Highly compact graphite-coated diamond powder, and preparation method and application thereof

Abstract

This invention belongs to the field of superhard materials technology, specifically relating to a highly dense graphite-coated diamond powder, its preparation method, and its application. The method includes the following steps: S1, heating the diamond powder to a certain temperature under vacuum conditions and performing a first etching treatment on the diamond powder using high-energy plasma; S2, under vacuum conditions, using low-temperature plasma chemical vapor deposition (PSCVD) with a carbon source and protective gas, depositing a carbon coating on the diamond powder surface; S3, under vacuum conditions, performing a second etching treatment on the surface of the obtained carbon coating using high-energy plasma to obtain highly dense graphite-coated diamond powder. This invention prepares a graphite layer on the surface of diamond powder, forming a graphite-diamond composite powder, which can solve the problem of insufficient wear resistance in synthesized PDC composite sheet materials due to the low density of diamond powder.

Description

Technical Field

[0001] This invention belongs to the field of superhard materials technology, specifically relating to a highly dense graphite-coated diamond powder, its preparation method, and its application. Background Technology

[0002] Polycrystalline diamond (PDC) drill bits are the primary drilling and production tools for oil and gas field drilling footage. PDC composite material is the core component of PDC drill bits, and its wear resistance significantly impacts drilling depth and efficiency. PDC composites are generally made by sintering diamond powder and cemented carbide substrate under high temperature and pressure. The initial density of the diamond powder has a crucial influence on the wear resistance of the PDC composite. Currently, domestically produced PDC composites suffer from insufficient wear resistance and impact resistance due to the low initial density of the diamond powder, making them unsuitable for deep / ultra-deep complex, dense, and difficult-to-drill formations. The low density of the diamond powder is mainly due to the hard contact between the powder particles, which easily forms large voids. Although secondary breakage of large powder particles occurs during high temperature and pressure processes, the hard contact between the powder particles still results in significant voids, leading to a persistently low density. Meanwhile, the inability to form a uniform particle interface leads to uneven distribution of cobalt among diamond particles during sintering, easily resulting in localized agglomeration. This prevents the formation of a stable and uniform cobalt network framework, consequently reducing the wear resistance of the prepared PDC composite sheet. Therefore, improving the density of diamond powder used in the synthesis of PDC composite sheets is a pressing issue that needs to be addressed in the development of high-wear-resistant and high-impact-resistant PDC composite sheet materials. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a highly dense graphite-coated diamond powder, its preparation method, and its applications. This invention prepares a graphite layer on the surface of diamond powder, forming a graphite-diamond composite powder, which solves the problem of insufficient wear resistance in synthesized PDC composite materials due to the low density of diamond powder in existing technologies.

[0004] The technical solution provided by this invention is as follows:

[0005] A method for preparing highly dense graphite-coated diamond powder includes the following steps:

[0006] S1. Under vacuum conditions, the diamond powder is heated to a certain temperature and then subjected to the first etching treatment by high-energy plasma.

[0007] S2. Under vacuum conditions, a carbon source and protective gas are introduced to deposit a carbon coating on the diamond powder using a low-temperature plasma chemical vapor deposition method to prepare a carbon coating on the surface of the diamond powder.

[0008] S3. Under vacuum conditions, the carbon coating surface obtained in step S2 is subjected to a second etching process by high-energy plasma to obtain highly dense graphite-coated diamond powder.

[0009] In the above technical solution:

[0010] In step S1, the original diamond powder is subjected to vacuum reduction treatment to etch away impurities on the powder surface.

[0011] In step S2, a carbon coating is deposited on the surface of diamond powder using microwave plasma chemical vapor deposition to form a graphite layer containing a graphite phase.

[0012] In step S2, hydrogen etching is performed on the surface of the graphite layer using microwave plasma chemical vapor deposition to remove large SP particles from the graphite layer surface. 2 The carbon-based particles are etched away, ultimately forming a uniform SP on the surface of the diamond powder. 2 Graphite layer.

[0013] Specifically, in step S1, the diamond powder raw material used is single-crystal diamond powder particles with a size of 0.2-60μm.

