Method for producing single crystal diamond, and single crystal diamond

Abstract

The invention relates to a method for producing single crystal diamond and single crystal diamond. Provided are: a method for producing a single crystal diamond, whereby it is possible to inexpensively synthesize a single crystal diamond having excellent durability in a short time; and a single crystal diamond. A method for producing a single crystal diamond by exposing a raw material comprising amorphous carbon and a carbon compound to a pressure and temperature of a thermodynamically stable region of the diamond in a phase equilibrium diagram of carbon using a high-temperature and high-pressure method, thereby synthesizing the single crystal diamond.

Description

[0001] This application is a divisional application of an application with an application date of April 28, 2022, an application number of 202280057088.3, and an invention title of "Method for Manufacturing Single-Crystal Diamond and Single-Crystal Diamond". Technical Field

[0002] The present invention relates to a method for manufacturing single-crystal diamond and single-crystal diamond. Background Art

[0003] Diamond particles used in industry are usually synthesized by the high-temperature and high-pressure method. As raw materials used in the synthesis, graphite and molten (also referred to as catalyst, solvent, or solute) metal (or their alloys and carbides) are usually used. For example, Patent Document 1 describes single-crystal diamond obtained by increasing 12 the concentration of C, thereby reducing the impurity concentration and not containing Ni in inevitable impurities. According to the same document, it is said that: since the impurity concentration is low, high hardness is shown, and since Ni is not contained in the impurities, the temperature dependence of hardness is improved. The synthesis of this single-crystal diamond is carried out based on the melt precipitation theory of generating diamond particles in the presence of molten metal.

[0004] On the other hand, a method of synthesizing diamond particles in a solid state without using a metal catalyst has been studied. For example, Patent Document 2 discloses a method for manufacturing diamond particles, the manufacturing method including the steps of: impregnating a powder of detonation nanodiamond (hereinafter, simply referred to as "DND") obtained by detonation synthesis with a saturated acyclic hydrocarbon or a monohydric alcohol, and maintaining the obtained composition at a static pressure of 5 to 8 GPa and a temperature of 1300 to 1800 °C for 10 to 60 seconds. Thus, in recent years, in the synthesis of diamond particles by the high-temperature and high-pressure method, a method that does not necessarily require molten metal has been revealed.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2013-202446

[0008] Patent Document 2: International Publication No. 2015 / 038031

[0009] Patent Document 3: International Publication No. 2018 / 101347 Summary of the Invention

[0010] Problems to be Solved by the Invention

[0011] The diamond requires the following processes: using a carbon material obtained by thermally cracking a high-purity hydrocarbon gas as a carbon source, synthesizing diamond by the high-temperature and high-pressure method, cutting out a seed crystal from the synthesized diamond, using the cut-out seed crystal and a Ni-free metal solvent as raw materials, and growing single-crystal diamond by the high-temperature and high-pressure method. However, in the invention described in Patent Document 1, the high-temperature and high-pressure method needs to be carried out twice, and it is necessary to extract and cut out the region where good-quality seed crystals exist. Therefore, it is difficult to achieve a low price for the manufactured diamond.

[0012] In addition, Patent Document 1 discloses the following solution: using an Fe-Co-Ti alloy as a metal catalyst as a raw material for synthesizing single-crystal diamond. However, when manufacturing single-crystal diamond using a metal solvent, it is inevitable that the elements in the catalyst remain in the diamond at the atomic level. When the elements in the metal catalyst remain as impurities in the single-crystal diamond particles, the arrangement of the crystal lattice becomes irregular and can also cause defects. Therefore, even without Ni, the hardness of the single-crystal diamond deteriorates.

[0013] Furthermore, abrasive materials and grinding materials are also required to have durability to withstand long-term use. Therefore, even if the hardness of single-crystal diamond is high, if the fracture strength is poor, the grinding speed is likely to decrease, and the durability deteriorates when used for grindstones.

[0014] In addition, Patent Document 2 discloses the following solution: using DND to synthesize crystalline diamond in a short time. It is not clear whether this crystalline diamond is single-crystal diamond or polycrystalline diamond, but the size of the diamond particles is 30 to 250 nm. Therefore, it is considered that single-crystal diamond particles may probably be manufactured. However, since diamond is used as a raw material, considering the stability of its surface state, it is considered difficult to synthesize single-crystal diamond particles in a short time. For the diamond particles synthesized by the invention described in Patent Document 2, assuming they are polycrystalline diamond, there is a concern that the durability is further worse than that of the diamond particles synthesized by the invention described in Patent Document 1. If DND is used as a raw material, the manufacturing cost is high. In addition, if one wants to forcibly manufacture single-crystal diamond particles, it is considered that further synthesis conditions under high pressure, high temperature, and long time are required, and the mass productivity deteriorates.

[0015] The subject of the present invention is to provide: a method for manufacturing single-crystal diamond and single-crystal diamond that can synthesize single-crystal diamond with excellent durability inexpensively and in a short time.

