JP6488146B2 - Coating method and gas sensor manufacturing method - Google Patents

Description

  The present invention relates to a film manufacturing method and a gas sensor manufacturing method.

  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 film such as a 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, there is a case where it is desired to form a film on a part of the surface of the object. In such a case, it is conceivable to form a film by plasma spraying after covering a region other than the region where the film is to be formed with a mask. However, for example, as shown in FIG. 11A, the end portion of the coating 991 formed on the upper surface of the object 901 may adhere to the mask 910. As a result, for example, as shown in FIG. 11B, the coating 991 may be peeled off when the mask 910 is removed.

  The present invention has been made to solve such a problem, and has as its main object to further suppress the peeling of the coating film when the mask is removed.

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

The method for producing the coating of the present invention comprises:
A method for producing a coating by plasma spraying, comprising:
(A) arranging a mask so as to cover a non-formation area adjacent to the formation area of the film; (b) forming the film in the formation area by plasma spraying;
(C) removing the mask;
Including
The mask has a gap forming portion that forms a gap opened to the formation region side at an end of the non-formation region when the mask is arranged in the step (a).
The height T of the opening of the gap is larger than the film thickness t of the coating formed in the step (b).
Is.

  In this method for producing a coating film of the present invention, the mask covering the non-formation area adjacent to the film formation area has a gap forming portion. When the mask is disposed so as to cover the non-forming region, the gap forming portion forms a gap that opens to the forming region side at the end of the non-forming region on the forming region side. Moreover, the height T of the opening of the gap is larger than the film thickness t of the coating film to be formed. Therefore, it becomes difficult for the edge part by the side of a mask among the coatings formed in a formation area by plasma spraying, and the edge part by the side of the formation area among masks. Thereby, peeling of the film when removing the mask can be further suppressed. In this case, the coating film may be a porous body.

  In the film manufacturing method of the present invention, the height T may be twice or more the film thickness t. If it carries out like this, since the edge part by the side of a mask among coatings will become more difficult to contact the edge part by the side of a formation area among masks, peeling of the film at the time of removing a mask can further be suppressed.

In the coating film manufacturing method of the present invention, the gap forming portion is perpendicular to the opening surface of the gap and is formed in the step (b) with the mask disposed in the step (a). The area S of the gap may be 0.2 mm ² or more when viewed in a cross section parallel to. In this way, the gap is sufficiently large, and even if the end of the film is formed so as to enter the gap, the film and the mask are unlikely to contact each other. Therefore, peeling of the coating film when removing the mask can be further suppressed.

  In the coating film manufacturing method of the present invention, the gap forming portion is perpendicular to the opening surface of the gap and is formed in the step (b) with the mask disposed in the step (a). The length M of the portion exposed to the gap in the non-formed region may be 1 mm or more when viewed in a cross section parallel to the surface. In this way, even if the exposed portion of the non-formation region in the gap (= the portion where the mask is not in direct contact) is sufficient, and the end of the film is formed so as to enter the gap. The film and the mask are difficult to contact. Therefore, peeling of the coating film when removing the mask can be further suppressed.

  In the coating film manufacturing method of the present invention, the gap forming portion has a shape that is spaced apart from the non-formation region and protrudes toward the formation region with the mask disposed in the step (a). May be.

  In the film manufacturing method of the present invention, the mask may be made of metal or resin. In this case, the mask may be made of a heat resistant resin, a water repellent resin, or a resin having heat resistance and water repellency.

  In the method for producing a film of the present invention, the mask may be made of a water-repellent resin or may be coated with a water-repellent coating. If it carries out like this, it can suppress that the formation material of a film adheres to a mask in a process (b). Therefore, peeling of the film when removing the mask in the step (c) can be further suppressed.

The manufacturing method of the gas sensor of the present invention includes:
A gas sensor manufacturing method comprising: a sensor element; and a film formed on a surface of the sensor element,
A first step of preparing the sensor element;
A second step of forming the coating film in the formation region by using a part of the surface of the sensor element as the formation region by the method for manufacturing a coating film according to any one of claims 1 to 5;
Is included.

  In this gas sensor manufacturing method of the present invention, a coating film is formed on a part of the surface of the sensor element by any one of the above-described coating film manufacturing methods of the present invention. Therefore, the effect which suppresses peeling of the film at the time of removing a mask similarly to the manufacturing method of the film mentioned above is acquired. Thereby, the yield of a gas sensor improves.

