JP3195758B2 - Nitrogen oxide sensor - Google Patents

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 a nitrogen oxide concentration.

[0002]

2. Description of the Related Art A typical solid oxide type nitrogen oxide sensor which has been disclosed so far is disclosed, for example, in Japanese Patent Application Laid-Open No. 4-1.
There is one described in Japanese Patent No. 42455. This sensor is provided an electrode and the reference electrode using nitrate ion conductor in detection target atmosphere, to measure the electromotive force generated between the electrodes, shows a sensitivity to NO and NO ₂ I have. However, since the sensitivities to NO and NO ₂ are different, the NO _X concentration cannot be detected in the measurement atmosphere where both gases coexist, and neither NO nor NO ₂ concentration can be detected.

In order to improve the sensitivity to NO and NO ₂ , an electromotive force sensor in which an oxidation catalyst for NO is coated or mixed on a sub-electrode has been proposed (Japanese Patent Laid-Open No. 6-1237).
No. 26). According to this method, the detection of the NO _X concentration for possible NO in gas to NO and NO ₂ coexist in the oxidized to NO ₂ single gas becomes possible. However, its accuracy as in the conventional analytical method is determined by the oxidizing ability of the catalyst, resulting in a different value from the actual of the NO _X concentration. Further, these sensors have a problem in moisture resistance and heat resistance because nitrate is used for the sub-electrode, and practical use is almost difficult from the viewpoint of long-term stability.

On the other hand, a sensor utilizing the semiconductor properties of various oxides to measure the electrical conductivity change based the NO _X concentration is reported. For example, JP-A-6-160324 proposes a sensor using tin oxide as a gas sensitive body. However, even in this sensor, NO and NO ₂
Since sensitivity to different, it can not detect the NO _X concentration in the measurement atmosphere in which both the gas coexist.

Recently, a method for detecting the NO _X concentration NO _X gas electrochemically electrolyte from electrolytic current value at that time has been proposed (SAE TECHNICAL PAPER 960334 or JP-A 8-271476 JP). The detection principle of this sensor itself is an extension of an electrolytic current sensor which has been widely used for other gases. Specifically, two chambers were provided in the ion conductor, oxygen was sucked by an oxygen pump in the first chamber, the oxygen concentration in the measurement atmosphere was reduced to almost zero, NO ₂ was reduced to NO, and the second chamber was provided. A voltage is applied to the electrode to ionize oxygen generated by the reduction of NO in the measurement atmosphere, and its electrolytic current is detected to detect N.
A sensor for detecting the O _X concentration. NO _X concentration detected in the sensor depends largely on the performance of the oxygen pump. In addition, when the concentration of the gas to be detected is low, the interference of the residual oxygen concentration in the measurement atmosphere is large, and the signal current is very small. it has been difficult to detect the NO _X concentration.

The present inventors have proposed a NO _X sensor electromotive force type, JP-A 6-194605, JP-A No. 6-21
No. 6698 and Japanese Patent Application Laid-Open No. 6-216699. However, in these configurations, although the sensitivity to NO or NO ₂ gas is good, there has been a problem that the NO or NO ₂ gas interferes with each other or is interfered by the reducing gas. Furthermore, the present inventors have proposed a configuration that is not affected by reducing gas (Japanese Patent Application No. 8-85419). This sensor arrangement is to form an oxygen pump and NO _X sensing electrode for Kumikomu oxygen into the solid electrolyte body, at the same time NO gas when the oxidation of the reducing gas was achieved, suppressing interfering with NO ₂ gasified . However, with respect to the problem of mutual interference of NO or NO ₂ gas, this configuration does not always provide sufficient measures.

[0007]

Among the nitrogen oxide gases, the gas response characteristics particularly to the NO gas and the NO ₂ gas are different, so that mutual interference occurs in an atmosphere where both gases coexist. In addition, nitrogen oxide gas is easily affected by reducing gas such as hydrocarbon gas and CO gas.
These issues are resolved at the same time, large NO _X sensitivity output and its concentration dependency is detected, the structure of the nitrogen oxide sensor is required that can accurately detect NO _X concentration even under noisy for automobiles . Therefore, an object of the present invention is to provide a sensor that can meet these requirements.

