JPH09264872A - Gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure to-be-detected gas concentration with high accuracy by forming an electrode an both surfaces of a pair of solid electrolytes to form both sensor elements, forming a cavity, which leads to outside, between both elements with a supporting body, and finding difference of electromotive farce between the electrodes of each element. SOLUTION: Electrodes 1, 2 and 5, 6 are formed on both surfaces of each zirconia solid electrolyte 3 and 7, to constitute two sets of oxygen sensor elements 4 and 8. A supporting structure body 9 of zirconia is put between the elements 4 and 8, and an atmosphere introducing path 10 which introduces a reference gas is farmed at the central part. The reference gas is brought into contact with electrodes 2 and 5 of the introducing path 10 in the structure body 9, and a to-be-detected gas is brought into contact with the electrodes 1 and 6 on the outside of the sensors. When the element 4 is an element which does not sense the to-be-detected gas, and the element 8 is an element which senses the to-be-detected gas and the gas which the element 4 senses, the concentration of the to-be-detected gas is accurately measured while not affected by concentration of other gas, especially oxygen gas, based on difference of the electromotive farce of the elements 4 and 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is an exhaust gas component of an internal combustion engine, environment control, medical, agricultural, CO in the fermentation industry, etc., NO _x, detection or concentration measurement such extensive use of hydrocarbons such as various gases The present invention relates to a possible gas sensor, and more particularly to a gas sensor capable of measuring a desired gas concentration extremely accurately regardless of the concentrations of other gases.

[0002]

2. Description of the Related Art CO and N which are exhaust gas components of an internal combustion engine
O _x, and various hydrocarbons, etc., from the social situation of the global environment protection, devices for detecting the degradation limit of the apparatus and the catalyst to perform optimum combustion control of the internal combustion engine to detect the emissions have been studied . These devices have a gas sensor for detecting or measuring the concentration of the gas component as an essential component,
Various studies have been made.

There are mainly two types of gas sensors that have been conventionally used: a semiconductor type sensor and a concentration cell type sensor. The semiconductor-type sensor utilizes a change in the resistance value of the semiconductor that occurs in proportion to the detected gas concentration. As the semiconductor-type sensor, the perovskite-type sensor containing La disclosed in JP-A-6-222028 is used. A sensor having a semiconductor made of an oxide, a sensor having a semiconductor containing lanthanum oxide and antimony oxide as main components disclosed in JP-A-6-229964, and JP-A-6-22996.
Formula disclosed in 5 JP A _{1 over x} A _'y BO ₄ to A
_{2-y A 'y BO 4} (A and A' is an alkaline earth metal or rare earth metal, B is a transition element) General disclosure sensor having a semiconductor comprising a compound represented by, in JP-A-5-332967 A sensor having a semiconductor made of a compound represented by the formula ABO ₂₊ δ (A is a group IIa element, B is a divalent element), and a general formula A _1-x A disclosed in JP-A-5-332968. There is a sensor having a semiconductor made of a compound represented by _x MO ₂ ± δ.

In the concentration cell type sensor, by coating a solid electrolyte such as zirconia with a material having catalytic activity for a detection gas, an electromotive force corresponding to the gas concentration is generated in the solid electrolyte, and the gas concentration is generated from the electromotive force. And a sensor using the lithium ion conductive solid electrolyte disclosed in JP-A-6-265520 and JP-A-1-27.
There is one using the zirconia solid electrolyte disclosed in Japanese Patent No. 7751.

[0005]

However, in any of the above-mentioned sensors, the specificity to the target gas,
That is, it was difficult to measure the exact concentration of the desired gas without being affected by other gases. As a solution to this, a pair of first and second electrodes are provided on a cylindrical zirconia solid electrolyte having a closed end and a closed end, as disclosed in Japanese Patent Laid-Open No. 7-306178. By burning a material that has a catalytic effect on the exhaust gas component, the oxygen concentration changes as the exhaust gas component burns or decomposes, and the gas component in the test gas is detected by the electromotive force due to the oxygen concentration difference. There is something to do.

However, in the gas sensor disclosed in Japanese Unexamined Patent Publication No. 7-306178, the oxygen concentration in the exhaust gas fluctuates and the electromotive force generated is also greatly affected. Therefore, the accuracy with respect to the desired gas varies with the oxygen concentration. There was a drawback that it got worse with it. In order to improve this drawback, the first and second electrodes 10 as shown in FIG.
2 and 103 are both disposed on the same surface of the same solid electrolyte 101, the third electrode 104 is disposed on the surface facing the same, and the catalyst layer 105 is formed on the first electrode 102.
The gas concentration is measured using the difference between the electromotive force between the second electrode 103 and the third electrode 104 and the electromotive force between the second electrode 103 and the third electrode 104. In addition, conduction leakage of oxygen ions is generated between the second electrodes, and the measurement accuracy deteriorates.

In view of the above-mentioned circumstances, therefore, the present invention provides an oxygen ion conductive solid electrolyte for oxygen concentration change caused by oxidative combustion or decomposition reduction of exhaust gas components, particularly gas components such as CO, NO _x and hydrocarbons. In the gas sensor that measures by using, it is basically necessary to manufacture and provide a gas sensor that enables highly accurate measurement of a desired gas without being affected by external factors such as fluctuations in oxygen concentration in exhaust gas. Purpose.

[0008]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors in accordance with the above object, the first oxygen-ion conductive solid electrolyte and the first solid electrolyte formed on one surface of the first solid electrolyte are obtained. A first sensor element comprising an electrode and a second electrode formed on one surface facing the first electrode; a second oxygen ion conductive solid electrolyte; and formed on one surface of the second solid electrolyte A second sensor element including a third electrode and a fourth electrode formed on one surface facing the third electrode, and between the first sensor element and the second sensor element. A support structure having a gap facing the first electrode and the third electrode, which is sandwiched and communicates with the outside; and a support structure between the first electrode and the second electrode. Due to the difference between the electric power and the electromotive force between the third electrode and the fourth electrode, the concentration of the detection gas is increased. We developed a gas sensor and measuring the, and completed the present invention.

It is preferable that the support structure has a heating means including an insulating portion having oxygen ion non-conductivity.
The heating means includes a surface of the support structure that contacts the first sensor element, a surface of the support structure that contacts the second sensor element, and
Are preferably formed. Furthermore, it is preferable that a catalyst layer made of a substance having a catalytic activity with respect to the detection gas is formed on at least one of the second electrode and the fourth electrode.

According to the present invention, by combining various combinations of the solid electrolyte, the electrode, the catalyst layer, the heating means, etc., extremely precise and specific measurement can be performed for a desired gas. In addition, since the leakage of oxygen ions from each sensor element can be blocked, there is no deterioration in measurement accuracy, and since a heating means that can heat each sensor element uniformly and in a short time can be attached, measurement due to the influence of temperature can be performed. It is possible to prevent deterioration of accuracy

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, a first oxygen ion conductive solid electrolyte, a first electrode formed on one surface of the first solid electrolyte, and one surface opposite to the first electrode are formed. A first sensor element including the formed second electrode, and a second sensor element
Sensor element comprising an oxygen ion conductive solid electrolyte, a third electrode formed on one surface of the second solid electrolyte, and a fourth electrode formed on one surface facing the third electrode And a support structure that is sandwiched between the first sensor element and the second sensor element and that has a void facing the first electrode and the third electrode that communicate with the outside. And measuring the concentration of the detection gas by the difference between the electromotive force between the first electrode and the second electrode and the electromotive force between the third electrode and the fourth electrode. There is a gas sensor characterized in that

As the first or second solid electrolyte,
There is no particular limitation as long as it is a sintered body that conducts oxygen ions.
Various materials such as rO ₂ and LaGaO ₃ can be used,
The composition of the first and second solid electrolytes can be changed depending on the detection gas. When used as a sensor for automobile exhaust gas, a material that can withstand use at high temperatures, such as the zirconia solid electrolyte described in JP-A-54-4913, can be used. When a zirconia solid electrolyte is used, the method for producing the zirconia solid electrolyte is, for example, zirconia (ZrO ₂ ) and yttria (Y ₂ O ₃ ).
Can be produced by adding a predetermined amount of the above, pulverizing, calcination, and then molding this into a desired shape and calcining. The shape of the solid electrolyte is not particularly limited, but it is preferable that the solid electrolyte has a flat plate shape in consideration of the accuracy of gas concentration measurement.

The support structure may take various forms as long as it has a structure that forms a void communicating with the outside between the first electrode of the first solid electrolyte and the third electrode of the second solid electrolyte. In addition, various materials can be used as long as they can withstand the desired temperature. Further, the support structure may be made of the same material or may be an assembly made of various constituents, and several kinds of materials may be mixed. Further, the support structure preferably has an insulating portion that blocks oxygen conductivity between the first solid electrolyte and the second solid electrolyte,
As the insulating portion, various types can be used as long as they block oxygen conductivity. Furthermore, it is preferable to have a heating means inside, and a ceramic heater or the like may be integrated in the support structure. In this case, in order to electrically insulate the heater from the support structure, it is preferable that the insulating portion be electrically non-conductive or that an electrically non-conductive insulating portion be separately provided. The heating means may be arranged symmetrically with respect to the first sensor element and the second sensor element in the support structure so as to uniformly heat the first sensor element and the second sensor element. preferable. Particularly preferably the first
One is formed at a position in contact with the second sensor element and the other is formed at a position in contact with the second sensor element.

The material of the first to fourth electrodes is preferably platinum, gold, silver, copper, or an alloy containing them, which is a good electrical conductor. The electrode, using the above metal or a compound thereof or a paste in which an organic binder or the like is mixed, electroplating, electroless plating, hot dipping, thermal spraying, vapor deposition, ion plating, mechanical plating, Alternatively, it is preferably produced by forming a metal film on a predetermined surface of the solid electrolyte by a known method such as a printing method. In particular, it is preferable to use gold, platinum, or a paste containing them from the viewpoint of corrosion resistance. Further, these solid electrolyte and each electrode may be integrally fired. Also, using a metal mesh, or adding a flammable substance such as organic beads to a paste containing a metal,
The electrode may be made porous by burning it off after coating.

On one or both of the second electrode and the fourth electrode exposed to the outside, a catalyst layer made of a substance having catalytic activity to the detection gas is formed in accordance with the gas to be detected. You can The catalyst layer can be prepared, for example, by applying a paste containing a substance having a catalytic activity to the detection gas and then firing the paste integrally.

In order to measure a desired gas concentration using the gas sensor according to the present invention, the reference gas is used for the first and third electrodes of the void in the support structure, and the detection gas is used for the second and fourth electrodes on the outer surface of the gas sensor. To contact. At this time, the first
The sensor element of is made insensitive to the detection gas, and the second
If the sensor element is a sensor that is sensitive to the detection gas and the gas that the first sensor element is sensitive to, the concentration of the detection gas can be determined from the difference between the electromotive forces generated by these two sensor elements, especially the concentration of other gases, especially oxygen. Accurate measurement is possible without being affected by the gas concentration.

In the gas sensor according to the present invention, the material of the solid electrolyte and the electrode, the heating temperature, and when the catalyst layer is provided, the material of the catalyst layer and the like are changed according to the gas to be detected, so that the gas concentration can be extremely high and specific. It is possible to measure. That is, for example, in the case of detecting a gas component which starts combustion at around 300 ° C. to 400 ° C. such as hydrocarbon or CO, a solid electrolyte such as LaGaO ₃ having excellent oxygen ion conductivity at low temperature is used and the second electrode is used. Materials with poor oxidation catalyst ability such as gold,
By using a material such as platinum or rhodium having an excellent oxidation catalytic ability for the fourth electrode, the electromotive force between the first and second electrodes and the electromotive force between the third and fourth electrodes depending on the detected gas concentration are A difference is generated, which allows hydrocarbons, CO, etc. to be accurately
Moreover, the measurement can be performed without the influence of the oxygen concentration.

When a flammable gas is detected, for example, a perovskite type oxide (LaFeO) is used for the fourth electrode.
₍₃ etc.), etc., by using a material having an oxidation catalyst capacity superior to that of gold but inferior to platinum, and heating the solid electrolyte near the temperature at which the detection gas burns with a heater,
It is possible to selectively measure the concentrations of combustible detection gases such as hydrocarbons and CO having different spontaneous ignition points. FIG. 6 is a graph showing the ignition temperature of combustible gas that can be measured by the gas sensor according to the present invention. In FIG. 6, the horizontal axis represents the substance name of combustible gas, and the vertical axis represents the ignition temperature (° C.).

Further, when measuring the concentration of NO gas, for example, a catalyst layer is provided on the second and fourth electrodes, and a hydrocarbon which is a main component of the catalyst layer is used as a catalyst on the second electrode.
By providing the fourth electrode with a catalyst having a strong oxidation catalyst ability to oxidize and burn CO and the like, and a strong oxidation catalyst ability to oxidize other hydrocarbons such as CO and CO to NO A proportional electromotive force difference can be obtained.

[0020]

Embodiments of the present invention will be described below in more detail. However, the invention is in no way limited to these examples.

Example 1 FIG. 1 is a schematic sectional view of a gas sensor of Example 1, and FIG. 3 shows the components of the gas sensor of Example 1 in the order of stacking. The gas sensor of FIGS. 1 and 3 has two sets of oxygen sensor elements 4 and 8 composed of electrodes 1 and 2 and zirconia solid electrolytes 3 and 7 on which electrodes 5 and 6 are formed.
And an atmosphere introduction path 1 for guiding the reference gas to the sensor element portion in the central portion, which is sandwiched between the two sets of sensor elements 4 and 8.
Insulating the heaters 11a and 11b made of platinum-ceramic mixed material, which are formed by a support structure 9 made of zirconia installed so as to form 0, and which are thick film printed on the upper and lower surfaces of the support structure 9 in the same pattern. It is arranged with the layers 14a, b. Electrode 1 and electrode 6 are catalytic layers 12 and 1 respectively.
3 encapsulates the outer part. This heater 11a,
b and the zirconia solid electrolyte are electrically and oxygen-ion conductively insulated by the insulating layers 14a and 14b made of alumina.

As shown in FIG. 3, the components of this gas sensor are, in order, a secondary electrode 2 as a first sensor element portion.
1, overcoat 22, electrode (-pole) 23, insulation coat 24, zirconia sheet 25, insulation coat 26, electrode (+ pole) 27, bonding coat 28, 87% Pt-13% Rh as a support structure part Line (hereinafter, "13% PR
Line ”) 29, insulating coat 30, heater 31, insulating coat 32, zirconia sheet 33, insulating coat 34,
Heater 35, insulation coat 36, 13% PR line 37, second
As the sensor element portion of the, the laminating coat 38, the electrode (+ electrode) 39, the insulating coat 40, the zirconia sheet 4
1, the insulating coat 42, the electrode (-electrode) 43, and the overcoat 44 are laminated.

<Embodiment 2> FIG. 2 shows a schematic sectional view of a gas sensor of Embodiment 2, and FIG. 4 shows the components of the gas sensor of Embodiment 2 in the order of stacking. The gas sensor of FIGS. 2 and 4 includes two sets of oxygen sensor elements 54 and 58, which are electrodes 51 and 52 and zirconia solid electrolytes 53 and 57 on which electrodes 55 and 56 are formed, and two sets of the sensor elements 54. Formed of a support structure 59 having a zirconia solid electrolyte disposed between the first and second electrodes 58, 58 so as to form an air introduction path 60 for guiding the reference gas to the sensor element portion in the central portion. Reference numeral 59 is a pair of heaters 61 made of a platinum-ceramic mixed material, which is thick-film printed with a pattern in the center thereof.
a and b are arranged. The electrodes 51 and 56 are covered with catalyst layers 62 and 63, respectively, on their outer portions.
The heaters 61a, 61b and the zirconia solid electrolyte are electrically and oxygen-ion conductively insulated by insulating layers 64a, 64b made of alumina. In the gas sensor of the present embodiment, the area of the electrodes 52 and 55 can be made larger than that of the first embodiment, so the output reliability as a sensor is improved.

As shown in FIG. 4, the components of this gas sensor are, in order, a secondary electrode 7 as a first sensor element portion.
1, overcoat 72, electrode (-pole) 73, insulation coat 74, zirconia sheet 75, insulation coat 76, electrode (+ pole) 77, bonding coat 78, 13% PR line 79 as a support structure, reinforcement Coat 80, zirconia sheet 81, bonding coat 82, heater 83, insulating coat 84, zirconia sheet 85, insulating coat 86,
The heater 87, the bonding coat 88, the zirconia sheet 89, the reinforcing coat 90, the 13% PR line 91, the bonding coat 92 as the second sensor element portion, the electrode (+ electrode)
In this embodiment, 93, insulating coat 94, zirconia sheet 95, insulating coat 96, electrode (-electrode) 97, and overcoat 98 are laminated.

[0025]

According to the present invention, the concentration of a specific gas is
Measurement can be performed with extremely high accuracy without being affected by other gases, and since heating means capable of heating each sensor element uniformly and in a short time can be attached, deterioration of measurement accuracy due to the influence of temperature can be prevented. Since the leak of oxygen ions of each sensor element can be prevented and the measurement accuracy is not deteriorated, the desired gas can be obtained by combining various combinations of the solid electrolyte, the electrode, the catalyst layer, and the heating means. It is possible to make extremely precise and specific measurements with respect to.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a gas sensor according to a first embodiment of the present invention.

FIG. 2 is a schematic sectional view of a gas sensor according to a second embodiment of the present invention.

FIG. 3 is a schematic perspective view showing the configuration of the gas sensor according to the first embodiment of the present invention.

FIG. 4 is a schematic perspective view showing a configuration of a gas sensor according to a second embodiment of the present invention.

FIG. 5 is a schematic sectional view showing a conventional gas sensor.

FIG. 6 is a graph showing ignition points of various combustible gases.

[Explanation of symbols]

1, 2 ... Electrode, 3 ... Solid electrolyte, 4 ... Sensor element,
5, 6 ... Electrode, 7 ... Solid electrolyte, 8 ... Sensor element,
9 ... Support structure, 10 ... Atmosphere introduction path, 11a, b ...
Heater, 12, 13 ... Catalyst layer, 14a, b ... Insulating layer,
21 ... Secondary electrode, 22 ... Overcoat, 23 ... Electrode (-electrode), 24 ... Insulation coat, 25 ... Zirconia sheet, 26 ... Insulation coat, 27 ... Electrode (+ pole), 28
... Lamination coat, 29 ... 13% PR line, 30 ...
Insulation coat, 31 ... Heater, 32 ... Insulation coat, 33
... Zirconia sheet, 34 ... Insulation coat, 35 ... Heater, 36 ... Insulation coat, 37 ... 13% PR line, 38
... Bonding coat, 39 ... Electrode (+ pole), 40 ...
Insulation coat, 41 ... Zirconia sheet, 42 ... Insulation coat, 43 ... Electrode (-electrode), 44 ... Overcoat,
51, 52 ... Electrode, 53 ... Solid electrolyte, 54 ... Sensor element, 55, 56 ... Electrode, 57 ... Solid electrolyte, 58
... Sensor element, 59 ... Support structure, 60 ... Atmosphere introducing path, 61a, b ... Heater, 62, 63 ... Catalyst layer, 64
a, b ... Insulating layer, 71 ... Secondary electrode, 72 ... Overcoat, 73 ... Electrode (-electrode), 74 ... Insulation coat, 7
5 ... Zirconia sheet, 76 ... Insulation coat, 77 ...
Electrode (+ electrode), 78 ... Laminating coat, 79 ... 13
% PR line, 80 ... Reinforcement coat, 81 ... Zirconia sheet, 82 ... Laminating coat, 83 ... Heater, 84 ...
Insulating sheet, 85 ... Zirconia sheet, 86 ... Insulating coat, 87 ... Heater, 88 ... Laminating sheet, 8
9 ... Zirconia sheet, 90 ... Reinforcement coat, 91 ...
13% PR line, 92 ... Laminating coat, 93 ... Electrode (+ electrode), 94 ... Insulation coat, 95 ... Zirconia sheet, 96 ... Insulation coat, 97 ... Electrode ( -Pole), 98 ...
・ Overcoat, 101 ... Solid electrolyte, 102, 10
3, 104 ... Electrode, 105 ... Catalyst layer

Claims (5)

[Claims] 1. A first oxygen ion conductive solid electrolyte, a first electrode formed on one surface of the first solid electrolyte, and the first electrode.
Sensor element comprising a second electrode formed on one surface facing the other electrode, a second oxygen ion conductive solid electrolyte, and a third electrode formed on one surface of the second solid electrolyte And a second sensor element composed of a fourth electrode formed on one surface facing the third electrode, and sandwiched between the first sensor element and the second sensor element and externally provided. A support structure having a void facing the first electrode and the third electrode that communicate with each other, and an electromotive force between the first electrode and the second electrode; A gas sensor, characterized in that the concentration of the detection gas is measured by the difference between the electromotive force between the third electrode and the fourth electrode. 2. The gas sensor according to claim 1, wherein the support structure has heating means including an insulating portion having oxygen ion non-conductivity. 3. The heating means is formed on a surface of the support structure that contacts the first sensor element and on a surface of the support structure that contacts the second sensor element. Gas sensor according to. 4. A catalyst layer made of a substance having catalytic activity to a detection gas is formed on at least one of the second electrode and the fourth electrode. The gas sensor according to any one of 1 to 3. 5. A ceramic structure having an internal void communicating with the outside, a first electrode formed on one surface of an inner wall of the ceramic structure surrounding the void, and a surface provided with the first electrode. A second electrode formed on one surface of the ceramic structure that faces the ceramic structure, and a third electrode formed on one surface of an inner wall of the ceramic structure that faces the first electrode with the gap. A fourth electrode formed on one surface of the third electrode that faces the third electrode with the ceramic structure sandwiched between the first electrode and the second electrode of the ceramic structure. The portion sandwiched between the third
The electrode sandwiched between the fourth electrode and the fourth electrode is made of an oxygen ion conductive solid electrolyte, and the electromotive force between the first electrode and the second electrode, and the third electrode The fourth
A gas sensor, characterized in that the concentration of the detection gas is measured by the difference between the electromotive force and the electromotive force between the electrodes.