A method for preparing a heat-conducting foamed carbon and a heat-conducting foamed carbon prepared thereby

Abstract

The application discloses a preparation method of heat-conducting foamed carbon and the heat-conducting foamed carbon. The preparation method comprises the following steps: (1) uniformly mixing and crushing pitch components, porous graphite and optional heat-conducting reinforcing materials, and then performing compression molding; (2) treating the preformed material obtained in the step (1) at 450-700 DEG C for more than 10 minutes under normal pressure to obtain a formed material; and (3) performing high-temperature treatment on the formed material obtained in the step (2) at a temperature of more than 900 DEG C under normal pressure and in a protective atmosphere to obtain a foamed carbon material. The application adopts a normal pressure preparation process, and the process is simple and low in cost. Moreover, the low-density porous structure is realized by effectively connecting the porous graphite, the pore size is multi-level distributed, and the liquid phase and a large amount of phase change materials can be better bound.

Description

Technical Field

[0001] This invention relates to a method for preparing thermally conductive foamed carbon and the thermally conductive foamed carbon itself, which can be used as a thermally conductive material, electromagnetic shielding material, and wave-absorbing material, and can be applied in fields such as chemical engineering, aerospace, and electronics. When used as a thermally conductive framework for phase change materials, it can effectively confine liquid phase change materials. Background Technology

[0002] Thermally conductive carbon foam is a three-dimensional network of lightweight porous material with advantages such as low density, high thermal conductivity, corrosion resistance, and low coefficient of expansion. In particular, its isotropic thermal conductivity makes it highly valuable in many fields, such as new energy, aerospace, energy-saving buildings, and chemical industry.

[0003] Thermally conductive foamed carbon is currently typically prepared from mesophase pitch through a pressurized foaming process, with a typical microstructure being a cellular structure. For example, CN201810643104.2 describes the preparation of a graphene foamed carbon composite material, which has a cellular structure, with most pores larger than 50 micrometers. CN200310105053.1 describes a foamed carbon material prepared by self-reaction foaming using coal-based intermediate-temperature pitch and petroleum-based mesophase pitch as raw materials, which also exhibits a cellular structure.

[0004] Furthermore, existing thermally conductive foamed carbon requires mesophase pitch as a raw material to ensure thermal conductivity, necessitating a pressurized foaming process that is complex and costly. For example, the technical route in CN101164875A involves adding particles with catalytic graphitization properties to mesophase pitch as raw materials. This preparation process does not require the addition of a foaming agent or oxidative stabilization treatment; instead, it directly utilizes the light component gas released during heating of the mesophase pitch to foam, which then solidifies at a specific temperature to produce foamed carbon. However, the entire process is carried out in a high-pressure reactor at 2-4 MPa. This pressurized preparation process is limited by equipment, allowing only intermittent production and resulting in high costs.

[0005] CN104446587A discloses a method for preparing thermally conductive graphite sheets, which includes mixing expanded graphite, carbon fiber and mesophase pitch evenly in a solvent, drying and pulverizing them, then pre-pressing them into shape, pre-oxidizing them at 250-330 degrees Celsius for 1-4 hours, and finally performing high-temperature hot pressing treatment at 5-50 MPa. Therefore, on the one hand, the pressing process is complex and costly, and on the other hand, its purpose is to prepare dense graphite sheets. The material performance indicators and preparation requirements are fundamentally different from those of foamed carbon materials.

[0006] Furthermore, when used as a thermally conductive framework for phase change materials, the art seeks to fill the foamed carbon material with more phase change material to achieve higher energy storage density / phase change enthalpy in the composite material. However, research has found that due to the large pore size (pore diameter between 50-1000 micrometers), filling with more phase change material easily leads to significant leakage problems; in addition, increasing the proportion of phase change material also tends to significantly reduce thermal conductivity. Therefore, there is an incentive to develop a foamed carbon material that can meet the requirements of high filling volume while also possessing good thermal conductivity and effectively binding liquid phase change material. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing thermally conductive foamed carbon. The method successfully produces thermally conductive foamed carbon using an atmospheric pressure preparation process. The process route is simple, resulting in low process cost.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for preparing thermally conductive carbon foam, the method comprising the following steps:

[0010] (1) The asphalt component is crushed and then dry-mixed with porous graphite and optionally thermally conductive reinforcing material to achieve uniform mixing, and then pressed into shape.

[0011] (2) The preform obtained in step (1) is treated at 450-700℃ for more than 10 minutes under normal pressure to obtain the molding material;

[0012] (3) The molding material obtained in step (2) is subjected to high temperature treatment at a temperature above 900°C under normal pressure and in a protective atmosphere to obtain foamed carbon material.

[0013] The asphalt component is mesophase asphalt; in the preform, porous graphite accounts for 30%-60% by mass, mesophase asphalt accounts for 40-70% by mass, and thermally conductive reinforcing material accounts for 0-20% by mass.

[0014] In step (1) of the present invention, the asphalt component is pulverized and then mixed uniformly with porous graphite and optionally a thermally conductive reinforcing material. In one embodiment, the asphalt component is pulverized and then dry-mixed with porous graphite and optionally a thermally conductive reinforcing material to achieve uniform mixing, for example, by dry mixing at room temperature.

[0015] In one embodiment, the mesophase content of the mesophase asphalt is not less than 60%, such as 80% or 100%; in another embodiment, the softening point of the mesophase asphalt is 150-400℃, such as 180, 220, 250, 280, 300, 350 or 380℃, preferably 200-360℃; in this invention, the mesophase asphalt is pulverized before mixing to ensure thorough mixing; in one embodiment, after pulverization, the particle size of the mesophase asphalt is not less than 100 mesh (Taylor standard sieve), preferably not less than 200 mesh, such as 200-1000 mesh, such as 300, 500 or 800 mesh, to facilitate the subsequent formation of multi-level pores.

[0016] In this invention, the porous graphite can be one or more of graphene, expanded graphite, high thermal conductivity carbon felt, foamed graphite, and carbon nanotubes; in one embodiment, the bulk density of the porous graphite is not less than 100, preferably not less than 200, such as 220, 250, 300, 330, or 350; in another embodiment, the porous graphite is preferably one or more of expanded graphite and carbon nanotubes, and the bulk density is preferably 200-350, which is beneficial for the mixing and dispersion of mesophase pitch and for generating hierarchical pores that are more conducive to filling phase change materials.

[0017] In this invention, when the porous graphite in step (1) is a combination of multiple components, its bulkiness refers to the average bulkiness of the porous graphite composition, which is equal to the sum of the products of the weight parts of each component and the bulkiness divided by the sum of the weight parts of each component. For example, when the porous graphite is composed of expanded graphite and carbon nanotubes, its bulkiness is equal to (Z1*P1+Z2P2) / (Z1+Z2); where Z1 is the weight part of expanded graphite, Z2 is the weight part of carbon nanotubes, P1 is the bulkiness of expanded graphite, and P2 is the bulkiness of carbon nanotubes.

[0018] In step (1) of this invention, the mixed raw materials are pressed and molded to obtain a preform, which serves as the basis for subsequent processing. In one embodiment, the molding pressure is preferably 3-20 MPa, such as 5, 8, 10, 15, or 18 MPa, which helps to reduce the adverse foaming effects in subsequent steps. In this invention, after molding, the density of the preform can be 0.035-0.5 g / cm³. 3 For example, 0.04, 0.05, 0.1, 0.2, 0.4 or 0.45; during molding, the holding time can be 1-10 minutes, such as 2, 5 or 8 minutes.

[0019] In one embodiment, the preform contains 40%-60% porous graphite by mass, such as 42%, 45%, 50%, 55%, or 58%, 30%-45% asphalt material by mass, such as 32%, 35%, 40%, or 43%, and 0-10% thermally conductive reinforcing material by mass, such as 2%, 5%, or 8%. The thermally conductive reinforcing material, used to enhance the thermal conductivity of the thermally conductive carbon foam, is well-known in the art and can be one or more of natural graphite, high thermal conductivity carbon fiber, and boron nitride, wherein high thermal conductivity carbon fiber refers to carbon fiber with a thermal conductivity ≥2000 W / mK. It should be understood that in this invention, when the mass percentage of a component is 0, it means that the component is not present. For example, in this invention, when the high-temperature treatment in subsequent step (3) is sufficiently high, such as above 3000°C, allowing the carbon foam to be fully graphitized, since graphite itself has good thermal conductivity, the addition of the thermally conductive reinforcing material can be considered unnecessary.

[0020] In step (2) of this invention, the preform obtained in step (1) is treated at 450-700°C for at least 10 minutes under normal pressure to allow the preform to solidify and significantly reduce foaming, thereby obtaining the molded material. In one embodiment, the treatment temperature is 450-650°C, such as 470, 500, 550, 600, or 620°C, and the treatment time can be 10-60 minutes, such as 20, 30, or 50 minutes. Excessive time is detrimental to efficiency. In this invention, during the heat treatment in step (2), the treatment atmosphere can be an air atmosphere or a protective atmosphere. For cost considerations, an air atmosphere can be chosen. In this invention, unless otherwise specified, the aforementioned treatment atmosphere is an air atmosphere.

[0021] In step (3) of the present invention, the molding material obtained in step (2) is subjected to high-temperature treatment at a temperature above 900°C under normal pressure and a protective atmosphere to obtain foamed carbon material; the protective atmosphere can be a nitrogen atmosphere or an inert gas atmosphere. In one embodiment, the high-temperature treatment temperature is 1000-3200°C, such as 1200, 1500, 2000, 2500 or 3000°C. Different treatment temperatures can yield foamed carbon materials with different thermal diffusivity. Therefore, the corresponding treatment temperature can be selected according to the target thermal diffusivity. For example, to obtain a better thermal diffusivity, the high-temperature treatment temperature can be increased, such as to 2800°C or even 3000°C or 3200°C, so as to facilitate full graphitization; or, the foamed carbon material obtained by the present invention through high-temperature treatment (such as below 2000°C, 2500°C or even below 2800°C) is further treated at a temperature above 2800°C, such as 3000°C or 3200°C, to improve the thermal diffusivity, so as to facilitate full graphitization.

[0022] The present invention also provides a thermally conductive foam carbon preparation; the thermally conductive foam carbon has a multi-level pore size distribution, wherein the pore size distribution in the range of 0.01-5 μm (excluding 5 μm) is not less than 20%, preferably 22-60%, such as 25%, 30%, 40%, 45%, 50%, 55% or 58%; the pore size distribution in the range of 5-150 μm is not less than 10%, preferably 12-45%, such as 15%, 20%, 25%, 30%, 35%, 40% or 42%; and the pore size distribution in the range of 150-1000 μm (excluding 150 μm) is not less than 8%, preferably 10-60%, such as 12%, 15%, 20%, 30%, 40%, 45%, 50%, 55% or 58%.

[0023] In one embodiment, the density of the thermally conductive foam carbon of the present invention is 0.03-0.4 g / cm³. 3 For example, 0.05, 0.1, 0.2, or 0.3 g / cm³. 3 In one embodiment, the thermally conductive foam carbon is composed of graphite and amorphous carbon components, wherein the graphite content can be 40%-100%, such as 60%, 80%, 90%, or 95%, and the amorphous carbon content can be 0-60%. In another embodiment, the graphite content of the thermally conductive foam carbon is 90% or even 95% or higher, so as to have a relatively higher thermal diffusivity at its low density level.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] (1) Unlike existing technologies, the novel foamed carbon proposed in this invention has a non-porous structure, which differs from the traditional foaming structure. In this invention, powdered asphalt is dispersed and mixed in loose porous graphite and molded under certain pressure. Subsequent heating effectively reduces foaming, and the asphalt material and porous graphite material bond together to form a low-density porous structure with a multi-level pore size distribution, particularly abundant at 50 micrometers (e.g., 5 micrometers). Therefore, even when filled with a large amount of phase change material, the liquid phase change material can be effectively bound. After five cycles of "melting-solidification" in the phase change composite material, the mass loss is less than 10%. Simultaneously, the fine thermally conductive skeleton of the foamed carbon in this invention also gives the entire composite material a high thermal conductivity, for example, when the density of the foamed carbon is 0.045 g / cm³. 3 At that time, 10 grams of foamed carbon filled with 115 grams of paraffin phase change material had a thermal conductivity of 6.5 W / mK;

[0026] (2) The density of the foamed carbon material obtained by this invention is 0.03-0.4 g / cm³. 3 Thermal diffusivity greater than 20 mm 2 / s, utilizing the effective overlap between porous graphite to achieve a multi-level pore size distribution, wherein the pore size distribution in the range of 0.01-5μm is not less than 20%, for example 22-60%; the pore size distribution in the range of 5-150μm is not less than 10%, for example 12-45%; and the pore size distribution in the range of 150-1000μm is not less than 8%, for example 10-60%.

[0027] (3) The phase change composite material prepared by combining the foamed carbon of the present invention with the phase change material has a thermal conductivity of 5-30 W / mK and can be used for lithium battery thermal management to maintain the battery temperature below 50°C; in addition, the filling amount of phase change material such as paraffin can reach more than 85% (the ratio of the filling amount of paraffin to the total amount).

[0028] (4) The present invention adopts an atmospheric pressure preparation process, which is simple and has low cost. Detailed Implementation

[0029] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the listed embodiments.

[0030] Example 1

[0031] Asphalt with a softening point of 360℃ and a mesophase content of 100% was pulverized and passed through a 200-mesh sieve. 50 parts of asphalt, 40 parts of expanded graphite (bulkness 200, carbon content 99.9%), and 10 parts of high thermal conductivity carbon fiber (thermal conductivity approximately 2000 W / mK) were mixed. The mixture was pressed into shape in a mold at a pressure of 7 MPa for 3 minutes. It was then fired at 600℃ for 30 minutes to obtain the molded material. The molded material was then subjected to high-temperature treatment at 1600℃ in a protective atmosphere to obtain foamed carbon material.

[0032] Tests showed that the density of the foamed carbon material was 0.1 g / cm³. 3 Thermal diffusivity 45mm 2 / s, graphite content 55%, amorphous carbon content 45%. Pore size distribution: 0.01-5μm 35%, 5-150μm 40%, 150-1000μm 25%.

[0033] Example 2

[0034] Asphalt with a softening point of 300℃ and a mesophase content of 80% was pulverized and passed through a 500-mesh sieve. 55 parts asphalt, 40 parts carbon nanotubes (300% bulk), and 5 parts natural graphite were mixed. The mixture was pressed into shape in a mold at a pressure of 15 MPa for 3 minutes. It was then fired at 500℃ for 20 minutes to obtain the molded material. Finally, it was treated at 3000℃ in a protective atmosphere to obtain foamed carbon material.

[0035] Tests showed that the density of the foamed carbon material was 0.2 g / cm³. 3 Thermal diffusivity 200 mm 2 / s, graphite content 99.5%, amorphous carbon content 0.5%. Pore size distribution: 0.01-5μm 55%, 5-150μm 35%, 150-1000μm 10%.

[0036] Example 3

[0037] Asphalt with a softening point of 250℃ and a mesophase content of 60% was pulverized and passed through a 300-mesh sieve. 60 parts of asphalt and 40 parts of expanded graphite (bulk density 250) were mixed. The mixture was then pressed into shape in a mold at a pressure of 3 MPa for 1 minute. It was then fired at 450℃ for 25 minutes to obtain the molded material. Finally, it was treated at 1000℃ in a protective atmosphere to obtain foamed carbon material.

[0038] Tests showed that the density of the foamed carbon material was 0.05 g / cm³. 3 Thermal diffusion system 20mm 2 / s, graphite content 40%, amorphous carbon content 60%. Pore size distribution: 0.01-5μm 25%, 5-20μm 15%, 20-250μm 15%, 250-1000μm 45%.

[0039] Comparative Example 1

[0040] Repeat Example 1, except that the processing temperature is 400 degrees Celsius, and the resulting material is loose powder, and foamed carbon material cannot be obtained.

[0041] Comparative Example 2

[0042] Example 2 was repeated, except that the formula was changed to 10 parts asphalt, 10 parts carbon nanotubes (300 bulk), and 80 parts natural graphite, resulting in a dense powder, but not a multi-level porous foamed carbon material.

[0043] Comparative Example 3

[0044] Example 3 was repeated, except that the porous graphite component had a bulk density of less than 50, making it impossible to obtain a density of less than 0.5 g / cm³. 3 The molding material cannot produce multi-level porous carbon foam material.

[0045] Example 4

[0046] The foamed carbon obtained in Example 2 was composited with a phase change material (the phase change material was phase change paraffin, with a phase change temperature of 38°C). The composite process was as follows: the phase change material was heated to a liquid state, and 10 grams of thermally conductive foamed carbon was immersed in the liquid phase change material under vacuum conditions until adsorption saturation (adsorption amount 65 grams) was achieved, resulting in a foamed carbon phase change composite material. The thermal conductivity of the foamed carbon phase change composite material at room temperature was 30 W / mK. Testing showed that after five cycles of melting and solidification, the mass loss of the phase change composite material was less than 5%, indicating that it could form effective binding.

[0047] Example 5

[0048] The foamed carbon prepared in Example 3 was subjected to graphitization treatment at 3000℃ to obtain a foamed carbon material with a density of 0.045 g / cm³. 3 Thermal diffusion system 45mm 2 / s. Then, it is composited with a phase change material (the phase change material is phase change paraffin, phase change temperature 38℃). The composite process is as follows: the phase change material is heated to a liquid state, and 10 grams of thermally conductive carbon foam is immersed in the liquid phase change material under vacuum conditions until adsorption saturation (adsorption amount 115 grams), resulting in a phase change composite carbon foam material. The thermal conductivity of the phase change composite carbon foam material at room temperature is 6.5 W / mK. Testing showed that after 5 cycles of "melting-solidification," the mass loss of the phase change composite material was less than 10%, indicating that it can form effective binding.

Claims

1. A method for preparing thermally conductive carbon foam, the method comprising the following steps: (1) The asphalt component is crushed and then dry-mixed with porous graphite and thermally conductive reinforcing material to achieve uniform mixing, and then pressed into shape; wherein, the porous graphite accounts for 30%-60% by mass, the asphalt component is mesophase asphalt, the mesophase asphalt accounts for 40-70% by mass, and the thermally conductive reinforcing material accounts for 0-20% by mass; (2) The preform obtained in step (1) is treated at 450-700℃ for more than 10 minutes under normal pressure to obtain the molding material; (3) The molding material obtained in step (2) is subjected to high temperature treatment at a temperature above 900°C under normal pressure and in a protective atmosphere to obtain foamed carbon material; The porous graphite has a bulk density of not less than 100; the porous graphite is one or more of graphene, expanded graphite, high thermal conductivity carbon felt, foamed graphite, and carbon nanotubes. The mesophase asphalt contains no less than 60% mesophase, has a softening point of 150-400℃, and a particle size of no less than 100 mesh.

2. The preparation method according to claim 1, characterized in that, The porous graphite has a bulk density of not less than 200; the porous graphite is one or more of expanded graphite and carbon nanotubes.

3. The preparation method according to claim 1 or 2, characterized in that, The softening point of the mesophase pitch is 200-360℃, and the particle size is 200-1000 mesh.

4. The preparation method according to claim 1, characterized in that, In step (1), the molding pressure is 3-20 MPa and the molding time is 1-10 min.

5. The preparation method according to claim 3, characterized in that, In step (1), the molding pressure is 3-20 MPa, and the molding time is 1-10 min; the density of the preform is 0.035-0.5 g / cm³. 3 .

6. The preparation method according to any one of claims 1-2 and 4-5, characterized in that, The preform contains 40%-60% porous graphite, 30%-45% asphalt components, and 0-10% thermally conductive reinforcing materials.

7. The preparation method according to any one of claims 1-2 and 4-5, characterized in that, The thermally conductive enhancement material includes one or more of natural graphite, high thermal conductivity carbon fiber, and boron nitride.

8. The preparation method according to claim 6, characterized in that, The thermally conductive enhancement material includes one or more of natural graphite, high thermal conductivity carbon fiber, and boron nitride.

9. The preparation method according to any one of claims 1-2, 4-5 and 8, characterized in that, The processing time in step (2) is 10-60 min, and the processing temperature is 450-650℃.

10. The preparation method according to any one of claims 1-2, 4-5 and 8, characterized in that, In step (3), the protective atmosphere is a nitrogen atmosphere or an inert gas atmosphere; the high-temperature treatment temperature is 1000-3200℃.

11. The preparation method according to claim 9, characterized in that, In step (3), the protective atmosphere is a nitrogen atmosphere or an inert gas atmosphere; the high-temperature treatment temperature is 1000-3200℃.

12. A thermally conductive foamed carbon prepared by the method according to claim 1, characterized in that, The thermally conductive carbon foam has a multi-level pore size distribution, wherein the pore size distribution in the range of 0.01-5μm is not less than 20%; the pore size distribution in the range of 5-150μm is not less than 10%; and the pore size distribution in the range of 150-1000μm is not less than 8%.

13. The thermally conductive foamed carbon according to claim 12, characterized in that, The pore size distribution is 22-60% for pore sizes ranging from 0.01 to 5 μm; 12-45% for pore sizes ranging from 5 to 150 μm; and 10-60% for pore sizes ranging from 150 to 1000 μm.

14. The thermally conductive foamed carbon according to claim 12 or 13, characterized in that, The density of the thermally conductive carbon foam is 0.03-0.4 g / cm³. 3 .

15. The thermally conductive foamed carbon according to claim 14, characterized in that, The thermally conductive foam carbon is composed of graphite and amorphous carbon, wherein the graphite content is 40%-100% and the amorphous carbon content is 0-60%.