Silicon carbide micropowder and method for producing the same

Abstract

This invention discloses a silicon carbide micropowder and its preparation method, relating to the field of semiconductor technology. The preparation method includes reacting elemental silicon and elemental carbon in a vacuum environment to obtain a first silicon carbide powder; processing the first silicon carbide powder into a second silicon carbide powder with a D50 of 0.5mm-2.5mm; and cleaning the second silicon carbide powder to obtain silicon carbide micropowder; wherein the cleaning includes electrochemical cleaning using a magnetic field synergistic with a pulsed field. No fluoride or chloride ions are introduced during the cleaning process, and no volatile acids are generated in the neutral electrolyte; metallic impurities (such as Fe and Cr) are enriched by cathode deposition with a recovery rate ≥95%, resulting in near-zero heavy metal emissions; ozone is continuously added through a closed-loop system, and unreacted ozone is converted into O2 by a catalyst and discharged, effectively controlling waste gas generation; the wastewater after cleaning treatment can meet the GB 8978-2002 Class I emission standard after simple neutralization, and is expected to be widely applied.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and more specifically, to a silicon carbide micropowder and its preparation method. Background Technology

[0002] The preparation process of silicon carbide materials typically includes cleaning the resulting silicon carbide material. Conventional cleaning involves acid pickling to remove surface impurities and residual contaminants. While acid pickling effectively cleans the silicon carbide surface, it also leads to significant raw material loss and the accumulation of metallic impurities. These problems not only increase the production cost of silicon carbide materials but also result in substantial losses of raw materials due to corrosion. The introduced metallic ion impurities affect the electrical properties of the material and device yield. Furthermore, it generates wastewater, waste gas, and waste residue containing harmful substances, placing enormous pressure on subsequent environmental treatment and significantly increasing overall manufacturing costs, thus limiting its application in a wider range of fields.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide silicon carbide micro powder and its preparation method to solve the above-mentioned technical problems.

[0005] This invention is implemented as follows:

[0006] In a first aspect, embodiments of the present invention provide a method for preparing silicon carbide micro powder, comprising the following steps:

[0007] Silicon and carbon were reacted in a vacuum environment in a certain proportion to obtain the first silicon carbide powder.

[0008] The first silicon carbide powder is made into a second silicon carbide powder with a D50 of 0.5mm-2.5mm, and the second silicon carbide powder is cleaned to obtain silicon carbide micro powder; wherein, the cleaning includes electrochemical cleaning with magnetic field synergistic pulse field.

[0009] In an optional embodiment, the rotational speed of the magnetic field is 300 rpm-1200 rpm, and the magnetic field strength is 0.1T-1T; the silicon carbide micropowder moves in a spiral motion with a radius of 0.5mm-2mm under the drive of the magnetic field, during which eddy currents with an intensity of 10 are formed. 4 s -1 -10 6 s -1 vortex field;

[0010] And / or, the frequency of the pulse field is 10Hz-100Hz, the duty cycle is 30%-70%, and the peak voltage is 15V.

[0011] In an alternative embodiment, the magnetic field includes a ring-shaped permanent magnet array connected to alternating current, the ring-shaped permanent magnet array including alternating N-pole and S-pole, and coils surrounding the N-pole and S-pole.

[0012] In an optional implementation, the rotational speed of the magnetic field is 500 rpm-700 rpm, and the magnetic field strength is 0.2T-0.5T;

[0013] And / or, the frequency of the pulse field is 30Hz-80Hz, and the duty cycle is 30%-50%.

[0014] In an optional embodiment, the time for a single cleaning cycle is 10-18 minutes, and the concentration of silicon carbide micropowder is ≤1 kg / m³. 3 Electrolyte.

[0015] In an optional embodiment, during the cleaning process, an oxidant is continuously added to most of the electrolytes; wherein the electrolytes include a carbonate solution with a concentration of 0.08 mol / L to 0.2 mol / L, and the oxidant includes ozone with a concentration of 5 ppm to 50 ppm.

[0016] In an optional embodiment, the total fluoride content in the wastewater after cleaning is 0 mg / L, the total heavy metal content is <0.1 mg / L, the COD value is ≤80 mg / L, and the pH value of the wastewater is 6-8.

[0017] And / or, in the cleaned solid waste, the organic filter residue is 0 kg / kg solid waste, the heavy metal sludge is <0.001 kg / kg solid waste, the loss rate of silicon carbide powder is <0.1%, and the recovery rate of cathode enriched metal is ≥95%;

[0018] And / or, no acid washing gas was detected in the cleaned exhaust gas, and the ozone residue was <0.05 ppm;

[0019] And / or, after cleaning, the process also includes post-treatment of silicon carbide micro powder, which includes washing the silicon carbide micro powder with water 2-3 times and then drying it at a temperature of 115℃-125℃.

[0020] In an optional embodiment, the silicon carbide micro powder contains ≤10ppm of metallic impurities and ≤0.06wt% of free carbon; wherein the metallic impurities include Fe, Al and Cr.

[0021] In an optional embodiment, the molar ratio of silicon to carbon is (1.05-1.1):1, the vacuum degree is 30 mbar to 100 mbar, and the temperature for preparing the first silicon carbide powder is 1800℃-2400℃, and the time is 5h-30h.

[0022] Secondly, embodiments of the present invention provide a silicon carbide micro powder, which is prepared by the preparation method described above.

[0023] The present invention has the following beneficial effects:

[0024] The method for preparing silicon carbide micropowder provided in this invention does not introduce fluoride or chloride ions during the cleaning process, and the neutral electrolyte does not generate volatile acids; the cathode deposits and enriches metallic impurities (such as Fe and Cr) with a recovery rate of ≥95%, resulting in near-zero emissions of heavy metals; ozone is continuously added through a closed-loop system, and unreacted ozone is converted into O2 by a catalyst and discharged, effectively controlling the amount of waste gas generated; the wastewater after the cleaning process can meet the GB 8978-2002 Class I emission standard after simple neutralization, and is expected to be widely applied. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the cleaning equipment.

[0027] Explanation of main component symbols: 1-positive electrode; 2-negative electrode; 3-material placement component; 4-cleaning equipment; 5-electrolyte; 6-ring permanent magnet array; 7-first magnetic pole; 8-second magnetic pole. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0029] In the preparation of silicon carbide micro powder, the common acid washing methods have many shortcomings. The main types of pollutants, their sources and corresponding hazards are summarized in Table 1.

[0030] Table 1 Common types of pickling contaminants and their hazards

[0031]

[0032] The silicon carbide micropowder and its preparation scheme provided by this invention involve a cleaning process. This process focuses on the cleaning reagents and methods, employing electrochemical cleaning combined with magnetic and electric field mechanisms, without adding any acidic substances. Throughout the system, the rotating magnetic field continuously updates the reaction interface on the surface of the silicon carbide micropowder, avoiding the passivation failure of traditional electrochemical methods. This facilitates a balance between impurity removal and the integrity of the silicon carbide micropowder, effectively reducing the content of metallic impurities and free carbon in the powder. The entire preparation process is simplified, safe, and easy to implement, and is expected to be widely applied. The specific implementation process is as follows:

[0033] In a first aspect, embodiments of the present invention provide a method for preparing silicon carbide micro powder, comprising the following steps:

[0034] Silicon and carbon were reacted in a vacuum environment in a certain proportion to obtain the first silicon carbide powder.

[0035] The first silicon carbide powder is made into a second silicon carbide powder with a D50 of 0.5mm-2.5mm, and the second silicon carbide powder is cleaned to obtain silicon carbide micro powder; wherein, the cleaning includes electrochemical cleaning with magnetic field synergistic pulse field.

[0036] It should be noted that the cleaning system is free of fluorine / chlorine ions: the cleaning includes electrochemical cleaning with magnetic field synergistic pulse field, wherein electrolyte 5 is a carbonate solution, and ozone system is continuously added, with no halogen introduced; heavy metal emissions are near zero, metal ions migrate directionally to the cathode for deposition and recovery under the electric field, the cathode deposition enriches metal impurities, and the recovery rate is ≥95%; the wastewater after cleaning can meet the GB 8978-2002 Class I discharge standard after simple neutralization.

[0037] It should be noted that this invention does not impose particular limitations on the preparation method and equipment for second silicon carbide powder with a D50 of 0.5mm-2.5mm, and appropriate selections can be made according to actual needs, such as ball mills, vibratory mills, and air jet mills.

[0038] This invention involves preparing a first silicon carbide powder into a second silicon carbide powder with a D50 of 0.5mm-2.5mm, followed by cleaning. This process has the following advantages: the smaller silicon carbide particles have a larger surface area, allowing for efficient removal of incompletely reacted silicon, residual carbon, dust, and organic impurities introduced during preparation, thus improving the purity of the resulting silicon carbide micropowder. Furthermore, the preparation of small-particle, cleaned silicon carbide micropowder is beneficial for downstream applications, ensuring optimal mechanical, thermal, and electrical properties in applications such as composite materials and semiconductor devices.

[0039] In an optional embodiment, silicon carbide micropowder forms eddy currents with an intensity of 10 under a rotating magnetic field with an intensity of 0.1T-1T. 4s -1 -10 6 s -1 The eddy current field; furthermore, the magnetic field strength is 0.2T-0.5T.

[0040] It should be noted that the rotating magnetic field includes a ring-shaped permanent magnet array connected to alternating current. The ring-shaped permanent magnet array includes alternating N poles (denoted as the first magnetic pole 7 or the second magnetic pole 8) and S poles (denoted as the second magnetic pole 8 or the first magnetic pole 7), as well as coils surrounding the N poles and S poles.

[0041] The rotating magnetic field causes the charged second silicon carbide powder to move in a spiral motion in the electrolyte 5, powered by a servo motor. During this process, the radius of the spiral motion trajectory R = 0.5mm-2mm, and the collision frequency between the second silicon carbide powder particles increases by 3 times, which is beneficial for efficiently breaking the impurity adsorption layer. Under the induction of the alternating magnetic field, a micro eddy current field is formed on the surface of the second silicon carbide powder, which helps to prevent particle agglomeration and achieve 100% single particle cleaning.

[0042] In an optional embodiment, the magnetic field is provided by a neodymium iron boron magnet with a single pole strength of 0.5T. In other embodiments of the invention, reasonable selections and substitutions can be made as needed.

[0043] And / or, the frequency of the pulse field is 10Hz-100Hz, the duty cycle is 30%-70%, and the peak voltage is 15V.

[0044] The pulsed electric field generates a periodic oxidation / reduction reaction on the surface of the second silicon carbide powder, Fe 3+ Preferential dissolution of metal ions; alternating magnetic field induces the formation of micro-eddy current field (eddy current intensity > 10) on the surface of silicon carbide micro powder. 4 s -1 This prevents particle aggregation, achieving 100% single-particle cleaning and significantly improving cleaning efficiency.

[0045] The present invention does not impose any particular limitation on the electrodes that provide the electric field. Specifically, in the embodiments of the present invention, the electrodes in the electric field include an anode with a titanium alloy mesh structure and a cathode made of stainless steel; in other embodiments, reasonable selection can be made according to actual needs.

[0046] In an optional embodiment, during the cleaning process, the electrode is placed in a mixture of silicon carbide micro powder and electrolyte 5, the mixture is placed inside the cleaning device 4, and the magnetic field is placed outside the cleaning device 4.

[0047] In an optional embodiment, the cleaning device 4 includes a material placement component 3 with an aperture (not shown) of 0.2mm-0.4mm; the rotating magnetic field is provided by a ring-shaped permanent magnet array 6 connected to alternating current, the ring-shaped permanent magnet array 6 including alternating N poles (denoted as first magnetic pole 7) and S poles (denoted as second magnetic pole 8), and coils surrounding the N poles and S poles. A schematic diagram of the cleaning device 4 is shown below. Figure 1 For ease of understanding, the electrodes providing the pulsed electric field (positive electrode 1, negative electrode 2), the ring-shaped permanent magnet array 6 providing the magnetic field, and the material holder 3 containing silicon carbide powder are located at different vertical heights. It should be noted that during the cleaning process, the electric field, magnetic field, and material holder 3 are located at the same vertical height.

[0048] In other embodiments of the present invention, the shape and specifications of the material placement component 3, the cleaning device 4, and the annular permanent magnet array 6 can be reasonably adjusted according to actual needs.

[0049] The placement component 3 facilitates the loading and unloading of silicon carbide powder into the cleaning equipment 4, as well as subsequent post-processing operations. It also prevents the formation of a high-intensity eddy current field within the cleaning equipment 4, thus avoiding increased powder loss. In this embodiment, the placement component 3 is made of titanium alloy, but other materials can be selected based on actual needs.

[0050] It should be noted that the present invention does not impose a specific limit on the number of titanium alloy feeding components 3, which can be reasonably adjusted according to the actual amount of silicon carbide micro powder being processed. The aperture of the titanium alloy feeding component 3 is slightly smaller than the D50 size of the second silicon carbide powder to avoid too much second silicon carbide powder entering the cleaning equipment 4 during the cleaning process, thereby increasing the subsequent processing steps and cost.

[0051] In an optional embodiment, the silicon carbide micro powder undergoes a spiral motion with a radius of 0.5 mm to 2 mm under the drive of a rotating magnetic field, wherein the rotational speed of the magnetic field is 300 rpm to 1200 rpm.

[0052] Furthermore, the rotational speed of the magnetic field is 500 rpm-700 rpm.

[0053] When the rotation speed of the magnetic field is less than 300 rpm, the Lorentz force is insufficient to overcome Brownian motion, resulting in chaotic movement trajectory of silicon carbide micropowder and low cleaning efficiency. When the rotation speed of the magnetic field is greater than 1000 rpm, the speed reaches the limit speed, and its shear force exceeds the tensile strength of SiC (≈500 MPa), causing particle breakage and increasing the loss rate of silicon carbide micropowder.

[0054] In an optional implementation, the optimal rotational speed of the magnetic field is 600 rpm, at which point the centrifugal acceleration α = ω 2 r≈100m / s 2This allows the relative velocity of the mixed system consisting of the second silicon carbide powder and electrolyte 5 to reach 100 mm / s, reducing the boundary layer thickness to 1 μm and significantly decreasing the free carbon content. In other embodiments, the concentration of the silicon carbide powder being processed can be reasonably adjusted.

[0055] And / or, the frequency of the pulse field is 30Hz-80Hz, and the duty cycle is 30%-50%.

[0056] If the frequency of the pulse field is in the low-frequency region (10 Hz-30 Hz), the electric field period is long, the ion migration is sufficient but the reaction rate is low, and the magnetic field is required to enhance mass transfer. If the frequency of the pulse field is in the high-frequency region (>80 Hz), the double layer is not fully charged and discharged, the effective voltage decreases, and the eddy current thermal effect intensifies, and the temperature of the mixed system increases.

[0057] In an optional implementation, the optimal frequency of the pulse field is 50 Hz: at this frequency, the pulse period matches the ion relaxation time, and unsteady diffusion enhancement is achieved under the drive of the magnetic field, resulting in a significant reduction in the content of metal impurities and a significant improvement in the metal extraction efficiency.

[0058] If the pulse field has a low duty cycle (<30%), the short energizing time suppresses the oxygen evolution side reaction, but insufficient reduction cycle easily leads to Fe... 2+ Re-adsorption results in a high content of metal impurities. If the pulse field has a high duty cycle (>70%), continuous anodizing leads to passivation of the silicon carbide micropowder surface, and the adhesion of hydrogen bubbles causes agglomeration, resulting in an increased loss rate of silicon carbide micropowder.

[0059] In an optional implementation, the duty cycle of the pulsed field is 50%, at which point the oxidation / reduction half-cycle is balanced, satisfying the reactions of the cathode and anode, and maintaining the pH stability of the mixed system during the cleaning process: wherein the anode reaction is Fe→Fe 2+ +2e - The cathode reaction is 2H₂O + 2e⁻ - →H2+2OH - In other embodiments, the concentration of the silicon carbide powder being processed can be adjusted accordingly.

[0060] In an optional embodiment, the time for a single cleaning cycle is 10-18 minutes, and the concentration of silicon carbide micropowder is ≤1 kg / m³. 3 Electrolyte 5.

[0061] It should be noted that the cleaning process of the present invention mainly includes three stages: the first cleaning process lasts from 0 min to 8 min, during which the electrochemical dissolution of metal ions mainly occurs, and the removal rate of metal impurities is 65% / min-75% / min; the second cleaning process lasts from 8 min to 15 min, during which free carbon ozone oxidation and in-situ oxidation of carbon by active oxygen free radicals (·OH) mainly occur, and the decarbonization rate is 0.01wt% / min-0.03wt% / min; the third cleaning process lasts from >15 min, during which SiC bulk oxidation and mechanical wear mainly occur, the harmful effects are dominant, the loss rate of silicon carbide micro powder increases, and this stage is not conducive to cleaning.

[0062] In an optional implementation, the optimal time for a single cleaning cycle is 15 minutes; in other implementations, the time can be adjusted reasonably according to the concentration of the silicon carbide powder being processed.

[0063] In an optional embodiment, during the cleaning process, an oxidant is continuously added to the electrolyte 5; wherein the electrolyte 5 comprises a carbonate solution with a concentration of 0.08 mol / L to 0.2 mol / L, and the oxidant comprises ozone with a concentration of 5 ppm to 50 ppm.

[0064] This invention does not impose any particular limitation on the type of carbonate, which can be reasonably selected according to actual needs, such as sodium carbonate, potassium carbonate, etc. For example, the concentration of the carbonate solution can be selected from any one of 0.08 mol / L, 0.1 mol / L, 0.12 mol / L, 0.15 mol / L, 0.18 mol / L, and 0.2 mol / L, or other values ​​within the range of 0.08 mol / L to 0.2 mol / L; the amount of ozone used can be selected from any one of 5 ppm, 15 ppm, 20 ppm, 25 ppm, 30 ppm, and 50 ppm, or other values ​​within the range of 5 ppm to 50 ppm.

[0065] The electrochemical cleaning setup enables in-situ oxidation and carbon removal during electrolysis. Specifically, the generated reactive oxygen free radicals (·OH) oxidize free carbon on the surface: C + 4·OH → CO2 + 2H2O. Since electrolyte 5 is neutral and no acidic substances are added, no acid mist is generated during the cleaning process.

[0066] The continuous addition of ozone is beneficial for decomposing the silica gel layer: SiO2·nH2O+O3→H4SiO4+O2.

[0067] In the embodiments of the present invention, the system providing ozone is a closed-loop system, wherein undecomposed O3 is converted into O2 and emitted through a catalytic bed (MnO2 / Al2O3). Therefore, in the detection of the exhaust gas after cleaning, the residual ozone is <0.05 ppm.

[0068] In an optional embodiment, the total fluoride content in the wastewater after cleaning is 0 mg / L, the total heavy metal content is <0.1 mg / L, the COD value is ≤80 mg / L, and the pH value of the wastewater is 6-8.

[0069] And / or, in the cleaned solid waste, the organic filter residue is 0 kg / kg solid waste, the heavy metal sludge is <0.001 kg / kg solid waste, the loss rate of silicon carbide powder is <0.1%, and the recovery rate of cathode enriched metal is ≥95%;

[0070] And / or, no acid washing gas was detected in the cleaned exhaust gas, and the ozone residue was <0.05 ppm;

[0071] And / or, after cleaning, the process also includes post-treatment of silicon carbide micro powder, which includes washing the silicon carbide micro powder with water 2-3 times and then drying it at a temperature of 115℃-125℃.

[0072] It should be noted that the present invention does not impose any particular limitation on the number of times the silicon carbide micro powder is washed with water or on the drying time, which can be reasonably adjusted according to the actual amount of material being processed.

[0073] In an optional embodiment, the silicon carbide micro powder contains ≤10ppm of metallic impurities and ≤0.06wt% of free carbon; wherein the metallic impurities include Fe, Al and Cr.

[0074] In an optional embodiment, the molar ratio of silicon to carbon is (1.05-1.1):1, the vacuum degree is 30 mbar to 100 mbar, and the temperature for preparing the first silicon carbide powder is 1800℃-2400℃, and the time is 5h-30h.

[0075] Secondly, embodiments of the present invention provide a silicon carbide micro powder, which is prepared by the preparation method described above.

[0076] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0077] Example 1

[0078] This embodiment provides a silicon carbide micro powder, which is prepared by the following method:

[0079] (1) Preparation of silicon carbide powder

[0080] Silicon and carbon were reacted in a vacuum environment at a molar ratio of 1.05:1 to obtain the first silicon carbide powder; wherein the vacuum degree was 80 mbar; the temperature for preparing the first silicon carbide powder was 2000℃ and the time was 15 h; and the first silicon carbide powder was α-SiC.

[0081] (2) Cleaning treatment

[0082] The first silicon carbide powder obtained in step (1) was ground into a second silicon carbide powder with a D50 of 1.0 mm using a ball mill, and the second silicon carbide powder was then cleaned. The first silicon carbide powder had a mass of 1 kg and an Fe content of 45 ppm. The second silicon carbide powder was loaded into a 0.4 mm aperture holder 3 and placed in a cleaning device 4. The electrolyte 5 in the cleaning device 4 was 1 ml. 3 The electrode is placed inside the material placement part 3, and the magnetic field is placed radially outside the cleaning equipment 4, and at the same vertical height as the electrode.

[0083] The cleaning process includes electrochemical cleaning using a magnetic field combined with a pulsed field. The relevant substances and parameters are as follows:

[0084] Electrolyte 5 is 0.1 mol / L Na2CO3 electrolyte, with 20 ppm ozone continuously introduced during the process; the applied pulsed electric field has a pulse frequency of 50 Hz, a peak voltage of 15 V, a duty cycle of 50%, and an alternating current; the anode is a titanium alloy mesh structure, and the cathode is made of stainless steel; eddy currents with an intensity of 10 are formed during the process. 5 s -1 The eddy current field was formed; the magnetic field strength was 0.3T and the rotation speed was 600rpm; the cleaning cycle was 15min.

[0085] (3) Post-processing

[0086] After the second silicon carbide powder was electrochemically cleaned in step (2), it was washed twice with deionized water and then dried in a vacuum drying oven at 120°C for 1.2 hours to obtain silicon carbide micro powder.

[0087] Example 2

[0088] This embodiment provides a silicon carbide micro powder, the preparation method of which is the same as that in the embodiment, the only difference being:

[0089] (2) Cleaning treatment

[0090] The pulse frequency of the applied pulsed electric field is 30 Hz.

[0091] Example 3

[0092] This embodiment provides a silicon carbide micro powder, the preparation method of which is the same as that in the embodiment, the only difference being:

[0093] (2) Cleaning treatment

[0094] The pulse frequency of the applied pulsed electric field is 100 Hz.

