Method for producing silicon nitride

Abstract

The application provides a preparation method of silicon nitride, comprising the following steps: direct reaction: passing silane gas and ammonia gas into a reactor, controlling the temperature of the reactor to be 600-900 DEG C, and making the silane gas and the ammonia gas react to form amorphous silicon nitride; phase transformation: controlling the reactor to be heated to 1000-1300 DEG C, and passing silicon powder into the reactor, so that the amorphous silicon nitride obtained in the direct reaction step is transformed into alpha-phase silicon nitride, and the silicon powder reacts with the ammonia gas to obtain alpha-phase silicon nitride. According to the application, the silane gas and the ammonia gas are made to react at low temperature to form amorphous silicon nitride, the energy consumption and the production cost of the reaction are reduced, then the temperature is increased and the silicon powder is passed in, the amorphous silicon nitride is transformed into alpha-phase silicon nitride, and the silicon powder acts as a diluent for the nitriding reaction, so that the quality and the purity of the alpha-phase silicon nitride powder obtained finally are high.

Description

Technical Field

[0001] This application relates to the field of silicon nitride production technology, and in particular to a method for preparing silicon nitride. Background Technology

[0002] Silicon nitride (Si3N4), as an important high-temperature structural ceramic material, possesses a series of advantages, including high hardness, high strength, wear resistance, high temperature resistance, low coefficient of thermal expansion, high thermal conductivity, good thermal shock resistance, and low density. It has extremely broad application prospects in fields such as ceramic engines, machining, microelectronics, space science, and nuclear power engineering. Examples include silicon nitride ceramic tools (such as cutting tools), ceramic bearings, automotive engine valves, automotive turbochargers, heaters, and various wear-resistant, high-temperature-resistant, and corrosion-resistant parts.

[0003] Currently, the main methods for preparing silicon nitride include direct silicon powder nitridation, carbothermal reduction, silicon halide ammonolysis, and precursor methods. Among these, direct silicon powder nitridation is the most widely used method in China. This method is relatively simple, inexpensive, and uses polycrystalline or monocrystalline silicon as raw materials. However, the silicon powder nitridation process has some problems. For example, silicon powder nitridation is an exothermic reaction, and the nitridation rate must be carefully controlled; otherwise, a "silicon flow" phenomenon can easily occur in local areas, affecting the powder quality. Furthermore, the silicon nitride powder produced by this process is in block form and must be ball-milled to obtain fine powder, which is inefficient and easily introduces impurities.

[0004] In addition, the direct nitridation of silicon powder involves high reaction temperatures, requires sophisticated equipment, and has high production costs. Summary of the Invention

[0005] The purpose of this application is to provide a method for preparing silicon nitride, which first reacts silane gas and ammonia gas at a lower temperature to form amorphous silicon nitride, and then raises the temperature to introduce silicon powder for nitriding, thus solving the problems of high reaction temperature and easy occurrence of "silicon flow" in the prior art.

[0006] To achieve one of the above-mentioned objectives, one embodiment of this application provides a method for preparing silicon nitride, comprising the following steps:

[0007] Direct reaction: Silane gas and ammonia gas are introduced into the reactor, and the reactor temperature is controlled at 600-900℃. Silane gas and ammonia gas react to form amorphous silicon nitride. Phase transformation: The reactor temperature is controlled to be raised to 1000-1300℃, and silicon powder is introduced into the reactor. The amorphous silicon nitride obtained in the direct reaction step is transformed into α-phase silicon nitride. At the same time, the silicon powder reacts with ammonia to obtain α-phase silicon nitride.

[0008] In one embodiment of this application, the silane gas is silane, the flow rate of the silane is 0.8-1.2 kg / min, and the flow rate of the ammonia gas is 0.65-1.5 kg / min.

[0009] In one embodiment of this application, the silicon powder is introduced into the reactor using nitrogen as a carrier gas, with the flow rate of the silicon powder into the reactor being 4-6 kg / min and the flow rate of the nitrogen being 4-8 kg / min.

[0010] In one embodiment of this application, the reaction pressure of silane gas and ammonia gas in the direct reaction step is 130-150 kPa.

[0011] In one embodiment of this application, the pressure at which amorphous silicon nitride is converted into α-phase silicon nitride in the phase transformation step is 170-190 kPa.

[0012] In one embodiment of this application, in the direct reaction step, silane gas and ammonia gas are preheated at 180-200°C before being introduced into the reactor.

[0013] In one embodiment of this application, the reactor is a fluidized bed reactor, and a spiral guide plate is provided inside the fluidized bed reactor to agitate the solid matter inside the fluidized bed reactor.

[0014] In one embodiment of this application, the fluidized bed reactor further includes a silane gas storage tank, an ammonia gas storage tank, and a mixer. Silane gas and ammonia gas are introduced into the mixer from the silane gas storage tank and the ammonia gas storage tank, respectively, and after being preheated in the mixer, they are introduced into the fluidized bed reactor.

[0015] In one embodiment of this application, the purity of silane gas and ammonia gas is ≥99.9%, the purity of silicon powder is ≥99.9%, and the particle size is 1-10 μm.

[0016] In one embodiment of this application, the silicon nitride obtained by the reaction has a purity of ≥99.9999% and an α phase content of ≥95%.

[0017] One or more technical solutions provided in this application have at least the following technical effects or advantages: In the silicon nitride preparation method provided in this application, silane gas and ammonia gas are first reacted at a lower temperature to form amorphous silicon nitride, and then silicon powder is introduced for nitriding at a higher temperature. The amorphous silicon nitride serves as a seed crystal and can generate α-phase silicon nitride before silicon powder nitriding. The α-phase silicon nitride serves as a diluent to control the silicon powder nitriding reaction and avoid the "silicon flow" phenomenon. Detailed Implementation

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] This application provides a method for preparing silicon nitride, comprising the following steps: Direct reaction: Silane gas and ammonia gas are introduced into the reactor, and the reactor temperature is controlled at 600-900℃. Silane gas and ammonia gas react to form amorphous silicon nitride. Phase transformation: The reactor temperature is controlled to be raised to 1000-1300℃, and silicon powder is introduced into the reactor. The amorphous silicon nitride obtained in the direct reaction step is transformed into α-phase silicon nitride. At the same time, the silicon powder reacts with ammonia to obtain α-phase silicon nitride.

[0020] This application obtains amorphous silicon nitride powder by reacting silane gas and ammonia gas at a relatively low temperature (600-900℃). The reaction temperature is much lower than the temperature required for silicon powder nitridation, which can reduce the production energy consumption and cost of silicon nitride preparation.

[0021] The silicon nitride obtained from the direct reaction step is amorphous silicon nitride. Amorphous silicon nitride has a loose structure, low density, low hardness, poor strength, and poor thermal stability, resulting in limited application value. By raising the temperature to 1000-1300℃, the amorphous silicon nitride, acting as a seed crystal, undergoes a phase transformation to form α-phase silicon nitride powder. Simultaneously, silicon powder is introduced into the reactor, where it reacts with ammonia gas at high temperature to obtain α-phase silicon nitride.

[0022] Amorphous silicon nitride, used as a seed crystal, undergoes a phase transformation that occurs preferentially over the reaction between silicon powder and ammonia. The α-phase silicon nitride powder formed from the phase transformation of amorphous silicon nitride powder can act as a diluent for the nitriding reaction of silicon powder, absorbing some of the heat generated by the reaction between silicon powder and ammonia, thus ensuring a uniform temperature distribution and preventing the silicon powder from melting due to excessively high local temperatures, which would lead to a "silicon flow" phenomenon. This controls the progress of the silicon powder nitriding reaction, ensuring that the nitriding reaction can proceed continuously and stably, thereby improving the quality of the silicon nitride powder.

[0023] In addition, the reaction of silane gas and ammonia gas not only produces amorphous silicon nitride, but also generates hydrogen gas. Hydrogen gas can act as a reducing agent in the reactor to prevent silicon powder from being oxidized, and it can also reduce the silicon oxide layer on the surface of the silicon powder introduced into the reactor or the silicon oxide formed after oxidation during the reaction, thereby improving the purity of the silicon nitride product.

[0024] In some embodiments of this application, the silane gas is silane, the flow rate of which is 0.8-1.2 kg / min, and the flow rate of the ammonia gas is 0.65-1.5 kg / min. When silane and ammonia react to produce silicon nitride, their molar ratio is 3:4. When silane and ammonia are introduced, ammonia is kept in excess to ensure that the silane reacts completely without residue, thus avoiding waste of silane.

[0025] In some embodiments of this application, the silicon powder is introduced into the reactor using nitrogen as a carrier gas, with the flow rate of the silicon powder into the reactor being 4-6 kg / min and the flow rate of the nitrogen being 4-8 kg / min.

[0026] Nitrogen can not only serve as a carrier gas to uniformly feed silicon powder into the reactor, but also as a nitrogen source for the nitriding reaction of silicon powder. When the ammonia gas reacts with the silane gas in the direct reaction step, and the remaining ammonia gas is insufficient to completely consume the silicon powder, the excess nitrogen gas participates in the nitriding reaction of the silicon powder, which can ensure that the silicon powder is completely consumed.

[0027] In some embodiments of this application, the reaction pressure of silane gas and ammonia gas in the direct reaction step is 130-150 kPa.

[0028] Before introducing silane and ammonia gas into the reactor, the reactor is first evacuated to prevent the oxidation of amorphous silicon nitride and silicon powder added during the phase transformation step, which would generate unnecessary impurities. After evacuation, silane and ammonia gas are introduced into the reactor, raising the internal pressure to 130-150 kPa.

[0029] Controlling the reaction pressure of silane gas and ammonia gas above atmospheric pressure can promote the forward reaction, improve reaction efficiency, and reduce equipment wear and tear, thereby lowering equipment maintenance costs. In some embodiments of this application, the pressure at which amorphous silicon nitride is converted to α-phase silicon nitride during the phase transformation step is 170-190 kPa. Slightly increasing the pressure can promote the conversion of amorphous silicon nitride to α-phase silicon nitride and also promote the forward nitriding reaction of silicon powder, thereby improving conversion efficiency and reaction efficiency.

[0030] In some embodiments of this application, in the direct reaction step, silane gas and ammonia gas are preheated at 180-200°C before being introduced into the reactor.

[0031] Preheating silane and ammonia gases before they enter the reactor serves two purposes. First, it ensures that the gases reach a suitable initial reaction temperature before entering the reactor, reducing the temperature drop within the reactor and thus shortening the required heating time after the gases enter, thereby increasing the reaction rate and efficiency. It also reduces the temperature gradient within the reactor, resulting in a more uniform reaction, minimizing side reactions, and ensuring the stability and safety of the reaction process. Second, preheating reduces the reactor's heat load, lowers energy consumption, and extends the equipment's lifespan.

[0032] In some embodiments of this application, the reactor is a fluidized bed reactor, and a spiral guide plate is provided inside the fluidized bed reactor to agitate the solid matter inside the fluidized bed reactor.

[0033] The reactor is made of high-temperature and corrosion-resistant materials, such as stainless steel or quartz. An efficient heating system is installed outside the reactor, enabling precise temperature control. Heating can be achieved through electric heating or induction heating. Inside the reactor, a spiral baffle plate agitates the silicon powder and silicon-nitrogen intermediates, keeping the solids in a fluidized state and preventing solid deposition that could affect decomposition / reaction efficiency.

[0034] During the reaction, after the fluidized bed reactor is evacuated, silane gas and ammonia gas are introduced to a preset pressure, and then the gas supply is stopped. After the direct reaction step is completed, nitrogen gas carrying silicon powder is introduced to a preset pressure and heated in the phase transformation step to start the phase transformation and silicon powder nitriding reaction.

[0035] Of course, the required gas can also be continuously introduced and controlled at a preset pressure, and the solid material can be returned to the fluidized bed reactor through filtration or other means.

[0036] In some embodiments of this application, the fluidized bed reactor further includes a silane gas storage tank, an ammonia gas storage tank, and a mixer. Silane gas and ammonia gas are introduced into the mixer from the silane gas storage tank and the ammonia gas storage tank, respectively, and after being preheated in the mixer, they are introduced into the fluidized bed reactor.

[0037] Silane gas and ammonia gas are stored in silane gas storage tanks and ammonia gas storage tanks, respectively. Silane gas and ammonia gas are introduced into the mixer according to preset quantities through flow controllers. They are mixed in the mixer to form a uniform reaction atmosphere, which promotes the efficient reaction of the two in the reactor. At the same time, silane gas and ammonia gas are preheated in the mixer to 180-200°C before being introduced into the fluidized bed reactor to reduce the temperature rise time after entering the reactor.

[0038] In some embodiments of this application, the fluidized bed reactor is further provided with a tail gas treatment device to treat the tail gas after the reaction, such as silane gas, ammonia gas, nitrogen gas, and hydrogen gas, in order to prevent environmental pollution. The tail gas treatment device can be an absorption tower or a burner, etc., to remove harmful substances in the tail gas or convert them into harmless substances.

[0039] In some embodiments of this application, the purity of silane gas and ammonia gas is ≥99.9%, the purity of silicon powder is ≥99.9%, and the particle size is 1-10 μm. Using high-purity silane gas, ammonia gas, and silicon powder as raw materials avoids introducing impurities. Smaller silicon powder particle size results in a larger specific surface area, increasing the contact area between silicon powder and ammonia / nitrogen gas, thereby enhancing the reactivity of silicon powder with ammonia / nitrogen gas and increasing the reaction rate.

[0040] In the silicon nitride preparation method provided in this application, the direct reaction step at low temperature can greatly reduce the energy consumption and production cost of silicon nitride production; the α-phase silicon nitride formed by the phase transformation of amorphous silicon nitride serves as a diluent during the nitriding reaction of silicon powder, ensuring that the nitriding reaction can proceed continuously and stably, improving the quality of silicon nitride powder, and thus obtaining high-quality (purity ≥99.9999%) α-phase silicon nitride powder (α-phase content ≥95%) under conditions of lower energy consumption and cost.

[0041] The technical solution of this application will be further described below with reference to some specific embodiments.

[0042] Example 1 Direct reaction: The fluidized bed reactor was evacuated, and silane was introduced into the mixer at a rate of 0.8 kg / min. Ammonia was introduced into the mixture at a rate of 1.0 kg / min. After mixing, the mixture was preheated to 180°C in the mixer and then introduced into the fluidized bed reactor, which was pre-set to 650°C, until the pressure reached 130 kPa. The reaction was carried out for 5 hours to obtain amorphous silicon nitride. The purity of the silane gas and the ammonia gas was 99.9%. Phase transformation: The fluidized bed reactor is heated to 1050℃ and pressurized to 175kPa. Nitrogen gas carrying silicon powder is introduced into the fluidized bed reactor at a rate of 4kg / min and a rate of 5kg / min. The reaction is carried out for 3 hours to obtain α-phase silicon nitride.

[0043] XRD analysis showed that the purity of the α-phase silicon nitride was 99.9999%, and the purity of the α-phase was 95.7%.

[0044] Example 2 Direct reaction: The fluidized bed reactor was evacuated, and silane was introduced into the mixer at a rate of 0.9 kg / min. Ammonia was introduced into the mixture at a rate of 1.1 kg / min. After mixing, the mixture was preheated to 190°C in the mixer and then introduced into the fluidized bed reactor, which was pre-set to 750°C, until the pressure reached 135 kPa. The reaction was carried out for 5.5 hours to obtain amorphous silicon nitride. The purity of the silane gas and the ammonia gas was 99.9%. Phase transformation: The fluidized bed reactor was heated to 1150℃ and pressurized to 180kPa. Nitrogen gas carrying silicon powder was introduced into the fluidized bed reactor at a rate of 4.3 kg / min and a rate of 6 kg / min. The reaction was carried out for 2 hours to obtain α-phase silicon nitride.

[0045] XRD analysis showed that the purity of the α-phase silicon nitride was 99.9999%, and the purity of the α-phase was 95.8%.

[0046] Example 3 Direct reaction: The fluidized bed reactor was evacuated, and silane was introduced into the mixer at a rate of 1 kg / min. Ammonia was introduced into the mixture at a rate of 1.35 kg / min. After mixing, the mixture was preheated to 185°C in the mixer and then introduced into the fluidized bed reactor, which was pre-set to 870°C, until the pressure reached 145 kPa. The reaction was carried out for 4 hours to obtain amorphous silicon nitride. The purity of the silane gas and the ammonia gas was 99.9%. Phase transformation: The fluidized bed reactor is heated to 1200℃ and pressurized to 180kPa. Nitrogen gas carrying silicon powder is introduced into the fluidized bed reactor at a rate of 5kg / min and a rate of 7kg / min. The reaction is carried out for 3.5 hours to obtain α-phase silicon nitride.

[0047] XRD analysis showed that the purity of the α-phase silicon nitride was 99.99999%, and the α-phase content was 96%.

[0048] Example 4 Direct reaction: The fluidized bed reactor was evacuated, and silane was introduced into the mixer at a rate of 1.2 kg / min. Ammonia was introduced into the mixture at a rate of 1.5 kg / min. After mixing, the mixture was preheated to 200°C in the mixer and then introduced into the fluidized bed reactor, which was pre-set to 900°C, until the pressure reached 150 kPa. The reaction was carried out for 3 hours to obtain amorphous silicon nitride. The purity of the silane gas and the ammonia gas was 99.9%. Phase transformation: The fluidized bed reactor is heated to 1250℃ and pressurized to 190kPa. Nitrogen gas carrying silicon powder is introduced into the fluidized bed reactor at a rate of 6 kg / min and 8 kg / min. The reaction is carried out for 2 hours to obtain α-phase silicon nitride.

[0049] XRD analysis showed that the purity of the α-phase silicon nitride was 99.99999%, and the α-phase purity was 96.7%.

[0050] It should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0051] The detailed descriptions listed above are merely specific descriptions of feasible implementation methods of this application and are not intended to limit the scope of protection of this application. All equivalent implementation methods or modifications made without departing from the spirit of the art of this application should be included within the scope of protection of this application.

Claims

1. A method for preparing silicon nitride, characterized in that, Includes the following steps: Direct reaction: Silane gas and ammonia gas are introduced into the reactor, and the reactor temperature is controlled at 600-900℃. Silane gas and ammonia gas react to form amorphous silicon nitride. Phase transformation: The reactor temperature is controlled to be raised to 1000-1300℃, and silicon powder is introduced into the reactor. The amorphous silicon nitride obtained in the direct reaction step is transformed into α-phase silicon nitride. At the same time, the silicon powder reacts with ammonia to obtain α-phase silicon nitride.

2. The method for preparing silicon nitride according to claim 1, characterized in that, The silane gas is silane, and the flow rate of the silane is 0.8-1.2 kg / min. The flow rate of the ammonia gas is 0.65-1.5 kg / min.

3. The method for preparing silicon nitride according to claim 2, characterized in that, The silicon powder is introduced into the reactor using nitrogen as a carrier gas at a flow rate of 4-6 kg / min, and the nitrogen flow rate is 4-8 kg / min.

4. The method for preparing silicon nitride according to claim 1, characterized in that, In the direct reaction step, the reaction pressure of silane gas and ammonia gas is 130-150 kPa.

5. The method for preparing silicon nitride according to claim 1, characterized in that, In the phase transformation step, the pressure for converting amorphous silicon nitride into α-phase silicon nitride is 170-190 kPa.

6. The method for preparing silicon nitride according to claim 1, characterized in that, In the direct reaction step, silane gas and ammonia gas are preheated at 180-200°C before being introduced into the reactor.

7. The method for preparing silicon nitride according to claim 6, characterized in that, The reactor is a fluidized bed reactor, and a spiral guide plate is installed inside the fluidized bed reactor to agitate the solid matter inside the reactor.

8. The method for preparing silicon nitride according to claim 7, characterized in that, The fluidized bed reactor also includes a silane gas storage tank, an ammonia gas storage tank, and a mixer. Silane gas and ammonia gas are introduced into the mixer from the silane gas storage tank and the ammonia gas storage tank, respectively, and after being preheated in the mixer, they are introduced into the fluidized bed reactor.

9. The method for preparing silicon nitride according to claim 1, characterized in that, The purity of silane gas and ammonia gas is ≥99.9%, the purity of silicon powder is ≥99.9%, and the particle size is 1-10μm.

10. The method for preparing silicon nitride according to any one of claims 1 to 9, characterized in that, The silicon nitride obtained from the reaction has a purity of ≥99.9999% and an α phase content of ≥95%.