JPH05180797A - Oxygen concentration sensor - Google Patents

Abstract

PURPOSE:To achieve a prevention of an electrode from peeling and higher durability and performance of a sensor by producing a number of grooves with the width thereof larger than the particle size of ceramics of a sensor element base material on the surface thereof to make ceramic particles adhere to the surface thereof with the particle size being almost the same as the width of the grooves. CONSTITUTION:A cylindrical sensor element 1 whose one end is closed with zirconia particles of an average particle size of about 1-2mum is formed and a number of grooves 2 are formed in the direction orthogonal to the length of the element 1 on the outer surface thereof with both the width and depth of about 10-28mum. Then, the element 1 is dipped into a suspension which contains zirconia particles 3 of about 1-2mum being mixed with the second zirconia particles 3 with an average particle size of about 10-20mum, a binder, a solvent, a plasticizer and the like and then, the particles 3 are made to adhere onto the element 1 by baking. Thereafter, internal and external platinum electrodes 4 and 5 with a specified shape are formed on the inner and outer surfaces of the element 1 and a protective layer 6 is formed on the electrode 4. As a result, the particles 3 are fitted into the grooves 2 and bonded firmly on the outer surface of the element 1 being dispersed evenly. Thus, the electrode 4 is bonded on the outer surface of the element 1 evenly and firmly either.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen concentration sensor, and more particularly to an oxygen concentration sensor in which electrodes are hard to peel off.

[0002]

2. Description of the Related Art As an oxygen concentration sensor used as an exhaust gas sensor, for example, a zirconia type oxygen concentration sensor or a titania type oxygen concentration sensor can be cited. Zirconia type oxygen concentration sensor is a solid electrolyte zirconia is a cup-shaped element, the oxygen concentration in the exhaust gas is detected by using the electromotive force generated by the oxygen concentration difference between the inside and outside of this element .. Further, the titania-type oxygen concentration sensor detects the oxygen concentration in the exhaust gas by utilizing the fact that the electric resistance of the titania element which is an oxide semiconductor changes depending on the oxygen concentration.

By the way, in any of the various types of oxygen concentration sensors as described above, a pair of electrodes are provided on the surface of the sensor element for electrically extracting a detection signal corresponding to the oxygen concentration. ing. The electrodes are often formed by a so-called printing method in which a noble metal paste such as a platinum paste is applied and then baked. However, if a platinum electrode is directly formed on the sensor element base material, when the oxygen concentration sensor is used for a long time, the electrode performance may be deteriorated due to peeling of the electrode due to poor adhesion between the platinum electrode and the sensor element base material or aggregation of platinum particles. The problem of decreasing

In order to solve the above-mentioned problems, conventionally, of a pair of front and back surfaces of a sensor element substrate (eg, zirconia element or titania element) made of first ceramic particles (eg, zirconia particles or titania particles). Second ceramic particles made of the same material as the first ceramic particles and having an average particle size larger than that of the first ceramic particles are attached to at least one surface, and an electrode (for example, a platinum electrode) is further deposited thereon. An oxygen concentration sensor formed by forming is used. In this case, the second ceramic particles are deposited on the flat sensor element substrate surface by means of coating or dipping.

When, for example, zirconia particles having a predetermined property are attached to the surface of the zirconia element by using the above method, the surface of the zirconia element becomes uneven and the surface area increases, so that an electrode formed on the surface of the zirconia element, for example, a platinum electrode is It firmly adheres to the surface of the zirconia element and prevents the platinum particles from aggregating.

[0006]

However, even when the zirconia particles having a predetermined property are adhered to the surface of the zirconia element and the platinum electrode is formed on the zirconia particle as described above, the zirconia particles should be evenly adhered to the element surface. Is difficult, resulting in uneven adhesion of zirconia particles,
In the part where the zirconia particles are not adhered, the problems of electrode peeling and platinum particle aggregation still tend to occur. Further, even if the particle size of the zirconia particles varies, the particle size is not selected at the time of adhesion, so that zirconia particles of various particle sizes adhere to the surface of the zirconia element, and the electrode is formed on this. In this case, unevenness is likely to occur.

The present invention is to solve the above-mentioned problems of the prior art. The object of the present invention is to improve the durability and performance of the oxygen in which the electrode is less likely to be peeled off as compared with the conventional oxygen concentration sensor. It is to provide a concentration sensor.

[0008]

That is, the oxygen concentration sensor of the present invention comprises a sensor element substrate comprising a first ceramic particle, the first and second surfaces of which are provided on at least one of the front and back surfaces. In an oxygen concentration sensor in which second ceramic particles having an average particle size larger than that of the ceramic particles are attached, and electrodes are further formed on the second ceramic particles, the average particle size of the second ceramic particles on the surface of the sensor element substrate. A large number of grooves having a width substantially equal to the diameter are formed, and the second ceramic particles are adhered to the surface on which the grooves are formed.

The material of the first ceramic particles may be a material conventionally used as a material for a sensor element substrate, for example, zirconia, titania or the like optionally containing a conventional additive component such as yttria. Properties such as the shape and average particle size of the first ceramic particles are appropriately selected depending on the intended performance of the sensor element.

The size and shape of the sensor element substrate are not particularly limited. The shape of the sensor element base material may be, for example, various shapes such as a cylindrical shape, a prismatic shape, a cylindrical shape, and a rectangular tube shape, or a combination thereof. Further, as the method of molding the sensor element base material, a conventional method such as a method using a molding die, a method of laminating ceramic green sheets, or a method of combining these can be used.

As the material for the second ceramic particles, those conventionally used in this field can be used similarly to the material for the first ceramic particles. The material of the second ceramic particles may be the same as or different from the material of the first ceramic particles. It is convenient that the same material improves mutual adhesiveness. In this case, the second ceramic particles may be formed by a conventional method using the first ceramic particles as a raw material. The shape and average particle size of the second ceramic particles are appropriately selected such that the average particle size is larger than that of the first ceramic particles. The coating thickness of the second ceramic particles is appropriately selected, but is usually several tens μm to several hundreds μm.
Is preferred. The second ceramic particles may be attached to both of the front and back surfaces of the sensor element substrate, which are paired, or one of them (usually the outer surface).

The electrodes may be formed, for example, by a printing method using a noble metal paste containing platinum, palladium, gold, silver or the like, or may be formed by another conventional method such as a plating method. .. The number, size, shape, etc. of the electrodes are appropriately selected. If desired, a ceramic such as spinel may be coated on the electrode by a thermal spraying method or a dipping method to form a protective layer.

The groove formed on the surface of the sensor element has a width similar to the average particle diameter of the second ceramic particles, for example, a width of several tens of μm, and a part of the second ceramic particles enter therein. Anything can be used. The groove may be formed in various shapes such as a linear shape, a sawtooth shape, a curved shape, or a combination thereof as a planar shape. Further, the plurality of grooves may be formed in various shapes such as a parallel shape, a cross shape, a radial shape, a concentric shape, or a combination thereof. Further, the cross-sectional shape of the groove may be various shapes such as a semicircular shape, a U-shape, a V-shape, and a rectangular shape as long as it can accommodate a part of the second ceramic particles. Since the ceramic particles are usually spherical, the cross-sectional shape of the groove is preferably semicircular or U-shaped.

As a means for forming the groove, a conventional groove forming means can be used. For example, the surface of the sensor element base material may be cut, or at the same time when the sensor element base material is formed, a molding die is used. It may be formed. Furthermore, these methods may be used in combination.

The method of putting a portion of the second ceramic particles in the groove can be carried out by a conventional method, for example, by coating or spraying a suspension of the second ceramic particles containing a suitable binder with the sensor element substrate. It can be performed by immersing the sensor element substrate in the suspension.

[0016]

Since a large number of grooves having a width similar to the average particle diameter of the second ceramic particles are formed on the surface of the sensor element base material, and the second ceramic particles are adhered to the grooved surface, A part of the second ceramic particles enters the groove and is uniformly and firmly bonded to the sensor element base material by the anchor effect, and peeling of the electrode formed thereon and aggregation of the electrode material particles are prevented.

[0017]

The present invention will be described in more detail with reference to the following examples and comparative examples. In the following Examples and Comparative Examples, for the sake of explanation, a case of an oxygen concentration sensor using a zirconia element that is a solid electrolyte will be described, but the present invention relates to the case of an oxygen concentration sensor using another element. Of course, it is also applicable.

Example 1 A cylindrical sensor element 1 having one end closed as shown in FIG. 1 using first zirconia particles having an average particle size of 1 to 2 μm.
Formed. Then, on the outer surface of the sensor element 1 (the portion where the outer electrode is to be provided), the width and depth are both 10 to 2
A large number of 0 μm grooves 2 were formed by cutting in a direction orthogonal to the length direction of the sensor element 1. Then, a sensor was added to the suspension containing the second zirconia particles 3 having an average particle diameter of 10 to 20 μm, polyvinyl alcohol as a binder, trichloroethane as a solvent, ethanol and a plasticizer, and 1 to 2 μm zirconia particles mixed with a peptizer. Element 1
After soaking, take out and dry at about 120 ° C for 2 hours, then about 1
The second zirconia particles 3 were attached onto the sensor element 1 by firing at 50 ° C. for 2 hours.

Next, an outer platinum electrode 4 and an inner platinum electrode 5 having a predetermined size, shape and thickness were formed on the inner surface and outer surface of the sensor element 1 by a printing method or a plating method.
After that, a protective layer 6 having a predetermined thickness was formed on the outer platinum electrode 4 by using a ceramic such as spinel by a thermal spraying method or a dipping method.

FIG. 2 shows an enlarged view of portion A in FIG. As is apparent from FIG. 2, since the second zirconia particles 3 are fitted in the grooves 2, they are uniformly dispersed on the outer surface of the sensor element 1 and firmly bonded to the outer surface of the sensor element 1. Therefore, the outer platinum electrode 4 formed on the second zirconia particles 3 is also uniformly formed on the outer surface of the sensor element 1 and firmly bonded to the outer surface of the sensor element 1 via the second zirconia particles 3. is doing. Further, it can be seen that the second zirconia particles 3 (for example, the width of the groove 2 and the particle size are almost equal) which are likely to enter the groove 2 preferentially enter the groove 2.

As shown in FIG. 3, the sensor element 1 was assembled in the sensor holder 7 and other components were mounted to obtain the oxygen concentration sensor of Example 1. In FIG. 3, 8 is a protective cover and 9 is another.
Is a flange, 10 and 11 are outer cylinders, 12 is a spring, 13,
14 and 15 are bushes, 16 is a filler, and 17 is a lead wire.

[0022] except for using Example 2 plate-shaped sensor element 1 in the same manner as in Example 1 to obtain an oxygen concentration sensor of Example 2.

[0023] except that the coated zirconia paste having a predetermined concentration, instead of immersing the sensor element 1 in Example 3 zirconia suspension on the sensor element 1 in the same manner as in Example 1, the oxygen concentration sensor of Example 3 Obtained.

[0024] except for using Example 4 plate-shaped sensor element 1 in the same manner as in Example 3, to obtain an oxygen concentration sensor of Example 4.

[0025] Except for not forming the groove 2 in Comparative Example sensor element 1 in the same manner as in Example 1 to obtain an oxygen concentration sensor of the comparative example. Figure 6
A partially enlarged view of the sensor element 1 of the oxygen concentration sensor of the comparative example is shown in FIG. As is apparent from FIG. 6, since the second zirconia particles 3 do not have the grooves 2 and the adhesion state of the second zirconia particles 3 is non-uniform, the portions where the second zirconia particles 3 are attached to the outer surface of the sensor element 1 There is. Further, when the particle diameters of the second zirconia particles 3 vary, it can be seen that the second zirconia particles 3 having various particle diameters are nonuniformly attached to the outer surface of the sensor element 1.

Performance Comparison Test The oxygen concentration sensor of Example 1 and the oxygen concentration sensor of Comparative Example were mounted on an exhaust system of an automobile and a running test was conducted to examine the relationship between the running distance and the sensor output. The results are shown in FIG. As is apparent from FIG. 4, the sensor output of the oxygen concentration sensor of Example 1 did not decrease even when the traveling distance increased, but the sensor output of the oxygen concentration sensor of the comparative example began to decrease due to the increase of the traveling distance. ..

5 (a) and 5 (b) show the changes over time in the outputs of the oxygen concentration sensor of Example 1 and the oxygen concentration sensor of Comparative Example in the white circle of Example 1 and the white star of Comparative Example, respectively. .. As shown in FIG. 5A, in the oxygen concentration sensor of the first embodiment, the output regularly changes in a sinusoidal shape with time. On the other hand, as shown in FIG. 5B, it can be seen that the output of the oxygen concentration sensor of the comparative example changes irregularly in a sawtooth wave shape with time, and the performance of the oxygen concentration sensor deteriorates.

[0028]

The oxygen concentration sensor of the present invention has the structure as described above, and a large number of grooves having a width similar to the average particle size of the second ceramic particles are formed on the surface of the sensor element substrate. Since the second ceramic particles are made to adhere to the surface where is formed, a part of the second ceramic particles enters the groove,
The anchor effect uniformly and firmly binds to the sensor element substrate, prevents peeling of the electrode formed thereon and aggregation of electrode material particles, and improves the durability and performance of the oxygen concentration sensor.

Further, since the second ceramic particles are evenly adhered to the surface of the sensor element base material, the influence of thermal expansion is made uniform when firing the sensor element base material or when using the oxygen concentration sensor, The improved strength prevents cracking of the device.

Furthermore, since variations in performance among individual sensor elements are reduced, productivity is improved and production cost is also reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of a sensor element of an oxygen concentration sensor according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of a portion A of the sensor element of FIG.

FIG. 3 is a cross-sectional view of the oxygen concentration sensor according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between a mileage and a sensor output when the oxygen concentration sensors of the present invention and a comparative example are mounted on an automobile.

FIG. 5 is a diagram showing a change over time in sensor output after traveling a long distance when the oxygen concentration sensors of the present invention and the comparative example are mounted on an automobile.

FIG. 6 is a partially enlarged sectional view of a sensor element of an oxygen concentration sensor of a comparative example.

[Explanation of symbols]

 1 Sensor Element 2 Groove 3 Second Zirconia Particle 4 Outer Platinum Electrode 5 Inner Platinum Electrode 6 Protective Layer 7 Sensor Holder 8 Protective Cover 9 Flange 10,11 Outer Cylinder 12 Spring 13,14,15 Bush 16 Filler 17 Lead Wire

Claims (1)

[Reference number] C1176 [Claims] 1. A second ceramic particle having an average particle size larger than that of the first ceramic particle on at least one surface of a pair of front and back surfaces of a sensor element substrate made of the first ceramic particle. Is attached, further in the oxygen concentration sensor having an electrode formed thereon, in the surface of the sensor element base material, a large number of grooves having a width similar to the average particle diameter of the second ceramic particles are formed, An oxygen concentration sensor characterized in that the second ceramic particles are adhered to the surface on which the groove is formed.