Drying method of graphene powder

Abstract

The invention relates to the technical field of graphene drying, in particular to a graphene powder drying method which comprises the steps that firstly, graphene powder to be dried is put into a reaction container, then the reaction container is placed in a furnace tube, a heating source is started until the temperature of the furnace tube rises to the preset temperature, and then the graphene powder is dried; then the reaction container is placed in a heating area of a heating source to heat the graphene powder to be dried, the graphene powder to be dried is moved into the heating area from the outside of the heating area, water vapor in the graphene powder to be dried is rapidly vaporized, meanwhile, graphene sheet layers adsorbed together due to Van der Waals' force are rapidly expanded, and the graphene powder to be dried is obtained. And the breakage of the specific surface area of the to-be-dried graphene powder in the drying process is weakened.

Description

Technical Field

[0001] The present application relates to the technical field of graphene drying, and in particular to a method for drying graphene powder. Background Art

[0002] CVD graphene is a new method for large-scale production of graphene powder, following redox and mechanical exfoliation. This method uses molten metal as a catalyst, introducing a carbon source gas into the molten metal. The growing graphene then floats on the liquid surface and is blown out with the airflow. As long as the carbon source gas is continuously introduced, the graphene powder can continue to grow. However, as the graphene powder is blown out, some metal powder adheres to the graphene surface and is blown out to a collection device. Therefore, it is necessary to purify the metal impurities on the graphene surface. However, due to the high energy consumption and cost of high-temperature purification, the common purification method in the industry is still to use chemical methods to corrode the metal impurities. The graphene filter cake is then washed and filtered to obtain a dry graphene powder.

[0003] However, after water washing and filtration, the graphene microsheets in the filter cake undergo interfacial adsorption under the action of van der Waals forces. Oven drying of the graphene filter cake will result in obvious stacking and attachment of the dried graphene microsheets, thereby reducing the specific surface area of the graphene powder and affecting its electrical conductivity, thermal conductivity and mechanical properties in the composite material.

[0004] In order to solve the above problems, the present application provides a method for drying graphene powder. Summary of the Invention

[0005] In response to the above-mentioned problems of the prior art, the present application provides a method for drying graphene powder, which significantly reduces the adsorption and adhesion of graphene microplatelets during the drying process, thereby reducing the loss of specific surface area of the graphene powder to be dried during the drying process, and can also significantly improve the drying process efficiency and shorten the drying cycle. The method mainly uses a heating device, which includes a furnace tube, a reaction vessel and a heat source, and the method includes:

[0006] S1: loading the graphene powder to be dried into the reaction container, and placing the reaction container in the furnace tube;

[0007] S2: starting the heating source until the furnace temperature rises to a preset temperature, and the reaction container is located outside the heating area of the heating source;

[0008] S3: placing the reaction container in the heating area of the heating source to heat the graphene powder to be dried, and cooling it after a certain period of time to obtain dried graphene powder.

[0009] In a possible embodiment, placing the reaction container within the heating area of the heating source to heat the graphene powder to be dried includes: moving the reaction container into the heating area of the heating source to heat the graphene powder to be dried; or moving the heating source so that the heating area of the heating source is moved to the tube wall where the reaction container is located to heat the graphene powder to be dried.

[0010] In a possible implementation manner, the method satisfies at least one of the following characteristics:

[0011] When the furnace temperature is increased in step S2, the distance between the tube wall where the reaction container is located and the heating area of the heating source is ≥50 cm;

[0012] The time for the reaction container to move relatively into the heating area of the heating source is 2 to 3 seconds.

[0013] In a possible implementation manner, the heating process of the graphene powder to be dried is carried out in a negative pressure environment.

[0014] In a possible implementation manner, when the reaction container is placed in the heating area of the heating source, the interior of the furnace tube is evacuated to place the heating area of the heating source in a negative pressure environment.

[0015] In a possible implementation manner, the vacuuming of the interior of the furnace tube is performed by reducing the pressure in steps. During the step-by-step pressure reduction process, the decompression rate of the vacuuming treatment in each step is gradually reduced.

[0016] In a possible implementation manner, the step-by-step pressure reduction includes a first pressure reduction process, a second pressure reduction process, and a third pressure reduction process;

[0017] The pressure range in the furnace tube during the first pressure reduction process is 100KPa to 10KPa, and the required first pressure reduction time is 25 to 40s;

[0018] The pressure in the furnace tube during the second pressure reduction process ranges from 10 kPa to 3 kPa, and the required second pressure reduction time is 2.5 to 3.5 minutes;

[0019] The pressure range of the furnace tube in the third pressure reduction treatment is 3KPa to 150Pa, and the required third pressure reduction time is 7 to 10 minutes.

[0020] In a possible implementation manner, the cooling method in step S3 is quenching.

[0021] In a possible embodiment, the cooling in step S3 includes: in response to the heating time of the graphene powder to be dried reaching a preset time, placing the reaction container outside the heating area of the heating source, and obtaining the dried graphene powder after cooling.

[0022] In a possible embodiment, placing the reaction container outside the heating area of the heating source includes: moving the reaction container outside the heating area of the heating source to cool the graphene powder; or moving the heating source so that the heating area of the heating source is moved away from the tube wall where the reaction container is located to cool the graphene powder.

[0023] In a possible implementation manner, the method satisfies at least one of the following characteristics:

[0024] The cooling time required for the cooling treatment in step S3 is 18 to 30 minutes;

[0025] In the case of the cooling treatment in step S3, the distance between the tube wall where the reaction container is located and the heating area of the heating source is ≥50 cm;

[0026] The time it takes for the reaction container to move relatively to outside the heating area of the heating source is 2 to 4 seconds.

[0027] In a possible embodiment, after the heating time of the graphene powder to be dried reaches a preset time and before cooling, the method further includes: introducing an inert gas into the heating area of the heating source to place the interior of the furnace tube under normal pressure.

[0028] In a possible embodiment, the reaction container includes a shell and a lid provided on the shell, wherein the lid is provided with a plurality of cover holes, and the cover holes can allow water vapor to be discharged and can limit the discharge of the graphene powder.

[0029] In a possible embodiment, the reaction container satisfies at least one of the following characteristics:

[0030] The diameter of the cover hole is 0.1-0.2 mm, and the hole density on the cover is 15-25 per cm 2 ;

[0031] There is a gap between the housing and the cover, and the gap ranges from 0 to 0.2 mm;

[0032] The thickness of the shell and the cover are both in the range of 5 to 10 mm.

[0033] In a possible implementation manner, the method satisfies at least one of the following characteristics:

[0034] The volume of the graphene powder to be dried in the reaction container does not exceed 80% of the volume of the reaction container;

[0035] The bulk density of the dried graphene powder is ≤0.012 g / cm 3 ;

[0036] The specific surface area of the dried graphene powder is ≥240m 2 / g.

[0037] In a possible implementation manner, the method satisfies at least one of the following characteristics:

[0038] The preset temperature of the furnace in step S2 is 450-650°C;

[0039] The heating time of the graphene powder to be dried is 1.5 to 2.5 hours;

[0040] During the heating process of the furnace temperature in step S2, the process further includes: introducing an inert gas into the interior of the furnace tube so that the heating area of the heating source is in an inert atmosphere.

[0041] Based on the above technical solution, this application has the following beneficial effects:

[0042] The graphene powder drying method of the present application adopts a heating device, which includes a furnace tube, a reaction container and a heating source. The method includes the following steps: first, the graphene powder to be dried is loaded into the reaction container, and then the reaction container is placed in the furnace tube, the reaction container is located outside the heating area of the heating source, the heating source is started until the temperature of the furnace rises to a preset temperature, and then the reaction container is placed in the heating area of the heating source to heat the graphene powder to be dried, and the graphene powder to be dried is moved from outside the heating area to the heating area, that is, the reaction container containing the graphene powder to be dried is quickly moved from a region close to room temperature to a region close to room temperature. It is placed in the heating area, so that under the driving force of rapid temperature rise, the water vapor in the graphene powder to be dried is vaporized in a short time, and instantaneous high pressure is locally generated between the graphene microsheets, accompanied by violent expansion of the gas, which quickly separates the graphene microsheets in an adsorbed and superimposed state, reducing the loss of specific surface area of the graphene powder to be dried during the drying process, and improving the electrical conductivity, thermal conductivity and mechanical properties of the graphene powder in the composite material. In addition, compared with the traditional oven drying method, the graphene drying method of the present application can significantly improve the drying process efficiency, shorten the drying cycle, reduce costs, and is conducive to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] To more clearly illustrate the technical solution of this application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are merely some embodiments of this application, and those skilled in the art can derive other drawings based on these drawings without inventive effort.

