JP2003344348A - Oxygen sensor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an oxygen sensor element that avoids the occurrence of warpage and has superior durability to a heat cycle. <P>SOLUTION: The oxygen sensor element is provided with; a flat substrate 2 made of a ceramic solid electrolyte having an atmospheric introduction hole 3; a reference electrode 4 formed on the inner wall of the atmospheric introduction hole 3; a measurement electrode 5 formed on the outer surface of the substrate 2 that opposes the reference electrode 4; a first ceramic insulating layer 7 provided inside the substrate 2; a heating element 6 provided in the insulating layer 7; and a second ceramic insulating layer 8 provided at a nearly symmetrical position to the first ceramic insulating layer 7 in the substrate 2 made of a solid electrolyte. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plate-shaped oxygen sensor element.

[0002]

2. Description of the Related Art In recent years, environmental problems have been highlighted, and efforts have been made in each industry to prioritize the global environment. Especially, in the automobile industry, as represented by exhaust gas regulations, CO ₂ , CO, and H in exhaust gas are changed year by year.
It is required to reduce the amounts of C and NOx. Among them, in order to further reduce the above-mentioned gas in the exhaust gas, it is important to efficiently burn the fuel inside the heat engine, and for that purpose the residual oxygen amount in the exhaust gas is measured instantaneously. However, there is an increasing demand for an oxygen sensor element that can quickly feed back the information to the combustion system.

Such an oxygen sensor element has hitherto used the heat of the exhaust gas to raise the temperature of the cup-type oxygen sensor element and bring out the sensor function. However, exhaust gas is in a state of being discharged until the sensor function appears, and it has become impossible to comply with the recent strict exhaust gas regulations. Therefore, by providing a heater inside the cup-type oxygen sensor element and positively heating by this heater, the sensor function can be made to appear faster, and information can be fed back more responsively. However, since the cup-type oxygen sensor element is large in size and the sensor portion and the heater are separated from each other, there is a limit in making the sensor function appear faster.

Therefore, recently, by integrating a plate-shaped oxygen sensor element and a plate-shaped ceramic heater by firing, the size can be reduced and the temperature rising speed can be increased as compared with the cup type, resulting in faster sensor function. Is emerging.

[0005]

However, in the above plate-shaped oxygen sensor element, a ceramic green sheet of solid electrolyte such as zirconia forming the sensor portion and a ceramic green such as alumina in which a heating element such as tungsten is embedded. Laminate and adhere to the sheet, degreasing,
When firing, there was a problem that warpage occurred during firing. Further, there is a problem in that the manufacturing yield is reduced due to the warp, the ceramic material, the electrode material, and the like are wasted, which leads to an increase in cost. Further, stress is generated by repeating temperature rising and cooling, and therefore the object of the present invention is to suppress the occurrence of warp and
An object of the present invention is to provide an oxygen sensor element having excellent durability even in heat cycles.

[0006]

According to the present invention, a plate-shaped substrate made of a ceramic solid electrolyte having an air introduction hole, a reference electrode formed on the inner wall of the air introduction hole, and a reference electrode facing the reference electrode. The measurement electrode formed on the outer surface of the base body, the first ceramic insulating layer provided inside the base body, the heating element provided inside the ceramic insulating layer, and the first base body made of the solid electrolyte. The above object can be achieved by the oxygen sensor element including the ceramic insulating layer and the second ceramic insulating layer provided in a substantially symmetrical position.

In particular, the first ceramic insulating layer and the second ceramic insulating layer
When the main components of the ceramic insulating layer are the same, it is easy to adjust the firing conditions and stress balance.

Further, the position where the second ceramic insulating layer is formed is not sandwiched between the reference electrode and the measurement electrode, and particularly the portion where the air introduction hole is formed is the sensor portion. It does not affect the sensor performance of.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION An example of the oxygen sensor element of the present invention will be described with reference to FIG. 1 (a) schematic plan view and (b) XX sectional view. According to the oxygen sensor element 1 of FIG. 1, the substrate 2 made of a plate-shaped solid electrolyte is provided with a hollow atmosphere introduction hole 3 whose one end is sealed, and a part of the inner wall of the atmosphere introduction hole 3 is provided. The reference electrode 4 is adhered and formed, and the measurement electrode 5 that comes into contact with the gas to be measured is formed on the outer surface of the solid electrolyte substrate 2 facing the reference electrode 4 to form the sensor portion A. . Further, on the surface of the substrate 2 or on the inner wall of the air introduction hole 3, an electrode lead 51 and an electrode pad 52 whose one end is electrically connected to the reference electrode 4 and the measurement electrode 5 are formed.

On the other hand, the reference electrode 3 of the air introduction hole 3 of the substrate 2
A ceramic insulating layer 7 containing a heating element 6 is provided inside the base body 2 on which the heating element 6 is not formed, and the heating section 6 and the ceramic insulating layer 7 form a heater portion B.

In the present invention, the ceramic insulating layer 8 is provided at a position substantially symmetrical to the ceramic insulating layer 7 containing the heating element 6. Conventionally, when the ceramic insulating layer 8 is not provided, the ceramic insulating layer 7 containing the heating element 6 is formed on one side of the air introducing hole 3 of the oxygen sensor element 1, so that the ceramic insulating layer 7 is not formed. When viewed from the whole, it is formed in a biased position. Therefore, the base body 2 and the ceramic insulating layer 7 made of the solid electrolyte during firing are used.
When viewed from the whole of the oxygen sensor element 1 due to the difference in firing shrinkage behavior and the coefficient of thermal expansion, strain occurs between the vicinity where the sensor part A is formed and the vicinity where the heater part B is formed, and this distortion causes warpage. Is likely to occur, and damage is likely to occur due to repeated heat cycles.

On the other hand, when the ceramic insulating layer 8 is formed, the strains generated by the ceramic insulating layer 7 are canceled by the strains generated by the formation of the ceramic insulating layer 8, so that warpage occurs and thermal cycling occurs. It is possible to effectively prevent the occurrence of breakage in the.

The location where the ceramic insulating layer 8 is formed is substantially symmetrical to the location where the ceramic insulating layer 7 is formed. The substantially symmetrical position is a sectional view of the oxygen sensor element 1. In the case where the ceramic insulating layer 7 is formed in a region lower than the center line p, as shown in FIG. The insulating layer 8 may be formed in a region above the center line p.

Further, according to the present invention, it is desirable that the ceramic insulating layer 8 has the same main component as the ceramic insulating layer 7 having the heating element 6 built therein, and in particular, the ceramic insulating layer 8 is made of substantially the same composition. Most desirable. This is because it is possible to easily design and control the oxygen sensor element 1 by making the firing shrinkage behavior and the thermal expansion characteristics of the two the same or similar.

Further, since the ceramic insulating layers 7 and 8 need to be insulators in order to incorporate the heating element 6, the ceramic insulating layer 8 is provided between the measurement electrode 5 and the reference electrode 4. It cannot be formed. Therefore, according to the present invention, since the ceramic insulating layer 8 is provided in a part of the portion where the air introduction hole 3 is formed, the sensor performance of the sensor unit A is not affected, which is most desirable.

The total thickness t of the ceramic insulating layer 7 containing the heating element 6 is usually 5 to 100 μm, especially 10 μm.
˜50 μm, ceramic insulating layer 8
Is 0.8t to the thickness t of the ceramic insulating layer 7.
1.5t is suitable.

Further, the ceramic insulating layer 8 does not necessarily have to be one layer, and may be formed of, for example, a plurality of layers 8a and 8b of two or more layers as shown in the schematic sectional view of FIG. Is. Even in such a case, it is desirable that the total thickness of the ceramic insulating layers 8a and 8b be within the above range.

Although the theoretical air-fuel ratio oxygen sensor (λ sensor) is illustrated in FIG. 1 above, the present invention is also applicable to a wide range sensor element. FIG. 3 is a schematic cross-sectional view for explaining the typical structure thereof. According to the oxygen sensor element of FIG. 3, the electrode pair of the reference electrode 4 and the measurement electrode 5 is formed on the opposing surfaces of the base 2a, and the space 10 is formed above the measurement electrode 5 by the base 2b. . The space 10 is closed by a base body 2c, and a diffusion hole 11 having a size of 0.1 to 0.5 mm for taking in exhaust gas is formed in the base body 2c. With such a configuration, the air-fuel ratio in the exhaust gas is controlled by controlling the current flowing between the electrode pair according to the oxygen concentration in the exhaust gas that has passed through the diffusion hole 11.

