Low-leakage graphene-based phase change material and preparation method thereof

Abstract

The invention belongs to the technical field of phase change materials, and particularly relates to a low-leakage graphene-based phase change material and a preparation method thereof. Coupling packaging of the phase change material is achieved through the compact shell plated through magnetron sputtering and the three-dimensional porous graphene aerogel. According to the anisotropic three-dimensional porous graphene aerogel, the phase-change material is packaged for the first time by utilizing the ultrahigh capillary action, the existence of peripheral open micropores is reduced by a micro-nano-scale compact shell formed by magnetron sputtering, and meanwhile, due to the abundant heat conduction ways of the graphene aerogel, the heat conductivity of the phase-change material is improved; and finally, the composite phase change material with ultralow leakage rate, high heat conductivity and high heat storage density is obtained. The leakage problem of the phase change material during phase change can be effectively solved, leakage of the phase change material in the heat absorption-cooling process is prevented, and then reduction of the phase change heat storage density is effectively avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of phase change materials, and particularly relates to a low-leakage graphene-based phase change material and a preparation method thereof. Background Art

[0002] As excellent thermal management materials, phase change materials have characteristics such as high heat storage density, adjustable temperature, and good chemical stability. They can store and release latent heat during the melting and solidification processes, enabling electronic devices to maintain an appropriate operating temperature. Therefore, they show broad application prospects in industrial waste heat recovery, electronic device thermal management, artificial satellites, etc. According to chemical composition, phase change materials are divided into inorganic phase change materials and organic phase change materials. Compared with inorganic phase change materials, organic phase change materials have lower corrosivity and are not prone to supercooling or phase separation. However, there is a problem of easy leakage at high temperatures, which greatly limits their application. CN105602530B discloses a preparation method of an organic gel composite phase change material. First, an organic wet gel is prepared by the condensation reaction of an amino group and an aldehyde, and then the phase change core material solution is dispersed in the organic gel carrier material by a solution impregnation method, and the solvent is removed at a higher temperature to obtain a covalent organic gel composite phase change material. This material can effectively avoid the problem of phase change core material leakage, but the low thermal conductivity of the organic matter makes the phase change material have a slow thermal response. CN108342187A discloses a preparation method of a high-thermal-conductivity graphene aerogel composite phase change material with controllable shape. A graphene aerogel with controllable shape is prepared by reducing graphene oxide with ethylenediamine and gelatin, and then the organic phase change material is mixed with the graphene aerogel by a physical adsorption method to obtain a graphene aerogel composite phase change material. This aerogel can solve the problem of the single shape of traditional graphene aerogel composite phase change materials, but since the graphene aerogel is an open-cell material, there are still problems such as leakage. CN114106779B discloses a preparation method of a carbon nanotube aerogel-based composite shaped phase change material. Using organosilane and carbon nanotubes as raw materials, a composite carbon nanotube aerogel is prepared by hydrolysis reaction and freeze-drying, and then the phase change material is immersed in it by vacuum impregnation, and finally a carbon nanotube aerogel-based composite shaped phase change material is obtained. The carbon nanotube aerogel exhibits a hierarchical porous structure and can effectively encapsulate the phase change material. In the above methods, through the capillary action of the gel micropores, the gel can fully adsorb the liquid phase change material, which can effectively improve the leakage problem of the organic phase change material. However, due to the presence of open micropores at the edge of the aerogel, this undoubtedly increases the leakage risk during the solid-liquid phase change of the phase change material. Therefore, the wide use of these composite phase change materials is still limited. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to overcome the deficiencies of the above-mentioned existing technologies, and to provide a low-leakage graphene-based phase change material and a preparation method thereof. The present invention realizes the coupled encapsulation of the phase change material through the dense outer shell of magnetron sputtering plating and the three-dimensional porous graphene aerogel. The anisotropic three-dimensional porous graphene aerogel first encapsulates the phase change material by using ultra-high capillary action, and the dense outer shell reduces the existence of peripheral open micropores and further encapsulates the phase change material. At the same time, due to the rich heat conduction pathways of the graphene aerogel, a composite phase change material with an ultra-low leakage rate, high thermal conductivity, and high heat storage density is finally obtained.

[0004] To achieve the above object, the technical solution of the present invention is as follows:

[0005] The present invention provides a preparation method of a low-leakage graphene-based phase change material, comprising the following steps:

[0006] Step 1: Subject the graphene oxide slurry to directional freezing, freeze-drying, high-temperature carbonization, and ultra-high-temperature graphitization to obtain a three-dimensional porous graphene aerogel;

[0007] Step 2: Immerse the liquid phase change material into the three-dimensional porous graphene aerogel by vacuum impregnation, and cool to obtain a graphene composite phase change material;

[0008] Step 3: Subject the graphene composite phase change material to magnetron sputtering to obtain a low-leakage graphene-based phase change material.

[0009] Further, in Step 1, the temperature of directional freezing is (-100°C) - (-198°C), and the time of freeze-drying is 24 - 72 hours.

[0010] Further, in Step 1, the temperature of high-temperature carbonization is 500 - 1200°C, and the temperature of ultra-high-temperature graphitization is 2000 - 3200°C.

[0011] Further, in Step 1, the pore diameter of the three-dimensional porous graphene aerogel is 20 - 150 μm.

[0012] Further, in Step 2, the vacuum degree of vacuum impregnation is 0.1 MPa - 0.01 Pa.

[0013] Further, in Step 2, the phase change material is an alkane, an alcohol, or an inorganic salt.

[0014] Further, in Step 3, the conditions of magnetron sputtering are: the sputtering time is 20 - 100 min, the metal target is one or a combination of several of aluminum, copper, titanium, tungsten, nickel, silver, gold, and platinum, and the sputtering thickness is 10 nm - 100 μm.

[0015] On the other hand, the present invention provides a low-leakage graphene-based phase change material prepared by the preparation method as described above. Under the combined action of a dense metal shell deposited by magnetron sputtering and a three-dimensional porous graphene aerogel, the phase change material is coupled and encapsulated.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] (1) The present invention designs a two-stage encapsulation strategy for the phase change material. On the basis of the traditional three-dimensional porous graphene encapsulation, a micro-nano metal shell self-encapsulation is further adopted, which can effectively prevent the leakage of the phase change material through the outer openings of the three-dimensional porous graphene during the melting-cooling process, thereby ensuring the heat storage density of the phase change material.

[0018] (2) In the present invention, a micro-nano metal shell encapsulation is adopted. Since the metal is a high thermal conductivity material, after encapsulation, it can further enhance the heat transfer ability of the three-dimensional porous graphene, further improve the thermal conductivity of the low-leakage graphene phase change composite material, and then improve the thermal response ability of the graphene phase change composite material.

[0019] (3) The micro-nano metal shell encapsulation process of the present invention is simple, has good encapsulation uniformity, can realize batch encapsulation of large-size samples, and has good industrialization prospects.

[0020] (4) Compared with the graphene composite phase change material without metal encapsulation, the leakage rate (leakage amount / total mass) of the low-leakage graphene-based phase change material prepared by the present invention is reduced by 65.5%, and the thermal conductivity is increased by 67%. Description of the Drawings

[0021] Figure 1 Graphene phase change composite material encapsulated with copper metal in Example 1 (a) physical picture and (b) microscopic morphology picture;

[0022] Figure 2 Microscopic morphology diagram of three-dimensional porous graphene in Example 2;

[0023] Figure 3 Pictures of the constant temperature leakage experiment results of the graphene phase change composite material at 70 °C in Example 2;

[0024] Figure 4 Distribution of dense copper elements on the surface layer of the graphene phase change composite material encapsulated with copper in Example 3;

[0025] Figure 5 DSC curve of the graphene phase change composite material encapsulated with silver after 50 thermal cycles in Example 5;

[0026] Figure 6 Thermal diffusivity and thermal conductivity of the graphene phase change composite material encapsulated with copper in Example 5. Detailed Embodiments

[0027] In order to facilitate the understanding of the present invention, the present invention will be described more fully below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0028] Example 1

[0029] (1) Pour 10 mL of 5 g / L graphene oxide slurry into a container, ultrasonically disperse it, and place the container in a low-temperature environment of -196°C for directional freezing to form graphene oxide hydrogel; then freeze-dry for 24 hours to obtain a three-dimensional porous graphene oxide aerogel. Then, the graphene oxide aerogel is carbonized at a high temperature of 800°C for 2 hours to obtain a three-dimensional porous reduced graphene oxide aerogel. Finally, a three-dimensional porous graphene aerogel is prepared by ultra-high temperature graphitization at 2500°C for 1 hour.

[0030] (2) The three-dimensional porous graphene aerogel is placed in a container containing melted paraffin phase change material (melting point 63°C), and then placed in a vacuum device. The vacuum device is then evacuated to 0.06 MPa, so that the phase change material is encapsulated in the three-dimensional porous graphene aerogel, and then cooled to obtain a graphene composite phase change material.

[0031] (3) Use 2000-grit sandpaper to polish the graphene composite phase change material to make the surface flat and smooth, and fix it on the base of the magnetron sputtering instrument. Use copper metal as the target material. The magnetron sputtering system is evacuated by a mechanical pump. When the vacuum degree drops below 5Pa, the molecular pump and mechanical pump are used to continue evacuating. Then, the gas flow meter is turned on and magnetron sputtering is started under the protection of argon atmosphere. After sputtering for 30 minutes, a dense metal shell with a thickness of 186nm is formed. After sputtering, the sample is taken out and turned over. Under the same operating conditions, the reverse side is magnetron sputtered for a certain period of time to obtain a copper metal-encapsulated graphene-based phase change material.

