Aerogel with dual orientation network and preparation method and application thereof

Abstract

The present application relates to aerogel with double orientation network and its preparation method and application, specifically discloses a kind of preparation method of aerogel with double orientation network, comprising the following steps: 1) filler, polymer binder and water are mixed and handled, to obtain filler mixture;2) double orientation forming device is placed in advance in low-temperature refrigeration medium, filler mixture is added to double orientation forming device, freezing treatment is carried out to form ice mixture, then freeze-drying treatment is carried out, to obtain aerogel precursor;3) the aerogel precursor is sintered heat treatment, to obtain aerogel;Wherein, the double orientation forming device is the container that is constituted by metal cylinder ring and gasket located at the bottom of metal cylinder ring.The present application is widely applicable, and the structure of aerogel has distinctive double orientation characteristics, the preparation process is simple, the reaction condition is relatively mild and the yield is high, the anisotropy coefficient of aerogel is controllable, and has good application prospect in many fields.

Description

Technical Field

[0001] This invention belongs to the field of porous materials technology, specifically, it relates to an aerogel with a dual-orientation network, its preparation method, and its application. Background Technology

[0002] Aerogels are porous materials that have attracted widespread attention in recent years due to their unique microstructure and promising applications in fields such as adsorption and environmental protection, energy storage, tissue engineering, and structural composite materials. The applications of aerogels involve their mass transfer behavior, and the microstructure of aerogels is a major influencing factor on their mass transfer performance. Conventional aerogels have disordered microstructures. To improve the mass transfer performance of aerogels in specific directions, researchers have conducted extensive studies on aerogels with oriented and ordered microstructures.

[0003] Optimizing the microstructure of aerogels has always been a key technical challenge in aerogel preparation. The microstructure of aerogels is related to assembly techniques and the morphology of assembly units. Currently, the most researched aerogels are those with unidirectional networks. Cryocasting is a commonly used method for preparing aerogels with unidirectional networks; this method is simple, environmentally friendly, and efficient. The prepared aerogels have an oriented microstructure in the axial direction, thus exhibiting excellent mass transfer properties in that direction. Unidirectional aerogels have shown great application potential in thermally conductive composite materials and adsorption fields. The Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, has published several related patents.

[0004] However, many applications place more stringent demands on the performance of aerogels. Aerogels not only need to exhibit good mass transfer behavior in the axial direction, but also need to ensure the regularity of mass transfer channels in the planar direction. Therefore, aerogels with bi-oriented networks face greater application requirements and technical challenges than aerogels with uni-oriented networks. Currently, publicly available patent documents rarely mention aerogels with bi-oriented networks, their preparation methods, or applications.

[0005] Therefore, it is of great significance to invent a simple, rapid and universal method for preparing aerogels with a dual-orientation network. Summary of the Invention

[0006] In view of the problems mentioned in the background art, the purpose of this invention is to overcome the shortcomings of the prior art and provide a universal method for preparing aerogels with a dual-orientation network. This method is widely applicable to zero-dimensional particles, one-dimensional tubular / linear materials, and two-dimensional materials, and is not limited by the type and morphology of the material. This method provides a new approach to optimizing the microstructure of aerogels and solves the current technical bottleneck.

[0007] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows:

[0008] The first aspect of this invention provides a method for preparing an aerogel with a dual-orientation network, comprising the following steps:

[0009] Step 1: Mix the filler, polymer binder, and water at a mass ratio of 1:0.01-0.05:3-50 to obtain a filler mixture;

[0010] Step 2: Place the dual-orientation molding device in a low-temperature cooling medium beforehand, add the filler mixture to the dual-orientation molding device, freeze it to form a frozen mixture, and then freeze-dry it to obtain the aerogel precursor.

[0011] Step 3: Perform sintering heat treatment on the aerogel precursor to obtain aerogel;

[0012] The dual-orientation forming device is a container consisting of a metal cylindrical ring and a gasket located at the bottom of the metal cylindrical ring.

[0013] In the technical solution of this invention, the filler is any substance that does not chemically react with water at room temperature. The filler can be zero-dimensional particles, one-dimensional tubular / linear materials, two-dimensional micro / nano materials, or three-dimensional particulate materials, with the filler being a micro / nano material. Preferably, the size of the filler is 50 nm to 100 μm, for example, 100 nm, 300 nm, 500 nm, 1 μm, 3 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, or 100 μm.

[0014] In some embodiments, the filler is selected from at least one of alumina, magnesium oxide, zinc oxide, aluminum nitride, boron nitride, silicon carbide, and graphene. Aerogels can be prepared based on the method of the present invention as long as the target filler does not chemically react with water and can be dispersed in water.

[0015] Preferably, the filler is selected from, but is not limited to, any one of the following: granular, filamentous, or sheet-like materials, or a free combination thereof. Any one of the following: granular, filamentous, or sheet-like materials, or a free combination thereof, can be used to prepare an aerogel based on the method of this invention. The particle size of the filler is 50 nm to 100 μm.

[0016] In the technical solution of this invention, the polymer binder is selected from at least one of polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, polyacrylamide, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, or hydroxypropyl methyl cellulose. Using these polymer binders can effectively increase the viscosity of the solution, thereby improving the dispersibility of the filler in water, preventing filler agglomeration, and improving the mechanical properties of the aerogel precursor, thus facilitating subsequent sintering heat treatment.

[0017] In the technical solution of the present invention, the mixing process is carried out by a planetary mixer. The filler, polymer binder and water are mixed in a certain mass ratio to obtain a uniform filler mixture in a short time.

[0018] In the technical solution of this invention, the metal in the cylindrical metal ring is any metallic substance that does not chemically react with water at room temperature, preferably at least one of copper, silver, gold, platinum, molybdenum, tungsten, nickel, aluminum, iron, zinc, tin, and lead. As long as the target metal does not chemically react with water, it can be used to prepare the cylindrical metal ring described in this patent. Selecting these metals can effectively promote the formation of a radial temperature gradient and improve the radial structural regularity of the aerogel precursor, thereby facilitating the obtaining of an aerogel with a dual-orientation network.

[0019] In the technical solution of this invention, the length ratio of the outer diameter to the height of the metal cylindrical ring is 0.25 to 4:1. For example, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, and 3.5:1.

[0020] In the technical solution of this invention, the height of the metal cylindrical ring is 1 to 5 cm. For example, 1 cm, 2 cm, 3 cm, 4 cm, and 5 cm.

[0021] In the technical solution of this invention, the wall thickness of the metal cylindrical ring is 50 to 500 μm. For example, 100 μm, 200 μm, 300 μm, 400 μm, and 450 μm.

[0022] By controlling the length ratio of the outer diameter to the height of the metal cylindrical ring, as well as the height and wall thickness of the metal cylindrical ring, the anisotropy and structural regularity of the aerogel microstructure can be controlled.

[0023] In the technical solution of the present invention, the gasket is prepared by curing a polymer matrix, wherein the polymer matrix is ​​at least one of epoxy resin, polyurethane, phenolic resin, unsaturated polyester, amino resin, polyethylene, polypropylene, polyvinyl chloride, polystyrene or polysiloxane.

[0024] In one embodiment, the diameter of the polymer circular gasket is equal to the inner diameter of the metal cylindrical ring, and the length ratio of the thickness of the polymer circular gasket to the height of the metal cylindrical ring is 0.01 to 0.5:1.

[0025] In the technical solution of the present invention, the dual-orientation molding device is used to place a polymer gasket into a metal cylindrical ring and place it at the bottom to form a container that can hold liquid.

[0026] In the technical solution of the present invention, the cryogenic refrigeration medium is at least one of liquid nitrogen or liquid helium;

[0027] In the technical solution of this invention, the freezing process involves adding a filler mixture to a dual-orientation molding device and indirectly contacting it with a cryogenic cooling medium, thereby initiating a continuous self-assembly molding process. During freezing, the water in the filler mixture freezes and compresses the filler, forming a dual-orientation network microstructure. During freezing, ice crystals grow simultaneously in two directions: a radial direction from the periphery to the center and an axial direction from the bottom to the top. At least one-quarter of the metal cylindrical ring in the dual-orientation molding device is immersed in the cryogenic cooling medium. The metal cylindrical ring can rapidly cool; immersion of only one-quarter is sufficient to ensure that the metal cylindrical ring quickly cools to a temperature close to that of the freezing medium.

[0028] In the technical solution of the present invention, the freeze-drying process involves placing the frozen product into a freeze dryer to sublimate the ice.

