JPH035314A - Method for synthesizing diamond powder - Google Patents

Abstract

PURPOSE:To synthesize high purity diamond with high productivity by introducing a carbon source into a plasma flame and carrying out rapid cooling by contact with a moving solid cooling body. CONSTITUTION:A pressure in a reaction chamber is regulated to a reduced pressure of 0.1-600torr, preferably 10-400torr, and hydrogen gas, argon, etc., are introduced into the above reaction chamber to produce plasma by using direct current, high frequency waves, microwaves, etc. Subsequently, a carbon source (in which the ratio of the number of carbon atoms to the number of hydrogen atoms is regulated to 0.0001-10), such as acetylene, is introduced to the above plasma, which is brought into contact with a cooling body (400-1400 deg.C surface temp.) rotating (1-20000rpm) by an external motor or vibrating (>=0.01Hz) by means of an ultrasonic vibrator, etc. By this method, the diamond powder is precipitated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for efficiently producing diamond powder of high purity used for diamond sintered bodies processed for polishing and grinding.

[Prior art]

Conventionally, the following method is known as a method for synthesizing diamond powder using a gas phase method.

(1) As shown in JP-A No. 63-158195, an organic compound or carbon material is introduced into a high-temperature plasma and decomposed or evaporated to precipitate diamond.
Thermal plasma CVD method.

(2) (JP-A-63-156009) A high-frequency or microwave plasma CVD method that uses an organic compound, hydrogen, and a nucleus for producing diamond, and deposits diamond on the nucleus.

However, these methods have the following drawbacks. In other words, in method (1), cooling gas is injected into the space of the plasma tail flame to rapidly cool the reaction mixture containing active species in the plasma and precipitate diamond. It is extremely difficult to control the temperature in the reaction region and the region where gases collide and diamond precipitates.

As a result, reproducibility is poor, temperature distribution tends to occur in the reaction region, which makes it easy for non-diamond-like carbon to be mixed in, and it is difficult to increase the supersaturation degree of diamond formation, which limits the amount of diamond powder produced. have. In method (2), a foreign substance is added as a nucleus to facilitate the precipitation of diamond, and the resulting powder becomes a composite powder with the foreign substance that was used as a nucleus. Furthermore, since it uses electrodeless high frequency or microwave discharge, there is a limit to the concentration of raw materials, and it has the disadvantage that it is not possible to increase the amount of diamond powder produced.

[Problem to be solved by the invention]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for solving the above-mentioned drawbacks and synthesizing diamond powder of good purity with high productivity.

[Means to solve the problem]

As a result of extensive research, the present inventors have discovered that the productivity of diamond powder with good purity can be improved by mechanically or electrically moving the cooling body, and have completed the present invention. That is, in order to achieve the above object, the present invention provides a method for producing diamond by introducing a carbon source into plasma generated by electric discharge under reduced pressure, and bringing this plasma flame into contact with a solid cooling body to rapidly cool it. The cooling body is characterized in that the cooling body is moved mechanically and/or electrically.

[Effect]

The discharge used in the present invention is not particularly limited, and may be, for example, any one of direct current, high frequency, microwave, low frequency alternating current, or a combination thereof, or the application of a magnetic field or electric field.

As the gas used for the plasma in the present invention, hydrogen gas, inert gases such as argon, helium, neon, and xenon, nitrogen gas, and oxygen gas can be used alone or in a mixture of two or more gases. This includes ammonia, carbon dioxide,
- Carbon oxide etc. may coexist.

The carbon source used in this study may be gas, liquid, or solid as long as it dissociates in plasma to generate active species such as carbon-containing ionic species and radical species. Examples of carbon sources include saturated hydrocarbons such as methane, ethane, and propane; unsaturated hydrocarbons such as ethylene, propylene, and acetylene; aromatic hydrocarbons such as benzene; alicyclic hydrocarbons such as cyclohexane and cyclopropane; ethanol; Alcohols such as propatool, tert-butyl alcohol, ethers such as dimethyl ether and diethyl ether, aldehydes such as formaldehyde and acetaldehyde, ketones such as acetone, methyl chloride,
Halides such as acetyl bromide, carboxylic acids such as formic acid, acetic acid, oxalic acid, malonic acid, esters such as methyl formate and formate esters, acid amides such as acetate amide, amines such as methylamine and trimethylamine, Examples include polymer compounds such as polyethylene and boropropylene, organic compounds containing sulfur such as thiophene, organic compounds containing phosphorus such as phosphine, carbon oxide, carbon dioxide, and graphite.

These carbon source substances may be one type or a mixture of two or more types. When the carbon source is liquid or solid, it is used in the plasma using an inert gas such as argon or helium or hydrogen gas as a carrier gas. supply to.

In the method of the present invention, the reaction of the carbon source in the plasma is carried out in the presence of hydrogen, but this hydrogen gas may be introduced into the reaction system as a gas for plasma generation, or as a sheath gas or carrier. It may also be introduced as a gas or the like. Furthermore, there are no restrictions on the method of introducing the carbon source into the plasma.

In the method of the present invention, the quantitative ratio of the hydrogen gas introduced into the reaction system to the carbon source is preferably such that the ratio of the number of carbon atoms/the number of hydrogen atoms in the carbon source is 0.0001 to 10. If this ratio is too large, graphite tends to precipitate, and if this ratio is too low, too little diamond is produced.

In the present invention, methods for mechanically and/or electrically moving the cooling body include a method of rotating the cooling body with an external motor, and a method of vibrating the cooling body using an ultrasonic vibrator, an electromagnet, a motor, etc. The rotation speed is preferably in the range of 1 to 20,000 rpm. If it is slower than that, there will be no effect of rotating it, and if it is faster than that, the gas turbulence on the surface of the cooling body will become large and the cooling effect will be lost, and on the contrary, the diamond precipitation rate will be slow (and the equipment cost will increase). .The vibration given is 0.
The frequency is preferably 0.01 Hz or higher. Below that, the vibrating effect is lost.

The reaction pressure used in the present invention is 0.1 to 600 torr.
The range of r is preferably 10 to 400 torr. At a pressure lower than Q, l torr, diamond precipitation is extremely slow, and at a pressure higher than 600 torr, the gas temperature becomes high and graphite or amorphous carbon tends to be mixed in.

The material of the cooling body used in the present invention is m in the periodic table.
Examples include simple substances or compounds belonging to groups a to ■, Ib to IVb. For example, steel, tungsten, molybdenum, silicon, tantalum, graphite, etc., stainless steel,
Examples include compounds such as quartz glass, alumina, silicon carbide, silicon nitride, boron carbide, boron nitride, and aluminum nitride. This cooling body is cooled with a refrigerant such as water, and the surface temperature of the cooling body is set to be 400 to 1400°C.

A method of implementing the present invention will be explained using schematic diagrams. FIG. 1 shows an apparatus for synthesizing diamond powder using direct current discharge. Figure 2 shows an apparatus for synthesizing diamond powder using high frequency discharge.

In Fig. 1, 1 is a DC plasma torch, 2 is a DC power source, 3 is a water-cooled reaction vessel, 4 is a vertically movable and rotatable cooling body, 5 is a water-cooled light plate, and 6 is a plasma generation gas inlet. , 7 is a raw material gas inlet, 8 is a sheath gas (gas flowing spirally along the inner wall of the water-cooled reaction vessel) inlet, 9 is a gas supply device, and 10 is a vacuum exhaust device with a pressure adjustment function inside the reaction vessel. show.

During the reaction, after evacuating the inside of the reaction vessel to a vacuum level of 0.01 torr or more, the plasma generating gas inlet 6 is opened.
After the plasma is stabilized, a sheath gas, in this case an atmosphere conditioning gas and a reaction gas, hydrogen or a mixture of an inert gas and hydrogen gas, is flowed through the inlet 8. The cooling body 4 and the water cooling light are used to place the plate 5 in a predetermined position (with a surface temperature of 400 to 1400°C).
After the reactor is installed at a position of 10, the inside of the reaction vessel is adjusted to a predetermined pressure using the exhaust device 10, and the cooling body 4 is rotated.

Next, a carbon source is introduced from the introduction lower and is decomposed or excited in the plasma to generate active species, whereby diamond powder is precipitated and deposited on the inner wall 3 of the water-cooled reaction vessel and the water-cooled light on the dish 5.

In Fig. 2, 11 is a vibration device, 12 is a work coil for high frequency generation, 13 is a high frequency power source, and the others are the first
Same as the figure. During the reaction, as in the case of direct current discharge, after evacuating the inside of the reaction vessel to a vacuum level of 0.01 torr or more, argon is flowed through the plasma generating gas inlet 6 and the sheath gas inlet 8 to cause discharge and generate plasma. After the plasma is generated and stabilized, the sheath gas inlet 8
Hydrogen gas is further supplied as an atmosphere conditioning gas and a reaction gas. After placing the dish 5 in a predetermined position, the water cooling light adjusts the inside of the reaction vessel to a predetermined pressure using an exhaust device 10, and vibrates the cooling body 4. Next, a carbon source is introduced through the introduction lower,
Diamond powder is precipitated by decomposition or excitation in the plasma to generate active species, and the diamond powder is deposited on the inner wall 3 of the water-cooled reaction vessel and the water-cooled light plate 5.

〔Example〕

Example 1 Using the apparatus shown in Fig. 1, the inside of the reaction vessel was 0.01 to
After evacuation to rr, argon was flowed at 201/min as a plasma generation gas to generate DC plasma, and hydrogen was flowed through the sheath gas inlet 8 at 41/min. Next, the pressure inside the reaction vessel was adjusted to 50 torr, the copper cooling body was raised to a position where the surface temperature was about 800°C, and after rotating at 2500 rpm, acetylene was injected at 0.41/min from the raw material gas inlet. DC power source 8
The reaction was carried out for 1 hour at kW. Note that the surface temperature was measured using a radiation thermometer.

As a result, the inner wall of the water-cooled reaction tube and the water-cooled light weighed about 6g from the dish.
of powder was obtained. The obtained powder was found to be cubic diamond from the results of X-ray diffraction and Raman scattering spectroscopy. Furthermore, observation using a scanning electron microscope (SEM) revealed that the obtained powder was a spherical powder with a diameter of about 0.3 μm.

Example 2 Using the apparatus shown in Figure 2, the inside of the reaction vessel was heated to 0.01 torr.
After evacuation to r, argon gas was flowed at 181/min through the plasma generation gas inlet 6 and argon gas was flowed through the sheath gas inlet 8 at 301/min to generate high frequency plasma. Next, 1017 ml of hydrogen was added to the sheath gas, and the pressure inside the reaction vessel was adjusted to 300 torr. After stabilizing the plasma, the tungsten cooling body was installed at a position where the surface temperature was approximately 900℃, and the vibration frequency was set to 26GH.
z, it was vibrated by an ultrasonic vibrator with a rated output of 300W. Furthermore, methane was flowed at 71/min from the raw material gas introduction lower, and reaction was carried out for 1 hour using a high-frequency power source with manual power of 30 kW.

As a result, the inner wall of the water-cooled reaction tube and the water-cooled light weighed approximately 8 g from the dish.
of powder was obtained. The obtained powder was found to be cubic diamond based on >1 diffraction and Raman scattering spectrum measurements. Furthermore, SEM observation revealed that the obtained powder was a spherical powder with a diameter of about 0.2 μm.

Comparative Example 1 Using the apparatus of Example 1, the reaction was carried out for 1 hour under the same conditions as in Example without rotating the cooling body. When the inner wall of the water-cooled reaction tube and the water-cooled light were A powder was obtained. X-ray diffraction and Raman scattering spectra, SE
It was found that it was cubic diamond powder with a diameter of about 0.3 μm.

Comparative Example 2 Using the apparatus of Example 2, the reaction was carried out for 1 hour under the same conditions as Example 2 without vibrating the cooling body, and the inner wall of the water-cooled reaction tube and the water-cooled light were approximately 4 g powder was obtained. X-ray diffraction and Raman scattering spectra, SEM
It was found that the powder was cubic diamond powder with a diameter of about 0.2 μm.

〔Effect of the invention〕

According to the present invention, diamond powder with good purity can be synthesized efficiently and with high productivity.

[Brief explanation of drawings]

FIG. 1 shows a longitudinal cross-sectional view of an apparatus for synthesizing diamond powder using a direct current discharge and FIG. 2 a high-frequency discharge. 1... DC plasma torch, 2... DC power supply, 3...
... Water-cooled reaction vessel, 4... Cooling body, 5... Water-cooled light plate, 6... Plasma generation gas inlet, 7... Raw material gas inlet, 8... Sheath gas inlet, 9 ... Gas supply device, 10... Vacuum exhaust device, II... Vibration device, 12... Work coil, 13... High frequency power supply. Figure 1

Claims (1)

[Claims] A method of precipitating diamond powder by introducing a carbon source into plasma generated by electric discharge under reduced pressure and rapidly cooling the plasma flame by bringing it into contact with a cooling body made of a solid material, the method comprising: A method for synthesizing diamond powder characterized by electrically moving the powder.