Nano silicon carbide whisker and preparation method thereof

Abstract

The invention relates to a nano silicon carbide whisker and a preparation method thereof, and the preparation method comprises the following steps: (1) carrying out acid process treatment on fly ash by using an acid solution, so that the content of key impurity elements in the fly ash accounts for 2-11% of the total mass of the treated fly ash, and obtaining acid-treated fly ash; (2) mixing the acid-treated fly ash with a first carbon source to obtain a mixture; and (3) covering the mixture with a second carbon source, roasting in a reducing atmosphere to obtain a roasted material which comprises a nano silicon carbide whisker layer and a total impurity layer positioned below the silicon carbide whisker layer, and removing the total impurity layer to obtain the nano silicon carbide whisker. According to the preparation method, the low-cost fly ash is taken as a raw material, the advantages of low preparation cost and relatively high product yield can be taken into account through the synergistic effect of moderate acid treatment, raw material position setting and roasting in the reducing atmosphere, and good morphology and relatively high purity of the nano silicon carbide crystal whiskers are ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial solid waste resource utilization, and in particular to a nano silicon carbide whisker and a preparation method thereof. BACKGROUND

[0002] Silicon carbide whisker (SiCw) is a single crystal fiber with nanometer to micron diameter and high orientation, and its crystal structure is similar to that of diamond. SiCw is known as "the king of whiskers" and has high strength, high melting point, low density, high elastic modulus, low thermal expansion rate, and properties of wear resistance, corrosion resistance, and high temperature oxidation resistance. SiCw is mainly used in toughening occasions requiring high temperature and high strength application materials. The addition of SiCw can significantly improve the fracture toughness and bending strength of the matrix material. As an excellent reinforcing and toughening agent, SiCw toughened ceramic-based, metal-based and polymer-based composite materials have been widely used in mechanical, chemical, national defense, energy, environmental protection and other fields.

[0003] At present, various technologies for preparing silicon carbide whiskers have been developed, such as pyrolysis of organic precursors, arc discharge reaction, chemical vapor deposition reaction, laser ablation reaction, solvothermal reaction and carbothermal reduction reaction. The most mature technology is to use carbon black, silica powder or rice husk as raw material, add catalyst, and heat to high temperature in an electric furnace to synthesize.

[0004] CN105329895B discloses a method for preparing a large amount of silicon carbide nanowhiskers on the surface of carbon materials without catalyst by using bitumen organic solvent-soluble components or resin organic solvent-soluble components as carbon source and organic silicon as silicon source. CN116695253A discloses a method for preparing silicon carbide whiskers with high yield by mixing catalyst precursor with rice husk carbon, carbon powder and carbon fiber, and then carrying out mixed heating, preparation and pretreatment of silicon source matrix, carbonization reaction treatment and post-treatment of carbonization reaction. However, the above methods have problems such as high cost, harsh reaction conditions, and difficulty in industrialization.

[0005] Carbothermal reduction reaction is considered to be the most suitable method for industrial application and popularization of silicon carbide whiskers due to its wide adaptability of raw materials, no need for toxic organic precursors, and low equipment requirements. For example, CN111392730A discloses a method for preparing silicon carbide whiskers from silicon dioxide, silicon and other raw materials, which can obtain whiskers with an aspect ratio greater than 25, a whisker diameter of 200 nm to 1 μm, and a large whisker diameter. However, the method has problems such as high cost of required raw materials, low yield, complex reaction process, difficult control of product purity, only partial fiber morphology, and poor product crystal form.

[0006] Meanwhile, fly ash is a kind of fly ash generated after high-temperature combustion of coal, and has become the largest single solid waste in China, with an annual emission of 600 million tons. Although the utilization rate of fly ash in China is as high as 70%, a large amount of fly ash is still stored, causing serious environmental pollution problems. At present, fly ash is mainly used as raw material for cement, concrete, building bricks and other public building materials, and is mixed with backfilling materials for mine backfilling, and its consumption almost entirely depends on these traditional ways, which has problems of low technical content, low product added value and small market capacity in some areas. As a kind of secondary resource rich in active silicon components, fly ash is in urgent need of high-value utilization technology.

[0007] CN113248242A discloses a preparation method, which is synthesized by using silicon dioxide and fly ash as silicon source, and crushed lignite as carbon source in solution, and then sintering to obtain silicon carbide whiskers, the whiskers have high straight crystal rate and can effectively play a bridging effect, and then the silicon carbide whiskers are modified by carbon nanotubes to obtain modified nano silicon carbide whiskers which can significantly improve the bending strength, but the preparation cost is still high, and the product purity and yield still need to be improved.

[0008] Therefore, it is an urgent problem to provide a silicon carbide whisker preparation method which can balance the advantages of low cost and high product yield, and ensure that the silicon carbide whisker has good morphology and high purity. SUMMARY

[0009] To solve the above technical problems, the purpose of the present application is to provide a kind of nano silicon carbide whisker and its preparation method. The present application uses low-cost fly ash as raw material, and through the synergistic effect of moderate acid treatment, setting of raw material placement position and sintering in reducing atmosphere, the slow release and adsorption of silicon monoxide gas from the raw material are effectively controlled, thereby forming a microenvironment in the upper second carbon source where silicon monoxide gas and reducing gas coexist, creating conditions suitable for the growth of nano silicon carbide whiskers, so as to balance the advantages of low preparation cost and high product yield, and ensure good morphology and high purity of nano silicon carbide whiskers.

[0010] To achieve this purpose, the present application adopts the following technical solutions:

[0011] In a first aspect, the present application provides a preparation method of nano silicon carbide whisker, which comprises:

[0012] (1) using acid to treat fly ash by acid method, so that the content of key impurity elements in fly ash accounts for 2-11% of the total mass of treated fly ash, to obtain acid-treated fly ash; wherein the key impurity elements include iron, magnesium and calcium elements;

[0013] (2) mixing the acid-treated fly ash with a first carbon source to obtain a mixture;

[0014] (3) covering the mixture with a second carbon source and calcining under a reducing atmosphere to obtain a calcined material, wherein the calcined material comprises a nano-silicon carbide whisker layer and a total impurity layer located below the silicon carbide whisker layer, and the total impurity layer is removed to obtain the nano-silicon carbide whisker.

[0015] In the present application, the content of the key impurity element in step (1) accounts for 2-11% of the total mass of the acid-treated fly ash, for example, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or 11%, etc.

