JPH08271467A - Nitrogen oxide sensor - Google Patents

Abstract

PURPOSE: To provide a highly reliable NOX gas sensor having stabilized detection characteristics in which no noise is produced even if gas components of HC, CO, etc., are present in the detection environment by disposing the electrode at a section for detecting a gas principally comprising a composite oxide represented by a specified formula. CONSTITUTION: An electrode 2 is disposed at a section 1 for detecting a gas principally comprising a composite oxide represented by a formula; Bi2+x (Sr1-a Caa )2-x-y-b LnyCu1+b O2 (where, Ln is a rare earth metal, 0<=x<=0.5, 0<=x+y<=1, 0<=a<=1, -0.1<=b<=x/2, z>=6), and a heater 4 is disposed on the rear surface. Almost all rare earth metal can be employed including La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb, Lu and Y. The composite oxide exhibits electric conductivity equivalent to that of metal at 350 deg.C or above. It is practically operated at 200-500 deg.C by normally heated by means of a heater 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitrogen oxide sensor for detecting nitrogen oxide contained in the atmosphere or exhaust gas.

[0002]

2. Description of the Related Art As an example of a gas sensor for detecting nitrogen oxides in exhaust gas, a nitrogen oxide gas (hereinafter sometimes referred to as NO _x gas) detecting element disclosed in Japanese Patent Laid-Open No. 3-13854 is disclosed. can give. FIG. 25 shows a plan view of a NO _x gas sensor using this NO _x gas detection element. In FIG. 25, 32 is a heater, 33 is a lead wire for a heater, 34 is a gas detector fixed on the heater 32, 35 is an electrode formed at both ends of the gas detector 34, and 36 is the electrode. It is a lead wire drawn from the electrode 35.

The gas detector 34 is made of, for example, a semiconductor which is a compound obtained by adding a small amount of Al or the like to TiO ₂ and sintering it, and applies a specified DC voltage to the heater 32 through the heater lead wire 33. Gas detector 3
The surface temperature of No. 4 can be set to about 400 ° C. When gas molecules are physically adsorbed on the surface of the gas detection unit 34, the resistance changes according to the adsorption amount, and an output voltage is taken out from the electrode lead wire 36. The adsorption amount is known from this voltage. Can measure the concentration of gas molecules.

[0004] Japanese Patent Laid-Open No. 3-13854, a conventional semiconductor type NO _x gas sensing element, NO _x in the exhaust gas components
Hydrocarbons (hereinafter, H
It is described that it hardly reacts with a gas such as C) or carbon monoxide (hereinafter sometimes referred to as CO) and is not affected by the coexisting gas component, that is, does not become noise.

However, according to the present inventors, the NO
_{When the x} sensing element was evaluated in detail, it was found that the resistivity of the gas sensing element changed due to the presence of HC or CO (described in detail in Comparative Example 1).

As described above, there is no sensor that can detect NO _x with high accuracy without being affected by coexisting gases such as HC and CO.

Conventional of the NO _x gas detection sensor in NO _x
The resistance characteristic of the gas detection element varies significantly depending on the presence or absence of coexisting gases HC and CO in a NO _x environment such as NO. Especially, when this sensor is added to the exhaust gas treatment system, malfunction occurs, which is important. There is a problem that it may invite.

[0008]

The present invention 0005] has been made in view of the points of the, HC on detected NO _x environment,
Even if a gas component such as CO coexists, the coexisting gas component does not become noise, the NO _x gas detection characteristic is stable, and a nitrogen oxide sensor equipped with a highly reliable NO _x gas detection element is provided. The purpose is to provide.

[0009]

The present invention provides a compound represented by the formula (I): Bi _{2 + x} (Sr _1-a Ca _a ) _2-xyb Ln _y Cu _{1 + b} O _z (I) (wherein Ln is It is a rare earth metal, and x, y, z, a and b satisfy the following relational expression: 0 ≦ x ≦ 0.
5, 0 ≦ x + y ≦ 1, 0 ≦ a ≦ 1, −0.1 ≦ b ≦ x /
The present invention relates to a nitrogen oxide sensor provided with a gas detecting section containing a complex oxide represented by 2, z ≧ 6) as a main component and an electrode provided in the detecting section.

The present invention also has the formula (II): Bi ₂ Sr _2-y Nd _y CuO _z (II) (where y and z satisfy the following relational expression: 0 <y <1, The present invention relates to a nitrogen oxide sensor including a gas detecting section containing a composition represented by z ≧ 6) as a main component and an electrode provided in the detecting section.

The present invention also provides the formula (III): Bi ₂ Sr _{2-y + a} La _y Cu _1-b O _z (III) (wherein y, z and a satisfy the following relational expressions): Yes: 0 <y ≦ 1.2, 0 ≦ a ≦ 0.2, 0 ≦ b ≦ 0.
The present invention relates to a nitrogen oxide sensor including a gas detection section containing a composition represented by 2, z ≧ 6) as a main component and an electrode provided in the detection section.

The present invention also provides the formula (IV): Bi ₂ Sr _2-x M _{2 + x} Cu ₂ O _z (IV) (where x is 0 or the following relational expression: 0.15 ≦ x ≦
In the case of x = 0, M satisfies the following relational expression: M = Ln ′ _1-y X _y (where Ln ′ is Pr, N
d, Sm, Eu, Gd, Tb, Dy, Y, Ho, Er or Tm, X is Ce or Th, and y satisfies the following relational expression: 0.1 ≦ y ≦ 0.4. ), Or the following relational expression: M = Nd _1-y Y _y (where y is the following relational expression: 0 <y ≦ 0.24), or M is Gd Or Pr, z satisfies the following relational expression: z ≧ 10, and x satisfies the following relational expression: 0.15 ≦ x ≦ 0.3, M is the following relational expression: M = Ln _1-y L
a _y (where Ln is Dy, Gd, Eu, or Sm, y is the following relational expression: 0.15 ≦ y ≦ 0.2), and z is the following relational expression: :
The present invention relates to a nitrogen oxide sensor provided with a gas detection section mainly composed of a complex oxide represented by z ≧ 10) and an electrode provided in the detection section.

The present invention also provides a composite oxide represented by the formula (I) or formula (IV) or a composition represented by the formula (II) or formula (III) contained in the gas detector. The present invention relates to a nitrogen oxide sensor which exhibits metallic electric conductivity at a temperature higher than a use temperature.

In the present invention, the content of the complex oxide represented by the above formula (I) or (IV) or the composition represented by the above (II) or (III) contained in the above gas detector. Relates to a nitrogen oxide detection sensor having a volume ratio of 25% or more.

The present invention also constitutes the complex oxide represented by the formula (I) or (IV) or the composition represented by the (II) or (III) contained in the gas detection section. Al element contained in addition to metal element is 1
It relates to a nitrogen oxide sensor which is less than wt%.

The present invention also constitutes the complex oxide represented by the formula (I) or (IV) or the composition represented by the (II) or (III) contained in the gas detecting section. Pb element contained in addition to metal element is 5
It relates to a nitrogen oxide sensor which is less than or equal to wt%.

In the present invention, the gas detection section is reacted with the complex oxide represented by the formula (I) or (IV), or the composition represented by the formula (II) or (III). It relates to a nitrogen oxide sensor in which an insulating material is mixed.

In the present invention, the insulator material is MgO.
Alternatively, it relates to a nitrogen oxide sensor which is SrTiO ₃ .

The present invention also relates to a nitrogen oxide detection sensor in which the gas detection section is in the form of a bulky thin plate, and the electrodes are made of a material having oxidation resistance and corrosion resistance.

The present invention also relates to a nitrogen oxide sensor in which the gas detecting portion is in the form of a film and the electrodes are made of a material having oxidation resistance and corrosion resistance.

The present invention also relates to a nitrogen oxide sensor in which the electrodes are bipolar electrodes.

In the present invention, the electrode is located between a pair of electrodes to which a voltage is applied and a current is passed, and another pair of electrodes for detecting a voltage between the electrodes. A nitrogen oxide sensor consisting of a pair of electrodes.

The present invention also relates to a nitrogen oxide sensor provided with a heater for heating the gas detecting section.

The present invention also relates to a nitrogen oxide sensor provided with a catalyst filter near or on the surface of the gas detecting section.

The present invention also relates to a nitrogen oxide sensor in which fine particles of a platinum group metal are dispersed or carried inside or on the surface of the gas detecting section.

The present invention also relates to a nitrogen oxide sensor in which the platinum group metal is Pt or Pd.

[0027]

The present inventors have paid attention to the fact that the compound having the Bi-2201 phase and the compound having the Bi-2222 phase have selective sensing characteristics for NO _x gas, and the gas detecting section made of these compounds is used. He has invented a nitrogen oxide sensor having the same.

The composite oxide represented by the above formula (I) or (IV), or the composition represented by the above formula (II) or (III) used in the gas detecting portion of the nitrogen oxide sensor of the present invention is It exhibits a metallic electric conductivity at a temperature of at least about 350 ° C.

Here, the temperature of about 350 ° C. or higher is a temperature including a substantial use temperature of the composite oxide or the composition as a nitrogen oxide sensor, and is composed of the composite oxide or the composition. Nitrogen oxide sensor is usually 20
It is used at a temperature of 0 to 500 ° C. (use temperature).

"Metallic electrical conductivity" refers to the characteristic that the electrical resistivity monotonically increases as the temperature rises (hereinafter, the one having metallic electrical conductivity may be simply referred to as metal. On the other hand, sometimes it is simply non-metal that shows non-metallic electrical conductivity). Since the complex oxide or composition used in the gas detection part utilizes a phenomenon accompanied by a rapid increase in resistivity when transitioning from a metal to a non-metal as described later, it may have metallic electric conductivity. preferable.

The complex oxide in the present invention has the formula (I)
Alternatively, it means a single-phase material having a composition represented by the formula (IV), and the composition of the present invention is mainly composed of the complex oxide of the present invention and contains an unidentifiable impurity phase, but It refers to a multiphase material whose composition matches the composition represented by formula (II) or formula (III), and includes raw materials such as constituent metal oxides, carbonates, hydroxides, nitrates or oxalates. The molar ratio of the metal elements used is the same as the ratio of the metal elements in the composition of the target complex oxide or composition represented by formula (I), formula (II), formula (III) or formula (IV). After weighing, mixing and press-forming as described above, it can be produced by a method of heat-treating at an appropriate temperature and time in an atmosphere of an appropriate oxygen partial pressure.

The so-called Bi-2201 phase composite oxide or Bi-22 represented by the above formula (I) or formula (IV)
22-phase complex oxide, or the above formula (II) or (II
When a nitrogen oxide is physically adsorbed on a gas detection part composed mainly of a composition mainly composed of a so-called Bi-2201 phase composite oxide represented by I), Bi-2201
Holes, which are carriers responsible for electric conduction of the phase composite oxide or the Bi-2222 phase composite oxide, are deprived.

The above-mentioned "hole" refers to a conductive carrier having the same size as an electron but having the opposite sign, that is, a positive charge. The hole density is called the hole concentration.

Here, the Bi-2201 phase ideally means BiO face / BiO face / SrO face / CuO ₂ face / SrO.
Phase with a layered structure with the plane as the period (ideal composition is Bi
₂ Sr ₂ CuO ₆ ), and the Bi-2222 phase ideally means BiO face / BiO face / SrO face / CuO ₂ face / M
Surface / O ₂ surface / M surface / CuO ₂ plane / SrO plane (M is a trivalent to tetravalent metal) is a phase (ideal composition having a layered structure in which a periodic _{Bi 2 Sr 2 M 2 Cu 2} O ₁₀ ).

In the Bi-2201 phase composite oxide or the Bi-2222 phase composite oxide, the resistivity increases as the hole concentration (n _H ) decreases, and the non-metal (non-metal) concentration decreases as the critical concentration (n _C ) or less decreases. State). The amount of nitrogen oxides physically adsorbed on the gas detection part made of the composite oxide or the composition changes (increases) according to the concentration of nitrogen oxides in the gas phase. −
The hole concentration of 2201 phase composite oxide or Bi-2222 phase composite oxide changes (decreases) and the resistivity changes (increases).
By doing so, the concentration of nitrogen oxides can be measured. Also, for coexisting gas components such as HC and CO, Bi-2
Physical adsorption hardly occurs in the 201-phase composite oxide or the Bi-2222-phase composite oxide, and the hole concentration hardly changes. Therefore, in this gas detector, the resistivity change occurs only by the concentration of nitrogen oxides in the gas phase,
Since this change in resistivity can be detected by the electrode provided in the gas detection unit, it exhibits a gas detection ability selective to nitrogen oxides and can have a sufficient function as a sensor for detecting nitrogen oxides.

The complex oxide usable in the present invention is represented by the formula (I): Bi _{2 + x} (Sr _1-a Ca _a ) _2-xyb Ln _y Cu _{1 + b} O _z (I) (wherein Ln Is a rare earth metal, and x, y, z, a and b satisfy the following relational expressions: 0 ≦ x ≦ 0.
5, 0 ≦ x + y ≦ 1, 0 ≦ a ≦ 1, −0.1 ≦ b ≦ x /
2, a complex oxide represented by z ≧ 6).

As the rare earth metal, La, Ce, P
r, Nd, Sm, Eu, Gd, Dy, Ho, Er, Y
Almost all rare earth elements such as b, Lu and Y can be mentioned.

Further, in the above relation of x, y, x, a and b, when x is less than 0 or x exceeds 0.5, the structure of the phase becomes unstable, and when x + y is less than 0, the phase becomes unstable. Structure becomes unstable, on the other hand, when x + y exceeds 1, the hole concentration becomes too low and becomes close to a non-metal, and when b is less than -0.1 or b exceeds x / 2, the phase structure is unstable. become.
When z approaches 6, the hole concentration becomes low and it becomes close to non-metal. The value of z changes depending on the oxygen partial pressure during production, and the higher this value, the higher the hole concentration. However, from the viewpoint of production, the upper limit is about 6.6. Manufacture under pressure is required.

As a preferred specific example of this composite oxide,
Examples thereof include Bi _2.2 Sr _1.75 Cu _1.05 O _z (z is not measured) or Bi ₂ Sr _1.2 Nd _0.8 CuO _z (z is not measured).

These complex oxides can be obtained by a method of weighing, mixing, press-molding and heat-treating a powder material such as an oxide or carbonate of a constituent metal element (hereinafter, this method may be referred to as a ceramic process). You can

The composition which can be used in the present invention includes
Formula _{(II): Bi 2 Sr 2} -y Nd y CuO z (II) ( wherein, is intended to satisfy a relational expression of y and z Hatsugi: 0 <y <1, z ≧ 6) with a composition represented Can be given.

In the above relation of y and z, y is 0
If it is less than this, Nd is not contained in this composition, and it becomes difficult to form 2201 phase. On the other hand, if y is 1 or more, the hole concentration is too low to be non-metallic, and z approaches 6. And the hole concentration becomes low and it becomes close to non-metal.
Since this composition is a multiphase mixture, the upper limit of z is not specified.

As a preferred specific example of this composite oxide,
For example, Bi ₂ Sr _1.6 Nd _0.6 CuO _z can be cited, which contains Bi-2201 phase as a main component and Bi ₁₇ Sr ₁₆ Cu ₇
When impurities such as O _z are contained, Bi-2201
There may be a single phase.

These compositions can be obtained by the former case (including impurities) in the ceramic process, and the latter case (single phase) in the thin film synthesis method such as laser ablation.

Another composition which can be used in the present invention is represented by the formula (III): Bi ₂ Sr _2-ya La _y Cu _1-b O _z (III) (wherein y, z and a are as follows: The relational expressions are satisfied: 0 <y ≦ 1.2, 0 ≦ a ≦ 0.2, 0 ≦ b ≦ 0.
2, a composition represented by z ≧ 6).

In the above relation of y, z and a, y
Is 0, the Bi-2201 phase is not generated, and when y exceeds 1.2, it becomes a nonmetal and the sensitivity cannot be obtained, and a is 0.
When it is less than 1, the sensitivity as a sensor is low, while a is 0.
When it exceeds 2, the ratio of the Bi-2201 phase to be generated decreases, and when z approaches 6, the hole concentration becomes low and it becomes close to a nonmetal. Since this composition is a multiphase mixture, the upper limit of z is not specified.

Specific preferred examples of this composition include Bi ₂ SrLaCu _0.8 O _z and Bi ₂ Sr _1.2.
La _1.2 CuO _{z and the} like can be mentioned.

These compositions consist of Bi ₂ O ₃ , SrCO ₃ ,
Raw material powders of La ₂ O ₃ and CuO were weighed, mixed and press-molded so that the molar ratio of the metal elements was the above composition, and the mixture was press-molded, for example, at a temperature of about 800 ° C. for about 10 hours,
After calcination in air, crush and press-mold 840
It can be obtained by a method of baking in the air at a temperature of about 30 ° C. for about 30 hours.

Another composite oxide usable in the present invention is represented by the formula (IV): Bi ₂ Sr _2-x M _{2 + x} Cu ₂ O _z (IV) (where x is 0 or Relational expression: 0.15 ≦ x ≦
In the case of x = 0, M satisfies the following relational expression: M = Ln ′ _1-y X _y (where Ln ′ is Pr, N
d, Sm, Eu, Gd, Tb, Dy, Y, Ho, Er or Tm, X is Ce or Th, and y satisfies the following relational expression: 0.1 ≦ y ≦ 0.4. ), Or the following relational expression: M = Nd _1-y Y _y (where y is the following relational expression: 0 <y ≦ 0.24), or M is Gd Or Pr, z satisfies the following relational expression: z ≧ 10, and x satisfies the following relational expression: 0.15 ≦ x ≦ 0.3, M is the following relational expression: M = Ln ' _1-y
La _y (where Ln ′ is Dy, Gd, Eu or Sm, y is the following relational expression: 0.15 ≦ y ≦ 0.2), and z is the following relation: A complex oxide represented by the formula: satisfying z ≧ 10.

The above x, y, z, M, and Ln 'of the formula (IV) are
And X, x = 0 and M satisfies the following relational expression: M = Ln ′ _1-y X _y , the preferable Ln ′ is P from the viewpoint that the Bi-2222 phase is generated.
r, Nd, Sn, Eu, Gd, Tb, Dy, Y, Ho,
Er or Tm, preferable X is Ce or Th from the viewpoint of forming the Bi-2222 phase, and y is 0.1.
If it is less than or more than 0.4, the Bi-2222 phase becomes unstable, and if z approaches 10, the hole concentration becomes low and it becomes close to a nonmetal. The value changes depending on the oxygen partial pressure in production, and the larger this value, the higher the hole concentration.
From the viewpoint of production, the upper limit is about 10.5, and production under a high oxygen pressure is necessary to produce a product exceeding this.

Further, the above-mentioned x, y, z, M of the formula (IV),
In the relationship between Ln ′ and X, when x = 0 and M satisfies the following relational expression: M = Nd _1-y Y _y , preferable Ln ′ is from the viewpoint that the Bi-2222 phase is generated. , Pr, Nd, Sm, Eu, Gd, Tb, Dy,
Y, Ho, Er or Tm, preferred X is Bi-
Ce or Th from the viewpoint of generating 2222 phase,
When y is 0 or y exceeds 0.24, Bi-2222
The phase becomes unstable, and if z is less than 10, the hole concentration becomes low and the phase becomes nonmetallic. In this case, the upper limit of the value of z is about 10.5 from the viewpoint of production, and in order to produce a value exceeding this, production under high oxygen pressure is necessary.

Further, in the relation of x, y, z, M and Ln 'in the equation (IV), x is the following relational expression 0.15
If it satisfies ≦ x ≦ 0.3, Bi-222
Due to the stable structure of the two phases, preferred Ln ′ is D
y, Gd, Eu, or Sm, and when y is less than 0.15 or y exceeds 0.2, the Bi-2222 phase becomes unstable, and when z approaches 10, the hole concentration decreases and becomes closer to nonmetal. . In this case, the upper limit of the value of z is about 10.3 from the viewpoint of production, and in order to produce a value exceeding this, production under a high oxygen pressure is necessary.

Further, in the formula (IV), when x is not 0 or x is not within the range of 0.15≤x≤0.3, from the viewpoint of structural stability of the Bi-2222 phase, high pressure synthesis is performed. And a special synthesis method such as a thin film manufacturing method is required.

Specific preferred examples of these composite oxides include, for example, Bi ₂ Sr _1.8 La _0.35 Dy _1.85 Cu.
₂ O _{z and the} like.

These composite oxides include Bi ₂ O ₃ and SrCO.
Raw material powders such as ₃ , La ₂ O ₃ , Dy ₂ O ₃ and CuO are weighed, mixed and press-molded. For example, they are pre-baked at about 800 ° C. for about 10 hours in the air, crushed and then press-molded. Pre-baking is performed again in the atmosphere at about 850 ° C for about 10 hours, and after crushing and press molding, it is performed at about 940 ° C in the atmosphere for 1 hour.
It can be obtained by a method of baking for about 5 hours.

In the nitrogen oxide sensor, Al
_When a method of forming a film on a ₂ O ₃ substrate by screen printing or the like and performing a heat treatment is used, an Al element may be mixed as an impurity in the gas detection portion. A complex oxide represented by the above formula (I) or formula (IV), or a formula (II)
Alternatively, if the composition represented by the formula (III) contains 1% by weight or more of Al element, B can be obtained even at a low temperature of 500 ° C.
The reaction between the i-2201-phase composite oxide or the Bi-2222-phase composite oxide and this Al element occurs, and the N
Selective sensitivity to _Ox gas tends to be reduced or lost. That is, although the characteristic of the increase in resistivity due to the adsorption of NO _x gas is maintained, the increase in resistivity depending on the concentration of CO gas also occurs, and it is not possible to detect only the concentration of NO _x gas. Tends to be possible. In order to maintain sufficient selectivity, the content of Al element needs to be less than 1% by weight.

In the nitrogen oxide sensor, when a raw material powder such as CuO or Bi ₂ O _{3 having} low purity is used, the Pb element may be mixed as an impurity in the gas detection portion. In many of the composite oxides represented by the formula (I) or the formula (IV) or the compositions represented by the formula (II) or the formula (III), the Bi site is replaced with the Pb element. For example, 10% of Bi element
When Pb is replaced with Pb element, the selectivity for NO _x gas is maintained, but the sensitivity is extremely lowered. In order to maintain sufficient sensitivity to NO _x gas, the content of Pb element must be at least 5% by weight or less.

In the nitrogen oxide sensor, Bi-
It is preferable that the gas detection unit includes an insulator material that does not react with the 2201 phase or the Bi-2222 phase. Examples of the insulating material include MgO and SrTiO ₃ .

Addition of such an insulator material to the Bi-2201 phase composite oxide, the Bi-2222 phase composite oxide or a composition containing these composite oxides, for example, by a method of dispersing them in a granular state. As a result, the resistivity of the gas detection unit can be increased to a desired value without impairing the electrical characteristics of the Bi-2201 phase or the Bi-2222 phase.

By increasing the resistivity of the gas detector,
Since the change in resistivity depending on the concentration of NO _x gas is large, the sensitivity of concentration detection is improved. Further, since the presence of such an additive disturbs the denseness of the composite oxide or composition forming the detection part, the atmospheric gas easily penetrates into the interior of the composite oxide or composition. Further, the detection sensitivity is improved, and the adsorption and desorption of NO _x gas can be performed in a short time, so that the response speed of detection is increased.

However, if the total amount of the additives is 75% by weight or more, the resistivity of the detecting section becomes extremely high, which makes detection difficult.

It is preferable that the gas detecting portion in the nitrogen oxide sensor has a bulky thin plate shape. Here, the bulk shape means a sintered body with a thickness of about several millimeters, and the gas detection part having such a shape increases the mechanical strength of the gas detection part and holds the detection part. The substrate to be used can be omitted.

Further, in the nitrogen oxide sensor, it is further preferable that the gas detecting portion is in the form of a thin film from the viewpoint of downsizing and weight saving of the sensor.

Further, the change in the resistivity of the gas detector is detected by the electrode made of a metal material. For example, when trying to detect NO _{x in} automobile exhaust gas, the metal may be oxidized or corroded by the exhaust gas,
It preferably has oxidation resistance and corrosion resistance. Specific examples of the metal include noble metals such as Ag, Au and Pt.

As the electrode, it is preferable to use an electrode composed of two pairs of electrodes.

Of these two pairs of electrodes, one pair is for supplying a constant current to the detection section, and the other pair is for the above-mentioned 1 pair.
The electrodes are provided with a proper distance between the pair of electrodes and detect a change in resistivity of the gas detection unit by a change in voltage.

Even if it is composed of a pair of electrodes, it can be measured by a method of incorporating a nitrogen oxide sensor into an equivalent circuit as shown in FIG. 11 (which will be described in detail in Examples). By using two pairs of electrodes as described above, it is effective in that the connection resistance and interface resistance between the gas detector and the electrodes can be ignored.

Further, in the nitrogen oxide sensor of the present invention, a heater for heating the gas detecting section is provided.

The heater may be any heater as long as it can heat the gas detector to an appropriate temperature, and is provided in the vicinity of the gas detector. The suitable heating temperature of the gas detecting part in the present invention depends on the kind of the compound constituting the gas detecting part, but it is 800 ° C. or lower as the temperature at which the complex oxide or the composition in the present invention is stably present, and the sensor performance. Is more preferably 300 to 500 ° C.

As the heater, a high melting point metal such as Pt, Ru or Rh can be used.

Further, it is preferable that the nitrogen oxide sensor of the present invention is provided with a catalyst filter from the viewpoint of improving the preferable selective detection characteristics of NO _x . This catalyst filter is provided on or near the surface of the nitrogen oxide sensor. It is provided in.

By using this catalyst filter,
Since a mixed gas such as HC or CO other than NO _x can be sufficiently removed, noise of the gas such as HC or CO coexisting with NO _x can be further suppressed.

As the catalyst filter, Pt or P
d and the like, and those having low reactivity with the compound of the present invention are preferable.

Further, in the nitrogen oxide sensor of the present invention, it is preferable that the platinum group metal fine particles are dispersed inside the gas detecting portion or are carried on the surface thereof.
Here, the term “support” means a state of being physically attached.

Since the platinum group metal fine particles are dispersed inside the gas detecting portion or are carried on the surface, noise of gases such as HC and CO coexisting with nitrogen oxides can be further suppressed, which is preferable. It is preferable from the viewpoint of improving the selective detection characteristic of NO _x .

Examples of the platinum group metal include Pt, Pd, Rh and the like.
t or Pd is preferable, and fine particles produced from a high-purity metal are preferable from the viewpoint of high catalytic performance.

An embodiment of the nitrogen oxide sensor of the present invention (hereinafter, also referred to as embodiment A) will be described below with reference to the drawings.

1 and 2 are plan views (front surface and back surface) of the nitrogen oxide sensor of the present invention. In FIGS. 1 and 2, 1 is a gas detection portion (front surface), 1b is a back surface of the gas detection portion, 2 is an electrode, 3 is an electrode lead wire, 4 is a heater, and 5 is a heater heater lead wire.

The gas detector is made of Bi ₂ O ₃ , SrC.
O ₃ , Nd ₂ O ₃ , CuO, CaCO ₃ , Pr ₆ O ₁₁ , Ce
An appropriate oxide such as O ₂ or Ln ₂ O ₃ (where Ln is a rare earth element other than Ce, Pr and Nd) or an appropriate amount of a carbonate or nitrate is uniformly mixed to obtain a desired shape. It can be obtained by a method of sintering into a sintered body or a method of processing a sintered body into a desired shape.

In the above-mentioned sintering method, the sintering is carried out in the atmosphere, and the sintering temperature is preferably 600 to 900 ° C. from the viewpoint of improving mechanical strength and compound purity, and 750 to 750. The temperature is more preferably 800 ° C., and the sintering time is 1 in view of productivity and stability of quality.
It is preferably -30 hours, more preferably 5-20 hours.

The thickness of the gas detecting portion is preferably 1 to 2 mm from the viewpoint of electrode formation and handling during installation, and the surface area is 0.2 to 1 cm ² from the viewpoint of miniaturization.
It is preferred that

By these methods, a sintered body composed of the composite oxide represented by the above formula (I) or (IV) or the composition represented by the above formula (II) or (III) is obtained. Get the gas detector. These sintered bodies are bulk materials,
That is, since it is an integrally molded product, it generally has high mechanical strength.

For the above-mentioned reason, it is preferable to add the above-mentioned insulator material or platinum group metal to the above-mentioned sintered body at the time of mixing the raw material of the detecting portion, or to add it to the surface of the detecting portion by a method such as wiping.

Subsequently, an electrode is provided on the surface of the sintered body. Examples of the electrodes include a method in which a pair of electrodes is provided on one surface of the sintered body, or a method in which a plurality of pairs of electrodes are provided for performance adjustment and the like, and mask printing is easy. A method of providing a pair of electrodes on one surface of the sintered body is preferable. In addition to the method of providing a pair of electrodes on one surface, an electrode arrangement having two opposing surfaces as a pair can be considered.

As the electrode material, a metal material such as Ag, Au or Pt, which has suitable corrosion resistance and oxidation resistance as described above, is preferable.

A paste-like material prepared by kneading the metal powder of these metal materials and a binder made of an organic material such as television neol, linseed oil, castor oil or emulgen is formed on one surface of the sintered body as desired. The above-mentioned electrode is obtained by a method such as mask printing on a shape and firing the mask in the atmosphere at about 750 ° C. for about 1 hour.

The shape of the electrodes is a pair of parallel 2
The shape of a straight line (having an appropriate width) or the shape of two pairs of combs that are combined with each other can be given. The electrode shown in FIG. 1 has a pair of parallel straight lines.

The thickness of the electrode is 0.0 from the viewpoint of productivity.
It is preferably 5 to 0.10 mm, and the surface area is preferably 0.05 to 0.10 cm ² for the same reason.

Subsequently, a voltage is applied to the pair of electrodes, and lead wires 3 of the electrodes for measuring the resistivity of the gas detecting portion are provided. As the lead wire, Au or the like is used in consideration of corrosion resistance.

Subsequently, the heater 4 is provided on the back surface of the gas detector. The heater is only required to be capable of heating the gas detection part to an appropriate temperature, and is preferably provided in the vicinity of the gas detection part, preferably directly on the back surface of the gas detection part, from the viewpoint of thermal efficiency.

The heater is mask-printed with a paste-like material obtained by kneading a metal powder such as Pt, Ru, or Rh and an organic material similar to the binder for the electrode to form a desired shape. In general, it can be obtained by a method such as firing at about 950 ° C. for about 1 hour. The heater may have any shape as long as it can uniformly and uniformly heat the gas detector.

Subsequently, the lead wire 5 of the electrode for applying a voltage to the heater is provided. Au or the like is used as the lead wire.

Next, another embodiment (embodiment B) of the nitrogen oxide sensor of the present invention will be described with reference to the drawings.

FIG. 3 shows a plan view (surface) of another nitrogen oxide sensor of the present invention. In FIG. 3, 6 is a gas detection part (front surface), 7 is a first electrode, 8 is a lead wire of a first electrode, 9 is a second electrode, 10 is a lead wire of a second electrode, 1
Reference numeral 1 indicates a lead wire of the heater.

A heating heater (not shown) similar to that of the embodiment A is provided on the back surface of the gas detector 6. The gas detector 6 is the same as the gas detector 1 of the above-described embodiment A, but the same method is used, and the first electrode 7 and the lead wire 8 of the first electrode are connected to the electrode 2 of the above-described embodiment A. In the same manner as the lead wire 3 of the electrode and the lead wire 3 of the electrode, the lead wire 11 of the heater is the same as the lead wire 5 of the heater of the embodiment A described above.

Subsequently, the pair of second electrodes 9 is provided at an appropriate position between the pair of first electrodes 7. Examples of the shape of the second electrode include a pair of two parallel straight lines (having an appropriate width). The second electrode can be made of the same material as the first electrode by the same method. Generally, the first electrode and the second electrode can be provided in the same step.

Subsequently, the lead wire 10 of the second electrode is provided on the pair of second electrodes 9. As the lead wire, the same lead wire as the first electrode can be used.

From the viewpoint of productivity, the thickness of the second electrode is preferably 0.05 to 0.10 mm, and the surface area is 0.05 to 0.10 cm ² for the same reason. Is preferred.

In this embodiment, a DC voltage is applied to the pair of first electrodes 7 through the lead wire 8 of the first electrode to cause a current to flow in the gas detecting section 6, and the pair of second electrodes 7 The resistivity of the gas detector 6 can be obtained by detecting the voltage between the electrodes 9 through the lead wire 10 of the second electrode. According to this method, as described above, the connection resistance and interface resistance between the gas detection section and the first electrode, and the connection resistance and interface resistance between the gas detection section and the second electrode can be ignored. For this reason, there is little variation in the resistivity of the gas detection unit detected by each nitrogen oxide sensor between manufacturing lots of nitrogen oxide sensors, stable products can be manufactured, and the product yield is good. Further, this is also preferable in gas detection accuracy.

Next, still another embodiment (embodiment C) of the nitrogen oxide sensor of the present invention will be described with reference to the drawings.

FIG. 4 is a plan view of yet another nitrogen oxide sensor of the present invention. Further, FIG. 5 is the plan view (FIG. 4).
FIG. 6 is a sectional view taken along line aa in FIG. In FIGS. 4 and 5, 12 is a substrate, 13 is a gas detector, 14 is an electrode, 15
Is a lead wire of the electrode, 16 is a heater, and 17 is a lead wire of the heater.

The substrate 12 can be obtained by processing or polishing a material such as MgO or SrTiO ₃ .

Since the thickness of the substrate is easy to obtain,
The surface area is preferably 0.2 to 1.0 mm, and the surface area is preferably 0.2 to 1.0 cm ² from the viewpoint of miniaturization.

Bi ₂ O ₃ and SrC are formed on one surface of the substrate.
O ₃ , Nd ₂ O ₃ , CuO, CaCO ₃ , Pr ₆ O ₁₁ , Ce
O ₂ or Ln ₂ O ₃ (where, Ln is Ce, a rare earth element except Pr and Nd) appropriate for appropriate oxides or carbonates or nitrates and the amount and TV ne ol, linseed oil,
A method of screen-printing a paste-like material prepared by kneading an organic substance such as castor oil or emulgen, or a method of spin-coating a paste-like material made of the same material as the above-mentioned one so that the viscosity is lowered, A film of paste-like material is obtained, which is fired and sintered together with the substrate.

This sintering is carried out in the atmosphere, and the sintering temperature is 60 from the viewpoint of decomposing the contained organic substances and improving the compound purity.
It is preferably 0 to 900 ° C., and 750 to 800 ° C.
Is more preferable, and the sintering time is preferably 1 to 30 hours, more preferably 5 to 20 hours, from the viewpoint of productivity and stability of quality.

The thickness of the gas detecting portion is preferably 0.05 to 0.1 mm because it can be easily formed.

By these methods, a film of a sintered body composed of the composite oxide represented by the above formula (I) or (IV) or the composition represented by the above formula (II) or (III). The gas detection part can be provided on the base material.

Subsequently, on the gas detection part 13, the same material as that of the electrode 2 and the electrode lead wire 3 of the embodiment A is used, and the electrode 14 and the electrode lead wire 15 are obtained by the same method.

Subsequently, on the substrate 12, the same material as that of the heater 4 and the lead wire 5 of the heater of the embodiment A is used, and the electrode 14 and the lead wire 15 of the heater are obtained by the same method. .

The nitrogen oxide sensor of this embodiment has gas sensitivity characteristics similar to those of the nitrogen oxide sensor of embodiment A, and further, the saturation rate of change in resistivity due to nitrogen oxide is fast, so that it can be achieved in a short time. Has the advantage that it can be measured.

Next, still another embodiment (embodiment D) of the nitrogen oxide sensor of the present invention will be described with reference to the drawings.

FIG. 6 is a plan view of still another nitrogen oxide sensor of the present invention. FIG. 7 is the plan view (FIG. 6).
6 is a cross-sectional view taken along line bb in FIG. 6 and 7, 18 is a gas detection unit, 19 is an electrode, 20 is an electrode lead wire, 21 is a heater, 22 is a heater heater lead wire, and 23 is a catalyst.

The gas detecting section 18 is obtained by using the same material as the gas detecting section 1 of the embodiment A and using the same method.

Subsequently, the same material as that of the electrode 2 and the electrode lead wire 3 of the above-mentioned embodiment A is used on the surface of the gas detection portion 18, and the electrode 19 and the electrode lead wire 20 are obtained by the same method.

Next, on the other surface (rear surface) of the gas detecting portion 18, the same material as that of the heater 4 and the lead wire 5 of the heater of the embodiment A is used, and the electrode 21 and the heater are heated by the same method. Get the heater lead wire 22.

Subsequently, the catalyst layer 23 is provided on the gas detecting portion 18 provided with the electrode 19. Examples of the material for the catalyst layer include those in which a noble metal such as Pt or Pd is contained in activated alumina or zeolite in an amount of about 5%.

As the catalyst layer 23, a material formed into a honeycomb structure by using the above-mentioned material is fixed to the gas detecting portion 18 by using an inorganic adhesive, or the above-mentioned material is pulverized or kneaded. Gas solution 1 in solution form
No. 8 can also be obtained by printing on the surface by a method such as screen printing and then sintering it in the air at about 600 ° C. for about 1 hour.

When the catalyst layer has a honeycomb structure, the size of the honeycomb is preferably several millimeters and the thickness of the layer is preferably 5 to 10 mm. If the catalyst layer is sintered by the above method,
The thickness of the catalyst layer is preferably 0.01 to 0.05 mm from the viewpoint of easy formation and gas permeability.

The nitrogen oxide sensor of this embodiment has an advantage that noises such as CO and HC that coexist with nitrogen oxides can be more preferably eliminated.

A nitrogen oxide sensor combining the features of the respective embodiments described above can also be preferably used.

The above-mentioned respective embodiments are all examples having a heater.
For example, when applied to an engine (internal combustion engine) of an automobile or various combustors, the nitrogen oxide sensor without the heater may be used. In this case, the gas detection unit can be heated by the combustion waste heat of the internal combustion engine, the combustor, etc., and the gas sensitivity characteristics similar to those of the above-described respective embodiments can be obtained.

[0122]

The present invention will be described below based on examples of the nitrogen oxide sensor of the present invention, but the present invention is not limited to these examples.

[Example 1] (1) Preparation of gas detection part The powder of Bi ₂ O ₃ , SrCO ₃ , Nd ₂ O ₃ and CuO was used, and the molar ratio of each metal element in the composition was Bi: Sr: N
d: Cu = 2: 2-y: y: 1 (where y is 0.2,
0.4, 0.6, 0.8, 1.0 and 1.2)
20 g of each sample was weighed so that each sample would be uniformly mixed and heat-treated in the atmosphere at 800 ° C. for 20 hours, and then the obtained product was pulverized. Mixing and pulverization were performed using a porcelain mortar and pestle.

Then, the obtained pulverized product is 10 mm × 10.
It is pressed into a plate with a thickness of 1 mm and a thickness of 1 mm, and it is 84 in the air.
Firing was performed at 0 ° C. for 30 hours to obtain a sintered body.

Each of the above sintered bodies was evaluated by a powder X-ray diffraction method using MPX (3000) manufactured by Mac Science. This X-ray diffraction pattern is shown in FIG. FIG.
In, the horizontal axis represents the diffraction angle of X-rays (2θ (deg)), and the vertical axis represents the relative intensity of X-rays (arb.units). For comparison, the X-ray diffraction pattern of the composition with y = 0 is also shown.

For example, y = 0 has a peak derived from phase B indicated by a triangle in the figure (the peak derived from phase B is described in the literature (Ikeda et al., "Powder and powder metallurgy"). Third
B, No. 6, No. 5 (1989), p. 108)
Referred to the peak derived from the phase). Here, the B phase is Bi-
It has a distorted structure of 2201 phase and is said to belong to a monoclinic crystal. The detailed structure is unknown, but its composition is Bi ₁₇
It refers to a phase identified as Sr ₁₆ Cu ₇ O _Z.

Further, for example, y = 0.8 has a peak derived from the Bi-2201 phase indicated by a circle in the figure (the peak derived from the Bi-2201 phase is described in the literature (T. Den.
Other reference was made to the peak derived from the Bi-2201 phase of the composite oxide described in "Jpn.J.Appl.Phys., Vol127 (1988) L1620").

For y of 0.2, 0.4 and 0.6, the peak derived from the Bi-2201 phase was mainly present, but it was found that the peak derived from the B phase also coexists. It can be seen that the coexistence ratio of the peaks decreases as the value of y increases.

If y exceeds 0.8, Bi-2 is used.
Although the peak derived from the 201 phase is the main, a peak derived from neither the Bi-2201 phase nor the B phase was observed, and it is considered that impurities were increased.

From the above X-ray diffraction results, Bi: Sr:
Nd: Cu = 2: 2-y: y: 1, that is, Bi: Sr +
From the compounding composition of Nd: Cu = 2: 2: 1, if y = 0, that is, if Nd is not contained, a B phase compound is obtained, and the value of y increases, that is, the substitution amount of Nd with Sr increases. And B
The phase becomes unstable, mainly the Bi-2201 phase occurs, the proportion of the coexisting B phase decreases, and when the y value is 0.8 or more, the B phase does not occur and when the y value is 1.0 or more. Bi-22
It was found that Nd did not form a solid solution in the 01-phase compound.

Next, the temperature dependence of the resistivity of the sintered body in a dry atmosphere was evaluated using a prototype high temperature electrical resistance measuring device by the AC four terminal method.

The results are shown in FIG. 9 (y is 0.2, 0.4, 0.6).
And 0.8) and FIG. 10 (y is 1.0 and 1.2). 9 and 10, the horizontal axis represents the measurement temperature (° C.) and the vertical axis represents the resistivity (Ω · cm).

As shown in FIG. 9, the value of y, that is, Nd
It can be seen that when the content ratio of is less than 0.6, the resistivity monotonically increases with increasing temperature from room temperature to 600 ° C. and is metallic. Further, when the value of y is 0.8, the resistivity decreases as the measurement temperature rises up to about 300 ° C. and is non-metallic, and at about 300 ° C. or higher, the resistivity decreases with the measurement temperature rise. It was found to be metallic, and a phase transition phenomenon was observed at about 300 ° C.

Further, as shown in FIG. 10, it can be seen that the resistivity does not change with respect to the change of the measurement temperature especially at high temperature when the value of y, that is, the Nd content is 1.0 or more.

(2) Production of Nitrogen Oxide Sensor 1 mm × 8 mm on the surface of the gas detecting portion which is the sintered body.
A pair of electrodes having a thickness of 50 μm were provided in parallel at an interval of 5 mm. The electrode is mask-printed with a paste material made by kneading silver metal powder and an organic material, and then 750 in the air.
It was obtained by firing at 1 ° C. for 1 hour.

Next, a heater having the shape shown in FIG. 2 was provided on the back surface of the sintered body (the surface opposite to the surface on which the electrodes were provided). The heater was obtained by mask-printing a material in the form of a paste by kneading platinum metal powder and an organic substance, and baking the paste in the atmosphere at 950 ° C. for 1 hour.

The nitrogen oxide sensor having the structure shown in FIGS. 1 and 2 was obtained by the above method.

(3) Evaluation of Nitrogen Oxide Sensor The nitrogen oxide sensor having the above structure was incorporated in the equivalent circuit test apparatus shown in FIG. In FIG. 11, 24 is a nitrogen oxide sensor, 25 is a gas detection unit resistance of the nitrogen oxide sensor, 26 is a heater resistance of the nitrogen oxide sensor, 27 is a fixed resistance of an equivalent circuit, and V is a gas detection unit resistance. Indicates the voltage generated across both ends of.

A voltage of DC 3 V or higher was applied to the heater to heat the surface temperature of the gas detector to 200 ° C. or higher. Further, by applying a voltage of DC1V to the connection circuit between the fixed resistance and the gas detection unit resistance, the voltage V generated at both ends of the gas detection unit resistance is measured, and the gas detection unit resistivity is calculated from this voltage V. It was calculated by the following formula.

R _S = (V / (V ₀ −V)) × _RL (where R _S is the resistivity of the gas detection unit resistance, R _L is the resistivity of the fixed resistance, and V is the resistance of the gas detection unit. Voltage generated across both ends,
V ₀ is the applied voltage of the connection circuit between the fixed resistance and the gas detection unit resistance).

The nitrogen oxide sensor incorporated in the above-mentioned circuit was placed in a clean air atmosphere to measure the resistivity (hereinafter sometimes referred to as Ra) of the gas detection part, and then 0.5% was measured in this clean air. The resistivity of the gas detection unit (hereinafter, Rg is set in an atmosphere mixed with volume% nitric oxide (NO)).
Sometimes it was measured).

Both Ra and Rg were measured by changing the surface temperature of the gas detection part in the range of 200 to 400 ° C.

FIG. 12 shows the ratio of Rg to Ra and Rg / Ra (hereinafter sometimes referred to as sensitivity ratio) in the case of the composition having y of 0.6. In FIG. 12, the horizontal axis represents the surface temperature of the gas detection unit and the vertical axis represents the sensitivity ratio.

According to FIG. 12, this nitrogen oxide sensor is
It can be seen that in the surface temperature range of 200 to 400 ° C., the sensitivity ratio near 300 ° C. is highest.

However, in this measurement, the gas detection response speed is faster when the surface temperature is higher than the low temperature side.

FIG. 13 shows the sensitivity ratios of the above compositions in which y is 0.2, 0.4, 0.6 and 0.8. here,
The surface temperature of the gas detection part was evaluated by maintaining it at 350 ° C., where both the sensitivity ratio and the response speed are suitable.

According to FIG. 13, the value of y is 0.2 or more and 0.8.
It can be seen that the following have an effective sensitivity ratio, and those with a y value of 0.2 or more and 0.6 or less have a more suitable sensitivity ratio. Although not shown in FIG. 13, the sensitivity ratio was very low when the value of y was 1.0 or more.
As shown in FIG. 10, the value of y is 1.
In No. 0, the hole concentration of Bi-2201 phase is considerably low, so that the hole concentration is below the critical concentration at 350 ° C., and it is in a nonmetallic state. Therefore, it is presumed that the change in the hole concentration due to the adsorption of nitric oxide is small and thus the change in the resistivity, that is, the sensitivity ratio is low.

Next, the sensitivity ratio to carbon monoxide (CO), carbon dioxide (CO ₂ ) and hydrocarbon (HC) which are coexisting gas components at the surface temperature of the gas detection part of 350 ° C. was determined for the above-mentioned nitric oxide. It was measured by the same method as the measurement of. Propane gas (C ₃ H ₈ ) was used as the hydrocarbon. Sensitivity ratio in a mixed gas atmosphere in which 1% by volume of carbon monoxide is mixed with clean air,
The sensitivity ratio in a mixed gas atmosphere in which clean air is mixed with 1% by volume of carbon dioxide and the sensitivity ratio in a mixed gas atmosphere in which clean air is mixed with 1% by volume of propane gas are 0. Using a nitrogen oxide sensor having the above-mentioned composition of 2, 0.4, 0.6 and 0.8 as a gas detection part, 350 ° C.
The sensitivity ratio of the carbon monoxide mixed gas was 1.02 in all nitrogen oxide sensors when measured under the surface temperature of
In the case of the carbon dioxide mixed gas sensitivity ratio and the propane gas mixed gas, the change in the resistivity of the gas detector was below the detection accuracy. This indicates that these sensors have a detection sensitivity that is selective for nitrogen oxides.

In addition, when exhausting combustion gas from an internal combustion engine or a combustor, in addition to the coexistent gas, water vapor may be mixed in or a low oxygen concentration state (oxygen deficiency state) may occur. A nitrogen oxide sensor that does not show sensitivity even under such changes in conditions is desired. Therefore, the surface temperature of the gas detector is set to 3
Set to a constant temperature of 50 ° C, change relative humidity to 10-80% (20 ° C), with or without humidity (water vapor) dependency.
Oxygen concentration was changed to 0 to 20% depending on the presence or absence of oxygen concentration dependency, and the change in resistivity of each sensor (y was 0.2, 0.4, 0.6 and 0.8) was measured. As a result, in all the sensors, the change in the resistivity of the gas detection part was below the measurement accuracy. From this, it can be seen that the characteristics of the gas detection unit do not change even with these water vapor and low oxygen concentrations (oxygen deficiency state), and the gas detection unit has a stable sensitivity ratio to nitrogen oxides.

In the case of this example, the main phase of the composition having y of 0.6 or less was Bi-based on the X-ray diffraction pattern shown in FIG.
2201 phase, but also includes B phase. The present inventors have discovered that this B phase also has a selective sensitivity to NO _x gas ("Nozaki et al., 1994 (1994) Autumn 55th Annual Meeting of Japan Society of Applied Physics" Proceedings of the lecture,
No. See page 1, 65). Therefore, only the data relating to the composition in which y is 0.6 or less indicates that the Bi-2201 phase has NO _x.
It cannot be determined if it has selective sensitivity to gas. However, since it is determined by the X-ray diffraction pattern of FIG. 8 that the compositions in which y is 0.8 and 1.0 do not include the B phase, the Bi-2201 phase also has a selective sensitivity to NO _x gas. It can be said to have.

[Example 2] The existence of the Bi-2201 phase is 1
Discovered in 987 (C. Michel et al. Z. Phys. B68.1987,
P421, J. Akimitusu et al. Jpn. J. Appl. Phys. 26 (198
7) L2080), in addition to the example in which a part of Sr is replaced with Nd, a part of Sr is La, Ce, Pr, Sm, Eu, G
It is also known that many rare earth metals such as d, Dy and Ho can be substituted (T. Den et al. Jpn. J. Appl. Phys., vol.
27 (1988) L1620). In addition, Bi-220 containing no Sr
The existence of one phase is also known. For example, the literature (Y. Takemur
a et al. Jpn. J. Appl. Phys. 27 (1988) L1864) has Bi ₂
CaLaCuO _z was published in the literature (H. Sasakura et al. Jpn. J. Ap.
pl. Phys. 27 (1988) L1864) contains Bi ₂ Ca _2-y Pr _y C
uO _z (0.5 ≦ y ≦ 1) is also reported in the literature (H. Sasakura
Other Physica C 234 (1994) 307) has Bi _{2 + x} Ca _2-xy L
n _y CuO _z (Ln = La, Pr, Nd, Sm, Eu, G
d) is reported. According to these synthesis conditions, Table 1
A gas detection part made of the composition shown in Fig. 1 was prepared, and an electrode was provided on the gas detection part by the same method as in Example 1. Then, a change in resistivity under a temperature condition from room temperature to 600 ° C in a dry atmosphere, and The sensitivity ratio at 350 ° C. to 0.5% by volume nitric oxide (NO) gas-mixed clean air was measured. In this example and the subsequent examples, the heater was not provided in the gas detection part, and the nitrogen oxide detection sensor was installed in the tubular furnace capable of controlling the ambient temperature to control the temperature of the gas detection part.
Table 1 shows the results. In Table 1, ○ in the sensitivity ratio column
Indicates that the value of Rg / Ra is 1.1 or more. △ indicates Rg /
If the value of Ra is larger than 1.1 and smaller than 1, it means that
Shows no sensitivity within the range of this measurement (Rg / Ra
Is 1), and ○ in the metallic column indicates that the metallic conductivity at 350 ° C., and × indicates the non-metallic conductivity at 350 ° C.
The column of phases represents the phases contained in the sample, and “impurities” represent the coexistence of slight unknown impurities. As shown in Table 1, it is understood that the materials exhibiting a good sensitivity ratio (that is, Rg / Ra value of 1.1 or more) exhibit metallic electrical conductivity. However, part of the Bi site is Pb
It can also be seen that the one substituted with is reduced in the sensitivity ratio to the NO _x gas although the selectivity to the NO _x gas is retained.

[0152]

[Table 1]

[Embodiment 3] For example, Bi _2-w Pb _w Sr
_{In the} composition represented by _1.8-w Nd _{0.2 + w} CuO _z , the valence of each metal ion is approximately +3 for Bi and +2 for Pb.
It is known that the valence, Sr is +2, and Nd is +3. Therefore, even if the value of w in the composition formula is changed, it is considered that the change in the average valence of Cu is small unless the oxygen amount z changes significantly. It is known that the hole concentration in the system of these compositions and complex oxides is proportional to δ when the average valence of Cu is + (2 + δ). Therefore, it is estimated that the change in hole concentration is small even if the value of w in the above composition formula is changed. In the above composition formula obtained by baking the electrode with Ag paste, w is 0, 0.2, 0.4, 0.
The composition of 6 and 0.8 was fired in the air, and the fired product was provided with electrodes in the same manner as in Example 1 to obtain a nitrogen oxide sensor, and the resistivity at 350 ° C. in the air was measured. However, this resistivity showed almost no difference due to the difference in the value of w. These nitrogen oxide sensors were placed in a dry atmosphere, 0.5% by volume NO gas mixed clean air,
1 volume% CO gas mixed clean air and 1 volume% C ₃ H ₈
The electrical resistivity at 350 ° C. in clean air mixed with gas was measured. It was found that the change of the resistivity with respect to the CO and CH coexisting gas was less than the measurement accuracy, and that all the samples had excellent selective detection.

FIG. 14 shows the relationship between the sensitivity ratio to NO _x gas and the Pb composition content. In FIG. 14, the vertical axis represents the sensitivity ratio (Rg / Ra) and the horizontal axis represents the Pb composition content (w). As shown in FIG. 14, it can be seen that the sensitivity ratio sharply decreases when the Bi element is replaced by the Pb element. As described above, it is not preferable that the Pb element is mixed in the Bi-2201 phase. If Pb element is included, w
Value of about 0.2 or less, that is, Pb element is preferably 5% by weight or less.

[Example 4] BiO _1.5 -SrO-CuO
The phase diagram of the ternary system has been studied in detail, and it is known that in this ternary composition, the stoichiometric composition of the Bi-2201 phase compound has some extent. For example, the literature (Ikeda et al., Powder and powder metallurgy No. 3
Vol. 6, No. 5 (1989) p. 108) shows the state diagram shown in FIG. FIG. 15 shows Ba ₂ O ₃ and SrCO.
FIG. 3 shows a phase diagram of a BiO _1.5 —SrO—CuO ternary system obtained by firing a mixture of ₃ and CuO at 840 ° C. in the atmosphere. As shown in FIG. 15, Bi: S
In the composition of r: Cu = 2: 2: 1 (indicated by point B in the figure), a mixed phase containing the B phase (Bi ₁₇ Sr ₁₆ Cu ₇ O _z ) as the main component is obtained, and the Bi-2201 phase is obtained. It turns out that is not generated. On the other hand, the Bi-2201 phase occurs in the region marked A in the figure, and Bi _{2 + x} Sr _2-x Cu _1-y O _z (0.1 <
It is shown that the composition range is x0.5, 0 <y <x / 2). On the other hand, a part of Sr is rare earth metal (L
n) substituted BiO _1.5- (Sr _1-x Ln _x ) O _z -Cu
The phase diagram of the quasi-ternary system of O is unknown, and there is a difference from the unsubstituted system. That is, even if Bi: (Sr _1-x Ln _x ): Cu = 2: 2: 1, the B phase cannot be obtained by substituting Ln to a certain degree or more, and almost a single phase of the Bi-2201 phase can be obtained. In this case, it is not known how the stoichiometric composition of the Bi-2201 phase extends.

Therefore, in the formula: Bi ₂ Sr _2-y Ln _y CuO _z , Bi: (Sr _0.5 L) where Ln = La and y = 1
a _0.5 ): Cu = 2: 2: 1 with a focus on Bi, (S
r _0.5 La _0.5 ) or Cu composition ± 20
Six types of samples were prepared, which were increased or decreased by%. The composition of these six types of samples is shown in the state diagram of FIG. 9 (however, SrO (Sr _0.5
La _0.5 ) O _1.25 )) and the numbers (1) to (6). (1) is a sample in which the Cu element is reduced by 20%, that is, the composition is Bi ₂ SrLaCu _0.8 O _z . Similarly, (2) increases (Sr _0.5 La _0.5 ) by 20%, and (3)
Is a composition in which the Bi element is decreased by 20%, (4) is an increase in the Cu element by 20%, (5) is a composition in which (Sr _0.5 La _0.5 ) is decreased by 20%, and (6) is a composition in which the Bi element is increased by 20%. In the air, a mixture of raw material powders weighed and mixed with these blending compositions,
The X-ray diffraction pattern of the sample baked at 840 ° C. for 30 hours is shown in FIG. In FIG. 17, the vertical axis represents the X-ray diffraction intensity I.
(Cps), the horizontal axis represents the diffraction angle 2θ (deg),
(1) to (6) show the diffraction patterns of the above-mentioned respective compositions. The peak marked with a circle in FIG. 17 corresponds to the Bi-2201 phase, but many peaks due to other impurities are also seen. However,
It can be seen that the sample (4) (increasing the Cu element by 20%) is relatively close to a single phase. From this data Bi-2201
Lattice constants estimated assuming that the crystal structure of the phase is tetragonal are shown in FIGS. 18 and 19. FIG. 18 shows the a-axis length, and FIG. 19 shows the c-axis length. As shown in FIG. 18 and FIG.
Axial length and c-axis length show good correlation, and samples (1) and (2)
The lattice constants of (3) and (3) are shorter than those of the samples (4), (5) and (6). The above results show that BiO _1.5 − (Sr _1-x
Also in the phase diagram of the quasi-ternary system of Ln _x ) O _z -CuO, B
It was found that the stoichiometric composition of the i-2201 phase has a spread and its lattice constant greatly changes depending on the composition.

These samples were also provided with electrodes in the same manner as in Example 1, and the resistivity at 350 ° C. was measured in a dry atmosphere and a 0.5% NO _x gas mixed clean air atmosphere. The obtained sensitivity ratio (Rg / Ra) is 1.50 for sample (1), 1.20 for sample (2), 1.07 for sample (3), and sample (4).
Is 1.05, sample (5) is 1.06, and sample (6) is 1.
It was 03. Incidentally, the sensitivity ratio was 1.1 in the almost single-phase sample of Bi ₂ SrLaCuO _z . From the above results, it was found that the sensitivity to NO _x gas strongly depends on the stoichiometric composition of the Bi-2201 phase or the lattice constant, and is good on the Cu decreasing side or the (Sr _1-x Ln _x ) increasing side. It was

[Embodiment 5] The sensitivity ratio is Bi-
Since it was found to strongly depend on the stoichiometric composition of the 2222 phase, Example 1 was reviewed and an attempt was made to prepare a sample containing no B phase. When Nd is not substituted, the composition range in which a single phase of Bi-2201 phase is obtained is Bi _{2 + x} Sr _2-x Cu _{1 + y} O
_Since it is known that _z (0.1 <x <0.5, 0 <y <x / 2), it is near the middle of this composition range (the middle is
x = 0.3, y = 0.075)
_2.2 Sr _1.75 Cu _1.05 O _z was selected. The chemical formula here is such that the number of moles of all metal elements is converted to ₅ , that is, Bi _{5 (2 + x) / (5 + y)} Sr _{5 (2-x) / (5 + y)} Cu.
_Since the display is _{5 (1 + y) / (5 + y)} O _z , x =
0.228 and y = 0.063. Therefore, an attempt was made to prepare a sample in which a part of Sr in this composition was replaced with Nd. The compounding composition is Bi _2.2 Sr _1.75-y Nd _y Cu _1.05 O
_z (y = 0, 0.2, 0.4, 0.6, 0.8, 1.
0). The synthesis conditions were the same as in Example 1. When powder X-ray diffraction of the obtained sample was performed, y = 0, 0.
2, 0.4 is a single phase of the Bi-2201 phase, and when the value of y is more than that, the Bi-2201 phase is the main phase but contains impurities, and the amount thereof increases with the increase of y. I knew that. _{BiO 1.5 -Sr 1-y Nd y} O 1 + y / 2 -CuO phase diagram y = 0 shown in FIG. 15 with increasing y pseudo ternary
It was found that the composition region in which a single phase of the Bi-2201 phase was obtained also changed depending on y.

Therefore, the obtained single-phase sample only 350
The gas sensitivity characteristics to 0 ° C. and 0.5% NO were evaluated. The results are shown in Fig. 20. In the composition selected in this example, not only +3 valent Nd is substituted by y mole on +2 valent Sr site, but also approximately +3 valent Bi is substituted by 0.2 mole and +2 valent Cu is substituted by 0.05 mole. Can be considered. In order to compare the results of Example 1 and this example, it is easier to understand that samples having similar hole concentrations correspond to each other. Compared to Example 1, the y mol Nd-substituted sample in this example is:
This corresponds to the y + 0.2 sample from the viewpoint of hole concentration.
Therefore, in FIG. 20, the horizontal axis is y + 0.2. Further, the results of Example 1 in FIG. 13 are also shown with the horizontal axis y.
As shown in FIG. 20, in the case of the present embodiment as well, it can be seen that the sensitivity ratio monotonously decreases as y increases (the hole concentration decreases), but the rate of change thereof is rapid. Almost Bi-
The sensitivity ratio of the sample of y = 0.8 in the single phase of 2201 phase is not on the curve (indicated by the broken line in the figure) obtained by extrapolating the curve of the sensitivity ratio of the present embodiment. . Therefore,
It can be said that the hole density is not the only factor that determines the sensitivity ratio.

Example 6 Next, Bi ₂ Sr _1.4 Nd _{0.6 was used.}
10% by weight of Al ₂ O ₃ powder was added to the CuO _z powder, and a sintered body similar to that of Example 1 was produced using this as a raw material. When the phase was identified by X-ray diffraction, Bi-220
Several unknown peaks were found in addition to the diffraction peak derived from the 1st phase. Also, the lattice constant of the Bi-2201 phase is Al
_A slight difference from the value of the Bi-2201 phase before the addition of ₂ O ₃ was observed. An electrode was provided on this sintered body by the same method as in Example 1, and the gas sensitivity characteristics were measured in an atmosphere at a temperature of 350 ° C. As a result, the sensitivity ratio for the 0.5% by volume NO _x gas-mixed clean air was only about 15% lower than that for the sample without Al ₂ O ₃ , but for the 1% by volume CO gas-mixed clean air. Therefore, the resistivity was further increased.
This result is presumed to be due to the loss of the selectivity for the NO _x gas due to the incorporation of Al in the Bi-2201 phase. Therefore, addition of Al ₂ O ₃ to the Bi-2201 phase is not preferable. When Al is contained, it is preferably less than 1% by weight of the whole.

[Embodiment 7] When an insulating material which does not react with the Bi-2201 phase is contained / dispersed in the gas detection part containing the Bi-2201 phase as a main component, what kind of change occurs in the gas sensitivity characteristics. An experiment was conducted to find out. As such an insulating material, some are known as a substrate material used for thin film synthesis of MgO or SrTiO ₃ or other oxide superconducting material. Here, MgO is selected as an example, and powders of MgO and Bi ₂ Sr _1.4 Nd _0.6 CuO _z are mixed at a volume ratio of 1-v: v (1 ≧ v ≧ 0.2), and after press molding, Firing was performed in the air at 840 ° C. for 30 hours. An Ag electrode was baked on these samples, and the resistance at 350 ° C. in the atmosphere was measured. The obtained resistivity rapidly increased with decreasing v, and became unmeasurable at v <0.23. The relationship between the electric conductivity (reciprocal of resistivity) and v is almost a straight line, and this straight line is extrapolated to 0 when v is 0.2. Next, the resistivity at 350 ° C. was measured in 0.5% by volume NO gas-mixed clean air. The relationship between the obtained sensitivity ratio (Rg / Ra) and v is shown in FIG. As shown in FIG. 21, the sensitivity ratio monotonically increases as v decreases. It is presumed that this result is because the addition of MgO deteriorates the sinterability and makes it easier for the atmospheric gas to permeate into the gas detection portion. In fact, in particular v <0.
The sinterability of sample 5 was very poor.

As described above, the sensitivity is improved as the volume ratio of the Bi-2201 phase is reduced, but the element resistance is also increased. If the resistance of the element becomes too high, the circuit for measuring the resistance becomes complicated. Therefore, it is necessary to control the element resistance value within a certain range by adjusting the element size and the MgO content. These insulator materials have a resistance value (about 100 k) that can measure the element resistance value.
It can be seen that the volume ratio is preferably 75% or less of the whole in order to be Ω) or less.

Example 8 Bi ₂ O ₃ , SrCO ₃ and La ₂
O ₃ , Ln ₂ O ₃ (Ln = Sm, Eu, Gd, Dy), C
Each powder of uO was mixed with Bi: Sr: La: Ln: Cu = 2: 2.
Weighed so as to be -x: 2-y: x + y: 2 and mixed well. Here, in the case of Ln = Sm and Eu, x = 0.
3, and y = 1.6, and when Ln = Gd and Dy, x
= 0.2 and y = 1.65. 600 kg of mixed powder
It was press-molded at a pressure of f / cm ² , calcinated in the air at 800 ° C. for 10 hours, and then pulverized. The obtained powder was press-molded again at 600 kgf / cm ² , calcinated in the air at 850 ° C. for 10 hours, and then pulverized. The obtained powder was press-molded into a flat plate at 1000 kgf / cm ² , and fired at 940 ° C. for 15 hours in the atmosphere. When the powder X-ray diffraction of the obtained sintered body was performed,
As shown in akakura et al., Physica C 218 (1993) 695), it was confirmed that the compound was almost a single phase of Bi-2222 phase compound. Electrodes were provided on these samples in the same manner as in Example 1, and the resistivity at 350 ° C. was measured in a dry atmosphere and a 0.5% by volume NO gas-mixed clean air atmosphere.
As a result, as shown in Table 1, all samples were 350 ° C.
Above, metallic electric conductivity was exhibited, and the sensitivity ratio was also good. In particular, the case where Ln = Dy showed a good sensitivity ratio, but it is presumed that this sample is inferior in sinterability and has a low density, so that the atmospheric gas easily permeates into the inside of the sample.

The Bi-2222 phase has Bi ₂ Sr ₂ (Ln _1-x X _x ) ₂ Cu ₂ shown in the literature (Y. Tokura et al., Nature 342 (1989) 890) in addition to the above composition. _Oz (Ln is a rare earth metal; X = Ce, Th) and literature (A. Schilling e
Bi ₂ Sr ₂ Ln ₂ Cu ₂ O _z (Ln = Gd, Pr, Nd _1-x shown in Tal., Physica C 185-189 (1991) 659).
Y _x ), etc. are also known. Bi-22 of these compositions
The 22 phase also shows metallic electrical conductivity at 350 ° C. or higher, and showed sensitivity to NO gas at 350 ° C.

[Embodiment 9] In the above Embodiments 1 to 8, 1
Although a pair of first electrodes is provided and a DC voltage is applied to the pair of electrodes to obtain the resistance of the gas detection unit, for example, another electrode is formed in an intermediate region where the pair of first electrodes is formed. A method of determining the resistivity of the gas detector may be adopted by providing a second electrode having a pair of linear shapes (see FIG. 3). In the case of this method, a DC voltage is applied to the pair of first electrodes through the lead wire of the first electrode to pass a current, and the voltage across the other pair of second electrodes is applied to the second electrode. The resistivity of the gas detector is obtained by detecting it through the lead wire. As a result, the connection resistance or interface resistance between the gas detection section and the first electrode, or the connection resistance or interface resistance between the gas detection section and the second electrode can be ignored. Very stable and less variation, and good yield. It can also be said that the gas detection accuracy is good.

[Embodiment 10] In Embodiment 10, description will be made on the case where the gas detector is formed in a film shape (FIGS. 4 and 5).
reference). As a gas detection film forming method, for example, a method of screen-printing a paste prepared by kneading a composition powder and an organic material on a ceramic substrate, a method of spin-coating a paste having a low viscosity on the substrate, and a vapor deposition method or a sputtering method. A method of forming an object thin film is also possible. The nitrogen oxide detection sensor in this case is shown in FIGS. 4 and 5, and the first gas sensor is formed by forming a gas detection film on a ceramic substrate and forming a pair of linear shapes facing the surface of the gas detection film, for example. When the electrodes are formed and further the heater is formed on the back surface of the ceramic substrate, the gas sensitivity characteristic almost similar to that of the first embodiment can be secured, and the object of the present invention can be achieved.

FIG. 22 shows the results of measurement of NO gas absorption / desorption response in a film-shaped nitrogen oxide detection sensor having a composition of Bi ₂ Sr _1.4 Nd _0.6 CuO _z (see FIGS. 4 and 5).
Is shown in the sensitivity characteristic diagram of. In FIG. 22, the vertical axis represents the element resistance value (Ω), and the horizontal axis represents the elapsed time (minutes). Also,
In FIG. 22, IN indicates that 0.5% NO gas was adsorbed and sealed in the gas detection unit, and OUT indicates that NO gas was released by blowing air onto the gas detection unit. As shown in FIG. 22, the film of Example 9 had higher sensitivity than the bulk body of Example 1, and the saturation time of the characteristic was short and the performance was good.

[Embodiment 11] A gas detecting portion and a first electrode or a second electrode constructed by the same method as in Embodiment 9 are formed, and then a noble metal element of Pt or Pd is further formed on the active alumina or zeolite. It is also effective to selectively detect nitrogen oxides if a combustion catalyst or reduction / removal catalyst capable of removing the above-mentioned coexisting gases HC, CO, etc. by the oxidative exothermic reaction is adhered to about 5% of the above. .

A side sectional view of the present sensor is shown in FIG. 23. A honeycomb combustion catalyst 31 is fixed on the gas detector 28 and the first electrode 29. The result of the gas experiment conducted using this sensor is shown in the sensitive characteristic diagram of FIG. In FIG. 24, the vertical axis represents the element resistance value (Ω), the horizontal axis represents the concentration (%) of the measurement gas, the solid line in the figure shows the data with the catalyst 31 provided, and the broken line shows the data without the catalyst 31 provided. Show the data. The measurement was carried out under clean air mixed with CO gas and NO gas, respectively. In the case without the honeycomb combustion catalyst 31 shown by the solid line, the resistance value of the gas detection unit 28 is slightly increased with respect to CO, and the gas detection unit 28 has some gas sensitivity.
On the other hand, in the case of the honeycomb combustion catalyst 31 shown by the broken line, it is understood that CO has no sensitivity and no dependence.

As a method of forming the combustion catalyst on the gas detecting portion, the first electrode and the second electrode, there is the following method, which is known to have the same characteristics as described above.

(1) Zeolite containing an element such as Pt or Pd in an amount of about 5% is made into a solution and screen-printed on the surface of the gas detection unit 1 to a thickness of about 50 μm and sintered. Method.

(2) A method of containing and dispersing an element such as Pt or Pd in the gas detector 1.

[Comparative Example 1] A NO _x gas detecting element described in JP-A-3-13854 (TFN-11 (trade name portable type NO _x concentration meter manufactured by Tokuyama Soda / SEGLO GIKEN)) (see FIG. 25). The gas detection characteristics of NO, HC and CO were evaluated by. Figure 26 shows the evaluation results.
Shown in In FIG. 26, the vertical axis represents the resistance value (kΩ) of the gas detection element, and the horizontal axis represents the concentration (%) of the measurement gas. In this evaluation, the temperature of the NO _x gas detecting element was set to about 450 ° C. As is clear from FIG. 26, the resistance of the sensing element increases as the concentration of NO increases, while the resistance of HC and CO decreases as the concentration increases. That is, according to this measurement, according to the NO _x gas detecting element described in JP-A-3-13854, the resistance value of the gas detecting element changes due to the presence of the coexisting gas component HC or CO, which causes the NO _x gas concentration to be detected. Therefore, it has been found that it causes an adverse effect (noise).

Next, using the same gas detecting element as described above, the element temperature is set to about 450 ° C., and NO is 0.
The measurement of NO _x was started in an atmosphere of 5% constant, and 20 minutes after the start of measurement, the gas-sensitive characteristics were measured when HC and CO were adsorbed and enclosed. This measurement result is shown in FIG.
Shown in In FIG. 27, the vertical axis represents the resistance value (kΩ) of the gas detection element, and the horizontal axis represents the elapsed time (minutes) of measurement. FIG.
As is clear from the above, the element resistance of the gas detection element was constant while the coexisting gas components HC and CO were absent.
After the adsorption and encapsulation of O, it decreased significantly.

[0175]

According to the nitrogen oxide sensor of the present invention, the gas detecting portion has a Bi-2201 phase composite oxide or B
i-2222 phase complex oxide or since a composition containing these composite oxides having selective sensing characteristics for NO _x gases.

Further, in the nitrogen oxide sensor according to the present invention, since the gas detecting portion has a metallic electric conductivity at the working temperature or higher, the hole concentration is lowered by the adsorption of NO gas, so that the metal-nonmetal transition occurs. This results in a large resistance change.

Further, in the nitrogen oxide sensor according to the present invention, the gas detecting portion has the Bi-2201 phase composite oxide or its composition or the Bi-2222 phase composite oxide or this composition in a total amount of 25% by weight or more. Therefore, the resistivity of the detection section does not become extremely high, and sufficient detection characteristics can be obtained.

Further, the nitrogen oxide sensor according to the present invention has the complex oxide represented by the above formula (I) or (IV) mixed in the gas detection portion as an impurity, or the complex oxide represented by the formula (II) or (III). Since the Al element contained in the composition shown in addition to the metal element is less than 1% by weight, it has selective detection sensitivity to NO _x gas.

Further, the nitrogen oxide sensor according to the present invention comprises the compound oxide represented by the above formula (I) or (IV) mixed in the gas detection portion as an impurity, or the complex oxide represented by the formula (II) or (III). Since the Pb element contained in the composition represented in addition to the metal element is 5% by weight or less, it has sufficient detection sensitivity for NO _x gas.

Further, in the nitrogen oxide sensor of the present invention, the resistance of the gas detecting section is improved by including an insulating material such as MgO or SrTiO ₃ which does not react with the Bi-2201 phase or the Bi-2222 phase in the gas detecting section. it is possible to increase the rate to a desired value, in order to resistivity changes depending on the concentration of the NO _x gas is increased to improve the sensitivity of the density detection. Further, since the presence of such an additive disturbs the denseness of the composite oxide or composition forming the detection part, the atmospheric gas easily penetrates into the interior of the composite oxide or composition. Further, the detection sensitivity is improved, and the adsorption and desorption of NO _x gas can be performed in a short time, so that the response speed of detection is increased.

Further, in the nitrogen oxide sensor according to the present invention, the gas detecting portion has a bulky thin plate shape,
It is possible to increase the strength of the gas detector and to manufacture it at low cost.

Further, the nitrogen oxide sensor according to the present invention has the gas detecting portion in the form of a film, so that the sensitivity and the responsiveness can be improved, although they are more expensive than those in the bulk thin plate shape.

Further, in the nitrogen oxide sensor of the present invention, since the change in the resistivity of the gas detecting portion can be measured by the electrodes having the oxidation resistance and the corrosion resistance, the reliability and reproducibility are high, and The life will be extended.

In the nitrogen oxide sensor of the present invention, the change in the resistivity of the gas detecting section is made up of two pairs of electrodes, so that the connection resistance and interface resistance between the gas detecting section and the electrodes are changed. Can be ignored.

Further, in the nitrogen oxide sensor of the present invention, by providing the heater for heating the gas detecting section, the gas detecting section can be heated to a desired temperature and the gas can be detected under the optimum conditions.

Further, in the nitrogen oxide sensor of the present invention, by providing a catalyst filter, it is possible to sufficiently remove a mixed gas other than NO _x , such as HC and CO, so that gas such as HC and CO that coexists with NO _x. Noise can be further suppressed, and preferable selective detection characteristics of NO _x can be improved.

Further, in the nitrogen oxide sensor of the present invention, fine particles of platinum group metal such as Pt or Pd are dispersed inside the gas detecting portion or are carried on the surface of the gas, so that, for example, HC or CO other than NO _x can be obtained. Since the mixed gas such as HC can be sufficiently removed, the noise of the gas such as HC and CO coexisting with NO _x can be further suppressed, and the preferable NO
The selective detection characteristic of _x can be improved.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a nitrogen oxide sensor of the present invention.

FIG. 2 is a bottom view showing an embodiment of the nitrogen oxide sensor of the present invention.

FIG. 3 is a plan view showing another embodiment of the nitrogen oxide sensor of the present invention.

FIG. 4 is a plan view showing still another embodiment of the nitrogen oxide sensor of the present invention.

FIG. 5 a of the nitrogen oxide sensor of the present invention in FIG.
FIG.

FIG. 6 is a plan view showing still another embodiment of the nitrogen oxide sensor of the present invention.

7 b of the nitrogen oxide sensor of the present invention in FIG.
It is a -b line sectional view.

FIG. 8 is a powder X-ray diffraction pattern of Bi ₂ Sr _2-y Nd _y CuO _z , which is a composition constituting the detection part of the nitrogen oxide sensor of the present invention.

FIG. 9 is a diagram showing the temperature dependence of the resistivity of Bi ₂ Sr _{2 -y} Nd _y CuO _z , which is a composition constituting the detection part of the nitrogen oxide sensor of the present invention.

FIG. 10 is a diagram showing the temperature dependence of the resistivity of Bi ₂ Sr _{2 -y} Nd _y CuO _z , which is a composition constituting the detection part of the nitrogen oxide sensor of the present invention.

FIG. 11 is a diagram of an equivalent circuit for measuring the resistivity of the detection portion of the nitrogen oxide sensor used in Examples 1 to 8.

FIG. 12 shows the temperature dependence of the sensitivity ratio of the composition constituting the detection part of the nitrogen oxide sensor of Example 1, Bi ₂ Sr _{2 -y} Nd _y CuO _z , to 0.5 vol% NO gas mixed clean air. FIG.

13 is a diagram showing the relationship between the sensitivity ratio of Bi ₂ Sr _{2 -y} Nd _y CuO _z at 350 ° C., which is the composition of the detector of the nitrogen oxide sensor of Example 1, and the value of y indicating the composition of the composition. FIG.

FIG. 14 is a composite oxide constituting the detection part of the nitrogen oxide sensor of Example 3, Bi _2-w Pb _w Sr1.8 _-w Nd _0.2-w C.
is a diagram showing the relationship between the value of w illustrating a configuration of a sensitivity ratio and composition in 350 ° C. of uO _z.

FIG. 15 is a phase diagram of a BiO _1.5 —SrO—CuO ternary system described in the literature at 840 ° C. in the atmosphere.

FIG. 16 shows BiO _1.2 − (Sr _0.5 L in Example 4).
a _0.5) is an illustration of the composition of the ternary O _1.25 -CuO.

FIG. 17 is an X-ray diffraction pattern of compositions (1) to (6) constituting the detection part of the nitrogen oxide sensor of Example 4.

FIG. 18 is a diagram showing the lattice constants of the Bi-2201 phase of compositions (1) to (6) constituting the detection part of the nitrogen oxide sensor of Example 4.

FIG. 19 is a diagram showing the lattice constants of the Bi-2201 phase of the compositions (1) to (6) constituting the detection part of the nitrogen oxide sensor of Example 4.

FIG. 20: Composition of Bi ₂ Sr _1.75-y Nd _y Cu _1.05 O _z , which is a composition constituting the detection part of the nitrogen oxide sensor of Example 5,
Y + 0.2 showing the sensitivity ratio at 50 ° C. and the composition of the composition
It is a figure which shows the relationship with the value of.

21 is a graph showing the composition of the detection part of the nitrogen oxide sensor of Example 7, Bi ₂ Sr1.4Nd0.6CuO _{z, in} which MgO is contained / dispersed in a volume ratio of v: v−1. .5
It is a figure which shows the sensitivity ratio in 350 degreeC with respect to the volume% NO gas mixed clean air.

FIG. 22 is a response characteristic diagram showing evaluation results of NO gas adsorption / desorption responsiveness of the nitrogen oxide sensor of Example 9.

23 is a side view of the nitrogen oxide sensor of Example 11. FIG.

FIG. 24 is a response characteristic diagram showing evaluation results of NO gas adsorption / desorption responsiveness of the nitrogen oxide sensor of Example 11.

FIG. 25 is a plan view of a conventional nitrogen oxide sensor.

26 is a NO _X, sensitive characteristic diagram showing the results of gas measurement experiment of HC and CO in nitrogen oxide sensor of Comparative Example 1 (nitrogen oxide sensor of the prior art).

FIG. 27 is a response characteristic diagram showing the result of a gas measurement experiment of NO _X , HC and CO of the nitrogen oxide sensor of Comparative Example 1 (conventional nitrogen oxide sensor).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 gas detection part, 1b gas detection part (back surface), 2 electrodes, 3 electrode lead wire, 4 heating heater, 5 heating heater lead wire, 6 gas detection part, 7 first electrode, 8
1st electrode lead wire, 9 2nd electrode, 10 2nd
Electrode lead wire, 11 heater heater lead wire, 12
Substrate, 13 Gas detection part, 14 electrodes, 15 electrode lead wire, 16 heating heater, 17 heating heater lead wire, 18 Gas detection part, 19 electrode, 20 electrode lead wire, 21 heating heater, 22 heating heater lead Wire, 23 catalyst layer, 24 nitrogen oxide sensor, 25 gas detection part resistance, 26 heating heater resistance, 27 fixed resistance, 28 gas detection part, 29 electrode, 30 heating heater, 31 honeycomb combustion catalyst, 32 heating heater, 3
3 Lead wire of heater, 34 Gas detector, 35
Electrode, 36-electrode lead wire.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Yoshida 2-14-40 Ofuna, Kamakura City Mitsubishi Electric Corporation Living Environment Research and Development Center (72) Inventor Katsuaki Yasui 840 Chiyoda-cho, Himeji Mitsubishi Electric Stock Association Inside the Himeji Works

Claims (18)

[Claims] 1. A formula _{(I): Bi 2 + x} (Sr 1-a Ca a) 2-xyb Ln y Cu 1 + b O z (I) ( wherein, Ln is a rare earth metal, x, y , Z, a and b satisfy the following relations: 0 ≦ x ≦ 0.
5, 0 ≦ x + y ≦ 1, 0 ≦ a ≦ 1, −0.1 ≦ b ≦ x /
2. A nitrogen oxide sensor provided with a gas detection section containing a complex oxide represented by z ≧ 6) as a main component and an electrode provided in the detection section. 2. Formula (II): Bi ₂ Sr _2-y Nd _y CuO _z (II) (where y and z satisfy the following relational expression: 0 <y <1, z ≧ 6). A nitrogen oxide sensor comprising a gas detecting section containing a composition represented by the above as a main component, and an electrode provided in the detecting section. 3. Formula (III): Bi ₂ Sr _{2-y + a} La _y Cu _1-b O _z (III) (where y, z and a satisfy the following relational expression: 0 < y ≦ 1.2, 0 ≦ a ≦ 0.2, 0 ≦ b ≦ 0.
2. A nitrogen oxide sensor provided with a gas detection part containing a composition represented by z ≧ 6) as a main component and an electrode provided in the detection part. 4. Formula (IV): Bi ₂ Sr _2-x M _{2 + x} Cu ₂ O _z (IV) (where x is 0 or the following relational expression: 0.15 ≦ x ≦
In the case of x = 0, M satisfies the following relational expression: M = Ln ′ _1-y X _y (where Ln ′ is Pr, N
d, Sm, Eu, Gd, Tb, Dy, Y, Ho, Er or Tm, X is Ce or Th, and y satisfies the following relational expression: 0.1 ≦ y ≦ 0.4. ), Or the following relational expression: M = Nd _1-y Y _y (where y is the following relational expression: 0 <y ≦ 0.24), or M is Gd Or Pr, z satisfies the following relational expression: z ≧ 10, and x satisfies the following relational expression: 0.15 ≦ x ≦ 0.3, M is the following relational expression: M = Ln _1-y L
a _y (where Ln is Dy, Gd, Eu, or Sm, y is the following relational expression: 0.15 ≦ y ≦ 0.2), and z is the following relational expression: :
A nitrogen oxide sensor having a gas detecting section mainly composed of a complex oxide represented by z ≧ 10 and an electrode provided in the detecting section. 5. The formula (I) included in the gas detector.
5. The complex oxide represented by the formula (IV), or the composition represented by the formula (II) or the formula (III) exhibits metallic electric conductivity at a temperature of use or higher. Nitrogen Oxide Sensor. 6. The formula (I) included in the gas detector.
6. The nitrogen according to claim 1, wherein the content of the complex oxide represented by the formula (IV) or the composition represented by the (II) or (III) is 25% or more by volume. Oxide detection sensor. 7. The formula (I) included in the gas detector.
7. The composite element represented by the formula (IV) or the Al element contained in addition to the metal element constituting the composition represented by the (II) or (III) is less than 1% by weight. 5. The nitrogen oxide sensor according to any one of 1. 8. The formula (I) included in the gas detector.
7. The Pb element contained in addition to the metal oxide constituting the composite oxide represented by formula (IV) or the composition represented by (II) or (III) is 5% by weight or less. 5. The nitrogen oxide sensor according to any one of 1. 9. The composite oxide represented by the formula (I) or (IV), or the formula (I
9. The nitrogen oxide sensor according to claim 1, wherein an insulator material that does not react with the composition represented by I) or the formula (III) is mixed. 10. The insulator material is MgO or SrT.
The nitrogen oxide sensor according to claim 1, which is iO ₃ . 11. The nitrogen oxide detection according to claim 1, wherein the gas detection portion is in the shape of a bulky thin plate, and the electrode is formed of a material having oxidation resistance and corrosion resistance. Sensor. 12. The nitrogen oxide sensor according to claim 1, wherein the gas detection portion is in the form of a film, and the electrode is formed of a material having oxidation resistance and corrosion resistance. 13. The nitrogen oxide sensor according to claim 1, wherein the electrode has two poles. 14. The electrode comprises a pair of electrodes for applying a voltage and passing a current, and another pair of electrodes positioned between the pair of electrodes for detecting a voltage. Item 13. A nitrogen oxide sensor according to any one of items 1 to 12. 15. The nitrogen oxide sensor according to claim 1, further comprising a heater for heating the gas detector. 16. The nitrogen oxide sensor according to claim 1, wherein a catalyst filter is provided near or on the surface of the gas detection unit. 17. The fine particles of platinum group metal are dispersed or carried inside or on the surface of the gas detector.
17. The nitrogen oxide sensor according to any one of 1 to 16. 18. The nitrogen oxide sensor according to claim 17, wherein the platinum group metal is Pt or Pd.