1 is a schematic perspective view of a gas sensor 100. FIG. AA sectional drawing of FIG. Explanatory drawing of the mask 110. FIG. Explanatory drawing of the 2nd process using the mask 110. FIG. Explanatory drawing of the 2nd process using the mask 110. FIG. CC sectional drawing of FIG.4 (b). DD sectional drawing of FIG.4 (b). The fragmentary sectional view of the mask 210 of a modification. The fragmentary sectional view of the mask 310 of a modification. The fragmentary sectional view of the mask 410 of a modification. Explanatory drawing which shows a mode that the mask 910 is removed after forming the film 991 by the conventional method.

  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 is 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, and the porosity of the coating layer 24 is 10%-60%, for example. 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 t (see FIG. 2) 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. In the present embodiment, the thickness t of the porous protective layers 91a to 91e is the same value.

  Next, a method for manufacturing the gas sensor 100 will be described. The manufacturing method of the gas sensor 100 includes a first step of preparing the sensor element 101, a first step of forming porous protective layers 91 a to 91 d as coatings in the formation region 102 using a part of the surface of the sensor element 101 as the formation region 102. 2 steps.

  First, the first step will be described. In the first step, the sensor element 101 is prepared by manufacturing the sensor element 101 before forming the porous protection part 90. 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. 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. In the first step, the manufactured sensor element 101 may be prepared instead of manufacturing the sensor element 101.

  Next, the second step will be described. The second step includes (a) a step of disposing a mask 110 so as to cover the non-formation region 103 adjacent to the formation region 102 of the porous protective layers 91a to 91d, and (b) porous in the formation region 102 by plasma spraying. Forming the protective layers 91a to 91d, and (c) removing the mask 110.

  First, the mask 110 used in the step (a) will be described. FIG. 3 is an explanatory diagram of the mask 110. FIG. 3A is a perspective view of the mask 110 as viewed from the upper right front, and FIG. 3B is a B view of FIG. 3A. The mask 110 is a member for covering the non-formation region 103 other than the formation region 102 in which the porous protective layers 91a to 91d are formed in the sensor element 101 by inserting the sensor element 101 into the internal space 112c. The mask 110 is a substantially rectangular parallelepiped box-shaped member, and includes a main body portion 112, a bottom portion 113, and a gap forming portion 114. The main body 112 includes a main body end surface 112a which is a front end surface, a main body opening 112b formed in the main body end surface 112a, and a substantially rectangular parallelepiped internal space 112c formed from the main body opening 112b to the bottom 113. I have. The main body opening 112b has substantially the same height and width as the sensor element 101, and the internal space 112c can be inserted into the sensor element 101 through the main body opening 112b. The bottom 113 is a plate-like member connected to the rear end of the main body 112, and closes the rear end of the internal space 112c. The gap forming portion 114 is formed in front of the main body portion end surface 112 a of the main body portion 112. The gap forming portion 114 is a square frame-shaped member that protrudes forward from the main body portion 112, and forms a gap forming portion opening 115 on the front end surface. The gap forming part 114 protrudes forward from the front side of the main body part 112 from the upper side of the main body part end surface 112a, and the front part of the main body part 112 protrudes from the lower side to the front side of the main body part end surface 112a. The gap forming portion 114b, the gap forming portion 114c protruding forward from the left side of the main body portion end surface 112a among the front ends of the main body portion 112, and the front end of the main body portion 112 protruding forward from the right side of the main body portion end surface 112a. 114d. A space surrounded by the gap forming portions 114a to 114d and the main body end surface 112a is opened to the outside through the gap forming portion opening 115 and communicates with the internal space 112c through the main body portion opening 112b. The gap forming portion opening 115 has a larger area than the main body portion opening 112b. The upper surface of the gap forming portion 114 a is located on the same plane as the upper surface of the main body portion 112. Similarly, the lower surface, the left surface, and the right surface of the gap forming portions 114b, 114c, and 114d are located on the same plane as the lower surface, the left surface, and the right surface of the main body portion 112, respectively. The lower surface of the gap forming portion 114a (the upper surface of the inner peripheral surface of the gap forming portion 114) is positioned above the main body opening 112b by a height T (see FIG. 3B). Similarly, the upper surface, the right surface, and the left surface of the gap forming portions 114b, 114c, and 114d are respectively positioned below, left, and right by a height T from the main body opening 112b. The front end surfaces of the gap forming portions 114a to 114d are on the same plane, and the length from the front end surface to the main body end surface 112a is separated by a length M (see FIG. 3A).

  The material of the mask 110 is a metal member such as SUS (stainless steel), carbon steel, or chromium molybdenum steel. The mask 110 may be a resin member. The resin used for the mask 110 is preferably a heat-resistant resin having heat resistance that can be used for plasma spraying, and examples thereof include fluororesins such as Teflon (registered trademark) (polytetrafluoroethylene), nylon (registered trademark), and the like. The resin used for the mask 110 is preferably a water-repellent resin, and examples thereof include fluororesins such as Teflon and nylon. Further, the surface of the mask 110 may be water repellent coated. The material of the water-repellent coating is preferably one having heat resistance, and examples thereof include water-repellent resins such as Teflon and nylon, DLC (diamond-like carbon), Si-containing DLC, and the like. Since the mask 110 is made of water-repellent resin or the mask 110 is coated with water-repellent coating, a powder sprayed material 134 (described later), which is a material for forming the porous protective layer 91 in the step (b), is applied to the mask 110. Since adhesion is suppressed, peeling of the porous protective layer 91 when removing the mask 110 in the step (c) can be further suppressed. Further, in the present embodiment, the main body 112 and the gap forming portion 114 are integrally formed members, and the bottom 113 is attached to the main body 112 with, for example, welding or bolts. However, the present invention is not limited thereto, and the main body portion 112 and the gap forming portion 114 may be separate members, or a member in which the main body portion 112 and the bottom portion 113 are integrally formed. Further, the gap forming portions 114a to 114d are not integrally formed and may be members different from each other.

  Next, the second process using the mask 110 will be described. 4 and 5 are explanatory diagrams of the second process using the mask 110. FIG. First, in the step (a), the sensor element 101 and the mask 110 prepared in the first step are prepared (FIG. 4A), and the sensor element 101 is inserted into the internal space 112c from the main body opening 112b of the mask 110. The end is inserted to position the mask 110 (FIG. 4B).

  A positional relationship between the sensor element 101 and the mask 110 in a state where the mask 110 is arranged in the step (a) will be described. 6 is a cross-sectional view taken along the line CC in FIG. 4B, and FIG. 7 is a cross-sectional view taken along the line DD in FIG. FIG. 6 is a cross-sectional view taken along the center in the left-right direction of the sensor element 101, and shows a state when viewed in a cross section perpendicular to the gap forming portion opening 115 and parallel to the vertical direction. FIG. 6 also shows a plasma gun 120 and a porous protective layer 91a used for plasma spraying, which will be described later. FIG. 7 is a cross-sectional view taken along the vertical center of the sensor element 101, and shows a state when viewed in a cross-section perpendicular to the gap forming portion opening 115 and parallel to the left-right direction. As shown in FIGS. 6 and 7, in step (a), the sensor element 101 is inserted into the internal space 112c so that the rear end of the sensor element 101 is in contact with the bottom 113, and the mask 110 is positioned (arranged). Here, the distance from the front end face of the mask 110 to the rear end of the internal space 112c (see FIG. 3) is predetermined so as to be (length of sensor element in the longitudinal direction−distance L). As a result, as shown in FIG. 6, the formation region 102 a, which is a region from the front end surface to the distance L in the rear surface of the upper surface of the sensor element 101, is not covered with the mask 110. A certain non-formation region 103 a is covered with the mask 110. Similarly, the formation region 102b that is the region from the front end surface to the distance L toward the rear side of the lower surface of the sensor element 101 is not covered with the mask 110, and the non-formation region 103b that is the other region of the lower surface is masked 110. Similarly, on the left surface and the right surface of the sensor element 101, the formation regions 102c and 102d are not covered with the mask 110, and the non-formation regions 103c and 103d are covered with the mask 110. (See FIG. 7). Note that the formation regions 102a to 102d and the non-formation regions 103a to 103d may be referred to as the formation region 102 and the non-formation region 103, respectively, unless otherwise distinguished.

  Further, the mask 110 has the above-described gap forming portion 114a. In the state shown in FIG. 6, the gap forming portion 114a protrudes toward the forming region 102a (front side). Thus, a gap 116a is formed that is sandwiched between the lower surface of the gap forming portion 114a and the upper surface (non-forming region 103a) of the sensor element 101. The gap 116a is a gap (space) having a gap opening 117a that opens toward the formation region 102a at the end (front end) on the formation region 102a side of the non-formation region 103a. The height of the gap opening 117a at the front end portion of the gap 116a, that is, the distance between the front lower end of the gap forming portion 114a and the upper surface of the sensor element 101 is the same as the height T described above. In the cross section of FIG. 6, the length in the front-rear direction of the portion exposed to the gap 116 a in the non-forming region 103 a is the same as the length M described above. The gap 116a is a quadrangular region having an area S (= height T × length M) in the cross section of FIG. Thus, in the step (a), the mask 110 is arranged on the sensor element 101 so that the gap 116a having the height T, the length M, and the area S is formed by the gap forming portion 114a. Similarly, the gap forming portion 114b forms a gap 116b having a gap opening 117b opened to the forming region 102b side at the end (front end) on the forming region 102b side of the non-forming region 103b. Further, as shown in FIG. 7, the gap forming portions 114c and 114d allow the gap opening 117c opened to the forming regions 102c and 102d at the end (front end) on the forming regions 102c and 102d side of the non-forming regions 103c and 103d. , 117d having gaps 116c, 116d, respectively, are formed. The gap openings 117a to 117d are a part of the gap forming part opening 115 shown in FIG. In the present embodiment, the gaps 116b to 116d in the cross sections of FIGS. 6 and 7 are all the same in height T, length M, and area S as the gap 116a. Note that the gaps 116a to 116d and the gap openings 117a to 117d may be referred to as the gap 116 and the gap opening 117, respectively, unless they are particularly distinguished.

Here, the height T of the gap 116a is larger than the film thickness t of the porous protective layer 91a formed in the step (b). Similarly, the gaps 116b to 116d are larger than the film thickness t of the corresponding porous protective layers 91b to 91d. Further, the height T of the gap 116 is preferably at least twice the film thickness t. The length M is 1 mm or more, and the area S is 0.2 mm ² or more.

  Once the step (a) is performed, the step (b) of forming the porous protective layers 91a to 91d in the formation regions 102a to 102d by plasma spraying is then performed. Plasma spraying using the plasma gun 120 will be described with reference to FIG. FIG. 6 shows a state in which 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 a plasma state is ejected from the nozzle 126a downward as shown in FIG. 6 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. Note that the plasma spraying is performed, for example, in an atmosphere of air and room temperature. Although not particularly limited, the direction of thermal spraying of the plasma gun 120 (the direction of the nozzle 126a) is 30 ° to 90 ° with respect to the formation surface (formation region 102a) of the porous protective layer 91a in the sensor element 101. It is. In this embodiment, the angle is 90 ° (the direction of the nozzle 126a is perpendicular to the upper surface of the sensor element 101).

  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 of the sensor element 101 on which the porous protective layer 91 is formed (the upper surface of the coating layer 24a in FIG. 6) 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. 6) according to the area where the porous protective layer 91 is formed. In this case, the distance W is within the above-mentioned range. Is preferably maintained. The time for plasma spraying may be appropriately determined according to the film thickness t and area of the porous protective layer 91 to be formed.

  When plasma spraying is performed on the upper surface of the sensor element 101 (upper surface of the coating layer 24a) as described above, the mask 110 covers the non-formation region 103a as shown in FIG. The thermal spray material 134 adheres to form a porous protective layer 91a having a film thickness t. At this time, as described above, the height T of the gap opening 117a of the gap 116a is larger than the film thickness t. Therefore, on the boundary between the formation region 102a and the non-formation region 103a, the gap forming portion 114a and the porous protective layer 91a are likely to be separated in the thickness direction (vertical direction) of the porous protective layer 91a. Therefore, the end (rear end) on the mask 110 side of the formed porous protective layer 91a is less likely to contact the end on the formation region 102a side (front end of the gap forming portion 114a) of the mask 110.

  In the step (b), the porous protective layers 91b to 91d are also formed one by one in the same manner except that the surfaces to be formed on the sensor element 101 are different. The porous protective layer 91b is formed on the surface of the coating layer 24b as described above. The porous protective layers 91c to 91d are directly formed on the surface of the main body (each layer 1 to 6) of the sensor element 101. Here, since the mask 110 covers the non-formation regions 103b to 103d, the porous protection layers 91b to 91d having a film thickness t are formed in the formation regions 102b to 102d, similarly to the porous protection layer 91a. Further, the height T of the gap openings 117b to 117d of the gaps 116b to 116d is larger than the film thickness t. Therefore, the end portion (rear end) on the mask 110 side of the formed porous protective layers 91b to 91d is the end portion on the formation region 102b to 102d side (front end of the gap forming portions 114b to 114d) of the mask 110. Is difficult to touch. In the step (b), the state in which the porous protective layers 91a and 91b are first formed is FIG. 4C, and the state in which the porous protective layers 91c and 91d are subsequently formed is FIG. 5A. As shown to Fig.5 (a), the formed porous protective layers 91a-91d will be in the state connected with the mutually adjacent layer.

