JPH03102256A - Oxygen sensor - Google Patents

Abstract

PURPOSE:To enable stable measurement of dissolved oxygen in water for a long period by constructing an oxygen sensor of a sensor element having an oxygen ion conductor and a pair of electrodes and of a porous partition wall. CONSTITUTION:A sensor element M is constructed of an oxygen ion conductor 1 formed to be of small thickness and constituted of stabilized zirconia, of porous electrodes 2A and 2B which are laminated on the counter surfaces of the conductor and whereon a prescribed voltage is impressed, etc. On the side of a stem 10 whereon the sensor element M is disposed, a mesh cover 12 (first air-permeable partition wall) covering the sensor element M wholly and preventing impurities such as dust is fitted, and moreover an air-permeable Teflon film 13 (second air-permeable partition wall) preventing the invasion of a solution and allowing a gas (oxygen gas) dissolved in the solution to pass through is fitted on the inner surface of the cover 12. A porous partition wall 14 is constructed of this cover 12 and the film 13. By this partition wall 14, it is possible to prevent the invasion of the solution and to allow only the gas to pass through, and thus the concentration of oxygen dissolved in water can be measured effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a limiting current type oxygen sensor capable of measuring the concentration of oxygen dissolved in water.

"Prior Art and its Problems" Conventionally, galvanic cell type and polar graph type oxygen sensors have been known as sensors capable of measuring dissolved oxygen.

Both of these types of oxygen sensors are electrochemical sensors that use an electrolyte, and the sample gas inlet of the oxygen sensor is equipped with FEP (tetrafluoroethylene copolymer of bovine fluoropropylene), etc. A diaphragm is provided.

By the way, since the oxygen sensor is an electrochemical sensor, it has a problem that its lifespan ends as the electrolyte is consumed, and it cannot withstand continuous use over a long period of time, and its function as a sensor stops at a certain point. In addition, the above-mentioned oxygen sensor is highly dependent on the performance of the diaphragm, and as a result, the material forming the diaphragm is subject to severe deterioration, which also poses the problem of not being able to withstand long-term continuous use.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a limiting current type oxygen sensor that can stably measure dissolved oxygen in water over a long period of time.

"Means for Solving the Problems" In order to achieve the above object, the first invention provides an oxygen ion conductor made of a thin solid electrolyte, and an oxygen ion conductor laminated on each surface of the oxygen ion conductor. a sensor element having a pair of electrodes to which a predetermined voltage is applied;
It is provided with a porous partition wall that prevents solution from entering and has air permeability.

In a second aspect of the invention, the porous partition wall includes a first breathable partition wall provided to cover the sensor element, and a second breathable partition wall provided inside the first breathable partition wall. I try to do that.

"Operation" According to these inventions, the porous partition wall provided to completely cover the sensor element prevents solution from entering and allows only gas to pass through, effectively controlling the concentration of oxygen dissolved in water. can be measured. In addition, the porous partition wall is one that selectively allows oxygen to pass through, like a conventional galvanic cell type, and is a film made of lopyrene, etc., or a porous film thereof (for example, one in which fine pores have been made by electron beam irradiation, etc.).
It is possible to select a highly durable material with extremely low material deterioration, such as porous ceramic.

"Embodiment" An embodiment of the present invention will be described with reference to FIGS. 1(A) to 3.

First, the general structure of the sensor element M will be explained with reference to FIG. 3. This sensor element M is made of thin stabilized zirconia (for example, Z rot-8Y, O.
porous electrodes 2A and 2B which are laminated on both sides of the oxygen ion conductor 1 and to which a predetermined voltage is applied, and an oxygen ion conductor 1 which is formed from the oxygen ion conductor 1; a ceramic canopy 4 that is joined by a glass 3 and forms a microspace 4A between it and the electrode 2B;
The heater 5 is provided on the inner surface of the ceramic cannob 4 and directly applies heat to the oxygen ion conductor 1 to improve the responsiveness of the oxygen ion conductor 1. At the center of the oxygen ion conductor 1, a gas diffusion hole IA is formed so as to communicate with the microspace 4A, thereby controlling the rate of diffusion.

In the oxygen ion conductor 1 of the oxygen sensor configured as described above, when a constant voltage is applied to the heater 5 and a constant sensor monitoring voltage is applied to the electrodes 2A and 2B, An ion current using oxygen ions as carriers flows due to the oxygen pumping action, and the surrounding oxygen concentration is measured from the current value of this ion current.

In the sensor element M, the gas diffusion hole IA is formed in the center of the oxygen ion conductor 1, but the gas diffusion hole may be formed on the ceramic cap 4 side.

Next, a waterproof structure of an oxygen sensor incorporating the sensor element M configured as described above will be explained with reference to FIG. 1(A).

In this figure, the reference numeral 10 indicates a stem serving as a base, and a terminal 11 formed of a conductor is supported on the stem 10. Further, a sensor element M is attached to the upper end of these terminals 11 at a certain height from the stem 10, and between these terminals 11 and the heater 5 and electrodes 2A and 2B of the sensor element M. is provided with a wire IIA that supports the sensor element M and connects each other in a conductive state.

Further, on the side of the stem 10 where the sensor element M is arranged, a mesh cover 12 (first breathable partition) that completely covers the sensor element M and removes impurities such as dust.
Further, on the inner surface of this messine cover 12, there is a Teflon membrane 1 having air permeability that prevents solution from entering and allows gas (oxygen gas) dissolved in the solution to pass through.
3 (second breathable partition wall) is attached.

Note that this Teflon film 13 has a thickness of 0. Ol~1
．． A porous film with a pore size of about 0 [mm] and a pore diameter of about 0.1 to 10 (μ) is used, but if the film is thin, a film without pores may also be used depending on the purpose. , as the porous film, for example,
Those with fine holes drilled by electron beam irradiation or the like are used.

In addition, in this example, the porous film has heat resistance,
Although the highly durable Teflon membrane 13 is used, an FEP membrane, an inexpensive polypropylene membrane, a porous ceramic, or the like may also be used.

Further, the mesh cover 12 and the Teflon film 13 constitute a porous partition wall l4 shown in the claims.
3 and 3 may be fused together and integrated instead of being separated.

The concentration of oxygen gas dissolved in water was measured using the waterproof limiting current type oxygen sensor configured as described above.

As a result, when this oxygen sensor is actually placed in water and measurements are taken, as time passes, the oxygen in the sensor element M and the dissolved oxygen in the water reach a state of vapor-liquid equilibrium, resulting in a specific amount of dissolved oxygen. Then, it becomes a specific sensor output. In other words, it was confirmed that there is a correlation between the amount of dissolved oxygen and the sensor output, and that when the amount of dissolved oxygen changes, the sensor output also changes accordingly. Furthermore, when the relationship between dissolved oxygen concentration and sensor output was investigated, it was confirmed that a very good linear relationship was obtained.

On the other hand, this oxygen sensor utilizes the oxygen ion conductivity of stabilized zirconia, and unlike electrochemical sensors such as galvanic sensors, it does not reach the end of its life due to consumption of the electrolyte, and is basically semi-permanent. It has the advantage that it can be used at high temperatures, and it has also been confirmed that it can operate even in high temperature solutions of 50°C or higher.

(Experimental Example) In order to investigate the relationship between the dissolved oxygen concentration and sensor output described above, the following experiment was conducted.

First, fill a 2g flask with water and add 20 [III] of pure nitrogen.
After confirming the saturation state (dissolved oxygen concentration at this time was 0 ppm), the waterproof type limiting current type oxygen sensor was put in and the change in sensor output was measured.

As a result, the sensor output, which was approximately 0.209V in the atmosphere, decreased over time and eventually reached OQ399.
Stable at V.

Similarly, the oxygen concentration is 12.5%, 20.9%, 2
The sample solution was bubbled with 9.9% gas to reach a saturated state (at this time, the dissolved oxygen concentration was 5pp).
+a, 8 ppm, and 13 ppm), the above-mentioned waterproof type limiting current type oxygen sensor was introduced, and the sensor output when stable was measured.

The results can be summarized in the "Sensor output when stable" section of the table below, and if this is graphed, it will look like Figure 2 (indicated by "○" in Figure 2).

As can be seen from this graph, it was confirmed that there was a very good linear relationship between the dissolved oxygen concentration [ppm] and the sensor output [V].

In addition, the sample solution set as above was created using a polarographic type dissolved oxygen sensor (Hanna Portable Oxygen Meter HI8543), and the results were similar to those of the waterproof type oxygen sensor shown in this example. The output was exactly the same as the sensor output (the measurement results are indicated by "x" in FIG. 2).

This confirmed that the waterproof limiting current type oxygen sensor shown in this example can be fully utilized as an oxygen sensor for measuring dissolved oxygen in water.

In addition, in this experimental example, a porous partition wall 14 made of a mesh cover 12 and a Teflon film l3 is placed on the outside of the sensor element M.
However, as shown in FIG. 1(B), a metal sintered body or a ceramic sintered body formed of a porous material that is porous enough to allow liquid to pass is placed outside the porous partition wall l4. l5 may be provided. The reason why such a sintered body 15 is provided outside the porous partition wall 14 is to prevent the sample liquid from directly entering the porous partition wall 14 when this waterproof oxygen sensor is immersed in a sample liquid. For example, the water pressure that enters the Teflon membrane 13 may put an excessive burden on it, or the Teflon membrane l
This is to prevent 3 from being torn. That is, the sample liquid is brought into gentle contact with the porous partition wall l4 using the sintered body 15, and the sample liquid is guided into the porous partition wall 14 over a certain period of time, thereby increasing the water pressure of the sample liquid. This prevents sudden action on the Teflon film 13.

Further, in this embodiment, the Teflon membrane 13 was used to prevent the solution from entering and to allow only gas to pass through, but instead of this Teflon membrane I3, the pore size was adjusted to allow only gas to pass through. A sintered body 15 as shown in (B) may be provided.

In addition, in FIG. 1(B), what is indicated by the symbol l6 is a case/case that entirely houses the oxygen sensor shown in FIG. 1(A).
The cable shown by reference numeral I7 is a cable in which the terminal 11 is housed.

"Effects of the Invention" As explained in detail above, according to the present invention, the porous partition wall provided to completely cover the sensor element prevents solution from entering and allows only gas to pass through. ,
The concentration of oxygen dissolved in water can be effectively measured.

In addition, the porous partition wall may be one that selectively allows oxygen to pass through, such as a conventional galvanic cell type, but it may also be one that allows gas to pass through but not liquid. It is possible to select highly durable materials with extremely low material deterioration, such as films, porous films, porous ceramics, etc., and the effect is that the concentration of oxygen dissolved in water can be measured stably and effectively over a long period of time. is obtained.

[Brief explanation of drawings]

1(A) to 3 are diagrams showing a first embodiment of the present invention, in which FIG. 1(A) is an external view showing the overall schematic configuration, and FIG. Fig. 2 is a graph showing the dissolved oxygen measurement results of the oxygen sensor; Fig. 3 is Fig. 1 (A.) and Fig. 1 (B).
FIG. 2 is a schematic configuration diagram showing a sensor element M used in an oxygen sensor. 1...Oxygen ion 2# electric body, 2A/2B...
... Electrode, 10 ... Stem, l4 ... Porous partition wall (
12... 71 Non-Yukahar (first breathable partition wall), I3...Teflon membrane (second breathable partition wall)), 1
5...Sintered body (porous partition wall), M...Sensor element.

Claims (2)

[Claims] (1) A sensor element having an oxygen ion conductor made of a solid electrolyte, a pair of electrodes laminated on each surface of the oxygen ion conductor to which a predetermined voltage is applied, and a sensor element provided to cover the sensor element. An oxygen sensor comprising: a porous partition wall that prevents solution from entering and has air permeability. (2) The porous partition wall is composed of a first breathable partition wall provided to cover the sensor element, and a second breathable partition wall provided inside the first breathable partition wall. The oxygen sensor according to claim 1, characterized in that: