Silicon nitride ceramic and method for producing the same

Abstract

The application discloses silicon nitride ceramic and a preparation method thereof, and belongs to the ceramic field. The preparation method is as follows: in an organic solvent, taking beta-phase silicon nitride powder as aggregate, taking amorphous-phase silicon nitride powder as activator, taking a beta-diketone rare earth complex as a sintering aid, and taking a mixture of polysilazane and PVB as a binder, after forming treatment, high-temperature sintering is performed to obtain the silicon nitride ceramic; the density of the ceramic material is 3.05-3.29 g / cm 3 , the bending strength is 750-1100 MPa, and the thermal conductivity is 65-130 W / (m.K). The silicon nitride ceramic obtained by the application has the advantages of high densification degree, high mechanical strength and high thermal conductivity, and has a wide application scene.

Description

Technical Field

[0001] This invention belongs to the field of ceramics and relates to a silicon nitride ceramic and its preparation method. Background Technology

[0002] Silicon nitride is an excellent advanced ceramic material with numerous superior properties. Silicon nitride ceramics combine low density, high strength, high hardness, high insulation, high thermal conductivity, high temperature resistance, corrosion resistance, wear resistance, thermal shock resistance, and oxidation resistance, making it considered the ceramic material with the best overall performance. These properties endow silicon nitride with universal applicability, leading to its widespread application in aerospace, semiconductor manufacturing, energy, medical devices, and communications, among other fields.

[0003] However, as semiconductor devices evolve towards higher power, higher frequency, and greater integration, these components generate a significant amount of heat during operation. Statistics show that heat-related failures account for up to 55% of device failures, highlighting heat as a key factor in semiconductor device failure. Furthermore, in fields such as new energy vehicles and modern rail transportation, high-power devices must withstand complex operating conditions including bumps and vibrations. Traditional silicon nitride ceramic materials suffer from low strength and poor thermal conductivity, limiting their application in some demanding fields.

[0004] Patent application No. 202010197262.7, published on July 3, 2020, discloses a high thermal conductivity silicon nitride ceramic and its preparation method. This patent uses magnesium silicon nitride as a sintering aid, and obtains silicon nitride ceramic through spray granulation, pressing, debinding, and gas pressure sintering. The silicon nitride ceramic is then subjected to hot isostatic pressing and annealing heat treatment to improve its thermal conductivity. Patent application No. 202210605665.X, published on May 31, 2022, discloses a method for preparing a high thermal conductivity silicon nitride ceramic substrate. This patent uses silicon powder / silicon nitride powder as raw materials, and obtains the silicon nitride ceramic substrate through spray granulation, isostatic pressing, vacuum debinding, nitriding treatment, and sintering. Patent application No. 202310023868.2, with a publication date of March 14, 2023, discloses a method for preparing high thermal conductivity silicon nitride ceramics. The patent first refines and oxidizes silicon nitride raw material powder, then adds a certain amount of β-phase seed crystals and rare earth oxide sintering aids to the powder, mixes and forms a ceramic blank, and then performs gas pressure sintering to obtain silicon nitride ceramic material.

[0005] Based on the above search results, currently, in the process of preparing silicon nitride ceramics:

[0006] (1) Using alpha or beta silicon nitride powder as raw material, oxygen-containing sintering aids such as rare earth oxides and alkaline earth metal oxides or oxygen-free sintering aids such as magnesium silicon nitride are added. The sintering aids and silicon nitride raw powder are ball-milled in aqueous phase, resulting in high oxygen content in the sintered powder and low thermal conductivity of silicon nitride ceramics; during solid-phase ball milling, the sintering aids are prone to agglomeration and cannot be uniformly dispersed on the surface of silicon nitride raw powder, resulting in poor strength and low reliability of the sintered ceramics;

[0007] (2) When spray granulation is performed, PVA series and PVB series are used as binders. After degumming and sintering, more pores are generated inside the ceramic, resulting in low density of the ceramic. The generated pores will hinder the formation of the internal thermal conductive network of the ceramic, affecting the further improvement of the thermal conductivity of the ceramic.

[0008] In summary, there is currently a lack of a high-strength, high-thermal-conductivity silicon nitride ceramic and its preparation method in this field. Summary of the Invention

[0009] 1. The problem to be solved

[0010] To address the problems of poor strength, low intrinsic thermal conductivity, and low density in existing silicon nitride ceramics, this invention provides a method for preparing silicon nitride ceramics. By optimizing the raw material formulation, the prepared silicon nitride ceramics exhibit high strength, high thermal conductivity, and high density.

[0011] 2. Technical Solution

[0012] To address the aforementioned technical challenges, this invention utilizes β-phase silicon nitride powder as aggregate, amorphous silicon nitride powder as activator, β-diketone rare earth complex as sintering aid, and a mixture of polysilazane and a small amount of PVB as binder to achieve the preparation of high thermal conductivity and high strength silicon nitride ceramics. Details are as follows:

[0013] A method for preparing silicon nitride ceramics involves mixing β-phase silicon nitride powder as aggregate, amorphous silicon nitride powder as activator, β-diketone rare earth complex as sintering aid, and a mixture of polysilazane and PVB as binder in an organic solvent in a mixer to obtain a stable slurry. After molding, the sintering is carried out at high temperature to obtain silicon nitride ceramics.

[0014] Furthermore, the rare earth content in the β-diketone rare earth complex accounts for 1.5% to 5.5% of the total mass of the preparation reaction system.

[0015] Furthermore, the β-diketone rare earth complex is one or more of tri(acetylacetone) rare earth, tri(2,2,6,6-tetramethyl-3,5-heptanedione) rare earth, and tri(1,3-diphenyl-1,3-propanedione) rare earth mixed in any proportion, wherein the rare earth is selected from one or more of yttrium, ytterbium, europium, and lanthanum.

[0016] Furthermore, the median particle size D50 of β-phase silicon nitride powder is ≤3 micrometers, and the median particle size D50 of amorphous silicon nitride powder is ≤1 micrometer.

[0017] Furthermore, in the mixture of polysilazane and PVB, the mass ratio of polysilazane to PVB is 1:(0.15 to 0.20).

[0018] Furthermore, the polysilazane is one or more of phenyl polysilazane, ethynyl polysilazane, propylene polysilazane, and perhydropolysilazane.

[0019] Furthermore, the molding process includes compression molding, wherein the compression molding pressure is 100-200 MPa.

[0020] Furthermore, before compression molding, the material is spray-granulated to obtain silicon nitride granulated powder with a particle size of 10-150 micrometers; after compression molding, high-temperature debinding is performed at a temperature of 300-600℃ for 10 hours to obtain debinded silicon nitride ceramic green body; after high-temperature debinding, cold isostatic pressing is performed to obtain a further densified silicon nitride ceramic green body, wherein the pressure of cold isostatic pressing is 150-300 MPa and the holding time is 1-5 minutes.

[0021] Furthermore, in the high-temperature sintering, the sintering temperature is 1600–1900℃, and the holding time is 1–10 hours.

[0022] Furthermore, the mass percentages of each material are as follows:

[0023] Organic solvents 35%–55%;

[0024]

[0025] The organic solvent is one or more of acetone, ethyl acetate, and butyl acetate, and the total mass percentage of each material is 100%.

[0026] A silicon nitride ceramic, prepared by the above method, has a density of 3.05–3.29 g / cm³. 3 Its flexural strength is 750–1100 MPa, and its thermal conductivity is 65–130 W / (m·K).

[0027] The above technical solution has the following significant advantages:

[0028] (1) Using β-phase silicon nitride powder and a small amount of amorphous silicon nitride powder as raw materials, the abnormal growth of β-silicon nitride during sintering is avoided. At the same time, amorphous silicon nitride powder has high sintering activity and can effectively utilize the dissolution-precipitation mechanism to promote the densification sintering of β-silicon nitride.

[0029] (2) Using β-diketone rare earth complex as a sintering aid, which does not contain water of crystallization, and can remove the hydroxyl groups on the surface of silicon nitride powder through the substitution reaction that occurs at the interface, thereby reducing the oxygen content of silicon nitride; the rare earth β-diketone complex sintering aid is dissolved in an organic solvent and fully mixed in a mixer, so that the sintering aid is uniformly coated on the surface of silicon nitride powder, thereby achieving uniform dispersion of the sintering aid in silicon nitride powder, thus avoiding the problems of poor reliability and low strength of silicon nitride ceramics caused by uneven mixing of sintering aid and silicon nitride powder.

[0030] (3) A mixture of polysilazane and a small amount of PVB is used as a binder. During the sintering process, polysilazane is converted into silicon nitride, which plays a filling role between β-silicon nitride grains, reducing the formation of ceramic pores, reducing ceramic volume shrinkage, and improving the density of ceramic. The in-situ generated silicon nitride ceramic is integrated with the main raw material to form a new thermal conductivity path, which improves the intrinsic thermal conductivity of ceramic.

[0031] 3. Beneficial effects

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] After adopting the above method, the present invention has the following advantages: Since an organic solvent is used as the dispersion medium, silicon nitride powder in a certain mass ratio is mixed with a certain amount of organic solvent and binder in a certain order to form a slurry. After homogenization in a mixer, it is spray granulated, molded, degummed, cold isostatically pressed and sintered at high temperature. After sintering, silicon nitride ceramics are obtained. The obtained silicon nitride ceramics have advantages such as high densification, high mechanical strength and high thermal conductivity, and have a wide range of applications. Attached Figure Description

[0034] Figure 1 The XRD pattern of the silicon nitride ceramic in Example 1 is shown below.

[0035] Figure 2 Here is a SEM image of the fracture surface of the silicon nitride ceramic in Example 2;

[0036] Figure 3 This is a SEM image of the fracture surface of the silicon nitride ceramic in Example 4. Detailed Implementation

[0037] The present invention will be further described below with reference to specific embodiments.

[0038] Example 1

[0039] (1) 31wt% β-phase silicon nitride powder, 5wt% amorphous silicon nitride powder and 9wt% sintering aid (3wt% yttrium acetylacetonate (III) (CAS: 15554-47-9, purchased from Shanghai Myriel Biochemical Technology Co., Ltd.), 3wt% ytterbium acetylacetonate (III) (CAS: 14284-98-1, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.), 3wt% lanthanum acetylacetonate (III) (CAS: 14284-88-9, purchased from Shanghai Myriel Biochemical Technology Co., Ltd.) were added to 40wt% acetone, wherein the mass percentage of rare earth elements yttrium, ytterbium and lanthanum was 2.9%, and 15wt% PVB / perhydropolysilazane (mass ratio of PVB and perhydropolysilazane was 15:85) was used as a binder, and the mixture was added to a mixer and mixed evenly to obtain a stable slurry;

[0040] (2) The above mixed slurry was spray granulated to obtain granulated powder with a median particle size of 100 micrometers;

[0041] (3) The obtained granulated powder is molded by compression molding at a pressure of 100 MPa.

[0042] (4) The obtained silicon nitride ceramic green body was debonded at high temperature. The debonding temperature was 400℃ and the debonding time was 10h.

[0043] (5) The obtained degummed silicon nitride ceramic blank is subjected to cold isostatic pressing. The pressure of cold isostatic pressing is 200 MPa and the holding time is 4 min.

[0044] (6) The obtained further densified silicon nitride ceramic blank was sintered without pressure at a temperature of 1600℃ for 4 hours in an atmosphere of N2.

[0045] The sintered product is the silicon nitride ceramic described in this invention, with a density of 3.05 g / cm³. 3 The flexural strength is 750 MPa, and the thermal conductivity is 65 W / (m·K). XRD analysis showed that the β-phase silicon nitride content was 100%, meaning that all amorphous silicon nitride was converted to β-phase silicon nitride. The results are as follows: Figure 1 As shown.

[0046] Example 2

[0047] (1) 50wt% β-phase silicon nitride powder, 5wt% amorphous silicon nitride powder and 5wt% sintering aid (1wt% yttrium acetylacetonate (III), 1wt% europium tris(2,2,6,6-tetramethyl-3,5-heptane) (CAS:15522-71-1, purchased from Shanghai Mairui Biochemical Technology Co., Ltd.), 3wt% lanthanum acetylacetonate (III)) were added to 35wt% acetone / butyl acetate mixed solvent (the mass ratio of acetone and butyl acetate was 34:66), wherein the mass percentage of rare earth elements yttrium, europium and lanthanum was 1.5%, and 5wt% PVB / ethynyl polysilazane (the mass ratio of PVB, ethynyl polysilazane and perhydropolysilazane was 17:50:33) was used as a binder and added to a mixer and mixed evenly to obtain a stable mixed slurry;

[0048] (2) The above mixed slurry was spray-granulated to obtain granulated powder with a median particle size of 110 micrometers;

[0049] (3) The obtained granulated powder is molded by compression molding at a pressure of 150 MPa.

[0050] (4) The obtained silicon nitride ceramic green body is subjected to high-temperature debinding at a temperature of 500℃ for 10 hours.

[0051] (5) The obtained degummed silicon nitride ceramic blank is subjected to cold isostatic pressing. The pressure of cold isostatic pressing is 300 MPa and the holding time is 3 min.

[0052] (6) The obtained further densified silicon nitride ceramic blank was subjected to gas pressure sintering at a temperature of 1900℃ and a holding time of 8h. The atmosphere was high-purity nitrogen and the nitrogen pressure was 6MPa.

[0053] The sintered product is the silicon nitride ceramic described in this invention, with a density of 3.21 g / cm³. 3 The flexural strength is 980 MPa, the thermal conductivity is 130 W / (m·K), and the fracture surface was observed by SEM. The results are as follows. Figure 2 As shown in the figure, the β-phase silicon nitride is a rod-shaped crystal with a uniform morphology and a large aspect ratio, which is beneficial to the formation of a heat-conducting network.

[0054] Example 3

[0055] (1) 30wt% β-phase silicon nitride powder, 15wt% amorphous silicon nitride powder and 15wt% sintering aid (ytterbium acetylacetonate (III)) were added to 35wt% acetone / butyl acetate mixed solvent (the mass ratio of acetone and butyl acetate was 34:66), wherein the mass percentage of rare earth element ytterbium was 5.5%, and 5wt% PVB / polysilazane (the mass ratio of PVB, propylene polysilazane and perhydropolysilazane was 17:50:33) was used as a binder. The mixture was added to a mixer and mixed evenly to obtain a stable mixed slurry.

[0056] (2) The above mixed slurry was spray-granulated to obtain granulated powder with a median particle size of 110 micrometers;

[0057] (3) The obtained granulated powder is molded by compression molding at a pressure of 170 MPa.

[0058] (4) The obtained silicon nitride ceramic green body was debonded at high temperature. The debonding temperature was 550℃ and the debonding time was 10h.

[0059] (5) The obtained degummed silicon nitride ceramic blank is subjected to cold isostatic pressing. The pressure of cold isostatic pressing is 280 MPa and the holding time is 3 min.

[0060] (6) The obtained further densified silicon nitride ceramic blank was subjected to gas pressure sintering at a temperature of 1800℃ and a holding time of 10h. The atmosphere was high-purity nitrogen and the nitrogen pressure was 4Mpa.

[0061] The sintered product is the silicon nitride ceramic described in this invention, with a density of 3.19 g / cm³. 3 It has a flexural strength of 860 MPa and a thermal conductivity of 118 W / (m·K).

