JP7333248B2 - Sensor element and gas sensor - Google Patents

Description

The present invention relates to sensor elements and gas sensors.

2. Description of the Related Art Conventionally, there has been known a gas sensor provided with a sensor element for detecting the concentration of a specific gas such as NOx in a gas to be measured such as automobile exhaust gas. Among such gas sensors, there is known one that includes a protective layer that covers the surface of the sensor element, and that the protective layer has a space (for example, Patent Document 1). In Patent Document 1, the protective layer has an exposed space where the surface of the element body is exposed. This exposed space can suppress cooling of the element body when water adheres to the surface of the protective layer, and can improve water resistance of the element body.

JP 2016-188853 A

By the way, when the sensor element detects the concentration of the specific gas in the gas to be measured, the concentration of the detected specific gas may vary even if the concentration of the specific gas does not actually fluctuate.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems, and a main object of the present invention is to suppress variations in concentration of a specific gas detected by a sensor element.

The present invention employs the following means in order to achieve the above main object.

The sensor element of the present invention is
A sensor element for detecting a specific gas concentration in a gas to be measured,
an element main body having an oxygen ion-conducting solid electrolyte body and provided therein with a measured gas flow section for introducing and circulating a measured gas;
a measuring electrode disposed on the inner peripheral surface of the measured gas flow portion;
a reference electrode disposed in the element main body and exposed to a reference gas serving as a reference for detecting the concentration of the specific gas;
a porous protective layer covering part of the surface of the element body;
with
The protective layer has an inlet protective layer that covers a gas inlet serving as an inlet of the gas flow section to be measured and at least a portion of the surface where the gas inlet is open on the surface of the element body. ,
The inlet protective layer has an internal space,
At least one of the arithmetic average roughness Rap of the inner peripheral surface of the inner space of the inlet protective layer being 8 μm or more, or the arithmetic average roughness Rac of the adhesive surface of the protective layer to the element body being greater than satisfies the conditions of
It is.

This sensor element includes a measurement electrode disposed on the inner peripheral surface of the gas flow portion to be measured, and a reference electrode exposed to a reference gas serving as a reference for detecting the specific gas concentration. This sensor element can detect the specific gas concentration in the gas to be measured based on the voltage between the measurement electrode and the reference electrode. Further, the sensor element includes an inlet protective layer covering the gas inlet serving as the inlet of the gas flow part to be measured and at least a part of the surface where the gas inlet is open on the surface of the element body. there is Then, whether the arithmetic mean roughness Rap of the inner peripheral surface of the internal space of the inlet protective layer is 8 μm or more or is larger than the arithmetic mean roughness Rac of the adhesive surface of the protective layer with the element body. Satisfy at least one condition. That is, the arithmetic mean roughness Rap of the inner peripheral surface of the internal space of the introduced protective layer is relatively large, and the unevenness of the inner peripheral surface is relatively large. As a result, when the gas to be measured passes through the inner space of the inlet protective layer from the outside of the protective layer and reaches the gas inlet, the unevenness of the inner peripheral surface of the inner space disturbs the gas to be measured in the inner space. A flow is generated, and the gas to be measured is agitated by the turbulent flow, and the specific gas concentration in the gas to be measured is homogenized. Therefore, variations in the specific gas concentration in the measured gas introduced into the measured gas flow section are suppressed, and voltage fluctuations between the measurement electrode and the reference electrode due to variations in the specific gas concentration are suppressed. be. As a result, it is possible to suppress variations in the concentration of the specific gas detected by the sensor element.

In this case, the arithmetic mean roughness Rap may be 100 μm or less. If the arithmetic mean roughness Rap is more than 100 μm, the measured gas becomes difficult to flow due to the unevenness of the inner peripheral surface of the inner space of the inlet protective layer, and the gas to be measured becomes difficult to reach the gas inlet, resulting in the response of the sensor element. performance may be reduced. When the arithmetic mean roughness Rap is 100 μm or less, such a decrease in responsiveness can be suppressed. The gas inlet may open into the internal space of the inlet protective layer. The internal space of the inlet protective layer may be an exposed space where the surface of the element body is exposed. The element body may have an elongated shape having a longitudinal direction. The element main body may have an elongated rectangular parallelepiped shape.

In the sensor element of the present invention, the arithmetic mean roughness Rap may be 10 μm or more. When the arithmetic mean roughness Rap is 10 μm or more, the effect of suppressing variations in specific gas concentration detected by the sensor element is enhanced. The arithmetic mean roughness Rap may be 20 μm or more, or may be 30 μm or more.

In the sensor element of the present invention, the arithmetic mean roughness Rac may be 0.1 μm or more and 1.0 μm or less. When the arithmetic mean roughness Rac is 0.1 μm or more, the adhesion strength between the element main body and the protective layer can be secured. When the arithmetic mean roughness Rac is 1.0 μm or less, the strength of the protective layer can be secured.

In the sensor element of the present invention, the surface of the element body has a surface in which the gas introduction port is open and one or more adjacent surfaces that are in contact with the surface at sides of the surface, and the protection The layer has an adjacent surface protective layer covering at least a portion of the one or more adjacent surfaces, the adjacent surface protective layer directly communicating with the internal space of the inlet protective layer, and It may have an internal space that satisfies at least one of the arithmetic mean roughness Ras of the peripheral surface being 8 μm or more and being greater than the arithmetic mean roughness Rac. By doing so, the presence of the adjacent surface protective layer can improve the water resistance of the element body. Moreover, since the adjacent surface protective layer has an internal space, heat conduction in the thickness direction of the adjacent surface protective layer from the outside of the adjacent surface protective layer toward the element body can be suppressed by the internal space, and the element body is water resistant. is better. In addition, since the internal space of the adjacent surface protective layer and the internal space of the inlet protective layer are in direct communication, the internal space of the adjacent surface protective layer is relatively wide, and the element main body is water resistant. is further improved. Further, the arithmetic mean roughness Ras of the inner peripheral surface of the inner space of the adjacent surface protective layer satisfies at least one condition of 8 μm or more or greater than the arithmetic mean roughness Rac. That is, the adjacent surface protective layer has an internal space in which the arithmetic mean roughness Ras of the inner peripheral surface is relatively large. As a result, the unevenness of the inner space of the adjacent surface protective layer causes a turbulent flow in the gas to be measured in the inner space, making it difficult for the gas to be measured to flow from the inner space of the inlet protective layer into the inner space of the adjacent surface protective layer. . Therefore, the gas to be measured in the inner space of the adjacent surface protective layer easily flows into the gas to be measured circulation portion from the gas inlet, thereby improving the responsiveness of the sensor element. That is, the internal space of the adjacent surface protective layer and the internal space of the inlet protective layer are in direct communication with each other, so that the water resistance of the element main body is improved and the arithmetic mean roughness Ras is relatively large. can suppress the decrease in responsiveness due to the direct communication between the two spaces. Here, "directly communicating" means communicating without passing through pores in the protective layer.

In the sensor element of the present invention, the element body may have an elongated shape with a longitudinal direction, and the surface on which the gas introduction port is open may be an end surface in the longitudinal direction.

In this case, the element main body is a laminate in which a plurality of the solid electrolyte bodies are laminated in a lamination direction perpendicular to the longitudinal direction, and the surface of the element main body includes the end face and sides of the end face. and a plurality of adjacent surfaces in contact with each other, the protective layer having an adjacent surface protective layer covering the plurality of adjacent surfaces, and the adjacent surface protective layer covering the adjacent surfaces in the stacking direction An inner space, an outer protective layer positioned outside the inner space, and an outer protective layer positioned outside the inner space and adhered to the surface of the element main body positioned inside the inner space are provided on the portions covering the upper and lower surfaces located at both ends of the and an inner protective layer comprising: By doing so, the presence of the inner protective layer in contact with the upper and lower surfaces increases the heat capacity of the element body (more precisely, the element body and the inner protective layer). Therefore, even if a thermal shock reaches the element main body side from the outside, the rapid temperature change of the element main body is suppressed. As a result, the water resistance of the element body is improved.

A gas sensor of the present invention includes the sensor element according to any one of the aspects described above. Therefore, this gas sensor can obtain the same effect as the sensor element of the present invention described above, for example, the effect of suppressing the variation in concentration of the specific gas detected by the sensor element.

3 is a perspective view of the sensor element 101; FIG. FIG. 2 is a cross-sectional view schematically showing the configuration of the gas sensor 100; FIG. 3 is an enlarged view of the periphery of the measured gas flow section 9 of FIG. 2; BB sectional view of FIG. Sectional drawing of the protective layer 184 of a modification. Sectional drawing of the protective layer 284 of a modification. Sectional drawing of the protective layer 284 of a modification. 7 is a graph showing the relationship between the arithmetic mean roughness Rap and the variation rate of the detected value of the sensor element 101 in Experimental Examples 1 to 7;

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of a sensor element 101 included in a gas sensor 100 according to one embodiment of the invention. FIG. 2 is a cross-sectional view schematically showing the configuration of the gas sensor 100. As shown in FIG. The cross-sectional portion of the sensor element 101 in FIG. 2 is the AA cross section in FIG. FIG. 3 is an enlarged view of the periphery of the measured gas circulation section 9 of FIG. FIG. 4 is a cross-sectional view along BB in FIG. In FIG. 4, illustration of the inside of the cross section of the element main body 102 other than the gas flow part 9 to be measured is omitted. The sensor element 101 has a long rectangular parallelepiped shape. do. Also, the width direction of the sensor element 101 (the direction perpendicular to the front-back direction and the up-down direction) is defined as the left-right direction.

The gas sensor 100 is attached to a pipe such as an exhaust gas pipe of a vehicle, for example, and used to measure the concentration of specific gases such as NOx and O ₂ contained in the exhaust gas as the gas to be measured. In this embodiment, the gas sensor 100 measures the NOx concentration as the specific gas concentration. The gas sensor 100 has a sensor element 101 . The sensor element 101 includes an element body 102 and a porous protective layer 84 covering the element body 102 . Note that the element body 102 refers to the portion of the sensor element 101 other than the protective layer 84 .

As shown in FIG. 2, the sensor element 101 includes a first substrate layer 1, a second substrate layer 2, and a third substrate layer 3 each made of an oxygen ion conductive solid electrolyte layer such as zirconia (ZrO ₂ ). , a first solid electrolyte layer 4, a spacer layer 5, and a second solid electrolyte layer 6 are stacked in this order from the bottom as viewed in the drawing. Also, the solid electrolyte forming these six layers is dense and airtight. The sensor element 101 is manufactured by, for example, performing predetermined processing and circuit pattern printing on ceramic green sheets corresponding to each layer, laminating them, and firing them to integrate them.

A gas introduction port 10 and a first diffusion The rate-controlling part 11, the buffer space 12, the second diffusion rate-controlling part 13, the first internal space 20, the third diffusion rate-controlling part 30, and the second internal space 40 communicate with each other in this order. formed adjacent to each other.

The gas introduction port 10 , the buffer space 12 , the first internal space 20 , and the second internal space 40 are formed by hollowing out the spacer layer 5 . The space inside the sensor element 101 is defined by the upper surface of the first solid electrolyte layer 4 at the bottom and the side surface of the spacer layer 5 at the side.

Each of the first diffusion rate-controlling part 11, the second diffusion rate-controlling part 13, and the third diffusion rate-controlling part 30 is provided as two horizontally long slits (the openings of which have the longitudinal direction in the direction perpendicular to the drawing). . A space from the gas introduction port 10 to the second internal space 40 is called a measured gas flow portion 9 . The measured gas flow portion 9 is formed in a substantially rectangular parallelepiped shape. The longitudinal direction of the measured gas flow portion 9 is parallel to the front-rear direction.

In addition, at a position farther from the tip side than the measured gas circulation portion 9, between the upper surface of the third substrate layer 3 and the lower surface of the spacer layer 5, a side portion of the first solid electrolyte layer 4 is provided. A reference gas introduction space 43 is provided at a position defined by . For example, atmospheric air is introduced into the reference gas introduction space 43 as a reference gas when measuring the NOx concentration.

The atmosphere introduction layer 48 is a layer made of porous ceramics, and the reference gas is introduced into the atmosphere introduction layer 48 through the reference gas introduction space 43 . Also, the atmosphere introduction layer 48 is formed so as to cover the reference electrode 42 .

The reference electrode 42 is an electrode formed in a manner sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4, and as described above, is connected to the reference gas introduction space 43 around it. An atmosphere introduction layer 48 is provided. Further, as will be described later, it is possible to measure the oxygen concentration (oxygen partial pressure) in the first internal space 20 and the second internal space 40 using the reference electrode 42 .

In the measured gas circulation portion 9, the gas inlet 10 is a portion that is open to the external space, and the gas to be measured is taken into the sensor element 101 from the outer space through the gas inlet 10. ing. The first diffusion control portion 11 is a portion that imparts a predetermined diffusion resistance to the gas to be measured introduced from the gas inlet 10 . The buffer space 12 is a space provided for guiding the gas to be measured introduced from the first diffusion rate controlling section 11 to the second diffusion rate controlling section 13 . The second diffusion control portion 13 is a portion that imparts a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 12 into the first internal space 20 . When the gas to be measured is introduced from the outside of the sensor element 101 into the first internal space 20, the pressure fluctuation of the gas to be measured in the external space (the pulsation of the exhaust pressure if the gas to be measured is automobile exhaust gas) ) is not directly introduced into the first internal space 20, but rather is introduced into the first diffusion rate-determining portion 11, the buffer space 12, the second After pressure fluctuations of the gas to be measured are canceled out through the diffusion control section 13 , the gas is introduced into the first internal cavity 20 . As a result, pressure fluctuations of the gas to be measured introduced into the first internal cavity 20 are almost negligible. The first internal space 20 is provided as a space for adjusting the oxygen partial pressure in the gas to be measured introduced through the second diffusion control section 13 . The oxygen partial pressure is adjusted by operating the main pump cell 21 .

The main pump cell 21 includes an inner pump electrode 22 having a ceiling electrode portion 22a provided on substantially the entire lower surface of the second solid electrolyte layer 6 facing the first internal cavity 20, and an upper surface of the second solid electrolyte layer 6. This is an electrochemical pump cell composed of an outer pump electrode 23 provided in a region corresponding to the ceiling electrode portion 22a and a second solid electrolyte layer 6 sandwiched between these electrodes.

The inner pump electrode 22 is formed across the upper and lower solid electrolyte layers (the second solid electrolyte layer 6 and the first solid electrolyte layer 4) that define the first internal cavity 20 and the spacer layer 5 that provides side walls. there is Specifically, a ceiling electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 that provides the ceiling surface of the first internal cavity 20, and a bottom electrode portion 22a is formed on the upper surface of the first solid electrolyte layer 4 that provides the bottom surface. A spacer layer in which electrode portions 22b are formed, and side electrode portions (not shown) constitute both side wall portions of the first internal cavity 20 so as to connect the ceiling electrode portion 22a and the bottom electrode portion 22b. 5, and arranged in a tunnel-shaped structure at the arrangement portion of the side electrode portion.

The inner pump electrode 22 and the outer pump electrode 23 are formed as porous cermet electrodes (for example, cermet electrodes of Pt and ZrO ₂ containing 1% Au). The inner pump electrode 22 that comes into contact with the gas to be measured is made of a material that has a weakened ability to reduce NOx components in the gas to be measured.

In the main pump cell 21, a desired pump voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23 to generate a positive or negative pump current between the inner pump electrode 22 and the outer pump electrode 23. By flowing Ip0, it is possible to pump oxygen in the first internal space 20 to the external space, or to pump oxygen in the external space into the first internal space 20 .

In order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere in the first internal space 20, the inner pump electrode 22, the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4 , the third substrate layer 3 and the reference electrode 42 constitute an electrochemical sensor cell, that is, an oxygen partial pressure detection sensor cell 80 for main pump control.

By measuring the electromotive force V0 in the oxygen partial pressure detection sensor cell 80 for controlling the main pump, the oxygen concentration (oxygen partial pressure) in the first internal space 20 can be known. Furthermore, the pump current Ip0 is controlled by feedback-controlling the pump voltage Vp0 of the variable power supply 25 so that the electromotive force V0 becomes a target value. Thereby, the oxygen concentration in the first internal space 20 can be maintained at a predetermined constant value.

The third diffusion control section 30 applies a predetermined diffusion resistance to the gas under measurement whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the main pump cell 21 in the first internal space 20, thereby reducing the gas under measurement. It is a portion that leads to the second internal space 40 .

The second internal space 40 is provided as a space for performing processing related to measurement of nitrogen oxide (NOx) concentration in the gas under measurement introduced through the third diffusion control section 30 . The NOx concentration is measured mainly in the second internal space 40 where the oxygen concentration is adjusted by the auxiliary pump cell 50 and further by the operation of the measuring pump cell 41 .

In the second internal space 40, after the oxygen concentration (oxygen partial pressure) is adjusted in advance in the first internal space 20, the gas to be measured introduced through the third diffusion control section 30 is further subjected to the auxiliary pump cell 50. The oxygen partial pressure is adjusted by As a result, the oxygen concentration in the second internal space 40 can be kept constant with high accuracy, so that the gas sensor 100 can measure the NOx concentration with high accuracy.

The auxiliary pump cell 50 includes an auxiliary pump electrode 51 having a ceiling electrode portion 51a provided over substantially the entire lower surface of the second solid electrolyte layer 6 facing the second internal cavity 40, and an outer pump electrode 23 (outer pump electrode 23 any suitable electrode outside the sensor element 101 ) and the second solid electrolyte layer 6 .

The auxiliary pump electrode 51 is arranged in the second internal space 40 in the same tunnel-like structure as the inner pump electrode 22 provided in the first internal space 20 . That is, the ceiling electrode portion 51a is formed on the second solid electrolyte layer 6 that provides the ceiling surface of the second internal space 40, and the first solid electrolyte layer 4 that provides the bottom surface of the second internal space 40 has , bottom electrode portions 51b are formed, and side electrode portions (not shown) connecting the ceiling electrode portions 51a and the bottom electrode portions 51b are formed on the spacer layer 5 that provides side walls of the second internal cavity 40. It has a tunnel-like structure formed on both walls. As with the inner pump electrode 22, the auxiliary pump electrode 51 is also made of a material having a weakened ability to reduce NOx components in the gas to be measured.

In the auxiliary pump cell 50, by applying a desired voltage Vp1 between the auxiliary pump electrode 51 and the outer pump electrode 23, oxygen in the atmosphere inside the second internal cavity 40 is pumped out to the external space, or It is possible to pump from the space into the second internal cavity 40 .

In order to control the oxygen partial pressure in the atmosphere inside the second internal space 40, the auxiliary pump electrode 51, the reference electrode 42, the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte The layer 4 and the third substrate layer 3 constitute an electrochemical sensor cell, that is, an oxygen partial pressure detection sensor cell 81 for controlling the auxiliary pump.

The auxiliary pump cell 50 performs pumping with the variable power supply 52 whose voltage is controlled based on the electromotive force V1 detected by the oxygen partial pressure detecting sensor cell 81 for controlling the auxiliary pump. Thereby, the oxygen partial pressure in the atmosphere inside the second internal cavity 40 is controlled to a low partial pressure that does not substantially affect the measurement of NOx.

Along with this, the pump current Ip1 is used to control the electromotive force of the oxygen partial pressure detection sensor cell 80 for main pump control. Specifically, the pump current Ip1 is input as a control signal to the oxygen partial pressure detection sensor cell 80 for controlling the main pump, and the above-described target value of the electromotive force V0 is controlled, thereby The gradient of the oxygen partial pressure in the gas to be measured introduced into the second internal space 40 is controlled so that it is always constant. When used as a NOx sensor, the main pump cell 21 and the auxiliary pump cell 50 work to keep the oxygen concentration in the second internal cavity 40 at a constant value of approximately 0.001 ppm.

The measuring pump cell 41 measures the NOx concentration in the gas to be measured in the second internal space 40 . The measurement pump cell 41 includes a measurement electrode 44 provided on the upper surface of the first solid electrolyte layer 4 facing the second internal space 40 and at a position spaced apart from the third diffusion control section 30 , and an outer pump electrode 23 . , a second solid electrolyte layer 6 , a spacer layer 5 and a first solid electrolyte layer 4 .

The measurement electrode 44 is a porous cermet electrode. The measurement electrode 44 also functions as a NOx reduction catalyst that reduces NOx present in the atmosphere within the second internal cavity 40 . Furthermore, the measurement electrode 44 is covered with a fourth diffusion control section 45 .

The fourth diffusion rate controlling portion 45 is a membrane made of a ceramic porous body. The fourth diffusion control section 45 plays a role of limiting the amount of NOx flowing into the measurement electrode 44 and also functions as a protective film for the measurement electrode 44 . In the measurement pump cell 41, oxygen generated by decomposition of nitrogen oxides in the atmosphere around the measurement electrode 44 can be pumped out, and the amount of oxygen generated can be detected as a pump current Ip2.

Also, in order to detect the oxygen partial pressure around the measuring electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, the measuring electrode 44 and the reference electrode 42 form an electrochemical sensor cell, i.e. An oxygen partial pressure detection sensor cell 82 for controlling the measuring pump is configured. The variable power supply 46 is controlled based on the electromotive force V2 detected by the oxygen partial pressure detection sensor cell 82 for controlling the measuring pump.

The measured gas guided into the second internal space 40 reaches the measuring electrode 44 through the fourth diffusion control section 45 under the condition that the oxygen partial pressure is controlled. Nitrogen oxides in the gas to be measured around the measuring electrode 44 are reduced (2NO→N ₂ +O ₂ ) to generate oxygen. The generated oxygen is pumped by the measuring pump cell 41. At this time, the electromotive force V2 detected by the measuring pump controlling oxygen partial pressure detecting sensor cell 82 becomes constant (target value). Thus, the voltage Vp2 of the variable power supply 46 is controlled. Since the amount of oxygen generated around the measuring electrode 44 is proportional to the concentration of nitrogen oxides in the gas to be measured, the pump current Ip2 in the pump cell 41 for measurement is used to measure the nitrogen oxides in the gas to be measured. The concentration will be calculated.

Further, if the measurement electrode 44, the first solid electrolyte layer 4, the third substrate layer 3 and the reference electrode 42 are combined to constitute an oxygen partial pressure detecting means as an electrochemical sensor cell, the measurement electrode 44 can be It is possible to detect the electromotive force corresponding to the difference between the amount of oxygen generated by the reduction of the NOx components in the surrounding atmosphere and the amount of oxygen contained in the reference atmosphere, thereby determining the concentration of the NOx components in the gas to be measured. is also possible.

An electrochemical sensor cell 83 is composed of the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23, and the reference electrode 42. The oxygen partial pressure in the gas to be measured outside the sensor can be detected from the electromotive force Vref obtained by the sensor cell 83 .

In the gas sensor 100 having such a configuration, by operating the main pump cell 21 and the auxiliary pump cell 50, the oxygen partial pressure is always kept at a constant low value (a value that does not substantially affect NOx measurement). A gas to be measured is supplied to the measuring pump cell 41 . Therefore, the NOx concentration in the gas to be measured is determined based on the pump current Ip2 that flows when the oxygen generated by the reduction of NOx is pumped out of the measuring pump cell 41 in substantially proportion to the concentration of NOx in the gas to be measured. It is possible to know.

Further, the sensor element 101 is provided with a heater section 70 that plays a role of temperature adjustment for heating and keeping the sensor element 101 warm in order to increase the oxygen ion conductivity of the solid electrolyte. The heater section 70 includes heater connector electrodes 71 , heaters 72 , through holes 73 , heater insulating layers 74 , and pressure dissipation holes 75 .

The heater connector electrode 71 is an electrode formed so as to be in contact with the lower surface of the first substrate layer 1 . By connecting the heater connector electrode 71 to an external power supply, power can be supplied to the heater section 70 from the outside.

The heater 72 is an electric resistor that is sandwiched between the second substrate layer 2 and the third substrate layer 3 from above and below. The heater 72 is connected to the heater connector electrode 71 through the through hole 73, and generates heat by being supplied with power from the outside through the heater connector electrode 71, thereby heating the solid electrolyte forming the sensor element 101 and keeping it warm. .

Further, the heater 72 is embedded over the entire area from the first internal space 20 to the second internal space 40, and it is possible to adjust the entire sensor element 101 to a temperature at which the solid electrolyte is activated. ing.

The heater insulating layer 74 is an insulating layer formed on the upper and lower surfaces of the heater 72 with an insulator such as alumina. The heater insulating layer 74 is formed for the purpose of providing electrical insulation between the second substrate layer 2 and the heater 72 and electrical insulation between the third substrate layer 3 and the heater 72 .

The pressure dissipation hole 75 is a portion that penetrates the third substrate layer 3 and is provided so as to communicate with the reference gas introduction space 43. The pressure dissipation hole 75 is provided for the purpose of alleviating an increase in internal pressure accompanying a temperature increase in the heater insulating layer 74. formed.

The element body 102 is partially covered with a porous protective layer 84, as shown in FIGS. Here, since the sensor element 101 has a rectangular parallelepiped shape, as shown in FIGS. 1 to 4, the first surface 102a (upper surface), It has six surfaces: a second surface 102b (lower surface), a third surface 102c (left surface), a fourth surface 102d (right surface), a fifth surface 102e (front end surface), and a sixth surface 102f (rear end surface). ing. The protective layer 84 includes first to fifth protective layers formed on five surfaces (first to fifth surfaces 102a to 102e) of the six surfaces (first to sixth surfaces 102a to 102f) of the element body 102, respectively. It includes layers 84a-84e. The fifth protective layer 84e (an example of an inlet protective layer) includes a fifth surface 102e, which is one end surface in the longitudinal direction (here, the front-rear direction) of the element body 102, and a gas inlet opening in the fifth surface 102e. 10 (see FIG. 3). The first to fourth protective layers 84a to 84d (an example of adjacent surface protective layers) are provided on four surfaces (first to fourth surfaces 102a to 102d, adjacent surface example) is covered (see FIGS. 3 and 4). The first to fifth protective layers 84a to 84e are collectively referred to as a protective layer 84. As shown in FIG. The protective layer 84 covers a portion of the element body 102 to protect that portion. The protective layer 84 plays a role of suppressing cracks in the element body 102 caused by adhesion of moisture or the like in the gas to be measured, for example.

As shown in FIGS. 3 and 4, the first protective layer 84a includes a first inner space 90a, a first outer protective layer 85a positioned outside the first inner space 90a, and a first outer protective layer 85a positioned inner than the first inner space 90a. and a first inner protective layer 86a located at . The first inner protective layer 86a is in contact with the first surface 102a. The first inner protective layer 86 a covers the outer pump electrode 23 . Similarly, the second protective layer 84b has a second internal space 90b, a second outer protective layer 85b, and a second inner protective layer 86b. The second inner protective layer 86b is in contact with the second surface 102b. The third protective layer 84c has a third internal space 90c and a third outer protective layer 85c located outside the third internal space 90c. The third protective layer 84c does not have a protective layer inside the third internal space 90c. Therefore, the third surface 102c is exposed in the third internal space 90c (see FIG. 4). Similarly, the fourth and fifth protective layers 84d and 84e have fourth and fifth internal spaces 90d and 90e and fourth and fifth outer protective layers 85d and 85e. The fourth and fifth surfaces 102d and 102e are exposed in the fourth and fifth internal spaces 90d and 90e, respectively (see FIGS. 3 and 4). The gas introduction port 10 is exposed in the fifth internal space 90e. The first to fifth outer protective layers 85a to 85e are collectively referred to as an outer protective layer 85, the first and second inner protective layers 86a and 86b are collectively referred to as an inner protective layer 86, and the first to fifth internal spaces 90a to 90e. are generically called an internal space 90 . The inner peripheral surfaces of the first to fifth internal spaces 90a to 90e are referred to as first to fifth inner peripheral surfaces 94a to 94e, respectively, and are collectively referred to as inner peripheral surfaces 94. As shown in FIG.

Adjacent layers of the first to fifth outer protective layers 85a to 85e are connected to each other, and the entire outer protective layer 85 covers the tip portion of the element body 102. FIG. The first and second inner protective layers 86a and 86b directly cover the portions of the first and second surfaces 102a and 102b covered by the first and second outer protective layers 85a and 85b, respectively. Therefore, the first and second surfaces 102a and 102b are not exposed in the first and second internal spaces 90a and 90b. Adjacent spaces of the first to fifth internal spaces 90a to 90e communicate directly with each other, and the internal space 90 as a whole forms one space. "Direct communication" means communication without passing through pores in the protective layer 84 (here, the outer protective layer 85 and the inner protective layer 86). The outer protective layer 85 and the inner protective layer 86 are in contact only at the rear end of the protective layer 84 (see FIG. 3). More specifically, the first outer protective layer 85a and the first inner protective layer 86a are in contact at the rear ends, and similarly the second outer protective layer 85b and the second inner protective layer 86b are in contact at the rear ends. are doing. The third and fourth outer protective layers 85c and 85d of the outer protective layer 85 are in contact with the third and fourth surfaces 102c and 102d only at their rear end portions. The fifth outer protective layer 85e is not in contact with the element body 102. As shown in FIG.

When viewed in a direction perpendicular to the first surface 102a, the first protective layer 84a overlaps the entire region of the first surface 102a from the front end of the element body 102 toward the rear to a distance L (see FIG. 3). are doing. The same applies to the second to fourth protective layers 84b to 84d. The same applies to each of the first to fourth outer protective layers 85a to 85d and the first and second inner protective layers 86a and 86b. The fifth protective layer 84e overlaps the entire fifth surface 102e when viewed from a direction perpendicular to the fifth surface 102e (here, when viewed along the front-to-back direction). That is, the fifth protective layer 84e covers the entire fifth surface 102e including the gas inlet 10. As shown in FIG. Since the protective layer 84 is a porous body, the gas to be measured can flow through the inside of the protective layer 84 and reach the inside of the gas introduction port 10 and the gas to be measured circulating portion 9 .

