Preparation method of normal-pressure heat-conducting foamed carbon and heat-conducting foamed carbon

Abstract

The application discloses a preparation method of heat-conducting foamed carbon under normal pressure and heat-conducting foamed carbon, and the preparation method comprises the following steps: (1) uniformly mixing porous graphite and heat-conducting reinforcing materials, and performing compression molding; (2) dissolving a pitch component in a solvent; (3) immersing the preformed material obtained in the step (1) into the solution obtained in the step (2), so that the pitch component enters the preformed material, and the solvent is dried to obtain an impregnated material; and (4) treating the impregnated material obtained in the step (3) at 450-900 DEG C for more than 0.5 hours under normal pressure and in a protective atmosphere, so as to obtain foamed carbon material. The application adopts a normal pressure preparation process, and the process is simple and low in cost. In addition, the low-density multi-level pore structure formed by bonding the loose porous graphite and the heat-conducting reinforcing materials through the pitch component has small pore diameters, and can better bind the liquid phase change material.

Description

Technical Field

[0001] This invention relates to a method for preparing thermally conductive foamed carbon under normal pressure and the thermally conductive foamed carbon itself. It can be used as a thermally conductive material, electromagnetic shielding material, and microwave 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, to achieve higher energy storage density / phase change enthalpy in the composite material, there is a desire in the art to fill the carbon foam material with more phase change material. However, studies have found that due to the large pore size (pore diameter between 50-1000 micrometers), filling with more phase change material easily leads to leakage problems. Therefore, there is an incentive to develop a carbon foam material that can effectively confine the phase change material; in addition, increasing the proportion of phase change material can also significantly reduce thermal conductivity. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing thermally conductive foamed carbon under normal pressure. The method successfully prepares thermally conductive foamed carbon under normal pressure, with a simple process route and 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 under normal pressure, the method comprising the following steps:

[0010] (1) Mix porous graphite with thermally conductive reinforcing material evenly, press and shape to obtain preform material;

[0011] (2) Dissolve the asphalt components in a solvent;

[0012] (3) Immerse the preform obtained in step (1) into the solution obtained in step (2) so that the asphalt component enters the preform and dry the solvent to obtain the impregnated material;

[0013] (4) The impregnation material obtained in step (3) is treated at 450-900℃ for more than 30 minutes under normal pressure and in a protective atmosphere to obtain the molding material;

[0014] (5) The molding material obtained in step (4) is subjected to high temperature treatment at a temperature above 1000°C under normal pressure and in a protective atmosphere to obtain foamed carbon material.

[0015] The impregnating material comprises 50%-70% porous graphite, 30%-50% asphalt component, and 0-20% thermally conductive reinforcing material; the asphalt component is mesophase asphalt.

[0016] In step (1) of this invention, porous graphite is mixed uniformly with an optional thermally conductive reinforcing material. In one embodiment, the porous graphite and the optional thermally conductive reinforcing material are dry-mixed to achieve uniform mixing, for example, at room temperature. It should be understood that when the amount of thermally conductive reinforcing material is zero, mixing is not required, and subsequent molding processes are performed directly.

[0017] 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 this invention. In one embodiment, the density of the preform can be 0.3-0.6 g / cm³. 3 For example, 0.35, 0.4, 0.45, 0.5, or 0.55 can help reduce the adverse foaming effects of subsequent steps. In this invention, the molding pressure can be 5-20 MPa, such as 6, 8, 10, 15, or 18 MPa. In this invention, the holding time during molding can be 1-10 minutes, such as 2, 5, or 8 minutes.

[0018] 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, such as 100, 200, 220, 250, 300, 330, 350, or 450; in another embodiment, the porous graphite is preferably one or more of graphene, expanded graphite, and carbon nanotubes, and the bulk density is preferably 200-400, 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.

[0019] 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.

[0020] In step (2) of the present invention, the asphalt component is dissolved in a solvent; the solvent may be one or more of quinoline, heavy oil, tetrahydrofuran, solvent oil and carbon tetrachloride.

[0021] In one embodiment, the mesophase content of the mesophase pitch is not less than 80%, such as 90% or 100%; in another embodiment, the softening point of the mesophase pitch is 200-370°C, such as 210, 230, 250, 280, 300, 330 or 360°C, preferably 220-350°C; in this invention, the mass ratio of the mesophase pitch to the solvent in the solution obtained by dissolution can be 1:8-1:1, such as 1:5 or 1:2.

[0022] In step (3) of the present invention, the preform obtained in step (1) is immersed in the solution obtained in step (2) so that the asphalt component enters the preform and the solvent is dried. Those skilled in the art will understand that this process can be repeated once or multiple times until the content of asphalt component in the dried impregnated material reaches the target requirement.

[0023] In one embodiment, the impregnating material comprises 50-60% porous graphite by mass, such as 52%, 55%, or 58%; 30-45% bitumen component by mass, such as 32%, 35%, 40%, or 43%; and 5-20% thermally conductive reinforcing material by mass, such as 8%, 10%, 15%, or 18%. 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.

[0024] In step (4) of this invention, the impregnated material obtained in step (3) is treated at 450-900°C for at least 30 minutes under normal pressure and a protective atmosphere to facilitate molding and greatly reduce foaming, thereby obtaining a molded material. In one embodiment, the treatment temperature is 500-800°C, such as 500, 520, 550, 600, 700, 750 or 780°C, and the treatment time can be 0.5-6 hours, such as 1, 2, 3 or 5 hours. Excessive time is not conducive to improving efficiency.

[0025] In step (5) of the present invention, the molding material obtained in step (4) is subjected to high-temperature treatment at a temperature above 1000°C under normal pressure and a protective atmosphere to obtain foamed carbon material. 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, so 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, 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.

[0026] In this invention, the protective atmosphere can be a nitrogen atmosphere or an inert gas atmosphere.

[0027] 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 0.01-50 μm (excluding 50 μm) is not less than 20%, preferably 25-50%, such as 30%, 35%, 40%, or 45%; the pore size distribution in the range of 50-250 μm is not less than 30%, preferably 35-55%, such as 40%, 45%, 47%, 50%, or 52%; and the pore size distribution in the range of 250-1000 μm (excluding 250 μm) is not less than 10%, preferably 10-30%, such as 13%, 15%, 20%, 25%, or 28%.

[0028] In one embodiment, the density of the thermally conductive foam carbon of the present invention is 0.20-0.6 g / cm³. 3 For example, 0.25, 0.3, 0.4, 0.45, 0.48, 0.5, 0.55, or 0.58 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.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] (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, porous graphite is pre-formed and then impregnated to disperse asphalt within the porous graphite. This effectively reduces foaming during subsequent heating, and the asphalt material and porous graphite material bond together to form a low-density hierarchical porous structure with a multi-level pore size distribution, particularly abundant at 50 micrometers. Therefore, even when filled with a large amount of phase change material, the liquid phase change material is effectively bound. At the same time, the fine thermally conductive skeleton of the foamed carbon of this invention also enables the entire composite material to have high thermal conductivity, for example, when the density of the foamed carbon is 0.25 g / cm³. 3 At that time, 10 grams of foamed carbon were used to fill 60 grams of phase change material, and the thermal conductivity of the foamed carbon phase change composite material was 35 W / mK;

[0031] (2) The foamed carbon material obtained by the present invention utilizes the effective overlap between porous graphite to achieve a multi-level distribution of pore size, wherein the pore size distribution in the pore size range of 0.01-50μm is not less than 20%, for example 25-50%; the pore size distribution in the pore size range of 50-250μm is not less than 30%, for example 35-55%; and the pore size distribution in the pore size range of 250-1000μm is not less than 10%, for example 10-30%.

[0032] (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 more than 12 W / mK. It can be used for lithium battery thermal management and can keep the battery temperature below 50°C. In addition, the filling amount of phase change material such as paraffin is more than 60% (the ratio of the filling amount of paraffin to the total amount). After testing, the mass loss of the foamed carbon phase change composite material is less than 5% after 5 cycles of "melting-solidification", which can form an effective binding of liquid phase change material.

[0033] (4) The present invention adopts an atmospheric pressure preparation process, which is simple and has low cost. Detailed Implementation

[0034] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the listed embodiments.

