A transparent nanocrystalline diamond and its low-temperature compressive strength preparation method

Abstract

This invention provides a method for preparing transparent polycrystalline diamond nanoparticles at low temperatures, comprising the following steps: S1: Mixing: Using hydrogen-modified carbon nanospheres as raw materials, the raw materials are mixed after removing moisture and impurities; S2: Pressing: The mixed raw materials are pressed into cylindrical shapes according to the size of the synthesis chamber using a hydraulic press; S3: Assembly: The cylindrical raw materials are placed into a heating container and then assembled in the synthesis chamber; S4: Synthesis: The pressure is controlled at 9.0-15 GPa, the temperature at 1250-2300℃, and the holding time is 1-15 min, to synthesize the raw materials assembled in step S3 to obtain the product; S5: Cooling and depressurization: After the product synthesized in step S4 is cooled and depressurized, transparent polycrystalline diamond nanoparticles are obtained. This invention provides a low-cost and relatively simple method for preparing transparent polycrystalline diamond nanoparticles at low temperatures, which has high commercial and promotional value.

Description

Technical Field

[0001] This invention relates to the field of nanocrystalline diamond preparation, and more specifically, to a transparent nanocrystalline diamond and a method for preparing it under low-temperature compression. Background Technology

[0002] Superhard polycrystalline diamond (NPD) materials have important applications in aerospace, geological exploration, oil extraction, and precision machining. While single-crystal diamond materials have extremely high hardness, they are prone to fracture along the 111-plane, forming cleavage planes. Polycrystalline diamond (NPD), typically formed by the direct transformation of various carbon allotropes under high temperature and pressure, is a polycrystalline aggregate composed of directly bonded nanodiamond grains (D≤100nm). It exhibits better thermal stability and wear resistance than single-crystal diamond, and its hardness is generally higher. Furthermore, it possesses isotropic characteristics and superior mechanical properties, making it a significant indicator of a nation's manufacturing level and playing a crucial role in high-tech and defense sectors.

[0003] Due to the strong covalent nature of diamond, its sinterability is extremely poor, and the mechanical properties of sintered polycrystalline diamond (NPD) are difficult to surpass those of single-crystal diamond. Although commercially available NPDs are isotropic, binders (such as cobalt and nickel) significantly reduce their hardness, wear resistance, and thermal stability. Nanocrystalline NPDs, which do not contain any sintering aids, successfully avoid the drawbacks of the aforementioned two types of diamond materials. Therefore, there is an urgent need to develop sintering-free nanocrystalline NPD materials. The main methods for directly preparing NPDs are chemical vapor deposition (CVD) and high-temperature, high-pressure (HPHT). CVD-prepared NPDs have uneven grain sizes and obvious orientations, with weak intergranular interactions and relatively low hardness (80-100 GPa). HPHT-prepared NPDs have fine grain sizes and strong covalent bonds between grains, achieving a hardness as high as 110-140 GPa. They outperform single-crystal diamond (SD) and polycrystalline diamond (PCD) materials in terms of hardness, fracture toughness, and oxidation resistance. Currently, large-scale production of NPD faces the challenge of demanding synthesis conditions (≥15GPa, 2300~2500℃), while the high pressure in the chamber limits the size of NPD preparation, making mass production of large-size NPD difficult. T. Irifune et al. prepared large-size NPD with a size exceeding 10mm using a 6000t press, but still face the challenges of long production cycles and high costs.

[0004] Therefore, the key to promoting the industrialization of NPD lies in reducing the temperature and pressure range of preparation, thereby increasing sample size and reducing preparation costs. Exploring suitable carbon sources to reduce preparation conditions is the key to solving the above problems. Therefore, designing new precursors to produce diamond under milder conditions is of great importance for reducing energy and time barriers and understanding the diamond conversion mechanism. Summary of the Invention

[0005] One of the technical problems to be solved by the present invention is to provide a method for preparing transparent nano-polycrystalline diamond at low temperature and pressure, so as to solve the problem that conventional nano-polycrystalline diamond requires harsh synthesis conditions, high temperature and high pressure and high cost in preparation.

[0006] To address the above problems, this invention provides a method for preparing transparent nanocrystalline diamond at low temperatures, comprising the following steps:

[0007] S1: Mixing: Using hydrogen-modified carbon nanospheres as raw materials, the raw materials are mixed after removing moisture and impurities to obtain hydrogen-modified carbon materials;

[0008] S2: Briquetting: Using a hydraulic press, hydrogen-modified carbon materials are pressed into cylindrical raw materials according to the size of the synthesis chamber;

[0009] S3: Assembly: The block-shaped cylindrical raw material is loaded into a heating container and placed into a synthesis chamber for assembly;

[0010] S4: Synthesis: The pressure is controlled at 9.0-15 GPa, the temperature at 1250-2300℃, and the holding time is 1-15 min. The raw materials assembled in step S3 are synthesized to obtain the product.

[0011] S5: Cooling and depressurization: After the product synthesized in step S4 is cooled and depressurized, a transparent nano-polycrystalline diamond material is obtained.

[0012] As a preferred embodiment, in step S1, the temperature for removing moisture and impurities is 200°C.

[0013] As a preferred embodiment, in step S1, the particle size of the hydrogen-modified carbon nanomaterial is 30-50 nm, and the morphology of the carbon nanomaterial is spherical.

[0014] As a preferred embodiment, in step S3, the heating method of the heating container is as follows: heating is performed using a metal rhenium tube, magnesium oxide is used as the pressure transmission medium, and hexagonal boron nitride is used to protect the synthesis cavity.

[0015] As a preferred embodiment, in step S4, the synthesis pressure is 10-15 GPa and the synthesis temperature is 1350-1850℃.

[0016] As a preferred embodiment, step S5, the cooling and depressurization includes the following steps: after the sample has cooled naturally to room temperature, the pressure is depressurized to normal pressure to obtain the transparent nano-polycrystalline diamond material.

[0017] Another technical problem to be solved by the present invention is to provide a transparent nanocrystalline diamond prepared by the above method, wherein the diamond prepared has high hardness, fracture toughness and oxidation resistance.

[0018] To address the aforementioned problems, this invention provides a transparent nanocrystalline diamond, which is prepared using any of the above-mentioned preparation methods.

[0019] Beneficial effects:

[0020] This invention provides a low-temperature compression molding method for preparing transparent polycrystalline nanodiamonds. The process is simple and eliminates the need for complex steps such as adding sintering aids. By adjusting temperature and pressure, the crystal structure and transparency of the polycrystalline nanodiamonds are controlled, resulting in bulk polycrystalline nanodiamonds with high transparency. This low-temperature compression molding method significantly reduces the temperature and pressure requirements of traditional methods. The synthesized transparent polycrystalline nanodiamonds are beneficial for optimizing their optical and mechanical properties, overcoming the problems of harsh synthesis conditions, high temperature and pressure, and high cost associated with conventional polycrystalline nanodiamond preparation. Attached Figure Description

[0021] Figure 1 This is an X-ray diffraction pattern of the hydrogen-modified carbon nanosphere raw material used in the experiment;

[0022] Figure 2 This is the Raman scattering pattern of the hydrogen-modified carbon nanosphere raw material used in the experiment;

[0023] Figure 3 This is a scanning electron microscope image of the hydrogen-modified carbon nanosphere raw material used in the experiment;

[0024] Figure 4 These are X-ray diffraction patterns of nanocrystalline diamond prepared at different temperatures under a pressure of 10 GPa in Example 1.

[0025] Figure 5 These are X-ray diffraction patterns of nanocrystalline diamond prepared at different temperatures under a pressure of 15 GPa in Example 2.

[0026] Figure 6 This is the X-ray diffraction pattern of nano-polycrystalline diamond prepared under different pressures at a temperature of 1800℃ in Example 3;

[0027] Figure 7This is a transmission electron microscope image of the nanocrystalline diamond prepared under the conditions of 15 GPa pressure and 1800 °C in Example 1.

[0028] Figure 8 This is an optical photograph of transparent nanocrystalline diamond prepared under a pressure of 15 GPa in Example 1;

[0029] Figure 9 This is an optical photograph of transparent nanocrystalline diamond prepared under a pressure of 10 GPa in Example 2. Detailed Implementation

[0030] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] This invention provides a method for preparing transparent nanocrystalline diamond at low temperature, comprising the following steps:

[0032] S1: Mixing: Using hydrogen-modified carbon nanospheres as raw materials, the raw materials are mixed after removing moisture and impurities to obtain hydrogen-modified carbon materials;

[0033] S2: Briquetting: Using a hydraulic press, hydrogen-modified carbon materials are pressed into cylindrical raw materials according to the size of the synthesis chamber;

[0034] S3: Assembly: The block-shaped cylindrical raw material is loaded into a heating container and placed into a synthesis chamber for assembly;

[0035] S4: Synthesis: The pressure is controlled at 9.0-15 GPa, the temperature at 1250-2300℃, and the holding time is 1-15 min. The raw materials assembled in step S3 are synthesized to obtain the product.

[0036] S5: Cooling and depressurization: After the product synthesized in step S4 is cooled and depressurized, a transparent nano-polycrystalline diamond material is obtained.

[0037] Preferably, in step S1, the temperature for removing moisture and impurities is 200°C.

[0038] Preferably, in step S1, the particle size of the hydrogen-modified carbon nanomaterial is 30-50 nm, and the morphology of the carbon nanomaterial is spherical.

[0039] Preferably, in step S3, the heating method of the heating container is: heating with a metal rhenium tube, using magnesium oxide as the pressure transmission medium, and using hexagonal boron nitride to protect the synthesis cavity.

[0040] Preferably, in step S4, the synthesis pressure is 10-15 GPa and the synthesis temperature is 1350-1850℃.

[0041] Preferably, in step S5, the cooling and depressurization includes the following steps: after the sample has cooled naturally to room temperature, the pressure is depressurized to normal pressure to obtain the transparent nano-polycrystalline diamond material.

[0042] The present invention also provides a transparent nanocrystalline diamond, which is prepared by any of the above preparation methods.

[0043] The following section elaborates on the above-mentioned solution of the present invention using actual data:

[0044] The experiments described in the following examples were performed using a 10 / 5 experimental assembly on a 1000t Walker-type two-stage press; in the embodiments of the present invention, the X-ray diffraction pattern, Raman scattering pattern, and scanning electron microscope image of the hydrogen-modified carbon nanosphere raw material used are respectively... Figure 1 , Figure 2 , Figure 3 As shown.

[0045] Example 1:

[0046] This embodiment provides a method for preparing transparent nanocrystalline diamond at low temperature, including the following steps:

[0047] S1: Mixing: Using hydrogen-modified carbon nanospheres as raw materials, moisture and adsorbed impurities are removed at 200℃, and then the mixture is prepared.

[0048] S2: Briquetting: Using a hydraulic press to press the raw materials of the mixture into cylindrical shapes according to the size of the synthesis chamber;

[0049] S3: Assembly: The block-shaped cylindrical raw material is loaded into a heating container and placed into a synthesis chamber for assembly. The assembly chamber is heated by a metal rhenium tube, magnesium oxide is used as the pressure transmission medium, and hexagonal boron nitride is used to protect the chamber.

[0050] S4: Synthesis: The synthesis pressure is controlled at 10 GPa, the synthesis temperature is 1400-1800℃, and the holding time is 15 min. The raw materials assembled in step S3 are synthesized to obtain the product.

[0051] S5: Cooling and depressurization: After the sample synthesized in step S4 stops heating, the sample is naturally cooled to room temperature and then depressurized to obtain transparent nano-polycrystalline diamond material.

[0052] Example 2:

[0053] This embodiment provides a method for preparing transparent nanocrystalline diamond at low temperature, including the following steps:

[0054] S1: Mixing: Using hydrogen-modified carbon nanospheres as raw materials, moisture and adsorbed impurities are removed at 200℃, and then the mixture is prepared.

[0055] S2: Briquetting: Using a hydraulic press to press the raw materials of the mixture into cylindrical shapes according to the size of the synthesis chamber;

[0056] S3: Assembly: The blocky cylindrical raw material is loaded into a heating container and placed into a synthesis chamber for assembly. The assembly uses graphite heating, pyrophyllite as a pressure transmission medium, and hexagonal boron nitride to protect the synthesized sample.

[0057] S4: Synthesis: The synthesis pressure is controlled at 15 GPa, the synthesis temperature is 1250-2300℃, and the holding time is 15 min. The raw materials assembled in step S3 are synthesized to obtain the product.

[0058] S5: Cooling and depressurization: After the sample synthesized in step S4 stops heating, the sample is naturally cooled to room temperature and then depressurized to obtain transparent nano-polycrystalline diamond material.

[0059] Example 3:

[0060] This embodiment provides a method for preparing transparent nanocrystalline diamond at low temperature, including the following steps:

[0061] S1: Mixing: Using hydrogen-modified carbon nanospheres as raw materials, moisture and adsorbed impurities are removed at 200℃, and then the mixture is prepared.

[0062] S2: Briquetting: Using a hydraulic press to press the raw materials of the mixture into cylindrical shapes according to the size of the synthesis chamber;

[0063] S3: Assembly: The blocky cylindrical raw material is loaded into a heating container and placed into a synthesis chamber for assembly. The assembly uses graphite heating, pyrophyllite as a pressure transmission medium, and hexagonal boron nitride to protect the synthesized sample.

[0064] S4: Synthesis: The synthesis pressure is controlled at 9-15 GPa, the synthesis temperature is 1800℃, and the holding time is 15 min. The raw materials assembled in step S3 are synthesized to obtain the product.

[0065] S5: Cooling and depressurization: After the sample synthesized in step S4 stops heating, the sample is naturally cooled to room temperature and then depressurized to obtain transparent nano-polycrystalline diamond material.

[0066] Example 4:

[0067] This embodiment provides a method for preparing transparent nanocrystalline diamond at low temperature, including the following steps:

[0068] S1: Mixing: Using hydrogen-modified carbon nanospheres as raw materials, moisture and adsorbed impurities are removed at 200℃, and then the mixture is prepared.

[0069] S2: Briquetting: Using a hydraulic press to press the raw materials of the mixture into cylindrical shapes according to the size of the synthesis chamber;

[0070] S3: Assembly: The block-shaped cylindrical raw material is loaded into a heating container and placed into a synthesis chamber for assembly. The assembly chamber is heated by a metal rhenium tube, magnesium oxide is used as the pressure transmission medium, and hexagonal boron nitride is used to protect the chamber.

[0071] S4: Synthesis: The synthesis pressure is controlled at 9 GPa, the synthesis temperature at 1250℃, and the holding time is 15 min. The raw materials assembled in step S3 are synthesized to obtain the product.

[0072] S5: Cooling and depressurization: After the sample synthesized in step S4 stops heating, the sample is naturally cooled to room temperature and then depressurized to obtain transparent nano-polycrystalline diamond material.

[0073] Example 5:

[0074] This embodiment provides a method for preparing transparent nanocrystalline diamond at low temperature, including the following steps:

[0075] S1: Mixing: Using hydrogen-modified carbon nanospheres as raw materials, moisture and adsorbed impurities are removed at 200℃, and then the mixture is prepared.

[0076] S2: Briquetting: Using a hydraulic press to press the raw materials of the mixture into cylindrical shapes according to the size of the synthesis chamber;

[0077] S3: Assembly: The block-shaped cylindrical raw material is loaded into a heating container and placed into a synthesis chamber for assembly. The assembly chamber is heated by a metal rhenium tube, magnesium oxide is used as the pressure transmission medium, and hexagonal boron nitride is used to protect the chamber.

[0078] S4: Synthesis: The synthesis pressure is controlled at 15 GPa, the synthesis temperature is 2300℃, and the holding time is 1 min. The raw materials assembled in step S3 are synthesized to obtain the product.

[0079] S5: Cooling and depressurization: After the sample synthesized in step S4 stops heating, the sample is naturally cooled to room temperature and then depressurized to obtain transparent nano-polycrystalline diamond material.

[0080] Relevant optical diffraction experiments were conducted on the embodiments of Examples 1-3 above, such as... Figure 4 As shown in Figures 5 and 6, these are the X-ray diffraction patterns of the nanocrystalline diamond prepared in Examples 1, 2, and 3, respectively. Figure 7The image shows the morphology of the nano-polycrystalline diamond prepared under the conditions of 15 GPa pressure and 1800℃ in Example 1, indicating that the grains of the nano-polycrystalline diamond are at the nanoscale. Figure 8 This is an optical photograph of transparent nanocrystalline diamond prepared under a pressure of 15 GPa in Example 1; Figure 9 This is an optical photograph of the transparent polycrystalline diamond nanoparticles prepared under a pressure of 10 GPa in Example 2. It shows that the prepared polycrystalline diamond nanoparticles are all transparent samples with no pores between the grains, thin grain boundaries, and strong intergranular bonding, which realizes the direct bonding of diamond nanoparticles and indicates that the material has a high hardness value.

[0081] The above embodiments further demonstrate that the low-temperature compression preparation method for transparent nano-polycrystalline diamond of the present invention has a simple process flow and does not require complex processes such as adding sintering aids. By adjusting the temperature and pressure, the crystal structure and transparency of the nano-polycrystalline diamond are adjusted, and bulk nano-polycrystalline diamond with high transparency is prepared. This overcomes the problems of harsh synthesis conditions, high temperature and high pressure, and high cost in the preparation of conventional nano-polycrystalline diamond.

[0082] While the disclosure is as stated above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the protection scope of this invention.

Claims

1. A method for preparing transparent nanocrystalline diamond at low temperature, characterized in that, Includes the following steps: S1: Mixing: Using hydrogen-modified carbon nanospheres as raw materials, the hydrogen-modified carbon nanospheres have a particle size of 30-50 nm and the nano-carbon material has a spherical morphology. The raw materials are mixed after removing moisture and adsorbed impurities at 200 °C to obtain hydrogen-modified carbon material. S2: Pressing: Using a hydraulic press, the hydrogen-modified carbon material is pressed into cylindrical raw materials according to the size of the synthesis chamber; S3: Assembly: The cylindrical raw material in block form is loaded into a heating container and placed into a synthesis chamber for assembly. The heating method of the heating container is: heating with a metal rhenium tube, using magnesium oxide as the pressure transmission medium, and using hexagonal boron nitride to protect the synthesis chamber. S4: Synthesis: The synthesis pressure is controlled at 10 GPa, the synthesis temperature is 1800℃, and the holding time is 15 min. The raw materials assembled in step S3 are synthesized to obtain the product. S5: Cooling and depressurization: After the product synthesized in step S4 has cooled naturally to room temperature, the pressure is depressurized to normal pressure to obtain the transparent nano-polycrystalline diamond material.

2. A transparent nanocrystalline diamond, characterized in that, The transparent nanocrystalline diamond was prepared using the preparation method described in claim 1.

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