[0016] In the present application, the fly ash obtained by a conventional coal combustion process is used as a raw material, which is widely available and low in cost. Through the synergistic effect of moderate acid treatment, the setting of the raw material placement position and calcination under a reducing atmosphere, the slow release and adsorption of silicon monoxide gas are effectively controlled, a microenvironment in which silicon monoxide gas and reducing gas coexist is formed in the upper layer of the second carbon source, and conditions suitable for the growth of nano-silicon carbide whiskers are created, thereby achieving the advantages of low preparation cost and high product yield, and ensuring that the prepared nano-silicon carbide whiskers have good morphology and high purity.

[0017] The preparation method used in the present application first discovers through element analysis of fly ash that the fly ash contains a large amount of silicon dioxide component, which can be reduced to silicon monoxide gas during carbothermal reduction calcination. The silicon monoxide gas slowly overflows from the mixture during the reaction process and enters the second carbon source layer covered on the upper surface of the mixture. The reducing gas in the reaction system can only slowly penetrate into the carbon source layer due to the presence of the upper layer of the second carbon source layer, thereby forming a microenvironment in which low-concentration silicon monoxide gas and low-concentration reducing gas coexist in the upper layer of the second carbon source layer, creating conditions suitable for the growth of nano-silicon carbide whiskers with good morphology and high purity. Under these conditions, the slowly escaping silicon monoxide gas reacts with the second carbon source layer above it to prepare nano-silicon carbide whiskers with good morphology and high purity.

[0018] Furthermore, the acid treatment process of the fly ash in the present application can remove part of the impurity elements such as calcium, magnesium and iron in the fly ash, on the one hand, the content of low-melting-point phases in the reaction system can be moderately reduced to prevent excessive sintering of the mixture, which can lead to densification and affect the discharge of silicon monoxide gas, thereby increasing the yield of the obtained nano-silicon carbide whiskers; on the other hand, a certain amount of liquid phase can be contained in the reaction system by moderately retaining part of the calcium, magnesium and iron impurities, thereby playing a role in adsorbing and slowly releasing silicon monoxide, maintaining the silicon monoxide gas concentration in the reaction system at an appropriate level, and promoting the growth of nano-silicon carbide whiskers. In addition, the retained part of the iron can also play a role in catalyzing the reaction.

[0019] Preferably, the acid solution in step (1) comprises any one or a combination of at least two of sulfuric acid solution, hydrochloric acid solution, nitric acid solution or phosphoric acid solution.

[0020] Preferably, the concentration of the acid solution in step (1) is 0.2-5.0 mol / L, for example 0.2 mol / L, 0.3 mol / L, 0.5 mol / L, 0.8 mol / L, 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, 3.0 mol / L, 3.5 mol / L, 4.0 mol / L, 4.5 mol / L or 5.0 mol / L, etc.

[0021] In the present application, too low acid concentration will result in too little impurity leaching amount, failing to achieve the purpose of moderate impurity removal, leading to lower yield of prepared nanometer silicon carbide whiskers; too high acid concentration will result in too much impurity leaching amount, too little amount of liquid phase produced in the reaction system, also leading to decreased yield of generated nanometer silicon carbide whiskers, and low aspect ratio and poor morphology of the product.

[0022] Preferably, the temperature of the acid treatment in step (1) is 30-60℃, for example 30℃, 33℃, 36℃, 39℃, 42℃, 45℃, 48℃, 51℃, 54℃, 57℃ or 60℃, etc.

[0023] In the present application, too low acid treatment temperature will result in too slow impurity leaching rate and too low impurity leaching rate, failing to achieve the purpose of moderate impurity removal, leading to lower yield of prepared nanometer silicon carbide whiskers; too high acid treatment temperature will result in too high impurity leaching rate, too little amount of low-melting-point phase in the reaction system, and too little amount of liquid phase produced in the carbothermal reduction reaction process, which is not conducive to regulating the concentration of silicon monoxide in the reaction system, and it is difficult to generate nanometer silicon carbide whiskers with large aspect ratio and good morphology.

[0024] Preferably, the time of the acid treatment in step (1) is 0.5-5 h, for example 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h or 5 h, etc.

[0025] Preferably, the liquid-solid ratio of the acid solution to fly ash in step (1) is 3-10 L / kg, for example 3 L / kg, 4 L / kg, 5 L / kg, 6 L / kg, 7 L / kg, 8 L / kg, 9 L / kg or 10 L / kg, etc.

[0026] In the present application, the "liquid-solid ratio of the acid treatment in step (1) is 3-10 L / kg" means that 1 kg of fly ash raw material is subjected to acid treatment in 3-10 L of acid solution.

[0027] The various parameters set in the acid treatment of the present application cooperate with each other, which can effectively achieve the purpose of moderate acid treatment, moderately retain part of the impurities in the system, so that the reaction system contains an appropriate amount of liquid phase, thereby playing the role of adsorption and slow release of silicon monoxide gas, maintaining the silicon monoxide gas concentration in the reaction system at an appropriate level, promoting the growth of nanoscale silicon carbide whiskers with good morphology, and more conducive to improving the yield and purity of the obtained nanoscale silicon carbide whiskers.

[0028] Preferably, the content of the iron element in step (1) accounts for 1-5% of the total mass of the acid-treated fly ash, such as 1%, 2%, 3%, 4% or 5%, etc.

[0029] Preferably, the content of the magnesium element in step (1) accounts for 0.5-3% of the total mass of the acid-treated fly ash, such as 0.5%, 1%, 1.5%, 2%, 2.5% or 3%, etc.

[0030] Preferably, the content of the calcium element in step (1) accounts for 0.5-3% of the total mass of the acid-treated fly ash, such as 0.5%, 1%, 1.5%, 2%, 2.5% or 3%, etc.

[0031] Preferably, the mass ratio of the fly ash to the first carbon source in step (1) is 1:(0.01-0.30), preferably 1:(0.05-0.20), such as 1:0.01, 1:0.05, 1:0.10, 1:0.15, 1:0.20, 1:0.25 or 1:0.30, etc.

[0032] In the present application, if the mass ratio of the fly ash to the first carbon source is too large, the amount of the first carbon source is insufficient, and the silicon dioxide in the fly ash cannot be fully converted into silicon monoxide, resulting in too low content and yield of the generated nanoscale silicon carbide whiskers; if the mass ratio of the fly ash to the first carbon source is too small, the first carbon source is excessive, which can cause the generated silicon monoxide gas in the mixture to easily contact with the excessive first carbon source to generate silicon carbide in situ, and the silicon carbide is mixed with the remaining impurities in the fly ash, which is difficult to separate, and high-purity nanoscale silicon carbide whiskers cannot be obtained, and a large amount of silicon monoxide gas is consumed, resulting in a decrease in the yield of the finally obtained nanoscale silicon carbide whiskers.

[0033] Preferably, the first carbon source in step (2) and the second carbon source in step (3) independently comprise any one or a combination of at least two of activated carbon, carbon black, graphene or carbon nanotubes, and further preferably carbon black.

[0034] Preferably, the thickness of the second carbon source in step (3) is 10-200% of the thickness of the mixture, preferably 50-100%, such as 10%, 20%, 30%, 40%, 50%, 70%, 100%, 120%, 150%, 170%, or 200%, etc.

[0035] In the present application, the thickness of the second carbon source covering the mixture is too thin to provide sufficient gas-phase second carbon source, and the silicon monoxide gas easily escapes and cannot generate silicon carbide whiskers at the appropriate location; the thickness of the second carbon source is too thick, the reaction produces too much gas-phase second carbon source, the concentration is too high, which destroys the growth conditions of the whiskers, and at the same time, the excess second carbon source also increases the cost.

[0036] Preferably, the reducing atmosphere in step (3) is any one or a combination of at least two of hydrogen, methane, ethane, or acetylene.

[0037] The hydrogen gas used in the present application can react with the second carbon source to generate alkane gas-phase products, and react with silicon monoxide to generate nano-silicon carbide whiskers, while methane, ethane, and acetylene can directly react with silicon monoxide to generate nano-silicon carbide whiskers.

[0038] Preferably, the flow rate of the reducing gas in the reducing atmosphere in step (3) is 0.1-10.0 L / min, such as 0.1 L / min, 0.15 L / min, 0.3 L / min, 0.6 L / min, 1.0 L / min, 1.5 L / min, 2.0 L / min, 2.5 L / min, 3.0 L / min, 3.5 L / min, 4.0 L / min, 4.5 L / min, 5.0 L / min, 5.5 L / min, 6.0 L / min, 6.5 L / min, 7.0 L / min, 7.5 L / min, 8.0 L / min, 8.5 L / min, 9.0 L / min, 9.5 L / min, or 10.0 L / min, etc.

[0039] The flow rate of the reducing gas in the reducing atmosphere of the present application is too low, the amount of reducing gas in the system is too small, and the reaction rate is too low. Further, when the flow rate of the reducing gas is too low, the concentration of silicon monoxide gas will be relatively high, which is not conducive to the generation of whiskers and is more likely to generate particles, thereby reducing the purity and yield of the generated nano-silicon carbide whiskers; if the gas flow rate is too high, the concentration and partial pressure of the reducing gas will be too high, which will destroy the growth environment of the nano-silicon carbide whiskers, resulting in a decrease in the yield of the nano-silicon carbide whiskers.

[0040] Preferably, the temperature of the roasting in step (3) is 1100-1900℃, preferably 1200-1600℃, such as 1100℃, 1150℃, 1200℃, 1250℃, 1300℃, 1350℃, 1400℃, 1450℃, 1500℃, 1550℃, 1600℃, 1650℃, 1700℃, 1750℃, 1800℃, 1850℃ or 1900℃, etc.

[0041] In the present application, if the roasting temperature is too low, the carbothermal reduction reaction cannot be carried out; if the roasting temperature is too high, the carbothermal reduction reaction rate is too fast, resulting in too high concentration of silicon monoxide gas in the reaction system, and it is difficult to obtain nano silicon carbide whiskers.

[0042] Preferably, the time of the roasting in step (3) is 0.5-8h, preferably 1-5h, such as 0.5h, 1.0h, 1.5h, 2.0h, 2.5h, 3.0h, 4.0h, 5.0h, 6.0h, 7.0h or 8.0h, etc.

[0043] Preferably, the method for removing the total impurity layer in step (3) comprises peeling.

[0044] The total impurity layer obtained in the preparation method of the present application can be converted into corundum and silicon carbide, and can be used as raw material for abrasives or refractory materials, and is expected to realize full-component high-value utilization of fly ash, and has good application prospect.

[0045] Preferably, after step (3), the method further comprises step (4): performing carbon removal treatment on the nano silicon carbide whiskers.

[0046] Preferably, the method for the carbon removal treatment is calcination.

[0047] In the present application, the nano silicon carbide whiskers are subjected to calcination treatment, and the carbon impurities in the crude nano silicon carbide whiskers are removed through the calcination process.

[0048] Preferably, the temperature of the carbon removal treatment is 500-950℃, such as 500℃, 550℃, 600℃, 700℃, 800℃, 900℃ or 950℃, etc.

[0049] Preferably, the time of the carbon removal treatment is 0.5-5.0h, such as 0.5h, 1.0h, 1.5h, 2.0h, 2.5h, 3.0h, 3.5h, 4.0h, 4.5h or 5.0h, etc.

[0050] Preferably, step (4) further comprises performing acid etching on the product after the carbon removal treatment.

[0051] The nano silicon carbide whisker prepared by the method has a small amount of silicon carbide on the surface which is oxidized to silicon dioxide. In order to further improve the purity of the nano silicon carbide whisker, the product after carbon removal by calcination is subjected to hydrofluoric acid etching purification to remove the silicon dioxide obtained by oxidation of the silicon carbide on the surface of the silicon carbide whisker.

[0052] Preferably, the acid etching employs an acid solution comprising a hydrofluoric acid solution.

[0053] Preferably, the concentration of the hydrofluoric acid solution is 4.5-22.5 mol / L, further preferably 8.0-15.0 mol / L, for example 4.5 mol / L, 6.5 mol / L, 8.5 mol / L, 10.5 mol / L, 12.5 mol / L, 14.5 mol / L, 16.5 mol / L, 18.5 mol / L, 20.5 mol / L or 22.5 mol / L, etc.

[0054] Preferably, the liquid-solid ratio of the hydrofluoric acid solution to the product after carbon removal treatment is 5-50 L / kg, for example 5 L / kg, 10 L / kg, 15 L / kg, 20 L / kg, 25 L / kg, 30 L / kg, 35 L / kg, 40 L / kg, 45 L / kg or 50 L / kg, etc.

[0055] Preferably, the temperature of the acid etching is 20-80℃, for example 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃ or 80℃, etc.

[0056] Preferably, the time of the acid etching is 0.5-5 h, for example 0.5 h, 1.0 h, 1.5 h, 2.0 h, 2.5 h, 3.0 h, 4.0 h or 5.0 h, etc.

[0057] As a preferred technical solution, the preparation method comprises the following steps:

[0058] (1) mixing fly ash and an acid solution at a liquid-solid ratio of 3-10 L / kg, and acid treatment at 30-60℃ for 0.5-5 h to make the content of key impurity elements in the fly ash account for 2-11% of the total mass of the treated fly ash, to obtain acid-treated fly ash;

[0059] The key impurity elements include iron element, magnesium element and calcium element, the content of the iron element accounts for 1-5% of the total mass of the acid-treated fly ash, the content of the magnesium element accounts for 0.5-3% of the total mass of the acid-treated fly ash, and the content of the calcium element accounts for 0.5-3% of the total mass of the acid-treated fly ash; the acid solution includes any one or a combination of at least two of a sulfuric acid solution, a hydrochloric acid solution, a nitric acid solution or a phosphoric acid solution, and the concentration of the acid solution is 0.2-5.0 mol / L;

[0060] (2) The acid-treated fly ash is mixed with the first carbon source according to a mass ratio of 1:(0.01-0.30) to obtain a mixture;

[0061] (3) The second carbon source is covered on the mixture, the thickness of the second carbon source is 10-200% of the thickness of the mixture, and roasting is performed under a reducing atmosphere with a gas flow rate of 0.1-10.0 L / min, the temperature of the roasting is 1100-1900°C, and the time is 0.5-8 h, to obtain a roasted material, the roasted material includes an upper layer material and a lower layer material, the upper layer material is separated from the lower layer material to obtain a crude nano silicon carbide whisker and an impurity phase;

[0062] In the step (2), the first carbon source and the second carbon source in the step (3) independently include any one or a combination of at least two of activated carbon, carbon black, graphene or carbon nanotube, and is further preferably carbon black; and the reducing atmosphere in the step (3) is any one or a combination of at least two of hydrogen, methane, ethane or acetylene;

[0063] (4) The crude nano silicon carbide whisker is calcined at 500-950°C for 0.5-5.0 h to remove residual carbon source, the product after the carbon removal treatment is mixed with a hydrofluoric acid solution with a concentration of 4.5-22.5 mol / L according to a liquid-solid ratio of 5-50 L / kg, and acid etching is performed at a temperature of 20-80°C for 0.5-5 h to obtain the nano silicon carbide whisker.

[0064] In a second aspect, the present application provides a nano silicon carbide whisker prepared by the preparation method in the first aspect.

[0065] Preferably, the average diameter of the nano silicon carbide whisker is 50-150 nm, for example, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm or 150 nm, etc.

[0066] Preferably, the average length of the nanometer silicon carbide whisker is 5-50 μm, such as 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm or 50 μm, etc.

[0067] Preferably, the average length-diameter ratio of the nanometer silicon carbide whisker is (30-1000):1, such as 30:1, 50:1, 100:1, 200:1, 300:1, 400:1, 500:1, 600:1, 700:1, 800:1, 900:1 or 1000:1, etc.

[0068] Preferably, the nanometer silicon carbide whisker is white powder.

[0069] The present application successfully prepares the nanometer silicon carbide whisker with nanometer average diameter, large average length-diameter ratio, good morphology and high purity. There is no related paper or patent reporting the synthesis of white silicon carbide whisker.

[0070] Compared with the prior art, the present application has at least the following beneficial effects:

[0071] (1) The present application uses low-cost fly ash as raw material, and through the synergistic effect of moderate acid treatment, setting of raw material placement position and roasting under reducing atmosphere, effectively controls the slow release and adsorption of silicon monoxide gas, forms a microenvironment of coexistence of silicon monoxide gas and reducing gas in the upper second carbon source, and creates conditions suitable for the growth of nanometer silicon carbide whisker, so as to take into account the advantages of low preparation cost and high yield, and ensure good morphology and high purity of the nanometer silicon carbide whisker.

[0072] (2) The total impurity layer obtained by the present application using fly ash as raw material can be converted into corundum and silicon carbide, which can be used as raw material for abrasives or refractory materials, realizing full-component high-value utilization of fly ash, and having good economic and environmental benefits.

[0073] (3) The nanometer silicon carbide whisker prepared by the present application has excellent morphology with nanometer average diameter and average length-diameter ratio of more than 250, and the purity is as high as more than 99wt%, and the yield of the product can reach 60-64%. BRIEF DESCRIPTION OF DRAWINGS

[0074] Figure 1 is a sample diagram of the nanometer silicon carbide whisker prepared by Example 1 of the present application.

[0075] Figure 2 is an XRD diagram of the nanometer silicon carbide whisker prepared by Example 1 of the present application.

[0076] Figure 3is a SEM image of the nano-silicon carbide whisker prepared by the embodiment 1 of the present application.

[0077] Figure 4 is a SEM image of the nano-silicon carbide whisker prepared by the comparative example 1 of the present application.

[0078] Figure 5 is a SEM image of the nano-silicon carbide whisker prepared by the comparative example 2 of the present application.

[0079] Figure 6 is a SEM image of the nano-silicon carbide whisker prepared by the comparative example 3 of the present application.

[0080] Figure 7 is a SEM image of the nano-silicon carbide whisker prepared by the comparative example 4 of the present application. DETAILED DESCRIPTION

[0081] The technical solutions of the present application are further illustrated by the specific embodiments in combination with the accompanying drawings. However, the following examples are only simple examples of the present application, and do not represent or limit the protection scope of the present application, and the protection scope of the present application is subject to the claims.

[0082] The fly ash used in the following examples is from the fly ash provided by Xi'an thermal power plant

[0083] Embodiment 1

[0084] The present embodiment provides a preparation method of nano-silicon carbide whisker, which comprises the following steps:

[0085] (1) The fly ash is mixed with 1 mol / L hydrochloric acid solution according to the liquid-solid ratio of 5L / kg, and is treated by acid method at 60℃ for 1.5h, so that the contents of iron element, magnesium element and calcium element in the fly ash are about 5%, 1% and 1% respectively, to obtain the acid-treated fly ash;

[0086] (2) The acid-treated fly ash is uniformly mixed with carbon black according to the mass ratio of 1:0.1 to obtain a mixture;

[0087] (3) The mixture is placed in a crucible, carbon black is covered on the mixture, the thickness of the carbon black is 100% of the thickness of the mixture, and the mixture is calcined in a hydrogen atmosphere with a gas flow rate of 0.15L / min for 3h, the calcination temperature is 1500℃, to obtain a calcined material, the calcined material includes the upper layer of crude nano-silicon carbide whisker and the lower layer of total impurity layer, the upper layer material and the lower layer material in the calcined material are stripped to obtain the crude nano-silicon carbide whisker;

[0088] (4) the crude nanometer silicon carbide whisker is calcined at 800 DEG C for 3h to remove residual carbon black, the carbon-removed product is mixed with a hydrofluoric acid solution with a concentration of 11.2 mol / L according to a liquid-solid ratio of 20L / kg, and acid etching is performed at a temperature of 30 DEG C for 1.5h to obtain the nanometer silicon carbide whisker.

[0089] The actual sample diagram of the nanometer silicon carbide whisker prepared in the embodiment is shown in FIG. 2. Figure 1 As shown in the diagram, the nanometer silicon carbide whisker prepared by the preparation process adopted in the embodiment is white in macroscopic view, and there is no related paper or patent reporting the synthesis of white silicon carbide whisker at present.

[0090] The XRD diagram of the nanometer silicon carbide whisker prepared in the embodiment is shown in FIG. 3. Figure 2 As shown in the diagram, compared with the standard peak diagram (JCPDS 29-1129), the sample presents five typical peaks at 35.6°, 41.4°, 60.0°, 71.8° and 75.5°, which correspond to the

[111] ,

[200] ,

[220] ,

[311] and

[222] β-SiC crystal faces respectively.

[0091] The SEM diagram of the nanometer silicon carbide whisker prepared in the embodiment is shown in FIG. 4. Figure 3 As shown in the diagram, the nanometer silicon carbide whisker obtained in the embodiment has good fiber morphology, long length and small diameter.

[0092] Embodiment 2

[0093] The embodiment provides a preparation method of nanometer silicon carbide whisker, and the preparation method comprises the following steps:

[0094] (1) fly ash is mixed with a phosphoric acid solution with a concentration of 0.5 mol / L according to a liquid-solid ratio of 3L / kg, and acid treatment is performed at 30 DEG C for 2h, so that the contents of iron element, magnesium element and calcium element in the fly ash are about 5%, 1% and 3% respectively, to obtain acid-treated fly ash;

[0095] (2) the acid-treated fly ash is uniformly mixed with carbon black according to a mass ratio of 1:0.05 to obtain a mixture;

[0096] (3) the mixture is placed in a crucible, carbon black is covered on the mixture, the thickness of the carbon black is 70% of the thickness of the mixture, calcination is performed in a methane atmosphere with a gas flow rate of 1L / min for 7h, the calcination temperature is 1200 DEG C, to obtain calcined material, the calcined material comprises upper crude nanometer silicon carbide whisker and lower total impurity layer, the upper material is stripped from the lower material to obtain the crude nanometer silicon carbide whisker;

[0097] (4) The crude nanometer silicon carbide whisker is calcined at 500°C for 2h to remove residual carbon black, and the carbon-removed product is mixed with a hydrofluoric acid solution with a concentration of 8mol / L at a solid-liquid ratio of 10L / kg, and acid etching is performed at 50°C for 1h to obtain the nanometer silicon carbide whisker.

[0098] Example 3

[0099] The embodiment provides a preparation method of a nanometer silicon carbide whisker, and the preparation method comprises the following steps:

[0100] (1) Fly ash is mixed with a nitric acid solution with a concentration of 3mol / L at a liquid-solid ratio of 8L / kg, and acid treatment is performed at 50°C for 4h, so that the contents of iron elements, magnesium elements and calcium elements in the fly ash are about 5%, 1% and 1% respectively, to obtain acid-treated fly ash;

[0101] (2) The acid-treated fly ash is uniformly mixed with carbon black at a mass ratio of 1:0.2 to obtain a mixture;

[0102] (3) The mixture is placed in a crucible, graphene is covered on the mixture, the thickness of the graphene is 100% of the thickness of the mixture, and the mixture is calcined in an ethane atmosphere with a gas flow rate of 8L / min for 5h at a calcination temperature of 1400°C to obtain a calcined material, the calcined material comprises upper crude nanometer silicon carbide whiskers and a lower total impurity layer, and the upper material and the lower material in the calcined material are stripped to obtain the crude nanometer silicon carbide whisker;

[0103] (4) The crude nanometer silicon carbide whisker is calcined at 700°C for 4h to remove residual graphene, and the carbon-removed product is mixed with a hydrofluoric acid solution with a concentration of 12mol / L at a solid-liquid ratio of 40L / kg, and acid etching is performed at 40°C for 4h to obtain the nanometer silicon carbide whisker.

[0104] Example 4

[0105] The embodiment provides a preparation method of a nanometer silicon carbide whisker, and the preparation method comprises the following steps:

[0106] (1) Fly ash is mixed with a sulfuric acid solution with a concentration of 1mol / L at a liquid-solid ratio of 7L / kg, and acid treatment is performed at 40°C for 3h, so that the contents of iron elements, magnesium elements and calcium elements in the fly ash are about 5%, 1% and 3% respectively, to obtain acid-treated fly ash;

[0107] (2) The acid-treated fly ash is uniformly mixed with carbon black at a mass ratio of 1:0.15 to obtain a mixture;

[0108] (3) Put the mixture into a crucible, cover the mixture with activated carbon, the thickness of the activated carbon is 90% of the thickness of the mixture, and bake the mixture in an acetylene atmosphere with a gas flow rate of 6 L / min for 4 h at a baking temperature of 1600℃ to obtain a baked material, the baked material includes an upper layer of crude nano silicon carbide whiskers and a lower layer of a total impurity layer, and the upper layer of the baked material is separated from the lower layer to obtain the crude nano silicon carbide whiskers;

[0109] (4) The crude nano silicon carbide whiskers are calcined at 800℃ for 3 h to remove residual activated carbon, and the carbon-removed product is mixed with a hydrofluoric acid solution with a concentration of 10 mol / L at a solid-liquid ratio of 25 L / kg, and acid etched at a temperature of 50℃ for 2 h to obtain the nano silicon carbide whiskers.

[0110] Example 5

[0111] The present embodiment provides a preparation method of nano silicon carbide whiskers, wherein the temperature of the reaction of the fly ash and the hydrochloric acid solution in step (1) is changed to 20℃, and the other conditions are the same as those in Example 1.

[0112] Example 6

[0113] The present embodiment provides a preparation method of nano silicon carbide whiskers, wherein the temperature of the reaction of the fly ash and the hydrochloric acid solution in step (1) is changed to 70℃, and the other conditions are the same as those in Example 1.

[0114] Example 7

[0115] The present embodiment provides a preparation method of nano silicon carbide whiskers, wherein the concentration of the hydrochloric acid solution in step (1) is changed to 0.1 mol / L, and the other conditions are the same as those in Example 1.

[0116] Example 8

[0117] The present embodiment provides a preparation method of nano silicon carbide whiskers, wherein the concentration of the hydrochloric acid solution in step (1) is changed to 6 mol / L, and the other conditions are the same as those in Example 1.

[0118] Example 9

[0119] The present embodiment provides a preparation method of nano silicon carbide whiskers, wherein the mass ratio of the purified fly ash to the carbon black in step (1) is changed to 1:0.01, and the other conditions are the same as those in Example 1.

[0120] Example 10

[0121] The present example provides a preparation method of nano silicon carbide whiskers, wherein the mass ratio of the purified fly ash to carbon black in step (1) is changed to 1:0.25, and the other conditions are the same as those in Example 1.

[0122] Example 11

[0123] The present example provides a preparation method of nano silicon carbide whiskers, wherein the mass ratio of the purified fly ash to carbon black in step (1) is changed to 1:0.005, and the other conditions are the same as those in Example 1.

[0124] Example 12

[0125] The present example provides a preparation method of nano silicon carbide whiskers, wherein the mass ratio of the purified fly ash to carbon black in step (1) is changed to 1:0.35, and the other conditions are the same as those in Example 1.

[0126] Example 13

[0127] The present example provides a preparation method of nano silicon carbide whiskers, wherein the thickness of the carbon black in step (2) is changed to 10% of the thickness of the mixture, and the other conditions are the same as those in Example 1.

[0128] Example 14

[0129] The present example provides a preparation method of nano silicon carbide whiskers, wherein the thickness of the carbon black in step (2) is changed to 200% of the thickness of the mixture, and the other conditions are the same as those in Example 1.

[0130] Example 15

[0131] The present example provides a preparation method of nano silicon carbide whiskers, wherein the thickness of the carbon black in step (2) is changed to 5% of the thickness of the mixture, and the other conditions are the same as those in Example 1.

[0132] Example 16

[0133] The present example provides a preparation method of nano silicon carbide whiskers, wherein the thickness of the carbon black in step (2) is changed to 210% of the thickness of the mixture, and the other conditions are the same as those in Example 1.

[0134] Example 17

[0135] The present example provides a preparation method of nano silicon carbide whiskers, wherein the gas flow rate in step (2) is changed to 0.1 L / min, and the other conditions are the same as those in Example 1.

[0136] Example 18

[0137] The present example provides a preparation method of nano silicon carbide whiskers, wherein the gas flow rate in step (2) is changed to 10 L / min, and the other conditions are the same as those in Example 1.

[0138] Example 19

[0139] The present example provides a preparation method of nano silicon carbide whiskers, wherein the gas flow rate in step (2) is changed to 0.05 L / min, and the other conditions are the same as those in Example 1.

[0140] Example 20

[0141] The present example provides a preparation method of nano silicon carbide whiskers, wherein the gas flow rate in step (2) is changed to 12 L / min, and the other conditions are the same as those in Example 1.

[0142] Example 21

[0143] The present example provides a preparation method of nano silicon carbide whiskers, wherein the calcination process for removing residual carbon black in step (4) is omitted, and the other conditions are the same as those in Example 1.

[0144] Example 22

[0145] The present example provides a preparation method of nano silicon carbide whiskers, wherein the acid etching process using hydrofluoric acid solution in step (4) is omitted, and the other conditions are the same as those in Example 1.

[0146] Comparative Example 1

[0147] The present comparative example provides a preparation method of nano silicon carbide whiskers, wherein the acid treatment in step (1) is omitted, and the fly ash raw material is directly mixed with carbon black, and the other conditions are the same as those in Example 1.

[0148] The SEM image of the nano silicon carbide whiskers prepared in the present comparative example is shown in FIG. 1. Figure 4 As can be seen from the figure, the nano silicon carbide whiskers obtained in the present comparative example are similar to those in the examples, but many silicon carbide particles are produced, resulting in a significant reduction in the yield of nano silicon carbide whiskers.

[0149] Comparative Example 2

[0150] The present comparative example provides a preparation method of nano silicon carbide whiskers, wherein the fly ash is mixed with an 8 mol / L hydrochloric acid solution according to a liquid-solid ratio of 20 L / kg, and is subjected to acid treatment at 90°C for 6 h, so that the contents of calcium, magnesium, and iron in the fly ash are all <1%, and the other conditions are the same as those in Example 1.

[0151] The SEM image of the nanometer silicon carbide whisker prepared in the present comparative example is shown in Figure 5 As shown in the figure, the fiber size of the nanometer silicon carbide whisker obtained in the present comparative example is not uniform, a large amount of silicon carbide particles are produced, and the yield of the nanometer silicon carbide whisker is reduced.

[0152] Comparative Example 3

[0153] The present comparative example provides a preparation method of nanometer silicon carbide whisker, wherein the preparation method does not cover carbon black on the mixture, but directly mixes the carbon black with the mixture, and the rest of the conditions are the same as those in Example 1.

[0154] The SEM image of the product prepared in the present comparative example is shown in Figure 6 As shown in the figure, the product obtained in the present comparative example is silicon carbide in the form of worms, not straight crystals, the surface is rough, and is mixed with impurities, which is difficult to separate effectively.

[0155] Comparative Example 4

[0156] The present comparative example provides a preparation method of nanometer silicon carbide whisker, wherein the preparation method replaces the hydrogen atmosphere in step (2) with an argon atmosphere, and the rest of the conditions are the same as those in Example 1.

[0157] The SEM image of the product prepared in the present comparative example is shown in Figure 7 As shown in the figure, the product obtained in the present comparative example is silicon carbide particles, and no whisker is produced.

[0158] The morphology, purity and yield of the samples prepared in all of Examples 1-22 and Comparative Examples 1-4 are analyzed, wherein the yield of the obtained sample = (the mass of the actually obtained nanometer silicon carbide whisker / the mass of the theoretically obtained nanometer silicon carbide whisker) x 100%, and the results are shown in Table 1:

[0159] Table 1

[0160]

[0161]

[0162] It can be seen from the test results that:

[0163] (1) It can be seen from Examples 1 to 4 that the present application uses low-cost fly ash as raw material, and through the synergistic effect of moderate acid treatment, the setting of the raw material placement position and the roasting under the reducing atmosphere, the slow release and adsorption of silicon monoxide gas are effectively controlled, the microenvironment of the coexistence of silicon monoxide gas and reducing gas is formed in the upper carbon source, and the conditions suitable for the growth of nanometer silicon carbide whisker are created, so as to be able to take into account the advantages of low preparation cost and high product yield, and to ensure good morphology and high purity of the nanometer silicon carbide whisker.

[0164] (2) Through the comparison of Example 1 and Examples 5-6, it can be seen that in the present application, if the acid treatment temperature is too low, the impurity leaching rate is too slow, and the impurity leaching rate is too low, which cannot achieve the purpose of moderate impurity removal, thereby resulting in a decrease in the yield of the obtained nanometer silicon carbide whiskers; if the acid treatment temperature is too high, the impurity leaching rate is too high, which will result in too small amount of low-melting-point phases in the reaction system, and too small amount of liquid phases generated in the carbothermal reduction reaction process, which is not conducive to the regulation of the concentration of silicon monoxide in the reaction system, and the product yield is decreased, and it is difficult to generate nanometer silicon carbide whiskers with large aspect ratio and good morphology.

[0165] (3) Through the comparison of Example 1 and Examples 7-8, it can be seen that in the present application, if the acid concentration is too low, the impurity leaching amount is too small, which cannot achieve the purpose of moderate impurity removal, and the product yield is decreased; if the acid concentration is too high, the impurity leaching amount is too much, and the amount of liquid phases generated in the reaction system is too small, which results in a decrease in the product yield, and at the same time, the aspect ratio of the obtained product is low and the morphology is poor.

[0166] (4) Through the comparison of Example 1 and Examples 9-12, it can be seen that in the present application, if the mass ratio of fly ash to the first carbon source is too large, the amount of the first carbon source is insufficient, and the silicon dioxide in the fly ash cannot be fully converted into silicon monoxide, which results in a decrease in the content and yield of the generated nanometer silicon carbide whiskers; if the mass ratio of fly ash to the first carbon source is too small, the amount of the first carbon source is excessive, which will result in that the generated silicon monoxide gas in the mixture is easy to contact with the excessive first carbon source to generate silicon carbide in situ, and the silicon carbide is mixed with the remaining impurity phases in the fly ash, which is difficult to separate, and high-purity nanometer silicon carbide whiskers cannot be obtained, and a large amount of consumed silicon monoxide gas makes the yield of the finally obtained nanometer silicon carbide whiskers decrease.

[0167] (5) Through the comparison of Example 1 and Examples 13-16, it can be seen that if the thickness of the second carbon source covered on the mixture is too thin, it cannot provide enough gaseous second carbon source, and the silicon monoxide gas is easy to escape and cannot generate silicon carbide whiskers at a suitable position; if the thickness of the second carbon source is too thick, the amount of gaseous second carbon source generated in the reaction is too much, and the concentration is too high, which destroys the growth conditions of the whiskers, and at the same time, the excessive second carbon source also increases the cost.

[0168] (6) Through the comparison of Example 1 and Examples 17-20, it can be seen that in the present application, if the flow rate of the reducing gas in the reducing atmosphere is too low, the amount of reducing gas in the system is too small, and the reaction rate is too low, and further, when the flow rate of the reducing gas is too low, the concentration of silicon monoxide gas is relatively high, which is not conducive to the generation of whiskers, and particles are more likely to be generated, thereby resulting in a decrease in the purity and yield of the generated nanometer silicon carbide whiskers; if the gas flow rate is too high, the concentration and partial pressure of the reducing gas are too high, which will destroy the growth environment of the nanometer silicon carbide whiskers, and even the whiskers cannot be generated, resulting in a decrease in the yield of the nanometer silicon carbide whiskers.

[0169] (8) Through the comparison of Example 1 and Examples 21-22, it can be seen that, in the present application, if the calcination process for removing the carbon source is not used, the purity of the obtained nanometer silicon carbide whiskers is reduced; if the acid etching process is not used, a small amount of silicon dioxide exists on the surface of the nanometer silicon carbide, so that the purity of the obtained nanometer silicon carbide whiskers is low.

[0170] (9) Through the comparison of Example 1 and Comparative Examples 1-2, it can be seen that, in the present application, by acid treatment of the fly ash raw material, part of the impurities in the system is moderately reserved, so that the reaction system contains an appropriate amount of liquid phase, thereby playing a role of adsorbing and slowly releasing silicon monoxide, and promoting the growth of nanometer silicon carbide whiskers. When the fly ash is not subjected to acid treatment, the purpose of moderate impurity removal cannot be achieved, so that the yield of the prepared nanometer silicon carbide whiskers is low (as shown in Figure 4 ). If the acid treatment is excessive, the liquid phase is too small, which will affect the release of silicon monoxide gas, and it is difficult to obtain nanometer silicon carbide whiskers with a large aspect ratio and good morphology (as shown in Figure 5 ).

[0171] (10) Through the comparison of Example 1 and Comparative Example 3, it can be seen that, in the present application, if no carbon source is covered on the mixture, the silicon monoxide gas generated in the mixture will contact with the carbon source to generate in situ worm-like silicon carbide (as shown in Figure 6 ), the whisker is curved and the surface is rough, and the silicon carbide is mixed with the remaining impurities in the fly ash, which is difficult to separate, and high-purity nanometer silicon carbide whiskers cannot be obtained.

[0172] (11) Through the comparison of Example 1 and Comparative Example 4, it can be seen that, in the present application, if other non-reducing atmospheres or atmospheres without carbon source are used, the microenvironment of coexistence of silicon monoxide gas and reducing gas cannot be formed, and nanometer silicon carbide whiskers cannot be formed, and the product is granular silicon carbide (as shown in Figure 7 ).

[0173] In summary, in the present application, low-cost fly ash is used as raw material, and through the synergistic effect of moderate acid treatment, the setting of the raw material placement position and the calcination under reducing atmosphere, the slow release and adsorption of silicon monoxide gas are effectively controlled, the microenvironment of coexistence of silicon monoxide gas and reducing gas is formed in the upper carbon source, and the conditions suitable for the growth of nanometer silicon carbide whiskers are created, so that the advantages of low preparation cost can be taken into account, and the good morphology and high purity of the nanometer silicon carbide whiskers are ensured.

[0174] The applicant states that the above description is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and it should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the present application can be easily thought out by those skilled in the art, and all of them fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for producing nanometer-sized silicon carbide whiskers, characterized by, The preparation method comprises: (1) using an acid liquid to perform acid treatment on fly ash, so that the content of key impurity elements in the fly ash accounts for 2-11% of the total mass of the treated fly ash, to obtain acid-treated fly ash; wherein the key impurity elements include iron elements, magnesium elements and calcium elements; (2) mixing the acid-treated fly ash with a first carbon source to obtain a mixture; (3) covering a second carbon source on the mixture, and performing roasting under a reducing atmosphere to obtain a roasted material, wherein the roasted material comprises a nano-silicon carbide whisker layer and a total impurity layer located below the silicon carbide whisker layer, and the total impurity layer is removed to obtain the nano-silicon carbide whisker.

2. The production method according to claim 1, characterized by, The acid liquid in step (1) comprises any one or a combination of at least two of a sulfuric acid solution, a hydrochloric acid solution, a nitric acid solution or a phosphoric acid solution; Preferably, the concentration of the acid liquid in step (1) is 0.2-5.0 mol / L; Preferably, the temperature of the acid treatment in step (1) is 30-60℃; Preferably, the time of the acid treatment in step (1) is 0.5-5h; Preferably, the liquid-solid ratio of the acid liquid to fly ash in step (1) is 3-10 L / kg; Preferably, the content of the iron elements in the acid-treated fly ash accounts for 1-5% of the total mass of the acid-treated fly ash; Preferably, the content of the magnesium elements in the acid-treated fly ash accounts for 0.5-3% of the total mass of the acid-treated fly ash; Preferably, the content of the calcium elements in the acid-treated fly ash accounts for 0.5-3% of the total mass of the acid-treated fly ash.

3. The production method according to claim 1 or 2, characterized by, The mass ratio of the fly ash to the first carbon source in step (2) is 1:(0.01-0.30), preferably 1:(0.05-0.20); Preferably, the first carbon source in step (2) and the second carbon source in step (3) independently comprise any one or a combination of at least two of activated carbon, carbon black, graphene or carbon nanotubes, and are further preferably carbon black.

4. The production method according to any one of claims 1 to 3, characterized by, The thickness of the second carbon source in step (3) is 10-200% of the thickness of the mixture, preferably 50-100%; Preferably, the reducing atmosphere in step (3) is any one or a combination of at least two of hydrogen, methane, ethane or acetylene; Preferably, the flow rate of the reducing gas in the reducing atmosphere in step (3) is 0.1-10.0 L / min.

5. The method of any one of claims 1-4, wherein, The roasting temperature in step (3) is 1100-1900℃, preferably 1200-1600℃; Preferably, the roasting time in step (3) is 0.5-8h, preferably 1-5h; Preferably, the way of removing the total impurity layer in step (3) comprises peeling.

6. The method of any one of claims 1-5, wherein, The step (3) further comprises step (4): performing carbon removal treatment on the nano-silicon carbide whisker; Preferably, the way of the carbon removal treatment is calcination; Preferably, the temperature of the carbon removal treatment is 500-950℃; Preferably, the time of the carbon removal treatment is 0.5-5.0h.

7. The production method according to claim 6, characterized by, The step (4) further comprises performing acid etching on the product after the carbon removal treatment; Preferably, the acid liquid used in the acid etching comprises a hydrofluoric acid solution. Preferably, the concentration of the hydrofluoric acid solution is 4.5-22.5 mol / L, further preferably 8.0-15.0 mol / L; Preferably, the liquid-solid ratio of the hydrofluoric acid solution to the product after the carbon removal treatment is 5-50 L / kg; Preferably, the temperature of the acid etching is 20-80℃; Preferably, the time of the acid etching is 0.5-5h.

8. The method of any one of claims 1-7, wherein, The preparation method comprises the following steps: (1) mixing fly ash with acid solution according to a liquid-solid ratio of 3-10 L / kg, and acid-treating at 30-60℃ for 0.5-5h to make the content of key impurity elements in the fly ash account for 2-11% of the total mass of the treated fly ash, thereby obtaining acid-treated fly ash; wherein the key impurity elements include iron element, magnesium element and calcium element, the content of the iron element accounts for 1-5% of the total mass of the acid-treated fly ash, the content of the magnesium element accounts for 0.5-3% of the total mass of the acid-treated fly ash, and the content of the calcium element accounts for 0.5-3% of the total mass of the acid-treated fly ash; the acid solution includes any one or a combination of at least two of sulfuric acid solution, hydrochloric acid solution, nitric acid solution or phosphoric acid solution, and the concentration of the acid solution is 0.2-5.0 mol / L; (2) mixing the acid-treated fly ash with a first carbon source according to a mass ratio of 1:(0.01-0.30) to obtain a mixture; (3) covering a second carbon source on the mixture, the thickness of the second carbon source being 10-200% of the thickness of the mixture, and performing roasting under a reducing atmosphere with a gas flow rate of 0.1-10.0 L / min, the roasting temperature being 1100-1900℃ and the roasting time being 0.5-8h, thereby obtaining a roasted material, the roasted material including upper layer material and lower layer material, and stripping the upper layer material from the lower layer material to obtain crude nano silicon carbide whiskers and a total impurity layer; wherein the first carbon source in step (2) and the second carbon source in step (3) independently include any one or a combination of at least two of activated carbon, carbon black, graphene or carbon nanotube, further preferably carbon black; and the reducing atmosphere in step (3) is any one or a combination of at least two of hydrogen, methane, ethane or acetylene; (4) calcining the crude nano silicon carbide whiskers at 500-950℃ for 0.5-5.0h to remove residual carbon source, mixing the product after the carbon removal treatment with a hydrofluoric acid solution with a concentration of 4.5-22.5 mol / L according to a liquid-solid ratio of 5-50 L / kg, and performing acid etching at a temperature of 20-80℃ for 0.5-5h, thereby obtaining the nano silicon carbide whiskers.

9. Nano silicon carbide whiskers prepared by the preparation method according to any one of claims 1-8.

10. The nano-sized silicon carbide whisker according to claim 9, wherein The average diameter of the nano silicon carbide whiskers is 50-150 nm; Preferably, the average length of the nano silicon carbide whiskers is 5-50 μm; Preferably, the average length-diameter ratio of the nano silicon carbide whiskers is (30-1000):1; Preferably, the nano silicon carbide whiskers are white powder.

Images