[0062] Example 4

[0063] (1) 25wt% β-phase silicon nitride powder, 5wt% amorphous silicon nitride powder and 10wt% sintering aid (3wt% lanthanum acetylacetonate (III), 3wt% ytterbium acetylacetonate (III), 4wt% tris(1,3-diphenyl-1,3-propanedione)(1,10-phenanthroline) europium (CAS:17904-83-5, purchased from Shanghai Yingxin Laboratory Equipment Co., Ltd.) were added to 55wt% acetone / ethyl acetate mixed solvent (the mass ratio of acetone and ethyl acetate was 34:66), wherein the mass percentage of rare earth elements lanthanum, ytterbium and europium was 2.7%, and 5wt% PVB / polysilazane (the mass ratio of PVB, propylene polysilazane and perhydropolysilazane was 17:50:33) was used as a binder. The mixture was added to a mixer and mixed evenly to obtain a stable mixed slurry.

[0064] (2) The above mixed slurry was spray-granulated to obtain granulated powder with a median particle size of 90 micrometers;

[0065] (3) The obtained granulated powder is molded by compression molding at a pressure of 200 MPa.

[0066] (4) The obtained silicon nitride ceramic green body was debonded at high temperature. The debonding temperature was 600℃ and the debonding time was 10h.

[0067] (5) The obtained degummed silicon nitride ceramic blank is subjected to cold isostatic pressing. The pressure of cold isostatic pressing is 250 MPa and the holding time is 3 min.

[0068] (6) The obtained further densified silicon nitride ceramic blank was subjected to vacuum hot pressing sintering at a temperature of 1750℃ and a holding time of 9h.

[0069] The sintered product is the silicon nitride ceramic described in this invention, with a density of 3.29 g / cm³. 3 The flexural strength is 1100 MPa, the thermal conductivity is 105 W / (m·K), and the fracture surface was observed by SEM. The results are as follows. Figure 3 As shown in the figure, β-phase silicon nitride with different aspect ratios is distributed in an alternating manner, exhibiting a bimodal structure, which is beneficial to improving the fracture toughness of ceramics.

[0070] Comparative Example 1

[0071] (1) 40wt% acetone, 15wt% PVB, 36wt% α-phase silicon nitride powder and 9wt% sintering aid (3wt% yttrium oxide, 3wt% ytterbium oxide and 3wt% lanthanum oxide) are added to a mixer and mixed evenly to obtain a stable mixed slurry, wherein the mass percentage of rare earth elements yttrium, ytterbium and lanthanum is 7.6%;

[0072] (2) The above mixed slurry was spray-granulated to obtain granulated powder with a median particle size of 50 micrometers;

[0073] (3) The obtained granulated powder is molded by compression molding at a pressure of 100 MPa.

[0074] (4) The obtained silicon nitride ceramic green body was debonded at high temperature. The debonding temperature was 400℃ and the debonding time was 10h.

[0075] (5) The obtained degummed silicon nitride ceramic blank is subjected to cold isostatic pressing. The pressure of cold isostatic pressing is 200 MPa and the holding time is 4 min.

[0076] (6) The obtained further densified silicon nitride ceramic blank was sintered without pressure at a temperature of 1600℃ for 4 hours in an atmosphere of N2.

[0077] The sintered product is the silicon nitride ceramic described in this invention, with a density of 3.12 g / cm³. 3 The flexural strength was 280 MPa, and the thermal conductivity was 28 W / (m·K). Compared with Example 1, both were pressureless sintering, and the flexural strength and thermal conductivity of the silicon nitride ceramic in Comparative Example 1 were much lower than those in Example 1.

[0078] Comparative Example 2

[0079] (1) 55wt% β-phase silicon nitride powder and 5wt% sintering aid (1wt% yttrium acetylacetonate (III), 1wt% europium tris(2,2,6,6-tetramethyl-3,5-heptane), 3wt% lanthanum acetylacetonate (III)) were added to 35wt% acetone / butyl acetate mixed solvent (the mass ratio of acetone and butyl acetate was 34:66), wherein the mass percentage of rare earth elements yttrium, europium and lanthanum was 1.5%, and 5wt% PVB / polysilazane (the mass ratio of PVB, ethynyl polysilazane and perhydropolysilazane was 17:50:33) was used as a binder and added to a mixer and mixed evenly to obtain a stable mixed slurry;

[0080] (2) The above mixed slurry was spray-granulated to obtain granulated powder with a median particle size of 110 micrometers;

[0081] (3) The obtained granulated powder is molded by compression molding at a pressure of 150 MPa.

