Hexagonal boron nitride ceramic material, preparation method and application thereof

Abstract

The application belongs to the technical field of ceramic matrix composite materials, and particularly relates to a hexagonal boron nitride ceramic material and a preparation method and application thereof. The hexagonal boron nitride ceramic material prepared by the application is prepared from raw materials including hexagonal boron nitride powder and a composite sintering aid, wherein the composite sintering aid is composed of magnesium oxide powder, aluminum oxide powder, silicon dioxide powder and rare earth oxide powder. The preparation method includes raw material mixing, ball milling and drying, and vacuum rapid hot-press sintering. In the application, rare earth ions exist in the form of amorphous state in a magnesium-aluminum-silicate glass network, and the hexagonal boron nitride ceramic material with high compactness, high directional arrangement texture and excellent mechanical properties is prepared by utilizing the differential regulation of different radius rare earth ions on the liquid phase generation and rheological viscosity of the glass network. The ceramic material can also be effectively protected by in-situ generation of a high-melting-point oxide barrier layer under a high-temperature molten metal corrosion environment, so that the corrosion resistance of the ceramic material is improved.

Description

Technical Field

[0001] This invention belongs to the field of ceramic matrix composite technology, specifically relating to a hexagonal boron nitride ceramic material, its preparation method, and its application. Background Technology

[0002] Hexagonal boron nitride (h-BN) possesses a unique crystal structure, excellent thermal shock resistance, and ease of processing, making it suitable for applications such as horizontal continuous casting separation rings, metal smelting crucibles, amorphous nozzles, and high-temperature metal electrolytic cells. However, due to the strong covalent bonds and low diffusion coefficient of hexagonal boron nitride, it is difficult to achieve high-density sintering at high temperatures. Currently, the hot-pressed sintering temperature of hexagonal boron nitride ceramic materials prepared domestically and internationally generally needs to reach around 2000℃ and the sintering pressure needs to reach above 25 MPa to achieve a relatively high density, which is insufficient to meet the mechanical property requirements of most components.

[0003] Furthermore, research indicates that the texture (i.e., the degree of grain orientation) of h-BN ceramics has a decisive influence on its thermal conductivity, lubrication, corrosion resistance, and mechanical properties in specific directions. High-texture h-BN ceramics can concentrate the superior properties of the ab plane of the grains on the working surface of macroscopic components, thus exhibiting comprehensive performance far exceeding that of randomly oriented materials in applications such as molten metal contact, directional thermal conduction, and low-friction lubrication. However, h-BN grains obtained by traditional pressureless or hot-pressing sintering are mostly randomly arranged, making it difficult to form a highly oriented texture. This results in the inability to fully utilize the mechanical and thermophysical properties of the material in specific directions. Simultaneously, in molten metal environments such as high-temperature molten iron, h-BN is prone to oxidation corrosion and even structural collapse, thus failing to solve the problem of high-temperature molten metal corrosion.

[0004] Therefore, how to effectively control the directional arrangement of h-BN grains and obtain high-texture materials while achieving high densification, and at the same time take into account their resistance to high-temperature molten metal corrosion, has always been an unsolved technical problem in this field. Summary of the Invention

[0005] To address the needs of existing technologies, the purpose of this invention is to provide a hexagonal boron nitride ceramic material, its preparation method, and its applications. This invention addresses the technical shortcomings of traditional hexagonal boron nitride ceramic materials, such as difficulty in sintering to achieve density and low hardness and strength, which makes them unsuitable for harsh operating conditions. It provides a hexagonal boron nitride ceramic material with high density, highly oriented texture, and excellent mechanical properties, along with its preparation method. This invention utilizes rare earth ions in an amorphous form within a magnesium aluminosilicate glass network. By employing differentiated control of the liquid phase formation and rheological viscosity of the glass network using rare earth ions of different radii, a hexagonal boron nitride ceramic material with high density, highly oriented texture, and excellent mechanical properties is prepared. Furthermore, it can effectively protect the matrix by generating a high-melting-point oxide barrier layer in situ under high-temperature molten metal corrosion environments, thereby improving the corrosion resistance of the ceramic material.

[0006] Specifically, the present invention provides the following technical solution: In a first aspect, the present invention provides a hexagonal boron nitride ceramic material, wherein, by mass percentage, the raw material components of the hexagonal boron nitride ceramic material comprise: 70%~90% hexagonal boron nitride powder and 10%~30% composite sintering aid; wherein, the mass percentage of each component in the composite sintering aid to the total amount of the composite sintering aid is as follows: 10%~25% magnesium oxide, 25%~45% aluminum oxide, 40%~60% silicon dioxide, and 10%~23% rare earth oxides; The rare earth oxide is selected from one or more of lanthanum oxide, yttrium oxide, scandium oxide, cerium oxide, neodymium oxide, gadolinium oxide, dysprosium oxide, erbium oxide, and ytterbium oxide.

[0007] Preferably, the raw material composition of the hexagonal boron nitride ceramic material, by mass percentage, includes: 70%~75% hexagonal boron nitride powder and 25%~30% composite sintering aid; wherein, the mass percentage of each component in the composite sintering aid to the total amount of the composite sintering aid is as follows: 10%~15% magnesium oxide, 28%~32% aluminum oxide, 18%~22% rare earth oxides, and the balance is silicon dioxide.

[0008] Preferably, the raw material composition of the hexagonal boron nitride ceramic material, by mass percentage, includes: 85%~90% hexagonal boron nitride powder and 10%~15% composite sintering aid; wherein, the mass percentage of each component in the composite sintering aid to the total amount of the composite sintering aid is as follows: 10%~12% magnesium oxide, 25%~28% aluminum oxide, 18%~23% rare earth oxides, and the balance is silicon dioxide.

[0009] Preferably, the raw material composition of the hexagonal boron nitride ceramic material, by mass percentage, includes: 78%~82% hexagonal boron nitride powder, and 18%~22% composite sintering aid; wherein, the mass percentage of each component in the composite sintering aid to the total amount of the composite sintering aid is as follows: 10%~15% magnesium oxide, 28%~32% aluminum oxide, 18%~23% rare earth oxides, and the balance is silicon dioxide.

[0010] Preferably, in the hexagonal boron nitride ceramic material, rare earth ions exist in an amorphous form in the magnesium aluminum silicate glass network, and the hexagonal boron nitride ceramic material has a hexagonal boron nitride grain orientation structure with an absolute texture value greater than 1500.

[0011] Preferably, in a high-temperature molten metal corrosion environment, the magnesium and aluminum ions in the internal glass phase of the hexagonal boron nitride ceramic material diffuse to the surface and react in situ to form a high-melting-point oxide barrier layer.

[0012] Preferably, the hexagonal boron nitride powder has a purity of ≥99.0% and a particle size of 1~2 μm; the magnesium oxide, aluminum oxide, silicon dioxide and rare earth oxides are all nano-sized powders with a purity of ≥99.9%.

[0013] A second aspect of the present invention provides a method for preparing the hexagonal boron nitride ceramic material described in the first aspect, comprising the following steps: Hexagonal boron nitride powder and composite sintering aid are mixed, ball-milled and dried, and the resulting product is hot-pressed and sintered under vacuum to obtain hexagonal boron nitride ceramic material.

[0014] Preferably, the ball milling conditions are: ball-to-material ratio of 3:1, anhydrous ethanol as the grinding medium, rotation speed of 200~400 r / min, and ball milling time of 5~8 h; the drying temperature is 75~85℃, and the drying time is 10~15 h.

[0015] Preferably, the hot pressing sintering is performed using a rapid hot pressing method, that is, heating from an initial temperature of 600~750℃ to 1500~1900℃ at a heating rate of 1~100℃ / min, holding time of 5~60 min, and applying an axial pressure of 10~50MPa.

[0016] Preferably, the vacuum degree of the vacuum condition is ≤10 Pa.

[0017] A third aspect of the present invention provides the application of the hexagonal boron nitride ceramic material described in the first aspect in the preparation of high-temperature molten metal contact components.

[0018] The beneficial effects achieved by one or more technical solutions of the present invention are as follows: (1) In the hexagonal boron nitride ceramic material prepared by the present invention, rare earth ions exist in the magnesium aluminum silicate glass network in an amorphous form. There are no rare earth-related crystallization peaks in the X-ray diffraction pattern, and the hexagonal boron nitride grains are highly oriented and the absolute value of texture is greater than 1500. The preparation method includes three steps: raw material mixing, ball milling and drying, and vacuum hot pressing sintering. Compared with the prior art, this application can complete sintering under significantly milder conditions: the temperature can be as low as 1600℃ (reduced by 200℃), the holding time is as short as 10 minutes (reduced to 1 / 9), the pressure is as low as 10 MPa (reduced to 1 / 3), and no cold pressing pretreatment is required. The process flow is simplified and the production efficiency is greatly improved.

[0019] (2) The hexagonal boron nitride ceramic material prepared by this invention achieves a synergistic effect of high density, high texture, and high mechanical properties. By introducing rare earth ions with different radii, the liquid phase generation kinetics and rheological viscosity of the magnesium aluminosilicate glass network are differentially regulated. This effectively reduces the steric hindrance of liquid phase mass transfer and the resistance to h-BN lamellar rearrangement at high temperatures, thereby promoting material densification while achieving highly oriented h-BN grains, significantly improving the bending strength of the material. Specifically, the bulk density reaches 2.02~2.31 g / cm³. 3 The absolute value of the texture is as high as 1731~2970, and the bending strength is nearly 5 times higher than that of the unmodified system (from 15.9 MPa to 90.5 MPa).

[0020] (3) In the high-temperature molten metal corrosion environment, the hexagonal boron nitride ceramic material prepared by this invention can diffuse Mg, Al and other elements in the glass phase inside the material to the surface and react in situ to form a dense high-melting-point oxide barrier layer. This corrosion layer acts as an effective physical shield, significantly delaying the process of molten metal erosion into the matrix, thereby effectively protecting the matrix structure and extending the service life of the material under harsh working conditions.

[0021] (4) This invention, through innovative design of raw materials and preparation methods, prepares hexagonal boron nitride composite ceramic materials with reinforcing phase precipitation inside the composite phase and at the phase interface with the hexagonal boron nitride matrix phase; it can also obtain reinforcing phases with different contents and morphologies at the phase interface and in the composite phase by different sintering temperatures and heat treatment times; it improves the overall performance of the product by improving interface bonding and precipitated phase reinforcement; thus effectively solving the technical defects of traditional hexagonal boron nitride ceramic materials in the prior art, which have low hardness and strength, making it difficult to meet the performance requirements of harsh working conditions. Specifically, by adjusting the type of rare earth ions (using radius differences to control liquid phase rheology), rare earth content (10%~24%), and additive dosage (10%~30%), a flexible balance can be achieved between densification, texturing, and corrosion resistance to meet the needs of different working conditions.

[0022] (5) The high-texture, corrosion-resistant hexagonal boron nitride ceramic material prepared by this invention can be widely used in high-temperature molten metal contact scenarios, including but not limited to: horizontal continuous casting separation rings (utilizing the low friction and corrosion resistance properties brought by high texture), metal smelting crucibles (utilizing the corrosion resistance of the in-situ generated barrier layer), amorphous nozzles (utilizing directional heat conduction and thermal shock resistance properties), and high-temperature metal electrolytic cells (utilizing electrical insulation and resistance to fluoride salt corrosion properties). In addition, this material can also be extended to the fields of directional heat dissipation substrates for high-power electronic devices and high-temperature lubrication components, and has significant industrial practical value and broad market prospects. Attached Figure Description

[0023] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0024] Figure 1 The XRD patterns of La-30-1600, Y-30-1600 and Sc-30-1600 obtained in Examples 1 to 3 of this invention are shown. Figure 2 The XRD patterns of Sc-30-1600 prepared in Example 3 and Sc24-30-1600 prepared in Comparative Example 3 are shown below. Figure 3 SEM images of Sc-30-1600, Sc-15-1800, and Sc-10-1800 obtained in Examples 3 and 7-8 of the present invention; Figure 4 This is a cross-sectional SEM image of Sc-15-1800 obtained in Example 7 of the present invention when subjected to high-temperature erosion by molten iron. Figure 5 This is a schematic diagram of the preparation process of the hexagonal boron nitride ceramic material obtained in an embodiment of the present invention. Detailed Implementation

[0025] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0026] As mentioned above, given the inherent characteristics of hexagonal boron nitride (h-BN) ceramics, such as strong covalent bonds and low diffusion coefficients, sintering densification is extremely difficult. Therefore, sintering aids are typically introduced under high temperature and high pressure conditions to improve sintering behavior. In existing technologies, the mechanisms of action of sintering aids mainly include: 1) forming a solid solution with the main crystalline phase, increasing the concentration of point defects, improving the ion diffusion coefficient and powder surface energy, and increasing the sintering driving force; 2) forming a continuous liquid phase at grain boundaries, transforming evaporation-condensation mass transfer into a faster dissolution-precipitation mass transfer, promoting particle rearrangement and densification, thereby effectively filling the voids in the "card-room structure" of h-BN grains, reducing porosity, and achieving densification sintering at lower temperatures.

