A Green Preparation Method for Silicon Nitride Ceramics

Abstract

This invention discloses a green preparation method for silicon nitride ceramics, belonging to the field of silicon nitride preparation technology. The method includes: dry mixing silicon powder with a sintering aid to obtain a mixed powder; forming a green body from the mixed powder; subjecting the green body to a nitriding reaction to obtain a nitrided material; and sintering the nitrided material in a nitrogen atmosphere to obtain silicon nitride ceramics. Specifically, 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 the green body; when the particle size of the silicon powder exceeds 3 μm, the mixed powder is first dry-milled and then cold-isostatically pressed to form the green body. This preparation method is simple, easy to operate, and low in cost. The preparation process does not involve drying or debinding, shortening the product production cycle and saving energy costs compared to traditional wet ball milling methods. Furthermore, this preparation method avoids the use of organic solvents or organic binders, thus avoiding environmental pollution caused by the debinding process and achieving net-zero carbon emissions.

Description

Technical Field

[0001] This invention relates to the field of silicon nitride preparation technology, and more specifically, to a green preparation method for silicon nitride ceramics. Background Technology

[0002] Silicon nitride (Si3N4) is one of the most important fine ceramic materials. Silicon nitride ceramics possess excellent properties such as low density, high hardness, high strength, high toughness, high thermal conductivity, high wear resistance, high insulation, high weather resistance, low coefficient of thermal expansion, and good biocompatibility. These properties lead to their wide application in chemical and metallurgical industries (e.g., ceramic sleeves, casting crucibles), mechanical industries (e.g., bearing balls, sealing rings), semiconductors (e.g., heat dissipation ceramic substrates for power modules), aerospace (e.g., wave-transparent materials), and biomedicine (e.g., artificial joints). However, the high cost has always been a significant factor limiting the widespread application of high-performance silicon nitride ceramics.

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

[0004] In the SRBSN method, to promote the nitriding of silicon powder preforms and subsequent sintering, in addition to reducing the particle size of the raw silicon powder, nitriding accelerators or sintering aids also need to be added. To obtain a mixed powder, water or ethanol is typically used as the mixing medium (solvent), and ball milling is performed using a drum mill or planetary mill to achieve a uniform mixture of the raw silicon powder and additives such as sintering aids. Then, drying is carried out using rotary evaporation or spray granulation methods. Furthermore, to improve the molding behavior of the mixed powder and increase the strength of the preform, organic polymers such as polyvinyl alcohol (PVA) or polyvinyl butyral (PVB) are usually added to the ball milling medium as a binder.

[0005] However, using water as a ball milling medium can cause silicon powder oxidation, which hinders the silicon powder nitriding reaction and damages the final material properties. In addition, the use of binders introduces a debinding process, which not only causes environmental problems but also increases energy costs.

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

[0007] The present invention aims to provide a green preparation method for silicon nitride ceramics to solve or improve the above-mentioned technical problems.

[0008] This invention can be implemented as follows:

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

[0010] Silicon powder and sintering aids are dry-mixed to obtain a mixed powder; the mixed powder is made into a green body; the green body is subjected to a nitriding reaction to obtain a nitrided material; the nitrided material is sintered in a nitrogen atmosphere to obtain silicon nitride ceramic;

[0011] When the particle size of 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 silicon powder exceeds 3μm, the mixed powder is first subjected to dry sand milling to ensure that the particle size of silicon powder does not exceed 3μm; then the mixed powder after dry sand milling is subjected to cold isostatic pressing 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 sintering aid to silicon powder is 1:99 to 10:90.

[0014] In an optional embodiment, the sintering aids include metal oxides and rare earth oxides.

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

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

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

[0018] In an optional implementation, dry sand milling includes at least one of the following features:

[0019] Feature 1: Dry sand milling is carried out in a closed environment with nitrogen protection;

[0020] Feature 2: The mixed powder is first mixed with the grinding aid, and then dry sand milling is performed.

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

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

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

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

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

[0026] Feature 4: The nitriding reaction takes 8 to 120 hours;

[0027] Feature 5: During the nitriding reaction, the flow rate of nitrogen gas is 0.5 L / min to 20 L / 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 0.1 MPa to 10 MPa.

[0031] The beneficial effects of this invention include:

[0032] The method for preparing silicon nitride ceramics provided by this invention is simple, easy to operate, and low in cost. The preparation process eliminates the need for drying and binder removal steps, which not only shortens the product production cycle compared to traditional wet ball milling but also saves energy costs. Furthermore, this preparation method avoids the use of organic solvents or organic binders, thereby preventing environmental pollution caused by the binder removal process and achieving green preparation of silicon nitride ceramics with net-zero carbon emissions. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 A flowchart of a green preparation method for silicon nitride ceramics provided by the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0036] The following is a detailed description of the green preparation method for silicon nitride ceramics provided by the present invention.

[0037] This invention provides a green preparation method for silicon nitride ceramics. Please refer to... Figure 1 The process includes the following steps: dry mixing silicon powder with sintering aids to obtain a mixed powder; forming the mixed powder into a green body; subjecting the green body to a nitriding reaction to obtain a nitrided material; and sintering the nitrided material in a nitrogen atmosphere to obtain silicon nitride ceramic.

[0038] When the particle size of 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 silicon powder exceeds 3μm, the mixed powder is first subjected to dry sand milling to ensure that the particle size of silicon powder does not exceed 3μm; then the mixed powder after dry sand milling is subjected to cold isostatic pressing to form a blank.

[0039] In some alternative 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 sintering aid to silicon powder can be from 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 more typical embodiments, the molar ratio of sintering aid to silicon powder is 7:93 to 8:92.

[0041] Sintering aids form a liquid phase during the high-temperature melting process, which is beneficial for promoting the rearrangement and densification of silicon nitride particles. If the amount of sintering aids is too small, it is not conducive to obtaining silicon nitride with high density; if the amount of sintering aids is too large, it can easily lead to material deformation and performance degradation, such as thermal conductivity and high-temperature performance.

[0042] In some alternative implementations, sintering aids include metal oxides and rare earth oxides.

[0043] The metal oxide may include at least one of Li₂O, MgO, Al₂O₃, TiO₂, and ZrO₂, which are more conducive to promoting the densification of silicon nitride than calcium oxide or barium oxide. Rare earth oxides 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 a mixture of yttrium oxide and magnesium oxide.

[0044] By way of example, the molar ratio of metal oxides to rare earth oxides in sintering aids can be from 2:5 to 3:5. For example, sintering aids may include yttrium oxide and aluminum oxide in a molar ratio of 2:5, or 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 above-mentioned rare earth oxide and metal oxide to no more than 3 μm is more conducive to grinding the silicon source finely during the dry sand milling process, thereby increasing the relative density of the green blank.

[0046] In some alternative implementations, dry mixing can be carried out using industrially common mixing equipment, such as dual-motion mixers, dual-motion fly knife mixers, three-dimensional motion mixers, V-type mixers, or double-cone mixers.

[0047] In this invention, dry sand milling is carried out in a closed environment with nitrogen protection to avoid oxidation of silicon powder during the sand milling process.

[0048] In some optional embodiments, the sand milling may be performed only once; in other optional embodiments, the sand milling may be performed two, three, four or more times, depending on the actual situation, with the particle size of the sand-milled silicon powder not exceeding 3μm.

[0049] Preferably, the mixed powder is first mixed with the grinding aid, and then dry sand milling is performed.

[0050] The grinding aid may include at least one of ethanol, ethylene glycol, triethanolamine, and stearic acid. The amount of grinding aid added can be 0.1 wt% to 1.5 wt% of the mixed powder, such as 0.1 wt%, 0.2 wt%, 0.5 wt%, 0.8 wt%, 1.0 wt%, 1.2 wt%, or 1.5 wt%, or other values ​​within the range of 0.1 wt% to 1.5 wt%. In this invention, the amount of grinding aid used is small, and it only serves to assist grinding, unlike the traditional wet ball milling method that uses ethanol or similar solvents.

[0051] The grinding beads used in the dry sand milling process can be, for example but not exclusively, zirconia beads or silicon nitride beads, and the particle size of the grinding beads is preferably no more than 5 mm, such as 3 mm.

[0052] After dry sand milling, the particle size of silicon powder in the resulting powder should not exceed 3μm, so as to avoid the formation of coarse structure after nitriding due to excessively large silicon powder particle size, which would result in poor densification effect after sintering.

[0053] It should be noted that this invention creatively utilizes dry sand milling of the mixed powder after dry mixing, combined with the use of grinding aids and control of the particle size of the silicon powder after dry sand milling. On the one hand, this eliminates the drying and debinding processes in the traditional wet ball milling process, which not only shortens the product production cycle but also saves energy costs. The significant cost reduction helps to accelerate the widespread application of silicon nitride ceramic materials. On the other hand, the dry sand milling process for silicon powder eliminates the use of organic solvents or organic binders, thereby eliminating the environmental pollution caused by burning organic binders (debinding) and achieving net-zero carbon emissions.

[0054] In some alternative embodiments, the pressure for 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 alternative implementations, the dry-milled mixed powder (which may be referred to as "milled powder") can be pre-formed before cold isostatic pressing. Pre-forming can be performed, for example, by loading the dry-milled mixed powder into a mold and evacuating the mold under vacuum conditions. Alternatively, pre-forming can be performed by loading the dry-milled mixed powder into a mold and pre-pressing the mold (the pre-pressing pressure can be set according to actual needs).

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

[0057] In some alternative embodiments, the nitriding reaction temperature can be between 1300°C and 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 more typical embodiments, the nitriding reaction temperature is 1400°C.

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

[0059] In some optional embodiments, the flow rate of nitrogen gas during the nitriding reaction can be from 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 0.5 L / min, the nitriding rate will be slow, prolonging the nitriding reaction time and increasing energy consumption. If the nitrogen flow rate is greater than 20 L / min, the nitrogen flow rate on the sample surface will be too high, hindering the diffusion of nitrogen from the sample surface to the interior, thus slowing down the nitriding rate. In addition, a higher nitrogen flow rate will increase nitrogen consumption, thereby increasing the cost of nitrogen usage.

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

[0062] In some alternative embodiments, the sintering temperature can be between 1800°C and 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 more typical embodiments, the sintering temperature is 1900°C.

[0063] The nitrogen pressure during the sintering process can be from 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, or other values ​​within the range of 0.1 MPa to 10 MPa. In some typical embodiments, the nitrogen pressure during the gas pressure sintering process is 1 MPa.

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

[0065] In this 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 will be further described in detail below with reference to embodiments.

[0067] Example 1

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

[0069] Based on the molar ratio of Si3N4, Y2O3, and Al2O3 after nitriding being 93:5:2, weigh out 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) 500g of the powder was placed in a three-dimensional mixer, and 5g of anhydrous ethanol was added for thorough mixing. Then, it was sand-milled twice in a 1L sand mill using 3mm diameter zirconia beads. The sand-milling process was carried out in a closed environment under nitrogen protection, at a speed of 960rpm, for 1min per milling, to obtain sand-milled powder. 4.5g of the sand-milled powder was placed in a 20mm diameter stainless steel mold and pre-compressed in a tablet press with a uniaxial pressure of 30MPa to obtain a pre-compressed preform. The pre-compressed preform was then cold isostatically pressed at 200MPa to obtain the final preform. The final preform was placed in a boron nitride crucible and then placed in an alumina tube furnace and held at 1400℃ for 8h under nitrogen flow rate of 1L / min to obtain the nitride material. The nitriding material was then placed in a boron nitride crucible and placed in a graphite pressure sintering furnace. The temperature was raised to 1900℃ under a nitrogen pressure of 1MPa and held for 6 hours. After sintering, the furnace was cooled to room temperature, and the sintered sample was taken out, which is silicon nitride ceramic.

[0070] Example 2

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

[0072] Example 3

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

[0074] Example 4

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

[0076] Example 5

[0077] The difference between this embodiment and Example 2 is that, based on the molar ratio of Si3N4, Y2O3, and MgO after nitriding being 92:5:3, Si powder (purity 99.9%, particle size D) was weighed. 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 anhydrous ethanol as a grinding aid is 1.5 wt% of the mixed powder.

[0080] Example 7

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

[0082] Example 8

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

[0084] Example 9

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

[0086] Example 10

[0087] The difference between this embodiment and Embodiment 1 is that the particle size of the silicon powder is 3μm, and the Si powder, Y2O3 powder and Al2O3 powder are directly pre-pressed and processed after dry mixing.

[0088] Example 11

[0089] The difference between this embodiment and Embodiment 1 is that the particle size of the silicon powder is 1μm, and the Si powder, Y2O3 powder and Al2O3 powder are directly pre-pressed and processed after dry mixing.

[0090] Comparative Example 1

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

[0092] Comparative Example 2

[0093] The difference between this comparative example and Example 1 is that the sanding was performed only once.

[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 hours.

[0098] Comparative Example 5

[0099] The difference between this comparative example and Example 1 is that the nitrogen flow rate during the nitriding reaction 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℃.

[0102] Test case

[0103] The particle size, relative density of the green blank, nitriding rate, and relative density of the sintered sample of the grinding materials involved in Examples 1 to 11 and Comparative Examples 1 to 6 were compared, and the results are shown in Table 1.

[0104] The bulk density of nitrided and sintered samples was determined using the Archimedes method; the apparent density of the green blank was calculated using its geometric dimensions (volume) and weight (relative density = apparent density × 100% / theoretical density); the nitriding rate was calculated based on the weight gain before and after nitriding; X-ray diffraction analysis of the nitrided and sintered samples was performed using a Malvern Panalytical Empyrean S3 powder X-ray diffractometer, and the absence of silicon diffraction peaks indicated complete nitriding; the relative density of the nitrided and sintered samples was calculated as bulk density × 100% / theoretical density.

[0105] Table 1 Results

[0106]

[0107] As shown in Table 1, the method provided by this invention can effectively prepare silicon nitride ceramics with a density higher than 95% without using wet ball milling. Furthermore, the method provided by this invention is simple, easy to operate, and time-efficient, which can significantly reduce production costs and achieve net-zero carbon emissions.

[0108] As can be seen from the examples and comparative examples, when the preparation conditions are not set properly, 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 silicon nitride ceramic preparation method provided by this invention is simple, easy to operate, and low in cost. The preparation process eliminates the need for drying and binder removal steps, which not only shortens the product production cycle but also saves energy costs compared to traditional wet ball milling methods. Furthermore, this preparation method avoids the use of organic solvents or organic binders, thereby preventing environmental pollution caused by the binder removal process and achieving green preparation of silicon nitride ceramics with net-zero carbon emissions.

[0110] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A green preparation method for silicon nitride ceramics, characterized in that, Includes the following steps: Silicon powder and sintering aids are dry-mixed to obtain a mixed powder. The mixed powder is prepared into a blank; the blank is subjected to a nitriding reaction to obtain a nitrided material; the nitrided material is sintered in a nitrogen atmosphere to obtain silicon nitride ceramic; the green preparation method does not include a drying process or a binder removal process; wherein, when the particle size of the silicon powder does not exceed 3 μm, the mixed powder is directly subjected to cold isostatic pressing to prepare a blank; when the particle size of the silicon powder exceeds 3 μm, the mixed powder is first subjected to dry sand milling to ensure that the particle size of the silicon powder does not exceed 3 μm; then the dry-milled mixed powder is subjected to cold isostatic pressing to form a blank; Dry sand milling is carried out in a closed environment under nitrogen protection; the mixed powder is first mixed with a grinding aid, and then dry sand milling is performed; the grinding aid includes at least one selected from ethanol, ethylene glycol, triethanolamine, and stearic acid; the amount of the grinding aid added is 0.1wt% to 1.5wt% of the mixed powder; The pressure for cold isostatic pressing is 150MPa~500MPa; The nitriding reaction temperature is 1300℃~1500℃; the nitriding reaction time is 8h~120h; during the nitriding reaction, the nitrogen flow rate is 0.5L / min~20L / min; The sintering temperature is 1800℃~2000℃; the nitrogen pressure during the sintering process is 0.1MPa~10MPa; The molar ratio of the sintering aid to the silicon powder is 1:99 to 10:90; the sintering aid includes metal oxides and rare earth oxides in a molar ratio of 2:5 to 3:5; the metal oxide is aluminum oxide or magnesium oxide, and the rare earth oxide is yttrium oxide.

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.

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