JP2017198659A - Gas sensor element and gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor element and a gas sensor which can detect gas in a low temperature environment (300°C or lower).SOLUTION: A gas sensor element 3 of a gas sensor has a protective layer 31 over an external electrode 27, and the protective layer has a low thermal conductivity layer 32 providing heat insulating effects. This can suppress the temperature drop in an element body 21 through the heat insulating effects of the low thermal conductivity layer 32 even when the temperature of an exhaust gas drops, and the active state can be therefore maintained. The protective layer 31 of the gas sensor element 3 has a catalyst-containing layer 33, whereby a part of exhaust gas which reaches the external electrode 27 via the protective layer 31 will cause a gas equilibration reaction in the catalyst-containing layer 33 and the gas equilibration reaction will be easily generated when the gas reaches the external electrode 27. This makes it possible to detect gas if the active state of the element body 21 becomes lower, and increase in the accuracy of gas detection can be thus allowed.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a gas sensor element including a solid electrolyte body and a pair of electrodes, and a gas sensor including the gas sensor element.

  A gas sensor element for detecting a specific gas (eg, oxygen, NOx, etc.) contained in a measurement target gas (eg, exhaust gas) and a gas sensor including such a gas sensor element are known. The gas sensor element includes a solid electrolyte body and a pair of electrodes arranged so as to sandwich the solid electrolyte body.

By the way, demands for reducing emissions (such as air pollutants) in exhaust gas from internal combustion engines are increasing year by year, and emission regulations are being strengthened.
As a gas sensor used for gas detection in exhaust gas, for example, there is a gas sensor with a heater including a gas sensor element for detecting gas and a heater for activating the gas sensor element. In addition, the gas sensor may be strongly required to be low in cost depending on the application, and a heaterless gas sensor that does not include a heater may be employed for such a demand.

  Such a gas sensor can detect a gas when the gas sensor element is activated by heating of at least one of the heater and the exhaust gas. For this reason, in the gas sensor, it is important that the gas sensor element has excellent characteristics (gas heat receiving property) that can efficiently use heat from at least one of the heater and the exhaust gas for activation of the gas sensor element. .

  In response to such a demand for improving gas heat receiving properties, a material (cerium oxide, lanthanum oxide, calcium oxide) as a promoter is added to the protective layer that covers the measurement electrode of the gas sensor element (the electrode that contacts the measurement target gas). A gas sensor element having the above configuration has been proposed (Patent Document 1). In such a gas sensor element, the catalytic activity of the measurement electrode can be improved by the cocatalyst, and the characteristics of the gas sensor element at a low temperature are improved.

Japanese Patent Laid-Open No. 06-160332

  However, depending on the application of the gas sensor, gas detection in a lower temperature zone (for example, 300 ° C. or lower) may be required. Under such more severe conditions, the gas sensor element including the above-described promoter is used. Even in this case, activation of the measurement electrode may be insufficient and gas detection may not be possible.

  Therefore, an object of the present invention is to provide a gas sensor element capable of detecting gas even in a low temperature (300 ° C. or lower) environment, and a gas sensor including such a gas sensor element.

A gas sensor element according to one aspect of the present invention includes a solid electrolyte body, a pair of electrodes, and a protective layer.
The pair of electrodes are arranged so as to sandwich the solid electrolyte body. The pair of electrodes includes a measurement electrode in contact with the measurement target gas and a reference electrode in contact with the reference gas.

The protective layer is made of a porous material that covers the measurement electrode. The protective layer includes at least a low thermal conductivity layer and a catalyst-containing layer.
The low thermal conductivity layer is formed in a porous shape, and has a thermal conductivity equal to or lower than that of the solid electrolyte body.

The catalyst-containing layer is formed in a porous shape and contains a catalyst that promotes the gas equilibration reaction of the measurement target gas.
In this gas sensor element, since the protective layer covering the measurement electrode includes the low thermal conductivity layer, the heat retention effect by the low thermal conductivity layer can be obtained. For this reason, about the site | part in which a pair of electrode is formed among solid electrolyte bodies, it can reduce that calorie | heat amount is discharge | released outside via a protective layer, and can suppress the temperature fall in the activated solid electrolyte body. In other words, the solid electrolyte body that has been activated by receiving the amount of heat from the measurement target gas can suppress its own temperature decrease due to the heat retention effect of the low thermal conductivity layer even when the temperature of the measurement target gas decreases. The activated state can be maintained. For this reason, since this gas sensor element can utilize the heat | fever from measurement object gas efficiently, gas heat receiving property can be improved.

  In this gas sensor element, the protective layer covering the measurement electrode includes the catalyst-containing layer, so that part of the measurement target gas that reaches the measurement electrode via the protective layer undergoes a gas equilibration reaction in the catalyst-containing layer. The gas equilibration reaction is likely to occur when the measurement electrode is reached. Thereby, even if it is a case where the activation state of a solid electrolyte body falls, since gas detection becomes possible, gas detection accuracy can be improved.

Therefore, according to this gas sensor element, gas detection is possible even in a low temperature (300 ° C. or lower) environment.
Next, in the gas sensor element described above, the low thermal conductivity layer may be disposed in the protective layer at a position closer to the measurement electrode than the catalyst-containing layer.

Thus, the temperature decrease of the solid electrolyte body can be further suppressed by disposing the low thermal conductivity layer at a position closer to the measurement electrode than the catalyst-containing layer.
In addition, when the measurement target gas passes through the protective layer and reaches the measurement electrode, the gas equilibration reaction of the measurement target gas is sufficiently accelerated by passing through the catalyst-containing layer before the low thermal conductivity layer. Gas detection accuracy can be improved.

Next, in the gas sensor element described above, the solid electrolyte body may be formed in a bottomed cylindrical shape or a plate shape.
That is, the specific shape of the gas sensor element includes, for example, a bottomed cylinder type or a plate type.

  A gas sensor according to another aspect of the present invention is a gas sensor including a gas sensor element that detects a specific gas contained in a measurement target gas, and includes any of the gas sensor elements described above as the gas sensor element.

  As described above, a gas sensor including any one of the gas sensor elements described above can detect a gas even in a low temperature (300 ° C. or lower) environment.

According to the gas sensor element of the present invention, gas detection is possible even in a low temperature (300 ° C. or lower) environment.
Further, according to the gas sensor of the present invention, gas detection is possible even in a low temperature (300 ° C. or lower) environment.

It is explanatory drawing which shows the state which fractured | ruptured the gas sensor in the axis line O direction. It is a front view which shows the external appearance of a gas sensor element. It is sectional drawing which shows the structure of a gas sensor element. It is the expanded sectional view which expanded the area | region D1 enclosed with the dotted line among the gas sensor elements shown in FIG. It is a test result of the evaluation test for evaluating the gas heat receiving property of a gas sensor element. It is the simulation result of the element temperature obtained by the heat-transfer analysis by simulation about each of Example 1 and Comparative Example 1. FIG. It is a test result of the evaluation test for evaluating the low temperature operability of a gas sensor. It is a perspective view of a plate type gas sensor element. It is a typical exploded perspective view of a plate type gas sensor element. It is a partial expanded sectional view of the front end side of a plate type gas sensor element.

Embodiments to which the present invention is applied will be described below with reference to the drawings.
In addition, this invention is not limited to the following embodiment at all, and it cannot be overemphasized that various forms may be taken as long as it belongs to the technical scope of this invention.

[1. First Embodiment]
[1-1. overall structure]
As a first embodiment, an oxygen sensor (hereinafter also referred to as a gas sensor 1) that detects the oxygen in exhaust gas by attaching the tip portion of the exhaust pipe to the exhaust pipe of the internal combustion engine so as to protrude into the exhaust pipe is taken as an example. explain. In addition, the gas sensor 1 is provided in the exhaust pipe of vehicles, such as a motor vehicle or a motorcycle, for example.

First, the structure of the gas sensor 1 of this embodiment is demonstrated using FIG.
In FIG. 1, the downward direction in the drawing is the front end side of the gas sensor, and the upward direction in the drawing is the rear end side of the gas sensor.

  The gas sensor 1 includes a gas sensor element 3, a separator 5, a closing member 7, a terminal fitting 9, and a lead wire 11. Further, the gas sensor 1 includes a metal shell 13, a protector 15, and an outer cylinder 16 that are arranged so as to cover the periphery of the gas sensor element 3, the separator 5, and the closing member 7. The outer cylinder 16 includes an inner outer cylinder 17 and an outer outer cylinder 19.

  The gas sensor 1 is a so-called heater-less sensor that does not include a heater for heating the gas sensor element 3, and detects oxygen by activating the gas sensor element 3 using the heat of exhaust gas.

FIG. 2 is a front view showing the appearance of the gas sensor element 3.
The gas sensor element 3 is formed using a solid electrolyte body having oxygen ion conductivity, has a bottomed cylindrical shape with a closed end 25, and has a cylindrical element body 21 extending in the direction of the axis O. doing. On the outer periphery of the element main body 21, an element collar portion 23 protruding outward in the radial direction is provided.

The solid electrolyte body constituting the element body 21 is a partially stabilized zirconia sintered body obtained by adding yttria (Y ₂ O ₃ ) or calcia (CaO) as a stabilizer to zirconia (ZrO ₂ ). It is configured. The solid electrolyte constituting the element body 21 is not limited to these, and includes “solid solution of alkaline earth metal oxide and ZrO ₂ ”, “solid solution of rare earth metal oxide and ZrO ₂ ”, and the like. May be used. Further, those containing HfO ₂ may be used as the solid electrolyte body constituting the element body 21.

  An outer electrode 27 (see FIG. 3 described later) is formed on the outer peripheral surface of the element body 21 at the distal end portion 25 of the gas sensor element 3. The outer electrode 27 is made of porous Pt or Pt alloy. The outer electrode 27 is covered with a porous protective layer 31. Therefore, in FIG. 2, the protective layer 31 is illustrated, but the outer electrode 27 is not illustrated.

An annular lead portion 28 made of Pt or the like is formed on the tip end side (lower side in FIG. 2) of the element flange 23.
A vertical lead portion 29 made of Pt or the like is formed between the outer electrode 27 and the annular lead portion 28 on the outer peripheral surface of the element body 21 so as to extend in the axial direction. The vertical lead portion 29 electrically connects the outer electrode 27 and the annular lead portion 28.

  On the other hand, an inner electrode 30 is formed on the inner peripheral surface of the element body 21 of the gas sensor element 3. The inner electrode 30 is a porous Pt or Pt alloy. In the front end portion 25 (detection portion) of the gas sensor element 3, the outer electrode 27 is exposed to the measurement target gas via the protective layer 31, and the inner electrode 30 is exposed to the reference gas (atmosphere). The oxygen concentration is detected.

  The separator 5 is a cylindrical member formed of an electrically insulating material (for example, alumina). The separator 5 has a through hole 35 through which the lead wire 11 is inserted at the center of the axis. The separator 5 is disposed so that a gap 18 is provided between the separator 5 and the inner outer cylinder 17 covering the outer peripheral side.

  The closing member 7 is a cylindrical seal member made of an electrically insulating material (for example, fluororubber). The closing member 7 includes a protruding portion 36 that protrudes radially outward at the rear end thereof. The closing member 7 includes a lead wire insertion hole 37 through which the lead wire 11 is inserted at the center of the shaft. The front end surface 95 of the closing member 7 is in close contact with the rear end surface 97 of the separator 5, and the side outer peripheral surface 98 on the front end side of the protruding portion 36 of the closing member 7 is in close contact with the inner surface of the inner outer cylinder 17. . That is, the closing member 7 closes the rear end side of the outer cylinder 16.

The rear end facing surface 99 of the closing member 7 sandwiches the flange portion 89b of the lead wire protection member 89 between the front end facing surface 19a of the reduced diameter portion 19g of the outer outer cylinder 19.
Among these, the reduced diameter portion 19 g extends radially inward from the rear end side of the closing member 7, and the distal-facing surface 19 a of the reduced diameter portion 19 g is provided as a surface facing the distal end side of the gas sensor 1. ing. A lead wire insertion portion 19c for inserting the lead wire 11 and the lead wire protection member 89 is formed in the central region of the reduced diameter portion 19g.

  The lead wire protection member 89 is a cylindrical member having an inner diameter that can accommodate the lead wire 11 and is made of a material having flexibility, heat resistance, and insulation (for example, a glass tube or a resin tube). Yes. The lead wire protection member 89 is provided for protecting the lead wire 11 from flying objects (stone, water, etc.) from the outside.

  The lead wire protection member 89 includes a plate-like flange portion 89b that protrudes outward in the vertical direction in the axial direction at the distal end side end portion 89a. The collar portion 89b is formed not over a part of the lead wire protection member 89 in the circumferential direction but over the entire circumference.

The flange portion 89b of the lead wire protection member 89 is sandwiched between the front end facing surface 19a of the reduced diameter portion 19g of the outer cylinder 16 (specifically, the outer outer cylinder 19) and the rear end facing surface 99 of the closing member 7. The
The terminal fitting 9 is made of a conductive material (for example, Inconel 750 (trade name of Inconel, UK)), and is a cylindrical member made of a conductive material for taking out the sensor output to the outside. The terminal fitting 9 is electrically connected to the lead wire 11 and is disposed so as to be in electrical contact with the inner electrode 30 of the gas sensor element 3. The terminal fitting 9 is provided with a flange portion 77 protruding outward in the radial direction (direction perpendicular to the axial direction) on the rear end side. The flange portion 77 includes three plate-like flange pieces 75.

The lead wire 11 includes a core wire 65 and a covering portion 67 that covers the outer periphery of the core wire 65.
The metal shell 13 is a cylindrical member formed of a metal material (for example, iron or SUS430). The metal shell 13 is provided with a stepped portion 39 projecting radially inward on the inner peripheral surface. The step portion 39 is provided to support the element flange 23 of the gas sensor element 3.

  A threaded portion 41 for attaching the gas sensor 1 to the exhaust pipe is formed on the outer peripheral surface on the distal end side of the metal shell 13. A hexagonal portion 43 is formed on the rear end side of the threaded portion 41 of the metal shell 13 to engage the attachment tool when the gas sensor 1 is attached to or detached from the exhaust pipe. Further, a cylindrical portion 45 is provided on the rear end side of the hexagonal portion 43 in the metal shell 13.

  The protector 15 is a protective member that is formed of a metal material (for example, SUS310S) and covers the distal end side of the gas sensor element 3. The protector 15 is fixed so that its rear edge is sandwiched between the element flange 23 of the gas sensor element 3 and the stepped portion 39 of the metal shell 13 via the packing 88.

  In the rear end region of the element flange 23 of the gas sensor element 3, the ceramic powder 47 made of talc and the alumina are formed between the metal shell 13 and the gas sensor element 3 from the front end side to the rear end side. The ceramic sleeve 49 is disposed.

  Furthermore, on the inner side of the rear end portion 51 of the cylindrical portion 45 of the metal shell 13, there are a metal ring 53 formed of a metal material (for example, SUS430) and an inner outer tube 17 formed of a metal material (for example, SUS304L). The tip portion 55 is disposed. The distal end portion 55 of the inner outer cylinder 17 is formed in a shape that extends radially outward. That is, the rear end portion 51 of the tubular portion 45 is crimped, so that the front end portion 55 of the inner outer tube 17 is interposed between the rear end portion 51 of the tubular portion 45 and the ceramic sleeve 49 via the metal ring 53. The inner outer cylinder 17 is fixed to the metal shell 13.

  A cylindrical filter 57 formed of a resin material (for example, PTFE) is disposed on the outer periphery of the inner outer cylinder 17, and an outer outer cylinder 19 formed of, for example, SUS304L is disposed on the outer periphery of the filter 57. Has been placed. The filter 57 can be ventilated but can suppress the intrusion of moisture.

  Then, the inner outer cylinder 17, the filter 57, and the outer outer cylinder 19 are integrally fixed by caulking the caulking portion 19b of the outer outer cylinder 19 radially inward from the outer peripheral side. Further, the caulking portion 19 h of the outer outer cylinder 19 is caulked inward in the radial direction from the outer peripheral side, whereby the inner outer cylinder 17 and the outer outer cylinder 19 are integrally fixed, and the lateral outer peripheral surface of the closing member 7. 98 comes into close contact with the inner surface of the inner outer cylinder 17.

  The inner outer cylinder 17 and the outer outer cylinder 19 are provided with vent holes 59 and 61, respectively, and the inside and outside of the gas sensor 1 can be ventilated through the vent holes 59 and 61 and the filter 57. .

[1-2. Gas sensor element]
The configuration of the gas sensor element 3 will be described. In particular, the configuration of the tip portion 25 provided with the protective layer 31 will be mainly described.

As described above, the gas sensor element 3 includes the element body 21, the outer electrode 27, the annular lead portion 28, the vertical lead portion 29, the inner electrode 30, and the protective layer 31.
FIG. 3 is a cross-sectional view showing the configuration of the gas sensor element 3. FIG. 4 is an enlarged cross-sectional view in which a region D1 surrounded by a dotted line in the gas sensor element 3 shown in FIG. 3 is enlarged.

At the distal end portion 25 of the gas sensor element 3, the outer electrode 27 and the inner electrode 30 are disposed so as to sandwich the element body 21.
The protective layer 31 is formed so as to cover the outer electrode 27. The protective layer 31 includes a low thermal conductivity layer 32 and a catalyst-containing layer 33. In the protective layer 31, the low thermal conductivity layer 32 is disposed closer to the outer electrode 27 than the catalyst-containing layer 33.

  The low thermal conductivity layer 32 is made of zirconia (5YSZ) stabilized with 5 mol% yttria. The low thermal conductivity layer 32 is formed in a porous shape with a porosity of 13%. The low thermal conductivity layer 32 has a thickness dimension of 80 μm. The low thermal conductivity layer 32 has a thermal conductivity of 2.0 [W / m · K].

The element body 21 has a thermal conductivity of 2.5 [W / m · K]. For this reason, the low thermal conductivity layer 32 has a lower thermal conductivity than the element body 21.
The catalyst-containing layer 33 is formed of spinel (MgAl ₂ O ₄ ) and titania (TiO ₂ ). The catalyst-containing layer 33 carries a noble metal (at least one of Pt, Pd, and Rh). This noble metal functions as a catalyst for promoting the gas equilibration reaction of various gases contained in the exhaust gas. The catalyst-containing layer 33 is formed in a porous shape with a porosity of 52%. The catalyst-containing layer 33 has a thickness dimension of 100 μm.

The element body 21 has a thickness dimension of 500 μm (detector region), the outer electrode 27 has a thickness dimension of 3 μm, and the inner electrode 30 has a thickness dimension of 3 μm.
[1-3. Manufacturing method of gas sensor element]
A method for manufacturing the gas sensor element 3 will be described.

First, as a powder of a solid electrolyte body that is a material of the element body 21, zirconia (ZrO ₂ ) added with 5 mol% of yttria (Y ₂ O ₃ ) as a stabilizer (also referred to as “5YSZ”), Furthermore, what added alumina powder is prepared. When the total material powder of the element body 21 is 100% by mass, the content of 5YSZ is 99.6% by mass, and the content of alumina powder is 0.4% by mass. After the powder is pressed, an unsintered molded body is obtained by cutting the powder so as to have a cylindrical shape.

  Next, a slurry containing platinum (Pt) and zirconia is applied to each formation position of the outer electrode 27, the annular lead portion 28, the vertical lead portion 29, and the inner electrode 30 in the green compact.

  At this time, as a slurry for forming the outer electrode 27, the annular lead portion 28, and the vertical lead portion 29, a slurry in which 15% by mass of monoclinic zirconia is added to platinum (Pt) is used. The slurry for forming the inner electrode 30 is 15% by mass of “mixed powder of 99.6% by mass of 5YSZ / 0.4% by mass of alumina” (the same composition as the element body 21) with respect to platinum (Pt). Use the added one.

  Next, the unfired low thermal conductivity layer 32 is formed by applying a slurry that becomes the low thermal conductivity layer 32 after firing so as to cover the entire outer electrode 27 in the green compact, by dipping. This slurry is obtained by adding carbon as a pore forming material (a pore forming material) to a mixed powder of 5YSZ / 0.4 mass% alumina. The ratio of 5YSZ / 0.4% by mass alumina mixed powder and carbon in the slurry is 87% by volume of 5YSZ / 0.4% by mass alumina mixed powder and 13% by volume of carbon.

Next, the unsintered molded body to which each of the above-described slurries was applied was subjected to a drying treatment and then fired at 1350 ° C. for 1 hour.
Next, among the fired bodies obtained by firing the unsintered green body, a slurry that becomes the catalyst-containing layer 33 after firing is applied by a dipping method so as to cover the entire low thermal conductivity layer 32, A catalyst-containing layer 33 for firing is formed. This slurry is composed of spinel powder and titania powder.

  Next, the fired body to which the slurry was applied was subjected to a drying treatment, and then fired at 1000 ° C. for 1 hour, whereby the catalyst-containing layer 33 was formed. Thereafter, a portion where the catalyst-containing layer 33 is formed in the fired body is dipped in an aqueous solution containing a noble metal (chlorinated Pt acid solution + nitric acid Pd solution + nitric acid Rh solution), followed by drying treatment, and further heat treatment at 800 ° C. did.

By performing such a manufacturing process, the gas sensor element 3 is obtained.
The gas sensor element 3 thus manufactured constitutes a part of the gas sensor 1 by being assembled with the separator 5, the closing member 7, the terminal fitting 9, the lead wire 11, and the like.

[1-4. Gas sensor element evaluation test]
The test results of the evaluation test carried out for evaluating the gas heat receiving property of the gas sensor element to which the present invention is applied will be described.

In addition, gas heat receiving property is a characteristic which shows whether the heat | fever from measurement object gas (exhaust gas etc.) can be utilized efficiently for activation of a gas sensor element among the characteristics of a gas sensor element.
In this evaluation test, the gas sensor element is attached to a known burner measurement device in a state where the gas sensor element is assembled to the gas sensor, the internal resistance of the gas sensor element is measured by a burner measurement method, and the activation state of the gas sensor element is determined. The heat receiving property was evaluated. Specifically, the sensor output at an air-fuel ratio λ = 0.9 (rich) at a gas temperature of 300 ° C. is detected by an oscilloscope using two resistance elements (1 MΩ, 100 kΩ) having different resistance values, and based on the output difference. The internal resistance of the gas sensor element was calculated. Since the internal resistance of the gas sensor element decreases as it enters the activated state, it can be determined whether or not it is in the activated state based on the internal resistance.

  In this evaluation test, the gas sensor element of the present invention manufactured by the above manufacturing method is used as Example 1, and the gas sensor element manufactured by a manufacturing method different from the above manufacturing method is used as Comparative Example 1. The evaluation test was conducted by measuring the internal resistances of Example 1 and Comparative Example 1.

  The gas sensor element of Comparative Example 1 is not a manufacturing method in which an unsintered compact and a slurry that becomes the low thermal conductivity layer 32 after firing are fired at the same time. It was manufactured by a manufacturing method for forming the low thermal conductivity layer 32.

  In addition, the thickness dimension of the protective layer 31 of the gas sensor element of Example 1 (the total dimension of the respective thickness dimensions of the low thermal conductivity layer 32 and the catalyst-containing layer 33) and the protective layer 31 of the gas sensor element of Comparative Example 1 The thickness dimension (the total dimension of the thickness dimensions of the low thermal conductivity layer 32 and the catalyst-containing layer 33) was 180 μm.

In this evaluation test, six samples were used as the gas sensor elements of Example 1, and six samples were used as the gas sensor elements of Comparative Example 1, and the internal resistance of each was measured.
FIG. 5 shows test results of an evaluation test for evaluating the gas heat receiving property of the gas sensor element.

The internal resistance of Example 1 is distributed in the range of 80 kΩ to 100 kΩ, and the internal resistance of Comparative Example 1 is distributed in the range of 100 kΩ to 140 kΩ.
According to this test result, it can be seen that the internal resistance of Example 1 is lower than the internal resistance of Comparative Example 1, and thus is in a higher activated state. In addition, regarding the variation in internal resistance in each of the six samples, the variation in Example 1 is smaller than that in Comparative Example 1, and thus it can be seen that an error in sensor output due to individual differences hardly occurs.

  Here, for each of Example 1 and Comparative Example 1, the simulation results of the element temperature obtained by the heat transfer analysis by simulation are shown in FIG. The simulation result of the element temperature of Example 1 was 293 ° C., and the simulation result of the element temperature of Comparative Example 1 was 290 ° C. From this, the difference in element temperature due to the difference in gas heat receiving property can be cited as a factor in which Example 1 showed a low internal resistance compared to Comparative Example 1. In this simulation, the temperature of the element when the sensor was exposed to an environment where the gas temperature was 300 ° C. was analyzed.

  The low thermal conductivity layer 32 formed by simultaneous firing with the green compact as in Example 1 has a lower thermal conductivity than the low thermal conductivity layer 32 formed by spinel spraying as in Comparative Example 1. Therefore, the heat retention effect is increased. Specifically, the thermal conductivity of the low thermal conductivity layer 32 of Example 1 is 2.0 [W / m · K], and the thermal conductivity of the low thermal conductivity layer 32 of Comparative Example 1 is 10 [W / m. m · K].

  The thermal conductivity of the element body 21 of Example 1 and Comparative Example 1 is 2.5 [W / m · K]. For this reason, in Example 1, the thermal conductivity of the low thermal conductivity layer 32 is a value lower than the thermal conductivity of the element body 21, and in Comparative Example 1, the thermal conductivity of the low thermal conductivity layer 32 is the element. The value is higher than the thermal conductivity of the main body 21.

  Thereby, since the gas sensor element of Example 1 can utilize the heat | fever from measurement object gas efficiently for activation compared with the gas sensor element of the comparative example 1, it becomes the thing excellent in gas heat receiving property. For this reason, since the element temperature becomes higher and gas detection is possible in Example 1 even under the condition where the temperature of the gas to be measured is lower (300 ° C. or lower) than that in Comparative Example 1, the temperature is low (300 It is excellent in activation performance (low temperature operability) at ℃ or less).

[1-5. Gas sensor evaluation test]
Test results of an evaluation test carried out for evaluating the low temperature operability of the gas sensor to which the present invention is applied will be described.

In addition, low temperature operability is a characteristic which shows the activation performance in low temperature (300 degrees C or less) among the characteristics of a gas sensor.
In this evaluation test, the sensor output waveform is obtained with the passage of time from the start of the engine of the two-wheeled vehicle in a state where the gas sensor is assembled at the most downstream position of the exhaust pipe in the two-wheeled vehicle (specifically, a position 300 mm away from the engine head). Thus, the low temperature operability of the gas sensor was evaluated. Specifically, the sensor output waveform in the idling state was detected after the engine was started. The temperature of the exhaust gas at the gas sensor mounting position in the exhaust pipe was about 250 ° C.

  In this evaluation test, a gas sensor including the gas sensor element of the present invention is used as Example 2, and a gas sensor including a gas sensor element different from the present invention is used as Comparative Examples 2 and 3, and Example 2 is used. The sensor output waveforms of Comparative Examples 2 and 3 were detected.

  The gas sensor element of Example 2 was obtained by adding carbon as a pore-forming material to the mixed powder of 5YSZ / 0.4 mass% alumina as a slurry that becomes the low thermal conductivity layer 32 after firing in the above manufacturing method. It is the gas sensor element manufactured using. The ratio of 5YSZ / 0.4% by mass alumina mixed powder and carbon in the slurry is 87% by volume of 5YSZ / 0.4% by mass alumina mixed powder and 13% by volume of carbon. In other words, the gas sensor element of Example 2 is a gas sensor element in which the porosity of the low thermal conductivity layer 32 is 13% and the catalyst-containing layer 33 carries a noble metal catalyst of Pt, Pd, and Rh.

  The gas sensor element of Comparative Example 2 was obtained by adding carbon as a pore-forming material to the mixed powder of 5YSZ / 0.4 mass% alumina as a slurry that becomes the low thermal conductivity layer 32 after firing in the above manufacturing method. Further, after forming the catalyst-containing layer 33, the gas sensor element was manufactured without being immersed in an aqueous solution containing a noble metal. The ratio of 5YSZ / 0.4% by mass alumina mixed powder and carbon in the slurry is 87% by volume of 5YSZ / 0.4% by mass alumina mixed powder and 13% by volume of carbon. That is, the gas sensor element of Comparative Example 2 is a gas sensor element in which the porosity of the low thermal conductivity layer 32 is 13% and the noble metal catalyst is not supported on the catalyst-containing layer 33.

  The gas sensor element of Comparative Example 3 was obtained by adding carbon as a pore-forming material to a mixed powder of 5YSZ / 0.4 mass% alumina as a slurry that becomes the low thermal conductivity layer 32 after firing in the above manufacturing method. It is the gas sensor element manufactured using. The ratio of 5YSZ / 0.4% by mass alumina mixed powder and carbon in the slurry is 75% by volume of 5YSZ / 0.4% by mass alumina mixed powder and 25% by volume of carbon. That is, the gas sensor element of Comparative Example 3 is a gas sensor element in which the low thermal conductivity layer 32 has a porosity of 25% and the catalyst-containing layer 33 carries a noble metal catalyst of Pt, Pd, and Rh.

FIG. 7 shows test results of an evaluation test for evaluating the low temperature operability of the gas sensor.
According to this test result, in the gas sensor of Example 2, the sensor output fluctuates in accordance with the oxygen concentration in the exhaust gas after the elapsed time from the engine start time of 118 seconds, and the sensor output waveform is It is normal.

  In the gas sensor of Comparative Example 2, the sensor output does not fluctuate according to the oxygen concentration in the exhaust gas during the period from the engine start time to “0 sec to 207 sec”, and the sensor output waveform is normal. Absent. In other words, in Comparative Example 2, the elapsed time from the engine starting time “period from 100 sec to 207 sec” is determined as a failure because the gas sensor does not operate normally, so the elapsed time from the engine starting time is 207 sec or more. Otherwise, normal gas detection cannot be performed.

  In the gas sensor of Comparative Example 3, the sensor output waveform is normal when the elapsed time from the engine start time is “a period from 100 sec to 162 sec”, but the sensor output waveform is not normal during the “period from 162 sec to 222 sec”. That is, in Comparative Example 3, normal gas detection cannot be performed unless the elapsed time from the engine start time is 222 seconds or more.

  Among these test results, according to the comparison between Example 2 and Comparative Example 2, when the noble metal catalyst is supported on the catalyst-containing layer 33, the noble metal catalyst is supported on the catalyst-containing layer 33. In comparison, it can be seen that the low temperature operability of the gas sensor is improved. That is, since the gas equilibration reaction of the exhaust gas can be promoted by providing the catalyst-containing layer 33 on which the noble metal catalyst is supported, a part of the exhaust gas reaching the outer electrode 27 via the protective layer 31 is a catalyst-containing layer. A gas equilibration reaction occurs at 33, and the gas equilibration reaction is likely to occur when the outer electrode 27 is reached. As a result, even if the activation state of the element body 21 (solid electrolyte body) is lowered, gas detection is possible, so that the gas detection accuracy in Example 2 can be improved as compared with Comparative Example 2.

  Further, according to the comparison between Example 2 and Comparative Example 3, when the porosity of the low thermal conductivity layer 32 is relatively small, the low temperature operability of the gas sensor is greater than when the porosity is relatively large. Can be seen to improve. Thus, by forming a relatively dense layer as the low thermal conductivity layer 32, the amount of exhaust gas reaching the outer electrode 27 can be limited. That is, by limiting the amount of exhaust gas processed by the outer electrode 27, a sensor output corresponding to the oxygen concentration in the exhaust gas can be stably obtained.

  From these facts, in Example 2, the porosity of the low thermal conductivity layer 32 is relatively small as compared with Comparative Examples 2 and 3, or the noble metal catalyst is supported on the catalyst-containing layer 33. Gas detection accuracy can be improved and stable sensor output can be realized.

[1-6. effect]
As described above, in the gas sensor element 3 provided in the gas sensor 1 of the present embodiment, the protective layer 31 includes the low thermal conductivity layer 32 and the catalyst-containing layer 33. The low thermal conductivity layer 32 has a thermal conductivity lower than that of the element body 21. The catalyst-containing layer 33 is formed to contain a catalyst that promotes the gas equilibration reaction of the exhaust gas.

  In the gas sensor element 3, the protective layer 31 covering the outer electrode 27 includes the low thermal conductivity layer 32, so that the heat retention effect by the low thermal conductivity layer 32 is obtained. For this reason, it is possible to reduce the amount of heat released to the outside through the protective layer 31 with respect to the portion where the pair of electrodes (outer electrode 27, inner electrode 30) is formed in the element body 21, and the activated element. A temperature drop in the main body 21 can be suppressed.

  In other words, the element body 21 that has been activated by receiving the amount of heat from the exhaust gas can suppress a decrease in its temperature due to the heat retention effect of the low thermal conductivity layer 32 even when the temperature of the exhaust gas decreases. The activated state can be maintained. For this reason, since this gas sensor element 3 can utilize the heat | fever from measurement object gas efficiently, gas heat receiving property can be improved.

  In the gas sensor element 3, the protective layer 31 that covers the outer electrode 27 includes the catalyst-containing layer 33, so that a part of the exhaust gas that reaches the outer electrode 27 through the protective layer 31 is the catalyst-containing layer 33. A gas equilibration reaction occurs, and the gas equilibration reaction is likely to occur when the outer electrode 27 is reached. Thereby, even if it is a case where the activation state of the element main body 21 falls, since gas detection becomes possible, gas detection accuracy can be improved.

Therefore, according to the gas sensor element 3, gas detection is possible even in a low temperature (300 ° C. or lower) environment without performing heating by a heater.
Next, in the gas sensor element 3, the low thermal conductivity layer 32 is disposed in the protective layer 31 at a position closer to the outer electrode 27 than the catalyst-containing layer 33.

As described above, the temperature change of the element body 21 can be further suppressed by disposing the low thermal conductivity layer 32 at a position closer to the outer electrode 27 than the catalyst-containing layer 33.
Further, when the exhaust gas (measurement target gas) passes through the protective layer 31 and reaches the outer electrode 27, it passes through the catalyst-containing layer 33 before the low thermal conductivity layer 32, so that the gas equilibrium of the measurement target gas is achieved. The chemical reaction can be sufficiently promoted, and the gas detection accuracy can be improved.

[1-7. Correspondence of wording]
Here, the correspondence of words in the present embodiment will be described.
The gas sensor 1 corresponds to an example of a gas sensor, the gas sensor element 3 corresponds to an example of a gas sensor element, the element body 21 corresponds to an example of a solid electrolyte body, the outer electrode 27 corresponds to an example of a measurement electrode, and the inner electrode 30 Corresponds to an example of a reference electrode.

The protective layer 31 corresponds to an example of a protective layer, the low thermal conductivity layer 32 corresponds to an example of a low thermal conductivity layer, and the catalyst-containing layer 33 corresponds to an example of a catalyst-containing layer.
[2. Second Embodiment]
[2-1. Plate type gas sensor element]
The solid electrolyte body of the gas sensor element is not limited to the bottomed cylinder type, and may be a plate type. Therefore, a plate type gas sensor element 100 will be described as a second embodiment.

  FIG. 8 is a perspective view of the plate-type gas sensor element 100. FIG. 9 is a schematic exploded perspective view of a plate-type gas sensor element. FIG. 10 is a partial enlarged cross-sectional view of the front end side of the plate type gas sensor element.

The plate type gas sensor element 100 includes an element body 101 and a porous protective layer 120.
As shown in FIG. 9, the element body 101 includes an oxygen concentration detection cell 130, a reinforcing protection layer 111, an air introduction hole layer 107, and a lower surface layer 103. In FIG. 9, the porous protective layer 120 is not shown.

  The oxygen concentration detection cell 130 includes a solid electrolyte body 105 and a pair of electrodes (a reference electrode 104 and a measurement electrode 106). The reference electrode 104 and the measurement electrode 106 are arranged so as to sandwich the solid electrolyte body 105.

  The reference electrode 104 includes a reference electrode portion 104a and a reference lead portion 104L. The reference lead portion 104L is formed so as to extend from the reference electrode portion 104a along the longitudinal direction of the solid electrolyte body 105.

  The measurement electrode 106 includes a measurement electrode portion 106a and a detection lead portion 106L. The detection lead portion 106L is formed so as to extend from the measurement electrode portion 106a along the longitudinal direction of the solid electrolyte body 105.

The reinforcement protection layer 111 includes a reinforcement part 112 and an electrode protection part 113a.
The reinforcing portion 112 is a plate-like member for protecting the solid electrolyte body 105 by sandwiching the detection lead portion 106 </ b> L with the solid electrolyte body 105. The reinforcing part 112 is formed of the same material as the solid electrolyte body, and includes a protective part arrangement space 112a that penetrates in the thickness direction of the plate.

  The electrode protection part 113a is made of a porous material and is arranged in the protection part arrangement space 112a. The electrode protection unit 113a protects the measurement electrode unit 106a by suppressing the sublimation of the measurement electrode unit 106a so as to sandwich the measurement electrode unit 106a with the solid electrolyte body 105.

  The plate-type gas sensor element 100 of the present embodiment is a so-called oxygen concentration electromotive force type gas sensor that can detect the oxygen concentration using the value of the voltage (electromotive force) generated between the electrodes of the oxygen concentration detection cell 130. (Λ sensor) is configured.

  The lower surface layer 103 and the air introduction hole layer 107 are laminated on the reference electrode 104 so as to sandwich the reference electrode 104 with the solid electrolyte body 105. The air introduction hole layer 107 is formed in a substantially U shape with an opening at the rear end side. An internal space surrounded by the solid electrolyte body 105, the air introduction hole layer 107, and the lower surface layer 103 constitutes an air introduction hole 107h. The reference electrode 104 is disposed so as to be exposed to the atmosphere (reference gas) introduced into the atmosphere introduction hole 107h.

  Thus, the element main body 101 is a laminated body in which the lower surface layer 103, the air introduction hole layer 107, the reference electrode 104, the solid electrolyte body 105, the measurement electrode 106, and the reinforcing protective layer 111 are laminated. The element body 101 is formed in a plate shape.

  The terminal of the reference lead portion 104L is electrically connected to the detection element side pad 121 on the solid electrolyte body 105 through a conductor formed in a through hole 105a provided in the solid electrolyte body 105. The reinforcing protective layer 111 is formed to have a shorter dimension in the axial direction (left-right direction in FIG. 9) than the end of the detection lead portion 106L. The terminals of the detection element side pads 121 and the detection lead portions 106L are exposed to the outside from the rear end of the reinforcing protective layer 111 and are electrically connected to external terminals (not shown) for connecting external circuits.

  Next, the porous protective layer 120 will be described. As shown in FIG. 8, the porous protective layer 120 is provided so as to cover the entire circumference on the tip side of the plate-type gas sensor element 100 (element body 101).

  As shown in FIG. 10, the porous protective layer 120 is formed so as to include the front end surface of the plate-type gas sensor element 100 (element main body 101) and to extend to the rear end side along the axial direction (left-right direction in the figure). ing. Further, as shown in FIG. 8, the porous protective layer 120 is formed so as to completely surround the plate-like four surfaces (front surface, back surface, right side surface, and left side surface) of the element body 101.

  Furthermore, the porous protective layer 120 is formed so as to cover at least a region including at least the reference electrode portion 104a and the measurement electrode portion 106a (this region constitutes a detection portion) in the element body 101 in the axial direction. . In the present embodiment, the porous protective layer 120 further extends from this region to the rear end.

  The plate-type gas sensor element 100 may be exposed to poisonous substances such as silicon and phosphorus contained in the exhaust gas, or water droplets in the exhaust gas may adhere. Therefore, by covering the outer surface of the plate-type gas sensor element 100 with the porous protective layer 120, it is possible to prevent poisonous substances from being captured or to prevent water droplets from directly contacting the plate-type gas sensor element 100.

Next, component compositions such as a solid electrolyte body, a protective layer, and a porous protective layer, which are features of the present invention, will be described.
Similarly to the element body 21 of the first embodiment, the solid electrolyte body 105 is a partially stabilized zirconia sintered body obtained by adding yttria (Y ₂ O ₃ ) or calcia (CaO) as a stabilizer to zirconia (ZrO ₂ ). Consists of union. The solid electrolyte body 105 contains zirconia as a main component, and 50 to 83.3 mass% of the zirconia is tetragonal zirconia.

The measurement electrode 106 is mainly composed of Pt and contains monoclinic zirconia. The measurement electrode 106 may contain a ceramic component other than monoclinic zirconia.
The “main component” refers to a component that exceeds 50% by mass with respect to all components constituting the target portion (solid electrolyte body 105, measurement electrode 106, etc.). The solid electrolyte body 105 has a thickness dimension of 200 μm, the measurement electrode 106 has a thickness dimension of 3 μm, and the reference electrode 104 has a thickness dimension of 3 μm.

The portion of the porous protective layer 120 that covers at least the measurement electrode 106 is formed of spinel (MgAl ₂ O ₄ ) and titania (TiO ₂ ), similar to the catalyst-containing layer 33 of the first embodiment. A noble metal (at least one of Pt, Pd, and Rh) is supported. This noble metal functions as a catalyst for promoting the gas equilibration reaction of various gases contained in the exhaust gas. The porous protective layer 120 is formed in a porous shape with a porosity of 52%. The portion of the porous protective layer 120 that covers the measurement electrode 106 has a thickness dimension of 100 μm.

  Note that the portion of the porous protective layer 120 that covers at least the measurement electrode 106 refers to a portion that overlaps the measurement electrode 106 in the stacking direction of the element body 101. The portion of the porous protective layer 120 that covers the measurement electrode 106 has a thickness dimension of 100 μm.

  The electrode protection part 113a is formed of zirconia (5YSZ) stabilized with 5 mol% yttria, like the low thermal conductivity layer 32 of the first embodiment. The electrode protection part 113a is formed in a porous shape with a porosity of 13%. The electrode protection part 113a has a thickness dimension of 80 μm. The electrode protection part 113a has a thermal conductivity of 2.0 [W / m · K].

The solid electrolyte body 105 has a thermal conductivity of 2.5 [W / m · K]. For this reason, the electrode protection part 113 a has a lower thermal conductivity than the solid electrolyte body 105.
[2-2. effect]
As described above, the plate-type gas sensor element 100 of the second embodiment includes the electrode protection part 113a and the porous protection layer 120.

The electrode protection part 113 a has a thermal conductivity lower than that of the solid electrolyte body 105. The porous protective layer 120 is formed containing a catalyst that promotes the gas equilibration reaction of the exhaust gas.
In the plate-type gas sensor element 100, by providing the electrode protection part 113a that covers the measurement electrode 106, the heat retention effect by the electrode protection part 113a can be obtained. For this reason, it is possible to reduce the amount of heat released to the outside through the electrode protection part 113a in the portion where the pair of electrodes (the measurement electrode 106 and the reference electrode 104) is formed in the solid electrolyte body 105, and the activated state The temperature drop in the element body 101 can be suppressed.

  In other words, the element body 101 that has been activated by receiving the amount of heat from the exhaust gas can suppress a decrease in its temperature due to the heat retention effect of the electrode protection portion 113a even when the temperature of the exhaust gas is reduced. Can be maintained. For this reason, since the plate-type gas sensor element 100 can efficiently utilize the heat from the measurement target gas, the gas heat receiving property can be improved.

  Further, the plate type gas sensor element 100 includes the porous protective layer 120 that covers the measurement electrode 106 via the electrode protection part 113a, so that the exhaust gas that reaches the measurement electrode 106 via the porous protective layer 120 is included. A part of the porous protective layer 120 causes a gas equilibration reaction, and the gas equilibration reaction is likely to occur when the measurement electrode 106 is reached. Thereby, even if it is a case where the activation state of the element main body 101 falls, since gas detection becomes possible, gas detection accuracy can be improved.

Therefore, according to the plate-type gas sensor element 100, it is possible to detect a gas even in a low temperature (300 ° C. or lower) environment without heating by a heater.
[2-3. Correspondence of wording]
Here, the correspondence of words in the present embodiment will be described.

  The plate-type gas sensor element 100 corresponds to an example of a gas sensor element, the element body 101 corresponds to an example of a solid electrolyte body, the measurement electrode 106 corresponds to an example of a measurement electrode, and the reference electrode 104 corresponds to an example of a reference electrode. .

  The electrode protection part 113a and the porous protection layer 120 correspond to an example of a protection layer, the electrode protection part 113a corresponds to an example of a low thermal conductivity layer, and the porous protection layer 120 corresponds to an example of a catalyst-containing layer.

[3. Other Embodiments]
As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, In the range which does not deviate from the summary of this invention, it is possible to implement in various aspects.

  In the above embodiment, various numerical values (thermal conductivity, thickness dimension, porosity, etc.) in the protective layer and the element body (solid electrolyte body) are specified, but these various numerical values are limited to the above numerical values. However, any value can be adopted as long as it is included in the technical scope of the present invention. For example, the thermal conductivity of the low thermal conductivity layer is not limited to a value lower than the thermal conductivity of the element body (solid electrolyte body), and may be the same value as the element body (solid electrolyte body). Further, the porosity of the low thermal conductivity layer can take any value within a range of 5 to 20%. Furthermore, the thickness dimension of the protective layer (the total dimension of the thickness dimensions of the low thermal conductivity layer and the catalyst-containing layer) can take any value within the range of 30 to 300 μm.

  Next, the stacking order of the low thermal conductivity layer and the catalyst-containing layer in the protective layer is not limited to the same order as in the above embodiment. For example, the catalyst-containing layer is larger than the low-thermal conductivity layer so that the distance between the low thermal conductivity layer and the measurement electrode (outer electrode 27) is larger than the distance between the catalyst-containing layer and the measurement electrode (outer electrode 27). You may comprise a protective layer in the position near a measurement electrode. Even with such a protective layer, gas heat detection can be improved by the heat retention effect of the low thermal conductivity layer, and gas detection can be achieved by promoting the gas equilibration reaction of the gas to be measured by the catalytic effect of the catalyst-containing layer. Accuracy can be improved.

  Next, the protective layer is not limited to the configuration including only the low thermal conductivity layer and the catalyst-containing layer, and may further include another layer. For example, the protective layer 31 of the first embodiment may include a catalyst protective layer formed so as to cover the entire catalyst-containing layer 33. By providing this catalyst protective layer, volatilization of the catalyst component (noble metal component) in the catalyst-containing layer can be suppressed, and a decrease in gas detection accuracy due to volatilization of the catalyst component (noble metal component) can be suppressed.

  Next, in the above-described embodiment, the gas sensor including the cylindrical gas sensor element has been described as the gas sensor. However, the gas sensor to which the present invention is applied may be a gas sensor including a plate-type gas sensor element. In addition, since the gas sensor provided with a plate type gas sensor element is well-known, the description about a detailed structure is abbreviate | omitted.

  Next, in the method for producing a gas sensor element, in producing the low thermal conductivity layer, a raw material having the same specific surface area or a larger specific surface area is used as a raw material for the low thermal conductivity layer than the raw material for the element body (solid electrolyte body). May be used. By using the raw material whose specific surface area is defined in this way, the sinterability at the time of firing is improved, so that the pores formed inside the low thermal conductivity layer after firing are only the pores formed by the pore former. It becomes. Thereby, the porosity of the low thermal conductivity layer can be accurately adjusted by the pore former.

  Next, in the above embodiment, the heaterless gas sensor has been described as the gas sensor, but the gas sensor to which the present invention is applied may be a gas sensor with a heater including a heater for heating the gas sensor element. Such a gas sensor can efficiently use the heat from the exhaust gas for the activation of the gas sensor element in addition to the heating by the heater, so that the gas can be detected even in a low temperature (300 ° C. or lower) environment.

  Examples of the heater include a rod heater that is formed in a rod shape and contacts a cylindrical inner surface of the bottomed cylindrical gas sensor element, and a plate heater stacked on the plate gas sensor element.

  DESCRIPTION OF SYMBOLS 1 ... Gas sensor, 3 ... Gas sensor element, 5 ... Separator, 7 ... Closure member, 9 ... Terminal metal fitting, 11 ... Lead wire, 13 ... Main metal fitting, 15 ... Protector, 16 ... Outer cylinder, 21 ... Element main body, 23 ... Element 25: tip part, 27 ... outer electrode, 28 ... annular lead part, 29 ... longitudinal lead part, 30 ... inner electrode, 31 ... protective layer, 32 ... low thermal conductivity layer, 33 ... catalyst-containing layer.

Claims (4)

A gas sensor element comprising: a solid electrolyte body; and a pair of electrodes arranged to sandwich the solid electrolyte body,
The pair of electrodes includes a measurement electrode that contacts a measurement target gas, and a reference electrode that contacts a reference gas,
A porous protective layer covering the measurement electrode is provided,
The protective layer includes at least a low thermal conductivity layer and a catalyst-containing layer,
The low thermal conductivity layer is formed in a porous shape, and the thermal conductivity is the same as or lower than that of the solid electrolyte body,
The catalyst-containing layer is formed in a porous shape and contains a catalyst that promotes a gas equilibration reaction of the measurement target gas.
Gas sensor element. The low thermal conductivity layer is disposed in the protective layer at a position closer to the measurement electrode than the catalyst-containing layer.
The gas sensor element according to claim 1. The solid electrolyte body is formed in a bottomed cylindrical shape or a plate shape,
The gas sensor element according to claim 1 or 2. A gas sensor including a gas sensor element for detecting a specific gas contained in a measurement target gas,
The gas sensor element according to any one of claims 1 to 3 as the gas sensor element.
Gas sensor.