Method for producing high-purity large-size hexagonal diamond
By directly converting highly oriented pyrolytic graphite into large-size hexagonal diamond under high temperature and pressure, the problem of preparing pure-phase bulk hexagonal diamond has been solved, providing a high-purity and high-hardness material for use in superhard materials and semiconductor devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHENGZHOU UNIV
- Filing Date
- 2025-03-04
- Publication Date
- 2026-05-12
AI Technical Summary
Existing technologies make it difficult to prepare pure-phase bulk hexagonal diamond, which limits the study of its physical properties, and the accurate identification of hexagonal diamond is complex and difficult.
Highly oriented pyrolytic graphite was cut into cylinders along the c-axis and assembled in a high-pressure heating synthesis assembly. The cylinders were heated and pressurized at 1300–1900℃ and 20–25 GPa for 10–20 minutes to control the sliding and bonding growth of graphite, directly transforming it into high-purity, large-size hexagonal diamond.
The preparation of high-purity, large-size hexagonal diamonds with dimensions of 1–2 mm has been achieved. These diamonds exhibit significant thermal stability and high hardness, making them suitable for superhard materials and semiconductor devices.
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Figure CN120094492B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of superhard materials technology, specifically relating to a method for preparing high-purity hexagonal diamond. Background Technology
[0002] Hexagonal diamond, also known as lonsdaleite, has attracted considerable attention due to its theoretically predicted extremely high hardness and its potential role as a mineralogical marker of meteorite impact events. Since its initial discovery in meteorites, the synthesis of bulk, pure-phase hexagonal diamond has been a key technological focus in the field.
[0003] Currently, a common method is to compress graphite precursors under high temperature and pressure, and then prepare hexagonal diamond using detonation or impact compression of the graphite sample. However, because cubic diamond is thermodynamically more stable and preferentially forms in the synthesized product, only a small amount of hexagonal diamond or graphite is present in the product. Typically, these multiphase mixtures require identification using X-ray diffraction and selected area electron diffraction, but the overlapping characteristics of cubic and hexagonal diamonds make accurate identification of hexagonal diamond complex and difficult. Studies have shown that structural evidence previously attributed to hexagonal diamond may actually correspond to cubic diamond with stacking faults or cubic nanotwins, casting doubt on the validity of the hexagonal diamond phase. Therefore, the existence of hexagonal diamond remains controversial and elusive.
[0004] The inability to prepare pure-phase bulk hexagonal diamond crystals currently hinders further research into its properties. Therefore, the preparation of pure-phase bulk hexagonal diamond materials remains an urgent need in this field. Summary of the Invention
[0005] In view of this, some embodiments disclose a method for preparing high-purity, large-size hexagonal diamond, including the following steps:
[0006] S1. Cut along the c-axis of highly oriented pyrolytic graphite to obtain cylindrical highly oriented pyrolytic graphite, which is used as a raw material precursor.
[0007] S2. Assemble the raw material precursors in a high-pressure heating synthesis assembly;
[0008] S3. The high-pressure heating synthesis component is heated and pressurized to the set pressure and set temperature, and held at the set temperature to obtain high-purity, large-size hexagonal diamonds; wherein the set temperature is 1300~1900℃, the set pressure is 20~25GPa, and the set time is 10~20min.
[0009] Furthermore, in some embodiments of the method for preparing high-purity, large-size hexagonal diamond, step S2, assembling the raw material precursor in a high-pressure heating synthesis assembly, includes:
[0010] S21. Place the rhenium plate heater into the lanthanum chromate heating tube, and roll the rhenium plate heater into a cylindrical shape so that it fits tightly against the inner wall of the lanthanum chromate heating tube.
[0011] S22. Place the raw material precursor into the alumina sample tube, and place alumina sheets above and below the raw material precursor to confine the raw material precursor within the alumina sample tube.
[0012] S23. Place the alumina sample tube into the middle of the lanthanum chromate heating tube;
[0013] S24. Place an alumina cylindrical plug at the bottom of the lanthanum chromate heating tube and a four-hole alumina ceramic tube at the top of the lanthanum chromate heating tube to confine the alumina sample tube in the middle of the lanthanum chromate heating tube; wherein, a tungsten-rhenium thermocouple is inserted into the four-hole alumina ceramic tube for temperature calibration.
[0014] S25. Finally, the lanthanum chromate heating tube is placed into the magnesium oxide octahedral mold to complete the assembly and obtain the high-pressure heating synthesis component.
[0015] In some embodiments, a method for preparing high-purity, large-size hexagonal diamond is disclosed. In step S3, a high-pressure heating synthesis component is placed in a large-cavity press for heating and pressurization, and a synthesis reaction is carried out under set conditions. After the reaction is completed, the pressure is reduced at a set depressurization rate and the temperature is reduced at a set cooling rate to obtain high-purity, large-size hexagonal diamond.
[0016] Furthermore, in some embodiments, the method for preparing high-purity large-size hexagonal diamonds is disclosed, with the pressurization rate set to 2 GPa / h, the heating rate to 200℃ / min, and the depressurization rate set to 1 GPa / h.
[0017] Some embodiments disclose a method for preparing high-purity large-size hexagonal diamonds. After the reaction is completed, the sample is quenched and cooled to room temperature, and then depressurized to atmospheric pressure at a set rate to obtain high-purity large-size hexagonal diamonds.
[0018] Some embodiments disclose a method for preparing high-purity, large-size hexagonal diamonds, wherein the size of the high-purity, large-size hexagonal diamonds is on the millimeter scale.
[0019] The present invention discloses a method for preparing high-purity, large-size hexagonal diamonds. This method utilizes highly oriented pyrolytic graphite cut along the c-axis as a precursor, and under specified conditions, completely transforms the highly oriented pyrolytic graphite into high-purity, large-size hexagonal diamonds with dimensions ranging from 1 to 2 mm. The hexagonal diamonds prepared by this method do not require an intermediate phase transformation of graphite but undergo a direct structural transformation from graphite to diamond, and can be synthesized under relatively low pressure. This method has significant application prospects in fields such as superhard materials and semiconductor devices. Attached Figure Description
[0020] Figure 1 This is the XRD pattern of the sample obtained in Example 1;
[0021] Figure 2 This is the Raman spectrum of the sample obtained in Example 1;
[0022] Figure 3 These are the XRD patterns of the samples obtained in Example 2 and Comparative Example 1;
[0023] Figure 4 These are aberration electron microscope images of the sample obtained in Example 1;
[0024] Figure 5 These are the Vickers hardness test results of the sample obtained in Example 1;
[0025] Figure 6 These are the thermal stability test results of the sample obtained in Example 1;
[0026] Figure 7 The morphology of the cold-pressed experimental sample obtained in Comparative Example 2 is shown.
[0027] Figure 8 The XRD pattern of the sample obtained in Comparative Example 3 is shown below.
[0028] Figure 9 This is a schematic diagram of the high-pressure heating synthesis component setup in Example 1.
[0029] Figure Labels
[0030] 1. Alumina sample tube 2. Alumina sheet
[0031] 3. Rhenium plate heater; 4. Lanthanum chromate heating tube
[0032] 5. Alumina four-hole ceramic tube; 6. Alumina cylindrical plug.
[0033] 7. Thermocouple 8. Magnesium oxide octahedral mold
[0034] 100 Raw material precursors Detailed Implementation
[0035] The term "embodiment" used herein, as an example, is not necessarily to be construed as superior to or better than other embodiments. Performance testing in these embodiments of the invention, unless otherwise specified, employs conventional testing methods in the art. It should be understood that the terminology used in these embodiments is merely for describing particular implementations and is not intended to limit the scope of the disclosure of these embodiments.
[0036] Unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of this invention pertain; other experimental methods and technical means not specifically noted in the embodiments of this invention refer to experimental methods and technical means commonly used by one of ordinary skill in the art.
[0037] The terms “basic” and “approximately” as used herein are used to describe small fluctuations. For example, they can refer to less than or equal to ±5%, such as less than or equal to ±2%, such as less than or equal to ±1%, such as less than or equal to ±0.5%, such as less than or equal to ±0.2%, such as less than or equal to ±0.1%, such as less than or equal to ±0.05%. Numerical data presented or expressed in range format herein are used for convenience and brevity only, and should therefore be flexibly interpreted to include not only the explicitly listed values that define the range, but also all independent values or subranges contained within the range. For example, a numerical range of “1–5%” should be interpreted to include not only the explicitly listed values from 1% to 5%, but also the independent values and subranges within the indicated range. Thus, this numerical range includes independent values such as 2%, 3.5%, and 4%, and subranges such as 1%–3%, 2%–4%, and 3%–5%, etc. This principle also applies to ranges that list only one value. Furthermore, this interpretation applies regardless of the width of the range or the characteristics described.
[0038] In this document, including in the claims, conjunctions such as "comprising," "including," "with," "having," "containing," "involving," and "accommodating" are understood to be open-ended, meaning "including but not limited to." Only the conjunctions "consisting of" and "composed of" are closed conjunctions.
[0039] To better illustrate the content of this invention, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that the invention can be practiced even without certain specific details. In the embodiments, some methods, means, instruments, and devices well-known to those skilled in the art are not described in detail, in order to highlight the main points of the invention.
[0040] Without conflict, the technical features disclosed in the embodiments of the present invention can be combined arbitrarily, and the resulting technical solution belongs to the content disclosed in the embodiments of the present invention.
[0041] In some embodiments, the method for preparing high-purity, large-size hexagonal diamond includes the following steps:
[0042] S1. Cut along the c-axis of highly oriented pyrolytic graphite to obtain cylindrical highly oriented pyrolytic graphite, which is used as a raw material precursor.
[0043] S2. Assemble the raw material precursor in a high-pressure heating synthesis assembly; in some embodiments, this specifically includes:
[0044] S21. Place the rhenium plate heater into the lanthanum chromate heating tube, and roll the rhenium plate heater into a cylindrical shape so that it fits tightly against the inner wall of the lanthanum chromate heating tube.
[0045] S22. Place the raw material precursor into the alumina sample tube, and place alumina sheets above and below the raw material precursor to confine the raw material precursor within the alumina sample tube.
[0046] S23. Place the alumina sample tube into the middle of the lanthanum chromate heating tube;
[0047] S24. Place an alumina cylindrical plug at the bottom of the lanthanum chromate heating tube and a four-hole alumina ceramic tube at the top of the lanthanum chromate heating tube to confine the alumina sample tube in the middle of the lanthanum chromate heating tube; wherein, a tungsten-rhenium thermocouple is inserted into the four-hole alumina ceramic tube for temperature calibration.
[0048] S25. Finally, the lanthanum chromate heating tube is placed into the magnesium oxide octahedral mold to complete the assembly and obtain the high-pressure heating synthesis component.
[0049] S3. The high-pressure heating synthesis component is heated and pressurized to a set pressure and temperature, and held at that temperature for a set time to obtain high-purity, large-size hexagonal diamonds. The set temperature is 1300–1900℃, the set pressure is 20–25 GPa, and the set time is 10–20 min. Generally, during the pressurization process under set conditions, the highly oriented pyrolytic graphite precursor in the high-pressure heating synthesis component compresses the high-temperature pyrolytic graphite along the c-axis, restricting its lateral sliding and causing it to buckle in a serrated manner. This results in orthogonal stacking of the pyrolytic graphite layers, followed by bonding growth at the increased temperature, yielding highly crystalline hexagonal diamonds. The transformation process is complete, resulting in large-size hexagonal diamonds. For example, the high-pressure heating synthesis component is placed in a large-cavity press for heating and pressurization, and the synthesis reaction is carried out under set conditions. After the reaction is completed, the pressure is reduced at a set depressurization rate, and the temperature is reduced at a set cooling rate to obtain high-purity, large-size hexagonal diamonds.
[0050] Some embodiments disclose a method for preparing high-purity, large-size hexagonal diamond, with the pressurization rate set to 2 GPa / h, the heating rate to 200 °C / min, and the depressurization rate set to 1 GPa / h.
[0051] Some embodiments disclose a method for preparing high-purity large-size hexagonal diamonds. After the reaction is completed, the sample is quenched and depressurized to room temperature, and then depressurized to atmospheric pressure at a set rate to obtain high-purity large-size hexagonal diamonds.
[0052] Some embodiments disclose a method for preparing high-purity large-size hexagonal diamonds, the resulting high-purity large-size hexagonal diamonds having a size in the millimeter range, for example, 1 to 2 mm.
[0053] The technical details are further illustrated below with reference to the embodiments.
[0054] Example 1
[0055] In Example 1, the method for preparing high-purity, large-size hexagonal diamond includes the following steps:
[0056] S1. Cut along the c-axis of the highly oriented pyrolytic graphite to obtain a cylinder of highly oriented pyrolytic graphite with a diameter of 1-2 mm and a height of 0.5-1 mm, which is used as a raw material precursor;
[0057] S2. Assemble the raw material precursors in a high-pressure heating synthesis assembly; such as... Figure 9 As shown, it specifically includes:
[0058] S21. Place the rhenium plate heater 3 into the lanthanum chromate heating tube 4, and roll the rhenium plate heater 3 into a cylindrical shape so that it is tightly attached to the inner wall of the lanthanum chromate heating tube 4.
[0059] S22. Place the raw material precursor 100 into the alumina sample tube 1, and place an alumina sheet 2 above and below the raw material precursor 100 to confine the raw material precursor 100 within the alumina sample tube 1; wherein the highly oriented pyrolytic graphite layer of the raw material precursor 100 is kept horizontal, and the c-axis of the highly oriented pyrolytic graphite cylinder is kept vertically upward; the alumina sheets 2 inside the alumina sample tube 1 are located at the upper and lower ends of the raw material precursor 100 to restrict the raw material precursor 100 within the alumina sample tube 1 to prevent it from sliding, and to prevent the raw material precursor from deforming under the pressure of the metal thermocouple;
[0060] S23. Place the alumina sample tube 1 into the middle of the lanthanum chromate heating tube 4;
[0061] S24. An alumina cylindrical plug 6 is placed at the bottom of the lanthanum chromate heating tube 4, and an alumina four-hole ceramic tube 5 is placed at the top of the lanthanum chromate heating tube 4, thus confining the alumina sample tube 1 in the middle of the lanthanum chromate heating tube 4; wherein, a tungsten-rhenium thermocouple 7 is inserted into the alumina four-hole ceramic tube 5 for temperature calibration.
[0062] S25. Finally, the lanthanum chromate heating tube 4 is placed into the magnesium oxide octahedral mold 8 with a side length of 8mm to complete the assembly and obtain the high-pressure heating synthesis component. Typically, the magnesium oxide octahedral mold has a cylindrical cavity adapted to the lanthanum chromate heating tube 4 between its two relatively parallel surfaces. The cylindrical cavity runs through the two parallel surfaces, and the annular cavity is used to house the lanthanum chromate heating tube 4.
[0063] S3. Place the high-pressure heating component into the Kawai-type large-cavity press, heat and pressurize to the set pressure and set temperature, hold for the set time, then quench to cool the product sample to room temperature, and depressurize to normal pressure at the set rate to obtain high-purity hexagonal diamond.
[0064] Among them, a cemented carbide anvil with a side length of 25.4 mm and a truncated side length of 3 mm was used as the secondary pressure anvil; the set temperatures were 700, 1300, 1700, 1900 and 2100℃, the set pressure was 20 GPa, the pressurization rate was 2 GPa / h, the set time was 10 min, and the depressurization rate was 1 GPa / h.
[0065] The sample obtained in Example 1 was subjected to XRD and Raman spectroscopy tests, and the results are as follows: Figure 1 , Figure 2 As shown, the results indicate that the samples obtained at set temperatures of 1300, 1700, and 1900 are pure hexagonal diamond; while the samples obtained at set temperatures of 700℃ and 2100℃ are graphite / hexagonal diamond mixed phase and cubic / hexagonal diamond mixed phase, respectively.
[0066] The hexagonal diamond sample obtained at 1300℃ was processed into a transmission electron microscopy (TEM) sample using a focused ion beam. The structure of the transmitted sample was then comprehensively characterized using aberration-corrected TEM. Figure 4 As shown, the results indicate that the sample has a typical hexagonal diamond structure.
[0067] Hexagonal diamond samples obtained at 1300, 1700, and 1900℃ were subjected to Vickers hardness tests under a 1 kg load. The results are as follows: Figure 5 As shown, the Vickers hardness value of the sample obtained at 1300℃ is 162±9GPa; the Vickers hardness value of the sample obtained at 1700℃ is 145±8GPa; and the Vickers hardness value of the sample obtained at 1900℃ is 151±11GPa.
[0068] The thermal stability of the hexagonal diamond sample obtained at 1300℃ was tested in air, and the results are as follows: Figure 6 As shown, the results indicate that the sample exhibits significant thermal stability, with an initial oxidation temperature of 1121 K.
[0069] Example 2
[0070] In Example 2, the preparation method of high-purity large-size hexagonal diamond is the same as in Example 1, wherein the pressure is set to 22 GPa;
[0071] The obtained hexagonal diamond sample was subjected to XRD pattern analysis, and the results are as follows: Figure 3 As shown; the results indicate that the sample obtained in Example 2 is pure-phase hexagonal diamond.
[0072] Comparative Example 1
[0073] In Comparative Example 1, the preparation method of hexagonal diamond was carried out in accordance with Example 1; wherein, the pressure value was set to 15 GPa and the temperature was set to 1300 and 1900 °C respectively.
[0074] The XRD pattern of the sample obtained in Comparative Example 1 was tested, and the results are as follows: Figure 3 As shown, the test results indicate that in Comparative Example 1, the sample obtained at 1300℃ is mainly composed of graphite phase, while the sample obtained at 1900℃ is mainly composed of cubic diamond phase.
[0075] Comparative Example 2
[0076] In Comparative Example 2, the randomly stacked sample of highly oriented pyrolytic graphite and the orderly vertically stacked sample along the c-axis were used as raw material precursors for cold pressing experiments; the experimental process was the same as in Example 1; the pressure was set at 20 GPa and no temperature was increased.
[0077] The sample obtained in Comparative Example 2 was characterized by scanning electron microscopy, such as... Figure 7 As shown in the figure; where figures a and b represent the changes in disordered stacked samples, and figures c and d represent the changes in ordered vertically stacked samples; the results show that ordered stacked highly oriented pyrolytic graphite is flatter and has fewer wrinkles after cold pressing, which is beneficial for its transformation into hexagonal diamond.
[0078] Comparative Example 3
[0079] In Comparative Example 3, flake graphite, randomly stacked highly oriented pyrolytic graphite (HOPG disordered stacking) and ordered vertically stacked highly oriented pyrolytic graphite (HOPG ordered stacking) along the c-axis were used as raw material precursors, and high-pressure experiments were carried out respectively. The experimental process was the same as in Example 1. The pressure was set at 20 GPa and the temperature was set at 1300℃.
[0080] The XRD pattern of the sample obtained in Comparative Example 3 was tested, and the results are as follows: Figure 8 As shown, the sample synthesized using flake graphite as a precursor is pure-phase cubic diamond; the sample synthesized using disordered stacking of HOPG as a precursor is mainly cubic diamond; and the sample synthesized using highly oriented pyrolytic graphite stacked vertically along the c-axis as a precursor is pure-phase hexagonal diamond. This demonstrates that the strategy of controlling graphite slippage by quasi-uniaxial pressure to synthesize hexagonal diamond can achieve the expected technical effect.
[0081] The present invention discloses a method for preparing high-purity, large-size hexagonal diamonds. This method uses c-axis cylindrical highly oriented pyrolytic graphite as a raw material precursor and, under set conditions, completely converts the highly oriented pyrolytic graphite into high-purity, large-size hexagonal diamonds with a size of 1-2 mm. This method has significant application prospects in fields such as superhard materials and semiconductor devices.
[0082] The technical solutions and technical details disclosed in the embodiments of this invention are merely illustrative of the inventive concept of this invention and do not constitute a limitation on the technical solutions of the embodiments of this invention. Any conventional changes, substitutions, or combinations made to the technical details disclosed in the embodiments of this invention have the same inventive concept as this invention and are within the protection scope of the claims of this invention.
Claims
1. A method for preparing high-purity, large-size hexagonal diamond, characterized in that, Including the following steps: S1. Cut along the c-axis of highly oriented pyrolytic graphite to obtain cylindrical highly oriented pyrolytic graphite, which is used as a raw material precursor. S2. Assembling the raw material precursors in a high-pressure heating synthesis assembly; specifically including: S21. Place the rhenium plate heater into the lanthanum chromate heating tube, and roll the rhenium plate heater into a cylindrical shape so that it fits tightly against the inner wall of the lanthanum chromate heating tube. S22. Place the raw material precursor into the alumina sample tube, and place alumina sheets above and below the raw material precursor to confine the raw material precursor within the alumina sample tube. S23. Place the alumina sample tube into the middle of the lanthanum chromate heating tube; S24. Place an alumina cylindrical plug at the bottom of the lanthanum chromate heating tube and a four-hole alumina ceramic tube at the top of the lanthanum chromate heating tube to confine the alumina sample tube in the middle of the lanthanum chromate heating tube; wherein, a tungsten-rhenium thermocouple is inserted into the four-hole alumina ceramic tube for temperature calibration. S25. Finally, the lanthanum chromate heating tube is placed into the magnesium oxide octahedral mold to complete the assembly and obtain the high-pressure heating synthesis component. S3. The high-pressure heating synthesis component is placed in a large-cavity press for heating and pressurization, and a synthesis reaction is carried out under set conditions. After the reaction is completed, the sample is quenched and cooled to room temperature, and then depressurized to atmospheric pressure at a set rate to obtain high-purity large-size hexagonal diamond. The set temperature is 1300-1900℃, the set pressure is 20-25GPa, the set time is 10-20min, the pressurization rate is set to 2GPa / h, the heating rate is 200℃ / min, and the depressurization rate is set to 1GPa / h. The size of the high-purity large-size hexagonal diamond is in the millimeter range.