A method of high temperature high pressure welding of diamond

Abstract

The high-temperature and high-pressure welding method for diamond described in this invention uses diamond film or diamond block as raw material, and the process steps are as follows: (1) Cut the raw material into at least two initial samples of the required shape and size, ultrasonically clean the initial samples to remove surface impurities, and then perform surface graphitization treatment to obtain the samples to be welded; (2) Place the samples to be welded in the package with the welding surface facing the welding surface, or place the samples to be welded in the package with the welding surface facing the welding surface and fill the gap between the welding surfaces with welding flux, and then encapsulate them after compaction to form the blank to be welded; (3) Place the blank to be welded into a static high-pressure device, and weld for 60 to 3600 seconds under the conditions of pressure of 6.5 to 25 GPa and temperature of 1800 to 2500℃. After the welding time is reached, cool down and depressurize to room temperature and normal pressure, and then take out the encapsulated diamond after high-temperature and high-pressure welding, and remove the encapsulation material and impurities attached to the diamond surface by cleaning.

Description

Technical Field

[0001] This invention belongs to the field of synthetic diamond technology, and specifically relates to a method for preparing thick-film / large-size diamond. Background Technology

[0002] Due to its excellent properties in terms of force, heat, light, and electricity, diamond has become a crucial functional material. As a result, the demand for thick-film / large-size diamond is increasing.

[0003] Currently, the main methods for preparing synthetic diamonds are high-temperature high-pressure (HPHT) and chemical vapor deposition (CVD). The HPHT method uses a static high-pressure device to convert graphite or other non-diamond carbon into diamond under high temperature and pressure. During this process, the breaking and reconnection of carbon-carbon covalent bonds requires overcoming a high energy barrier. Therefore, to lower the activation energy, a catalyst must be introduced during the HPHT synthesis. This makes it difficult to control the impurity content of the resulting diamond, and the preparation of large-particle diamonds requires a long holding time. For example, CN202110100312.X discloses a method for growing large-particle diamonds under high temperature and pressure. A seed crystal is placed in a catalyst and molded to obtain a catalyst-encapsulated seed crystal composite. Then, a carbon source is used to encapsulate the composite to form a diamond growth preform. The diamond preform is then grown under high temperature and pressure using a static high-pressure device. According to its embodiments, the holding time is 2.5–6 hours. Chemical vapor deposition (CVD) utilizes a chemical reaction between a gaseous precursor and a substrate under specific conditions to deposit a diamond film. Therefore, the main problems with CVD in preparing thick / large-size diamond films are the difficulty in obtaining large-size substrates, the long deposition time, and the inevitable introduction of impurity gases such as N and H during the deposition process as the thickness increases, which severely affects the performance of the diamond film (see "Research Status of Preparation and Processing of Large-Size Single-Crystal Diamond Substrates for Semiconductors," Liu Junjie et al., Journal of Artificial Crystals, Vol. 52, No. 10, October 2023). Summary of the Invention

[0004] The purpose of this invention is to provide a high-temperature and high-pressure welding method for diamond, so as to solve the technical problems of difficult preparation of thick-film / large-size diamond, long preparation cycle and high impurity content.

[0005] The high-temperature and high-pressure welding method for diamond described in this invention uses diamond film or diamond block as raw material, and the process steps are as follows:

[0006] (1) Preparation of the sample to be welded

[0007] The raw material is cut and processed into at least two initial samples of the required shape and size. Then, the initial samples are ultrasonically cleaned to remove surface impurities and then subjected to surface graphitization treatment to obtain at least two samples to be welded.

[0008] (2) Forming the weld blank

[0009] Using a chemically stable material with a purity of ≥99% as the packaging material, the packaging material is made into a package that matches the shape, size and quantity of the sample to be welded; the sample to be welded prepared in step (1) is placed in the package with the welding surface facing the welding surface, and after being compacted, it is sealed to form a welded blank; or the sample to be welded prepared in step (1) is placed in the package with the welding surface facing the welding surface and welding flux is filled between the welding surfaces, and after being compacted, it is sealed to form a welded blank.

[0010] (3) High-temperature and high-pressure welding and removal of wrapping materials and impurities

[0011] The weld blank formed in step (2) is placed into the assembly of the static high pressure device, and then the assembly containing the weld blank is placed into the static high pressure device. Welding is then performed for 60s to 3600s under a pressure of 6.5GPa to 25GPa and a temperature of 1800℃ to 2500℃. After the welding time is reached, the temperature and pressure are reduced to room temperature and normal pressure. Then the encapsulated diamond after high temperature and high pressure welding is taken out, and the encapsulation material and impurities on the surface of the diamond are removed by cleaning.

[0012] In the above method, the thickness of the raw diamond film and the size of the diamond block are not limited because, in terms of the high temperature and high pressure welding mechanism between diamonds (using the bonding and growth between diamond grains under high temperature and high pressure to connect multiple diamonds into a whole), there are no requirements for the thickness of the diamond film to be welded and the size of the diamond block. However, the thickness of the diamond film prepared by the existing technology is generally less than 2 mm, and the particle size of the diamond block is generally less than 2 mm.

[0013] In the above method, the raw material diamond film or diamond bulk material can be either single crystal or polycrystalline.

[0014] The surface graphitization treatment of the initial sample in step (1) of the above method includes three methods: laser etching, vacuum heat treatment, and high temperature and high pressure treatment. However, the specific method used should be based on whether the raw material of the initial sample has been polished. When the raw material of the initial sample is an unpolished single-crystal or polycrystalline diamond film or diamond bulk, the graphitization treatment of the initial sample surface in step (1) can be performed using any one of the following methods: laser etching, vacuum heat treatment, or high temperature and high pressure treatment. Alternatively, a combination of vacuum heat treatment followed by laser etching, or a combination of high temperature and high pressure treatment followed by laser etching can be used. When the raw material of the initial sample is a polished single-crystal or polycrystalline diamond film or diamond bulk, the graphitization treatment of the initial sample surface can be performed using vacuum heat treatment or high temperature and high pressure treatment. Alternatively, a combination of vacuum heat treatment followed by laser etching, or a combination of high temperature and high pressure treatment followed by laser etching can be used.

[0015] The laser etching method uses a laser frequency of 10Hz to 40Hz, a laser power of 5W to 100W, and the laser etching pattern can be linear or nonlinear; the vacuum heat treatment method has a vacuum degree of <10. -2 Pa, the heat treatment temperature is 800℃~1700℃, and the heat treatment time is 10min~90min; the high temperature and high pressure treatment method has a treatment pressure of 1GPa~5GPa, a treatment temperature of 1400℃~1800℃, and a treatment time of 10min~60min.

[0016] In the above method, the encapsulation material in step (2) is preferably tantalum (Ta), rhenium (Re), niobium (Nb), molybdenum (Mo), or platinum (Pt).

[0017] In the above method, the welding agent in step (2) is graphite powder or diamond powder, preferably diamond powder, because diamond powder can prevent the weld from shrinking.

[0018] In step (3) of the above method, the pressure increase rate from atmospheric pressure to welding pressure and the pressure decrease rate from welding pressure to atmospheric pressure are 3GPa / h to 5GPa / h, and the temperature increase rate from room temperature to welding temperature and the temperature decrease rate from welding temperature to room temperature are 100℃ / min to 300℃ / min.

[0019] In step (3) of the above method, acid and anhydrous ethanol are used to clean and remove the coating material and impurities attached to the diamond surface; the acid is at least one of nitric acid solution, hydrofluoric acid solution, hydrochloric acid solution, and sulfuric acid solution; the coating material is first removed by soaking in acid, and then the impurities attached to the diamond surface are removed by ultrasonic cleaning with anhydrous ethanol.

[0020] Compared with the prior art, the present invention has the following beneficial technical effects:

[0021] (1) The method described in this invention uses diamond films or diamond blocks obtained by high temperature and high pressure (HPHT) method and chemical vapor deposition (CVD) method as raw materials. Multiple diamonds are connected into one piece by high temperature and high pressure welding, utilizing the bonding or growth between diamond grains under high temperature and high pressure conditions, thereby obtaining thick diamond films / large-size diamonds, providing a new technical solution for the preparation of thick diamond films / large-size diamonds.

[0022] (2) Since the sample to be welded in the method of the present invention is prepared from raw diamond film or diamond block, the sample to be welded is placed in the package and then sealed after compaction, or the sample to be welded is placed in the package and the welding agent is filled between the welding surfaces, and then sealed after compaction. The package is made of chemically stable material with a purity of ≥99%, and the welding agent is graphite powder or diamond powder. Therefore, the introduction of impurities can be avoided during the high temperature and high pressure welding process, and the purity of the welded diamond is guaranteed.

[0023] (3) The welding time of the method described in this invention is 60s to 3600s, which greatly shortens the preparation cycle compared with the existing high temperature and high pressure (HPHT) method and chemical vapor deposition (CVD) method for preparing diamond thick film / large-size diamond. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the assembly of the static high-pressure device. In the diagram, 1 is a magnesium oxide octahedron, 2 is a zirconium oxide plug, 3 is a zirconium oxide tube, 4 is a heating tantalum tube, 5 is the sample to be welded, 6 is the inclusion body, and 7 is hexagonal boron nitride.

[0025] Figure 2 Optical images of the initial sample of a non-transparent diamond film;

[0026] Figure 3 Comparison of optical photographs of the initial non-transparent diamond film sample and the welded sample obtained by surface graphitization treatment using laser etching.

[0027] Figure 4 The images show a comparison of optical photographs of the initial transparent diamond film sample and the welded sample obtained by surface graphitization treatment using the high temperature and high pressure method. In Figure (a), the initial transparent diamond film sample is shown, and in Figure (b), the welded sample obtained by surface graphitization treatment using the high temperature and high pressure method is shown.

[0028] Figure 5 Optical images of diamond thick films obtained by high-temperature and high-pressure welding in Example 1;

[0029] Figure 6 Optical images of diamond thick films obtained by high-temperature and high-pressure welding in Example 2;

[0030] Figure 7 Optical images of diamond thick films obtained by high-temperature and high-pressure welding in Example 3;

[0031] Figure 8 The image shows the SEM image of the diamond thick film weld obtained by high temperature and high pressure welding in Example 1. In Figure (b), the image is an enlarged view of the white framed part of Figure (a).

[0032] Figure 9 The image shows the SEM image of the diamond thick film weld obtained by high temperature and high pressure welding in Example 2. In Figure (b), the image is an enlarged view of the white framed part of Figure (a).

[0033] Figure 10 The image shows the SEM image of the diamond thick film weld obtained by high temperature and high pressure welding in Example 3. In Figure (b), the image is an enlarged view of the white framed part of Figure (a).

[0034] Figure 11 The image shows the XRD pattern of the diamond thick film weld obtained by high temperature and high pressure welding in Example 1.

[0035] Figure 12 The image shows the XRD pattern of the diamond thick film weld obtained by high temperature and high pressure welding in Example 2.

[0036] Figure 13 The image shows the XRD pattern of the diamond thick film weld obtained by high temperature and high pressure welding in Example 3. Detailed Implementation

[0037] The high-temperature and high-pressure welding method for diamond according to the present invention will be further described below through embodiments and in conjunction with the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] In the following embodiments, the static high pressure device is a domestically produced hinged six-sided top pressure machine, model DS 6×8MN, manufactured by Zhangjiakou Prospecting Machinery Factory; the diamond film used as raw material is purchased from the market.

[0039] Example 1

[0040] In this embodiment, the raw material is an opaque CVD polycrystalline diamond film with a thickness of 1.0 mm and an unpolished surface. The process steps are as follows:

[0041] (1) Preparation of the sample to be welded

[0042] The raw material was cut into three circular initial samples with a diameter of 3.0 mm and a thickness of 1.0 mm. Then, each initial sample was ultrasonically cleaned with anhydrous ethanol to remove surface impurities. After the anhydrous ethanol on the surface of each initial sample evaporated naturally, a laser etching machine was used to graphitize the two circular surfaces at both ends of one initial sample to form a weldable sample with two welding surfaces. The circular surfaces at one end of the other two initial samples were graphitized to form two weldable samples with only one welding surface. The laser etching process was: frequency 40 Hz, power 45 W, and the etching pattern was linear stripes with a spacing of 0.01 mm.

[0043] (2) Forming the weld blank

[0044] Using 0.025mm thick tantalum foil as the wrapping material, the wrapping material is made into a wrapping body that matches the shape, size and quantity of the flux sample; the three samples to be welded prepared in step (1) are placed in the wrapping body with the welding surfaces facing each other, and the welding flux is filled between the welding surfaces. After compaction, the wrapping body is sealed to form a welding blank. The welding flux is 8000 mesh ultrafine graphite powder with a filling thickness of 0.2mm.

[0045] (3) High-temperature and high-pressure welding and removal of wrapping materials and impurities

[0046] The weld blank formed in step (2) is placed into the assembly of the static high pressure device, and then the assembly containing the weld blank is placed into the static high pressure device. The pressure is increased to 15 GPa at a rate of 5 GPa / h and kept constant. The temperature is then increased to 2100℃ at a rate of 300℃ / min and held for 60s. After the welding time is reached, the temperature is first reduced to room temperature at a rate of 300℃ / min, and then the pressure is reduced to normal pressure at a rate of 3 GPa / h. Then the encapsulated diamond after high temperature and high pressure welding is taken out and placed in a mixed acid composed of nitric acid and hydrofluoric acid (the volume ratio of nitric acid to hydrofluoric acid is 3:1) for 8 hours to remove the encapsulating material. Then the impurities attached to the diamond surface are removed by ultrasonic cleaning with anhydrous ethanol, thus obtaining the welded diamond thick film.

[0047] Optical photographs of the polished diamond thick film are shown below. Figure 5 SEM images of the diamond thick film weld joints are shown below. Figure 8 The XRD pattern of the diamond thick film weld joint is shown in [reference needed]. Figure 11 .from Figure 5 It can be seen that the three welded samples were formed into an integrated structure through high-temperature and high-pressure welding; from Figure 8 It can be seen that the weld thickness at the weld joint is approximately 50 μm; from Figure 11 It can be seen that the composition of the weld joint is pure phase diamond.

[0048] Example 2

[0049] In this embodiment, the raw material is an opaque CVD polycrystalline diamond film with a thickness of 1.0 mm and an unpolished surface. The process steps are as follows:

[0050] (1) Preparation of the sample to be welded

[0051] The raw material was cut into two circular initial samples with a diameter of 3.0 mm and a thickness of 1.0 mm. Then, each initial sample was ultrasonically cleaned with anhydrous ethanol to remove surface impurities. After the anhydrous ethanol on the surface of each initial sample evaporated naturally, a laser etching machine was used to graphitize one end of the circular surface of the two initial samples to form two welded samples with only one welding surface. The laser etching process was: frequency 40 Hz, power 45 W, and the etching pattern was linear stripes with a spacing of 0.01 mm.

[0052] (2) Forming the weld blank

[0053] Using 0.025mm thick tantalum foil as the wrapping material, the wrapping material is made into a wrapping body that matches the shape, size and quantity of the flux sample; the two samples to be welded prepared in step (1) are placed in the wrapping body with the welding surfaces facing each other, and the flux is filled between the welding surfaces. After compaction, the wrapping body is sealed to form a welded blank; the flux is composed of 10μm diamond powder and 0.5μm diamond powder in a mass ratio of 6:4. The two diamond powders are mixed in a mixer for 8 hours to ensure thorough mixing, and then pre-compacted under 3GPa pressure as the flux for filling, with a filling thickness of 0.2mm;

[0054] (3) High-temperature and high-pressure welding and removal of wrapping materials and impurities

[0055] The weld blank formed in step (2) is placed into the assembly of the static high pressure device, and then the assembly containing the weld blank is placed into the static high pressure device. The pressure is increased to 10 GPa at a rate of 5 GPa / h and kept constant. The temperature is then increased to 1800℃ at a rate of 300℃ / min and held for 300s. After the welding time is reached, the temperature is first reduced to room temperature at a rate of 300℃ / min, and then the pressure is reduced to atmospheric pressure at a rate of 3 GPa / h. The encapsulated diamond after high temperature and high pressure welding is then taken out and placed in a mixed acid composed of nitric acid and hydrofluoric acid (the volume ratio of nitric acid to hydrofluoric acid is 3:1) for 8 hours to remove the encapsulating material. Then, the impurities attached to the diamond surface are removed by ultrasonic cleaning with anhydrous ethanol, thus obtaining the welded diamond thick film.

[0056] Optical photographs of the polished diamond thick film are shown below. Figure 6 SEM images of the diamond thick film weld joints are shown below. Figure 9 The XRD pattern of the diamond thick film weld joint is shown in [reference needed]. Figure 12 .from Figure 6 It can be seen that the two samples were welded together under high temperature and high pressure to form an integrated structure; from Figure 9 It can be seen that the weld thickness at the weld joint is approximately 200 μm; from Figure 12 It can be seen that the composition of the weld joint is pure phase diamond.

[0057] Example 3

[0058] In this embodiment, the raw material is an opaque CVD polycrystalline diamond film with a thickness of 1.0 mm and an unpolished surface. The process steps are as follows:

[0059] (1) Preparation of the sample to be welded

[0060] The raw material was cut into two circular initial samples with a diameter of 3.0 mm and a thickness of 1.0 mm. Then, each initial sample was ultrasonically cleaned with anhydrous ethanol to remove surface impurities. After the anhydrous ethanol on the surface of each initial sample evaporated naturally, a laser etching machine was used to graphitize one end of the circular surface of the two initial samples to form two welded samples with only one welding surface. The laser etching process was: frequency 40 Hz, power 45 W, and the etching pattern was linear stripes with a spacing of 0.01 mm.

[0061] (2) Forming the weld blank

[0062] Using 0.025mm thick tantalum foil as the wrapping material, the wrapping material is made into a wrapping body that matches the shape, size and quantity of the flux sample; the two samples to be welded prepared in step (1) are placed in the wrapping body with the welding surface facing the welding surface, and after being compacted, they are sealed to form a welding blank;

[0063] (3) High-temperature and high-pressure welding and removal of wrapping materials and impurities

[0064] The weld blank formed in step (2) is placed into the assembly of the static high pressure device, and then the assembly containing the weld blank is placed into the static high pressure device. The pressure is increased to 15 GPa at a rate of 5 GPa / h and kept constant. The temperature is increased to 2100℃ at a rate of 300℃ / min and held for 600s. After the welding time is reached, the temperature is first reduced to room temperature at a rate of 300℃ / min, and then the pressure is reduced to normal pressure at a rate of 3 GPa / h. Then the encapsulated diamond after high temperature and high pressure welding is taken out and placed in a mixed acid composed of nitric acid and hydrofluoric acid (the volume ratio of nitric acid to hydrofluoric acid is 3:1) for 8 hours to remove the encapsulating material. Then the impurities attached to the diamond surface are removed by ultrasonic cleaning with anhydrous ethanol, and the welded diamond thick film is obtained.

[0065] Optical photographs of the polished diamond thick film are shown below. Figure 7SEM images of the diamond thick film weld joints are shown below. Figure 10 The XRD pattern of the diamond thick film weld joint is shown in [reference needed]. Figure 13 .from Figure 7 It can be seen that the two samples were welded together under high temperature and high pressure to form an integrated structure; from Figure 10 It can be seen that the weld thickness at the weld joint is approximately 20 μm; from Figure 13 It can be seen that the composition of the weld joint is pure phase diamond.

[0066] Example 4

[0067] In this embodiment, the raw material is an opaque CVD polycrystalline diamond film with a thickness of 1.0 mm and an unpolished surface. The process steps are as follows:

[0068] (1) Preparation of the sample to be welded

[0069] The raw material was cut and processed into four circular initial samples with a diameter of 3.5 mm and a thickness of 1.0 mm. Then, each initial sample was ultrasonically cleaned with anhydrous ethanol to remove surface impurities. After the anhydrous ethanol on the surface of each initial sample evaporated naturally, the surface of the four initial samples was graphitized using a high temperature and high pressure method to obtain four samples to be welded. The high temperature and high pressure graphitization process used a domestic hinged six-sided press. Each initial sample was wrapped with graphite and placed in the hinged six-sided press. The processing pressure was 2 GPa and the processing temperature was 1700℃. The temperature and pressure rise and fall process was as follows: the pressure was increased to 2 GPa at a pressurization rate of 0.2 GPa / min and kept constant, then the temperature was increased to 1700℃ at a heating rate of 200℃ / min and held for 30 min. After the holding period, the temperature was reduced to room temperature at a cooling rate of 200℃ / min, and then the pressure was reduced to atmospheric pressure at a depressurization rate of 0.2 GPa / min.

[0070] (2) Forming the weld blank

[0071] Using 0.025mm thick tantalum foil as the wrapping material, the wrapping material is made into a wrapping body that matches the shape, size and quantity of the flux sample; the four samples to be welded prepared in step (1) are placed in the wrapping body with the welding surface facing the welding surface, and after being compacted, they are sealed to form a welding blank;

[0072] (3) High-temperature and high-pressure welding and removal of wrapping materials and impurities

[0073] The weld blank formed in step (2) is placed into the assembly of the static high pressure device, and then the assembly containing the weld blank is placed into the static high pressure device. The pressure is increased to 10 GPa at a rate of 5 GPa / h and kept constant. The temperature is then increased to 1800℃ at a rate of 300℃ / min and held for 1800s. After the welding time is reached, the temperature is first reduced to room temperature at a rate of 300℃ / min, and then the pressure is reduced to normal pressure at a rate of 3 GPa / h. Then the encapsulated diamond after high temperature and high pressure welding is taken out and placed in a mixed acid composed of nitric acid and hydrofluoric acid (the volume ratio of nitric acid to hydrofluoric acid is 3:1) at 100℃ for 6 hours to remove the encapsulating material. Then the impurities attached to the diamond surface are removed by ultrasonic cleaning with anhydrous ethanol, thus obtaining the welded diamond thick film.

[0074] Example 5

[0075] In this embodiment, the raw material is a 1.0 mm thick transparent CVD single-crystal diamond film with an unpolished surface, and the process steps are as follows:

[0076] (1) Preparation of the sample to be welded

[0077] The raw material was cut into two circular initial samples with a diameter of 3.5 mm and a thickness of 1.0 mm. Each initial sample was then ultrasonically cleaned with anhydrous ethanol to remove surface impurities. After the anhydrous ethanol on the surface of the cleaned initial samples evaporated naturally, the surfaces of the two initial samples were graphitized using a combination of high temperature and high pressure followed by laser etching to obtain two samples to be welded. The graphitization process was as follows: The high temperature and high pressure graphitization process used a domestically produced hinged six-sided press. Each initial sample was wrapped in graphite and placed in the hinged six-sided press. The pressure was first increased to 2 GPa at a rate of 0.2 GPa / min and maintained thereafter, and then increased at a rate of 200℃ / min. The temperature was raised to 1700℃ and held for 30 minutes. After holding, the temperature was lowered to room temperature at a rate of 200℃ / min, and then the pressure was reduced to atmospheric pressure at a rate of 0.2 GPa / min. The diamond film treated with high temperature and high pressure graphitization was placed in a mixed acid composed of nitric acid and hydrofluoric acid (volume ratio of nitric acid to hydrofluoric acid is 3:1) for acid washing to remove surface impurities, and then ultrasonically cleaned with anhydrous ethanol. After the anhydrous ethanol on the surfaces of the two diamond films evaporated, one end of each circular surface was treated with a laser etching machine to form a welding surface. The laser etching frequency was 40 Hz, the power was 45 W, and the etching pattern was linear stripes with a spacing of 0.1 mm.

[0078] (2) Forming the weld blank

[0079] Using 0.025mm thick tantalum foil as the wrapping material, the wrapping material is made into a wrapping body that matches the shape, size and quantity of the flux sample; the two samples to be welded prepared in step (1) are placed in the wrapping body with the welding surface facing the welding surface, and after being compacted, they are sealed to form a welding blank;

[0080] (3) High-temperature and high-pressure welding and removal of wrapping materials and impurities

[0081] The weld blank formed in step (2) is placed into the assembly of the static high pressure device, and then the assembly containing the weld blank is placed into the static high pressure device. The pressure is increased to 12 GPa at a rate of 5 GPa / h and kept constant. The temperature is then increased to 2000℃ at a rate of 300℃ / min and held for 3600s. After the welding time is reached, the temperature is first reduced to room temperature at a rate of 300℃ / min, and then the pressure is reduced to normal pressure at a rate of 3 GPa / h. Then the encapsulated diamond after high temperature and high pressure welding is taken out and placed in a mixed acid composed of nitric acid and hydrofluoric acid (the volume ratio of nitric acid to hydrofluoric acid is 3:1) at 100℃ for 6 hours to remove the encapsulating material. Then the impurities attached to the diamond surface are removed by ultrasonic cleaning with anhydrous ethanol, and the welded diamond thick film is obtained.

[0082] Example 6

[0083] In this embodiment, the raw material is an opaque polycrystalline diamond film prepared by the high-temperature, high-pressure (HPHT) method with a thickness of 1.0 mm and an unpolished surface. The process steps are as follows:

[0084] (1) Preparation of the sample to be welded

[0085] The raw material was cut into four circular initial samples with a diameter of 4.0 mm and a thickness of 1.0 mm. Then, each initial sample was ultrasonically cleaned with anhydrous ethanol to remove surface impurities. After the anhydrous ethanol on the surface of each initial sample evaporated naturally, a laser etching machine was used to graphitize the circular surfaces at both ends of two of the initial samples to form weldable samples with two welding surfaces. The circular surfaces at one end of the other two initial samples were graphitized to form weldable samples with only one welding surface. The laser etching process was: frequency 40 Hz, power 45 W, and the etching pattern was linear stripes with a spacing of 0.01 mm.

[0086] (2) Forming the weld blank

[0087] Using 0.025mm thick tantalum foil as the wrapping material, the wrapping material is made into a wrapping body that matches the shape, size and quantity of the flux sample; the four samples to be welded prepared in step (1) are placed in the wrapping body with the welding surface facing the welding surface, and after being compacted, they are sealed to form a welding blank;

[0088] (3) High-temperature and high-pressure welding and removal of wrapping materials and impurities

[0089] The weld blank formed in step (2) is placed into the assembly of the static high pressure device, and then the assembly containing the weld blank is placed into the static high pressure device. The pressure is increased to 16 GPa at a rate of 5 GPa / h and kept constant. The temperature is then increased to 2200℃ at a rate of 300℃ / min and held for 600s. After the welding time is reached, the temperature is first reduced to room temperature at a rate of 300℃ / min, and then the pressure is reduced to atmospheric pressure at a rate of 3 GPa / h. The encapsulated diamond after high temperature and high pressure welding is then taken out and placed in a mixed acid composed of nitric acid and hydrofluoric acid (the volume ratio of nitric acid to hydrofluoric acid is 3:1) at 100℃ for 6 hours to remove the encapsulating material. Then, the impurities attached to the diamond surface are removed by ultrasonic cleaning with anhydrous ethanol, thus obtaining the welded diamond thick film.

Claims

1. A high-temperature, high-pressure welding method for diamond, characterized in that... Using diamond film or diamond bulk as raw material, the process steps are as follows: (1) Preparation of the sample to be welded The raw material is cut and processed into at least two initial samples of the required shape and size. Then, the initial samples are ultrasonically cleaned to remove surface impurities and then subjected to surface graphitization treatment to obtain at least two samples to be welded. The raw material is an unpolished single-crystal or polycrystalline diamond film or diamond block, or a polished single-crystal or polycrystalline diamond film or diamond block. When the raw material of the initial sample is an unpolished single-crystal or polycrystalline diamond film or diamond bulk, the graphitization treatment of the initial sample surface shall be performed by any one of the following methods: laser etching, vacuum heat treatment, or high temperature and high pressure treatment, or by a combination of vacuum heat treatment followed by laser etching or high temperature and high pressure treatment followed by laser etching. When the raw material of the initial sample is a polished single-crystal or polycrystalline diamond film or diamond bulk, the graphitization treatment of the initial sample surface adopts a vacuum heat treatment method or a high-temperature and high-pressure treatment method, or a combination of vacuum heat treatment followed by laser etching or high-temperature and high-pressure treatment followed by laser etching. (2) Forming the weld blank Using a chemically stable material with a purity of ≥99% as the packaging material, the packaging material is made into a package that matches the shape, size and quantity of the sample to be welded; the sample to be welded prepared in step (1) is placed in the package with the welding surface facing the welding surface, and after being compacted, it is sealed to form a welded blank; or the sample to be welded prepared in step (1) is placed in the package with the welding surface facing the welding surface and welding flux is filled between the welding surfaces, and after being compacted, it is sealed to form a welded blank. (3) High temperature and high pressure welding and removal of wrapping materials and impurities The weld blank formed in step (2) is placed into the assembly of the static high pressure device, and then the assembly containing the weld blank is placed into the static high pressure device. Welding is then performed for 60s to 3600s under a pressure of 6.5GPa to 25GPa and a temperature of 1800℃ to 2500℃. After the welding time is reached, the temperature and pressure are reduced to room temperature and normal pressure. Then the encapsulated diamond after high temperature and high pressure welding is taken out, and the encapsulation material and impurities attached to the surface of the diamond are removed by cleaning.

2. The high-temperature and high-pressure welding method for diamond according to claim 1, characterized in that... The laser etching method uses a laser frequency of 10 Hz to 40 Hz, a laser power of 5 W to 100 W, and the laser etching pattern can be linear or non-linear; the vacuum heat treatment method uses a vacuum degree of <10. -2 Pa, the heat treatment temperature is 800℃~1700℃, and the heat treatment time is 10min~90min; the high temperature and high pressure treatment method has a treatment pressure of 1 GPa~5GPa, a treatment temperature of 1400℃~1800℃, and a treatment time of 10min~60min.

3. The high-temperature and high-pressure welding method for diamond according to claim 1 or 2, characterized in that... The packaging material mentioned in step (2) is tantalum, rhenium, niobium, molybdenum or platinum.

4. The high-temperature and high-pressure welding method for diamond according to claim 1 or 2, characterized in that... The welding agent mentioned in step (2) is graphite powder or diamond powder.

5. The high-temperature and high-pressure welding method for diamond according to claim 3, characterized in that... The welding agent mentioned in step (2) is graphite powder or diamond powder.

6. The high-temperature and high-pressure welding method for diamond according to claim 1 or 2, characterized in that... In step (3), the pressure increase rate from atmospheric pressure to welding pressure and the pressure decrease rate from welding pressure to atmospheric pressure are 3GPa / h to 5GPa / h, and the temperature increase rate from room temperature to welding temperature and the temperature decrease rate from welding temperature to room temperature are 100℃ / min to 300℃ / min.

7. The high-temperature and high-pressure welding method for diamond according to claim 3, characterized in that... In step (3), the pressure increase rate from atmospheric pressure to welding pressure and the pressure decrease rate from welding pressure to atmospheric pressure are 3 GPa / h to 5 GPa / h, and the temperature increase rate from room temperature to welding temperature and the temperature decrease rate from welding temperature to room temperature are 100℃ / min to 300℃ / min.

8. The high-temperature and high-pressure welding method for diamond according to claim 4, characterized in that... In step (3), the pressure increase rate from atmospheric pressure to welding pressure and the pressure decrease rate from welding pressure to atmospheric pressure are 3 GPa / h to 5 GPa / h, and the temperature increase rate from room temperature to welding temperature and the temperature decrease rate from welding temperature to room temperature are 100℃ / min to 300℃ / min.

9. The high-temperature and high-pressure welding method for diamond according to claim 5, characterized in that... In step (3), the pressure increase rate from atmospheric pressure to welding pressure and the pressure decrease rate from welding pressure to atmospheric pressure are 3 GPa / h to 5 GPa / h, and the temperature increase rate from room temperature to welding temperature and the temperature decrease rate from welding temperature to room temperature are 100 ℃ / min to 300 ℃ / min.

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