High-purity silicon carbide powder for ceramics and preparation process thereof

Abstract

The application belongs to the technical field of silicon carbide powder preparation, and relates to high-purity silicon carbide powder for ceramics and a preparation process thereof. The preparation process comprises the following steps: S1: adding an ethanol aqueous solution into a reaction kettle, adjusting the pH to 2.5-3.0, adding a silicon source, reacting, adding a polyphenol compound, heating, mixing, cooling, and obtaining a homogeneous sol; S2: under the assistance of ultrasonic waves, uniformly dispersing fluorine-containing polymer nanoemulsion in the homogeneous sol, and then spray drying to obtain precursor microsphere powder; and S3: under an inert atmosphere, placing the precursor microsphere powder in an atmosphere furnace, performing gradient heating treatment, and then, under an air atmosphere, heat-treating at 550-600 DEG C to obtain high-purity silicon carbide powder. The high-purity silicon carbide powder prepared by the method has the advantages of ultrahigh purity, uniform and controllable submicron particle size, excellent dispersibility and high sintering activity.

Description

Technical Field

[0001] This invention belongs to the field of silicon carbide powder preparation technology, and more specifically, relates to a high-purity silicon carbide powder for ceramics and its preparation process, which is applicable to fields such as ceramic parts for semiconductor manufacturing, high-temperature kiln furniture and wear-resistant ceramic products. Background Technology

[0002] Silicon carbide (SiC) ceramics, with their high hardness, excellent high-temperature mechanical properties, high thermal conductivity, and outstanding oxidation and corrosion resistance, have irreplaceable application value in high-end industrial fields such as semiconductor wafer processing fixtures, bulletproof armor, high-temperature kiln furniture, and aerospace hot-end components. With the rapid development of 5G communication and the third-generation semiconductor industry, the global annual demand for high-purity, ultrafine, and easily sinterable high-performance ceramic-grade SiC powder is increasing daily.

[0003] Currently, the mainstream methods for preparing SiC powder in industry include carbothermal reduction and precursor conversion. Carbothermal reduction requires reactions at ultra-high temperatures above 2000℃, resulting in extremely high energy consumption. Furthermore, the prepared powder has coarse particle size and high impurity content, requiring multiple crushing and acid washing purification processes before it can be used for ceramic preparation, making it difficult to meet the purity requirements of high-end semiconductor fields. Although precursor conversion improves the dispersion uniformity of silicon and carbon sources to some extent through liquid-phase mixing and lowers the reaction temperature, existing technologies still struggle to completely overcome the technical bottleneck of incomplete reaction during the high-temperature synthesis stage at 1500℃ to 1700℃. To achieve high conversion rates, existing technologies often require extended holding times or further increases in calcination temperatures, which in turn leads to severe coarsening of SiC grains, intensified hard agglomeration, and a significant reduction in the sintering activity of the powder.

[0004] The patent application document with publication number CN102718217A discloses a method for preparing high-purity silicon carbide. The specific steps are as follows: (1) After mixing silica sol and graphene oxide at a weight percentage of 100:16-36, the mixture is first subjected to ultrasonic treatment for 15-30 minutes at an ultrasonic frequency of 20-120kHz, and then stirred vigorously for 2-4 hours to obtain a composite precursor. The silica sol is an acidic silica sol with a silica content of 5%-30%, a pH value of 2-7, and a particle size of 6-30nm. The graphene oxide is a carbon material with a good sheet structure; (2) After the composite precursor is cured and dried in a drying oven for 48 hours, it is ground in a high-speed ball mill for 2 hours to obtain a fine and homogeneous powder precursor; (3) The powder precursor is placed in a high-temperature tube furnace, and argon gas with a purity of 99.99% is introduced. The carbonothermic reduction reaction is carried out at 1400~1600℃ for 2~8 hours to obtain a crude silicon carbide micro powder; (4) The crude silicon carbide micro powder is soaked in an inorganic acid for 2~4 hours and then filtered. The filter residue is sintered at 400~700℃ for 1~9 hours in the presence of air to remove unreacted carbon. After cooling, silicon carbide powder with a content of not less than 99% is obtained.

