A method for preparing fly ash derived high thermal conductivity mullite ceramic by molten salt filling

Abstract

The application relates to a method for preparing fly ash derived high-thermal-conductivity mullite ceramics by using molten salt filling, and relates to a method for preparing high-thermal-conductivity mullite ceramics. The application aims at solving the problem that the prior art cannot use fly ash to prepare high-thermal-conductivity mullite ceramics. The preparation method comprises the following steps: 1, uniformly mixing crushed fly ash and an aluminum source by ball milling; 2, sintering reaction; and 3, vacuum impregnation treatment in high-temperature molten inorganic salt. The application is used for preparing fly ash derived high-thermal-conductivity mullite ceramics by using molten salt filling.

Description

Technical Field

[0001] The invention relates to a method for preparing high thermal conductivity mullite ceramics. Background Art

[0002] Fly ash is one of the main solid wastes generated by coal-fired power plants. It is a fine gray or off-white powder composed primarily of silicates and aluminates. Due to its tiny particles and large surface area, fly ash easily diffuses in the air, causing environmental pollution. Compared with traditional landfill disposal methods, using fly ash to prepare mullite porous ceramics not only has higher economic added value but also reduces the environmental burden. However, due to the poor thermal conductivity of mullite itself, existing technologies are unable to use fly ash to prepare mullite ceramics with high thermal conductivity, which limits its application potential in the field of heat transfer. Summary of the Invention

[0003] The present invention aims to solve the problem that the prior art cannot use fly ash to produce high thermal conductivity mullite ceramics, and provides a method for preparing fly ash-derived high thermal conductivity mullite ceramics by using molten salt filling.

[0004] A method for preparing fly ash-derived high thermal conductivity mullite ceramics by using molten salt filling is completed by the following steps:

[0005] 1. Crush the fly ash, then mix the crushed fly ash and aluminum source by ball milling, and finally sieve to obtain a uniformly mixed powder;

[0006] 2. Sintering the uniformly mixed powder in an air atmosphere at a temperature of 1150°C to 1350°C for 0.5h to 3h, and cooling the furnace after the reaction to obtain fly ash-derived mullite ceramics;

[0007] 3. The fly ash-derived mullite ceramic is vacuum impregnated in a high-temperature molten inorganic salt, and then naturally cooled after being taken out to obtain the fly ash-derived high thermal conductivity mullite ceramic.

[0008] The beneficial effects of the present invention are:

[0009] 1. In the present invention, when the mass percentage of the aluminum source in the mixed uniform powder is 14%, the fly ash-derived porous mullite ceramic produced has mullite whiskers with a diameter of about 100 nm and an aspect ratio of 1:7, and has an apparent porosity of 51%. Then, by introducing molten inorganic salt to fill the mullite ceramic, the thermal conductivity below the melting point of the inorganic salt is improved.

[0010] 2. The maximum operating temperature of the fly ash-derived high thermal conductivity mullite ceramic prepared in the present invention is 758°C to 893°C.

[0011] 3. The preparation method of the present invention is simple, the process is easy to control, and it is suitable for large-scale industrial production. The present invention uses fly ash as raw material, which reduces costs, maximizes the high-value-added resource utilization of fly ash in heat transfer related fields, and improves my country's comprehensive utilization capacity of fly ash. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a microscopic morphology of the fly ash-derived mullite ceramic prepared in step 2 of Example 3;

[0013] Figure 2 This is a comparison chart of the porosity of fly ash-derived mullite ceramics prepared in step 2 of Examples 1 to 5;

[0014] Figure 3 This is the element distribution diagram of the fly ash-derived high thermal conductivity mullite ceramic prepared in step 3 of Example 3;

[0015] Figure 4 This is a comparison chart of the thermal conductivities of the fly ash-derived mullite ceramic prepared in step 2 of Examples 1 to 5 and the fly ash-derived high thermal conductivity mullite ceramic prepared in step 3. DETAILED DESCRIPTION

[0016] Specific embodiment 1: This embodiment is a method for preparing fly ash-derived high thermal conductivity mullite ceramics by filling with molten salt, which is completed by the following steps:

[0017] 1. Crush the fly ash, then mix the crushed fly ash and aluminum source by ball milling, and finally sieve to obtain a uniformly mixed powder;

[0018] 2. Sintering the uniformly mixed powder in an air atmosphere at a temperature of 1150°C to 1350°C for 0.5h to 3h, and cooling the furnace after the reaction to obtain fly ash-derived mullite ceramics;

[0019] 3. The fly ash-derived mullite ceramic is vacuum impregnated in a high-temperature molten inorganic salt, and then naturally cooled after being taken out to obtain the fly ash-derived high thermal conductivity mullite ceramic.

[0020] Principle: Fly ash contains substances such as silicon dioxide. Fly ash is used as raw material, and an aluminum source is introduced as a reactant. After reaction under high temperature environment, 3Al2O3·2SiO2 mullite component is achieved.

[0021] The formation of high-hardness mullite ceramics prepared by reaction mainly follows the following chemical reaction process:

[0022] Formation of mullite:

[0023] SiO2 (quartz phase) → SiO2 (cristobalite phase)

[0024] SiO2 (quartz phase) + SiO2 (cristobalite phase) → SiO2 (liquid amorphous phase)

[0025] 3Al2O3+2SiO2(liquid amorphous phase)→3A12O3·2SiO2(mullite phase).

[0026] The beneficial effects of this embodiment are:

[0027] 1. In this embodiment, when the mass percentage of the aluminum source in the mixed uniform powder is 14%, the fly ash-derived porous mullite ceramic produced has mullite whiskers with a diameter of about 100 nm and an aspect ratio of 1:7, and has an apparent porosity of 51%. Then, by introducing molten inorganic salt to fill the mullite ceramic, the thermal conductivity below the melting point of the inorganic salt is improved.

[0028] 2. The maximum operating temperature of the fly ash-derived high thermal conductivity mullite ceramic prepared in this embodiment is 758°C to 893°C.

[0029] 3. The preparation method of this embodiment is simple, the process is easy to control, and it is suitable for large-scale industrial production. This embodiment uses fly ash as raw material to reduce costs, maximize the high-value-added resource utilization of fly ash in heat transfer related fields, and improve my country's comprehensive utilization capacity of fly ash.

[0030] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the fly ash is crushed into blocks with a size of less than 75 μm in step 1. Other steps are the same as those in specific embodiment 1.

[0031] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that the aluminum source in step 1 is one or a combination of aluminum oxide, bauxite, and kaolin. Other aspects are the same as specific embodiment 1 or 2.

[0032] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the ball milling in step 1 is performed at a rotation speed of 250 to 400 r / min and a ball-to-material ratio of (1 to 2):1 for 2 to 6 hours. Other aspects are the same as specific embodiments 1 to 3.

[0033] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the sieving in step 1 is performed through a 200-mesh sieve. Other aspects are the same as specific embodiments 1 to 4.

[0034] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that the mass percentage of the aluminum source in the mixed powder in step 1 is 0% to 28%. Other aspects are the same as specific embodiments 1 to 5.

[0035] When the mass percentage of the aluminum source in the uniformly mixed powder described in step 1 is 0%, since the fly ash originally contains a small amount of aluminum oxide, the reaction of 3Al2O3+2SiO2 (liquid phase amorphous phase) → 3A12O3·2SiO2 (mullite phase) can also occur to generate a small amount of mullite, so it still belongs to mullite ceramics.

[0036] Specific embodiment 7: This embodiment differs from any one of specific embodiments 1 to 6 in that, in step 2, the temperature of the uniformly mixed powder is first raised to 300°C to 500°C at a rate of 5°C / min to 10°C / min under air atmosphere, and then raised to 1150°C to 1350°C at a rate of 2°C / min to 2.5°C / min. Other steps are the same as specific embodiments 1 to 6.

[0037] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that the high-temperature molten inorganic salt in step 3 is high-temperature molten sodium fluoride or high-temperature molten potassium fluoride. Other aspects are the same as specific embodiments 1 to 7.

[0038] The melting point of the sodium fluoride is 993°C, and the melting point of the potassium fluoride is 858°C.

[0039] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that the vacuum impregnation treatment in step 3 is carried out under a vacuum degree of 0.1 Pa to 1 Pa for 0.5 to 2 hours. Other aspects are the same as specific embodiments 1 to 8.

[0040] Specific embodiment 10: This embodiment differs from specific embodiments 1 to 9 in that the mass percentage of inorganic salt in the fly ash-derived high thermal conductivity mullite ceramic prepared in step 3 is 10.01% to 50.02%. Other aspects are the same as specific embodiments 1 to 9.

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

[0042] Example 1:

[0043] A method for preparing fly ash-derived high thermal conductivity mullite ceramics by using molten salt filling is completed by the following steps:

[0044] First, the fly ash was crushed, and then the crushed fly ash was mixed with the aluminum source by ball milling at a rotation speed of 300 r / min and a ball-to-material ratio of 1:1 for 4 hours, and finally sieved to obtain a uniformly mixed powder;

[0045] 2. The mixed powder is placed in a corundum crucible, and in an air atmosphere, the temperature is first raised to 500°C at a rate of 5°C / min, then raised to 1300°C at a rate of 2.5°C / min, and finally sintered in an air atmosphere at a temperature of 1300°C for 2 hours. After the reaction is completed, the furnace is cooled to obtain fly ash-derived mullite ceramics;

[0046] 3. Under the condition of vacuum degree of 0.1 Pa, the fly ash-derived mullite ceramics were vacuum impregnated in high-temperature molten inorganic salt for 2 hours, taken out and naturally cooled to obtain fly ash-derived high thermal conductivity mullite ceramics.

[0047] In step 1, the fly ash is crushed into blocks with a size of less than 75 μm.

[0048] The aluminum source in step 1 is alumina powder with a purity of 99.98%, sourced from Inner Mongolia Haite Huacai Technology Co., Ltd.

[0049] The sieving described in step 1 is to pass through a 200-mesh sieve.

[0050] The fly ash described in step 1 comes from bulk fly ash of Inner Mongolia Zhalainuoer Coal Industry Co., Ltd., and its composition is SiO2 content 27.76wt%, Al2O3 content 12.78wt%, Fe2O3 content 26.68wt%, CaO content 15.09wt%, MgO content 1.29wt%, Na2O content 11.42wt%, and K2O content 4.98wt%.

[0051] The mass percentage of the aluminum source in the uniformly mixed powder described in step 1 is 0%.

[0052] The high-temperature molten inorganic salt in step 3 is high-temperature molten sodium fluoride (melting point 993° C.).

[0053] The mass percentage of inorganic salt in the fly ash-derived high thermal conductivity mullite ceramic prepared in step three is 10.01%.

[0054] The maximum operating temperature of the fly ash-derived high thermal conductivity mullite ceramic prepared in step three is 893°C.

[0055] Example 2: This example differs from Example 1 in that the mass percentage of the aluminum source in the uniformly mixed powder in Step 1 is 7%, and the mass percentage of the inorganic salt in the fly ash-derived high thermal conductivity mullite ceramic prepared in Step 3 is 20.32%. Other steps are the same as in Example 1.

[0056] Example 3: This example differs from Example 1 in that the mass percentage of the aluminum source in the uniformly mixed powder in Step 1 is 14%; and the mass percentage of the inorganic salt in the fly ash-derived high thermal conductivity mullite ceramic prepared in Step 3 is 30.15%. Other steps are the same as in Example 1.

[0057] Example 4: This example differs from Example 1 in that the mass percentage of the aluminum source in the uniformly mixed powder in Step 1 is 21%, and the mass percentage of the inorganic salt in the fly ash-derived high thermal conductivity mullite ceramic prepared in Step 3 is 40.83%. Other steps are the same as in Example 1.

[0058] Example 5: This example differs from Example 1 in that the mass percentage of the aluminum source in the uniformly mixed powder in Step 1 is 28%, and the mass percentage of the inorganic salt in the fly ash-derived high thermal conductivity mullite ceramic prepared in Step 3 is 50.02%. Other steps are the same as in Example 1.