[0016] Solutions for solving the problems

[0017] From the viewpoint of manufacturing single-crystal diamond that can be synthesized inexpensively and in a short time, the inventors first examined the structure of diamond particles manufactured by the manufacturing method described in Patent Document 2. As a result, the following insight was obtained: Grain boundaries remain between DNDs even after synthesis, and the diamond particles described in Patent Document 2 are polycrystalline diamond. Therefore, in order to manufacture single-crystal diamond particles in a short time, it is necessary not to use diamond particles as raw materials.

[0018] Therefore, the inventors studied a method for synthesizing single-crystal diamond without using a metal catalyst as a raw material as described in Patent Document 1, and furthermore, without using diamond particles as a raw material as described in Patent Document 1. Here, as a synthesis method in which the raw material does not contain a metal catalyst or diamond particles, for example, Patent Document 3 discloses an example of synthesizing polycrystalline diamond particles using only graphite as a raw material. However, in Patent Document 3, the particle size of the diamond particles was only a tiny diamond of about 10 to 100 nm in the examples. Therefore, in order to use it as an abrasive grain, it is necessary to sinter the tiny diamond, and in order to manufacture polycrystalline diamond, the manufacturing process becomes complicated and the price cannot be suppressed. In addition, even if the polycrystalline diamond is sintered, there are grain boundaries, so the durability is poor.

[0019] The inventors conducted in-depth research to synthesize micron-sized single-crystal diamond by the high-temperature high-pressure method. In order for graphite to grow as single-crystal diamond, it is necessary to introduce a raw material that serves as a starting point for graphite to transform into single-crystal diamond in a high-temperature high-pressure environment. It is also considered that if the raw material itself is also incorporated into the single-crystal diamond, lattice distortion and defects can be sufficiently avoided.

[0020] Here, it is considered that the metal catalyst that has been used conventionally is likely to wet graphite when melted, increasing the dissolution rate of graphite, and thus is effective for the transformation from graphite to diamond. However, as described above, the metal catalyst remains in the single-crystal diamond particles, thus hindering the improvement of the crushing strength. In addition, graphite is usually a crystal of the hexagonal crystal system, and in order to orient carbon atoms into diamond belonging to the isometric crystal system, a large orientation energy is required, and it is difficult to manufacture diamond in a short time.

[0021] The inventors conducted a re-study of the raw materials so that the raw materials used in the manufacture of diamond directly contribute to the growth of diamond. As raw materials that directly contribute to the growth of single-crystal diamond, carbon compounds and amorphous carbon that are concerned about the formation of pores due to gasification in the high-temperature high-pressure method were deliberately used. As a result, unexpectedly, the following insights were obtained: micron-sized single-crystal diamond with less lattice distortion and defects was synthesized in a short time. Furthermore, the following insight was also obtained: The carbon of the raw material is amorphous carbon rather than crystallized graphite, and single-crystal diamond can be manufactured in a short time, so it becomes possible to achieve low cost.

[0022] Furthermore, the following insights were obtained: The obtained single-crystal diamond particles slightly retain crystal nuclei and / or crystal defects derived from carbon compounds. The following insights were obtained: Even if crystal nuclei and crystal defects remain, the crystal orientation is consistent throughout the particles, and the synthesized particles are single-crystal diamond. Additionally, the following insight was obtained: The single-crystal diamond synthesized in this way does not use a metal catalyst, so its purity is extremely high, and the components other than carbon in the decomposed carbon compound are released to the outside and do not remain in the single-crystal diamond particles. Therefore, the impurities in the crystal are extremely few. At the same time, the insight that it has high durability was also obtained.

[0023] The present invention based on these insights is as follows.

[0024] (1) A method for manufacturing single-crystal diamond, characterized in that it is a method for manufacturing single-crystal diamond using the high-temperature and high-pressure method, and a raw material composed of amorphous carbon and a carbon compound is exposed to the pressure and temperature in the thermodynamically stable region of diamond in the carbon phase equilibrium diagram to synthesize diamond.

[0025] (2) The method for manufacturing single-crystal diamond according to the above (1), wherein the amorphous carbon is carbon black.

[0026] (3) The method for manufacturing single-crystal diamond according to the above (1) or the above (2), wherein the pressure in the thermodynamically stable region is 5 to 10 GPa and the temperature is 1300 to 1800 °C.

[0027] (4) The method for manufacturing single-crystal diamond according to any one of the above (1) to the above (3), wherein the time for which the raw material is exposed to the aforementioned thermodynamically stable region is 1 to 300 seconds.

[0028] (5) The method for manufacturing single-crystal diamond according to any one of the above (1) to the above (4), wherein the carbon compound is an organic compound.

[0029] (6) The method for manufacturing single-crystal diamond according to the above (5), wherein the organic compound is a polyol.

[0030] (7) The method for manufacturing single-crystal diamond according to the above (5) or the above (6), wherein the carbon constituting the organic compound has sp3 hybrid orbitals.

[0031] (8) The method for manufacturing single-crystal diamond according to the above (1) or the above (4), wherein the carbon compound is pentaerythritol.

[0032] (9) A single-crystal diamond having crystal nuclei and / or crystal defects derived from a carbon compound.

[0033] (10) The single-crystal diamond according to (9) above, wherein the carbon compound is an organic compound.

[0034] (11) The single-crystal diamond according to (10) above, wherein the organic compound is a polyol.

[0035] (12) The single-crystal diamond according to (11) above, wherein the carbon constituting the organic compound has sp3 hybrid orbitals.

[0036] (13) The single-crystal diamond according to (9) above, wherein the carbon compound is pentaerythritol.

[0037] (14) The single-crystal diamond according to any one of (9) to (13) above, having an average particle size of 0.25 to 50 μm or less. Description of the Drawings

[0038] Figure 1 It is a block diagram showing the manufacturing process of the single-crystal diamond particles of the present invention.

[0039] Figure 2 It is a perspective view of the pressurizing part in a high-temperature and high-pressure device of an anvil opposed type.

[0040] Figure 3 It is a partial cross-sectional perspective view of the pressurizing part of the high-pressure device used in the manufacturing process of the single-crystal diamond particles, Figure 3 where (a) is a semi-circular type, Figure 3 and (b) is a semi-ring type.

[0041] Figure 4 It is a phase equilibrium diagram of carbon.

[0042] Figure 5 It is a photograph of the single-crystal diamond of the present invention, Figure 5 where (a) is a photograph of the appearance of the specimen after high-temperature and high-pressure treatment, Figure 5 and (b) is Figure 5 an SEM photograph of the diamond in the specimen shown in (a).

[0043] Figure 6 It is a diagram showing a Raman spectrum, Figure 6 where (a) is the Raman spectrum of graphite and carbon black, Figure 6 and (b) is the Raman spectrum of pentaerythritol, Figure 6 and (c) is the Raman spectrum of natural diamond and the single-crystal diamond manufactured under the conditions of Example 2.

[0044] Figure 7 It is a photograph of a transmission electron microscope (TEM) image of the diamond particles, Figure 7 where (a) and Figure 7(b) of Example 2 is a single crystal diamond particle, Figure 7 (c) of Figure 7 and (d) of Comparative Example 8 are polycrystalline diamond particles.

[0045] Figure 8 It is a TEM photograph of the carbon black used in the examples. Detailed Description of the Invention

[0046] 1. Outline of the Method for Manufacturing Single Crystal Diamond

[0047] The method for manufacturing single crystal diamond of the present invention is a method for manufacturing single crystal diamond using the high temperature and high pressure method, in which a raw material composed of amorphous carbon and a carbon compound is exposed to the pressure and temperature in the thermodynamically stable region of diamond in the phase equilibrium diagram of carbon, thereby synthesizing diamond.

[0048] The manufacturing method of the present invention is an epoch-making method that dares to use a carbon compound and amorphous carbon, which are treated as impurities in the high temperature and high pressure method and are considered to be the cause of pores due to decomposition components, as starting materials for synthesizing single crystal diamond particles. Here, in the method for synthesizing diamond using chemical vapor deposition, it is difficult to manufacture single crystal diamond particles of 1 μm or more from powders such as graphite, carbon black, and amorphous carbon. Therefore, in order to synthesize single crystal diamond particles, the high temperature and high pressure method is the best. The following will be described in detail with reference to the drawings.

[0049] Figure 1 is a block diagram showing the manufacturing process of the single crystal diamond particles of the present invention. Specifically, the method for manufacturing single crystal diamond of the present invention is as Figure 1 shown, and is the following steps: (1) a step of mixing starting materials composed of amorphous carbon and a carbon compound; (2) a step of introducing the mixed raw materials into a pressure medium; (3) a step of exposing the mixed raw materials to the pressure and temperature in the thermodynamically stable region of diamond in the phase equilibrium diagram of graphite. These will be described in detail below.

[0050] (1) Step of Mixing Starting Materials Composed of Amorphous Carbon and a Carbon Compound

[0051] The "amorphous carbon" used in the manufacturing method of the present invention refers to a non-crystalline state and is composed of carbon or the like that does not have a constant crystal structure. Among these, solids that are easy to handle are preferred, and carbon black is preferred. In addition, inevitable impurities may also be included.

[0052] It should be noted that in the present invention, those having a constant crystal structure such as diamond and graphite are excluded from the "amorphous carbon" in the present invention. In addition, the "carbon compound" described later is also excluded from the "amorphous carbon".

[0053] In the manufacturing method of the present invention, single crystal diamond can be manufactured without being limited by the purity of the raw material. Preferably, the impurity concentration of the amorphous carbon containing carbon black is less than 30 ppm, and the arithmetic average particle size is 16 to 200 nm. More preferably 16 to 100 nm, and further preferably 16 to 70 nm. If it is in this range, there is no need to complicate the temperature curve and the pressure curve.

[0054] The carbon compound used in the present invention is not particularly limited as long as it is a compound containing C. For example, it includes inorganic compound materials and organic materials, and the inorganic compound materials contain carbon monoxide, carbon dioxide, cyanic acid, cyanate, thiocyanate. However, it does not contain amorphous carbon and metal salts. The carbon compound is not particularly limited as long as it is a substance such as a tire, toner, hair, wood, waste plastic, etc. that can be thermally cracked and carbonized. When using such recycled resources, as long as it is pulverized to a small size in a manner that is easy to carbonize by thermal cracking, it can be used as a raw material. In addition, it also includes: solids such as coal, coke, charcoal, coal (coal ash), vitreous carbon, liquids such as naphtha (gasoline), kerosene, light oil, heavy oil, and gases such as natural gas.

[0055] In addition, the carbon compound is preferably an organic compound, preferably a liquid or solid at room temperature, and particularly preferably an individual that is easy to handle as a raw material. In order for elements that do not contribute to diamond not to remain during synthesis and to decompose during synthesis and be released to the outside, the organic compound is more preferably composed of hydrogen, oxygen, and carbon, and preferably has hydrogen and / or a hydroxyl group and carbon.

[0056] In addition to the above, the carbon compound used in the present invention includes aliphatic hydrocarbons, aromatic hydrocarbons, and alicyclic hydrocarbons. They can be saturated hydrocarbons or unsaturated hydrocarbons, and in addition, they can also be monomers, oligomers, or polymers.

[0057] For example: methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, decane and other alkanes, ethylene (ethylene), propylene (propylene), butene (butene), pentene, hexene, heptene, octene, nonene, decene and other alkenes, acetylene (acetylene), propyne (methyl acetylene), butyne, pentyne, hexyne, heptyne, octyne, nonyne, decyne and other alkynes, cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane and other cycloalkanes, allene (allene), butadiene, pentadiene (1,3-pentadiene), hexadiene, heptadiene, octadiene, nonadiene, decadiene and other alkanedienes. They can also be alcohols having a hydroxyl group such as methanol, ethanol, propanol, etc., and can have substituents such as a sulfo group, a nitro group, a nitroso group, an epoxy group, an aldehyde group, an amino group, an acyl group, a carbonyl group, a carboxyl group, etc., and can be oligomers thereof, or polymers such as polyethylene, polypropylene, polyethylene terephthalate, etc.

[0058] In addition, similar to single-crystal diamond, it is preferable that a shoulder peak is visible in the Raman spectrum at around 1330 - 1340 cm -1 Furthermore, the organic compound preferably has carbon atoms with sp 3 hybrid orbitals, and the number of carbon atoms is preferably 1 - 10, more preferably 4 - 6, and particularly preferably 5. A polyol is particularly preferably used as the organic compound. As the polyol, a 3 - to 8 - valent alcohol is preferred, and a 4 - valent alcohol is more preferred. Further, it is preferred that all carbon elements in the polyol have sp 3 hybrid orbitals.

[0059] Diamond has a tetrahedral structure with sp 3 hybrid orbitals. When this carbon structure exists in a carbon compound, it functions as a crystal nucleus during synthesis. Therefore, in order to more effectively promote the growth of diamond, it is preferred that the carbon compound contains a carbon structure with sp 3 hybrid orbitals and preferably has branches. Furthermore, in addition to these, the carbon compound preferably has a structure close to the tetrahedral structure of diamond. In addition to these, it is most preferred that a tetrahedral structure is formed by 5 carbon atoms. Hydroxyl groups may be present at these ends, and from the viewpoint of being released as desorbed gas when heated, a polyol is preferred.

[0060] In the present invention, the reason for being able to synthesize single - crystal diamond with excellent durability in a short time with high yield and at low cost by using the above - mentioned preferred amorphous carbon and carbon compound is speculated as follows.

[0061] In the existing high - temperature and high - pressure method, molten metal and graphite are used. The molten metal melts at high temperature, and thus graphite is decomposed by the molten metal to generate diamond. However, amorphous carbon, which is carbon without a constant crystal structure, has a random structure. Therefore, compared with those having a specific structure, it is easier to undergo a structural transformation into diamond. Therefore, high energy required for the structural change of graphite based on molten metal as in the prior art is not needed, and as long as there is an organic compound with sp 3 hybrid orbitals as a nuclear substance, which becomes the starting point for the transformation from carbon to diamond, it is speculated that the generation of diamond is easy.

[0062] In addition, the hydroxyl groups in the raw materials exposed to the high - temperature and high - pressure environment react with amorphous carbon and are desorbed as CO and CO2. The remaining carbon with sp 3 hybrid orbitals becomes the crystal nucleus, which is the smallest structure of the diamond crystal. Then, starting from this crystal nucleus, the amorphous carbon is transformed into the diamond structure. Therefore, it is speculated that in the present invention, single - crystal diamond particles with few defects and excellent durability can be manufactured inexpensively and with high yield.

[0063] As polyhydric alcohols, for example, the following can be mentioned: ethylene glycol, propylene glycol, diethylene glycol, trimethylene glycol, tetraethylene glycol, triethylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, 2,3-butanediol, 1,2-butanediol, 2-methyl-1,3-propanediol, 3-methyl-1,2-butanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,2-pentanediol, 1,5-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 2,3-dimethyltrimethylene glycol, tetramethylene glycol, 3-methyl-4,3-pentanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 2,5-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, tricyclodecane dimethanol, hydroxypivalic acid neopentyl glycol ester, glycerol, trimethylolethane, trimethylolpropane, diglycerol, xylitol, triglycerol, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, tris(2-hydroxyethyl) isocyanurate, sorbitol, mannoheptitol, sucrose, etc.

[0064] Among these, as trihydric alcohols, glycerol, trimethylolpropane, etc. can be mentioned. As tetrahydric alcohols, pentaerythritol, diglycerol, etc. can be mentioned. As pentahydric alcohols, xylitol, etc. can be mentioned. As hexahydric alcohols, sorbitol, etc. can be mentioned. As heptahydric alcohols, mannoheptitol, etc. can be mentioned. As octahydric alcohols, sucrose, etc. can be mentioned. Among these, tetrahydric alcohols are preferred, and pentaerythritol is most preferred.

[0065] The above carbon compounds can be one kind or a mixture of two or more kinds, and the above carbon compounds may contain inevitable impurities. In the case of containing inevitable impurities, it has no influence on the above effects.

[0066] In the present invention, in the combination of amorphous carbon and a carbon compound, it is preferred that the amorphous carbon is carbon black and the carbon compound is a polyhydric alcohol having an sp 3 hybrid orbital and a tetrahedral structure, and the combination of carbon black and pentaerythritol is most preferred. If it is this combination, sometimes 95% or more, preferably 99% or more, is converted into diamond with respect to the total weight of the raw materials.

[0067] Regarding the mixing ratio of amorphous carbon and the carbon compound, from the viewpoint of the pressure attenuation caused by the volume shrinkage during the conversion of amorphous carbon into diamond, in terms of mass ratio, it is desirable that (amorphous carbon):(carbon compound) = 7:3 to 4:6, and particularly desirable is 6:4 to 5:5. After weighing amorphous carbon and the carbon compound within the above range, the starting materials are mixed. The mixing method can be a general method. For example, the above starting materials are put into a powder mixer and mixed for about 1 to 30 minutes under atmospheric pressure or reduced pressure. Thus, a mixed powder of 100 μm or less is obtained.

[0068] (2) Step of introducing the mixed raw materials into the pressure medium

[0069] Load the mixed powder prepared as described above into a pressure medium equipped with, for example, a graphite heater, and set it in the pressurizing section of a high-temperature and high-pressure device.

[0070] The high-temperature and high-pressure device used in the synthesis of diamond particles based on the high-temperature and high-pressure method is not particularly limited as long as it can maintain 5 to 10 GPa for about 1 minute at 1000 to 1400 °C as described later. In order to perform synthesis under such conditions, it is necessary to apply a static external force to the mixed raw materials with an anvil. As the pressurizing form for applying the external force, various pressurizing forms can be adopted. For example, there can be cited: an anvil-cylinder type such as a belt type represented by uniaxial pressurization, a semi-ring type of an anvil opposed type, a semi-circle type, a regular tetrahedron type of multi-axial pressurization, a multi-anvil type, etc.

[0071] Figure 2 Fig. is a perspective view of the pressurizing section 1 in a high-temperature and high-pressure device of an anvil opposed type. A pressure medium 20 formed of calcium carbonate or the like is provided on the lower anvil 10. In the cavity 30 at the central part of the pressure medium 20, for example, the mixed raw materials loaded in a graphite tube are introduced. Then, the lower anvil 10 provided with the mixed raw materials in the pressure medium 20 is pressed against the upper anvil 40 to form a high-pressure and high-temperature state of the raw materials described later, and single-crystal diamond particles are synthesized.

[0072] Figure 3 Fig. is a partial cross-sectional perspective view showing the pressurizing section of the high-pressure device used in the manufacturing process of single-crystal diamond particles. Figure 3 (a) of Fig. is a semi-circle type. Figure 3 (b) of Fig. is a semi-ring type. As Figure 3 shown in (a) of Fig., in the semi-circle type, the pressure medium 50 with raw materials introduced into the recessed part 51 at the central part is clamped by the upper and lower anvils 60 and 70. By moderately flattening the pressure medium in the recessed part under high pressure, the pressure applied to the raw materials can be prevented from decreasing. As Figure 3 shown in (b) of Fig., in the semi-ring type, a ring-shaped recessed part 82 is further provided around the recessed part 81 at the central part. The ring-shaped recessed part 82 is formed in a ring shape when viewed from above the drawing plane. The pressure medium 80 is flattened and leaks from the recessed part 81, but the flow of the flattened pressure medium can be prevented by the ring-shaped recessed part 82. Therefore, the decrease in pressure can be suppressed while the pressurizing time elapses. Figure 3 In (b) of Fig., one ring-shaped recessed part 82 is provided, but it is preferable to further provide other ring-shaped recessed parts around it.

[0073] (3) Exposing the mixed raw materials to the pressure and temperature within the thermodynamically stable region of diamond in the phase equilibrium diagram of graphite

[0074] After setting the raw materials in the high-pressure device as described above, the raw materials are exposed to a specified pressure and temperature on the anvil. Figure 4 is the phase equilibrium diagram of graphite. As Figure 4 shown, in the region above the graphite-diamond equilibrium line, diamond is thermodynamically stable. In this region, the pressure and temperature are set. In addition, the curves of pressure and temperature are not particularly limited. Based on considerations of the homogenization of the temperature and pressure of the starting raw materials, the recrystallization of graphite, nucleation, and particle growth, various conditions can be determined and carried out. Generally, it is desirable to gradually increase the pressure and temperature slowly, but it takes time until the synthesis of diamond is completed.

[0075] From this perspective, it is preferable that the pressure in the thermodynamically stable region is 5 to 10 GPa and the temperature is 1300 to 1800 °C. If the pressure is 5 GPa or more, micro-sized diamond particles are obtained. In addition, a high conversion rate from carbon black to diamond is obtained. The same is true if the temperature is 1300 °C or more. The pressure is further preferably 6 GPa or more, and the temperature is further preferably 1400 °C or more.

[0076] On the other hand, if the pressure is 10 GPa or less, it does not cause an excessive load on the pressurizing device. In addition, the pressure medium does not leak from the gap, and the initial pressure is maintained without depending on the passage of time. In addition, as Figure 4 shown, if the applied pressure is within the above range, it is only necessary to enter the thermodynamically stable region, and it is not necessary to form a temperature higher than required. The pressure is more preferably 9.5 GPa or less, further preferably 8 GPa or less, the temperature is more preferably 1700 °C or less, and further preferably 1600 °C or less. In the present invention, from the viewpoint of the yield of diamond, it is preferable to raise the pressure to the above range and then lower the temperature to the above range.

[0077] The time for exposing the raw materials to the thermodynamically stable region is preferably 1 to 300 seconds. If it is within this time, a high conversion rate from carbon black to diamond is obtained. In addition, if it is within 300 seconds, the decrease in pressure caused by the leakage of the flattened pressure medium from the gap can be suppressed. The time for exposing the raw materials to the thermodynamically stable region is more preferably 2 to 70 seconds, further preferably 3 to 10 seconds, and particularly preferably 4 to 7 seconds or less. It should be noted that this time range is the time for exposure to the thermodynamically stable region, and it is preferably the time when the pressure and temperature are within the above ranges.

[0078] The pressure curve and the temperature curve are not particularly limited, and the pressurization rate and the heating rate can be set as long as they are within the specifications of the device. The pressurization rate is preferably fast, as long as it is 0.5 GPa / second or more, and more preferably 3 GPa / second or more. The heating rate is also preferably fast, as long as it is 300 °C / second or more.

[0079] Under the above conditions, the starting material is exposed to high temperature and high pressure, whereby the carbon black is instantaneously converted into single crystal diamond, and the carbon of the carbon compound is incorporated into the single crystal diamond. Therefore, according to the suitable manufacturing method of the single crystal diamond of the present invention, it can be manufactured in a short time of several seconds to several tens of seconds with a high yield of 90% or more, or 99% or more.

[0080] 2. Single crystal diamond

[0081] (1) Outline of single crystal diamond

[0082] The single crystal diamond particles of the present invention manufactured by the above-described manufacturing method of single crystal diamond have crystal nuclei and / or crystal defects derived from a carbon compound. In the case of existing diamond particles, when crystal nuclei and crystal defects remain, crystal interfaces are formed on the surfaces containing these, resulting in polycrystals. However, in the single crystal diamond of the present invention, the crystal orientation is consistent in all regions including these and their peripheries, and the synthesized diamond particles are single crystals. Along with this, the single crystal diamond of the present invention has an as-grown surface that does not undergo addition such as crushing, that is, a so-called smooth crystal plane.

[0083] In addition, since the single crystal diamond particles of the present invention do not use a metal catalyst as described above, the purity is extremely high, and components other than the carbon of the decomposed carbon compound do not remain in the single crystal diamond particles but are released to the outside. Therefore, the defects are extremely few. As a result, high durability can be achieved.

[0084] (2) Crystal nuclei and / or crystal defects derived from a carbon compound

[0085] The single crystal diamond particles of the present invention have crystal nuclei and / or crystal defects derived from a carbon compound. When stress is applied to the single crystal diamond particles from the outside, the stress is relieved by the crystal nuclei and crystal defects, and single crystals are formed, so that high durability is exhibited.

[0086] The crystal nuclei and crystal defects in the present invention can be easily confirmed by TEM or the like. For example, as shown in (a) of Figure 7 , the vertical and horizontal lines are crystal defects, and the central part thereof is a crystal nucleus. Figure 7 The lines in (a) of are defects, but these defects were accidentally observed on the surface of the specimen and did not reach the depth of the particle. Even if such weak defects exist, the crystal orientation is consistent in all regions including the crystal nucleus and its periphery, so that high durability can be exhibited.

[0087] The crystal nuclei and crystal defects in the present invention are derived from the carbon compound described in the above manufacturing method. For the carbon compound, it is the same as described above, so the description is omitted. The crystal nuclei possessed by the single crystal diamond particles of the present invention are those in which a certain structure of the carbon compound before generation remains. The number thereof is preferably 1 to 3, and as long as there is 1, the stress can be sufficiently relieved.

[0088] (3) Average particle size

[0089] The average particle size of the single-crystal diamond particles of the present invention is preferably 0.25 to 50 μm, more preferably 1 to 30 μm, still more preferably 2 to 30 μm, particularly preferably 3 to 30 μm, and most preferably 4 to 28 μm. If it is within this range, the particles are not overly large, and thus, they can be used in a wide range of applications. In the present invention, for example, the volume average diameter D50 value of a particle size distribution measuring machine using the laser diffraction scattering method (e.g., manufactured by Malvern Instruments, model: Mastersizer2000, manufactured by Microtrac BEL Corp., model: Microtrac MT3000, Microtrac UPA, etc.) can be used as the average particle size.

[0090] (4) Raman spectrum

[0091] The single-crystal diamond particles of the present invention preferably have a sharp peak near 1332 cm -1 similarly to natural single-crystal diamond. Therefore, the lattice distortion and defects are extremely few, and excellent durability is exhibited.

[0092] Examples

[0093] The present invention is not limited to the examples shown below.

[0094] 1. Production of diamond particles

[0095] First, carbon black powder (trade name: manufactured by Tokai Carbon Co., Ltd., TOKABLACK #4500) or graphite having an arithmetic average particle size of 40 nm is used as amorphous carbon, and pentaerythritol (manufactured by Tokyo Chemical Industry Co., Ltd., product number (P0039)), xylitol (manufactured by Tokyo Chemical Industry Co., Ltd., product number (X0018)), a product obtained by cutting polyethylene (manufactured by Nisshin Chemical Co., Ltd., product name: Kitchen Pack) with a commercially available pair of scissors, or methanol (manufactured by Kanto Chemical Co., Inc., product number: 25183-70) is used as a carbon compound. As shown in Table 1, they are weighed and put into a powder mixer to obtain a mixed powder. When using DND, DND powder having a volume average diameter D50 value of 2 to 100 nm measured by a particle size distribution measuring machine using the laser diffraction scattering method (e.g., manufactured by Microtrac BEL Corp., model: Microtrac UPA) is used. As shown in Table 1, this DND powder and pentaerythritol are weighed and put into a powder mixer to obtain a mixed powder. These mixed powders are filled into a graphite tube and introduced into the cavity portion of a disc-shaped CaCO3 pressure medium.

[0096] The synthesis of diamond is carried out in a "semicircular" high-pressure chamber. The applied pressure is corrected using the approximate curve of the phase change of Bi, Tl, and Ba at room temperature commonly used in the high-temperature and high-pressure method, and is set as the pressure indicated by the oil pressure gauge. The heating temperature is corrected from the input power and temperature using a thermocouple, and is the temperature obtained from the input power. The raw material is heated by direct heating in which an electric current flows through a graphite heater. Using these setups, the powdered raw material is exposed to high temperature and high pressure under the conditions shown in Table 1.

[0097] The sample synthesized by the high-temperature and high-pressure method is as Figure 5 shown in (a). At the moment when the pressure reduction is completed, it is in a state of being mixed with the pressure medium. Therefore, first, the particles of the pressure medium are removed by a sieve, and then, it is washed with deionized water. Next, the powder is put into a liquid of bromoform (CHBr3) to separate the carbon black from the diamond particles. The diamond particles are filtered and washed with deionized water to obtain diamond particles.

[0098] Arbitrarily extract 2 grains from the obtained diamond particles. As Figure 5 shown in (a), observe with an optical microscope (Optical Microscope: OM). As Figure 5 shown in (b), observe the morphology of the obtained particles with a field emission scanning electron microscope (Field Emission Scanning Electron Microscope; FE-SEM). The identification of diamond is carried out by Raman spectroscopy as Figure 6 shown in (c) (device name manufactured by JASCO Corporation: Laser Raman Spectroscopy Device, model NRS-7500). As Figure 7 shown, investigate the crystallinity in the transmission electron microscope (device name manufactured by JEOL Ltd.: Transmission Electron Microscope: TEM, model name: JEM-ARM200F) image. In addition, observe whether graphite is mixed in the carbon black used in this example in the transmission electron microscope image.

[0099] The yield is obtained by multiplying by 100 the value obtained by dividing the total mass of the obtained diamond particles by the total mass of the raw materials (%). If it is not 0%, single crystal microdiamonds can be manufactured. If the yield is 90% or more, it can be said to be a high yield. If the yield is 99% or more, it is an extremely high yield, and early implementation is expected.

[0100] The average particle size of the obtained crystals is measured as the volume average particle size D50 as the average particle size by a particle size distribution measuring machine using the laser diffraction scattering method (for example, manufactured by Malvern Instruments, model: Mastersizer2000).

[0101] When the particle size is 1 μm or more and single-crystal diamond can be produced, the evaluation is marked as "〇". When single-crystal microdiamond cannot be produced, it is marked as "-". When it is polycrystalline, it is marked as "polycrystalline".

[0102] The results are shown in Table 1.

[0103] [Table 1]

[0104]

[0105] As shown in Table 1, the diamond particles of the examples are all single crystals, and crystal nuclei can be confirmed. In particular, Examples 1, 2, and 4 show that single-crystal microdiamond particles with high yields are obtained in a short time.

[0106] On the other hand, for the diamond particles of Comparative Example 1 and Comparative Example 2, carbon black or pentaerythritol is not used, so diamond particles cannot be produced. For the diamond particles of Comparative Example 3, graphite is used as a raw material. Therefore, it is known that diamond grows with pentaerythritol as a crystal nucleus, but there will be crystal interfaces and it becomes polycrystalline. For the diamond particles of Comparative Examples 4 to 7, since the manufacturing conditions are not suitable, single-crystal microdiamond particles cannot be produced. For Comparative Example 8, DND is used as a raw material. Therefore, in the thermodynamically stable region, DND exists stably as diamond. Thus, it is known that DND grows with pentaerythritol as a crystal nucleus, but there will be crystal interfaces and it becomes polycrystalline.

[0107] Figure 6 For the figure showing the Raman spectrum, Figure 6 (a) thereof is the Raman spectrum of graphite and carbon black, Figure 6 and (b) thereof is the Raman spectrum of pentaerythritol, Figure 6 and (c) thereof is the Raman spectrum of natural diamond and single-crystal diamond particles produced under the conditions of Example 2. The graphite and carbon black used in this example, as Figure 6 shown in (a), show significantly different Raman spectra. In graphite, a sharp peak near 1580 cm -1 and a shoulder peak near 1330 cm -1 are visible. On the other hand, since carbon black is amorphous carbon, no sharp peak is seen near 1580 cm -1 . Thus, it is confirmed that the crystal structures of graphite and carbon black are significantly different.

[0108] It should be noted that since carbon black is amorphous carbon, no peak should be seen in the Raman spectrum, but shoulder peaks are visible near 1330 cm -1 and near 1580 cm -1 . However, as will be described later, Figure 8In this example, there is no graphite in the carbon black used. Therefore, the shoulder peak visible in the Raman spectrum of the carbon black is not the graphite mixed into the raw material, but the part of the carbon black that becomes graphite due to the laser during Raman spectroscopy measurement. As Figure 6 shown in (b) of -1 , in pentaerythritol, a small shoulder peak is visible around 1330 - 1340 cm Figure 6 -1 . Therefore, it can be known that it is optimal as the crystal nucleus that becomes the starting point of diamond growth. As shown in (c) of

[0109] Figure 7 Figure 7 Figure 7 Figure 7 Figure 7 Figure 7 Figure 7 Figure 7 Figure 7

[0110] Figure 8 Figure 8

[0111]

[0112] shown in (d) of Figure 7 Figure 7

[0110] Figure 8 Figure 8

[0111] Description of reference numerals

[0112] 1 Pressure part, 10, 40, 60, 70 Anvil, 20, 50, 80 Pressure medium, 30 Cavity, 51, 81 Concave part, 82 Annular concave part

Claims

1. A single crystal diamond particle, characterized in that, It has smooth crystal planes, an average particle size of 0.25 to 50 μm, crystal defects derived from a carbon compound on its surface, and is manufactured by the following method for manufacturing single-crystal diamond. The method mixes raw materials composed of amorphous carbon and a carbon compound having hydrogen and / or hydroxyl groups and a carbon structure with sp 3 hybrid orbitals in a mixing ratio of the amorphous carbon: the carbon compound = 7:3 to 4:6 by mass ratio, and holds it for 1 to 300 seconds under the conditions of a pressure of 5 to 10 GPa and a temperature of 1300 to 1800 °C to synthesize diamond.

2. The single crystal diamond particles according to claim 1, having an average particle size of 1 to 30 μm.

3. The single-crystal diamond particle according to claim 1 or 2, wherein The amorphous carbon is carbon black, and the carbon compound is at least one of aliphatic hydrocarbons, alcohols, and polyols.

4. The single-crystal diamond particle according to claim 3, wherein, The aliphatic hydrocarbon is polyethylene, the alcohol is methanol, and the polyol is pentaerythritol or xylitol.

5. The single crystal diamond particle according to claim 1 or 2, wherein, There is a peak near 1332 cm in the Raman spectrum -1 .

6. The single-crystal diamond particle according to claim 3, wherein, There is a peak near 1332 cm in the Raman spectrum -1 .

7. The single-crystal diamond particle according to claim 4, wherein There is a peak near 1332 cm in the Raman spectrum -1 ​

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