JP7693391B2 - Carbon electrodes for fluorine electrolysis equipment - Google Patents

Description

The present invention relates to a carbon electrode for a fluorine electrolysis device and a method for manufacturing a carbon electrode for a fluorine electrolysis device.

Fluorine gas is used in a variety of fields, including semiconductor manufacturing, uranium enrichment, and fluorine-related products. Fluorine gas is obtained by electrolyzing a molten salt containing hydrofluoric acid, and a carbon electrode is commonly used as the anode in this reaction.

Patent Document 1 describes a method for producing fluorine using porous carbon with an electrical resistivity anisotropy ratio of 1.3 or less as an anode material, as a production method that is unlikely to cause the so-called anode effect, a phenomenon in which an electrically insulating film forms on the anode surface and current suddenly stops flowing when fluorine is produced electrolytically using carbon as the anode material, and that can be continued stably for a long period of time.

Japanese Patent Application Publication No. 3-53090

However, as described in Patent Document 1, a porous anode material is used, and a density of, for example, 1.0 to 1.3 g/cm ³ is considered to be desirable. In such low-density carbon materials, the bonds between carbon particles are weak, and as consumption progresses, the internal particles tend to fall off.

In view of the above-mentioned problems, the present invention aims to provide a carbon electrode for a fluorine electrolysis device in which particles are unlikely to fall off even when the density is low, and a method for manufacturing a carbon electrode for a fluorine electrolysis device.

The carbon electrode for a fluorine electrolysis device of the present invention is
A carbon electrode for a fluorine electrolysis device comprising a porous carbon-based material,
The porous carbon-based material has carbon-based particles and a carbonaceous binder that binds the carbon-based particles to each other, forming secondary particles,
The secondary particles are not independent but are bonded to each other.

In the carbon electrode for a fluorine electrolysis device of the present invention, the secondary particles that make up the porous carbon-based material are not independent but are bonded to each other, so that particles or fine powder that have fallen from the inside are prevented from coming out to the outside of the material. This makes it possible to provide a carbon electrode for a fluorine electrolysis device that is less contaminated.

The carbon electrode for a fluorine electrolysis device of the present invention preferably has the following configuration:

The carbon electrode for the fluorine electrolysis device has an attachment portion and an immersion portion, the attachment portion has a processed surface, and the immersion portion has an unprocessed surface.

The part that is immersed in the electrolyte is an unmachined surface, so the surface is not damaged by machining, and particle shedding can be prevented, especially in the early stages of use. In addition, because most of the hard carbonaceous material is used with its unmachined surface, difficult shaping can be kept to a minimum.

The carbon electrode for the fluorine electrolysis device has a maximum pore size of 50 to 1000 μm.

If the maximum pore diameter is 50 μm or more, the molten salt can easily penetrate into the pores, and the surface area involved in electrolysis can be increased. If the maximum pore diameter is 1000 μm or less, the decrease in surface area is suppressed, and the surface area involved in electrolysis can be increased.

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

When the bulk density is 1.0 g/cm3 or ^more , sufficient strength is obtained as a carbon electrode for a fluorine electrolysis device. When the bulk density is 1.5 g/cm3 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.

Next, the method for producing a carbon electrode for a fluorine electrolysis apparatus of the present invention comprises the steps of:
a raw material process of kneading carbon particles with pitch having a softening point of 70 to 200° C. to obtain raw material powder;
a molding step of placing the raw material powder in a mold having a shape of a carbon electrode and heating the raw material powder 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;
Includes.

According to the method for manufacturing carbon electrodes for fluorine electrolysis devices of the present invention, raw material powder is obtained by kneading carbon particles with pitch having a softening point of 70°C or higher, so that they do not adhere to each other at room temperature, and the particle size can be adjusted to a desired particle size at room temperature. In addition, because pitch having a softening point of 200°C or lower is kneaded, there is no need to expose the pitch to high temperatures when melting it for kneading, and condensation reactions do not easily proceed at the pitch melting stage, making it possible to prevent an increase in the softening point. In addition, in the subsequent molding process, the desired shape of carbon electrodes for fluorine electrolysis devices can be easily obtained because the particles are easily fused by heat.

