JP6827239B2 - Manufacturing method of silver-silver chloride electrode - Google Patents

Description

The present invention relates to a method for manufacturing a silver-silver chloride electrode for measuring an electric field strength in seawater or soil.

As the silver-silver chloride electrode for measuring the electric field strength in seawater or soil, a silver-silver chloride electrode produced by a sintering method is used. This electrode is obtained by compression molding silver powder and chlorinating the surface of the compression molded product.

As a silver-silver chloride electrode, those disclosed in Patent Documents 1 and 2 are known. In the techniques of Patent Documents 1 and 2, a silver-silver chloride electrode composed of a sintered body of a mixed powder of silver-silver chloride and a silver plate integrally bonded to one side is used.

As a method for producing a silver-silver chloride electrode, the one disclosed in Patent Document 3 is known. In the technique of Patent Document 3, a conductive paste composed of silver oxide having a particle size of 1 μm or more and 2 μm or less, silver chloride having a particle size of 1 μm or more and 2 μm or less, and a heat-resistant paste is printed on an alumina substrate, and then 440. A method for producing a silver-silver chloride electrode produced by firing at ° C. for 10 minutes is used.

As a method for producing a biological electrode, the one disclosed in Patent Document 4 is known. In the technique of Patent Document 4, a method for producing a biological electrode in which a conductive electrode substrate and a mixture of silver, silver chloride and boron oxide are pelletized and then supported on the electrode substrate is used. Further, Patent Document 4 exemplifies an anodic oxidation method, a sintering method, a paste method and the like as a method for producing a silver-silver chloride electrode.

Further, as a silver-silver chloride electrode for measuring a bioelectric potential, those disclosed in Non-Patent Documents 1 and 2 are known. In the techniques of Non-Patent Documents 1 and 2, an electrode obtained by chlorinating a silver surface having a fine wire shape or a disk shape is used. These electrodes are used to measure the weak current of a living body.

Japanese Unexamined Patent Publication No. 5-176903 Japanese Unexamined Patent Publication No. 5-176904 Japanese Unexamined Patent Publication No. 5-142189 Japanese Unexamined Patent Publication No. 2006-280735

WARNER INSTRUMENTS "Ag / AgCl Pellet, Disc and Wire Electrodes; Silver Wire" BaSi “Silver / Silver Chloride Reference Electrode” Chibu Homma and Toshimichi Watanabe "Measurement of biopotential and potential fluctuation in tea plants" (summary) Osaka University Graduate School of Medicine / Graduate School of Frontier Biosciences "History of Bioelectrical Signal Research"

As the silver-silver chloride electrode, those disclosed in Patent Documents 1 to 4 and Non-Patent Documents 1 and 2 are known. However, many of them are not premised on being used as a silver-silver chloride electrode for measuring the electric field strength in seawater or soil.

Here, the silver-silver chloride electrode having a dry surface is put into seawater. In the silver-silver chloride electrode having fine pores, seawater permeates deep into the pores and the particle surface is uniformly wetted, the potential difference between the pair of silver-silver chloride electrodes becomes small, and a stable state is reached. The conventional silver-silver chloride electrode has a problem that it takes a long time to reach this stable state.

Further, when the silver-silver chloride electrode has a fine wire shape, it is suitable for measuring the electric field strength in a region where a weak current of μA level flows. However, in the region where a current of mA or more flows, there is a problem that intergranular corrosion progresses rapidly and the silver-silver chloride electrode is quickly consumed.

Further, in the conventional silver powder, since the diameter of the particles is small, a large number of closed pores are formed, and the specific surface area of the molded body that contributes to the measurement of the electric field strength cannot be increased. Here, the closed pores are cavities having no openings on the surface of the molded product. Therefore, it is difficult to reduce the detectable electric field strength. Therefore, there is a problem that the sensitivity in measuring the electric field strength of the silver-silver chloride electrode is low.

The present invention is for solving the above problems, the time required for the silver-silver chloride electrode to reach a stable state after being put into seawater is short, the deterioration of the silver-silver chloride electrode is suppressed, and the sensitivity in measuring the electric field strength is high. The purpose is to obtain a method for producing a high silver-silver chloride electrode.

(1) The method for producing a silver-silver chloride electrode of the present invention includes a molding step of molding a molded body of silver powder, a sintering step of sintering the molded body of the silver powder, and the sintered silver. A method for producing a silver-silver chloride electrode, which comprises a surface chloride step of chlorinating the surface of a sintered body of powder. The silver powder is composed of agglomerated particles having a sphere equivalent diameter of 30 μm or more and 150 μm or less, and the agglomeration The particle size of the single particles constituting the particles is 1 μm or more and 50 μm or less, the sphere equivalent diameter of the cumulative weight of the aggregated particles of 50% is 70 μm or more and 100 μm or less, and the aspect ratio is more than 2.0 and 2.5 or less. The composition contains 20% by weight or more and 35% by weight or less of the agglomerated particles, and 5% by weight or more and 10% by weight or less of the agglomerated particles having an aspect ratio of more than 2.5 and 5.0 or less.

Here, the reason why the spheres are composed of aggregated particles having an equivalent diameter of 30 μm or more is to prevent the pores on the chlorinated surface of the sintered body of silver powder from becoming too small and the permeation rate of seawater from decreasing. Is.
The reason why it is composed of agglomerated particles having a sphere equivalent diameter of 150 μm or less is that the surface area is maintained and the contact resistance with seawater is kept at a low level with respect to a predetermined thickness of the sintered body of silver powder.
The reason why the particle size of the single particle is 1 μm or more is that the pores are easily clogged with a relatively small amount when isolated.
The reason why the particle size of the single particle is 50 μm or less is that if it is too large, it is difficult to mold and there is a limitation in the manufacturing process of the silver powder.
The reason why the sphere equivalent diameter of 50% of the cumulative weight of the agglomerated particles is 70 μm or more is to avoid that the diameter of the pores becomes too small and the permeation rate of seawater decreases.
The reason why the equivalent sphere diameter of 50% of the cumulative weight of the agglomerated particles is 100 μm or less is to avoid a decrease in the surface area of the silver powder molded product and a decrease in sensitivity as an electrode.
The reason why the aggregated particles having an aspect ratio of more than 2.0 and 2.5 or less are contained is that when particles having a large aspect ratio are mixed, the filling rate can be lowered and the pore volume can be increased.
The reason why the agglutinated particles having an aspect ratio of more than 2.0 and 2.5 or less are contained in an amount of 20% by weight or more is that when the ratio is low, the effect of lowering the filling rate is reduced.
The reason why the agglutinated particles having an aspect ratio of more than 2.0 and 2.5 or less are contained in an amount of 50% by weight or less is that if the aspect ratio is too large, it is difficult to mold and there is a limitation in the production process of silver powder.
The reason for containing agglomerated particles with an aspect ratio of more than 2.5 and 5.0 or less is that when long particles with a large aspect ratio are mixed, the strength of the molded body is maintained, the filling rate is lowered, and the pore volume is reduced. This is because it can be enhanced.
The reason why the agglutinated particles having an aspect ratio of more than 2.5 and 5.0 or less are contained in an amount of 5% by weight or more is that when the ratio is low, the effect of maintaining the strength of the molded product is small.
The reason why the agglutinated particles having an aspect ratio of more than 2.5 and 5.0 or less are contained in an amount of 10% by weight or less is that if the aspect ratio is too large, it becomes difficult to mold.

(2) In the molding step, the molded product of the silver powder is compression-molded, and in the sintering step, the thickness of the sintered body of the silver powder is formed to be 2 mm or more and 3 mm or less.

The reason for forming the thickness of the sintered body of silver powder to be 2 mm or more is to suppress a decrease in the adhesive strength of the silver wire when compression molding is performed while incorporating a silver wire having a diameter of 1 mm as a lead wire.
The reason for forming the thickness of the sintered body of the silver powder to be 3 mm or less is to avoid that it takes time for seawater to permeate into the pores and it takes time to reach a stable state.

(3) In the molding step, a silver wire or strip-shaped silver whose tip is chemically treated is inserted into the molded body of the silver powder and integrally molded.

(4) In the molding step, the molded body of the silver powder is formed on the base material.

(5) As the base material, silver or a metal plate having a low ionization tendency in seawater having electrical characteristics close to the silver is used, and the molded product of the silver powder formed on the base material in the molding step. The thickness is 0.3 mm or more and 1.0 mm or less.

(6) As the base material, a ceramic plate to which the porous or silver powder easily adheres is used.
The thickness of the molded product of the silver powder formed on the base material in the molding step is 0.3 mm or more and 1.0 mm or less.

The reason why the thickness of the silver powder molded product is 0.3 mm or more is to avoid a decrease in surface area and a decrease in sensitivity as an electrode.
The reason why the thickness of the silver powder molded product is 1.0 mm or less is to avoid a long time until the potential difference between the pair of electrodes stabilizes due to the influence of the permeation rate of seawater.

According to the method for producing a silver-silver chloride electrode according to the present invention, no special mechanism is required for storage and maintenance, and when the surface is placed in seawater from a dry state, seawater quickly enters the pores. It is possible to produce a silver-silver chloride electrode that permeates into and operates stably in a short time.
Further, a thin film layer of silver chloride can be formed deep inside the pores, and a silver-silver chloride electrode whose deterioration is suppressed even when the detection signal level is high can be manufactured.
Further, it is possible to manufacture a silver-silver chloride electrode which is small in size, has a small distance between electrodes, and has higher sensitivity in measuring electric field strength than conventional electrodes.

It is a flowchart which shows the manufacturing method of the silver-silver chloride electrode which concerns on Embodiment 1 of this invention. It is a figure which shows the cross-sectional photograph of the silver-silver chloride wire which part of the silver chloride layer was corroded and peeled off. It is a figure which shows the SEM photograph of the silver powder in Example 1 of Embodiment 1 of this invention. It is a figure which shows the SEM photograph of the silver powder in the comparative example 2 of Embodiment 1 of this invention. It is a figure which shows the SEM photograph of the silver powder in the comparative example 3 of Embodiment 1 of this invention. It is a figure which shows the characteristic of the silver-silver chloride electrode in Examples 1 and 2 and Comparative Examples 1 and 3 of Embodiment 1 of this invention. It is explanatory drawing which shows the cross section of the structure of the silver-silver chloride electrode which concerns on Embodiment 2 of this invention. It is a figure which shows the characteristic of the silver-silver chloride electrode in Examples 3-6 and Comparative Examples 4 and 5 of Embodiment 1 of this invention. It is a figure which shows the relationship between the thickness and the stabilization time of the silver-silver chloride electrode in Examples 3-6 and Comparative Examples 4 and 5 of Embodiment 2 of this invention.

Hereinafter, embodiments of the method for producing a silver-silver chloride electrode according to the present invention will be described. The form of the drawings is an example, and does not limit the present invention. In addition, those having the same reference numerals in the respective figures are the same or equivalent thereof, which are common to the entire text of the specification. Further, in the drawings below, the relationship between the sizes of the constituent members may differ from the actual one.

Embodiment 1.
As a method for producing a silver-silver chloride electrode, silver powder having the following composition is used. Specifically, the silver powder is composed of agglomerated particles having a sphere-equivalent diameter of 30 μm or more and 150 μm or less. In the silver powder, the particle size of the single particles constituting the aggregated particles is 1 μm or more and 50 μm or less. The silver powder has a sphere equivalent diameter of 50% of the cumulative weight of the agglomerated particles of 70 μm or more and 100 μm or less. The silver powder contains 20% by weight or more and 35% by weight or less of agglutinated particles having an aspect ratio of more than 2.0 and 2.5 or less. The silver powder has a composition containing 5% by weight or more and 10% by weight or less of agglutinated particles having an aspect ratio of more than 2.5 and 5.0 or less.

FIG. 1 is a flowchart showing a method for manufacturing a silver-silver chloride electrode according to the first embodiment of the present invention.
As shown in FIG. 1, the method for producing a silver-silver chloride electrode includes a molding step, a sintering step, and a surface chloride step. Hereinafter, each process will be described in order.

(Molding process)
In the molding step, a silver powder molded body having the above composition is compression molded. Further, in the molding step, a silver wire whose tip is chemically treated is inserted into a silver powder molded body and integrally molded.
In addition, instead of the silver wire having the tip portion chemically treated, a strip-shaped silver having the tip portion chemically treated may be inserted into the silver powder molded body and integrally molded.

