A ceramic material, its preparation and use

Abstract

The application discloses a ceramic material and a preparation method and application thereof. A main phase of the ceramic material comprises cubic boron nitride, hexagonal boron nitride and rare earth oxide, the volume fraction of the hexagonal boron nitride is greater than that of the cubic boron nitride, the elastic modulus of the ceramic material is greater than 15 GPa, and the nanoindentation hardness of the ceramic material is not less than 250 MPa. The preparation method comprises the following steps: 1) mixing cubic boron nitride and rare earth oxide to obtain mixed powder of rare earth doped cubic boron nitride; and 2) performing hot-pressing sintering on the mixed powder to promote in-situ phase transition of the rare earth oxide catalyzed cubic boron nitride to hexagonal boron nitride, so that the ceramic material is obtained. The method can effectively improve the density and mechanical properties of the ceramic material, and the ceramic material has good stability at high temperature. The ceramic material has strong mechanical properties and high density, and can be applied to the field of wave-transparent ceramics.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ceramic material preparation, and relates to a ceramic material and a preparation method and application thereof. BACKGROUND

[0002] Hexagonal boron nitride (hBN) is a material with a graphite-like structure, in which B atoms and N atoms in each layer form a six-membered ring network through covalent bonds, and the layers are combined by van der Waals force. Compared with silicon nitride ceramic materials, hBN has higher thermal stability, lower density, lower dielectric constant, lower dielectric loss, lower thermal expansion coefficient, and a decomposition temperature of more than 3000 DEG C. These characteristics make hBN have extremely high application potential. However, due to the difficulty in forming a tight stack during sintering of the layered structure of hBN, the strong covalent bond limits the atomic self-diffusion, so that sintering of hBN is difficult. The current sintered product has low density, poor bending strength, is easy to absorb moisture, and has poor rain erosion resistance. Therefore, single-phase BN ceramic materials have not been truly applied in the field of wave-transparent materials.

[0003] In order to solve these defects, researchers have adopted various methods, among which the most commonly used is to introduce a second phase to improve the strength and sintering performance of hBN ceramic materials.

[0004] CN111848179B discloses a method for preparing high-strength boron nitride ceramics by adding zirconium diboride or boron powder to boron nitride powder and adopting hot-pressing sintering process. The obtained ceramics have good mechanical properties and high-temperature resistance. However, this method requires sintering at a high temperature of 1800 DEG C to 2100 DEG C, which has high energy consumption. Moreover, the mechanical properties of the boron nitride ceramics are low, and the density is low.

[0005] CN104177091A discloses a preparation method of high-density hexagonal boron nitride ceramic material. The method coats SiO2 on the surface of hBN powder, and adopts discharge plasma sintering or hot isostatic pressing sintering to prepare a dense hBN block material. However, the surface coating process of this method is complex, and the density of the prepared hBN block material can only reach 86.4%, which needs to be further improved.

[0006] CN110395988A discloses a preparation method of high-strength boron nitride ceramics. The method first pre-presses and then hot-presses or discharge plasma sintering single-particle-size nanometer cubic boron nitride powder to prepare high-strength boron nitride ceramics. However, the nanometer cubic boron nitride powder used in this method has high cost, and the processing technology is complex.

[0007] Therefore, it is necessary to further explore a preparation method of a ceramic material based on boron nitride with a simple preparation process, so that a ceramic material with high density and strong mechanical properties can be obtained, which is a technical problem to be solved at present. SUMMARY

[0008] In view of the above problems existing in the prior art, the purpose of the present application is to provide a ceramic material and a preparation method and use thereof.

[0009] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0010] In a first aspect, the present application provides a ceramic material, wherein the main phase of the ceramic material comprises cubic boron nitride, hexagonal boron nitride and rare earth oxide, the volume fraction of the hexagonal boron nitride is greater than the volume fraction of the cubic boron nitride, the elastic modulus of the ceramic material is > 15 GPa, and the nanoindentation hardness of the ceramic material is not less than 250 MPa.

[0011] In the present application, the volume fraction of hexagonal boron nitride and the fraction of cubic boron nitride are calculated based on the total volume of the two (hexagonal boron nitride and cubic boron nitride) being 100%.

[0012] In the present application, the elastic modulus of the ceramic material may, for example, be 15.5 GPa, 16 GPa, 17 GPa, 18 GPa, 20 GPa, 21 GPa, 23 GPa, 25 GPa, 26 GPa, 28 GPa or 30 GPa.

[0013] In the present application, the nanoindentation hardness of the ceramic material may, for example, be 250 MPa, 260 MPa, 270 MPa, 280 MPa, 290 MPa, 300 MPa, 315 MPa, 330 MPa, 340 MPa, 350 MPa, 375 MPa, 400 MPa, 420 MPa, 440 MPa, 460 MPa, 480 MPa, 500 MPa, 525 MPa, 550 MPa, 575 MPa, 600 MPa, 630 MPa, 660 MPa, 690 MPa, 720 MPa or 760 MPa.

[0014] In the present application, the density of the ceramic material is > 85%, for example, 85.5%, 86%, 86.5%, 87%, 87.5%, 88%, 89%, 90%, 92%, 93%, 94%, 95%, 96% or 96.5% and the like.

[0015] The ceramic material of the present application takes cubic boron nitride and hexagonal boron nitride as the main phase, and limits the volume ratio relationship of the two, which has strong mechanical properties and high density, and can be applied in the field of wave-transparent ceramics.

[0016] The following are preferred technical solutions of the present application, but not as a limitation of the technical solutions provided by the present application. Through the following preferred technical solutions, the technical purposes and beneficial effects of the present application can be better achieved and implemented.

[0017] Preferably, the density of the ceramic material is greater than 2.2 g / cm 3 , for example 2.2 g / cm 3 , 2.21 g / cm 3 , 2.23 g / cm 3 , 2.25 g / cm 3 , 2.26 g / cm 3 , 2.28 g / cm 3 , 2.29 g / cm 3 or 2.30 g / cm 3 , etc.

[0018] Preferably, the volume fraction of the hexagonal boron nitride is 75%-99%, for example 75%, 77%, 78%, 80%, 82.5%, 85%, 88%, 90%, 91%, 92%, 93%, 95%, 96% or 98%, etc., preferably 90%-99%, based on the total volume of the cubic boron nitride and the hexagonal boron nitride being 100%.

[0019] Preferably, the volume fraction of the cubic boron nitride is 1%-25%, for example 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 13%, 14%, 15%, 17%, 19%, 20%, 21.5%, 23% or 25%, etc., preferably 1%-10%, based on the total volume of the cubic boron nitride and the hexagonal boron nitride being 100%.

[0020] Preferably, the ceramic material further comprises a rare earth oxide.

[0021] Preferably, the rare earth oxide comprises at least one of Eu2O3, Yb2O3 and Gd2O3.

[0022] Preferably, the mass content of the rare earth oxide is 1wt%-10wt%, for example 1wt%, 2wt%, 2.5wt%, 3wt%, 4wt%, 4.5wt%, 5wt%, 6wt%, 7wt%, 7.5wt%, 8wt%, 9wt% or 10wt%, etc., based on the total mass of the ceramic material being 100%.

[0023] In a second aspect, the present application provides a preparation method of the ceramic material according to the first aspect, the preparation method comprising the following steps:

[0024] (1) mixing cubic boron nitride and rare earth oxide to obtain mixed powder of rare earth doped cubic boron nitride;

[0025] (2) performing hot-press sintering on the mixed powder to promote in-situ phase transition of cubic boron nitride catalyzed by rare earth oxide to hexagonal boron nitride, thereby obtaining the ceramic material.

[0026] The application provides a method for preparing a ceramic material by a rare earth catalytic solid phase transition method, which uses rare earth oxide as a catalyst to promote in-situ phase transition of cubic boron nitride catalyzed by rare earth oxide to hexagonal boron nitride during hot-press sintering, and cubic boron nitride expands in volume when it turns into hexagonal boron nitride. The method of the application can effectively improve the density and mechanical properties of the ceramic material by pre-doping cubic boron nitride with rare earth and then performing in-situ phase transition, and the ceramic material has good stability at high temperatures.

[0027] The raw materials used in the method of the application are easy to obtain, the operation is simple, and the process conditions are easy to control, which is conducive to industrial production.

[0028] Preferably, the particle size D50 of the cubic boron nitride in step (1) is 1 μm-2 μm, for example, 1 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm or 2 μm, etc.

[0029] Preferably, the rare earth oxide in step (1) comprises at least one of Eu2O3, Yb2O3 and Gd2O3.

[0030] Preferably, the particle size D50 of the rare earth oxide in step (1) is 2 μm-4 μm, for example, 2 μm, 2.2 μm, 2.3 μm, 2.5 μm, 2.7 μm, 3 μm, 3.3 μm, 3.5 μm, 3.6 μm, 3.8 μm or 4 μm, etc.

[0031] The preparation method of the application uses a micron-sized particle size as a raw material for the preparation of a ceramic material, which can not only obtain a material with high density and high mechanical properties, but also effectively reduce production costs and is suitable for industrial production.

[0032] As a preferred technical solution of the method for preparing the ceramic material, the mixing method in step (1) is wet ball milling, and the method for preparing the mixed powder of rare earth doped cubic boron nitride by wet ball milling comprises the following steps: mixing cubic boron nitride powder, rare earth oxide and a dispersant, ball milling, drying the ball-milled material, and obtaining the mixed powder.

[0033] Preferably, the grinding balls used in the ball milling process comprise at least one of silicon nitride (Si3N4) grinding balls and zirconium oxide (ZrO2) grinding balls.

[0034] Preferably, the dispersant comprises at least one of ethanol, isopropyl alcohol and acetone. Among them, ethanol can adopt anhydrous ethanol.

[0035] Preferably, the rotation speed of the ball mill is 300 rpm-500 rpm, such as 300 rpm, 325 rpm, 350 rpm, 370 rpm, 380 rpm, 400 rpm, 425 rpm, 450 rpm, 460 rpm, 480 rpm or 500 rpm, etc.

[0036] Preferably, the time of the ball mill is 4h-6h, such as 4h, 4.2h, 4.5h, 4.6h, 4.8h, 5h, 5.3h, 5.6h or 6h, etc.

[0037] Preferably, after the ball mill, the grinding balls are removed by filtration to obtain the material after ball mill.

[0038] Preferably, the mesh size of the screen used in the filtration is 70 mesh-90 mesh, such as 70 mesh, 80 mesh or 90 mesh.

[0039] Preferably, the temperature of the drying is 80℃-100℃, such as 80℃, 85℃, 88℃, 90℃, 95℃ or 100℃, etc.

[0040] Preferably, the time of the drying is 8h-20h, such as 8h, 10h, 11h, 12h, 14h, 15h, 16h, 18h or 20h, etc.

[0041] As a preferred technical solution of the preparation method of the ceramic material, before the drying, the material after ball mill is subjected to rotary evaporation, the temperature of the rotary evaporation is 45℃-60℃, such as 45℃, 47℃, 50℃, 55℃ or 60℃, etc.; the rotation speed of the rotary evaporation is 30rpm-60rpm, such as 30rpm, 35rpm, 40rpm, 45rpm, 50rpm, 55rpm or 60rpm, etc. By rotary evaporation before drying, the time of subsequent drying can be shortened, and the production efficiency is improved.

[0042] As a preferred technical solution of the preparation method of the ceramic material, the method further comprises grinding and sieving the mixed powder before hot-pressing sintering;

[0043] Preferably, the mesh size of the screen used in the sieving is 175 mesh-230 mesh, such as 180 mesh, 200 mesh, 220 mesh or 230 mesh; the number of times of the sieving is 2-3 times.

[0044] In the present application, the mesh number of the screen is different, and the aperture on the screen is different, so that materials with certain particle size can be obtained. For example, the mesh number is 200 meshes, and the aperture on the screen is 0.074 mm. The material of the screen is not specifically limited in the present application, for example, it can be a stainless steel screen.

[0045] As a preferred technical solution of the preparation method of the ceramic material, in the process of hot-pressing sintering, the sintering temperature is 1600-1900℃, for example, 1600℃, 1650℃, 1680℃, 1700℃, 1730℃, 1750℃, 1800℃ or 1900℃, etc.

[0046] Preferably, the heating rate of the hot-pressing sintering is 8-12℃ / min, for example, 8℃ / min, 9℃ / min, 10℃ / min, 11℃ / min or 12℃ / min, etc.

[0047] Preferably, in the process of hot-pressing sintering, the sintering pressure is 40-50MPa, for example, 40MPa, 42MPa, 43MPa, 45MPa, 47MPa, 48MPa or 50MPa, etc.

[0048] Preferably, the pressure holding time of the hot-pressing sintering is 60-120min, for example, 60min, 65min, 70min, 75min, 80min, 85min, 90min, 95min, 100min, 105min, 110min, 115min or 120min, etc.

[0049] Preferably, the hot-pressing sintering is carried out under the protection of a protective gas, and the protective gas includes at least one of N2, He, Ne and Ar.

[0050] As a preferred technical solution of the preparation method of the ceramic material, the preparation method comprises the following steps:

[0051] (1) Ball-milling mixing: weighing cubic boron nitride powder with particle size D50 of 1-2μm, and rare earth oxide Re2O3 with particle size D50 of 2-4μm, using anhydrous ethanol as a dispersant, wet ball-milling mixing uniformly to obtain a mixed slurry, wherein Re is a rare earth element;

[0052] (2) Drying and sieving: filtering the mixed slurry in step (1) to remove the milling balls, removing the anhydrous ethanol by rotary evaporation, grinding and sieving after drying, to obtain a mixed powder of Re2O3 doped cubic boron nitride;

[0053] (3) hot-pressing sintering: a proper amount of the mixed powder in step (2) is weighed and put into a sintering graphite mold, and then the sintering graphite mold containing the mixed powder is put into a hot-pressing sintering device to perform hot-pressing sintering under the protection of a protective gas; during the hot-pressing sintering, the sintering temperature is 1600-1900℃, the heating rate of the hot-pressing sintering is 8-12℃ / min, and the pressure-maintaining time of the hot-pressing sintering is 60-120min;

[0054] (4) ceramic demolding: after the hot-pressing sintering device is cooled to room temperature, the graphite mold is taken out, and the ceramic material is obtained by demolding.

[0055] In a third aspect, the present application provides a use of the ceramic material according to the first aspect as a wave-transparent ceramic.

[0056] The numerical range of the present application includes not only the point values listed above, but also any point values between the above numerical ranges that are not listed, and the present application does not list the specific point values included in the range for the sake of brevity and simplicity.

[0057] Compared with the prior art, the present application has the following beneficial effects:

[0058] (1) The ceramic material of the present application takes cubic boron nitride and hexagonal boron nitride as the main phase and limits the volume ratio relationship of the two, has strong mechanical properties and high density, and can be applied to the field of wave-transparent ceramics.

[0059] (2) The present application provides a method for preparing a ceramic material by a rare earth catalytic solid phase transformation method, which uses rare earth oxides as catalysts to promote the in-situ phase transformation of cubic boron nitride to hexagonal boron nitride catalyzed by rare earth oxides during hot-pressing sintering. The volume expansion of cubic boron nitride to hexagonal boron nitride can effectively improve the density and mechanical properties of the ceramic material, and the ceramic material has good stability at high temperatures. BRIEF DESCRIPTION OF DRAWINGS

[0060] Figure 1 is the XRD spectrum of the ceramic material of Examples 1-3 and Comparative Example 1.

[0061] Figure 2 is the SEM image of the ceramic material in Examples 1-3 and Comparative Example 1, wherein (a) corresponds to Example 1, (b) corresponds to Example 2, (c) corresponds to Example 3, and (d) corresponds to Comparative Example 1.

[0062] Figure 3 is the EDS spectrum analysis diagram of the ceramic material in Examples 1-3 and Comparative Example 1, wherein (a) corresponds to Example 1, (b) corresponds to Example 2, (c) corresponds to Example 3, and (d) corresponds to Comparative Example 1. DETAILED DESCRIPTION

[0063] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments description will be briefly introduced as follows. Obviously, the following drawings only show some of the embodiments of the present application, and therefore should not be considered as a limitation to the scope, and other related drawings can also be obtained by those skilled in the art without any creative effort.

[0064] The specific embodiments described herein are intended for illustration purposes only and are not intended to limit the present application.

[0065] Embodiment 1

[0066] A ceramic material, a main phase of the ceramic material comprising cubic boron nitride, hexagonal boron nitride and rare earth oxide, the rare earth oxide being Gd2O3, the volume fraction of the cubic boron nitride being 6% and the volume fraction of the hexagonal boron nitride being 94% based on 100% of the total volume of the cubic boron nitride and the hexagonal boron nitride, and the mass content of the rare earth oxide being 3wt% based on 100% of the total mass of the ceramic material.

[0067] The preparation method of the ceramic material provided by the embodiment comprises the following steps:

[0068] (1) Ball milling mixing: a certain mass of cubic boron nitride powder (particle size D50 = 1 μm) is weighed by a balance and added into a ball milling tank, then rare earth oxide Gd2O3 (particle size D50 = 3 μm) is added, and anhydrous ethanol is used as a dispersant for wet ball milling mixing;

[0069] In the process of ball milling, silicon nitride milling balls are used, the ball milling speed is 300 rpm, and the time length is 4 h;

[0070] (2) Drying and sieving: the milling balls are filtered out using a 80-mesh stainless steel screen, the anhydrous ethanol is removed by rotary evaporation, the temperature of rotary evaporation is 50℃, the speed of rotary evaporation is 30 rpm, after drying at 80℃ for 10 h, the dried mixed powder is ground by a mortar, and sieved by a 200-mesh screen for 2 times to obtain the mixed powder of Gd2O3 doped cubic boron nitride;

[0071] (3) Hot-pressing sintering: 5 g of the mixed powder of Gd2O3 doped cubic boron nitride is weighed and put into a sintering graphite mold, then the sintering graphite mold containing the mixed powder is put into a hot-pressing sintering equipment for hot-pressing sintering;

[0072] In the process of hot-pressing sintering, the sintering temperature is 1700℃, the heating speed is 8℃ / min, the sintering pressure is 40 MPa, the pressure holding time is 90 min, and the sintering atmosphere is N2;

[0073] (4) Ceramic demolding: after waiting for the hot-pressing sintering equipment to cool to room temperature, the graphite mold is taken out, and the ceramic material is demolded.

[0074] Example 2

[0075] A ceramic material, a main phase of the ceramic material comprising cubic boron nitride, hexagonal boron nitride and rare earth oxide, the rare earth oxide being Eu2O3, the volume fraction of the cubic boron nitride being 4% and the volume fraction of the hexagonal boron nitride being 96% based on 100% of the total volume of the cubic boron nitride and the hexagonal boron nitride, the mass content of the rare earth oxide being 5wt% based on 100% of the total mass of the ceramic material.

[0076] The preparation method of the ceramic material provided in the embodiment comprises the following steps:

[0077] (1) Ball milling mixing: a certain mass of cubic boron nitride powder (particle size D50 = 1.5 μm) is weighed by a balance and added into a ball milling tank, then rare earth oxide Eu2O3 (particle size D50 = 4 μm) is added, and anhydrous ethanol is used as a dispersant for wet ball milling mixing;

[0078] In the process of ball milling, silicon nitride milling balls are used, the ball milling rotation speed is 400 rpm, and the time length is 5 h;

[0079] (2) Drying and sieving: the milling balls are filtered out using a 80-mesh stainless steel screen, the anhydrous ethanol is removed by rotary evaporation, the rotary evaporation temperature is 50°C, the rotary evaporation rotation speed is 30 rpm, after drying at 100°C for 10 h, the dried mixed powder is ground by a mortar, and sieved by a 200-mesh screen for 3 times to obtain a Eu2O3-doped cubic boron nitride mixed powder;

[0080] (3) Hot-pressing sintering: 5 g of the Eu2O3-doped cubic boron nitride mixed powder is weighed and put into a sintering graphite mold, then the sintering graphite mold containing the mixed powder is put into a hot-pressing sintering equipment for hot-pressing sintering;

[0081] In the process of hot-pressing sintering, the sintering temperature is 1800°C, the heating speed is 10°C / min, the sintering pressure is 50 MPa, the pressure holding time is 120 min, and the sintering atmosphere is N2;

[0082] (4) Ceramic demolding: after waiting for the hot-pressing sintering equipment to cool to room temperature, the graphite mold is taken out, and the ceramic material is demolded.

[0083] Example 3

[0084] A ceramic material, a main phase of the ceramic material comprising cubic boron nitride, hexagonal boron nitride and rare earth oxide, the rare earth oxide being Yb2O3, a volume fraction of the cubic boron nitride being 23% and a volume fraction of the hexagonal boron nitride being 77% based on a total volume of the cubic boron nitride and the hexagonal boron nitride being 100%, and a mass content of the rare earth oxide being 7wt% based on a total mass of the ceramic material being 100%.

[0085] The preparation method of the ceramic material provided in the embodiment comprises the following steps:

[0086] (1) Ball milling mixing: a certain mass of cubic boron nitride powder (particle size D50 = 2 μm) is weighed by a balance and added into a ball milling tank, then rare earth oxide Yb2O3 (particle size D50 = 3.5 μm) is added, and anhydrous ethanol is used as a dispersant for wet ball milling mixing;

[0087] In the process of ball milling, silicon nitride milling balls are used, the rotation speed of the ball milling is 350 rpm, and the time length is 6 h;

[0088] (2) Drying and sieving: the milling balls are filtered out by using a 80-mesh stainless steel screen, the anhydrous ethanol is removed by rotary evaporation, the temperature of the rotary evaporation is 50℃, the rotation speed of the rotary evaporation is 30 rpm, after drying at 90℃ for 15 h, the dried mixed powder is ground by a mortar, and sieved by a 200-mesh screen for 3 times to obtain the mixed powder of Yb2O3 doped cubic boron nitride;

[0089] (3) Hot-pressing sintering: 5 g of the mixed powder of Yb2O3 doped cubic boron nitride is weighed and put into a sintering graphite mold, then the sintering graphite mold containing the mixed powder is put into a hot-pressing sintering equipment for hot-pressing sintering;

[0090] In the process of hot-pressing sintering, the sintering temperature is 1600℃, the heating speed is 10℃ / min, the sintering pressure is 45 MPa, the pressure maintaining time is 90 min, and the sintering atmosphere is N2;

[0091] (4) Ceramic demolding: after the hot-pressing sintering equipment is cooled to room temperature, the graphite mold is taken out to obtain the ceramic material.

[0092] Embodiment 4

[0093] A ceramic material and a preparation method thereof, the preparation method of the ceramic material is only different from that of embodiment 1 in that the sintering temperature is 1500℃.

[0094] In the main phase of the ceramic material of the embodiment, a volume fraction of the hexagonal boron nitride is 79% and a volume fraction of the cubic boron nitride is 21% based on a total volume of the cubic boron nitride and the hexagonal boron nitride being 100%.

[0095] Example 5

[0096] A ceramic material and a method for producing the same, the method for producing the ceramic material being different from that of Example 1 only in that the sintering temperature is 1900°C.

[0097] In the main phase of the ceramic material of this example, the volume fraction of cubic boron nitride is 2% and the volume fraction of hexagonal boron nitride is 98% based on 100% of the total volume of the cubic boron nitride and the hexagonal boron nitride.

[0098] Example 6

[0099] A ceramic material and a method for producing the same, the method for producing the ceramic material being different from that of Example 1 only in that the sintering pressure is 30 MPa.

[0100] In the main phase of the ceramic material of this example, the volume fraction of cubic boron nitride is 3% and the volume fraction of hexagonal boron nitride is 97% based on 100% of the total volume of the cubic boron nitride and the hexagonal boron nitride.

[0101] Example 7

[0102] A ceramic material and a method for producing the same, the method for producing the ceramic material being different from that of Example 1 only in that the sintering pressure is 60 MPa.

[0103] In the main phase of the ceramic material of this example, the volume fraction of cubic boron nitride is 14% and the volume fraction of hexagonal boron nitride is 86% based on 100% of the total volume of the cubic boron nitride and the hexagonal boron nitride.

[0104] Example 8

[0105] A ceramic material and a method for producing the same, the method for producing the ceramic material being different from that of Example 1 only in that the amount of the rare earth oxide used in the production method is changed so that the mass content of the rare earth oxide in the ceramic material produced is 0.5%.

[0106] The main phase of the ceramic material of this example includes cubic boron nitride, hexagonal boron nitride and a rare earth oxide, the volume fraction of the cubic boron nitride is 16% and the volume fraction of the hexagonal boron nitride is 84% based on 100% of the total volume of the cubic boron nitride and the hexagonal boron nitride; and the mass content of the rare earth oxide is 0.5% based on the total mass of the ceramic material.

[0107] Example 9

[0108] A ceramic material and a method for producing the same, the method for producing the ceramic material being different from that of Example 1 only in that the amount of the rare earth oxide used in the production method is changed so that the mass content of the rare earth oxide in the ceramic material produced is 11%.

[0109] The main phase of the ceramic material of the embodiment comprises cubic boron nitride, hexagonal boron nitride and rare earth oxide, the volume fraction of the cubic boron nitride is 4% and the volume fraction of the hexagonal boron nitride is 96% based on 100% of the total volume of the cubic boron nitride and the hexagonal boron nitride; and the mass content of the rare earth oxide is 10% based on the total mass of the ceramic material.

[0110] Comparative Example 1

[0111] A ceramic material and a preparation method thereof, wherein the preparation method of the ceramic material is only different from that of Example 1 in that no rare earth oxide Gd2O3 is added in step (1), and the ball milling mixing is performed according to the same process as that of Example 1.

[0112] The ceramic material of the embodiment comprises cubic boron nitride and hexagonal boron nitride, the volume fraction of the cubic boron nitride is 96% and the volume fraction of the hexagonal boron nitride is 4% based on 100% of the total volume of the cubic boron nitride and the hexagonal boron nitride.

[0113] Performance test:

[0114] (1) Density test: the density test of the sample is performed by using the Archimedes drainage method.

[0115] (2) Elastic modulus test: the elastic modulus test of the sample is performed by using the G200 nanoindenter of the United States of America is the technology company. The sample is polished and polished before the test.

[0116] (3) Nanoindentation hardness test: the nanoindentation hardness test of the sample is performed by using the G200 nanoindenter of the United States of America is the technology company. The sample is polished and polished before the test.

[0117] (4) Densification test: the actual density of the sample is measured by using the Archimedes drainage method, and the densification of the sample is calculated by combining the theoretical density of the sample obtained according to the XRD analysis result.

[0118] (5) XRD test: the sample is tested and analyzed by using the X'Pert-PRO X-ray diffractometer of the Netherlands PANalytical Philips company. Cu Kα ray is used as the light source, the wavelength λ is 0.15406

[0119] nm, the tube voltage and current are 40kV and 30mA respectively, and the scanning range 2θ is 10°-90°.

[0120] (6) SEM test: the surface morphology of the sample is observed by using the Gemini 300 hot field emission scanning electron microscope of the Germany Zeiss company, and the acceleration voltage is 2kV. The sample is surface gold spraying treated before the test.

[0121] (7) EDS spectrum analysis: EDS spectrum analysis of the sample was performed using Ultim Max electron spectrometer of Oxford Instruments, UK, with an accelerating voltage of 15 kV. The sample was treated by surface spraying before testing.

[0122] The tests of (1)-(7) were performed on the ceramic materials of Examples 1-9 and Comparative Example 1, and the results are shown in Table 1.

[0123] Table 1

[0124]

[0125] As shown in Table 1, by using rare earth oxides as catalysts, the in-situ phase transition of cubic boron nitride to hexagonal boron nitride is promoted during hot-pressing sintering, and the volume expansion occurs when cubic boron nitride turns into hexagonal boron nitride, which can effectively improve the density and mechanical properties of the ceramic material. The ceramic material has good stability at high temperature. In Comparative Example 1, no rare earth oxides are added, so that the ceramic material obtained after hot-pressing sintering mainly exists in the phase of cubic boron nitride, and has low mechanical properties and density.

[0126] As shown in Table 1, by using rare earth oxides as catalysts, the in-situ phase transition of cubic boron nitride to hexagonal boron nitride is promoted during hot-pressing sintering, and the volume expansion occurs when cubic boron nitride turns into hexagonal boron nitride, which can effectively improve the density and mechanical properties of the ceramic material. The ceramic material has good stability at high temperature. In Comparative Example 1, no rare earth oxides are added, so that the ceramic material obtained after hot-pressing sintering mainly exists in the phase of cubic boron nitride, and has low mechanical properties and density.

[0127] As shown in Table 1, by using rare earth oxides as catalysts, the in-situ phase transition of cubic boron nitride to hexagonal boron nitride is promoted during hot-pressing sintering, and the volume expansion occurs when cubic boron nitride turns into hexagonal boron nitride, which can effectively improve the density and mechanical properties of the ceramic material. The ceramic material has good stability at high temperature. In Comparative Example 1, no rare earth oxides are added, so that the ceramic material obtained after hot-pressing sintering mainly exists in the phase of cubic boron nitride, and has low mechanical properties and density.

[0128] As shown in Table 1, by using rare earth oxides as catalysts, the in-situ phase transition of cubic boron nitride to hexagonal boron nitride is promoted during hot-pressing sintering, and the volume expansion occurs when cubic boron nitride turns into hexagonal boron nitride, which can effectively improve the density and mechanical properties of the ceramic material. The ceramic material has good stability at high temperature. In Comparative Example 1, no rare earth oxides are added, so that the ceramic material obtained after hot-pressing sintering mainly exists in the phase of cubic boron nitride, and has low mechanical properties and density.

