Novel high-temperature and high-pressure large single crystal diamond and synthesis method thereof

Abstract

The invention discloses a novel high-temperature and high-pressure large single crystal diamond and a synthesis method thereof, and belongs to the technical field of artificial diamond synthesis. According to the method, a synthesis block assembly structure is improved, a carbon source and a nickel-containing plug material in a special ratio are adopted, the synthesis process is divided into multiple stages, and different temperatures, pressures and change rates are set respectively, so that the high-temperature and high-pressure large single crystal diamond is obtained. Therefore, the crystal growth environment can be accurately controlled. The method specifically comprises the following steps: in the first stage, slowly raising temperature and pressure and keeping temperature and pressure for 48 hours; the second stage is constant-speed boosting and cooling for 144 hours; and in the third stage, boosting and cooling speeds are further reduced, and temperature and pressure gradients are reduced. The diamond large single crystal synthesized by the method has the advantages of uniform granularity, high purity, low crystal cracking rate, few impurities and the like, is suitable for jewel-grade and high-performance industrial application, is stable in process and is suitable for batch production.

Description

Technical Field

[0001] This invention relates to the field of synthetic diamond technology, and in particular to a novel high-temperature, high-pressure large single-crystal diamond and its synthesis method. Background Technology

[0002] Diamond is a material with numerous superior properties, including extremely high hardness, high breakdown voltage, high thermal conductivity, and chemical stability. High-quality large single-crystal diamond, or Type IIa diamond, is a superhard material with exceptional properties. Its notable characteristics include the absence of metallic impurities and non-metallic impurities such as nitrogen, boron, and hydrogen, and the absence of stress and defects within the crystal. This type of diamond crystal exhibits a colorless and transparent appearance, possessing excellent optical transparency, high light transmittance, and high thermal conductivity. Therefore, it is considered one of the most promising gem-quality materials, and it also shows broad prospects in thermal, acoustic, optical, and electronic applications. Its high purity and low defect density make it a preferred material for high-end jewelry, thermal management components, optical devices, and high-performance electronic products.

[0003] With the advancement of scientific research and the development of high-temperature and high-pressure technology, my country has now optimized the length and angle of the small inclined side of the top hammer and the pressure transmission sealing material of the hinged six-sided top press. The pressure and temperature generated are now fully capable of meeting the synthesis conditions for large single crystals of diamond-grade diamond. The pressure is about 5-6 GPa and the temperature generally does not exceed 1400 ℃.

[0004] As the volume of diamond crystals gradually increases, the growth surface of the crystals gradually moves towards the high-temperature end of the synthesis chamber, and the synthesis temperature gradually increases. This leads to an unstable growth environment inside the chamber, which will reduce the quality of the diamonds and may even cause "cracks".

[0005] The invention patent with patent application number CN202210691796.4 discloses a method for synthesizing octahedral diamond, including preparing alloy catalyst powder, adding high-purity graphite powder to LiAlH4 and mixing it with the alloy catalyst powder to obtain raw materials, putting them into a high-speed wet granulator for mixing and granulation, adding the granular mixture into a mold to obtain core plates, seeding between the core plates and stacking and pressing them to obtain core columns, placing the core columns in a vacuum furnace to remove dispersing solvents, oxygen and other impurities, vacuum packaging the core columns after they come out of the furnace, putting the core columns into diamond synthesis blocks, and then putting them into a six-sided top press for synthesis. The beneficial effects of this invention are that by adjusting the different proportions of alloy catalyst powder, mixing it with high-purity graphite powder, uniformly adding LiAlH4 to the high-purity graphite powder, and adopting a synthesis process with multi-stage gradual increase in pressure and power, the growth of special crystal-type octahedral diamond can be better controlled. The octahedral diamond synthesized by this invention has good crystal consistency, high crystal face integrity, high purity, and high impact resistance. However, this invention has the disadvantages of low weight of individual crystals, low yield per unit, and does not address the applicability of the process for single long-term production (more than 10 days), as well as the quality issues of diamonds under long-term production. Summary of the Invention

[0006] The purpose of this invention is to provide a novel high-temperature, high-pressure large single-crystal diamond and its synthesis method. The synthesized diamond has a particle size of 5.5-6 mm. This invention aims to solve the problem in existing production processes where, as the synthesis cycle lengthens, the diamond crystal growth volume gradually increases, the crystal growth surface gradually moves towards the high-temperature end of the synthesis cavity, and the synthesis temperature gradually rises. This leads to uneven growth temperature of the large single-crystal diamond within the cavity, resulting in unstable temperature and pressure within the cavity and an increased diamond cracking rate. This invention divides the synthesis cycle of large single-crystal diamond into multiple stages and implements different temperature and pressure processes at different stages, thereby improving crystal quality and yield.

