Method for producing highly oriented graphite-coated carbon-based material

Abstract

To provide a method for producing a highly oriented graphite-coated carbonaceous material by which a highly oriented graphite coating having a high degree of graphitization can be formed by a simple method.SOLUTION: A method for producing a highly oriented graphite-coated carbon-based material, comprising an assembling step of obtaining an assembly in which a metal layer is adhered to a surface of a carbon-based base material, a heating step of heating the assembly to 800 °C to 1800 °C, a cooling step of cooling the assembly, and a removing step of removing the metal layer from the cooled assembly, wherein a metal constituting the metal layer has a solid solution region on the metal side in a carbon-metal binary phase diagram.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a highly oriented graphite-coated carbon-based material. [Background technology]

[0002] Carbon-based materials, including graphite, pyrolytic carbon, C / C composites, and glassy carbon, are widely used in high-temperature, metallurgical, and semiconductor fields because carbon itself has high heat resistance and chemical stability.

[0003] Generally, the higher the degree of graphitization of graphite material, the less oxidizable and chemically stable it is. This is because the most common crystalline structure of carbon is a highly anisotropic hexagonal system crystalline structure consisting of the a-axis direction along which hexagonal mesh planes bonded by covalent bonds extend, and the c-axis direction along which the hexagonal mesh planes are bonded by van der Waals forces. Furthermore, as graphitization progresses, the crystals grow, increasing the number of basal planes and decreasing the number of edge planes. While the basal planes are extremely unreactive, the edge planes are composed of unsaturated sp 2 Because it has electrons, it is easily attacked and is more reactive than the basal surface.

[0004] Taking into account the characteristics of such carbon-based materials, Patent Document 1 describes a method for producing a pyrolytic carbon-coated graphite material with better oxidation resistance and reactivity resistance, in which a graphite substrate is coated with 2.0 g / cm at a temperature of 1600-2200°C. 3 The document describes a method for producing a pyrolytic carbon-coated graphite material, which is characterized by coating the material with pyrolytic carbon having a bulk density of 1000 or more and then heat-treating the material at a temperature of 2500°C or higher. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 63-210088 Summary of the Invention [Problem to be solved by the invention]

[0006] The invention described in Patent Document 1 produces a pyrolytic carbon-coated graphite material with excellent oxidation resistance and reactivity resistance by treating it at high temperatures, but as the temperature rises, the vapor pressure of carbon increases, and the sublimation temperature is reached at around 3600°C. When carbon begins to sublimate from the surface, the rearranged carbon atoms on the surface become disordered, and the carbon atoms themselves volatilize, so there is a limit to how much the treatment temperature can be increased to produce a highly crystalline pyrolytic carbon coating (highly oriented graphite coating). Furthermore, increasing the temperature requires a large amount of energy.

[0007] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method for producing a highly-oriented graphite-coated carbon-based material, which can form a highly-oriented graphite coating with a high degree of graphitization by a simple method. [Means for solving the problem]

[0008] The method for producing a highly oriented graphite-coated carbon-based material of the present invention comprises an assembling step of obtaining an assembled body in which a metal layer is adhered to the surface of a carbon-based substrate, a heating step of heating the assembled body to 800°C to 1800°C, a cooling step of cooling the assembled body, and a removal step of removing the metal layer from the cooled assembled body, wherein the metal constituting the metal layer has a solid solution region on the metal side in a carbon-metal binary phase diagram.

[0009] In the method for producing a highly oriented graphite-coated carbon-based material of the present invention, in the combining step, the metal layer is preferably adhered to the carbon-based substrate by electroplating, electroless plating, or physical vapor deposition.

[0010] In the method for producing a highly oriented graphite-coated carbon-based material of the present invention, the metal is preferably Ni or Fe.

[0011] In the method for producing a highly oriented graphite-coated carbon-based material of the present invention, the heating temperature in the heating step is preferably equal to or lower than the eutectic temperature of the region where the solid solution of the metal and carbon and the liquid phase coexist.

[0012] In the method for producing a highly oriented graphite-coated carbon-based material of the present invention, the thickness of the metal layer is preferably 100 μm or less.

