Green preparation method of silicon nitride ceramic

Abstract

The invention discloses a green preparation method of silicon nitride ceramic, and belongs to the technical field of silicon nitride preparation. The method comprises the following steps: carrying out dry mixing on silicon powder and a sintering aid to obtain mixed powder; preparing the mixed powder into a biscuit; carrying out nitridation reaction on the biscuit to obtain a nitrided material; and sintering the nitrided material in a nitrogen atmosphere to obtain the silicon nitride ceramic. Wherein when the particle size of the silicon powder does not exceed 3 microns, the mixed powder is directly subjected to cold isostatic pressing to prepare a biscuit; when the particle size of the silicon powder exceeds 3 microns, carrying out dry sanding on the mixed powder and then carrying out cold isostatic pressing to prepare a biscuit; the preparation method is simple, easy to operate and low in cost, drying and glue discharging are not carried out in the preparation process, and compared with a traditional wet ball milling mode, the product production period is shortened, and the energy consumption cost is saved. In addition, the preparation method avoids the use of an organic solvent or an organic binder, thereby avoiding the pollution to the environment in the glue discharging process and realizing clean zero carbon emission.

Description

Technical Field

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

[0002] Silicon nitride (Si3N4) is one of the most important fine ceramic materials. Silicon nitride ceramics have excellent properties such as low density, high hardness, high strength, high toughness, high thermal conductivity, high wear resistance, high insulation, high weather resistance, low thermal expansion coefficient and good biocompatibility. They are widely used in chemical metallurgy (such as ceramic sleeves, melting crucibles), mechanical industry (such as bearing balls, sealing rings), semiconductors (such as heat dissipation ceramic substrates for power modules), aerospace (such as wave-transmitting materials), biomedicine (such as artificial joints) and other fields. However, the high cost has always been an important reason restricting the widespread application of high-performance silicon nitride ceramics.

[0003] According to the raw materials used, the preparation methods of silicon nitride ceramics can be divided into two types: direct sintering (Sintering of Si3N4 powder compacts, SSN) and reaction-bonded sintering (Sintered reaction-bonded Si3N4, SRBSN). Compared with the SSN method, the SRBSN method is considered to be the most promising preparation method for low-cost, high-performance silicon nitride ceramics because of its advantages such as cheap silicon powder raw materials, 60% nitriding weight gain, easy processing of RBSN and lower sintering shrinkage.

[0004] In the SRBSN method, in order to promote the nitridation and later sintering of the silicon powder blank, in addition to reducing the particle size of the raw silicon powder, it is also necessary to add a nitridation promoter or a sintering aid. In order to obtain a mixed powder, water or ethanol is usually used as a mixing medium (solvent), and a drum ball mill or a planetary ball mill is used for ball milling to achieve a uniform mixing of the raw silicon powder and additives such as sintering aids. Then use rotary evaporation or spray granulation to dry. In addition, in order to improve the compression behavior of the mixed powder and increase the strength of the blank, it is usually necessary to add organic polymers such as polyvinyl alcohol (PVA) or polyvinyl butyral (PVB) as a binder to the ball milling medium.

[0005] However, water as a ball-milling medium will cause oxidation of silicon powder and hinder the nitridation reaction of silicon powder and damage the performance of the final material. In addition, the use of binders will introduce a debinding process, which will not only cause environmental problems but also increase energy consumption costs.

[0006] In view of this, the present invention is proposed. Summary of the invention

[0007] The purpose of the present invention includes providing a green preparation method of silicon nitride ceramics to solve or improve the above technical problems.

[0008] The present invention can be implemented like this:

[0009] In a first aspect, the present invention provides a green preparation method of silicon nitride ceramics, comprising the following steps:

[0010] The silicon powder is mixed with a sintering aid by a dry method to obtain a mixed powder; the mixed powder is made into a green blank; the green blank is subjected to a nitriding reaction to obtain a nitrided material; the nitrided material is sintered in a nitrogen atmosphere to obtain a silicon nitride ceramic;

[0011] Among them, when the particle size of the silicon powder does not exceed 3μm, the mixed powder is directly subjected to cold isostatic pressing to form a blank; when the particle size of the silicon powder exceeds 3μm, the mixed powder is first dry-grinded to make the particle size of the silicon powder not exceed 3μm; then the dry-grinded mixed powder is cold isostatically pressed to form a blank.

[0012] In an optional embodiment, the average particle size of the silicon powder does not exceed 45 μm.

[0013] In an optional embodiment, the molar ratio of the sintering aid to the silicon powder is 1:99 to 10:90.

[0014] In an alternative embodiment, the sintering aid includes metal oxides and rare earth oxides.

[0015] In an alternative embodiment, the metal oxide includes at least one of Li2O, MgO, Al2O3, TiO2 and ZrO2.

[0016] In an alternative embodiment, the rare earth oxide includes at least one of Y2O3, CeO2, La2O3, Nd2O3, Sm2O3 and Lu2O3.

[0017] In an alternative embodiment, the sintering aid is a mixture of yttrium oxide and aluminum oxide, or the sintering aid is a mixture of yttrium oxide and magnesium oxide.

[0018] In an optional embodiment, dry sanding includes at least one of the following features:

[0019] Feature 1: Dry sand grinding is carried out in a closed and nitrogen-protected environment;

[0020] Feature 2: The mixed powder is first mixed with a grinding aid and then dry-grinded.

[0021] In an alternative embodiment, the grinding aid comprises at least one of ethanol, ethylene glycol, triethanolamine and stearic acid.

[0022] In an optional embodiment, the amount of grinding aid added is 0.1 wt% to 1.5 wt% of the mixed powder.

[0023] In an optional embodiment, the pressure of cold isostatic pressing is 150 MPa to 500 MPa.

[0024] In an optional embodiment, the nitridation reaction includes at least one of the following features:

[0025] Feature 3: The temperature of the nitriding reaction is 1300℃~1500℃;

[0026] Feature 4: The nitridation reaction time is 8h to 120h;

[0027] Feature 5: During the nitridation reaction, the flow rate of nitrogen is 0.5L / min to 20L / min.

[0028] In an optional embodiment, sintering includes at least one of the following features:

[0029] Feature 6: The sintering temperature is 1800℃~2000℃;

[0030] Feature 7: The nitrogen pressure during the sintering process is 0.1MPa~10MPa.

[0031] The beneficial effects of the present invention include:

[0032] The preparation method of silicon nitride ceramics provided by the present invention is simple, easy to operate, and low in cost. No drying process and debinding process are performed during the preparation process. Compared with the traditional wet ball milling method, it not only shortens the product production cycle, but also saves energy consumption costs. In addition, the preparation method avoids the use of organic solvents or organic binders, thereby avoiding the pollution to the environment caused by the debinding process, and realizing the green preparation of silicon nitride ceramics with net zero carbon emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0034] Figure 1 The present invention provides a flow chart of the green preparation method of silicon nitride ceramics. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0036] The green preparation method of silicon nitride ceramics provided by the present invention is specifically described below.

[0037] The present invention provides a green preparation method of silicon nitride ceramics. Figure 1 , comprising the following steps: dry-mixing silicon powder and a sintering aid to obtain a mixed powder; making the mixed powder into a green blank; subjecting the green blank to a nitriding reaction to obtain a nitrided material; sintering the nitrided material in a nitrogen atmosphere to obtain a silicon nitride ceramic;

[0038] Among them, when the particle size of the silicon powder does not exceed 3μm, the mixed powder is directly subjected to cold isostatic pressing to form a blank; when the particle size of the silicon powder exceeds 3μm, the mixed powder is first dry-grinded to make the particle size of the silicon powder not exceed 3μm; then the dry-grinded mixed powder is cold isostatically pressed to form a blank.

[0039] In some optional embodiments, the average particle size of the silicon powder does not exceed 45 μm. The purity of the silicon powder is preferably not less than 98%.

[0040] In some optional embodiments, the molar ratio of the sintering aid to the silicon powder can be 1:99 to 10:90, such as 1:99, 2:98, 3:97, 4:96, 5:95, 6:94, 7:93, 8:92, 9:91 or 10:90, or other values ​​within the range of 1:99 to 10:90. In some typical embodiments, the molar ratio of the sintering aid to the silicon powder is 7:93 to 8:92.

[0041] The sintering aid forms a liquid phase during the high-temperature melting process, which is beneficial to promote the rearrangement and densification of silicon nitride particles. If the amount of sintering aid is too little, it is not conducive to obtaining high-density silicon nitride; if the amount of sintering aid is too much, it is easy to cause material deformation and performance degradation, such as thermal conductivity, high-temperature performance, etc.

[0042] In some alternative embodiments, the sintering aid includes metal oxides and rare earth oxides.

[0043] The metal oxide may include at least one of Li2O, MgO, Al2O3, TiO2 and ZrO2, and the above metal oxides can promote the densification of silicon nitride more than calcium oxide or barium oxide. The rare earth oxide may include at least one of Y2O3, CeO2, La2O3, Nd2O3, Sm2O3 and Lu2O3. In some preferred embodiments, the sintering aid is a mixture of yttrium oxide and aluminum oxide, or the sintering aid is a mixture of yttrium oxide and magnesium oxide.

[0044] As an example, in the sintering aid, the molar ratio of the metal oxide to the rare earth oxide may be 2:5 to 3:5. For example, the sintering aid may include yttrium oxide and aluminum oxide in a molar ratio of 2:5, or include yttrium oxide and magnesium oxide in a molar ratio of 5:3.

[0045] In some optional embodiments, the purity of the rare earth oxide is not less than 99%, and the average particle size is preferably controlled to be no more than 3 μm, such as about 1 μm. The purity of the metal oxide is not less than 99%, and the average particle size is preferably controlled to be no more than 3 μm, such as about 0.5 μm. Controlling the average particle size of the rare earth oxide and the metal oxide to no more than 3 μm is more conducive to grinding the silicon source during the dry sand milling process, thereby increasing the relative density of the green blank.

[0046] In some optional embodiments, dry mixing can be performed using mixing equipment commonly used in industry, such as a double-motion mixer, a double-motion flying knife mixer, a three-dimensional motion mixer, a V-type mixer, or a double-cone mixer.

[0047] In the present invention, dry sand milling is performed in a closed nitrogen-protected environment to prevent oxidation of silicon powder during the sand milling process.

[0048] In some optional embodiments, the number of sanding may be only 1 time; in some other optional embodiments, the number of sanding may be 2 times, 3 times, 4 times or more times. The number of sanding is set according to the actual situation, and the particle size of the silicon powder after sanding does not exceed 3 μm.

[0049] Preferably, the mixed powder is first mixed with a grinding aid and then dry-grinded.

[0050] Wherein, the grinding aid can include at least one of ethanol, ethylene glycol, triethanolamine and stearic acid. The addition amount of the grinding aid can be 0.1wt% to 1.5wt% of the mixed powder, such as 0.1wt%, 0.2wt%, 0.5wt%, 0.8wt%, 1.0wt%, 1.2wt% or 1.5wt%, or other values ​​within the scope of 0.1wt% to 1.5wt%. In the present invention, the amount of the grinding aid is small, and it only plays a grinding aid effect, which is different from the method of using ethanol as a solvent in traditional wet ball milling.

[0051] The grinding beads used in the dry sand grinding process can be exemplified but not limited to zirconium oxide beads or silicon nitride beads, and the particle size of the grinding beads is preferably not more than 5 mm, such as 3 mm.

[0052] After dry sand grinding, the particle size of the silicon powder in the obtained powder does not exceed 3 μm, so as to avoid the silicon powder particle size being too large, resulting in the formation of a coarse structure after nitridation, and then resulting in poor densification effect after sintering.

[0053] It should be noted that the present invention creatively performs dry sand grinding on the mixed powder after dry mixing, combines the use of grinding aids and controls the particle size of the silicon powder after dry sand grinding. On the one hand, it omits the drying process and debinding process in the traditional wet ball milling process, which not only shortens the product production cycle, but also saves energy consumption costs. The greatly reduced cost helps to accelerate the widespread application of silicon nitride ceramic materials. On the other hand, through the dry sand grinding process of silicon powder, the use of organic solvents or organic binders is eliminated, thereby eliminating the pollution to the environment caused by burning organic binders (debinding), and achieving net zero carbon emissions.

[0054] In some optional embodiments, the pressure of cold isostatic pressing can be 150MPa to 500MPa, such as 150MPa, 200MPa, 250MPa, 300MPa, 350MPa, 400MPa, 450MPa or 500MPa, or other values ​​within the range of 150MPa to 500MPa.

[0055] In some optional embodiments, the dry sand-milled mixed powder (which may be referred to as "sand-milled powder") may be preformed first, and then cold isostatically pressed. Preforming may be performed, for example, in the following manner: the dry sand-milled mixed powder is placed in a mold, and the mold is evacuated under vacuum conditions. In addition, preforming may also be performed in the following manner: the dry sand-milled mixed powder is placed in a mold, and the mold is pre-pressed (the pre-pressing pressure may be set according to actual needs).

