Carbon electrode for fluorine electrolyzer

Abstract

To provide a carbon electrode for a fluorine electrolysis device with which particles hardly fall even when density of a carbon-based material is low, and to provide a production method of the carbon electrode for the fluorine electrolysis device.SOLUTION: In a carbon electrode for a fluorine electrolysis device containing a porous carbon-based material having secondary particles constituted of carbon-based particles and a carbonaceous binder making the carbon-based particles combine with each other, the secondary particles are not existing independently but combined with each other. A production method of the carbon electrode for the fluorine electrolysis device includes: a raw material forming step to obtain raw material powder by kneading the carbon-based particles and pitch with softening point of 70-200°C; a molding step to obtain a molding by putting the raw material powder in a molding tool with a shape of the carbon electrode and heating it to a temperature higher than the softening point; and a sintering step to obtain a sintered compact by sintering the molding.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a carbon electrode for a fluorine electrolyzer and a method for manufacturing the carbon electrode for a fluorine electrolyzer.

Background Art

[0002] Fluorine gas is used in various fields such as semiconductor manufacturing, uranium enrichment, and fluorine-related products. Fluorine gas is obtained by electrolyzing a molten salt containing hydrofluoric acid, and in this reaction, a carbon electrode is widely used as the anode.

[0003] Patent Document 1 describes a manufacturing method in which, when electrolytic production of fluorine is performed using carbon as the anode material, a so-called anode effect, in which an electrically insulating film is formed on the anode surface and the current suddenly stops flowing, is unlikely to occur and can stably continue for a long period. The method uses carbon having an electrical resistance anisotropy ratio of 1.3 or less and being porous as the anode material.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, as described in Patent Document 1, a porous anode material is used. For example, it is desirable that the density is 1.0 to 1.3 g / cm 3 . In such a low-density carbon material, the bond between carbon particles is weak, and as consumption progresses, the internal particles are likely to fall off.

[0006] In view of the above problems, an object of the present invention is to provide a carbon electrode for a fluorine electrolyzer and a method for manufacturing the carbon electrode for a fluorine electrolyzer in which particles are unlikely to fall off even if the density is low.

Means for Solving the Problem

[0007] The carbon electrode for a fluorine electrolyzer of the present invention is a carbon electrode for a fluorine electrolyzer containing a porous carbon-based material, wherein the porous carbon-based material forms secondary particles composed of carbon-based particles and a carbonaceous binder that binds the carbon-based particles to each other, and the secondary particles are bound to each other without being independent.

[0008] In the carbon electrode for a fluorine electrolyzer of the present invention, since the secondary particles formed by the porous carbon-based material are bound to each other without being independent, it is possible to suppress particles and fine powders that have fallen off from the inside from coming out to the outside of the material. Therefore, it is possible to provide a carbon electrode for a fluorine electrolyzer with less contamination.

[0009] The carbon electrode for a fluorine electrolyzer of the present invention preferably has the following aspects.

[0010] The carbon electrode for a fluorine electrolyzer has a mounting portion and an immersion portion, the mounting portion has a machined surface, and the immersion portion has an unprocessed surface.

[0011] Since the immersion portion immersed in the electrolytic solution is an unprocessed surface, it is not damaged on the surface by machining, and particularly, particle dropout can be prevented in the initial stage of use. In addition, since most of the hard carbonaceous material is used as an unprocessed surface, difficult shape processing can be minimized.

[0012] The carbon electrode for a fluorine electrolyzer has a maximum pore diameter of 50 to 1000 μm.

[0013] When the maximum pore diameter is 50 μm or more, the molten salt easily penetrates into the pores, and the surface area involved in electrolysis can be increased. When the maximum pore diameter is 1000 μm or less, a decrease in the surface area can be suppressed, and the surface area involved in electrolysis can be increased.

[0014] The carbon electrode for the fluorine electrolysis device has a bulk density of 1.0 to 1.5 g / cm 3 .

[0015] When the bulk density is 1.0 g / cm 3 or more, sufficient strength can be obtained as the carbon electrode for the fluorine electrolysis device. When the bulk density is 1.5 g / cm 3 or less, a sufficient amount of pores can be secured inside, and electrolysis can occur not only on the electrode surface but also inside the pores, enabling efficient production of fluorine.

[0016] Subsequently, the method for manufacturing the carbon electrode for the fluorine electrolysis device of the present invention includes a raw material step of kneading carbon-based particles and a pitch having a softening point of 70 to 200 °C to obtain raw material powder, a molding step of putting the raw material powder into a molding die in the shape of a carbon electrode and heating it to a temperature higher than the softening point to obtain a molded body, a firing step of firing the molded body to obtain a fired body, .

[0017] According to the method for manufacturing the carbon electrode for the fluorine electrolysis device of the present invention, since carbon-based particles and a pitch having a softening point of 70 °C or higher are kneaded to obtain raw material powder, they do not adhere to each other at room temperature, and the particle size can be adjusted to a predetermined particle size at room temperature. Also, since a pitch having a softening point of 200 °C or lower is kneaded, it is not necessary to expose it to a high temperature even when melting the pitch for kneading, and the condensation reaction hardly proceeds at the stage of melting the pitch, preventing an increase in the softening point. Further, in the subsequent molding step, it can be easily fused by heat and the shape of the carbon electrode for the fluorine electrolysis device can be easily obtained.

[0018] Also, in order to obtain a porous material, since it is fused by heat without applying pressure to obtain the shape of the carbon electrode for the fluorine electrolysis device, a porous body in which secondary particles having a wide particle size distribution are bonded to each other can be obtained, and a large number of continuous pores exist, and the volatile components contained in the raw material powder can be removed without accumulating inside in the subsequent firing step. Furthermore, in order to obtain a porous material, it is fused by heat without applying pressure to obtain the shape of a carbon electrode for a predetermined fluorine electrolyzer. Therefore, there is no dimensional change due to pressure, and the shape of the mold directly becomes the shape of the molded body. For this reason, a carbon electrode for a fluorine electrolyzer with high dimensional accuracy can be obtained after firing.

[0019] Also, the method for manufacturing a carbon electrode for a fluorine electrolyzer according to the present invention preferably has the following aspects.

[0020] The method further includes a processing step of surface processing a part of the fired body to form a mounting portion and making the remaining part an immersion portion.

[0021] According to the method for manufacturing a carbon electrode for a fluorine electrolyzer of the present invention, originally, a material having a shape close to that of a carbon electrode for a fluorine electrolyzer is obtained. By processing the mounting portion that contacts the metal clamp for supplying current, a highly accurate mounting portion can be obtained, and the contact resistance can be reduced.

[0022] In the processing step, a mounting hole is further processed in the mounting portion.

[0023] By providing a mounting hole in the mounting portion, the connection reliability with the metal clamp for supplying current can be enhanced. The mounting hole may be either a through hole or a non-through hole, and may be a straight hole or a threaded hole.

[0024] The molding die is provided with a core pin at a position corresponding to the mounting hole.

[0025] A core pin is a pin installed in a molding die and is a member that forms a hole in a molded body. A carbon electrode for a fluorine electrolyzer is a carbonaceous material, and it is difficult to perform drilling. In the method for manufacturing a carbon electrode for a fluorine electrolyzer of the present invention, since it is molded by heat without applying pressure in the molding step, even if a core pin is inserted in the process of molding particulate raw materials with low fluidity, a strong force is not applied to the core pin, and it is not necessary to firmly fix it to the die. For this reason, a hole can be formed at a predetermined position with high accuracy.

[0026] Note that the material of the core pin is not particularly limited. If it is to be removed after molding, metals, ceramics, etc. can be used. If it is to be burned without being removed after molding, it is preferable to use organic substances such as wood, paper, and resin.

[0027] In the molding step, heating is performed for 10 minutes or more.

[0028] By heating for 10 minutes or more in the molding step, the fusion of the pitch is promoted, and the secondary particles can be surely bonded to each other. Also, in the molding step, since the mold can be propagated to directly heat the raw material powder from the heat source, fusion can be achieved earlier than the molecular weight increase due to the condensation of the pitch, and strong bonding can be achieved.

[0029] In the firing step, the molded body is buried and fired in a packing material having an average particle size larger than the average particle size of the raw material powder.

[0030] In the firing step, the pitch easily melts and deforms, which causes volatiles to be generated from the pitch. However, by burying the molded body in the packing material, deformation is suppressed. Furthermore, since the average particle size of the packing material is coarser (larger) than that of the raw material powder, the generated volatiles can be quickly discharged, preventing cracks and foaming due to excessive volatiles.

[0031] The average particle size of the raw material powder is 50 to 1500 μm.

[0032] By setting the average particle size of the raw material powder to 50 to 1500 μm, a carbon electrode for a fluorine electrolysis device with a large specific surface area and high strength can be obtained.

