JPS62263458A - Oxygen sensor element - Google Patents

Abstract

PURPOSE:To suppress the irregularity of a limit current value, by providing an adjusting means for adjusting the diameter of a diffusion hole in which a wire material is inserted and a seal layer. CONSTITUTION:A wire material 9 for adjusting the diameter of the diffusion hole 8 of a diffusion resistor 7 is inserted in said diffusion hole 8. The material quantity of the wire material has m.p. at least equal to or higher than the operation temp. of a sensor element and excellent oxidation resistance because the sensor element is heated to operable temp. Next, a diffusion resistor holding member (or resistor 7) is provided with a seal layer 10 so as to form a constant space from the surface of the cathode 2b of a solid electrolyte body 1. The seal layer 10 is constituted of a glass paste 10a and heat resistant fine particles 10b. The material quality of the paste 10a pref. has coefficient of thermal expansion equal to that of the electrolyte body 1 or the member 6 (or resistor 7). A material having m.p. higher than the working temp. of the paste 10a is adapted to the fine particles 10b. By this method, the irregularity of the limit current value of the sensor element can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an oxygen sensor element for detecting oxygen concentration in an atmospheric gas, and in particular to a limiting current type oxygen sensor element using an oxygen ion conductive solid electrolyte. It is.

BACKGROUND OF THE INVENTION Conventionally, this type of oxygen sensor element is as shown in FIG.
For example, Pt is applied to both sides of an oxygen ion conductive solid electrolyte body 1 (hereinafter referred to as solid electrolyte body) made of ZrO2, y2o3 material.
, a porous electrode 2 (anode 2a, cathode 2b) made of conductive paste such as Pd, and further the cathode 2b
(1111 solid electrolyte body 1 surface and diffusion resistor 4 provided with diffusion holes 3 with a diameter of 100 μm or less to restrict oxygen inflow)
It has a structure in which the glass layer 5 is bonded with a vitreous adhesive and a layer 5 is provided.

In this configuration, after heating the oxygen sensor element to a temperature at which it can operate as an oxygen sensor, when a DC voltage is applied between the electrodes 2, an ionization reaction of oxygen molecules occurs on the surface of the cathode 2b, and the ionized oxygen ions are transferred to the solid electrolyte body 1. Inside positive i2
Move towards a. At this time, the inflow of atmospheric gas is restricted by the diffusion holes 3 provided in the diffusion resistor 4, and the inflow of oxygen into the cathode 2b becomes diffusion rate-determining. The generated current becomes constant after a certain voltage as the applied voltage increases. This constant current is the limiting current, and since this is proportional to changes in oxygen concentration in the atmospheric gas, changes in oxygen concentration can be measured by detecting this limiting current.

Problems to be Solved by the Invention However, the material of the diffused resistor 4 is often limited to ceramics in terms of heat resistance and corrosion resistance. When a ceramic material is used as the diffused resistor 4, the diameter is 10
It is practically difficult to drill diffusion holes of 0 μm or less with precision, and there is a problem in that the value of the limiting current ultimately varies greatly due to variations that occur in each process of assembling the oxygen sensor element. Ta.

Furthermore, although a glassy adhesive is used to bond the diffused resistor 4 and the solid electrolyte 1, the wettability of the glass at the adhesive interface deteriorates when the two are heated and fused together without any load. There has been a problem in that communicating cavities are likely to occur at the bonded interface, and atmospheric gas leaks from these cavities, making it impossible to obtain limiting current characteristics. On the other hand, if the adhesive is applied with a load, the glass will flow into the electrode 2 (negative electrode 2b) and cover the electrode surface, causing the dissociation and adsorption ability of oxygen to be suppressed, increasing the variation in the limiting current value. There was a problem.

The present invention has been made to solve these conventional problems, and aims to provide an oxygen sensor element that suppresses variations in the limiting current value and can always provide stable limiting current characteristics.

Means for Solving the Problems In order to solve the problems described above, the oxygen sensor element of the present invention has the following features:
A means for adjusting the hole diameter by inserting a wire into a diffusion hole formed in the diffusion resistor, and a glass paste and a working temperature of the glass paste so as to form a certain space between the diffusion resistor and the solid electrolyte body. It has a structure in which a sealing layer is provided which is made of a mixture of heat-resistant particles having a higher melting point.

Effects According to the present invention, with the above-described configuration, even if the diameter of the diffusion hole formed in the diffusion resistor varies greatly, a constant diameter can be obtained by inserting a wire corresponding to the variation into the diffusion hole. In addition, even if heat fusion is applied under load to improve the adhesion of the Sea) V layer, fine particles with a melting point higher than the working temperature of the glass paste contained in the Sea W layer support the diffusion resistor (in a certain space). ), thereby preventing the molten glass from flowing out onto the electrode surface due to compression.

Embodiments Hereinafter, embodiments of the present invention will be described based on the accompanying drawings.

FIG. 1 is a schematic cross-sectional view of an oxygen sensor element that is an embodiment of the present invention. In the same figure, 1 is an oxygen ion conductive solid electrolyte body, ZrO2・Y 203, ZrO2・C
aO1Zr02 ・Mho%CaO2・Y2O3, Ce
O2・CaO1Th02・Y2O3, Th02・CaO
, B i 203 ・E r 203, B i 203
・Y2O3, B i 203 ・Nb, solid solutions such as 205 can be mentioned, but are not particularly limited. A pair of electrodes 2 are formed on both sides of the solid electrolyte body 1 . Materials for the electrode 2 include metals whose main components are Pt, Pd, Au, etc., which have excellent ability to dissociate (ionize) oxygen molecules, and porous materials are particularly preferred.

Reference numeral 6 denotes a diffusion resistor holding member, into which a diffusion resistor 7 provided with diffusion holes 8 for atmospheric gas is inserted. Since the materials of the diffusion resistor holding member 6 and the diffusion resistor 7 are bonded to the solid electrolyte body 1, materials having the same coefficient of thermal expansion as the solid electrolyte body 1 are used. For example, if the solid electrolyte body 1 is
When a solid solution of rO2/Y2O3 is applied, the diffused resistor holding member 6 is made of ZrO2/Y2O3 ceramic, F/L.
/Stellite, K2O・PbO・Si○2 thread galame glass 20-2() Pb()Si02 series galanu, Na2
( ) BaO・5i02 glass or the like is applied. Further, the diffusion resistor 7 is also preferably made of the same material as the diffusion resistor holding member, but is preferably made of a glass-based material that allows easy processing of the diffusion holes 8. In the embodiment, the diffused resistor holding member 6 and the diffused resistor 7 are distinguished, but they may be integrated.

A wire 9 is inserted into the diffusion hole 8 of the diffusion resistor 7 to adjust the diameter of the diffusion hole. Since the material of the wire 9 is heated to a temperature at which the oxygen sensor element can operate, it is preferable to use a material that has a melting point at least higher than the operating temperature and has excellent oxidation resistance, such as PT, Au, Ic tenene, or glass fiber. , ceramic fiber, etc.

Next, a sealing layer 10 is provided on the aforementioned diffused resistor holding member 6 (or diffused resistor 7) so that a certain space is formed with the surface of the shadow W2b of the solid electrolyte body 1. This sealing layer 10 is composed of glass paste 10a and heat-resistant fine particles 10b. As mentioned above, the material of the glass paste should preferably have a coefficient of thermal expansion equivalent to that of the solid electrolyte body 1 and the diffused resistor holding member 6 (t or diffused resistor 7). Further, the heat-resistant fine particles 10b are made of a material having a melting point higher than the working temperature of the glass paste 10a, such as ZrO2, T
Metal oxide powder such as iO2, Ae203, Ba04
Examples include '102Si○2 series and SiO2 Gala 7 powder.

Next, its action and effects will be explained based on specific experimental examples.

The constituent materials and manufacturing method of the oxygen sensor element of the present invention are as follows.

Solid electrolyte body-Z r 02 ・Y2O3 (Y2O38
mo e%), 10X 10X0.4 mm Electrode-Pt paste Electrode diameter 6 mm A film thickness of approximately 5 mm was printed on both sides of the solid electrolyte by screen printing.
Forming a μm electrode film (firing temperature 850°C) Diffused resistor holding member - fustellite, outer diameter 10mm
, inner diameter 1 mm, thickness 0.8 mm, thermal expansion coefficient 10 x 1
0-6X°C Diffused resistor with 2O-Pbo/5i02 glass capillary, thermal expansion coefficient 9.5 x 10-6/'C outer diameter 1
mm, length 5mm, insert this capillary into the fully diffused resistor holding member and seal it with glass paste wire - Au wire, insert this wire into the capillary and adjust the diffusion hole diameter Seal layer - outer diameter 9mm, inner diameter 7mm, glass Paste-pb○, ZnO・B2O3 based glass beanute
Thermal expansion coefficient 9.7×10-6/C heat-resistant fine particles-BaO
・T i 02/5i02 series galame glass powder average about 5
1 g of 0μ Nigarasu paste was mixed with 10 m of heat-resistant fine particles, 9 was printed on the surface of the solid electrolyte body by screen printing, and a diffusion resistor holding member into which the diffusion resistor was inserted was combined with a load of approximately 50 g. and baked (firing temperature 450
°C) and form a sealing layer on the diffused resistor (glass capillary) during the manufacturing process.
Oxygen sensor elements were fabricated using two types of diffusion pore diameters: 90 μm and 130 μm. After pulling out the lead wire from the electrode of this oxygen sensor element, it was heated to 450°C in air and a DC voltage was applied between the electrodes.
．． The current generated within the range of 2.5 mm showed a constant value.

The current that shows this constant value is the limiting current, and the oxygen sensor element with a diffusion hole diameter of 90 μm is approximately 220 μA and 120 μm.
m was approximately 400 μA. This limiting current is approximately expressed by the following equation.

I g = K - S/e where Ie: limit current value: proportionality constant S: opening area of diffusion hole (capillary opening area) e: length of diffusion hole (capillary length) From the above equation, the oxygen sensor element It turns out that the reason why the limiting currents differ is due to the difference in the diameter of the diffusion holes, and if the diameters of the diffusion holes are made the same, the same limiting current can be obtained.

If the limiting current value is set to 100 μA, the diameter of the diffusion hole will be approximately 60 μm from the formula. The diameter of the diffusion hole and the Au inserted into it for the two types of oxygen sensor elements mentioned above.
! The diameter of the Au wire was calculated so that the space created by the difference in diameter of li would be approximately 60 μm in terms of diameter. As a result, the diameter of the diffusion pore of 120 μm was 104 μm.
Au m.

It was found that it is sufficient to insert an Au wire with a diameter of 67 μm into a hole having a diameter of 90 μm.

Therefore, when an Au wire having the diameter calculated for each of the oxygen sensor elements described above was inserted into the diffusion hole and the limiting current was measured in the same manner as described above, a value of about 100 μA was obtained for both. Therefore, even if the diameter of the diffusion hole provided in the diffusion resistor in the oxygen sensor element varies greatly, by inserting a wire such as an Au wire into the diffusion hole, it is possible to maintain a constant diameter, thereby suppressing variations in the limiting current value. At the same time, it becomes possible to set the desired limit current value.

In addition, the same procedure was carried out using wires made of Pt1 Nutenless, glass fiber, and ceramic fiber instead of the Au wire, and it was confirmed that almost the same effect as in the case of the Au wire was obtained.

Next, we examined the limiting current under the same conditions as above for an oxygen sensor element fabricated according to the oxygen sensor element manufacturing method described above, and an oxygen sensor element fabricated as a comparative example in which the sealing layer was made of only glass paste and with and without loading. Characteristics were evaluated. Note that the number of oxygen sensor elements manufactured was n = 1.
It was set to 0.

The results are shown in the table below.

Table Comparison of characteristics of each oxygen sensor element * In Comparative Example 1, in which all the pore diameters of the diffusion holes were the same, the reason why the resulting current value was low and the variation was large was that only the glass paste was heated and fused by applying weight. At this time, the glass flows out to the electrode surface (cathode side χ,
This is because the electrode surface was coated to suppress the ionization reaction of oxygen molecules, and it is thought that the value of the limiting current differed depending on the degree of coverage.

On the other hand, in Comparative Example 2, when C1 was heat-fused without applying any load, the wettability of the glass at the bonding interface deteriorated, and communicating cavities were likely to occur at the bonding interface. It is thought that atmospheric gas leaked from the cavity, impairing the function of the diffused resistor and preventing the limiting current characteristics from being obtained. In fact, as a result of optical microscopic observation, cavities were confirmed. Further, the reason why the variations in the devices with which the limiting current characteristics were obtained is large is thought to be due to the presence of minute cavities in the sealing layer.

The reason why the present invention was able to obtain a nearly constant limiting current characteristic at n=10°C is that the application of weight during bonding suppresses the formation of cavities at the bonding interface, and the sealing layer Since there is glass powder with a melting point higher than the working temperature of the adhesive, this powder particle supports the diffusion resistor holding member (or the diffusion resistor) and prevents the molten glass from flowing out to the electrode surface due to compression. This is thought to be due to the prevention of

In addition, instead of glass powder, Zr○2 powder, TlO2
The same procedure was carried out using Ae203 powder, and the same effect as that of the glass powder was obtained.

Effects of the Invention As described above, the oxygen sensor element of the present invention provides the following effects.

(1) By inserting a heat-resistant wire into the diffusion hole formed in the diffusion resistor, the diameter of the diffusion hole can be easily adjusted, so that the desired level of limiting current characteristics can be obtained, and the diameter of the diffusion hole can be easily adjusted. Even if there is a large variation during processing, by inserting a wire rod with a diameter that corresponds to this variation, variation in the limiting current value of the oxygen sensor element can be suppressed.

(2) Since the heat-resistant fine particles present in the C/L/layer and having a melting point higher than the working temperature of the glass paste support the diffused resistor holding member (or the diffused resistor), a load is applied. Even when heated and fused, it is possible to prevent the glass from flowing out to the electrode surface due to compression, and since the glass is loaded, the wetting of the glass at the bonding interface improves, suppressing the formation of cavities, and improving the limiting current characteristics of the oxygen sensor element. is always obtained stably.

(3) In the present invention, the diameter of the diffusion hole can be adjusted after the device is fabricated, so there is no need for strict control over dimensional accuracy in the process of forming the diffusion hole of the diffusion resistor, which simplifies the process and improves productivity. .

[Brief explanation of drawings]

FIG. 1 is a sectional view of an oxygen sensor element showing an embodiment of the present invention, and FIG. 2 is a sectional view of a conventional oxygen sensor element. 6... Diffused resistor holding member, 7... Diffused resistor, 9... Heat resistant wire, 10...
・Seal layer, 10a...Glass paste, 10
b...Fine particles. Name of agent: Patent attorney Toshio Nakao and 1 other person7-
One side main electrolyte body 2--11 Electrolyte 2a--Anode 2b-Cathode 6- Diffusion resistor holding member Fig. 1 7° Diffusion resistor 8-- Diffusion hole b 2a (-5-1 )

Claims (3)

[Claims] (1) An oxygen ion conductive solid electrolyte body having a pair of electrodes formed on both sides, a diffusion resistor having a gas diffusion hole located on one surface of the solid electrolyte body, and the solid electrolyte body. It consists of a sealing layer provided to form a certain space between the electrolyte body and the diffusion resistor, and a hole diameter adjusting means made of a wire inserted into the diffusion hole for adjusting the diameter of the diffusion hole. Oxygen sensor element. (2) The oxygen sensor element according to claim 1, wherein the sealing layer is made of a mixture of glass paste and heat-resistant fine particles having a melting point higher than the working temperature of the glass paste. (3) The oxygen sensor element according to claim 1, wherein the wire serving as the pore size adjusting means is made of one selected from the group consisting of Pt, Au, stainless steel, glass fiber, and ceramic fiber.