JPH08101149A - Gas sensor - Google Patents

Abstract

PURPOSE: To provide a gas sensor which prevents propagation of sintering in a gas sensitive layer on the cathode side and suppresses a deterioration due to such change with time that a response lag is generated for a change in the gas concentration. CONSTITUTION: The gas sensor is composed of a pair of electrodes 16a, 16b consisting of an anode and a cathode and a porous gas sensitive layer 24 which encloses the electrodes 16a, 16b, contains oxides of a transition metal such as titania having gas sensitivity, and whose electric resistance varies in accordance with the gas composition and/or concentration, wherein a sintering inhibiting agent to inhibit sintering of the layer 24 is added to that part of the layer 24 which is situated around the cathode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas detector for detecting a gas component or its concentration,
In particular, it relates to a gas detector using a gas-sensitive transition metal oxide.

[0002]

2. Description of the Related Art Conventionally, an oxygen gas detector has been used as a gas detector for detecting the presence or concentration of gas.
Combustible gas detectors have been put to practical use. Among these, there is one using a gas-sensitive metal oxide having a characteristic that its electric resistance changes when it comes into contact with gas. For example, oxides of transition metal elements such as TiO2 CoO and NiO can be used as oxygen sensors.

The transition metal oxides exemplified here are non-stoichiometric compounds. Then, the amount of charge carriers (holes, electrons) in this non-stoichiometric compound changes depending on the partial pressure of oxygen gas in the surroundings. Therefore, the conductivity changes according to the partial pressure of oxygen gas in the surroundings.

[0004]

Among the above oxygen sensors, for example, in a TiO2 sensor, an ionic current due to a bias between the cathode and the anode causes the
As the Ti4 + becomes deficient, the oxygen deficiency becomes less due to the excess of O2-. Therefore, the anode and TiO2
The resistance between the gas-sensitive layers increases, and the resistance value of the gas-sensitive layers becomes different from the initial state and deteriorates. On the other hand, even on the cathode side, due to the ion current, Ti4 + is in an excessive state and O2- is in an insufficient state, but since O2- is supplied from the atmosphere, the porous gas-sensitive layer made of TiO2 is sintered. And the surface area is reduced. Such progress of sintering of the gas-sensitive layer causes a delay in response to changes in gas concentration.

The present invention has been made as a result of investigating the problems of the above-mentioned conventional techniques, and an object of the present invention is to provide a gas detector which is less deteriorated due to aging.

[0006]

The present invention adopts the following means in order to solve the above problems. That is, the first invention includes a pair of electrodes composed of an anode and a cathode, and a pair of electrodes covering the electrodes, containing a gas-sensitive transition metal oxide, and having an electric resistance that changes according to a gas component and / or a gas concentration. A gas detector comprising a porous gas-sensitive layer, wherein the gas-sensitive layer around the anode is added with an electron donor additive containing an element having a higher valence than the transition metal. Use as a summary.

The second invention includes a pair of electrodes consisting of an anode and a cathode, a pair of electrodes covering the electrodes, containing a gas-sensitive transition metal oxide, and having an electric resistance depending on a gas component and / or a gas concentration. A gas detector having a porous gas sensitive layer that changes, and a gas detector characterized in that a sintering inhibitor that suppresses sintering of the gas sensitive layer is added to the gas sensitive layer around the cathode. Use as a summary.

Further, a third aspect of the present invention includes a pair of electrodes consisting of an anode and a cathode, a pair of electrodes covering the electrodes, containing a gas-sensitive transition metal oxide, and having an electric resistance depending on a gas component and / or a gas concentration. The gas detector is characterized in that it has a porous gas-sensitive layer having a variable surface area, and the surface area of the gas-sensitive layer around the cathode is smaller than that on the anode side.

Here, the above-mentioned electrode is not particularly limited as long as it is a heat-resistant conductor, but in general, one containing tungsten, molybdenum, gold or platinum group as a main component is used. As the gas-sensitive metal oxide used in the gas-sensitive layer, the substance may be selected according to the gas component to be detected, but as the commonly used substances, TiO2, SnO
Examples thereof include transition metal oxides such as 2, CoO, ZnO, Nb2O5, Cr2O3, and NiO. In the present invention, any one or a combination of two or more of these may be used.

As the donor additive, for example, in an oxygen sensor containing TiO2 as a main component, there are cations and their oxides such as Ta5 + and Nb5 +, which have a larger ionic valence than Ti4 +. Further, in the second invention, as a sintering inhibitor, for example, in an oxygen sensor containing TiO2 as a main component, a base material of ZrO2 containing Y2O3 as a stabilizer or an oxide such as CeO2 is used. is there.

