JPH0492806A - Production of fine graphite powder - Google Patents

Abstract

PURPOSE:To produce fine graphite powder in which carbon net planes are oriented in one direction by treating specific carbonaceous fiber with a sulfuric acid-containing solution, then quick heating the treated fiber and disintegrating the fiber. CONSTITUTION:With 97-60vol.% concentrated sulfuric acid at 96wt.% concentration, is mixed 3-40vol.% concentrated nitric acid at 68wt.% concentration. Thereby, an acid solution is prepared and then added to ribbon-like carbon fiber having the carbon networks vertically laminated relatively to the longitudinal direction of the fiber, 3.354-3.380Angstrom spacing (d002) thereof, a rectangular or flat elliptical cross section thereof, the major axis of the cross section of >=2 times based on the minor axis, 0.05-0.7mum width and several mum to tens of mum length without any hollow pore parts so as to provide 1-300 ml sulfuric acid based on 1g fiber. The mixture is heated at >=30 deg.C while being stirred to carry out oxidation treatment. The resultant fiber is then filtered, washed with water and dried. The obtained carbon fiber is heated at >=10 deg.C/min rate, kept at >=600 deg.C for >=1sec and then disintegrated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field to which the Invention Pertains] The present invention relates to fine graphite powder, and more particularly to fine graphite powder in which carbon mesh surfaces are aligned in one direction, and a method for producing the same.

[Conventional technology] Fine graphite powder has electrical conductivity, thermal conductivity, mobility, heat resistance,
It has excellent chemical stability and is widely used as conductive coatings, industrial lubricants, antistatic agents, battery materials, heat dissipation materials, and additives for various composites.

For these applications, it is often required that the graphite fine powder has a size of lpm or less.

The conventional method for producing fine graphite powder is to mechanically crush and classify lumps of natural graphite or artificial graphite, but graphite is a highly anisotropic material made of laminated layers of developed carbon networks. Therefore, the carbon mesh surface itself is difficult to break, but on the other hand, the layered direction of the mesh surface is soft and slippery, and such materials can be crushed to 1 μm or less in any three-dimensional direction. That is difficult.

In addition, although it is possible to reduce the particle size to 1 μm or less by mechanical pulverization in some areas, it is very difficult to reduce the particle size to 1 μm or less as a whole. In order to obtain this, an extremely large amount of crushing energy is required.

As a means to solve this problem, there are known methods such as graphitizing carbon powder that is easy to crush, such as coke, and heat treating carbon black, which is originally a fine carbon powder with a particle size of 1 μm or less. It is being

[Problems to be Solved by the Invention] However, in the method using coke or the like, it is difficult to obtain submicron-order fine graphite powder, which is the intended purpose, because it aggregates and coalesces during the graphitization process.

On the other hand, even in the method of graphitizing carbon black, increasing the degree of graphitization itself has its own problems, and, like the coke crushing method, there are problems of agglomeration and coalescence during the graphitization process.

In both cases, when we focus on the microstructure of the fine graphite powder, we find that it is not a graphite structure in which the carbon network surfaces are neatly layered, but a disordered structure, which is different from the structure that is imagined when we call it graphite. Many have different structures.

Furthermore, in both cases, 2000
It is necessary to process at a high temperature of .degree. C. or higher, which poses difficulties in terms of production costs as well as limitations in terms of equipment, including ease of handling.

[Means for Solving the Problem] As a result of intensive study, the inventors of the present invention found that if they selected a starting carbon material with a structure in which fine graphite networks were originally gathered together and crushed it, the above-mentioned results could be achieved. Not only can we solve problems that were difficult to solve with conventional technology, but we are also able to produce graphite fine powder with an almost ideal morphology and microstructure, which was previously thought to be impossible. As a result, the present invention was completed.

That is, an object of the present invention is to provide an unprecedented method for producing fine graphite powder, which has a particle size on the order of submicrons and a controlled microstructure in which the graphite network surface is oriented in one direction. be.

This purpose is achieved by laminating the carbon mesh planes substantially perpendicularly to the length direction of the fibers, and the distance between the planes (d002) is 3.3.
54 to 3.380, and has substantially no hollow pores, the cross section of the fiber is rectangular or flat oval, and the long axis of the cross section is at least twice as large as the short axis. This can be easily achieved by a method for producing fine graphite powder, which is characterized in that it is subjected to oxidation treatment in an acid solution containing sulfuric acid, and then subjected to rapid heating treatment and crushed.

The present invention will be explained in detail below.

The starting carbon material used in the present invention is not particularly limited as long as it has a structure in which fine graphite network planes are assembled, but it has a microstructure in which fine graphite planes are stacked in a one-dimensional direction. is desirable.

Examples of such carbon materials include ribbon-shaped carbon fibers (patent application No. 1-286673) for which the present inventors have applied for a patent.
(No.).

The carbon fibers are fine fibrous carbon produced by the catalytic action of ultrafine metal particles using carbon oxide as a raw material, and have a fiber width of 0.05 to 0.7 μm and a length of several to several tens of pm,
It has a very characteristic microstructure in which the carbon network planes are uniformly stacked perpendicular to the fiber axis, and has a high degree of graphitization even though it is produced at a relatively low temperature.

For example, the d002 (distance between carbon network planes) of the fiber obtained by the reaction at 700°C is 3.366, which is very close to the value of 3.354 for graphite single crystal, and the value of Mering and Me
The degree of graphitization is estimated to be 86% when calculated from the ire formula.

To obtain such highly graphitized carbon, it is usually 2500~
Considering that heat treatment at 3000°C is required, fibers with a high degree of direct graphitization were obtained at an unusually low temperature.

The fibrous carbon is used together with a mixed gas of carbon oxide and hydrogen (mixing ratio 1:1) as a catalyst raw material for fiber growth. Iron pentacarbonyl is added so that the total carbon atom weight is 100 and the iron weight is 1 to 20. 550 to 800
60e /
It can be obtained by continuous insertion at a rate of around hr (Japanese Patent Application No. 1-286673).

Fibrous carbon, which has an ideal microstructure and morphology as a starting material for obtaining fine graphite powder, in which the submicron autograph obtained in this way is laminated in a one-dimensional direction and becomes fibrous, is By crushing as shown in Figure 1, fine graphite powder with a controlled microstructure is obtained.

The method for crushing the carbon fibers is to take advantage of the high graphitizability of this fiber and insert sulfuric acid as an intercalan between the layers used in the production of well-known expanded graphite, followed by heat treatment. It is preferable to crush it by a method such as The oxidation treatment is carried out in an acid solution containing sulfuric acid, more preferably a mixed acid of sulfuric acid and nitric acid. % solution), the volume ratio of sulfuric acid l
Nitric acid is 97/3 to 60/40, more preferably 9515 to 80/20. Regarding the blending of sulfuric acid and the carbon fiber, 1 g of sulfuric acid in the acid solution is used for 1 g of fiber.
It is desirable to use up to 300 ml, more preferably 10 to 200 ml, and the temperature is preferably 30°C or higher, more preferably 50°C or higher, with stirring.

The acid solution treated with the carbon fibers is poured into a large amount of water, and the product is filtered, thoroughly washed with water, and then dried.

The carbon fiber after this sulfuric acid treatment is at least 100C7
The temperature is raised for at least 100°C minutes, preferably at least 100°C minutes, and
The temperature is maintained at 0°C or higher, preferably 800°C or higher for at least 1 second.

Although it is difficult to raise the temperature too rapidly in an electric furnace, the sample, which has been kept at a low temperature, is quickly moved to the heating zone of the electric furnace, which has been preheated to a predetermined temperature. You can also do this by

[Examples] The present invention will be described in more detail below based on Examples, but the present invention is not limited to the Examples unless the gist thereof is exceeded.

Example 1 A mixed acid of concentrated sulfuric acid and concentrated nitric acid (
Add 60 ml of 9:1) and heat at 100°C while stirring.
It was allowed to react for 0 minutes. Drop this into 600m1 of pure water,
After stirring well, the mixture was filtered, washed with water, and dried.

100° away from the heating zone at the end of a quartz reaction tube preheated to 1000°C and placed in an electric furnace.
A quartz container containing the sulfuric acid-treated carbon fibers was placed at a position below C, and the container was quickly moved and held for 3 minutes under a nitrogen atmosphere.

When the sample thus obtained was observed under an electron microscope, the carbon fibers were crushed to produce fine graphite powder, and as shown in Figure 2, the carbon network surface of this fine graphite powder was oriented in one direction. It was confirmed that it has a controlled microstructure.

Table 1 shows the physical properties of the obtained graphite fine powder.

The specific surface area was determined by the nitrogen adsorption method.

X-ray diffraction was measured by the staircase scanning method based on the Jakushin method using silicon single crystal powder as an internal standard.

Table 1 (Effects of the Invention) According to the present invention, fibrous carbon in which highly graphitized carbon network surfaces are stacked substantially perpendicularly to the length direction of the fibers is treated with an acid solution containing sulfuric acid. , followed by rapid heating treatment and crushing to easily produce unprecedented graphite fine powder under relatively low temperature conditions, which has a controlled microstructure in which the carbon network surface is oriented in one direction. I can do it.

The obtained graphite fine powder of the present invention can be widely used as a conductive paint, an industrial lubricant, an antistatic agent, a battery material, a heat dissipating material, and various composite additives.

[Brief explanation of drawings]

Claims (2)

[Claims] (1) The carbon mesh planes are stacked substantially perpendicularly to the length direction of the fibers, and the distance between the planes (d_0_0_2) is 3.35.
4 to 3.380 Å, and has substantially no hollow pores, the cross section of the fiber is rectangular or flat elliptical, and the long axis of the cross section is at least twice as large as the short axis. A method for producing fine graphite powder, which comprises oxidizing it in an acid solution containing sulfuric acid, followed by rapid heating treatment and crushing it. (2) The method for producing fine graphite powder according to claim 1, wherein the oxidation treatment is performed in a mixed acid solution containing sulfuric acid and nitric acid.