Method for forming controllable coating on surface of diamond

Abstract

The invention discloses a method for forming a controllable coating on the surface of diamond, which comprises the following steps of: uniformly mixing an adhesive, the diamond and a carbide forming substance in sequence, and drying in a vacuum or non-oxidizing atmosphere to obtain the diamond with the carbide forming substance attached on the surface; then uniformly mixing with halogen salt molten salt to obtain a mixture; pressing the mixture into a block; and calcining the block in a neutral or reducing atmosphere to form a coating on the surface of the diamond. Diamond and carbide forming substances of carbon salt forming elements are tightly attached through an adhesive, halogen salt fused salt and treated diamond particles / powder are pressed and formed, and the micro-reaction area with the diamond as a framework, the surface of the diamond particles / powder as a reaction bed and the halogen salt fused salt as a fluid medium is obtained. And the synthesis of the carbide is efficiently regulated and controlled, and the effect that the surface layer can be regulated and controlled to generate finer carbide grains at a lower reaction temperature is successfully achieved.

Description

Technical Field

[0001] The invention belongs to the field of surface engineering, and in particular relates to a method for forming a controllable coating on a diamond surface. Background Art

[0002] Diamond possesses exceptional physical and chemical properties, such as ultra-high hardness, excellent thermal conductivity, and good stability, playing a key role in numerous applications. Limited by diamond production technology, it typically exists in forms such as powder, granules, and flakes. To fully realize its high performance, it must be combined with a matrix material to create blocks of varying geometries for convenient application. However, the high chemical inertness and low surface energy of diamond surfaces result in poor bonding with the matrix. Blocks often lack a firm grip on the diamond and can even easily fall out of the matrix. These shortcomings hinder the full realization of diamond's performance advantages and significantly restrict its application. Surface modification of diamond particles / powders, specifically the formation of a reactive coating, can effectively address these issues. This coating securely bonds to the diamond particles / powder while also providing excellent adhesion to the matrix. This reactive coating effectively bridges the gap between the inert diamond and the matrix.

[0003] For example, in diamond-reinforced metal-matrix composites, the interfacial bonding between the diamond, as a reinforcing phase, and the matrix is key to achieving excellent thermophysical properties, directly affecting heat conduction efficiency and thermal stability. However, due to the poor wettability of diamond particles / powder with the metal matrix, they cannot directly bond with the metal through metallurgy, diffusion, or other methods during the bonding process, resulting in the formation of a large number of defects at the composite interface, significantly reducing the thermal conductivity of the composite. Generally, based on practical feasibility in the engineering field, Ni-based or Cu-based coatings are formed on the surface of diamond particles through electroplating or chemical plating. However, these metal-based coatings, in addition to coating the diamond thickly, still do not wet or bond with the diamond particles / powder. In order to simultaneously improve the bonding between the coating and the diamond and reduce the coating thickness, advanced technologies such as magnetron sputtering and metal vapor deposition are used. Specific alloying elements (such as Ti, Cr, W, V, Zr, etc.) can be uniformly deposited on the diamond surface to form a thin metal layer. Subsequently, a carbide layer is formed during high-temperature treatment. This layer can improve the wettability of both and enhance the interfacial bonding strength. However, the above technologies are inefficient, require high costs for equipment and raw materials, and have complex production processes. They are also very difficult to mass-produce uniformly coated diamonds, especially for diamond fine particles and diamond powder.

[0004] Currently, halide molten salts are mixed with metal powder and diamond particles / powder. After heating, the halide molten salts melt into a liquid phase, promoting the formation of a carbide coating on the surface of the diamond particles / powder by the metal powder. This coating bonds well with the diamond particles / powder and can also achieve good bonding with the substrate. However, due to the uncontrollable reaction conditions and high reaction temperatures, the resulting coating often cracks, separates, and peels off. Since the coating thickness reaches the micron level, it cannot form a coating of suitable thickness for fine diamond particles and diamond powder. Summary of the Invention

[0005] To overcome the problem of uneven carbide coatings prepared on diamond surfaces in the prior art, the present invention aims to provide a method for forming a controllable coating on a diamond surface. This method can prepare a uniform coating on the diamond surface, and the coating has fine grains and the thickness of the coating can be finely controlled, thereby improving the interface and bonding strength between the diamond and the substrate material.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for forming a controllable coating on a diamond surface comprises the following steps:

[0008] The adhesive is mixed with diamond and then mixed evenly with a carbide-forming substance, and then dried under vacuum or a non-oxidizing atmosphere to obtain diamond with a carbide-forming substance attached to its surface;

[0009] The diamond particles with carbide-forming substances attached to their surfaces are uniformly mixed with a halide molten salt to obtain a mixture;

[0010] Press the mixture into blocks;

[0011] The block is calcined in a neutral or reducing atmosphere to form a coating on the diamond surface.

[0012] Furthermore, after the adhesive and diamond are mixed and before being evenly mixed with the carbide-forming material, the diamond is acid-washed and alkali-washed; the non-oxidizing atmosphere is nitrogen or argon.

[0013] Furthermore, the mass ratio of the adhesive to the diamond is 1:(20-300).

[0014] Furthermore, the carbide-forming substance is W, Ti, Cr, V, B, Mo, Zr or Nb.

[0015] Furthermore, the molar ratio of the carbide-forming substance to the diamond is 1:(5-25).

[0016] Furthermore, the drying temperature is 40-300° C., and the drying time is 10-60 min.

[0017] Furthermore, the adhesive is polyvinyl alcohol, silica sol or water glass; the pressing pressure is 10 to 50 MPa, and the pressing time is 0.5 min to 60 min.

[0018] Furthermore, the halide molten salt is a mixture of NaCl, KCl, LiCl, CaCl2, MgCl2, NaF, KF and LiF in a mass ratio of 1:(0.5-2):(0-6):(0-1.8):(0-1.8):(0-1.2):(0-1.2):(0.5-1.2).

[0019] Furthermore, the neutral atmosphere is nitrogen or argon, and the reducing atmosphere is a mixed atmosphere containing hydrogen; the calcination temperature is 400-1000° C., and the calcination time is 30 min-360 min.

[0020] Further, heating is performed to 400-1000° C. at a heating rate of 1-20° C. / min.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention forms a liquid-phase micro-reaction zone through a molten salt system, greatly reducing the reaction temperature and controlling the reaction rate, obtaining a controllable near-nanoscale coating, and realizing the effective preparation of controllable coatings on the surfaces of diamond particles, powders, and sheets, and effectively reducing the heat treatment temperature, and preparing a complete and uniform carbide coating on the diamond surface. The present invention obtains diamond particles / powders coated with carbide-forming material powders through an adhesive, which directly allows the diamond and carbide-forming material to fit closely together. By pressing the treated diamond particles / powders with halide molten salts, a micro-reaction zone with diamond as the skeleton, the surface of the diamond particles / powder as the reaction bed, and the halide molten salt as the fluid medium is obtained, which more efficiently regulates the synthesis of carbides and successfully achieves the effect of regulating the generation of finer carbide grains in the interface layer at a lower reaction temperature. Finally, a carbide coating with a thickness of less than 1 μm and uniformity on the diamond surface is obtained, providing a solution for the further application of diamond-reinforced composite materials.

[0023] Furthermore, the reaction products of carbide-forming substances and diamond particles / powder vary at different temperatures. For example, the reaction between tungsten and diamond can form WC and WC2 phases. By adjusting the temperature and establishing micro-reaction zones, the coating composition and thickness can be flexibly controlled. Unreacted carbide-forming substance particles adhering to the surface can also be subjected to subsequent heat treatment to produce a carbide reaction coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a flow chart of the present invention;

[0025] Figure 2 The X-ray diffraction pattern of the tungsten carbide coated diamond particles prepared in Example 1;

[0026] Figure 3 This is a surface scanning electron microscope image of the tungsten carbide coated diamond particles prepared in Example 1;

[0027] Figure 4 This is a surface grain map of the tungsten carbide coated diamond particles prepared in Example 1;

[0028] Figure 5 This is a surface scanning electron microscope image of titanium carbide coated diamond particles prepared by single calcination in Example 2;

[0029] Figure 6 This is a surface scanning electron microscope image of titanium carbide coated diamond particles prepared by secondary calcination in Example 2. DETAILED DESCRIPTION

[0030] To make the technical solution and improvement effect of the present invention clearer, the operation process of the present invention is further described in detail below. It should be noted that the specific implementation described here is only used to explain the present invention and is not used to limit the present invention.

[0031] In order to solve the problem that under the traditional molten salt method strategy, when the reaction temperature is low, the fluidity and activity of the molten salt system are limited, and the metal powder of the carbide-forming element cannot be fully and efficiently transported to the diamond surface, resulting in uneven coating, which in turn has a negative impact on the interface bonding strength. A method for forming a controllable coating on the diamond surface is adopted. By designing a micro-reaction zone, the distance between the diamond and the metal particles of the carbide-forming element is pre-compressed to shorten the distance between the diamond and the carbide-forming element, so that the metal particles of the carbide-forming element participating in the reaction are effectively transported under the action of the molten salt, and the carbide synthesis is more efficiently regulated, successfully achieving the effect of regulating the generation of finer carbide grains in the interface layer at a lower reaction temperature. Finally, a thin and uniform carbide coating is coated on the diamond surface. The molten salt method adopted in the present invention greatly reduces the reaction temperature under the molten salt system, making it easier for the carbide metal particles to diffuse and flow in the molten salt system at low temperature, providing a reaction basis for the preparation of nano-modified coatings.

[0032] The present invention provides a method for preparing a controllable coating on a diamond surface. By designing a micro-reaction zone, the surface coating can be precisely controlled and prepared at a relatively low temperature. Advantages include a low reaction temperature, fine coating grains, and easy and precise control of coating thickness, which can be less than 1 μm. Low-temperature coating preparation avoids damage to the diamond, significantly improving the interface and bonding strength between the diamond and the matrix material. Diamond particles, powders, flakes, and the like, used as a reinforcing phase, can form a good composite with the matrix. This method is suitable not only for large particles but also for diamonds with diameters of several microns, nearly like powders. Furthermore, the method is convenient, easy to use, and low-cost.

[0033] The specific method is as follows: Pre-treated diamonds are mixed with a trace amount of adhesive in a ball mill to form a sticky film on the surface of the diamond particles. A small amount of carbide-forming metal powder is then mixed evenly with the sticky diamond. After complete drying in a neutral or reducing atmosphere, the metal powder is coated on the surface of the diamond particles / powder. The coated diamond particles are mixed with molten salt in a ball mill to obtain a mixed powder. The mixed powder is then placed in a mold and pressed into a relatively dense block using a press. The block is then placed in a crucible and heated for a period of time in an inert or neutral atmosphere, followed by furnace cooling. Finally, the treated block mixture is placed in water to dissolve excess halide salt and sieve out the diamond particles. The excess carbide-forming substances are then removed by acid washing, cleaned, and filtered through an appropriate filter to remove the diamond particles / powder. If necessary, the filtered diamond particles / powder can be subjected to a slightly higher heat treatment temperature in a neutral or reducing atmosphere for a period of time to promote further complete conversion. The present invention utilizes pre-coating and micro-reaction zones to create a close bond between diamond and the carbide-forming material of carbide-forming elements. This allows for more efficient control of carbide synthesis within the molten salt phase, successfully achieving the goal of precisely controlling the formation of finer carbide grains at the interface layer at relatively low reaction temperatures. This ultimately creates a thin and uniform carbide coating on the diamond surface, fully leveraging the diamond's performance in the field of thermal management materials.

[0034] Specifically, a method of forming a controllable coating on a diamond surface of the present invention comprises the following steps:

[0035] Step 1: Diamond particles with a particle size range of 1 to 1500 μm are first immersed in dilute hydrochloric acid (mass concentration of 5 to 20%), heated to 50 to 80°C, and stirred for 10 to 60 minutes. After separation and washing, they are added to a NaOH solution (mass concentration of 10 to 30%), and then heated to 50 to 80°C in an alkaline solution and stirred for 10 to 60 minutes to remove impurities on the diamond surface. Subsequently, the diamond particles are repeatedly washed with deionized water until their surface is neutral. Finally, the diamond particles are dried to obtain pre-treated diamonds for use;

[0036] Step 2: Mixing a binder (such as polyvinyl alcohol, silica sol or water glass) with the pretreated diamond in a mass ratio of 1: (20-300) and placing them in a ball mill for uniform mixing. Then, adding a carbide-forming element (such as W, Ti, Cr, V, B, Mo, Zr or Nb) in a molar ratio of 1: (5-25) to the pretreated diamond, mixing them uniformly, and drying them at 40-300° C. for 10-60 minutes under vacuum or a non-oxidizing atmosphere to adhere or coat the carbide-forming material powder onto the surface of the diamond particles / powder.

