JP6577408B2 - Gas sensor element and gas sensor - Google Patents

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.

As a gas sensor, a sensor is known that includes a gas sensor element whose electrical characteristics change according to the concentration of a specific gas component in a gas to be measured.
For example, Patent Document 1 discloses a bottomed cylindrical solid electrolyte body with a closed tip, an inner electrode (reference electrode) formed on the inner surface of the solid electrolyte body, and a tip portion of the outer surface of the solid electrolyte body. A gas sensor element is disclosed that includes an outer electrode (detection electrode) formed on the substrate. Such a gas sensor is suitably used, for example, for detecting the gas concentration of a specific gas contained in exhaust gas discharged from a combustor or an internal combustion engine.

  Patent Documents 2 and 3 disclose various conductive oxides. These conductive oxides can be used as electrode materials for gas sensor elements. If the conductive oxide disclosed in Patent Documents 2 and 3 is used as the electrode material of the gas sensor element, an electrode having a sufficiently low electric resistance value can be obtained, whereby a gas sensor element with improved gas detection accuracy can be obtained. Further, by using the conductive oxide disclosed in Patent Documents 2 and 3 as the electrode material of the gas sensor element, a cheaper gas sensor element can be obtained as compared with the case where only the noble metal is used as the electrode material.

JP 2009-63330 A Japanese Patent No. 3417090 International Publication No. 2013/1507779

  However, the gas sensor (gas sensor element) may require gas detection in a lower temperature zone (for example, 300 ° C. or lower) depending on the application. Even if the gas sensor element described above is used, activation of the electrode is not possible. In some cases, gas detection may not be possible.

  In addition, gas sensors (gas sensor elements) may be used in an environment where temperature changes are severe depending on applications, and the above gas sensor elements are insufficient in resistance to thermal shock caused by temperature changes (cooling cycle resistance). Therefore, the gas sensor element may be damaged due to thermal shock.

  Accordingly, the present invention provides a gas sensor element that can detect a gas even in a low temperature (300 ° C. or lower) environment and is less likely to be damaged by a thermal shock caused by a temperature change, and a gas sensor including such a gas sensor element. Objective.

A gas sensor element according to one aspect of the present invention includes a solid electrolyte body and a pair of electrodes.
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.

At least one of the measurement electrode and the reference electrode has a multilayer structure in which a reaction preventing layer, an electrode layer, and a lead layer are laminated in order from the side close to the solid electrolyte body.
The reaction preventing layer and the electrode layer each contain rare earth-added ceria.

  Each of the electrode layer and the lead layer is formed including a conductive oxide layer. This conductive oxide layer has a perovskite phase represented by a composition formula: LaaMbNicOx (M is one or more of Co and Fe, a + b + c = 1, 1.25 ≦ x ≦ 1.75) and has a perovskite crystal structure. contains. A, b, and c in the composition formula satisfy 0.459 ≦ a ≦ 0.535, 0.200 ≦ b ≦ 0.475, and 0.025 ≦ c ≦ 0.350.

The thickness dimension of the reaction preventing layer is smaller than the thickness dimension of the lead layer. The thickness dimension of the electrode layer is not less than the thickness dimension of the reaction preventing layer and not more than the thickness dimension of the lead layer.
In this gas sensor element, since the electrode layer and the lead layer are configured to include the conductive oxide layer containing the perovskite phase described above, compared to the case where the electrode layer and the lead layer are configured using a noble metal, Can be manufactured at low cost.

  The reaction preventing layer has a thickness dimension smaller than the thickness dimension of the lead layer, and the thickness dimension is less than or equal to the thickness dimension of the electrode layer. The reaction preventing layer having such a configuration has higher thermal shock resistance in the cooling and heating cycle than the reaction preventing layer formed with a thickness dimension larger than that of the lead layer and the electrode layer.

  Since the thickness dimension of the lead layer is larger than the thickness dimension of the reaction preventing layer, the electrical resistance value in the lead layer can be reduced, and the internal resistance value as a gas sensor element can be reduced. Gas detection is possible even in a low temperature (300 ° C. or lower) environment.

Therefore, this gas sensor element is advantageous in that it is inexpensive, has thermal shock resistance, and has low temperature operability.
In addition, an electrode layer and a lead layer can be manufactured further cheaply by comprising the conductive oxide layer which has the above-mentioned perovskite phase as a main component. Here, “having a perovskite phase as a main component” means that the conductive oxide layer contains the most perovskite phase.

  Next, in the gas sensor element described above, the reaction preventing layer, the electrode layer, and the lead layer are formed so that the reaction preventing layer has the lowest porosity among the porosity of the reaction preventing layer, the electrode layer, and the lead layer. May be.

Since the porosity of the reaction preventing layer is the lowest, the density of the reaction preventing layer is increased, so that the interface resistance value between the solid electrolyte body and the electrode layer can be reduced.
Next, in the gas sensor element described above, the thickness dimension of the reaction preventing layer, the thickness dimension of the electrode layer, and the thickness dimension of the lead layer satisfy the above-mentioned magnitude relationship, and the thickness dimension of the reaction preventing layer is It may be in the range of 1 to 10 μm, the thickness dimension of the electrode layer may be in the range of 3 to 30 μm, and the thickness dimension of the lead layer may be in the range of 5 to 40 μm.

  By setting the thickness dimensions of the reaction preventing layer, the electrode layer, and the lead layer in this way, the gas sensor element can be prevented from being damaged by thermal shock, and the low temperature operability of the gas sensor element is improved.

  Next, in the gas sensor element described above, the porosity of the reaction preventing layer is in the range of 0 to 10%, the porosity of the electrode layer is in the range of 10 to 30%, and the porosity of the lead layer is May be in the range of 35-60%.

  By setting the respective porosities of the reaction preventing layer, the electrode layer, and the lead layer in this manner, the gas sensor element can be prevented from being damaged by thermal shock, and the low temperature operability of the gas sensor element is improved.

Next, in the gas sensor element described above, the reference electrode may have a multilayer structure in which a reaction preventing layer, an electrode layer, and a lead layer are laminated.
The solid electrolyte body and the pair of electrodes (reference electrode, measurement electrode) are at a high temperature (for example, a temperature exceeding 300 ° C.) at the time of gas detection. Among these, the reference electrode becomes a low temperature reference gas (atmosphere) at the time of gas detection Because of contact, damage due to thermal shock is likely to occur.

  On the other hand, since the reference electrode has a multilayer structure in which a reaction preventing layer, an electrode layer, and a lead layer are laminated, damage to the reference electrode due to thermal shock can be suppressed, and thermal shock resistance as a gas sensor element is improved. .

Next, in the gas sensor element described above, the solid electrolyte body may be a bottomed cylinder type or a plate type.
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.

  A gas sensor including any one of the gas sensor elements described above is advantageous in that it is inexpensive, has thermal shock resistance, and has low temperature operability.

  According to the gas sensor element and the gas sensor of the present invention, there are advantageous effects such as low cost, thermal shock resistance, and low temperature operability.

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 and the area | region D2 enclosed with the dotted line among the gas sensor elements shown in FIG. It is explanatory drawing showing the cross-sectional SEM image before and after the thermal cycle test in the gas sensor element of Example 1. FIG. It is explanatory drawing showing the cross-sectional SEM image before and after the thermal cycle test in the gas sensor element of a comparative example. 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. It is a partial expanded sectional view of the area | region in which the reference electrode part of a reference electrode is formed among plate-type gas sensor elements.

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. is 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 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.
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, as shown in FIG. 1, 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 formed by forming a porous material including a rare earth-added ceria, a perovskite phase, and the like. At the front end portion 25 (detection unit) of the gas sensor element 3, the outer electrode 27 is exposed to the measurement target gas, and the inner electrode 30 is exposed to the reference gas (atmosphere), thereby detecting the oxygen concentration in the measurement target gas. Yes.

  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 the rear edge thereof is sandwiched between the element flange portion 23 of the gas sensor element 3 and the step portion 39 of the metal shell 13 via a packing 88 formed of a conductive material. Yes.

  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. Is arranged. 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.
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, and the inner electrode 30.

FIG. 3 is a cross-sectional view showing the configuration of the gas sensor element 3. 4 is an enlarged cross-sectional view in which the region D1 and the region D2 surrounded by the dotted line in the gas sensor element 3 shown in FIG. 3 are 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 element body 21 and the pair of electrodes (the outer electrode 27 and the inner electrode 30) constitute an oxygen concentration cell and generate an electromotive force (voltage) corresponding to the gas concentration of the measurement target gas. That is, the oxygen concentration in the measurement target gas is detected by exposing the outer electrode 27 to the measurement target gas and the inner electrode 30 to the reference gas (atmosphere) at the tip 25 (detection unit) of the gas sensor element 3. is doing.

  As described above, the outer electrode 27 is electrically connected to the annular lead portion 28 via the vertical lead portion 29. The annular lead portion 28 is electrically connected to the metal shell 13 via a packing 88 made of a conductive material and the protector 15. An electrode protective layer (not shown) for protecting the outer electrode 27 may be formed so as to cover the outer electrode 27. Note that the shape and arrangement of the outer electrode 27 are merely examples, and various other shapes and arrangements can be employed.

  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 formed by forming a porous material including a rare earth-added ceria, a perovskite phase, and the like. The inner electrode 30 has an inner detection electrode part 30a and an inner lead part 30b.

  The inner detection electrode part 30 a is formed so as to cover the inner surface of the tip part 25 of the element body 21. The inner lead portion 30b is connected to the rear end side of the inner detection electrode portion 30a and is electrically connected to the terminal fitting 9 (see FIG. 1). The inner detection electrode part 30a and the inner lead part 30b are formed so as to cover the entire inner surface of the element body 21 as a whole.

  That is, the element body 21 of the gas sensor element 3 has the outer electrode 27 and the inner detection electrode portion 30a formed in the front end side region F1, and the inner lead portion 30b formed in the rear end side region F2. The tip end region F1 of the element body 21 corresponds to the tip portion 25 of the element body 21.

  As shown in FIG. 4, the inner detection electrode portion 30 a has a multilayer structure in which a reaction preventing layer 31, an electrode layer 32, and a tip lead layer 33 a (lead layer 33) are laminated in order from the side closer to the element body 21.

  The leading lead layer 33a forms the lead layer 33 together with a trailing lead layer 33b described later. That is, the lead layer 33 includes a leading end lead layer 33a and a trailing end lead layer 33b.

The reaction preventing layer 31 is an oxide layer formed of rare earth-added ceria. The rare earth-added ceria is a ceria to which a rare earth oxide other than ceria is added. As the “rare earth oxide other than ceria”, La ₂ O ₃ , Gd ₂ O ₃ , Sm ₂ O ₃ , Y ₂ O _{3 and the} like can be used. The content ratio of the rare earth element RE in such rare earth-added ceria is, for example, in the range of 10 mol% or more and 50 mol% or less in terms of the molar fraction {RE / (Ce + RE)} of cerium and the rare earth element RE. it can. Such rare earth-added ceria is an insulator at a low temperature (room temperature), but functions as a solid electrolyte having oxygen ion conductivity at a high temperature (use temperature of the gas sensor 1). For this reason, the reaction preventing layer 31 functions as a layer for electrically connecting the electrode layer 32 and the element body 21 when the gas sensor 1 is used (when the gas sensor element 3 is used). The reaction preventing layer 31 has a function of making it difficult for the reaction between La of the electrode layer 32 and ZrO _{2 of the} element body 21 to occur during the manufacturing (firing) of the gas sensor element 3. By providing such a reaction preventing layer 31, it is possible to suppress the formation of a lanthanum zirconate layer (reaction layer) due to the reaction between La of the electrode layer 32 and ZrO _{2 of the} element body 21.

The electrode layer 32 and the lead layer 33 are configured to include a crystal phase (perovskite phase) having a perovskite oxide crystal structure that satisfies the following composition formula.
LaaMbNicOx (1)
Here, the element M represents one or more of Co and Fe, and a + b + c = 1 and 1.25 ≦ x ≦ 1.75. The coefficients a, b, and c preferably satisfy the following relationship.

0.459 ≦ a ≦ 0.535 (2a)
0.200 ≦ b ≦ 0.475 (2b)
0.025 ≦ c ≦ 0.350 (2c)
The perovskite-type conductive oxide having the composition represented by the above composition formula has a conductivity of 250 S / cm or more at room temperature (25 ° C.) and a B constant of 600 K or less, and does not satisfy these relationships. Compared to this, it has good characteristics such as high conductivity and small B constant. In addition, since the perovskite type conductive oxide has a lower activation energy of the interface resistance than the noble metal electrode, the interface resistance can be sufficiently reduced even at a low temperature. If the Pt electrode is left in an atmosphere of about 600 ° C. in the atmosphere, the Pt electrode is oxidized and the interface resistance is increased. On the other hand, the perovskite type conductive oxide has an advantage that such a change with time hardly occurs.

Regarding the coefficients b and c, the following (3b) and (3c) may be satisfied instead of the above (2b) and (2c).
0.200 ≦ b ≦ 0.375 (3b)
0.125 ≦ c ≦ 0.300 (3c)
In this case, the conductivity can be further increased and the B constant can be further decreased.

  Regarding the coefficient x of O (oxygen) in the above formula (1), when all the conductive oxides having the above composition are composed of a perovskite phase, theoretically, x = 1.5. However, since oxygen may deviate from the stoichiometric composition, as a typical example, the range of x is defined as 1.25 ≦ x ≦ 1.75.

  The electrode layer 32 includes the perovskite phase and the rare earth-added ceria. Since such an electrode layer 32 has both ionic conductivity and electronic conductivity properties at a high temperature (when the gas sensor 1 is used), it exhibits a sufficiently low interface resistance value.

The lead layer 33 is composed of the above-described perovskite phase as a main component and does not contain rare earth-added ceria.
The thickness dimension T1 of the reaction preventing layer 31 is 2 μm, the thickness dimension T2 of the electrode layer 32 is 11 μm, and the thickness dimension T3 of the lead layer 33 is 16 μm. Further, the porosity B1 of the reaction preventing layer 31 is 1%, the porosity B2 of the electrode layer 32 is 21%, and the porosity B3 of the lead layer 33 is 46%.

  The inner lead portion 30 b has a multilayer structure including a rear end lead layer 33 b (lead layer 33) and a lanthanum zirconate layer 34. The lanthanum zirconate layer 34 is disposed closer to the element body 21 than the rear end lead layer 33b.

The rear end lead layer 33b is formed with the same composition as the front end lead layer 33a of the inner detection electrode portion 30a described above.
However, the content ratio of the perovskite phase in the front lead layer 33a constituting the inner detection electrode portion 30a is the same as or more than the content ratio of the perovskite phase in the rear lead layer 33b constituting the inner lead portion 30b. May be.

The lanthanum zirconate layer 34 is a layer formed by a reaction between lanthanum (La) contained in the rear end lead layer 33b and ZrO ₂ contained in the element body 21 during the firing of the inner lead portion 30b. Such a lanthanum zirconate layer 34 is also referred to as “reaction layer 34” below. When the lanthanum zirconate layer 34 is formed, the adhesion between the lanthanum zirconate layer 34 and the rear end lead layer 33b and between the lanthanum zirconate layer 34 and the element body 21 is increased. Improves impact resistance. Therefore, in the portion where the inner lead portion 30b exists, the mechanical impact resistance can be improved by forming the lanthanum zirconate layer 34 between the rear end lead layer 33b and the element body 21.

[1-3. Manufacturing method of gas sensor element]
A method for manufacturing the gas sensor element 3 will be described.
In the first step, a green compact is produced.

In the first step, first, as a powder of a solid electrolyte body that is a material of the element body 21, zirconia (ZrO ₂ ) is added with 5 mol% of yttria (Y ₂ O ₃ ) as a stabilizer (also referred to as “5YSZ”). ) To which alumina powder is further added. 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, in the second step, a slurry of conductive oxide (with ceria) (slurry of electrode layer 32), slurry of conductive oxide (without ceria) (slurry of lead layer 33), and reaction preventing layer Slurry.

