JPH11142364A - Electrode for electrochemical measurement - Google Patents

Abstract

(57) [Problem] To prevent a change in an electrode area in a state of being immersed and used in an electrolytic solution composed of a molten salt at a relatively high temperature. SOLUTION: An electrode 11 for electrochemical measurement is used by being immersed in a molten salt electrolyte 12. Electrode 11 for electrochemical measurement has a cylindrical electrode rod 11a and an electrode rod 11a which is loosely fitted to electrode rod 11a at room temperature and immersed at least in electrolyte 12.
And a cylindrical insulating portion 11b having a length surrounding the peripheral surface of the electrode rod 11 and having a smaller coefficient of thermal expansion than the electrode rod 11a. Is configured to adhere to the inner surface of the insulating portion 11b.
It is preferable that the electrode rod 11a be made of graphite and the insulating part 11b be made of boron nitride.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode for electrochemical measurement used by being immersed in an electrolytic solution. More specifically, the present invention relates to a molten salt in which an electrolytic solution is melted at a relatively high temperature, and to an electrode for electrochemical measurement used by being immersed in the high-temperature molten salt.

[0002]

2. Description of the Related Art Conventionally, in each analysis field such as environmental analysis, food analysis and medical analysis, electrochemical measurement is widely used because it is a high-speed and high-sensitivity measurement method. Electrochemical measurement is also an excellent measuring method in that the operation is simpler than a measuring method using a chemical reaction, and its application range is expanded. The method used in electrochemical measurement includes an amperometric measurement method that applies and holds a constant potential to the measurement electrode, such as voltammetry, and detects changes in the amount of flowing current, and a measurement method, such as polarography. Various measuring methods such as a potentiometric measuring method for detecting a potential change of an electrode are used, and all of them measure by detecting a change of a measuring electrode.

[0003] In the measurement electrodes used in these electrochemical measurements, the regulation of the area of the sensitive part is an important technical issue. Various electrodes have been devised. For example, as shown in FIG. 4A, a conductive part 2 suspended by a wire 1 is covered with Pyrex glass 3, or as shown in FIG. Of the flag-shaped electrode 7 with the refractory ceramics 8
And the like are known. As described above, by performing measurement while keeping the electrode area constant by coating with Pyrex glass 3 or refractory ceramics 8, the reliability of the measured value can be improved.

[0004]

However, in the case where the periphery of the conductive part 2 is covered, there is a problem that the solution permeates into the joint between the conductive part 2 and the glass 3 during the measurement, and the thin wire 6 is used. In the method, there is a problem that the electrolytic solution creeps up due to a so-called meniscus effect due to a surface area of the fine wire 6 or a surface tension at a solution interface between the flag-shaped electrode 7 and the fine wire 6. The infiltration of the solution or the creeping up of the electrolytic solution causes a problem in that the electrode area fluctuates and the reliability of the measured values is reduced. On the other hand, when a molten salt that is melted at a relatively high temperature is used for the electrolytic solution, the electrode for electrochemical measurement that is immersed in this high-temperature molten salt has a fixed electrode area for the high-temperature electrolytic solution. Also need to be kept. SUMMARY OF THE INVENTION An object of the present invention is to provide an electrochemical measurement capable of preventing a change in an electrode area in a state of being immersed in an electrolytic solution composed of a molten salt having a relatively high temperature and accurately controlling a liquid contact area of an electrode sensitive portion. To provide an electrode for use.

[0005]

The invention according to claim 1 is
As shown in FIG. 1, this is an improvement of the electrochemical measurement electrode 11 used by being immersed in the molten salt electrolyte 12. The characteristic configuration is that the electrode rod 11a has a length that surrounds the cylindrical electrode rod 11a and the peripheral surface of the electrode rod 11a that is loosely fitted to the electrode rod 11a at room temperature and immersed at least in the electrolyte 12.
and a cylindrical insulating portion 11b having a smaller coefficient of thermal expansion than a, and the peripheral surface of the electrode rod 11a is in close contact with the inner surface of the insulating portion 11b due to the difference in the coefficient of thermal expansion in the molten state of the molten salt 12. There.

