JP2589664Y2 - Oxygen sensor - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a limiting current type oxygen sensor using a zirconia-based solid electrolyte substrate having oxygen ion conductivity.

[0002]

2. Description of the Related Art Oxygen sensors using a zirconia-based solid electrolyte substrate are classified into an oxygen concentration cell type and a limiting current type according to the difference in operation principle. In an oxygen concentration cell type oxygen sensor, a reference gas having a known oxygen concentration (for example, air) is brought into contact with one electrode and a gas to be measured is brought into contact with the other electrode to measure an electromotive force generated due to a difference in oxygen concentration. By doing so, the oxygen concentration in the gas to be measured is detected.

On the other hand, in a limiting current type oxygen sensor, a pair of electrodes is formed on the surface of an oxygen ion conductive solid electrolyte substrate, and the oxygen gas in the gas to be measured reaches one of the electrodes. Structurally suppressed (producing a diffusion-controlled state of oxygen gas molecules), a voltage is applied between the electrodes, and the oxygen molecules are ionized and moved through the solid electrolyte substrate (producing an ionic current). The concentration of oxygen gas is measured by measuring a current value (limit current value) flowing therebetween. This limiting current type oxygen sensor is easy to use because it does not require a reference gas required for a concentration cell type sensor, and has recently been mounted on home electric appliances and the like.

FIG. 3 shows an example of a limiting current type oxygen sensor. In this oxygen sensor 10, porous electrodes 3a and 3b are provided on both surfaces of the solid electrolyte substrate 2, and a power supply is connected so that the electrode 3a is used as a cathode. Cathode 3
On the side a, an internal chamber 5 is formed by the solid electrolyte substrate 2, the sealing member 4, and the spacer 40. The internal chamber 5 is formed by the holes of the porous electrodes 3a and 3b and the solid electrolyte substrate. 2 communicates with the outside only through the minute diffusion holes 6.

In this type of sensor, it is preferable to heat the oxygen sensor itself to about 400 ° C. in order to increase the ionic conductivity of the solid electrolyte. For this reason, a heater 7 is formed on the outer surface of the sealing member 4. Have been. The solid electrolyte substrate 2 is generally formed of a zirconia-based material (for example, zirconia / yttria), and the electrodes 3a and 3b are generally formed of a platinum-based material.

In the limiting current type sensor having the above-described cross-sectional structure, a sensor 10a having a rectangular planar shape as shown in FIG. 4 has been generally used.

In the sensor 10a including the sealing member 4 and the substrate 2 having a rectangular planar shape, the sealing member 4 and the substrate 2
Since the corners have a lower temperature than other parts, it is difficult to uniformly heat them, and a temperature distribution easily occurs in the sealing member 4 and the substrate 2. When such a temperature distribution occurs, thermal stress tends to be generated particularly at the corners of the sealing member 4 or the substrate 2, and as a result, cracks occur in the sealing member 4 or the substrate 2, and further, the spacer 40 in contact with them. There was something. If a crack occurs, the airtightness of the internal chamber cannot be maintained, and accurate detection of the oxygen concentration cannot be performed.

As shown in FIG. 5, a sensor 10b manufactured using a circular sealing member 4 (and the substrate 2) has also been developed. In this sensor 10b, since no corner is formed, a large temperature difference rarely occurs in the sealing member 4 or the substrate 2, and therefore, there is no portion where thermal stress is particularly concentrated. Therefore, the sensor 10a shown in FIG.
The occurrence of cracks is smaller than that of However,
Since the sealing member 4 and the substrate 2 must be circular, it is difficult to apply a batch process for cutting out many small substrates (or sealing members) from one large member. In other words, this type of sensor is inferior in productivity, especially in mass productivity.

Accordingly, it is an object of the present invention to provide a limiting current type oxygen sensor which overcomes the above-mentioned disadvantages, has good productivity (mass productivity), and has a long service life.

[0010]

Means for Solving the Problems In view of the above object, as a result of intensive studies, the present inventor found that when forming an internal chamber using a rectangular solid electrolyte substrate and a sealing member, the corner of the substrate and the sealing member were formed. If the diagonal directions of the substrate and the sealing member are shifted so that the corners of the substrate do not overlap (or do not approach), the thermal stress at the respective corners of the substrate and the sealing member is reduced and cracks are less likely to occur. Discovered and completed the present invention.

That is, the oxygen sensor of the present invention comprises: (a) a rectangular zirconia-based solid electrolyte substrate; (b) porous electrodes formed one on each side of the substrate; and (c) a rectangular electrode. A dense sealing member provided on the substrate so as to form an internal chamber on one of the electrodes, and (d) a heater provided on the surface of the sealing member,
A limiting current type oxygen sensor in which a diffusion hole communicating the internal chamber and the outside world is formed in the substrate or the sealing member, and in a plan view thereof, a corner of the sealing member and a corner of the substrate. There are no diagonal lines so that
It is characterized by having been done.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a plan view showing an oxygen sensor according to an embodiment of the present invention, and FIG. 2 is a sectional view taken along line AA of FIG.

First, as shown in FIG.
Is a dense solid electrolyte substrate 2 having oxygen ion conductivity
And porous electrodes 3a and 3b provided on both surfaces of the solid electrolyte substrate 2, a dense sealing member 4 having a heater 7 formed on the surface thereof, and between the sealing member 4 and the solid electrolyte substrate 2. And a spacer 40 arranged. As can be easily understood from FIG. 2, an internal chamber 5 is formed on the electrode 3a by the solid electrolyte substrate 2, the sealing member 4, and the spacer 40.
Here, diffusion holes 6 are formed in the solid electrolyte substrate 2 to cause a diffusion-controlled state of oxygen gas, and only the holes of the porous electrodes 3a and 3b and the diffusion holes 6 (the internal chamber 5) are formed.
A) communicates with the outside. In addition, the diffusion hole 6 does not need to be provided in the solid electrolyte substrate 2 and can be provided in the sealing member 4.

Next, in the embodiment shown in FIG. 1, the solid electrolyte substrate 2 and the sealing member 4 are both formed in a square shape, but the present invention is not limited to a square shape, and the lengths of the two sides are different. It may be rectangular. Therefore, the term “rectangle” used in this specification includes both a square and the rectangle.

On the surface of the sealing member 4, a heater 7 is formed in a meandering manner. As shown in FIG. 1, the heater 7 is meandered at equal intervals and as evenly as possible in the vertical and horizontal directions, so that the portion of the solid electrolyte substrate 2 on which the porous electrodes are formed is heated at least uniformly. It is preferable to do so. The heater 7 does not need to be formed in a pattern as shown in FIG. 1, and any pattern can be used as long as the portion of the solid electrolyte substrate 2 on which the porous electrode is formed is heated at least uniformly. Good.

In the sensor 1 of this embodiment, the sealing member 4 is in close contact with the solid electrolyte substrate 2 such that the diagonal of the sealing member 4 intersects the diagonal of the solid electrolyte substrate 2 at substantially 45 °. In other words, in the plan view shown in FIG. 1, the corners of the solid electrolyte substrate 2 and the corners of the sealing member 4 alternately
And they are arranged at equal intervals. In FIG. 1, an oxygen sensor 1
Is symmetric.

With such a structure, there is no portion in the oxygen sensor 1 where the temperature becomes extremely low.
That is, the corners of the substrate 2 where the temperature is the lowest and the corners of the sealing member 4 where the temperature is the lowest do not overlap, and they are arranged alternately and at equal intervals. Because it is. Therefore, there is no place where a particularly large thermal stress is applied, and the occurrence of cracks can be prevented.

In the sensor 1 of this embodiment, as can be seen from FIGS. 1 and 2, the spacer 40 is formed in a cylindrical shape. Further, the electrode 3a includes a circular portion and a band-shaped portion, and the circular portion is disposed in the spacer 40. The end 30 of the strip portion of the electrode 3a protrudes from the spacer 40 and appears outside. This protruding end 30
And the lead wire 11 is connected. With such a structure, it is not necessary to penetrate the lead wire 11 through the inside of the spacer 40, and the manufacture of the sensor is easy. Note that the end 30 of the electrode 3a that protrudes beyond the spacer 40 (actually protrudes from the space between the spacer 40 and the solid electrolyte substrate 2).
Is sealed with a vitreous material, so that gas outside the sensor does not enter the internal chamber 5 from the end 30 of the electrode 3a (through the strip of the electrode 3a). The lead wire 12 is connected to the electrode 3b (not shown in FIG. 1).

A power supply and an ammeter or a resistor (not shown) are connected in series between the lead wires 11 and 12 connected to the electrodes 3a and 3b, respectively, and flow into the solid electrolyte substrate by oxygen ions. Current is detected.

Next, each member of the oxygen sensor 1 will be described. (1) Solid Electrolyte Substrate As the solid electrolyte substrate 2, a zirconia-based substrate that is a conductor of oxygen ions is used. At this time, it is preferable to use zirconia to which at least one of yttria, calcia, ceria and the like is added as a stabilizer.

(2) Porous electrode Electrodes 3a, 3b formed on the surface of solid electrolyte substrate 2
Is made of a porous conductive material. Since the electrodes 3a and 3b function as catalyst activation electrodes, metals such as Pt, Ag, and Pd or alloys thereof, or La _x Sr _(1-x) CoO ₃ ,
La _x Sr _(1-x) Co _y Ni _(1-y) O ₃ , La _x Sr _(1-x) Mn
It is preferable to use an oxide having a perovskite structure such as O ₃ and La _x Sr _(1-x) Co _y Mn _(1-y) O ₃ . Further, a mixture of these materials or a mixture of each of the above substances and a hardly sinterable material such as zirconia may be used.

The porosity of the porous electrode only needs to be such that diffusion of oxygen gas is not limited at least in the electrode, and the interface between the solid electrolyte substrate and the electrode is preferably as large as possible.

(3) Sealing Member The sealing member 4 is preferably formed from a member mainly composed of oxide ceramics, carbide ceramics or nitride ceramics. At least the sealing member is dense,
It is preferable that the material is sufficiently stable even when heated by a heater and has a thermal expansion coefficient close to that of the solid electrolyte substrate or the spacer. Further, a material having sufficient strength to withstand an impact such as a drop during use is preferable.

(4) Spacer As the spacer 40, it is preferable to use a dense inorganic substance (a vitreous substance) having the same coefficient of thermal expansion as the solid electrolyte substrate 2.

In the present embodiment, the sealing member 4 and the spacer 40 are used, and these and the solid electrolyte substrate 2
However, the present invention is not limited to this, and it is also possible to adopt a structure in which an internal chamber is formed by one sealing member formed integrally with a spacer portion at an edge portion and the solid electrolyte substrate 2. it can.

(5) Heater The heater 7 formed on the surface of the sealing member 4 is for heating the solid electrolyte substrate to a predetermined temperature, functions as a heater, and is made of a stable material. . A heater pattern can be formed on a film by a screen printing method or a chemical vapor deposition method using a paste by using a photolithography technique or the like.

In the embodiment shown in FIGS. 1 and 2, the heater 7 is formed on the outer surface of the sealing member 4. However, the present invention is not limited to this. The heater 7 can also be formed.

(6) Lead Wires The lead wires 11 and 12 connected to the electrodes 3a and 3b are as follows.
Pt, Au, Ag, Ni wire and the like can be used. The lead wire can be attached by a connectable method such as welding, fusion or baking with a paste.

Although the present invention has been described with reference to the accompanying drawings, the present invention is not limited thereto, and various modifications can be made without departing from the spirit of the present invention.

For example, the sealing member 4 and / or the solid electrolyte substrate 2 need not necessarily be formed in a square shape, but may be formed in a desired rectangular shape. However, a rectangle in which one side is extremely longer than the other side is not desirable.

[0031]

As described above, the oxygen sensor according to the present invention has a rectangular (or square) solid electrolyte substrate and a sealing member, and their diagonals do not point in the same direction. Since the corners are not overlapped with each other, the thermal stress that tends to occur at those corners is reduced, and defects such as cracks are less likely to occur. Therefore, the oxygen sensor according to the present invention has high reliability and long life.

Further, the oxygen sensor according to the present invention uses a square or rectangular substrate and a sealing member which are usually used, so that a so-called batch process can be applied to the production, and the productivity (mass productivity) can be improved. Also excellent.

The oxygen sensor of the present invention can be widely used in room monitors for ordinary households, oxygen deficiency monitors for industrial use, oxygen concentration detecting devices for controlling oxygen concentration, and the like.

[Brief description of the drawings]

FIG. 1 is a plan view illustrating an oxygen sensor according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a sectional view showing an example of a conventional limiting current type oxygen sensor.

FIG. 4 is a plan view showing an example of a conventional limiting current type oxygen sensor.

FIG. 5 is a plan view showing another example of a conventional limiting current type oxygen sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 10 Oxygen sensor 2, Solid electrolyte board 3a, 3b Electrode 4 Sealing member 5 Inner chamber 6 Diffusion hole 7 Heater 11, 12 Lead wire 40 Spacer

Claims (2)

(57) [Scope of request for utility model registration] (A) a rectangular zirconia-based solid electrolyte substrate, (b) a porous electrode formed one on each side of the substrate, and (c) a rectangular contour, A dense sealing member provided on the substrate so as to form an internal chamber on one electrode, and (d) a heater provided on the surface of the sealing member,
A limiting current type oxygen sensor in which a diffusion hole communicating the internal chamber and the outside world is formed in the substrate or the sealing member, and in a plan view thereof, a corner of the sealing member and a corner of the substrate. There are no diagonal lines so that
Oxygen sensor, characterized by being. 2. The oxygen sensor according to claim 1, wherein
An oxygen sensor, wherein the substrate and the sealing member are both square, and a diagonal between them is substantially 45 °.