High-density boron nitride ceramic material as well as preparation method and application thereof

Abstract

The invention relates to a high-density boron nitride ceramic material as well as a preparation method and application thereof. The high-density boron nitride ceramic material comprises a main phase, a second phase and an additive, the main phase comprises h-BN, the second phase comprises Al2Y4O9, and the additive comprises chopped BN fibers. The strength of the BN composite ceramic material is enhanced by adding the chopped BN fibers into the high-density boron nitride ceramic material, meanwhile, the excellent wave-transparent performance of the BN ceramic is kept, meanwhile, the Al2Y4O9 can ensure that the boron nitride ceramic material with higher density is obtained through sintering under a relatively low-temperature condition, so that the energy consumption is reduced, the chopped BN fibers are combined with an h-BN main phase, and the energy consumption is reduced. Deformation of the h-BN main phase can be restrained, meanwhile, deformation of the h-BN main phase is restrained by the h-BN, and therefore the mutual enhancement effect is achieved; in addition, the mechanical property is further improved due to deflection of fibers or BN crystal grains when the fibers are broken and cracked, and the bending strength of the high-density boron nitride ceramic material is improved due to the comprehensive action.

Description

Technical Field

[0001] The invention relates to the technical field of ceramic materials, and in particular to a high-density boron nitride ceramic material and a preparation method and application thereof. Background Art

[0002] h-BN ceramic matrix composites have good high temperature oxidation resistance, excellent dielectric properties and good corrosion resistance. As an ideal material for the wave-transmitting components of high-speed aircraft such as the new generation of radomes and antenna windows, they have always attracted attention in the aerospace field. 2 The covalent bond hybrid structure has a large atomic diffusion activation energy, and its unique lamellar morphology makes it easy to form a card house structure when stacked, which makes it difficult to sinter single-phase h-BN to a dense state. Therefore, domestic and foreign researchers have added Al2O3, AlN, SiO2, Y2O3, ZrO2, Si3N4, MAS (magnesium aluminum silicate glass) and other substances as the second phase in the form of units or multiples to h-BN on the basis of improving the high-temperature sintering process, producing a liquid phase at high temperature, promoting the adhesion and particle rearrangement of h-BN particles, and improving the sintering performance and densification degree of ceramics, so as to obtain h-BN composite ceramics with excellent comprehensive performance. In order to strengthen and toughen h-BN ceramics and obtain h-BN ceramic-based composites with stronger mechanical properties, many scholars have prepared a series of continuous fiber-reinforced h-BN composites through the polymer precursor impregnation-pyrolysis process (PIP), such as SiO2f / BN, SiO2f / BN–Si3N4, Nextel-720f / BN and Si-N-Of / BN composites. Among them, the preparation of continuous BN fiber-reinforced h-BN composites requires a fiber braid, which puts high demands on the fiber braiding performance and greatly increases the preparation cost. At the same time, among the existing BN precursors, polyborazane is more active, and the other BN precursors have decarbonization problems as impregnants, so there is currently no more suitable BN precursor impregnation solution.

[0003] CN111848179B discloses a method for preparing a high-strength boron nitride ceramic that can be used in an ultra-high temperature environment. The boron nitride-based ceramic composite material is made of 0-25wt.% zirconium diboride, 0-15wt.% boron powder and 60-100wt.% hexagonal boron nitride powder through a hot pressing sintering process. The ceramic mechanical properties of this method are good, but the high temperature of 1800-2100°C is required during sintering, and the energy consumption is large. CN110240488A discloses a high-temperature resistant and wave-transmitting ceramic-based composite material and a preparation method thereof. The method uses silicon nitride fiber as a reinforcing phase and boron nitride obtained by conversion of cycloborazine as a precursor as a matrix. The prepared ceramic-based composite material has excellent high-temperature stability, high-temperature mechanical properties and high-temperature dielectric properties, but its preparation cycle is long and the synthetic preparation process is complicated and cumbersome. CN107986806B discloses an alumina fiber reinforced nitride-based wave-transparent composite material and a preparation method thereof. The method makes full use of the strong high-temperature oxidation resistance of alumina fiber and the good thermal, mechanical and electrical comprehensive properties of boron nitride matrix, so that the high-temperature mechanical properties and dielectric properties of the composite material are improved. However, the preparation process is relatively complicated, and the dielectric constant of the alumina fiber used is relatively large, about 9, and the temperature resistance is relatively low, about 1400°C.

[0004] Therefore, there is an urgent need to provide a fiber-reinforced boron nitride composite ceramic material with high density, high strength and excellent wave transmission performance, and to develop a preparation method for a high-density boron nitride ceramic material with low sintering temperature, low energy consumption and relatively simple preparation process. Summary of the invention

[0005] In order to solve the above technical problems, the purpose of the present invention is to provide a high-density boron nitride ceramic material and a preparation method and application thereof. The high-density boron nitride ceramic material provided by the present invention uses short-cut BN fibers as additives to enhance the bending strength of BN composite ceramic materials while maintaining the excellent wave transmission performance of BN ceramics. The short-cut BN fiber-reinforced boron nitride ceramic material is more likely to achieve quasi-isotropy in a plane, which is beneficial to improving the strain failure, fracture toughness and elastic modulus of boron nitride ceramics, and has a certain strengthening effect on boron nitride ceramics. In addition, due to the presence of short-cut BN fibers, fiber breakage and crack deflection when encountering fibers or BN grains further improve the mechanical properties, so that the boron nitride ceramic material can achieve high density and bending strength at a lower sintering temperature, which reduces energy consumption compared with traditional high-temperature sintering, and effectively avoids the negative impact of high-temperature volatilization of low-melting point additives on the ceramic structure and performance.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a high-density boron nitride ceramic material, which includes a main phase, a second phase and an additive; the main phase includes h-BN, the second phase includes Al2Y4O9, and the additive includes chopped BN fibers.

[0008] The "high density" mentioned in the present invention refers to a density ≥ 90%.

[0009] The present invention enhances the strength of the high-density boron nitride ceramic material by adding short-cut BN fibers to the material, while maintaining the excellent wave transmission performance of the BN ceramic, and enables the prepared boron nitride ceramic material to achieve high density and bending strength at a relatively low sintering temperature, thereby reducing energy consumption; the short-cut BN fibers are combined with the h-BN main phase to constrain the deformation of the h-BN main phase, while the deformation of the short-cut BN fibers themselves is constrained by the h-BN, and the fiber breakage and cracks are deflected when encountering the fiber or the BN grain, further improving the mechanical properties, and the combined effect improves the bending strength of the high-density boron nitride ceramic material; in addition, the addition of the short-cut BN ceramic fibers can also stabilize the dielectric properties of the boron nitride ceramic material.

[0010] 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 preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0011] Preferably, the average length of the chopped BN fibers is 2-3 mm, for example, 2.0 mm, 2.1 mm, 2.2 mm, 2.3 mm, 2.4 mm, 2.5 mm, 2.6 mm, 2.7 mm, 2.8 mm, 2.9 mm or 3 mm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0012] The present invention further enhances the strength of the BN composite ceramic material by controlling the average length of the short-cut BN fibers in the high-density boron nitride ceramic material within a specific range, while maintaining the excellent wave transmission performance of the BN ceramic. If the average length of the short-cut BN fibers is too short, less than 2 mm, the fiber pull-out effect will also be weakened, the fiber reinforcement effect will be weakened, and the bending strength of the composite ceramic material will decrease; if the average length of the short-cut BN fibers is too long, greater than 3 mm, the longer fibers will be intertwined during the mixing process, making it difficult to mix evenly, resulting in a lower density of the final boron nitride ceramic material and poor strength uniformity.

[0013] The diameter of the chopped BN fibers is 10-13 μm, for example, 10 μm, 10.2 μm, 10.4 μm, 10.6 μm, 10.8 μm, 11 μm, 11.2 μm, 11.4 μm, 11.6 μm, 11.8 μm, 12 μm, 12.2 μm, 12.4 μm, 12.6 μm, 12.8 μm or 13 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0014] Preferably, the density of the high-density boron nitride ceramic material is ≥90%, for example, it can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 10%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0015] The bending strength of the high-density boron nitride ceramic material is ≥150 MPa, for example, it can be 150 MPa, 170 MPa, 190 MPa, 210 MPa or 230 MPa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0016] The bending strength of the high-density boron nitride ceramic material provided by the present invention is ≥150MPa, which is nearly twice as high as the bending strength of the boron nitride ceramic material prepared without adding chopped BN fibers.

[0017] Preferably, based on the total mass of the high-density boron nitride ceramic material as 100%, the content of the second phase is 15-20wt%, for example, it can be 15wt%, 15.5wt%, 16wt%, 16.5wt%, 17wt%, 17.5wt%, 18wt%, 18.5wt%, 19wt%, 19.5wt% or 20wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] Taking the total mass of the high-density boron nitride ceramic material as 100%, the content of the additive is 14-20wt%, for example, it can be 14wt%, 14.5wt%, 15wt%, 15.5wt%, 16wt%, 16.5wt%, 17wt%, 17.5wt%, 18wt%, 18.5wt%, 19wt%, 19.5wt% or 20wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable, and the balance is the main phase.

[0019] The present invention further enhances the strength of the BN composite ceramic material by controlling the contents of the additive and the second phase in the high-density boron nitride ceramic material within a specific range, while maintaining the excellent wave transmission performance of the BN ceramic. If the content of the second phase is less than 15wt%, the sintering-promoting effect thereof is weakened, the density is reduced, and the strength of the high-density boron nitride composite ceramic material is reduced; if the content of the second phase is greater than 20wt%, the wave transmission performance of the ceramic material is reduced; if the content of the additive is less than 14wt%, a good reinforcement effect cannot be achieved, and the bending strength of the prepared boron nitride ceramic material is low; if the content of the additive is greater than 20wt%, more short-cut BN fibers are stacked on each other to easily form pores, and the increase in pores leads to limited reinforcement effect of the short-cut BN fibers, which in turn has an adverse effect on the organizational structure and bending strength of the composite ceramic.

[0020] In a second aspect, the present invention provides a method for preparing the high-density boron nitride ceramic material as described in the first aspect, the preparation method comprising the following steps:

[0021] (1) B2O3 powder, AlN powder and Y2O3 powder are first mixed to obtain a first mixture, and h-BN powder and the first mixture are second mixed to obtain a ceramic powder mixture;

[0022] (2) the chopped BN fibers and anhydrous ethanol are mixed for a third time to obtain a chopped BN fiber slurry;

[0023] (3) the ceramic powder mixture obtained in step (1) and the chopped BN fiber slurry obtained in step (2) are mixed in a fourth step to obtain a composite slurry, and then subjected to rotary evaporation and drying in sequence to obtain a ceramic composite powder;

[0024] (4) pre-pressing and sintering the ceramic composite powder obtained in step (3) to obtain the high-density boron nitride ceramic material;

[0025] There is no particular order in which steps (1) and (2) are performed.

[0026] In the preparation method provided by the present invention, AlN powder acts as a wave-transmitting ceramic to enhance the multiphase performance, and Y2O3 powder acts as a sintering aid to promote the densification sintering of h-BN; in the initial stage of sintering, that is, under relatively low temperature conditions, B2O3 powder can form a liquid phase, which firstly plays a role in wetting h-BN, and secondly can promote the diffusion and rearrangement of h-BN grains. When the sintering enters the high temperature stage, the single B2O3 powder will volatilize under high temperature conditions to form pores in the boron nitride ceramic material, affecting the density and mechanical properties of the boron nitride ceramic material. In the present invention, due to the addition of AlN powder and Y2O3 powder, at the high temperature stage, B2O3, AlN and Y2 O3 undergoes a chemical reaction to generate Al2Y4O9 which is retained in the h-BN ceramic matrix, thereby effectively avoiding the negative impact of high-temperature volatilization of the low-melting point additive (B2O3 powder) on the ceramic structure and performance; in addition, the chopped BN fibers and anhydrous ethanol are mixed to obtain chopped BN fiber slurry, so that the fibers are evenly dispersed, and the mixing process does not use a ball milling dispersion method, thereby preventing mechanical damage to the chopped BN fibers during the ball milling process, and then the ceramic powder mixture is mixed with the chopped BN fiber slurry, and a high-density boron nitride ceramic material is obtained through sintering. The preparation method is simple and easy to operate, and the prepared high-density boron nitride ceramic material has high density and bending strength.

[0027] Preferably, the molar ratio of the B2O3, AlN and Y2O3 powders in step (1) is 1:(0.8-1.2):(1.8-2.2), for example, it can be 1:0.8:1.8, 1:0.8:2, 1:0.8:2.2, 1:1:1.8, 1:1:2, 1:1:2.2, 1:1.2:1.8, 1:1.2:2 or 1:1.2:2.2, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 1:1:2.

[0028] The coordinated proportions of B2O3, AlN and Y2O3 in the present invention can better reduce the subsequent sintering temperature and further improve the density and bending strength of the prepared high-density boron nitride ceramic material.

[0029] Preferably, the average particle size of the B2O3 powder is 1-2μm, for example, it can be 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm or 2μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] Preferably, the average particle size of the AlN powder is 1-2 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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] Preferably, the average particle size of the Y2O3 powder is 40-100nm, for example, it can be 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm or 100nm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] Preferably, the average particle size of the h-BN powder is <150 nm, for example, it may be 149 nm, 145 nm, 140 nm, 135 nm, 130 nm, 125 nm, 120 nm, 115 nm, 110 nm, 105 nm or 100 nm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] Preferably, the mass ratio of the h-BN powder to the first mixture is 1:(0.2-0.3), for example, 1:0.2, 1:0.25 or 1:0.3, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable, preferably 1:0.25.

[0034] The present invention further controls the mass ratio of h-BN powder and the first mixture to meet the range of 1:(0.2-0.3), so that the prepared high-density boron nitride ceramic material can have high bending strength at a lower sintering temperature; the second phase in the present invention mainly functions to promote sintering. Due to the addition of the second phase, the sintering temperature required for the material to reach the conventional required density and bending strength is greatly reduced, thereby reducing energy consumption. If the content of the second phase is too much, the wave transmission performance of the material will be reduced.

[0035] Preferably, the first mixing and the second mixing methods each independently comprise a first mechanical stirring.

[0036] Preferably, the rotation speed of the first mechanical agitator is 300-500rpm, for example, it can be 300rpm, 320rpm, 340rpm, 360rpm, 380rpm, 400rpm, 420rpm, 440rpm, 460rpm, 480rpm or 500rpm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] Preferably, the first mechanical stirring time is 30-90 min, for example, it can be 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min or 90 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] Preferably, the mass ratio of the chopped BN fibers to anhydrous ethanol in step (2) is 1:(100-500), for example, 1:100, 1:150, 1:200, 1:250, 1:300, 1:350, 1:400, 1:450 or 1:500, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0039] The present invention further controls the mass ratio of the chopped BN fibers and anhydrous ethanol to meet the range of 1: (100-500), so that the chopped BN fibers can be better dispersed, and at the same time, it is beneficial to the subsequent uniform dispersion and mixing of the ceramic powder mixture, so that the prepared high-density boron nitride ceramic material has higher bending strength and density.

[0040] Preferably, the third mixing comprises a first ultrasonic vibration.

[0041] Preferably, the frequency of the first ultrasonic vibration is 30-40 kHz, for example, 30 kHz, 35 kHz or 40 kHz, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0042] Preferably, the duration of the first ultrasonic vibration is 20-30 min, for example, 20 min, 25 min or 30 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0043] Preferably, the mass ratio of the chopped BN fibers to the ceramic powder mixture in the chopped BN fiber slurry in step (3) is 1:(6-9), for example, it can be 1:6, 1:6.5, 1:7, 1:7.5, 1:8, 1:8.5 or 1:9, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0044] The present invention further controls the mass ratio of the chopped BN fiber slurry to the ceramic powder mixture to meet the range of 1: (6-9), which is not only conducive to a more uniform dispersion between the two, but also enables the chopped BN fibers to have a suitable mass content in the ceramic powder mixture, so that the prepared high-density boron nitride ceramic material has higher bending strength and density; if the mass ratio of the chopped BN fiber slurry to the ceramic powder mixture is greater than 1: 6, that is, there is too much chopped BN fiber slurry, more BN fibers will be introduced, and more BN fibers will be easily stacked to form pores, which will have an adverse effect on the organizational structure and bending strength of the composite ceramic; if the mass ratio of the chopped BN fiber slurry to the ceramic powder mixture is less than 1: 9, that is, there is too little chopped BN fiber slurry, too few BN fibers will be introduced, and the effect of enhancing the strength of the ceramic boron nitride ceramic will not be achieved.

[0045] Preferably, the fourth mixing method includes a second mechanical stirring and a second ultrasonic vibration.

[0046] Preferably, the second mechanical stirring and the second ultrasonic vibration are performed simultaneously.

[0047] In the present invention, the second mechanical stirring and the second ultrasonic vibration are effectively combined to promote the uniform mixing of the ceramic powder mixture and the chopped BN fiber slurry, so that the chopped BN fibers are evenly dispersed. Compared with the ball milling mixing method, the second mechanical stirring and the second ultrasonic vibration are carried out simultaneously, which effectively ensures the uniformity of the obtained ceramic composite powder, reduces the mechanical damage of the chopped BN fibers in the process, maintains the integrity of the morphology and structure of the chopped BN fibers, and is conducive to the reinforcing effect of the chopped BN fibers in the composite ceramics.

[0048] Preferably, the rotation speed of the second mechanical agitator is 300-500rpm, for example, it can be 300rpm, 320rpm, 340rpm, 360rpm, 380rpm, 400rpm, 420rpm, 440rpm, 460rpm, 480rpm or 500rpm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0049] Preferably, the frequency of the second ultrasonic vibration is 30-40kHz, for example, it can be 30kHz, 31kHz, 32kHz, 33kHz, 34kHz, 35kHz, 36kHz, 37kHz, 38kHz, 39kHz or 40kHz, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0050] Preferably, the time of the second ultrasonic vibration is 40-60 min, for example, it can be 40 min, 42 min, 44 min, 46 min, 48 min, 50 min, 52 min, 54 min, 56 min, 58 min or 60 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0051] Preferably, the temperature of the cooling liquid during the rotary evaporation is -2°C-10°C, for example, it can be -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, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0052] Preferably, the rotary evaporation temperature is 50-80°C, for example, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0053] Preferably, the rotation speed during the rotary evaporation is 40-60rpm, for example, it can be 40rpm, 42rpm, 44rpm, 46rpm, 48rpm, 50rpm, 52rpm, 54rpm, 56rpm, 58rpm or 60rpm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0054] Preferably, the drying temperature is 80-100°C, for example, it can be 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, 92°C, 94°C, 96°C, 98°C or 100°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0055] Preferably, the drying time is 2-5 h, for example, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h or 5 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0056] Preferably, the pre-pressing and sintering process in step (4) comprises the following steps:

[0057] The ceramic composite powder in step (3) is loaded into a steel mold for pre-pressing, and demolding is performed to obtain a green embryo; the obtained green embryo is placed in a graphite mold of the same diameter, and the graphite mold is placed in a rapid hot pressing sintering device for sintering; after the sintering device is cooled to room temperature, the graphite mold is taken out and demolded to obtain the high-density boron nitride ceramic material.

[0058] Preferably, the pre-pressing temperature in step (4) is 20-30°C, for example, it can be 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C or 30°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0059] Preferably, the pre-pressing pressure is 30-50MPa, for example, it can be 30MPa, 32MPa, 34MPa, 36MPa, 38MPa, 40MPa, 42MPa, 44MPa, 46MPa, 48MPa or 50MPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0060] Preferably, the holding time of the pre-pressing is 5-10 minutes, for example, it can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes or 10 minutes, but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0061] Preferably, the sintering temperature is 1450-1550°C, for example, it can be 1450°C, 1460°C, 1470°C, 1480°C, 1490°C, 1500°C, 1510°C, 1520°C, 1530°C, 1540°C or 1550°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0062] The obtained ceramic composite powder is sintered in the present invention, and the sintering temperature is much lower than the temperature (1700°C) for preparing traditional BN ceramic materials. The addition of the second phase promotes sintering, that is, a ceramic material with equal strength and density is obtained. The sintering temperature used in the method of the present invention is lower than that used in conventional methods, which greatly reduces the cost and energy consumption in the material preparation process. The preparation process is easy to control, and it is convenient to prepare large-size ceramic components.

[0063] Preferably, the sintering heating rate is 90-120°C / min, for example, it can be 90°C / min, 92°C / min, 94°C / min, 96°C / min, 98°C / min, 100°C / min, 102°C / min, 104°C / min, 106°C / min, 108°C / min, 110°C / min, 112°C / min, 114°C / min, 116°C / min, 118°C / min or 120°C / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0064] Preferably, the sintering holding time is 10-20 min, for example, it can be 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min or 20 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0065] Preferably, the sintering pressure is 40-60 MPa, for example, it can be 40 MPa, 42 MPa, 44 MPa, 46 MPa, 48 MPa, 50 MPa, 52 MPa, 54 MPa, 56 MPa, 58 MPa or 60 MPa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0066] The sintering pressure refers to the pressure in the graphite mold;

[0067] Preferably, the sintering vacuum degree is <10Pa, for example, it can be 9Pa, 8Pa, 7Pa, 6Pa, 5Pa, 4Pa, 3Pa, 2Pa or 1Pa, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0068] The vacuum degree of sintering refers to the vacuum degree in the sintering device;

[0069] In a third aspect, the present invention provides an application of the high-density boron nitride ceramic material as described in the first aspect, wherein the high-density boron nitride ceramic material is used in a radome, an antenna window or a wave-transmitting component.

[0070] The raw materials used in the high-density boron nitride ceramic material provided by the present invention are easy to obtain, the preparation process is easy to control, the production cost is low, and it is convenient to prepare large-size ceramic components. It has high density, bending strength and stable dielectric properties, and can be used as a manufacturing material for antenna covers, antenna windows or wave-transmitting components.

[0071] Compared with the prior art, the present invention has at least the following beneficial effects:

[0072] (1) The present invention enhances the strength of BN composite ceramic materials by adding short-cut BN fibers to high-density boron nitride ceramic materials, while maintaining the excellent wave transmission performance of BN ceramics. At the same time, it can be sintered under relatively low temperature conditions to obtain a higher-density boron nitride ceramic material, thereby reducing energy consumption. The short-cut BN fibers are combined with the h-BN main phase to constrain the deformation of the h-BN main phase, and their own deformation is constrained by the h-BN, thereby achieving a mutual reinforcement effect; in addition, the fiber breakage and crack deflection when encountering the fiber or BN grain further improve the mechanical properties, and the combined effect improves the bending strength of the high-density boron nitride ceramic material;

[0073] (2) In the preparation method provided by the present invention, B2O3 powder can form a liquid phase at a relatively low temperature to promote the diffusion and rearrangement of h-BN grains, AlN powder acts as a wave-transmitting ceramic to enhance the multiphase, and Y2O3 powder acts as a common sintering aid to promote the densification sintering of h-BN. Under high temperature conditions, B2O3, AlN and Y2O3 react chemically to generate Al2Y4O9 which is retained in the h-BN ceramic matrix, effectively avoiding the negative impact of high-temperature volatilization of low-melting-point additives on the ceramic structure and performance. In addition, chopped BN fibers and anhydrous ethanol are mixed to obtain chopped BN fiber slurry, so that the fibers are evenly dispersed. The mixing process does not use a ball milling dispersion method, thereby preventing mechanical damage to the chopped BN fibers during the ball milling process. Then, the ceramic powder mixture is mixed with the chopped BN fiber slurry, and a high-density boron nitride ceramic material is obtained after sintering. The preparation method is simple and easy to operate, and the prepared high-density boron nitride ceramic material has high density and bending strength.

[0074] (3) The raw materials used in the high-density boron nitride ceramic material provided by the present invention are easy to obtain, the preparation process is easy to control, the production cost is low, and it is convenient to prepare large-size ceramic components. It has high density, bending strength and stable dielectric properties, and can be used as a material for making antenna covers, antenna windows or wave-transmitting components. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 It is the XRD spectrum of Examples 1-2, 6-7 and Comparative Example 1-2 of the present invention;

[0076] Figure 2 This is a SEM morphology image of the fracture of the high-density boron nitride ceramic material obtained in Example 1 of the present invention;

[0077] Figure 3 This is a SEM morphology of the fiber distribution of the high-density boron nitride ceramic material obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0078] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and through specific implementation methods. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0079] In the following examples, unless otherwise specified, all reagents and consumables were purchased from conventional reagent manufacturers in the field; unless otherwise specified, the experimental methods and technical means used were conventional methods and means in the field.

[0080] Example 1

[0081] This embodiment provides a high-density boron nitride ceramic material, which includes a main phase, a second phase and an additive, wherein the main phase includes h-BN, the second phase includes Al2Y4O9, and the additive includes chopped BN fibers;

[0082] The average length of the chopped BN fibers is 2.5 mm and the diameter is 12 μm;

[0083] Based on the total mass of the high-density boron nitride ceramic material being 100%, the content of the second phase is 18wt%, the content of the additive is 17wt%, and the remainder is the main phase.

[0084] The preparation method of the high-density boron nitride ceramic material provided in this embodiment comprises the following steps:

[0085] (1) B2O3 powder, AlN powder and Y2O3 powder were first mechanically stirred at 400 rpm for 70 min in a molar ratio of 1:1:2 to obtain a first mixture, and h-BN powder and the first mixture were first mechanically stirred at 400 rpm for 70 min in a molar ratio of 1:0.25 to obtain a ceramic powder mixture;

[0086] (2) chopped BN fibers and anhydrous ethanol were subjected to a first ultrasonic vibration at 35 kHz for 25 minutes in a mass ratio of 1:300 to obtain chopped BN fiber slurry;

[0087] (3) The chopped BN fibers in the chopped BN fiber slurry obtained in step (2) and the ceramic powder mixture obtained in step (1) are subjected to a second mechanical stirring and a second ultrasonic vibration for 50 minutes at a rotation speed of 400 rpm and a frequency of 35 kHz in a mass ratio of 1:7 to obtain a composite slurry, and then rotary evaporation is performed under the conditions of a coolant temperature of 10° C., a rotary evaporation temperature of 60° C., and a rotary speed of 50 rpm, and then dried at 90° C. for 3 hours to obtain a ceramic composite powder;

[0088] (4) the ceramic composite powder obtained in step (3) is loaded into a steel mold, maintained at a pressure of 25° C. and 40 MPa for 8 minutes, and demolded to obtain a ceramic blank; the obtained blank is placed in a graphite mold of the same diameter, the graphite mold is placed in a rapid hot pressing sintering device, and the temperature is increased to 1500° C. at a heating rate of 100° C. / min under a vacuum degree of 5 Pa, and sintered at a pressure of 50 MPa for 50 minutes; after the sintering device is cooled to room temperature, the graphite mold is taken out and demolded to obtain the high-density boron nitride ceramic material;

[0089] There is no particular order in which steps (1) and (2) are performed.

[0090] The XRD pattern of the prepared high-density boron nitride ceramic material is shown in Figure 1 As shown, it can be seen that the phases of the obtained high-density boron nitride ceramic material are h-BN and Al2Y4O9;

[0091] The fracture morphology of the prepared high-density boron nitride ceramic material is as follows: Figure 2 As shown in the figure, the collective pullout of the chopped BN fibers and the fibrous holes left after some of the fibers were pulled out can be seen. The fibers and the BN matrix are composited, and the fiber orientations are inconsistent. The fracture surface is uneven and staggered. The pullout of the BN fibers and the cracks encounter fiber deflection to effectively consume the fracture energy, which is beneficial to improve the mechanical properties of the composite ceramics.

[0092] The SEM morphology of the fiber distribution of the prepared high-density boron nitride ceramic material is as follows: Figure 3 As shown, it can be seen that the chopped BN fibers are evenly distributed in the ceramic matrix and have random orientations, which is conducive to obtaining isotropic ceramic materials.

[0093] Example 2

[0094] This embodiment provides a high-density boron nitride ceramic material, which includes a main phase, a second phase and an additive, wherein the main phase includes h-BN, the second phase includes Al2Y4O9, and the additive includes chopped BN fibers;

[0095] The average length of the chopped BN fibers is 2 mm and the diameter is 10 μm;

[0096] Based on the total mass of the high-density boron nitride ceramic material being 100%, the content of the second phase is 15wt%, the content of the additive is 20wt%, and the remainder is the main phase.

[0097] The preparation method of the high-density boron nitride ceramic material provided in this embodiment comprises the following steps:

[0098] (1) B2O3 powder, AlN powder and Y2O3 powder were first mechanically stirred at 300 rpm for 90 min at a molar ratio of 1:1:2 to obtain a first mixture, and h-BN powder and the first mixture were first mechanically stirred at 300 rpm for 90 min at a molar ratio of 1:0.2 to obtain a ceramic powder mixture;

[0099] (2) chopped BN fibers and anhydrous ethanol were subjected to a first ultrasonic vibration at 30 kHz for 20 minutes in a mass ratio of 1:100 to obtain chopped BN fiber slurry;

[0100] (3) The chopped BN fibers in the chopped BN fiber slurry obtained in step (2) and the ceramic powder mixture obtained in step (1) are subjected to a second mechanical stirring and a second ultrasonic vibration for 60 minutes at a rotation speed of 300 rpm and a frequency of 40 kHz in a mass ratio of 1:6 to obtain a composite slurry, and then rotary evaporation is performed under the conditions of a coolant temperature of -2°C, a rotary evaporation temperature of 50°C, and a rotation speed of 40 rpm, and then dried at 80°C for 5 hours to obtain a ceramic composite powder;

[0101] (4) the ceramic composite powder obtained in step (3) is loaded into a steel mold, maintained at a pressure of 20° C. and 30 MPa for 10 minutes, and demolded to obtain a ceramic blank; the obtained blank is placed in a graphite mold of the same diameter, the graphite mold is placed in a rapid hot pressing sintering device, and the temperature is increased to 1550° C. at a heating rate of 90° C. / min under a vacuum degree of 9 Pa, and sintered at a pressure of 40 MPa for 40 minutes; after the sintering device is cooled to room temperature, the graphite mold is taken out and demolded to obtain the high-density boron nitride ceramic material;

[0102] There is no particular order in which steps (1) and (2) are performed.

[0103] Example 3

[0104] This embodiment provides a high-density boron nitride ceramic material, which includes a main phase, a second phase and an additive, wherein the main phase includes h-BN, the second phase includes Al2Y4O9, and the additive includes chopped BN fibers;

[0105] The average length of the chopped BN fibers is 3 mm and the diameter is 13 μm;

[0106] Based on the total mass of the high-density boron nitride ceramic material being 100%, the content of the second phase is 20wt%, the content of the additive is 14wt%, and the remainder is the main phase.

[0107] The preparation method of the high-density boron nitride ceramic material provided in this embodiment comprises the following steps:

[0108] (1) B2O3 powder, AlN powder and Y2O3 powder were first mechanically stirred at 500 rpm for 30 min at a molar ratio of 1:1:2 to obtain a first mixture, and h-BN powder and the first mixture were first mechanically stirred at 500 rpm for 30 min at a molar ratio of 1:0.3 to obtain a ceramic powder mixture;

[0109] (2) chopped BN fibers and anhydrous ethanol were subjected to a first ultrasonic vibration at 20 kHz for 30 minutes in a mass ratio of 1:500 to obtain a chopped BN fiber slurry;

[0110] (3) The chopped BN fibers in the chopped BN fiber slurry obtained in step (2) and the ceramic powder mixture obtained in step (1) are subjected to a second mechanical stirring and a second ultrasonic vibration for 40 minutes at a rotation speed of 500 rpm and a frequency of 30 kHz in a mass ratio of 1:9 to obtain a composite slurry, and then rotary evaporation is performed under the conditions of a coolant temperature of 8° C., a rotary evaporation temperature of 80° C., and a rotary speed of 60 rpm, and then dried at 100° C. for 2 hours to obtain a ceramic composite powder;

[0111] (4) the ceramic composite powder obtained in step (3) is loaded into a steel mold, maintained at a pressure of 30° C. and 50 MPa for 5 minutes, and demolded to obtain a ceramic blank; the obtained blank is placed in a graphite mold of the same diameter, the graphite mold is placed in a rapid hot pressing sintering device, and the temperature is increased to 1450° C. at a heating rate of 120° C. / min under a vacuum degree of 1 Pa, and sintered at a pressure of 60 MPa for 20 minutes; after the sintering device is cooled to room temperature, the graphite mold is taken out and demolded to obtain the high-density boron nitride ceramic material;

[0112] There is no particular order in which steps (1) and (2) are performed.

[0113] Example 4

[0114] This embodiment provides a high-density boron nitride ceramic material. The high-density boron nitride ceramic is different from that of Embodiment 1 only in that the average length of the chopped BN fibers is 1 mm. The preparation method thereof is the same as that of Embodiment 1.

[0115] Example 5

[0116] This embodiment provides a high-density boron nitride ceramic material. The high-density boron nitride ceramic is different from that of Embodiment 1 only in that the average length of the chopped BN fibers is 5 mm. The preparation method thereof is the same as that of Embodiment 1.

[0117] Example 6

[0118] This embodiment provides a high-density boron nitride ceramic material. The high-density boron nitride ceramic is different from that of Embodiment 1 only in that, when preparing the high-density boron nitride ceramic material, the mass ratio of the ceramic powder mixture to the chopped BN fiber slurry in step (3) is 1:12.

[0119] Example 7

[0120] This embodiment provides a high-density boron nitride ceramic material. The high-density boron nitride ceramic is different from that of Embodiment 1 only in that, when preparing the high-density boron nitride ceramic material, the mass ratio of the ceramic powder mixture to the chopped BN fiber slurry in step (3) is 1:4.

[0121] Comparative Example 1

[0122] This comparative example provides a boron nitride ceramic material, which is different from Example 1 only in that, when preparing the boron nitride ceramic material, step (1) and step (2) are not performed and chopped BN fiber slurry is not added in step (3). The specific steps include:

[0123] (1) mechanically stirring the h-BN powder at 300 rpm for 90 min to obtain a ceramic powder;

[0124] (2) subjecting the ceramic powder obtained in step (1) to a second mechanical stirring and a second ultrasonic vibration at 300 rpm and 40 kHz for 60 min, and then subjecting the ceramic powder to rotary evaporation at a coolant temperature of -2°C, a rotary evaporation temperature of 50°C, and a rotary speed of 40 rpm, and then drying at 80°C for 5 h to obtain a ceramic powder;

[0125] (3) The ceramic powder obtained in step (2) is loaded into a steel mold, maintained at a pressure of 20° C. and 30 MPa for 10 minutes, and demolded to obtain a ceramic blank; the obtained blank is placed in a graphite mold of the same diameter, and the graphite mold is placed in a rapid hot pressing sintering device, and the temperature is increased to 1450° C. at a heating rate of 90° C. / min under a vacuum degree of 4 Pa, and sintered at a pressure of 40 MPa for 40 minutes; after the sintering device is cooled to room temperature, the graphite mold is taken out and demolded to obtain the boron nitride ceramic material.

