Preparation method of SiC fiber / lignite / fly ash high-strength heat storage ceramic

Abstract

The invention discloses a preparation method of SiC fiber / lignite / fly ash high-strength heat storage ceramic, and belongs to the field of heat storage ceramic. The invention aims to solve the problem that the fly ash-based heat storage ceramic with high-strength carbon-based heat-conducting filler cannot be prepared in the prior art. The method comprises the following steps: 1, pyrolyzing lignite powder at high temperature to obtain graphitized lignite powder; 2, mixing the graphitized lignite powder, silicon carbide nanowires, solar salt and fly ash; 3, pressing; and 4, sintering. The method is used for preparing the SiC fiber / lignite / fly ash high-strength heat storage ceramic.

Description

Technical Field

[0001] The present invention belongs to the field of heat storage ceramics. Background Art

[0002] Fly ash porous ceramics have important applications in the field of heat storage. They are usually used as the matrix of phase change heat storage materials. By improving the thermal conductivity and material stability, the thermal response efficiency of the heat storage system is significantly enhanced. Its unique porous structure not only provides a large specific surface area, enhancing the heat transfer efficiency between the matrix and the phase change material, but also effectively prevents the leakage of the phase change material during the solid-liquid phase change process. Fly ash, as the main raw material, has a wide source and low cost, and its preparation process realizes the resource utilization of waste, reflecting good economic efficiency and environmental friendliness. In addition, high thermal conductivity is crucial for optimizing the heat storage efficiency, which can improve the heat storage and release rate of the phase change material and the energy utilization efficiency of the system. However, the existing methods for improving the thermal conductivity of fly ash porous ceramics mainly rely on introducing carbon-based thermal conductive fillers (such as graphite, carbon nanotubes, etc.). Although these methods can effectively improve the thermal conductivity, they will cause the material strength to rapidly decline with the increase in the addition amount of the thermal conductive filler, making it difficult to meet the mechanical requirements of practical applications. So far, there has been no technology that can prepare fly ash-based heat storage ceramics with high-strength carbon-based thermal conductive fillers. Summary of the Invention

[0003] The present invention aims to solve the problem that the existing technology cannot prepare fly ash-based heat storage ceramics with high-strength carbon-based thermal conductive fillers, and further provides a preparation method for SiC fiber / lignite / fly ash high-strength heat storage ceramics.

[0004] A preparation method for SiC fiber / lignite / fly ash high-strength heat storage ceramics is carried out according to the following steps:

[0005] 1. Pyrolyze the lignite powder at high temperature to obtain graphitized lignite powder;

[0006] 2. Mix the graphitized lignite powder, silicon carbide nanowires, solar salt and fly ash to obtain ceramic raw powder;

[0007] 3. Press the ceramic raw powder into a ceramic green body;

[0008] 4. Sinter the ceramic green body in a nitrogen atmosphere to obtain SiC fiber / lignite / fly ash high-strength heat storage ceramics.

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

[0010] 1. In the present invention, silicon carbide nanowires are used as both thermal conductive fillers and mechanical reinforcement phases. After being mixed with graphitized lignite powder, solar salt, and fly ash, and then pressed and sintered, a fly ash-based heat storage ceramic with both high thermal conductivity and high strength is prepared. The addition of silicon carbide nanowires can disperse stress through the load transfer mechanism, thereby obtaining greater mechanical strength.

[0011] 2. When the total mass of graphitized lignite powder and silicon carbide nanowires accounts for 5% of the total mass of the ceramic raw powder in the present invention, and the mass ratio of graphitized lignite powder to silicon carbide nanowires is 4:1, the thermal conductivity of the prepared SiC fiber / lignite / fly ash high-strength heat storage ceramic is as high as 4.106 W / (m·K), and it has a compressive strength of 480.01 MPa and a latent heat calorific value of 65.61 kJ / kg.

[0012] 3. The present invention optimizes the thermal conductivity, mechanical strength, and heat storage performance of the heat storage ceramic by adding silicon carbide nanowires, and has broad application prospects. Using conventional raw materials such as graphitized lignite and fly ash not only reduces the production cost, but also realizes the efficient resource utilization of waste, improves the economic efficiency and environmental friendliness of the ceramic material, and is suitable for large-scale industrial production. Description of the Drawings

[0013] Figure 1 It is the Raman spectrum of the lignite powder and the prepared graphitized lignite powder in Step 1 of Example 1;

[0014] Figure 2 It is the XRD spectrum of the silicon carbide nanowires in Step 2 of Example 1;

[0015] Figure 3 It is the SEM spectrum of the silicon carbide nanowires in Step 2 of Example 1;

[0016] Figure 4 It is the thermal conductivity spectrum of the graphitized lignite powder prepared in Step 1 of Example 1 and the silicon carbide nanowires in Step 2;

[0017] Figure 5 It is the thermal conductivity spectrum of the SiC fiber / lignite / fly ash high-strength heat storage ceramics prepared in Examples 1 to 5;

[0018] Figure 6 It is the compressive strength spectrum of the SiC fiber / lignite / fly ash high-strength heat storage ceramics prepared in Examples 1 to 5;

[0019] Figure 7 It is the latent heat calorific value spectrum of the SiC fiber / lignite / fly ash high-strength heat storage ceramics prepared in Examples 1 to 5. Detailed Embodiments

[0020] Specific Embodiment 1: A preparation method of a high-strength heat storage ceramic of SiC fiber / lignite / fly ash is carried out according to the following steps:

[0021] 1. Pyrolyze the lignite powder at high temperature to obtain graphitized lignite powder;

[0022] 2. Mix the graphitized lignite powder, silicon carbide nanowires, solar salt and fly ash to obtain ceramic raw powder;

[0023] 3. Press the ceramic raw powder into a ceramic green body;

[0024] 4. Sinter the ceramic green body in a nitrogen atmosphere to obtain a high-strength heat storage ceramic of SiC fiber / lignite / fly ash.

[0025] The principle of the heat storage process of the high-strength heat storage ceramic of SiC fiber / lignite / fly ash prepared in this specific embodiment is as follows:

[0026] Endothermic process: solid solar salt → liquid solar salt;

[0027] Exothermic process: liquid solar salt → solid solar salt.

[0028] The beneficial effects of this embodiment are as follows:

[0029] 1. In this embodiment, silicon carbide nanowires are used as both thermal conductive fillers and mechanical strengthening phases at the same time. After being mixed with graphitized lignite powder, solar salt and fly ash, and then pressed and sintered, a fly ash-based heat storage ceramic with both high thermal conductivity and high strength is prepared. The addition of silicon carbide nanowires can disperse stress through the load transfer mechanism, thereby obtaining greater mechanical strength.

[0030] 2. In this embodiment, when the total mass of the graphitized lignite powder and silicon carbide nanowires accounts for 5% of the total mass of the ceramic raw powder, and the mass ratio of the graphitized lignite powder to the silicon carbide nanowires is 4:1, the thermal conductivity of the prepared high-strength heat storage ceramic of SiC fiber / lignite / fly ash is as high as 4.106 W / (m·K), and it has a compressive strength of 480.01 MPa and a latent heat value of 65.61 kJ / kg.

[0031] 3. In this embodiment, the addition of silicon carbide nanowires optimizes the thermal conductivity, mechanical strength and heat storage performance of the heat storage ceramic, and has broad application prospects. Using conventional raw materials such as graphitized lignite and fly ash not only reduces the production cost, but also realizes the efficient resource utilization of waste, improves the economy and environmental friendliness of ceramic materials, and is suitable for large-scale industrial production.

