Method for preparing SiC-based porous material from balsa wood and lignite

Abstract

The invention relates to a method for preparing a SiC-based porous material, in particular to a method for preparing a SiC-based porous material from balsa wood and lignite. The invention aims to solve the problems that the existing SiC-based porous material is high in preparation cost and difficult to prepare, and the functions of high heat insulation, high wave absorption and electromagnetic protection are difficult to consider at the same time, and the problem of low utilization rate of lignite is solved. The preparation method comprises the following steps: 1, carrying out ball-milling mixing and sieving treatment on the lignite, the adhesive, the dispersing agent and the deionized water; secondly, the blocky balsa wood is placed in the mixed slurry and subjected to vacuum impregnation; 3, freeze drying and carbonization; and 4, carbon thermal reduction. The method is used for preparing the SiC-based porous material from the balsa wood and the lignite.

Description

Technical Field

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

[0002] With the widespread use of electromagnetic waves in radar systems, large aircraft and weapons and equipment in modern military face the threat of exposure. Therefore, the development of materials that can absorb radar waves and have lightweight and thermal insulation properties has become the key and has important research significance. Silicon carbide (SiC) has broad prospects in the field of lightweight, broadband, high-temperature resistant absorbing materials due to its low density, excellent thermal stability, high mechanical strength, anti-oxidation and corrosion resistance, and excellent electromagnetic wave absorption performance. It is especially suitable for complex environments, but the existing SiC-based porous materials have high preparation costs and difficulties, and it is difficult to take into account high thermal insulation, high wave absorption and electromagnetic protection functions at the same time. As a low-rank coal, lignite is abundant in resources but has low utilization rate, which has an impact on the environment. Summary of the invention

[0003] The present invention aims to solve the problems of high preparation cost and difficulty in preparation of existing SiC-based porous materials, and difficulty in taking into account high thermal insulation, high wave absorption and electromagnetic protection functions at the same time, and to solve the problem of low utilization rate of lignite, and provide a method for preparing SiC-based porous materials using balsa wood and lignite.

[0004] A method for preparing a SiC-based porous material using balsa wood and lignite is completed by the following steps:

[0005] 1. The lignite, adhesive, dispersant and deionized water are ball-milled, mixed and sieved, and finally degassed under vacuum conditions to obtain a mixed slurry;

[0006] 2. placing block balsa wood in the mixed slurry and vacuum impregnating it to obtain a balsa wood and lignite mixture;

[0007] 3. freeze-drying the balsa wood-lignite mixture, and then carbonizing it in an argon atmosphere at a temperature of 600° C. to 800° C. to obtain a carbonized balsa wood-lignite mixture;

[0008] 4. Using the carbonized balsa wood and lignite mixture as the carbon source and the mixture of silicon and silicon dioxide as the silicon source, the silicon source is laid on the bottom of the graphite crucible, and then the carbon source is placed on the silicon source, and a carbon thermal reduction reaction is carried out in an argon atmosphere at a temperature of 1250°C to 1600°C, thereby completing the method for preparing SiC-based porous materials using balsa wood and lignite.

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

[0010] First, balsa wood is abundant in source, grows fast, is light in weight, has 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 if it is carbonized at high temperature under an inert atmosphere, the inherent wood structure can still be retained. The porous structure helps to enhance the impedance matching between electromagnetic waves and materials and the multiple reflections of electromagnetic waves inside the material, that is, it can enhance the material's ability to absorb electromagnetic waves.

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

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

[0013] Fourth, the SiC-based porous material prepared by the present 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. The SiC-based porous material is mixed with paraffin in a mass ratio of 3:7. When the thickness is 0.3mm, the effective wave absorption frequency band is 7.57GHz to 14.6GHz, and the minimum reflection loss is -56.8226dB.

