Preparation method of high-density graphite thick film

Abstract

The invention belongs to the field of functional films, and particularly relates to a preparation method of an integrated high-density graphite thick film. According to the preparation method, the upper surface and the lower surface of a single graphite film are subjected to functionalization treatment by using an auxiliary agent, so that the interfacial compatibility of the graphite film is improved, and the high-density graphite thick film is prepared by stacking a plurality of functionalized graphite films and then carrying out hot pressing treatment. According to the invention, functional groups and structural defects are introduced into the surface of the graphite film to promote interface fusion among multiple layers of graphite films, so that the integrated high-density and high-thickness graphite film is obtained. The method is simple in process, controllable in thickness layer number and easy in scale amplification, and widens the application range of the graphite film in the fields of thermal management, electromagnetic shielding, energy storage, nuclear technology and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of functional films, and particularly relates to a preparation method of an integrated high-density graphite thick film. BACKGROUND

[0002] High-quality graphite films have shown broad application value in the fields of electronic information, 5G communication, thermal management, etc. due to their high in-plane thermal conductivity (-2000 W / mK), low density (2.26 g / cm3), low thermal expansion coefficient and stable thermal chemical properties. With the increasing integration of electronic devices, the serious heat accumulation problem has gradually attracted people's attention, and the low heat dissipation flow of traditional low-thickness graphite films has been unable to meet the current demand. In order to improve the heat dissipation flow, high-thickness graphite films need to be prepared. However, with the existing film-forming and graphitization process of polymer-based graphite films and graphene films, it is difficult to maintain the alignment orientation of polymer molecular chains and graphene nanosheets at high thickness, so the thermal conductivity of the prepared graphite thick film will decrease significantly with the increase of thickness. And the current technology of bonding graphite films by commercial adhesives will produce more obvious interface thermal resistance in the structure of the graphite thick film, further affecting the performance of the graphite thick film. Therefore, under the premise of ensuring the thermal conductivity of the graphite film, how to prepare high-quality and high-density integrated graphite thick films is a problem that needs to be solved in this field. SUMMARY

[0003] In order to solve the problems in the prior art, the purpose of the present application is to provide a preparation method of an integrated high-density graphite thick film. The method fuses the interlayer interface of the graphite film by chemical functionalization of the surface of the graphite film and heat pressing treatment, so as to obtain a high-quality and high-density graphite thick film, thereby solving the problems of poor orientation and reduced thermal conductivity of the graphite film with the increase of thickness.

[0004] The design idea of the present application is:

[0005] The present application improves the interface bonding strength and interface carbon atom activity of the graphite film by surface functionalization modification treatment, and further promotes the diffusion of carbon atoms at the graphite interface by means of laminated heat pressing, so as to realize the interlayer structure fusion of the graphite film at high temperature and obtain a high-density graphite thick film.

[0006] In order to solve the above technical problems, the technical scheme of the present application is:

[0007] The present application provides a preparation method of a high-density graphite thick film, comprising the following steps:

[0008] (1) Functionalization treatment is performed on the upper and lower surfaces of the single-piece graphite film using an auxiliary agent to produce structural defects and functional groups on the surface of the graphite film, so as to improve the interface compatibility thereof;

[0009] (2) Stack at least two pieces of the graphite film treated in step (1) and make the interface between the film layers fuse by a lamination hot-pressing treatment to obtain a high-density graphite thick film.

[0010] Further, the graphite film raw material includes, but is not limited to, a pyrolytic carbon film prepared by a chemical vapor deposition method, a polymer film such as a polyimide film, a synthetic graphite film prepared by a carbonization and graphitization method, a graphene film prepared by a thermal reduction of an oxidized graphene film or an intrinsic graphene assembly method. The graphite film preparation method includes one or more combinations of a carbon source chemical vapor deposition method, a polymer film carbonization and graphitization method, a thermal reduction of an oxidized graphene film method, or an intrinsic graphene assembly method.

[0011] Further, the graphite film has a thickness ranging from 0.1 to 5000 μm and a density ranging from 1.0 to 2.26 g / cm 3 , and a C / O atomic ratio greater than 10.

[0012] Further, the functionalization type includes one or a combination of oxidation, amination, and sulfonation.

[0013] Further, in step (1), the functionalization treatment method includes one or a combination of a liquid functionalization etching, a plasma treatment, and an ozone treatment.

