Silicon nitride ceramic and its preparation method and application

Abstract

The present invention belongs to the field of silicon nitride ceramic technology, and specifically relates to a silicon nitride ceramic and its preparation method and application. The preparation method comprises the following steps: S1, mixing α-Si3N4, silicon powder, sintering aid, dispersant, and solvent for a first ball milling to obtain slurry A; S2, mixing slurry A, a binder, and a plasticizer for a second ball milling to obtain slurry B; S3, tape-casting slurry B, sintering, cooling, and obtaining silicon nitride ceramic; sintering aids include magnesium silicon nitride and rare earth oxides; heating to 1100-1300°C at a rate of 5-30°C / min for a first sintering of 1-6h, heating to 1400-1450°C at a rate of 0.1-10°C / min for a second sintering of 2-5h, and heating to 1750-1950°C at a rate of 3-20°C / min for a third sintering of 3-8h; the obtained silicon nitride ceramic has high density and takes into account both thermal conductivity and mechanical properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of silicon nitride ceramics, and in particular relates to a silicon nitride ceramic and a preparation method and application thereof. Background Art

[0002] To reduce environmental pollution, efficient use of electricity has become a key link. Electronic devices, as the core technology to achieve this goal, have been widely used in many fields such as wind power generation and new energy vehicles. This development trend places more stringent requirements on the heat dissipation substrates in electronic devices. Traditional ceramic substrates, such as AlN and BeO, have poor mechanical properties, which greatly limits their further development. In contrast, silicon nitride ceramics, with their excellent theoretical thermal conductivity and good mechanical properties, are gradually becoming the mainstream heat dissipation material for electronic devices.

[0003] Silicon nitride ceramics are high-performance structural ceramics, boasting properties such as high hardness, high wear resistance, excellent thermal shock resistance, good chemical stability, and a low coefficient of thermal expansion. They are widely used in a wide range of fields, including aerospace. However, traditional sintering methods make it difficult to produce high-density and stable silicon nitride ceramics. Furthermore, the preparation process is extremely complex to achieve high density, placing stringent demands on raw material purity and sintering technology. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect of poor density of silicon nitride ceramics obtained by existing preparation methods, thereby providing a silicon nitride ceramic and its preparation method and application.

[0005] To this end, the present invention provides the following technical solutions:

[0006] A first aspect of the present invention provides a method for preparing a silicon nitride ceramic, wherein the method comprises the following steps:

[0007] S1, α-Si3N4, silicon powder, sintering aid, dispersant, and solvent are mixed and ball-milled for the first time to obtain slurry A;

[0008] S2, mixing slurry A, a binder, and a plasticizer, and performing a second ball milling to obtain slurry B;

[0009] S3, tape-casting the slurry B, sintering, and cooling to obtain silicon nitride ceramics;

[0010] Wherein, the sintering aid includes magnesium silicon nitride and rare earth oxide;

[0011] The sintering conditions include: heating to 1100-1300°C at a rate of 5-30°C / min for a first sintering of 1-6 hours, heating to 1400-1450°C at a rate of 0.1-10°C / min for a second sintering of 2-5 hours, and heating to 1750-1950°C at a rate of 3-20°C / min for a third sintering of 3-8 hours.

[0012] In the present invention, α-Si3N4, silicon powder, sintering aid, dispersant and solvent are mixed and ball milled for the first time. Sometimes, in order to make the mixing more uniform, the silicon powder and sintering aid are first mixed with part of the solution, and the proportion of the part of the solution is 10-30 vol% based on the volume of the solution; then the dispersant is added, and then the α-Si3N4 and the remaining solvent are added and mixed.

[0013] In the present invention, the α-Si3N4 is a conventional raw material in the art. Typically, but not limiting, the purity of α-Si3N4 is 90-99.5%, which prevents impurities from forming defects inside the ceramic.

[0014] In the present invention, the purity of the silicon powder is 95-99.5%.