[0032] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is as follows: The lignite powder described in Step 1 is specifically obtained by using a vibration mill with steel balls having a diameter of 6 mm to 10 mm as the crushing medium, under the conditions of a vibration frequency of 20 Hz to 50 Hz, a volume filling amount of the total volume of the balls and the material in the grinding tank of 20% to 75%, and a mass ratio of the balls to the material of (1 to 2):1. The lignite blocks are vibrated and ground for 6 h to 24 h, and finally sieved to obtain the lignite powder. Others are the same as Specific Embodiment 1.

[0033] Specific Embodiment 3: The difference between this embodiment and one of Specific Embodiments 1 or 2 is as follows: The sieving is specifically carried out by using a 200-mesh to 300-mesh sieve. Others are the same as Specific Embodiment 1 or 2.

[0034] Specific Embodiment 4: The difference between this embodiment and one of Specific Embodiments 1 to 3 is as follows: The high-temperature pyrolysis described in Step 1 is specifically carried out according to the following steps: Under vacuum conditions, at a rate of 5 °C / min to 10 °C / min, the temperature is raised to 800 °C to 1000 °C, and then at a rate of 2.5 °C / min to 5 °C / min, the temperature is raised to 1700 °C to 2000 °C. Under vacuum and at a temperature of 1700 °C to 2000 °C, pyrolysis is carried out for 3 h to 6 h, and finally under vacuum conditions, the temperature is lowered to room temperature at a rate of 2.5 °C / min to 5 °C / min. Others are the same as Specific Embodiment 3.

[0035] Specific Embodiment 5: The difference between this embodiment and one of Specific Embodiments 1 to 4 is as follows: The mass ratio of the graphitized lignite powder to the silicon carbide nanowires described in Step 2 is (3 to 7):1. Others are the same as Specific Embodiments 1 to 4.

[0036] Specific Embodiment 6: The difference between this embodiment and one of Specific Embodiments 1 to 5 is as follows: The total mass of the graphitized lignite powder and the silicon carbide nanowires described in Step 2 accounts for 5% to 10% of the total mass of the ceramic raw powder. Others are the same as Specific Embodiments 1 to 5.

[0037] Specific Embodiment 7: The difference between this embodiment and one of Specific Embodiments 1 to 6 is as follows: The mass ratio of the solar salt to the fly ash described in Step 2 is 1:(1 to 1.5). Others are the same as Specific Embodiments 1 to 6.

[0038] Specific Embodiment 8: The difference between this embodiment and one of Specific Embodiments 1 to 7 is as follows: The mixing described in Step 2 is specifically carried out by using a ribbon mixer. Under the condition of a stirring rate of 50 r / min to 100 r / min, the graphitized lignite powder, the silicon carbide nanowires, the solar salt and the fly ash are stirred and mixed for 5 min to 15 min. Others are the same as Specific Embodiments 1 to 7.

[0039] Embodiment 9: The difference between this embodiment and any one of Embodiments 1 to 8 is that: in Step 3, the pressing is specifically carried out under the condition of a pressure of 20 MPa to 200 MPa for 2 min to 5 min of compression molding. Others are the same as those in Embodiments 1 to 8.

[0040] Embodiment 10: The difference between this embodiment and any one of Embodiments 1 to 9 is that: in Step 4, the sintering is specifically carried out in a nitrogen atmosphere at a rate of 5 °C / min to 10 °C / min, heated to 800 °C to 1000 °C, and then sintered for 2 h to 4 h under the conditions of a nitrogen atmosphere and a temperature of 800 °C to 1000 °C, and finally cooled to room temperature at a rate of 5 °C / min to 10 °C / min in a nitrogen atmosphere. Others are the same as those in Embodiments 1 to 9.

