JPH05240834A - Oxygen sensor and manufacture thereof - Google Patents

Abstract

PURPOSE:To manufacture an oxygen sensor, which is excellent in detecting accuracy, above all the measuring accuracy of low-concentration oxygen gas, by the easy method. CONSTITUTION:In an oxygen sensor, an electrochemical pump part, wherein first and second electrode 4 and 5 are formed on a first zirconia ceramics electrolyte member 1, and an electrochemical sensor part, wherein third and fourth electrodes 6 and 7 are formed on a second zirconia ceramics solid electrolyte member 2, are arranged through a tightly sealed space, which is formed in a sealing shape of the zirconia ceramics solid electrolyte members and a mica- glass ceramics sealing member 3 in the sealing shape. When the oxygen sensor is manufactured, the zirconia ceramics solid electrolyte members and the mica- glass ceramics sealing member are heated and bonded.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor particularly excellent in measuring low-concentration oxygen gas and a method for manufacturing the same.

[0002]

2. Description of the Related Art Zirconia has been applied to oxygen sensors because it exhibits perfect oxygen ion conductivity at 600 to 800 ° C. Generally, the oxygen concentration of the test gas is obtained from the Nernst theoretical formula using air as the reference gas. When actually measured by this method, the oxygen concentration up to about 0.1% can be measured by using this Nernst's theoretical formula, whereas in the oxygen concentration range below that, the device is stabilized and the theoretical It will be very difficult to get the value data. For example, when the oxygen concentration of the test gas is as low as 10 ppm, the measurement accuracy becomes poor. The reason is that electrochemical gas permeation, that is, movement of oxygen ions corresponding to electron conduction, which is slightly present in the solid electrolyte, occurs from the air side electrode toward the test side electrode, and the oxygen concentration near the test gas side electrode Is supposed to change. As an improvement measure, a point contact type or double tube type sensor has been proposed.
Vol. 21, No. 11, page 7 (1983), all have complicated structures and have a problem in stability over a long period of time.

On the other hand, a method in which an electrochemical sensor section and an electrochemical oxygen pump are used in combination and the oxygen concentration of the reference gas is actively controlled by using the electrochemical oxygen pump is particularly suitable for lean-bar system air-fuel ratio control of automobiles. Is being developed with the aim of applying to the sensor element. Since this sensor element is not in contact with a gas having a constant oxygen concentration because the whole sensor element is exposed to the test gas whose oxygen concentration constantly changes, that is, the exhaust gas of the automobile, oxygen in the exhaust gas of the vehicle is removed using an oxygen pump. The reference gas is supplied to the inside of the sensor to produce a reference gas containing a high concentration of oxygen. However, it is difficult to strictly control the oxygen concentration of the reference gas obtained in this way, and although it can be used as a so-called λ type sensor required for automobile air-fuel ratio control, it cannot be used for applications that require strict measurement accuracy. Absent.

Since zirconia ceramics have high hardness and low toughness, they are not easy to machine. In the past, products formed from powder and sintered were often used without being processed. However, due to strong demands from the application aspect such as the present invention, the manufacturing and processing techniques of ceramic parts have been rapidly advanced, and the applications as precision functional material parts are expanding. For this purpose, not only the removal of a part of the material such as cutting and polishing, but also the need to combine other substances such as adhesion and adhesion and the same kind of substance has been increased. The method of using the same kind of ceramic material in the present invention can be divided into solid phase adhesion such as using an intervening layer, heating and pressure bonding, and melt bonding such as laser welding, electron beam welding and welding by electric discharge. Here, melt bonding has recently received attention, but there are relatively few cases. The reason is that the device is insufficient, the cost is high, and there is a problem with the bonding jig. On the other hand, solid phase adhesion is a commonly used method. At present, the cost of bonding oxygen sensor elements is
Considering adhesion, adhesive strength, damage to other members, etc., only solid-phase adhesion can be used. As the bonding method, a method of heating a zirconia material with metallic aluminum interposed (Japanese Patent Laid-Open No. 59-217682) and a method of thinly brazing Ti, Zr, etc. on the surface of the zirconia material (Japanese Patent Laid-Open No. 60-81)
069), using a bonding paste made by kneading a zirconia powder and an organic binder (JP-A-62-2).
30681), a method using an adhesive made of crystallized glass of oxide and a rare earth oxide (Japanese Patent Laid-Open No. 63-1592).
63) Then, there is a method (Japanese Patent Laid-Open No. 01-145382) for obtaining strong adhesion by plastic deformation of zirconia, and various methods have been tried in this way. Thus, various bonding methods for zirconia have been tried. But,
In the method of interposing a metal such as Al or Ti on the bonding surface, there are problems in electrical insulation and adhesive strength at high temperature. The method of interposing ceramic powder or the like is inferior in denseness and causes molecular gas permeation. Further, a method of adhering by plastic working is also conceivable, but it requires a temperature of 1300 ° C. or higher,
There is also a problem in the dimensional accuracy of the adhesive.

[0005]

SUMMARY OF THE INVENTION The present inventors have completed the present invention as a result of intensive studies in view of the above-mentioned problems in bonding existing oxygen sensors and ceramics to each other. An object of the present invention is to provide an oxygen sensor excellent in detection accuracy, particularly low-concentration oxygen gas measurement accuracy, and a manufacturing method thereof. Other objects and effects of the present invention will be apparent from the following description.

[0006]

The above-described object is to provide an electrochemical pump portion having first and second electrodes formed on a first zirconia ceramics solid electrolyte member and a second zirconia ceramics solid electrolyte member. The electrochemical sensor part having the third and fourth electrodes formed therein is arranged via a sealed space formed in a sealing shape by the zirconia ceramics solid electrolyte member and the mica glass ceramics sealing member. Oxygen sensor and

This is achieved by a method of manufacturing an oxygen sensor, characterized in that a zirconia ceramics solid electrolyte member and a mica glass ceramics sealing member are heated and adhered when manufacturing the oxygen sensor.

An example of an embodiment of the oxygen sensor of the present invention will be described with reference to the drawings. 1 and 2 are explanatory views showing an example of the oxygen sensor according to the present invention. In FIG. 1, 1 is a first zirconia ceramics solid electrolyte member, 2 is a second zirconia ceramics solid electrolyte member, 3 is a mica glass ceramics sealing member, 4
Is a first electrode, 5 is a second electrode, 6 is a third electrode, 7 is a fourth electrode, 8 is a voltmeter, and 9 is a DC power supply. In FIG. 2, 1 is a first zirconia ceramics solid electrolyte member, 2 is a second zirconia ceramics solid electrolyte member, 3 is a mica glass ceramics sealing member, 4
Is a first electrode, 5 is a second electrode, 6 is a third electrode, 7 is a fourth electrode, 8 and 8'are voltmeters, and 9 is a DC power supply.

The oxygen sensor shown in FIG. 1 has a first zirconia ceramics solid electrolyte member 1 and a second zirconia ceramics solid electrolyte member 2 each having a first
Electrode 4 and second electrode 5, and third electrode 6 and fourth electrode 7 are provided, and first zirconia ceramic solid electrolyte member 1, second zirconia ceramic solid electrolyte member 2 and mica glass It is integrated via a sealed space (hereinafter abbreviated as a chamber) formed by the ceramics sealing member 3. Then, when a voltage is applied between the third electrode 6 and the fourth electrode 7 arranged via the second solid electrolyte member 2 by the DC power supply 9, an electrochemical pump portion is formed. In addition, the first electrode 4 and the second electrode 5 arranged via the first solid electrolyte member 1
And the voltmeter 8 form an electrochemical sensor section. To measure the oxygen gas concentration using such an oxygen sensor, for example, the first electrode 4 is used as the test gas and the fourth electrode 7 is used.
When contacting the air with air to measure the concentration of the test gas, when a constant direct current voltage is applied between the third electrode 6 and the fourth electrode, it functions as an electrochemical pump and is dependent on the supplied voltage. The voltage corresponding to the ratio P ₃ / P ₁ of the oxygen partial pressure P ₁ in the air and the oxygen partial pressure P ₃ in the chamber is made constant. When the voltage becomes constant, the voltmeter 8 reads the electromotive force corresponding to the ratio P ₂ / P ₃ of the oxygen partial pressure P ₂ in the test gas and the oxygen partial pressure P _{3 in} the chamber, and the Nernst (Nernst) The concentration of the test gas is calculated by the formula.

The oxygen sensor of FIG. 2 is the second sensor of the sensor of FIG.
The zirconia ceramic solid electrolyte of 2 is divided into 2 and 2'and an insulating mica glass ceramics sealing member is inserted between them, and the third electrode 6 and the fourth electrode 7 are connected to each other through the solid electrolyte member 2. Third through member 2 '
The electrode 6'and the fourth electrode 7'of the
A voltage is applied by a DC power supply 9 between the electrodes to form an electrochemical pump section, and a voltmeter 8'is provided between the electrodes 6'and 7 '.
Is provided to control the current supplied from the DC power supply. To measure the oxygen gas concentration using such an oxygen sensor,
For example, the first electrode 4 is used as the test gas, and the fourth electrodes 7, 7 '
When the sample gas is measured by contacting it with air and measuring the concentration of the test gas, the voltage between the third electrode 6'and the fourth electrode 7'is detected by the voltmeter 8'and the DC power source 9 is used. The supplied current is controlled (the voltage of the voltmeter 8'is controlled so that the oxygen gas partial pressure P ₃ in the chamber becomes a desired partial pressure). The voltmeter 8 reads the electromotive force corresponding to the ratio P ₂ / P ₃ of the oxygen partial pressure P ₂ in the test gas and the oxygen partial pressure in the chamber, and the concentration of the test gas is calculated by the Nernst equation.

In the mica glass ceramics used as the sealing member in the present invention, fluorine mica has a volume fraction of 30.
% Or more is preferable. This is because it is necessary to maintain electrical insulation and to maintain machinability and to process into a sealing material or the like. The glass component of mica glass ceramics is preferably contained in a volume fraction of 20% or more. This is due to the fact that the denseness between the fluorine mica is maintained and the material that maintains the impermeability of molecular gas is required. Among the commercially available mica glass ceramics as this material, those produced by the glass crystallization method are preferable. When the heating temperature required for adhesion is 1100 ° C. or higher, fluoromica is decomposed from the surface of the mica glass ceramics, and an adhesive effect is produced, which is preferable. Further, if it is performed at 1300 ° C. or lower, the shape can be maintained even when processed into a sealing material or the like, which is preferable. The heating method is preferably an open type such as in air. The coefficient of thermal expansion of the solid electrolyte zirconia member is 10
Since it is × 10 ^-6 ° C ^-1 , and the thermal expansion coefficient of the mica glass ceramics is not damaged during heating and cooling, it is preferable to be included in the range of 11 × 10 ^-6 to 9 × 10 ^-6 ° C ^-1 . As this material, a material having a fluorine mica content of mica glass ceramics of 30 to 80% is preferable. The present invention will be specifically described below with reference to examples.

(Example) Tosoh zirconia powder (TZ
-6Y) is press-molded, fired and ground, and then a mica glass ceramic is placed between two zirconia plates having platinum electrodes on both sides thereof, an inner diameter of 23 mmφ and an outer diameter of 25 mm.
A ring-shaped product having a diameter of φ and a height of 2 mm was inserted and heated in an electric furnace to prepare an oxygen sensor as shown in FIG.
Fluorine mica volume content of mica glass ceramics used as a sealing member was changed as shown in Table 1.
Heat up to 200 ° C at a temperature rising rate of 100 ° C / h, hold at the same temperature for 1 hour, and then cool at a temperature lowering rate of 100 ° C / h,
Table 1 shows the results when the oxygen sensor shown in FIG. 1 was produced.

[Table 1]

Next, the oxygen sensor shown in FIG. 1 was prepared in the same manner as described above except that mica glass ceramics having a volume content of fluorine mica of 50% was used as a sealing member and the heating adhesion temperature was changed as shown in Table 2. did. The results are shown in [Table 2].

[Table 2]

To increase the sealing effect from the above table, 1
It is understood that it is preferable to heat and bond at a temperature of 100 ° C. or higher and 1300 ° C. or lower, and it is more preferable in the range of 1150 ° C.-1250 ° C. The oxygen sensor shown in FIG. 1 was prepared by using Vycor glass or Pyrex glass as a sealing member in place of the mica glass ceramics having a volume content of fluorine mica of 50%. The results are shown in Table 3.

[Table 3]

[0015]

According to the present invention, it is possible to easily prepare an oxygen sensor which is excellent in detection accuracy and particularly in low-concentration oxygen gas measurement accuracy.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of an embodiment of an oxygen sensor according to the present invention.

FIG. 2 is an explanatory diagram showing an example of an embodiment of an oxygen sensor according to the present invention.

[Description of Reference Signs] 1 first zirconia ceramic solid electrolyte member 2 second zirconia ceramic solid electrolyte member 3 mica glass ceramics sealing member 4 first electrode 5 second electrode 6 third electrode 7 fourth electrode 8 Voltmeter 9 DC power supply

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuyoshi Ina 2-3-3, 203 Imamiya, Minoh City, Osaka Prefecture (72) Inventor Takuji Yoshimura 2-10-10, Kitamidoka, Toyonaka City, Osaka Prefecture

Claims (2)

[Claims] 1. An electrochemical pump portion having first and second electrodes formed on a first zirconia ceramic solid electrolyte member, and third and fourth electrodes formed on a second zirconia ceramic solid electrolyte member. An oxygen sensor, wherein an electrochemical sensor part is arranged via a sealed space formed in a sealing shape by the zirconia ceramics solid electrolyte member and a mica glass ceramics sealing member. 2. A method for manufacturing an oxygen sensor, which comprises heating a zirconia ceramics solid electrolyte member and a mica glass ceramics sealing member to bond them when manufacturing the oxygen sensor.