[0013] In the method for producing a highly oriented graphite-coated carbon-based material of the present invention, the carbon-based substrate is preferably made of at least one material selected from the group consisting of graphite, a C / C composite material, pyrolytic carbon, and glassy carbon. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram showing an example of a process flow of the method for producing a highly oriented graphite-coated carbon-based material of the present invention. [Figure 2] FIG. 2 is a Ni-C binary phase diagram. [Figure 3] FIG. 3 is a stable Fe-C binary phase diagram. [Figure 4] FIG. 4 is a process flow diagram schematically illustrating an example of the peeling step. [Figure 5] FIG. 5 shows Raman spectra of the surfaces of the highly oriented graphite-coated carbon-based materials according to Examples 1 to 3 and Comparative Example 2 and the surface of the carbon-based substrate. [Figure 6] FIG. 6 is a diagram showing the relationship between the peak intensity ratio (D / G) in the Raman spectrum shown in FIG. 5 and the heating temperature. [Figure 7] FIG. 7 shows X-ray diffraction patterns of the surfaces of the carbon-based substrate, the metal layer, and the highly-oriented graphite-coated carbon-based material in Example 1, and the surface of the carbon-based substrate in Comparative Example 1 before and after heating. [Figure 8] FIG. 8 is an enlarged photograph of the surface of the metal layer in Example 1 before the heating step, observed with a scanning electron microscope. [Figure 9]FIG. 9 is an enlarged photograph of the surface of the highly oriented graphite-coated carbon-based material according to Example 2, observed with a scanning electron microscope. [Figure 10] FIG. 10 is an enlarged photograph of the surface of the highly oriented graphite-coated carbon-based material according to Example 1, observed with a scanning electron microscope. [Figure 11] FIG. 11 is an enlarged photograph of the surface of the highly oriented graphite-coated carbon-based material according to Example 3, observed with a scanning electron microscope. [Figure 12] FIG. 12 is an enlarged photograph of the surface of the highly oriented graphite-coated carbon-based material according to Comparative Example 2, observed with a scanning electron microscope. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be appropriately modified and applied within the scope of the present invention.

[0016] [Method for producing highly oriented graphite-coated carbon-based materials] The method for producing a highly oriented graphite-coated carbon-based material of the present invention comprises an assembling step of obtaining an assembled body in which a metal layer is adhered to the surface of a carbon-based substrate, a heating step of heating the assembled body to 800°C to 1800°C, a cooling step of cooling the assembled body, and a removal step of removing the metal layer from the cooled assembled body, wherein the metal constituting the metal layer has a solid solution region on the metal side in a carbon-metal binary phase diagram.

[0017] FIG. 1 is a diagram showing an example of a process flow of the method for producing a highly oriented graphite-coated carbon-based material of the present invention. As shown in FIG. 1, the method for producing a highly oriented graphite-coated carbon-based material of the present invention includes an assembling step of obtaining an assembled body in which a metal layer is adhered to one surface of a carbon-based substrate, a heating step of heating the assembled body at 800 to 1800°C, a cooling step of cooling the assembled body, and a removal step of removing the metal layer from the cooled assembled body.

[0018] The method for producing a highly oriented graphite-coated carbon-based material shown in FIG. 1 includes a combining step S1, a heating step S2, a cooling step S3, and a removing step S4.

[0019] In the combining step S1, the metal layer 20 is adhered to the surface of the carbon-based substrate 10 to obtain the combined body 100.

[0020] In the heating step S2, the combined body 100 is heated at 800°C to 1800°C. When the combined body 100 is heated at 800° C. to 1800° C., carbon atoms and metal atoms interpenetrate at the contact interface between the carbon-based substrate 10 and the metal layer 20 to form a solid solution layer 40 .

[0021] In the cooling step S3, the heated combined body 100 is cooled. When the heated combined body 100 is cooled, the solid solubility of carbon in the solid solution decreases, the solid solution layer 40 separates, and carbon atoms precipitate at the interface between the carbon-based substrate 10 and the metal layer 20. At this time, rearrangement of the carbon atoms occurs, and a highly oriented graphite layer (highly oriented graphite coating) 50, which is a graphite layer with a high degree of crystallinity (degree of graphitization), is formed on the surface of the carbon-based substrate 10.

[0022] In the removal step S4, the metal layer 20 is removed from the combined body 100. By removing the metal layer 20 from the combined body 100 that has undergone the heating step S2 and the cooling step S3, a highly-oriented graphite-coated carbon-based material 1 consisting of the carbon-based substrate 10 and the highly-oriented graphite layer 50 formed on the surface of the carbon-based substrate 10 can be obtained.

[0023] Hereinafter, each step constituting the method for producing a highly oriented graphite-coated carbon-based material of the present invention will be described.

[0024] [Combination process] In the combining step, a combined body is obtained in which the metal layer is adhered to the surface of the carbon-based substrate.

