JP2001242125A - Gas sensor element and gas sensor equipped therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor element, capable of effectively preventing generation of cracks not only in the baking of a manufacturing process but also in a cooling/heating cycle at use, and a gas sensor using the same. SOLUTION: A solid electrolyte element is divided into a body part 151 mainly developing gas detection capacity and a peripheral part 152 where there is no need for developing gas detection capacity and the peripheral part 152 is made thin to disperse the stress concentration of the solid electrolyte element. Furthermore, an pressing layer 162 is provided on the peripheral layer, on the surface opposite to the release direction of the solid electrolyte element, no only to suppress deformation of the peripheral part through thermal expansion but also to reduce the tensile force acting on the interface of a substrate and the solid electrolyte element to prevent generation of cracks.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small and inexpensive gas sensor element capable of detecting oxygen, NOx and the like contained in exhaust gas discharged from an internal combustion engine of an automobile or the like, and a gas sensor using the same.

[0002]

2. Description of the Related Art Conventionally, a cylindrical solid electrolyte body, or
2. Description of the Related Art A gas sensor element (hereinafter, simply referred to as an “element”) using a plate-shaped solid electrolyte body is known. Among them, Japanese Patent Application Laid-Open No. 7-55758 discloses an element having a plate-shaped solid electrolyte body as an element having a plate-shaped solid electrolyte body, the element having a plate-shaped solid electrolyte body laminated in contact with an alumina substrate. But,
Since there is a large difference in thermal expansion between the alumina substrate and the solid electrolyte body, in a gas sensor element having a solid electrolyte body laminated in contact with the alumina substrate, stress is generated at these interfaces after firing and cracks are generated. There was a thing. To solve this problem, Japanese Patent Application Laid-Open No. 9-304321 discloses a technique for suppressing the occurrence of cracks or the like by providing a stress relaxation portion in which the thickness of the outer edge of the solid electrolyte body is gradually reduced. However, cracks have not yet been sufficiently prevented.

[0003]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and it is an object of the present invention to provide a gas sensor element having a solid electrolyte body laminated in contact with a substrate made of a different material such as an alumina substrate. An object is to prevent generation of cracks at an interface.

[0004]

According to the present invention, the peripheral portion of a solid electrolyte body provided on an insulating substrate is formed thin and a suppression layer is provided on at least a part of the peripheral portion. It was completed based on the finding that cracks can be significantly prevented.

According to a first aspect of the present invention, there is provided a gas sensor element including an insulating base and a solid electrolyte disposed on the base, wherein the solid electrolyte comprises a main body, and a solid electrolyte. And a peripheral portion having a small thickness, and a suppression layer overlying at least a part of the peripheral portion.

[0006] It is preferable that the "substrate" has an insulating property at a temperature of 900 ° C which is 100 times or more that of a solid electrolyte. The “solid electrolyte body” only needs to have oxygen ion conductivity, and for example, a zirconia-based sintered body, LaGaO ₃ -based sintered body, or the like having oxygen ion conductivity can be used. The above "peripheral part" provided in the solid electrolyte layer
Is preferably 30 to 70%, more preferably 40 to 60% of the thickness of the “body”. Further, the thickness of the main body is preferably 20 to 150 μm (more preferably 30 to 100 μm). In particular, cracks can be sufficiently prevented by setting the thickness of the main body to 150 μm or less. The compositions of the main body and the peripheral portion may be the same or different. Further, they may be integrated or separate before firing.

The peripheral portion may be formed so as to become gradually thinner from the main body portion to the peripheral portion. However, as in the second invention, the peripheral portion is formed so as to become thinner stepwise at the boundary with the main body portion. can do. When forming in a step shape,
It can be formed by laminating unsintered sheets of different thicknesses. Further, the thickness can be changed stepwise by printing the paste in a superimposed manner. Forming the solid electrolyte body stepwise in this manner is simple and efficient in production.

The "suppression layer" is usually constituted by a part of the insulating layer, and is formed on the peripheral part so as to suppress at least a part of the peripheral part. This suppression layer usually has higher insulating properties than the peripheral part. Further, the peripheral portion can be provided via an interposition layer as in the third invention without directly contacting the base. Thereby, the area where the solid electrolyte body and the substrate having a different composition are in contact with each other can be reduced, and the stress can be dispersed and the occurrence of cracks can be prevented. This intercalation layer
Usually, it is constituted by a part of the insulating layer. Therefore, the suppression layer and the insertion layer may be integrated. Since the suppression layer and the interposed layer each directly contact the peripheral layer of the solid electrolyte body, it is preferable that the composition is close to the composition of the solid electrolyte body as long as it has sufficient insulating properties with respect to the solid electrolyte body. Thereby, the difference in thermal expansion can be reduced. Specifically, the suppression layer and the interposed layer can contain less than 15% by mass (more preferably, less than 10% by mass) of a component constituting the solid electrolyte body.

When no intervening layer is provided, the total thickness of the peripheral portion and the suppression layer is preferably equal to the thickness of the main body. Further, when an interposing layer is provided, as in the fourth invention,
It is preferable that the total thickness of the peripheral portion, the suppression layer, and the insertion layer is equal to the thickness of the main body portion. However, being equal to each other may not only mean exactly the same, but also cause a difference of about −60 to 60% (more preferably −40 to 40%). As described above, by making the total thickness of the peripheral portion and the suppression layer and / or the interposed layer equal to the thickness of the main body portion, the stress balance is optimized, and the occurrence of cracks can be effectively prevented. .

Further, the base is preferably plate-shaped as in the fifth invention, and the solid electrolyte body is preferably formed in a layered form in contact with at least a part of one surface of the base. As described above, in the production of the solid electrolyte body, it is preferable to perform lamination printing of unfired sheets or lamination printing of paste. In this case, the substrate on which these are laminated is preferably in the form of an integral plate. This particularly facilitates handling during manufacture. It is preferable that a reference electrode is formed on the solid electrolyte body in contact with the substrate-side surface of the solid electrolyte body and a detection electrode is formed on the other surface, as in the sixth invention.

In the gas sensor element according to the first to sixth aspects of the present invention, as in the seventh aspect, the solid electrolyte body contains 10 to 80% by mass (more preferably 40 to 60% by mass)
% By mass). If the content of the component constituting the base exceeds 80% by mass, it is difficult to obtain sufficient characteristics as a solid electrolyte body, which is not preferable. On the other hand, if it is 10% by mass or less, it is difficult to sufficiently reduce the difference in thermal expansion coefficient. This can further improve the problem caused by the difference in the coefficient of thermal expansion. In particular, as in the eighth invention, the solid electrolyte body preferably contains zirconia and alumina as main components, and the substrate preferably contains alumina as a main component. A gas sensor element provided with such a solid electrolyte body containing a large amount of alumina has low cost and high durability.

In the gas sensor element which exhibits the gas detecting ability by forming the reference oxygen source as described above and sufficiently holding the reference oxygen source, the main body needs to be airtight to hold the reference oxygen source. I do. For this reason, it is necessary to have a thickness that can secure this airtightness. However, the peripheral portion of the solid electrolyte body that is not used for gas detection can be made thinner because it is not necessary to ensure airtightness. In this way, the solid electrolyte body is divided into a main body part that mainly exhibits gas detection ability and a peripheral part that does not need to exhibit gas detection ability, and the thickness of the peripheral part is reduced, so that the stress concentration of the solid electrolyte body is reduced. Can be dispersed.

Furthermore, by laminating the suppression layer on the peripheral portion, deformation of the peripheral portion due to thermal expansion can be suppressed. In a gas sensor element having no suppression layer, a force accompanying deformation due to a difference in thermal expansion coefficient between the solid electrolyte body and the base acts to separate them. For this reason, it was necessary to endure the tensile stress of peeling at the interface, but the durability of the substrate made of a different material with respect to the tensile force was not sufficient, and it is considered that cracks would occur. In the gas sensor element according to the first to eighth aspects of the present invention, the suppression layer is provided on the side opposite to the direction in which the solid electrolyte body is separated, so that the tensile force acting on the interface between the substrate and the solid electrolyte body is reduced, and the generation of cracks is reduced. It is thought that it can be largely prevented.