[0082] (4) The obtained silicon nitride ceramic green body is subjected to high-temperature debinding at a temperature of 500℃ for 10 hours.

[0083] (5) The obtained degummed silicon nitride ceramic blank is subjected to cold isostatic pressing. The pressure of cold isostatic pressing is 300 MPa and the holding time is 3 min.

[0084] (6) The obtained further densified silicon nitride ceramic blank was subjected to gas pressure sintering at a temperature of 1900℃ and a holding time of 8h. The atmosphere was high-purity nitrogen and the nitrogen pressure was 6MPa.

[0085] The sintered product is the silicon nitride ceramic described in this invention, with a density of 3.15 g / cm³. 3 The flexural strength was 330 MPa and the thermal conductivity was 45 W / (m·K). Compared with Example 2, under the same sintering process conditions, the flexural strength and thermal conductivity of the silicon nitride ceramic prepared in Comparative Example 2 were much lower than those in Example 2.

[0086] Comparative Example 3

[0087] (1) 30 wt% β-phase silicon nitride powder, 15 wt% amorphous silicon nitride powder and 15 wt% sintering aid (ytterbium oxide) were added to 35 wt% acetone / ethyl acetate mixed solvent (the mass ratio of acetone and butyl acetate was 34:66), wherein the mass percentage of rare earth elements yttrium, europium and lanthanum was 13%, and 5 wt% PVB / polysilazane (the mass ratio of PVB, propylene polysilazane and perhydropolysilazane was 17:50:33) was used as a binder. The mixture was added to a mixer and mixed evenly to obtain a stable mixed slurry.

[0088] (2) The above mixed slurry was spray-granulated to obtain granulated powder with a median particle size of 110 micrometers;

[0089] (3) The obtained granulated powder is molded by compression molding at a pressure of 170 MPa.

[0090] (4) The obtained silicon nitride ceramic green body was debonded at high temperature. The debonding temperature was 550℃ and the debonding time was 10h.

[0091] (5) The obtained degummed silicon nitride ceramic blank is subjected to cold isostatic pressing. The pressure of cold isostatic pressing is 280 MPa and the holding time is 3 min.

[0092] (6) The obtained further densified silicon nitride ceramic blank was subjected to gas pressure sintering at a temperature of 1800℃ and a holding time of 10h. The atmosphere was high-purity nitrogen and the nitrogen pressure was 4Mpa.

[0093] The sintered product is the silicon nitride ceramic described in this invention, with a density of 3.21 g / cm³. 3 The flexural strength was 420 MPa, and the thermal conductivity was 41 W / (m·K). Compared with Example 3, under the same sintering process conditions, the flexural strength and thermal conductivity of the silicon nitride ceramic prepared in Comparative Example 3 were much lower than those in Example 3.

[0094] Comparative Example 4

[0095] (1) 25wt% β-phase silicon nitride powder, 5wt% amorphous silicon nitride powder and 10wt% sintering aid (3wt% lanthanum acetylacetonate (III), 3wt% ytterbium acetylacetonate (III), 4wt% tris(1,3-diphenyl-1,3-propanedione)(1,10-phenanthroline) europium) were added to 55wt% acetone / ethyl acetate mixed solvent (the mass ratio of acetone and butyl acetate was 34:66), wherein the mass percentage of rare earth elements lanthanum, ytterbium and europium was 2.7%, and 5wt% PVB was used as a binder. The mixture was added to a mixer and mixed evenly to obtain a stable slurry.

[0096] (2) The above mixed slurry was spray granulated to obtain granulated powder with a median particle size of 95 micrometers;

[0097] (3) The obtained granulated powder is molded by compression molding at a pressure of 200 MPa.

[0098] (4) The obtained silicon nitride ceramic green body was debonded at high temperature. The debonding temperature was 600℃ and the debonding time was 10h.

[0099] (5) The obtained degummed silicon nitride ceramic blank is subjected to cold isostatic pressing. The pressure of cold isostatic pressing is 250 MPa and the holding time is 3 min.

[0100] (6) The obtained further densified silicon nitride ceramic blank was subjected to vacuum hot pressing sintering at a temperature of 1750℃ and a holding time of 9h.

[0101] The sintered product is the silicon nitride ceramic described in this invention, with a density of 3.26 g / cm³. 3 The flexural strength was 560 MPa, and the thermal conductivity was 49 W / (m·K). Compared with Example 4, under the same sintering process conditions, the flexural strength and thermal conductivity of the silicon nitride ceramic in Comparative Example 4 were much lower than those in Example 4.

[0102] The above embodiments have described in detail the purpose and effects of the present invention. It should be understood that the above embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the concept and scope of the present invention. All modifications, equivalent substitutions, improvements, etc., made by those skilled in the art or by adopting the technical concept and technical solution of the present invention within the spirit and principles of the present invention and without departing from the design concept of the present invention are within the protection scope of the present invention.

Claims

1. A method for preparing silicon nitride ceramics, characterized in that: In an organic solvent, β-phase silicon nitride powder is used as aggregate, amorphous silicon nitride powder as activator, β-diketone rare earth complex as sintering aid, and a mixture of polysilazane and PVB as binder. After molding, silicon nitride ceramics are obtained by high-temperature sintering. The median particle size D50 of the β-phase silicon nitride powder is ≤3 μm, the median particle size D50 of the amorphous silicon nitride powder is ≤1 μm, and the rare earth content in the β-diketone rare earth complex accounts for 1.5%~5.5% of the total mass of the preparation reaction system. The mass percentages of each material are as follows: Organic solvents 35%~55%; β-phase silicon nitride powder 25%~50%; Amorphous silicon nitride powder 5%~15%; Sintering aids 5%~15%; Adhesive 5%~15%; The organic solvent is one or more of acetone, ethyl acetate, and butyl acetate, and the total mass percentage of each material is 100%.

2. The method for preparing silicon nitride ceramic according to claim 1, characterized in that: The β-diketone rare earth complex is a mixture of one or more of tri(acetylacetone) rare earth, tri(2,2,6,6-tetramethyl-3,5-heptanedione) rare earth, and tri(1,3-diphenyl-1,3-propanedione) rare earth in any proportion, wherein the rare earth is selected from one or more of yttrium, ytterbium, europium, and lanthanum.

3. The method for preparing silicon nitride ceramic according to claim 1, characterized in that: In the mixture of polysilazane and PVB, the mass ratio of polysilazane to PVB is 1: (0.15~0.20).

4. The method for preparing silicon nitride ceramic according to claim 3, characterized in that: Polysilazane is one or a mixture of phenyl polysilazane, ethynyl polysilazane, propylene polysilazane, and perhydropolysilazane.

5. The method for preparing silicon nitride ceramic according to claim 1, characterized in that: The molding process includes compression molding, with a compression molding pressure of 100~200MPa.

6. A method for preparing silicon nitride ceramic according to claim 5, characterized in that: Before compression molding, the material is spray-granulated to obtain silicon nitride granulated powder with a particle size of 10-150 micrometers. After compression molding, high-temperature debinding is performed at a temperature of 300-600℃ for 10 hours to obtain debinded silicon nitride ceramic green body. After high-temperature debinding, cold isostatic pressing is performed at a pressure of 150-300 MPa for 1-5 minutes. During high-temperature sintering, the sintering temperature is 1600-1900℃ for 1-10 hours.

7. A silicon nitride ceramic, characterized in that: The ceramic material obtained by any one of claims 1 to 6 has a density of 3.05 to 3.29 g / cm³. 3 Its flexural strength is 750~1100 MPa, and its thermal conductivity is 65~130 W / (m·K).

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