A low-temperature high thermal conductivity polymer composite material and its preparation method

Abstract

This invention discloses a low-temperature high thermal conductivity polymer composite material and its preparation method, belonging to the field of magnetic confinement nuclear fusion technology. This invention uses a specific process to composite a low-temperature high thermal conductivity filler with a polymer matrix. Compared to the microstructure of conventional polymer thermally conductive composite materials, this material has a quasi-continuous thermally conductive network formed by the low-temperature high thermal conductivity filler surrounding the polymer. At low temperatures (e.g., 4K), when the volume percentage of the thermally conductive filler is 50%, it can reach 100 W·m³. ‑1 ·K ‑1 The low-temperature high thermal conductivity polymer composite material of this invention exhibits significantly higher thermal conductivity than other polymer composite materials under the same thermally conductive filler volume percentage. It can be applied in low-temperature heat and mass transfer fields such as superconducting magnets, and possesses advantages such as lightweight, low-temperature resistance, and ease of processing. Furthermore, the preparation method of the low-temperature high thermal conductivity polymer composite material of this invention is simple and reliable, offering significant advantages in mass production.

Description

Technical Field

[0001] This invention belongs to the field of magnetic confinement nuclear fusion technology, and particularly relates to a low-temperature high thermal conductivity polymer composite material and its preparation method. Background Technology

[0002] The toroidal field coil box is a key component of a tokamak device, functioning to protect the internal superconducting coils and provide a structural interface for adjacent magnet systems. During tokamak operation, the toroidal field coil box is exposed to various heat sources, including thermal radiation, conduction, eddy current heating, winding AC losses, and nuclear heat, resulting in significant heat deposition on its surface. Without high-performance cooling channels, this heat will be transferred to the coils through the insulation layer, potentially affecting the coils' superconducting performance. The cooling channels for the toroidal field coil box mainly consist of cooling channels, cooling pipes, and thermally conductive materials. Compared to welding and brazing methods, using polymer composite materials to manufacture cooling channels offers advantages such as less coil box deformation, lighter weight, and higher implementation efficiency. In recent years, polymer composite materials have been widely used as thermally conductive materials in the manufacture of cooling channels for superconducting magnet structural components or heat transfer components. Therefore, developing low-temperature, high-thermal-conductivity polymer composite materials is crucial for the stable operation of low-temperature superconducting coils such as toroidal field magnets.

[0003] For related technologies, please refer to Chinese invention patent with announcement number CN117672554A, which discloses a cooling structure and manufacturing method of a tokamak device coil box. This invention sets a cooling pipe and a heat-conducting powder that completely wraps the cooling pipe in a cooling tank, so that the cooling tank and the cooling pipe can conduct heat through the heat-conducting powder to form a flexible heat-conducting network. This avoids the failure of the heat-conducting medium due to centripetal force after the longitudinal field coil is energized, and improves the stability of heat exchange between the cooling pipe and the cooling tank.

[0004] In response to the aforementioned technologies, and in order to improve the heat exchange efficiency between the cooling pipe and the cooling tank, this invention proposes a low-temperature high thermal conductivity polymer composite material and its preparation method, which is compatible with the thermally conductive powder proposed in the above invention. Summary of the Invention

[0005] To improve the thermal conductivity of the cooling channel of the longitudinal field coil box, this invention provides a low-temperature high thermal conductivity polymer composite material and its preparation method.

[0006] The present invention provides a low-temperature high thermal conductivity polymer composite material and its preparation method, which adopts the following technical solution:

[0007] The low-temperature high thermal conductivity polymer composite material of this invention comprises the following raw materials: polymer powder, thermally conductive powder, and adhesive. The volume ratio of the polymer powder to the thermally conductive powder is 1:(0.1-1), and the ratio can be adjusted according to the thermal conductivity requirements of the applicable working conditions. The particle size of the thermally conductive powder is less than 1 / 10 of the particle size of the polymer powder. The small-particle-size thermally conductive powder is distributed around the large-particle-size polymer powder to form a quasi-continuous three-dimensional network. The polymer powder and the thermally conductive powder, as well as the thermally conductive powders themselves, are bonded together by the adhesive. The polymer powder can be polyimide powder, polyetherimide powder, or epoxy resin powder, with a particle size of 10μm-200μm. The thermally conductive powder is copper powder, nickel powder, tin powder, aluminum powder, magnesium powder, or alloy powder containing the above metals, with a particle size of 1μm-20μm. The adhesive is a thermosetting epoxy resin with a room temperature viscosity of less than 2000 cP.

[0008] The present invention discloses a method for preparing a low-temperature high thermal conductivity polymer composite material, comprising the following steps: S1. Mixing thermally conductive powder with polymer powder to obtain a mixed powder; S2. Adding an adhesive to the mixed powder and mixing the mixed powder with the adhesive to obtain a wetted mixed powder; S3. Placing the wetted mixed powder in a mold for extrusion molding and then heating and curing. In step S2, the volume of adhesive added is 0.4-2 times the volume of the mixed powder. In step S3, the pressure applied during extrusion is 1-10 MPa.

[0009] By adopting the above technical solution, polyimide powder, polyetherimide powder, or epoxy resin powder is used as the polymer powder.

[0010] Preferably, polyimide is used as the polymer powder.

[0011] By adopting the above technical solution, copper powder, nickel powder, iron powder, silver powder, lead powder, tin powder, aluminum powder, magnesium powder, and alloy powder containing the above metals are used as heat-conducting powders.

[0012] Preferably, copper powder is used as the thermally conductive powder.

[0013] In summary, the present invention has at least one of the following beneficial technical effects:

[0014] 1. Metal powder with electronic thermal conductivity forms a quasi-continuous phase in the composite material, which significantly improves the low-temperature thermal conductivity of the polymer composite material;

[0015] 2. Compared with discrete composite materials prepared by traditional solid-liquid two-phase mixing methods of thermally conductive fillers and polymer adhesives, the polymer composite material of the present invention can exhibit higher thermal conductivity under the same thermally conductive filler volume fraction.

[0016] 3. The preparation method described in this invention avoids the problem of high-density thermally conductive fillers settling in the polymer matrix during the preparation of traditional polymer composite materials. Attached Figure Description

[0017] Figure 1 This is a microscopic morphology diagram of a low-temperature high thermal conductivity polymer composite material of the present invention.

[0018] Figure 2 This is a schematic diagram of the microstructure of a low-temperature high thermal conductivity polymer composite material according to the present invention.

[0019] Figure 3 This is a schematic diagram of a method for preparing a low-temperature high thermal conductivity polymer composite material according to the present invention.

[0020] Wherein: 1 represents thermally conductive powder, 2 represents polymer powder, 12 represents mixed powder, 3 represents adhesive, 123 represents wetting mixed powder, 4 represents tableting mold, and 5 represents composite material. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only for explaining the present invention, and the scope of protection of the present invention should include all the contents of the claims. Moreover, through the description of the following embodiments, those skilled in the art can fully implement all the contents of the claims of the present invention.

[0022] The present invention will be further described in detail below with reference to the embodiments.

[0023] The materials and tools used in the preparation examples, embodiments, and comparative examples provided in this invention are all commercially available products, and their specifications and manufacturers are as follows:

[0024] In the examples, the polymer powders were: polyetherimide powder (PEI), 150-200 mesh (<104μm), from Jiaxin Polymer Materials (Taobao store); high-purity copper powder, 5μm, from Chengxin Rare Metal Materials Factory (Taobao store); and an adhesive mixture of MY510 epoxy resin and ARADUR 5200 curing agent, with a mass ratio of MY510:ARADUR 5200 = 2.5:1, from Huntsman Corporation. Tools included a press from Tianjin Tianguang Optical Instrument Co., Ltd., and a tableting mold from Rishunxing Mold Factory (Taobao store).

[0025] In the specified proportions, the silver powder is specification S110971, with a particle size of approximately 5 μm, and is manufactured by Shanghai Aladdin Biotechnology Co., Ltd. The adhesive is a mixture of MY510 epoxy resin and ARADUR 5200 curing agent, with a mass ratio of MY510:ARADUR 5200 = 2.5:1, manufactured by Huntsman Corporation.

[0026] Example 1:

[0027] like Figure 2 and Figure 3 As shown, following the preparation steps, 8.9g of copper powder (thermal conductive powder 1) and 1.1g of polyetherimide powder (polymer powder 2) were placed in a mortar and stirred until homogeneous to obtain mixed powder 12. 1.3g of adhesive 3 was added to mixed powder 12, and the mixed powder 12 and adhesive 3 were placed in a mortar and stirred until homogeneous to obtain wetted mixed powder 123. Wetted mixed powder 123 was placed in a tableting mold 4 and extruded under a pressure of 3MPa. The extruded wetted mixed powder was placed in an oven and heated to 85℃ at a heating rate of 5℃ / h, held at that temperature for 10 hours, and then cooled to room temperature to obtain the polymer composite material 5 of Example 1. The microstructure of the obtained composite material 5 is shown in the figure. Figure 1 As shown.

[0028] Example 2:

[0029] 8.9 g of copper powder (thermally conductive powder 1, particle size 5 μm) and 1.1 g of polyetherimide powder (polymer powder 2, particle size 104-150 μm, median particle size approximately 127 μm) were placed in a mortar and stirred until homogeneous to obtain mixed powder 12. 1.3 g of adhesive 3 was added to mixed powder 12, and the mixed powder 12 and adhesive 3 were placed in a mortar and stirred until homogeneous to obtain wetted mixed powder 123. Wetted mixed powder 123 was placed in a tableting mold 4 and extruded under a pressure of 3 MPa. The extruded wetted mixed powder was placed in an oven and heated to 85 °C at a heating rate of 5 °C / h, held at that temperature for 10 hours, and then cooled to room temperature to obtain the polymer composite material 5 of Example 2.

[0030] Example 3:

[0031] 8.9 g of copper powder (thermally conductive powder 1, particle size 5 μm) and 1.1 g of polyetherimide powder (polymer powder 2, particle size 180-250 μm, median particle size approximately 215 μm) were placed in a mortar and stirred until homogeneous to obtain mixed powder 12. 1.3 g of adhesive 3 was added to mixed powder 12, and the mixed powder 12 and adhesive 3 were placed in a mortar and stirred until homogeneous to obtain wetted mixed powder 123. Wetted mixed powder 123 was placed in a tableting mold 4 and extruded under a pressure of 3 MPa. The extruded wetted mixed powder was placed in an oven and heated to 85 °C at a heating rate of 5 °C / h, held at that temperature for 10 hours, and then cooled to room temperature to obtain the polymer composite material 5 of Example 3.

[0032] Comparative Example 1:

[0033] 10.5 g of silver powder (5 μm particle size) and 1.2 g of adhesive were mixed in a mortar and then placed in an oven. The mixture was heated to 85 °C at a heating rate of 5 °C / h, held at that temperature for 10 hours, and then cooled to room temperature to obtain the polymer composite material of Comparative Example 1. This method is a traditional process that only mixes and cures the thermally conductive filler with the adhesive (polymer matrix), without using large-particle-size polymer powder as the dispersed phase.

[0034] Performance testing:

[0035] The thermal conductivity of the composite materials in the examples and comparison examples was tested using the Power Physical Measurement System (PPMS) developed by Quantum Design, Inc., USA. The specific test results are shown in Table 1:

[0036] Table 1. Thermal conductivity of composite materials from different embodiments and comparative examples at 4K.

[0037]

[0038] Test Result Analysis:

[0039] 1. Comparative analysis of Examples 1-3 and Comparative Example 1:

[0040] Table 1 clearly shows the thermal conductivity (100 W·m⁻¹) of the composite materials (50% filler volume fraction) prepared by the method of this invention in Examples 1-3 at 4 K. -1 ·K -1 95 W·m -1 ·K -1 65 W·m -1 ·K -1 The yield was significantly higher than that of the composite material in Comparative Example 1 prepared using traditional methods (0.1 W·m⁻¹). -1 ·K -1 ).

[0041] The main reason for this significant difference is the fundamental difference in microstructure. This invention utilizes thermally conductive powder (copper powder) with a particle size much smaller than that of the polymer powder, combined with specific mixing and molding processes, to effectively "encapsulate" the thermally conductive powder around the polymer powder, forming a "quasi-continuous three-dimensional thermally conductive network" after curing (e.g., ...). Figure 1 , Figure 2 (As shown). This structure greatly facilitates heat transfer within the metal powder network (electronic thermal conductivity is dominant), significantly improving the overall thermal conductivity of the composite material.

[0042] In contrast, Comparative Example 1 employed a traditional solid-liquid mixing method, where silver powder was simply dispersed within an adhesive (epoxy resin) matrix and cured. The silver powder lacked effective, direct, and continuous contact paths, being isolated by a large amount of low thermal conductivity polymer matrix, resulting in a "discrete" thermally conductive structure. At low temperatures, the thermal conductivity of the polymer matrix was extremely low (typically less than 0.1 W·m). -1 ·K -1 This severely hinders heat transfer, resulting in a very low overall thermal conductivity (0.1 W·m). -1 ·K -1 ).

[0043] Analysis of the effect of particle size ratio on thermal conductivity (Example 1 vs Example 2 vs Example 3):

[0044] Table 1 shows that, while keeping the particle size (5 μm) and volume fraction (50%) of the thermally conductive powder (copper powder) constant, the particle size of the polymer powder (i.e., the ratio of the particle size of the thermally conductive powder to that of the polymer powder) has a significant impact on the thermal conductivity of the final composite material.

[0045] When the polymer powder particle size is small (Example 1, approximately 89 μm) and the thermally conductive powder particle size (5 μm) is approximately 1 / 18 of that, the resulting quasi-continuous network is the most dense and effective, exhibiting the highest thermal conductivity (102 W·m). -1 ·K -1 ).

[0046] As the polymer powder particle size increases (Example 2, approximately 127 μm, particle size ratio approximately 1 / 25; Example 3, approximately 215 μm, particle size ratio approximately 1 / 43), although the thermally conductive powder can still be distributed around it, the amount of polymer powder per unit volume decreases, and the interparticle spacing increases. This requires the thermally conductive powder to traverse longer paths when constructing a continuous network, which may affect the connectivity and continuity of the network (e.g., increased path tortuosity), resulting in a decrease in thermal conductivity (95 W·m, respectively). -1 ·K -1 and 65 W·m -1 ·K -1 ).

[0047] The above results verify the importance of the technical feature that the particle size of the thermally conductive powder is less than 1 / 10 of the polymer powder particle size. A smaller particle size ratio (i.e., finer thermally conductive powder and relatively coarser polymer powder) is more conducive to forming an efficient and dense quasi-continuous thermally conductive network, thereby achieving higher low-temperature thermal conductivity. Example 1 (particle size ratio ≈ 1 / 18 < 1 / 10) exhibited the highest thermal conductivity, followed by Example 2 (≈ 1 / 25 < 1 / 10), while Example 3 (≈ 1 / 43 < 1 / 10) had the lowest but was still significantly better than Comparative Example 1. When the particle size ratio is greater than 1 / 10 (e.g., the thermally conductive powder particle size is too large or the polymer powder particle size is too small), it is difficult to effectively form this quasi-continuous network with its encapsulated structure, and the improvement in thermal conductivity will be greatly reduced.

[0048] Summarize:

[0049] This invention successfully constructs a quasi-continuous thermally conductive structure by encapsulating and bonding a thermally conductive powder (small particle size) around a polymer powder (large particle size dispersed phase) into a network, overcoming the bottleneck of low thermal conductivity in traditional polymer-based composites at low temperatures. Performance test data (Table 1) fully demonstrates the superiority of this structure, especially the achievement of 100 W·m at a low temperature (4K). -1 ·K -1 The thermal conductivity is on the order of magnitude high. Furthermore, through comparative examples with different particle size ratios (Examples 1-3), it was verified that a particle size of less than 1 / 10 of the polymer powder particle size is one of the key technical characteristics for forming an efficient quasi-continuous network and obtaining excellent low-temperature thermal conductivity. The preparation method of this invention is simple and reliable, easy to mass-produce, and has broad application prospects in low-temperature heat and mass transfer fields such as superconducting magnets.

[0050] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A low-temperature high thermal conductivity polymer composite material, characterized in that: The raw materials include: polymer powder, thermally conductive powder, and adhesive; The volume ratio of the polymer powder to the thermally conductive powder is 1:(0.1-1); The particle size of the thermally conductive powder is less than 1 / 10 of the particle size of the polymer powder; In the microstructure of the polymer composite material, thermally conductive powder is distributed around the polymer powder to form a quasi-continuous three-dimensional thermally conductive network, and the polymer powder and the thermally conductive powder, as well as the thermally conductive powder and the thermally conductive powder, are bonded together by an adhesive. The composite material has a thermal conductivity of 100 W·m at a low temperature of 4K. -1 ·K -1 ; The polymer powder has a particle size of 10μm-200μm, and the thermally conductive powder has a particle size of 1μm-20μm.

2. The low-temperature high thermal conductivity polymer composite material according to claim 1, characterized in that: The polymer powder is polyetherimide powder, polyimide powder, or epoxy resin powder.

3. The low-temperature high thermal conductivity polymer composite material according to claim 1, characterized in that: The thermally conductive powder is one or more of copper powder, nickel powder, iron powder, silver powder, lead powder, tin powder, aluminum powder, and magnesium powder, or an alloy powder containing the above metals.

4. The low-temperature high thermal conductivity polymer composite material according to claim 1, characterized in that: The adhesive is a thermosetting epoxy resin.

5. The low-temperature high thermal conductivity polymer composite material according to claim 4, characterized in that: The thermosetting epoxy resin adhesive has a room temperature viscosity of less than 2000 cP.

6. A method for preparing a low-temperature high thermal conductivity polymer composite material as described in any one of claims 1-5, characterized in that: Includes the following steps: S1. Mix the thermally conductive powder with the polymer powder to obtain a mixed powder; S2. Add adhesive to the mixed powder and mix the mixed powder with the adhesive to obtain a wetted mixed powder; S3. Place the wetted and mixed powder in a mold, extrude it under a pressure of 1-10 MPa, and then heat it to cure.

7. The method for preparing a low-temperature high thermal conductivity polymer composite material according to claim 6, characterized in that: In step S2, the volume of adhesive added is 0.4-2 times the volume of the mixed powder.

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