[0029] In the technical solution of this invention, sintering is carried out at a temperature of 300℃~2500℃ for 1h~12h;

[0030] Preferably, the sintering is performed at a temperature of 300℃ to 400℃ before the sintering heat treatment, and the pre-sintering time is 4h to 6h.

[0031] A second aspect of the present invention provides an aerogel, which is prepared by the preparation method described in the present invention, wherein the ratio of the thermal conductivity of the aerogel in the radial and axial directions is 0.4 to 1.2, and the anisotropy coefficient of the aerogel is 0.4 to 1.2.

[0032] A third aspect of the present invention provides a system for preparing aerogels with a dual orientation network, the system comprising a dual orientation molding apparatus, the dual orientation molding apparatus being a container consisting of a metal cylindrical ring and a gasket located at the bottom of the metal cylindrical ring.

[0033] Preferably, the metal in the cylindrical metal ring is any metallic substance that does not chemically react with water at room temperature, and is preferably at least one of copper, silver, gold, platinum, molybdenum, tungsten, nickel, aluminum, iron, zinc, tin, and lead.

[0034] Preferably, the ratio of the outer diameter to the height of the metal cylindrical ring is 0.25 to 4:1.

[0035] Preferably, the height of the metal cylindrical ring is 1 to 5 cm.

[0036] Preferably, the wall thickness of the metal cylindrical ring is 50–500 μm.

[0037] Preferably, the gasket is prepared by curing a polymer matrix, wherein the polymer matrix is ​​at least one selected from epoxy resin, polyurethane, phenolic resin, unsaturated polyester, amino resin, polyethylene, polypropylene, polyvinyl chloride, polystyrene, or polysiloxane.

[0038] Preferably, the diameter of the polymer circular gasket is equal to the inner diameter of the metal cylindrical ring, and the length ratio of the thickness of the polymer circular gasket to the height of the metal cylindrical ring is 0.01 to 0.5:1.

[0039] In the technical solution of the present invention, the system further includes a cryogenic refrigeration medium, preferably liquid nitrogen or liquid helium.

[0040] In the technical solution of the present invention, the system further includes a freeze-drying device. In the technical solution of the present invention, the system further includes a sintering device. Preferably, the sintering device can provide a temperature of 300℃-3000℃.

[0041] In the technical solution of the present invention, the system further includes a mixing device. Preferably, the mixing device is selected from a planetary mixer.

[0042] A fourth aspect of the present invention provides the use of aerogels prepared by the method of the present invention as thermally conductive composite materials.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] 1. The aerogel prepared by this invention differs from traditional aerogels. The aerogel prepared by this invention possesses a dual-oriented network microstructure with regular channels in both the radial and axial directions, thus exhibiting excellent mass transfer performance. The aerogel prepared by the method of this invention has superior comprehensive structural characteristics and tunability; therefore, it can be more widely applied in fields such as thermally conductive composite materials, environmental protection, sensors, military, and aerospace.

[0045] 2. The present invention proposes a method for preparing aerogels with a dual-orientation network by mixing fillers, polymer binders and water to form a homogeneous filler mixture. The filler mixture only needs to be subjected to freezing treatment, freeze drying and sintering heat treatment. This method makes the applicable material range wide, the aerogel size controllable, the preparation process simple and the reaction conditions relatively mild. It effectively solves the technical bottlenecks of the narrow applicable material range and complex preparation process of existing conventional methods, and broadens the application prospects of aerogels in various fields. Attached Figure Description

[0046] Figure 1 This is a flowchart illustrating the general method for preparing an aerogel with a dual-orientation network according to the present invention.

[0047] Figure 2 This is a schematic diagram illustrating the principle of a dual-orientation molding apparatus for preparing an aerogel with a dual-orientation network, which is universally applicable to this invention.

[0048] Figure 3 Electron photographs of the boron nitride aerogel prepared in Example 1 during the freezing process;

[0049] Figure 4 An electron micrograph of the graphene aerogel prepared in Example 2. Detailed Implementation

[0050] The present invention will be further described in detail below with reference to embodiments and comparative examples, but the implementation of the present invention is not limited thereto. Specifically, the following embodiments are included:

[0051] To make the technical problem to be solved, the technical solution, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0052] This invention provides a method for preparing aerogels with a dual-orientation network. The general process steps for preparing aerogels with a dual-orientation network according to this invention are as follows: Figure 1 As shown, it includes the following steps:

[0053] S01. The filler, polymer binder and water are mixed at a mass ratio of 1:0.01 to 0.05:3 to 50 to obtain a filler mixture;

[0054] S02. The dual-orientation molding device is pre-placed with a low-temperature cooling medium, the filler mixture is dripped into the dual-orientation molding device, and frozen to form a frozen mixture. The mixture is then freeze-dried to obtain an aerogel precursor.

[0055] S03. The aerogel precursor is subjected to first and second sintering heat treatments to obtain aerogel.

[0056] The dual-orientation molding apparatus used in this invention is an improvement on the traditional single-orientation apparatus. While ensuring the existence of an axial temperature gradient, a radial temperature gradient is introduced to guide ice crystals to grow simultaneously along both the radial and axial directions during freezing, constructing a microstructure with a dual-orientation network. The wall thickness of the metal cylindrical ring affects the radial temperature gradient, while the thickness of the polymer gasket affects the axial temperature gradient. By combining parameters such as the ratio of the outer diameter to the height of the metal cylindrical ring, the anisotropy of the aerogel structure can be controlled. Specifically, Figure 2This diagram illustrates the principle of a bi-orientation molding apparatus for preparing an aerogel with a bi-orientation network, a method applicable to this invention. First, the bi-orientation molding apparatus is pre-cooled in a cryogenic medium. A filler mixture is then dropped into the apparatus, and a localized cryogenic self-assembly process immediately occurs. Ice crystals grow simultaneously along the radial and axial directions, following the temperature gradient. As the ice crystals increase in size, the filler in the mixture is repelled and aggregates between adjacent ice crystals. Freezing promotes the formation of an oriented framework along the temperature gradient, imparting anisotropic properties to the material. The cryogenic self-assembly process continues until all the water in the filler mixture has turned into ice. The ice is then sublimated by freeze-drying to obtain an aerogel precursor with a bi-orientation network.

[0057] Based on the general method for preparing aerogels with a dual-orientation network described above, the following embodiments of the present invention also provide several aerogel materials. Naturally, these aerogel materials are prepared using the general method for preparing aerogels with a dual-orientation network described above. Specifically, the following embodiments are included:

[0058] Example 1

[0059] The preparation method of boron nitride aerogel provided in Example 1 is as shown in Appendix 1. Figure 1 As shown, the specific steps include the following:

[0060] S11: Mix boron nitride microsheets with a size of 5μm, polyvinyl alcohol and water at a mass ratio of 1:0.01:5 and stir in a planetary mixer to obtain a homogeneous boron nitride mixture;

[0061] S12: The dual-orientation molding apparatus is pre-placed in liquid nitrogen. A boron nitride mixture is dripped into the apparatus and frozen to form a frozen mixture. This mixture is then freeze-dried to obtain a boron nitride aerogel precursor. The dual-orientation molding apparatus includes a copper cylindrical ring and an epoxy resin gasket at the bottom of the copper cylindrical ring. The ratio of the outer diameter to the height of the copper cylindrical ring is 0.5:1. The height of the copper cylindrical ring is 4.5 cm, and the wall thickness is 200 μm. The epoxy resin gasket is 2 cm thick, and its diameter is equal to the inner diameter of the copper cylindrical ring. At least one-quarter of the copper cylindrical ring is immersed in liquid nitrogen.

[0062] S13: The boron nitride aerogel precursor is subjected to sintering heat treatment process. The first sintering heat treatment temperature is 350℃ and the sintering time is 4h; the second sintering temperature is 900℃ and the sintering time is 10h.

[0063] The boron nitride aerogel prepared in Example 1 of this invention was analyzed. Electron images of the boron nitride aerogel during the freezing process are shown below. Figure 3As shown, radial ice crystal growth dominates during freezing, resulting in a greater radial network within the aerogel, while the proportion of the axial network decreases in comparison. The composite material of boron nitride aerogel filled with epoxy resin exhibits thermal conductivity of 3.56 W / mK in the radial direction and 3.43 W / mK in the axial direction, with an anisotropy coefficient of 1.04.

[0064] Example 2

[0065] The preparation method of the graphene aerogel provided in Example 2 is as shown in the appendix. Figure 1 As shown, the specific steps include the following:

[0066] S21: Graphene with a size of 20μm, carboxymethyl cellulose and water are mixed at a mass ratio of 1:0.01:40 and stirred in a planetary mixer to obtain a homogeneous graphene mixture;

[0067] S22: The dual-orientation molding device is pre-placed in liquid nitrogen. A graphene mixture is dripped into the device and frozen to form a frozen mixture. This mixture is then freeze-dried to obtain a graphene aerogel precursor. The dual-orientation molding device includes a silver cylindrical ring and a polysiloxane gasket at the bottom of the ring. The ratio of the outer diameter to the height of the silver cylindrical ring is 0.3:1. The height of the ring is 3 cm, and its wall thickness is 100 μm. The polysiloxane gasket is 1 cm thick and has a diameter equal to the inner diameter of the ring. At least one-quarter of the silver cylindrical ring is immersed in liquid nitrogen.

[0068] S23: The graphene aerogel precursor is subjected to sintering heat treatment process. The first sintering heat treatment temperature is 300℃ and the sintering time is 4h; no second sintering treatment is performed.

[0069] The graphene aerogel prepared in Example 2 of this invention was analyzed, and the electron micrograph of the graphene aerogel is shown below. Figure 4 As shown, a distinct radial network structure can be observed. The graphene aerogel-filled epoxy resin composite material exhibits thermal conductivity of 0.52 W / mK in the radial direction and 0.49 W / mK in the axial direction, with an anisotropy coefficient of 1.06 for the aerogel.

[0070] Example 3

[0071] The preparation method of the alumina aerogel provided in Example 3 is as shown in the appendix. Figure 1 As shown, the specific steps include the following:

[0072] S31: Mix alumina particles with a size of 500nm, polyvinylpyrrolidone and water at a mass ratio of 1:0.03:10 and stir in a planetary mixer to obtain a homogeneous alumina mixture;

[0073] S32: The dual-orientation molding apparatus is pre-placed in liquid nitrogen. An alumina mixture is dripped into the apparatus and frozen to form a frozen mixture. This mixture is then freeze-dried to obtain an alumina aerogel precursor. The dual-orientation molding apparatus includes a tin cylindrical ring and a phenolic resin gasket. The ratio of the outer diameter to the height of the tin cylindrical ring is 3:1. The height of the tin cylindrical ring is 1 cm, and its wall thickness is 400 μm. The thickness of the phenolic resin gasket is 0.1 cm, and its diameter is equal to the inner diameter of the tin cylindrical ring. At least one-quarter of the tin cylindrical ring is immersed in liquid nitrogen.

[0074] S33: The alumina aerogel precursor is subjected to sintering heat treatment. The first sintering heat treatment temperature is 400℃, and the sintering time is 6h; the second sintering temperature is 1300℃, and the sintering time is 10h.

[0075] The alumina aerogel prepared in Example 3 of the present invention was analyzed. The thermal conductivity of the alumina aerogel-filled epoxy resin composite material was measured to be 0.72 W / mK in the radial direction and 1.25 W / mK in the axial direction. The anisotropy coefficient of the aerogel was 0.58.

[0076] Example 4

[0077] The preparation method of boron nitride aerogel provided in Example 4 is as shown in Appendix 4. Figure 1 As shown, the specific steps include the following:

[0078] S41: 15μm boron nitride microsheets, polyvinyl alcohol and water are mixed in a mass ratio of 1:0.01:5 and stirred in a planetary mixer to obtain a homogeneous boron nitride mixture;

[0079] S42: The dual-orientation molding apparatus is pre-placed in liquid nitrogen. A boron nitride mixture is dripped into the apparatus and frozen to form a frozen mixture. This mixture is then freeze-dried to obtain a boron nitride aerogel precursor. The dual-orientation molding apparatus includes a copper cylindrical ring and an epoxy resin gasket at the bottom of the copper cylindrical ring. The ratio of the outer diameter to the height of the copper cylindrical ring is 0.5:1. The height of the copper cylindrical ring is 4.5 cm, and the wall thickness is 200 μm. The epoxy resin gasket has a thickness of 2 cm and a diameter equal to the inner diameter of the copper cylindrical ring. At least one-quarter of the copper cylindrical ring is immersed in liquid nitrogen.

[0080] S43: The boron nitride aerogel precursor is subjected to sintering heat treatment process. The first sintering heat treatment temperature is 350℃ and the sintering time is 4h; the second sintering temperature is 900℃ and the sintering time is 10h.

[0081] The boron nitride aerogel prepared in Example 4 of this invention was analyzed. The thermal conductivity of the boron nitride aerogel-filled epoxy resin composite material was measured to be 3.85 W / mK in the radial direction and 3.38 W / mK in the axial direction. The anisotropy coefficient of the aerogel was 1.14.

[0082] Example 5

[0083] The preparation method of boron nitride aerogel provided in Example 5 is as shown in the appendix. Figure 1 As shown, the specific steps include the following:

[0084] S51: Mix boron nitride micron sheets with a size of 5μm, polyvinyl alcohol and water at a mass ratio of 1:0.01:5 and stir in a planetary mixer to obtain a homogeneous boron nitride mixture;

[0085] S52: The dual-orientation molding apparatus is pre-placed in liquid nitrogen. A boron nitride mixture is dripped into the apparatus and frozen to form a frozen mixture. This mixture is then freeze-dried to obtain a boron nitride aerogel precursor. The dual-orientation molding apparatus includes a copper cylindrical ring and an epoxy resin gasket at the bottom of the copper cylindrical ring. The ratio of the outer diameter to the height of the copper cylindrical ring is 1:1. The height of the copper cylindrical ring is 4.5 cm, and the wall thickness is 200 μm. The thickness of the epoxy resin gasket is 2 cm, and the diameter of the epoxy resin gasket is equal to the inner diameter of the copper cylindrical ring. At least one-quarter of the copper cylindrical ring is immersed in liquid nitrogen.

[0086] S53: The boron nitride aerogel precursor is subjected to sintering heat treatment process. The first sintering heat treatment temperature is 350℃ and the sintering time is 4h; the second sintering temperature is 900℃ and the sintering time is 10h.

[0087] The boron nitride aerogel prepared in Example 5 of the present invention was analyzed. The thermal conductivity of the boron nitride aerogel-filled epoxy resin composite material was measured to be 3.34 W / mK in the radial direction and 2.96 W / mK in the axial direction. The anisotropy coefficient of the aerogel was 1.13.

[0088] Example 6

[0089] The preparation method of boron nitride aerogel provided in Example 6 is as shown in Appendix 6. Figure 1 As shown, the specific steps include the following:

[0090] S61: Mix boron nitride microsheets with a size of 5μm, polyvinyl alcohol and water at a mass ratio of 1:0.01:5 and stir in a planetary mixer to obtain a homogeneous boron nitride mixture;

[0091] S62: The dual-orientation molding apparatus is pre-placed in liquid nitrogen. A boron nitride mixture is dripped into the apparatus and frozen to form a frozen mixture. This mixture is then freeze-dried to obtain a boron nitride aerogel precursor. The dual-orientation molding apparatus includes a copper cylindrical ring and an epoxy resin gasket at the bottom of the copper cylindrical ring. The ratio of the outer diameter to the height of the copper cylindrical ring is 0.3:1. The height of the copper cylindrical ring is 5 cm, and its wall thickness is 100 μm. The epoxy resin gasket has a thickness of 2.5 cm and a diameter equal to the inner diameter of the copper cylindrical ring. At least one-quarter of the copper cylindrical ring is immersed in liquid nitrogen.

[0092] S63: The boron nitride aerogel precursor is subjected to sintering heat treatment process. The first sintering heat treatment temperature is 350℃ and the sintering time is 4h; the second sintering temperature is 900℃ and the sintering time is 10h.

[0093] The boron nitride aerogel prepared in Example 6 of the present invention was analyzed. The thermal conductivity of the boron nitride aerogel-filled epoxy resin composite material was measured to be 3.77 W / mK in the radial direction and 3.70 W / mK in the axial direction. The anisotropy coefficient of the aerogel was 1.02.

[0094] Example 7

[0095] The preparation method of boron nitride aerogel provided in Example 7 is as shown in Appendix 7. Figure 1 As shown, the specific steps include the following:

[0096] S71: Mix boron nitride micron sheets with a size of 5μm, polyvinyl alcohol and water at a mass ratio of 1:0.01:5 and stir in a planetary mixer to obtain a homogeneous boron nitride mixture;

[0097] S72: The dual-orientation molding apparatus is pre-placed in liquid nitrogen. A boron nitride mixture is dripped into the apparatus and frozen to form a frozen mixture. This mixture is then freeze-dried to obtain a boron nitride aerogel precursor. The dual-orientation molding apparatus includes a copper cylindrical ring and an epoxy resin gasket at the bottom of the copper cylindrical ring. The ratio of the outer diameter to the height of the copper cylindrical ring is 3.5:1. The height of the copper cylindrical ring is 2 cm, and the wall thickness is 400 μm. The thickness of the epoxy resin gasket is 0.1 cm, and the diameter of the epoxy resin gasket is equal to the inner diameter of the copper cylindrical ring. At least one-quarter of the copper cylindrical ring is immersed in liquid nitrogen.

[0098] S73: The boron nitride aerogel precursor is subjected to sintering heat treatment process. The first sintering heat treatment temperature is 350℃ and the sintering time is 4h; the second sintering temperature is 900℃ and the sintering time is 10h.

[0099] The boron nitride aerogel prepared in Example 7 of the present invention was analyzed. The thermal conductivity of the boron nitride aerogel-filled epoxy resin composite material was measured to be 1.63 W / mK in the radial direction and 3.66 W / mK in the axial direction. The anisotropy coefficient of the aerogel was 0.45.

[0100] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the embodiments described above. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

[0101] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method of preparing an aerogel having a dual orientation network, characterized in that, The method comprises the following steps: Step 1: mixing the filler, the polymer binder and water according to the mass ratio of 1:0.01-0.05:3-50 to obtain a filler mixture; Step 2: placing the bioriented molding device in a low-temperature refrigeration medium in advance, adding the filler mixture into the bioriented molding device, performing a freezing treatment to form an ice mixture, and then performing a freeze-drying treatment to obtain an aerogel precursor; Step 3: performing a sintering heat treatment on the aerogel precursor to obtain an aerogel; The bioriented molding device is a container composed of a metal cylindrical ring and a gasket located at the bottom of the metal cylindrical ring; At least one quarter of the metal cylindrical ring in the bioriented molding device is immersed in the low-temperature refrigeration medium; The low-temperature refrigeration medium is at least one of liquid nitrogen or liquid helium; The freezing treatment is to drop the filler mixture into the bioriented molding device and indirectly contact with the low-temperature refrigeration medium, thereby triggering a continuous self-assembly molding process; The filler is any substance that does not chemically react with water at room temperature; The filler includes aluminum oxide, magnesium oxide, zinc oxide, aluminum nitride, boron nitride, silicon carbide, and graphene; The polymer binder is at least one of polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, polyacrylamide, carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, or hydroxypropyl methyl cellulose; The gasket is a polymer circular gasket prepared by curing a polymer matrix selected from at least one of epoxy resin, polyurethane, phenolic resin, unsaturated polyester, amino resin, polyethylene, polypropylene, polyvinyl chloride, polystyrene, or polysiloxane; The length ratio of the outer diameter to the height of the metal cylindrical ring is 0.25-4:1 The wall thickness of the metal cylindrical ring is 50-500 μm; The length ratio of the thickness of the polymer circular gasket to the height of the metal cylindrical ring is 0.01-0.5:

1.

2. The method of claim 1, wherein: The appearance of the filler is any one or more of granular, linear, or flaky.

3. The method of claim 1, wherein: The particle size of the filler is 50 nm-100 μm.

4. The method of claim 1, wherein: The metal in the metal cylindrical ring is any metal substance that does not chemically react with water at room temperature, and the metal is selected from at least one of copper, silver, gold, platinum, molybdenum, tungsten, nickel, aluminum, iron, zinc, tin, and lead.

5. The method of claim 1, wherein: The height of the metal cylindrical ring is 1-5 cm.

6. The method of claim 1, wherein: The sintering heat treatment is sintering at a temperature of 300ºC-2500ºC for 1 h-12 h.

7. The method of claim 1, wherein: Pre-sintering is performed at a temperature of 300ºC-400ºC before the sintering heat treatment, and the pre-sintering time is 4 h-6 h.

8. The method for preparing the aerogel with a bioriented network according to claim 1, wherein: The freeze-drying treatment is to place the ice product into a freeze-drying machine to sublimate the ice.

9. The aerogel with a bioriented network prepared by the method according to any one of claims 1-8.

10. The aerogel with a bioriented network according to claim 9 as an application in a heat-conducting composite material.

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