Salt template induced hierarchical porous graphite foam material and preparation and application thereof
The preparation of hierarchical porous graphite foam by salt template induction method solves the problem that existing graphite foam materials cannot achieve hierarchical pore structure, improves the adsorption and shaping ability and heat transfer performance of phase change materials, and is suitable for thermal management of high-power electronic devices.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- INST OF COAL CHEM CHINESE ACAD OF SCI
- Filing Date
- 2024-01-16
- Publication Date
- 2026-05-29
AI Technical Summary
Existing graphite foam materials cannot achieve a hierarchical pore structure distribution, thus failing to serve as an enhanced heat transfer carrier. This results in poor adsorption and shaping capabilities of phase change materials, making them prone to leakage and slow response.
A salt template induction method is used to form hierarchical porous graphite foam by ball milling a salt template and reacting it with naphthalene-based mesophase pitch powder. The process includes ball milling, reaction, washing, carbonization and graphitization steps. By controlling the amount of salt template added and the reaction conditions, interconnected structures with millimeter-scale, micrometer-scale and nanometer-scale pore sizes are formed.
A hierarchical porous graphite foam structure was achieved, which enhanced the adsorption and shaping ability of phase change materials and improved heat capacity, heat transfer rate and heat transfer efficiency, making it suitable for thermal management of high-power electronic devices.
Smart Images
Figure CN117902572B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a graphite foam material, specifically to a salt template-induced hierarchical porous graphite foam material and its preparation and application. Background Technology
[0002] In recent years, with the development of aviation and aerospace, and the miniaturization and intelligence of electronic devices, short-duration high-power devices and periodic devices with high power density have been widely used. During short periods of operation, the large amount of heat generated by these devices inevitably leads to a sharp increase in heat density, causing the system's operating temperature to rise and affecting the stability and lifespan of the electronic devices. Therefore, there is an urgent need for effective thermal management of electronic components and equipment to prevent device failure due to overheating.
[0003] Currently, a feasible approach is to develop phase change materials and thermal storage technologies with high volumetric heat storage density, rapid heat absorption, high reliability, and small temperature fluctuations to achieve rapid absorption of high-flux heat. Graphite foam, as a novel carbon material with a three-dimensional network structure, has broad application prospects in advanced manufacturing and weaponry fields such as high-power heat exchangers, high-power laser weapons, and high-temperature electromagnetic shielding due to its lightweight, high thermal conductivity, excellent mechanical properties, and thermal shock resistance. The three-dimensional carbonaceous framework of graphite foam plays a crucial role in enhancing heat transfer and shaping the adsorption of phase change materials. Existing literature 1 (patent publication numbers CN101049928A and CN114956067A) reports a method for preparing graphite foam with uniform pore size by optimizing the physicochemical properties of mesophase pitch using surfactants and oxygen. However, the graphite foam prepared by this foaming process has excessively large internal pore sizes and a single pore size distribution, failing to obtain a hierarchical porous structure containing millimeter, micrometer, and nanopores simultaneously. Therefore, the poor adsorption and shaping ability of phase change materials easily leads to leakage of phase change substances. The closed-cell structure also limits the storage and transportation of phase change materials, resulting in a slow response speed. Reference 2 (patent publication number CN111825078A) reports a method for preparing three-dimensional graphene foam materials with the assistance of a pore-forming agent. The obtained three-dimensional porous structure is mainly composed of micron-sized pores, but it cannot achieve a hierarchical pore structure distribution, resulting in poor overall mechanical properties and thermal conductivity far inferior to graphite foam. Furthermore, the pore-forming agent is a metal powder, which is relatively expensive. Therefore, these existing graphene foam materials cannot serve as enhanced heat transfer carriers and are difficult to widely apply in phase change thermal storage technology. Summary of the Invention
[0004] The purpose of this invention is to provide a salt template-induced hierarchical porous graphite foam material and its preparation and application, which solves the problem that existing materials cannot achieve hierarchical pore structure distribution and cannot be used as enhanced heat transfer carriers.
