Microcapsule with chemical and physical heat storage capacity and preparation method thereof

Abstract

The invention discloses a microcapsule with chemical and physical heat storage capacity and a preparation method thereof. The invention relates to the technical field of heat storage microcapsules. The preparation method comprises the following steps that S1, aluminum powder or aluminum-based alloy powder is placed in high-temperature water vapor or deionized water at the temperature of 100 DEG C, and porous aluminum powder or aluminum-based alloy powder is obtained after filtering and drying; s2, porous aluminum powder or aluminum-based alloy powder is placed in a metal compound solution to be subjected to a reduction reaction, and pretreated aluminum powder or aluminum-based alloy powder is obtained after filtering and drying; s3, calcium nitrate tetrahydrate or magnesium nitrate hexahydrate is added into deionized water, and then the pretreated aluminum powder or aluminum-based alloy powder is added; evaporating the solution to obtain a microcapsule precursor; and S4, carrying out heat treatment on the microcapsule precursor in flowing gas. The microcapsule with a complete structure is formed while consumption of raw materials is low, phase change latent heat of metal is kept to the maximum extent, and an oxide shell layer on the surface has the characteristic of chemical reaction heat storage.

Description

Technical Field

[0001] The invention relates to the technical field of heat storage microcapsules, and in particular to a microcapsule with chemical and physical heat storage capabilities and a preparation method thereof. Background Art

[0002] Aluminum-based alloys have been a hot topic in recent years as phase change thermal storage materials due to their suitable phase change temperature, high phase change latent heat and excellent thermal conductivity. They can be used in solar thermal power generation, valley power utilization and industrial waste heat recovery. Like other metals or alloys, aluminum-based alloys will have liquid phase when used at high temperatures, and have disadvantages such as fluidity and corrosion of the base material, so they must be encapsulated. Microencapsulation of thermal storage materials is a more appropriate choice. Microcapsules have the advantages of strong processability and high heat storage capacity, so they have become the research object of many scholars.

[0003] The patented technology of "An Al / Al2O3 thermal storage material and its preparation method" (201010127955.5) uses aluminum powder as raw material and prepares Al2O3 coated Al powder core-shell composite phase change thermal storage material by cooling in oxygen atmosphere after atomization. The patented technology of "A high-temperature phase change thermal storage microcapsule based on aluminum silicon alloy and its preparation method" (CN 108300426A) 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 stirring in a water bath, and then adds a mixed solution of aluminum silicon alloy powder and acetic acid, and then filters, washes, dries and sinters after standing to obtain a high-temperature phase change thermal storage microcapsule based on aluminum silicon alloy. The patented technology of "A high-temperature phase-change heat storage microcapsule with a whisker / fiber coating layer and its preparation method" (CN 114634798 B) is to place aluminum-based alloy powder in high-temperature water vapor for 10-60 minutes to obtain surface-modified aluminum-silicon alloy powder; then place the surface-modified aluminum-silicon alloy powder in a hydrothermal reactor filled with glucose aqueous solution, and perform hydrothermal reaction at 160-180℃ for 4-7 hours. After high-temperature sintering, aluminum-based microcapsules with whisker / fiber coating are obtained.

[0004] The limitations of aluminum-based microcapsules prepared in the prior art are: first, the microcapsules only rely on the phase change of the core to store heat, and the ceramic shell layer will occupy a certain proportion, and the heat storage capacity of the microcapsules is very limited; second, the formed ceramic shell layer has poor thermal shock stability, is easy to break during use, and has a short service life. Summary of the invention

[0005] The purpose of the present invention is to address the above-mentioned deficiencies in the prior art and to provide a microcapsule with chemical and physical heat storage capabilities and a preparation method thereof.

[0006] A method for preparing microcapsules with chemical and physical heat storage capacity of the present invention comprises the following steps:

[0007] S1. placing aluminum powder or aluminum-based alloy powder in high-temperature steam or 100° C. deionized water for a period of time, filtering and drying to obtain porous aluminum powder or aluminum-based alloy powder;

[0008] S2, placing the porous aluminum powder or aluminum-based alloy powder in a metal compound solution for reduction reaction, depositing metal nanoparticles on the surface of the porous aluminum powder or aluminum-based alloy powder, filtering and drying to obtain pretreated aluminum powder or aluminum-based alloy powder;

[0009] S3, adding calcium nitrate tetrahydrate or magnesium nitrate hexahydrate into deionized water, and after completely dissolving, adding pretreated aluminum powder or aluminum-based alloy powder; heating the mixed solution and placing it in a vacuum environment to evaporate the solution to obtain a microcapsule precursor;

[0010] S4, heat-treating the microcapsule precursor in a flowing gas according to the following temperature increase regime and then naturally cooling the microcapsules to obtain microcapsules with chemical and physical heat storage capacity;

[0011] The heating system is to heat to 500℃ at a heating rate of 10℃ / min and keep it at that temperature for 1h; then heat to 900-1200℃ at a heating rate of 5℃ / min and keep it at that temperature for 2-4h;

[0012] The flowing gas is nitrogen or air.

[0013] Furthermore, in step S2, the metal nanoparticles include one or more of nano Fe, Ni, and Co particles.

[0014] Furthermore, in step S2, the reduction reaction is carried out at 40-60°C.

[0015] Furthermore, step S1 is maintained for 10-60 minutes.

[0016] Furthermore, the particle size of the aluminum powder or aluminum-based alloy powder is ≤74 μm.

[0017] Furthermore, the aluminum-based alloy powder contains Si, and the Si content is less than 40wt%.

[0018] Furthermore, the aluminum-based alloy powder contains Si and Fe.

[0019] Furthermore, in step S3, the mixed solution is heated to 70-90°C.

[0020] Furthermore, the temperature of the high temperature steam is 100-400°C.

[0021] A microcapsule with chemical and physical heat storage capacity prepared by the above preparation method.

[0022] The present invention forms a porous diaspore gel layer on the surface of the aluminum-based alloy by treating with high-temperature steam or 100°C deionized water, which has a large number of open pores and a large specific surface area. Then, nanoparticles are deposited on the surface of the alloy powder, and the nanoparticles are deposited in the open pores on the surface, thereby increasing the specific surface area of ​​the alloy powder and reducing the aperture of the open pores. The small pores formed by the accumulation of the nanoparticles increase the number of pores on the surface as a whole. A CaO precursor or a MgO precursor is obtained by solvent-evaporation and attached to the surface of the alloy powder. During the heat treatment process, the temperature is first raised to 500°C and kept warm, and after dehydration, porous Al2O3 and CaO or MgO coating are formed. After the alloy is melted, the porous shell expands with the alloy, and the aluminum melt enters the porous shell.

[0023] As the temperature continues to rise, when the flowing atmosphere is air, the metal aluminum melt infiltrates through the gaps and comes into contact with oxygen to react, and reacts with CaO or MgO during the continuous heat treatment process to form a calcium aluminum oxide shell or a magnesium aluminum oxide shell. The chemical heat storage effect is achieved through the water absorption and dehydration reaction of calcium aluminum oxide or magnesium aluminum oxide.

[0024] When the flowing atmosphere is nitrogen, under the catalytic action of nanoparticles, the Al melt in the porous shell reacts with nitrogen to form whiskers / fibers interspersed in the porous Al2O3 and CaO or MgO coating layers, and the insulation process forms a complete double-shell structure with whisker / fiber toughening. After the cooling is completed, Alloy@Al2O3@CaO microcapsules or Alloy@Al2O3@MgO microcapsules with whisker / fiber toughening are formed, realizing the integration of chemical and physical heat storage.

[0025] The microcapsules prepared by the present invention consume less raw materials and form microcapsules with complete structures, which retain the metal phase change latent heat to the greatest extent, and the oxide shell layer on the surface has the characteristic of chemical reaction heat storage. The phase change latent heat of the microcapsules is 300-450 J / g and the chemical heat is 100-300 J / g.

[0026] The dense Al2O3 / AlN on the surface of the microcapsule prepared by the present invention can prevent direct contact between metal and oxygen, and the porous CaO or MgO or calcium aluminum oxide or magnesium aluminum oxide layer can greatly improve the toughness of the microcapsule shell layer and relieve the thermal stress during the heating and cooling process. Therefore, the microcapsule has excellent thermal cycle performance, and the phase change retention rate after 1000 cycles is above 85%.

[0027] The present invention provides a method for preparing microcapsules with chemical and physical heat storage capabilities, which has the advantages of simple preparation process, low cost and easy industrial production; the prepared microcapsules can realize physical heat storage and chemical heat storage at the same time, have a large total heat storage density, low specific heat storage cost, and good thermal cycle stability, and are suitable for long-term energy storage fields such as solar thermal power generation, valley electricity utilization and waste heat recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a scanning electron microscope image of the aluminum-silicon alloy microcapsules prepared in flowing air in Example 2;

[0029] Figure 2 This is a scanning electron microscope image of the aluminum-silicon alloy microcapsules prepared in flowing nitrogen in Example 6. DETAILED DESCRIPTION

[0030] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0031] Example 1

[0032] A method for preparing microcapsules with chemical and physical heat storage capacity of the present invention comprises the following steps:

[0033] Step 1: Place aluminum powder in 100°C water vapor for 20 minutes, filter and dry to obtain porous aluminum powder or aluminum-based alloy powder;

[0034] Step 2: placing the porous aluminum powder in a metal compound solution, performing a reduction reaction at 40° C., depositing metal nano Fe particles on the surface of the porous alloy powder, and obtaining pretreated aluminum powder after filtering and drying.

[0035] Step 3: Add calcium nitrate tetrahydrate into deionized water, and after it is completely dissolved, add pretreated aluminum powder. Heat the mixed solution to 80°C, and place it in a vacuum environment to evaporate the solution to obtain a microcapsule precursor;

[0036] Step 4: Place the microcapsule precursor in a tube furnace and perform heat treatment in flowing air according to the following heating schedule:

[0037] The temperature was raised to 500°C at a rate of 10°C / min and kept at that temperature for 1 hour. The temperature was then raised to 1100°C at a rate of 5°C / min and kept at that temperature for 2 hours. After natural cooling, a microcapsule with chemical and physical heat storage capacity was obtained.

[0038] Examples 1 to 8 are shown in the following table:

[0039]

[0040] Figure 1This is a scanning electron microscope image of the aluminum-silicon alloy microcapsules prepared in flowing air in Example 2; it can be seen from the figure that the surface of the microcapsules presents a loose and porous morphology, which is formed by the dehydration of the oxide in the outer shell layer, indicating that a dehydration reaction occurs during the heating process and the microcapsules do not leak.

[0041] Figure 2 This is a scanning electron microscope image of the aluminum-silicon alloy microcapsule prepared in flowing nitrogen in Example 6. From the image, it can be seen that the surface of the microcapsule is composed of a large number of oxide particles, and the oxide particles are interspersed and connected by whiskers to form a complete shell layer, which improves the toughness of the microcapsule shell layer.

[0042] For matters not mentioned above, the prior art applies.

[0043] Although some specific embodiments of the present invention have been described in detail through examples, those skilled in the art should understand that the above examples are for illustration only and are not intended to limit the scope of the present invention. Those skilled in the art to which the present invention belongs may make various modifications or supplements to the specific embodiments described or replace them in a similar manner, but they will not deviate from the direction of the present invention or exceed the scope defined by the attached claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc. made to the above embodiments based on the technical essence of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing microcapsules with chemical and physical heat storage capacity, characterized in that: The steps include: S1. placing aluminum powder or aluminum-based alloy powder in high-temperature steam or 100° C. deionized water for a period of time, filtering and drying to obtain porous aluminum powder or aluminum-based alloy powder; S2, placing the porous aluminum powder or aluminum-based alloy powder in a metal compound solution for reduction reaction, depositing metal nanoparticles on the surface of the porous aluminum powder or aluminum-based alloy powder, filtering and drying to obtain pretreated aluminum powder or aluminum-based alloy powder; S3, adding calcium nitrate tetrahydrate or magnesium nitrate hexahydrate into deionized water, and after completely dissolving, adding pretreated aluminum powder or aluminum-based alloy powder; The mixed solution is heated and placed in a vacuum environment to evaporate the solution to obtain a microcapsule precursor; S4, heat-treating the microcapsule precursor in a flowing gas according to the following temperature increase regime and then naturally cooling the microcapsules to obtain microcapsules with chemical and physical heat storage capacity; The heating system is to heat to 500℃ at a heating rate of 10℃ / min and keep it at that temperature for 1h; then heat to 900-1200℃ at a heating rate of 5℃ / min and keep it at that temperature for 2-4h; The flowing gas is nitrogen or air.

2. The preparation method according to claim 1, characterized in that In step S2, the metal nanoparticles include one or more of nano Fe, Ni, and Co particles.

3. The preparation method according to claim 1, characterized in that: In step S2, the reduction reaction is carried out at 40 to 60°C.

4. The preparation method according to claim 1, characterized in that: The step S1 is maintained for 10-60 minutes.

5. The preparation method according to claim 1, characterized in that: The particle size of the aluminum powder or aluminum-based alloy powder is ≤74 μm.

6. The preparation method according to claim 1, characterized in that: The aluminum-based alloy powder contains Si, and the Si content is less than 40wt%.

7. The preparation method according to claim 1, characterized in that: The aluminum-based alloy powder contains Si and Fe.

8. The preparation method according to claim 1, characterized in that: In step S3, the mixed solution is heated to 70-90°C.

9. The preparation method according to claim 1, characterized in that: The temperature of high temperature steam is 100-400°C.

10. A microcapsule having chemical and physical heat storage capacity prepared by the preparation method according to any one of claims 1 to 9.

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