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

[0015] That is, the SiC-based porous material prepared by the present invention has high thermal insulation, high wave absorption and electromagnetic protection functions at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0017] Figure 2 This is a scanning electron microscope image of the SiC-based porous material prepared in Example 1;

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

[0019] Figure 4 This is a diagram of the wave absorption performance of the SiC-based porous material prepared in Example 1. DETAILED DESCRIPTION

[0020] Specific implementation method 1: This implementation method is a method for preparing SiC-based porous materials using balsa wood and lignite, which is completed in the following steps:

[0021] 1. The lignite, adhesive, dispersant and deionized water are ball-milled, mixed and sieved, and finally degassed under vacuum conditions to obtain a mixed slurry;

[0022] 2. placing block balsa wood in the mixed slurry and vacuum impregnating it to obtain a balsa wood and lignite mixture;

[0023] 3. freeze-drying the balsa wood-lignite mixture, and then carbonizing it in 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 and lignite mixture as the carbon source and the mixture of silicon and silicon dioxide as the silicon source, the silicon source is laid on the bottom of the graphite crucible, and then the carbon source is placed on the silicon source, and a carbon thermal reduction reaction is carried out in an argon atmosphere at a temperature of 1250°C to 1600°C, thereby completing the method for preparing SiC-based porous materials using balsa wood and lignite.

[0025] Principle: This specific implementation adopts a new carbon source and a silicon source to form a dual carbon source reaction system. The lignite is filled into the pores of balsa wood by vacuum impregnation. The reaction of the carbon source and the silicon source is regulated by freeze drying, high temperature carbonization and carbon thermal reduction to prepare SiC with a developed three-dimensional interconnected porous structure. The SiC inherits the porous structure of balsa wood very well, and forms a unique morphology of SiC nanowires filling a three-dimensional interconnected porous structure. This unique structural feature contributes to the multiple reflection-absorption of electromagnetic waves inside the material.

[0026] This specific implementation method uses biomass as a carbon source as the SiC ceramic matrix, which gives new value to wood, broadens its application field, conforms to the concept of environmental protection, and has market prospects. Its three-dimensional porous structure not only improves the microwave scattering and absorption capabilities, but also has a good thermal insulation effect. 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, which is conducive to energy diversification and sustainable development.

[0027] The beneficial effects of this embodiment are:

[0028] First, balsa wood is abundant in source, grows fast, is light in weight, has 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 if it is carbonized at high temperature under an inert atmosphere, the inherent wood structure can still be retained. The porous structure helps to enhance the impedance matching between electromagnetic waves and materials and the multiple reflections of electromagnetic waves inside the material, that is, it can enhance the material's ability to absorb electromagnetic waves.

[0029] 2. Lignite is an organic material containing oxygen and carbon, which has a high carbon content and a low ash content. This embodiment uses cheap and abundant lignite as one of the components of the carbon source to react with a silicon source to prepare a SiC-based porous material, which efficiently utilizes lignite, a cheap coal resource, reduces the cost of raw materials, and solves the problem of low lignite utilization.

[0030] 3. This method has a simple preparation process, low raw material cost, is suitable for large-scale production, improves the comprehensive utilization efficiency of balsa wood and lignite resources, and reduces environmental pollution.

[0031] 4. 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. The SiC-based porous material is mixed with paraffin in a mass ratio of 3:7. When the thickness is 0.3mm, the effective wave absorption frequency band is 7.57GHz to 14.6GHz, and the minimum reflection loss is -56.8226dB.

[0032] 5. The SiC-based porous material prepared in this embodiment has good thermal insulation performance, and the thermal conductivity of the SiC-based porous material is 0.062 W / (m·K).

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

[0034] Specific embodiment 2: This embodiment is different from specific embodiment 1 in that: the lignite described in step 1 is lignite from Zhalainuoer, Inner Mongolia; the adhesive described in step 1 is one or a combination of sodium carboxymethyl cellulose, polyvinyl alcohol and phenolic resin; the dispersant described in step 1 is a mixture of tetramethylammonium hydroxide and polyvinyl pyrrolidone, and the mass ratio of tetramethylammonium hydroxide to polyvinyl pyrrolidone is 1:(1-10). The rest is the same as specific embodiment 1.

[0035] Specific implementation method 3: This implementation method is different from specific implementation method 1 or 2 in that: the mass ratio of the adhesive to lignite in step 1 is 1:(10-30); the mass ratio of the adhesive to dispersant in step 1 is 1:(1-10); the mass ratio of the adhesive to deionized water in step 1 is 1:(30-50). Others are the same as specific implementation method 1 or 2.

[0036] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that: the ball milling mixing in step 1 is specifically carried out at a rotation speed of 150 rpm to 500 rpm for 2 h to 10 h; the sieving treatment in step 1 is carried out through a sieve of 800 mesh to 1200 mesh. The rest is the same as specific embodiments 1 to 3.

[0037] Specific implementation method 5: This implementation method is different from specific implementation methods 1 to 4 in that: the block balsa wood in step 2 is basalt balsa wood chips with a thickness of 4 mm to 6 mm; the mass ratio of the block balsa wood in step 2 to the mixed slurry is 1:(1 to 10). Other aspects are the same as specific implementation methods 1 to 4.

[0038] Specific embodiment 6: This embodiment is different from specific embodiments 1 to 5 in that the vacuum impregnation described in step 2 is carried out at room temperature and a pressure of -0.1 MPa to -0.5 MPa for 10 to 12 hours. The rest is the same as specific embodiments 1 to 5.

[0039] Specific embodiment 7: This embodiment differs from Specific embodiments 1 to 6 in that the freeze drying in step 3 is performed at a temperature of -60°C to -80°C for 5h to 12h. The rest is the same as Specific embodiments 1 to 6.

[0040] Specific embodiment eight: This embodiment differs from specific embodiments one to seven in that: in step three, under an argon atmosphere, the temperature is first raised to 300°C to 500°C at a heating rate of 3°C / min to 5°C / min, then raised to 600°C to 800°C at a heating rate of 1°C / min to 3.5°C / min, then carbonized for 2h to 4h under an argon atmosphere and 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. The rest is the same as specific embodiments one to seven.

[0041] Specific embodiment 9: This embodiment differs from any one of specific embodiments 1 to 8 in that the molar ratio of the carbon source to the silicon source in step 4 is 1:(4-8); the molar ratio of silicon to silicon dioxide in the mixture of silicon and silicon dioxide in step 4 is (1-10):1. The rest is the same as specific 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] 4. Using the carbonized balsa wood lignite mixture as the carbon source and the mixture of silicon and silicon dioxide as the silicon source, the silicon source is laid on the bottom of the graphite crucible, and then the carbon source is placed on the silicon source. Under an argon atmosphere, the temperature is first increased to 800°C at a heating rate of 10°C / min, then increased to 1000°C at a heating rate of 5°C / min, and then increased to 1500°C at a heating rate of 2.5°C / min. Carbothermal reduction reaction is carried out under argon atmosphere and temperature of 1500°C for 2h, and then cooled to 1000°C at a cooling rate of 2.5°C / min, then cooled to 800°C at a cooling rate of 5°C / min, and finally cooled to room temperature at a cooling rate of 10°C / min to obtain a 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 described in step one is lignite from Zhalainuoer Coal Industry in Inner Mongolia, 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 the range of 1 μm to 2 μm, and the average particle size is 1.75 μm; the average particle size of silicon described in step four is 100 nm; the average particle size of silicon dioxide described in step four is 200 nm.

[0054] The adhesive described in step one is sodium carboxymethyl cellulose; the dispersant described in step one is a mixture of tetramethylammonium hydroxide and polyvinyl pyrrolidone, and the mass ratio of the tetramethylammonium hydroxide to the polyvinyl pyrrolidone is 1:1.

[0055] The block-shaped balsa wood described in step 2 is basalt balsa wood chips, and the size is 30mm×30mm×4mm.

[0056] Figure 1 This is the XRD spectrum 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 This is a scanning electron microscope image 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 10nm and 20nm, and a large number of plush SiC nanowires appear in the SiC-based porous material. The diameter of the SiC nanowires is about tens to hundreds of nanometers, and the length is several microns to hundreds of microns, 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 are shown in Figure 2. The average pore size of the SiC-based porous material prepared in Example 1 is 14.3213 nm and the BET specific surface area is 10.3393 m 2 / g.

