A method for producing a single crystal diamond
By combining rare earth salts, nickel salts, iron salts, and citric acid with expanded graphite, the problem of uneven mixing between graphite and catalyst was solved, achieving efficient preparation of high-quality single-crystal diamond and improving yield and thermal stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUNAN LIANGCHENG NEW MATERIAL TECH CO LTD
- Filing Date
- 2025-06-27
- Publication Date
- 2026-05-29
AI Technical Summary
Existing technologies make it difficult to achieve uniform mixing of graphite and catalyst, resulting in low efficiency and poor quality of synthetic diamonds, especially affecting the quality of single-crystal diamonds.
A combination of rare earth salts, nickel salts, iron salts, and citric acid with expanded graphite was used to form a colloid by adjusting the pH value. Then, single-crystal diamond was synthesized under high temperature and high pressure. The loose and porous structure of expanded graphite was used to achieve uniform mixing of metal catalyst and graphite, and composite ferrite intercalation was formed during vacuum sintering to improve catalytic activity.
It improves the yield and quality of single-crystal diamond, enhances the catalytic effect, makes diamond growth more uniform and coarser in size, improves thermal stability, and reduces the content of bound oxygen.
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Figure CN120679424B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of synthetic diamond technology, specifically a method for preparing single-crystal diamond. Background Technology
[0002] Natural diamond is a mineral formed deep within the Earth, stable under high temperature and pressure conditions, either as a single crystal or polycrystalline form. Diamond is favored by researchers and industry professionals primarily because of its superior properties compared to ordinary materials. These properties are mainly reflected in five aspects: optics, mechanics, thermal, chemistry, and electricity, and can be widely used in many fields such as industry, medicine, science and technology, and national defense.
[0003] The origin of natural diamonds remains a mystery. They are mostly found in kimberlite, but whether they are formed within kimberlite or transported to the surface by being encased in it remains inconclusive in current research. Due to modern industrialization and technological advancements, the demand for high-performance materials like diamonds has increased significantly. However, the scarcity of natural diamond sources and the severe shortage of diamond reserves have spurred the rapid development of research into synthetic diamonds and related industries. Finally, in 1955, GE in the United States achieved the first reproducible synthesis of diamonds using graphite and nickel under high temperature and pressure. Since then, the technology for synthesizing single crystal diamonds abroad has made new breakthroughs every few years, leading to increasingly mature theoretical research and synthesis processes for synthetic diamonds, and a flourishing development of the diamond application and jewelry industries.
[0004] As an indispensable auxiliary material in the synthesis of synthetic diamonds, catalysts not only reduce the temperature and pressure required for the conversion of graphite to diamond, but also significantly influence the quality and crystal morphology of the resulting diamonds. Powdered catalysts can be thoroughly mixed with graphite powder. Compared to flake catalysts, powdered catalysts significantly increase the contact area between the catalyst and graphite within the limited high-temperature and high-pressure synthesis chamber, as well as the yield of synthesized diamonds. They also offer advantages such as easier adjustment of alloy composition and superior synthesis environment and economic benefits compared to flake catalysts. However, due to the extremely small particle size of graphite and catalyst, and their significant difference in specific gravity, achieving uniform mixing is difficult. Currently, the commonly used method is to add a binder, press into shape, and then granulate. This method is inefficient, and incomplete post-treatment of the binder can also affect the quality of the synthesized diamonds. Summary of the Invention
[0005] Purpose of the invention: To address the above-mentioned technical problems, this invention proposes a method for preparing single-crystal diamond.
[0006] The technical solution adopted is as follows:
[0007] A method for preparing single-crystal diamond is as follows:
[0008] Rare earth salts, nickel salts, iron salts, and citric acid are added to deionized water to prepare a solution. Expanded graphite is added, and the pH of the solution is adjusted to 7-8. The solution is stirred in a water bath at 70-90℃ until a colloid is formed. The colloid is dried, and then held at 400-500℃ for 10-60 minutes. After that, it is vacuum sintered at 1400-1500℃ for 30-60 minutes and assembled into a synthetic block. Finally, single-crystal diamond is synthesized under high temperature and high pressure.
