Core-shell structure diamond micro-powder and preparation method thereof

Abstract

The application discloses a kind of core-shell structure diamond micro powder and preparation method thereof, using highly dispersed few-layer graphene oxide solution to wrap diamond micro powder, then the diamond micro powder wrapped by graphene oxide is reduced to obtain the core-shell structure diamond micro powder wrapped by graphene, the obtained core-shell structure diamond micro powder, graphene is evenly coated on diamond particle outside, after coating, diamond particle is uniformly distributed, dense accumulation arrangement on microstructure, can reduce the friction between diamond micro powder particles under high pressure in the synthesis process of composite sheet, make it more dense accumulation, can solve the uneven distribution of prior art graphene in diamond micro powder, can prevent the residue of excess graphene in sintering process, and help the migration of metal catalyst and the formation of D-D bond, improve the performance of final product, prepare high-density high-strength diamond composite sheet.

Description

Technical Field

[0001] This invention relates to the field of diamond composite sheet materials technology. More specifically, this invention relates to a core-shell structured diamond micropowder and its preparation method. Background Technology

[0002] During the synthesis of polycrystalline diamond composite sheets, under high pressure, diamond microparticles undergo sliding, rearrangement, and breakage. During rearrangement, finer particles tend to gradually fill the gaps between coarser particles, resulting in a dense polycrystalline diamond composite sheet. To obtain high-density polycrystalline diamond composite sheets and improve diamond-doped diamond (DD) bonding, the diamond composite sheet is generally subjected to high-temperature vacuum heat treatment with microparticles before sintering. This pre-graphitization of the diamond microparticles facilitates relative sliding between diamond particles, promotes particle rearrangement for densification, protects the integrity of the diamond particles, reduces high-pressure breakage, and improves DD bonding.

[0003] Currently, in research on polycrystalline diamond composite sheets both domestically and internationally, the introduction of graphene is mostly achieved by directly adding graphene powder and mixing it with diamond micropowder. For example, in the application No. 201910029344.8, "A method for preparing graphene-reinforced polycrystalline diamond," 0.05-0.3 wt% graphene is added to the diamond micropowder by mass ratio. This can provide good lubrication between diamond particles, reduce frictional resistance between particles under high pressure, and promote diamond fragmentation. Filling the gaps improves the strength and wear resistance of polycrystalline diamond. For example, the application No. 202010860958.3, "A polycrystalline diamond composite sheet with good heat resistance and its preparation method", adds 0.1-0.2% graphene to diamond micro powder in the polycrystalline diamond layer, which breaks through the technical bottleneck of high toughness, high heat resistance and high wear resistance of polycrystalline diamond composite sheets. The prepared polycrystalline diamond composite sheet has excellent heat resistance and wear resistance compared with diamond composite sheets obtained by existing technology.

[0004] The main problem with this type of method is that graphene powder is prone to agglomeration and is difficult to disperse evenly in diamond micro powder, which is not conducive to the uniform dispersion of metal catalysts in the subsequent sintering process. Summary of the Invention

[0005] One object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages that will be described later.

[0006] Another objective of this invention is to provide a core-shell structured diamond micropowder and its preparation method, so as to solve the technical problem that graphene is difficult to uniformly disperse in polycrystalline diamond layer diamond micropowder in the prior art.

[0007] To achieve these objectives and other advantages according to the present invention, in one aspect, the present invention provides a core-shell structured diamond micropowder comprising a micron-sized diamond particle core and a few-layer graphene shell encapsulating the diamond particle core, wherein the C / O ratio of the few-layer graphene shell is greater than 10, and the relationship between the size s of the graphene sheets in the graphene shell and the diameter d of the diamond micropowder is πd. 2 <s<1.5πd 2 .

[0008] Preferably, the few-layer graphene shell is obtained by reducing graphene oxide, and the number of graphene oxide layers is 1-10.

[0009] Preferably, the diamond micron powder has a particle size of 1-50 micrometers.

[0010] Preferably, the diamond micro powder is crushed diamond single crystal or raw diamond powder.

[0011] On the other hand, the present invention also provides a method for preparing core-shell structured diamond micron powder.

