A method for preparing silicon nitride nano-powder

Abstract

The application discloses a preparation method of silicon nitride nano-powder, relates to the technical field of inorganic non-metallic nano-material preparation, and is characterized by a direct nitriding reaction link of silicon vapor and nitrogen plasma. The method uses high-purity silicon vapor prepared by an existing process as raw material, introduces the high-purity silicon vapor into a nitrogen plasma reaction area, and under specific process conditions, the silicon vapor and the nitrogen plasma rapidly generate a nitriding reaction to form a silicon nitride nano-particle precursor. After condensation, collection and simple subsequent treatment, high-purity silicon nitride nano-powder is obtained. The core reaction link of the application does not need to prepare a solid silicon powder intermediate, has high reaction efficiency, high product purity and good dispersity, solves the problems of easy agglomeration and high impurity content of silicon nitride powder in the prior art, and the product can be applied to high-end fields such as high-temperature structural ceramics and semiconductor packaging.

Description

Technical Field

[0001] This invention relates to the field of inorganic non-metallic nanomaterial preparation technology, specifically to a method for preparing silicon nitride nanopowder, and particularly to a process step involving the direct reaction of silicon vapor and nitrogen plasma to generate silicon nitride. Background Technology

[0002] Silicon nitride (Si3N4) nanopowder possesses excellent properties such as high strength, high hardness, high temperature resistance, corrosion resistance, and good insulation, and is widely used in high-end fields such as high-temperature structural ceramics, semiconductor packaging, and wear-resistant coatings.

[0003] A Chinese patent, CN 103072960 B, discloses a method for producing nano-silicon nitride powder. This method uses a plasma-transferred arc to heat solid silicon raw materials in a crucible, generating nano-silicon powder, which then reacts with nitriding reaction gas to produce silicon nitride powder. However, this method still requires the preparation of a solid silicon powder intermediate. Impurities are easily introduced into the solid silicon powder during preparation, grinding, and conveying, and agglomeration is likely to occur during the high-temperature reaction. Another Chinese patent, CN 114920218 A, discloses a process for preparing nitride nanopowder materials. This method transports solid raw materials to a high-temperature nitrogen plasma nitriding chamber for evaporation and atomization, followed by multiple nitriding and spheroidization processes to form nitride powder. However, this method still starts with solid raw materials, posing a risk of solid particle agglomeration and impurity introduction. A Chinese patent with publication number CN 113200528 A discloses a method for preparing high-purity α-phase silicon nitride powder. This method uses high-purity silicon powder and a catalyst as raw materials, and rapidly generates amorphous silicon nitride through a plasma reactor. However, this method also requires solid silicon powder as a raw material and necessitates the addition of a catalyst, increasing the risk of impurity introduction.

[0004] Currently, the main methods for preparing silicon nitride nanopowder include high-temperature nitridation of silicon powder, vapor-phase synthesis, and sol-gel methods. Among them: High-temperature nitriding of silicon powder: Solid silicon powder needs to be prepared first, and then reacted with nitrogen at high temperature. This method has problems such as low reaction efficiency, easy agglomeration of powder, and difficulty in improving product purity.

[0005] Gas-phase synthesis method: This method often uses silicon tetrachloride to react with ammonia. During the reaction, chlorine-containing impurities are generated, which are difficult to remove completely and affect product quality.

[0006] Sol-gel method: The preparation cycle is long and the product particle size distribution is uneven, which cannot meet the needs of high-end fields.

[0007] Existing technologies include patents for preparing gaseous SiO by hydrogen plasma reduction of quartz sand, followed by further hydrogen plasma reduction of the gaseous SiO to generate silicon vapor. This process can yield high-purity silicon vapor. However, how to efficiently prepare high-purity silicon nitride nanoparticles using this high-purity silicon vapor while avoiding the shortcomings of the existing preparation methods remains a pressing technical problem.

[0008] This invention provides a technical solution for the direct reaction of silicon vapor and nitrogen plasma to generate silicon nitride, which has high reaction efficiency and excellent product quality, and can effectively solve the problems existing in the prior art. Summary of the Invention

[0009] This invention aims to solve the problems of low reaction efficiency, easy product agglomeration, and high impurity content in existing silicon nitride preparation processes. It utilizes the direct reaction between silicon vapor and nitrogen plasma to achieve the efficient preparation of high-purity silicon nitride nanopowder.

[0010] Technical solution This invention provides a method for preparing silicon nitride nanopowder, the core of which lies in the direct nitriding reaction of silicon vapor and nitrogen plasma.

[0011] The preparation method includes the following steps: High-purity silicon vapor is introduced into a nitrogen plasma reaction zone, allowing the silicon vapor to directly react with nitrogen plasma to form a nitriding reaction, generating silicon nitride nanoparticle precursors. The nitriding reaction is carried out under plasma conditions, wherein the plasma reaction zone temperature is 7000K-11000K and the reaction chamber pressure does not exceed 10 K. -1 Pa-10 -3 Pa; the reaction products were condensed and collected to obtain silicon nitride nanopowder.

[0012] Specifically, the method includes a pre-preparation step, a core reaction step, and a post-processing step: I. Pre-preparation stage Silicon vapor can be prepared using existing processes. Preferably, high-purity silica sand is used as raw material, and a hydrogen plasma reduction process is employed. First, the silica sand is reduced to prepare gaseous SiO; subsequently, the gaseous SiO is further reduced in a hydrogen plasma environment to generate high-purity silicon vapor (purity ≥ 99.9%). The silicon vapor should be free of significant solid impurities and oxide impurities.

[0013] II. Core Reaction Phase The high-purity silicon vapor is preferably buffered and stabilized by a flow guiding device before being precisely introduced into the nitrogen plasma reaction zone.

[0014] Nitrogen plasma is generated by ionization of nitrogen gas with a purity of ≥99.999% by a plasma generator. The nitrogen gas must be purified of impurities such as moisture and oxygen beforehand to prevent the introduction of byproducts.

[0015] Under the set process conditions, silicon vapor and nitrogen plasma undergo a rapid nitriding reaction to directly generate silicon nitride nanoparticle precursors.

[0016] The conditions for the core nitriding reaction can be adjusted according to the actual equipment capabilities, with the plasma reaction zone temperature not lower than 7000K and the reaction chamber pressure not higher than 10. -1 The conditions at Pa allow for the full nitridation of silicon vapor. As a preferred range, the following process conditions yield better reaction results: nitrogen plasma generator power 30-90 kW, plasma reaction zone temperature 7000-10000 K, silicon vapor flow rate 5-15 L / min, nitrogen flow rate 20-40 L / min, silicon vapor to nitrogen flow rate ratio 1:3-1:5, and reaction chamber pressure 10... -2 -10 -3 Pa, silicon vapor residence time 300-800ms.

[0017] Reaction principle: Silicon vapor (Si(g)) reacts with nitrogen plasma (N... + N2 + (Active particles) undergo rapid chemical reactions under high temperature and high energy conditions: 3Si(g) + N + / N2 + (g) → Si3N4(s) This reaction is exothermic and requires no additional heating.

[0018] III. Follow-up Processing The reaction products are collected after rapid condensation. Preferably, a multi-stage cooling structure is used, with a first-stage cooling temperature of 800-1000℃ and a second-stage cooling temperature of 200-300℃. Collection employs a combination of cyclone separator and bag filter collection. The collected silicon nitride nanoparticles undergo simple purification and drying to remove trace adsorbed impurities, further ensuring product purity.

[0019] Product characteristics The silicon nitride nanopowder prepared by the method of this invention has a particle size distribution of 20-100nm, a purity of ≥99.9%, a crystal form of β-Si3N4, high particle sphericity, good dispersibility, and no obvious agglomeration, which can meet the high-end application requirements of high-temperature structural ceramics, semiconductor packaging and other fields.

[0020] Beneficial effects Compared with the prior art, the present invention has the following beneficial effects: No solid silicon powder intermediate is required: silicon vapor reacts directly with nitrogen plasma, eliminating the need for silicon powder preparation, grinding, and transportation steps, shortening the process, and improving reaction efficiency. Compared with existing technologies such as CN103072960B, CN114920218A / B, and CN113200528A, this invention eliminates the need for preparing solid silicon powder or nano-silicon powder intermediates, fundamentally avoiding the problem of solid particle agglomeration.

[0021] High product purity: Avoids introducing impurities during solid grinding and conveying, with a purity of ≥99.9%. It adopts a direct gas-phase reaction path with no solid contact throughout the process, significantly reducing the risk of impurity introduction.

[0022] Controllable particle size and good dispersibility: By adjusting plasma parameters, gas flow rate, residence time, etc., spherical particles with 20-100nm and no agglomeration can be obtained.

[0023] Avoiding chlorine impurities: This invention does not use silicon tetrachloride or ammonia, produces no chlorine or corrosive byproducts, and is environmentally friendly. Compared to the gas-phase synthesis method (silicon tetrachloride + ammonia), this invention produces no chlorine byproducts, has higher product purity, and fundamentally solves the equipment corrosion problem.

[0024] It has good synergy with existing silicon vapor preparation processes: it can be directly connected to existing silicon vapor production lines and has good prospects for industrial application.

[0025] Clear process conditions and easy industrialization: This invention clarifies the key process conditions for achieving complete silicon vapor nitridation (temperature ≥7000K, pressure ≤10). -1 Under these conditions (Pa), high-purity silicon nitride nanopowder can be stably obtained, exhibiting good industrial operability. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the production system used in the silicon nitride nanopowder preparation method of the present invention.

[0027] In the diagram: 1-Silicon vapor supply device; 2-Flow guiding and buffering device; 3-Nitrogen plasma generator; 4-Nitrogen plasma reaction chamber; 5-Multi-stage condenser; 6-Cyclone separator; 7-Bag collector; 8-Vacuum system. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments. Embodiments 1-3 are preferred embodiments of the present invention, and embodiments 4-5 are embodiments with a wide parameter range, used to demonstrate that the present invention can be implemented under the conditions defined in claim 1 (temperature ≥ 7000K, pressure ≤ 10). -1 Full nitridation of silicon vapor can be achieved at all Pa levels.

[0029] Example 1 (Preferred Example)

[0030] Pre-processing: Using existing technology, high-purity quartz sand is used as raw material to prepare gaseous SiO by hydrogen plasma reduction. The gaseous SiO is then reduced by hydrogen plasma to obtain silicon vapor with a purity of 99.9%.

[0031] Core reaction: The silicon vapor is buffered and stabilized by a flow guide device, then introduced into the nitrogen plasma reaction zone at a flow rate of 8 L / min; nitrogen gas (99.999% purity, with moisture and oxygen removed beforehand) is ionized by a plasma generator to produce nitrogen plasma, with a nitrogen introduction flow rate of 30 L / min; the nitrogen plasma generator power is controlled at 60 kW, the plasma reaction zone temperature is maintained at 9000 K, and the reaction chamber pressure is controlled at 5 × 10⁻⁶. -3 Pa, silicon vapor reacts rapidly with nitrogen plasma to form silicon nitride nanoparticle precursors.

[0032] Condensation and collection: A multi-stage cooling structure is adopted, with a first-stage cooling temperature of 900℃ and a second-stage cooling temperature of 250℃, to rapidly condense the reaction products; silicon nitride nanopowder is collected by a combination of cyclone separator and bag filter.

[0033] Subsequent processing: The collected powder is simply purified and dried to remove trace amounts of adsorbed impurities, yielding the final product.

[0034] Testing revealed that the silicon nitride nanopowder prepared in this embodiment had a particle size distribution of 30-80 nm, a purity of 99.92%, a crystal form of β-Si3N4, high particle sphericity, good dispersibility, and no obvious agglomeration.

[0035] Example 2 (Preferred Example)

[0036] Pre-processing: Using the same existing process as in Example 1, silicon vapor with a purity of 99.95% was obtained.

[0037] Core reaction: Silicon vapor flow rate 5 L / min, nitrogen flow rate 20 L / min (flow ratio 1:4); nitrogen plasma generator power 40 kW, plasma reaction zone temperature 8000 K, reaction chamber pressure 10 K. -2 Pa, with the remaining conditions consistent with Example 1.

[0038] Condensation collection and subsequent processing: Same as in Example 1.

[0039] Testing revealed that the silicon nitride nanopowder prepared in this embodiment had a particle size distribution of 20-60 nm, a purity of 99.91%, a crystal form of β-Si3N4, and good dispersibility.

[0040] Example 3 (Preferred Example)

[0041] Pre-processing: Using the same existing process as in Example 1, silicon vapor with a purity of 99.9% was obtained.

[0042] Core reaction: Silicon vapor flow rate 15 L / min, nitrogen flow rate 4 L / min (flow ratio 1:3); nitrogen plasma generator power 90 kW, plasma reaction zone temperature 10000 K, reaction chamber pressure 10 -3 Pa, with the remaining conditions consistent with Example 1.

[0043] Condensation collection and subsequent processing: Same as in Example 1.

[0044] Testing revealed that the silicon nitride nanopowder prepared in this embodiment had a particle size distribution of 60-100 nm, a purity of 99.93%, a crystal form of β-Si3N4, and no obvious agglomeration.

[0045] Example 4 (Wide parameter range example 1: High temperature conditions) To demonstrate that the present invention can still achieve full nitridation of silicon vapor at higher temperatures within the temperature range (≥7000K) defined in claim 1, this embodiment uses power and temperature conditions higher than those in Example 3.

[0046] Pre-treatment: Same as in Example 1, to obtain silicon vapor with a purity of 99.9%.

[0047] Core reaction: Silicon vapor flow rate is 12 L / min, nitrogen flow rate is 35 L / min; nitrogen plasma generator power is 100 kW, plasma reaction zone temperature is 11000 K, and reaction chamber pressure is 5 × 10⁻⁶. -3 Pa, with the remaining conditions consistent with Example 1.

[0048] Condensation collection and subsequent processing: Same as in Example 1.

[0049] Testing revealed that the silicon nitride nanopowder prepared in this example had a particle size distribution of 40-90 nm, a purity of 99.91%, a crystal form of β-Si3N4, and good dispersibility. The results showed that even under conditions of 100 kW power and 11000 K temperature, silicon vapor could still be fully nitrided, and no unreacted silicon residue or product decomposition was observed.

[0050] Example 5 (Wide parameter range example 2: Low temperature and low pressure conditions) To demonstrate that the present invention meets the critical conditions defined in claim 1 (temperature 7000K, pressure 10), -1 Sufficient nitridation of silicon vapor can still be achieved near Pa. In this embodiment, the power and temperature conditions are lower than those in Example 2.

[0051] Pre-treatment: Same as in Example 1, to obtain silicon vapor with a purity of 99.9%.

[0052] Core reaction: Silicon vapor flow rate is 6 L / min, nitrogen flow rate is 25 L / min; nitrogen plasma generator power is 30 kW, plasma reaction zone temperature is 7000 K, and reaction chamber pressure is 5 × 10⁻⁶. -2 Pa, with the remaining conditions consistent with Example 1.

[0053] Condensation collection and subsequent processing: Same as in Example 1.

[0054] Testing revealed that the silicon nitride nanopowder prepared in this example had a particle size distribution of 25-70 nm, a purity of 99.90%, and a crystal form of β-Si3N4. The unreacted silicon residue in the product was approximately 3%, which is still within an acceptable range (≤5%). The results indicate that under conditions of 30 kW power, 7000 K temperature, and 5 × 10⁻⁶ pressure, the desired silicon content is achieved. -2 Under the conditions of Pa, silicon vapor can still achieve essentially complete nitridation, proving that the critical conditions defined in claim 1 (temperature ≥ 7000 K, pressure ≤ 10 Pa) are met. -1 Pa) can achieve the inventive objective of this invention.

[0055] Table 1 Comparison of the method of the present invention with the prior art

[0056] The method of this invention can be directly integrated with existing high-purity silicon vapor production lines without the need for additional solid silicon powder preparation. Equipment investment is moderate, and continuous production is easily achieved. Using this method, a silicon nitride nanopowder production line with an annual output of over one ton can be constructed. The product can be applied to high-end fields such as high-temperature structural ceramics and semiconductor packaging, demonstrating promising industrial application prospects.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing silicon nitride nanopowder, characterized in that, The method comprises the following steps: introducing high-purity silicon vapor into a nitrogen plasma reaction area, and making the silicon vapor directly react with nitrogen plasma to generate silicon nitride nanoparticle precursors; the reaction is carried out under plasma conditions, wherein the temperature of the plasma reaction area is 7000K-11000K, the pressure of the reaction cavity is not higher than 10 -1 Pa-10 -3 Pa; and the reaction product is condensed and collected to obtain silicon nitride nanopowder.

2. The preparation method according to claim 1, characterized in that, The nitrogen plasma is generated by ionization of nitrogen gas by a plasma generator. The power of the plasma generator and the flow rate of nitrogen gas are sufficient to make the temperature of the nitrogen plasma reaction zone reach the required temperature.

3. The preparation method according to claim 1, characterized in that, The ratio of silicon vapor flow rate to nitrogen flow rate ensures that the silicon vapor is fully nitrided, with unreacted silicon residue ≤5%.

4. The preparation method according to claim 1, characterized in that, The residence time of the silicon vapor in the nitrogen plasma reaction region is sufficient for the silicon vapor to be completely converted into silicon nitride.

5. The preparation method according to claim 1, characterized in that, The process conditions for the nitriding reaction are as follows: nitrogen plasma generator power 30-90kW, plasma reaction zone temperature 8000-10000K, silicon vapor flow rate 5-15L / min, nitrogen flow rate 20-40L / min, silicon vapor to nitrogen flow ratio 1:3-1:5, and reaction chamber pressure 10... -2 -10 -3 Pa, the residence time of silicon vapor in the nitrogen plasma reaction region is 300-800 ms.

6. The preparation method according to claim 1, characterized in that, The high-purity silicon vapor is obtained by reducing quartz sand to gaseous SiO, and then reducing the gaseous SiO to hydrogen plasma again. The purity of the silicon vapor is ≥99.9%.

7. The preparation method according to claim 1, characterized in that, The nitrogen plasma is generated by ionization of nitrogen gas with a purity of ≥99.999% by a plasma generator. The nitrogen gas needs to be purified of moisture and oxygen impurities beforehand.

8. The preparation method according to claim 1, characterized in that, Before the silicon vapor is introduced, it is buffered and stabilized by a flow guiding device to avoid airflow fluctuations affecting the uniformity of the reaction.

9. The preparation method according to claim 1, characterized in that, The condensation adopts a multi-stage cooling structure, with a first-stage cooling temperature of 800-1000℃ and a second-stage cooling temperature of 200-300℃; the collection adopts a combination of cyclone separator and bag collection.

10. The preparation method according to claim 1, characterized in that, The silicon nitride nanopowder has a particle size distribution of 20-100 nm, a purity of ≥99.9%, a crystal form of β-Si3N4, high particle sphericity, good dispersibility, and no obvious agglomeration.

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