[0129] The ceramic materials of Examples 1-3 and Comparative Example 1 were subjected to tests (5)-(7), and the results are as follows:

[0130] The ceramic materials of Examples 1-3 and Comparative Example 1 were subjected to XRD tests, and the results are as shown in FIG. 2. Figure 1 As can be seen from the figure, the diffraction peaks of cubic boron nitride and hexagonal boron nitride appear simultaneously in the spectrum of the ceramic material of Example 1, which are respectively attributed to unconverted cubic boron nitride and converted hexagonal boron nitride. In the spectrum of the ceramic material of Example 2, the diffraction intensity of hexagonal boron nitride is significantly higher than that of cubic boron nitride, indicating that most of the cubic boron nitride is converted into well-crystallized hexagonal boron nitride. The diffraction peaks of cubic boron nitride and hexagonal boron nitride appear simultaneously in the spectrum of the ceramic material of Example 3, which are respectively attributed to unconverted cubic boron nitride and converted hexagonal boron nitride. In the spectrum of the ceramic material of Comparative Example 1, although there are diffraction peaks of hexagonal boron nitride, the height is much lower than that of cubic boron nitride, indicating that only a small amount of cubic boron nitride is converted into hexagonal boron nitride.

[0131] The ceramic materials of Examples 1-3 and Comparative Example 1 were subjected to SEM tests, and the results are as shown in FIG. 3. Figure 2 Figure 2 In the figure, (a) corresponds to Example 1, (b) corresponds to Example 2, (c) corresponds to Example 3, and (d) corresponds to Comparative Example 1. As can be seen from the figure, in the ceramic material of Example 1, the flaky morphology of the hexagonal boron nitride grains is relatively obvious and highly dense, which is due to the volume expansion of the conversion of cubic boron nitride into hexagonal boron nitride when hot-pressing sintering at 1800°C, and the obvious catalytic phase transition effect of Gd2O3 on cubic boron nitride. In the ceramic material of Example 2, the flaky morphology of the hexagonal boron nitride grains is relatively obvious and highly dense, which is due to the volume expansion of the conversion of cubic boron nitride into hexagonal boron nitride when hot-pressing sintering at 1800°C, and the obvious catalytic phase transition effect of Eu2O3 on cubic boron nitride. In the ceramic material of Example 3, the flaky morphology of the hexagonal boron nitride grains is relatively obvious and highly dense. In the ceramic material of Comparative Example 1, the morphology of the cubic boron nitride powder can be clearly distinguished, and the density is also relatively low.

[0132] The ceramic materials of Examples 1-3 and Comparative Example 1 were subjected to EDS spectrum analysis, and the results are as shown in FIG. 4. Figure 3 Figure 3 ​​In the figure, (a) corresponds to example 1, (b) corresponds to example 2, (c) corresponds to example 3, (d) corresponds to comparative example 1. As can be seen from the figure, in the ceramic material of example 1, in addition to the peaks of boron element and nitrogen element, there are peaks of gadolinium and oxygen in the ceramic, which indicates that Gd2O3 still exists in the form of oxide in the ceramic. In the ceramic material of example 2, in addition to the peaks of boron element and nitrogen element, the spectrum peaks of europium and oxygen are clearly visible. In the ceramic material of example 3, in addition to the peaks of boron element and nitrogen element, the spectrum peaks of ytterbium and oxygen are clearly visible. In the ceramic material of comparative example 1, only the peaks of boron element and nitrogen element are visible, and the peaks of rare earth element and oxygen are not visible, which indicates that there is no rare earth oxide in it.

[0133] In summary, by using rare earth oxide as a catalyst, the in-situ phase transition of cubic boron nitride to hexagonal boron nitride catalyzed by rare earth oxide is promoted during the process of hot-pressing sintering, and the volume expansion occurs when cubic boron nitride turns to hexagonal boron nitride, which can effectively improve the density and mechanical properties of the ceramic material. The ceramic material has good stability at high temperature.

[0134] The applicant declares that the detailed method of the present application is illustrated by the above examples, but the present application is not limited to the above detailed method, that is, it does not mean that the present application must rely on the above detailed method to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of each raw material of the product of the present application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A ceramic material, characterized in that, The main phase of the ceramic material comprises cubic boron nitride and hexagonal boron nitride, the elastic modulus of the ceramic material is greater than 15 GPa, the nanoindentation hardness of the ceramic material is not less than 250 MPa, and the density of the ceramic material is greater than 85%; The volume fraction of the hexagonal boron nitride is 90%-99% based on the total volume of the cubic boron nitride and the hexagonal boron nitride being 100%; the volume fraction of the cubic boron nitride is 1%-10%; The ceramic material further comprises rare earth oxides; the mass content of the rare earth oxides is 1wt%-10wt% based on the total mass of the ceramic material being 100%; The ceramic material is prepared by the following method, which comprises the following steps: (1) mixing cubic boron nitride and rare earth oxides to obtain a mixed powder of rare earth doped cubic boron nitride; (2) hot-pressing sintering the mixed powder to promote in-situ phase transition of the rare earth oxide catalyzed cubic boron nitride to hexagonal boron nitride to obtain the ceramic material; The hot-pressing sintering is carried out under the protection of a protective gas, and the protective gas comprises at least one of N2, He, Ne and Ar; The particle size D50 of the rare earth oxide in step (1) is 2µm-4µm; The particle size D50 of the cubic boron nitride in step (1) is 1µm-2µm.