[0035] Example 1

[0036] 50 parts of expanded graphite (300 bulk) and 5 parts of high thermal conductivity carbon fiber (thermal conductivity approximately 2000 W / mK, the same below) were mixed evenly and then pressed into a mold with a molding density of 0.4 g / cm³. 3 Asphalt with a softening point of 230℃ and a mesophase content of 60% was dissolved in solvent oil. The preform was then vacuum-impregnated in the solvent oil containing the mesophase asphalt for 30 minutes. After drying, the weight gain was 45 parts. The above material was then subjected to constant temperature at 600℃ for 60 minutes under normal pressure and nitrogen atmosphere. The removed sample was then treated at 3000℃. This yielded a thermally conductive carbon foam material with a density of 0.35 g / cm³. 3 Thermal diffusion system 25mm 2 / s. The pore size distribution is as follows: 0.01-50μm (excluding 50 μm) accounts for 30%, 250-1000μm accounts for 45%, and 250-1000μm (excluding 250 μm) accounts for 25%.

[0037] Example 2

[0038] 30 parts expanded graphite (200 bulk), 20 parts graphene (200 bulk), 10 parts natural graphite, and 10 parts high thermal conductivity carbon fiber were mixed evenly and then pressed into a mold with a molding density of 0.5 g / cm³. 3Asphalt with a softening point of 270℃ and a mesophase content of 80% was dissolved in heavy oil. The preform was then vacuum-impregnated in the solvent oil of the mesophase asphalt for 30 minutes. It was then removed and dried. This process was repeated twice to increase the weight of the preform by 30 parts per cubic centimeter through impregnation. The above material was then subjected to constant temperature at 800℃ for 150 minutes under normal pressure and nitrogen atmosphere. The removed sample was then treated at 3000℃. This yielded a thermally conductive carbon foam material with a density of 0.48 g / cm³. 3 Thermal diffusion coefficient 80mm 2 / s. The pore size distribution is as follows: 0.01-50μm (excluding 50 μm) accounts for 35%, 250-1000μm accounts for 44%, and 250-1000μm (excluding 250 μm) accounts for 21%.

[0039] Example 3

[0040] 20 parts expanded graphite (50% bulk), 35 parts carbon nanotubes (400% bulk), 5 parts boron nitride, and 10 parts high thermal conductivity carbon fiber were mixed evenly and then pressed into a mold with a density of 0.35 g / cm³. 3 Asphalt with a softening point of 330℃ and a mesophase content of 100% was dissolved in heavy oil. The preform was then vacuum-impregnated in the solvent oil of the mesophase asphalt for 30 minutes. It was then removed and dried. This process was repeated 1-2 times to increase the weight of the preform to 30 parts per cubic centimeter. The above material was then subjected to constant temperature at 550℃ for 50 minutes under normal pressure and nitrogen atmosphere. The removed sample was then treated at 3000℃. This yielded a thermally conductive foamed carbon material with a density of 0.3 g / cm³. 3 Thermal diffusivity 80 mm 2 / s. The pore size distribution is as follows: 0.01-50μm (excluding 50 μm) accounts for 45%, 250-1000μm accounts for 42%, and 250-1000μm (excluding 250 μm) accounts for 13%.

[0041] Example 4

[0042] The difference from Example 1 is that the high-temperature treatment of the obtained impregnated material was performed at 1600°C. This resulted in a thermally conductive carbon foam material with a density of 0.38 g / cm³. 3 Thermal diffusion system 15mm 2 / s. The pore size distribution is as follows: 0.01-50μm (excluding 50 μm) accounts for 33%, 250-1000μm accounts for 47%, and 250-1000μm (excluding 250 μm) accounts for 20%.

[0043] Comparative Example 1

[0044] Repeat Example 1, except that the processing temperature was 300 degrees Celsius. The resulting material had extremely poor strength and a thermal diffusivity of less than 15 mm. 2 / s.

[0045] Comparative Example 2

[0046] Example 2 was repeated, except that the porosity of the porous graphite was 50, and the multi-level porous foamed carbon material of the present invention could not be obtained.

[0047] Comparative Example 3

[0048] Repeat Example 2, except that the impregnation material is a mixture of raw materials in a solvent, dried and pulverized to obtain an irregularly shaped, multi-sized aggregated powder, rather than a foamed carbon material with a uniform structure.

[0049] Example 4

[0050] 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 25 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 65 W / mK. Testing showed that after five cycles of melting and solidification, the mass loss of the foamed carbon phase change composite material was less than 3%, indicating that it could form effective binding.

[0051] Example 5

[0052] The foamed carbon obtained in Example 3 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 52 grams) was achieved, resulting in a phase change composite foamed carbon material. The thermal conductivity of the phase change composite foamed carbon material at room temperature was 50 W / mK. Testing showed that after five cycles of melting and solidification, the mass loss of the foamed carbon phase change composite material was less than 4%, indicating that it could form effective binding.

Claims

1. A method for preparing thermally conductive carbon foam using an atmospheric pressure method, the preparation method comprising the following steps: (1) Mix porous graphite with thermally conductive reinforcing material evenly, press and mold to obtain preform material; (2) Dissolve the asphalt components in a solvent; (3) Immerse the preform obtained in step (1) into the solution obtained in step (2) so that the asphalt component enters the preform and dry the solvent to obtain the impregnated material; (4) The impregnated material obtained in step (3) is treated at 450-900℃ for more than 30 minutes under normal pressure and in a protective atmosphere to obtain the molding material; (5) The molding material obtained in step (4) is subjected to high temperature treatment at a temperature above 1000°C under normal pressure and in a protective atmosphere to obtain foamed carbon material. In the impregnation material, porous graphite accounts for 50%-70% by mass, asphalt component accounts for 30-50% by mass, and thermally conductive reinforcing material accounts for 0-20% by mass; the asphalt component is mesophase asphalt; and the porosity of the porous graphite is not less than 100.

2. The production method according to claim 1, characterized by, The porous graphite is one or more of graphene, expanded graphite, high thermal conductivity carbon felt, foamed graphite, and carbon nanotubes.

3. 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 graphene, expanded graphite, and carbon nanotubes.

4. The production method according to any one of claims 1 to 3, characterized by, The mesophase pitch has a mesophase content of 80-100% and a softening point of 230-370℃.

5. The preparation method according to claim 1, characterized in that, The impregnating material contains 50%-60% porous graphite, 30%-45% asphalt components, and 5%-20% thermally conductive reinforcing materials.

6. The preparation method according to claim 4, characterized in that, The impregnating material contains 50%-60% porous graphite, 30%-45% asphalt components, and 5%-20% thermally conductive reinforcing materials.

7. The production method according to any one of claims 1 to 3 and 5 to 6, characterized by, The thermally conductive reinforcing material includes one or more of natural graphite, high thermal conductivity carbon fiber, and boron nitride.

8. The preparation method according to claim 7, characterized in that, The solvent is one or more of quinoline, heavy oil, tetrahydrofuran, solvent oil, and carbon tetrachloride.

9. The production method according to any one of claims 1 to 3, 5 to 6 and 8, characterized by, The density of the preform is 0.3-0.6 g / cm³. 3 .

10. The production method according to any one of claims 1 to 3, 5 to 6 and 8, characterized by, The processing time in step (4) is 0.5-6 hours and the processing temperature is 500-800℃.

11. The preparation method according to claim 9, characterized in that, The processing time in step (4) is 0.5-6 hours and the processing temperature is 500-800℃.

12. The heat conductive carbon foam produced by the production method according to any one of claims 1 to 11, characterized by, The thermally conductive carbon foam has a multi-level pore size distribution, wherein the pore size distribution in the range of 0.01-50μm is not less than 20%; the pore size distribution in the range of 50-250μm is not less than 30%; and the pore size distribution in the range of 250-1000μm is not less than 10%.

13. The thermally conductive foamed carbon of claim 12, wherein, The pore size distribution is 25-50% for pores with a pore size range of 0.01-50 μm; 35-55% for pores with a pore size range of 50-250 μm; and 10-30% for pores with a pore size range of 250-1000 μm.

14. The thermally conductive foamed carbon according to claim 12 or 13, characterized in that, The heat conductive foamed carbon has a density of 0.2-0.6 g / cm 3 .

15. The thermally conductive foamed carbon of claim 14, wherein, 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%.