Heat storage microcapsule with shell layer of shell-imitating structure and preparation method thereof

Abstract

The application discloses a heat storage microcapsule with a shell layer of imitated shell structure and a preparation method thereof. The preparation method comprises the following steps: S1, washing an aluminum-based alloy powder by using a dilute oxalic acid solution to obtain a pretreated aluminum-based alloy powder; S2, placing the pretreated aluminum-based alloy powder in a NiCl2 solution to obtain a microcapsule precursor; S3, placing the microcapsule precursor in a high-temperature furnace containing an oxygen atmosphere, controlling the gas flow rate to be 1-6 ml / min, heating to 900-1200 DEG C at a heating rate of 3-10 DEG C / min, keeping for 2-5 hours, and cooling at a cooling rate of 3-10 DEG C / min to obtain the heat storage microcapsule with the shell layer of imitated shell structure. The application has the characteristics of low raw material cost, simple preparation process and easy realization of industrial production; the prepared heat storage microcapsule with the shell layer of imitated shell structure can improve the heat utilization rate and utilization efficiency, has a high use temperature and a long service life.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat storage materials, and particularly relates to a heat storage microcapsule with a shell layer of a shell-imitating structure and a preparation method thereof. BACKGROUND

[0002] Heat storage technology is an important means to improve the utilization rate of renewable energy and the utilization efficiency of non-renewable energy, and can achieve the purpose of flexible heat source allocation. Aluminum-silicon alloy has been proved to be an excellent heat storage material, which has a high heat storage density, a high thermal conductivity, and a suitable phase change temperature, and is suitable for heat energy storage systems of photothermal power generation and industrial waste heat recovery. However, the molten liquid of aluminum-silicon alloy may leak at high temperature, which may cause corrosion and safety problems to the base material or the packaging container. Therefore, it is of great significance to package the aluminum-silicon alloy to ensure its stability in use. At present, the packaging methods for aluminum-based alloy mainly include macroscopic packaging and microencapsulation. Compared with macroscopic packaging, the microcapsule has the advantages that it has good secondary processability and can be prepared into heat storage bricks, heat storage balls, honeycomb ceramics or heat storage fluids, and the shell layer of the microcapsule has a small specific gravity and a higher heat storage density than the macroscopic capsule.

[0003] There are many methods for preparing high-temperature phase change heat storage microcapsules in the prior art, for example: an Al / Al2O3 heat storage material and a preparation method thereof (201010127955.5) patent technology, which uses aluminum powder as raw material and prepares Al2O3-coated Al powder core-shell composite phase change heat storage material by atomization and oxygen atmosphere cooling method. The core-shell structure of the composite phase change heat storage material has high requirements for equipment, complex preparation process, difficult to control, thin shell layer, and is difficult to meet the strength requirements. The Chinese patent with publication number CN108300426A discloses a high-temperature phase change heat storage microcapsule based on aluminum-silicon alloy and a preparation method thereof. The technology mixes aluminum-silicon alloy powder, aluminum chloride and ethyl acetate in proportion, adds a mixed solution of aluminum-silicon alloy powder and anhydrous ethanol under water bath stirring, and then adds a mixed solution of aluminum-silicon alloy powder and acetic acid. After standing, filtering, washing and drying, the high-temperature phase change heat storage microcapsule based on aluminum-silicon alloy is obtained by calcining. However, the latent heat retention rate of the prepared microcapsule is not high, and the microcapsule shell layer cannot withstand multiple changes of thermal stress, and the thermal cycle performance is poor, and the service life is limited. A whisker-toughened phase change heat storage microcapsule and a preparation method thereof (202011169834.7) patent technology, aluminum or aluminum-silicon alloy powder is placed in pressurized steam, then immersed in silica sol precursor, pH value is adjusted, and filtered; the filtered residue is dried, and then placed in a muffle furnace, and calcined at 1050-1250℃ in air atmosphere to obtain a whisker-toughened phase change heat storage microcapsule. The heat storage density and thermal cycle performance need to be improved. The patent technology of "a high-temperature phase change heat storage microcapsule with whisker / fiber coating layer and a preparation method thereof" (CN202210085306) mixes the surface-treated alloy powder with the glucose solution, and then obtains the microcapsule precursor through hydrothermal reaction, and the microcapsule with composite whisker / fiber is obtained by controlling the calcination system and oxygen content. However, the preparation cost of the process is high, and the thermal cycle stability still has room for improvement. SUMMARY

[0004] The purpose of the present application is to overcome the above-mentioned deficiencies of the prior art, and to provide a heat storage microcapsule with a shell layer of imitated shell structure and a preparation method thereof.

