JPS6123959A - Collating electrode for high-temperature and high-pressure water - Google Patents

Abstract

PURPOSE:To prevent an electrolyte, etc., from leaking by forming the liquid junction of the collating electrode in a specific shape. CONSTITUTION:The liquid junction of the collating electrode formed of a container 1 which is equipped with a bellows 3, etc., and made of ethylene tetrafluoride, etc., is shaped in a frustum of a cone and inserted into a container body. In this constitution, even if the electrolyte 2 in the container 1, the container 1, etc., expand in different states as the water temperature in an autoclave rises, the clearance formed between the liquid junction and container body is blocked automatically with the conic part of the liquid junction 4. When the temperature falls, on the other hand, outward leakage of the electrolyte, inward leakage of water, etc., are prevented similarly.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an electrochemical measuring instrument, particularly for measuring the oxidation/reduction electrode (surface potential, corrosion potential) of a metal material (sample electrode) in high temperature/high pressure water. This invention relates to a reference electrode that provides an indispensable reference potential.

[Background of the invention]

High-temperature/high-pressure water reference electrodes are roughly divided into two types, internal reference electrodes and external reference electrodes, depending on how the electrodes are installed. The former is installed inside an autoclave.

Used at the same temperature as the sample electrode. The latter is placed outside the autoclave and is normally used at room temperature. Although potentials measured using external reference electrodes are useful for investigating relative changes, internal reference electrodes are necessary for thermodynamic investigation of corrosion reactions.

A practical problem with internal reference electrodes for high-temperature, high-pressure water is that the electrodes deteriorate in a relatively short period of time, and one of the causes of this is the sealing caused by the difference in thermal expansion coefficient between the electrode container and the internal liquid. It is thought that the parts may have become defective. In contrast, the container is made of thin-walled polytetrafluoroethylene resin (PIFE) to provide flexibility and to alleviate pressure changes caused by thermal expansion of the internal liquid.

However, it is difficult to completely eliminate the pressure difference between the inside and outside of the container when the temperature rises or falls, and when the temperature rises, the electrolyte leaks into the autoclave, contaminating the water inside the autoclave. Moreover, when the temperature falls, the inside of the container becomes negative pressure, water in the autoclave flows in, and the electrolyte is diluted, causing deterioration of the electrodes.

Particularly under BWR conditions, since high-purity water is used, electrolyte leakage during temperature rise has a large effect on the quality of reactor water.

[Purpose of the invention]

An object of the present invention is to provide an internal reference electrode for high-temperature/high-pressure water having a structure that can effectively prevent electrolyte leakage, which is essential for application under BWR conditions.

[Summary of the invention] As a result of experimentally investigating the correlation between the electrolyte leak behavior in a conventional internal reference electrode and the temperature cycle of temperature rise and fall, we found that
During the temperature rising process, the pressure inside the container becomes higher than that outside due to thermal expansion of the electrolytic solution inside the container, and the electrolytic solution leaks to the outside of the container. On the other hand, during the cooling process, as the electrolyte contracts, the pressure inside the container becomes lower than that outside, and water from outside the container leaks into the container, diluting the electrolyte. It was also found that, in addition to the liquid junction, the gap formed by the difference in thermal expansion coefficient between the liquid junction and the container has a large contribution to the leak path.

Based on these experimental facts, in order to effectively prevent external leakage of the electrolyte, the liquid junction is shaped like a truncated cone, and the pressure inside the container generated during the heating process is used to reduce the thermal expansion of the liquid junction and the container. The present invention was developed based on the idea of automatically eliminating the gap formed by the difference in rate.

A feature of the present invention is that in a reference electrode for electrochemical measurement consisting of an electrode, an electrolyte, an electrode/electrolyte holding container, and a liquid junction, the diameter of the liquid junction is larger on the inside of the container than on the outside. The main body of the container is shaped like a trapezoidal cone.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an example of the internal structure of an internal reference electrode for high-temperature/high-pressure water to which the present invention is applied; 1 is a PTFE container;
2 is a 0.01 kmoQ-m-" KCQ aqueous solution, 3 is a PTFE bellows, 4 is a trapezoidal liquid junction made of porous alumina sintered body, 5 is an Ag wire, and 6 is AgCQ, which is the so-called silver /Constituting a silver halide electrode.First
The electrode shown in the figure is immersed in pure water in an autoclave, heated together with the water in the autoclave, and used as an internal reference electrode for high-temperature, high-pressure water. FIG. 2 is a diagram schematically showing the deformation behavior of the liquid junction during the temperature rising/cooling process. The body expansion coefficient of PTFE is 5.4 Xl0-'/K,
That of water is 1.41 Xl0-a/K, and that of alumina is 8. It is OX10-S/. Therefore, the electrodes in Figure 1 can be adjusted from room temperature to 285, which is the BWR reactor water temperature condition.
When the temperature rises to 558 K, the electrolytic solution in the container expands approximately 25% more than the volume of the container. The volumetric expansion is absorbed by the extension of the bellows part, but since the bellows part has a spring constant, an internal pressure corresponding to the product of the spring constant and the extension of the bellows part is generated within the container.

Now, as shown in Figure 2, if the length of the container containing the electrolyte is Q (■), the cross-sectional area is S (alT), and the spring constant is K (kg/am), then the volume of the electrolyte is Expansion (25
%), the internal pressure P (ICg/a#) is expressed by the following formula.

For example, Q = 10 cm, S = 1 ti
, k = 1 kg/an, then P = 2.5
kg/af.

On the other hand, in the liquid junction part, the liquid junction entry part of the container expands about 30% more than the alumina liquid junction. Assuming uniform thermal expansion of the container, the diameter of the junction will increase by about 10%.

Now, as shown in Figure 2, the liquid junction diameter on the inside of the container is a
(■), and the diameter at 285°C is 1. I Xa(cn),
1. I Xb (an).

For example, if a = 1 and b = 0.7 gloss, then 285℃
The diameter of each is 1.1 ■.

It becomes 0.77an. That is, a gap of about 0.1 an is generated between the liquid junction and the container body. However, as mentioned above, the internal pressure due to the volume expansion of the electrolyte, 2
．． Because 5 kg/ln is applied, the liquid junction moves from the inside of the container to the outside, as shown in Figure 2, and a gap of approximately 0.1 mark is created between the liquid junction and the container body. It will be automatically blocked. Therefore, by using a truncated cone-shaped liquid junction as shown in FIG. 1, it is possible to effectively prevent the electrolyte from flowing outside during the temperature rising process.

In addition, in the present invention, an example has been shown in the case of a silver/silver halide electrode, but metal/metal oxide electrodes and metal/metal sulfate electrodes described in the documents cited in the background of the invention may also be used. It can be generally applied to reference electrodes for high temperature and high pressure water, such as calomel electrodes, which are composed of an electrode, an electrolyte, an electrode/electrolyte holding container, and a liquid junction, and the same effects as in the above embodiments are exhibited. In addition, the material of the container is PTF.
A material other than E may be used, but in the case of stainless steel, for example, corrosion products caused by the electrolyte will have a negative effect on the electrode.

Modification Example 1 FIG. 3 is a diagram showing a modification example of the invention embodiment shown in FIG.
- 6 are the same as in FIG. 1, 7 is a Teflon liquid junction presser, and 8 is a spring. By adding a Teflon liquid junction retainer 7 and a spring 8, it not only prevents gaps from forming when the temperature rises, but also creates a negative pressure inside the container relative to the outside when the temperature falls, causing water to leak into the autoclave. To reliably prevent in-leakage to the third part. becomes possible. Therefore, not only can water in the autoclave be prevented from being contaminated, but also dilution of the electrolytic solution can be prevented, so that the life of the reference electrode can be extended.

Modified Example 2 FIG. 4 is a diagram showing a modified example of the embodiment of the invention shown in FIG. 3, in which the shape of the truncated cone of the liquid junction is such that the diameter of the inner side of the container is larger than the diameter of the outer side.

In this case, the advantage is that the liquid junction can be attached to the container body from outside the container, but it is also possible to generate a pressure higher than the internal pressure in order to prevent external leakage of the electrolyte due to thermal expansion of the electrolyte. A spring is essential.

Modification 3 1st. Third. Figure 4 shows the electrode/electrolyte holding container.
Although a thick-walled Teflon container with a bellows structure was used, similar effects can be expected by using a conventionally used thin-walled Teflon container without a bellows structure.

〔Effect of the invention〕

According to the present invention, the following effects can be achieved.

1. It is possible to automatically prevent external leakage of electrolyte during the temperature raising process, and the oxidation/reduction potential of metal materials in high-temperature water can be measured without changing the quality of pure water in the autoclave. .

2. - It is possible to automatically prevent dilution of the electrolytic solution due to in-leakage of water during the temperature-lowering process, and it is possible to prevent deterioration of the reference electrode due to dilution of the electrolytic solution.

[Brief explanation of drawings]

Fig. 1 is an internal structure diagram of an internal reference electrode for high temperature/high pressure water according to an embodiment of the present invention, Fig. 2 is an explanatory diagram showing the deformation behavior of the liquid junction according to the present invention during the temperature rising/falling process, and Fig. 3 Figure, 4th
The figure is an internal structure diagram of an internal reference electrode for high temperature/high pressure water according to a modification of the present invention. 1... PTFE container, 4... Liquid junction, 5... Ag
Line, 6...-33' 1st eye 39th mouth

Claims (1)

[Claims] 1. In a reference electrode for electrochemical measurement consisting of an electrode, an electrolyte, an electrode/electrolyte holding container, and a liquid junction, the liquid junction part is shaped like a trapezoid and is inserted into the main body of the container. Reference electrode for water.