Preparation method of SiC

Abstract

The invention discloses a preparation method of SiC, which comprises the following steps: dispersing biomass in water, adding a modifier with oxidizability for modification to obtain acidic functional group modified biochar, uniformly dispersing the modified biochar, water glass and metal salt in water, transferring into a hydrothermal kettle, and carrying out hydrothermal reaction to obtain the SiC. The preparation method comprises the following steps: preparing a carbon-silicon precursor, filtering and drying the carbon-silicon precursor, carrying out a carbon thermal reduction reaction in an argon atmosphere to obtain a SiC crude product, carrying out high-temperature calcination on the obtained SiC crude product to remove unreacted carbon, soaking the obtained SiC crude product in an acid or alkali to remove unreacted impurities, washing, filtering, and drying to obtain a SiC finished product. According to the method, equipment is simple, irritant gas cannot be generated, and the SiC production method which is low in cost and green is provided.

Description

Technical Field

[0001] The present application relates to the technical field of SiC preparation, and in particular to a method for preparing SiC. Background Art

[0002] SiC (silicon carbide) is a covalent compound composed of carbon and silicon atoms with a diamond-like tetrahedral structure. It has high heat resistance, chemical stability and electronic properties, and is an important structural material and semiconductor material. Silicon carbide with a high specific surface area has more surface active sites, interacts more frequently with the surrounding environment, and exhibits higher activity in reactions such as catalysis and adsorption. It has broad application prospects in high-temperature radiation, high-frequency and high-power devices, aerospace, automobiles, radar communications, oil exploration, and catalysis.

[0003] The preparation methods of high specific area silicon carbide mainly include the shape memory synthesis method proposed by Ledoux et al. using silicon powder, silicon oxide, activated carbon, etc. as raw materials, and the sol-gel combined with low-temperature carbon thermal reduction method proposed by Guo Xiangyun et al. using phenolic resin, ethyl orthosilicate, etc. as raw materials; the former has complex equipment and high production cost, while the latter requires the use of bromine-containing surfactants, and irritating gases are generated during the production process, which requires special treatment. Therefore, it is of great significance to study and develop a clean and efficient method for producing high specific surface area SiC. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the purpose of the present application is to provide a clean and efficient method for preparing SiC with a high specific surface area.

[0005] In order to achieve the above objectives, this application adopts the following technical solutions:

[0006] The present application discloses a method for preparing SiC, which comprises the following steps:

[0007] Preparation of carbon-silicon precursor: biochar, water glass and metal salt are uniformly dispersed in water, and then transferred to a hydrothermal reactor for heating treatment to obtain a carbon-silicon precursor, wherein the metal salt is iron, cobalt or nickel salt;

[0008] Carbothermal reduction: The carbon silicon precursor is filtered and dried, and then subjected to carbothermal reduction reaction under an argon atmosphere to obtain a crude SiC product;

[0009] Post-treatment: high temperature calcination to remove unreacted carbon, soaking with acid or alkali to remove unreacted impurities, washing, filtering and drying to obtain SiC finished products.

[0010] In some embodiments of the present application, before the preparation of the carbon silicon precursor, the following steps are further included:

[0011] Modification of biochar: Disperse the biochar in water, add an oxidizing modifier, stir evenly under a certain temperature, wash and dry to obtain biochar modified with acidic functional groups.

[0012] In some embodiments of the present application, the modifier includes at least one of nitric acid, sulfuric acid, phosphoric acid, hydrogen peroxide, potassium permanganate, and potassium perchlorate.

[0013] In some embodiments of the present application, the modification conditions of the biochar include: reacting at 40 to 90° C. for 2 to 12 hours.

[0014] In some embodiments of the present application, in the preparation of the carbon-silicon precursor, the molar ratio of carbon to silicon in the biochar, water glass and metal salt used is 1:1-8, and the molar ratio of metal salt to silicon is 0.05-1:1.

