A method of controlling the growth rate of a diamond

Abstract

The application provides a method for controlling diamond growth speed, comprising the following steps: S1) baking: a certain amount of high-purity graphite powder and ultra-high-purity metal oxide powder are baked in an oven at 120 DEG C or above for 24 hours; S2) weighing: the mass fraction ratio of the metal oxide powder and the graphite powder is 9.5:0.5-0:10; S3) mixing: the powders with various proportions weighed in step S2) are respectively added into different ball milling tanks, and the mass proportion fraction of the metal oxide mixed powder is S4) pressing: the diameter of the carbon source in the diamond synthesis cavity is generally about 25-38 mm, and the overall thickness is generally 4.00-5.00 mm; the carbon source is distributed in a gradient and is shaped; S5) finishing and preserving. The application changes the density of the graphite in each layer in the synthesis process by adjusting the proportion and thickness value of the metal oxide and the graphite in the carbon source, thereby controlling the dissolution speed of the graphite in the metal catalyst and the precipitation speed of the graphite at the low-temperature end of the catalyst in the synthesis process, and significantly improving the quality of the synthesized diamond.

Description

Technical Field

[0001] This invention belongs to the field of superhard material synthesis, specifically relating to a method for controlling the diamond growth rate during the high-temperature and high-pressure synthesis of synthetic diamonds. Background Technology

[0002] Beyond the jewelry industry, diamonds, as an ultra-hard material, hold an extremely important position in many fields. Currently, the main commercially successful synthesis methods include chemical vapor deposition (CVD) and high-temperature, high-pressure (HPHT). In recent years, with breakthroughs in HPHT technology for synthesizing gem-quality diamonds on a six-sided press, large diamond (3-5 carats) technology has been developed, and related technologies for even larger diamonds are still under research.

[0003] As is well known, the HPHT method for synthesizing gem-quality diamond is based on the thermocline method. Graphite or similar materials serve as the carbon source at the high-temperature end, while the diamond seed crystal is located at the low-temperature end, with a metal catalyst in between. At approximately 1400℃ and a pressure of 5-6 GPa, the carbon source dissolves in the metal catalyst and precipitates at the low end under the influence of the temperature gradient, completing the C / C bond formation of the graphite sp. 2 To Diamond SP 3 The transformation of the structure is a significant drawback. However, the temperature range for synthesizing the optimal crystal zone of diamonds using the thermal difference method is very narrow (only 30℃) and is greatly affected by the structure, materials, and processes, making it very difficult to meet this requirement during synthesis. Especially in the synthesis of larger jewelry-grade diamonds, the temperature gradient changes continuously as the grain size increases, making it easy to introduce impurities such as graphite or metal catalysts during growth, which severely reduces the quality of the diamond.

[0004] To solve this problem, the conventional approach is to redesign and explore an alternative cavity structure, but this is quite difficult.

[0005] Based on the above situation, the present invention provides a method for controlling the growth rate of diamonds. By improving the carbon source (generally high-purity graphite) in the existing cavity structure, the growth rate of diamonds is regulated by controlling the amount of graphite dissolved in the catalyst, thereby achieving the synthesis of high-quality large-particle diamonds without changing the existing cavity structure design. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for controlling the growth rate of diamonds. This method is simple, low-cost, and suitable for mass production, with significant implementation effects, wide applicability, and great application potential.

[0007] The technical solution of this invention is: a method for controlling the growth rate of diamonds, wherein the preparation process of the carbon source includes the following steps:

[0008] S1) Baking: A certain amount of high-purity graphite powder and ultra-high-purity metal oxide powder are spread evenly in a stainless steel tray and baked in an oven at 120℃ or above for 24 hours;

[0009] S2) Weighing: Weigh the metal oxide powder and high-purity graphite powder respectively according to the mass ratio of metal oxide powder to graphite powder of 9.5:0.5 to 0:10;

[0010] S3) Mixing: Add the various proportions of powder weighed in step S2) to different ball mill jars, and mark them according to the mass proportions of the metal oxide mixed powder, i.e., the first proportion, the second proportion, the third proportion, and the fourth proportion. Then add the pre-cleaned and dried zirconia ceramic grinding balls of different sizes, and ball mill them for 24 hours to ensure that they are fully mixed.

[0011] S4) Pressing: After mixing, remove the special steel mold for pressing the carbon source, and conduct a trial press to determine the powder dosage and molding pressure. The diameter of the carbon source in the diamond synthesis cavity is generally about 25-38 mm, and the overall thickness is generally 4.00-5.00 mm; the carbon source is distributed in a gradient according to the proportion of metal oxide powder and formed.

[0012] S5) Finishing and Storage: Use a grinding wheel to finish the carbon source pressed in step 4) (tolerance ±0.02mm). After finishing, dry and store in a 70℃ oven.

[0013] Furthermore, the molding step in step S4 above is as follows:

[0014] a) Integrated molding: When the thickness of a single layer d < 1 mm, subsequent fine grinding is difficult to perform, and integrated molding is the only option. That is, first, a first layer of powder mixture in a first proportion is added to the steel mold, spread out, then a second proportion of powder is added and spread out, then a third proportion of powder is added and spread out, and so on; after all the powder is added, the whole piece is pressed into shape.

[0015] After pressing, during finishing, the side with higher carbon source content can be finely ground with a grinding wheel to meet the requirements. The amount of powder required for each layer to reach the specified thickness can be confirmed based on the test pressing results;

[0016] b) Segmented molding: When the thickness of a single layer d ≥ 1 mm, choose integrated molding or segmented molding; segmented molding means that after powders of various proportions are directly pressed and molded and trimmed to obtain carbon sources of different proportions and thicknesses, they are combined to achieve the original carbon source height requirements.

[0017] During assembly, the appropriate ratio of carbon source combinations needs to be selected based on the diamond's growth rate. The side with a higher proportion of metal oxide powder is closer to the metal catalyst.

[0018] Further, the mixing step in step S3 above is as follows: the mass ratio of the metal oxide mixed powder to the zirconia ceramic grinding ball is 10:1.

[0019] Furthermore, for synthetic diamond targets below 1 ct, the mass ratio of the first proportion of metal oxide powder to graphite powder is selected within the range of 6:4 to 9:1, and the mass ratio of the second proportion of oxide powder to graphite powder is selected within the range of 5:5 to 0:10. The thickness d of the first layer of powder with the first proportion after pressing is... A The thickness d of the second layer of powder after pressing is in the range of 0.50–2.50 mm. B The range is 2.50 to 3.50 mm of excess thickness.

[0020] Preferably, the mass ratio of the metal oxide powder and graphite powder in the first ratio is 7:3, and the thickness d A The thickness is 1.50 mm; the second ratio of metal oxide powder to graphite powder is selected at a mass ratio of 2:8, and the thickness range is the excess thickness (i.e., the original carbon source thickness and the first layer thickness d). A (Difference).

[0021] Furthermore, when the target size of the synthetic diamond is 1–3 ct, the mass ratio of the first proportion of metal oxide powder to graphite powder is selected from 6:4 to 9:1, the mass ratio of the second proportion of oxide powder to graphite powder is selected from 8.5:1.5 to 9.5:0.5, and the mass ratio of the third proportion of metal oxide powder to graphite powder is selected from 2:8 to 0:10. The thickness d after pressing the first proportion of mixed powder is... A The thickness d after pressing of the second proportion of mixed powder ranges from 0.50 to 1.50 mm. B The range is 1.50–2.50 mm. The thickness after pressing the third proportion powder is the remaining thickness (i.e., the original carbon source thickness plus the first layer thickness d). A Second layer thickness d B (The value after that).

[0022] Preferably, the first ratio of oxide powder to graphite powder is 7:3 parts by mass, and its thickness is 1.00 mm; the second ratio of oxide powder to graphite powder is 9:1 by mass, and its thickness is 2.00 mm; the third ratio of oxide powder to graphite powder is 1:9 by mass, and the remaining thickness is 1.00 to 2.50 mm.

[0023] Preferably, the metal oxide powder in step S1 is Al2O3, MgO, or ZrO2, with a purity of superior grade and a particle size of less than 20 μm.

[0024] Preferably, the above-mentioned superior-purity metal oxide powder is Al2O3 or MgO powder with a particle size of less than 5 μm. The high-purity graphite powder has a purity of 99.99% and a particle size of less than 5 μm.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1) By adjusting parameters such as the ratio and thickness of metal oxides and graphite in each layer of the carbon source, the density of graphite in each layer during the synthesis process can be changed, thereby controlling the dissolution rate of graphite in the metal catalyst and the precipitation rate at the low temperature end of the catalyst. This effectively avoids the serious inclusion problem that is common in the growth of large diamond particles caused by excessively rapid dissolution and precipitation of the carbon source, thereby improving the A-grade yield and significantly improving the quality of synthetic diamonds.

[0027] 2) The method is simple and highly operable. Only minor adjustments to the existing structure and synthesis process are needed; that is, using the carbon source described in this patent instead of the original carbon source is sufficient to achieve the growth of large diamond particles. This effectively avoids the complex, tedious, and highly challenging process of redesigning the cavity. It can be used for the production of large diamond particles on various structures and presses.

[0028] 3) This method can be used not only for the synthesis of diamonds under 3 carats, but also for the production and synthesis of diamonds over 3 carats. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the gradient carbon source structure of the present invention;

[0030] Among them, 1-first layer; 2-second layer; 3-third layer. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1

[0033] A method for controlling diamond growth rate, wherein the carbon source preparation process includes the following steps:

[0034] 1) Baking: Take a certain amount of high-purity graphite powder and ultra-high-purity MgO powder, spread them evenly in a stainless steel tray, and bake them in an oven at 120℃ or above for 24 hours.

[0035] 2) Weighing: The mass ratio of MgO powder to high-purity graphite powder is 7:3 (denoted as A1), 9:1 (denoted as B1), 2:8 (denoted as C1) and 1:9 (denoted as D1).

[0036] 3) Mixing: 300 g of each of the various proportions of powder weighed in step 2) are added to different ball mill jars. After marking them, 30 g of zirconia ceramic grinding balls of different sizes that have been cleaned and dried are added to each jar. The mixture is then ball milled and mixed for 24 h to ensure that it is fully and evenly mixed.

[0037] 4) Pressing: After mixing, sieve out the zirconia grinding balls. Take out the special steel mold for pressing the carbon source, and conduct a trial press to determine the powder dosage and molding pressure. For a 650mm cylinder diameter press, the diameter of the carbon source in a certain type of structural composite block is approximately 38.00 mm, and the overall thickness is 4.50 mm, so one-piece molding can be selected.

[0038] When producing diamonds weighing less than 1 carat, a one-piece molding process can be used. The first layer consists of powder in ratio A1 (1.50 mm thick, approximately 5.10 g). This powder is spread evenly in the mold and pressed flat with a pressure bar. Then, powder in ratio C1 (3.00 mm thick, approximately 8.00 g) is added, spread evenly, and pressed at 15 MPa for 30 seconds to form the final shape.

[0039] When the production target is 1-3 ct diamonds, the first layer is powder with a ratio of A1 (thickness about 1.00 mm, mass about 3.40 g). After spreading it in the mold and pressing it flat with a pressure bar, powder with a ratio of B1 (thickness about 2.00 mm, mass about 7.45 g) is added. After spreading it in the mold and pressing it flat with a pressure bar, powder with a ratio of D1 (thickness about 1.50 mm, mass about 4.50 g) is added. After spreading it flat, it is pressed into shape on a press at 15 MPa for 30 seconds.

[0040] For this type of structure, when producing diamond products smaller than 1 ct, the carbon source can also be formed in segments. Specifically, approximately 5.10 g of powder in the mixture from step 3) with a proportion of A1 is weighed and molded under 15 MPa pressure for 30 seconds using the same mold to obtain the A1 layer of carbon source. Then, 8.00 g of powder with a proportion of C1 is weighed and molded under the same 15 MPa pressure for 30 seconds to obtain the C1 layer of carbon source. In use, combining A1 and C1 can also achieve the same integrated molding effect.

[0041] 5) Finishing and Storage: Use a grinding wheel to finish the carbon source pressed in step 4) (the main machining surface is the side with higher graphite content), with a tolerance of ±0.02 mm. After finishing, it can be used in the synthesis block to replace the original carbon source (the side with higher metal oxide content is closer to the catalyst). When not in use, dry and store in a 70°C oven under air atmosphere to prevent moisture absorption.

[0042] To verify its effectiveness, on the 650 press, we used the existing cavity structure and our integrated and segmented carbon sources. By extending the holding time, we successfully obtained diamonds that met the target requirements and were of A-grade quality.

[0043] Example 2

[0044] A method for controlling diamond growth rate, wherein the carbon source preparation process includes the following steps:

[0045] Steps 1), 3), and 5) are the same as in Example 1.

[0046] 2) Weighing: Weigh the powder according to the mass ratio of MgO powder to high-purity graphite powder of 6:4 (denoted as A2) and 5:5 (denoted as B2).

[0047] 4) Pressing: After mixing, remove the special steel mold for pressing the carbon source and perform a trial press to determine the powder dosage and molding pressure. For a 650mm cylinder diameter press, the carbon source diameter in a certain type of composite block is approximately 38.00 mm, and the overall thickness is 4.50 mm, allowing for integrated molding.

[0048] When producing diamonds smaller than 1 carat, the first layer uses powder in ratio A2 (2.50 mm thick, approximately 8.05 g). After being spread evenly in the mold and pressed down with a pressure bar, powder in ratio B2 (2.00 mm thick, approximately 6.20 g) is added, spread evenly, and then pressed at 15 MPa to form the final product. For this type of structure, when producing products smaller than 1 carat, the carbon source can also be formed in segments.

[0049] To verify its effectiveness, we successfully obtained a diamond weighing approximately 0.5 ct that met the Grade A requirement by using the existing cavity and appropriately extending the holding time on a 650 press.

[0050] Example 3

[0051] A method for controlling diamond growth rate, wherein the carbon source preparation process includes the following steps:

[0052] Steps 1), 3), and 5) are the same as in Example 1.

[0053] 2) Weighing: The mass ratio of MgO powder to high-purity graphite powder is 6:4 (referred to as A3) or 0 parts: 10 parts (referred to as B3).

[0054] 4) Pressing: After mixing, remove the special steel mold for pressing the carbon source and conduct a trial press to determine the powder dosage and molding pressure. For a 650mm cylinder press, the carbon source diameter in a certain type of composite block is approximately 38mm, and the overall thickness is 4.5mm, allowing for integrated molding. When producing diamonds under 1 ct, the first layer uses powder with a ratio of A3 (2.5mm thickness, approximately 8.05g). After spreading it in the mold and pressing it once with a pressure bar, powder with a ratio of B3 (2mm thickness, approximately 4.60g) is added. After spreading it, it is pressed at 15 MPa. Similarly, this carbon source can also be molded in segments.

[0055] Similarly, on the 650 press, we successfully obtained diamonds weighing approximately 0.5ct that met Grade A requirements by using the existing cavity and extending the holding time.

[0056] Example 4

[0057] A method for controlling diamond growth rate, wherein the carbon source preparation process includes the following steps:

[0058] Steps 1), 3), and 5) are the same as in Example 1.

[0059] 2) Weighing: The mass ratio of MgO powder to high-purity graphite powder is 6:4 (referred to as A4), 9.5 parts: 0.5 parts (referred to as B4), and 0 parts: 10 parts (referred to as C4).

[0060] 4) Pressing: After mixing, remove the special steel mold for pressing the carbon source and perform a trial press to determine the powder dosage and molding pressure. For a 650mm cylinder press, the carbon source diameter in a certain type of structural composite block is approximately 38mm, and the overall thickness is 4.50mm, allowing for integrated molding. When producing 1-3 ct diamonds, the first layer uses powder with a ratio of A4 (1.50mm thickness, approximately 4.85g). After spreading it in the mold and pressing it once with a pressure rod, add powder with a ratio of B4 (approximately 1.50mm thickness, approximately 5.65g). Spread it in the mold, press it once with a pressure rod, and then add powder with a ratio of C4 (approximately 1.50mm thickness, approximately 3.45g). After spreading it, press it at 15 MPa. Similarly, this carbon source can also be molded in segments and then assembled to replace the original carbon source.

[0061] Similarly, on the 650 press, we successfully obtained diamonds weighing between 1 and 3 carats with quality meeting Grade A requirements by using the existing cavity and extending the holding time.

[0062] Example 5

[0063] A method for controlling diamond growth rate, wherein the carbon source preparation process includes the following steps:

[0064] 1) Baking: Take a certain amount of high-purity graphite powder and ultra-high-purity Al2O3 powder, spread them evenly in a stainless steel tray, and bake them in an oven at 120℃ or above for 24 hours.

[0065] 2) Weighing: The mass ratio of Al2O3 powder to high-purity graphite powder is 7:3 (denoted as A5) or 2:8 (denoted as B5).

[0066] 3) Mixing: 300 g of each of the various proportions of powder weighed in step 2) are added to the ball mill jar, marked, and 30 g of zirconia ceramic grinding balls of different particle sizes that have been cleaned and dried are added to each jar. The mixture is then ball-milled for 24 h to ensure thorough mixing.

[0067] 4) Pressing: After mixing, remove the special steel mold for pressing the carbon source and perform a trial press to determine the powder dosage and molding pressure. For a 550mm cylinder diameter press, the carbon source diameter in a certain type of composite block is approximately 25mm, and the overall thickness is 5mm, so integrated molding can be selected.

[0068] When producing diamonds under 1 carat, the first layer uses powder with a ratio of A5 (1.50 mm thick, approximately 2.50 g). This powder is spread evenly in the mold, pressed flat with a pressure rod, and then powder with a ratio of B5 (3.5 mm thick, approximately 4.20 g) is added. After spreading, it is pressed at 10 MPa to form the final shape. For this type of structure, when the thickness of a single carbon source layer is greater than 1 mm, a segmented molding and then splicing method can also be adopted.

[0069] Step 5) is the same as in Example 1.

[0070] To verify its effectiveness, we successfully obtained diamonds of approximately 0.5 carats with quality meeting Grade A requirements by using the existing cavity and extending the holding time on a 550 press.

[0071] Example 6

[0072] A method for controlling diamond growth rate, wherein the carbon source preparation process includes the following steps:

[0073] Steps 1), 3), and 5) are the same as in Example 5.

[0074] 2) Weighing: The mass ratio of Al2O3 powder to high-purity graphite powder is 6:4 (referred to as A6), 9.5 parts: 0.5 parts (referred to as B6), and 0 parts: 10 parts (referred to as C6).

[0075] 4) Pressing: After mixing, remove the special steel mold for pressing the carbon source and perform a trial press to determine the powder dosage and molding pressure. For a 550mm cylinder diameter press, the carbon source diameter in a certain type of structural composite block is approximately 25mm and the thickness is 5mm, which can be selected for one-piece molding.

[0076] When producing diamonds between 1 and 3 carats, the first layer consists of powder in a ratio of A6 (1.50 mm thick, approximately 2.40 g). After being spread evenly in the mold and pressed down with a pressure bar, powder in a ratio of B6 (approximately 1.50 mm thick, approximately 2.90 g) is added. This is followed by spreading evenly in the mold, pressing down with a pressure bar, and then adding powder in a ratio of C6 (approximately 2.00 mm thick, approximately 2.05 g). After spreading evenly, the mixture is pressed at 10 MPa to form the final shape. Similarly, this carbon source can also be produced by segmented molding followed by assembly.

[0077] On the 550 press, we successfully obtained diamonds ranging from 1 to 3 carats in size and meeting Grade A quality requirements by using the existing cavity and extending the holding time.

[0078] The molding process of this invention is specifically as follows:

[0079] a) Integrated Molding: When the thickness of a single layer d < 1 mm, subsequent fine grinding is difficult to perform, and integrated molding is the only option. This involves first adding the first layer of powder mixture A to the steel mold, leveling it, then adding powder of ratio B and leveling it, followed by adding powder of ratio C and leveling it, and so on. After all the powder has been added, the entire piece is pressed into shape. After pressing, during fine grinding, a grinding wheel can be used to appropriately grind the side with higher carbon source content to meet the requirements. The amount of powder required for each layer to reach the specified thickness can be confirmed based on the results of prior test pressing.

[0080] b) Segmented Molding: When the single-layer thickness d ≥ 1 mm, either integrated molding or segmented molding can be selected. This involves directly pressing and refining powders of various proportions to obtain carbon source materials of different ratios and thicknesses, which are then combined to achieve the required carbon source height. During assembly, the combination of carbon source proportions needs to be rationally selected based on the diamond growth rate. The side with a higher proportion of metal oxide powder is closer to the metal catalyst.

[0081] Before pressing, the present invention requires a trial pressing for two purposes: first, to determine the process parameters during pressing (including the pressing pressure and holding time); and second, to determine the amount of powders in various proportions (which needs to be determined according to the target size of the diamond production).

[0082] Generally, the mass of carbon in the carbon source is no less than 1.5 times the mass of the diamond to be transformed.

[0083] For carbon sources with a diameter Φ≥30 mm and a thickness d≥3 mm after molding, the molding pressure range is 12~15 MPa, and the holding pressure is 30 s; for carbon sources with a diameter Φ<30 mm and a thickness d<3 mm after molding, the molding pressure range is 6~12 MPa, and the holding pressure is 30 s.

[0084] The aforementioned metal oxide powder can be Al2O3, MgO, ZrO2, etc., with a purity of superior grade and a particle size of less than 20 μm.

[0085] Preferably, the superior purity metal oxide powder is Al2O3 or MgO powder with a particle size of less than 5 μm.

[0086] Preferably, the graphite powder used is high-purity graphite with a purity of not less than 99.99%.

[0087] This invention designs and uses a gradient carbon source instead of the existing pure carbon source. That is, different amounts of metal oxide powder are added to the carbon source. By realizing microporous channels of different concentrations that are spontaneously formed during diamond synthesis, the amount of carbon source dissolved in the metal catalyst is controlled. This controls the precipitation rate of carbon at low temperatures, thereby controlling the growth rate of diamond and preventing the formation of inclusions due to excessive growth.

[0088] Comparative Examples

[0089] Similarly, instead of using the gradient carbon source mentioned above, pure graphite is directly pressed into a carbon source. By using the existing cavity structure and extending the holding time, the resulting diamond rough has very serious inclusions, making it impossible to produce diamonds larger than 1 carat with quality meeting the A grade requirements.

[0090] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for controlling the growth rate of diamonds, characterized in that, The preparation process of a carbon source includes the following steps: S1) Baking: Take a certain amount of high-purity graphite powder and ultra-high-purity metal oxide powder, spread them evenly in a stainless steel tray, and bake them in an oven at 120℃ or above for 24 hours. The metal oxide powder is Al2O3, MgO, or ZrO2. S2) Weighing: Weigh the metal oxide powder and high-purity graphite powder separately according to a certain mass ratio; S3) Mixing: The various mass ratios of the mixed powder weighed in step S2) are added to different ball mill jars for mixing. The mixed powders are marked according to the mass ratios of the first, second and third proportions. Then, different sizes of zirconia ceramic grinding balls that have been cleaned and dried are added to each jar. The mixture is ball milled for 24 hours to ensure that it is fully mixed. S4) Pressing: After mixing, take out the special steel mold for pressing carbon source, and perform a test press to determine the amount of powder and molding pressure; the diameter of the carbon source in the synthetic block is 25.00~38.00 mm, and the overall thickness is 4.00~5.00 mm; For synthetic diamond targets below 1 ct, the mass ratio of metal oxide powder to graphite powder in the first proportion of mixed powder ranges from 6:4 to 9:1, and the mass ratio of metal oxide powder to graphite powder in the second proportion of mixed powder ranges from 5:5 to 0:

10. or When the target size of the synthetic diamond is 1 to 3 ct, the mass ratio of metal oxide powder to graphite powder in the first proportion of the mixed powder ranges from 6:4 to 9:1, the mass ratio of metal oxide powder to graphite powder in the second proportion of the mixed powder ranges from 8.5:1.5 to 9.5:0.5, and the mass ratio of metal oxide powder to graphite powder in the third proportion of the mixed powder ranges from 2:8 to 0:

10. The first to third proportions of the mixture powder are added sequentially to the steel mold, wherein the first proportion of the mixture powder is closer to the metal catalyst; S5) Finishing and storage: Use a grinding wheel to finish the carbon source pressed in step S4), with a tolerance of ±0.02 mm, and dry and store it in a 70℃ oven.

2. The method as described in claim 1, characterized in that, The molding step in step S4) is as follows: a) Integrated molding: When the thickness of a single layer d < 1 mm, subsequent fine grinding is difficult to operate, so integrated molding can only be selected: that is, first add the first layer of mixed powder in the first proportion to the steel mold, spread it out, then add the second proportion of mixed powder and spread it out, then add the third proportion of mixed powder and spread it out, and then press the whole thing into shape after the mixed powder is added. After pressing, the side with high graphite content is finely ground with a grinding wheel during finishing to meet the requirements; the amount of powder required for each layer to reach the specified thickness is confirmed based on the results of the pre-press test. b) Segmented molding: When the thickness of a single layer d ≥ 1 mm, integrated molding or segmented molding can be selected; the segmented molding means that powders of various proportions are first directly pressurized and molded to obtain carbon source units with different proportions and thicknesses, and then combined to meet the original carbon source height requirements.

3. The method as described in claim 1, characterized in that, The mixing step in step S3) is as follows: the mass ratio of the mixed powder to the zirconia ceramic grinding ball is 10:

1.

4. The method as described in claim 1, characterized in that, For synthetic diamond targets below 1 ct, the thickness d of the first proportion of mixed powder after pressing... A The thickness d of the second proportion of mixed powder ranges from 0.50 to 2.50 mm. B The range is the remaining thickness.

5. The method as described in claim 4, characterized in that, The mass ratio of metal oxide powder to graphite powder in the first proportion of the mixed powder is 7:3, and the thickness d A The thickness is 1.50 mm; the mass ratio of metal oxide powder to graphite powder in the second proportion of mixed powder is 2:8, and the remaining thickness is 2.50 ~ 3.50 mm.

6. The method as described in claim 1, characterized in that, When the target size of the synthetic diamond is 1~3 ct, the thickness d of the first ratio of mixed powder after pressing is... A The thickness d of the second proportion of mixed powder ranges from 0.50 to 1.50 mm. B The thickness d of the third proportion of the mixed powder ranges from 1.50 to 2.50 mm. C Select the remaining thickness.

7. The method as described in claim 6, characterized in that, The mass ratio of metal oxide powder to graphite powder in the first proportion of the mixed powder is 7:3, and its thickness d A The thickness is 1.00 mm; the mass ratio of metal oxide powder to graphite powder in the second proportion of the mixed powder is 9:1, and its thickness d is... B The thickness is 2.00 mm; the mass ratio of metal oxide powder to graphite powder in the third proportion of the mixed powder is 1:9, and the remaining thickness is 1.00 to 2.50 mm.

8. The method as described in claim 1, characterized in that, The metal oxide powder in step S1 is of superior purity and has a particle size of less than 20 μm.

9. The method as described in claim 8, characterized in that, The superior purity metal oxide powder is Al2O3 or MgO powder with a particle size of less than 5 μm.

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