[0059] The SiC-based porous material and paraffin prepared in Example 1 were weighed at a mass ratio of 3:7, and then the paraffin was placed on the SiC-based porous material. In a vacuum drying and heating box, the paraffin was evacuated and heated to melt the paraffin, and the paraffin was vacuum impregnated into the SiC-based porous material, and 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 was prepared; Figure 4 This is a diagram of the wave absorption performance 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] The thermal conductivity of the SiC-based porous material prepared in Example 1 was tested to be 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 done in the following steps:

1. The lignite, adhesive, dispersant and deionized water are ball-milled, mixed and sieved, and finally degassed under vacuum conditions to obtain a mixed slurry; 2. placing block balsa wood in the mixed slurry and vacuum impregnating it to obtain a balsa wood and lignite mixture; 3. freeze-drying the balsa wood-lignite mixture, and then carbonizing it in an argon atmosphere at a temperature of 600° C. to 800° C. to obtain a carbonized balsa wood-lignite mixture; 4. Using the carbonized balsa wood and lignite mixture as the carbon source and the mixture of silicon and silicon dioxide as the silicon source, the silicon source is laid on the bottom of the graphite crucible, and then the carbon source is placed on the silicon source, and a carbon thermal reduction reaction is carried out in an argon atmosphere at a temperature of 1250°C to 1600°C, thereby completing the method for preparing SiC-based porous materials using balsa wood and lignite.

2. The method for preparing SiC-based porous material by using balsa wood and lignite according to claim 1, characterized in that The lignite described in step one is lignite from Zhalainuoer, Inner Mongolia; the adhesive described in step one is one or a combination of several of sodium carboxymethyl cellulose, polyvinyl alcohol and phenolic resin; the dispersant described in step one is a mixture of tetramethylammonium hydroxide and polyvinyl pyrrolidone, and the mass ratio of tetramethylammonium hydroxide to polyvinyl pyrrolidone is 1:(1-10).

3. The method for preparing SiC-based porous material by using balsa wood and lignite according to claim 1, characterized in that The mass ratio of the adhesive in step 1 to lignite is 1:(10-30); the mass ratio of the adhesive in step 1 to dispersant is 1:(1-10); the mass ratio of the adhesive in step 1 to deionized water is 1:(30-50).

4. The method for preparing SiC-based porous material by using balsa wood and lignite according to claim 1, characterized in that The ball milling mixing described in step 1 is specifically performed at a rotation speed of 150 rpm to 500 rpm for 2 h to 10 h; the screening treatment described in step 1 is performed through a sieve of 800 mesh to 1200 mesh.

5. The method for preparing SiC-based porous material by using balsa wood and lignite according to claim 1, characterized in that The block balsa wood described in step 2 is basalt balsa wood chips with a thickness of 4 mm to 6 mm; the mass ratio of the block balsa wood described in step 2 to the mixed slurry is 1:(1 to 10).

6. The method for preparing SiC-based porous material by using balsa wood and lignite according to claim 1, characterized in that The vacuum impregnation described in step 2 is specifically carried out at room temperature and a pressure of -0.1 MPa to -0.5 MPa for 10 to 12 hours.

7. The method for preparing SiC-based porous material by using balsa wood and lignite according to claim 1, characterized in that The freeze drying described in step 3 is specifically freeze drying at a temperature of -60°C to -80°C for 5h to 12h.

8. The method for preparing SiC-based porous material by using balsa wood and lignite according to claim 1, characterized in that In step three, under an argon atmosphere, the temperature is first increased to 300°C~500°C at a heating rate of 3°C / min~5°C / min, then increased to 600°C~800°C at a heating rate of 1°C / min~3.5°C / min, and then carbonized under an argon atmosphere and a temperature of 600°C~800°C for 2h~4h, and finally cooled to room temperature at a cooling rate of 5°C / min~10°C / min.

9. The method for preparing SiC-based porous material by using balsa wood and lignite according to claim 1, characterized in that The molar ratio of the carbon source to the silicon source in step 4 is 1:(4-8); the molar ratio of silicon to silicon dioxide in the mixture of silicon and silicon dioxide in step 4 is (1-10):

1.

10. The method for preparing SiC-based porous material by using balsa wood and lignite according to claim 1, characterized in that In step 4, under an argon atmosphere, the temperature is first increased to 800°C-900°C at a heating rate of 8°C / min-10°C / min, then increased to 1000°C-1200°C at a heating rate of 3°C / min-5°C / min, and then increased to 1250°C-1600°C at a heating rate of 2°C / min-5°C / min. Carbothermal reduction reaction is carried out under argon atmosphere and temperature of 1250°C-1600°C for 2h-4h, and then first cooled to 1000°C-1200°C at a cooling rate of 2°C / min-5°C / min, then cooled to 800°C-900°C at a cooling rate of 3°C / min-5°C / min, and finally cooled to room temperature at a cooling rate of 8°C / min-10°C / min.

Images