[0027] The technical solution of this invention is to introduce rare earth ions (La / Y / Sc, etc.) in a specific content range (10~24 wt%) as modifiers for magnesium aluminosilicate glass networks. By utilizing the differences in the radii of different rare earth ions, the generation kinetics and rheological viscosity of the liquid phase are precisely controlled, thereby achieving a synergistic effect of high density, high texture (oriented grain arrangement) and resistance to high-temperature molten metal corrosion at lower temperatures, shorter times, and lower pressures.

[0028] In detail, during liquid-phase assisted hot pressing sintering, the sintering behavior is directly controlled by the amount and viscosity of the liquid phase. Sufficient liquid phase provides physical lubrication, reduces solid-phase frictional resistance, and allows h-BN sheets to rotate smoothly under hot-pressing stress; lower liquid phase viscosity further weakens the viscous resistance to grain rotation, accelerates liquid phase mass transfer, and promotes the anisotropic preferential growth of h-BN grains.

[0029] In the sintering aid system of this invention, the introduction of rare earth ions interacts with the aid components at a lower temperature, altering the reaction pathway, inhibiting the formation of complex intermediate crystalline phases in conventional solid-state reactions, and promoting the early transformation of the material into an amorphous or trace liquid phase, laying the foundation for subsequent wetting and densification. The "network depolymerization ability" of rare earth ions allows them to act as network modifiers. By introducing non-bridging oxygen to break the silicon-oxygen framework, deep depolymerization not only promotes the early formation of the liquid phase but also significantly reduces the viscous resistance of the high-temperature liquid phase. After entering the fully liquid phase, "steric hindrance" replaces "network depolymerization ability" as the core factor determining rheological viscosity and lubrication effect. Therefore, by controlling the type of rare earth ions and the sintering process, this invention achieves precise control over the properties of h-BN ceramics.

[0030] Furthermore, although h-BN ceramics do not have a definite melting point under standard pressure and do not soften below 3000℃, their resistance is significantly affected by the environmental atmosphere: they are prone to oxidation in oxidizing atmospheres above 800℃, and there is a risk of complete corrosion when in contact with molten iron. In this application, when the ceramic is immersed in molten iron for corrosion, magnesium and aluminum ions in the internal additives diffuse to the high-temperature surface and combine with oxygen and silicon to form a corrosion layer. This corrosion layer acts as a barrier, preventing the ceramic matrix from directly contacting the molten iron, thereby significantly improving the material's corrosion resistance.

[0031] The specific plan is as follows: In a first typical embodiment of the present invention, a hexagonal boron nitride ceramic material is provided. The raw material components of the hexagonal boron nitride ceramic material, by mass percentage, include: 70%~90% hexagonal boron nitride powder and 10%~30% composite sintering aid; wherein, the mass percentage of each component in the composite sintering aid is as follows: magnesium oxide 10%~25%, aluminum oxide 25%~45%, silicon dioxide 40%~60%, and rare earth oxides 10%~24%. The rare earth oxide is selected from one or more of lanthanum oxide, yttrium oxide, scandium oxide, cerium oxide, neodymium oxide, gadolinium oxide, dysprosium oxide, erbium oxide, and ytterbium oxide.

[0032] In one or more embodiments of this implementation, the raw material components of the hexagonal boron nitride ceramic material, by mass percentage, include: 70%~75% hexagonal boron nitride powder and 25%~30% composite sintering aid; wherein, the mass percentage of each component in the composite sintering aid to the total amount of the composite sintering aid is as follows: 10%~15% magnesium oxide, 28%~32% aluminum oxide, 18%~22% rare earth oxides, and the balance is silicon dioxide.

[0033] In one or more embodiments of this implementation, the raw material components of the hexagonal boron nitride ceramic material, by mass percentage, include: 85%~90% hexagonal boron nitride powder and 10%~15% composite sintering aid; wherein, the mass percentage of each component in the composite sintering aid to the total amount of the composite sintering aid is as follows: 10%~12% magnesium oxide, 25%~28% aluminum oxide, 18%~23% rare earth oxides, and the balance is silicon dioxide.

[0034] In one or more embodiments of this implementation, the raw material components of the hexagonal boron nitride ceramic material, by mass percentage, include: 78%~82% hexagonal boron nitride powder, and 18%~22% composite sintering aid; wherein, the mass percentage of each component in the composite sintering aid to the total amount of the composite sintering aid is as follows: magnesium oxide 10%~15%, aluminum oxide 28%~32%, rare earth oxides 18%~23%, and the balance is silicon dioxide.