The distance L shown in FIG. 3 is based on the range in which the element main body 102 is exposed to the gas to be measured in the gas sensor 100, the position of the gas flow part 9 to be measured, and the like (0<distance L<longitudinal direction of the element main body 102 length). Further, it is preferable that the distance L is set to be longer than the longitudinal length of the measured gas flow section 9 provided inside the element main body 102 . As shown in FIGS. 2 to 4, the measured gas circulation portion 9 has a longitudinal direction along the longitudinal direction (here, the front-rear direction) of the element main body 102, and the distance L is the length of the measured gas circulation portion 9 in the longitudinal direction. It will be longer than that. In this embodiment, as shown in FIG. 1, the element body 102 has different lengths in the front-rear direction, widths in the left-right direction, and thicknesses in the up-down direction, and length>width>thickness. there is Also, the distance L is a value larger than the width and thickness of the element body 102 .

The protective layer 84 is made of porous material such as alumina porous material, zirconia porous material, spinel porous material, cordierite porous material, titania porous material, or magnesia porous material. In this embodiment, the protective layer 84 is made of an alumina porous body. Although not particularly limited, the thickness of the protective layer 84 is, for example, 100 μm to 1000 μm, and the porosity of the protective layer 84 is, for example, 5% to 85%. The thickness of the outer protective layer 85 may be, for example, 50 μm to 800 μm. The thickness of the inner protective layer 86 may be, for example, 5 μm to 50 μm. The thickness (height) of the internal space 90 may be, for example, 5 μm to 800 μm. The outer protective layer 85 and the inner protective layer 86 may have different porosities and materials. At least one of the outer protective layer 85 and the inner protective layer 86 may have multiple layers.

The arithmetic average roughness Rap of the fifth inner peripheral surface 94e of the fifth inner space 90e is a relatively large value. Specifically, the arithmetic mean roughness Rap satisfies at least one of the conditions of being 8 μm or more and being greater than the arithmetic mean roughness Rac of the bonding surface 97 of the protective layer 84 with the element body 102 . Although details will be described later, this causes a turbulent flow in the fifth internal space 90e and suppresses variations in the NOx concentration detected by the sensor element 101. FIG. In the present embodiment, the fifth inner peripheral surface 94e has only the fifth outer inner peripheral surface 95e that is the surface on the inner side (the element body 102 side) of the fifth outer protective layer 85e (see FIG. 3). Therefore, the value of the arithmetic mean roughness Ra of the fifth outer inner peripheral surface 95e is defined as the arithmetic mean roughness Rap. Further, in the present embodiment, the bonding surface 97 includes a first bonding surface 97a, which is a bonding surface between the first inner protective layer 86a and the first surface 102a, and a bonding surface between the second inner protective layer 86b and the second surface 102b. and a second adhesive surface 97b, which is a surface. Therefore, the average value of the arithmetic average roughness Ra of the first adhesive surface 97a and the arithmetic average roughness Ra of the second adhesive surface 97b is defined as the arithmetic average roughness Rac. In this embodiment, the arithmetic mean roughness Rap is assumed to satisfy both of the two conditions described above.

The arithmetic mean roughness Rap is preferably 10 μm or more. When the arithmetic mean roughness Rap is 10 μm or more, the effect of suppressing variations in the NOx concentration detected by the sensor element 101 is enhanced. The arithmetic mean roughness Rap may be 20 μm or more, or may be 30 μm or more. The arithmetic mean roughness Rap may be 100 μm or less. The arithmetic mean roughness Rac may be 0.1 μm or more and 1.0 μm or less. When the arithmetic mean roughness Rac is 0.1 μm or more, the adhesion strength between the element main body 102 and the protective layer 84 can be ensured. When the arithmetic mean roughness Rac is 1.0 μm or less, the strength of the protective layer 84 can be secured.

Here, the arithmetic mean roughness Rap is obtained by cutting the protective layer 84 to expose the inner peripheral surface to be measured (here, the fifth outer inner peripheral surface 95e), and applying light by a method according to JIS B 0601:2013. A value measured using an interferometer. Moreover, let the arithmetic mean roughness Rac be the value measured as follows. First, the sensor element 101 is cut so that the cross section perpendicular to the bonding surface 97 serves as an observation surface, and the cut surface is filled with resin and polished to obtain an observation sample. Next, the magnification of the scanning electron microscope (SEM) is set to 300 times, and the observation surface of the prepared observation sample with a field of view of approximately 350 μm×250 μm is photographed. Next, based on the luminance data of each pixel of the obtained image, a luminance histogram is created for all pixels. Then, the brightness of each pixel is tri-valued by setting the brightness value of the portion between the three peaks (troughs) appearing in the histogram as a threshold, and comparing the brightness of each pixel with the threshold. As a result, it is possible to distinguish whether each pixel is a constituent particle of the protective layer 84, a pore of the protective layer 84, or the element main body 102. FIG. Then, a boundary line between the constituent particles of the protective layer 84 and the element body 102 is drawn, and this boundary line is defined as the "real surface cross-sectional curve" of the bonding surface 97 defined in JIS B 0601:2013. Then, based on this cross-sectional curve of the real surface, the arithmetic average roughness Ra measured by performing image processing according to the method according to JIS B 0601:2013 is defined as the arithmetic average roughness Rac.

Further, it is preferable that the arithmetic average roughness of the inner peripheral surface of the first to fourth internal spaces 90a to 90d directly communicating with the fifth internal space 90e is relatively large. Specifically, the arithmetic average roughness Ras of the first to fourth inner peripheral surfaces 94a to 94d of the first to fourth internal spaces 90a to 90d is 8 μm or more or larger than the arithmetic average roughness Rac. At least one condition is preferably satisfied. Here, the arithmetic mean roughness Ras of the first to fourth inner peripheral surfaces 94a to 94d are defined as arithmetic mean roughnesses Ra1s to Ra4s, respectively. In this case, at least one of the arithmetic mean roughnesses Ra1s to Ra4s preferably satisfies at least one of the above two conditions.

Arithmetic mean roughness Ra1s will be described. In the present embodiment, the first inner peripheral surface 94a includes a first outer inner peripheral surface 95a that is a surface on the inner side (on the element body 102 side) of the first outer protective layer 85a, and an outer surface (on the side of the element body 102) on the outer side of the first inner protective layer 86a. 1 inner space 90a side) and a first inner inner peripheral surface 96a (see FIG. 3). In this case, when the arithmetic average roughness Ra of at least one of the first outer inner peripheral surface 95a and the first inner inner peripheral surface 96a is assumed to be the arithmetic average roughness Ra1s, the arithmetic average roughness Ra1s is the above-mentioned two At least one of the conditions is preferably satisfied. In other words, the arithmetic average roughness Ra of at least one of the first outer inner peripheral surface 95a and the first inner inner peripheral surface 96a preferably satisfies at least one of the two conditions described above. In the present embodiment, the arithmetic mean roughness Ra (=Ra1s) of the first outer inner peripheral surface 95a satisfies both of the above two conditions.

Arithmetic mean roughness Ra2s will be described. In the present embodiment, the second inner peripheral surface 94b includes a second outer inner peripheral surface 95b that is a surface on the inner side (on the element body 102 side) of the second outer protective layer 85b and an outer surface (on the side of the element body 102) on the outer side of the second inner protective layer 86b. 2, a second inner inner peripheral surface 96b which is a surface on the inner space 90b side (see FIG. 3). In this case, similarly to the arithmetic average roughness Ra1s, when the arithmetic average roughness Ra of at least one of the second outer inner peripheral surface 95b and the second inner inner peripheral surface 96b is defined as the arithmetic average roughness Ra2s, this arithmetic Preferably, the average roughness Ra2s satisfies at least one of the two conditions described above. In the present embodiment, the arithmetic mean roughness Ra (=Ra2s) of the second outer inner peripheral surface 95b satisfies both of the above two conditions.

Arithmetic mean roughness Ra3s will be described. In the present embodiment, the third inner peripheral surface 94c has only the third outer inner peripheral surface 95c that is the inner side (element body 102 side) of the third outer protective layer 85c (see FIG. 4). Therefore, the value of the arithmetic mean roughness Ra of the third outer inner peripheral surface 95c is defined as the arithmetic mean roughness Ra3s. Similarly, the fourth inner peripheral surface 94d has only the fourth outer inner peripheral surface 95d, which is the inner side (element body 102 side) of the fourth outer protective layer 85d (see FIG. 4). Therefore, the value of the arithmetic mean roughness Ra of the fourth outer inner peripheral surface 95d is defined as the arithmetic mean roughness Ra4s. In this embodiment, each of the arithmetic mean roughnesses Ra3s and Ra4s is assumed to satisfy both of the two conditions described above.

Similar to the arithmetic average roughness Rap, the arithmetic average roughness Ra1s to Ra4s are obtained by cutting the protective layer 84 and exposing the inner peripheral surface to be measured (here, the first to fourth outer inner peripheral surfaces 95a to 94d). and measured using an optical interferometer in accordance with JIS B 0601:2013.

As can be seen from FIGS. 3 and 4, the first to fifth inner peripheral surfaces 94a to 94e are all inner peripheral surfaces inside the outer protective layer 85 (on the element main body 102 side). Therefore, in the present embodiment, the arithmetic mean roughness Ra1s to Ra4s are set to the same value, and the arithmetic mean roughness Rap is also set to be the same value. However, each of the arithmetic mean roughnesses Rap, Ra1s to Ra4s may have different values. Also, the arithmetic mean roughness Ras (more specifically, one or more of the arithmetic mean roughnesses Ra1s to Ra4s) may be 10 μm or more, 20 μm or more, or 30 μm or more. The arithmetic mean roughness Ras may be 100 μm or less.

A method of manufacturing the gas sensor 100 thus configured will be described below. In the method of manufacturing the gas sensor 100 , the element body 102 is first manufactured, and then the protective layer 84 is formed on the element body 102 to manufacture the sensor element 101 .

A method for manufacturing the element body 102 will be described. First, six unsintered ceramic green sheets are prepared. Then, corresponding to each of the layers 1 to 6, each green sheet is provided with a plurality of sheet holes used for positioning during printing and lamination, necessary through holes, etc., in advance. In addition, the green sheet that will be the spacer layer 5 is previously provided with a space that will be the gas flow part 9 to be measured by a punching process or the like. Next, patterns such as electrodes and heaters are printed on each ceramic green sheet. After forming various patterns in this manner, the green sheet is dried. After that, they are laminated to form a laminate. In addition, a part of the laminate that becomes a space such as the measured gas circulation portion 9 may be filled with a vanishing material (for example, an organic material such as carbon or theobromine) that disappears during firing. The laminate thus obtained includes a plurality of element bodies 102 . The laminated body is cut into pieces of the size of the element body 102 and fired at a predetermined firing temperature to obtain the element body 102 .

Next, a method for forming the protective layer 84 on the element body 102 will be described. First, the inner protective layer 86 is formed on the surface of the element body 102 . The inner protective layer 86 can be formed by various methods such as mold casting, screen printing, dipping, and plasma spraying. When forming the inner protective layer 86 by screen printing or plasma spraying, the first to fifth inner protective layers 86a to 86e may be formed one by one. Next, the disappearing body is formed in the shape of the inner space 90 by applying the disappearing body on the inner protective layer 86 and drying it. Application of the eliminator can be performed by, for example, screen printing, gravure printing, inkjet printing, or the like. Alternatively, the disappearing body may be formed by repeating the application and drying a plurality of times. Examples of the material of the vanishing body include organic materials such as carbon and theobromine described above, as well as thermally decomposed polymers such as vinyl resins. Subsequently, an outer protective layer 85 is formed on the outer side of the inner protective layer 86 and the vanishing body. The outer protective layer 85 can be formed by a method similar to that for the inner protective layer 86 . This forms a protective layer 84 with a vanishing body in the shape of the internal space 90 . After that, the vanishing body is extinguished by burning. As a result, the vanishing body portion becomes the internal space 90, and the protective layer 84 having the internal space 90 is formed. Thus, the protective layer 84 is formed on the element body 102 to obtain the sensor element 101 . When the protective layer 84 is formed by mold casting, screen printing, or dipping, the slurry forming the outer protective layer 85 and the inner protective layer 86 is solidified or dried, and then the slurry is baked to form the protective layer 84. do. In this case, the burning of the protective layer 84 and the burning of the vanishing body may be performed at the same time. Further, when the outer protective layer 85 and the inner protective layer 86 are formed by plasma spraying, the vanishing body may be burnt out after both are formed.

Methods for relatively increasing the arithmetic mean roughness Rap and Ras include, for example, the following. First, a case will be described where the arithmetic mean roughnesses Rap and Ras are relatively increased by increasing the arithmetic mean roughnesses Ra of the first to fifth outer inner peripheral surfaces 95a to 95e. In this case, for example, the outer protective layer 85 is formed by plasma spraying, and the amount of plasma generating gas used for plasma spraying is reduced, or the distance between the plasma gun and the element main body 102 is increased. The speed at which the constituent particles of the protective layer 85 collide with the vanishing body is made relatively weak. This suppresses the constituent particles of the outer protective layer 85 from being crushed and flattened when colliding with the vanishing object, and increases the arithmetic average roughness Ra of the first to fifth outer inner peripheral surfaces 95a to 95e. can be done. Also, by using a soft material for the vanishing body, it is possible to suppress crushing of the constituent particles of the outer protective layer 85 when colliding with the vanishing body. Roughness Ra can be increased. Alternatively, the arithmetic average roughness Ra of the first to fifth outer inner peripheral surfaces 95a to 95e can be reduced by increasing the particle size of the powder thermal spray material (raw material powder constituting the outer protective layer 85) used for plasma spraying. You can also make it bigger. As a method for increasing the arithmetic mean roughness Ra of the first and second inner inner peripheral surfaces 96a and 96b, for example, the inner protective layer 86 is made up of a plurality of layers in the thickness direction and adhered to the element body 102. For example, the particle size of the constituent particles used for forming the layer exposed to the internal space 90 may be made larger than the constituent particles used for forming the layer exposed to the internal space 90 . Alternatively, the arithmetic mean roughness Ra may be increased by roughening the first and second inner peripheral surfaces 96a and 96b after the inner protective layer 86 is formed.

In addition, when the protective layer 84 has a plurality of layers (here, the outer protective layer 85 and the inner protective layer 86) in the thickness direction, the innermost layer (here, the inner protective layer 86) is formed by, for example, a mold casting method, a screen Preferably, a slurry is formed on the surface of the element body 102 using printing or dipping, and the inner protective layer 86 is formed by firing the slurry integrally with the element body 102 . The surface of the element body 102 often has a relatively small arithmetic mean roughness Ra, and the inner protective layer 86 that is directly adhered to the element body 102 tends to have low adhesion to the element body 102. , the adhesion between the element body 102 and the inner protective layer 86 can be enhanced. In addition, the surface of the inner protective layer 86 that contacts the outer protective layer 85 (here, the rear end portion of the surface of the inner protective layer 86) has a larger arithmetic mean roughness Ra than the surface of the element body 102. is preferred. By doing so, the adhesion between the inner protective layer 86 and the outer protective layer 85 can be enhanced. The arithmetic mean roughness Ra of the surface of the inner protective layer 86 that contacts the outer protective layer 85 may be 1 μm or more and 10 μm or less, or 1 μm or more and 5 μm or less. Not only the surface of the inner protective layer 86 that contacts the outer protective layer 85 but also the first and second inner inner peripheral surfaces 96a and 96b exposed to the internal space 90 have an arithmetic mean roughness Ra of 1 μm or more and 10 μm or less. or 1 μm or more and 5 μm or less.

Further, when the outer protective layer 85 is manufactured, the outer protective layer 85 (first to fifth outer protective layers 85a to 85e) is integrally formed into a cap shape (cylindrical shape with a bottom, box shape with one side open). , as a protective layer. For example, a cap-shaped unfired body having the shape of the outer protective layer 85 is produced using a mold casting method, and the element body 102 (the element body when the inner protective layer 86 is provided) is placed inside the cap-shaped unfired body. The outer protective layer 85 may be produced by inserting the tip side of 102 and the inner protective layer 86) and then firing the unfired body. In this case, by making the shape of the unfired body into a shape having a space support portion such as a columnar portion or a stepped portion inside (therefore, the outside protective layer 85 which is the unfired body after firing also has a space support portion). ), it is also possible to form the internal space 90 between the outer protective layer 85 and the element body 102 by means of a space supporting portion without using a vanishing body having the shape of the internal space 90 . Further, when the outer protective layer 85 is manufactured by inserting the element body 102 into the cap-shaped unfired body, the internal space 90 between the outer protective layer 85 and the element body 102 is located on the rear end side of the element body 102. It may have an opening facing In this case, plugging portions may be formed so as to block the openings by plasma spraying or the like. The plugging portions are preferably made of a porous material having the same main component as that of the outer protective layer 85 . Further, the arithmetic average roughness Rap and Ras can be adjusted by the shape of the irregularities (surface roughness) on the surface of the molding die when the unfired body to be the outer protective layer 85 is produced.

Once the sensor element 101 is obtained in this manner, it is housed in a predetermined housing, incorporated into a main body (not shown) of the gas sensor 100, and connected to various power sources, etc., thereby obtaining the gas sensor 100. FIG.

When the gas sensor 100 configured in this manner is used, the gas to be measured in the pipe reaches the sensor element 101, passes through the protective layer 84, and flows into the gas introduction port 10. As shown in FIG. Then, the sensor element 101 measures the concentration of NOx in the measured gas flowing into the measured gas circulation section 9 from the gas introduction port 10 by measuring the voltage between the measuring electrode 44 and the reference electrode 42 (electromotive force V2 in this case). Detect based on For example, the value of the electromotive force V2 or the value of the pump current Ip2 that flows by controlling the voltage Vp2 so that the electromotive force V2 is constant is output (measured) from the sensor element 101, thereby representing the specific gas concentration. value is obtained.

In the sensor element 101 of the present embodiment, the arithmetic mean roughness Rap of the fifth inner peripheral surface 94e (here, the fifth outer inner peripheral surface 95e) of the inlet protective layer (here, the fifth protective layer 84e) is At least one of the conditions of being 8 μm or more and being larger than the arithmetic average roughness Rac of the bonding surface 97 of the protective layer 84 to the element body 102 is satisfied. That is, the arithmetic mean roughness Rap of the fifth outer inner peripheral surface 95e is relatively large, and the unevenness of the fifth outer inner peripheral surface 95e is relatively large. As a result, when the gas to be measured passes through the fifth internal space 90e from the outside of the protective layer 84 and reaches the gas introduction port 10, the unevenness of the fifth outer inner peripheral surface 95e causes the measured gas to pass through the fifth internal space 90e. Turbulence occurs in the measurement gas. The gas to be measured is stirred by the turbulent flow, and the NOx concentration in the gas to be measured is made uniform. Therefore, variations in the NOx concentration in the measured gas introduced into the measured gas circulation section 9 are suppressed, so that the electromotive force V2 between the measurement electrode 44 and the reference electrode 42 caused by variations in the NOx concentration is reduced. Fluctuations are suppressed. Thereby, variations in the NOx concentration detected by the sensor element 101 can be suppressed.

According to the gas sensor 100 of the present embodiment described in detail above, the sensor element 101 includes the measurement electrode 44 arranged on the inner peripheral surface of the measured gas circulation section 9 and the concentration of the specific gas (NOx concentration in this case). and a reference electrode 42 exposed to a reference gas (atmosphere in this case) that serves as a reference for detection. The sensor element 101 has an inlet covering the surface of the element main body 102, the gas introduction port 10 serving as the inlet of the gas flow section 9 to be measured, and at least a portion of the fifth surface 102e where the gas introduction port 10 is open. A protective layer (here, the fifth protective layer 84e) is provided. The fifth inner peripheral surface 94e (here, the fifth outer inner peripheral surface 95e) of the fifth inner space 90e of the fifth protective layer 84e has an arithmetic mean roughness Rap of 8 μm or more, or It satisfies at least one of the conditions that the roughness is larger than the arithmetic mean roughness Rac of the bonding surface 97 with the element main body 102 . That is, the arithmetic average roughness Rap of the fifth outer inner peripheral surface 95e is relatively large. Thereby, variations in the NOx concentration detected by the sensor element 101 can be suppressed.

Further, when the arithmetic mean roughness Rap is larger than 100 μm, the fifth inner peripheral surface 94e (here, the fifth outer inner peripheral surface 95e) of the fifth internal space 90e possessed by the inlet protective layer (here, the fifth protective layer 84e) Due to the unevenness of the sensor element 101, the flow of the gas to be measured becomes difficult, and it becomes difficult for the gas to be measured to reach the gas introduction port 10, which may reduce the responsiveness of the sensor element 101. When the arithmetic mean roughness Rap is 100 μm or less, such a decrease in responsiveness can be suppressed.

Further, when the arithmetic mean roughness Rap is 10 μm or more, the effect of suppressing variations in the NOx concentration detected by the sensor element 101 is enhanced. When the arithmetic mean roughness Rac is 0.1 μm or more, the adhesion strength between the element main body 102 and the protective layer 84 can be ensured. The strength of the protective layer 84 can be ensured by setting the arithmetic mean roughness Rac to 1.0 μm or less.

Furthermore, the surface of the element main body 102 includes a fifth surface 102e where the gas inlet 10 is open, and a plurality of adjacent surfaces (here, first to fourth surfaces) that are in contact with the fifth surface 102e on the sides of the fifth surface 102e. 102a-102d). The protective layer 84 has adjacent surface protective layers (here, first to fourth protective layers 84a to 84d) covering the first to fourth surfaces 102a to 102d, and the first to fourth protective layers 84a to 84d. directly communicates with the fifth internal space 90e of the fifth protective layer 84e, and the arithmetic mean roughness Ras (here Ra1s ˜Ra4s) is 8 μm or more or greater than the arithmetic mean roughness Rac. Here, when the sensor element 101 is used, moisture contained in the gas to be measured may adhere to the surface of the sensor element 101 . As described above, the element body 102 is adjusted to a temperature (for example, 800° C.) at which the solid electrolyte is activated by the heater 72. Cracks may occur in the body 102 . In the sensor element 101 of the present embodiment, the existence of the first to fourth protective layers 84a to 84d suppresses a rapid drop in the temperature of the element body 102, thereby improving the water resistance of the element body 102. Moreover, since the first to fourth protective layers 84a to 84d have the first to fourth internal spaces 90a to 90d, the first to fourth protective layers 84a to 84d extend toward the element body 102 from the outside of the first to fourth protective layers 84a to 84d. Heat conduction in the thickness direction of each of the protective layers 84a-84d can be suppressed by the first to fourth internal spaces 90a-90d, and the water resistance of the element body 102 is further improved. In addition, since the first to fourth internal spaces 90a to 90d and the fifth internal space 90e are in direct communication, the first to fourth internal spaces 90a to 90d are relatively wide, and the element main body The water resistance of 102 is further improved. Furthermore, at least one of the arithmetic average roughness Ras of the first to fourth inner peripheral surfaces 94a to 94d of the first to fourth internal spaces 90a to 90d is 8 μm or more or larger than the arithmetic average roughness Rac meet the conditions. That is, the first to fourth protective layers 84a to 84d have first to fourth internal spaces 90a to 90d in which the arithmetic average roughness Ras of the first to fourth inner peripheral surfaces 94a to 94d is relatively large. . As a result, turbulent flow is generated in the gas to be measured in the first to fourth internal spaces 90a to 90d due to the unevenness of the first to fourth internal spaces 90a to 90d, and the flow from the fifth internal space 90e to the first to fourth internal spaces It becomes difficult for the gas to be measured to flow into 90a to 90d. Therefore, the gas to be measured in the fifth internal space 90e easily flows from the gas inlet 10 into the gas-to-be-measured circulation portion 9, and the responsiveness of the sensor element 101 is improved. That is, since the first to fourth internal spaces 90a to 90d and the fifth internal space 90e are in direct communication, the water resistance of the element body 102 is improved, and the arithmetic mean roughness Ras is relatively large. By doing so, it is possible to suppress a decrease in responsiveness due to direct communication between the two spaces.

Furthermore, the element main body 102 is a laminate in which a plurality of solid electrolyte bodies are laminated in a lamination direction (vertical direction) perpendicular to the longitudinal direction. The surface of the element body 102 includes a fifth surface 102e, which is an end surface in the longitudinal direction, and a plurality of adjacent surfaces (here, first to fourth surfaces 102a to 102d) that are in contact with the fifth surface 102e on the sides of the fifth surface 102e. ) and The protective layer 84 has adjacent surface protective layers (here, first to fourth protective layers 84a to 84d) covering the first to fourth surfaces 102a to 102d. The first to fourth protective layers 84a to 84d cover the upper surface (here, the first surface 102a) and the lower surface (here, the second surface 102b) located at both ends in the stacking direction of the first to fourth surfaces 102a to 102d. The first and second internal spaces 90a and 90b and the first and second internal spaces 90a and 90b located outside the first and second internal spaces 90a and 90b are provided in the covering portions (here, the first and second protective layers 84a and 84b), respectively. , second outer protective layers 85a and 85b, first and second inner protective layers 86a and 86b positioned inside the first and second internal spaces 90a and 90b and adhered to the surface of the element body 102, have. Since the first and second inner protective layers 86a and 86b are in contact with the first surface 102a and the second surface 102b, the element body 102 (more precisely, the element body 102 and the first and second inner protective layers 86a, 86b) are increased in heat capacity. Therefore, even if a thermal shock reaches the element body 102 side from the outside, a rapid temperature change of the element body 102 is suppressed. As a result, the water resistance of the element body 102 is improved.

It goes without saying that the present invention is not limited to the above-described embodiments, and can be implemented in various forms as long as they fall within the technical scope of the present invention.

For example, while the protective layer 84 includes an inner protective layer 86 in the embodiments described above, the protective layer 84 need not include the inner protective layer 86 . FIG. 5 is a cross-sectional view of a protective layer 184 that is a modified example of this case. The protective layer 184 has an outer protective layer 85 and an internal space 90, and the first to fifth surfaces 102a to 102e, which are the surfaces of the element body 102, are exposed to the internal space 90. FIG. In this case, the bonding surface 97 of the protective layer 184 serves as the bonding surface between the outer protective layer 85 and the element body 102 (for example, the first and second bonding surfaces 97a and 97b shown in FIG. 5). Arithmetic mean roughness Rac is determined based on this.

Although the inner protective layer 86 has the first and second inner protective layers 86a and 86b in the embodiment described above, it is not limited to this. The inner protective layer 86 may cover one or more of the first to fifth surfaces 102a to 102e. For example, like the protective layer 284 of the modified example shown in FIGS. may In the protective layer 284, the third to fifth inner peripheral surfaces 94c to 94e have third to fifth outer inner peripheral surfaces 95c to 95e and third to fifth inner inner peripheral surfaces 96c to 96e. In this case, the bonding surface 97 of the protective layer 284 serves as the bonding surface between the inner protective layer 86 and the element body 102 (the first to fifth bonding surfaces 97a to 97e shown in FIGS. 6 and 7). Arithmetic mean roughness Rac is determined based on surface 97 . Specifically, in the examples of FIGS. 6 and 7, the average value of the arithmetic mean roughness Ra of each of the first to fifth bonding surfaces 97a to 97e is defined as the arithmetic mean roughness Rac. In the example of FIGS. 6 and 7, the fifth surface 102e is covered with the fifth inner protective layer 86e, so neither the fifth surface 102e nor the gas introduction port 10 is exposed to the fifth internal space 90e.

Although the first to fifth internal spaces 90a to 90e communicate directly with each other in the above-described embodiment, the present invention is not limited to this. For example, the fifth internal space 90e may directly communicate with at least one of the first to fourth internal spaces 90a to 90d, or directly communicate with any of the first to fourth internal spaces 90a to 90d. may not be in communication.

Although each of the first to fifth protective layers 84a to 84e has one internal space in the above-described embodiment, they may have two or more internal spaces. When there are a plurality of fifth internal spaces 90e, the value of the arithmetic mean roughness Ra of the inner peripheral surface of the inner space closest to the gas inlet 10 among the plurality of fifth internal spaces 90e is defined as the arithmetic mean roughness Rap and

In the embodiment described above, the protective layer 84 had the first to fifth protective layers 84a to 84e, but the protective layer 84 includes at least the inlet protective layer (the fifth protective layer 84e in the embodiment described above). It is good if there is The protective layer 84 may have no adjacent surface protective layer (the first to fourth protective layers 84a to 84d in the embodiment described above), or may have at least one adjacent surface protective layer.

In the above-described embodiment, the longitudinal direction of the measured gas circulation portion 9 is parallel to the longitudinal direction of the element main body 102, but the present invention is not limited to this. Moreover, although the gas introduction port 10 of the measured gas circulation portion 9 is opened on the fifth surface 102e, it may be opened on another surface such as the first surface 102a. In other words, the inlet protective layer is not limited to the fifth protective layer 84e.

In the above-described embodiment, the element body 102 has a rectangular parallelepiped shape. For example, the element body 102 may have the shape of a polygonal prism or cylinder.

Although not particularly described in the above-described embodiment, each of the first to fifth internal spaces 90a to 90e included in the protective layer 84 is formed in the constituent materials of the protective layer 84 (for example, the outer protective layer 85 and the inner protective layer 86). It is a size that can be distinguished from the pores of That is, pores in the outer protective layer 85 and the inner protective layer 86 are not included in the internal space 90 . The internal space 90 (each of the first to fifth internal spaces 90a to 90e) is a space different from the pores in the protective layer 84 and larger than the pores. For example, the volume of the portion of the first internal space 90a that exists in the region directly above the first surface 102a may be 0.03 mm ³ or more, 0.04 mm ³ or more, or 0.07 mm ³ . 0.5 mm ³ or more, or 1.5 mm ³ or more. The volume of the portion of the second internal space 90b that exists in the area immediately below the second surface 102b may be 0.03 mm ³ or more, 0.04 mm ³ or more, or 0.07 mm ³ or more. It may be 0.5 mm ³ or more, or 1.5 mm ³ or more. The volume of the portion of the third internal space 90c that exists in the region to the left of the third surface 102c may be 0.015 mm ³ or more, 0.2 mm ³ or more, or 0.4 mm ³ or more. good too. The volume of the portion of the fourth internal space 90d that exists in the area to the right of the fourth surface 102d may be 0.015 mm ³ or more, 0.2 mm ³ or more, or 0.4 mm ³ or more. good too. The volume of the portion of the fifth internal space 90e that exists in the area in front of the fifth surface 102e may be 0.010 mm ³ or more, 0.1 mm ³ or more, or 0.2 mm ³ or more. Alternatively, it may be 0.3 mm ³ or more. Here, the “region right above the first surface 102a” means a region existing in a direction perpendicular to the first surface 102a with respect to the first surface 102a, and includes the upper left, upper right, etc. of the first surface 102a. do not have. The same applies to the ``area immediately below the second surface 102b'', the ``left area of the third surface 102c'', the ``right area of the fourth surface 102d'', and the ``area in front of the fifth surface 102e''. be. Further, when the first internal space 90a has a plurality of spaces, at least one of the plurality of spaces has a volume of 0.03 mm 3 or more and 0.03 mm ³ or more of a portion existing in the region right above the first surface 102a. 04 mm ³ or more, 0.07 mm ³ or more, 0.5 mm ³ or more, or 1.5 mm ³ or more. The volume may be 0.03 mm ³ or more, 0.04 mm ³ or more, 0.07 mm ³ or more, 0.5 mm ³ or more, or 1.5 mm ^{3 or} more. Similarly, when each of the second to fifth internal spaces 90b to 90e has a plurality of spaces, at least one of the plurality of spaces may satisfy the above numerical range of volumes, or a plurality of The volumetric numerical ranges described above may be satisfied for the total space. The height of the first internal space 90a may be 40% or more and 70% or less of the height from the first surface 102a to the upper surface of the first outer protective layer 85a. Similarly, the height of the second internal space 90b may be 40% or more and 70% or less of the height from the second surface 102b to the lower surface of the second outer protective layer 85b. The height of the third internal space 90c may be 40% or more and 70% or less of the height from the third surface 102c to the left surface of the third outer protective layer 85c. The height of the fourth internal space 90d may be 40% or more and 70% or less of the height from the fourth surface 102d to the right surface of the fourth outer protective layer 85d. The height of the fifth internal space 90e may be 40% or more and 70% or less of the height from the fifth surface 102e to the front surface of the fifth outer protective layer 85e. The height of the first internal space 90a may be 5 times or more, or 10 times or more, the average pore diameter of the protective layer 84 (according to mercury porosimetry). Similarly, the height of each of the second to fifth internal spaces 90b to 90e may be five times or more, or ten times or more the average pore diameter of the protective layer .

In the above-described embodiment, the element main body 102 is a laminate having a plurality of solid electrolyte layers (layers 1 to 6), but it is not limited to this. The element main body 102 may include at least one oxygen ion conductive solid electrolyte layer. For example, in FIG. 2, the layers 1 to 5 other than the second solid electrolyte layer 6 may be structural layers made of a material other than the solid electrolyte (for example, layers made of alumina). In this case, each electrode of element body 102 may be arranged on second solid electrolyte layer 6 . For example, the measurement electrode 44 in FIG. 2 may be arranged on the bottom surface of the second solid electrolyte layer 6 . Further, the reference gas introduction space 43 is provided in the spacer layer 5 instead of the first solid electrolyte layer 4, and the air introduction layer 48 is provided in the second solid electrolyte layer 4 instead of providing it between the first solid electrolyte layer 4 and the third substrate layer 3. It may be provided between the electrolyte layer 6 and the spacer layer 5 , and the reference electrode 42 may be provided behind the second internal space 40 and on the lower surface of the second solid electrolyte layer 6 .

In the above-described embodiment, the gas sensor 100 that detects the NOx concentration was exemplified, but the present invention may be applied to a gas sensor that detects the oxygen concentration or a gas sensor that detects the ammonia concentration.

An example in which a sensor element is specifically manufactured will be described below as an example. Experimental Examples 2 to 11 correspond to examples of the present invention, and Experimental Example 1 corresponds to a comparative example. In addition, the present invention is not limited to the following examples.

[Experimental example 1]
A sensor element 101 having the structure shown in FIGS. First, the element body 102 shown in FIGS. 1 to 4 having a length of 67.5 mm, a width of 4.25 mm, and a thickness of 1.45 mm was produced. In fabricating the element main body 102, the ceramic green sheets corresponding to the layers 1 to 6 were formed by tape forming by mixing zirconia particles to which 4 mol % of yttria as a stabilizer was added, an organic binder, and an organic solvent. Patterns of electrodes and the like were printed on each of the six green sheets. Of the six green sheets, the surface of the green sheet that will be the second solid electrolyte layer 6 (the surface that will be the first surface 102a) and the surface of the green sheet that will be the first substrate layer 1 (the surface that will be the second surface 102b) , a slurry that becomes the inner protective layer 86 (the first and second inner protective layers 86a and 86b) after firing was formed by screen printing. A slurry for forming the inner protective layer 86 was prepared as follows. The particle size of the raw material powder (alumina powder) is D50 = 5 µm, the volume ratio is 10 vol%, the binder solution (polyvinyl acetal and butyl carbitol) is 40 vol%, the auxiliary solvent (acetone) is 45 vol%, and the dispersant (poly 5 vol % of oxyethylene styrenated phenyl ether), and mixed for 3 hours at 200 rpm in a pot mill mixer to prepare a paste. After printing the pattern of each electrode and the slurry for the inner protective layer 86, six green sheets were laminated and fired to fabricate the element body 102 having the inner protective layer 86. FIG.

Next, the inner space 90 and the outer protective layer 85 were formed in the element body 102 having the inner protective layer 86 . Specifically, first, a disappearing body made of a vinyl resin is screen-printed on each of the first inner protective layer 86a, the second inner protective layer 86b, and the third to fifth surfaces 102c to 102e of the element body 102. formed by The vanishing body was formed to have the shape of the internal space 90 (first to fifth internal spaces 90a to 90e). Next, the outer protective layer 85 (first to fifth outer protective layers 85a to 85e) was formed on the surface of the vanishing body by plasma spraying using a plasma spray gun (Simplex Pro-90 manufactured by Oerlikon Metco). The plasma spraying conditions for forming the first outer protective layer 85a were as follows. A mixture of argon gas (flow rate: 50 L/min) and hydrogen (flow rate: 2 L/min) was used as the plasma generation gas. The applied voltage for plasma generation was a DC voltage of 100V and the current was 200A. Alumina powder having an average particle size of 30 μm was used as raw material particles (powder thermal spraying material) for forming the first outer protective layer 85a. Argon gas (flow rate: 5 L/min) was used as the carrier gas for supplying the raw material particles. The thermal spraying direction of the plasma gun was perpendicular to the first surface 102a, and the distance between the plasma gun and the first surface 102a was 120 mm. Plasma spraying was carried out in the air and at room temperature. The second to fifth outer protective layers 85b to 85e are also formed by plasma spraying in the same manner as the first outer protective layer 85a. The plasma spraying conditions were all the same. After forming the first to fifth outer protective layers 85a to 85e in this way, the vanishing body was burnt out to form an internal space 90. As shown in FIG. As described above, the sensor element 101 of Experimental Example 1 was obtained.

In the sensor element 101 of Experimental Example 1, the first inner protective layers 86a and 86b had a thickness of 50 μm and a porosity of 50%. The arithmetic average roughness Rac of the bonding surface 97 of the first inner protective layer 86a and the second inner protective layer 86b was measured by the method described above and found to be 1 μm. The first to fifth outer protective layers 85a to 85e had a thickness of 200 μm and a porosity of 20%. When the arithmetic mean roughness Ras (=Ra1s to Ra4s) of the first to fourth outer inner peripheral surfaces 95a to 95d was measured by the method described above using an optical interferometer (optical measuring instrument Zygo), all were 1 μm. Ta. The arithmetic mean roughness Rap of the fifth outer inner peripheral surface 95e was also measured by the above-described method and found to be 1 μm. The measured values of the arithmetic mean roughness Ras (=Ra1s to Ra4s) are measured from one point in the center of each of the first to fourth outer inner peripheral surfaces 95a to 95d and from there in the longitudinal direction (front and back direction) of the sensor element 101. ) and two points 1 mm apart from each other. The measured value of the arithmetic average roughness Rap was calculated as the average value of a total of three points, one point in the center of the fifth outer inner peripheral surface 95e and two points separated therefrom by 1 mm. The thickness of the first and second internal spaces 90a and 90b (the distance in the thickness direction between the outer protective layer 85 and the inner protective layer 86) was 200 μm. The thickness of the third to fifth internal spaces 90c to 90e was 200 μm.

[Experimental Examples 2 to 7]
An experiment was conducted in the same manner as in Experimental Example 1, except that the plasma spraying conditions for forming the outer protective layer 85 were changed so that the arithmetic mean roughnesses Rap and Ras were larger than in Experimental Example 1. Sensor elements 101 of Examples 2-7 were fabricated. The conditions of the plasma spraying are as follows: the above distance is 150 mm in Experimental Example 2, the distance is 180 mm in Experimental Example 3, the distance is 200 mm in Experimental Example 4, the distance is 200 mm in Experimental Example 5, and the average particle size of the alumina powder is In Experimental Example 6, the distance was 200 mm and the average particle diameter of the alumina powder was 40 μm, and in Experimental Example 7 the distance was 200 mm and the average particle diameter of the alumina powder was 50 μm. In each of Experimental Examples 2 to 7, the arithmetic mean roughness Rap and the arithmetic mean roughness Ras were the same value.

[Evaluation Test of Variation of Detected Values]
A gas sensor provided with the sensor element 101 of Experimental Example 1 was attached to an exhaust pipe of an automobile. Then, the heater 72 was energized to raise the temperature to 800° C., thereby heating the sensor element 101 . Next, the automobile gasoline engine (1.8 L) was operated under predetermined operating conditions (engine speed 4500 rpm, air/fuel A/F value 11.0, load torque 130 Nm, exhaust gas gauge pressure 60 kPa, The temperature of the exhaust gas was 800° C.). Then, each pump cell 21, 41, 50 described above was operated to start measuring the NOx concentration by the sensor element 101. FIG. Measurement of the value of the pump current Ip2 (value corresponding to the NOx concentration in the exhaust gas) was started 10 seconds after the start of operation of each pump cell, and the measurement was continued for 10 seconds. Then, the difference between the maximum value and the minimum value of the pump current Ip2 during the measurement period was derived as a value representing the variation in the NOx concentration detected by the sensor element 101 (detected value of the sensor element 101). Similar values were derived for Experimental Examples 2 to 7 as well. Assuming that the value derived in Experimental Example 1 was 100%, the value derived in each of Experimental Examples 2 to 7 was expressed as a percentage, and the variation ratio of the detection value of the sensor element 101 was obtained.

Table 1 shows the arithmetic average roughness Rap, Rac, Ras and the variation rate of the detection value of the sensor element 101 in each of Experimental Examples 1 to 7. FIG. 8 is a graph showing the relationship between the arithmetic mean roughness Rap and the variation rate of the detected value of the sensor element 101 in Experimental Examples 1-7.

As can be seen from Table 1 and FIG. 8, in comparison with Experimental Example 1 in which the arithmetic mean roughness Rap is less than 8 μm and Rap=Rac, in Experimental Examples 2 to 7 in which Rap>Rac, the sensor element 101 The variation rate of detected values was small. Moreover, in Experimental Examples 1 to 7, there was a tendency that the larger the arithmetic mean roughness Rap, the smaller the rate of variation in the detected value of the sensor element 101 . Further, when the arithmetic mean roughness Rap is less than 8 μm (Experimental Examples 1 to 4), the larger the arithmetic mean roughness Rap, the more the rate of variation in the detected value of the sensor element 101 tends to decrease rapidly. When the arithmetic mean roughness Rap was 8 μm or more (Experimental Examples 5 to 7), the fluctuation rate of the detected value was almost the same even when the arithmetic mean roughness Rap was increased. Therefore, if the arithmetic mean roughness Rap is 8 μm or more, it is considered that variations in the NOx concentration detected by the sensor element 101 can be sufficiently suppressed.

[Experimental Examples 8 to 11]
The sensor element 101 is obtained by changing plasma spraying conditions for the first to fourth outer protective layers 85a to 85d and the fifth outer protective layer 85e so that the arithmetic mean roughness Rap and the arithmetic mean roughness Ras are different values. They were prepared as Experimental Examples 8 to 11. Experimental Examples 8 to 11 were all the same as Experimental Example 5 except for the plasma spraying conditions when forming the first to fourth outer protective layers 85a to 85d. Regarding the plasma spraying conditions for forming the first to fourth outer protective layers 85a to 85d, Experimental Example 8 is the same as Experimental Example 2, Experimental Example 9 is the same as Experimental Example 4, and Experimental Example 10 is the same. The conditions were the same as in Experimental Example 5, and the conditions in Experimental Example 11 were the same as in Experimental Example 6. Therefore, in Experimental Example 10, the sensor element 101 was produced under the same manufacturing conditions as in Experimental Example 5, including the plasma spraying conditions when forming the first to fourth outer protective layers 85a to 85d.

[Responsive evaluation test]
A gas sensor provided with the sensor element 101 of Experimental Example 8 was attached to an automobile exhaust pipe. Then, the heater 72 was energized to raise the temperature to 800° C., thereby heating the sensor element 101 . Next, nitrogen was used as the base gas, and a model gas obtained by mixing a predetermined concentration of oxygen and 70 ppm of NO was used as the gas to be measured. Further, the pump cells 21, 41 and 50 described above were operated to start measuring the NOx concentration by the sensor element 101. FIG. After the value of the pump current Ip2 (the value corresponding to the NOx concentration in the gas to be measured) stabilizes, the NO concentration of the gas to be measured flowing through the pipe is changed from 70 ppm to 500 ppm. We investigated the time change of the value. When the value of the pump current Ip2 exceeds 10%, where the value of the pump current Ip2 immediately before the NO concentration is changed is 0% and the value when the pump current Ip2 changes and stabilizes after the NO concentration is changed is 100%. The response time (sec) for detecting the NOx concentration was the elapsed time from when it exceeded 90%. A shorter response time means a higher response of the sensor element 101 . For Experimental Examples 8 to 11, response times were similarly measured. The measurement of the response time was performed multiple times for each experimental example, and each average value was used as the response time for each experimental example.

Table 2 shows the arithmetic mean roughness Rap, Rac, Ras and the response time of the sensor element 101 in each of Experimental Examples 8-11.

As can be seen from Table 2, the response time of the sensor element 101 is It was short. Further, in Experimental Examples 8 to 11, there was a tendency that the larger the arithmetic mean roughness Ras, the shorter the response time of the sensor element 101 . Further, from a comparison of Experimental Examples 8 to 11, Experimental Examples 10 and 11, in which the arithmetic mean roughness Ras is 8 μm or more, are superior to Experimental Examples 8 and 9, in which the arithmetic mean roughness Ras is less than 8 μm. A tendency for the response time to shorten rapidly was observed. Therefore, it is considered that the responsiveness of the sensor element 101 is sufficiently high if the arithmetic mean roughness Ras is 8 μm or more.

REFERENCE SIGNS LIST 1 first substrate layer 2 second substrate layer 3 third substrate layer 4 first solid electrolyte layer 5 spacer layer 6 second solid electrolyte layer 9 measured gas flow portion 10 gas introduction port 11 th 1 diffusion control section 12 buffer space 13 second diffusion control section 20 first internal cavity 21 main pump cell 22 inner pump electrode 22a ceiling electrode section 22b bottom electrode section 23 outer pump electrode 25 variable power supply , 30 third diffusion control section, 40 second internal space, 41 pump cell for measurement, 42 reference electrode, 43 reference gas introduction space, 44 measurement electrode, 45 fourth diffusion control section, 46 variable power supply, 48 atmosphere introduction layer, 50 auxiliary pump cell, 51 auxiliary pump electrode, 51a ceiling electrode portion, 51b bottom electrode portion, 52 variable power supply, 70 heater portion, 71 heater connector electrode, 72 heater, 73 through hole, 74 heater insulating layer, 75 pressure dissipation hole, 80 Oxygen partial pressure detection sensor cell for main pump control 81 Oxygen partial pressure detection sensor cell for auxiliary pump control 82 Oxygen partial pressure detection sensor cell for measurement pump control 83 Sensor cell 84 Protective layer 84a to 84e First to fifth protective layers , 85 outer protective layer, 85a to 85e first to fifth outer protective layer, 86 inner protective layer, 86a to 86e first to fifth inner protective layer, 90 inner space, 90a to 90e first to fifth inner space, 94 inner peripheral surface 94a to 94e first to fifth inner peripheral surface 95a to 95e first to fifth outer inner peripheral surface 96a to 96e first to fifth inner inner peripheral surface 97 adhesive surface 97a to 97e First to fifth adhesive surfaces 100 gas sensor 101 sensor element 102 element body 102a to 102f first to sixth surfaces 184, 284 protective layer.

Claims (7)

A sensor element for detecting a specific gas concentration in a gas to be measured,
an element main body having an oxygen ion-conducting solid electrolyte body and provided therein with a measured gas flow section for introducing and circulating a measured gas;
a measuring electrode disposed on the inner peripheral surface of the measured gas flow portion;
a reference electrode disposed in the element main body and exposed to a reference gas serving as a reference for detecting the concentration of the specific gas;
a porous protective layer covering part of the surface of the element body;
with
The protective layer has an inlet protective layer that covers a gas inlet serving as an inlet of the gas flow section to be measured and at least a portion of the surface where the gas inlet is open on the surface of the element body. ,
The inlet protective layer has an internal space,
The arithmetic average roughness Rap of the inner peripheral surface of the inner space of the introduction port protective layer is 10 μm or more .
sensor element. The arithmetic mean roughness Rap is greater than the arithmetic mean roughness Rac of the surface of the protective layer bonded to the element body,
A sensor element according to claim 1 . The arithmetic mean roughness Rac is 0.1 μm or more and 1.0 μm or less.
3. A sensor element according to claim 2 . the surface of the element body has a surface on which the gas introduction port is open and one or more adjacent surfaces that are in contact with the surface at sides of the surface;
The protective layer has an adjacent surface protective layer covering at least a portion of the one or more adjacent surfaces,
The adjacent surface protective layer communicates directly with the internal space of the inlet protective layer, and has an inner peripheral surface with an arithmetic average roughness Ras of 8 μm or more or larger than the arithmetic average roughness Rac. have an interior space that satisfies at least one of the conditions,
4. A sensor element according to claim 2 or 3 . The element body has an elongated shape with a longitudinal direction,
The surface on which the gas introduction port is open is the end surface in the longitudinal direction,
The sensor element according to any one of claims 1-4. The element body is a laminate obtained by laminating a plurality of the solid electrolyte bodies in a lamination direction perpendicular to the longitudinal direction,
the surface of the element body has the end surface and a plurality of adjacent surfaces that are in contact with the end surface at sides of the end surface;
The protective layer has an adjacent surface protective layer covering the plurality of adjacent surfaces,
The adjacent surface protective layer has an internal space, an outer protective layer positioned outside the internal space, and an internal an inner protective layer positioned inside the space and adhered to the surface of the element body;
6. A sensor element according to claim 5. A gas sensor comprising the sensor element according to any one of claims 1 to 6.

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