Preparation method and system for producing high-purity silicon carbide raw material by using silica aerogel

Abstract

The invention relates to the field of silicon carbide raw material preparation, in particular to a preparation method and system for producing a high-purity silicon carbide raw material through silica aerogel, and the method comprises the following steps that S1, the silica aerogel and a metal reducing agent are mixed and heated at a high temperature in an argon inert atmosphere, a first product is generated, and the first product contains monatomic silicon; s2, after cooling, carrying out acid pickling on the first product by using diluted hydrochloric acid, and filtering to obtain a granular second product; and S3, repeatedly washing the second product with deionized water, and drying after washing to finally obtain the silicon particles. According to the scheme, the reaction speed is increased, the reaction time is shortened, silicon dioxide and the reducing agent can fully react in a short time, and the preparation efficiency of silicon is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of silicon carbide raw material preparation, and particularly relates to a method and system for producing high-purity silicon carbide raw material by using silicon aerogel. BACKGROUND

[0002] Silicon is an important raw material for the growth of silicon carbide crystals, and the purity of silicon directly affects the preparation quality of silicon carbide crystals. The higher the purity of silicon, the better the quality of the crystals.

[0003] In the prior art, there are many methods for preparing silicon, such as high-temperature reduction method, silane reduction method, chlorination method, etc. Among them, the high-temperature reduction method is the most commonly used method for producing silicon in industry. This method uses a reducing agent to reduce silicon dioxide to silicon at high temperature.

[0004] However, the traditional high-temperature reduction method mixes silicon dioxide and a reducing agent, and the contact area between the two needs to be improved. The reaction time between the two is relatively long, and the reaction speed and the degree of reaction are both to be improved. SUMMARY

[0005] The present application aims to provide a method and system for producing high-purity silicon carbide raw material by using silicon aerogel, in order to improve the reaction speed, reduce the reaction time, and enable silicon dioxide and a reducing agent to react fully in a short period of time, thereby improving the efficiency of silicon production.

[0006] In one aspect, to achieve the above-mentioned purpose, the present application adopts the following technical scheme: a method for producing high-purity silicon carbide raw material by using silicon aerogel, comprising the following steps: S1. Mix silicon aerogel with a metal reducing agent, heat at high temperature in an argon inert atmosphere to generate a first product, and the first product contains elemental silicon; S2. After cooling, use dilute hydrochloric acid to acid wash the first product, and filter to obtain a granular second product; S3. Then repeatedly rinse the second product with deionized water, and after rinsing, dry to obtain silicon particles.

[0007] The principle and advantages of the present scheme are: the silicon aerogel is used as the silicon source, and the silicon aerogel is a kind of porous and extremely light solid material, which is called "solid smoke". Since the silicon aerogel has a porous structure, the silicon aerogel has a very large specific surface area, which can be up to several hundred square meters per gram. In this way, the reducing agent can enter the pores of the silicon aerogel. The reducing agent can not only contact the silicon aerogel on the outside, but also enter the inside of the silicon aerogel to contact the silicon aerogel. Therefore, the reducing agent and the silicon aerogel have a large reaction contact area. After the silicon aerogel is mixed with the reducing agent, the silicon aerogel can be fully mixed and contacted with the reducing agent, thereby helping to accelerate the reaction rate and improve the reaction efficiency. After the reaction speed is increased, the reaction time is reduced, thereby facilitating the improvement of the preparation efficiency of silicon.

[0008] In addition, the inventors have unexpectedly found that using silicon aerogel as a silicon source to prepare silicon can produce silicon with higher purity, and the purity of the silicon can reach more than 7 nine (99.99999%). Through the present scheme, the reason why high-purity silicon can be prepared is summarized as follows: 1. Compared with other types of silicon sources, the starting material of the silicon aerogel is usually a high-purity silicon alkoxide. The purity of the starting material of the silicon aerogel is high itself. In addition, the silicon aerogel is usually prepared by sol-gel method. The silicon aerogel itself can effectively remove impurities through acid washing or solvent exchange during the preparation process, thereby making the purity of the silicon aerogel itself higher. 2. The contact area between the silicon aerogel and the metal reducing agent is large, and the reaction is rapid and complete, thereby avoiding the residual silicon dioxide or intermediate products due to incomplete reaction. 3. By performing acid washing in S2 and deionized water cleaning in S3, the by-products generated by the reaction and the reducing agent not involved in the reaction can be removed, thereby avoiding being mixed in the silicon as impurities.

[0009] In summary, through the present scheme, the preparation efficiency of silicon can be greatly improved, and the preparation purity of silicon can also be improved, which has a significant effect.

[0010] On the other hand, in order to achieve the above-mentioned purpose, the present application adopts the following technical scheme: a system for producing high-purity silicon carbide raw material by using silicon aerogel, comprising, An argon source is used to provide argon; An evaporator is connected to the argon source, and the argon in the argon source enters the evaporator. The evaporator is used to change the metal reducing agent into a gaseous state; A reactor is connected to the evaporator, and the reactor is used to mix the gaseous metal reducing agent with the silicon aerogel. The silicon aerogel and the metal reducing agent are heated at high temperature in the reactor.

[0011] The principle and advantages of the present scheme are: the solid metal reducing agent is put into the evaporator, the evaporator is heated, the evaporator heats the metal reducing agent to make it into gaseous metal reducing agent, then the argon source provides argon, the argon enters the evaporator, the argon enters the reactor as a carrier gas together with the gaseous metal reducing agent, the metal reducing agent contacts the silica aerogel and reacts in the reactor to generate silicon. By using the present scheme, since the metal reducing agent is a gas, the gaseous metal reducing agent is more easily entered into the pores of the silica aerogel than the solid metal reducing agent, thereby more conducive to ensuring that the silica aerogel and the metal reducing agent are in full contact, which helps to accelerate the reaction rate and improve the reaction efficiency, thereby improving the preparation efficiency and quality of silicon, and solving the problem that the solid metal reducing agent is not easy to enter the pores of the silica aerogel.

[0012] Another reason why the present scheme changes the metal reducing agent into a gas is that the silica aerogel has extremely light characteristics. If the solid metal reducing agent is mixed with the silica aerogel, the density of the metal reducing agent and the silica aerogel will not be consistent, which will cause the two to separate, which is not conducive to the full contact of the silica aerogel and the metal reducing agent. However, through the present scheme, the gaseous metal reducing agent has a certain diffusivity and can flow in different silica aerogels, thereby facilitating the full contact of the silica aerogel and the metal reducing agent.

[0013] Preferably, as an improvement, the reducing agent is sodium or magnesium.

[0014] Preferably, as an improvement, the temperature of the high-temperature heating in S1 is 700-900°C.

[0015] Preferably, as an improvement, in S1, the silica aerogel and the metal reducing agent are mixed and high-temperature heated in the reactor; the metal reducing agent enters the reactor as a gas.

[0016] Preferably, as an improvement, the evaporator is provided with a molybdenum boat or a tantalum boat, and the solid metal reducing agent is placed in the molybdenum boat or the tantalum boat.

[0017] The molybdenum boat or the tantalum boat is used to hold the solid metal reducing agent. Molybdenum or tantalum has extremely high stability in argon and can be used as an inert container. The metal reducing agent placed in the molybdenum boat or the tantalum boat will not react with molybdenum (or tantalum), avoiding the entry of container impurities during the process of the metal reducing agent becoming gaseous. In addition, molybdenum or tantalum has a very high melting point and high-temperature strength, and can maintain its shape without softening and deforming during the process of heating the metal reducing agent to become gaseous. In addition, molybdenum or tantalum has excellent thermal conductivity, which is conducive to heating the metal reducing agent and will not hinder the heating of the metal reducing agent.

[0018] Preferably, as an improvement, a vent pipe is connected between the evaporator and the reactor, and an insulating layer or a heating part is arranged on the outer wall of the vent pipe. Thus, the gas of the metal reducing agent generated in the evaporator enters the reactor through the vent pipe. The insulating layer is used to insulate the vent pipe or the heating part is used to heat the vent pipe, so that the vent pipe can maintain a certain temperature, avoiding the gasification of the metal reducing agent in the vent pipe.

