JPH03220322A - Fluorinated graphite fiber and production thereof - Google Patents

Abstract

PURPOSE:To obtain the title fiber having excellent stability and conductivity, capable of readily blending with a thermoplastic resin, etc., and suitable for conductive composite material, etc., by graphitizing a carbon fiber grown in vapor phase and obtained by pyrolyzing a carbon compound to provide a graphite fiber having three-dimensional crystal structure and bring the resultant graphite into contact with fluorine. CONSTITUTION:A carbon fiber grown in vapor phase and obtained by pyrolyzing a hydrocarbon compound in non-oxidizing atmosphere in the presence of a catalyst carried on a substrate is graphitized to afford a graphite fiber having three dimensional crystal structure being parallel to fiber axis in hexagonal net face of carbon ad annually oriented in a state of annual ring. The resultant graphite fiber is brought into contact with fluorine to provide the aimed fiber having length of repeating cycle in c axis direction of crystal being within 5-24Angstrom and being lighter than a metal and capable of effectively providing conductivity even in small amount.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to carbon fibers suitable for use in conductive composite materials and the like.

[Conventional technology]

Carbon fiber is lightweight, has excellent mechanical strength, and has good electrical conductivity, so it is used in a variety of application fields by combining metals, plastics, carbon materials, etc. into composite materials.

By the way, carbon materials have inferior conductivity compared to metal materials, so research is underway to improve the conductivity of carbon materials. It is known that intercalation compounds with improved conductivity can be obtained by inserting . Furthermore, a covalently bonded intercalation compound obtained by reacting graphite with fluorine was said to exhibit insulating properties, but it is now possible to create a covalent intercalation compound obtained by reacting graphite with fluorine. It is also known that conductive intercalation compounds can be obtained. However, such intercalation compounds are in the form of powder, and when used as a composite material, it is difficult to obtain uniform and stable conductivity, and there are also problems in that the strength is reduced.

On the other hand, the crystal structure of pinch-type graphite fibers and PAN-type graphite fibers does not develop very well, and intercalation compounds with excellent conductivity have not been obtained, and it is difficult to achieve uniform dispersion as a composite material. That's difficult. Furthermore, on the other hand, there are graphite fibers obtained by graphitizing vapor-grown carbon fibers with a crystal structure that is closer to perfect, and then reacted with nitric acid, metal chlorides, bromine, etc., but these are not stable. It has disadvantages such as poor resistance, electrical resistance increases over time, and equipment that comes into contact with it corrodes due to decomposition products.

[Problem to be solved by the invention]

Therefore, the present invention has developed a graphite intercalation compound fiber that has outstanding stability in the atmosphere and thermal stability, has good conductivity, and is easy to blend with thermoplastic resins and is suitable for use in conductive composite materials. intended to provide.

[Means to solve the problem]

The object of the present invention as described above is to provide an interlayer compound of graphite fibers and fluorine having a three-dimensional crystal structure in which the carbon hexagonal mesh planes are substantially parallel to the fiber axis and oriented in the form of growth rings. This is achieved by using fluorinated graphite fibers characterized by a mixture of repeat period lengths in the C-axis direction ranging from 5 to 24 angstroms.

The fluorinated graphite fiber of the present invention can be produced by graphitizing vapor-grown carbon fiber obtained by thermally decomposing a hydrocarbon compound in a non-oxidizing atmosphere in the presence of a catalyst supported on a substrate to form a carbon hexagonal network surface. It can be produced by obtaining graphite fibers having a three-dimensional crystal structure in which the graphite is substantially parallel to the fiber axis and oriented in the form of growth rings, and then contacting it with fluorine. Furthermore, vapor-grown carbon fiber obtained by contacting an ultrafine metal catalyst suspended in a high-temperature zone with a hydrocarbon compound is graphitized so that the carbon hexagonal network surface is substantially parallel to the fiber axis and It can also be produced by obtaining graphite fibers with a ring-oriented three-dimensional crystal structure and then contacting them with fluorine.

The carbon fiber that is the material of the fluorinated graphite fiber of the present invention contains hydrocarbon compounds such as aromatic hydrocarbons such as toluene, benzene, and naphthalene, and aliphatic hydrocarbons such as propane, ethane, and ethylene, preferably benzene or naphthalene. The raw material is gasified and a catalyst made of ultrafine metal, such as iron, nickel, iron-nickel alloy, etc. with a particle size of 100 to 300 angstroms, is produced in a reaction zone at 900 to 1500° C. with a carrier gas such as hydrogen. It is obtained by contacting and decomposing.

The carbon fibers obtained in this manner are heat-treated at a temperature of 1500 to 3500°C, preferably 2500 to 3000°C, for 3 to 120 minutes, preferably 30 to 60 minutes, in an atmosphere of an inert gas such as argon. The graphite fiber has a three-dimensional crystal structure in which the hexagonal mesh planes are substantially parallel to the fiber axis and oriented in the form of tree rings. In this case, if the heat treatment temperature is lower than 1,500°C, the carbon crystal structure will not develop sufficiently, while if it exceeds 3,500°C, the effect will not be particularly enhanced and it is not economical. Further, when the heat treatment time is shorter than 10 minutes, the heat treatment effect is not sufficient and the degree of development of the crystal structure varies greatly, while on the other hand, when the heat treatment time exceeds 120 minutes, no further improvement is observed.

The carbon fibers thus obtained may be purified as necessary before or after the heat treatment for graphitization, and may be pulverized using a ball mill, rotor speed mill, cutting mill, or other suitable pulverizer. You may. Although such pulverization is not essential, it is preferable to carry out because it facilitates the formation of intercalation compounds and improves the dispersibility when compounding with other materials.

In fluorinating the graphite fiber thus obtained, the temperature is 200°C or lower, preferably -10 to 120°C, for 10 minutes or more, preferably 48 to 72 hours, and the pressure is 10°C.
A method of contacting with fluorine gas at a temperature of 0 Torr or more, preferably 3°O to 1500 Torr is used. At this time, a catalyst such as silver fluoride can be used to promote fluorination.

In proceeding with the above-mentioned fluorination, if the contact temperature between the graphite fiber and the fluorine gas exceeds 200°C, covalently bonded fluorinated graphite is produced, and fibers with excellent conductivity cannot be obtained.

Further, the pressure of the fluorine gas needs to be at least 100 Torr; if it is lower than this, the desired fluorinated intercalation compound cannot be obtained. Further, the contact time between the graphite fiber and the fluorine is required to be 10 minutes or more, and depending on the reaction temperature and pressure, for example, 40 hours or more at normal temperature and normal pressure is suitable. However, if the reaction time becomes too long, the crystal structure will deviate from the desired range, resulting in a decrease in conductivity, which is not desirable.

The fluorinated graphite fiber obtained by applying the above manufacturing conditions has a composition of CsF to C3°F, and the length of the repetition period in the C-axis direction of the crystal is
. is 5 to 24 angstroms.

[Example 1] A liquid in which metallic iron catalyst particles with a particle size of 300 angstroms or less are dispersed in alcohol is applied onto a mullite ceramic plate. A substrate on which the catalyst is dispersed and adhered is placed in a horizontal tubular electric furnace. Then, the temperature was raised to 1000-1)00°C for catalytic decomposition by introducing a mixed gas of benzene and hydrogen to obtain carbon fibers having a length of 2 to 30 m and a diameter of 5 to 50 m.

Next, this carbon fiber was placed in an electric furnace and maintained at 2950 to 3000°C for 30 minutes in an argon atmosphere to graphitize it. The obtained graphite fiber Angstrom, crystal size C-axis direction L
It was confirmed that c(002) was 1000 angstroms or more.

1 g of graphite fiber X obtained in this way and about 1 mg of powdered silver fluoride were mixed lightly and placed in a nickel boat in a nickel reaction tube, and after sufficiently evacuating, high purity fluorine gas was introduced at room temperature. Keeping the pressure at 760 Torr 72
Allowed time to react. Thereafter, argon was introduced into the reaction tube to replace the gas inside, and fluorine was introduced into an alumina-filled adsorption tower to be adsorbed, and fluorinated graphite fiber A was recovered.

Elemental analysis of the obtained fluorinated graphite fiber A revealed that C
, , F composition.

Furthermore, when we measured the length of the repetition period in the C-axis direction of the crystal using X-ray diffraction, we obtained values of 9.42 angstroms and 12.6 angstroms, indicating that the number of intercalation compound stages is 2 and 3. It turned out to be a mixture.

Next, the electrical resistance of this fluorinated graphite fiber A was measured by the DC 4-terminal method, and the stability was investigated by measuring the electrical resistance again after the device was placed in the atmosphere for 3 months. 25 again
High temperature stability was investigated by measuring the electrical resistance after 30 minutes and 3 hours of holding at 0''C.

These measurement results are shown in Table 1 in comparison with the measurement results for untreated graphite fibers X.

Table 1 Electrical resistivity (μΩcn+) A 4.5 No change 4.6 5. OX
6Q 5Q [Example 2
] 1000~1) Metallic iron catalyst particles with a particle size of about 300 angstroms are suspended in a vertical tubular electric furnace whose temperature is adjusted to 00°C without flowing hydrogen from below, and a mixed gas of benzene and hydrogen is added to the metal catalyst particles. was introduced from below and subjected to catalytic decomposition to obtain carbon fibers having a length of 0.01 to 1 m and a diameter of 0.1 to 0.5 μm. Next, this carbon fiber was pulverized for 20 minutes at a rotation speed of 50° rpm using a planetary ball mill (Model P-5, Fritsch Japan Co., Ltd.).