[0126] Comparative Example 2

[0127] This comparative example provides a boron nitride ceramic material, which is different from Example 1 only in that, when preparing the boron nitride ceramic material, step (2) is not performed and step (3) does not add chopped BN fiber slurry. The specific steps include:

[0128] (1) B2O3 powder, AlN powder and Y2O3 powder were first mechanically stirred at 300 rpm for 90 min at a molar ratio of 1:0.5:4 to obtain a first mixture, and h-BN powder and the first mixture were first mechanically stirred at 300 rpm for 90 min at a molar ratio of 1:0.2 to obtain a ceramic powder mixture;

[0129] (2) subjecting the ceramic powder mixture obtained in step (1) to a second mechanical stirring and a second ultrasonic vibration at 300 rpm and 40 kHz for 60 min, and then subjecting the mixture to rotary evaporation at a coolant temperature of -2°C, a rotary evaporation temperature of 50°C, and a rotary speed of 40 rpm, and then drying at 80°C for 5 h to obtain a ceramic powder;

[0130] (3) The ceramic powder obtained in step (2) is loaded into a steel mold, maintained at a pressure of 20° C. and 30 MPa for 10 minutes, and demolded to obtain a ceramic blank; the obtained blank is placed in a graphite mold of the same diameter, and the graphite mold is placed in a rapid hot pressing sintering device, and the temperature is increased to 1450° C. at a heating rate of 90° C. / min under a vacuum degree of 4 Pa, and sintered at a pressure of 40 MPa for 40 minutes; after the sintering device is cooled to room temperature, the graphite mold is taken out and demolded to obtain the boron nitride ceramic material.

[0131] Test Method

[0132] The boron nitride ceramics obtained in Examples 1-7 and Comparative Examples 1-2 were tested: the actual density of the ceramic block was measured using the Archimedean principle; and the density was obtained by calculating the ratio of the actual density to the theoretical density; the composite ceramic bending strength was tested using a SinterWDW-20kN testing machine according to the three-point bending strength test standard GB / T6569-2006 "Fine Ceramics Bending Strength Test Method", with a sample size of 3mm×4mm×35mm, a span of 30mm, and a loading rate of 0.5mm / min. The results are recorded in Table 1.

[0133] Table 1

[0134] <![CDATA[Density / g / cm 3 > Density / % Bending strength / MPa Example 1 2.17 92.91 172.72 Example 2 2.11 92.16 169.74 Example 3 2.22 93.34 178.43 Example 4 2.19 93.07 144.86 Example 5 2.08 90.25 156.78 Example 6 2.21 93.48 76.44 Example 7 2.07 85.96 113.31 Comparative Example 1 1.71 75.43 71.62 Comparative Example 2 2.29 95.09 91.33

[0135] The test results show that:

[0136] (1) It can be seen from Examples 1-3 that the present invention enhances the strength of the BN composite ceramic material by adding chopped BN fibers to the high-density boron nitride ceramic material, while maintaining the excellent wave transmission performance of the BN ceramic, and can be sintered under relatively low temperature conditions to obtain a higher-density boron nitride ceramic material, thereby reducing energy consumption. The chopped BN fibers are combined with the h-BN main phase to constrain the deformation of the h-BN main phase, and their own deformation is constrained by the h-BN, thereby achieving a mutual reinforcement effect; in addition, the fiber breakage and crack deflection when encountering the fiber or BN grain further improve the mechanical properties. The combined effect improves the bending strength of the high-density boron nitride ceramic material. The density of the prepared high-density boron nitride ceramic material is 2.11 g / cm 3 Above, the density is above 92% and the bending strength is above 169MPa.

[0137] (2) By comparing Example 1 with Examples 4-5, it can be seen that the present invention further enhances the strength of the BN composite ceramic material by further controlling the average length and diameter of the chopped BN fibers in the high-density boron nitride ceramic material within a reasonable and specific range, while maintaining the excellent wave transmission performance of the BN ceramic. If the average length of the chopped BN fibers is too short, less than 2 mm, the fiber pull-out effect will also be weakened, the fiber reinforcement effect will be weakened, and the bending strength of the composite ceramic material will decrease; if the average length of the chopped BN fibers is too long, greater than 3 mm, the longer fibers will be intertwined during the mixing process, making it difficult to mix evenly, resulting in a lower density of the final boron nitride ceramic material and poor strength uniformity.

[0138] (3) By comparing Example 1 with Examples 6-7, it can be seen that the present invention further controls the mass ratio of the chopped BN fiber slurry to the ceramic powder mixture to meet the range of 1: (6-9), which is not only conducive to a more uniform dispersion between the two, but also enables the chopped BN fibers to have a suitable mass content in the ceramic powder mixture, so that the prepared high-density boron nitride ceramic material has higher bending strength and density; It can be seen from Example 6 that when the mass ratio of the chopped BN fiber slurry to the ceramic powder mixture is 1:4, that is, too much chopped BN fiber slurry, more BN fibers will be introduced, and more BN fibers will be easily stacked to form pores, which will have an adverse effect on the organizational structure and bending strength of the composite ceramic; It can be seen from Example 7 that when the mass ratio of the chopped BN fiber slurry to the ceramic powder mixture is 1:16, that is, too little chopped BN fiber slurry, too little BN fiber will be introduced, and the effect of enhancing the strength of the ceramic boron nitride ceramic will not be achieved.

[0139] (4) By comparing Example 1 with Comparative Example 1, it can be seen that if step (1) and step (2) are not performed when preparing the boron nitride ceramic material and the chopped BN fiber slurry is not added in step (3), the density of the boron nitride ceramic material is only 1.71 g / cm 3 , the density is only 75.43%, and the bending strength is only 71.62MPa; This indicates that the present invention uses short-cut BN fibers as an additive to cooperate with the second phase Al2Y4O9 to enhance the density and bending strength of high-density boron nitride ceramic materials, which is beneficial to improving the strain failure, fracture toughness and elastic modulus of boron nitride ceramics, and has a certain strengthening effect on boron nitride ceramics. It can also be sintered under relatively low temperature conditions to obtain a higher-density boron nitride ceramic material, thereby reducing energy consumption and effectively avoiding the negative impact of high-temperature volatilization of low-melting-point additives on the ceramic structure and performance.

[0140] (5) By comparing Example 1 with Comparative Example 2, it can be seen that when preparing the boron nitride ceramic material, step (2) is not performed and step (3) does not add chopped BN fiber slurry, then the density of the boron nitride ceramic material is 2.29 g / cm 3 , density is 95.09%, and flexural strength is 91.33MPa; it indicates that the present invention adopts short-cut BN fibers as additives to enhance the strength and flexural strength of BN composite ceramic materials, and the short-cut BN fiber reinforced boron nitride ceramic materials are more likely to achieve quasi-isotropy in one plane, which is beneficial to improve the strain failure, fracture toughness and elastic modulus of boron nitride ceramics, and play a certain reinforcing role on boron nitride ceramics.

[0141] In summary, the present invention enhances the strength of BN composite ceramic materials by adding short-cut BN fibers to high-density boron nitride ceramic materials, while maintaining the excellent wave transmission performance of BN ceramics, and can be sintered under relatively low temperature conditions to obtain higher-density boron nitride ceramic materials, thereby reducing energy consumption. The short-cut BN fibers are combined with the h-BN main phase to constrain the deformation of the h-BN main phase, and their own deformation is constrained by the h-BN, thereby achieving a mutual reinforcement effect; in addition, the fiber breakage and crack deflection when encountering fibers or BN grains further improve the mechanical properties, and the combined effect improves the bending strength of the high-density boron nitride ceramic material.

[0142] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A high-density boron nitride ceramic material, characterized in that: The high-density boron nitride ceramic material comprises a main phase, a second phase and an additive; The main phase includes h-BN, the second phase includes Al2Y4O9, and the additive includes chopped BN fibers.

2. The high-density boron nitride ceramic material according to claim 1, characterized in that: The average length of the chopped BN fibers is 2-3 mm and the diameter is 10-13 μm; Preferably, the high-density boron nitride ceramic material has a density of ≥90% and a bending strength of ≥150 MPa.

3. The high-density boron nitride ceramic material according to claim 1 or 2, characterized in that: Based on the total mass of the high-density boron nitride ceramic material being 100%, the content of the second phase is 15-20wt%, the content of the additive is 14-20wt%, and the remainder is the main phase.

4. A method for preparing a high-density boron nitride ceramic material according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: (1) B2O3 powder, AlN powder and Y2O3 powder are first mixed to obtain a first mixture, and h-BN powder and the first mixture are second mixed to obtain a ceramic powder mixture; (2) the chopped BN fibers and anhydrous ethanol are mixed for a third time to obtain a chopped BN fiber slurry; (3) the ceramic powder mixture obtained in step (1) and the chopped BN fiber slurry obtained in step (2) are mixed in a fourth step to obtain a composite slurry, and then subjected to rotary evaporation and drying in sequence to obtain a ceramic composite powder; (4) pre-pressing and sintering the ceramic composite powder obtained in step (3) to obtain the high-density boron nitride ceramic material; There is no particular order in which steps (1) and (2) are performed.

5. The preparation method according to claim 4, characterized in that: The molar ratio of B2O3, AlN and Y2O3 powders in step (1) is 1:(0.8-1.2):(1.8-2.2), preferably 1:1:2; Preferably, the average particle size of the B2O3 powder is 1-2 μm; Preferably, the average particle size of the AlN powder is 1-2 μm; Preferably, the average particle size of the Y2O3 powder is 40-100 nm; Preferably, the average particle size of the h-BN powder is <150 nm; Preferably, the mass ratio of the h-BN powder to the first mixture is 1:(0.2-0.3), preferably 1:0.25; Preferably, the first mixing and second mixing methods each independently include a first mechanical stirring; Preferably, the rotation speed of the first mechanical agitator is 300-500 rpm; Preferably, the first mechanical stirring time is 30-90 min.

6. The preparation method according to claim 4 or 5, characterized in that: The mass ratio of the chopped BN fibers to anhydrous ethanol in step (2) is 1:(100-500); Preferably, the third mixing comprises a first ultrasonic vibration; Preferably, the frequency of the first ultrasonic vibration is 30-40kHz; Preferably, the first ultrasonic vibration duration is 20-30 minutes.

7. The preparation method according to any one of claims 4 to 6, characterized in that: The mass ratio of the chopped BN fibers to the ceramic powder mixture in the chopped BN fiber slurry of step (3) is 1:(6-9); Preferably, the fourth mixing method includes a second mechanical stirring and a second ultrasonic vibration; Preferably, the second mechanical stirring and the second ultrasonic vibration are performed simultaneously; Preferably, the rotation speed of the second mechanical stirring is 300-500 rpm; Preferably, the frequency of the second ultrasonic vibration is 30-40kHz; Preferably, the second ultrasonic vibration time is 40-60 minutes; Preferably, the temperature of the cooling liquid during the rotary evaporation is -2°C-10°C; Preferably, the temperature of the rotary evaporation is 50-80°C; Preferably, the rotation speed during the rotary evaporation is 40-60 rpm; Preferably, the drying temperature is 80-100°C; Preferably, the drying time is 2-5 hours.

8. The preparation method according to any one of claims 4 to 7, characterized in that: The pre-pressing and sintering process in step (4) comprises the following steps: The ceramic composite powder in step (3) is loaded into a steel mold for pre-pressing, and demolding is performed to obtain a green embryo; the obtained green embryo is placed in a graphite mold of the same diameter, and the graphite mold is placed in a rapid hot pressing sintering device for sintering; after the sintering device is cooled to room temperature, the graphite mold is taken out and demolded to obtain the high-density boron nitride ceramic material.

9. The preparation method according to any one of claims 4 to 8, characterized in that: The pre-pressing temperature in step (4) is 20-30° C. Preferably, the pre-pressing pressure is 30-50 MPa; Preferably, the holding time of the pre-pressing is 5-10 minutes; Preferably, the sintering temperature is 1450-1550°C; Preferably, the heating rate of the sintering is 90-120°C / min; Preferably, the sintering holding time is 10-20 minutes; Preferably, the sintering pressure is 40-60 MPa; Preferably, the vacuum degree of the sintering is less than 10Pa.

10. An application of the high-density boron nitride ceramic material according to any one of claims 1 to 3, characterized in that: The high-density boron nitride ceramic material is used in a radome, an antenna window or a wave-transmitting component.

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