Hexagonal boron nitride ceramic and preparation method thereof

Abstract

The present invention provides a hexagonal boron nitride ceramic and a preparation method thereof. The hexagonal boron nitride ceramic comprises a main phase and a dispersed phase, wherein the main phase comprises h-BN and the dispersed phase comprises Al2Y4O9. The hexagonal boron nitride ceramic has an apparent porosity of ≤5% and a density of ≥90%. The preparation method comprises mixing h-BN with a sintering aid and then sintering to obtain a high-density hexagonal boron nitride ceramic containing a specific crystal phase component. The obtained hexagonal boron nitride ceramic has an elastic modulus of ≥20.0 GPa and a flexural strength of ≥100 MPa. The preparation method is simple in process, is conducive to the preparation of large-sized boron nitride ceramic components, and has a relatively low sintering temperature, which is conducive to reducing costs and promoting large-scale industrial production.

Description

Technical Field

[0001] The invention belongs to the field of ceramic materials and relates to hexagonal boron nitride ceramics and a preparation method thereof. Background Art

[0002] At present, hexagonal boron nitride (h-BN) is commonly known as "white graphite". It has a layered crystal structure similar to graphite. The interlayer atoms are bonded by van der Waals bonds, which has good lubricity and thermal conductivity. The B and N atoms in the h-BN layer are connected by sp 2 Due to covalent bonding and high electron binding energy (about 192eV), the atomic diffusion rate during the sintering process of h-BN ceramics is slow. Only when the temperature is increased (usually above 1500°C) to increase the atomic diffusion rate, the h-BN ceramics begin to show signs of sintering. In addition, the h-BN grains have a card house structure, and the stacking produces many pores, making the densification sintering of h-BN ceramics more difficult.

[0003] High-temperature sintering is currently the only industrially viable method for preparing boron nitride ceramics on a large scale. It can be broadly categorized into three methods: atmospheric pressure sintering, hot pressing sintering, and spark plasma sintering. To obtain dense h-BN ceramics, high temperature and high pressure are typically employed, along with the addition of sintering aids. These aids primarily serve three purposes: first, at high temperatures, they form a continuous liquid phase between the h-BN grains, promoting heat and mass transfer; second, they fill the pores between the h-BN grains, promoting ceramic densification; and third, they inhibit the continued growth of the h-BN grains at the grain boundaries, reducing pore size.

[0004] For example, CN108017393A, CN104177091, and CN104193341B prepare hexagonal boron nitride ceramics by dry pressing and isostatic pressing followed by pressureless sintering. Although the process is simple, the absence of pressure during sintering can easily lead to deformation and cracking of the ceramics due to thermal stress. Furthermore, the ceramics sintered by this method generally have low density.

[0005] CN110395988A discloses a high-strength boron nitride ceramic and its preparation method. The boron nitride ceramic is prepared by hot pressing or spark plasma sintering of single-particle nano-cubic boron nitride. While this method is simple to prepare, the synthesis of the cubic boron nitride raw material is complex and expensive, resulting in a relatively high cost for the boron nitride ceramic produced by this method.

[0006] CN111848179B discloses a method for preparing high-strength boron nitride ceramics that can be used in ultra-high temperature environments. The method comprises adding zirconium diboride or boron powder to boron nitride powder and adopting a hot pressing sintering process to prepare high-strength boron nitride ceramics. This method has low raw material costs and good mechanical properties of the ceramics. However, the diffusion of boron nitride during sintering is relatively difficult, and the sintering temperature needs to reach a high temperature of 1800-2100°C, resulting in high energy consumption.

[0007] Therefore, it is necessary to further explore a preparation method for boron nitride ceramics with low raw material cost and easy availability, relatively simple preparation process, and high finished product density. Summary of the Invention

[0008] In view of the problems existing in the prior art, the object of the present invention is to provide a hexagonal boron nitride ceramic and a preparation method thereof, wherein the hexagonal boron nitride ceramic comprises a main phase and a dispersed phase, the main phase comprising h-BN, and the dispersed phase comprising Al2Y4O9; the hexagonal boron nitride ceramic has an apparent porosity of ≤5% and a density of ≥90%; the preparation method obtains a high-density hexagonal boron nitride ceramic containing a specific crystal phase component by mixing h-BN with a sintering aid and then sintering, and the obtained hexagonal boron nitride ceramic has an elastic modulus of ≥20.0 GPa and a flexural strength of ≥100 MPa; the preparation method is simple in process and has a low sintering temperature, which is conducive to reducing costs and promoting large-scale industrial production.

[0009] To achieve this object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a hexagonal boron nitride ceramic comprising a main phase and a dispersed phase, wherein the main phase comprises h-BN and the dispersed phase comprises Al2Y4O9; the hexagonal boron nitride ceramic has an apparent porosity of ≤5% and a density of ≥90%.

[0011] The present invention uses h-BN and a sintering aid capable of generating Al2Y4O9, such as Y2O3, B2O3 and AlN, and mixes and sinters them to obtain a hexagonal boron nitride ceramic containing a specific crystal phase composition and structure, that is, the main crystal phase is hexagonal boron nitride h-BN, and a small amount of dispersed phase Al2Y4O9 is dispersed, so that the obtained hexagonal boron nitride ceramic has the characteristics of high density and high elastic modulus.

