Method and device for removing sulfur element in silicon carbide raw material and silicon carbide powder

Abstract

The invention relates to the technical field of silicon carbide growth, and discloses a method and a device for removing a sulfur element in a silicon carbide raw material and silicon carbide powder. The method for removing the sulfur element in the silicon carbide raw material comprises the following steps: carrying out first reaction on the silicon carbide raw material and an alkali solvent in a microwave field to obtain first powder; performing ultrasonic water washing on the first powder to obtain second powder; performing a second reaction on the second powder and a reducing agent to reduce insoluble sulfides in the second powder to obtain third powder; performing a third reaction on the third powder and an oxidizing agent to oxidize the silicon elementary substance in the third powder to obtain fourth powder; and carrying out ultrasonic washing on the fourth powder to obtain the silicon carbide powder. The method for removing the sulfur element in the silicon carbide raw material is high in desulfurization efficiency, low in cost and environmentally friendly, and the obtained silicon carbide powder is stable in performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silicon carbide growth, in particular, to a method and device for removing sulfur elements from silicon carbide raw materials and silicon carbide powder. BACKGROUND

[0002] At present, as the third generation of wide band gap semiconductor material, silicon carbide has excellent performance such as wide band gap, high thermal conductivity and fast electron saturation drift speed, and has wide application prospects in high-temperature, high-frequency and high-power electronic devices and optoelectronic devices. However, sulfur elements are easily introduced into silicon carbide powder during smelting and processing, which mainly exist in the form of sulfides such as FeS2, CaS and SiS2. In semiconductor applications, sulfur will become an electron trap, reducing the carrier mobility. Therefore, effectively removing sulfur elements from silicon carbide powder is a key link to improve its application value.

[0003] The existing silicon carbide desulfurization technology has many deficiencies, for example, the traditional alkali fusion method needs to be carried out at a high temperature of 1200℃ or above, has high energy consumption and a reaction time of 2-4 hours, and is easy to cause silicon carbide particles to sinter and agglomerate. Although the acid immersion method can remove part of the soluble sulfides, it has limited effect on the insoluble sulfides, and generates a large amount of acid wastewater, which has high environmental protection treatment cost. In addition, the high-temperature reduction method needs to be operated at a temperature of 1000℃ or above and in a strong reducing atmosphere, relies on large equipment and has large equipment investment, and is not suitable for small and medium-sized enterprises. Therefore, developing a new method for removing sulfur elements from silicon carbide raw materials is one of the current challenges.

[0004] SUMMARY The present application aims to at least partially solve one of the technical problems in the related art. To this end, one object of the present application is to provide a method and device for removing sulfur elements from silicon carbide raw materials and silicon carbide powder. The method for removing sulfur elements from silicon carbide raw materials according to the present application can efficiently remove sulfur elements from silicon carbide powder, and can achieve efficient, economical and green desulfurization.

[0005] In a first aspect, the present application provides a method for removing sulfur elements from silicon carbide raw materials, comprising: causing a first reaction of the silicon carbide raw materials and an alkali flux in a microwave field to obtain a first powder; performing ultrasonic water washing on the first powder to obtain a second powder; causing a second reaction of the second powder and a reducing agent to reduce insoluble sulfides in the second powder to obtain a third powder; causing a third reaction of the third powder and an oxidizing agent to oxidize elemental silicon in the third powder to obtain a fourth powder; performing ultrasonic water washing on the fourth powder to obtain silicon carbide powder.

[0006] The method for removing sulfur elements in silicon carbide raw materials in the application has at least the following beneficial effects: 1. High desulfurization efficiency: microwave alkali fusion efficiently converts insoluble sulfides, ultrasonic water washing strengthens the removal of soluble sulfides, and low-temperature reduction deeply removes residual sulfur. The three work together to make the desulfurization rate reach more than 98%, and the sulfur content of the treated powder can be reduced to less than 5ppm, which is much better than the traditional alkali fusion method (82%-85%) and acid leaching method (75%-80%); 2. Low energy consumption and cost: microwave heating reduces the alkali fusion temperature to 450-550℃, which is more than 50% lower than the traditional alkali fusion method (about 1200℃), and the total energy consumption is reduced by 40%-50%; using industrial-grade sodium carbonate and hydrogen gas can reduce the raw material cost by 60% compared with special desulfurizing agents; 3. Green and environmentally friendly: The ultrasonic water washing filtrate can be recycled as sodium sulfide, and the low-temperature reduction tail gas can be discharged after being absorbed by lye, without generating a large amount of harmful waste water and waste gas, which meets the environmental protection requirements; 4. Stable performance of powder: The mild reaction conditions avoid sintering and agglomeration of silicon carbide particles, the crystal structure is complete, and the particle agglomeration rate is less than 2%; 5. Strong adaptability to industrialization: The equipment used is conventional industrial equipment, the investment cost is low, the operation steps are simple, and continuous production can be realized, which is suitable for different scale enterprises.

[0007] In addition, the method according to the above embodiments of the application can also have the following additional technical features: In some embodiments, the first reaction of the silicon carbide raw material and the alkali flux in the microwave field includes: mixing the silicon carbide raw material and the alkali flux to obtain a first mixture; The first mixture is subjected to the first reaction in the microwave field.

[0008] In some embodiments, at least one of the following conditions is met: The alkali flux includes at least one of sodium carbonate and potassium carbonate, preferably sodium carbonate; The rotation speed of the first mixing is 300-400 rpm; The time of the first mixing is 5-10 min; The microwave frequency is 24-2500 MHz; The microwave power is 800-1200 W.

[0009] In some embodiments, at least one of the following conditions is met: The particle size of the alkali flux is 100-200 mesh; The particle size of the silicon carbide raw material is 5-50 microns; The temperature of the first reaction is 450-550℃; The first reaction time is 20 min to 30 min; The first reaction temperature rising rate is 15 ℃ / min to 25 ℃ / min; The mass ratio of the silicon carbide raw material to the alkali flux is 1: (0.8-1.2).

[0010] In some embodiments, the ultrasonic water washing of the first powder includes: after mixing the first powder and water, sequentially performing ultrasonic water washing, filtration, and drying to obtain the second powder.

[0011] In some embodiments, at least one of the following conditions is met: The mass ratio of the first powder to the water is 1: (3-5); The ultrasonic water washing temperature is 25 ℃ to 40 ℃; The ultrasonic water washing time is 15 min to 20 min; The drying temperature is 80 ℃ to 100 ℃; The drying time is 1 h to 2 h; The drying vacuum degree is -0.08 MPa to 0.1 MPa.

[0012] In some embodiments, at least one of the following conditions is met: The reducing agent includes at least one of hydrogen and carbon monoxide; The oxidizing agent includes a mixed gas of oxygen and nitrogen; The second reaction temperature is 300 ℃ to 400 ℃; The second reaction time is 5 min to 10 min; The second reaction temperature rising rate is 10 ℃ / min to 15 ℃ / min; The third reaction temperature is 300 ℃ to 350 ℃; The third reaction time is 5 min to 8 min.

[0013] In the second aspect of the present application, a silicon carbide powder is prepared by the method described above. Thus, the silicon carbide powder has stable performance and low sulfur content.

[0014] In some embodiments, the content of sulfur in the silicon carbide powder is ≤5 ppm.

[0015] In the third aspect of the present application, a device for removing sulfur from a silicon carbide raw material is provided, which includes: A mixer is used to mix the silicon carbide raw material and the alkali flux to obtain a first mixture; a microwave reactor connected with the mixing machine, used for causing the first mixture to have a first reaction to obtain a first powder; an ultrasonic cleaning tank connected with the microwave reactor, used for performing ultrasonic water washing on the first powder to obtain a solid-liquid mixture of the first powder; a filter connected with the ultrasonic cleaning tank, used for realizing solid-liquid separation on the solid-liquid mixture of the first powder to obtain a wet-state powder; a drying machine connected with the filter, used for drying the wet-state powder to obtain a second powder; a tube furnace connected with the drying machine, used for providing a place for a redox reaction; a lye absorption tower connected with the tube furnace, used for absorbing gas in the tube furnace; a screen connected with the tube furnace, used for screening the powder. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 FIG. 1 is a structural schematic diagram of a device for removing sulfur elements in silicon carbide raw materials according to an embodiment of the present application. DETAILED DESCRIPTION

[0017] Embodiments of the present application are described in detail below. The embodiments described below are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0018] The present application is based on the following findings and recognitions of the applicant: As described above, the current alkali fusion method, acid leaching method and high-temperature reduction method all have certain drawbacks. The inventors consider that microwave heating has the characteristics of volume heating, high thermal efficiency and fast heating speed, which can significantly reduce the alkali fusion reaction temperature and time. Ultrasonic water washing can use cavitation effect to strengthen mass transfer and improve the removal efficiency of soluble sulfides. Low-temperature reduction can deeply remove residual insoluble sulfides under mild conditions. If the three are combined to remove sulfur, i.e., through the synergy of the three core units of microwave-assisted alkali fusion, ultrasonic water washing and low-temperature reduction, a continuous and efficient silicon carbide powder desulfurization system is constructed, which realizes the whole process desulfurization from raw material pretreatment to finished product collection, and is expected to solve the defects of related desulfurization methods and achieve efficient, economical and green desulfurization effect.

[0019] Therefore, in a first aspect, the present application provides a method for removing sulfur elements in silicon carbide raw materials, comprising: S10: causing the silicon carbide raw materials and the alkali flux to have a first reaction in a microwave field to obtain a first powder.

[0020] In the step, first mixing silicon carbide raw material and alkali flux to obtain a first mixture, and then making the first mixture undergo a first reaction in a microwave field. The insoluble sulfide in the silicon carbide raw material and the alkali flux undergo a double decomposition reaction or an oxidation reaction, and the sulfur element in the silicon carbide raw material is converted into a water-soluble sulfide. After the first reaction is completed, the temperature of the first powder is reduced to below 100 DEG C, and then the subsequent step is started.

[0021] In some embodiments, the temperature of the first reaction is 450 DEG C to 550 DEG C. Specifically, it can be 450 DEG C, 470 DEG C, 500 DEG C, 530 DEG C, 550 DEG C, etc. In this application, the "volume heating effect" and "dielectric polarization effect" of the microwave are used to achieve efficient alkali fusion. In the microwave field, the molecules of the alkali flux quickly absorb energy and heat up due to dielectric polarization, avoiding the heat conduction loss of traditional heating, so that the material can reach the reaction activity threshold at 450 DEG C to 550 DEG C (more than 650 DEG C lower than traditional heating). At the same time, the local strong electric field generated by the microwave polarization can weaken the lattice bond energy of the sulfide, accelerate the ion diffusion, and further promote the progress of the first reaction. In this process, the alkali flux and the insoluble sulfide in the powder undergo a double decomposition reaction or an oxidation reaction, and the sulfur element is converted into a water-soluble sulfide.

[0022] In some embodiments, the temperature of the first reaction is 450 DEG C to 550 DEG C. Specifically, it can be 450 DEG C, 470 DEG C, 500 DEG C, 530 DEG C, 550 DEG C, etc. In this application, the "volume heating effect" and "dielectric polarization effect" of the microwave are used to achieve efficient alkali fusion. In the microwave field, the molecules of the alkali flux quickly absorb energy and heat up due to dielectric polarization, avoiding the heat conduction loss of traditional heating, so that the material can reach the reaction activity threshold at 450 DEG C to 550 DEG C (more than 650 DEG C lower than traditional heating). At the same time, the local strong electric field generated by the microwave polarization can weaken the lattice bond energy of the sulfide, accelerate the ion diffusion, and further promote the progress of the first reaction. In this process, the alkali flux and the insoluble sulfide in the powder undergo a double decomposition reaction or an oxidation reaction, and the sulfur element is converted into a water-soluble sulfide.

[0023] In some embodiments, the temperature of the first reaction is 450 DEG C to 550 DEG C. Specifically, it can be 450 DEG C, 470 DEG C, 500 DEG C, 530 DEG C, 550 DEG C, etc. In this application, the "volume heating effect" and "dielectric polarization effect" of the microwave are used to achieve efficient alkali fusion. In the microwave field, the molecules of the alkali flux quickly absorb energy and heat up due to dielectric polarization, avoiding the heat conduction loss of traditional heating, so that the material can reach the reaction activity threshold at 450 DEG C to 550 DEG C (more than 650 DEG C lower than traditional heating). At the same time, the local strong electric field generated by the microwave polarization can weaken the lattice bond energy of the sulfide, accelerate the ion diffusion, and further promote the progress of the first reaction. In this process, the alkali flux and the insoluble sulfide in the powder undergo a double decomposition reaction or an oxidation reaction, and the sulfur element is converted into a water-soluble sulfide.

[0024] In some embodiments, the alkali flux includes at least one of sodium carbonate and potassium carbonate. The above-mentioned alkali flux has good wave-absorbing properties in the microwave field, can quickly heat up, and makes the reaction more efficient and uniform. At the same time, the above-mentioned alkali flux can react with the insoluble sulfide in the silicon carbide raw material to generate a water-soluble sulfide at a certain temperature. When the alkali flux is sodium carbonate, the cost is lower, and the dielectric properties of sodium carbonate are more matched with the temperature of the first reaction.

[0025] In some embodiments, the alkali flux is a mixed alkali with a mass ratio of sodium carbonate to potassium carbonate of 1:1. In this way, the reaction temperature can be further reduced by 50 DEG C to 80 DEG C, which is suitable for high-sulfur-content powder processing.

[0026] For example, when calcium sulfide (CaS) exists in the silicon carbide raw material, the specific reaction formula is: CaS + Na2CO3→ Na2S + CaCO3↓. The reaction utilizes the ion potential difference between Na+ and Ca2+ to make the more stable CaCO3 precipitate, thereby promoting the reaction to proceed in the forward direction. + The ion potential difference between Na+ and Ca2+ makes the more stable CaCO3 precipitate, thereby promoting the reaction to proceed in the forward direction. 2+

[0027] When iron sulfide (FeS2) exists in the silicon carbide raw material, the specific reaction formula is: 4FeS2+ 16Na2CO3+ O2→ 8Na2S + 2Fe2O3+ 16CO2↑. The microwave promotes O2 (a trace amount in the air) to participate in the reaction, oxidizing FeS2 to Fe2O3, while S2- combines with Na+ to form Na2S. 2+ 3+ 2- +

[0028] In some embodiments, the mass ratio of the silicon carbide raw material and the alkali flux is 1: (0.8-1.2). Specifically, it can be 1:0.8, 1:1, 1:1.2, or any range between any two of them. The above mass ratio can basically ensure that the alkali flux is uniformly coated on the surface of the silicon carbide raw material, so as to completely convert the insoluble sulfide in the silicon carbide raw material into water-soluble sulfide. This can basically avoid the problem that insufficient alkali flux cannot fully convert the sulfur element, and that excessive alkali flux may increase the burden of subsequent removal of the alkali flux.

[0029] In some embodiments, the microwave frequency is 24-2500 MHz (specifically, it can be 24 MHz, 100 MHz, 500 MHz, 1000 MHz, 2000 MHz, 2500 MHz, etc.) and the microwave power is 800-1200 W (specifically, it can be 800 W, 900 W, 1000 W, 1100 W, 1200 W, etc.) when the first reaction is performed. Within the above range of microwave frequency, the dielectric polarization effect of the alkali flux is strong, which can quickly absorb energy and uniformly heat, avoiding the heat conduction loss of traditional heating. Within the above range of microwave power, the material can stably maintain the temperature in the reaction interval of 450-550°C. It will neither cause slow heating and low reaction efficiency due to too low power, nor cause local overheating due to too high power.

[0030] ​​​​​In some embodiments, the rotation speed of the first mixing is 300 rpm-400 rpm (specifically, it can be 300 rpm, 320 rpm, 340 rpm, 360 rpm, 380 rpm, 400 rpm, etc.), and the time of the first mixing is 5 min-10 min (specifically, it can be 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, etc.). The above range can ensure that the alkali flux is uniformly coated on the surface of the silicon carbide raw material, and further promote the stable and uniform performance of the first reaction. The core principle of this step is to achieve full contact of solid-solid interface through mechanical mixing, to create homogeneous reaction conditions for the subsequent alkali fusion reaction (first reaction), and to avoid the occurrence of problems such as incomplete local reaction.

[0031] The specific mixing method is not limited. For example, the silicon carbide raw material and the alkali flux can be placed in a double-helix mixer for mixing.

[0032] In some embodiments, the particle size of the alkali flux is 100 mesh-200 mesh. Specifically, it can be 100 mesh, 150 mesh, 200 mesh, or any range between any two of them. The particle size of the silicon carbide raw material is 5 microns-50 microns. Specifically, it can be 5 microns, 10 microns, 20 microns, 30 microns, 40 microns, 50 microns, etc. Thus, it is helpful to further ensure the full performance of the alkali fusion reaction.

[0033] S20: ultrasonic water washing the first powder to obtain a second powder.

[0034] In this step, the first powder with a temperature lower than 100°C is ultrasonic water washed to remove the sulfides easily soluble in water in the first powder. Specifically, it includes: mixing the first powder and water, and then sequentially performing ultrasonic water washing, filtering, and drying to obtain the second powder.

[0035] In some embodiments, the mass ratio of the first powder to water is 1:(3-5). Specifically, it can be 1:3, 1:4, 1:5, or any range between any two of them. Thus, it can ensure that the first powder is fully dispersed in water, thereby ensuring the efficiency of water washing to remove sulfides easily soluble in water under ultrasonic conditions. The water used here is deionized water.

[0036] In this step, the ultrasonic method is not limited. For example, the mixture of the first powder and deionized water can be placed in an ultrasonic device for processing. After starting the ultrasonic device, the core relies on the "ultrasonic cavitation effect" to enhance mass transfer. When ultrasonic waves of 20 kHz to 40 kHz propagate in water, micro-bubbles (cavitation bubbles) are periodically formed, and when the bubbles burst instantaneously, local high temperature (about 5000K), high pressure (about 50 MPa), and micro-jet (flow rate up to 100 m / s) are generated. This effect can break the liquid film boundary layer attached to the surface of the silicon carbide particles, destroy the adsorption force between Na2S and the second powder particles, and accelerate the diffusion of soluble sulfide into the water phase. The core physicochemical process of this step is the dissolution and ionization reaction of Na2S: Na2S + H2O → 2Na + + HS - + OH - ; HS - + H2O H2S + OH - The local microenvironment generated by ultrasonic cavitation promotes the forward movement of the ionization equilibrium and improves the dissolution rate.

[0037] In some embodiments, the temperature of the ultrasonic water washing is 25°C to 40°C (specifically, it can be 25°C, 30°C, 35°C, 40°C, etc.). The time of ultrasonic water washing is 15 to 20 min (specifically, it can be 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, etc.). Thus, the ultrasonic can be performed at room temperature, and the conditions are relatively mild. The ultrasonic time in the above range can sufficiently remove the water-soluble sulfide in the first powder.

[0038] In some embodiments, the drying temperature is 80°C to 100°C. For example, it can be 80°C, 90°C, 100°C, etc. The drying time is 1h to 2h. For example, it can be 1h, 1.5h, 2h, etc. In the above range, the water remaining in the powder can be completely removed to obtain a dry second powder.

[0039] In some embodiments, the vacuum degree of drying is -0.08MPa to 0.1MPa. Specifically, it can be -0.08MPa, -0.06MPa, -0.04MPa, -0.02MPa, 0.1MPa, etc. Thus, it helps to improve the drying efficiency; at the same time, it avoids the entry of external gas to affect the purity of the product. The principle of vacuum drying is to use the vacuum environment to reduce the boiling point of water, to quickly remove the free water and part of the bound water attached to the surface of the powder at a lower temperature, to avoid the agglomeration of the powder caused by high-temperature drying, and to prevent water from entering the subsequent step and mixing with hydrogen to form explosive gas.