[0015] In some embodiments of the present application, the metal salt includes any one of ferric nitrate, cobalt nitrate, nickel nitrate, ferric chloride, nickel chloride, and cobalt chloride.

[0016] In some embodiments of the present application, the biochar, water glass and metal salt are uniformly dispersed in water and then transferred to a hydrothermal kettle for heating treatment, specifically comprising:

[0017] The biochar, water glass and metal salt are uniformly dispersed in water, and then transferred to a hydrothermal kettle, heated to 165-220° C., and reacted for 1.5-12 hours.

[0018] In some embodiments of the present application, filtering and drying the carbon silicon precursor and then performing a carbothermal reduction reaction under an argon atmosphere specifically includes:

[0019] The carbon silicon precursor is filtered and dried, and then heated to 1250-1650° C. in an argon atmosphere for reaction for 2-22 hours.

[0020] In some embodiments of the present application, the high temperature calcination to remove unreacted carbon specifically includes:

[0021] The crude SiC is calcined at 600-950°C for 2-5.5 hours to remove unreacted carbon.

[0022] In some embodiments of the present application, in the post-treatment, the acid includes a mixed solution of HCl and HF in a volume ratio of 1:1; the alkali includes a KOH solution or a NaOH solution with a concentration of 0.8 to 6.5 mol / L.

[0023] Beneficial effects:

[0024] The preparation method of SiC provided in the present application greatly reduces the production cost by using abundant biochar as the carbon source, and the biochar has a rich pore structure, which can increase the specific surface area of ​​the SiC product; in addition, the carbon silicon precursor is prepared by hydrothermal treatment, which can improve the uniform compounding of the carbon precursor and the silicon precursor, thereby improving the sufficiency of the carbon and silicon reaction in the carbon thermal reduction reaction and improving the yield of the product. The preparation method has simple equipment and does not produce irritating gases during the production process, providing a green process for the preparation of high specific surface area SiC. DETAILED DESCRIPTION

[0025] The present application provides a method for preparing SiC. To make the purpose, technical solution and effect of the present application clearer and more specific, the present application is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0026] Unless otherwise specified, the equipment, reagents, raw materials, etc. used in the following examples are all common commercially available products.

[0027] The present application provides a method for preparing SiC, specifically a method for preparing SiC with a high specific surface area. The method has simple equipment and does not generate irritating gas during the production process. It is a green method for preparing SiC with a high specific surface area.

[0028] Specifically, the preparation method comprises the following steps:

[0029] Step S100, preparation of carbon silicon precursor: evenly dispersing biochar, water glass and metal salt in water, and then transferring them to a hydrothermal kettle for heating treatment to obtain a carbon silicon precursor.

[0030] Biochar is a solid material rich in carbon that is processed by pyrolysis technology from biomass such as plant roots, wood chips, wheat straw, and animal manure. Since biomass is a renewable energy source with a wide range of sources, biochar is abundant in sources and low in cost.

[0031] Biochar has a rich pore structure, which can increase the specific surface area of ​​SiC products and make SiC have better water absorption and higher reaction activity.

[0032] In the above, biochar, water glass and metal salt are dispersed in a hydrothermal kettle for hydrothermal reaction, which can achieve uniform compounding of carbon precursor and silicon precursor, and is beneficial for the full reaction of carbon and silicon in the subsequent high-temperature carbon thermal reduction reaction, thereby improving the yield of the product.

[0033] Among them, in the above reaction, the addition amount of biochar, water glass and metal salt is uniformly dispersed in water according to the ratio of carbon to silicon of 1:1 to 8 and the molar ratio of metal salt to silicon of 0.05 to 1:1. The addition amount of biochar, water glass and metal salt is within the above ratio range, the raw materials can fully react with each other, the ratio of the generated carbon silicon precursor is high, and the waste of raw materials is reduced.

