A method for preparing silicon dioxide nanopowder

Abstract

The present invention relates to a method for preparing silicon monoxide nanopowder, and belongs to the technical field of non-metallic powder material preparation. The present invention uses SiO2 aerogel powder with a three-dimensional continuous structure surface as raw material, adsorbs hydrogen molecules on the surface of the powdered SiO2 aerogel, and axially feeds an argon-excited inductively coupled plasma torch. The hydrogen molecules are excited by the argon plasma torch to form a highly active hydrogen-rich plasma, which undergoes a reduction reaction with the SiO2 aerogel powder having the characteristics of high specific surface area and high porosity. The generated silicon monoxide vapor is quenched by argon downstream of the reaction device to obtain highly dispersible silicon monoxide nanopowder. This method overcomes the defects of the traditional solid-solid reaction method for preparing silicon monoxide, which has a slow reaction rate and low raw material conversion rate, and at the same time solves the safety problems existing in the traditional method of producing silicon monoxide by hydrogen reduction, thereby greatly improving production efficiency and safety.

Description

Technical Field

[0001] The invention belongs to the technical field of non-metallic powder material preparation, and particularly relates to a method for preparing silicon monoxide nanopowder. Background Art

[0002] Industrially, silicon dioxide is mainly synthesized by vapor deposition. After mixing elemental silicon with silicon dioxide, a neutralization reaction occurs under negative pressure (<1Pa) and 1300℃~1500℃. The silicon dioxide formed escapes in the form of steam. The reaction formula is:

[0003] Si+SiO2=2SiO

[0004] Silicon oxide vapor cools and deposits on the reactor's condenser plates, forming black, amorphous silicon oxide deposits. By adjusting the raw material ratios and process conditions, silicon oxide materials with varying oxygen contents can be produced. While this method achieves the production of silicon oxide, it still has some drawbacks. First, as a solid-solid reaction, the reaction between elemental silicon and silicon dioxide requires demanding conditions and a low reaction rate, necessitating refinement of the raw materials and uniform mixing to increase the reaction interface and facilitate the reaction. Refining the raw materials is not only energy-consuming and time-consuming, but more importantly, fine silicon powder is highly reactive, making it prone to dust explosions during production and use. Second, the intrinsic thermal conductivity of elemental silicon and silicon dioxide is low, further reducing their heat transfer performance in powder form. This makes it difficult for the material accumulated in the core of the reaction to reach the reaction temperature, resulting in low raw material conversion. Furthermore, as the reaction proceeds, the escape of silicon oxide gaseous products causes the previously well-contacted, densely packed raw materials to become loose and porous, further reducing the reaction rate and raw material conversion. Currently, the single-furnace production of silicon oxide synthesized using vapor deposition is ≤10kg, the production cycle is as long as 20 to 40 hours, and the raw material conversion rate is ≤60%. These shortcomings severely limit the large-scale production of silicon oxide. Finally, the vapor deposition method directly condenses silicon oxide vapor onto the surface of a condenser plate, resulting in amorphous silicon oxide blocks that require cumbersome secondary processing (such as crushing, heat treatment, and grading) to disperse them to the nanoscale. Secondary processing of amorphous silicon oxide easily triggers disproportionation reactions of silicon oxide, and the processed products also generally suffer from defects such as poor dispersibility and low tap density.

[0005] In addition, silicon dioxide vapor can be obtained by mixing carbon and silicon dioxide powder in a certain proportion and then reducing them at 1600°C and 1.013KPa. The reaction formula is:

[0006] C+2SiO2=CO2+2SiO

[0007] As a solid-solid reaction, this method still suffers from the drawbacks of low reaction rate and low raw material conversion rate. Furthermore, to promote the reaction, carbon is generally added in excess as a reducing agent. This results in the reaction product containing not only silicon oxide but also residual silicon carbide and carbon impurities that affect the purity of silicon oxide. The generated carbon monoxide poses certain hazards to the environment and production safety.

[0008] Silicon dioxide can also be obtained by reducing it with hydrogen at a high temperature of 1200-1700℃ and then sublimating it in a vacuum. The chemical reaction formula is:

[0009] SiO2+H2=SiO+H2O

[0010] Because the gas-solid reaction rate is much higher than traditional solid-solid reactions, this method offers a high reaction rate and environmentally friendly reaction products. However, this reaction involves the use of hydrogen, which is highly hazardous. Leakage can easily cause explosions, and at high temperatures, it can also cause hydrogen embrittlement in the reactor, placing extremely high demands on the reactor's materials and design.

[0011] As an important material processing technology, plasma has been increasingly used in the preparation of positive and negative electrode materials for lithium batteries in recent years. In particular, in the field of nanomaterial preparation, plasma technology offers higher production efficiency than traditional methods such as liquid phase and ball milling, while also reducing or eliminating the use of process control agents or surfactants. Specifically for the preparation of silicon-based anode materials, patent CN109796017 vaporizes dried silicon monoxide in a plasma torch and condenses it to produce nano-silicon monoxide with uniform particle size, high purity, no hard agglomerates, and stable chemical properties. However, this method uses silicon monoxide with a particle size of 0.5 to 75 μm as the raw material. Nano-sizing the silicon monoxide is achieved through the material's physical state changes during the plasma treatment. However, the silicon monoxide raw material still relies on traditional methods for preparation, thus failing to address the problem of nano-silicon monoxide preparation from the perspective of new material synthesis. Patent CN116692870 utilizes electric or microwave heating to react silica (SiO2) with hydrogen to produce silicon monoxide. A plasma generator is then used to generate hydrogen plasma to enhance the reducibility of the hydrogen, which then reacts with silicon dioxide to produce powdered silicon. Although this invention utilizes a hydrogen plasma-based gas-solid reaction to achieve the preparation of silicon, greatly improving production efficiency, it still uses a high-temperature fluidized bed as a reactor in the silicon monoxide production stage. The hydrogen and silica (SiO2) in the reaction tank are heated by electricity or microwaves, and react at 1200-1700°C to produce silicon monoxide. During the reaction, the reaction tank is filled with free high-temperature hydrogen, so safety issues such as hydrogen leakage and high-temperature hydrogen embrittlement of the reactor still exist. Moreover, the final target product of this method is powdered industrial silicon, and the state of silicon monoxide as an intermediate product of the reaction is not mentioned in the invention. Summary of the Invention

[0012] The present invention aims to provide a method for preparing silicon oxide nanopowder. This method uses SiO2 aerogel powder with hydrogen adsorbed on its surface as raw material. A plasma torch is used to excite hydrogen to form a highly active hydrogen-rich plasma. The resulting silicon oxide vapor is then quenched with argon gas downstream of the reactor to produce the silicon oxide nanopowder. This method overcomes the shortcomings of traditional solid-solid reaction methods for preparing silicon oxide, such as slow reaction rates and low raw material conversion rates. It also addresses safety concerns associated with traditional hydrogen reduction methods for producing silicon oxide, significantly improving production efficiency and safety.

[0013] The above-mentioned purpose of the present invention is mainly achieved through the following technical solutions:

[0014] A method for preparing silicon dioxide nanopowder comprises the following steps:

[0015] (1) placing SiO2 aerogel powder in a sealed container, evacuating the sealed container, and heating the SiO2 aerogel powder until the pressure in the sealed container no longer changes, thereby removing the gas molecules adsorbed on the surface of the SiO2 aerogel powder;

[0016] (2) filling the sealed container containing the degassed SiO2 aerogel powder obtained in step (1) with hydrogen to a pressure of 95.0 to 105.0 kPa, and maintaining the pressure for a period of time until the pressure in the sealed container no longer changes, so that the hydrogen molecules are adsorbed on the surface of the degassed SiO2 aerogel powder;

[0017] (3) The SiO2 aerogel powder adsorbing hydrogen molecules obtained in step (2) is fed into an argon-excited inductively coupled plasma torch for plasma heat treatment, whereby the SiO2 aerogel powder reacts with the hydrogen molecules adsorbed on the surface to produce silicon dioxide gas;

[0018] (4) The silicon dioxide gas obtained in step (3) is separated from the plasma torch, and the silicon dioxide gas is quenched and dispersed during the falling process to condense to obtain silicon dioxide nanopowder.

[0019] The SiO2 aerogel powder in step (1) has a particle size range of 200 to 500 μm and a specific surface area of ​​500 m 2 / g.

[0020] When the sealed container is evacuated in step (1), the pressure inside the sealed container is ≤1Pa.

[0021] The heating temperature in step (1) is 50-150°C.

[0022] The process parameters of the plasma heat treatment in step (3) are as follows: plasma power is 30kW~100kW, center gas flow rate is 40slpm~60slpm argon, sheath gas flow rate is 200slpm~800slpm argon, carrier gas flow rate is 20slpm~50slpm argon, system pressure is 100kPa~120kPa, and powder feeding rate is 200g / min~1000g / min.

[0023] The gas used in the quenching and dispersion process of step (4) is argon, and the cooling rate of silicon dioxide gas is ≥2×10 4 K / s.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects:

[0025] (1) The present invention uses SiO2 aerogel powder with a three-dimensional continuous structure surface as raw material, and utilizes its high specific surface area and high porosity to adsorb hydrogen molecules on the surface of the powdered SiO2 aerogel and send it into the reaction device, so that the hydrogen molecules are in full contact with SiO2 while restricting the free movement of the hydrogen molecules, thereby greatly improving the safety of the production process.

