Method for preparing beta-SiC containing whisker structure from rice husks

Abstract

The invention provides a method for preparing beta-SiC containing a whisker structure from rice husks, and belongs to the field of comprehensive utilization of resources and inorganic non-metallic materials. The method comprises the following steps: carbonizing rice hulls in a protective atmosphere to obtain rice hull ash, removing impurities from the rice hull ash, and fully mixing the rice hull ash with NaCl and H3BO3 to obtain a rice hull ash mixture; and putting the two groups of rice hull ash mixtures into the same atmosphere furnace, introducing shielding gas, enabling the gas to sequentially pass through the H3BO3 mixture and the NaCl mixture in sequence, heating to 1300-1600 DEG C at a heating rate of 2-10 DEG C / min, performing high-temperature treatment for 1-5 hours, washing and drying the obtained solid, and firing in air to obtain beta-SiC. The silicon carbide product with high commercial value is prepared from the cheap rice hulls, hydrofluoric acid and other high-toxicity and high-corrosivity raw materials are not needed in the preparation process, the heat treatment temperature is low, large-scale production can be easily achieved, the problems that an existing industrial carbon thermal reduction method is large in process pollution and high in energy consumption can be solved, the production cost is reduced, and the method is suitable for industrial production. And industrial popularization and application are facilitated.

Description

Technical Field

[0001] The invention belongs to the field of comprehensive resource utilization and inorganic non-metallic materials, and relates to a method for preparing beta-SiC containing a whisker structure from rice husks. Background Art

[0002] Rice husk is a byproduct of rice processing. It is rich in biomass carbon and silicon dioxide, which makes it of great utilization value. In-situ synthesis of silicon carbide using silicon dioxide and biomass carbon in rice husk can effectively utilize this agricultural byproduct.

[0003] Among various rice husk utilization methods, patent CN103803982B discloses a method for preparing porous silicon carbide stacked from rice husks. This method involves impregnating and stacking rice husks in phenolic resin and then placing them in a vacuum furnace for carbonization. The carbonized product is then mixed with silicon powder and placed in a vacuum furnace for silicification at 1420-1750°C to obtain porous silicon carbide stacked from rice husks. Patent CN106316447B discloses a method for preparing rice husk-based porous silicon carbide ceramic materials. This method involves uniformly mixing rice husks and a mixture consisting of silicon powder, a carbon source, a catalyst, and a binder to form a blank, then drying the ingredients into a ligand and placing them in a reducing atmosphere at 1300°C-1500°C to obtain a rice husk-based porous silicon carbide ceramic material. Patent CN112093801B discloses a method for preparing rice husk-based nano-silicon carbide / carbon composite materials. The method comprises mixing the carbonized rice husk obtained by carbonizing the rice husk and the nano-silicon dioxide and magnesium powder obtained by heat treatment of the rice husk in a certain proportion, and then ball milling them, and heating them to 500-1000°C under the condition of passing protective gas to obtain a rice husk-based nano-silicon carbide / carbon composite material. Patent CN106395787B discloses a method for preparing a porous silicon carbide material based on rice husk. The method comprises soaking the rice husk in a NaOH solution, adding a nickel nitrate solution, ultrasonically oscillating and heating the material, and then filtering the material to obtain a filter residue, mixing the filter residue with pectinase, adding alumina and ammonium fluoride to grind, keeping the temperature, mixing with liquid nitrogen and letting it stand, and then mixing with hydrochloric acid, filtering the filter residue, drying and crushing it to obtain a porous silicon carbide material.

[0004] In the above patents, although rice husks are used as precursors to prepare silicon carbide, additional carbon sources or silicon sources are still added when using the carbon source and silicon source in rice husks to prepare silicon carbide, and the elements in rice husks are not fully utilized. Some patents first separate carbon and silicon dioxide, and then use silicon dioxide as a silicon source to prepare silicon carbide materials. The synthesis steps are cumbersome. Some patents use overly expensive materials, activated substances or high temperatures in the process of preparing silicon carbide, which not only increases production costs, but also generates a large amount of waste liquid, wastes energy, and pollutes the environment. Most patents do not consider the impact of the production process on the environment and the cost of raw materials. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a method for preparing β-SiC containing a whisker structure from rice husks, wherein the β-SiC is prepared by carbonization, pickling, grinding, mixing and high-temperature heating, and the whisker-like structure is included without adding additional carbon source and silicon source, thereby reducing production costs, saving energy consumption and not polluting the environment.

[0006] The present invention is achieved through the following technical solutions: (1) carbonizing the washed and dried rice husk under a protective atmosphere to obtain rice husk ash; (2) acid-washing the rice husk ash obtained in step (1), and then filtering, washing, drying, and sieving; (3) The rice husk ash obtained in step (2) is divided into two groups, and the groups are fully mixed with NaCl and H3BO3 respectively; the mixture of NaCl and rice husk ash and the mixture of H3BO3 and rice husk ash are placed in the same atmosphere furnace and a protective gas is introduced, and the gas is passed through the mixture of H3BO3 and rice husk ash and the mixture of NaCl and rice husk ash in sequence, and high-temperature treatment is performed in the atmosphere furnace; the high-temperature treatment temperature is 1300-1600° C., and the treatment time is 1-5 hours; (4) The rice husk ash mixture treated in step (3) is taken out, pickled, filtered, washed, dried, and then burned in air to remove carbon to obtain β-SiC.

[0007] Preferably, the protective gas in step (1) is Ar.

[0008] Preferably, the carbonization temperature in step (1) is 300-600° C., and the carbonization time is 0.5-2.5 h.

[0009] Preferably, the acid used in the pickling treatment in step (2) is hydrochloric acid with a concentration of 0.5 to 2.5 mol / l.

[0010] Preferably, the protective gas in step (3) is Ar.

[0011] Preferably, the protective gas flow rate in step (3) is controlled at 60-200 ml / min.

[0012] Preferably, the heating rate during high temperature treatment in step (3) is controlled at 2-10°C / min.

[0013] Preferably, the calcination temperature in step (4) is 500-800° C., and the calcination time is 1-5 hours.

[0014] Beneficial effects of the present invention: (1) The scheme adopted by the present invention can allow a reaction that cannot proceed smoothly at a lower reaction temperature by dividing the reactants into two parts, so that the intermediate generated by one of the reactants catalyzes the other reactant to smoothly generate the desired product, and then further remove impurities to obtain a pure final product.

[0015] (2) The prepared β-SiC contains a whisker-like structure. When β-SiC is used as an additive such as an abrasive or refractory material, the whisker-like structure can increase the compactness between its molecules, thereby increasing the mechanical strength and improving the performance of the material.

[0016] (3) The method of the present invention can fully utilize the carbon source and silicon source in rice husk. During the preparation process, neither additional carbon source nor additional silicon source needs to be introduced, thereby maximizing the utilization of rice husk resources and reducing production costs.

[0017] (4) The method of the present invention does not require separation of the carbon source and the silicon source and can be directly prepared. The final product is easy to remove impurities and purify. The operation steps are simple. As a carbon thermal reduction method, the production temperature is low and the energy consumption is low.

[0018] (5) No toxic or harmful substances are introduced or produced during the production process, which complies with the production concept of green chemistry and is environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a process flow chart of β-SiC preparation.

[0020] Figure 2 This is the XRD diagram of the mixed solid of NaCl and rice husk ash after being treated at 1400° C. in step (3) of Example 4.

[0021] Figure 3 This is a SEM image of the mixed solid of NaCl and rice husk ash after treatment at 1400° C. in step (3) of Example 4.

[0022] Figure 4 This is the XRD pattern of the finally prepared β-SiC solid with whisker structure.

[0023] Figure 5 This is the SEM image of the final prepared β-SiC solid with whisker structure.

[0024] Figure 6 It is the XRD diagram of Examples 1 to 4. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further explained and illustrated in the form of specific embodiments below.

[0026] Example 1 (1) The washed and dried rice husk was carbonized at 500 °C for 1 h in an Ar atmosphere to obtain rice husk ash; (2) The rice husk ash obtained in step (1) is pickled with 1 mol / l hydrochloric acid, and then filtered, washed, dried, and sieved; (3) placing the rice husk ash treated in step (2) into an atmosphere furnace and introducing Ar gas, controlling the gas flow rate to 100 ml / min, heating the furnace at a heating rate of 5°C / min to 1400°C and maintaining the temperature for 4 h; (4) The rice husk ash treated in step (3) is taken out, pickled, filtered, washed, dried, and then calcined in air at 700° C. for 4 h to obtain a product. The product is characterized by XRD, and no SiC is generated.

[0027] Example 2 (1) The washed and dried rice husk was carbonized at 500 °C for 1 h in an Ar atmosphere to obtain rice husk ash; (2) The rice husk ash obtained in step (1) is pickled with 1 mol / l hydrochloric acid, and then filtered, washed, dried, and sieved; (3) The rice husk ash treated in step (2) and NaCl were fully mixed in a mass ratio of 1:1 (the change in the ratio would not result in a significant difference), placed in an atmosphere furnace and introduced with Ar, the gas flow rate was controlled at 100 ml / min, and the temperature was raised to 1400°C at a heating rate of 5°C / min in the atmosphere furnace and maintained for 4 h; (4) The rice husk ash mixture treated in step (3) is taken out, pickled, filtered, washed, dried, and then calcined in air at 700° C. for 4 h to obtain a product. The product is characterized by XRD, and no SiC is generated.

