Hexagonal diamond and preparation method thereof
By applying quasi-uniaxial pressure and local high temperature gradient on graphite materials, the complexity and high cost of high temperature and high pressure in the preparation of hexagonal diamonds were solved, and the preparation of hexagonal diamonds with high purity and good crystal structure was achieved.
Patent Information
- Application Number
- CN202310971789.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-08-03
- Publication Date
- 2025-10-03
- Estimated Expiration
- 2043-08-03
AI Technical Summary
The preparation of hexagonal diamond in the existing technology requires high temperature and high pressure conditions, which is complicated and costly to operate, making it difficult to achieve large-scale mass production, and the quality of the prepared crystals is relatively low.
By applying quasi-uniaxial pressure and local high temperature to the graphite material, pressure and temperature gradients in different directions are applied to promote the nucleation and growth of hexagonal diamond and reduce the pressure conditions required for phase transition.
The preparation of hexagonal diamond with high purity and good crystal structure is achieved, which reduces the preparation cost and energy consumption and improves the crystal quality.
Smart Images
Figure CN117085595B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of diamond preparation, in particular to a hexagonal diamond and a preparation method thereof. Background Art
[0002] Diamond is one of the hardest naturally occurring substances on Earth and one of the most recognizable and precious gemstones. Composed of pure carbon, it possesses a unique crystal structure and remarkable physical properties. Diamond is widely recognized for its exceptional hardness. Rated 10 on the Mohs hardness scale, it is the highest hardness, making it an ideal material for many industrial and scientific fields, particularly for the manufacture of cutting, grinding, and abrasive tools. Diamond's hardness allows it to remain stable under extreme conditions, resisting wear and corrosion. Diamond's properties stem from its unique sp 3 Hybrid structure, each carbon atom is sp 3 The hybrid orbital forms covalent bonds with the other four carbon atoms to form a regular tetrahedron. 3 Hybrid carbon has two crystalline forms: cubic diamond (CD) and hexagonal diamond (HD). Hexagonal diamond, due to its structural superiority, possesses superior mechanical properties compared to cubic diamond. However, due to the difficulty of preparing it, research on it is currently limited.
[0003] The phase transition from graphite to diamond has been a subject of considerable interest for decades. Graphite and diamond are two distinct crystalline forms of carbon, each with distinct crystal structures and physical properties. Graphite is a layered material, its crystal structure composed of hexagonal layers of carbon atoms stacked together. This gives it excellent electrical conductivity and lubricity. Diamond, on the other hand, consists of tightly packed carbon atoms forming a cubic crystal structure, resulting in exceptional hardness and optical transparency. The phase transition between graphite and diamond, known as the graphite-diamond transition, is a significant physical phenomenon occurring under high-temperature and high-pressure conditions deep within the Earth. When carbon atoms are exposed to extreme heat and pressure, they rearrange themselves to form a diamond structure, transforming from graphite to diamond. The graphite-diamond transition is of great significance in geology. This phase transition underlies the formation of rocks and minerals that make up the Earth's interior. By studying the graphite-diamond transition, geologists gain insight into the high-temperature and high-pressure conditions within the Earth's interior and infer its internal structure and evolutionary history.
[0004] Furthermore, the graphite-diamond phase transition is also being studied and applied in the laboratory. By simulating the high temperature and high pressure conditions of the Earth's mantle and utilizing powerful pressure devices and high-temperature furnaces, scientists have successfully achieved the phase transition from graphite to diamond. This has provided important information on phase transition processes and the properties of diamond for the fields of materials science and high-pressure physics.
[0005] However, the preparation technology of hexagonal diamond so far requires the use of high temperature and high pressure conditions, the operation and control process is quite complicated, and the equipment and material costs are high. In addition, the synthesis process of diamond requires a lot of time and energy, and there is a certain failure rate. The existing technology obtains hexagonal diamond samples by using DAC to process single crystal graphite disks under high temperature and high pressure. This is a complex and high-cost preparation process. The preparation technology still has certain limitations and it is difficult to meet the standards of mass production. In addition, due to the limitations of preparation conditions, the samples used in the existing technology are single crystal graphite samples with a size of 60×20 microns in the shape of a disk, and the corresponding prepared crystal quality is relatively small. Summary of the Invention
[0006] The present invention aims to overcome the shortcomings of the existing technology by providing a hexagonal diamond and a method for its preparation. Through visualization and data analysis, the present invention achieves a comprehensive interpretation of the material's phase transition mechanism at both macroscopic and microscopic levels, as well as at both pictorial and numerical levels. This interpretation clarifies the underlying reasons for the different products produced under different experimental conditions, explains the low yield of hexagonal diamond and the predominant presence of twins in the experiment, and proposes an experimental protocol for large-scale hexagonal diamond synthesis based on the phase transition mechanism.
[0007] To achieve the above object, the technical solution adopted by the present invention is:
[0008] In a first aspect, the present invention provides a method for preparing hexagonal diamond, comprising the following steps:
[0009] (1) applying quasi-uniaxial pressure: applying pressure to the graphite material in the three dimensions x, y, and z, wherein the pressure in the x direction is 12-40 GPa, the pressure in the y direction is 12-40 GPa, and the pressure in the z direction is 15-50 GPa, and the pressure in the z direction is greater than the pressure in the x and y directions;
[0010] (2) Heating: The graphite material is heated to 300-2000K and maintained for 1 minute to 5 hours to obtain hexagonal diamond.
[0011] In the present invention, different pressures are first applied to a graphite material in three dimensions, creating a quasi-uniaxial pressure. This causes the graphite material to exhibit a different response in the direction of maximum force than in the other two directions. The graphite material is then heated to produce hexagonal diamond. The hexagonal diamond produced by this method has high purity and a good crystal structure.
[0012] Preferably, in step (2), the central area of the graphite material is first heated to 900-2000K, the temperature of the peripheral area is maintained at 300-900K, and maintained for 1min-2h, and then the graphite material is heated as a whole to 900-1600K and maintained for 1min-3h to obtain hexagonal diamond.
[0013] The present invention first locally heats the graphite material, creating a temperature gradient. The heated area is at high temperature and high pressure, while the surrounding area is at high pressure and low temperature. This locally high temperature creates thermal field stress in the graphite material, which leads to hexagonal diamond nucleation. After the hexagonal diamond nucleation, the entire material is heated to drive the diamond nucleus growth, thus producing hexagonal diamond. The localized heating method reduces the applied pressure, allowing the graphite material to undergo phase transition even under lower pressure. The resulting hexagonal diamond has higher purity and a better crystal structure.
[0014] Preferably, the pressure in the x-direction in step (1) is the same as the pressure in the y-direction.
[0015] Preferably, in step (1), the pressure in the x-direction is 15-25 GPa, the pressure in the y-direction is 15-25 GPa, and the pressure in the z-direction is 18-30 GPa.
[0016] Preferably, in step (1), the pressure in the x-direction is 20 GPa, the pressure in the y-direction is 20 GPa, and the pressure in the z-direction is 30 GPa.
[0017] Preferably, in step (1), the pressure in the x-direction is 30 GPa, the pressure in the y-direction is 30 GPa, and the pressure in the z-direction is 40 GPa.
[0018] Preferably, the temperature of the central area in step (2) is 1500K.
[0019] Preferably, the temperature of the peripheral area in step (2) is 500K.
[0020] Preferably, the heating temperature of the graphite material in step (2) is 1000K.
[0021] In a second aspect, the present invention also provides a hexagonal diamond prepared by the above method.
[0022] Compared with the prior art, the present invention has the following beneficial effects:
[0023] (1) This technical solution uses a quasi-uniaxial compression method to obtain hexagonal diamond as the product of the graphite phase transition. If pressure is applied by other means, such as absolute uniaxial pressure or hydrostatic pressure, the graphite phase transition product obtained is mostly cubic diamond, rather than the target product hexagonal diamond with better mechanical properties.
[0024] (2) This technical solution uses a local high temperature method to reduce the pressure conditions required for phase transition. Under the pressure conditions where the product is hexagonal diamond, the sample must be nucleated by the local high temperature method. Nucleation is very difficult under the conditions of overall high temperature heating. This technical solution achieves the goal of reducing reaction conditions through the combined action of quasi-uniaxial pressure compression and local high temperature methods. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Figure 1 Figure 2 shows the nucleation mechanism of hexagonal diamond and the microscopic structure of the resulting hexagonal diamond in Example 2 of the present invention. Figures a, b, c, and d are the atomic structures of the graphite material at different times. In this mechanism, the (001) plane of the graphite is parallel to the (100) plane of the hexagonal diamond.
[0026] Figure 2 This is a schematic diagram of the microscopic simulation structure of hexagonal diamond under the conditions of x, y being 30 GPa and z being 40 GPa in Example 3 of the present invention, a is the hexagonal diamond grown at 1000K, and b is the hexagonal diamond grown at 1500K. DETAILED DESCRIPTION
[0027] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below with reference to specific embodiments, but the protection scope and implementation methods of the present invention are not limited thereto.
[0028] Unless otherwise specified, the materials and reagents used in the following examples are commercially available.
[0029] Example 1
[0030] A method for preparing hexagonal diamond comprises the following steps:
[0031] (1) Applying quasi-uniaxial pressure: applying different pressures to the graphite material in the directions of three dimensions x, y, and z, wherein the confining pressure direction includes the x direction and the y direction, and the applied direction includes the z direction. The pressure in the x direction is 15 GPa, the pressure in the y direction is 15 GPa, and the pressure in the z direction is 20 GPa;
[0032] (2) Heating: The graphite material is heated to 1000K and maintained for 2 hours to obtain hexagonal diamond.
[0033] Example 2
[0034] A method for preparing hexagonal diamond comprises the following steps:
[0035] (1) Apply quasi-uniaxial pressure:
[0036] Different pressures are applied to the graphite material in the three dimensions xyz, where the pressure in the z direction is greater than that in the x and y directions. The pressure in the x direction is 15 GPa, the pressure in the y direction is 15 GPa, and the pressure in the z direction is 20 GPa, resulting in an effect of applying approximately unidirectional pressure, namely quasi-uniaxial pressure. This causes the graphite material to exhibit a completely different response in the direction of maximum force than in the other two directions. Since the c-axis of graphite is parallel to the direction of maximum pressure, the interlayer spacing of the graphite surface changes, while the compression in other directions of the crystal is small.
[0037] (2) Local temperature rise, forming a temperature gradient:
[0038] Heat up one area of the graphite material while keeping the other areas constant. This creates a temperature gradient in the graphite material. The heated area is at a high temperature and high pressure state of 900K, while the surrounding atoms are at a high pressure and low temperature state of 300K. This is maintained for 1 hour.
[0039] At this point, the graphite material forms thermal field stress at a local high temperature, and hexagonal diamond nucleation occurs: Due to the formation of a temperature gradient, different regions of the graphite material are affected by different temperatures and will expand or contract at different rates. Due to the boundary conditions of the graphite material, some regions may not be able to expand or contract freely, which leads to the generation of internal stress, namely thermal field stress. This thermal field stress changes the energy barrier for the graphite phase transition to hexagonal diamond, reducing the nucleation potential energy in the high-temperature region of the graphite material, which can overcome the nucleation potential energy and promote the nucleation of hexagonal diamond.
[0040] Then the whole material is heated to drive the diamond nucleus to grow into a single crystal: the graphite material is heated as a whole, the whole heating temperature is 1000K, and it is maintained for 2 hours to obtain hexagonal diamond.
[0041] After the hexagonal diamond nuclei have formed, heating the graphite material as a whole will no longer directly drive the formation of new nuclei. Once nuclei are formed and begin to grow, they continue to grow into larger crystals without forming new nuclei. During the overall heating process, the existing nuclei are affected by the temperature, and the thermal vibration energy of the atoms or molecules within them is enhanced, promoting the accelerated growth rate of the crystal, rather than forming new individual nuclei and driving the diamond nuclei to grow into single crystals.
[0042] Maintaining localized high temperatures after nucleation can cause unnecessary expansion in certain areas of the sample, generating additional localized stress that can ultimately cause the sample to crack or break, affecting crystal quality. Furthermore, at high overall temperatures, the kinetic energy of atoms in the non-phase-transitioned regions increases, promoting the transfer and release of localized stress and improving the crystal quality of the product.
[0043] The crystal structure and chemical composition of the samples were characterized by using X-ray diffraction and Raman spectroscopy; then, the morphology and microstructure of the samples were observed and analyzed using scanning electron microscopy and transmission electron microscopy. Figure 1 As shown; through the above technical analysis means, the hexagonal diamond sample prepared by the present invention has the characteristics of higher purity and better crystal structure than the preparation results of the prior art.
[0044] Example 3
[0045] The difference from Example 1 is that in step (1), the pressure in the x-direction is 30 GPa, the pressure in the y-direction is 30 GPa, and the pressure in the z-direction is 40 GPa. The rest is the same as Example 1.
[0046] like Figure 2 As shown, the hexagonal diamond obtained in Example 3 is of better quality.
[0047] Example 4
[0048] The difference from Example 1 is that in step (1), the pressure in the x-direction is 20 GPa, the pressure in the y-direction is 20 GPa, and the pressure in the z-direction is 30 GPa. The rest is the same as Example 1.
[0049] Example 5
[0050] The difference from Example 1 is that in step (1), the pressure in the x-direction is 12 GPa, the pressure in the y-direction is 12 GPa, and the pressure in the z-direction is 15 GPa. The rest is the same as Example 1.
[0051] Example 6
[0052] The difference from Example 2 is that the temperature of the heating area in step (2) is 1500K and the temperature of the peripheral area is 500K. The rest is the same as Example 2.
[0053] Example 7
[0054] The difference from Example 2 is that the temperature of the heating area in step (2) is 2000K and the temperature of the peripheral area is 900K. The rest is the same as Example 2.
[0055] Example 8
[0056] The difference from Example 2 is that the overall heating temperature in step (2) is 900K, and the rest is the same as Example 2.
[0057] The hexagonal diamond samples prepared in the above embodiment have higher purity and better crystal structure than those prepared in the prior art.
[0058] Comparative Example 1
[0059] The difference from Example 1 is that in step (1), the pressure in the x-direction is 50 GPa, the pressure in the y-direction is 50 GPa, and the pressure in the z-direction is 50 GPa, and the rest are the same as in Example 1. In this case, the pressure in the z-direction is equal to the pressures in the x-direction and y-direction, and the product prepared is a mixture of cubic diamond and hexagonal diamond, and the purity of the hexagonal diamond is relatively low.
[0060] Comparative Example 2
[0061] The difference from Example 1 is that in step (1), the pressure in the x-direction is 30 GPa, the pressure in the y-direction is 30 GPa, and the pressure in the z-direction is 20 GPa, and the rest is the same as in Example 1. At this time, the pressure in the z-direction is less than the pressure in the x-direction and y-direction, and the graphite material is distorted and transformed into nanocubic diamond.
[0062] Comparative Example 3
[0063] The difference from Example 1 is that the heating temperature in step (2) is 800K, and the rest is the same as Example 1. At this time, the heating temperature is lower than the protection range defined by the present invention, and cannot reduce the energy conditions required for the phase change of graphite, resulting in the failure of the phase change of graphite.
[0064] Comparative Example 4
[0065] The difference from Example 1 is that the heating temperature in step (2) is 2200 K, and the rest is the same as Example 1. At this time, the heating temperature is higher than the protection range defined by the present invention, and graphite is converted into cubic diamond.
[0066] 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 the technical solutions of the present invention may be modified or replaced by equivalents 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: The following steps are involved: (1) applying quasi-uniaxial pressure: applying pressure to the graphite material in the three dimensions x, y, and z, wherein the pressure in the x direction is 12-40 GPa, the pressure in the y direction is 12-40 GPa, and the pressure in the z direction is 15-50 GPa, and the pressure in the z direction is greater than the pressure in the x and y directions; (2) Heating: The graphite material is heated to 300-2000K and maintained for 1 minute to 5 hours to obtain hexagonal diamond.
2. The method for preparing hexagonal diamond according to claim 1, wherein In the step (2), the central area of the graphite material is first heated to 900-2000K, the temperature of the peripheral area is maintained at 300-900K, and maintained for 1 minute to 2 hours, and then the entire graphite material is heated to 900-1600K and maintained for 1 minute to 3 hours to obtain hexagonal diamond.
3. The method for preparing hexagonal diamond according to claim 1 is characterized in that, In the step (1), the pressure in the x-direction is the same as the pressure in the y-direction.
4. The method for preparing hexagonal diamond according to claim 1, wherein: In the step (1), the pressure in the x-direction is 15-25 GPa, the pressure in the y-direction is 15-25 GPa, and the pressure in the z-direction is 18-30 GPa.
5. The method for preparing hexagonal diamond according to claim 4, wherein: In step (1), the pressure in the x-direction is 20 GPa, the pressure in the y-direction is 20 GPa, and the pressure in the z-direction is 30 GPa.
6. The method for preparing hexagonal diamond according to claim 3, wherein: In step (1), the pressure in the x-direction is 30 GPa, the pressure in the y-direction is 30 GPa, and the pressure in the z-direction is 40 GPa.
7. The method for preparing hexagonal diamond according to claim 2, wherein: The temperature of the central area in step (2) is 1500K.
8. The method for preparing hexagonal diamond according to claim 2, wherein: The temperature of the surrounding area in step (2) is 500K 。 9. The method for preparing hexagonal diamond according to claim 1, wherein: The heating temperature of the graphite material in the step (2) is 1000K.
10. A hexagonal diamond prepared by the preparation method according to any one of claims 1 to 9.