[0034] Furthermore, the above-mentioned biochar, water glass and metal salt are uniformly dispersed in water, and then transferred to a hydrothermal kettle, heated to 165-220°C, and reacted for 1.5-12 hours; carbon and silicon can be effectively cross-linked in the above temperature range, and the reaction time of 1.5-12 hours can ensure that carbon and silicon are fully composited.

[0035] The metal salt is an iron, cobalt or nickel salt. The metal ions in the iron, cobalt or nickel salt can promote the formation of SiC, and can adjust the size and distribution of silicon carbide grains, thereby improving the structure and performance of silicon carbide.

[0036] Specifically, the metal salt includes at least one of iron nitrate, cobalt nitrate, nickel nitrate, iron chloride, nickel chloride, and cobalt chloride. Nitrates of iron, cobalt, and nickel and chlorides of iron, cobalt, and nickel are soluble in water, and nitrates and chlorides are relatively easy to remove after the SiC crude product is generated, which is convenient for the purification of the SiC crude product.

[0037] Furthermore, the biochar may be modified before the preparation of the carbon silicon precursor.

[0038] Specifically, the modification process of the biochar includes:

[0039] The biochar is dispersed in water, an oxidizing modifier is added, and the mixture is stirred evenly under certain temperature conditions so that the biochar can fully contact and react with the modifier. After washing and drying, the biochar modified with acidic functional groups is obtained.

[0040] Biochar has rich pore structures and surface functional groups. Reacting with oxidizing modifiers can introduce more acidic oxygen-containing functional groups on the surface of biochar, thereby improving the neutralization effect of biochar on alkaline substances in water glass in subsequent reactions, thereby reducing the corrosion of alkaline substances in water glass to equipment during the SiC production process.

[0041] Specifically, the modifier can be selected from one or more of nitric acid, sulfuric acid, phosphoric acid, hydrogen peroxide, potassium permanganate, and potassium perchlorate. The above modifier is miscible with water or relatively soluble in water, and has strong oxidizing properties. After the biochar is dispersed in water, the oxygen-containing acidic functional groups in the above modifier can be quickly connected to the surface of the biochar. The stronger the oxidizing property of the modifier, the better the neutralization ability of the modified biochar to the alkaline substances in the water glass, and the less corrosion of the alkaline substances in the water glass to the equipment when preparing SiC.

[0042] Specifically, the biochar and the modifier react at 40-90°C for 2-12 hours. The modifier has strong oxidizing properties. If the reaction temperature is too high, the reaction rate is too high, the reaction is violent, and the controllability of the reaction is too low; if the reaction temperature is too low, the reaction rate is too low, and the reaction time is long. At the above temperature, the biochar and the modifier can react stably, and the reaction controllability is high. The above reaction time allows the surface of the biochar to be evenly and stably connected with enough acidic groups.

[0043] Furthermore, the modified biochar is washed with water and ethanol successively, and then dried to obtain the modified biochar. The modifier used in biochar modification is basically soluble in water, so washing with water can remove the excess modifier on the surface of the biochar; in addition, ethanol can dissolve most of the above modifiers and can take away the moisture on the surface of the biochar, reduce the moisture content of the biochar, and shorten the drying time of the biochar.

[0044] Step S200: filtering and drying the carbon silicon precursor, and then performing a carbothermal reduction reaction under an argon atmosphere to obtain a SiC crude product.

[0045] Specifically, in the above carbon thermal reduction reaction, the carbon silicon precursor is placed in an argon atmosphere and heated to 1250-1650°C for 2-22 hours. The higher the reaction temperature, the higher the yield of SiC obtained, but the porosity of SiC decreases, thereby reducing the specific surface area of ​​SiC; the lower the reaction temperature, the lower the yield of SiC, the higher the porosity of SiC, thereby increasing the specific surface area of ​​SiC. The above temperature and reaction time allow the prepared SiC to have a higher specific surface area and a suitable yield.

[0046] Step S300, high temperature calcination to remove unreacted carbon, acid soaking to remove unreacted impurities, washing, filtering, and drying to obtain a SiC finished product.

[0047] Specifically, the crude SiC product is calcined at 600-950° C. for 2-5.5 hours to remove unreacted carbon.

[0048] For example, the acid may be a mixed solution of HCl and HF in a volume ratio of 1:1. HCl can remove the metal salt added in the carbon silicon precursor reaction, and HF can remove the unreacted SiO2 in the product, thereby improving the purity of the carbon silicon precursor.

[0049] In other embodiments, the SiC crude product after calcination and cooling can also be soaked in alkali to remove unreacted impurities. Exemplarily, the alkali can be a KOH solution or a NaOH solution with a concentration of 0.8 to 6.5 mol / L. Compared with using acid to remove unreacted impurities in the SiC crude product, especially using HF, using alkali to remove impurities is more environmentally friendly. The KOH solution or NaOH solution of the above concentration is more sufficient to basically remove the impurity components in SiC.

[0050] Furthermore, the SiC after impurities are removed is washed with water and ethanol in sequence, and then dried. During the washing process of SiC, it can be washed once with water and ethanol respectively, or washed multiple times with water and ethanol respectively, and the number of washing times can be determined according to whether the impurity components are completely cleaned.

[0051] In the above, in order to avoid introducing new impurities, the water used can be deionized water. In order to reasonably control production costs, the ethanol used in the washing process can be analytically pure. Of course, in order to improve the purity of the product, the ethanol used in the washing process can also be of higher purity.

[0052] The present application will be described in more detail below through examples and comparative examples, but the present application is not limited to the following examples.

[0053] Example 1

[0054] 1 g of biochar was ultrasonically dispersed in 60 mL of deionized water, 10 mL of H2O2 was added and stirred at 50 °C for 5 h, then washed with water and ethanol in turn, and dried to obtain biochar modified with acidic functional groups.

[0055] The modified biochar, water glass and cobalt nitrate were evenly dispersed in 100 mL of deionized water at a carbon-silicon molar ratio of 1:2.5 and a metal salt-silicon molar ratio of 0.25:1, and then transferred to a hydrothermal autoclave to react at 200°C for 6 hours to obtain a carbon-silicon precursor.

[0056] The carbon silicon precursor was filtered and dried, and then subjected to carbothermal reduction reaction at 1350°C for 5 h in an argon atmosphere to obtain a crude SiC product.

[0057] The crude SiC obtained above was placed in a high-temperature furnace, heated to 800°C, and calcined at high temperature for 2 hours to remove unreacted carbon. It was then soaked in a mixed acid of HCl and HF in a volume ratio of 1:1 to remove silicon dioxide and other impurities. It was washed with water and ethanol in turn and dried to obtain high specific surface area SiC.

[0058] The specific surface area of ​​the SiC prepared above is 36.5 m 2 / g, the yield is 14.9%; after the high-temperature furnace for high-temperature calcining SiC crude product was reused 20 times, the high-temperature furnace refractory material had slight corrosion.

[0059] Example 2

[0060] The unmodified biochar, water glass and cobalt nitrate were uniformly dispersed in 100 mL of deionized water at a carbon-silicon molar ratio of 1:2.5 and a metal salt-silicon molar ratio of 0.25:1, and then transferred to a hydrothermal autoclave to react at 200°C for 6 hours to obtain a carbon-silicon precursor.

[0061] The carbon silicon precursor was filtered and dried, and then subjected to carbothermal reduction reaction at 1350°C for 5 h in an argon atmosphere to obtain a crude SiC product.

[0062] The crude SiC obtained above was placed in a high-temperature furnace, heated to 800°C, and calcined at high temperature for 2 hours to remove unreacted carbon. It was then soaked in a mixed acid of HCl and HF in a volume ratio of 1:1 to remove silicon dioxide and other impurities. It was washed with water and ethanol in turn and dried to obtain high specific surface area SiC.

[0063] The specific surface area of ​​the SiC prepared above is 34.8 m 2 / g, the yield is 13.5%; after the high-temperature furnace for high-temperature calcining SiC crude product was reused 5 times, the high-temperature furnace refractory material had slight corrosion.

[0064] Example 3

[0065] 1 g of biochar was ultrasonically dispersed in 60 mL of deionized water, 10 mL of H2O2 was added and stirred at 50 °C for 5 h, then washed with water and ethanol in turn, and dried to obtain biochar modified with acidic functional groups.

[0066] The modified biochar, water glass and cobalt nitrate were evenly dispersed in 100 mL of deionized water at a carbon-silicon molar ratio of 1:2.5 and a metal salt-silicon molar ratio of 0.25:1, and then transferred to a hydrothermal autoclave to react at 200°C for 6 hours to obtain a carbon-silicon precursor.

[0067] The carbon silicon precursor was filtered and dried, and then subjected to carbothermal reduction reaction at 1450°C for 5 h in an argon atmosphere to obtain a crude SiC product.

[0068] The crude SiC obtained above was placed in a high-temperature furnace, heated to 800°C, and calcined at high temperature for 2 hours to remove unreacted carbon. It was then soaked in a mixed acid of HCl and HF in a volume ratio of 1:1 to remove silicon dioxide and other impurities. It was washed with water and ethanol in turn and dried to obtain high specific surface area SiC.

[0069] The specific surface area of ​​the SiC prepared above is 31.5 m 2 / g, the yield is 16.3%; after the high-temperature furnace for high-temperature calcining SiC crude product was reused 20 times, the high-temperature furnace refractory material had slight corrosion.

[0070] Example 4

[0071] 1 g of biochar was ultrasonically dispersed in 60 mL of deionized water, 10 mL of H2O2 was added and stirred at 80 °C for 5 h, then washed with water and ethanol in turn, and dried to obtain biochar modified with acidic functional groups.

[0072] The modified biochar, water glass and cobalt nitrate were evenly dispersed in 100 mL of deionized water at a carbon-silicon molar ratio of 1:2.5 and a metal salt-silicon molar ratio of 0.25:1, and then transferred to a hydrothermal autoclave to react at 200°C for 6 hours to obtain a carbon-silicon precursor.

[0073] The carbon silicon precursor was filtered and dried, and then subjected to carbothermal reduction reaction at 1350°C for 5 h in an argon atmosphere to obtain a crude SiC product.

[0074] The crude SiC obtained above was placed in a high-temperature furnace, heated to 800°C, and calcined at high temperature for 2 hours to remove unreacted carbon. It was then soaked in a mixed acid of HCl and HF in a volume ratio of 1:1 to remove silicon dioxide and other impurities. It was washed with water and ethanol in turn and dried to obtain high specific surface area SiC.

[0075] The specific surface area of ​​the SiC prepared above is 35.1 m 2 / g, the yield is 14.6%; after the high-temperature furnace for high-temperature calcining SiC crude product was reused 20 times, there was no obvious corrosion phenomenon in the high-temperature furnace refractory material.

[0076] Example 5

[0077] 1 g of biochar was ultrasonically dispersed in 60 mL of deionized water, 10 mL of HNO3 was added and stirred at 50 °C for 5 h, then washed with water and ethanol in turn, and dried to obtain biochar modified with acidic functional groups.

[0078] The modified biochar, water glass and cobalt nitrate were evenly dispersed in 100 mL of deionized water at a carbon-silicon molar ratio of 1:2.5 and a metal salt-silicon molar ratio of 0.25:1, and then transferred to a hydrothermal autoclave to react at 200°C for 6 hours to obtain a carbon-silicon precursor.

[0079] The carbon silicon precursor was filtered and dried, and then subjected to a carbon thermal reduction reaction at 1350° C. for 5 h under an argon atmosphere to obtain a crude SiC product.

[0080] The crude SiC obtained above was placed in a high-temperature furnace, heated to 800°C, and calcined at high temperature for 2 hours to remove unreacted carbon. It was then soaked in a mixed acid of HCl and HF in a volume ratio of 1:1 to remove silicon dioxide and other impurities. It was washed with water and ethanol in turn and dried to obtain high specific surface area SiC.

[0081] The specific surface area of ​​the SiC prepared above is 34.6 m 2 / g, the yield is 15.1%; after the high-temperature furnace for high-temperature calcining SiC crude product was reused 20 times, there was no obvious corrosion phenomenon in the high-temperature furnace refractory material.

[0082] Example 6

[0083] 1 g of biochar was ultrasonically dispersed in 60 mL of deionized water, 10 mL of H2O2 was added and stirred at 50 °C for 5 h, then washed with water and ethanol in turn, and dried to obtain biochar modified with acidic functional groups.

[0084] The modified biochar, water glass and cobalt nitrate were evenly dispersed in 100 mL of deionized water at a carbon-silicon molar ratio of 1:1 and a metal salt-silicon molar ratio of 0.25:1, and then transferred to a hydrothermal autoclave to react at 200°C for 6 hours to obtain a carbon-silicon precursor.

[0085] The carbon silicon precursor was filtered and dried, and then subjected to carbothermal reduction reaction at 1350°C for 5 h in an argon atmosphere to obtain a crude SiC product.

[0086] The crude SiC obtained above was placed in a high-temperature furnace, heated to 800°C, and calcined at high temperature for 2 hours to remove unreacted carbon. It was then soaked in a mixed acid of HCl and HF in a volume ratio of 1:1 to remove silicon dioxide and other impurities. It was washed with water and ethanol in turn and dried to obtain high specific surface area SiC.

[0087] The specific surface area of ​​the SiC prepared above is 23.8 m 2 / g, the yield is 3.6%; after the high-temperature furnace for high-temperature calcining SiC crude product was reused 20 times, the high-temperature furnace refractory material had slight corrosion.

[0088] Example 7

[0089] 1 g of biochar was ultrasonically dispersed in 60 mL of deionized water, 10 mL of H2O2 was added and stirred at 50 °C for 5 h, then washed with water and ethanol in turn, and dried to obtain biochar modified with acidic functional groups.

[0090] The modified biochar, water glass and cobalt nitrate were evenly dispersed in 100 mL of deionized water at a carbon-silicon molar ratio of 1:8 and a metal salt-silicon molar ratio of 0.25:1, and then transferred to a hydrothermal autoclave to react at 200°C for 6 hours to obtain a carbon-silicon precursor.

[0091] The carbon silicon precursor was filtered and dried, and then subjected to carbothermal reduction reaction at 1350°C for 5 h in an argon atmosphere to obtain a crude SiC product.

[0092] The crude SiC obtained above was placed in a high-temperature furnace, heated to 800°C, and calcined at high temperature for 2 hours to remove unreacted carbon. It was then soaked in a mixed acid of HCl and HF in a volume ratio of 1:1 to remove silicon dioxide and other impurities. It was washed with water and ethanol in turn and dried to obtain high specific surface area SiC.

[0093] The specific surface area of ​​the SiC prepared above is 37.4 m 2 / g, the yield is 14.2%; after the high-temperature furnace for high-temperature calcining SiC crude product was reused 20 times, the high-temperature furnace refractory material had slight corrosion.

[0094] Example 8

[0095] 1 g of biochar was ultrasonically dispersed in 60 mL of deionized water, 10 mL of H2O2 was added and stirred at 50 °C for 5 h, then washed with water and ethanol in turn, and dried to obtain biochar modified with acidic functional groups.

