JP2002066302A - Nanodiamond and method for preparing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide nanodiamond having a uniform nano size particle diameter useful for a diamond sintered body, slurry abrasive or the like and to provide a method for preparing the nanodiamond. SOLUTION: The nanodiamond is synthesized by heating carbon nanotubes at >=1,600 deg.C under pressure as high as >=10 GPa.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nanodiamond and a method for producing the same. More specifically, the invention of this application relates to a nanodiamond having a nanosized uniform particle size, which is useful as a diamond sintered body, a slurry-like abrasive, or the like, and a method for producing the same.

[0002]

2. Description of the Related Art Diamond is widely used in various industrial fields such as cutting and polishing. For example, in the electronics industry, the capacity of hard disks has been rapidly increased, and the accuracy of grinding has been increasing in terms of improving the surface accuracy of recording media and reducing the interval for writing and reading signals of a magnetic head. The improvement is remarkable. For the grinding and polishing of such a recording medium and a magnetic head, extremely fine diamond particles of so-called micron size or less are used. In particular, as a diamond slurry or a diamond paste, an artificial diamond powder having a D50 value in the nano order by classification is used.

[0003] Artificial diamond is synthesized by a method of synthesizing diamond in the form of a film by a vapor phase (low pressure) synthesis method typified by a chemical vapor deposition method (CVD) or the like, and by a high-pressure synthesis method that simulates natural conditions. A method of synthesizing a granular diamond is known. The high-pressure synthesis method further includes three methods: an impact method, a flux method, and a high-temperature high-pressure method.
Are classified into two methods.

In the impact method, a dynamic impact is applied by, for example, detonating an explosive to directly convert a raw material having a graphite structure into particles having a diamond structure, thereby obtaining granular diamond. However, in this method, since explosives are used, there are problems that various restrictions are imposed on the production process and that unconverted substances such as amorphous carbon and graphite are often mixed, so that it is difficult to obtain a single phase of diamond. .

[0005] In the flux method, for example, a metal catalyst such as iron or cobalt is used, and graphite as a raw material powder is subjected to static pressure of 4 to 6 GPa and 1500 to 2000 GPa.
This is a method of dissolving in a metal catalyst at a temperature of ° C. and then depositing. This method has the disadvantage that it is difficult to control the size of the diamond to be produced because it is a synthetic method involving nucleation.

[0006] The high-temperature high-pressure method is, for example, a high static pressure of 13 to 16 GPa and 3000 to
By holding the raw graphite powder at a high temperature of 4000 ° C. and achieving the stable conditions for diamond,
In this method, graphite powder is directly phase-transformed into diamond.

However, none of the above-mentioned methods has been able to obtain single-phase diamond fine particles having a uniform particle size on the order of nanometers.

On the other hand, it is known that ballas, which is a naturally produced high-purity diamond polycrystal, has extremely high mechanical strength due to the small diameter of the sintered diamond particles. In the study of diamond sintered bodies, it is required to realize a diamond sintered body similar to this ballast, in which nano-sized diamonds are randomly oriented. However, when the grain size of the diamond used is reduced, the crystal grain boundaries increase, so that the amount ratio of the sintering aid increases, and contradiction arises in that ballast containing no sintering aid is far apart. Was gone.

Accordingly, the invention of this application has been made in view of the above circumstances, and solves the problems of the prior art, and is a single phase, useful as a slurry-like abrasive, etc.
An object of the present invention is to provide a nanodiamond having a uniform particle size of nanosize and a method for producing the same.

[0010]

Accordingly, the invention of this application provides the following invention to solve the above problems.

That is, first, the invention of this application provides a nanodiamond characterized in that carbon nanotubes are synthesized by being heated to 1600 ° C. or more at a high pressure of 10 GPa or more. I do.

Secondly, according to the first aspect of the present invention, a nanodiamond characterized in that the carbon nanotube is synthesized by being heated to 1800 ° C. or more at a high pressure of 15 GPa or more, No. 3 provides a nanodiamond characterized by a uniform particle size of 20 to 50 nm, and fourth, a nanodiamond characterized by being octahedral and self-shaped.

A fifth aspect is the method for producing nanodiamond according to any one of the first to fourth aspects, wherein
Pressing the carbon nanotubes to 10 GPa or more,
Provided is a method for producing nanodiamond, wherein the method is heated to 00 ° C. or higher. Sixthly, the present invention provides the method for producing nanodiamond according to the fifth aspect, wherein the carbon nanotubes are pressurized to 10 GPa or more and heated to 1600 ° C. or more.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The invention of this application has the features as described above, and will be described below.

First, the nanodiamond of the invention of this application is characterized in that carbon nanotubes are synthesized by heating carbon nanotubes to 1600 ° C. or more at a high pressure of 10 GPa or more.

The carbon nanotube has a structure in which carbon hexagonal mesh planes are closed in a cylindrical shape or a multilayer structure in which these cylinders are nested, and has a diameter of several nm to several tens of nanometers.
m and very thin. As such carbon nanotubes, those manufactured by various generally known methods can be used. For example, a method in which an arc discharge is generated between carbon electrodes to grow on a cathode surface of a discharge carbon electrode, a method in which SiC is irradiated with a laser beam to be heated and sublimated, and a method in which CVD is performed by chemical vapor deposition (CVD) ) Is exemplified.