[0012] The hexagonal boron nitride ceramic has an apparent porosity of ≤5%, for example, 5%, 4.5%, 4%, 3.5%, 3%, 2.5%, 2%, 1.5% or 1%, and a density of ≥90%, for example, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99%, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0013] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0014] As a preferred technical solution of the present invention, the mass fraction of the main phase is 80% to 95%, for example, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, etc., and the mass fraction of the dispersed phase is 5% to 20%, for example, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0015] Preferably, the elastic modulus of the hexagonal boron nitride ceramic is ≥20.0 GPa, for example, 20.0 GPa, 20.5 GPa, 21.0 GPa, 21.5 GPa, 22.0 GPa, 22.5 GPa, 23.0 GPa, 23.5 GPa, 24.0 GPa, 24.5 GPa or 25.0 GPa, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0016] Preferably, the flexural strength of the hexagonal boron nitride ceramic is ≥100 MPa, for example, 100 MPa, 105 MPa, 110 MPa, 115 MPa, 120 MPa, 125 MPa, 130 MPa, 135 MPa, 140 MPa, 145 MPa or 150 MPa, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0017] In a second aspect, the present invention provides a method for preparing the hexagonal boron nitride ceramic according to the first aspect, comprising the following steps:

[0018] h-BN is mixed with a sintering aid, wherein the sintering aid includes Y2O3, B2O3 and AlN, and sintered to obtain hexagonal boron nitride ceramics.

[0019] The preparation method adopts a method of adding a mixture of AlN, B2O3 and Y2O3 to h-BN powder to assist sintering. The hexagonal boron nitride ceramic prepared by sintering methods such as spark plasma sintering has high density and high elastic modulus. In addition, the raw materials used in the method are easy to obtain, the process conditions are easy to control, the production cost is relatively low, and large-scale preparation is possible.

[0020] AlN, B2O3 and Y2O3 not only generate dispersed phase and BN, but also act as additives. Among them, B2O3 has a melting point of 470℃. After exceeding the melting point, it turns into liquid, which can promote the rearrangement of BN particles and promote sintering. Too much B2O3 will reduce the high-temperature performance of the ceramic, and too little will not promote sintering enough. AlN has high hardness, low dielectric constant and dielectric loss. As an added phase, it plays a strengthening role when used in an appropriate amount without significantly reducing the dielectric properties of BN ceramics. Too much AlN will lead to a decrease in dielectric properties, and too little will not have a sufficient strengthening effect. Y2O3, as a sintering aid, promotes the sintering of BN and AlN. Too much Y2O3 will reduce the high-temperature performance of the ceramic, and too little will not promote sintering enough.

[0021] As a preferred technical solution of the present invention, the mass ratio of B2O3, AlN and Y2O3 is 1:(1-2):(4-7), for example, 1:1:4, 1:1:5, 1:1:6, 1:1:7, 1:1.1:4, 1:1.1:5, 1:1.1:6, 1:1.1:7, 1:1.2:4, 1:1.2:5, 1:1.2:6, 1:1.2:7, 1:1.3:4, 1:1.3:5, 1:1.3:6, 1:1.3:7, 1:1.4:4, 1:1.4:5, 1:1.4:6, 1:1.4:7, 1:1.5:4, 1:1.5:5, 1:1.5:6, 1:1.5:7, 1:1.6:4, 1:1.6:5, 1:1.6:6, 1:1.6:7, 1:1.7:4, 1:1.7:5, 1:1.7:6, 1:1.7:7, 1:1.8:4, 1:1.8:5, 1:1.8:6, 1:1.8:7, 1:1.9:4, 1:1.9:5, 1:1.9:6, 1:1.9:7, 1:2:4, 1:2:5, 1:2:6 or 1:2:7, etc., but are not limited to the listed values, other values ​​not listed within the above numerical range are also applicable.

[0022] When B2O3, AlN and Y2O3 are used as sintering aids, it is preferred to configure B2O3, AlN and Y2O3 according to the stoichiometric ratio of the generated "Al2Y4O9" and "BN", and control the molar amount and molar ratio. Preferably, the molar ratio of B2O3, AlN and Y2O3 is 1:2:2.

[0023] Preferably, the mass of the sintering aid accounts for 5% to 20% of the total mass of the sintering aid and the h-BN, for example, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0024] As a preferred technical solution of the present invention, the h-BN is a powder with a particle size of 100 to 200 nm, for example, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm or 200 nm, etc., but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0025] Preferably, the B2O3 is a powder with a particle size of 1 to 2 μm, for example, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm or 2 μm, etc., but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0026] Preferably, the AlN is a powder with a particle size of 1 to 2 μm, for example, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm or 2 μm, etc., but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0027] Preferably, the Y2O3 is a powder with a particle size of 50 to 100 nm, for example, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm or 100 nm, etc., but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0028] As a preferred technical solution of the present invention, the mixing method includes first mixing h-BN powder and a sintering aid into dry powder, then preparing the mixture into slurry, and grinding the mixture.

[0029] Preferably, the solvent for preparing the slurry includes anhydrous ethanol.

[0030] Preferably, the mass ratio of dry powder to solvent for preparing the slurry is (0.6-1.5):1, for example, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1 or 1.5:1, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0031] Preferably, the grinding method comprises ball milling.

[0032] Preferably, Si3N4 grinding balls are used in the ball milling.

[0033] The present invention preferably performs grinding, on the one hand to disperse and refine the powder agglomerates to achieve an appropriate particle size, and on the other hand to ensure that the powders are evenly mixed. When the particle size is appropriate and evenly dispersed in the h-BN powder, it is beneficial to ensure the effect of subsequent compression molding. The grinding is preferably wet grinding. In the case of dry grinding, the main h-BN powder tends to adhere to the inner wall and is difficult to access, thereby causing the mixed powder ratio to change. On the other hand, the particles of wet grinding are relatively more uniform. The present invention preferably uses Si3N4 grinding balls for ball milling powder mixing. Compared with grinding balls made of materials such as Al2O3, it can effectively avoid the introduction of oxide grinding ball impurities under high-energy and long-term ball milling.

[0034] Preferably, the ball-to-material mass ratio of the ball mill is (1-3):1, for example 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1, 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1 or 3:1, etc., but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0035] Preferably, the grinding time is 4 to 24 hours, for example, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours or 24 hours, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0036] Preferably, the grinding rotation direction is changed every 30 to 60 minutes, for example, 30 minutes, 33 minutes, 36 minutes, 39 minutes, 42 minutes, 45 minutes, 48 ​​minutes, 51 minutes, 54 minutes, 57 minutes or 60 minutes, etc., but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0037] As a preferred technical solution of the present invention, before sintering, drying, crushing, screening and forming are carried out in sequence.

[0038] Preferably, the drying comprises rotary evaporation and oven drying.

[0039] Preferably, the device used for rotary evaporation comprises a rotary evaporator.

[0040] Preferably, the temperature of the coolant of the rotary evaporator is -2 to 10°C, for example, -2°C, -1°C, 0°C, 1°C, 2°C, 3°C, 4°C, 5°C, 6°C, 7°C, 8°C, 9°C or 10°C, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0041] Preferably, the temperature of the heating fluid of the rotary evaporator is 40-70°C, for example, 40°C, 43°C, 46°C, 49°C, 52°C, 55°C, 58°C, 61°C, 64°C, 67°C or 70°C, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0042] Preferably, the rotation speed of the rotary evaporator is 10 to 60 rpm, for example, 10 rpm, 15 rpm, 20 rpm, 25 rpm, 30 rpm, 35 rpm, 40 rpm, 45 rpm, 50 rpm, 55 rpm or 60 rpm, etc., but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0043] Preferably, the device used for drying includes a vacuum drying oven.

[0044] Preferably, the drying temperature is 80-100°C, for example, 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, 92°C, 94°C, 96°C, 98°C or 100°C, and the drying time is 6-8h, for example, 6h, 6.2h, 6.4h, 6.6h, 6.8h, 7h, 7.2h, 7.4h, 7.6h, 7.8h or 8h, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0045] The present invention preferably adopts a combination of rotary evaporation and vacuum drying after ball milling to more completely remove the solvent anhydrous ethanol in the mixed slurry, and more efficiently obtains a uniformly mixed BN composite powder.

[0046] As a preferred technical solution of the present invention, the crushing includes grinding.

[0047] Preferably, the mesh size of the sieve used for screening is 170 to 230 mesh, such as 170 mesh, 180 mesh, 190 mesh, 200 mesh, 210 mesh, 220 mesh or 230 mesh, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0048] Preferably, the sieving is repeated 2 to 3 times.

[0049] Preferably, the forming method comprises using a steel mold and pre-pressing with a tablet press, demoulding to obtain a green blank, and sintering the green blank.

[0050] Preferably, the pre-pressing temperature is 15-35°C, for example, 15°C, 17°C, 19°C, 21°C, 23°C, 25°C, 27°C, 29°C, 31°C, 33°C or 35°C, etc., but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0051] Preferably, the pre-pressing pressure is 20 to 60 MPa, for example, 20 MPa, 25 MPa, 30 MPa, 35 MPa, 40 MPa, 45 MPa, 50 MPa, 55 MPa or 60 MPa, and the holding time is 5 to 15 min, for example, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min or 15 min, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0052] As a preferred technical solution of the present invention, the sintering method includes spark plasma sintering.

[0053] The present invention preferably adopts spark plasma sintering, which is more efficient and energy-saving than hot pressing sintering, saving time cost and economic cost of sintering sample preparation. From the perspective of time alone, the efficiency of spark plasma sintering is about 3 times that of hot pressing, and the size of the sample that can be sintered is between 12.5 and 200 mm.

[0054] Preferably, the spark plasma sintering method includes using a graphite mold and using graphite paper to separate the sample to be sintered from the contact surface of the graphite mold.

[0055] Preferably, after sintering and demolding, a sandblaster is used to remove the graphite carbon paper coated on the surface of the ceramic sample. This is efficient and convenient, and can avoid damage to the sample surface caused by manual grinding or scraping. At the same time, it is more energy-saving and safer than the grinding method.

[0056] Preferably, the sintering heating rate is 50 to 130°C / min, for example, 50°C / min, 60°C / min, 70°C / min, 80°C / min, 90°C / min, 100°C / min, 110°C / min, 120°C / min or 130°C / min, etc., but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0057] Preferably, the sintering temperature is 1500-1900°C, for example, 1500°C, 1550°C, 1600°C, 1650°C, 1700°C, 1750°C, 1800°C, 1850°C or 1900°C, and the holding time is 5-20 min, for example, 5 min, 8 min, 10 min, 12 min, 14 min, 16 min, 18 min or 20 min, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0058] Preferably, the sintering pressure is 20 to 70 MPa, for example, 20 MPa, 25 MPa, 30 MPa, 35 MPa, 40 MPa, 45 MPa, 50 MPa, 55 MPa, 60 MPa, 65 MPa or 70 MPa, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0059] Preferably, the sintering vacuum degree is less than 10Pa, such as 9Pa, 8Pa, 7Pa, 6Pa, 5Pa, 4Pa, 3Pa, 2Pa or 1Pa, etc., but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0060] The present invention does not limit the specific sintering process and equipment model. In actual operation, the sintering temperature, holding time, sintering pressure, etc. should be adjusted according to the actual situation to sinter the sample densely. In theory, the higher the sintering temperature and the longer the holding time, the more conducive to particle rearrangement and particle diffusion, which promotes sintering, but the energy consumption will be higher; the greater the pressure, the denser the ceramic. The vacuum requirement is to prevent the sample from being oxidized during the sintering process and the introduction of unfavorable oxides. Therefore, a vacuum degree of <10Pa can meet the needs. Of course, a lower vacuum degree or an inert atmosphere such as Ar can be selected as needed. It is further preferred that the sintering temperature is 1600-1700℃, the holding time is 5-10min, and the sintering pressure is 45-60MPa.

