JPS6117950A - Formation of electrode in detecting part of oxygen sensor - Google Patents

Abstract

PURPOSE:To prevent exfoliation for a long period and to decrease resistance by providing a catalytically active metallic layer atop the noble metal paste baked to an uncalcined oxygen ion conductive solid electrolyte molding (solid electrolyte), etc. CONSTITUTION:The noble metal paste 2 is coated on the uncalcined solid electrolyte (or calcined body) 1 so as to penetrate the paste into the layer of the electrolyte 1 and is calcined at the temp. at which the noble metal 2 does not evaporate. An aq. soln. of chloride of a catalytically active metal such as platinum, rhodium or palladium or the alloy thereof is coated on the layer of the metal 2 to provide the metallic layer 3 thereon. Said layer is baked at the temp. at which the catalytic activity is not lost or said metal or the alloy thereof is plated thereon. The adhesion is thus improved and the exfoliation is obviated for a long period; in addition, the resistance is decreased.

Description

[Detailed description of the invention] (Technical field to which the invention pertains) The present invention relates to a method for forming electrodes of an oxygen sensor detection section.

(Prior art and its problems) - Conventionally, electrodes were formed by applying platinum base to an unfired oxygen ion conductive solid electrolyte (hereinafter referred to as solid electrolyte) compact or calcined body, and then baking the platinum base. Ta.

The oxygen sensor obtained by this electrode formation method has the advantage of long life, but has the disadvantage of high resistance.

To address the above drawbacks, attempts have been made to make electrodes by baking a glass-containing platinum base into a solid electrolyte sintered body at low temperatures, but the drawback is that the inclusion of glass impedes the diffusion of oxygen ions. Furthermore, a low-resistance oxygen sensor has been proposed in which a solid electrolyte sintered body is directly plated with platinum, but with this method, the electrodes are thin and the adhesion to the sintered body is weak, resulting in the electrodes peeling off. The disadvantage is that the oxygen sensor is easily used and the life of the oxygen sensor is short.

(Object of the Invention) An object of the present invention is to provide a method for forming electrodes of an oxygen sensor detecting section without such drawbacks.

(Means for Solving the Problems) The inventors of the present invention have conducted various studies in view of the above-mentioned shortcomings, and have found that a noble metal base is applied to an unfired solid electrolyte molded body or a calcined body, and then fired to bake the precious metal base. Then, when a catalytically active metal layer was provided on the soil surface, an oxygen sensor without the above-mentioned drawbacks could be obtained.

The present invention is a method for forming electrodes of an oxygen sensor detection part, in which a noble metal base is coated on an unfired solid electrolyte molded body or a calcined body, and then the noble metal base is baked, and a catalytically active metal layer is then formed on the upper surface of the noble metal base. Regarding.

In detail, as shown in Fig. 2, a noble metal base is applied to an unfired solid electrolyte molded body or a calcined body, the noble metal base is soaked in the solid electrolyte layer, and fired at a temperature at which the precious metal does not evaporate. A noble metal 2 is introduced into a layer of a strong solid electrolyte 1. Further, a catalytically active metal layer is provided on the 20 layers of noble metal, and as shown in FIG. 1, metal particles 3 are closely attached to the 20 layers of noble metal to form an electrode.

If metal particles are brought into close contact with the noble metal layer as described above, the surface area of the part that will become an electrode will be larger than that of the structure shown in Figure 2, and furthermore, in order to bring the metal particles into close contact, baking is performed at a relatively low temperature. Since a catalytically active electrode is formed by applying plating or plating, a structure having a lower resistance than that shown in FIG. 2 can be obtained, thereby achieving the object of the present invention.

In the present invention, the catalytically active metal layer is formed by coating an aqueous chloride solution of a metal such as platinum, rhodium, palladium, or an alloy thereof at a temperature that does not cause loss of catalytic activity (1200° C. or less in the case of platinum).

In the case of rhodium, it is baked at 1300 degrees Celsius or less, in the case of palladium it is baked at 1000 degrees Celsius or less), or it is provided by plating with the above metal or alloy.

If metal or alloy plating is applied, baking shall be performed as necessary.

(Example) The present invention will be explained in detail below.

Example 1 Zirconia stabilized with Ittria, inner diameter 8mm.

1 bag tubular molded product with a wall thickness of 1 mm and a length of 100 mm
The product was fired at 100° C. for 1 hour to obtain one bag of tubular calcined product.

Next, a platinum base coat was applied to the inner and outer surfaces of the bag-tube-shaped calcined product and baked at 1560° C. for 1 hour to form a platinum layer. The area of the platinum layer at this time was 1 cm''.Furthermore, a chloroplatinic acid aqueous solution was applied to the platinum layer-E.
The platinum particles were baked at 800° C. for 1 hour to make them adhere to each other, thereby forming the electrode of the oxygen sensor detection section.

Example 2 The electrode of the oxygen sensor detection part was formed in the same manner as in Example 1, except that electroless platinum plating was applied instead of the chloroplatinic acid aqueous solution in Example 1.

Example 3 A chlorinated rhodic acid aqueous solution was applied on the platinum layer formed on the inner and outer surfaces of the bag-tubular calcined product obtained in Example 1.

Baked at 900℃ for 1 hour to make the rhodium particles adhere,
The electrodes of the oxygen sensor detection section were formed.

Example 4 A chloropalladium acid aqueous solution was applied on the platinum layer formed on the inner and outer surfaces of the bag-tubular calcined product obtained in Example 1, and baked at 700°C for 1 hour to make the palladium particles adhere to each other, allowing oxygen sensor detection. electrodes were formed.

□ When we observed the electrodes of the oxygen sensor detection part obtained in each example, we confirmed that the electrodes were firmly adhered to the sintered body of the solid electrolyte and there was no problem with peeling off, as shown in Figure 1. Ta.

Next, air is flowed through the inner circumferential sides of the oxygen sensor forming the electrode of the oxygen sensor detection part according to the embodiment of the present invention and the conventional oxygen sensor. Flow 11) m of nitrogen gas containing oxygen on the outer circumferential side to generate an electromotive force, then vary the oxygen sensor temperature and measure the resistance by the voltage drop method (7). As shown in Fig. 3, it can be seen that the oxygen sensor in which the electrode of the oxygen sensor detecting section according to the embodiment of the present invention is formed has a lower resistance than the conventional oxygen sensor.

In the examples, platinum plating is used, but the same effect can be obtained by using rhodium plating or palladium plating.

(Effects of the Invention) The present invention applies a noble metal base to an unfired solid electrolyte molded body or a calcined body, and then bakes the noble metal base through firing 1, and then provides a catalytically active metal layer on the top surface. It is possible to form the electrode of the oxygen sensor 6-detecting part which has good adhesion with the oxygen sensor 6 and has good adhesion with the oxygen sensor 6 without worrying about peeling over a long period of time, and which has a lower resistance than the conventional oxygen sensor.

[Brief explanation of the drawing]

FIG. 1 is an enlarged sectional view of an oxygen sensor in which an electrode of an oxygen sensor detection part is formed according to an embodiment of the present invention, FIG. 2 is an enlarged sectional view of a conventional oxygen sensor, and FIG. 3 is an embodiment of the present invention. 2 is a graph showing the relationship between temperature and resistance of an oxygen sensor in which an electrode of an oxygen sensor detection section is formed and a conventional oxygen sensor. Explanation of symbols 1. Solid electrolyte 2. Precious Metals 3, Metal Particles No. 10 Calculation 20 Certain 3 Figure 1 戊 (C) 〼 11 1K Application No. 138597 2, Name of the invention: Electrode formation method for oxygen sensor detection section 3, Relationship with the case of the person making the amendment Name of patent applicant (445) Hitachi Chemical Co., Ltd. 4, Agent 5, Drawings subject to amendment Figure 3 6, Contents of correction 3 B Hani 11 ("C)

Claims (1)

[Claims] 1. An oxygen sensor detection unit characterized in that a noble metal base is applied to an unfired oxygen ion conductive solid electrolyte molded body or a calcined body, and then fired to bake the noble metal base, and then a catalytically active metal layer is provided on the top surface. electrode formation method.