JPH0664006B2 - Oxygen sensor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor for measuring an oxygen concentration in an atmospheric gas, and more particularly 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, an oxygen sensor of this type has an electrode membrane 2 (anode 2a, anode 2a) made of a metal such as platinum on both sides of a solid electrolyte plate 1 made of, for example, zirconia-based ceramic having oxygen ion conductivity. Cathode 2b) and further said cathode 2b
For forming a closed space on the solid electrolyte plate 1 on the side
The character-shaped lid body 3 is arranged, and further, the lid body 3 is provided with an oxygen diffusion hole 4 for communicating an external space and a closed space. The diffusion hole 4 is sized to diffuse a smaller amount of oxygen than the oxygen delivery capacity of the cathode 2b.

In this configuration, when the direct current voltage is applied between the electrodes 2 after heating the oxygen sensor to an operable temperature, an ionization reaction of oxygen molecules occurs at the cathode 2b, and the ionized oxygen ions pass through the solid electrolyte plate 1 into the anode 2a. Move towards anode 2a
At that time, a molecular reaction of oxygen ions occurs and the oxygen ions are discharged to the outside 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 cathode 2b is diffusion-controlled. As a result, the current generated by the movement of oxygen ions in the solid electrolyte plate 1 shows a constant value after a certain voltage as the applied voltage increases. This constant current is the limiting current. Since this is almost proportional to the oxygen concentration in the atmosphere gas, the oxygen concentration can be measured by detecting the limiting current. (For example, JP-A-59-192953 and JP-A-60-252254) Problems to be Solved by the Invention The material of the lid body 3 in which the diffusion holes 4 are formed is ceramic from the viewpoint of heat resistance and corrosion resistance. Materials are often applied. The size of the diffusion hole 4 is arbitrarily set depending on the operating temperature of the oxygen sensor and the size of the limiting current. However, it is desirable to keep the operating temperature as low as possible in order to ensure long-term reliability of the oxygen sensor. In the solid electrolyte of zirconia-based ceramic, the minimum operating temperature is about 400 from the viewpoint of oxygen ion transport capacity.
℃. In order to obtain a practical limit current value at this operating temperature, the diffusion hole 4 has an extremely small diameter of several tens of μm and a length of several mm. Therefore, it is practically difficult to perform the drilling process for the diffusion holes 4 in the ceramic material with high accuracy, and the characteristics vary greatly, and the fine processing leads to poor productivity and high cost. there were.

Further, in the configuration in which the diffusion hole 4 is formed in the upper portion of the lid body 3, dust, foreign matter, etc. enter the diffusion hole 4 to change or close the diameter thereof during the manufacturing process or actual use of the oxygen sensor. I have a concern. As a result, there is a problem that the oxygen sensor characteristics change over time, which causes malfunction.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide an oxygen sensor which is excellent in workability and productivity, has less variation in characteristics, and can realize stable characteristics over a long period of time. .

Means for Solving the Problems In order to solve the above problems, the oxygen sensor of the present invention has a solid electrolyte plate, electrode films formed on both surfaces of the solid electrolyte plate, and a starting end surrounding one of the electrode films. And spiral ends arranged so that the ends of the spiral spacers are spaced from each other on the solid electrolyte plate, partition walls facing each other of the spiral spacer, and spiral diffusion holes surrounded by the solid electrolyte plate and the seal plate. It is a thing.

Operation In the above configuration of the present invention, since the spiral diffusion hole is formed at the same time when the spiral spacer, the solid electrolyte plate and the seal plate are bonded, it is possible to perform difficult drilling work like the diffusion hole in the conventional oxygen sensor. In addition, it is unnecessary, and since the diffusion hole of the present invention is formed in parallel with the solid electrolyte plate, the spiral diffusion hole prevents intrusion of dust or foreign matter. Further, since the spiral diffusion hole is formed around the electrode film, the opening area and length of the diffusion hole can be designed to be large, and the dimensional accuracy is improved.

Embodiments Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a first embodiment of the present invention and is shown in FIG.
Is an exploded perspective view of the oxygen sensor, and FIG. 6B is a partially cutaway perspective view of the oxygen sensor.

In FIGS. 1 (a) and 1 (b), 1 is a solid electrolyte plate having oxygen ion conductivity, and electrode films 2 are formed on both surfaces thereof. A spiral spacer 5 is arranged on one surface of the solid electrolyte plate 1 so as to surround the electrode film 2, the start end and the end are spaced from each other, and a seal plate 6 is further arranged. The diffusion hole 7 of the present invention is formed in a spiral space surrounded by the partition walls of the spiral spacer 5 facing each other, the solid electrolyte plate 1 and the seal plate 6,
Oxygen diffuses into the electrode film 2 through the space.

Examples of the material of the solid electrolyte plate 1 include zirconia-based ceramics, which is the most practical in terms of long-term reliability, stability of characteristics, and the like. Among them, zirconia to which yttria is added is preferable.

Examples of the material of the electrode film 2 include platinum, gold, palladium and silver, but are not particularly limited.

The spiral spacer 5 is required to have heat resistance sufficient to withstand the operating temperature of the oxygen sensor and adhesiveness that realizes airtightness between the solid electrolyte plate 1 and the seal plate 6, and the material thereof is glass,
Examples include metals.

When the glass material to which the zirconia-based ceramic as a solid electrolyte plate 1, it is desirable thermal expansion is _{comparable, PbO-ZnO-B 2 O} 3 -SiO 2 system, K 2 _O-PbO-Si
O ₂ system, Na ₂ O-K ₂ O-PbO-SiO ₂ system, Na ₂ O-CaO-
Examples thereof include SiO ₂ type and K ₂ O—CaO—SiO ₂ type glasses.
By the way, in the case where the spiral spacer 5 is made of only glass, when the seal plate 6 is placed on the upper part and then heated and fired, the seal plate 6 is settled by softening of the glass and the gap of the spiral spacer 5, that is, the diffusion hole 4 is formed. Large dimensional variation. In the present invention, in order to prevent this, heat resistant particles having a melting point higher than that of the glass component are dispersed in the glass component. The heat-resistant particles prevent the seal plate 6 from settling, and a stable gap can be formed. By adjusting the sizes of the heat resistant particles, the dimensional accuracy of the gap is improved.

The screen printing method is most suitable as the means for forming the spiral spacer 5. In this case, the heat-resistant particles are appropriately added to the paste containing the glass component, mixed and dispersed, and the solid electrolyte plate 1 is formed by using the pattern of the spiral spacer 5.
Is printed so as to surround the electrode film 2.

On the other hand, when the spiral spacer 5 is made of metal, a titanium foil sandwiched between silver brazing foils is most suitable. The reason is that titanium has a coefficient of thermal expansion close to that of the zirconia-based ceramic applied as the solid electrolyte plate 1, heat resistance,
It has excellent adhesiveness. The silver brazing foil and the titanium foil are formed into the spiral spacer 5 by laser processing or the like.
The one processed into the pattern is used. The gap of the spiral spacer 5 is determined by the thicknesses of the silver brazing foil and the titanium foil, and a stable gap size is always obtained.

Examples of the material of the seal plate 6 include zirconia-based ceramics, forsterite, and the glass described in the spiral spacer 5 from the viewpoint of thermal expansion coefficient and heat resistance. The glass used as the seal plate 6 has a higher melting point than that of the glass used in the spiral spacer 5.

As described above, the spiral diffusion hole 7 of the present invention is composed of the partition walls facing each other of the spiral spacer 5, the spiral space surrounded by the solid electrolyte plate 1 and the seal plate 6, and the seal plate 6 is formed by the spiral spacer. After being placed on top of No. 5, it is formed by the following method.

Bonding by heating and baking when the spacer is glass printed.

In the case of silver brazing foil and titanium foil, brazing by heating and melting in vacuum or inert gas.

In the limiting current type oxygen sensor, the limiting current is approximated by the following equation.

Il = K · S / l · Po ₂ Where, Il: Limiting current K: Proportional constant S: Oxygen diffusion hole opening area l: 〃 length (diffusion distance) Po ₂ : Oxygen partial pressure From the above equation, It can be seen that the limiting current is proportional to the opening area of the diffusion hole through which oxygen diffuses and inversely proportional to the length of the diffusion hole. In order to realize the limiting current, the diffusion holes need to be sized to diffuse a smaller amount of oxygen than the oxygen ion transport capacity of the solid electrolyte plate. For example, in the present invention, if the limiting current value in air is 100 μA, the size of the spiral diffusion hole 7 is such that oxygen corresponding to the limiting current value is diffusion limited, and the opening area is 400 μm (helical diffusion hole 7 Width) x 50 μm (height of spiral diffusion hole 7), the length is
The distance is 25 mm (the distance from the start end to the end of the spiral diffusion hole 7). The oxygen sensor having the spiral-shaped diffusion hole 7 having the above-mentioned size is used as the current value conversion of the oxygen ion transport ability of the solid electrolyte plate 1.
By heating to a temperature of 100 μA or more, limiting current characteristics are obtained, and it functions as an oxygen sensor.

The size of the spiral diffusion hole 7 is appropriately set according to the operating temperature of the oxygen sensor and the size of the required limiting current,
It is not limited.

Next, the operation and effect will be described based on a concrete experimental example.

The oxygen sensor constituent material and manufacturing method in the first embodiment of the present invention shown in FIG. 1 are as follows.

The spiral diffusion hole 7 was designed so that the limiting current value was 100 μA (in air). Further, a glass printed film was used as the spiral spacer 5 as an oxygen sensor A, and a titanium foil sandwiched between silver brazing foils was used as an oxygen sensor B.

Solid electrolyte plate 1 ZrO ₂ · Y ₂ O ₃ ceramic (Y ₂ O ₃ 8 mol%), size 1
2 × 12 × 0.4tmm electrode film 2 Pt paste, electrode diameter 6mm, film thickness about 5μm Apply on both sides of solid electrolyte plate 1 by screen printing method, and calcination at 850 ° C for 10 minutes. A printed film made of Pt paste for connecting lead wires was formed on the cathode side only as shown in FIG.

Helical spacer 5 A: Glass printing film glass _{... PbO-ZnO-B 2 O} 3 -SiO 2 based glass paste refractory particles ... BaO-TiO ₂ -SiO ₂ based glass powder having an average particle size of 5
0 μm A mixture of 1 mg of the glass paste and 10 mg of the glass powder was used to form a spiral spacer 5 on one surface of the solid electrolyte plate 1 by surrounding the electrode film 2 by screen printing.
The spiral spacer 5 has the shape shown in FIG. 1, and the size of the spiral diffusion hole 7 is set to be the size shown in the above example.

Width of spiral spacer 5 0.5mm B: Titanium foil sandwiched by silver brazing foil The titanium spacer sandwiched between the silver brazing foils is laser-processed to form the spiral spacer 5 shown in FIG. 1 so that the size of the spiral diffusion hole 7 becomes the size shown in the above example, and the solid electrolyte plate is formed. The electrode film 2 is arranged on the first electrode 1.

Width of spiral spacer 5 0.5 mm Seal plate ZrO ₂ · Y ₂ O ₃ ceramic (Y ₂ O ₃ 8 mol%) Dimensions 11 × 12 × 0.5 tmm Seal plate 6 is arranged on spiral spacer 5 Adhesion of the above-mentioned members and formation of spiral diffusion hole 7 a: 450 ° C., 30 minutes of heating and burning B: 10 ^{- 4} torr below 800 ° C. under vacuum, 5 minutes of brazing oxygen sensor a was fabricated in this manner, the B Attach a lead wire (Pt) to the electrode film 2 and apply voltage at 400 ° C in air.
The current characteristics were evaluated. As a result, the produced oxygen sensor A,
For both B, the current showed a constant value in the applied voltage range of 1V to 2.2V. It was confirmed that the current showing this constant value is the limiting current and functions as an oxygen sensor. Further, both of the limiting current values showed about 100 μA, and it was confirmed that the above-mentioned spiral diffusion hole was formed as designed.

When the limiting current value in air is set to 100 μA, the size of the conventional diffusion hole 4 shown in FIG. 3 is 30 μm in diameter and 1 m in length.
It becomes m. On the other hand, the spiral diffusion hole 7 of the present invention shown in FIG.
The size is 400 μm in width, 50 μm in height, and 25 mm in length. (The sizes of the diffusion holes of the related art and the present invention shown here are representative examples of high practicability.) Here, when the opening size of both diffusion holes varies by 10%, the limiting current value is about 20.
% Will vary. It is difficult to accurately process a minute hole such as the conventional diffusion hole 4, and the area of the opening is small.
It is inevitable that it will vary by more than 10%. On the other hand, since the spiral diffusion hole 7 of the present invention is formed around the electrode film 2, both the opening area and the length can be made 20 times or more. The fact that the opening area can be designed to be large has an effect that the variation in the limiting current value can be reduced because the variation can be reduced as compared with the conventional case. The variation of the opening area of the spiral diffusion hole 7 according to the present invention is within 10%, and the limiting current value is within ± 20%.

Further, according to the present invention, since the spiral diffusion hole 7 is formed by the combination of the solid electrolyte 1, the spiral spacer 5 and the seal plate 6 which are adhered to each other, it is not necessary to perforate the ceramic as in the conventional case. Therefore, since it is formed by an extremely simple method, it is possible to realize excellent productivity and low cost.

Further, in the present invention, since the spiral diffusion hole 7 is formed in parallel with the solid electrolyte plate 1, it is possible to prevent dust and foreign matter from entering the diffusion hole during the manufacturing process of the oxygen sensor and in actual use, and to stabilize the characteristics. In addition, reliability can be improved over a long period of time.

Next, another embodiment of the present invention will be described. 2 is different from the above-mentioned embodiment in that the total length of the spiral spacer 5 is short, that is, the length of the spiral diffusion hole 7 is short, and a higher limiting current value than that in the above-mentioned embodiment is required. This is the case.

The shape of the spiral spacer 5 (spiral diffusion hole 7) is not limited to the round shape shown in the embodiment, and may be a triangle or a quadrangle.

3 is different from that of the above embodiment in that the oxygen inlet of the spiral diffusion hole 7 is connected to the solid electrolyte plate 1 and the seal plate 6.
The oxygen sensor of the above-mentioned embodiment can be realized because the filter function for preventing the intrusion of dust and foreign matter in the gap between the solid electrolyte plate 1 and the seal plate 6 can be realized by arranging the oxygen sensor inside the end part of the oxygen sensor. It is possible to stabilize characteristics and further improve reliability.

In the embodiment, ZrO ₂ · Y ₂ O ₃ ceramic is used as the seal plate 6, and PbO—ZnO—B ₂ O is used as the glass of the spiral spacer 5.
_{Although the 3-} SiO ₂ based glass has been described, the same effects as those in the above-described examples can be obtained with other materials described in the specification. Also,
The shapes of the seal plate 6 and the solid electrolyte plate 1 are not limited to the shapes shown in FIGS. 1 to 3.

Effects of the Invention As described above, the oxygen sensor of the present invention has the following effects.

(1) Since the size of the oxygen diffusion hole can be made larger than in the conventional case, the relative variation of the diffusion hole can be reduced, and the variation of the limiting current value can be reduced.

(2) The diffusion holes are formed by bonding a spiral spacer made of a glass printed film or a metal foil, a solid electrolyte plate and a seal plate. Therefore, since it can be formed by an extremely simple method, it is possible to realize excellent productivity and low cost.

(3) Since the diffusion hole is formed in parallel with the solid electrolyte plate, dust and foreign matter can be prevented from entering the diffusion hole, and the characteristics can be stabilized and the long-term reliability can be improved.

[Brief description of drawings]

FIG. 1a is an exploded perspective view of an oxygen sensor showing a first embodiment of the present invention, FIG. 1b is a partially cutaway perspective view of the oxygen sensor, and FIG.
FIG. A is an exploded perspective view of an oxygen sensor showing a second embodiment of the present invention, FIG. B is a partially cutaway perspective view of the oxygen sensor, and FIG.
Is an exploded perspective view of an oxygen sensor showing a third embodiment of the present invention, FIG. 4b is a partially exploded perspective view of the oxygen sensor, and FIG. 4 is a sectional view of a conventional oxygen sensor. 1 ... Solid electrolyte plate, 5 ... Helical spacer, 6 ... Seal plate, 7 ... Helical diffusion hole.

Claims (2)

[Claims] 1. A solid electrolyte plate having oxygen ion conductivity, electrode films formed on both sides of the solid electrolyte plate, and surrounding one of the electrode films, a start end and an end are spaced from each other on the solid electrolyte plate. A spiral spacer arranged to have, a sealing plate arranged on the spiral spacer so as to face the solid electrolyte plate, a partition wall facing the spiral spacer, and a seal between the solid electrolyte plate. An oxygen sensor comprising a spiral diffusion hole surrounded by a plate. 2. The spacer is a mixture of glass and heat resistant particles,
The oxygen sensor according to claim 1, comprising any one of titanium foils sandwiched between silver brazing foils.