[0040] In some embodiments, the specific operation of the filtration is not limited. For example, a filter can be used to filter at a filtration pressure of 0.3-0.5 MPa. The principle of filtration is to separate solid and liquid by pressure difference. Meanwhile, a filter cloth with a pore size of 5-10 pm is used. The filter cloth can trap silicon carbide particles (particle size ≥ 5 pm) in the second powder, while allowing the filtrate containing Na + , HS - and plasma to pass through. The filtrate containing sodium sulfide is collected in a special recovery tank for subsequent resource extraction of sodium sulfide, realizing the recycling of the filtrate.

[0041] S30: The second powder and the reducing agent are subjected to a second reaction, so that the insoluble sulfide in the second powder is reduced to obtain a third powder.

[0042] In this step, the strong reducing property of hydrogen or carbon monoxide is utilized, and hydrogen is preferably used to react with the insoluble sulfide (such as SiS2, which has high chemical stability and cannot be removed by the previous steps) remaining in the second powder under mild conditions. The reaction formula is: SiS2+2H2→Si+2H2S↑. This reaction is an exothermic reaction that can proceed spontaneously once it is started. Although the generated elemental Si is chemically stable, it is free on the surface of the silicon carbide particles, which affects the purity of the final powder and the subsequent sintering density, and needs to be removed in the subsequent steps. For example, the second reaction can be carried out in a tube furnace.

[0043] In some embodiments, the hydrogen flow rate can be controlled at 50 mL / min-100 mL / min. Specifically, it can be 50 mL / min, 60 mL / min, 70 mL / min, 80 mL / min, 90 mL / min, 100 mL / min, etc. In this way, both the sufficient reducing atmosphere and the waste of hydrogen can be avoided.

[0044] In some embodiments, the temperature of the second reaction is 300°C-400°C. Specifically, it can be 300°C, 320°C, 340°C, 360°C, 380°C, 400°C, etc. This temperature range can activate the Si-S bond to facilitate the above-mentioned reduction reaction. At the same time, the silicon carbide particles are avoided to be reduced (the reduction temperature of SiC needs to be ≥1200°C).

[0045] In some embodiments, the time of the second reaction is 5 min-10 min. Specifically, it can be 5 min, 10 min or any value between them. In this way, the insoluble sulfide remaining in the second powder can be fully converted to H2S.

[0046] In some embodiments, the temperature increasing rate of the second reaction is 10 ℃ / min~15 ℃ / min. Specifically, the temperature increasing rate of the second reaction can be 10 ℃ / min, 11 ℃ / min, 12 ℃ / min, 13 ℃ / min, 14 ℃ / min, 15 ℃ / min, etc. Thus, it is helpful for the second reaction to proceed stably and uniformly.

[0047] In some embodiments, the H2S generated in the second reaction can be absorbed using a sodium hydroxide solution with a mass fraction of 10%~15%. The tail gas treatment is achieved by using an acid-base neutralization reaction, and the reaction formula is: H2S+2NaOH→Na2S+2H2O (when H2S is in excess: H2S+NaOH→NaHS+H2O). The generated sodium sulfide can be recycled for industrial production, and the clean gas (SO2 concentration≤10 mg / m 3 ) after absorption is discharged after reaching the standard.

[0048] S40: The third powder and an oxidizing agent are subjected to a third reaction, so that the elemental silicon in the third powder is oxidized to obtain a fourth powder.

[0049] In this step, the elemental Si generated in the previous reduction reaction (second reaction) will affect the purity of the powder and the subsequent processing performance, so an oxidation-removal process needs to be matched synchronously in the reduction stage, i.e., the third powder and an oxidizing agent are subjected to a third reaction, so that the elemental silicon in the third powder is oxidized.

[0050] In some embodiments, the temperature of the third reaction is 300 ℃~350 ℃. Specifically, it can be 300 ℃, 310 ℃, 320 ℃, 330 ℃, 340 ℃, 350 ℃, etc. Within the above temperature range, the oxidation reaction rate of silicon is moderate, and local overheating and powder caking will not occur due to too fast reaction.

[0051] In some embodiments, the time of the third reaction is 5 min~8 min. Specifically, it can be 5 min, 6 min, 7 min, 8 min, etc. Thus, the sufficient oxidation of elemental silicon is ensured.

[0052] For example, after the second reaction is completed, a mixed gas of oxygen and nitrogen with a volume fraction of 5%~10% (total flow rate of 50 mL / min~80 mL / min) is introduced into the tube furnace, and the temperature is kept at 330 ℃ for 6 min. The elemental Si is oxidized to generate SiO2 (third reaction). The reaction formula is: Si+O2→SiO2.

[0053] S50: The fourth powder is subjected to ultrasonic water washing to obtain a silicon carbide powder.

[0054] In this step, the SiO2 generated in the third reaction can be removed by subsequent ultrasonic water washing. For example, deionized water and the fourth powder are mixed, and then ultrasonic water washing, filtration and drying are sequentially performed to obtain the silicon carbide powder.

[0055] At room temperature, SiO2 can slowly react with water to generate a small amount of silicic acid (SiO2+H2O H2SiO3), and the cavitation effect of ultrasonic water washing can achieve efficient removal of SiO2.

[0056] In some embodiments, the parameters of ultrasonic water washing, filtration and drying in S50 are consistent with those of ultrasonic water washing in S10, which aims to remove the SiO2 generated by oxidation and ensure that there is no residual impurity in the powder.

[0057] In some embodiments, after drying, the obtained silicon carbide powder is slowly cooled to room temperature. The silicon carbide powder is screened using a 100-mesh to 120-mesh screen to remove impurities. The core principle is to use the particle size classification effect of screening to remove a small amount of agglomerated particles (particle size ≥ 150 μm) that may be formed during the reaction, thereby ensuring uniform particle size of the finished product. The cooling principle is to avoid oxidation of the high-temperature fourth powder when it comes into contact with air (silicon carbide is stable at room temperature, and is easily oxidized to SiO2 at ≥800 ℃), and to prevent rapid cooling from causing internal stress in the particles.

[0058] In a second aspect of the present application, a silicon carbide powder is provided, which is obtained by the method for removing sulfur elements from a silicon carbide raw material described above. The silicon carbide powder has stable performance and low sulfur content.

[0059] In some embodiments, the content of sulfur elements in the silicon carbide powder is ≤5 ppm.

[0060] In a third aspect of the present application, a device for removing sulfur elements from a silicon carbide raw material is provided, which is described with reference to Figure 1 , and includes a mixer 1, a microwave reactor 2, an ultrasonic cleaning tank 3, a filter 4, a drying machine 5, a tube furnace 6, an alkali liquor absorption tower 7, and a screen 8. The mixer 1 is used to mix the silicon carbide raw material and the alkali flux to obtain a first mixture. The microwave reactor 2 is connected to the mixer 1 and is used to make the first mixture undergo a first reaction to obtain a first powder. The ultrasonic cleaning tank 3 is connected to the microwave reactor 2 and is used to perform ultrasonic water washing on the first powder to obtain a solid-liquid mixture of the first powder. The filter 4 is connected to the ultrasonic cleaning tank 3 and is used to perform solid-liquid separation on the solid-liquid mixture of the first powder to obtain a wet-state powder. The drying machine 5 is connected to the filter 4 and is used to dry the wet-state powder to obtain a second powder. The tube furnace 6 is connected to the drying machine 5 and is used to provide a place for the oxidation-reduction reaction. The alkali liquor absorption tower 7 is connected to the tube furnace 6 and is used to absorb the gas (H2S) in the tube furnace. The screen 8 is connected to the tube furnace 5 and is used to screen the powder.

[0061] The method for removing sulfur elements in silicon carbide raw materials in the present application has at least the following beneficial effects: 1. High desulfurization efficiency: microwave alkali fusion efficiently converts insoluble sulfides, ultrasonic water washing strengthens the removal of soluble sulfides, and low-temperature reduction deeply removes residual sulfur. The three work together to make the desulfurization rate reach more than 98%, and the sulfur content of the treated powder can be reduced to less than 5 ppm, which is much better than the traditional alkali fusion method (82%-85%) and acid leaching method (75%-80%); 2. Low energy consumption and cost: Microwave heating reduces the alkali fusion temperature to 450-550°C, which is more than 50% lower than the traditional alkali fusion method (about 1200°C), and the total energy consumption is reduced by 40%-50%. The use of industrial-grade sodium carbonate and hydrogen reduces the raw material cost by 60% compared with special desulfurizing agents; 3. Green and environmentally friendly: The ultrasonic water washing filtrate can be recycled as sodium sulfide, and the low-temperature reduction tail gas can be discharged after being absorbed by lye, without generating a large amount of harmful waste water and waste gas, meeting environmental protection requirements; 4. Stable powder performance: Mild reaction conditions avoid sintering and agglomeration of silicon carbide particles, and the crystal structure is complete, with a particle agglomeration rate of less than 2%; 5. Strong adaptability to industrialization: The equipment used is conventional industrial equipment, with low investment cost and simple operation steps, and can realize continuous production, suitable for different scale enterprises.

[0062] The present application will be described below with reference to specific examples. It should be noted that these examples are merely descriptive and do not limit the present application in any way. If the specific techniques or conditions are not specified in the examples, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions.

