A hexagonal diamond and its preparation method

Abstract

This invention discloses a hexagonal diamond and its preparation method, relating to the technical field of diamond preparation. A method for preparing hexagonal diamond includes the following steps: stacking several HOPG sheets along the direction of the top hammer of a double-sided press; then installing retaining rings around the stacked HOPG sheets along the horizontal direction of the HOPG sheets; placing the HOPG sheets with the retaining rings installed into the synthesis chamber of the double-sided press; then applying a pressure of 20-25 GPa to the synthesis chamber; heating the synthesis chamber to 1000-1800 K; and holding the temperature and pressure for 0.2-24 hours to obtain hexagonal diamond. This method for preparing hexagonal diamond reduces the lateral stress on the raw material, avoids buckling, wrinkling, and deformation of the HOPG block's microstructure, maintains the uniform orientation of the HOPG block, and results in hexagonal diamond with high purity, excellent crystal structure, and large volume size.

Description

Technical Field

[0001] This invention relates to the technical field of diamond preparation, and more particularly to a hexagonal diamond and its preparation method. Background Technology

[0002] As a well-known high-performance material, diamond possesses numerous superior properties, including maximum hardness, maximum thermal conductivity, minimum compressibility, widest light transmission band, radiation resistance, and resistance to strong acids and alkalis. Therefore, it has become an indispensable material in many fields such as industry, science and technology, and national defense. The properties of diamond stem from its unique spline properties. 3 Hybrid structure, each carbon atom is sp 3 The hybrid orbitals form covalent bonds with the other four carbon atoms, constituting a regular tetrahedron. Diamond has many polymorphs, such as cubic diamond and hexagonal diamond; among them, hexagonal diamond has attracted particular attention due to its superior mechanical properties caused by its excellent structure. However, due to the difficulty in its preparation, current research on it is still relatively limited.

[0003] For decades, the mass production of hexagonal diamond has been a subject of widespread interest. To date, high-temperature and high-pressure conditions are commonly used in the preparation of hexagonal diamond, provided by a six-sided press. However, when pressure is applied using this press, the lateral pressure inevitably disrupts the orientation consistency of the graphite, causing internal buckling and wrinkling. Therefore, this synthesis method has not yet yielded hexagonal diamond samples with practical applications.

[0004] However, all current techniques for synthesizing hexagonal diamond require high temperature and high pressure conditions, and are often costly. Under high pressure, graphite samples must not exhibit any buckling or wrinkling at the microscopic level. Large-volume presses are difficult to operate, time-consuming, and have a low success rate. Furthermore, the main method for synthesizing hexagonal diamond currently involves applying quasi-uniaxial stress using a six-sided press, but the lateral pressure applied by the six-sided press inevitably disrupts the orientation consistency of graphite, causing internal buckling and wrinkling, making it fundamentally impossible to synthesize hexagonal diamond. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a hexagonal diamond and its preparation method. This invention is the first to use a two-sided top press to directionally compress a uniformly oriented HOPG block to prepare hexagonal diamond. This reduces the lateral stress on the raw material, avoids buckling, wrinkling, and deformation of the HOPG block's microstructure, maintains the uniform orientation of the HOPG block, meets the necessary conditions for preparing hexagonal diamond, and ensures the superior performance of the obtained product. This results in hexagonal diamond with high purity, excellent crystal structure, and large size.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing hexagonal diamond, comprising the following steps:

[0008] (1) Stack several HOPG sheets along the direction of the top hammer of the double-sided press, and then install fixing rings around the stacked HOPG sheets along the horizontal direction of the HOPG sheets; the plane direction of the HOPG sheets is perpendicular to the direction of the top hammer.

[0009] (2) Place the HOPG sheet with the fixed ring installed into the synthesis chamber of the double-sided press, then apply a pressure of 20-25 GPa to the synthesis chamber, heat the synthesis chamber to 1000-1800 K, and keep it at the temperature and pressure for 0.2-24 h to obtain hexagonal diamond.

[0010] The principle of this invention is as follows: First, several HOPG sheets are stacked oriented along the direction of the top hammers of a double-sided press. Then, fixing rings are installed around the HOPG sheets along the horizontal direction, so that the fixing rings completely wrap around the HOPG sheets, thereby forming a confining pressure around the HOPG sheets and preventing buckling, wrinkling, and deformation of the microstructure of the HOPG sheets. Then, the double-sided press is turned on, and the top hammers squeeze the pressure-transmitting medium (i.e., the fixing rings), so that part of the pressure-transmitting medium is distributed between the top hammers to act as a sealing edge. The pressure-transmitting medium and the sealing edge area are mainly characterized by flow deformation. As the pressure applied to the synthesis chamber increases, the sealing edge is squeezed and thins with a small amount of flow. At the same time, the volume of the synthesis chamber decreases accordingly. During this process, only a small amount of pressure is transmitted. The pressure medium flows between the top hammers, acting as a sealing edge. The pressure transmission medium area of ​​the pressure chamber is mainly characterized by elastic deformation, while the elastic deformation and flow deformation of the sealing edge area coexist. When the pressure is applied to 20-25 GPa, it cannot be increased further to avoid the top hammers of the two-sided press machine from breaking. Then, the heating system inside the press machine is activated to raise the temperature of the synthesis chamber to 1000-1800K. Then, the pressure and heat preservation stage begins. The volume of the high-pressure chamber shrinks. Since the sealing edge is already very thin and basically no longer flows, both the pressure transmission medium and the sealing edge are mainly characterized by elastic deformation. This makes it difficult for the external applied pressure to push the top hammer forward to supplement the pressure in the pressure chamber area. Finally, after heat preservation and pressure preservation for 0.2-24 hours, the diamond nucleus is promoted to grow into a single crystal, thus obtaining hexagonal diamond.

[0011] Preferably, the number of HOPG sheets is 1-100.

[0012] Preferably, the fixing ring in step (1) is a PVC ring.

[0013] Preferably, in step (1), the HOPG sheet has a length of 2-5 mm, a width of 2-5 mm, and a thickness of 1-3 mm.

[0014] The present invention uses several HOPG sheets of specific sizes to better stack and form hexagonal diamond nuclei, thereby allowing them to grow into hexagonal diamonds more effectively.

[0015] Preferably, in step (2), a pressure of 12-14 GPa is first applied to the synthesis chamber, then the synthesis chamber is heated to 1000-1800 K, and then the pressure is continued to be applied to 20-25 GPa.

[0016] The present invention first applies a specific range of pressure to the synthesis cavity, which can suppress the lateral slippage of graphite and is beneficial to obtaining HD (high resolution) hexagonal diamond.

[0017] Preferably, when applying pressure in step (2), the synthesis chamber is pre-pressed first, with a pressure of 4-6 GPa and a pre-pressing time of 30 min-2 h.

[0018] The present invention pre-compresses the synthesis chamber, making it less likely for the volume to collapse drastically due to excessive pressure, thus making the synthesis chamber less prone to damage.

[0019] Preferably, the heat preservation and pressure maintenance time of the synthesis cavity in step (2) is 5-10 hours.

[0020] Preferably, the temperature of the synthesis chamber in step (2) is 1200-1600K.

[0021] The synthesis chamber of this invention, within the aforementioned temperature range, is conducive to further promoting diamond nucleation, thereby enabling hexagonal diamond to form an excellent crystal structure.

[0022] Secondly, the present invention also provides a hexagonal diamond prepared by the above method.

[0023] Preferably, the diameter of the hexagonal diamond along the direction perpendicular to the graphite

[001] plane is 2-5 micrometers.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) The present invention uses a two-sided top press to process HOPG blocks with uniform orientation to obtain hexagonal diamond nuclei. By applying quasi-uniaxial stress along the stacking direction of HOPG blocks, the uniform orientation of HOPG blocks is maintained during the compression process, thus ensuring the subsequent synthesis of hexagonal diamonds with excellent properties.

[0026] (2) The present invention uses a winding double-sided top press, and PVC rings are added around the HOPG block in advance to form confining pressure during the compression process. At the same time, the direction of the top hammer of the double-sided top press is always consistent with the directional arrangement direction of the HOPG block. The directional arrangement of the HOPG block is maintained throughout the compression process. The target product hexagonal diamond primary nucleus can be prepared by the method of the present invention. At the same time, the target product can be synthesized quickly and at low cost, and has broad application prospects. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the preparation process of the hexagonal diamond described in this invention.

[0028] Figure 2 This is a schematic diagram of the structure of the double-sided press of the present invention. The direction along

[001] in the figure is the direction of the graphite

[001] surface.

[0029] Figure 3 This is a schematic diagram of the nucleation mechanism of hexagonal diamond described in Example 1 and the microscopic simulated structure of the formed hexagonal diamond. b, c, d, and e are the phase transition processes of graphite materials during the nucleation and growth stage.

[0030] Figure 4 This is a schematic diagram of the nucleation mechanism of diamond described in Comparative Example 1 and the microscopic simulated structure of the formed diamond. a is a schematic diagram of a six-sided press, b, c, d, and e are phase transition processes of graphite material during the nucleation and growth stage, and F represents the direction of pressure applied to the synthesis cavity. Detailed Implementation

[0031] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments, but the scope of protection and implementation of the present invention are not limited thereto.

[0032] Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0033] Example 1

[0034] A method for preparing hexagonal diamond includes the following steps:

[0035] (1) Pretreatment of HOPG (Highly Oriented Pyrolytic Graphite) blocks: HOPG blocks are mechanically cut into HOPG sheets with a length of 5mm, a width of 5mm, and a thickness of 1mm to form hexagonal diamond nuclei, thus facilitating their growth into hexagonal diamonds; a schematic diagram of the double-sided press is shown below. Figure 2 As shown, Figure 2 The direction along the

[001] axis, i.e. the direction of the graphite

[001] surface, is the same as the direction of the top hammer of the two-sided press.

[0036] (2) Oriented stacking of HOPG sheets: Six HOPG sheets are oriented and stacked along the c-axis direction. The direction of the top hammer of the two-sided press is also the direction of the graphite

[001] surface. Then, PCV rings are installed along the horizontal direction of the HOPG sheets to form a confining pressure in the two-sided press.

[0037] (3) Apply quasi-uniaxial pressure using a double-sided press: Place 6 HOPG sheets and PCV rings into the synthesis chamber of the double-sided press, then turn on the press to pre-press the synthesis chamber. The pressure during pre-pressing is 4 GPa and the pre-pressing time is 1 hour.

[0038] At this time, the top hammer squeezes the pressure transmission medium, causing some of the pressure transmission medium to be distributed between the butanol to act as a sealing edge. The pressure transmission medium and the sealing edge area are mainly characterized by flow deformation.

[0039] (4) Uniform heating and pressurization to promote diamond nucleation: The pressure in the synthesis chamber was continued to reach 12 GPa, and then the temperature in the synthesis chamber was increased to 1500 K. The pressure was continued to reach 20 GPa, and the hexagonal diamond sample was obtained after holding the temperature and pressure for 5 hours. The specific preparation process is as follows: Figure 1 As shown;

[0040] When the synthesis chamber is pressurized, the sealing edge is squeezed and thinned by a small amount of flow. At this time, the volume of the pressure chamber decreases, and only a small amount of pressure-transmitting medium flows between the top hammers to act as the sealing edge. The pressure-transmitting medium area of ​​the pressure chamber is mainly elastically deformed, while the elastic deformation and flow deformation of the sealing edge area coexist. When the pressure rises to 12 GPa, the internal heating system is activated to raise the temperature of the synthesis chamber to 1500 K. The pressure is then continued to be applied to 20 GPa, and finally, the temperature and pressure are maintained for 5 hours to promote the growth of diamond nuclei into single crystals.

[0041] When the heat preservation and pressure holding stage begins, the volume of the high-pressure cavity shrinks. Since the sealing edge is already very thin and basically no longer flows, the pressure transmission medium and the sealing edge are mainly elastically deformed. The strength of the sealing edge material increases with the increase of pressure, making it difficult for the external loading pressure to push the top hammer forward to supplement the pressure in the pressure cavity area. Most of the external loading is consumed in the sealing edge area, so the cavity pressure basically no longer increases. Continuing to increase the external loading may cause the top hammer to break. After heat preservation and pressure holding of the synthesis cavity, the hexagonal diamond sample is obtained.

[0042] After cooling and depressurization, the sample was verified to be single-crystal hexagonal diamond: after the pressure in the high-pressure chamber began to decrease, the top hammer was pressed down by the sealing edge under the action of external force, while cooling and depressurization were carried out at the same time. The crystal structure and chemical composition of the sample were characterized by X-ray diffraction and Raman spectroscopy. Then, the morphology and microstructure of the sample were observed and analyzed by scanning electron microscopy and transmission electron microscopy.

[0043] Through the above technical analysis methods, the results are as follows: Figure 3 As shown, Figure 3 The entire nucleation and growth process is divided into four stages in chronological order, with b, c, d, and e corresponding to the first, second, third, and fourth stages, respectively.

[0044] according to Figure 3 It can be seen that hexagonal diamond was indeed produced by the method described in this invention, and Figure 3 The diamond nuclei maintain their directional alignment throughout the growth process, without wrinkling or deformation. Therefore, the hexagonal diamond samples prepared by this invention have higher purity, better crystal structure, and larger volume size compared to those prepared by existing technologies.

[0045] Example 2

[0046] The difference from Example 1 is that the pressure during pre-compression in step (3) is 5 GPa and the pre-compression time is 30 min, while the other steps are the same as in Example 1.

