Boron element doped boron nitride, binder-free polycrystalline cubic boron nitride and preparation method and application of boron element doped boron nitride and binder-free polycrystalline cubic boron nitride

Abstract

The invention provides boron element doped boron nitride, binderless polycrystalline cubic boron nitride, and a preparation method and application of the boron element doped boron nitride and the binderless polycrystalline cubic boron nitride. The content of the boron element in the boron element doped boron nitride is 45-48wt%. The preparation method of the boron element doped boron nitride comprises the following steps: uniformly mixing a boron nitride raw material with another boron-containing substance, and then carrying out vacuum high-temperature treatment. The preparation method of the binder-free polycrystalline cubic boron nitride comprises the following steps: by taking the boron element doped boron nitride as a raw material, synthesizing the binder-free polycrystalline cubic boron nitride through static pressure molding and high-temperature and high-pressure treatment. The binder-free polycrystalline cubic boron nitride takes boron doped boron nitride as a raw material, so that the density of the prepared binder-free polycrystalline cubic boron nitride can be improved, the grain boundary defect can be improved, the heat-conducting property of the binder-free polycrystalline cubic boron nitride is further improved, and the binder-free polycrystalline cubic boron nitride is applied to the field of heat management as a heat-conducting material.

Description

Technical Field

[0001] The present invention relates to the technical field of superhard materials, and in particular to boron-doped boron nitride, binder-free polycrystalline cubic boron nitride, and a preparation method and application thereof. Background Art

[0002] As the integration of electronic devices becomes higher and higher, the heat generated by the devices per unit time increases sharply. If the generated heat cannot be conducted in time, it will have an extremely adverse effect on the working efficiency and working life of the electronic devices. Therefore, modern industry has put forward more stringent requirements on the thermal conductivity of heat dissipation materials. Cubic boron nitride (cBN) is a sphalerite structure with a crystal structure similar to diamond, and its thermal conductivity is second only to diamond. Theoretically calculated thermal conductivity of cubic boron nitride is as high as 1300 W / (mK), which is much higher than ceramic materials such as AlN and SiC. At the same time, cBN has excellent thermal stability and low thermal expansion coefficient, which is very suitable for heat dissipation substrates of high-power electronic devices.

[0003] The application of single-crystal cubic boron nitride in the field of thermal conductivity is limited by its size (usually less than millimeter level), while polycrystalline cubic boron nitride can overcome the above-mentioned size disadvantages of single-crystal cubic boron nitride. Polycrystalline cubic boron nitride can be divided into binder polycrystalline cubic boron nitride (PCBN) and binderless polycrystalline cubic boron nitride (BCBN). PCBN has a thermal conductivity that is affected by the presence of the second phase, and its thermal conductivity is usually 80-130 W / (mK). Since BCBN does not contain other phases, its thermal conductivity is greatly improved compared to PCBN. For example, Bushyla (Sintering of binderless cubic boron nitrideand its modification by β-Si 3 N 4 Additive for hard machining applications[J].International Journal of Refractory Metals and Hard Materials, 2020, 86(105100): 1-12) mentioned that the thermal conductivity of BCBN prepared under 7.7 GPa and 2300℃ reached 200 W / (mK).

[0004] BCBN has excellent thermal conductivity, low thermal expansion coefficient and excellent thermal stability, and has a very broad application prospect in the field of thermal management. However, BCBN is not easy to sinter, and its low density and grain boundary defects restrict its thermal conductivity from being further improved. Summary of the invention

[0005] In view of this, the main purpose of the present invention is to provide a boron-doped boron nitride, binderless polycrystalline cubic boron nitride and its preparation method and application, mainly by doping the raw materials of BCBN with boron to increase the density of BCBN and improve grain boundary defects, thereby further improving the thermal conductivity of BCBN.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A boron-doped boron nitride, wherein the boron content is 45-48wt%.

[0007] A method for preparing the boron-doped boron nitride comprises: firstly uniformly mixing the boron nitride raw material and the boron-containing substance, then performing vacuum high-temperature treatment, and then removing the excess boron-containing substance, so as to obtain the boron-doped boron nitride.

[0008] Based on the above preparation method, the ratio of the mass of the boron nitride raw material to the mass of the boron element in the boron-containing substance is 9:1-7:3, so as to ensure that the above boron-doped boron nitride can be obtained.

[0009] Based on the above preparation method, the parameters of the vacuum high temperature treatment include: vacuum degree 10 -1 -10 -3 pa, processing temperature 1500-1800℃, processing time 1-2 h.

[0010] A method for preparing BCBN comprises: using the boron-doped boron nitride as a raw material, and synthesizing BCBN through static pressing and high-temperature and high-pressure treatment.

[0011] Based on the above, the static pressure forming process includes: applying a static pressure of 50-100 Mpa to the boron-doped boron nitride for 5-15 s to obtain a density of 1.7-2.2 g / cm 3 preforms.

[0012] Based on the above, the high temperature and high pressure treatment includes: sintering the preform under high temperature and high pressure for 10-30 min under the conditions of 7-10 GPa and 1600-2100°C.

[0013] A BCBN prepared by the above preparation method, wherein the thermal conductivity of the BCBN is 240-310 W / (mK).

[0014] An application of the above BCBN as a thermal conductive material in the field of thermal management.

[0015] Compared with the prior art, the boron-doped boron nitride provided by the present invention causes the original lattice of the boron nitride raw material therein to be distorted and in a high-energy state, thereby reducing the sintering conditions of BCBN and improving the density of BCBN. On the other hand, the doping of boron elements can passivate the grain boundaries and reduce the defects of the grain boundaries inside BCBN; thereby, the BCBN provided by the present invention is composed only of cubic boron nitride phase, avoiding the adverse effect of the second phase existing in PCBN on the thermal conductivity of the material, so that BCBN has higher thermal conductivity, and the thermal conductivity coefficient can reach 240-310 W / (mK). BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The XRD pattern of BCBN synthesized in Example 1 of the present invention; Figure 2 The XRD pattern of BCBN synthesized in Example 5 of the present invention; Figure 3 This is the XRD pattern of BCBN synthesized in Example 6 of the present invention. DETAILED DESCRIPTION

[0017] In the present invention, unless otherwise specified and / or described, all numerical values ​​involving the amount of components are "weight". Unless otherwise specified, the terms used in the present invention are commonly used in the field, and the preparation processes, test methods, etc. used in each embodiment are conventional means well known to those skilled in the art unless otherwise specified, and the raw materials and equipment used can be obtained from public commercial channels.

[0018] The present invention mainly performs boron doping treatment on BCBN raw materials to increase the density of BCBN and improve grain boundary defects, thereby achieving the purpose of improving the thermal conductivity of BCBN.

[0019] Specifically, the first aspect of the present invention provides a boron-doped boron nitride as a BCBN raw material, wherein the boron content is 45-48 wt%, such as 45 wt%, 45.5 wt%, 46 wt%, 46.5 wt%, 47 wt%, 47.5 wt%, 48 wt%, etc.; in this way, not only the compactness of the subsequently prepared BCBN can be improved, but also the grain boundary defects inside the BCBN can be significantly reduced, and the thermal conductivity of the BCBN can be significantly improved. If the doped boron content is too low, the improvement effect of the thermal conductivity of BCBN is not obvious. On the other hand, as the high-temperature diffusion doping proceeds, the doping process becomes increasingly difficult to carry out. The upper limit of the boron content in the boron-doped boron nitride is about 48%.

[0020] The boron-doped boron nitride is boron-doped hexagonal boron nitride, boron-doped cubic boron nitride or any combination thereof.

[0021] The second aspect of the present invention provides a method for preparing the above-mentioned boron-doped boron nitride, comprising: first uniformly mixing the boron nitride raw material with another boron-containing substance, then performing a vacuum high-temperature treatment, and then removing excess boron-containing substance therefrom to obtain the above-mentioned boron-doped boron nitride.

[0022] Wherein, the boron nitride raw material is hexagonal boron nitride, cubic boron nitride powder or a mixture of the two. Preferably, the particle size of the boron nitride raw material is 0.5-10 μm. The other boron-containing material includes elemental boron or a boron compound, and the boron compound can be boric acid, aluminum boride (AlB 2 ) and other substances, and are not the boron nitride raw materials.

[0023] To ensure that the boron content in the boron-doped boron nitride is 45-48 wt %, the ratio of the mass of the boron nitride raw material to the mass of the boron element in the other boron-containing material is preferably 9:1-7:3, such as 9:1, 8.5:1.5, 8:2, 7.5:2.5, 7:3, etc.

[0024] The preparation method of the boron-doped boron nitride specifically includes: firstly, the boron nitride raw material is mixed with the boron-containing substance, then placed in a vacuum high-temperature furnace for vacuum high-temperature treatment for 1-2 hours, and then the excess boron-containing substance is removed by pickling or water to obtain boron-doped boron nitride as the subsequent BCBN raw material. The parameters of the vacuum high-temperature treatment include: vacuum degree 10 -1 - 10 -3 pa, processing temperature 1500-1800℃.

[0025] The pickling method comprises: firstly heating the product after vacuum high temperature treatment to 50-70°C in concentrated nitric acid and keeping the temperature constant for 20-40 min; then washing with pure water and drying to obtain the boron element doped boron nitride; at this time, the boron nitride raw material is water-insoluble elemental boron, aluminum boride (AlB 2 When the boron nitride raw material is boric acid, the product after vacuum high temperature treatment can be rinsed with water to obtain pure boron-doped boron nitride.

[0026] The third aspect of the present invention provides a method for preparing BCBN, comprising: using the above-mentioned boron-doped boron nitride as a raw material, and synthesizing BCBN through static pressing and high temperature and high pressure treatment.

[0027] The static pressing process is a prior art, and its main purpose is to dope boron nitride with boron to form a blank, so as to carry out a subsequent high temperature and high pressure sintering process. Specifically, the static pressing process includes: applying a static pressure of 50-100 Mpa for 5-15 s to the boron doped boron nitride to obtain a blank with a density of 1.7-2.2 g / cm 3More specifically, the boron-doped boron nitride is first loaded into a metal tantalum cup, and then a press is used to perform static pressure molding for 5-15 minutes at 50-100 Mpa to obtain a preform with a density of 1.7-2.2 g / cm 3 preformed products.

[0028] The high temperature and high pressure treatment is basically the existing technology, which mainly includes: sintering the preform under high temperature and high pressure for 10-30 min under the conditions of 7-10 Gpa and 1600-2100°C. Specifically, the steps of the high temperature and high pressure treatment include: first loading the preform into a high temperature and high pressure assembly block, and then synthesizing BCBN under high temperature and high pressure under the conditions of 7-10Gpa and 1600-2100°C. Among them, the high pressure in the high temperature and high pressure treatment process is preferably 7-9 Gpa, such as 7 Gpa, 7.5Gpa, 8 Gpa, 8.5 Gpa, 9 Gpa, etc.; the high temperature is preferably 1800-2100°C, such as 1800°C, 1850°C, 1900°C, 1950°C, 2000°C, 2050°C, 2100°C, etc.

[0029] Furthermore, the preparation method of BCBN also includes the steps of: after synthesizing BCBN at high temperature and high pressure, annealing and cooling, and removing the metal tantalum cup with a mixed acid solution to obtain pure phase BCBN. The mixed acid solution is prepared by uniformly mixing a hydrofluoric acid solution (40 wt%) and concentrated nitric acid (68 wt%) in a mass ratio of 1:1-1:3.

[0030] The fourth aspect of the present invention provides a BCBN prepared by the above method, wherein the thermal conductivity of the BCBN is 240-310 W / (mK).

[0031] A fifth aspect of the present invention provides an application of the above-mentioned BCBN as a thermal conductive material in the field of thermal management, wherein the thermal management field relates to electronic equipment, aerospace, automobiles, and the like.

[0032] The present invention will be further described below in conjunction with specific implementation modes.

[0033] Example 1 (1) Hexagonal boron nitride powder with a particle size of 0.5-1 μm and elemental boron are mixed in a mass ratio of 9:1 to obtain a mixed powder. The mixed powder is then placed in a vacuum at a degree of 10 -2 Pa, and treated in a vacuum furnace at 1600 °C for 1 h. The mixed powder after vacuum treatment was placed in concentrated nitric acid and heated to 55 °C and kept warm for 30 min, then washed with pure water and dried to obtain hexagonal boron nitride doped with boron.

[0034] (2) The boron-doped hexagonal boron nitride obtained in (1) was placed in a metal tantalum cup and subjected to static pressure molding under a press with a pressure of 60 MPa and a holding time of 10 s to obtain a preform. The density of the preform was 1.78 g / cm 3 .

[0035] (3) The preform obtained in (2) is combined with a pressure transmission medium, a heating component, and a heat preservation component to form an assembly block, which is then placed in a six-sided top press for synthesis. The synthesis pressure is 8 Gpa, the synthesis temperature is 1900°C, and the insulation time is 10 min. After the synthesis is completed and the pressure is released and cooled, the synthesis block is placed in a mixed solution of hydrofluoric acid and concentrated nitric acid in a ratio of 1:1 to remove the metal tantalum cup wrapped on the surface of the synthesis block, thereby obtaining a high thermal conductivity BCBN.