[0044] Figure 1 Schematic diagram of the structure of the graphene powder to be dried before it moves to the heating area in Example 1.

[0045] Figure 2 This is a schematic diagram of the structure in which the graphene powder to be dried is located in the heating area in Example 1.

[0046] Figure 3 This is a schematic structural diagram of the cooling treatment of the graphene powder to be dried in Example 1.

[0047] Figure 4 This is the SEM image of the graphene powder after drying in Example 1.

[0048] Figure 5 SEM image of the dried graphene powder in Comparative Example 1.

[0049] In the figure: 1-furnace tube, 11-first low-temperature zone, 12-second low-temperature zone, 2-reaction vessel, 3-heating area, 4-thermal insulation, 5-push rod, 6-safety valve. DETAILED DESCRIPTION

[0050] The following will be combined with the accompanying drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0051] For the following defined terms, these definitions shall apply unless a different definition is given in the claims or elsewhere in this specification. All numerical values, whether or not explicitly indicated, are defined herein as being modified by the term "about". The term "about" generally refers to a numerical range that one of ordinary skill in the art would consider equivalent to the stated value to produce substantially the same properties, functions, results, etc. A numerical range indicated by a lower value and an upper value is defined to include all numerical values included in the numerical range and all subranges included in the numerical range.

[0052] It should be noted that the terms "first," "second," and the like in the specification and claims of this application and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a particular order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "including," "having," and any variations thereof are intended to cover non-exclusive inclusions.

[0053] The following describes a method for drying graphene powder provided in an embodiment of the present application, using a heating device comprising a furnace tube 1, a reaction vessel 2, and a heating source. The method comprises:

[0054] S1: The graphene powder to be dried is loaded into a reaction vessel 2, and the reaction vessel 2 is placed in a furnace tube 1; in some embodiments, the method for preparing the graphene powder to be dried includes: etching the graphene prepared by the CVD method with a chemical reagent to remove impurities, washing and filtering the graphene filter cake with water, and crushing the graphene filter cake to obtain the graphene powder to be dried.

[0055] In some embodiments, the container 2 includes a shell and a lid provided on the shell, wherein the lid is provided with a plurality of cover holes, which can allow water vapor to be discharged and can limit the discharge of graphene powder.

[0056] The stacked graphene microsheets in the reaction vessel 2 are randomly interlaced and overlapped, making it more difficult for them to escape from the small-sized micropores than discrete single microsheets. Therefore, the diameter of the cover holes can be appropriately larger than the diameter of the graphene microsheets. This not only reduces the resistance to water vapor discharge during the drying process, but also prevents the graphene powder from escaping from the cover holes during the drying process. In some embodiments, the diameter of the cover holes is 0.1-0.2 mm, and the hole density on the cover is 15-25 / cm 2 The upper limit of the diameter of the cover hole can be, but not limited to, 0.2 mm, 0.19 mm, 0.18 mm, etc., and the lower limit of the diameter of the cover hole can be, but not limited to, 0.1 mm, 0.11 mm, 0.12 mm, etc. It can be understood that the diameter of the cover hole can also be any point value within the above range, which is not enumerated here. The upper limit of the hole density on the cover can be, but not limited to, 25 holes / cm 2 , 24 pieces / cm 2 , 23 pieces / cm 2 The lower limit of the hole density on the cover can be, but is not limited to, 15 holes / cm 2 , 16 pieces / cm 2 , 17 pieces / cm 2 etc.; It is understandable that the hole density on the cover can also be any point value within the above range, which is not enumerated here.

[0057] However, when the aperture of the lid is large, although it can maintain a good discharge of water vapor, which is beneficial to the drying of the graphene powder, and can avoid the problem that the lid is blown open due to excessive pressure inside the reaction vessel 2, causing the graphene powder to be scattered in the furnace tube, making it difficult to collect, the high-speed steam airflow generated under the combined action of huge pressure drop and instantaneous high temperature will discharge a large amount of graphene powder from the hole, and when the aperture of the lid is small, the water vapor inside the container 2 is difficult to discharge in time, resulting in excessive pressure inside the container 2, the lid is blown open, which may cause safety risks, and there will also be problems such as graphene powder being blown out and scattered in the furnace tube, making it difficult to collect; further limit the hole density on the lid to avoid the mechanical strength of the lid being low due to large hole density, especially when the container to be filled is When the container of dried graphene is quickly moved from near room temperature to a high-temperature zone, the temperature changes dramatically, which may cause the lid to break. At the same time, it also avoids the low pore density, which slows the discharge rate of water vapor during the drying process, thereby reducing the drying rate. In addition, the low pore density will also affect the pressure drop rate inside the reaction container during the vacuum pumping process, causing the vaporization rate of water in the graphene powder to be dried to slow down, making it take a relatively long time for the water molecule film between the graphene microsheets to evaporate and escape. Therefore, instantaneous high pressure cannot be formed locally between the graphene microsheets, and the graphene microsheets that are in a superimposed and attached state due to the interfacial adsorption induced by the water molecule film between the sheets cannot be effectively separated, resulting in a reduction in the specific surface area of the graphene after drying, thereby affecting its electrical and thermal conductivity and other properties in the composite material.

[0058] In some embodiments, there is a gap between the shell and the lid, and the gap ranges from 0 to 0.2 mm. The upper limit of the gap may be, but is not limited to, 0.2 mm, 0.19 mm, 0.18 mm, etc., and the lower limit of the gap may be, but is not limited to, 0 mm, 0.05 mm, 0.1 mm, etc.; it is understandable that the gap may also be any point value within the above range, which is not enumerated here. By limiting the gap range between the shell and the lid, the airtightness of the reaction vessel 2 is ensured, and the graphene powder is prevented from being blown out by the steam flow. Preferably, the gap ranges from 0 to 0.1 mm, which further ensures the airtightness of the reaction vessel 2.

[0059] In some embodiments, the thickness of the shell and the lid ranges from 5 to 10 mm. The upper limit of the thickness of the shell and the lid can be, but is not limited to, 10 mm, 9.7 mm, 9.4 mm, etc., and the lower limit of the thickness of the shell and the lid can be, but is not limited to, 5 mm, 5.3 mm, 5.6 mm, etc.; it is understandable that the thickness of the shell and the lid can also be any point value within the above range, which is not enumerated here. Through this arrangement, the mechanical strength of the reaction vessel 2 is improved, and the problem of damage to the material of the reaction vessel 2 caused by rapid temperature increase and decrease is avoided. When the thickness of the shell and the lid is thicker, the mass of the reaction vessel 2 will inevitably increase. When the container is moved from the low temperature zone of the furnace tube to the heating zone and when it is moved out of the heating zone, the friction between the inner wall of the container and the furnace tube will also be greater, which may cause greater damage to the inner wall of the furnace tube. Furthermore, when the shell and lid are thick, the heat transfer efficiency is reduced, which is not conducive to the rapid heating of the graphene powder to be dried inside the container and the rapid vaporization of the water in the powder. This prevents the graphene microplatelets in the adsorbed and attached state from quickly separating under the action of gas expansion, thereby affecting the specific surface area of the graphene powder after drying. In addition, when the lid is thick, the pore length increases, resulting in greater resistance to water vapor discharge at high temperatures. The pressure drop rate in the container during vacuuming will also decrease, thereby reducing the vaporization efficiency of the water in the powder, ultimately affecting the specific surface area of the graphene powder after drying. Preferably, the thickness of the shell and lid ranges from 5 to 8 mm. In some embodiments, the volume occupied by the graphene powder to be dried in the reaction vessel 2 does not exceed 80% of the volume of the reaction vessel 2. Preferably, the volume occupied by the graphene powder to be dried in the reaction vessel 2 does not exceed 60 to 80% of the volume of the reaction vessel 2. The reaction vessel 2 containing the graphene to be dried is quickly placed in the heating area of the heating source, and when the vacuum pump is turned on to evacuate the vacuum, the water in the powder is rapidly vaporized to form a large amount of water vapor, and a portion of space is reserved between the graphene powder and the lid. This portion of space can serve as a buffer to prevent the water vapor from being unable to be discharged in time, resulting in an increase in the internal pressure of the container and thus causing the lid to be pushed open, causing the graphene powder in the container 2 to be scattered in large quantities in the furnace tube 1, which is not conducive to the recovery of the material after drying and may even cause a safety risk at the moment the lid is opened. In addition, under the combined effect of instantaneous high temperature and sudden drop in vacuum pressure, the water in the powder is rapidly vaporized to form a large amount of water vapor, which will instantly blow up the graphene powder in the container. A portion of space is reserved between the graphene powder and the lid to prevent the pores on the lid from being blocked, thereby blocking the discharge of water vapor. Furthermore, if the reserved space is too small, high pressure may build up inside the container, which could not only force the lid open but also inhibit the rapid evaporation of moisture in the powder. Consequently, it would be impossible to generate instantaneous high pressure between the graphene microplatelets to quickly separate the adsorbed and bonded graphene microplatelets, thereby reducing the specific surface area of the dried graphene powder. If the reserved space is too large, the amount of graphene powder placed in the reaction vessel 2 would be small, which would be detrimental to improving drying efficiency.