[0047] Example 3

[0048] The difference from Example 1 is that in step (4), the pressure in the synthesis chamber is continued to be applied to 14 GPa, the temperature in the synthesis chamber is raised to 1200 K, and the pressure is continued to be applied to 20 GPa. All other steps are the same as in Example 1.

[0049] Example 4

[0050] The difference from Example 1 is that in step (4), the pressure in the synthesis chamber is continued to be applied to 12 GPa, the temperature in the synthesis chamber is raised to 1800 K, and the pressure is continued to be applied to 25 GPa. All other steps are the same as in Example 1.

[0051] The hexagonal diamond samples prepared in the above embodiments have higher purity, better crystal structure, and larger volume size compared with the preparation results of the prior art.

[0052] Comparative Example 1

[0053] The difference from Example 1 is that in step (3), a six-sided press is used to apply pressure to the six HOPG sheets; all other steps are the same as in Example 1. Using a six-sided press disrupts the orientation consistency of the graphite, causing internal buckling and wrinkling, making it impossible to synthesize hexagonal diamond. Figure 4 As shown, Figure 4 The entire nucleation and growth process is divided into four stages in chronological order, with b, c, d, and e corresponding to the first, second, third, and fourth stages, respectively.

[0054] Figure 4The diamond nucleus exhibits significant buckling, wrinkling, and deformation during growth, making it impossible to prepare hexagonal diamonds.

[0055] Comparative Example 2

[0056] The difference from Example 1 is that in step (4), the pressure in the synthesis chamber is further applied to 8 GPa, then the temperature in the synthesis chamber is raised to 1200 K, and the pressure is further applied to 10 GPa. All other steps are the same as in Example 1. At this time, the pressure in the synthesis chamber is lower than the protection range defined by the present invention, which causes graphite to be unable to be converted into diamond.

[0057] Comparative Example 3

[0058] The difference from Example 1 is that the temperature of the synthesis chamber in step (4) is 800K, while the other steps are the same as in Example 1. At this time, the temperature inside the synthesis chamber is lower than the protection range defined by the present invention, which prevents graphite from undergoing a phase transition.

[0059] Comparative Example 4

[0060] The difference from Example 1 is that the temperature of the synthesis chamber in step (4) is 2000K, while the other steps are the same as in Example 1. At this time, the temperature inside the synthesis chamber is higher than the protection range defined by this invention, and the graphite is transformed into cubic diamond.

[0061] Comparative Example 5

[0062] The difference from Example 1 is that no PVC ring is installed around the HOPG sheet in step (2), while the other steps are the same as in Example 1. In this case, the absence of a retaining ring around the HOPG sheet disrupts the orientation consistency of the graphite during compression, causing the graphite to buckle and form wrinkles, making it impossible to synthesize hexagonal diamond.

[0063] 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 scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing hexagonal diamond, characterized in that, Includes the following steps: (1) Stack several HOPG sheets along the direction of the top hammer of the double-sided press, and then install a fixing ring around the stacked HOPG sheets along the horizontal direction of the HOPG sheets; the plane direction of the HOPG sheets is perpendicular to the direction of the top hammer; the fixing ring is a PVC ring. (2) Place the HOPG sheet with the fixed ring installed into the synthesis chamber of the double-sided press, then apply a pressure of 20-25 GPa to the synthesis chamber, heat the synthesis chamber to 1000-1800 K, and keep it at the temperature and pressure for 0.2-24 h to obtain hexagonal diamond.

2. The method for preparing hexagonal diamond as described in claim 1, characterized in that, In step (1), the HOPG sheet has a length of 2-5 mm, a width of 2-5 mm, and a thickness of 1-3 mm.

3. The method for preparing hexagonal diamond as described in claim 1, characterized in that, In step (2), a pressure of 12-14 GPa is first applied to the synthesis chamber, then the temperature of the synthesis chamber is raised to 1000-1800 K, and then the pressure is continued to be applied to 20-25 GPa.

4. The method for preparing hexagonal diamond as described in claim 3, characterized in that, When applying pressure in step (2), the synthesis chamber is first pre-pressed. The pressure during pre-pressing is 4-6 GPa, and the pre-pressing time is 30 min-2 h.

5. The method for preparing hexagonal diamond as described in claim 1, characterized in that, The heat preservation and pressure maintenance time of the synthesis cavity in step (2) is 5-10 hours.

6. The method for preparing hexagonal diamond as described in claim 1, characterized in that, The temperature of the synthesis chamber in step (2) is 1200-1600K.

7. Hexagonal diamond prepared by the method for preparing hexagonal diamond according to any one of claims 1-6.

8. The hexagonal diamond as described in claim 7, characterized in that, The diameter of the hexagonal diamond along the direction perpendicular to the graphite base is 2-5 micrometers.

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