A method for synthesizing polycrystalline diamond

Abstract

This invention provides a method for synthesizing polycrystalline diamond, belonging to the field of polycrystalline diamond preparation technology. The method for synthesizing polycrystalline diamond provided by this invention includes the following steps: mixing diamond micropowder with a metal powder catalyst and a solvent, followed by drying to obtain a mixed micropowder; subjecting the obtained mixed micropowder to high-temperature and high-pressure sintering to obtain polycrystalline diamond; the high-temperature and high-pressure sintering involves: loading the mixed micropowder into an assembly unit, and then pressurizing and energizing the assembly unit; the assembly unit includes an insulating tube and conductive current collectors disposed at both ends of the insulating tube. Results from the embodiments show that the polycrystalline diamond synthesized using the catalyst provided by this invention has a uniform crystal structure, excellent quality, and no metal oxides appear inside the crystal.

Description

Technical Field

[0001] This invention relates to the field of polycrystalline diamond preparation technology, and in particular to a method for synthesizing polycrystalline diamond. Background Technology

[0002] Currently, there are two main methods for synthesizing polycrystalline diamond using catalysts. One method involves mixing diamond powder and catalyst and placing the mixture into a circular metal cup, with a circular heating element surrounding the cup. The other method involves directly mixing diamond powder and catalyst and then placing the mixture into a heating element. These heating elements can be graphite tubes, metal tubes, conductive carbon tubes, etc., and can indirectly heat the diamond powder and catalyst inside the metal cup, or be directly heated by the heating element. However, both methods suffer from the same problem: the heat transfer from the heating element to the diamond powder and catalyst requires a certain time, resulting in a temperature gradient in the synthesized polycrystalline diamond. The outer layer near the heating element has a higher temperature than the center, leading to a gradient in the quality of the polycrystalline diamond and causing uneven quality. This also results in high energy consumption. Furthermore, both methods also suffer from localized catalyst oxidation, leading to the inclusion of metal oxides and numerous structural defects in the polycrystalline diamond.

[0003] Therefore, there is an urgent need to provide a method for synthesizing polycrystalline diamond that can avoid the problems of uneven quality of polycrystalline diamond caused by temperature gradient changes during the synthesis process and the presence of oxidizing catalyst impurities in the polycrystalline diamond. Summary of the Invention

[0004] The purpose of this invention is to provide a method for synthesizing polycrystalline diamond. The polycrystalline diamond obtained by the synthesis method provided by this invention has a uniform crystal structure, no oxidizing catalyst impurities in the structure, few crystal defects, and excellent quality.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for synthesizing polycrystalline diamond, comprising the following steps:

[0007] (1) Diamond micro powder is mixed with metal powder catalyst and solvent and then dried to obtain mixed micro powder;

[0008] (2) The mixed micro powder obtained in step (1) is subjected to high temperature and high pressure sintering to obtain diamond polycrystalline material; the high temperature and high pressure sintering is: the mixed micro powder is loaded into the assembly unit, and then the assembly unit is pressurized and energized; the assembly unit includes an insulating tube and conductive current collectors disposed at both ends of the insulating tube.

[0009] Preferably, the metal powder catalyst in step (1) comprises the following components by mass percentage: 0-80% cobalt, 0-30% iron, 0-40% nickel and 0-35% silver; wherein the mass percentages of cobalt, iron, nickel and silver are not all 0.

[0010] Preferably, the metal powder catalyst comprises the following components in weight percentage: 10-75% cobalt, 10-25% iron, 10-35% nickel and 10-32% silver.

[0011] Preferably, the particle size of the metal powder catalyst is 0.1 to 10 μm.

[0012] Preferably, the diamond micron powder in step (1) has a particle size of 0.1 to 70 μm.

[0013] Preferably, the mass ratio of diamond micro powder to metal powder catalyst in step (1) is (80-100):(1-15).

[0014] Preferably, the mixing method in step (1) is ball milling.

[0015] Preferably, the ball mill rotates at a speed of 100–150 r / min, and the ball milling time is 1–5 h.