[0005] To achieve the above objectives, the present invention provides a method for preparing a salt-template-induced hierarchical porous graphite foam material, the method comprising:
[0006] (1) The salt was ball-milled, sieved to obtain salt with a particle size ≤48μm, and dried;
[0007] When the salt template particle size is too large, it forms a large number of millimeter-scale pore structures, destroys the three-dimensional heat conduction network, and causes a large amount of leakage when used as a phase change material carrier, making it impossible to shape the phase change material.
[0008] (2) Under an inert gas atmosphere, naphthalene-based mesophase pitch powder and dried salt were reacted and stirred at 300-320°C and cooled to obtain graphite foam precursor.
[0009] (3) Grind the obtained precursor, heat it to 420-500℃ and react it under an inert gas atmosphere with a pressure of 2.0-3.5 MPa, cool it naturally and release the gas to obtain graphite foam raw material.
[0010] (4) The obtained graphite foam raw material is washed, dried, and then carbonized and graphitized to obtain graphite foam; wherein the carbonization is carried out by heating to 800-1000℃ at a rate of 2-5℃ / min and holding at the temperature; the graphitization is carried out by heating to 2600-2800℃ at a rate of 5-10℃ / min and holding at the temperature.
[0011] Preferably, in step (1), the ball milling is performed in cycles of 40-80 minutes of forward operation followed by a 20-30 minute stop, and then 40-80 minutes of reverse operation, for a total of 10-20 cycles. The salt includes any one or more of chlorides, nitrates, and carbonates. The salt is water-soluble to facilitate template removal and must be stable and non-decomposable during the foaming stage (400-500℃).
[0012] Preferably, in step (2), the mass ratio of the naphthalene-based mesophase pitch powder to the dried salt is 50:(1-9). Excessive addition of the salt template affects the pitch melting and foaming process, hindering foaming and affecting the formation of the ligament structure. It prevents the formation of a continuous heat-conducting network channel, causing the pore structure to collapse and affecting the overall pore structure, thus preventing the filling of the phase change material.
[0013] More preferably, the mass ratio of the naphthalene-based mesophase pitch powder to the dried salt is 50:(1-6).
[0014] Preferably, in step (2), the stirring rate is 100-150 r / min and the time is 6-8 h; the inert gas is nitrogen.
[0015] Preferably, in step (3), the heating rate is 0.5 to 5 °C / min; and the isothermal reaction time is 2 to 3 h.
[0016] Preferably, in step (4), the drying temperature is 120-150°C and the drying time is 5-10 hours.
[0017] Preferably, in step (4), the holding time during carbonization is 60 to 120 minutes; and the holding time during graphitization is 30 to 120 minutes.
[0018] This invention provides a salt template-induced hierarchical porous graphite foam material prepared by the method described above.
[0019] Preferably, the material contains millimeter-sized, micrometer-sized, and nanometer-sized pores, and the millimeter-sized, micrometer-sized, and nanometer-sized pores are interconnected.
[0020] This invention provides an application of the salt template-induced hierarchical porous graphite foam material as described above in a phase change thermal storage carrier.
[0021] This invention discloses a salt-template-induced hierarchical porous graphite foam material, its preparation, and its application. This invention solves the problem that existing materials cannot achieve a hierarchical pore structure distribution and therefore cannot be used as enhanced heat transfer carriers. It has the following advantages:
[0022] 1. The salt template of this invention utilizes a unique pore-forming mechanism. Its angular, planar structure easily overcomes viscous resistance, has high density, and settles quickly, allowing it to easily penetrate the asphalt and achieve efficient pore-forming. The salt template is inexpensive and can be completely removed and recycled after foaming, leaving no residue and not affecting subsequent carbonization and graphitization processes.
[0023] 2. Compared with the prior art, this invention proposes for the first time to introduce the salt template method and the foaming method in the graphite foam precursor to construct a hierarchical porous and interconnected structure, and for the first time successfully constructs a hierarchical porous graphite foam with multiple modes of millimeter pores, micrometer pores and nanometer pores.
[0024] 3. The hierarchical porous graphite foam of this invention possesses excellent mechanical properties, making it suitable as a heat transfer enhancer and ensuring reusability in phase change thermal storage technology. The hierarchical pore structure of the graphite foam also offers the following advantages in phase change thermal storage technology:
[0025] (1) Increase heat capacity: Hierarchical porous graphite foam usually has a large pore volume, which helps the phase change material to be absorbed into the pores, accommodate more phase change material, maintain good adsorption performance of phase change material, increase heat capacity, absorb and release more heat, and improve heat exchange effect.