  In the present embodiment, the porous protective layer 91e is also formed in the step (b). The porous protective layer 91e is formed in the same manner as the porous protective layers 91a to 91d described above, except that the porous protective layer 91e is formed on the front end surface of the sensor element 101. However, since the front end surface of the sensor element 101 is not covered with the mask 110, the porous protective layer 91 e is formed so as to cover the entire front end surface of the sensor element 101. Further, the porous protective layer 91e is connected to the adjacent porous protective layers 91a to 91d. As described above, the porous protective layers 91 a to 91 e are formed on the top, bottom, left, and right surfaces and the front end surface of the sensor element 101 to form the porous protection portion 90. Thereafter, in step (c), the sensor element 101 is pulled out from the internal space 112c, and the mask 110 is removed (FIG. 5B). As described above, the gas sensor 100 is obtained by performing the second step including the steps (a) to (c).

  In the manufacturing method of the gas sensor 100 of the present embodiment described in detail above, the mask 110 covering the non-formation region 103 adjacent to the formation region 102 of the porous protective layer 91 (91a to 91d) has the gap formation portion 114. . When the mask 110 is disposed in the step (a) so as to cover the non-forming region 103 by the gap forming portion 114, the end (front end) on the forming region 102 side of the non-forming region 103 is moved to the forming region 102 side. An open gap 116 is formed. Further, the inner peripheral surface of the gap forming portion 114 is positioned up and down and left and right by a height T from the main body portion opening 112b, and the height T of the opening of the gap 116 is the height of the porous protective layer 91 to be formed. It is larger than the film thickness t. Therefore, the end (rear end) on the mask 110 side of the porous protective layer 91 formed in the formation region 102 by plasma spraying and the end (front end) on the formation region 102 side of the mask 110 are in contact with each other. It becomes difficult. Thereby, peeling of the porous protective layer 91 at the time of removing the mask 110 at a process (c) can be suppressed more. Further, by setting the height T to be twice or more the film thickness t, the end of the porous protective layer 91 formed in the formation region 102 on the mask 110 side and the end of the mask 110 on the formation region 102 side. Since it becomes more difficult to contact, the peeling of the porous protective layer 91 when removing the mask 110 can be further suppressed. In addition, since the porous protective layer 91 and the gap forming portion 114 are separated in the thickness direction of the porous protective layer 91 as the height T is larger, the effect that the porous protective layer 91 and the mask 110 are less likely to contact each other. Rise. The height T may be less than the distance W, but may be, for example, 10% or less of the distance W, or 40 times or less of the film thickness t.

The gap forming portion 114 is a cross section perpendicular to the opening surface of the gap 116 and parallel to the thickness direction of the porous protective layer 91 formed in the step (b) with the mask 110 disposed in the step (a). When viewed, the shape is such that the area S is 0.2 mm ² or more. Therefore, even if the gap 116 has a sufficient size and is formed so that the end portion of the porous protective layer 91 enters the gap 116, the porous protective layer 91 and the mask 110 are not easily in contact with each other. For example, in FIG. 6, a part of the powder sprayed material 134 may enter the gap 116 a, so that the porous protective layer 91 a may also cover a part of the non-formation region 103 a. Even in such a case, the larger the area S, the less the porous protective layer 91 and the mask 110 (for example, the main body end surface 112a) are in contact with each other. If the area S is 0.2 mm ² or more, the effect of being difficult to contact is sufficient, and the peeling of the porous protective layer 91 when removing the mask 110 in the step (c) can be further suppressed.

  Further, the gap forming portion 114 is separated from the front end face by a length M from the main body end face 112a, and is perpendicular to the opening surface of the gap 116 with the mask 110 disposed in the step (a). The length M is 1 mm or more when viewed in a cross-section parallel to the thickness direction of the porous protective layer 91 formed in (1). Therefore, the exposed portion of the non-formation region 103 in the gap 116 (= the portion where the mask 110 is not in direct contact) is sufficiently large, so that the end of the porous protective layer 91 enters the gap 116. Even if formed, the porous protective layer 91 and the mask 110 are difficult to contact. Therefore, similarly to the case where the area S is large, peeling of the porous protective layer 91 when removing the mask 110 can be further suppressed.