This pulverized carbon fiber was placed in an electric furnace and maintained at 2960 to 3000°C for 30 minutes in an argon atmosphere to graphitize it.

The obtained fibers were found to have a three-dimensional crystal structure in which the carbon hexagonal mesh planes were parallel to the fiber axis and oriented in the form of tree rings, and the lattice constant d0゜2 was 3.3.
7 to 3.40 angstroms, crystal size C-axis direction L
It was confirmed that the graphite fiber had excellent orientation with c(002) of 310 angstroms.

The thus obtained graphite fiber Y was fluorinated by the same procedure as in Example 1, and fluorinated graphite fiber B was recovered.

Elemental analysis of the obtained fluorinated graphite fiber B revealed that C
It was found that it had a composition of a, sF.

Also, the length of the repetition period in the C-axis direction of the crystal was determined by X-ray diffraction method. When measured, values of 9.42 angstroms and 12.6 angstroms were obtained, indicating that the number of stages of the intercalation compound was a mixture of 2 and 3 stages.

1 g of powder of such fluorinated graphite fiber B has a diameter of IC1.
) was placed in a cylinder made of insulating material, sandwiched between upper and lower brass electrodes, and compressed with a pressure of up to It/cm2, and the electrical resistance between the upper and lower electrodes was measured, and the packing density was 1.6 g/c.
The volume resistivity at m3 was determined.

Furthermore, after the device was placed in the atmosphere for 3 months, the electrical resistance was measured again to examine stability. Also, after 30 minutes at 250℃ and 3
The high temperature stability was investigated by measuring the electrical resistance after a period of time.

These measurement results are shown in Table 2 in comparison with the measurement results for untreated graphite fiber Y.

[Example 3] Metallic iron catalyst particles with a particle size of about 100 angstroms were suspended in a vertical tubular electric furnace whose temperature was adjusted to 1000-1) 00°C, and benzene, hydrogen, -carbon oxide, and carbon dioxide were suspended. A mixed gas was introduced from below to cause catalytic decomposition, thereby obtaining carbon fibers having a length of 0.01 to 3 mm and a diameter of 1 to 5 μm. Next, this carbon fiber was crushed in the same manner as in Example 2, graphitized to obtain graphite fiber Z, and further fluorinated to obtain powder of fluorinated graphite fiber C.

The composition and crystal structure of this fluorinated graphite fiber C powder are as follows:
It was completely the same as the fluorinated graphite fiber B obtained in Example 2.

Furthermore, Example 2 regarding the powder of this fluorinated graphite fiber C
Volume resistivity was measured in the same manner as above, and stability in air and high temperature stability were also investigated.

These measurement results are shown in Table 2 in comparison with the measurement results for untreated graphite fiber Z.

Table 2 Electrical resistivity (10-'Ωcm) No change No change = Leaving at 250°C [Example 4] Using graphite fiber Fluorination was carried out in the same manner as in Example 1, except that the reaction was carried out for 48 hours to obtain a fluorinated graphite fiber.

Elemental analysis of the obtained fluorinated graphite fiber revealed that C
It was found that it had a composition of 2° and 2F.

In addition, when the repeating period length Ie in the C-axis direction of the crystal was measured by X-ray diffraction, values of 16.42 angstroms and 19.80 angstroms were obtained, indicating that the number of intercalation compound stages is 4 and 5. It turned out to be.

Next, the electrical resistance of this fluorinated graphite fiber was measured in Example 1.
It was measured using the same DC 4-terminal method.

The measurement results are shown in Table 3 in comparison with the measurement results for fluorinated graphite fiber A and untreated graphite fiber X.

[Comparative Example 1] Using graphite fiber X obtained by the same procedure as Example 1,
Fluorination was carried out in the same manner as in Example 1, except that the fluorine pressure was maintained at 760 Torr and the reaction was carried out for 24 hours, to obtain fluorinated graphite fiber E.

Elemental analysis of the obtained fluorinated graphite fiber E revealed that C
It was found that it had a composition of 4° and 3F.

Also, the length of the repetition period in the C-axis direction of the crystal was determined by X-ray diffraction method. When measured, it was found that the structure of graphite fibers X remained strongly, and the formation of interlayer compounds having a periodic structure could not be confirmed.

Furthermore, the electrical resistance of this fluorinated graphite fiber E was measured using the same direct current four-probe method as in Example 1, and the results are shown in Table 3.

[Example 5] Using graphite fiber X obtained by the same procedure as Example 1,
1444 at room temperature while keeping the fluorine pressure at 760 Torr.
Fluorination was carried out in the same manner as in Example 1, except that the reaction was carried out for 4 hours, to obtain fluorinated graphite fiber F.

Elemental analysis of the obtained fluorinated graphite fiber F revealed that
It was found that it had a composition of C5,,F.

Also, the length of the repetition period in the C-axis direction of the crystal was determined by X-ray diffraction method. When measured, we obtained a very strong value of 5.14 angstroms and a weak value of 9.38 angstroms, indicating that the intercalation compound consists mostly of stage number 1, with a small amount of stage number 2 mixed in. It turns out.

The electrical resistance of this fluorinated graphite fiber F was measured using the same direct current four-terminal method as in Example 1, and the results are shown in Table 3.

Table 3 Sample Electrical resistivity (μΩcm) A4.5 D5.3 El 45 8 Xo 60 : Control example [Example 6] Using graphite fiber Y obtained by the same procedure as Example 2,
Fluorination was carried out by the same method as in Example 4,
Fluorinated graphite fiber G was obtained.

Elemental analysis of the obtained fluorinated graphite fiber G revealed that C
2□1. It was found that it had a composition of F.

In addition, when the repeating period length IC in the C-axis direction of the crystal was measured by X-ray diffraction method, 13.6.17.1 and 2
A value of 0.8 angstroms was obtained, and the number of intercalation compound stages was found to be a mixture of 3.4 and 5.

The electrical resistance of this fluorinated graphite fiber G was measured by the same powder method as in Example 2, and the volume resistivity when the packing density was 1.6 g/cm' was calculated for fluorinated graphite fiber B and untreated graphite fiber. Table 4 shows a comparison with the measurement results for Y.

[Example 7] Using graphite fiber Y obtained by the same procedure as Example 2,
Fluorination was carried out by the same method as in Example 5,
Fluorinated graphite fiber H was obtained.

Elemental analysis of the obtained fluorinated graphite fiber H revealed that 2C
It was found that it had a composition of 6,,F.

When the repeating period length Io in the C-axis direction of the crystal was measured by X-ray diffraction, a weak peak of 5.17 angstroms and strong peaks of 9.41 and 12.78 angstroms were obtained, indicating that the intercalation compound It was found that the majority were stage 2 and 3 with a small amount of stage 1 mixed in.

The electrical resistance of this fluorinated graphite fiber H was measured by the same powder method as in Example 2, and the results are shown in Table 4.

[Example 8] Using graphite fiber Z obtained by the same procedure as in Example 3,
Fluorination was performed in the same manner as in Example 4 to obtain fluorinated graphite fiber I.

Elemental analysis of the obtained fluorinated graphite fiber I revealed that C
It was found that it had a composition of 10,1)F.

Also, the length of the repetition period in the C-axis direction of the crystal was determined by X-ray diffraction method. When measured, values of 16.4 angstroms and 19.8 angstroms were obtained, indicating that the number of intercalation compound stages was a mixture of 4 and 5.

The electrical resistance of this fluorinated graphite fiber I was measured by the same powder method as in Example 2, and the results were
The results are also shown in Table 4 in comparison with the measurement results for untreated graphite fiber Z.

Table 4 [Effects of the Invention] The fluorinated graphite fiber of the present invention is lighter than metal, has higher conductivity than conventional carbon materials, and maintains higher stability than conventional graphite intercalation compounds. There is. Moreover, it has good dispersibility in synthetic resins and the like, and can effectively impart conductivity even in small amounts, making it suitable for use in composite materials and the like.

Claims (3)

[Claims] (1) Consists of an interlayer compound of graphite fibers and fluorine having a three-dimensional crystal structure in which the carbon hexagonal mesh planes are substantially parallel to the fiber axis and oriented in the form of tree rings, and the repetition period in the c-axis direction of the crystal is A fluorinated graphite fiber characterized by having a mixture of lengths ranging from 5 to 24 angstroms. (2) Vapor-grown carbon fiber obtained by thermally decomposing a hydrocarbon compound in a non-oxidizing atmosphere in the presence of a catalyst supported on a substrate is graphitized so that the carbon hexagonal network surface is substantially aligned with the fiber axis. A method for producing a fluorinated graphite fiber according to claim (1), which comprises obtaining graphite fibers having a three-dimensional crystal structure parallel to and oriented in the form of tree rings, and then contacting them with fluorine. (3) Vapor-grown carbon fiber obtained by contacting an ultrafine metal catalyst suspended in a high-temperature zone with a hydrocarbon compound is graphitized so that the carbon hexagonal network plane is substantially parallel to the fiber axis and A method for producing fluorinated graphite fibers according to claim (1), characterized in that graphite fibers having a three-dimensional crystal structure oriented in a ring shape are obtained and then brought into contact with fluorine.