[0063] Example 1 Raw materials: 1000 g of industrial-grade silicon carbide raw material with a sulfur content of 85 ppm and a particle size of 10 μm; Microwave alkali fusion: The silicon carbide raw material and 800 g of sodium carbonate (150 mesh) were added to a double-helix mixer and mixed at 350 rpm for 8 min, then sent to a microwave reactor, with a microwave power of 1000 W, a microwave frequency of 1000 MHz, and a temperature rise to 500°C for 25 min; Ultrasonic water washing: After cooling, the material was added to 4000 g of deionized water, ultrasonically treated at 30 kHz for 20 min, and filtered at 30°C using a plate and frame filter (pressure 0.4 MPa) to collect the powder; Low-temperature reduction: The powder was dried in a vacuum at 90°C for 1.5 h, then sent to a tube furnace, with a hydrogen flow rate of 80 mL / min, and a temperature rise to 350°C for 18 min; Desiliconization: After the reduction reaction, the temperature of the tube furnace was kept at 350 ℃, the hydrogen valve was closed, and the vacuum pump was turned on to remove the residual H2S gas by pumping the furnace to a vacuum of -0.05 MPa; then the vacuum pump was turned off, and oxygen-nitrogen mixed gas (oxygen volume fraction 8%, nitrogen volume fraction 92%, total flow rate 60 mL / min) was introduced for 7 min; Post-treatment: After reduction, the powder was first cooled by nitrogen blowing, then 3000 g of deionized water was added for ultrasonic treatment at 20 kHz for 10 min, filtered by a plate frame, vacuum dried at 90 ℃ for 1 h, and finally sieved through a 100 mesh sieve.

[0064] Results: The sulfur content in the obtained silicon carbide powder was 1.2 ppm, the desulfurization rate was 98.6%, the concentration of recovered sodium sulfide solution reached 7.2%, and the particle morphology was complete without agglomeration.

[0065] Example 2 Raw materials: 2000 g of silicon carbide powder with a sulfur content of 120 ppm and a particle size of 40 μm; Microwave alkali fusion: The silicon carbide raw material and 2400 g of sodium carbonate (150 mesh) were added to a double helix mixer and mixed at 400 rpm for 10 min, then introduced into a microwave reactor, with a microwave power of 1200 W, a microwave frequency of 2000 MHz, and a temperature of 550 ℃ for 30 min; Ultrasonic water washing: 10000 g of deionized water was added, and ultrasonic treatment was carried out at 40 kHz for 18 min, then filtered at 40 ℃ using a plate frame filter (pressure 0.4 MPa) to collect the powder; Low-temperature reduction: The powder was vacuum dried at 100 ℃ for 1 h, then introduced into a tube furnace, with a hydrogen flow rate of 100 mL / min, and heated to 400 ℃ for 20 min; Desiliconization: After the reduction reaction, the temperature of the tube furnace was kept at 350 ℃, the hydrogen valve was closed, and the vacuum pump was turned on to remove the residual H2S gas by pumping the furnace to a vacuum of -0.05 MPa; then the vacuum pump was turned off, and oxygen-nitrogen mixed gas (oxygen volume fraction 8%, nitrogen volume fraction 92%, total flow rate 60 mL / min) was introduced for 7 min; Desiliconization: After the reduction reaction, the temperature of the tube furnace was kept at 350 ℃, the hydrogen valve was closed, and the vacuum pump was turned on to remove the residual H2S gas by pumping the furnace to a vacuum of -0.05 MPa; then the vacuum pump was turned off, and oxygen-nitrogen mixed gas (oxygen volume fraction 8%, nitrogen volume fraction 92%, total flow rate 60 mL / min) was introduced for 7 min;

[0066] Post-treatment: After reduction, the powder was first cooled by nitrogen blowing, then 3000 g of deionized water was added for ultrasonic treatment at 20 kHz for 10 min, filtered by a plate frame, vacuum dried at 90 ℃ for 1 h, and finally sieved through a 100 mesh sieve.

[0067] Results: The sulfur content in the obtained silicon carbide powder was 2.5 ppm, the desulfurization rate was 97.9%, the concentration of the recovered sodium sulfide solution reached 8%, which could be directly used for industrial production, the particle morphology was complete, and there was no agglomeration phenomenon.

[0068] Comparative Example 1 (traditional alkali fusion method) The raw material of Example 1 was subjected to a sodium carbonate alkali fusion method (1200°C, alkali material ratio 1:1, holding for 3 hours), followed by water washing and drying.

[0069] Results: The desulfurization rate was 83.5%, the sulfur content after treatment was 14.1 ppm, the unit energy consumption was 2.6 times that of Example 1, and 8 L / kg of alkaline wastewater was produced.

[0070] Comparative Example 2 (acid leaching method) The raw material of Example 1 was subjected to 10% hydrochloric acid solution leaching (liquid-solid ratio 5:1, stirring at 80°C for 2 hours). Results: The desulfurization rate was 78.2%, the sulfur content after treatment was 18.5 ppm, 9.5 L / kg of acidic wastewater was produced, and neutralization treatment was required.

[0071] Detection method Sulfur content: high-frequency induction furnace combustion-infrared absorption method, the sample was heated and combusted in an oxygen atmosphere, the sulfur element was converted into SO2 gas, the characteristic absorption peak intensity of SO2 was measured by an infrared detector, and the standard curve was compared for quantitative determination. Sulfur content (ppm) = (detection signal value x calibration coefficient) / sample mass (g), and the average value was taken for 3 parallel tests.

[0072] Agglomeration rate: a certain amount of dried silicon carbide powder was weighed and placed in a standard test sieve; the standard test sieve was placed on a vibrating sieve shaker for vibration screening; the residual particles on the sieve were collected, dried to constant weight, and then weighed. Agglomeration rate = (agglomerate mass / total sample mass) x 100%, and the average value was taken for 2 parallel tests.

[0073] Detection results The specific results of Examples 1-2 and Comparative Examples 1-2 are shown in Table 1.

[0074] Table 1

[0075] Conclusion: It can be seen that the desulfurization method in the present application has significant advantages over the traditional alkali fusion method and acid leaching method, with a desulfurization rate of 97.9%-98.6%, a sulfur content of the treated powder of only 1.2-2.5 ppm, and a particle agglomeration rate of ≤1.5%; the unit energy consumption is as low as 4.2-4.8 kW The h / kg is reduced by more than 50% compared with the traditional alkali fusion method, and the wastewater production is only 0.5-0.6 L / kg (recoverable), without a large amount of harmful wastewater discharge, and has multiple advantages of high efficiency, energy saving, environmental protection and stable powder performance, and stronger industrial applicability.

[0076] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms is not necessarily directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. Furthermore, different embodiments or examples described in the present specification and the features of different embodiments or examples can be combined and modified by those skilled in the art without contradiction within the scope of the present application.

[0077] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

Claims

1. A method for removing sulfur from silicon carbide raw materials, characterized in that, include: The silicon carbide raw material and the alkali flux undergo a first reaction in a microwave field to obtain the first powder. The first powder is subjected to ultrasonic water washing to obtain the second powder; The second powder and the reducing agent undergo a second reaction, reducing the insoluble sulfides in the second powder to obtain the third powder. The third powder and the oxidant undergo a third reaction, causing the elemental silicon in the third powder to be oxidized, resulting in a fourth powder. The fourth powder is subjected to ultrasonic water washing to obtain silicon carbide powder.

2. The method according to claim 1, characterized in that, The process of causing the silicon carbide raw material and the alkaline flux to undergo a first reaction in a microwave field includes: The silicon carbide raw material and the alkali flux are first mixed to obtain a first mixture; The first mixture is subjected to the first reaction in a microwave field.

3. The method according to claim 2, characterized in that, At least one of the following conditions must be met: The alkaline flux includes at least one of sodium carbonate and potassium carbonate, preferably sodium carbonate; The rotation speed of the first mixing is 300 rpm to 400 rpm; The first mixing time is 5 min to 10 min; The microwave frequency is 24MHz~2500MHz; The microwave power is 800W~1200W.

4. The method according to claim 1, characterized in that, At least one of the following conditions must be met: The particle size of the alkali flux is 100 mesh to 200 mesh; The particle size of the silicon carbide raw material is 5 micrometers to 50 micrometers; The temperature of the first reaction is 450℃~550℃; The first reaction takes 20 to 30 minutes; The heating rate of the first reaction is 15 °C / min to 25 °C / min; The mass ratio of silicon carbide raw material to alkali flux is 1:(0.8~1.2).

5. The method according to claim 1, characterized in that, The ultrasonic water washing of the first powder includes: mixing the first powder with water, and then sequentially performing ultrasonic water washing, filtration, and drying to obtain the second powder.

6. The method according to claim 5, characterized in that, At least one of the following conditions must be met: The mass ratio of the first powder to the water is 1:(3~5); The temperature of the ultrasonic water washing is 25℃~40℃; The ultrasonic water washing time is 15 min to 20 min; The drying temperature is 80℃~100℃; The drying time is 1 hour to 2 hours; The vacuum degree of the drying process is -0.08MPa to 0.1MPa.

7. The method according to claim 1, characterized in that, At least one of the following conditions must be met: The reducing agent includes at least one of hydrogen and carbon monoxide; The oxidant comprises a mixture of oxygen and nitrogen. The temperature of the second reaction is 300℃~400℃; The second reaction takes 5 to 10 minutes; The heating rate for the second reaction is 10 °C / min to 15 °C / min; The temperature of the third reaction is 300℃~350℃; The time for the third reaction is 5 to 8 minutes.

8. A silicon carbide powder, characterized in that, It is prepared by the method described in any one of claims 1 to 7.

9. The silicon carbide powder according to claim 8, characterized in that, The sulfur content in the silicon carbide powder is ≤5ppm.

10. An apparatus for removing sulfur from silicon carbide raw materials, characterized in that, include: A mixer is used to mix silicon carbide raw materials and alkaline flux to obtain a first mixture; A microwave reactor, connected to the mixer, is used to cause the first mixture to undergo a first reaction to obtain a first powder. An ultrasonic cleaning tank, connected to the microwave reactor, is used to ultrasonically wash the first powder to obtain a solid-liquid mixture of the first powder. A filter, connected to the ultrasonic cleaning tank, is used to separate the solid and liquid mixture of the first powder to obtain wet powder. A dryer, connected to the filter, is used to dry the wet powder to obtain a second powder. A tubular furnace, connected to the dryer, is used to provide a site for redox reactions; An alkali absorption tower, connected to the tubular furnace, is used to absorb the gas in the tubular furnace; A sieve, connected to the tubular furnace, is used to sieve powder materials.

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