Moreover, in order to obtain a porous material, a predetermined shape of a carbon electrode for a fluorine electrolysis device is obtained by fusing the material with heat without applying pressure, so that even secondary particles having a wide particle size distribution can be bonded to each other to obtain a porous body, and in addition, a large number of continuous pores are present, so that volatile matters contained in the raw material powder can be removed in the subsequent firing step without accumulating inside the raw material powder.
Furthermore, since the porous material is fused by heat without applying pressure to obtain a predetermined shape of a carbon electrode for a fluorine electrolysis device, there is no dimensional change due to pressure and the shape of the mold becomes the shape of the molded product as it is, so that a carbon electrode for a fluorine electrolysis device with high dimensional accuracy can be obtained after firing.

The method for producing a carbon electrode for a fluorine electrolysis device of the present invention preferably has the following features:

The method further includes a processing step in which a portion of the fired body is surface-processed to form an attachment portion and the remaining portion is made into an immersion portion.

The manufacturing method of carbon electrodes for fluorine electrolysis devices of the present invention allows the production of materials with a shape similar to that of carbon electrodes for fluorine electrolysis devices, and by machining the attachment part that comes into contact with the metal clamp that supplies the current, a highly accurate attachment part can be obtained, thereby reducing contact resistance.

In the processing step, mounting holes are further drilled into the mounting portion.

By providing a mounting hole in the mounting portion, the reliability of the connection with the metal clamp that supplies current can be improved. The mounting hole may be either a through hole or a blind hole, and may also be a straight hole or a screw hole.

The mold has a core pin at a position corresponding to the mounting hole.

A core pin is a pin installed in a molding die and is a component that forms holes in the molded body. Carbon electrodes for fluorine electrolysis devices are made of carbonaceous material, and drilling holes in them is difficult. In the manufacturing method for carbon electrodes for fluorine electrolysis devices of the present invention, molding is performed by heat without applying pressure in the molding process, so even if a core pin is inserted in the process of molding granular raw materials with low fluidity, no strong force is applied to the core pin and it does not need to be firmly fixed to the die. This makes it possible to drill holes in the specified positions with high precision.

There are no particular restrictions on the material of the core pin. If the core pin is to be removed after molding, metal, ceramic, etc. can be used. If the core pin is to be burned instead of being removed after molding, it is preferable to use organic materials such as wood, paper, and resin.

The molding process involves heating for 10 minutes or more.

By heating for 10 minutes or more during the molding process, the fusion of the pitch is promoted, and the secondary particles can be reliably bonded to each other. Also, during the molding process, heat can be transmitted through the mold and directly from the heat source to the raw powder, so the particles can be fused more quickly and bonded more firmly than the pitch can be condensed to increase its molecular weight.

In the firing process, the compact is embedded in a packing material whose average particle size is larger than the average particle size of the raw material powder, and then fired.

During the firing process, the pitch melts and becomes easily deformed, which causes volatile matter to be generated from the pitch, but by embedding the compact in packing material, deformation is suppressed, and because the average particle size of the packing material is coarser (larger) than the raw material powder, the generated volatile matter can be quickly discharged, preventing cracks and foaming caused by excess volatile matter.

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

By setting the average particle size of the raw material powder to 50 to 1500 μm, it is possible to obtain carbon electrodes for fluorine electrolysis devices that have a large specific surface area and high strength.

According to the carbon electrode for fluorine electrolysis of the present invention, the secondary particles that constitute the porous carbon-based material are not independent but are bonded to each other, so that particles and fine powder that have fallen from the inside of the electrode are prevented from coming out to the outside of the electrode. This makes it possible to provide a carbon electrode for fluorine electrolysis that is less contaminated.

In addition, according to the manufacturing method of the carbon electrode for a fluorine electrolysis device of the present invention, the raw material powder is obtained by kneading carbon particles with pitch having a softening point of 70°C or higher, so that 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. Furthermore, since pitch having a softening point of 200°C or lower is kneaded, there is no need to expose the pitch to high temperatures when melting it for kneading, and the condensation reaction is less likely to proceed at the pitch melting stage, and the pitch is easily fused by heat in the subsequent molding process, making it easy to obtain the desired shape of the carbon electrode for a fluorine electrolysis device.

In addition, to obtain the porous material, the material is fused with heat without pressure to obtain the desired shape of the carbon electrode for the fluorine electrolysis device. This means that even secondary particles with a wide particle size distribution can be bonded together to obtain a porous body, and there are many continuous pores, which means that volatile matter contained in the raw material powder can be removed in the subsequent firing process without accumulating inside.

In addition, to obtain the porous material, the desired shape of the carbon electrode for the fluorine electrolysis device is obtained by thermal fusion without applying pressure, so there is no dimensional change due to pressure, and the shape of the mold becomes the shape of the molded product as it is. As a result, it is possible to obtain a carbon electrode for the fluorine electrolysis device with high dimensional accuracy after firing.

FIG. 1 shows a flow diagram of a manufacturing process for a porous carbon material according to an embodiment of the present invention. FIG. 2 is a schematic diagram of a manufacturing process of a porous carbon-based material according to an embodiment of the present invention, in which (a) shows the raw material carbon particles and pitch, (b) shows the raw material powder obtained in the raw material step, (c) shows the packed raw material powder before molding in the molding step, (d) shows a portion of an integrated molded body obtained by combining the raw material powders after molding in the molding step, and (e) shows a portion of a porous carbon-based material (sintered body) obtained in the firing step. FIG. 3 is a flow diagram of a conventional manufacturing process for a porous carbon-based material, in which (a) shows the raw material carbon particles and pitch, (b) shows the raw material powder obtained in the raw material process, (c) shows the packed raw material powder before molding in the molding process, (d) shows a part of a molded body obtained by combining the raw material powder after molding in the molding process, and (e) shows a part of a porous carbon-based material (fired body) obtained in the firing process. FIG. 4 is a flow diagram of a conventional manufacturing process for isotropic graphite material, in which (a) shows the raw material carbon-based particles and pitch, (b) shows a kneaded product of the raw materials, (c) shows raw material powder obtained by pulverizing the kneaded product, (d) shows the packed raw material powder before molding in the molding step, (e) shows a part of a molded body obtained by bonding the raw material powders after molding in the molding step, and (f) shows a part of an isotropic graphite material obtained by the firing and graphitization steps. FIG. 5 shows an example of a method for producing a carbon electrode for a fluorine electrolysis device, in which (a) shows a molding die, (b) shows a molding die containing a raw material powder, (c) shows a sintered body, and (d) shows a carbon electrode for a fluorine electrolysis device having an attachment portion formed by a processing step. 6A and 6B are schematic diagrams showing the process of forming mounting holes using a drill, in which (a) is a schematic diagram showing the case where no pilot holes are formed, and (b) is a schematic diagram showing the case where pilot holes are formed. FIG. 7 shows another example of the method for producing a carbon electrode for a fluorine electrolysis device, in which (a) shows a mold, (b) shows a mold with a core pin installed, (c) shows a mold containing a raw material powder, (d) shows a sintered body, (e) shows a carbon electrode for a fluorine electrolysis device with an attachment portion formed by a processing step, and (f) shows a carbon electrode for a fluorine electrolysis device with an attachment hole formed by a processing step. FIG. 8 shows a graph of the pore distribution of the example and comparative examples 1 and 2. FIG. 9 shows a polarizing microscope photograph (a drawing substitute photograph) of the porous carbon material of the example embedded in resin. FIG. 10 shows a polarizing microscope photograph (a drawing substitute photograph) of the porous carbon-based material of Comparative Example 1 embedded in resin. FIG. 11 shows a polarizing microscope photograph (a drawing substitute photograph) of the isotropic graphite material of Comparative Example 2 embedded in resin. FIG. 12 shows a modification of the embodiment in which the molding step and the firing step are carried out simultaneously.

To explain the carbon electrode for a fluorine electrolysis device of the present invention and the manufacturing method of the carbon electrode for a fluorine electrolysis device, we will explain the carbon electrode for a fluorine electrolysis device that contains a porous carbon-based material according to an embodiment of the present invention, a carbon electrode for a fluorine electrolysis device that contains a conventional porous carbon-based material, and a carbon electrode for a fluorine electrolysis device that contains a conventional isotropic graphite material, while comparing the manufacturing methods, material structures, etc.

