A method for preparing boron nitride fiber

Abstract

The present invention provides a method for preparing boron nitride fibers. The method utilizes liquid-phase self-assembly and directional freezing techniques. The adhesive action of xanthan gum promotes the uniform accumulation and orderly arrangement of boron nitride within the xanthan gum framework, forming a continuous heat transfer network. In the present invention, xanthan gum acts as an adhesive, while boron nitride nanosheets serve as a heat conductor. In a liquid environment, xanthan gum molecules and boron nitride nanosheets mix to form a uniformly dispersed system. The method achieves the orderly growth of ice crystals, which in turn promotes the self-assembly of the boron nitride nanosheets and xanthan gum into liquid boron nitride fibers. After freeze-drying, solid boron nitride fibers are obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of nano material processing, in particular to a method for preparing boron nitride fiber. Background Art

[0002] In recent years, the emergence of 5G communication technology has accelerated progress in major scientific and technological fields such as big data, the Internet of Things, cloud computing, and artificial intelligence, thereby driving the development of integrated circuits and their associated industrial clusters. The increasing power density of electronic components is placing increasingly stringent demands on their thermal management systems. The development and preparation of efficient thermal interface materials (TIMs) to dissipate heat from microelectronic devices has become a key technology influencing the future development of thermal management techniques and the fabrication of advanced integrated circuits.

[0003] In recent years, thermally conductive polymers prepared by induced orientation of insulating two-dimensional thermally conductive fillers represented by boron nitride have demonstrated excellent in-plane thermal conductivity. The development of high-quality boron nitride fibers can effectively improve the thermal conductivity of boron nitride nanocomposites. Existing technologies use template guidance, electrospinning, and fiber coating to prepare various thermally conductive boron nitride fibers. The boron nitride nanosheets (BNNs) in the fibers have structural defects such as disordered stacking, sparse dispersion, and large micropores, which make it impossible to form a continuous thermal conductive network chain, hinder the long-range orderly transmission of phonons, and affect the heat diffusion rate. Summary of the Invention

[0004] The present invention aims to provide a method for preparing boron nitride fibers to solve the technical problem of unsatisfactory thermal conductivity of boron nitride fibers in the prior art.

[0005] To achieve the above object, the present invention provides a method for preparing boron nitride fiber, the specific steps of which are as follows:

[0006] (1) Xanthan gum was added to deionized water and stirred slowly for 1 hour to obtain a 2-20 mg / mL xanthan gum aqueous solution;

[0007] (2) Boron nitride was then added to deionized water and ultrasonically dispersed to obtain a 14 mg / mL boron nitride dispersion;

[0008] (3) Finally, the xanthan gum aqueous solution, the boron nitride dispersion and deionized water were mixed and stirred at a volume ratio of 2:1:1 for 5 minutes to obtain a mixed solution, which was directionally freeze-dried to obtain the boron nitride fiber.

[0009] Preferably, in step (1), the stirring rate of the slow stirring is 100 to 300 r / min.

[0010] Preferably, in step (2), the particle size of boron nitride is 5 to 10 μm and is purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0011] Preferably, in step (2), the process conditions for ultrasonic dispersion are: frequency 40 kHz, power 75 W, and time 10 minutes.

[0012] Preferably, in step (3), the process conditions for directional freeze drying are: first freezing with liquid nitrogen at -196°C until the liquid is completely solidified and frozen (freezer freezing cannot achieve the directional freezing function), and then transferring the frozen sample to a vacuum freeze dryer for vacuum freeze drying.

[0013] Further preferably, the process conditions of vacuum freeze drying are: vacuum degree 5 to 20 Pa, temperature -50 to -55°C, and freeze drying time 5 to 7 days.

[0014] The present invention has the following beneficial effects:

[0015] The present invention adopts liquid phase self-assembly technology and directional freezing technology, and promotes the uniform accumulation and neat arrangement of boron nitride in the xanthan gum skeleton through the adhesive effect of xanthan gum, thereby forming a continuous heat transfer network.

[0016] First, the right ratio of boron nitride to xanthan gum and water is crucial for successfully preparing high-quality, uniformly arranged boron nitride fibers. The applicants determined the optimal ratio through experimental screening. Too low a boron nitride solution concentration prevents the formation of a densely packed boron nitride arrangement and a uniform fiber structure. Too high a boron nitride content leads to clustering of boron nitride nanosheets, preventing a uniform stacking arrangement. In the present invention, xanthan gum acts as an adhesive, while the boron nitride nanosheets serve as a heat conductor. In a liquid environment, the xanthan gum molecules and boron nitride nanosheets mix to form a uniformly dispersed system.

[0017] Secondly, the freezing method can determine the arrangement of the fibers. The applicant obtained high-quality boron nitride fibers by freezing with liquid nitrogen. During the liquid nitrogen cryogenic freezing process, a directional freezing technique was used, using the highly anisotropic solidification behavior of water in the orientation temperature field as a template to controllably orient the boron nitride / xanthan gum. Specifically, the boron nitride / xanthan gum was placed in a temperature gradient aqueous solution, and the water was cooled to form vertical icicles. As the temperature dropped, the internal moisture solidified along the temperature gradient, while the boron nitride / xanthan gum was squeezed between the ice crystal columns, which then acted as physical confinement. Subsequently, the frozen sample was placed in a freeze dryer to dry, the ice crystals vaporized, and the remaining boron nitride / xanthan gum oriented fibers were left. The present invention achieves the orderly growth of ice crystals, and the process of ice crystal growth promotes the self-assembly of boron nitride nanosheets and xanthan gum into liquid boron nitride fibers. After drying, solid-state boron nitride fibers were obtained.

[0018] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0020] Figure 1 1 is a scanning electron microscope image of the boron nitride fiber obtained in an embodiment of the present invention, wherein A is a scanning electron microscope image, B is a partial enlarged image of A, and C is a partial enlarged image of B;

[0021] Figure 2 This is a scanning electron microscope image of the boron nitride fiber obtained in Comparative Example 1;

[0022] Figure 3 This is a scanning electron microscope image of the boron nitride fiber obtained in Comparative Example 2;

[0023] Figure 4 This is a scanning electron microscope image of the boron nitride fiber obtained in Comparative Example 3;

[0024] Figure 5 This is a scanning electron microscope image of the boron nitride fiber obtained in Comparative Example 4;

[0025] Figure 6 This is a scanning electron microscope image of the boron nitride fiber obtained in Comparative Example 5;

[0026] Figure 7 This is a scanning electron microscope image of the boron nitride fiber obtained in Comparative Example 6; DETAILED DESCRIPTION

[0027] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered by the claims.

[0028] Example 1:

[0029] A method for preparing boron nitride fiber, the specific steps are as follows:

[0030] (1) Xanthan gum was added to deionized water and stirred slowly at 100 rpm for 1 hour to obtain a 2 mg / mL xanthan gum aqueous solution;

[0031] (2) Boron nitride (particle size 10 μm, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) was then added to deionized water and ultrasonically dispersed to obtain a 14 mg / mL boron nitride dispersion;

[0032] (3) Finally, the xanthan gum aqueous solution, the boron nitride dispersion and deionized water were mixed and stirred at a volume ratio of 2:1:1 for 5 minutes to obtain a mixed solution, which was directionally freeze-dried to obtain the boron nitride fiber.

[0033] In step (2), the process conditions of ultrasonic dispersion are: frequency 40 kHz, power 75 W, and time 10 minutes.

[0034] In step (3), the process conditions for directional freeze drying are: first freezing with liquid nitrogen at -196°C until the liquid is completely solidified and frozen (freezer freezing cannot achieve the directional freezing function), and then transferring the frozen sample to a vacuum freeze dryer for vacuum freeze drying; the process conditions for vacuum freeze drying are: vacuum degree 5 Pa, temperature -50°C, and freeze drying time 5 days.

[0035] from Figure 1 It can be seen that the obtained boron nitride fibers are uniform and continuous as a whole ( Figure 1 Middle A), after magnification, we can see that the boron nitride nanosheets on the boron nitride fiber are densely packed and evenly arranged ( Figure 1 B and C) in the figure prove that high-quality boron nitride fibers were synthesized in Example 1.

[0036] Example 2:

[0037] A method for preparing boron nitride fiber, the specific steps are as follows:

[0038] (1) Xanthan gum was added to deionized water and stirred slowly at 300 rpm for 1 hour to obtain a 20 mg / mL xanthan gum aqueous solution;

[0039] (2) Boron nitride (particle size 10 μm, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) was then added to deionized water and ultrasonically dispersed to obtain a 14 mg / mL boron nitride dispersion;

[0040] (3) Finally, the xanthan gum aqueous solution, the boron nitride dispersion and deionized water were mixed and stirred at a volume ratio of 2:1:1 for 5 minutes to obtain a mixed solution, which was directionally freeze-dried to obtain the boron nitride fiber.

[0041] In step (2), the process conditions of ultrasonic dispersion are: frequency 40 kHz, power 75 W, and time 10 minutes.

[0042] In step (3), the process conditions for directional freeze drying are: first freezing with liquid nitrogen at -196°C until the liquid is completely solidified and frozen (freezer freezing cannot achieve the directional freezing function), and then transferring the frozen sample to a vacuum freeze dryer for vacuum freeze drying; the process conditions for vacuum freeze drying are: vacuum degree 20Pa, temperature -55°C, and freeze drying time 7 days.

[0043] Example 3:

[0044] A method for preparing boron nitride fiber, the specific steps are as follows:

[0045] (1) Xanthan gum was added to deionized water and stirred slowly at 100 rpm for 1 hour to obtain a 14 mg / mL xanthan gum aqueous solution;

[0046] (2) Boron nitride (particle size 10 μm, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) was then added to deionized water and ultrasonically dispersed to obtain a 14 mg / mL boron nitride dispersion;

[0047] (3) Finally, the xanthan gum aqueous solution, the boron nitride dispersion and deionized water were mixed and stirred at a volume ratio of 2:1:1 for 5 minutes to obtain a mixed solution, which was directionally freeze-dried to obtain the boron nitride fiber.

[0048] In step (2), the process conditions of ultrasonic dispersion are: frequency 40 kHz, power 75 W, and time 10 minutes.

[0049] In step (3), the process conditions for directional freeze drying are: first freezing with liquid nitrogen at -196°C until the liquid is completely solidified and frozen (freezer freezing cannot achieve the directional freezing function), and then transferring the frozen sample to a vacuum freeze dryer for vacuum freeze drying; the process conditions for vacuum freeze drying are: vacuum degree 20Pa, temperature -50°C, and freeze drying time 7 days.

[0050] Comparative Example 1

[0051] The concentration of the boron nitride dispersion was 2 mg / mL, and the rest was the same as in Example 1.

[0052] from Figure 2 It can be seen that the obtained product fibers are not formed.

[0053] Comparative Example 2

[0054] The concentration of the boron nitride dispersion was 6 mg / mL, and the rest was the same as in Example 1.

[0055] from Figure 3 It can be seen that the obtained product fibers are not formed.

[0056] Comparative Example 3

[0057] The concentration of the boron nitride dispersion was 20 mg / mL, and the rest was the same as in Example 1.

[0058] from Figure 4 It can be seen that the boron nitride nanosheets of the obtained product are arranged unevenly.

[0059] Comparative Example 4

[0060] The graphene oxide solution was poured into the xanthan gum solution, stirred evenly, directionally frozen using liquid nitrogen, and then freeze-dried in a freeze dryer. The rest was the same as in Example 1.

[0061] from Figure 5 It can be seen that fibrous graphene oxide fibers cannot be obtained.

[0062] Comparative Example 5

[0063] The graphene nanosheet solution was poured into the xanthan gum solution, stirred evenly, directionally frozen using liquid nitrogen, and then freeze-dried in a freeze dryer. The rest was the same as in Example 1.

[0064] from Figure 6 It can be seen that graphene nanosheet fibers cannot be obtained.

[0065] Comparative Example 6

[0066] The same procedures as in Example 1 were followed except that xanthan gum was replaced with cellulose.

[0067] from Figure 7 It can be seen that uniform long fibers cannot be formed.

[0068] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing boron nitride fiber, characterized in that: The specific steps are as follows: (1) Xanthan gum was added to deionized water and stirred slowly for 1 hour to obtain a 2-20 mg / mL xanthan gum aqueous solution; (2) Boron nitride was then added to deionized water and ultrasonically dispersed to obtain a 14 mg / mL boron nitride dispersion; (3) finally, the xanthan gum aqueous solution, the boron nitride dispersion and deionized water were mixed and stirred at a volume ratio of 2:1:1 for 5 minutes to obtain a mixed solution, and then directionally freeze-dried to obtain the boron nitride fiber; In step (2), the particle size of boron nitride is 5 to 10 μm and is purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; In step (3), the process conditions for directional freeze drying are: first freezing at -196°C in liquid nitrogen until the liquid is completely solidified and frozen, and then transferring the frozen sample to a vacuum freeze dryer for vacuum freeze drying; The process conditions of vacuum freeze drying are: vacuum degree 5 to 20 Pa, temperature -50 to -55°C, and freeze drying time 5 to 7 days.

2. The method for preparing boron nitride fiber according to claim 1, wherein: In step (1), the stirring rate of the slow stirring is 100 to 300 r / min.

3. The method for preparing boron nitride fiber according to claim 1, wherein: In step (2), the process conditions of ultrasonic dispersion are: frequency 40 kHz, power 75 W, and time 10 minutes.

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