Preparation method of diamond particles and diamond particles

Abstract

The invention provides a preparation method of diamond particles and the diamond particles. The preparation method comprises the following steps that S1, a heat source is arranged above a closed container, a graphite crucible is placed in the closed container, the top of the graphite crucible serves as a high-temperature end, the bottom of the graphite crucible serves as a low-temperature end, and other optional carbon sources, solid cosolvents and diamond seed crystals are placed in the graphite crucible according to the sequence from the high-temperature end to the low-temperature end; wherein the solid cosolvent comprises a liquid metal and a transition metal alloy; the melting point of the liquid metal is lower than 300 DEG C; and S2, in the presence of protective gas, heating the closed container through a heat source, so that the solid cosolvent is molten to form a cosolvent melt, and carbon provided by dissolving the inner wall of the graphite crucible through the cosolvent melt and optional other carbon sources are deposited at the diamond seed crystals to form diamond particles. According to the preparation method provided by the invention, equipment is simple, and the traditional complex diamond preparation process is simplified.

Description

Technical Field

[0001] The invention relates to a method for preparing diamond particles and the diamond particles, belonging to the technical field of diamond preparation. Background Art

[0002] Diamond is considered to be the most promising material for preparing the next generation of high-power, high-frequency, high-temperature and low-power loss electronic devices, and is hailed by the industry as the "ultimate semiconductor". It has the characteristics of high carrier mobility, high carrier saturation drift rate and large breakdown field strength, which enable diamond semiconductor devices to operate in harsh environments such as high frequency, high power, high voltage and strong radiation. Diamond particles have a low friction coefficient, extremely high hardness, excellent wear resistance, and stable chemical properties, and can be used in machinery, electronics, medical and other fields. The existing technology usually uses CVD (Chemical Vapor Deposition) and HTHP (High Temperature High Pressure) preparation methods, which often require harsh preparation environments, special preparation equipment and a large amount of energy consumption, and thus bring huge production costs.

[0003] Specifically, CVD is a process in which a gas phase precursor undergoes a chemical reaction at high temperature to deposit a diamond coating on the surface of the substrate. Commonly used precursor gases include methane (CH4) and hydrogen. It is usually carried out at a high temperature of 1000°C to 1500°C. The precursor gas decomposes at high temperature and reacts chemically with the surface of the substrate to form a uniform diamond coating. Its advantages are high coating quality, dense and uniform, and strong adhesion between the coating and the substrate. Its disadvantages are that the gas raw materials are expensive, the equipment cost is high, and the precursor gas is usually corrosive.

[0004] HPHT is a technology that simulates the conditions of diamond formation deep in the earth and synthesizes diamond under high temperature and high pressure. Under pressure exceeding 5GPa and high temperature of 1200℃ to 1500℃, a carbon source and a catalyst are placed in a closed reactor to accelerate the process of graphite conversion to diamond. For example, Reference 1 uses Fe 75 Ni 25 The alloy was used as a catalyst to successfully synthesize diamond particles. In the HPHT method, the pressure and temperature inside the reactor greatly increase the solubility of carbon, overcome the energy barrier of diamond synthesis, and the carbon atoms are dissolved in the catalyst and begin to deposit. The disadvantages of this method are also obvious, including high equipment costs, lengthy synthesis processes, complex operation requirements of multi-step pressure and temperature control or multiple power changes, and long synthesis time.

[0005] It can be seen that although those skilled in the art have conducted a series of studies on the preparation method of diamond particles, their studies cannot be said to be sufficient and there is room for further improvement.

[0006] References:

[0007] Cited literature 1: Bin Xu, Mu-sen Li, Jian-hong Gong etal. An investigation ofathin metal film covering on HPHT as-grown diamond from Fe–Ni–C system [J]. Materials Science and Engineering A. 396 (2005), 352–359. Summary of the invention

[0008] Problem that the invention aims to solve

[0009] In view of the above problems, it is necessary to provide a diamond preparation method with low equipment raw material cost, controllable particle size and morphology, short reaction cycle, simplicity and ease, which can reduce equipment requirements and simplify the traditional complex diamond preparation process.

