Low-thermal-conductivity light-heat conversion composite phase change material, and preparation method and application thereof

Abstract

The application belongs to the technical field of phase change heat storage materials, and particularly relates to a low-thermal-conductivity light-heat-conversion composite phase change material and a preparation method and application thereof, and comprises the following steps: (1) after the pretreated expanded perlite is immersed in a silver nitrate solution, a sodium citrate solution is added to perform a hydrothermal reaction, and a silver / expanded perlite composite is prepared; (2) after the hydrated inorganic salt and a nucleating agent are mixed and melted, the silver / expanded perlite composite is added and mixed, and after cooling, the low-thermal-conductivity light-heat-conversion composite phase change material is obtained. The expanded perlite is used as an adsorption material, and compared with carbon materials such as expanded graphite and graphene, the price is low, and the low thermal conductivity of the composite material is ensured; the silver nanoparticles are prepared by using a mild hydrothermal method, the process is simple and economical, and the surface plasmon resonance effect is used to compensate for the poor light absorption capacity of the expanded perlite. The expanded perlite and the silver nanoparticles synergistically act, and low thermal conductivity and high light-heat conversion are simultaneously achieved.

Description

Technical Field

[0001] This invention belongs to the field of phase change thermal storage materials technology, specifically relating to a low thermal conductivity photothermal conversion composite phase change material, its preparation method, and its application. Background Technology

[0002] Phase change thermal energy storage technology utilizes the characteristic of materials to absorb or release a large amount of latent heat during phase change to achieve heat storage. Photothermal conversion phase change materials (PCCs) are based on conventional PCCs but endowed with the ability to efficiently absorb solar radiation, simultaneously achieving solar photothermal conversion and heat storage. The performance of PCCs in solar thermal storage is influenced not only by the material's heat storage density, photothermal conversion efficiency, and phase change temperature, but also by its thermal conductivity. High thermal conductivity PCCs are suitable for large-scale solar thermal storage, while low thermal conductivity is required for applications such as building exterior wall insulation.

[0003] Currently, most widely studied photothermal conversion phase change materials (PCCs) utilize carbon materials as light absorption enhancers, such as expanded graphite, carbon nanotubes, and graphite fibers. However, the composite PCCs formed by these carbon materials and PCCs typically have high thermal conductivity, failing to meet the requirements for low thermal conductivity. Expanded perlite, as an inexpensive and readily available building material, has low thermal conductivity. Studies have shown that using expanded perlite as an adsorbent can prepare composite PCCs with low thermal conductivity. However, both expanded perlite and PCC raw materials have weak absorption capacity for solar radiation. Therefore, the resulting composite PCC cannot effectively absorb solar radiation.

[0004] The localized surface plasmon resonance effect of silver nanoparticles gives them a strong ability to absorb solar radiation. If silver nanoparticles can be uniformly dispersed in phase change materials (PCMs), composite PCMs with photothermal conversion capabilities can be obtained. However, silver nanoparticles have high surface energy and are prone to aggregation. Directly mixing silver nanoparticles with expanded perlite or PCMs makes it difficult to obtain monodisperse silver nanoparticles, which not only affects the photothermal conversion performance of the PCM but also adversely impacts the material's uniformity and mechanical properties. Due to the large-scale aggregation of silver nanoparticles, a high silver content is required to achieve the desired photothermal conversion effect. A higher silver content not only increases the thermal conductivity of the composite material but also increases the manufacturing cost. Therefore, how to uniformly disperse silver nanoparticles in expanded perlite or PCMs is crucial for preparing low-thermal-conductivity photothermal conversion composite PCMs. Summary of the Invention

[0005] The purpose of this invention is to provide a low thermal conductivity photothermal conversion composite phase change material, its preparation method and application, thereby overcoming the shortcomings of the prior art and achieving a low thermal conductivity while ensuring the heat storage density and photothermal conversion performance of the phase change material.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a low thermal conductivity photothermal conversion composite phase change material, comprising the following steps:

[0008] (1) After impregnating the pretreated expanded perlite with silver nitrate solution, sodium citrate solution was added to carry out a hydrothermal reaction to obtain a silver / expanded perlite composite.

[0009] (2) After mixing and melting the hydrated inorganic salt and nucleating agent, add the silver / expanded perlite composite and mix. After cooling, a low thermal conductivity photothermal conversion composite phase change material is obtained.

[0010] In some other embodiments, in step (1), the pretreatment method of the expanded perlite is to heat the expanded perlite at 400-500℃ for 1-5 hours, and the particle size of the expanded perlite is 10-30 mesh.