The gas detector of the present invention can be produced, for example, by providing a gas sensitive layer or the like on a ceramic substrate by a hybrid technique such as a thick film technique. Alternatively, it may be formed into a disk type, a bead type or the like used in a thermistor or the like without using the thick film technique or the like.

Further, a heating element may be provided in the vicinity of the gas-sensitive layer for the purpose of reducing fluctuations in the temperature characteristics of the gas detector during measurement. Then, a part of this heating element and one electrode of the gas detector may be connected to apply a voltage to the gas sensitive layer to reduce the number of terminals and simplify the measurement circuit.

[0013]

In the first aspect of the invention, due to the ion current due to the bias between the anode and the cathode, the shortage of Ti4 + on the anode side and O
Even if the amount of 2-excess, the cations in the gas-sensitive layer on the anode side are increased due to the donor additive added to the gas-sensitive layer on the anode side. And the reduced donor additive constitutes the bonding lattice of the gas sensitive layer. Therefore, the change with time of the interelectrode resistance of the gas sensitive layer is reduced.

In the second invention, the gas sensitive layer around the cathode is
The ion current causes an excess of Ti4 +, and the surface area due to sintering is reduced by O2- supplied from the ambient gas atmosphere, but the sintering inhibitor suppresses the sintering of the gas-sensitive layer around the cathode. Therefore, the change with time of the responsiveness to the change in the gas-sensitive concentration is reduced.

Further, in the third invention, as in the second invention, the adsorption area of the gas-sensitive layer on the cathode side is made small in advance in order to suppress the sintering on the cathode side. Since the rate of decrease of the adsorption area can be reduced, changes in responsiveness and the like over time are reduced.

[0016]

As described above, according to the gas detector of the present invention, deterioration due to use can be reduced and stable characteristics can be obtained. Then, according to the first aspect of the present invention, by adding the donor additive to the periphery of the anode, it is possible to suppress deterioration due to an increase in resistance around the anode.

Further, according to the second invention, sintering of the gas sensitive layer on the cathode side is suppressed by the sintering inhibitor on the cathode side, and according to the third invention, the gas sensitive layer on the cathode side is suppressed. Since the specific surface area of the layer is made small in advance, the change in specific surface area due to sintering from the initial state is small, and deterioration of responsiveness can be reduced.

[0018]

Embodiments of the present invention will be described with reference to the drawings. Note that the scale of each drawing is different for the sake of explanation. First, an embodiment of the present invention will be described with reference to FIG. The present embodiment is an oxygen gas detector 10 using TiO2 as a gas sensitive layer.

As shown in the partially broken perspective view of FIG. 1, the terminals 13a, 13b,
Detection electrodes 16a, 16b and thermal resistance electrode 16e connected to platinum lead wires 14a, 14b, 14e at 13e
And the like. Further, a first ceramic laminated plate 18 integrated with the ceramic substrate 12 on the ceramic substrate 12 and the electrode pattern 16 and a second ceramic on the first ceramic laminated plate 18 are formed. The laminated plates 19 are laminated. Anode side and cathode side lower window portions 20a and 20b divided by a partition portion 18a are formed on the first ceramic laminated plate 18, and further, both lower window portions are formed on the second ceramic laminated plate 19. Two
0a, 20b and the upper window portion 20 forming the window portion 20
c is formed.

Anode-side and cathode-side lower windows 20a and 20b of the window 20 are filled with anode-side and cathode-side pastes having the compositions shown in Table 1 to form the anode-side and cathode-side gas-sensitive lower layers. 24a and 24b are formed, and the upper window portion 20c is filled with a TiO2 paste forming a normal gas-sensitive layer of TiO2 to form a gas-sensitive upper layer 24c. The gas sensitive layer 24 is formed by these layers. In addition, the ceramic substrate 12
Spherical granulated particles 22 are interposed between the gas-sensitive layer 24 and the gas-sensitive layer 24.

Next, the manufacturing process of the oxygen gas detector 10 will be described with reference to FIGS. 2 wt% of alumina, 3 wt% of magnesia, and 5 wt% of sintering aid (silica, calcia, etc.) in a pot mill
Mix for 0 hours. Then, 12% by weight of polyvinyl butyral and 4% by weight of dibutyl phthalate were added to the mixture as an organic binder, and methyl ethyl ketone, toluene and the like were added as a solvent. Further, the mixture is mixed in a pot mill for 15 hours to form a slurry, and the substrate and laminating green sheets 12A, 18A and 19A are formed by the doctor plate method.

The shape of the green sheet is 47.8 mm × 4.0 mm × 0.8 in the green sheet for substrate 12A.
mmt, first and second stacking green sheets 18A, 1
It is 47.8 mm × 4.0 mm × 0.28 mmt at 9A. Then, the first green sheet for lamination 18A
Forms the two anode-side and cathode-side lower window parts partitioned by the partition part 18a with a size of 3.05 mm × 0.8 mm, and further comprises the upper window part 20c of the second stacking green sheet 19A of 3 It is formed with dimensions of 0.05 mm × 2.0 mm.

Next, platinum black and sponge-like platinum are
It is mixed at a ratio of 2: 1 and 10% by weight of the material mixture of the green sheet used above is added, and a solvent such as butyl carbidol and Ethocel is added to obtain an electrode paste. Next, the electrode pattern 16 is formed on the substrate green sheet 12A by thick film printing using the electrode paste adjusted in. As described above, as the electrode pattern 16, the detection electrode patterns 16a and 16b, the thermal resistance electrode pattern 16e that serves as a heater for heating the gas-sensitive layer 24, and the terminal pattern 13a that serves as a terminal of both patterns 16, 13b and 13e are formed. (FIG. 2 (a) (b)) Then, the terminal patterns 13a, 13b, 13e
The platinum lead wires 14a, 14b, 1 having a diameter of 0.2 mm
4e are respectively connected (FIG. 3 (a) (b)).

Next, the substrate green sheet 12
The first stacking green sheet 18A on A, and the second
The laminated green sheet 19A is laminated and thermocompression-bonded to form a laminated body. At this time, the green sheet for lamination 18
The detection electrode pattern 16 is provided on the windows 20 of A and 19A.
The tips of a and 16b are exposed. Then, it is made of the same material as the green sheet adjusted in the window 20.
A ceramic substrate 12 which is made integral by dispersing and adhering spherical granulated particles (secondary particles) 22 of 0 to 150 mesh for 2 hours at 1500 ° C. in substantially the same atmosphere as the atmosphere. And ceramic laminate 18,1
9 is formed (FIGS. 4A and 4B).

When the spherical granulated particles 22 are dispersed and adhered and fired as described above, each particle 22 becomes a ceramic substrate 12.
Dispersed on top to form an uneven surface. Next, the window portions 20 of the ceramic laminated plates 18 and 19 are filled with a gas-sensitive metal oxide containing TiO2 as a main component. Here, first, the sample N in Table 1 is used.
o. An anode side paste as shown in 5 is prepared.

That is, with respect to 100 parts by weight of TiO2 powder having an average particle size of 1.2 μm calcined at 1200 ° C. for 1 hour in air, Ta2O5 having an average particle size of 0.5 μm was used as a donor additive for increasing electron conductivity. 5 parts by weight was added, 20 parts by weight of platinum black was added as a catalyst, and 2 parts by weight of 3% by weight of ethyl cellulose was further added as a binder. These were added to butycarbitol (2- (2-butoxyethoxy) ethanol. (Commercial name), and the viscosity is adjusted to 300 poise to prepare a TiO2 paste. And
This anode side TiO2 paste is applied as a 20 to 50 [mu] m thick film on the anode pattern 16a in the anode side lower window portion 20a (Fig. 5 (a) (b)).

On the other hand, as for the cathode side paste, first the anode side Ti
TiO2 with an average particle size of 3.5 μm larger than the particle size of O2 powder
As a sintering inhibitor, Y2 was added to 100 parts by weight of the powder.
Then, 5 parts by weight of ZrO2 containing 7 mol% of O3 and 20 parts by weight of platinum black as a catalyst are added, and the same procedure as in the anode paste is performed. Then, this cathode-side paste is applied in a thickness of 20 to 50 μm in the cathode-side lower window portion 20b.

Next, the paste applied over both the anode and cathode electrodes is prepared. First, with respect to 100 parts by weight of TiO 2 powder having an average particle size of 1.2 μm, 10 parts by weight of platinum black is used as a catalyst. Parts and 1 part by weight of rhodium black are added and adjusted in the same manner as the above paste to make a paste. Then, paste this paste into the upper window part 20 on both layers.
Print 50 to 500 μm thick film on c.

After that, the laminated body that has undergone the above steps is left to stand in the air at 1200 ° C. for 1 hour to be fired (FIG. 6 (a) (b)). Samples of gas detectors are prepared by changing the composition of the paste on the anode side and the paste on the cathode side used in the above steps as shown in Table 1. After assembling this sample into an oxygen sensor, the response speed and durability of each sample are measured by the following experiments. The results of the experiment are shown in Table 2. ○ Response speed test The sample assembled as an oxygen sensor is exposed to the exhaust gas of a propane gas burner. This propane gas burner has an exhaust temperature of 350 ° C., and has an air fuel ratio of fuel excess (hereinafter referred to as rich, air fuel ratio λ = 0.9) and fuel shortage (hereinafter referred to as lean λ = 1.1) every one second. ) Is controlled to change between.

Gas detector 1 when exhaust gas is rich
The voltage applied to the sensor is adjusted so that the output of 0 is 1V and the output of lean is 0V. As the response speed, the time when the output of the gas detector 10 changes from 300 mV to 600 mV when the atmosphere changes from lean to rich and the time when the output changes from 600 mV to 300 mV when the atmosphere changes from rich to lean are measured. . ○ Durability test A sample assembled as an oxygen sensor is attached to an actual vehicle, and it is operated according to a specified durability pattern, and the durability is examined from the change in response speed before and after operation. That is, the oxygen sensor S
Is a commercially available 2000cc with EFI 3 as shown in FIG.
Exhaust pipe M between the engine Eng of the three-way catalyst car and the three-way catalyst THC
attached to an. Then, the control unit Uni controls the operating state of the engine according to the output of the oxygen sensor S. The output of the sensor S is detected by the circuit shown in FIG. Here, B is a power supply and Rc is a comparison resistance.

The engine Eng is operated for 300 hours in the endurance pattern shown in FIG. The solid line in the figure shows the temperature of the sample, and the broken line shows the temperature of the exhaust gas. The response speeds Tlr and Trl described above are measured before and after this operation, and the change is taken as the result of durability. That is, it is determined that the sample having less change in response speed before and after the operation has more excellent durability. In Table 1, before operation is described as initial and after operation as after durability test.

[0032]

[Table 1]

[0033]

[Table 2]

From the above experiment, as shown in Table 2, the following was found. Sample No. When the gas sensitive layer around the anode contains Ta2O5 or Nb2O5 as in Nos. 2 and 4 to 7, the resistance RT between the electrodes hardly changes from the initial value to the value after the durability test, and the sample No. The effect is remarkable as compared with 1 and 3.

Sample No. 3-7, ZrO2 containing 7 mol% Y2O3 or C in the gas sensitive layer around the cathode.
When the sintering inhibitor of eO2 is included, the response times Tlr and Trl of rich and lean are not so different between the initial value and the value after the durability test, and the sample does not contain the sintering inhibitor. N
o. The effect is remarkable as compared with 1 and 2.

Sample No. As shown in FIG. 2, even when the sintering inhibitor is not added to the gas-sensitive layer on the anode side, there is no change in the resistance value before and after the durability test.
It can be seen that sintering proceeds mainly on the cathode side. In addition, the sample No. 4 and sample No. As is clear from comparison with No. 5, by increasing the particle size of TiO2 from 1.2 μm to 3.5 μm to reduce the surface area of the gas-sensitive layer in advance, the progress of sintering is suppressed and the response time Tlr , Trl can be reduced.

As described above, the changes in the response times Tlr and Trl of the resistance value RT can be confirmed by the following experiment. That is, as shown in FIG. 10, a third electrode 16f is provided outside the anode pattern 16a and the cathode pattern 16b in the gas sensitive layer, and (a) the third electrode 16f is on the negative side, and both electrode patterns are provided. 16a and 16b are connected to the plus side, (b) The third electrode 16f is connected to the plus side, both electrode patterns 16a and 16b are connected to the minus side, and the resistance value RT and the response times Tlr and Trl are measured. The result of (a) is shown in FIG. 11, and the result of (b) is shown in FIG.

As a result, according to the connection of (a), with the sample containing the donor additive of Sample 2 in Table 1, no change in the resistance value RT was observed before and after the durability test (Fig. 11 ( I)). This shows that the donor additive can compensate for the shortage of Ti4 + on the anode side and the reduction of defects due to the excess of O2-.

Further, according to the connection of (b), in the case of adding the sintering inhibitor of Sample 3 in Table 1, there is almost no change in response time (Fig. 12 (b)). From this, the sintering that proceeds on the cathode side can be prevented by the sintering inhibitor.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view showing an oxygen sensor according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of manufacturing of an example.

FIG. 3 is an explanatory diagram of manufacturing of an example.

FIG. 4 is an explanatory diagram of manufacturing of the example.

FIG. 5 is an explanatory diagram of manufacturing of the example.

FIG. 6 is an explanatory diagram of manufacturing of the example.

FIG. 7 is a diagram for explaining the procedure of a durability test using an oxygen sensor in an internal combustion engine.

FIG. 8 is a diagram for explaining the procedure of a durability test using an oxygen sensor in an internal combustion engine.

FIG. 9 is a durability pattern diagram of the test.

FIG. 10 is an explanatory diagram illustrating an operation of the embodiment.

FIG. 11 is a graph showing characteristics of the same example.

FIG. 12 is a graph showing characteristics of the same example.

[Explanation of symbols]

 10 ... Oxygen sensor (gas detector), 12 ... Ceramic substrate, 16, 16a, 16b ... Electrode pattern (electrode), 18 ... First ceramic laminated plate, 19 ... Second Ceramic laminated plate, 20 ... Window part, 24 ... Gas sensitive layer

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[Procedure amendment]

[Submission date] May 23, 1995

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

Title of the invention Gas detector

[Claims]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas detector for detecting a gas component or its concentration,
In particular, it relates to a gas detector using a gas-sensitive transition metal oxide.

[0002]

2. Description of the Related Art Conventionally, an oxygen gas detector has been used as a gas detector for detecting the presence or concentration of gas.
Combustible gas detectors have been put to practical use. Among these, there is one using a gas-sensitive metal oxide having a characteristic that its electric resistance changes when it comes into contact with gas. For example, oxides of transition metal elements such as TiO ₂ , CoO, and NiO can be used as the oxygen gas detector .

The transition metal oxides exemplified here are non-stoichiometric compounds. Then, the amount of charge carriers (holes, electrons) in this non-stoichiometric compound changes depending on the partial pressure of oxygen gas in the surroundings. Therefore, the conductivity changes according to the partial pressure of oxygen gas in the surroundings.

[0004]

By the way, the above oxygen gas is used.
Among scan detector, for example, in the titania sensor, for ion current due to the bias between the cathode and the anode, the cathode side
, For the ion current, it becomes the state of excess Ti ^4+, it becomes the O ^2- starved of, O ^2- is porous gas-sensitive layer consisting of a Runode titania is replenished from the atmosphere Sintering
Advances. That is, as the sintering progresses, the particles gradually fuse together.
Particles that make up the porous gas-sensitive layer
Of these, the total surface area of particles around the cathode is reduced. That
Thus , due to the progress of the sintering of the gas sensitive layer, a response delay occurs with respect to the change of the gas concentration.

The present invention has been made as a result of investigating the problems of the above-mentioned conventional techniques, and an object of the present invention is to provide a gas detector which is less deteriorated due to aging.

[0006]

The present invention adopts the following means in order to solve the above problems. That is, the present invention
Is a pair of electrodes consisting of an anode and a cathode , and a porous gas-sensitive layer covering the electrodes, containing a gas-sensitive transition metal oxide, and having an electric resistance that changes according to the gas component and / or the gas concentration. When provided with, the gas-sensitive layer near the cathode, shall be the subject matter of the gas detector, characterized in that the addition of sintering inhibitor to inhibit the sintering of the sensitive gas layer.

Here, the above-mentioned electrode is not particularly limited as long as it is a heat-resistant conductor, but in general, one containing tungsten, molybdenum, gold or platinum group as a main component is used. As the gas-sensitive metal oxide used in the gas-sensitive layer, the substance may be selected according to the gas component to be detected, but as the commonly used substances, TiO ₂ , SnO
₂ , transition metal oxides such as CoO, ZnO, Nb ₂ O ₅ , Cr ₂ O ₃ , and NiO are included. In the present invention, any one or a combination of two or more of these may be used. Good.

In the present invention , as a sintering inhibitor, for example, in an oxygen sensor containing titania as a main component, ZrO 2 is used.
_{There is} a base material containing Y ₂ O ₃ as a stabilizer in the base material of ₂ , or an oxide such as CeO ₂ . The gas detector of the present invention can be produced, for example, by providing a gas sensitive layer or the like on a ceramic substrate by a hybrid technique such as a thick film technique. Alternatively, it may be formed into a disk type, a bead type or the like used in a thermistor or the like without using the thick film technique or the like.

Further, a heating element may be provided in the vicinity of the gas sensitive layer for the purpose of reducing the fluctuation of the temperature characteristic of the gas detector at the time of measurement. Then, a part of this heating element and one electrode of the gas detector may be connected to apply a voltage to the gas sensitive layer to reduce the number of terminals and simplify the measurement circuit.

[0010]

[Function] A sintering inhibitor is, for example, Ti ⁴⁺ by direct current.
By coupling with O ^2- movement and by the movement of the normally
If so, suppress the progress of sintering of the gas-sensitive layer on the cathode side.
And will interfere with this bond between Ti ⁴⁺ and O ²⁻ , for example.
Such components (specifically, ZrO ₂ —Y ₂ O ₃ and CeO ₂ are
Sintering is suppressed by adding (experimentally effective)
To reduce the change in responsiveness over time.

That is, the gas-sensitive layer around the cathode becomes, for example, in an excess state of Ti ⁴⁺ due to an ionic current, and the sintering progresses due to O ^{2 −} supplied from the atmosphere of the surrounding gas.
Although the sum of the surface areas of the side particles decreases, in the present invention,
Since sintering of the gas sensitive layer near the cathode is suppressed by sintering inhibitor, the responsiveness of the temporal change with respect to the change-sensitive gas concentration Ru is reduced.

[0012]

As described above, according to the gas detector of the present invention, deterioration due to use can be reduced and stable characteristics can be obtained. Then, according to the present invention, by sintering inhibitor on the cathode side, the sintering of the cathode side of the gas-sensitive layer is suppressed
Therefore , the change in specific surface area due to sintering from the initial state is small, and the deterioration of responsiveness can be reduced.

[0013]

Embodiments of the present invention will be described with reference to the drawings. Note that the scale of each drawing is different for the sake of explanation. First, an embodiment of the present invention will be described with reference to FIG . The present embodiment is an oxygen gas detector 10 using TiO ₂ as a gas sensitive layer.

As shown in the partially cutaway perspective view of FIG.
On the ceramic substrate 12, the terminals 13a, 13b, 13
The electrode patterns 16 such as the detection electrodes 16a and 16b and the thermal resistance electrodes 16e connected to the platinum lead wires 14a, 14b and 14e by e are formed, and the ceramic substrate 1 and the ceramic substrate 1 are further formed on the electrode pattern 16.
The first ceramic laminate 18 integrated with the second ceramic laminate 18 and the second ceramic laminate 19 are laminated on the first ceramic laminate 18 respectively. The first ceramic laminated plate 18 is formed with anode side and cathode side lower window portions 20a and 20b divided by a partition portion 18a, and further,
The second ceramic laminated plate 19 has two lower window parts 20.
a, 20 b and Uemado portion 20c which together form the window portion 20 is formed.

The anode side and cathode side lower window portions 20a and 20b of the window portion 20 are filled with the anode side and cathode side pastes having the compositions shown in Table 1 to form the anode side and cathode side gas-sensitive lower layers 24a. , 24b are formed, the more the upper window portion 20c, the gas sensitive layer 24c and TiO ₂ paste forming the normal of the TiO ₂ in the gas-sensitive layer is filled is formed. The gas sensitive layer 2 is formed by each of these layers.
4 are formed. In addition, the spherical granulated particles 2 for preventing the separation between the ceramic substrate 12 and the gas sensitive layer 24.
2 is interposed.

Next, will be described with reference to FIG. 2 through 6 a manufacturing process of the oxygen gas detector 10. 2 wt% of alumina, 3 wt% of magnesia, and 5 wt% of sintering aid (silica, calcia, etc.) in a pot mill
Mix for 0 hours. Then, 12% by weight of polyvinyl butyral and 4% by weight of dibutyl phthalate were added to the mixture as an organic binder, and methyl ethyl ketone, toluene and the like were added as a solvent. Further, the mixture is mixed in a pot mill for 15 hours to form a slurry, and the substrate and laminating green sheets 12A, 18A, 19A are formed by a doctor blade method.

The shape of the green sheet is 47.8 mm × 4.0 mm × 0.8 in the green sheet 12A for substrates.
mm ^t , first and second stacking green sheets 18A, 1
It is 47.8 mm × 4.0 mm × 0.28 mm ^t at 9A. Then, the first green sheet for lamination 18A
Forms the two anode-side and cathode-side lower window parts partitioned by the partition part 18a with a size of 3.05 mm × 0.8 mm, and further comprises the upper window part 20c of the second stacking green sheet 19A of 3 It is formed with dimensions of 0.05 mm × 2.0 mm.

Next, platinum black and sponge-like platinum
The green syrup used in the above was blended in a ratio of 2: 1.
Butyl carbide
Solvent, etc., to form an electrode paste.
You. Next, thick film printing using the electrode paste adjusted in
The electrode pattern on the green sheet 12A for the substrate
16 is formed. The electrode pattern 16 has been described above.
Sea urchin, detection electrode patterns 16a and 16b, and
The thermal resistance electrode pattern serving as a heater for heating the spray layer 24.
Terminal 16e and a terminal pattern that serves as terminals for both patterns 16 described above.
The turns 13a, 13b, 13e are formed. (FIG.
(A) (b)) Thereafter, the terminal patterns 13a, 13b, 13e
The platinum lead wires 14a, 14b, 1 having a diameter of 0.2 mm
Connect 4e respectively (Figure 3(A) (b)).

Next, the substrate green sheet 12
The first stacking green sheet 18A on A, and the second
The laminated green sheet 19A is laminated and thermocompression-bonded to form a laminated body. At this time, the green sheet for lamination 18
The detection electrode pattern 16 is provided on the windows 20 of A and 19A.
The tips of a and 16b are exposed. Then, it is made of the same material as the green sheet adjusted in the window 20.
A ceramic substrate 12 which is made integral by dispersing and adhering spherical granulated particles (secondary particles) 22 of 0 to 150 mesh for 2 hours at 1500 ° C. in substantially the same atmosphere as the atmosphere. And ceramic laminate 18,1
9 is formed ( FIGS. 4A and 4B ).

When the spherical granulated particles 22 are dispersed and adhered and fired as described above, each particle 22 is formed into a ceramic substrate 12.
Dispersed on top to form an uneven surface. Next, the window portions 20 of the ceramic laminated plates 18 and 19 are filled with a gas-sensitive metal oxide containing TiO ₂ as a main component. Here, first, the sample No. 1 in Table 1 is used.
An anode side paste as shown in 4 is prepared.

That is, with respect to 100 parts by weight of TiO ₂ powder having an average particle size of 1.2 μm, which was calcined at 1200 ° C. for 1 hour, Ta having an average particle size of 0.5 μm was used as a donor additive for increasing electron conductivity. 5 parts by weight of ₂ O ₅ was added, 20 parts by weight of platinum black was added as a catalyst, and only 2 parts by weight of 3% by weight of ethyl cellulose was added as a binder. These were added to butycarbitol (2- (2- Butoxyethoxy) ethanol (trade name) and mixed to obtain a viscosity of 300 poise to prepare a TiO ₂ paste. And
This anode side TiO ₂ paste is applied as a 20 to 50 μm thick film on the anode pattern 16a in the anode side lower window portion 20a ( FIGS. 5A and 5B ).

On the other hand, as for the paste on the cathode side, first, Ti on the anode side is prepared.
TiO _{2 having an} average particle size of 3.5 μm larger than that of O ₂ powder
As a sintering inhibitor, Y ₂ was added to 100 parts by weight of the powder.
Then, 5 parts by weight of ZrO ₂ containing 7 mol% of O ₃ and 20 parts by weight of platinum black as a catalyst were added, and the same procedure as in the anode paste was performed. Then, this cathode-side paste is applied in a thickness of 20 to 50 μm in the cathode-side lower window portion 20b.

Next, the paste applied to both the anode and cathode electrodes is prepared. First, 100 parts by weight of TiO ₂ powder having an average particle size of 1.2 μm is used as a catalyst for platinum black 10 Add 1 part by weight of rhodium black and 1 part by weight of rhodium black to prepare a paste in the same manner as the above paste. Then, paste this paste into the upper window part 20 on both layers.
Print 50 to 500 μm thick film on c.

After that, the laminated body that has undergone the above steps is
Bake by leaving it in the air at 1200 ° C for 1 hour (Figure 6
(A) (b)). Anode side and shade used in the above steps
The composition of the pole-side pasteTable 1Change likeOxygen gas detection
vesselMake a sample of. This sampleOxygen gas detectorAssembled in
After standing, the response speed and
Measure endurance. The result of the experimentTable 2Shown in. ○ Response speed test In the exhaust gas of propane gas burnerOxygen gas detectorWhen
And expose the assembled sample. This propane gas bar
The exhaust gas temperature is 350 ° C and the air fuel ratio
Is excessive fuel (hereinafter referred to as rich, air-fuel ratio λ = 0.
9) and fuel shortage (hereinafter referred to as lean, λ = 1.1)
Controlled to change between.

Oxygen gas detection when exhaust gas is rich
The voltage applied to the oxygen gas detector is adjusted so that the output of the detector is 1V and the output when lean is 0V. As the response speed, the output of the oxygen gas detector 10 when the atmosphere changes from lean to rich is 300 mV to 600 mV.
Measure the time to change to mV and the time to change the output from 600 mV to 300 mV when the atmosphere changes from rich to lean. ○ Durability test A sample assembled as an oxygen gas detector is attached to an actual vehicle, and it is operated in a prescribed durability pattern, and the durability is examined from the change in response speed before and after operation. That is, oxygen gas
The detector S is a commercially available 2000cc EF as shown in FIG.
It is attached to the exhaust pipe Man between the engine Eng of the 3-way catalyst car with I and the 3-way catalyst THC. And the control unit Uni
Controls the operating state of the engine according to the output of the oxygen gas detector S. The output of the oxygen gas detector S is detected by the circuit shown in FIG. Here, B is a power supply and Rc is a comparison resistance.

The engine Eng is operated for 300 hours in the endurance pattern shown in FIG . The solid line in the figure shows the temperature of the sample, and the broken line shows the temperature of the exhaust gas. The response speeds Tlr and Trl described above are measured before and after this operation, and the change is taken as the result of durability. That is, it is determined that the sample having less change in response speed before and after the operation has more excellent durability. In Table 2 , before operation is described as initial and after operation is described as after durability test. Also, RT should be rich
The resistance value between the electrodes 13a and 13b is shown.

[0027]

[Table 1]

[0028]

[Table 2]

From the above experiment, as shown in Table 2 , the following was found. Sample No. of the example . 2-6, if the gas sensitive layer around the cathode contains ZrO ₂ containing 7 mol% Y ₂ O ₃ or a CeO ₂ sintering inhibitor, the response times Tlr and Trl of rich and lean are given. Indicates that there is not much difference between the initial value and the value after the endurance test, and the ratio without sintering inhibitor is
Comparative sample No. Compared with 1 , the effect is remarkable.

Incidentally, the sample No. of the comparative example . As shown in Fig. 1, even when no sintering inhibitor was added to the gas-sensitive layer on the anode side, there was no change in the resistance value before and after the durability test. it is that the minute <br/> whether to proceed.

[ Brief description of drawings]

FIG. 1 is a partially cutaway perspective view showing an oxygen gas detector according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of manufacturing of an example.

FIG. 3 is an explanatory diagram of manufacturing of an example.

FIG. 4 is an explanatory diagram of manufacturing of the example.

FIG. 5 is an explanatory diagram of manufacturing of the example.

FIG. 6 is an explanatory diagram of manufacturing of the example.

FIG. 7 is a diagram for explaining the procedure of a durability test using an oxygen gas detector in an internal combustion engine.

FIG. 8 is a diagram for explaining the procedure of a durability test in which an oxygen gas detector is used in an internal combustion engine.

[9] Ru durable pattern diagram der of the test.

[Explanation of Codes] 10 ... Oxygen gas detector , 12 ... Ceramic substrate, 16, 16a, 16b ... Electrode pattern (electrode), 18 ... First ceramic laminated plate, 19 ... 2 ceramic laminated plate, 20 ... window portion, 24 ... gas sensitive layer

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 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Akio Takami 14-18 Takatsuji-cho, Mizuho-ku, Nagoya, Aichi Nihon Special Ceramics Co., Ltd.

Claims (3)

[Claims] 1. A pair of electrodes consisting of an anode and a cathode, and a porous electrode covering the electrodes and containing a gas-sensitive transition metal oxide, the electric resistance of which changes depending on the gas component and / or the gas concentration. A gas detector comprising: a gas-sensitive layer; and an electron donor additive containing an element having a higher valence than the transition metal, added to the gas-sensitive layer around the anode. 2. A pair of electrodes consisting of an anode and a cathode, and a porous electrode covering the electrodes and containing a gas-sensitive transition metal oxide, the electric resistance of which changes depending on the gas component and / or the gas concentration. A gas detector comprising: a gas-sensitive layer; and a sintering inhibitor that suppresses sintering of the gas-sensitive layer is added to the gas-sensitive layer around the cathode. 3. A pair of electrodes consisting of an anode and a cathode, and a porous electrode covering the electrodes, containing a gas-sensitive transition metal oxide, and having an electric resistance that changes depending on the gas component and / or the gas concentration. A gas detector comprising: a gas-sensitive layer; and a surface area of the gas-sensitive layer around the cathode is smaller than that on the anode side.