JPH0238962A - Electrochemical sensor - Google Patents

Abstract

PURPOSE:To improve a high temp. water resistant life and an electrode life by sealing a semiconductor electrode, counter electrode and reference electrode by ceramics sealing having a small difference in thermal expansion. CONSTITUTION:The semiconductor electrode 4 is formed by diffusion joining of the conductive electrode 12 with aluminum as a spacer to a TiO2 single crystal 11 doped with Nb2O5 and is sealed by diffusion joining thereof together with the counter electrode 3 to ceramics 13, 14. An electrode chamber 21 of the reference electrode 7 is sealed by diffusion joining of a crucible 24 consisting of a reverse osmosis membrane made of alumina and the ceramics 18 fixed with the electrode. Further, the platinum electrodes 5, 6 which detect the concn. of the KCl in an internal electrolyte are installed in addition to a silver-silver chloride electrode 20 as the reference electrode to the electrode chamber 21. These electrodes are fixed via bolts 9 to a housing 8. The fixed part is formed with the sealing via shims 10 made of titanium.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an electrochemical sensor for measuring the quality of high-temperature water and the corrosion characteristics of metals in high-temperature water, and particularly for measuring the quality of core cooling water in light water reactors and heavy water reactors. and an electrochemical sensor suitable for measuring and monitoring corrosion characteristics of core cooling system piping.

[Conventional technology]

Currently, pH measurement of high-temperature, high-pressure water using atomic couplants, etc.
Due to restrictions on the electrode's heat resistance and high-temperature sealing properties, high-temperature water is cooled to room temperature. For example, an example of a conventional pH measurement sensor using a hydrogen electrode is the Electrochemistry Handbook pp.27.
9-285. Corrosion Prevention Technology 34 (1985) ppL32~
134). All of these measurement techniques are performed with the water to be measured at a temperature close to room temperature, and cannot be applied to high-temperature, high-pressure water where the temperature of the water to be measured exceeds the boiling point.

On the other hand, an attempt to directly measure the pH of high-temperature water using a semiconductor electrode was recently reported in "Anti-Corrosion Technology." According to the report, the flat band potential obtained from the impedance obtained by applying alternating current of various amplitudes to a semiconductor made of a titanium oxide single crystal doped with niobium is pH
This means that it changes depending on the situation. This relationship shows that it is possible to measure the pH of high-temperature water because it has little temperature dependence.

[Problem to be solved by the invention]

For the structure of a sensor used to measure water quality in a plant that handles high-temperature, high-pressure water, it is essential that maintenance such as replacing the electrolyte used in the sensor or replacing the electrodes if they are damaged is essential. Furthermore, it is desirable to have a maintenance-free structure that does not require replacement of the electrolyte, but the above-mentioned conventional technology does not meet the requirements for ease of maintenance, heat resistance, or sealing required in plants that handle high-temperature, high-pressure water. Technical issues related to the practical use of semiconductor electrodes, such as gender, are not disclosed.

The present invention aims to solve the above problems.

This is intended to improve the high temperature water resistance life of the sensor sealing part and the life of the electrodes.

[Means to solve the problem]

The above object is achieved by making the semiconductor electrode, reference electrode, and counter electrode, which are the constituent elements of a sensor for electrochemically measuring the quality of high-temperature water, as follows.

NbzO, which is chemically stable in high-temperature water, is used for the semiconductor electrode.
A T' i 0 z single crystal doped with a was used and was diffusion bonded to a conductive electrode made of copper or its alloy, aluminum or its alloy, or stainless steel using aluminum as a spacer. By using aluminum as a spacer.

By reducing the difference in the work function of the plane electrode at the bonding interface between the TiOz single crystal and the conductive electrode, the influence of the electric double layer formed at the bonding interface during impedance measurement was reduced. Furthermore, sealing was achieved by diffusion bonding alumina (AQzOa) ceramic to the outer surface of the bonded semiconductor electrode.

In order to prevent the reference electrode from leaking its internal electrolyte from the electrode chamber into the measurement environment, the electrode chamber is sealed by diffusion bonding between a crucible made of an alumina reverse osmosis membrane and a ceramic terminal to which the electrode is fixed. ing.

Furthermore, in addition to the silver-silver chloride electrode as a reference electrode, a platinum electrode was installed in the electrode chamber to detect the KCl concentration in the internal electrolyte, and the electrical conductivity inside the electrode chamber was measured using these electrodes. The structure allows accurate evaluation of reference potential even if the KClIIA degree of the internal electrolyte changes. For this reason,
It is no longer necessary to maintain the KCl concentration of the internal electrolyte constant as in the prior art.

[Effect]

The principles of pH measurement and electrical conductivity measurement will be explained.

pH measurement: @When the vapor chemical sensor is filled with water to be measured, the surface potential of the semiconductor electrode changes depending on the concentration of H ions in the aqueous solution.
Affected by base dissociation reactions. Now, when the surface potential of the semiconductor electrode is verified using the verification tl electrode and a potential equivalent to this is periodically applied between the counter electrode and the semiconductor electrode, the capacitance component of the impedance tends to depend on pH.

The relationship is shown in Figure 3. The figure shows the relationship (tendency) between the potential and the capacitive component of the impedance when the potential is applied to the semiconductor electrode at a constant cycle while changing the potential. Here, the capacitive impedance is It was shown that the capacitive impedance corresponding to each potential, expressed as its reciprocal, decreases as it moves toward the acidic side.

Electrical conductivity 2 From the above impedance measurement, electrical conductivity can be determined from its resistance component. Now, when impedance is measured while keeping the potential constant and varying the frequency, the equivalent impedance is expressed as follows.

Here, Rsol: Resistance of the aqueous solution Rf: Resistance of the semiconductor electrode j: Complex number (jωC represents complex impedance) C: Electric double layer capacitance at the interface between the semiconductor electrode and the aqueous solution ω: Angular frequency (2πf) As a result, the fourth The resistance of the aqueous solution can be determined from the vector diagram shown in the figure.

Furthermore, when one end of the bridge circuit is connected to the platinum electrode installed inside the reference electrode and the electrical resistance inside the electrode chamber is measured, KC
Electrical resistance can be changed according to lm degrees.

〔Example〕

An embodiment of the present invention will be described below with reference to a sectional view of an electrochemical sensor shown in FIG.

As shown in FIG. 1, the electrochemical sensor of the present invention is a T i Oz doped with NbzO6 equipped with a platinum counter electrode 3.
A reference electrode 7 consisting of a single crystal semiconductor electrode 4 and a silver-silver chloride electrode provided with a platinum electrode 5.6 was fixed to a housing 8 with bolts 9.

These fixing parts are sealed with titanium shims 10 interposed therebetween. The water to be measured is introduced into and discharged from the electrochemical sensor as indicated by the white arrow, making it possible to reliably measure the quality of high-temperature, high-pressure water.

Details of each part of the electrochemical sensor of the present invention will be explained.

The housing 8 is necessary for arranging and fixing the reference electrode, semiconductor electrode, and counter electrode in the required positions, and maintaining a measurement environment in which high-temperature, high-pressure water is stably introduced and discharged. is shown in Figure 2.

From the viewpoint of corrosion resistance and strength, the casing 8 is preferably made of austenitic stainless steel, titanium, or an alloy thereof.

In FIG. 2, the convex portions 8a of each part of the casing have a shape necessary for fixing bolts 9 and sealing with shims 10.

The semiconductor electrode 4 has the structure shown in FIG. In the figure, Ti
The 0z single crystal semiconductor 11 is diffusion bonded to a copper m-pole 12 using aluminum as a spacer. This results in
The feature is that the difference in work function between the TiOx single crystal and the copper electrode at the welded interface is reduced, thereby reducing the influence of the electric double layer capacitance formed at the interface during impedance measurement.

Additionally, the same polarity was added to the ceramic 13 for sealing.
Diffusion bonding is used instead of rubber or Teflon seals as in conventional technology. At the diffusion bonding interface, an aluminum mini-ram spacer and glass were combined to prevent electrode damage due to thermal expansion difference.

The counter electrode 3 was diffusion bonded to the ceramic 14 and sealed. By further bonding these to the ceramic 13, water intrusion from the liquid contact side of the semiconductor 11 was sealed.

These electrodes are fixedly sealed to the electrode housing 15 with fukuronuts 16. Further, the electrode body 15 is cooled by a cooling pipe 17 through which cooling water flows, and finally the vaporized moisture is also removed by pushing the sleeve 19 inside the electrode body 15 with a flocron nut 18 and pressurizing the Teflon seal ring 20 to achieve sealing. The procedure for assembling 0 semiconductor electrodes is shown in FIG.

The structure of the reference electrode 7 is as shown in FIG.

In the figure, the reference electrode is a silver-silver chloride electrode, and its shape is such that molten silver chloride 20 is welded to the tip of a silver electrode 19 that is insulated and fixed in a ceramic 18 by diffusion bonding. Further, platinum electrodes 5 and 6 are insulated and fixed to the ceramic 18 by diffusion bonding.

Thereby, the KC and Q concentrations in the electrode chamber 21 are constantly detected.

That is, since there is a quantitative relationship between KCl concentration and electrical conductivity, by connecting both terminals of the platinum electrodes 5 and 6 to one end of the AC bridge circuit, KCl in the internal electrolyte of the electrode chamber 21 can be reduced. Concentration can be monitored.

Therefore, it is possible to check the potential without using the internal electrolyte at a certain concentration, and in the present invention, it is also possible to check the potential by using the ceramic agent 22 that can extract KCl6. Replenishment and replacement can be omitted for a long time. Of course, K(l extraction ceramic agent 22
It is also possible to check the potential using only the internal electrolyte without using the internal electrolyte.

The ft electrode chamber 21 includes a filter 23 to prevent dust from adhering to the vicinity of the electrode, and a crucible 24 made of an alumina reverse osmosis membrane.
This shows a space in which the ceramic 18 and the ceramic 18 are diffusion bonded, and this space is always filled with an aqueous solution containing KCl.

The aluminum crucible 24 is fixed to the electrode housing 26 with a fukuro nut 25 and sealed with a shim 10.

A rectifying chamber 27 is fixed to the fukuronut 25 in order to remove the influence of the flow rate of the water to be measured entering the electrode chamber 21.

The outer surface of the housing 26 is a cooling pipe 28 through which cooling water is passed.
The sleeve 30 is pushed into the electrode using a fukuronut 29, and the Teflon seal ring 31 is pressurized to achieve sealing.

A measurement example is shown in FIG. 9, which shows the relationship between the impedance measurement results for aqueous solutions with different pHs and the reciprocal (1/C'') of the capacitance component C of the impedance for each potential.

The figure shows that the capacity gradually decreases as the pH shifts to the acidic side, indicating pH dependence.

[Effects of the Invention] According to the present invention, high-temperature, high-pressure water can be reliably measured by integrating a semiconductor electrode, a counter electrode, and a reference electrode necessary for electrochemical measurement of the pH of high-temperature water.

Additionally, we have solved the problem of sealing high-temperature, high-pressure water, which was the most difficult problem with conventional technology, using ceramic diffusion bonding technology.

Furthermore, it is equipped with a function to self-monitor the KCV 11 degrees of the internal electrolyte of the reference electrode, so it can be used for a long period of time.

Eliminates the need to replace the internal electrolyte.

In addition, if we develop a unique KCl extraction ceramic agent and install it in the reference electrode chamber, it will be possible to measure the potential for an even longer period of time.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an electrochemical sensor according to an embodiment of the present invention, FIG. 2 is an enlarged sectional view of the casing shown in FIG. FIG. 4 is a vector diagram of the mi impedance of the semiconductor electrode, and FIG. 5 is an enlarged sectional view of the semiconductor electrode in FIG. 1. Fig. 6 is an exploded cross-sectional view showing the procedure for assembling the semiconductor electrode shown in Fig. 5, Fig. 7 is an enlarged cross-sectional view of the reference electrode shown in Fig. 1, and Fig. 8 is an assembly of the reference electrode shown in Fig. 7. FIG. 9 is an exploded sectional view showing the procedure, and a characteristic diagram showing a measurement example. 1... Alkaline aqueous solution, 2... Acidic aqueous solution, 3...
・Opposite. 4... Semiconductor electrode, 5, 6... Platinum electrode, 7... Reference electrode, 8... Housing, 9... Volt, 10... Shim, 11... Ti0z... Single Crystal semiconductor, 12.
...Copper electrode, 13°14.18...Ceramic, 1
5... Live temperature body electrode housing. 16.25.29...Fukuronut, 17.28...
・Cooling tube, 19... Silver electrode, 2o... Silver chloride, 21
... Electrode chamber, 22 ... KCl extraction ceramic agent, 2
3... Filter, 24... Alumina reverse osmosis membrane crucible, 26... Reference electrode housing, 27... Rectification chamber, 3
0...Sleeve, 31...Teflon seal ring,
A...pH 9,21 mouth...pH6,7, C...P
H1,7゜nel Kikutakume 1 intoxication r I death 1--71 Shitori 1'h71 Ikuzu diagram)

Claims (1)

[Claims] 1. A semiconductor electrode for measuring impedance of high-temperature water;
In an electrochemical sensor for high-temperature, high-pressure water that integrally houses a reference electrode for comparing the electrode potential, a counter electrode, and the above-mentioned electrode, heat and water resistance is imparted to the semiconductor electrode, the counter electrode, and the reference electrode by ceramic sealing with a small difference in thermal expansion. An electrochemical sensor for high temperature and high pressure water. 2. An electrochemical sensor characterized in that, in the semiconductor electrode described above, formation of an electric double layer during impedance measurement is prevented by bringing the semiconductor and the conductive electrode into ohmic contact by diffusion bonding using aluminum as a spacer. 3. A voltage chemical sensor characterized in that, in the reference electrode described above, the electrode chamber is sealed with a ceramic to prevent KCl elution from the internal electrolyte. 4. As mentioned above, a pair of electrodes that can measure the electrical conductivity of the aqueous solution inside the electrode chamber is installed in the reference electrode to self-monitor the KCl concentration of the internal electrolyte, thereby making it possible to correct the reference potential. An electrochemical sensor featuring: