A boron nitride aerogel / phase change thermal conductive composite material and a preparation method thereof

Abstract

The present application relates to a boron nitride aerogel / phase change heat conduction composite material and a preparation method thereof. The preparation method of the boron nitride aerogel / phase change heat conduction composite material comprises the following steps: (1) pouring a graphene oxide dispersion liquid into a mold and placing it in a low-temperature environment for freeze casting, then freeze-drying and heat-treating the freeze-cast sample to obtain a three-dimensional centripetal structure graphene aerogel; (2) using the three-dimensional centripetal structure graphene aerogel as a template, depositing boron nitride on the surface of graphene through in-situ reaction by using a chemical vapor deposition process to obtain a graphene / boron nitride hybrid aerogel; (3) performing heat etching and high-temperature oxidation treatment on the graphene / boron nitride hybrid aerogel to remove the graphene component to obtain a radiating structure boron nitride aerogel; and (4) immersing a phase change material into the radiating structure boron nitride aerogel by using a vacuum-assisted impregnation method under heating conditions, and obtaining the boron nitride aerogel / phase change heat conduction composite material after solidification.

Description

Technical Field

[0001] This invention belongs to the field of phase change thermally conductive composite materials technology, specifically relating to a boron nitride aerogel / phase change thermally conductive composite material and its preparation method. Background Technology

[0002] With the miniaturization, high integration, and increasing power density of power equipment and electronic devices, heat dissipation has become a significant challenge. Overheating caused by heat accumulation can greatly reduce the operating efficiency, reliability, and lifespan of these devices, and may even pose a fire risk. Today, the demand for high-performance thermal management materials is constantly increasing in many engineering fields, including power transmission, energy storage, and integrated circuits. In this context, high thermal conductivity materials with excellent mechanical, electrical insulation, and fire resistance properties are urgently needed to solve heat dissipation problems.

[0003] Phase change materials (PCMs), as thermal management materials, have been widely used in various fields due to their large heat storage capacity and isothermal properties during phase change. Organic PCMs, especially paraffin wax and polyethylene glycol (PEG), have attracted much attention due to their high latent heat, excellent cycle stability, and non-toxicity. However, organic PCMs generally also suffer from problems such as low inherent thermal conductivity and leakage, which severely limit their applications. To overcome these problems, high thermal conductivity fillers (such as graphene and carbon nanotubes) are widely used to enhance the thermal conductivity of PCMs. Phase change composite materials based on three-dimensional thermally conductive fillers have become an effective means to improve the performance of phase change materials.

[0004] Hexagonal boron nitride (h-BN), similar in structure to graphite and also known as white graphite, possesses excellent electrical insulation properties, high thermal conductivity, high thermal stability, and oxidation resistance. BN typically imparts higher electrical insulation and thermal conductivity to PCMs. Therefore, infiltrating PCMs into BN aerogels will facilitate the preparation of composite PCMs with high thermal conductivity but electrical insulation, potentially useful in microelectronic devices. However, due to the inert surface properties of boron nitride and the weak interactions between the networks, constructing boron nitride aerogels remains challenging. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a method for preparing boron nitride aerogel / phase change thermally conductive composite material, wherein the thermally conductive filler inside the composite material has a radial structure, which can endow the composite material with isotropic high thermal conductivity.

[0006] In a first aspect, the present invention provides a method for preparing a boron nitride aerogel / phase change thermally conductive composite material, the preparation method comprising the following steps:

[0007] (1) Pour the graphene oxide dispersion into a mold, then place it in a low temperature environment for freeze casting, and then freeze-dry and heat-treat the frozen casting sample to obtain a three-dimensional centripetal graphene aerogel.

[0008] (2) Using the three-dimensional centripetal graphene aerogel as a template, boron nitride is deposited on the graphene surface through in-situ reaction using chemical vapor deposition process to obtain graphene / boron nitride hybrid aerogel.

[0009] (3) The graphene / boron nitride hybrid aerogel is subjected to thermal etching and high-temperature oxidation treatment to remove the graphene component and obtain a radial boron nitride aerogel.

[0010] (4) The phase change material is immersed in the radial structure boron nitride aerogel under heating conditions using a vacuum-assisted impregnation method, and the boron nitride aerogel / phase change thermal conductive composite material is obtained after curing.

[0011] Preferably, the concentration of the graphene oxide dispersion is 2–14 mg / mL.

[0012] Preferably, the mold is a hollow mold, and is preferably in the shape of a cube, cuboid, or cylinder; wherein the inner diameter of the cylindrical hollow mold is 6-20 mm, the height is 6-20 mm, and the mold wall thickness is 0.5-2 mm.

[0013] Preferably, the cryogenic casting is carried out in liquid nitrogen, with the cryogenic casting temperature controlled between -196°C and -80°C, and the time being 3 to 10 minutes, preferably 5 minutes.

[0014] Preferably, the heat treatment process is as follows: heating to 800-2000°C at a rate of 1-10°C / min under an argon atmosphere and holding at that temperature for 1-4 hours.

[0015] Preferably, the temperature of the chemical vapor deposition process is 700–1600°C, and the deposition time is 20–80 min.

[0016] Preferably, the hot etching and high-temperature oxidation process is carried out in air at a temperature of 600–800°C for 20–60 minutes.

[0017] Preferably, the phase change material is an organic phase change material, preferably paraffin or polyethylene glycol; the ratio of boron nitride aerogel to phase change material is 0.02-0.1g:0.5-1g.

[0018] Preferably, in the vacuum-assisted impregnation method, the heating temperature is 60-150°C, the vacuum degree is 1-100 kPa, and the impregnation time is 20 min-2 h, preferably 20-40 min.

[0019] Secondly, the present invention provides a boron nitride aerogel / phase change thermally conductive composite material obtained according to the above preparation method.

[0020] Beneficial effects

[0021] This invention determines the microscopic orientation of boron nitride aerogel by customizing the sacrificed graphene aerogel junctions. The centripetal orientation of the boron nitride aerogel originates from centripetal cryogenic casting. During cryogenic casting, a temperature gradient is formed from the solution surface to the solution center, i.e., a centripetal temperature gradient. Under the influence of this centripetal temperature gradient, ice crystals grow from the inner surface of the mold towards the center. The graphene oxide sheets in the dispersion are squeezed to the ice crystal interface by the ice crystals, replicating the outline of the ice crystals to complete the orientation process. Therefore, the boron nitride aerogel obtained after thermal etching and oxidation to remove the graphene components also has a similar structure, and this ordered orientation helps to achieve efficient heat dissipation as a thermally conductive filler. Attached Figure Description

[0022] Figure 1 The structural orientation diagram of the boron nitride aerogel prepared in Example 1;

[0023] Figure 2 Microscopic morphology of the boron nitride aerogel / phase change thermally conductive composite material prepared in Example 1;

[0024] Figure 3 DSC curves of the boron nitride aerogel / phase change thermally conductive composite material prepared in Example 1;

[0025] Figure 4 , 5 The images show the microstructure of the boron nitride aerogel / phase change thermally conductive composite material samples prepared in Comparative Examples 1 and 2. Detailed Implementation

[0026] The present invention is further illustrated by the embodiments described below. It should be understood that the embodiments described below are for illustrative purposes only and are not intended to limit the present invention.

[0027] In this disclosure, graphene oxide is used as raw material, and graphene aerogel is obtained by centripetal freeze-drying and heat treatment. Based on the graphene aerogel template, boron nitride aerogel with a centripetal orientation radial structure is obtained by sacrificial template method. Finally, solid-liquid organic phase change material is impregnated by heating-assisted vacuum to obtain a composite thermally conductive phase change material with ordered thermally conductive filler.

[0028] The following exemplifies a method for preparing the boron nitride aerogel / phase change thermally conductive composite material provided by the present invention. The preparation method may include the following steps.

[0029] (1) Preparation of three-dimensional centripetal graphene aerogel. The graphene oxide dispersion was poured into a mold and then placed in a low-temperature environment for cryogenic casting. The cryogenically cast sample was then freeze-dried and heat-treated to obtain the three-dimensional centripetal graphene aerogel.

[0030] In some embodiments, the concentration of the graphene oxide dispersion can be 2–14 mg / mL. Too low a graphene concentration will prevent the formation of a three-dimensional framework; too high a concentration will result in material waste.

[0031] In some embodiments, the mold can be a hollow mold, preferably in the shape of a cube, cuboid, or cylinder. Specifically, the inner diameter of the cylindrical hollow mold can be 6–20 mm, the height can be 6–20 mm, and the mold wall thickness can be 0.5–2 mm, which is beneficial for obtaining boron nitride aerogels of different sizes subsequently.

[0032] In some embodiments, the cryocasting can be performed in liquid nitrogen, with the cryocasting temperature controlled between -196°C and -80°C, and the time between 3 and 10 minutes, preferably 5 minutes. Maintaining a low cryocasting temperature can promote smaller aerogel pore sizes and more stable structures; at the same time, controlling the freezing time can ensure complete freezing.

[0033] In some embodiments, the heat treatment process can be as follows: heating to 800–2000°C at a rate of 1–10°C / min under an argon atmosphere and holding at that temperature for 1–4 hours. This heat treatment can thermally reduce graphene oxide to graphene. The higher the reduction temperature, the higher the degree of graphene reduction; the heat treatment is performed under argon to ensure that the reduced graphene will not oxidize.

[0034] (2) Preparation of graphene / boron nitride hybrid aerogel. Using the above-mentioned three-dimensional centripetal graphene aerogel as a template, boron nitride was deposited on the graphene surface through in-situ reaction using chemical vapor deposition (CVI) process to obtain the graphene / boron nitride hybrid aerogel.

[0035] In some embodiments, the temperature of the chemical vapor deposition process can be 700–1600°C, and the deposition time can be 20–80 min.

[0036] In some embodiments, the boron nitride ceramic precursor may be selected from boron trichloride and ammonia, trichlorocycloborazine, and diethanolamine borate.

[0037] (3) Preparation of pure boron nitride aerogel. The above graphene / boron nitride hybrid aerogel was subjected to thermal etching and high-temperature oxidation treatment to remove the graphene component, resulting in a radially structured boron nitride aerogel.

[0038] In some embodiments, the thermal etching and high-temperature oxidation process can be carried out in air at a temperature of 600–800°C for a time of 20–60 minutes.

[0039] If the temperature of the thermal etching high-temperature oxidation process is too low, the graphene will not be completely oxidized and removed; if the temperature is too high, boron nitride will be oxidized, and the designed sample cannot be obtained. At the same time, if the time of the thermal etching high-temperature oxidation process is too short, the graphene will not be completely oxidized; if the oxidation process time is too long, boron nitride will be slightly oxidized, which is detrimental to its performance.

[0040] (4) Preparation of boron nitride aerogel / phase change thermally conductive composite material. The above-mentioned boron nitride aerogel and phase change material were placed together in a drying oven. Under heating conditions, the phase change material was immersed in the boron nitride aerogel using a vacuum-assisted impregnation method. After curing, the boron nitride aerogel / phase change thermally conductive composite material was obtained.

[0041] In some embodiments, the phase change material can be an organic phase change material, preferably paraffin wax or polyethylene glycol; the ratio of boron nitride aerogel to phase change material can be 0.02–0.1 g: 0.5–1 g. If the ratio is too low, a continuous thermally conductive framework cannot be formed, resulting in poor enhancement of the composite material's thermal conductivity; if boron nitride has a reinforcing effect, excessive dosage will lead to the formation of a more complex and irregular ceramic polymer composite material.

[0042] In some embodiments, the heating temperature in the vacuum-assisted impregnation method can be 60–150°C, the vacuum degree can be 1–100 kPa, and the impregnation time can be 20 min–2 h, preferably 20–40 min.

[0043] In some embodiments, the curing process can be natural cooling.

[0044] This invention determines the microscopic orientation of boron nitride aerogel by customizing the sacrificed graphene aerogel junctions. The centripetal orientation of the boron nitride aerogel originates from centripetal cryogenic casting. During cryogenic casting, a temperature gradient is formed from the solution surface to the solution center, i.e., a centripetal temperature gradient. Under the influence of this centripetal temperature gradient, ice crystals grow from the inner surface of the mold towards the center. The graphene oxide sheets in the dispersion are squeezed to the ice crystal interface by the ice crystals, replicating the outline of the ice crystals to complete the orientation process. Therefore, the boron nitride aerogel obtained after thermal etching and oxidation to remove the graphene components also has a similar structure, and this ordered orientation helps to achieve efficient heat dissipation as a thermally conductive filler.

