A method for preparing SiC-based porous materials using balsa wood and lignite

Abstract

A method for preparing SiC-based porous materials using balsa wood and lignite, which relates to a method for preparing SiC-based porous materials. The present invention aims to solve the problems of high preparation cost, difficult preparation of existing SiC-based porous materials, and the difficulty in simultaneously achieving high thermal insulation, high wave absorption, and electromagnetic protection functions, as well as the problem of low utilization rate of lignite. The preparation method is as follows: First, lignite, adhesive, dispersant, and deionized water are subjected to ball milling, mixing, and sieving. Second, block-shaped balsa wood is placed in the mixed slurry and vacuum impregnated. Third, freeze-drying and carbonization are carried out. Fourth, carbothermal reduction. The present invention is used for preparing SiC-based porous materials using balsa wood and lignite.

Description

Technical Field

[0001] The present invention relates to a method for preparing SiC-based porous materials. Background Art

[0002] With the wide application of electromagnetic waves in radar systems, large aircraft and weaponry in modern military face the threat of exposure. Therefore, developing materials that can absorb radar waves while possessing lightweight and heat insulation properties has become crucial and holds significant research significance. Silicon carbide (SiC), due to its low density, excellent thermal stability, high mechanical strength, oxidation and corrosion resistance, and outstanding electromagnetic wave absorption performance, has broad prospects particularly in the field of lightweight, broadband, and high-temperature wave-absorbing materials, especially suitable for complex environments. However, the existing SiC-based porous materials are costly to prepare, difficult to fabricate, and it is challenging to simultaneously achieve high heat insulation, high wave absorption, and electromagnetic protection functions. Lignite, as a low-rank coal, is rich in resources but has low utilization rate and impacts the environment. Summary of the Invention

[0003] The present invention aims to solve the problems of high preparation cost, difficult preparation, and the inability to simultaneously achieve high heat insulation, high wave absorption, and electromagnetic protection functions of existing SiC-based porous materials, as well as the low utilization rate of lignite, and provides a method for preparing SiC-based porous materials using balsa wood and lignite.

[0004] A method for preparing SiC-based porous materials using balsa wood and lignite is completed according to the following steps:

[0005] I. Ball-mill and screen the lignite, adhesive, dispersant, and deionized water, and finally degas under vacuum conditions to obtain a mixed slurry;

[0006] II. Immerse the block-shaped balsa wood in the mixed slurry under vacuum to obtain a balsa wood-lignite mixture;

[0007] III. Freeze-dry the balsa wood-lignite mixture, and then carbonize it under an argon atmosphere at a temperature of 600°C to 800°C to obtain a carbonized balsa wood-lignite mixture;

[0008] IV. Using the carbonized balsa wood-lignite mixture as the carbon source and a mixture of silicon and silicon dioxide as the silicon source, lay the silicon source at the bottom of a graphite crucible, then place the carbon source on the silicon source, and carry out a carbothermal reduction reaction under an argon atmosphere at a temperature of 1250°C to 1600°C, thus completing the method for preparing SiC-based porous materials using balsa wood and lignite.

[0009] The beneficial effects of the present invention are:

[0010] 1. Balsa wood is rich in sources, grows fast, has a light mass, low density, and has a fine internal structure and interconnected channels. Its natural three-dimensional network skeleton structure can be used as a template to prepare functional materials. Even when high-temperature carbonization is carried out in an inert atmosphere, the inherent wood structure can still be retained. The porous structure helps to enhance the impedance matching between electromagnetic waves and the material and the multiple reflections of electromagnetic waves inside the material, that is, it can enhance the absorption ability of the material to electromagnetic waves.

[0011] 2. Lignite is an oxygen-containing and carbon-containing organic material with a high carbon content and a low ash content. In this invention, cheap and abundant lignite is used as one of the components of the carbon source to react with the silicon source to prepare SiC-based porous materials, which efficiently utilizes this cheap coal resource of lignite, reduces the cost of raw materials, and solves the problem of low utilization rate of lignite.

[0012] 3. The preparation process of this method is simple, the raw material cost is low, it is suitable for large-scale production, improves the comprehensive utilization efficiency of balsa wood and lignite resources, and reduces environmental pollution.

[0013] 4. The SiC-based porous material prepared by this invention has the advantages of light weight, low cost, good wave absorption performance, and wide absorption frequency band. The main crystal phase of the prepared SiC-based porous material is 3C-SiC. When the SiC-based porous material is mixed with paraffin in a mass ratio of 3:7 and the thickness is 0.3 mm, the effective wave absorption frequency band is 7.57 GHz to 14.6 GHz, and the minimum reflection loss is -56.8226 dB.

[0014] 5. The SiC-based porous material prepared by this invention has good heat insulation performance, and the thermal conductivity of this SiC-based porous material is 0.062 W / (m·K).

[0015] That is, the SiC-based porous material prepared by this invention takes into account high heat insulation, high wave absorption, and electromagnetic protection functions at the same time. Description of the Drawings

[0016] Figure 1 XRD pattern of the SiC-based porous material prepared in Example 1;

[0017] Figure 2 Scanning electron micrograph of the SiC-based porous material prepared in Example 1;

[0018] Figure 3 Adsorption-desorption curve and pore size distribution curve of the SiC-based porous material prepared in Example 1;

[0019] Figure 4 Wave absorption performance diagram of the SiC-based porous material prepared in Example 1. Detailed Embodiments

[0020] Embodiment 1: A method for preparing SiC-based porous materials using balsa wood and lignite is completed according to the following steps:

[0021] 1. Ball-mill and sieve the lignite, binder, dispersant, and deionized water, and finally degas under vacuum to obtain a mixed slurry.

[0022] 2. Immerse the block of balsa wood in the mixed slurry under vacuum to obtain a balsa wood-lignite mixture.

[0023] 3. Freeze-dry the balsa wood-lignite mixture, and then carbonize it under an argon atmosphere at a temperature of 600 °C to 800 °C to obtain a carbonized balsa wood-lignite mixture.

[0024] 4. Using the carbonized balsa wood-lignite mixture as the carbon source and a mixture of silicon and silicon dioxide as the silicon source, lay the silicon source at the bottom of the graphite crucible, then place the carbon source on the silicon source, and carry out a carbothermal reduction reaction under an argon atmosphere at a temperature of 1250 °C to 1600 °C, thus completing the method for preparing SiC-based porous materials using balsa wood and lignite.

[0025] Principle: This specific embodiment uses a new combination of carbon source and silicon source to form a dual-carbon source reaction system. The lignite is impregnated under vacuum and filled in the pores of the balsa wood. Through steps such as freeze-drying, high-temperature carbonization, and carbothermal reduction, the reaction between the carbon source and the silicon source is regulated to prepare SiC with a developed three-dimensional interconnected porous structure. This SiC well inherits the porous structure of the balsa wood and forms a unique morphology with SiC nanowires filling the three-dimensional interconnected porous structure. This unique structural feature helps the multiple reflection-absorption of electromagnetic waves inside the material.

[0026] This specific embodiment uses biomass as the carbon source for the SiC ceramic matrix, endows wood with new value, broadens its application fields, conforms to the environmental protection concept, and has market prospects. Its three-dimensional porous structure not only improves the microwave scattering and absorption capabilities but also has good heat insulation effects. Applying lignite to improve biomass silicon carbide absorbing ceramics can not only promote the industrialization of materials but also enhance the application value of lignite, contributing to energy diversification and sustainable development.

[0027] The beneficial effects of this embodiment are:

[0028] 1. Balsa wood is rich in sources, grows fast, is light in weight and low in density, and has a fine internal structure and interconnected channels. Its natural three-dimensional network skeleton structure can be used as a template to prepare functional materials. Even under high-temperature carbonization in an inert atmosphere, the inherent wood structure can still be retained. The porous structure helps to enhance the impedance matching between electromagnetic waves and the material and the multiple reflections of electromagnetic waves inside the material, that is, it can enhance the absorption ability of the material to electromagnetic waves.

[0029] Second, lignite is an oxygen- and carbon-containing organic material with a relatively high carbon content and a relatively low ash content. In this embodiment, inexpensive and abundant lignite is used as one of the components of the carbon source to react with the silicon source to prepare the SiC-based porous material, which efficiently utilizes this inexpensive coal resource of lignite, reduces the cost of raw materials, and solves the problem of low utilization rate of lignite.

[0030] Third, the preparation process of this method is simple, the raw material cost is low, it is suitable for large-scale production, improves the comprehensive utilization efficiency of balsa wood and lignite resources, and reduces environmental pollution.

[0031] Fourth, the SiC-based porous material prepared in this embodiment has the advantages of light weight, low cost, good wave absorption performance, and wide absorption frequency band. The main crystal phase of the prepared SiC-based porous material is 3C-SiC. When the SiC-based porous material and paraffin are mixed at a mass ratio of 3:7 and the thickness is 0.3 mm, the effective wave absorption frequency band is 7.57 GHz to 14.6 GHz, and the minimum reflection loss is -56.8226 dB.

[0032] Fifth, the SiC-based porous material prepared in this embodiment has good heat insulation performance, and the thermal conductivity of this SiC-based porous material is 0.062 W / (m·K).

[0033] That is, the SiC-based porous material prepared in this embodiment takes into account the functions of high heat insulation, high wave absorption, and electromagnetic protection at the same time.

[0034] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that: the lignite described in Step 1 is the lignite from Zhalainuoer, Inner Mongolia; the binder described in Step 1 is one or a combination of sodium carboxymethylcellulose, polyvinyl alcohol, and phenolic resin; the dispersant described in Step 1 is a mixture of tetramethylammonium hydroxide and polyvinylpyrrolidone, and the mass ratio of the tetramethylammonium hydroxide to the polyvinylpyrrolidone is 1:(1-10). Others are the same as Specific Embodiment 1.

[0035] Specific Embodiment 3: The difference between this embodiment and one of Specific Embodiments 1 or 2 is that: the mass ratio of the binder to the lignite described in Step 1 is 1:(10-30); the mass ratio of the binder to the dispersant described in Step 1 is 1:(1-10); the mass ratio of the binder to deionized water described in Step 1 is 1:(30-50). Others are the same as Specific Embodiment 1 or 2.

[0036] Specific Embodiment 4: The difference between this embodiment and one of Specific Embodiments 1 to 3 is that: the ball milling and mixing described in Step 1 is specifically carried out under the condition of a rotation speed of 150 rpm to 500 rpm for 2 h to 10 h; the sieving treatment described in Step 1 is through a sieve mesh of 800 meshes to 1200 meshes. Others are the same as Specific Embodiments 1 to 3.

[0037] Specific Embodiment 5: The difference between this embodiment and any one of Embodiments 1 to 4 is as follows: the blocky balsa wood described in Step 2 is balsa wood chips with a thickness of 4 mm to 6 mm; the mass ratio of the blocky balsa wood to the mixed slurry described in Step 2 is 1:(1 to 10). Others are the same as those in Embodiments 1 to 4.

[0038] Specific Embodiment 6: The difference between this embodiment and any one of Embodiments 1 to 5 is as follows: the vacuum impregnation described in Step 2 is specifically carried out under the conditions of room temperature and a pressure of -0.1 MPa to -0.5 MPa for 10 h to 12 h. Others are the same as those in Embodiments 1 to 5.

[0039] Specific Embodiment 7: The difference between this embodiment and any one of Embodiments 1 to 6 is as follows: the freeze-drying described in Step 3 is specifically carried out under the conditions of a temperature of -60°C to -80°C for 5 h to 12 h. Others are the same as those in Embodiments 1 to 6.

[0040] Specific Embodiment 8: The difference between this embodiment and any one of Embodiments 1 to 7 is as follows: in an argon atmosphere in Step 3, first heat up at a heating rate of 3°C / min to 5°C / min to 300°C to 500°C, then heat up at a heating rate of 1°C / min to 3.5°C / min to 600°C to 800°C, then carbonize for 2 h to 4 h under the conditions of an argon atmosphere and a temperature of 600°C to 800°C, and finally cool down to room temperature at a cooling rate of 5°C / min to 10°C / min. Others are the same as those in Embodiments 1 to 7.

[0041] Specific Embodiment 9: The difference between this embodiment and any one of Embodiments 1 to 8 is as follows: the molar ratio of the carbon source to the silicon source in Step 4 is 1:(4 to 8); the molar ratio of silicon to silicon dioxide in the mixture of silicon and silicon dioxide in Step 4 is (1 to 10):1. Others are the same as those in Embodiments 1 to 8.

[0042] Specific embodiment ten: This embodiment differs from specific embodiments one to nine in that: in step four, under argon atmosphere, the temperature is first raised to 800°C to 900°C at a heating rate of 8°C / min to 10°C / min, then raised to 1000°C to 1200°C at a heating rate of 3°C / min to 5°C / min, then raised to 1250°C to 1600°C at a heating rate of 2°C / min to 5°C / min, and carbon thermal reduction reaction is carried out under argon atmosphere and temperature of 1250°C to 1600°C for 2h to 4h, then first lowered to 1000°C to 1200°C at a cooling rate of 2°C / min to 5°C / min, then lowered to 800°C to 900°C at a cooling rate of 3°C / min to 5°C / min, and finally lowered to room temperature at a cooling rate of 8°C / min to 10°C / min. Others are the same as specific embodiments one to nine.

[0043] The following examples are used to verify the beneficial effects of the present invention:

[0044] Embodiment 1:

[0045] A method for preparing a SiC-based porous material using balsa wood and lignite is completed by the following steps:

[0046] 1. Ball mill the lignite, adhesive, dispersant and deionized water at a rotation speed of 300 rpm for 10 h, then pass through a 800-mesh sieve, and finally degas under vacuum for 2 h to obtain a mixed slurry;

[0047] The mass ratio of the adhesive to lignite is 1:10; the mass ratio of the adhesive to dispersant is 1:1; the mass ratio of the adhesive to deionized water is 1:30;

[0048] 2. placing the block of balsa wood in the mixed slurry, and vacuum impregnating it for 12 hours at room temperature and a pressure of -0.1 MPa to obtain a balsa wood-lignite mixture;

[0049] The mass ratio of the balsa wood to the mixed pulp is 1:5;

[0050] 3. Freeze-dry the balsa wood-lignite mixture at -80°C for 12 hours, then heat it to 300°C at a heating rate of 5°C / min in an argon atmosphere, then heat it to 600°C at a heating rate of 1°C / min, then carbonize it at 600°C in an argon atmosphere for 2 hours, and finally cool it to room temperature at a cooling rate of 5°C / min to obtain a carbonized balsa wood-lignite mixture;

[0051] IV. Using the carbonized mixture of light lignite as the carbon source and the mixture of silicon and silicon dioxide as the silicon source, lay the silicon source at the bottom of the graphite crucible, then place the carbon source on the silicon source. Under an argon atmosphere, first heat it at a heating rate of 10 °C / min to 800 °C, then heat it at a heating rate of 5 °C / min to 1000 °C, and then heat it at a heating rate of 2.5 °C / min to 1500 °C. Carry out a carbothermal reduction reaction for 2 h under an argon atmosphere and at a temperature of 1500 °C. Then first cool it at a cooling rate of 2.5 °C / min to 1000 °C, then cool it at a cooling rate of 5 °C / min to 800 °C, and finally cool it at a cooling rate of 10 °C / min to room temperature to obtain the SiC-based porous material;

[0052] The molar ratio of the carbon source to the silicon source is 1:4; the molar ratio of silicon to silicon dioxide in the mixture of silicon and silicon dioxide is 1:1.

[0053] The lignite mentioned in Step I is the lignite of Inner Mongolia Zhalainuoer Coal Industry, in which the mass percentage of moisture in the lignite is 16%, the mass percentage of organic carbon in the lignite is 60%, the mass percentage of inorganic carbon in the lignite is 12%, the mass percentage of ash in the lignite is 12%, the particle size is mainly concentrated in 1 μm - 2 μm, and the average particle size is 1.75 μm; the average particle size of the silicon mentioned in Step IV is 100 nm; the average particle size of the silicon dioxide mentioned in Step IV is 200 nm.

[0054] The adhesive mentioned in Step I is sodium carboxymethyl cellulose; the dispersant mentioned in Step I is a mixture of tetramethylammonium hydroxide and polyvinylpyrrolidone, and the mass ratio of tetramethylammonium hydroxide to polyvinylpyrrolidone is 1:1.

[0055] The blocky balsa wood mentioned in Step II is balsa wood chips with a size of 30 mm × 30 mm × 4 mm.

[0056] Figure 1 It is the XRD pattern of the SiC-based porous material prepared in Example 1. As can be seen from the figure, the main crystal phase of the SiC-based porous material is 3C-SiC.

[0057] Figure 2 It is the scanning electron micrograph of the SiC-based porous material prepared in Example 1; as can be seen from the figure, the SiC-based porous material has a developed three-dimensional interconnected porous structure and very thin pore walls, the pore diameter is between 10 nm and 20 nm, and a large number of fluffy SiC nanowires appear in the SiC-based porous material. The diameter of the SiC nanowires is about dozens to hundreds of nanometers, and the length is several micrometers to hundreds of micrometers, forming a unique morphology of SiC nanowires filling the three-dimensional interconnected porous structure.

[0058] Figure 3The adsorption-desorption curve and pore size distribution curve of the SiC-based porous material prepared in Example 1; the average pore size of the SiC-based porous material prepared in Example 1 obtained by BET test is 14.3213 nm, and the BET specific surface area is 10.3393 m 2 / g.

[0059] Weigh the SiC-based porous material prepared in Example 1 and paraffin according to a mass ratio of 3:7, then place the paraffin on the SiC-based porous material, in a vacuum drying and heating oven, evacuate and heat to melt the paraffin, and the paraffin is vacuum-impregnated into the SiC-based porous material. Finally, a coaxial ring shape with a thickness of 0.3 mm, an inner diameter of 3 mm and an outer diameter of 7 mm is made; Figure 4 The wave absorption performance diagram of the SiC-based porous material prepared in Example 1. As can be seen from the figure, the SiC-based porous material exhibits excellent wave absorption performance, almost covering 7.57 GHz to 14.6 GHz, and the minimum reflection loss can reach -56.8226 dB.

[0060] After testing, the thermal conductivity of the SiC-based porous material prepared in Example 1 is 0.062 W / (m·K).

Claims

1. A method for preparing SiC-based porous materials using balsa wood and lignite, characterized in that It is completed according to the following steps: First, lignite, binder, dispersant and deionized water are ball-milled and mixed and passed through a sieve with a mesh size of 800 to 1200 meshes, and finally degassed under vacuum conditions to obtain a mixed slurry; The lignite is the lignite of Inner Mongolia Hulunbuir Coal Industry, in which the mass percentage of water in the lignite is 16%, the mass percentage of organic carbon in the lignite is 60%, the mass percentage of inorganic carbon in the lignite is 12%, the mass percentage of ash in the lignite is 12%, the particle size is mainly concentrated in 1μm to 2μm, and the average particle size is 1.75μm; The dispersant is a mixture of tetramethylammonium hydroxide and polyvinylpyrrolidone, and the mass ratio of the tetramethylammonium hydroxide to the polyvinylpyrrolidone is 1:(1 to 10); The mass ratio of the binder to the lignite is 1:(10 to 30); the mass ratio of the binder to the dispersant is 1:(1 to 10); the mass ratio of the binder to the deionized water is 1:(30 to 50); Second, the block balsa wood is placed in the mixed slurry and vacuum-impregnated for 10h to 12h at room temperature and a pressure of -0.1MPa to -0.5MPa to obtain a balsa wood-lignite mixture; The block balsa wood is balsa wood chips, with a thickness of 4mm to 6mm; the mass ratio of the block balsa wood to the mixed slurry is 1:(1 to 10); Third, under the condition of a temperature of -60°C to -80°C, the balsa wood-lignite mixture is freeze-dried for 5h to 12h, and then under an argon atmosphere, it is first heated to 300°C to 500°C at a heating rate of 3°C / min to 5°C / min, and then heated to 600°C to 800°C at a heating rate of 1°C / min to 3.5°C / min, and then carbonized for 2h to 4h under an argon atmosphere and at a temperature of 600°C to 800°C, and finally cooled to room temperature at a cooling rate of 5°C / min to 10°C / min to obtain a carbonized balsa wood-lignite mixture; Fourth, using the carbonized balsa wood-lignite mixture as a carbon source and a mixture of silicon and silicon dioxide as a silicon source, the silicon source is laid at the bottom of a graphite crucible, and then the carbon source is placed on the silicon source. Under an argon atmosphere, it is first heated to 800°C to 900°C at a heating rate of 8°C / min to 10°C / min, then heated to 1000°C to 1200°C at a heating rate of 3°C / min to 5°C / min, and then heated to 1250°C to 1600°C at a heating rate of 2°C / min to 5°C / min. Under an argon atmosphere and at a temperature of 1250°C to 1600°C, a carbothermal reduction reaction is carried out for 2h to 4h, and then it is first cooled to 1000°C to 1200°C at a cooling rate of 2°C / min to 5°C / min, then cooled to 800°C to 900°C at a cooling rate of 3°C / min to 5°C / min, and finally cooled to room temperature at a cooling rate of 8°C / min to 10°C / min, thus completing the method for preparing SiC-based porous materials using balsa wood and lignite; The average particle size of the silicon is 100nm; the average particle size of the silicon dioxide is 200nm; The molar ratio of the carbon source to the silicon source is 1:(4 - 8); the molar ratio of silicon to silicon dioxide in the mixture of silicon and silicon dioxide is (1 - 10):

1.

2. The method for preparing SiC-based porous material using balsa wood and lignite according to claim 1, wherein The adhesive described in Step 1 is one or a combination of sodium carboxymethylcellulose, polyvinyl alcohol, and phenolic resin.

3. A method for preparing SiC-based porous materials using balsa wood and lignite according to claim 1, characterized in that The ball milling and mixing in Step 1 is specifically carried out under the condition that the rotation speed is 150 rpm - 500 rpm for 2 h - 10 h.

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