[0026] (2) Increase surface area: Hierarchical porous graphite foam usually has a high specific surface area, that is, a large effective surface area per unit volume, which can increase the heat exchange contact area with the surrounding environment, thereby improving heat transfer efficiency.
[0027] (3) Improve heat transfer rate: Due to its hierarchical porous structure (a large number of interconnected pores composed of micron-sized pores and millimeter-sized pores), graphite foam can provide more channels and paths to transfer heat, which can accelerate the heat transfer speed, effectively alleviate the thermal expansion problem, and improve the heat transfer rate. Attached Figure Description
[0028] Figure 1 This is the EDS energy spectrum of the graded porous graphite foam material raw material prepared in Example 2 of the present invention.
[0029] Figure 2 This is a SEM image of the graphite foam prepared without salt in Comparative Example 1 of this invention.
[0030] Figure 3 This is a SEM image of the graded porous graphite foam material prepared in Example 2 of the present invention.
[0031] Figure 4 This is a SEM image of the porous graphite foam material prepared in Comparative Example 2 of the present invention.
[0032] Figure 5 This is a SEM image of the porous graphite foam material prepared in Comparative Example 3 of this invention.
[0033] Figure 6 This is a pore size distribution diagram of the graphite foam prepared without salt in Comparative Example 1 of the present invention.
[0034] Figure 7 This is a pore size distribution diagram of the graded porous graphite foam material obtained in Example 2 of the present invention.
[0035] Figure 8 This is a physical image of the graded porous graphite foam material prepared in Example 2 of the present invention. Detailed Implementation
[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0037] Example 1
[0038] A method for preparing a salt template-induced hierarchical porous graphite foam material, the method comprising:
[0039] (1) Sodium chloride salt was loaded into a ball mill jar and ball milled with zirconia ceramic balls of 5 mm, 3 mm and 1 mm particle sizes (the mass ratio of zirconia ceramic balls of 5 mm, 3 mm and 1 mm particle sizes was 3:5:2). The ball milling time was as follows: 40 min forward running, 20 min stop, then 40 min reverse running, and the cycle was repeated 10 times before stopping. The ball-milled salt template was passed through a 300 mesh sieve (pore size ≤48 μm) and dried for storage.
[0040] (2) 50g of pulverized naphthalene-based mesophase pitch and 5g of dried salt were placed into a three-necked flask, high-purity nitrogen was introduced, and the reaction was carried out at 300℃ with stirring. The stirring rate was 100r / min and the reaction time was 6h. After the reaction was completed and cooled, the graphite foam precursor was obtained.
[0041] (3) The obtained precursor was ground and placed in a mold, and then loaded into a reaction vessel. The reaction conditions were: high-purity nitrogen gas was introduced and pressurized to 2.0 MPa, the temperature was raised to 420°C at a heating rate of 0.5°C / min and kept at a constant temperature for 2 hours, then cooled naturally and the gas was released to obtain graphite foam raw material.
[0042] (4) The obtained graphite foam raw material is repeatedly washed with deionized water, and the salt template is completely removed from the foam. It is then dried at 120°C. The dried foam raw material is then carbonized and graphitized to obtain salt template-induced hierarchical porous graphite foam material. The carbonization process is as follows: the temperature is increased to 800°C at a rate of 2°C / min and held for 60 min. The graphitization process is as follows: the temperature is increased to 2800°C at a rate of 5°C / min and held for 60 min.
[0043] Example 2
[0044] The preparation method of a salt template-induced hierarchical porous graphite foam material is basically the same as that in Example 1, except that:
[0045] In step (1), the ball milling time is: 60 minutes of forward operation followed by 30 minutes of shutdown, then 60 minutes of reverse operation, repeated 15 times before shutdown;
[0046] In step (2), 50g of pulverized naphthalene-based mesophase pitch and 4g of salt were placed into a three-necked flask, high-purity nitrogen was introduced, the heating temperature was set to 310℃, and the mixture was stirred at a stirring rate of 120r / min for 7h.
[0047] In step (3), the reaction conditions are as follows: high-purity nitrogen gas is introduced and pressurized to 3.0 MPa, the temperature is increased to 430°C at a heating rate of 1°C / min and the reaction is kept at a constant temperature for 2 hours;
[0048] In step (4), the carbonization process is specifically: heating to 900℃ at a rate of 1.5℃ / min and holding for 60min; the graphitization process is specifically: heating to 2800℃ at a rate of 3℃ / min and holding for 60min.
[0049] Example 3
[0050] The preparation method of a salt template-induced hierarchical porous graphite foam material is basically the same as that in Example 1, except that:
[0051] In step (1), the ball milling time is: 80 minutes of forward running, 30 minutes of stopping, and then 80 minutes of reverse running, and so on for 20 cycles before stopping.
[0052] In step (2), 50g of pulverized naphthalene-based mesophase pitch and 3g of salt were placed into a three-necked flask, high-purity nitrogen was introduced, the heating temperature was set to 320℃, and the mixture was stirred at a stirring rate of 150r / min for 8h.
[0053] In step (3), the reaction conditions are as follows: high-purity nitrogen gas is introduced and pressurized to 3.5 MPa, the temperature is increased to 430°C at a heating rate of 2°C / min and the reaction is kept at a constant temperature for 2 hours;
[0054] In step (4), the drying temperature is adjusted from 120℃ to 150℃; the carbonization process is as follows: the temperature is increased to 1000℃ at a rate of 4℃ / min and held for 60min; the graphitization process is as follows: the temperature is increased to 2800℃ at a rate of 7℃ / min and held for 60min.
[0055] Example 4
[0056] The preparation method of a salt template-induced hierarchical porous graphite foam material is basically the same as that in Example 1, except that:
[0057] In step (1), the ball mill operation procedure is as follows: run in the forward direction for 80 minutes, stop for 30 minutes, then run in the reverse direction for 80 minutes, repeat 20 times, and then stop.
[0058] In step (2), 50g of pulverized naphthalene-based mesophase pitch and 2g of salt were placed into a three-necked flask, high-purity nitrogen was introduced, the heating temperature was set to 320℃, and the mixture was stirred at a stirring rate of 150r / min for 8h.
[0059] In step (3), the reaction conditions are: pressurize to 4 MPa by introducing high-purity nitrogen gas, heat to 450°C at a heating rate of 5°C / min and react at a constant temperature for 3 hours;
[0060] In step (4), the drying temperature is adjusted from 120℃ to 150℃; the carbonization process is specifically: the temperature is increased to 1000℃ at a rate of 4℃ / min and held for 60min; the graphitization process is specifically: the temperature is increased to 2800℃ at a rate of 10℃ / min and held for 60min.
[0061] Comparative Example 1
[0062] The preparation method of a salt template-induced hierarchical porous graphite foam material is basically the same as that in Example 1, except that:
[0063] Step (1) is missing;
[0064] No salt is added in step (2);
[0065] Graphite foam was obtained by performing the same operation as in Example 1.
[0066] Example 5
[0067] The preparation method of a salt template-induced hierarchical porous graphite foam material is basically the same as that in Example 1, except that:
[0068] In step (1), the ball milling time is: 80 minutes of forward running, 30 minutes of stopping, and then 80 minutes of reverse running, repeated 20 times before stopping;
[0069] In step (2), 50g of pulverized naphthalene-based mesophase pitch and 1g of salt were placed into a three-necked flask, high-purity nitrogen was introduced, the heating temperature was set to 320℃, and the mixture was stirred at a stirring rate of 150r / min for 8h.
[0070] In step (3), the reaction conditions are: pressurize to 5 MPa by introducing high-purity nitrogen gas, heat to 450°C at a heating rate of 2°C / min and keep the temperature constant for 3 hours;
[0071] In step (3), the drying temperature is adjusted from 120℃ to 150℃; the carbonization process is as follows: the temperature is increased to 1000℃ at a rate of 2℃ / min and held for 60min; the graphitization process is as follows: the temperature is increased to 2800℃ at a rate of 7℃ / min and held for 60min.