[0045] This invention employs centripetal freeze casting to obtain a distinctly oriented internal structure and lamellar orientation. The ordered structure often exhibits superior thermal insulation performance compared to the disordered structure obtained through freeze drying, thus reducing heat loss paths when used as a thermally conductive filler. Furthermore, the structure obtained through centripetal freeze casting imparts a negative Poisson's ratio effect to the aerogel. This metamaterial property makes it more stable, not only elastic but also capable of remaining stable under repeated cyclic compression.

[0046] The boron nitride aerogel / phase change thermally conductive composite material obtained by the preparation method provided by the present invention has a thermal conductivity of 0.6 to 3 W / m·K.

[0047] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention fall within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0048] Example 1

[0049] The preparation method of the boron nitride aerogel / phase change thermally conductive composite material provided in Example 1 includes the following steps:

[0050] (1) Graphene oxide was added to deionized water and ultrasonically dispersed to obtain a graphene oxide dispersion with a concentration of 10 mg / mL. Then, the graphene oxide dispersion was poured into a cylindrical hollow copper mold until it overflowed. After that, it was sealed with a copper sheet and then placed in liquid nitrogen at -196℃ for freezing and casting for 5 min. After that, the frozen sample was completely frozen and vacuum freeze-dried for 48 h. Finally, it was heated to 1000℃ at a rate of 5℃ / min under an argon atmosphere and held for 2 h to obtain a three-dimensional centripetal graphene aerogel.

[0051] (2) Place the graphene aerogel obtained in step (1) in a tube furnace to deposit BN at a deposition temperature of 1500℃ and a deposition time of 50min to obtain graphene / boron nitride hybrid aerogel.

[0052] (3) The graphene / boron nitride hybrid aerogel obtained in step (2) is placed in a muffle furnace and oxidized at 700°C to obtain boron nitride aerogel composed of pure boron nitride.

[0053] (4) The boron nitride aerogel obtained in step (3) is placed in a vacuum drying oven with paraffin and impregnated in a vacuum oven at 80°C for 2 hours with a vacuum degree of 20Pa. After curing, the boron nitride aerogel / phase change thermal conductive composite material is obtained.

[0054] Tests showed that the thermal conductivity of the boron nitride aerogel / phase change thermal conductive composite material prepared in Example 1 was 2.1 W / m·K.

[0055] Figure 1 The diagram shows the structural orientation of the boron nitride aerogel prepared in Example 1. As can be seen from the diagram, the internal lamellars of boron nitride converge towards the center of the sample, exhibiting a radial centripetal orientation, which is determined by the cryogenic casting process.

[0056] Figure 2 The images show the microstructure of the boron nitride aerogel / phase change thermally conductive composite material prepared in Example 1. The left image shows the orientation of boron nitride in the composite material, and the right image shows the tight bonding between boron nitride and paraffin. As can be seen from the images, after vacuum-assisted impregnation, the orientation of the boron nitride sheets did not change significantly, and the material exhibited good density.

[0057] Figure 3 The DSC curves for the boron nitride aerogel / phase change thermally conductive composite material prepared in Example 1 are shown. BNM-1, 2, 3, and 4 represent the final composite materials obtained at deposition temperatures of 1600℃, 1300℃, 1100℃, and 900℃, respectively. The left graph shows the DSC curve during endothermic melting, and the right graph shows the DSC curve during exothermic solidification. As can be seen from the figures, the lowest latent heat of phase change in the phase change composite material is 164.4 J / g (exothermic) and 162.9 J / g (endothermic).

[0058] Example 2

[0059] The preparation method of this Example 2 is the same as that of Example 1, the main difference being that the deposition time of chemical vapor deposition of BN in step (2) is 20 min.

[0060] Example 3

[0061] The preparation method of this Example 3 is the same as that of Example 1, the main difference being that the deposition time of chemical vapor deposition of BN in step (2) is 30 min.

[0062] Example 4

[0063] The preparation method of this Example 4 is the same as that of Example 1, the main difference being that the deposition time of chemical vapor deposition of BN in step (2) is 40 min.

[0064] Example 5

[0065] The preparation method of this Example 5 is the same as that of Example 1, the main difference being that the deposition time of chemical vapor deposition of BN in step (2) is 60 min.

[0066] Example 6

[0067] The preparation method of Example 6 is the same as that of Example 1, the main difference being that the phase change material impregnated in step (4) is polyethylene glycol.

[0068] Example 7

[0069] The preparation method of Example 7 is the same as that of Example 1, the main difference being that the heating temperature in step (4) is 60°C.

[0070] Comparative Example 1

[0071] The preparation method of Comparative Example 1 is the same as that of Example 1, the main difference being that the freeze casting temperature in step (1) is -80℃.

[0072] Comparative Example 2

[0073] The preparation method of Comparative Example 2 is the same as that of Example 1, the main difference being that the freeze casting temperature in step (1) is -20℃.

[0074] Figure 4 , 5 The images show the microstructure of the boron nitride aerogel / phase change thermally conductive composite material samples prepared in Comparative Examples 1 and 2. As can be seen from the images, the samples obtained in Comparative Examples 1 and 2 cannot form a continuous and stable framework, making it difficult to obtain phase change thermally conductive composite materials with good performance.

[0075] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A method for preparing a boron nitride aerogel / phase change thermally conductive composite material, characterized in that, The preparation method includes the following steps: (1) Pour the graphene oxide dispersion into the mold, then place it in a low temperature environment for freeze casting, and then freeze-dry and heat-treat the frozen casting sample to obtain a three-dimensional centripetal graphene aerogel. (2) Using the three-dimensional centripetal graphene aerogel as a template, boron nitride is deposited on the graphene surface through in-situ reaction using chemical vapor deposition process to obtain graphene / boron nitride hybrid aerogel. (3) The graphene / boron nitride hybrid aerogel is subjected to thermal etching and high-temperature oxidation treatment to remove the graphene component and obtain a radial boron nitride aerogel. (4) The phase change material is immersed in the radial structure boron nitride aerogel under heating conditions using a vacuum-assisted impregnation method, and the boron nitride aerogel / phase change thermal conductive composite material is obtained after curing.

2. The preparation method according to claim 1, characterized in that, The concentration of the graphene oxide dispersion is 2–14 mg / mL.

3. The preparation method according to claim 1, characterized in that, The mold is a hollow mold.

4. The preparation method according to claim 3, characterized in that, The hollow mold is in the shape of a cube, cuboid, or cylinder; wherein, the inner diameter of the cylindrical hollow mold is 6–20 mm, the height is 6–20 mm, and the mold wall thickness is 0.5–2 mm.

5. The preparation method according to claim 1, characterized in that, The cryogenic casting is carried out in liquid nitrogen, with the temperature controlled between -196℃ and -80℃, and the time being 3 to 10 minutes.

6. The preparation method according to claim 5, characterized in that, The specified time is 5 minutes.

7. The preparation method according to claim 1, characterized in that, The heat treatment process is as follows: under an argon atmosphere, heat to 800-2000℃ at a rate of 1-10℃ / min and hold for 1-4 hours.

8. The preparation method according to claim 1, characterized in that, The chemical vapor deposition process is carried out at a temperature of 700–1600℃ and a deposition time of 20–80 min.

9. The preparation method according to claim 1, characterized in that, The hot etching and high-temperature oxidation process is carried out in air at a temperature of 600–800°C for 20–60 minutes.

10. The preparation method according to claim 1, characterized in that, The phase change material is an organic phase change material; the ratio of the radially structured boron nitride aerogel to the phase change material is 0.02-0.1g:0.5-1g.

11. The preparation method according to claim 10, characterized in that, The phase change material is paraffin wax and polyethylene glycol.

12. The preparation method according to claim 1, characterized in that, In the vacuum-assisted impregnation method, the heating temperature is 60–150°C, the vacuum degree is 1–100 kPa, and the impregnation time is 20 min–2 h.

13. The preparation method according to claim 12, characterized in that, The immersion time is 20 to 40 minutes.

14. A boron nitride aerogel / phase change thermally conductive composite material obtained by the preparation method according to claim 1.

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