[0060] In some embodiments, the material of the reaction container 2 includes at least one of quartz glass, corundum, silicon carbide ceramics, graphite, and stainless steel. Preferably, the material of the reaction container 2 is graphite.

[0061] S2: Start the heating source until the furnace temperature rises to a preset temperature, and the reaction vessel 2 is located outside the heating area 3 of the heating source;

[0062] In some embodiments, the heating source may be a tubular furnace.

[0063] In some embodiments, the preset temperature of the furnace is 450-650°C. The upper limit of the preset temperature of the furnace may be, but not limited to, 650°C, 640°C, 630°C, etc., and the lower limit of the preset temperature of the furnace may be, but not limited to, 450°C, 460°C, 470°C, etc.; it is understandable that the preset temperature of the furnace can also be any point value within the above range, which is not enumerated here. Preferably, the preset temperature of the furnace is 500-600°C. If the preset temperature of the furnace is too high, the water vapor formed by the vaporization of water in the powder will ablate the graphene microsheets if it cannot be discharged in time, affecting the structural integrity of the graphene microsheets and causing the conductivity of the graphene microsheets to deteriorate. In addition, water vapor at higher temperatures will change the surface properties of graphene (such as the grafting of oxygen-containing free radicals), making the surface adsorption of the graphene film stronger, thereby causing the initially separated graphene sheets to be stacked and adsorbed again. However, the preset furnace temperature is too low, and the vaporization of water in the powder fails to form a sufficiently high instantaneous pressure to quickly separate the graphene microsheets that are superimposed and attached due to interfacial adsorption, resulting in a low specific surface area of the dried graphene powder, which affects its performance in composite materials.

[0064] In addition, the preset temperature in the present application is much higher than the boiling point of the solvent water. Compared with the oven drying in the prior art, the drying efficiency of the present application is higher, the energy consumption is reduced, and the drying time is greatly shortened.

[0065] In some embodiments, during the heating process, the furnace tube 1 is further heated by introducing an inert gas to maintain an inert atmosphere in the heating region 3 of the heat source. This configuration avoids oxidation of the graphene powder during the drying process due to excessive air content in the high-temperature environment, which could lead to a decrease in overall performance.

[0066] Specifically, the flow rate of the inert gas is in the range of 3 to 10 L / min. Placing the reaction vessel 2 behind the heating area 3 of the heating source and turning off the inert gas before starting the vacuum pump to evacuate the chamber facilitates rapid reduction of the pressure inside the furnace tube.

[0067] Specifically, the inert gas includes at least one of nitrogen, helium and argon. Preferably, the inert gas is nitrogen.

[0068] In some embodiments, as shown in the attached Figure 1 As shown, the furnace tube 1 includes a first low-temperature zone 11 and a heating area 3 of a heating source, and the reaction container 2 is located outside the heating area 3 of the heating source, including: the reaction container 2 is located in the first low-temperature zone 11 of the furnace tube 1.

[0069] S3: placing the reaction container 2 in the heating area 3 of the heating source to heat the graphene powder to be dried, and cooling it after a certain period of time to obtain dried graphene powder.

[0070] In some embodiments, placing the reaction container 2 in the heating area 3 of the heating source to heat the graphene powder to be dried includes: moving the reaction container 2 into the heating area 3 of the heating source to heat the graphene powder to be dried.

[0071] Specifically, as attached Figure 1-2 As shown, the furnace tube 1 includes a first low-temperature zone 11 and a heating area 3 of a heating source, and the heating device includes a push rod 5, which moves the reaction vessel 2 to the heating area 3 of the heating source to heat the graphene powder to be dried, including: using the push rod 5 to move the reaction vessel 2 in the first low-temperature zone 11 of the furnace tube 1 to the heating area 3 of the heating source to heat the graphene powder to be dried.

[0072] Specifically, the temperature of the first low-temperature zone 11 of the furnace tube 1 is 10-35°C. It is understood that the first low-temperature zone 11 of the furnace tube 1 can be any value within the above range, which is not enumerated here. Preferably, the temperature of the first low-temperature zone 11 of the furnace tube 1 is 20-35°C. More preferably, the temperature of the first low-temperature zone 11 of the furnace tube 1 is 30°C.

[0073] In some embodiments, the reaction container 2 is placed in the heating area 3 of the heating source to heat the graphene powder to be dried, including: moving the heating source until the heating area 3 of the heating source moves to the tube wall where the reaction container 2 is located to heat the graphene powder to be dried.

[0074] Whether moving the reaction vessel 2 or the heating source, the reaction vessel 2 can be placed in the heating area 3 for heating. The above two modes of movement can place the graphene powder from the area with lower temperature in the heating area 3. In some embodiments, when the furnace temperature in step S2 is increased, the distance between the tube wall where the reaction vessel 2 is located and the heating area 3 of the heating source is ≥50 cm. The tube wall where the reaction vessel 2 is located here refers to the position of the reaction vessel 2 in the furnace tube. Heat insulation members 4 are provided on both sides of the heating area 3. By limiting the distance and arranging the heat insulation members, the heating area 3 of the heating source is prevented from affecting the temperature of the position of the reaction vessel 2 by radiation or conduction, and at the same time, the time for the reaction vessel to move to the heating area 3 is extended due to excessive travel, so that the graphene powder can be quickly moved from the furnace tube position with lower temperature to the heating area 3 with higher temperature, thereby generating a larger temperature rise rate in the graphene powder to be dried in a very short time, and assisting in the sudden drop in the pressure of vacuuming. As a result, within a very short period of time, a high instantaneous vapor pressure is generated between the graphene microsheets in the reaction vessel 2, causing the gas to expand rapidly. This causes the graphene microsheets, which are superimposed and attached due to the interfacial adsorption induced by the water molecule film, to rapidly separate from each other, thereby avoiding the problem of the graphene powder not suffering from a reduction in specific surface area due to the drying process. Preferably, the distance between the tube wall where the reaction vessel 2 is located and the heating area 3 of the heat source is 50 to 70 cm.

[0075] In some embodiments, the time for the reaction vessel 2 to move relative to the heating area 3 of the heating source is 2 to 3 s. The upper limit of the time may be, but not limited to, 3 s, 2.9 s, 2.8 s, etc., and the lower limit of the time may be, but not limited to, 2 s, 2.1 s, 2.2 s, etc.; it is understandable that the time may also be any point value within the above range, which is not enumerated here. By limiting the time, the movement speed of the reaction vessel 2 or the heating source is faster and the heating is uniform. In this way, the quality consistency of the graphene powder after drying in the container is better. In addition, a higher temperature rise rate and instantaneous temperature are obtained in a very short time, which is conducive to forming an instantaneous high pressure between the graphene powder microsheets to be dried under the sudden pressure drop assisted by vacuum extraction, thereby being able to quickly separate the graphene microsheets in an adsorbed and superimposed state.

