Method for preparing Ti-doped silicon carbide from lignite

Abstract

The invention discloses a method for preparing Ti-doped silicon carbide from lignite, and belongs to the field of preparation of silicon carbide. The invention aims to solve the problems of low utilization capacity of lignite, narrow wave-absorbing frequency band of silicon carbide and poor wave-absorbing performance in the prior art. The method comprises the following steps: 1, preparing a titanium source solution; 2, uniformly mixing a silicon source and lignite powder, then adding the mixture into the titanium source solution, drying and grinding; solid powder is obtained; and 3, high-temperature calcination and carbon removal. The method is used for preparing the Ti-doped silicon carbide from the lignite.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of silicon carbide. Background Art

[0002] Lignite, also known as firewood coal, is the lowest rank of mineral coal. It is a brownish-black, dull, low-grade coal between peat and bituminous coal. It has strong chemical reactivity, is easy to weather in the air, not easy to store and transport over long distances, and causes serious air pollution when burned.

[0003] Silicon carbide, also known as carborundum, is the most widely used and economical one among non-oxide high-tech refractory raw materials such as C, N, and B in modern times. It has a wide range of applications in many fields. However, the existing silicon carbide has a narrow wave absorption frequency band and poor wave absorption performance. Summary of the Invention

[0004] The present invention aims to solve the problems of low utilization ability of existing lignite, narrow wave absorption frequency band of silicon carbide, and poor wave absorption performance, and further provides a method for preparing Ti-doped silicon carbide using lignite.

[0005] A method for preparing Ti-doped silicon carbide using lignite is carried out according to the following steps:

[0006] First, a titanium source is added to absolute ethanol, stirred at a low speed until evenly mixed, and then left standing to obtain a titanium source solution;

[0007] The titanium source is a mixture of tetrabutyl titanate and barium titanate, and the mass ratio of tetrabutyl titanate to barium titanate is 1:(0.5 - 2);

[0008] Second, a silicon source and lignite powder are mixed evenly, then added to the titanium source solution to obtain a mixed solution. Deionized water is added to the mixed solution, stirred at room temperature, and finally dried and ground to obtain a solid powder;

[0009] Third, under an argon atmosphere, the solid powder is subjected to high-temperature calcination and carbon removal in sequence, and finally ground and ultrasonicated, thus completing the method for preparing Ti-doped silicon carbide using lignite.

[0010] The beneficial effects of the present invention are as follows:

[0011] 1. The lignite selected in the present invention is from Inner Mongolia Zhalainuoer Coal Industry. This lignite is rich in a large amount of carbon, with a high carbon content, and the rest is water and ash impurities. The ash is composed of oxides of various metals and silicon dioxide, etc. Appropriate metal particles can promote the VLS reaction and are beneficial to the formation of silicon carbide.

[0012] 2. Introduce a powder-phase solid, allowing it to interact with the carbon component in lignite through a solid-phase reaction to achieve the formation of SiC. The method of the present invention is simple, the process is easy to control, and large-scale production can be achieved through a one-step reaction, improving the comprehensive utilization ability of lignite.

[0013] 3. By introducing a titanium source in the present invention, the mixture of tetrabutyl titanate and barium titanate has a high dielectric constant and low dielectric loss, and can achieve excellent wave absorption ability of titanium-doped SiC with a wide wave absorption frequency band. The nanometer particles generated by the present invention have regular shapes, smooth surfaces, a diameter of about 50 nm, belong to β-SiC, and the crystal phase is the 3C phase, which is a high-quality raw material powder for manufacturing high-performance silicon carbide ceramics. Description of the Drawings

[0014] Figure 1 XRD spectra of Ti-doped silicon carbide prepared in Examples 1 to 4;

[0015] Figure 2 Scanning electron microscope image of Ti-doped silicon carbide prepared in Example 2;

[0016] Figure 3 Wave absorption performance diagram of Ti-doped silicon carbide prepared in Example 2. Detailed Embodiments

[0017] Detailed Embodiment 1: A method for preparing Ti-doped silicon carbide using lignite in this embodiment is carried out according to the following steps:

[0018] 1. Add the titanium source to absolute ethanol, stir at a low speed until evenly mixed, and then let it stand to obtain a titanium source solution;

[0019] The titanium source is a mixture of tetrabutyl titanate and barium titanate, and the mass ratio of tetrabutyl titanate to barium titanate is 1:(0.5 - 2);

[0020] 2. Mix the silicon source and lignite powder evenly, then add them to the titanium source solution to obtain a mixed solution. Add deionized water to the mixed solution, stir at room temperature, and finally dry and grind to obtain a solid powder;

[0021] 3. Under an argon atmosphere, perform high-temperature calcination and carbon removal on the solid powder in sequence, and finally grind and ultrasonicate to complete the method for preparing Ti-doped silicon carbide using lignite.

[0022] The principle is: Using lignite as a raw material to introduce a carbon source as a reactant, and subsequently introducing a silicon source while adding a titanium source to generate titanium-doped SiC under high-temperature sintering reaction.

[0023] The beneficial effects of this embodiment are:

[0024] 1. The lignite selected in this embodiment is sourced from Inner Mongolia Zhalainuoer Coal Industry. This lignite is rich in a large amount of carbon, with a high carbon content, and the rest is moisture and ash impurities. The ash is composed of oxides of various metals and silica, etc. Appropriate metal particles can promote the VLS reaction and are beneficial to the formation of silicon carbide.

[0025] 2. Powder-phase solids are introduced to interact with the carbon component in the lignite through solid-phase reactions to achieve the formation of SiC. The method of the present invention is simple, the process is easy to control, and one-step reaction can be used for large-scale production, improving the comprehensive utilization ability of lignite.

[0026] 3. In this embodiment, by introducing a titanium source, the mixture of tetrabutyl titanate and barium titanate has a high dielectric constant and low dielectric loss, and can achieve excellent wave absorption ability of titanium-doped SiC with a wide wave absorption bandwidth. The nano-particles generated in this embodiment have regular shapes, smooth surfaces, a diameter of about 50 nm, belong to β-SiC, and the crystal phase is the 3C phase, which is a high-quality raw material powder for manufacturing high-performance silicon carbide ceramics.

[0027] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that the mass ratio of the titanium source to the volume of absolute ethanol in Step 1 is 1 g:(2 - 5) mL. Others are the same as Specific Embodiment 1.

[0028] Specific Embodiment 3: The difference between this embodiment and one of Specific Embodiments 1 or 2 is that the low-speed stirring in Step 1 is specifically carried out under the conditions of a rotation speed of 100 r / min - 500 r / min and stirring for 10 min - 30 min. Others are the same as Specific Embodiment 1 or 2.

[0029] Specific Embodiment 4: The difference between this embodiment and one of Specific Embodiments 1 to 3 is that the lignite powder in Step 2 is obtained specifically according to the following steps: Under the condition of a temperature of 40°C - 80°C, the lignite blocks are dried for 2 h - 4 h, and then under the conditions of a rotation speed of 200 r / min - 500 r / min and a ball-to-material mass ratio of (1 - 2):1, ball milling is carried out for 0.5 h - 6 h; and cemented carbide grinding balls are used as grinding balls during the ball milling process. Others are the same as Specific Embodiment 3.

[0030] Specific Embodiment 5: The difference between this embodiment and one of Specific Embodiments 1 to 4 is that the silicon source in Step 2 is one or a combination of several of silicon dioxide, silicon powder, silica, and organosilicon. Others are the same as Specific Embodiments 1 to 4.

[0031] Specific Embodiment Six: The difference between this embodiment and any one of Specific Embodiments One to Five is as follows: In Step 2, the mass ratio of the lignite powder to the silicon source is (1 - 3):3; the molar ratio of the silicon source to the titanium source in the titanium source solution in Step 2 is 100:(0.5 - 10); the addition amount of deionized water in Step 2 is 5% - 10% of the mass of the mixed solution. Others are the same as those in Specific Embodiments One to Five.

[0032] Specific Embodiment Seven: The difference between this embodiment and any one of Specific Embodiments One to Six is as follows: In Step 2, add deionized water to the mixed solution, and then under the conditions of room temperature and a stirring speed of 200 r / min - 500 r / min, stir for 2 h - 5 h, then under the condition of a temperature of 100°C - 120°C, dry for 10 h - 14 h, and finally grind. Others are the same as those in Specific Embodiments One to Six.

[0033] Specific Embodiment Eight: The difference between this embodiment and any one of Specific Embodiments One to Seven is as follows: The high-temperature calcination in Step 3 is specifically carried out according to the following steps: Under an argon atmosphere, first heat up at a rate of 2°C / min - 5°C / min to 400°C - 500°C, then continue to heat up at a rate of 2°C / min - 10°C / min to 700°C - 800°C, then heat up at a rate of 2°C / min - 5°C / min to 900°C - 1000°C, and finally heat up at a rate of 2.5°C / min - 3°C / min to 1400°C - 1550°C, and under the conditions of an argon atmosphere and a temperature of 1400°C - 1550°C, keep warm for 1 h - 5 h. After heat preservation, under an argon atmosphere, first cool down at a rate of 2.5°C / min - 3°C / min to 900°C - 1000°C, then cool down at a rate of 2°C / min - 5°C / min to 700°C - 800°C, then cool down at a rate of 2°C / min - 10°C / min to 400°C - 500°C, and finally cool down to room temperature at a rate of 2°C / min - 5°C / min. Others are the same as those in Specific Embodiments One to Seven.

[0034] Specific Embodiment Nine: The difference between this embodiment and any one of Specific Embodiments One to Eight is as follows: The carbon removal in Step 3 is specifically carried out according to the following steps: Under an argon atmosphere, first heat up at a rate of 5°C / min - 10°C / min to 400°C - 500°C, then heat up at a rate of 3°C / min - 5°C / min to 600°C - 700°C, and under the conditions of an argon atmosphere and a temperature of 600°C - 700°C, keep warm for 2 h - 4 h. After heat preservation, under an argon atmosphere, first cool down at a rate of 3°C / min - 5°C / min to 400°C - 500°C, then cool down at a rate of 5°C / min - 10°C / min to room temperature. Others are the same as those in Specific Embodiments One to Eight.

[0035] Specific Embodiment 10: The difference between this embodiment and any one of Specific Embodiments 1 to 9 is that: in Step 3, the flow rate of the argon atmosphere is 20 mL / min to 100 mL / min, and the purity is ≥99.99%; in Step 3, the ultrasonic treatment is specifically carried out under the condition of an ultrasonic power of 100 W to 300 W for 0.5 h to 1 h. Others are the same as in Specific Embodiments 1 to 9.

[0036] The following examples are used to verify the beneficial effects of the present invention:

[0037] Example 1:

[0038] A method for preparing Ti-doped silicon carbide from lignite is carried out according to the following steps:

[0039] I. Add a titanium source to absolute ethanol, and under the condition of a rotation speed of 150 r / min, stir at a low speed for 15 min until evenly mixed, and then let it stand to obtain a titanium source solution;

[0040] The titanium source is a mixture of tetrabutyl titanate and barium titanate in a mass ratio of 1:2; the mass ratio of the titanium source to the volume of absolute ethanol is 1 g:5 mL;

[0041] II. Mix the silicon source and lignite powder evenly, and then add them to the titanium source solution to obtain a mixed solution. Add deionized water to the mixed solution, and then stir at room temperature and a stirring speed of 300 r / min for 2 h. Then, dry at a temperature of 100 °C for 12 h, and finally grind to obtain a solid powder;

[0042] The silicon source is a mixture of silicon dioxide and silicon powder in a molar ratio of 1:1; the mass ratio of the lignite powder to the silicon source is 2:3; the molar ratio of the silicon source to the titanium source in the titanium source solution is 100:0.5; the addition amount of deionized water is 10% of the mass of the mixed solution;

[0043] III. Under an argon atmosphere, the solid powder is sequentially subjected to high-temperature calcination and carbon removal, and finally ground and ultrasonically treated to obtain Ti-doped silicon carbide.

