JPH05312768A - Oxigen sensor - Google Patents

Abstract

PURPOSE:To simplyfy production process and reduce the production cost by suppressing the dispersion of limiting current characteristic to the utmost and unnecessitating any electrode preparation through separate processes for both surfaces of ion conductor. CONSTITUTION:An oxigen sensor is provided with at least one pair of electrodes 43 and 44 on one surface of an ion conductor 34 and a covered layer 45 on a negative electrode 44 at least, and the portion 45a of the layer 45 locating upward on the electrode is made of inorganic material that can pass through oxigen, while the portion 45b of the layer 45 is made of airtightening metallic material with a proper matching property for inorganic material. When the electrodes are applied with a specified voltage, the oxigen put into the ion conductor will flow in the ion conductor through oxigen pumping action, so that oxigen concentration of sample gas can be measured by measuring the current value because the oxigen ion is used as a carrier. The inorganic material is formed by anode-oxidizing the portion locating upward on the electrode of metallic layer covering the electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a limiting current type oxygen sensor which is suitable for use in preventing oxygen deficiency accidents in basements and in combustion management of engines and boilers.

[0002]

2. Description of the Related Art Conventionally, a limiting current type oxygen sensor using stabilized zirconia as an ionic conductor has been proposed and put into practical use. This oxygen sensor uses pure zirconia (Z
An oxide such as yttria (Y ₂ O ₃ ), magnesia (MgO) or calcia (CaO) is added to the rO ₂ ) as an additive for several meters.
Stabilized zirconia, which is a solid solution of about ol% and retains a fluorite type cubic crystal at low temperature, is used as an ion conductor. It can detect a wide range of oxygen partial pressure, has a fast response speed, and has an electromotive force. Since it has various characteristics such as stable and usable in high temperature atmosphere, it prevents various oxygen deficiency accidents in a closed room such as a basement, measures oxygen concentration in molten steel, combustion control of engine and boiler, pollution measurement, etc. It is a sensor that is suitable for the purpose.

As the oxygen sensor, for example, an oxygen sensor having a thick film structure as shown in FIG. 8 is known. This oxygen sensor 1 is formed on both surfaces of an ionic conductor 2 made of a thin solid electrolyte having ionic conductivity such as stabilized zirconia (eg, ZrO ₂ -8 mol% Y ₂ O ₃ ). And the porous platinum electrodes 3 and 4 to which a constant sensor monitoring voltage is applied, and the ionic conductor 2.
A ceramic cap 7 which is bonded to the electrode 3 side by crystallized glass 5, 5 and has a gas diffusion hole 6 vertically penetrating in the central portion, and a heater for heating formed on the upper surface of the ceramic cap 7. 8 is generally configured. The ceramic cap 7 may be replaced with an inorganic porous material having extremely high oxygen permeability, such as porous alumina. In the oxygen sensor 1, when a predetermined voltage is applied to the heater 8 and a predetermined voltage is applied between the electrodes 3 and 4, the gas diffusion hole 6 is formed.
Oxygen in the sample gas taken into the ionic conductor 2 through the ionic conductor 2 flows as ions in the ionic conductor 2 by the oxygen pumping action, and the oxygen concentration in the sample gas is determined from the current value using the oxygen ions as carriers. Is measured.

Further, like the oxygen sensor 11 shown in FIG.
Without forming the gas diffusion hole 6 in the ceramic cap 7, the gas diffusion hole 12 penetrating vertically in the central portion of the ionic conductor 2.
It is also known that formed. Also in the oxygen sensor 11 having this configuration, oxygen in the sample gas taken in from the gas diffusion holes 12 of the ionic conductor 2 flows as ions in the ionic conductor 2 due to the oxygen pumping action. The oxygen concentration in the sample gas is measured from the value of the electric current using as a carrier.

