JP2016065852A - Gas sensor production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor production method capable of more surely suppressing peeling of a porous protection layer.SOLUTION: A formation step of forming a porous protection part 90 comprising porous protection layers 91a-91e which are respectively formed on five surfaces of six surfaces of a long and rectangular sensor element 101, comprises: a step b for forming two porous protection layers 91a, 91b whose formation areas are widest, first; a step c for forming porous protection layers 91c, 91d which are not formed, of the porous protection part 90, so as to connect the at least two porous protection layers 91a, 91b which have been formed; and a step d for forming the porous protection layer 91e so as to connect the porous protection layers 91a-91d which have been formed. The two porous protection layers 91a, 91b which are formed first, are positioned on upper and lower surfaces which are opposite surfaces of the six surfaces of the sensor elements 101.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a method for manufacturing a gas sensor.

  Conventionally, a gas sensor including a sensor element that detects a concentration of a predetermined gas such as NOx in a gas to be measured such as an exhaust gas of an automobile is known. In such a gas sensor, it is known to form a porous protective layer on the surface of the sensor element. For example, Patent Documents 1 and 2 describe forming a porous protective layer by attaching heat-resistant particles such as alumina to the surface of a sensor element by plasma spraying. By forming this porous protective layer, for example, deterioration of the measurement electrode on the surface of the sensor element, cracking of the sensor element due to moisture adhesion, and the like can be suppressed.

JP2013-54025A Japanese Patent No. 3766572

  By the way, in forming such a porous protective layer on the surface of the sensor element, the adhesion between the porous protective layer and the sensor element surface is poor, and the porous protective layer may peel off after the formation.

  The present invention has been made to solve such a problem, and has as its main object to further suppress peeling of the porous protective layer.

The manufacturing method of the gas sensor of the present invention includes:
A gas sensor manufacturing method comprising: a long rectangular parallelepiped sensor element; and a porous protective part having a porous protective layer formed on at least three of the six surfaces of the sensor element. ,
(A) preparing the sensor element;
(B) a step of precedingly forming the two porous protective layers having the widest formation area among the porous protective portions;
(C) forming an unformed porous protective layer among the porous protective portions so as to be connected to at least two formed porous protective layers;
Is included.

  In the gas sensor manufacturing method of the present invention, when forming a porous protective portion having a porous protective layer formed on at least three surfaces of six surfaces of a long rectangular parallelepiped sensor element, The two widest porous protective layers are pre-formed. In this way, since the two porous protective layers having the largest formation area are first formed, the two porous protective layers are formed with the sensor element as compared with the case of forming another porous protective layer with a narrow formation area. Easy to adhere. Then, an unformed porous protective layer is formed in the porous protective portion so as to be connected to at least two formed porous protective layers. Thereby, the porous protective layer formed later is connected to at least two formed porous protective layers, so that it is difficult to peel off from the sensor element even if the formation area is small. By the above, peeling of a porous protective layer can be suppressed more. Here, “the two porous protective layers having the widest formation area among the porous protection portions” have the same formation area (the two formation areas of the two porous protection layers are the first). May be. In addition, when there is one porous protective layer having the largest formation area, “two porous protective layers having the largest formation area among the porous protection portions” have different formation areas (two porous protection layers). The area of the protective layer may be 1st or 2nd). Any of the two porous protective layers formed in advance may be formed first or simultaneously. The “at least two porous protective layers already formed” is not limited to the two porous protective layers previously formed in the step (b) but also includes the porous protective layers formed in the step (c). For example, when the porous protective portion has a porous protective layer formed on each of four or more surfaces, the porous protective layer first formed in step (c) is always connected to the two previously formed porous protective layers. However, if the porous protective layer to be formed thereafter is connected to at least two porous protective layers already formed in any of the steps (b) and (c), Good. However, since the previously formed porous protective layer has high adhesion to the sensor element, any porous protective layer formed in the step (c) should connect at least the two previously formed porous protective layers. It is preferable to form.

  In the gas sensor manufacturing method of the present invention, in the step (b), the two previously formed porous protective layers may be positioned on opposite surfaces of the six surfaces of the sensor element. Good. In this way, in step (c), the porous protective layer formed to be connected to the two previously formed porous protective layers is connected to the two porous protective layers on both sides of the formation surface. Therefore, the effect of suppressing peeling is enhanced.

  In the gas sensor manufacturing method of the present invention, in the step (b), of the surfaces on which the two porous protective layers are formed, the end on the surface side on which the porous protective layer is formed in the step (c) The porous protective layer may be formed in advance in a region including the portion. If it carries out like this, it will become easy to connect the two porous protective layers formed previously, and the porous protective layer formed later.

  In the gas sensor manufacturing method of the present invention, in the step (a), an arithmetic average of a region where the porous protective layer is formed in at least one of the steps (b) and (c) in the surface of the sensor element. The roughness Ra may be 2.0 to 5.0 μm. If it carries out like this, a porous protective layer will become easy to stick to the surface of a sensor element, and peeling of a porous protective layer can be controlled more. In addition, it is more preferable that arithmetic mean roughness Ra of the area | region where the said porous protective layer is formed at least in the said process (b) is 2.0-5.0 micrometers among the surfaces of a sensor element.

  In this case, in the step (a), a coating layer is formed in a region where the porous protective layer is formed in at least one of the steps (b) and (c) on the surface of the sensor element. The arithmetic average roughness Ra of the surface of the coating layer may be 2.0 to 5.0 μm. By doing so, for example, even when the arithmetic average roughness Ra of the surface of the sensor element body is difficult to be set to 2.0 to 5.0 μm, the porous protective layer easily adheres to the surface of the sensor element (= the surface of the coating layer). An effect is obtained.

  In the gas sensor manufacturing method of the present invention, in the step (a), a coating layer is formed on the surface of the sensor element in a region where the porous protective layer is formed in at least one of the steps (b) and (c). The porosity of the coating layer may be 10 to 71%. By setting the porosity of the coating layer to 10% or more, the porous protective layer partially enters into the pores of the coating layer and easily adheres to the surface of the sensor element (= the surface of the coating layer). By setting the porosity of the coating layer to 71% or less, the strength of the coating layer becomes sufficient, and peeling of the coating layer can be suppressed.

  In the gas sensor manufacturing method of the present invention, in the steps (b) and (c), the porous protective layer may be formed by plasma spraying. When the porous protective layer is formed by plasma spraying, unlike the case where the porous protective layer is formed by dipping or the like, for example, the porous protective layer is formed for each surface of the sensor element. In this case, in the steps (b) and (c), in the state where the distance W between the plasma gas outlet of the plasma gun and the surface of the sensor element on which the porous protective layer is formed is 50 mm to 300 mm. Thermal spraying may be performed. By setting the distance W to 50 mm or more, the material particles of the porous protective layer sprayed from the plasma gun are suppressed from physical shock and thermal shock when colliding with the sensor element, and the sensor element is cracked. It can be suppressed more. Further, by setting the distance W to 300 mm or less, it is possible to suppress the raw material particles from being excessively dispersed on the surface of the sensor element and to form the porous protective layer more reliably. The distance W may be 120 mm to 250 mm.

  In the method for producing a gas sensor of the present invention, the porous layers are formed on one end surface in the longitudinal direction and four surfaces perpendicular to the one end surface by the steps (b) and (c), respectively. A protective layer may be formed to form the porous protective portion covering a region from one end in the longitudinal direction of the sensor element to the distance L in the longitudinal direction of the sensor element (where 0 <distance L <Length in the longitudinal direction of the sensor element). By forming the porous protective layer on the five surfaces in this manner, for example, the effect of protecting the sensor element by the porous protective portion is enhanced as compared with the case where the porous protective layer is formed only on the four or less surfaces. .

  In the gas sensor manufacturing method of the present invention, the distance between the sensor element and the surface of the porous protective layer is defined as a distance in the thickness direction, and at least one unformed porous protective layer is formed in the step (c). In this case, the distance in the thickness direction of the porous protective layer to be formed is not more than 10 times the distance in the thickness direction of at least one of the formed porous protective layers connected at the time of forming the porous protective layer. It may be made to become. By doing so, the area to which the porous protective layer to be formed later and the formed porous protective layer are connected is sufficiently large, and the mass of the porous protective layer to be formed later is sufficiently small. The peeling of the porous protective layer formed from can be further suppressed.