[0072] Example 6
[0073] The preparation method of a salt template-induced hierarchical porous graphite foam material is basically the same as that in Example 1, except that:
[0074] In step (1), the ball mill operation procedure is as follows: run in the forward direction for 40 minutes, stop for 30 minutes, then run in the reverse direction for 40 minutes, repeat 20 times, and then stop.
[0075] In step (2), 50g of crushed petroleum mesophase pitch and 3g of salt were placed into a three-necked flask, high-purity nitrogen was introduced, the heating temperature was set to 310℃, and the mixture was stirred at a stirring rate of 100r / min for 8h.
[0076] In step (3), the reaction conditions are as follows: high-purity nitrogen gas is introduced and pressurized to 2.5 MPa, the temperature is increased to 450°C at a heating rate of 2°C / min and the reaction is kept at a constant temperature for 2 hours;
[0077] In step (4), the drying temperature is adjusted from 120℃ to 150℃, and the carbonization process is specifically as follows: the temperature is increased to 800℃ at 2℃ / min, and no heat preservation is performed.
[0078] Example 7
[0079] The preparation method of a salt template-induced hierarchical porous graphite foam material is basically the same as that in Example 1, except that:
[0080] In step (1), the ball milling time is: 60 minutes of forward operation followed by 30 minutes of shutdown, then 60 minutes of reverse operation, repeated 20 times before shutdown;
[0081] In step (2), 50g of pulverized coal-based mesophase pitch and 3g of salt were placed into a three-necked flask, inert gas was introduced, the heating temperature was set to 320℃, and the mixture was stirred at a stirring rate of 120r / min for 8h.
[0082] In step (3), the reaction conditions are as follows: high-purity nitrogen gas is introduced and pressurized to 4.0 MPa, the temperature is increased to 450°C at a heating rate of 2°C / min and the reaction is kept at a constant temperature for 2 hours.
[0083] In step (4), the drying temperature is adjusted from 120℃ to 150℃; the carbonization process is as follows: the temperature is increased to 900℃ at a rate of 3℃ / min and held for 60min; the graphitization process is as follows: the temperature is increased to 2700℃ at a rate of 5℃ / min and held for 60min.
[0084] Example 8
[0085] The preparation method of a salt template-induced hierarchical porous graphite foam material is basically the same as that in Example 1, except that:
[0086] In step (1), sodium chloride is changed to sodium carbonate, and the ball milling time is: 80 minutes of forward running, 30 minutes of stopping, and then 80 minutes of reverse running, and so on for 15 cycles before stopping.
[0087] In step (2), 50g of pulverized naphthalene-based mesophase pitch and 3g of salt were placed into a three-necked flask, inert gas was introduced, the heating temperature was set to 310℃, and the mixture was stirred at a stirring rate of 120r / min for 8h.
[0088] In step (3), the reaction conditions are: high-purity nitrogen gas is introduced and pressurized to 2.5 MPa, the temperature is increased to 450°C at a rate of 2°C / min and the reaction is kept at a constant temperature for 2 hours;
[0089] In step (4), the drying temperature is adjusted from 120℃ to 150℃; the carbonization process is as follows: the temperature is increased to 800℃ at a rate of 2℃ / min and held for 70min; the graphitization process is as follows: the temperature is increased to 2700℃ at a rate of 8℃ / min and held for 60min.
[0090] Example 9
[0091] The preparation method of a salt template-induced hierarchical porous graphite foam material is basically the same as that in Example 1, except that:
[0092] In step (1), sodium chloride is changed to sodium carbonate, and the ball milling time is: 60 minutes of forward running, 30 minutes of stopping, and then 60 minutes of reverse running, and the cycle is repeated 20 times before stopping.
[0093] In step (2), 50g of pulverized naphthalene-based mesophase pitch and 3g of salt were placed into a three-necked flask, inert gas was introduced, the heating temperature was set to 310℃, and the mixture was stirred at a stirring rate of 130r / min for 8h.
[0094] In step (3), the reaction conditions are: pressurize to 3 MPa by introducing high-purity nitrogen gas, heat to 450°C at a rate of 2°C / min and react at a constant temperature for 2 hours;
[0095] In step (4), the drying temperature is adjusted from 120℃ to 150℃; the carbonization process is as follows: the temperature is increased to 1000℃ at a rate of 4℃ / min and held for 80min; the graphitization process is as follows: the temperature is increased to 2700℃ at a rate of 5℃ / min and held for 60min.
[0096] Comparative Example 2
[0097] The preparation method of a salt template-induced hierarchical porous graphite foam material is basically the same as that in Example 1, except that:
[0098] In step (1), the ball milling time is as follows: run in the forward direction for 30 minutes, stop for 20 minutes, then run in the reverse direction for 30 minutes, repeat 5 times and then stop; the ball-milled salt template is passed through a 120-mesh sieve (pore size is much larger than 48μm).
[0099] Comparative Example 3
[0100] The preparation method of a salt template-induced hierarchical porous graphite foam material is basically the same as that in Example 1, except that:
[0101] In step (1), the mass of salt is adjusted from 5g to 10g.
[0102] Experiment Example 1: Structural Characterization and Performance Verification
[0103] 1. Structure
[0104] The present invention characterizes the materials obtained in Example 2 and Comparative Example 1.
[0105] like Figure 8 The image shown is a physical picture of the graded porous graphite foam material prepared in Example 2 of the present invention.
[0106] like Figure 1 The image shows the EDS energy spectrum of the graded porous graphite foam material raw material prepared in Example 2 of this invention. Figure 1 It can be seen that the salt template is evenly dispersed in the foam raw material.
[0107] like Figure 2 The image shown is a SEM image of the graphite foam prepared in Comparative Example 1 without the addition of salt. Figure 2 It is known that without a salt template, under self-foaming conditions, graphite foam has a low open-cell ratio, a large number of closed-cell structures, poor connectivity between pores, and pore sizes that are basically similar. Closed cells will reduce the storage space of phase change materials, and the poor connectivity between pores will affect the thermal response rate.
[0108] like Figure 3 The image shown is a SEM image of the hierarchical porous graphite foam material prepared in Example 2 of this invention. Figure 3 It is evident that the salt template method for preparing hierarchical porous graphite foam in this invention constructs an interconnected macropore and micropore structure within a three-dimensional network, significantly improving the porosity and connectivity between pores. This also enhances thermal response speed and storage capacity.
[0109] like Figure 4 The image shown is a SEM image of the porous graphite foam material prepared in Comparative Example 2 of this invention. Figure 4 It is known that when the salt template particle size is too large, a large number of millimeter-scale pore structures are formed, the three-dimensional heat conduction network is destroyed, and when it acts as a phase change material carrier, it will cause a lot of leakage and cannot achieve the shaping of the phase change material. This violates the application and original intention of the hierarchical pore design of this invention.
[0110] like Figure 5 The image shown is a SEM image of the porous graphite foam material prepared in Comparative Example 3 of this invention. Figure 5It is known that when the amount of salt template added is excessive, the excessive salt affects the asphalt melting and foaming process, which is not conducive to foaming and affects the formation of ligament structure. It is impossible to form a continuous heat conduction network channel, the pore structure collapses, the overall pore structure is affected, and it is impossible to fill the phase change material. This also violates the application and original intention of the graded pore design of this invention.
[0111] like Figure 6 The diagram shows the pore size distribution of the graphite foam prepared in Comparative Example 1 of this invention without the addition of salt. Figure 6 As can be seen, in this case, the pore size distribution of the graphite foam is a single pore size distribution, mainly concentrated in the large pore range. No obvious pore distribution gradient is observed.
[0112] like Figure 7 The diagram shows the pore size distribution of the hierarchical porous graphite foam material obtained in Example 2 of this invention. Figure 7 It can be seen that the pore size distribution of the hierarchical porous graphite foam induced by the salt template method of the present invention is no longer a single pore size distribution, but a pore size distribution gradient appears, which further verifies the internal hierarchical porous structure.
[0113] The graded porous graphite foam materials prepared in Examples 1, 3-9 all exhibited a gradient in pore size distribution.
[0114] 2. Performance
[0115] The properties of the hierarchical porous graphite foams prepared in Comparative Example 1 and Examples 1-9 were tested, and the specific results are shown in Table 1.
[0116] Table 1. Performance of graded porous graphite foam
[0117]
[0118] As shown in Table 1, from Example 4 to Example 1, with the increase of salt template addition, the template plays a major role in site occupancy, increasing porosity, improving the degree of classification, and decreasing density. Therefore, the thermal conductivity gradually decreases, but the final thermal conductivity remains at a high level, indicating that the introduction of the template did not significantly affect the thermal conductivity. In contrast, Comparative Example 1, without the addition of salt template, has a high thermal conductivity but low porosity and poor open-cell structure. In Example 5, the density increases slightly after adding a small amount of salt template, possibly because the small amount of salt promotes the condensation of naphthalene-based mesophase pitch, resulting in a slightly higher density and thermal conductivity. In Examples 6 and 7, the raw materials are petroleum pitch and coal pitch. Compared to naphthalene-based mesophase pitch, these two types of pitch are more difficult to graphitize, ultimately leading to lower thermal conductivity. In Examples 8 and 9, the salt template is replaced with sodium carbonate, resulting in graphite foams with similar performance and structure to those obtained with sodium chloride template (Example 3). Further explanation demonstrates that salt templates can induce highly thermally conductive hierarchical porous graphite foam: controlling the amount of salt template added can effectively control the degree of hierarchical structure within the graphite foam; the more salt template, the better the hierarchical structure. However, in Comparative Example 3, excessive addition of salt template caused the internal pore structure to collapse, reducing porosity and significantly decreasing thermal conductivity, thus affecting the overall structure. Furthermore, the salt template particle size should not be too large; in Comparative Example 2, the excessively large particle size resulted in numerous millimeter-scale pore structures, disrupting the three-dimensional thermal conductivity network. When acting as a phase change material carrier, this led to significant leakage, making it impossible to solidify the phase change material.
[0119] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.
Claims
1. A method for preparing a salt-template-induced hierarchical porous graphite foam material, characterized in that, The method includes: (1) The salt was ball-milled, sieved to obtain salt with a particle size ≤48μm, and dried; (2) Under an inert gas atmosphere, naphthalene-based mesophase pitch powder and dried salt were reacted at 300~320 °C and stirred, and then cooled to obtain graphite foam precursor; (3) Grind the obtained precursor, heat it to 420-500℃ and react it at a constant temperature under an inert gas atmosphere with a pressure of 2.0-3.5 MPa, cool it naturally and release the gas to obtain graphite foam raw material. (4) The obtained graphite foam raw material is washed, dried, and then carbonized and graphitized to obtain graphite foam; wherein, the carbonization is carried out by heating to 800-1000℃ at a rate of 2-5℃ / min and holding at the temperature; the graphitization is carried out by heating to 2600-2800℃ at a rate of 5-10℃ / min and holding at the temperature. In step (1), the ball mill is run in the forward direction for 40-80 minutes, then stopped for 20-30 minutes, and then run in the reverse direction for 40-80 minutes as a group, and the cycle is repeated 10-20 times; the salt contains any one or more of chloride, nitrate and carbonate. In step (2), the mass ratio of the naphthalene-based mesophase pitch powder to the dried salt is 50: (1~9).
2. The preparation method according to claim 1, characterized in that, In step (2), the stirring rate is 100~150 r / min and the time is 6~8 h; the inert gas is nitrogen.
3. The preparation method according to claim 1, characterized in that, In step (3), the heating rate is 0.5~5℃ / min; the isothermal reaction time is 2~3 h.
4. The preparation method according to claim 1, characterized in that, In step (4), the drying temperature is 120~150 ℃ and the time is 5~10 h.
5. The preparation method according to claim 1, characterized in that, In step (4), the holding time during carbonization is 60-120 min; the holding time during graphitization is 30-120 min.
6. A salt template-induced hierarchical porous graphite foam material prepared by the preparation method as described in claim 1.
7. The salt-template-induced hierarchical porous graphite foam material according to claim 6, characterized in that, The material contains millimeter-scale, micrometer-scale, and nanometer-scale pores, and these pores are interconnected.
8. The application of a salt template-induced hierarchical porous graphite foam material as described in claim 6 or 7 in a phase change thermal storage carrier.