[0035] In one or more embodiments of this implementation, rare earth ions exist in an amorphous form in the magnesium aluminum silicate glass network of the hexagonal boron nitride ceramic material, and the hexagonal boron nitride ceramic material has a hexagonal boron nitride grain orientation structure with an absolute texture value greater than 1500.

[0036] In one or more embodiments of this implementation, under high-temperature molten metal corrosion environment, magnesium and aluminum ions in the internal glass phase of the hexagonal boron nitride ceramic material diffuse to the surface and react in situ to generate a high-melting-point oxide barrier layer.

[0037] In one or more embodiments of this implementation, the purity of the hexagonal boron nitride powder is ≥99.0%, and the particle size is 1~2 μm; the magnesium oxide, aluminum oxide, silicon dioxide and rare earth oxides are all nano-sized powders with a purity of ≥99.9%.

[0038] A second typical embodiment of the present invention provides a method for preparing the above-mentioned hexagonal boron nitride ceramic material, comprising the following steps: Hexagonal boron nitride powder and composite sintering aid are mixed, ball-milled and dried, and the resulting product is hot-pressed and sintered under vacuum to obtain hexagonal boron nitride ceramic material.

[0039] In one or more embodiments of this implementation, the ball milling conditions are: ball-to-material ratio of 3:1, anhydrous ethanol as the grinding medium, rotation speed of 200~400 r / min, and ball milling time of 5~8 h; the drying temperature is 75~85℃, and the drying time is 10~15 h.

[0040] In one or more embodiments of this implementation, the hot pressing sintering is carried out using a rapid hot pressing method, that is, heating from an initial temperature of 600~750℃ to 1500~1900℃ at a heating rate of 1~100℃ / min, holding time of 5~60min, and applying axial pressure of 10~50 MPa.

[0041] In one or more embodiments of this implementation, the vacuum degree of the vacuum condition is ≤10 Pa.

[0042] A third typical embodiment of the present invention provides an application of the above-mentioned hexagonal boron nitride ceramic material in the preparation of high-temperature molten metal contact components.

[0043] In this respect, the texture originates from the generation of liquid phase in the system during sintering, which causes hexagonal boron nitride to rotate under uniaxial pressure. The addition of an appropriate amount of rare earth elements will modify the liquid phase (controlling the amount of liquid phase generated and the viscosity of the liquid phase), thereby improving the sintering effect and obtaining a high texture.

[0044] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0045] Example 1: This example provides a hexagonal boron nitride ceramic material and its preparation method. In this embodiment, the raw material components of the hexagonal boron nitride ceramic material, by mass percentage, include: 70% hexagonal boron nitride powder and 30% composite sintering aid; wherein, the mass percentage of each component in the composite sintering aid to the total amount of the composite sintering aid is as follows: 11% magnesium oxide, 28% aluminum oxide, 41% silicon dioxide, and 20% rare earth oxide (lanthanum oxide).

[0046] The specific preparation method is as follows (see the schematic diagram of the specific preparation process). Figure 5 (as shown) (1) Raw material mixing: Hexagonal boron nitride powder, magnesium oxide powder, aluminum oxide powder, silicon dioxide powder and rare earth oxide powder are mixed according to the above mass percentage ratio to obtain the first product; wherein, the purity of hexagonal boron nitride powder is ≥99.0% and the particle size is 1~2μm; the purity of magnesium oxide powder, aluminum oxide powder, silicon dioxide powder and rare earth oxide powder is ≥99.9% and they are all nano-sized powders.

[0047] (2) Ball milling and drying: The first product is fed into a ball mill and ball milled for 6 h at a ball-to-material ratio of 3:1, anhydrous ethanol as the grinding medium, and a rotation speed of 300 r / min until the powder is fully mixed and uniform. Then, it is dried in an oven at 80°C for 12 h to obtain the second product.

[0048] (3) Hot pressing sintering: The second product is placed in a graphite mold and rapidly hot-pressed to obtain product 1. The process conditions for rapid hot pressing sintering are as follows: the temperature is increased from 700℃ to 1600℃ at a heating rate of 50℃ / min, and held at this temperature for 10min. During the sintering process, the vacuum degree is always kept less than or equal to 10 Pa, and the applied axial pressure is 30 MPa, denoted as La-30-1600.

[0049] Example 2: This example provides a hexagonal boron nitride ceramic material and its preparation method. The difference between this embodiment and Example 1 is that the rare earth oxide is yttrium oxide, while the other component types, contents and preparation methods are the same as in Example 1, denoted as Y-30-1600.