[0008]

A nitrogen oxide sensor according to the present invention uses an ion conductive solid electrolyte body, has at least a pair of electrodes, and has an oxygen pump section for electrochemically pumping or discharging oxygen gas and a NO pump. _The detection electrode for detecting _X gas and the NO _X gas detection unit provided with its counter electrode are integrated, and one electrode of the oxygen pump unit and the detection electrode or the detection electrode and the counter electrode of the NO _X gas detection unit are set to the detection target atmosphere. disposed cans chamber communicating, in an environment heated to a predetermined temperature range in the heating mechanism equipped, a configuration for detecting the NO _X gas concentration by the potential difference between the sensing electrode and the counter electrode, whereby the oxygen pump the oxygen concentration of the NO _X gas detector is an oxygen concentration controlled to be 0.01% to 10% by parts. As a result, nitrogen oxide gas in the atmosphere to be detected, in particular, NO gas among NO gas and NO ₂ gas, is oxidized and converted into NO ₂ gas, NO ₂ or more nitrogen peroxide gas and a mixed gas thereof, and detected. NO _X between the pole and the counter electrode
The concentration of nitrogen oxide gas can be detected by detecting a potential difference based on the concentration. In addition, the oxygen concentration in the can chamber was set to 0.1.
By controlling the range of 01 to 10%, while suppressing interference with NO _X gas to oxidize the reducing gas such as hydrocarbon gas or CO gas, to detect the NOx concentration with high accuracy.

[0009] Incidentally, NO ₂ or more nitrogen peroxide gas (e.g., N ₂ O _5), the direction the direction of the sensor output in the method of the present invention is the same as the NO ₂ gas, i.e., the sensor output with increasing concentration increases Therefore, there is no obstacle.

[0010]

1 and 2 show an example of a nitrogen oxide sensor constituted by a single chamber according to the present invention. Hereinafter, the present invention will be described in detail using this configuration as an example. The plate-shaped solid electrolyte body 1 or 2 is made of various solid electrolyte bodies including stabilized zirconia and partially stabilized zirconia, and can be used as long as it is an oxygen ion conductive material regardless of the amount of the stabilizer and the amount added. . Oxygen pump section 3
Has a plate-shaped solid electrolyte body 1 and a pair of electrodes 3a, 3b disposed on both surfaces thereof, and applies a predetermined voltage to both electrodes 3a, 3b to operate as an oxygen pump. The electrodes 3a,
3b is not particularly limited as long as it is an electrode material that is subjected to electrochemical pumping, and a known material can be used. After a paste of the electrode material is formed by a known film forming method such as screen printing, a predetermined temperature is applied. It is obtained by firing.
It is more preferable that the electrode is finer by sputtering film formation or the like and has more active sites involved in the pump action.

The NO _x gas detecting section is composed of a solid electrolyte member 2, a detecting electrode 4 and a counter electrode 5. At least the detection electrode 4 is formed in a can chamber 18 in which the electrode 3a of the oxygen pump section 3 is formed. The counter electrode 5 may be arranged in the can chamber 18 similarly to the detection electrode 4. However, when the counter electrode 5 has a considerable activity with respect to the NO _X gas, it affects the signal based on the NO _X concentration detected by the detection electrode 4. Therefore, it is more preferable that the counter electrode 5 is provided in the air duct portion 19 communicating with the atmosphere serving as the reference atmosphere. Further, the detection electrode 4 and / or the counter electrode 5 may be formed on the solid electrolyte 1 constituting the oxygen pump section. The sensing electrode 4 is particularly limited as long as the electrode material or form having activity against NO _X gas is not, can be used known ones, forming a paste of the electrode material by a known film formation method such as screen printing After that, it is obtained by firing at a predetermined temperature. It is more preferable that the electrode to increase the active sites involved in and NO _X gases responds with fine by a sputtering deposition. Although NO _X gas detector or oxygen concentration of the can interior can be detected accurately NO _X gas concentration if from 0.01 to 10% oxygen concentration 0.1
% Or less in the slow response speed, the response speed with somewhat reduced of the NO _X sensitivity in reverse to the oxygen concentration of 5% or more,
It is more preferable that the oxygen concentration range of the sensor to be mounted on a site requiring a fast response speed is 0.1 to 5%.

In the case of an automobile, the concentration of oxygen present in the exhaust gas atmosphere is wide depending on the combustion state, that is, A / F. In order to sufficiently oxidize NO gas, hydrocarbon gas and CO gas in the oxygen pump section 3, the oxygen concentration of the whole within the can chamber 18 not oxygen or more equivalents of even oxygen fold it Kumikon NO _X gas detector only needs 0.01 to 10
% Is more preferably operated. The auxiliary oxygen pump portion 8 it is sufficient to be configured to any of the solid electrolyte body 2 at least a solid electrolyte body 1 or NO _X gas detecting electrode 4 is formed, at least the solid electrolyte body is formed into a plate-like 1 or It has one of the solid electrolyte members 2, an electrode 8a fixed to the one solid electrolyte member and arranged in the can chamber 18 and an electrode 8b arranged outside the can chamber, and a predetermined voltage is applied to both electrodes 8a and 8b. To operate as an auxiliary oxygen pump. That is, when the oxygen concentration in the chamber 18 is lower than the predetermined concentration range, the electrode 8 outside the chamber, which is configured to communicate with the atmosphere.
b. Oxygen pump to pump oxygen from b. Conversely, when the oxygen concentration in the can 18 is higher than a predetermined concentration range, the oxygen pump is operated so as to discharge oxygen from the electrode 8a in the can 18. The electrodes 8a, 8b
The electrode material is not particularly limited as long as it is an electrode material which is electrochemically pumped similarly to the electrodes 3a and 3b. The electrode material paste is formed by a film forming method such as screen printing and then fired at a predetermined temperature. Is obtained by It is more preferable that the electrode is finer by sputtering film formation or the like and has more active sites involved in the pump action.

[0013] NO _X gas detector or even NO _X gas detected by constituting the oxygen sensor portion for controlling the oxygen concentration in Kanshitsu 18 is highly accurate. At the site of a within the can chamber 18 proximate the NO _X gas detector, to form a solid electrolyte 1 or electrode 7 of oxygen concentration detection 2, NO
_The oxygen concentration is measured by the potential difference between the electrode 7 and the counter electrode 5 of the _X gas detection unit. Here, it is more preferable that the counter electrode 5 is provided in the air duct portion 19 communicating with the atmosphere serving as the reference atmosphere. By controlling the driving voltage of the oxygen pump unit 3 and / or the auxiliary oxygen pump unit 8 based on the oxygen concentration measured by the oxygen sensor unit,
Can control the oxygen concentration of the can chamber 18, it is possible to detect the NO _X gas concentration with high accuracy. The oxygen concentration detecting electrode 7 is obtained by forming a paste of an electrode material by a film forming method such as screen printing and then baking it at a predetermined temperature.

[0014] In the configuration of the present invention, action of the nitrogen oxide gas with the oxygen pump unit NO ₂ gas, and NO ₂ or more nitrogen peroxide gas and their mixed gas, and N
Since the O _x gas detector measures the potential difference generated through the solid electrolyte, the operating temperature is important to ensure that these operations are performed, and the oxygen pump and the NO _x gas detector are heated. 400-750 ° C depending on mechanism
It is necessary to control the temperature range. That is, 400 ° C
At lower temperatures below, the ionic conductivity of the solid electrolyte body itself is poor, making it difficult to detect a stable output. on the other hand,
At a high temperature of 750 ° C. or higher, it is difficult to oxidize NO gas, and the measurement intended by the present application cannot be performed. At least NO _X gas detector for this has to be maintained at a temperature within the above range, more preferably in the temperature range of 500 to 700 ° C.. The heating mechanism, bonding the partition wall member 15 and 14 with the solid electrolyte body 2 or the air duct 19 to the plate-shaped heater 6 embedded with good stability platinum heater oxygen pumping unit or NO _X gas detector configured For example, a means such as use of Of course, the heater 6, the oxygen pumping portion may be a NO _X gas detector arranged on both surfaces so that can be individually temperature controlled, and the temperature control is feedback control by the electric resistance value of the heater itself,
Alternatively, a method of separately performing feedback control using a temperature sensor such as a thermocouple is appropriately employed.

The gas in the measurement atmosphere is introduced from the gas introduction hole 10 into the can chamber 18. The oxygen concentration in the can chamber 18, or more precisely, the oxygen concentration in the NO _X gas detecting section is set to be 0.
It is necessary to control the voltage applied to the oxygen pump unit 3 so that at least NO gas is oxidized to NO ₂ gas in the nitrogen oxide gas at 01 to 10%. Considering the long-term stability of the electrodes 3a and 3b constituting the oxygen pump section 3 and the solid electrolyte body on which both electrodes are formed, the applied voltage is 1.5.
Desirably is V or less, the oxygen concentration of 0.01 of the gas inlet 10 is converted and NO _X gas detector of the nitrogen oxide gas
It is necessary to have a gas diffusion resistance that enables control of 10% to 10%. When the auxiliary oxygen pump unit 8 for adjusting the oxygen concentration in the can chamber 18 to 0.01 to 10% is configured, the voltage applied to the auxiliary oxygen pump unit 8 is 1.5 V or less and the oxygen The gas introduction hole 10 has gas diffusion resistance so as to be controllable.

[0016] forming an oxidation catalyst 11 of the NOx gas in the can chamber 18, the effect to prevent the NO _X gas is converted in an oxygen pump unit 3 is NO gas was reduced again It is a target. Further, it is more preferable that the oxidation catalyst body 11 is filled in the can chamber 18.

[0017] In case of at least facing the sensing electrode 4 to form the electrodes 3a and NO _X gas detector of the oxygen pump portion, the porous body during at least a sensing electrode 4 and the electrode 3a 1
By disposing 2 and narrowing the distance between these electrodes, the NO _x gas gas-converted by the oxygen pump section 3 can be immediately detected by the NO _x gas detection electrode. This porous body 12
Is more effective by sharing the oxidation catalyst 11. Further, the porous body 12 can be extracted signal output of the NO _X gas detector without being affected by the voltage driving the oxygen pump unit 3 as long as the material has an electrically highly insulating. However, even when the porous body 12 has an electron conductivity, the circuit constituting the circuit and NO _X gas detecting portion constituting the oxygen pump unit can be used without problems if separate circuit entirely.

FIGS. 3 and 4 show an example of a nitrogen oxide sensor composed of two chambers according to the present invention. Less than,
This configuration will be described in detail as an example, but the basic configuration such as a constituent material and a method for forming the same is similar to that described in detail in FIG. The solid electrolyte body 1 constituting the oxygen pump section 3 is formed in a plate shape and has a pair of electrodes 3a, 3b on both surfaces thereof.
A predetermined voltage is applied to b to operate as an oxygen pump. The electrode 3a constituting the oxygen pump unit 3 is formed in a first can chamber 18 formed by the partition 16 and is provided with nitrogen oxide gas, particularly NO gas and NO ₂ gas, in the atmosphere to be detected.
Among the gases, NO gas is oxidized and converted into NO ₂ gas, NO ₂ or more NO gas and mixed gas thereof, and reducing interfering gas coexisting with NO _X gas such as hydrocarbon gas and CO gas. It is operated in a direction in which oxygen gas having an oxygen equivalent or more necessary for oxidizing the oxygen is pumped into the first can chamber 18.

The NO _x gas detecting section comprises a solid electrolyte member 2, a detecting electrode 4 and a counter electrode 5. At least the detection electrode 4 is formed in a second can chamber 23 formed by the partition 16. Although the counter electrode 5 may be disposed in the second can chamber 23 similarly to the detection electrode 4, it is more preferable to provide the counter electrode 5 in the air duct 19 communicating with the atmosphere serving as the reference atmosphere. Further, the detection electrode 4 and / or the counter electrode 5 may be formed in the solid electrolyte 1 constituting the oxygen pump section 3.

[0020] Although NO _X gas detector or oxygen concentration of the can interior can be detected accurately NO _X gas concentration if 0.01% to 10%, more preferably an oxygen concentration range of 0.1% to 5% This is as described above. Therefore, the auxiliary oxygen pump unit 8 for controlling the oxygen concentration in the second can chamber 23
It is more preferable to operate. The auxiliary oxygen pump portion 8 it is sufficient to be configured in any of at least the solid electrolyte body 1 or NO _X gas sensing electrode 4 solid electrolyte 2 which is formed, at least one of the solid electrolyte body is formed into a plate-like 1 Alternatively, it has an electrode 8a disposed inside the can chamber and an electrode 8b disposed outside the can chamber, and applies a predetermined voltage to both electrodes 8a and 8b to operate as an oxygen pump. That is, when the oxygen concentration in the second chamber 23 is lower than the predetermined concentration range, the oxygen pump is performed so as to pump oxygen from the outside electrode 8b of the chamber that is configured to communicate with the atmosphere. Conversely, when the oxygen concentration in the second can chamber 23 is higher than a predetermined concentration range, the electrode 8a in the second can chamber 23
Operate the oxygen pump to expel oxygen from the The oxygen concentration in the second can 23 is measured by the oxygen sensor unit. At a site adjacent to the NO _X gas detector a within the second cans chamber 23, the solid electrolyte 1 or 2 to form an electrode 7 of oxygen concentration detection, share a counter electrode 5 of the NO _X gas detector The oxygen concentration is measured based on the potential difference generated between the electrode 7 and the electrode 7. Here, it is more preferable that the counter electrode 5 is provided in the air duct portion 19 communicating with the atmosphere serving as the reference atmosphere. By controlling the drive voltage of the auxiliary oxygen pump unit based on the oxygen concentration measured by the oxygen sensor unit, the second can chamber 2 is controlled.
Can control the oxygen concentration in the 3, it is possible to detect the NO _X concentration with high accuracy.

The oxygen sensor section 3 formed in the first chamber 18 oxidizes the nitrogen oxide gas to at least NO ₂ and oxidizes the reducing gas coexisting in the measurement atmosphere gas to NO _x. Interference with gas can be eliminated. Further, the first can chamber 18 and the second can chamber 23
By forming or filling an oxidation catalyst within, it can be converted NO _X gas reaches the NO _X gas detector without being reduced again, to detect the NO _X concentration with high accuracy. The heating mechanism in the configuration of the present invention conforms to that described in detail in FIG.

The gas in the measurement atmosphere is introduced into the first can chamber 18 from the gas introduction hole 10 and is introduced into the second can chamber 23 through the communication hole 21 from the first can chamber to the second can chamber. You. The voltage applied to the oxygen pump unit 3 is controlled so that the nitrogen oxide gas is oxidized to at least NO ₂ or more. Considering the long-term stability of the electrodes 3a and 3b forming the oxygen pump section 3, the applied voltage is desirably 1.5 V or less. Therefore, at least one of the gas introduction hole 10 and the communication hole 21 has gas diffusion resistance. When the auxiliary oxygen pump unit 8 for adjusting the oxygen concentration in the second chamber 23 to 0.01 to 10% or more is formed, the communication hole 21 from the first chamber to the second chamber is connected to the electrode 8a and the second chamber. The gas diffusion resistance is such that the oxygen concentration can be controlled when the voltage applied to 8b is 1.5 V or less.

[0023] In any of the configurations described in FIGS. 1-4, by using the output signal of the oxygen sensor portion disposed in the can chamber, by correcting the output signal of the NO _X gas detector electromotive force of the NO _X gas By detecting as a value, the influence of the coexisting oxygen concentration can be suppressed, and the detection accuracy of the nitrogen oxide gas is increased. The NO _X sensing electrode 4 is oxygen and N
When complicated by electrochemical reaction of O _X results in a mixed potential comprising, by forming the counter electrode 5 and the NO _X sensing electrode 4 in the same cans chamber, the effect of oxygen concentration coexisting It is hard to receive, and the detection accuracy of the nitrogen oxide gas is increased, and it is not necessary to separately form an air duct for the counter electrode.

The electrochemically using an oxygen pump for discharging or Komu draw oxygen, oxygen concentration of the NO _X gas detector is controlled in the range of 0.01% to 10%, mutual oxidized nitrogen oxide gas NO gas A highly sensitive and stable nitrogen oxide sensor is provided by eliminating interference and coexisting reducing gas interference. Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples.

[0025]

EXAMPLES (Example 1) Figure 1 of the oxygen pumping portion 3 of the structure, the auxiliary oxygen pumping portion 8, NO _X gas detector 4, the following materials nitrogen oxide sensor consists of an oxygen sensor unit 7 Produced by the procedure. The oxygen pump section 3 uses a 6 mol% yttria-stabilized zirconia green sheet molded and processed into t0.2 × w6 × 180 mm, and forms an electrode by applying a Pt paste by screen printing in the can chamber and the air duct. did. The NO _X gas detector 4 is made of the same material as the oxygen pump,
Using a green sheet having dimensions, a composite oxide paste of NiCr ₂ O ₄ was applied in a can chamber by screen printing to form a green sheet. The counter electrode is P in the air duct by screen printing.
It was formed by applying a t paste. Note that the NiCr ₂ O ₄ composite oxide paste is made of NiCr 2
_The powder was obtained by pulverizing and drying ₂ O ₄ powder with a ball mill and then mixing ethyl cellulose and a diluent. The auxiliary oxygen pump section 8 was also provided on the green sheet constituting the oxygen pump section, downstream of the oxygen pump section. An electrode was formed by applying a Pt paste by screen printing in both the can chamber and the air duct. Oxygen sensor unit 7, was constructed on the green sheets constituting the NO _X gas detector. The electrode for detecting the oxygen concentration in the can chamber was formed by applying a Pt paste by screen printing. Its counter electrode is shared with the counter electrode of the NO _X gas detector. The heater 6 was formed by screen printing a high-purity Pt paste different from that for the electrodes. A high-purity alumina print layer was formed on a green sheet of the same material and dimensions as the oxygen pump section, a heater pattern was printed thereon, and a high-purity alumina print layer was further laminated.
The size of the gas introduction hole was t0.1 × w0.5 × 11 mm. The thickness of the green sheet of the partition wall constituting the can chamber is 4
It was set to 0 μm.

The green sheet on which the electrodes and heaters are formed as described above is laminated, and at 1400 ° C.
By firing for 5 hours, the oxygen pumping portion, NO _X gas detector, to produce a nitrogen oxide sensor heater integrated.
The produced sensor was kept at 600 ° C. with an embedded heater, placed in a simulated gas having a known composition, and its output was examined. The auxiliary oxygen pump was controlled so that the oxygen concentration in the canister was 4%. The oxygen pump applied a voltage so as to pump oxygen into the can chamber. Table 1 shows the results. NO ₂ regardless of C ₃ H ₆ , CO and oxygen concentrations
An output proportional to the logarithm of the + NO gas concentration was obtained.

[0027]

[Table 1]

The oxygen pumping portion of the configuration of (Embodiment 2) FIG. 3, the auxiliary oxygen pumping portion, NO _X gas detector, to produce a nitrogen oxide sensor consists of an oxygen sensor unit. The materials, materials, dimensions and firing conditions constituting each part are the same as in Example 1.
Is the same as Oxygen pump portion to the first cans chamber, NO _X gas detector, auxiliary oxygen pump section constituted the oxygen sensor portion to the second cans chamber. The counter electrode was formed in the air duct, and the counter electrode of the oxygen sensor was also used. The produced sensor was kept at 600 ° C. with an embedded heater, placed in a simulated gas having a known composition, and its output was examined. The auxiliary oxygen pump was controlled so that the oxygen concentration in the canister was 4%. The oxygen pump applied a voltage so as to pump oxygen into the can chamber.
Table 2 shows the results. An output proportional to the logarithm of the NO ₂ + NO gas concentration was obtained without being affected by the concentrations of C ₃ H ₆ , CO and oxygen.

[0029]

[Table 2]

[0030] (Example 3) oxygen pumping portion of the arrangement of FIG. 3, the auxiliary oxygen pumping portion, NO _X gas detector, to produce a nitrogen oxide sensor consists of an oxygen sensor unit, the oxygen of the second cans chamber concentration were investigated on their response speed and NO _X sensitivity. The oxygen concentration in the can was measured by an oxygen sensor and controlled by an auxiliary oxygen pump. The materials, materials, dimensions, and firing conditions constituting each part are the same as in the second embodiment. The fabricated sensor was 600
℃ to hold, placed in NO _X gas 50ppmNO + 50ppmNO _2, were examined their output. The result is shown in FIG. An oxygen concentration of 0.01% or less, NO _X sensitivity response speed of greater markedly increased. Further, an oxygen concentration of 10% or more, NO _X sensitivity is somewhat smaller, the response speed was significantly increased.

The oxygen pumping portion of the structure (Example 4) FIG. 1, the auxiliary oxygen pumping portion, NO _X gas detector, the oxygen sensor unit, to produce a nitrogen oxide sensor consists of a porous material. Can chamber partition green sheet constituting the can chamber is 40 μm
Thick Satoshi oxygen pumping electrode and the NO _X sensing electrode cans chamber was in contact through a porous alumina film. Were also prepared even sensor oxygen pump electrode and the NO _X sensing electrode cans chamber was in contact via a porous membrane carrying palladium alumina. Oxygen pump, auxiliary oxygen pump, N
O _X gas detector, and the material constituting the oxygen sensor portion,
The material, dimensions and firing conditions are the same as in the first embodiment. The counter electrode was formed in the air duct, and the counter electrode of the oxygen sensor was also used. The fabricated sensor was 600
° C, 50 to 400 ppm NO + 50 ppm NO ₂ N
O _X gas placed in, we examined its output. The auxiliary oxygen pump was controlled so that the oxygen concentration in the canister was 4%. FIG. 6 shows the result. For comparison, the results measured using the sensor shown in Example 2 are also shown. Compared to sensors without the porous body of Example 2, the oxygen pumping electrode and the NO _X sensing electrode when placed so as to be in contact through a porous alumina film, NO _X concentration dependency of the sensor output is increased . In that case the porous film is a porous membrane carrying palladium alumina, NO _X concentration dependency of the sensor output becomes larger further.

With the nitrogen oxide sensor of the present invention, nitrogen oxide gas, particularly NO gas and NO
_{By 2} to oxidize NO gas among the gas, to convert NO ₂ gas, NO ₂ or more in nitrogen peroxide gas and their mixed gas, detects a potential difference which is based the NO _X concentration between the sensing electrode and the counter electrode The nitrogen oxide gas concentration can be detected.
In addition, the concentration of nitrogen oxide can be detected without interference from a reducing gas such as a hydrocarbon gas represented by C ₃ H ₆ or a CO gas.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a nitrogen oxide sensor composed of a single chamber according to the present invention.

FIG. 2 is an exploded perspective view of a nitrogen oxide sensor composed of one can chamber according to the present invention.

FIG. 3 is a schematic sectional view of a nitrogen oxide sensor composed of two cans according to the present invention.

FIG. 4 is an exploded perspective view of a nitrogen oxide sensor composed of two cans according to the present invention.

FIG. 5 is a diagram showing the oxygen concentration dependence of sensor output and response speed of a nitrogen oxide sensor composed of two cans according to the present invention.

Figure 6 shows the effect of the porous body in relation of the NO _X concentration and the sensor output of the nitrogen oxide sensor constructed from one canister chamber according to the invention.

[Explanation of symbols]

1,2 solid electrolyte body 3a, the electrode 8a constituting the 3b oxygen pump unit, 8b electrode 4 constituting the auxiliary oxygen pump unit NO _X gas sensing electrode 5 counter electrode 6 heater 7 oxygen concentration detecting electrode 10 gas introducing hole 21 first Communication hole from the can chamber to the second can chamber 11 Oxidation catalyst body 12 Porous body 14 Atmospheric duct forming body 15 Atmospheric duct partition body 19 Atmospheric duct 16 Can chamber partition body 17 Heater forming body 18 First can chamber 23 Second can Room

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takashi Ono 4-14-1, Suehiro, Kumagaya-shi, Saitama Pref. RIKEN Kumagaya Plant (72) Inventor Akira Kunimoto 4-1-1, Suehiro, Kumagaya-shi, Saitama (56) References JP-A-4-142455 (JP, A) JP-A-6-123726 (JP, A) JP-A-6-160324 (JP, A) JP-A 8-271476 (JP, A) JP-A-8-43346 (JP, A) JP-A-8-62178 (JP, A) JP-A-8-62174 (JP, A) JP-A-9-274011 (JP, A) JP-A-11-23523 (JP, A) JP-A-11-14592 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27/416 G01N 27/409 G01N 27/419

Claims (15)

(57) [Claims] [Claim 1 further comprising at least a pair of electrodes provided on the solid electrolyte body, and electrochemically pumped inclusive or spit oxygen pump unit oxygen gas, NO _X formed in the solid electrolyte body
A NO _X gas detector having a sensing electrode and its counter electrode to detect the gas, are integrated with the oxygen pump and the NO _X gas detector, of one of the oxygen pumping portion electrode and the NO _X gas detector sensing electrode or sensing electrode and a counter electrode is arranged in the can interior in communication with the detection target atmosphere, further comprising a heating mechanism for holding the oxygen pumping portion and NO _X gas detector to a predetermined temperature range, in the detection target atmosphere Nitrogen oxide gas, in particular, NO gas out of NO gas and NO ₂ gas, is oxidized and converted into NO ₂ gas, NO ₂ or more nitrogen peroxide gas and mixed gas thereof, and hydrocarbon-based gas and CO gas oxidizing the reducing interfering gases coexisting with NO _X gas detoxification, such a sensor arrangement for detecting the NO _X gas concentration by a potential difference between the sensing electrode and the counter electrode, NO _X gas analyzer Oxygen concentration of parts is 0.01% to 10%
A nitrogen oxide sensor characterized in that the oxygen concentration is controlled by an oxygen pump section so that Wherein provided at least a pair of electrodes on the solid electrolyte body, and the oxygen pumping portion Komu draw oxygen gas electrochemically, NO is provided a sensing electrode and its counter electrode to detect the NO _X gas to the solid electrolyte body _X integrated gas detector, sensing electrode or sensing electrode and the counter electrode of one electrode the NO _X gas detector of the oxygen pumping portion is disposed in the can chamber which communicates with the detection target atmosphere, the oxygen pumping portion and NO the _X gas detector comprises a heating mechanism for holding the predetermined temperature range, and oxidizing the NO gas among the nitrogen oxide gas in the detection target atmosphere at an oxygen pump unit, in particular NO gas and NO ₂ gas, NO ₂ gas , converts NO ₂ or more in nitrogen peroxide gas and their mixed gas, is oxidized to harmless reducing interfering gases coexisting with NO _X gas such as hydrocarbon gas and CO gas Narrowing pumped oxygen or more equivalents of oxygen required in order, a sensor arrangement for detecting the NO _X gas concentration by a potential difference between the sensing electrode and the counter electrode, 0.01 oxygen concentration of the NO _X gas detector and the oxygen sensor portion for detecting the oxygen concentration of the auxiliary oxygen pumping portion and the NO _X gas detector for controlling at 10% of the range is located,
A nitrogen oxide sensor, wherein a driving voltage of an auxiliary oxygen pump unit is controlled based on an oxygen concentration measured by the oxygen sensor unit. 3. Oxidizing nitrogen oxide gas, particularly NO gas, of NO gas and NO ₂ gas in the atmosphere to be detected,
After being converted to NO ₂ gas, NO ₂ or more nitrogen peroxide gas and a mixed gas thereof, an oxidation catalyst for preventing the gas from being reduced again before reaching the NO _X gas detecting section. nitrogen oxide sensor according to claim 1 or 2, characterized in that the medium is formed between the oxygen pump portion and the NO _X gas detector. Identical to wherein the oxygen pump unit or the oxygen pumping portion and each one of the electrodes and the NO _X gas detector of the sensing electrode or sensing electrode and a counter electrode of the oxygen pump unit consisting of the auxiliary oxygen pumping portion, communicates with the detection target Atmosphere And the gas introduction hole is provided with NO _X
2. A gas diffusion resistance in which a voltage applied to an oxygen pump unit and an auxiliary oxygen pump unit for controlling the oxygen concentration of the gas detection unit at 0.01 to 10% is 1.5 V or less. 4. The nitrogen oxide sensor according to any one of claims 1 to 3. 5. At least the sensing electrode of one of the electrodes of the oxygen pump portion and the NO _X gas detector is, nitrogen oxides according to claim 4 in which each electrode surface in the can chamber, characterized in that disposed opposite Object sensor. Nitrogen oxide sensor according to claim 5, the porous body is characterized in that it is filled between the 6. One electrode of the oxygen pump portion and the NO _X gas detector at least sensing electrode. Claim 6 7. oxygen pumping portion one electrode NO _X gas detector at least the sensing electrode and the porous body filled between the of, and having an electrically high insulation 2. The nitrogen oxide sensor according to 1. 8. Place the one electrode of the oxygen pump portion at a site adjacent to the gas introduction hole, characterized in that arranged at least the sensing electrode of the NO _X gas detector downstream of the oxygen pump electrodes claims Item 6. The nitrogen oxide sensor according to Item 4. 9. A first can chamber defined by the solid electrolyte body and communicating with the atmosphere to be detected, and a second can chamber communicating further downstream thereof, wherein one electrode of the oxygen pump section is the first can. It is arranged in the room, and NO _X gas detector of the sensing electrode or sensing electrode and a counter electrode to the second canister chamber, an auxiliary oxygen pump unit for controlling the oxygen concentration of the second canister chamber, detects the oxygen concentration 4. The nitrogen oxide sensor according to claim 2, wherein an oxygen sensor unit for performing the operation is provided, and at least a driving voltage of the auxiliary oxygen pump unit is controlled based on the oxygen concentration measured by the oxygen sensor. 10. A nitrogen oxide gas in a detection target atmosphere introduced into a first can chamber, in particular, NO gas among NO gas and NO ₂ gas is oxidized, and NO ₂ gas and nitrogen peroxide gas of NO ₂ or more are oxidized. and thereby converted to their mixed gas, when detoxifying oxidizing the reducing interfering gases coexisting with NO _X gas such as hydrocarbon gas and CO gas,
The gas introduction hole has a gas diffusion resistance such that the voltage applied to an oxygen pump section disposed in the first chamber is 1.5 V or less and the amount of oxygen is equal to or more than the oxygen equivalent required for the oxidation reaction. 10. The nitrogen oxide sensor according to 9. 11. A nitrogen oxide gas in a detection target atmosphere introduced into a first can chamber, particularly, NO gas among NO gas and NO ₂ gas is oxidized, and NO ₂ gas, NO ₂ or more nitrogen peroxide gas is used. and thereby converted to their mixed gas, when detoxifying oxidizing the reducing interfering gases coexisting with NO _X gas such as hydrocarbon gas and CO gas,
The communication hole from the first can chamber to the second can chamber is a gas diffusion chamber where the voltage applied to the oxygen pump section disposed in the first can chamber is 1.5 V or less and the amount of oxygen is equal to or more than the oxygen equivalent required for the oxidation reaction. The nitrogen oxide sensor according to claim 9, having a resistance. 12. When the oxygen concentration in the second can chamber is controlled to 0.01 to 10% by the auxiliary oxygen pump section, a communication hole from the first can chamber to the second can chamber is applied to the auxiliary oxygen pump section. The nitrogen oxide sensor according to any one of claims 9 to 11, wherein the nitrogen oxide sensor has a gas diffusion resistance that can be controlled at a voltage of 1.5 V or less. 13. An output signal from an oxygen sensor section disposed in a can chamber is used for correcting an output signal from a NO _X gas detection section and detecting the output signal as an electromotive force value of NO _X gas. The nitrogen oxide sensor according to claim 1. 14. Of the oxygen pumping electrodes or the NO _X sensing electrode, at least NO _X sensing electrode, excellent heat resistance,
14. The nitrogen oxide sensor according to claim 1, wherein a porous protective film having an oxidation catalytic ability is formed. 15. produce mixed potential formed by complicated electrochemical reactions of the NO _X sensing electrode the oxygen and NO _X, the NO _X
Nitrogen oxide sensor according to any of claims 1 to 14, characterized in that to measure the potential difference based the NO _X gas concentration between the detection electrode and the counter electrode.