[0005] In this scheme, liquid-phase mixing is achieved through macroscopic physical blending of silica sol and graphene oxide. However, this method cannot achieve nanoscale uniform dispersion of carbon and silicon sources. Graphene oxide sheets are prone to stacking and agglomeration, and the difference in surface charge between the two phases easily leads to micro-phase separation, forming local carbon-rich / silicon-rich regions. This inherent defect directly results in the carbothermic reduction products exhibiting elongated and irregular morphologies, with severe interparticle overlap and significant hard agglomeration. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art, solve the technical problems of low purity, uneven particle size, and easy agglomeration of existing silicon carbide powder, and provide a high-purity silicon carbide powder for ceramics and its preparation process.

[0007] To achieve the above-mentioned objectives, this invention provides a process for preparing high-purity silicon carbide powder for ceramics, the technical solution of which includes the following steps: S1: Add an aqueous ethanol solution to the reaction vessel, adjust the pH to 2.5~3.0, add a silicon source, react for 100~150 min, add a polyphenol compound, heat to 50~70℃, mix for 240~360 min, cool, and obtain a homogeneous sol. S2: Under ultrasonic assistance, the fluoropolymer nanoemulsion is uniformly dispersed in a homogeneous sol and then spray-dried to obtain precursor microsphere powder; S3: Under an inert atmosphere, the precursor microsphere powder is placed in an atmosphere furnace, heated to 500~600℃, held for 100~150min, then heated to 900~1100℃, held for 100~150min, then heated to 1500~1600℃, held for 200~300min, and after cooling, it is heated to 550~600℃ for 100~150min in an air atmosphere to obtain high-purity silicon carbide powder.

[0008] This invention first involves pre-hydrolyzing a silicon source and then subjecting it to a dehydration condensation reaction with polyphenolic compounds to form a three-dimensional molecular network linked by Si-OC covalent bonds, achieving uniform distribution of the silicon and carbon sources at the molecular scale. Next, an ultrasonically assisted dispersion of a fluoropolymer nanoemulsion is carried out in a sol system, followed by spray drying for instantaneous solidification to lock in the uniform dispersion of each component, resulting in a homogeneous precursor microsphere powder. Subsequently, a segmented programmed temperature heat treatment process is employed. First, a three-dimensional interconnected mesoporous network is constructed in situ based on the pyrolysis of the fluoropolymer. Then, the structural transformation of the amorphous silica-coated carbon nanotube skeleton is completed, overcoming the solid-phase diffusion barrier caused by the dense layer of SiC products in traditional carbothermal reduction reactions, achieving full conversion of silicon / carbon components. Finally, low-temperature heat treatment in an air atmosphere selectively removes trace amounts of residual free carbon, preparing a high-purity silicon carbide powder with high purity, controllable uniform particle size, no obvious hard agglomeration, and excellent sintering activity.

[0009] The volume-to-mass ratio of the silicon source, polyphenolic compound and fluorinated polymer nanoemulsion (based on solid content) described in this invention is (400~600) mL: (120~180) g: (7~11) g.

[0010] The silicon source described in this invention is either methyltrimethoxysilane or methyltriethoxysilane.

[0011] The silicon source involved in this invention hydrolyzes under acidic conditions to generate a large number of active silanol groups, which can efficiently undergo dehydration condensation reactions with the phenolic hydroxyl groups of subsequently added polyphenolic compounds to form a stable Si-OC covalent network, thereby achieving stable binding of the silicon source and carbon source at the molecular scale.

[0012] The polyphenolic compounds described in this invention are selected from at least one of tannic acid and gallic acid.

[0013] The polyphenolic compounds described in this invention include tannic acid and gallic acid.