[0050] Example 3: This example provides a hexagonal boron nitride ceramic material and its preparation method. The difference between this embodiment and Example 1 is that the rare earth oxide is scandium oxide, while the other component types, contents and preparation methods are the same as in Example 1, denoted as Sc-30-1600.

[0051] Example 4: This example provides a hexagonal boron nitride ceramic material and its preparation method. The difference between this embodiment and Embodiment 1 is that: The raw material components of the hexagonal boron nitride ceramic material, by mass percentage, include: 80% hexagonal boron nitride powder, 20% composite sintering aid, and the other component types, contents and preparation methods are the same as in Example 1, denoted as La-20-1600.

[0052] Example 5: This example provides a hexagonal boron nitride ceramic material and its preparation method. The difference between this embodiment and Example 4 is that the rare earth oxide is yttrium oxide, while the other component types, contents and preparation methods are the same as in Example 4, denoted as Y-20-1600.

[0053] Example 6: This example provides a hexagonal boron nitride ceramic material and its preparation method. The difference between this embodiment and Example 4 is that the rare earth oxide is scandium oxide, while the other component types, contents and preparation methods are the same as in Example 4, denoted as Sc-20-1600.

[0054] Example 7: This example provides a hexagonal boron nitride ceramic material and its preparation method. The difference between this embodiment and embodiment 3 is as follows: (1) The raw material components of the hexagonal boron nitride ceramic material, by mass percentage, include: 85% hexagonal boron nitride powder and 15% composite sintering aid; (2) In step (3), the peak temperature of rapid hot pressing sintering is 1800℃; The types, contents, and preparation methods of other components are the same as in Example 3, and are denoted as Sc-15-1800.

[0055] Example 8: This example provides a hexagonal boron nitride ceramic material and its preparation method. The difference between this embodiment and embodiment 3 is as follows: (1) The raw material components of the hexagonal boron nitride ceramic material, by mass percentage, include: 90% hexagonal boron nitride powder and 10% composite sintering aid; (2) In step (3), the peak temperature of rapid hot pressing sintering is 1800℃; The types, contents, and preparation methods of other components are the same as in Example 3, and are denoted as Sc-10-1800.

[0056] Comparative Example 1: The difference between this comparative example and Example 3 is that no composite sintering aid was added, and the peak temperature of rapid hot pressing sintering in step (3) was 1800℃; the other component types, contents and preparation methods are the same as in Example 3.

[0057] Comparative Example 2: The difference between this comparative example and Example 3 is that rare earth oxides were not added to the composite sintering aid, while the other component types, contents, and preparation methods are the same as in Example 3.

[0058] Comparative Example 3: The difference between this comparative example and Example 3 is that the amount of rare earth oxides added in the composite sintering aid is adjusted to 24 wt.%, while the other component types, contents and preparation methods are the same as in Example 3, denoted as Sc24-30-1600.

[0059] Experimental Example 1: In this experimental example, the structure of the hexagonal boron nitride ceramic materials prepared in Examples 1-3 and Comparative Examples 1-3 was determined. like Figure 1 As shown in the XRD pattern, compared with Comparative Example 2, the hexagonal boron nitride ceramic materials prepared in Examples 1-3 of this invention do not contain magnesium, aluminum, silicon, or rare earth-related phases. Rare earth ions (lanthanum, yttrium, scandium) act as network modifiers to promote the depolymerization of the silicate framework. like Figure 2 As shown in the XRD pattern, when the rare earth content in Comparative Example 3 is too high, Sc will preferentially form a high melting point phase with Si and O, thereby reducing the amount of liquid phase generated during sintering at high temperature and weakening the sintering effect. like Figure 3 As shown in the SEM images, the hexagonal boron nitride ceramic materials prepared in Examples 3 and 7-8 of this invention have obvious layered structures in their microstructure. The rare earth modified liquid phase can more fully wet the h-BN particles, promote particle rearrangement and effectively fill the pores. In the cross-sectional morphology, the h-BN sheets show a highly compact stacked state.

[0060] like Figure 4 As shown, the SEM cross-sectional morphology of Sc-15-1800 after 30 min of high-temperature corrosion by molten iron shows that the surface corrosion layer acts as a barrier, preventing direct contact between the ceramic matrix and the molten iron, thereby enhancing the overall corrosion resistance of the ceramic. (When the ceramic is immersed in molten iron for corrosion, magnesium and aluminum ions present in the internal additives of the ceramic diffuse to the surface at high temperature and combine with oxygen and silicon to form a corrosion layer. This layer acts as a barrier, preventing direct contact between the ceramic matrix and the molten iron, thereby enhancing the overall corrosion resistance of the ceramic.)