[0025] The method for adhering a metal layer to the surface of a carbon-based substrate is not particularly limited, but examples thereof include electroplating, electroless plating, and physical vapor deposition. When electroplating, electroless plating, or physical vapor deposition is used, sufficient adhesion between the metal layer and the carbon-based substrate can be ensured, making it easier to form a solid solution layer in the heating step.

[0026] In the combining step, the carbon-based substrate and the metal layer may simply be brought into contact (overlapped together). In this case, it is preferable to flatten the surface of the carbon-based substrate (the surface in contact with the metal layer) and the surface of the metal layer (the surface in contact with the carbon-based substrate), since this ensures adhesion between the carbon-based substrate and the metal layer.

[0027] (carbon-based substrate) The carbon-based substrate is a substrate mainly composed of carbon, and serves as a substrate on which a highly oriented graphite layer, which will be described later, is formed. The shape of the carbon-based substrate is not particularly limited, and may be, for example, a plate-like shape or a shape having recesses or protrusions.

[0028] The carbon-based substrate is preferably made of at least one material selected from the group consisting of graphite, a C / C composite material, pyrolytic carbon, and glassy carbon. The above material has a high carbon concentration, and therefore can form a good highly oriented graphite layer.

[0029] (metal layer) The metal layer is a layer made of a metal that is brought into close contact with the surface of the carbon-based substrate.

[0030] The metal constituting the metal layer has a solid solution region on the metal side in the carbon-metal binary phase diagram. The "metal side" refers to the region in the carbon-metal binary system where the metal is the main component (where the metal accounts for the majority of the weight).

[0031] The above metal preferably has a solid solution region in the high temperature region (for example, 800° C. or higher) in the carbon-metal binary phase diagram, but does not have a solid solution region at room temperature (25° C.).

[0032] When a metal that does not form a solid solution at all in a carbon-metal binary phase diagram is used, i.e., when the metal does not have a solid solution region, carbon does not dissolve in the metal in the heating step described below, and precipitation of carbon atoms and rearrangement of carbon during cooling are unlikely to occur. Therefore, the formation of a highly oriented graphite layer due to rearrangement of carbon is unlikely to occur. In this specification, not having a solid solution region does not exclude the case where there is no solid solution region at all, but it is sufficient that the solid solubility limit at room temperature (25°C) is overwhelmingly smaller than the solid solubility limit at the eutectic temperature in the region where a solid solution of metal and carbon and a liquid phase coexist, for example, 1 / 10,000 or less.

[0033] In the carbon-metal binary phase diagram, if a solid solution phase exists at room temperature as well as in the high-temperature region, the solid solution phase formed during the heating process will be maintained during cooling, making it difficult for carbon atoms to precipitate or rearrange. Therefore, the formation of highly oriented graphite layers due to carbon rearrangement is unlikely.

[0034] In the carbon-metal binary phase diagram, examples of metals that have a solid solution region on the metal side include Ni and Fe.

[0035] Among these, Ni is preferred because Ni carbide does not exist in the phase diagram and compounds such as NiC are not easily produced. In the phase diagram with carbon (binary phase diagram), Ni and Fe have a solid solution region on the metal side at high temperatures above 800°C, but no solid solution region exists at room temperature. This facilitates the formation of a carbon-metal solid solution during the heating process and the reprecipitation (rearrangement) of carbon atoms upon cooling.

[0036] The thickness of the metal layer is preferably 100 μm or less. When the thickness of the metal layer is 100 μm or less, the metal layer can be plastically deformed and peeled off little by little, which makes it easier to remove the metal layer in the removal step. Furthermore, even when the heating step is performed at a temperature equal to or higher than the melting point of the metal constituting the metal layer, if the thickness of the metal layer is 100 μm or less, the metal layer deforms into a ball shape on the surface of the carbon-based substrate, thereby preventing excessive contact between the carbon-based substrate and the metal layer during the heating step and excessive penetration of metal atoms into the solid solution layer. Furthermore, the metal deformed into a ball shape is easy to remove. Furthermore, by tilting the carbon-based substrate or orienting the metal layer side downward, most of the metal layer falls after melting, making it easier to remove.

[0037] [Heating process] In the heating step, the combined body is heated at 800°C to 1800°C. A solid solution layer is formed at the contact interface between the carbon-based substrate and the metal layer by heating the combined body 100 at 800°C to 1800°C. The solid solution layer is also called an intrusion layer because it is formed by carbon atoms intruding into the metal layer or metal atoms intruding into the carbon-based substrate.

[0038] Since the heating temperature in the heating step is 800°C to 1800°C, less energy is required compared to the method described in Patent Document 1, in which heating is performed at a temperature of 2500°C or higher. Furthermore, heating devices for heating at temperatures of 2500°C or higher tend to be large and suffer significant wear and tear on various components due to heat, but heating devices for heating at temperatures between 800°C and 1800°C can be small.

[0039] The heating temperature in the heating step may be adjusted as appropriate depending on the type of metal constituting the metal layer. For example, the heating temperature in the heating step is preferably equal to or lower than the melting point of the metal constituting the metal layer. When the heating temperature in the heating step is equal to or lower than the melting point of the metal, the metal layer is less likely to melt at locations other than the contact interface between the carbon-based substrate and the metal layer, and excessive penetration of metal atoms into the carbon-based substrate can be prevented, resulting in less metal remaining in the highly oriented graphite layer.

[0040] The heating temperature in the heating step is preferably equal to or lower than the eutectic temperature in the region where a metal-carbon solid solution and a liquid phase coexist in a carbon-metal binary phase diagram. If the heating temperature in the heating step is equal to or lower than the eutectic temperature in the region where a metal-carbon solid solution and a liquid phase coexist, the highly oriented graphite layer is formed solely by solid-phase diffusion without the involvement of a liquid phase, and metal atoms penetrate deep into the carbon-based substrate, making it difficult for carbon particles to become liberated. As a result, metal atoms are less likely to remain in the highly oriented graphite layer during the cooling step.

[0041] The temperature rise rate in the heating step is preferably 100°C / h to 300°C / h. If the heating rate is too high, the temperature at the contact interface between the carbon-based substrate and the metal layer may overshoot, making it difficult to form a solid solution layer, whereas if the heating rate is too low, excessive energy consumption results in poor energy efficiency.

[0042] The formation of solid solutions and the solubility limit in a carbon-metal binary system will be explained with reference to FIGS. 2 and 3.

[0043] FIG. 2 is a Ni-C binary phase diagram. The leftmost composition contains 100 wt% Ni, and the carbon content increases toward the right. As shown in Figure 2, Ni-C can form a Ni-C solid solution (γ solid solution in the region indicated by γ in Figure 2) containing a maximum of 0.56 wt% (2.70 atm% in atomic weight ratio) of carbon. In other words, at the eutectic temperature (1320°C) in the region where the solid solution of Ni and carbon coexists with the liquid phase, the solid solubility limit reaches its maximum value, which is 0.56 wt%. That is, it is understood that Ni has a solid solution region on the metal side in the carbon-metal binary phase diagram.

[0044] For example, if the metal layer is made of Ni, when the combined body is heated to around 1320°C, the eutectic temperature where a solid solution of Ni and carbon and a liquid phase coexist, the carbon atoms that make up the carbon-based substrate diffuse (penetrate) into the metal layer at the contact interface between the carbon-based substrate and the metal layer, forming a Ni-C solid solution (γ solid solution) containing up to 0.56 wt% carbon atoms. When cooled, the Ni-C phase precipitates as a single phase. At this time, the precipitated carbon atoms rearrange to form a highly oriented graphite layer.

[0045] For example, if the heating temperature in the heating step exceeds the eutectic temperature of 1,320°C, the metal layer will first liquefy little by little while forming a solid solution with carbon. If the melting rate is uneven, particles will fall off on the carbon substrate side, causing the surface to become rough. In such a case, metal atoms remain on the carbon-based substrate during cooling, and the metal is likely to be left behind in the deposited graphite coating. Furthermore, if the heating temperature in the heating step exceeds the melting point of Ni, the solubility of carbon in liquid Ni increases, making it easier for carbon particles to become liberated in the Ni melt, and making the surface more prone to roughening. Therefore, when the metal constituting the metal layer is Ni, the heating temperature in the heating step is preferably below the melting point of Ni, and further preferably below the eutectic temperature in the region where a solid solution of Ni and carbon and a liquid phase coexist.

[0046] FIG. 3 is a stable Fe-C binary phase diagram. In the Fe-C component system, the stable system is graphite on the carbon side, and the metastable system is Fe3C. The leftmost composition contains 100 wt% Fe, and the carbon (graphite) content increases toward the right. As shown in Figure 3, Fe-C can form Fe-C solid solutions containing up to 2.11 wt% carbon (α solid solution in the region indicated by α, α + γ solid solution in the region indicated by α + γ, and γ solid solution in the region indicated by γ in Figure 3). In other words, at the eutectic temperature (1153°C) in the region where the solid solution of Fe and carbon and the liquid phase coexist, the solid solubility limit shows a maximum value of 2.11 wt%. In other words, Fe can be said to have a solid solution region on the metal side in the carbon-metal binary phase diagram.

[0047] If the heating temperature in the heating step exceeds the eutectic temperature of 1153°C, the metal layer will first liquefy little by little while forming a solid solution with carbon. If the melting rate is uneven, particles will fall off on the carbon substrate side, causing the surface to become rough. In such a case, metal atoms remain on the carbon-based substrate during cooling, and the metal is likely to be left behind in the deposited graphite coating. Furthermore, if the heating temperature in the heating step exceeds the melting point of Fe, the solubility of carbon in liquid Fe increases, making it easier for carbon particles to become liberated in the Fe melt, and making the surface more prone to roughening. Therefore, when the metal constituting the metal layer is Fe, the heating temperature in the heating step is preferably below the melting point of Fe, and further below the eutectic temperature in the region where a solid solution of Fe and carbon and a liquid phase coexist.

[0048] In the Fe-C binary phase diagram (stable system) shown in FIG. 3, the eutectic temperature between the liquid phase and the solid phase is 1153°C.

[0049] The holding time at the maximum temperature in the heating step is preferably 1 hour to 12 hours. If the holding time is less than 1 hour, the diffusion of carbon atoms into the metal layer hardly progresses, and a solid solution layer may not be formed sufficiently. If the holding time exceeds 12 hours, the diffusion of carbon atoms into the metal layer proceeds too much, which makes it easier for carbon particles to be liberated and causes the surface to become rough.

[0050] [Cooling process] In the cooling step, the assembly is cooled. When the combined body is cooled after the heating process, the solubility of carbon in the solid solution decreases, the solid solution layer (intercalation layer) separates, and carbon atoms precipitate at the interface between the carbon-based substrate and the metal. At this time, the carbon atoms rearrange, forming a graphite layer (graphite film) with a high degree of crystallinity (graphitization).

[0051] In the cooling step, the assembly that has been subjected to the heating step is preferably cooled to room temperature, where room temperature means, for example, 25°C. The cooling rate in the cooling step is not particularly limited, but natural cooling is preferred to promote rearrangement of carbon (graphite).

[0052] [Removal process] In the removal step, the metal layer is removed from the cooled combination. The combined product that has been subjected to the heating and cooling steps is subjected to a removal step in which the metal layer disposed on the surface of the carbon-based substrate is removed, thereby obtaining a carbon-based substrate having a highly oriented graphite layer formed on the surface thereof, i.e., a highly oriented graphite-coated carbon-based material. At this time, the highly oriented graphite layer has a high degree of graphitization, so that peeling is likely to occur within the highly oriented graphite layer.

[0053] The method for removing the metal layer from the combined body is not particularly limited, but examples include removal by mechanical force (for example, with a metal spatula, bamboo spatula, sandpaper, or blade) and removal by laser irradiation. In the removal step, it is not necessary to remove the entire metal layer disposed on the surface of the carbon-based substrate.

[0054] By the above procedure, a highly oriented graphite-coated carbonaceous material can be obtained.

[0055] [Peeling process] The obtained highly oriented graphite layer is oriented in a direction parallel to the surface of the carbon-based substrate (plane direction), and therefore can be easily peeled off from the carbon-based substrate by applying a mechanical force. The highly oriented graphite layer peeled off from the carbon-based substrate has the same crystal structure as graphite and corresponds to so-called graphene. Therefore, graphene can be obtained by carrying out a peeling step of peeling off the highly oriented graphite layer from the surface of the highly oriented graphite-coated carbon-based material obtained in the above step.

[0056] In other words, a method that includes the above-mentioned peeling step in addition to the combining step, heating step, cooling step, and removing step that constitute the method for producing a highly oriented graphite-coated carbon-based material of the present invention is also a method for producing graphene.

[0057] FIG. 4 is a process flow diagram schematically illustrating an example of the peeling step. As shown in FIG. 4, in the peeling step S5, the highly oriented graphite layer 50 is peeled off from the surface of the highly oriented graphite-coated carbon-based material 1, thereby obtaining graphene 51.

[0058] As a method for peeling off the highly oriented graphite layer from the surface of the highly oriented graphite-coated carbon-based material, for example, a method in which an adhesive tape is used and the adhesive layer is removed with a solvent or the like can be mentioned.

[0059] The present specification discloses the following:

[0060] The present disclosure (1) provides a method for manufacturing a carbon-based substrate by combining a metal layer and a carbon-based substrate. a heating step of heating the combined body to 800°C to 1800°C; a cooling step of cooling the combined body; a removing step of removing the metal layer from the cooled combination; The method for producing a highly oriented graphite-coated carbon-based material is characterized in that the metal constituting the metal layer has a solid solution region on the metal side in a carbon-metal binary phase diagram.

[0061] The present disclosure (2) is the method for producing a highly-oriented graphite-coated carbon-based material according to the present disclosure (1), wherein in the combining step, the metal layer is adhered to the carbon-based substrate by an electroplating method, an electroless plating method, or a physical vapor deposition method.

[0062] The present disclosure (3) is a method for producing a highly oriented graphite-coated carbon-based material in any combination with any of the present disclosures (1) and (2), in which the metal is Ni or Fe.

[0063] The present disclosure (4) is a method for producing a highly oriented graphite-coated carbon-based material in any combination with any of the present disclosures (1) to (3), wherein the heating temperature in the heating step is equal to or lower than the eutectic temperature of a region where the solid solution of the metal and carbon and a liquid phase coexist.

[0064] The present disclosure (5) is a method for producing a highly oriented graphite-coated carbon-based material in any combination with any of the present disclosures (1) to (4), wherein the thickness of the metal layer is 100 μm or less.

[0065] The present disclosure (6) is a method for producing a highly oriented graphite-coated carbon-based material in any combination with any of the present disclosures (1) to (5), wherein the carbon-based substrate is made of at least one material selected from the group consisting of graphite, a C / C composite, pyrolytic carbon, and glassy carbon.

[0066] [Example] EXAMPLES Hereinafter, examples will be given that more specifically disclose the present invention, but the present invention is not limited to these examples.

[0067] Example 1 (Combination process) Isotropic graphite material ET-10 (Φ10×2 mm) manufactured by Ibiden Co., Ltd. was used as the carbon-based substrate, and a metal layer (thickness 10 μm) made of Ni was formed on the surface by electroless plating and adhered to the surface to prepare an assembly.

[0068] (Heating process) The assembly was then heated to 1400° C. in an inert atmosphere (argon atmosphere). The temperature was increased at a rate of 200°C / h, and the holding time at 1400°C was set to 2 hours.

[0069] (cooling process) Next, the assembly that had undergone the heating step was cooled by natural cooling, and it took 24 hours for it to cool to room temperature.

[0070] (Removal process) The metal layer was then removed from the combined body that had undergone the heating process. The metal layer was melted by the heating step and deformed into a ball shape, and adhered to the surface of the carbon-based substrate. Metal deposits on the surface of the carbon-based substrate were removed by mechanical force using a blade to obtain a highly oriented graphite-coated carbon-based material.

[0071] Example 2 A highly oriented graphite-coated carbon-based material was obtained in the same manner as in Example 1, except that the heating temperature in the heating step was changed to 1000°C.

[0072] Example 3 A highly oriented graphite-coated carbon-based material was obtained in the same manner as in Example 1, except that the heating temperature in the heating step was changed to 1600°C.

[0073] (Comparative Example 1) The carbon substrate with the pyrolytic carbon coating was heated at 3000°C in an inert atmosphere to promote crystallization of the pyrolytic carbon. The size of the carbon substrate was 20 × 20 × 0.1 mm, and the thickness of the pyrolytic carbon coating was 40 μm.

[0074] (Comparative Example 2) A highly oriented graphite-coated carbon-based material was obtained in the same manner as in Example 1, except that the heating temperature in the heating step was changed to 2000°C.

[0075] (Raman spectroscopy analysis) Raman spectroscopy was measured on the surfaces of the highly oriented graphite-coated carbon-based materials according to Examples 1 to 3 and Comparative Example 2, and on the surface of the carbon-based substrate according to Example 1. The conditions for Raman spectroscopy were set as follows. The results are shown in Figure 5. [Raman Spectroscopic Conditions] Measurement equipment: Horiba Ltd., Microscopic Laser Raman Spectrometer LabRAM HR800 Excitation wavelength: 632.81 nm

[0076] FIG. 5 shows Raman spectra of the surfaces of the highly oriented graphite-coated carbon-based materials according to Examples 1 to 3 and Comparative Example 2 and the surface of the carbon-based substrate. From Figure 5, the G band (1580 cm ) originating from the basal plane of graphite is -1 It can be seen that the surfaces of the highly oriented graphite-coated carbon-based materials according to Examples 1 to 3 and Comparative Example 2, in which peaks (peaks in the vicinity of the graphite) were observed, and the surfaces of the carbon-based substrates, contain graphite.

[0077] However, on the surface of the highly oriented graphite-coated carbon-based material according to Comparative Example 2 and the surface of the carbon-based substrate, the D band (1350 cm ) derived from the edge plane of graphite was observed. -1 A peak in the vicinity was also observed. From this, it can be said that the graphite layer formed on the surface of the carbon-based substrate used in Example 1 and on the surface of the highly oriented graphite-coated carbon-based material according to Comparative Example 2 has a low degree of crystallinity.

[0078] On the other hand, it is clear that a highly crystalline graphite layer is formed on the surface of the highly oriented graphite-coated carbon-based materials according to Examples 1 to 3, where the D band is barely detectable.

[0079] The reason why the D band was observed on the surface of the highly oriented graphite-coated carbon-based material according to Comparative Example 2 (the crystallinity was low) is thought to be that the heating temperature in the heating process was high, which increased the solubility of carbon in the Ni melt and caused solidification without going through a solid solution, resulting in a disordered crystal structure.

[0080] FIG. 6 is a diagram showing the relationship between the peak intensity ratio (D / G) in the Raman spectrum shown in FIG. 5 and the heating temperature. As can be seen from FIG. 6, in Examples 1 to 3 where the heating temperature was 1000 to 1600°C, D / G was close to 0, whereas in Comparative Example 2 where the heating temperature was 2000°C, D / G was approximately 0.6.

[0081] Note that a large D / G ratio means that the D band peak intensity is strong relative to the G band peak intensity, i.e., that the orientation (crystallinity) is low. Therefore, the larger the D / G ratio, the lower the orientation (crystallinity) of the graphite formed on the surface of the carbon-based substrate.

[0082] Considering the above and the results of FIG. 6, it can be said that the heating temperature in the heating step is more preferably 1000°C to 1600°C.

[0083] (X-ray diffraction analysis) The surface states of the carbon-based substrates according to Example 1 and Comparative Example 1 before and after the heat treatment were compared by X-ray diffraction (ray source: CuKα), and the results are shown in FIG. FIG. 7 shows X-ray diffraction patterns of the surfaces of the carbon-based substrate, the metal layer, and the highly-oriented graphite-coated carbon-based material in Example 1, and the surface of the carbon-based substrate in Comparative Example 1 before and after heating. The diffraction peak near 2θ=26° is a diffraction peak derived from the (002) [basal plane] of graphite, and the diffraction peak near 2θ=44.5° is a diffraction peak derived from the (111) of Ni.

[0084] From the results in FIG. 7, it can be seen that in both Example 1 and Comparative Example 1, the half-width of the diffraction peak of graphite (002) (the diffraction peak appearing near 2θ=26° in FIG. 6) became smaller by heating, and therefore it can be said that the orientation (crystallinity) of the graphite on the surface was improved by heating. That is, it can be said that a highly oriented graphite layer was formed in Example 1, and that the crystallinity of the pyrolytic carbon was increased in Comparative Example 1.

[0085] However, the half width of the diffraction peak of the graphite (002) of Example 1 after heating is smaller than the half width of the diffraction peak of the graphite (002) of Comparative Example 1. Therefore, it can be said that the highly oriented graphite layer formed by heating to 1400°C while in close contact with the metal layer and then cooling has a higher degree of crystallinity (higher orientation) than the pyrolytic carbon layer formed by the heating process at 3000°C.

[0086] Considering that Comparative Example 1 is heated at 3000°C, the method of Example 1, which can increase the crystallinity (orientation) of the graphite layer by heating at 1400°C compared to Comparative Example 1, can be said to be a simpler method than Comparative Example 1 and can further increase the crystallinity (orientation) of the graphite layer.

[0087] (Surface observation using a scanning electron microscope) The surface of the metal layer before the heating step in Example 1 was observed with a scanning electron microscope (accelerating voltage 5 kV, magnification: 500 times), and the results are shown in FIG. Under similar conditions, the surfaces (surfaces from which the metal layer was removed) of the highly oriented graphite-coated carbon-based materials according to Examples 1 to 3 and Comparative Example 2 were observed with a scanning electron microscope (magnification: 500x). The results are shown in Figures 9 to 12. The scale is 100 µm / 10 divisions in all cases.

[0088] FIG. 8 is an enlarged photograph of the surface of the metal layer in Example 1 before the heating step, observed with a scanning electron microscope. As shown in FIG. 8, a metal film was formed on the surface of the metal layer before the heating step, and no exposed carbon-based substrate was observed.

[0089] FIG. 9 is an enlarged photograph of the surface of the highly oriented graphite-coated carbon-based material according to Example 2, observed with a scanning electron microscope. As shown in FIG. 9, the surface of the highly oriented graphite-coated carbon-based material according to Example 2 contains a mixture of areas where the metal layer has been peeled off (black areas) and areas where the metal layer has not been peeled off (white areas).

[0090] FIG. 10 is an enlarged photograph of the surface of the highly oriented graphite-coated carbon-based material according to Example 1, observed with a scanning electron microscope. As shown in Fig. 10, most of the metal layer had been removed from the surface of the highly-oriented graphite-coated carbon-based material according to Example 1, compared to the highly-oriented graphite-coated carbon-based material according to Example 2 shown in Fig. 9, and part of the metal layer that was not completely removed remained in the form of balls. It can be inferred that these ball-shaped metal layers were formed by part of the metal layer being deformed into spheres during the heating process.

[0091] FIG. 11 is an enlarged photograph of the surface of the highly oriented graphite-coated carbon-based material according to Example 3, observed with a scanning electron microscope. 11, most of the metal layer was removed from the surface of the highly-oriented graphite-coated carbon-based material according to Example 3, and the remaining part of the metal layer remained in the form of balls. It is presumed that the ball-shaped metal layer was formed by melting part of the metal layer during the heating process and deforming into a spherical shape.

[0092] Furthermore, the shape of the metal layer shown in Fig. 11 had higher sphericity than the shape of the metal layer according to Example 1 shown in Fig. 10. This is presumably because the molten metal took on a shape closer to a perfect sphere as a result of being heated at a higher temperature.

[0093] FIG. 12 is an enlarged photograph of the surface of the highly oriented graphite-coated carbon-based material according to Comparative Example 2, observed with a scanning electron microscope. 12, no metal layer was observed on the surface of the highly-oriented graphite-coated carbon-based material according to Comparative Example 2. It is believed that the metal layer either dissolved into the carbon-based substrate to form a solid solution, or volatilized due to the high-temperature conditions. This coincides with the fact that a D-band peak was observed in the highly oriented graphite-coated carbon-based material according to Comparative Example 2 in the Raman spectrum shown in FIG.

[0094] From the above results, it was confirmed that by using the method for producing a highly oriented graphite-coated carbon-based material of the present invention, a highly oriented graphite-coated carbon-based material with a high degree of graphitization can be produced by a method easier than conventional methods. [Explanation of symbols]

[0095] 1 Highly oriented graphite-coated carbon material 10 Carbon-based substrates 20 metal layer 40 Solid solution layer (penetration layer) 50 Highly oriented graphite layer 51 Exfoliated highly oriented graphite layers (graphene) 100 Combinations S1 Combination process S2 heating process S3 cooling process S4 removal process S5 Peeling process

Claims

1. a combining step of obtaining a combined body in which a metal layer is adhered to the surface of a carbon-based substrate; a heating step of heating the combined body to 800°C to 1800°C; a cooling step of cooling the combined body; a removing step of removing the metal layer from the cooled combination; A method for producing a highly oriented graphite-coated carbon-based material, wherein the metal constituting the metal layer has a solid solution region on the metal side in a carbon-metal binary phase diagram.

2. 2. The method for producing a highly oriented graphite-coated carbon-based material according to claim 1, wherein in the combining step, the metal layer is adhered to the carbon-based substrate by electroplating, electroless plating, or physical vapor deposition.

3. 3. The method for producing a highly oriented graphite-coated carbon-based material according to claim 1, wherein the metal is Ni or Fe.

4. 3. The method for producing a highly oriented graphite-coated carbon-based material according to claim 1, wherein the heating temperature in the heating step is equal to or lower than the eutectic temperature of a region where the solid solution of the metal and carbon and a liquid phase coexist.

5. 3. The method for producing a highly oriented graphite-coated carbon-based material according to claim 1, wherein the metal layer has a thickness of 100 μm or less.

6. 3. The method for producing a highly-oriented graphite-coated carbon-based material according to claim 1, wherein the carbon-based substrate is made of at least one material selected from the group consisting of graphite, a C / C composite material, pyrolytic carbon, and glassy carbon.

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