[0096] The modified biochar, water glass and cobalt nitrate were evenly dispersed in 100 mL of deionized water at a carbon-silicon molar ratio of 1:2.5 and a metal salt-silicon molar ratio of 0.05:1, and then transferred to a hydrothermal autoclave to react at 200°C for 6 hours to obtain a carbon-silicon precursor.

[0097] The carbon silicon precursor was filtered and dried, and then subjected to carbothermal reduction reaction at 1350°C for 5 h in an argon atmosphere to obtain a crude SiC product.

[0098] The crude SiC obtained above was placed in a high-temperature furnace, heated to 800°C, and calcined at high temperature for 2 hours to remove unreacted carbon. It was then soaked in a mixed acid of HCl and HF in a volume ratio of 1:1 to remove silicon dioxide and other impurities. It was washed with water and ethanol in turn and dried to obtain high specific surface area SiC.

[0099] The specific surface area of ​​the SiC prepared above is 28.2 m 2 / g, the yield is 8.6%; after the high-temperature furnace for high-temperature calcining SiC crude product was reused 20 times, the high-temperature furnace refractory material had slight corrosion.

[0100] Example 9

[0101] 1 g of biochar was ultrasonically dispersed in 60 mL of deionized water, 10 mL of H2O2 was added and stirred at 50 °C for 5 h, then washed with water and ethanol in turn, and dried to obtain biochar modified with acidic functional groups.

[0102] The modified biochar, water glass and cobalt nitrate were uniformly dispersed in 100 mL of deionized water at a carbon-silicon molar ratio of 1:2.5 and a metal salt-silicon molar ratio of 1:1, and then transferred to a hydrothermal autoclave to react at 200°C for 6 hours to obtain a carbon-silicon precursor.

[0103] The carbon silicon precursor was filtered and dried, and then subjected to carbothermal reduction reaction at 1350°C for 5 h in an argon atmosphere to obtain a crude SiC product.

[0104] The crude SiC obtained above was placed in a high-temperature furnace, heated to 800°C, and calcined at high temperature for 2 hours to remove unreacted carbon. It was then soaked in a mixed acid of HCl and HF in a volume ratio of 1:1 to remove silicon dioxide and other impurities. It was washed with water and ethanol in turn and dried to obtain high specific surface area SiC.

[0105] The specific surface area of ​​the SiC prepared above is 33.7 m 2 / g, the yield is 7.3%; after the high-temperature furnace for high-temperature calcining SiC crude product was reused 20 times, the high-temperature furnace refractory material had slight corrosion.

[0106] It can be seen from the above Examples 1 to 9 that the preparation method provided in the present application can obtain SiC with a high specific surface area, and the yield can reach more than 16%.

[0107] The difference between Example 1 and Example 2 is that the biochar in Example 2 has not been modified by a modifier. By comparing the SiC prepared in Example 1 and Example 2, it can be seen that the biochar can be modified by an oxidant before reacting with water glass. The number of acidic oxygen-containing functional groups on the surface of the biochar can be increased, and the neutralization effect of the biochar on the alkaline substances in the water glass can be improved, thereby reducing the corrosion of the alkaline substances in the water glass to the equipment during the preparation of SiC.

[0108] It can be seen from Examples 1 and 3 that the temperature of the carbon thermal reduction reaction in Example 3 is higher than that of the carbon thermal reduction reaction in Example 1. Therefore, on the basis of other identical experimental conditions, within the scope disclosed in the present application, the higher the temperature of the carbon thermal reduction reaction, the more complete the reaction, the higher the yield of SiC, and the lower the specific surface area of ​​SiC.

[0109] It can be seen from Examples 1 and 4 that the modification temperature of the biochar in Example 4 is higher than the modification temperature of the biochar in Example 1. Therefore, within the scope disclosed in the present application, increasing the modification temperature of the biochar can increase the number of functional groups modified on the surface of silicon carbide and improve the neutralization effect of the biochar on the alkaline groups in water glass, thereby reducing the corrosion to the equipment during the preparation of SiC.

[0110] In summary, the present application can significantly reduce the cost of the product by adopting abundant biochar as the carbon source, and the biochar has a rich pore structure, so that the prepared SiC product has a higher specific surface area; the biochar is modified by an oxidizing modifier, which can increase the number of acidic oxygen-containing functional groups on the surface of the biochar and improve the neutralization effect of the biochar on the alkaline substances in the water glass, thereby reducing the corrosion of the alkaline substances in the water glass to the SiC production equipment and improving the equipment utilization rate.

[0111] In addition, the carbon silicon precursor is treated by a hydrothermal reaction before the carbothermal reduction reaction, so that the carbon precursor and the silicon precursor can be evenly compounded, thereby improving the sufficiency of the reaction of carbon and silicon in the carbothermal reduction reaction and improving the yield of the product.

[0112] It is understandable that those skilled in the art can make equivalent substitutions or changes based on the technical solution and application concept of the present application, and all these changes or substitutions should fall within the protection scope of the claims attached to the present application.

Claims

1. A method for preparing SiC, characterized in that: The steps include: Preparation of carbon-silicon precursor: biochar, water glass and metal salt are uniformly dispersed in water, and then transferred to a hydrothermal reactor for heating treatment to obtain a carbon-silicon precursor, wherein the metal salt is iron, cobalt or nickel salt; Carbothermal reduction: The carbon silicon precursor is filtered and dried, and then subjected to carbothermal reduction reaction under an argon atmosphere to obtain a crude SiC product; Post-treatment: high temperature calcination to remove unreacted carbon, soaking with acid or alkali to remove unreacted impurities, washing, filtering and drying to obtain SiC finished products.

2. The preparation method according to claim 1, characterized in that: Before the preparation of the carbon silicon precursor, the method further comprises: Modification of biochar: Disperse the biochar in water, add an oxidizing modifier, stir evenly under a certain temperature, wash and dry to obtain biochar modified with acidic functional groups.

3. The preparation method according to claim 1 or 2, characterized in that: The modifier includes at least one of nitric acid, sulfuric acid, phosphoric acid, hydrogen peroxide, potassium permanganate and potassium perchlorate.

4. The preparation method according to claim 2, characterized in that: The modification conditions of the biochar include: reacting at 40 to 90° C. for 2 to 12 hours.

5. The preparation method according to claim 1, characterized in that: In the preparation of the carbon-silicon precursor, the biochar, water glass and metal salt used have a molar ratio of carbon to silicon of 1:1-8 and a molar ratio of metal salt to silicon of 0.05-1:

1.

6. The preparation method according to claim 1, characterized in that: The metal salt includes at least one of ferric nitrate, cobalt nitrate, nickel nitrate, ferric chloride, nickel chloride and cobalt chloride.

7. The preparation method according to claim 1, characterized in that: The biochar, water glass and metal salt are uniformly dispersed in water and then transferred to a hydrothermal kettle for heating treatment, specifically comprising: The biochar, water glass and metal salt are uniformly dispersed in water, and then transferred to a hydrothermal kettle, heated to 165-220° C., and reacted for 1.5-12 hours.

8. The preparation method according to claim 1, characterized in that: The carbon silicon precursor is filtered and dried, and then subjected to a carbon thermal reduction reaction under an argon atmosphere, specifically comprising: The carbon silicon precursor is filtered and dried, and then heated to 1250-1650° C. in an argon atmosphere for reaction for 2-22 hours.

9. The preparation method according to claim 1, characterized in that: The high temperature calcination to remove unreacted carbon specifically includes: The crude SiC is calcined at 600-950°C for 2-5.5 hours to remove unreacted carbon.

10. The preparation method according to claim 1, characterized in that: In the post-treatment, the acid includes a mixed solution of HCl and HF in a volume ratio of 1:1; the alkali includes a KOH solution or a NaOH solution with a concentration of 0.8 to 6.5 mol / L.