Specifically, the tip of a silver wire having a diameter of 1 mm as a lead wire is bent within a size range smaller than the size of the silver-silver chloride electrode. The bent portion and the silver wire from the bent portion to the lead portion are boiled and washed with alcohol such as methyl alcohol or ethyl alcohol.
Next, the bent portion and the lead portion of the silver wire are immersed in a 5 to 20% by weight aqueous nitric acid solution at 50 to 70 ° C. for about 3 minutes.
The silver wire washed with pure water is annealed in an electric furnace at 450 to 600 ° C. for 5 minutes.
Using a mold, the bent portion and the silver powder having the above composition are integrally molded to a predetermined thickness at a molding pressure of 1.5 MPa or less. As a result, a silver powder molded product is obtained.

(Sintering process)
In the sintering process, the silver powder molded body is sintered. Further, in the sintering step, the thickness of the sintered body of silver powder is formed to be 2 mm or more and 3 mm or less.

Specifically, the silver powder molded product is sintered in an electric furnace at 450 to 600 ° C. for 15 minutes. As a result, a silver powder sintered body having a thickness of 2 mm or more and 3 mm or less is obtained.

(Surface chloride process)
In the surface chlorination step, the surface of the sintered body of the sintered silver powder is chlorinated.

Specifically, in the case of manufacturing a silver-silver chloride electrode for measuring the undersea electric current strength, a silver powder sintered body is placed on the anode in an aqueous sodium chloride solution of about 3.5% by weight, and the silver electrode is used. Is placed on the cathode, and a DC current of 5 to 20 mA is applied for about 24 hours to form a silver chloride film on the surface of the sintered body of silver powder. As a result, the surface of the sintered body of silver powder is chlorinated.

In the case of a silver-silver chloride electrode for measuring the electric current strength in soil, a sintered body of silver powder is placed on the anode and a silver electrode is placed on the cathode in an aqueous potassium chloride solution of about 3.8% by weight. , 5 to 20 mA of DC current is applied for 20 hours or more to form a silver chloride film on the surface of the sintered body of silver powder. As a result, the surface of the sintered body of silver powder is chlorinated.

(Action, effect)
Generally, a molded and sintered particle has pores having a diameter proportional to the average particle size of the constituent particles. It is known that the amount of liquid leaked from a pinhole or the like is proportional to the fourth power of the diameter of the hole and inversely proportional to the viscosity.
Based on the formula of this analysis example, the permeation rate in the pores in seawater is calculated. For example, when the pore diameter is 1 μmφ, the permeation rate of seawater is about 0.16 μm / s in the sea at a depth of 50 m.
On the other hand, when the pore diameter is 10 μmφ, the permeation rate of seawater is about 16 μm / s in the sea at a depth of 50 m, which is 100 times higher than that when the pore diameter is 1 μmφ.
That is, assuming that the average pore diameter when composed of particles having an average particle diameter of 6 μm is about 1 μmφ, the average pore diameter when composed of particles having an average particle diameter of 60 μm is about 10 μmφ, and the permeation time of seawater is It can be seen that it is 1/100 of the case where the particles are composed of particles having an average particle size of 6 μm.

In the method for producing a silver-silver chloride electrode according to the first embodiment, the particles are composed of aggregated particles having a sphere equivalent diameter of 30 μm or more and 150 μm or less, and the particle size of the single particles constituting the aggregated particles is 1 μm or more and 50 μm or less. A silver powder having a composition in which the cumulative weight of the agglomerated particles is 50% and the equivalent sphere diameter is 70 μm or more and 100 μm or less is used. Thereby, the pore diameter after molding and sintering this silver powder can be increased.
Here, when the sphere equivalent diameter is smaller than 30 μm, the generated pore diameter becomes too small, the permeation rate of seawater decreases, and it takes time to stabilize as a pair of electrodes. On the other hand, when the equivalent diameter of the sphere exceeds 150 μm, the surface area of the silver powder molded body decreases, so that the detectable electric field strength increases and the sensitivity decreases.
Further, when the particle size of the single particle is smaller than 1 μm, the pores are likely to be clogged with a relatively small amount when isolated. On the other hand, when the particle size of the single particle exceeds 50 μm, if it is too large, it is difficult to mold and it is caught in the limitation in the manufacturing process of the silver powder.
Further, when the sphere equivalent diameter of the cumulative weight of 50% of the aggregated particles is smaller than 70 μm, the diameter of the pores becomes too small, the permeation rate of seawater decreases, and it takes time to stabilize as a pair of electrodes. It will be. On the other hand, when the diameter equivalent to a sphere having a cumulative weight of 50% of the aggregated particles exceeds 100 μm, the surface area of the silver powder molded product becomes small and the sensitivity as an electrode decreases.

In the method for producing a silver-silver chloride electrode according to the first embodiment, the silver-silver chloride electrode contains 20% by weight or more and 35% by weight or less of agglomerated particles having an aspect ratio of more than 2.0 and 2.5 or less. , A silver powder having a composition containing 5% by weight or more and 10% by weight or less of agglomerated particles having an aspect ratio of more than 2.5 and 5.0 or less is used. As a result, the filling property at the time of molding is improved by the blocking effect, shrinkage and densification at the time of sintering are hindered, the pore diameter after sintering can be maintained, and many open pores on the surface can be maintained. In addition, the thickness of compression molding can be reduced while using silver powder having a large sphere-equivalent diameter.
Here, the aspect ratio is the ratio of the major axis to the minor axis (= major axis / minor axis) of the aggregated particles. Spherical particles with a particle size distribution tend to have higher filling properties. It is well known that when spheres with a particle size ratio of 1:10 are mixed, particles with a small particle size have a maximum packing density when the mixing ratio is 20 to 30% by weight, and the pores contained therein are reduced. Has been done. On the other hand, when long particles having a large aspect ratio are mixed, the filling rate can be lowered and the pore volume can be increased while maintaining the strength of the molded product.
Here, when agglomerated particles having an aspect ratio of more than 2.0 and 2.5 or less are included, if particles having a large aspect ratio are mixed, the filling rate can be lowered and the pore volume can be increased. When the agglutinated particles having an aspect ratio of more than 2.0 and 2.5 or less are contained in an amount of less than 20% by weight, the ratio becomes too low and the effect of lowering the filling rate is reduced. On the other hand, when agglutinated particles having an aspect ratio of more than 2.0 and 2.5 or less are contained in an amount of more than 35% by weight, if the amount is too large, it is difficult to mold and the silver powder is limited in the manufacturing process. It ends up.
Further, when agglomerated particles having an aspect ratio of more than 2.5 and 5.0 or less are contained, if long agglomerated particles having a large aspect ratio are mixed, the filling rate is lowered while maintaining the strength of the molded body. , The pore volume can be increased. When the agglutinated particles having an aspect ratio of more than 2.5 and 5.0 or less are contained in an amount of less than 5% by weight, if the ratio is too low, the effect of maintaining the strength of the molded product becomes small. On the other hand, when agglutinated particles having an aspect ratio of more than 2.5 and 5.0 or less are contained in an amount of more than 10% by weight, if the amount is too large, it becomes difficult to mold.

In the method for producing a silver-silver chloride electrode according to the first embodiment, the silver-silver chloride electrode uses a silver powder having a composition containing 5% by weight or more of agglomerated particles having an aspect ratio of more than 2.5 and 5.0 or less. Therefore, silver powder having a large equivalent diameter of spheres can be used. As a result, the thickness of the sintered body of silver powder to be compression-molded and sintered while incorporating a silver wire having a diameter of 1 mm as a lead wire can be formed to be 2 mm or more and 3 mm or less.
When long agglomerated particles having a large aspect ratio are mixed, the filling rate can be lowered and the thickness of the sintered body of silver powder can be formed to 3 mm or less while maintaining the strength of the molded body of silver powder. When the thickness of the sintered body of the silver powder is formed to be 2 mm or less, there is a drawback that the adhesive strength of the silver wire as the lead wire inserted into the silver-silver chloride electrode is lowered. Further, when the equivalent diameter of the sphere exceeds 150 μm, the adhesive strength is further lowered.

In the method for producing a silver-silver chloride electrode according to the first embodiment, a silver wire or strip-shaped silver whose tip is chemically treated is inserted into a molded body, integrally molded, and sintered to silver-chloride. Manufacture silver electrodes. As a result, the adhesive strength of the lead wire of the silver-silver chloride electrode can be increased.

In the conventional silver powder obtained by compression molding and chlorinating the surface thereof, the average particle size of the constituent silver-silver chloride electrodes is as small as 4 μm or more and 8 μm or less. Therefore, the average pore diameter of the conventional silver-silver chloride electrode is as small as 0.7 μm or more and 1.3 μm or less. Therefore, when a conventional silver-silver chloride electrode having a dry surface is put into seawater, the seawater permeates deep into the pores and the particle surface is uniformly wetted, and between the pair of silver-silver chloride electrodes. The potential difference became small, and it took a long time to reach a stable state.
On the other hand, the silver-silver chloride electrode produced by the method for producing a silver-silver chloride electrode according to the first embodiment has a large average pore diameter of 4 μm or more and 10 μm or less. Therefore, when a silver-silver chloride electrode with a dry surface is put into seawater, the seawater permeates deep into the pores and the particle surface is uniformly wetted, resulting in a potential difference between the pair of silver-silver chloride electrodes. It becomes smaller and takes less time to reach a stable state.

Further, the average pore diameter of the conventional silver-silver chloride electrode is as small as 0.7 μm or more and 1.3 μm or less, and the packing density is high. Therefore, the proportion of the open pores on the surface was small. Such a conventional silver-silver chloride electrode cannot increase the specific surface area of the molded product, which contributes to the measurement of the electric field strength. Therefore, in order to increase the sensitivity, the area of the silver-silver chloride electrode had to be increased.
On the other hand, in the silver-silver chloride electrode produced by the method for producing a silver-silver chloride electrode according to the first embodiment, the average pore diameter is as large as 4 μm or more and 10 μm or less as described above. Therefore, the specific surface area of the molded product that contributes to the measurement of the electric field strength can be increased. Therefore, it is not necessary to increase the area of the silver-silver chloride electrode in order to increase the sensitivity, and the size can be reduced.

Further, in the conventional silver powder, since the particle diameter is small and the packing density is high, a large number of closed pores are generated. Therefore, the specific surface area of the molded product, which contributes to the measurement of the electric field strength, cannot be increased, and it is difficult to reduce the detectable electric field strength. Here, the closed pores mean a cavity having no opening on the surface of the molded product.
On the other hand, in the silver-silver chloride electrode produced by the method for producing a silver-silver chloride electrode according to the first embodiment, the diameter of the silver powder particles is as large as 30 μm or more and the filling density is low, so that closed pores are generated. Can be suppressed. Therefore, the specific surface area of the molded product that contributes to the measurement of the electric field strength can be increased, and the detectable electric field strength can be reduced. Therefore, the sensitivity is high.

FIG. 2 is a cross-sectional photograph of a silver-silver chloride wire in which a part of the silver chloride layer is corroded and peeled off.
The conventional fine wire-shaped silver-silver chloride electrode is suitable for measuring the electric field strength in a region where a weak current of μA level flows. However, as shown in FIG. 2, in this electrode, intergranular corrosion rapidly progressed in the region where a current of mA or more flows, and the silver-silver chloride electrode was consumed quickly.
On the other hand, in the silver-silver chloride electrode manufactured by the method for producing a silver-silver chloride electrode according to the first embodiment, since the area of the particle-to-particle junction is large, even in a region where a current of μA level or mA or more flows. , The progress of intergranular corrosion is alleviated, and the durability of the silver-silver chloride electrode is improved.

In the conventional method for manufacturing a silver-silver chloride electrode, in the method of directly fixing the lead wire end to the sintered body with silver paste, the adhesive strength of the lead wire is low, and the lead wire may be peeled off.
On the other hand, in the silver-silver chloride electrode manufactured by the method for producing a silver-silver chloride electrode according to the first embodiment, since the electrode is integrally sintered with the particles, the adhesive strength of the lead wire is high and the lead wire is peeled off. It is difficult to do, and the durability of the silver-silver chloride electrode is improved.

As described above, according to the method for producing a silver-silver chloride electrode according to the first embodiment, when it is installed in seawater from a state where the surface is dried without requiring a special mechanism for storage and maintenance. Seawater quickly permeates the inside of the pores, and a silver-silver chloride electrode that operates stably in a short time can be manufactured.
Further, a thin film layer of silver chloride can be formed deep inside the pores, and a silver-silver chloride electrode whose deterioration is suppressed even when the detection signal level is high can be manufactured.
Further, since it is small and the distance between the electrodes is small, it is easy to identify the position of the target object even at a relatively short distance. Further, since the specific surface area is large and the potential difference between the pair of electrodes is very small, it is possible to manufacture a silver-silver chloride electrode whose sensitivity in measuring the electric field strength is 1000 times or more higher than that of the conventional electrode.

(Example 1)
FIG. 3 is a diagram showing an SEM photograph of the silver powder in Example 1 of the first embodiment of the present invention.
The silver powder of Example 1 shown in FIG. 3 has the same composition as that of the first embodiment. The silver powder of Example 1 is composed of agglomerated particles having a sphere-equivalent diameter of 30 μm or more and 140 μm or less. The silver powder of Example 1 has a sphere-equivalent diameter of 89 μm with a cumulative weight of 50% of the aggregated particles. Further, the silver powder of Example 1 has an average particle size of 26 μm as a single particle when dispersed with a 40 W homogenizer. The silver powder of Example 1 contained 7.8% by weight of agglutinated particles having an aspect ratio of more than 2.5 and 5.0 or less. Using this silver powder, a molded product having a diameter of 25 mm was prepared and sintered to prepare a silver-silver chloride electrode having a silver chloride film formed on the surface. The thickness of this electrode was 3.1 mm.

(Example 2)
Using the same silver powder as in Example 1, a molded product having a diameter of 25 mm was prepared and sintered to prepare a silver-silver chloride electrode having a silver chloride film formed on the surface. The thickness of this electrode was 2.9 mm.

(Comparative Example 1)
Using the same silver powder as in Example 1, a molded product having a diameter of 25 mm was prepared and sintered to prepare a silver-silver chloride electrode having a silver chloride film formed on the surface. The thickness of this electrode was 3.6 mm.

(Comparative Example 2)
FIG. 4 is a diagram showing an SEM photograph of silver powder in Comparative Example 2 of Embodiment 1 of the present invention.
The silver powder of Comparative Example 2 shown in FIG. 4 is composed of agglomerated particles having a sphere-equivalent diameter of 20 μm or more and 85 μm or less. The silver powder of Comparative Example 2 has a sphere-equivalent diameter of 53 μm with a cumulative weight of 50% of agglomerated particles. The silver powder of Comparative Example 2 has an average particle size of 26 μm as a single particle when dispersed with a 40 W homogenizer. The silver powder of Comparative Example 2 contains 3.1% by weight of particles having an aspect ratio of more than 2.5 and 5.0 or less. Using this silver powder, a molded product having a diameter of 25 mm was prepared and sintered to prepare an electrode having a silver chloride film formed on the surface. The thickness of this electrode was 3.2 mm.

(Comparative Example 3)
FIG. 5 is a diagram showing an SEM photograph of silver powder in Comparative Example 3 of Embodiment 1 of the present invention.
The silver powder of Comparative Example 3 shown in FIG. 5 is composed of agglomerated particles having a sphere-equivalent diameter of 10 μm or more and 95 μm or less. The silver powder of Comparative Example 3 has a sphere-equivalent diameter of 53 μm with a cumulative weight of 50% of agglomerated particles. The silver powder of Comparative Example 3 has an average particle size of 6.9 μm as a single particle when dispersed with a 40 W homogenizer. The silver powder of Comparative Example 3 contains 0.5% by weight of particles having an aspect ratio of more than 2.5 and 5.0 or less. Using this silver powder, a molded product having a diameter of 25 mm was prepared and sintered to prepare an electrode having a silver chloride film formed on the surface. The thickness of this electrode was 3.3 mm.

FIG. 6 is a diagram showing the characteristics of the silver-silver chloride electrodes in Examples 1 and 2 and Comparative Examples 1 to 3 according to the first embodiment of the present invention.
For actual use in seawater, it is desirable that the stabilization time is 30 minutes or less and the offset potential between the silver and silver chloride electrodes is low. The stability of the offset potential depends on the method of forming the silver chloride film. The stabilization time depends on the thickness of the sintered body of the silver powder and the shape and average particle size of the particles constituting the silver powder. This is clear from FIG.

As shown in FIG. 6, in the silver-silver chloride electrodes of Examples 1 and 2, the stabilization time from being put into seawater to reaching the stable state could be 30 minutes or less. It has been confirmed that the silver-silver chloride electrodes according to Examples 1 and 2 exhibit stable characteristics in a one-year actual sea level test.

On the other hand, in the silver-silver chloride electrode of Comparative Example 1, the stabilization time was long while using the same silver powder as in Example 1. This is because the thickness of the sintered body of silver powder was larger than 3 mm.
In addition, the silver-silver chloride electrodes of Comparative Examples 2 and 3 had a longer stabilization time than the silver-silver chloride electrodes of Comparative Example 1. In each of these silver-silver chloride electrodes of Comparative Examples 1 to 3, the bulk density of the sintered body of silver powder is high, and the open porosity is small.
The silver-silver chloride electrodes of Comparative Examples 2 and 3 were all difficult to mold, and both had to increase the pressure during molding. As a result, the open porosity was small and the average pore diameter was small.
The reason why the silver-silver chloride electrodes of Comparative Examples 2 and 3 were difficult to mold is considered to be the shape, particle size and particle size distribution of the silver powder.
In the raw material silver powder of the silver-silver chloride electrode of Comparative Example 2, the proportion of agglomerated particles having a large aspect ratio was small, and the size of the maximum particle size equivalent to a sphere was small. Further, in the raw material silver powder of the silver-silver chloride electrode of Comparative Example 3, there were almost no aggregated particles having a large aspect ratio, and the average diameter of the single particles was small.

Embodiment 2.
Hereinafter, the second embodiment will be described. In the second embodiment, the points different from the first embodiment will be mainly described.
As a method for producing a silver-silver chloride electrode, silver powder having the same composition as that of the first embodiment is used. The method for producing a silver-silver chloride electrode includes a molding step, a sintering step, and a surface chlorination step, as in the first embodiment shown in FIG.

FIG. 7 is an explanatory view showing a cross section of the structure of the silver-silver chloride electrode 100 according to the second embodiment of the present invention.
As shown in FIG. 7, the silver-silver chloride electrode 100 produced in the second embodiment has a silver-silver chloride electrode portion 1 composed of a sintered body of silver powder whose surface is chloride, and silver-silver chloride. It includes a base material 2 that supports the silver chloride electrode portion 1, and a thin round bar 3 of the same material that is integrally processed, screwed, or silver brazed with the base material 2.

(Molding process)
In the molding step, a silver powder molded body having the above composition is compression molded. Further, in the molding step, a silver wire whose tip is chemically treated is inserted into a silver powder molded body and integrally molded. In the molding process, a silver powder molded body is formed on the base material. Further, the thickness of the molded body of silver powder formed on the base material in the molding step is set to 0.3 mm or more and 1.0 mm or less.
In addition, instead of the silver wire having the tip portion chemically treated, a strip-shaped silver having the tip portion chemically treated may be inserted into the silver powder molded body and integrally molded.

A case where a metal plate having a low ionization tendency in seawater having silver or similar electrical characteristics is used as the base material of the silver-silver chloride electrode will be described.
Specifically, a metal plate of a predetermined shape such as silver, gold, or platinum, which is a base material of a silver-silver chloride electrode, is boiled and washed with alcohol such as methyl alcohol or ethyl alcohol. Next, one side of this metal plate is coated with a resin and immersed in a 5 to 20% by weight aqueous nitric acid solution at 50 to 70 ° C. for about 3 minutes.
The metal plate is washed with pure water to remove the resin coating layer, and then annealed in an electric furnace at 450 to 600 ° C. for 5 minutes.
Using a mold, silver powder having the above composition is formed on the chemically treated surface of this metal plate at a molding pressure of 1.5 MPa or less, and the thickness of the silver powder molded body is reduced to 0.3 mm or more and 1.0 mm or less. Integral molding process. As a result, a molded product of silver powder formed on the base material is obtained.

Further, a case where a ceramic plate to which porous or silver powder having the above composition easily adheres is used as the base material of the silver-silver chloride electrode will be described.
Specifically, a ceramic material such as cordierite, alumina, or magnesia, which is the base material of the silver-silver chloride electrode, is used as the base material of the silver-silver chloride electrode. In this case, in the case of a dense ceramic material, it is desirable that the surface roughness is 20 μm or more, and it is desirable to perform sandblasting treatment on one side as necessary.
The base material of this ceramic material is washed with pure water to remove inorganic deposits on the surface. At this time, an ultrasonic cleaner can also be used.
Next, the base material of this ceramic material is boiled and washed with alcohol such as methyl alcohol and ethyl alcohol.

When a ceramic material is used as the base material, a strip-shaped silver plate having a thickness of 0.3 mm is prepared as a material for attaching the lead wire.
This silver plate is boiled and washed with alcohol such as methyl alcohol and ethyl alcohol.
Next, the silver plate is immersed in a 5 to 20% by weight aqueous nitric acid solution at 50 to 70 ° C. for about 3 minutes. Further, the silver plate is washed with pure water and annealed in an electric furnace at 450 to 600 ° C. for 5 minutes.
Using a mold, a silver powder having the above composition and a chemically treated strip-shaped silver plate are formed on a surface of a ceramic material having a surface roughness of 20 μm or more at a pressure of 1.5 MPa or less. Then, the thickness of the silver powder molded body is integrally molded to 0.3 mm or more and 1.0 mm or less. As a result, a molded product of silver powder formed on the base material is obtained.

(Sintering process)
In the sintering process, the silver powder molded body is sintered.

Specifically, the silver powder molded product is sintered in an electric furnace at 450 to 600 ° C. for 15 minutes.

(Surface chloride process)
In the surface chlorination step, the surface of the sintered body of the sintered silver powder is chlorinated.

When a metal plate is used as the base material, the lead wire is attached to the side from which the resin coating layer has been removed, then coated again with resin, and the silver powder is fired in an aqueous solution of about 3.5% by weight of sodium chloride. The body is placed on the anode and the silver electrode is placed on the cathode, and a DC current of 5 to 20 mA is applied for about 24 hours to form a silver chloride film on the surface of the silver powder sintered body. As a result, the surface of the sintered body of silver powder is chlorinated.

On the other hand, when a ceramic material is used as the base material, a lead wire is attached to a strip-shaped silver plate, and then the sintered body of this silver powder is placed on the anode in a 3.5 wt% sodium chloride aqueous solution. At the same time, a silver electrode is placed on the cathode, and a DC current of 5 to 20 mA is applied for about 24 hours to form a silver chloride film on the surface of the sintered body of the silver powder. As a result, the surface of the sintered body of silver powder is chlorinated.

(Action, effect)
In the method for producing a silver-silver chloride electrode according to the second embodiment, the silver-silver chloride electrode has a silver powder molded body having a thickness of 0.3 mm or more and 1.0 mm or less. In this case, a silver powder molded body is formed on a metal base material such as silver, gold, or platinum or a porous base material, and this is chloride to form a silver-silver chloride electrode. Alternatively, a silver powder molded body is formed on a base material of a ceramic material such as cordierite, alumina, or magnesia or a base material of a porous body, and this is chloride to form a silver-silver chloride electrode.
Here, if the thickness of the silver powder molded product is made thinner than 0.3 mm, the surface area becomes smaller and the sensitivity as an electrode decreases. On the other hand, if the thickness of the silver powder molded body is made thicker than 1.0 mm, the stabilization time until the potential difference between the pair of electrodes stabilizes becomes longer due to the influence of the permeation rate of seawater.

The melting point of silver chloride is 449 ° C. in the conventional silver powder and silver chloride powder which are made into a paste, applied on a substrate, and sintered. Therefore, it must be sintered at a temperature of 449 ° C. or lower. In this case, the sintering strength was low, and the bonding force with the base material and the bonding force between the particles were small. Further, when a sintered body having a small particle size is used, it is difficult to form a sintered body that is porous and has a large specific surface area. Therefore, it was necessary to take steps such as pelletizing a mixture of silver, silver chloride and boron oxide before using it. With these silver-silver chloride electrodes, it is possible to measure the potential level of the living body due to the presence of inclusions, but it is not suitable for measuring the extremely weak electric field strength below that level.
On the other hand, the silver-silver chloride electrode produced by the method for producing a silver-silver chloride electrode according to the second embodiment can be sintered at a temperature exceeding 450 ° C., and therefore has a bonding force with a base material and a bonding force between particles. Can be raised.

Conventional silver-silver chloride electrodes, especially those for living organisms, have the following measured potentials. For example, in the case of tea plants, the fluctuation is about 10 mV depending on the presence or absence of solar radiation, and the fluctuation is about 30 mV depending on the fertilization of ammonium sulfate. In addition, in squid experiments, it has been confirmed that a temporary influx of sodium ions into nerve cells causes the membrane potential to change to the positive side and generate an action potential. Since this phenomenon is electrochemical, it has a large relationship with the ion concentration, and its potential is several tens of mV or more. Therefore, if the DCO (Direct Current Offset Voltage) is about 1 to 10 mV, it can be sufficiently used.
On the other hand, in the silver-silver chloride electrode manufactured by the method for producing a silver-silver chloride electrode according to the second embodiment, since the DCO is 10 μV or less, the sensitivity can be increased to about the background noise level in seawater.

The large silver-silver chloride electrode is placed in a container to hold the silver-silver chloride electrode in an aqueous chloride solution to maintain surface stability, and is porous to maintain contact with the outside world. Has ceramics, etc. When not installed in seawater, it must have an airtight cap to prevent volatilization and dissipation of water from this container, and the salinity of the aqueous chloride solution should be matched with the salinity of seawater. Without it, there is a problem that the offset potential between the pair of electrodes cannot be lowered.
On the other hand, the silver-silver chloride electrode produced by the method for producing the silver-silver chloride electrode according to the second embodiment has a thickness of 1.0 mm or less without lowering the strength of the silver-silver chloride electrode. The pores can be controlled to a length effective for measuring the electric field strength, and the time required for stabilizing the potentials of the pair of electrodes can be shortened.

(Example 3)
The silver powder of Example 3 has the same composition as that of Embodiment 1. The silver powder of Example 3 is composed of aggregated particles having a sphere-equivalent diameter of 30 μm or more and 140 μm or less. The silver powder of Example 3 has a sphere-equivalent diameter of 89 μm with a cumulative weight of 50% of the agglomerated particles. The silver powder of Example 3 has an average particle size of 26 μm as a single particle when dispersed with a 40 W homogenizer. The silver powder of Example 3 contains 7.8% by weight of agglutinated particles having an aspect ratio of more than 2.5 and 5.0 or less. Using this silver powder, a silver chloride plate having a thickness of 1.0 mm is compression-molded to a diameter of 25 mm and a thickness of 0.5 mm using a mold on a chemically treated surface, and sintered to form a silver chloride film on the surface. A silver-silver chloride electrode was prepared.

(Example 4)
As a base material, a strip-shaped silver plate having a thickness of 0.3 mm, which was chemically treated with the silver powder shown in Example 3 having a thickness of 1.0 mm, was compression-molded on a cordierite-ceramic plate, sintered, and silver chloride on the surface. An electrode with a film was prepared.

(Example 5)
As a base material, a silver powder shown in Example 3 having a thickness of 1.0 mm and a chemically treated strip of silver plate having a thickness of 0.3 mm were integrally compression-molded and sintered on a porous cozierite-ceramic plate. An electrode having a silver chloride film formed on the surface was prepared.

(Example 6)
On the chemically treated surface of a silver plate having a thickness of 1.0 mm, 5.1 weight of agglomerated particles having an average particle size substantially equal to that of the silver powder shown in Example 3 and an aspect ratio of more than 2.5 and 5.0 or less. A silver powder with a composition of% is used. Then, an electrode having a diameter of 25 mm and a thickness of 0.5 mm was compression-molded using a mold and sintered to prepare an electrode having a silver chloride film formed on the surface.

(Comparative Example 4)
The silver powder of Comparative Example 4 is composed of aggregated particles having a sphere-equivalent diameter of 10 μm or more and 95 μm or less. The silver powder of Comparative Example 4 has a sphere-equivalent diameter of 53 μm with a cumulative weight of 50% of agglomerated particles. The silver powder of Comparative Example 4 has an average particle size of 6.9 μm as a single particle when dispersed with a 40 W homogenizer. The silver powder of Comparative Example 4 contains 0.5% by weight of agglutinated particles having an aspect ratio of more than 2.5 and 5.0 or less. Using this silver powder, a 1.0 mm thick silver powder and a 0.3 mm thick strip-shaped silver plate chemically treated on a porous cozierite-ceramic plate are compression-molded, sintered, and chloride on the surface. An electrode having a silver film formed was prepared.

(Comparative Example 5)
The silver powder of Comparative Example 5 is composed of agglomerated particles having a sphere-equivalent diameter of 20 μm or more and 85 μm or less. The silver powder of Comparative Example 5 has a sphere-equivalent diameter of 53 μm with a cumulative weight of 50% of the agglomerated particles. The silver powder of Comparative Example 5 has an average particle size of 26 μm as a single particle when dispersed with a 40 W homogenizer. The silver powder of Comparative Example 5 contains 3.1% by weight of agglutinated particles having an aspect ratio of more than 2.5 and 5.0 or less. Using this silver powder, one side of a silver plate with a thickness of 1.0 mm was chemically treated on a chemically treated surface with a mold to be compression-molded to a diameter of 25 mm and a thickness of 0.5 mm, sintered, and a silver chloride film on the surface. The generated electrode was prepared.

FIG. 8 is a diagram showing the characteristics of the silver-silver chloride electrodes in Examples 3 to 6 and Comparative Examples 4 and 5 according to the first embodiment of the present invention. FIG. 9 is a diagram showing the relationship between the thickness of the silver-silver chloride electrode and the stabilization time in Examples 3 to 6 and Comparative Examples 4 and 5 of the second embodiment of the present invention.
For actual use in seawater, it is desirable that the stabilization time is 30 minutes or less and the offset potential between the silver and silver chloride electrodes is low. The stability of the offset potential depends on the method of forming the silver chloride film. The stabilization time depends on the thickness of the sintered body of the silver powder and the shape and average particle size of the particles constituting the silver powder. This is clear from FIG.

As shown in FIGS. 8 and 9, in the silver-silver chloride electrodes of Examples 3 to 6, the stabilization time from being put into seawater to reaching the stable state could be 18 minutes or less. It has been confirmed that the silver-silver chloride electrodes according to Examples 3 to 6 show stable characteristics in a one-year actual sea level test.

On the other hand, in Comparative Examples 4 and 5, it took 35 minutes or more to stabilize the electrodes.

As described above, according to the first and second embodiments, the method for producing a silver-silver chloride electrode includes a molding step of molding a molded body of silver powder. The method for producing a silver-silver chloride electrode includes a sintering step of sintering a molded product of silver powder. The method for producing a silver-silver chloride electrode includes a surface chlorination step of chlorinating the surface of a sintered body of sintered silver powder. In the method for producing a silver-silver chloride electrode, the silver powder is composed of agglomerated particles having a sphere equivalent diameter of 30 μm or more and 150 μm or less. In the silver powder, the particle size of the single particles constituting the aggregated particles is 1 μm or more and 50 μm or less. The silver powder has a sphere equivalent diameter of 50% of the cumulative weight of the agglomerated particles of 70 μm or more and 100 μm or less. The silver powder contains 20% by weight or more and 50% by weight or less of agglutinated particles having an aspect ratio of more than 2.0 and 2.5 or less. The silver powder contains 5% by weight or more and 10% by weight or less of agglutinated particles having an aspect ratio of more than 2.5 and not more than 5.0. The silver-silver chloride electrode is made of silver powder having the above composition.
According to this configuration, no special mechanism is required for storage and maintenance, and when the surface is placed in seawater from a dry state, seawater quickly permeates the inside of the pores and stabilizes in a short time. A working silver-silver chloride electrode can be produced.
Further, a thin film layer of silver chloride can be formed deep inside the pores, and a silver-silver chloride electrode whose deterioration is suppressed even when the detection signal level is high can be manufactured.
Further, it is possible to manufacture a silver-silver chloride electrode which is small in size, has a small distance between electrodes, and has higher sensitivity in measuring electric field strength than conventional electrodes.

In the method for producing a silver-silver chloride electrode, a silver powder molded product is compression-molded in the molding step. In the method for producing a silver-silver chloride electrode, the thickness of the sintered body of silver powder is formed to be 2 mm or more and 3 mm or less in the sintering step.
According to this configuration, since the thickness of the sintered body of silver powder is formed to be 2 mm or more, it is possible to suppress a decrease in the adhesive strength of the silver wire when compression molding is performed while incorporating a silver wire having a diameter of 1 mm as a lead wire. can do. Further, since the thickness of the sintered body of the silver powder is formed to be 3 mm or less, the time required to reach the stable state can be shortened regardless of the time required for the permeation of seawater into the pores.

In the method for producing a silver-silver chloride electrode, in the molding step, a silver wire or strip-shaped silver whose tip is chemically treated is inserted into a silver powder molded body and molded as a unit.
According to this configuration, silver wire or strip-shaped silver whose tip is chemically treated as a lead wire is inserted into a silver powder molded body and molded as a unit, so that a silver-silver chloride electrode can be easily manufactured. You can. Moreover, the connection between the electrode of the silver-silver chloride electrode and the lead wire can be easily performed.

In the method for producing a silver-silver chloride electrode, a silver powder molded body is formed on a base material in the molding step.
According to this configuration, the thickness can be reduced to 1.0 mm or less without lowering the strength of the silver-silver chloride electrode, so that the pores can be controlled to a length effective for measuring the electric field strength, and the pair of electrodes can be used. The time required to stabilize the potential can be shortened.

In the method for producing a silver-silver chloride electrode, a metal plate having a low ionization tendency in seawater having silver or similar electrical characteristics is used as a base material. In the method for producing a silver-silver chloride electrode, the thickness of the silver powder molded body formed on the base material in the molding step is 0.3 mm or more and 1.0 mm or less.
According to this configuration, it is easy to match the shape of the base material with the shape of the mounting portion to have a curvature and to mount the lead wire on the silver-silver chloride electrode.

As a method for producing a silver-silver chloride electrode, a ceramic plate to which porous or silver powder easily adheres is used as a base material. In the method for producing a silver-silver chloride electrode, the thickness of the silver powder molded body formed on the base material in the molding step is 0.3 mm or more and 1.0 mm or less.
According to this configuration, in the case of a porous substrate, seawater permeates from the back surface, so when silver powder is attached to the cylindrical inner surface, background noise of the electric field signal due to turbulence of seawater is generated. It can be lowered. Further, in the case of a ceramic plate to which silver powder easily adheres, by adhering the silver powder to the cylindrical inner surface, a large-area electrode can be formed as a towed or stationary electrode, so that a long distance electrode can be formed. Can measure weak electric field signals.

It should be noted that each of the embodiments disclosed this time is an example in all respects and is not restrictive. The scope of the present invention is shown by the scope of claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1 Silver chloride electrode part, 2 base material, 3 round bar, 100 silver chloride electrode.

Claims (6)

The molding process of molding a silver powder molded body and
A sintering step of sintering the molded product of the silver powder, and
A surface chlorination step for chlorinating the surface of the sintered silver powder
A method for producing a silver-silver chloride electrode containing
The silver powder is
It is composed of aggregated particles with a sphere equivalent diameter of 30 μm or more and 150 μm or less.
The particle size of the single particles constituting the aggregated particles is 1 μm or more and 50 μm or less.
The sphere equivalent diameter of the cumulative weight of the aggregated particles of 50% is 70 μm or more and 100 μm or less.
20% by weight or more and 50% by weight or less of the agglomerated particles having an aspect ratio of more than 2.0 and 2.5 or less, and 5% by weight or more of the agglomerated particles having an aspect ratio of more than 2.5 and 5.0 or less. A method for producing a silver-silver chloride electrode having a composition containing 10% by weight or less. In the molding step, the molded body of the silver powder is compression molded.
The method for producing a silver-silver chloride electrode according to claim 1, wherein in the sintering step, the thickness of the sintered body of the silver powder is formed to be 2 mm or more and 3 mm or less. The silver-silver chloride electrode according to claim 1 or 2, wherein in the molding step, a silver wire or strip-shaped silver whose tip is chemically treated is inserted into the molded body of the silver powder and integrally molded. Production method. The method for producing a silver-silver chloride electrode according to claim 1, wherein in the molding step, the molded body of the silver powder is formed on a base material. As the base material, a metal plate having a low ionization tendency in seawater having silver or similar electrical properties was used.
The method for producing a silver-silver chloride electrode according to claim 4, wherein the thickness of the molded product of the silver powder formed on the base material in the molding step is 0.3 mm or more and 1.0 mm or less. As the base material, a ceramic plate to which the porous or silver powder easily adheres is used.
The method for producing a silver-silver chloride electrode according to claim 4, wherein the thickness of the molded product of the silver powder formed on the base material in the molding step is 0.3 mm or more and 1.0 mm or less.

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