[0044] The lignite powder described in Step II is specifically obtained according to the following steps: Dry the lignite blocks at a temperature of 60 °C for 4 h, and then under the conditions of a rotation speed of 300 r / min and a ball-to-material mass ratio of 1:1, ball-mill for 2 h; and use titanium oxide grinding balls as grinding balls during the ball-milling process; the lignite blocks are from Hulun Buir Zhalainuoer Coal Industry Co., Ltd., and the main components of the lignite are: water content 16 wt.%, ash content 12 wt.%, organic carbon content 60 wt.%, inorganic carbon content 12 wt.%, and the particle size is mainly concentrated in 20 μm to 50 μm;

[0045] The high-temperature calcination described in Step 3 is specifically carried out as follows: Under an argon atmosphere, first heat up at a rate of 5 °C / min to 500 °C, then continue to heat up at a rate of 10 °C / min to 800 °C, then heat up at a rate of 5 °C / min to 1000 °C, and finally heat up at a rate of 2.5 °C / min to 1500 °C, and under the conditions of an argon atmosphere and a temperature of 1500 °C, keep the temperature for 2 h. After heat preservation, under an argon atmosphere, first cool down at a rate of 2.5 °C / min to 1000 °C, then cool down at a rate of 5 °C / min to 800 °C, then cool down at a rate of 10 °C / min to 500 °C, and finally cool down to room temperature at a rate of 5 °C / min;

[0046] The carbon removal described in Step 3 is specifically carried out as follows: Under an argon atmosphere, first heat up at a rate of 10 °C / min to 500 °C, then heat up at a rate of 5 °C / min to 700 °C, and under the conditions of an argon atmosphere and a temperature of 700 °C, keep the temperature for 2 h. After heat preservation, under an argon atmosphere, first cool down at a rate of 5 °C / min to 500 °C, then cool down at a rate of 10 °C / min to room temperature;

[0047] The flow rate of the argon atmosphere described in Step 3 is 40 mL / min, and the purity ≥ 99.99%.

[0048] The ultrasonic treatment described in Step 3 is specifically carried out under the condition of an ultrasonic power of 200 W for 0.5 h.

[0049] Example 2: The difference between this example and Example 1 is that the molar ratio of the titanium source in the silicon source and titanium source solution described in Step 2 is 100:1. Others are the same as in Example 1.

[0050] Example 3: The difference between this example and Example 1 is that the molar ratio of the titanium source in the silicon source and titanium source solution described in Step 2 is 100:5. Others are the same as in Example 1.

[0051] Example 4: The difference between this example and Example 1 is that the molar ratio of the titanium source in the silicon source and titanium source solution described in Step 2 is 100:10. Others are the same as in Example 1.

[0052] In this example, a tube furnace is used. In actual production for large-scale sintering, it is possible to first evacuate the vacuum and then introduce a protective gas before sintering.

[0053] Figure 1 XRD spectra of the Ti-doped silicon carbide prepared for Examples 1 to 4; As can be seen from the figure, strong diffraction peaks of SiC and titanium compounds are generated in the final product, and it belongs to β-SiC with a crystal phase of 3C phase, indicating that the method of this example realizes the introduction of silicon carbide components and titanium compounds.

[0054] Figure 2Scanning electron microscope image of the Ti-doped silicon carbide prepared in Example 2. As can be seen from the figure, in an Ar atmosphere, the generated nanoparticles have regular shapes, smooth surfaces, and a diameter of approximately 50 nm.

[0055] Mix the Ti-doped silicon carbide prepared in Example 2 with paraffin and test it using the coaxial method; Figure 3 Absorbing property diagram of the Ti-doped silicon carbide prepared in Example 2. As can be seen from the figure, the RL value of the reflectivity of Ti-doped SiC at a thickness of 5 mm is -24.27 dB, the absorption bandwidth is 3.8 GB - 4.7 GB, and the absorbing property is excellent.

Claims

1. A method for preparing Ti-doped silicon carbide using lignite, characterized in that It is carried out in the following steps:

1. Add the titanium source into anhydrous ethanol, stir at a low speed until the mixture is uniformly mixed, and then let it stand to obtain a titanium source solution; The titanium source is a mixture of tetrabutyl titanate and barium titanate, and the mass ratio of tetrabutyl titanate to barium titanate is 1:(0.5-2); 2. Mix the silicon source and lignite powder evenly, then add them to the titanium source solution to obtain a mixed solution, add deionized water to the mixed solution, stir at room temperature, and finally dry and grind to obtain a solid powder; 3. Under an argon atmosphere, the solid powder is sequentially subjected to high-temperature calcination and carbon removal, and finally ground and ultrasonicated to complete the method of preparing Ti-doped silicon carbide using lignite.

2. The method for preparing Ti-doped silicon carbide using lignite according to claim 1, characterized in that The mass ratio of the titanium source described in step 1 to the volume ratio of anhydrous ethanol is 1 g: (2-5) mL.

3. The method for preparing Ti-doped silicon carbide using lignite according to claim 1, characterized in that The low-speed stirring described in step 1 specifically involves stirring for 10 min to 30 min at a rotation speed of 100 r / min to 500 r / min.

4. The method for preparing Ti-doped silicon carbide using lignite according to claim 1, characterized in that The lignite powder described in step 2 is obtained specifically by the following steps: drying the lignite block at a temperature of 40°C to 80°C for 2h to 4h, and then ball milling for 0.5h to 6h at a rotation speed of 200r / min to 500r / min and a ball-to-material mass ratio of (1 to 2):1; and cemented carbide grinding balls are used as grinding balls during the ball milling process.

5. The method for preparing Ti-doped silicon carbide using lignite according to claim 1, characterized in that The silicon source described in step 2 is one or a combination of silicon dioxide, silicon powder, silica and organosilicon.

6. The method for preparing Ti-doped silicon carbide using lignite according to claim 1, characterized in that The mass ratio of the lignite powder to the silicon source in step 2 is (1-3):3; the molar ratio of the silicon source in step 2 to the titanium source in the titanium source solution is 100:(0.5-10); the amount of deionized water added in step 2 is 5% to 10% of the mass of the mixed solution.

7. The method for preparing Ti-doped silicon carbide using lignite according to claim 1, characterized in that In step 2, deionized water is added to the mixed solution, and then stirred for 2h to 5h at room temperature and a stirring speed of 200r / min to 500r / min, and then dried for 10h to 14h at a temperature of 100°C to 120°C, and finally ground.

8. The method for preparing Ti-doped silicon carbide using lignite according to claim 1, characterized in that The high temperature calcination described in step 3 is specifically carried out according to the following steps: in an argon atmosphere, firstly, the temperature is raised to 400°C to 500°C at a rate of 2°C / min to 5°C / min, then the temperature is further raised to 700°C to 800°C at a rate of 2°C / min to 10°C / min, then the temperature is raised to 900°C to 1000°C at a rate of 2°C / min to 5°C / min, and finally the temperature is raised to 1400°C to 1550°C at a rate of 2.5°C / min to 3°C / min, and Under the conditions of argon atmosphere and temperature of 1400℃~1550℃, keep warm for 1h~5h. After keeping warm, in argon atmosphere, first cool down to 900℃~1000℃ at a rate of 2.5℃ / min~3℃ / min, then cool down to 700℃~800℃ at a rate of 2℃ / min~5℃ / min, then cool down to 400℃~500℃ at a rate of 2℃ / min~10℃ / min, and finally cool down to room temperature at a rate of 2℃ / min~5℃ / min.

9. The method for preparing Ti-doped silicon carbide using lignite according to claim 1, characterized in that The carbon removal described in step three is specifically carried out according to the following steps: under an argon atmosphere, first heat the temperature to 400°C~500°C at a rate of 5°C / min~10°C / min, then heat the temperature to 600°C~700°C at a rate of 3°C / min~5°C / min, and keep warm for 2h~4h in an argon atmosphere and a temperature of 600°C~700°C. After keeping warm, under an argon atmosphere, first cool the temperature to 400°C~500°C at a rate of 3°C / min~5°C / min, and then cool to room temperature at a rate of 5°C / min~10°C / min.

10. The method for preparing Ti-doped silicon carbide using lignite according to claim 1, characterized in that The flow rate of the argon atmosphere described in step 3 is 20 mL / min to 100 mL / min, and the purity is ≥ 99.99%; the ultrasound described in step 3 is specifically performed at an ultrasound power of 100 W to 300 W for 0.5 h to 1 h.

Images