JPH10132778A - Manufacture of silver-silver chloride electrode having silver chloride layer on surface of silver substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a high-precision silver.silver chloride electrode by electrolytically oxidizing a silver substrate worked mechanically and polished chemically, in a solution containing chloride ions, and chloridizing the surface layer part of the silver substrate. SOLUTION: A silver substrate obtained by cutting a silver round bar of a diameter 10mm and a purity 99.9% into a length of 40mm for example, and degreasing, wet-polishing, and washing it, connecting a lead wire to its one side after that, and covering the periphery of the lead wire connected part with a thermally shrinking tube with an adhesive leaving a specified test surface as it is, and a silver plate as an electrode are prepared. This silver substrate with a lead wire is polished chemically by dissolving its surface, by dipping it in a mixed solution, in a agitated state, composed of 10% of saturated chromium oxide (valence VI) solution, 5% of hydrochloric acid, and the remaining of distilled water for about a minute. The silver substrate with a lead wire obtained by polishing and the silver plate are dipped in a 0.75N hydrochloric acid solution, and a current is caused to flow by a current density of 1.0mA/cm<2> for about one hour with the silver substrate with a lead wire as an anode and with the silver plate as a cathode. Consequently, it becomes possible to manufacture silver-silver chloride electrodes having silver chloride layers on the surfaces of silver substrates with lead wires.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the potential of a metal in an electrolyte, the current flowing in the electrolyte, or the measurement of minute potential changes in a living body. Silver / silver chloride electrode (hereinafter referred to as silver / silver chloride
A silver chloride electrode).

[0002]

2. Description of the Related Art As a sensor for measuring a metal potential in an electrolyte such as seawater, measuring a current flowing in the electrolyte, or measuring an electric signal of a minute potential change of a living body,
Conventionally, silver / silver chloride electrodes have been used. As a method for producing the silver / silver chloride electrode, a method of forming a silver chloride layer on the surface of a silver substrate by electrolyzing a silver substrate obtained by machining in a solution containing chloride ions, or a method of forming a silver substrate. A method of forming a silver chloride layer on the surface of a silver substrate by immersion in molten silver chloride is known.

[0003] The error of the silver / silver chloride electrode manufactured by the above-described conventional silver / silver chloride electrode manufacturing method is usually several hundreds of microvolts.
On the other hand, since the potential measured in measuring the potential of the metal in the electrolyte is several hundred mV, the above-mentioned error does not cause any particular problem. In addition, in the potential measurement using a combination with a pH sensor or another ion-selective sensor, a calibration operation using a standard solution is performed. Therefore, in this case, the above-described error does not cause any particular problem.

[0004]

However, since the potential difference measured by measuring an electrocardiogram, an electroencephalogram, or the like, or measuring a current flowing in an electrolytic solution is less than several mV, the silver / chloride produced by the conventional method is used. The silver electrode has a drawback that it is not possible to measure with sufficient accuracy.

[0005]

Means for Solving the Problems Accordingly, the present inventors have:
As a result of conducting various tests and researches to elucidate the error factors of the silver / silver chloride electrode manufactured by such a conventional method, (a) the silver substrate obtained by performing machining such as cutting and polishing includes:
Fine scratches, damaged layers, and structural changes occur on the surface of the silver substrate, and the effects of these machining processes are the main causes of errors.The silver substrates obtained by performing machining such as cutting and polishing are chemically polished. Alternatively, electropolishing removes fine scratches, deformed layers, and structural changes on the surface of the silver substrate caused by machining, and the silver substrate that has been subjected to chemical polishing or electrolytic polishing is electrolyzed in a solution containing chloride ions. The silver / silver chloride electrode obtained by oxidizing and chlorinating the surface layer of the silver substrate greatly improves the measurement accuracy and greatly reduces the dispersion of the measured values. (B) Formed on the surface of the silver substrate The crystal grain size of the silver substrate surface layer portion converted to the silver chloride layer is preferably as fine as possible. In order to obtain a silver substrate surface layer portion having fine crystal grains, the silver substrate surface layer portion is salified to obtain a silver chloride layer. To form
It can be obtained by reducing this silver chloride layer,
(C) After the surface layer of the silver substrate is salified to form a silver chloride layer, the operation of reducing the silver chloride layer to form a silver layer is repeated as the silver substrate surface layer has finer crystal grains. And (d) subjecting the silver substrate obtained by mechanical processing to chemical polishing or electrolytic polishing, and applying a plating method, dry plating to the surface of the chemically or electrolytically polished silver substrate. A silver coating layer is formed by a method or the like, and a silver chloride layer is formed by converting a surface portion or the entire surface of the silver coating layer to a silver chloride layer to form a silver chloride layer. Research results have shown that the electrodes can significantly improve the measurement accuracy and prevent variations in measured values due to silver / silver chloride electrodes.

The present invention has been made on the basis of the above research results. (1) A silver substrate obtained by machining is subjected to chemical polishing or electrolytic polishing, and the chemical or electrolytic polishing is performed. A method for producing a silver / silver chloride electrode in which the surface of the silver substrate is chlorinated by electrolytically oxidizing the silver substrate thus obtained in a solution containing chloride ions, (2) chemically polishing or electrolytically polishing the silver substrate obtained by machining. Polishing, the silver substrate subjected to the chemical polishing or the electrolytic polishing is electrolytically oxidized in a solution containing chloride ions to form a silver chloride layer on the surface of the silver substrate by salting the surface layer portion of the silver substrate, The obtained silver chloride layer on the surface of the silver substrate is electrolytically reduced to be converted into a silver layer having fine crystal grains, and the silver layer having fine crystal grains obtained by the conversion is electrolytically oxidized again to obtain a chloride layer. How to make silver / silver chloride electrode to form silver layer (3) The silver substrate obtained by machining is subjected to chemical polishing or electropolishing, and the chemically or electropolished silver substrate is electrolytically oxidized in a solution containing chloride ions to form a surface layer of the silver substrate. A silver chloride layer is formed on the surface of the silver substrate by chlorinating the portion, and the silver chloride layer on the surface of the obtained silver substrate is electrolytically reduced to be converted into a silver layer having fine crystal grains. The operation of converting to a silver layer having fine crystal grains by electrolytic reduction is repeated twice or more to form a silver layer having finer crystal grains, and then the obtained silver layer having finer crystal grains is obtained. A method for producing a silver / silver chloride electrode for forming a silver chloride layer by electrolytic oxidation of
It is characterized by the following.

[0007] As described above, it is necessary to form a new silver layer on the surface of the silver substrate which is not affected by minute grinding flaws caused by machining such as cutting and polishing, a layer affected by processing, and a change in structure. As a means for forming a new silver layer on the surface of a silver substrate, a plating method such as electroplating or electroless plating, or a method of forming a silver coating layer by dry plating such as vacuum evaporation or ion plating is known. The plating method is more preferable than the dry plating method as a method of forming the silver coating layer. When comparing the electroplating method and the electroless plating method among the plating methods, the electroplating method has a relatively high current density and plating solution concentration. Since the crystal grain size of the silver coating layer can be freely reduced, it is preferable to form the silver coating layer by an electroplating method in the method for producing a silver / silver chloride electrode of the present invention.

Accordingly, the present invention provides (4) a method of chemically polishing or electrolytically polishing a silver substrate obtained by machining, forming a silver coating layer on the surface of the silver substrate, and forming the silver substrate having the silver coating layer formed thereon. A method for producing a silver / silver chloride electrode for forming a silver chloride layer on the surface of a silver substrate by salifying a silver coating layer by electrolytic oxidation in a solution containing chloride ions, (5) silver obtained by machining After the substrate is chemically or electrolytically polished, a silver coating layer is formed on the surface of the silver substrate by electroplating, and the silver substrate having the silver coating layer formed thereon is electrolytically oxidized in a solution containing chloride ions to form a silver coating layer. And a method for producing a silver / silver chloride electrode for forming a silver chloride layer on the surface of a silver substrate by salification.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION 10 mm in diameter, purity: 99.9%
Of silver round bar of 40mm length, degreasing, wet polishing,
After washing, a lead wire is connected to one side, and a silver base covered with a heat-shrinkable tube with an adhesive around the lead wire connection portion except for a predetermined test surface (hereinafter referred to as a silver base with a lead).
Was prepared. Further, a silver plate was prepared as an electrode.

Example 1 A prepared silver substrate with a lead wire was immersed in a mixed solution of a saturated solution of chromium oxide (VI value): 10%, hydrochloric acid: 5%, and the balance: distilled water for 1 minute with stirring. The surface was dissolved and chemically polished. A silver substrate with a lead wire and a silver plate obtained by chemical polishing are immersed in a 0.75N hydrochloric acid solution, and the silver substrate with a lead wire is used as an anode, and the silver plate is used as a cathode at 1.0 mA / cm.
By energizing one hour ² of current density, No. with silver chloride layer on the silver surface of the substrate with Leads 1 to No. Five silver specimens of silver / silver chloride were manufactured.

Example 2 A silver substrate with a lead wire obtained by chemical polishing in Example 1
Immerse the silver plate in 0.1N silver nitrate solution,
1.0 mA / cm with body as cathode and silver plate as anode ^TwoCurrent
Silver substrate with lead wire by energizing for 3 hours at density
A silver plating layer having fine crystal grains on the surface was formed. this
The silver substrate with the lead wire and the silver plate
Immerse in a 0.75N hydrochloric acid solution, and place the silver
1.0 mA / cm using a pole and a silver plate as a cathode^TwoAt the current density of
Apply electricity for 1 hour to chloride the surface of the silver plating layer
Convert to a silver layer and form a silver chloride layer on the silver plating layer.
And a silver substrate having a silver chloride layer
o. 1 to No. 5-5 sample silver / silver chloride electrodes were manufactured
Was.

Example 3 A silver substrate with leads and a silver plate obtained by chemical polishing in Example 1 were immersed in a 0.1N silver nitrate solution, and the silver substrate with leads was used as a cathode and the silver plate was used as an anode at 10 mA / A. A silver plating layer was formed on the surface of the silver substrate with leads by applying a current at a current density of 1 cm ² for 1 hour. The silver substrate with the lead wire and the silver plate on which the silver plating layer was formed were immersed in a 0.75N hydrochloric acid solution, and the silver substrate with the lead wire was used as an anode and the silver plate was used as a cathode at a current density of 1.0 mA / cm ^2. For a period of time, and the silver plating layer on the surface of the silver substrate with the lead wire was salified to form a silver chloride layer. 1 to No. 5/5 sample silver
A silver chloride electrode was manufactured.

Example 4 The prepared silver base material having a lead wire was prepared by adding ethanol: 40%,
Phosphoric acid: 40%, balance: dipped in a mixed solution of distilled water,
3.0 mA / cm using silver substrate with lead wire as anode ^TwoCurrent
Energize for 5 minutes at the density to dissolve the surface of the silver substrate with lead wires
Then, electrolytic polishing was performed. This electrolytically polished
Silver substrate with silver wire and silver plate in 0.1N silver nitrate solution
Immersion, silver base with lead wire as cathode, silver plate as anode
1.0mA / cm^TwoWith a current density of 3 hours and lead
A silver plating layer with fine crystal grains is formed on the surface of the silver substrate with wires.
Formed. With the silver plating layer obtained in this way
Immerse silver substrate with lead wire and silver plate in 0.75N hydrochloric acid solution
The silver substrate with the lead wire was used as an anode and the silver plate was used as a cathode.
0mA / cm^TwoWith current density of 1 hour, with lead wire
Convert the surface layer of the silver plating layer on the surface of the silver substrate to a silver chloride layer
To form a silver chloride layer on the silver plating layer.
No. 1 having a silver chloride layer on the surface of a silver substrate with a lead wire. 1 to N
o. Five silver specimens of silver / silver chloride were manufactured.

Example 5 A prepared silver substrate with a lead wire was placed in a nitrogen gas for 2 hours.
Anneal by holding at 00 ° C for 3 hours, and place in a 3N nitric acid solution for 1 hour.
It was immersed for a time to dissolve the surface of the silver substrate with lead wires, and was subjected to chemical polishing. The chemically polished silver substrate with the lead wire and the silver plate are immersed in a 0.1 N silver nitrate solution, and the silver substrate with the lead wire is used as a cathode and the silver plate is used as an anode at a current density of 1.0 mA / cm ² for 3 hours. A silver plating layer having fine crystal grains was formed on the surface of the silver substrate with leads. The silver substrate with the lead wire having the silver plating layer and the silver plate thus obtained are immersed in a 0.75N hydrochloric acid solution, and the silver substrate with the lead wire is used as an anode, and the silver plate is used as a cathode and has a current of 1.0 mA / cm ² . An electric current is applied for 1 hour at a current density, and a silver chloride layer is formed on the silver plating layer by converting the surface layer of the silver plating layer on the surface of the silver substrate with the lead wire into a silver chloride layer. No. 1 having a silver chloride layer. 1 to No. Five silver specimens of silver / silver chloride were manufactured.

Example 6 A silver substrate with a lead wire obtained by chemical polishing in Example 1
Immerse the silver plate in 0.75N hydrochloric acid solution,
1.0 mA / cm with body as anode and silver plate as cathode ^TwoCurrent
Energize for 1 hour at the density to remove the surface layer of the silver base with lead wire.
Converted to silver chloride layer. Next, reverse the polarity
1.0 mA / cm with silver substrate as cathode and silver plate as anode
^TwoFor 1 hour at a current density of
By reducing the silver chloride layer in the surface layer,
It was converted to a silver layer with fine grains. Furthermore this fine
Silver substrate with lead wire and silver plate having silver layer with crystal grains
Immersed in 0.75N hydrochloric acid solution,
1.0 mA / cm using anode and silver plate as cathode^TwoCurrent density
For 1 hour, and re-clean the silver layer on the surface of the silver substrate with the lead wire.
By converting to a silver chloride layer, a silver chloride layer
No. 1 to No. 5/5 silver / silver chloride electrodes
Manufactured.

[0016] The surface forming silver substrate with leads silver chloride layer obtained in Example 7 Example 6, further a cathode of silver base leaded, silver plate and the anode of 1.0 mA / cm ² A current was applied for 1 hour at a current density, and the silver chloride layer on the surface of the silver substrate with leads was converted into a silver layer having smaller crystal grains than the silver layer obtained in Example 6. The silver substrate with a lead wire having a finer silver layer having a finer crystal grain obtained in this way was further added to a silver plate.
Dipped in a 75N hydrochloric acid solution, the silver substrate with the lead wire was used as an anode,
A silver plate was used as a cathode, a current was passed at a current density of 1.0 mA / cm ² for 1 hour, and a silver chloride layer was formed again on the surface of the silver substrate with leads. 1 to No. Five silver specimens of silver / silver chloride were manufactured.

Conventional Example 1 The prepared silver base with lead wire was used together with a silver plate as it was.
Dipped in a 75N hydrochloric acid solution, the silver substrate with the lead wire was used as an anode,
A silver plate was used as a cathode, a current was passed at a current density of 1.0 mA / cm ² for 1 hour, and a silver chloride layer was formed on the surface of a silver substrate with leads. 1 to No. Five silver specimens of silver / silver chloride were manufactured.

For each silver / silver chloride electrode obtained in Examples 1 to 7 and Conventional Example 1, an arbitrary sample was used as a reference electrode (No.
1), and dipped in a 3.5% NaCl solution with other silver / silver chloride electrodes (No. 2, No. 3, No. 4, No. 5) produced by the same method. After one day, soak 1
After 5 days, 30 days after immersion, the potential was measured three times. Table 1 shows the measured potential one day after immersion, and Table 2 shows the measured potential 15 days after immersion.
Table 3 shows the measured potential 30 days after the immersion.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

[Table 3]

From the results shown in Tables 1 to 3, the conventional example 1
The average value and the standard deviation of the potential difference with respect to the reference electrode are 500
Although many of them show a value of μV or more, the average value and the standard deviation of the potential difference from the reference electrode in Examples 1, 6, and 7 are 30 μV.
The average value and the standard deviation of the potential difference from the reference electrode in other examples are 10 μV or less, and particularly, Example 3 often shows around 1 μV except for one day after immersion, which is very high. It can be seen that the accuracy is shown.

[0023]

As described above, according to the method of the present invention, silver / silver chloride electrodes with extremely high precision can be easily provided in large quantities at low cost as compared with the conventional method. It has the effect that it has.

Claims (5)

[Claims] A silver substrate obtained by machining is subjected to chemical polishing or electrolytic polishing, and the chemically or electrolytically polished silver substrate is electrolytically oxidized in a solution containing chloride ions to form a silver substrate. A method for producing a silver / silver chloride electrode having a silver chloride layer on the surface of a silver substrate, wherein the surface layer is salified. 2. The silver chloride layer on the surface of the silver substrate obtained in claim 1 is electrolytically reduced to be converted into a silver layer having fine crystal grains, and the silver layer has fine crystal grains obtained by the conversion. A method for producing a silver / silver chloride electrode having a silver chloride layer on the surface of a silver substrate, wherein the silver layer is electrolytically oxidized again to form a silver chloride layer. 3. The silver chloride layer on the surface of the silver substrate obtained in claim 1 is converted into a silver layer having fine crystal grains by electrolytic reduction, and the silver chloride layer is finely reduced by electrolytic reduction. The operation of converting into a silver layer having grains is repeated twice or more to form a silver layer having finer grains, and then the obtained silver layer having finer grains is electrolytically oxidized to form a silver chloride layer. A method for producing a silver / silver chloride electrode having a silver chloride layer on a surface of a silver substrate, characterized by being formed. 4. A silver substrate obtained by machining is chemically or electrolytically polished, and then a silver coating layer is formed on the surface of the silver substrate. The silver substrate having the silver coating layer formed thereon is placed in a solution containing chloride ions. A method for producing a silver / silver chloride electrode having a silver chloride layer on the surface of a silver substrate, comprising forming a silver chloride layer on the surface of the silver substrate by chlorinating the silver coating layer by electrolytic oxidation. 5. The silver coating layer formed on the surface of the silver substrate is formed by electroplating.
A method for producing a silver / silver chloride electrode as described in the above.