According to a ninth aspect of the present invention, there is provided a gas sensor including the gas sensor according to any one of the first to eighth aspects. This gas sensor is inexpensive and has high durability. The form of the gas sensor 2 is not particularly limited. For example, the element 1 is disposed in the metal shell 21, and the outer surface of the metal shell 21 is arranged so that the detection unit disposed on the front side projects into the exhaust pipe or the like. Mounting screw part 42 formed in
And can be used after being exposed to the gas to be measured (exhaust gas). (See Fig. 6)

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail by way of examples. In the following, each part before and after firing is indicated by the same reference numeral for convenience. [1] Manufacturing of Device Having Peripheral Part and Suppressing Layer on Peripheral Part A method of manufacturing the device will be described with reference to FIG. (1) Preparation of unsintered alumina sheet Alumina powder (purity 99.99% or more, average particle size 0.3
μm) 100 parts by mass (hereinafter simply referred to as “parts”), 14 parts of butyral resin and 7 parts of dibutyl phthalate were blended and mixed using a mixed solvent consisting of toluene and methyl ethyl ketone to form a slurry. Four types of green sheets having different thicknesses and sizes were produced by the method. The first green sheet 11a has a thickness of 0.4
mm, 5 cm in length, the second green sheet 11b is 0.25 mm in thickness, 5 cm in length, the third green sheet 18a is 0.25 mm in thickness, 4 cm in length, and the fourth green sheet 18b is 0.4mm thick, 3.5 length
cm. After firing, the first green sheet becomes the first base 11a, the second green sheet becomes the second base 11b,
The third green sheet becomes the reinforcing layer 18a, and the fourth green sheet becomes the reinforcing layer 18b.

(2) Formation of heater pattern Alumina powder (purity 99.99% or more, average particle size 0.3
μm) A conductive layer paste containing 4 parts of platinum powder and 100 parts of platinum powder is printed on one surface of a first green sheet 11a (which becomes the lower half of the base after firing) to form a heating portion pattern 12a.
After drying, the heater lead pattern 12b was printed and dried to form the heater pattern 12 (to become the heating resistor 22 after firing). A through hole 1 near the base end of the first green sheet 11a for conducting the heating resistor.
11a was formed, and a heater pad pattern 19a was printed and dried at a position corresponding to the through-hole 111a on the back surface (after firing, it becomes an electrode pad for connecting terminals). Second green sheet 1 from above heater pattern 12
1b (the upper half of the substrate after firing) was laminated and pressure bonded.

(3) Formation of Buffer Layer Pattern A buffer layer pattern is formed on the second green sheet 11b of the ceramic laminate prepared in (2) using a buffer layer paste containing 80 parts of alumina and 20 parts of zirconia. 13
(To become a buffer layer after firing) to a thickness of 40 ± 10μ
Let dry. (4) Formation of Reference Electrode Pattern On the buffer layer pattern formed in (3), using the conductive layer paste used in (2), the electrode portion pattern 141a
(To become a reference electrode after firing) and electrode lead 141b
The reference electrode pattern 14a (which becomes a reference electrode after firing) becomes 20 μm ±
Printed and dried to a thickness of 10.

(5) Formation of First Solid Electrolyte Layer Pattern Zirconia powder (purity 99.9% or more, average particle diameter 0.3
μm) 50 parts and alumina powder (purity 99.99% or more,
50 parts, average particle size 0.3 mm), butyl carbitol 3
3.3 parts, dibutyl phthalate 0.8 part, dispersant 0.5
Parts and 20 parts of binder, add the required amount of acetone,
After mixing for a time, acetone was evaporated to prepare a solid electrolyte layer paste. This paste for solid electrolyte is printed and dried to a thickness of 13 mm and a thickness of 25 ± 10 μm in the length direction of the first green sheet (and the second green sheet) so as to cover the electrode portion 141a of the reference electrode pattern 14a,
The first solid electrolyte layer pattern 15a (which becomes a part of the main body portion and the peripheral portion of the solid electrolyte body after firing) was formed.

(6) Formation of first insulating layer pattern A necessary amount of acetone was added to 50 parts of butyl carbitol to the green sheet prepared in (1) and mixed for 4 hours. Paste was prepared. This insulating layer paste is printed and dried at a thickness of 25 ± 10 μm on a portion of the buffer layer pattern 13 where the first solid electrolyte layer pattern 15a is not printed.
An insulating layer pattern 16a was formed. After firing, it becomes a part of the insulating layer.

(7) Formation of Second Solid Electrolyte Layer Pattern The same solid electrolyte paste as in (5) is formed with a length of 8 mm,
Printing and drying to a thickness of 5 ± 10 μm, the second solid electrolyte layer pattern 15b (becomes a part of the solid electrolyte body after firing)
Was formed. That is, it has a 50 μm-thick portion serving as a main body after firing and a 25 μm-thick portion serving as a peripheral portion after firing.

(8) Formation of Second Insulating Layer Pattern The same insulating layer paste as in (6) is printed to a thickness of 25 ± 10 μm on the first insulating layer pattern 16a on which the second solid electrolyte layer pattern is not formed. After drying, a second insulating layer pattern 16b (a part of the insulating layer after firing, and in particular, a part on the first solid electrolyte pattern becomes the suppression layer 162 after firing) was formed.

(9) Formation of detection electrode pattern Second solid electrolyte layer pattern 1 formed in (7) to (8)
5b and the second insulating layer pattern 16b, using the conductive layer paste adjusted in (2), an electrode portion pattern 141a to be a detection electrode after firing (to be a detection electrode portion after firing).
And the electrode lead portion pattern 142b (which becomes the detection electrode lead portion after firing) is
Printing and drying were performed to a thickness of ± 10 μm. (10) Formation of protective layer pattern A resin powder having an average particle size of 50 μm was mixed with the same insulating layer paste as in (6) to prepare a protective layer paste, and a 10 mm length was formed on the second solid electrolyte layer pattern 17b. , Thickness 50
Printing and drying were performed at ± 20 μm to form a protective layer pattern 17 (which becomes a protective layer after firing). (11) Lamination of Third and Fourth Green Sheets The third green sheet 118a and the fourth green sheet 18b (each of a part of the reinforcing layer after firing are formed so as to cover portions except for the protective layer pattern formed in (10)). ) Were laminated.

(12) Degreasing and firing The laminate obtained in (1) to (11) is heated from room temperature to 420 ° C. at a rate of 10 ° C./hour in an air atmosphere, and held for 2 hours. The organic binder was degreased. Thereafter, in an air atmosphere, the temperature is increased to 1100 ° C. at a rate of 100 ° C./hour, and further increased to 1520 ° C. at a rate of 60 ° C./hour, held for 1 hour, and baked. There were obtained 300 gas sensor elements in which such a solid electrolyte body was provided with a main body part and a peripheral part, and the solid electrolyte body and the sensing electrode lead were separated by the suppression layer.

[2] Manufacture of a device having a suppression layer and an interposed layer According to the steps (7) and (8) of [1], after forming and drying the first solid electrolyte pattern 15a, the first insulating layer is formed. The pattern 16a (a part of which becomes the insertion layer 163) was formed and dried. Next, a second solid electrolyte layer pattern 15b (a part of which becomes the peripheral layer 162) having a larger area than the first solid electrolyte pattern 15a is formed on the first solid electrolyte pattern.
After drying, the second insulating layer pattern 16b was formed and dried. Thereafter, a third solid electrolyte pattern having a smaller area than the second solid electrolyte pattern not shown in FIG. 1 is further formed and dried, and a third insulating layer pattern (a part of which becomes the suppression layer 162) is formed. -It was dried. Otherwise, in the same manner as in [1], 300 devices were obtained. (FIG. 3
reference)

[3] Manufacture of Element Having Only Interposed Layer According to the steps (7) and (8) of [1], after forming and drying the first solid electrolyte pattern 15a, the first insulating layer pattern 16a is formed. (Partially becoming the insertion layer 163) was formed and dried. Next, a second solid electrolyte layer pattern 15b (a part of which becomes the peripheral layer 162) having a larger area than the first solid electrolyte pattern 15a is formed on the first solid electrolyte pattern.
After drying, the second insulating layer pattern 16b was formed and dried. In other respects, the device was changed to 30 in the same manner as in [1].
0 were obtained. (See Fig. 4)

[4] Manufacture of Element without Peripheral Part In the steps (7) and (8) of [1], the size of the second solid electrolyte layer pattern 15b is changed to the first solid electrolyte pattern 15a.
Then, 300 elements were obtained in the same manner as in [1] except that the size of the second insulating layer pattern 16b was adjusted to the size of the first insulating layer pattern 16a. (See Fig. 5)

[5] Evaluation of the rate of occurrence of cracks and the like due to firing 1200 elements obtained in [1] to [4] are submerged in water so that at least the solid electrolyte portion is completely immersed, and the reference electrode The resistance value between water and water was measured to evaluate the presence or absence of cracks. As a result, in the element having no peripheral portion obtained in [4], the distance between the solid electrolyte body and the insulating layer (T
At position), 183 cracks were found. That is, the crack occurrence rate was 60%. On the other hand, in the devices obtained in [1] to [3], no crack was generated, and the crack generation rate was 0%.

[6] Cooling / heating cycle durability test Using the device obtained in [1] to [4] and evaluated as having no crack in the test of [5], a resistance heating element of 16 V was used. 10 cycles of a heat cycle test in which the solid electrolyte body is heated until the temperature of the solid electrolyte body reaches about 1000 ° C., then the application of the voltage is stopped, and the solid electrolyte body is left until the temperature of the solid electrolyte body reaches room temperature. Was. Thereafter, the occurrence of cracks was evaluated by the same test as in [5]. As a result, cracks occurred in 29% of the devices obtained in [4], while cracks occurred in the devices obtained in [1] to [3] at 0%. From these results, it can be seen that the device of the present invention is a device having high durability in which no crack is generated during firing and no crack is generated in a heat cycle test after firing.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram for explaining a manufacturing process of a gas sensor element of the present invention.

FIG. 2 is a cross-sectional view of one example of the gas sensor element of the present invention.

FIG. 3 is a cross-sectional view of another example of the gas sensor element of the present invention.

FIG. 4 is a cross-sectional view of another example of the gas sensor element of the present invention.

FIG. 5 is a cross-sectional view of an example of a gas sensor element outside the scope of the present invention.

FIG. 6 is a sectional view of the gas sensor of the present invention.

[Explanation of symbols]

1; gas sensor element, 11a; first base, 11b; second
Substrate, 111; Through hole, 12; Heating resistor, 12
1; heating section; 122; heater lead section; 13; buffer layer;
14a; reference electrode, 14b; detection electrode, 15; solid electrolyte layer, 151; main body layer, 152; peripheral layer, 16a;
Insulating layer, 16b; second insulating layer, 162; suppression layer, 16
3; interposed layer, 17; protective layer, 18; first reinforcing layer, 18b
2nd reinforcement layer, 2; gas sensor, 21: metal shell, 21
1; metal shell screw part.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kunio Yanagi 14-18, Takatsuji-cho, Mizuho-ku, Nagoya Japan F-term (reference) 2G004 BB04 BE01 BE13 BF04 BJ03 BM07 5G301 CA12 CA28 CD01 CD10

Claims (9)

[Claims] 1. A gas sensor element comprising a substrate having an insulating property and a solid electrolyte disposed on the substrate, wherein the solid electrolyte comprises a main body and a peripheral portion having a thickness smaller than the main body. A gas sensor element comprising: a pressure suppression layer provided on at least a part of the peripheral portion. 2. The gas sensor element according to claim 1, wherein the solid electrolyte body has a stepped shape at a boundary between the main body and the peripheral part. 3. The gas sensor element according to claim 1, further comprising an intervening layer in contact with the peripheral portion. 4. The gas sensor element according to claim 3, wherein a total thickness of the peripheral portion, the suppression layer, and the interposition layer is equal to a thickness of the main body. 5. The substrate according to claim 1, wherein the substrate has a plate shape, and the solid electrolyte body is formed in a layer on one surface of the substrate.
The gas sensor element according to any one of claims 4 to 4. 6. The solid electrolyte body according to claim 1, wherein a reference electrode is formed in contact with the surface of the solid electrolyte body on the substrate side, and a detection electrode is formed in contact with the other surface. The gas sensor element according to any one of the preceding claims. 7. The gas sensor element according to claim 1, wherein the solid electrolyte body contains 10 to 80% by mass of a component constituting the base. 8. The gas sensor element according to claim 7, wherein the solid electrolyte body contains zirconia and alumina as main components, and the substrate contains alumina as a main component. 9. A gas sensor comprising the gas sensor element according to claim 1. Description: