Method for preparing high-strength fly ash heat storage composite material by sodium sulfate assisted sintering

Abstract

The invention discloses a method for preparing a high-strength fly ash heat storage composite material through sodium sulfate assisted sintering, and belongs to the field of heat storage ceramics. The invention aims to solve the problem that a high-strength fly ash heat storage composite material cannot be manufactured in the prior art. The method comprises the following steps: 1, ball-milling and uniformly mixing sodium sulfate powder and fly ash powder; 2, sintering reaction; 3, adding carbonate powder; 4, compression molding; and 5, sintering the blank. The method is used for preparing the high-strength fly ash heat storage composite material through sodium sulfate auxiliary sintering.

Description

Technical Field

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

[0002] High strength is one of the key properties of shaped phase change materials in practical applications. It not only ensures the structural stability of the materials under high temperature and multiple cycle conditions, but also significantly extends their service life. At present, fly ash-based shaped phase change materials mainly use chemically stable carbonates as phase change materials. During the phase change process, the interaction between carbonates and fly ash is weak, resulting in relative slippage of fly ash particles under external forces when carbonates melt, thus leading to a significant decrease in the mechanical properties of the materials. At present, there is no technology that can effectively improve the compressive strength on the basis of using the mixed pressing method to prepare fly ash heat storage materials. Summary of the Invention

[0003] The present invention aims to solve the problem that the prior art cannot manufacture high-strength fly ash heat storage composite materials, and further provides a method for preparing high-strength fly ash heat storage composite materials by sodium sulfate-assisted sintering.

[0004] A method for preparing high-strength fly ash heat storage composite materials by sodium sulfate-assisted sintering is carried out according to the following steps:

[0005] 1. Ball-mill and mix sodium sulfate powder and fly ash powder evenly to obtain sodium sulfate / fly ash mixed powder;

[0006] 2. Under the condition of a temperature of 900 °C to 1100 °C, sinter and react the sodium sulfate / fly ash mixed powder for 2 h to 3 h, and then naturally cool it to room temperature to obtain sodium sulfate / sodium silicate / fly ash composite powder;

[0007] 3. Add carbonate powder to the sodium sulfate / sodium silicate / fly ash composite powder, and then ball-mill and mix evenly to obtain sodium sulfate / sodium silicate / fly ash / carbonate prefabricated powder;

[0008] 4. Press the sodium sulfate / sodium silicate / fly ash / carbonate prefabricated powder into a mold to obtain a dense heat storage material green body;

[0009] 5. Under the condition of a temperature of 800 °C to 900 °C, sinter the dense heat storage material green body to obtain high-strength fly ash heat storage composite materials.

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

[0011] 1. The present invention uses the sodium sulfate / sodium silicate / fly ash powder generated by the reaction of sodium sulfate and fly ash as raw materials, and utilizes the bonding effect of sodium silicate to improve the mechanical properties of the heat storage composite material, which is innovative and practical. Its advantages lie in significantly improving the mechanical strength and heat storage performance of the composite material, while realizing the high-value utilization of waste resources such as fly ash, reflecting the concept of green environmental protection and the idea of circular economy. This method has high efficiency and controllable cost, is applicable to fields such as high-temperature heat storage and clean energy storage, and has good application prospects.

[0012] 2. When the mass ratio of the sodium sulfate powder to the fly ash powder in the present invention is 1:10, the density of the prepared high-strength fly ash heat storage composite material can reach 1.8 g / cm 3 , the latent heat of phase change value is 73.54 kJ / kg, and the compressive strength at 850 °C is 288.29 MPa, that is, the mechanical test is carried out above the melting point of the carbonate, and good mechanical properties can still be maintained. Description of the Drawings

[0013] Figure 1 SEM pattern of the sodium sulfate / fly ash mixed powder prepared in Step 1 of Example 1;

[0014] Figure 2 XRD patterns of the sodium sulfate / fly ash mixed powder prepared in Step 1 of Example 1 and the sodium sulfate / sodium silicate / fly ash composite powder prepared in Step 2, 1 is the sodium sulfate / fly ash mixed powder, and 2 is the sodium sulfate / sodium silicate / fly ash composite powder;

[0015] Figure 3 SEM pattern of the sodium sulfate / sodium silicate / fly ash composite powder prepared in Step 2 of Example 1;

[0016] Figure 4 Density pattern of the high-strength fly ash heat storage composite materials prepared in Examples 1 to 5;

[0017] Figure 5 Latent heat storage pattern of the high-strength fly ash heat storage composite materials prepared in Examples 1 to 5;

[0018] Figure 6 Compressive strength pattern at 850 °C of the high-strength fly ash heat storage composite materials prepared in Examples 1 to 5. Detailed Embodiments

[0019] Detailed Embodiment 1: A method for preparing a high-strength fly ash heat storage composite material by sodium sulfate-assisted sintering is carried out according to the following steps:

[0020] 1. Ball-mill and mix the sodium sulfate powder and the fly ash powder evenly to obtain a sodium sulfate / fly ash mixed powder;

[0021] II. Under the condition that the temperature is 900°C to 1100°C, sinter the sodium sulfate / fly ash mixed powder for 2h to 3h, and then naturally cool it to room temperature to obtain a sodium sulfate / sodium silicate / fly ash composite powder;

[0022] III. Add carbonate powder to the sodium sulfate / sodium silicate / fly ash composite powder, and then ball-mill and mix evenly to obtain a sodium sulfate / sodium silicate / fly ash / carbonate prefabricated powder;

[0023] IV. Press the sodium sulfate / sodium silicate / fly ash / carbonate prefabricated powder into a shape to obtain a dense green body of the heat storage material;

[0024] V. Under the condition that the temperature is 800°C to 900°C, sinter the dense green body of the heat storage material to obtain a high-strength fly ash heat storage composite material.

[0025] In this specific embodiment, the fly ash particles are sintered during the molten salt melting process, effectively improving the mechanical strength of the fly ash and improving its overall performance. At present, there is no related technology that can sinter fly ash particles during the melting process of inorganic salts to prepare high-strength heat storage ceramics.

[0026] The formation reaction mechanism of sodium silicate in step II of this specific embodiment is as follows:

[0027] 2Na2SO4 + 2SiO2 → 2Na2SiO3 + 2SO2 + O2 (reaction temperature 900°C to 1100°C);

[0028] The principle of the latent heat storage process of the high-strength fly ash heat storage composite material prepared in step V of this specific embodiment is as follows:

[0029] Endothermic process: solid carbonate → liquid carbonate;

[0030] Exothermic process: liquid carbonate → solid carbonate.

[0031] The beneficial effects of this embodiment are:

[0032] 1. This embodiment uses the sodium sulfate / sodium silicate / fly ash powder generated by the reaction of sodium sulfate and fly ash as raw materials, and uses the bonding effect of sodium silicate to improve the mechanical properties of the heat storage composite material, which is innovative and practical. Its advantages are that it significantly improves the mechanical strength and heat storage performance of the composite material, and at the same time realizes the high-value utilization of waste resources such as fly ash, reflecting the concept of green environmental protection and the idea of circular economy. This method has high efficiency and controllable cost, is suitable for high-temperature heat storage and clean energy storage and other fields, and has good application prospects.

[0033] 2. When the mass ratio of sodium sulfate powder to fly ash powder in this embodiment is 1:10, the density of the prepared high-strength fly ash thermal energy storage composite material can reach 1.8 g / cm 3 , the latent heat of phase change value is 73.54 kJ / kg, and the compressive strength at 850 °C is 288.29 MPa, that is, the mechanical test is carried out above the melting point of the carbonate, and good mechanical properties can still be maintained.

[0034] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that: the particle size of the sodium sulfate powder described in Step 1 is 100 mesh to 200 mesh; the particle size of the fly ash powder described in Step 1 is 120 mesh to 200 mesh; the mass ratio of the sodium sulfate powder to the fly ash powder in Step 1 is 1:(10 - 30). Others are the same as Specific Embodiment 1.

[0035] Specific Embodiment 3: The difference between this embodiment and one of Specific Embodiments 1 or 2 is that: the sintering reaction is carried out in an air atmosphere in Step 2 and Step 5. Others are the same as Specific Embodiment 1 or 2.

