CN-120094492-B - Preparation method of high-purity large-size hexagonal diamond

Abstract

The embodiment of the invention discloses a preparation method of high-purity large-size hexagonal diamond, which comprises the steps of S1, cutting along a C-axis of high-orientation pyrolytic graphite to obtain cylindrical high-orientation pyrolytic graphite serving as a raw material precursor, S2, assembling the raw material precursor into a high-pressure heating synthesis assembly, S3, heating and pressurizing the high-pressure heating synthesis assembly to set pressure and set temperature, and preserving heat for set time to obtain the high-purity hexagonal diamond, wherein the set temperature is 1300-1900 ℃, the set pressure is 20-25 GPa, and the set time is 10-20 min. The preparation method of the high-purity large-size hexagonal diamond disclosed by the embodiment of the invention uses the cylindrical high-orientation pyrolytic graphite cut along the c-axis as a raw material precursor, and fully converts the high-orientation pyrolytic graphite into the high-purity large-size hexagonal diamond under the set condition, wherein the dimension is 1-2 mm, and the preparation method has important application prospects in the fields of superhard materials, semiconductor devices and the like.

Inventors

• SHAN CHONGXIN
• YANG XIGUI
• Lai Shoulong

Assignees

• 郑州大学

Dates

Publication Date

20260512

Application Date

20250304

Claims (1)

1. 1. The preparation method of the high-purity large-size hexagonal diamond is characterized by comprising the following steps: S1, cutting along a c-axis of high-orientation pyrolytic graphite to obtain cylindrical high-orientation pyrolytic graphite serving as a raw material precursor; s2, assembling the raw material precursor in a high-pressure heating synthesis assembly, wherein the method specifically comprises the following steps: S21, placing the rhenium piece heater into a lanthanum chromate heating pipe, and rolling the rhenium piece heater into a cylinder shape to be tightly attached to the inner wall of the lanthanum chromate heating pipe; S22, placing raw material precursors into an alumina sample tube, respectively placing aluminum oxide sheets on the upper part and the lower part of the raw material precursors, and limiting the raw material precursors into the alumina sample tube; S23, placing an alumina sample tube into the middle part of the inside of the lanthanum chromate heating tube; S24, placing an alumina column plug at the lower part of the lanthanum chromate heating pipe, and placing an alumina four-hole ceramic pipe at the upper part of the lanthanum chromate heating pipe to limit an alumina sample pipe at the inner middle part of the lanthanum chromate heating pipe, wherein a tungsten-rhenium thermocouple is penetrated into the alumina four-hole ceramic pipe for calibrating the temperature; S25, finally, placing the lanthanum chromate heating pipe into a magnesium oxide octahedral die to complete assembly, and obtaining a high-pressure heating synthesis assembly; And S3, placing the high-pressure heating synthesis assembly into a large-cavity press for heating and pressurizing, and carrying out synthesis reaction under a set condition, wherein a sample obtained after the reaction is quenched, dimension-reduced to room temperature, and then pressure-released to normal pressure at a set rate to obtain the high-purity large-size hexagonal diamond, the set temperature is 1300-1900 ℃, the set pressure is 20-25 GPa, the set time is 10-20 min, the pressurizing rate is 2GPa/h, the heating rate is 200 ℃/min, the pressure-releasing rate is 1GPa/h, and the size of the high-purity large-size hexagonal diamond is millimeter level.

Description

Preparation method of high-purity large-size hexagonal diamond Technical Field The invention belongs to the technical field of superhard materials, and particularly relates to a preparation method of high-purity hexagonal diamond. Background Hexagonal diamond, also known as lambertian, has received considerable attention due to its theoretically predicted ultra-high hardness and potential role as a mineralogical marker for the event of merle impact. Since hexagonal diamond was first discovered in merle, synthesis of bulk pure phase hexagonal diamond has been a technical hotspot in this area. At present, a common method is to compress a graphite precursor at high temperature and high pressure, prepare hexagonal diamond by using a detonation method or impact compression graphite sample, however, cubic diamond is formed in a synthesized product preferentially due to higher thermodynamic stability, so that only a small amount of hexagonal diamond or graphite exists in the product. Typically, these multiphase mixture products require identification using x-ray diffraction and selective electron diffraction, but because of the overlapping nature of cubic and hexagonal diamonds, precise identification of hexagonal diamonds is complex and difficult. Studies have shown that the structural evidence previously attributed to hexagonal diamond may actually correspond to cubic diamond or cubic nano twins with stacked faults, making the availability of hexagonal diamond phases problematic. Thus, the presence of hexagonal diamond remains full of contention and elusive. The inability to prepare pure phase bulk hexagonal diamond crystals at present also prevents further investigation of their physical properties. Thus, there remains a pressing need in the art to produce pure phase hexagonal diamond bulk materials. Disclosure of Invention In view of this, some embodiments disclose a method of preparing high purity large-sized hexagonal diamond, comprising the steps of: S1, cutting along a c-axis of high-orientation pyrolytic graphite to obtain cylindrical high-orientation pyrolytic graphite serving as a raw material precursor; s2, assembling the raw material precursor in a high-pressure heating synthesis assembly; And S3, heating and pressurizing the high-pressure heating synthesis assembly to a set pressure and a set temperature, and preserving heat and setting to obtain the high-purity large-size hexagonal diamond, wherein the set temperature is 1300-1900 ℃, the set pressure is 20-25 GPa, and the set time is 10-20 min. Further, some embodiments disclose a method for preparing high purity large-sized hexagonal diamond, in step S2, assembling a raw material precursor in a high pressure heating synthesis assembly comprising: S21, placing the rhenium piece heater into a lanthanum chromate heating pipe, and rolling the rhenium piece heater into a cylinder shape to be tightly attached to the inner wall of the lanthanum chromate heating pipe; S22, placing raw material precursors into an alumina sample tube, respectively placing aluminum oxide sheets on the upper part and the lower part of the raw material precursors, and limiting the raw material precursors into the alumina sample tube; S23, placing an alumina sample tube into the middle part of the inside of the lanthanum chromate heating tube; S24, placing an alumina column plug at the lower part of the lanthanum chromate heating pipe, and placing an alumina four-hole ceramic pipe at the upper part of the lanthanum chromate heating pipe to limit an alumina sample pipe at the inner middle part of the lanthanum chromate heating pipe, wherein a tungsten-rhenium thermocouple is penetrated into the alumina four-hole ceramic pipe for calibrating the temperature; and S25, finally, placing the lanthanum chromate heating pipe into a magnesium oxide octahedral die to complete assembly, and obtaining the high-pressure heating synthetic component. In the preparation method of the high-purity large-size hexagonal diamond disclosed by some embodiments, in the step S3, a high-pressure heating synthesis assembly is placed into a large cavity press for heating and pressurizing, 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 temperature reduction rate, so that the high-purity large-size hexagonal diamond is obtained. Further, some examples disclose methods of preparing high purity large sized hexagonal diamond with a pressurization rate set at 2GPa/h, a heating rate at 200℃/min, and a pressure relief rate set at 1GPa/h. According to the preparation method of the high-purity large-size hexagonal diamond disclosed by some embodiments, a sample obtained after the reaction is quenched and cooled to room temperature, and then the pressure is relieved to normal pressure at a set rate, so that the high-purity large-size hexagonal diamond is obtained. Some examples disc