[0009] Furthermore, the molar ratio of the rare earth salt, nickel salt, iron salt, and citric acid is x:1:2-x:8; 0<x≤0.1.
[0010] Furthermore, the total mass ratio of the rare earth salt, nickel salt, iron salt, and citric acid to the mass ratio of deionized water is 1:3-6.
[0011] Furthermore, the mass ratio of the expanded graphite to the solution is 1:1-3.
[0012] Furthermore, the expanded graphite has a loose, porous, worm-like structure.
[0013] Furthermore, the preparation method of the expanded graphite is as follows:
[0014] After washing and drying the flaky graphite, place it in a mixed acid solution composed of sulfuric acid and nitric acid and stir evenly. Then add potassium permanganate and continue stirring for 1-5 hours. Filter, wash with water, dry, and then heat at 900-1000℃ for 1-5 minutes.
[0015] Furthermore, the mass concentration of sulfuric acid is 90-98%, and the mass concentration of nitric acid is 50-60%.
[0016] Furthermore, the mass ratio of sulfuric acid to nitric acid is 3-5:1.
[0017] Furthermore, the amount of potassium permanganate used is 5-10% of the mass of the flake graphite.
[0018] Furthermore, during high-temperature and high-pressure synthesis, the pressure is first increased to 1-2 GPa, and the temperature is increased to 550-650℃ while maintaining the pressure. This process is then maintained for 30-60 minutes. Next, the pressure is increased to 4-4.5 GPa, and the temperature is increased to 1300-1350℃ while maintaining the pressure. After maintaining the pressure for 20-25 hours, the pressure is released and the temperature is lowered to 1-2 GPa and 300-350℃. This process is maintained for 1-5 hours, and the temperature is then restored to normal. Finally, the temperature is allowed to cool naturally to room temperature.
[0019] The beneficial effects of this invention are:
[0020] This invention provides a method for preparing single-crystal diamond. Expanded graphite has a loose, porous, worm-like structure. Rare earth salts, nickel salts, and iron salts are deposited in the expanded graphite at a high temperature of 400-500℃ to form a composite ferrite intercalation. Subsequently, a metal catalyst is obtained by carbothermal reduction during vacuum sintering at 1400-1500℃. This method achieves uniform mixing of the metal catalyst and graphite, and also increases the contact area between the metal catalyst and graphite, thereby improving the quality of the prepared single-crystal diamond. The added rare earth elements can reduce the content of bound oxygen, improve the catalytic activity of the metal catalyst, enhance the catalytic effect, increase the nucleation rate of diamond, and make the diamond growth more uniform, with coarser particle size and better thermal stability. Attached Figure Description
[0021] Figure 1 This is an optical image of the single-crystal diamond prepared in Example 1. Detailed Implementation
[0022] Unless otherwise specified in the examples, the conditions were performed under standard conditions or as recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products. Techniques not mentioned in this invention refer to existing technologies. Unless otherwise specified, the following examples and comparative examples are parallel experiments, using the same processing steps and parameters.
[0023] Example 1:
[0024] A method for preparing single-crystal diamond:
[0025] 50g of 100-mesh flake graphite was washed and dried, then placed in 150g of a mixed acid solution consisting of sulfuric acid (98% by mass) and nitric acid (52% by mass) in a mass ratio of 4:1 and stirred for 30 minutes to make it uniform. Then, 3g of potassium permanganate was added and stirring was continued for 2.5 hours. The mixture was then filtered, washed repeatedly with water, dried, and then heated at 950℃ for 3 minutes to obtain expanded graphite with a loose, porous structure and a worm-like structure. A solution was prepared by adding 0.01 mol ytterbium nitrate pentahydrate, 0.1 mol nickel nitrate hexahydrate, 0.19 mol ferric nitrate nonahydrate, and 0.8 mol citric acid to 200 ml of deionized water. The solution was then mixed with expanded graphite at a mass ratio of 1:2. The pH of the solution was adjusted to 7-8 with ammonia. The mixture was stirred in an 80°C water bath for 5 hours until a colloid was formed. The colloid was dried, heated to 450°C for 30 minutes, then vacuum sintered at 1450°C for 40 minutes. After returning to room temperature, the mixture was pressed into a core block at 10 MPa. The core block and {111} seed crystals were then assembled into a composite block. Synthesized under high temperature and high pressure in a hinged SPD6×1200 six-sided hydraulic press. The synthesis process involved first pressurizing to 1.5 GPa, holding at pressure and then heating to 600℃ for 45 minutes. The pressure was then increased to 4.5 GPa, held at pressure, and heated to 1350℃ for 24 hours. Afterward, the pressure was released and the temperature was lowered to 1.5 GPa and 320℃, held at temperature and pressure for 2.5 hours, and then restored to normal pressure. The crystals were then naturally cooled to room temperature and removed, boiled in dilute nitric acid solution for 30 minutes, and then boiled in aqua regia solution for 2 hours. Finally, they were ultrasonically treated in anhydrous ethanol for 15 minutes and dried. The optical image is shown below. Figure 1 As shown, the surface is intact and smooth.
[0026] Example 2:
[0027] A method for preparing single-crystal diamond:
[0028] 50g of 100-mesh flake graphite was washed and dried, then placed in 150g of a mixed acid solution consisting of sulfuric acid (98% by mass) and nitric acid (52% by mass) in a mass ratio of 4:1 and stirred for 30 minutes to make it uniform. Then, 5g of potassium permanganate was added and stirring was continued for 5 hours. The mixture was then filtered, washed repeatedly with water, dried, and then heated at 1000℃ for 5 minutes to obtain expanded graphite with a loose, porous structure and a worm-like structure. A solution was prepared by adding 0.01 mol ytterbium nitrate pentahydrate, 0.1 mol nickel nitrate hexahydrate, 0.19 mol ferric nitrate nonahydrate, and 0.8 mol citric acid to 200 ml of deionized water. The solution was then mixed with expanded graphite at a mass ratio of 1:3. The pH of the solution was adjusted to 7-8 with ammonia. The mixture was stirred in an 80°C water bath for 5 hours until a colloid was formed. The colloid was dried, first held at 500°C for 60 minutes, then vacuum sintered at 1500°C for 60 minutes. After returning to room temperature, the mixture was pressed into a core block at 10 MPa. The core block and {111} seed crystals were then assembled into a synthetic... The blocks were synthesized under high temperature and high pressure in a domestically produced hinged SPD6×1200 six-sided hydraulic press. During synthesis, the pressure was first increased to 2 GPa, and the temperature was increased to 650℃ and held for 60 min. Then the pressure was increased to 4.5 GPa, and the temperature was increased to 1350℃ and held for 25 h. After that, the pressure was released and the temperature was lowered to 2 GPa and 350℃ and held for 5 h. After restoring to normal pressure, the blocks were naturally cooled to room temperature and removed. They were then boiled in a dilute nitric acid solution for 30 min. The resulting single crystal diamonds were then boiled in aqua regia solution for 2 h. Finally, they were ultrasonically treated in anhydrous ethanol for 15 min and dried.
[0029] Example 3:
[0030] A method for preparing single-crystal diamond:
[0031] 50g of 100-mesh flake graphite was washed and dried, then placed in 150g of a mixed acid solution consisting of sulfuric acid (98% by mass) and nitric acid (52% by mass) in a mass ratio of 4:1 and stirred for 30 minutes to make it uniform. Then, 2.5g of potassium permanganate was added and stirring was continued for 1 hour. The mixture was then filtered, washed repeatedly with water, dried, and then heated at 900℃ for 1 minute to obtain expanded graphite with a loose, porous structure and a worm-like structure. A solution was prepared by adding 0.01 mol ytterbium nitrate pentahydrate, 0.1 mol nickel nitrate hexahydrate, 0.19 mol ferric nitrate nonahydrate, and 0.8 mol citric acid to 200 ml of deionized water. The solution was then mixed with expanded graphite at a mass ratio of 1:1. The pH of the solution was adjusted to 7-8 with ammonia. The mixture was stirred in an 80°C water bath for 5 hours until a colloid was formed. The colloid was dried, first held at 400°C for 10 minutes, then vacuum sintered at 1400°C for 30 minutes. After returning to room temperature, it was pressed into a core block under 10 MPa. The core block and {111} seed crystals were then assembled into a composite material. The diamond was synthesized in a domestically produced hinged SPD6×1200 six-sided hydraulic press under high temperature and high pressure. During synthesis, the pressure was first increased to 1 GPa, and the temperature was increased to 550℃ and held for 30 min. Then the pressure was increased to 4 GPa, and the temperature was increased to 1300℃ and held for 20 h. After that, the pressure was released and the temperature was reduced to 1 GPa and 300℃. After holding for 1 h, the temperature was restored to normal and then naturally cooled to room temperature. The diamond was then boiled in a dilute nitric acid solution for 30 min. The resulting single crystal diamond was then boiled in aqua regia solution for 2 h. Finally, it was ultrasonically treated in anhydrous ethanol for 15 min and then dried.
[0032] Comparative Example 1:
[0033] It is basically the same as Example 1, except that 100-mesh flake graphite is used instead of expanded graphite with a worm-like structure.
[0034] A method for preparing single-crystal diamond:
[0035] A solution was prepared by adding 0.01 mol ytterbium nitrate pentahydrate, 0.1 mol nickel nitrate hexahydrate, 0.19 mol ferric nitrate nonahydrate, and 0.8 mol citric acid to 200 ml of deionized water. This solution (1:2 mass ratio) was then mixed with 100-mesh flake graphite. The pH was adjusted to 7-8 with ammonia. The mixture was stirred in an 80°C water bath for 5 hours until a colloid was formed. The colloid was dried, then heated to 450°C for 30 minutes, followed by 1450°C for 40 minutes. After returning to room temperature, the mixture was pressed into a core block at 10 MPa. The core block and {111} seed crystals were then assembled into a composite block. The diamond was synthesized under high temperature and high pressure in a domestically produced hinged SPD6×1200 six-sided hydraulic press. During synthesis, the pressure was first increased to 1.5 GPa, and the temperature was increased to 600℃ and held for 45 min. Then the pressure was increased to 4.5 GPa, and the temperature was increased to 1350℃ and held for 24 h. After that, the pressure was released and the temperature was lowered to 1.5 GPa and 320℃ and held for 2.5 h. After returning to normal pressure, the diamond was naturally cooled to room temperature and removed. It was then boiled in a dilute nitric acid solution for 30 min. The resulting single crystal diamond was then boiled in aqua regia solution for 2 h. Finally, it was ultrasonically treated in anhydrous ethanol for 15 min and dried.
[0036] In this comparative example, because 100-mesh flake graphite was used instead of expanded graphite, the loose and porous worm-like structure was lacking. The in-situ generated composite ferrite was difficult to intercalate or deposit between layers, which led to a decrease in the uniformity of mixing between the metal catalyst and graphite obtained by subsequent reduction, and consequently a decrease in the various properties of the prepared diamond.
[0037] Comparative Example 2:
[0038] It is basically the same as Example 1, except that ytterbium nitrate pentahydrate is not added.
[0039] A method for preparing single-crystal diamond:
[0040] 50g of 100-mesh flake graphite was washed and dried, then placed in 150g of a mixed acid solution consisting of sulfuric acid (98% by mass) and nitric acid (52% by mass) in a mass ratio of 4:1 and stirred for 30 minutes to make it uniform. Then, 3g of potassium permanganate was added and stirring was continued for 2.5 hours. The mixture was then filtered, washed repeatedly with water, dried, and then heated at 950℃ for 3 minutes to obtain expanded graphite with a loose, porous structure and a worm-like structure. A solution was prepared by adding 0.1 mol nickel nitrate hexahydrate, 0.2 mol ferric nitrate nonahydrate, and 0.8 mol citric acid to 200 ml of deionized water. This solution (1:2 mass ratio) was mixed with expanded graphite. The pH of the solution was adjusted to 7-8 with ammonia. The mixture was stirred in an 80℃ water bath for 5 hours until a colloid was formed. The colloid was dried, first held at 450℃ for 30 minutes, then vacuum sintered at 1450℃ for 40 minutes. After returning to room temperature, it was pressed into a core block under 10 MPa. The core block and {111} seed crystals were then assembled into a composite block. This was then processed using a domestically produced hinged SP... Synthesized under high temperature and high pressure in a D6×1200 six-sided hydraulic press. The synthesis process involves first pressurizing to 1.5 GPa, maintaining the pressure and raising the temperature to 600℃, holding the temperature and pressure for 45 minutes, then increasing the pressure to 4.5 GPa, maintaining the pressure and raising the temperature to 1350℃, holding the pressure for 24 hours, then depressurizing and cooling to 1.5 GPa and 320℃, holding the temperature and pressure for 2.5 hours, then restoring to normal pressure and naturally cooling to room temperature. The diamond is then placed in a dilute nitric acid solution and boiled for 30 minutes. The resulting single-crystal diamond is then boiled in aqua regia solution for 2 hours, and finally ultrasonically treated in anhydrous ethanol for 15 minutes and dried.
[0041] In this comparative example, the absence of ytterbium nitrate pentahydrate resulted in the absence of ytterbium in the metal catalyst obtained from the subsequent reduction, which led to a decrease in various properties of the prepared diamond.
[0042] Comparative Example 3:
[0043] The process is basically the same as in Example 1, except that the alloy powder catalyst is mixed with expanded graphite using a ball milling method.
[0044] A method for preparing single-crystal diamond:
[0045] 50g of 100-mesh flake graphite was washed and dried, then placed in 150g of a mixed acid solution consisting of sulfuric acid (98% by mass) and nitric acid (52% by mass) in a mass ratio of 4:1 and stirred for 30 minutes to make it uniform. Then, 3g of potassium permanganate was added and stirring was continued for 2.5 hours. The mixture was then filtered, washed repeatedly with water, dried, and then heated at 950℃ for 3 minutes to obtain expanded graphite with a loose, porous structure and a worm-like structure. A solution was prepared by adding 0.01 mol ytterbium nitrate pentahydrate, 0.1 mol nickel nitrate hexahydrate, 0.19 mol ferric nitrate nonahydrate, and 0.8 mol citric acid to 200 ml of deionized water. The pH of the solution was adjusted to 7-8 with ammonia. The solution was stirred in an 80°C water bath for 5 h until a colloid was formed. The colloid was dried, kept at 450°C for 30 min, and then vacuum sintered at 1450°C for 40 min under a hydrogen atmosphere. After returning to room temperature, an alloy powder catalyst was obtained. The alloy powder catalyst was mixed with expanded graphite by ball milling for 5 h and then pressed into a core block under 10 MPa. The core block and {111} seed crystal were then assembled. The synthesized blocks were synthesized under high temperature and high pressure in a domestically produced hinged SPD6×1200 six-sided hydraulic press. During synthesis, the pressure was first increased to 1.5 GPa, and the temperature was increased to 600℃ and held for 45 min. Then the pressure was increased to 4.5 GPa, and the temperature was increased to 1350℃ and held for 24 h. After that, the pressure was released and the temperature was lowered to 1.5 GPa and 320℃ and held for 2.5 h. After returning to normal pressure, the blocks were naturally cooled to room temperature and removed. They were then boiled in a dilute nitric acid solution for 30 min. The resulting single-crystal diamonds were then boiled in aqua regia solution for 2 h. Finally, they were ultrasonically treated in anhydrous ethanol for 15 min and dried.
[0046] In this comparative example, the metal catalyst obtained by reduction and the expanded graphite ball milling and mixing are not as uniform as the metal catalyst and expanded graphite obtained by carbothermal reduction of the composite ferrite first generated in situ between the expanded graphite layers in Example 1. This results in a decrease in various properties of the prepared diamond.
[0047] Comparative Example 4:
[0048] It is basically the same as Comparative Example 3, except that the alloy powder catalyst is replaced with commercially available Fe... 70 Ni 30 Alloy powder catalyst is used as a substitute.
[0049] A method for preparing single-crystal diamond:
[0050] 50g of 100-mesh flake graphite was washed, dried, and then placed in 150g of a mixed acid solution consisting of sulfuric acid (98% by mass) and nitric acid (52% by mass) in a 4:1 mass ratio. The mixture was stirred for 30 minutes to ensure homogeneity. Then, 3g of potassium permanganate was added, and stirring continued for 2.5 hours. The mixture was then filtered, repeatedly washed with water, dried, and finally heated at 950℃ for 3 minutes to obtain loose, porous expanded graphite with a worm-like structure. Commercially available Fe... 70 Ni 30 Alloy powder catalyst was mixed with expanded graphite ball milling for 5 hours and then pressed into a core block under 10 MPa. The core block and {111} seed crystal were then assembled into a synthetic block and synthesized under high temperature and high pressure in a domestically produced hinged SPD6×1200 six-sided hydraulic press. During synthesis, the pressure was first increased to 1.5 GPa, and the temperature was increased to 600℃ and held for 45 minutes. Then the pressure was increased to 4.5 GPa, and the temperature was increased to 1350℃ and held for 24 hours. After that, the pressure was released and the temperature was lowered to 1.5 GPa and 320℃. After holding for 2.5 hours, the pressure was restored to normal and the block was naturally cooled to room temperature. The block was then boiled in dilute nitric acid solution for 30 minutes. The resulting single crystal diamond was then boiled in aqua regia solution for 2 hours. Finally, it was ultrasonically treated in anhydrous ethanol for 15 minutes and dried.
[0051] This indicates that the metal catalyst in Comparative Example 3 has a better catalytic effect on single-crystal diamond than commercially available Fe catalysts. 70 Ni 30 Alloy powder catalyst.
[0052] Comparative Example 5:
[0053] It is basically the same as Comparative Example 4, except that expanded graphite is replaced with 100-mesh flake graphite.
[0054] A method for preparing single-crystal diamond:
[0055] Commercially available Fe 70 Ni 30 Alloy powder catalyst was mixed with 100-mesh flake graphite ball milled for 5 hours and then pressed into a core block under 10 MPa. The core block and {111} seed crystal were then assembled into a synthetic block and synthesized under high temperature and high pressure in a domestically produced hinged SPD6×1200 six-sided hydraulic press. During synthesis, the pressure was first increased to 1.5 GPa, and the temperature was increased to 600℃ and held for 45 minutes. Then the pressure was increased to 4.5 GPa, and the temperature was increased to 1350℃ and held for 24 hours. After that, the pressure was released and the temperature was lowered to 1.5 GPa and 320℃. After holding for 2.5 hours, the pressure was restored to normal and the block was naturally cooled to room temperature. The block was then boiled in a dilute nitric acid solution for 30 minutes. The resulting single crystal diamond was then boiled in aqua regia solution for 2 hours. Finally, it was ultrasonically treated in anhydrous ethanol for 15 minutes and dried.
[0056] This indicates that expanded graphite with a loose, porous, worm-like structure is more suitable as a raw material for preparing single-crystal diamond compared to flake graphite.
[0057] Performance testing:
[0058] The single-crystal diamonds synthesized in Examples 1-3 and Comparative Examples 1-5 of the present invention were used as samples.
[0059] The standard for diamond particle size testing is based on the national standard GB / T 6406-1996 "Particle Size of Superhard Abrasive Diamond or Cubic Boron Nitride". The equipment used is a vibrating screen and a standard test sieve to screen the diamond particles. The size of each particle size is determined by the mesh size of two adjacent screens. For example, when particles can pass through a 35-mesh screen but cannot pass through a 40-mesh screen, the particle size of these particles is called 35 / 40, and so on.
[0060] The compressive strength is the load value at which a single diamond breaks under static pressure. The compressive strength of a single particle is measured using the German Dia Test-SI automatic static compressive strength tester. Each grain is subjected to pressure from the anvil. As the pressure gradually increases, it continues until the grain breaks. The resistance to pressure per unit area during breakage is the compressive strength.
[0061] Thermal shock strength (TTI) is characterized by holding diamond particles at a certain temperature for a certain time, cooling them, and then using a steel ball and a mold to conduct an impact test at a set frequency and number of impacts, based on the proportion of undamaged diamond particles. The TTI test conditions are: holding at 1100℃ for ten minutes in an argon atmosphere, and measuring according to the requirements of JB / T10987-2010 "Method for Determination of Impact Toughness of Superhard Abrasive Synthetic Diamond".
[0062] The use of materials such as iron and nickel during diamond synthesis allows them to enter the diamond crystal, giving it magnetism. The strength of this magnetism reflects the amount of impurities present. The fewer impurities a diamond contains, the weaker its magnetism; conversely, the more impurities, the stronger its magnetism. Magnetic susceptibility is measured using an HRC-2 diamond magnetic susceptibility analyzer.
[0063] The test results are shown in Table 1 below:
[0064]
[0065] As shown in Table 1 above, the single-crystal diamond synthesized by the method of the present invention has a high yield and high hydrostatic strength and thermal shock toughness, low magnetic susceptibility, high purity, and low impurity content.
[0066] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for preparing single-crystal diamond, characterized in that, Specifically as follows: Rare earth salts, nickel salts, iron salts, and citric acid are added to deionized water to prepare a solution. Expanded graphite is added, and the pH of the solution is adjusted to 7-8. The solution is stirred in a water bath at 70-90℃ until a colloid is formed. The colloid is dried, and the solution is first kept at 400-500℃ for 10-60 minutes. Then, it is vacuum sintered at 1400-1500℃ for 30-60 minutes and assembled into a synthetic block. Finally, single crystal diamond is synthesized under high temperature and high pressure. The expanded graphite has a loose, porous, worm-like structure.
2. The method for preparing single-crystal diamond as described in claim 1, characterized in that, The molar ratio of the rare earth salt, nickel salt, iron salt, and citric acid is x:1:2-x:8; 0<x≤0.
1.
3. The method for preparing single-crystal diamond as described in claim 1, characterized in that, The total mass ratio of the rare earth salts, nickel salts, iron salts, and citric acid to the deionized water is 1:3-6.
4. The method for preparing single-crystal diamond as described in claim 1, characterized in that, The mass ratio of the expanded graphite to the solution is 1:1-3.
5. The method for preparing single-crystal diamond as described in claim 1, characterized in that, The preparation method of the expanded graphite is as follows: After washing and drying the flaky graphite, place it in a mixed acid solution composed of sulfuric acid and nitric acid and stir evenly. Then add potassium permanganate and continue stirring for 1-5 hours. Filter, wash with water, dry, and then heat at 900-1000℃ for 1-5 minutes.
6. The method for preparing single-crystal diamond as described in claim 5, characterized in that, The mass concentration of sulfuric acid is 90-98%, and the mass concentration of nitric acid is 50-60%.
7. The method for preparing single-crystal diamond as described in claim 5, characterized in that, The mass ratio of sulfuric acid to nitric acid is 3-5:
1.
8. The method for preparing single-crystal diamond as described in claim 5, characterized in that, The amount of potassium permanganate used is 5-10% of the mass of flake graphite.
9. The method for preparing single-crystal diamond as described in claim 1, characterized in that, During high-temperature and high-pressure synthesis, first pressurize to 1-2 GPa, maintain pressure and raise temperature to 550-650℃, maintain temperature and pressure for 30-60 min, then pressurize to 4-4.5 GPa, maintain pressure and raise temperature to 1300-1350℃, maintain pressure for 20-25 h, then depressurize and lower temperature to 1-2 GPa and 300-350℃, maintain temperature and pressure for 1-5 h, then restore to normal pressure and allow to cool naturally to room temperature.