[0059] Figure 1 This is a microscopic morphology of the fly ash-derived mullite ceramic prepared in step 2 of Example 3. As can be seen from the figure, when the mass percentage of the aluminum source in the mixed uniform powder is 14%, mullite whiskers with a diameter of about 100 nm and an aspect ratio of 1:7 are produced in the final product, indicating that mullite ceramics were successfully prepared using the method of this example.

[0060] Figure 2 This is a comparison chart of the porosity of fly ash-derived mullite ceramics prepared in step 2 of Examples 1 to 5. As can be seen from the figure, when the mass percentage of the aluminum source in the mixed powder is 14%, the prepared mullite ceramic is a porous ceramic with an apparent porosity of 51%.

[0061] Figure 3 This is the element distribution diagram of the fly ash-derived high-thermal-conductivity mullite ceramic prepared in step 3 of Example 3. As shown in the figure, when the mass percentage of the aluminum source in the mixed powder is 14%, after the inorganic salt filling, the NaF inorganic salt fills the pores of the porous mullite ceramic and is evenly distributed throughout the ceramic.

[0062] Figure 4This is a comparison chart of the thermal conductivity of the fly ash-derived mullite ceramic prepared in step 2 of Examples 1 to 5 and the fly ash-derived high-thermal-conductivity mullite ceramic prepared in step 3. As can be seen from the figure, when the mass percentage of the aluminum source in the mixed powder is 14%, the thermal conductivity of the prepared mullite porous ceramic increases from 0.6005 W / (m·K) to 1.1322 W / (m·K) after inorganic salt filling. When the mass percentage of the aluminum source in the mixed powder is 28%, the thermal conductivity of the prepared mullite porous ceramic increases from 0.4327 W / (m·K) to 1.4816 W / (m·K) after inorganic salt filling.

Claims

1. A method for preparing fly ash-derived high thermal conductivity mullite ceramics by using molten salt filling, characterized in that It is done in the following steps: First, crush the fly ash, then mix the crushed fly ash with the aluminum source by ball milling at a rotation speed of 250r / min~400r / min and a ball-to-material ratio of (1~2):1 for 2h~6h, and finally pass through a 200-mesh sieve to obtain a uniformly mixed powder; The mass percentage of the aluminum source in the uniformly mixed powder is 7% to 28%; the aluminum source is aluminum oxide; The fly ash is bulk fly ash from Zhalainuoer, Inner Mongolia, and has the following components: SiO2 content 27.76wt%, Al2O3 content 12.78wt%, Fe2O3 content 26.68wt%, CaO content 15.09wt%, MgO content 1.29wt%, Na2O content 11.42wt%, and K2O content 4.98wt%.

2. In an air atmosphere, first heating the uniformly mixed powder to 300°C~500°C at a rate of 5°C / min~10°C / min, then heating to 1150°C~1350°C at a rate of 2°C / min~2.5°C / min, and sintering the uniformly mixed powder for 0.5h~3h in an air atmosphere at a temperature of 1150°C~1350°C. After the reaction is completed, the powder is cooled in the furnace to obtain fly ash-derived mullite ceramics; 3. Vacuum impregnation of fly ash-derived mullite ceramics in a high-temperature molten inorganic salt, and then naturally cooling the ceramics to obtain fly ash-derived mullite ceramics with high thermal conductivity; The mass percentage of inorganic salts in the prepared fly ash-derived high thermal conductivity mullite ceramics ranges from 10.01% to 50.02%; The high-temperature molten inorganic salt is high-temperature molten sodium fluoride or high-temperature molten potassium fluoride.

2. The method for preparing fly ash-derived high thermal conductivity mullite ceramics by using molten salt filling according to claim 1, characterized in that In step 1, the fly ash is crushed into blocks with a size of less than 75 μm.

3. The method for preparing fly ash-derived high thermal conductivity mullite ceramics by using molten salt filling according to claim 1, characterized in that The vacuum impregnation treatment in step 3 is specifically performed under a vacuum degree of 0.1 Pa to 1 Pa for 0.5 h to 2 h.

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