JPH06242065A - Manufacture of limit current type oxygen sensor - Google Patents

Abstract

PURPOSE:To provide a method for manufacturing a limit current type oxygen sensor in which characteristics are improved and fluctuation is suppressed through a simple process. CONSTITUTION:A Pt anode electrode 2 and a cathode electrode 3 are formed on an ion conductive substrate 1 while a heater electrode 5 is formed through an insulation layer 4 on the side where the cathode electrode 3 is formed and net-like carbon fibers 6 are mounted thereon followed by screen printing of crystallized glass material 7. It is then fired and the glass material 7 is crystallized to form a crystallized glass seal layer 8. At the same time, the net-like carbon fibers 6 are decomposed and evaporated thus forming a porous gas diffusion layer 9 on the bottom of the glass seal layer 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a limiting current type oxygen sensor.

[0002]

2. Description of the Related Art A ceramic oxygen sensor using yttrium (Y) -stabilized zirconium oxide (ZrO2 --Y2 O3) as an ion conductor (solid electrolyte) has been known. In the bulk type ceramic oxygen sensor, a ZrO2 --Y2 O3 ionic conductor bulk is obtained by press molding and firing, and a porous Pt electrode having a catalytic action is formed by printing and firing Pt paste.

[0003]

In such a ceramic oxygen sensor, in order to obtain the limiting current characteristic, it is necessary to provide a gas diffusion hole for supplying oxygen gas to the cathode electrode in a diffusion rate-determining manner. Various methods have been conventionally proposed to form the gas diffusion holes, but a complicated process such as forming a hole in the substrate is required, and variations in element characteristics due to the complicated process. It was also big.

It is an object of the present invention to provide a method of manufacturing a limiting current type oxygen sensor, which is capable of obtaining excellent characteristics with little variation in a simple process.

[0005]

A method of manufacturing a limiting current type oxygen sensor according to the present invention comprises forming an anode electrode and a cathode electrode on an ion conductive substrate and highly decomposing on the surface of the substrate on which the cathode electrode is formed. After placing a reticulated body made of dot material and printing a crystallized glass material on it, by decomposing the reticulated body while crystallizing the crystallized glass material by heat treatment, the bottom is porous. It is characterized in that a crystallized glass sealing layer having a gas diffusion layer is formed. Here, the high decomposition point material is carbon fiber, graphite, boron-containing carbon, or the like, which decomposes into gas and volatilizes and decomposes above the softening temperature of the crystallized glass material and below the crystallization temperature.

[0006]

According to the present invention, when the crystallized glass sealing layer is formed on the ion conductive substrate having the electrodes formed thereon, the reticulate body made of a high decomposition point material such as carbon fiber is printed prior to printing the glass material. And is baked at a temperature above the glass transition temperature and below the softening temperature of the crystallized glass. By resolving and volatilizing the reticulate body while crystallizing the glass in this firing process, a reticulated gas diffusion layer can be formed at the bottom of the crystallized glass sealing layer. According to the method of the present invention, a mesh-shaped gas diffusion layer can be formed very easily. In addition, since a mesh of a high decomposition point material is used as a material for forming the gas diffusion layer, a method of forming a large number of elements on a large substrate and dicing the element has excellent characteristics with little variation. It can be mass-produced.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a manufacturing process of a limiting current type oxygen sensor according to an embodiment of the present invention. The ion conductive substrate 1 has, for example, an area of 10 cm × 10 cm and a thickness of 0.
It is a plate with a large area of 15 mm ZrO2-8% Y2O3.
It is created by the doctor blade method. As shown in FIG. 1A, a porous Pt anode electrode 2 is formed on one surface of the substrate 1, and a porous Pt cathode electrode 3 is formed on the other surface of the substrate 1 so as to face it. These Pt electrodes 2 and 3 are
It is formed by printing and firing Pt paste.

After that, a heater electrode 5 is disposed on the substrate surface on the side where the cathode electrode 3 is formed so as to surround the cathode electrode 3 with an insulating layer 4 interposed therebetween. The insulating layer 4 is, for example, crystallized glass, and the heater electrode 5 is the same Pt electrode as the anode and cathode electrodes 2 and 3. Next, the cathode electrode 3
Further, a reticulated body (hereinafter referred to as a net-shaped carbon fiber) 6 made of carbon fiber, which is an inorganic material having a high decomposition point, is placed on the substrate surface on the side where the heater electrode 5 is formed, and the crystallized glass material 7 is placed thereon. Screen print.

After that, heat treatment and baking are performed. The firing temperature is
The temperature is set in the range from the transition temperature of the glass material 7 to the softening temperature and below, and above the decomposition point of the net-like carbon fiber 6, for example, about 1000 ° C. As a result, the glass material 7 containing the nucleating agent is crystallized to form the crystallized glass sealing layer 8 as shown in FIG. 1 (b). At the same time as this firing process, the net-like carbon fibers 6 are decomposed and volatilized. As the net carbon fiber 6 is decomposed and volatilized, a porous gas diffusion layer 9 is formed at the bottom of the crystallized glass sealing layer 8 as shown in FIG. 1 (b).

Finally, dicing is performed at the position shown by the arrow in FIG. 1B to separate each sensor element of about 3 mm × 3 mm.
2 (a) and 2 (b) are a plan view and a sectional view taken along the line AA 'of each of the sensor elements thus formed separately. The anode electrode 2, the cathode electrode 3 and the heater electrode 5 are connected to respective electrode terminals 11, 12, 13, 1 as shown in the figure.
4 is patterned so as to be led out to one side of the element which is not covered with the crystallized glass sealing layer 8. The gas diffusion layer 9 is continuously formed along the interface between the cathode electrode 3 and the heater electrode 5 at the bottom of the crystallized glass sealing layer 8, and oxygen gas diffuses from the side surface of the element substrate through the gas diffusion layer 9. It is supplied at a rate-determining rate. Thereby, the limiting current characteristic is obtained.

According to this embodiment, an oxygen sensor having a mesh-like lateral hole type gas diffusion layer is formed by a simple process of screen-printing and firing a crystallized glass material after placing net carbon fibers. can get. This oxygen sensor is 400
When measured in an air atmosphere at ℃, a very clear limiting current characteristic was observed. The characteristics of the sensor element made from the same substrate had small variations and had good reproducibility.

FIG. 3 shows a manufacturing process of another embodiment of the present invention. The parts corresponding to those in the previous embodiment are designated by the same reference numerals as those in the previous embodiment, and detailed description thereof will be omitted. In this embodiment, as shown in FIG. 3A, the Pt anode electrode 2 and the Pt cathode electrode 3 arranged laterally adjacent to one surface of the ion conductive substrate 1 are formed by screen printing and firing. is doing. Then, as in the previous example, the Pt heater electrode 5 was formed via the insulating layer 4 such as crystallized glass, the net-like carbon fiber 6 was placed thereon, and the crystallized glass material 7 was screen-printed thereon. Bake. At this time, the net-like carbon fibers 6 are oxidized and decomposed by heating, and volatilized and disappear. Then, as shown in FIG. 3 (b), a porous gas diffusion layer 9 is formed at the bottom of the crystallized glass sealing layer 8 together with it. Finally, dicing is performed at the position of the arrow shown in FIG.

4 (a) and 4 (b) are a plan view and a sectional view taken along the line AA 'of the sensor element obtained in this embodiment. According to this embodiment, as in the previous embodiment, it is possible to obtain a limiting current type oxygen sensor having excellent characteristics with a very simple process and little variation between elements.

The present invention is not limited to the above embodiment. For example, in the examples, in order to form the gas diffusion layer at the same time in the step of firing the crystallized glass, the net-like carbon fiber is used, but the same reticulate body is formed by using another high decomposition point material such as graphite. A gas diffusion layer can be formed on the. Further, in the examples, the ion conductive plate-like body was used as the substrate, but the ion conductive substrate referred to in the present invention is, for example, Z
It also includes an insulating substrate such as rO2 -BN as a starting substrate on which an ion conductor film is formed.

[0015]

As described above, according to the method of the present invention, a lateral hole type gas diffusion layer is formed by decomposing and volatilizing a reticulated body made of a material having a high decomposition point during the firing of crystallized glass. It is possible to obtain an oxygen sensor which can be easily formed and exhibits a limiting current characteristic with little variation.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a manufacturing process of an embodiment of the present invention.

FIG. 2 is a plan view and a sectional view of a sensor element according to the same embodiment.

FIG. 3 is a cross-sectional view showing a manufacturing process of another embodiment.

FIG. 4 is a plan view and a sectional view of a sensor element according to the same embodiment.

[Explanation of symbols]

1 ... Ion conductive substrate, 2 ... Pt anode electrode, 3 ... P
t cathode electrode, 4 ... Insulating layer, 5 ... Pt heater electrode, 6
... Net carbon fiber, 7 ... Crystallized glass material, 8 ... Crystallized glass sealing layer, 9 ... Gas diffusion layer. 11, 12, 1
3, 14 ... Electrode terminals.

Front page continuation (72) Inventor Issei Ishibashi 1-5-1, Kiba, Koto-ku, Tokyo Fujikura Ltd. (72) Inventor Yoshinori Kato 1-1-5, Kiba, Koto-ku, Tokyo Fujikura Ltd. Within

Claims (1)

[Claims] 1. A step of forming an anode electrode and a cathode electrode on an ion conductive substrate, and placing a net made of a high decomposition point material on the surface of the substrate on which the cathode electrode is formed, and crystallizing on the net. Forming a crystallized glass encapsulation layer having a porous gas diffusion layer at the bottom by the step of printing the crystallized glass material and by performing heat treatment to decompose the reticulate body while crystallizing the crystallized glass material And the process of
A method for manufacturing a limiting current type oxygen sensor, comprising: