JPS61167857A - Gaseous oxygen sensor - Google Patents

Abstract

PURPOSE:To make internal resistance smaller and electrode area larger and to obtain a large output in a gaseous oxygen sensor provided with a detecting part on a base by providing electrodes on both sides of the plate-shaped detecting part so as to make a pair. CONSTITUTION:The base 1 is made of Al2O3 into a rectangular plate shape. A stress release layer A2 consists of Al2O3/ZrO2, more preferably the sintered mixture composed of about 0.5-3 Al2O3 and stabilized or partially stabilized ZrO2 and forms part of a U-shaped passage 7. The stress relieving layer B3 has the same outside shape as the outside shape of the base 1 and is provided with part of the passage 7. The detecting part 4 consists of a ZrO2 solid electrolyte stabilized by Y2O3. A measuring electrode 5 is provided atop the detecting part 4 and a reference electrode 6 is provided on the bottom surface thereof. The electrode 6 is connected to the external air via a passage 7 formed of the layers 2, 3 and the base 1. Since the electrodes 5, 6 are provided on both sides of the detecting part 4, the sensor which is quickly activated in a relatively low temp. state is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an oxygen gas sensor used for air-fuel ratio control of automobiles, etc.

[Prior Art] Conventionally, for example, in combustion equipment such as internal combustion engines, in order to improve fuel efficiency and emissions, the oxygen concentration in the exhaust gas has been detected and the air-fuel mixture combusted in the combustion vessel has been adjusted to near the stoichiometric air-fuel ratio. There are devices that perform so-called feedback control. As an oxygen gas sensor used in this type of control device to detect the oxygen concentration in exhaust gas, for example, a porous electrode layer is coated on a Zr0z 0z-based solid to form a pair of electrodes, and one electrode is Some are configured to conduct the measurement gas to one electrode and the reference gas to the other electrode.

Oxygen gas sensors using such Zr0z 0z-based solids are manufactured using plate-shaped Zr0z 0z-based solids for ease of manufacture.
After forming electrodes on both sides of a system solid body, a passage for introducing outside air to one electrode is often formed, and in this case, the support of the sensor is a 2rQ2 system solid electrolyte plate.

However, Zr0z 0z-based solid has poor insulation properties, so
In order to make accurate measurements, it was necessary to sandwich an insulating layer made of highly insulating material such as alumina or magnesia spinel between the conductor connecting the electrodes and the terminals and the solid electrolyte, which made manufacturing complicated.

Furthermore, since Zr0z 0z-based solids are relatively expensive, there has been a demand to reduce the amount used.

Therefore, it is proposed, for example, to provide a detection section made of a Zr0z 0z-based solid on a support made of another material, as disclosed in JP-A-56
-16865.

[Problems to be Solved by the Invention] However, the coefficient of thermal expansion of the ZrO2-based electrolyte is about 10×10, and Alt is most suitable as a support in terms of insulation and strength at high temperatures.

There is a considerable difference from 8.0X10 of 3. Therefore,
If the Zr0z 0z solid body and the Al2O3/ZrOzOa support are directly bonded, the bonded portion may peel off or the entire body may be deformed due to this difference in coefficient of thermal expansion. Also, Zr0z
The coefficient of thermal expansion of the 0z-based solid is very similar to that of metals, so metals are sometimes used as supports, but this requires the provision of an insulating layer, which poses the problem of difficulty in obtaining a sufficient insulating layer. .

The above-mentioned Japanese Patent Application Laid-Open No. 56-16865 uses an insulating coated metal plate as a support, and a Zr layer with a thickness of about 0°1 ms is placed on the support.
An O2-based solid electrolyte plate is provided as a detection part, and this z
``One side of the 02 series solid electrolyte plate is tightly bonded to the support, and a measurement electrode and a reference electrode are provided on the other side, with the reference electrode communicating with the outside air through a passage.

As a result, the internal resistance increases and the output decreases, making it impractical.

Means for Solving Problem E] The present invention was made by considering it from a completely different perspective from the conventional technology, and in order to solve the above problem as a structure of the invention, the following Technological measures were adopted.

That is, the oxygen gas sensor of the present invention includes a plate-shaped detection section made of a ZrO2-based solid electrolyte, a pair of electrodes provided on both sides of the detection section, and a thermal expansion coefficient of A.
It is between l2O3/ZrOzOs and zr02 solid electrolyte, can be sintered simultaneously with Al2O3 and ZrO2 solid electrolyte, and has sufficient insulating properties to form multiple conductor patterns directly on the surface. a stress relaxation layer on which the detection section is placed and an opening for forming a passage for introducing outside air into one electrode surface of the detection section; and a support made of 120g of A4, on which the support is placed.

The support is made of 120 g of commonly used A, and may contain a sintering aid as long as the amount is small enough not to impair insulation.

As the ZrO2-based solid electrolyte used as the detection part, it is possible to use ZrO2 with 4 to 15101% of a stabilizer such as Y2O1, Cao, MllO, etc. added thereto.

The coefficient of thermal expansion used as a stress relaxation layer is between that of AJ1203 and ZrO2-based solid electrolyte, and it can be sintered simultaneously with 80203 and Zr0z-based solid electrolyte, and it is also possible to directly sinter multiple conductor patterns on the surface. As a material having sufficient insulating properties for formation, a mixture and sintering of A120a and stabilized or partially stabilized ZrO2 is preferable because it has excellent mechanical strength and thermal shock resistance.

Among them, the II ratio AJIOs/Zr0z of AlzOa and stabilized or partially stabilized ZrO2 is 0.5 to 3.
A value of 0.7 to 2 is particularly preferred. A
nzOs/Zr 027! If it is smaller than 10.5, the electrical insulation properties at high temperatures will be poor, and the difference in coefficient of thermal expansion with AM203 will be too large, resulting in lack of durability, and if it is larger than 3, Z
The durability of the bonded portion with the rO2 solid electrolyte is lost. Further, a mixed sintered product of Al2O3 and unstabilized Zr0z has excellent mechanical strength and thermal shock resistance, but is not preferable because the coefficient of thermal expansion is too small.

The material of the conductor that forms the electrode provided in the detection part, the terminal for taking out the output to the outside, and the conductor part that connects the electrode and the terminal should be heat resistant and conductive if the main component is gold or platinum metal element. It is used for problems such as. In particular, platinum is preferable for the conductor in terms of catalytic properties and cost, and it is more preferable if the conductor contains an appropriate amount (for example, 20% by weight) of the same material as the substrate on which it is provided, since the expansion coefficient will be close to that of the substrate. Furthermore, AjLz03 is applied to the outer surface of the electrode in contact with the measurement gas.
It is preferable to provide a porous protective layer such as.

Since this protective layer is thin (approximately 50 microns), there is no need to consider thermal stress between it and the electrodes.

The sensing portion is configured such that one side is in contact with the measurement gas and the other side is in contact with the outside air via a passage provided in the stress relaxation layer, and is supported by the periphery of the opening in the stress relaxation layer. Therefore, the sensing part only needs to be thick enough to support itself, so it can be made thinner, resulting in a higher output voltage due to the reduction in internal resistance.Also, by appropriately increasing the area of the opening and the sensing part, Output current can be easily increased.

The present oxygen gas sensor is formed by laminating the above-mentioned support, stress relaxation layer, and detection part, but the stress relaxation layer and support having a passage for introducing the measurement gas are also provided on the electrode side that comes into contact with the measurement gas. They may be laminated, and in this way warping due to differences in expansion coefficients can be almost completely prevented.

Furthermore, by appropriately configuring the shape of the passageway (in particular, the inner height), the passageway can be used as a diffusion resistance section for working gas components such as oxygen, or it can be used as a diffusion resistance section for working gas components such as oxygen, or to prevent the action of oxygen etc. on the electrode surface that comes into contact with the measurement gas. It is also possible to form a so-called polarographic oxygen gas sensor by laminating diffusion-limiting porous layers that exhibit diffusion resistance to gas components.

Further, it is preferable to provide a heating element on the support or the stress relaxation layer because it can reduce the temperature dependence of the output of the present oxygen gas sensor. The heating element can be provided in the same manner as the electrical conductor described above. Further, by using this heating element, it is possible to create a temperature gradient between the support body and the detection part, thereby making it possible to further alleviate warping due to a difference in expansion coefficient.

Such an oxygen gas sensor is made by, for example, kneading a mixture of Hetachi 2O3, stress relaxation layer material, ZrO2, and a stabilizer with an organic binder and forming a green sheet using a doctor blade method, etc., and shaping the resulting green sheet into a predetermined shape. Punch or cut it, print a paste that will become an electrode, conductor, or heating element in a predetermined position using a screen method, etc., stack and press the raw sheets of the support, stress relaxation layer, and solid electrolyte, and apply an organic binder. After removal, it is manufactured by firing at 1400 to 1600°C for about 4 hours. Further, if necessary, a porous protective layer such as AJ1203 may be printed on top of printing a paste that becomes a conductor.

[Action J In a II gas sensor in which a detection part is provided on a support,
By providing electrodes in pairs on both sides of the plate-shaped sensing portion, internal resistance can be reduced, the area of the electrodes can be increased, and a large output can be obtained.

Stress created by mixing and sintering A120g and stabilized or partially stabilized 2rot! llll mineral expansion rate is A
The izOs and Zr0z solid base materials are intermediate in quality.

For example, Al2O3/ZrOzOa/ZrO2-1゜0
When , A9.20a and stabilized or partially stabilized Z
The coefficient of thermal expansion of the mixed sintered body with r0z is 8.8X10, which is the same as that of Al2O3 (8,8X10) and ZrO
It is approximately midway between the 2-system solid electrolyte (10×10 ).

When a mixed sintered body of AizOa and 7r02 having such properties is used as a relaxing layer between AizOa 203 and ZrO2 solid electrolyte, thermal stress is relaxed and peeling of the joint does not occur, and the expansion coefficient is Warpage caused by differences is also reduced.

Furthermore, since the stress relaxation layer made of AizOs and Zr0z has sufficient insulation properties, conductors can be directly arranged and formed on the same surface of the stress relaxation layer.

[Example] A first example of the present invention will be described using an explanatory diagram in FIG. 1, a perspective view in FIG. 2, and an end view in FIG. 3. Note that the scale of these figures has been partially changed for the purpose of explanation.

The oxygen gas sensor of this example has a rectangular plate shape.
Support 1 made of zOa, Al2O3 with AjlzOa/Zr02 (partially stabilized zirconia) of 1.0 and z"02
It is U-shaped and is made of a mixed sintered material with a passage 7 to be described later.
The stress relief 11A2 forming a part of the support body 1 and the outer shape of the support body 1
The stress relaxation layer B3 is the same as that and is provided with a part of the passage 7 described later, and the Z is stabilized by roughly Y20m.
r Q z A detection section 4 made of a solid photoelectrolyte body. Incidentally, on the upper surface of the detection section 4, a measurement electrode 5 is installed.
A standard electrode 6 is provided on the bottom surface of the standard electrode 6.
is connected to the outside air via a passage 7 formed by the relaxation layer bodies A2, B3 and the support 1. In addition, the measurement electrode 5
and the standard electrode 6 is a conductor track 8 provided on the relaxation ffA2.
．． 9 to the measuring terminal 10.11. Note that the measurement electrode 5 and the conductor path 8 are connected through a through hole. Further, a heating element 12 is provided on the surface of the support 1 on the passage 7 side, and the sensor can be heated by connecting a power source to the heating element terminals 13 and 14.

Further, a porous A1203 protective layer 15 is provided to cover the measurement electrode 5.

The manufacturing of this example can be carried out, for example, as follows.

(2) Zr02 powder, an appropriate amount of Y2O8 powder, and a binder are kneaded, and a green sheet with a thickness of 0.5 mm is formed by a known method.

■ Al2O3 is also made into a raw sheet with a thickness of 1.0 mm in the same manner as in ■.

■ An in which the weight ratio of A text 20s/ZrO2 is 1.0
A mixture of zOa and partially stabilized ZrO2 made by adding 5m01% of Y2O3 to Zr02 was also prepared in the same manner as in ■ to have a thickness of Q,
Make a 6mm raw sheet.

■ Cut the green sheet produced by ■, ■, and ■ into a predetermined shape. Additionally, provide through holes where necessary.

AuzOa raw sheet is 7X64mm to serve as a support.
7r 02 partially stabilized with AnzOa in the rectangle of
In order to provide stress relaxation ffA and B, the raw sheet has a U-shaped outer diameter of 7 x 64 mm and a concave portion of 4 x 62 mm, and a U-shaped sheet with an outer diameter of 7 x 54 mm and an opening of 4 x 1 Q mm where the solid electrolyte body and the outside air come into contact. Each rectangular raw sheet made of Y2O11 and Zr0z is cut into a rectangle of 7 x 18 mm and formed into a solid electrolyte body.

(2) Electrodes and conductors are formed on each formed cut-out raw sheet by screen printing using a PT paste containing 20% by weight of the same material as each raw sheet.

On the raw sheet corresponding to the support, a paste is printed as a heating element on the side that will become a passage, and a paste is printed as a conductor path 8.9 and a measurement terminal 10111 on the side in contact with the measurement gas of stress relaxation FjtA, and a solid electrolyte A paste is printed as electrodes 5.6 on both sides of the raw sheet corresponding to the body, and about 50% of AJ120a, which becomes the porous protective layer 15, is printed on the measurement electrode 5.
Print to a thickness of 0 μm.

(2) Cut raw sheets corresponding to the support, relaxation layers A and B, and the detection part are laminated and pressure-bonded.

■ The laminate formed by
C. for about 4 hours to obtain the oxygen gas sensor of this example.

In the oxygen gas sensor of this example manufactured as described above, the bonded portion did not peel off due to thermal expansion, and there was little warping. In addition, this embodiment has the effect of lowering costs because it is sufficient to use a relatively expensive Zr 02 solid electrolyte only in the portion that detects oxygen gas.

A second embodiment of the present invention will be described using the explanatory diagram in FIG. 4 and the perspective view in FIG. 5. Note that the scale of these figures has been partially changed for illustrative purposes.

The oxygen gas sensor of this example is a rectangular plate-shaped Al
A support A21 made of 2O3, a U-shaped support B22 made of Al2O5 forming a part of a passage 28 to be described later, and a support B22 made of Al2O5 having the same external shape as the support A21 and forming a part of a passage 28 to be described later. Support body C23 made of A4120B and A
4120 s/Z Al2 with rO2 of 1.0
A stress relaxation layer 24 made of a mixed sintered material of Zr 02 partially stabilized with Og and 5mo 1% Y2O3 has the same external shape as the detection section 25 described later and is provided with a part of the passage 2B described later. It further includes a detection section 25 made of a Zr 02 solid electrolyte stabilized by Y2O3. Furthermore, on the upper surface of the detection part 25 of the solid electrolyte body, there is a measurement electrode 2
6 is provided with a standard electrode 27 on its lower surface, and the standard electrode 27 is connected to the outside air via a passage 28 formed by the supports A21, B22, C23 and the stress relaxation layer 24. The measuring electrode 26 and the standard electrode 27 are also connected to a measuring terminal 31.32 via a conductor track 29.30 provided on the support C23. Furthermore, support A2
A heating element 33 is provided on the side of the passage 28 of 1.
The sensor can be heated by connecting a power source to the heating element terminals 34,35. Furthermore, a porous protective layer 36 of Al2O3 is provided to protect the measuring electrode 26.

In addition to the effects of the first example, the M gas sensor of this example manufactured in the same manner as the first example has the advantage that the joint of materials with different coefficients of thermal expansion is a part of the longitudinal direction. Since there are few areas subject to thermal stress, there is almost no warpage.

FIG. 6 is an explanatory diagram of a conventional oxygen gas sensor in which a detection section is provided on a support.

In this figure, 50 is alumina on a metal plate 50'']-
51 is a heating element, 52 is Zr 02
Detection part made of a thick film of solid electrolyte, 53 is a measurement electrode, 5
Reference numeral 4 denotes a standard electrode covered by a lid 56 having a passage 55, and is in contact with the outside air through the passage 55. This conventional oxygen gas sensor uses a standard electrode, 54
Since it is necessary to provide the measurement electrode 53 and the measurement electrode 53 on one surface of the membrane-like solid electrolyte, the internal resistance between the two electrodes increases, resulting in poor activation when used in relatively low-temperature gas. .

[Effects of the Invention] Since the oxygen gas sensor of the present invention has electrodes provided on both sides of the detection section, an oxygen gas sensor that is activated quickly at relatively low temperatures can be obtained.

Furthermore, in the oxygen gas sensor of the present invention, since the insulators of the support and the stress relaxation layer are large, the conductor path connecting the electrode and the terminal can be provided directly on the support or the stress relaxation layer. There is no need to particularly devise the shape of. This simplifies manufacturing.

Furthermore, it is possible to use less ZrO2-based solid electrolyte, which often uses rare earth metals, which are relatively scarce resources, resulting in a resource-saving effect.

Furthermore, since the thickness of the detection section can be made thinner than that of the conventional one, the output voltage can be increased, and therefore an oxygen gas sensor with high sensitivity can be obtained.

Furthermore, in the case of so-called polarographic applications, power is saved.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the first embodiment of the present invention, Fig. 2 is a perspective view thereof, Fig. 3 is an A-A end view thereof, and Fig. 4 is an explanatory diagram of the second embodiment of the invention. , FIG. 5 is a perspective view thereof, and FIG. 6 is an explanatory diagram of a conventional oxygen gas sensor. 1.21.22.23.50...Support support A, B
, C 2.3.24... Stress relaxation layer A, B Stress relaxation layer 4.25.52... Sensing section 5.6.26.27.53.54... Electrode 7.28.
55...Aisle

Claims (1)

[Claims] 1. A plate-shaped detection section made of a ZrO_2-based solid electrolyte, a pair of electrodes provided on both sides of the detection section, and a thermal expansion coefficient between that of Al_2O_3 and a ZrO_2-based solid electrolyte, and It can be sintered simultaneously with Al_2O_3 and ZrO_2-based solid electrolytes, and has sufficient insulating properties to form a plurality of conductor patterns directly on the surface. An oxygen sensor comprising: a stress relaxation layer having an opening that forms a passage for introducing outside air into one electrode surface of the detection section; and a support made of Al_2O_3 on which the stress relaxation layer is placed. gas sensor. 2 The stress relaxation layer is made of Zr stabilized or partially stabilized with Al_2O_3
2. The oxygen gas sensor according to claim 1, wherein the oxygen gas sensor is composed of O_2 and has a weight ratio of Al_2O_3/ZrO_2 of 0.5 to 3. 3. The stress relaxation layer A has an opening corresponding to one of the electrodes of the detection section near one end in the longitudinal direction, and has a pair of conductor paths connecting the negative pair of electrodes and the terminal; One end corresponding to the opening of the stress relaxation layer A is closed,
3. The oxygen gas sensor according to claim 1, wherein the other end is an open end, and the stress relaxation layer B is laminated with the opening and the open end communicating with each other. 4. The oxygen gas sensor according to any one of claims 1 to 3, which has a heating element on a support.