In addition, in such an oxygen sensor, a pair of electrodes may be formed on both surfaces sandwiching the base body 2c to function as a pumping cell.

It should be noted that the space 10 may be filled with porous ceramics in order to give the element strength. Further, the diffusion hole 11 can be formed not only on the upper surface of the element but also on the side surface and the tip. Furthermore, the diffusion hole 11
Need only function as a hole for taking in a certain amount of exhaust gas into the space. Therefore, the diffusion hole 11 may be formed of a large number of holes or may be formed of a ceramic porous layer.

According to the present invention, an oxygen cell as shown in FIG.
Also in the sensor element, the ceramic insulation with the built-in heating element 6
The ceramic insulating layer 8 is formed at a position substantially symmetrical to the edge layer 7.
It In this case, the ceramic insulating layer 8 is as shown in FIG.
Then, the base body 2b forming the space 10 is attached to the ceramic insulating layer.
8 is desirable. In addition,
A part or all of the base body 2d forming the entry hole 3 is ceramic
It may be replaced by the insulating layer 8. (Solid Electrolyte) Base in Oxygen Sensor Element 1 of the Present Invention
The solid electrolyte used as 2 is ZrO 2.₂And TiO₂Na
, Which can be formed by a known ceramic solid electrolyte
However, in terms of its performance, it consists of a zirconia-based solid electrolyte
Is desirable. Zirconia solid electrolyte and stabilizer
And then Y₂O₃And Yb₂O₃, Sc₂O₃, Sm₂O₃, N
d ₂O₃, Dy₂O₃1 to 1 of rare earth oxides such as
30% by mol, preferably 3-15% by mol
Standardized ZrO₂Or stabilized ZrO₂Is used.
In addition, ZrO₂Replace 1 to 20 atomic% of Zr with Ce
ZrO₂Oxygen ion conductivity by using
The effect is that it becomes larger and the responsiveness is further improved.
is there. Further, for the purpose of improving the sinterability, the above ZrO₂
Against Al₂O₃And SiO₂Can be added
Yes, but if contained in a large amount, creep at high temperature
Since the characteristics deteriorate, Al₂O₃And SiO₂Nozono
The total amount added should be 5% by weight or less, especially 2% by weight or less.
And is desirable. (Electrode) The surface of the solid electrolyte substrate 2 or the air introduction hole 3
The reference electrode 4, the measurement electrode 5 and the electrode formed on the inner wall,
The electrode lead 51 and the electrode pad 52 are both platinum,
Or platinum, rhodium, palladium, ruthenium,
And an alloy with one selected from the group of gold and gold. Well
Also, prevents metal grain growth in the electrode during sensor operation.
Purpose, the responsiveness of platinum particles, solid electrolyte and gas
For the purpose of increasing the contact point at the so-called three-phase interface with the body,
1-50% by volume of the above-mentioned ceramic solid electrolyte component, especially
Mix in the above electrodes 4 and 5 at a ratio of 10 to 30% by volume.
Good. The electrode shape can be square or elliptical.
Good. The thickness of the electrodes 4 and 5 is 3 to 20 μm, and
It is preferably 5 to 10 μm. (Ceramic insulating layer) On the other hand, a ceramic for embedding the heating element 6
The insulating layer 7 and the ceramic insulating layer 8 are made of Al
₂O₃At least selected from the group of mullite, spinel
If the relative density of one type of ceramic is 80% or more,
Composed of dense ceramics with a porosity of 5% or less
Is desirable, especially Al₂O₃Ceramics
Is desirable. Sinterability is improved in the above ceramics.
Various sintering aids, such as Al₂O₃Ceramics
In the case of, the total amount of oxides of Mg, Ca and Si is 1 to 10
The ceramic insulating layer 7, which may be contained in an amount of
In 8, the content of alkali metals such as Na and K
As a result of migration,
In order to reduce the electrical insulation between the heaters, in terms of oxide weight
It is desirable to control it to 50 ppm or less. Also relative
By setting the density within the above range, the substrate strength is high.
As a result, increasing the mechanical strength of the oxygen sensor itself
This is because you can (Porous layer) In addition, the surface of the measurement electrode 5 is shown in FIG.
Form a ceramic porous layer 9 for protection, as shown in FIG.
Is desirable. This ceramic porous layer 9 is
Zircon having a thickness of 10 to 800 μm and a porosity of 10 to 50%
Is it a group of konia, alumina, γ-alumina and spinel?
Be formed of at least one selected from
Is desirable. The thickness of the porous layer 9 is thinner than 10 μm
Or if the porosity exceeds 50%, electrode poisoning substance
When P, Si, etc. easily reach the electrode and the electrode performance deteriorates.
There is a match. On the other hand, the thickness of the porous layer 9 is 800μ
m or the porosity is less than 10%
The diffusion rate of gas and gas in the porous layer 9 becomes slow, and
The response may be poor. In particular, the thickness of the porous layer 9
Although it depends on the porosity, 100 to 500 μm is suitable.
It is right. (Heater) In the ceramic insulating layer 7 in the heater section B
Embedded heating element 6 and leads to heating element 6 (not shown)
Is platinum alone as the metal, or platinum and rhodium,
An alloy with one selected from the group of radium and ruthenium
Can be used. In this case, the resistance between the heating element 8 and the lead is
The anti-ratio should be controlled in the range of 9: 1 to 7: 3 at room temperature.
Preferably.

In the oxygen sensor element 1 of the present invention, the total thickness of the element is 0.8 to 2.0 mm, particularly 1.0.
.About.1.7 mm, and the length of the element is preferably 40 to 60 mm, and particularly preferably 45 to 55 mm in view of the rapid temperature rising property and the mounting condition of the element in the engine. (Manufacturing Method) Next, the manufacturing method of the oxygen sensor element of the present invention will be described with reference to the exploded perspective view of FIG. 4 by taking the oxygen sensor element of FIG. 1 as an example.

First, a solid electrolyte green sheet 20 is prepared. This green sheet 20 is obtained by, for example, appropriately adding a molding organic binder to a ceramic solid electrolyte powder having oxygen ion conductivity of zirconia, a doctor blade method, an extrusion molding, or a hydrostatic molding (rubber press). Alternatively, it is manufactured by a known method such as press forming. It is also possible to use a plurality of thin green sheets that are stacked to have a predetermined thickness.

Next, on both surfaces of the green sheet 20, the pattern 21, the lead pattern 22 and the electrode pad pattern 23 which will be the measurement electrode 5 and the reference electrode 4, respectively.
For example, a conductive paste containing platinum is used to print and form the slurry by a dip method, screen printing, pad printing, or roll transfer. Further, through holes (not shown) and the like are appropriately formed in the green sheet 20 and filled with a conductive paste to connect electrodes and the like between the front and back of the sheet.

Next, a green sheet having the air introduction hole 24 formed therein is prepared. At this time, according to the present invention, a slurry of at least one ceramic selected from the group consisting of alumina, mullite, and spinel is applied to the surface of the zirconia green sheet 25 having the air introduction hole 24 in a predetermined thickness. Then, the ceramic insulating layer 26 is applied. The air introduction hole 24 is opened by punching or the like, or is press-molded using a mold in which the air introduction hole 24 is formed by press molding. In addition, the green sheet 20
A green sheet 27 made of the same material as that for closing the opposite side of the air introduction hole 24 is prepared.

Then, the green sheets 20 and 2 described above.
5 and 27 are mechanically laminated and bonded while interposing an adhesive such as an acrylic resin or an organic solvent, or while applying pressure with a roller or the like.

At this time, a porous slurry for forming the ceramic porous layer 9 shown in FIG. 1 may be applied by printing on the surface of the pattern 21 which becomes the measuring electrode 5.

Next, as shown in FIG. 4, on the surface of the zirconia green sheet 28 produced in the same manner as the green sheet 20, at least one selected from the group consisting of ceramic insulators such as alumina, mullite and spinel. An insulating paste containing ceramics is printed by a slurry dip method, screen printing, pad printing, or roll transfer to form a ceramic insulating layer 29a.

Next, a heater pattern 30 for forming the heating element 6 is printed and applied on the surface of the ceramic insulating layer 29a. Then, again, the insulating paste is applied onto the heater pattern 30 to form the ceramic insulating layer 2
By forming 9b, a laminated body of the heater part B is manufactured.

Further, conductor vias may be formed in the zirconia green sheet 28 and the ceramic insulating layers 29a and 29b so as to connect with electrode pads (not shown) for leading out the heater pattern to the outside.

When the heater B is manufactured, the ceramic insulating layers 29a and 29b are formed by printing and applying the insulating slurry as described above, or by using the insulating slurry by a doctor blade method or the like. An insulating sheet may be formed by a sheet forming method and laminated.

Thereafter, the above green sheets are bonded and integrated by interposing an adhesive such as an acrylic resin or an organic solvent or by mechanically bonding the two while applying pressure with a roller or the like. Are fired at the same time. Firing is performed in air or in an inert gas atmosphere at 130
Baking is performed at a temperature range of 0 ° C to 1700 ° C for 1 to 10 hours.
During the firing, in order to suppress the warpage of the sensor portion during firing, it is possible to further reduce the warpage by placing a smooth substrate such as alumina as a weight on the laminate.

Thereafter, if necessary, at least one kind of porous ceramic layer selected from the group consisting of alumina, zirconia, and spinel is formed on the surface of the measurement electrode 21 after firing by a plasma spraying method or the like. An oxygen sensor element in which the sensor unit and the heater unit are integrated can be formed.

[0034]

EXAMPLES Example 1 First, an acrylic binder, a solvent and a medium were mixed with zirconia powder having an average particle size of 0.8 μm and stirred for 48 hours to obtain a slurry. Then, the slurry is formed by doctor blade forming and dried to produce a zirconia green sheet having a thickness of 180 μm, which is laminated with a contact liquid to produce zirconia green sheets A, B, C and D having a predetermined thickness. did.

An acrylic binder and terpineol were mixed with alumina powder having an average particle size of 0.5 μm, and the mixture was mixed with a three-roll roll for 10 times and then diluted with terpineol to adjust the viscosity. Paste A
Was prepared.

Furthermore, an acrylic binder and terpineol were mixed with platinum powder having an average particle size of 1 μm, and the mixture was mixed with a triple roll for 10 passes, and then diluted with terpineol to adjust the viscosity of the electrode paste and A heater paste was prepared.

First, a pattern of a reference electrode, a measurement electrode, an electrode lead, an electrode pad, etc. was formed by screen printing on the zirconia green sheet A using the above electrode paste.

On the surface of the zirconia green sheet B, the insulating paste A was used to form a ceramic insulating layer having a thickness of 30 μm by the doctor blade method. Then, the zirconia green sheet B was punched into a groove shape having a detection portion having a width of 1.6 mm and a length of 11 mm with a die to form an air introduction hole.

Further, the insulating paste A was applied on the surface of the zirconia green sheet C by screen printing to form a ceramic insulating layer having a thickness of 15 μm. Then, on the surface of the ceramic insulating layer, a heater having a thickness of 15 μm, a lead pattern or the like is printed and applied by screen printing using the heater paste, and then the insulating paste is further screen printed and dried. Then, a ceramic insulating layer having a total thickness of 30 μm was formed, and a ceramic insulating layer having a heating element therein was formed on the surface of the zirconia green sheet C.

Thereafter, the zirconia green sheet A having the electrode pattern formed thereon, the zirconia green sheet B having the air introduction hole formed therein and the ceramic insulating layer formed thereon,
The zirconia green sheet D and the zirconia green sheet C on which a ceramic insulating layer having a heating element were formed were positioned in this order, and they were laminated in close contact with a contact liquid, and pressed to obtain a green laminate. Then, this green laminate was fired at 1400 ° C. for 2 hours to produce an oxygen sensor element. The produced oxygen sensor element has a length of 46 mm, a width of 3 mm, and a thickness of 1.5 mm.

With respect to the 50 oxygen sensor elements thus produced, the warpage was measured with a surface roughness meter. The warp was measured by operating the stylus of a surface roughness meter in the longitudinal direction of the device when the warp was set with the measurement electrode facing upward, and calculating the average of 50 of them. As a result, the warp was 35 μm.

After the temperature of this oxygen sensor element was raised from room temperature to 1000 ° C. in about 20 seconds and then forcedly cooled to room temperature by a fan, the temperature cycle was defined as one cycle, which was repeated 20,000 times. As a result of measuring the rate of occurrence of cracks, no occurrence of cracks was observed in any of the 20 cracks. (Example 2) Green sheet E of zirconia having a thickness of 180 μm formed by the doctor blade method of Example 1
The insulating paste A of Example 1 was applied to the surfaces of Nos. 1 and E2 to form ceramic insulating layers each having a thickness of 15 μm. Then, the zirconia green sheets E1 and E2 on which the ceramic insulating layer is formed are laminated using a contact liquid, and then punched into a groove shape having a width of 1.6 mm and a length of 11 mm with a die to form an air introduction hole. did.

Then, the laminated body of the green sheets E1 and E2 having the air introduction holes formed as described above is
An oxygen sensor element was prepared and evaluated in the same manner as in Example 1 except that the air introducing hole of Example 1 was replaced with the zirconia sheet B on which the ceramic insulating layer was formed. As a result, the warp is 38 μm,
No cracks were found at all. Example 3 An acrylic binder and terpineol were mixed with forsterite powder having an average particle size of 0.5 μm, and the mixture was mixed 10 times with a three-roll mill, and then diluted with terpineol to adjust the viscosity. Sex paste B was obtained.

Then, instead of the insulating paste A of Example 1, this insulating paste B was applied to the surface of the zirconia green sheet B of Example 1 to form a ceramic insulating layer having a thickness of 30 μm. Then, the zirconia green sheet B on which the ceramic insulating layer was formed was punched into a groove having the same size as in Example 1 to form an air introduction hole.
An oxygen sensor element was prepared and evaluated in the same manner as in Example 1 except that this was replaced with the zirconia green sheet B having the air introduction holes of Example 1. As a result, the warp was 42 μm, and no crack was observed. (Comparative Example) The same procedure as in Example 1 was carried out except that the green sheet having the insulating layer formed thereon was not used in Example 1 and the green sheet having no insulating layer was used. As a result, the warpage was 105 μm. Further, after the thermal cycle test, the generation of cracks was observed in 15 of the 20 oxygen sensors.

[0045]

As described in detail above, according to the present invention,
By forming a second ceramic insulating layer at a position substantially symmetrical to this ceramic insulating layer in addition to the ceramic insulating layer having a heating element therein, generation of warpage of the sensor element is suppressed and thermal cycle is performed. The durability against can be increased.

[Brief description of drawings]

1A is a schematic plan view and FIG. 1B is a sectional view taken along line xx for explaining an example of an oxygen sensor element of the present invention.

FIG. 2 is a schematic sectional view for explaining another example of the oxygen sensor element of the present invention.

FIG. 3 is a schematic cross-sectional view for explaining another example of the oxygen sensor element of the present invention.

FIG. 4 is an exploded perspective view for explaining a method of manufacturing the oxygen sensor element of FIG. 1 as a method of manufacturing the oxygen sensor element of the present invention.

[Explanation of symbols]

1 Oxygen sensor element 2 base 3 Atmosphere introduction hole 4 Reference electrode 5 measuring electrodes 6 heating element 7, 8 Ceramic insulation layer

Claims (4)

[Claims] 1. A plate-shaped substrate made of a ceramic solid electrolyte having an air introduction hole, a reference electrode formed on the inner wall of the air introduction hole, and a measurement electrode formed on the outer surface of the substrate facing the reference electrode. A first ceramic insulating layer provided inside the base, a heating element provided inside the insulating layer, and a base made of the solid electrolyte at a position substantially symmetrical to the first ceramic insulating layer. An oxygen sensor element, comprising: a second ceramic insulating layer provided. 2. The oxygen sensor element according to claim 1, wherein the first ceramic insulating layer and the second ceramic insulating layer have the same main component. 3. The oxygen sensor element according to claim 1, wherein the formation position of the second ceramic insulating layer is not sandwiched between the reference electrode and the measurement electrode. 4. The oxygen sensor element according to claim 3, wherein a position where the second ceramic insulating layer is formed is a portion where the air introduction hole is formed.