Method for preparing high-purity nano silicon-carbon-oxygen ceramic powder by pyrolyzing silicon-carbon composite aerogel through microwave induction graphite tube fluidized bed

Abstract

The invention discloses a method for preparing high-purity nano silicon-carbon-oxygen ceramic powder by pyrolyzing silicon-carbon composite aerogel through a microwave induction graphite tube fluidized bed, relates to a preparation method of the high-purity nano silicon-carbon-oxygen ceramic powder, and aims to solve the technical problems that the purity of nano silicon carbide powder prepared by the conventional method is low, and the particle size is difficult to be less than 100nm and is not uniform. The method comprises the following steps: 1, pre-hydrolyzing monoaromatic ring silane, polyaromatic ring silane, straight-chain silane, silicate ester or orthosilicic acid serving as an initial raw material, adding ammonia gas, basic silane or silazane, reacting to prepare wet gel, replacing, aging, and removing a solvent to obtain silicon-carbon composite aerogel; and 2, after the surface of the silicon-carbon composite aerogel is subjected to impurity removal and purification, the silicon-carbon composite aerogel is conveyed to a microwave induction graphite tube fluidized bed for pyrolysis and carbonization, and the nano silicon-carbon-oxygen ceramic powder is obtained. The particle size of the silicon-carbon-oxygen ceramic powder is 100-500nm, the purity reaches 6N, and the silicon-carbon-oxygen ceramic powder can be used in the field of semiconductors.

Description

Technical Field

[0001] The invention relates to a method for preparing high-purity nano silicon carbon oxygen ceramic powder, and belongs to the field of multifunctional inorganic materials. Background Art

[0002] In the semiconductor manufacturing process, silicon carbide ceramics are used to make grinding discs because of their high hardness and low wear. Silicon carbide grinding discs can maintain flatness and parallelism when grinding or polishing silicon wafers at high speed, thereby improving the quality of the wafers. High-temperature heat treatment is often required in the production process of semiconductor devices, and silicon carbide ceramic fixtures are used for transportation, because the heat resistance and stability of silicon carbide can ensure that it will not damage the wafer at high temperatures, while preventing the diffusion of metal ion pollution, ensuring the quality of semiconductor devices. Therefore, in the production process of high-end semiconductor chips such as integrated circuit manufacturing and artificial intelligence, high-purity and precision silicon carbide ceramic structural parts are required. These structural parts include ceramic worktables, guide rails, reflectors, ceramic suction cups, etc. of photolithography machines, all of which have extremely high requirements for the purity and precision of materials. The extremely high requirements for the purity and precision of silicon carbide ceramic materials in the above-mentioned application fields have put forward extremely high requirements for silicon carbide ceramic raw materials, that is, nano-silicon carbide high-purity powders, which are mainly reflected in the requirements for purity, particle size and uniformity, and surface activity. Therefore, the reliable preparation of 6N high-purity nano-SiC powder has become a core issue restricting the development of high-purity SiC ceramics.

[0003] Currently, there are three main methods for preparing nano-silicon carbide ceramic powder, namely mechanical grinding, sol-gel method and CVD method.

[0004] (1) The mechanical grinding method is to crush the block silicon carbide step by step through crushing equipment such as Raymond mill, air flow mill and sand mill, and then through various screening technologies to finally obtain nano silicon carbide. The biggest disadvantage of this method is that it inevitably introduces various metal and non-metal impurities in the crushing equipment and grinding media. Even through acid washing, it is impossible to prepare silicon carbide nanomaterials with a purity greater than 3N. At the same time, due to multi-stage crushing and screening, the process consumes huge energy and is inefficient, and it is difficult for the particles to be less than 500 nanometers. In fact, they can only be regarded as submicron particles, rather than nano silicon carbide materials in the true sense.

[0005] (2) The sol-gel method uses sol-gel technology to introduce carbon precursors or tiny carbon materials into the silica sol system, and then obtains silicon carbide nanopowders through high-temperature carbon thermal reduction. This method can prepare nano-silicon carbide, but due to the introduction of catalysts in the silica sol process and the contamination of carbon-based resins, it is also impossible to prepare silicon carbide nanomaterials with a purity exceeding 3N. In addition, silicon and carbon elements are not mixed at the molecular interface, and the silicon / carbon molar ratio of the final product cannot fully achieve the stoichiometric ratio of silicon carbide.

[0006] (3) The CVD method uses methylchlorosilane as the raw material and can prepare silicon carbide nanopowders in a reducing atmosphere. However, this method has extremely high requirements on the corrosion resistance and precision of the production equipment materials. The reaction process produces more than ten by-products such as monomethyltrichlorosilane, dimethyldichlorosilane, hydrogen-containing chlorosilane, trichlorosilane, and silicon tetrachloride. The large amount of chlorine-containing by-products needs to be treated and environmentally friendly, as well as the extremely low raw material utilization rate, which makes the production cost high and unsuitable for large-scale industrialization. In addition, the product surface energy is too high and mostly exists in the form of agglomerates, which is not suitable for the preparation requirements of high-purity silicon carbide ceramics. Summary of the invention

[0007] The present invention aims to solve the technical problems that the nano silicon carbide powder prepared by the existing method has low purity, the particle size is difficult to be less than 100nm and is non-uniform, and provides a method for preparing high-purity nano silicon carbon oxygen ceramic powder by microwave induced graphite fluidized bed pyrolysis of silicon-carbon composite aerogel.

[0008] The method for preparing high-purity nano silicon carbon oxygen ceramic powder by microwave-induced graphite fluidized bed pyrolysis of silicon-carbon composite aerogel is carried out according to the following steps:

[0009] 1. Preparation of silicon-carbon composite aerogel:

[0010] (1) Preparation of pre-hydrolysis liquid: using monoaromatic silane, polyaromatic silane, linear silane, silicate or orthosilicic acid as starting raw materials, adding water-containing organic alcohol as solvent and acidic catalytic silane monomer as hydrolysis catalyst in sequence to obtain raw material liquid; stirring the raw material liquid at a temperature of 25 to 50° C. and a stirring speed of 150 to 600 r / min for 0.5 to 12 hours to hydrolyze the raw material to obtain a pre-hydrolysis liquid; controlling the hydrolysis degree of various raw material monomers by the amount of acidic silane, the concentration of hydrolysis raw materials, the reaction temperature and the stirring speed; controlling the consistency of the hydrolysis speed by the raw material addition sequence and the addition speed, thereby suppressing the occurrence of disordered polymerization reaction of each raw material;

[0011] (2) Preparation of wet gel: Ammonia, basic silane or silazane are introduced into the pre-hydrolyzed liquid in the stirred tank equipment, and then the reaction solvent is added, and the mixture is stirred for 0.5 to 12 hours at a temperature of 15 to 50°C and a pressure of normal pressure to obtain a wet gel. The temperature is adjusted in this step to prepare a wet gel with controllable colloidal particle size and adjustable solid content. The wet gel particles are controlled within the range of 20 to 500 nm, and the solid content is controlled within the range of 60% to 30%.

[0012] (3) Solvent replacement and purification of wet gel: The wet gel is placed in an ultrasound-assisted rapid self-absorption stirring system, and a replacement reagent is added to perform reverse pulse solvent replacement to obtain a high-purity wet gel; the closed solvent and a small amount of anion and ammonium particles in the wet gel are replaced by reverse pulse solvent replacement;

[0013] (4) Aging and skeleton strengthening of high-purity wet gel: The high-purity wet gel is placed in a light wave aging system with a wavelength of 200-400nm ultraviolet light and 800-1100nm infrared light for 0.5-2h to obtain a wet gel with constant temperature aging and skeleton strengthening;

[0014] (5) Preparation of silicon-carbon composite aerogel: The constant temperature aged and skeleton-strengthened wet gel is input into a microwave tube drying fluidized bed through a plunger pump for solvent removal and drying to obtain silicon-carbon composite aerogel powder; this step avoids the problem of low microwave penetration depth by using PP or tetrafluoroplastic tubes arranged in a matrix. After the wet gel slurry enters the fluidized bed, it enters each tube through a distribution plate for solvent removal and drying to obtain silicon-carbon composite aerogel powder, wherein the silicon-carbon ratio of the silicon-carbon composite aerogel powder is 1:1;

[0015] 2. Preparation of Nano-SiC Oxygen Ceramic Powders:

[0016] (1) Surface purification of silicon-carbon composite aerogel powder: silicon-carbon composite aerogel powder is added to a quartz rotary furnace through a quantitative bin, and high-temperature water vapor at a temperature of 120 to 180° C. is introduced into the quartz rotary furnace. The treatment is performed for 3 to 10 hours under the conditions of a water vapor addition amount of 1 to 10 kg / h and a rotary furnace speed of 10 to 60 r / min. After the treatment, the system vacuum is controlled at 1 to 100 Pa within 1 to 10 hours to obtain aerogel powder with a clean surface. In this step, high-temperature water vapor is used to desorb air and water vapor adsorbed on the surface of the silicon-carbon composite aerogel powder;

[0017] (2) Preparation of Nano-SiC Oxygen Ceramic Powders:

[0018] The cleaned aerogel powder is transported to a microwave-induced graphite tube fluidized bed through a venturi-type pneumatic conveying device, and argon or hydrogen is used as an auxiliary fluidizing gas. The microwave power is adjusted to raise the system temperature to 260-1200°C, and fluidized pyrolysis carbonization is performed under negative pressure, normal pressure or pressurized conditions. The residence time of the aerogel powder in the microwave-induced graphite tube fluidized bed is 0.1-1h, and nano-silicon carbon oxygen ceramic powder is obtained. In this step, in-situ carbonization and degreasing are performed during the fluidized pyrolysis carbonization process, the size and basic morphology of the original aerogel particles are maintained, and nano-silicon carbon oxygen ceramic powder with controllable particle size is obtained.

[0019] Furthermore, the monoaromatic ring silane in step 1 (1) is phenyltrimethoxysilane, phenyltriethoxysilane, methylphenyldimethoxysilane, methylphenyldiethoxysilane, dimethylphenylmethoxysilane or dimethylphenylethoxysilane.

[0020] Furthermore, the polyaromatic silane in step 1 (1) is diphenyldimethoxysilane or diphenyldiethoxysilane.

[0021] Furthermore, the linear silane described in step 1 (1) is trimethylmethoxysilane, trimethyltriethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, dodecylsilane or hydrogen-substituted dialkoxysilane of the above silanes.

[0022] Furthermore, the organic alcohol in step 1 (1) is methanol, ethanol or isobutanol.

[0023] Furthermore, the acidic catalytic silane monomer in step 1 (1) is trichlorosilane, silicon tetrachloride, dichlorosilane, methylchlorosilane or methylhydrochlorosilane.

[0024] Furthermore, the mass percentage concentration of the starting material in the raw material solution in step 1 (1) is 6% to 30%.

[0025] Furthermore, the mass of the acidic catalytic silane monomer added in step 1 (1) is 0.1% to 5% of the mass of the raw material.