Further, like an oxygen sensor 21 shown in FIG. 10, a ceramic cap 2 having an airtight glass film 22 formed on the entire inner surface of the electrode 3 of the ionic conductor 2 is formed.
A structure covered with 3 is also known. Also in the oxygen sensor 21 having this configuration, oxygen in the sample gas taken in from the gas diffusion holes 12 of the ionic conductor 2 flows as ions in the ionic conductor 2 due to the oxygen pumping action. The oxygen concentration in the sample gas is measured from the value of the electric current using as a carrier.

Further, as the thin film type oxygen sensor,
For example, an oxygen sensor 31 having a structure as shown in FIG. 11 is known. The oxygen sensor 31 includes an oxygen permeable substrate 3
2 has a structure in which an electrode 33, an ion conductor 34, and an electrode 35 are sequentially stacked on top of 2. And this oxygen sensor 31
In the above, oxygen in the sample gas taken in from the substrate 32 side flows as ions in the ionic conductor 34 by the oxygen pumping action, and the oxygen concentration in the sample gas is determined from the current value using the oxygen ions as carriers. Is measured.

[0007]

In the oxygen sensors 1 to 31 described above, since the electrodes are formed on both sides of the ionic conductor such as stabilized zirconia, the ionic current characteristics thereof are ionic conductivity. This greatly depends on the thickness of the bodies 2 and 34, and these ionic conductors 2 and 34 are required to be highly controlled in thickness. However, in the actual manufacturing process, the screen printing method is preferably used in the case of a thick film, and the sputtering or the like is preferably used in the case of a thin film. It is extremely difficult to control with high accuracy, and there is a drawback in that variations in ion current characteristics cannot be reduced. Further, in the above oxygen sensors 1 to 31, it is necessary to accurately form the electrodes 3 and 4 (33, 35) on both surfaces of the ionic conductor 2 (34) by separate steps, which complicates the manufacturing process. At the same time, there was a drawback that the manufacturing cost also increased. Since these drawbacks are obstacles when introducing an automated line or the like, the oxygen sensors 1 to 31 described above are
Generally, mass production was difficult.

The present invention has been made in view of the above circumstances, and solves the above-mentioned drawbacks and has an excellent feature such as high reliability, downsizing, low power consumption, and low cost. To provide.

[0009]

In order to solve the above problems, the present invention employs the following oxygen sensor. That is, in the oxygen sensor according to claim 1, at least a pair of electrodes are formed on one surface of the ionic conductor, a coating layer is formed on at least a negative electrode of these electrodes, and the electrode is located above the coating layer. The part to be formed is made of an inorganic material capable of passing oxygen, and the part other than the above is made of a metal material having good airtightness with the inorganic material, and by applying a predetermined voltage to these electrodes. ,
Oxygen in the sample gas taken into the ionic conductor flows as ions in the ionic conductor by an oxygen pumping action, and the oxygen concentration in the sample gas is determined from the current value using the oxygen ions as carriers. It is characterized by being measured.

The oxygen sensor according to a second aspect is the oxygen sensor according to the first aspect, wherein the inorganic material is formed by anodizing a portion of a metal layer covering the electrode, which is located above the electrode. Is characterized by.

The above-mentioned inorganic material capable of passing oxygen is, for example, porous ceramics such as porous alumina (Al ₂ O ₃ ) and porous yttria-stabilized zirconia containing 1 to 15 mol% of Y ₂ O _3. Is preferred. In addition, the metal material having good airtightness that is compatible with the inorganic material is a metal that is a constituent element of the porous ceramics and has airtightness, for example, aluminum (Al) metal for porous alumina, or porous metal. 2 to 3 parts of yttrium (Y) for high quality yttria-stabilized zirconia
A zirconium (Zr) alloy added with 0 mol% is preferable.

[0012]

In the oxygen sensor according to the first aspect of the present invention, oxygen in the sample gas taken into the ionic conductor through an inorganic material capable of passing oxygen is oxygen-pumping action to cause the ionic conductivity. Oxygen concentration in the sample gas is measured from the current value in which ions flow in the body, especially in the surface layer of the ionic conductor, and the oxygen ions serve as carriers.