[0014] Specifically, in step S2 or S3, the carbon coating formed is a graphite layer with a thickness of 0.01-0.1 μm.

[0015] Specifically, step S1 includes the following steps:

[0016] a) Place the diamond powder into the vacuum chamber and evacuate the vacuum chamber to the set value;

[0017] b) After evacuating to the set value, heat the diamond powder and the reaction chamber to the set temperature;

[0018] c) After the vacuum chamber is heated to the set temperature, a mixture of hydrogen and argon gas in a certain proportion is introduced to form a high-energy plasma, which is used to etch the diamond powder for the first time.

[0019] Preferred:

[0020] In step a), the vacuum is evacuated to 1×10⁻⁶. -3 Pa-5×10 -3 Pa;

[0021] In step b), the temperature is heated to 550-750℃;

[0022] In step c), the flow rate of the hydrogen and argon mixture is 10-30 sccm;

[0023] In step c), the etching voltage is 1.2-1.5 kV;

[0024] In step c), the etching time is 10-45 min.

[0025] Based on the above technical solution, it is possible to ensure that etching removes impurities from the powder surface.

[0026] Specifically, step S2 includes the following steps:

[0027] d) After step S1 is completed, an alkane precursor gas is introduced to carry out a chemical reaction, and a carbon coating is generated on the surface of the diamond powder.

[0028] e) After deposition is completed, the heat preservation stage begins.

[0029] Preferred:

[0030] In step d), the alkane precursor gas is selected from any one or more combinations of methane, ethane, ethylene, acetylene, propane, propylene, or propyne;

[0031] In step d), the flow rate of the alkane precursor gas is 100-300 sccm;

[0032] In step d), the carbon coating deposition pressure is 1×10⁻⁶. 1 Pa-6×10 1 Pa;

[0033] In step d), the carbon coating deposition temperature is 550-750℃;

[0034] In step d), the carbon coating deposition time is 5-40 min;

[0035] In step e), the heat preservation time is 30-60 minutes.

[0036] Based on the above technical solution, it is possible to ensure the deposition of a carbon coating on the surface of diamond powder, forming a graphite layer containing a graphite phase.

[0037] Specifically, step S3 includes the following steps:

[0038] f) After step S2 is completed, stop the supply of argon and alkane precursor gas, maintain the supply of hydrogen gas, keep the temperature up, stop the supply of hydrogen gas after the temperature is up, and raise the temperature in a controlled manner to the set temperature.

[0039] g) After heating to the set temperature, hydrogen gas is introduced again, and hydrogen plasma is used for secondary etching. After etching for a period of time, the hydrogen gas is stopped, and the temperature is controlled to room temperature to obtain highly dense graphite-coated diamond powder.

[0040] Preferred:

[0041] In step f), the hydrogen flow rate is 50-100 sccm;

[0042] In step f), the heat preservation temperature is 200-400℃, and the heat preservation time is 30-60min;

[0043] In step f), the heating temperature is 850-950℃;

[0044] In step g), the hydrogen flow rate for the secondary etching is 10-100 sccm;

[0045] In step g), the secondary etching time is 5-30 min;

[0046] In step g), the secondary etching voltage is 1.2-1.5 kV;

[0047] In step g), the controllable cooling rate is 3-8℃ / min.

[0048] Based on the above technical solution, it is possible to ensure the formation of uniform SP on the surface of diamond powder. 2 Graphite layer.

[0049] The present invention also provides a highly dense graphite-coated diamond powder prepared according to the above preparation method. The powder comprises diamond powder particles and a graphite layer coating the surface of the diamond powder particles. Its density is 2.75-2.9 g·cm³. -3 .

[0050] This invention also provides the application of the aforementioned highly dense graphite-coated diamond powder in the preparation of polycrystalline diamond composite sheets. The average coefficient of friction of the PDC composite material prepared under high temperature and high pressure is 0.05-0.12.

[0051] Specifically, the sintering temperature was 1550℃ and the sintering pressure was 7.5GPa. After sintering the PDC composite material, the surface of the prepared PDC composite material was polished and its friction coefficient was tested.

[0052] In the above technical solution, the diamond powder raw material used is raw diamond powder, which can be commercially available diamond powder.

[0053] In the above technical solution, the diamond powder is uniformly dispersed during each etching process, thereby ensuring that each powder particle is fully etched:

[0054] Raw diamond powder is placed in a metal tray equipped with a rotating device. The tray is positioned in the center of the plasma sphere. At the start of the experiment, the rotating device is activated and set to a certain speed, causing the powder to rotate within the metal tray. This ensures that the plasma and powder are in full and uniform contact, thereby ensuring that each powder particle is fully etched and a carbon coating is deposited.

[0055] The beneficial effects of this invention are as follows:

[0056] By applying the technical solution of this invention, a graphite layer is prepared on the surface of diamond powder to form a graphite-diamond composite powder. On the one hand, the graphite layer on the surface of the diamond powder can increase the lubricity between the powder particles and reduce the proportion of voids due to hard contact, thereby increasing the number of powder particles per unit volume and the density of the powder. On the other hand, after a second hydrogen plasma etching, the large graphite particles on the diamond surface can be transformed into fine and uniform graphite particles, thereby reducing the phenomenon of large graphite particles falling off during the subsequent diamond powder gradation and compaction process (the large graphite particles falling off will hinder the diffusion of Co elements during the composite sheet pressing process, leading to a decrease in the bonding of diamond powder). It can also improve the roundness and fluidity of the powder surface during high-temperature and high-pressure synthesis, forming a uniform diamond powder interface structure, significantly improving the wettability of cobalt elements in the cemented carbide substrate between the diamond powder particles, forming a uniformly distributed cobalt element skeleton network structure, thereby significantly enhancing the wear resistance and impact resistance of the PDC composite sheet.

[0057] In summary, diamond powder coated with a graphite layer can significantly improve the density of diamond powder, thereby improving the uniformity of cobalt element distribution in the diamond composite sheet structure, and thus significantly improving the wear resistance and impact resistance of existing PDC composite sheets. Attached Figure Description

[0058] Figure 1 This is a SEM image of the single-crystal diamond powder material used in Example 1.

[0059] Figure 2 This is a morphological image of the material obtained after the first etching in Example 1.

[0060] Figure 3 The image shows the surface morphology of the highly dense graphite-coated diamond powder prepared in Example 1.

[0061] Figure 4 This is a cross-sectional morphology diagram of the highly dense graphite-coated diamond powder prepared in Example 1.

[0062] Figure 5 The surface Raman test image of the highly dense graphite-coated diamond powder prepared in Example 1.

[0063] Figure 6 The average friction coefficient of PDC composite material prepared from the highly dense graphite-coated diamond powder prepared in Example 1 at 1550°C and 7.5 GPa is shown in the figure. Detailed Implementation

[0064] The principles and features of the present invention are described below. The embodiments given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0065] Unless otherwise specified, the test methods used in the embodiments are conventional methods; unless otherwise specified, the materials and reagents used are commercially available.

[0066] The highly dense graphite-coated diamond powder prepared by this invention includes original diamond powder particles and a graphite layer coated on the surface of the original diamond powder particles.

[0067] The raw diamond powder used is single-crystal diamond powder with a particle size of 0.2-60 μm. A graphite layer is coated onto the surface of the single-crystal diamond powder particles using microwave plasma deposition technology. The thickness of the graphite layer coating on the surface of the single-crystal diamond powder particles is 0.01-0.5 μm. The graphite layer on the surface of the diamond powder can increase the lubricity between the diamond powder particles and reduce the voids that exist between the powder particles due to hard contact. Preferably, the thickness of the graphite layer is 0.05-0.08 μm.

[0068] The prepared high-density graphite-coated diamond powder has a density as high as 2.75-2.9 g·cm³. -3 The composite sheet material prepared by using highly dense graphite-coated diamond powder under high temperature and high pressure conditions of 1550℃ and 7.5GPa has an average friction coefficient of 0.05-0.12.

[0069] The preparation method of high-density graphite-coated diamond powder includes: vacuum reduction treatment of raw diamond powder to remove impurities and form a hydrogen-containing interface layer; deposition of a carbon coating on the surface of the diamond powder using isostatic plasma chemical vapor deposition (ISPD) to form a graphite layer containing a graphite phase; and hydrogen etching treatment of the graphite layer surface using IPD to obtain large-size SPs on the graphite layer surface. 2 Graphite particles are etched into a fine, uniform, and dense graphite layer, which eventually forms a uniform and dense graphite layer on the surface of diamond powder, thus obtaining a highly dense graphite-coated diamond powder.

[0070] Plasma etching removes impurities from the surface of raw diamond powder, improving its purity. Plasma deposition grows a graphite layer on the powder surface. Compared to uncoated diamond powder, this increases lubricity between powder particles, reducing voids caused by hard contact and increasing the number of particles per unit volume and powder density. Furthermore, a second hydrogen plasma etching process transforms large graphite particles on the diamond surface into fine, uniform particles, reducing the shedding of large graphite particles during subsequent gradation and compaction (large graphite particles hinder Co diffusion during composite pressing, reducing diamond powder bonding). This improves the smoothness and flowability of the powder surface during high-temperature, high-pressure synthesis, creating a uniform diamond powder interface structure. This significantly improves the wettability of cobalt in the cemented carbide substrate within the diamond powder, forming a uniformly distributed cobalt skeletal network structure, thereby significantly enhancing the wear resistance and impact resistance of the PDC composite sheet.

[0071] In a preferred embodiment, the raw diamond powder and the reaction chamber are heated to a temperature of 560-720°C; the flow rate of the hydrogen + argon mixed gas is 12-25 sccm; and the first etching time is 35-50 min.

[0072] In a preferred embodiment, after the first etching is completed, acetylene gas is introduced at 50-200 sccm; the carbon coating deposition temperature is 560-700℃, and the deposition pressure is 2×10⁻⁶. 1 -4×10 1 Pa; the deposition time for carbon-based coatings is 20-30 min.

[0073] In a preferred embodiment, the second plasma etching temperature is 850-950°C, the hydrogen flow rate of the etching gas is 50-90 sccm, and the second plasma etching time is 10-25 min.

[0074] The temperature and processing time of the first and second plasma etching processes are not limited to the ranges mentioned above. Limiting them to the ranges is beneficial to further improve the lubricity between diamond powders and reduce the voids between powders, thereby further improving the density of the diamond powders and the wear resistance of the PDC composite sheet material prepared from the highly dense graphite-coated diamond powders.

[0075] Example 1

[0076] Preparation of high-density graphite-coated diamond powder:

[0077] 1. Place the raw diamond powder into the vacuum chamber and evacuate the chamber to a vacuum level of 1×10⁻⁶. -3 Pa;

[0078] 2. The original diamond powder and the reaction chamber are heated to 580°C;

[0079] 3. After the vacuum chamber is heated to 580℃, a hydrogen + argon mixture is introduced at a flow rate of 15 sccm to form a high-energy plasma to perform the first etching on the original diamond powder. The etching time is 45 min and the etching voltage is 1.35 kV.

[0080] 4. After the first etching is completed, acetylene gas is introduced at 100 sccm to form a carbon-based coating on the surface of the etched diamond powder; the deposition pressure of the carbon coating is 2 × 10⁻⁶. 1 Pa, the carbon coating deposition time is 30 min, and the deposition temperature is 730℃;

[0081] 5. After carbon deposition is completed, stop introducing all gases except hydrogen and start the heat preservation stage. The heat preservation temperature is 380℃ and the heat preservation time is 45min.

[0082] 6. After the carbon coating on the surface of the diamond powder is heated, stop the hydrogen gas supply and proceed with a controlled heating process, raising the temperature to 900℃.

[0083] 7. After the temperature is raised to 900℃, hydrogen gas is introduced again at 80 sccm to form hydrogen plasma. The hydrogen plasma is used to perform a second etching process on the diamond powder coated with carbon. The second etching time is 15 min and the etching voltage is 1.35 kV.

[0084] 8. After the second etching is completed, stop the hydrogen gas supply and cool down in a controlled manner at 5℃ / min. After cooling down to room temperature, highly dense graphite-coated diamond powder is obtained.

[0085] Measurement:

[0086] Figure 1 This is a SEM image of the single-crystal diamond powder material used in Example 1. Figure 1 It can be seen that the surface of the single-crystal diamond powder material used is free of impurities.

[0087] Figure 2 This is a morphological image of the material obtained after the first etching in Example 1. Figure 2 It can be seen that a layer of graphite is coated on the surface of the diamond powder.

[0088] Figure 3 This is a surface morphology image of the highly dense graphite-coated diamond powder prepared in Example 1. Figure 3 It can be seen that after the second etching, the graphite particles on the surface of the highly dense graphite-coated diamond powder are significantly smaller and more evenly distributed.

[0089] Figure 4 This is a cross-sectional morphology diagram of the highly dense graphite-coated diamond powder prepared in Example 1. Figure 4 The results showed that the thickness of the graphite layer in the highly dense graphite-coated diamond powder was approximately 0.076 μm.

[0090] Figure 5 This is a surface Raman spectral image of the highly dense graphite-coated diamond powder prepared in Example 1. Figure 5 It can be seen that the highly dense graphite-coated diamond powder is produced by SP 2 Phase graphite layer and SP 3 Composition of single-crystal diamond matrix.

[0091] Figure 6 The graph shows the average friction coefficient of PDC composite material prepared from the highly dense graphite-coated diamond powder prepared in Example 1 at 1550°C and 7.5 GPa. Figure 6 It can be seen that the average coefficient of friction of the PDC composite material prepared from the highly dense graphite-coated diamond powder prepared in Example 1 at 1550℃ and 7.5GPa is 0.05.

[0092] Example 2

[0093] The method is the same as in Example 1, except that in step 3, the temperature of the first plasma etching is 750°C.

[0094] The results showed that the density of the highly dense graphite-coated diamond powder was 2.75 g·cm³. -3 The coefficient of friction of the PDC composite sheet prepared from the highly dense graphite-coated diamond powder is 0.12.

[0095] Example 3

[0096] The method is the same as in Example 1, except that in step 3, the deposition temperature is 550°C.

[0097] The results showed that the density of the highly dense graphite-coated diamond powder was 2.78 g·cm³. -3 The coefficient of friction of the PDC composite sheet prepared from the highly dense graphite-coated diamond powder is 0.11.

[0098] Example 4

[0099] The method is the same as in Example 1, except that in step 4, the acetylene gas flow rate is 300 sccm.

[0100] The results showed that the density of the highly dense graphite-coated diamond powder was 2.78 g·cm³. -3 The coefficient of friction of the PDC composite sheet prepared from the highly dense graphite-coated diamond powder is 0.10.

[0101] Comparative Example 1

[0102] The method is the same as in Example 1, except that in step 3, the first plasma etching is not performed.

[0103] The results showed that the density of the prepared graphite-coated diamond powder was 2.21 g·cm³. -3 The coefficient of friction of the PDC composite sheet prepared from the graphite-coated diamond powder is 0.65.

[0104] Comparative Example 2

[0105] The method is the same as in Example 1, except that in step 4, the deposition temperature is 755°C.

[0106] The results showed that the density of graphite-coated diamond powder was 2.45 g·cm³. -3 The coefficient of friction of the PDC composite sheet prepared from the graphite-coated diamond powder is 0.48.

[0107] Comparative Example 3

[0108] The method is the same as in Example 1, except that in step 7, a second plasma etching is not performed.

[0109] The results showed that the density of graphite-coated diamond powder was 2.30 g·cm³. -3 The coefficient of friction of the PDC composite sheet prepared from the highly dense graphite-coated diamond powder is 0.59.

[0110] 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 preparing highly dense graphite-coated diamond powder, characterized in that, Includes the following steps: S1. Under vacuum conditions, the diamond powder is heated to a certain temperature and then subjected to the first etching treatment by high-energy plasma. S2. Under vacuum conditions, a carbon source and protective gas are introduced to deposit a carbon coating on diamond powder by low-temperature plasma chemical vapor deposition, thereby preparing a carbon coating on the surface of the diamond powder. S3. Under vacuum conditions, the carbon coating surface obtained in step S2 is subjected to a second etching process by high-energy plasma to obtain highly dense graphite-coated diamond powder.

2. The method for preparing highly dense graphite-coated diamond powder according to claim 1, characterized in that, Step S1 includes the following steps: a) Place the diamond powder into the vacuum chamber and evacuate the vacuum chamber to the set value; b) After evacuating to the set value, heat the diamond powder and the reaction chamber to the set temperature; c) After the vacuum chamber is heated to the set temperature, a mixture of hydrogen and argon gas in a certain proportion is introduced to form a high-energy plasma, which is used to etch the diamond powder for the first time.

3. The method for preparing highly dense graphite-coated diamond powder according to claim 2, characterized in that: In step a), the vacuum is evacuated to 1×10⁻⁶. -3 Pa-5×10 -3 Pa; In step b), the temperature is heated to 550-750℃; In step c), the flow rate of the hydrogen and argon mixture is 10-30 sccm; In step c), the etching voltage is 1.2-1.5 kV; In step c), the etching time is 10-45 min.

4. The method for preparing highly dense graphite-coated diamond powder according to claim 1, characterized in that, Step S2 includes the following steps: d) After step S1 is completed, an alkane precursor gas is introduced to carry out a chemical reaction, and a carbon coating is generated on the surface of the diamond powder. e) After deposition is completed, the heat preservation stage begins.

5. The method for preparing highly dense graphite-coated diamond powder according to claim 4, characterized in that: In step d), the alkane precursor gas is selected from any one or more combinations of methane, ethane, ethylene, acetylene, propane, propylene, or propyne; In step d), the flow rate of the alkane precursor gas is 100-300 sccm; In step d), the carbon coating deposition pressure is 1×10⁻⁶. 1 Pa-6×10 1 Pa; In step d), the carbon coating deposition temperature is 550-750℃; In step d), the carbon coating deposition time is 5-40 min; In step e), the insulation temperature is 550-750℃; In step e), the heat preservation time is 30-60 minutes.

6. The method for preparing highly dense graphite-coated diamond powder according to claim 1, characterized in that, Step S3 includes the following steps: f) After step S2 is completed, stop the supply of argon and alkane precursor gas, maintain the supply of hydrogen gas, keep the temperature up, stop the supply of hydrogen gas after the temperature is up, and raise the temperature in a controlled manner to the set temperature. g) After heating to the set temperature, hydrogen gas is introduced again, and hydrogen plasma is used for secondary etching. After etching for a period of time, the hydrogen gas is stopped, and the temperature is controlled to room temperature to obtain highly dense graphite-coated diamond powder.

7. The method for preparing highly dense graphite-coated diamond powder according to claim 1, characterized in that: In step f), the hydrogen flow rate is 50-100 sccm; In step f), the heat preservation temperature is 200-400℃, and the heat preservation time is 30-60min; In step f), the heating temperature is 850-950℃; In step g), the hydrogen flow rate for the secondary etching is 10-100 sccm; In step g), the secondary etching time is 5-30 min; In step g), the secondary etching voltage is 1.2-1.5 kV; In step g), the controllable cooling rate is 3-8℃ / min.

8. The method for preparing highly dense graphite-coated diamond powder according to any one of claims 1 to 7, characterized in that: In step S1, the diamond powder raw material used is single-crystal diamond powder particles with a size of 0.2-60μm; In step S2 or S3, the carbon coating formed is a graphite layer with a thickness of 0.01-0.1 μm.

9. A highly dense graphite-coated diamond powder prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The density is 2.75-2.9 g·cm³. -3 .

10. An application of the highly dense graphite-coated diamond powder according to claim 9, characterized in that: Used to prepare polycrystalline diamond composite sheets.

Images