JPH0915196A - Production of oxygen sensor - Google Patents

Abstract

PURPOSE: To provide an oxygen sensor having a diffusion rate layer equipped with fine open voids. CONSTITUTION: Electrodes 6, 7 are laminated on the upper and rear surfaces of a second sheet 2 being a sheet for a thin-walled solid electrolyte layer formed of a zirconia powder. A sheet 4 for forming a thin-walled diffusion rate layer formed from a mixture obtained by mixing a carbon powder with the zirconia powder is used to coat the electrode 6. When the whole is baked at about 1450 deg.C, the carbon powder of the sheet 4 is burnt off to form voids and the sheet 4 becomes the diffusion rate layer 4A. The atmosphere is introduced into atmosphere introducing pares 31 and exhaust gas is introduced into the diffusion rate layer 4A to detect the concn. of oxygen.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an oxygen sensor. The oxygen sensor according to the present invention is used, for example, for air-fuel ratio control of an internal combustion engine of a vehicle, exhaust gas purification, combustion control of a boiler, and the like.

[0002]

2. Description of the Related Art Conventionally, an oxygen sensor for detecting oxygen has been provided. As the oxygen sensor, as shown in FIG. 6, a solid electrolyte layer 100 having oxygen ion permeability,
Some solid electrolyte layers 100 are provided with a pair of electrodes 101 and 102 respectively coated on both sides, and a diffusion rate controlling layer 103 coated on the electrode 102 serving as a cathode.

The basic principle of the oxygen sensor will be described by taking the case of detecting the oxygen concentration contained in the exhaust gas as an example. That is, the diffusion-controlling layer 103 is arranged on the exhaust gas side and the electrode 101, which is the anode, is arranged on the atmosphere side. Then, when a voltage is applied between the electrodes 101 and 102 at a certain temperature or higher, oxygen molecules emit electrons and are ionized on the side of the electrode 102 that is the cathode. Further, the ionized oxygen moves inside the solid electrolyte layer 100 toward the electrode 101 serving as the anode, and becomes oxygen molecules again at the electrode 101 serving as the anode. Then, as described above, by covering the electrode 102, which is the cathode, with the diffusion-controlling layer 103 that restricts the arrival of oxygen molecules in the exhaust gas, an output current proportional to the oxygen concentration of the exhaust gas is obtained,
This makes it possible to obtain the oxygen concentration of the exhaust gas.

A large number of minute holes are formed in the diffusion-controlling layer 103 for passage of exhaust gas. In order to obtain a good diffusion rate controlling property, it is not preferable that the size of the holes is too small or too large, and generally 400 to 800.
It is said that about angstroms, particularly about 500 to 700 angstroms are preferable. By the way, as a manufacturing method for manufacturing the oxygen sensor having the diffusion-controlling layer 103 described above, JP-A-60-107560 discloses that a sheet for solid electrolyte is coated with a ceramic slurry and the slurry is coated with liquid nitrogen. A technique is disclosed in which water in a frozen state is sublimated by freezing and then decompressing, and a diffusion-controlling layer having continuous pores is formed in association with the sublimation.
Furthermore, in this publication, resin is mixed with ceramic slurry,
A technique is disclosed in which the resin is burned off after coating the slurry to form pores.

Further, in Japanese Patent Laid-Open No. 2-141653,
A technique for forming the above diffusion controlling layer having pores by a ceramic powder spraying method is disclosed.

[0006]

SUMMARY OF THE INVENTION The present invention provides a method of manufacturing an oxygen sensor having a diffusion coating layer having continuous minute pores, which is different from the method described above. This is an issue. In order to achieve the above object, the present inventor has eagerly developed an oxygen sensor having a diffusion-controlling layer. Then, particles of polyvinyl alcohol (PVA) having a small particle diameter are included in a ceramic slurry together with water as a solvent, and are removed together with water by burning in a firing process, thereby forming a diffusion rate controlling layer having pores. Developed the technology to do. However, although this technique can form relatively small pores, the particles tend to increase in size during the manufacturing process due to swelling, agglomeration, and the like, and the size tends to vary due to swelling and agglomeration. Therefore, according to the above-mentioned technique, there is a limit in forming a diffusion-controlling layer having fine and uniform pores and having a good diffusion-controlling performance.

[0007]

Therefore, the present inventor adopts carbon-based powder particles that are insoluble in all commonly used solvents such as water and organic solvents, to form fine and uniform pores. The present inventors have completed the method of the present invention by finding out that it is advantageous to form a diffusion-controlling layer having a good diffusion-controlling property and confirming it by a test.

That is, in the method for manufacturing an oxygen sensor according to the present invention, both surfaces of a sheet for a solid electrolyte layer, which is a solid electrolyte layer having oxygen ion permeability, and a fixed electrolyte layer sheet, are coated. An oxygen sensor by sequentially performing a laminating step for obtaining an element laminated body including a pair of electrodes and a diffusion controlling layer forming sheet covered with one electrode, and a firing step for firing the element laminated body. In the method for producing an oxygen sensor, the sheet for forming a diffusion-controlling layer of an element laminate contains carbon-based powder particles, burns out the carbon-based powder particles in the firing step, and creates continuous pores. The diffusion-controlling layer forming sheet is formed into a diffusion-controlling layer.

[0009]

According to the method of the present invention, the sheet for forming the diffusion-controlling layer of the element laminate contains carbon-based powder particles. As the carbon-based powder particles, carbonaceous particles and graphite particles can be adopted. The carbonaceous powder is generally referred to as amorphous carbon that does not show a clear crystalline state, or microcrystalline carbon that has a low degree of crystal growth.

Carbon powder particles such as carbon black powder and natural graphite powder can be used. The average particle diameter of the carbon-based powder particles forming the pores is appropriately changed according to the type of oxygen sensor, the desired diameter of the pores, etc., but the upper limit of the average particle diameter is 1.5 μm, 1.0 μm, 0. It can be set to 0.8 μm, and the lower limit values can be set to 0.2 μm, 0.4 μm, and 0.6 μm. For example, the average particle size of the carbon-based powder particles can be 0.7 μm to 0.9 μm, for example 0.8 μm.

The solid electrolyte layer sheet can be generally formed of zirconia powder. The diffusion-controlling layer-forming sheet can be usually formed of zirconia powder. Since the particle size of zirconia powder is considered to affect the size of pores,
The average particle size of the zirconia powder is appropriately changed according to the type of oxygen sensor. Therefore, the upper limit of the average particle size of zirconia powder can be 0.5 μm, 0.3 μm, 0.2 μm,
The lower limit can be set to 0.05 μm and 0.08 μm. For example, the average particle size of zirconia powder is 0.07 μm to 0.2 μm.
For example, it can be 0.1 μm.

According to the method of the present invention, in the firing step,
The carbon-based powder particles contained in the diffusion-controlling layer-forming sheet are burnt out in the firing step. Thereby, continuous voids are formed, and the diffusion-controlling-layer-forming sheet becomes the diffusion-controlling layer. The above-mentioned firing temperature is appropriately selected depending on the type of the sheet for forming the solid electrolyte layer or the sheet for forming the diffusion-controlling layer, but in the case of zirconia, it is generally 1400 to 1500.
It can be about ° C.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The method of the present invention can be carried out in the following modes. The sheet for the solid electrolyte layer contains zirconia as a main component. The diffusion-controlling-layer-forming sheet contains zirconia as a main component, and contains carbon-based powder particles having an average particle size of about 0.8 μm.

[0014]

Embodiments of the present invention will be described below. First, FIG. 1 is a perspective view of the element laminated body 8 in the manufacturing process. FIG. 2 shows a cross section of the element laminate 8. First, the manufacture of the element stack 8 will be described. 100 parts by weight of zirconia powder (average particle size: 0.1 μm) as a raw material powder, 15 parts by weight of ion-exchanged water as a solvent, 4 parts by weight of methyl cellulose as an organic binder, and 7 parts by weight of glycerin as a surfactant. prepare. Then, these are uniformly stirred and mixed with a stirrer to form a first mixture. Then, the first mixture is charged into an extrusion molding machine, and the sheet-shaped continuous material is discharged from the discharge port thereof by the operation of the extrusion molding machine.

The above continuous material is dried by a dryer,
Punching into a predetermined shape with a punching machine, thereby obtaining the first sheet 1, the second sheet 2 functioning as a solid electrolyte layer sheet, and the structural material sheet 3 shown in FIG. For example, the thickness of the first sheet 1 can be 0.6 to 1.3 mm. Second sheet 2
Can have a thickness of 0.1 to 0.3 mm. Structural material sheet 3
Can have a thickness of 0.6 to 1.3 mm. Structural material sheet 3
Is an inner wall surface 3 forming an air introduction hole 3i communicating with the atmosphere.
a to 3c.

Next, carbon powder having an average particle diameter of 0.8 μm (specifically, amorphous carbon powder) is added to the material having the same composition as the above-mentioned first kneaded material. The amount of carbon powder added was 10 parts by weight with respect to 100 parts by weight of zirconia powder. The preferable addition amount is 3 to 30 parts by weight, particularly 6 to 20 parts by weight. Then, these are uniformly mixed and stirred to form a second mixture. This second mixture is molded into a predetermined thickness with an extruder to obtain a sheet-shaped material for the diffusion controlling layer.

The above diffusion controlling layer material is dried by a dryer and punched into a predetermined shape by a punching machine to obtain a diffusion controlling layer sheet 4 shown in FIG. Therefore, the diffusion-controlling layer sheet 4 contains carbon powder. Next, platinum paste is applied to the front and back of the second sheet 2 by a screen printing method to stack the electrodes 6 and 7.

Next, the lower sheet 1 and the structural sheet 3 are watered.
About 2kgf / cm ^TwoPressurize with
You. Furthermore, a sheet 4 for diffusion controlling layer coated with water is laminated.
Then, the element laminated body 8 is obtained. Next, oxygen content
In the air as an atmosphere, the element laminated body 8 was
Heating in the firing pattern (including the degreasing process)
Oil and bake. As a result, the second sheet 2 is permeable to oxygen ions.
It becomes a solid electrolyte layer having a transient property. Also in the firing process
The carbon powder particles react with oxygen components and burn out.
The continuous voids are formed, and the diffusion-controlling layer forming sheet is formed.
4 is the diffusion rate controlling layer. This produces an oxygen sensor
Is done.

The firing pattern is as follows. Room temperature to 450 ° C 20 ° C / hour 450 to 1450 ° C 50 ° C / hour 1450 ° C 1 hour hold 1450 ° C to room temperature 200 ° C / hour When detecting the oxygen concentration of exhaust gas, the above Like
The manufactured oxygen sensor-9 was set in the test device shown in FIG.
To The oxygen sensor-9 is connected through a resistor 91 and a voltmeter 92.
Connected to the DC power source 90. The oxygen sensor-9
Test chamber 9 between the exhaust gas introduction path 96 and the atmosphere communication hole 97
It is located at 8. Application of oxygen sensor-9 in this state
When the voltage is gradually increased, the saturation characteristics as shown in Fig. 5 are obtained.
The lines A1, A2, A3 are obtained. Marked on the saturation characteristic line A1
When the applied voltage is Vo, the output current is I ₁It is. Saturation characteristic line
In A2, the output current is I when the applied voltage is Vo._TwoIt is.
In the saturation characteristic line A3, the output current is I when the applied voltage is Vo.
_ThreeIt is. Since such saturation characteristics are obtained, diffusion
The diffusion-controlling layer 4A having pores with rate-controlling property was obtained.
Is confirmed.

As described above, according to this embodiment, the diffusion-controlling-layer-forming sheet 4 of the element laminate 8 contains carbon powder, and the carbon powder particles are burned out in the firing step. , Continuous voids are formed, and the diffusion-controlling-layer-forming sheet 4 becomes a diffusion-controlling layer. Here, the particles of the carbon powder have a small particle diameter, and the sphericity of the particle shape is high. Furthermore, the particles of carbon powder are basically insoluble in ion-exchanged water as a solvent.

Therefore, unlike the above-described polyvinyl alcohol (PVA) and the like, it is possible to avoid the phenomenon of increasing the particle size due to swelling, aggregation and the like of the powder particles. Therefore, it is advantageous to incorporate fine particles into the diffusion-controlling layer forming sheet 4. Therefore, the pores formed by the burning of the carbon powder in the firing step are minute. Therefore, the diffusion-controlling layer 4A having a good diffusion-controlling property can be obtained.

According to this embodiment, the pore size of the diffusion-controlling layer 4A is 2 when measured by the impregnation porosity method.
It was 00 to 1500 angstroms, and the average was about 660 angstroms. This measuring method is a method in which mercury is impregnated into the holes deaerated under high vacuum by pressurization. According to the present embodiment, the carbon powder includes a form that is completely burned in the firing process, or a form in which the carbon powder is largely burned but a part thereof remains.

[0023]

According to the method of the present invention, since carbon-based powder particles are used, it is advantageous to manufacture an oxygen sensor having a diffusion-controlling layer having micropores of uniform size. According to the method of the present invention, since the carbon-based powder particles are burned off in the firing step required in the production of the oxygen sensor, it is not necessary to separately provide the pore forming step, and the productivity is good. .

[Brief description of the drawings]

FIG. 1 is a perspective view of an element stack.

FIG. 2 is a cross-sectional view of a main part of an element laminated body.

FIG. 3 is a plan view of a first sheet, a second sheet, a structural material sheet and the like.

FIG. 4 is a configuration diagram of a test apparatus.

FIG. 5 is a graph showing the relationship between applied voltage and output current.

FIG. 6 is a configuration diagram according to a conventional technique for explaining the principle of an oxygen sensor.

[Explanation of symbols]

In the figure, 2 is a second sheet (sheet for solid electrolyte layer), 4 is a sheet for diffusion controlling layer, 6 and 7 are electrodes, and 8 is an element laminate.

Claims (1)

[Claims] 1. A sheet for a solid electrolyte layer which becomes a solid electrolyte layer having oxygen ion permeability, a pair of electrodes respectively coated on both surfaces of the fixed electrolyte layer sheet, and one of the electrodes. Manufacture of an oxygen sensor, in which an oxygen sensor is manufactured by sequentially performing a laminating step for obtaining an element laminated body including a coated diffusion controlling layer forming sheet and a firing step for firing the element laminated body. In the method, the sheet for forming the diffusion-controlling layer of the element laminate contains carbon-based powder particles, and the carbon-based powder particles are burnt out in the firing step to form continuous pores and the diffusion. A method for manufacturing an oxygen sensor, characterized in that the rate controlling layer forming sheet is a diffusion rate controlling layer.