[0036] The BCBN prepared in this embodiment was subjected to XRD detection, and the results were as follows: Figure 1 As shown. Figure 1 It can be seen that the polycrystalline cubic boron nitride prepared by the method provided in this embodiment is composed of only cubic boron nitride CBN, without other phases; thus, it is proved that the method provided in this embodiment can successfully prepare binderless polycrystalline cubic boron nitride BCBN material.

[0037] Example 2 (1) Cubic boron nitride powder with a particle size of 4-6 μm and elemental boron were mixed in a mass ratio of 8.5:1.5 to obtain a mixed powder. The mixed powder was then placed in a vacuum of 10 -1 Pa, and treated in a vacuum furnace at 1500 °C for 1 h. The mixed powder after vacuum treatment was placed in concentrated nitric acid and heated to 60 °C and kept warm for 30 min, then washed with pure water and dried to obtain cubic boron nitride doped with boron.

[0038] (2) The boron-doped cubic boron nitride obtained in (1) was placed in a metal tantalum cup and subjected to static pressure molding under a press with a pressure of 90 MPa and a holding time of 10 s to obtain a preform. The density of the preform was 2.08 g / cm 3 .

[0039] (3) The preform obtained in (2) is combined with a pressure transmitting medium, a heating component, and a heat-insulating component to form an assembly block, which is then placed in a six-sided top press for synthesis. The synthesis pressure is 8.5 Gpa, the synthesis temperature is 2000°C, and the insulation time is 10 min. After the synthesis is completed and the pressure is released and cooled, the synthesized block is placed in a mixed solution of hydrofluoric acid and concentrated nitric acid in a ratio of 1:1 to remove the metal tantalum cup wrapped on the surface of the synthesized block, thereby obtaining a high thermal conductivity BCBN.

[0040] Example 3 (1) Hexagonal boron nitride with a particle size of 1-5 μm, cubic boron nitride powder with a particle size of 0.5-2 μm and elemental boron are mixed in a mass ratio of 4:4:2 to obtain a mixed powder. The mixed powder is then placed in a vacuum at a temperature of 10 -3 Pa, and treated in a vacuum furnace at 1500°C for 1 h. The mixed powder after vacuum treatment was placed in concentrated nitric acid and heated to 60°C and kept warm for 30 min, and then washed and dried with pure water to obtain a mixed powder of hexagonal boron nitride and cubic boron nitride doped with boron.

[0041] (2) The boron nitride mixed powder doped with boron obtained in (1) was placed in a metal tantalum cup and subjected to static pressing under a press with a pressure of 90 MPa and a holding time of 10 s to obtain a preform. The density of the preform was 1.91 g / cm 3 .

[0042] (3) The preform obtained in (2) is combined with a pressure transmitting medium, a heating component, and a heat-insulating component to form an assembly block, which is then placed in a six-sided top press for synthesis. The synthesis pressure is 9 Gpa, the synthesis temperature is 2100°C, and the insulation time is 30 min. After the synthesis is completed and the pressure is released and cooled, the synthesized block is placed in a mixed solution of hydrofluoric acid and concentrated nitric acid in a ratio of 1:2 to remove the metal tantalum cup wrapped on the surface of the synthesized block, thereby obtaining a high thermal conductivity BCBN.

[0043] Comparative Example 1: The raw materials used in this comparative example are consistent with those in Example 1, but no boron doping treatment is performed, and the subsequent operations and synthesis conditions are the same as those in Example 1.

[0044] Comparative Example 2: The raw materials used in this comparative example are consistent with those in Example 2, but no boron doping treatment is performed, and the subsequent operations and synthesis conditions are the same as those in Example 2.

[0045] Comparative Example 3: The raw materials used in this comparative example are consistent with those in Example 3, but no boron doping treatment is performed, and the subsequent operations and synthesis conditions are the same as those in Example 3.

[0046] Example 4 (1) Hexagonal boron nitride powder with a particle size of 0.5-1 μm and elemental boron are mixed in a mass ratio of 7:3 to obtain a mixed powder. The mixed powder is then placed in a vacuum at a degree of 10 -2 Pa, and treated in a vacuum furnace at 1800 °C for 2 h. The mixed powder after vacuum treatment was placed in concentrated nitric acid and heated to 70 °C and kept warm for 30 min, then washed with pure water and dried to obtain hexagonal boron nitride doped with boron.

[0047] (2) The boron-doped hexagonal boron nitride obtained in (1) was placed in a metal tantalum cup and subjected to static pressure molding under a press with a pressure of 60 MPa and a holding time of 10 s to obtain a preform. The density of the preform was 1.77 g / cm 3 .

[0048] (3) The preform obtained in (2) is combined with a pressure transmission medium, a heating component, and a heat preservation component to form an assembly block, which is then placed in a six-sided top press for synthesis. The synthesis pressure is 8 Gpa, the synthesis temperature is 1900°C, and the insulation time is 10 min. After the synthesis is completed and the pressure is released and cooled, the synthesis block is placed in a mixed solution of hydrofluoric acid and concentrated nitric acid in a ratio of 1:1 to remove the metal tantalum cup wrapped on the surface of the synthesis block, thereby obtaining a high thermal conductivity BCBN.

[0049] Example 5 (1) Mix the hexagonal boron nitride powder with a particle size of 0.5-1 μm and the boron element in boric acid in a ratio of 8:2 to obtain a mixed powder. Then, place the mixed powder under vacuum at a temperature of 10 -3 Pa, and treated in a vacuum furnace at a temperature of 1700°C for 1.5 h. The mixed powder after vacuum treatment was washed with pure water and dried to obtain hexagonal boron nitride powder doped with boron element.

[0050] (2) The boron-doped cubic boron nitride obtained in (1) was placed in a metal tantalum cup and subjected to static pressure molding under a press with a pressure of 90 MPa and a holding time of 10 s to obtain a preform. The density of the preform was 1.81 g / cm 3 .

[0051] (3) The preform obtained in (2) is combined with a pressure transmitting medium, a heating component, and a heat-insulating component to form an assembly block, which is then placed in a six-sided top press for synthesis. The synthesis pressure is 8.5 Gpa, the synthesis temperature is 2000°C, and the insulation time is 10 minutes. After the synthesis is completed and the pressure is released and cooled, the synthesis block is placed in a mixed solution of hydrofluoric acid and concentrated nitric acid in a ratio of 1:1 to remove the metal tantalum cup wrapped on the surface of the synthesis block, thereby obtaining high-conductivity BCBN.

[0052] The BCBN prepared in this embodiment was subjected to XRD detection, and the results were as follows: Figure 2 As shown. Figure 2 It can be seen that the polycrystalline cubic boron nitride prepared by the method provided in this embodiment is composed of only cubic boron nitride CBN, without other phases; thus, it is proved that the method provided in this embodiment can successfully prepare binderless polycrystalline cubic boron nitride BCBN material.

[0053] Example 6 (1) The mass of hexagonal boron nitride powder with a particle size of 0.5-1 μm and AlB 2 The boron elements in the mixture were mixed in a ratio of 7:3 to obtain a mixed powder. -3 Pa, and treated in a vacuum furnace at 1500 °C for 1.5 h. The mixed powder after vacuum treatment was placed in concentrated nitric acid and heated to 70 °C and kept warm for 30 min, and then washed with pure water and dried to obtain hexagonal boron nitride powder doped with boron element.

[0054] (2) The hexagonal boron nitride mixed powder doped with boron obtained in (1) was placed in a metal tantalum cup and subjected to static pressing under a press with a pressure of 90 MPa and a holding time of 10 s to obtain a preform. The density of the preform was 1.79 g / cm 3 .

[0055] (3) The preform obtained in (2) is combined with a pressure transmitting medium, a heating component, and a heat-insulating component to form an assembly block, and then placed in a six-sided top press for synthesis. The synthesis pressure is 7 Gpa, the synthesis temperature is 1900°C, and the insulation time is 30 minutes. After the synthesis is completed and the pressure is released and cooled, the synthesis block is placed in a mixed solution of hydrofluoric acid and concentrated nitric acid in a ratio of 1:2 to remove the metal tantalum cup wrapped on the surface of the synthesis block, thereby obtaining high-conductivity BCBN.

[0056] The BCBN prepared in this embodiment was subjected to XRD detection, and the results were as follows: Figure 3 As shown. Figure 3 It can be seen that the polycrystalline cubic boron nitride prepared by the method provided in this embodiment is composed of only cubic boron nitride CBN, without other phases; thus, it is proved that the method provided in this embodiment can successfully prepare binderless polycrystalline cubic boron nitride BCBN material.

