A SiC ceramic based on an integrated liquid-phase sintering aid, its preparation method and application

Abstract

This invention discloses a SiC ceramic based on an integrated liquid-phase sintering aid and its preparation method. The integrated liquid-phase sintering aid is an AlON-RE2O3 composite system, wherein RE2O3 nanoparticles are attached to the surface of AlON submicron particles. When the aid is mixed with SiC raw materials, during high-temperature sintering, the Al-RE-Si-O-N liquid phase environment (composition / content) of SiC particles at different locations is the same. Therefore, the liquid-phase mass transfer and the densification process of dissolution-precipitation remain unified during sintering, resulting in SiC ceramics with uniform and refined grain size. This invention requires only a small amount of aid (1wt%-3wt%) to achieve densification of SiC ceramics (relative density greater than 99%) and effectively reduces the intergranular phases common in liquid-phase sintering. The grain boundaries of the SiC ceramics are clean, thus improving the high-temperature mechanical properties and thermal conductivity of SiC ceramic products.

Description

Technical Field

[0001] This invention belongs to the field of SiC ceramics, specifically relating to a SiC ceramic based on an integrated liquid-phase sintering aid, its preparation method, and its application. Background Technology

[0002] Silicon carbide (SiC) is an important high-temperature structural ceramic widely used in machinery, petrochemicals, aerospace, nuclear energy, and electronics due to its excellent physical and chemical properties (including high hardness, high modulus, wear resistance, high-temperature stability, high thermal conductivity, low coefficient of thermal expansion, and resistance to chemical corrosion). Besides being used as a traditional industrial material for high-temperature kiln furniture, various grinding media, bearings, seals, nozzles, impellers, cutting tools, and heat exchangers, SiC also serves as a novel high-performance material for bulletproof armor, space mirrors, fixtures in semiconductor wafer fabrication, and nuclear fuel cladding, thus playing a vital role in national economy and defense security.

[0003] As a typical strongly covalently bonded material, SiC has a very low self-diffusion coefficient for Si and C atoms, resulting in poor sintering activity. Even under high temperature and pressure, it is difficult to obtain densified SiC without the addition of additives. Since the 1970s, researchers have conducted extensive research on the sintering mechanism, process, and densification of SiC, successively preparing dense SiC ceramics through solid-state sintering and liquid-state sintering methods. Commonly used additives in solid-state sintering include boron (B) and carbon (C) components (such as B4C+C, BN+C, BP+C, AlB2+C, etc.), achieving densification through the solid solution of B and the elimination of the oxide layer on the SiC surface by C. SiC prepared by solid-state sintering can achieve high density and lacks an intergranular glassy phase, possessing excellent high-temperature mechanical properties. However, it requires very high sintering temperatures (usually above 2100℃), which can lead to excessive grain growth and reduced mechanical strength of the SiC material.

[0004] Since the 1990s, researchers have studied the mechanism of SiC preparation via liquid-phase sintering. Liquid-phase sintering is achieved through the melting of a single component and the formation of a eutectic between two or more components. The generation of the liquid phase changes the mass transfer mode of the system from diffusion to viscous flow and dissolution, thus providing a high-diffusion-rate path, thereby increasing the sintering speed and reducing the sintering temperature. Furthermore, the resulting grain size is small, and the liquid phase remaining between the grains changes the fracture mode of SiC ceramics from transgranular fracture to intergranular fracture. Liquid-phase sintering aids are mainly Al2O3-RE2O3 (where RE2O3 is rare earth element oxides such as Y2O3, Er2O3, Yb2O3, Sc2O3, and Lu2O3), among which Al2O3-Y2O3 is the most comprehensively and thoroughly studied liquid-phase sintering aid. When the temperature is above 1750℃, Al2O3 reacts with Y2O3 to form Y3Al5O3.12 Al2O3 (YAG), YAlO3 (YAP), or Y4Al2O9 (YAM) are added to form a low-melting-point liquid phase with SiO2 on the SiC surface to promote the sintering reaction. However, the reaction between Al2O3 and SiC at high temperatures generates volatile substances, resulting in weight loss of the product and negatively impacting the sintering process and the final properties of the product. Therefore, it is generally necessary to increase the amount of sintering aid (greater than 10 wt%) and embed powder rich in Al2O3 to reduce weight loss and ensure sufficient liquid phase presence. Adding AlN to the liquid phase aid can suppress the volatilization of Al components, but directly adding multi-component powders of AlN, Al2O3, and RE2O3 to SiC raw materials can easily cause uneven mixing, leading to local segregation of SiC ceramics. This affects the uniformity of the microstructure and mechanical properties of SiC ceramics, thus failing to meet the manufacturing requirements of large-size or complex-shaped high-quality devices. In addition, existing SiC preparation processes also suffer from problems such as large amounts of liquid phase additives and easy residues of intergranular phases, which have a significant impact on the corrosion resistance and high-temperature mechanical properties of SiC materials. Summary of the Invention

[0005] To improve the above-mentioned technical problems, the present invention provides a SiC ceramic based on an integrated liquid phase sintering aid, its preparation method and application, which solves the problems inherent in the existing method of sequentially adding AlN, Al2O3 and RE2O3 aids, such as uneven distribution of aids (including uneven distribution of the sintering aid as a whole and uneven distribution of the components constituting the aid) and excessive amount of aids, which cause the presence of intergranular phases in the sintered SiC ceramic.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0007] This invention provides an AlON-RE2O3 material comprising AlON and RE2O3 supported on AlON, wherein RE represents a rare earth element selected from at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y and Sc; preferably Y.

[0008] According to an embodiment of the present invention, the AlON is in the form of particles. Exemplarily, the AlON are nearly ellipsoidal particles. Exemplarily, the particle size of the AlON is in the submicron range, for example, the particle size of the AlON is 200–600 nm.

[0009] According to an embodiment of the present invention, the RE2O3 is in the form of particles. Exemplarily, the RE2O3 is a near-spherical particle. Exemplarily, the particle size of the RE2O3 is in the nanometer range, for example, the particle size of the RE2O3 is 20–100 nm.

[0010] According to an embodiment of the present invention, the RE2O3 particles are uniformly loaded on the surface of the AlON particles.

[0011] According to an embodiment of the present invention, the mass ratio of RE2O3 loaded on AlON to AlON is (0.45 to 4.6):1, with exemplary ratios being 1.14:1, 2.28:1, 3.42:1, and 4.56:1.

[0012] According to an embodiment of the present invention, the AlON is a solid solution compound formed by AlN and Al2O3. Preferably, the molar ratio of AlN to Al2O3 is (0.25 to 0.52):1, and an exemplary ratio is 0.38:1.

[0013] The present invention also provides a method for preparing the above-mentioned AlON-RE2O3 material, comprising obtaining a homogeneous precursor containing elements such as Al, RE, O, and C by hydrothermal precipitation reaction of a solution containing Al source, RE source and soluble carbon source, and then preparing the AlON-RE2O3 material by carbothermal reduction nitridation reaction.

[0014] In one embodiment of the invention, the Al source is provided by a compound containing the element Al, such as by a salt containing the element Al, preferably aluminum nitrate.

[0015] In one embodiment of the invention, the RE source is provided by a compound containing RE, such as a salt containing RE, preferably yttrium nitrate.

[0016] In one embodiment of the present invention, the molar ratio of Al to RE is (0.5-5):1; exemplary ratios are 0.5:1, 0.67:1, 1:1, and 2:1.

[0017] In one embodiment of the present invention, the soluble carbon source is a water-soluble carbohydrate, preferably sucrose.

[0018] In one embodiment of the present invention, the molar ratio of the soluble carbon source (such as sucrose) to Al is (0.1 to 0.17):1; for example, it is 0.14:1.

[0019] In one embodiment of the invention, the hydrothermal precipitation reaction is carried out in the presence of a homogeneous precipitant. Exemplarily, the homogeneous precipitant is a compound that can decompose to produce hydroxide or carbonate ions, such as urea.

[0020] In one embodiment of the present invention, the molar ratio of the homogeneous precipitant to the metal ions (total molar amount of Al and RE elements) is (1-4):1; for example, it is 2:1.

[0021] In one embodiment of the present invention, the temperature of the hydrothermal precipitation reaction is 150-220°C, exemplarily 180°C; the time of the hydrothermal precipitation reaction is 6-24 hours, exemplarily 15 hours.

[0022] In one embodiment of the present invention, the temperature of the carbothermic reduction nitriding reaction is 1300-1800°C, exemplarily 1600°C; and the time of the carbothermic reduction nitriding reaction is 1-6 hours, exemplarily 4 hours.

[0023] The present invention also provides the application of the above-mentioned AlON-RE2O3 material as a sintering aid in the preparation of SiC ceramics.

[0024] The present invention also provides a method for preparing SiC ceramics, comprising using the above-mentioned AlON-RE2O3 material as a sintering aid, mixing it with SiC raw materials, sintering, and preparing SiC ceramics.

[0025] According to an embodiment of the present invention, the amount of AlON-RE2O3 material used is 1wt%-3wt% of the mass of SiC raw material; exemplary examples are 1wt%, 2wt%, and 3wt%.

[0026] According to an embodiment of the present invention, the sintering method may be pressureless sintering and / or hot pressing sintering.

[0027] In one embodiment of the present invention, the pressureless sintering temperature is 1700-1950℃, exemplarily 1800℃; the pressureless sintering heating rate is 5-20℃ / min, exemplarily 10℃ / min; and the pressureless sintering holding time is 2-4 hours, exemplarily 2 hours.

[0028] In one embodiment of the present invention, the hot pressing sintering temperature is 1600-1850℃, exemplarily 1700℃; the hot pressing sintering pressure is 20-40MPa, exemplarily 30MPa; the hot pressing sintering heating rate is 5-20℃ / min, exemplarily 10℃ / min; and the hot pressing sintering holding time is 0.5-2 hours, exemplarily 1 hour.

[0029] In one embodiment of the present invention, the sintering atmosphere is a vacuum (vacuum degree better than 20 Pa), argon or nitrogen.

[0030] According to an embodiment of the present invention, the particle size of the SiC raw material is 0.1 to 5 μm; for example, it is 0.5 μm.

[0031] According to an embodiment of the present invention, the mixing method is ball milling. For example, the solvent used for ball milling is water or anhydrous ethanol; the solid content of the slurry during ball milling is 30-60 wt%; the grinding balls used are SiC ceramic balls; the ball-to-material ratio is 3:1 to 10:1, exemplarily 5:1; the ball milling speed is 150-250 rpm, exemplarily 200 rpm; the ball milling time is 6-24 hours, exemplarily 24 hours.

[0032] According to an embodiment of the present invention, the preparation method further includes drying the mixed materials. For example, the drying method may be vacuum heating drying, freeze drying, or spray drying. For example, the freeze drying temperature is -50 to -30°C, exemplarily -40°C; the freeze drying time is 6 to 24 hours, exemplarily 12 hours.

[0033] According to an embodiment of the present invention, the preparation method further includes forming a green body from the dried ceramic powder. For example, the green body is formed by dry pressing (e.g., pressure of 10-30 MPa, exemplarily 20 MPa) combined with cold isostatic pressing (pressure of 100-250 MPa, exemplarily 200 MPa).

[0034] In this invention, the AlON-RE2O3 liquid phase additive has a uniform composition at all positions on the SiC matrix. During the sintering process, the additive will form the same Al-RE-Si-ON liquid phase composition with the silicon dioxide (SiO2) on the SiC surface in situ, thereby promoting the densification of SiC.

[0035] According to an embodiment of the present invention, the preparation method of the obtained SiC ceramic includes the following steps:

[0036] (1) Pre-synthesis of AlON-RE2O3 material by hydrothermal-carbothermal reduction nitridation method: Add homogeneous precipitant to a solution containing Al source, RE source and soluble carbon source, and obtain a homogeneous precursor containing Al, RE, O and C elements through hydrothermal precipitation reaction. Then, AlON-RE2O3 material is prepared by carbothermal reduction nitridation reaction.

[0037] (2) Mixing SiC raw material powder with pre-synthesized additives: Using AlON-RE2O3 material as an additive, SiC raw material powder and AlON-RE2O3 additives are mixed by ball milling to obtain a slurry; the slurry is dried and sieved to obtain ceramic powder for sintering;

[0038] (3) Sintering of SiC ceramics: The ceramic powder to be sintered is made into a blank and then sintered to obtain SiC ceramics.

[0039] The present invention also provides SiC ceramics prepared by the above preparation method.

[0040] According to an embodiment of the present invention, the relative density of the SiC ceramic is greater than 99%; exemplary values ​​are 99.1, 99.3, 99.5, 99.7, and 99.9.

[0041] According to an embodiment of the present invention, the SiC ceramic does not contain any phases other than SiC, and there are no obvious residual intergranular liquid phase components.

[0042] This invention controls the carbon content in the system by controlling the amount of sucrose used. During the carbothermic reduction nitridation reaction, carbon, aluminum oxide, and nitrogen react to form aluminum nitride, which further reacts with aluminum oxide to form AlON. In other words, by controlling the carbon content, the amount of aluminum nitride generated is controlled, thereby controlling the equivalent AlN content in AlON.

[0043] The present invention also provides the application of the above-mentioned SiC ceramics in the fields of machinery, petrochemicals, aerospace, nuclear energy, and electronics.

[0044] The present invention also provides a ceramic article containing the above-mentioned SiC ceramic.

[0045] The beneficial effects of this invention are:

[0046] Studies have found that adding AlN to completely or partially replace Al2O3 in the liquid-phase sintering of SiC can form an Al-RE-Si-ON system, which can suppress the decomposition and volatilization of Al components, thereby reducing the use of embedded powder and reducing weight loss during sintering. However, in current SiC preparation processes, AlN, Al2O3, and RE2O3 powders are directly added to SiC raw materials and mixed through ball milling, stirring, and other methods. For this multi-component composite additive system, the dispersibility of each component (AlN, Al2O3, and RE2O3) varies, and they are separated to varying degrees by SiC powder particles. Therefore, it is impossible to guarantee that there is the same proportion of additive components in any region at the source (i.e., the sintering additive is unevenly distributed, including the overall uneven distribution of the sintering additive and the uneven distribution of each component constituting the sintering additive), which easily causes local segregation, resulting in different densification degrees of SiC ceramics, and thus affecting the uniformity and consistency of the microstructure and mechanical properties of SiC ceramics. Furthermore, the existing SiC preparation process uses a large amount of mixed additives of AlN, Al2O3, and RE2O3, and after sintering, obvious intergranular oxide phases (such as Y4Al2O9 (YAM), YAlO3 (YAP), Y3Al5O3) exist at the grain boundaries between SiC grains. 12(YAG, etc.) This significantly impacts the corrosion resistance and high-temperature mechanical properties of SiC materials, thus limiting the application and development of SiC ceramics. In view of this, this invention utilizes a hydrothermal method to obtain the precursor and combines it with a carbothermal reduction nitridation method to pre-synthesize an AlON-RE2O3 integrated additive (where AlN and Al2O3 form an AlON compound, equivalent to AlN and Al2O3 having uniform composition at the molecular level; AlON material is a single-phase compound with uniform Al, O, and N elements at the molecular level, simultaneously achieving the roles of AlN and Al2O3 additives in SiC ceramic sintering). RE2O3 nanoparticles are loaded on the surface of AlON particles, in close contact, and uniformly distributed at the submicron scale. After the integrated additive is mixed with SiC raw materials for compaction, the various components of the AlON-RE2O3 integrated additive are uniformly distributed in the SiC matrix according to a preset ratio (i.e., the additive components in each part will not deviate from the ideal ratio). During the further high-temperature sintering process, the Al-RE-Si-ON liquid phase environment (composition / content) of SiC particles at different locations is the same. Therefore, the liquid phase mass transfer and the densification process of dissolution-precipitation can be kept unified, resulting in a uniform internal microstructure of the prepared SiC ceramic. This, in turn, helps to ensure the uniform and stable mechanical properties of large-size SiC ceramic products. In addition, since the additive components (including the overall distribution of the additives and the distribution of each component constituting the additives) in all parts of the SiC matrix are uniformly distributed, only a small amount (1wt%-3wt%) is needed to achieve efficient densification of SiC ceramics, making the relative density of SiC ceramics greater than 99%. This also effectively reduces the intergranular phases commonly found in liquid phase sintering. The SiC ceramics prepared by this invention have clean grain boundaries (no oxide residues were detected by X-ray diffraction and scanning electron microscopy). Ceramic products prepared from the SiC ceramics of this invention have good high-temperature mechanical properties and thermal conductivity. Attached Figure Description

[0047] Figure 1 This is a TEM image of the AlON-Y2O3 integrated additive pre-synthesized in Example 2 of the present invention.

[0048] Figure 2 This is an elemental composition distribution diagram of the AlON-Y2O3 integrated additive pre-synthesized in Example 2 of the present invention.

[0049] Figure 3 The image shows the XRD pattern of the AlON-Y2O3 integrated additive pre-synthesized in Example 2 of this invention.

[0050] Figure 4 The image shows the XRD pattern of the SiC ceramic prepared in Example 2 of this invention.

[0051] Figure 5This is a cross-sectional SEM image of the SiC ceramic prepared in Example 2 of the present invention.

[0052] Figure 6 The image shows the XRD pattern of the SiC ceramic prepared in Comparative Example 1 of this invention.

[0053] Figure 7 This is a cross-sectional SEM image of the SiC ceramic prepared in Comparative Example 1 of this invention. Detailed Implementation

[0054] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0055] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0056] In the following embodiments, X-ray powder diffraction analysis was performed using a benchtop X-ray diffractometer (Miniflex-600, Rigaku); microstructure analysis was performed using a scanning electron microscope (Phenom G2, Phenom-World) and a field emission transmission electron microscope (Talos-F200X, Thermo Fisher); the density of SiC ceramics was measured using a smart density balance (GH-300C, Xiamen Qunlong Instruments); and the three-point bending strength was determined according to GB / T 6569-2006 Test Method for Bending Strength of Fine Ceramics.

[0057] Example 1

[0058] A method for preparing SiC ceramic material includes the following steps:

[0059] (1) Pre-synthesis of AlON-Y2O3 integrated additive: 37.51g aluminum nitrate nonahydrate (0.1mol), 38.30g yttrium nitrate hexahydrate (0.1mol), and 4.80g sucrose (0.014mol) were added to 100ml of deionized water, wherein the molar ratio of sucrose to Al was 0.14:1; 24g urea (0.4mol) was added to the solution, wherein the molar ratio of urea to metal ions (Al ions and Y ions) was 2:1. After the above solution was stirred evenly, it was transferred to a polytetrafluoroethylene-lined hydrothermal reactor and hydrothermally reacted at 200℃ for 15 hours to obtain the precursor, which was then freeze-dried at -40℃ for 12 hours. The precursor was placed in a graphite crucible and transferred to a tube furnace. Carbothermic reduction nitridation was performed under nitrogen atmosphere at a reaction temperature of 1600℃ for 4 hours, yielding an integrated AlON-Y2O3 additive (where the equivalent AlN:Al2O3:Y2O3 molar ratio was 0.64:1.68:2, calculated by back-calculating the nitrogen content in AlON-Y2O3 obtained from testing).

[0060] (2) Mixing SiC raw material powder with pre-synthesized additive: Weigh 50g of SiC raw material powder (particle size 0.5μm), 1g of AlON-Y2O3 integrated additive prepared in step (1), add 50g of anhydrous ethanol and 250g of SiC grinding balls (diameter 3mm), and ball mill for 24 hours at a speed of 200rpm. Pour out the resulting slurry, dry it in a vacuum oven at 100℃ for 12 hours, and pass it through a 100-mesh sieve to obtain SiC powder containing sintering additive.

[0061] (3) Sintering of SiC ceramics: 30g of ceramic powder containing sintering aids prepared in step (2) was placed into a 50mm diameter metal mold and dry-pressed at 20MPa. After demolding, it was isostatically pressed at 200MPa to form a green body. The green body was placed in a graphite crucible and sintered without pressure in a carbon tube furnace at a sintering temperature of 1800℃, a heating rate of 10℃ / min, a holding time of 2 hours, and an argon atmosphere to obtain high-density SiC ceramics.

[0062] Example 2

[0063] A method for preparing SiC ceramic material includes the following steps:

[0064] (1) Pre-synthesis of AlON-Y2O3 integrated additive: 37.51g aluminum nitrate nonahydrate (0.1mol), 19.15g yttrium nitrate hexahydrate (0.05mol), and 4.80g sucrose (0.014mol) were added to 100ml of deionized water, wherein the molar ratio of sucrose to Al was 0.14:1; 18g urea was added to the solution, and its molar ratio with metal ions (Al ions and Y ions) was 2:1. After the above solution was stirred evenly, it was transferred to a polytetrafluoroethylene-lined hydrothermal reactor and hydrothermally reacted at 200℃ for 15 hours to obtain the precursor, which was then freeze-dried at -40℃ for 12 hours. The precursor was placed in a graphite crucible and transferred into a tube furnace. Nitrogen gas was introduced for carbothermic reduction nitridation. The carbothermic reduction reaction temperature was 1600℃ and the holding time was 4 hours to obtain an AlON-Y2O3 integrated additive (where the equivalent AlN:Al2O3:Y2O3 molar ratio was 0.64:1.68:1).

[0065] (2) Mixing SiC raw material powder with pre-synthesized additive: Weigh 50g of SiC raw material powder (particle size 0.5μm), 1g of AlON-Y2O3 integrated additive prepared in step (1), add 50g of anhydrous ethanol and 250g of SiC grinding balls (diameter 3mm), and ball mill for 24 hours at a speed of 200rpm. Pour out the resulting slurry, dry it in a vacuum oven at 100℃ for 12 hours, and pass it through a 100-mesh sieve to obtain SiC powder containing sintering additive.

[0066] (3) Sintering of SiC ceramics: 30g of ceramic powder containing sintering aids prepared in step (2) was placed into a 50mm diameter metal mold and dry-pressed at 20MPa. After demolding, it was isostatically pressed at 200MPa to form a green body. The green body was placed in a graphite crucible and sintered without pressure in a carbon tube furnace at a sintering temperature of 1800℃, a heating rate of 10℃ / min, a holding time of 2 hours, and an argon atmosphere to obtain high-density SiC ceramics.

[0067] Figure 1 The image shows the transmission electron microscope (TEM) morphology of the AlON-Y2O3 integrated additive pre-synthesized in Example 2. It can be observed from the image that the AlON particles in the AlON-Y2O3 integrated additive are nearly ellipsoidal with a particle size of about 200 nm; the Y2O3 particles are nearly spherical with a particle size of about 50 nm, and the Y2O3 particles are uniformly loaded on the surface of the AlON particles.

[0068] Figure 2 The figure shows the elemental composition distribution of the AlON-Y2O3 integrated additive pre-synthesized in Example 2. As can be seen from the figure, the larger ellipsoidal particles contain Al, O, and N components, which are AlON particles; while the smaller spherical particles contain Y and O components, which are Y2O3 particles.

[0069] Figure 3 The image shows the XRD pattern of the AlON-Y2O3 integrated additive pre-synthesized in Example 2. It can be observed from the image that the phases of the composite additive are AlON and Y2O3.

[0070] Figure 4 The image shows the XRD phase analysis spectrum of the SiC ceramic prepared in Example 2. As can be seen from the image, the ceramic contains only the SiC phase.

[0071] Figure 5 The image shows a scanning electron microscope (SEM) image of the cross-section of the SiC ceramic prepared in Example 2. As can be seen from the image, the SiC grains are uniform in size, the grain boundaries are clean, and there is no residual liquid phase material between the grains.

[0072] Example 3

[0073] A method for preparing SiC ceramic material includes the following steps:

[0074] (1) Pre-synthesis of AlON-Y2O3 integrated additive: 37.51g aluminum nitrate nonahydrate (0.1mol), 57.45g yttrium nitrate hexahydrate (0.15mol), and 4.80g sucrose (0.014mol) were added to 100ml of deionized water, wherein the molar ratio of sucrose to Al was 0.14:1; 30g urea was added to the solution, and its molar ratio with metal ions (Al ions and Y ions) was 2:1. After the above solution was stirred evenly, it was transferred to a polytetrafluoroethylene-lined hydrothermal reactor and hydrothermally reacted at 200℃ for 15 hours to obtain the precursor, which was then freeze-dried at -40℃ for 12 hours. The precursor was placed in a graphite crucible and transferred into a tube furnace. Nitrogen gas was introduced for carbothermic reduction nitridation. The carbothermic reduction reaction temperature was 1600℃ and the holding time was 4 hours to obtain an AlON-Y2O3 integrated additive (where the equivalent AlN:Al2O3:Y2O3 molar ratio was 0.64:1.68:3).

[0075] (2) Mixing SiC raw material powder with pre-synthesized additive: Weigh 50g of SiC raw material powder (particle size 0.5μm), 1g of AlON-Y2O3 integrated additive prepared in step (1), add 50g of anhydrous ethanol and 250g of SiC grinding balls (diameter 3mm), and ball mill for 24 hours at a speed of 200rpm. Pour out the resulting slurry, dry it in a vacuum oven at 100℃ for 12 hours, and pass it through a 100-mesh sieve to obtain SiC powder containing sintering additive.

[0076] (3) Sintering of SiC ceramics: 30g of ceramic powder containing sintering aids prepared in step (2) was placed into a 50mm diameter metal mold and dry-pressed at 20MPa. After demolding, it was isostatically pressed at 200MPa to form a green body. The green body was placed in a graphite crucible and sintered without pressure in a carbon tube furnace at a sintering temperature of 1800℃, a heating rate of 10℃ / min, a holding time of 2 hours, and an argon atmosphere to obtain high-density SiC ceramics.

[0077] Example 4

[0078] A method for preparing SiC ceramic material includes the following steps:

[0079] (1) Pre-synthesis of AlON-Y2O3 integrated additive: 37.51g aluminum nitrate nonahydrate (0.1mol), 76.6g yttrium nitrate hexahydrate (0.2mol), and 4.80g sucrose (0.014mol) were added to 100ml of deionized water, wherein the molar ratio of sucrose to Al was 0.14:1; 36g urea was added to the solution, and its molar ratio with metal ions (Al ions and Y ions) was 2:1. After the above solution was stirred evenly, it was transferred to a polytetrafluoroethylene-lined hydrothermal reactor and hydrothermally reacted at 200℃ for 15 hours to obtain the precursor, which was then freeze-dried at -40℃ for 12 hours. The precursor was placed in a graphite crucible and transferred into a tube furnace. Nitrogen gas was introduced for carbothermic reduction nitridation. The carbothermic reduction reaction temperature was 1600℃ and the holding time was 4 hours to obtain an AlON-Y2O3 integrated additive (where the equivalent AlN:Al2O3:Y2O3 molar ratio was 0.64:1.68:4).

[0080] (2) Mixing SiC raw material powder with pre-synthesized additive: Weigh 50g of SiC raw material powder (particle size 0.5μm), 1g of AlON-Y2O3 integrated additive prepared in step (1), add 50g of anhydrous ethanol and 250g of SiC grinding balls (diameter 3mm), and ball mill for 24 hours at a speed of 200rpm. Pour out the resulting slurry, dry it in a vacuum oven at 100℃ for 12 hours, and pass it through a 100-mesh sieve to obtain SiC powder containing sintering additive.

[0081] (3) Sintering of SiC ceramics: 30g of ceramic powder containing sintering aids prepared in step (2) was placed into a 50mm diameter metal mold and dry-pressed at 20MPa. After demolding, it was isostatically pressed at 200MPa to form a green body. The green body was placed in a graphite crucible and sintered without pressure in a carbon tube furnace at a sintering temperature of 1800℃, a heating rate of 10℃ / min, a holding time of 2 hours, and an argon atmosphere to obtain high-density SiC ceramics.

[0082] Example 5

[0083] A method for preparing SiC ceramic material includes the following steps:

[0084] (1) Pre-synthesis of AlON-Y2O3 integrated additive: 37.51g aluminum nitrate nonahydrate (0.1mol), 19.15g yttrium nitrate hexahydrate (0.05mol), and 4.80g sucrose (0.014mol) were added to 100ml of deionized water, wherein the molar ratio of sucrose to Al was 0.14:1; 18g urea was added to the solution, and its molar ratio with metal ions (Al ions and Y ions) was 2:1. After the above solution was stirred evenly, it was transferred to a polytetrafluoroethylene-lined hydrothermal reactor and hydrothermally reacted at 200℃ for 15 hours to obtain the precursor, which was then freeze-dried at -40℃ for 12 hours. The precursor was placed in a graphite crucible and transferred into a tube furnace. Nitrogen gas was introduced for carbothermic reduction nitridation. The carbothermic reduction reaction temperature was 1600℃ and the holding time was 4 hours to obtain an AlON-Y2O3 integrated additive (where the equivalent AlN:Al2O3:Y2O3 molar ratio was 0.64:1.68:1).

[0085] (2) Mixing SiC raw material powder with pre-synthesized additive: Weigh 50g of SiC raw material powder (particle size 0.5μm), 0.5g of AlON-Y2O3 integrated additive prepared in step (1), add 50g of anhydrous ethanol and 250g of SiC grinding balls (diameter 3mm), and ball mill for 24 hours at a speed of 200rpm. Pour out the resulting slurry, dry it in a vacuum oven at 100℃ for 12 hours, and pass it through a 100-mesh sieve to obtain SiC powder containing sintering additive.