[0032] like Figure 1 As shown, the surface of the graphene-based phase change material prepared in this embodiment is copper red, and the thickness of the metal shell is 186 nm, which is attached to the surface of the graphene phase change composite material.

[0033] Example 2

[0034] The preparation steps are basically the same as those in Example 1, except that: in step (1), 2 L of graphene oxide slurry with a concentration of 15 g / L is poured into a container, and the temperature of directional freezing is -150°C; freeze drying is for 72 hours; in step (2), an alcohol phase change material (melting point is 50°C) is used; in step (3), the sputtering time is 50 min, and a dense metal shell with a thickness of 2 μm is formed.

[0035] As Figure 2 shown, the pore size of the three-dimensional porous graphene prepared in this example is 50 μm, presenting long strip-shaped pores. As Figure 3 shown, by heating at a constant temperature of 70 °C for 5 minutes, it can be seen that the leakage rate (leakage amount / total mass) of the graphene-based composite material encapsulated by the metal shell is as low as 0.29%, and compared with the unencapsulated phase change composite material (0.84%), its leakage rate is reduced by 65.5%.

[0036] Example 3

[0037] The preparation steps are basically the same as those in Example 1, except that: in step (2), an inorganic salt phase change substance (melting point is 50 °C), and the vacuum equipment is evacuated to 3 Pa.

[0038] As Figure 4 shown, the copper distribution on the surface of the graphene-based phase change material prepared in this example is very uniform and dense.

[0039] Example 4

[0040] The preparation steps are basically the same as those in Example 1, except that: in step (2), an inorganic salt phase change substance (melting point is 50 °C), and the vacuum equipment is evacuated to 3 Pa; in step (3), silver metal is used as the target.

[0041] Example 5

[0042] The preparation steps are basically the same as those in Example 1, except that: in step (1), the ultra-high temperature graphitization temperature is 2800 °C; in step (2), the vacuum equipment is evacuated to 1 Pa; in step (3), silver metal is used as the target, and the sputtering time is 100 min to form a dense metal shell with a thickness of 100 μm.

[0043] As Figure 5 shown, after 50 melting-cooling cycles, the melting enthalpy (heat storage density) and solidification enthalpy of the low-leakage graphene phase change composite material only decreased by 0.28% and 1.51%, indicating that the phase change composite material has an extremely low leakage rate. As Figure 6 shown, the thermal conductivity of the graphene-based phase change material is increased from 0.73 W / mK to 1.22 W / mK, and the thermal conductivity is increased by 67%.

[0044] The above are only examples for better explaining the present invention, and are not intended to limit it. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall fall within the scope covered by the present invention.

Claims

1. A method for preparing a low leakage graphene-based phase change material, characterized in that it comprises the following steps: Step 1: Directional freezing, freeze drying, high temperature carbonization, and ultra-high temperature graphitization of graphene oxide slurry to obtain a three-dimensional porous graphene aerogel; Step 2: Infusing the liquid phase change material into the three-dimensional porous graphene aerogel by vacuum impregnation, and cooling, to obtain a graphene composite phase change material; Step 3: magnetron sputtering the graphene composite phase change material to obtain a low leakage graphene-based phase change material.

2. A method for preparing a low-leakage graphene-based phase change material according to claim 1, characterized in that the temperature of directional freezing in step 1 is (-100°C)-(-198°C), and the freeze-drying time is 24-72 hours.

3. A method for preparing a low-leakage graphene-based phase change material according to claim 1, wherein the temperature of the high-temperature carbonization in step 1 is 500-1200°C, and the temperature of the ultra-high-temperature graphitization is 2000-3200°C.

4. The method for preparing a low-leakage graphene-based phase change material according to claim 1, wherein the pore size of the three-dimensional porous graphene aerogel in step 1 is 20-150 μm.

5. The method for preparing a low-leakage graphene-based phase change material according to claim 1, wherein the vacuum degree of the vacuum impregnation in step 2 is 0.1 MPa-0.01 Pa.

6. The method for preparing a low-leakage graphene-based phase change material according to claim 1, wherein the phase change material in step 2 is an alkane, an alcohol or an inorganic salt.

7. A method for preparing a low-leakage graphene-based phase change material according to claim 1, characterized in that the conditions of magnetron sputtering in step 3 are: the sputtering time is 20-100 min, the metal target material is one or a combination of aluminum, copper, titanium, tungsten, nickel, silver, gold, platinum, and the sputtering thickness is 10nm-100μm.

8. The low leakage graphene-based phase change material obtained by the preparation method according to any one of claims 1 to 7 has the characteristic that the phase change material is coupled and packaged under the joint action of the dense metal shell plated by magnetron sputtering and the three-dimensional porous graphene aerogel.

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