°C or lower for carbon molded base materials. There is no particular limitation on the heat treatment time, but generally a time in the range of 1 minute to 120 minutes is sufficient.

The electrical conductivity of the carbon-based heat-treated product thus obtained is significantly higher than that of the original pyrolyzed product, ranging from 10 ² to
Improved to 10 ⁴ S/cm. In other words, it is considered to have an easily graphitizable carbon structure. It was totally unexpected that it would exhibit such conductivity at relatively low temperatures of 800°C to 2500°C.

More importantly, by doping this heat-treated product with an electron acceptor or an electron donor, the conductivity is further improved, reaching 10 ³ to ^{10 5} S/cm. The dopant is not particularly limited, but compounds that have been found to have high conductivity in conjugated polymers such as graphite, polyacetylene, and polypyrrole can be effectively used.

The doping method can be carried out by a known method, ie, a method of direct contact with a dopant in a gas phase or liquid phase, an electrochemical method, an ion implantation method, or the like.

Specifically, electron acceptors include halogen compounds: bromine, etc., Lewis acids: iron trichloride, arsenic pentafluoride, antimony pentafluoride, boron trifluoride, sulfur trioxide, aluminum trichloride, antimony pentachloride, etc. , protonic acids: nitric acid, sulfuric acid, chlorosulfonic acid, etc., electron donors: alkali metals: lithium, potassium, rubidium, cesium, etc., alkaline earth metals: calcium, strontium, barium, etc., other rare earth metals: ( Sm, Eu, Yo),
Acid amides: potassium amide, calcium amide, etc. are exemplified. There is no particular restriction on the amount of doping, but the preferred content is 0.1% per weight of the heat-treated product.
~150%, especially 10% to 100%.

The highly conductive composition of the carbon-based heat-treated material and the dopant according to the present invention can be used in various applications that provide conductivity. In addition to further increasing the conductivity of carbon-based substrates, it is also characterized by the ability to easily process the surfaces of insulating molded substrates such as quartz glass and ceramics to significantly increase their conductivity, making it ideal for a variety of electronic and electrical materials. Application is possible.

The present invention will be described in more detail with reference to Examples below, but the present invention is not limited thereto.

Example 1 A quartz glass furnace core tube (30 mmφ x 700 mmL) was inserted into a resistance wire-heated horizontal tubular electric furnace (450 mmL), and a glass container for storing and supplying raw materials was inserted into one end of the furnace core tube. Furthermore, the device was constructed so that inert gas could be introduced from the top. A quartz plate (2 cm x 5 cm) was placed as a base material in the furnace core tube at the center of the electric furnace.

2 grams of p-xylylene dichloride as a raw material was placed in the above-mentioned glass container, and 100 ml of nitrogen gas was passed per minute to raise the temperature in the electric furnace to 950°C. Furthermore, a ribbon heater for heating the raw material is wrapped around the exposed part of the quartz glass furnace core tube from the electric furnace, and then p-
xylylene dichloride with a ribbon heater, 180
It was heated to ℃ and poured into the furnace core tube in the gas phase to perform thermal decomposition. After continuing the thermal decomposition for 1 hour, the electric furnace and ribbon heater were turned off, and the sample was taken out after cooling to room temperature. A homogeneous, silvery-white, shiny deposit of pyrolytic carbon had formed on the quartz plate. The electrical conductivity of this pyrolysis deposit was 84/S/cm.

The obtained deposit was in the form of a thin film and could be peeled off from the quartz plate. This was carried out in an argon gas atmosphere using a graphite electrically heated tubular furnace.
Heat treatment was performed at 2500°C and 2750°C for 15 minutes.

The electrical conductivity of the heat-treated products obtained was 5.7×10 ³ S/
cm, improved to 9.7×10 ³ S/cm. Furthermore, when sulfuric anhydride was used as an electron acceptor compound and gas phase doping was performed at room temperature for 3 days using a conventional method, the conductivities were further improved to 9.9×10 ⁴ S/cm and 7.1×10 ⁴ S/cm. did.

The electrical conductivity of the pyrolysis deposits without heat treatment was not improved by vapor phase doping with sulfuric anhydride.

Example 2 P-xylylene dichloride was prepared under the same conditions as in Example 1 except that polyacrylonitrile carbon fiber (diameter 7μ) was used as the base material instead of the quartz plate.
Pyrolysis at 950°C was carried out for 1 hour. When the obtained pyrolytic carbon-coated carbon fiber was observed with a scanning electron microscope, it was found that it was uniformly coated with a carbon layer having a thickness of about 0.5 μm.

This was heat-treated at 2500°C for 15 minutes in an argon atmosphere using a graphite electrically heated tubular furnace. The electrical conductivity of the obtained heat-treated product is 1.7×10 ³ S/
improved to cm. Furthermore, when this was subjected to gas phase doping with anhydrous sulfuric acid for 3 days, the result was 1.4×10 ⁴ S/
cm and further improved. In addition, the doping rate with nitric acid was 2.0×10 ⁴ S/cm. On the other hand, when the carbon fiber used as the base material was heat-treated at 2500°C under the same conditions, it was 1.2 × 10 ³ S/cm, but the value doped with sulfuric anhydride was 5 × 10 ³ S/cm, and the value doped with nitric acid was 6 The improvement in conductivity was small at ×10 ³ S/cm. This fact indicates that the pyrolytic carbon-coated carbon fiber makes a large contribution to improving conductivity.

Example 3 P-xylylene dichloride was thermally decomposed at 950°C under the same conditions as in Example 1 except that alumina fibers (diameter 20μ) and quartz short fibers (diameter 110μ) were used as the base material instead of the quartz plate. I did it for an hour. In both cases, a homogeneous pyrolytic carbon coating was formed on each fiber. The electrical conductivity of each fiber obtained was 120S/cm,
It was 180S/cm.

When pyrolytic carbon-coated alumina fibers were heat-treated at 1500°C and pyrolytic carbon-coated quartz wool was heat-treated at 1200°C, the electrical conductivity of the former improved to 1.7×10 ³ S/cm and the latter to 870 S/cm. When this was doped with sulfuric anhydride, the conductivity was 3.0×10 ³ S/cm and 1.0×
This was further improved to 10 ³ S/cm.

The conductivity of carbon-coated fibers that were not heat-treated did not improve even when doped with anhydrous sulfuric acid.

Example 4 Thermal decomposition was carried out in the same manner as in Example 1, except that allyl chloride or ethyl iodide was used instead of p-xylylene dichloride in Example 1, and the evaporation was performed at room temperature without using the evaporative heating ribbon heater. The electrical conductivities of the pyrolysis deposits at 900° C. for 1 hour were 568 S/cm and 210 S/cm ² , respectively. The conductivity of the film-like material peeled off from the quartz plate base material and heat-treated at 2500℃ for 15 minutes was 7.6×10 ³ 3/cm, respectively.
It improved to 2.1×10 ³ S/cm.

Example 5 In place of p-xylylene chloride in Example 1, p-diiodobenzene was used. Pyrolysis was carried out at 900°C for 1 hour. The electrical conductivity of pyrolysis deposits is
It was 300S/cm. The film-like material peeled off from the quartz plate base material was heat-treated at 2500°C for 15 minutes, and its electrical conductivity improved to 6.3×10 ³ S/cm.

Claims (1)

[Claims] 1. An organic compound having a saturated or carbon-carbon double bond and containing a halogen atom is thermally decomposed at a temperature of 500°C or higher in an inert atmosphere, and then at an even higher temperature and 3500°C. Highly conductive carbon-based heat-treated material obtained by heat treatment at the following temperatures. 2. Thermal decomposition of an organic compound having a saturated or carbon-carbon double bond and containing a halogen atom at a temperature of 500°C or higher in an inert atmosphere, and then heat-treating it at an even higher temperature and a temperature of 3500°C or lower. A highly conductive composition containing a carbon-based heat-treated product obtained by and a dopant as essential components.