Advantages of the Invention

[0033] According to the carbon electrode for a fluorine electrolysis device of the present invention, since the secondary particles constituting the porous carbon-based material are bonded to each other without being independent, particles and fine powders that have fallen off from the inside of the electrode are suppressed from coming out to the outside of the electrode. Therefore, a carbon electrode for a fluorine electrolysis device with less contamination can be provided.

[0034] Further, according to the method for manufacturing a carbon electrode for a fluorine electrolyzer of the present invention, since carbon-based particles and a pitch having a softening point of 70°C or higher are kneaded to obtain raw material powder, they do not adhere to each other at room temperature, and the particle size can be adjusted to a predetermined particle size at room temperature. Further, since a pitch having a softening point of 200°C or lower is kneaded, it is not necessary to expose the pitch to a high temperature even when melting the pitch for kneading, and the condensation reaction hardly proceeds at the stage of melting the pitch, and in the subsequent forming step, it is easily fused by heat and the shape of a predetermined carbon electrode for a fluorine electrolyzer can be easily obtained.

[0035] Also, in order to obtain a porous material, since the shape of a predetermined carbon electrode for a fluorine electrolyzer is obtained by heat fusion without applying pressure, a porous body in which even secondary particles having a wide particle size distribution are bonded to each other can be obtained, and a large number of continuous pores are present, and volatile components contained in the raw material powder can be removed without accumulating inside in the subsequent firing step.

[0036] Furthermore, in order to obtain a porous material, since the shape of a predetermined carbon electrode for a fluorine electrolyzer is obtained by heat fusion without applying pressure, there is no dimensional change due to pressure, and the shape of the mold becomes the shape of the molded body as it is. For this reason, a carbon electrode for a fluorine electrolyzer with high dimensional accuracy can be obtained after firing.

Brief Description of the Drawings

[0037]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Embodiments for Carrying Out the Invention

[0038] To explain the carbon electrode for a fluorine electrolyzer and the manufacturing method of the carbon electrode for a fluorine electrolyzer of the present invention, a carbon electrode for a fluorine electrolyzer including a porous carbon-based material according to an embodiment of the present invention, a carbon electrode for a fluorine electrolyzer including a conventional porous carbon-based material, and a carbon electrode for a fluorine electrolyzer including a conventional isotropic graphite material will be described while comparing the manufacturing method, the structure of the material, and the like.

[0039] Fig. 1 shows the manufacturing process of the carbonaceous porous carbon-based material for the carbon electrode for a fluorine electrolyzer which is an embodiment of the present invention.

[0040] As shown in Fig. 1, the carbonaceous porous carbon-based material of the embodiment of the present invention is obtained by kneading carbon-based particles and a pitch having a softening point of 70 to 200°C to obtain raw material powder (raw material process), putting the raw material powder into a mold and heating it to a temperature higher than the softening point to obtain a molded body having a predetermined shape (molding process), and firing the molded body (firing process).

[0041] (Raw Material Process) In the kneading process of the present embodiment, as shown in Fig. 2(a), carbon-based particles and a pitch having a softening point of 70 to 200°C are kneaded to obtain the raw material powder shown in Fig. 2(b). The raw material powder is an aggregate of particles in which the carbon-based particles are bonded to each other by a binder, and corresponds to secondary particles obtained through a firing process or a graphitization process. The carbon-based particles are not particularly limited, and for example, pulverized carbon-based particles such as pitch coke, graphite, and glassy carbon can be used. Among them, pitch coke has good compatibility with pitch and can obtain a strong bond, and can be preferably used as the carbon-based particles of the present invention.

[0042] The raw material powder obtained in the raw material process may be used for molding as it is, but if there is an appropriate particle size range suitable for the porous carbon-based material for the carbon electrode of the fluorine electrolysis device, the particle size may be adjusted during the raw material process. As methods for adjusting the particle size, techniques such as classification and pulverization can be used. When adjusting the particle size by pulverization, by making the carbon-based particles sufficiently smaller than the particle diameter of the raw material powder, the generation of exposed surfaces without the adhesion of the binder after pulverization can be prevented.

[0043] The desirable average particle diameter of the carbon-based particles is 50 to 500 μm. When the average particle diameter of the carbon-based particles is 50 μm or more, the amount of pitch required in the raw material process can be reduced, and in the subsequent firing process, the disappearance of pores due to the deformation of secondary particles and foaming due to the generated gas can be prevented. The average particle diameter of the carbon-based particles is preferably 70 μm or more, and more preferably 100 μm or more. Also, when the average particle diameter of the carbon-based particles is 500 μm or less, the generation of exposed surfaces not covered by the binder can be prevented. The average particle diameter of the carbon-based particles is preferably 400 μm or less. The average particle diameter of the carbon-based particles can be measured with a laser diffraction particle size distribution analyzer.

[0044] The pitch used in this embodiment has a softening point of 70 to 200 °C. By kneading the carbon-based particles and the pitch with a softening point of 70 °C or higher to obtain the raw material powder, the adhesion of the raw material powder at room temperature can be suppressed, and the particle size of the raw material powder can be adjusted so as to have a predetermined particle diameter at room temperature. The softening point is preferably 90 °C or higher, and more preferably 100 °C or higher. Also, by kneading the carbon-based particles and the pitch with a softening point of 200 °C or lower to obtain the raw material powder, it is not necessary to expose the raw material powder to a high temperature for kneading, and the progress of the condensation reaction at the stage of melting the pitch during kneading can be suppressed, and the increase in the softening point can be prevented. The softening point is preferably 180 °C or lower, and more preferably 160 °C or lower.

[0045] In this embodiment, the kneading temperature is preferably 150 to 300 °C and higher than the softening point of the pitch. By setting the kneading temperature to 150 °C or higher and higher than the softening point of the pitch, the pitch can be sufficiently melted and the carbon-based particles can be bonded to each other. The kneading temperature is more preferably 180 °C or higher. By setting the kneading temperature to 300 °C or lower, polycondensation of the pitch can be prevented and the moldability of the raw material powder can be ensured. The kneading temperature is more preferably 280 °C or lower.

[0046] In addition, in order to obtain a porous carbon-based material for a carbon electrode for a fluorine electrolysis device, the main bonding action is mainly due to heat and hardly any pressure is applied. Therefore, even if the secondary particles have a wide particle size distribution, a porous body in which they are bonded to each other can be obtained, and continuous pores are likely to be formed. In the subsequent firing process, the volatile components contained in the raw material powder can be removed without accumulating inside.

[0047] In this embodiment, it is preferable to end the kneading at the stage of uniformly mixing while melting the pitch. Specifically, the kneading time is preferably 30 minutes or less. When the kneading time is 30 minutes or less, polycondensation of the pitch can be suppressed and a decrease in the adhesiveness of the raw material powder can be prevented. The kneading time is more preferably 20 minutes or less, and even more preferably 10 minutes or less.

[0048] (Particle size adjustment) The raw material powder obtained in the raw material process (Fig. 2(b)) is preferably subjected to particle size adjustment as necessary. By performing particle size adjustment, a porous carbon-based material for a carbon electrode of a fluorine electrolyzer with a predetermined porosity and particle size distribution can be obtained. As the method for particle size adjustment, techniques such as classification and pulverization can be used. When adjusting the particle size by pulverization, since the raw material powder in which carbon-based particles are solidified with pitch is pulverized, many secondary particles with adhesion in which carbon-based particles are entangled with pitch are obtained. On the other hand, raw material particles without adhesion, such as raw material powder in which carbon-based particles are broken or the binder pitch is peeled off, are also obtained simultaneously. In the method for manufacturing a carbon electrode for a fluorine electrolyzer of the present invention, since it is mainly molded by the fusion action due to heat, even such raw material powder without adhesion can be combined with each other without being independent.

[0049] The average particle size of the raw material powder used in this embodiment is preferably 50 to 1500 μm. When the average particle size of the raw material powder is 50 μm or more, pores of sufficient size can be obtained, and a porous carbon-based material for a carbon electrode of a fluorine electrolyzer that is easy to use for various applications can be obtained. The average particle size of the raw material powder is more preferably 80 μm or more, and even more preferably 100 μm or more. When the average particle size of the raw material powder is 1500 μm or less, when it is put into a mold and molded, the size of the unevenness formed on the surface can be reduced, and a porous carbon-based material for a carbon electrode of a fluorine electrolyzer with a smooth surface can be obtained. The average particle size of the raw material powder is more preferably 1200 μm or less, and even more preferably 1000 μm or less.

[0050] (Molding process) In the molding process of this embodiment, the obtained raw material powder (Fig. 2(b)) is put into a mold (Fig. 2(c)) and heated to a temperature higher than the softening point of pitch to obtain a molded body having a predetermined shape shown in Fig. 2(d). As shown in Fig. 2(d), in this embodiment, since it is held in a state of being heated to a temperature higher than the softening point of pitch, even small raw material powder or raw material powder from which the binder has peeled off are combined with each other without being released and integrated.