[0015] In the present invention, the solvent is a conventional solvent in the art. Typically, but not limited to, the solvent includes at least one of anhydrous ethanol, acetone, isopropyl alcohol, and ethyl acetate.

[0016] In the present invention, the rare earth oxide is a conventional oxide in the art. Typically, but not limitedly, the rare earth oxide includes at least one of gadolinium oxide (Gd2O3), lutetium oxide (Lu2O3), lanthanum oxide (La2O3), ytterbium oxide (Yb2O3), yttrium oxide (Y2O3), europium oxide (Eu2O3), and scandium oxide (Sc2O3).

[0017] In the present invention, the dispersant is a conventional dispersant in the art. Typically, but not limitedly, the dispersant includes an organic dispersant; optionally, the dispersant includes at least one of triolein, triethyl phosphate, sodium polyacrylate, and castor oil.

[0018] In the present invention, the binder is a conventional binder in the art. Typically, but not limitedly, the binder includes a high molecular polymer binder; optionally, the binder includes at least one of polyvinyl butyral, polyvinyl alcohol, and polyvinyl acetate.

[0019] In the present invention, the plasticizer is a conventional plasticizer in the art. Typically, but not limited to, the plasticizer includes at least one of a carboxylic acid ester compound and a polyol compound; optionally, the plasticizer includes at least one of dibutyl phthalate and glycerol.

[0020] In the present invention, the ball milling conditions are conventional ball milling conditions in the art. Typically, but not limitedly, the first ball milling has a rotation speed of 80-500 r / min, a temperature of 10-40°C, and a time of 12-24 h; the second ball milling has a rotation speed of 80-500 r / min, a temperature of 10-40°C, and a time of 12-36 h.

[0021] In the present invention, the particle size of the reagent is a conventional particle size in the art. Typically, but not limiting, the median particle size of the α-Si3N4 is 0.8-1.0 μm; the median particle size of the silicon powder is 0.7-2 μm; and the median particle size of the sintering aid is 0.2-1.5 μm.

[0022] In the present invention, after tape casting, a drying step is performed to obtain a blank, which is then cut and debinded to obtain a green blank. Drying is performed under conventional conditions in the art, typically, but not limited to, drying at room temperature for 6-8 hours. Debinding is performed under conventional conditions in the art, typically, but not limited to, heating to 600-650°C at a rate of 1-3°C / h and maintaining the temperature at 600-650°C for 2-3 hours. After debinding, the temperature is cooled to room temperature to obtain a green blank.

[0023] According to the present invention, the mass ratio of the magnesium silicon nitride to the rare earth oxide is 1:(0.5-6).

[0024] According to the present invention, the oxygen content of the silicon powder is 0.05-0.7 wt % based on the mass of the silicon powder.

[0025] According to the present invention, the mass ratio of the α-Si3N4, silicon powder, sintering aid, dispersant and solvent is 100:(60-180):(10-20):(0.5-7):(60-350).

[0026] According to the present invention, the mass ratio of the magnesium silicon nitride to the rare earth oxide is 1:(0.7-3).

[0027] According to the present invention, the oxygen content of the silicon powder is 0.05-0.2 wt % based on the mass of the silicon powder.

[0028] According to the present invention, the mass ratio of the α-Si3N4, silicon powder, sintering aid, dispersant and solvent is 100:(60-75):(10-18):(0.5-5):(80-200).

[0029] According to the present invention, the mass ratio of the α-Si3N4, binder and plasticizer is 1:(0.3-0.7):(0.03-0.07).

[0030] According to the present invention, the mass ratio of the α-Si3N4, binder and plasticizer is 1:(0.3-0.5):(0.03-0.05).

[0031] According to the present invention, the sintering conditions include: heating to 1200-1250°C at a rate of 15-20°C / min for a first sintering time of 1-4 hours, heating to 1420-1450°C at a rate of 0.1-5°C / min for a second sintering time of 2-5 hours, and heating to 1770-1950°C at a rate of 3-15°C / min for a third sintering time of 4-6 hours.

[0032] According to the present invention, the cooling conditions include: cooling to 1400°C at a rate of 3-10°C / min, and then cooling from 1400°C to room temperature at a natural cooling rate.

[0033] A second aspect of the present invention provides a silicon nitride ceramic produced by the aforementioned preparation method.

[0034] A third aspect of the present invention provides an application of the aforementioned silicon nitride ceramic in the fields of aerospace, wind power generation, and new energy vehicles.

[0035] In the present invention, when silicon nitride ceramics are used in specific applications, typically but not limitedly, the silicon nitride ceramics can be first packaged into a device and then used.

[0036] The technical solution of the present invention has the following advantages:

[0037] 1. The present invention provides a method for preparing silicon nitride ceramics, wherein the preparation method comprises the following steps: S1, mixing α-Si3N4, silicon powder, sintering aid, dispersant, and solvent, and performing a first ball milling to obtain slurry A; S2, mixing slurry A, a binder, and a plasticizer, and performing a second ball milling to obtain slurry B; S3, tape-casting slurry B, sintering, and cooling to obtain silicon nitride ceramics; wherein the sintering aid comprises magnesium silicon nitride and rare earth oxide. The sintering conditions include: heating to 1100-1300°C at a rate of 5-30°C / min for a first sintering period of 1-6 hours, heating to 1400-1450°C at a rate of 0.1-10°C / min for a second sintering period of 2-5 hours, and heating to 1750-1950°C at a rate of 3-20°C / min for a third sintering period of 3-8 hours. The silicon nitride ceramics prepared by the present invention have high density and can take into account both thermal conductivity and mechanical properties. Compared with other crystal forms of Si3N4 (such as β-Si3N4), α-Si3N4 has higher sintering activity and the material density obtained after sintering is higher; α-Si3N4 and silicon powder can promote nitridation reaction, optimize material structure, and improve density. The use of the two together can also reduce the process requirements for sintering temperature and pressure, and reduce energy consumption; magnesium silicon nitride can reduce the oxygen content of the product. The inventor accidentally discovered that when magnesium silicon nitride and rare earth oxides are selected as sintering aids, the two can synergistically react with impurities on the surface of α-Si3N4 to generate a low-melting-point liquid phase. In the early stage of sintering, the liquid phase infiltrates α-Si3N4, making it easier for α-Si3N4 to move and rearrange, reducing porosity and achieving initial densification of the material; the first sintering can form The skeleton is formed and organic matter is excluded to achieve the initial densification of the material; the second sintering can melt the sintering aid to form a low-viscosity liquid phase, promote the movement and rearrangement of α-Si3N4, and reduce the closed porosity; the third sintering can promote crystal growth and close stacking to achieve complete densification of the material; at the same time, S1, α-Si3N4, silicon powder, sintering aid, dispersant, and solvent are mixed and ball-milled for the first time to obtain slurry A; S2, slurry A, binder and plasticizer are ball-milled for the second time to obtain slurry B; the first ball milling makes the raw materials more evenly dispersed, and the second ball milling solves the bonding and molding problems. By adding in steps and ball milling twice, the raw materials are prevented from affecting each other, the uniformity is improved, the differences caused by component segregation in local areas are avoided, and the density of silicon nitride ceramics is improved.

[0038] 2. In the present invention, the specific mass ratio of magnesium silicon nitride to rare earth oxide can optimize the material structure, make atomic diffusion and material migration smoother, and more effectively fill the pores inside the green body during the sintering process, thereby improving the density of silicon nitride ceramics and further optimizing the mechanical properties and thermal conductivity of silicon nitride ceramics.

[0039] 3. In the present invention, the specific oxygen content of silicon powder can further reduce phonon scattering, increase phonon free path, further adjust the density of silicon nitride ceramics, and further improve the mechanical properties and thermal conductivity of silicon nitride ceramics.

[0040] 4. In the present invention, the specific mass ratio of α-Si3N4, silicon powder, sintering aid, and dispersant can further make the substances evenly dispersed, prepare uniform and stable silicon nitride ceramics, and improve the density of silicon nitride ceramics.

[0041] 5. In the present invention, the specific mass ratio of α-Si3N4, binder and plasticizer can further improve the density of silicon nitride ceramics.

[0042] 6. In the present invention, the specific cooling conditions can further adjust the microstructure of the silicon nitride ceramic, thereby further improving the mechanical properties and thermal conductivity of the silicon nitride ceramic. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0044] Figure 1 is an electron microscope image of the silicon nitride ceramic of Example 1;

[0045] Figure 2 is an electron microscope image of the silicon nitride ceramic of Example 2;

[0046] Figure 3 This is an electron microscope image of the silicon nitride ceramic of Comparative Example 1. DETAILED DESCRIPTION

[0047] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0048] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0049] The viscosity was tested using a rotational viscometer;

[0050] The purity of α-Si3N4 powder is 95%;

[0051] The purity of silicon powder is 99.5%; the oxygen content of silicon powder is based on the mass of silicon powder;

[0052] The weight average molecular weight of polyvinyl butyral is 30,000 g / mol.

[0053] Example 1

[0054] This embodiment provides a method for preparing silicon nitride ceramics, comprising the following steps:

[0055] S1, mixing α-Si3N4 powder with a median particle size of 0.8 μm, silicon powder with a median particle size of 2 μm and an oxygen content of 0.3 wt%, magnesium silicon nitride powder with a median particle size of 1.2 μm, and gadolinium oxide powder with a median particle size of 1 μm, adding castor oil, and then adding anhydrous ethanol, wherein the mass ratio of α-Si3N4 powder, silicon powder, sintering aid (magnesium silicon nitride powder and gadolinium oxide powder), castor oil, and anhydrous ethanol is 100:74.1:12.9:3.3:166.6; the mass ratio of magnesium silicon nitride powder to gadolinium oxide powder is 1:1.14; performing the first ball milling at a speed of 380 r / min, a temperature of 25° C., and a time of 12 h to obtain slurry A;

[0056] S2, mixing slurry A obtained in S1, polyvinyl butyral, and diisobutyl phthalate, wherein the mass ratio of α-Si3N4 powder, polyvinyl butyral, and diisobutyl phthalate is 1:0.6:0.05; performing a second ball milling at a speed of 380 r / min, a temperature of 25°C, and a time of 24 h; after the ball milling is completed, degassing under a vacuum degree of 0.05 Pa to obtain slurry B with a viscosity of 8500 mPa·s at 23°C;

[0057] S3, the slurry B is tape-casted and then dried at 25 ° C for 6 hours to obtain a green body; after cutting, the binder is removed in a debinding furnace. During the debinding process, the temperature is raised to 600 ° C at a rate of 1 ° C / h, kept at 600 ° C for 2 hours, and then cooled to room temperature to obtain a green body with a green body thickness of 560 μm; the green body is placed in a boron nitride crucible, placed in a sintering furnace with a nitrogen pressure of 6 MPa, and the temperature is raised to 1200 ° C at a rate of 15 ° C / min for the first sintering for 1 hour, and the temperature is raised to 1400 ° C at a rate of 0.1 ° C / min for the second sintering for 2 hours, and the temperature is raised to 1900 ° C at a rate of 3 ° C / min for the third sintering for 4 hours, and the temperature is lowered to 1400 ° C at a rate of 3 ° C / min. It is naturally cooled to room temperature to obtain silicon nitride ceramics; the electron microscope picture of silicon nitride ceramics is shown as follows Figure 1 As shown, from Figure 1It can be seen that the structure of silicon nitride ceramics is relatively complete, with few defects and cracks.

[0058] Example 2

[0059] This embodiment provides a method for preparing silicon nitride ceramics, comprising the following steps:

[0060] S1, α-Si3N4 powder with a median particle size of 0.8 μm, silicon powder with a median particle size of 2 μm and an oxygen content of 0.5 wt%, magnesium silicon nitride powder with a median particle size of 1.2 μm, yttrium oxide powder with a median particle size of 1 μm, and ytterbium oxide powder with a median particle size of 1 μm are mixed, triolein and triethyl phosphate are added, and then anhydrous ethanol is added, wherein the α-Si3N4 powder, silicon powder, sintering aids (magnesium silicon nitride powder, The mass ratio of yttrium oxide powder and ytterbium oxide powder), dispersant (triolein and triethyl phosphate in a mass ratio of 1:1), and anhydrous ethanol was 100:63.2:11.2:3.2:132.9; the mass ratio of magnesium silicon nitride powder and rare earth oxide (yttrium oxide powder and ytterbium oxide powder in a mass ratio of 1:1) was 1:0.77; the first ball milling was performed at a speed of 360 r / min, a temperature of 10°C, and a time of 15 hours to obtain slurry A;

[0061] S2, mixing slurry A obtained in S1, polyvinyl butyral, and diisobutyl phthalate, wherein the mass ratio of α-Si3N4 powder, polyvinyl butyral, and diisobutyl phthalate is 1:0.61:0.05; performing a second ball milling at a speed of 360 r / min, a temperature of 40°C, and a time of 36 h; after the ball milling is completed, degassing is carried out under a vacuum degree of 0.05 Pa to obtain slurry B with a viscosity of 10100 mPa·s at 23°C;

[0062] S3, the slurry B is tape-casted and then dried at 30 ° C for 6 hours to obtain a green body; after cutting, it is debinded in a degreasing furnace. During debinding, the temperature is raised to 600 ° C at a rate of 1 ° C / h, kept at 600 ° C for 2 hours, and then cooled to room temperature to obtain a green body with a green body thickness of 520 μm; the green body is placed in a boron nitride crucible, placed in a sintering furnace with a nitrogen pressure of 6 MPa, and heated to 1300 ° C at a rate of 15 ° C / min for the first sintering for 1 hour, heated to 1400 ° C at a rate of 0.1 ° C / min for the second sintering for 2 hours, heated to 1900 ° C at a rate of 3 ° C / min for the third sintering for 4 hours, cooled to 1400 ° C at a rate of 3 ° C / min, and naturally cooled to room temperature to obtain silicon nitride ceramics; the electron microscope picture of silicon nitride ceramics is as follows Figure 2 As shown, from Figure 2 The structure of silicon nitride ceramics is relatively complete, and the number of defects, cracks and holes is still within an acceptable range.

[0063] Example 3

[0064] This embodiment provides a method for preparing silicon nitride ceramics, comprising the following steps:

[0065] S1, α-Si3N4 powder with a median particle size of 0.8 μm, silicon powder with a median particle size of 2 μm and an oxygen content of 0.7 wt%, magnesium silicon nitride powder with a median particle size of 1.2 μm, ytterbium oxide powder with a median particle size of 1 μm, yttrium oxide powder with a median particle size of 1.2 μm, and scandium oxide powder with a median particle size of 1.1 μm are mixed, triolein and triethyl phosphate are added, and then anhydrous ethanol is added, wherein the α-Si3N4 powder, silicon powder, sintering aid (silicon nitride) The mass ratio of magnesium powder, ytterbium oxide powder, yttrium oxide powder, and scandium oxide powder), dispersant (triolein and triethyl phosphate in a mass ratio of 1:1), and anhydrous ethanol is 100:178.8:18:6.2:322.8; the mass ratio of magnesium silicon nitride powder and rare earth oxide (ytterbium oxide powder, yttrium oxide powder, and scandium oxide powder in a mass ratio of 1:1:1) is 1:1.21; the first ball milling is performed at a speed of 360 r / min, a temperature of 40°C, and a time of 12 hours to obtain slurry A;

[0066] S2, mixing slurry A obtained in S1, polyvinyl butyral, and diisobutyl phthalate, wherein the mass ratio of α-Si3N4 powder, polyvinyl butyral, and diisobutyl phthalate is 1:1.15:0.11; performing a second ball milling at a speed of 360 r / min, a temperature of 40°C, and a time of 24 h; after the ball milling is completed, degassing is carried out under a vacuum degree of 0.05 Pa to obtain slurry B with a viscosity of 9200 mPa·s at 23°C;

[0067] S3, the slurry B is tape-cast and then dried at 40 ° C for 6 hours to obtain a green body; after cutting, the binder is removed in a debinding furnace. During the debinding process, the temperature is raised to 600 ° C at a rate of 1 ° C / h, and after being kept at 600 ° C for 2 hours, it is cooled to room temperature to obtain a green body with a thickness of 440 μm; the green body is placed in a boron nitride crucible, and placed in a sintering furnace with a nitrogen pressure of 3 MPa, and the temperature is raised to 1200 ° C at a rate of 10 ° C / min for the first sintering for 2 hours, and the temperature is raised to 1400 ° C at a rate of 0.1 ° C / min for the second sintering for 3 hours, and the temperature is raised to 1920 ° C at a rate of 3 ° C / min for the third sintering for 8 hours, and the temperature is lowered to 1450 ° C at a rate of 2 ° C / min. It is naturally cooled to room temperature to obtain silicon nitride ceramics.

[0068] Example 4

[0069] This embodiment provides a method for preparing silicon nitride ceramics, comprising the following steps:

[0070] The method of Example 1 is the same, except that in step S1, the mass ratio of magnesium silicon nitride powder to gadolinium oxide powder is 1:4.

[0071] Example 5

[0072] This embodiment provides a method for preparing silicon nitride ceramics, comprising the following steps:

[0073] The method of Example 1 is the same, except that in step S1, the oxygen content of the silicon powder is 0.5 wt % based on the mass of the silicon powder.

[0074] Example 6

[0075] This embodiment provides a method for preparing silicon nitride ceramics, comprising the following steps:

[0076] The method of Example 1 is the same, except that in step S1, the mass ratio of α-Si3N4 powder, silicon powder, sintering aid (magnesium silicon nitride powder and gadolinium oxide powder in a mass ratio of 1:1.14), castor oil, and anhydrous ethanol is 100:120:20:7:300.

[0077] Example 7

[0078] This embodiment provides a method for preparing silicon nitride ceramics, comprising the following steps:

[0079] The method of Example 1 is the same, except that in step S2, the mass ratio of α-Si3N4 powder, polyvinyl butyral, and diisobutyl phthalate is 1:0.7:0.07.

[0080] Example 8

[0081] This embodiment provides a method for preparing silicon nitride ceramics, comprising the following steps:

[0082] The method of Example 1 is the same, except that, in step S3, the method of "raising the temperature to 1200°C at a rate of 15°C / min for the first sintering for 1 hour, raising the temperature to 1400°C at a rate of 0.1°C / min for the second sintering for 2 hours, and raising the temperature to 1900°C at a rate of 3°C / min for the third sintering for 4 hours" is changed to "raising the temperature to 1300°C at a rate of 10°C / min for the first sintering for 6 hours, raising the temperature to 1400°C at a rate of 10°C / min for the second sintering for 2 hours, and raising the temperature to 1750°C at a rate of 20°C / min for the third sintering for 6 hours".

[0083] Example 9

[0084] This embodiment provides a method for preparing silicon nitride ceramics, comprising the following steps:

[0085] The method of Example 1 is the same, except that “cooling to 1400° C. at a rate of 3° C. / min and naturally cooling to room temperature” is changed to “naturally cooling to room temperature”.

[0086] Comparative Example 1

[0087] This comparative example provides a method for preparing silicon nitride ceramics, comprising the following steps:

[0088] According to the method of Example 4, the difference is that α-Si3N4 is replaced with β-Si3N4 of equal mass. The electron microscope image of silicon nitride ceramic is as follows: Figure 3 As shown, from Figure 3 It can be seen that due to the insufficient density of silicon nitride ceramics, the material is loose and there are a large number of obvious defects on the surface.

[0089] Comparative Example 2

[0090] This comparative example provides a method for preparing silicon nitride ceramics, comprising the following steps:

[0091] The method of Example 4 is the same as that of Example 4, except that in step S1, the α-Si3N4 powder is replaced with silicon powder of equal mass, and the mass ratio of silicon powder, sintering aid, castor oil and anhydrous ethanol is 174.1:12.9:3.3:166.6.

[0092] Comparative Example 3

[0093] This comparative example provides a method for preparing silicon nitride ceramics, comprising the following steps:

[0094] The method of Example 4 is the same as that of Example 4, except that in step S1, the silicon powder is replaced with α-Si3N4 of equal mass, and the mass ratio of α-Si3N4 powder, sintering aid, castor oil and anhydrous ethanol is 174.1:12.9:3.3:166.6.

[0095] Comparative Example 4

[0096] This comparative example provides a method for preparing silicon nitride ceramics, comprising the following steps:

[0097] The method of Example 5 is the same as that of Example 5, except that in step S1, magnesium silicon nitride is replaced with aluminum nitride of equal mass, and the total mass of the sintering aid remains unchanged.

[0098] Comparative Example 5

[0099] This comparative example provides a method for preparing silicon nitride ceramics, comprising the following steps:

[0100] The method of Example 5 is the same as that of Example 5, except that in step S1, the gadolinium oxide powder is replaced with magnesium silicon nitride powder of the same mass, and the total mass of the sintering aid remains unchanged.

[0101] Comparative Example 6

[0102] This comparative example provides a method for preparing silicon nitride ceramics, comprising the following steps:

[0103] The method of Example 1 is the same, except that in step S3, the green body is heated to 1900°C at a rate of 15°C / min in a sintering furnace with a nitrogen pressure of 6 MPa and sintered for 7 hours, then cooled to 1400°C at a rate of 3°C / min and naturally cooled to room temperature.

[0104] Comparative Example 7

[0105] The method of Example 1 is the same, except that in step S3, the green body is heated to 1400°C at a rate of 15°C / min in a sintering furnace with a nitrogen pressure of 6 MPa for a first sintering for 0.5 h, then heated to 1620°C at a rate of 20°C / min for a second sintering for 2 h, and then heated to 1850°C at a rate of 5°C / min for a third sintering for 4 h.

[0106] Comparative Example 8

[0107] The method of Example 1 is the same, except that in step S3, the green body is heated to 900°C at a rate of 15°C / min in a sintering furnace with a nitrogen pressure of 6 MPa for the first sintering for 8 hours, then heated to 1200°C at a rate of 0.05°C / min for the second sintering for 2 hours, and then heated to 2000°C at a rate of 5°C / min for the third sintering for 4 hours.

[0108] Test Case

[0109] (1) Density test method: The density of the silicon nitride ceramics in the examples and comparative examples was calculated by dividing the bulk density by the theoretical density. The bulk density was measured by the Archimedean drainage method, and the average value was obtained by three tests.

[0110] The specific test results are shown in Table 1;

[0111] Table 1 Density of silicon nitride ceramics

[0112]

[0113] (2) The flexural strength was tested by a three-point bending test, specifically comprising: testing the silicon nitride ceramics of the embodiment and the comparative example with a size of 23×40 mm in a universal testing machine, recording the maximum load value measured, and calculating the flexural strength, using the standard GB / T 6569-2006;

[0114] The fracture toughness was tested by indentation method, using the standard GB / T 44304-2024;

[0115] Thermal conductivity characterizes thermal conductivity, and the standard adopted is GB / T 22588-2008;

[0116] The specific test results are shown in Table 2;

[0117] Table 2 Mechanical properties and thermal conductivity of silicon nitride ceramics

[0118]

[0119] The silicon nitride ceramics of Comparative Examples 1-8 have acceptable flexural strength, but low thermal conductivity, and cannot provide a balance between thermal conductivity and mechanical properties.

[0120] Comparing Example 1 with Example 4, it can be seen that the specific mass ratio of magnesium silicon nitride and rare earth oxide can optimize the material structure, make atomic diffusion and material migration smoother, and more effectively fill the pores inside the green body during the sintering process, thereby improving the density of the silicon nitride ceramic, and further optimizing the mechanical properties and thermal conductivity of the silicon nitride ceramic.

[0121] Comparing Example 1 with Example 5, it can be seen that the specific oxygen content of silicon powder can further reduce phonon scattering, increase phonon free path, further adjust the density of silicon nitride ceramics, and further improve the thermal conductivity of silicon nitride ceramics.

[0122] Comparing Example 1 with Example 6, it can be seen that the specific mass ratio of α-Si3N4, silicon powder, sintering aid, and dispersant can further evenly disperse the substances, prepare uniform and stable silicon nitride ceramics, and improve the density of silicon nitride ceramics.

[0123] Comparing Example 1 with Example 7, it can be seen that the specific mass ratio of α-Si3N4, binder, and plasticizer can further improve the density of silicon nitride ceramics.

[0124] Comparing Example 1 with Example 9, it can be seen that the specific cooling conditions can further adjust the microstructure of the ceramic, thereby further improving the mechanical properties and thermal conductivity of the silicon nitride ceramic.

[0125] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing silicon nitride ceramics, characterized in that: The preparation method comprises the following steps: S1, α-Si3N4, silicon powder, sintering aid, dispersant, and solvent are mixed and ball-milled for the first time to obtain slurry A; S2, mixing slurry A, a binder, and a plasticizer, and performing a second ball milling to obtain slurry B; S3, tape-casting the slurry B, sintering, and cooling to obtain silicon nitride ceramics; Wherein, the sintering aid includes magnesium silicon nitride and rare earth oxide; The mass ratio of the α-Si3N4, silicon powder, sintering aid, dispersant and solvent is 100:(60-75):(10-18):(0.5-5):(80-200); The sintering conditions include: heating to 1100-1300°C at a rate of 5-30°C / min for a first sintering of 1-6 hours, heating to 1400-1450°C at a rate of 0.1-10°C / min for a second sintering of 2-5 hours, and heating to 1750-1950°C at a rate of 3-20°C / min for a third sintering of 3-8 hours.

2. The preparation method according to claim 1, characterized in that The mass ratio of the magnesium silicon nitride to the rare earth oxide is 1:(0.5-6); And / or, based on the mass of the silicon powder, the oxygen content of the silicon powder is 0.05-0.7 wt %.

3. The preparation method according to claim 2, characterized in that The mass ratio of the magnesium silicon nitride to the rare earth oxide is 1:(0.7-3).

4. The preparation method according to claim 2, characterized in that Based on the mass of the silicon powder, the oxygen content of the silicon powder is 0.05-0.2 wt %.

5. The preparation method according to claim 1, characterized in that The mass ratio of the α-Si3N4, binder and plasticizer is 1:(0.3-0.7):(0.03-0.07).

6. The preparation method according to claim 5, characterized in that The mass ratio of the α-Si3N4, binder and plasticizer is 1:(0.3-0.5):(0.03-0.05).

7. The preparation method according to claim 1, characterized in that The sintering conditions include: heating to 1200-1250°C at a rate of 15-20°C / min for a first sintering period of 1-4 hours, heating to 1420-1450°C at a rate of 0.1-5°C / min for a second sintering period of 2-5 hours, and heating to 1770-1950°C at a rate of 3-15°C / min for a third sintering period of 4-6 hours. And / or, the cooling conditions include: cooling to 1400° C. at a rate of 3-10° C. / min, and cooling to room temperature.

8. A silicon nitride ceramic prepared by the preparation method according to any one of claims 1 to 7.

9. Application of the silicon nitride ceramic according to claim 8 in the fields of aerospace, wind power generation, and new energy vehicles.

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