[0086] (3) Sintering of SiC ceramics: 30g of ceramic powder containing sintering aids prepared in step (2) was placed into a 50mm diameter metal mold and dry-pressed at 20MPa. After demolding, it was isostatically pressed at 200MPa to form a green body. The green body was placed in a graphite crucible and sintered without pressure in a carbon tube furnace at a sintering temperature of 1800℃, a heating rate of 10℃ / min, a holding time of 2 hours, and an argon atmosphere to obtain high-density SiC ceramics.

[0087] Example 6

[0088] A method for preparing SiC ceramic material includes the following steps:

[0089] (1) Pre-synthesis of AlON-Y2O3 integrated additive: 37.51g aluminum nitrate nonahydrate (0.1mol), 19.15g yttrium nitrate hexahydrate (0.05mol), and 4.80g sucrose (0.014mol) were added to 100ml of deionized water, wherein the molar ratio of sucrose to Al was 0.14:1; 18g urea was added to the solution, with a molar ratio of urea to metal ions (Al ions and Y ions) of 2:1. After the above solution was stirred evenly, it was transferred to a polytetrafluoroethylene-lined hydrothermal reactor and hydrothermally reacted at 200℃ for 15 hours to obtain the precursor, which was then freeze-dried at -40℃ for 12 hours. The precursor was placed in a graphite crucible and transferred into a tube furnace. Nitrogen gas was introduced for carbothermic reduction nitridation. The carbothermic reduction reaction temperature was 1600℃ and the holding time was 4 hours to obtain an AlON-Y2O3 integrated additive (where the equivalent AlN:Al2O3:Y2O3 molar ratio was 0.64:1.68:1).

[0090] (2) Mixing SiC raw material powder with pre-synthesized additive: Weigh 50g of SiC raw material powder (particle size 0.5μm), 1.5g of AlON-Y2O3 integrated additive prepared in step (1), add 50g of anhydrous ethanol and 250g of SiC grinding balls (diameter 3mm), and ball mill for 24 hours at a speed of 200rpm. Pour out the resulting slurry, dry it in a vacuum oven at 100℃ for 12 hours, and pass it through a 100-mesh sieve to obtain SiC powder containing sintering additive.

[0091] (3) Sintering of SiC ceramics: 30g of ceramic powder containing sintering aids prepared in step (2) was placed into a graphite mold with a diameter of 50mm and placed in a hot pressing sintering furnace for hot pressing sintering. The sintering temperature was 1700℃, the pressure of hot pressing sintering was 30MPa, the heating rate was 10℃ / min, the holding time was 1 hour, and the sintering atmosphere was argon. High density SiC ceramics were prepared.

[0092] Comparative Example 1

[0093] A method for preparing SiC ceramic material includes the following steps:

[0094] (1) Using AlN, Al2O3, and Y2O3 as auxiliary components (molar ratio AlN:Al2O3:Y2O3 = 0.64:1.68:1), 0.31g AlN, 2.02g Al2O3, and 2.67g Y2O3 were added sequentially to 50g SiC raw material, with the addition amount being 10wt% of the SiC powder mass. 50g anhydrous ethanol was added, and 250g SiC grinding balls (3mm in diameter) were used for ball milling for 24 hours at a speed of 200rpm. The resulting slurry was poured out, dried in a vacuum oven at 100℃ for 12 hours, and passed through a 100-mesh sieve to obtain SiC powder containing sintering aids.

[0095] (2) Sintering of SiC ceramics: 30g of ceramic powder containing sintering aids prepared in step (1) was placed into a 50mm diameter metal mold and dry-pressed at 20MPa. After demolding, it was isostatically pressed at 200MPa to form a green body. The green body was placed in a graphite crucible and sintered without pressure in a carbon tube furnace at a sintering temperature of 1800℃, a heating rate of 10℃ / min, a holding time of 2 hours, and an argon atmosphere to obtain high-density SiC ceramics.

[0096] Figure 6 The image shows the XRD phase analysis spectrum of the SiC ceramic prepared in Comparative Example 1. It can be seen from the image that the ceramic contains SiC phase, as well as YAM and YAP phases.

[0097] Figure 7 The image shows a cross-sectional scanning electron microscope (SEM) image of the SiC ceramic prepared in Comparative Example 1. It can be seen from the image that the SiC grain size varies greatly and there are obvious residual liquid phase substances at the grain boundaries.

[0098] Comparative Example 2

[0099] A method for preparing SiC ceramic material includes the following steps:

[0100] (1) Using AlN, Al2O3, and Y2O3 as auxiliary components (molar ratio AlN:Al2O3:Y2O3 = 0.64:1.68:1), 0.09g AlN, 0.61g Al2O3, and 0.8g Y2O3 were added sequentially to 50g SiC raw material, with the addition amount being 3wt% of the SiC powder mass. 50g anhydrous ethanol was added, and 250g SiC grinding balls (3mm in diameter) were used for ball milling for 24 hours at a speed of 200rpm. The resulting slurry was poured out, dried in a vacuum oven at 100℃ for 12 hours, and passed through a 100-mesh sieve to obtain SiC powder containing sintering aids.

[0101] (2) Sintering of SiC ceramics: 30g of ceramic powder containing sintering aids prepared in step (1) was placed into a 50mm diameter metal mold and dry-pressed at 20MPa. After demolding, it was isostatically pressed at 200MPa to form a green body. The green body was placed in a graphite crucible and sintered without pressure in a carbon tube furnace at a sintering temperature of 1800℃, a heating rate of 10℃ / min, a holding time of 2 hours, and an argon atmosphere to obtain high-density SiC ceramics.

[0102] The relative densities of the SiC ceramics prepared in Examples 1-6 and Comparative Examples 1-2 are calculated as follows: (Relative density = Actual measured density value / Theoretical density value * 100%, where the theoretical density of SiC is 3.21 g / cm³). 3The XRD phase composition, intergranular material, and three-point bending strength (MPa) were tested and compared, and the results are shown in Table 1 below:

[0103] Table 1

[0104]

[0105]

[0106] By comparing the relative density, XRD phase, and intergranular material of SiC ceramics prepared in Examples 1-6 and Comparative Examples 1-2, it was found that when the AlON-Y2O3 integrated additive pre-synthesized in this invention is used, the amount of AlON-Y2O3 integrated additive added can be significantly reduced, and the relative density and flexural strength of the SiC ceramics prepared thereby are significantly improved, and only the SiC phase is detected.

[0107] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An AlON-RE2O3 material, characterized in that, It includes AlON and RE2O3 supported on AlON, wherein RE represents a rare earth element selected from at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y and Sc; The AlON is in granular form; The mass ratio of RE₂O₃ loaded on AlON to AlON is (0.45~4.6):1; The AlON is a solid solution compound formed by AlN and Al2O3, with a molar ratio of AlN to Al2O3 of (0.25~0.52):1; The RE2O3 is in granular form; The preparation method of the AlON-RE2O3 material includes obtaining a homogeneous precursor containing Al, RE, O, and C elements by hydrothermal precipitation reaction of a solution containing Al source, RE source, and soluble carbon source, and then preparing it by carbothermal reduction nitridation reaction. The Al source is provided by a salt containing the element Al; The RE source is provided by a salt containing RE elements; The soluble carbon source is a water-soluble carbohydrate; The molar ratio of Al to RE is (0.5~5):1; The molar ratio of the soluble carbon source to Al is (0.1~0.17):1; The homogeneous precipitant used in the hydrothermal precipitation reaction is urea; The molar ratio of the homogeneous precipitant to the total molar amount of Al and RE elements is (1~4):1; The temperature of the hydrothermal precipitation reaction is 150-220℃; the time of the hydrothermal precipitation reaction is 6-24 hours. The temperature of the carbothermic reduction nitriding reaction is 1300-1800℃; the time of the carbothermic reduction nitriding reaction is 1-6 hours.

2. The AlON-RE2O3 material as described in claim 1, characterized in that, The Al source is aluminum nitrate; The RE source is yttrium nitrate; The soluble carbon source is sucrose; The molar ratio of sucrose to Al is (0.1~0.17):

1.

3. The AlON-RE2O3 material as described in claim 1, characterized in that, The AlON particles are nearly ellipsoidal; the particle size of the AlON is in the submicron range. The RE2O3 is a near-spherical particle; the particle size of the RE2O3 is in the nanometer range.

4. The AlON-RE2O3 material as described in claim 3, characterized in that, The particle size of the AlON is 200~600nm; The particle size of the RE2O3 is 20~100nm.

5. The use of the AlON-RE2O3 material according to any one of claims 1-4 as a sintering aid in the preparation of SiC ceramics.

6. A method for preparing SiC ceramics, characterized in that, The method includes using the AlON-RE2O3 material as described in any one of claims 1-4 as a sintering aid, mixing it with SiC raw materials, and then sintering to prepare SiC ceramics.

7. The preparation method according to claim 6, characterized in that, The amount of AlON-RE2O3 material used is 1wt%-3wt% of the mass of SiC raw material; And / or, the sintering method is pressureless sintering or hot pressing sintering; the pressureless sintering temperature is 1700-1950℃; the pressureless sintering heating rate is 5~20℃ / min; the pressureless sintering holding time is 2-4 hours; The hot pressing sintering temperature is 1600-1850℃; the hot pressing sintering pressure is 20-40MPa; the hot pressing sintering heating rate is 5~20℃ / min; and the hot pressing sintering holding time is 0.5-2 hours.

8. A SiC ceramic, characterized in that, It is prepared using the preparation method described in claim 6 or 7.

9. The application of the SiC ceramic as described in claim 8 in the fields of machinery, petrochemicals, aerospace, nuclear energy, and electronics.

10. A ceramic product, characterized in that, It contains the SiC ceramic as described in claim 8.

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