[0041] The following examples are used to verify the beneficial effects of the present invention:

[0042] Example 1:

[0043] A preparation method of a SiC fiber / lignite / fly ash high-strength heat storage ceramic is carried out according to the following steps:

[0044] 1. Under vacuum conditions, the lignite powder is heated to 1000 °C at a rate of 10 °C / min, and then heated to 2000 °C at a rate of 5 °C / min. Under vacuum and at a temperature of 2000 °C, it is pyrolyzed for 6 h, and finally cooled to room temperature at a rate of 5 °C / min under vacuum conditions to obtain graphitized lignite powder;

[0045] 2. Using a ribbon mixer, under the condition of a stirring rate of 100 r / min, the graphitized lignite powder, silicon carbide nanowires, solar salt and fly ash are stirred and mixed for 15 min to obtain ceramic raw powder;

[0046] The mass ratio of the graphitized lignite powder to the silicon carbide nanowires is 4:1;

[0047] The total mass of the graphitized lignite powder and the silicon carbide nanowires accounts for 5% of the total mass of the ceramic raw powder;

[0048] The mass ratio of the solar salt to the fly ash is 1:1;

[0049] 3. Under the condition of a pressure of 200 MPa, the ceramic raw powder is compression molded for 5 min to obtain a ceramic green body;

[0050] IV. Under a nitrogen atmosphere, the ceramic green body is heated to 1000 °C at a rate of 5 °C / min, then sintered for 4 h under a nitrogen atmosphere at a temperature of 1000 °C, and finally cooled to room temperature at a rate of 5 °C / min under a nitrogen atmosphere to obtain the SiC fiber / lignite / fly ash high-strength heat storage ceramic.

[0051] The lignite powder described in Step 1 is specifically obtained by using a vibration mill with steel balls of 10 mm in diameter as the crushing medium, under the conditions of a vibration frequency of 50 Hz, a volume filling ratio of the total volume of balls and materials in the grinding tank of 50%, and a mass ratio of balls to materials of 2:1, vibrating and grinding the lignite blocks for 24 h, and finally sieving through a 300-mesh sieve to obtain the lignite powder; the lignite blocks are from Zhalainuoer Coal Industry Co., Ltd., with a water content of 16 wt.%, an ash content of 12 wt.%, an organic carbon content of 60 wt.%, an inorganic carbon content of 12 wt.%, and the particle size mainly concentrated in 20 μm - 30 μm, and an average particle size of 25 μm.

[0052] The fly ash described in Step 2 is from Zhalainuoer Coal Industry Co., Ltd., with a silicon dioxide content of 62 wt.%, an aluminum oxide content of 30 wt.%, an iron oxide content of 5 wt.%, and other alkali metal oxides of 3 wt.%; the average particle size is 95 μm.

[0053] The solar salt and silicon carbide nanowires described in Step 2 are from Inner Mongolia Haitai Huacai Technology Co., Ltd.; the sodium chloride in the solar salt described in Step 2 is 86 wt.%, sodium sulfate is 10 wt.%, magnesium chloride is 2.7 wt.%, calcium chloride is 1.2 wt.%, and other compounds are 0.1 wt.%; the average diameter of the silicon carbide nanowires described in Step 2 is 50 nm, and the average length is 15 μm.

[0054] Measured by ion chromatography, the mass percentage of the solar salt in the SiC fiber / lignite / fly ash high-strength heat storage ceramic prepared in Example 1 is 45.86%; and the measured thermal conductivity is 4.106 W / (m·K), and the compressive strength is 480.01 MPa.

[0055] Example 2: The difference between this example and Example 1 is that: the mass ratio of the graphitized lignite powder to the silicon carbide nanowires described in Step 2 is 3:1. Others are the same as Example 1.

[0056] The thermal conductivity of the SiC fiber / lignite / fly ash high-strength heat storage ceramic prepared in Example 2 is 3.294 W / (m·K), and the compressive strength is 500.52 MPa.

[0057] Example 3: The difference between this example and Example 1 is that: the mass ratio of the graphitized lignite powder to the silicon carbide nanowires described in Step 2 is 5:1. Others are the same as Example 1.

[0058] The thermal conductivity of the SiC fiber / lignite / fly ash high-strength heat storage ceramic prepared in Example 3 is 4.491 W / (m·K), and the compressive strength is 390.21 MPa.

[0059] Example 4: The difference between this example and Example 1 is that the mass ratio of the graphitized lignite powder to the silicon carbide nanowires described in Step 2 is 6:1. Others are the same as in Example 1.

[0060] The thermal conductivity of the SiC fiber / lignite / fly ash high-strength heat storage ceramic prepared in Example 4 is 5.058 W / (m·K), and the compressive strength is 340.57 MPa.

[0061] Example 5: The difference between this example and Example 1 is that the mass ratio of the graphitized lignite powder to the silicon carbide nanowires described in Step 2 is 7:1. Others are the same as in Example 1.

[0062] The thermal conductivity of the SiC fiber / lignite / fly ash high-strength heat storage ceramic prepared in Example 5 is 5.247 W / (m·K), and the compressive strength is 280.22 MPa.

[0063] Figure 1 It is the Raman spectrum of the lignite powder and the prepared graphitized lignite powder described in Step 1 of Example 1; as can be seen from the figure, the G peak of the lignite powder is significantly enhanced compared with the D peak after pyrolysis, indicating that the graphitized lignite powder is successfully prepared by the method in the example.

[0064] Figure 2 It is the XRD spectrum of the silicon carbide nanowires described in Step 2 of Example 1; as can be seen from the figure, the main phase of the silicon carbide nanowires is β-SiC.

[0065] Figure 3 It is the SEM spectrum of the silicon carbide nanowires described in Step 2 of Example 1; as can be seen from the figure, the average diameter of the silicon carbide nanowires is 50 nm, and the average length is 15 μm. The high aspect ratio is beneficial to heat conduction and stress dispersion.

[0066] Figure 4 It is the thermal conductivity spectrum of the graphitized lignite powder prepared in Step 1 of Example 1 and the silicon carbide nanowires described in Step 2; as can be seen from the figure, the thermal conductivity of the graphitized lignite powder is 36.99 W / (m·K), which is significantly higher than the thermal conductivity of the silicon carbide nanowires, 25.26 W / (m·K).

[0067] Figure 5Thermal conductivity spectra of the high-strength heat storage ceramics of SiC fiber / lignite / fly ash prepared in Examples 1 to 5; As can be seen from the figure, when the total mass percentage of graphitized lignite powder and silicon carbide nanowires in the ceramic raw powder is 5%, and the mass ratio of lignite powder to silicon carbide nanowires is 4:1, the thermal conductivity of the ceramic raw powder is 4.106 W / (m·K), indicating that the high-strength heat storage ceramics of SiC fiber / lignite / fly ash prepared by the method in the examples have excellent thermal conductivity performance.

[0068] Tested according to the GB / T 1964-2023 standard; Figure 6 Compressive strength spectra of the high-strength heat storage ceramics of SiC fiber / lignite / fly ash prepared in Examples 1 to 5; As can be seen from the figure, when the total mass percentage of graphitized lignite powder and silicon carbide nanowires in the ceramic raw powder is 5%, and the mass ratio of lignite powder to silicon carbide nanowires is 4:1, the compressive strength of the high-strength heat storage ceramics of SiC fiber / lignite / fly ash is 480.01 MPa, indicating that the high-strength heat storage ceramics of SiC fiber / lignite / fly ash have been successfully prepared by the method in the examples.

[0069] Figure 7 Latent heat calorific value spectra of the high-strength heat storage ceramics of SiC fiber / lignite / fly ash prepared in Examples 1 to 5; As can be seen from the figure, when the total mass percentage of graphitized lignite powder and silicon carbide nanowires in the ceramic raw powder is 5%, and the mass ratio of lignite powder to silicon carbide nanowires is 4:1, the latent heat calorific value of the high-strength heat storage ceramics of SiC fiber / lignite / fly ash is 65.61 kJ / kg, indicating that the high-strength heat storage ceramics of SiC fiber / lignite / fly ash successfully prepared by the method in the examples have excellent heat storage performance.

Claims

1. A method for preparing SiC fiber / lignite / fly ash high-strength thermal storage ceramics, characterized in that It is carried out in the following steps:

1. Pyrolyzing lignite powder at high temperature to obtain graphitized lignite powder; 2. mixing graphitized lignite powder, silicon carbide nanowires, solar salt and fly ash to obtain ceramic raw powder; 3. Pressing ceramic raw powder into ceramic embryos; Fourth, the ceramic green body is sintered in a nitrogen atmosphere to obtain SiC fiber / lignite / fly ash high-strength heat storage ceramics.

2. The method for preparing a SiC fiber / lignite / fly ash high-strength thermal storage ceramic according to claim 1, characterized in that The lignite powder described in step one is specifically produced by a vibration mill, with steel balls having a diameter of 6 mm to 10 mm as the crushing medium. Under the conditions of a vibration frequency of 20 Hz to 50 Hz, a volume filling amount of the total volume of the ball material in the grinding tank of 20% to 75% and a ball material mass ratio of (1 to 2): 1, the lignite block is vibrated for 6 h to 24 h, and finally sieved to obtain lignite powder.

3. The method for preparing a SiC fiber / lignite / fly ash high-strength thermal storage ceramic according to claim 2, characterized in that The sieving is performed by using a 200-300 mesh screen.

4. The method for preparing a SiC fiber / lignite / fly ash high-strength thermal storage ceramic according to claim 1, characterized in that The high-temperature pyrolysis described in step 1 is specifically carried out according to the following steps: under vacuum conditions, the temperature is increased to 800°C to 1000°C at a rate of 5°C / min to 10°C / min, and then the temperature is increased to 1700°C to 2000°C at 2.5°C / min to 5°C / min, and pyrolysis is performed for 3h to 6h under vacuum and a temperature of 1700°C to 2000°C, and finally under vacuum conditions, the temperature is reduced to room temperature at a rate of 2.5°C / min to 5°C / min.

5. The method for preparing a SiC fiber / lignite / fly ash high-strength thermal storage ceramic according to claim 1, characterized in that The mass ratio of the graphitized lignite powder to the silicon carbide nanowires described in step 2 is (3-7):

1.

6. The method for preparing a SiC fiber / lignite / fly ash high-strength thermal storage ceramic according to claim 1, characterized in that The total mass of the graphitized lignite powder and the silicon carbide nanowires described in step 2 accounts for 5% to 10% of the total mass of the ceramic raw powder.

7. The method for preparing a SiC fiber / lignite / fly ash high-strength thermal storage ceramic according to claim 1, characterized in that The mass ratio of solar salt to fly ash in step 2 is 1:(1-1.5).

8. The method for preparing a SiC fiber / lignite / fly ash high-strength thermal storage ceramic according to claim 1, characterized in that The mixing described in step 2 is specifically performed by using a ribbon mixer to stir and mix the graphitized lignite powder, silicon carbide nanowires, solar salt and fly ash for 5 minutes to 15 minutes at a stirring rate of 50 r / min to 100 r / min.

9. The method for preparing a SiC fiber / lignite / fly ash high-strength thermal storage ceramic according to claim 1, characterized in that The pressing described in step 3 is specifically performed under a pressure of 20 MPa to 200 MPa for 2 to 5 minutes.

10. The method for preparing a SiC fiber / lignite / fly ash high-strength thermal storage ceramic according to claim 1, characterized in that The sintering described in step 4 is specifically to heat up to 800℃~1000℃ at a rate of 5℃ / min~10℃ / min in a nitrogen atmosphere, then sinter for 2h~4h in a nitrogen atmosphere and at a temperature of 800℃~1000℃, and finally cool to room temperature at a rate of 5℃ / min~10℃ / min in a nitrogen atmosphere.

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