JPH03218453A - Oxygen sensor and its production - Google Patents

Abstract

PURPOSE:To prevent the expansion in the fluctuation in threshold current value by disposing plural beginning ends which enclose cathode electrode films and come into contact with an ambient space and one terminal end on a solid electrolyte plate to have spacings from each other. CONSTITUTION:Spiral spacers 5 disposed in such a manner that the plural beginning ends 51 to 53 which enclose the electrode films 2 formed on both surfaces of the solid electrolyte plate 1 having an oxygen ion conductivity and come into contact with the ambient space and one terminal end 54 have the spacings from each other are disposed on the electrolyte plate 1. Diffusion holes 7 are formed in the spiral spaces enclosed by the partition walls of the spacers 5, the electrolyte plate 1 and a sealing plate 6 when the spacers 5 are covered with the sealing plate 6. Oxygen diffuses through this space to the electrode films 2. The diffusion quantity of the oxygen is determined approximately by the diffusion holes 7 constituted between the terminal end 54 and the beginning end 51 nearest this end and, therefore, if the beginning ends 51 to 53 are successively closed in order of the ends nearer the terminal end 53, the adjustment of the diffusion resistance value in an increasing direction, i.e. the threshold current value in a decreasing direction is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an oxygen sensor for measuring oxygen concentration in the environment, and in particular to a limiting current type oxygen sensor using an oxygen ion conductive solid electrolyte. 2. Description of the Related Art Conventionally, as shown in FIG. 4, this type of oxygen sensor has a solid electrolyte plate 1 made of, for example, zirconia ceramic material having oxygen ion conductivity, and a metal electrode film 2 (anode 2a) made of platinum or the like on both sides. , a negative electrode 2b), and further the negative electrode 2b).
A U-shaped lid 3 is placed on the solid electrolyte plate 1 on the b side to provide a sealed space.
In addition, the lid body 3 is provided with an oxygen diffusion hole 4 that communicates the external space with the closed space. In this configuration, when the oxygen sensor is heated to an operable temperature and then a DC voltage is applied between the electrodes 2, an ionization reaction of oxygen molecules occurs at the anode i2b, and the ionized oxygen ions pass through the solid electrolyte plate 1 to the anode 2a. A molecularization reaction of oxygen ions occurs at positive i2a toward the ion, and the oxygen ions are discharged into the external space. On the other hand, the inflow of oxygen into the closed space is restricted by the diffusion hole 4 provided in the lid 3, and the inflow of oxygen into the negative i2b is diffusion-controlled. As a result, the current generated by the movement of oxygen ions in the solid electrolyte plate remains constant after a certain voltage as the applied voltage increases. This constant current is the limiting current. Since this is approximately proportional to the oxygen concentration in the atmospheric gas, the oxygen concentration can be measured by detecting the limiting current. (For example, JP-A-59-19
(No. 2953, Japanese Unexamined Patent Publication No. 1983-252254) Problems to be Solved by the Invention The size of the diffusion hole 4 can be arbitrarily set depending on the operating temperature and the limit current of the oxygen sensor. However, to ensure long-term reliability of oxygen sensors, it is desirable to keep the operating temperature as low as possible. The minimum operating temperature of a zirconia-based ceramic solid electrolyte is approximately 400°C due to its ability to transport oxygen ions. In order to obtain a practical limiting current value at this operating temperature, the diffusion hole 4 must be extremely small, with a diameter of several tens of μm and a length of several square meters. However, it has been difficult to precisely control the shape of the diffusion hole 4. For this reason, the limit electric current
(There was a problem that the variation in a was large.

The present invention has been made to solve such conventional problems, and an object of the present invention is to provide an oxygen sensor with small variations in limiting current value.

Means for Solving the Problems In order to solve the above problems, the oxygen sensor of the present invention includes: a solid electrolyte plate having oxygen ion conductivity; a cathode electrode film formed on one surface of the solid electrolyte plate; A positive scraping electrode film formed on the other surface of the temporary solid electrolyte, a plurality of starting ends and a terminal end surrounding the cathode electrode film and in contact with the surrounding space are spaced apart from each other on the solid electrolyte slope. a spacer disposed on the spacer, a seal plate disposed on the spacer to face the solid electrolyte plate, a partition wall facing the spacer, the solid electrolyte plate, and the seal plate. It is equipped with a spiral diffusion hole with multiple starting points. Operation In the above structure of the present invention, a spiral diffusion hole having a plurality of starting ends and one ending end is formed between the solid electrolyte plate and the sealing plate. The diffusion resistance value of a diffusion hole is mainly determined by the spiral diffusion hole formed between one end and the starting end closest to it.
By closing them in the order of their proximity, it is possible to adjust the diffusion resistance value to a larger value, that is, the limiting current value to a smaller value.

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

FIG. 1 shows an embodiment of the present invention, and FIG. 1 (al is an exploded perspective view of an oxygen sensor, and FIG. 1) is a partially cutaway perspective view of the oxygen sensor. Figure 1(a). In (b), electrodes Il! are placed on both sides of the solid electrolyte plate l having oxygen ion conductivity. 2 is formed. A spiral spacer 5 surrounding the electrode film 2 and having a plurality of starting ends 5l, 52, 53 and a terminal end 54 spaced apart from each other is disposed on one surface of the solid electrolyte plate l, and a sealing plate 6 is further disposed. The diffusion hole 7 is formed by a spiral space surrounded by the opposing partition walls of the spiral spacer 5, the solid electrolyte plate 1, and the seal 6, and oxygen flows through this space to the electrode M2.
It spreads to. For the solid electrode plate 1, zirconia-based ceramics, especially zirconia doped with isotria, are often used. The t-electrode film 2 is made of platinum, gold, palladium, silver, etc., but is not particularly limited. The helical spacer 5 has heat resistance sufficient to withstand the operating temperature of the oxygen sensor,
Airtightness is required between the solid electrolyte plate 1 and the seal plate 6, and glass and metal can be used as the material. For example, if a thick fired glass film is used, the spiral spacer 5 shown in FIG. 1 can be easily obtained. For the sealing plate 6, a ceramic plate such as zirconia ceramic or forsterite is used. The coefficients of thermal expansion of each of the solid electrolyte plate 1, the spiral spacer 5, and the seal plate 6 are selected so as to be as similar as possible. In the embodiment shown in FIG. 1, three starting ends 5l, 5253
is shown, it is also easy to form three or more starting points. As described above, the oxygen sensor of the present invention has a plurality of starting ends, but the amount of oxygen diffused into the electrode film 2 is determined by the spiral formed between one ending 54 and the starting end 5l closest to it. The shape is almost determined by the diffusion hole 7. Therefore 5
1 is closed, the amount of oxygen diffused is the spiral diffusion hole 7 formed between one 54 and the starting end 52 closest to it.
It is almost determined by In this way, by sequentially closing the starting ends 5l, 52, and 53 in the order of proximity to one terminal end 54, the diffusion resistance bond can be increased, that is, the limiting current value can be adjusted to be decreased.

When the plurality of starting ends 51 and 52 are closed in the order of proximity to one terminal end 54 in this way, as shown in FIG. It is desirable to place it so that it is located on the surface of l. This is because the positions of the starting ends 5l and 52 can be easily distinguished, making the closing work easier. Note that the same effect can be obtained even if the plurality of starting ends 5l, 52, and 53 are similarly arranged so as to be located on the surface of the seal plate 6.

For example, the starting end 5l is closed by forming a closing material 8 so as to completely block the starting end 5l, as shown in FIG. As a method for closing the plurality of starting ends 51 and 52 in this manner, a method of coating the starting ends with a fluid inorganic material and then firing them is preferable. The material to be closed not only reliably covers the starting ends 51 and 52, but also has heat resistance sufficient to withstand the operating temperature of the oxygen sensor, as well as the solid electrolyte plate 1 and the seal plate, similar to the material of the spiral spacer 5. 6 is required.
Fluid inorganic materials such as glass paste for thick films or slurry containing ceramic powder exhibit good fluidity at room temperature, so it is possible to reliably coat the starting ends 5L and 52, and also to form a solid electrolyte by firing after coating. Plate l and sticker 4Ii
This is because it adheres tightly to 6 and forms a dense solid with excellent heat resistance. For example, SiO. , BaOZnO, Cab,
Nap, K! The paste for thick films, which is mainly composed of powder such as O, is baked at 700 to 900°C, so that it adheres closely to the solid electrolyte plate 1 and the seal plate 6, and forms an airtight glass with heat resistance of 500°C or more. can be easily obtained. In addition, slurries containing alumina powder and zirconia powder also have a
By firing at 900°C, a ceramic with excellent adhesion and heat resistance, similar to thick film paste, can be obtained. This ceramic is normally porous with many small holes, but it has a sufficiently large resistance value compared to the diffusion resistance value of the spiral diffusion hole, so it has a sufficient blocking effect on oxygen diffusion. exists. Effects of the Invention As described above, the oxygen sensor of the present invention provides the following effects. (1) By closing a plurality of starting ends in the order of proximity to the terminal end, the diffusion resistance value of the spiral diffusion hole can be adjusted in the direction of increasing it, that is, the limiting current value can be decreased. (2) By coating the starting end with a fluid inorganic material and then firing it, it is possible to close the starting end with excellent adhesion, heat resistance, and airtightness.

[Brief explanation of drawings]

FIG. 1(a) is a sectional view of an oxygen sensor element showing an embodiment of the present invention.

Claims (5)

[Claims] (1) A solid electrolyte plate having oxygen ion conductivity, a cathode electrode film formed on one surface of the solid electrolyte plate, an anode electrode film formed on the other surface of the solid electrolyte plate, and the cathode. a spacer that surrounds the electrode film and has a plurality of starting ends and one end that are in contact with the surrounding space and are arranged at intervals on the solid electrolyte plate; and a spacer that faces the solid electrolyte plate on the spacer. An oxygen sensor comprising: a spiral diffusion hole surrounded by opposing partition walls of the spacer, the solid electrolyte plate, and the seal plate. (2) The oxygen sensor according to claim 1, wherein the plurality of starting ends are located outside the end of the seal plate and on the surface of the solid electrolyte plate. (3) The method for manufacturing an oxygen sensor according to claim 1, wherein a part of the plurality of starting ends is covered with a fluid inorganic material and then fired to close a part of the plurality of starting ends. (4) The method for manufacturing an oxygen sensor according to claim 3, wherein the fluid inorganic material is thick film glass paste. (5) The method for manufacturing an oxygen sensor according to claim 3, wherein the fluid inorganic material is a slurry containing ceramic powder.