In the production of a slurry of conductive oxide (with ceria) (slurry of electrode layer 32), for example, the raw material powder mixture is weighed and then wet mixed and dried to adjust the raw material powder mixture. To do. At this time, for example, La (OH) ₃ or La ₂ O ₃ , Co ₃ O ₄ , Fe ₂ O ₃ , and NiO can be used as the raw powder for the perovskite phase. In addition to CeO ₂ , La ₂ O ₃ , Gd ₂ O ₃ , Sm ₂ O ₃ , Y ₂ O _{3 and the} like can be used as the rare earth-added ceria raw material powder. These raw material powder mixtures are calcined at 700 to 1200 ° C. for 1 to 5 hours in an air atmosphere to prepare calcined powder. Then, the calcined powder is pulverized by a wet ball mill or the like and adjusted to a predetermined particle size, and then dissolved in a solvent such as terpineol or butyl carbitol together with a binder such as ethyl cellulose to produce a slurry.

In this embodiment, LFN (LaFe _0.5 Ni _0.5 O ₃ ) powder having a specific surface area of 8.0 [m ² / g] is used as the raw material powder for the perovskite phase, and the raw material for rare earth-added ceria is used. As the powder, GDC (20 mol% Gd—CeO ₂ ) powder having a specific surface area of 30.0 [m ² / g] was used. Moreover, in this embodiment, the raw material powder mixture prepared so that LFN powder and GDC powder might each be 50 volume% was used.

The production step of the conductive oxide (without ceria) slurry (slurry of the lead layer 33) does not mix at least the rare earth-added ceria raw material powder compared to the production step of the conductive oxide (with ceria) slurry. The difference is that a pore former is added. In the production of the slurry of conductive oxide (without ceria), for example, the raw material powder mixture is prepared by weighing the raw material powder of the conductive oxide and then wet-mixing and drying. In the present embodiment, LFN (LaFe _0.5 Ni _0.5 O ₃ ) powder having a specific surface area of 1.5 [m ² / g] was used as the raw material powder for the perovskite phase. A slurry obtained by adding 30% by volume of carbon to this powder was dissolved in a solvent such as terpineol or butyl carbitol together with a binder such as ethyl cellulose.

In the preparation of the slurry for the reaction preventing layer, the raw material powder of the rare earth-added ceria is dissolved in a solvent such as terpineol or butyl carbitol together with a binder such as ethyl cellulose to prepare a slurry. In addition to CeO ₂ , La ₂ O ₃ , Gd ₂ O ₃ , Sm ₂ O ₃ , Y ₂ O _{3 and the} like can be used as the rare earth-added ceria raw material powder. In the present embodiment, GDC (20 mol% Gd—CeO ₂ ) powder having a specific surface area of 10 [m ² / g] was used as the rare earth-added ceria. As described above, the reaction preventing layer 31 is formed of rare earth-added ceria.

Next, in a 3rd process, each slurry is apply | coated to the formation part of the outer side electrode 27, the inner side detection electrode part 30a, and the inner side lead part 30b among unsintered molded objects.
First, a noble metal slurry such as a Pt paste is applied to the formation part of the outer electrode 27, and a rare earth-added ceria slurry is applied to the formation part of the reaction preventing layer 31. After application of the slurry for the reaction preventing layer 31, the slurry for the electrode layer 32 is applied, and then the slurry for the lead layer 33 (the tip lead layer 33a of the inner detection electrode portion 30a, the rear end lead layer 33b of the inner lead portion 30b). Apply.

  As described above, the electrode layer 32 includes a perovskite phase and a rare earth-added ceria. On the other hand, the lead layer 33 (front end lead layer 33a, rear end lead layer 33b) does not contain rare earth-added ceria and is composed only of a perovskite phase. Therefore, in the third step, the slurry suitable for each part is prepared by using the two types of conductive oxide slurry (with ceria and without ceria) produced in the second step and the slurry of the reaction preventing layer 31. Apply.

That is, when applying the slurry of the electrode layer 32, the conductive oxide (ceria-containing) slurry is applied to the portion where the electrode layer 32 is formed (the portion where the slurry of the reaction preventing layer 31 is applied).
Further, when applying the slurry of the lead layer 33 (the tip lead layer 33a and the rear lead layer 33b), the inner detection electrode portion 30a formation portion (the slurry application portion of the electrode layer 32) and the inner lead portion 30b are formed. A slurry of conductive oxide (without ceria) is applied to each of the portions. In the present embodiment, the leading end lead layer 33a and the trailing end lead layer 33b are formed of the same conductive oxide. In addition, what is necessary is just to apply | coat the slurry of a different composition to each part, when making the composition of each conductive oxide of the front-end lead layer 33a and the rear-end lead layer 33b differ.

  In the next fourth step, the green compact coated with each slurry is dried and then fired at a predetermined firing temperature (for example, 1250 ° C. or higher and 1450 ° C. or lower (preferably 1350 ± 50 ° C.)). . In this firing step, a reaction layer 34 is formed between the rear end lead layer 33b of the inner lead portion 30b and the element main body 21, but between the electrode layer 32 of the inner detection electrode portion 30a and the element main body 21. Since the reaction preventing layer 31 is formed, the reaction layer 34 is not formed.

As described above, the reaction layer 34 is a layer formed by a reaction between lanthanum (La) contained in the inner lead portion 30 b and ZrO ₂ contained in the element body 21. The thickness dimension of the reaction layer 34 increases as the firing temperature increases, and increases as the content ratio of the rare earth-added ceria decreases. Therefore, it is possible to adjust the thickness of the reaction layer 34 by adjusting these parameters (firing temperature, content ratio of rare earth-added ceria).

The gas sensor element 3 can be manufactured by performing each of the above steps.
[1-4. Gas sensor element evaluation test]
Test results of an evaluation test carried out to evaluate the thermal shock resistance and low temperature operability of the gas sensor element to which the present invention is applied will be described.