[0016] Preferably, in step (2), the temperature of high-temperature and high-pressure sintering is 1200-1600℃, the pressure of high-temperature and high-pressure sintering is 5-6 GPa, and the time of high-temperature and high-pressure sintering is 20-300s.

[0017] Preferably, the heating rate to the temperature of the high-temperature and high-pressure sintering is 80–160 °C / s.

[0018] This invention provides a method for synthesizing polycrystalline diamond, comprising the following steps: mixing diamond micropowder with metal powder catalyst and solvent and drying to obtain mixed micropowder; subjecting the obtained mixed micropowder to high-temperature and high-pressure sintering to obtain polycrystalline diamond; wherein the high-temperature and high-pressure sintering comprises: loading the mixed micropowder into an assembly unit, and then pressurizing and energizing the assembly unit; wherein the assembly unit includes an insulating tube and conductive current collectors disposed at both ends of the insulating tube. The method for synthesizing polycrystalline diamond provided by this invention utilizes the electrical and thermal conductivity of a metal powder catalyst, which can form a closed circuit with the conductive current collectors at both ends of an insulating tube. Under energized conditions, it achieves self-heating, directly providing a heat source for rapid and uniform heating of the diamond micropowder without generating a heat transfer gradient. The diamond micropowder inside the insulating tube can simultaneously undergo graphitization and form a diamond phase, ultimately forming polycrystalline diamond, resulting in a more uniform crystal structure. Furthermore, using a metal powder catalyst in the synthesis of polycrystalline diamond, after mixing with the diamond micropowder, results in a larger contact area, which is more conducive to the full utilization of heat for catalytic synthesis. Additionally, under energized conditions in the conductive current collector, the oxidized portion of the catalyst can be electrolytically reduced, restoring catalytic activity and preventing the metal powder catalyst from being oxidized, thus reducing defects in the synthesized polycrystalline diamond. The results of the embodiments show that the polycrystalline diamond synthesized using the catalyst provided by this invention has a uniform crystal structure, excellent quality, and no oxidized catalyst impurities appear inside the crystal.

[0019] In addition, the method for synthesizing polycrystalline diamond provided by this invention is simple, easy to implement, and has easy-to-control parameters and low cost. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the assembly unit structure used in step (2) of Embodiment 1 of the present invention;

[0021] Figure 2 This is a scanning electron microscope image of the diamond polycrystalline material obtained in Example 2 of the present invention. Detailed Implementation

[0022] This invention provides a method for synthesizing polycrystalline diamond, comprising the following steps:

[0023] (1) Diamond micro powder is mixed with metal powder catalyst and solvent and then dried to obtain mixed micro powder;

[0024] (2) The mixed micro powder obtained in step (1) is subjected to high temperature and high pressure sintering to obtain diamond polycrystalline material; the high temperature and high pressure sintering is: the mixed micro powder is loaded into the assembly unit, and then the assembly unit is pressurized and energized; the assembly unit includes an insulating tube and conductive current collectors disposed at both ends of the insulating tube.

[0025] This invention involves mixing diamond micro powder with metal powder catalyst and solvent, followed by drying to obtain mixed micro powder.

[0026] The present invention does not have any special requirements on the source of the diamond micro powder; commercially available diamond micro powder known in the art or diamond micro powder prepared by conventional methods can be used.

[0027] In this invention, the particle size of the diamond micro powder is preferably 0.1 to 70 μm, more preferably 5 to 30 μm.

[0028] In this invention, the diamond micropowder is preferably pretreated before use. The pretreatment preferably includes: first, melting and boiling in molten sodium hydroxide; then, cooling the melted product and sequentially washing and drying it; next, boiling the dried product in aqua regia; and finally, cooling the boiled product and sequentially washing and drying it to obtain the diamond micropowder. This invention does not have special requirements for the concentration of the aqua regia; a conventional concentration is sufficient. In this invention, the melting and boiling times are preferably 0.2–2 hours, more preferably 0.5–1 hour. By performing the above pretreatment on the diamond micropowder before use, this invention can remove protoporphyrite, lipids, and metallic impurities from its surface, which is more conducive to obtaining high-quality diamond polycrystals.

[0029] In this invention, the metal powder catalyst preferably comprises the following components by mass percentage: 0-80% cobalt, 0-30% iron, 0-40% nickel, and 0-35% silver; wherein the mass percentages of cobalt, iron, nickel, and silver are not simultaneously 0; more preferably, it comprises the following components by mass percentage: 10-75% cobalt, 10-25% iron, 10-35% nickel, and 10-32% silver. By controlling the composition of the metal powder catalyst within the above range, this invention can enable the metal powder catalyst to have higher catalytic activity, increase the growth rate of diamond polycrystals, reduce crystal defects in diamond polycrystals during synthesis, thereby obtaining diamond polycrystals of higher quality; moreover, it has good wettability with diamond micropowder, lowers the synthesis temperature, promotes graphitization of the diamond micropowder surface, thereby fully converting it into the diamond phase and forming polycrystals.

[0030] In this invention, the particle size of the metal powder catalyst is preferably 0.1–10 μm, more preferably 0.5–5 μm. By using a metal powder catalyst with a particle size within the above range, the present invention allows for more uniform mixing with diamond micropowder, resulting in a larger contact area between the catalyst and the diamond micropowder, faster and more uniform heat transfer, and is more conducive to obtaining high-quality diamond polycrystalline materials.

[0031] In this invention, the preferred method for preparing the metal powder catalyst includes mixing two or more of cobalt powder, iron powder, nickel powder, and silver powder to obtain the metal powder catalyst. This invention does not impose any particular limitation on the mixing operation; conventional mixing methods in the art can be used to mix the components uniformly.

[0032] In this invention, the preferred mass ratio of diamond micropowder to metal powder catalyst is (80-100):(1-15), more preferably (85-95):(5-10), and most preferably (90-92):(6-8). By controlling the mass ratio of diamond micropowder to catalyst within the above range, this invention is more conducive to promoting the graphitization of the diamond micropowder surface, thereby enabling it to fully transform into the diamond phase and form polycrystalline structures.

[0033] In this invention, the solvent is preferably anhydrous ethanol. There is no particular limitation on the amount of anhydrous ethanol used, as long as it is sufficient to ensure uniform mixing of the diamond micropowder and the catalyst.

[0034] In this invention, the preferred method for mixing the diamond micron powder with the metal powder catalyst and solvent is ball milling. The preferred milling speed is 100–150 r / min, more preferably 120–130 r / min; the preferred milling time is 1–5 h, more preferably 3–4 h. By selecting the ball milling mixing method and controlling the milling parameters within the above ranges, this invention can achieve a more uniform mixing of the diamond micron powder and the metal powder catalyst. Simultaneously, the friction and collision between powder particles during ball milling further enhances the reactivity of the diamond polycrystals with the catalyst, thereby completing the synthesis with lower energy consumption.

[0035] The present invention does not have special requirements for the drying operation after mixing diamond micro powder with metal powder catalyst and solvent. The drying operation known to those skilled in the art can be used to fully remove the solvent and moisture from the mixed micro powder.

[0036] After drying, the present invention preferably passes the dried product through a 100-mesh sieve to obtain a mixed micro powder. By passing the dried product through a 100-mesh sieve, the present invention can eliminate agglomerates during ball milling and drying, making the mixed micro powder more dispersed.

[0037] After obtaining the mixed micro powder, the present invention performs high-temperature and high-pressure sintering on the mixed micro powder to obtain diamond polycrystalline.

[0038] In this invention, the high-temperature and high-pressure sintering involves: loading the mixed micro-powder into an assembly unit, and then pressurizing and energizing the assembly unit; the assembly unit includes an insulating tube and conductive current collectors disposed at both ends of the insulating tube. By performing the above operations before high-temperature and high-pressure sintering, this invention allows the current in the conductive current collector to conduct electricity through the metal powder catalyst, causing the metal powder catalyst to heat the metal powder. The heat generated by the catalyst directly acts on the diamond micro-powder, preventing the formation of a heat transfer gradient and ensuring more uniform heating. This avoids the formation of a structural gradient during the synthesis of diamond polycrystalline materials, ensuring that the diamond polycrystalline materials have a uniform crystal structure and superior quality.

[0039] In this invention, the temperature of the high-temperature and high-pressure sintering is preferably 1200–1600℃, more preferably 1250–1550℃, and most preferably 1300–1500℃; the pressure of the high-temperature and high-pressure sintering is preferably 5–6 GPa, more preferably 5.2–5.8 GPa, and most preferably 5.4–5.6 GPa; the time of the high-temperature and high-pressure sintering is preferably 20–300 s, more preferably 50–250 s, and most preferably 100–200 s. By controlling the temperature, pressure, and time of the high-temperature and high-pressure sintering within the above ranges, this invention is more conducive to promoting the graphitization of the diamond micropowder surface, thereby enabling it to fully transform into the diamond phase and form polycrystalline structures.

[0040] In this invention, the heating rate to the high-temperature, high-pressure sintering temperature is preferably 80–160 °C / s, more preferably 90–155 °C / s, and most preferably 100–120 °C / s. By controlling the heating rate during high-temperature, high-pressure sintering within the above range, this invention allows the oxidized portion of the catalyst to be re-electrolytically reduced and its catalytic activity restored during the heating process. This is more conducive to promoting the graphitization of the diamond micropowder surface, thereby enabling it to fully transform into the diamond phase and form polycrystalline structures.

[0041] The method for synthesizing polycrystalline diamond provided by this invention produces polycrystalline diamond crystals with more uniform crystals and free from catalyst oxides and other crystal defects, resulting in higher quality polycrystalline diamond crystals. Moreover, the synthesis method is simple, easy to implement, and has easy-to-control parameters, and is low in cost.

[0042] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0043] Example 1

[0044] A method for synthesizing polycrystalline diamond comprises the following steps:

[0045] (1) Diamond micro powder was mixed with metal powder catalyst and solvent and then dried at 80℃ and sieved through 100 mesh to obtain mixed micro powder; wherein, the particle size of diamond micro powder is 5μm and it is pretreated before use; the pretreatment of diamond micro powder is as follows: first, it is melted in molten sodium hydroxide for 1h, then the melted product is cooled and washed and dried in sequence, then the dried product is boiled in aqua regia for 0.5h, and finally the boiled product is cooled and washed and dried in sequence to obtain diamond micro powder; the mass ratio of diamond micro powder (95g) to catalyst (5g) is 95:5; the solvent is anhydrous ethanol (40g); the mixing method is ball milling; the ball milling speed is 120r / min, the ball milling time is 3h, and the ball milling medium is 500g stainless steel balls;

[0046] The metal powder catalyst is composed of the following components in mass percentage: 40% cobalt, 15% iron, 30% nickel and 15% silver; the particle size of the metal powder catalyst is 0.5-5 μm; the metal powder catalyst is prepared by mixing cobalt powder, iron powder, nickel powder and silver powder evenly to obtain the metal powder catalyst.

[0047] (2) Take 8.5g of the mixed micro powder obtained in step (1) and load it into the assembly unit. Then pressurize and energize the assembly unit to perform high-temperature and high-pressure sintering to obtain a diamond polycrystal with a diameter of 13mm and a height of 18mm. The assembly unit is an insulating tube and conductive current collectors set at both ends of the insulating tube. The high-temperature and high-pressure sintering temperature is 1550℃, the high-temperature and high-pressure sintering pressure is 5GPa, the high-temperature and high-pressure sintering time is 50s, and the heating rate is 155℃ / s.

[0048] Example 1 Step (2) The structural composition diagram of the assembly unit used is shown below. Figure 1 As shown.

[0049] Depend on Figure 1 As can be seen, conductive current collectors are provided at both ends of the insulator. The mixed micro powder is placed in the insulator. Utilizing the conductivity of the catalyst, current can be passed into the mixed micro powder by energizing the conductive current collector. The catalyst can generate heat under the action of the current, directly providing heat to the diamond micro powder without forming a heat transfer gradient, resulting in faster and more uniform heating. Moreover, under the action of the current, the oxidized part of the catalyst can undergo electrolysis, regaining catalytic activity.

[0050] Example 2

[0051] A method for synthesizing polycrystalline diamond comprises the following steps:

[0052] (1) Diamond micro powder was mixed with metal powder catalyst and solvent and then dried at 80℃ and sieved through 100 mesh to obtain mixed micro powder; wherein the particle size of diamond micro powder was 10μm and it was pretreated before use; the pretreatment of diamond micro powder was to first melt and boil in molten sodium hydroxide for 1h, then cool the melted product and wash and dry it in sequence, then boil the dried product in aqua regia for 0.5h, and finally cool the boiled product and wash and dry it in sequence to obtain diamond micro powder; the mass ratio of diamond micro powder (90g) to catalyst (10g) was 90:10; the solvent was anhydrous ethanol (40g); the mixing method was ball milling; the ball milling speed was 120r / min, the ball milling time was 3h, and the ball milling medium was 500g stainless steel balls;

[0053] The metal powder catalyst is composed of the following components in mass percentage: 40% cobalt, 15% iron, 30% nickel and 15% silver; the particle size of the metal powder catalyst is 0.5-5 μm; the metal powder catalyst is prepared by mixing cobalt powder, iron powder, nickel powder and silver powder evenly to obtain the metal powder catalyst.

[0054] (2) Take 16.5g of the mixed micro powder obtained in step (1) and load it into the assembly unit. Then, pressurize and energize the assembly unit to perform high-temperature and high-pressure sintering to obtain a diamond polycrystal with a diameter of 13mm and a height of 18mm. The assembly unit is an insulating tube and conductive current collectors set at both ends of the insulating tube. The high-temperature and high-pressure sintering temperature is 1550℃, the high-temperature and high-pressure sintering pressure is 5GPa, the high-temperature and high-pressure sintering time is 50s, and the heating rate is 155℃ / s.

[0055] The microstructure of the diamond polycrystal prepared in Example 2 was observed using a scanning electron microscope (SEM), and the obtained SEM images are shown below. Figure 2 As shown.

[0056] Depend on Figure 2 It can be seen that the diamond polycrystal synthesized using the catalyst provided by this invention has a uniform crystal structure, excellent quality, and no metal oxides appear inside the crystal.

[0057] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for synthesizing polycrystalline diamond, comprising the following steps: (1) Diamond micro powder is mixed with metal powder catalyst and solvent and then dried to obtain mixed micro powder; (2) The mixed micro powder obtained in step (1) is subjected to high temperature and high pressure sintering to obtain diamond polycrystalline material; the high temperature and high pressure sintering is: the mixed micro powder is loaded into the assembly unit, and then the assembly unit is pressurized and energized; the assembly unit includes an insulating tube and conductive current collectors disposed at both ends of the insulating tube; The metal powder catalyst in step (1) comprises the following components by mass percentage: 0-80% cobalt, 0-30% iron, 0-40% nickel and 0-35% silver; wherein the mass percentages of cobalt, iron, nickel and silver are not all 0. The mass ratio of diamond micro powder to metal powder catalyst in step (1) is (80~100):(1~15); The mixing method in step (1) is ball milling; In step (2), the temperature of high-temperature and high-pressure sintering is 1200~1600℃, the pressure of high-temperature and high-pressure sintering is 5~6GPa, the time of high-temperature and high-pressure sintering is 20~300s, and the heating rate to the temperature of high-temperature and high-pressure sintering is 80~160℃ / s.

2. The synthesis method according to claim 1, characterized in that, The particle size of the metal powder catalyst is 0.1~10μm.

3. The synthesis method as described in claim 1, characterized in that, The particle size of the diamond micro powder in step (1) is 0.1~70μm.

4. The synthesis method according to claim 1, characterized in that, The ball mill rotates at a speed of 100-150 r / min, and the milling time is 1-5 h.

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