[0061] As a preferred technical solution of the present invention, the preparation method comprises the following steps:

[0062] B2O3, AlN and Y2O3 powders are weighed and mixed in a mass ratio of 1:(1-1.5):(4-7), wherein the h-BN powder has a particle size of 100-200 nm, the B2O3 powder has a particle size of 1-2 μm, the AlN powder has a particle size of 1-2 μm, and the Y2O3 powder has a particle size of 50-100 nm, which is recorded as BAY powder and used as an additive;

[0063] Then, h-BN powder and BAY powder are mixed to obtain a ceramic powder mixture, which is recorded as M powder, wherein the mass content of BAY powder is 5% to 20%;

[0064] Add M powder to anhydrous ethanol to prepare a slurry with a mass ratio of M powder to anhydrous ethanol = (0.6-1.5):1. Use Si3N4 grinding balls with a ball-to-ethanol mass ratio of (1-3):1 and ball mill for 4-24 hours, changing the rotation direction of the grinding ball mill every 30-60 minutes.

[0065] The temperature of the cooling liquid of the rotary evaporator is set to -2 to 10°C, the temperature of the heating fluid is set to 40 to 70°C, and the rotation speed is set to 10 to 60 rpm. After ball milling and filtering to remove the grinding balls, the uniformly mixed slurry is subjected to rotary evaporation to remove anhydrous ethanol, and then placed in a vacuum drying oven at 80 to 100°C for 6 to 8 hours. Then, it is ground and crushed, and the mesh size is controlled to 170 to 230 mesh, and sieved 2 to 3 times to prepare a BN composite powder.

[0066] The BN composite powder is loaded into a steel mold and pre-pressed using a tablet press. The pre-pressing temperature is controlled at 15-35°C, the pressure is 20-60 MPa, and the holding time is 5-15 minutes. The mold is then removed to obtain a green body of the h-BN ceramic.

[0067] The green blank is placed in a graphite mold of appropriate size, and the inner wall contacting the green blank is separated by graphite paper. Then the graphite mold is placed in a spark plasma sintering device, and the heating rate is controlled to be 50-130℃ / min, the pressure is 20-70MPa, and the vacuum degree is less than 10Pa. It is sintered at 1500-1900℃ for 5-20min.

[0068] After the discharge plasma sintering equipment is cooled to room temperature, the graphite mold is taken out and demoulded, and the graphite paper on the surface is removed by a sandblasting machine to obtain hexagonal boron nitride ceramics.

[0069] Compared with the existing technical solutions, the present invention has at least the following beneficial effects:

[0070] The present invention utilizes a first additive containing Y2O3 as a rare earth sintering aid, which is mixed with a second additive containing B2O3 and / or AlN and h-BN, followed by sintering. This produces a highly dense, high-elastic-modulus hexagonal boron nitride ceramic with a specific crystalline phase composition and structure: h-BN as the primary crystalline phase, with a small amount of Al2Y4O9 dispersed therein. The resulting hexagonal boron nitride ceramic exhibits an apparent porosity of ≤5%, a density of ≥90%, an elastic modulus of ≥20.0 GPa, and a flexural strength of ≥100 MPa. It can be used as a wave-transmitting material in applications such as radomes and antenna windows, or in related fields. The preparation method is simple, facilitates the production of large-scale boron nitride ceramic components, and has a low sintering temperature, reducing costs and facilitating large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 1-4 and 1-2 are X-ray diffraction patterns of the hexagonal boron nitride ceramics obtained in Examples 1-4 and Comparative Examples 1-2;

[0072] Figure 2 is a SEM surface morphology of the hexagonal boron nitride ceramic obtained in Example 1;

[0073] Figure 3is a SEM backscattered electron image of the hexagonal boron nitride ceramic obtained in Example 1;

[0074] Figure 4 1 is an EDS spectrum analysis diagram of the hexagonal boron nitride ceramic obtained in Example 1;

[0075] Figure 5 This is a macroscopic morphology of the hexagonal boron nitride ceramic obtained in Example 1. DETAILED DESCRIPTION

[0076] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0077] It should be apparent to those skilled in the art that the embodiments are only intended to help understand the present invention and should not be considered as specific limitations of the present invention.

[0078] Example 1

[0079] This embodiment provides a hexagonal boron nitride ceramic, and the preparation method of the hexagonal boron nitride ceramic is as follows:

[0080] (1) B2O3, AlN, and Y2O3 powders were weighed and mixed in a mass ratio of 1:1:5, wherein the h-BN powder had a particle size of 100-200 nm, the B2O3 powder had a particle size of 1-2 μm, the AlN powder had a particle size of 1-2 μm, and the Y2O3 powder had a particle size of 50-100 nm, which was recorded as BAY powder and used as an additive;

[0081] h-BN powder and BAY powder are then mixed to obtain a ceramic powder mixture, which is recorded as M powder, wherein the mass content of BAY powder is 20%;

[0082] (2) M powder was added to anhydrous ethanol to prepare a slurry with a mass ratio of M powder to anhydrous ethanol = 0.6:1. Si3N4 grinding balls were used with a ball-to-ethanol mass ratio of 1:1. The ball milling was performed for 4 h, and the rotation direction of the grinding ball mill was changed every 30 min.

[0083] (3) The temperature of the cooling liquid (water) of the rotary evaporator was set to -2°C, the temperature of the heating fluid (silicone oil or water) was set to 50°C, and the rotation speed was set to 30 rpm. The uniformly mixed slurry obtained after ball milling and filtering out the grinding balls was subjected to rotary evaporation to remove anhydrous ethanol, and then placed in a vacuum drying oven at 80°C for 8 h. Then, it was ground and crushed, and the mesh size of the sieve was controlled to 200 mesh and the pore size was 0.074 mm. The sieving was repeated twice to prepare BN composite powder;

[0084] (4) The BN composite powder was placed in a steel mold and pre-pressed using a tablet press at room temperature with a pressure of 20 MPa for 5 min, and then demolded to obtain a green body of h-BN ceramics;

[0085] (5) The green blank is placed in a graphite mold of appropriate size, and the inner wall contacting the green blank is separated by graphite paper. The graphite mold is then placed in a spark plasma sintering device, and the heating rate is controlled to be 100°C / min, the pressure is 45MPa, and the vacuum degree is less than 10Pa. The product is sintered at 1700°C for 10min.