[0095] Example 4

[0096] This embodiment provides a silicon carbide micro powder, the preparation method of which is the same as that in the embodiment, the only difference being:

[0097] (2) Cleaning treatment

[0098] The rotational speed at which the magnetic field is applied is 300 rpm.

[0099] Example 5

[0100] This embodiment provides a silicon carbide micro powder, the preparation method of which is the same as that in the embodiment, the only difference being:

[0101] (2) Cleaning treatment

[0102] The rotational speed at which the magnetic field is applied is 1200 rpm.

[0103] Example 6

[0104] This embodiment provides a silicon carbide micro powder, the preparation method of which is the same as that in the embodiment, the only difference being:

[0105] (2) Cleaning treatment

[0106] The first silicon carbide powder obtained in step (1) was ground into a second silicon carbide powder with a D50 of 1.5 mm by ball milling.

[0107] Example 7

[0108] This embodiment provides a silicon carbide micro powder, the preparation method of which is the same as that in the embodiment, the only difference being:

[0109] (2) Cleaning treatment

[0110] The concentration of silicon carbide micro powder is 1.2 kg / m³. 3 Electrolyte 5.

[0111] Example 8

[0112] This embodiment provides a silicon carbide micro powder, the preparation method of which is the same as that in the embodiment, the only difference being:

[0113] (2) Cleaning treatment

[0114] Ozone at 16 ppm was continuously introduced during the cleaning process.

[0115] Example 9

[0116] This embodiment provides a silicon carbide micro powder, the preparation method of which is the same as that in the embodiment, the only difference being:

[0117] (2) Cleaning treatment

[0118] The peak voltage of the applied pulsed electric field is 12V.

[0119] Example 10

[0120] This embodiment provides a silicon carbide micro powder, the preparation method of which is the same as that in the embodiment, the only difference being:

[0121] (2) Cleaning treatment

[0122] The magnetic field strength applied is 0.5T.

[0123] Comparative Example 1

[0124] This comparative example provides a silicon carbide micro powder, the preparation method of which is the same as that in the examples, the only difference being:

[0125] (2) Cleaning treatment

[0126] The applied current is direct current, and the voltage of the direct current electric field is 15V.

[0127] No magnetic field was applied.

[0128] Comparative Example 2

[0129] This comparative example provides a silicon carbide micro powder, which is prepared by the same method as in Example 1, except that the cleaning process includes the following steps:

[0130] First, pretreatment

[0131] Silicon carbide powder was ground to a D50 of 1.0 mm, washed several times with deionized water by stirring, and then filtered and dried. The stirring time was 20 minutes, the washing was performed twice, and the drying temperature was 100℃.

[0132] Second, acid leaching treatment

[0133] Acid preparation: The mixed acid system consists of 10% vol hydrofluoric acid (HF) and 18% vol hydrochloric acid (HCl).

[0134] Solid-liquid ratio: The mass ratio of silicon carbide powder to acid solution is 1:7. Ensure that the powder is completely submerged and that there is sufficient acid solution for the reaction.

[0135] To ensure a more thorough acid leaching process, heating and stirring were performed. The heating temperature was 80°C, the stirring speed was 300 rpm, and the acid leaching time was 15 hours.

[0136] Third, post-processing

[0137] The acid-leached silicon carbide powder was cooled to room temperature. It was then filtered using an acid-resistant vacuum filtration device, and the filter cake was repeatedly washed with a large amount of deionized water until the pH of the washing solution was close to neutral.

[0138] The washed filter cake was transferred to a corrosion-resistant oven for drying at 110°C for 8 hours to avoid particle agglomeration or oxidation caused by excessively high temperatures.

[0139] Comparative Example 3

[0140] This comparative example provides a silicon carbide micro powder, the preparation method of which is the same as that in Example 1, the only difference being:

[0141] (2) Cleaning treatment

[0142] The applied current is direct current.

[0143] Comparative Example 4

[0144] This comparative example provides a silicon carbide micro powder, the preparation method of which is the same as that in Example 1, the only difference being:

[0145] (2) Cleaning treatment

[0146] No magnetic field was applied.

[0147] Comparative Example 5

[0148] This comparative example provides a silicon carbide micro powder, the preparation method of which is the same as that in Example 1, the only difference being:

[0149] (2) Cleaning treatment

[0150] Ozone was not introduced during the cleaning process.

[0151] Comparative Example 6

[0152] This comparative example provides a silicon carbide micro powder, the preparation method of which is the same as that in Example 1, the only difference being:

[0153] (2) Cleaning treatment

[0154] The second silicon carbide powder is directly loaded into the cleaning equipment 4 for cleaning.

[0155] Experimental Example 1

[0156] This experiment was used to study the effect of cleaning time on the total amount of metal impurities and the free carbon content in the final silicon carbide micro powder. The relevant results are shown in Table 2.

[0157] The parameters in the preparation process were the same as in Example 1, with the only difference being the duration of the cleaning cycle. The methods for testing metallic impurities and free carbon were gas chromatography-mass spectrometry (GC-MS) and inductively coupled plasma mass spectrometry (ICP-MS).

[0158] Table 2 Cleaning Time and Corresponding Results

[0159]

[0160] As can be seen from the data in Table 2, after 15 minutes of cleaning, the content of metal impurities and free carbon both decreased to a low level and remained stable. Further increasing the cleaning time did not significantly reduce the content of metal impurities and free carbon. Therefore, considering cost and economic efficiency, 15 minutes of cleaning yielded the best results.

[0161] Test Example 1

[0162] This test example tested the silicon carbide micro powders prepared in Examples 1-5 and Comparative Examples 1-2 in the following ways: metal impurities, free carbon, silicon carbide micro powder loss rate and unit energy consumption. The phenomena observed during the preparation process were summarized, and the test results are shown in Table 3.

[0163] In the test items, the test methods for metal impurities and free carbon are the same as those in Experiment 1. The test method for silicon carbide micro-particle loss rate is to weigh and calculate the loss before and after cleaning. The test method for unit energy consumption is to multiply the power of the equipment operation by the equipment operation time.

[0164] Table 3 Test items and corresponding results and phenomena

[0165]

[0166] As shown in Table 3, the most effective cleaning method was to use 0.1 mol / L Na2CO3 electrolyte 5, with continuous introduction of 20 ppm ozone; the applied pulsed electric field had a pulse frequency of 50 Hz, a peak voltage of 15 V, a duty cycle of 50%, and an alternating current; the anode was a titanium alloy mesh structure, and the cathode was made of stainless steel; during this process, an eddy current intensity of 10 was formed. 5 s -1 The eddy current field was applied; the magnetic field strength was 0.3T, and the rotation speed was 600 rpm; the cleaning cycle lasted for 15 minutes. Reducing the pulse frequency (Example 2) resulted in more than twice the content of metal impurities and free carbon after cleaning compared to Example 1; similarly, increasing the pulse frequency (Example 3) was also detrimental to reducing the content of metal impurities and free carbon after cleaning. Decreasing the rotation speed of the magnetic field (Example 4) resulted in higher content of metal impurities and free carbon after cleaning compared to Example 1, and increased unit energy consumption; increasing the rotation speed of the magnetic field (Example 5) caused mechanical collision and breakage of the silicon carbide micropowder, resulting in smaller particle diameters and leakage from the basket, leading to decreased yield and increased unit energy consumption.

[0167] This test case also compares the performance of Example 1 and Comparative Example 2 and summarizes it in Table 4.

[0168] Table 4 Test Items and Performance Comparison

[0169]

[0170] As can be seen from the data in Table 4, the electrochemical cleaning method using magnetic field combined with pulsed field reduces the metal impurity content by about 10 times, the free carbon content by 5-10 times, the cleaning time by 4 times, and the powder loss rate by 5 times compared with the traditional acid washing method, and no acidic hazardous waste liquid is generated in the cleaning solution.

[0171] Test Example 2

[0172] This test case analyzes the wastewater composition in the preparation of silicon carbide micro powder in Example 1 and Comparative Example 2. The relevant information on total fluoride content, total heavy metal content, COD value and pH value is summarized in Table 5.

[0173] The test methods for total fluorine content and total heavy metal content are GC-MS, the test method for COD value is potassium dichromate method, and the test method for pH value is pH meter.

[0174] Table 5 Wastewater Composition Analysis

[0175]

[0176] As can be seen from the data in Table 5, the wastewater generated by this method has no fluoride discharge, and the total amount of heavy metals is <0.1mg / L, which is 99.8% lower than that of traditional pickling. The organic pollution content in the water body is reduced by 98.4% compared with traditional pickling. The wastewater is neutral and can be discharged directly without dilution or neutralization with a large amount of water.

[0177] Test Example 3

[0178] This test case analyzes the waste gas composition in the silicon carbide micro powder prepared in Example 1 and Comparative Example 2. The relevant information on pickling gas, volatile organic compounds and ozone residue is summarized in Table 6.

[0179] The test methods for pickling gases are ion chromatography, for volatile organic compounds are GC-MS, and for ozone residues are ultraviolet spectrophotometers.

