Purification method of primary monocrystal diamond powder

Abstract

The invention relates to a method for purifying primary monocrystal diamond powder, which comprises the following steps of: (1) pretreatment stage: pretreating diamond particles subjected to coarse separation, and carrying out ultrasonic treatment and cleaning by adopting a mixed acid of a hydrochloric acid solution with the mass percent concentration of 30% and a nitric acid solution with the mass percent concentration of 50%; (2) treating for 60-90 minutes at the temperature of 80-120 DEG C by adopting a microwave-assisted ionic liquid method, then carrying out solid-liquid separation, and recovering ionic liquid; (3) carrying out ultrasonic wave-hydrogen peroxide composite oxidation treatment on the treated diamond; and (4) carrying out ultrapure water ultrasonic cleaning on the diamond subjected to composite oxidation treatment, and then carrying out vacuum drying. Physical field, green chemistry and mild oxidation technologies are organically combined, the highest temperature of the whole process does not exceed 120 DEG C, etching, oxidation and lattice damage caused by high temperature and strong acid to the diamond surface are avoided from the source, the integrity and high strength of primary single crystals can be kept, and the method is suitable for large-scale production. And a novel efficient, high-quality and environment-friendly diamond purification path is formed.

Description

Technical Field

[0001] This invention relates to a method for purifying virgin single-crystal diamond powder, belonging to the field of synthetic diamond preparation. Background Technology

[0002] Diamond possesses exceptional hardness and the highest thermal conductivity, along with stable chemical properties, making it a promising material for industrial manufacturing, chemical production, and optical research. In my country, diamond production primarily employs the static high-pressure method. This method involves mixing graphite with a specific proportion of catalyst metal powder, assembling it with a pressure-transmitting medium into a synthetic block, and then using a six-sided press under high temperature and pressure to synthesize diamond. The diamond, along with residual graphite, catalyst metal, and a small amount of pyrophyllite, is mixed into a dense synthetic rod, which requires purification. To ultimately obtain high-purity diamond particles, the current conventional approach involves first initially crushing the synthetic rod (or block), then ball milling it for further crushing, followed by removing the catalyst metal using electrolysis or acid leaching. Finally, a shaking table is used to initially separate the graphite and diamond, yielding refined synthetic diamond material. Diamond is chemically stable and not dissolved by strong acids or alkalis, while catalyst metal, graphite, pyrophyllite, and dolomite can be removed through chemical reactions, achieving the goal of purifying diamond. Existing chemical treatment processes require the use of large amounts of acids and alkalis, which generates a large amount of waste liquid. The waste liquid treatment is costly, poses significant environmental risks, and consumes a lot of energy. Summary of the Invention

[0003] This invention provides a method for purifying virgin single-crystal diamond powder, which solves the problems of generating a large amount of waste liquid, high waste liquid treatment costs, high environmental risks, and high energy consumption in the existing chemical diamond purification process.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for purifying virgin single-crystal diamond powder includes the following steps: (1) Pretreatment stage: The coarsely separated diamond particles are pretreated by a mixture of 30% hydrochloric acid solution and 50% nitric acid solution, with a volume ratio of hydrochloric acid to nitric acid of 1:1-2 and a solid-liquid ratio of diamond particles to mixed acid of 1g:2-3ml. The mixture is then ultrasonically treated and cleaned. (2) Microwave-assisted ionic liquid method was used, 80-120℃ for 60 min, then solid-liquid separation was performed and the ionic liquid was recovered; (3) The diamond treated above is subjected to ultrasonic-hydrogen peroxide composite oxidation treatment. (4) The diamonds that have undergone composite oxidation treatment are ultrasonically cleaned with ultrapure water and then vacuum dried.

[0005] Furthermore, preferably: step (1) also includes ultrasonic treatment, specifically: ultrasonic treatment is performed at 40-50°C, with an ultrasonic power of 300W, a frequency of 40kHz, and a treatment time of 30-45min, and then the mixture is rinsed with deionized water until neutral.

[0006] Furthermore, preferably, the ionic liquid described in step (2) comprises, by mass percentage, 3% to 5% tea saponin, 2% to 4% sodium lignin sulfonate, and the balance being diethyl 1-ethyl-3-methylimidazolium phosphate.

[0007] Furthermore, preferably: the microwave-assisted ionic liquid method specifically involves: a stepped microwave power program, with the power at 400W for the first stage (0-30min) to rapidly heat the system to 80℃; and the power adjusted to 200W for the second stage (30-60min) to maintain the system temperature at 90-100℃ for the reaction.

[0008] Furthermore, preferably: the ultrasonic-hydrogen peroxide composite oxidation treatment: using ultrapure water as a solvent, adding hydrogen peroxide (H2O2) to make its mass percentage concentration at 5%-10%, adding a trace amount of sodium hydroxide, adjusting the pH value of the oxidation solution to 9-10, and then treating with ultrasound at 30-40kHz and 200-300W at 70-80℃ for 60-90min.

[0009] Furthermore, preferably: the ultrapure water ultrasonic cleaning is specifically a segmented ultrasonic water washing, the first stage: ultrasonic power 600W, frequency 40kHz, water temperature 50℃, cleaning for 10-20min; the second stage: ultrasonic power 300W, frequency 80kHz, water temperature 50℃, cleaning for 20-30min.

[0010] The beneficial effects of this invention are: The method of the present invention designs a three-stage targeted removal process for the three most common impurities in diamond (metal catalyst, graphite, and pyrophyllite): Step (1) mixed acid ultrasonic pretreatment can effectively remove most of the metal impurities; Step (2) the composite ionic liquid has excellent selective intercalation and dissolution ability for graphite and pyrophyllite under microwave assistance, and microwave heating provides efficient and uniform bulk phase heating, which significantly accelerates the exfoliation reaction of ionic liquid on graphite; Step (3) ultrasonic-hydrogen peroxide composite oxidation treatment can gently remove residual trace amounts of non-diamond carbon without damaging the diamond matrix.

[0011] This invention successfully combines physical fields (microwaves, ultrasound), green chemistry (composite ionic liquids), and mild oxidation technology. The highest temperature of the entire process does not exceed 120°C, and it avoids highly corrosive reagents such as concentrated sulfuric acid and hydrofluoric acid. It eliminates the etching, oxidation, and lattice damage to the diamond surface caused by high temperature and strong acid from the source. It is particularly beneficial to maintain the integrity and high strength of the original single crystal, forming a new efficient, high-quality, and environmentally friendly diamond purification path with good industrialization prospects.

[0012] The method of this invention innovatively introduces two natural, biodegradable plant-based components, tea saponin and sodium lignin sulfonate, into the ionic liquid, which effectively enhances the peeling efficiency.

[0013] Tea saponin is an excellent natural nonionic surfactant. Its hydrophilic (glycan chain) and hydrophobic (glycoside) structure can significantly reduce the surface tension of ionic liquids, making it easier for it to penetrate into the layered structure of graphite and the gaps between the pyrophyllite layers. Through the wedge effect, it can strongly peel off their bond with the diamond surface. At the same time, its good foaming properties can carry the peeled light graphite and pyrophyllite fragments to the liquid surface during the subsequent washing process, making it easy to separate.

[0014] Sodium lignosulfonate, as an anionic polymer, has macromolecular chains that can adsorb onto the surface of exfoliated graphite nanosheets and pyrophyllite particles. Through electrostatic repulsion and steric hindrance, it prevents these particles from re-aggregating or redepositing onto the diamond surface, thus stabilizing them in the ionic liquid. In addition, its phenolic hydroxyl and sulfonic acid groups can weakly complex metal ions in pyrophyllite, aiding in the exfoliation process.

[0015] The composite ionic liquid of this invention forms an integrated cleaning system of penetration-stripping-stabilization: tea saponin opens and penetrates the impurity interface; the ionic liquid intercalates and dissolves graphite; sodium lignin sulfonate stabilizes the stripped fragments in a timely manner, ensuring thorough separation. This not only significantly improves the cleaning efficiency and separation effect of graphite and pyrophyllite, but also shows great potential in terms of environmental protection, safety and cost. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 Micrograph of raw diamond powder before processing; Figure 2 This is a micrograph of the processed raw diamond powder. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are also described.

[0019] Example 1 A method for purifying virgin single-crystal diamond powder includes the following steps: (1) Pretreatment stage: The coarsely separated diamond particles (25-30 μm) are pretreated by a mixture of 30% hydrochloric acid solution and 50% nitric acid solution. The mixing ratio is 1:2 (volume ratio of hydrochloric acid to nitric acid) and 1g:3ml (solid-liquid ratio of diamond particles to mixed acid). Ultrasonic treatment and cleaning are performed. The ultrasonic treatment is performed at 50℃ with an ultrasonic power of 300W, a frequency of 40kHz, and a treatment time of 40min. Then, the particles are cleaned with deionized water until neutral. (2) The microwave-assisted ionic liquid method was adopted. The solution was treated at 120°C for 90 min, followed by solid-liquid separation and recovery of the ionic liquid. The ionic liquid, by mass percentage, included 4% tea saponin, 3% sodium lignosulfonate, and 93% 1-ethyl-3-methylimidazolium phosphate. The microwave-assisted ionic liquid method was specifically as follows: the microwave power was programmed in a stepwise manner. In the first stage, 0-30 min, the power was 400W to rapidly raise the system temperature to 80°C. In the second stage, 30-60 min, the power was adjusted to 200W to maintain the system temperature at 90-100°C for the reaction. (3) The diamond treated above is subjected to ultrasonic-hydrogen peroxide composite oxidation treatment. The ultrasonic-hydrogen peroxide composite oxidation treatment is as follows: ultrapure water is used as solvent, hydrogen peroxide (H2O2) is added to make its mass percentage 10%, a trace amount of sodium hydroxide is added, the pH value of the oxidation solution is adjusted to 10, and then ultrasonic waves at 40kHz and 300W are used at 80℃ for 90min. (4) The diamond treated with composite oxidation is ultrasonically cleaned with ultrapure water and then vacuum dried. The ultrasonic cleaning with ultrapure water is specifically a segmented ultrasonic water washing. The first stage: ultrasonic power 600W, frequency 40kHz, water temperature 50℃, cleaning for 20min; the second stage: ultrasonic power 300W, frequency 80kHz, water temperature room temperature, cleaning for 30min, and then vacuum dried at 80℃ for 3h to obtain native single crystal diamond powder.

[0020] Comparative Example 1 The process is basically the same as in Example 1, except that the ionic liquid in step (2) is 1-ethyl-3-methylimidazolium phosphate diethyl ester.

[0021] Comparative Example 2 It is basically the same as Example 1, except that the ionic liquid in step (2) includes 4% tea saponin and 96% 1-ethyl-3-methylimidazolium phosphate by mass percentage.

[0022] Comparative Example 3 It is basically the same as Example 1, except that the ionic liquid in step (2) includes 3% sodium lignosulfonate and 97% diethyl 1-ethyl-3-methylimidazolium phosphate by mass percentage.

[0023] Comparative Example 4 It is basically the same as Example 1, except that the ionic liquid in step (2) includes, by mass percentage, 3% tea saponin, 2% sodium lignin sulfonate, and 95% diethyl 1-ethyl-3-methylimidazolium phosphate.

[0024] Comparative Example 5 It is basically the same as Example 1, except that the ionic liquid in step (2) includes, by mass percentage, 5% tea saponin, 4% sodium lignin sulfonate, and 91% diethyl 1-ethyl-3-methylimidazolium phosphate.

[0025] According to GB / T 23942-2009 standard, diamond impurities were determined using a 7300V instrument. The specific results are as follows: Table 1. Results of diamond surface impurity measurement in different embodiments

[0026] As shown in Table 1, the microwave composite ionic liquid method of this invention has a good cleaning and removal effect on impurities in diamond powder. The total amount of impurities removed is about 22 ppm, which is more than 78% lower than that of Comparative Example 1. The composite ionic liquid of this invention forms an integrated cleaning system of penetration-exfoliation-stabilization: tea saponin opens and penetrates the impurity interface; the ionic liquid intercalates and dissolves graphite; sodium lignosulfonate stabilizes the exfoliated fragments in time, ensuring thorough separation. This not only significantly improves the cleaning efficiency and separation effect of graphite and pyrophyllite, but also shows great potential in terms of environmental protection, safety and cost. In particular, it has obvious advantages over using 1-ethyl-3-methylimidazolium phosphate as the ionic liquid alone, the combination of 1-ethyl-3-methylimidazolium phosphate and tea saponin, and the combination of 1-ethyl-3-methylimidazolium phosphate and sodium lignosulfonate, especially for the removal of iron and silicon.

[0027] As can be seen from Comparative Examples 4 and 5, when the addition amount of tea saponin and sodium lignin sulfonate reaches 5% tea saponin and 4% sodium lignin sulfonate, the cleaning effect is basically the same as that of Example 1. Therefore, the following experiments will use the range of 3% to 5% tea saponin and 2% to 4% sodium lignin sulfonate to screen for the optimal solution.

[0028] Example 2 A method for purifying virgin single-crystal diamond powder includes the following steps: (1) Pretreatment stage: The coarsely separated diamond particles (25-30μm) are pretreated by a mixture of 30% hydrochloric acid solution and 50% nitric acid solution. The mixing ratio is 1:1 (volume ratio of hydrochloric acid to nitric acid) and the solid-liquid ratio of diamond particles to mixed acid is 1g:2ml. Ultrasonic treatment and cleaning are performed. The ultrasonic treatment is performed at 40℃ with an ultrasonic power of 300W, a frequency of 40kHz, and a treatment time of 45min. Then, the particles are cleaned with deionized water until neutral. (2) The microwave-assisted ionic liquid method was adopted. The solution was treated at 120°C for 90 min, followed by solid-liquid separation and recovery of the ionic liquid. The ionic liquid, by mass percentage, included 3% tea saponin, 4% sodium lignin sulfonate, and 93% 1-ethyl-3-methylimidazolium phosphate. The microwave-assisted ionic liquid method was specifically as follows: the microwave power was programmed in a stepwise manner. In the first stage, 0-30 min, the power was 400W to rapidly raise the system temperature to 80°C. In the second stage, 30-60 min, the power was adjusted to 200W to maintain the system temperature at 90-100°C for the reaction. (3) The diamond treated above is subjected to ultrasonic-hydrogen peroxide composite oxidation treatment. The ultrasonic-hydrogen peroxide composite oxidation treatment is as follows: ultrapure water is used as solvent, hydrogen peroxide (H2O2) is added to make its mass percentage 5%, a trace amount of sodium hydroxide is added, the pH value of the oxidation solution is adjusted to 9, and then ultrasonic waves at 30kHz and 200W are used at 70℃ for 60min. (4) The diamond treated with composite oxidation is ultrasonically cleaned with ultrapure water and then vacuum dried. The ultrasonic cleaning with ultrapure water is specifically a segmented ultrasonic water washing. The first stage: ultrasonic power 600W, frequency 40kHz, water temperature 50℃, cleaning for 10min; the second stage: ultrasonic power 300W, frequency 80kHz, water temperature room temperature, cleaning for 20min, and then vacuum dried at 80℃ for 3h to obtain native single crystal diamond powder.

[0029] Example 3 A method for purifying virgin single-crystal diamond powder includes the following steps: (1) Pretreatment stage: The coarsely separated diamond particles (25-30 μm) are pretreated by a mixture of 30% hydrochloric acid solution and 50% nitric acid solution. The mixing ratio is 1:2 (volume ratio of hydrochloric acid to nitric acid) and 1g:3ml (solid-liquid ratio of diamond particles to mixed acid). Ultrasonic treatment and cleaning are performed. The ultrasonic treatment is performed at 50℃ with an ultrasonic power of 300W, a frequency of 40kHz, and a treatment time of 45min. Then, the particles are cleaned with deionized water until neutral. (2) The microwave-assisted ionic liquid method was adopted. The solution was treated at 120°C for 70 min, followed by solid-liquid separation and recovery of the ionic liquid. The ionic liquid, by mass percentage, included 3% tea saponin, 3% sodium lignosulfonate, and 94% 1-ethyl-3-methylimidazolium phosphate. The microwave-assisted ionic liquid method was specifically as follows: the microwave power was programmed in a stepwise manner. In the first stage, 0-30 min, the power was 400W to rapidly raise the system temperature to 80°C. In the second stage, 30-60 min, the power was adjusted to 200W to maintain the system temperature at 90-100°C for the reaction. (3) The diamond treated above is subjected to ultrasonic-hydrogen peroxide composite oxidation treatment. The ultrasonic-hydrogen peroxide composite oxidation treatment is as follows: ultrapure water is used as solvent, hydrogen peroxide (H2O2) is added to make its mass percentage 8%, a trace amount of sodium hydroxide is added, the pH value of the oxidation solution is adjusted to 10, and then ultrasonic waves at 40kHz and 300W are used at 80℃ for 90min. (4) The diamond treated with composite oxidation is ultrasonically cleaned with ultrapure water and then vacuum dried. The ultrasonic cleaning with ultrapure water is specifically a segmented ultrasonic water washing. The first stage: ultrasonic power 600W, frequency 40kHz, water temperature 50℃, cleaning for 20min; the second stage: ultrasonic power 300W, frequency 80kHz, water temperature room temperature, cleaning for 30min, and then vacuum dried at 80℃ for 3h to obtain native single crystal diamond powder.

[0030] Example 4 A method for purifying virgin single-crystal diamond powder includes the following steps: (1) Pretreatment stage: The coarsely separated diamond particles (25-30 μm) are pretreated by mixing a 30% hydrochloric acid solution and a 50% nitric acid solution. The mixing ratio is 1:2 (volume ratio of hydrochloric acid to nitric acid) and the solid-liquid ratio of diamond particles to mixed acid is 1g:2ml. Ultrasonic treatment and cleaning are performed. The ultrasonic treatment is performed at 50℃ with an ultrasonic power of 300W, a frequency of 40kHz, and a treatment time of 30min. Then, the particles are cleaned with deionized water until neutral. (2) The microwave-assisted ionic liquid method was adopted. The solution was treated at 100°C for 90 min, followed by solid-liquid separation and recovery of the ionic liquid. The ionic liquid, by mass percentage, included 3% tea saponin, 2% sodium lignin sulfonate, and 95% 1-ethyl-3-methylimidazolium phosphate. The microwave-assisted ionic liquid method was specifically as follows: the microwave power was programmed in a stepwise manner. In the first stage, 0-30 min, the power was 400W to rapidly raise the system temperature to 80°C. In the second stage, 30-60 min, the power was adjusted to 200W to maintain the system temperature at 90-100°C for the reaction. (3) The diamond treated above is subjected to ultrasonic-hydrogen peroxide composite oxidation treatment. The ultrasonic-hydrogen peroxide composite oxidation treatment is as follows: ultrapure water is used as solvent, hydrogen peroxide (H2O2) is added to make its mass percentage 10%, a trace amount of sodium hydroxide is added, the pH value of the oxidation solution is adjusted to 10, and then ultrasonic waves at 40kHz and 300W are used at 80℃ for 70min. (4) The diamond treated with composite oxidation is ultrasonically cleaned with ultrapure water and then vacuum dried. The ultrasonic cleaning with ultrapure water is specifically a segmented ultrasonic water washing. The first stage: ultrasonic power 600W, frequency 40kHz, water temperature 50℃, cleaning for 20min; the second stage: ultrasonic power 300W, frequency 80kHz, water temperature room temperature, cleaning for 30min, and then vacuum dried at 80℃ for 3h to obtain native single crystal diamond powder.

[0031] According to GB / T 23942-2009 standard, diamond impurities were determined using a 7300V instrument. The specific results are as follows: Table 2. Results of diamond surface impurity measurement in different embodiments

[0032] As can be seen from the table above, the diamond powder processed by the method of the present invention has high purity and low impurity content, reaching the ppm level. In particular, the diamond powder prepared by the method of Example 3 has the best purity.

[0033] Example 5 The method stability test was conducted using the method described in Example 3, and the test was repeated 20 times. The data obtained are as follows: Table 3 Results of diamond surface impurity determination in Example 5

[0034] The diamond powder before and after treatment was observed using a microscope, such as... Figure 1 and 2 As shown. By Figure 1As can be seen, when the diamond powder before treatment is magnified 100 times, impurities are clearly visible on the diamond (the black part within the circle in the image). When the diamond powder after treatment is magnified 100 times, the impurity content on the particle surface is below 20 ppm. Microscopic images show that the diamond particles after treatment are regular hexagonal octahedral crystals, without aggregated crystals, with a concentrated particle size distribution and low impurity content, reaching the ppm level.

[0035] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for purifying a raw single crystal diamond powder, characterized by, It comprises the following steps: (1) Pretreatment stage: the rough diamond particles are pretreated, a mixed acid of 30% hydrochloric acid solution and 50% nitric acid solution is used, the mixing ratio is 1:1-2, the solid-liquid ratio of diamond particles to mixed acid is 1g:2-3ml, ultrasonic treatment, and cleaning; (2) Microwave-assisted ionic liquid method, 80-120℃, 60min, then solid-liquid separation, and recovery of ionic liquid; (3) Ultrasonic-hydrogen peroxide composite oxidation treatment is performed on the diamond treated above; (4) The composite oxidation treated diamond is ultrasonically cleaned with ultrapure water, and then vacuum dried.

2. The purification method according to claim 1, characterized in that: The ultrasonic treatment in step (1) is specifically: ultrasonic treatment is carried out at 40-50℃, the ultrasonic power is 300W, the frequency is 40kHz, and the treatment time is 30-45min, then deionized water is used for cleaning to neutral.

3. The purification method according to claim 1, characterized by: The microwave-assisted ionic liquid method in step (2) comprises tea saponin 3%-5%, lignosulfonate sodium 2%-4%, and the rest is 1-ethyl-3-methylimidazole diethyl phosphate according to mass percentage.

4. The purification method according to claim 3, characterized in that: The microwave-assisted ionic liquid method is specifically: the microwave power adopts a stepwise program, the first stage is 0-30min, the power is 400W, the system is quickly heated to 80℃, the second stage is 30-60min, the power is adjusted to 200W, and the system temperature is maintained at 90-100℃ for reaction.

5. The purification method according to claim 1, characterized by: The ultrasonic-hydrogen peroxide composite oxidation treatment is: ultrapure water is used as solvent, hydrogen peroxide is added, the mass percentage concentration is 5%-10%, a small amount of sodium hydroxide is added, the pH value of the oxidation liquid is adjusted to 9-10, then ultrasonic treatment is carried out at 30-40kHz, power 200-300W, 70-80℃, for 60-90min.

6. The purification method according to claim 1, characterized by: The ultrasonic cleaning with ultrapure water is specifically: segmented ultrasonic water cleaning, the first stage: ultrasonic power 600W, frequency 40kHz, water temperature 50℃, cleaning 10-20min; the second stage: ultrasonic power 300W, frequency 80kHz, water temperature room temperature, cleaning 20-30min.

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