Boron nitride nanotube / silicon nitride composite powder, preparation method and application thereof

Abstract

The present application relates to the technical field of materials, and particularly relates to a boron nitride nanotube / silicon nitride composite powder, a preparation method and application thereof, the preparation method comprising the following steps: mixing silicon powder, boron powder, silicon nitride diluent and ammonium salt mixed with ammonia gas to prepare reaction raw materials; and performing combustion synthesis on the reaction raw materials in hydrogen / nitrogen mixed gas to prepare the boron nitride nanotube / silicon nitride composite powder. The preparation method of the embodiment can obtain the boron nitride nanotube / silicon nitride composite powder with high alpha phase content, high uniformity and good dispersibility. The low volume fraction of the dispersed boron nitride nanotube in the composite powder is in-situ compounded in the silicon nitride powder, which can ingeniously solve the problems of insufficient strength, toughness and thermal conductivity of the ceramic bulk after sintering of the silicon nitride powder, and provides a new technical path for batch sintering of the silicon nitride powder, high-performance silicon nitride substrate, structural parts, bearings and other application directions.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and in particular to a boron nitride nanotube / silicon nitride composite powder, its preparation method, and its application. Background Technology

[0002] Silicon nitride has high thermal conductivity, good dielectric properties, high bending strength and fracture toughness, and is widely used in high-performance ceramic bearings, high-performance ceramic substrates, and high-performance cutting tools.

[0003] There are currently two main industrial preparation methods for silicon nitride powder raw materials: one is the liquid ammonia method, which has high requirements for equipment and raw materials, is prone to environmental pollution, and has problems such as high cost, by-products that easily pollute the environment, and difficulty in achieving large-scale production; the other is the silicon powder nitriding method, which has a series of problems such as high technical difficulty, high energy consumption, and unstable products.

[0004] Combustion synthesis of silicon nitride powder offers advantages such as low cost and large-scale production, making it a primary method for silicon nitride powder preparation. However, combustion-synthesized silicon nitride powder exhibits poor consistency, and silicon nitride ceramics prepared from this powder often suffer from low strength, thermal conductivity, and toughness. This results in low yields for mass-produced silicon nitride substrates or structural components, posing a challenge to the large-scale application of silicon nitride ceramics.

[0005] When conventional silicon nitride powder is reinforced with boron nitride nanotubes or other reinforcing agents to improve its sintering performance, the aggregation problem of boron nitride nanotubes often necessitates mechanical ball milling to disperse the silicon nitride composite powder after the addition of boron nitride nanotubes. This ensures a highly uniform mixture of the silicon nitride and boron nitride nanotube phases. However, during mechanical ball milling, the boron nitride nanotube reinforcement is easily subjected to mechanical collisions, leading to intrinsic defects. This results in a significant reduction in the intrinsic strength and thermal conductivity of the reinforcement, making it difficult to achieve a substantial improvement in the performance of silicon nitride ceramic bulk materials prepared by sintering boron nitride nanotube / silicon nitride powder.

[0006] Therefore, the search for a high-performance composite powder preparation method that can mass-produce high-strength, high-toughness, and high-thermal-conductivity silicon nitride ceramic blocks by sintering has become a research hotspot. Summary of the Invention

[0007] To address the technical problems of insufficient strength, toughness, and thermal conductivity of sintered blocks obtained from silicon nitride powder prepared by the above-mentioned combustion synthesis method, this invention provides a boron nitride nanotube / silicon nitride composite powder, its preparation method, and its application. Dispersed boron nitride nanotubes are generated in situ within the silicon nitride powder, achieving in-situ composite and efficient dispersion of the silicon nitride powder and the boron nitride nanotube reinforcement. The toughness and thermal conductivity of the silicon nitride ceramic block formed by sintering after adding boron nitride nanotubes to silicon nitride are significantly improved.

[0008] In one aspect, the present invention provides a method for preparing boron nitride nanotube / silicon nitride composite powder, the method comprising the following steps: in an ammonia atmosphere, silicon powder, boron powder, silicon nitride diluent, and ammonium salt are mixed uniformly in a mass ratio of (50-60):(5-10):(20-30):(10-15) to prepare combustion synthesis raw materials; the synthesis raw materials are combusted in a hydrogen / nitrogen mixture to prepare boron nitride nanotube / silicon nitride composite powder; wherein the α-Si3N4 content m in the boron nitride nanotube / silicon nitride composite powder is in the range of m≥93%.

[0009] Further, wherein the mass ratio of silicon powder to silicon nitride diluent is (5:1) to (3:1); and / or, the mass ratio of silicon powder to ammonium salt is (10:1) to (3:1); and / or, the mass ratio of boron powder to ammonium salt is (10:1) to (1:2).

[0010] Further, in the ammonia atmosphere, the pressure of the ammonia is 100 to 50000 Pa; and / or, the ammonium salt is selected from at least one of ammonium chloride and ammonium fluoride; and / or, the silicon nitride diluent is selected from at least one of α-Si3N4, β-Si3N4, and boron nitride.

[0011] Further, wherein the particle size of the silicon powder is 1–50 μm; and / or the particle size of the boron powder is 2–10 μm; and / or the particle size of the silicon nitride diluent is 1–8 μm.

[0012] Further, the method for uniformly mixing silicon powder, boron powder, silicon nitride diluent, and ammonium salt is as follows: ball milling is performed under the action of grinding balls; the mass ratio of grinding balls to combustion synthesis raw materials is (5:1) to (300:1); and / or, the mass ratio of silicon powder to grinding balls is (10:1) to (100:1); and / or, the mass ratio of boron powder to grinding balls is (10:1) to (100:1); and / or, the mass ratio of silicon nitride diluent to grinding balls is (10:1) to (100:1); and / or, the mass ratio of ammonium salt to grinding balls is (10:1) to (100:1); and / or, the composition of the grinding balls includes at least one of silicon nitride, tungsten carbide, zirconium oxide, and stainless steel.

[0013] Furthermore, in the hydrogen / nitrogen mixture, the total pressure of hydrogen and nitrogen is 1 to 15 MPa; and / or, in the hydrogen / nitrogen mixture, the volume ratio of hydrogen to nitrogen is (1:99) to (20:80).

[0014] Furthermore, the step of combustion synthesis of raw materials includes: placing the raw materials in a porous ceramic permeable crucible and igniting the raw materials using an electric tungsten filament; wherein the porosity of the porous ceramic permeable crucible is 90-98%; and / or the current of the electric tungsten filament is 20-150A.

[0015] In another aspect, the present invention provides a boron nitride nanotube / silicon nitride composite powder obtained by the above-described method for preparing boron nitride nanotube / silicon nitride composite powder.

[0016] In another aspect, the present invention provides an application of the above-mentioned boron nitride nanotube / silicon nitride composite powder in the preparation of silicon nitride ceramic bulk.

[0017] Furthermore, the method for preparing the silicon nitride ceramic bulk includes: isostatically pressing a sintering aid and boron nitride nanotube / silicon nitride composite powder to obtain a green body; sintering the green body in a nitrogen atmosphere to obtain the silicon nitride ceramic bulk body; wherein the sintering aid includes at least one of yttrium oxide, magnesium oxide, and magnesium silicon nitride; and / or, the isostatic pressing pressure is 20–500 MPa; and / or, the nitrogen atmosphere pressure is 0.1–15 MPa; and / or, the sintering temperature is 1600–2200 °C; and / or, the sintering time is 10–50 h.

[0018] The technical solution provided by this invention has the following advantages:

[0019] The method for preparing boron nitride nanotube / silicon nitride composite powder of the present invention utilizes the reaction heat of combustion synthesis to generate highly dispersed boron nitride nanotubes in situ, avoiding the agglomeration and dispersion problems when directly adding boron nitride nanotubes, and greatly improving the thermal conductivity and toughness of silicon nitride, thus paving the way for the preparation of high-performance silicon nitride with both high strength and high toughness.

[0020] Specifically, a combustion synthesis method is employed where silicon powder, boron powder, silicon nitride diluent, and ammonium salt are mixed in an ammonia atmosphere via ball milling. This allows the ammonia and hydrogen halides (ammonium chloride decomposes into ammonia and hydrogen chloride; ammonia fluoride decomposes into ammonia and hydrogen fluoride) formed by the decomposition of the ammonium salt to form complete adsorption of amino and halide ions (chloride or fluoride ions) on the surface of the silicon powder. This instills polarity in the silicon powder, promoting efficient dispersion and uniform catalytic reaction, resulting in a highly homogenized combustion synthesis raw material. The material is then placed in a crucible made of boron nitride fibers. Finally, a mixture of hydrogen and nitrogen is introduced for combustion, synthesizing boron nitride nanotube / silicon nitride composite powder. This powder is then used to prepare silicon nitride ceramic blocks with good thermal conductivity and fracture toughness.

[0021] The silicon nitride ceramic bulk prepared from boron nitride nanotube / silicon nitride composite powder exhibits excellent thermal conductivity and fracture toughness because: firstly, ball milling allows for the uniform dispersion of boron powder on the surface of the silicon powder raw material synthesized through combustion; secondly, during the combustion reaction of the silicon powder raw material loaded with nano-boron, a small amount of boron nitride nanotubes are generated simultaneously with the synthesis of silicon nitride. Due to the uniform dispersion of boron and silicon powder after ball milling, the in-situ synthesized boron nitride nanotubes can achieve good uniform dispersion within the synthesized silicon nitride powder, resulting in a uniform distribution of boron nitride nanotubes within the silicon nitride grains and grain boundaries in the sintered silicon nitride ceramic bulk. The uniform formation of boron nitride nanotubes in silicon nitride powder can significantly increase the grain boundary density of silicon nitride after sintering, effectively hindering dislocation slip and crack deflection between silicon nitride grain boundaries. At the same time, it breaks the limitation of heat flow transmission between silicon nitride grain boundaries by low thermal conductivity glass, and establishes an efficient heat conduction path, thereby enabling the sintered silicon nitride ceramic bulk to exhibit better thermal conductivity, fracture toughness and ceramic strength. Attached Figure Description

[0022] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0024] Figure 1 This is a SEM image of the boron nitride nanotube / silicon nitride composite powder prepared in Example 1 of this invention;

[0025] Figure 2 The image shows the XRD pattern of the boron nitride nanotube / silicon nitride composite powder prepared in Example 1 of this invention.

[0026] Figure 3 The image shows a low-magnification (5000x) SEM image of the boron nitride nanotube / silicon nitride composite powder prepared in Example 1 of this invention after sieving and classification.

[0027] Figure 4 The image shows a high-magnification (20,000x) SEM image of the boron nitride nanotube / silicon nitride composite powder prepared in Example 1 of this invention after sieving and classification. Detailed Implementation

[0028] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0029] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0030] According to an embodiment of the present invention, a method for preparing boron nitride nanotube / silicon nitride composite powder is provided, the method comprising the following steps: in an ammonia atmosphere, silicon powder, boron powder, silicon nitride diluent, and ammonium salt are mixed uniformly in a mass ratio of (50-60):(5-10):(20-30):(10-15) to prepare combustion synthesis raw materials; in a hydrogen / nitrogen mixture, the synthesis raw materials are combusted to carry out a combustion reaction to prepare boron nitride nanotube / silicon nitride composite powder; wherein, the α-Si3N4 content m in the boron nitride nanotube / silicon nitride composite powder is in the range of m≥93%.

[0031] The method for preparing boron nitride nanotube / silicon nitride composite powder in this invention uses silicon powder, silicon nitride diluent, boron powder and ammonium salt as raw materials. It utilizes ball milling to prepare combustion synthesis raw materials with high uniformity. Through this low-cost combustion synthesis technology, boron nitride nanotube / high-purity alpha phase silicon nitride composite powder can be synthesized on a large scale. The silicon nitride ceramic block obtained by sintering it has high thermal conductivity and good fracture toughness.

[0032] In some embodiments of the present invention, a method for preparing boron nitride nanotube / silicon nitride composite powder includes the following steps:

[0033] (1) Preparation of combustion synthesis raw materials

[0034] Silicon powder, boron powder, silicon nitride diluent, and ammonium salt are added to a ball mill jar in a certain proportion. High-pressure ammonia gas is introduced, and after adding a certain proportion of grinding balls, the mixture is ball-milled to form a uniformly mixed combustion synthesis raw material.

[0035] (2) Preparation of boron nitride nanotube / silicon nitride composite powder

[0036] Weigh a certain mass of the combustion synthesis raw material prepared in step (1) and place it in a porous ceramic permeable crucible. Place the porous ceramic permeable crucible with the combustion synthesis raw material in a high-pressure container and introduce a hydrogen / nitrogen mixture at a certain pressure. Then, ignite the combustion synthesis raw material with an electric tungsten wire to prepare boron nitride nanotube / silicon nitride composite powder.

[0037] In some embodiments of the present invention, in step (1), the mass ratio of silicon powder, boron powder, silicon nitride diluent, and ammonium salt is (50-60):(5-10):(20-30):(10-15), for example, it can be 52:6:21:11, 54:7:24:12, 56:8:26:13, 58:9:27:13.4, 59:10:28:14.5, 60:5:20:14.8, etc.

[0038] In some embodiments of the present invention, in step (1), the silicon powder particle size is 1 to 50 μm, for example, it can be 13 μm, 16 μm, 23 μm, 39 μm, 46 μm, etc.; preferably 20 μm.

[0039] In some embodiments of the present invention, in step (1), the particle size of the boron powder is 2 to 10 μm, for example, it can be 3 μm, 4 μm, 6 μm, 8 μm, 9 μm, etc.; preferably 5 μm.

[0040] In some embodiments of the present invention, in step (1), the particle size of the silicon nitride diluent is 1 to 8 μm, for example, it can be 2 μm, 3 μm, 4 μm, 6 μm, 7 μm, etc.; preferably 4 μm.

[0041] In some embodiments of the present invention, in step (1), the mass ratio of silicon powder to grinding balls is (10:1) to (100:1), for example, it can be 16:1, 32:1, 46:1, 58:1, 72:1, 82:1, 96:1, etc., preferably 50:1; the mass ratio of boron powder to grinding balls is (10:1) to (100:1), for example, it can be 14:1, 31:1, 45:1, 56:1, 71:1, 79:1, 98:1, etc. The preferred ratio is 50:1; the mass ratio of silicon nitride diluent to grinding balls is (10:1) to (100:1), for example, it can be 18:1, 36:1, 49:1, 63:1, 73:1, 85:1, 99:1, etc., preferably 50:1; the mass ratio of ammonium salt to grinding balls is (10:1) to (100:1), for example, it can be 21:1, 36:1, 45:1, 64:1, 76:1, 89:1, 98:1, etc., preferably 50:1.

[0042] In some embodiments of the present invention, in step (1), the pressure of ammonia in the ball mill jar is 100 to 50000 Pa, for example, it can be 568 Pa, 10896 Pa, 28905 Pa, 38792 Pa, 48968 Pa, etc., preferably 1000 Pa.

[0043] In some embodiments of the present invention, in step (1), the grinding ball is composed of silicon nitride, tungsten carbide, zirconium oxide, and stainless steel, preferably tungsten carbide.

[0044] In some embodiments of the present invention, in step (1), the mass ratio of the grinding ball to the mass of the combustion synthetic raw material is (5:1) to (300:1), for example, it can be 39:1, 108:1, 186:1, 236:1, 298:1, etc., preferably 200:1.

[0045] In some embodiments of the present invention, in step (1), the mass ratio of silicon powder to silicon nitride diluent is (5:1) to (3:1), for example, it can be 4.9:1, 4.2:1, 3.6:1, 3.4:1, 3.2:1, etc., preferably 3:1.

[0046] In some embodiments of the present invention, in step (1), the ratio of silicon powder to ammonium salt is (10:1) to (3:1), for example, it can be 9.6:1, 8.2:1, 6.1:1, 5.2:1, 4.1:1, 3.2:1, etc., preferably 10:1.

[0047] In some embodiments of the present invention, in step (1), the mass ratio of boron powder to ammonium salt is (10:1) to (1:2), for example, it can be 9.6:1, 7.2:1, 5.1:1, 4.2:1, 3.1:1, 2.2:1, etc., and the preferred ratio is 1:1.

[0048] In some embodiments of the present invention, in step (2), the mass of the combustion synthesis raw material prepared in step (1) is weighed as 1 to 5 kg, for example, it can be 1.4 kg, 2.3 kg, 3.3 kg, 3.9 kg, 4.3 kg, 4.9 kg, etc., preferably 5 kg.

[0049] In some embodiments of the present invention, in step (2), the porosity of the porous ceramic permeable crucible is 90-98%, for example, it can be 91%, 93%, 94%, 96%, 97%, etc., preferably 98%.

[0050] In some embodiments of the present invention, in step (2), the total pressure of the hydrogen / nitrogen mixture is 1 to 15 MPa, for example, it can be 1.8 MPa, 3.9 MPa, 5.2 MPa, 6.8 MPa, 9.3 MPa, 14.6 MPa, preferably 9 MPa.

[0051] In some embodiments of the present invention, in step (2), the volume ratio of hydrogen to nitrogen in the hydrogen / nitrogen mixture is (1:99) to (20:80), for example, it can be 1:86, 1:72, 1:66, 1:56, 1:43, etc.; preferably 1:90.

[0052] In some embodiments of the present invention, in step (2), the current of the energized tungsten wire is 20 to 150 A, for example, it can be 29 A, 46 A, 82 A, 96 A, 128 A, 148 A, etc.; preferably 150 A.

[0053] According to an embodiment of the present invention, a boron nitride nanotube / silicon nitride composite powder obtained by the above-described method for preparing boron nitride nanotube / silicon nitride composite powder is provided.

[0054] According to an embodiment of the present invention, an application of the above-described boron nitride nanotube / silicon nitride composite powder in the preparation of silicon nitride ceramic bulk is provided.

[0055] In some embodiments of the present invention, a method for preparing a silicon nitride ceramic bulk includes the following steps:

[0056] (a) Grinding and pulverizing boron nitride nanotube / silicon nitride composite powder;

[0057] (b) Add sintering aid to the boron nitride nanotube / silicon nitride composite powder obtained in step (a), and perform isostatic pressing to obtain a green body;

[0058] (c) In a nitrogen atmosphere, the blank obtained in step (b) is sintered at high temperature to obtain a silicon nitride ceramic block.

[0059] In some embodiments of the present invention, in step (a), after the boron nitride nanotube / silicon nitride composite powder is ground and pulverized, the particle size of the obtained boron nitride nanotube / silicon nitride composite powder is 0.7 to 2 μm, for example, it can be 0.9 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.9 μm, etc.

[0060] In some embodiments of the present invention, in step (b), the sintering aid includes at least one of yttrium oxide, magnesium oxide, and magnesium silicon nitride.

[0061] In some embodiments of the present invention, in step (b), the pressure of the isostatic pressing of the blank is 20 to 500 MPa, for example, it can be 36 MPa, 98 MPa, 169 MPa, 286 MPa, 328 MPa, 419 MPa, 497 MPa, etc.

[0062] In some embodiments of the present invention, in step (c), the nitrogen atmosphere pressure is 0.1 to 15 MPa, for example, it can be 0.6 MPa, 1.3 MPa, 3.9 MPa, 5.4 MPa, 9.8 MPa, 12.3 MPa, 14.6 MPa, etc.; the sintering temperature is 1600 to 2200°C, for example, it can be 1689°C, 1738°C, 1826°C, 1976°C, 2183°C, etc.; the sintering time is 10 to 50 h, for example, it can be 11 h, 19 h, 26 h, 34 h, 39 h, 42 h, 49 h, etc.

[0063] The technical solution of the present invention will be further explained and illustrated below through specific embodiments.

[0064] All reagents used in the following examples are commercially available.

[0065] Preparation of boron nitride nanotube / silicon nitride composite powder

[0066] Example 1

[0067] A method for preparing boron nitride nanotube / silicon nitride composite powder includes the following steps:

[0068] (1) Preparation of combustion synthesis raw materials

[0069] A total of 100g of raw material powder (silicon powder, boron powder, silicon nitride diluent, and ammonium chloride) was added to a ball mill jar. The silicon powder had a particle size of 20μm, the boron powder had a particle size of 5μm, the silicon nitride diluent had a particle size of 4μm, and the ammonium chloride had a particle size of 2μm. The raw materials were mixed in a mass ratio of 50:10:30:10. The stainless steel grinding media balls in the ball mill jar weighed 5000g. After evacuating the ball mill tube, 1000Pa high-pressure ammonia gas was introduced, and then the mixture was ball-milled at 100rpm to form a uniformly mixed combustion synthesis raw material.

[0070] (2) Preparation of boron nitride nanotube / silicon nitride composite powder

[0071] The combustion synthesis raw material obtained in step (1) was placed in a porous ceramic permeable crucible with a porosity of 90%. The crucible with the combustion synthesis raw material was placed in a high-pressure container, and a nitrogen-hydrogen mixture (with a hydrogen content of 10%) at a pressure of 6 MPa was introduced. Then, the raw material powder was ignited using an electric tungsten wire at a current of 80 A to prepare boron nitride nanotube / silicon nitride composite powder. The obtained boron nitride nanotube / silicon nitride composite powder was characterized by SEM and XRD, and the results are as follows: Figure 1 , Figure 2 As shown. Among them, Figure 3This is a low-magnification (5000x) SEM image of the boron nitride nanotube / silicon nitride composite powder after sieving and classification. Figure 4 This is a high-magnification (20,000x) SEM image of boron nitride nanotube / silicon nitride composite powder after sieving and classification.

[0072] Figure 1 SEM image of the boron nitride nanotube / silicon nitride composite powder prepared in step (2); from Figure 1 As can be seen, the boron nitride nanotube / silicon nitride composite powder has a complete morphology.

[0073] Figure 2 XRD pattern of boron nitride nanotube / silicon nitride composite powder prepared in step (2); from Figure 2 As can be seen from the data, the α-Si3N4 content m in the prepared boron nitride nanotube / silicon nitride composite powder is m = 95.8%.

[0074] from Figure 3 and Figure 4 In the images, the morphology of boron nitride nanotubes and silicon nitride composite powder can be clearly seen at different magnifications.

[0075] Example 2

[0076] A method for preparing boron nitride nanotube / silicon nitride composite powder includes the following steps:

[0077] (1) Preparation of combustion synthesis raw materials

[0078] A total of 100g of raw material powder (silicon powder, boron powder, silicon nitride diluent, and ammonium chloride) was added to a ball mill jar. The silicon powder had a particle size of 20μm, the boron powder had a particle size of 5μm, the silicon nitride diluent had a particle size of 4μm, and the ammonium chloride had a particle size of 2μm. The raw materials were mixed in a mass ratio of 60:10:20:15 for silicon powder, boron powder, silicon nitride diluent, and ammonium chloride. The tungsten carbide grinding media in the ball mill jar had a mass of 3000g. After evacuating the ball mill tube, 1000Pa high-pressure ammonia gas was introduced, and then the mixture was ball-milled at a speed of 80rpm to form a uniformly mixed combustion synthesis raw material.

[0079] (2) Preparation of boron nitride nanotube / silicon nitride composite powder

[0080] The combustion synthesis raw material obtained in step (1) is placed in a porous ceramic permeable crucible with a porosity of 90%. The crucible with the combustion synthesis raw material is placed in a high-pressure container and a nitrogen-hydrogen mixture with a pressure of 7 MPa (of which the hydrogen content is 10%) is introduced. Then, the raw material powder is ignited by an electric tungsten wire under a current of 80 A to prepare boron nitride nanotube / silicon nitride composite powder. In the prepared boron nitride nanotube / silicon nitride composite powder, the α-Si3N4 content m is m=95.6%.

[0081] Example 3

[0082] A method for preparing boron nitride nanotube / silicon nitride composite powder includes the following steps:

[0083] (1) Preparation of combustion synthesis raw materials

[0084] A total of 100g of raw material powder (silicon powder, boron powder, silicon nitride diluent, and ammonium chloride) was added to a ball mill jar. The silicon powder had a particle size of 20μm, the boron powder had a particle size of 5μm, the silicon nitride diluent had a particle size of 4μm, and the ammonium chloride had a particle size of 2μm. The raw materials were mixed in a mass ratio of 60:5:20:10 for silicon powder, boron powder, silicon nitride diluent, and ammonium chloride. The mass of the zirconium oxide grinding media grinding balls in the ball mill jar was 5000g. After evacuating the ball mill tube, 1000Pa high-pressure ammonia gas was introduced, and then the mixture was ball-milled at 100rpm to form a uniformly mixed combustion synthesis raw material.

[0085] (2) Preparation of boron nitride nanotube / silicon nitride composite powder

[0086] The combustion synthesis raw material obtained in step (1) is placed in a porous ceramic permeable crucible with a porosity of 90%. The crucible with the raw material is placed in a high-pressure container and a nitrogen-hydrogen mixture with a pressure of 6 MPa (of which the hydrogen content is 10%) is introduced. Then, the raw material powder is ignited by an electric tungsten wire under a current of 80 A to prepare boron nitride nanotube / silicon nitride composite powder. In the prepared boron nitride nanotube / silicon nitride composite powder, the α-Si3N4 content m is m=94%.

[0087] Example 4

[0088] A method for preparing boron nitride nanotube / silicon nitride composite powder includes the following steps:

[0089] (1) Preparation of combustion synthesis raw materials

[0090] A total of 100g of raw material powder (silicon powder, boron powder, silicon nitride diluent, and ammonium chloride) was added to a ball mill jar. The silicon powder had a particle size of 20μm, the boron powder had a particle size of 5μm, the silicon nitride diluent had a particle size of 4μm, and the ammonium chloride had a particle size of 2μm. The raw materials were mixed in a mass ratio of 60:5:20:15. The mass of the silicon nitride grinding media grinding balls in the ball mill jar was 5000g. After evacuating the ball mill tube, 1000Pa high-pressure ammonia gas was introduced, and then the mixture was ball-milled at 100rpm to form a uniformly mixed combustion synthesis raw material.

[0091] (2) Preparation of boron nitride nanotube / silicon nitride composite powder

[0092] The combustion synthesis raw material obtained in step (1) was placed in a porous ceramic permeable crucible with a porosity of 90%. The crucible with the combustion synthesis raw material was placed in a high-pressure container and a nitrogen-hydrogen mixture with a pressure of 6 MPa (of which the hydrogen content was 10%) was introduced. Then, the combustion synthesis raw material powder was ignited by an electric tungsten wire at a current of 80 A to prepare boron nitride nanotube / silicon nitride composite powder. In the prepared boron nitride nanotube / silicon nitride composite powder, the α-Si3N4 content m was m = 93.6%.