[0007] A novel method for synthesizing high-temperature, high-pressure large single-crystal diamond, the method comprising the following steps:

[0008] (1) Select flake graphite powder and diamond micro powder to prepare carbon source powder;

[0009] (2) The carbon source powder in step (1) is put into a high-speed wet granulator for mixing and granulation to obtain a 20-40 mesh granular mixture;

[0010] (3) Add the granular mixture prepared in step (2) into the mold and press it with a four-column press to obtain the core column sheet;

[0011] (4) Place the core column sheet prepared in step (3) in a vacuum furnace and vacuum treat it at 1100℃-1300℃. After taking it out of the furnace, vacuum package the core column.

[0012] (5) Select barium zirconate powder as the raw material for the plugging material, and put it into a high-speed wet granulator for granulation to obtain granules;

[0013] (6) Add the granules prepared in step (5) into the mold and press them with a four-column press to obtain barium zirconate core sheets with a thickness of 4 mm ± 0.05 mm;

[0014] (7) Place the barium zirconate core prepared in step (6) in a vacuum furnace and vacuum treat it at 1300℃-1500℃. After taking it out of the furnace, vacuum package the core.

[0015] (8) Stack the core sheets from step (7) with barium zirconate core sheets on top and nickel sheets on the bottom, and press the stacked core sheets with a four-column press to obtain a core with a height of 8mm ± 0.05mm;

[0016] (9) Place the core sheet prepared in step (4) and the core prepared in step (8) into the diamond synthesis block, and then put the diamond synthesis block into a six-sided press for synthesis. The actual synthesis pressure and temperature are controlled by the pressure curve and the power control curve, respectively. The synthesis is carried out by first raising the temperature and pressure, then keeping the temperature and pressure, and then through multiple stages of pressure increase and multiple stages of power decrease.

[0017] Steps (1) to (9) are performed in sequence.

[0018] Preferably, the carbon source powder in step (1) comprises the following components in parts by weight: 30-40% flake graphite powder and 60-70% diamond micro powder. The flake graphite powder has a purity of 99.995% or higher and a mesh size of 400 mesh or finer. The diamond micro powder has a particle size of 100 / 200, a purity of ≥99.8%, and a crystal form of type IIa.

[0019] Specifically, the carbon source powder may include any component in the range of 30-40% by weight, such as 30% flake graphite powder, 32% flake graphite powder, 34% flake graphite powder, 36% flake graphite powder, and 40% flake graphite powder; and any value of diamond micron powder in the range of 60%-70%, such as 70% diamond micron powder, 68% diamond micron powder, 66% diamond micron powder, 64% diamond micron powder, and 60% diamond micron powder.

[0020] Preferably, in any of the above embodiments, the barium zirconate powder has a purity of ≥98.5% and a mesh size of 300 mesh or finer.

[0021] In any of the above schemes, the preferred option is that in step (4), the core column prepared in step (3) is placed in a vacuum furnace and vacuum-treated at 1100℃-1300℃, and the core column is vacuum-packed after being taken out of the furnace.

[0022] Specifically, the temperature during vacuum treatment can be any value within the range of 1100℃-1300℃, such as 1100℃, 1150℃, 1200℃, 1250℃, or 1300℃.

[0023] In any of the above schemes, the preferred option is that in step (7), the barium zirconate core prepared in step (6) is placed in a vacuum furnace and vacuum treated at 1300℃-1500℃, and the core is vacuum packaged after being taken out of the furnace.

[0024] Specifically, the temperature during vacuum treatment can be any value within the range of 1100℃-1300℃, such as 1300℃, 1350℃, 1400℃, 1450℃, or 1500℃.

[0025] The preferred embodiment of any of the above schemes is that the nickel sheet described in step (8) has a purity of ≥99.0% and a thickness of 2mm ± 0.05mm.

[0026] In any of the above schemes, the preferred option is that, in step (8), the control pressure curve is specifically as follows: the six-sided top press is pressurized at a rate greater than 60 MPa / hour to increase the pressure in the cavity from 0 MPa to 75-90 MPa, and then the pressure is maintained for a period of time in the pressure holding stage. Then, the pressure is increased at a rate of 2-3 MPa / hour and maintained for a period of time. Then, the pressure is increased at a rate of 1-1.5 MPa / hour and maintained for a period of time. Finally, the pressure is released naturally.

[0027] Specifically, a six-sided press is used to increase the pressure inside the chamber from 0 MPa to any value within the range of 75-90 MPa at a pressurization rate greater than 60 MPa / hour, such as 75 MPa, 80 MPa, 85 MPa, or 90 MPa. After that, a pressure holding phase is entered and maintained for a period of time. Then, the pressure is increased at a constant rate of 2-3 MPa / hour and maintained for a period of time. Next, the pressure is increased at a constant rate of 1-1.5 MPa / hour and maintained for a period of time. Finally, the pressure is released naturally.

[0028] The preferred option among the above schemes is that, after step (8), the pressure holding period is 48 hours.

[0029] In any of the above schemes, the preferred option is that in step (8), the pressure holding stage is maintained for 48 hours, and then the pressure is increased at a constant rate of 2-3 MPa / hour (the pressure increase rate can be 2 MPa / hour, 2.5 MPa / hour, or 3 MPa / hour) for 144 hours, and then the pressure is increased at a constant rate of 1-1.5 MPa / hour (the pressure increase rate here can be 1 MPa / hour, 1.2 MPa / hour, 1.3 MPa / hour, or 1.5 MPa / hour) for 144 hours, and finally the pressure is released naturally.

[0030] In any of the above schemes, the preferred option is that in step (8), the stacking weight ratio of the barium zirconate core and the nickel sheet is 60%-80% for the barium zirconate core and 20%-40% for the nickel sheet.

[0031] Specifically, during stacking, the barium zirconate core can be any value within the range of 60%-80%, such as 60%, 70%, or 80%; the nickel can be any value within the range of 20%-40%, such as 20%, 30%, or 40%.

[0032] In any of the above schemes, the preferred power control curve is as follows: the initial power is 7.5-8.5KW, maintained for a period of time, then enters the heat preservation stage, maintained for a period of time, then cools down at a uniform rate of 0.04-0.055 W / h, maintained for a period of time, then cools down at a uniform rate of 0.02-0.03W / h, maintained for a period of time, and finally cools down naturally.

[0033] In any of the above schemes, the preferred option is that in step (8), the power control curve is as follows: the initial power is 7.5-8.5KW, maintained for 1 hour, then enters the heat preservation stage, maintained for 48 hours, then cools down at a constant rate of 0.04-0.055 W / hour and maintained for 144 hours, then cools down at a constant rate of 0.02-0.03W / hour and maintained for 144 hours, and finally cools down naturally.

[0034] Specifically, the initial power is any value within the range of 7.5-8.5kW, such as 7.5kW, 8kW, or 8.5kW, and is maintained for 1 hour; then it enters the heat preservation stage and is maintained for 48 hours; then it is cooled at a uniform rate of 0.04-0.055 W / hour (the heating rate can be any value within the range of 0.04-0.055 W / hour, such as 0.04W / hour, 0.045W / hour, 0.05W / hour, or 0.055W / hour) and maintained for 144 hours; then it is cooled at a uniform rate of 0.02-0.03 W / hour (the heating rate can be any value within the range of 0.02-0.03 W / hour, such as 0.02W / hour, 0.025W / hour, or 0.03W / hour) and maintained for 144 hours; finally, it is allowed to cool naturally.

[0035] A novel high-temperature, high-pressure large single-crystal diamond is obtained by any of the synthesis methods described above.

