JPH0552752U - Oxygen sensor - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to provide a limiting current type oxygen sensor having excellent productivity. The present invention relates to a gas permeable substrate 11 and the substrate 1.
At least one pair of electrodes 12 and 13 formed on one surface of the substrate 1 at a distance from each other, the electrodes 12 and 13 and the substrate 11
An oxygen sensor of a limiting current type composed of an ion conductor layer 14 formed on the upper surface of the gas permeable substrate 11, and has a structure in which other constituent elements such as electrodes are formed on one surface side of the gas permeable substrate 11, which is excellent. Mass productivity can be obtained.

Description

[Detailed description of the device]

[0001]

[Industrial application]

 The present invention relates to a limiting current type oxygen sensor, and more particularly to an oxygen sensor having excellent productivity.

[0002]

[Prior Art]

 Conventionally, various structures of the limiting current type oxygen sensor have been proposed, but when roughly classified, for example, a thick film type and a thin film type as shown in FIGS. Be done.

In the thick film type oxygen sensor C ₁ of FIG. 3, electrodes 2 and 3 are provided on both surfaces of an ion conductor plate 1 made of zirconia or the like, and ion conduction on one side (upper side in the figure) of the electrode 3 is conducted. The body plate 1 is covered with a cap 4 for forming a diffusion chamber R, a gas diffusion hole 5 communicating with the diffusion chamber R is provided in the center of the cap 4, and a heater 6 for heating is provided on a part of the surface thereof. It is a thing.

The thin-film oxygen sensor C ₂ of FIG. 4 is also provided with electrodes 2 and 3 on both surfaces of an ion conductor plate 1 such as zirconia, and one electrode 2 side (lower side in the figure). Is provided with a gas permeable substrate 7 in place of the gas diffusion hole.

In the case of using any of the oxygen sensors C ₁ and C ₂ described above, when the oxygen sensor C ₁ or C ₂ is used, the entire sensor is heated (about 400 ° C.) by the heater 6 for heating, an external heating means, etc. The oxygen concentration is measured by energizing 3 and determining the limiting current value.

[0006]

[Problems to be solved by the device]

However, in the case of each of these oxygen sensors C ₁ and C ₂ , from the viewpoint of manufacturing, there were the following problems to be solved. (1) First, since it is necessary to provide the electrodes 2 and 3 on both sides of the ion conductor plate 1 in any of the oxygen sensors C ₁ and C ₂ , after forming one electrode, the other electrode is formed. However, there is a problem that the manufacturing process is complicated and the mass productivity is poor. (2) Furthermore, in the case of such a double-sided electrode structure, the ion current characteristics thereof are greatly affected by the thickness of the ion conductor plate 1, so it is necessary to control this plate thickness with high accuracy. High manufacturing technology was required. (3) In the case of the thin film type oxygen sensor C ₂ , conventionally, a material such as alumina or steatite is generally used as the gas permeable substrate 7, and a doctor blade method, a uniaxial or hydrostatic press is used. There are porous substrates obtained by adjusting the pressing pressure when forming and firing by a forming method such as the above, or by adding an organic binder. There was a problem that the limit current value obtained varied due to the fact that the control was rather troublesome and the reproducibility was poor. Furthermore, this substrate has a problem that thermal shock resistance is poor and cracks are likely to occur due to heating when the sensor is used.

The present invention has been made in view of such a conventional situation, and a major feature thereof is to provide a sensor which is structurally excellent in productivity.

[0008]

[Means for Solving the Problems]

 The present invention is directed to a limiting current consisting of a gas-permeable substrate, at least a pair of electrodes formed on one surface of the substrate at a distance from each other, and an ion conductor layer formed on the electrodes and the substrate. Type oxygen sensor.

[0009]

[Action]

 As described above, according to the present invention, since the other components such as the electrodes are formed on one side of the gas permeable substrate, excellent mass productivity can be obtained.

[0010]

【Example】

FIG. 1 shows an embodiment of a limiting current type oxygen sensor C _{11 according to} the present invention. 11 is a gas permeable substrate made of continuous porous machinable ceramic or the like, and 12 and 13 are A pair of electrodes made of white gold or the like formed on one surface side of the gas permeable substrate 11 with a slight distance therebetween, and 14 an ion conductor layer made of zirconia or the like formed on the electrodes 12 and 13 and the substrate 11. Is.

In the oxygen sensor C ₁₁ , the gas permeable substrate 11 serves as a sensor pedestal and serves to obtain a diffusion-controlling hole which is essential in a limiting current type oxygen sensor. Therefore, the porosity of the substrate 11 is required to be a continuous type, that is, a structure in which small holes are continuous in some way on the front and back sides (upper and lower sides) of the substrate to allow gas permeation. The machinable ceramics used as such members are composed of α or β cordierite, aluminum titanate, zirconia, aluminum nitride, silicon nitride, boron nitride, etc. Since it has the same characteristics as the level and can be machined, it can easily machine to the desired thickness and shape, and the stress during machining is easily relieved from its structure, so cracks occur during machining. In addition, since it has high thermal shock resistance, it has the advantage that cracking does not easily occur even when the sensor is heated.

Examples of such machinable ceramics include, for example, Asahi Glass Co., Ltd.'s Lotech MC, Lotech CF, Lotech TC, Lotech TF, and Lotech Z (all are trade names), and Nihon Heavy Chemical Industry's silicon nitride. Examples include SN-S and SN-B (both are trade names). In particular, these machinable ceramics have a much smaller variation in porosity than conventional porous alumina, etc., and the resulting variation in the limiting current value can also be suppressed to a small level, and the pore diameter is also extremely small. Since it is small, it is excellent in smoothness, and good adhesion can be obtained in the formation of the electrodes 12 and 13 and the ion conductor layer 14.

The shape of the gas permeable substrate 11 is not particularly limited and may be, for example, a disc shape or a rectangular shape, and the thickness t ₁ thereof is, for example, 01. ~ 1.0 mm is preferable.

The electrodes 12 and 13 are formed by a sputtering method, a screen printing method or the like. The thickness t ₂ is preferably 1 to 5 μm in the case of the sputtering method and 1 to 3 μm in the case of the screen printing method, and the separation distance (slit width) δ between the electrodes 12 and 13 is as much as possible. It is desirable to make the width narrow, and this makes it possible to manufacture a high-performance oxygen sensor such as a low-temperature operation and high response, and for example, it may be about 0.1 to 20 μm.

The ion conductor layer 14 coated on the electrodes 12 and 13 and the gas permeable substrate 11 is formed by, for example, a sputtering method, and the thickness t ₃ thereof is preferably about 5 to 100 μm. ..

When the oxygen sensor C ₁₁ having such a configuration is heated to about 400 ° C. by an external heating means and the like and the electrodes 12 and 13 are energized and placed in an oxygen atmosphere, FIG. As described above, oxygen molecules (O ₂ ) outside the sensor are taken into the minus electrode 12 side through the small holes of the gas permeable substrate 11, electrons are given there, and the ion conductor layer formed between the electrodes 12 and 13 is formed. In the 14th part, oxygen ions (O ²⁻ ) move to the plus electrode 13 side, where electrons are lost to become oxygen molecules (O ₂ ) which are discharged to the outside through the small holes of the gas permeable substrate 11. An ion current is generated by the action of such oxygen molecules, and a limiting current value corresponding to the oxygen concentration in the oxygen atmosphere is obtained. The target oxygen concentration can be determined from this limiting current value.

Incidentally, in the oxygen sensor C ₁₁ as described above, the gas permeable substrate 11 is a disk type made of low-tech Z, and its size (diameter) is L = 5 mm and its thickness is t _1. = 0.3 mm, the thickness of the platinum electrodes 12 and 13 is t ₂ = 5 μm, the slit width is δ = 10 μm, and the thickness of the zirconia ion conductor layer 14 is t ₃ = 50 μm. As a result, the current characteristic curve shown in FIG. 2 was obtained. From this current characteristic curve, it is understood that the limiting current value I of 40 μA can be obtained by the applied voltage of 0.7 to 1.4V.

In the above embodiment, the pair of electrodes was used, but the present invention is not limited to this.

[0019]

[Effect of the device]

 As is apparent from the above description, the oxygen sensor according to the present invention has the following excellent effects. (1) First, since the electrodes and ionic conductor layers, which are the constituent elements of the sensor, are formed on one side of the gas permeable substrate, the manufacturing process is simpler than the conventional double-sided electrode structure. , And excellent mass productivity can be obtained. In other words, in the case of the double-sided electrode structure, it is necessary to first form an electrode on one surface of the substrate and then to form another electrode on the other surface of the substrate by turning the substrate over. On the other hand, the present invention has an advantage that the step of turning over the substrate and the step of forming the electrode twice are unnecessary.

(2) Further, as compared with the conventional thick film type sensor, a cap having a gas diffusion hole is not required, and it can be manufactured in two steps of an electrode forming step for a substrate and an ion conductor layer forming step. The cost can be reduced by reducing the number of steps.

(3) In addition, in the conventional oxygen sensor, the control of the thickness of the ionic conductor portion was a factor that greatly affects the sensor characteristics. However, in the present invention, the slit width of at least a pair of both electrodes is used. Since the amount of ionic conductors such as zirconia can be controlled accurately, the control of sensor characteristics becomes extremely possible. For this reason, it is possible to obtain an advantage that it is unnecessary to control the thickness of the conventional ionic conductor, which is difficult to control with high accuracy.

(4) Further, when a machinable ceramic is used as the gas permeable substrate, it is easy to process, and cracks are less likely to occur due to stress during processing and heating during use.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of an oxygen sensor according to the present invention.

FIG. 2 is a graph showing a current characteristic curve obtained by the oxygen sensor of FIG.

FIG. 3 is a vertical sectional view showing an example of an oxygen sensor having a conventional structure.

FIG. 4 is a vertical sectional view showing another example of an oxygen sensor having a conventional structure.

[Explanation of symbols]

C ₁₁ oxygen sensor, 11 gas permeable substrate, 12 electrode, 13 electrode, 14 ion conductor layer,

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Creator Yoshinori Kato 1-5-1, Kiba, Koto-ku, Tokyo Inside Fujikura Electric Wire Co., Ltd.

Claims (1)

[Scope of utility model registration request] 1. A limiting current type of gas-permeable substrate comprising: a gas-permeable substrate; at least a pair of electrodes formed on one surface of the substrate at a distance from each other; and an ion conductor layer formed on the electrode and the substrate. Oxygen sensor.