Figure 1 shows the manufacturing process for a carbonaceous porous carbon-based material for carbon electrodes in a fluorine electrolysis device, which is an embodiment of the present invention.

As shown in FIG. 1, the carbonaceous porous carbon-based material according to an embodiment of the present invention is manufactured through a raw material process in which carbon particles are mixed with pitch having a softening point of 70 to 200°C to obtain raw material powder, a molding process in which the raw material powder is placed in a mold and heated to a temperature higher than the softening point to obtain a molded body of a predetermined shape, and a sintering process in which the molded body is sintered.

(Raw material process)
In the kneading step of this embodiment, as shown in Fig. 2(a), carbon-based particles and pitch with 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 carbon-based particles bound to each other by a binder, and corresponds to secondary particles obtained through a firing step or a graphitization step. 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 is compatible with pitch and can provide a strong bond, and can be preferably used as the carbon-based particles of the present invention.

The raw material powder obtained in the raw material process may be used for molding as is, but if there is an appropriate particle size range for a porous carbon-based material for carbon electrodes in fluorine electrolysis devices, the particle size may be adjusted during the raw material process. Methods for particle size adjustment include classification and pulverization. When particle size adjustment is performed by pulverization, the carbon-based particles should be made sufficiently smaller than the particle size of the raw material powder to prevent the occurrence of exposed surfaces to which the binder does not adhere after pulverization.

The average particle size of the carbon-based particles is preferably 50 to 500 μm. If the average particle size of the carbon-based particles is 50 μm or more, the amount of pitch required in the raw material process can be reduced, and the disappearance of pores due to deformation of secondary particles and foaming due to generated gas can be prevented in the subsequent firing process. The average particle size of the carbon-based particles is preferably 70 μm or more, and more preferably 100 μm or more.
Furthermore, when the average particle size of the carbon-based particles is 500 μm or less, it is possible to prevent the occurrence of an exposed surface that is not covered with the binder.The average particle size of the carbon-based particles is preferably 400 μm or less.
The average particle size of the carbon-based particles can be measured by a laser diffraction particle size distribution analyzer.

The pitch used in this embodiment has a softening point of 70 to 200° C. By obtaining raw material powder by kneading carbon-based particles with pitch having a softening point of 70° C. or higher, it is possible to suppress adhesion of the raw material powder to each other at room temperature and to adjust the particle size of the raw material powder to a predetermined particle size at room temperature. The softening point is preferably 90° C. or higher, and more preferably 100° C. or higher.
In addition, by obtaining a raw material powder by kneading carbon-based particles with pitch having a softening point of 200° C. or less, it is not necessary to expose the raw material powder to high temperatures for kneading, and it is possible to suppress the progress of a condensation reaction at the stage of melting the pitch during kneading, thereby preventing an increase in the softening point. The softening point is preferably 180° C. or less, more preferably 160° C. or less.

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 at 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 together. The kneading temperature is more preferably 180° C. or higher.
By setting the kneading temperature at 300° C. or less, polycondensation of the pitch can be prevented and moldability of the raw material powder can be ensured. The kneading temperature is more preferably 280° C. or less.

In addition, the process for obtaining porous carbon-based materials for carbon electrodes in fluorine electrolysis devices mainly relies on thermal fusion, and almost no pressure is applied, so that even secondary particles with a wide particle size distribution can be bonded together to obtain a porous body, and continuous pores can be easily formed, making it possible to remove volatile matter contained in the raw material powder in the subsequent firing process without it accumulating inside.

In this embodiment, it is preferable to end the kneading when the pitch is melted and mixed uniformly, and specifically, the kneading time is preferably 30 minutes or less. If 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.

(particle size adjustment)
The raw material powder ( FIG. 2( b )) obtained in the raw material step is preferably subjected to particle size adjustment as necessary. By performing particle size adjustment, a porous carbon-based material for a carbon electrode for a fluorine electrolysis device having a predetermined porosity and particle size distribution can be obtained. Methods such as classification and pulverization can be used for particle size adjustment. When particle size adjustment is performed by pulverization, a raw material powder in which carbon-based particles are solidified with pitch is pulverized, so that many adhesive secondary particles in which the carbon-based particles are entangled with pitch are obtained, while non-adhesive raw material particles are also obtained at the same time, such as raw material powder in which the carbon-based particles are destroyed or the pitch serving as a binder is peeled off. In the method for producing a carbon electrode for a fluorine electrolysis device of the present invention, molding is performed mainly by a fusion action due to heat, so that even such non-adhesive raw material powders can be bonded to each other without becoming independent.

The average particle diameter of the raw material powder used in the present embodiment is preferably 50 to 1500 μm. When the average particle diameter 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 for a fluorine electrolysis device that can be easily used for various applications can be obtained. The average particle diameter of the raw material powder is more preferably 80 μm or more, and further preferably 100 μm or more.
When the average particle size of the raw material powder is 1500 μm or less, the size of the irregularities formed on the surface when molded in a molding die can be reduced, and a porous carbon-based material for a carbon electrode for a fluorine electrolysis device having 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.

(molding process)
In the molding process of this embodiment, the obtained raw material powder (FIG. 2(b)) is placed in a mold (FIG. 2(c)) and heated to a temperature higher than the softening point of the pitch to obtain a molded body of a predetermined shape as shown in FIG. 2(d). As shown in FIG. 2(d), in this embodiment, the raw material powder is heated and maintained at a temperature higher than the softening point of the pitch, so that even small raw material powder particles or raw material powder particles from which the binder has peeled off are not separated but are bonded to each other and integrated.

In this embodiment, heat is applied to the raw material powder, so even non-adhesive raw material powder can be incorporated into the secondary particles and integrated, suppressing the generation of independent, free carbon-based particles.

In the molding process of this embodiment, the desired heating time is 10 minutes or more. Since the molding process uses heat to form the powder, extending the heating time can soften the raw material powder more and fuse it firmly. A heating time of 20 minutes or more is more preferable, and 40 minutes or more is even more preferable.

The forming process of this embodiment does not necessarily need to be prepared separately as a forming process, and the initial stage of the subsequent firing process can be the forming process. For example, as shown in FIG. 12, raw material powder may be placed in a strong container, covered, and then buried in packing material for firing. In FIG. 12(a), raw material powder is filled in a combustible container, in FIG. 12(b), the above container is buried in a firing container filled with packing material, and in FIG. 12(c), the temperature is raised, the raw material powder is melted and molded, and fired to obtain a fired body. The container is preferably air-permeable so that the generated gas does not accumulate, but may be made of a material that becomes air-permeable when heated. In the initial stage of firing, the raw material powder is fused to each other and formed into a predetermined shape. If the temperature is further raised, the generated gas passes through the air-permeable container and is discharged to the outside, and the molded body thermally shrinks as the temperature rises. In addition, it is preferable that the container is combustible. If the container is combustible, it will carbonize during the firing process and will no longer retain its original shape. Since it is embedded in packing material, the packing material follows the shrinkage of the molded body, preventing deformation. As a breathable, flammable container, cardboard with many holes punched in it to ensure breathability can be used.

In addition, in the molding process of this embodiment, as long as the temperature range is such that fusion occurs, molding may be performed using not only heat but also pressure. By applying pressure, the shape of the molding die can be transferred, and a porous carbon-based material for carbon electrodes for fluorine electrolysis devices with high dimensional accuracy can be obtained.

In order to clarify the features of the present invention, the following describes conventional porous carbon-based materials and conventional dense isotropic carbon-based materials (isotropic graphite materials), focusing in particular on the molding process.

In conventional porous carbon materials, carbon particles and pitch shown in FIG. 3(a) are kneaded to obtain raw material powder shown in FIG. 3(b). Then, the molding process shown in FIG. 3(c) and (d) and the sintering process shown in FIG. 3(e) are performed. FIG. 3(c) shows the stage before molding, and FIG. 3(d) shows the stage after molding. In conventional methods, the molding process shown in FIG. 3(c) and (d) is performed mainly by the action of pressure without melting the pitch. Therefore, the contact points of particles to which pressure is applied are strongly bonded, whereas the contact points of particles to which pressure is not applied cannot be strongly bonded. In the production of porous carbon materials, coarse raw material powder is used, so large voids are formed at the stage of filling the mold, and it is difficult to apply sufficient pressure to the raw material powder that has entered the large voids. Therefore, it is unable to be integrated with other particles and becomes a free secondary particle, which does not contribute to the strength of the material and only generates particles.

In addition, in conventional isotropic graphite materials, carbon particles and pitch shown in FIG. 4(a) are mixed to obtain a lump-shaped mixture as shown in FIG. 4(b). The mixture is then pulverized to obtain raw material powder as shown in FIG. 4(c). The raw material powder is then molded under high pressure to obtain a molded body as shown in FIG. 4(d) and (e), and the molded body is then subjected to a sintering process as shown in FIG. 4(f) and graphitized as necessary to obtain an isotropic graphite material. Note that FIG. 4(d) shows the stage before molding, and FIG. 4(e) shows the stage after molding.

In conventional graphitic isotropic carbon-based materials (isotropic graphite materials), the raw powder after grinding is fine, so large voids are unlikely to form during molding, and pressure is easily distributed evenly, making it difficult for free particles to form. In addition, because the voids themselves are fine, even if free secondary particles are present, they are contained inside and are unlikely to cause particles.

(Firing process)
In the sintering step of this embodiment according to the present invention, the obtained molded body ( FIG. 2( d )) is heated in an inert atmosphere to obtain a sintered body shown in FIG. 2( e ). In this embodiment, the sintered body becomes a porous carbon-based material for a carbon electrode for a fluorine electrolysis device.

The firing temperature is preferably, for example, 700 to 2000°C. By firing at 700°C or higher, volatile matter is sufficiently removed from the compact, making it usable as a porous carbon-based material for carbon electrodes for fluorine electrolysis devices. The firing temperature is more preferably 800°C or higher, and even more preferably 900°C or higher.

In addition, by carrying out the calcination at 2000°C or less, it is possible to impart sufficient hardness to the porous carbon-based material, and obtain a porous carbon-based material that can be used, for example, in an electrolytic electrode. The calcination temperature is more preferably 1800°C or less, and even more preferably 1500°C or less.

In the manufacturing method according to the present embodiment of the present invention, the raw material powder is softened in the molding process, so the pitch is not fully polycondensed in the raw material process. As a result, it contains a lot of volatile matter, but since it is porous after molding, the decomposition gas is quickly diffused to the outside, and densification and sealing of pores caused by carbonization of the volatile matter inside the molded body can be prevented, and cracks can be prevented.

In the firing process of this embodiment of the present invention, it is preferable that the average particle size of the packing material is coarser (larger) than that of the raw material powder. If the average particle size of the packing material is coarser than that of the raw material powder, the tar-like product generated from the compact will not remain within the compact but will quickly diffuse, promoting the formation of pores in the porous body.

In the porous carbon-based material for carbon electrodes for fluorine electrolysis devices obtained through the above processes, the secondary particles are bonded to each other without being independent, at least inside the material, and the presence of free particles is suppressed. Therefore, it is possible to suppress the leakage of particles and fine powder from the surface of the material.

In this embodiment, the maximum pore diameter is preferably 50 to 1000 μm. If the maximum pore diameter is 50 μm or more, the molten salt can easily penetrate 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 further preferably 100 μm or more.
When the maximum pore diameter is 1000 μm or less, the decrease in surface area is suppressed and the surface area participating in electrolysis can be increased. The maximum pore diameter is more preferably 800 μm or less, and further preferably 500 μm or less.
The maximum pore diameter can be measured by mercury intrusion porosimetry.

(Processing process)
In the processing step of this embodiment, at least a part of the obtained sintered body ( FIG. 2( e )) is surface-processed to form an attachment portion, and the remaining part other than the attachment portion is made into an immersion portion to be immersed in an electrolytic solution. The sintered body obtained in the sintering step is obtained as a material having a shape similar to that of a carbon electrode for a fluorine electrolysis device, and by processing the attachment portion that comes into contact with a metal clamp that supplies current, a highly accurate attachment portion can be obtained and contact resistance can be reduced.

In the processing step, it is desirable to machine mounting holes in the mounting portion. Providing mounting holes in the mounting portion can increase the reliability of the connection with the metal clamp that supplies current. The mounting holes may be either through holes or blind holes, and may also be straight holes or screw holes.

Figure 5 shows an example of a method for manufacturing a carbon electrode for a fluorine electrolysis device. As shown in Figure 5(a), a mold 1 that matches the shape of the carbon electrode is prepared, and as shown in Figure 5(b), the raw material powder 2 obtained in the raw material process is placed in the mold 1, and a molding process is carried out. As shown in Figure 5(c), the molded body obtained in Figure 5(b) is sintered to obtain a sintered body 3. As shown in Figure 5(d), a processing process is performed to perform surface processing (flat processing in this example) on the sintered body 3 to form an attachment part 11. Furthermore, a mounting hole 15 is formed in the attachment part 11, thereby completing the carbon electrode 10 for a fluorine electrolysis device. The remaining part other than the attachment part 11 is the immersion part 12 that is immersed in the electrolyte.

To reduce the contact resistance between the mounting part 11 and the metal clamp, the mounting part 11 is preferably machined, for example, into a cylindrical or flat shape. If it is cylindrical, it can be machined using a centerless processing machine or lathe using a grinding wheel, and if it is flat, it can be ground using a surface grinder or milling machine. Furthermore, to firmly connect to the metal clamp, a mounting hole 15 such as a through hole or a screw hole can be formed in the mounting part 11. If the mounting hole 15 is a screw hole, the metal clamp can be fixed even if it is a non-through hole.

However, the carbon electrode for the fluorine electrolysis device of the present invention is made of a carbonaceous material and is therefore hard. When drilling the mounting hole 15 using a drill, as shown in FIG. 6(a), the machining ability of the center of the drill 20, which has a slow peripheral speed, is poor, and the tip of the drill 20 is prone to wear and breakage.

To prevent this, as shown in FIG. 6(b), a method is considered in which pilot holes 15a that serve as the bases for the mounting holes 15 are drilled in advance in the molded body during the molding process. In this case, the center of the drill 20, which has a slow peripheral speed, is not involved in the machining, and the tip of the drill 20 can be prevented from being worn out or broken. FIG. 7 shows an example of a manufacturing method for a carbon electrode for a fluorine electrolysis device in which such pilot holes 15a are formed in the molding process. In this example, as shown in FIG. 7(a), a molding die 1 similar to that shown in 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 during the manufacturing process of the molding die 1.

The core pin 7 is a pin installed in the mold 1, and is a member that forms holes in the molded body and the fired body. Carbon electrodes for fluorine electrolysis devices are made of carbonaceous material, and drilling holes in them is difficult. In the manufacturing method for carbon electrodes for fluorine electrolysis devices of this embodiment, the electrodes are molded by heat without applying pressure in the molding process. Therefore, even if a core pin is present in the process of molding the particulate raw material with low fluidity, no strong force is applied to the core pin, and it does not need to be firmly fixed to the mold. This allows holes to be drilled at the specified positions with high precision.

There are no particular limitations on the material of the core pin 7, but if it is to be removed after molding, it is sufficient that it is heat-resistant to the temperatures during molding, and there are no particular limitations on the material, such as metal, ceramic, resin, wood, etc. If it is not to be removed after molding and is to be carbonized during firing, pulp, wood, resin, etc. can be used.

When forming pilot holes 15a using core pins 7, they are placed further outward than the actual position and further away from the actual spacing, taking into account the firing shrinkage of the molded body. The direction in which core pins 7 extend is not particularly limited, and may be the thickness direction or length direction of the molded body. In the manufacturing method of this embodiment, molding is performed with almost no pressure applied, so misalignment or deformation is unlikely to occur in any direction.

As shown in FIG. 7(c), the raw material powder 2 obtained in the raw material process is placed in a 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 a fired body 3. Since a core pin 7 is installed in the mold 1, a pilot hole 15a is formed in the fired body 3.

As shown in FIG. 7(e), a surface treatment (flat surface treatment in this example) is performed on the area including the pilot hole 15a of the sintered body 3 in the processing step to form the mounting portion 11. As shown in FIG. 7(f), a drill 20 is advanced along the pilot hole 15a in the manner shown in FIG. 6(b) to form the mounting hole 15, completing the carbon electrode 10 for a fluorine electrolysis device. The remaining portion other than the mounting portion 11 is the immersion portion 12 that is immersed in the electrolyte.

As shown in FIG. 6(b), if the pilot hole 15a is pre-formed, the load on the center of the drill 20, which is the most difficult to machine, can be reduced, and the mounting hole 15 can be easily drilled during the machining process. In addition, if the mounting hole 15 is a through hole, cutting powder can be discharged downward, and the temperature rise of the cutting edge due to friction can be reduced.

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 Figures 5 and 7, but also in the length direction, and the core pin 7 is designed and installed based on the direction in which the mounting hole 15 is formed.

(Example)
100 parts by weight of amorphous pitch coke with an average particle size of 300 μm as carbon-based particles and 25 parts by weight of pitch with a softening point of 150° C. as 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 put into the continuous kneader quickly melted and was 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 progressed polycondensation.

The resulting mixture was then coarsely crushed and passed through a 2 mm sieve to adjust the particle size. The average particle size of the resulting raw material powder was 900 μm.

The obtained raw material powder was filled into a metal mold with an opening of 600 x 300 mm and a depth of 80 mm, a metal lid was placed on top, the surroundings were heated to 200°C, and after holding for 120 minutes, the lid was slowly pressed down to adjust the overall shape. The pressure applied at this time was only the weight of the lid, and was 2 kPa.

After cooling, the mixture was removed from the mold, packed in a calcination can, embedded in packing coke having an average particle size of 5 mm, and calcined at 900° C. to obtain a calcined body.
Next, a part of the fired body was surface-processed to form a mounting portion and the remaining portion was processed to form an immersion portion, thereby producing a carbon electrode for a fluorine electrolysis device.

(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. and 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.

(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 the mixture was kneaded for 200 minutes. During the kneading process, the pitch polycondensed and its softening point rose to 200° C. or higher. 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.

The resulting mixture was pulverized to obtain a raw material powder with 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 resulting molded body was sintered 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.

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

Figure 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 together by heat during molding, with rounded corners, and no free secondary particles were observed. Furthermore, even after ultrasonic cleaning 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.

Figure 10 shows a polarizing microscope photograph 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 cause particles remained inside the pores (free secondary particles). Furthermore, when ultrasonic cleaning was performed using water as in the examples, particle generation from the pores was confirmed.

11 shows a polarizing microscope photograph 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 are no large pores to begin with, and the presence of free secondary particles that cause particles could not be confirmed. Even if free secondary particles exist, they are believed to be confined inside the fine pores and are unlikely to escape to the outside.
When ultrasonic cleaning was performed using water in the same manner as in the example, particles were observed to be generated from the pores. It is presumed that the particles inside the pores were knocked out by the strong cleaning power.

Reference Signs List 1 Mold 2 Raw material powder 3 Sintered body 7 Core pin 11 Mounting portion 12 Immersion portion 15 Mounting hole 15a Pilot hole 20 Drill

Claims (3)

A carbon electrode for a fluorine electrolysis device comprising a porous carbon-based material,
The porous carbon-based material has carbon-based particles and a carbonaceous binder that binds the carbon-based particles to each other, forming secondary particles,
The secondary particles are not independent but are bonded to each other,
The carbon electrode for a fluorine electrolysis device has a bulk density of 1.0 to 1.5 g/cm ³ . The carbon electrode for a fluorine electrolysis device has an attachment portion and an immersion portion,
2. The carbon electrode for a fluorine electrolysis device according to claim 1, wherein the attachment portion has a processed surface, and the immersion portion has an unprocessed surface. The carbon electrode for a fluorine electrolysis device according to claim 1 or 2, wherein the carbon electrode for a fluorine electrolysis device has a maximum pore size of 50 to 1000 μm.

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