Catalyst for cultured diamonds and diamond cultivation method

Abstract

The present invention provides a catalyst for growing diamonds and a diamond growth method. The catalyst is used in a high-temperature, high-pressure synthesis chamber with a cavity diameter greater than or equal to 40 mm, comprising: the synthesis chamber comprises a central region and several annular edge regions surrounding the central region, each region being provided with a metal catalyst. The melting point of the metal catalyst provided in each region gradually increases from the central region outward, matching the temperature gradient distribution within the synthesis chamber, so that all metal catalysts in the synthesis chamber have a uniform melting point. In this way, the catalyst for growing diamonds increases the temperature growth range of diamonds within the catalyst solvent, solving the problem of uneven temperature within large cavities with a diameter greater than 40 mm. This allows for excellent growth of grown diamonds in both the edge and center regions of the synthesis chamber, resulting in substantially consistent size and clarity of grown diamonds in both the edge and center regions, resulting in relatively high uniformity and quality.

Description

Technical Field

[0001] The present invention relates to the field of diamond cultivation, and in particular to a catalyst for diamond cultivation suitable for a large synthetic cavity and a diamond cultivation method. Background Art

[0002] As the technology for artificially synthesizing large single-crystal diamonds matures, the cultured diamond market is experiencing a surge due to its cost-effectiveness and environmental friendliness. The temperature gradient method is a key approach for synthesizing large single-crystal diamonds using high-temperature, high-pressure methods. This method utilizes the spatial distribution of temperature within a molten catalyst to generate carbon transport from a carbon source to a seed crystal, achieving epitaxial growth of diamond crystals. Graphite, the carbon source, is located at the high-temperature end of the cavity, while the seed crystal is located at the low-temperature end. Driven by a temperature gradient, carbon diffuses from the high-concentration region at the high-temperature end to the low-concentration region at the low-temperature end, achieving growth on the seed crystal.

[0003] The process of synthesizing large single crystal diamond using the temperature gradient method at high temperature and high pressure is as follows:

[0004] .

[0005] In the temperature gradient method, the catalytic metal acts as a solvent in the diamond transformation process. Graphite dissolves atomically under high temperature and high pressure until it reaches saturation, and then precipitates as diamond from the solution that is supersaturated with carbon. The solution formed by carbon and metal under high temperature and high pressure conditions is unsaturated with graphite and supersaturated with diamond, thus creating a so-called continuous solution, which allows graphite to continuously dissolve and diamond to continuously crystallize and precipitate.

[0006] Currently, the most commonly used metal catalysts on the market are Fe- and Ni-based catalysts, such as FeMnCo, FeNi, and NiMnCo. Because the diamond growth temperature range of these catalysts is only 10°C, they are very mature for small-cavity synthesis processes with cavity diameters less than 40 mm. However, as the cavity diameter exceeds 40 mm, the external heating method causes the temperature difference between the cavity edge and the center to exceed 10°C, ultimately resulting in excessively high cavity edge temperatures and high levels of impurities and inclusions in the grown diamonds. The low temperature at the center of the cavity prevents the production of diamonds or the growth of skeletal crystals. This results in low yields and high costs for large-cavity diamond cultivation. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a catalyst for cultured diamonds and a method for cultivating large single-crystal cultured diamonds. By regulating the catalyst composition, the problems of low cultured diamond yield and high cost when the diameter of the high-temperature and high-pressure synthesis chamber is not less than 40 mm are solved.

[0008] In order to achieve the above-mentioned purpose, the present invention protects the following technical solutions:

[0009] A catalyst for growing diamonds, used in a high-temperature, high-pressure synthesis chamber with a chamber diameter greater than or equal to 40 mm, comprising: the synthesis chamber consisting of a central area and a plurality of annular edge areas arranged around the central area, each area being provided with a metal catalyst, and the melting point of the metal catalyst arranged in each area gradually increases from the central area outwards and matches the temperature gradient distribution in the synthesis chamber, so that all metal catalysts in the synthesis chamber have a uniform melting degree.

[0010] Based on the above, the metal catalyst located in the central region is the first metal catalyst, which is a conventional metal catalyst, such as an Fe-based catalyst or a Ni-based catalyst, and is composed of at least two elements selected from Fe, Ni, Co, Mn, Cu, Cr, Al, and Mg. Preferably, the diameter of the central region is less than or equal to 30 mm.

[0011] Based on the above, the metal catalyst disposed on the edge region comprises, based on 100 parts by mass, 97-99.5 parts of the first metal catalyst and 0.5-3 parts of a rare earth metal. The rare earth metal is at least one of cerium (Ce), neodymium (Nd), erbium (Er), iridium (Ir), and tantalum (Ta).

[0012] Based on the above, when the diameter of the synthesis chamber is 40 to 50 mm, the synthesis chamber consists of the central area and an edge area, and the metal catalyst located on the edge area is the second metal catalyst, which includes 97 to 99.5 parts of the first metal catalyst and 0.5 to 3 parts of the rare earth metal.

[0013] Based on the above, when the diameter of the synthesis chamber is 50-60 mm, the synthesis chamber consists of the central region and two edge regions, wherein the second metal catalyst is disposed on the edge region near the central region, and the third metal catalyst is disposed on the edge region located at the outermost edge. The second metal catalyst comprises 98-99.5 parts of the first metal catalyst and 0.5-2 parts of the rare earth metal, and the third metal catalyst comprises 97-98.5 parts of the first metal catalyst and 1.5-3 parts of the rare earth metal. Preferably, the inner diameter of the edge region where the second metal catalyst is located is less than or equal to 30 mm, and the outer diameter is less than or equal to 50 mm.

[0014] A diamond cultivation method comprises: placing the above-mentioned diamond cultivation catalyst on a crystal bed, and cultivating diamond roughs in a synthesis cavity with a cavity diameter greater than or equal to 40 mm under high temperature and high pressure using a temperature gradient method.

[0015] Based on the above, the synthesis pressure of the cultured diamond rough is 5-5.6 GPa, the temperature is 1300-1350°C, and the holding time is 36-96 hours. Preferably, the synthesis pressure is 5.2-5.4 GPa, the synthesis temperature is 1320-1330°C, and the holding time is 48-72 hours.

[0016] Therefore, the catalyst for cultured diamonds provided by the present invention regulates the catalyst composition based on the characteristic that the temperature in the central area of the synthesis chamber is lower than the temperature in its peripheral areas, and metal catalysts of different compositions are arranged in different areas. This makes the melting point of the catalyst in the central area lower than the melting point of the catalyst in the peripheral areas, and matches the temperature distribution in the synthesis chamber. This ensures that the melting state of all catalysts in the synthesis chamber is basically consistent, thereby increasing the temperature growth range of diamonds in the catalyst solvent, solving the problem of uneven temperature inside large cavities with a diameter of more than 40 mm, and achieving excellent growth of cultured diamonds in both the peripheral and central areas of the synthesis chamber. The cultured diamonds in the peripheral and central areas are basically consistent in size and clarity, and have relatively high uniformity and quality.

[0017] Furthermore, the present invention changes the melting point of the catalyst located in the edge area by adding rare earth elements to the catalyst arranged in the edge area, so that the melting state of all catalysts in the synthesis cavity is basically consistent, thereby improving the uniformity and quality of the growth of cultured diamond crystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of catalyst distribution when the diameter of the synthesis cavity provided in Example 1 of the present invention is 40 mm.

[0019] Figure 2 This is a photo of a single synthetic cultured diamond with a synthetic cavity diameter of 40 mm; Figure 2 A is a photograph of a cultured diamond synthesized in a single pass using the catalyst provided in Example 1. Figure 2 B is comparative example 1 using Fe 60 -Ni 40 Photograph of cultured diamonds synthesized by metal catalysts in a single pass. Figure 2 C is the comparative example 2 using Fe 59.5 -Ni 40 -Ta 0.5 Photograph of cultured diamonds produced using a metal-catalyzed single-pass synthesis.

[0020] Figure 3 Schematic diagram of catalyst distribution when the diameter of the synthesis cavity provided in Example 2 of the present invention is 50 mm.

[0021] Figure 4 This is a photo of a single synthetic cultured diamond with a synthetic cavity diameter of 50 mm; Figure 4A is a photograph of a cultured diamond synthesized in a single pass using the catalyst provided in Example 2. Figure 4 B is a photograph of a cultured diamond synthesized in a single pass using a FeMnCo metal catalyst in comparative example 3, wherein the element weights of Fe:Mn:Co are 5:1:4.

[0022] Figure 5 This is a schematic diagram of the distribution of catalysts when the diameter of the synthesis cavity is 60 mm in Examples 3 and 4 of the present invention, wherein: Figure 5 A is the catalyst distribution diagram of Example 3, Figure 5 B is the catalyst distribution diagram of Example 4.

[0023] Figure 6 This is a photo of a single synthetic cultured diamond with a synthetic cavity diameter of 60 mm; Figure 6 A is a photograph of a cultured diamond synthesized in a single pass using the catalyst provided in Example 3. Figure 6 B is a photograph of a cultured diamond synthesized in a single pass using the metal catalyst provided in Example 4. Figure 6 C is the comparative example 4 using (NiMnCo) 98.5 -Nd 1.5 Photograph of a cultured diamond produced using a metal catalyst in a single-pass synthesis. The element weight ratio is Ni:Mn:Co:3:1:3. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is further described in detail below through specific implementation methods. x ” represents, wherein M represents one or more metal elements, and x represents the mass fraction of the metal element in the metal catalyst.

[0025] Example 1

[0026] See also Figure 1 In the embodiment 1 of the present invention, a catalyst for growing diamonds is provided when the synthesis cavity is 40 mm, which is composed of a first metal catalyst 1 located in the center area and a second metal catalyst 2 located in the edge area, and the center area and the edge area are concentrically arranged, and the diameter of the center area is 25 mm. In this embodiment, the first metal catalyst 1 is a conventional Fe 60 -Ni 40 Metal catalyst (consisting of Fe and Ni uniformly mixed in a mass ratio of 60:40), the second metal catalyst 2 is Fe 59.5 -Ni 40 -Ta 0.5 Metal catalyst (consisting of Fe, Ni and Ta uniformly mixed in a mass ratio of 59.5:40:0.5).

[0027] This embodiment also provides a method for growing diamonds using the catalyst, comprising: Figure 1 The first metal catalyst 1 and the second metal catalyst 2 are placed on a crystal bed with a diameter of 40 mm in the synthesis cavity. 42 seed crystals are arranged in three layers inside and outside the crystal bed. The crystal bed is kept at a pressure of 5.4 GPa and a temperature of 1320°C for 48 hours. Figure 2 As shown in A, 39 rough diamonds of 1 to 3 carats are grown, and excellent diamond growth can be achieved in both the edge and center areas of the cavity, obtaining cultured diamond particles with good size uniformity and high quality.

[0028] Comparative Examples 1 and 2 each provide a metal catalyst, which differs from Example 1 mainly in that each comparative example uses a single-component metal catalyst instead of the two metal catalysts in Example 1, wherein Comparative Example 1 uses the first metal catalyst 1 in Example 1, which is a traditional Fe 60 -Ni 40 Metal catalyst; Comparative Example 2 uses the second metal catalyst 2 in Example 1 using Fe 59.5 -Ni 40 -Ta 0.5 Metal catalyst.

[0029] The method for preparing cultured diamonds in a 40 mm diameter synthesis cavity using the metal catalysts provided in Comparative Examples 1 and 2 is basically the same as that in Example 1. The results are as follows: Figure 2 B and 2C.

[0030] from Figure 2 It can be seen that: Figure 2 A single batch of 39 rough diamonds of 1 to 3 carats were prepared, and the clarity of all of them could reach 1B grade, with a weight distribution of 1 to 3 carats. This shows that their uniformity and quality are relatively good.

[0031] Figure 2 B only produced 23 rough diamonds weighing 0.5 to 4 carats in a single batch. This was mainly due to the uneven temperature field inside and outside the cavity. The seed crystals at the edge of the cavity were too hot, resulting in obvious impurities or inclusions inside the cultured diamond crystals, making them black in color. The seed crystals in the center were too cold, resulting in some cultured diamonds being extremely small in size, not fully growing into skeletal crystals, and even failing to produce cultured diamonds. As a result, the crystal quality of the cultured diamonds produced in a single batch was greatly reduced. Specifically, 5 rough diamonds had a clarity of D grade, 9 had a clarity of C grade, and 9 had a clarity of 2B grade. Their weight was distributed between 0.5 and 4 carats, and their sizes were uneven.

[0032] Figure 2C only prepared 26 diamond roughs of 0.5 to 4 carats in a single batch, 18 of which had a clarity of C grade and 8 had a clarity of 2B grade. The weight distribution ranged from 0.5 to 4 carats and the sizes were uneven.

[0033] It can be seen that although the cultured diamonds prepared in Comparative Example 2 are improved compared with Comparative Example 1, the increase is not large. This is mainly because when the diameter of the synthesis cavity is greater than or equal to 40 mm, the temperature difference between the central area and the edge area reaches more than 13°C, and the single-component catalyst cannot meet the crystal growth requirements.

[0034] Example 2

[0035] See also Figure 3 This embodiment provides a catalyst for growing diamonds with a synthesis cavity of 50 mm. The catalyst is basically the same as the catalyst provided in Example 1, and is composed of a first metal catalyst 1 and a second metal catalyst 2. The main difference is that: in this embodiment, the diameter of the central area is 30 mm, the first metal catalyst 1 is a traditional FeMnCo metal catalyst, which is composed of a uniform mixture of Fe, Mn and Co in a mass ratio of 5:1:4, and the second metal catalyst 2 is (FeMnCo) 99 -Ir1 metal catalyst (consisting of a uniform mixture of FeMnCo metal catalyst and Ir in a mass ratio of 99:1).

[0036] Comparative Example 3 provides a metal catalyst, which differs from Example 2 mainly in that this comparative example uses the first metal catalyst 1 in Example 2 to replace all catalysts in Example 2, that is, Comparative Example 3 only uses FeMnCo metal catalyst as solvent.

[0037] Example 2 and Comparative Example 3 also provide a diamond cultivation method, comprising: placing a corresponding metal catalyst on a crystal bed with a synthesis cavity diameter of 50 mm, arranging 42 seed crystals in three layers inside and outside the crystal bed, and keeping the temperature at a pressure of 5.2 GPa and a temperature of 1330°C for 72 hours, so as to prepare a diamond blank in a single step. Figure 4 .

[0038] from Figure 4 It can be seen that: Figure 4 A prepared 23 cultured diamond roughs, whose clarity can reach 1A and 1B levels, and their weight is concentrated between 2 and 3 carats. It can be seen that their uniformity and quality are relatively good. Figure 4B produced only 18 rough diamonds weighing 0.5 to 4 carats in a single batch. One rough diamond had a clarity of D, 10 had a clarity of 2B, and 7 had a clarity of 2A. The weight of the rough diamonds was concentrated between 0.5 and 4 carats, resulting in extremely uneven clarity and size. When the cavity diameter exceeded 50 mm, the temperature inside the cavity varied by approximately 17°C. Using a single-component catalyst resulted in inconsistent melting conditions between the cavity and the edges, affecting crystal growth.

[0039] Example 3

[0040] This embodiment provides a catalyst for growing diamonds when the synthesis cavity is 60 mm, which is basically the same as the catalyst provided in Example 2. Figure 5 As shown in A, both are composed of a first metal catalyst 1 and a second metal catalyst 2. The main difference is that: in this embodiment, the first metal catalyst 1 is a traditional NiMnCo metal catalyst, which is composed of a uniform mixture of Ni:Mn:Co in a mass ratio of 3:1:3, and the second metal catalyst 2 is (NiMnCo) 98.5 Nd 1.5 Metal catalyst (composed of a uniform mixture of NiMnCo metal catalyst and Nd in a mass ratio of 98.5:1.5).

[0041] Example 4

[0042] This embodiment provides a catalyst for growing diamonds when the synthesis cavity is 60 mm, and its distribution structure is as follows: Figure 5 As shown in Figure B, from the inside to the outside, it consists of a first metal catalyst 1 located in the center area, a second metal catalyst 2, and a third metal catalyst 3 located in the outermost edge area. The area where the second metal catalyst 2 is located is sandwiched between the center area and the outermost edge area. In this embodiment, the diameter of the center area is 30 mm, the inner diameter of the second edge area is 30 mm and the outer diameter is 45 mm, and the inner diameter of the third edge area is 45 mm and the outer diameter is 60 mm. The first metal catalyst 1 is a traditional NiMnCo metal catalyst, and the second metal catalyst 2 is (NiMnCo) 98.5 Nd 1.5 Metal catalyst, the third metal catalyst 3 is (NiMnCo) 97 Ce3 metal catalyst.

[0043] Comparative Example 4 provides a metal catalyst, which differs from Examples 3 and 4 mainly in that: this comparative example uses the second metal catalyst 2 (NiMnCo) 98.5 Nd 1.5 The metal catalyst acts as a solvent to replace all the catalysts in the synthesis chamber with a diameter of 60 mm.

[0044] Examples 3 to 4 and Comparative Example 4 also provide a diamond cultivation method, comprising: placing the corresponding metal catalyst on a crystal bed with a synthesis cavity diameter of 60 mm, arranging 33 seed crystals in three layers inside and outside the crystal bed, and keeping the temperature at a pressure of 5.4 GPa and a temperature of 1330°C for 96 hours, and preparing a single diamond. Figure 6 Rough lab-grown diamond shown.

[0045] from Figure 6 It can be seen that: Figure 6 A single batch of 25 rough diamonds ranging from 0.7 to 4 carats were prepared. There were obvious inclusions inside the crystals, and some products were extremely small and incompletely grown. Among them, the clarity of 7 rough diamonds was C grade, the clarity of 11 rough diamonds was 2B grade, and the clarity of 7 rough diamonds was 2A grade. The product sizes were uneven, with the smallest weighing 0.7 carats and the largest weighing 4 carats.

[0046] Figure 6 Figure B shows a single batch of 33 rough diamonds weighing 3 to 4 carats, with a clarity of 1B and 2A. The products are uniform in size and their weight is concentrated between 3 and 4 carats.

[0047] Figure 6 C shows a single preparation of 27 diamond roughs ranging from 0.5 to 3 carats, of which 11 have a clarity of C, 15 have a clarity of 2B, and 1 has a clarity of 2A. The product sizes are uneven, with the smallest weighing 0.5 carats and the largest weighing 3 carats.

[0048] When the cavity diameter is above 60 mm, the temperature difference inside the cavity reaches more than 25°C. Even a two-component catalyst cannot meet the optimal crystal growth requirements. Using a three-component catalyst can make the catalysts in different areas reach the same melting state, ensuring good crystal growth.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to preferred embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or some technical features can be replaced by equivalents without departing from the spirit of the technical solutions of the present invention. They should all be included in the scope of the technical solutions claimed for protection by the present invention.

Claims

1. A method for growing diamonds, comprising: Placing a catalyst for growing diamonds on a crystal bed, using a temperature gradient method, under high temperature and high pressure, in a synthesis cavity with a cavity diameter greater than or equal to 40 mm, to grow diamond rough; The synthesis chamber is composed of a central region and a plurality of annular edge regions arranged around the central region. A metal catalyst is arranged on each region. The melting point of the metal catalyst arranged on each region gradually increases from the central region outward and matches the temperature gradient distribution in the synthesis chamber, so that the melting degree of the metal catalyst in the synthesis chamber is consistent. The metal catalyst located on the central area is a first metal catalyst, which is an Fe-based catalyst or a Ni-based catalyst and is composed of at least two elements of Fe, Ni, Co, Mn, Cu, Cr, Al, and Mg; the metal catalyst arranged on the annular edge area includes 97 to 99.5 parts of the first metal catalyst and 0.5 to 3 parts of a transition metal, calculated on a basis of 100 parts by mass, and the transition metal is at least one of cerium, neodymium, erbium, iridium, and tantalum.

2. The cultivation method according to claim 1, wherein The diameter of the central area is less than or equal to 30 mm.

3. The cultivation method according to claim 1 or 2, characterized in that When the diameter of the synthesis cavity is 40-50 mm, the synthesis cavity is composed of the central area and an annular edge area.

4. The cultivation method according to claim 1, wherein When the diameter of the synthesis chamber is 50 to 60 mm, the synthesis chamber consists of the central area and two annular edge areas, wherein a second metal catalyst is arranged on the annular edge area close to the central area, and a third metal catalyst is arranged on the annular edge area located at the outermost edge; based on 100 parts by mass, the second metal catalyst includes 98 to 99.5 parts of the first metal catalyst and 0.5 to 2 parts of the transition metal; based on 100 parts by mass, the third metal catalyst includes 97 to 98.5 parts of the first metal catalyst and 1.5 to 3 parts of the transition metal.

5. The cultivation method according to claim 4, wherein The inner diameter of the annular edge region where the second metal catalyst is located is less than or equal to 30 mm, and the outer diameter is less than or equal to 50 mm.

6. The cultivation method according to claim 1, wherein The synthesis pressure of the cultured diamond rough is 5 to 5.6 GPa, the temperature is 1300 to 1350° C., and the holding time is 36 to 96 hours.

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