[0014] The tannic acid molecules involved in this invention contain a large number of ortho-phenolic hydroxyl groups, which can undergo efficient dehydration condensation with silanol groups to form a high-density covalent cross-linked network, while providing a stable and uniform carbon source for the carbothermic reduction reaction. Gallic acid has higher reactivity than the ortho-phenolic hydroxyl groups of tannic acid, and can react rapidly with silanol groups to fill the gaps between tannic acid molecules, forming a "macromolecule-small molecule" gradient cross-linked structure.

[0015] The fluoropolymer nanoemulsion described in this invention is any one of polytetrafluoroethylene nanoemulsion, polyvinylidene fluoride nanoemulsion, and fluorinated ethylene propylene copolymer nanoemulsion.

[0016] The fluoropolymer nanoemulsion described in this invention is a polytetrafluoroethylene nanoemulsion.

[0017] The fluoropolymers involved in this invention can gradually release fluorine-containing active groups through thermal decomposition during heat treatment, effectively achieving in-situ pore formation and triggering of chemical vapor transport reactions, without leaving any harmful solid residues.

[0018] The ultrasonic-assisted process parameters described in this invention are: power 800~1000W, frequency 20~30kHz, and time 45~60min.

[0019] The spray drying process parameters of the present invention are as follows: inlet air temperature is 180~190℃, outlet air temperature is 85~90℃, atomizing disc rotation speed is 15000~17000rpm, and feed rate is 25~35mL / min.

[0020] The spray drying parameters involved in this invention can achieve instantaneous solidification of the sol, quickly lock in the uniform dispersion state of each component, avoid component migration and phase separation during the drying process, and stably obtain precursor microspheres with good sphericity and uniform particle size.

[0021] In step S2 of this invention, under ultrasonic assistance, the fluoropolymer nanoemulsion is first uniformly dispersed in a homogeneous sol, and then the fluorosilane coupling agent pre-hydrolyzed solution is added under ultrasonic conditions. The mixture is ultrasonically dispersed for 30-40 minutes and finally spray-dried.

[0022] In the fluorosilane coupling agent pre-hydrolyzed solution described in this invention, the amount of fluorosilane coupling agent used is 1% to 2% of the amount of silicon source used.

[0023] The preparation method of the fluorosilane coupling agent pre-hydrolyzed solution of the present invention includes the following steps: Add the fluorosilane coupling agent to an aqueous ethanol solution, adjust the pH of the system to 4.0-5.0, heat to 60-75℃, hydrolyze for 90-120 min, cool, and obtain a pre-hydrolyzed solution of the fluorosilane coupling agent.

[0024] The fluorosilane coupling agent described in this invention is perfluorooctyltriethoxysilane.

[0025] The pre-hydrolyzed fluorosilane coupling agent involved in this invention can be further modified into a covalent network to achieve uniform molecular-level dispersion of the fluorine source, forming a synergistic effect with the fluoropolymer nanoemulsion, further enhancing the reaction efficiency and impurity removal effect in the subsequent heat treatment process, while improving the stability of the network structure.

[0026] The present invention also provides a high-purity silicon carbide powder for ceramics prepared by the above-mentioned preparation process; based on the molecular-level uniform dispersion of silicon and carbon sources in the precursor system, the synergistic regulation of fluorine sources and the synergistic effect of segmented heat treatment process, the high-purity silicon carbide powder prepared has high purity, good dispersibility, no obvious hard agglomeration, and excellent sintering activity, which can meet the preparation requirements of high-end silicon carbide ceramics.

[0027] Compared with existing technologies, the advantages of this invention are as follows: First, it employs a liquid-phase copolymerization process of silicon source and polyphenolic compounds, constructing a covalent network through dehydration condensation reaction, achieving uniform dispersion of silicon and carbon sources at the molecular scale. Through the synergistic control of the introduction of fluorine-containing components and segmented programmed temperature heat treatment, in-situ pore formation, enhanced reaction kinetics, and removal of metal impurities are simultaneously achieved. Full conversion of silicon and carbon components can be achieved at relatively low temperatures, resulting in silicon carbide powder with excellent comprehensive performance. Second, it avoids the problems of uneven dispersion of carbon and silicon sources and agglomeration of graphene oxide sheets caused by macroscopic physical blending. The resulting silicon carbide powder has a more regular particle morphology, and its purity and particle size uniformity are significantly improved. Attached Figure Description

[0028] Figure 1 This is a scanning electron microscope image of the high-purity silicon carbide powder prepared in Example 1 of the present invention; Figure 2 This is a scanning electron microscope image of the high-purity silicon carbide powder prepared in Example 2 of the present invention. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0030] Unless otherwise specified, the raw materials used in this embodiment and comparative example are all commercially available. Among them, the polytetrafluoroethylene nanoemulsion is industrial grade, with a solid content of 60wt% and a particle size distribution of 20~50nm.

[0031] Example 1 The preparation process of high-purity silicon carbide powder for ceramics in this embodiment includes the following steps: S1: 500 mL of anhydrous ethanol and 1000 mL of deionized water were injected into a 2000 mL reactor with a Teflon liner. The pH of the system was adjusted to 2.5 using 36% hydrochloric acid. Mechanical stirring was started at 400 rpm. 500 mL of methyltrimethoxysilane was added dropwise at a uniform rate. After the addition was complete, the mixture was stirred at 25 °C for 120 min. Then, 150 g of tannic acid powder was added at once. The temperature was raised to 60 °C and stirred at 500 rpm for 300 min. The mixture was then cooled to room temperature to obtain a homogeneous sol. S2: Transfer the homogeneous sol to an ultrasonic disperser with a power of 800W and a frequency of 20kHz. Under ultrasonic conditions, add 15g of polytetrafluoroethylene nanoemulsion at a rate of 1mL / min. After the addition is complete, continue ultrasonic dispersion for 60min. Pump the mixture into a centrifugal spray dryer with the inlet air temperature set to 180℃, the outlet air temperature set to 85℃, the atomizing disc speed set to 15000rpm, and the feed rate set to 25mL / min to obtain precursor microsphere powder. S3: The precursor microsphere powder was loaded into a high-purity graphite crucible and pushed into a tube furnace. High-purity argon gas was introduced at a flow rate of 500 mL / min. The heating program was set as follows: the temperature was increased to 500℃ at a rate of 5℃ / min and held for 120 min. Then, under the protection of high-purity argon gas (flow rate 500 mL / min), the temperature was increased to 1000℃ at a rate of 3℃ / min and held for 120 min. Then, the temperature was increased to 1550℃ at a rate of 5℃ / min and held for 240 min. The temperature was then allowed to cool naturally to room temperature. The mixture was then transferred to an air muffle furnace and heated to 600℃ at a rate of 10℃ / min and held for 120 min. After cooling, the mixture was pulverized and sieved to obtain high-purity silicon carbide powder.

[0032] Example 2 The preparation process of high-purity silicon carbide powder for ceramics in this embodiment includes the following steps: S1: 500 mL of anhydrous ethanol and 1000 mL of deionized water were injected into a 2000 mL reactor with a Teflon liner. The pH of the system was adjusted to 3.0 using 36% hydrochloric acid. Mechanical stirring was started at 400 rpm. 400 mL of methyltriethoxysilane was added dropwise at a uniform rate. After the addition was complete, the mixture was stirred at 25 °C for 100 min. Then, 120 g of tannic acid powder was added at once. The temperature was raised to 50 °C and stirred at 500 rpm for 240 min. The mixture was then cooled to room temperature to obtain a homogeneous sol. S2: The homogeneous sol was transferred to an ultrasonic disperser with a power of 800W and a frequency of 20kHz. 12g of polytetrafluoroethylene nanoemulsion was added dropwise at a rate of 1mL / min under ultrasonic conditions. After the addition was completed, ultrasonic dispersion was continued for 60min. The mixture was then pumped into a centrifugal spray dryer with the inlet air temperature set to 180℃, the outlet air temperature set to 85℃, the atomizing disc speed set to 15000rpm, and the feed rate set to 25mL / min to obtain precursor microsphere powder. S3: The precursor microsphere powder was loaded into a high-purity graphite crucible and pushed into a tube furnace. High-purity argon gas was introduced at a flow rate of 500 mL / min. The heating program was set as follows: the temperature was increased to 500℃ at a rate of 5℃ / min and held for 150 min. Then, under the protection of high-purity argon gas (flow rate 500 mL / min), the temperature was increased to 900℃ at a rate of 3℃ / min and held for 150 min. Then, the temperature was increased to 1500℃ at a rate of 5℃ / min and held for 300 min. The temperature was then allowed to cool naturally to room temperature. The temperature was then transferred to an air muffle furnace and increased to 550℃ at a rate of 10℃ / min and held for 150 min. After cooling, the temperature was pulverized and sieved to obtain high-purity silicon carbide powder.

[0033] Example 3 The preparation process of high-purity silicon carbide powder for ceramics in this embodiment includes the following steps: S1: 500 mL of anhydrous ethanol and 1000 mL of deionized water were injected into a 2000 mL reactor with a Teflon liner. The pH of the system was adjusted to 2.5 using 36% hydrochloric acid. Mechanical stirring was started at 400 rpm. 600 mL of methyltriethoxysilane was added dropwise at a uniform rate. After the addition was complete, the mixture was stirred at 25 °C for 100 min. Then, 180 g of tannic acid powder was added at once. The temperature was raised to 70 °C and stirred at 500 rpm for 360 min. The mixture was then cooled to room temperature to obtain a homogeneous sol. S2: Transfer the homogeneous sol to an ultrasonic disperser with a power of 1000W and a frequency of 30kHz. Under ultrasonic conditions, add 18.5g of polytetrafluoroethylene nanoemulsion at a rate of 1mL / min. After the addition is complete, continue ultrasonic dispersion for 45min. Pump the mixture into a centrifugal spray dryer with the inlet air temperature set to 190℃, the outlet air temperature set to 90℃, the atomizing disc speed set to 17000rpm, and the feed rate set to 35mL / min to obtain precursor microsphere powder. S3: The precursor microsphere powder was loaded into a high-purity graphite crucible and pushed into a tube furnace. High-purity argon gas was introduced at a flow rate of 500 mL / min. The heating program was set as follows: the temperature was increased to 600℃ at a rate of 5℃ / min and held for 100 min. Then, under the protection of high-purity argon gas (flow rate 500 mL / min), the temperature was increased to 1100℃ at a rate of 3℃ / min and held for 100 min. Then, the temperature was increased to 1600℃ at a rate of 5℃ / min and held for 200 min. The temperature was then allowed to cool naturally to room temperature. The mixture was then transferred to an air muffle furnace and heated to 600℃ at a rate of 10℃ / min. After holding for 100 min, the mixture was cooled, pulverized, and sieved to obtain high-purity silicon carbide powder.

[0034] Example 4 The difference between this embodiment and Embodiment 1 is that: S1: 500 mL of anhydrous ethanol and 1000 mL of deionized water were injected into a 2000 mL reactor with a Teflon liner. The pH of the system was adjusted to 2.5 using 36% hydrochloric acid. Mechanical stirring was started at 400 rpm. 500 mL of methyltrimethoxysilane was added dropwise at a uniform rate. After the addition was complete, the mixture was stirred at 25 °C for 120 min. Then, 130 g of tannic acid powder and 20 g of gallic acid powder were added at once. The temperature was raised to 60 °C and stirred at 500 rpm for 300 min. The mixture was then cooled to room temperature to obtain a homogeneous sol. Everything else is the same as in Example 1.

[0035] Example 5 The difference between this embodiment and embodiment 4 is that: S2: The homogeneous sol was transferred to an ultrasonic disperser with a power of 800W and a frequency of 20kHz. 15g of polytetrafluoroethylene nanoemulsion was added dropwise at a rate of 1mL / min under ultrasonic conditions. After the addition was completed, ultrasonic dispersion was continued for 60min. While maintaining ultrasonic conditions, fluorosilane coupling agent pre-hydrolysis solution was added, and ultrasonic dispersion was continued for 30min. The mixture was then pumped into a centrifugal spray dryer with the inlet air temperature set to 180℃, the outlet air temperature set to 85℃, the atomizing disc speed set to 15000rpm, and the feed rate set to 25mL / min to obtain precursor microsphere powder. The preparation method of the fluorosilane coupling agent pre-hydrolyzed solution is as follows: Add 5 mL of perfluorooctyltriethoxysilane to 50 mL of anhydrous ethanol-water solution (volume ratio of anhydrous ethanol to water is 5:1), adjust the pH of the system to 5.0 with 5% dilute hydrochloric acid, heat to 60 °C, hydrolyze for 120 min, cool, and obtain a pre-hydrolyzed solution of fluorosilane coupling agent.

[0036] The obtained fluorosilane coupling agent pre-hydrolyzed solution must be added entirely to this embodiment.

[0037] The rest is the same as in Example 4.

[0038] Example 6 The difference between this embodiment and embodiment 5 is as follows: S2: Transfer the homogeneous sol to an ultrasonic disperser with a power of 800W and a frequency of 20kHz. Under ultrasonic conditions, add 15g of polytetrafluoroethylene nanoemulsion at a rate of 1mL / min. After the addition is complete, continue ultrasonic dispersion for 60min. While maintaining ultrasonic conditions, add the fluorosilane coupling agent pre-hydrolyzed solution and continue ultrasonic dispersion for 40min. Pump the solution into a centrifugal spray dryer with the inlet air temperature set to 180℃, the outlet air temperature set to 85℃, the atomizing disc speed set to 15000rpm, and the feed rate set to 25mL / min to obtain precursor microsphere powder. The preparation method of the fluorosilane coupling agent pre-hydrolyzed solution is as follows: 10 mL of perfluorooctyltriethoxysilane was added to 100 mL of anhydrous ethanol-water solution (volume ratio of anhydrous ethanol to water was 5:1). The pH of the system was adjusted to 4.0 with 5% dilute hydrochloric acid. The temperature was raised to 75 °C and hydrolyzed for 90 min. After cooling, a pre-hydrolyzed solution of fluorosilane coupling agent was obtained.

[0039] The obtained fluorosilane coupling agent pre-hydrolyzed solution must be added entirely to this embodiment.

[0040] The rest is the same as in Example 5.

[0041] Comparative Example 1 The difference between this comparative example and Example 1 is as follows: S2: Pump the homogeneous sol into a centrifugal spray dryer, set the inlet air temperature to 180℃, the outlet air temperature to 85℃, the atomizing disc speed to 15000rpm, and the feed rate to 25mL / min to obtain precursor microsphere powder. Everything else is the same as in Example 1.