[0057] Composition and performance testing The boron content in the boron-doped boron nitride prepared in Examples 1-6 and the corresponding boron nitride raw materials was tested respectively with reference to the industry standard boron nitride chemical analysis method, that is, the boron content in the boron nitride raw materials before and after boron doping was tested, and the test results are shown in Table 1.

[0058] The density (detected by Archimedes drainage method) and thermal conductivity (detected by Xiaxi TC3000E thermal conductivity meter) of the BCBN obtained in Examples 1-6 and Comparative Examples 1-3 were respectively detected, and the test results are shown in Table 2.

[0059] Table 1 Boron content of boron nitride raw materials before and after boron doping sample Before doping(wt%) After doping (wt%) Example 1 43.58 45.15 Example 2 43.72 45.65 Example 3 43.61 46.24 Example 4 43.52 47.81 Example 5 43.46 45.23 Example 6 43.63 46.56 Table 2 BCBN performance test results sample Density(%) Thermal conductivity [W / (mK)] Example 1 97.63 258 Comparative Example 1 96.82 189 Example 2 98.43 293 Comparative Example 2 97.12 202 Example 3 98.06 307 Comparative Example 3 97.35 195 Example 4 98.03 283 Example 5 97.57 246 Example 6 97.44 253 Combined with Table 1 and Table 2, from the comparison results of Examples 1-3 and Comparative Examples 1-3, under the same other conditions, the BCBN prepared using the boron-doped boron nitride provided by the embodiment of the present invention as a raw material has a better density, indicating that the boron-doped boron nitride is easier to sinter under high temperature and high pressure. This shows that the content of boron in the boron-doped boron nitride has an important influence on the density and thermal conductivity of the final BCBN.

[0060] It can be seen that the boron-doped boron nitride prepared in the embodiment of the present invention causes the original lattice of the corresponding hexagonal boron nitride or cubic boron nitride to be distorted and in a high-energy state, thereby reducing the sintering conditions of BCBN and improving the density of BCBN. On the other hand, the doping of boron can passivate the grain boundaries and reduce the defects of the internal grain boundaries of BCBN; thereby, the embodiment of the present invention can successfully prepare and provide BCBN material, avoiding the adverse effect of the second relative material thermal conductivity existing in PCBN, so that the thermal conductivity of BCBN can reach 240-310 W / (mK), and can be used as a thermal conductive material for application in electronic equipment, aerospace, automobiles and other fields.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or some technical features can be replaced by equivalents without departing from the spirit of the technical solution of the present invention, which should be included in the scope of the technical solution for protection of the present invention.

Claims

1. A boron-doped boron nitride, characterized in that: The boron content is 45-48wt%.

2. The boron-doped boron nitride according to claim 1, characterized in that: It is boron-doped hexagonal boron nitride, boron-doped cubic boron nitride or any combination of the two.

3. A method for preparing boron-doped boron nitride according to claim 1, comprising: The boron nitride raw material is firstly uniformly mixed with another boron-containing substance, and then subjected to vacuum high-temperature treatment; wherein the boron nitride raw material is hexagonal boron nitride, cubic boron nitride powder or a mixture of the two, and the other boron-containing substance includes elemental boron or a boron compound.

4. The preparation method according to claim 3, characterized in that The parameters of the vacuum high temperature treatment include: vacuum degree 10 -1 -10 -3 pa, processing temperature 1500-1800℃, processing time 1-2 h.

5. The preparation method according to claim 3 or 4, characterized in that: The ratio of the mass of the boron nitride raw material to the mass of the boron element in the other boron-containing material is 9:1-7:

3.

6. A method for preparing binder-free polycrystalline cubic boron nitride comprises: The boron-doped boron nitride according to claim 1 or 2 is used as a raw material, and binder-free polycrystalline cubic boron nitride is synthesized by static pressing and high temperature and high pressure treatment.

7. The preparation method according to claim 6, characterized in that The static pressure forming process comprises: applying a static pressure of 50-100 MPa to the boron-doped boron nitride for 5-15 s to obtain a density of 1.7-2.2 g / cm 3 preformed products.

8. The preparation method according to claim 6 or 7, characterized in that: The high temperature and high pressure treatment comprises: sintering the preform under high temperature and high pressure for 10-30 min under the conditions of 7-10 GPa and 1600-2100° C.

9. Binder-free polycrystalline cubic boron nitride obtained by the preparation method according to any one of claims 6 to 8.

10. Use of the binderless polycrystalline cubic boron nitride according to claim 9 as a thermal conductive material in the field of thermal management.

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