[0005] The preparation method of the heat storage microcapsule with the shell layer of imitated shell structure comprises the following steps:

[0006] S1, washing aluminum-based alloy powder with dilute oxalic acid solution to obtain pretreated aluminum-based alloy powder;

[0007] S2, placing the pretreated aluminum-based alloy powder in a NiCl2 solution, heating to a certain temperature and reacting for a period of time to obtain a microcapsule precursor;

[0008] S3, placing the microcapsule precursor into a high-temperature furnace with an oxygen-containing atmosphere, controlling the gas flow rate to be 1-6 ml / min, and heating at a rate of 3-10 DEG C / min to 900-1200 DEG C, and keeping for 2-5 h, and cooling at a rate of 3-10 DEG C / min to obtain heat storage microcapsules with a shell layer having a shell structure simulating a shell.

[0009] Further, in step S3, the oxygen concentration in the oxygen-containing atmosphere is greater than 5%.

[0010] Further, in step S1, the specific operation is to place the aluminum-based alloy powder into a dilute oxalic acid solution and stir in a water bath for 20-40 min, and the water bath temperature is 40-60 DEG C.

[0011] Further, in step S2, the reaction temperature is 70-100 DEG C, and the reaction time is 10-20 min.

[0012] Further, in step S2, the concentration of the NiCl2 solution is 0.05-0.2 g / L.

[0013] Further, the particle size of the aluminum-based alloy powder is 20-80 mu m.

[0014] Further, the Al content in the aluminum-based alloy powder is not less than 80 wt%, which can ensure that there is sufficient and uniformly distributed aluminum on the surface of the alloy, and the surface aluminum will be consumed to form a shell layer during the preparation process.

[0015] A heat storage microcapsule with a shell layer having a shell structure simulating a shell is prepared by the above method.

[0016] The present application first pretreats commercially available aluminum-based alloy powder in the first step, washes the powder using an oxalic acid solution, removes the surface oxide film, and enables the metal aluminum to directly contact with the external medium, which facilitates the next step of processing. In the second step, the alloy powder is further treated using a NiCl2 solution, which enables the metal nickel particles to be deposited on the alloy surface through a displacement reaction, and enables the aluminum to easily undergo a hydration reaction to produce flaky AlOOH, and the crystals are arranged on the alloy surface to form a pre-coated shell layer. Measurement shows that the specific surface area of the microcapsule precursor is increased by several times compared to the specific surface area of the raw aluminum-based alloy powder, which indicates that the pre-treatment indeed forms a porous structure on the surface of the microcapsule precursor. During the heating process, thermal stress and volume expansion will cause cracks in the pre-coated shell layer on the alloy surface, and when the temperature exceeds the melting point of the alloy, the melt will leak to the surface of the sample through the cracks.

[0017] When the temperature reaches the melting point of the alloy, the alloy leaks out of the crack, and the part first contacted with oxygen will react to form an alumina film under the catalysis of nickel particles, thereby slowing down the outflow of the alloy. Here, we control the flow rate of the gas during the reaction process to balance the outflow of the melt and the formation rate of the oxidation film. The continuous expansion of the alloy causes the alloy in the core to continuously flow outward, resulting in the continuous diffusion of the outflowing melt along the porous surface. Due to the complex porous structure of the surface, the flow rate of the alloy on the surface is slow, and the melt surface first contacted with oxygen will react to form an alumina film, thereby inhibiting the radial flow of the melt and expanding horizontally along the alloy surface. During the constant temperature stage, no volume expansion occurs, and as the leaked melt continues to oxidize, a uniform and dense shell layer with a shell-like structure is formed, preventing the continuous penetration of oxygen. During the cooling process, the cooling rate is controlled, and due to the shrinkage of the melt, a negative pressure is slowly formed inside the shell layer, thereby leaving an expansion space. Similarly, the shell of a shell-like structure such as a shellfish is thin but has ultra-high strength, and such a structure also gives the microcapsule shell layer high strength and toughness, which can withstand thermal stress generated by thermal cycling.

[0018] The heat storage microcapsule with a shell layer having a shell-like structure prepared by the present application has a heat storage density of 350-480 J / g, a thermal conductivity of 70.5-120.3 W / (m·K), and a specific heat capacity of 1.1-1.7 J / (g·K). After 5000 thermal cycles, the heat storage density retention rate is not less than 95%.

[0019] Therefore, the present application has the characteristics of low raw material cost, simple preparation process and easy industrial production; the prepared heat storage microcapsule with a shell layer having a shell-like structure can improve the utilization rate and efficiency of heat, has a high use temperature and a long service life, and is suitable for fields such as solar thermal power generation, high-temperature heat exchange of industrial furnaces, and heat recovery of high-temperature industrial waste gas. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The cross-sectional view and surface view of the heat storage microcapsule with a shell layer having a shell-like structure prepared in Example 3. DETAILED DESCRIPTION

[0021] The following are specific embodiments of the present application, which further describe the technical solutions of the present application, but the present application is not limited to these embodiments.

[0022] Example 1

[0023] Preparation of a heat storage microcapsule with a shell layer having a shell-like structure includes the following steps:

[0024] (1) 10 g of metal Al-Si powder (Al content of 90 wt%, particle size of metal powder of 50 μm) was placed in a dilute oxalic acid solution and stirred in a water bath for 30 min to obtain pretreated metal powder;

[0025] (2) The pretreated metal powder was placed in 100 mL of a NiCl2 solution with a concentration of 0.05 g / L, heated to 80°C, and stirred for 15 min to obtain a microcapsule precursor;

[0026] (3) The microcapsule precursor was placed in a high-temperature furnace with an oxygen content of 10%, the gas flow rate was 3 ml / min, and the temperature was raised to 900°C at a rate of 3°C / min, and the temperature was maintained for 3 h, and then cooled at a rate of 5°C / min to obtain a heat storage microcapsule with a shell layer having a shell structure.

[0027] Example 2

[0028] Preparation of a heat storage microcapsule with a shell layer having a shell structure includes the following steps:

[0029] (1) 15 g of metal Al powder (Al content of 99.9 wt%, particle size of metal powder of 53 μm) was placed in a dilute oxalic acid solution and stirred in a water bath for 20 min to obtain pretreated metal powder;

[0030] (2) The pretreated metal powder was placed in 100 mL of a NiCl2 solution with a concentration of 0.1 g / L, heated to 70°C, and stirred for 20 min to obtain a microcapsule precursor;

[0031] (3) The microcapsule precursor was placed in a high-temperature furnace with an oxygen content of 10%, the gas flow rate was 1 ml / min, and the temperature was raised to 1200°C at a rate of 10°C / min, and the temperature was maintained for 5 h, and then cooled at a rate of 3°C / min to obtain a heat storage microcapsule with a shell layer having a shell structure.

[0032] Example 3

[0033] Preparation of a heat storage microcapsule with a shell layer having a shell structure includes the following steps:

[0034] (1) 20 g of metal Al-Si powder (Al content of 88 wt%, particle size of metal powder of 48 μm) was placed in a dilute oxalic acid solution and stirred in a water bath for 40 min to obtain pretreated metal powder;

[0035] (2) The pretreated metal powder was placed in 100 mL of a NiCl2 solution with a concentration of 0.15 g / L, heated to 90°C, and stirred for 15 min to obtain a microcapsule precursor;

[0036] (3) The microcapsule precursor is placed in a high-temperature furnace with 21% oxygen content, the gas flow rate is 6ml / min, the temperature is raised to 1000℃ at a rate of 5℃ / min, and the temperature is kept for 5h, and then the microcapsule precursor is cooled at a rate of 5℃ / min to obtain the heat storage microcapsule with shell layer of imitated shell structure.

[0037] Figure 1 The cross-sectional view and surface view of the heat storage microcapsule with shell layer of imitated shell structure prepared in the present embodiment.

[0038] The specific surface area of the raw material is 0.16m 2 / g, and the specific surface area of the microcapsule precursor is 3.67m 2 / g, which is increased by about 23 times, indicating that steps (1) and (2) form a porous structure on the surface of the microcapsule precursor.

[0039] Example 4

[0040] The preparation of a heat storage microcapsule with shell layer of imitated shell structure includes the following steps:

[0041] (1) 17g of metal Al-Si powder (Al content is 80wt%, and the particle size of the metal powder is 42μm) is placed in a dilute oxalic acid solution and stirred in a water bath for 40min to obtain a pretreated metal powder;

[0042] (2) The pretreated metal powder is placed in a 100mL NiCl2 solution with a concentration of 0.2g / L, heated to 100℃, and stirred for 10min to obtain a microcapsule precursor;

[0043] (3) The microcapsule precursor is placed in a high-temperature furnace with 21% oxygen content, the gas flow rate is 6ml / min, the temperature is raised to 1000℃ at a rate of 5℃ / min, and the temperature is kept for 5h, and then the microcapsule precursor is cooled at a rate of 5℃ / min to obtain the heat storage microcapsule with shell layer of imitated shell structure.

[0044] Table 1 Performance table of examples 1-4

[0045] Example 1 Example 2 Example 3 Example 4 Latent heat value / J g -1 ]] 450 350 480 420 Cycling temperature / °C 500-700 600-750 500-700 500-700 Latent heat retention rate after 5000 thermal cycles / % 100 95 100 100 Thermal conductivity / W m -1 K -1 ]]> 80.1 120.3 73.8 70.5

[0046] As can be seen from Table 1, the heat storage microcapsule with shell layer of imitated shell structure prepared by the present application has a heat storage density of 350-480J / g, a thermal conductivity of 70.5-120.3W / (m﹒K), and a specific heat capacity of 1.1-1.7J / (g﹒K); and the heat storage density retention rate is not less than 95% after 5000 thermal cycles.

[0047] The above not involved, applicable to the prior art.

[0048] Although some specific embodiments of the present application have been described in detail by way of example with reference to the drawings, it is to be understood that the above examples are intended to be illustrative only and are not intended to limit the scope of the present application, and that various modifications and changes can be made by those skilled in the art to the particular embodiments described without departing from the spirit and scope of the present application. It is intended that the scope of the present application be limited only by the broadest interpretation of the appended claims to be accorded under 35 U.S.C. § 112.

Claims

1. A method for preparing heat storage microcapsules having a shell layer with a shell-like structure, characterized by, The method comprises the following steps: S1, washing the aluminum-based alloy powder with a dilute oxalic acid solution to obtain pretreated aluminum-based alloy powder; S2, placing the pretreated aluminum-based alloy powder in a NiCl2 solution, heating to a certain temperature and reacting for a period of time to obtain a microcapsule precursor; S3, placing the microcapsule precursor in a high-temperature furnace containing an oxygen-containing atmosphere, controlling the gas flow rate to be 1-6 ml / min, heating to 900-1200℃ at a rate of 3-10℃ / min, maintaining for 2-5 h, and cooling at a rate of 3-10℃ / min to obtain a heat storage microcapsule with a shell layer having a shell structure similar to a shell.

2. The method for preparing a heat storage microcapsule with a shell-like structure as described in claim 1, characterized in that, In step S3, the oxygen concentration in the oxygen-containing atmosphere is greater than 5%.

3. The method of claim 1, wherein the shell layer has a shell structure mimicking a shell of a mollusk. In step S1, the specific operation is to place the aluminum-based alloy powder in a dilute oxalic acid solution, water bath stirring for 20-40 min, and the water bath temperature is 40-60℃.

4. The method of claim 1, wherein the shell layer has a shell structure mimicking a shell of a mollusk. In step S2, the reaction temperature is 70-100℃, and the reaction time is 10-20 min.

5. The method of claim 1, wherein the shell layer has a shell structure mimicking a shell of a mollusk. In step S2, the concentration of the NiCl2 solution is 0.05-0.2 g / L.

6. The method of claim 1, wherein the shell layer has a shell structure mimicking a shell of a mollusk. The particle size of the aluminum-based alloy powder is 20-80 μm.

7. The method of claim 1, wherein the shell layer has a shell structure mimicking a shell of a mollusk. The Al content in the aluminum-based alloy powder is not less than 80 wt%.

8. A heat storage microcapsule with a shell layer having a shell structure similar to a shell, which is prepared by the preparation method of any one of claims 1-7.

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