[0026] Furthermore, the basic silane in step 1 (2) is aminopropyltrimethoxysilane, aminopropyltriethoxysilane, hexamethyldisilazane, aminoethylaminopropyltrimethoxysilane or secondary aminosilane.

[0027] Furthermore, the silazane in step 1 (2) is hexamethylsilazane or polysilazane.

[0028] Furthermore, the amount of ammonia, basic silane or silazane added in step 1 (2) is based on the solid content of the pre-hydrolyzed solution, and the solid content is converted into the amount of silicon dioxide. The amount of ammonia, basic silane or silazane added is 0.1% to 5% of the amount of silicon dioxide.

[0029] Furthermore, the reaction solvent in step 1 (2) is methanol, ethanol, methanol or a mixture of ethanol and ultrapure water.

[0030] Furthermore, the amount of the reaction solvent added in step 1 (2) is based on the total volume of the solid phase material in the pre-hydrolyzed solution, and the volume of the reaction solvent is 1 to 3 times the volume of the solid phase material.

[0031] Furthermore, the replacement reagent in step 1 (3) is one or a mixture of methanol, ethanol and n-butane.

[0032] Furthermore, the added volume of the displacement reagent in step 1 (3) is 1 to 5 times the volume of the gel;

[0033] Furthermore, the microwave tube drying fluidized bed described in step 1 (5) comprises: a microwave generating unit 1, a waveguide transmission unit 2, a fluidized bed pressure vessel 3 with a classifying wheel and a cyclone separator, a microwave transparent tube matrix unit 4, an inert fluidizing gas control unit 5, a quantitative feeding unit 6, a powder collecting unit 7 and an organic solvent condensation recovery unit 8; an overflow port 3-1 is provided at the upper end of the fluidized bed pressure vessel 3 with a classifying wheel and a cyclone separator, and the overflow port 3-1 is connected to the powder collecting unit 7, and a group of tubes 4-3 are provided in the microwave transparent tube matrix unit 4, and the tubes 4-3 are double-layer non-uniform-height jacketed tubes composed of an inner tube 4-1 and an outer tube 4-2, and a The jacket 4-4 and the lower end of the outer tube 4-2 are provided with a jacket opening 4-5, the microwave generating unit 1 is connected with the waveguide transmission unit 2, the waveguide transmission unit 2 is connected with the microwave transparent tube matrix unit 4, the upper end of the outer tube 4-2 is inserted into the fluidized bed pressure vessel 3 with a classifying wheel and a cyclone separator from the lower end of the fluidized bed pressure vessel 3 with a classifying wheel and a cyclone separator, the lower end of the inner tube 4-1 is connected with the quantitative feeding unit 6, the jacket 4-4 is connected with the inert fluidizing gas control unit 5 through the jacket opening 4-5, the upper expansion section of the fluidized bed pressure vessel 3 with a classifying wheel and a cyclone separator is connected with the powder collecting unit 7, and the top of the fluidized bed pressure vessel 3 with a classifying wheel and a cyclone separator is connected with the organic solvent condensation recovery unit 8.

[0034] Furthermore, the microwave transparent tube matrix unit 4 in the microwave tube drying fluidized bed described in step 1 (5) is made of polytetrafluoroethylene or polyethylene.

[0035] Furthermore, the diameter of the tubes in the microwave transparent tube matrix unit 4 in the microwave tube drying fluidized bed described in step 1 (5) is 2 to 10 cm.

[0036] Furthermore, the inner tube 4-1 in the microwave tube drying fluidized bed described in step 1 (5) has a length of 1 to 5 meters, a tube wall thickness of 1 to 5 mm, and is made of polytetrafluoroethylene or polyethylene.

[0037] Furthermore, in the microwave tube drying fluidized bed described in step 1 (5), the length of the inner tube 4-1 is 1 / 3-3 / 4 of the length of the outer tube 4-2, the diameter ratio of the inner tube 4-1 to the outer tube 4-2 is 1:2-4:5, and the distance between two adjacent tubes 4-3 is 1-10 cm.

[0038] Furthermore, the method for removing the solvent and drying the wet gel in step 1 (5) in a microwave tube drying fluidized bed is:

[0039] ①, put the wet gel into the quantitative feeding unit 6, and preheat it by light wave or microwave heating, the preheating temperature is 5-10°C lower than the bubble point;

[0040] ②, the preheated slurry is conveyed to the inner tube 4-1 of the microwave transparent tube matrix unit 4 in a closed manner, the microwave output power is adjusted, the pump head pressure and the operating pressure of the fluidized bed pressure vessel 3 with a classifying wheel and a cyclone separator are coordinated to adjust the rising film movement speed, to ensure that at least 95% of the solvent in the slurry is vaporized, and the fluidized bed pressure vessel 3 with a classifying wheel and a cyclone separator completes the drying and solvent removal process under normal pressure or negative pressure, and the negative pressure is -60kPa to -95kPa;

[0041] ③. Adjust the power of the microwave heating power supply of the microwave generating unit 1 to 60% to 90%. The microwave generated by the magnetron is directly absorbed by the polar solvent through the tube array 4-3 after being transmitted through the waveguide. The solvent is quickly heated and vaporized. The temperature is increased to the bubble point at a heating rate of 5 to 25°C / min. A large amount of gas is generated instantly during vaporization. The gas carries the insulating powder into the outer tube 4-2 and enters the upper expansion section of the fluidized bed pressure vessel 3 with a classifying wheel and a cyclone separator together with the inert fluidizing gas.

[0042] ④. In the expansion section, the powder-gas separation is achieved through the synergistic effect of gravity sedimentation, classification by the classifying wheel and the internal cyclone. The powder enters the powder collecting unit 7 through the overflow port 3-1 and is collected to obtain silicon-carbon composite aerogel powder;

[0043] ⑤. The mixture of inert gas and evaporated organic solvent passes through the organic solvent condensation recovery unit 8, and the evaporated organic solvent is collected through multi-stage condensation and tail gas compression condensation. The non-condensable gas after compression and condensation is washed in the elution tower, dried in the cold dryer and circulated to the inert fluidized gas control unit 5 for reuse.

[0044] Furthermore, the negative pressure in step 2 (2) refers to a vacuum degree of 1000 to 90000 Pa;

[0045] Furthermore, the pressurization in step 2 (2) refers to a pressure of 0.15 to 1 MPa.

[0046] Furthermore, the microwave-induced graphite tube fluidized bed described in step 2 (2) is composed of a microwave generating unit 9, a waveguide transmission unit 10, a fluidized bed pressure vessel 11 with a classifying wheel and a cyclone separator, a tube matrix unit 12, an inert fluidizing gas control unit 13, a precursor resin powder quantitative feeding unit 14, a degreasing and carbonizing powder collecting unit 15 and a condensation recovery unit 16. The fluidized bed pressure vessel 11 with a classifying wheel and a cyclone separator is provided with an overflow port 11-1 at the upper end, and the overflow port 11-1 is connected to the degreasing and carbonizing powder collecting unit 15. The tube matrix unit 12 is provided with a group of tubes 12-3, and the tubes 12-3 are double-layer non-uniform jacketed tubes composed of an inner tube 12-1 and an outer tube 12-2. A jacket 12-4 is provided between the inner tube 12-1 and the outer tube 12-2. A jacket port 12-5 is provided at the lower end of the outer tube 12-2. The inner tube 12-1 is long. The length is 1 / 11 to 3 / 4 of the length of the outer tube 12-2, the inner tube 12-1 is a tapered tube that is narrow at the bottom and thick at the top, the microwave generating unit 9 is connected to the waveguide transmission unit 10, the waveguide transmission unit 10 is connected to the tube matrix unit 12, the upper end of the outer tube 12-2 is inserted into the fluidized bed pressure vessel 11 with a classifying wheel and a cyclone separator from the lower end of the fluidized bed pressure vessel 11 with a classifying wheel and a cyclone separator, the lower end of the inner tube 12-1 is connected to the precursor resin powder quantitative feeding unit 14, the inner tube 12-1 of the tube array 12-3 and the jacket 12-4 of the outer tube 12-2 are connected to the inert fluidizing gas control unit 13 through the jacket port 12-5, the upper expansion section of the fluidized bed pressure vessel 11 with a classifying wheel and a cyclone separator is connected to the powder collection unit 15 after degreasing and carbonization, and the top of the fluidized bed pressure vessel 11 with a classifying wheel and a cyclone separator is connected to the condensation recovery unit 16.

[0047] Furthermore, the inner tube 12-1 of the microwave induced graphite tube fluidized bed is 1 to 5 meters long, made of isostatic graphite or silicon carbide, has a wall thickness of 1 to 3 mm, and has a diameter of 2 to 7 cm.

[0048] Furthermore, the wall thickness of the inner tube 12 - 1 of the microwave induced graphite tube fluidized bed is 1 to 1.5 mm.

[0049] Furthermore, the cone angle of the conical inner tube 12-1 of the microwave induced graphite tube fluidized bed is 1 to 10 degrees, and the cone angle is adjustable, and the ratio of the upper end diameter of the inner tube to the outer tube diameter is 1:2 to 4:5.

[0050] Furthermore, the diameter of the tubes 12 - 3 in the tube matrix unit of the microwave induced graphite tube fluidized bed is 8 to 12 cm.

[0051] Furthermore, the distance between two adjacent tubes 12 - 3 of the microwave induced graphite tube fluidized bed is 1 to 10 cm.

[0052] Furthermore, the steps of using microwave-induced graphite tube-coiled fluidized bed to pyrolyze and carbonize aerogel powder are as follows: according to the processing amount of aerogel powder of 500g to 5000g / hour, the inert fluidizing gas control unit 13 is started, the microwave generator of the microwave generating unit 9 is started, the output power is adjusted to 80% to 90% of the power output, the system is heated to 260 to 1200°C, the microwave electromagnetic wave is transmitted to the tube matrix unit 12 through the waveguide transmission unit 10, the aerogel powder enters the tube matrix unit 12 from the jacket 12-4 along with the inert gas, degreases and carbonizes under negative pressure, normal pressure or pressurized state, the carbonized particles meet the inert gas introduced into the jacket 12-4, and the temperature of the inert gas is controlled to be 200 to 700°C and the gas flow rate is controlled to be 0.05 to 100°C through the inert fluidizing gas control unit 13. 0.5m / s, the particles after degreasing and pyrolysis enter the upper part of the fluidized bed pressure vessel 11 with a classifying wheel and a cyclone separator along with the inert gas and the organic gas generated by pyrolysis, the particles enter the classifying wheel and the cyclone separator in the fluidized bed pressure vessel 11 with the classifying wheel and the cyclone separator, and finally enter the powder collection unit 15 after degreasing and carbonization through the overflow port 11-1, and then are collected in the powder silo, a small amount of non-condensable gas enters the condensation recovery unit 16, a large amount of organic vapor enters the cyclone in the fluidized bed pressure vessel 11 with the classifying wheel and the cyclone separator, and after powder and gas separation, enters the condensation recovery unit 16, the organic vapor is cooled by the condensation recovery unit 16, and then collected in the mixed liquid storage tank, the non-condensable gas is incinerated by the incinerator, the tail gas is eluted by the elution tower and purified by the cold dryer, and then converted into high-purity inert gas for recycling.

[0053] Furthermore, the ultrasonically assisted rapid self-priming stirring system described in step 1 (3) is composed of a kettle body 17 with a jacket 17-1, a motor 18, a self-priming stirring paddle 19 and 6 microwave radiation emitters 20; 6 microwave radiation waveguide openings 17-2 are evenly distributed on the circumference of the upper end cover of the kettle body 17, and the 6 microwave radiation emitters 20 are respectively installed on the microwave radiation waveguide openings 17-2, and an inlet and outlet 17-3 and an air inlet 17-4 are set at the bottom of the kettle body 17.

[0054] The present invention first prepares a wet gel with a particle size of 20 to 500 nm and a solid content of 6% to 30%, and then replaces and ages the wet gel, removes the solvent and dries it to obtain a silicon-carbon composite aerogel powder; then removes impurities from the surface of the silicon-carbon composite aerogel powder and pyrolyzes and carbonizes it to obtain a nano silicon-carbon-oxygen ceramic powder. The nano silicon-carbon-oxygen ceramic powder has a particle size of 100 to 500 nm, a purity of 6N, and a silicon-carbon ratio of 1:1. The nano silicon-carbon-oxygen ceramic powder can be carbon-thermally reduced to prepare a nano silicon carbide powder with a particle size of 50 to 300 nm, which can be used in the semiconductor field. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 This is a schematic diagram of the structure of the microwave tube drying fluidized bed in Example 1;

[0056] Figure 2 It is a schematic diagram of the tube structure of the microwave tube drying fluidized bed;

[0057] Figure 3 This is a schematic diagram of the structure of the microwave-induced graphite tube fluidized bed in Example 1;

[0058] Figure 4 It is a schematic diagram of the structure of the tubes of the microwave induced graphite tube fluidized bed;

[0059] Figure 5 It is a structural schematic diagram of an ultrasonic-assisted rapid self-priming stirring system;

[0060] Figure 6 This is a scanning electron microscope photograph of the nano-silicon carbon oxide ceramic powder obtained in Example 1. DETAILED DESCRIPTION

[0061] The beneficial effects of the present invention are verified by the following examples.

[0062] Example 1: The method of preparing high-purity nano-silicon carbon oxygen ceramic powder by pyrolyzing silicon-carbon composite aerogel in a microwave-induced graphite tube fluidized bed of this embodiment is carried out according to the following steps:

[0063] 1. Preparation of silicon-carbon composite aerogel:

[0064] (1) Preparation of pre-hydrolysis liquid: 4 kg of propyltrimethoxysilane, 6 kg of phenyltrimethoxysilane, 80.5 kg of methanol, and 0.5 kg of trichlorosilane were added to a reaction tank; the raw material liquid was stirred at a temperature of 40° C. and a stirring speed of 300 r / min for 6 h to hydrolyze the mixed silane to obtain a pre-hydrolysis liquid; the solid mass percentage of the pre-hydrolysis liquid was 6.8%,

[0065] (2) Preparation of wet gel: 1.5 kg of aminopropyltrimethoxysilane and 10 kg of methanol were added to the pre-hydrolyzed liquid in a stirred tank, and the mixture was stirred for 6 h at a temperature of 25° C. and a pressure of normal pressure to obtain a wet gel; the wet gel particles prepared in this step were in the range of 50 to 800 nm and had a solid content of 6.98%;

[0066] (3) Solvent replacement and purification of wet gel: An ultrasonic-assisted rapid self-priming stirring system is used for reverse pulse solvent replacement. The ultrasonic-assisted rapid self-priming stirring system consists of a kettle 17 with a jacket 17-1, a motor 18, a self-priming stirring paddle 19 and six microwave radiation emitters 20; six microwave radiation waveguide ports 17-2 are evenly distributed on the circumference of the upper end cover of the kettle 17, and the six microwave radiation emitters 20 are respectively installed on the microwave radiation waveguide ports 17-2. A material inlet and outlet port is set at the bottom of the kettle 17. Port 17-3 and air inlet 17-4, the kettle body 17 is lined with polytetrafluoroethylene; 5 kg of wet gel is placed in the kettle body 17, 20 kg of replacement reagent methanol is added, 20 kg of replacement reagent methanol is introduced from the inlet and outlet 17-3 at a flow rate of 20 kg / hour, and nitrogen is introduced into the kettle body 17 through the air inlet 17-4. Nitrogen is circulated internally by the action of self-absorption slurry to promote solvent exchange efficiency. After full replacement for 1 hour, it flows out from the inlet and outlet 17-3 at the bottom of the reactor to obtain high-purity wet gel;

[0067] (4) Aging and skeleton strengthening of high-purity wet gel: The high-purity wet gel was placed in a light wave aging system with a composite wavelength of 200-400 nm ultraviolet light and 800-1100 nm infrared light for 1 h to obtain a wet gel that was aged at a constant temperature and had a skeleton strengthened;

[0068] (5) Preparation of silicon-carbon composite aerogel: The wet gel after constant temperature aging and skeleton strengthening is introduced into a microwave tube drying fluidized bed through a plunger pump; the microwave tube drying fluidized bed comprises a microwave generating unit 1, a waveguide transmission unit 2, a fluidized bed pressure vessel 3 with a classifying wheel and a cyclone separator, a microwave transparent tube matrix unit 4 made of tetrafluoroethylene plastic, an inert fluidizing gas control unit 5, a quantitative feeding unit 6, a powder collecting unit 7 and an organic solvent condensation recovery unit 8; the fluidized bed pressure vessel 3 with a classifying wheel and a cyclone separator is provided with an overflow port 3-1 at the upper end, and the overflow port 3-1 is connected to the powder collecting unit 7; the microwave transparent tube matrix unit 4 is provided with a group of tubes 4-3 with a diameter of 5 cm, and the tubes 4-3 are double-layer non-uniform height jacketed tubes composed of an inner tube 4-1 and an outer tube 4-2; the inner tube 4-1 is 3 meters long, with a tube wall thickness of 1.5 mm, and is made of tetrafluoroethylene plastic; the inner tube 4-1 is 3 meters long, with a tube wall thickness of 1.5 mm, and is made of tetrafluoroethylene plastic; the inner tube 4-2 is 1.5 mm thick, and is made of tetrafluoroethylene plastic; the inner tube 4-1 is 1.5 mm thick ... The length of the outer tube 4-1 is 3 / 4 of the length of the outer tube 4-2, the diameter ratio of the inner tube 4-1 to the outer tube 4-2 is 1:2, and the distance between two adjacent tubes 4-3 is 8 cm; a jacket 4-4 is provided between the inner tube 4-1 and the outer tube 4-2, and a jacket opening 4-5 is provided at the lower end of the outer tube 4-2. The microwave generating unit 1 is connected to the waveguide transmission unit 2, and the waveguide transmission unit 2 is connected to the microwave transparent tube matrix unit 4. The upper end of the outer tube 4-2 is inserted from the lower end of the fluidized bed pressure vessel 3 with a classifying wheel and a cyclone separator into the fluidized bed pressure vessel 3 with a classifying wheel and a cyclone separator, the lower end of the inner tube 4-1 is connected to the quantitative feeding unit 6, the jacket 4-4 is connected to the inert fluidizing gas control unit 5 through the jacket opening 4-5, the upper expansion section of the fluidized bed pressure vessel 3 with a classifying wheel and a cyclone separator is connected to the powder collecting unit 7, and the top of the fluidized bed pressure vessel 3 with a classifying wheel and a cyclone separator is connected to the organic solvent condensation recovery unit 8;

[0069] The wet gel is placed in a quantitative feeding unit 6, which is made of stainless steel and preheated by microwave heating, with the preheating temperature being 8°C below the bubble point;

[0070] The preheated wet gel is conveyed to the inner tube 4-1 of the microwave transparent tube matrix unit 4 in a closed manner, the microwave output power is adjusted, the pump head pressure and the operating pressure of the fluidized bed pressure vessel 3 with a classifying wheel and a cyclone separator are adjusted in coordination, and then the rising film moving speed is adjusted to ensure that at least 95% of the solvent in the wet gel is vaporized, and the fluidized bed pressure vessel 3 with a classifying wheel and a cyclone separator completes the drying and solvent removal process at a negative pressure of -80 kPa;

[0071] The power of the microwave heating power supply of the microwave generating unit 1 is adjusted to 80%. The microwave generated by the magnetron is transmitted through the waveguide and directly absorbed by the polar solvent through the tube array 4-3. The solvent is quickly heated and vaporized. The temperature is increased to the bubble point at a heating rate of 15°C / min. A large amount of gas is generated instantly during vaporization. The gas carries the insulating powder into the outer tube 4-2 and enters the upper expansion section of the fluidized bed pressure vessel 3 with a classifying wheel and a cyclone separator together with the inert fluidizing gas.

[0072] In the expansion section, the powder-gas separation is achieved through the synergistic effect of gravity sedimentation, classification by the classifying wheel and the internal cyclone, and the powder enters the powder collecting unit 7 through the overflow port 3-1 to obtain silicon-carbon composite aerogel powder;

[0073] The mixture of inert gas and evaporated organic solvent passes through the organic solvent condensation recovery unit 8, and the evaporated organic solvent is collected through multi-stage condensation and tail gas compression condensation. The non-condensable gas after compression condensation is washed by the elution tower, dried by the cold dryer, and circulated to the inert fluidized gas control unit 5 for reuse;

[0074] In this step, the problem of low microwave penetration depth is avoided by using tetrafluoroplastic tubes arranged in a matrix. After the wet gel slurry enters the fluidized bed, it enters each tube through a distribution plate, and the solvent is removed and dried to obtain silicon-carbon composite aerogel powder.

[0075] 2. Preparation of Nano-SiC Oxygen Ceramic Powders:

[0076] (1) Surface purification of silicon-carbon composite aerogel powder: 0.5 kg of silicon-carbon composite aerogel powder was added to a quartz rotary furnace through a quantitative bin, and high-temperature water vapor at a temperature of 160° C. was introduced into the quartz rotary furnace. The treatment was carried out for 3 hours at a water vapor flow rate of 1 kg / hour and a rotary furnace speed of 15 r / min. After the treatment, the vacuum was reduced to 50 Pa within 4 hours to obtain a clean aerogel powder with a clean surface. In this step, high-temperature water vapor was used to desorb the air and water vapor adsorbed on the surface of the silicon-carbon composite aerogel powder;

[0077] (2) Preparation of Nano-SiC Oxygen Ceramic Powders:

[0078] The cleaned aerogel powder is transported to the microwave-induced graphite tube fluidized bed through a venturi pneumatic conveying device; the microwave-induced graphite tube fluidized bed is composed of a microwave generating unit 9, a waveguide transmission unit 10, a fluidized bed pressure vessel 11 with a classifying wheel and a cyclone separator, a tube matrix unit 12, an inert fluidizing gas control unit 13, a precursor resin powder quantitative feeding unit 14, a degreasing and carbonized powder collecting unit 15 and a condensation recovery unit 16, and the fluidized bed pressure vessel with a classifying wheel and a cyclone separator An overflow port 11-1 is provided at the upper end of the tube matrix unit 11, and the overflow port 11-1 is connected to the powder collection unit 15 after degreasing and carbonization. A group of tubes 12-3 with a diameter of 11 cm are provided in the tube matrix unit 12, and the distance between two adjacent tubes 12-3 is 4 cm; the tube matrix unit 12-3 is a double-layer non-uniform jacket tube composed of an inner tube 12-1 and an outer tube 12-2, the inner tube 12-1 is 3 meters long, the material is isostatic graphite 3, the inner tube wall thickness is 1 mm, and the inner tube diameter is 5 cm; ... -1 and the outer tube 12-2 are provided with a jacket 12-4, the outer tube 12-2 is provided with a jacket opening 12-5 at the lower end, the inner tube 12-1 is 1 / 2 of the length of the outer tube 12-2, the inner tube 12-1 is a tapered tube with a narrow bottom and a thick top and a taper angle of 10°, the microwave generating unit 9 is connected to the waveguide transmission unit 10, the waveguide transmission unit 10 is connected to the tube matrix unit 12, the upper end of the outer tube 12-2 is inserted from the lower end of the fluidized bed pressure vessel 11 with a classifying wheel and a cyclone separator The fluidized bed pressure vessel 11 of the separator, the lower end of the inner tube 12-1 is connected to the precursor resin powder quantitative feeding unit 14, the inner tube 12-1 of the tube array 12-3 and the jacket 12-4 of the outer tube 12-2 are connected to the inert fluidizing gas control unit 13 through the jacket port 12-5, the upper expansion section of the fluidized bed pressure vessel 11 with a classifying wheel and a cyclone separator is connected to the degreasing and carbonized powder collection unit 15, and the top of the fluidized bed pressure vessel 11 with a classifying wheel and a cyclone separator is connected to the condensation recovery unit 16;

[0079] According to the processing amount of 1000g / hour of aerogel powder, the inert fluidizing gas control unit 13 is started, the microwave generator of the microwave generating unit 9 is started, the output power is adjusted to 80% of the power output, the system is heated to 1100°C, and the microwave electromagnetic wave is transmitted to the tube matrix unit 12 through the waveguide transmission unit 10. The aerogel powder enters the tube matrix unit 12 from the jacket 12-4 along with the inert gas, and is fluidized pyrolysis and carbonized under the condition of a vacuum degree of 90000Pa. The carbonized particles meet the inert gas introduced into the jacket 12-4, and the temperature of the inert gas is controlled to 550°C and the gas flow rate to 0.4m / s through the hydrogen fluidizing gas control unit 13. After degreasing and pyrolysis, the particles enter the upper part of the fluidized bed pressure vessel 11 with a classifying wheel and a cyclone separator along with the inert gas and the organic gas generated by the pyrolysis. The particles enter the fluidized bed pressure vessel 11 with a classifying wheel and a cyclone separator. The classifying wheel and cyclone separator in the fluidized bed pressure vessel 11 finally enter the degreasing and carbonizing powder collection unit 15 through the overflow port 11-1, and then collect the nano silicon carbon oxygen ceramic powder into the powder silo. The residence time of the aerogel powder in the microwave pyrolysis graphite tube fluidized bed is 0.3h; a small amount of non-condensable gas enters the condensation recovery unit 16, and a large amount of organic vapor enters the cyclone and powder gas separation in the fluidized bed pressure vessel 11 with a classifying wheel and a cyclone separator, and then enters the condensation recovery unit 16. After the organic vapor is cooled by the condensation recovery unit 16, it is collected in the mixed liquid storage tank, the non-condensable gas is incinerated by the incinerator, and the tail gas is eluted by the elution tower and purified by the cold dryer, and then converted into a high-purity inert gas for recycling; this step is in-situ carbonization and degreasing during the fluidized pyrolysis carbonization process, which maintains the size and basic morphology of the original particles of the aerogel, and obtains nano silicon carbon oxygen ceramic powder with controllable particle size.

[0080] The scanning electron microscope photo of the nano-silicon carbon oxide ceramic powder obtained in this Example 1 is as follows Figure 6 As shown, from Figure 6 It can be seen that the particle size of the nano silicon carbon oxide ceramic powder is 100-500nm. After testing, the purity of the nano silicon carbon oxide ceramic powder reaches 6N, and the silicon carbon ratio is 1:1.

[0081] By using the silicon carbide ceramic powder to perform carbothermal reduction, uniform silicon carbide particles with a particle size of 50 to 300 nm can be obtained.

Claims

1. A method for preparing high-purity nano-silicon carbon oxygen ceramic powder by pyrolyzing silicon-carbon composite aerogel in a microwave-induced graphite tube fluidized bed, characterized in that The method proceeds as follows:

1. Preparation of silicon-carbon composite aerogel: (1) Preparation of a pre-hydrolysis solution: using monoaromatic silane, polyaromatic silane, linear silane, silicate or orthosilicic acid as a starting material, sequentially adding an aqueous organic alcohol as a solvent and an acidic catalytic silane monomer as a hydrolysis catalyst to obtain a raw material solution; stirring the raw material solution at a temperature of 25 to 50° C. and a stirring speed of 150 to 600 r / min for 0.5 to 12 hours to hydrolyze the raw material to obtain a pre-hydrolysis solution; (2) Preparation of wet gel: Ammonia, basic silane or silazane are introduced into the pre-hydrolyzed liquid in a stirred tank device, and then a reaction solvent is added, and the mixture is stirred for 0.5 to 12 hours at a temperature of 15 to 50° C. and a pressure of normal pressure to obtain a wet gel; (3) Solvent replacement and purification of wet gel: The wet gel is placed in an ultrasound-assisted rapid self-absorption stirring system, and a replacement reagent is added to perform reverse pulse solvent replacement to obtain a high-purity wet gel; (4) Aging and skeleton strengthening of high-purity wet gel: The high-purity wet gel is placed in a light wave aging system with a wavelength of 200-400nm ultraviolet light and 800-1100nm infrared light for 0.5-2h to obtain a wet gel with constant temperature aging and skeleton strengthening; (5) Preparation of silicon-carbon composite aerogel: The wet gel after constant temperature aging and skeleton strengthening is input into a microwave tube drying fluidized bed through a plunger pump for solvent removal and drying to obtain silicon-carbon composite aerogel powder; 2. Preparation of Nano-SiC Oxygen Ceramic Powders: (1) Surface purification of silicon-carbon composite aerogel powder: adding silicon-carbon composite aerogel powder into a quartz rotary furnace through a quantitative bin, introducing high-temperature steam at a temperature of 120 to 180° C. into the quartz rotary furnace, treating for 3 to 10 hours under the conditions of a steam addition amount of 1 to 10 kg / hour and a rotary furnace speed of 10 to 60 r / min, and controlling the system vacuum degree at 1 to 100 Pa within 1 to 10 hours after the treatment to obtain aerogel powder with a clean surface; (2) Preparation of Nano-SiC Oxygen Ceramic Powders: The cleaned aerogel powder is transported to a microwave-induced graphite tube fluidized bed through a Venturi pneumatic conveying device. Argon or hydrogen is used as an auxiliary fluidizing gas. The microwave power is adjusted to raise the system temperature to 260-1200°C. The aerogel powder is fluidized, pyrolyzed and carbonized under negative pressure, normal pressure or pressurized conditions. The residence time of the aerogel powder in the microwave-induced graphite tube fluidized bed is 0.1-1h to obtain nano-silicon carbon oxygen ceramic powder.

2. The method for preparing high-purity nano-silicon carbon oxygen ceramic powder by pyrolyzing silicon-carbon composite aerogel in a microwave-induced graphite tube fluidized bed according to claim 1, characterized in that: The monoaromatic ring silane described in step 1 (1) is phenyltrimethoxysilane, phenyltriethoxysilane, methylphenyldimethoxysilane, methylphenyldiethoxysilane, dimethylphenylmethoxysilane or dimethylphenylethoxysilane.

3. The method for preparing high-purity nano-silicon carbon oxygen ceramic powder by pyrolyzing silicon-carbon composite aerogel in a microwave-induced graphite tube fluidized bed according to claim 1 or 2, characterized in that: The polyaromatic silane in step 1 (1) is diphenyldimethoxysilane or diphenyldiethoxysilane.

4. The method for preparing high-purity nano-silicon carbon oxygen ceramic powder by pyrolyzing silicon-carbon composite aerogel in a microwave-induced graphite tube fluidized bed according to claim 1 or 2, characterized in that: The linear silane described in step 1 (1) is trimethylmethoxysilane, trimethyltriethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, dodecylsilane or hydrogen-substituted dialkoxysilane of the above silanes.

5. The method for preparing high-purity nano-silicon carbon oxygen ceramic powder by pyrolyzing silicon-carbon composite aerogel in a microwave-induced graphite tube fluidized bed according to claim 1 or 2, characterized in that: The organic alcohol described in step 1 (1) is methanol, ethanol or isobutanol.

6. The method for preparing high-purity nano-silicon carbon oxygen ceramic powder by pyrolyzing silicon-carbon composite aerogel in a microwave-induced graphite tube fluidized bed according to claim 1 or 2, characterized in that: The acidic catalytic silane monomer described in step 1 (1) is trichlorosilane, silicon tetrachloride, dichlorosilane, methylchlorosilane or methylhydrochlorosilane.

7. The method for preparing high-purity nano-silicon carbon oxygen ceramic powder by pyrolyzing silicon-carbon composite aerogel in a microwave-induced graphite tube fluidized bed according to claim 1 or 2, characterized in that: The mass percentage concentration of the starting material in the raw material solution described in step 1 (1) is 6% to 30%.

8. The method for preparing high-purity nano-silicon carbon oxygen ceramic powder by pyrolyzing silicon-carbon composite aerogel in a microwave-induced graphite tube fluidized bed according to claim 1 or 2, characterized in that: The added mass of the acidic catalytic silane monomer described in step 1 (1) is 0.1% to 5% of the mass of the raw material.

9. The method for preparing high-purity nano-silicon carbon oxygen ceramic powder by pyrolyzing silicon-carbon composite aerogel in a microwave-induced graphite tube fluidized bed according to claim 1 or 2, characterized in that: The basic silane described in step 1 (2) is aminopropyltrimethoxysilane, aminopropyltriethoxysilane, hexamethyldisilazane, aminoethylaminopropyltrimethoxysilane or secondary aminosilane.

10. The method for preparing high-purity nano-silicon carbon oxygen ceramic powder by pyrolyzing silicon-carbon composite aerogel in a microwave-induced graphite tube fluidized bed according to claim 1 or 2, characterized in that: The silazane described in step 1 (2) is hexamethylsilazane or polysilazane.

Images