[0056] In the present invention, the green billet can be directly subjected to nitridation reaction, or the green billet can be first processed and then subjected to nitridation reaction according to the shape and size of the product.

[0057] In some optional embodiments, the temperature of the nitridation reaction may be 1300° C. to 1500° C., such as 1300° C., 1350° C., 1400° C., 1450° C. or 1500° C., or other values ​​within the range of 1300° C. to 1500° C. In some typical embodiments, the temperature of the nitridation reaction is 1400° C.

[0058] In some optional embodiments, the nitridation reaction time can be 8 h to 120 h, such as 8 h, 12 h, 24 h, 48 h, 96 h, 100 h, 108 h or 120 h, etc., or other values ​​within the range of 8 h to 120 h. In some typical embodiments, the nitridation reaction time is 8 h.

[0059] In some optional embodiments, during the nitridation reaction, the flow rate of nitrogen can be 0.5 L / min to 20 L / min, such as 0.5 L / min, 1 L / min, 2 L / min, 3 L / min, 4 L / min, 5 L / min, 6 L / min, 7 L / min, 8 L / min, 9 L / min, 10 L / min, 11 L / min, 12 L / min, 13 L / min, 14 L / min, 15 L / min, 16 L / min, 17 L / min, 18 L / min, 19 L / min or 20 L / min, or other values ​​within the range of 0.5 L / min to 20 L / min.

[0060] If the nitrogen flow rate is less than 0.5L / min, the nitriding speed will be slow, the nitriding reaction time will be prolonged, and the energy consumption will be increased; if the nitrogen flow rate is greater than 20L / min, the nitrogen flow rate on the sample surface will be too high, thereby hindering the diffusion of nitrogen from the sample surface to the inside, thereby slowing down the nitriding speed. In addition, a larger nitrogen flow rate will increase the nitrogen consumption, thereby increasing the cost of nitrogen use.

[0061] In the present invention, the nitrided material can be directly sintered, or it can be processed first and then sintered according to the shape and size of the product.

[0062] In some optional embodiments, the sintering temperature may be 1800° C. to 2000° C., such as 1800° C., 1850° C., 1900° C., 1950° C. or 2000° C., or other values ​​within the range of 1800° C. to 2000° C. In some typical embodiments, the sintering temperature is 1900° C.

[0063] The nitrogen pressure during the sintering process can be 0.1 MPa to 10 MPa, such as 0.1 MPa, 0.5 MPa, 1 MPa, 2 MPa, 3 MPa, 4 MPa, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa or 10 MPa, etc., or other values ​​within the range of 0.1 MPa to 10 MPa. In some typical embodiments, the nitrogen pressure during gas pressure sintering is 1 MPa.

[0064] If the sintering temperature is 1800°C, the nitrogen pressure should not be lower than 0.1MPa, otherwise it will cause decomposition of silicon nitride; if the sintering temperature is 1900°C, the nitrogen pressure should not be lower than 1MPa, otherwise it will cause decomposition of silicon nitride; if the sintering temperature is 2000°C, the nitrogen pressure should not be lower than 10MPa, otherwise it will cause decomposition of silicon nitride.

[0065] In the present invention, the relative density of the prepared silicon nitride product is not less than 95%, such as 95%, 96%, 97%, 98% or 99%.

[0066] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0067] Example 1

[0068] This embodiment provides a green preparation method of silicon nitride ceramics, comprising the following steps:

[0069] According to the molar ratio of Si3N4, Y2O3 and Al2O3 after nitridation of 93:5:2, Si powder (purity 99.9%, particle size D 50 =8μm), Y2O3 powder (purity 99%, particle size D 50 =1μm) and Al2O3 powder (purity 99%, particle size D 50 =0.5μm) totaling 500g was put into a three-dimensional mixer, and 5g of anhydrous ethanol was added for thorough mixing. Then, zirconia beads with a diameter of 3mm were used in a 1L sand mill for sand grinding, and the number of sand grinding times was 2 times. The above sand grinding process was carried out in a closed and nitrogen-protected environment, the sand grinding speed was 960rpm, and the sand grinding time for each time was 1min to obtain sand grinding powder. 4.5g of the sand grinding powder was placed in a stainless steel mold with a diameter of 20mm, and then pre-pressed in a tablet press with a uniaxial pressure of 30MPa to obtain a pre-pressed blank; then the pre-pressed blank was cold isostatically pressed at 200MPa to obtain the final blank. The final blank obtained was placed in a boron nitride crucible, and then placed in an alumina tube furnace, and kept warm for 8h at a nitrogen flow rate of 1L / min and a temperature of 1400°C to obtain a nitrided material. The nitride material is then placed in a boron nitride crucible and placed in a graphite gas pressure sintering furnace, and the temperature is raised to 1900°C and kept at this temperature for 6 hours under a nitrogen pressure of 1 MPa; after sintering, the furnace is cooled to room temperature, and the sintered sample is taken out, which is silicon nitride ceramics.

[0070] Example 2

[0071] The difference between this embodiment and embodiment 1 is that the number of sanding times is 3 times.

[0072] Example 3

[0073] The difference between this embodiment and embodiment 1 is that the number of sanding times is 4 times.

[0074] Example 4

[0075] The difference between this embodiment and embodiment 1 is that the particle size D of Si powder is 50 5μm.

[0076] Example 5

[0077] The difference between this embodiment and embodiment 2 is that: according to the molar ratio of Si3N4, Y2O3 and MgO after nitridation being 92:5:3, Si powder (purity 99.9%, particle size D 50 =8μm), Y2O3 powder (purity 99%, particle size D 50 =1μm) and MgO powder (purity 99%, particle size D 50 =0.5μm).

[0078] Example 6

[0079] The difference between this embodiment and embodiment 1 is that the amount of the grinding aid anhydrous ethanol is 1.5wt% of the mixed powder.

[0080] Example 7

[0081] The difference between this embodiment and embodiment 1 is that: according to the molar ratio of Si3N4, Y2O3 and MgO after nitridation being 90:5:5, Si powder (purity 99.9%, particle size D 50 =8μm), Y2O3 powder (purity 99%, particle size D 50 =1μm) and MgO powder (purity 99%, particle size D 50 =0.5 μm). The grinding aid is ethylene glycol.

[0082] Example 8

[0083] The difference between this embodiment and embodiment 1 is that: according to the molar ratio of Si3N4, La2O3 and ZrO2 after nitridation being 90:1:9, Si powder (purity 99.9%, particle size D 50 =8μm), La2O3 powder (purity 99%, particle size D 50 =1μm) and ZrO2 powder (purity 99%, particle size D 50 =0.5 μm). The grinding aid is triethanolamine.

[0084] Example 9

[0085] The difference between this embodiment and embodiment 1 is that: according to the molar ratio of Si3N4, CeO2 and TiO2 after nitridation being 99:0.5:0.5, Si powder (purity 99.9%, particle size D50 =8μm), CeO2 powder (purity 99%, particle size D 50 =1μm) and TiO2 powder (purity 99%, particle size D 50 =0.5 μm). The grinding aid is stearic acid.

[0086] Example 10

[0087] The difference between this embodiment and embodiment 1 is that the particle size of silicon powder is 3 μm, and Si powder, Y2O3 powder and Al2O3 powder are directly subjected to pre-pressing and subsequent processes after being dry-mixed.

[0088] Embodiment 11

[0089] The difference between this embodiment and embodiment 1 is that the particle size of silicon powder is 1 μm, and Si powder, Y2O3 powder and Al2O3 powder are directly subjected to pre-pressing and subsequent processes after being dry-mixed.

[0090] Comparative Example 1

[0091] The difference between this comparative example and Example 1 is that: before sand grinding, no grinding aid was used; and the sand grinding was performed only once.

[0092] Comparative Example 2

[0093] The difference between this comparative example and Example 1 is that the sanding times are only one.

[0094] Comparative Example 3

[0095] The difference between this comparative example and Example 1 is that the nitriding temperature is 1600°C.

[0096] Comparative Example 4

[0097] The difference between this comparative example and Example 1 is that the nitriding time is 5 h.

[0098] Comparative Example 5

[0099] The difference between this comparative example and Example 1 is that during the nitridation reaction, the flow rate of nitrogen is 22 L / min.

[0100] Comparative Example 6

[0101] The difference between this comparative example and Example 1 is that the sintering temperature is 1500°C.

[0102] Test example

[0103] The particle size of the sanding materials, the relative density of the green blanks, the nitriding rate, and the relative density of the sintered samples involved in the above-mentioned Examples 1 to 11 and Comparative Examples 1 to 6 are compared, and the results are shown in Table 1.

[0104] Among them, the Archimedes method is used to determine the volume density of the nitrided and sintered samples; the apparent density of the blank is calculated using the geometric size (volume) and weight of the blank, and the relative density of the blank = apparent density × 100% / theoretical density); the nitriding rate is calculated based on the weight gain before and after nitriding; the nitrided and sintered samples are subjected to X-ray diffraction analysis using a Malvern Panalytical Empyrean S3 powder X-ray diffractometer, and if no diffraction peak of silicon is detected, it means that the nitriding is complete; the relative density of the nitrided and sintered samples = volume density × 100% / theoretical density.

[0105] Table 1 Results

[0106]

[0107] It can be seen from Table 1 that the method provided by the present invention can effectively prepare silicon nitride ceramics with a density higher than 95% without using wet ball milling. In addition, the method provided by the present invention has a simple process, is easy to operate, and takes a short time, which can greatly reduce production costs and achieve net zero carbon emissions.

[0108] It can be seen from the comparison between the examples and the comparative examples that when the preparation conditions are not properly set, it is difficult to prepare silicon nitride ceramics with a density higher than 95%, that is, it is difficult to obtain silicon nitride ceramics of qualified quality.

[0109] In summary, the preparation method of silicon nitride ceramics provided by the present invention is simple, easy to operate, and has low cost. No drying process and debinding process are performed during the preparation process. Compared with the traditional wet ball milling method, it not only shortens the product production cycle, but also saves energy consumption costs. In addition, the preparation method avoids the use of organic solvents or organic binders, thereby avoiding the pollution to the environment caused by the debinding process, and realizing the green preparation of silicon nitride ceramics with net zero carbon emissions.

[0110] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A green preparation method for silicon nitride ceramics, characterized in that: The following steps are involved: Dry-mixing silicon powder and a sintering aid to obtain a mixed powder; The mixed powder is made into a green blank; the green blank is subjected to a nitriding reaction to obtain a nitrided material; the nitrided material is sintered in a nitrogen atmosphere to obtain a silicon nitride ceramic; When the particle size of the silicon powder does not exceed 3 μm, the mixed powder is directly subjected to cold isostatic pressing to form a green blank; when the particle size of the silicon powder exceeds 3 μm, the mixed powder is first subjected to dry sand grinding to make the particle size of the silicon powder not exceed 3 μm; The dry-grinded mixed powder is then cold isostatically pressed to form a green blank.

2. The green preparation method according to claim 1, characterized in that: The average particle size of the silicon powder does not exceed 45 μm.

3. The green preparation method according to claim 1, characterized in that: The molar ratio of the sintering aid to the silicon powder is 1:99 to 10:

90.

4. The green preparation method according to claim 3, characterized in that: The sintering aid includes metal oxides and rare earth oxides; Preferably, the metal oxide includes at least one of Li2O, MgO, Al2O3, TiO2 and ZrO2; Preferably, the rare earth oxide includes at least one of Y2O3, CeO2, La2O3, Nd2O3, Sm2O3 and Lu2O3; More preferably, the sintering aid is a mixture of yttrium oxide and aluminum oxide, or the sintering aid is a mixture of yttrium oxide and magnesium oxide.

5. The green preparation method according to claim 1, characterized in that: Dry sanding includes at least one of the following features: Feature 1: Dry sand grinding is carried out in a closed and nitrogen-protected environment; Feature 2: The mixed powder is first mixed with a grinding aid and then dry-grinded.

6. The green preparation method according to claim 5, characterized in that: The grinding aid includes at least one of ethanol, ethylene glycol, triethanolamine and stearic acid.

7. The green preparation method according to claim 5 or 6, characterized in that: The addition amount of the grinding aid is 0.1wt% to 1.5wt% of the mixed powder.

8. The green preparation method according to claim 1, characterized in that: The pressure of cold isostatic pressing is 150MPa~500MPa.

9. The green preparation method according to claim 1, characterized in that: The nitridation reaction includes at least one of the following characteristics: Feature 3: The temperature of the nitriding reaction is 1300℃~1500℃; Feature 4: The nitridation reaction time is 8h to 120h; Feature 5: During the nitridation reaction, the flow rate of nitrogen is 0.5L / min to 20L / min.

10. The green preparation method according to claim 1, characterized in that: Sintering includes at least one of the following features: Feature 6: The sintering temperature is 1800℃~2000℃; Feature 7: The nitrogen pressure during the sintering process is 0.1MPa~10MPa.

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