[0076] In some embodiments, the heating time of the graphene powder to be dried is 1.5 to 2.5 hours. The upper limit of the heating time may be, but is not limited to, 2.5 hours, 2.4 hours, 2.3 hours, etc., and the lower limit of the heating time may be, but is not limited to, 1.5 hours, 1.6 hours, 1.7 hours, etc.; it is understandable that the heating time can also be any point value within the above range, which is not enumerated here. Preferably, the heating time of the graphene powder to be dried is 1.6 to 2.2 hours. Further preferably, the heating time of the graphene powder to be dried is 2 hours. When the heating time is too long, the carbon lattice structure of the graphene may change, causing the graphene microsheets to re-stack and adsorb, thereby reducing the specific surface area of the dried graphene, thereby affecting its electrical conductivity, thermal conductivity and other properties in the composite material; when the heating time is too short, the moisture may not be completely removed, thereby affecting the comprehensive performance of the graphene powder.

[0077] In some embodiments, the heating device includes a first thermal insulation member, a second thermal insulation member, and a third thermal insulation member. The first thermal insulation member and the second thermal insulation member are arranged on both sides of the reaction vessel 2, and the third thermal insulation member is arranged on the side of the heating area away from the reaction vessel 2. The thermal insulation member 4 is arranged on both sides of the heating area 3 and on both sides of the container 2. It can ensure that the temperature of the heating area is uniform during the heating process of the furnace heating source and after the reaction vessel is moved to the heating area after reaching the preset temperature, which is conducive to ensuring the consistency of the quality of the graphene powder obtained by drying using the drying method of the present application. Specifically, the material of the thermal insulation member 4 is frosted quartz, alumina ceramic fiber, aluminum silicate ceramic fiber, zirconium oxide ceramic fiber or silicon carbide ceramic fiber.

[0078] In some embodiments, the method further comprises: placing the reaction vessel 2 in the heating zone 3 of the heating source, and evacuating the interior of the furnace tube 1 so that the heating process of the graphene powder to be dried in the heating zone 3 of the heating source is in a negative pressure environment. In the negative pressure environment, the boiling point of water is lowered, so that the residual water in the graphene powder can be quickly vaporized, thereby improving the drying efficiency. At the same time, the graphene powder to be dried is rapidly heated from near room temperature in a very short time and is at a higher instantaneous temperature. In addition, the rapid pressure drop during the vacuuming process causes a large pressure difference between the inside and outside of the reaction vessel, so that the inside of the reaction vessel is in a lower pressure state. Thus, under the dual driving forces of the pressure suddenly dropping to a state close to a medium vacuum state and the temperature quickly rising to a level far above the boiling point of water, an instantaneous high pressure is formed between the micro-sheets of the graphene powder to be dried, thereby quickly separating the graphene micro-sheets in an adsorbed and superimposed state, thereby avoiding the reduction of the specific surface area of the graphene during the drying process. In addition, in the negative pressure environment, the concentration of oxygen and water vapor in the heating area can be significantly reduced, thereby effectively protecting the graphene from oxidation etching.

[0079] In some embodiments, after the reaction vessel 2 containing the graphene powder to be dried is placed in the heating zone 3 of the heat source, a preset time interval is required before the interior of the furnace tube 1 is evacuated. During this stage, the graphene to be dried can be preheated at a low temperature, so that when the vacuum pump is turned on and the pressure drops suddenly, the interior of the graphene powder to be dried is at a higher instantaneous temperature, which is conducive to the rapid vaporization of water. As a result, the rapid vaporization and expansion of water between the locally overlapped microflakes of the graphene powder generates a higher instantaneous pressure, separating the adsorbed graphene microflakes, thereby reducing the loss of the specific surface area of the graphene powder caused by the drying process.

[0080] However, if the preset time is too long, a large amount of water will evaporate and escape freely before vacuuming, making it impossible to form a synergistic effect of instantaneous high temperature and instantaneous negative pressure. It is also impossible to effectively separate the graphene microsheets that are in a superimposed and attached state due to the interfacial adsorption induced by the water molecule film between the sheets, resulting in a decrease in the specific surface area of the graphene after drying, thereby affecting its electrical conductivity and thermal conductivity in the composite material. In addition, if the preset time is too long, the water vapor will stay in the heating area for too long, which will not only ablate the graphene microsheets, affecting the structural integrity of the graphene microsheets and making the graphene conductivity worse, but also change the surface properties of the graphene at higher temperatures (such as the grafting of oxygen-containing free radicals), making the surface adsorption of the graphene film stronger, thereby causing the stacking adsorption between the initially separated graphene sheets to occur again, resulting in a lower specific surface area of the graphene powder after drying. Specifically, the preset time is 3 to 5 seconds.

[0081] In some embodiments, the heating device includes a safety valve 6, and a flange is provided on the furnace tube, with the safety valve 6 fixedly connected to the flange. Because the reaction vessel containing the graphene powder to be dried is instantly placed from a region near room temperature into the heating region before the vacuum pump is activated to evacuate the interior of the furnace tube cavity, the time interval between these operations is very short, and the safety valve is provided on the furnace tube flange. Therefore, the drying method of the present application does not pose safety risks such as damage to the furnace tube or collapse of the flange due to increased internal pressure in the furnace tube, thereby improving the safety performance of the drying method.

[0082] In some embodiments, vacuuming the interior of the furnace tube 1 is performed by stepwise depressurization. During the stepwise depressurization process, the decompression rate of each step of the vacuuming process gradually decreases. In this embodiment, the stepwise depressurization is achieved by adjusting the driving frequency and valve opening of the multi-stage vacuum pump.

[0083] By adopting the step-by-step pressure reduction method, on the one hand, the graphene powder to be dried is subjected to the combined effects of rapid temperature increase and sudden pressure drop, and the local overlapping micro-sheets of the graphene powder are subjected to instantaneous high pressure due to the rapid vaporization and expansion of water, which separates the graphene micro-sheets in an adsorbed state, thereby reducing the loss of the specific surface area of the graphene powder caused by the drying process; on the other hand, the step-by-step pressure reduction method can prevent the graphene micro-sheets that are in the process of separation or have been separated from being re-overlapped and stuck together under the subsequent excessively rapid vacuum pressure drop and in a higher temperature environment, resulting in a decrease in the specific surface area of the graphene powder after drying, thereby affecting its performance as an additive in composite materials.

[0084] In some embodiments, the step-by-step depressurization includes a first depressurization process, a second depressurization process, and a third depressurization process;

[0085] The pressure in the furnace tube 1 during the first depressurization process ranges from 100 kPa to 10 kPa, and the required first depressurization time is 25 to 40 seconds. It is understood that the pressure in the furnace tube 1 and the required first depressurization time during the first depressurization process can be any value within the above range, and are not enumerated here. Preferably, the required first depressurization time is 25 to 35 seconds.

[0086] The pressure range inside the furnace tube 1 during the second pressure reduction treatment process is 10KPa~3KPa, and the required second pressure reduction time is 2.5~3.5min; it can be understood that the pressure inside the furnace tube 1 during the second pressure reduction treatment process and the required second pressure reduction time can be any point value within the above range, which is not enumerated here.

[0087] The pressure in furnace tube 1 during the third depressurization process ranges from 3 kPa to 150 Pa, and the required third depressurization time is 7 to 10 minutes. It is understood that the pressure in furnace tube 1 and the required third depressurization time during the third depressurization process can be any value within the above ranges, and are not enumerated here. Preferably, the required third depressurization time is 8 to 10 minutes.

[0088] By limiting the pressure range and depressurization duration of the depressurization process in each step, not only can the instantaneous high temperature generated by the rapid temperature rise and the large pressure difference formed inside and outside the reaction vessel when vacuuming cause the pressure in the reaction vessel to drop suddenly, the two form a synergistic effect, so that the micro-sheets and micro-sheets of the locally superimposed graphene powders are subjected to instantaneous high pressure due to the rapid vaporization and expansion of water, and the graphene micro-sheets in the adsorbed state are separated. It is also possible to avoid the graphene micro-sheets that are separated or have been separated from being superimposed and pasted together again under a subsequent excessively fast vacuum pressure drop and in a higher temperature environment. In short, through this operation, it is possible to avoid the drying process causing a reduction in the specific surface area of the graphene powder, thereby helping to improve its performance as an additive in a composite material. In some embodiments, the cooling method in step S3 is quenching. By adopting a quenching method to cool, the microscopic morphology of the graphene is maintained, and the graphene microsheets are prevented from undergoing adaptive structural adjustments due to the small temperature gradient change during the slow cooling process, so that the separated graphene microsheets are re-overlapped and bonded, resulting in a decrease in the specific surface area of the powder, thereby affecting its performance as an additive in composite materials. In some embodiments, the cooling in step S3 includes: in response to the heating time of the graphene powder to be dried reaching a preset time, placing the reaction vessel 2 outside the heating area 3 of the heating source, and after cooling, obtaining a dried graphene powder. Specifically, air cooling can be used to assist in cooling during the cooling process.

[0089] After the heating time of the graphene powder to be dried reaches a preset time, the reaction vessel 2 is placed outside the heating area 3 of the heat source, which can quickly move the graphene powder from the higher temperature area to the lower temperature area. The larger temperature drop helps maintain the microscopic morphology of the graphene and prevents the graphene microsheets from undergoing adaptive structural adjustments due to the small temperature gradient during the slow cooling process. This can cause the separated graphene microsheets to overlap and bond again, resulting in a reduction in the specific surface area of the powder and affecting its performance as an additive in the composite material.

[0090] In some embodiments, placing the reaction container 2 outside the heating region 3 of the heating source includes: moving the reaction container 2 outside the heating region 3 of the heating source to cool the graphene powder.

[0091] Specifically, as attached Figure 3 As shown, the furnace tube 1 includes a second low-temperature zone 12 and a heating area 3 of a heating source, and the heating device includes a push rod 5. The reaction vessel 2 is moved outside the heating area 3 of the heating source to cool the graphene powder, including: using the push rod 5 to move the reaction vessel 2 from the heating area 3 of the heating source to the low-temperature zone of the furnace tube 1 to cool the graphene powder.

[0092] Specifically, the temperature of the second low-temperature zone 12 of the furnace tube 1 is 10-35°C. It is understood that the temperature of the second low-temperature zone 12 of the furnace tube 1 can be any value within the above range, which is not enumerated here. Preferably, the temperature of the second low-temperature zone 12 of the furnace tube 1 is 20-35°C. More preferably, the temperature of the second low-temperature zone 12 of the furnace tube 1 is 30°C.

[0093] In some embodiments, placing the reaction vessel 2 outside the heating area 3 of the heating source includes: moving the heating source until the heating area 3 of the heating source is moved away from the tube wall where the reaction vessel 2 is located to cool the graphene powder. The tube wall where the reaction vessel 2 is located here refers to the position of the reaction vessel 2 in the furnace tube. Whether moving the reaction vessel 2 or moving the heating area 3 of the heating source, the reaction vessel 2 can be placed outside the heating area 3 for cooling. Both of the above-mentioned moving methods can quickly move the graphene powder from a higher temperature area to a lower temperature area. The larger temperature drop helps to maintain the microscopic morphology of the graphene and avoid the graphene microsheets undergoing adaptive structural adjustment due to the small temperature gradient change during the slow cooling process, so that the separated graphene microsheets are re-overlapped and bonded, resulting in a decrease in the specific surface area of the powder, thereby affecting its performance as an additive in the composite material. In some embodiments, the cooling time required for the cooling treatment in step S3 is 18 to 30 minutes. The upper limit of the cooling time may be, but is not limited to, 30 min, 29 min, 28 min, etc., and the lower limit of the cooling time may be, but is not limited to, 18 min, 19 min, 20 min, etc.; it is understandable that the cooling time may also be any point value within the above range, which is not enumerated here. By limiting the cooling time, it is avoided that the furnace tube and the reaction vessel 2 may be cracked or damaged due to excessive cooling speed; however, if the cooling speed is too slow, due to the small change in the temperature gradient, the graphene microsheets undergo adaptive structural adjustment, causing the separated graphene microsheets to overlap and bond again, resulting in a decrease in the specific surface area of the powder, thereby affecting its performance as an additive in the composite material. Preferably, the cooling time required for the cooling treatment in step S3 is 18 to 25 min.

[0094] In some embodiments, during the cooling process in step S3, the distance between the tube wall where the reaction vessel 2 is located and the heating area 3 of the heating source is ≥ 50 cm. By limiting this distance, and under the combined action of the thermal insulation, the heating area 3 of the heating source is prevented from heating the reaction vessel 2 by heat radiation or conduction. As a result, after the reaction vessel 2 is removed from the high-temperature zone, it is almost completely insulated from the radiation or conduction heating of the furnace heating source, thereby achieving a sudden cooling effect. Preferably, the distance between the tube wall where the reaction vessel 2 is located and the heating area 3 of the heating source is 50 to 70 cm.

[0095] In some embodiments, the time for the container 2 to move relative to the outside of the heating area 3 of the heating source is 2 to 4 seconds. The upper limit of the time may be, but is not limited to, 4 seconds, 3.9 seconds, 3.8 seconds, etc., and the lower limit of the time may be, but is not limited to, 2 seconds, 2.1 seconds, 2.2 seconds, etc.; it is understandable that the time can also be any point value within the above range, which is not enumerated here. By limiting this time, the movement speed of the reaction container 2 or the heating source is faster, so that the graphene powder in the reaction container 2 can be quenched from a high temperature in a very short time, thereby avoiding differences in the quality of the graphene powder at different positions in the container after drying.

[0096] In some embodiments, after the graphene powder to be dried has been heated for a predetermined period of time and before cooling, the method further includes: introducing an inert gas into the heating region 3 of the heat source to maintain the interior of the furnace tube 1 at atmospheric pressure. This arrangement prevents air from leaking into the high-temperature graphene powder when the reaction vessel 2 containing the graphene is removed from the heating region of the heat source, thereby preventing oxidation.

[0097] Specifically, the inert gas includes at least one of nitrogen, helium, argon and neon. Preferably, the inert gas is nitrogen.

[0098] In some embodiments, the bulk density of the dried graphene powder is ≤0.012 g / cm 3 Preferably, the bulk density of the dried graphene powder is 0.007 to 0.012 g / cm 3 ;

[0099] In some embodiments, the specific surface area of the dried graphene powder is ≥240 m 2 / g. Preferably, the specific surface area of the dried graphene powder is 240 to 258 m 2 The drying method of the present application can obtain graphene powder with a lower bulk density and a higher specific surface area, indicating that the stacking, bonding, or overlapping of the graphene microsheets after drying is effectively alleviated, thereby helping to improve the electrical conductivity, thermal conductivity, and mechanical properties of the graphene powder as an additive in composite materials.

[0100] In some embodiments, the composite material made from the dried graphene powder has a tensile strength of ≥22.8 MPa. Preferably, the composite material made from the dried graphene powder has a tensile strength in the range of 22.8 to 23.5 MPa.

[0101] In some embodiments, the composite material made from the dried graphene powder has an elongation at break of ≥9.12%. Preferably, the composite material made from the dried graphene powder has an elongation at break in the range of 9.12-9.55%.

[0102] In some embodiments, the resistivity of the composite film made from the dried graphene powder is ≤2.90Ω.cm. Preferably, the resistivity of the composite film made from the dried graphene powder is in the range of 2.50 to 2.90Ω.cm.

[0103] In some embodiments, the thermal conductivity of the composite film made of the dried graphene powder is ≥8.51 W / (mK). Preferably, the thermal conductivity of the composite film made of the dried graphene powder is in the range of 8.51 to 9.13 W /

[0104] The mechanical properties of the composite material made of the dried graphene powder obtained by the drying method of the present application are greatly improved, and the resistivity of the composite film made of the dried graphene powder is reduced, and its thermal conductivity is improved.

[0105] The graphene powder drying method in the present application is to quickly place the reaction container containing the graphene powder to be dried from a region close to room temperature to a heating region, then start the vacuum pump to evacuate the interior of the furnace tube cavity, and in a relatively short period of time the pressure drops sharply to a state close to a medium vacuum, so that a large pressure difference is generated inside and outside the reaction container. At the same time, due to the heating effect of the high-temperature region, the temperature of the graphene powder to be dried is rapidly increased to a temperature far above the boiling point of water. In this way, under the dual driving forces of large pressure drop and rapid temperature rise, the water in the graphene powder is rapidly vaporized, and local instantaneous high pressure is generated between the graphene microsheets, accompanied by violent expansion of the gas, which quickly separates the graphene microsheets in an adsorbed and superimposed state, thereby reducing the loss of specific surface area of the graphene powder to be dried during the drying process, and improving the electrical conductivity, thermal conductivity and mechanical properties of the graphene powder in the composite material. Compared with traditional oven drying or freeze-drying methods, the graphene drying method of the present application can significantly improve the drying process efficiency, shorten the drying cycle, reduce costs, and is conducive to large-scale production.

[0106] The following describes specific embodiments of the present application in conjunction with the above-mentioned method for drying graphene powder. The following examples describe the technical solutions of the present application in more detail. These examples are intended for illustrative purposes only, as various modifications and variations within the scope of the present disclosure are obvious to those skilled in the art. The reagents used in the examples can be obtained commercially or synthesized according to conventional methods and can be used directly without further treatment. The instruments and devices used in the examples can also be obtained commercially.

[0107] Example 1

[0108] This embodiment provides a method for drying graphene powder, which specifically includes the following steps:

[0109] S1: Graphene prepared by CVD is corroded with chemical reagents to remove impurities, then washed and filtered to obtain a graphene filter cake, the graphene filter cake is crushed to obtain graphene powder to be dried, the graphene powder to be dried is placed in a reaction vessel 2, and the reaction vessel 2 is placed in the first low-temperature zone 11 of the furnace tube 1; the aperture of the cover of the reaction vessel 2 is 0.1 mm, and the hole density on the cover is 15 / cm 2 The volume of the graphene powder to be dried in the reaction vessel 2 does not exceed 80% of the volume of the reaction vessel 2;

[0110] S2: Start the heating source of the tubular furnace body until the furnace temperature rises to 450°C. The reaction vessel 2 is located in the first low-temperature zone 11 of the furnace tube 1. The temperature of the first low-temperature zone is 35°C. During the heating process, nitrogen is introduced into the furnace tube at a flow rate of 5 L / min.

[0111] S3: Use the push rod 5 to move the reaction container 2 from the first low-temperature zone 11 of the furnace tube 1 to the heating area 3 of the tubular furnace body, wherein the moving time is 2s, and the distance between the first low-temperature zone 11 of the furnace tube 1 and the heating area 3 of the tubular furnace body is 50cm. Turn off the nitrogen before turning on the vacuum pump for vacuuming. After a preset time of 5s, vacuum the inside of the furnace tube 1 so that the inside of the furnace tube is in a negative pressure environment, and heat it in the negative pressure environment for 2.5h. The vacuuming of the inside of the furnace tube 1 is mainly carried out in a step-by-step pressure reduction method, which includes a first pressure reduction treatment, a second pressure reduction treatment, and a third pressure reduction treatment. During the first pressure reduction treatment, the pressure range of the furnace tube 1 is 100KPa to 10KPa, and the required first pressure reduction time is 40s. During the second pressure reduction treatment, the pressure range of the furnace tube 1 is 10KPa to 3KPa, and the required second pressure reduction time is 3.5min. During the third pressure reduction treatment, the pressure range of the furnace tube 1 is 3KPa to 150Pa, and the required third pressure reduction time is 10min.

[0112] S4: Close the vacuum pump valve and introduce nitrogen into the furnace tube 1 until the interior of the furnace tube 1 is at normal pressure. Then use the push rod 5 to move the reaction vessel 2 from the heating area 3 to the second low-temperature zone 12 of the furnace tube 1. The moving time is 4 seconds. After cooling for 18 minutes, the dried graphene powder is obtained. The distance between the second low-temperature zone 12 and the heating area 3 of the furnace tube 1 is 50 cm, and the temperature of the second low-temperature zone 12 is 30°C.

[0113] Example 2

[0114] This embodiment provides a method for drying graphene powder. The similarities with Example 1 are not repeated here. The difference from Example 1 is that: S2: Start the heating source of the tubular furnace body until the furnace temperature rises to 650°C, the reaction vessel 2 is located in the first low-temperature zone 11 of the furnace tube 1, and the temperature of the first low-temperature zone 11 is 25°C.

[0115] Example 3

[0116] This embodiment provides a method for drying graphene powder. The similarities with Example 1 are not repeated here. The difference from Example 1 is that the heating time in the negative pressure environment in step S3 is 1.5 hours.

[0117] Example 4

[0118] This embodiment provides a method for drying graphene powder. The similarities with Example 1 are not repeated here. The difference from Example 1 is that the cooling time in step S4 is 30 minutes.

[0119] Example 5

[0120] This embodiment provides a method for drying graphene powder. The similarities with Example 1 are not repeated here. The difference from Example 1 is that the heating time in the negative pressure environment in step S3 is 2 hours.

[0121] Example 6

[0122] This embodiment provides a method for drying graphene powder. The similarities with Example 1 are not repeated here. The difference from Example 1 is that: the heating source of the tubular furnace body is started until the furnace temperature rises to 500°C, the reaction vessel 2 is located in the first low-temperature zone 11 of the furnace tube 1, and the temperature of the first low-temperature zone 11 is 25°C.

[0123] Example 7

[0124] This embodiment provides a method for drying graphene powder. The similarities with Example 1 are not repeated here. The difference from Example 1 is that the cooling time in step S4 is 25 minutes.

[0125] Comparative Example 1

[0126] This comparative example provides a method for drying graphene powder, which specifically comprises the following steps:

[0127] The graphene prepared by the CVD method is corroded with chemical reagents to remove impurities, and then washed and filtered to obtain a graphene filter cake. The graphene filter cake is crushed to obtain graphene powder to be dried. The graphene powder to be dried is placed in a beaker and dried for 21 hours in a conventional experimental oven at a drying temperature of 110°C to obtain dried graphene powder. The model of the conventional experimental oven is Zhetu TGF-9070A.

[0128] Comparative Example 2

[0129] This comparative example provides a method for drying graphene powder. The similarities with Example 1 are not repeated here. The difference from Example 1 is that: S2: start the tubular furnace heating source until the furnace temperature rises to 750°C, and the container 2 is located in the first low-temperature zone 11 of the furnace tube 1, and the temperature of the first low-temperature zone 11 is 30°C.

[0130] Comparative Example 3

[0131] This comparative example provides a method for drying graphene powder. The similarities with Example 1 are not repeated here. The difference from Example 1 is that: S3: The push rod 5 is used to move the reaction vessel 2 from the first low-temperature zone 11 of the furnace tube 1 to the heating area 3 of the tubular furnace body, wherein the moving time is 2s and the heating in the heating area 3 is 3.5h.

[0132] Comparative Example 4

[0133] This comparative example provides a method for drying graphene powder. The similarities with Example 1 are not repeated here. The difference from Example 1 is that the heating time in the negative pressure environment in step S3 is 1 hour.

[0134] Comparative Example 5

[0135] This comparative example provides a method for drying graphene powder, and the similarities with Example 1 are not repeated here. The difference from Example 1 is that the cooling time in step S4 is 35 minutes.

[0136] Comparative Example 6

[0137] The graphene prepared by the CVD method is corroded with chemical reagents to remove impurities, and then washed and filtered to obtain a graphene filter cake. The graphene filter cake is mixed with water to obtain a mixed solution. The concentration of graphene in the mixed solution is 0.2%. The mixed solution is ultrasonically dispersed for 4 hours, quenched with liquid nitrogen, and then transferred to a freeze dryer for freeze-drying treatment. The freeze-drying treatment time is 60 hours to obtain dried graphene powder.

[0138] Comparative Example 7

[0139] This comparative example provides a method for drying graphene powder, and the similarities with Example 1 are not repeated here. The difference from Example 1 is that the preset time in step S3 is 8s.

[0140] Comparative Example 8

[0141] This comparative example provides a method for drying graphene powder, and the similarities with Example 1 are not repeated here. The difference from Example 1 is that:

[0142] S2: Use the push rod 5 to move the reaction container 2 from the first low-temperature zone 11 of the furnace tube 1 to the heating zone 3 of the tubular furnace body. The moving time is 2 seconds, and the distance between the first low-temperature zone 11 of the furnace tube 1 and the heating zone 3 of the tubular furnace body is 50 cm.

[0143] S3: After a preset time of 5 seconds, the interior of the furnace tube 1 is evacuated so that the interior of the furnace tube is in a negative pressure environment. At the same time, the heating source of the tubular furnace body is started until the furnace temperature rises to 450°C and the furnace is heated in a negative pressure environment for 2.5 hours. The interior of the furnace tube 1 is evacuated mainly by a step-by-step pressure reduction method, which includes a first pressure reduction treatment, a second pressure reduction treatment and a third pressure reduction treatment. The pressure range of the furnace tube 1 during the first pressure reduction treatment is 100KPa to 10KPa, and the required first pressure reduction time is 40s. The pressure range of the furnace tube 1 during the second pressure reduction treatment is 10KPa to 3KPa, and the required second pressure reduction time is 3.5min. The pressure range of the furnace tube 1 during the third pressure reduction treatment is 3KPa to 150Pa, and the required third pressure reduction time is 10min.

[0144] S4: Without closing the vacuum pump valve, nitrogen is introduced into the furnace tube 1 until the interior of the furnace tube 1 is in a normal pressure environment, and then the push rod 5 is used to move the reaction vessel 2 from the heating area 3 to the second low-temperature zone 12 of the furnace tube 1. The moving time is 4 seconds. After cooling for 18 minutes, the dried graphene powder is obtained. The distance between the second low-temperature zone 12 and the heating area 3 of the furnace tube 1 is 50 cm, and the temperature of the second low-temperature zone 12 is 30°C.

[0145] Comparative Example 9

[0146] This comparative example provides a method for drying graphene powder. The similarities with Example 1 are not repeated here. The difference from Example 1 is as follows: S2: the reaction vessel 2 is moved from the first low-temperature zone 11 of the furnace tube 1 to the heating zone 3 of the tube furnace body by using a push rod 5, wherein the moving time is 2 s, the distance between the first low-temperature zone 11 of the furnace tube 1 and the heating zone 3 of the tube furnace body is 50 cm, and nitrogen is introduced into the furnace tube at a flow rate of 5 L / min;

[0147] S3: After a preset time of 3 to 5 seconds, the heating source of the tubular furnace is started until the furnace temperature reaches 450°C and heating is carried out at normal pressure for 2.5 hours;

[0148] S4: The reaction vessel 2 is moved from the heating zone 3 to the second low-temperature zone 12 of the furnace tube 1 using the push rod 5. The moving time is 4 seconds. After cooling for 18 minutes, the dried graphene powder is obtained. The distance between the second low-temperature zone 12 and the heating zone 3 of the furnace tube 1 is 50 cm, and the temperature of the second low-temperature zone 12 is 30°C.

[0149] Comparative Example 10

[0150] This comparative example provides a method for drying graphene powder, and the similarities with Example 1 are not repeated here. The difference from Example 1 is that:

[0151] S2: Start the heating source of the tubular furnace body until the furnace temperature rises to 450°C. The reaction vessel 2 is located in the first low-temperature zone 11 of the furnace tube 1. The temperature of the first low-temperature zone is 35°C. During the heating process, nitrogen is introduced into the furnace tube at a flow rate of 5 L / min.

[0152] S3: Use push rod 5 to move reaction vessel 2 from first low-temperature zone 11 of furnace tube 1 to heating zone 3 of the tube furnace. The moving time is 2 seconds, and the distance between first low-temperature zone 11 of furnace tube 1 and heating zone 3 of the tube furnace is 50 cm. Heat at normal pressure for 2.5 hours.

[0153] S4: The reaction vessel 2 is moved from the heating zone 3 to the second low-temperature zone 12 of the furnace tube 1 using the push rod 5. The moving time is 4 seconds. After cooling for 18 minutes, the dried graphene powder is obtained. The distance between the second low-temperature zone 12 and the heating zone 3 of the furnace tube 1 is 50 cm, and the temperature of the second low-temperature zone 12 is 30°C.

[0154] Comparative Example 11

[0155] This comparative example provides a method for drying graphene powder. The similarities with comparative example 10 are not repeated here. The difference from comparative example 10 is that the furnace temperature in step S2 is 110°C, and the treatment time of normal pressure heat treatment is 21h.

[0156] The above examples and comparative examples adopt the following testing methods:

[0157] 1. The bulk density of the graphene powders of the embodiment and the comparative example was tested using a natural bulk density meter (Dandong Haoyu HYL-103). The test results are shown in Table 1.

[0158] 2. The specific surface area of the graphene powders obtained in the examples and comparative examples was measured using a specific surface area analyzer (JW-DX). The test results are shown in Table 1.

[0159] 3. The moisture content of the dried graphene powder was tested using an infrared moisture meter (Yishite ST-100A). The test results are shown in Table 1.

[0160] 4. Use CHNSO element analyzer (Thermo Fisher FlashSmart) to test the oxygen content in the dried graphene powder;

[0161] 5. The mass of the graphene powder to be dried in Examples 1-7 and Comparative Examples 1-11 is the same. The mass of the dried graphene powder obtained in Comparative Example 1 is recorded as m 参照 The mass of the dried graphene powder obtained in Examples 1-7 and Comparative Examples 2-11 is recorded as m 测试 , by calculating the formula (m 测试 -m 参照 ) / m 测试 ×100% to calculate the carbon mass loss rate of the graphene powder after drying in the embodiment and the comparative example.

[0162] 6. The dried graphene powder was tested by Raman spectrometer (Renishaw inVia Reflex, UK). D / I G The defect degree of the dried graphene powder was obtained by ratio calculation.

[0163] 7. Evaluation of the conductive properties of the dried graphene powder: 3% of the dried graphene powder was added to a 40% solid content TPU solution, and the mixture was evenly mixed by mechanical stirring. Then, a film was coated on PET using a small automatic coating machine. After drying, the film thickness was measured to be 60 μm. The resistivity of the composite film was tested using a four-probe resistivity tester (XGSZ-F4, Xigao Huadian). The test results are shown in Table 1.

[0164] 8. Evaluation of thermal conductivity of dried graphene powder: 3% dried graphene powder was added to a 40% solid content TPU solution, and the mixture was mechanically stirred to mix evenly. Then, a film was coated on PET using a small automatic coating machine. After drying, the film thickness was measured to be 60 μm. The thermal conductivity of the composite film was tested using a laser thermal conductivity tester (LFA467). The test results are shown in Table 1.

[0165] 9. Mechanical Properties Evaluation of Dried Graphene Powder in Composite Materials: 3% of the dried graphene powder obtained in the examples and comparative examples was added to PP powder, and the workpieces obtained by premixing, melt mixing, and injection molding were tested for tensile strength and elongation at break of the composite materials using a universal material testing machine. The test results are shown in Table 1.

[0166] 10. The morphology of the graphene powders obtained in the examples and comparative examples was characterized using a SEM scanning electron microscope (FEI-Navo Nano SEM450). The test results are shown in Figure 10. Figure 4-5 As shown, Figure 4 This is the morphology of the graphene powder obtained in Example 1. It can be seen that there is no obvious stacking and adhesion between the graphene sheets. Figure 5 This is the morphology of the graphene powder obtained in Comparative Example 1. It can be seen that there is obvious stacking and adhesion between the graphene sheets.

[0167] The following Table 1 statistically records the test data in the embodiments and comparative examples:

[0168] Table 1

[0169]

[0170]

[0171] With reference to Table 1 and the accompanying drawings, in combination with Example 1 and Comparative Example 1, it can be seen that the specific surface area of the dried graphene powder is significantly reduced by oven drying, and the electrical conductivity, thermal conductivity and mechanical properties of the composite molded workpiece obtained by using the graphene powder as an additive are significantly reduced.

[0172] In combination with Example 1 and Comparative Example 2, it can be seen that if the heating temperature is too high, the conductive properties of the dried graphene powder will be significantly reduced, that is, the resistivity of the composite film will increase significantly. This may be because the high heating temperature affects the structural integrity of the graphene microsheets, the specific surface area is reduced, and the packing density is increased. This may be because water vapor will change the surface properties of graphene at a higher temperature, making the surface adsorption force of the graphene film stronger, thereby causing the initially separated graphene sheets to be stacked and adsorbed again.

[0173] Combining Example 1 and Comparative Examples 3-4, it can be seen that a heating time that is too long or too short will affect the comprehensive performance of the powder after drying. This may be because the carbon lattice structure of the graphene changes due to a too long heating time, causing the graphene microsheets to stack and adsorb again, thereby reducing the specific surface area of the graphene after drying. If the heating time is too short, the moisture cannot be completely removed, affecting the comprehensive performance of the graphene powder.

[0174] Combining Example 1 and Comparative Example 5, it can be seen that a too long cooling time will affect the comprehensive performance of the powder after drying. This may be because the cooling speed is too slow. Due to the small change in the temperature gradient, the graphene microsheets undergo adaptive structural adjustment, causing the separated graphene microsheets to overlap and bond again, resulting in a decrease in the specific surface area of the powder, thereby affecting the comprehensive performance of the powder after drying.

[0175] In combination with Example 1 and Comparative Example 6, it can be seen that the comprehensive performance of the graphene powder obtained by the drying method of the present application is equivalent to that obtained by freeze-drying, which proves that the quality of the graphene powder obtained by the drying method of the present application is higher, and compared with the freeze-drying method, the drying method of the present application has a shorter drying cycle, is easy to scale up production, and has higher drying efficiency.

[0176] Combining Example 1 and Comparative Example 7, it can be seen that if the preset time is too long, the comprehensive performance of the graphene powder will be affected. This is mainly because the water vapor stays in the heating area for too long, which not only ablates the graphene microsheets, affecting the structural integrity of the graphene microsheets and making the graphene conductivity worse, but also changes the surface properties of the graphene (such as the grafting of oxygen-containing free radicals) at higher temperatures, making the surface adsorption of the graphene film stronger, and then causing the initially separated graphene sheets to stack and adsorb again, resulting in a lower specific surface area of the dried graphene powder.

[0177] In combination with Example 1 and Comparative Example 8, it can be seen that when the heating area of the furnace tube is heated to the preset temperature, the vacuum pump is in the open state and the graphene powder to be dried is heated synchronously. In this way, the heating rate of the graphene powder to be dried in the reaction container is slowed down, and a large amount of water vaporizes and escapes before reaching the preset temperature, and the synergistic effect of instantaneous high temperature and instantaneous negative pressure cannot be formed, which in turn reduces the overall performance of the graphene powder.

[0178] In combination with Example 1 and Comparative Example 9, it can be seen that when the heating area of the furnace tube is heated to a preset temperature at normal pressure under nitrogen protection, the graphene powder to be dried is heated simultaneously. This method is also adopted because the temperature of the graphene powder to be dried in the reaction vessel is slowed down, and the water vaporization between the graphene sheets cannot form instantaneous high pressure. At the same time, there is no synergistic effect of the instantaneous negative pressure of vacuum extraction, which makes the vaporization rate of water in the graphene powder slow, making it impossible to quickly separate the graphene microsheets in the adsorbed and superimposed state.

[0179] In combination with Example 1 and Comparative Examples 10-11, it can be seen that when the graphene powder is dried at normal pressure and reaches a preset temperature, the graphene powder to be dried is moved to a heating area, but the vacuum pump is not turned on for vacuuming. Relying solely on instantaneous high temperature to try to separate the graphene microsheets that are attached and overlapped due to interface adsorption has a very limited effect. On the contrary, the water vapor discharge rate will slow down, the graphene oxygen content will increase, and the defects will increase, which will ultimately reduce the overall performance of the graphene powder.

[0180] Therefore, compared with the conventional oven drying method, the drying method of the present application can better preserve the microscopic morphology of the graphene powder, and avoid the problem of obvious stacking and attachment of the graphene microsheets after drying due to interfacial adsorption between the graphene microsheets in the filter cake after water washing and filtration under the action of van der Waals force, thereby avoiding the loss of the specific surface area of the graphene powder during the drying process, thereby helping to improve its electrical conductivity, thermal conductivity and mechanical properties in the composite material.

[0181] The above description has fully disclosed the specific embodiments of this application. It should be noted that any changes made by those skilled in the art to the specific embodiments of this application do not depart from the scope of the claims of this application. Accordingly, the scope of the claims of this application is not limited to the above specific embodiments.

Claims

1. A method for drying graphene powder, using a heating device, wherein the heating device includes a furnace tube, a reaction container and a heating source, characterized in that: The method comprises: S1: loading the graphene powder to be dried into the reaction container, and placing the reaction container in the furnace tube; S2: starting the heating source until the furnace temperature rises to a preset temperature, and the reaction container is located outside the heating area of the heating source; S3: placing the reaction container in the heating area of the heating source to heat the graphene powder to be dried, and cooling it after a certain period of time to obtain dried graphene powder.

2. The method according to claim 1, characterized in that Placing the reaction container within the heating area of the heating source to heat the graphene powder to be dried includes: moving the reaction container into the heating area of the heating source to heat the graphene powder to be dried; or moving the heating source so that the heating area of the heating source is moved to the tube wall where the reaction container is located to heat the graphene powder to be dried.

3. The method according to claim 2, characterized in that The method satisfies at least one of the following characteristics: When the furnace temperature is increased in step S2, the distance between the tube wall where the reaction container is located and the heating area of the heating source is ≥50 cm; The time for the reaction container to move relatively into the heating area of the heating source is 2 to 3 seconds.

4. The method according to any one of claims 1 to 3, characterized in that The method further includes: heating the graphene powder to be dried in a negative pressure environment.

5. The method according to any one of claims 1 to 3, characterized in that When the reaction container is placed in the heating area of the heating source, the interior of the furnace tube is evacuated to place the heating area of the heating source in a negative pressure environment.

6. The method according to claim 5, characterized in that The vacuuming of the interior of the furnace tube is performed by step-by-step pressure reduction. During the step-by-step pressure reduction, the pressure reduction rate of each step of the vacuuming treatment is gradually reduced. The step-by-step pressure reduction includes a first pressure reduction treatment, a second pressure reduction treatment, and a third pressure reduction treatment. The pressure range in the furnace tube during the first pressure reduction process is 100KPa to 10KPa, and the required first pressure reduction time is 25 to 40s; The pressure in the furnace tube during the second pressure reduction process ranges from 10 kPa to 3 kPa, and the required second pressure reduction time is 2.5 to 3.5 minutes; The pressure range of the furnace tube in the third pressure reduction treatment is 3KPa to 150Pa, and the required third pressure reduction time is 7 to 10 minutes.

7. The method according to any one of claims 1 to 3, characterized in that The cooling method in step S3 is quenching.

8. The method according to any one of claims 1 to 3, characterized in that The cooling in step S3 includes: in response to the heating time of the graphene powder to be dried reaching a preset time, placing the reaction container outside the heating area of the heating source, and cooling to obtain the dried graphene powder.

9. The method according to claim 8, characterized in that Placing the reaction container outside the heating area of the heating source includes: moving the reaction container outside the heating area of the heating source to cool the graphene powder; or moving the heating source so that the heating area of the heating source is moved away from the tube wall where the reaction container is located to cool the graphene powder.

10. The method according to claim 9, characterized in that The method satisfies at least one of the following characteristics: The cooling time required for the cooling treatment in step S3 is 18 to 30 minutes; In the case of the cooling treatment in step S3, the distance between the tube wall where the reaction container is located and the heating area of the heating source is ≥50 cm; The time for the reaction container to move relative to the outside of the heating area of the heating source is 2 to 4 seconds; After the heating time of the graphene powder to be dried reaches a preset time and before cooling, the method further includes: introducing an inert gas into the heating area of the heating source to keep the interior of the furnace tube at normal pressure.

11. The method according to any one of claims 1 to 3, characterized in that The reaction container includes a shell and a lid provided on the shell, wherein the lid is provided with a plurality of cover holes, wherein the cover holes can allow water vapor to be discharged and can limit the discharge of the graphene powder, and the reaction container meets at least one of the following characteristics: The diameter of the cover hole is 0.1-0.2 mm, and the hole density on the cover is 15-25 per cm 2 ; There is a gap between the housing and the cover, and the gap ranges from 0 to 0.2 mm; The thickness of the shell and the cover are both in the range of 5 to 10 mm.

12. The method according to any one of claims 1 to 3, characterized in that The method satisfies at least one of the following characteristics: The volume of the graphene powder to be dried in the reaction container does not exceed 80% of the volume of the reaction container; The bulk density of the dried graphene powder is ≤0.012 g / cm 3 ; The specific surface area of the dried graphene powder is ≥240m 2 / g; The preset temperature of the furnace in step S2 is 450-650°C; The heating time of the graphene powder to be dried is 1.5 to 2.5 hours; During the heating process of the furnace temperature in step S2, the process further includes: introducing an inert gas into the interior of the furnace tube so that the heating area of the heating source is in an inert atmosphere.

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