[0061] Test Example 1: This test example demonstrates the performance testing of ceramic samples prepared in the examples and comparative examples. Testing process: (1) Bending strength: The bending strength of the specimens was evaluated using the three-point bending method. The material was processed into rectangular strips with a length of 25 mm, a width of 3 mm, and a height of 4 mm. The experiment was conducted under conditions of a 20 mm span and a loading rate of 0.5 mm / min. Each group of specimens was measured at least three times to obtain average data. The bending strength was calculated based on the following:

[0062] In the formula: — Bending strength, MPa; —Maximum load at which the specimen fractures, in N; —Specimen span, mm; —Sample width, mm; —Sample thickness, mm.

[0063] (2) Bulk density determination: The bulk density of the sample was measured by Archimedes' displacement method, and the buoyant weight of the sample when it was completely submerged in deionized water was measured. The actual density of deionized water is recorded as 1.0 g / cm³. 3 , recorded as The actual density of the sample is denoted as The final formula for calculating the actual density of the sample is as follows:

[0064] in: —The weight (g) of the sample in air after drying; —The weight (g) of the sample in air after it has completely absorbed water; —The weight of the sample in water (g); —The density of deionized water at room temperature is taken as 1.0 g / cm³. 3 .

[0065] (3) Texture determination: The orientation preference index was calculated according to the following formula. [24, 87, 137, 138] :

[0066] In the formula and These represent the intensities of the diffraction peaks on the top and side surfaces, respectively. IOP = ± 1 indicates that the h-BN grains are randomly arranged in the ceramic; IOP > 1 indicates that the c-axis of the h-BN grains tends to be perpendicular to the pressure direction; conversely, if IOP < 1, it indicates that the c-axis of the h-BN grains tends to be parallel to the pressure direction. Furthermore, the larger the absolute value of IOP, the higher the degree of texture.

[0067] The specific test results are shown in Table 1: Table 1

[0068] Analysis of the data in Table 1 shows that: Compared with pure hexagonal boron nitride ceramics sintered under the same temperature conditions but without the addition of rare earth modified sintering aids (Comparative Example 1), and hexagonal boron nitride multiphase ceramics with no rare earth oxides added and excessive rare earth oxides added (Comparative Example 2), the products obtained in Examples 1 to 8 of the present invention have significantly improved comprehensive performance.

[0069] Compared with Comparative Example 3, which had the same amount of composite sintering aids but different amounts of rare earth oxides, the ceramic samples prepared in Examples 1-3 of this invention had higher bulk density, resulting in better sintering effect and more compact samples.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A hexagonal boron nitride ceramic material, characterized in that, The raw material components of the hexagonal boron nitride ceramic material, by mass percentage, include: 70%~75% hexagonal boron nitride powder and 25%~30% composite sintering aid; wherein, the mass percentage of each component in the composite sintering aid to the total amount of the composite sintering aid is as follows: 10%~15% magnesium oxide, 28%~32% aluminum oxide, 18%~22% rare earth oxides, and the balance is silicon dioxide; The rare earth oxide is selected from one or more of lanthanum oxide, yttrium oxide, scandium oxide, cerium oxide, neodymium oxide, gadolinium oxide, dysprosium oxide, erbium oxide, and ytterbium oxide; In the hexagonal boron nitride ceramic material, rare earth ions exist in an amorphous form in the magnesium aluminosilicate glass network; The hexagonal boron nitride ceramic material is obtained by mixing hexagonal boron nitride powder and composite sintering aid, ball milling, drying, and then hot pressing and sintering the product under vacuum conditions. The hot pressing sintering is performed using a rapid hot pressing method, that is, the initial temperature is raised from 600~750℃ to 1500~1900℃, the heating rate is 1~100℃ / min, the holding time is 5~60 min, and the axial pressure is 10~50 MPa; the vacuum degree of the vacuum condition is ≤10 Pa. The hexagonal boron nitride ceramic material has a hexagonal boron nitride grain orientation structure with an absolute texture value greater than 1500.

2. A hexagonal boron nitride ceramic material, characterized in that, The raw material composition of the hexagonal boron nitride ceramic material, by mass percentage, includes: 85%~90% hexagonal boron nitride powder and 10%~15% composite sintering aid; wherein, the mass percentage of each component in the composite sintering aid to the total amount of the composite sintering aid is as follows: 10%~12% magnesium oxide, 25%~28% aluminum oxide, 18%~23% rare earth oxides, and the balance is silicon dioxide; The rare earth oxide is selected from one or more of lanthanum oxide, yttrium oxide, scandium oxide, cerium oxide, neodymium oxide, gadolinium oxide, dysprosium oxide, erbium oxide, and ytterbium oxide; In the hexagonal boron nitride ceramic material, rare earth ions exist in an amorphous form in the magnesium aluminosilicate glass network; The hexagonal boron nitride ceramic material is obtained by mixing hexagonal boron nitride powder and composite sintering aid, ball milling, drying, and then hot pressing and sintering the product under vacuum conditions. The hot pressing sintering is performed using a rapid hot pressing method, that is, the initial temperature is raised from 600~750℃ to 1500~1900℃, the heating rate is 1~100℃ / min, the holding time is 5~60 min, and the axial pressure is 10~50 MPa; the vacuum degree of the vacuum condition is ≤10 Pa. The hexagonal boron nitride ceramic material has a hexagonal boron nitride grain orientation structure with an absolute texture value greater than 1500.

3. A hexagonal boron nitride ceramic material, characterized in that, The raw material composition of the hexagonal boron nitride ceramic material, by mass percentage, includes: 78%~82% hexagonal boron nitride powder, and 18%~22% composite sintering aid; wherein, the mass percentage of each component in the composite sintering aid to the total amount of the composite sintering aid is as follows: 10%~15% magnesium oxide, 28%~32% aluminum oxide, 18%~23% rare earth oxides, and the balance is silicon dioxide; The rare earth oxide is selected from one or more of lanthanum oxide, yttrium oxide, scandium oxide, cerium oxide, neodymium oxide, gadolinium oxide, dysprosium oxide, erbium oxide, and ytterbium oxide; In the hexagonal boron nitride ceramic material, rare earth ions exist in an amorphous form in the magnesium aluminosilicate glass network; The hexagonal boron nitride ceramic material is obtained by mixing hexagonal boron nitride powder and composite sintering aid, ball milling, drying, and then hot pressing and sintering the product under vacuum conditions. The hot pressing sintering is performed using a rapid hot pressing method, that is, the initial temperature is raised from 600~750℃ to 1500~1900℃, the heating rate is 1~100℃ / min, the holding time is 5~60 min, and the axial pressure is 10~50 MPa; the vacuum degree of the vacuum condition is ≤10 Pa. The hexagonal boron nitride ceramic material has a hexagonal boron nitride grain orientation structure with an absolute texture value greater than 1500.

4. The hexagonal boron nitride ceramic material as described in claim 1, characterized in that, In the high-temperature molten metal corrosion environment, the magnesium and aluminum ions in the internal glass phase of the hexagonal boron nitride ceramic material diffuse to the surface and react in situ to form a high-melting-point oxide barrier layer.

5. The hexagonal boron nitride ceramic material as described in claim 1, characterized in that, The hexagonal boron nitride powder has a purity of ≥99.0% and a particle size of 1~2 μm; the magnesium oxide, aluminum oxide, silicon dioxide and rare earth oxides are all nano-sized powders with a purity of ≥99.9%.

6. A method for preparing a hexagonal boron nitride ceramic material according to any one of claims 1 to 5, characterized in that, Includes the following steps: Hexagonal boron nitride powder and composite sintering aid are mixed, ball-milled and dried, and the resulting product is hot-pressed and sintered under vacuum to obtain hexagonal boron nitride ceramic material.

7. The preparation method according to claim 6, characterized in that, The ball milling conditions are as follows: ball-to-material ratio 3:1, anhydrous ethanol as the grinding medium, rotation speed 200~400 r / min, ball milling time 5~8 h; the drying temperature is 75~85℃, and the drying time is 10~15 h.

8. The preparation method according to claim 6, characterized in that, The hot pressing sintering is performed using a rapid hot pressing method, that is, the initial temperature is raised from 600~750℃ to 1500~1900℃, the heating rate is 1~100℃ / min, the holding time is 5~60 min, and the axial pressure is 10~50 MPa; the vacuum degree of the vacuum condition is ≤10 Pa.

9. The application of the hexagonal boron nitride ceramic material according to any one of claims 1 to 5 in the preparation of high-temperature molten metal contact components.

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