1 is a schematic perspective view of a gas sensor 100. FIG. AA sectional drawing of FIG. Explanatory drawing of plasma spraying using the plasma gun 120. FIG. FIG. 3 is an explanatory diagram showing a state in which a porous protective part 90 is formed on the sensor element 101. The cross-sectional schematic diagram which shows a mode that the porous protective layers 91c and 91d are formed. Sectional drawing of the gas sensor 100 of a modification.

  Next, a schematic configuration of the gas sensor 100 including the sensor element 101 which is an example of the embodiment of the present invention will be described. FIG. 1 is a perspective view schematically showing an example of the configuration of the gas sensor 100. FIG. 2 is a cross-sectional view taken along the line AA of FIG. The gas sensor 100 detects the concentration of a predetermined gas such as NOx in a gas to be measured such as an exhaust gas of an automobile by the sensor element 101. The sensor element 101 has a long rectangular parallelepiped shape. The longitudinal direction of the sensor element 101 (left-right direction in FIG. 1) is the front-rear direction, and the thickness direction of the sensor element 101 (up-down direction in FIG. 1) is vertical. The direction. The width direction of sensor element 101 (the direction perpendicular to the front-rear direction and the up-down direction) is the left-right direction. FIG. 1 shows the sensor element 101 as viewed from the upper right front. FIG. 2 is a cross-sectional view of the sensor element 101 taken along the center in the left-right direction.

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 ). The first solid electrolyte layer 4, the spacer layer 5, and the second solid electrolyte layer 6 are elements having a structure in which the layers are laminated in this order from the bottom in the drawing. The solid electrolyte forming these six layers is dense and airtight. The sensor element 101 is manufactured, for example, by performing predetermined processing and circuit pattern printing on a ceramic green sheet corresponding to each layer, stacking them, and firing and integrating them.

  One end portion (front end portion) of the sensor element 101, and between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4, the gas inlet 10 and the first diffusion In a mode in which the rate-limiting portion 11, the buffer space 12, the second diffusion-controlling portion 13, the first internal space 20, the third diffusion-controlling portion 30, and the second internal space 40 are communicated in this order. Adjacently formed.

  The gas introduction port 10, the buffer space 12, the first internal space 20, and the second internal space 40 are provided on the lower surface of the second solid electrolyte layer 6 with the upper portion provided in a state in which the spacer layer 5 is cut out. The space inside the sensor element 101 is defined by the lower part being the upper surface of the first solid electrolyte layer 4 and the side parts being the side surfaces of the spacer layer 5.

  Each of the first diffusion rate controlling unit 11, the second diffusion rate controlling unit 13, and the third diffusion rate controlling unit 30 is provided as two horizontally long slits (the opening has a longitudinal direction in a direction perpendicular to the drawing). . In addition, the site | part from the gas inlet 10 to the 2nd internal space 40 is also called a gas distribution part.

  Further, at a position farther from the front end side than the gas circulation part, the side part is partitioned by the side surface of the first solid electrolyte layer 4 between the upper surface of the third substrate layer 3 and the lower surface of the spacer layer 5. The reference gas introduction space 43 is provided at the position. For example, the atmosphere is introduced into the reference gas introduction space 43 as a reference gas when measuring the NOx concentration.

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

  The reference electrode 42 is an electrode formed in such a manner that it is sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4. As described above, the reference electrode 42 leads to the reference gas introduction space 43. An air 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 gas circulation part, the gas inlet 10 is a part opened to the external space, and the gas to be measured is taken into the sensor element 101 from the external space through the gas inlet 10. The first diffusion control unit 11 is a part that provides a predetermined diffusion resistance to the gas to be measured taken from the gas inlet 10. The buffer space 12 is a space provided to guide the gas to be measured introduced from the first diffusion rate controlling unit 11 to the second diffusion rate controlling unit 13. The second diffusion rate limiting unit 13 is a part 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 to the inside of the first internal space 20, the pressure fluctuation of the gas to be measured in the external space (exhaust pressure pulsation if the gas to be measured is an automobile exhaust gas) ), The gas to be measured that is suddenly taken into the sensor element 101 from the gas inlet 10 is not directly introduced into the first internal space 20, but the first diffusion control unit 11, the buffer space 12, the second After the concentration variation of the gas to be measured is canceled through the diffusion control unit 13, the gas is introduced into the first internal space 20. As a result, the concentration fluctuation of the gas to be measured introduced into the first internal space 20 becomes almost negligible. The first internal space 20 is provided as a space for adjusting the partial pressure of oxygen in the gas to be measured introduced through the second diffusion rate limiting unit 13. The oxygen partial pressure is adjusted by the operation of 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 space 20, and an upper surface of the second solid electrolyte layer 6. An electrochemical pump cell comprising an outer pump electrode 23 provided in a manner exposed to the external space in a region corresponding to the ceiling electrode portion 22a, and a second solid electrolyte layer 6 sandwiched between these electrodes. is there.

  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 inner space 20, and the spacer layer 5 that provides side walls. Yes. 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 space 20, and a bottom portion is formed on the upper surface of the first solid electrolyte layer 4 that provides the bottom surface. Spacer layers in which the electrode portions 22b are formed and the side electrode portions (not shown) constitute both side walls of the first internal space 20 so as to connect the ceiling electrode portions 22a and the bottom electrode portions 22b. 5 is formed on the side wall surface (inner surface), and is disposed in a tunnel-shaped structure at the portion where the side electrode portion is disposed.

The inner pump electrode 22 and the outer pump electrode 23 are formed as a porous cermet electrode (for example, a cermet electrode of Pt and ZrO ₂ containing 1% of Au). The inner pump electrode 22 in contact with the gas to be measured is formed using a material that has a reduced reduction ability for the NOx component in the gas to be measured.

  In the main pump cell 21, a desired pump voltage Vp 0 is applied between the inner pump electrode 22 and the outer pump electrode 23, and the pump current is positive or negative between the inner pump electrode 22 and the outer pump electrode 23. By flowing Ip0, oxygen in the first internal space 20 can be pumped into the external space, or oxygen in the external space can be pumped into the first internal space 20.

  Further, 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, a main pump control oxygen partial pressure detection sensor cell 80.

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

  The third diffusion control unit 30 provides 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, and the gas under measurement is supplied to the gas under measurement. This is the part that leads to the second internal space 40.

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

  In the second internal space 40, after the oxygen concentration (oxygen partial pressure) is adjusted in the first internal space 20 in advance, the auxiliary pump cell 50 further supplies the gas to be measured introduced through the third diffusion control unit. The oxygen partial pressure is adjusted. Thereby, since the oxygen concentration in the second internal space 40 can be kept constant with high accuracy, 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 on substantially the entire lower surface of the second solid electrolyte layer 6 facing the second internal space 40, and an outer pump electrode 23 (outer pump electrode 23). The auxiliary electrochemical pump cell is configured by the second solid electrolyte layer 6 and the sensor element 101 and an appropriate electrode on the outside.

  The auxiliary pump electrode 51 is disposed in the second internal space 40 in the same tunnel configuration as the inner pump electrode 22 provided in the first internal space 20. That is, the ceiling electrode portion 51 a 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 is formed on the first solid electrolyte layer 4. The bottom electrode part 51b is formed, and the side electrode part (not shown) connecting the ceiling electrode part 51a and the bottom electrode part 51b is provided on the spacer layer 5 that provides the side wall of the second internal space 40. It has a tunnel-type structure formed on both wall surfaces. Note that the auxiliary pump electrode 51 is also formed using a material having a reduced reducing ability with respect to the NOx component in the gas to be measured, like the inner pump electrode 22.

  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 in the second internal space 40 is pumped to the external space, or It is possible to pump into the second internal space 40 from the space.

  Further, in order to control the oxygen partial pressure in the atmosphere in 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 auxiliary pump control oxygen partial pressure detection sensor cell 81.

  The auxiliary pump cell 50 performs pumping by the variable power source 52 that is voltage-controlled based on the electromotive force V1 detected by the auxiliary pump control oxygen partial pressure detection sensor cell 81. Thereby, the oxygen partial pressure in the atmosphere in the second internal space 40 is controlled to a low partial pressure that does not substantially affect the measurement of NOx.

  At the same time, 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 main pump control oxygen partial pressure detection sensor cell 80, and the electromotive force V0 is controlled, so that the third diffusion rate limiting unit 30 controls the second internal space. The gradient of the oxygen partial pressure in the gas to be measured introduced into the gas 40 is controlled so as to be always constant. When used as a NOx sensor, the oxygen concentration in the second internal space 40 is maintained at a constant value of about 0.001 ppm by the action of the main pump cell 21 and the auxiliary pump cell 50.

  The measurement 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 a top surface of the first solid electrolyte layer 4 facing the second internal space 40 and spaced from the third diffusion rate-determining portion 30, an outer pump electrode 23, The electrochemical pump cell is constituted by the second solid electrolyte layer 6, the spacer layer 5, and the 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 in the second internal space 40. Further, the measurement electrode 44 is covered with a fourth diffusion rate controlling part 45.

  The 4th diffusion control part 45 is a film | membrane comprised with a ceramic porous body. The fourth diffusion control unit 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 the decomposition of nitrogen oxides in the atmosphere around the measurement electrode 44 can be pumped out, and the generated amount can be detected as the pump current Ip2.

  In order to detect the oxygen partial pressure around the measurement electrode 44, an electrochemical sensor cell, that is, a first solid electrolyte layer 4, a third substrate layer 3, a measurement electrode 44, and a reference electrode 42, that is, A measurement pump control oxygen partial pressure detection sensor cell 82 is configured. The variable power supply 46 is controlled on the basis of the electromotive force V2 detected by the measurement pump control oxygen partial pressure detection sensor cell 82.

The gas to be measured introduced into the second internal space 40 reaches the measurement electrode 44 through the fourth diffusion rate-determining unit 45 under the condition where the oxygen partial pressure is controlled. Nitrogen oxide in the gas to be measured around the measurement electrode 44 is reduced (2NO → N ₂ + O ₂ ) to generate oxygen. The generated oxygen is pumped by the measurement pump cell 41. At this time, the variable power source is set so that the control voltage V2 detected by the measurement pump control oxygen partial pressure detection sensor cell 82 becomes constant. 46 voltage Vp2 is controlled. Since the amount of oxygen generated around the measurement electrode 44 is proportional to the concentration of nitrogen oxide in the gas to be measured, the nitrogen oxide in the gas to be measured using the pump current Ip2 in the measurement pump cell 41. The concentration will be calculated.

  In addition, if the measurement electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42 are combined to form an oxygen partial pressure detecting means as an electrochemical sensor cell, The electromotive force according to the difference between the amount of oxygen generated by the reduction of the NOx component in the surrounding atmosphere and the amount of oxygen contained in the reference atmosphere can be detected, thereby the concentration of the NOx component in the gas to be measured Is also possible.

  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 constitute an electrochemical sensor cell 83. The oxygen partial pressure in the gas to be measured outside the sensor can be detected by 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 the measurement of NOx). A gas to be measured is supplied to the measurement pump cell 41. Therefore, the NOx concentration in the measurement gas is determined based on the pump current Ip2 that flows when oxygen generated by the reduction of NOx is pumped out of the measurement pump cell 41 in proportion to the NOx concentration in the measurement gas. You can know.

  Furthermore, the sensor element 101 includes a heater unit 70 that plays a role of temperature adjustment for heating and maintaining the sensor element 101 in order to increase the oxygen ion conductivity of the solid electrolyte. The heater unit 70 includes a heater connector electrode 71, a heater 72, a through hole 73, a heater insulating layer 74, and a pressure dissipation hole 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 source, power can be supplied to the heater unit 70 from the outside.

  The heater 72 is an electric resistor formed in a form 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 when power is supplied from the outside through the heater connector electrode 71, thereby heating and keeping the solid electrolyte forming the sensor element 101. .

  The heater 72 is embedded over the entire area from the first internal space 20 to the second internal space 40, and the entire sensor element 101 can be adjusted 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 by an insulator such as alumina. The heater insulating layer 74 is formed for the purpose of obtaining 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 dissipating hole 75 is a portion that is provided so as to penetrate the third substrate layer 3 and communicate with the reference gas introduction space 43, and is for the purpose of alleviating the increase in internal pressure accompanying the temperature increase in the heater insulating layer 74. Formed.

  The sensor element 101 includes a coating layer 24 as shown in FIGS. The coating layer 24 includes a coating layer 24a that covers the upper surface of the sensor element 101 (the upper surface of the second solid electrolyte layer 6), a coating layer 24b that covers the lower surface of the sensor element 101 (the lower surface of the first substrate layer 1), It has. Note that the coating layer 24 a also covers the surface of the outer pump electrode 23. The coating layer 24 b does not cover the heater connector electrode 71 on the lower surface of the sensor element 101. Therefore, the coating layer 24b does not prevent the supply of electric power to the heater connector electrode 71 from the outside. The coating layer 24 is made of porous ceramics such as alumina, zirconia, spinel, cordierite, and magnesia. In the present embodiment, the coating layer 24 is a porous ceramic made of alumina. Although it does not specifically limit, the film thickness of the coating layer 24 is 5-50 micrometers, for example. The porosity of the coating layer 24 is preferably 10% to 71%. The porosity of the coating layer 24 may be 70% or less, or 60% or less. Moreover, it is preferable that arithmetic mean roughness Ra of the surface (the upper surface of the coating layer 24a, and the lower surface of the coating layer 24b) of the coating layer 24 shall be 2.0-5.0 micrometers. Although not particularly limited, the arithmetic average roughness Ra of the surface of the main body of the sensor element 101 on which the coating layer 24 is formed (the upper surface of the second solid electrolyte layer 6 and the lower surface of the first substrate layer 1) is: For example, it is 0.3 to 1.0 μm.

  Further, as shown in FIGS. 1 and 2, the sensor element 101 is partially covered with a porous protective part 90. The porous protection part 90 includes porous protection layers 91a to 91e formed on five surfaces of the six surfaces of the sensor element 101, respectively. The porous protective layer 91a covers a part of the upper surface of the sensor element 101 (the upper surface of the coating layer 24a). The porous protective layer 91b covers a part of the lower surface of the sensor element 101 (the lower surface of the coating layer 24b). The porous protective layer 91 c covers a part of the left surface of the sensor element 101. The porous protective layer 91d covers a part of the right surface of the sensor element 101. The porous protective layer 91e covers the entire front end surface of the sensor element 101. In addition, each of the porous protective layers 91a to 91d is the entire surface from the front end face of the sensor element 101 to the distance L (see FIG. 2) in the surface of the sensor element 101 on which the porous protective layers 91a to 91d are formed. Covering. The porous protective layer 91a also covers the portion where the outer pump electrode 23 is formed. The porous protective layer 91e also covers the gas inlet 10, but since the porous protective layer 91e is a porous body, the gas to be measured flows through the porous protective layer 91e and reaches the gas inlet. Is possible. The porous protection part 90 covers a part of the sensor element 101 (a part from the front end surface of the sensor element 101 to the distance L) and protects the part. The porous protection unit 90 plays a role of suppressing the occurrence of cracks in the sensor element 101 due to, for example, moisture in the gas to be measured attached thereto. Further, the porous protective layer 91a plays a role of suppressing deterioration of the outer pump electrode 23 by suppressing oil components and the like contained in the measurement gas from adhering to the outer pump electrode 23. The distance L is a range of (0 <distance L <length in the longitudinal direction of the sensor element) based on the range in which the sensor element 101 is exposed to the gas to be measured in the gas sensor 100, the position of the outer pump electrode 23, and the like. Stipulated in Hereinafter, the porous protective layers 91a to 91e may be referred to as the porous protective layer 91 unless particularly distinguished.

  In the present embodiment, as shown in FIG. 1, the sensor element 101 has a length in the front-rear direction, a width in the left-right direction, and a thickness in the vertical direction, and length> width> thickness. Yes. Further, the distance L is assumed to be larger than the width and thickness of the sensor element 101. Therefore, among the porous protection layers 91a to 91e, the formation area of the porous protection layers 91a and 91b (= distance L × width of the sensor element 101) is the largest, and then the formation area of the porous protection layers 91c and 91d ( = Distance L × thickness of sensor element 101) is wide, and the formation area of porous protective layer 91e (= width of sensor element 101 × thickness) is the narrowest.

  The porous protective layer 91 is made of a porous material such as an alumina porous material, a zirconia porous material, a spinel porous material, a cordierite porous material, a titania porous material, or a magnesia porous material. In the present embodiment, the porous protective layer 91 is made of an alumina porous body. Although not particularly limited, the thickness of the porous protective layer 91 is, for example, 100 to 700 μm, and the porosity of the porous protective layer 91 is, for example, 10% to 40%. In addition, since adhesive force becomes high, it is preferable that coating layer 24a, 24b and the porous protective layers 91a and 91b formed in the surface are the same materials.

  Next, a method for manufacturing the gas sensor 100 will be described. In the manufacturing method of the gas sensor 100, first, the sensor element 101 is manufactured, and then the porous protection part 90 is formed on the sensor element 101.

  First, a method for manufacturing the sensor element 101 before forming the porous protection part 90 will be described. First, six green ceramic green sheets are prepared. And each corresponding to each of the 1st substrate layer 1, the 2nd substrate layer 2, the 3rd substrate layer 3, the 1st solid electrolyte layer 4, the spacer layer 5, and the 2nd solid electrolyte layer 6, A pattern such as an electrode, an insulating layer, and a resistance heating element is printed on the ceramic green sheet. Further, a paste that becomes the coating layer 24a after firing is screen-printed on the surface of the ceramic green sheet that becomes the second solid electrolyte layer 6 (the surface that becomes the upper surface of the sensor element 101). Similarly, a paste that becomes the coating layer 24b after firing is screen-printed on the surface of the ceramic green sheet that becomes the first substrate layer 1 (the surface that becomes the lower surface of the sensor element 101). The paste used as the coating layers 24a and 24b is a mixture of the raw material powder (alumina powder in this embodiment) made of the material of the coating layer 24 described above, an organic binder, an organic solvent, and the like. The paste is preferably adjusted in advance so that the arithmetic average roughness Ra of the surface of the coating layer 24 after firing is 2.0 to 5.0 μm. Although not particularly limited thereto, for example, the particle size of the raw material powder is D50 = 2 to 20 μm, the volume ratio is 5 to 20 vol%, the binder solution is 20 to 40 vol%, and the cosolvent is 30 to 50 vol%. The paste is prepared by mixing 1 to 5 vol% of the dispersant and mixing the mixture for 2 to 6 hours at a rotation speed of 50 to 250 rpm, so that the arithmetic average roughness Ra of the surface of the coating layer 24 after firing is 2. It can be set to 0-5.0 micrometers. The paste is preferably adjusted in advance so that the porosity of the coating layer 24 after firing is 10% to 71%. For example, the porosity of the coating layer 24 after firing is 10 by adjusting the blending ratio of the pore former to be included in the paste, adjusting the particle size of the raw material powder, or adjusting the blending ratio of the binder solution. It can adjust so that it may become% -71%. After forming various patterns in this way, the green sheet is dried. Then, they are laminated to form a laminate. The laminated body thus obtained includes a plurality of sensor elements 101. The laminate is cut into pieces of the sensor element 101 and fired at a predetermined firing temperature to obtain the sensor element 101. A method of manufacturing the sensor element 101 by laminating a plurality of green sheets is known, and is described in, for example, Japanese Patent Application Laid-Open Nos. 2008-164411 and 2009-175099.

  Next, a method for forming the porous protection part 90 on the sensor element 101 will be described. In the present embodiment, the porous protective layers 91a to 91e of the porous protective portion 90 are formed one by one by plasma spraying. FIG. 3 is an explanatory diagram of plasma spraying using the plasma gun 120. FIG. 3 shows a state where the porous protective layer 91a is formed as an example, and the plasma gun 120 is shown in cross section. The plasma gun 120 includes an anode 126 and a cathode 128 that serve as electrodes for generating plasma, and a substantially cylindrical outer peripheral portion 122 that covers them. The outer peripheral portion 122 includes an insulating portion (insulator) 123 for insulating from the anode 126. At the lower end of the outer peripheral portion 122, a powder supply portion 132 for supplying a powder sprayed material 134 that is a material for forming the porous protective layer 91 is formed. A water cooling jacket 124 is provided between the outer peripheral portion 122 and the anode 126, thereby enabling the anode 126 to be cooled. The anode 126 is formed in a cylindrical shape, and has a nozzle 126a that opens downward. A plasma generating gas 130 is supplied between the anode 126 and the cathode 128 from above. Such a plasma gun 120 is known and is described in, for example, Patent Document 1 described above.

  When the porous protective layer 91a is formed, a voltage is applied between the anode 126 and the cathode 128 of the plasma gun 120, and arc discharge is performed in the presence of the supplied plasma generating gas 130 to generate plasma. The working gas 130 is brought into a high temperature plasma state. The gas in the plasma state is ejected from the nozzle 126a downward in FIG. 3 as a high-temperature and high-speed plasma jet. On the other hand, the powder spraying material 134 is supplied from the powder supply unit 132 together with the carrier gas. Accordingly, the powder sprayed material 134 is heated and melted and accelerated by the plasma, collides with the surface (upper surface) of the sensor element 101, and rapidly solidifies to form the porous protective layer 91a. The direction of thermal spraying of the plasma gun 120 (the direction of the nozzle 126a) is not particularly limited as long as the porous protective layer 91a can be formed. The porous protective layers 91b to 91e are also formed one by one in the same manner except that the surface to be formed on the sensor element 101 is different. The porous protective layers 91a and 91b are respectively formed on the surfaces of the coating layers 24a and 24b as described above. The porous protective layers 91c to 91e are directly formed on the surface of the main body (each layer 1 to 6) of the sensor element 101. Note that the plasma spraying is performed, for example, in an atmosphere of air and room temperature.

  Here, as the plasma generating gas 130, for example, an inert gas such as an argon gas can be used. Further, since plasma is easily generated, it is preferable to use a mixture of argon and hydrogen as the plasma generating gas 130. Although not particularly limited, the flow rate of argon gas is, for example, 40 to 50 L / min, and the flow rate of hydrogen is, for example, 9 to 11 L / min. The voltage applied between the anode 126 and the cathode 128 is a DC voltage of 50 to 70 V, for example, and the current is 500 to 550 A, for example.

  The powder sprayed material 134 is a powder that becomes the material of the porous protective layer 91 described above, and is alumina powder in this embodiment. Although it does not specifically limit, the particle size of the powder spraying material 134 is 10 micrometers-30 micrometers, for example. As the carrier gas used for supplying the powder spray material 134, for example, the same argon gas as the plasma generating gas 130 can be used. Although not particularly limited, the flow rate of the carrier gas is, for example, 3 to 4 L / min.

  When performing plasma spraying, the distance W between the nozzle 126a, which is the plasma gas outlet in the plasma gun 120, and the surface on which the porous protective layer 91 is formed in the sensor element 101 (the upper surface of the coating layer 24a in FIG. 3) is 50 mm. It is preferable to set it to -300 mm. The distance W may be 120 mm to 250 mm. Further, plasma spraying may be performed while appropriately moving the plasma gun 120 (moving left and right in FIG. 3) according to the area where the porous protective layer 91 is formed. In this case, the distance W is within the above-described range. Is preferably maintained. The time for plasma spraying may be appropriately determined according to the film thickness and area of the porous protective layer 91 to be formed. In the case where the porous protective layer 91 is formed on a part of the surface of the sensor element 101 (region from the front end to the distance L) like the porous protective layer 91a to the porous protective layer 91d. A region where the porous protective layer 91 is not formed may be covered with a mask.

  Next, the formation order of the porous protective layers 91a to 91e will be described. FIG. 4 is an explanatory view showing a state in which the porous protection part 90 is formed on the sensor element 101. First, with respect to the sensor element 101 (FIG. 4A) prepared as described above, the porous protective layer 91a, which is the two porous protective layers 91 having the largest formation area among the porous protective portions 90, 91b is formed in advance (FIG. 4B). Note that either the porous protective layer 91a or the porous protective layer 91b may be formed first. Thereby, the area | region from the front end to the distance L is covered with the porous protective layers 91a and 91b among the upper surface and lower surface of the sensor element 101. FIG.

  Subsequently, porous protective layers 91c to 91e, which are unformed porous protective layers 91 in the porous protective portion 90, are formed by plasma spraying. In the present embodiment, the porous protective layers 91c and 91d are first formed on the left and right surfaces of the sensor element 101, respectively (FIG. 4C). Any of the porous protective layer 91c and the porous protective layer 91d may be formed first. Thereby, the area | region from the front end to the distance L is covered with the porous protective layers 91c and 91d among the left surface and the right surface of the sensor element 101. FIG. Since the porous protective layers 91a and 91b are already formed, for example, when the porous protective layer 91d is formed, the upper end (side portion along the front-rear direction) of the right surface of the sensor element 101 is porous. The protective layer 91a (the right end portion thereof) is present, and the porous protective layer 91b (the right end portion thereof) is present at the lower end (side portion along the front-rear direction) of the right surface. The porous protective layer 91d covers the right surface of the sensor element 101 and is formed so as to be connected to the porous protective layers 91a and 91b (between the porous protective layers 91a and 91b). Similarly, the porous protective layer 91c is formed so as to be connected to the porous protective layer 91a (the left end portion thereof) and the porous protective layer 91b (the left end portion thereof).

  Next, an unformed porous protective layer 91e in the porous protective portion 90 is formed by plasma spraying (FIG. 3D). Thereby, the front end surface of the sensor element 101 is covered with the porous protective layer 91e. The porous protective layers 91a to 91d are formed in advance, and the porous protective layer 91e is formed so as to be connected to the porous protective layers 91a to 91d (front end portions thereof). As described above, the porous protective layers 91 a to 91 e are respectively formed on the upper, lower, left, and right surfaces and the front end surface of the sensor element 101 to form the porous protective portion 90, thereby obtaining the gas sensor 100.

  Here, the correspondence between the components of the present embodiment and the components of the present invention will be clarified. The sensor element 101 of this embodiment corresponds to the sensor element of the present invention, the porous protection part 90 corresponds to the porous protection part, and the porous protection layers 91a and 91b are formed in advance in the step (b). The porous protective layer 91c corresponds to the porous protective layer formed in the step (c). The porous protective layers 91d and 91e also correspond to the porous protective layer formed in the step (c). Further, the front end surface of the sensor element 101 corresponds to “one end surface in the longitudinal direction of the surface of the sensor element”.

  In the manufacturing method of the gas sensor 100 according to the present embodiment described in detail above, the porous protective portion having the porous protective layers 91a to 91e formed on the five surfaces among the six surfaces of the long rectangular parallelepiped sensor element. In forming 90, two porous protective layers 91a and 91b having the largest formation area are formed in advance. Thus, since the two porous protective layers 91a and 91b having the largest formation area are first formed, the porous protective layer 91a is formed as compared with the case of forming the other porous protective layers 91c to 91e having a narrow formation area. , 91b are easily in close contact with the sensor element 101. And unformed porous protective layers 91c-91e are formed among porous protective parts 90 so that it may connect with at least two porous protective layers 91 (91a, 91b) which have been formed. Thereby, the porous protective layers 91c to 91e formed later are connected to at least two porous protective layers 91 that have been formed, so that the porous protective layers 91c to 91e are hardly peeled off from the sensor element 101 even if the formation area is small. As described above, peeling of the porous protective layer 91 can be further suppressed.

  The two porous protective layers 91 a and 91 b formed in advance are positioned on the upper and lower surfaces which are surfaces opposite to each other among the six surfaces of the sensor element 101. Therefore, the porous protective layers 91c to 91e formed to be connected to the two previously formed porous protective layers 91a and 91b are connected to the two porous protective layers 91a and 91b on both sides of the formation surface. Therefore, the effect of suppressing peeling is enhanced.

  Further, of each surface (upper and lower surfaces) forming the two porous protective layers 91a and 91b, a region including the end portion (right end, left end, front end) on the surface side where the porous protective layers 91c to 91e are formed. The porous protective layers 91a and 91b are formed in advance. Therefore, it becomes easy to connect the two previously formed porous protective layers 91a and 91b and the porous protective layers 91c to 91e to be formed later.

  Furthermore, coating layers 24a and 24b are formed on the upper and lower surfaces of the sensor element surface including the region where the porous protective layers 91a and 91b are formed. By setting the arithmetic average roughness Ra of the surfaces of the coating layers 24 a and 24 b to 2.0 to 5.0 μm, the porous protective layers 91 a and 91 b are in close contact with the surface of the sensor element 101 (the surface of the coating layer 24). It becomes easy and peeling of porous protective layers 91a and 91b can be controlled more.

  Also, coating layers 24a and 24b are formed on the upper and lower surfaces of the sensor element surface including the region where the porous protective layers 91a and 91b are formed. By setting the porosity of the coating layer 24 to 10% or more, the porous protective layers 91a and 91b partially enter the pores of the coating layer 24 and adhere to the surface of the sensor element 101 (= the surface of the coating layer 24). It becomes easy to do. Further, by setting the porosity of the coating layer 24 to 71% or less, the strength of the coating layer 24 becomes sufficient, and peeling of the coating layer 24 can be suppressed.

  In addition, the porous protective layer 91 is formed by plasma spraying. When the porous protective layer 91 is formed by plasma spraying, the porous protective layer 91 is formed on each surface of the sensor element 101, unlike the case where a plurality of porous protective layers are collectively formed by dipping or the like. Therefore, the significance of applying the present invention is high. In addition, by setting the distance W between the nozzle 126a of the plasma gun 120 and the surface of the sensor element 101 on which the porous protective layer 91 is formed to 50 mm or more, the raw material particles of the porous protective layer 91 sprayed from the plasma gun 120 ( It is possible to suppress the occurrence of cracks in the sensor element 101 by suppressing the physical shock and thermal shock when the powder sprayed material 134) collides with the sensor element 101. Further, by setting the distance W to 300 mm or less, it is possible to suppress the raw material particles from being excessively dispersed on the surface of the sensor element 101 and to form the porous protective layer 91 more reliably.

  In addition, a porous protective layer 91 is formed on each of the front end surface which is one end surface in the longitudinal direction of the surface of the sensor element 101 and the upper, lower, left and right surfaces which are four surfaces perpendicular to the front end surface. A porous protective portion 90 is formed to cover a region from one end in the longitudinal direction of 101 to a distance L in the longitudinal direction of the sensor element 101. Thus, by forming the porous protective layer 91 on the five surfaces, the sensor element 101 is protected by the porous protective portion 90 as compared with the case where the porous protective layer 91 is formed only on the four or less surfaces, for example. The effect to do increases.

  It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

  For example, in the above-described embodiment, the coating layer 24 covers the region where the porous protective layers 91a and 91b are not formed on the upper surface and the lower surface of the sensor element 101. However, the present invention is not limited to this. The coating layers 24a and 24b only need to cover at least the regions where the porous protective layers 91a and 91b are formed. In addition, a coating layer may be formed on one or more of the regions where the porous protective layers 91c to 91e are formed on the surface of the sensor element 101. Alternatively, the sensor element 101 may not include the coating layer 24.

  In the above-described embodiment, it has been described that the porous protective layers 91a and 91b are easily adhered to the sensor element 101 by setting the arithmetic average roughness Ra of the surface of the coating layer 24 to 2.0 to 5.0 μm. However, the arithmetic average roughness Ra of the region where the porous protective layer 91 is formed in the surface of the sensor element 101 may be 2.0 to 5.0 μm. For example, even when the sensor element 101 does not include the coating layer 24, the arithmetic average roughness Ra of the surface of the main body (layer 1 to layer 6) of the sensor element 101 may be 2.0 to 5.0 μm. In this case, the arithmetic average roughness Ra may be set to 2.0 to 5.0 μm, for example, by roughening the surface of the main body of the sensor element 101 with sandblasting or the like.

  In the embodiment described above, the porous protective layer 91 of the porous protective part 90 is formed by plasma spraying, but is not limited thereto. Even if it is another formation method, the effect which suppresses peeling of the porous protective layer 91 more similarly to this embodiment is acquired by forming the porous protective layers 91a-91e in the order mentioned above. For example, the porous protective layer 91 may be formed by screen printing in the same manner as the coating layer 24. In this case, the porous protective layers 91a and 91b may be formed in advance by screen printing the paste, drying and baking, and then the porous protective layers 91c to 91e may be printed, dried and fired. Moreover, you may form one or more among the porous protective layers 91a-91e with a method and material different from others.

  In the above-described embodiment, the porous protective layers 91c and 91d are first formed after the porous protective layers 91a and 91b are formed in advance. However, the present invention is not limited to this. After the porous protective layers 91a and 91b are formed in advance, the porous protective layer 91e may be formed first. However, in the order of the above-described embodiment, when the porous protective layer 91e is formed, the porous protective layer 91e can be formed so as to be connected to the four porous protective layers 91a to 91d. On the other hand, after forming the porous protective layers 91a and 91b in advance, when the porous protective layer 91e is first formed, only the porous protective layers 91a and 91b are already formed. The porous protective layer 91 is connected. Here, the porous protective layer 91 having a smaller formation area tends to have a lower adhesion with the sensor element 101. For this reason, the porous protective layer 91e having the smallest formation area is preferably formed last in order to be connected to as many porous protective layers 91 as possible. That is, the order of forming the remaining porous protective layer 91 after the prior lamination in the porous protective portion 90 is such that the porous protective layer 91 having a smaller formation area has a larger number of formed porous protective layers at the time of formation. It is preferable to set the order so as to tend to be connected to 91.

  In the embodiment described above, the porous protection part 90 includes the porous protection layers 91a to 91e, but is not limited thereto. The porous protection part 90 only needs to have a porous protection layer 91 formed on at least three of the six surfaces of the sensor element 101. For example, the porous protective layer 91e may not be provided in the above-described embodiment. Moreover, although all the porous protective layers 91a-91d shall cover the distance L from the front end of the sensor element 101, it is not restricted to this. For example, one or more of the porous protective layers 91a to 91d may be different in length in the longitudinal direction (distance L in the present embodiment) from the other.

  In the embodiment described above, the porous protective layer 91a covers a region from the front end to the distance L in the upper surface of the sensor element 101, and the porous protective layer is also formed on the left end, right end, and front end of the upper surface of the sensor element 101. Although 91a is assumed to exist, the present invention is not limited to this. For example, the porous protective layer 91a may not be formed up to the right end of the upper surface of the sensor element 101 (the side portion along the front-rear direction of the upper surface of the sensor element 101) (for example, the porous protective layer 91a is the right end). Etc.). Even in such a case, the porous protective layer 91d can be formed so as to be connected to the porous protective layer 91a by forming the porous protective layer 91d so as to protrude slightly to the upper surface side of the sensor element 101. . The same applies to the left end and the front end of the upper surface of the sensor element 101 in the porous protective layer 91a. The same applies to the porous protective layer 91b.

  In the above-described embodiment, the porous protective layers 91a and 91b positioned on the upper and lower surfaces, which are surfaces opposite to each other, of the sensor element 101 are formed in advance, but the present invention is not limited to this. For example, a case is considered in which the upper and lower thicknesses and the left and right widths of the sensor element 101 are the same, and the formation areas of the porous protective layers 91a to 91d are the same and widest. In such a case, any two of the porous protective layers 91a to 91d may be formed in advance. For example, the porous protective layers 91a and 91c may be formed in advance. In this case, since the porous protective layers 91b and 91d cannot be formed so as to be connected to the porous protective layers 91a and 91c, the porous protective layer 91e is first formed after the porous protective layers 91a and 91c are formed. Will do. Thereafter, the porous protective layer 91d is formed so as to be connected to the porous protective layers 91a and 91e, or the porous protective layer 91b is formed so as to be connected to the porous protective layers 91c and 91e. Finally, the remaining porous protective layer 91 (91b or 91d) is formed so as to connect at least two porous protective layers 91 that have been formed. However, in order to increase the effect of suppressing peeling, it is preferable that the two porous protective layers 91 positioned on the opposite surfaces are formed in advance.

  In the embodiment described above, the distance L is larger than the width and thickness of the sensor element 101, but is not limited thereto. For example, when the distance L is smaller than the width and thickness of the sensor element 101, the formation area of the porous protective layer 91e is the largest. In this case, the porous protective layer 91e and the porous protective layer 91 having the next largest formation area are formed in advance.

  In the embodiment described above, when forming at least one unformed porous protective layer 91 among the porous protective portions 90 with the distance between the sensor element 101 and the surface of the porous protective layer 91 being the thickness direction distance. The distance in the thickness direction of the porous protective layer 91 to be formed is not more than 10 times the distance in the thickness direction of at least one of the formed porous protective layers 91 connected when the porous protective layer 91 is formed. It is preferable to make it. This will be described with reference to FIG. FIG. 5 is a schematic cross-sectional view showing how the porous protective layers 91c and 91d are formed so as to be connected to the formed porous protective layers 91a and 91b. FIG. 5A is a schematic cross-sectional view before the formation of the porous protective layers 91c and 91d, and FIG. 5B is a schematic cross-sectional view after the formation of the porous protective layers 91c and 91d. FIGS. 5A and 5B schematically show cross sections of the sensor element 101 of FIGS. 4B and 4C cut perpendicularly to the longitudinal direction (front-rear direction), respectively. In FIG. 5A, the distance between the surface of the sensor element 101 (second solid electrolyte layer 6) and the surface of the porous protective layer 91a (the upper surface in FIG. 5A) is shown as a distance A. A is the thickness direction distance of the porous protective layer 91a. Similarly, the distance between the surface of the sensor element 101 (first substrate layer 1) and the surface of the porous protective layer 91b (the lower surface in FIG. 5A) is shown as a distance B, and this distance B is the porous protection. The distance in the thickness direction of the layer 91b. When the porous protective layer 91c is formed as shown in FIG. 5B, at least one thickness direction of the formed porous protective layers 91a and 91b connected when the porous protective layer 91c is formed. It is preferable that the distance is 10 times or less. That is, the distance C, which is the distance in the thickness direction of the porous protective layer 91c to be formed, is preferably 10 times or less of at least one of the distance A and the distance B. Here, the larger the distance A and the distance B, the larger the area in which the porous protective layer 91c and the porous protective layers 91a and 91b are connected when the porous protective layer 91c is formed. Peeling tends to be more suppressed. Moreover, since the porous protective layer 91c is thin, that is, the mass is small as the distance C is small, peeling of the porous protective layer 91c tends to be further suppressed. And if distance C is 10 times or less of at least one of distance A and distance B, peeling of the porous protective layer 91c will be suppressed more by these effects. In addition, it is more preferable that the distance C is 10 times or less with respect to both the distance A and the distance B. Similarly, when forming the porous protective layer 91d, the distance D, which is the distance in the thickness direction of the porous protective layer 91d, is preferably 10 times or less of at least one of the distance A and the distance B. It is more preferable that the ratio is 10 times or less for both A and distance B. Since the distance in the thickness direction is “the distance between the sensor element and the surface of the porous protective layer 91”, another layer such as the coating layer 24 exists between the sensor element 101 and the porous protective layer 91. In this case, not only the thickness of the porous protective layer 91 but also the thickness including other layers is the thickness direction distance. For example, in FIG. 5, the distance A which is the distance in the thickness direction of the porous protective layer 91a is the sum of the thickness of the porous protective layer 91a and the thickness of the coating layer 24a. On the other hand, when there is no other layer between the sensor element 101 and the porous protective layer 91, the thickness of the porous protective layer 91 is the thickness direction distance. For example, as shown in FIG. 5B, the distance C that is the distance in the thickness direction of the porous protective layer 91c is equal to the thickness of the porous protective layer 91c. In the embodiment described above, when the porous protective layer 91e shown in FIG. 4D is formed, the porous protective layers 91a to 91d are already formed, and the porous protective layer 91e is porous. It is connected to any of the quality protective layers 91a to 91d. In this case, it is preferable that the thickness direction distance of the porous protective layer 91e is 10 times or less with respect to at least one of the thickness direction distances (distances A to D) of the porous protective layers 91a to 91d. In addition, each thickness direction distance of the porous protective layer 91 is good also as 100 micrometers-700 micrometers, and good also as 100 micrometers-500 micrometers.

In the above-described embodiment, it is described that the coating layers 24a and 24b and the porous protective layers 91a and 91b formed on the surfaces thereof are preferably the same material. However, the coating layers 24a and 24b are porous. The same material as the quality protective layers 91a and 91b may be included. In this case, the coating layers 24a and 24b are made of the same material (for example, zirconia (ZrO ₂ )) as the solid electrolyte layer (the second solid electrolyte layer 6 and the first substrate layer 1 in the above-described embodiment) on which the coating layers 24a and 24b are formed. It is preferable to include. The coating layers 24a and 24b include the same material as the solid electrolyte layer on which the coating layers 24a and 24b are formed, and the same material as the porous protective layer 91 formed on the surface of the coating layers 24a and 24b. It becomes easier to bond the layer and the porous protective layer 91.

  In the above-described embodiment, the sensor element 101 of the gas sensor 100 includes the first internal space 20 and the second internal space 40, but is not limited thereto. For example, a third internal space may be further provided. FIG. 6 shows a cross-sectional view of a gas sensor 100 according to a modified example in this case. As shown in the figure, in the gas sensor 100 of this modification, the measurement electrode 44 is not covered with the fourth diffusion rate-determining part 45. Instead, between the auxiliary pump electrode 51 and the measurement electrode 44, a fourth diffusion rate controlling unit 60 similar to the third diffusion rate controlling unit 30 is formed. As a result, the second internal space 40, the fourth diffusion-controlling portion 60, and the third internal space 61 are formed adjacent to each other in this order, and constitute a part of the gas circulation portion. ing. The auxiliary pump electrode 51 is disposed in the second internal space 40, and the measurement electrode 44 is disposed on the upper surface of the first solid electrolyte layer 4 facing the third internal space 61. In the gas sensor 100 of this modification, since the fourth diffusion rate controlling unit 60 functions in the same manner as the fourth diffusion rate controlling unit 45 in FIG. 2, the NOx concentration in the gas to be measured is detected as in the above-described embodiment. Can do. Moreover, also when manufacturing the gas sensor 100 of this modification, the effect similar to embodiment mentioned above is acquired by using the manufacturing method similar to embodiment mentioned above. For example, peeling of the porous protective layer 91 can be further suppressed.

  In the above-described embodiment, the gas sensor of the present invention is embodied in the gas sensor 100 including the variable power sources 25, 46, 52, etc., but the gas sensor of the present invention includes these variable power sources 25, 46, 52, You may embody as a gas sensor (For example, the gas sensor provided with the sensor element 101, the coating layer 24, and the porous protection part 90) except structures, such as external wiring.

  Hereinafter, an example in which the gas sensor 100 is specifically manufactured will be described as an experimental example. Experimental Examples 1, 2, 5-9, and 11-20 correspond to Examples of the present invention, and Experimental Examples 3, 4, and 10 correspond to Comparative Examples. In addition, this invention is not limited to a following example.

[Experiment 1]
As Experimental Example 1, 20 gas sensors 100 were produced according to the method for producing the gas sensor 100 of the embodiment described above. Specifically, first, the sensor element 101 having a length in the front-rear direction of 67.5 mm, a width in the left-right direction of 4.25 mm, and a thickness in the vertical direction of 1.45 mm was manufactured. In preparing the sensor element 101, the paste for forming the coating layer 24 was adjusted 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 co-solvent (acetone) is 45 vol%, the dispersant (poly These were prepared with 5 vol% of oxyethylene styrenated phenyl ether) and mixed for 3 hours with a pot mill mixer at 200 rpm to prepare a paste. Moreover, when the film thickness of the coating layer 24 was measured about the produced sensor element 101, all were about 10-20 micrometers. Further, the arithmetic average roughness Ra of the surfaces of the coating layers 24a and 24b was about 2.4 μm. The dimension of the sensor element 101 is a dimension including the coating layer 24. The porosity of the coating layer 24 was about 20%.

  Subsequently, the porous protective layer 91 was formed in the order of the porous protective layers 91 a, 91 b, 91 c, 91 d, 91 e on the surface of the sensor element 101 to form the porous protective portion 90, thereby providing the gas sensor 100. The plasma spraying conditions for forming the porous protective layer 91 were as follows. As the plasma generating gas 130, a mixture of argon gas (flow rate 50 L / min) and hydrogen (flow rate 10 L / min) was used. The voltage applied between the anode 126 and the cathode 128 was a DC voltage of 70V. The current was 500A. As the powder spray material 134, an alumina powder having a particle size distribution in the range of 10 μm to 30 μm was used. The carrier gas used to supply the powder spray material 134 was argon gas (flow rate 4 L / min). The distance W was 150 mm. The distance L was 10 mm. Moreover, plasma spraying was performed in the atmosphere of air and room temperature. The direction of thermal spraying of the plasma gun 120 (the direction of the nozzle 126a) was set perpendicular to the formation surface of the porous protective layer 91 in the sensor element 101. The film thicknesses of the formed porous protective layers 91a to 91e were all about 450 μm. None of the 20 gas sensors 100 of Experimental Example 1 had the porous protective layer 91 peeled off.

[Experiment 2]
Twenty gas sensors 100 were produced in the same manner as in Experimental Example 1 except that the formation order of the porous protective layer 91a and the porous protective layer 91b in Experimental Example 1 was reversed. That is, in Experimental Example 2, the porous protective layer 91 was formed in the order of the porous protective layers 91b, 91a, 91c, 91d, and 91e. In all of the 20 gas sensors 100 of Experimental Example 2, the porous protective layer 91 was not peeled off.

[Experiment 3]
Twenty gas sensors 100 were produced in the same manner as in Experimental Example 1 except that the porous protective layers 91c and 91d were first formed among the porous protective layers 91a to 91e. That is, in Experimental Example 3, the porous protective layer 91 was formed in the order of the porous protective layers 91c, 91d, 91a, 91b, 91e. Of the 20 gas sensors 100 of Experimental Example 3, two of the porous protective layers 91a and 91d were peeled off. In addition, it is thought that the porous protective layer 91a peeled with peeling of the porous protective layer 91d.

[Experimental Example 4]
Twenty gas sensors 100 were produced in the same manner as in Experimental Example 1 except that the porous protective layer 91e was first formed among the porous protective layers 91a to 91e. That is, in Experimental Example 4, the porous protective layer 91 was formed in the order of the porous protective layers 91e, 91a, 91b, 91c, and 91d. Of the 20 gas sensors 100 of Experimental Example 4, peeling of the porous protective layer 91e occurred in three of them.

  From the results of Experimental Examples 1 to 4, the porous protective layers 91a and 91b having the widest formation area are formed in advance, and then the porous protective layer 91c is connected so that at least two formed porous protective layers 91 are connected. It was confirmed that the peeling of the porous protective layer 91 can be further suppressed by forming ~ 91e.

[Experimental Examples 5 to 10]
In Experimental Examples 5 to 9, 20 gas sensors 100 were produced in the same manner as in Experimental Example 1 except that the distance W when performing plasma spraying was variously changed. Specifically, in Experimental Example 5, the distance W was set to 30 mm. In Experimental Example 6, the distance W was set to 100 mm. In Experimental Example 7, the distance W was 150 mm. In Experimental Example 8, the distance W was 200 mm. In Experimental Example 9, the distance W was 250 mm. In any of the 20 gas sensors 100 of Experimental Examples 5 to 9, no peeling of the porous protective layer 91 occurred. In addition, when the distance W was set to 320 mm as Experimental Example 10, the powder spray material 134 was dispersed too much and the porous protective layer 91 was not formed.

  In Experimental Examples 5 to 9, the produced 20 gas sensors 100 were inspected for cracks. Specifically, first, the main pump cell 21, the auxiliary pump cell 50, the oxygen partial pressure detection sensor cell 80 for main pump control, the oxygen partial pressure detection sensor cell 81 for auxiliary pump control, etc. are actuated in the atmospheric air, and the first internal air is discharged. The oxygen concentration in the in-house 20 was controlled to be kept at a predetermined constant value. In this state, after waiting for the pump current Ip0 to stabilize, the value of the pump current Ip0 was measured. And the presence or absence of the crack of the sensor element 101 was determined based on whether the pump current Ip0 exceeded a predetermined threshold value. When a crack is generated in the sensor element 101, oxygen easily flows into the first internal space 20 through the crack portion, and the value of the pump current Ip0 increases. For this reason, when the pump current Ip0 exceeds a predetermined threshold value determined by experiment, it is determined that the sensor element 101 is cracked. In Experimental Example 5, cracks occurred in all 20 gas sensors 100. In Experimental Example 6, cracks occurred in the five gas sensors 100. In Experimental Examples 7 to 9, no cracks occurred in any of the 20 samples.

  From the results of Experimental Examples 5 to 10, it is considered that the occurrence of cracks in the sensor element 101 can be further suppressed by setting the distance W to 50 mm or more. Moreover, it is thought that the porous protective layer 91 can be more reliably formed by setting the distance W to 300 mm or less.

[Experimental Examples 11 to 20]
In Experimental Examples 11 to 20, 20 gas sensors 100 were produced in the same manner as in Experimental Example 1 except that the porosity of the coating layer 24 was variously changed. Specifically, in the adjustment of the paste for forming the coating layer 24, the sensor elements 101 of Experimental Examples 11 to 20 were manufactured in the same manner as Experimental Example 1 except for the following points. In Experimental Example 11, a raw material powder (alumina powder) was pulverized to have a particle size of D50 = 0.5 μm, and the binder volume ratio was set to ¼ (= 10 vol%). In Experimental Example 12, the volume ratio of the binder was ¼ (= 10 vol%). In Experimental Example 13, the volume ratio of the binder was halved (= 20 vol%). In Experimental Example 14, the sensor element 101 was produced in the same manner as in Experimental Example 1. In Experimental Example 15, 0.225 vol% of a pore former (theobromine) was added to the paste. In Experimental Example 16, 0.85 vol% of a pore former (theobromine) was added to the paste. In Experimental Example 17, 1.75 vol% of a pore former (theobromine) was added to the paste. In Experimental Example 18, 4.25 vol% of a pore former (theobromine) was added to the paste. In Experimental Example 19, 6.5 vol% of a pore former (theobromine) was added to the paste. In Experimental Example 20, 10 vol% of a pore former (theobromine) was added to the paste. The porosity of the coating layer 24 of Experimental Examples 11 to 20 is 5.3%, 10.24%, 15.36%, 20.78%, 37.2%, 51.1%, and 60.7%, respectively. 64.86%, 70.1% and 75%. Moreover, when the film thickness of the coating layer 24 was measured about the sensor element 101 of Experimental example 11-20, all were about 10 micrometers. In addition, the arithmetic average roughness Ra of the surfaces of the coating layers 24a and 24b of Experimental Examples 11 to 20 were both about 2 μm.

  The volume ratio of the raw material powder, the particle diameter of the raw material powder, the volume ratio of the pore former, the volume ratio of the binder, the porosity of the coating layer in the preparation of the paste for forming the coating layer 24 in Experimental Examples 11 to 20, and Table 1 summarizes the number of peeled porous protective layers 91 or coating layers 24 out of 20.

  As shown in Table 1, in Experimental Example 11 in which the porosity of the coating layer 24 was less than 10%, peeling of the porous protective layer 24 occurred in 2 out of 20 samples. Further, in Experimental Example 20 in which the porosity of the coating layer 24 was over 71%, the coating layer 24 was peeled off for two of the twenty. In Experimental Example 20, it is considered that the coating layer 24 peeled off due to the collision of the alumina powder during plasma spraying, and the peeling occurred because the strength of the coating layer 24 was low. On the other hand, in each of Experimental Examples 12 to 19, no peeling of the porous protective layer 91 or the coating layer 24 occurred in any of the 20 samples. From the above results, it is considered that peeling of the porous protective layer 91 can be suppressed by setting the porosity of the coating layer to 10% or more. In addition, it is considered that when the porosity of the coating layer 24 is 71% or less, peeling of the coating layer 24 can be suppressed, and consequently peeling of the porous protective layer 91 can be suppressed.

  DESCRIPTION OF SYMBOLS 1 1st board | substrate layer, 2nd board | substrate layer, 3rd board | substrate layer, 4th 1st solid electrolyte layer, 5 spacer layer, 6 2nd solid electrolyte layer, 10 gas inlet, 11 1st diffusion control part, 12 buffer Space, 13 Second diffusion rate limiting part, 20 First internal space, 21 Main pump cell, 22 Inner pump electrode, 22a Ceiling electrode part, 22b Bottom electrode part, 23 Outer pump electrode, 24, 24a, 24b Coating layer, 25 Variable Power source, 30 3rd diffusion rate limiting part, 40 2nd internal space, 41 measurement pump cell, 42 reference electrode, 43 reference gas introduction space, 44 measurement electrode, 45 4th diffusion rate limiting part, 46 variable power supply, 48 atmosphere introduction layer , 50 Auxiliary pump cell, 51 Auxiliary pump electrode, 51a Ceiling electrode part, 51b Bottom electrode part, 52 Variable power supply, 60 4th diffusion rate limiting part, 61 3rd internal space, 70 Heater part, 71 Heater connector electrode, 72 Heater, 73 Through hole, 74 Heater insulation layer, 75 Pressure diffusion hole, 76, 76a-76c Heater lead wire, 80 Main pump control oxygen partial pressure detection sensor cell, 81 Auxiliary pump control Oxygen partial pressure detection sensor cell, 82 Oxygen partial pressure detection sensor cell for measurement pump control, 83 Sensor cell, 90 Porous protective part, 91, 91a to 91e Porous protective layer, 100 Gas sensor, 101 Sensor element, 120 Plasma gun, 122 Outer peripheral part, 123 insulating part, 124 water cooling jacket, 126 anode, 126a nozzle, 128 cathode, 130 gas for generating plasma, 132 powder supply part, 134 powder spraying material.

Claims (9)

A gas sensor manufacturing method comprising: a long rectangular parallelepiped sensor element; and a porous protective part having a porous protective layer formed on at least three of the six surfaces of the sensor element. ,
(A) preparing the sensor element;
(B) a step of precedingly forming the two porous protective layers having the widest formation area among the porous protective portions;
(C) forming an unformed porous protective layer among the porous protective portions so as to be connected to at least two formed porous protective layers;
The manufacturing method of the gas sensor containing this. In the step (b), the two previously formed porous protective layers are positioned on opposite surfaces of the six surfaces of the sensor element.
The manufacturing method of the gas sensor of Claim 1. In the step (b), among the respective surfaces forming the two porous protective layers, the porous region is formed in a region including an end portion on the surface side where the porous protective layer is formed in the step (c). Pre-form a protective layer,
The manufacturing method of the gas sensor of Claim 1 or 2. In the step (a), the arithmetic average roughness Ra of the surface of the sensor element in which the porous protective layer is formed in at least one of the steps (b) and (c) is 2.0-5. 0.0 μm,
The manufacturing method of the gas sensor of any one of Claims 1-3. In the step (a), a coating layer is formed in a region where the porous protective layer is formed in at least one of the steps (b) and (c) on the surface of the sensor element. The arithmetic average roughness Ra of the surface is 2.0 to 5.0 μm,
The manufacturing method of the gas sensor of Claim 4. In the step (a), a coating layer is formed in a region where the porous protective layer is formed in at least one of the steps (b) and (c) on the surface of the sensor element. The porosity is 10 to 71%.
The manufacturing method of the gas sensor of any one of Claims 1-5. In the steps (b) and (c), the porous protective layer is formed by plasma spraying.
The manufacturing method of the gas sensor of any one of Claims 1-6. By the steps (b) and (c), the porous protective layer is formed on one end surface of the sensor element in the longitudinal direction and four surfaces perpendicular to the one end surface. Forming the porous protective portion covering a region from one end in the longitudinal direction of the element to the distance L in the longitudinal direction of the sensor element (where 0 <distance L <length in the longitudinal direction of the sensor element);
The manufacturing method of the gas sensor of any one of Claims 1-7. The distance between the sensor element and the surface of the porous protective layer as a thickness direction distance,
In the step (c), when forming at least one unformed porous protective layer, the thickness direction distance of the porous protective layer to be formed is connected when the porous protective layer is formed. Not more than 10 times the distance in the thickness direction of at least one of the formed porous protective layers;
The manufacturing method of the gas sensor of any one of Claims 1-8.