[0180] Table 6. Analysis of waste gas composition

[0181]

[0182] As can be seen from the data in Table 6, this cleaning method does not introduce acid cleaning gases or volatile organic compounds.

[0183] Test Example 4

[0184] This test case analyzes the solid waste (i.e. waste residue) composition in the silicon carbide micro powder prepared in Example 1 and Comparative Example 2. The relevant information on heavy metal sludge, organic filter residue, and ineffective loss of silicon carbide micro powder is summarized in Table 7.

[0185] Among them, the test method for sludge containing heavy metals is ICP-MS, the test method for organic filter residue is GC-MS measurement after solvent extraction, and the test method for ineffective loss of silicon carbide micro powder is weighing after drying.

[0186] Table 7 Solid Waste Composition Analysis

[0187]

[0188] As can be seen from the data in Table 7, this cleaning method reduces the amount of heavy metal sludge and organic filter residue by more than 99% and reduces particulate loss by 80%.

[0189] In summary, the method for preparing silicon carbide micropowder provided in this embodiment of the invention introduces no fluoride or chloride ions during the cleaning process, and the neutral electrolyte 5 produces no volatile acids; the cathode deposits and enriches metallic impurities (such as Fe and Cr) with a recovery rate of ≥95%, resulting in near-zero emissions of heavy metals; ozone is continuously added through a closed-loop system, and unreacted ozone is converted into O2 by a catalyst and discharged, effectively controlling the amount of waste gas generated; the wastewater after the cleaning process can meet the GB 8978-2002 Class I emission standard after simple neutralization, and is expected to be widely applied.

[0190] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for producing silicon carbide micropowder, characterized by, The method comprises the following steps: proportionally reacting silicon and carbon in a vacuum environment to obtain a first silicon carbide powder; the first silicon carbide powder is made into a second silicon carbide powder with a D50 of 0.5mm-2.5mm, and the second silicon carbide powder is cleaned to obtain a silicon carbide micro powder; wherein the cleaning comprises electrochemical cleaning in cooperation with a magnetic field and a pulse field; during the electrochemical cleaning, an electrode is placed in a mixed system of the silicon carbide micro powder and an electrolyte; The silicon carbide micropowder forms an eddy current field with an eddy current intensity of 10 4 s -1 -10 6 s -1 in a rotating magnetic field with a strength of 0.1 T-1 T. the frequency of the pulse field is 10Hz-100Hz, the duty cycle is 30%-70%, and the peak voltage is 15V; during the cleaning, an oxidizing agent is continuously added to the electrolyte; wherein the electrolyte comprises a carbonate solution with a concentration of 0.08mol / L-0.2mol / L, and the oxidizing agent comprises 5ppm-50ppm of ozone.

2. The production method according to claim 1, characterized by, The silicon carbide micro powder makes spiral motion with a radius of 0.5mm-2mm under the driving of the rotating magnetic field, wherein the rotating speed of the magnetic field is 300rpm-1200rpm.

3. The production method according to claim 1 or 2, characterized by, The rotating speed of the magnetic field is 500rpm-700rpm, and the strength of the magnetic field is 0.2T-0.5T. And / or, the frequency of the pulse field is 30Hz-80Hz, and the duty cycle is 30%-50%.

4. The method of claim 1, wherein, The time of single washing is 10-18 min, the concentration of the silicon carbide micro powder is ≤1 kg / m 3 Electrolyte.

5. The preparation method according to claim 1, characterized in that, In the wastewater after cleaning, the total content of fluorides is 0mg / L, the total content of heavy metals is <0.1mg / L, the COD value is ≤80mg / L, and the pH value of the wastewater is 6-8; And / or, in the solid waste after cleaning, the organic filter residue is 0kg / kg of solid waste, the heavy metal sludge is <0.001kg / kg of solid waste, the loss rate of the silicon carbide powder is <0.1%, and the recovery rate of the cathode enriched metal is ≥95%; And / or, in the exhaust gas after cleaning, no pickling gas is detected, and the residual ozone is <0.05ppm; And / or, after the cleaning, the silicon carbide micro powder is further treated, which comprises cleaning the silicon carbide micro powder with water for 2-3 times and then drying at a temperature of 115℃-125℃.

6. The method of claim 1, wherein, In the silicon carbide micro powder, the content of metal impurities is ≤10ppm, and the content of free carbon is ≤0.06wt%; wherein the metal impurities include Fe, Al and Cr.

7. The preparation method according to claim 1, characterized in that, The molar ratio of the silicon to the carbon is (1.05-1.1):1, the vacuum degree is 30mbar to 100mbar, the temperature for preparing the first silicon carbide powder is 1800℃-2400℃, and the time is 5h-30h.

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