JPH02189454A - Sensor of concentration of oxygen - Google Patents

Abstract

PURPOSE:To enable execution of highly precise measurement without being affected by the temperature and pressure of working environment by laminating a pinhole rate-determining layer wherein molecular diffusion is dominant and a porous rate-determining layer wherein Knudsen diffusion is dominant. CONSTITUTION:A measuring element 16 is constructed by providing a platinum electrode 14 on both surfaces of a zirconia sheet 12 which is an ion-conductive solid electrolyte. A pinhole plate 20 is bonded on a plate material 18 which is bonded to the electrode 14, and a pinhole 20a is made beforehand at a posi tion which is to be located on the central axis of the measuring element 16. Moreover, a porous layer 24 is joined on the plate around the position whereat the pinhole 20a is made. As to the relation between the diffusion rate determina tion of oxygen molecules by the porous layer 24 and the diffusion rate determina tion by the pinhole 20a, the latter is designed to be larger slightly than the former. By laminating the pinhole 20a being a diffusion rate-determining layer wherein molecular diffusion is dominant and the porous layer 24 being a diffu sion rate-determining layer wherein Knudsen diffusion is dominant, in this way, both actions of shielding of temperature dependence and shielding of pressure dependence can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an oxygen concentration sensor that can measure oxygen concentration by using an ionically conductive solid electrolyte as an oxygen pump.

[Prior Art] Conventionally, the following configuration has been known as an oxygen-related sensor for measuring oxygen concentration, which uses an ion-conductive solid electrolyte as an oxygen pump.

As shown in FIG. 9, platinum electrodes 52, which have a catalytic effect to promote the ionization of oxygen molecules, are formed on both sides of the partition wall 5o made of an ion-conductive solid electrolyte such as zirconia. A platinum lead wire is attached to the platinum electrode 52, and a constant voltage V is applied to the partition wall 50.

On the other hand, on the cathode side of the partition wall 50, a diffusion-limiting layer section 54 is provided that limits the diffusion rate of oxygen molecules to a predetermined range.
The diffusion rate of oxygen molecules to the cathode side electrode site of 0 is limited. More specifically, this diffusion-controlling layer section 54 may be a pinhole-type diffusion-controlling layer that uses holes with a predetermined diameter, or a porous-type diffusion-controlling layer that uses a porous layer with predetermined pores. Either layer is used.

The oxygen/seismic intensity sensor configured as shown in FIG.
As can be easily understood from the output characteristics shown in the figure, when the applied voltage (2) is selected to the optimum value (2) of 0, the current (2) flowing through the partition wall 50 is the acid fZ? It is known that it is proportional to n degrees.

Therefore, conventional oxygen/seismic intensity sensors are widely used in fields that require measurement of oxygen moisture over a relatively wide range.

[Problems to be Solved by the Invention] However, the following problems are still unresolved in conventional oxygen moisture sensors, and the field of application is limited, or there are problems with measurement accuracy.

As mentioned above, there are two types of diffusion-controlling portions 54 shown in FIG. 9, specifically, a pinhole-type diffusion-controlling layer and a porous-type diffusion-controlling layer. The action of these diffusion-limiting parts 54 is as follows:
It looks like this:

In the pinhole type diffusion control layer, molecular diffusion within small pores of a predetermined diameter is dominant, and the desired diffusion control effect is achieved. In other words, the inside of the pore is a free space for oxygen molecules, and diffusion is restricted here by molecular collisions. Therefore, the pinhole type diffusion control layer has a large temperature dependence based on the well-known molecular diffusion characteristics, and the output current of an oxygen/seismic intensity sensor that uses this layer is approximately proportional to the absolute temperature T to the 0°75th power. It is almost unaffected by the pressure P.

On the other hand, in a porous diffusion-controlling layer, Knudsen diffusion within predetermined pores is dominant, and the desired diffusion-controlling effect is achieved. Therefore, this type of diffusion-limiting layer is adopted (oxygen)
The output current I of the seismic intensity sensor changes in proportion to approximately the 0.8th power of the pressure P based on the known characteristic of Knudsen diffusion, and is substantially unaffected by temperature.

Therefore, conventionally, an oxygen moisture sensor configured with a diffusion control layer that exhibits more appropriate characteristics has been selected depending on the environment in which oxygen moisture measurement is required.

For example, an oxygen sensor used in an environment with rapid temperature changes is constructed with a porous diffusion-controlling layer in which Knudsen diffusion, which has little temperature dependence, is dominant. On the other hand, an oxygen moisture sensor that is intended to be used in an environment with severe pressure changes uses a pinhole type diffusion control layer.

However, in the actual environment in which the oxygen concentration sensor is used, both temperature and pressure generally change, and it is extremely rare for either of them to be stable. Therefore, no matter which type of oxygen humidity sensor is selected, the actual results of the oxygen humidity detection by the oxygen humidity sensor will include measurement errors due to changes in temperature or pressure. There was a problem with low accuracy. Especially in environments where temperature and pressure vary over a wide range,
For example, this poses a major problem when using an oxygen temperature sensor in the exhaust gas of an internal combustion engine. To deal with this, for example, in order to measure the oxygen moisture content in the exhaust gas of an internal combustion engine, we have added a configuration that corrects the measurement results of an oxygen moisture sensor that uses a porous diffusion control layer based on the exhaust temperature. However, new problems have arisen, such as increasing the size and complexity of the device configuration, lowering reliability, and increasing costs.

The present invention was made to solve the above problems, and
It is an object of the present invention to provide an excellent oxygen moisture sensor whose measurement accuracy does not depend on the temperature and pressure of the environment in which it is used, and which can measure oxygen moisture with high measurement accuracy even under any harsh environment.

[Means for Solving the Problems] The configuration of the oxygen moisture sensor of the present invention, which has been made to achieve the above object, is as follows: A predetermined voltage is applied to an ion-conducting solid electrolyte, An oxygen partial pressure measuring section that measures the oxygen partial pressure ratio of the gas by ionizing oxygen molecules and moving the oxygen ions to the anode side electrode and measuring the ion current caused by the movement, and a cathode of the oxygen partial pressure measuring section. an oxygen moisture sensor comprising: a diffusion-limiting layer section provided on the side and limiting the rate-limiting diffusion of oxygen molecules to the negative and electrode side electrode portions to a predetermined value; The diffusion-limiting layer is composed of a pinhole-limiting layer in which Knudsen diffusion is dominant, and a porous control layer in which Knudsen diffusion is dominant. The gist is what was done.

[Function] The oxygen temperature sensor of the present invention has a pinhole rate-limiting layer that exerts a diffusion rate-limiting effect due to molecular diffusion for the oxygen partial pressure measuring section that measures the oxygen partial pressure ratio of gas by measuring the oxygen ion current. A diffusion-limiting layer section is provided in which a porous rate-limiting layer exhibiting a diffusion-limiting effect due to Knudsen diffusion is laminated, and the diffusion rate is set to a predetermined value by combining the diffusion rate-limiting effects of each layer.

That is, macroscopically, the diffusion-limiting layer section formed by stacking these two types of diffusion-limiting layers functions to determine the rate-limiting rate of diffusion of oxygen molecules into the oxygen partial pressure measuring section to a predetermined value. Microscopically, the pressure dependence of oxygen molecule diffusion is shielded by a pinhole rate-limiting layer that acts as a diffusion rate-limiting layer due to molecular diffusion.
The temperature dependence of oxygen molecule diffusion is shielded by a porous rate-limiting layer that exerts a diffusion rate-limiting effect due to Knudsen diffusion, and the rate-limiting rate of diffusion of oxygen molecules to the oxygen partial pressure measuring section is made stable and independent of temperature and pressure. It has the effect of

Therefore, the pore diameter of the bottle ball regulating layer constituting the diffusion regulating section in the present invention is large enough to provide a free space for oxygen molecules, and is within the range of 1011 m to 1 mm in order to achieve the desired diffusion regulation. It is desirable that there be.