[0036] Specific Embodiment 4: The difference between this embodiment and one of Specific Embodiments 1 to 3 is that: in Step 2, the sodium sulfate / fly ash mixed powder is heated to 900 °C to 1100 °C at a heating rate of 2 °C / min to 5 °C / min. Others are the same as Specific Embodiment 3.

[0037] Specific Embodiment 5: The difference between this embodiment and one of Specific Embodiments 1 to 4 is that: the carbonate powder described in Step 3 is sodium carbonate powder or potassium carbonate powder; the particle size of the carbonate powder described in Step 3 is 100 mesh to 200 mesh. Others are the same as Specific Embodiments 1 to 4.

[0038] Specific Embodiment 6: The difference between this embodiment and one of Specific Embodiments 1 to 5 is that: the mass ratio of the sodium sulfate / sodium silicate / fly ash composite powder to the carbonate powder in Step 3 is (1 - 3):1. Others are the same as Specific Embodiments 1 to 5.

[0039] Specific Embodiment 7: The difference between this embodiment and one of Specific Embodiments 1 to 6 is that: the ball milling and mixing evenly described in Step 1 and Step 3 is specifically carried out under the conditions of a rotation speed of 200 r / min to 400 r / min and a ball-to-material mass ratio of (2 - 4):1, and ball milling for 4 h to 8 h. Others are the same as Specific Embodiments 1 to 6.

[0040] Specific Embodiment 8: The difference between this embodiment and one of Specific Embodiments 1 to 7 is that: the pressing and forming described in Step 4 is specifically carried out under the condition of a pressure of 20 MPa to 200 MPa for 1 min to 5 min. Others are the same as Specific Embodiments 1 to 7.

[0041] Embodiment Nine: The difference between this embodiment and any one of Embodiments One to Eight is that: in Step Five, the dense green body of the heat storage material is heated to 800°C to 900°C at a rate of 0.5°C / min to 2°C / min. Others are the same as those in Embodiments One to Eight.

[0042] Embodiment Ten: The difference between this embodiment and any one of Embodiments One to Nine is that: in Step Five, the dense green body of the heat storage material is sintered for 2 h to 4 h under the condition that the temperature is 800°C to 900°C. Others are the same as those in Embodiments One to Nine.

[0043] The following examples are used to verify the beneficial effects of the present invention:

[0044] Example One:

[0045] A method for preparing a high-strength fly ash heat storage composite material by sodium sulfate-assisted sintering is carried out according to the following steps:

[0046] I. Under the conditions of a rotation speed of 400 r / min and a ball-to-material mass ratio of 4:1, the sodium sulfate powder and the fly ash powder are ball-milled and mixed for 8 h to obtain a sodium sulfate / fly ash mixed powder;

[0047] The average particle size of the sodium sulfate powder is 200 mesh; the average particle size of the fly ash powder is 200 mesh; the mass ratio of the sodium sulfate powder to the fly ash powder is 1:10;

[0048] II. In an air atmosphere, the sodium sulfate / fly ash mixed powder is heated to 1100°C at a heating rate of 5°C / min. Under the conditions of an air atmosphere and a temperature of 1100°C, the sodium sulfate / fly ash mixed powder is sintered and reacted for 3 h, and then naturally cooled to room temperature to obtain a sodium sulfate / sodium silicate / fly ash composite powder;

[0049] III. Sodium carbonate powder is added to the sodium sulfate / sodium silicate / fly ash composite powder, and then under the conditions of a rotation speed of 400 r / min and a ball-to-material mass ratio of 4:1, it is ball-milled and mixed for 8 h to obtain a sodium sulfate / sodium silicate / fly ash / carbonate preform powder;

[0050] The carbonate powder is sodium carbonate powder; the average particle size of the carbonate powder is 140 mesh; the mass ratio of the sodium sulfate / sodium silicate / fly ash composite powder to the carbonate powder is 1:1;

[0051] IV. Under the condition of a pressure of 200 MPa, the sodium sulfate / sodium silicate / fly ash / carbonate preform powder is pressed into shape for 5 min to obtain a dense green body of the heat storage material;

[0052] V. Under an air atmosphere, the dense green body of the heat storage material was heated to 900 °C at a rate of 2 °C / min, and then sintered for 4 h under an air atmosphere at a temperature of 900 °C to obtain a high-strength fly ash heat storage composite material.

[0053] In Step II, the container used for the sintering reaction is an alumina crucible.

[0054] In Step V, the reaction equipment used for the sintering reaction is a muffle furnace.

[0055] The fly ash powder described in Step I is sourced from Zhalainuoer Coal Industry Co., Ltd.; the fly ash powder is a hollow spherical powder, and its specific composition is as follows: the mass percentage of water is 1%, the mass percentage of carbon is 1%, the mass percentage of silicon dioxide is 50%, the mass percentage of aluminum oxide is 18%, the mass percentage of iron oxide is 12%, the mass percentage of calcium oxide is 15%, and the mass percentage of other oxides is 3%.

[0056] The sodium sulfate powder and sodium carbonate powder described in Step I and Step III are sourced from Inner Mongolia Haitahua Materials Technology Co., Ltd., and their purities are both greater than 95%.

[0057] Through ion chromatography testing, the mass percentage of sodium silicate in the high-strength fly ash heat storage composite material prepared in this example was measured to be 4.50%.

[0058] Example 2: The difference between this example and Example 1 is that: in Step I, the mass ratio of the sodium sulfate powder to the fly ash powder is 1:15; the mass percentage of sodium silicate in the high-strength fly ash heat storage composite material prepared in Step V is 3.02%. Others are the same as in Example 1.

[0059] Example 3: The difference between this example and Example 1 is that: in Step I, the mass ratio of the sodium sulfate powder to the fly ash powder is 1:20; the mass percentage of sodium silicate in the high-strength fly ash heat storage composite material prepared in Step V is 2.23%. Others are the same as in Example 1.

[0060] Example 4: The difference between this example and Example 1 is that: in Step I, the mass ratio of the sodium sulfate powder to the fly ash powder is 1:25; the mass percentage of sodium silicate in the high-strength fly ash heat storage composite material prepared in Step V is 1.87%. Others are the same as in Example 1.

[0061] Example 5: The difference between this example and Example 1 is that: in Step I, the mass ratio of the sodium sulfate powder to the fly ash powder is 1:30; the mass percentage of sodium silicate in the high-strength fly ash heat storage composite material prepared in Step V is 1.60%. Others are the same as in Example 1.

[0062] Figure 1SEM pattern of the sodium sulfate / fly ash mixed powder prepared in Step 1 of Example 1; As can be seen from the figure, the sodium sulfate / fly ash mixed powder prepared from sodium sulfate powder and fly ash powder is mainly composed of fly ash hollow spheres and sodium sulfate blocks.

[0063] Figure 2 XRD patterns of the sodium sulfate / fly ash mixed powder prepared in Step 1 of Example 1 and the sodium sulfate / sodium silicate / fly ash composite powder prepared in Step 2, where 1 is the sodium sulfate / fly ash mixed powder and 2 is the sodium sulfate / sodium silicate / fly ash composite powder; As can be seen from the figure, sodium silicate is produced by the sintering reaction of the sodium sulfate / fly ash mixed powder.

[0064] Figure 3 SEM pattern of the sodium sulfate / sodium silicate / fly ash composite powder prepared in Step 2 of Example 1; As can be seen from the figure, the fly ash hollow microspheres disappear in the sodium sulfate / sodium silicate / fly ash composite powder.

[0065] Figure 4 Density pattern of the high-strength fly ash heat storage composite material prepared in Examples 1 to 5; As can be seen from the figure, when the mass ratio of the sodium sulfate powder to the fly ash powder in Step 1 of Example 1 is 1:10, the density of the prepared high-strength fly ash heat storage composite material is 1.8 g / cm 3 。

[0066] Figure 5 Latent heat storage pattern of the high-strength fly ash heat storage composite material prepared in Examples 1 to 5; As can be seen from the figure, when the mass ratio of the sodium sulfate powder to the fly ash powder in Step 1 of Example 1 is 1:10, the latent heat of the prepared high-strength fly ash heat storage composite material is 73.54 kJ / kg.

[0067] The high-temperature pressure testing machine MTSDW-G20 of MTS (Shandong) Testing Instrument Co., Ltd. was used as the testing instrument, and the compressive strength test at 850 °C was carried out according to the standard of ISO 14544:2013 "Fine Ceramics (Advanced Ceramics, Advanced Technical Ceramics) - Determination of Mechanical Properties - Compressive Properties of Ceramic Composites at High Temperatures". Figure 6 Compressive strength pattern of the high-strength fly ash heat storage composite material prepared in Examples 1 to 5 at 850 °C; As can be seen from the figure, when the mass ratio of the sodium sulfate powder to the fly ash powder in Step 1 of Example 1 is 1:10, the compressive strength of the prepared high-strength fly ash heat storage composite material at 850 °C is 288.29 MPa, that is, the mechanical test is carried out above the melting point of sodium carbonate, and good mechanical properties can still be maintained.

Claims

1. A method for preparing a high-strength fly ash heat storage composite material by sodium sulfate-assisted sintering, characterized in that It is carried out in the following steps:

1. Mixing the sodium sulfate powder and the fly ash powder evenly by ball milling to obtain a sodium sulfate / fly ash mixed powder; 2. Sintering the sodium sulfate / fly ash mixed powder at a temperature of 900°C to 1100°C for 2h to 3h, and then naturally cooling to room temperature to obtain a sodium sulfate / sodium silicate / fly ash composite powder; 3. Adding carbonate powder to the sodium sulfate / sodium silicate / fly ash composite powder, and then ball milling to mix evenly to obtain sodium sulfate / sodium silicate / fly ash / carbonate prefabricated powder; Fourth, pressing and molding the sodium sulfate / sodium silicate / fly ash / carbonate prefabricated powder to obtain a dense heat storage material embryo; 5. Sinter the dense heat storage material green body at a temperature of 800°C to 900°C to obtain a high-strength fly ash heat storage composite material.

2. The method for preparing a high-strength fly ash heat storage composite material by sodium sulfate-assisted sintering according to claim 1, characterized in that The particle size of the sodium sulfate powder described in step one is 100 mesh to 200 mesh; the particle size of the fly ash powder described in step one is 120 mesh to 200 mesh; the mass ratio of the sodium sulfate powder to the fly ash powder described in step one is 1:(10-30).

3. The method for preparing a high-strength fly ash heat storage composite material by sodium sulfate-assisted sintering according to claim 1, characterized in that In step 2 and step 5, the sintering reaction is carried out in an air atmosphere.

4. The method for preparing a high-strength fly ash heat storage composite material by sodium sulfate-assisted sintering according to claim 1, characterized in that In step 2, the sodium sulfate / fly ash mixed powder is heated to 900° C. to 1100° C. at a heating rate of 2° C. / min to 5° C. / min.

5. The method for preparing a high-strength fly ash heat storage composite material by sodium sulfate-assisted sintering according to claim 1, characterized in that The carbonate powder described in step three is sodium carbonate powder or potassium carbonate powder; the particle size of the carbonate powder described in step three is 100 mesh to 200 mesh.

6. The method for preparing a high-strength fly ash heat storage composite material by sodium sulfate-assisted sintering according to claim 1, characterized in that The mass ratio of the sodium sulfate / sodium silicate / fly ash composite powder to the carbonate powder described in step three is (1-3):

1.

7. The method for preparing a high-strength fly ash heat storage composite material by sodium sulfate-assisted sintering according to claim 1, characterized in that The ball milling mixing described in step 1 and step 3 is specifically carried out for 4h to 8h at a rotation speed of 200r / min to 400r / min and a ball-to-material mass ratio of (2 to 4):

1.

8. The method for preparing a high-strength fly ash heat storage composite material by sodium sulfate-assisted sintering according to claim 1, characterized in that The pressing and molding described in step 4 is specifically performed under a pressure of 20 MPa to 200 MPa for 1 to 5 minutes.

9. The method for preparing a high-strength fly ash heat storage composite material by sodium sulfate-assisted sintering according to claim 1, characterized in that In step five, the temperature of the dense heat storage material embryo is raised to 800°C to 900°C at a rate of 0.5°C / min to 2°C / min.

10. The method for preparing a high-strength fly ash heat storage composite material by sodium sulfate-assisted sintering according to claim 1, characterized in that In step five, the dense heat storage material green body is sintered at a temperature of 800° C. to 900° C. for 2 h to 4 h.

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