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CN-122010118-A - Method for preparing electronic grade silicon carbide by using fly ash dynamic impurity removal-gas phase purification method

CN122010118ACN 122010118 ACN122010118 ACN 122010118ACN-122010118-A

Abstract

The invention relates to the technical field of preparation methods of silicon carbide, in particular to a method for preparing electronic grade silicon carbide by a fly ash dynamic impurity removal-gas phase purification method. Pretreating fly ash raw materials by KOH solution, carrying out acid leaching in oxalic acid/citric acid mixed solution, introducing chlorine-containing gas to remove impurities, mixing with biomass carbon source, heating and reducing in nitrogen-hydrogen mixed gas, and introducing silicon vapor to carry out high-temperature reaction to obtain the high-purity beta-SiC. The process does not need presintering and pore-forming agents, and breaks through the limitation of a sandwich structure. The dynamic aluminum-silicon ratio feedback system based on viscosity real-time regulation effectively solves the problem of impurity regeneration caused by difficulty in accurate regulation of aluminum-silicon ratio in a fly ash hydrothermal melting method, the Cl gas phase deep impurity removal technology enables mullite to be decomposed into volatile chloride under high pressure, the limit of acid leaching impurity removal is broken through, and a silicon vapor partial pressure control model is used for realizing beta phase directional crystallization by accurately regulating and controlling gas phase SiO concentration to inhibit alpha-SiC generation.

Inventors

  • TAN ZENGQIANG
  • WANG FENGYANG
  • LI JIANGAO
  • FAN HUIPENG
  • LENG JING
  • GAO YANG

Assignees

  • 西安热工研究院有限公司
  • 华能沁北发电有限责任公司

Dates

Publication Date
20260512
Application Date
20260206

Claims (10)

  1. 1. The method for preparing the electronic grade silicon carbide by the dynamic impurity removal-gas phase purification method of the fly ash is characterized by comprising the following steps of: (1) Fly ash pretreatment-aluminum-silicon ratio precise regulation and control Mixing fly ash with KOH solution, adding the mixture into a reaction kettle, sealing, gradually heating to 110-130 ℃ by heating an oil bath, monitoring the viscosity change of a reaction system in real time, and automatically adjusting the hydrothermal reaction temperature and time by a feedback system to stabilize the Al/Si ratio; (2) Staged acid leaching-gas phase cooperative impurity removal Primary acid leaching, namely pouring the molten pulverized fuel ash into a graded leaching tank after the pulverized fuel ash is melted by potassium hydroxide, adding a mixed acid solution consisting of oxalic acid and citric acid, uniformly stirring, and heating and preserving heat; Transferring into a high-pressure reaction kettle, reacting at high temperature and high pressure by taking chlorine gas or hydrogen chloride gas as a gas phase transmission medium to form volatile AlCl 3 by Al, continuously removing oxygen partial pressure in the system to decompose mullite, and finally enabling the Al/Si ratio to reach 2-3 to obtain impurity-removing powder; (3) In situ beta-SiC crystalline phase induction Ball-milling and mixing the impurity-removed powder and a biomass carbon source according to the weight ratio of 1:2, placing the mixture in a vacuum tube furnace, vacuumizing to below 10Pa, The first stage, namely slowly heating to 1300-1400 ℃ and preserving heat under the mixed atmosphere of N 2 and H 2 ; the second stage, injecting dimethyl dichlorosilane; And in the third stage, slowly heating to 1550-1650 ℃ and preserving heat under a carbon-rich reducing atmosphere of CH 4 and O 2 .
  2. 2. The method for preparing electronic grade silicon carbide by using the dynamic impurity removal and gas phase purification method for fly ash, which is characterized by comprising the following steps of (1), wherein the fly ash is any one of power plant fly ash, steel mill slag or iron mill slag, preferably, the mass fraction of KOH solution in step (1) is 10-15%, and the liquid-solid ratio of KOH solution to fly ash is 0.8 mL/1 g.
  3. 3. The method for preparing electronic grade silicon carbide by using the dynamic impurity removal and gas phase purification method for fly ash according to claim 1, wherein in the step (2), the concentration of oxalic acid in the mixed acid solution is 10-15%, the concentration of citric acid is 5-10%, and the liquid-solid ratio of the mixed acid solution to the fly ash is 4:1.
  4. 4. The method for preparing electronic grade silicon carbide by using the dynamic impurity removal and gas phase purification method for fly ash according to claim 1, wherein in the step (2), the temperature is kept at 80 ℃ for 2 hours.
  5. 5. The method for preparing electronic grade silicon carbide by using the dynamic impurity removal and gas phase purification method for fly ash according to claim 1, wherein in the step (2), the reaction is carried out for 8 hours at 240 ℃ and 2.5 MPa.
  6. 6. The method for preparing electronic grade silicon carbide by using the dynamic impurity removal and gas phase purification method of fly ash according to claim 1, wherein in the step (3), the biomass carbon source is one or more of water wood flower, needle wood, eucalyptus wood, bamboo wood or rice husk.
  7. 7. The method for preparing electronic grade silicon carbide by using the dynamic impurity removal and gas phase purification method for fly ash according to claim 1, wherein in the step (3), the volume ratio of N 2 to H 2 is (8-10): 1.
  8. 8. The method for preparing electronic grade silicon carbide by using the dynamic impurity removal and gas phase purification method for fly ash according to claim 1, wherein in the step (3), the temperature is raised to 1300-1400 ℃ at a rate of 3-8 ℃ per minute and kept for 0.5-2h in the first stage.
  9. 9. The method for preparing electronic grade silicon carbide by using the dynamic impurity removal and gas phase purification method for fly ash according to claim 1, wherein in the step (3), the volume ratio of CH 4 to O 2 is (1.5-2.5): 1.
  10. 10. The method for preparing electronic grade silicon carbide by using the dynamic impurity removal and gas phase purification method for fly ash according to claim 1, wherein in the step (3), the temperature is raised to 1550-1650 ℃ at a rate of 3-8 ℃ per minute and kept for 2-4 hours in the third stage.

Description

Method for preparing electronic grade silicon carbide by using fly ash dynamic impurity removal-gas phase purification method Technical Field The invention relates to the technical field of preparation methods of silicon carbide, in particular to a method for preparing electronic grade silicon carbide by a fly ash dynamic impurity removal-gas phase purification method. Background In the technical field of preparing electronic grade silicon carbide from fly ash, the prior art such as CN102583468A and CN119039021A, although certain progress is made in extracting alumina from fly ash and preparing low-expansion structural ceramics, the key problems of preparing high-purity electronic grade silicon carbide cannot be effectively solved by the technologies. CN102583468a, although solving the problems of equipment corrosion and process chain shortening by ammonium sulfate activation process, is not related to the preparation of silicon carbide, and it is not mentioned how to control the crystal phase and purity of silicon carbide. In the preparation method of the low-expansion structural ceramic disclosed in CN119039021A, although raw materials such as coal gangue and secondary aluminum ash are utilized, the final product is not silicon carbide, and a specific technical scheme for extracting and purifying the silicon carbide from the fly ash is not provided. These prior art techniques have the disadvantage of not being effective in controlling and removing impurities from fly ash, particularly in making highly pure, highly oriented beta-SiC phases difficult to achieve, while also being ineffective in utilizing carbon sources and controlling the partial pressure of silicon vapor to promote oriented crystallization of beta-SiC. In addition, the prior art has room for improvement in terms of cost control and environmental friendliness, such as improvement of raw material utilization rate and reagent circulation rate, and realization of a closed loop process with zero wastewater discharge. Disclosure of Invention In order to overcome the defects of the prior art, the invention provides a method for preparing electronic grade silicon carbide by using a fly ash dynamic impurity removal-gas phase purification method, which aims to solve the problems of metal ion toxicity, easy silicon dioxide hydrolysis, long process flow and high cost in the preparation of the silicon carbide by using the fly ash. A method for preparing electronic grade silicon carbide by a fly ash dynamic impurity removal-gas phase purification method comprises the following steps: (1) Fly ash pretreatment-aluminum-silicon ratio precise regulation and control Mixing fly ash with KOH solution, adding the mixture into a reaction kettle, sealing, gradually heating to 110-130 ℃ by heating an oil bath, monitoring the viscosity change of a reaction system in real time, and automatically adjusting the hydrothermal reaction temperature and time by a feedback system to stabilize the Al/Si ratio; (2) Staged acid leaching-gas phase cooperative impurity removal Primary acid leaching, namely pouring the molten pulverized fuel ash into a graded leaching tank after the pulverized fuel ash is melted by potassium hydroxide, adding a mixed acid solution consisting of oxalic acid and citric acid, uniformly stirring, and heating and preserving heat; transferring into a high-pressure reaction kettle, and reacting at high temperature and high pressure by taking chlorine (Cl 2) or hydrogen chloride (HCl) gas as a gas phase transmission medium, wherein the chlorine/hydrogen chloride directly reacts with aluminosilicate such as mullite to generate gaseous volatile products such as aluminum chloride (AlCl 3), so as to realize deep impurity removal, and finally, the Al/Si ratio reaches 2-3, thereby obtaining impurity-removed powder; (3) In situ beta-SiC crystalline phase induction Ball-milling and mixing the impurity-removed powder and a biomass carbon source according to the weight ratio of 1:2, placing the mixture in a vacuum tube furnace, vacuumizing to below 10Pa, The first stage, namely slowly heating to 1300-1400 ℃ and preserving heat under the mixed atmosphere of N 2 and H 2; the second stage, injecting dimethyl dichlorosilane; And in the third stage, slowly heating to 1550-1650 ℃ and preserving heat under a carbon-rich reducing atmosphere of CH 4 and O 2. Preferably, in the step (1), the fly ash is any one of power plant fly ash, steel mill slag or iron mill slag. Preferably, in the step (1), the mass fraction of the KOH solution is 10-15%, and the liquid-solid ratio of the KOH solution to the fly ash is 0.8:1. Preferably, in the step (2), the concentration of oxalic acid in the mixed acid solution is 10-15%, the concentration of citric acid is 5-10%, and the liquid-solid ratio of the mixed acid solution to the fly ash is 4:1. Preferably, in step (2), the temperature is maintained at 80 ℃ for 2 hours. Preferably, in step (2), the reaction is carried out at 240℃and 2.5MPa