JPH0395454A - Limiting current-type oxygen sensor - Google Patents

Abstract

PURPOSE:To improve processability and productivity and to stabilize characteristics for a long term by allowing a spiral spacer to tightly and rigidly secure a solid electrolytic plate with a seal plate through heating and melting of a protruding body of a mixture of glass and heat-proof very fine particles of a predetermined particle size and a film made of glass. CONSTITUTION:A spiral spacer 5 is placed between one surface of a solid electrolytic plate 1 and a seal plate 6. The solid electrolytic plate 1 with conductivity of oxygen ions has electrode films 2 formed at either face thereof. A protruding body 5a of a mixture of glass of the spacer 5 and heat-proof very fine particles of a predetermined particle size is tightly secured, via a film 5b made of glass, between the electrolytic plate 1 and seal plate 6 through heating and melting. A scattering hole 7 is formed in the spiral room and the oxygen is scattered through this room to the electrode film 2. Therefore, the scattering hole 7 is formed with good productivity simultaneously when the electrolytic plate 1, seal plate 6 and spacer 5 are bonded. Since the scattering hole 7 is formed parallel to the electrolytic plate 1, invasion of dust or foreign substance can be prevented. Moreover, the scattering hole 7 can be formed in the periphery of the electrode film 2 with a large opening area and a large length, thus improving the accuracy in size.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an oxygen sensor for measuring the oxygen concentration in an atmospheric gas, and particularly relates 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. 5, this type of oxygen sensor has electrode films 2 (anode 2a, anode 2a, A U-shaped lid 3 is placed on the solid electrolyte plate 1 on the cathode 2b side to form a sealed space, and the lid 3 is provided with an external space and a sealed space. The structure includes oxygen diffusion holes 4 that communicate with each other. Note that the diffusion hole 4 is formed in a size that allows a smaller amount of oxygen to spread than the oxygen delivery capacity of the cathode 2b.

In this configuration, the oxygen sensor is heated to an operating temperature.
After heating, when a DC voltage is applied between the electrodes 2, the cathode 2b
An ionization reaction of oxygen molecules occurs, and the ionized oxygen ions move toward the anode 2a in the solid electrolyte plate 1. A moleculeization reaction of oxygen ions occurs at the anode 2a and is 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 exhibits a constant value 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-59-192953
(Japanese Patent Application Laid-open No. 60-252254) Problems to be Solved by the Invention As the material of the lid body 3 in which the expansion hole 4 is formed, a ceramic material is preferably used from the viewpoint of heat resistance and corrosion resistance. many. The size of the diffusion hole 4 is arbitrarily set depending on the operating temperature of the oxygen sensor and the magnitude of the limiting current.

However, to ensure long-term reliability of the oxygen sensor, it is desirable to lower the operating temperature as much as possible.

A solid electrolyte made of zirconia ceramic has a minimum operating temperature of about 400°C from the viewpoint of 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 mm. Therefore, it is practically difficult to drill the diffusion holes 4 in ceramic materials with high precision, and there are problems such as large variations in characteristics, poor productivity due to micromachining, and high costs. there were.

In addition, in a structure in which the diffusion hole 4 is formed in the upper part of the lid body 3, dust or foreign matter may enter the diffusion hole 4 and change its diameter or block it during the manufacturing process or actual use of the oxygen sensor. There are concerns that As a result, there is a problem in that the oxygen sensor characteristics change over time, causing malfunction.

The present invention has been made to solve these conventional problems, and aims to provide an oxygen sensor that has excellent workability and productivity, has little variation in characteristics, and can realize stable characteristics over a long period of time. do.

Means for Solving the Problems In order to solve the above problems, the oxygen sensor of the present invention includes a solid electrolyte plate, an electrode film formed on both sides of the solid electrolyte plate, and a starting end and a point surrounding one of the electrode films. : a helical spacer whose ends are spaced apart from each other on the solid electrolyte machine, and a helical diffusion hole surrounded by opposing partition walls of the helical spacer, the solid electrolyte plate, and the seal plate. The helical spacer has a structure in which the solid electrolyte plate and the seal plate are closely fixed by heating and melting a protrusion made of a mixture of glass and heat-resistant fine particles of a predetermined size and a film made of glass. There is.

Function: In the above structure of the present invention, the spiral diffusion hole is formed at the same time as the spiral spacer, the solid electrolyte plate, and the seal plate are bonded together, so unlike the diffusion hole in the conventional oxygen sensor, the difficult drilling process is not required. This is not necessary, and since the diffusion holes of the present invention are formed parallel to the solid electrolyte plate, the gA spiral expansion holes are prevented from entering dust, foreign matter, and the like. Furthermore, since the spiral diffusion hole is formed around the electrode membrane, the opening area and length of the diffusion hole can be designed to be large, improving dimensional accuracy.

In addition, the helical spacer tightly fixes the solid electrolyte plate and the seal plate by heating and melting the projections made of glass in which heat-resistant fine particles of a predetermined size are dispersed and the membrane made of octopus. The two plates are firmly attached to each other by the glass on both sides, and the dimensional accuracy of the gears and holes (that is, the diffusion holes) between the two plates is further improved.

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

FIG. 1 shows an embodiment of the limiting current type oxygen sensor of the present invention, and FIG. 1(a) is an exploded perspective view of the oxygen sensor, and FIG.
) is a partially cutaway perspective view of the oxygen sensor.

In FIGS. 1(a) and 1(b), ▪ indicates a solid electrolyte plate having oxygen ion conductivity, and electrode films 2 are formed on both sides of the solid electrolyte plate. A spiral spacer 5 which surrounds the electrode film 2 and whose starting and ending ends are spaced apart from each other is disposed on one side of the solid electrolyte plate 1, and further a sealing plate 6 is disposed. The diffusion hole 7 of the present invention is defined by a spiral space surrounded by the opposing partition walls of the spiral diffuser 5, the solid electrolyte plate 2, and the seal plate 6,
Oxygen diffuses into the electrode film 2 through the space.

On the other hand, the spiral spacer 5 is a protrusion 5a made of a mixture of glass and heat-resistant fine particles of a predetermined particle size, and is tightly fixed to the solid electrolyte plate 1 and the seal plate 6 by heating and melting through a film body 5b made of glass. ing.

As the material for the solid electrolyte plate 1, zirconia-based ceramics are the most practical in terms of long-term reliability and stability of characteristics, and among these, zirconia doped with Il-lia is preferable.

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

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

The glass material is zirconia-based CeraQ as the solid electrolyte plate 1.
When applying '7', it is desirable that the thermal expansion is the same, and
20-Pb○1Si○2 series, Nax O-K2 0-P
b○-Si○2 system, Na. ○CaO-Si02 series, K2
0-Ca〇1Si○2 system, BaO-Si○2-Na20
Examples include glass. By the way, when the spiral spacer 5 is made of only glass, when the seal plate 6 is placed on the top and heated and burned, the seal plate 6 sinks due to the softening of the glass, and the gap of the spiral spacer 5, that is, the diffusion hole. 4
The variation in dimensions becomes thicker. In the present invention, in order to prevent this, heat-resistant particles having a melting point higher than that of the glass are dispersed in the glass. The heat-resistant particles prevent the seal plate 6 from settling, and a stable gap shape can be realized. The dimensional accuracy of the gap can be improved by adjusting the size of the heat-resistant particles to a predetermined particle diameter.

Screen printing is the most suitable method for forming the spiral spacer 5. In this case, an appropriate amount of the heat-resistant particles is added to the paste containing the glass component, mixed and dispersed, and then the solid electrolyte plate is
The protrusions 5a are formed by printing on the surface of the electrode film 2 so as to surround the electrode film 2, and then drying and baking.

On the other hand, when the protrusion 5a is closely fixed to the seal plate 6, the seal vi. 6, a sufficient degree of adhesion cannot be obtained and a limiting current cannot be obtained. In the present invention, in order to prevent this, the solid electrolyte 1 and the sealing plate 6 are tightly fixed through a film 5b made of glass, so that the solid electrolyte 1 and the sealing plate 6 are perfectly adhered by the glass.

As the material for the temporary seal 6, zirconia ceramics and forsterite are used in consideration of thermal expansion coefficient and heat resistance. FIG. 2(a) shows the structure of the seal plate 6 used in the limiting current type oxygen sensor which is an embodiment of the present invention, and FIG. 2(b) shows a cross-sectional view taken along line AA'' in the same figure.

A heater 8 is formed on the seal plate 6 by a printing method.
Furthermore, a film body 5b is coated on top thereof by a glass paste printing method. With this heater 8, the solid electrolyte plate 1
is heated and its oxygen ion conductivity increases. On the other hand, the membrane body 5b
This prevents deterioration of the heater 8 due to corrosive harmful gases and improves its durability, and also ensures close fixation between the solid electrolyte plate 1 and the seal plate 6 of the helical spacer 5, thereby improving its manufacturing reliability. is increasing.

Note that the heater 8 is not limited to the above-described embodiment, and may be formed in a portion of the seal plate 8 where the membrane body 5b is not formed, a portion of the solid electrolyte plate 1, or the like. Also,
Indirect heating from an external source other than the oxygen sensor element may also be used. The material used is platinum, nichrome wire, etc.

Next, its action and effects will be explained based on specific experimental examples.

The construction materials and manufacturing method of the oxygen sensor in the 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 200 μA (in air).

◆Solid electrolyte plate 1 Zr○2 ・Y203 ceramic ('i' z○38
no p. %), dimensions 12X12X0.4tm
m.

●Electrode film 2 Form a film with an electrode diameter of 6 mm and a film thickness of approximately 5 μm using PT paste. It was coated on both sides of the solid electrolyte plate 1 by screen printing and baked at 820°C for 10 minutes.

◆Helical spacer 5 Glass/BaO-Si○2-Na20 glass space 1
- Heat-resistant particles=-B a O-T i 02-S iO.
Based glass powder average particle size 50 μm For 1 g of the glass paste, 10% of the glass powder
(2) Using the mixture, a spiral spacer protrusion 5a surrounding the electrode film 2 is coated on one surface of the solid electrolyte plate 1 by screen printing using a printing method, followed by IO firing at 820°C.

The protrusion 5a of the helical spacer has the shape shown in FIG. 1, and the helical diffusion hole 7 has an opening area of 800 μm.
m (width of helical diffusion hole 7) x 40 μm (width of helical diffusion hole 7)
height), the length is 11 holes (distance from the starting end to the ending end of the spiral diffusion hole 7). On the other hand, its width is 0.8m
It is m.

◆Membrane 5b Using Ba○-NazOSi○2 glass base 1,
A film of about 10 μm was applied to one side of the seal plate 6 by screen printing, and burned at 820° C. for 10 minutes.

●Seal plate 6 is forsterite and its dimensions are 12X12X0
．． 5'mm0 The solid electrolyte plate 1 and the seal plate 6 are tightly fixed together by heating and melting the protrusion 5a of the spiral spacer and the membrane 5b (820°C x 10 minutes).

A lead wire (Pt) was attached to the electrode film 2 of the oxygen sensor thus produced, and the voltage-current characteristics were evaluated by heating in air at 400°C. The results are shown in FIG.

A saturation current, that is, a limiting current, is obtained at each oxygen concentration,
Furthermore, the limiting current value had a characteristic proportional to the oxygen concentration as shown in FIG.

Furthermore, in the present invention, since the spiral diffusion hole 7 is formed parallel to the solid electrolyte plate 1, the manufacturing process of the oxygen sensor is
During actual use, it was possible to prevent dust and foreign matter from entering the diffusion holes, stabilizing the characteristics and improving long-term reliability.

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

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

(2) Since the diffusion holes are formed parallel to the solid electrolyte plate, dust and foreign matter can be prevented from entering the diffusion holes, and characteristics can be stabilized and long-term reliability can be improved.

(3) Since the diffusion holes are tightly fixed by heating and melting the helical spacer made of a glass printed film, the fixed electrolyte plate, and the seal plate, it can be formed by an extremely simple method, resulting in excellent productivity and low cost. Become.

(4) The helical smoother is a protrusion made of glass that has separated heat-resistant fine particles of a predetermined particle size, and the solid electrolyte plate and the seal plate are closely fixed together through a membrane made of glass. The two plates are brought into close contact with each other by the glass on both sides, and the dimensional accuracy of the gap (diffusion hole) between the two plates is further improved. In particular, the diffusion hole dimensional accuracy is maintained using heat-resistant fine particles of a predetermined particle size, and the adhesion method by heating and melting the glass used for the protrusion and membrane body is resistant to bonding deviation between the solid electrolyte plate and the seal plate, and improves manufacturing yield. It is effective in greatly improving

(5) By forming the protrusions on the solid electrolyte plate and forming the membrane body into a seal plate, the electrode membrane on the solid electrode slope can secure a large area, and accordingly, the current load per unit area of the electrode can be reduced. becomes smaller.

Therefore, the interfacial resistance in the electrode film is reduced, thereby increasing the performance and durability of the electrode film.

(6) By forming a membrane on the sealing plate and also providing a heater and covering it with the membrane, deterioration of the heater due to harmful gases can be prevented and the life span can be improved. Furthermore, since the membrane body also serves to tightly fix the solid electrolyte plate and the seal plate, materials can be saved and manufacturing man-hours can be reduced. Furthermore, since a heater is attached to this oxygen sensor, it has a compact shape.

[Brief explanation of drawings]

FIG. 1(a) is an exploded perspective view of a limiting current type oxygen sensor that is an embodiment of the present invention, FIG. 1(b) is a partially cutaway perspective view of the same oxygen sensor, and FIG. A plan view of a seal plate used in a limiting current type oxygen sensor which is an embodiment of the invention, No. 2
Figure (b) is a sectional view of AA' cotton in Figure 2 (a),
FIG. 4 is a voltage-current characteristic diagram showing the effects of the present invention, FIG. 4 is an oxygen concentration current characteristic diagram showing the effects of the present invention, and FIG. 5 is a sectional view of a conventional limiting current type oxygen sensor. 1... Solid electrolyte plate, 2... Electrode membrane,
5... Helical smoother, 5a... Protrusion, 5b... Membrane, 6... Seal plate,
7... Diffusion hole, 8... Heater.

Claims (3)

[Claims] (1) An oxygen ion conductive solid electrolyte plate having electrode films formed on both sides, and a spiral spacer surrounding one of the electrode films so that its starting end and ending end are spaced apart from each other on the solid electrolyte board. , a seal plate disposed on the helical spacer so as to face the solid electrolyte plate, and a diffusion hole is surrounded by the opposing partition walls of the helical spacer, the solid electrolyte, and the seal plate. is formed, and the helical spacer is a protrusion made of a mixture of glass and heat-resistant fine particles of a predetermined particle size, and the solid electrolyte plate and the seal plate are tightly fixed by heating and melting through a film body made of glass. Limit current type oxygen sensor. (2) The limiting current type oxygen sensor according to claim 1, wherein the protrusion is formed on a solid electrolyte plate, and the membrane body is formed on a seal plate. (3) The limiting current type oxygen sensor according to claim 1, further comprising a heater and a membrane covering the heater.