A pretreatment process for inhibiting abnormal growth of diamond single crystal under high temperature and high pressure

Abstract

The application discloses a pretreatment process for inhibiting abnormal growth of diamond single crystal under high temperature and high pressure. The application firstly performs high-temperature micropore structuring treatment on a carbon source, forms uniform micropore structures in the carbon source, and constructs a uniform and dense metal carbide passivation layer on the surface of the carbon source, so that the carbon release rate of the carbon source is accurately controlled; then a high-uniformity catalyst powder is prepared by using a static magnetic field coupling ultrasonic vibration assisted smelting method, so that the problems of catalyst melt component segregation and flow disorder are effectively improved; finally, a synthesis system with a dense structure and a stable interface is obtained through a laminated assembly combined with a cold isostatic pressing pre-pressing process. Through the synergistic effect of accurate carbon control of the carbon source, catalyst homogenization and dense assembly structure, the abnormal growth of the diamond single crystal is inhibited, the crystal defect density is greatly reduced, the crystal morphology regularity and the single crystal product yield are improved, and the process is stable and has strong repeatability.

Description

Technical Field

[0001] This invention relates to the field of superhard material synthesis technology, and more specifically to a pretreatment process for suppressing abnormal growth of diamond single crystals under high temperature and high pressure. Background Technology

[0002] High temperature and high pressure (HTHP) is the mainstream technology for preparing industrial-grade and gem-quality diamond single crystals. Its core principle is to utilize metal catalysts (such as Fe, Ni, Co, Mn, and their alloys) under high temperature and high pressure conditions to effectively lower the energy barrier for the transformation of graphite into diamond, promoting the epitaxial growth of carbon atoms on the surface of the diamond seed crystal, thereby obtaining high-quality diamond single crystals. However, in actual industrial production, diamond single crystals are prone to abnormal growth phenomena, severely restricting product quality and production. These mainly include: 1) Polycrystalline and twinning formation: Multiple crystal nuclei or twin boundaries are unexpectedly formed on or inside the target single crystal, directly destroying the integrity of the crystal structure and leading to a decrease in single crystal purity; 2) Inclusion aggregation and banded structures: Impurities in the metal catalyst or system are non-uniformly encapsulated inside the growing crystal, forming a banded structure with concentrated defects, disrupting the continuity of the crystal; 3) Irregular morphology: The crystal growth process deviates from the ideal octahedral or cubic-octahedral morphology, resulting in abnormal morphologies such as steps and hill-like protrusions, affecting the appearance and performance uniformity of the crystal.

[0003] The aforementioned abnormal growth phenomena deteriorate the mechanical, thermal, and optical uniformity of diamond single crystals, directly leading to low product yield, large performance dispersion, increased industrial production costs, and limiting the application of diamond single crystals in high-end fields. In existing technologies, the industry mainly attempts to control the diamond single crystal growth process and suppress abnormal growth by optimizing the temperature gradient and pressure curve within the growth chamber or adjusting the catalyst composition. However, these methods require extremely high precision in equipment control, are difficult to operate, and are costly. Furthermore, they often only alleviate the abnormal growth phenomenon and cannot solve the problem at its root.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a pretreatment process for suppressing abnormal growth of diamond single crystals under high temperature and high pressure in order to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention specifically adopts the following technical solution: A pretreatment process for suppressing abnormal growth of diamond single crystals under high temperature and high pressure includes the following steps.

[0007] S1. The carbon source is processed into a block or sheet, and then the carbon source is sequentially structured into micropores and passivated with a surface carbide layer to obtain a carbon source sheet.

[0008] Furthermore, the specific methods for microporous structuring include: Under inert atmosphere or vacuum conditions, the carbon source is treated at 1800~2200℃ for 5~30 min, and closed or semi-closed micropores are formed inside the carbon source.

[0009] Furthermore, the pore size of the micropores is 0.1~2μm.

[0010] The formed carbon source contains a large amount of amorphous carbon, residual organic matter, ash, and other impurities. Simultaneously, the carbon lattice exhibits structural imperfections such as defects and grain boundary voids. Under high-temperature conditions of 1800–2200℃, the following important processes occur: 1) Amorphous carbon undergoes thermal decomposition, breaking down into small molecule carbon species; residual organic matter, ash and other impurities volatilize and escape upon heating, leaving initial pores inside the carbon source; 2) The graphite microcrystals in the carbon source undergo high-temperature graphitization rearrangement, resulting in more regular carbon layer stacking. Simultaneously, volume shrinkage occurs, generating thermal stress inside the carbon source, which promotes further expansion and interconnection of the initial pores, ultimately forming a closed or semi-closed microporous structure. 3) By controlling the processing time to 5-30 min, excessive sintering of the carbon source can be avoided, which could lead to micropore collapse or interconnection, thus stabilizing the micropore size within the micrometer range of 0.1-2 μm. This size of micropore provides sufficient reaction sites and adsorption space while preserving the mechanical strength of the carbon source bulk, preventing a loose structure.

[0011] Furthermore, the specific method for constructing the surface carbide passivation layer includes: A carbon source that has undergone microporous structuring is placed in an environment containing Ti, Zr, Cr or W element vapors and heated to 1200~1500℃ under vacuum for 1~4 hours, resulting in the formation of a metal carbide layer on the surface of the carbon source.

[0012] Furthermore, the thickness of the metal carbide layer is 10~500 nm.

[0013] In a vacuum environment, metallic raw materials such as Ti, Zr, Cr, and W sublimate into metal atom vapor upon heating. This metal vapor possesses excellent diffusivity, allowing it to uniformly cover the surface of the microporous structured carbon source, including the openings of the surface micropores, providing a uniform reactant interface for subsequent reactions. Simultaneously, the vacuum condition prevents the metal vapor from reacting with oxygen to form metal oxides, ensuring the activity of the metal atoms.

[0014] The carbon source surface after microporous structuring treatment has a certain roughness and pore openings, which can increase the adsorption area of ​​metal vapor, promote the contact between metal atoms and carbon atoms, make the passivation layer more tightly bonded to the carbon source matrix, and prevent the passivation layer from falling off. The passivation layer seals the openings of the surface micropores, which can prevent the internal micropores from being blocked or contaminated in subsequent applications, while inhibiting the oxidation of the carbon source and carbon loss, thus ensuring the functional stability of the internal micropores. The resulting carbon source sheet has internal micropores that provide ample reaction sites, adsorption sites, and material transport channels, while the surface passivation layer provides stable protection. This gives the carbon source sheet both excellent reactivity and good high-temperature resistance, oxidation resistance, and corrosion resistance.

[0015] S2. The metal catalyst alloy is melted under vacuum or argon protection to prevent high-temperature oxidation and impurity generation, ensuring compositional purity. High-temperature melting melts all alloy components, achieving initial uniform diffusion of elements. During melting, a static magnetic field perpendicular to gravity with a strength ≥0.5T is applied to suppress melt convection and gravitational segregation using Lorentz force, refining grain embryos. Simultaneously, electromagnetic stirring or ultrasonic vibration at a frequency of 20~40kHz is used to enhance melt mixing, eliminate compositional inhomogeneity, and achieve dual homogenization of melt structure and composition. After holding at high temperature, the homogenized melt is rapidly cooled into ingots, then crushed and sieved to obtain catalyst powder. Rapid cooling inhibits grain growth and elemental segregation, forming fine-grained alloy ingots and improving catalyst activity. Crushing and sieving mechanically produces uniformly sized powder from the alloy ingots, preventing agglomeration and ensuring effective contact with the carbon source sheet.

[0016] Furthermore, the particle size of the catalyst powder is 100~300 mesh.

[0017] S3. From bottom to top, carbon source sheet, mixing layer, diamond seed crystal, mixing layer, and carbon source sheet are placed to obtain a stacked structure. This symmetrical assembly method forms a symmetrical stacked structure, ensuring uniform carbon supply to the upper and lower carbon source sheets, while placing the diamond seed crystal in the central core position and uniformly wrapped by the mixing layer. The stacked structure is placed in a high-purity pyrophyllite assembly block or ceramic assembly block and cold isostatically pre-pressed at room temperature. The mixed layer comprises 0.1-1.0% by mass of diamond micron powder and the balance being catalyst powder.

[0018] Furthermore, the diamond micropowder has a particle size of less than 1 μm.

[0019] Furthermore, the pressure of the cold isostatic pre-pressing is 100~300MPa, and the pressure is held for 5~15min.

[0020] This invention addresses the problems of uneven carbon source dissolution, unstable catalyst melt flow, poor component interface contact, and seed crystal contamination by microporous structuring and carbide passivation modification of the carbon source, magnetic field-ultrasonic synergistic melting and homogenization of the catalyst, and the construction of a symmetrical stacked structure combined with cold isostatic pressing. It eliminates the causes of defects such as polycrystalline twins, inclusions, and morphological distortion from the source, and achieves stable and orderly epitaxial growth of diamond single crystals under high temperature and high pressure conditions, significantly improving the integrity of single crystals and product yield.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This process prepares a carbon source sheet with a porous interior and a dense surface by constructing a microporous structure and a surface carbide passivation layer. The closed or semi-closed micropores of 0.1~2μm inside can provide sufficient reaction sites and adsorption space while maintaining the mechanical strength of the carbon source block. The dense metal carbide layer of 10~500nm on the surface can effectively seal the micropore openings of the carbon source surface, prevent the internal micropores from being contaminated by external impurities, and prevent the carbon species inside the carbon source from diffusing outward. In addition, the passivation layer has extremely high chemical stability, high temperature resistance and oxidation resistance, which can isolate the contact between external oxygen and corrosive gases and the carbon source matrix, inhibit the oxidation and corrosion of the carbon source under high temperature conditions, and improve the service life of the carbon source sheet. 2. A symmetrical stacked structure is adopted, in which carbon source sheet, mixing layer, diamond seed crystal, mixing layer, and carbon source sheet are placed sequentially from bottom to top. This ensures uniform carbon supply to the upper and lower carbon source sheets, while placing the diamond seed crystal in the central core position and uniformly wrapped by the mixing layer. The diamond micro powder with a mass fraction of 0.1~1.0% and a particle size of <1μm in the mixing layer can act as a crystal nucleation aid to promote subsequent diamond growth. At the same time, it works synergistically with the catalyst powder to fill the gap between the carbon source sheet and the seed crystal, improving the contact tightness. 3. Cold isostatic pressing at room temperature (100-300 MPa) for 5-15 minutes can induce slight plastic deformation in the components of the laminated structure through uniform fluid pressure, eliminating internal gaps and achieving tight bonding. At the same time, it fixes the shape of the laminated structure and prevents delamination and misalignment during subsequent transfer and reaction processes. This solves the problems of delamination and poor contact that are common in conventional assembly methods, and provides a stable structural foundation for carbon source transport, catalyst catalysis, and diamond growth in subsequent high-temperature and high-pressure reactions. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and 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. The materials and instruments used in the following embodiments are all commercially available.

[0023] A pretreatment process for suppressing abnormal growth of diamond single crystals under high temperature and high pressure includes the following steps S1 to S3.

[0024] S1. The carbon source is processed into a block or sheet, and then the carbon source is sequentially structured into micropores and passivated with a surface carbide layer to obtain a carbon source sheet.

[0025] Furthermore, the specific methods for microporous structuring include: Under inert atmosphere or vacuum conditions, the carbon source is treated at 1800~2200℃ for 5~30 min, and closed or semi-closed micropores are formed inside the carbon source.

[0026] Furthermore, the pore size of the micropores is 0.1~2μm.

[0027] Furthermore, the specific method for constructing the surface carbide passivation layer includes: A carbon source that has undergone microporous structuring is placed in an environment containing Ti, Zr, Cr or W element vapors and heated to 1200~1500℃ under vacuum for 1~4 hours, resulting in the formation of a metal carbide layer on the surface of the carbon source.

[0028] Furthermore, the thickness of the metal carbide layer is 10~500 nm.

[0029] S2. The metal catalyst alloy is smelted under vacuum or argon protection. During the smelting process, a static magnetic field with a magnetic field strength ≥0.5T perpendicular to the direction of gravity is applied. At the same time, electromagnetic stirring or ultrasonic vibration with a frequency of 20~40kHz is used for assistance. After heat preservation, the homogenized melt is rapidly cooled into ingots, and then crushed and sieved to obtain catalyst powder.

[0030] Furthermore, the particle size of the catalyst powder is 100~300 mesh.

[0031] S3. Place carbon source sheet, mixed layer, diamond seed crystal, mixed layer and carbon source sheet from bottom to top to obtain a stacked structure. Place the stacked structure into a high-purity pyrophyllite assembly block or ceramic assembly block and perform cold isostatic pressing at room temperature. The mixed layer comprises 0.1-1.0% by mass of diamond micron powder and the balance being catalyst powder.

[0032] Furthermore, the particle size of the diamond powder is less than 1 μm.

[0033] Furthermore, the pressure of the cold isostatic pre-pressing is 100~300MPa, and the pressure is held for 5~15min.

[0034] The present invention will be further described below with reference to specific embodiments and comparative examples.

[0035] Example 1 This embodiment provides a pretreatment process for suppressing abnormal growth of diamond single crystals under high temperature and high pressure, including the following steps: S1. The graphite carbon source is processed into sheets and treated at 2000℃ for 15 min under an argon atmosphere to obtain closed micropores with a pore size of 0.5~1μm; Ti vapor is introduced under vacuum and kept at 1350℃ for 2 h to form an 80nm TiC passivation layer, thus obtaining the carbon source sheet. S2. The Fe-Ni-Co catalyst alloy is vacuum melted, a 0.8T vertical static magnetic field is applied, and ultrasonic vibration at 30kHz is used for assistance. After heat preservation, it is rapidly cooled, crushed and sieved to obtain catalyst powder. S3. The mixed layer consists of 0.5% diamond micro powder with a particle size of 0.5μm and the remainder is catalyst powder. The mixture is stacked in the following order: carbon source sheet - mixed layer - diamond seed crystal - mixed layer - carbon source sheet. A high-purity pyrophyllite assembly block is then inserted and cold isostatically pressed at 200MPa for 10 minutes.

[0036] Example 2 The difference between this embodiment and Embodiment 1 is that: S1. Argon atmosphere treatment at 1800℃ for 5 min, micropore diameter 0.1~0.5μm; vacuum Ti vapor treatment at 1200℃ for 1 h to form a 10nm TiC passivation layer; S2, catalyst alloy melting, with a 0.5T vertical static magnetic field and 20kHz ultrasonic vibration assistance; S3, mixed layer diamond micro powder mass fraction 0.1%, particle size <1μm; cold isostatic pressing 100MPa for 5min; The remaining steps are the same as in Example 1.

[0037] Example 3 The difference between this embodiment and Embodiment 1 is that: S1. Argon atmosphere treatment at 2200℃ for 30 min, micropore diameter 1~2μm; vacuum Ti vapor treatment at 1500℃ for 4 h to form a 500nm TiC passivation layer. S2, catalyst alloy melting, with a 1.0T vertical static magnetic field and 40kHz ultrasonic vibration assistance; S3, mixed layer diamond micro powder mass fraction 1.0%, particle size <1μm; cold isostatic pressing 300MPa for 15min; The remaining steps are the same as in Example 1.

[0038] Comparative Example 1 The difference between this comparative example and Example 1 is that this comparative example uses ordinary graphite sheets, conventional Fe-Ni-Co catalyst for melting, and direct assembly, without microporous structuring, carbide passivation, magnetic field-ultrasonic melting, or cold isostatic pressing. The remaining steps are the same as in Example 1.

[0039] Comparative Example 2 The difference between this comparative example and Example 1 is that the carbon source in this comparative example is only structured into micropores, and no metal carbide passivation layer is constructed. The remaining steps are the same as in Example 1.

[0040] To fully verify the effect of the pretreatment process of the present invention on the suppression of abnormal growth of diamond single crystals under high temperature and high pressure, the examples 1-3 and comparative examples 1-2 were compared and analyzed from six core dimensions: twin and polycrystalline defects, metal inclusions and banded structure defects, crystal morphology regularity, carbon source dissolution uniformity, catalyst melt stability and final single crystal yield. The comparison results are shown in Table 1.

[0041] The testing methods for each indicator are as follows: (1) Twin and polycrystalline defects: The polished cross section of diamond single crystal was observed using an optical microscope and a scanning electron microscope (SEM). Multiple fields of view were randomly selected to count the number of twin and polycrystalline defects per unit area and calculate the defect density. (2) Metal inclusions and banded defects: The internal structure of the crystal was observed using a polarizing microscope, and the proportion of crystals containing metal inclusions and banded defects was counted. (3) Crystal morphology regularity: The overall morphology, crystal face and crystal edge integrity of diamond single crystals were observed using a stereomicroscope; (4) Uniformity of carbon source dissolution: After synthesis, the assembly block was disassembled and the microstructure and elemental distribution of the residual carbon source were observed by SEM-EDS to qualitatively evaluate the uniformity of carbon source dissolution. (5) Catalyst melt stability: Metallographic and SEM-EDS analysis was performed on the catalyst alloy ingot, and the melt stability was qualitatively evaluated based on component segregation and microstructure uniformity. (6) Single crystal yield: Count the total number of crystals produced in a single synthesis, screen out qualified single crystals without twins, without inclusions and with regular morphology, and calculate the percentage of qualified crystals.

[0042] Table 1 Comparison Results As shown in Examples 1-3, Comparative Examples 1-2, and Table 1, Examples 1-3 achieve synergistic regulation of carbon release rate through carbon source microporous structuring and metal carbide passivation layer, combined with static magnetic field-ultrasonic vibration coupling to homogenize the catalyst melt, and cold isostatic pressing to improve the compactness of the assembled structure. This suppresses abnormal diamond single crystal growth from three dimensions: carbon supply, melt stability, and growth interface. Example 1 represents the optimal process parameters, achieving a single crystal yield of 94-96%; Examples 2 and 3 represent the upper and lower limits of the process parameters, still exhibiting good defect suppression effects. Comparative Example 1 used ordinary graphite sheets and conventional Fe-Ni-Co catalyst for direct assembly, without microporous structure, carbide passivation, magnetic field-ultrasonic melting, or cold isostatic pressing. The carbon source lacked micropores and a passivation layer, resulting in disordered carbon release, rapid local dissolution and desorption, and drastic fluctuations in carbon concentration. The catalyst melting, without a magnetic field-ultrasonic approach, led to severe component segregation and intense melt turbulence. Assembly was loose, and interface stability was poor. Ultimately, a large number of twins and polycrystalline materials were generated, with significant metal inclusions and banded structures, severely distorted crystal morphology, and a single-crystal yield of only 33-43%, highlighting the problem of abnormal growth. In Comparative Example 2, the carbon source was only microporously structured without constructing a metal carbide passivation layer. While micropores can improve carbon release uniformity to some extent, they cannot precisely control the carbon diffusion rate. Under high temperature and pressure, local carbon release from the carbon source is too rapid, leading to carbon oversaturation at the growth front and inducing twins, metal inclusions, and banded structures. Although the catalyst and assembly pretreatment met the standards and the melt stability was good, carbon supply control was insufficient. The final single-crystal yield was only 53-60%, with more defects than in the previous example.

Claims

1. A pretreatment process for suppressing abnormal growth of diamond single crystals under high temperature and high pressure, characterized in that, Includes the following steps: S1. The carbon source is processed into a block or sheet, and then the carbon source is sequentially structured into micropores and passivated with a surface carbide layer to obtain a carbon source sheet. S2. The metal catalyst alloy is smelted under vacuum or argon protection. During the smelting process, a static magnetic field with a magnetic field strength ≥0.5T perpendicular to the direction of gravity is applied. At the same time, electromagnetic stirring or ultrasonic vibration with a frequency of 20~40kHz is used for assistance. After heat preservation, the homogenized melt is rapidly cooled into ingots, and then crushed and screened to obtain catalyst powder. S3. Place carbon source sheet, mixed layer, diamond seed crystal, mixed layer and carbon source sheet from bottom to top to obtain a stacked structure. Place the stacked structure into a high-purity pyrophyllite assembly block or ceramic assembly block and perform cold isostatic pressing at room temperature. The mixed layer comprises 0.1-1.0% by mass of diamond micron powder and the balance being catalyst powder.

2. The pretreatment process for suppressing abnormal growth of diamond single crystals under high temperature and high pressure according to claim 1, characterized in that, The specific methods for microporous structuring include: Under inert atmosphere or vacuum conditions, the carbon source is treated at 1800~2200℃ for 5~30 min, and closed or semi-closed micropores are formed inside the carbon source.

3. The pretreatment process for suppressing abnormal growth of diamond single crystals under high temperature and high pressure according to claim 1, characterized in that, The pore size of the micropores is 0.1~2μm.

4. The pretreatment process for suppressing abnormal growth of diamond single crystals under high temperature and high pressure according to claim 1, characterized in that, The specific method for constructing the surface carbide passivation layer includes: A carbon source that has undergone microporous structuring is placed in an environment containing Ti, Zr, Cr or W element vapors and heated to 1200~1500℃ under vacuum for 1~4 hours, resulting in the formation of a metal carbide layer on the surface of the carbon source.

5. The pretreatment process for suppressing abnormal growth of diamond single crystals under high temperature and high pressure according to claim 4, characterized in that, The thickness of the metal carbide layer is 10~500 nm.

6. The pretreatment process for suppressing abnormal growth of diamond single crystals under high temperature and high pressure according to claim 1, characterized in that, The particle size of the catalyst powder is 100~300 mesh.

7. The pretreatment process for suppressing abnormal growth of diamond single crystals under high temperature and high pressure according to claim 1, characterized in that, The diamond micro powder has a particle size of less than 1 μm.

8. The pretreatment process for suppressing abnormal growth of diamond single crystals under high temperature and high pressure according to claim 1, characterized in that, The pressure of the cold isostatic pre-compression is 100~300MPa, and the pressure is held for 5~15min.

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