[0086] (6) After the discharge plasma sintering equipment is cooled to room temperature, the graphite mold is taken out and demolded, and the graphite paper on the surface is removed by a sandblasting machine to obtain hexagonal boron nitride ceramics.

[0087] Example 2

[0088] This embodiment provides a hexagonal boron nitride ceramic, and the preparation method of the hexagonal boron nitride ceramic is as follows:

[0089] (1) B2O3, AlN, and Y2O3 powders were weighed and mixed in a mass ratio of 1:1.2:6, wherein the h-BN powder had a particle size of 100-200 nm, the B2O3 powder had a particle size of 1-2 μm, the AlN powder had a particle size of 1-2 μm, and the Y2O3 powder had a particle size of 50-100 nm, which was recorded as BAY powder and used as an additive;

[0090] h-BN powder and BAY powder are then mixed to obtain a ceramic powder mixture, which is recorded as M powder, wherein the mass content of BAY powder is 15%;

[0091] (2) Add M powder to anhydrous ethanol to prepare a slurry with a mass ratio of M powder to anhydrous ethanol = 1:1. Use Si3N4 grinding balls with a ball-to-powder mass ratio of 2:1 and ball mill for 8 h. Change the rotation direction of the grinding ball mill every 60 min.

[0092] (3) The temperature of the cooling liquid (water) of the rotary evaporator was set to 0°C, the temperature of the heating fluid (silicone oil or water) was set to 60°C, and the rotation speed was set to 40 rpm. The uniformly mixed slurry obtained after ball milling and filtering out the grinding balls was subjected to rotary evaporation to remove anhydrous ethanol, and then placed in a vacuum drying oven at 90°C for 7 hours. Then, the slurry was ground and crushed, and the mesh size was controlled to 200 mesh and the pore size was 0.074 mm. The sieving was repeated 3 times to prepare BN composite powder.

[0093] (4) The BN composite powder was placed in a steel mold and pre-pressed using a tablet press at room temperature with a pressure of 30 MPa and a holding time of 5 min, and then demolded to obtain a green body of h-BN ceramics;

[0094] (5) The green blank is placed in a graphite mold of appropriate size, and the inner wall contacting the green blank is separated by graphite paper. The graphite mold is then placed in a spark plasma sintering device, and the heating rate is controlled to be 110°C / min, the pressure is 40 MPa, and the vacuum degree is less than 10 Pa. The product is sintered at 1800°C for 5 min.

[0095] (6) After the discharge plasma sintering equipment is cooled to room temperature, the graphite mold is taken out and demolded, and the graphite paper on the surface is removed by a sandblasting machine to obtain hexagonal boron nitride ceramics.

[0096] Example 3

[0097] This embodiment provides a hexagonal boron nitride ceramic, and the preparation method of the hexagonal boron nitride ceramic is as follows:

[0098] (1) B2O3, AlN, and Y2O3 powders were weighed and mixed in a mass ratio of 1:2:6.5, wherein the h-BN powder had a particle size of 100-200 nm, the B2O3 powder had a particle size of 1-2 μm, the AlN powder had a particle size of 1-2 μm, and the Y2O3 powder had a particle size of 50-100 nm, which was recorded as BAY powder and used as an additive;

[0099] h-BN powder and BAY powder are then mixed to obtain a ceramic powder mixture, which is recorded as M powder, wherein the mass content of BAY powder is 10%;

[0100] (2) Add M powder to anhydrous ethanol to prepare a slurry with a mass ratio of M powder to anhydrous ethanol = 1.5:1. Use Si3N4 grinding balls with a ball-to-powder mass ratio of 2.5:1 and ball mill for 12 hours. Change the rotation direction of the grinding ball mill every 60 minutes.

[0101] (3) The temperature of the cooling liquid (water) of the rotary evaporator was set to 5°C, the temperature of the heating fluid (silicone oil or water) was set to 55°C, and the rotation speed was set to 50 rpm. The uniformly mixed slurry obtained after ball milling and filtering out the grinding balls was subjected to rotary evaporation to remove anhydrous ethanol, and then placed in a vacuum drying oven at 100°C for 6 hours. Then, it was ground and crushed, and the mesh size of the sieve was controlled to 200 mesh and the pore size was 0.074 mm. The sieving was repeated twice to prepare BN composite powder;

[0102] (4) The BN composite powder was placed in a steel mold and pre-pressed using a tablet press at room temperature with a pressure of 50 MPa and a holding time of 10 min, and then demolded to obtain a green body of h-BN ceramics;

[0103] (5) The green blank is placed in a graphite mold of appropriate size, and the inner wall contacting the green blank is separated by graphite paper. The graphite mold is then placed in a spark plasma sintering device, and the heating rate is controlled to be 100°C / min, the pressure is 50 MPa, and the vacuum degree is less than 10 Pa. The product is sintered at 1700°C for 10 min.

[0104] (6) After the discharge plasma sintering equipment is cooled to room temperature, the graphite mold is taken out and demolded, and the graphite paper on the surface is removed by a sandblasting machine to obtain hexagonal boron nitride ceramics.