The coating layer formed on at least the negative electrode is made of an inorganic material that allows oxygen to pass through the portion of the coating layer located above the electrode, and the portion other than the above is the inorganic material. By using a metal material that has good airtightness and consistency, it is possible to selectively pass oxygen only to the upper part of the negative electrode, making it possible to minimize the variation in the limiting current characteristics of the oxygen sensor. Become. Further, by effectively utilizing the characteristics of the surface layer of the ionic conductor, the thickness of the ionic conductor only needs to be a thickness that sufficiently satisfies the mechanical strength, and it is not necessary to control it with high precision.

By forming electrodes on one surface of the ionic conductor, it is not necessary to attach electrodes to both surfaces of the ionic conductor in separate steps, which simplifies the manufacturing process and reduces the manufacturing cost. ..

Further, in the oxygen sensor according to the present invention, the portion of the metal layer covering the electrode located above the electrode is anodized to be an inorganic material capable of allowing oxygen to pass therethrough. The material changes to the inorganic material continuously, the stress generated on the joint surface between the metal material and the inorganic material is reduced, and the durability can be improved. Further, the porosity of the inorganic material can be adjusted by adjusting the magnitude of the applied voltage or the current.

[0016]

Embodiments of the oxygen sensor of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 shows an oxygen sensor 4 according to Embodiment 1 of the present invention.
FIG. 2 is a front sectional view showing 1. The oxygen sensor 41 includes a silicon (Si) substrate 42, stabilized zirconia formed on the upper surface of the Si substrate 42 (e.g., ZrO ₂ over 8mol
% Y ₂ O ₃ ) etc., and a positive electrode 43 and a negative electrode 44 of rectangular porous platinum formed at an interval of 10 μm on the upper surface of the ion conductor 34.
And the inorganic material coating layer 4 formed on the negative electrode 44.
5 and 5 are roughly configured.

The portion 45a of the coating layer 45 located above the negative electrode 44 is made of porous alumina (Al ₂ O ₃ ) which is an inorganic material capable of passing oxygen, and the portion 45b other than the above is made of dense aluminum. Each of them is made of a metal material which is airtight and has a good compatibility with the inorganic material made of (Al).

As the above-mentioned inorganic material capable of passing oxygen, in addition to the above-mentioned porous alumina, for example, Z
and rO ₂ over _{8mol% Y 2 O 3, ZrO} 2 over 3mol% Y ₂ O ₃
Porous yttria-stabilized zirconia such as, for example, are preferably used. In addition to the Al, as the metal material having good airtightness with the inorganic material, for example, ZrO
Zr chromatography for _{2-8mol% Y 2 O 3 16mol%} Y
With respect to the zirconium alloy of ZrO _{2 -3} mol% Y ₂ O ₃ , the zirconium alloy of Zr-6 mol% Y is preferably used.

Next, a method of forming the coating layer 45 will be described with reference to FIG.
It will be explained based on. As shown in FIG. 5A, the ion conductor 34, the positive electrode 43, and the negative electrode 44 are sequentially formed on the upper surface of the Si substrate 42, and then the Al film 51 is formed on the negative electrode 44.
Are formed (substrate 52).

Next, the positive side of the output end of the constant current power source is connected to the negative electrode 44, the negative side is connected to a separately prepared stainless steel plate 53, and these substrates 52 and stainless steel plate 53 are connected to 4N phosphoric acid ( It is immersed in an H ₃ PO ₄ ) aqueous solution 54, and a predetermined current is passed between the substrate 52 and the stainless steel plate 53 ((b) of the same figure). During this time, the portion 51a of the Al film 51 on the negative electrode 44 is anodized and changed to porous alumina. In this way, the coating layer 45 is formed on the negative electrode 44.
Can be formed.

FIG. 3 is a diagram showing the limiting current characteristics of the oxygen sensor 41. This figure is a graph showing the magnitude of the electric current obtained when the oxygen sensor 41 is heated to 300 ° C. and the magnitude of the voltage applied between the electrodes 43 and 44 is changed. From FIG. 3, the oxygen sensor 41 of the first embodiment is shown.
It is understood that indicates a good limiting current characteristic. Moreover,
The variation of the limiting current characteristics is small, and the porous alumina of the coating layer 45 is extremely uniform.

As described above, according to the oxygen sensor 41 of the above embodiment, the thin film ionic conductor 34 formed on the upper surface of the Si substrate 42 and the positive electrode formed on the upper surface of the ionic conductor 34. 43 and the negative electrode 44, and the inorganic material coating layer 45 formed on the negative electrode 44, oxygen can be selectively passed only to the upper portion of the negative electrode 44. It is possible to make the variation in the limiting current characteristic of the sensor extremely small. Further, by effectively utilizing the characteristics of the surface layer of the ionic conductor 34,
The thickness of the ionic conductor 34 may be a thickness that sufficiently satisfies the mechanical strength, and it is not necessary to control it with high precision.

Further, since the positive electrode 43 and the negative electrode 44 are formed on one surface of the ionic conductor 34, the manufacturing process can be simplified and the manufacturing cost can be reduced.

Further, since the metal of the portion 45a located above the negative electrode 44 of the coating layer 45 is anodized, an inorganic material (porous alumina) capable of passing oxygen is formed. The change of the metal material to the inorganic material becomes continuous, the thermal and mechanical stress generated at the joint surface between the metal material and the inorganic material can be reduced, and the durability can be improved. Further, the porosity of the inorganic material can be adjusted by adjusting the magnitude of the applied voltage or the current. Therefore, oxygen in the sample gas can be selectively passed, and the sensitivity as an oxygen sensor can be improved.

(Second Embodiment) FIG. 4 is a front sectional view showing an oxygen sensor 61 according to a second embodiment of the present invention. This oxygen sensor 61 is roughly composed of a Si substrate 42, an ionic conductor 34, a positive electrode 43 and a negative electrode 44, and an inorganic material coating layer 62 formed on these electrodes 43, 44. There is. The portions 62a and 62b of the coating layer 62 located above the electrodes 43 and 44 are made of porous alumina, and the other portions 62c, ... Are made of dense Al.

As for the coating layer 62, similarly to the coating layer 45 of the first embodiment, an Al film is formed on the electrodes 43 and 44, and the portions of the Al film located above the electrodes 43 and 44 are anodized. It can be formed by This oxygen sensor 6
Also in 1, the same operation as the oxygen sensor 41 described above
The effect can be obtained.

(Third Embodiment) FIG. 5 is a front sectional view showing an oxygen sensor 71 according to a third embodiment of the present invention. The oxygen sensor 71 has an oxide film (SiO ₂ film) 7 on the surface of the Si substrate 42.
2 is formed, and the ionic conductor 34,
The positive electrode 43 and the negative electrode 44 are sequentially formed, and the negative electrode 44
The coating layer 45 is formed on the above. Also in this oxygen sensor 71, the same action and effect as those of the oxygen sensors 41 and 61 described above can be obtained.

(Embodiment 4) FIG. 6 is a front sectional view showing an oxygen sensor 81 according to Embodiment 4 of the present invention. In this oxygen sensor 81, an ion conductor 34, five pairs of positive electrodes 43 and negative electrodes 44 are sequentially formed on a Si substrate 42, and a coating layer 45 is formed on each negative electrode 44.

FIG. 7 is a diagram showing the limiting current characteristics of the oxygen sensor 81. In this figure, the oxygen sensor 81 is
The magnitude of the current obtained when heated to 00 ° C. and the magnitude of the voltage applied between the electrodes 43 and 44 was changed was plotted. From FIG. 7, the oxygen sensor 81 of the fourth embodiment is shown.
It is understood that indicates a good limiting current characteristic.

Also in this oxygen sensor 81, the same action and effect as those of the oxygen sensors 41, 61, 71 described above can be obtained.

[0031]

As described in detail above, according to the oxygen sensor of claim 1 of the present invention, at least a pair of electrodes is formed on one surface of the ionic conductor, and at least the negative electrodes of these electrodes are formed. A coating layer is formed on the electrode, and the portion of the coating layer located above the electrode is made of an inorganic material that allows oxygen to pass through, and the portion other than the above is a metal having a good airtightness with the inorganic material. Made of materials,
By applying a predetermined voltage to these electrodes, oxygen in the sample gas taken into the ionic conductor flows as ions in the ionic conductor due to the oxygen pumping action, and the oxygen ions serve as carriers. From the current value to
Since the oxygen concentration in the sample gas is to be measured, oxygen can be selectively passed only through the negative electrode upper part, and the variation in the limiting current characteristic of the oxygen sensor can be made extremely small. Further, by effectively utilizing the characteristics of the surface layer of the ionic conductor, the thickness of the ionic conductor only needs to be a thickness that sufficiently satisfies the mechanical strength, and it is not necessary to control it with high precision.

By forming electrodes on one surface of the ionic conductor, it is not necessary to attach electrodes to both surfaces of the ionic conductor in separate steps, which simplifies the manufacturing process and reduces the manufacturing cost. ..

According to the oxygen sensor of the second aspect, in the oxygen sensor of the first aspect, the inorganic material anodizes a portion of the metal layer covering the electrode, which is located above the electrode. Since the change of the metallic material to the inorganic material is continuous, the thermal and mechanical stress generated at the joint surface between the metallic material and the inorganic material can be reduced, and the durability is improved. Can be made Further, the porosity of the inorganic material can be adjusted by adjusting the magnitude of the applied voltage or the current. Therefore, oxygen in the sample gas can be selectively passed, and the sensitivity as an oxygen sensor can be improved.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a method of forming a coating layer of the oxygen sensor of Example 1 of the present invention.

FIG. 3 is a diagram showing a limiting current characteristic of the oxygen sensor of Example 1 of the present invention.

FIG. 4 is a front sectional view showing an oxygen sensor according to a second embodiment of the present invention.

FIG. 5 is a front sectional view showing an oxygen sensor of Example 3 of the present invention.

FIG. 6 is a front sectional view showing an oxygen sensor of Example 4 of the present invention.

FIG. 7 is a diagram showing a limiting current characteristic of the oxygen sensor of Example 4 of the present invention.

FIG. 8 is a front sectional view showing a conventional oxygen sensor.

FIG. 9 is a front cross-sectional view showing a conventional oxygen sensor.

FIG. 10 is a front sectional view showing a conventional oxygen sensor.

FIG. 11 is a front sectional view showing a conventional oxygen sensor.

[Explanation of symbols]

41 ... Oxygen sensor, 42 ... Substrate, 34 ... Ion conductor, 43 ... Positive electrode, 44 ... Negative electrode, 45 ... Coating layer, 61 ... Oxygen sensor, 62 ... Coating layer, 71 ... Oxygen sensor, 72 ... Oxide film, 81 ... Oxygen sensor.

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

Claims (2)

[Claims] 1. At least a pair of electrodes is formed on one surface of an ionic conductor, a coating layer is formed on at least a negative electrode of these electrodes, and a portion of the coating layer located above the electrodes passes oxygen. In addition to being made of an inorganic material that can be made to exist, the portions other than the above are made of a metal material that has good airtightness with the inorganic material, and by applying a predetermined voltage to these electrodes, Oxygen in the sample gas taken in by the oxygen ion pumping action flows as ions in the ionic conductor, from the current value using the oxygen ions as carriers,
An oxygen sensor, wherein the oxygen concentration in the sample gas is measured. 2. The oxygen sensor according to claim 1, wherein the inorganic material is formed by anodizing a portion of a metal layer covering the electrode, which is located above the electrode.