Preparation method and application of novel boron nitride-carbon nitride heterostructure heat-conducting filler

Abstract

The invention discloses a preparation method and application of a novel boron nitride-carbon nitride heterostructure heat-conducting filler. According to the preparation method disclosed by the invention, melamine is taken as a precursor on a two-dimensional filler BNNS prepared by stripping, and the melamine is converted into flaky graphite phase carbon nitride (g-C3N4) through high-temperature treatment, so that the g-C3N4-coated BNNS heterostructure filler is formed. Wherein g-C3N4 with good heat-conducting property uniformly grows on the surface of a BNNS sheet layer, so that the structural defect of BNNS is filled up, and a connecting site for the BNNS to act with a polymer matrix is provided for the BNNS. The g-C3N4-coated BNNS novel heterostructure filler prepared by the method can solve the problem of intrinsic thermal conductivity reduction caused by BNNS structure defects, and can also reduce the interface thermal resistance between the BNNS filler and a matrix to a certain extent.

Description

Technical Field

[0001] The present invention belongs to the field of thermal conductive materials, and in particular relates to a preparation method and application of a novel boron nitride-carbon nitride heterostructure thermal conductive filler. Background Art

[0002] With significant advances in the integration and miniaturization of microelectronic devices, the continuous increase in device power density has posed unprecedented challenges. The large amounts of heat generated during operation can negatively impact device safety, performance, and lifespan, thereby limiting the development of microelectronics and wireless communications. Therefore, effective thermal management has become a pressing issue. In particular, with the rise of fifth-generation mobile communication networks, the high-density integrated systems they utilize, the Internet of Things (IoT), and artificial intelligence (AI) all require effective thermal management technologies. In this context, heat dissipation materials used in thermal management must possess both high thermal conductivity and electrical insulation properties. Polymers are widely used in this field due to their electrical insulation, low cost, ease of processing, and lightweight properties. However, their intrinsic thermal conductivity is too low to meet these requirements. Therefore, the addition of highly thermally conductive fillers is being used to improve the thermal conductivity of polymers.

[0003] BNNS has high thermal conductivity (130-400W m -1 K -1 ), electrically insulating, and with a high aspect ratio, making it an ideal filler for preparing thermally conductive composite materials. Most BNNS are prepared from h-BN by mechanically and chemically exfoliating the h-BN layer to destroy the interlayer van der Waals forces. However, the strong mechanical forces and violent chemical reactions during the preparation process inevitably damage the BNNS crystal structure, which seriously reduces its intrinsic thermal conductivity. Most people skilled in the art compensate for the problem of reduced intrinsic thermal conductivity of BNNS by adding BNNS and another two-dimensional high thermal conductivity filler (mostly graphene) to the polymer matrix at the same time.

[0004] Furthermore, BNNS have few surface functional groups and are chemically inert, making them difficult to effectively interact with the matrix. This results in poor interfacial compatibility and uneven filler distribution in the composite material, leading to a significant discrepancy between experimental and theoretical thermal conductivity values. Technologists in this field have chemically modified BNNS with various modifiers to enhance their interfacial interaction with the polymer matrix, thereby improving the thermal conductivity of the composite material.

[0005] Therefore, the current preparation process for BNNS-based composite materials has two limitations: 1. The chemical or mechanical exfoliation methods used in the BNNS preparation process can damage its structure to a certain extent, thereby introducing defect sites that affect its intrinsic thermal conductivity. 2. The surface inertness of BNNS causes it to introduce a large amount of interfacial thermal resistance at the filler-matrix interface when used as a filler in a polymer matrix.

[0006] Currently, the method of improving the poor intrinsic thermal conductivity of BNNS by introducing another two-dimensional high thermal conductivity filler has several limitations: 1. Conventional two-dimensional high thermal conductivity fillers are relatively expensive, significantly increasing the overall cost of the composite material; 2. The newly introduced two-dimensional high thermal conductivity filler has no interaction sites with the BNNS, resulting in a large amount of interfacial thermal resistance between the new filler and the BNNS, making the thermal conductivity improvement efficiency of the composite material lower than expected; 3. It does not substantially address the defects in the BNNS crystal structure. In addition, the method of chemically modifying the surface-inert BNNS to improve its interfacial interaction with the polymer matrix has certain problems: 1. The chemical modification process often involves high temperature and pressure or strong acid and strong base reagents, which further destroy the BNNS crystal structure and reduce the intrinsic thermal conductivity of the BNNS; 2. Most chemical modifiers do not have heat transfer capabilities, and their introduction may affect the heat transfer efficiency of the composite material; 3. The complexity of the chemical modification process increases costs, and improper subsequent disposal of strong acid and strong base modifiers can cause environmental pollution. Summary of the Invention

[0007] The present invention is aimed at the problems existing in the above-mentioned prior art and provides a method for preparing a novel heterostructured thermal conductive filler of boron nitride-carbon nitride and its application. The present invention uses melamine as a precursor on the two-dimensional filler BNNS obtained by peeling, and converts melamine into flaky graphite phase carbon nitride (g-C3N4) by high temperature treatment to form a g-C3N4@BNNS heterostructured filler. The g-C3N4 with good thermal conductivity grows evenly on the surface of the BNNS layer, fills the structural defects of the BNNS, and provides the BNNS with a connection site for forming an effect with the polymer matrix. The g-C3N4@BNNS novel heterostructured filler prepared by the present invention can not only solve the problem of reduced intrinsic thermal conductivity caused by the structural defects of the BNNS, but also reduce the interfacial thermal resistance between the BNNS filler and the matrix to a certain extent.

[0008] The preparation method of the novel boron nitride-carbon nitride heterostructure thermal conductive filler of the present invention comprises the following steps:

[0009] Step 1: Preparation of BNNS

[0010] 0.5 g of h-BN was added to 500 mL of a mixed solvent of isopropanol and water, stirred magnetically until uniform, and then placed in an ultrasonic machine for ultrasonic treatment for 24 hours. The sonicated mixture was centrifuged at 1000 rpm for 10 minutes to remove the unpeeled h-BN in the lower layer. The supernatant was centrifuged at 10000 rpm for 10 minutes, and the sediment was vacuum dried at 70°C for 24 hours to obtain BNNS.

[0011] Step 2: Preparation of g-C3N4@BNNS

[0012] 0.2g of melamine was added to 20mL of deionized water, heated in a waterbath at 80°C, and magnetically stirred for 30 minutes. To this solution, 0.2g of BNNS was added, stirred at 80°C for 12 hours, and ultrasonically dispersed for 1 hour. The mixture was centrifuged at 10,000 rpm for 10 minutes, and the sediment was freeze-dried for 24 hours. The dried sample was annealed in a tube furnace and then cooled to room temperature to obtain g-C3N4@BNNS, a novel boron nitride-carbon nitride heterostructure thermally conductive filler.

[0013] In step 1, the volume ratio of isopropyl alcohol to water in the mixed solvent of isopropyl alcohol and water is 1:1.

[0014] In step 2, the mass ratio of melamine to BNNS is 2:1 to 1:2, preferably 1:1.

[0015] In step 2, the annealing is carried out in a nitrogen atmosphere or an argon atmosphere at 450-600° C. for 3-8 hours with a heating rate of 2.5° C. / min.

[0016] The invention discloses an application of a novel boron nitride-carbon nitride heterostructure thermally conductive filler in the preparation of an epoxy resin thermally conductive composite material.

[0017] The specific steps include:

[0018] To a 10 mL 1 wt% aqueous solution of hydroxyethyl cellulose (HEC), 0.5-2 g of g-C3N4@BNNS was added. The mixture was stirred for 30 minutes, sonicated for 1 hour, poured into a mold, frozen from the bottom up with liquid nitrogen, and freeze-dried in a freeze dryer for 24 hours to obtain a g-C3N4@BNNS skeleton. The g-C3N4@BNNS skeleton was then infused with an epoxy resin mixture (epoxy resin, catalyst, curing agent = 100:100:5) and cured at 120°C to form a g-C3N4@BNNS / epoxy resin thermally conductive composite. A BNNS / epoxy resin thermally conductive composite was also prepared to verify the excellent thermal conductivity of the g-C3N4@BNNS heterostructured thermally conductive filler.

[0019] The mass content of g-C3N4@BNNS in the g-C3N4@BNNS / epoxy resin thermal conductive composite material is 5-30%.

[0020] The present invention aims to reinforce h-BN, which has low cost and average performance, through this method, thereby improving its application performance.

[0021] The present invention utilizes melamine as a precursor to be evenly distributed on the surface of BNNS, and prepares g-C3N4@BNNS heterogeneous structure filler by in-situ conversion method. Among them, melamine is converted into g-C3N4 with good thermal conductivity in situ, and is connected to BNNS defect sites through chemical bonds, thereby compensating for the crystal defects of BNNS and improving its intrinsic thermal conductivity. In addition, g-C3N4 has certain chemical activity, and BNNS establishes a connection with the polymer matrix with the help of g-C3N4, thereby improving the interface strength of the filler-matrix and thus improving the thermal conductivity of the composite material. This invention constructs a new type of heterogeneous structure thermal conductive filler g-C3N4@BNNS on the basis of simple preparation process, no toxic solvents are used in the process, and low cost. The filler not only has high intrinsic thermal conductivity, but also combines well with the polymer matrix, so that the polymer-based composite material prepared on this basis has excellent thermal conductivity while maintaining good mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a flow chart for preparing the g-C3N4@BNNS heterostructure of the present invention.

[0023] Figure 2 This is a scanning electron microscope image of the g-C3N4@BNNS heterostructure of the present invention.

[0024] Figure 3 This is a comparison chart of thermal conductivity of g-C3N4@BNNS / epoxy resin and BN / epoxy resin with different filler ratios.

[0025] Figure 4 This is a comparison chart of the tensile strength of g-C3N4@BNNS / epoxy resin and BN / epoxy resin with different filler ratios.

[0026] Figure 5 This is a comparison chart of the thermal conductivity of g-C3N4@BNNS / epoxy resin prepared at the same filler content (14.4wt%) prepared by g-C3N4@BNNS synthesized at different mass ratios of melamine to BNNS. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further analyzed and explained below through specific embodiments.

[0028] Example 1: Preparation of BNNS

[0029] 0.5 g of h-BN was added to 500 mL of a mixed solvent of isopropanol and water (the volume ratio of isopropanol to water was 1:1), magnetically stirred until uniform, and then placed in an ultrasonic machine for ultrasonic treatment for 24 hours. The sonicated mixture was centrifuged at 1000 rpm for 10 minutes to remove the unpeeled h-BN in the lower layer. The supernatant was centrifuged at 10000 rpm for 10 minutes, and the sediment was vacuum dried at 70°C for 24 hours to obtain BNNS.

[0030] Example 2: Preparation of g-C3N4@BNNS

[0031] 0.2g of melamine was added to 20mL of deionized water, heated in a waterbath at 80°C, and magnetically stirred for 30 minutes. To this solution, 0.2g of BNNS was added, stirred at 80°C for 12 hours, and ultrasonically dispersed for 1 hour. The mixture was centrifuged at 10,000 rpm for 10 minutes, and the sediment was freeze-dried for 24 hours. The dried sample was placed in a tube furnace under nitrogen protection and heated at a rate of 2.5°C / min to 550°C. The temperature was maintained for 4 hours, and then cooled to room temperature to obtain a novel boron nitride-carbon nitride heterostructure thermally conductive filler, g-C3N4@BNNS.

[0032] Example 3: Preparation of BNNS / epoxy resin thermal conductive composite material

[0033] A 1 wt% aqueous solution of hydroxyethyl cellulose was prepared, to which different masses of g-C3N4@BNNS were added to form mixtures with concentrations of 50 mg / mL, 100 mg / mL, 150 mg / mL, and 200 mg / mL, respectively. The mixtures were stirred for 30 minutes and sonicated for 1 hour. Once homogeneously mixed, 5 mL of each mixture was poured into a mold, frozen from the bottom up with liquid nitrogen, and freeze-dried in a freeze dryer for 24 hours to obtain a g-C3N4@BNNS skeleton. The g-C3N4@BNNS skeleton was then infused with an epoxy resin mixture (epoxy resin, catalyst, and curing agent = 100:100:5) until the skeleton was submerged. The mixture was then cured at 120°C to form a g-C3N4@BNNS / epoxy resin thermally conductive composite. Simultaneously, BNNS / epoxy resin thermally conductive composites were prepared to verify the excellent thermal and mechanical properties of the g-C3N4@BNNS heterostructured thermally conductive filler.

[0034] Among them, epoxy resin is EPON TM Resin 862, the catalyst is methylhexahydrophthalic anhydride, and the curing agent is 2,4,6-tris(dimethylaminomethyl)phenol.

Claims

1. A method for preparing a novel boron nitride-carbon nitride heterostructure thermal conductive filler, characterized in that The steps include: Step 1: Preparation of BNNS h-BN is added to a mixed solvent of isopropyl alcohol and water, stirred magnetically and then ultrasonicated. The mixture is centrifuged at low speed to remove the unpeeled h-BN in the lower layer, and the supernatant is centrifuged at high speed. The sediment is vacuum dried to obtain BNNS. Step 2: Preparation of g-C3N4@BNNS 0.2 g of melamine was added to 20 mL of deionized water, heated in a water bath at 80°C, and magnetically stirred for 30 minutes. 0.2 g of BNNS was added to the above solution, and stirring was continued at 80°C for 12 hours, followed by ultrasonic dispersion for 1 hour. The mixture was centrifuged at high speed, and the obtained sediment was freeze-dried. The dried sample was annealed in a tube furnace and cooled to room temperature after annealing to obtain a new boron nitride-carbon nitride heterostructure thermal conductive filler g-C3N4@BNNS.

2. The preparation method according to claim 1, wherein: In step 1, the volume ratio of isopropyl alcohol to water in the mixed solvent of isopropyl alcohol and water is 1:

1.

3. The preparation method according to claim 1, wherein: In step 1, the low-speed centrifugation treatment is performed at 1000 rpm for 10 min.

4. The preparation method according to claim 1, wherein: In step 1, the high-speed centrifugation is performed at 10,000 rpm for 10 minutes.

5. The preparation method according to claim 1, wherein: In step 2, the mass ratio of melamine to BNNS is 2:1 to 1:

2.

6. The preparation method according to claim 5, characterized in that: The mass ratio of melamine to BNNS is 1:

1.

7. The preparation method according to claim 1, wherein: In step 2, the annealing is carried out in a nitrogen atmosphere or an argon atmosphere at 450-600° C. for 3-8 hours with a heating rate of 2.5° C. / min.

8. Use of the novel heterostructured thermal conductive filler of boron nitride-carbon nitride prepared by the preparation method according to any one of claims 1 to 7 in the preparation of epoxy resin thermal conductive composite materials.

9. The use according to claim 8, characterized in that: Prepare 10 mL of a 1 wt% hydroxyethyl cellulose aqueous solution, add 0.5-2 g of g-C3N4@BNNS, stir for 30 minutes, ultrasonicate for 1 hour, pour into a mold, freeze from bottom to top using liquid nitrogen, and freeze-dry in a freeze dryer for 24 hours to obtain a g-C3N4@BNNS skeleton structure; then fill the g-C3N4@BNNS skeleton with an epoxy resin mixture, and after curing, form a g-C3N4@BNNS / epoxy resin thermal conductive composite material.

10. The use according to claim 9, characterized in that: The mass content of g-C3N4@BNNS in the g-C3N4@BNNS / epoxy resin thermal conductive composite material is 5-30%.

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