2. The ceramic material of claim 1, wherein, The ceramic material has a density greater than 2.2 g / cm3 3 .

3. The ceramic material of claim 1, wherein, The rare earth oxide comprises at least one of Eu2O3, Yb2O3 and Gd2O3.

4. A method of producing a ceramic material as claimed in any one of claims 1 to 3, characterised in that, The preparation method comprises the following steps: (1) mixing cubic boron nitride and rare earth oxides to obtain a mixed powder of rare earth doped cubic boron nitride; (2) hot-pressing sintering the mixed powder to promote in-situ phase transition of the rare earth oxide catalyzed cubic boron nitride to hexagonal boron nitride to obtain the ceramic material; The hot-pressing sintering is carried out under the protection of a protective gas, and the protective gas comprises at least one of N2, He, Ne and Ar; The particle size D50 of the rare earth oxide in step (1) is 2µm-4µm; The particle size D50 of the cubic boron nitride in step (1) is 1µm-2µm.

5. The method of producing a ceramic material according to claim 4, characterized in that, The rare earth oxide in step (1) comprises at least one of Eu2O3, Yb2O3 and Gd2O3.

6. The method of producing a ceramic material according to claim 4, characterized in that, The mixing method in step (1) is wet ball milling, and the method for preparing the mixed powder of rare earth doped cubic boron nitride by wet ball milling comprises the following steps: mixing cubic boron nitride powder, rare earth oxides and a dispersing agent, drying the milled material after ball milling to obtain the mixed powder.

7. The method of producing a ceramic material according to claim 6, characterized in that, The grinding balls used in the ball milling process comprise at least one of silicon nitride grinding balls and zirconium oxide grinding balls.

8. The method of producing a ceramic material according to claim 6, characterized in that, The dispersing agent comprises at least one of ethanol, isopropyl alcohol and acetone.

9. The method of producing a ceramic material according to claim 6, characterized in that, The rotation speed of the ball milling is 300rpm-500rpm.

10. The method of producing a ceramic material according to claim 6, characterized in that, The ball milling time is 4h-6h.

11. The method of producing a ceramic material according to claim 6, characterized in that, After the ball milling, the grinding balls are removed by filtration to obtain the milled material.

12. The method of producing a ceramic material according to claim 11, characterized in that, The mesh number of the screen used in the filtration is 70-90.

13. The method of producing a ceramic material according to claim 6, characterized in that, The drying temperature is 80°C-100°C.

14. The method of producing a ceramic material according to claim 6, characterized in that, The drying time is 8h-20h.

15. The method of producing a ceramic material according to claim 6, characterized in that, Before the drying, the ball-milled material is subjected to rotary evaporation at a temperature of 45-60℃ and a rotation speed of 30-60rpm.

16. The method of producing a ceramic material according to claim 4, characterized in that, The method further comprises grinding and sieving the mixed powder before hot-press sintering.

17. The method of producing a ceramic material according to claim 16, characterized in that, The sieving is performed 2-3 times using a sieve with a mesh size of 175-230.

18. The method of producing a ceramic material according to claim 4, characterized in that, During the hot-press sintering, the sintering temperature is 1600-1900℃.

19. The method of producing a ceramic material according to claim 4, characterized in that, The heating rate of the hot-press sintering is 8-12℃ / min.

20. The method of producing a ceramic material according to claim 4, wherein During the hot-press sintering, the sintering pressure is 40-50MPa.

21. The method of producing a ceramic material according to claim 4, characterized in that, The pressure holding time of the hot-press sintering is 60-120min.

22. The method of producing a ceramic material according to claim 4, characterized in that, The preparation method comprises the following steps: (1) Ball-milling mixing: Cubic boron nitride powder with a particle size D50 of 1-2µm is weighed and mixed with rare earth oxide Re2O3 with a particle size D50 of 2-4µm by wet ball-milling using anhydrous ethanol as a dispersant to obtain a mixed slurry, wherein Re is a rare earth element; (2) Drying and sieving: The mixed slurry in step (1) is filtered to remove the milling balls, rotary evaporated to remove the anhydrous ethanol, and then ground and sieved after drying to obtain a mixed powder of Re2O3-doped cubic boron nitride; (3) Hot-press sintering: An appropriate amount of the mixed powder in step (2) is weighed and placed in a sintering graphite mold, which is then placed in a hot-press sintering device for hot-press sintering under the protection of a protective gas. During the hot-press sintering, the sintering temperature is 1600-1900℃, the heating rate is 8-12℃ / min, and the pressure holding time is 60-120min; (4) Ceramic demolding: After the hot-press sintering device cools to room temperature, the graphite mold is removed to obtain the ceramic material.

23. Use of a ceramic material according to any one of claims 1 to 3, characterized in that The ceramic material is used as a wave-transparent ceramic.

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