[0010] Solutions for solving problems

[0011] In order to solve the above problems, the inventors studied and found that by immersing the diamond seed crystal in liquid metal (at least one of tin, gallium, indium, etc.) in a common induction heating furnace, the graphite crucible will dissolve with the help of a transition metal alloy flux (such as an alloy composed of two or more elements such as iron, nickel, cobalt, cerium, etc.), and supersaturate the diamond seed crystal region located at the lowest temperature, and carbon atoms are deposited and the carbon atom arrangement is converted from the hexagonal layered structure of graphite to the spatial tetrahedral atomic structure of diamond by liquid metal catalysis, diamond nucleation, and carbon recrystallization into a micron diamond structure. This method can achieve the regulation of diamond growth characteristics and morphology through the adjustment of temperature gradient and carbon-liquid metal-transition metal alloy system.

[0012] The present invention first provides a method for preparing diamond particles, which comprises the following steps:

[0013] S1: Arrange a heat source above a sealed container, place a graphite crucible in the sealed container, make the top of the graphite crucible a high-temperature end, and the bottom of the graphite crucible a low-temperature end, and place other optional carbon sources, solid solvents, and diamond seed crystals in the graphite crucible in the order from the high-temperature end to the low-temperature end; wherein the solid solvent comprises liquid metal and transition metal alloy; and the liquid metal is a metal having a melting point below 300°C;

[0014] S2: In the presence of a protective gas, the sealed container is heated by a heat source to melt the solid solvent to form a solvent melt, and the carbon provided by the solvent melt dissolving the inner wall of the graphite crucible and optional other carbon sources are deposited on the diamond seed crystal to form diamond particles.

[0015] According to the preparation method of the present invention, the other carbon sources include single-layer graphene powder and / or multi-layer graphene powder.

[0016] According to the preparation method of the present invention, the molar ratio of the liquid metal to the transition metal alloy is 7:3 to 8:2; and / or,

[0017] The liquid metal includes a combination of one or more of tin, gallium and indium; and / or,

[0018] The transition metal alloy includes a combination of two or more of iron, nickel, cobalt and cerium,

[0019] Preferably, the transition metal alloy comprises an iron-nickel alloy and / or an iron-nickel-cerium alloy.

[0020] More preferably, in the iron-nickel alloy, the molar ratio of iron to nickel is 1:0.5 to 1:1.5,

[0021] In the iron-nickel-cerium alloy, the molar ratio of iron, nickel and cerium is 1:(0.5-1.5):(0.2-0.5).

[0022] According to the preparation method of the present invention, in step S2, the pressure in the closed container is 0.6-1 atm.

[0023] According to the preparation method of the present invention, the protective gas includes a combination of one or more of argon, methane and hydrogen.

[0024] According to the preparation method of the present invention, in step S2, the temperature of the top of the solvent melt is 1400-1500° C., and the temperature gradient from the top to the bottom of the solvent melt is 10-40K / cm.

[0025] According to the preparation method of the present invention, in step S2, after heating to the reaction temperature, the step further includes rotating the graphite crucible, and the rotation rate is 5 to 20 rpm.

[0026] According to the preparation method of the present invention, the {100} face or the {111} face of the diamond seed crystal is the growth face.

[0027] According to the preparation method of the present invention, in step S2, the deposition time is 30 to 180 minutes.

[0028] In addition, the present invention also provides diamond particles, wherein the diamond particles are obtained according to the preparation method of the present invention, and the diamond particles are tetrahedral to octahedral micron diamond particles.

[0029] Effects of the Invention

[0030] The method for preparing diamond particles provided by the present invention has the advantages of low equipment and raw material cost, controllable particle size and morphology, short reaction cycle, simplicity and ease of operation, and can reduce equipment requirements and simplify the traditional complex diamond preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A scanning electron microscope image of the micron diamond particles obtained in Example 1 is shown. DETAILED DESCRIPTION

[0032] The following is a detailed description of the present invention. The following description of the technical features is based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples. It should be noted that:

[0033] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints numerical values ​​A and B.

[0034] In the present specification, a numerical range expressed using "above" or "below" means a numerical range including the number.

[0035] In this specification, the word "may" means both performing a certain process and not performing a certain process.

[0036] In this specification, the use of "optional" or "optional" indicates that certain substances, components, execution steps, application conditions and other factors are used or not used.

[0037] In this specification, the "normal temperature" or "room temperature" used means an indoor ambient temperature of "23±2°C".

[0038] In this specification, the unit names used are all international standard unit names, and unless otherwise stated, the "%" used indicates weight or mass percentage.

[0039] In the present specification, the use of "substantially" means that the standard deviation from a theoretical model or theoretical data is within a numerical range of 5%, preferably 3%, and more preferably 1%.

[0040] In this specification, when the terms “include” and / or “comprise” are used, they indicate the existence of features, steps, operations, devices, components and / or their combinations.

[0041] In this specification, the references to "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", etc., mean that the specific elements (e.g., features, structures, properties and / or characteristics) described in connection with the embodiments are included in at least one embodiment described herein, and may or may not exist in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0042] <First aspect>

[0043] A first aspect of the present invention provides a method for preparing diamond particles, comprising the following steps:

[0044] S1: Arrange a heat source above a sealed container, place a graphite crucible in the sealed container, make the top of the graphite crucible a high-temperature end, and the bottom of the graphite crucible a low-temperature end, and place other optional carbon sources, solid solvents, and diamond seed crystals in the graphite crucible in the order from the high-temperature end to the low-temperature end; wherein the solvent comprises liquid metal and transition metal alloy; and the liquid metal is a metal with a melting point lower than 300°C;

[0045] S2: In the presence of a protective gas, the sealed container is heated by a heat source to melt the solid solvent to form a solvent melt, and the carbon provided by the solvent melt dissolving the inner wall of the graphite crucible and optional other carbon sources are deposited on the diamond seed crystal to form diamond particles.

[0046] The following is a detailed description of each step.

[0047] Step S1

[0048] In step S1, a heat source is arranged above a sealed container, and a graphite crucible is placed below the heat source, so that the top of the graphite crucible becomes a high temperature end due to being close to the heat source after being heated by the heat source, and the bottom becomes a low temperature end. Optional other carbon sources, solid co-solvents, and diamond seed crystals are placed in the graphite crucible in the order from the high temperature end to the low temperature end. After heating in the steps described below, the inner wall of the graphite crucible and the optional other carbon sources are dissolved in the co-solvent at the high temperature end, and carbon is supersaturated at the diamond seed crystals at the low temperature end, thereby precipitating diamond particles.

[0049] There is no particular limitation on the heat source, and it can be selected as needed. In some specific implementation schemes, an induction coil is used as the heat source, and the number of turns of the induction coil can be 20 to 30 turns.

[0050] The sealed container is not particularly limited and can be selected as required, for example, it can be an induction heating furnace, etc. The method of the present invention can be used to synthesize diamond particles in a simple device.

[0051] The main carbon source in the present invention comes from the graphite crucible. While serving as a container, the inner wall of the graphite crucible can also be dissolved with the help of a solvent to provide a carbon source. Compared with the six-sided top press used in the traditional high-temperature and high-pressure method for synthesizing diamond particles, the present invention uses a simple closed container and a graphite crucible to achieve the synthesis of diamond particles, which has higher economic benefits.

[0052] The present invention does not specifically limit the other carbon sources, and may include, for example, single-layer graphene powder or multi-layer graphene powder. Preferably, the purity of the single-layer graphene powder or multi-layer graphene powder may be above 99%, preferably above 99.5%, and more preferably above 99.9%.

[0053] In the present invention, the solid solvent comprises liquid metal and transition metal alloy. The addition of the solid solvent as a catalyst can reduce the phase change activation energy in the process of graphite to diamond transformation.

[0054] In some specific embodiments, the molar ratio of the liquid metal to the transition metal alloy is 7:3 to 8:2, for example, 7.2:2.8, 7.5:2.5, 7.8:2.2, etc.

[0055] The liquid metal does not refer to a metal with a melting point below 300°C, such as a combination of one or more metals such as tin, gallium, and indium. Among them, tin is preferred. The structure of the tin surface shows greater disorder at high temperatures (1400°C). Although tin is considered to be a carbon-insoluble metal, its high surface activity relaxes the atomic gaps, allowing carbon atoms to diffuse and rearrange rapidly, forming short-lived surface clusters, which help carbon to be adsorbed on the surface of the liquid metal, aggregate together, and promote nucleation. In the present invention, in an environment where a transition metal alloy helps catalysis, the transition metal combines with tin to reduce the formation energy of the carbon cluster, and the nucleation point further develops into a stable diamond carbon structure. In addition, tin not only has the above-mentioned strong surface activity characteristics of liquid metals, but is also in the same family as carbon. The three-dimensional tetrahedral structure of tin can catalyze carbon to inherit its tetrahedral atomic structure, easily forming SnV color centers in diamond, and promoting carbon atoms from sp 2 Hybridization to sp 3 Hybridization, rearrangement into diamond lattice structure, promoting diamond nucleation.

[0056] The transition metal alloy includes a combination of two or more of iron, nickel, cobalt and cerium.

[0057] The transition metal alloy is preferably an iron-nickel alloy, and the main reasons are: 1) the iron-nickel alloy has a high carbon solubility, which can dissolve the graphite crucible to provide a rich carbon source for the growth of diamond, promote the diffusion of carbon in the alloy, and help accelerate the nucleation and growth process of diamond; 2) iron and nickel are both efficient metals that catalyze the growth of diamond, and they work synergistically to increase the growth rate of diamond; 3) the dissolved carbon atoms and transition metal atoms form carbides Fe3C and Ni3C, which are unstable at high temperatures and exist instantaneously. They are easy to decompose and release high-energy carbon atoms, and are more likely to rearrange into a diamond structure; 4) the interaction between iron and nickel metal atoms and carbon atoms helps to break the strong covalent bonds in graphite, promote the movement and reorganization of carbon atoms, reduce the activation energy required for the rearrangement of carbon atoms, and make sp 3 The transformation occurs at lower temperature and pressure, forming a three-dimensional tetrahedral structure.

[0058] In some specific embodiments, in the iron-nickel alloy, the molar ratio of iron to nickel may be 1:0.5 to 1:1.5, for example, 1:0.75, 1:1, 1:1.25, etc.

[0059] Furthermore, the transition metal alloy can also be an iron-nickel-cerium alloy. The introduction of cerium has at least the following advantages: 1) Cerium has a low melting point (about 798°C), and its addition can reduce the migration barrier of carbon atoms on the surface of liquid metal, which is conducive to the rapid movement and rearrangement of carbon atoms on the surface of liquid metal; 2) The addition of cerium can greatly increase the solubility of carbon, activate carbon atoms by forming and decomposing carbides CeC2 and Ce2C, further reduce the energy barrier, and expand the diamond stability area to lower temperature and pressure; 3) Its incompletely filled 4f orbital allows cerium to transform between +3 and +4 valence states, and 4f electrons may participate in the electron exchange or transfer process with carbon atoms, affecting the electron cloud distribution and reaction activity of carbon atoms, overlapping with the orbit of carbon atoms, and promoting the carbon atoms from sp 2 Hybridization to sp 3 Hybridization.

[0060] In some specific embodiments, in the iron-nickel-cerium alloy, the molar ratio of iron, nickel and cerium can be 1:(0.5-1.5):(0.2-0.5), for example, 1:0.75:0.2, 1:0.75:0.35, 1:0.75:0.5, 1:1:0.2, 1:1:0.35, 1:1:0.5, 1:1.25:0.2, 1:1.25:0.35, 1:1.5:0.5, etc. As a high-energy close-packed plane, the {111} plane usually has a higher impurity concentration. During the growth process, the diamond is etched, and the CC at the vacancy first breaks and continuously expands outward. The macroscopic manifestation is the appearance of triangular corrosion pits on the {111} plane. By increasing the cerium doping content, the triangular defects show a trend of decreasing size, increasing density and decreasing depth. Therefore, by adjusting the cerium doping amount, the defect size, depth and density of the diamond {111} plane can be regulated.

[0061] Step S2

[0062] In step S2, in the presence of a protective gas, the sealed container is heated by a heat source to melt the solid solvent to form a solvent melt, and the carbon provided by the solvent melt dissolving the inner wall of the graphite crucible and optional other carbon sources are deposited on the diamond seed crystal to form diamond particles.

[0063] In some specific embodiments, step S2 includes: opening a vacuum pump and a vacuum valve to evacuate the gas in the furnace chamber as a closed container, subsequently introducing a protective gas, turning on a heating power supply, and heating the graphite crucible under the action of induction heating to melt the solid block solvent. After reaching the preset reaction temperature, the graphite crucible is rotated to increase the carbon convection supply so that the graphite crucible is dissolved. After a specific reaction time, carbon is supersaturated in the diamond seed crystal region at the lowest temperature, carbon atoms are deposited, and the carbon atom arrangement is converted from the hexagonal layered structure of graphite to the spatial tetrahedral atomic structure of diamond through liquid metal catalysis, diamond nucleation, and carbon recrystallization to form diamond particles.

[0064] The type of the protective gas is not particularly limited and may include a combination of one or more of argon, methane, and hydrogen. When the protective gas includes methane, the liquid metal can adsorb and activate methane, and its high-energy surface helps the CH bond to break, significantly reducing the CH bond dissociation energy, generating methyl (CH3) and hydrogen (H) radicals, which are adsorbed on the surface of the liquid metal, activating and aggregating carbon, and further promoting diamond nucleation.

[0065] In step S2, the pressure in the sealed container is 0.6 to 1 atm, for example, 0.7 atm, 0.75 atm, 0.8 atm, 0.85 atm, 0.9 atm, etc. As the reaction proceeds, the pressure in the sealed container rises, and the vacuum pump and the vacuum valve are opened to evacuate the gas in the furnace chamber to maintain the pressure at 0.6 to 1 atm. The present invention effectively reduces the reaction pressure required for the synthesis of diamond particles by introducing liquid metal as a catalyst, and the synthesis of diamond particles can be completed at 0.6 to 1 atmospheres.

[0066] In step S2, the temperature of the top of the flux melt is 1400-1500°C, for example, 1420°C, 1440°C, 1450°C, 1460°C, 1480°C, etc. The higher the temperature, the more octahedral transformation tendency the generated diamond particles have; and the temperature gradient from the top of the flux melt to the bottom of the flux melt is 10-40K / cm, for example, 15K / cm, 20K / cm, 25K / cm, 30K / cm, 35K / cm, etc. The temperature gradient is controlled to dissolve the graphite crucible at the high temperature end, and tetrahedral to octahedral micron diamond particles are precipitated at the low temperature end due to supersaturation.

[0067] In step S2, after heating to the reaction temperature, the step of rotating the graphite crucible is further included, and the rotation rate is 5 to 20 rpm, for example, 8 rpm, 10 rpm, 12 rpm, 14 rpm, 16 rpm, 18 rpm, etc. The rotation of the graphite crucible can promote carbon solute convection. When the rotation rate is 5 to 20 rpm, the greater the crucible rotation speed, the stronger the solution vortex, which promotes crucible corrosion, more sufficient carbon supply, and larger diamond particles.

[0068] In step S2, the {100} face or the {111} face of the diamond seed crystal is the growth face. The {100} face is preferably used as the growth face, and the co-solvent as a catalyst can help stabilize the {100} face, thereby controlling the growth morphology of the diamond and improving the uniformity and purity of the finished product. The {111} face is a high-energy close-packed face and usually has a higher impurity concentration.

[0069] In step S2, the deposition time is 30 to 180 minutes, for example, 50 minutes, 70 minutes, 90 minutes, 110 minutes, 130 minutes, 150 minutes, 170 minutes, etc. The deposition time is calculated from the time when the upper surface of the melt reaches the required temperature. The longer the deposition time, the more sufficient the growth time, and the larger the generated diamond particles. When the deposition time exceeds 180 minutes, as the deposition time continues to increase, the diamond particle size no longer increases further, which is related to the gradual decrease in the surface activity of the liquid metal, indicating that the liquid metal is a key factor in promoting the transformation of graphite into diamond phase deformation nuclei.

[0070] <Second Aspect>

[0071] A second aspect of the present invention provides diamond particles, which are synthesized by the method provided by the first aspect.

[0072] The diamond particles are tetrahedral to octahedral micron diamond particles. The particle size of the diamond particles is 1 to 5 μm, for example, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, etc.

[0073] Example

[0074] The embodiments of the present invention will be described in detail below in conjunction with the examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific conditions are specified in the examples, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0075] Example 1

[0076] A graphite crucible is placed in an induction heating furnace. High-purity single-layer graphene powder (purity> 99%), solid block solvent (Sn 80 Fe 10 Ni 10 ), diamond seed crystal (with {100} face as growth face), open vacuum pump and vacuum valve to evacuate the gas in the furnace chamber, then introduce argon protection, the pressure in the growth chamber is 0.8atm, turn on the heating power, heat the graphite crucible at 15KW by induction heating, melt the tin-iron-nickel solid block solvent in the crucible, and the high-purity single-layer graphene powder and the inner wall of the graphite crucible dissolved by the melted tin-iron-nickel melt provide the carbon required for diamond synthesis. The infrared thermometer measured that the upper part of the melt reached 1450°C and then maintained for 180 minutes of growth. The heat field distribution in the induction heating furnace cavity was set to make the upper surface temperature of the alloy melt in the crucible 1450°C, and the temperature gradient from the top to the bottom of the melt was 30K / cm. The graphite crucible was rotated at 5rpm to increase the carbon convection supply, so that the graphite crucible was dissolved, and the carbon was supersaturated in the diamond seed crystal area at the lowest temperature. Carbon atoms were deposited and converted by catalysis of tin liquid metal. The carbon was recrystallized to form a micron diamond structure. The heating power was then reduced to 0KW, and the temperature was lowered until the growth furnace temperature reached room temperature. The crystal was taken out to complete the growth. The diamond particles obtained in Example 1 were photographed by scanning electron microscopy as shown in the figure. Figure 1 As shown by Figure 1It can be seen that while there are a large number of tetrahedral diamonds, there are also some triangular micron diamond particles, that is, the diamond particles obtained in Example 1 are tetrahedral to octahedral micron-sized diamonds with a particle size of about 1 to 4 μm, in which the morphology of the diamond is dominated by the (100) face, and the secondary {111} face may exist.

[0077] Example 2

[0078] A graphite crucible is placed in the induction heating furnace. The solid block solvent (Sn 78 Fe 10 Ni 10 Ce2), diamond seed crystal (with {111} face as growth face), open vacuum pump and vacuum valve to evacuate the gas in the furnace chamber, then introduce methane and hydrogen mixed gas (mixing ratio 10 / 100), the pressure in the growth chamber is 0.9atm, turn on the heating power, heat the graphite crucible at 15KW by induction heating, melt the solid tin-iron-nickel-cerium block solvent in the crucible, and the carbon required for diamond synthesis is dissolved by methane and the melted tin-iron-nickel-cerium melt on the inner wall of the graphite crucible to provide. The upper part of the melt was measured by an infrared thermometer to reach 1400°C and then maintained for 120 minutes of growth. The heat field distribution in the induction heating furnace cavity was set to make the upper surface temperature of the alloy melt in the crucible 1400°C, and the temperature gradient from the top to the bottom of the melt was 35K / cm. The graphite crucible was rotated at 10rpm to increase the carbon convection supply, so that the graphite crucible was dissolved, and the carbon was supersaturated in the diamond seed crystal area at the lowest temperature. Carbon atoms were deposited and catalyzed by tin liquid metal. Carbon was recrystallized to form a micron diamond structure, and then the heating power was reduced to 0KW, and the temperature was lowered until the growth furnace temperature reached room temperature, and the crystal was taken out to complete the growth. Compared with the diamond particles obtained in Example 1, the diamond particles obtained in Example 2 have more triangular micron diamond particles, and octahedral micron diamond particles appear, with a particle size of about 1 to 3μm.

[0079] Example 3

[0080] A graphite crucible is placed in the induction heating furnace. The solid block solvent (Sn 50 Ga 30 Fe 10 Ni 10), diamond seed crystal (with {100} face as growth face), open vacuum pump and vacuum valve to evacuate the gas in the furnace chamber, then introduce methane and hydrogen mixed gas (10 / 100), the pressure in the growth chamber is 0.8atm, turn on the heating power, heat the graphite crucible at 15KW by induction heating, melt the solid SnGaFeNi block material in the crucible as a solvent, and the carbon required for diamond synthesis is dissolved by methane and the melted SnGaFeNi melt on the inner wall of the graphite crucible. The upper part of the melt is measured by an infrared thermometer and then maintained for 80 minutes of growth after reaching 1430°C. The heat field distribution in the induction heating furnace cavity is set to make the upper surface temperature of the alloy melt in the crucible 1430°C, and the temperature gradient from the top to the bottom of the melt is 25K / cm. The graphite crucible is rotated at 15rpm to increase the carbon convection supply, so that the graphite crucible is dissolved, and the carbon is supersaturated in the diamond seed crystal area at the lowest temperature. Carbon atoms are deposited and catalyzed by tin and gallium liquid metals. Carbon recrystallizes to form a micron diamond structure, and then the heating power is reduced to 0KW, and the temperature is lowered until the growth furnace temperature reaches room temperature, and the crystal is taken out to complete the growth. The diamond particles obtained in Example 3 are a large number of tetrahedral to octahedral micron-sized diamonds with a particle size of about 1 to 4μm.

[0081] It should be noted that, although the technical solution of the present invention is introduced with specific examples, those skilled in the art will appreciate that the present invention should not be limited thereto.

[0082] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the market, or to enable other persons of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A method for preparing diamond particles, characterized in that: The following steps are involved: S1: Arrange a heat source above a sealed container, place a graphite crucible in the sealed container, make the top of the graphite crucible a high-temperature end, and the bottom of the graphite crucible a low-temperature end, and place other optional carbon sources, solid solvents, and diamond seed crystals in the graphite crucible in the order from the high-temperature end to the low-temperature end; wherein the solid solvent comprises liquid metal and transition metal alloy; and the liquid metal is a metal having a melting point below 300°C; S2: In the presence of a protective gas, the sealed container is heated by a heat source to melt the solid solvent to form a solvent melt, and the carbon provided by the solvent melt dissolving the inner wall of the graphite crucible and optional other carbon sources are deposited on the diamond seed crystal to form diamond particles.

2. The preparation method according to claim 1, characterized in that: The other carbon sources include single-layer graphene powder and / or multi-layer graphene powder.

3. The preparation method according to claim 1 or 2, characterized in that: The molar ratio of the liquid metal to the transition metal alloy is 7:3 to 8:2; and / or, The liquid metal includes a combination of one or more of tin, gallium, and indium; and / or, The transition metal alloy includes a combination of two or more of iron, nickel, cobalt and cerium, Preferably, the transition metal alloy comprises an iron-nickel alloy and / or an iron-nickel-cerium alloy. More preferably, in the iron-nickel alloy, the molar ratio of iron to nickel is 1:0.5 to 1:1.5, In the iron-nickel-cerium alloy, the molar ratio of iron, nickel and cerium is 1:(0.5-1.5):(0.2-0.5).

4. The preparation method according to any one of claims 1 to 3, characterized in that: In step S2, the pressure in the sealed container is 0.6-1 atm.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The protective gas includes one or more of argon, methane and hydrogen.

6. The preparation method according to any one of claims 1 to 5, characterized in that: In step S2, the temperature of the top of the solvent melt is 1400-1500°C, and the temperature gradient from the top to the bottom of the solvent melt is 10-40K / cm.

7. The preparation method according to any one of claims 1 to 6, characterized in that: In step S2, after heating to the reaction temperature, the step of rotating the graphite crucible is also included, and the rotation rate is 5 to 20 rpm.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The {100} face or the {111} face of the diamond seed crystal is a growth face.

9. The preparation method according to any one of claims 1 to 8, characterized in that: In step S2, the deposition time is 30 to 180 minutes.

10. A diamond particle, characterized in that: The diamond particles are obtained according to the preparation method according to any one of claims 1 to 9, and the diamond particles are tetrahedral to octahedral micron diamond particles.

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