JPH0545331A - Oxygen sensor device - Google Patents

Abstract

(57) [Summary] [Purpose] An oxygen sensor element in which the adhesion between the solid electrolyte and the measuring electrode does not deteriorate even when exposed to a high-temperature measurement gas for a long time, and peeling of the measuring electrode does not easily occur. provide. [Constitution] In an oxygen sensor element 1 for detecting a concentration of oxygen in a gas to be measured by providing a reference electrode 3 and a measuring electrode 5 on the surface of a solid electrolyte 2, a solid electrolyte is mainly formed on the surface of the solid electrolyte 2 on the measuring electrode 5 side. An oxygen sensor element 1 in which a base layer 4 made of a material 4a of the same kind as that of 2 and platinum or a platinum group alloy 4b is formed, and a measurement electrode 5 made of platinum or a platinum group alloy is formed thereon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor element used for detecting the oxygen concentration of various combustion equipment,
For example, the present invention relates to an oxygen sensor element used as an oxygen sensor element for air-fuel ratio control used in an exhaust gas purification system for purifying exhaust gas emitted from a combustion engine of an automobile or the like.

[0002]

2. Description of the Related Art In a conventional oxygen sensor element, for example, an oxygen sensor element for controlling an air-fuel ratio used in an exhaust gas purification system of an automobile has a crucible-shaped solid like an oxygen sensor element 11 shown in FIG. A reference electrode 13 containing a precious metal such as Pt as a main component is formed on the inner surface of the electrolyte 12, and a measuring electrode 14 containing a precious metal such as Pt is also formed on the outer surface, and the measuring electrode 14 is exposed to exhaust gas. Has a structure in which a ceramic protective layer 15 such as spinel is provided.

In such an oxygen sensor element 11,
The electrodes 13 and 14 formed on the solid electrolyte 12 are made of a metal having heat resistance and a catalytic action, for example, a noble metal such as platinum. Then, as a method for forming these electrodes 13 and 14, there are a vacuum vapor deposition method, a chemical vapor deposition method, an electroless plating method and the like.

[0004]

However, the oxygen sensor element 11 for controlling the air-fuel ratio used in such a conventional automobile exhaust gas purification system is exposed to high-temperature exhaust gas for a long time. In particular, there is a problem that the sintering of the measuring electrode 14 progresses, the adhesiveness with the surface of the solid electrolyte 12 is deteriorated, and the measuring electrode 14 may be peeled off. The challenge was to eliminate even more possibilities.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and provides the adhesion between the solid electrolyte and the measuring electrode even when exposed to a gas to be measured such as high temperature exhaust gas for a long time. It is an object of the present invention to provide an oxygen sensor element in which the measurement electrode does not deteriorate and peeling of the measurement electrode does not easily occur.

[0006]

The present invention provides an oxygen sensor element for detecting a concentration of oxygen in a gas to be measured by providing a reference electrode and a measurement electrode on the surface of a solid electrolyte, and a solid electrolyte on the surface of the measurement electrode. It is characterized in that an underlayer mainly composed of the same kind of material as the solid electrolyte and platinum or a platinum group alloy is formed, and a measurement electrode composed of platinum or a platinum group alloy is formed thereon. The structure of the invention relating to the sensor element serves as means for solving the above-mentioned conventional problems.

In the oxygen sensor element according to the present invention, as the solid electrolyte, ZrO ₂ is added to Y ₂ O ₃ or CaO.
A divalent or trivalent metal oxide such as ZrO ₂ is used which is added in a partially stabilizing or stabilizing component ratio.
A powder obtained by (temporarily) firing a mixed powder of powder and Y ₂ O ₃ or CaO powder and then re-pulverizing it to form partially stabilized or stabilized zirconia is used.

A film-shaped or crucible-shaped solid electrolyte can be obtained by pressure-molding and partially calcining such partially stabilized or stabilized zirconia powder.

A reference electrode and a measurement electrode are provided on the surface of the solid electrolyte. Before the measurement electrode is provided, the surface of the solid electrolyte on the measurement electrode side is mainly made of the same material as the solid electrolyte and platinum or a platinum group alloy. Is formed, and the measurement electrode is provided on the underlayer.

In this case, the average particle size of the solid electrolyte forming the underlayer is preferably around 50 μm, and the particle size of the platinum or platinum group alloy forming the underlayer is 50 μm or less. It is desirable that

Further, the electrical resistance of the underlayer at room temperature is more preferably set to a value of 1 kilo ohm or more, and the same kind of material as the solid electrolyte, platinum or platinum is used so as not to function as an electrode for extracting electromotive force. It is desirable to adjust the component ratio with the platinum group alloy and use it as a mixture which is made fluid by an appropriate organic binder.

It is desirable that the fluid mixture is adhered to the surface of the pre-calcined solid electrolyte in the form of a film by printing or dipping and is applied so that the calcined thickness is about 50 μm.

Further, when the measurement electrode is provided on the surface of the underlayer and the reference electrode is provided on the surface of the solid electrolyte, platinum or platinum group alloy is used by vacuum deposition, chemical vapor deposition, electroless plating or the like. The film is formed in a film thickness of about 1 μm.

After that, ceramics such as spinel and mullite are formed on the surface of the measuring electrode to a thickness of 10 by plasma spraying or the like.
An oxygen sensor element provided with a protective layer is formed by forming a film having a thickness of about 0 μm.

In such an oxygen sensor element, the solid electrolyte and the underlayer are firmly adhered to each other by containing the same kind of material, and the measuring electrode formed on the underlayer has the above-mentioned unevenness of the underlayer. The film is firmly adhered to the underlayer, and the adhesion strength of the protective layer formed on the measurement electrode is also increased.

By the way, it is desirable that the electrical resistance value of the underlayer at room temperature be 1 k ohm or more, because if the underlayer itself acts as a measuring electrode, the gas diffusion of the underlayer is not good, This is because there is a possibility that the oxygen sensor element has poor controllability due to poor responsiveness to changes in the air-fuel ratio due to reasons such as insufficient catalytic activity of the underlayer. Therefore, by providing a function only for improving the adhesion strength of the measuring electrode and the protective layer to the underlayer, the component ratio of platinum or a platinum group alloy is lowered, and the resistance value is 1 kΩ or more. It can be said that it is desirable that

[0017]

In the oxygen sensor element according to the present invention,
On the surface of the solid electrolyte on the measurement electrode side, an underlayer mainly made of the same material as the solid electrolyte and platinum or platinum group alloy is formed, and the measurement electrode made of platinum or platinum group alloy is formed on it. The adhesion strength of the measurement electrode to the solid electrolyte through the underlayer is further improved, and the adhesion of the measurement electrode to the solid electrolyte is reduced even when exposed to a measured gas such as high-temperature exhaust gas for a long time. As a result, peeling of the measurement electrode hardly occurs, and problems such as a decrease in sensor electromotive force and deterioration of responsiveness due to peeling of the measurement electrode can be prevented.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an oxygen sensor element according to an embodiment of the present invention.
Is provided with a reference electrode 3 made of platinum in contact with the atmosphere on the inner surface of a solid electrolyte 2 made of partially stabilized zirconia in the shape of a crucible, and the outer surface of the solid electrolyte 2 is mainly made of the same material 4a as the solid electrolyte 2. And a platinum or platinum group alloy 4b are formed as an underlayer 4, a measurement electrode 5 made of platinum is provided on the underlayer 4, and a ceramic protective layer 6 made of spinel is provided on the measurement electrode 5. It is what makes up.

In manufacturing the oxygen sensor element 1 having such a structure, first, ZrO ₂ is mixed with 6 mol of Y ₂ O ₃ .
% To obtain a partially stabilized zirconia powder by crushing, calcination, and re-crushing, and then press-molding this powder into a cylinder with one end closed and calcination
The solid electrolyte 2 has a crucible shape.

Next, a mixed powder of the same partially stabilized zirconia powder (average particle size; 50 μm) and platinum powder (average particle size; 50 μm) as in the solid electrolyte 2 is prepared.
The electrical resistance of the underlayer 4 at room temperature has a resistance value of 1 kilo ohm or more, and the ratio of these components is set so that it does not function as an electromotive force extraction electrode.
The mixture was adjusted to 6 and made fluid by an organic binder, and then the fluid mixture was attached to the surface of the calcined crucible-shaped solid electrolyte 2 by dipping, and the surface layer thickness after firing was 50 μm. It was applied to the front and back.

Next, using platinum as a material, a reference electrode 3 having a thickness of 1 μm is formed on the inner surface of the solid electrolyte 2 by a vacuum deposition method, and a base electrode 4 having a thickness of 1 μm is provided on the outer surface of the solid electrolyte 2. A measurement electrode 4 was formed, and a protective layer 6 made of spinel and having a thickness of 100 μm was formed on the measurement electrode 5 by plasma spraying to obtain an oxygen sensor element 1 having a structure shown in FIG.

On the surface of the oxygen sensor element 1 thus obtained, the underlayer 4 having irregularities with a thickness of about 5 μm or more is present.
Was obtained.

The measurement electrode 5 formed on the underlayer 4 was firmly adhered to the underlayer 4 due to the unevenness of the underlayer 4. Similarly, the adhesion strength of the protective layer 6 formed on the measurement electrode 5 was also increased.

Further, since platinum mixed in the underlayer 4 is sintered with the measuring electrode 5 and a part of the measuring electrode 5 penetrates into the underlayer 4 like a wedge, the platinum mixed with the underlayer 4 It helped to dramatically improve the adhesion strength.

FIG. 3 exemplifies the result of conducting a severe durability test at 1200 ° C. in air for a long time. In the conventional oxygen sensor element 11 having the structure shown in FIG. Since the peeling occurred from the surface of the solid electrolyte 12 and the response time was long after the long-term durability test, the response was deteriorated.
In the oxygen sensor element 1 of the present invention having the structure shown in FIG. 3, the measurement electrode 5 was not peeled off, and the responsiveness was deteriorated due to deterioration over time, and good results were obtained.

In another embodiment, the underlayer 4 is made of Al ₂
Using a mixture of a metal oxide such as O ₃ or TiO ₂ and platinum or a platinum group alloy, the average particle size of Al ₂ O ₃ is the same as that of a material (stabilized or partially stabilized zirconia) of the solid electrolyte. When the diameter was ½ or less and 20 mol% was mixed, the Al ₂ O ₃ particles were allowed to enter the gaps of the zirconia particles to form a more dense underlayer 4.

[0028]

According to the oxygen sensor element of the present invention,
On the surface of the solid electrolyte on the measurement electrode side, an underlayer mainly made of the same material as the solid electrolyte and platinum or a platinum group alloy is formed, and the measurement electrode made of platinum or a platinum group alloy is formed on it. Further, the adhesion strength of the measurement electrode to the surface of the solid electrolyte via the underlayer is improved, and the peeling of the measurement electrode can be prevented even during long-term use, which is a remarkably excellent effect.

[Brief description of drawings]

1A and 1B show an embodiment of an oxygen sensor element according to the present invention, FIG. 1A is an overall sectional explanatory view, and FIG. 1B is a partially enlarged sectional explanatory view.

FIG. 2 is a graph showing the results of a durability test at 1200 ° C. in air.

FIG. 3 shows a conventional oxygen sensor element, FIG. 3 (a) is an overall cross-sectional explanatory view, and FIG. 3 (b) is a partially enlarged cross-sectional explanatory view.

[Explanation of symbols]

 1 Oxygen Sensor Element 2 Solid Electrolyte 3 Reference Electrode 4 Underlayer 4a Same Material as Solid Electrolyte 4b Platinum or Platinum Group Alloy 5 Measuring Electrode

Claims (1)

[Claims] 1. An oxygen sensor element for detecting a concentration of oxygen in a gas to be measured by providing a reference electrode and a measurement electrode on the surface of a solid electrolyte, wherein the surface of the solid electrolyte on the measurement electrode side is mainly made of the same material as that of the solid electrolyte. And an underlayer made of platinum or a platinum group alloy, and a measurement electrode made of platinum or a platinum group alloy formed on the underlayer.