JPS63156009A - Synthesis of fine diamond powder - Google Patents

Abstract

PURPOSE:To obtain fine powder of spherical polycrystalline diamond which is not bonded to a substrate, by introducing the nuclei for forming diamond into plasma when fine diamond powder is formed by the plasma chemical vapor deposition process. CONSTITUTION:A nuclei-forming substance 13 (e.g. boron, silicon oxide, etc.) is mounted on a boat 8 for forming the nuclei, and the inside of a plasma forming chamber 11 is evacuated by an evacuating apparatus 2. Then, a gaseous mixture of a volatile org. compd. (e.g. methane) contg. carbon and H2 is supplied from a reaction gas feeding apparatus 1, and high frequency wave of >=100kHz is introduced by operating a high frequency wave generator 3 generating plasma. At the same time, the nuclei forming substance 13 is heated by a heating electric source 4, and the fine diamond powder is obtd. on a saucer 12 by forming the nuclei. In this case, plasma can be also generated by introducing microwave of >=300MHz using a microwave generator in place of the high frequency wave generator 3.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a method for synthesizing fine diamond powder.

Prior Art Conventional methods for synthesizing fine diamond powder include using graphite as a raw material, (1) high temperature and high pressure method using a metal catalyst, (2) impact compression method using gunpowder or explosives, or containing carbon such as hydrocarbons. Plasma chemical vapor deposition methods using volatile organic compounds are known.

The present invention relates to the method (3) above.

The present inventors previously prepared a gas containing a mixture of hydrogen and hydrocarbons passed through a microwave non-polar discharge, or a mixed gas of hydrogen and hydrocarbons passed through a microwave non-polar discharge.
A diamond synthesis method (Japanese Patent Application No. 56-204321) in which diamond is precipitated by decomposing hydrocarbons into a substrate heated to 0 to 1300°C, and hydrocarbons and hydrogen gas, or hydrocarbons and hydrogen gas, and inert gas. When microwave plasma is generated by introducing microwaves of 300 M + 1 z or more into a mixed gas of We have developed a synthesis method that allows a temperature of 300 to 1,300°C to be obtained and deposits diamond on a substrate. (Japanese Patent Application No. 57-109044) However, diamonds synthesized by these methods bond to the substrate and undergo nucleation growth on a substrate placed in plasma, and the resulting fine powder particles are halved by the substrate. It has the disadvantage that it is divided into two parts and is in the form of a single crystal.

OBJECTS OF THE INVENTION The present invention has been made to eliminate this drawback, and its purpose is to provide a method for synthesizing fine spherical polycrystalline diamond powder that has no bond to a substrate.

Structure of the Invention As a result of intensive research to achieve the above object, the present inventors found that by introducing and synthesizing the elements and compounds necessary for generating diamond nuclei into the plasma, a polycrystalline material having no bond with the substrate was produced. It was found that fine diamond powder with a shape of The present invention was completed based on this knowledge.

The gist of the present invention is to add 10% to a mixed gas of a volatile organic compound containing carbon and hydrogen.
A method for producing fine diamond powder, which is characterized in that a high frequency of 0 kHz or higher or a microwave of 300 MHz or higher is introduced to generate plasma, and a nucleus for diamond generation is introduced into the plasma to generate fine diamond powder. It's in the synthesis method.

The diamond-producing nuclei used in the method of the present invention belong to the m and rv groups of the periodic table.

Elements that can combine with carbon to form carbides in a mixed gas plasma of volatile organic compounds containing hydrogen and carbon, such as boron, silicon, aluminum, and elements that can decompose in the plasma to form carbides. Mention may be made of elemental compounds such as boron oxide, silicon oxide, aluminum oxide, boron nitride, silicon nitride, aluminum nitride, and allotropes of carbon such as graphite, amorphous carbon, carbyne.

Boron, aluminum, silicon, and carbon, which are elements that generate a large number of nuclei and can combine with carbon to form carbides in order to form a fine powder, are preferable, and in order to improve the purity of the diamond produced. Amorphous carbon and graphite are preferred.

The synthesis method of the present invention will be explained based on the drawings. FIG. 1 shows a schematic diagram of a method using high frequency plasma, and FIG. 2 shows a schematic diagram of a method using microwave plasma.

In Fig. 1, 1 is a reaction gas supply device, 2 is an exhaust device, 3 is a high frequency oscillator, 4 is a heating power source for nuclear generation, 7 is a coil for high frequency application, 8 is a heating boat for nuclear generation, and 11 is a plasma generator. Chamber, 12 is a saucer for the generated diamond, 13
15, 16, 17, and 18 indicate the nucleating material and the regulating valve.

To illustrate this operation, the nuclear generating material 1 is placed on the nuclear generating boat 8.
3, the exhaust device 2 is operated and the regulating valve 18 is adjusted to reduce the pressure inside the plasma generation chamber 11.

At the same time, hydrogen gas and a volatile organic compound containing carbon are supplied from the reaction gas supply device 1 through the regulating valve 15.16.degree. 17 to maintain a predetermined pressure. Next, the high frequency oscillator 3 is activated to generate plasma, and the heating power source 4 for nuclear generation
is activated to heat the nuclear generating material 13 and generate nuclei. As a result, fine diamond powder is obtained in the saucer 12.

In FIG. 2, a microwave oscillator 5 is used in place of the high-frequency oscillator 3 in FIG. 1, and a microwave oscillator 6 for nuclear generation is used in place of the heating power source 7 for nuclear generation.

After activating the microwave oscillator 5 to generate plasma, the nucleation microwave oscillator 6 is activated to induce plasma and heat and evaporate the nucleation material 13. Fine diamond powder is obtained in the saucer 12 in the same manner as in FIG. 1 in other respects.

The volatile organic compound containing carbon in the present invention includes:
For example, hydrocarbons such as methane, ethane, ethylene, acetylene, butane, alcohols such as methyl alcohol and ethyl alcohol, and ethers such as dimethyl ether and diethyl ether.

Examples include ketones such as acetone. The mixing ratio with hydrogen is in the range of 0.0001 to 100 in terms of the ratio of carbon atoms to hydrogen, but preferably in the range of 0.001 to 1.

Example 1 Using the apparatus shown in FIG. 1, using boron oxide as the nucleation material, placing it in the nucleation heating boat 8, and evacuating the inside of the plasma generation chamber 11 with the exhaust device 2, 100 ml/ll of a gas mixture of hydrogen and methane at 2% by volume
11n, and the plasma generation chamber 11 was maintained at 40 Torr. Next, the high frequency oscillator 3 was operated at an output of -1 to generate plasma, and then the nuclear generation heating power source 4 was activated to heat the nuclear generation heating boat 8 to about 2000°C. While clusters of boron atoms (groups of several or more atoms) generated by reacting with hydrogen on the heating boat 8 pass through the plasma, a spherical polycrystalline diamond of about 5000 angstroms is formed with the clusters as the core. A fine powder was produced and obtained on the saucer 12. When a nucleating substance was not used, a similar operation was performed to obtain half-divided, single-crystal fine particles of about 2 microns that were strongly bonded to the receiving plate.

Example 2 The apparatus shown in FIG. 2 was used, and a bundle of silicon powder was used as the nucleating material 13. After the plasma generation chamber 11 was evacuated by the exhaust device 2, a mixed gas of hydrogen and ethane in an amount of 0.5% by volume was flowed at a rate of 50 ml per minute to maintain the inside of the plasma generation chamber 11 at 30 Torr. Next, the microwave oscillator 5 is operated at an output of 500 to generate plasma, and then the microwave oscillator for nuclear generation 6 is operated at an output of 300- to generate plasma around the nuclear generating material 13. Nuclear generating material 13
was heated and evaporated. A spherical polycrystalline fine diamond powder of about 3000 angstroms was obtained on the saucer 12 with clusters of vaporized silicon atoms as nuclei.

Without the operation of the microwave oscillator 6 for nuclear generation, it was in the form of a single crystal that was combined with the saucer and divided into halves.