[0036] Beneficial effects

[0037] This invention provides a novel high-temperature, high-pressure large single-crystal diamond and its synthesis method. The method improves the assembly structure of the synthesis block by adjusting the carbon source formulation to create a new carbon source, and by optimizing the structure and formulation of the plug material in the traditional synthesis block by incorporating a novel nickel sheet formulation. The structure is constructed using stacked barium zirconate sheets made of nickel sheets. This application divides the synthesis process into multiple stages, setting different temperatures, pressures, and rates of change to ensure a stable crystal growth environment for producing high-quality large single-crystal diamonds (particle size 5.5-6 mm). Specifically, the process includes: a first stage of slow heating and pressurization followed by holding at that temperature and pressure for 48 hours; a second stage of uniform pressurization and cooling for 144 hours; and a third stage of further slowing down the pressurization and cooling rates to reduce temperature and pressure gradients. The large single-crystal diamond synthesized by this invention has advantages such as uniform particle size, high purity, low crystal cracking rate, and few impurities, making it suitable for gem-quality and high-performance industrial applications. Furthermore, the process is stable and suitable for mass production.

[0038] (1) The present invention adopts a synthesis process of first raising the temperature and pressure, then keeping the temperature and pressure, and then slowly raising the pressure and lowering the power for a long time in multiple stages, so as to better control the high-quality growth of diamond.

[0039] (2) By adding type IIa diamond micro powder to the carbon source and adjusting the ratio to mix with flake graphite powder, the present invention avoids the growth of diamond in the carbon source, reduces the self-consumption of the carbon source, and ensures the supply of carbon source to compete with the crystal bed.

[0040] (3) By adding nickel sheets to the plug material and adjusting the ratio to press them together with barium zirconate into a column, the present invention ensures that the diamond is not contaminated by impurities during the above-mentioned processing and further ensures the stability of the growth environment.

[0041] (4) The novel high-temperature and high-pressure large single-crystal diamond synthesis method of the present invention produces large single-crystal diamonds with a high proportion of A-grade material (i.e., the produced diamonds are graded as E or above, and no internal central impurities are observed under an optical microscope at a magnification of less than 2000x), high weight per crystal, a large number of diamonds produced per batch, large individual crystal size, a large number of crystals, low crystal cracking rate, and high purity. The process has good stability, can meet the needs of mass production and market demand, and can enable enterprises to obtain good economic benefits. Attached Figure Description

[0042] Figure 1 This is an internal assembly structure diagram of the novel high-temperature and high-pressure large single-crystal diamond synthesis method of the present invention;

[0043] Figure 2 The trend of pressure curve variation is shown in the novel high-temperature and high-pressure large single-crystal diamond synthesis method of the present invention.

[0044] Figure 3 The image shows a physical sample of a large single-crystal diamond synthesized using the novel high-temperature and high-pressure large single-crystal diamond synthesis method of this invention.

[0045] Figure 4 The image shows a physical diamond synthesized using existing synthetic methods.

[0046] Figure 5 Comparison of crack patterns under a high-magnification optical microscope using the synthesis method of this invention and existing synthesis methods;

[0047] Reference numerals: 1. Pyrophyllite composite block; 2. Steel ring; 3. Dolomite lining; 4. Heating tube; 5. Molybdenum sheet; 6. Pyrophyllite ring; 7. Plug; 8. Carbon source; 9. Metal catalyst; 10. Seed crystal. Detailed Implementation

[0048] The following embodiments are further illustrations of the present invention and serve as explanations of the technical content of the present invention. However, the essence of the present invention is not limited to the embodiments described below. Those skilled in the art can and should know that any simple changes or substitutions based on the spirit of the present invention should fall within the protection scope claimed by the present invention.

[0049] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0050] This invention provides a novel method for synthesizing large single-crystal diamond under high temperature and high pressure. The specific synthesis method includes the following steps:

[0051] (1) Select flake graphite powder and diamond micro powder to prepare carbon source powder: Specifically, select flake graphite powder with a purity of 99.995% or higher and a mesh size of 400 mesh or finer, and diamond micro powder with a particle size of 100 / 200, a purity of ≥99.8%, and a crystal form of type IIa. The weight percentage of the two is flake graphite powder: 40%, diamond micro powder: 60%.

[0052] (2) The raw materials in step (1) are put into a high-speed wet granulator for mixing and granulation to obtain 20-mesh granules;

[0053] (3) Add the granular mixture prepared in step (2) into the mold and press it with a four-column press to obtain a core column sheet with a thickness of 3mm ± 0.05mm;

[0054] (4) Place the core sheet prepared in step (3) in a vacuum furnace and vacuum treat it at 1100℃-1300℃ for 5 hours to remove impurities. After taking it out of the furnace, vacuum package the core sheet.

[0055] (5) Select barium zirconate powder with a purity of ≥98.5% and a mesh size of 300 as the raw material for the plugging material, and put it into a high-speed wet granulator for granulation to obtain granules with a mesh size of less than 100.

[0056] (6) Add the granules prepared in step (5) into the mold and press them with a four-column press to obtain barium zirconate core sheets with a thickness of 4 mm ± 0.05 mm;

[0057] (7) Place the barium zirconate core prepared in step (6) in a vacuum furnace and vacuum treat it at 1300℃-1500℃ for 2 hours to remove impurities. After taking it out of the furnace, vacuum package the core.

[0058] (8) Select nickel sheets with a purity of ≥99.0% and a thickness of 2mm±0.05mm. Stack the barium zirconate core sheets from step (7) with barium zirconate core sheets on the top layer and nickel sheets on the bottom layer. The stacking composition ratio is barium zirconate core sheets: 80% and nickel: 20%. Press the stacked core sheets with a four-column press to obtain a core with a height of 8mm±0.05mm.

[0059] (9) Place the core sheet prepared in step (4) and the core prepared in step (8) into the diamond synthesis block, and then put the diamond synthesis block into a six-sided press for synthesis. The actual synthesis pressure and temperature are guaranteed by controlling the pressure curve and the power control curve, respectively. The synthesis is carried out by first raising the temperature and pressure, then keeping the temperature and pressure, and then slowly raising the pressure and lowering the power for a long time.

[0060] Specifically, during synthesis in a six-sided press, such as Figure 1 As shown, the outer layer is a hollow column wrapped with a pyrophyllite composite block 1. The pyrophyllite composite block 1 is filled with a dolomite liner 3 and a pyrophyllite ring 6. The bottom is sealed with a molybdenum sheet 5. The side wall of the dolomite liner 3 is equipped with a heating tube 4. The inner cavity is arranged from bottom to top as follows: seed crystal 10, metal catalyst 9 (the catalyst is a mixture of 70% iron powder and 30% cobalt powder pressed into shape), carbon source 8 (made of flake graphite powder and diamond micro powder, with the weight percentage of flake graphite powder: 40% and diamond micro powder: 60%), and the top is sealed with a plug 7, a molybdenum sheet 5, and a steel ring 2 from bottom to top.

[0061] Specifically, such as Figure 2 As shown, the pressure control curve is as follows: the six-sided press is pressurized at a rate greater than 60 MPa / hour to increase the pressure in the cavity from 0 MPa to 75 MPa, then enters the pressure holding stage and maintains it for 48 hours. Then, the pressure is increased at a constant rate of 2 MPa / hour and maintained for 144 hours. Then, the pressure is increased at a constant rate of 1 MPa / hour and maintained for 144 hours. Finally, the pressure is naturally released. The power control curve is as follows: the initial power is 7.5 KW and maintained for 1 hour. Then, the heat preservation stage is entered and maintained for 48 hours. Then, the temperature is decreased at a constant rate of 0.04 W / hour and maintained for 144 hours. Then, the temperature is decreased at a constant rate of 0.02 W / hour and maintained for 144 hours. Finally, the temperature is naturally released, and the synthesis ends after cooling and depressurization.

[0062] The relevant properties of the diamond obtained after synthesis are shown in Table 1 below:

[0063] Table 1

[0064]

[0065] The large single-crystal diamond synthesized in this invention, such as Figure 3As shown, the proportion of A-grade material is high (i.e., the produced diamonds are graded E or higher in color, and no internal central impurities are observed when viewed under an optical microscope at a magnification of less than 2000x), the weight of a single crystal is high, the number of diamonds produced in a single batch is large, the size of a single crystal is large, the number of crystals is large, the cracking rate is low, and the clarity is high. Figure 4 The image shows a physical diamond synthesized using existing synthetic methods. It contains obvious inclusions and has many impurities.

[0066] Example 2

[0067] A novel high-temperature, high-pressure method for synthesizing large single-crystal diamond is similar to that in Example 1, except that the synthesis method specifically includes the following steps:

[0068] (1) Select flake graphite powder and diamond micro powder to prepare carbon source powder: Specifically, select flake graphite powder with a purity of 99.995% or higher and a mesh size of 400 mesh or finer, and diamond micro powder with a particle size of 100 / 200, a purity of ≥99.8%, and a crystal form of type IIa. According to the weight percentage, the flake graphite powder is 35% and the diamond micro powder is 65%.

[0069] (2) The carbon source powder from step (1) is put into a high-speed wet granulator for mixing and granulation to obtain a 30-mesh granular mixture;

[0070] (3) Add the granular mixture from step (2) into the mold and press it with a four-column press to obtain a core plate with a thickness of 4mm ± 0.05mm;

[0071] (4) Place the core column sheet prepared in step (3) in a vacuum furnace and vacuum treat it at 1100℃-1300℃ for 6 hours to remove impurities. After taking it out of the furnace, vacuum package the core column.

[0072] (5) Select barium zirconate powder with a purity of ≥98.5% and a mesh size of 300 as the raw material for plugging material, and put it into a high-speed wet granulator for granulation to obtain granules with a mesh size of less than 100.

[0073] (6) Add the granules prepared in step (5) into the mold and press them with a four-column press to obtain barium zirconate core sheets with a thickness of 4 mm ± 0.05 mm;

[0074] (7) Place the barium zirconate core in step (6) in a vacuum furnace and vacuum treat it at 1300℃-1500℃ for 3 hours to remove impurities. After taking it out of the furnace, vacuum package the core.

[0075] (8) Select nickel sheets with a purity of ≥99.0% and a thickness of 2mm±0.05mm. Stack the barium zirconate core sheets prepared in step (7) with barium zirconate core sheets on the top layer and nickel sheets on the bottom layer. The stacking composition ratio is barium zirconate: 70% and nickel: 30%. Press the stacked core sheets with a four-column press to obtain a core with a height of 8mm±0.05mm.

[0076] (9) Place the core sheet prepared in step (4) and the core prepared in step (8) into the diamond synthesis block, and then put the diamond synthesis block into a six-sided press for synthesis. The actual synthesis pressure and temperature are guaranteed by controlling the pressure curve and the power control curve, respectively. The synthesis is carried out by first raising the temperature and pressure, then keeping the temperature and pressure, and then slowly raising the pressure and lowering the power for a long time.

[0077] Specifically, the pressure control curve is as follows: the six-sided press is pressurized at a rate greater than 60 MPa / hour to increase the pressure inside the chamber from 0 MPa to 82.5 MPa, enters the pressure holding stage, and is maintained for 48 hours. Then, the pressure is increased at a constant rate of 2.5 MPa / hour and maintained for 144 hours. Then, the pressure is increased at a constant rate of 1.25 MPa / hour and maintained for 144 hours. Finally, the pressure is released naturally.

[0078] The power control curve is as follows: the initial power is 8KW, maintained for 1 hour, then enters the heat preservation stage, maintained for 48 hours, then the temperature is uniformly reduced at a rate of 0.0475W / hour and maintained for 144 hours, then the temperature is uniformly reduced at a rate of 0.025W / hour and maintained for 144 hours, and finally the temperature is naturally reduced. The synthesis ends after the temperature is reduced and the pressure is released.

[0079] The diamonds obtained after synthesis have a yield of 65 carats per diamond, and the relevant indicators are shown in Table 2 below:

[0080] Table 2

[0081]

[0082] Example 3

[0083] A novel high-temperature, high-pressure method for synthesizing large single-crystal diamond is similar to that in Example 1, except that the specific method includes the following steps:

[0084] (1) Select flake graphite powder and diamond micro powder to prepare carbon source powder: Specifically, select flake graphite powder with a purity of 99.995% or higher and a mesh size of 400 mesh or finer, and diamond micro powder with a particle size of 100 / 200, a purity of ≥99.8%, and a crystal form of type IIa. According to the weight percentage, the flake graphite powder is 30% and the diamond micro powder is 70%.

