WO1999022045A1

WO1999022045A1 - Electrode of an electrolytic bath for generating fluorine and isotropic carbonaceous block used therefor

Info

Publication number: WO1999022045A1
Application number: PCT/JP1998/004859
Authority: WO
Inventors: Tetsuro Tojo; Jiro Hiraiwa; Nobuatsu Watanabe; Masahide Sangawa
Original assignee: Toyo Tanso Co., Ltd.
Priority date: 1997-10-28
Filing date: 1998-10-27
Publication date: 1999-05-06

Abstract

A carbonaceous block for a positive electrode, which is inexpensive yet exhibiting a long life and excellent electrode characteristics, and an electrode using the carbonaceous block. The isotropic carbonaceous block is used as a positive electrode in an electrolytic bath which comprises a hydrogen fluoride-containing molten salt for generating fluorine, and has a bulk density of less than 1.6 g/cm3, a bending strength of more than 200 kgf/cm2, an average porous radius of more than 0.5 νm, a cumulative porous volume of more than 80 mm3/g, and a gas permeability of more than 0.1 cm2/s.

Description

Description Electrode of electrolytic bath for fluorine generation and isotropic carbonaceous block used for the electrode

The present invention relates to an electrode of an electrolytic bath for generating fluorine which is inexpensive and has excellent electrode characteristics, and an isotropic carbonaceous block used for the electrode. Background art

As an industrial method for producing fluorine, an electrolysis method of a molten salt containing hydrogen fluoride (hereinafter abbreviated as “HF”) is generally employed. In most cases, the so-called medium temperature method is used in which a mixed molten salt of potassium fluoride (hereinafter abbreviated as “HK J”) and HF is maintained at about 90. In order to carry out the process, a carbon material is used exclusively for the anode of the electrode of the fluorine electrolytic cell, and a metal such as iron is generally used for the cathode and the tank body, and Monel is used for the partition. Decomposition usually proceeds according to the general reaction formula (1) under the conditions of a current density of 7 to 10 O AZ dm ² and a bath voltage of 8.5 to 15 V, and fluorine is generated on the anode side partitioned by the partition wall. On the cathode side, hydrogen is obtained.

2 HF-→ F ₂ + H ₂ (1) In order to ensure the smooth operation of such electrolysis, carbon materials for anodes basically satisfy the following required electrode characteristics ① to ③ It is preferable.

(1) It must be possible to avoid the occurrence of the so-called anode effect, that is, the situation in which the voltage suddenly rises after the polarization has progressed to some extent and the current cannot be supplied. (2) To produce fluorine, increase the applied current density. However, the polarization of the anode usually progresses rapidly in proportion to the increase in the applied current density. This accelerates the anodic effect, increases the number of electrode (anode) replacements, and reduces production efficiency. Therefore, the anode effect can be suppressed even if the applied current density is slightly increased.

(3) During electrolysis, the carbon material itself as the anode is partially destroyed, collapsed, peeled off, etc., making it impossible to conduct electricity, or the resulting carbon powder mixes with the fluorine being recovered, lowering its purity. The carbon material itself, which is the anode, must have considerable strength so that it does not occur.

Until now, carbon materials that have been used as anodes for the production of fluorine, such as XJ, 'in du strial Electromica 1 P eocesses, Ed. By A. Kuhn, p p. 22, 1970, Elsevior ”, the pore radius was more than 5 / m. However, because of their large pore diameter, their mechanical strength was also low, and their self-damage prevention ability was low, so they could not satisfy the above requirements (1) and (3).

The present applicants have proposed an effective carbon material for an anode capable of solving the above problems and satisfying the required electrode characteristics, having sufficient strength and being hardly polarized, that is, effective for suppressing the anode effect. We succeeded in developing a carbonaceous block (isotropic carbonaceous block) with a specific resistance of less than 1.2 in the vertical and horizontal directions, which can increase the maximum current density in A patent has been obtained for the "manufacturing method" (Japanese Patent Publication No. 61-12994). The development of the isotropic carbonaceous blocks having such sufficient strength (high density and high strength), earlier fluorine only in the maximum current density of at most. 6 to 8 AZ dm ² extent in order to prevent the occurrence of anode effect those that did not perform the electrolytic production, we can continue the electrolysis stably at maximum current density of about 1 5 a / dm ² I got it. As a result, the efficiency of fluorine electrolysis, that is, the productivity of fluorine, was greatly improved. However, there is still room for improvement in the above carbonaceous block. That is, in the pre-sintering molding stage to obtain a high-density, high-strength isotropic carbonaceous block, cold isostatic pressing of about 1 ton Zcm ² (hereinafter referred to as “CI PJ molding”) is required. Because of this, the molding equipment was relatively large, and before that, a hard and brittle porous anode carbonaceous block with a bulk density of about 1.2 to 1.3 was produced on a relatively small scale. The molding cost was higher because the molding pressure was higher than when molding with a low-pressure extrusion molding machine.

In addition, in order to use the carbonaceous block after firing as an electrode, it is necessary to machine it into a shape and size with predetermined dimensions commensurate with the electrolytic capacity, but because of its high density and high strength, it is extremely It was difficult to process and the machining cost was high. High-density, high-strength isotropic carbonaceous blocks certainly have a long life and excellent electrolytic performance, but because molding costs are extremely high, machining costs are extremely high, and until product prices can be effectively reduced. Has not been improved.

An object of the present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electrode for an anode made of an isotropic carbonaceous material, which has a long life and excellent electrode characteristics but is inexpensive. The point is to provide an isotropic carbonaceous block used for it. Disclosure of the invention

The electrode made of an isotropic carbonaceous material used as the anode of the electrolytic bath for generating fluorine of the present invention, which has achieved the above object, has a bulk density of 1.egZcni ³ or less.

The bending strength is 2 O Ok gf / cm ² or more. An electrode made of such an isotropic carbonaceous material has a structure that is slightly weaker than the mechanical strength of the previously developed isotropic carbonaceous block, but has sufficient self-damage prevention ability. It is also possible to maintain a practical level, and further improve the ability to suppress the anode effect. As a result, machining becomes easier due to the reduced mechanical strength. Furthermore, since the molding pressure as a pre-process is low, general-purpose mold molding can be performed without using CIP molding. In addition, even in the case of CIP molding, it is possible to manufacture at low cost because of the low molding pressure. Therefore, the anode of the electrolytic bath for fluorine generation, which is inexpensive, has a longer life, and has excellent electrode characteristics, is significantly reduced by greatly reducing the costs required for machining and the former stage of molding and improving the ability to suppress the anode effect. An isotropic carbonaceous block can be provided.

Further, the isotropic carbonaceous material has an average pore radius of 0.5 im or more, a cumulative pore volume of 80 mm ³ Zg or more, and a gas permeability of 0.1 cm ² s or more. I do.

With such an isotropic carbonaceous material, it is possible to prevent the electrolytic bath from penetrating into the electrode. In addition, the wettability of the electrode surface can be ensured, and the bubbles of fluorine gas can be easily removed, and the electrode for fluorine electrolysis can be used more stably even under high current density electrolysis conditions.

An electrode using the isotropic carbonaceous material as described above, wherein a metal coating film is formed on a surface of the isotropic carbonaceous material at a junction with an electrically conductive support member. It is characterized by the following.

The surface corresponding to the joint with the support member is coated with a metal such as Ni or Cu by an appropriate method such as thermal spraying or electrolytic plating. As a result, it is possible to prevent the electrode from cracking due to Joule heat and arc discharge generated by corrosion of the joint during use.

Hereinafter, the present invention will be described in detail. (1) The inventors of the present invention first pointed out that the problem remaining in the previously developed isotropic carbonaceous block, that is, the problem that the cost required for molding and In order to find a solution near the limit, we believe that the mechanical strength of the block can be solved if it can be positively weakened to the point where self-damage can be avoided and good electrode characteristics can be maintained. Various experimental studies were repeated.

Furthermore, the present inventors have found, in the course of the study, that the anodic effect is less likely to occur during fluorine electrolysis when the porous is somewhat porous than when the isotropic carbonaceous block is dense. As a result of microscopic consideration of this phenomenon, the following findings were obtained.

That is, the reaction between fluorine generated on the anode made of a carbonaceous electrode and the carbon electrode during electrolysis generates fluorinated graphite having extremely low surface energy. In the portion where the fluorinated graphite is generated, the wettability between the anode and the bath becomes poor, and the portion becomes electrochemically inactive. The effective area of the anode decreases with increasing coverage of the anode surface with fluorinated graphite, and the current density increases. This is the main cause of anode overvoltage in fluorine electrolysis. When the coverage of graphite fluoride exceeds about 20 ° / ₀ , the voltage rises sharply and power cannot be supplied. This phenomenon is the anodic effect.

In a sufficiently dehydrated electrolytic bath (KF · 2HF), the reaction shown in equation (2) proceeds.

C _x ^† F "is called a fluorine-graphite intercalation compound, and the bonding state of C and F is a charge transfer type. Here, MF is Li F, Ni F ₂ , C a F _z , M g These are metal fluorides such as F ₂ and A 1 F ₃ , which are catalysts for promoting this reaction.These compounds are formed when fluorine species penetrate into the graphite layer.These are the large electronegativities of fluorine atoms. Π electrons in the graphite layer It is generated in holes by being attracted to nitrogen atoms. As a specific action, the electrical conductivity increases, and the polarity increases. The bath is an ionic melt, and the polarity between the bath and the electrode is greatly improved by improving the polarity of the electrode surface. This suppresses the anodic effect on the electrode surface where the fluorine-graphite intercalation compound is generated, and the fluorine generation reaction proceeds smoothly.

If the carbon electrode, which is the anode, is appropriately porous, fluorine gas in contact with the anode surface will enter the minute gap near the surface inside the anode. As a result, the film of fluorine bubbles generated on the anode is easily interrupted, and the surface of the anode is exposed at the interrupted portion, so that it is easily wetted with the bath again, the electrochemically active state is restored, and electrolysis is started. It turns out that we can continue further. Therefore, based on the above findings, the present inventors made the carbonaceous material for the anode dense enough to avoid self-damage, and reduced the surface on which the above-mentioned fluorine-graphite intercalation compound was formed, with the ability to suppress the anode effect. Further studies were conducted to find appropriate mechanical strength that can be made porous so as to contribute to improvement. As a result, finally, characteristics of "isotropic carbonaceous material, bulk density 1. 6 g Z cm ³ or less, a bending strength of 2 0 0 kgf Z cm ² or more, the average pore radius is 0. 5 m or more, cumulative pore volume of 80 mm ³ / g or more, gas permeability of 0.1 cm ² Z s or more ” This is a completed carbonaceous material.

(2) In order to obtain the above isotropic carbonaceous material, for example, use is made of a material obtained by adding a pitch binder of approximately the same weight or more to a fine powder aggregate, or Use aggregates that show large shrinkage during the heat treatment stage, such as raw coke, to achieve the necessary densification of the carbon material.Some are combined with aggregates such as denatured bitch-mesocarbon microbeads. This can be achieved by using a monolithic material in which the material is integrally formed. Here, the term “micro-mosaic structure” refers to a micro-mosaic structure in which the mesophase spherules whose size is 10 μπι or less are uniformly dispersed in an isotropic matrix like a mosaic during the process of heating the pitch to form mesophase spherules. Say. When a carbon material having such a structure is heated, the mosaic portion shrinks greatly, and a desired high-density material is easily obtained.

Further, as described above, so-called mesocarbon microbeads obtained by separating mesophase microspheres generated from pitch can be advantageously used as a raw material of the carbon electrode of the present invention as a monolithic material as it is. . If the atmosphere is controlled during the carbonization of the pitch, a non-graphitizable carbon material precursor is obtained in air and a graphitizable carbon material precursor is obtained in nitrogen gas.These precursors are called altered pitches. It can be used for producing the carbon electrode of the invention.

That is, the carbonaceous block for an anode of the present invention is, for example, a powder binder having a particle size of 3 to 20 / m. A mixture of 130 parts by weight of a binary material or a modified material such as a denatured pitch mesocarbon mic mouth bead is kneaded at about 150 to 250 ° C, cooled, pulverized, and then subjected to particle size adjustment. It can be manufactured by molding and finally heat-treating. The molding is carried out by CIP molding or die molding under a low pressure of about 100 to 600 kg / cm ² , preferably about 100 to 300 kg / cm ² , to form an isotropic block. The heat treatment temperature is usually from 1000 ° C to 1500 ° C, preferably from 1000 ° C to 1200 ° C. The isotropic carbonaceous block obtained in this way has a characteristic structure that is much more dense but moderately porous compared to the carbon material blocked by so-called extrusion molding. Has become. In addition, the raw material, such as altered pitch @ mesocarbon microbeads, should be a monolithic material with a nearly spherical Thus, as described above, the anisotropy of the specific resistance in the vertical and horizontal directions can be equal to or less than 1.2 even in mold molding.

The characteristics of the isotropic carbonaceous block for an anode of the present invention comprising such a structure are, as described above, at least 1.S gZcm ³ or less in terms of bulk density and 200 kg kgZcm ² or more in bending strength. It is necessary to be. More preferably, the bulk density is 1.25 to: L. 5 gZcm ³ and the flexural strength is 30 ° kgf Zcm ² or more. With the isotropic carbonaceous block for anode having such characteristics, the suppression of the anode effect is further improved, and the electrode characteristics can be further improved. In addition, machining can be easily performed into an electrode shape having a predetermined size corresponding to the electrolytic capacity, and the machining cost can be reduced. Further, since the molding pressure as a pre-process can be reduced, general-purpose mold molding can be performed without using CIP molding, and even in the case of using CIP molding, further downsizing can be achieved. Therefore, the cost for machining and the preceding stage, molding, are greatly reduced, and the ability to suppress the anodic effect is improved, so that it is inexpensive, has a longer life, and has excellent electrode characteristics. An anisotropic carbon block can be provided.

In addition, as the characteristics of the isotropic carbonaceous block for an anode of the present invention, the average pore radius is 0.5 / im or more, the cumulative pore volume is 80 mm ³ / g or more, and the gas permeability is 0.1 cm ² / s The above is also preferable. Such an isotropic carbon block prevents bubbles of fluorine gas generated on the electrode surface while preventing the electrolytic bath from penetrating into the electrode, and has a high current density as a fluorine electrolysis electrode. It can be used more stably up to electrolysis conditions. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic sectional view of an electrolytic cell included in a general electrolytic device. Fig. 2 shows the carbonaceous block (CIP molding method) used in Experimental Examples 1-4. FIG. 6 is a diagram showing the relationship between the cumulative pore volume and the average pore radius obtained by the mercury intrusion method for the obtained samples I to II).

Figure 3 is a schematic diagram of the gas permeability measuring equipment.

FIG. 4 is a table summarizing the measurement results of the respective characteristic values of the samples in Experimental Examples 1 to 9.

Figure 5 shows the constant current method in a KF · 2 HF electrolytic bath at 90 for the one material block (samples I to 得 obtained by the CIP molding method) used in Experimental Examples 1 to 4. FIG. 4 is a diagram showing a anodic current density-potential curve. Figure 6 shows the results obtained by the galvanostatic method in a 90 ° CK F · 2 HF electrolytic bath for the carbonaceous blocks (samples I to II obtained by the die molding method) used in Experimental Examples 5 to 8. FIG. 4 is a diagram showing an anode current density-potential curve.

FIG. 7 is a diagram showing the relationship between current density and fluorine gas bubble generation for the carbonaceous blocks (samples I to II obtained by the CIP molding method) used in Experimental Examples 1 to 4. BEST MODE FOR CARRYING OUT THE INVENTION

An electrolytic cell included in a general electrolytic apparatus that can obtain fluorine using the carbonaceous block according to the present invention will be described with reference to FIG. In FIG. 1, an electrolytic cell included in a general electrolytic apparatus is composed of an electrolytic cell body 1 forming an electrolytic bath 1a using a mixed molten salt (KF · 2HF), and an electrolytic cell immersed in the mixed molten salt. An anode 2 made of an isotropic carbonaceous block, a cathode 3 generally made of metal, and a partition wall 4 separating the anode 2 side and the cathode 3 side are provided. Here, 5 in the figure is a bus bar, 6 is an insulating material, 7 is an electrolytic cell lid made of metal, 8 is a cathode gas outlet, 9 is an anode gas outlet, 10 is a bolt for mounting the anode 2, 11 indicates a holding plate, and 12 indicates a metal-coated surface. The anode 2 made of a carbonaceous block is an L-shaped bus bar 5 made of metal. And a holding plate 11 and a supporting member such as a bolt 10 which can be electrically connected to the apparatus main body.

It is well known that carbon materials have higher specific resistance than metals. During the electrolysis, mixed molten salt (KF ■ 2HF) and generated gas (F ₂ ) enter between the bus bar 5 and the holding plate 11 and the anode 2. At this time, the conduction of the contact surface is partially inhibited by solidification of the mixed molten salt (KF ■ 2HF) or generated gas (F ₂ ), or reaction with the anode 2 made of carbon material and corrosion. . If this becomes severe, heat will be generated, or in extreme cases, electric discharge will occur, damaging the electrodes and rendering it impossible for electrolysis. In order to suppress this phenomenon, the surface 12 of the anode 2 made of a carbonaceous block, which is in contact with the bus bar 5 and the holding plate 11, is sprayed or plated with metal such as Ni or Cu. Is coated. This is because the contact resistance between the metal and the metal is lower than that between the carbon material and the metal. This makes it possible to maintain a stable energized state for a long period of time and to prevent electrode cracking.

Next, the present invention will be described in more detail with reference to experimental examples.

(Experimental examples 1-4, Experimental examples 5-8)

In Experimental Examples 1-4, four types of carbonaceous blocks for samples having different mechanical strengths adjusted by variously changing the molding pressure by the CIP molding method were investigated and evaluated for their ability to suppress the anodic effect. In Experimental Examples 5 to 8, the anodic effect suppressing ability of four other types of carbonaceous blocks for samples was investigated in the same manner as in Experimental Examples 1 to 4, except that the molding method was a mold molding method. evaluated. In Experimental Example 9, a carbonaceous block for a sample was prepared in the same manner as in Experimental Examples 1 to 4, except that the starting material used was mainly mesoporous microbeads.

First, the carbonaceous block raw materials for the samples of Experimental Examples 1 to 8 before molding were as follows. Was adjusted in the manner described above. That is, 90 parts by weight of coal tar pitch is added to 100 parts by weight of calcined petroleum coke powder pulverized to 325 mesh (Tyler) or less, and brought to about 150 to 250 ° C, preferably about 180 to 220 ° C. The mixture was kneaded under heating for a long time, the volatile content was adjusted, and the mixture was cooled to room temperature. Then, it was pulverized again to classify and collect pulverized products of 100 mesh (Tyler) or less, and used as raw materials for carbonaceous blocks for samples.

The carbonaceous block raw material for the sample in Experimental Example 9 was formed by CIP using mesocarbon microbeads having an average particle diameter of 10 to 40 m, and then fired at 1000 ° C.

Next, the obtained raw material was molded by four methods using both the CIP molding and the die molding while changing the pressure so as to obtain a product having dimensions of 340 XI 70 X thickness 70 (mm). The carbonaceous block for the anode as a sample was fired by firing nine types (for Experimental Examples 1 to 4, for Experimental Examples 5 to 8 and for Experimental Example 9) at 100 ° C. The test pieces were prepared, and five test pieces each of 10 × 10 × 10 mm and 10 × 10 × 60 mm were prepared, and each physical property was measured.

For the measurement of bulk density, use a test specimen of 10 x 10 x 60 mm (however, the dimensional tolerance is 10 ± 0.02, 5 ± 0.02, 60 ± 0.1). First, transfer the test piece to an air bath at 105 to 110 ° C, cool it every hour, and weigh it. This is repeated until a constant weight is reached. Next, measure the length of each test piece at three points, and determine the volume from the average size of each side. The bulk density of the test side is calculated by the following formula and rounded to three decimal places.

d = W / V

Where d bulk density

W Weight of dry specimen (g)

V volume (cm ³ ) The bulk density of the test pieces is shown by averaging the measured values of five test pieces rounded to two decimal places.

The hardness was measured by a Shore D type hardness tester using a test piece 1 ◦ X 10 X 6 Omm (however, dimensional tolerances 10 ± 0.02, 5 ± 0.02, 60 ± 0 1) Measure. The tester is used by placing it vertically on a stable table. Measurements are made at three points each on the pressurized surface and side surface during molding. However, the measurement points must not be repeated, close, or close to the end face. The reading of the measured value is an integer value. The test specimens should be kept for at least 2 hours in an air bath of 105 to 11 and cooled in a desiccator to reach room temperature. The hardness of the test piece is shown by rounding the average value of the measured values of the pressed surface and the side surface of the five test pieces to an integer.

For the specific resistance, the test piece used is 10 x 10 x 60 mm (however, the dimensional tolerance is 10 ± 0.02, 5 ± 0.02, 60 ± 0.1), and the following It is calculated by the formula and rounded to an integer.

p = {(v X A) / (I X L)} X 1 0 0 0

Where p is the specific resistance (Ωcm)

v: Voltage between voltage terminals (mV)

I: Current flowing through test piece (A)

A: Cross section of test piece (cm ² )

L: Voltage terminal distance (cm)

The flexural strength is 10 X 10 X 60 mm for the test piece (however, the dimensional tolerance is 10 ± 0.02, 5 ± 0.02, 60 ± 0.1), between the fulcrums The distance shall be 40 mm and measured with a universal material testing machine. The radius of curvature of the fulcrum at the fulcrum is 1.5 mm, the angle of the press wedge is 60 °, and the radius of curvature at the tip is 3 mm. Place the test piece horizontally on the abutment, apply a vertical load at the uniform speed in the center of the test piece, and measure the maximum load when the test piece breaks. Read on. The bending strength of the test piece is calculated by the following formula and rounded to one decimal place.

a _b = 3 P 1 / (2 bt ² )

Where cx _b : bending strength (kg / cni ² )

P: Maximum load (kg)

1: Distance between supporting points (cm)

b: Width of test piece (cm)

t: Specimen thickness (cm)

The bending strength of the test piece is shown by rounding the average of the measured values of five test pieces to an integer.

The compressive strength is measured by a universal material testing machine using a test piece of 10 × 10 × 10 mm (with a dimensional tolerance of ± 0.01). The width 10mm of the test piece, by applying a thick piece of the upper of the test piece molded pressing surface as a test pressing surface with a thickness of 10mm, pressurized to a central portion of the test piece at a uniform rate per second to about S k gZcm ² Read the maximum load on the scale plate when the test piece breaks. The compressive strength of the test piece is calculated by the following formula and rounded to an integer.

σ _c = P / A

Where σ. : Compressive strength (kg / cm ² )

P: Maximum load (kg)

A ■ · Area of pressed surface of test piece (cm ² )

For the compressive strength of the test pieces, the average value of the measured values of five test pieces is rounded to an integer.

Next, only the samples of Experimental Examples 1 to 4 were measured for the average pore radius, cumulative pore volume, and gas permeability.

The average pore radius and the measurement of the cumulative pore volume, maximum dimension Φ 1 2 X40mm below, using the following things pore volume 0. 5 mm ³ Zg as a test piece. this Is set on a mercury intrusion method measuring device (manufactured by Fisons). Surface tension of mercury is 480 dy nZcm, test piece and the contact angle 1 4 mercury 1. 3 ° and a pressure _{0. 1 5~1 0001 £ 8 (:} 111 as ^two ranges, a sample container filled with mercury Measurement is performed by gradually applying pressure to 內, and as a result, the curves shown in Fig. 2 are obtained, where the numbers given to the curves correspond to the test pieces of Experimental Examples 1 to 4, respectively. The vertical axis shows the cumulative pore volume, and the horizontal axis reading at the point located at the highest position of the cumulative pore volume of each curve is the average pore radius. Here, 31 in the figure is a gas transmittance measurement device, 32 is the first chamber, 33 is the test piece, 34 is the packing material, 35 is the second chamber, and 36 is the vacuum. The pump is shown The sample is processed into a disk shape of φ30 × 7 The test piece 33 is mounted on the interface between the first chamber 132 and the second chamber 135. Here, first, the vacuum pump After reducing the pressure in the first chamber 132 and the second chamber 35 using 36, the vacuum pump 36 is stopped, and the first chamber 32 is filled with nitrogen gas. It starts to flow from 33 into the second chamber 35. At this time, the gas flow rate Q of the flowing gas is obtained by the following equation.

Q = ((PB ₂ -PBi) / VB) / (T ₂ -Ti)

Where Q: gas ventilation (Pa · cm ³ / s)

PB,: pressure of second chamber 135 at time (P a) PB ₂ : pressure of second chamber 135 at time (P a) VB: volume of second chamber 135 (cm ³ )

Further, the gas permeability K can be obtained by substituting the obtained gas flow rate Q into the following equation of Darcy.

K = (Qt) / (ΔPA)

Where K: Gas permeability (cm ² / s)

Q: Gas ventilation (Pa · cm ³ / s)

Four t: Thickness of test piece (cm)

Δ ：: Pressure difference before and after gas passage between the first chamber 32 and the second chamber 35

Α: Gas permeation area (cm ² )

Figure 4 shows the results. The sample numbers (① to ⑨) in FIG. 4 correspond to the experimental example numbers (1 to 9).

Next, with respect to the carbonaceous blocks of Samples (1) to (4), an anode current density potential curve was obtained by a constant current method in a KF · 2HF electrolytic bath width of 90 ° C. The obtained curves are shown in Fig. 5 (in the case of CIP molding in Experimental Examples 1 to 4) and in Fig. 6 (in the case of excess molding in Experimental Examples 5 to 8).

As is clear from Fig. 4 and Fig. 5, at the stage of the carbonaceous block of sample 成形 (CIP molding pressure is 900 kg / cm ² , bulk density is 1.65 gZcm ³ , bending strength is 920 kgf Zcm ² ) Limiting current density 1 OA, dm when using carbon material by conventional extrusion (bulk density is usually 1.2 to 1.3 gZcm ³ and flexural strength is 1 ◦ _kg fcm ² or less) for anode about ² is obtained, further molding pressure is increased critical current density etc. Ho becomes bulk density and flexural strength is weakening low, it can be seen that inhibit anode effect capability is increased. In the case of a sample の with a bulk density of 1.47 g / cm ³ and a flexural strength of 680 kgf Zcm ² obtained at a CIP molding pressure of 100 kg / cm ² , the maximum current density of 4 OAZdni ² can be applied. No anodic effect occurred during electrolysis.

Further, as apparent from FIGS. 4 and 6, samples ⑧ carbonaceous blocks of (bulk density in molding pressure 900 k gZcm ² is 1. e gZcin ^3, the bending strength 1 129 kgf Zcm ²⁾ In this stage, a critical current density of about 1 OAZdm ² when using a carbon material by conventional extrusion molding for the anode is obtained, and the lower the molding pressure becomes, the lower the bulk density and bending strength become. It can be seen that the current density has increased and the ability to suppress the anodic effect has increased. The bulk density molding pressure was obtained at ^{1 00 kg / cm 2 1. 33} g / cm 3, in the case of bending strength 334 kgf / cm ² Sample ⑤, until the current density up to 40 A / dm ² Even when the voltage was applied, no anodic effect occurred during electrolysis.

In addition, from FIG. 4, the sample とする using mesocarbon microbeads as the main raw material showed almost the same density and bending strength as the sample した described above. Furthermore, even when the current density was applied up to a maximum of 4 OA and dm ² , no anodic effect occurred during the electrolysis, as in Sample I.

From Fig. 4, carbonaceous blocks with an average pore radius of 0.5 m or more, a cumulative pore volume of 8 Omm ³ Zg or more, and a gas permeability of 0.1 mm ² Zs or more (forming pressure of 100 kg / cm ² and 400 k / cm ² ) were also found to have good electrolytic properties. This is due to the fact that the pore distribution of the electrode has been optimized, and in addition to the atomization effect of the conventional fluorine-graphite intercalation compound, the bubbles of the fluorine gas generated on the electrode surface have been improved, and the electrode surface is always in contact with the electrolytic bath. It is thought that this contact is maintained stably, and as a result, this state is maintained up to a high current density.

Fig. 7 shows the relationship between the electrode current densities of the samples of Experimental Examples 1 to 4 and the number of fluorine gas bubbles generated by electrolysis at that time. The higher the molding pressure, the earlier the anode effect occurs and the electricity stops, and the generation of bubbles also stops. Molding until the pressure was 400 kg / cm of material ^{1 8 AZdm 2, 1 00 k} cm 2 is of the material has made a stable electrolytic up 40AZdm ^2, even if the number of occurrence of gas bubbles according to增加current density The increase is almost linear, and it can be seen that the state of gas generation with respect to the amount of current does not change much up to a high current density.

Comprehensively considering the results of Experimental Examples 1 to 9 above, As a lock, the electrode characteristics are improved by improving the suppression of the anodic effect, and while maintaining the ability to efficiently produce high-purity product fluorine, the characteristics such that its own machinability is good ( As described above, the mechanical strength is required to be at least 1. S gZcni ³ or less in terms of bulk density and 200 kgf / cm ² or more in bending strength. More preferably, the bulk density is 1.3 to: L. 5 gZcm ³ and the flexural strength is 300 kgf / cm ² or more.

Also, if the pores are too large, the electrolytic bath will permeate too much into the electrode and degassing will not be hindered. For this reason, by using an electrode having an average pore radius of 45 m or less, a cumulative pore volume of 100 Omm ³ / g or less, and a gas permeability of 3 cm ² s or less, the electrode can be used more stably for a long time.

The carbonaceous Proc the properties l OO e OO k gZcm ² about, preferably forming is carried out in conditions of a 100 to 300k g cm ² about a relatively low pressure. Therefore, not only can a small-scale CIP molding apparatus be used, but also a general-purpose mold molding apparatus can be used, so that the molding cost can be reduced as compared with the case where the conventional large-scale CIP apparatus needs to be used. The number of birds can be reduced.

(3) The HF-containing molten salt as the electrolytic bath for generating fluorine to which the carbonaceous block for an anode according to the present invention is applied is not particularly limited. For example, KF-HF (preferably KF-2HF), CF s F-HF yarn or NOF-HF system can be used.

In addition, in order to ensure stable operation during electrolysis, the assembly of the terminal for energization to the anode is devised to prevent infiltration of fluorine / hydrogen fluoride or bath into the terminal, and to reduce contact resistance. It is important not to increase. As a countermeasure, a flexible graphite sheet is sandwiched between the metal (usually copper) of the terminal for anode conduction and the carbon electrode, or a sprayed nickel-copper film or plating. Means such as forming a film is effective. This makes it possible to prevent the electrode from cracking. Industrial applicability

The electrode of the electrolytic bath for generating fluorine of the present invention and the isotropic carbonaceous block used for the electrode are constituted as described above, and are inexpensive but exhibit excellent electrode characteristics while exhibiting excellent electrode characteristics. Are suitable.

Claims

The scope of the claims

1. An electrode used as an anode of an electrolytic bath for fluorine generation consisting of a molten salt containing hydrogen fluoride, with a bulk density of 1. S gZcm ³ or less and a bending strength of 200 kgf Zcm ² or more. Electrode for electrolytic bath for fluorine generation made of carbonaceous material.

2. The isotropic carbonaceous material according to claim 1, wherein the average pore radius is 0.5 m or more, the cumulative pore volume is 8 Omm ³ Zg or more, and the gas permeability is 0.1 cm ² Zs or more. Electrode of electrolytic bath for fluorine generation.

3. An electrode which is used as an anode of an electrolytic bath for generating fluorine made of a molten salt containing hydrogen fluoride and which is an electrically conductive support member on the surface of the isotropic carbonaceous material according to claim 1 or 2. Electrode of electrolytic bath for fluorine generation with a gold coating film formed at the junction with the electrode.

4. The electrode of the electrolytic bath for generating fluorine according to claim 1, wherein the aggregate of the isotropic carbonaceous material has an average particle diameter of 3 to 20 μm.

5. The electrode of the electrolytic bath for generating fluorine according to claim 4, wherein the aggregate is mainly composed of mesocarbon microbeads.

6. An electrode for use as an anode of the fluorine generating electrolysis bath consisting of hydrogen fluoride-containing molten salt, the bulk density is formed from 1. 25~1. 6 gZcm ³ der Ru isotropic carbonaceous material Electrode of electrolytic bath for generating fluorine.

7. The electrode of the electrolytic bath for generating fluorine according to claim 6, wherein the bending strength of the isotropic carbonaceous material is 200 kgi / _C rn ² or more.

8. The average pore radius of the isotropic carbonaceous material is 0.5 or more, the accumulated air pore volume 80 mm ³ or more, Ru der gas permeability 0.1 1 cm ² Roh s or more claims 6 or 7 Les, The electrode of the electrolytic bath for fluorine generation according to any of the above.

9. At the joint between the isotropic carbonaceous material and the conductive support 9. The electrode of the electrolytic bath for generating fluorine according to claim 6, wherein a covering film is formed.

10. The electrode of the electrolytic bath for generating fluorine according to claim 6, wherein the aggregate of the isotropic carbonaceous material has an average particle diameter of 3 to 20 "m.

11. The electrode of the electrolytic bath for generating fluorine according to claim 10, wherein the aggregate mainly comprises mesocarbon microbeads.

1 2. An isotropic carbonaceous block used as the anode of a fluorine generation electrolytic bath composed of a molten salt containing hydrogen fluoride, with a bulk density of 1.6 g / crn ³ or less and a bending strength of 200 kgf. An isotropic carbonaceous block for the anode of a fluorine generation electrolytic bath formed of an isotropic carbonaceous material having a Zcm of ² or more.

13. The said isotropic carbonaceous material has an average pore radius of 0.5 μm or more, a cumulative pore volume of 8 Omm ³ Zg or more, and a gas permeability of 0.1 cm ² s or more. Isotropic carbonaceous block for anode of electrolytic bath for fluorine generation.