[0051] In this embodiment, since heat is applied to the raw material powder, even raw material powder without adhesion can be incorporated into secondary particles and integrated, and generation of independent and free carbon-based particles can be suppressed.

[0052] In the molding process of this embodiment, a desirable heating time is 10 minutes or more. Since molding is performed by the action of heat in the molding process, by increasing the heating time, the raw material powder can be softened more and firmly fused. The heating time is more preferably 20 minutes or more, and even more preferably 40 minutes or more.

[0053] The molding process of this embodiment does not necessarily have to be separately prepared as a molding process, and the initial stage of the subsequent firing process can be used as the molding process. For example, as shown in FIG. 12, raw material powder may be put into a strong container, covered, and then buried in a packing material and fired. In FIG. 12(a), the combustible container is filled with raw material powder. In FIG. 12(b), the above container is buried in a firing container filled with a packing material. In FIG. 12(c), the temperature is raised, and the raw material powder is melted and molded and fired to obtain a fired body. The container preferably has air permeability so that the generated product gas does not accumulate, but a material that becomes air permeable when heated may also be used. In the initial stage of firing, the raw material powders fuse with each other and are molded into a predetermined shape. When the temperature is further increased, the generated product gas passes through the air-permeable container and is discharged to the outside, and the molded body thermally shrinks as the temperature rises. Also, the container is preferably combustible. If the container is combustible, the container carbonizes during firing and does not retain its original shape. Since it is buried in the packing material, the packing material can follow the shrinkage of the molded body and deformation can be prevented. As an air-permeable and combustible container, thick paper with a number of holes drilled to ensure air permeability can be used.

[0054] Also, in the molding process of this embodiment, as long as it is a temperature range where fusion occurs, molding may be performed using not only heat but also pressure in combination. By applying pressure, the shape of the mold can be transferred, and a porous carbon-based material for a carbon electrode for a fluorine electrolyzer with high dimensional accuracy can be obtained.

[0055] Hereinafter, in order to clarify the features of the present invention, the conventional porous carbon-based materials and the conventional dense isotropic carbon-based materials (isotropic graphite materials) will be described, particularly focusing on the forming process.

[0056] In the conventional porous carbon-based materials, carbon-based particles and pitch shown in Fig. 3(a) are kneaded to obtain raw material powder shown in Fig. 3(b). Then, the forming processes shown in Figs. 3(c) and (d) and the firing process shown in Fig. 3(e) are performed. Fig. 3(c) shows the stage before forming, and Fig. 3(d) shows the stage after forming. In the conventional method, the forming processes shown in Figs. 3(c) and (d) are mainly performed by the action of pressure without melting the pitch. Therefore, strong bonding occurs at the contact points of the particles to which pressure is applied, while strong bonding cannot occur at the contact points of the particles to which no pressure is applied. In the production of porous carbon-based materials, since coarse raw material powder is used, large voids are formed at the stage of filling the mold, and it is difficult for sufficient pressure to be applied to the raw material powder that has entered the large voids. For this reason, it cannot be integrated with other particles and becomes free secondary particles, which do not contribute to the strength of the material and become foreign substances that only generate particles.

[0057] Also, in the conventional isotropic graphite materials, carbon-based particles and pitch shown in Fig. 4(a) are kneaded to obtain a massive kneaded product as shown in Fig. 4(b). The kneaded product is finely pulverized to obtain raw material powder shown in Fig. 4(c). Then, as shown in Figs. 4(d) and (e), after the raw material powder is formed under high pressure to obtain a formed body, through the firing process shown in Fig. 4(f) and graphitization as required, an isotropic graphite material is obtained. Note that Fig. 4(d) shows the stage before forming, and Fig. 4(e) shows the stage after forming.

[0058] In the conventional graphite-based isotropic carbon-based materials (isotropic graphite materials), since the raw material powder after pulverization is fine, large voids are unlikely to be formed during forming, and since pressure is easily propagated evenly, free particles are unlikely to be generated. Also, since the voids themselves are fine, even if there are secondary particles in a free state, they are confined inside and are unlikely to cause particles.

[0059] (Firing process) In the firing process of this embodiment according to the present invention, the obtained molded body (Fig. 2(d)) is heated in an inert atmosphere to obtain a fired body shown in Fig. 2(e). In this embodiment, the fired body becomes a porous carbon-based material for a carbon electrode of a fluorine electrolyzer.

[0060] The firing temperature is preferably, for example, 700 to 2000 °C. By performing the firing at 700 °C or higher, volatile components are sufficiently removed from the molded body, and it becomes possible to be used as a porous carbon-based material for a carbon electrode of a fluorine electrolyzer. The firing temperature is more preferably 800 °C or higher, and even more preferably 900 °C or higher.

[0061] Also, by performing the firing at 2000 °C or lower, sufficient hardness is imparted to the porous carbon-based material, and for example, a porous carbon-based material that can be used as an electrolysis electrode can be obtained. The firing temperature is more preferably 1800 °C or lower, and even more preferably 1500 °C or lower.

[0062] In the manufacturing method of this embodiment according to the present invention, since the raw material powder is softened in the molding process, the pitch is not sufficiently polycondensed at the stage of the raw material process. For this reason, it contains a lot of volatile components, but since it is porous in the first place after molding, the decomposition gas can be quickly diffused to the outside, and it is possible to prevent densification due to carbonization of the volatile components inside the molded body and sealing of pores, and prevent cracks.

[0063] In the firing process of this embodiment according to the present invention, it is preferable that the average particle diameter of the packing material is coarser (larger) than that of the raw material powder. When the average particle diameter of the packing material is coarser than that of the raw material powder, the tar-like product generated from the molded body does not stay inside the molded body and diffuses quickly, and it is possible to promote the formation of pores in the porous body.

[0064] The porous carbon-based material for a carbon electrode of a fluorine electrolyzer obtained through the above steps is such that, at least inside the material, the secondary particles are bonded to each other without being independent, and the presence of free particles is suppressed. Therefore, it is possible to suppress particles and fine powder from leaking out from the surface of the material.

[0065] In this embodiment, it is preferable that the maximum pore diameter is 50 to 1000 μm. When the maximum pore diameter is 50 μm or more, the molten salt easily penetrates into the pores, and the surface area involved in electrolysis can be increased. The maximum pore diameter is more preferably 80 μm or more, and even more preferably 100 μm or more. When the maximum pore diameter is 1000 μm or less, a decrease in the surface area can be suppressed, and the surface area involved in electrolysis can be increased. The maximum pore diameter is more preferably 800 μm or less, and even more preferably 500 μm or less. Note that the maximum pore diameter can be measured by the mercury intrusion method.

[0066] (Processing step) In the processing step of this embodiment, at least a part of the obtained fired body (Fig. 2(e)) is surface - processed to form a mounting portion, and the remaining portion other than the mounting portion is made into an immersion portion to be immersed in the electrolytic solution. The fired body obtained in the firing step is obtained as a material having a shape close to that of the carbon electrode for the fluorine electrolysis device. By processing the mounting portion that contacts the metal clamp for supplying current, a highly accurate mounting portion can be obtained, and the contact resistance can be reduced.

[0067] In the processing step, it is desirable to process a mounting hole in the mounting portion. By providing a mounting hole in the mounting portion, the connection reliability with the metal clamp for supplying current can be enhanced. The mounting hole may be either a through - hole or a non - through - hole, and may be a straight hole or a threaded hole.

[0068] Fig. 5 shows an example of the manufacturing method of the carbon electrode for the fluorine electrolysis device. As shown in Fig. 5(a), a molding die 1 conforming to the shape of the carbon electrode is prepared. As shown in Fig. 5(b), the raw material powder 2 obtained in the raw material step is put into the molding die 1, and the molding step is carried out. As shown in Fig. 5(c), the molded body obtained in Fig. 5(b) is fired to obtain a fired body 3. As shown in Fig. 5(d), by the processing step, the fired body 3 is surface - processed (in this example, planar processing) to form a mounting portion 11. Further, by forming a mounting hole 15 in the mounting portion 11, the carbon electrode 10 for the fluorine electrolysis device is completed. The remaining portion other than the mounting portion 11 is an immersion portion 12 to be immersed in the electrolytic solution.

[0069] In order to reduce the contact resistance between the mounting portion 11 and the metal clamp, the mounting portion 11 is preferably processed into, for example, a cylindrical shape or a planar shape. If it is cylindrical, it can be processed by a centerless grinding machine using a grinding wheel, a lathe, etc. If it is planar, it can be ground using a surface grinder, a milling machine, etc. Furthermore, in order to firmly connect with the metal clamp, mounting holes 15 such as through holes and screw holes can be formed in the mounting portion 11. When the mounting hole 15 is a screw hole, the metal clamp can be fixed even if it is a non-through hole.

[0070] By the way, since the carbon electrode for a fluorine electrolysis device of the present invention is a carbonaceous material, it is hard. When processing the mounting hole 15 using a drill, as shown in Fig. 6(a), the machining ability of the center part of the drill 20 with a slow peripheral speed is inferior, and the tip of the drill 20 is likely to be consumed or broken.

[0071] To prevent this, as shown in Fig. 6(b), a method of drilling a pilot hole 15a that serves as the basis of the mounting hole 15 in advance at the stage of the molded body in the molding process can be considered. In this case, the center part of the drill 20 with a slow peripheral speed is not involved in the machining, and it is possible to prevent the tip of the drill 20 from being consumed or broken. Fig. 7 shows an example of a manufacturing method of a carbon electrode for a fluorine electrolysis device that forms such a pilot hole 15a in the molding process. In this example, as shown in Fig. 7(a), a molding die 1 similar to Fig. 5(a) is prepared, but as shown in Fig. 7(b), a core pin 7 is installed in the molding die 1. The core pin 7 may be formed simultaneously at the manufacturing stage of the molding die 1.

[0072] The core pin 7 is a pin installed in the mold 1 and is a member for forming holes in the molded body and the fired body. The carbon electrode for the fluorine electrolysis device is made of a carbonaceous material, and drilling is difficult. Since the manufacturing method of the carbon electrode for the fluorine electrolysis device of the present embodiment is molded by heat without applying pressure in the molding process, even if there is a core pin in the process of molding a particulate raw material with low fluidity, no strong force is applied to the core pin and it is not necessary to firmly fix it to the mold. Therefore, a hole can be drilled at a predetermined position with high accuracy.

[0073] The material of the core pin 7 is not particularly limited. However, if it is to be removed after molding, it only needs to have heat resistance that can withstand the temperature during molding, and is not particularly limited such as metal, ceramic, resin, wood, etc. If it is not removed after molding and is carbonized during firing, pulp, wood, resin, etc. can be used.

[0074] When forming the pilot hole 15a using the core pin 7, considering the firing shrinkage of the molded body, it is arranged outside the actual position and at a distance from the actual interval. The extending direction of the core pin 7 is the thickness direction, length direction, etc. of the molded body, and is not particularly limited. In the manufacturing method of the present embodiment, since molding can be performed with almost no pressure applied, displacement and deformation are less likely to occur in any direction.

[0075] As shown in FIG. 7(c), the raw material powder 2 obtained in the raw material process is put into the mold 1, and the molding process is carried out. As shown in FIG. 7(d), the molded body obtained in FIG. 7(c) is fired to obtain the fired body 3. Since the core pin 7 is installed in the mold 1, the pilot hole 15a is formed in the fired body 3.

[0076] As shown in FIG. 7(e), in the machining process, surface machining (in this example, flat machining) is performed on the region including the pilot hole 15a of the fired body 3 to form the mounting portion 11. As shown in FIG. 7(f), in the manner shown in FIG. 6(b), the drill 20 is advanced along the pilot hole 15a to form the mounting hole 15, whereby the carbon electrode 10 for the fluorine electrolysis device is completed. The remaining portion other than the mounting portion 11 is the immersion portion 12 that is immersed in the electrolytic solution.

[0077] As shown in Fig. 6(b), if the pilot hole 15a is formed in advance, the load on the center of the drill 20, which is the most difficult to machine, can be suppressed, and the drilling of the mounting hole 15 in the machining process can be easily performed. Further, when the mounting hole 15 is a through hole, the cutting powder can be discharged downward, and the temperature rise of the cutting edge due to friction can be reduced.

[0078] Note that the direction of the mounting hole 15 is not particularly limited, and it may be formed not only in the thickness direction of the molded body (carbon electrode for fluorine electrolysis device) as in the examples of Figs. 5 and 7, but also in the length direction. The core pin 7 is designed and installed based on the forming direction of the mounting hole 15.

[0079] (Example) 100 parts by weight of amorphous pitch coke with an average particle diameter of 300 μm as carbon-based particles and 25 parts by weight of pitch with a softening point of 150 °C as a binder were used as raw materials and kneaded in a continuous kneader. The temperature of the continuous kneader was set to 250 °C. The pitch introduced into the continuous kneader was quickly melted and mixed with the carbon-based particles to obtain a kneaded product. The kneading time of the continuous kneader was 1 minute, and the pitch hardly underwent polycondensation.

[0080] Next, the obtained kneaded product was roughly pulverized, passed through a 2 mm sieve, and the particle size was adjusted. The average particle diameter of the obtained raw material powder was 900 μm.

[0081] The obtained raw material powder was filled into a metal mold with an opening of 600 × 300 mm and a depth of 80 mm, covered with a metal lid, heated to 200 °C around, held for 120 minutes, and then the lid was slowly pressed to adjust the overall shape. The pressing pressure at this time was only the self-weight of the lid, which was 2 kPa.

[0082] After cooling, it was taken out of the mold, packed into a firing can, buried in packing coke with an average particle diameter of 5 mm, and fired at 900 °C to obtain a fired body. Next, a part of the fired body was surface-machined to manufacture a carbon electrode for a fluorine electrolysis device, which further included a processing step of forming a mounting portion and making the remaining portion an immersion portion.

[0083] Comparative Example 1 A porous carbon material was produced in the same manner as in Example 1, except that the molding step was performed by pressing at 100° C. under a surface pressure of 15 MPa, and then processed in the same manner as in Example 1 to obtain a carbon electrode for a fluorine electrolysis device.

[0084] Comparative Example 2 60 parts by weight of pitch was added as a binder to 100 parts by weight of amorphous pitch coke with an average particle size of 15 μm as carbon particles, and kneaded for 200 minutes. Note that the pitch polycondensed during the kneading process, and its softening point rose to 200° C. or higher. Note that in this comparative example, a powdery raw material powder was not obtained in the raw material process, and a lump-like hard kneaded product was obtained, which could not be used as the raw material powder in the molding process as it is.

[0085] The obtained kneaded product was pulverized to obtain a raw material powder having an average particle size of 25 μm. The raw material powder was filled into a rubber bag and CIP molded at a molding pressure of 100 MPa. The obtained molded body was fired at 900° C. to obtain a dense carbonaceous material, which was then processed in the same manner as in Example 1 to obtain a carbon electrode for a fluorine electrolysis device.

[0086] Table 1 shows the physical properties of the carbonaceous materials obtained in the Examples and Comparative Examples. Fig. 8 shows the pore distributions in the Examples and Comparative Examples. The Examples show a large average pore diameter, although there is no significant difference in porosity between Comparative Examples 1 and 2. The Examples also show a higher bending strength than Comparative Example 1.

[0087] [Table 1]

[0088] Fig. 9 shows a polarizing microscope photograph of the cross section of the porous carbon-based material obtained in the example. The structure of the example was fused to each other by heat during molding, the corners were rounded, and no free secondary particles were observed. Furthermore, even when ultrasonically cleaned with water, no particles were generated from the pores. In other words, it can be understood that the secondary particles are not independent but are bonded to each other.

[0089] FIG. 10 shows a polarized light micrograph of the cross section of the porous carbon-based material obtained in Comparative Example 1. In the porous carbon-based material obtained in Comparative Example 1, fine secondary particles that caused the particles remained inside the pores (free secondary particles). Further, when ultrasonic cleaning was performed using water in the same manner as in the examples, generation of particles from the pores was confirmed.

[0090] FIG. 11 shows a polarized light micrograph of the cross section of the carbon-based material obtained in Comparative Example 2. In the dense carbon-based material obtained in Comparative Example 2, there were no large pores in the first place, and the presence of free secondary particles that caused the particles could not be confirmed. Even if free secondary particles were present, it was considered that they were confined inside fine pores and were difficult to flow out to the outside. In addition, when ultrasonic cleaning was performed using water in the same manner as in the examples, generation of particles from the pores was confirmed. It is presumed that the particles inside the pores were knocked out to the outside by the strong cleaning power.

Explanation of Reference Numerals

[0091] 1 Mold 2 Raw material powder 3 Fired body 7 Core pin 11 Mounting portion 12 Immersion portion 15 Mounting hole 15a Counterbore 20 Drill

Claims

1. A carbon electrode for a fluorine electrolyzer comprising a porous carbon-based material, wherein the porous carbon-based material comprises carbon-based particles and a carbonaceous binder that binds the carbon-based particles to each other to form secondary particles, the secondary particles are bonded to each other without being independent, and the carbon electrode for a fluorine electrolyzer has a bulk density of 1.0 to 1.5 g / cm ３ The carbon electrode for a fluorine electrolyzer.

2. The carbon electrode for a fluorine electrolyzer has a mounting portion and an immersion portion, The mounting portion has a machined surface, and the immersion portion has an un-machined surface. The carbon electrode for a fluorine electrolyzer according to Claim 1.

3. The carbon electrode for a fluorine electrolyzer has a maximum pore diameter of 50 to 1000 μm. The carbon electrode for a fluorine electrolyzer according to Claim 1 or 2.

Images