More specifically, in order to reduce the temperature dependence of the diffusion rate due to the pinhole rate-controlling layer, the diameter should be as small as possible, as shown in FIG. Therefore, its minimum diameter is approximately 10 μm due to manufacturing constraints, and its maximum diameter is 1
It will be about 0011m. Then, by changing the length of the hole with a diameter within this range, the diffusion control rate is adjusted to a desired value. The cross-sectional area of the hole is S [mm2], and the hole length is Q [m
m], the relationship between these ratios S/Q and the output current is proportional as shown in FIG. Therefore, from the viewpoint of setting the output current to the desired value and the responsiveness of the sensor,
It is preferable that S/Q is 0.15 to 0.30 [mm].

Furthermore, it is desirable to change the number of pinholes in the pinhole control layer according to the electrode area of the oxygen/temperature sensor, and it is preferable to drill one pinhole in an area ranging from 10 m2 to 50 mm. preferable.

The other porous rate-limiting layer constituting the diffusion rate-limiting part in the present invention is dominated by Knudsen diffusion of oxygen molecules;
The pore diameter is suitably in the range of 0.01 μm to 1 μm. In order to obtain the desired diffusion rate control, it is preferable to adjust the diffusion rate control by the thickness of the porous rate control layer from the viewpoint of suppressing variations in the output current. ), the porosity of the porous rate-controlling layer should be P [%], and the thickness should be Q [mm
], it is desirable that P/Q is about 100 to 1000.

In addition, in order to form a dense porous control layer by plasma spraying, the lamination of the diffusion control layer and the porous control layer of the hole control layer is performed so that the porous control layer is placed outside the oxygen concentration sensor. It is preferable to arrange.

Furthermore, the desired diffusion control is obtained by combining the diffusion control by the pinhole control layer and the diffusion control by the porous control layer, but the dependence on pressure or temperature is shielded by the respective diffusion control effects. It is preferable that each of the pinball rate-limiting layer and the porous rate-limiting layer exhibits the same degree of diffusion rate-limiting effect. Therefore, for boat fishing, when the final target diffusion rate is ``100'', the diffusion rate of each of the pinhole rate-limiting layer and the porous rate-limiting layer is preferably ``50±20''. However, depending on the environment in which the oxygen temperature sensor of this embodiment is used, the proportion of diffusion control may be changed as appropriate, taking into consideration which of the temperature and pressure is more strongly affected.

Note that the solid electrolyte used in the oxygen moisture sensor of the present invention may be any material as long as it has ionic conductivity, such as zirconia and ion tria.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to explain the present invention more specifically, one embodiment of the present invention will be described below with reference to the drawings.

[Example 3] FIG. 3 is a sectional view of an oxygen humidity sensor 10 which is an example of the present invention.

In this example, the ion conductive solid electrolyte is 6 mm.
X50mm, thickness 0. 2mm zirconia sheet 12
is used. Platinum electrodes 14 are formed over an area of 3 mm x 15 mm at opposing positions on both surfaces of this zirconia sheet, and a measuring section 16 is manufactured.

The plate material to be bonded to the cathode side (upper side of the drawing) of the platinum electrode 14 formed on the zirconia sheet 12 is made of the same material as the solid electrolyte and has a thickness of 0.5 mm. The measurement window 1 is a plate material of 5 mm and exposes only the measurement part 16 where the platinum electrode 14 is formed.
8a is bored. On this plate material 18, 6 mm
X 45 mm, thickness 0. A pinhole plate 20 made of the same material as the 5 mm fixed electrolyte is glued,
A pinhole 20a having a diameter of 0.05 mm is pre-drilled at a position on the pinhole plate 20 on the central axis of the measuring section 16 by laser processing.

That is, with the plate material 1 day and the pinhole plate 20,
A measurement space 22 is formed on the cathode side of the measurement section 1G, into which oxygen molecules are introduced under a predetermined diffusion rate.

Furthermore, the porous layer 24 is joined around the position where the pinhole 20a of the pinhole plate 20 is bored. Here, the porous layer 24 has an average pore diameter of 0.5 μm,
6mm x 20mm, thickness 0. It is a porous body with a 2 mm spinel sprayed layer.

Note that a duct 26 is formed on the other surface of the zirconia sheet 12, that is, on the anode side of the platinum electrode 14, for releasing oxygen molecules that have moved through the measurement section 16.

The rate-determining conditions for oxygen molecules diffusing into the measurement space 22 of this embodiment configured as described above are determined by the two types of diffusion rate-determining layers provided above the measurement space 22: the pinhole plate 20 and the porous JW 24. The result is as shown in FIG.

In other words, the output current I is limited to the desired value by combining two types of diffusion control layers. The relationship between the ball 20a and the diffusion rate limitation is designed so that the pinhole 20a has a slightly larger diffusion restriction. Specifically, the rate-determining ratio of the porous layer 24 is 40% with respect to the target rate-determining rate of diffusion, and the rate-determining ratio of the porous layer 24 is 40%.
The rate-determining ratio due to 0a is 60%.

In this way, the oxygen moisture sensor 1 of this embodiment includes the pinhole 20a, which is a diffusion-limiting layer in which molecular diffusion is dominant, and the porous layer 24, which is a diffusion-limiting layer in which Knudsen diffusion is dominant.
The measurement results of temperature dependence and pressure dependence of 0 are shown in Figures 5 and 7.
As shown in the figure.

FIG. 5 shows the experimental results of temperature dependence. When the oxygen humidity sensor 10 of this embodiment is placed in a gas with an oxygen humidity of 10% and a pressure of 30 kPa, a limiting current at which the output type tm I becomes flat can be obtained. Continue to apply a constant voltage of 0.7 [V], and increase the ambient temperature from 600 [' C] to 750 [' C]
For every 50[' CF, the limiting current I[
mA].

As shown in the figure, it can be seen that the limiting current of the oxygen-related sensor 10 of this example is extremely stable even over a wide range of temperature changes over 150['C].

The stability of this limiting current is compared to the conventional i! 1) In order to compare with that of the oxygen moisture sensor, two oxygen moisture sensors were fabricated that differed only in the structure of the diffusion control layer compared to the oxygen moisture sensor 10 of the example, and similar experiments were conducted. The results are shown in Figure 6. An oxygen moisture sensor that uses only a porous layer as a diffusion-limiting layer exhibits stable characteristics against temperature changes. Furthermore, the oxygen humidity sensor that uses only a pinhole as the diffusion control layer has a limiting current value that changes linearly as the temperature rises.

Comparing FIGS. 5 and 6 above, it can be seen that in the oxygen concentration sensor 10 of this embodiment, the temperature dependence of the limiting current is blocked by the action of the porous layer 24.

Next, the experimental results of the pressure dependence shown in FIG. 7 will be explained.

In this experiment, a constant voltage of 0.7 [V] similar to the experiment shown in Fig. 6 was applied to the oxygen concentration sensor 10 of the example, and the temperature was kept constant at 700 [°C] in an atmospheric atmosphere. Mama,
The change in limiting current is measured when the pressure is changed from 10 [kPa] to 100 [kPa].

As shown in FIG. 7, even when the pressure changes so greatly that it differs by one phase, the limiting current of the oxygen concentration sensor 10 of this embodiment is extremely stable and can be considered almost constant.

Figure 8 shows the results of a similar experiment conducted on the two types of seismic intensity sensors manufactured for comparison. As shown in the figure, the oxygen concentration sensor having a pinhole diffusion control layer has no pressure dependence and exhibits a stable limiting current value as in this example. However, an oxygen concentration sensor having a diffusion-limiting layer made of a porous layer, which had no temperature dependence, shows a strong pressure dependence in which the limiting current value increases in proportion to the increase in pressure.

As described above, the following effects are clear from the experimental results regarding the temperature dependence and pressure dependence of the oxygen concentration sensor 10 of the embodiment.

The oxygen concentration sensor 10 of this embodiment has a pinhole 20a and a porous layer 24 laminated to control the rate of diffusion of oxygen molecules. Therefore, it exhibits extremely high stability against changes in temperature and pressure, and can detect oxygen concentration with high accuracy even under harsh environments, greatly improving its versatility.

Further, there is no need to correct the detection results of the oxygen/seismic intensity sensor 10 of this embodiment according to changes in temperature or pressure, and the oxygen concentration detection device is simplified, smaller, and lighter, and costs are reduced. Can be done.

Although the above embodiment describes a laminated zirconia sheet type sensor, the structure of the present invention is not limited to the above embodiment, and similar effects can be obtained by configuring it as a bulk type sensor, for example. That is clear.

[Effects of the Invention] As explained above, according to the oxygen concentration sensor of the present invention,
The diffusion-controlling layer portion is constructed by laminating a pinhole-controlling layer in which molecular diffusion is predominant and a porous control layer in which Knudsen diffusion is predominant.

Therefore, it becomes an oxygen/seismic intensity sensor that has both the temperature-dependent shielding and pressure-dependent shielding functions that are the features of each diffusion control layer. Therefore, the measurement accuracy does not depend on the temperature and pressure of the usage environment, and oxygen concentration can be measured with high measurement accuracy even under any harsh environment. In other words, there is no need to correct the detection results of the oxygen concentration sensor according to changes in temperature or pressure, and the oxygen concentration detection device is simplified, smaller, and lighter, reducing costs and increasing versatility. is significantly improved.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the pinhole diameter and temperature dependence, Fig. 2 is an explanatory diagram of the relationship between the ratio of pinhole diameter area and pinhole length, and output current, and Fig. 3 is a cross section of the oxygen concentration sensor of the example. figure,
Fig. 4 is an output characteristic diagram of the same embodiment, Fig. 5 is a temperature dependence characteristic diagram of the same embodiment, Fig. 6 is a temperature dependence characteristic diagram of the conventional example, and Fig. 7 is a pressure dependence diagram of the above embodiment. FIG. 8 shows a pressure dependence characteristic diagram according to a conventional example, FIG. 9 shows a basic configuration diagram of an oxygen concentration sensor, and FIG. 10 shows a basic output characteristic diagram of an oxygen concentration sensor. . 10... Oxygen concentration sensor 12... Zirconia sheet 14... Platinum electrode 16... Measuring section 18.
... Plate material 20 ... Pinhole temporary 20a.
...Pinhole 22...Measurement space 24...Porous layer 24 Agent: Patent attorney Tsutomu Sadate (and 2 others) Fig. 1 Fig. 2 S/I (mm) Fig. 7 Pressure (KPal Pressure (KPal) Figure 3 Figure 4 Figure 5 Applied voltage (V) Temperature (℃) V. Applied voltage■

Claims (1)

[Claims] A predetermined voltage is applied to an ion-conducting solid electrolyte to ionize oxygen molecules existing at the cathode side electrode, and at the same time move the oxygen ions to the anode side electrode, and generate an ionic current due to the movement. an oxygen partial pressure measuring section that measures the oxygen partial pressure ratio of gas by measuring; and an oxygen partial pressure measuring section that is provided on the cathode side of the oxygen partial pressure measuring section and limits the diffusion rate of oxygen molecules to the cathode side electrode site to a predetermined value. an oxygen concentration sensor having a diffusion-limiting layer section, wherein the diffusion-limiting layer section is formed by laminating a pinhole regulating layer in which molecular diffusion is predominant and a porous regulating layer in which Knudsen diffusion is predominant; An oxygen concentration sensor characterized in that the diffusion-limiting rate is set to the predetermined value by combining the diffusion-limiting rates of the pinhole rate-limiting layer and the porous rate-limiting layer.