[0012] Preferably, the method includes the following steps:

[0013] S1. Prepare a graphene oxide solution with a carbon-to-oxygen ratio of 1.8-4;

[0014] S2. The graphene oxide solution is ultrasonically dispersed and diamond microparticles of a single particle size are added. The diameter d of the diamond microparticles satisfies the relationship πd. 2 <s<1.5πd 2 Continue sonication for 30 minutes to obtain a diamond / graphene oxide solution;

[0015] S3. Dry the diamond / graphene oxide solution to obtain diamond / graphene oxide powder;

[0016] S4. Reduce diamond / graphene oxide powder in a hydrogen atmosphere at a temperature of 600-1000℃ for 10-90 minutes to obtain diamond / graphene powder, wherein oxygen-containing functional groups are still present in the graphene composition and the C / O ratio is greater than 10, thus obtaining the core-shell structured diamond micro powder.

[0017] Preferably, step S1 specifically includes the following steps to control the carbon-oxygen ratio:

[0018] A1. Add graphite, sodium nitrate, and concentrated sulfuric acid to the reaction vessel and mix them mechanically under an ice-water bath at 0°C to obtain an initial mixture;

[0019] A2. Add potassium permanganate to the initial mixture and stir continuously for 3 hours in an ice-water bath at 0°C. Then raise the reaction temperature to 35°C and stir for 3 hours at this temperature. Add deionized water and raise the reaction temperature to 98°C to continue the reaction for 0.5 hours to obtain the initial reactant.

[0020] A3. Add hydrogen peroxide and deionized water to the initial reactants, and continue stirring the reaction for 0.5 h to obtain the oxidation product;

[0021] A4. First, wash the oxidation products with dilute hydrochloric acid, then wash repeatedly with deionized water until the pH is neutral, so that the carbon-oxygen ratio of graphene oxide is in the range of 1.8-4.

[0022] Preferably, step S1 further includes the following step after step A4:

[0023] S11. Standardize the concentration of the graphene oxide solution to obtain the standard solution;

[0024] S12. Take the standard solution and add deionized water to prepare a solution with a concentration of 1 mg / ml, then perform ultrasonic dispersion to obtain a dispersion.

[0025] S13. Measure the thickness of the graphene oxide sheets after the dispersion is dried. If the thickness is greater than 10 layers, return to step S12 to continue dilution until the thickness is no more than 10 layers.

[0026] S14. Measure the size s of the graphene oxide sheet for the dispersion that meets the layer thickness requirements.

[0027] Preferably, the concentration of the graphene oxide solution is not higher than 4 mg / ml.

[0028] Preferably, in step S3, the drying process is achieved by freeze-drying, and the freezing process uses liquid nitrogen for rapid freezing.

[0029] The present invention includes at least the following beneficial effects: The method for preparing core-shell structured diamond micropowder of the present invention uses a highly dispersed few-layer graphene oxide solution to coat diamond micropowder, and then reduces the graphene oxide-coated diamond micropowder under a hydrogen atmosphere to obtain graphene-coated core-shell structured diamond micropowder. In the obtained core-shell structured diamond micropowder, graphene is uniformly coated on the outside of diamond particles. The coated diamond particles are uniformly distributed and densely packed in the microstructure, which can reduce the friction between diamond micropowder particles under high pressure during composite sheet synthesis, making their packing more dense. It can solve the problem of uneven distribution of graphene in diamond micropowder in the prior art, prevent excess graphene residue in the sintering process, and help the migration of metal catalysts and the formation of DD bonds, improve the performance of the final product, and prepare high-density and high-strength diamond composite sheets.

[0030] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the core-shell structured diamond micron powder of the present invention;

[0032] Figure 2 The XPS spectrum of the diamond / graphene oxide powder obtained in step S3 is shown in the embodiment of the present invention.

[0033] Figure 3 The XPS spectrum of the core-shell structured diamond micropowder obtained in step S4 is shown in the embodiment of the present invention.

[0034] Figure 4 Optical micrographs of the core-shell structured diamond micropowder prepared in this invention were obtained using a Keyence microscope.

[0035] Figure 5 Optical micrographs of the diamond micropowder raw material of this invention obtained using a Keyence microscope;

[0036] Figure 6 An optical micrograph obtained using a Keyence microscope to show a comparative example of the present invention, showing the coating structure obtained by solid-phase mixing of diamond micropowder and graphene.

[0037] The accompanying diagram in the instruction manual is labeled as follows: 1. Diamond micro powder; 2. Graphene shell. Detailed Implementation

[0038] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0039] It should be noted that, unless otherwise specified, the experimental methods described in the following embodiments are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified. In the description of this invention, the terms "lateral", "longitudinal", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0040] The preparation method used in this invention is basically as follows:

[0041] First, a graphene oxide solution was prepared and dispersed to obtain a few-layer graphene oxide solution with a concentration not exceeding 4 mg / ml. Then, diamond micropowder was uniformly dispersed in the few-layer graphene oxide solution and ultrasonically coated for more than 30 min using a liquid phase coating method. The resulting product was then dried and reduced in a hydrogen atmosphere at 600-1000℃ for 10-90 min to obtain the final product, core-shell structured diamond micropowder.

[0042] In the preparation of graphene oxide solution, 2g of flake graphite and 0.5-2g of sodium nitrate were weighed and added to 30-60mL of concentrated sulfuric acid. The mixture was mechanically stirred for 0.5h in an ice-water bath at 0°C. Next, 4-8g of potassium permanganate was slowly added to the mixture, and the reaction was continued with stirring in an ice-water bath for 3h. Afterward, the reaction temperature was raised to 35°C and the mixture was stirred at this temperature for 3h. Then, 46mL of deionized water was slowly added to the flask, and the reaction temperature was raised to 98°C and the reaction was continued for 0.5h. After the above reaction was completed, 25-50mL of hydrogen peroxide and 200mL of deionized water were added to the reaction vessel, and the reaction was continued with stirring for 0.5h. Finally, the reaction product was washed first with dilute hydrochloric acid, and then repeatedly washed with deionized water until nearly neutral, thus obtaining the graphene oxide solution. The ratio of flake graphite to sodium nitrate and potassium permanganate is 1:0.5-1:2-4. By adjusting the experimental parameters in this process, the number of graphene oxide layers used can be controlled to be 1-10 layers, and the C / O ratio can be 1.8-4.

[0043] Specifically, the following implementation procedure can be used to prepare core-shell structured diamond micropowder samples:

[0044] (1) Preparation of graphene oxide solution

[0045] Weigh 2g of flake graphite and 1g of sodium nitrate using a Mettler balance, and place them together in a 500mL round-bottom three-necked flask. Then, add 46mL of concentrated sulfuric acid to the flask and mechanically stir the mixture in an ice-water bath at 0°C for 0.5h. Next, slowly add 6g of potassium permanganate to the mixture and continue stirring in an ice-water bath for 3h. Afterward, raise the reaction temperature to 35°C and stir at this temperature for 3h. Then, slowly add 46mL of deionized water to the flask and raise the reaction temperature to 98°C, continuing the reaction for 0.5h. After the above reaction is complete, add 36mL of hydrogen peroxide and 200mL of deionized water to the reaction vessel and continue stirring for 0.5h. Finally, wash the reaction product first with dilute hydrochloric acid, then repeatedly wash with deionized water until nearly neutral, obtaining a graphene oxide solution. The carbon-to-oxygen ratio of the graphene oxide obtained using the above parameters is controlled to be approximately 2.5.

[0046] (2) Calibration of graphene oxide solution concentration

[0047] To calibrate the concentration of graphene oxide prepared in step (1), the mass of the solute, m, is first obtained by drying a solution of a specific volume v. The mass of the solute, m, is then determined using the ratio of the obtained mass of the solute, m, to the volume of the solution, v, where ρ = m / v.

[0048] (3) Prepare a graphene oxide solution with a concentration of 1 mg / ml.

[0049] Take 20 ml of the solution from (2) after concentration calibration. According to the principle of solute mass conservation, the final sample volume V1 satisfies the following formula: ρ*20=1*V1. The volume of deionized water to be added is V2=V1-20. After adding V2 of deionized water, perform ultrasonic dispersion for more than 30 min to obtain a graphene oxide solution with a concentration of 1 mg / ml.

[0050] (4) Measurement of graphene oxide sheet thickness

[0051] Take 2-5 drops of the ultrasonically dispersed solution from (3), drop it onto a flat mica sheet surface and let it dry. Then observe it under an atomic force microscope and measure the layer thickness of the graphene oxide sheet. If the resulting graphene oxide sheet has a layer thickness greater than 10 layers, continue to dilute it until its thickness is less than 10 layers.

[0052] (5) Measurement of graphene oxide sheet size

[0053] Graphene oxide is a two-dimensional sheet material. Take 2-5 drops of the ultrasonically dispersed solution in (3), drop it onto the surface of copper foil and let it dry. Then observe it under a scanning electron microscope and measure the two-dimensional size s of the graphene oxide sheet.

[0054] (6) Preparation of diamond / graphene oxide solution

[0055] Take a 1 mg / ml graphene oxide solution from (3) that meets the measurement requirements of (4) and ultrasonically disperse it for 30 min. Then add diamond micro powder with a mass ratio of 99% to 99.99% of the graphene oxide. The diameter d of the diamond micro powder should satisfy πd. 2 <s<1.5πd 2 During the liquid phase coating process, samples with different diamond micropowder diameters need to be coated separately to prevent micropowder agglomeration. After sonication for 30 minutes, a diamond / graphene oxide solution is obtained.

[0056] (7) Preparation of diamond / graphene oxide core-shell structure

[0057] The solution obtained in (6) was dried to obtain diamond / graphene oxide powder. The drying process was carried out by freeze-drying. First, the ultrasonicated solution was rapidly frozen with liquid nitrogen, and then the sample was dried using a freeze dryer to obtain diamond / graphene oxide powder. The C / O ratio at this time was as follows: Figure 2 As shown.

[0058] (8) Preparation of diamond / graphene core-shell structure

[0059] The diamond / graphene oxide powder obtained in (7) was reduced at 600-1000℃ for 10-90 min under a hydrogen atmosphere to obtain diamond / graphene powder, i.e., core-shell structured diamond micropowder. Here, graphene refers to redox graphene, such as… Figure 3 As shown, a small number of oxygen-containing functional groups still exist, and the C / O ratio after reduction is greater than 10. Graphene obtained by the redox method has higher activity due to the remaining small number of oxygen-containing functional groups, which can improve the wettability of metal catalysts and further facilitate the migration of metal catalysts and the formation of DD bonds during sintering.

[0060] Optical micrographs of the core-shell structured diamond micropowder obtained in this invention were obtained under a Keyence microscope. The results are as follows: Figure 4 As shown; another diamond micron powder raw material from step (6) was taken and optical micrographs were obtained under a Keyence microscope, and the results are as follows. Figure 5 As shown in the figure; a comparative example was set up, in which a mixture of diamond micro powder and graphene with a mass fraction of 0.5% was prepared. The resulting mixture was ball-milled for 2 hours, and the resulting mixture was photographed under a Keyence microscope. The results are shown in the figure. Figure 6 As shown. Comparison Figure 4 , Figure 5 , Figure 6 ,exist Figure 6 The corresponding product contains black dots, indicating agglomerated graphene, which suggests that the diamond and graphene are not evenly dispersed. Figure 5 This corresponds to the state of the diamond micropowder structure itself. In the image, the diamond particles are bright in color overall. However, in the core-shell structure diamond micropowder obtained by the preparation method of this invention, graphene is wrapped on the surface of the diamond micropowder. In the image, the overall color of the wrapped diamond particles is darker, and no graphene agglomeration is observed, indicating that the coating effect, dispersion, and uniformity are good.

[0061] The method for preparing core-shell structured diamond micropowder of the present invention controls the carbon-oxygen ratio during the preparation of graphene oxide solution, thereby controlling the proportion of oxygen-containing functional groups and the activity of graphene oxide. This ensures that graphene oxide has good dispersibility in the mixed solution and can effectively adhere to the outside of each diamond particle. By controlling the number of graphene oxide layers, the microstructure size of the graphene-coated diamond particles can be controlled, resulting in a uniform core-shell structure with better dispersibility and preventing agglomeration. On the other hand, it also facilitates the subsequent reduction reaction of diamond / graphene oxide, improving the stability and controllability of microstructure formation, providing a larger specific surface area, reducing friction between diamond micropowder particles, and improving the compactness of the packing arrangement.

[0062] The method for preparing core-shell structured diamond micropowder of the present invention involves using a highly dispersed few-layer graphene oxide solution to coat diamond micropowder, followed by reduction of the graphene-coated diamond micropowder under a hydrogen atmosphere to obtain graphene-coated core-shell structured diamond micropowder. In the resulting core-shell structured diamond micropowder, graphene is uniformly coated in several layers around the diamond particles. The coated diamond particles are uniformly distributed and densely packed in the microstructure, which solves the problem of uneven graphene distribution in diamond micropowder in existing technologies. It also prevents excess graphene residue during the sintering process, facilitates the migration of metal catalysts and the formation of D-bonds, improves the performance of the final product, reduces friction between diamond micropowder particles under high pressure during composite sheet synthesis, and makes their packing more dense, thus preparing high-density, high-strength diamond composite sheets.

[0063] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for preparing core-shell structured diamond micropowder, characterized in that, It includes a micron-sized diamond particle core and a few-layer graphene shell covering the diamond particle core. The C / O ratio of the few-layer graphene shell is greater than 10. The relationship between the two-dimensional dimension s of the graphene sheet in the graphene shell and the diameter d of the diamond microparticles is πd. 2 < s <1.5πd 2 The diamond micropowder has a particle size of 1-50 micrometers, and the few-layer graphene shell is obtained by reducing graphene oxide, with the number of graphene oxide layers being 1-10. The core-shell structured diamond micropowder is prepared through the following steps: S1. Prepare a graphene oxide solution with a carbon-to-oxygen ratio of 1.8-4; The carbon-to-oxygen ratio is controlled through the following steps: A1. Add flake graphite, sodium nitrate, and concentrated sulfuric acid to the reaction vessel and mix them mechanically under an ice-water bath at 0°C to obtain an initial mixture; A2. Add potassium permanganate to the initial mixture. The ratio of flake graphite to sodium nitrate and potassium permanganate is 1:0.5-1:2-4. Stir continuously for 3 h in an ice-water bath at 0°C. Then raise the reaction temperature to 35°C and stir for 3 h at this temperature. Add deionized water and raise the reaction temperature to 98°C to continue the reaction for 0.5 h to obtain the initial reactant. A3. Add hydrogen peroxide and deionized water to the initial reactants, and continue stirring the reaction for 0.5 h to obtain the oxidation product; A4. First wash the oxidation products with dilute hydrochloric acid, then wash them repeatedly with deionized water until the pH is neutral, so that the carbon-oxygen ratio of graphene oxide is in the range of 1.8-4. S11. Standardize the concentration of the graphene oxide solution to obtain the standard solution; S12. Take the standard solution and add deionized water to prepare a solution with a concentration of 1 mg / ml, then perform ultrasonic dispersion to obtain a dispersion. S13. Measure the thickness of the graphene oxide sheets after the dispersion is dried. If the thickness is greater than 10 layers, return to step S12 to continue dilution until the thickness is no more than 10 layers. S14. Measure the two-dimensional dimensions s of the graphene oxide sheet for the dispersion that meets the layer thickness requirements; S2. The graphene oxide solution is ultrasonically dispersed, followed by the addition of diamond microparticles of a single particle size. The diameter d of the diamond microparticles satisfies the following relationship: Continue sonication for 30 minutes to obtain a diamond / graphene oxide solution; S3. Dry the diamond / graphene oxide solution to obtain diamond / graphene oxide powder; S4. Reduce diamond / graphene oxide powder in a hydrogen atmosphere at a temperature of 600-1000°C for 10-90 minutes to obtain diamond / graphene powder, wherein oxygen-containing functional groups are still present in the graphene composition and the C / O ratio is greater than 10, thus obtaining the core-shell structured diamond micro powder.

2. The method for preparing core-shell structured diamond micron powder as described in claim 1, characterized in that, The diamond micro powder is either crushed diamond single crystal or raw diamond powder.

3. The method for preparing core-shell structured diamond micron powder as described in claim 1, characterized in that, In step S3, the drying process is achieved by freeze-drying, and the freezing process uses liquid nitrogen for rapid freezing.

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