[0019] Preferably, as an improvement, a feeding part is fixedly arranged on the top of the reactor, and an annular feeding channel is arranged on the feeding part, and the bottom end of the feeding channel extends into the reactor; the vent pipe extends into the reactor from the bottom of the reactor, the center line of the vent pipe is collinear with the center line of the feeding channel, and a plurality of circumferentially distributed gas outlet holes are arranged on the side wall of the top of the vent pipe, and the top end of the vent pipe is blocked.

[0020] Thus, the powdered silica aerogel enters the feeding channel and falls down along the feeding channel. Since the center line of the vent pipe is collinear with the center line of the feeding channel, the silica aerogel leaking from the bottom of the feeding channel is located around the top of the vent pipe. At the same time, the gas of the metal reducing agent enters the vent pipe and flows to the top end of the vent pipe. Since the top end of the vent pipe is blocked, the gas can only blow out from the gas outlet holes in the radial direction of the vent pipe, so as to blow towards the silica aerogel around the top of the vent pipe, realizing the mixing of the metal reducing agent and the silica aerogel, and facilitating the metal reducing agent to enter the pores of the silica aerogel. At the same time, the gas blows the silica aerogel around the top of the vent pipe, so that the silica aerogel flowing out of the feeding channel does not block at the bottom of the feeding channel, which is conducive to the continuous feeding of the silica aerogel in the feeding channel. In addition, the gas is continuously blown out from the gas outlet holes, the silica aerogel is continuously fed and contacted with the gas, the silica aerogel is not stacked together when contacted with the gas, the silica aerogel is in a flowing state, and the silica aerogel is close to the gas outlet holes, so that the silica aerogel entering the reactor passes through the gas outlet holes at a close distance, thereby facilitating the sufficient contact between the silica aerogel and the gas.

[0021] Preferably, as an improvement, a blocking part is arranged in the reactor, the blocking part is located below the annular channel, the blocking part is sleeved on the vent pipe, and the gas outlet holes are located above the blocking part.

[0022] Thus, the blocking part can block the silica aerogel leaking from the feeding channel, and the gas blown out from the gas outlet holes blows the silica aerogel on the blocking part. In this way, the silica aerogel falling downward can be stopped by the blocking action of the blocking part, and then the gas blows the silica aerogel, avoiding the problem that the silica aerogel cannot be fully contacted with the gas due to the too fast downward movement of the silica aerogel without stopping, and further improving the contact between the gas and the silica aerogel.

[0023] Preferably, as an improvement, the top end of the feeding part is connected with a feeding box, the bottom of the feeding box is communicated with the feeding channel; the feeding part comprises a middle part and a sleeving part, the sleeving part is sleeved outside the middle part, and the gap between the sleeving part and the middle part is the feeding channel; the inside of the feeding box is provided with a guide cone fixed on the middle part.

[0024] Thus, the feeding box is used for containing the silica aerogel. The guide cone is conical, thereby being capable of guiding the silica aerogel to fall into the annular feeding channel. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is a schematic diagram of a preparation system for producing high-purity silicon carbide raw materials by using silica aerogel.

[0026] Figure 2 It is a structural schematic diagram of the connection of the feeding part, the reactor and the vent pipe.

[0027] Figure 3 It is Figure 2 It is an enlarged view of the middle A. DETAILED DESCRIPTION

[0028] The following will be further described in detail through specific embodiments: The reference signs in the drawings of the specification comprise: an argon source 1, an evaporator 2, a reactor 3, a first vent pipe 4, a second vent pipe 5, a heat preservation layer or heating part 6, a feeding box 7, a guide cone 8, a sleeving part 9, a middle part 10, a feeding channel 11, a blocking part 12 and an air outlet hole 13.

[0029] Embodiment 1 A preparation method for producing high-purity silicon carbide raw materials by using silica aerogel, comprising the following steps: S1, powder-shaped silica aerogel and solid metal reducing agent are put into a reactor (for example, an electric furnace, a high-temperature reaction kettle or a pipe furnace, etc.) to mix, the gas in the reactor is extracted, argon is introduced into the reactor, high-temperature heating is carried out in the argon inert atmosphere, and reaction is carried out for a period of time (8-10h) to generate a first product containing elemental silicon; the reducing agent in the embodiment is sodium or magnesium. The high-temperature heating temperature is 700-900℃. The weight ratio of the silica aerogel and the metal reducing agent in the embodiment is 10-20:1. Specifically, in the step, 80-100g of silica aerogel is mixed with 5-8g of metal reducing agent. The argon flow in the step is 100sccm. The elemental silicon generated in the step is 80-100nm.

[0030] S2, after cooling, the first product is pickled with 10% dilute hydrochloric acid, and a granular second product is obtained by filtration; S3, then the second product is repeatedly washed with deionized water, and after washing, drying (85 degrees Celsius) is performed, and finally, silicon particles having a particle size of less than 100 nm are obtained.

[0031] Comparative Example 1: Instead of using silicon aerogel, a conventional silicon dioxide is used as a silicon source, and the other processes are the same as the above-described silicon carbide raw material production method.

[0032] The purity of the silicon particles in this example is detected (using mass spectrometry ICP-MS or optical spectroscopy), and the inventors found that the purity of the silicon reached more than 7 nines (99.99999%), while the purity of the silicon in the comparative example was 99.9%.

[0033] Example 2 The difference between this example and Example 1 is that the metal reducing agent in S1 enters the reactor 3 as a gas.

[0034] This example also relates to a system for producing high-purity silicon carbide raw materials using silicon aerogel, which combines Figure 1 as shown, comprising, an argon source 1 for providing argon; an evaporator 2 in communication with the argon source 1, the argon in the argon source 1 entering the evaporator 2, the evaporator 2 containing a metal reducing agent, the evaporator 2 being used to change the metal reducing agent to a gaseous state; a reactor 3 in communication with the evaporator 2, the reactor 3 containing silicon aerogel, the gaseous metal reducing agent entering the reactor 3 and mixing with the silicon aerogel, the silicon aerogel and the metal reducing agent being heated at high temperature in the reactor 3.

[0035] In this example, a first air pipe 4 is connected between the argon source 1 and the evaporator 2, and a second air pipe 5 is connected between the evaporator 2 and the reactor 3. The outer side of the second air pipe 5 is provided with a heat preservation layer or a heating part 6, for example, by providing a heat preservation material, so that the inside of the second air pipe 5 can be heat preserved, or by heating through the heating part, so that the heating of the second air pipe 5 is achieved. The heating part can be a copper induction coil wrapped around the outside of the second air pipe 5, which is energized to heat the second air pipe 5. A silicon molybdenum rod or a tungsten wire can also be used as a heating body to directly embed or wrap around the second air pipe 5 to heat the second air pipe 5. In this example, the material of the second air pipe 5 is molybdenum or tantalum.

[0036] The evaporator 2 is provided with a molybdenum boat or a tantalum boat, and the solid metal reducing agent is placed in the molybdenum boat or the tantalum boat. The evaporator 2 is evacuated, and then heated, so that the metal reducing agent is heated to become gaseous metal reducing agent. The argon source 1 provides argon, which enters the evaporator 2 through the first gas pipe 4, and the gaseous metal reducing agent and the argon are mixed together and enter the second gas pipe 5. Since the second gas pipe 5 is provided with a heat preservation layer or a heating part 6, the gas can maintain a certain temperature in the second gas pipe 5 and will not condense. The gas enters the reactor 3 (the temperature of the reactor 3 is 700-900°C), and the metal reducing agent and the silica aerogel contact and react in the reactor 3 to generate silicon. The material of the reaction chamber of the reactor 3 in this embodiment is also molybdenum or tantalum.

[0037] In this embodiment, the metal reducing agent is a gas, which can enter the pores of the silica aerogel after entering the reactor 3. Compared with embodiment 1, the contact between the metal reducing agent and the silica aerogel is more sufficient.

[0038] In this embodiment, the weight ratio of the silica aerogel in the reactor 3 to the metal reducing agent used in the evaporator 2 is 10-20:1. The argon flow rate can be adjusted according to the actual reaction situation.

[0039] In this embodiment, the reaction time of the silica aerogel and the metal reducing agent is shortened to 5-6h, which is shorter than that in embodiment 1, so that the preparation efficiency is greatly improved. At the same time, the purity of the silicon particles prepared in this embodiment is detected, and the purity of the silicon reaches more than 7 nines (99.99999%).

[0040] Comparative example 2: The preparation method of embodiment 1 is used, but the reaction time is shortened to 5-6h, and the rest is the same as that of embodiment 1. The purity of the silicon particles prepared in this comparative example is detected, and the purity of the silicon is only 4 nines (99.99%).

[0041] Example 3 This embodiment is further optimized on the basis of embodiment 2.

[0042] In combination Figure 2 and Figure 3 As shown in the figures, the top of the reactor 3 is fixedly provided with a feeding part, which includes an intermediate part 10 and a sleeving part 9. The sleeving part 9 is tubular and is sleeved outside the intermediate part 10. There is a gap between the intermediate part 10 and the sleeving part 9, which is a feeding channel 11, and the feeding channel 11 is annular. The bottom end of the feeding channel 11 extends into the reactor 3.

[0043] The second vent pipe 5 extends into the reactor 3 from the bottom of the reactor 3, the center line of the second vent pipe 5 is collinear with the center line of the feeding channel 11, the top of the second vent pipe 5 is blocked, specifically, the top end of the second vent pipe 5 abuts against the bottom end of the middle part 10. The outer diameter of the second vent pipe 5 is equal to the outer diameter of the middle part 10. The sidewall of the top of the second vent pipe 5 is provided with a plurality of circumferentially distributed gas outlet holes 13. The inside of the reactor 3 is provided with a blocking part 12, the blocking part 12 is located below the annular channel, the blocking part 12 is fixed (for example, integrally fixed) on the second vent pipe 5, and the gas outlet holes 13 are located above the blocking part 12. The blocking part 12 is opposite to the feeding channel 11.

[0044] The top end of the feeding part in the embodiment is connected with a feeding box 7, the bottom of the feeding box 7 is in communication with the feeding channel 11. The inside of the feeding box 7 is provided with a guide cone 8 fixed on the middle part 10, the guide cone 8 is conical, the bottom diameter of the guide cone 8 is equal to the diameter of the middle part 10, and the guide cone 8 is used for guiding the powdered silica aerogel in the feeding box 7, so that the silica aerogel in the feeding box 7 can enter the feeding channel 11.

[0045] In specific implementation, the silica aerogel is placed in the feeding box 7, the silica aerogel enters the feeding channel 11 under the action of gravity and is blocked at the blocking part 12. Then, the gas in the feeding box 7, the reactor 3 and the feeding channel 11 is extracted, so that the feeding box 7, the reactor 3 and the feeding channel 11 do not contain air. The metal reducing agent gas flowing out of the evaporator 2 flows to the second vent pipe 5, the gas flows along the second vent pipe 5 and enters the reactor 3 along the second vent pipe 5. Since the temperature of the reactor 3 is lower than the temperature of the evaporator 2 and the second vent pipe 5 is partially inserted into the reactor 3, the part of the second vent pipe 5 in the reactor 3 (this part does not contain a heat preservation layer or a heating part 6) can radiate heat to the inside of the reactor 3, which is beneficial to heating the reactor 3 and reducing the energy consumption of the reactor 3 for maintaining a certain temperature.

[0046] The gas flows upward along the second aeration pipe 5 in the reactor 3, and due to the top end of the second aeration pipe 5 being blocked, the gas can only be blown out from the gas outlet hole 13 in the radial direction of the second aeration pipe 5, so as to be blown to the silica aerogel on the blocking part 12 around the top of the second aeration pipe 5, so as to realize the mixing of the metal reducing agent and the silica aerogel, and facilitate the metal reducing agent to enter the pores of the silica aerogel. At the same time, the gas blows the silica aerogel around the top of the second aeration pipe 5, and the silica aerogel is blown off from the blocking part 12 and falls to the bottom of the reactor 3, so that the silica aerogel flowing out of the feeding channel 11 does not block at the bottom of the feeding channel 11, which facilitates the feeding of the silica aerogel in the feeding channel 11. In addition, the gas is continuously blown out from the gas outlet hole 13, and the silica aerogel is continuously fed and contacted with the gas, the silica aerogel is not accumulated when contacted with the gas, the silica aerogel is in a flowing state, and the silica aerogel is close to the gas outlet hole 13, so that the silica aerogel entering the reactor 3 will pass through the gas outlet hole 13 at a close distance, thereby facilitating the sufficient contact between the silica aerogel and the gas.

[0047] In the embodiment, the reaction time of the silica aerogel and the metal reducing agent is shortened to 4h, which is further shortened compared with the reaction time in Embodiment 2. At the same time, the purity of the silica particles prepared in the embodiment is detected, and the purity of the silica reaches more than 7 nines (99.99999%).

[0048] Comparative Example 3: The preparation method of Embodiment 2 is adopted, but the reaction time is shortened to 4h, and the rest is the same as the preparation method of Embodiment 2. The purity of the silica particles prepared in the comparative example is detected, and the purity of the silica is only 5 nines (99.999%).

[0049] The above is only an embodiment of the present application, and the specific technical solutions and / or common knowledge of the scheme are not described in detail. It should be noted that for those skilled in the art, without departing from the technical solutions of the present application, a number of modifications and improvements can be made, which should also be considered as the protection scope of the present application, and these will not affect the effect and practicality of the patent. The protection scope claimed in the present application should be subject to the content of its claims, and the specific embodiments and the like in the specification can be used to explain the content of the claims.

Claims

1. A method for preparing high-purity silicon carbide raw materials using silica aerogel, characterized in that: Includes the following steps: S1. Mix the silica aerogel with a metal reducing agent and heat it at high temperature in an inert argon atmosphere to generate a first product, wherein the first product contains elemental silicon. S2. After cooling, the first product is acid-washed with dilute hydrochloric acid and filtered to obtain the granular second product. S3. Then, the second product is repeatedly rinsed with deionized water, and dried after rinsing to finally obtain silicon particles.

2. The method for preparing high-purity silicon carbide raw materials using silica aerogel according to claim 1, characterized in that: The reducing agent is sodium or magnesium.

3. The method for preparing high-purity silicon carbide raw materials using silica aerogel according to claim 1, characterized in that: The high-temperature heating temperature in S1 is 700-900℃.

4. The method for preparing high-purity silicon carbide raw materials using silica aerogel according to claim 1, characterized in that: In S1, the silica aerogel and the metal reducing agent are mixed and heated at high temperature in the reactor; the metal reducing agent enters the reactor as a gas.

5. A system for preparing high-purity silicon carbide raw materials using silica aerogel, characterized in that: include, An argon gas source, wherein the argon gas source is used to provide argon gas; An evaporator is connected to an argon source, and argon gas from the argon source enters the evaporator. The evaporator contains a metal reducing agent and is used to convert the metal reducing agent into a gaseous state. The reactor is connected to the evaporator. The reactor contains silica aerogel. A gaseous metal reducing agent enters the reactor and mixes with the silica aerogel. The silica aerogel and the metal reducing agent are heated at high temperature in the reactor.

6. The system for preparing high-purity silicon carbide raw materials using silica aerogel according to claim 5, characterized in that: The evaporator is equipped with a molybdenum boat or a tantalum boat, and a solid metal reducing agent is placed in the molybdenum boat or tantalum boat.

7. The system for preparing high-purity silicon carbide raw materials using silica aerogel according to claim 5, characterized in that: A vent pipe is connected between the evaporator and the reactor, and the outer wall of the vent pipe is provided with a heat insulation layer or a heating element.

8. The system for preparing high-purity silicon carbide raw materials using silica aerogel according to claim 7, characterized in that: The reactor is fixedly provided with a feed section at the top, and the feed section is provided with an annular feed channel, the bottom end of which extends into the reactor; the vent pipe extends into the reactor from the bottom, the center line of the vent pipe and the center line of the feed channel are collinear, the top side wall of the vent pipe is provided with multiple circumferentially distributed vent holes, and the top end of the vent pipe is sealed.

9. A system for preparing high-purity silicon carbide raw materials using silica aerogel according to claim 8, characterized in that: The reactor has a baffle inside, which is located below the annular channel and is fitted onto the vent pipe. The vent is located above the baffle.

10. A system for preparing high-purity silicon carbide raw materials using silica aerogel according to claim 8, characterized in that: The top of the feeding part is connected to the feeding box, and the bottom of the feeding box is connected to the feeding channel; the feeding part includes a middle part and a sleeve part, the sleeve part is sleeved on the outside of the middle part, and the gap between the sleeve part and the middle part is the feeding channel; the inside of the feeding box is provided with a guide cone fixed on the middle part.

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