[0026] (2) The reaction device of the present invention adopts argon-excited inductively coupled plasma, and SiO2 aerogel powder adsorbing hydrogen molecules is used as a reactant and is axially fed into the plasma torch. The reactant and the reaction product are both wrapped in the argon atmosphere, which avoids the oxidation of the reaction product and ensures the safety of the reaction process.

[0027] (3) The hydrogen molecules in the SiO2 aerogel powder that adsorbs hydrogen molecules of the present invention are excited by the high temperature of the argon plasma torch to form a highly active hydrogen-rich plasma, which reacts with the SiO2 aerogel powder having the characteristics of high specific surface area and high porosity. Compared with solid-solid reactions and traditional gas-solid reactions, the reaction process of this invention is only on the millisecond level, the reaction rate is greatly improved, and the raw material conversion rate exceeds 98%.

[0028] (4) The inductively coupled plasma of the present invention has an extremely high temperature gradient. The high temperature zone in the reaction device is only near the position of the inductively coupled plasma torch, which avoids heating of the entire reaction device. Therefore, the cooling rate of the silicon dioxide vapor and hydrogen leaving the plasma torch is extremely high. Combined with the quenching argon gas downstream of the inductively coupled plasma torch, the silicon dioxide vapor and hydrogen can be rapidly cooled. This condition is not only conducive to the formation of highly dispersed nano-silicon dioxide, but also can avoid hydrogen embrittlement of the reaction device caused by high-temperature hydrogen. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of a method for preparing silicon dioxide nanopowder according to the present invention;

[0030] Figure 2 This is an X-ray diffraction pattern of a silicon oxide nanopowder according to Example 1 of the present invention;

[0031] Figure 3 This is a transmission electron microscope photograph of silicon monoxide nanopowder according to Example 1 of the present invention. DETAILED DESCRIPTION

[0032] The present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments:

[0033] like Figure 1 The figure shows a principle diagram of a method for preparing silicon oxide nanopowder according to the present invention. The method for preparing silicon oxide nanopowder comprises the following steps:

[0034] (1) placing SiO2 aerogel powder in a sealed container, evacuating the sealed container, and heating the SiO2 aerogel powder until the pressure in the sealed container no longer changes, thereby removing the gas molecules adsorbed on the surface of the SiO2 aerogel powder;

[0035] (2) filling the sealed container containing the degassed SiO2 aerogel powder obtained in step (1) with hydrogen to a pressure of 95.0 to 105.0 kPa, and maintaining the pressure for a period of time until the pressure in the sealed container no longer changes, so that the hydrogen molecules are adsorbed on the surface of the degassed SiO2 aerogel powder;

[0036] (3) The SiO2 aerogel powder adsorbing hydrogen molecules obtained in step (2) is fed into an argon-excited inductively coupled plasma torch for plasma heat treatment, whereby the SiO2 aerogel powder reacts with the hydrogen molecules adsorbed on the surface to produce silicon dioxide gas;

[0037] (4) After the silicon dioxide gas obtained in step (3) leaves the high-temperature plasma torch, the silicon dioxide gas is quenched and dispersed during the falling process, and condensed to obtain silicon dioxide nanopowder.

[0038] Example 1

[0039] Preparation of highly dispersed silicon dioxide nanopowder with an average particle size of 20 nm comprises the following steps:

[0040] (1) SiO2 aerogel powder with a particle size range of 250 to 350 μm is placed in a sealed container, and the sealed container is evacuated to 0.1 Pa. At the same time, the SiO2 aerogel powder is heated to 100 ° C and degassed for 30 minutes until the pressure in the sealed container no longer changes, thereby removing the gas molecules adsorbed on the surface of the SiO2 aerogel powder.

[0041] (2) hydrogen was filled into a sealed container containing degassed SiO2 aerogel powder to a pressure of 101.0 kPa, and the pressure was maintained for 30 min until the final pressure in the sealed container reached 101.0 kPa, so that hydrogen molecules were adsorbed on the surface of the degassed SiO2 aerogel powder;

[0042] (3) The SiO2 aerogel powder adsorbing hydrogen molecules is fed into an argon-excited inductively coupled plasma torch for plasma heat treatment. The process parameters of the plasma heat treatment include:

[0043]

[0044] SiO2 aerogel powder reacts with hydrogen molecules adsorbed on the surface to produce silicon dioxide gas;

[0045] (4) After the silicon oxide gas leaves the high-temperature plasma torch, argon gas is used to quench and disperse the silicon oxide gas during the falling process. The cooling rate of the silicon oxide gas is 5×10 4 K / s, and condensed to obtain highly dispersed silicon dioxide nanopowder with an average particle size of 20 μm.

[0046] Figure 2 The figure shows the X-ray diffraction pattern of the highly dispersed silicon dioxide nanopowder with an average particle size of 20 μm prepared in this example; Figure 3 This is a transmission electron microscope photograph of the highly dispersed silicon dioxide nanopowder with an average particle size of 20 μm prepared in this example.

[0047] Example 2

[0048] Preparation of highly dispersed silicon dioxide nanopowder with an average particle size of 50 nm comprises the following steps:

[0049] (1) SiO2 aerogel powder with a particle size range of 300-400 μm is placed in a sealed container, and the sealed container is evacuated to 0.3 Pa. At the same time, the SiO2 aerogel powder is heated to 120 ° C and degassed for 20 minutes until the pressure in the sealed container no longer changes, thereby removing the gas molecules adsorbed on the surface of the SiO2 aerogel powder.

[0050] (2) hydrogen was filled into a sealed container containing degassed SiO2 aerogel powder to a pressure of 100.0 kPa, and the pressure was maintained for 20 min until the final pressure in the sealed container reached 101.0 kPa, so that hydrogen molecules were adsorbed on the surface of the degassed SiO2 aerogel powder;

[0051] (3) The SiO2 aerogel powder adsorbing hydrogen molecules is fed into an argon-excited inductively coupled plasma torch for plasma heat treatment. The process parameters of the plasma heat treatment include:

[0052]

[0053] SiO2 aerogel powder reacts with hydrogen molecules adsorbed on the surface to produce silicon dioxide gas;

[0054] (4) After the silicon oxide gas leaves the high-temperature plasma torch, argon gas is used to quench and disperse the silicon oxide gas during the falling process. The cooling rate of the silicon oxide gas is 4×10 4 K / s, and condensed to obtain highly dispersed silicon dioxide nanopowder with an average particle size of 50 μm.

[0055] The above description is only the best specific implementation method of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or replacements that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

[0056] The contents not described in detail in the specification of the present invention belong to the common knowledge of professionals in this field.

Claims

1. A method for preparing silicon dioxide nanopowder, characterized in that: The following steps are involved: (1) placing SiO2 aerogel powder in a sealed container, evacuating the sealed container, and heating the SiO2 aerogel powder until the pressure in the sealed container no longer changes, thereby removing the gas molecules adsorbed on the surface of the SiO2 aerogel powder; (2) filling the sealed container containing the degassed SiO2 aerogel powder obtained in step (1) with hydrogen to a pressure of 95.0 to 105.0 kPa, and maintaining the pressure for a period of time until the pressure in the sealed container no longer changes, so that the hydrogen molecules are adsorbed on the surface of the degassed SiO2 aerogel powder; (3) The SiO2 aerogel powder adsorbing hydrogen molecules obtained in step (2) is fed into an argon-excited inductively coupled plasma torch for plasma heat treatment, whereby the SiO2 aerogel powder reacts with the hydrogen molecules adsorbed on the surface to produce silicon dioxide gas; (4) The silicon dioxide gas obtained in step (3) is separated from the plasma torch, and the silicon dioxide gas is quenched and dispersed during the falling process to condense to obtain silicon dioxide nanopowder.

2. The method for preparing silicon dioxide nanopowder according to claim 1, wherein: The SiO2 aerogel powder in step (1) has a particle size range of 200 to 500 μm and a specific surface area of ​​500 m 2 / g.

3. The method for preparing silicon dioxide nanopowder according to claim 1, wherein: When the sealed container is evacuated in step (1), the pressure inside the sealed container is ≤1Pa.

4. The method for preparing silicon monoxide nanopowder according to claim 1, wherein: The heating temperature in step (1) is 50-150°C.

5. The method for preparing silicon monoxide nanopowder according to claim 1, wherein: The process parameters of the plasma heat treatment in step (3) are as follows: plasma power is 30kW~100kW, center gas flow rate is 40slpm~60slpm argon, sheath gas flow rate is 200slpm~800slpm argon, carrier gas flow rate is 20slpm~50slpm argon, system pressure is 100kPa~120kPa, and powder feeding rate is 200g / min~1000g / min.

6. The method for preparing silicon monoxide nanopowder according to claim 1, wherein: The gas used in the quenching and dispersion process of step (4) is argon, and the cooling rate of silicon dioxide gas is ≥2×10 4 K / s.

7. A silicon oxide nanopowder, characterized by: The method according to any one of claims 1 to 6 is prepared.

Images