JP2513234B2 - Oxygen concentration detector manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing an oxygen concentration detector having a closed space between an electrode and a diffusion-controlling layer.

(Prior Art) Although various types of oxygen concentration detectors have been known,
A limiting current type oxygen concentration detector has been developed as one of them. This limiting current type oxygen concentration detector is an element body with electrodes on both sides of a plate-shaped oxygen ion permeable solid electrolyte, and when a constant voltage is applied between both electrodes of this element body, one electrode (cathode) Since oxygen ions permeate from one side to the other electrode (anode) side, limiting the amount of oxygen ions entering (or leaving) at least one of the electrodes at that time causes a limit between both electrodes depending on the oxygen concentration in the measured gas. It utilizes the fact that an electric current flows.

This limiting current type oxygen concentration detector is, for example, as a method for limiting the diffusion rate of oxygen to one electrode surface of the element body, an oxygen concentration detection method in which a porous ceramic sprayed layer is formed directly on the electrode surface is used. Although a vessel is conventionally known, by providing a closed space between the electrode and the porous ceramic sprayed layer as shown in FIG. 3 or FIG. A container is proposed in Japanese Patent Laid-Open No. 60-13256. In FIG. 3, 21 is an oxygen ion permeable solid electrolyte cell, 22 is a cathode provided on the cell 21, 23 is an anode, 24 is an alumina holder for supporting the ceramic sprayed layer 26, 31 is a housing, 32 indicates a ceramic tube. This detector is manufactured as follows.

The solid electrolyte cell 21 is made of, for example, zirconia powder containing 8% yttria. Cell 21 of this powder compact
Platinum paste is applied to the taper portion 21 'and a part of the upper surface thereof, and then the paste is fired to sinter the powder compact and simultaneously form a lead portion 22' for taking out the cathode. After firing, cell
The upper and lower surfaces of 21 are plated with platinum, and unnecessary portions are scraped off to form the cathode 22 and the anode 23. On the other hand, for the ceramic sprayed layer, an alumina holder 24 having an opening at the center is used as shown in FIG.
A backing plate such as a metal plate that is better polished than the bottom surface in the 24 openings
25 is applied and the ceramic is sprayed from above to form a porous spray layer 26 having a thickness of 500 μm. Then remove the backing plate 25,
The obtained alumina holder 24 with the sprayed layer 26 is covered on the solid electrolyte cell 2, and the contact portion between the two is sealed and fixed with an inorganic adhesive 27, and a space 20 closed between the sprayed layer 26 and the cell 21 is obtained. Forming an oxygen concentration detecting element S ₀ . Next, the detection element S ₀ is installed in a cylindrical ceramic housing 31 having a built-in ceramic heater 31 ′, a ceramic tube 32 is fitted in the housing 31, and the detection element S ₀ is pressed and fixed. Get the detector to do. In the figure, 33 and 34 indicate lead wires.

Further, as shown in FIG. 5, the ceramic sprayed layer 26 has a very porous ceramic filter 28 having an average pore diameter of 10 to 50 μm fixed to the opening of the alumina holder 24 by an inorganic adhesive, and the ceramic filter 28 is coated with the above The ceramic sprayed layer 26 may be provided in the same manner as in.

Further, the oxygen concentration detector of FIG. 6 is an example applied to the element body in which the cathode 22 and the anode 23 are formed so as to correspond to the front and back surfaces of the end of the rectangular flat plate-shaped solid electrolyte cell 21, respectively. The rectangular alumina holder 24 with the ceramic sprayed layer 26 obtained in the above was provided so that there was a gap between the cathode 22 and the sprayed layer 26 to form an oxygen concentration detecting element.
In the figure, 35 indicates a ceramic support plate.

Further, as shown in FIG. 7 and FIG. 8, plates having different sizes of windows are overlapped, a porous ceramic sprayed layer is formed on the plates, and at the same time, a plate-shaped oxygen concentration detection is provided with a closed space. A vessel is proposed in Japanese Patent Application No. 61-196987.
In the figure, 41 and 45 are plates, 42 and 44 are spacers, 43 is a solid electrolyte, 46 and 47a are windows, 47 is a space, 48, 49, 50, 51, 5
2 and 53 are electrodes, 54 is an air introduction path, and 56 is a ceramic porous layer. Furthermore, a similar plate-like air-fuel ratio detector is proposed in Japanese Patent Application No. 61-178407.

(Problems to be Solved by the Invention) However, the oxygen concentration detector having a closed space between the electrode and the ceramic porous layer disclosed in the above-mentioned Japanese Patent Application No. 60-13256 has low temperature operability and durability. Excellent, but the third
As shown in the figure, it is difficult to secure airtightness because a closed space is created by the adhesive structure. Also, as shown in FIGS. 4 and 5, a ceramic sprayed layer is made in advance with another piece, and then assembled later. Since the number of parts is large and the parts are small, the process is complicated. Further, since the heater is located on the outermost side where it is cooled most, there is a problem that the heater efficiency is poor and a large amount of electric power is required.

Although the plate-shaped laminated oxygen concentration detector disclosed in Japanese Patent Application Nos. 61-196987 and 61-178407 shown in FIGS. 7 to 8 solves the above problems, , If the ceramic porous layer 56 is not thicker than the spacer 42, the closed space 47
However, there is a problem that it is difficult to perform thermal spray coating on a narrow portion with a uniform thickness, and heat easily causes cracks between the plate 41 and the ceramic porous layer 56.

The present invention is intended to solve the above problems, and an object of the present invention is to provide a method capable of easily manufacturing an oxygen concentration detector having a closed space between an electrode and a ceramic porous layer. It is a thing.

(Means for Solving Problems) A method for manufacturing an oxygen concentration detector according to the present invention is an electrode for measuring an oxygen concentration in the manufacture of a laminated oxygen concentration detector having a closed space between an electrode and a diffusion-controlling layer. After the element for covering the electrode is integrated by firing by making a space communicating with the outside by a hole for introducing gas, the hole is closed with an organic substance,
It is characterized in that a porous ceramic sprayed layer having a predetermined thickness is formed therein so as to cover the pores, and then heated to oxidize and vaporize and remove the organic matter.

In the present invention, the organic substance that closes the gas introduction hole is not particularly limited, but examples thereof include paper and plastics such as polyethylene, polypropylene, and polyester.

(Operation) When manufacturing an oxygen concentration detector in which ceramic green sheets are laminated to form a closed space between the electrode and the diffusion-controlling layer, a space that communicates with the outside through a gas introduction hole on the oxygen concentration measurement electrode A space can be easily provided on the electrode by making the electrode exist and covering the electrode. After that, when the hole is covered with an organic substance and a ceramic is sprayed on the hole so as to cover the hole, the organic substance supports the sprayed ceramic even if the organic substance is slightly decomposed. A porous ceramic sprayed layer of a predetermined thickness can be formed over the holes so that the holes are closed by the sprayed layer. Then, the organic matter is eliminated in a high-temperature oxidizing atmosphere, whereby a closed space can be provided between the electrode of the oxygen concentration detector and the porous ceramic sprayed layer which is the diffusion-controlling layer formed on the hole. .

(Example) The present invention will be described by way of an example with reference to the drawings.

As shown in FIG. 1 (a), the solid electrolyte 3 is formed on both surfaces in the vicinity of one end of the plate-shaped oxygen ion permeable solid electrolyte 3.
Pt by the printing method so that it becomes a pair on the front and back
Two pairs of electrodes 6 and 7 and electrodes 8 and 9 composed of the same are provided. Next, the outer shape is almost the same as that of the solid electrolyte 3, and the outer shape for forming the atmosphere introduction path 12 on the plate 5 made of ceramic in which the heating element 13 is provided at a position corresponding to the electrode by a printing method is used. Almost the same as the solid electrolyte 3, a frame-shaped spacer 4 having one end opened is laid so that the open end side is the opposite side of the heating element 13, and the solid electrolyte 3 is placed on the electrode 6,
The layers 7, 8 and 9 were placed on the heating element 13. Further, a spacer 2 made of ceramic having an outer shape substantially similar to that of the solid electrolyte 3 and having windows at positions corresponding to the electrodes 7 and 8 is laid thereon so that the windows are placed on both electrodes, and the outer shape is formed thereon. The plate 1 having substantially the same structure as that of the solid electrolyte 3 and having the holes 10 at positions corresponding to the positions between the electrodes 7 and 8 was stacked so that the holes 10 were located above the electrodes 7 and 8 and integrated by firing.

Then, in the hole 10 (diameter 2 mm) of the element obtained by firing as described above, as shown in FIG.
14 is rolled up into a cylindrical shape and embedded, and plate 1 and paper 14
Was made to be the same.

Next, as shown in FIG. 1 (c), spinel powder of MgO.Al ₂ O ₃ (average particle size 40 μm) was sprayed by a plasma gun 15 on the element in which the hole 10 was closed with paper 14 while rotating the element. . Hole 10
Is covered with the paper 14 so as to be flush with the plate 1, so that the sprayed ceramic does not enter the hole 10 and a porous ceramic sprayed layer having a thickness of 500 μm can be formed around the element. It was

Next, the element on which the sprayed layer 16 is formed is heated to 1000 ° C.
1 hour, the paper 14 embedded in the holes 10 is oxidized, vaporized, and evaporated from the porous ceramic sprayed layer 16 to the outside of the element, and the paper 14 is removed from the holes 10 to obtain the structure shown in FIG. An oxygen concentration detector having a closed space between the electrodes 7 and 8 and the porous ceramic sprayed layer 16 which is the diffusion-controlling layer as shown in d) was obtained. In addition, when the paper is made to disappear in a high temperature oxidizing atmosphere, it may be performed under pressure.

The electrodes 6 and 7 of the oxygen concentration detector are used as pump cells for sending oxygen from the atmosphere to the closed space, the electrodes 8 and 9 are used as measurement electrodes, a constant voltage is applied, and the air-fuel ratio (A / F) was changed and the current value was read. This output characteristic is shown in FIG. A certain voltage is applied to the electrodes 6 and 7 as pump cells even in a rich state, and oxygen gas is supplied from the air inlet 12 to the closed space 11 to provide an output current that can be measured by the electrodes 8 and 9. Get
An output current proportional to the air-fuel ratio was obtained in the air-fuel ratio from rich to lean.

(Effects of the Invention) Since the method for manufacturing an oxygen concentration detector of the present invention has the above-described configuration, a dedicated jig such as a thermal spraying patch plate or a masking material is not required when spraying the porous ceramic, and It does not require joining to form a space and can be easily manufactured.

Further, since the outer side of the element is covered with the thermal spray layer, the porous ceramic thermal spray layer can be formed uniformly and with a predetermined thickness. Furthermore, since the formed thermal spray layer adheres widely to the element, it is hard to peel off. It has many advantages.

[Brief description of drawings]

1 (a), (b), (c), and (d) are cross-sectional views for explaining the manufacturing process of the oxygen concentration detector of one embodiment of the present invention, and FIG. 2 is one embodiment of the present invention. FIG. 3 is a graph showing the output characteristics of the oxygen concentration detector of FIG. 3, FIG. 3 is a sectional view of a cylindrical oxygen concentration detector in which a conventional sprayed layer is joined, and FIG. 4 is a sectional view of a holder in which a conventional sprayed layer is formed. Fig. 5 is a sectional view of a holder in which a sprayed layer is formed on a conventional filter, Fig. 6 is a sectional view of a plate-shaped oxygen concentration detector in which a sprayed layer of the related art is joined, and Fig. 7 is a direct sprayed layer of the conventional type. FIG. 8 is a sectional view of the laminated oxygen concentration detector, and FIG. 8 is an exploded perspective view of the oxygen concentration detector of FIG. In the figure, 1 ... plate, 2 ... spacer 3 ... solid electrolyte, 6,7,8,9 ... electrode 10 ... hole, 11 ... space 14 ... paper, 16 ... sprayed layer

Claims (1)

(57) [Claims] 1. In the production of a laminated oxygen concentration detector having a closed space between an electrode and a diffusion-controlling layer, a space communicating with the outside is present on the oxygen concentration measuring electrode by a gas introduction hole. After firing and integrating the elements covering the electrodes,
The hole is closed with an organic substance, a porous ceramic sprayed layer having a predetermined thickness is formed thereon so as to cover the hole, and then heated to oxidize and vaporize the organic substance to remove the closed layer. Method of manufacturing oxygen concentration detector having space.