[0028] Example 3 (1) The washed and dried rice husk was carbonized at 500 °C for 1 h in an Ar atmosphere to obtain rice husk ash; (2) The rice husk ash obtained in step (1) is pickled with 1 mol / l hydrochloric acid, and then filtered, washed, dried, and sieved; (3) After the rice husk ash treated in step (2) and H3BO3 are fully mixed in a mass ratio of 1:1 (the change in the ratio will not lead to a significant difference), the mixture of H3BO3 and rice husk ash and the rice husk ash are placed in the same atmosphere furnace in sequence and Ar is introduced, the gas flow rate is controlled at 100 ml / min, and the gas is passed through the H3BO3 mixture and the rice husk ash in sequence, and the temperature is raised to 1400°C in the atmosphere furnace at a heating rate of 5°C / min and maintained for 4 hours; (4) The rice husk ash treated in step (3) is taken out, pickled, filtered, washed, dried, and then calcined in air at 700°C for 4 h to obtain a product. The product is characterized by XRD, and it is found that β-SiC is generated and a small amount of SiO2 remains.

[0029] Example 4 (1) The washed and dried rice husk was carbonized at 500 °C for 1 h in an Ar atmosphere to obtain rice husk ash; (2) The rice husk ash obtained in step (1) is pickled with 1 mol / l hydrochloric acid, and then filtered, washed, dried, and sieved; (3) The rice husk ash treated in step (2) was fully mixed with NaCl and H3BO3 in a mass ratio of 1:1 (the change in the ratio will not lead to significant differences) and divided into two groups. The mixture of NaCl and rice husk ash and the mixture of H3BO3 and rice husk ash were placed in the same atmosphere furnace and introduced with Ar, and the gas flow rate was controlled at 100 ml / min. The gas was passed through the H3BO3 mixture and the NaCl mixture in sequence, and the temperature was raised to 1400°C in the atmosphere furnace at a heating rate of 5°C / min and maintained for 4 hours; (4) The mixture of NaCl and rice husk ash treated in step (3) is taken out, acid-washed, filtered, washed, dried, and then calcined in air at 700°C for 4 h to obtain a product. The product is characterized by XRD, such as Figure 4 As shown, all the products in this embodiment are β-SiC.

[0030] As shown in Examples 1 and 2, rice husk ash and a mixture of rice husk ash and NaCl cannot generate SiC when subjected to high temperature treatment. It can be seen that NaCl itself does not have the ability to catalyze the conversion of rice husk ash SiO2 into SiC. As shown in Example 3, a mixture of H3BO3 and rice husk ash can catalyze the conversion of rice husk charcoal into β-SiC, but a small amount of SiO2 remains, and the silicon source cannot be fully utilized. From the experimental results of Example 4, it can be seen that after the high temperature treatment in step (3), β-SiC containing a whisker structure (such as Figure 3 ), but it also contains NaCl and residual carbon. After being treated in step (4), it can be seen from the XRD spectrum analysis that the obtained product only contains β-SiC, and it can be seen from the SEM image that it contains obvious whisker-like structure. It can be seen that the mixture of H3BO3 and rice husk ash catalyzes the mixture of NaCl and rice husk ash, so that all SiO2 is converted into β-SiC.

Claims

1. A method for preparing β-SiC containing whisker structure from rice husk, characterized in that: The specific steps of this method are as follows: (1) carbonizing the washed and dried rice husk under a protective atmosphere to obtain rice husk ash; (2) acid-washing the rice husk ash obtained in step (1), and then filtering, washing, drying, and sieving; (3) The rice husk ash obtained in step (2) is divided into two groups, and the groups are fully mixed with NaCl and H3BO3 respectively; the mixture of NaCl and rice husk ash and the mixture of H3BO3 and rice husk ash are placed in the same atmosphere furnace and a protective gas is introduced, and the gas is passed through the mixture of H3BO3 and rice husk ash and the mixture of NaCl and rice husk ash in sequence, and high-temperature treatment is performed in the atmosphere furnace; the high-temperature treatment temperature is 1300-1600° C., and the treatment time is 1-5 hours; (4) The rice husk ash mixture treated in step (3) is taken out, pickled, filtered, washed, dried, and then burned in air to remove carbon to obtain β-SiC.

2. The method for preparing β-SiC containing whisker structure from rice husk according to claim 1, characterized in that: The protective gas in step (1) is Ar.

3. The method for preparing β-SiC containing whisker structure from rice husk according to claim 1, characterized in that: The carbonization temperature of step (1) is 300-600° C., and the carbonization time is 0.5-2.5 h.

4. The method for preparing β-SiC containing whisker structure from rice husk according to claim 1, characterized in that: The acid used in the pickling treatment in step (2) is hydrochloric acid with a concentration of 0.5 to 2.5 mol / l.

5. The method for preparing β-SiC containing whisker structure from rice husk according to claim 1, characterized in that: The protective gas in step (3) is Ar.

6. The method for preparing β-SiC containing whisker structure from rice husk according to claim 1, characterized in that: The flow rate of the protective gas in step (3) is controlled at 60-200 ml / min.

7. The method for preparing β-SiC containing whisker structure from rice husk according to claim 1, characterized in that: During the high temperature treatment in step (3), the heating rate is controlled at 2 to 10°C / min.

8. The method for preparing β-SiC containing whisker structure from rice husk according to claim 1, characterized in that: The calcination temperature in step (4) is 500-800° C., and the calcination time is 1-5 hours.

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