[0085] (2) The carbon source powder from step (1) is put into a high-speed wet granulator for mixing and granulation to obtain a 40-mesh granular mixture.

[0086] (3) Add the granular mixture prepared in step (2) into the mold and press it with a four-column press to obtain a core plate with a thickness of 4mm ± 0.05mm;

[0087] (4) Place the core sheet prepared in step (3) in a vacuum furnace and vacuum treat it at 1100℃-1300℃ for 7 hours to remove impurities. After taking it out of the furnace, vacuum package the core sheet.

[0088] (5) Select barium zirconate powder with a purity of ≥98.5% and a mesh size of 300 as the raw material for the plugging material, and put it into a high-speed wet granulator for granulation to obtain granules with a mesh size of less than 100.

[0089] (6) The granules prepared in step (5) are added into the molds respectively, and barium zirconate core sheets with a thickness of 4 mm ± 0.05 mm are obtained by pressing them with a four-column press.

[0090] (7) Place the barium zirconate core prepared in step (6) in a vacuum furnace and vacuum treat it at 1300℃-1500℃ for 4 hours to remove impurities. After taking it out of the furnace, vacuum package the core.

[0091] (8) Select nickel sheets with a purity of ≥99.0% and a thickness of 2mm±0.05mm. Stack the barium zirconate core sheets prepared in step (7) with barium zirconate core sheets on the top layer and nickel sheets on the bottom layer. The stacking composition ratio is barium zirconate: 60% and nickel: 40%. Press the stacked barium zirconate core sheets with a four-column press to obtain cores with a height of 8mm±0.05mm.

[0092] (9) Place the core sheet prepared in step (4) and the core prepared in step (8) into the diamond synthesis block, and then put the diamond synthesis block into a six-sided press for synthesis. The actual synthesis pressure and temperature are guaranteed by controlling the pressure curve and the power control curve, respectively. The synthesis is carried out by first raising the temperature and pressure, then keeping the temperature and pressure, and then slowly raising the pressure and lowering the power for a long time.

[0093] Specifically, the pressure control curve is as follows: the six-sided press is pressurized at a rate greater than 60 MPa / hour to increase the pressure inside the chamber from 0 MPa to 90 MPa, enters the pressure holding stage, and is maintained for 48 hours. Then, the pressure is increased at a constant rate of 3 MPa / hour and maintained for 144 hours. Then, the pressure is increased at a constant rate of 1-1.5 MPa / hour and maintained for 144 hours. Finally, the pressure is released naturally.

[0094] The power control curve is as follows: the initial power is 8.5KW, maintained for 1 hour, then enters the heat preservation stage, maintained for 48 hours, then the temperature is uniformly reduced at a rate of 0.055 W / hour and maintained for 144 hours, then the temperature is uniformly reduced at a rate of 0.03W / hour and maintained for 144 hours, and finally the temperature is naturally reduced. The synthesis ends after the temperature is reduced and the pressure is released.

[0095] The relevant properties of the diamond obtained after synthesis are shown in Table 3 below:

[0096] Table 3

[0097]

[0098] Figure 5 The images show a comparison of crack patterns obtained using the synthesis method of this invention and existing synthesis methods under a high-magnification optical microscope. Figure 5 The image on the left shows a large single-crystal diamond formed using the synthesis method of this invention, while the image on the right shows a large single-crystal diamond formed using a synthesis method in the prior art. From... Figure 5 It can be seen that the synthesis method described in this paper results in a low crystallization rate and high purity.

[0099] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A novel method for synthesizing high-temperature, high-pressure large single-crystal diamond, characterized in that, The synthesis method includes the following steps: (1) Select flake graphite powder and diamond micro powder to prepare carbon source powder; (2) The carbon source powder from step (1) is put into a high-speed wet granulator for mixing and granulation to obtain a granular mixture; (3) Add the granular mixture prepared in step (2) into the mold and press it with a four-column press to obtain the core column sheet; (4) Place the core column prepared in step (3) in a vacuum furnace and vacuum treat it at 1100℃-1300℃. After taking it out of the furnace, vacuum package the core column. (5) Select barium zirconate powder as the raw material for the plugging material, and put it into a high-speed wet granulator for granulation to obtain granules; (6) Add the granules prepared in step (5) into the molds respectively, and press them with a four-column press to obtain barium zirconate core sheets; (7) Place the barium zirconate core prepared in step (6) in a vacuum furnace and vacuum treat it at 1300℃-1500℃. After taking it out of the furnace, vacuum package the core. (8) Stack the core sheets from step (7) with barium zirconate core sheets on the top layer and nickel sheets on the bottom layer, and press the stacked core sheets with a four-column press to obtain cores; (9) Place the core sheet prepared in step (4) and the core prepared in step (8) into the diamond synthesis block, and then put the diamond synthesis block into a six-sided press for synthesis. The actual synthesis pressure and temperature are controlled by pressure control curve and power control curve, respectively. The synthesis is carried out by first raising the temperature and pressure, then keeping the temperature and pressure, and then through multiple stages of pressure slow increase and multiple stages of power slow decrease. Steps (1) to (9) are performed in sequence.

2. The method for synthesizing novel high-temperature and high-pressure large single-crystal diamond according to claim 1, characterized in that, In step (1), the carbon source powder comprises the following components in parts by weight: flake graphite powder: 30-40%, diamond micro powder: 60-70%, wherein the flake graphite powder has a purity of 99.995% or higher and a mesh size of 400 mesh or finer; wherein the diamond micro powder has a particle size of 100 / 200, a purity of ≥99.8%, and a crystal form of type IIa.

3. The method for synthesizing novel high-temperature and high-pressure large single-crystal diamond according to claim 1, characterized in that, In step (5), the barium zirconate powder has a purity of ≥98.5% and a mesh size of 300 mesh or finer.

4. The method for synthesizing novel high-temperature and high-pressure large single-crystal diamond according to claim 1, characterized in that, The nickel sheet mentioned in step (8) has a purity of ≥99.0% and a thickness of 2mm ±0.05mm.

5. The method for synthesizing novel high-temperature and high-pressure large single-crystal diamond according to claim 1, characterized in that, Step (8), the control pressure curve is specifically as follows: pressurize the pressure inside the cavity from 0MPa to 75-90MPa at a pressurization rate of more than 60MPa / hour using the six-sided top press, enter the pressure holding stage and maintain it for a period of time, then increase the pressure at a uniform rate of 2-3 MPa / hour and maintain it for a period of time, then increase the pressure at a uniform rate of 1-1.5MPa / hour and maintain it for a period of time, and finally release the pressure naturally.

6. The method for synthesizing novel high-temperature and high-pressure large single-crystal diamond according to claim 5, characterized in that, In step (8), the stacking weight ratio of the barium zirconate core and the nickel sheet is 60%-80% barium zirconate core and 20%-40% nickel sheet.

7. The method for synthesizing novel high-temperature and high-pressure large single-crystal diamond according to claim 5, characterized in that, In step (8), the pressure is maintained for 48 hours, then the pressure is increased at a constant rate of 2-3 MPa / hour for 144 hours, then the pressure is increased at a constant rate of 1-1.5 MPa / hour for 144 hours, and finally the pressure is released naturally.

8. The method for synthesizing novel high-temperature and high-pressure large single-crystal diamond according to claim 1, characterized in that, In step (8), the power control curve is as follows: the initial power is 7.5-8.5KW, maintained for a period of time, then enters the heat preservation stage, maintained for a period of time, then cools down at a constant rate of 0.04-0.055 W / hour, maintained for a period of time, then cools down at a constant rate of 0.02-0.03W / hour, maintained for a period of time, and finally cools down naturally.

9. The method for synthesizing novel high-temperature and high-pressure large single-crystal diamond according to claim 8, characterized in that, In step (8), the power control curve is as follows: the initial power is 7.5-8.5KW, maintained for 1 hour, then enters the heat preservation stage, maintained for 48 hours, then cools down at a constant rate of 0.04-0.055 W / hour and maintained for 144 hours, then cools down at a constant rate of 0.02-0.03W / hour and maintained for 144 hours, and finally cools down naturally.

10. A novel high-temperature, high-pressure large single-crystal diamond, obtained by the synthesis method described in any one of claims 1-9.

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