Example 3 Using the apparatus shown in FIG. 2, a graphite molded body is used as the nucleation material, placed on the saucer 12, and after exhausting the inside of the plasma generation chamber 11 with the exhaust device 2, the reactant gas supply device 1 The regulating valves 15, 16, and 17 were adjusted to flow a mixed gas of 0.5% by volume of hydrogen and acetylene at a rate of 120 ml per minute, and the inside of the plasma generation chamber 11 was maintained at 20 Torr.

Next, the microwave oscillator 5 was operated at an output of 300 for both nucleation and diamond generation, and the graphite molded body of the nucleation material was maintained at 810°C. As a result, spherical polycrystalline diamond fine particles of about 2000 angstroms were obtained on the saucer and graphite compact.

Without the graphite compact, it was a single crystal that was bonded to the saucer and split in half.

Example 4 Using the apparatus shown in FIG. 1, aluminum oxide was used as the nucleation material, and this was placed in the heating boat 8 for nucleation.
After evacuating the inside of the plasma generation chamber 11 using the exhaust device 2,
100 ml/gas of hydrogen and methane mixed at 3% by volume
ll1in, and the plasma generation chamber 11 was heated to 30 Torr.
It was held at r. Next, the high frequency oscillator 3 was operated at an output of 1.2 - to generate plasma, and then the nuclear generation heating port 8 was heated to about 2500°C. While the clusters of aluminum atoms generated by reacting with hydrogen on the heating boat 8 pass through the plasma, spherical polycrystalline fine diamond powder of about 3000 angstroms is generated using the clusters as nuclei, and is placed on the saucer 12. obtained.

When aluminum oxide was not used, the particles were divided into halves, single crystals, and about 2 microns in size, which were strongly bonded to the saucer.

Example 5 Using the apparatus shown in Fig. 2, aluminum nitride was used as the nucleating material, and after the plasma generation chamber 11 was evacuated through the exhaust bag W2, a gas containing hydrogen mixed with ethylene at 1% by volume was added at a rate of 50 ml per minute. The inside of the plasma generation chamber 11 is heated to 30 Tor.
It was held at r. Next, the microwave oscillator 5 is operated at an output of 300 to generate plasma, and then the microwave oscillator for nuclear generation is operated at an output of 600W to generate plasma around the nucleating material 13 to generate nuclei. Heating and evaporation of substance 13 was performed. As a result, a spherical polycrystalline fine diamond powder of about 2000 angstroms was obtained on the saucer, with clusters of aluminum atoms produced by reaction with hydrogen activated in the plasma as the nucleus.

When the microwave oscillator 6 for nuclear generation was not operated, the single crystal particles were bonded to the saucer and divided into halves.

[Brief explanation of the drawing]

The drawings are diagrams showing embodiments of the present invention; FIG. 1 is a schematic diagram of the case in which plasma generated by high frequency waves is used, and FIG. 2 is a schematic diagram in the case that plasma generated by microwave waves is used. 1: Reaction gas supply device, 2: Exhaust device, 3: High frequency oscillator, 4: Heating power source for nuclear generation, 5: Microwave oscillator, 6: Microwave oscillator for nuclear generation, 7: High frequency application coil, 8: Nuclear generation heating boat, 9.10: Microwave waveguide, 11: Plasma generation chamber, 12: Receiver, 13: Nuclear generating material, 14: Nuclear generating material support, 15, 16.17
．． 18: Adjustment valve.

Claims (1)

[Claims] 1) Plasma is generated by introducing high frequency waves of 100 kHz or more or microwaves of 300 MHz or more into a mixed gas of a volatile organic compound containing carbon and hydrogen, and a plasma is generated in the plasma for diamond generation. 1. A method for synthesizing fine diamond powder, characterized in that a fine diamond powder is produced by introducing the nucleus of. 2) The nucleus for diamond formation is found in the periodic table IIIIV.
2. The method according to claim 1, wherein the element belongs to the group consisting of elements selected from the group consisting of elements that combine with carbon to form carbides in plasma, compounds of said elements that form carbides when decomposed in plasma, and allotropes of carbon. . 3) The method according to claim 1 or 2, wherein the nucleus for producing diamond is selected from boron, silicon, aluminum, oxides and nitrides thereof, and allotropes of carbon. Method.