JPH02186255A - Oxygen sensor element - Google Patents

Abstract

PURPOSE:To achieve a higher output accuracy and a higher anti-seismic property by using forsterite as material for a plate which is sealed to form a gap between the plate and a stabilized zirconia plate. CONSTITUTION:One top almost square is formed at a part of a stabilized zirconia plate 2 and a tiny hole 24 is formed at the center thereof 2. Then, the stabilized zirconia plate 2 is laminated with the forsterite plate 3 with the back thereof 2 facing the surface thereof 3 so as to position the top. Thus, a gap is formed between the stabilized zirconia plate 2 and the forsterite plate 3. The gap leads to an outside air only with the tiny hole 24 by sealing the plates airtight by a sealing glass 36.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a ceramic oxygen sensor element, and more particularly to an improvement of a limiting current type ceramic oxygen sensor element. This ceramic oxygen sensor is used for combustion control in boilers, automobile engines, etc., and oxygen deficiency monitoring in manholes, etc.

[Conventional technology]

The conventional limiting current type ceramic oxygen sensor element has platinum electrodes provided on the front and back surfaces of the stabilized zirconia plate 2 to connect the anode 21 and cathode 2 as shown in FIG.
2, and this stabilized zirconia plate 2 and cap 3
7 to form a gap therebetween, and the small hole 38 is sealed with a cap 37 (or stabilized zirconia plate 2).
It is formed by providing a space in the air gap and communicating the air gap with the outside air. A heater 31 is provided on the surface of the cap 37, and a constant current is passed through the heater lead wire 39 to heat the cap 37. The anode lead wire 27 is connected to the anode 21 and the cathode 22.
, cathode lead wires 28 are connected, and a constant voltage (monitoring voltage) is applied between the anode 2 and the cathode 22 by these. Then, the stabilized zirconia plate 2, which is a solid electrolyte, acts as an oxygen ion conductor, and due to its oxygen bombing effect and the concentration gradient of oxygen flowing through the small holes 38,
A current value corresponding to the oxygen concentration of the surrounding atmosphere can be obtained as a current flowing between the anode and the cathode 22. Here, the cap 37 is made of cubic stabilized zirconia (
811101%; Y2O3ZrO2) Since it is necessary to seal the cap 37 with the plate 2, the material of the cap 37 is conventionally a partially stabilized cubic zirconia (3 mol* Y2O3-ZrO2) having a similar coefficient of thermal expansion (see Table 2). ing. In addition, due to the demand for miniaturization of oxygen sensor elements, lead wires 27, 28, 39, etc. have a diameter of 0. IM platinum wire is used and bonded to each electrode with platinum paste.

[Problem to be solved by the invention]

However, partially stabilized zirconia has very low electrical insulation properties when exposed to high temperatures, so if the cap is made of partially stabilized zirconia as in the past, when heated by a heater, A leakage current flows between the electrodes, and this leakage current affects the current flowing between the anode and the cathode, causing an error in the measured value, which poses a problem in that it impedes accurate oxygen concentration measurement. In order to avoid this problem, it has been considered to improve electrical insulation by forming an alumina porous layer 82 on the interface between the partially stabilized zirconia cap 81 and the heater 31 as shown in FIG. Another problem arises in that the degree of adhesion of the heater 31 to the cap 81 is reduced, and earthquake resistance is significantly deteriorated. Additionally, there is considerable variation in insulation properties depending on the alumina coating conditions, which is difficult to control. Furthermore, in this case, an alumina coating step and its firing step are added, which deteriorates productivity and takes time, which is also disadvantageous in terms of cost. In addition, alumina (A1203) has a long track record as a heater substrate, so it may be possible to use it, but although it certainly has good electrical insulation, its coefficient of thermal expansion is smaller than that of stabilized zirconia (Table 2 (see ), it cannot be used because it is difficult to bond. By the way, I checked this leakage current by performing a test like the one above. The results are shown in Table 1 of Haggi. Table 1 In this test, a cap 37 with a diameter of 5 mm as shown in FIG. and a cathode lead 35, and this cap 37 is heated to 450°C.
Applying a DC voltage to the heater 31 so that it is heated to
This was done by measuring the leakage current and resistance value between the heater lead 32 and the cathode lead 35. In addition, the conventional method of using platinum wire as a lead wire and bonding it to each electrode with platinum paste requires connection work under a microscope, which is very inefficient. There is also the problem that accidents such as lead wires being cut or pulled out are likely to occur, and there are concerns about earthquake resistance. This invention is an oxygen sensor element with excellent productivity that eliminates error factors caused by heater leakage current and enables accurate oxygen concentration measurement without causing problems such as lead wire problems or deterioration of earthquake resistance. The purpose is to provide

[Means to solve the problem]

In order to achieve the above object, the oxygen sensor element according to the present invention includes a stabilized zirconia plate having an anode electrode and a cathode electrode formed on the front and back surfaces, respectively, and a space between the stabilized zirconia plate and the stabilized zirconia plate. A forsterite plate on which a heater, a heater lead part, an anode lead part, and a cathode lead part are printed, which are sealed so as to form a predetermined gap, is provided. 1 Effect] Forsterite is used as the material of the member corresponding to the cap 37 (Fig. 6) that is sealed to the stabilized zirconia plate, and this forsterite plate is equipped with a heater,
The heater lead part, anode lead part, and cathode lead part are formed by printing. This forsterite <2Mg0-8i02) is a material conventionally used as a ceramic material for electron tube envelopes, cathode ray tube envelopes, etc.
As shown in Figure 2, it has excellent electrical insulation properties, and its thermal expansion coefficient can be controlled to be almost the same as that of stabilized zirconia, and it also has good adhesion to stabilized zirconia plates. Table 2 *1: Bending strength [Kg/cm2] Cat: Maximum safe operating temperature ['C) *3: Coefficient of thermal expansion [1/'C] (40 to 400"C)
*4: Thermal conductivity [cal, /cm-s・'C] (20"
C) *5: Volume resistivity [Ω-cml (500'C)
Then, when a cap 37 as shown in FIG. 8 above was made using this forsterite and a leakage current test was performed, good results were obtained as shown in Table 1. Because forsterite has good insulating properties, it can be used not only as a heater for the cap itself, but also as a heater.
The heater lead part, anode lead part, and cathode lead part can be formed by printing instead of the conventional lead wires, thereby improving earthquake resistance. Also,
All can be formed through the printing process, resulting in high productivity.
It is suitable for mass production and can also be made compact. Therefore, by using forsterite as the cap material, it is possible to eliminate errors in output due to leakage current from the heater without changing the structure of conventional ceramic oxygen sensors, and improve earthquake resistance. In addition, it is possible to increase productivity and facilitate downsizing.

【Example】

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1A is a top view of an oxygen sensor element 1 according to an embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along the line B--B in FIG. be. As shown in these figures, the stabilized zirconia plate 2 is stacked on the forsterite plate 3, and the sealing glass 3 is
These are sealed to each other with a predetermined gap created between them via the wires 6. The stabilized zirconia plate 2 functions as an oxygen ion conductive plate, and is formed as a roughly circular plate as shown in FIGS. ing. An anode 21 is formed in the center of the front surface, and a cathode 22 is formed in the center of the back surface.
is formed, and the cathode lead 23 connected thereto is connected to the top portion 2.
It is formed in a. These are made, for example, by printing porous platinum electrodes. Furthermore, a small hole 24 is formed in the center of the stabilized zirconia plate 2. The forsterite plate 3 has a circular shape as a whole as shown in FIGS. 3A and 3B, but has one almost right-angled apex 3a similar to the stabilized zirconia plate 2, and 1 protruding from this apex 3a. one protrusion 3a'' and the other three protrusions 3
b, 3c, and 3d are formed. As shown in FIG. 3A, on the surface side of this forsterite plate 3, a cathode lead 35 is provided at the top 3a and a protrusion 3a'' projecting from the top, and an anode lead 3 is provided at the protrusion 3b in the opposite direction.
4 is formed. As shown in FIG. 3B, on the back side, a heater 31 is formed in the center, and two protrusions 3c
, 3d are formed with heater leads 32 and 33. All of these are formed, for example, by platinum paste printing. The stabilized zirconia plate 2 and forsterite plate 3 are arranged such that the back surface of the stabilized zirconia plate 2 (FIG. 2B) and the surface of the forsterite plate 3 (FIG. 3A) are at the top 2a.
, 3a are stacked so that they face each other. Then. Since the cathode lead 23 of the stabilized zirconia plate 2 and the cathode lead 35 of the forsterite plate 3 face each other, by interposing the platinum paste 26 between them, the cathode lead 35 of the forsterite plate 3
and the cathode 22 of the stabilized zirconia plate 2. Further, an anode 21 of the stabilized zirconia plate 2,
A platinum paste 25 is provided between the forsterite plate 3 and the anode lead 34 by printing or brushing to ensure electrical continuity therebetween. As a result, two of the four protrusions 3a, 3b, 3c, and 3d become the anode and cathode take-out parts, and the other two protrusions 3C3d serve as the heater take-out parts. A gap of approximately 10 μm to 100 μm is formed between the stabilized zirconia plate 2 and the forsterite plate 3, but the gap is closed by airtightly sealing these plates 2.3 with the sealing glass 36. is communicated with the outside air only through the small hole 24. These small holes 24 function as oxygen diffusion holes, but instead of being provided in the stabilized zirconia plate 2 as shown in these figures, they may also be provided in a part of the sealing glass 36 or a part of the forsterite plate 3. good. The oxygen sensor element 1 thus formed is shown in FIGS.
It is housed in a case (stem) 4 as shown in C. The case 4 is made of a ceramic having good electrical insulation properties, such as alumina, zircon, stearite, or forsterite, and is formed into a bottomed cylindrical shape with an open upper end. Four terminal pins 42 are installed in the case 4 so that the terminal pins 42 have four grooves 41 and their upper ends are exposed on the bottom surface of the grooves 41 . The oxygen sensor element 1 is arranged so that the four protrusions 3a, 3b, 3c, and 3d of the oxygen sensor element 1 are fitted into each of the four grooves 41, and the fifth
As shown in Figure C, each of the terminal pins 42 and the protrusions 3a'' are electrically connected to each of the protrusions 3a'', 3b, 3c, and 3d by solder 43.Instead of such soldering, a metal paste is applied and then fired. Thereafter, as shown in FIGS. 5A, B, and C, the lid 5 is placed on the top open side of the bottomed cylindrical case 4, and the cover 51 is attached to the side surface of the M5. The lid 5 is made of, for example, metal mesh, sintered metal, sintered plastic, or porous ceramic.The sensor unit is thus formed by housing the oxygen sensor element 1 in the case 4. In the sensor unit according to this embodiment, protrusions 3a', 3b, 3c, and 3d are formed on the forsterite plate 3 as described above, and an anode lead 34, a cathode lead 35, and a heater lead 32 are attached to each of the protrusions. .33
The protrusions are inserted into the grooves 41 of the case 4 for positioning. And this groove 41
The upper end of the terminal bin 42 is exposed on the bottom surface of the terminal bin 42, and each protrusion is inserted into the groove 41 to establish electrical continuity between the terminal bin and each lead. Therefore, positioning work during assembly is easy, and connection work between each lead and each terminal bin can also be easily performed.

【Effect of the invention】

According to the oxygen sensor element of the present invention, forsterite is used as the material of the plate sealed to form a gap between the stabilized zirconia plate used as the oxygen ion conductor. Moreover, not only the heater but also the heater lead, anode lead, and cathode lead are printed on this forsterite plate, which eliminates leakage current from the heater, improves output accuracy, and improves earthquake resistance. It is possible to improve productivity, further increase productivity, and make it possible to make it more compact. That is, since this forsterite plate has excellent electrical insulation properties, the heater and each lead portion can all be formed by printing, and productivity can be improved by introducing such a printing process. Since the lead parts and the like are formed by printing, problems such as earthquake resistance when connecting lead wires are solved, and it also contributes to compactness.

[Brief explanation of the drawing]

1A and 1B show an oxygen sensor element according to an embodiment of the present invention, in which FIG. 1A is a plan view seen from above;
Figure B is a cross-sectional view taken along the line B-B in Figure 1A, and Figures 2A and 2B show the stabilized zirconia plate of the same example.
is a front view, Figure 2B is a back view, Figures 3A and B show the forsterite plate of the same example, Figure 3A is a front view, Figure 3B is a back view, and Figure 4 is a front view. A, B, and C show the case in which the oxygen sensor element described above is housed, and FIG. 4A is a plan view seen from above, FIG.
Figure C is a sectional view taken along the line C-C of Figure 4A, Figures 5A, B,
C shows the oxygen sensor element housed in the case, and FIG. 5A is a plan view seen from above.
Figure B is a side view from the side, Figure 5C is C-C in Figure 5A.
6 is a sectional view of a conventional example, FIG. 7 is a sectional view showing a part of another conventional example, and FIG. 8 is a schematic diagram for explaining a leakage current test. DESCRIPTION OF SYMBOLS 1... Oxygen sensor element, 2... Stabilized zirconia plate, 3... Forsterite plate, 4... Case (stem), 5... Lid, 21... Anode, 22... Cathode, 23.35...Cathode lead, 24.38
...Small hole, 25.26...Platinum paste, 27...
・Anode lead wire, 28...Cathode lead wire, 3
1...Heater, 32.33...Heater lead,
34...Anode lead wire Tall lead wire, 41...
Groove, 42...Terminal pin, 43...Solder, 51...
Cover, 81... Partially stabilized zirconia cap, 8
2...Alumina porous layer. Joy 1 area

Claims (1)

[Claims] (1) A stabilized zirconia plate having an anode electrode and a cathode electrode formed on the front and back sides, respectively, is sealed so that a predetermined gap is formed between the stabilized zirconia plate and the stabilized zirconia plate. An oxygen sensor element comprising a heater, a forsterite plate on which a heater lead part, an anode lead part, and a cathode lead part are printed.