Needle-shaped single crystal diamond and preparation method thereof

Abstract

The present invention discloses a needle-shaped single crystal diamond and a preparation method thereof, belonging to the technical field of artificial diamonds. The preparation method of the needle-shaped single crystal diamond comprises the following steps: (1) assembling a core column and a synthetic block to obtain an assembly block, wherein the core column comprises heat insulating materials at both ends and a carbon source and a catalyst between the heat insulating materials; (2) placing the assembly block in a static high pressure device and first pressurizing it to ≥5GPa, then heating it to ≥1000°C, controlling diamond nucleation, and maintaining the temperature and pressure to carry out directional growth of diamond, with a growth time of ≥30min; (3) after the growth is completed, cooling and depressurizing, taking out the sample, removing the remaining carbon source and catalyst, and obtaining the needle-shaped single crystal diamond. The method of the present invention has simple and efficient steps, and does not use seed crystals. The obtained needle-shaped diamond single crystal has an aspect ratio of ≥4 and a high yield.

Description

Technical Field

[0001] The invention belongs to the technical field of artificial diamonds, and in particular relates to a needle-shaped single crystal diamond and a preparation method thereof. Background Art

[0002] Diamond has the characteristics of high hardness, high thermal conductivity, stable chemical properties, excellent corrosion resistance, etc., and is widely used in mechanical processing, oil drilling, national defense and military industries. Diamonds are divided into natural diamonds and artificial diamonds; natural diamonds are extremely rare in nature, basically non-renewable resources, and are only distributed in a few regions around the world; artificial diamonds have been a hot topic in the field of superhard material research in recent years, and their cost is significantly lower than that of natural diamonds, and they can be used for doping, and in some physical properties they can be comparable to or even far exceed those of natural diamonds.

[0003] At present, the synthesis of artificial diamonds generally adopts the temperature gradient method, which uses the catalysis of catalysts to convert carbon sources into diamonds under high temperature and high pressure; there must be a suitable temperature difference ΔT in the synthesis chamber, and the driving force for diamond growth is provided by the temperature difference. Compared with the traditional chemical vapor deposition method, the crystal surface of the crystal synthesized by the temperature gradient method is not limited by the size of the seed crystal surface.

[0004] A Chinese patent document with publication number CN114029002A discloses a method for synthesizing single crystal diamond. The method mainly uses activated graphite powder and diamond seeds as a mixed carbon source, first combines a sol-gel method and an in-situ reduction method to prepare sintered precursor particles containing a catalyst, and then places the sintered precursor particles in a single crystal diamond synthesis device that forms a temperature gradient for high temperature and high pressure treatment to synthesize large single crystal diamond.

[0005] A Chinese patent document with publication number CN110055585A discloses a method for artificially synthesizing large columnar diamond single crystals. In the invention, a carbon source, a catalyst, a seed crystal and a crystal bed are arranged in sequence from the high-temperature end to the low-temperature end of a cavity. The parameters of the synthesis process are: a synthesis pressure of 5 to 6 GPa, a cavity center temperature of 1260 to 1360°C, and a synthesis time of 10 to 30 hours; the seed crystal used is a long strip crystal face with an aspect ratio greater than 1.5; and the synthesized large columnar diamond single crystal is obtained.

[0006] The Chinese patent document with publication number CN111778555A discloses a low-stress diamond and a preparation method thereof, which comprises the following steps: S1: gradually heating the diamond to 1100-2300°C and keeping the temperature for 10min-8h; S2: gradually cooling the diamond to below 400°C and using a vacuum high-temperature device or a plasma device to complete the preparation of the low-stress diamond, wherein the vacuum high-temperature device is a vacuum tube furnace device, and the background vacuum degree is reduced by less than 10 -9mbar, and is protected by inert gases Ar and He; the plasma equipment is a microwave plasma equipment, and the background vacuum is less than 10 -5 mbar, and then introduce H2, or Ar and H2.

[0007] A Chinese patent document with publication number CN110523346A discloses a method for cultivating colored diamonds under high temperature and high pressure. The invention obtains artificially cultivated diamonds of different colors by artificially introducing impurity elements or creating internal defects in diamonds during the high temperature and high pressure synthesis process based on the different coloring mechanisms of diamonds of different colors. Specifically, high-purity boron powder and high-purity graphite are mixed in a certain proportion and vacuum reduction sintering is adopted, which effectively ensures the uniform distribution of boron elements in the carbon source and reduces the content of harmful impurities in the carbon source.

[0008] However, in the above-mentioned prior art, the synthetic diamond single crystals are all in regular crystal shape, changing from octahedron to cube with the temperature gradient, and there is no report on the synthesis of directional growth of needle-shaped diamond single crystals with high aspect ratio (≥4). Summary of the invention

[0009] The invention provides a method for preparing needle-shaped single crystal diamond, which does not use seed crystals, has simple and efficient steps and high yield. The aspect ratio of the prepared needle-shaped single crystal diamond is ≥4, and the length is controllable.

[0010] The specific technical solutions adopted are as follows:

[0011] A method for preparing needle-shaped single-crystal diamond comprises the following steps:

[0012] (1) Assembling a core column and a synthesis block to obtain an assembly block, wherein the core column includes heat insulation materials at both ends and a carbon source and a catalyst between the heat insulation materials; wherein the heat insulation materials provide a temperature gradient to ensure axial growth of the crystal;

[0013] (2) placing the assembled block in a static high-pressure device and first pressurizing it to ≥5 GPa, then heating it to ≥1000°C, controlling diamond nucleation, and maintaining the temperature and pressure for directional growth of diamond, with a growth time of ≥30 min;

[0014] (3) After the growth is completed, the sample is taken out after the temperature and pressure are lowered, and the remaining carbon source and catalyst are removed to obtain the needle-shaped single crystal diamond.

[0015] The inventive principle of the present invention is to control the spontaneous nucleation of the carbon source at the interface with the catalyst by regulating the temperature in HPHT, and to control the directional growth of diamond by the temperature gradient. The directional growth rate and aspect ratio of the needle-shaped single crystal diamond are effectively controlled by controlling the nucleation rate and the directional moving speed of the catalyst / diamond growth surface.

[0016] The carbon source is a carbonaceous material or a carbon-containing material. The carbonaceous material includes but is not limited to carbon rods, diamonds, graphite, carbon fibers, carbon nanotubes, etc. The carbon-containing material includes but is not limited to petroleum coke, asphalt, coal tar, plant charcoal, etc.

[0017] The catalyst is a transition metal element or a transition metal alloy, the transition metal element is Fe, Ni or Co, etc., and the transition metal alloy is a nickel-manganese alloy, an iron-nickel alloy, an iron-cobalt alloy or an iron-nickel-cobalt alloy.

[0018] The thermal insulation material is selected from low thermal conductivity materials such as zirconium oxide, magnesium oxide or samarium oxide. The thermal insulation material is designed, combined and proportioned according to the material and height, providing a certain temperature gradient to ensure the axial growth of the crystal.

[0019] Specifically, the carbon source and the catalyst are pressed into pieces and then assembled.

[0020] Preferably, the height ratio of the carbon source to the catalyst in the core column is 0.2-20:1; the height ratio of the heat insulating material at each end to the carbon source and the catalyst is 0.1-10:1.

[0021] Preferably, in step (2), the assembly block is placed in a static high pressure device and first pressurized to 5 GPa to 10 GPa, and then heated to 1000° C. to 2000° C. More preferably, the pressure increase rate during pressurization is 0.1 to 10 GP / min, and the heating rate during heating is 1° C. / min to 1000° C. / min.

[0022] Preferably, in step (3), the cooling rate during cooling is 1°C / min to 6000°C / min, and the pressure reduction rate during pressure reduction is ≤2 GPa / min.

[0023] Preferably, in step (3), the carbon source is removed by knocking, and the catalyst is removed by pickling. The pickling is to immerse the knocked block in an acid solution at 5°C to 200°C until the catalyst is completely removed.

[0024] More preferably, the acid solution is at least one of a nitric acid solution, a hydrochloric acid solution, and a sulfuric acid solution.

[0025] The present invention also provides needle-shaped single-crystalline diamonds prepared by the method for preparing needle-shaped single-crystalline diamonds, wherein the aspect ratio of the needle-shaped single-crystalline diamonds is ≥4.

[0026] Preferably, the aspect ratio of the needle-shaped single crystal diamond is 4-30.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention synthesizes needle-shaped single-crystal diamond by controlling the core column assembly method and temperature difference under high temperature and high pressure without using a seed crystal.

[0029] (2) The needle-shaped single crystal diamond obtained by the present invention has an aspect ratio of ≥4, a high yield, and controllable length. Its length and width can be controlled by controlling the growth time, temperature field gradient and nucleation rate. The needle-shaped single crystal diamond has unique potential applications in medical micro-needles, special optical devices, micro-drilling devices, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of the assembly blocks used to synthesize the needle-shaped single-crystal diamond.

[0031] Figure 2 This is a scanning electron microscope image of the needle-shaped single crystal diamond obtained by heat preservation and pressure maintenance growth for 48 hours in Example 1.

[0032] Figure 3 This is the Raman test spectrum of the needle-shaped single-crystal diamond synthesized in Example 1.

[0033] Figure 4 This is an optical microscope picture of the needle-shaped single crystal diamond obtained by heat preservation and pressure maintenance growth for 48 hours in Example 2.

[0034] Figure 5 This is a scanning electron microscope image of the needle-shaped single crystal diamond obtained by heat preservation and pressure maintenance growth for 48 hours in Example 3.

[0035] Figure numerals: 1 - conductive metal block, 2 - dolomite lining, 3 - first thermal insulation material, 4 - carbon source, 5 - heating layer, 6 - catalyst, 7 - second thermal insulation material, 8 - insulating layer, 9 - phyllite layer. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] Example 1

[0038] In this embodiment, the carbon source is graphite with a purity of 99.99% and a weight of 1.5 g; the catalyst is Fe 60 Co 40 Alloy, purity is 99.9%, grain size is 80μm, weight is 2.8g; after pressing the carbon source and catalyst, the height ratio is 2:1;

[0039] Specifically, the steps of synthesizing needle-shaped single crystal diamond under high temperature and high pressure are as follows:

[0040] (1) Figure 1 As shown, the core column includes a first thermal insulation material 3 (zirconium oxide) and a second thermal insulation material 7 (zirconium oxide) at both ends, as well as the above-mentioned carbon source 4 and the above-mentioned catalyst 6 between the thermal insulation materials. The core column and the synthetic block are assembled to obtain an assembled block, and the synthetic block includes a phyllite layer 9, an insulating layer 8, a heating layer 5, a dolomite lining 2 and a conductive metal block 1.

[0041] (2) placing the assembled block in a static high pressure device (hinged six-sided top press), first pressurizing it to 5 GPa at a pressure increase rate of 7 GPa / h, then heating it to 1300°C at a heating rate of 100°C / min, and maintaining the pressure and temperature at the above pressure and temperature for ≥1h to grow diamond;

[0042] (3) After the heat and pressure growth is completed, the temperature is reduced to room temperature and pressure at a cooling rate of 300°C / min and a pressure reduction rate of 10 GPa / h, and then the six-sided top press is returned and the sample is taken out, and the graphite on the surface of the sample is knocked off. The remaining sample is then placed in a mixed solution of concentrated nitric acid and concentrated hydrochloric acid in a ratio of 1:3 and heated to boiling (about 80°C) to remove the catalyst, and further ultrasonically cleaned with deionized water to remove the residual acid solution, and then dried to remove the surface moisture, to obtain the needle-shaped single crystal diamond.

[0043] The SEM image of the needle-shaped single crystal diamond synthesized in this example is as follows: Figure 2 As shown in the figure, many diamond single crystals grow in a directional needle-like shape, neatly arranged in one direction, and each diamond single crystal at the top presents a regular four-sided pyramid tip with an aspect ratio of about 6. Figure 3 As shown, Raman spectroscopy detected the characteristic peak of diamond at 1332 cm -1 , indicating that the synthesized product is diamond. The characteristic peak of diamond is sharp, indicating that the obtained diamond single crystal is of good quality and has fewer lattice defects.

[0044] Example 2

[0045] In this embodiment, the carbon source is graphite with a purity of 99.99% and a weight of 1.5 g; the catalyst is Fe 60 Co 40 Alloy, purity is 99.9%, grain size is 80μm, weight is 2.8g; after pressing the carbon source and catalyst, the height ratio is 2:1;

[0046] Specifically, the steps of synthesizing needle-shaped single crystal diamond under high temperature and high pressure are as follows:

[0047] (1) As in Example 1, the core column and the synthesis block are assembled to obtain an assembled block, wherein the core column includes a thermal insulation material (zirconia) at both ends and a carbon source and a catalyst between the thermal insulation materials;

[0048] (2) placing the assembled block in a static high pressure device (hinged six-sided top press), first pressurizing to 5 GPa at a pressure increase rate of 8 GPa / h, then heating to 1300°C at a heating rate of 80°C / min, and maintaining the pressure and temperature at the above pressure and temperature for ≥1h to grow diamond;

[0049] (3) After the heat and pressure growth is completed, the temperature is reduced to room temperature and pressure at a cooling rate of 200°C / min and a pressure reduction rate of 10 GPa / h, and then the six-sided top press is returned and the sample is taken out, and the graphite on the surface of the sample is knocked off. The remaining sample is then placed in a mixed solution of concentrated nitric acid and concentrated hydrochloric acid in a ratio of 1:3 and heated to boiling (about 80°C) to remove the catalyst, and further ultrasonically cleaned with deionized water to remove the residual acid solution, and then dried to remove the surface moisture, to obtain the needle-shaped single crystal diamond.

[0050] The optical microscope photograph of the needle-shaped single crystal diamond synthesized in this example is as follows: Figure 4 As shown, the diamond single crystal shown in the figure has a width of about 175 μm, a length of about 2000 μm, and an aspect ratio of about 11.4.

[0051] Example 3

[0052] In this embodiment, the carbon source is graphite with a purity of 99.99% and a weight of 1.5 g; the catalyst is Fe 60 Co 40 Alloy, purity is 99.9%, grain size is 80μm, weight is 2.8g; after pressing the carbon source and catalyst, the height ratio is 2:1;

[0053] Specifically, the steps of synthesizing needle-shaped single crystal diamond under high temperature and high pressure are as follows:

[0054] (1) As in Example 1, the core column and the synthesis block are assembled to obtain an assembled block, wherein the core column includes a thermal insulation material (zirconia) at both ends and a carbon source and a catalyst between the thermal insulation materials;

[0055] (2) placing the assembled block in a static high pressure device (hinged six-sided top press), first pressurizing to 5 GPa at a pressure increase rate of 8 GPa / h, then heating to 1300°C at a heating rate of 80°C / min, and maintaining the pressure and temperature at the above pressure and temperature for ≥1h to grow diamond;

[0056] (3) After the heat and pressure growth is completed, the temperature is reduced to room temperature and pressure at a cooling rate of 100°C / min and a pressure reduction rate of 10 GPa / h, and then the six-sided top press is returned and the sample is taken out, and the graphite on the surface of the sample is knocked off. The remaining sample is then placed in a mixed solution of concentrated nitric acid and concentrated hydrochloric acid in a ratio of 1:3 and heated to boiling (about 80°C) to remove the catalyst, and further ultrasonically cleaned with deionized water to remove the residual acid solution, and then dried to remove the surface moisture, to obtain the needle-shaped single crystal diamond.

[0057] The SEM image of the needle-shaped single crystal diamond synthesized in this example is as follows: Figure 5 shown.

[0058] Example 4

[0059] In this embodiment, the carbon source is an artificial graphite rod with a purity of 99.99% and a weight of 2 g; the catalyst is Fe 60 Co 40 Alloy, purity is 99.9%, grain size is 100μm, weight is 3g; after pressing the carbon source and catalyst, the height ratio is 2:1;

[0060] Specifically, the steps of synthesizing needle-shaped single crystal diamond under high temperature and high pressure are as follows:

[0061] (1) As in Example 1, the core column and the synthesis block are assembled to obtain an assembled block, wherein the core column includes a heat insulating material (magnesium oxide) at both ends and a carbon source and a catalyst between the heat insulating materials;

[0062] (2) placing the assembled block in a static high pressure device (hinged six-sided top press), first pressurizing to 5 GPa at a pressure increase rate of 8 GPa / h, then heating to 1300°C at a heating rate of 80°C / min, and maintaining the pressure and temperature at the above pressure and temperature for ≥1h to grow diamond;

[0063] (3) After the heat and pressure growth is completed, the temperature is reduced to room temperature and pressure at a cooling rate of 100°C / min and a pressure reduction rate of 10 GPa / h, and then the six-sided top press is returned and the sample is taken out, and the graphite on the surface of the sample is knocked off. The remaining sample is then placed in a mixed solution of concentrated nitric acid and concentrated hydrochloric acid in a ratio of 1:3 and heated to boiling (about 80°C) to remove the catalyst, and further ultrasonically cleaned with deionized water to remove the residual acid solution, and then dried to remove the surface moisture, to obtain the needle-shaped single crystal diamond.

