JPH0495766A - Manufacture of oxygen sensor - Google Patents

Abstract

PURPOSE:To avoid the formation of a hollow and the deterioration of an insulating layer part by a method wherein an organic precious metal ink is applied and baked onto a main body or the like of a solid electrolyte, and a plated layer is formed by plating on a part where a nucleus of precious metal is formed. CONSTITUTION:With using a transfer printing pad, an ink pattern part formed rectangular onto a transfer plate with an organic platinum ink of an organic platinum compound including an organic binder is transferred to the outer peripheral wall corresponding to a hole 11a at the tubular wall of a cylindrical main body 1A of a solid electrolyte, so that a film 4 for formation of a precious metal nucleus for a measuring electrode is formed. Moreover, the film 4 is baked for two hours at 700 deg.C, whereby a part 4A of the precious metal nucleus is formed. Thereafter, an insulating pipe 10 having the main body of the solid electrolyte with the precious metal nucleus is soaked into an electroless plating solution, thereby to form a plated layer 5 on the part 4A. Accordingly, a basic model of an oxygen sensor having an outer electrode 6 comprised of the forming part 4A and plated layer 5 on the forming part 4A is produced.

Description

Detailed Description of the Invention [Industrial Field of Application: 1] The present invention relates to a method for manufacturing an oxygen sensor, and more specifically, the present invention relates to a method for manufacturing an oxygen sensor, and more specifically, it has excellent adhesion of an electrode to a solid carp material body, and is accompanied by a method for manufacturing an oxygen sensor. The present invention relates to a method for manufacturing an oxygen sensor with excellent properties such as toxicity, insulation, productivity, and economic efficiency.

INDUSTRIAL APPLICATION This invention is utilized for a zirconia lambda sensor, an air-fuel ratio sensor, etc. in an internal combustion engine, various combustion equipment, etc., for example.

[Conventional technology]

Ceramic oxygen sensors are capable of detecting acid levels over a wide range, and have excellent characteristics such as quick response and the ability to be heated to high temperatures, making them suitable for combustion control, pollution measurement, etc. Widely used.

Such an oxygen sensor generally has electrodes such as a reference electrode and a measurement electrode formed on a predetermined portion of the solid electrolyte body.
Ru. As for the method of forming these electrodes, ■
A method of applying a paste mainly made of Pt onto an unfinished solid electrolyte body and firing it to form an electrode. ■ Forming an electrode by applying electroless plating with noble metal salt etc. to the area on the solid electrolyte body where the electrode is to be formed. It is known how to do it (
Special Publication No. 52-30699, Special Publication No. 59-2438
Publication No. 2, etc.).

[Problem to be solved by the invention]

However, in the conventional method (2) above, the sintering of the ceramic body and the formation of the electrode are performed by simultaneous firing, so the sintering temperature of the ceramic body becomes rate-determining. A hole is formed,
During use, it is easily affected by poisonous substances in the operating atmosphere. Further, in the electrode according to the conventional method (2), if a heat generating part is present on the surrounding main body with an insulating layer interposed therebetween, the insulation properties of the insulating layer part may be impaired.

Another possible method is to form electrodes by directly printing organic platinum paste on the solid electrolyte body, but with this method, it is difficult to obtain a sufficiently strong and adherent platinum film. The reason for this is, although not completely obvious, that the decomposition and desorption of the organic resin in the organic platinum paste and the sintering of the platinum proceed simultaneously during heat treatment, resulting in sintering that exceeds the adhesion to the solid electrolyte surface. This is thought to be due to the force acting on it. Further, in order to solve this problem, a glass component or the like must be added, but this method may impair the high catalytic activity required of the platinum film. In addition, the method of forming electrodes by directly printing organic platinum paste on the solid electrolyte body requires a large amount of platinum, which poses problems in economic terms. It is also inferior in workability.

The present invention solves the above-mentioned problems, and includes electrodes formed on a noble metal nucleation forming part formed of an organic noble metal ink (in particular, a noble metal content of 0.5 to 10% by weight) and a noble metal nucleation forming part formed thereon. The present invention provides a method for manufacturing an oxygen sensor that has excellent adhesion of the electrode to the solid electrolyte body by being composed of a plating layer, and has excellent properties such as toxicity resistance, insulation properties, and productivity. be.

Go 11! Means for Solving Problem i] The method for manufacturing an oxygen sensor according to the Suigun 1 invention includes a first step of forming an electrode on a solid electrolyte body, and a second step of forming an electrode protective layer that covers and protects the electrode. In the method for manufacturing an oxygen sensor, the first step includes forming a coating film made of an organic noble metal ink containing an organic noble metal compound on the solid electrolyte body, and then baking the coating film to attach noble metal nuclei. forming a forming part, and then forming a plating layer on the noble metal nucleating forming part by a plating method, so that the pre-disposed noble metal nucleating part is composed of the forming part and the plating layer formed on the forming part. The method is characterized in that the electrode is formed.

The above-mentioned "solid electrolyte main body" may be anything as long as it has ionic conductivity, for example, Zr0z -Y20s, Zr
A sintered body made of partially stabilized O2CaO or stabilized zirconia can be used. Further, the overall shape is not particularly limited, and examples thereof include a bottomed cylindrical body and a flat plate-like body. Further, the wall thickness is not particularly limited.

The "noble metal element" in the "organic noble metal compound" is one that has catalytic activity, and specifically includes Ag, Au, and platinum group elements (Ru, Os%Rh, Ir5Pd, Pt). Depending on the purpose and use, organometallic compounds containing one or more noble metal elements can be selected and used. Further, as shown in the second invention, the noble metal content in the organic noble metal ink may be 0.5 to 10% by weight (hereinafter simply referred to as "%") based on the total amount of the organic noble metal ink. preferable. 0.5
%, in the case of no vortex, too few nuclei are formed, so the electroless reaction rate during plating is slow, and there is a gap in practical use. On the other hand, if it exceeds 10%, the firing reaction of the noble metal proceeds at the same time as the organic resin comes out during sintering, making it impossible to obtain sufficient film strength of the plating layer.

The "baking" is performed to form a nucleus for activation, that is, a noble metal nucleus, on the solid electrolyte body using the organic noble metal ink containing the "organic noble metal compound." Here, "nuclei" refers to shaped bodies scattered mainly in the form of islands on the main body, and acts as a reduction reaction catalyst during the electroless plating reaction, but their size and shape are not particularly limited. . The nucleus is usually an independent hemispherical body with a diameter of 0.1 to 0.8 μm, but several hemispherical bodies may be overlapped. In addition, the baking conditions such as temperature and heating time are as follows.
It is determined depending on the type of organic noble metal ink, solid electrolyte body, purpose of use of the oxygen sensor, etc. Furthermore, the formation of a coating film of organic noble metal ink on the solid electrolyte body, etc. can be performed by screen printing, transfer, etc., but especially in the case of transfer, it is necessary to more accurately apply the coating film to the desired position on the curved surface. can be formed.

The "noble metal nucleation forming part" refers to a portion (region) where the "nuclei" are gathered.

The "plated layer" is deposited mainly on noble metal nuclei that are not connected to each other, and is formed in a layered manner by connecting these noble metal nuclei. Therefore, although the formation of the noble metal core alone does not result in conduction, the formation of this plating layer causes it to function as an electrode. Further, this plating layer does not necessarily have to be made of the same material as the noble metal nucleation forming part, and may be made of other kinds of noble metals, or even metals other than noble metals such as Ni. Note that if this material is of the same type, it has excellent adhesion, and if it is a noble metal material, it has excellent catalytic activity.

[Effect]

In the present invention, first, an organic noble metal ink is applied onto a solid electrolyte body, etc., and is baked, thereby forming an island-shaped noble metal core in firm adhesion. Next, a plating layer is formed by a plating method on the area where the noble metal nuclei have gathered, that is, on the noble metal nucleation formation portion. In this case, this plated layer also obtains a strong bond with the solid electrolyte main body through the noble metal nucleation forming portion. Therefore, the electrode made of the noble metal nucleation forming portion and the plating layer formed thereon has excellent adhesion to the solid electrolyte body.

In this way, there is no need to worry about the formation of a large number of pores in the formed electrode part, and the insulation properties of the insulating layer part will not be impaired, so it maintains sufficient performance as an oxygen sensor. I will do it.

Furthermore, since the electrodes are not discontinuous, it is not necessary to bake several layers, which is excellent in terms of productivity. Also,
It is also easy to reduce the amount of expensive organic noble metals used, which is excellent in terms of economy.

Further, to form a gap in which a plating layer is to be formed, electroless plating is performed by placing a solid electrolyte body or the like in which a noble metal is planted in a plating liquid tank containing a noble metal compound, for example. As a result, a plating layer is formed on the noble metal nucleation forming portion. Therefore, by forming the noble metal core forming portion into a desired shape, masking during plating becomes unnecessary.

〔Example〕

The present invention will be clarified by examples below.

(1) Preparation of test piece ■Product Nα1 As shown in Figure 1, Zr0-YzO with a thickness of 0.3 mm
−On one side of the green sheet (on the inside side),
Pt paste was applied by a printing method to form a coating film for the inner electrode (width = 2.6 mm, length = 6.5 mm, thickness = 15 μm).
) 2 and the coating film 31 for the inner lead drawer part connected to this
was formed. Also, on the other side of this green sheet (
Excluding the part that will become the outer electrode part 6 (on the outer surface),
Alumina paste was applied by a printing method to form a first insulating layer coating M8. Further, a coating film 32 for outer lead drawer portions is applied to a position corresponding to the coating film 31 for inner lead drawer portions on this first insulating layer coating film 8 in the same manner as the coating film for inner lead drawer portions. was formed. Furthermore, alumina paste was applied to one end of the outer lead drawer part coating film 32 (the part connected to the outer electrode 6) and a part other than the part where the outer electrode was to be formed, to form a second insulating layer coating film 9. . In addition, in order to provide stronger adhesion of the plating film to the part that will become the outer electrode 6, particles made of the same material as the solid electrolyte used for the green sheet (average particle diameter 50-6
0 μm) is applied.

In this case, the blending ratio (weight ratio) of zirconia particles and zirconia powder is 5:5 to 8:2, and the particles are 100
It is more preferable to use a material calcined at a temperature of 0 to 1350° C. than to use a material made only of zirconia particles with few sintered contacts.

Separately, a cylindrical insulator tube 10 is manufactured, which is made of the same material as the green sheet and has holes 11a and llb with a diameter of 1 mm arranged at 180° opposing positions. Next, as shown in Figure 2,
The green sheet with a coating film is wound around the insulator tube 9 so that the electrode 2 covers the holes 11a and llb, and then fired to form the solid electrolyte main body 1A, the inner electrode 2A, the inner lead drawer part 31A, and the outer lead drawer B52A. , a first insulating layer 8A and a second insulating layer 9A were obtained.

On the other hand, using a transfer printing pad (this printing machine; tampo printing machine), an organic platinum ink (viscosity: 80 ~200 poise, measured with a Brookfield DVH viscometer), the ink pattern part formed in a rectangular shape (2.5 mm x 6.5 mm x 0.1 mm) on the transfer plate was applied to the solid electrolyte body IAO tube wall of the cylindrical body. This was transferred onto the outer peripheral wall corresponding to the hole 11a provided in the hole 11a, thereby forming the coating film 4 for the noble metal core forming part for the measurement electrode. Incidentally, when the viscosity of this ink is 80 to 200 poise, it is excellent in actual workability and convenient for transfer.

Furthermore, this was baked at 700° C. for 2 hours to form a noble metal core forming portion 4A. Note that this nucleus is a hemispherical body with a diameter and height of about 0.3 μm. In addition, since the resistance value of this noble metal cored part shows infinity, it can be seen that the respective schools are not connected.

Next, the insulator tube 10 having the solid electrolyte body with a noble metal core was immersed in an electroless plating solution, and a plating layer 5 (see FIGS. 3 and 4) was formed on the noble metal core forming portion 4A. As a result, an oxygen sensor element body (Product No. 1) having an outer electrode 6 composed of a noble metal core forming portion 4A and a plating layer 5 formed thereon was manufactured. This plating was performed using an aqueous solution of a tetravalent Pt ammine complex salt and hydrazine as a reducing agent, and after precipitation and drying, heat treatment was performed in the atmosphere at 1000 to 1300° C. for 1 hour).

■Product Nos. 2 to 4 and reference products Nα1 to 4 Oxygen sensor body similar to Product No. 1, except that the platinum content in the organic platinum ink was 1.5 and 10% by weight, respectively. were manufactured and designated as actual products Nα2 to Nα4, respectively. Similarly, the platinum content in the organic platinum ink was set to 0.
2.15 and [0.50% by weight oxygen sensor bodies were manufactured and designated as comparative products Nα1 to Nα4, respectively.

■Products Nα5 to 6 Spinel was further sprayed on the entire outer periphery of the oxygen sensor body of product N111, and approximately 50%
An electrode protective layer 7 with a thickness of 0 to 150 μm is formed to form an oxygen sensor (
A practical product Nα5) was created. In addition, as shown in FIG. 5, an oxygen sensor having a structure in which a heater 12 is built into the alumina insulating layer of the oxygen sensor of Example No. 5 (Example No. 5) is used.
6) was also produced. Note that this heater 12 is arranged so as to surround the electrode portion in order to heat the element body (mainly the electrode).

■ Simultaneously fired comparison product (Nα5) Same as the tested product, Z r O2Y20 with thickness Q, 3mm.
．． Pt paste was applied onto the green sheet by a printing method to form a coating film for the inner electrode and a coating film for the inner lead lead-out portion connected thereto. In addition, the same Pt paste was used for the part facing the inner electrode through the sheet,
A coating film for the outer electrode and a coating film for the lead lead-out portion connected thereto were formed by the same method. Furthermore, in order to provide an insulating layer in areas other than the outer electrode portion, an alumina paste coating was applied to form an insulating layer coating.

Separately, a cylindrical insulator tube made of the same material as the green sheet and having holes with a diameter of 1 mm arranged at positions 180 degrees opposite to each other was manufactured. Next, the green sheet with the coating film is applied to this insulator,
After winding the electrode to cover the hole, which will be formed later, is fired to obtain the solid electrolyte body, the inner electrode, the inner lead lead part, the outer electrode, the outer lead lead part, and the insulating layer to form the oxygen sensor element. Created.

Next, on the entire outer periphery of this oxygen sensor body, the applied product N
Spinel was sprayed in the same way as α5, and the oxygen sensor (comparative product N
α5) was manufactured.

■Plated comparison product (No. 6) Electroless plating was performed using a tetravalent Pt ammine complex aqueous solution on a solid electrolyte body similar to that used in the actual product to form an electrode and an oxygen sensor element. Made the body.

Next, a heater and an alumina insulating layer similar to those of the implemented product Nα6 were provided to this oxygen sensor body to obtain a comparative product NCL.
6 oxygen sensors were manufactured.

Incidentally, an insulating layer similar to that of the actual product is also formed on the outer lead lead-out portion 32B of the oxygen sensor element related to the comparative product.

(2) Performance test and performance evaluation ■Initial adhesion The strength of the plating film on the element bodies of test products Nos. 1 to 4 and comparison products Nos. 1 to 4 was examined by a tape test.

In the case of comparative products No. 1, some of them were originally poorly plated and did not exhibit sufficient conduction resistance.

Moreover, in the case of comparative products Nα2 to Nα4, peeling was large and showed low adhesion.

On the other hand, in the case of Examples Nα1 to Nα4, no peeling occurred and high adhesion was exhibited.

■Durable adhesion The outer l rod portion 6 of the oxygen sensor of the tested product Nα5 and the comparative product Nα5 was continuously heated with a Bunsen burner, and changes over time in the adhesion between the electrode and the solid electrolyte body were investigated, and the results are shown in Figure 6. It was shown to.

In the comparison product No. 5 oxygen sensor, when heating was continued, the sensor internal resistance increased significantly, but in the implementation product No. 5 oxygen sensor, heating was continued to 120°C.
Even after 0 hours of continuous use, the sensor internal resistance increased only slightly. Incidentally, in some of the comparative products No. 5, peeling occurred between the electrode and the solid electrolyte body due to continuous heating for 500 hours.

■Insulating properties of the electrode protective layer The insulating properties of the alumina insulating layer were investigated using the oxygen sensors of tested product No. 6 and comparative product No. 6. That is, 800℃
Using a 50 V-DC insulation resistance meter, the resistance value was examined to evaluate the insulation between the heater embedded in the alumina insulating layer and the outer electrode. The results are shown in FIG.

In the comparative product, there was a large variation in insulation resistance, and some had an absolute value of about 10Ω, indicating that the insulation property was lower than that of the practical product. The cause of this is
In the electrode plating method for Comparative Product No. 6, masking was used to prevent plating from being deposited on areas other than the electrode portion, but this is thought to be due to incomplete masking.

In contrast, the insulating properties of the alumina insulating layer in this example product were sufficiently ensured.

■Toxification Resistance Test Product No.5 and Comparative Product No. 5 Oxygen sensors were attached to the designated exhaust gas pipes, and the toxicity resistance (resistance to lead poisoning) of each element was tested. The durability conditions were such that the Pb content in gasoline was 50 mg/g a 1, and a bench durability test (cycle pattern durability test including full throttle, medium speed range, and idle). The results are shown in FIGS. 8 and 9.

Figure 8 shows the elapsed time and the rich exhaust gas atmosphere (600 m
Figure 9 shows the relationship between the control air-fuel ratio and the sensor control frequency.

As shown in these figures, in the comparison product Nα5 oxygen sensor, the response deteriorates after 1000 hours (Fig. 8), the control frequency decreases, and the control air-fuel ratio characteristics also shift significantly toward the rich direction (Fig. 8). Figure 9). There is almost no such variation in the tested product. From the above, the comparative products are strongly affected by lead, which is a poisonous substance. This is because multiple pores are formed in the electrode part, and since the electrode is formed by high-temperature firing, there are few three-phase interfaces of gas-solid electrolyte-Pt, and therefore the reactivity with gas is poor, and Pt
This is because the effects of poisoning such as b.

On the other hand, the oxygen sensor of Example No. 5 does not have this problem and has extremely good poison resistance.

(3) Effects of Example As described above, according to the manufacturing method of the oxygen sensor according to the present example, the adhesion strength between the electrode and the solid electrolyte body can be improved, and the toxicity resistance, insulation, etc. of the sensor can be improved accordingly. It is possible to maintain and improve the performance of Furthermore, since it has a predetermined platinum concentration, it has excellent initial adhesion of the electrode.

It should be noted that the present invention is not limited to those shown in the above-mentioned specific embodiments, and may be modified in various ways within the scope of the present invention depending on the purpose and use.

〔Effect of the invention〕

By using the method for manufacturing an oxygen sensor according to the present invention, as shown in the above-mentioned effects, it is possible to improve the adhesion strength between the electrode and the solid electrolyte body, and also to prevent the electrode itself from peeling off from the solid electrolyte body when using the oxygen sensor. can.

Therefore, by configuring the electrode with a precious metal forming part and a plating layer formed on it, it has excellent adhesion with the solid electrolyte body and the density of the plating layer, and therefore has excellent toxicity resistance, insulation, etc. It is possible to maintain and improve the performance of

[Brief explanation of drawings]

Fig. 1 is a partial cross-sectional view showing a state in which a coating film for the inner electrode is formed on a green sheet which becomes the solid electrolyte body of the oxygen sensor element in the example, and Fig. FIG. 3 is a partial cross-sectional view of the oxygen sensor according to the embodiment. FIG. A partial cross-sectional view explaining the configuration, FIG. 5 is a partial cross-sectional view explaining the configuration of the outer electrode, etc. of the oxygen sensor in which the heater of Implementation Product No. 6 is embedded, No. 6! ! I is a graph showing changes in sensor internal resistance over time;
Figure 7 is a graph showing the results of evaluating the insulation properties of the alumina insulating layer using resistance values, Figure 8 is a graph showing the relationship between elapsed time and responsiveness from rich to lean exhaust gas atmosphere, and Figure 9 is It is a graph showing the relationship between controlled air-fuel ratio characteristics and control frequency of a sensor. 1; Green sheet, IA; Solid electrolyte main body, 2; Coating film for inner electrode, 2A; Inner electrode, 31; Side for inner lead extraction part ll! , 32 ; Coating film for outer lead drawer part;
31A; Inner lead drawer part, 32A: Outer lead drawer part, 4; Coating film for forming part for precious metal stacking, 4A; Precious metal stacking part for forming part, 5; Plating layer, 6; Electrode, 7; Electrode protective layer, 8; Coating film for first insulating layer, 8A; First insulating layer, 9; Second
Coating film for insulating layer, 9A; second insulating layer, 10; porcelain tube, 12;
Heater Figure 1 Patent Applicant NGK Spark Plug Co., Ltd. Representative Patent Attorney Kiyomichi Kojima Figure 2 Figure 5 Figure 6 Gin f'el (hr) Kanmai Akira No. 6 ni-teme, 6

Claims (2)

[Claims] (1) A first step of forming an electrode on the solid electrolyte body,
A method for manufacturing an oxygen sensor, comprising: a second step of forming an electrode protective layer that covers and protects the electrode, wherein the first step comprises forming an organic noble metal ink containing an organic noble metal compound on the solid electrolyte body. A coating film is formed, and then the coating film is baked to form a noble metal nucleation forming part, and then a plating layer is formed on the noble metal nucleation forming part by a plating method, so that the noble metal nucleation forming part and the noble metal nucleation forming part are formed. A method for manufacturing an oxygen sensor, characterized in that the electrode is formed from the plating layer formed on the forming part. (2) The noble metal content in the organic noble metal ink is 0.5 to 10% by weight based on the total amount of the organic noble metal ink.
A method for manufacturing an oxygen sensor according to the claims.