JPS6355147A - Electroconductive body made from carbon and clay - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to conductors obtained by sintering a mixture of clay and carbon, their electrodes, filter media, electromagnetic wave shielding materials, and electric or magnetic effects. The invention relates to a method for using it as a heating element that generates heat.

[Prior art and its problems] Conventionally, there are porous electrical conductors made of carbon solidified into a porous state (for example, porous carbon P-140 manufactured by Nippon Carbon Co., Ltd.). It has been used as an electrode in zinc-chlorine batteries and in electrolysis. However, conventional products obtained using carbons (a) cannot be said to have sufficient strength.

(b) It is difficult to mold.

(c) It cannot be said that the chemical stability is sufficient when used at high temperatures like electrodes for wet fuel cells.

(d) Poor compatibility with aqueous electrolyte.

(e) Generally expensive.

It has the following disadvantages.

[Means for solving the problem] Clay (or china clay) can be easily formed into a sintered body at a temperature of about 1000 degrees Celsius. This sintered body is produced relatively inexpensively and is widely used in daily life. Therefore, if a porous conductor with strength can be obtained by sintering a mixture of this clay and a relatively small amount of carbon, this material can compensate for some of the drawbacks of conventional porous conductors. can. For example, clay sintered bodies are generally easy to mold, inexpensive, strong, and have good wettability with water.

However, sintered clay is generally an insulator, and it is considered difficult to obtain a material that can achieve this purpose by mixing a relatively small amount of carbon. However, experimental findings have shown that porous conductors that achieve the above objectives can be obtained by sintering a mixture of carbon and clay, especially when porous carbon is used as the carbon. It was. Naturally, such porous materials can also be used as filter media.

In addition, when the conductor of the present invention is used as an electrode for a fuel cell, etc., a catalyst or its precursor may be impregnated into carbon, clay, or a sintered body before or after sintering, and any necessary treatments may be carried out. Let's do it. Furthermore, based on the above discovery, it has been found that a mixture of clay and carbon can be used not only for porous bodies but also for general conductive sintered bodies that are useful for various purposes. Examples of applications are shown below.

[Example 1] Powdered clay, carbon powder, and water were ground and mixed in a mortar, and then molded into a disk shape with a diameter of 13 mm using a press mold. This disk-shaped mixture was left to dry in the air at room temperature.

After drying, it was heated and sintered in an argon stream using an electric furnace. After the sample was placed in the electric furnace, the temperature was raised from room temperature at a rate of 300 degrees per hour, and after reaching a predetermined temperature, the sample was maintained at that temperature for 1 hour to perform sintering. The clay used is Kibushi clay produced in Sanage Town, Nishikamo District, Aichi Prefecture (hereinafter referred to as "Sanage Kibushi Clay"), or Rouseki produced in Yano Katsumitsuyama, Shobara City, Hiroshima Prefecture (hereinafter referred to as "Sanage Kibushi Clay").
Hereinafter, Katsumitsuzan Rouseki (abbreviated as Katsumitsuzan Rouseki) was used.

These clays are ground and then elutriated. When Sanage Kibushi clay was used, it was sintered by keeping it at 800 degrees for 1 hour, and when Katsumitsuzan Rouseki was used, it was sintered by keeping it at 1100 degrees for 1 hour.

Examples of carbon include Ketjenblack EC (sold by Lion Corporation), Ketjenblack EC-DJ600 (sold by Lion Corporation), or Toka Black #5500.
(Tokai Carbon Co., Ltd. product) was used. The former two are typical porous carbons that absorb approximately 950 mg or more of iodine per gram, and the N2 adsorption area according to the BET method is 1 gram.
This indicates a value of approximately 930 m2 or more per area. On the other hand, Toka Black #5500 absorbs about 260 mg of iodine per gram, and exhibits a value of 210 m2 per gram of N2 adsorption area according to the BET method.

The following types of sintered bodies were obtained using the above combination of clay and carbon.

Type A: Sanage Kibushi clay and Ketjen black
EC combination.

Type B: Sanage Kibushi clay and Ketjen Black
EC-DJ combination.

Type C: Sanage Kibushi clay and Touka Black #5500
A combination of

Type D: Katsumitsuzan wax stone and Ketjen black
EC combination.

These types of sintered bodies were subjected to measurements such as (a) porosity, (b) conductivity, (c) strength, and (d) thermogravimetric analysis, and the following results were obtained.

(a) Porosity: The sintered body was immersed in water and the air in the sintered body was released under reduced pressure to impregnate the sintered body with water.

Then, the porosity was calculated from the ratio of the apparent volume of the sintered body to the volume of water contained in the sintered body by the above operation. As a result, the following relationship was found between the carbon content in the sintered body and the porosity (porosity = volume of water contained in the sintered body ÷ apparent volume of the sintered body).

That is, for any type of sintered body, the porosity of the sintered body tended to increase as the carbon content of the sintered body increased. Here, the carbon content indicates the analytical value of carbon in the sintered body (therefore, the weight percentage of carbon),
It changes depending on the mixing ratio of clay and carbon. This definition will be used below regarding carbon content. Sanage Kibushi clay and Katsumitsuyama Rouseki are each made of 80% without mixing carbon.
The porosity of the sintered bodies obtained by sintering at 0 degrees and 1100 degrees for 1 hour was about 38% and 43%, respectively.

Type A sintered bodies have a carbon content of approximately 5%, 10%, and 15%.
%, 20%, and 22%, respectively, approximately 45% and 51%.
%, 55%, 58%, and 62%.

Type B sintered bodies have a carbon content of approximately 3%, 5%, and 10%.
, 15% and 20%, approximately 47% and 54%, respectively.
, 58%, 62%, and 65% porosity.

Type C sintered bodies have a carbon content of approximately 5%, 10%, 1
Approximately 43%, 48%, and 5% at 5% and 18%, respectively.
It showed a porosity of 1% and 54%.

The type D sintered body had a carbon content of about 1% and a porosity of about 58%. In general, the porosity of clay sintered bodies decreases and the strength increases by increasing the sintering temperature, so by further increasing the sintering temperature of the sample, it is possible to obtain a suitable porosity, higher strength, conductivity, etc. can get things.

Note that a mercury porosimeter is commonly used to measure porosity, but this method is thought to give a larger porosity than the above-mentioned porosity because the measurement is performed under pressure.

(b) Conductivity The conductivity of the sintered body at room temperature was measured, and the following relationship was observed between the conductivity and carbon content.

That is, for all types of sintered bodies, there was a tendency for the conductivity to increase as the carbon content increased. The conductivity was mainly determined by the two-point method.

Type A sintered bodies have a carbon content of approximately 2%, 3%, and 7%.
, 10%, 15%, 20%, and 22%, respectively, approximately 10-10Scm-1 (Siemens per centimeter), 10-6Scm-1, 10-1.7Scm-1, 1
0-0.7Scm-1, 10-0.2Scm-1, 10
The conductivity was 0.1 Scm-1 and 100.1 Scm-1.

Type B sintered bodies have carbon contents of approximately 3%, 5%, and 10
%, 15%, 20%, each about 10-4Sc
m-1, 10-2Scm-1, 10-0.4Scm-1
, 10-0.2 Scm-1, and 100.2 Scm-1.

Type C sintered bodies have a carbon content of approximately 3%, 5%, and 10%.
%, 15%, 19%, each about 10-9Sc
m-1, 10-5Scm-1, 10-1Scm-1, 1
The conductivity was 0-0.5 Scm-1 and 10-0.2 Scm-1.

Type D sintered bodies have a carbon content of approximately 2%, 5%, and 9%.
, respectively about 10-6 Scm-1, 10-2.
The conductivity was 3 Scm-1 and 10-1 Scm-1.

Regarding type D sintered bodies, it was difficult to measure the conductivity of samples with a carbon content of about 10% or more because their mechanical strength was insufficient.

(c) Strength The sintered body obtained by the above method described in this example has a strength of approximately 1
It is disc-shaped with a diameter of 0 mm. A sample with a thickness of about 2.5 mm was prepared for this disc-shaped sintered body. This sample was placed on a hard flat surface, and a metal cylinder with a diameter of 5 mm was applied from the top of the sample to approximately the center of the sample. Thereafter, a load was applied to the metal cylinder, and the fracture load value of the sintered body was determined. The fracture load value was calculated by dividing the load applied to the metal cylinder when the sintered body began to fracture by the cross-sectional area of the metal cylinder (0.196 cm2). As a result, for type A sintered bodies, when the carbon content was approximately 3.5%, 5.5%, 10.5%, 14%, and 19%, the fracture load values were 1200 kg/cm2 and 900 kg/cm2, respectively.
kg/cm2, 430kg/cm2, 170kg/cm
2,130 kg/cm2, indicating that this sintered body has high mechanical strength. This is an advantage in using this sintered body for electrodes, filter media, etc. For type B and type C sintered bodies, if their porosity is almost the same as that of type A sintered body, they can be folded by hand and have almost the same mechanical strength as type A sintered body. This was determined by testing the strength. Type D sintered bodies have a carbon content of approximately 0.5%, 2.5%, and 6%, respectively, and have a weight of 150 kg/cm2 and 60 kg/cm2, respectively, according to the measurement method described above.
, showed a breaking load value of 50 kg/cm2.

In addition, the metal cylinder used when calculating the above-mentioned breaking load value had sufficient hardness and mechanical strength. Further, the disc-shaped sintered body was placed on a hard flat surface with its flat surface in contact with a hard flat surface, and the fracture load value was measured. As the sintered body sample for measurement, a disk-shaped sample having a diameter of 10 mm and a thickness of about 2.5 mm similar to that described above may be cut out from a larger sintered body and used.

(d) Thermogravimetric analysis In order to investigate the chemical stability of the carbon in the above sintered body against oxygen in the air, type A,
Thermogravimetric analysis of Type B and Type C sintered bodies was conducted. As a result, it was found that the carbon in the sintered body exhibited greater resistance to oxidative decomposition during heating than the carbon in the raw material. For example, type A sintered bodies are first sintered at a temperature approximately 100 degrees higher than the temperature at which weight loss begins due to air oxidation in thermogravimetric analysis of the raw material Ketjenblack in air. It was found that weight loss occurs due to air oxidation of carbon in the body. Such high thermal stability indicates an advantage in using the present sintered body as an electrode or heating element of a wet fuel cell that operates at high temperatures. Type B and type C sintered bodies are also about 50 degrees and 1
It was found that the thermal stability in air at 5 degrees Celsius was improved.

[Example 2 and Applications] As shown in Example 1, the type A sintered body has electrical conductivity, sufficient mechanical strength, and chemical stability, so it is suitable as a battery electrode or an electrolysis electrode. . Type A below
An example of a battery using a sintered body of as an electrode is shown below. Similar batteries were obtained also when type B and type C sintered bodies were used.

A type A sintered body having a diameter of about 10 mm and a thickness of about 2.5 mm is impregnated with 0.11 ml of a 2.5 mol/l ZnI2 aqueous solution to form a positive electrode. A platinum plate as a current collector, this positive electrode, a glass fiber mat (G manufactured by Toyo Roshi Co., Ltd.) impregnated with 0.07 ml of a 2.5 mol/l ZnI2 aqueous solution
A-100 filter paper, diameter 10 mm) and a zinc plate as a negative electrode were stacked in this order to prepare a secondary battery. This secondary battery is charged with a constant current (direct current) of 10 mA for about 80 minutes to deposit iodine on the positive electrode and zinc on the negative electrode. After this, when charging is stopped and discharged at a constant current of 10 mA, the discharge voltage becomes 0.
．． Discharge could be performed for about 60 minutes until the voltage dropped to 8V. Such charge/discharge cycles could be repeated over 50 times. Furthermore, by placing a cation exchange membrane between the positive electrode and the negative electrode, the current efficiency of a similar secondary battery could be made nearly 100%. Note that these secondary batteries were used in a sealed manner to prevent water in the electrolyte from evaporating.

The above examples show that porous conductors of the present invention can be used as electrode materials. Such porous conductors have a large contact area when gases pass through them, and are therefore particularly suitable as electrodes in batteries using gaseous active materials such as hydrogen, oxygen, chlorine, etc. or,
Since the conductor of the present invention has relatively high conductivity, it can be used as a shielding material for electromagnetic waves or as a heating element that generates heat by the action of electricity or magnetism. When used as an electromagnetic wave shielding material or a heating element, the conductor does not necessarily have to be porous, and a conductive sintered body with small porosity obtained at a temperature higher than that shown in Example 1 may also be used. good. As mentioned above, above a certain temperature, the higher the sintering temperature, the smaller the porosity of clay sintered bodies, but the mechanical strength and hardness tend to increase. A similar tendency is observed in the case of the obtained sintered bodies, so from the viewpoint of mechanical strength, sintered bodies with small porosity obtained at higher temperatures are better as electromagnetic wave shielding materials and heating elements. There are many cases where it is good.

It is also believed that in a sintered body with smaller porosity obtained at a higher temperature, the distance between the carbon clusters becomes shorter and the contact between the carbon particles becomes better, resulting in higher conductivity. In fact, for the various types of sintered bodies obtained in Example 1, the average of the carbons dispersed in the sintered bodies was determined from the published particle size, carbon content, and porosity of the carbons. If you calculate the separation distance and plot the conductivity of the sintered body against this distance, the conductivity will increase as the distance becomes shorter for any type of sintered body, and a curve representing the relationship between the two will be obtained. was found to be quite similar for all sintered bodies. Due to this fact, when obtaining materials that require excellent mechanical strength and appropriate conductivity, such as electromagnetic wave shielding materials and the above-mentioned heating elements, it is necessary to increase the sintering temperature. In fact, it is often better to obtain a denser sintered body with smaller porosity. In addition, in order to reduce the separation distance between carbons and improve their electrical contact, and to smoothly sinter the clay particles and provide mechanical strength to the sintered body, the carbons to be used are Fine particles or thin fibers such as Chen Black EC, Toka Black #5500, and acetylene black are desirable, and porous carbon is generally more suitable for such purposes.

[Effect of the invention] According to the present invention, inexpensive clay is used as the main component of the raw material,
A conductor having mechanical strength and thermal and chemical stability can be obtained by a simple method.

The obtained conductor can be used for electrodes, filter media, electromagnetic wave shielding materials, heating elements that generate heat by electric or magnetic action, and the like.

Claims (7)

[Claims] (1) Obtained by sintering a mixture of clay and carbon, and
A conductor having a conductivity of 0^-^4Scm^-^1 (Siemens per centimeter) or more. (2) The conductor according to claim 1, wherein the carbon is porous carbon. (3) The conductor according to claim 1 or 2, which has a porosity of 40% or more. (4) The conductor according to any one of claims 1 to 3, wherein the content of carbon is 25% by weight or less. (5) For a disk-shaped conductor sample with a diameter of 10 mm and a thickness of 2.5 mm, place the sample on a hard plane with the flat surfaces touching, and pass the disk-shaped conductor sample through a hard cylindrical material with a diameter of 5 mm from the opposite side. The electrical conductor according to any one of claims 1 to 4, wherein the electrical conductor has a breaking load value of 50 kg/cm^2 or more when a load is applied to the center of the sample. body. (6) Any one of claims 1 to 5, characterized in that the carbon in the conductor has higher thermal stability in air than the carbon used as a raw material. The electrical conductor described. (7) A method of using the conductor according to any one of claims 1 to 6 as an electrode, a filter medium, an electromagnetic wave shielding material, or a heating element that generates heat by the action of electricity or magnetism.