[0037] Step 3: Add the diamond particles obtained in step 2 and the molten salt in a mass ratio of 1:(0.2~4) into a ball mill, and add zirconia balls with a ball-to-material ratio of (1~20):1. Then add a small amount of anhydrous ethanol and mix on a mixer for 6h~32h. Finally, dry the material and separate it from the zirconia balls to obtain a uniformly mixed raw material. The composition of the molten salt is NaCl:KCl:LiCl:CaCl2:MgCl2:NaF:KF:LiF in a mass ratio of 1:(0.5~2):(0~6):(0~1.8):(0~1.8):(0~1.2):(0~1.2):(0.5~1.2).

[0038] Step 4: Place the mixed raw materials into a steel mold, apply a pressure of 10 to 50 MPa on the press to form a relatively dense block, and hold the pressure for 0.5 to 60 minutes before taking out the sample. The formed sample is placed in a corundum crucible for later use;

[0039] Step 5: placing the corundum crucible containing the sample in step 4 into a tube furnace under a neutral atmosphere (such as nitrogen or argon, etc.) or a reducing atmosphere (such as an atmosphere containing hydrogen), heating to 400-1000°C at a heating rate of 1-20°C / min, and keeping the temperature for 30-360min, cooling with the furnace to obtain a treated bulk mixture;

[0040] Step 6: Place the treated block mixture in water to dissolve the excess halide salt, then remove the excess carbide-forming substances through acid washing, and filter out the diamond particles / powder with an appropriate filter after cleaning;

[0041] Step 7: If necessary, place the diamond particles / powder in step 6 in a neutral or reducing atmosphere at a temperature higher than 400-1000°C for a period of time (60 min) to convert the carbide-forming substances on the diamond surface into carbides as much as possible.

[0042] Example 1

[0043] like Figure 1 As shown, the method of forming a controllable coating on a diamond surface in this embodiment includes the following steps:

[0044] Step 1: Immerse 70μm diamond particles in dilute hydrochloric acid (mass concentration of 10%), heat to 60°C, and stir for 10 minutes. After separation and washing, add them to a NaOH solution (mass concentration of 30%), then heat to 70°C in an alkaline solution and stir for 20 minutes to remove impurities on the diamond surface. Subsequently, the diamond particles are repeatedly washed with deionized water until their surface is neutral. Finally, the diamond particles are dried to obtain pre-treated diamonds for use.

[0045] Step 2: Add 20g of the diamond particles treated in Step 1 to 3g of a 5% polyvinyl alcohol solution in a ball mill and mix thoroughly. Then, add the nano-W powder and dry the mixture at 50°C under vacuum for 60 minutes to obtain W-coated diamond particles. The mass ratio of diamond particles to polyvinyl alcohol is 400:3, and the molar ratio of W powder to diamond particles is 1:1.

[0046] Step 3: Take 25g of diamond particles coated with W powder and ternary molten salt (ternary molten salt is a mixture of sodium chloride, lithium chloride and potassium chloride with a molar ratio of 1:1:2) and add them to a ball mill. Then add 150g of zirconia balls and drop 200ml of anhydrous ethanol and wet mix on a mixer for 8 hours to ensure that the raw materials are evenly mixed. After the mixing is completed, the material in the ball mill is dried and separated by sieving with zirconia balls to obtain the raw material for standby use. Among them, the mass ratio of diamond particles to molten salt is 1:0.2;

[0047] Step 4: Take 20g of raw material and put it into a steel mold. Use a hydraulic press to apply a pressure of 30MPa to press it into a relatively dense block. After holding the pressure for 10 minutes, take out the sample and place the pre-pressed sample in a corundum crucible for later use.

[0048] Step 5: Place the corundum crucible containing the sample into a tube furnace, introduce argon gas, set the heating curve of the tube furnace, and heat it from room temperature to 800°C at a heating rate of 3°C / min. Keep it at this temperature for 180 minutes and then cool it down with the furnace.

[0049] Step 6: Remove the crucible, immerse the obtained block mixture in deionized water, heat it to 60°C, and crush the sample with a glass rod. Repeat the washing to remove the halide salt in the product, then wash it with dilute hydrochloric acid to remove excess W powder, and finally wash it repeatedly with deionized water and dry it. Sieve (250 mesh screen) to remove diamond particles, and form a controllable coating on the surface of the diamond particles.

[0050] from Figure 2 It can be seen that the coating is composed of WC / WC2 phase, indicating that the present method can achieve surface modification of diamond at a relatively low temperature.

[0051] from Figure 3 It can be seen that the tungsten carbide is evenly and continuously coated on the diamond surface, with good bonding and no peeling. The coating thickness is less than 1μm, which shows moderate thickness and no cracking or peeling.

[0052] from Figure 4 It can be seen that the grain size of the tungsten carbide coating is small, indicating that lowering the reaction temperature can fully refine the coating grains. Reducing the grain size can effectively improve the bonding between the coating and the diamond, and avoid the peeling of the diamond and the substrate material in the subsequent process.

[0053] Example 2

[0054] The method of forming a controllable coating on a diamond surface in this embodiment includes the following steps:

[0055] Step 1: Immerse 200μm diamond particles in dilute hydrochloric acid (mass concentration of 10%), heat to 50°C, and stir for 10 minutes. After separation and washing, add them to a NaOH solution (mass concentration of 15%), then heat to 60°C in an alkaline solution and stir for 20 minutes to remove impurities on the diamond surface. Subsequently, the diamond particles are repeatedly washed with deionized water until their surface is neutral. Finally, the diamond particles are dried to obtain pre-treated diamonds for use.

[0056] Step 2: Add 10g of diamond particles treated in Step 1 to 4g of 5% polyvinyl alcohol solution in a ball mill and mix thoroughly. Then, add Ti powder and dry the mixture at 50°C in a nitrogen atmosphere for 60 minutes to obtain Ti-coated diamond particles. The mass ratio of diamond particles to polyvinyl alcohol is 50:1, and the molar ratio of Ti powder to diamond particles is 1:20.

[0057] Step 3: Take 6g of diamond particles coated with Ti powder and 0.6g of ternary molten salt (ternary molten salt is a mixture of sodium chloride, lithium chloride and potassium chloride with a molar ratio of 1:1:3) and add them to a ball mill. Then add 6g of zirconia balls and drop a small amount of anhydrous ethanol and wet mix them on a mixer for 12 hours to ensure that the raw materials are evenly mixed. After the mixing is completed, the material in the ball mill is dried and separated by sieving with zirconia balls to obtain the raw material for standby use. Among them, the mass ratio of diamond particles to molten salt is 1:0.1;

[0058] Step 4: Take 10g of raw material and put it into a steel mold with a diameter of 5mm. Apply a pressure of 15MPa on the press to press it into a relatively dense block. After maintaining the pressure for 30 minutes, take out the sample and place the pre-pressed sample in a corundum crucible for later use.

[0059] Step 5: Place the corundum crucible containing the sample into a vacuum furnace, introduce nitrogen, set the temperature rise curve of the vacuum furnace, and heat it from room temperature to 600°C at a heating rate of 5°C / min. Keep it at this temperature for 180 minutes and then cool it down with the furnace.

[0060] Step 6: Remove the crucible, immerse the obtained block mixture in deionized water and heat it to 70°C, and crush the sample with a glass rod. Repeat the washing several times to remove the halide salt in the product, then wash it with dilute hydrochloric acid to remove excess W powder, and finally dry and sieve (150 mesh sieve) to remove diamond particles.

[0061] Step 7: Place the diamond particles processed in step 6 in a nitrogen atmosphere and keep the temperature at 900° C. for 60 minutes to promote the carbide-forming substances in the carbide coating to further transform into carbides as much as possible.

[0062] from Figure 5 It can be seen that after step six treatment, the diamond particles were successfully coated with a layer of nano-scale titanium carbide coating, which was uniform, continuous and had a high coverage rate. However, only a small amount of titanium powder remained on the diamond surface and a very small amount of peeling occurred.

[0063] from Figure 6 It can be seen that after the heat treatment in step seven, the surface coating of the diamond particles is smooth and complete without titanium powder accumulation and peeling.

[0064] Example 3

[0065] Step 1: Immerse 500μm diamond particles in dilute hydrochloric acid (5% by mass), heat to 80°C, and stir for 10 minutes. After separation and washing, add them to a NaOH solution (20% by mass), then heat to 70°C in an alkaline solution and stir for 20 minutes to remove impurities on the diamond surface. Subsequently, the diamond particles are repeatedly washed with deionized water until their surface is neutral. Finally, the diamond particles are dried to obtain pre-treated diamonds for use.

[0066] Step 2: Add 200g of the diamond particles treated in Step 1 to 30g of a 15% silica sol solution in a ball mill and mix thoroughly. Add Cr powder and dry the mixture at 40°C in a nitrogen atmosphere for 60 minutes to obtain Cr-coated diamond particles. The mass ratio of diamond particles to polyvinyl alcohol is 400:9, and the molar ratio of Cr powder to diamond particles is 1:5.

[0067] Step 3: Take 250g of diamond particles coated with Cr powder and ternary molten salt (molten salt is a mixture of NaCl, KCl and LiF in a molar ratio of 1:0.5:1.2) and add them to a ball mill. Then add 1500g of zirconia balls and drop 2000ml of anhydrous ethanol and wet mix on a mixer for 8 hours to ensure that the raw materials are evenly mixed. After the mixing is completed, the material in the ball mill is dried and separated by sieving with zirconia balls to obtain the raw material for later use. Among them, the mass ratio of diamond particles to molten salt is 1:0.2;

[0068] Step 4: Take 20g of raw material and put it into a steel mold. Apply a pressure of 20MPa on a hydraulic press to press it into a relatively dense block. After maintaining the pressure for 60 minutes, take out the sample and place the pre-pressed sample in a corundum crucible for later use.

[0069] Step 5: Place the corundum crucible containing the sample into a tube furnace, introduce argon gas, set the heating curve of the tube furnace, and heat it from room temperature to 700°C at a heating rate of 10°C / min. Keep it at this temperature for 360 minutes and then cool it down with the furnace.

[0070] Step 6: Remove the crucible, immerse the obtained block mixture in deionized water, heat it to 60°C, and crush the sample with a glass rod. Repeat the washing to remove the halide salt in the product, then wash it with dilute hydrochloric acid to remove excess Cr powder, and finally wash it repeatedly with deionized water and dry it. Sieve (250 mesh screen) to remove diamond particles, forming a controllable coating on the surface of the diamond particles.

[0071] Example 4

[0072] Step 1: Immerse 100μm diamond particles in dilute hydrochloric acid (mass concentration of 20%), heat to 50°C, and stir for 20 minutes. After separation and washing, add them to a NaOH solution (mass concentration of 20%), and then heat to 50°C in an alkaline solution and stir for 20 minutes to remove impurities on the diamond surface. Subsequently, the diamond particles are repeatedly washed with deionized water until their surface is neutral. Finally, the diamond particles are dried to obtain pre-treated diamonds for use.

[0073] Step 2: Add 40g of diamond particles treated in Step 1 to 20g of a 10% sodium silicate solution in a ball mill and mix thoroughly. Then, add the V powder and dry at 300°C in an argon atmosphere for 10 minutes to obtain diamond particles coated with V powder. The mass ratio of diamond particles to polyvinyl alcohol is 20:1, and the molar ratio of V powder to diamond particles is 1:15.

[0074] Step 3: Take 100g of diamond particles coated with V powder and binary molten salt (molten salt is a mixture of NaCl and KCl in a molar ratio of 1:2) and add them to a ball mill. Then add 600g of zirconia balls and drop 800ml of anhydrous ethanol and wet mix on a mixer for 8 hours to ensure that the raw materials are evenly mixed. After the mixing is completed, the material in the ball mill is dried and separated from the zirconia balls by sieving to obtain the raw material for later use. The mass ratio of diamond particles to molten salt is 1:4;

[0075] Step 4: Take 20g of raw material and put it into a steel mold. Apply 50MPa pressure on the hydraulic press to press it into a relatively dense block. After holding the pressure for 5 minutes, take out the sample and place the pre-pressed sample in a corundum crucible for later use.

[0076] Step 5: Place the corundum crucible containing the sample into a tube furnace, introduce argon gas, set the heating curve of the tube furnace, and heat it from room temperature to 800°C at a heating rate of 10°C / min. Keep it at this temperature for 30 minutes and then cool it down with the furnace.

[0077] Step 6: Remove the crucible, immerse the obtained block mixture in deionized water, heat it to 60°C, and crush the sample with a glass rod. Repeat the washing to remove the halide salt in the product, then wash it with dilute hydrochloric acid to remove excess V powder, and finally wash it repeatedly with deionized water and dry it. Sieve (250 mesh screen) to remove diamond particles, forming a controllable coating on the surface of the diamond particles.

[0078] Example 5

[0079] Step 1: Immerse 1μm diamond particles in dilute hydrochloric acid (mass concentration of 10%), heat to 60°C, and stir for 30 minutes. After separation and washing, add them to a NaOH solution (mass concentration of 10%), then heat to 80°C in an alkaline solution and stir for 10 minutes to remove impurities on the diamond surface. Subsequently, the diamond particles are repeatedly washed with deionized water until their surface is neutral. Finally, the diamond particles are dried to obtain pre-treated diamonds for use.

[0080] Step 2: 50g of diamond particles treated in step 1 were added to 4g of a 10% water glass solution in a ball mill and mixed evenly. Mo powder was then added to the mixture and dried at 100°C under vacuum for 30 minutes to obtain diamond particles coated with Mo powder. The mass ratio of diamond particles to polyvinyl alcohol was 125:1, and the molar ratio of Mo powder to diamond particles was 1:20.

[0081] Step 3: Take 50g of diamond particles coated with Mo powder and binary molten salt (molten salt is a mixture of KCl and LiCl in a molar ratio of 1:3) and add them to a ball mill. Then add 300g of zirconia balls and drop 400ml of anhydrous ethanol and wet mix on a mixer for 8 hours to ensure that the raw materials are evenly mixed. After the mixing is completed, the material in the ball mill is dried and separated by sieving with zirconia balls to obtain the raw material for later use. Among them, the mass ratio of diamond particles to molten salt is 1:1;

[0082] Step 4: Take 10g of raw material and put it into a steel mold. Apply a pressure of 25MPa on a hydraulic press to press it into a relatively dense block. After maintaining the pressure for 40 minutes, take out the sample and place the pre-pressed sample in a corundum crucible for later use.

[0083] Step 5: Place the corundum crucible containing the sample into a vacuum atmosphere furnace, introduce nitrogen, set the furnace heating curve, and heat it from room temperature to 1000°C at a heating rate of 20°C / min. Keep it at this temperature for 240 minutes and then cool it with the furnace.

[0084] Step 6: Take out the crucible, immerse the obtained block mixture in deionized water, heat it to 60°C, and crush the sample with a glass rod. Repeat the washing to remove the halide in the product, then wash it with dilute hydrochloric acid to remove excess Mo powder, and finally wash it repeatedly with deionized water and dry it. Sieve (250 mesh screen) to remove diamond particles, forming a controllable coating on the surface of the diamond particles.

[0085] Example 6

[0086] Step 1: Immerse 1500μm diamond particles in dilute hydrochloric acid (mass concentration of 10%), heat to 60°C, and stir for 30 minutes. After separation and washing, add them to a NaOH solution (mass concentration of 10%), then heat to 80°C in an alkaline solution and stir for 10 minutes to remove impurities on the diamond surface. Subsequently, the diamond particles are repeatedly washed with deionized water until their surface is neutral. Finally, the diamond particles are dried to obtain pre-treated diamonds for use.

[0087] Step 2: 600g of diamond particles treated in Step 1 were added to a 5% polyvinyl alcohol solution in a ball mill and mixed thoroughly. Nb powder was then added to the mixture and dried at 80°C in a nitrogen atmosphere for 50 minutes to obtain diamond particles coated with Nb powder. The mass ratio of diamond particles to polyvinyl alcohol was 300:1, and the molar ratio of Nb powder to diamond particles was 1:25.

[0088] Step 3: Take 200g of diamond particles coated with Nb powder and quaternary molten salt (molten salt is a mixture of NaCl, KCl, LiCl, and CaCl2 in a molar ratio of 1:1.5:1:0.5) and add them to a ball mill. Then add 1500g of zirconia balls and drop 2000ml of anhydrous ethanol and wet mix on a mixer for 8 hours to ensure that the raw materials are evenly mixed. After the mixing is completed, the material in the ball mill is dried and separated by sieving the zirconia balls to obtain the raw material for later use. Among them, the mass ratio of diamond particles to molten salt is 1:2;

[0089] Step 4: Take 5g of raw material and put it into a steel mold. Apply a pressure of 40MPa on a hydraulic press to press it into a relatively dense block. After holding the pressure for 10 minutes, take out the sample and place the pre-pressed sample in a corundum crucible for later use.

[0090] Step 5: Place the corundum crucible containing the sample into a vacuum furnace, introduce argon gas, set the heating curve of the tube furnace, and heat it from room temperature to 900°C at a heating rate of 1°C / min. Keep it at this temperature for 100 minutes and then cool it down with the furnace.

[0091] Step 6: Remove the crucible, immerse the obtained block mixture in deionized water, heat it to 60°C, and crush the sample with a glass rod. Repeat the washing to remove the halide salt in the product, then wash it with dilute hydrochloric acid to remove excess Nb powder, and finally wash it repeatedly with deionized water and dry it. Sieve (250 mesh screen) to remove diamond particles, forming a controllable coating on the surface of the diamond particles.

[0092] The present invention achieves uniform nanocarbide coating on the diamond surface through the molten salt method at a relatively low temperature, which can avoid damage to the diamond surface caused by high-temperature processes under traditional strategies, as well as the negative impact of uneven coating on interface bonding at low temperatures. It can effectively optimize the interface structure, significantly improve the wettability between diamond and matrix materials, greatly enhance the thermal conductivity performance of the composite material, and give full play to the application potential of diamond particles / powder in the field of thermal management materials.

[0093] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principles of the present invention. These improvements should also be regarded as the scope of protection of the present invention.

Claims

1. A method for forming a controllable coating on a diamond surface, characterized in that: The following steps are involved: The adhesive is mixed with diamond and then mixed evenly with a carbide-forming substance, and then dried under vacuum or a non-oxidizing atmosphere to obtain diamond with the carbide-forming substance attached to the surface; The diamond particles with carbide-forming substances attached to their surfaces are uniformly mixed with a halide molten salt to obtain a mixture; Press the mixture into blocks; The block is calcined in a neutral or reducing atmosphere to form a coating on the diamond surface.

2. The method for forming a controllable coating on a diamond surface according to claim 1, wherein: After the adhesive and diamond are mixed and then mixed evenly with the carbide-forming material, the diamond is acid-washed and alkaline-washed; the non-oxidizing atmosphere is nitrogen or argon.

3. The method for forming a controllable coating on a diamond surface according to claim 1, wherein: The mass ratio of the adhesive to the diamond is 1:(20-300).

4. The method for forming a controllable coating on a diamond surface according to claim 1, wherein: The carbide-forming substance is W, Ti, Cr, V, B, Mo, Zr or Nb.

5. The method for forming a controllable coating on a diamond surface according to claim 1, wherein: The molar ratio of carbide-forming material to diamond is 1:(5-25).

6. The method for forming a controllable coating on a diamond surface according to claim 1, wherein: The drying temperature is 40-300°C and the drying time is 10-60 minutes.

7. The method for forming a controllable coating on a diamond surface according to claim 1, wherein: The adhesive is polyvinyl alcohol, silica sol or water glass; the pressing pressure is 10 to 50 MPa, and the pressing time is 5 to 60 minutes.

8. The method for forming a controllable coating on a diamond surface according to claim 1, wherein: The halide molten salt is a mixture of NaCl, KCl, LiCl, CaCl2, MgCl2, NaF, KF and LiF in a mass ratio of 1:(0.5-2):(0-6):(0-1.8):(0-1.8):(0-1.2):(0-1.2):(0.5-1.2).

9. The method for forming a controllable coating on a diamond surface according to claim 1, wherein: The neutral atmosphere is nitrogen or argon, and the reducing atmosphere is a mixed atmosphere containing hydrogen; the calcination temperature is 400-1000° C., and the calcination time is 0.5 min-360 min.

10. The method for forming a controllable coating on a diamond surface according to claim 9, wherein: Heat to 400-1000°C at a heating rate of 1-20°C / min.

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