[0014] Further, for the liquid functionalization etching method, the functionalization treatment uses an auxiliary agent including one or a combination of sulfuric acid, nitric acid, hydrochloric acid, hydrogen peroxide, ammonia, urea, sulfur trioxide, chlorosulfonic acid, and fuming sulfuric acid.

[0015] Further, the high-density graphite thick film preparation method has a functionalization treatment temperature ranging from 20 to 200 °C and a treatment time of 0.1 to 100 h, i.e., for the liquid functionalization etching method, a functionalization treatment temperature ranging from 20 to 200 °C and a treatment time of 0.1 to 100 h; for the ozone treatment method, an ozone treatment time of 0.1 to 10 h and a treatment temperature ranging from 20 to 200 °C.

[0016] Further, the high-density graphite thick film preparation method has a functionalization treatment using a plasma treatment, and the plasma treatment has an atmosphere including one or a combination of hydrogen, oxygen, air, nitrogen, and argon and a power ranging from 10 to 500 W.

[0017] Further, the high-density graphite thick film preparation method has a functionalization treatment using an ozone treatment method, an ozone treatment time of 0.1 to 10 h, and a treatment temperature ranging from 20 to 200 °C.

[0018] Further, the preparation method of the high-density graphite thick film, the specific method for functionalizing the upper and lower surfaces of the graphite thin film using the auxiliary agent is selected from any one of the following methods:

[0019] Method one: heat treat the graphite thin film on a heating table at 120℃, and make the ozone gas generated by an ozone generator react with the graphite thin film in the atmospheric environment, and the treatment time is 0.5h;

[0020] Method two: place the graphite thin film in a plasma chamber, and etch and treat the graphite surface in one or a combined atmosphere of hydrogen, oxygen, air, nitrogen, and argon at a power of 200W for 0.1-0.5h;

[0021] Method three: place the graphite thin film in a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 7:3, and treat at 80℃ for 1h, then clean with deionized water after the treatment, and vacuum dry at 100℃ for 10h;

[0022] Method four: place the graphite thin film in a mixed solution of sulfuric acid and nitric acid with a volume ratio of 3:1, and heat treat at 80℃ for 5h to functionalize the surface with amino groups and oxidation, then clean with deionized water after the treatment, and vacuum dry at 100℃ for 10h.

[0023] Further, in the step (2) of the preparation method of the high-density graphite thick film, the heating mode in the heat pressing process includes one or a combination of resistance heating, induction heating, microwave heating, radiation heating, and Joule heating, the heating temperature ranges from 25-3300℃, the heating atmosphere includes one or a combination of vacuum, argon, nitrogen, hydrogen, and carbon dioxide, the temperature rising rate is 0.1-100℃ / min, the highest temperature holding time is 0.1-100h, and preferably, the heating temperature ranges from 100-3300℃, and the temperature rising rate is 1-20℃ / min.

[0024] Further, in the step (2), the pressing mode in the heat pressing process includes one or a combination of gas pressure, liquid pressure, and solid pressure, the applied pressure is 0.1-10GPa, and the pressing time is 0.1-10h.

[0025] Compared with the prior art, the application has the following advantages and beneficial effects:

[0026] 1、The present application utilizes the modification of the surface functionalization treatment of graphite thin film to produce structural defects and functional groups on the surface of graphite thin film, so that it has better interface bonding strength, improves the interface compatibility through the van der Waals force and hydrogen bond between the upper and lower surfaces of the graphite thin film, and the defect state graphene has lower diffusion activation energy than the perfect graphene, so that the interlayer carbon atom diffusion and rearrangement of the two layers of defect state graphene in contact with each other can effectively occur to realize the structural fusion between the interfaces, and the high-quality and high-density graphite thick film is prepared.

[0027] 2、The high-density graphite thick film prepared by the present application can effectively maintain the original high thermal conductivity of the graphite thin film, and the thermal conductivity can reach 1980W / mK, and after the interlayer fusion of the stacked high-temperature hot pressing treatment, the density is only reduced by 0.3% or less, and the thermal conductivity is only reduced by 1% or less.

[0028] 3、The present application has simple operation process, low cost and easy scale-up, and is suitable for the preparation and performance improvement of ultra-thick high-quality high-density graphite film, and expands the application range of graphite film in the fields of thermal management, electromagnetic shielding, nuclear technology and high-end instrument equipment. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The micro-interface structure schematic diagram of the high-density graphite thick film prepared for Example 1 under high-resolution transmission electron microscope.

[0030] Figure 2 The micro-interface structure schematic diagram of the high-density graphite thick film prepared for Example 2 under high-resolution transmission electron microscope.

[0031] Figure 3 The micro-interface structure schematic diagram of the high-density graphite thick film prepared for Comparative Example 1 under high-resolution transmission electron microscope. DETAILED DESCRIPTION

[0032] The present application prepares high-density and high-quality graphite thick film by the surface functionalization treatment modification of graphite thin film and the stacking hot pressing method, and the specific implementation process is as follows: high-quality graphite thin film is used as the stacking structure unit, the surface of the thin film is modified by chemical treatment to improve the interface compatibility, and the interface fusion between the graphite thin film layers is further promoted by hot pressing treatment, so that high-quality and high-density graphite thick film is obtained. After the surface functionalization modification and stacking hot pressing treatment, the density of the graphite thick film is reduced by 100% to 0.3%, and the thermal conductivity is reduced by 100% to 1%.

[0033] In the following, the present application is further described in detail through specific examples.

[0034] Example 1

[0035] In this embodiment, the preparation method of high-density high-quality graphite thick film includes the following steps:

[0036] (1) The graphite thin film prepared by two-layer chemical vapor deposition is used as a structural unit, the thickness of the graphite thin film is 1.0 μm, the density is 2.24 g / cm 3 , and the thermal conductivity is 1930 W / mK. The surface contact angle is 95°, and the surface C / O atomic ratio is 90.

[0037] (2) The graphite thin film is heated at 120°C on a heating table, and the ozone gas generated by the ozone generator is discharged to react with the graphite thin film in the atmospheric environment, and the treatment time is 0.5 h. The surface contact angle of the graphite thin film is 70° and 72°, respectively, and the surface C / O atomic ratio is 4.5.

[0038] (3) The functionalized surfaces of two graphite films are stacked and contacted, and are heat-pressed at 2200°C, 0.5 MPa pressure and in an argon atmosphere and are kept for 0.5 h to obtain a graphite thick film.

[0039] (4) The thickness of the graphite thick film is 2.0 μm, the density is 2.25 g / cm 3 , and the thermal conductivity is 1980 W / mK. The HRTEM cross-sectional structure corresponding to the interface of the graphite film is shown in Figure 1 , the surface functionalization and heat-pressing not only realize the interface fusion of the graphite film at high temperature, but also promote the structure repair, grain growth and interlayer structure densification of the graphite film, so that the density of the graphite thick film is increased by 0.5%, and the thermal conductivity is increased by 2.6%.

[0040] Figure 1 The micro-interface structure of the high-density graphite thick film prepared in this embodiment under high-resolution transmission electron microscopy is shown in the figure, and it can be seen from the figure that the two interfaces are highly fused, the carbon atom lattice of graphene is highly ordered along the c-axis direction, and there is no obvious gap between the interfaces.

[0041] Embodiment 2

[0042] In this embodiment, the preparation method of high-density high-quality graphite thick film includes the following steps:

[0043] (1) The graphite thin film prepared by two-layer chemical vapor deposition is used as a structural unit, the thickness of the graphite thin film is 1.0 μm, the density is 2.24 g / cm 3 , and the thermal conductivity is 1930 W / mK. The surface contact angle is 95°, and the surface C / O atomic ratio is 90.

[0044] (2) The graphite film is placed in a plasma chamber, and is subjected to etching treatment in an oxygen atmosphere at a power of 200 W for 0.5 h to oxidize the graphite surface. The average value of the contact angle of the graphite film surface is 78°, and the surface C / O atomic ratio is 4.4.

[0045] (3) The functionalized 10-layer graphite film is stacked in contact, and is subjected to hot-pressing treatment at 400°C, 0.2 MPa pressure, and in an argon atmosphere, and is kept for 0.2 h to obtain a graphite thick film.

[0046] (4) The thickness of the graphite thick film is measured to be 245 μm, the density is 2.21 g / cm 3 , and the thermal conductivity is 1735 W / mK. The surface hydrophilization and the hot-pressing treatment increase the density of the graphite thick film by 0.4%, and only reduce the thermal conductivity by 0.9%.

[0047] Figure 2 The micro-interface structure of the high-density graphite thick film prepared in this embodiment under high-resolution transmission electron microscopy is shown in the schematic diagram. As can be seen from the diagram, a high degree of fusion occurs between the two interfaces, and there is no obvious gap between the interfaces, and the integration between the two graphite film layers is successfully achieved.

[0048] Example 3

[0049] In this embodiment, the preparation method of the high-density high-quality graphite thick film comprises the following steps:

[0050] (1) One layer of polyimide-based graphite film and one layer of reduced graphene oxide film are used as structural units. The thickness of the polyimide-based graphite film is measured to be 25 μm, the density is 2.20 g / cm 3 , the thermal conductivity is 1750 W / mK, the surface contact angle is 98°, and the surface C / O atomic ratio is 76. The thickness of the reduced graphene oxide film is 28 μm, the density is 2.12 g / cm 3 , the thermal conductivity is 1680 W / mK, the surface contact angle is 87°, and the surface C / O atomic ratio is 20.

[0051] (2) The graphite film is placed in a concentrated sulfuric acid and hydrogen peroxide (volume ratio 7:3) mixed solution, and is treated at 80°C for 1 h. After the treatment, it is washed with deionized water, and then is vacuum dried at 100°C for 10 h. The surface contact angle of the polyimide-based artificial graphite film is measured to be 67°, and the surface C / O atomic ratio is 3.1. The surface contact angle of the reduced graphene oxide film is 65°, and the surface C / O atomic ratio is 2.7.

[0052] (3) The functionalized surfaces of the two graphite films are stacked in contact, and are subjected to hot-pressing treatment at 2000°C, 0.1 MPa pressure, and in an argon atmosphere, and are kept for 1 h to obtain a graphite thick film.

[0053] (4) The thickness of the graphite thick film is 52 μm, the density is 2.20 g / cm 3 , and the thermal conductivity is 1750 W / mK.

[0054] Example 4

[0055] In this embodiment, the preparation method of the high-density high-quality graphite thick film comprises the following steps:

[0056] (1) The thickness of the graphene film is 100 μm, the density is 2.15 g / cm 3 , and the thermal conductivity is 1700 W / mK. The surface contact angle is 96°, and the surface C / O atomic ratio is 80.

[0057] (2) The 20 pieces of graphite film are placed in a plasma chamber and etched in an air atmosphere at a power of 200 W for 0.5 h to oxidize the surface. The average value of the surface contact angle of the graphite film is 75°, and the surface C / O atomic ratio is 5.4.

[0058] (3) The functionalized graphene film is stacked in contact, and is heat-pressed at 3000°C, 0.4 MPa pressure, and in an argon atmosphere for 1 h to obtain a graphite thick film.

[0059] (4) The thickness of the graphite thick film is 1995 μm, the density is 2.16 g / cm 3 , and the thermal conductivity is 1745 W / mK. The surface functionalization and heat-pressing treatment increase the density of the graphite thick film by 0.5%, and increase the thermal conductivity by 2.6%.

[0060] Example 5

[0061] In this embodiment, the preparation method of the high-density high-quality graphite thick film comprises the following steps:

[0062] (1) The thickness of the graphene film is 100 μm, the density is 1.45 g / cm 3 , and the thermal conductivity is 10 W / mK. The surface contact angle is 85°, and the surface C / O atomic ratio is 20.

[0063] (2) The 5 pieces of graphite film are placed in a sulfuric acid-nitric acid (volume ratio 3:1) mixed solution, and are heat-treated at 80°C for 5 h to functionalize the surface with amino groups and oxidation. After washing with deionized water, vacuum drying is performed at 100°C for 10 h. The average value of the surface contact angle of the graphite film is 60°, the surface C / O atomic ratio is 7.2, and the C / N atomic ratio is 5.6.

[0064] (3) The functionalized five-layer graphene film stack was contacted, and heat-pressed at 2800℃, 0.1 MPa pressure, and in an argon atmosphere for 0.5 h, to obtain a graphite thick film.

[0065] (4) The graphite thick film had a thickness of 494 μm, a density of 2.18 g / cm 3 , and a thermal conductivity of 1820 W / mK. The surface functionalization and heat-pressing increased the density of the graphite thick film by 50%, and the thermal conductivity by 180 times.

[0066] Example 6

[0067] This example provides a method for preparing a high-density graphite thick film, and the specific steps are as follows:

[0068] (1) A three-layer chemical vapor deposition method was used to prepare a graphite thin film as a structural unit. The graphite thin film had a thickness of 50 μm, a density of 2.22 g / cm 3 , and a thermal conductivity of 1850 W / mK. The surface contact angle was 98°, and the surface C / O atomic ratio was 85.

[0069] (2) The graphite thin film was placed in a mixed solution of fuming sulfuric acid and chlorosulfonic acid at a volume ratio of 5:1, and was treated at 60℃ for 2 h for sulfonation. After treatment, the graphite thin film was repeatedly washed with deionized water until the pH value was neutral, and then was vacuum dried at 80℃ for 12 h. The surface contact angle of the graphite thin film was reduced to 55°, the surface C / O atomic ratio was reduced to 3.8, and the presence of sulfonic groups (-SO3H) was detected by FTIR characterization.

[0070] (3) Three sulfonated graphite thin films were stacked, with the functionalized surfaces in contact, and were heat-pressed at 2500℃, 0.8 MPa pressure, and in an argon atmosphere for 2 h, to obtain a graphite thick film.

[0071] (4) The graphite thick film had a final thickness of 148 μm, a density of 2.23 g / cm 3 (0.45% higher than the raw material), and a thermal conductivity of 1870 W / mK (1.1% higher than the raw material).

[0072] Comparative Example 1

[0073] In this comparative example, the method for preparing a graphite thick film included the following steps:

[0074] (1) A three-layer polyimide-based graphite film was used as a structural unit. The polyimide-based graphite thin film had a thickness of 25 μm, a density of 2.20 g / cm 3 , a thermal conductivity of 1750 W / mK, a surface contact angle of 100°, and a surface C / O atomic ratio of 76.

[0075] (2) The polyimide-based graphite film is not subjected to functional modification treatment.

[0076] (3) The three-layer polyimide-based graphite film is stacked and contacted, and is subjected to hot-pressing treatment under an argon atmosphere at 2800°C and a pressure of 0.1 MPa and is kept for 0.1 h to obtain a graphite thick film.

[0077] (4) The graphite thick film has a thickness of 80 μm, a density of 2.06 g / cm 3 , and a thermal conductivity of 1665 W / mK. Figure 3 The HRTEM cross-sectional structure of the graphite thick film prepared in this example at the interface of the corresponding graphite thick film is shown in the figure. It can be seen that the graphite film not subjected to surface functionalization treatment cannot be well fused at most regions after hot-pressing treatment.

[0078] Comparative Example 2

[0079] In the comparative example, the graphite thick film is prepared by the following steps:

[0080] (1) The three-layer polyimide-based graphite film is used as a structural unit, and the polyimide-based graphite film has a thickness of 25 μm, a density of 2.20 g / cm 3 , a thermal conductivity of 1750 W / mK, a surface contact angle of 100°, and a surface C / O atomic ratio of 76.

[0081] (2) The polyimide-based graphite film is placed on a heating table and is subjected to heat treatment at 150°C, and ozone gas generated by an ozone generator is led out and reacted with the graphite film in an atmospheric environment for 0.5 h. The graphite film has an average surface contact angle of 72° and an average surface C / O atomic ratio of 6.0.

[0082] (3) The three-layer polyimide-based graphite film is stacked and contacted, and is subjected to hot-pressing treatment under an argon atmosphere at 1500°C and a normal pressure and is kept for 1 h to obtain a graphite thick film.

[0083] (4) The graphite thick film has a thickness of 75 μm, a density of 2.20 g / cm 3 , and a thermal conductivity of 1758 W / mK. The graphite film subjected to surface functionalization treatment can still be fused at a normal pressure, and the graphite thick film has an unchanged density and a thermal conductivity increased by 0.5% under the action of high-temperature hot-pressing treatment.

[0084] Comparative Example 3

[0085] In the comparative example, the graphite thick film is prepared by the following steps:

[0086] (1) The thickness of the polyimide-based graphite film is 25 μm, the density is 2.20 g / cm 3 , the thermal conductivity is 1750 W / mK, the surface contact angle is 100°, and the surface C / O atomic ratio is 76.

[0087] (2) The polyimide-based graphite film is heated at 150°C on a heating table, and the ozone gas generated by an ozone generator is led out to react with the graphite film in the atmospheric environment for 0.5 h. The average value of the surface contact angle of the graphite film is 72°, and the average value of the surface C / O atomic ratio is 6.0.

[0088] (3) The three-layer polyimide-based graphite film is laminated and contacted, and is pressed at 30°C for 1 h under a pressure of 0.1 MPa to obtain a graphite thick film.

[0089] (4) The thickness of the graphite thick film is 75 μm, the density is 2.20 g / cm 3 , and the thermal conductivity is 1680 W / mK. The graphite film after the surface functionalization treatment can maintain good interface contact after the pressurization treatment at 30°C, and the density of the obtained graphite thick film is unchanged, but the thermal conductivity is reduced by 4% due to the surface oxidation treatment, which indicates that the heat treatment can effectively promote the repair and fusion of the interface structure and the in-plane structure, and further improve the crystallization quality and thermal conductivity of the graphite film.

[0090] The specific embodiments of the present application are described above. It should be understood that the present application is not limited to the specific embodiments described above, and various modifications or changes can be made by those skilled in the art within the scope of the claims, which do not affect the essential content of the present application.

Claims

1. A method for preparing a high-density graphite thick film, characterized in that: The following steps are involved: (1) The upper and lower surfaces of a single graphite film are functionalized with an additive to generate structural defects and functional groups on the surface of the graphite film to improve its interfacial compatibility; (2) stacking at least two graphite films processed in step (1), and performing a lamination hot pressing process to cause interface fusion between the film layers to obtain a highly dense graphite thick film.

2. The method for preparing a high-density graphite thick film according to claim 1, wherein The preparation method of the graphite film includes one or more combinations of carbon source chemical vapor deposition method, polymer film carbonization and graphitization method, graphene oxide film thermal reduction method or intrinsic graphene assembly method.

3. The method for preparing a high-density graphite thick film according to claim 2, wherein: The thickness of graphite film ranges from 0.1 to 5000 μm, and the density of graphite film ranges from 1.0 to 2.26 g / cm 3 , the C / O atomic ratio of the graphite film is greater than 10.

4. The method for preparing a high-density graphite thick film according to claim 1, wherein The functionalization type includes oxidation, amination, sulfonation or a combination thereof.

5. The method for preparing a high-density graphite thick film according to claim 1, wherein In step (1), the functionalization treatment method includes one or a combination of liquid phase functionalization etching, plasma treatment, and ozone treatment.

6. The surface functionalization treatment method according to claim 5, characterized in that: For the liquid phase functionalization etching method, the auxiliary agent used in the functionalization treatment includes one or a combination of sulfuric acid, nitric acid, hydrochloric acid, hydrogen peroxide, ammonia water, urea, sulfur trioxide, chlorosulfonic acid, and fuming sulfuric acid.

7. The method for preparing a high-density graphite thick film according to claim 5, wherein: The functionalization treatment temperature ranges from 20 to 200° C., and the treatment time ranges from 0.1 to 100 hours.

8. The method for preparing a high-density graphite thick film according to claim 5, wherein: The functionalization treatment adopts plasma treatment, the atmosphere of the plasma treatment is one or a combination of hydrogen, oxygen, air, nitrogen, and argon, and the power range is 10 to 500W.

9. The method for preparing a high-density graphite thick film according to claim 1, wherein: In step (2), the heating method in the hot pressing process includes one or a mixture of resistance heating, induction heating, microwave heating, radiation heating, and Joule heating, the heating temperature range is 25 to 3300°C, the heating atmosphere includes one or a mixture of vacuum, argon, nitrogen, hydrogen, and carbon dioxide, the heating rate is 0.1 to 100°C / min, and the maximum temperature holding time is 0.1 to 100h.

10. The method for preparing a high-density graphite thick film according to claim 1, wherein: In step (2), the pressurizing method during the hot pressing process includes one or a combination of air pressure, hydraulic pressure, and solid pressure, the applied pressure is 0.1 to 10 GPa, and the pressing time is 0.1 to 10 hours.

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