The electrode 11 for electrochemical measurement has an electrode rod 11a and an insulating part 11b, and the insulating part 11b has a length at least surrounding the peripheral surface of the electrode rod 11a immersed in the electrolytic solution 12. The peripheral surface of the electrode rod 11a is
In the state of use in close contact with the inner surface of b, only the lower surface of the electrode rod 11a functions as an electrode surface. Also, the insulating part 11b
Is configured to be loosely fitted to the electrode rod 11a at room temperature, thereby facilitating the production of the electrochemical measurement electrode 11,
In the molten state of the molten salt 12, the electrode rod 11
a so that the peripheral surface of the electrolyte solution a is in close contact with the inner surface of the insulating portion 11b.
The electrolyte solution 12 is prevented from seeping between the electrode rod 11a and the insulating portion 11b in a state where the electrode rod 11 is used by being immersed in the electrode.

The invention according to claim 2 is the invention according to claim 1, wherein the electrode rod 11a is made of graphite, and
b is an electrode for electrochemical measurement consisting of boron nitride. The coefficient of thermal expansion of the graphite electrode rod 11a is the same as that of the insulating portion 1 of boron nitride.
Since the thermal expansion coefficient is larger than 1b, the gap between the electrode rod 11a and the insulating portion 11b can be reliably eliminated in the molten state of the molten salt.

[0008]

Embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, an electrolytic solution 12 in which an electrode for electrochemical measurement 11 of the present invention is immersed is stored in a crucible 13. The crucible 13 is made of platinum or graphite. The crucible 13 is a bottomed cylindrical body, and a heater 14 is wound around the side peripheral surface of the crucible 13. The heater 14 is provided for heating the molten salt 12 put in the crucible 13 to a molten state. Electrode for electrochemical measurement 11 crucible 1
3 is provided so as to be immersed in the molten salt 12.

The electrode 11 includes a cylindrical electrode rod 11a and a cylindrical insulating part 11b surrounding the peripheral surface of the electrode rod 11a. The insulating part 11b is made of a material having a smaller coefficient of thermal expansion than the electrode rod 11a. You. In this embodiment, the electrode rod 11a is made of graphite, and the insulating part 11b is made of boron nitride having a smaller coefficient of thermal expansion than graphite. As shown in FIG. 3, the insulating portion 11b made of boron nitride
Has a length surrounding the peripheral surface of the electrode rod 11a which is loosely fitted to the electrode rod 11a at room temperature and immersed at least in the electrolyte solution 12. The degree of loose fitting of the insulating portion 11b to the electrode rod 11a depends on the difference in the coefficient of thermal expansion of the electrode rod 11a in the state where the insulating portion 11b is heated to the melting temperature of the molten salt 12 for electrochemical measurement, as shown in FIG. Is configured so that the peripheral surface thereof closely adheres to the inner surface of the insulating portion 11b. The peripheral surface of the electrode rod 11a is an insulating portion 11b.
In a use state in which the electrode rod 11a is in close contact with the inner surface, the lower surface of the electrode rod 11a and the lower surface of the insulating portion 11b are configured to be the same surface, and only the lower surface of the electrode rod 11a is configured to function as an electrode surface.

In the electrode 11 for electrochemical measurement configured as described above, the insulating portion 11b is loosely fitted to the electrode rod 11a at room temperature prior to use. On the other hand, a salt containing a metal salt as a raw material of the molten salt is put in the crucible 13, and the heater 14 is energized to heat the salt to a molten state. Next, at room temperature, the electrode for electrochemical measurement 11 in which the insulating portion 11b is loosely fitted to the electrode rod 11a is heated to the melting temperature of the molten salt. Due to this heating, the peripheral surface of the electrode rod 11a comes into close contact with the inner surface of the insulating part 11b due to the difference in the coefficient of thermal expansion between the electrode rod 11a and the insulating part 11b. The electrode 11 for electrochemical measurement heated to the melting temperature of the molten salt is thereafter immersed in the molten salt electrolyte 12 to serve as the electrode 11 for measurement. in this case,
Since the peripheral surface of the electrode rod 11a is in close contact with the inner surface of the insulating part 11b, the electrolyte 1 is placed between the electrode rod 11a and the insulating part 11b.
2 does not penetrate, thereby preventing the electrode area from fluctuating due to the penetration of the electrolytic solution 12.

[0011]

Next, embodiments of the present invention will be described. As shown in FIG. 1, an electrode 11 for electrochemical measurement was manufactured using graphite for the electrode rod 11a and boron nitride having a smaller coefficient of thermal expansion than graphite for the insulating part 11b. On the other hand, as a raw material of the molten salt, 142.3 g of LiF, 59.1 g of NaF, KF
Was placed in a platinum crucible 13 and the heater 14 was energized to heat the salt to 500 ° C. to be in a molten state.
Specifically, at room temperature, the diameter of the electrode rod 11a in the electrochemical measurement electrode 11 is set to 10.00 mm, the inner diameter of the insulating portion 11b is set to 10.02 mm, and the peripheral surface of the electrode rod 11a is heated to 500 ° C. It was configured to be in close contact with the inner surface of the insulating part 11b. The electrode 11 for electrochemical measurement thus constituted was preliminarily heated to 500 ° C. in an inert atmosphere, immersed in the molten salt 12, and left in that state for 5 hours.

After leaving for 5 hours, the electrode for electrochemical measurement 11
From the molten salt 12 and cooled to room temperature.
Observation was made on the contact portion between a and the insulating portion 11b. Observation of the contact portion was performed by cutting the electrode 11 in the vertical direction and
Observation was performed with a microscope of 0 magnification, and analysis of fluorine ions by EPMA analysis was performed. As a result of the observation, microscopic observation of the contact portion showed no trace of the molten salt seeping into the contact portion, and no residual fluorine ions at the contact interface in EPMA analysis. This is considered to be due to the fact that the peripheral surface of the electrode rod 11a was in close contact with the inner surface of the insulating portion 11b.

[0013]

As described above, according to the present invention, the electrode for electrochemical measurement is formed on the cylindrical electrode rod and the electrode rod is loosely fitted to the electrode rod at room temperature and at least immersed in the electrolyte. A cylindrical insulating portion having a length surrounding the surface and having a smaller coefficient of thermal expansion than the electrode rod, and a peripheral surface of the electrode rod is formed on the inner surface of the insulating portion due to a difference in coefficient of thermal expansion in a molten state of the molten salt. Because it is configured to be in close contact, only the lower surface of the electrode rod acts as an electrode surface when the peripheral surface of the electrode rod is in close contact with the inner surface of the insulating part, and the peripheral surface of the electrode rod contacts the inner surface of the insulating part. It prevents the electrolyte solution from soaking between the electrode rod and the insulating portion by being in close contact with each other. As a result, it is possible to prevent the fluctuation of the electrode area due to the penetration of the electrolyte in the state of being used by being immersed in the electrolyte composed of the molten salt at a relatively high temperature, and to accurately regulate the liquid contact area of the electrode sensitive portion. be able to. If the electrode rod is made of graphite and the insulating part is made of boron nitride, the coefficient of thermal expansion of the graphite electrode rod is larger than the coefficient of thermal expansion of the insulating part of boron nitride. It is possible to reliably eliminate the gap between the insulating portion.

[Brief description of the drawings]

FIG. 1 is a central longitudinal sectional view of an apparatus including an electrode for electrochemical measurement of the present invention.

FIG. 2 is an enlarged sectional view of a part A in FIG. 1 showing an electrode for electrochemical measurement used by being immersed in a molten salt electrolyte.

FIG. 3 is an enlarged sectional view corresponding to FIG. 2, showing an electrode for electrochemical measurement in a room temperature state.

FIG. 4A is a longitudinal sectional view showing a conventional electrode for electrochemical measurement in which the periphery of a conductive portion is covered with Pyrex glass. (B) A longitudinal sectional view showing a conventional electrode for electrochemical measurement in which a flag electrode is coated with a refractory ceramic.

[Explanation of symbols]

 11 Electrode for Electrochemical Measurement 11a Electrode Rod 11b Insulating Part 12 Molten Salt Electrolyte

Claims (2)

[Claims] 1. An electrochemical measurement electrode (11) which is used by being immersed in a molten salt electrolyte (12), wherein the electrode (11a) having a columnar shape and the electrode rod (11a) are allowed to float at room temperature. Electrode rod fitted and immersed at least in the electrolyte (12)
(11a) having a length surrounding the peripheral surface of the electrode rod (11a)
A cylindrical insulating portion (11b) having a smaller coefficient of thermal expansion, wherein the peripheral surface of the electrode rod (11a) is insulated by the difference in the coefficient of thermal expansion in the molten state of the molten salt (12). An electrode for electrochemical measurement, wherein the electrode is configured to be in intimate contact with the inner surface of the electrode. 2. An electrode (11a) made of graphite, and an insulating portion (11).
2. The electrode for electrochemical measurements according to claim 1, wherein b) comprises boron nitride.