Preparation method of high-purity large-size hexagonal diamond

Abstract

The embodiment of the invention discloses a preparation method of a high-purity large-size hexagonal diamond, which comprises the following steps: S1, cutting along the c axis of highly oriented pyrolytic graphite to obtain cylindrical highly oriented pyrolytic graphite as a raw material precursor; s2, assembling the raw material precursor in a high-pressure heating synthesis assembly; s3, the high-pressure heating synthesis assembly is heated and pressurized to set pressure and set temperature, heat preservation is conducted for set time, and the high-purity hexagonal diamond is obtained; wherein the set temperature ranges from 1300 DEG C to 1900 DEG C, the set pressure ranges from 20 GPa to 25 GPa, and the set time ranges from 10 min to 20 min. According to the preparation method of the high-purity large-size hexagonal diamond disclosed by the embodiment of the invention, cylindrical high-orientation pyrolytic graphite cut along a c axis is used as a raw material precursor, the high-orientation pyrolytic graphite is completely converted into the high-purity large-size hexagonal diamond under set conditions, and the size is 1-2 mm; the method has important application prospects in the fields of superhard materials, semiconductor devices and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of superhard materials, and in particular relates to a method for preparing high-purity hexagonal diamond. Background Art

[0002] Hexagonal diamond, also known as lonsdaleite, has received considerable attention due to its theoretically predicted ultrahigh hardness and potential role as a mineralogical marker of meteorite impact events. Since its first discovery in meteorites, the synthesis of bulk pure phase hexagonal diamond has been a technical hotspot in the field.

[0003] Currently, the common method is to compress graphite precursors under high temperature and pressure, and use detonation or shock compression to prepare hexagonal diamond from graphite samples; however, cubic diamond is thermodynamically more stable and is preferentially formed in the synthetic product, resulting in only a small amount of hexagonal diamond or graphite in the product. Usually, these multiphase mixture products need to be identified using x-ray diffraction and selected area electron diffraction, but the precise identification of hexagonal diamond is complex and difficult due to the overlapping characteristics of cubic diamond and hexagonal diamond. Studies have shown that structural evidence previously attributed to hexagonal diamond may actually correspond to cubic diamond or cubic nanotwins with stacking faults, making the validity of the existence of the hexagonal diamond phase questionable. Therefore, the existence of hexagonal diamond remains controversial and elusive.

[0004] The inability to prepare pure phase bulk hexagonal diamond crystals currently also hinders further research on its physical properties. Therefore, the preparation of pure phase hexagonal diamond bulk materials is still an urgent need in the field. Summary of the invention

[0005] In view of this, some embodiments disclose a method for preparing high-purity large-size hexagonal diamond, comprising the steps of:

[0006] S1, cutting along the c-axis of the highly oriented pyrolytic graphite to obtain cylindrical highly oriented pyrolytic graphite as a raw material precursor;

[0007] S2, assembling the raw material precursors in a high pressure heating synthesis assembly;

[0008] S3. Heat and pressurize the high-pressure heating synthesis component to a set pressure and a set temperature, and keep the temperature for a set time to obtain high-purity, large-size hexagonal diamond; wherein the set temperature is 1300-1900°C, the set pressure is 20-25GPa, and the set time is 10-20min.

[0009] Further, in some embodiments of the method for preparing high-purity large-size hexagonal diamond, in step S2, assembling the raw material precursor in a high-pressure heating synthesis assembly includes:

[0010] S21, placing the rhenium sheet heater into the lanthanum chromate heating tube, and rolling the rhenium sheet heater into a cylindrical shape so that it is closely attached to the inner wall of the lanthanum chromate heating tube;

[0011] S22, placing the raw material precursor into an alumina sample tube, placing alumina sheets above and below the raw material precursor, and confining the raw material precursor in the alumina sample tube;

[0012] S23, placing the alumina sample tube into the middle of the lanthanum chromate heating tube;

[0013] S24, placing an alumina columnar plug at the bottom of the lanthanum chromate heating tube, placing an alumina four-hole ceramic tube at the top of the lanthanum chromate heating tube, and restricting the alumina sample tube to the middle of the lanthanum chromate heating tube; wherein a tungsten-rhenium thermocouple is inserted into the alumina four-hole ceramic tube to calibrate the temperature;

[0014] S25. Finally, the lanthanum chromate heating tube is placed into the magnesium oxide octahedron mold to complete the assembly and obtain a high-pressure heating synthesis component.

[0015] Some embodiments disclose a method for preparing high-purity large-sized hexagonal diamonds. In step S3, a high-pressure heated 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 pressure relief rate, and the temperature is reduced at a set cooling rate to obtain high-purity large-sized hexagonal diamonds.

[0016] Furthermore, in some embodiments of the method for preparing high-purity large-size hexagonal diamond, the pressurization rate is set to 2 GPa / h, the heating rate is set to 200°C / min, and the pressure relief rate is set to 1 GPa / h.

[0017] Some embodiments disclose a method for preparing high-purity large-sized hexagonal diamond. After the reaction is completed, the sample obtained is quenched and cooled to room temperature, and then the pressure is released to normal pressure at a set rate to obtain high-purity large-sized hexagonal diamond.

[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 millimeter-level.

[0019] The method for preparing high-purity large-size hexagonal diamond disclosed in an embodiment of the present invention uses cylindrical highly oriented pyrolytic graphite cut along the c-axis as a raw material precursor, and under set conditions, the highly oriented pyrolytic graphite is completely converted into high-purity, large-size hexagonal diamond with a scale of 1 to 2 mm; the hexagonal diamond prepared by this method does not need to undergo an intermediate phase transition of graphite, but directly undergoes a structural transition from graphite to diamond, and can be synthesized under relatively low pressure; it has important application prospects in the fields of superhard materials, semiconductor devices, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is the XRD pattern of the sample obtained in Example 1;

[0021] Figure 2 is the Raman spectrum of the sample obtained in Example 1;

[0022] Figure 3 is the XRD pattern of the samples obtained in Example 2 and Comparative Example 1;

[0023] Figure 4 is the spherical aberration electron microscope image of the sample obtained in Example 1;

[0024] Figure 5 is the Vickers hardness test result of the sample obtained in Example 1;

[0025] Figure 6 is the thermal stability test result of the sample obtained in Example 1;

[0026] Figure 7 This is the morphology of the cold pressing test sample obtained in Comparative Example 2;

[0027] Figure 8 This is the XRD pattern of the sample obtained in Comparative Example 3;

[0028] Fig. 9 It is a schematic diagram of the arrangement of the high pressure heating synthesis assembly in Example 1.

[0029] Reference numerals

[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 columnar plug

[0033] 7 Thermocouple 8 Magnesium oxide octahedron mold

[0034] 100 Raw material precursor DETAILED DESCRIPTION

[0035] The word "embodiment" used herein as an "exemplary" does not necessarily mean that any embodiment described is superior or better than other embodiments. Performance index tests in the embodiments of the present invention are performed using conventional test methods in the art unless otherwise specified. It should be understood that the terms described in the embodiments of the present invention are only used to describe specific implementation methods and are not intended to limit the contents disclosed in the embodiments of the present invention.

[0036] Unless otherwise specified, the technical and scientific terms used herein have the same meanings as commonly understood by ordinary technicians in the technical field to which the embodiments of the present invention belong; other experimental methods and technical means not specifically specified in the embodiments of the present invention refer to experimental methods and technical means commonly used by ordinary technicians in the field.

[0037] The terms "substantially" and "approximately" 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%. The numerical data represented or presented in the range format herein are used only for convenience and brevity, and should therefore be flexibly interpreted as including not only the values ​​clearly listed as the limits of the range, but also all independent values ​​or sub-ranges contained in the range. For example, the numerical range of "1-5%" should be interpreted as including not only the clearly listed values ​​of 1% to 5%, but also the independent values ​​and sub-ranges within the range shown. Therefore, independent values ​​such as 2%, 3.5% and 4% and sub-ranges such as 1%-3%, 2%-4% and 3%-5% are included in this numerical range. This principle also applies to the range of only one numerical value. In addition, such an interpretation applies regardless of the width of the range or the characteristics described.

[0038] In this document, including in the claims, transitional words such as "comprises," "includes," "with," "having," "containing," "involving," "accommodating," etc. are understood to be open-ended, i.e., meaning "including but not limited to." Only the transitional words "consisting of" and "composed of" are closed transitional words.

[0039] In order to better illustrate the present invention, numerous specific details are provided in the specific examples below. It should be understood by those skilled in the art that the present invention can be implemented without certain specific details. In the embodiments, some methods, means, instruments, equipment, etc. well known to those skilled in the art are not described in detail in order to highlight the gist of the present invention.

[0040] Under the premise of no conflict, the technical features disclosed in the embodiments of the present invention may be arbitrarily combined, and the resulting technical solutions belong to the contents disclosed in the embodiments of the present invention.

[0041] In some embodiments, the method for preparing high-purity large-size hexagonal diamond comprises the steps of:

[0042] S1, cutting along the c-axis of the highly oriented pyrolytic graphite to obtain cylindrical highly oriented pyrolytic graphite as a raw material precursor;

[0043] S2, assembling the raw material precursors in a high pressure heating synthesis assembly; in some embodiments, specifically comprising:

[0044] S21, placing the rhenium sheet heater into the lanthanum chromate heating tube, and rolling the rhenium sheet heater into a cylindrical shape so that it is closely attached to the inner wall of the lanthanum chromate heating tube;

[0045] S22, placing the raw material precursor into an alumina sample tube, placing alumina sheets above and below the raw material precursor, and confining the raw material precursor in the alumina sample tube;

[0046] S23, placing the alumina sample tube into the middle of the lanthanum chromate heating tube;

[0047] S24, placing an alumina columnar plug at the bottom of the lanthanum chromate heating tube, placing an alumina four-hole ceramic tube at the top of the lanthanum chromate heating tube, and restricting the alumina sample tube to the middle of the lanthanum chromate heating tube; wherein a tungsten-rhenium thermocouple is inserted into the alumina four-hole ceramic tube to calibrate the temperature;

[0048] S25, finally placing the lanthanum chromate heating tube into the magnesium oxide octahedron mold to complete the assembly and obtain a high-pressure heating synthesis component;

[0049] S3. Heat and pressurize the high-pressure heating synthesis component to the set pressure and set temperature, and keep it warm for the set time to obtain high-purity, large-sized hexagonal diamond; wherein the set temperature is 1300-1900°C, the set pressure is 20-25GPa, and the set time is 10-20min. Generally, during the pressurization process under set conditions, the high-oriented pyrolytic graphite raw material precursor in the high-pressure heating synthesis component compresses the high-temperature pyrolytic graphite along the c-axis direction, restricts the lateral sliding of the high-temperature pyrolytic graphite and causes it to be serrated, so that the pyrolytic graphite layers are orthogonally stacked, and bonded growth occurs at elevated temperatures to obtain highly crystalline hexagonal diamonds, and the conversion process is complete, and large-sized hexagonal diamonds can be obtained; for example, 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 pressure is reduced at a set pressure relief rate, and the temperature is reduced at a set cooling rate to obtain high-purity large-sized hexagonal diamonds.

[0050] Some embodiments disclose a method for preparing high-purity large-size hexagonal diamond, wherein the pressurization rate is set to 2 GPa / h, the heating rate is set to 200°C / min, and the pressure relief rate is set to 1 GPa / h.

[0051] Some embodiments disclose a method for preparing high-purity large-sized hexagonal diamonds. After the reaction is completed, the sample obtained is quenched and reduced to room temperature, and then the pressure is released to normal pressure at a set rate to obtain high-purity large-sized hexagonal diamonds.

[0052] Some embodiments disclose methods for preparing high-purity large-size hexagonal diamonds, and the prepared high-purity large-size hexagonal diamonds have a size of millimeter level, for example, 1 to 2 mm.

[0053] The technical details are further illustrated below in conjunction with embodiments.

[0054] Example 1

[0055] In Example 1, the method for preparing high-purity large-size hexagonal diamond comprises the steps of:

[0056] S1, cutting along the c-axis of the highly oriented pyrolytic graphite to obtain a highly oriented pyrolytic graphite cylinder with a diameter of 1 to 2 mm and a height of 0.5 to 1 mm as a raw material precursor;

[0057] S2, assembling the raw material precursors in a high pressure heating synthesis assembly; Fig. 9 As shown, specifically including:

[0058] S21, placing the rhenium sheet heater 3 into the lanthanum chromate heating tube 4, and rolling the rhenium sheet heater 3 into a cylindrical shape so that it is close to the inner wall of the lanthanum chromate heating tube 4;

[0059] S22, placing the raw material precursor 100 into the alumina sample tube 1, placing an alumina sheet 2 on the upper and lower sides of the raw material precursor 100, and confining 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 sheet 2 in the alumina sample tube 1 is located at the upper and lower ends of the raw material precursor 100, so as to confine the raw material precursor 100 in the alumina sample tube 1 to prevent it from sliding, and to keep the raw material precursor from being deformed under the extrusion of the metal thermocouple;

[0060] S23, placing the alumina sample tube 1 into the middle of the lanthanum chromate heating tube 4;

[0061] S24, placing an alumina columnar plug 6 at the lower part of the lanthanum chromate heating tube 4, placing an alumina four-hole ceramic tube 5 at the upper part of the lanthanum chromate heating tube 4, and restricting 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 calibrating the temperature;

[0062] S25, finally, the lanthanum chromate heating tube 4 is placed in the magnesium oxide octahedron mold 8 with a side length of 8 mm, and the assembly is completed to obtain a high-pressure heating synthesis component; usually, the magnesium oxide octahedron mold is provided with a cylindrical chamber adapted to the lanthanum chromate heating tube 4 between its two relatively parallel surfaces, and the cylindrical chamber runs through the two parallel surfaces, and the annular chamber is used to set the lanthanum chromate heating tube 4;

[0063] S3, placing the high-pressure heating assembly into a Kawai-type large-cavity press, heating and pressurizing to a set pressure and a set temperature, keeping the temperature for a set time, then quenching to cool the product sample to room temperature, and unloading the pressure to normal pressure at a set rate to obtain high-purity hexagonal diamond;

[0064] Among them, a carbide anvil with a side length of 25.4 mm and a truncated side length of 3 mm was used as the secondary anvil; the set temperatures were 700, 1300, 1700, 1900 and 2100°C, the set pressure was 20 GPa, the pressurization rate was 2 GPa / h, the setting time was 10 min, and the pressure relief rate was 1 GPa / h.

[0065] The samples obtained in Example 1 were subjected to XRD and Raman spectroscopy tests, and the results were as follows: Figure 1 , Figure 2 As shown, the results show that the samples obtained at the set temperatures of 1300, 1700, and 1900 are pure hexagonal diamond; while the samples obtained at the set temperatures of 700℃ and 2100℃ are graphite / hexagonal diamond mixed phases and cubic / hexagonal diamond mixed phases, respectively;

[0066] The hexagonal diamond samples obtained at 1300°C were processed into transmission samples by focused ion beam, and the structure of the transmission samples was fully characterized by spherical aberration transmission electron microscopy, such as Figure 4 As shown, the results show that the sample has a typical hexagonal diamond structure;

[0067] The Vickers hardness test was performed on the hexagonal diamond samples obtained at 1300, 1700, and 1900°C under a load of 1 kg. The results are as follows: Figure 5 As shown, the Vickers hardness of the sample obtained at 1300°C is 162±9GPa; the Vickers hardness of the sample obtained at 1700°C is 145±8GPa, and the Vickers hardness of the sample obtained at 1900°C is 151±11GPa;

[0068] The thermal stability of the hexagonal diamond samples obtained at 1300°C was tested in air atmosphere. Figure 6 As shown, the results show that the sample exhibits remarkable thermal stability and the onset oxidation temperature is 1121K.

[0069] Example 2

[0070] In Example 2, the preparation method of high-purity large-size hexagonal diamond is carried out with reference to Example 1, wherein the set pressure is 22 GPa;

[0071] The obtained hexagonal diamond sample was tested by XRD spectrum, and the results are as follows: Figure 3 As shown; the results show 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 is carried out with reference to Example 1; wherein the set pressure value is 15 GPa, and the set temperatures are 1300 and 1900° C. respectively.

[0074] The sample obtained in Comparative Example 1 was subjected to XRD spectrum test, and the results are as follows: Figure 3 As shown, the test results show that in Comparative Example 1, the sample obtained at 1300°C is mainly graphite phase, and the sample obtained at 1900°C is mainly cubic diamond phase.

[0075] Comparative Example 2

[0076] In Comparative Example 2, a highly oriented pyrolytic graphite disordered stacking sample and an ordered vertical stacking sample along the c-axis were used as raw material precursors, respectively, and a cold pressing experiment was carried out; the experimental process was referred to Example 1; wherein the pressure was set to 20 GPa, and the temperature was not increased.

[0077] The samples obtained in Comparative Example 2 were characterized by scanning electron microscopy. Figure 7 As shown; Figures a and b represent the changes of disordered stacking samples, and Figures c and d represent the changes of ordered vertical stacking samples; the results show that the ordered stacked highly oriented pyrolytic graphite is flatter and has fewer wrinkles after cold pressing, which is conducive to its conversion into hexagonal diamond.

[0078] Comparative Example 3

[0079] In Comparative Example 3, flake graphite, highly oriented pyrolytic graphite with disordered stacking (HOPG disordered stacking) and highly oriented pyrolytic graphite with orderly vertical stacking along the c-axis (HOPG ordered stacking) were used as raw material precursors, and high-pressure experiments were carried out respectively. The experimental process referred to Example 1; wherein the set pressure was 20 GPa and the set temperature was 1300°C.

[0080] The sample obtained in Comparative Example 3 was subjected to XRD spectrum test, and the results were as follows: Figure 8 As shown, the sample synthesized with flake graphite as the precursor is pure cubic diamond; the sample synthesized with disordered stacking of HOPG as the precursor is mainly composed of cubic diamond phase; the sample synthesized with highly oriented pyrolytic graphite with orderly vertical stacking along the c-axis as the precursor is pure hexagonal diamond, indicating that the strategy of controlling the slip of graphite by quasi-uniaxial pressure to synthesize hexagonal diamond can achieve the expected technical effect.

[0081] The method for preparing high-purity large-size hexagonal diamond disclosed in an embodiment of the present invention utilizes c-axis cylindrical highly oriented pyrolytic graphite as a raw material precursor, and under set conditions, the highly oriented pyrolytic graphite is completely converted into high-purity large-size hexagonal diamond with a scale of 1 to 2 mm; it has important application prospects in the fields of superhard materials, semiconductor devices, etc.

[0082] The technical solutions disclosed in the embodiments of the present invention and the technical details disclosed in the embodiments are merely illustrative of the inventive concept of the present invention and do not constitute a limitation on the technical solutions of the embodiments of the present invention. Any conventional changes, replacements or combinations of the technical details disclosed in the embodiments of the present invention have the same inventive concept as the present invention and are within the protection scope of the claims of the present invention.

Claims

1. A method for preparing high-purity large-size hexagonal diamond, characterized in that: Includes steps: S1, cutting along the c-axis of the highly oriented pyrolytic graphite to obtain cylindrical highly oriented pyrolytic graphite as a raw material precursor; S2, assembling the raw material precursors in a high pressure heating synthesis assembly; S3. Heat and pressurize the high-pressure heating synthesis component to a set pressure and a set temperature, and keep it warm for a set time to obtain high-purity, large-sized hexagonal diamond; wherein the set temperature is 1300-1900°C, the set pressure is 20-25GPa, and the set time is 10-20min.

2. The method for preparing high-purity large-size hexagonal diamond according to claim 1, characterized in that: In step S2, assembling the raw material precursors in a high pressure heating synthesis assembly includes: S21, placing the rhenium sheet heater into the lanthanum chromate heating tube, and rolling the rhenium sheet heater into a cylindrical shape so that it is closely attached to the inner wall of the lanthanum chromate heating tube; S22, placing the raw material precursor into an alumina sample tube, placing alumina sheets above and below the raw material precursor, and confining the raw material precursor in the alumina sample tube; S23, placing the alumina sample tube into the middle of the lanthanum chromate heating tube; S24, placing an alumina columnar plug at the bottom of the lanthanum chromate heating tube, placing an alumina four-hole ceramic tube at the top of the lanthanum chromate heating tube, and restricting the alumina sample tube to the middle of the lanthanum chromate heating tube; wherein a tungsten-rhenium thermocouple is inserted into the alumina four-hole ceramic tube to calibrate the temperature; S25. Finally, the lanthanum chromate heating tube is placed into the magnesium oxide octahedron mold to complete the assembly and obtain a high-pressure heating synthesis component.

3. The method for preparing high-purity large-size hexagonal diamond according to claim 1, characterized in that: In step 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 pressure is reduced at a set pressure relief rate, and the temperature is reduced at a set cooling rate to obtain high-purity large-size hexagonal diamond.

4. The method for preparing high-purity large-size hexagonal diamond according to claim 3, characterized in that: in, The pressurization rate was set to 2 GPa / h, the heating rate was 200°C / min, and the pressure relief rate was set to 1 GPa / h.

5. The method for preparing high-purity large-size hexagonal diamond according to claim 3, characterized in that: After the reaction is completed, the sample obtained is quenched and reduced to room temperature, and then decompressed to normal pressure at a set rate to obtain high-purity large-size hexagonal diamond.

6. The method for preparing high-purity large-size hexagonal diamond according to claim 1, characterized in that: The size of the high-purity large-size hexagonal diamond is millimeter level.

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