[0011] In some other embodiments, in step (1), the concentration of the silver nitrate solution is 1-10 mM, the concentration of the sodium citrate solution is 0.1-0.5 M, and the molar ratio of silver nitrate to sodium citrate is 1:2-1:5.

[0012] In some other embodiments, in step (1), the impregnation is performed by stirring and mixing at 75-85°C for 10-60 minutes;

[0013] Alternatively, the hydrothermal reaction is carried out at a temperature of 75-85°C for a duration of 1-5 hours.

[0014] Alternatively, after the hydrothermal reaction is complete, the product may also undergo filtration, rinsing, and drying.

[0015] The drying process is carried out in a nitrogen atmosphere at 80-100℃ for 1-5 hours.

[0016] Preferably, in step (1), the impregnation is performed by stirring and mixing at 80°C for 30 minutes;

[0017] Alternatively, the hydrothermal reaction is carried out at a temperature of 80°C for 2 hours.

[0018] Alternatively, the drying process can be carried out in a nitrogen atmosphere at 100°C for 3 hours.

[0019] In some other embodiments, in step (2), the hydrated inorganic salt is one of sodium acetate trihydrate, calcium chloride hexahydrate, sodium thiosulfate pentahydrate, sodium carbonate decahydrate, and disodium hydrogen phosphate dodecahydrate;

[0020] The nucleating agent is one of disodium hydrogen phosphate, strontium chloride hexahydrate, and sodium silicate nonahydrate;

[0021] The nucleating agent is added at an amount of 1-5 wt.% of the hydrated inorganic salt.

[0022] In some other embodiments, in step (2), the mixing mass ratio of the hydrated inorganic salt to the silver / expanded perlite composite is (2-4):(3-1).

[0023] In a second aspect, the present invention provides a low thermal conductivity photothermal conversion composite phase change material obtained by the preparation method of the low thermal conductivity photothermal conversion composite phase change material described in the first aspect.

[0024] In some other embodiments, the invention includes an expanded perlite carrier and silver nanoparticles loaded on the expanded perlite carrier, the silver nanoparticles having a particle size of 10-100 nm.

[0025] Thirdly, the present invention provides the application of the low thermal conductivity photothermal conversion composite phase change material described in the second aspect in solar thermal systems, building energy conservation, heat dissipation of electronic equipment, and seawater desalination.

[0026] In some other embodiments, the application is in building energy conservation.

[0027] Phase change materials with low thermal conductivity and photothermal conversion properties, as provided in the second aspect of this invention, are filled into hollow acrylic sheets to prepare phase change bricks with dimensions of 30cm × 30cm × 2cm. Multiple phase change bricks are then laid flat on the roof of a building. During the day, when the sun shines, the phase change bricks absorb solar radiation and convert it into heat energy. Some of this heat is transferred to the interior, raising the indoor temperature, while excess heat is stored in the phase change material as latent heat. At night, when there is no sunlight, the heat stored in the phase change material during the day is released into the interior, maintaining the indoor temperature. By absorbing solar radiation and storing heat, the phase change material effectively increases the indoor temperature and reduces heating energy consumption.

[0028] The beneficial effects of this invention are:

[0029] 1) This invention pre-treats commercially available expanded perlite with heat to remove water and impurities adsorbed by the expanded perlite, which is beneficial for generating uniformly dispersed silver nanoparticles.

[0030] 2) The composite phase change material provided by this invention utilizes expanded perlite as an adsorbent to ensure low thermal conductivity of the composite material; silver nanoparticles are prepared in situ using a mild chemical reaction, which facilitates the uniform dispersion of silver nanoparticles on the surface of expanded perlite, and the surface plasmon resonance effect compensates for the poor light absorption capacity of expanded perlite. The synergistic effect of expanded perlite and silver nanoparticles simultaneously achieves low thermal conductivity and high photothermal conversion.

[0031] 3) This invention uses expanded perlite as the adsorbent material, which is cheaper than carbon materials such as expanded graphite and graphene. The thermal conductivity of the composite phase change material is as low as 0.16 W / (m·K), the solar photothermal conversion efficiency is greater than 85%, reaching a maximum of 91%, and the phase change temperature is 25-60℃. Silver nanoparticles are prepared using a mild hydrothermal method, which is simple and economical. Detailed Implementation

[0032] Unless otherwise specified, the raw materials used in the preparation of the low thermal conductivity photothermal conversion composite phase change material of this invention, including expanded perlite, silver nitrate, sodium citrate dihydrate, hydrated inorganic salts, and nucleating agents, are all commercially available products.

[0033] Example 1

[0034] (1) Weigh 30 grams of expanded perlite with a particle size of 18-30 mesh, put it into a muffle furnace, heat it to 400 degrees at a rate of 10℃ / min, and keep it at that temperature for 2 hours to obtain pretreated expanded perlite.

[0035] (2) Weigh 0.34 g of silver nitrate, dissolve it in 200 g of deionized water, and heat it to 80°C using a magnetic stirrer with heating function. Immerse the pretreated expanded perlite obtained in step (1) in the silver nitrate solution and stir continuously for 30 minutes. Weigh 1.776 g of sodium citrate dihydrate, dissolve it in 20 g of deionized water, and slowly add it to the mixture of expanded perlite and silver nitrate, stirring continuously for 2 hours.

[0036] (3) The mixture is filtered, rinsed three times with deionized water, and heated in a nitrogen muffle furnace at 100°C for 3 hours to remove the water adsorbed by the expanded perlite, thus obtaining silver / expanded perlite.

[0037] (4) Weigh 20 g of sodium acetate trihydrate, add 0.2 g of disodium hydrogen phosphate as a nucleating agent, mix evenly, and heat in an 80°C forced-air drying oven until melted. Mix evenly with the silver / expanded perlite obtained in step (3) by mechanical stirring, and cool to room temperature to obtain a low thermal conductivity photothermal conversion composite phase change material with a phase change temperature of about 58°C.

[0038] Example 2

[0039] (1) Weigh 20 grams of expanded perlite with a particle size of 18-30 mesh, put it into a muffle furnace, heat it to 400 degrees at a rate of 10℃ / min, and keep it at that temperature for 2 hours to obtain pretreated expanded perlite.

[0040] (2) Weigh 0.34 g of silver nitrate, dissolve it in 200 g of deionized water, and heat it to 80°C using a magnetic stirrer with heating function. Immerse the pretreated expanded perlite obtained in step (1) in the silver nitrate solution and stir continuously for 30 minutes. Weigh 1.176 g of sodium citrate dihydrate, dissolve it in 20 g of deionized water, and slowly add it to the mixture of expanded perlite and silver nitrate, stirring continuously for 2 hours.

[0041] (3) The mixture is filtered, rinsed three times with deionized water, and heated in a nitrogen muffle furnace at 100°C for 3 hours to remove the water adsorbed by the expanded perlite, thus obtaining silver / expanded perlite.

[0042] (4) Weigh 80 g of sodium acetate trihydrate, add 0.8 g of disodium hydrogen phosphate as a nucleating agent, mix evenly, and heat in an 80°C forced-air drying oven until melted. Mix evenly with the silver / expanded perlite obtained in step (3) by mechanical stirring, and cool to room temperature to obtain a low thermal conductivity photothermal conversion composite phase change material with a phase change temperature of about 58°C.

[0043] Example 3

[0044] (1) Weigh 30 grams of expanded perlite with a particle size of 18-30 mesh, put it into a muffle furnace, heat it to 400 degrees at a rate of 10℃ / min, and keep it at that temperature for 2 hours to obtain pretreated expanded perlite.

[0045] (2) Weigh 0.34 g of silver nitrate, dissolve it in 200 g of deionized water, and heat it to 80°C using a magnetic stirrer with heating function. Immerse the pretreated expanded perlite obtained in step (1) in the silver nitrate solution and stir continuously for 30 minutes. Weigh 1.176 g of sodium citrate dihydrate, dissolve it in 20 g of deionized water, and slowly add it to the mixture of expanded perlite and silver nitrate, stirring continuously for 2 hours.

[0046] (3) The mixture is filtered, rinsed three times with deionized water, and heated in a nitrogen muffle furnace at 100°C for 3 hours to remove the water adsorbed by the expanded perlite, thus obtaining silver / expanded perlite.

[0047] (4) Weigh 30 g of calcium chloride hexahydrate, add 0.6 g of strontium chloride hexahydrate as a nucleating agent, mix evenly, and heat in a 50°C forced-air drying oven until melted. Mix evenly with the silver / expanded perlite obtained in step (3) by mechanical stirring, and cool to room temperature to obtain a low thermal conductivity photothermal conversion composite phase change material with a phase change temperature of about 28°C.

[0048] Example 4

[0049] (1) Weigh 30 grams of expanded perlite with a particle size of 18-30 mesh, put it into a muffle furnace, heat it to 400 degrees at a rate of 10℃ / min, and keep it at that temperature for 2 hours to obtain pretreated expanded perlite.

[0050] (2) Weigh 0.34 g of silver nitrate, dissolve it in 200 g of deionized water, and heat it to 80°C using a magnetic stirrer with heating function. Immerse the pretreated expanded perlite obtained in step (1) in the silver nitrate solution and stir continuously for 30 minutes. Weigh 1.176 g of sodium citrate dihydrate, dissolve it in 20 g of deionized water, and slowly add it to the mixture of expanded perlite and silver nitrate, stirring continuously for 2 hours.

[0051] (3) The mixture is filtered, rinsed three times with deionized water, and heated in a nitrogen muffle furnace at 100°C for 3 hours to remove the water adsorbed by the expanded perlite, thus obtaining silver / expanded perlite.

[0052] (4) Weigh 30 g of disodium hydrogen phosphate dodecahydrate, add 1.2 g of sodium silicate nonahydrate, mix evenly, and heat in a 50°C forced-air drying oven until melted. Mix evenly with the silver / expanded perlite obtained in step (3) by mechanical stirring, and cool to room temperature to obtain a low thermal conductivity photothermal conversion composite phase change material with a phase change temperature of about 35°C.

[0053] Comparative Example 1

[0054] (1) Weigh 30 grams of expanded perlite with a particle size of 18-30 mesh, put it into a muffle furnace, heat it to 400 degrees at a rate of 10℃ / min, and keep it at that temperature for 2 hours to obtain pretreated expanded perlite.

[0055] (2) Weigh 20 g of sodium acetate trihydrate, add 0.2 g of disodium hydrogen phosphate as a nucleating agent, mix evenly, and heat in an 80°C forced-air drying oven until melted. Mix evenly with the pretreated expanded perlite obtained in step (1) by mechanical stirring, and cool to room temperature to obtain a composite phase change material with a phase change temperature of about 58°C.

[0056] Comparative Example 2

[0057] (1) Weigh 30 grams of expanded graphite with a particle size of 50 mesh, put it into a muffle furnace, heat it to 400 degrees at a rate of 10℃ / min, and keep it at that temperature for 2 hours.

[0058] (2) Weigh 20 g of sodium acetate trihydrate, add 0.2 g of disodium hydrogen phosphate as a nucleating agent, mix evenly, and heat in an 80°C forced-air drying oven until melted. Mix evenly with the expanded graphite obtained in step (1) by mechanical stirring, and cool to room temperature to obtain a composite phase change material with a phase change temperature of about 58°C.

[0059] Comparative Example 3

[0060] Unlike Example 1, step (1) is omitted, that is, the expanded perlite is not pretreated, and the other preparation steps are exactly the same as in Example 1.

[0061] Comparative Example 4

[0062] Unlike Example 1, 2 grams of 50 nm silver particles were directly mechanically mixed with pretreated expanded perlite, while the other preparation steps were exactly the same as in Example 1.

[0063] The performance tests of the embodiments and comparative examples are shown in Table 1.

[0064] Table 1 Material Test Results

[0065] Case Phase transition temperature (°C) Phase transition latent heat (J / g) Thermal conductivity W / (m·K) Photothermal conversion efficiency % Example 1 58.3 98.4 0.192 89 Example 2 58.8 201 0.263 85 Example 3 28.4 88.2 0.200 91 Example 4 35.4 108 0.221 85 Comparative Example 1 57.8 100.5 0.197 15 Comparative Example 2 57.5 104.4 3.62 88 Comparative Example 3 57.5 101.2 0.203 76 Comparative Example 4 57.5 90.3 0.355 56

[0066] As shown in Table 1, the composite phase change materials of Examples 1-4 have a maximum thermal conductivity of 0.263 W / (m·K) and a photothermal conversion efficiency greater than 85%, indicating the successful preparation of low thermal conductivity photothermal conversion composite phase change materials. The low thermal conductivity is attributed to the inherent thermal insulation properties of expanded perlite (thermal conductivity approximately 0.1 W / (m·K)). When expanded perlite is combined with inorganic hydrated salts, the thermal conductivity does not increase significantly. In Example 2, the mass ratio of hydrated inorganic salts to silver / expanded perlite is 4:1, the largest ratio, thus resulting in the largest latent heat of phase change. The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 did not load silver nanoparticles onto the surface of expanded perlite; therefore, the photothermal conversion efficiency of the composite phase change material is significantly lower than that of Example 1.

[0067] Comparative Example 2 used expanded graphite to replace the expanded perlite in Comparative Example 1. Although Comparative Example 2 showed a photothermal conversion efficiency of 88%, its thermal conductivity was as high as 3.62 W / (m·K), which could not meet the requirement of low thermal conductivity for building exterior walls. In Comparative Example 3, the expanded perlite was not pretreated, and impurities in the expanded perlite may have affected the formation of silver nanoparticles, thus resulting in a lower photothermal conversion efficiency.

[0068] Comparative Example 4 employed a mechanical mixing method. Due to the larger particle size of expanded perlite and the smaller particle size and tendency of silver nanoparticles to agglomerate, the mechanical mixing method resulted in poorer dispersion of the silver nanoparticles compared to the in-situ growth preparation in Example 1, leading to a lower photothermal conversion efficiency. Furthermore, compared to Example 1, silver particles accounted for 3.8% of the composite phase change material's mass in this comparative example, while the silver mass in Example 1 was almost negligible. This not only increased the thermal conductivity of the composite material but also reduced the latent heat of phase change.

[0069] In addition, the raw materials of this invention, expanded perlite and phase change material, are inexpensive and readily available, the preparation process is simple, the reaction conditions are mild, the cost is low, and they are suitable for large-scale production and application.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a low thermal conductivity photothermal conversion composite phase change material, characterized in that, Includes the following steps: (1) After impregnating the pretreated expanded perlite with silver nitrate solution, sodium citrate solution was added to carry out a hydrothermal reaction to obtain a silver / expanded perlite composite. (2) After mixing and melting hydrated inorganic salt and nucleating agent, silver / expanded perlite composite is added and mixed, and then cooled to obtain low thermal conductivity photothermal conversion composite phase change material; In step (1), the pretreatment method of the expanded perlite is to heat the expanded perlite at 400-500 ℃ for 1-5 h, and the particle size of the expanded perlite is 10-30 mesh.

2. The method for preparing the low thermal conductivity photothermal conversion composite phase change material according to claim 1, characterized in that, In step (1), the concentration of the silver nitrate solution is 1-10 mM, the concentration of the sodium citrate solution is 0.1-0.5 M, and the molar ratio of silver nitrate to sodium citrate is 1:2-1:

5.

3. The method for preparing the low thermal conductivity photothermal conversion composite phase change material according to claim 1, characterized in that, In step (1), the impregnation is carried out by stirring and mixing at 75-85 °C for 10-60 min; Alternatively, the hydrothermal reaction is carried out at a temperature of 75-85 °C for a time of 1-5 h; Alternatively, after the hydrothermal reaction is complete, the product may also undergo filtration, rinsing, and drying. The drying process is carried out in a nitrogen atmosphere at 80-100 ℃ for 1-5 hours.

4. The method for preparing the low thermal conductivity photothermal conversion composite phase change material according to claim 3, characterized in that, In step (1), the impregnation is performed by stirring and mixing at 80 °C for 30 min; Alternatively, the hydrothermal reaction is carried out at a temperature of 80 °C for a duration of 2 h; Alternatively, the drying process can be carried out in a nitrogen atmosphere at 100 °C for 3 hours.

5. The method for preparing the low thermal conductivity photothermal conversion composite phase change material according to claim 1, characterized in that, In step (2), the hydrated inorganic salt is one of sodium acetate trihydrate, calcium chloride hexahydrate, sodium thiosulfate pentahydrate, sodium carbonate decahydrate, and disodium hydrogen phosphate dodecahydrate; The nucleating agent is one of disodium hydrogen phosphate, strontium chloride hexahydrate, and sodium silicate nonahydrate; The nucleating agent is added at an amount of 1-5 wt.% of the hydrated inorganic salt.

6. The method for preparing the low thermal conductivity photothermal conversion composite phase change material according to claim 1, characterized in that, In step (2), the mixing mass ratio of the hydrated inorganic salt to the silver / expanded perlite composite is (2-4):(3-1).

7. A low thermal conductivity photothermal conversion composite phase change material obtained by the preparation method of the low thermal conductivity photothermal conversion composite phase change material according to any one of claims 1-6.

8. The low thermal conductivity photothermal conversion composite phase change material according to claim 7, characterized in that, It includes an expanded perlite carrier and silver nanoparticles loaded on the expanded perlite carrier, wherein the silver nanoparticles have a particle size of 10-100 nm.

9. The application of the low thermal conductivity photothermal conversion composite phase change material as described in claim 7 or 8 in solar thermal systems, building energy conservation, heat dissipation of electronic equipment, and seawater desalination.

10. The application according to claim 9, characterized in that, The application is in building energy conservation.