Method for preparing porous silicon carbide powder through short-time flash firing

Abstract

The invention relates to a method for preparing porous silicon carbide powder through short-time flash firing, which comprises the following steps: mixing coal gangue powder with coal tar according to a certain proportion, then pasting the mixed sample on a resistance heating material, carrying out high-current flash firing in a protective atmosphere to a high temperature, and carrying out heat preservation for a period of time to obtain powder containing silicon carbide, and dispersing the powder in acid to remove residual silicon dioxide and other impurities, and cleaning and drying to obtain the silicon carbide powder.

Description

Technical Field

[0001] This invention relates to a method for preparing porous silicon carbide powder by short-time flash calcination, and more particularly to a method for preparing porous silicon carbide powder by short-time flash calcination using industrial waste coal gangue and coal tar. Background Technology

[0002] Silicon carbide (SiC) is a high-performance ceramic and semiconductor material with important applications in multiple technological fields due to its unique physical and chemical properties. Silicon carbide is scarce in nature (its ore is called moissanite), and industrially, it is mostly obtained through artificial synthesis. Currently, among several relatively mature industrial methods for preparing silicon carbide powder, the Acheson process (also known as the traditional carbothermal reduction method) involves mixing high-purity quartz sand or pulverized quartz ore with petroleum coke, graphite, or anthracite fine powder, and then reacting the mixture at temperatures above 2000°C using a graphite electrode to synthesize α-SiC powder. However, on October 27, 2017, according to the list of carcinogens published by the International Agency for Research on Cancer (IARC) of the World Health Organization, the Acheson process was classified as a Group 2B carcinogen. Another method is the low-temperature carbothermal reduction of silica, which involves mixing fine silica powder with carbon powder and carrying out a carbothermal reduction reaction at temperatures ranging from 1500 to 1800°C to obtain β-SiC powder with higher purity. Although this method is similar to the Acheson method, it has a lower synthesis temperature and produces a β-type crystal structure. However, this method leaves a large amount of residual unreacted carbon and silicon dioxide, requiring effective desilication and decarburization treatment.

[0003] Patent CN 114835122A discloses a method for preparing silicon carbide aerogel powder from coal gangue. The method involves alkali-activated coal gangue followed by acid leaching to extract a silicon-rich solution. Resorcinol and formaldehyde are used as carbon sources, and ionic liquids are used as catalysts and templates. The silicon carbide aerogel powder is prepared by supercritical drying and spark plasma sintering. Patent CN 108046265A discloses a method for preparing silicon carbide from coal gangue and waste activated carbon. The coal gangue and activated carbon are mixed and pretreated, then heated at 1400-1700℃ for 3-10 hours to obtain silicon carbide powder. Patent CN108751199A discloses a method for preparing silicon carbide from aluminate slag extracted from coal gangue. The method involves microwave heating straw starch obtained from agricultural waste straw with coal gangue to obtain silicon carbide. The above three methods have drawbacks such as complex preparation processes, high calcination energy consumption, high carbon source costs, or cumbersome pretreatment. Summary of the Invention

[0004] To address the problems of existing silicon carbide preparation methods, such as carcinogenicity, high energy consumption, slow heating and cooling, and long preparation cycles, this invention proposes a method for preparing porous silicon carbide powder using short-time flash calcination. This method uses coal gangue and coal tar as raw materials, employing a rapid electric heating calcination technique in an inert atmosphere to shorten the calcination time to within 10 minutes, thereby producing porous silicon carbide. This significantly reduces energy consumption and improves the efficiency of silicon carbide preparation methods.

[0005] The technical solution adopted by the present invention to achieve the above-mentioned technical objectives is as follows.

[0006] A method for preparing porous silicon carbide powder by short-time flash calcination includes the following steps:

[0007] 1) Mix coal gangue powder and coal tar in a certain proportion until uniform, and add an appropriate amount of catalyst to obtain a viscous mixture;

[0008] 2) Adhere the viscous mixture to the surface of the resistance heating element, apply electricity, and flash-fire at high current to 1300-1800℃ in a protective atmosphere. Hold for 1-5 minutes, then allow to cool naturally to room temperature. Remove the flash-fired product from the surface of the resistance heating element.

[0009] 3) The flash-calcined product is calcined at 600-800℃ in air atmosphere for 1-5 hours, then acid-washed with sufficient hydrofluoric acid, then washed with water until neutral, and dried to obtain the porous silicon carbide powder.

[0010] This invention employs a short-time flash calcination method to prepare porous silicon carbide powder materials. During the flash calcination process, coal tar undergoes carbonization, and volatiles (such as H2 and CH4) generated from the decomposition of small molecule organic matter escape, leaving initial pores. Cracks formed by the uneven shrinkage of the carbon skeleton further expand the pores. Simultaneously, the siliceous components in coal gangue react with the carbon generated from the carbonization of coal tar at high temperatures to form silicon carbide. During the reaction, the escape of gaseous products and the volume changes between the solid and solid phases form new pores in the silicon carbide matrix. These factors collectively contribute to the formation of the porous structure of the silicon carbide sample.

[0011] Coal gangue's main components are Al2O3 and SiO2, and it also contains varying amounts of Fe2O3, etc. High-temperature carbonization results in the following reaction: Al2O3 + SiO2 + Fe2O3 + C → Al4C3 + SiC + Fe + CO + CO2. Hydrofluoric acid washing removes the roasting products Fe and Al4C3, and unreacted Al2O3, Fe2O3, and other oxides are also removed by hydrofluoric acid.

[0012] Furthermore, the particle size of the coal gangue powder is ≥80 mesh.

[0013] Furthermore, the SiO2 content in the coal gangue powder is ≥50wt%, and the Al2O3 content is ≤30wt%.

[0014] Furthermore, the coal tar is high-temperature coal tar with a benzene content ≤0.15wt%, anthracene content ≥26wt%, and naphthalene content ≥12wt%.

[0015] Furthermore, the mass ratio of coal gangue to high-temperature coal tar is 1:0.5-1.5.

[0016] Furthermore, the catalyst is one or more of ferric nitrate, cobalt nitrate, or nickel nitrate.

[0017] Furthermore, the resistance heating element is a resistance wire / rod or heating wire / rod with a resistance value of 10Ω~20Ω.

[0018] Furthermore, the protective atmosphere is one or more of argon, nitrogen, and helium.

[0019] Furthermore, the high current is 400A~500A.

[0020] Furthermore, the concentration of the hydrofluoric acid is 4 mol / L to 6 mol / L.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1) This invention uses industrial waste coal gangue as a silicon source and coal tar as a carbon source to prepare porous silicon carbide. On the one hand, it solves the problem of environmental pollution and resource waste caused by coal gangue industrial waste. On the other hand, compared with traditional methods of preparing silicon carbide, it effectively reduces the production cost of silicon carbide products and has significant economic and environmental benefits.

[0023] 2) The raw materials of this invention are abundant and inexpensive, the required equipment is simple, the operation process is simple and easy, the production cost is low, and the production cycle is short. Attached Figure Description

[0024] Figure 1 The images show the XRD patterns of the SiC samples prepared in Examples 1, 2, and 3 of this invention.

[0025] Figure 2 (a) Nitrogen adsorption isotherm and (b) pore size distribution of the SiC sample prepared in Example 4 of this invention.

[0026] Figure 3 (a) Nitrogen adsorption isotherm and (b) pore size distribution of the SiC sample prepared in Example 7 of this invention. Detailed Implementation

[0027] The present invention will be further described below with reference to the embodiments. However, the scope of the present invention is not limited to the following embodiments.

[0028] Example 1

[0029] 1) Mix 5g of coal gangue powder with 2.5ml of coal tar, add nickel nitrate catalyst and mix evenly to obtain a viscous mixed sample; 2) Adhere the above mixed sample to the surface of a resistance wire (Ф=50mm, 10Ω), flash-fire at 1500℃ with a high current of 420A in an argon atmosphere, hold for 2min, and allow to cool naturally to room temperature after the reaction. Remove the flash-fired product from the surface of the resistance heating element; 3) Oxidize the flash-fired product in air at 700℃ for 4h, then acid-wash with sufficient 4mol / L hydrofluoric acid, then wash with water until neutral, and dry to obtain the porous silicon carbide powder.

[0030] Example 2

[0031] 1) Mix 5g of coal gangue powder with 5ml of coal tar, add cobalt nitrate catalyst and mix evenly to obtain a viscous mixed sample; 2) Adhere the above mixed sample to the surface of a resistance wire (Ф=50mm, 15Ω), flash-calculate at 450A to 1800℃ in a helium atmosphere, hold for 5min, and allow to cool naturally to room temperature after the reaction. Remove the flash-calculated product from the surface of the resistance heating element; 3) Oxidize the flash-calculated product in air at 600℃ for 4h, then acid-wash with sufficient 5mol / L hydrofluoric acid, then wash with water until neutral, and dry to obtain the porous silicon carbide powder.

[0032] Example 3

[0033] 1) Mix 5g of coal gangue powder with 7.5ml of coal tar, add ferric nitrate catalyst and mix evenly to obtain a viscous mixed sample; 2) Adhere the above mixed sample to the surface of a resistance wire (Ф=50mm, 17Ω), flash-calculate at 500A to 1300℃ in an argon atmosphere, hold for 1min, and allow to cool naturally to room temperature after the reaction. Remove the flash-calculated product from the surface of the resistance heating element; 3) Oxidize the flash-calculated product in air at 700℃ for 2h, then acid-wash with sufficient 6mol / L hydrofluoric acid, then wash with water until neutral, and dry to obtain the porous silicon carbide powder.

[0034] The XRD patterns of the silicon carbide powders prepared in Examples 1 to 3 are shown below. Figure 1 .Depend on Figure 1 As can be seen, the main diffraction peaks at 36°, 43°, 60°, and 72° correspond to the (111), (110), (220), and (311) crystal planes of silicon carbide, respectively, indicating that the method of the present invention successfully prepared silicon carbide powder. The positions of the characteristic diffraction peaks in the XRD patterns of the silicon carbide powders prepared in Examples 4 to 7 are basically the same as those in Examples 1-3, so they will not be listed one by one.

[0035] Example 4

[0036] 1) Mix 5g of coal gangue powder with 15ml of coal tar, add cobalt nitrate catalyst and mix evenly to obtain a viscous mixed sample; 2) Adhere the above mixed sample to the surface of a resistance wire (Ф=50mm, 20Ω), flash-calculate at 470A to 1400℃ in a mixed atmosphere of argon and helium, hold for 2min, and allow to cool naturally to room temperature after the reaction. Remove the flash-calculated product from the surface of the resistance heating element; 3) Oxidize the flash-calculated product in air at 800℃ for 3h, then acid-wash with sufficient 5mol / L hydrofluoric acid, then wash with water until neutral, and dry to obtain the porous silicon carbide powder.

[0037] Figure 2 The following are examples of the nitrogen adsorption isotherm and pore size distribution of the SiC sample prepared in Example 4 of this invention. The nitrogen adsorption isotherm belongs to type IV in the IUPAC classification, with H1 hysteresis loop, indicating that the prepared silicon carbide powder has a porous structure. The pore size distribution shows that its pore size is mainly 3 nm.

[0038] Example 5

[0039] 1) Mix 5g of coal gangue powder with 9ml of coal tar, add cobalt nitrate catalyst and mix evenly to obtain a viscous mixed sample; 2) Adhere the above mixed sample to the surface of a resistance wire (Ф=50mm, 20Ω), flash-calculate at 450A to 1500℃ in a mixed atmosphere of argon and nitrogen, hold for 2min, and allow to cool naturally to room temperature after the reaction. Remove the flash-calculated product from the surface of the resistance heating element; 3) Oxidize the flash-calculated product in air at 800℃ for 4h, then acid-wash with sufficient 6mol / L hydrofluoric acid, then wash with water until neutral, and dry to obtain the porous silicon carbide powder.

[0040] Example 6

[0041] 1) Mix 2.5g of coal gangue powder with 5ml of coal tar, add cobalt nitrate catalyst and mix evenly to obtain a viscous mixed sample; 2) Adhere the above mixed sample to the surface of a resistance wire (Ф=50mm, 15Ω), flash-calculate at 480A to 1500℃ in a helium atmosphere, hold for 2min, and allow to cool naturally to room temperature after the reaction. Remove the flash-calculated product from the surface of the resistance heating element; 3) Oxidize the flash-calculated product in air at 700℃ for 4h, then acid-wash with sufficient 4mol / L hydrofluoric acid, then wash with water until neutral, and dry to obtain the porous silicon carbide powder.

[0042] Example 7

[0043] 1) Mix 3.5g of coal gangue powder with 5ml of coal tar, add ferric nitrate catalyst and mix evenly to obtain a viscous mixed sample; 2) Adhere the above mixed sample to the surface of a resistance wire (Ф=50mm, 18Ω), flash-calculate at 500A to 1300℃ in a helium atmosphere, hold for 3min, and allow to cool naturally to room temperature after the reaction. Remove the flash-calculated product from the surface of the resistance heating element; 3) Oxidize the flash-calculated product in air at 800℃ for 5h, then acid-wash with sufficient 4mol / L hydrofluoric acid, then wash with water until neutral, and dry to obtain the porous silicon carbide powder.

[0044] Figure 3 The following are the nitrogen adsorption isotherm and pore size distribution of the SiC sample prepared in Example 7 of this invention. The nitrogen adsorption isotherm belongs to type IV in the IUPAC classification, with H1 hysteresis loop, indicating that the prepared silicon carbide powder has a porous structure. The pore size distribution shows that its pore size is mainly 3.5 nm.

Claims

1. A method for preparing porous silicon carbide powder by short-time flash calcination, characterized in that... Includes the following steps: 1) Mix coal gangue powder and coal tar in a certain proportion until uniform, and add an appropriate amount of catalyst to obtain a viscous mixture; 2) Adhere the viscous mixture onto the surface of the resistance heating element, apply electricity, and flash-fire at high current to 1300-1800°C in a protective atmosphere. After holding for 1-5 minutes, allow it to cool naturally to room temperature. Remove the flash-fired product from the surface of the resistance heating element. 3) The flash-calcined product is calcined at 600-800℃ in air atmosphere for 1-5 hours, then acid-washed with sufficient hydrofluoric acid, then washed with water until neutral, and dried to obtain the porous silicon carbide powder.

2. The method for preparing porous silicon carbide powder by short-time flash calcination according to claim 1, characterized in that: The particle size of the coal gangue powder is ≥80 mesh.

3. The method for preparing porous silicon carbide powder by short-time flash calcination according to claim 1 or 2, characterized in that: The coal gangue powder contains ≥50wt% SiO2 and ≤30wt% Al2O3.

4. The method for preparing porous silicon carbide powder by short-time flash calcination according to claim 1, characterized in that: The coal tar is high-temperature coal tar with a benzene content ≤0.15wt%, anthracene content ≥26wt%, and naphthalene content ≥12wt%.

5. The method for preparing porous silicon carbide powder by short-time flash calcination according to claim 1, characterized in that: The mass ratio of coal gangue to high-temperature coal tar is 1:0.5-1.

5.

6. The method for preparing porous silicon carbide powder by short-time flash calcination according to claim 1, characterized in that: The catalyst is one or more of ferric nitrate, cobalt nitrate, or nickel nitrate.

7. The method for preparing porous silicon carbide powder by short-time flash calcination according to claim 1, characterized in that: The resistance heating element is a resistance wire / rod or heating wire / rod with a resistance value of 10Ω~20Ω.

8. The method for preparing porous silicon carbide powder by short-time flash calcination according to claim 1, characterized in that: The protective atmosphere is one or more of argon, nitrogen, and helium.

9. The method for preparing porous silicon carbide powder by short-time flash calcination according to claim 1, characterized in that: The high current is 400A~500A.

10. The method for preparing porous silicon carbide powder by short-time flash calcination according to claim 1, characterized in that: The concentration of the hydrofluoric acid is 4 mol / L to 6 mol / L.

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