Preparation method of silicon monoxide nano powder

Abstract

The invention relates to a preparation method of silicon monoxide nano powder, and belongs to the technical field of preparation of nonmetal powder materials. According to the method, SiO2 aerogel powder with a three-dimensional continuous structure surface is taken as a raw material, hydrogen molecules are adsorbed on the surface of powdery SiO2 aerogel, and the powdery SiO2 aerogel is axially fed into an inductively coupled plasma torch excited by argon. Hydrogen molecules are excited by an argon plasma torch to form high-activity hydrogen-rich plasma, the high-activity hydrogen-rich plasma and SiO2 aerogel powder with the characteristics of high specific surface area and high porosity are subjected to a reduction reaction, generated silicon monoxide steam is quenched by argon at the downstream of a reaction device, and the high-dispersity silicon monoxide nano powder is obtained. According to the method, the defects of low reaction rate and low raw material conversion rate of the traditional method for preparing silicon monoxide through solid-solid reaction are overcome, the safety problem of the traditional method for producing silicon monoxide through hydrogen reduction is solved, and the production efficiency and the safety are greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of non-metallic powder material preparation, and specifically relates to a method for preparing silicon dioxide 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+SiO 2 =2SiO

[0004] Silicon dioxide vapor is cooled and deposited on the reactor condensation plate to form black block amorphous silicon dioxide deposits. Silicon dioxide materials with different oxygen contents can be obtained by adjusting the raw material ratio and process conditions. Although this method has achieved the preparation of silicon dioxide, it still has some shortcomings. First, as a solid-solid reaction, the reaction conditions of elemental silicon and silicon dioxide are harsh and the reaction rate is low. It is necessary to increase the reaction interface by refining the raw materials and uniformly mixing to promote the reaction. Refining the raw materials is not only energy-consuming and time-consuming, but more importantly, the fine silicon powder is extremely active and can easily cause dust explosions during production and use. Secondly, the intrinsic thermal conductivity of elemental silicon and silicon dioxide is low, and its heat transfer performance in the powder state is further reduced, which makes it difficult for the materials accumulated in the core during the reaction to reach the reaction temperature, resulting in a low raw material conversion rate. Not only that, as the reaction proceeds, the escape of silicon dioxide gas products makes the densely packed raw materials that were originally fully contacted become loose and porous, which further reduces the reaction rate and raw material conversion rate. At present, the single furnace output of silicon oxide synthesized by vapor deposition method is ≤10kg, the production cycle is as long as 20 to 40 hours, and the raw material conversion rate is ≤60%. These defects seriously limit the large-scale production of silicon oxide. Finally, the vapor deposition method is to directly condense silicon oxide vapor on the surface of the condensation plate, and the obtained silicon oxide is amorphous block, which requires cumbersome secondary processing (such as crushing, heat treatment, and grading) to disperse it to the nanoscale. The secondary processing of amorphous silicon oxide is easy to cause the disproportionation reaction of silicon oxide, and the processed products also generally have defects such as poor dispersibility and low tap density.

[0005] In addition, carbon and silicon dioxide powder can be mixed in a certain proportion and then reduced at 1600°C and 1.013KPa to obtain silicon dioxide vapor. The reaction formula is:

[0006] C+2SiO 2 =CO 2 +2SiO

[0007] As a solid-solid reaction, this method still has the defects of low reaction rate and raw material conversion rate. In addition, in order to promote the reaction, carbon is generally added in excess as a reducing agent. This results in the presence of not only silicon oxide in the reaction product, but also residual silicon carbide and carbon impurities that affect the purity of silicon oxide. The generated carbon monoxide has 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 vacuum. The chemical reaction formula is:

[0009] SiO 2 +H 2 =SiO+H 2 O

[0010] Since the rate of gas-solid reaction is much higher than that of traditional solid-solid reaction, this method has a higher reaction rate and the reaction product is also environmentally friendly. However, this reaction involves the use of hydrogen, which is highly dangerous. It is not only easy to leak and cause explosion, but also causes hydrogen embrittlement of the reactor at high temperature. Therefore, it places extremely high demands on the material and design of the reactor.

[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. Especially in the field of nanomaterial preparation, compared with traditional methods such as liquid phase method and ball milling method, plasma technology has higher production efficiency and reduces or avoids the use of process control agents or surfactants. Specifically in the preparation of silicon-based negative electrode materials, patent CN109796017 vaporizes the dried silicon monoxide in a plasma torch and condenses to obtain nano silicon monoxide with uniform particle size, high purity, no hard agglomeration, and stable chemical properties. However, this method uses silicon monoxide with a particle size of 0.5 to 75 μm as a raw material, and realizes the nano-sizing of silicon monoxide through the physical state change of the material during the plasma treatment process. The silicon monoxide raw material still relies on traditional methods for preparation, so it fails to solve the preparation problem of nano silicon monoxide from the level of new material synthesis. Patent CN116692870 uses electric heating or microwave heating to make silica (SiO 2 ) reacts with hydrogen to generate silicon monoxide, and then a plasma generator is used to excite hydrogen plasma to improve the reducibility of hydrogen, and then react with silicon dioxide to obtain powdered silicon. Although this invention uses a gas-solid reaction based on hydrogen plasma to achieve the preparation of silicon, greatly improving production efficiency, it still uses a high-temperature fluidized bed as a reactor in the production of silicon monoxide, and uses electricity or microwaves to irradiate the hydrogen and silica (SiO 2) is heated to generate silicon monoxide at 1200-1700°C. 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. In addition, the final target product of this method is powdered industrial silicon, and silicon monoxide is an intermediate product of the reaction, and its state is not mentioned in the invention. Summary of the invention

[0012] The purpose of the present invention is to provide a method for preparing silicon dioxide nanopowder. 2 Aerogel powder is used as raw material, hydrogen is excited by a plasma torch to form a highly active hydrogen-rich plasma, and the silicon dioxide vapor generated by the reduction reaction is quenched by argon gas downstream of the reaction device to obtain silicon dioxide nanopowder. This method overcomes the defects of slow reaction rate and low raw material conversion rate of the traditional solid-solid reaction method for preparing silicon dioxide, and solves the safety problems of the traditional method of producing silicon dioxide by hydrogen reduction, greatly 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) SiO 2 The aerogel powder is placed in a sealed container, the sealed container is evacuated, and the SiO 2 The aerogel powder is heated until the pressure in the sealed container no longer changes, achieving SiO 2 Removal of adsorbed gas molecules on the surface of aerogel powder;

[0016] (2) Add the degassed SiO 2 The sealed container of aerogel powder is filled with hydrogen to 95.0-105.0 KPa and maintained for a period of time until the pressure in the sealed container does not change, so that the hydrogen molecules are adsorbed on the degassed SiO 2 Aerogel powder surface;

[0017] (3) The SiO2 adsorbed hydrogen molecules obtained in step (2) 2 Aerogel powder was fed into an argon-excited inductively coupled plasma torch for plasma heat treatment. 2 The aerogel powder reacts with 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] Step (1) SiO 2 Aerogel powder particle size range is 200~500μm, specific surface area ≥500m 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 gas, 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 SiO 2 Aerogel powder is used as raw material, and its high specific surface area and high porosity are used to adsorb hydrogen molecules on powdered SiO 2 The surface of the aerogel is fed into a reaction device to allow hydrogen molecules to react with SiO 2 While ensuring full contact, the free movement of hydrogen molecules is restricted, greatly improving the safety of the production process.

[0026] (2) In the reaction device of the present invention, argon is used to excite inductively coupled plasma to adsorb hydrogen molecules on SiO 2 Aerogel powder is used as a reactant and is axially fed into the plasma torch. The reactants and reaction products are all wrapped in an argon atmosphere, which prevents the reaction products from being oxidized while ensuring the safety of the reaction process.

[0027] (3) SiO2 adsorbing hydrogen molecules of the present invention 2 The hydrogen molecules in the aerogel powder are excited by the high temperature of the argon plasma torch to form a highly active hydrogen-rich plasma, which reacts with the SiO2 with high specific surface area and high porosity. 2 Compared with solid-solid reaction and traditional gas-solid reaction, the reaction process of aerogel powder is only in milliseconds, 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 only high temperature area in the reaction device is the position close to the inductively coupled plasma torch, which avoids heating of the entire reaction device. Therefore, the cooling rate of the silicon dioxide vapor and hydrogen gas 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 gas 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 dioxide nanopowder according to Example 1 of the present invention. DETAILED DESCRIPTION

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

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

[0034] (1) SiO 2 The aerogel powder is placed in a sealed container, the sealed container is evacuated, and the SiO 2 The aerogel powder is heated until the pressure in the sealed container no longer changes, achieving SiO 2 Removal of adsorbed gas molecules on the surface of aerogel powder;

[0035] (2) Add the degassed SiO 2 The sealed container of aerogel powder is filled with hydrogen to 95.0-105.0 KPa and maintained for a period of time until the pressure in the sealed container does not change, so that the hydrogen molecules are adsorbed on the degassed SiO 2 Aerogel powder surface;

[0036] (3) The SiO2 adsorbed hydrogen molecules obtained in step (2) 2 Aerogel powder was fed into an argon-excited inductively coupled plasma torch for plasma heat treatment. 2 The aerogel powder reacts with 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 to condense to obtain silicon dioxide nanopowder.

[0038] Example 1

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

[0040] (1) SiO with a particle size range of 250 to 350 μm 2 The aerogel powder is placed in a sealed container, which is evacuated to 0.1 Pa. 2 The aerogel powder was heated to 100 °C and degassed for 30 min until the pressure in the sealed container no longer changed, achieving SiO 2 Removal of gas molecules adsorbed on the surface of aerogel powder.

[0041] (2) Place the degassed SiO 2 The sealed container of aerogel powder is filled with hydrogen to 101.0 kPa, and the pressure is maintained for 30 minutes until the final pressure in the sealed container reaches 101.0 kPa, so that the hydrogen molecules are adsorbed on the degassed SiO 2 Aerogel powder surface;

[0042] (3) SiO2 that absorbs hydrogen molecules 2 The aerogel powder 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] SiO 2 The 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 oxide 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 oxide nanopowder with an average particle size of 20 μm prepared in this embodiment; 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] The preparation method of highly dispersed silicon dioxide nanopowder with an average particle size of 50 nm comprises the following steps:

[0049] (1) SiO with a particle size range of 300 to 400 μm 2 The aerogel powder is placed in a sealed container, which is evacuated to 0.3 Pa. 2 The aerogel powder was heated to 120°C and degassed for 20 min until the pressure in the sealed container no longer changed, achieving SiO 2 Removal of gas molecules adsorbed on the surface of aerogel powder.

[0050] (2) Place the degassed SiO 2 The sealed container of aerogel powder is filled with hydrogen to 100.0 kPa, and the pressure is maintained for 20 minutes until the final pressure in the sealed container reaches 101.0 kPa, so that the hydrogen molecules are adsorbed on the degassed SiO 2 Aerogel powder surface;

[0051] (3) SiO2 that absorbs hydrogen molecules 2 The aerogel powder 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] SiO 2 The 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 mode of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

[0056] The contents not described in detail in the specification of the present invention belong to the common knowledge of the 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 sent to an argon-excited inductively coupled plasma torch for plasma heat treatment, and the SiO2 aerogel powder reacts with the hydrogen molecules adsorbed on the surface to obtain 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, characterized in that: The SiO2 aerogel powder of 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, characterized in that: When the sealed container is evacuated in step (1), the pressure inside the sealed container is ≤1Pa.

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

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

7. A silicon oxide nanopowder, characterized in that: The method according to any one of claims 1 to 6 is used to prepare the compound.

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