[0093] Comparative Example 1

[0094] (1) Preparation of combustion synthesis raw materials

[0095] A total of 100g of raw material powder (silicon powder, silicon nitride diluent, and ammonium chloride) was added to a ball mill jar. The silicon powder had a particle size of 20μm, the silicon nitride diluent had a particle size of 4μm, and the ammonium chloride had a particle size of 2μm. The raw materials were mixed in a mass ratio of 60:30:10 for silicon powder, silicon nitride diluent, and ammonium chloride. The mass of the stainless steel grinding media in the ball mill jar was 5000g. After evacuating the ball mill tube, 1000Pa high-pressure ammonia gas was introduced, and then the mixture was ball-milled at 100rpm to form a uniformly mixed combustion synthesis raw material.

[0096] (2) Preparation of silicon nitride powder

[0097] The combustion synthesis raw material obtained in step (1) is placed in a porous ceramic permeable crucible with a porosity of 90%. The crucible with the combustion synthesis raw material is placed in a high-pressure container and a nitrogen-hydrogen mixture with a pressure of 6 MPa (the hydrogen content is 10%) is introduced. Then, the raw material powder is ignited by an electric tungsten wire under a current of 80 A to prepare silicon nitride powder. In the prepared silicon nitride powder, the α-Si3N4 content m is m = 93.6%.

[0098] Applications of boron nitride nanotube / silicon nitride composite powders

[0099] A method for preparing silicon nitride ceramic bulk using boron nitride nanotube / silicon nitride composite powder includes the following steps:

[0100] (a) Powder grinding

[0101] The boron nitride nanotube / silicon nitride composite powders prepared in Examples 1-4 and Comparative Example 1 were ground and pulverized.

[0102] (b) Preparation of the blank

[0103] The sintering aid yttrium oxide / magnesium oxide / silicon magnesium nitride was added to the boron nitride nanotube / silicon nitride composite powder obtained in step (a), and the powder was subjected to isostatic pressing at 200-400 Ma to obtain a green body.

[0104] (c) Preparation of silicon nitride ceramic matrix

[0105] In a nitrogen atmosphere of 1–2 Ma, the green body obtained in step (b) is sintered at 1750–1950 °C for 48 h to obtain a silicon nitride ceramic bulk.

[0106] (d) Performance Testing

[0107] The mechanical properties of the silicon nitride ceramic bulk obtained in step (c) were tested and analyzed. The specific mechanical property testing conditions are as follows: the mechanical property tests were conducted according to GB / T45767-2025.

[0108] The mechanical property test results are as follows:

[0109] (1) The boron nitride nanotube / silicon nitride composite powder prepared in Example 1, after sintering, yielded silicon nitride ceramic with a strength of 900 MPa and a fracture toughness of 11 MPa·m. 1 / 2 The thermal conductivity of the sintered body is 121 W / mK;

[0110] (2) The silicon nitride ceramic obtained after sintering the boron nitride nanotube / silicon nitride composite powder prepared in Example 2 has a strength of 700 MPa and a fracture toughness of 12 MPa·m. 1 / 2 The thermal conductivity of the sintered body is 125 W / mK.

[0111] (3) The silicon nitride ceramic obtained after sintering the boron nitride nanotube / silicon nitride composite powder prepared in Example 3 has a strength of 1100 MPa and a fracture toughness of 10 MPa·m. 1 / 2 The thermal conductivity of the sintered body is 109 W / mK;

[0112] (4) The silicon nitride ceramic block obtained by sintering the boron nitride nanotube / silicon nitride composite powder prepared in Example 4 has a strength of 900 MPa and a fracture toughness of 10 MPa·m. 1 / 2The thermal conductivity of the sintered body is 108 W / mK.

[0113] (5) The silicon nitride ceramic obtained after sintering of the boron nitride nanotube / silicon nitride composite powder prepared in Comparative Example 1 has a strength of 600 MPa and a fracture toughness of 7 MPa·m. 1 / 2 The thermal conductivity of the sintered body is 78 W / mK.

[0114] The specific results are listed in Table 1.

[0115] Table 1. Test results of mechanical properties of silicon nitride ceramic bulk materials

[0116] Number ceramic strength MPa )]]> Fracture toughness (MPa-m 1 / 2 ) Sintered body thermal conductivity (W / mK) Example 1 900 11 121 Example 2 700 12 125 Example 3 1100 10 109 Example 4 900 10 108 Comparative Example 1 600 7 78

[0117] Based on the data analysis in Table 1, the following conclusions can be drawn: the silicon nitride ceramic block obtained by sintering the boron nitride nanotube / silicon nitride composite powder prepared by the method of the present invention has high thermal conductivity and good fracture toughness.

[0118] In summary, the boron nitride nanotube / silicon nitride composite powder, its preparation method, and its applications according to embodiments of the present invention utilize silicon powder, silicon nitride diluent, boron powder, and ammonium salt as raw materials. Highly uniform reaction raw materials are prepared using ball milling, and high-purity alpha-phase silicon nitride and boron nitride nanotube composite powders are synthesized on a large scale through the low-cost combustion synthesis technique. The preparation method of the boron nitride nanotube / silicon nitride composite powder of the present invention avoids the agglomeration and dispersion problem of boron nitride nanotubes in silicon nitride powder and greatly improves the toughness, thermal conductivity, thermal shock resistance, dielectric properties, and wave transmission properties of the sintered silicon nitride ceramic block, thus broadening the application of silicon nitride in the fields of information communication, hypersonic load-bearing structures, and radar wave transmission.

[0119] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0120] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing boron nitride nanotube / silicon nitride composite powder, characterized in that, include: In an ammonia atmosphere, silicon powder, boron powder, silicon nitride diluent, and ammonium salt are mixed evenly in a mass ratio of (50-60):(5-10):(20-30):(10-15) to prepare combustion synthesis raw materials; The method for uniformly mixing silicon powder, boron powder, silicon nitride diluent, and ammonium salt is as follows: ball milling is performed under the action of grinding balls; The ammonium salt is selected from at least one of ammonium chloride and ammonium fluoride; The silicon nitride diluent is selected from at least one of α-Si3N4 and β-Si3N4; In a hydrogen / nitrogen mixture, the combustion synthesis raw materials undergo a combustion reaction to prepare boron nitride nanotube / silicon nitride composite powder, which is synthesized in situ. The steps involved in the combustion reaction of the synthetic raw materials include: The combustion synthesis raw material is placed in a porous ceramic permeable crucible and ignited by an electrically powered tungsten filament. The porous ceramic permeable crucible has a porosity of 90-98%. And / or, the current of the energized tungsten filament is 20 to 150 A; The α-Si3N4 content m in the boron nitride nanotube / silicon nitride composite powder has a value range of m≥93%.

2. The method for preparing boron nitride nanotube / silicon nitride composite powder according to claim 1, characterized in that, The mass ratio of silicon powder to silicon nitride diluent is (5:1) to (3:1); And / or, the mass ratio of the silicon powder to the ammonium salt is (10:1) to (3:1); And / or, the mass ratio of the boron powder to the ammonium salt is (10:1) to (1:2).

3. The method for preparing boron nitride nanotube / silicon nitride composite powder according to claim 2, characterized in that, In an ammonia atmosphere, the pressure of ammonia is 100–50000 Pa.

4. The method for preparing boron nitride nanotube / silicon nitride composite powder according to claim 3, characterized in that, The particle size of the silicon powder is 1–50 μm; And / or, the particle size of the boron powder is 2 to 10 μm; And / or, the particle size of the silicon nitride diluent is 1 to 8 μm.

5. The method for preparing boron nitride nanotube / silicon nitride composite powder according to claim 4, characterized in that, The mass ratio of silicon powder to grinding balls is (10:1) to (100:1); And / or, the mass ratio of the boron powder to the grinding balls is (10:1) to (100:1); And / or, the mass ratio of the silicon nitride diluent to the grinding balls is (10:1) to (100:1); And / or, the mass ratio of the ammonium salt to the grinding balls is (10:1) to (100:1); And / or, the grinding balls are composed of at least one of silicon nitride, tungsten carbide, zirconium oxide, and stainless steel.

6. The method for preparing boron nitride nanotube / silicon nitride composite powder according to claim 5, characterized in that, In a hydrogen / nitrogen mixture, the total pressure of hydrogen and nitrogen is 1–15 MPa; And / or, in a hydrogen / nitrogen mixture, the volume ratio of hydrogen to nitrogen is (1:99) to (20:80).

7. A boron nitride nanotube / silicon nitride composite powder obtained by the preparation method of boron nitride nanotube / silicon nitride composite powder according to any one of claims 1 to 6.

8. The application of the boron nitride nanotube / silicon nitride composite powder according to claim 7 in the preparation of silicon nitride ceramic bulk.

9. The application according to claim 8, characterized in that, Methods for preparing silicon nitride ceramic bulk materials include: The sintering aid and boron nitride nanotube / silicon nitride composite powder were subjected to isostatic pressing to obtain a green body. The blank is sintered in a nitrogen atmosphere to obtain a silicon nitride ceramic block; The sintering aid includes at least one of yttrium oxide, magnesium oxide, and magnesium silicon nitride. And / or, the pressure of isostatic pressing is 20–500 MPa; And / or, the pressure of the nitrogen atmosphere is 0.1–15 MPa; And / or, the sintering temperature is 1600~2200℃; And / or, the sintering temperature and time are 10 to 50 hours.

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