KR950003455B1 - Electrode manufacturing method of oxygen sensor - Google Patents

Abstract

The method improves productivity of oxygen sensor by coating the inside and outside surface of the sintered body with platinum. The oxygen sensor is manufactured by forming platium layers on the inside and outside of solid electrolyte (1) by sputtering, after placing an anode of solid electrolyte (1) between a plate-shape cathode (4) and a core-shape cathode (5).

Description

Electrode manufacturing method of oxygen sensor

1 is a schematic diagram of an electrode manufacturing apparatus used to manufacture an electrode of an oxygen sensor according to the present invention.

2 is a schematic diagram of an electrode manufacturing apparatus used to fabricate a conventional oxygen sensor electrode.

Figure 3 (a) is a cross-sectional view showing the platinum paste microstructure of each electrode produced by the method according to the present invention.

Figure 3 (b) is a cross-sectional view showing a platinum paste fine structure of each electrode manufactured by the electrode manufacturing method of the conventional oxygen sensor.

4 is a graph comparing the characteristic diagrams of the product oxygen sensor of the present invention and the conventional product oxygen sensor.

* Explanation of symbols for main parts of the drawings

1,11,21: solid electrolyte sintered body 2,12: reference electrode

3,13: detection electrode 4,5,14: cathode

6,15,16: Anode 7,18: power supply

8,19: Chamber 17: Masking jig

22: detection electrode electrode fine structure 23: reference electrode electrode fine structure

The present invention relates to a method for manufacturing an electrode of an oxygen sensor, and more particularly, the measurement time of the sensor itself with a homogeneous electrode formed by sputtering simultaneously on the outer and inner surfaces of the solid electrolyte sintered body. The present invention relates to a method for manufacturing an electrode of an oxygen sensor, which can shorten and improve the detection capability.

In general, what is widely used as a gas sensor using a solid electrolyte is currently limited to an oxygen sensor using stabilized zirconia, which is also called a zirconia sensor. The zirconia sensor has a structure in which a platinum paste electrode is fixed to both sides of a stabilized zirconia tube (ZrO ₂ including 8 mol% of Y ₂ O ₃ is widely used). Here, the technique of manufacturing the reference electrode as the inner electrode and the detection electrode as the outer electrode by fixing the platinum paste on both sides of the stabilizing zirconia tube is very important because it greatly affects the function of the manufactured oxygen sensor.

Conventionally, in manufacturing the reference electrode and the detection electrode of the oxygen sensor, a platinum ink is applied to the inner surface of the solid electrolyte sintered body using a brush or a printing tool, dried, and then sintered and adhered at a temperature of 600 to 1300 ° C. As shown in FIG. 2, the solid electrolyte sintered body 11 on which the reference electrode 12 was manufactured was placed on the anode plate 15, fixed with a masking jig 17, and then a power supply ( In 18), while supplying a constant voltage to the cathode (14) and the anode (16) using a platinum target or platinum ingot as a raw material, sputtering, vacuum deposition or chemical vapor deposition (chemical vapor deposition) The detection electrode 13 was prepared on the outer surface of the solid electrolyte using the method: CVD (US Pat. Nos. 3,844,920, 4,264,647, 4,400,255, Japanese Patent Publication Nos. 62-55620, 62-55621). ) .

However, the method is not only complicated by manufacturing the reference electrode and the detection electrode in a separate process, but also the reference electrode made by applying platinum ink or the like has a processing rate and a fine structure as shown in FIG. 3 (b). Differences occur for each product produced, and the applied thickness and the coated area do not have uniformity, and thus also differ from the detection electrodes produced by the sputtering method, vacuum deposition method, or chemical vapor deposition method after fabrication of the reference electrode. There was a disadvantage in reducing the performance of the oxygen sensor.

In order to solve this problem, US Patent No. 4,136,000 attempts to improve the performance of an oxygen sensor by chemically treating a reference electrode made of platinum ink with hydrochloric acid, hydrofluoric acid, etc., and US Patent No. 4,264,667 uses compressed air and a painting tool. However, the performance of the oxygen sensor was improved by manufacturing the reference electrode, but it was not sufficient to overcome the above-mentioned fundamental problems caused by applying the platinum ink to produce the reference electrode.

In addition, in order to solve the above problems, a method of manufacturing the reference electrode by sputtering may be considered. However, when the sputtering is performed, the coated portion has a directionality, and thus, the hole may not be coated on the detection electrode. It was not possible to manufacture reference electrodes having the same uniform shape.

Thus, the present invention is to install a core-type reference electrode manufacturing method having the same shape on the inner surface of the solid electrolyte sintered body and the electrode of the platinum paste on the outer and inner surfaces of the solid electrolyte sintered body by the sputtering method simultaneously with the formation of the detection electrode By fixing the structure, the manufacturing process of the electrode can be greatly simplified, and the productivity in manufacturing the oxygen sensor can be improved by about 2 to 3 times. Also, the difference in the oxygen sensor detection characteristics resulting from the manufacturing process difference between the reference electrode and the detection electrode can be eliminated. It is an object of the present invention to provide a method of manufacturing an electrode of an oxygen sensor, which has a reliable oxygen concentration measurement characteristic and is able to quickly detect the oxygen concentration in the exhaust gas.

Hereinafter, the present invention will be described in detail.

The present invention relates to a method for manufacturing an electrode of an oxygen sensor in which a reference electrode and a detection electrode are formed on an inner surface and an outer surface of a solid electrolyte sintered body, the method comprising: a cathode and a power supply for manufacturing a planar detection electrode connected to receive power from a power supply It is a method of manufacturing an electrode of an oxygen sensor by forming an electrode on the inner and outer surfaces of a solid electrolyte sintered body by simultaneous sputtering between the core-type reference electrode manufacturing cathodes having the same shape as the inner surface of the solid electrolyte sintered body connected to receive power. It is characterized by.

Such a present invention will be described in more detail as follows.

The present invention relates to simultaneously forming the reference electrode and the detection electrode by applying the sputtering method to the inner and outer surfaces of the solid electrolyte sintered body at the same time. As the solid electrolyte sintered body used in the present invention, Y ₂ is commonly used as a zirconia sintered body. Stabilized or partially stabilized zirconia sintered body (ZrO ₂ ), which is O ₃ , MgO and CaO alone or a mixture of two or more thereof, may be used, and among them, it is most preferable to use a zirconia sintered body containing 6 mol% of Y ₂ O _3. Do.

In addition, platinum, rhodium, and palladium alone or a mixture of two or more may be used as a cathode for preparing a core-type detection electrode having the same shape as the inner surface of the solid electrolyte sintered body and the planar reference electrode used in the present invention.

On the other hand, in the present invention, the sputtering process is a vacuum degree of 10 to 20mmTorr, the gas mixture ratio by volume ratio of Ar: N ₂ = 70: 30 to 40: 60, the power of the cathode for the reference electrode fabrication 5-15w / ㎠, for the detection electrode It is preferable to carry out under the conditions of 13 to 21 W / cm 2 of the power of the cathode, and when the sputtering is performed simultaneously on the surface of the solid electrolyte sintered body under such conditions, an oxygen sensor having an electrode to which the platinum paste according to the present invention is fixed Will be prepared.

In the above, the degree of vacuum is preferably 10 to 20 mmTorr. If the vacuum degree is less than 10 mmTorr, the microstructure of the manufactured electrode is too dense so that the diffusion rate of air in the electrode is slowed. It gets worse. In addition, the gas mixing ratio is preferably Ar: N ₂ = 70: 30 to 40: 60 in the volume ratio. When the mixing ratio of the N ₂ gas exceeds 60% in the volume ratio, the pore sizes of the reference electrode and the detection electrode are too large or The electrode productivity is lowered.

The reason why N ₂ gas is mixed and used in sputtering in addition to Ar gas is because N ₂ gas molecules act as impurities in a vacuum to scatter atoms of the target material that is sputtered at the target to have appropriate pores in the electrode.

And, the power of the reference electrode manufacturing method is 5 to 15w / ㎠, the power of the detection electrode manufacturing method is preferably 13 to 21w / ㎠, if out of the above range, the electrode productivity is lowered, or the electrode The microstructure of the nonuniformity results in a short lifetime of the cathode.

When the sputtering under the above conditions, the distance between the cathode for manufacturing the reference electrode and the inner surface of the solid electrolyte sintered body is limited, and the sputtering condition is changed by the power applied to the cathode within this limited distance.

Therefore, in the present invention, the distance between the cathode for producing the detection electrode and the solid electrolyte sintered body was 3 to 5 cm, and the distance between the solid electrolyte sintered body and the cathode for the reference electrode production was 0.2 to 0.3 cm.

Hereinafter, the present invention will be described with reference to the illustrated drawings.

1 is a diagram schematically showing an electrode manufacturing apparatus for carrying out the method of the present invention, in which a solid electrolyte sintered body is indicated by reference numeral 1, and the sintered body 1 is fixedly mounted on the anode plate 6, The straight cathode 4 for the manufacture of the detection electrode 3 is provided above the solid electrolyte sintered body 1, and the reference | standard which has the same shape as the inner surface of this sintered body 1 below the sintered body 1 A core-type cathode 5 which is made of an electrode 2 is provided. Each of the cathodes 4 and 5 is connected to a power supply 7 which supplies power. Therefore, when the solid electrolyte sintered body 1 is installed on the anode plate 6 and sputtered under the conditions described above through the cathodes 4 and 5 on both sides, the outer surface of the sintered body 1 and The reference electrode and the detection electrode are respectively formed on the inner surface at the same time.

Here, reference numeral 8 denotes a chamber in which sputtering can be performed.

Hereinafter, the present invention will be described in more detail based on examples.

[Examples 1 to 4]

Press-molded mixed powder consisting of 94 mol% of zirconia oxide and 6 mol% of yttrium oxide, processed to a certain size, and sintered at 1600 ° C. The outer diameter of the lower part is 15mm, the inner diameter of the lower part is 8mm, the thickness is 1mm and the density is 5.65g / A solid electrolyte sintered body of 2 cm 2 or more was produced. After the manufactured sintered body was washed, it was installed in a sputtering apparatus and sputtered under the conditions shown in Table 1 to form electrodes on the inner and outer surfaces of the sintered body, thereby manufacturing an oxygen sensor.

Performance tests were performed with the manufactured oxygen sensor, and the results are shown in Table 2 below, and the performance test was performed as follows. In addition, the cross section of the oxygen sensor manufactured as above is shown in FIG. 3 (a).

[Performance Test]

Oxygen sensor switching time when the combustion ratio of air / fuel changes the electromotive force value in the rich and lean regions and the combustion ratio of the air fuel while the heated sample gas prepared according to the present invention passes through the product Measure the internal resistance of the product at and 500 ℃ and the measured values are shown in Table 2 below.

Comparative Example 1

The performance test was carried out under the same conditions as in Example 1 of a Japanese electronic product A24-600 oxygen sensor manufactured by the conventional method and shown in Table 2 below, and the characteristics thereof are shown in FIG. In addition, the cross section of the oxygen sensor is shown in FIG.3 (b).

TABLE 1

TABLE 2

*: A24-600 Oxygen Sensor from Japan.

As shown in Fig. 3, it can be seen that the oxygen sensor manufactured according to the method of the present invention has the same shape as the microstructure of the reference electrode and the detection electrode as compared to the oxygen sensor manufactured by the conventional method. Regarding the reaction at the three-phase interface, the reaction formula generated at the three-phase interface of the solid electrolyte / cathode / air at the reference electrode is shown in the following equation [I], and the three-phase of the test gas / cathode / solid electrolyte at the detection electrode The reaction formula generated at the interface is shown in the following formula [II].

^{_{O 2 + 4e - → 2O 2}} - ... … … … … … … … … … … … … … … … … … … … … [Ⅰ]

^{_{20 2 - → O 2 + 4e}} - ... … … … … … … … … … … … … … … … … … … … … [II]

Since the reaction of formula [I] and formula [II] occurs quantitatively at the three-phase interface of solid electrolyte / cathode / air, the number of three-phase interface of solid electrolyte / cathode / air is higher than that of the conventional oxygen sensor. By generating a large amount and uniformity, it is possible to equilibrate the oxygen concentration change of the test gas to be measured within a faster time, thereby increasing the switching reaction time corresponding to the oxygen concentration change and increasing the adhesion between the reference electrode and the detection electrode and the solid electrolyte. The oxygen concentration can be measured accurately and precisely.

As can be seen in Table 2, the switching time, which is the main characteristic value of the oxygen sensor, was reduced by 30 to 50%, and the difference in electromotive force in the concentrated salt and lean regions was increased by 30%, indicating that the detection capability of the oxygen sensor was improved.

As described above, the present invention improves the productivity of the oxygen sensor by about 2 to 3 times as compared to the conventional method, and the oxygen sensor manufactured by the present invention reduces the switching reaction time, increases the measurement accuracy of the oxygen concentration, and increases the measurement accuracy. By reducing the exhaust gas purification efficiency can be increased.

In addition, the oxygen sensor manufactured according to the present invention is mainly used for oxygen sensors for automobiles, oxygen sensors for industrial boilers, etc., and in particular, when used as an oxygen sensor for automobiles, the sensor detection time is shortened in the initial start-up and various operating conditions. It also has a great effect on reducing environmental pollution by reducing the amount of harmful exhaust gas.

Claims (3)

In the electrode manufacturing method of the oxygen sensor by forming a reference electrode and a detection electrode on the inner and outer surfaces of the solid electrolyte sintered body, the power supply is supplied from a cathode and a cathode for producing a planar detection electrode connected to receive power from the power supply A method of manufacturing an electrode of an oxygen sensor, characterized in that an electrode is formed on the inner surface and the outer surface of a solid electrolyte sintered body by a simultaneous sputtering method between the core-type reference electrode fabrication cathodes having the same shape as the inner surface of the solid electrolyte sintered body connected to be received. The method according to claim 1, wherein the sputtering is a vacuum degree of 10 to 20mmTorr, the gas mixing ratio is a volume ratio of Ar: N ₂ = 70: 30 to 40: 60, the power of the cathode for the reference electrode fabrication 5-15w / ㎠, for the detection electrode A method for producing an electrode of an oxygen sensor, characterized in that the power of the cathode is set to 13 to 21 w / cm 2. The method of manufacturing an electrode of an oxygen sensor according to claim 1, wherein the cathode is made of platinum, rhodium and palladium alone or an alloy of two or more thereof as a material.

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