Hexagonal boron nitride powder and method for producing the same

Abstract

The application discloses hexagonal boron nitride powder and a preparation method thereof, and belongs to the technical field of ceramic material preparation. The raw materials of the hexagonal boron nitride powder include 45-60 parts of boric acid, 30-40 parts of melamine, 1-15 parts of an additive, and 1-5 parts of a water-soluble rare earth salt in terms of mass fraction; the additive includes any one or more of borax, barium carbonate and calcium carbonate. The high-purity hexagonal boron nitride powder is prepared through material mixing, suction filtration, drying and heat treatment; the particle size, morphology and crystallinity of the hexagonal boron nitride powder material are controlled by controlling the heat treatment temperature and introducing different additives and rare earths, so that the technical defects that the mechanical properties of products are low due to the insufficient sintering performance of traditional hexagonal boron nitride powder and the products are difficult to meet the performance requirements of severe working conditions are effectively solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of ceramic material preparation, and particularly relates to a hexagonal boron nitride powder and a preparation method thereof. BACKGROUND

[0002] The information disclosed in this Background section is for the purpose of increasing the understanding of the background of the application and does not necessarily pertain to the prior art that is already known in the art.

[0003] Hexagonal boron nitride (h-BN) has a unique crystal structure, excellent thermal shock resistance and easy processing, and can be used in various fields such as horizontal continuous casting separation ring, metal smelting crucible, amorphous nozzle and high-temperature metal electrolytic cell. However, the layered structure of h-BN leads to the flakiness of the powder, and the mutual lapping of the powder during high-temperature sintering process easily forms an arch bridge effect, which seriously hinders densification, and makes it a long-term technical problem to prepare high-density h-BN ceramics.

[0004] Currently, the sintering temperature of the prepared hot-pressed sintered hexagonal boron nitride ceramic material is generally above 1800 DEG C, and the sintering pressure is above 25 MPa, so as to achieve a relatively high density.

[0005] Therefore, it is very important to develop a new technical scheme that can balance high density and excellent intrinsic properties. SUMMARY

[0006] In order to solve the problems of the prior art, the present application provides a hexagonal boron nitride powder and a preparation method thereof. The present application realizes the morphology control of the hexagonal boron nitride powder by introducing different additives and rare earth elements, so as to improve the sintering performance.

[0007] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0008] In a first aspect of the present application, a hexagonal boron nitride powder is provided. The raw materials of the hexagonal boron nitride powder include, in mass fraction, 45-60 parts of boric acid, 30-40 parts of melamine, 1-15 parts of an additive, and 1-5 parts of a water-soluble rare earth salt.

[0009] The additive includes any one or several of borax, barium carbonate and calcium carbonate.

[0010] In some embodiments of the present application, the water-soluble rare earth salt is a rare earth nitrate, and the rare earth is a non-radioactive lanthanide series element.

[0011] In some embodiments of the present application, the particle size of the hexagonal boron nitride powder is 100 nm-5 microns.

[0012] The second aspect of the present application provides a preparation method of the hexagonal boron nitride powder of the first aspect, comprising:

[0013] The boric acid, the melamine, the auxiliary agent, the rare earth nitrate and the water are mixed, completely dissolved, then filtered and dried, and heat treated under a protective atmosphere to obtain the hexagonal boron nitride powder.

[0014] In some embodiments of the present application, the drying is drying at 60-80℃ for 20-25 h under vacuum.

[0015] In some embodiments of the present application, the drying is drying at 70℃ for 24 h under vacuum.

[0016] In some embodiments of the present application, the heat treatment is heating to 1200-1400℃ at a heating rate of 1-10℃ / min, and keeping for 120-240 min.

[0017] In some embodiments of the present application, the heat treatment is heating to 1300℃ at a heating rate of 5℃ / min, and keeping for 180 min.

[0018] In some embodiments of the present application, the heat treatment is heating to 1200℃ at a heating rate of 5℃ / min, and keeping for 180 min.

[0019] The third aspect of the present application provides an application of the hexagonal boron nitride powder of the first aspect in preparing a hexagonal boron nitride ceramic material, and the relative density of the hexagonal boron nitride ceramic material is 87%-91%.

[0020] In some embodiments of the present application, the preparation method of the hexagonal boron nitride ceramic material comprises:

[0021] The hexagonal boron nitride powder of the first aspect is sintered under vacuum at 650-750℃ at a heating rate of 40-60℃ / min to 1700-1800℃, and kept for 5-15 min to obtain the hexagonal boron nitride ceramic material.

[0022] The present application has the following beneficial effects:

[0023] The application provides a hexagonal boron nitride powder, and the morphology of the hexagonal boron nitride powder is controlled by introducing different additives and rare earth elements to improve the sintering capacity.

[0024] The application further provides a preparation method of the hexagonal boron nitride powder, and the hexagonal boron nitride powder is obtained through raw material mixing, filtration, drying and heat treatment. BRIEF DESCRIPTION OF DRAWINGS

[0025] The accompanying drawings, which form a part of the specification, are included to provide a further understanding of the application and are incorporated herein in conjunction with the description of the application. The drawings are not to be considered as part of the specification, and the explanation of the illustrative embodiments and their descriptions are used to explain the application and do not constitute improper limitations on the application.

[0026] Figure 1 In the technical scheme provided in Embodiment 3-Embodiment 8 of the application, the SEM morphology of the obtained hexagonal boron nitride powder product is shown, wherein (a) is the Na2B4O7-Eu sample of Embodiment 3, (b) is the Na2B4O7-Tb sample of Embodiment 4, (c) is the Na2B4O7-Ce sample of Embodiment 5, (d) is the BaCO3-Eu sample of Embodiment 6, (e) is the BaCO3-Tb sample of Embodiment 7, and (f) is the BaCO3-Ce sample of Embodiment 8.

[0027] Figure 2 In the technical scheme provided in Embodiment 11 of the application, the micro-morphology of the hexagonal boron nitride ceramic material prepared by using different hexagonal boron nitride powders is shown, wherein (a) is the Na2B4O7-La sample of Embodiment 1, and (b) is the BaCO3-Tb sample of Embodiment 7.

[0028] Figure 3 In the technical scheme provided in Embodiment 1-Embodiment 10 of the application, the flowchart of the preparation method of the hexagonal boron nitride powder is shown. DETAILED DESCRIPTION

[0029] In view of the fact that the cross-stacking support of the flaky h-BN particles in the sintering process makes it difficult for the obtained ceramic material to have a density higher than 90%, the application provides a hexagonal boron nitride powder and a preparation method thereof.

[0030] The application provides a hexagonal boron nitride powder, raw materials of which include, in mass fraction, 45-60 parts of boric acid, 30-40 parts of melamine, 1-15 parts of an additive, and 1-5 parts of a water-soluble rare earth salt.

[0031] The additive includes any one or several of borax, barium carbonate and calcium carbonate.

[0032] The hexagonal boron nitride crystal grains have a sheet layer structure, and the particle size, morphology and crystallinity of the hexagonal boron nitride powder are regulated by introducing different additives and rare earth elements, so that the sintering performance of the hexagonal boron nitride powder as a raw material is improved, and the density and mechanical properties of the product are improved.

[0033] Boric acid (H3BO3) is the main source of boron elements. Boric acid will undergo a stage decomposition during heating, first dehydrating to form metaboric acid (HBO2), and further heating to form boron trioxide (B2O3). This stage decomposition feature is conducive to the formation of active intermediates, providing sufficient boron source for the nitriding reaction. Compared with other boron sources (such as boric anhydride, boron halide, etc.), boric acid has the advantages of low price, low toxicity, safe handling, etc. Especially important is that the B2O3 produced by boric acid during heating has appropriate volatility and reactivity, which can react with nitrogen-containing compounds at a lower temperature to form boron nitride. In addition, the intermediate product formed by boric acid during heat treatment has high reactivity and adjustable porous structure, which provides a good carrier for the distribution of other additives and rare earth elements, so that the subsequent nitriding reaction can be more uniform and complete, thereby reducing the formation of impurities, improving the crystallinity and purity of the product.

[0034] Melamine (C3H6N6) is a nitrogen source, which contains up to 66% of nitrogen elements in its molecule, and has a high nitrogen content. Melamine will gradually decompose during heating to generate various nitrogen-containing intermediates and finally release nitrogen gas. This decomposition feature in a wide temperature range is conducive to providing a continuous nitrogen source throughout the reaction process, making the nitriding reaction more complete and complete. Compared with other nitrogen sources (such as urea, ammonium chloride, etc.), the decomposition process of melamine is more controllable, avoiding the problem of reaction violent fluctuation and uneven product particle size caused by instantaneous release of a large amount of nitrogen gas. Melamine can also coordinate with rare earth elements to promote the uniform distribution of rare earth elements in the reaction system, so as to better play its catalytic effect and grain boundary pinning effect.

[0035] The auxiliary agent used in the present application includes any one or several of borax, barium carbonate and calcium carbonate, which have unique functions and can produce synergistic effects in the reaction system. Borax (Na2B4O7·10H2O) can be used as an auxiliary boron source and a fluxing agent. The melting point of borax is relatively low (about 740°C), and it can form a liquid phase at the reaction temperature, thereby promoting the mass transfer and diffusion rate between raw materials, reducing the nitriding reaction temperature and shortening the reaction time. The sodium oxide produced by the decomposition of borax can form a eutectic with other components in the system, further reducing the overall melting point of the reaction system.

[0036] Barium carbonate (BaCO3) decomposes into barium oxide and carbon dioxide at high temperature, and the barium oxide can affect the crystallization behavior of hexagonal boron nitride as a mineralizer and structure directing agent. Barium ions have a large ionic radius and can insert between the layers of boron nitride, to some extent affecting the stacking mode of the layered structure and the growth orientation of the crystal. In addition, barium oxide can also react with B2O3 in the system to form a borate liquid phase, promoting the reaction and the growth of the crystal grains.

[0037] Calcium carbonate (CaCO3) decomposes into calcium oxide and carbon dioxide at high temperature, and the calcium oxide can affect the acid-base balance of the reaction system as an alkalinity regulator, thereby affecting the formation and transformation of intermediate products. Calcium ions have a certain catalytic activity and can promote the progress of the nitriding reaction. Calcium oxide can also react with impurities in the product (such as B2O3) to form calcium borate, which is easy to remove, thereby improving the purity of the final product.

[0038] The water-soluble rare earth salt introduced in the present application is an important innovation for performance regulation of hexagonal boron nitride. Rare earth elements have special catalytic activity and surface effect due to their unique electronic layer structure (4f electron layer), which can play an important role in the synthesis and subsequent sintering process of boron nitride.

[0039] Firstly, rare earth elements can act as catalysts to accelerate the progress of the nitriding reaction. Rare earth elements (such as La, Ce, etc.) can reduce the activation energy of the nitriding reaction and increase the reaction rate. Rare earth ions have high surface activity and can be adsorbed on the surface of boron nitride crystal nuclei, affecting the formation and growth kinetics of the crystal nuclei. By adjusting the concentration and type of rare earth ions, the size of boron nitride crystal grains can be precisely controlled, and ultra-fine powders of nanometer or sub-micron size can be obtained.

[0040] Secondly, rare earth elements tend to segregate at grain boundaries, producing pinning effects that inhibit abnormal grain growth. This effect is beneficial for obtaining boron nitride powder with uniform particle size and regular morphology. Rare earth elements (such as Y, La, etc.) also have a structure directing effect, which can promote the formation and regular arrangement of flaky boron nitride, which is of great significance for improving the anisotropic properties and sintering activity of the material.

[0041] Again, in the subsequent sintering process, rare earth elements can be used as sintering aids to promote the diffusion and migration of substances, reduce the sintering temperature, and improve the density of the product. Rare earth elements can also react with impurities (such as oxygen) in the material to form high-melting-point rare earth compounds, purify the grain boundary, and improve the high-temperature performance of the material. The introduction of rare earth elements can also improve the mechanical properties and thermal shock stability of boron nitride ceramics, making them more suitable for high-temperature structural applications.

[0042] In the present application, the water-soluble rare earth salt is a rare earth nitrate, and the rare earth is a non-radioactive lanthanide series element. Specifically, the non-radioactive lanthanide series element includes lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu), a total of 14 elements.

[0043] In the present application, the water-soluble rare earth salt is any one or several of lanthanum nitrate, cerium nitrate, praseodymium nitrate, neodymium nitrate, samarium nitrate, europium nitrate, terbium nitrate, gadolinium nitrate, dysprosium nitrate, holmium nitrate, erbium nitrate, thulium nitrate, ytterbium nitrate and lutetium nitrate.

[0044] The present application uses rare earth nitrate (such as lanthanum nitrate, cerium nitrate, etc.) to introduce rare earth elements. Compared with the rare earth oxides (such as lanthanum oxide, cerium oxide, etc.) commonly used in the prior art, the rare earth nitrate is a water-soluble compound, which can achieve uniform dispersion at the molecular level in the aqueous solution of boric acid and melamine, ensuring the highly uniform and fine distribution of rare earth elements in the final h-BN powder particles to realize the control of the powder morphology, thereby making the sintered sample have higher performance.

[0045] Boric acid and melamine constitute the basic framework of the reaction, providing the boron source and nitrogen source required for the synthesis of boron nitride. The introduction of the additive significantly improves the reaction kinetics and product morphology through various mechanisms such as forming a liquid phase, adjusting the reaction environment and guiding crystal growth. The addition of water-soluble rare earth salt finely controls the reaction process and crystal growth at atomic and nanometer scales, achieving precise control of the particle size, morphology and crystallinity of the product.

[0046] The synergistic effect of each component reduces the reaction temperature, shortens the reaction time, reduces energy consumption and production cost; improves the product quality, obtains boron nitride powder with uniform particle size, regular morphology and high crystallinity; through the control of the powder characteristics, the sintering performance in the subsequent sintering process is significantly improved, and finally the boron nitride ceramic product with high density and excellent mechanical properties is obtained, laying a solid foundation for its application in high-end fields.

[0047] In the present application, the particle size of the hexagonal boron nitride powder is 100 nm-5 μm.

[0048] Smaller particle size (especially submicron, such as 200 nm) means higher specific surface area and surface energy, which increases the driving force of sintering, facilitates mass transport and diffusion, and thus achieves higher density at lower temperature or shorter time. The increase of sintered body density usually directly leads to the enhancement of mechanical properties, such as bending strength and fracture toughness. Finer h-BN powder helps to obtain sintered body with more uniform microstructure, reduce defects, and is also beneficial to mechanical properties. The particle size and morphology of the powder will affect the arrangement of the grains during sintering. The particle size range helps to form a more ideal grain orientation structure, thereby optimizing specific properties.

[0049] The application also provides a preparation method of the above-mentioned h-BN powder, comprising:

[0050] The boric acid, melamine, additives, water-soluble rare earth salt and water are mixed, completely dissolved, then filtered and dried, and heat treated under a protective atmosphere to obtain the product.

[0051] The application directly prepares the h-BN powder with low agglomeration, fine particle size, low aspect ratio and complete crystallization by regulating the synthesis process. When the powder is used for hot-press sintering, the 'arch effect' between the flaky particles can be greatly reduced, and the densification is significantly promoted, so that the h-BN ceramic with a relative density of > 90% is successfully prepared, which breaks through the technical bottleneck of difficult sintering densification.

[0052] The application introduces rare earth elements and additives in the synthesis stage, which can continue to play a promoting role in the high-temperature sintering process, while achieving high density, the inherent high thermal conductivity, excellent electrical insulation and chemical stability of h-BN are maximally retained.

[0053] The preparation method provided by the application is simple, practical and easy to popularize.

[0054] In the application, the drying is performed at 60-80 ℃ under vacuum for 20-25 h.

[0055] In the application, the drying is performed at 70 ℃ under vacuum for 24 h.

[0056] In the application, the heat treatment is performed at a temperature increasing rate of 1-10 ℃ / min to 1200-1400 ℃, and maintained for 120-240 min.

[0057] The temperature of the heat treatment affects the particle size and morphology of the powder material. Therefore, the conditions of the heat treatment are studied, and the sintering performance is more optimal under the above-mentioned heat treatment conditions.

[0058] In the present application, the heat treatment is heating to 1300℃ at a temperature rising rate of 5℃ / min, and holding for 180 min.

[0059] In the present application, the heat treatment is heating to 1200℃ at a temperature rising rate of 5℃ / min, and holding for 180 min.

[0060] The hexagonal boron nitride powder material prepared by the preparation method provided by the present application can be further controlled in overall particle size by changing the temperature of heat treatment, so as to meet the sintering requirements of samples with different textures in production. The preparation method is simple, practical and easy to popularize.

[0061] The present application also provides an application of the hexagonal boron nitride powder in the preparation of a hexagonal boron nitride ceramic material, and the relative density of the hexagonal boron nitride ceramic material is 87%-91%.

[0062] It can be understood that the term relative density refers to the ratio of the actual density of the obtained hexagonal boron nitride ceramic material to the theoretical density (or true density), which is expressed in percentage. The actual density refers to the sintered body density measured by experimental methods (such as Archimedes drainage method). The theoretical density (true density) refers to the ideal maximum density value calculated based on the crystal structure and chemical composition of the material assuming that the material is completely free of any pores.

[0063] In the present application, the relative density of 87%-91% means that the actual density of the hexagonal boron nitride ceramic material prepared by the present application reaches 87%-91% of the theoretical ideal density. At the same time, it also means that only about 10% of the volume of the material is occupied by pores.

[0064] In the present application, the preparation method of the hexagonal boron nitride ceramic material comprises:

[0065] Under vacuum conditions, the hexagonal boron nitride powder is sintered by heating from 650-750℃ to 1700-1800℃ at a temperature rising rate of 40-60℃ / min, and holding for 5-15 min.

[0066] In order for those skilled in the art to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described in detail below in combination with specific examples.

[0067] Table 1 Hexagonal boron nitride powder raw material formula of examples 1-10 and comparative examples

[0068]

[0069] Example 1

[0070] The embodiment provides a hexagonal boron nitride powder product, and a preparation method thereof is as follows:

[0071] Step one, raw material mixing

[0072] Boric acid, melamine, an additive (borax), and a water-soluble rare earth salt (lanthanum nitrate) are added to deionized water according to the formula in Table 1, heated to 90 DEG C on a constant-temperature heating magnetic stirrer, stirred for 30 min to completely dissolve, and cooled to room temperature to obtain a first product.

[0073] Step two, vacuum filtration

[0074] The first product is subjected to vacuum filtration to obtain a second product.

[0075] Step three, vacuum drying

[0076] The second product is dried in a vacuum drying oven at 70 DEG C for 24 h to obtain a third product.

[0077] Step four, heat treatment

[0078] The third product is placed in a corundum crucible, heated to 1300 DEG C at a heating rate of 5 DEG C / min from 50 DEG C under nitrogen atmosphere protection, and kept at the temperature for 180 min to obtain a hexagonal boron nitride powder product, named as Na2B4O7-La sample.

[0079] The product is high-purity hexagonal boron nitride, has uniform particle size distribution (about 1 μm), and has a similar layer thickness to other rare earth element embodiments but a larger particle size. Compared with a hexagonal boron nitride powder prepared by the same preparation scheme but without the rare earth element, the particle size and morphology are significantly changed.

[0080] Embodiment 2

[0081] The embodiment provides a hexagonal boron nitride powder product, and a preparation method thereof is as follows:

[0082] The product is high-purity hexagonal boron nitride, has uniform particle size distribution (about 1 μm), and has a similar layer thickness to other rare earth element embodiments but a larger particle size. Compared with a hexagonal boron nitride powder prepared by the same preparation scheme but without the rare earth element, the particle size and morphology are significantly changed.

[0083] Embodiment 3

[0084] The embodiment provides a hexagonal boron nitride powder product, and the preparation method of the hexagonal boron nitride powder product is different from that of the embodiment 1, the use amounts of boric acid, melamine, an additive and a water-soluble rare earth salt are shown in Table 1, the additive is borax, the water-soluble rare earth salt is europium nitrate, and the rest steps are completely consistent with those of the embodiment 1. The obtained product is named as a Na2B4O7-Eu sample.

[0085] It is detected that the product is high-purity hexagonal boron nitride. Figure 1 It is observed from the SEM morphology of (a) in the table that the particle size distribution is relatively dispersed (100-600 nm), and the sheet layer morphology is regular. Compared with the hexagonal boron nitride powder prepared by the same preparation scheme but without adding a rare earth element, the particle size and the morphology are significantly changed.

[0086] Embodiment 4

[0087] The embodiment provides a hexagonal boron nitride powder product, and the preparation method of the hexagonal boron nitride powder product is different from that of the embodiment 1, the use amounts of boric acid, melamine, an additive and a water-soluble rare earth salt are shown in Table 1, the additive is borax, the water-soluble rare earth salt is terbium nitrate, and the rest steps are completely consistent with those of the embodiment 1. The obtained product is named as a Na2B4O7-Tb sample.

[0088] It is detected that the product is high-purity hexagonal boron nitride. Figure 1 It is observed from the SEM morphology of (b) in the table that the overall morphology of the powder is relatively broken, and small particles can be observed between sheet layers. Compared with the hexagonal boron nitride powder prepared by the same preparation scheme but without adding a rare earth element, the particle size and the morphology are significantly changed.

[0089] Embodiment 5

[0090] The embodiment provides a hexagonal boron nitride powder product, and the preparation method of the hexagonal boron nitride powder product is different from that of the embodiment 1, the use amounts of boric acid, melamine, an additive and a water-soluble rare earth salt are shown in Table 1, the additive is borax, the water-soluble rare earth salt is cerium nitrate, and the rest steps are completely consistent with those of the embodiment 1. The obtained product is named as a Na2B4O7-Ce sample.

[0091] It is detected that the product is high-purity hexagonal boron nitride. Figure 1 It is observed from the SEM morphology of (c) in the table that the sheet layer morphology is regular, and the particle size distribution is uniform (about 300 nm). Compared with the hexagonal boron nitride powder prepared by the same preparation scheme but without adding a rare earth element, the particle size and the morphology are significantly changed. Figure 1 It can be known that the overall morphology and the particle size distribution of the hexagonal boron nitride powder are greatly changed by adding the additive and introducing different rare earth elements.

[0092] Embodiment 6

[0093] The embodiment provides a hexagonal boron nitride powder product, and the preparation method of the hexagonal boron nitride powder product is different from that of the embodiment 1, the use amounts of boric acid, melamine, an additive and a water-soluble rare earth nitrate are shown in Table 1, the additive is barium carbonate, the water-soluble rare earth salt is europium nitrate, and the rest steps are completely consistent with those of the embodiment 1. The obtained product is named as a BaCO3-Eu sample.

[0094] The product is high-purity hexagonal boron nitride through detection. Figure 1 It is observed from the SEM morphology in (e) of FIG. 3 that the overall morphology of the powder is a mixture of irregular sheet layers and fine particles, and the average size is smaller. Compared with the hexagonal boron nitride powder prepared by the same preparation scheme but without the rare earth element, the particle size and morphology are significantly changed.

[0095] Embodiment 7

[0096] The embodiment provides a hexagonal boron nitride powder product, and the preparation method of the hexagonal boron nitride powder product is different from that of the embodiment 1, the use amounts of boric acid, melamine, an additive and a water-soluble rare earth nitrate are shown in Table 1, the additive is barium carbonate, the water-soluble rare earth salt is terbium nitrate, and the rest steps are completely consistent with those of the embodiment 1. The obtained product is named as a BaCO3-Tb sample.

[0097] The product is high-purity hexagonal boron nitride through detection. Figure 1 It is observed from the SEM morphology in (e) of FIG. 3 that the overall morphology of the powder is a mixture of irregular sheet layers and fine particles, and the average size is smaller. Compared with the hexagonal boron nitride powder prepared by the same preparation scheme but without the rare earth element, the particle size and morphology are significantly changed.

[0098] Embodiment 8

[0099] The embodiment provides a hexagonal boron nitride powder product, and the preparation method of the hexagonal boron nitride powder product is different from that of the embodiment 1, the use amounts of boric acid, melamine, an additive and a water-soluble rare earth nitrate are shown in Table 1, the additive is barium carbonate, the water-soluble rare earth salt is cerium nitrate, and the rest steps are completely consistent with those of the embodiment 1. The obtained product is named as a BaCO3-Ce sample.

[0100] The product is high-purity hexagonal boron nitride through detection. Figure 1 It is observed from the SEM morphology in (f) of FIG. 4 that the overall morphology of the powder is a mixture of irregular sheet layers and fine particles. Compared with the hexagonal boron nitride powder prepared by the same preparation scheme but without the rare earth element, the particle size and morphology are significantly changed.

[0101] Embodiment 9

[0102] The embodiment provides a hexagonal boron nitride powder product, and the preparation method of the hexagonal boron nitride powder product is different from that of the embodiment 1. The use amounts of boric acid, melamine, an additive and a water-soluble rare earth salt are shown in Table 1, the additive is barium carbonate, the water-soluble rare earth salt is cerium nitrate, the temperature is increased to 1200 DEG C at a temperature increasing speed of 5 DEG C / min under the protection of a nitrogen atmosphere, and the temperature is kept for 180 min. The other steps are completely same as those of the embodiment 1. The obtained product is named as a BaCO3-Ce-1200 sample.

[0103] The product is high-purity hexagonal boron nitride, and the morphology is a mixture of fibrous and lamellar.

[0104] Example 10

[0105] The embodiment provides a hexagonal boron nitride powder product, and the preparation method of the hexagonal boron nitride powder product is different from that of the embodiment 1. The use amounts of boric acid, melamine, an additive and a water-soluble rare earth salt are shown in Table 1, the additive is barium carbonate, the water-soluble rare earth salt is cerium nitrate, the temperature is increased to 1400 DEG C at a temperature increasing speed of 5 DEG C / min under the protection of a nitrogen atmosphere, and the temperature is kept for 180 min. The other steps are completely same as those of the embodiment 1. The obtained product is named as a BaCO3-Ce-1400 sample.

[0106] The product is high-purity hexagonal boron nitride, and the morphology is a mixture of fibrous and lamellar.

[0107] Comparative Example 1

[0108] The comparative example provides a hexagonal boron nitride powder product, and the preparation method of the hexagonal boron nitride powder product is different from that of the embodiment. The use amounts of boric acid, melamine and an additive are shown in Table 1, and the additive is borax. The other steps are completely same as those of the embodiment 1.

[0109] The product is fibrous.

[0110] Comparative Example 2

[0111] The comparative example provides a hexagonal boron nitride powder product, and the preparation method of the hexagonal boron nitride powder product is different from that of the embodiment. The use amounts of boric acid, melamine and an additive are shown in Table 1, and the additive is borax. The other steps are completely same as those of the embodiment 1.

[0112] The product is fibrous.

[0113] Comparative Example 3

[0114] The present comparative example provides a hexagonal boron nitride powder product, the preparation method of which is distinguished from the examples in that the amounts of boric acid, melamine and the additive are as shown in Table 1, and the additive is barium carbonate. The remaining steps are exactly the same as those of Example 1.

[0115] It is detected that the obtained product has unevenly sized sheet layer particles.

[0116] Example 11

[0117] The present example provides a hexagonal boron nitride ceramic material, the preparation steps of which are as follows:

[0118] The hexagonal boron nitride powder products obtained in the examples and comparative examples are respectively placed in a graphite mold to perform rapid hot-pressing sintering to obtain a hexagonal boron nitride ceramic material.

[0119] The method of rapid hot-pressing sintering is as follows: heating from 700℃ to 1750℃ at a heating rate of 50℃ / min, and keeping the temperature for 10 min during the sintering process, and the vacuum degree is always kept less than or equal to 10 Pa.

[0120] Table 2 Mechanical strength and density of hexagonal boron nitride ceramic material

[0121]

[0122] The microscopic morphology of the hexagonal boron nitride ceramic material prepared by using Na2B4O7-La is shown in FIG. (a) of Figure 2 , and the microscopic morphology of the hexagonal boron nitride ceramic material prepared by using BaCO3-Tb is shown in FIG. (b) of Figure 2 .

[0123] Compared with the hexagonal boron nitride ceramic material prepared by using the hexagonal boron nitride powder prepared by the same preparation method but without adding rare earth elements, the hexagonal boron nitride ceramic material sintered by using the hexagonal boron nitride powder prepared by the present example has higher bending strength and relative density.

[0124] In summary, by virtue of the innovative design of raw materials and preparation methods, the present application prepares a high-purity hexagonal boron nitride powder material; by introducing different rare earth elements and additives, the overall morphology, particle size distribution and crystallinity of the hexagonal boron nitride powder can be controlled to improve the sintering performance thereof during sintering and to meet the customized needs; thereby effectively solving the technical defects in the prior art that the sintering performance of traditional hexagonal boron nitride powder is insufficient, which results in low mechanical properties of the products and makes it difficult to meet the performance requirements in harsh working conditions.

[0125] The above merely provides the preferred embodiments of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the principles and technical scope of the present application shall fall into the scope of the present application.

Claims

1. A hexagonal boron nitride powder, characterized by, The raw materials include 45-60 parts of boric acid, 30-40 parts of melamine, 1-15 parts of an auxiliary agent, and 1-5 parts of a water-soluble rare earth salt by mass fraction; The auxiliary agent includes any one or several of borax, barium carbonate, and calcium carbonate; The water-soluble rare earth salt is a rare earth nitrate, and the rare earth is a non-radioactive lanthanide series element; The preparation method of the hexagonal boron nitride powder includes mixing boric acid, melamine, an auxiliary agent, a water-soluble rare earth salt, and water, completely dissolving, vacuum filtration, drying, and heat treatment in a protective atmosphere to obtain the hexagonal boron nitride powder; The drying is performed at 70-80℃ under vacuum for 20-25 h; The heat treatment is performed at a temperature increasing rate of 1-10℃ / min to 1200-1300℃, and maintained for 120-180 min; The relative density of the hexagonal boron nitride ceramic material is 87-91%.

2. The hexagonal boron nitride powder according to claim 1, wherein The particle size of the hexagonal boron nitride powder is 100 nm-5 μm.

3. A method of producing the hexagonal boron nitride powder according to claim 1 or 2, characterized by, The preparation method of the hexagonal boron nitride powder includes: mixing boric acid, melamine, an auxiliary agent, a water-soluble rare earth salt, and water, completely dissolving, vacuum filtration, drying, and heat treatment in a protective atmosphere to obtain the hexagonal boron nitride powder; The drying is performed at 70-80℃ under vacuum for 20-25 h; The heat treatment is performed at a temperature increasing rate of 1-10℃ / min to 1200-1300℃, and maintained for 120-180 min.

4. The production method according to claim 3, wherein The drying is performed at 70℃ under vacuum for 24 h.

5. The production method according to claim 3, wherein The heat treatment is performed at a temperature increasing rate of 5℃ / min to 1300℃, and maintained for 180 min.

6. The production method according to claim 3, wherein The heat treatment is performed at a temperature increasing rate of 5℃ / min to 1200℃, and maintained for 180 min.

7. Use of the hexagonal boron nitride powder according to claim 1 or 2 for the production of a hexagonal boron nitride ceramic material, characterized in that, The relative density of the hexagonal boron nitride ceramic material is 87-91%.

8. Use of the hexagonal boron nitride powder according to claim 7 for the production of a hexagonal boron nitride ceramic material, characterized in that, The preparation method of the hexagonal boron nitride ceramic material includes: sintering the hexagonal boron nitride powder of any one of claims 1-2 at a temperature increasing rate of 40-60℃ / min to 1700-1800℃ under vacuum, and maintained for 5-15 min to obtain the hexagonal boron nitride ceramic material.

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