JPH0477396A - Production of diamond particles - Google Patents

Abstract

PURPOSE:To obtain dense diamond particles of large particle size by disposing a solid covered with a vapor-deposited material which acts as the core for production of diamond in a reaction field where the source gas for synthesis of diamond decomposes, so that a diamond crystal layer is precipitated on the surface of the solid. CONSTITUTION:The material which acts as the core for production of diamond, such as molybudenum, cobalt, tungsten, etc., is deposited by gas phase vapor deposition, physical vapor deposition, or the like on the surface of a solid which endures against high temp., such as graphite, oxide ceramics, carbide ceramics, etc. Then the solid covered with the vepor-deposited core material is disposed in the reaction field where the source gas for synthesis of diamond (e.g. methane gas) decomposes by plasma, flame or hot filament, so that a diamond crystal layer is precipitated on the surface of the solid. Thus, the diamond particles can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing diamond particles.

[Conventional technology]

Conventionally, methods for precipitating diamond particles include, for example, JP-A-59-137311 and JP-A-61-
As disclosed in Japanese Patent Application Laid-open No. 168596 and Japanese Patent Application Laid-Open No. 62-216906, diamond synthesis raw material gas consisting of hydrogen and gaseous hydrocarbons is chemically processed by plasma using a high-pressure method, an explosion method, and a low-pressure method. It is known that diamond particles are precipitated on the surface of powder in a fluidized bed by activating highly reactive excited hydrogen atoms and hydrocarbon molecules.

In particular, diamond powder, which is widely used industrially, is obtained by crushing produced grains using a high-pressure method.

[Problem B to be Solved by the Invention] However, the high-pressure method has high energy costs and also has problems such as poor yields in order to make the particle size uniform because it crushes large grown particles.

Furthermore, since the explosion method is a type of high-pressure method, it has problems such as poor yield, noise insulation from explosions, and restrictions on factory location.

Furthermore, in the case of deposition on a substrate, the low-pressure method causes particle precipitation to occur on the surface and not in volume, making it impossible to deposit a large amount of powder.

Examples of this low-pressure method include those using a freeboard of a fluidized bed (see JP-A No. 62-216906) and those suspending in an air flow (see JP-A No. 61-168596).
etc., but even if it is possible to deposit on the order of 100 μm, it is only a few μm.
Precipitation of microparticles of the order of magnitude or less could not be carried out because their particle diameters were small, so they were carried by the airflow and could not be retained in the reaction section. In addition, the density of nuclear growth was extremely low, and there were also restrictions on the material on the solid surface (substrate) to be deposited, making it unsuitable for mass production.

The present invention was made to solve these conventional problems, and its purpose is to manufacture diamond particles that can increase the density of diamond precipitation and efficiently produce large quantities of diamond particles. The purpose is to provide a method.

[Means to solve the problem]

The method for producing diamond particles according to claim 1 includes placing a solid material on which a substance that is a nucleus for diamond generation is deposited in a reaction field where a raw material gas for diamond synthesis undergoes a decomposition reaction by plasma, flame, or hot filament;
This method deposits a diamond crystal layer on the solid surface.

The method for producing diamond particles according to claim 2 is characterized in that porous carbon particles on which a material that becomes the core of diamond generation is vapor-deposited are subjected to a decomposition reaction with raw material gas for diamond synthesis using plasma, flame, or hot filament in a fluidized bed or a rotary furnace. The porous carbon particles are fluidized or rolled in the carbon particles to precipitate a large amount of diamond particles within the porous carbon particles.

The method for producing diamond particles according to claim 3 is the method according to claim 2, wherein after the diamond particles are precipitated, the porous carbon particles are removed by incineration at 500 to 800°C.

[For production]

In the method for producing diamond particles to precipitate a diamond crystal layer according to claim 1, first, for example, graphite, amorphous carbonaceous materials, oxide/nitride/carbide ceramics, etc. are heated to a high temperature of about 1000°C. For example, Mo on a resistant solid surface.

Co, W, Si, etc., which are the core of diamond generation, are deposited using a vapor phase deposition method (including chemical vapor deposition (CVD method), physical vapor deposition (PVD method) (vacuum evaporation method, sputtering method, etc.)) Then, a solid material is created on which the material that forms the core of diamond formation is deposited. Next, hydrogen (which may include a carrier gas such as helium or argon) and a gaseous hydrocarbon (e.g. C)14°C'2H6,C3H5
, ethyl alcohol, methyl alcohol, etc.) is made chemically reactive by using plasma from a plasma gun (DC plasma, RF plasma, microwave plasma, etc.), flame from a combustion burner, hot filament, etc. A reaction field with a temperature of about 600 to 1100 °C (e.g., fixed bed, moving bed single rotary furnace, fluidized bed, (air flow layer, gas phase, etc.), and the above-mentioned solid is placed in this. As a result, the substance that is deposited on the solid surface and becomes the nucleus for diamond generation is activated, and a diamond crystal layer can be deposited on the solid surface.

In the method for producing diamond particles according to claim 2,
First, a substance that will become the nucleus of diamond generation, such as Mo, Co, WSi, etc., is applied to porous carbon particles whose particle size has been adjusted to a particle size of 40 μm or more that is easy to flow, using a vapor phase deposition method (chemical vapor deposition (CVD method)). , physical vapor deposition (PVD method) (including vacuum evaporation method, sputtering method, etc.),
Porous carbon particles are made by depositing a substance that becomes the nucleus for diamond generation on the surface and in the pores. The porous carbon particles are then introduced into a bubbling fluidized bed, circulating fluidized bed, or rotary furnace at normal or reduced pressure, and hydrogen (which may also include a carrier gas such as helium or argon) and gaseous Fluidization or rolling is performed using a raw material gas for diamond synthesis consisting of hydrocarbons (for example, CH, C2Hb, C31'18+ ethyl alcohol, methyl alcohol, etc.). Then, a plasma gun (DC plasma,
RF plasma, microwave plasma, etc.) or a combustion burner generates a flame or hot filament, which converts the raw material gas for diamond synthesis into chemically reactive excited hydrogen atoms and carbon molecules. It is activated to a temperature of about 600 to 1100°C that causes a reaction to precipitate diamond, and is activated on the material that is the nucleus of diamond generation deposited on the surface of the porous carbon particles and in the pores. A large number of diamonds can be deposited not only on the outer surface of the porous carbon particles but also on the inner pore surfaces thereof.

In the method for producing diamond particles according to claim 3,
Porous carbon particles corresponding to a matrix in which diamonds are formed on the surface and in the pores by the method for producing diamond particles according to claim 2 are heated at 500 to 800°C by a fluidized bed method.
The diamond fine particles can be recovered by incinerating and removing the porous carbon particles by burning at a relatively low temperature.

〔Example〕

Examples of the present invention will be specifically described below.

Example 1 This example relates to a method for producing diamond particles to precipitate a diamond crystal layer according to claim 1, and an outline of an apparatus used in the method is shown in FIGS. 1 and 2. .

First, molybdenum fine particles are deposited on a carbon porous plate by the CVD method to create a molybdenum vapor-deposited carbon porous plate 1.

This molybdenum vapor-deposited carbon porous plate 1, together with a cooling pipe 2, is made up of a molybdenum foil belt 3 having a hole 4 in the center.
It is hung on. This belt 3 is held by a spring 5. Further, water is passed through the cooling pipe 2.

On the other hand, below these, a DC plasma device 6 is provided. This DC plasma device 6 includes an anode 7,
A cathode 9 is arranged below the hole 8 provided in the anode 7 at a predetermined interval, and a raw material gas 10 for diamond synthesis is supplied from the gap between the two.

After disposing the carbon porous plate 1 subjected to molybdenum vapor deposition treatment, argon <5.21 (20° C./min) and hydrogen (2,61
20℃/min), methane (0,0651 (20℃)/min), arc discharge at a current of about 35A, voltage of about 20V,
The pressure was 300 Torr, the reaction time was 30 to 60 minutes, and the plasma jet 11 was connected to the molybdenum foil belt 3.
The beam was radiated toward a carbon porous plate 1 fixed with molybdenum vapor deposition.

As a result, the plasma jet 11 causes the molybdenum on the inner surface of the carbon porous plate 1, which has been subjected to the molybdenum vapor deposition process, to become a nucleus, which causes a reaction to precipitate diamond, and several tens of micrometers of diamond are precipitated on the surface. was completed.

Comparative Example 1 When a porous carbon plate without molybdenum vapor deposited was compared with one treated in the same manner as above, it was confirmed that the particle density increased dramatically and the particle size also increased significantly. . Moreover, it is thought that when molybdenum was not vapor-deposited, it took time for nucleation to occur, and the particle growth time within the same reaction time became shorter, resulting in a smaller grown particle size.

Example 2 This example relates to the method for producing diamond particles according to claim 2.

As porous carbon particles, the apparent density is 0.28-0.36
g/ctl, specific surface area of 900 to 1100 n(/g, average pore diameter of 20 to 40 μm, and porosity of 0.78 to 0.84).

First, molybdenum fine particles are deposited on porous carbon particles by the CVD method, and then porous carbon particles 12 which have been subjected to molybdenum vapor deposition treatment and whose particle size is adjusted to be easily fluidized are prepared.

Next, the porous carbon particles 1 subjected to molybdenum vapor deposition treatment are
2, diamond particles were produced using the apparatus shown in FIG.

First, porous carbon particles 12 that have been subjected to molybdenum vapor deposition are
The raw material gas for diamond synthesis (in this example, argon, hydrogen) is put into the fluidized bed reactor 13 and is pressurized into each of the containers 10a, 10b, 10c from the lower part of the fluidized bed reactor 13.

methane) 10 is supplied, and with this raw material gas 10 for diamond synthesis, the porous carbon particles 12 that have been subjected to molybdenum vapor deposition are fluidized, and the porous carbon particles 14 suspended in fluidization in the reaction vessel 13 of the fluidized bed apparatus are Form. Next, the DC plasma device 1 installed at the bottom of the fluidized bed device reaction vessel 13
5 generates plasma 16 and decomposes the raw material gas 10 for diamond synthesis in the fluidized bed at high temperature.
Porous carbon particles I subjected to molybdenum vapor deposition by causing a reaction to precipitate diamond at a temperature of about 1100'C.
2, diamond was deposited.

Note that a filter 22 is installed in the upper part of the fluidized bed apparatus reaction vessel 13.
An exhaust pipe 21 containing a built-in exhaust pipe is provided.

It was confirmed that diamond was precipitated not only on the surface but also inside the porous carbon particles obtained in this manner. Furthermore, it was confirmed that the particle density and particle size were increased compared to porous carbon particles on which molybdenum was not vapor-deposited and similarly treated. Furthermore, most of the precipitated particles were ball-shaped. This is thought to be because in the case of a porous body, the precipitation surface temperature is higher than that in a flat body.

Note that the method for manufacturing diamond particles according to claim 2 is not limited to the apparatus shown in FIG. 3, and similar effects can be obtained when using, for example, fluidized bed apparatuses shown in FIGS. 4 to 7. was completed.

In FIG. 4, a circulating fluidized bed cyclone 17 is provided to allow porous carbon particles to circulate and flow. At the top of the circulating fluidized bed cyclone 17, an exhaust pipe 21 containing a filter 22 is provided. Incidentally, a high frequency coil may be wound around the outer side of the fluidized bed apparatus reaction vessel 13 of the fluidized bed apparatus shown in FIG. 4 in some cases. Further, in FIG. 5, a large number of plasma guns 18 are arranged in a plane to cause a large amount of reaction, and a fluidized bed portion is formed over a wide area so that diamond can be generated. Furthermore, as in FIG. 5, in FIG. 6, a large number of burner combustors 19 are arranged in a plane to cause a large amount of reaction, a fluidized bed is formed over a wide area, and diamond can be generated by flame 20. This is how it was done. Furthermore, although not shown in the drawings, similar effects can be obtained by providing the apparatuses shown in FIGS. 5 and 6 with a circulating fluidized bed cyclone similar to that shown in FIG. was there.

Furthermore, the apparatus shown in FIG. 7 introduces carbon porous particles that have been subjected to molybdenum vapor deposition from a supply section 23 for continuously supplying them to the fluidized bed apparatus, and sends carbon porous particles containing diamond particles to a discharge section. 24, and a number of burner combustors 19 for generating flames 20 are provided at the bottom, similar to FIG. 6. Note that in the device shown in FIG. 7, the burner combustor 19 is similar to the device shown in FIG.
Similar effects can be obtained even if the DC plasma device 15 is used instead.

Example 3 This example relates to the method for producing diamond particles according to claim 3.

The porous carbon particles obtained in Example 2 with diamond precipitated on the surface and pores were heated to 500 to 800 particles by a flow method.
The porous carbon particles corresponding to the matrix were incinerated at a temperature of °C, and the precipitated diamond fine particles were collected.

〔Effect of the invention〕

As described above, according to the method for producing diamond particles according to claim 1, on the surface of the solid on which diamond is precipitated,
Since the diamond generation reaction is carried out by vapor depositing a substance that becomes the core of diamond generation, diamond particles with increased particle density and particle size can be obtained. However, any substance can be used as long as it can withstand the diamond generation reaction temperature of about 600 to 1100°C, so there is no restriction on solids precipitated as in the conventional low-pressure method. Furthermore, precipitation of fine particles becomes possible. Furthermore, since the diamond precipitated layer has a high particle density, it can also be used for decoration.

According to the method for producing diamond particles according to claim 2,
By using porous carbon particles on which a substance that forms the nucleus of diamond generation is deposited, it is possible to deposit diamonds on the surface and inside the pores. becomes more efficient.

Furthermore, when diamond is precipitated onto porous carbon particles, by coating the porous carbon particles with a substance that can become a nucleus for diamond generation by vapor deposition, the density of diamond precipitation can be dramatically increased. Furthermore, it is possible to precipitate a large amount of diamond by decomposing and reacting raw material gas for diamond synthesis with plasma, flame, or hot filament in a fluidized bed using porous carbon particles whose particle size is adjusted to facilitate fluidization. Become. In particular, if the process is carried out in a batch-type fluidized bed, fine diamond powder with a uniform particle size on the order of several μm can be produced, which is extremely useful as an abrasive, a raw material for powder metallurgy, etc.

Furthermore, since the diamond particles are held within the porous carbon particles, wear of the device due to the diamond particles can be suppressed.

According to the method for producing diamond particles according to claim 3,
After the diamond is precipitated, the porous carbon particles corresponding to the matrix are removed by incineration at a temperature of 500 to 800°C, so the porous carbon particles supporting the diamond disappear, and the diamond fine particles can be directly and easily recovered.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway front view of a device used in an embodiment according to claim 1. FIG. 2 is a partially cutaway side view of the apparatus used in the embodiment according to claim 1. FIG. 3 is a schematic explanatory diagram showing an apparatus used in an embodiment according to claim 2. 4 to 7 are schematic explanatory diagrams showing modifications of the apparatus used in the embodiment according to claim 2. [Explanation of symbols of main parts] 1... Carbon porous plate treated with molybdenum vapor deposition 6.15
. . . DC plasma device 10 . . . Raw material gas for diamond synthesis 11 . . . Plasma jet 12 . . . Molybdenum vapor-deposited porous carbon particles 13
... Fluidized bed reactor 14 ... Porous carbon particle section 16 ... Plasma 19 ... Burner combustor 20 ... Flame. Figure 5

Claims (3)

[Claims] (1) Placing a solid material on which a substance that becomes the core of diamond generation is deposited in a reaction field where raw material gas for diamond synthesis undergoes a decomposition reaction by plasma, flame, or hot filament, and depositing a diamond crystal layer on the solid surface. A method for producing diamond particles characterized by: (2) Porous carbon particles on which the material that forms the core of diamond generation is vapor-deposited are fluidized or rolled in a fluidized bed or rotary furnace where raw material gas for diamond synthesis undergoes a decomposition reaction using plasma, flame, or hot filament. , a method for producing diamond particles, characterized by precipitating a large amount of diamond particles within porous carbon particles. (3) In claim 2, after precipitating the diamond particles,
A method for producing dymoyand particles, which comprises removing porous carbon particles by incineration at 500 to 800°C.