The carbon nanotubes as a starting material are placed in a sealed high-pressure vessel such as a diamond anvil cell apparatus, for example, to place 10 g of carbon nanotubes.
A high static pressure of Pa or more is uniformly applied to maintain a high temperature of 1600 ° C. or more. Furthermore, at a high pressure of 15 GPa or more, 18
It can be maintained at a high temperature of 00 ° C. or higher. In other words, by realizing the stable condition of the diamond structure, the carbon nanotube is directly phase-transformed into diamond. The holding time at such a high temperature and high pressure can be about several tens of seconds to several minutes, depending on the temperature and pressure conditions. For example, about 1 carbon nanotube
When holding at a high temperature of about 1600 ° C. at a high pressure of 0 GPa, the holding time can be about several minutes. When holding the carbon nanotube at a high temperature of about 1800 ° C. at a high pressure of about 15 GPa, the holding time can be reduced. Can be set to about several tens of seconds.

As a result, nanodiamonds having a size substantially equal to the diameter of the nanotube used as a raw material can be obtained as an aggregate.

In addition, since the above-mentioned method is a reaction in a solid phase, it does not involve nucleation as seen in a dissolution reaction, so that nanodiamonds having a uniform size can be obtained. For example, by using an aggregate of carbon nanotubes having a diameter of 20 to 50 nm as a starting material, a particle size of 20
A uniform nanodiamond aggregate having a thickness of about 50 nm can be obtained.

Furthermore, according to the invention of this application, since it is synthesized under static pressure, there is little generation of distortion, and nanodiamond can be obtained as a self-shaped crystal having an octahedral structure.

Such a nano diamond is, for example,
It can be used as diamond slurry or diamond paste. Further, the nanodiamond of the invention of this application is expected to realize a diamond sintered body that does not contain any sintering aid and is similar to a natural high-purity diamond polycrystalline balass.

Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

[0023]

EXAMPLES Using multi-walled carbon nanotubes having diameters of about 20 to 50 nm as starting materials, nanodiamonds were produced by high-pressure synthesis. An outline of the diamond anvil cell device used for the synthesis is shown in a perspective view of FIG.
FIG. 2 is an enlarged side view of the vicinity of the sample chamber. The high-resolution scanning electron microscope (HRSEM) image and the electron energy loss spectrum of the multi-walled carbon nanotube used as the starting material are shown in FIGS.
(B).

As illustrated in FIGS. 1 and 2, first,
100 micron square x 20 multi-walled carbon nanotube
A sample (1) was prepared by shaping to a micron thickness and placed in a sample chamber (4) between the diamond anvil (2) with potassium bromide as a pressure medium (6). The pressure medium (6) serves to distribute pressure evenly over the surface of the sample (1) and the ruby used as pressure sensor. Next, using a screw device (not shown), a uniform pressure of 15 GPa was applied to the sample (1) via the diamond anvil (2) and the pressure medium (6). Then, the sample (1) is irradiated with a laser beam (5) obtained by condensing a carbon dioxide laser having an output of 100 W through a lens to a size of 100 microns, and the surface of the sample (1) is irradiated with a laser beam (5).
A temperature of 500K was generated.

The product sample thus obtained was observed with a high-resolution scanning electron microscope and a transmission electron microscope, and its electron bonding state was examined by electron energy loss spectroscopy. The results are shown in FIGS. 4, 5 and 6, respectively.
(A).

From FIGS. 4 and 5, it was confirmed that octahedral self-shaped nanodiamond aggregates having a uniform particle size of about 20 to 50 nm were formed. The electron diffraction pattern shown in the upper right of FIG. 5 was found to be consistent with the diffraction pattern of cubic diamond. FIG.
It was also confirmed that the electron energy loss spectrum of (a) matched the cubic diamond.

From the above, it was confirmed that the invention of this application realizes an octahedral self-shaped nanodiamond aggregate having a uniform particle size of about 20 to 50 nm.

Of course, the present invention is not limited to the above-described example, and it goes without saying that various embodiments are possible in detail.

[0029]

As described above in detail, according to the present invention, a nanodiamond having a uniform nanoparticle size and a method for producing the same useful as a diamond sintered body, a slurry-like abrasive, and the like are provided.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing an apparatus used for producing nanodiamond in an example.

FIG. 2 is a side sectional view schematically showing the vicinity of a sample chamber of an apparatus used for producing nanodiamond in an example.

FIG. 3 is a diagram illustrating a high-resolution scanning electron microscope image of a multi-walled carbon nanotube used as a starting material.

FIG. 4 is a diagram illustrating a high-resolution scanning electron microscope image of the obtained nanodiamond.

FIG. 5 is a diagram illustrating a transmission electron microscope image of the obtained nanodiamond and its electron beam diffraction pattern.

FIG. 6 is a diagram illustrating an electron beam energy loss spectrum showing an electronic bonding state of (a) the nanodiamond produced in the example and (b) the multi-walled carbon nanotube used as a starting material.

[Explanation of symbols]

 Reference Signs List 1 sample 2 diamond anvil 3 gasket 4 sample chamber 5 laser beam 6 pressure medium

Claims (6)

[Claims] 1. A nanodiamond, wherein the carbon nanotube is synthesized by being heated to 1600 ° C. or higher at a high pressure of 10 GPa or higher. 2. The nanodiamond according to claim 1, wherein the carbon nanotube is synthesized by heating at a high pressure of 15 GPa or more to 1800 ° C. or more. 3. The nanodiamond according to claim 1, wherein the particle diameter is 20 to 50 nm. 4. The nanodiamond according to claim 1, wherein the nanodiamond has an octahedral structure and is self-shaped. 5. The method for producing nanodiamond according to claim 1, wherein one of the carbon nanotubes is
A method for producing nanodiamond, comprising pressurizing to 0 GPa or more and heating to 1600 ° C or more. 6. The method according to claim 5, wherein the carbon nanotube is pressurized to 15 GPa or more and heated to 1800 ° C. or more.