[0105] Example 4

[0106] This embodiment provides a hexagonal boron nitride ceramic, and the preparation method of the hexagonal boron nitride ceramic is as follows:

[0107] (1) B2O3, AlN, and Y2O3 powders were weighed and mixed in a mass ratio of 1:1.5:6, wherein the h-BN powder had a particle size of 100-200 nm, the B2O3 powder had a particle size of 1-2 μm, the AlN powder had a particle size of 1-2 μm, and the Y2O3 powder had a particle size of 50-100 nm, which was recorded as BAY powder and used as an additive;

[0108] h-BN powder and BAY powder are then mixed to obtain a ceramic powder mixture, which is recorded as M powder, wherein the mass content of BAY powder is 10%;

[0109] (2) M powder was added to anhydrous ethanol to prepare a slurry with a mass ratio of M powder to anhydrous ethanol = 1.2:1. Si3N4 grinding balls were used with a ball-to-powder mass ratio of 3:1. The ball milling was performed for 24 h, and the rotation direction of the grinding ball mill was changed every 60 min.

[0110] (3) The temperature of the cooling liquid (water) of the rotary evaporator was set to 10°C, the temperature of the heating fluid (silicone oil or water) was set to 70°C, and the rotation speed was set to 60 rpm. The uniformly mixed slurry obtained after ball milling and filtering out the grinding balls was subjected to rotary evaporation to remove anhydrous ethanol, and then placed in a vacuum drying oven at 90°C for 7 hours. Then, it was ground and crushed, and the mesh size of the sieve was controlled to 200 mesh and the pore size was 0.074 mm. The sieving was repeated 3 times to prepare BN composite powder;

[0111] (4) The BN composite powder was placed in a steel mold and pre-pressed using a tablet press at room temperature at a pressure of 60 MPa for 15 min, and then demolded to obtain a green body of h-BN ceramics;

[0112] (5) The green blank is placed in a graphite mold of appropriate size, and the inner wall contacting the green blank is separated by graphite paper. The graphite mold is then placed in a spark plasma sintering device, and the heating rate is controlled to be 100°C / min, the pressure is 45MPa, and the vacuum degree is less than 10Pa. The product is sintered at 1900°C for 10min.

[0113] (6) After the discharge plasma sintering equipment is cooled to room temperature, the graphite mold is taken out and demolded, and the graphite paper on the surface is removed by a sandblasting machine to obtain hexagonal boron nitride ceramics.

[0114] Example 5

[0115] This embodiment provides a hexagonal boron nitride ceramic. In the preparation method of the hexagonal boron nitride ceramic, the amount of BAY powder is adjusted in step (1) so that the mass content of BAY powder in M ​​powder is adjusted from 20% to 2%. Other than this, the other conditions are exactly the same as those in Example 1.

[0116] Example 6

[0117] This embodiment provides a hexagonal boron nitride ceramic. In the preparation method of the hexagonal boron nitride ceramic, the amount of BAY powder is adjusted in step (1) so that the mass content of BAY powder in M ​​powder is adjusted from 20% to 5%. Other than this, the other conditions are exactly the same as those in Example 1.

[0118] Example 7

[0119] This embodiment provides a hexagonal boron nitride ceramic. In the preparation method of the hexagonal boron nitride ceramic, the amount of BAY powder is adjusted in step (1) so that the mass content of BAY powder in M ​​powder is adjusted from 20% to 10%. Other than this, the other conditions are exactly the same as those in Example 1.

[0120] Example 8

[0121] This embodiment provides a hexagonal boron nitride ceramic. In the preparation method of the hexagonal boron nitride ceramic, the amount of BAY powder is adjusted in step (1) so that the mass content of BAY powder in M ​​powder is adjusted from 20% to 23%. Other than this, the other conditions are exactly the same as those in Example 1.

[0122] Comparative Example 1

[0123] This comparative example provides a hexagonal boron nitride ceramic. In the preparation method of the hexagonal boron nitride ceramic, B2O3, AlN and Y2O3 are not used in step (1). The h-BN powder with a particle size of 100 to 200 nm is directly pre-pressed in step (4), and then steps (5) and (6) are performed. Apart from this, the other conditions are exactly the same as those in Example 1.

[0124] Comparative Example 2

[0125] This comparative example provides a hexagonal boron nitride ceramic. In the preparation method of the hexagonal boron nitride ceramic, AlN is not used in step (1), and the amounts of B2O3 and Y2O3 are kept unchanged. Apart from this, other conditions are exactly the same as those in Example 1.

[0126] Comparative Example 3

[0127] This comparative example provides a hexagonal boron nitride ceramic. In the preparation method of the hexagonal boron nitride ceramic, B2O3 is not used in step (1), and the amounts of AlN and Y2O3 are kept unchanged. Apart from this, other conditions are exactly the same as those in Example 1.

[0128] Comparative Example 4

[0129] This comparative example provides a hexagonal boron nitride ceramic. In the preparation method of the hexagonal boron nitride ceramic, Y2O3 is not used in step (1), and the amounts of AlN and B2O3 are kept unchanged. Apart from this, other conditions are exactly the same as those in Example 1.

[0130] Comparative Example 5

[0131] This comparative example provides a hexagonal boron nitride ceramic. In the preparation method of the hexagonal boron nitride ceramic, AlN and B2O3 are not used in step (1), and the amount of Y2O3 is kept unchanged. Apart from this, other conditions are exactly the same as those in Example 1.

[0132] Ⅰ. Composition and morphology characterization

[0133] Figure 1 3 is the XRD spectrum of the hexagonal boron nitride ceramics obtained in Examples 1-4 and Comparative Example 1. It can be seen from the figure that the main phase of the hexagonal boron nitride ceramics obtained in Examples 1-4 is h-BN, and also contains a certain amount of Al2Y4O9 dispersed phase, while Comparative Example 1 only has h-BN phase.

[0134] The hexagonal boron nitride ceramic matrix obtained in Example 1 is a BN phase and contains a dispersed phase of Al2Y4O9 yttrium aluminate. Figure 2 This is the SEM image of the hexagonal boron nitride ceramic obtained in Example 1, which shows that the ceramic is stacked in a card room structure. Figure 3 The backscattered image shows obvious element contrast. Figure 4 EDS energy spectrum analysis shows that the concentrated areas of the distribution of the three elements Al, Y, and O are consistent. Combined with the XRD results, it can be seen that Figure 3The white area represents Al2Y4O9, which is uniformly dispersed within the BN matrix. Test results indicate that the B, N, O, Al, and Y content of the hexagonal boron nitride ceramic prepared in Example 1 are 19.77%, 54.95%, 5.43%, 2.47%, and 17.38%, respectively. Using Image J, the area of ​​the white area was calculated and converted to volume fraction, revealing a mass content of 19.27% ​​for Al2Y4O9. Figure 5 This is a macroscopic morphology of the hexagonal boron nitride ceramic obtained in Example 1. The obtained hexagonal boron nitride ceramic has excellent appearance, morphology and product quality.

[0135] II. Performance Testing

[0136] The hexagonal boron nitride ceramics obtained in the Examples and Comparative Examples were tested: the apparent porosity and actual density of the ceramic blocks were measured using the Archimedean principle, and the density was calculated by calculating the ratio of actual density to theoretical density. The nanoindentation hardness and simplified elastic modulus of the ceramics were measured using a Bruker Hysitron TI980 nanoindenter, using a standard Berkovich indenter and loading-holding-unloading cycles of 5s, 2s, and 5s, respectively. The flexural strength of the ceramics was measured using a Sinter WDW-20kN testing machine according to the three-point flexural strength test standard GB / T 6569-2006, "Test Method for Flexural Strength of Fine Ceramics." The specimen dimensions were 3 mm × 4 mm × 35 mm, with a span of 30 mm and a loading rate of 0.5 mm / min. The results are reported in Table 1.

[0137] Table 1

[0138]

[0139]

[0140] As can be seen from Table 1:

[0141] The hexagonal boron nitride ceramics prepared in Examples 1-4 have an apparent porosity of ≤5%, a density of ≥90%, and all have an elastic modulus of ≥20.0GPa and a flexural strength of ≥100MPa. Compared with Examples 11 to 14, Example 1 has too little BAY powder mass, and the effect of promoting sintering and densification is weak. At the same time, the ceramic strength is also small. However, compared with Comparative Example 1, the density, porosity and strength are improved, indicating that BAY powder has a certain effect of promoting sintering and densification, but when the addition amount is small, the effect is small. Compared with Comparative Example 1, the pure BN ceramic in Example 1 is difficult to sinter, has a large apparent porosity (15.31%), and has low flexural strength. The addition of 20wt.% of BAY powder significantly improves the porosity, density and strength of the ceramic. Compared with Comparative Example 2, Example 1 does not add AlN powder. The liquid phase diffusion of B2O3 promotes particle rearrangement and the sintering promotion of Y2O3 plays a certain densification and sintering effect on the ceramic, but this effect is not as strong as the addition of BAY powder. Compared with Comparative Example 3, Example 1 does not add B2O3. Y2O3 can promote sintering as a sintering aid. At the same time, AlN can improve the flexural strength of the ceramic through the second phase reinforcement effect, but the effect of the two powders is not as strong as BAY powder. Compared with Comparative Example 4, Example 1 does not add Y2O3. B2O3 can promote BN diffusion through liquid phase sintering as a sintering aid, which plays a role in promoting sintering. At the same time, AlN can improve the flexural strength of the ceramic through the second phase reinforcement effect, but the effect of the two powders is not as strong as BAY powder. Compared with Comparative Example 5, Example 1 does not add B2O3 and AlN. It relies only on the sintering promotion effect of Y2O3. The sintering promotion and densification effect are small. BAY powder has excellent sintering promotion and densification effects. At the same time, the sintered ceramic has a higher flexural strength.

[0142] While the present invention is described through the above-described embodiments to illustrate the detailed structural features of the present invention, the present invention is not limited to these detailed structural features, nor does it necessarily rely on these detailed structural features for implementation. Those skilled in the art should understand that any improvements to the present invention, equivalent replacements for selected components, additions of auxiliary components, and selection of specific embodiments, etc., fall within the scope of protection and disclosure of the present invention.

[0143] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0144] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0145] In addition, the various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A hexagonal boron nitride ceramic, characterized in that: The hexagonal boron nitride ceramic comprises a main phase and a dispersed phase, wherein the main phase comprises h-BN and the dispersed phase comprises Al2Y4O9; the apparent porosity of the hexagonal boron nitride ceramic is ≤5% and the density is ≥90%; Calculated based on the mass of the hexagonal boron nitride ceramic being 100%, the mass fraction of the main phase is 80% to 95%, and the mass fraction of the dispersed phase is 5% to 20%; The preparation method of the hexagonal boron nitride ceramic comprises: mixing h-BN with a sintering aid, wherein the sintering aid comprises Y2O3, B2O3 and AlN, and sintering to obtain the hexagonal boron nitride ceramic.

2. The hexagonal boron nitride ceramic according to claim 1, characterized in that The elastic modulus of the hexagonal boron nitride ceramic is ≥20.0 GPa.

3. The hexagonal boron nitride ceramic according to claim 1, characterized in that The bending strength of the hexagonal boron nitride ceramic is ≥100 MPa.

4. A method for preparing the hexagonal boron nitride ceramic according to claim 1, characterized in that: The steps include: h-BN is mixed with a sintering aid, wherein the sintering aid includes Y2O3, B2O3 and AlN, and sintered to obtain hexagonal boron nitride ceramics.

5. The preparation method according to claim 4, characterized in that The mass ratio of B2O3, AlN and Y2O3 is 1:(1-2):(4-7).

6. The preparation method according to claim 4, characterized in that The mass of the sintering aid accounts for 5% to 20% of the total mass of the sintering aid and the h-BN.

7. The preparation method according to claim 4, characterized in that The h-BN is in powder form with a particle size of 100 to 200 nm.

8. The preparation method according to claim 4, characterized in that The B2O3 is in powder form with a particle size of 1 to 2 μm.

9. The preparation method according to claim 4, characterized in that The AlN is in powder form, and the particle size is 1 to 2 μm.

10. The preparation method according to claim 4, characterized in that The Y2O3 is in powder form with a particle size of 50 to 100 nm.

11. The preparation method according to claim 4, characterized in that The mixing method includes first mixing h-BN powder and a sintering aid into dry powder, then preparing the mixture into slurry, and grinding the mixture.

12. The preparation method according to claim 11, characterized in that The solvent for preparing the slurry includes anhydrous ethanol.

13. The preparation method according to claim 11, characterized in that The mass ratio of the dry powder to the solvent for preparing the slurry is (0.6-1.5):

1.

14. The preparation method according to claim 11, characterized in that The grinding method includes ball milling.

15. The preparation method according to claim 14, characterized in that The ball milling uses Si3N4 grinding balls.

16. The preparation method according to claim 14, characterized in that The ball-to-material mass ratio of the ball mill is (1-3):

1.

17. The preparation method according to claim 11, characterized in that The grinding time is 4 to 24 hours.

18. The preparation method according to claim 11, characterized in that The grinding rotation direction is changed every 30 to 60 minutes.

19. The preparation method according to claim 4, characterized in that Before sintering, the raw materials are dried, crushed, screened and formed in sequence.

20. The preparation method according to claim 19, characterized in that The drying includes rotary evaporation and oven drying.

21. The preparation method according to claim 20, characterized in that The device used in the rotary evaporation includes a rotary evaporator.

22. The preparation method according to claim 21, characterized in that The temperature of the coolant of the rotary evaporator is -2 to 10°C.

23. The preparation method according to claim 21, characterized in that The temperature of the heating fluid of the rotary evaporator is 40-70°C.

24. The preparation method according to claim 21, characterized in that The rotation speed of the rotary evaporator is 10 to 60 rpm.

25. The preparation method according to claim 20, characterized in that The device used for drying includes a vacuum drying oven.

26. The preparation method according to claim 20, characterized in that The drying temperature is 80-100° C. and the drying time is 6-8 hours.

27. The preparation method according to claim 19, characterized in that The crushing includes grinding.

28. The preparation method according to claim 19, characterized in that The mesh size of the sieve used in the sieving is 170 to 230 meshes.

29. The preparation method according to claim 19, characterized in that The sieving is repeated 2 to 3 times.

30. The preparation method according to claim 19, characterized in that The molding method includes using a steel mold and pre-pressing with a tablet press, demoulding to obtain a green blank, and sintering the green blank.

31. The preparation method according to claim 30, characterized in that The pre-pressing temperature is 15-35°C.

32. The preparation method according to claim 30, characterized in that The pre-pressing pressure is 20-60 MPa, and the holding time is 5-15 minutes.

33. The preparation method according to claim 4, characterized in that The sintering method includes spark plasma sintering.

34. The preparation method according to claim 33, characterized in that The spark plasma sintering method includes using a graphite mold and using graphite paper to separate the contact surface of the sample to be sintered from the graphite mold.

35. The preparation method according to claim 4, characterized in that The heating rate of the sintering is 50-130° C. / min.

36. The preparation method according to claim 4, characterized in that The sintering temperature is 1500-1900° C., and the heat preservation time is 5-20 minutes.

37. The preparation method according to claim 4, characterized in that The sintering pressure is 20-70 MPa.

38. The preparation method according to claim 4, characterized in that The vacuum degree of the sintering is less than 10Pa.

39. The preparation method according to any one of claims 5 to 38, characterized in that: The preparation method comprises the following steps: B2O3, AlN and Y2O3 powders were weighed and mixed in a mass ratio of 1:(1-2):(4-7), wherein the h-BN powder had a particle size of 100-200 nm, the B2O3 powder had a particle size of 1-2 μm, the AlN powder had a particle size of 1-2 μm, and the Y2O3 powder had a particle size of 50-100 nm, and were recorded as BAY powder as an additive; Then, h-BN powder and BAY powder are mixed to obtain a ceramic powder mixture, which is recorded as M powder, wherein the mass content of BAY powder is 5% to 20%; Add M powder to anhydrous ethanol to prepare a slurry with a mass ratio of M powder to anhydrous ethanol = (0.6-1.5):

1. Use Si3N4 grinding balls with a ball-to-ethanol mass ratio of (1-3):1 and ball mill for 4-24 hours, changing the rotation direction of the grinding ball mill every 30-60 minutes. The temperature of the cooling liquid of the rotary evaporator is set to -2 to 10°C, the temperature of the heating fluid is set to 40 to 70°C, and the rotation speed is set to 10 to 60 rpm. After ball milling and filtering to remove the grinding balls, the uniformly mixed slurry is subjected to rotary evaporation to remove anhydrous ethanol, and then placed in a vacuum drying oven at 80 to 100°C for 6 to 8 hours. Then, it is ground and crushed, and the mesh size is controlled to 170 to 230 mesh, and sieved 2 to 3 times to prepare a BN composite powder. The BN composite powder is loaded into a steel mold and pre-pressed using a tablet press. The pre-pressing temperature is controlled at 15-35°C, the pressure is 20-60 MPa, and the holding time is 5-15 minutes. The mold is then removed to obtain a green body of the h-BN ceramic. The green blank is placed in a graphite mold of appropriate size, and the inner wall contacting the green blank is separated by graphite paper. Then the graphite mold is placed in a spark plasma sintering device, and the heating rate is controlled to be 50-130℃ / min, the pressure is 20-70MPa, and the vacuum degree is less than 10Pa. It is sintered at 1500-1900℃ for 5-20min. After the discharge plasma sintering equipment is cooled to room temperature, the graphite mold is taken out and demoulded, and the graphite paper on the surface is removed by a sandblasting machine to obtain hexagonal boron nitride ceramics.

Images