JPH0346371Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] The present invention relates to a diaphragm oxygen electrode, which is a sensor for measuring dissolved oxygen. It has a particularly great value in measurement.

[Conventional technology]

A diaphragm oxygen electrode (hereinafter abbreviated as DO sensor) used to measure dissolved oxygen (DO) is composed of a cathode, an anode, a diaphragm, an electrolyte, and an electrolytic cell.

The cathode is made of platinum, the anode of the polarographic sensor is made of silver (lead for the galvanic sensor), the diaphragm is made of polyfluorinated ethylene, the electrolyte is made of potassium chloride, and the electrolytic cell is made of plastic or metal. It is used.

This DO sensor is suitable for river water, industrial water, waste water,
It is widely used for measuring DO in bioreactors, etc., but it is especially used in boiler water management, as DO causes corrosion.
Because it is necessary to remove DO in advance by adding an oxygen scavenger such as hydrazine and confirm its removal effect.
Emphasis is placed on the measurement and management of ultra-trace amounts of DO on the ppb order (ppm order in normal applications).

From the standpoint of ensuring plant safety, particularly strict DO monitoring is required for nuclear power boiler water. At nuclear power plants, the above-mentioned oxygen scavenger is added to the boiler water, and hydrogen gas is added and dissolved in order to protect the boiler from corrosion. However, there is no suitable measurement method, and the DO measurement relies on complicated manual analysis methods. This is the current situation.

[Problem that the invention attempts to solve]

If the DO measurement of the above-mentioned water water could be carried out continuously and automatically using a DO sensor, it would be possible to perform complete DO monitoring with less labor, but conventional DO sensors cannot be used for the following reasons.

In other words, with a platinum cathode, in the presence of hydrogen gas, the indication of the oxygen amount (oxygen reduction current) will deviate greatly in the negative direction, as shown by curve a in Figure 1, and DO measurement will not be possible at all. This was revealed through the inventor's experimental research.

This is thought to be due to the simultaneous occurrence of the oxidation reaction of hydrogen, since platinum has a strong catalytic ability for hydrogen.

[Purpose of invention]

The purpose of this invention is to solve the problem even in the presence of dissolved hydrogen.
Our objective is to provide a DO sensor that can accurately measure DO to ensure the safety of nuclear power plants.

[Means for solving problems]

The present invention was devised to solve the above-mentioned problems, and includes a diaphragm oxygen electrode in which a platinum cathode electrode is melt-sealed to the end of a glass tube. It is designed to form layers.

[Effect]

Since the DO sensor according to the present invention is coated with a gold plating layer, the platinum cathode electrode is not affected by hydrogen at all, so DO can be measured accurately.

In FIG. 1, curve b shows the meter reading when the device according to the present invention is used, and the meter reading does not change even if hydrogen gas is introduced.

Note that conventional DO using gold as the cathode material
There are sensors, but they don't fit well with the glass, so
It is practically impossible to use it by melt-sealing it in glass.

As a solution to this problem, there is an extremely complicated proposal, such as US Pat. No. 4,096,047 (Harley method), in which the cathode is crimped onto the sapphire insulator using a spring.

There are also products that use gold as a cathode sealed in organic insulating materials such as epoxy resins, but as they are used, the electrolyte gradually seeps into the space between the insulator and the gold, causing an increase in residual current. Therefore, it cannot be used for measuring extremely low concentrations of DO for a long time.

〔Example〕

FIG. 2 shows an embodiment of the present invention, in which 1 is a glass tube, 2 is a cathode made of platinum that is melt-sealed in a recess 1a provided at the end of the glass tube, and 3 is a lead wire.

The cathode 2 made of platinum has minute irregularities 2 on its surface.
A is applied, and a gold plating layer 4 is applied to the upper surface.

In addition, in the DO sensor, close contact between the surface of the cathode and the diaphragm 5 is necessary to ensure response and stability, but if the tension for close contact is too strong,
The electrolytic solution 6 is forced out from between the diaphragm 5 and the cathode 2, inhibiting the electrolytic reaction and reducing the current, making accurate measurement of DO impossible.

[Effect of idea]

In the present invention, platinum, a metal that is most completely encapsulated in glass, is used as the cathode electrode, so the above-mentioned problems in insulation technology when using gold do not occur.

Furthermore, in the present invention, since the cathode surface has a large number of fine uneven surfaces, even if the diaphragm is strongly stretched, the electrolyte remains in the recesses, ensuring extremely stable and rapid response.

Therefore, it is possible to automatically and continuously measure trace amounts of DO in deoxygenated water containing dissolved hydrogen gas.

Furthermore, since the reaction area becomes larger, the oxygen reduction reaction increases, resulting in a synergistic effect of increasing sensitivity by 50%. Also, compared to the Hare method, it has a simpler structure and is administered orally.

[Brief explanation of the drawing]

FIG. 1 is a comparison diagram of the hydrogen resistance of a conventional DO electrode and the DO electrode of the present invention, and FIG. 2 is a partially cutaway side view of an embodiment of the present invention. 1...Glass tube, 2...Platinum cathode electrode, 3...Lead wire, 4...Gold plating layer.

Claims (1)

[Scope of utility model registration request] A diaphragm oxygen electrode comprising a platinum cathode electrode melt-sealed to the end of a glass tube, characterized in that a gold plating layer having fine irregularities is formed on the surface of the platinum cathode electrode.