  The thermal shock resistance is an index representing the resistance to the thermal shock (stress) generated with temperature change, and among the gas sensor elements, the thermal shock resistance is inferior as the gas sensor element is easily damaged. The more resistant to thermal shock, the better the thermal shock resistance.

  The low temperature operability is an index indicating that gas detection is possible even in a low temperature (for example, 300 ° C. or lower) environment. Among the gas sensor elements, the higher the internal resistance value between the outer electrode and the inner electrode, the lower the low temperature operability, and the lower the internal resistance value between the outer electrode and the inner electrode, the lower the temperature operability. It is excellent.

  In this evaluation test, among the gas sensor elements, the thickness dimension T1 of the reaction prevention layer 31, the thickness dimension T2 of the electrode layer 32, the thickness dimension T3 of the lead layer 33, the porosity B1 of the reaction prevention layer 31, and the electrode layer 32 The thermal shock resistance and the low temperature operability of the gas sensor element were evaluated by changing the porosity B2 and the porosity B3 of the lead layer 33, respectively. Control of the thickness dimension in each layer can be realized by changing the number of times the slurry is applied at the time of production, the solid content concentration, and the like. Moreover, the control of the porosity in each layer can be realized by adjusting the amount of pore-forming material added during production.

Regarding the thermal shock resistance test, a thermal cycle test was performed on the gas sensor element, and the thermal shock resistance was evaluated based on whether or not a crack (breakage) occurred in the gas sensor element.
In this test, the gas sensor element 3 was changed from room temperature (20 ° C.) to 970 ° C. and then lowered to room temperature as one cycle. Based on the cross-sectional SEM image of the element, it was determined whether or not the gas sensor element 3 was damaged.

Regarding the low temperature operability test, the internal resistance value between the outer electrode 27 and the inner electrode 30 of the gas sensor element was measured, and the low temperature operability of the gas sensor element was evaluated based on the internal resistance value.
In this test, with the gas sensor element assembled to the gas sensor, the gas sensor was attached to a known burner measuring apparatus, and the internal resistance value of the gas sensor element was measured by a burner measurement method. Specifically, sensor output at an element temperature of 300 ° C. at an air-fuel ratio λ = 0.9 (rich) is detected with an oscilloscope using two resistance elements (1 MΩ, 100 kΩ) having different resistance values, and based on the output difference. The internal resistance value of the gas sensor element was calculated. A gas sensor element whose internal resistance value is in a gas detectable range (in this embodiment, 100 [kΩ] or less) is determined to have good low-temperature operability, and a gas sensor element whose internal resistance value deviates from the gas detectable range is selected. It was determined that the low temperature operability was poor.

  As the gas sensor elements of Examples 1 to 5 and the gas sensor element of the comparative example, the thickness dimension T1 of the reaction preventing layer 31, the thickness dimension T2 of the electrode layer 32, the thickness dimension T3 of the lead layer 33, and the reaction preventing layer 31 The gas sensor elements having the porosity B1, the porosity B2 of the electrode layer 32, and the porosity B3 of the lead layer 33, which are values shown in [Table 1], were used. In each gas sensor element, the evaluation results of the presence or absence of cracks (breakage) after the cooling / heating cycle test (after 100 cycles and 300 cycles) and the evaluation results of low temperature operability are shown in [Table 1].

FIG. 5 is an explanatory diagram showing cross-sectional SEM images before and after the cooling cycle test in the gas sensor element 3 of Example 1. FIG. 6 is an explanatory diagram showing cross-sectional SEM images before and after the cooling cycle test in the gas sensor element of the comparative example.

  As can be seen from the cross-sectional SEM image, in the gas sensor element 3 of Example 1, no damage occurred in any of the reaction prevention layer, the electrode layer, and the lead layer after the thermal cycle test, whereas the gas sensor of the comparative example In the element 3, after the thermal cycle test, a crack (breakage) from the lead layer to the solid electrolyte body (element body) via the electrode layer and the reaction preventing layer occurs.

  Among these test results, according to the comparison between Examples 1 to 5 and the comparative example, the thickness dimension of the reaction prevention layer is smaller than the thickness dimension of the lead layer, and the thickness dimension of the electrode layer is reaction prevention. As can be seen from the evaluation results after the thermal cycle test (after 300 cycles), the gas sensor element set to be equal to or greater than the thickness dimension of the layer is less susceptible to cracking (breakage).

  Of these test results, according to Examples 1 to 5 and the comparative example, the gas sensor element in which the thickness dimension of the lead layer is larger than the thickness dimension of the reaction preventing layer can be understood from the evaluation result of the low temperature operability. In addition, since the electrical resistance value in the lead layer can be reduced and the internal resistance value as the gas sensor element can be reduced, gas detection is possible even in a low temperature (300 ° C. or lower) environment where the activation state of the solid electrolyte body is low.

  Further, among the test results, according to Examples 1 to 5 and the comparative example, the gas sensor in which the porosity of the reaction preventing layer is set to the lowest among the porosities of the reaction preventing layer, the electrode layer, and the lead layer. As can be seen from the evaluation result of the low temperature operability, the element can reduce the interface resistance value between the solid electrolyte body and the electrode layer, and as a result, the internal resistance value as the gas sensor element can be further reduced. it can. For this reason, gas detection is possible even in a low temperature (300 ° C. or lower) environment where the activated state of the solid electrolyte body is low, and the low temperature operability of the gas sensor element is further improved.

  Further, according to the test results, “the thickness dimension of the reaction preventing layer is smaller than the thickness dimension of the lead layer”, “the thickness dimension of the electrode layer is equal to or larger than the thickness dimension of the reaction preventing layer, and the lead layer The thickness dimension T1 of the reaction preventing layer 31 is in the range of 1 to 10 μm, and the thickness dimension T2 of the electrode layer 32 is in the range of 3 to 30 μm. The gas sensor element 3 having the thickness dimension T3 of the lead layer 33 in the range of 5 to 40 μm can suppress the damage of the gas sensor element due to thermal shock, and the low temperature operability of the gas sensor element is improved.

  Furthermore, according to the test results, the porosity B1 of the reaction preventing layer 31 is in the range of 0 to 10%, the porosity B2 of the electrode layer 32 is in the range of 10 to 30%, and the porosity of the lead layer 33 is The gas sensor element 3 in which the rate B3 is in the range of 35 to 60% can suppress damage to the gas sensor element due to thermal shock, and the low temperature operability of the gas sensor element is improved.

[1-5. effect]
As described above, in the gas sensor element 3 provided in the gas sensor 1 of the present embodiment, the inner electrode 30 has the reaction preventing layer 31, the electrode layer 32, the lead layer 33 (the tip lead 33) in order from the side closer to the element body 21. It is a multilayer structure in which layers 33a) are stacked. The reaction preventing layer 31 and the electrode layer 32 each contain rare earth-added ceria. The electrode layer 32 and the lead layer 33 are each formed to include a conductive oxide layer containing the above-described perovskite phase.

  As described above, in the gas sensor element 3, since the electrode layer 32 and the lead layer 33 are configured to include the conductive oxide layer containing the perovskite phase, the electrode layer and the lead layer are configured using a noble metal. Compared to the case of manufacturing, it can be manufactured at a low cost.

  In the gas sensor element 3, the thickness dimension T1 (= 2 μm) of the reaction preventing layer 31 is smaller than the thickness dimension T3 (= 16 μm) of the lead layer 33, and the thickness dimension T2 (= 11 μm) of the electrode layer 32 is The reaction prevention layer 31 has a thickness dimension T1 or more and the lead layer 33 has a thickness dimension T3 or less.

  That is, in the gas sensor element 3, the thickness dimension T1 of the reaction preventing layer 31 is smaller than the thickness dimension T3 of the lead layer 33, and the thickness dimension T2 of the electrode layer 32 is equal to or larger than the thickness dimension T1 of the reaction preventing layer 31. Is set to According to the test results shown in the above [Table 1] (specifically, the comparison between Examples 1 to 5 and the comparative example), the gas sensor element 3 has a thickness dimension of the reaction preventing layer of the lead layer and The thermal shock resistance in the cooling / heating cycle is higher than that of the configuration in which the electrode layer is formed larger than each thickness dimension.

  The gas sensor element 3 has a configuration in which the thickness dimension T3 of the lead layer 33 is larger than the thickness dimension T1 of the reaction preventing layer 31, and the test results shown in the above [Table 1] 5 and Comparative Example), the electrical resistance value in the lead layer 33 can be reduced. Thereby, since the gas sensor element 3 can reduce the internal resistance value as a gas sensor element, gas detection is possible even in a low temperature (300 ° C. or lower) environment where the activation state of the element body 21 (solid electrolyte body) is low. .

Therefore, this gas sensor element 3 is advantageous in that it is inexpensive, has thermal shock resistance, and has low temperature operability.
Next, in the gas sensor element 3, the pores of the reaction preventing layer 31 out of the respective porosities (B1 = 1%, B2 = 21%, B3 = 46%) of the reaction preventing layer 31, the electrode layer 32, and the lead layer 33. The reaction preventing layer 31, the electrode layer 32, and the lead layer 33 are formed so that the rate B1 is the lowest.

Since the porosity B1 of the reaction preventing layer 31 is the lowest, the density of the reaction preventing layer 31 is increased, so that the interface resistance value between the element body 21 and the electrode layer 32 can be reduced.
The gas sensor 1 including such a gas sensor element 3 is advantageous in that it is inexpensive, has thermal shock resistance, and has low temperature operability.

[1-6. 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 reaction preventing layer 31 corresponds to an example of a reaction preventing layer, the electrode layer 32 corresponds to an example of an electrode layer, and the lead layer 33 (tip lead layer 33a) corresponds to an example of a lead 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. 7 is a perspective view of the plate-type gas sensor element 100. FIG. 8 is a schematic exploded perspective view of the plate-type gas sensor element 100. FIG. 9 is a partial enlarged cross-sectional view of the distal end side of the plate type gas sensor element 100. FIG. 10 is a partially enlarged cross-sectional view of a region where the reference electrode portion 104a of the reference electrode 104 is formed in the plate-type gas sensor element 100.

The plate type gas sensor element 100 includes an element body 101 and a porous protective layer 120.
As shown in FIG. 8, 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 addition, illustration of the porous protective layer 120 is abbreviate | omitted in FIG.

  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. As shown in FIG. 10, the reference electrode portion 104a has a multilayer structure in which a reaction preventing layer 104b, an electrode layer 104c, and a lead layer 104d are stacked in this order from the side closer to the solid electrolyte body 105. 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 that of the solid electrolyte body 105, and includes a protective part arrangement space 112a penetrating 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 part 113a protects the measurement electrode part 106a by sandwiching the measurement electrode part 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. 8) 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, as shown in FIG. 7, 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. 9, 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 extend to the rear end side along the axial direction (left-right direction in the figure). ing. Further, as shown in FIG. 7, 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 measurement electrode, and a reference electrode, 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.
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.).

Of the reference electrode portion 104a of the reference electrode 104, the reaction preventing layer 104b is an oxide layer formed of rare earth-added ceria. The rare earth-added ceria is a ceria to which a rare earth oxide other than ceria is added. As the “rare earth oxide other than ceria”, La ₂ O ₃ , Gd ₂ O ₃ , Sm ₂ O ₃ , Y ₂ O _{3 and the} like can be used. Such a reaction preventing layer 104b is an insulator at a low temperature (room temperature), but has an oxygen ion conductivity at a high temperature (when the plate-type gas sensor element 100 is used), and the electrode layer 104c and the solid electrolyte. It functions as a layer for electrically connecting the body 105. The reaction preventing layer 104b has a function of making it difficult to cause a reaction between La of the electrode layer 104c and ZrO ₂ of the solid electrolyte body 105 when the plate-type gas sensor element 100 is manufactured (at the time of firing). By providing such a reaction preventing layer 104b, it is possible to suppress the formation of a lanthanum zirconate layer (reaction layer) due to the reaction between La of the electrode layer 104c and ZrO ₂ of the solid electrolyte body 105.

  The electrode layer 104c includes a perovskite phase and a rare earth-added ceria. The perovskite phase contained in the electrode layer 104c has a perovskite-type oxide crystal structure that satisfies the above conditions (1), (2a), (2b), and (2c) as in the electrode layer 32 of the first embodiment. It is a crystal phase (perovskite phase) having Since such an electrode layer 104c has both ionic conductivity and electronic conductivity properties at a high temperature (when the plate-type gas sensor element 100 is used), it exhibits a sufficiently low interface resistance value.

  Similar to the lead layer 33 of the first embodiment, the lead layer 104d has a crystal phase having a perovskite oxide crystal structure that satisfies the above conditions (1), (2a), (2b), and (2c) ( Perovskite phase) as a main component. Note that the lead layer 104d of this embodiment does not contain rare earth-doped ceria.

The reference lead portion 104L is formed of the same material as the lead layer 104d.
The thickness dimension of the solid electrolyte body 105 is 200 μm, the thickness dimension of the measurement electrode 106 is 3 μm, the thickness dimension T4 of the reaction preventing layer 104b in the reference electrode portion 104a of the reference electrode 104 is 2 μm, The electrode layer 104c has a thickness dimension T5 of 11 μm, and the lead layer 104d has a thickness dimension T6 of 16 μm.

Further, the porosity B4 of the reaction preventing layer 104b is 1%, the porosity B5 of the electrode layer 104c is 21%, and the porosity B6 of the lead layer 104d is 46%.
In the porous protective layer 120, at least a portion covering the measurement electrode 106 is formed of spinel (MgAl ₂ O ₄ ) and titania (TiO ₂ ), and at least one of noble metals (Pt, Pd, Rh). Is carried. This noble metal functions as a catalyst for promoting the chemical reaction of oxygen contained in the exhaust gas. The porous protective layer 120 is formed in a porous shape with a porosity of 52%.

  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 made of zirconia (5YSZ) stabilized with 5 mol% yttria. 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.

[2-2. effect]
As described above, in the plate-type gas sensor element 100 of the second embodiment, the reference electrode portion 104a of the reference electrode 104 is in order from the side closer to the solid electrolyte body 105, the reaction preventing layer 104b, the electrode layer 104c, and the lead layer. This is a multilayer structure in which 104d are stacked. The reaction preventing layer 104b and the electrode layer 104c each contain rare earth-added ceria. The electrode layer 104c and the lead layer 104d are each formed including the conductive oxide layer containing the above-described perovskite phase.

  Thus, in the plate-type gas sensor element 100, since the electrode layer 104c and the lead layer 104d are configured to include the conductive oxide layer containing the above-described perovskite phase, the electrode layer and the lead layer are made of a noble metal. Compared with the case where it comprises, it can manufacture cheaply.

  In the plate-type gas sensor element 100, the thickness dimension T4 (= 2 μm) of the reaction preventing layer 104b is smaller than the thickness dimension T6 (= 16 μm) of the lead layer 104d, and the thickness dimension T5 (= 11 μm) of the electrode layer 104c. ) Is not less than the thickness dimension T4 of the reaction preventing layer 104b and not more than the thickness dimension T6 of the lead layer 104d.

  That is, in the plate type gas sensor element 100, the thickness dimension T4 of the reaction preventing layer 104b is smaller than the thickness dimension T6 of the lead layer 104d, and the thickness dimension T5 of the electrode layer 104c is the thickness dimension of the reaction preventing layer 104b. It is set to T4 or more. Such a plate-type gas sensor element 100 has higher thermal shock resistance in a cooling cycle than a configuration in which the thickness dimension of the reaction preventing layer is formed larger than the thickness dimensions of the lead layer and the electrode layer.

  The plate type gas sensor element 100 has a configuration in which the thickness dimension T6 of the lead layer 104d is larger than the thickness dimension T4 of the reaction preventing layer 104b, and can reduce the electric resistance value in the lead layer 104d. Thereby, since the plate-type gas sensor element 100 can reduce the internal resistance value as a gas sensor element, gas detection is possible even in a low temperature (300 ° C. or lower) environment where the activation state of the solid electrolyte body 105 is low.

Therefore, the plate-type gas sensor element 100 is advantageous in that it is inexpensive, has thermal shock resistance, and has low temperature operability.
Next, in the plate-type gas sensor element 100, the reaction preventing layer 104b out of the respective porosity (B4 = 1%, B5 = 21%, B6 = 46%) of the reaction preventing layer 104b, the electrode layer 104c, and the lead layer 104d. The reaction preventing layer 104b, the electrode layer 104c, and the lead layer 104d are formed so that the porosity B4 of the layer is the lowest.

  Since the porosity B4 of the reaction preventing layer 104b is the lowest, the density of the reaction preventing layer 104b is increased, so that the interface resistance value between the solid electrolyte body 105 and the electrode layer 104c can be reduced.

A gas sensor including such a plate-type gas sensor element 100 is advantageous in that it is inexpensive, has thermal shock resistance, and has low temperature operability.
[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 solid electrolyte body 105 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. To do.

The reaction preventing layer 104b corresponds to an example of a reaction preventing layer, the electrode layer 104c corresponds to an example of an electrode layer, and the lead layer 104d corresponds to an example of a lead 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 (thickness dimension, porosity, etc.) in the measurement electrode (outer electrode), the reference electrode (inner electrode), the solid electrolyte body (element body), etc. are specified. Is not limited to the above numerical values, and can take any value as long as it is included in the technical scope of the present invention.

  In the above embodiment, the gas sensor element has been described in which the reference electrode (inner electrode) has a multilayer structure (a multilayer structure in which a reaction preventing layer, an electrode layer, and a lead layer are laminated). It is not limited to. The gas sensor element to which the present invention is applied may be, for example, a gas sensor element in which the measurement electrode (outer electrode) has a multilayer structure (a multilayer structure in which a reaction preventing layer, an electrode layer, and a lead layer are laminated), or a reference electrode ( A gas sensor element in which each of the inner electrode) and the measurement electrode (outer electrode) has a multilayer structure may be used.

  Next, in the above 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 the plate type gas sensor element of the above second embodiment. . 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 above-described embodiment, the gas sensor element including the lead layer having the above-described perovskite phase as a main component and including no rare earth-added ceria has been described as the lead layer. However, the lead layer is limited to such a configuration. There is nothing. For example, the lead layer may have a configuration including rare earth-doped ceria, and the lead layer having such a configuration may reduce the internal resistance value between the outer electrode and the inner electrode when the gas sensor element is used. Is possible. However, in order to reduce the electrical resistance value of the lead layer at room temperature, it is preferable to adopt a configuration that does not include rare earth-doped ceria.

  Next, in the above-described embodiment, the form using the material in which M is Fe as the perovskite phase has been described, but the present invention is not limited to such a form. For example, even if the perovskite phase uses a material in which M is Co or a material in which M is a mixture of Fe and Co, the same effects as those in the above embodiment can be obtained.

  DESCRIPTION OF SYMBOLS 1 ... Gas sensor, 3 ... Gas sensor element, 13 ... Main metal fitting, 15 ... Protector, 21 ... Element main body, 23 ... Element collar part, 25 ... Tip part, 27 ... Outer electrode, 28 ... Annular lead part, 29 ... Vertical lead part 30 ... Inner electrode, 30a ... Inner sensing electrode part, 30b ... Inner lead part, 31 ... Reaction prevention layer, 32 ... Electrode layer, 33 ... Lead layer, 33a ... Front lead layer, 33b ... Rear end lead layer, 34 ... Lanthanum zirconate layer (reaction layer), 100 ... plate type gas sensor element, 101 ... element body, 104 ... reference electrode, 104a ... reference electrode portion, 104b ... reaction prevention layer, 104c ... electrode layer, 104d ... lead layer, 104L ... Reference lead 105, solid electrolyte body 106, measurement electrode 106a, measurement electrode 106L, detection lead 130, oxygen concentration detection cell.

Claims (7)

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,
At least one of the measurement electrode and the reference electrode has a multilayer structure in which a reaction preventing layer, an electrode layer, and a lead layer are laminated in order from the side close to the solid electrolyte body,
The reaction preventing layer and the electrode layer each contain rare earth-added ceria,
Each of the electrode layer and the lead layer has a perovskite crystal structure represented by a composition formula: LaaMbNicOx (M is one or more of Co and Fe, a + b + c = 1, 1.25 ≦ x ≦ 1.75). A conductive oxide layer containing a perovskite phase, wherein a, b, c are 0.459 ≦ a ≦ 0.535, 0.200 ≦ b ≦ 0.475, 0.025 ≦ c ≦ 0.350 Meets
The thickness dimension of the reaction preventing layer is smaller than the thickness dimension of the lead layer,
The thickness dimension of the electrode layer is not less than the thickness dimension of the reaction preventing layer and not more than the thickness dimension of the lead layer.
Gas sensor element. Of the porosity of the reaction preventing layer, the electrode layer, and the lead layer, the porosity of the reaction preventing layer is the lowest,
The gas sensor element according to claim 1. The thickness dimension of the reaction preventing layer, the thickness dimension of the electrode layer, and the thickness dimension of the lead layer each satisfy the above-mentioned magnitude relationship,
The thickness of the reaction preventing layer is in the range of 1 to 10 μm,
The thickness dimension of the electrode layer is in the range of 3 to 30 μm,
The thickness dimension of the lead layer is in the range of 5 to 40 μm.
The gas sensor element according to claim 1 or 2. The porosity of the reaction preventing layer is in the range of 0 to 10%,
The porosity of the electrode layer is in the range of 10-30%,
The porosity of the lead layer is in the range of 35-60%,
The gas sensor element according to any one of claims 1 to 3. The reference electrode has a multilayer structure in which the reaction preventing layer, the electrode layer, and the lead layer are laminated.
The gas sensor element according to any one of claims 1 to 4. The solid electrolyte body is a bottomed cylinder type or a plate type,
The gas sensor element according to any one of claims 1 to 5. A gas sensor including a gas sensor element for detecting a specific gas contained in a measurement target gas,
As the gas sensor element, comprising the gas sensor element according to any one of claims 1 to 6,
Gas sensor.