[0064] Comparative Example 1

[0065] In this comparative example, the carbon source is graphite with a purity of 99.99% and a weight of 2 g; the catalyst is Fe 60 Co 40 Alloy, purity is 99.9%, grain size is 100μm, weight is 3g; carbon source and catalyst are mixed and pressed into core column;

[0066] (1) Assembling the core column and the composite block to obtain an assembled block, wherein the core column does not include thermal insulation materials at both ends;

[0067] (2) placing the assembled block in a static high pressure device (hinged six-sided top press), first pressurizing to 5 GPa at a pressure increase rate of 8 GPa / h, then heating to 1300°C at a heating rate of 80°C / min, and maintaining the pressure and temperature at the above pressure and temperature for ≥1h to grow diamond;

[0068] (3) After the heat and pressure growth is completed, the temperature is reduced to room temperature and pressure at a cooling rate of 100°C / min and a pressure reduction rate of 10 GPa / h, then the hexahedral press is returned and the sample is taken out, and the graphite on the surface of the sample is knocked off. The remaining sample is then placed in a mixed solution of concentrated nitric acid and concentrated hydrochloric acid in a ratio of 1:3 and heated to boiling (about 80°C) to remove the catalyst, and further ultrasonic cleaning with deionized water is performed to remove the residual acid solution, and the surface moisture is removed by drying to obtain hexahedral diamond single crystal particles.

[0069] The embodiments described above provide a detailed description of the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements or similar substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing needle-shaped single-crystal diamond, characterized in that: The following steps are involved: (1) Assembling a core column and a synthetic block to obtain an assembled block, wherein the core column includes thermal insulation materials at both ends and a carbon source and a catalyst between the thermal insulation materials; the thermal insulation material is selected from zirconium oxide, magnesium oxide or samarium oxide; (2) Place the assembled block in a static high-pressure device and pressurize it to ≥5 GPa, then raise the temperature to ≥1000 °C to control diamond nucleation, and maintain the temperature and pressure for directional growth of diamond for ≥30 min; (3) After the growth is completed, the sample is taken out after cooling and reducing the pressure, and the remaining carbon source and catalyst are removed to obtain the needle-shaped single crystal diamond.

2. The method for preparing needle-shaped single crystal diamond according to claim 1, characterized in that: The carbon source is a carbonaceous material or a carbon-containing material. The carbonaceous material includes carbon rods, diamonds, graphite, carbon fibers or carbon nanotubes. The carbon-containing material includes petroleum coke, asphalt, coal tar or plant charcoal.

3. The method for preparing needle-shaped single-crystal diamond according to claim 1, characterized in that: The catalyst is a transition metal element or a transition metal alloy, the transition metal element is Fe, Ni or Co, and the transition metal alloy is a nickel-manganese alloy, an iron-nickel alloy, an iron-cobalt alloy or an iron-nickel-cobalt alloy.

4. The method for preparing needle-shaped single-crystal diamond according to claim 1, characterized in that: In step (2), the assembly block is placed in a static high pressure device and pressurized to 5 GPa to 10 GPa, and then heated to 1000°C to 2000°C.

5. The method for preparing needle-shaped single-crystal diamond according to claim 1, characterized in that: In step (3), the carbon source is removed by knocking, and the catalyst is removed by pickling. The pickling is to immerse the knocked block in an acid solution at 5°C to 200°C until the catalyst is completely removed.

6. The method for preparing needle-shaped single-crystal diamond according to claim 5, characterized in that: The acid solution is at least one of a nitric acid solution, a hydrochloric acid solution and a sulfuric acid solution.

7. Needle-shaped single-crystalline diamond obtained according to the method for preparing needle-shaped single-crystalline diamond according to any one of claims 1 to 6.

8. The needle-shaped single crystal diamond according to claim 7, characterized in that: The aspect ratio of the needle-shaped single crystal diamond is ≥4.

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