[0042] Comparative Example 2 The preparation process of high-purity silicon carbide powder for ceramics in this comparative example includes the following steps: S1: 500 mL of anhydrous ethanol and 1000 mL of deionized water were injected into a 2000 mL reactor with a Teflon liner. The pH of the system was adjusted to 2.5 using 36% hydrochloric acid. Mechanical stirring was started at 400 rpm. 500 mL of methyltrimethoxysilane was added dropwise at a uniform rate. After the addition was complete, the mixture was stirred at 25 °C for 120 min. Then, 150 g of tannic acid powder was added at once. The temperature was raised to 60 °C and stirred at 500 rpm for 300 min. The mixture was then cooled to room temperature to obtain a homogeneous sol. S2: The homogeneous sol was transferred to an ultrasonic disperser with a power of 800W and a frequency of 20kHz. 15g of polytetrafluoroethylene nanoemulsion was added dropwise at a rate of 1mL / min under ultrasonic conditions. After the addition was completed, ultrasonic dispersion was continued for 60min. The mixture was then placed in a forced-air drying oven at 120℃ for slow evaporation for up to 36h. After that, it was placed in a high-purity graphite crucible and pushed into a tube furnace. High-purity argon gas was introduced at a flow rate of 500mL / min. The temperature was increased to 1550℃ at a rate of 10℃ / min and held for 240min. The mixture was then allowed to cool naturally to room temperature and transferred to an air muffle furnace. The temperature was increased to 600℃ at a rate of 10℃ / min and held for 120min. After cooling, the mixture was pulverized and sieved to obtain high-purity silicon carbide powder.

[0043] Comparative Example 3 The preparation process of high-purity silicon carbide powder for ceramics in this comparative example includes the following steps: 200g of acidic silica sol with a SiO2 solid content of 50wt% (including 100g of nano-silica) and 66g of conductive carbon black powder were used as silicon and carbon sources, respectively. These, along with 15g of polytetrafluoroethylene nanoemulsion, were placed together in a planetary ball mill. Using anhydrous ethanol as the medium, the mixture was wet-milled at 600rpm for 24 hours. After drying in a 120℃ forced-air drying oven for 2 hours, the mixture was placed in a high-purity graphite crucible and pushed into a tubular atmosphere furnace. High-purity argon gas was introduced at a flow rate of 500mL / min, and the temperature was set to a specific range. Sequence: The temperature was increased to 500℃ at a rate of 5℃ / min and held for 120 min. Then, under the protection of high-purity argon (flow rate 500 mL / min), the temperature was increased to 1000℃ at a rate of 3℃ / min and held for 120 min. Then, the temperature was increased to 1550℃ at a rate of 5℃ / min and held for 240 min. After natural cooling to room temperature, the temperature was transferred to an air muffle furnace and increased to 600℃ at a rate of 10℃ / min. After holding for 120 min, the temperature was cooled, pulverized, and sieved to obtain high-purity silicon carbide powder.

[0044] Among them, the conductive carbon black is nano-sized conductive carbon black with an average particle size D50 of 20~50nm.

[0045] Performance testing The high-purity silicon carbide powders obtained in Examples 1-6 and Comparative Examples 1-3 were subjected to the following performance tests, and the test results are shown in Table 1. Among them, the preparation of ceramic samples: the silicon carbide powders obtained in each example and comparative example were all added with 3wt% boron carbide and 5wt% phenolic resin as sintering aids. Anhydrous ethanol was used as the ball milling medium, and the samples were ball-milled in a planetary ball mill for 4 hours. After drying and passing through a 200-mesh sieve, the samples were dry-pressed into green blanks under a pressure of 200 MPa. The green blanks were then sintered at 2150℃ for 2 hours under a high-purity argon atmosphere. After cooling in the furnace, the sintered samples were processed into standard bending test specimens of 3mm×4mm×36mm, and the bending strength was tested.

[0046] Table 1. Performance test data of high-purity silicon carbide powders prepared in Examples 1-6 and Comparative Examples 1-3

[0047] The performance test data in Table 1 is analyzed as follows: The silicon carbide powders prepared in Examples 1-6 of this invention have finer and more uniform particle size, higher main phase purity, and better acid corrosion resistance compared to Comparative Examples 1-3. The room temperature flexural strength of silicon carbide ceramics prepared in this way is significantly improved. This fully demonstrates that the core process design of this invention, which involves the molecular-level uniform dispersion of silicon and carbon sources and the synergistic segmented programmed heating heat treatment of fluorine-containing components, effectively solves the core pain points of traditional silicon carbide preparation processes, such as incomplete reaction, severe powder agglomeration, low purity, and poor sintering activity. This invention achieves the controllable preparation of high-purity, highly dispersed, and highly sintering active silicon carbide powders.

[0048] This embodiment is illustrated by... Figures 1-2 Scanning electron microscopy characterization revealed that the silicon carbide powder obtained was uniform in size, with no hard agglomerates formed by high-temperature sintering necks between particles, and no abnormally grown grains. It exhibited excellent dispersibility, which can effectively avoid the problems of uneven densification and abnormal grain growth caused by agglomerates during ceramic sintering, laying a good foundation for the high-performance preparation of silicon carbide ceramics.

Claims

1. A process for preparing high-purity silicon carbide powder for ceramics, characterized in that, The process includes the following steps: S1: Add an aqueous ethanol solution to a reaction vessel, adjust the pH to 2.5-3.0, add a silicon source, react for 100-150 min, wherein the silicon source is any one of methyltrimethoxysilane or methyltriethoxysilane, add a polyphenolic compound, heat to 50-70℃, mix for 240-360 min, cool, and obtain a homogeneous sol, wherein the polyphenolic compound is selected from at least one of tannic acid and gallic acid; S2: Under ultrasonic assistance, uniformly disperse the fluoropolymer nanoemulsion in the homogeneous sol, and then spray dry to obtain precursor microsphere powder, wherein the fluoropolymer nanoemulsion is polytetrafluoroethylene nanoemulsion, polyvinylidene fluoride nanoemulsion, or fluorinated ethylene propylene copolymer nanoemulsion. For any of the rice emulsions, the spray drying process parameters are as follows: inlet air temperature is 180~190℃, outlet air temperature is 85~90℃, atomizing disc speed is 15000~17000rpm, and feed rate is 25~35mL / min; S3: Under an inert atmosphere, the precursor microsphere powder is placed in an atmosphere furnace, heated to 500~600℃, held for 100~150min, then heated to 900~1100℃, held for 100~150min, then heated to 1500~1600℃, held for 200~300min, and after cooling, under an air atmosphere, held at 550~600℃ for 100~150min to obtain high-purity silicon carbide powder.

2. The preparation process of high-purity silicon carbide powder for ceramics according to claim 1, characterized in that, The volume-to-mass ratio of the silicon source, polyphenolic compound, and fluorinated polymer nanoemulsion (based on solid content) is (400~600) mL: (120~180) g: (7~11) g.

3. The preparation process of high-purity silicon carbide powder for ceramics according to claim 1, characterized in that, The polyphenolic compounds include tannic acid and gallic acid.

4. The preparation process of high-purity silicon carbide powder for ceramics according to claim 1, characterized in that, In step S2, under ultrasonic assistance, the fluoropolymer nanoemulsion is first uniformly dispersed in a homogeneous sol, and then the fluorosilane coupling agent pre-hydrolysis solution is added under ultrasonic conditions. The mixture is ultrasonically dispersed for 30-40 minutes and finally spray-dried.

5. The preparation process of high-purity silicon carbide powder for ceramics according to claim 4, characterized in that, In the fluorosilane coupling agent pre-hydrolyzed solution, the amount of fluorosilane coupling agent used is 1% to 2% of the amount of silicon source used.

6. The preparation process of high-purity silicon carbide powder for ceramics according to claim 4, characterized in that, The preparation method of the fluorosilane coupling agent pre-hydrolyzed solution includes the following steps: adding the fluorosilane coupling agent to an ethanol aqueous solution, adjusting the pH of the system to 4.0~5.0, heating to 60~75℃, hydrolyzing for 90~120 min, cooling, and obtaining the fluorosilane coupling agent pre-hydrolyzed solution.

7. A high-purity silicon carbide powder prepared by the preparation process according to any one of claims 1 to 6, used to improve the performance of ceramic products.

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