  Furthermore, the gap forming portion 114 has a shape that is separated from the non-forming region 103 and protrudes toward the forming region 102 (front side) in a state where the mask 110 is disposed in the step (a). Therefore, the gap 116 can be formed more reliably.

  Moreover, since the steps (a) to (c) are performed to further prevent the porous protective layer 91 from being peeled off when the mask 110 is removed, the yield of the gas sensor 100 is improved.

  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 embodiment described above, the gaps 116a to 116d are rectangular regions in the cross sections of FIGS. 8 to 10 are partial cross-sectional views of masks 210, 310, and 410 according to modified examples. The masks 210 to 410 have the same configuration as the mask 110 described above except that the shape of the gap forming portions 214 to 314 is different from that of the gap forming portion 114. Therefore, the same components as those of the mask 110 in the masks 210 to 410 are denoted by the same reference numerals, and detailed description thereof is omitted. FIGS. 8 to 10 are all cross-sectional views of the same cross section as FIG. 6 and illustrate the vicinity of the boundary between the formation region 102 a and the non-formation region 103 a on the upper surface of the sensor element 101.

  As shown in FIG. 8, the gap forming portion 214a of the mask 210 of the modified example protrudes forward from the main body portion 112, and the lower surface thereof is formed in an arcuate curved surface having an elliptical (or circular) cross section. . Note that the lower surface of the gap forming portion 214a has a shape that bulges downward and forward. When the mask 210 is disposed in the step (a), the gap forming portion 214a causes the gap having the gap opening 217a opened to the formation area 102a side at the end (front end) on the formation area 102a side of the non-formation area 103a. 216a is formed. The area S of the gap 216a is an area obtained by removing a quarter-shaped portion of an ellipse from a rectangular region having a height T × a length M, so that the area S = (height T × length M). ) − (Π × height T × length M × 1/4).

  As shown in FIG. 9, the gap forming portion 314a of the mask 310 according to the modified example protrudes forward from the main body portion 112, and the lower surface thereof is formed into an arcuate curved surface having an elliptical (or circular) cross section. . Note that the lower surface of the gap forming portion 314a has a shape recessed toward the upper rear, contrary to the gap forming portion 214a. When the mask 310 is disposed in the step (a), the gap forming portion 314a causes the gap having the gap opening 317a opened to the formation area 102a side at the end (front end) on the formation area 102a side of the non-formation area 103a. 316a is formed. The area S of the gap 216a is an elliptical quarter-shaped area, and therefore, the area S = (π × height T × length M × 1/4).

  As shown in FIG. 10, the lower surface of the gap forming portion 414a of the mask 410 of the modified example is formed in a flat plane (slope) whose cross section is a straight line from the upper front to the lower rear. When the mask 410 is disposed in the step (a), the gap forming portion 414a causes a gap having a gap opening 417a opened to the formation area 102a side at the end (front end) on the formation area 102a side of the non-formation area 103a. 416a is formed. Since the area S of the gap 416a is a triangular area, the area S = (height T × length M × 1/2).

  Also in the masks 210 to 410 of the modified examples shown in FIGS. 8 to 10, if the height T, the length M, and the area S are adjusted in the same manner as the above-described mask 110, respectively, The effect corresponding to is obtained. Although not shown in the drawings, in the masks 210 to 410 of the modified example, gaps (corresponding to the gaps 116b to 116d in the above-described embodiment) formed on the lower surface side and the left and right surface sides of the sensor element 101 are also gaps 216a. It has the same shape as ˜416a.

  Other than the masks 210 to 410 of the modification shown in FIGS. 8 to 10, the mask 110 may have any shape as long as a gap can be formed so that at least the height T is larger than the film thickness t. For example, the lower surfaces of the gap forming portions 214a and 314a in FIGS. 8 and 9 have an elliptical arc shape in cross-sectional view, but may have other curved shapes. Alternatively, a surface of the gap forming portion that faces the non-forming region 103 (for example, a lower surface in the case of the gap forming portions 114a to 414a) may have a shape formed by a combination of a straight line and a curved line in a sectional view. Further, in the masks 210 to 410, the height from the non-formation region 103a on the lower surfaces of the gap forming portions 214a to 414a tends to decrease toward the rear end, but is not limited thereto. For example, the height from the non-formation region 103a on the lower surface of the gap forming portion may tend to increase toward the rear end. That is, the shape of the gap may be such that there is a portion that is higher than the height T of the opening of the gap. In addition, the height from the non-formation region 103a of the lower surface of the gap forming portion may tend to increase (or decrease) on the way to the rear end and decrease (or increase) toward the rear end. .

In the embodiment described above, the area S is 0.2 mm ² or more. However, the present invention is not limited to this, and the area S only needs to exceed 0 mm ² . However, since the above-described effects can be obtained, the thickness is preferably 0.2 mm ² or more. Moreover, it is good also as 0.3 mm < ² > or more and 0.4 mm < ² > or more. Although not particularly limited, the area S may be 100 mm ² or less, for example.

  In the above-described embodiment, the length M is set to 1 mm or more. However, the length M is not limited to this, and it is sufficient that the length M exceeds 0 mm. However, since the above-described effects can be obtained, the thickness is preferably 1 mm or more, and may be 2 mm or more and 3 mm or more. The length M may be appropriately determined within a range less than the length in the longitudinal direction of the non-formation region 103 so that the main body 112 and the non-formation region 103 of the sensor element 101 are in sufficient contact and the mutual positional relationship is stabilized. it can. Although not particularly limited, the length M may be, for example, 30 mm or less.

  In the embodiment described above, the porous protective layers 91a and 91b are formed in the step (b), the porous protective layers 91c and 91d are formed, and the porous protective layer 91e is formed. The order of forming 91a to 91e is not limited to this, and any order may be used. Moreover, after forming the porous protective layers 91a to 91d in the step (b) and removing the mask 110 in the step (c), the porous protective layer 91e may be formed.

  In the embodiment described above, the gaps 116a to 116d formed in the state in which the mask 110 is arranged in the step (a) are all assumed to have the same values of height T, length M, and area S. It is not limited to this. 6 and 7, the gaps 116a to 116d have the same rectangular shape. However, the shape is not limited to this, and one or more of the gaps 116a to 116d may have a different shape. Also, regarding the film thickness t, one or more of the porous protective layers 91a to 91d may have different values.

  In the above-described embodiment, the porous protective layer 91 is formed by plasma spraying using the mask 110. However, any material that forms a coating film may be used. For example, the film to be formed is not limited to a porous body. Further, a film other than the protective layer such as the outer pump electrode 23 may be formed.

  In the embodiment described above, the mask 110 has the gap forming portions 114a to 114d. However, the present invention is not limited to this, and any mask having at least one of the gap forming portions 114a to 114d may be used. Further, the mask 110 has the bottom portion 113, but the bottom portion 113 may not be provided, and the internal space 112c may open to the rear end side. In this case, it is not necessary for the mask 110 to cover the entire non-formation region 103. For example, the sensor element 101 may be disposed so as to penetrate the internal space 112c of the mask 110 in the step (a). At this time, a part of the region on the rear end side 103 is exposed behind the mask 110, but the exposed portion is a region far from the formation region 102. Therefore, depending on the shape and orientation of the nozzle 126a of the plasma gun 120 and the length of the mask 110 in the front-rear direction, there is no problem even if it is exposed.

  In the above-described embodiment, the mask 110 can fix the sensor element 101 by inserting the sensor element 101 into the internal space 112c, and simultaneously covers the upper, lower, left, and right non-formation regions 103a to 103d of the sensor element 101. Not limited. For example, the mask 110 may be a substantially plate-like member having a gap forming portion and a thicker flat plate-like member. In this case, in the step (a), a mask is placed on the surface of the sensor element 101 so as to cover any one of the non-forming regions 103a to 103d, and the corresponding porous protective layer in the step (b). 91 may be formed. And when forming the porous protective layer 91 in two or more surfaces, what is necessary is just to change the mounting surface of a mask and to repeat process (a), (b) suitably.

  In the above-described embodiment, the coating layer 24 is formed on the upper surface and the lower surface of the sensor element 101, but is not limited thereto. Of the surface of the sensor element 101, a coating layer may be formed in one or more of the regions where the porous protective layers 91c to 91e are formed. 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 protection part 90 includes the porous protection layers 91a to 91e, but is not limited thereto. The porous protection part 90 should just have 1 or more among the porous protection layers 91a-91d. 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. Even in this case, if the shape of the mask 110 is adjusted so that a gap similar to the gap 116 described above is formed on the formation region 102 side in the non-formation region 103 when the mask 110 is arranged in the step (a). Good.

  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, the distance L may be smaller than at least one of the width and thickness of the sensor element 101.

  In the above-described embodiment, the method for manufacturing the gas sensor 100 has been described. However, a method for manufacturing a film may be used.

  Below, the example which produced the gas sensor concretely is demonstrated as an experiment example. Experimental examples 1 to 6 correspond to examples of the present invention, and experimental example 7 corresponds to a comparative example. In addition, this invention is not limited to a following example.

[Experimental Example 1]
As Experimental Example 1, a gas sensor similar to the gas sensor 100 of the above-described embodiment was manufactured except that the porous protective part 90 includes only the porous protective layer 91a. First, in the first step, a sensor element 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 up-down direction of 1.45 mm according to the method for manufacturing the gas sensor 100 of the embodiment described above. 101 was produced. 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.

In the second step, the porous protective layer 91a was formed on the surface of the sensor element 101, and the gas sensor of Experimental Example 1 was obtained. Specifically, first, the mask 110 was disposed so as to cover the non-formation region 103a of the sensor element 101 as in the above-described embodiment in the step (a). The distance L was 10 mm. At this time, a rectangular gap 116a having a height T = 5.0 mm, a length M = 3.0 mm, and an area S = 15.0 mm ² was formed by the gap forming portion 114a in the same cross section as FIG. The material of the mask 110 was metal.

  Next, the porous protective layer 91a was formed in the formation region 102a using the plasma gun 120 in the step (b). The plasma spraying conditions for forming the porous protective layer 91a 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 200 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 91a in the sensor element 101. The film thickness t of the formed porous protective layer 91a was 0.5 mm.

  And the mask 110 was removed at the process (c), and the gas sensor of Experimental example 1 was obtained. When a portion (near the non-formation region 103a in the formation region 102a) located in the vicinity of the mask 110 in the porous protective layer 91a after the step (c) was confirmed, no peeling occurred.

[Experiment 2]
With the shape of the gap forming portion 114a in Experimental Example 1 changed and the mask 110 placed in the step (a), the height T = 3.0 mm and the length M = 5.0 mm in the same cross section as FIG. A gas sensor of Experimental Example 2 was obtained by performing the same process as in Experimental Example 1 except that a rectangular gap 116a having an area S = 15.0 mm ² was formed. Also in Experimental Example 2, when the presence or absence of the peeling of the porous protective layer 91a was examined in the same manner as in Experimental Example 1, no peeling occurred.

[Experiment 3]
With the shape of the gap forming portion 114a in Experimental Example 1 changed and the mask 110 placed in the step (a), the height T = 1.0 mm and the length M = 3.0 mm in the same cross section as FIG. A gas sensor of Experimental Example 3 was obtained by performing the same process as in Experimental Example 1 except that a rectangular gap 116a having an area S = 3.0 mm ² was formed. Also in Experimental Example 3, when the presence or absence of the peeling of the porous protective layer 91a was examined in the same manner as in Experimental Example 1, no peeling occurred.

[Experimental Example 4]
Except for using the mask 410 shown in FIG. 10, the same process as in Experimental Example 1 was performed to obtain a gas sensor of Experimental Example 3. In the state where the mask 410 is disposed in the step (a), the gap forming portion 414a has a height T = 1.0 mm, a length M = 3.0 mm, and an area S = 1.5 mm ^{2 in the} same cross section as FIG. The triangular gap 416a was formed. Also in Experimental Example 4, when the presence or absence of peeling of the porous protective layer 91a was examined in the same manner as in Experimental Example 1, no peeling occurred.

[Experimental Example 5]
Except for using the mask 310 shown in FIG. 9, the same process as in Experimental Example 1 was performed to obtain a gas sensor of Experimental Example 5. In the state where the mask 310 is disposed in the step (a), the gap forming portion 314a causes the same cross section as FIG. 9 to have a height T = 1.0 mm, a length M = 3.0 mm, and an area S = about 2.4 mm. ^Two gaps 316a were formed. Also in Experimental Example 5, when the presence or absence of peeling of the porous protective layer 91a was examined in the same manner as in Experimental Example 1, peeling did not occur.

[Experimental Example 6]
Except for using the mask 210 shown in FIG. 8, the same process as in Experimental Example 1 was performed to obtain a gas sensor of Experimental Example 6. In the state where the mask 210 is arranged in the step (a), the gap forming portion 214a causes the same cross section as FIG. 8 to have a height T = 1.0 mm, a length M = 3.0 mm, and an area S = about 0.6 mm. ^Two gaps 216a were formed. Also in Experimental Example 6, when the presence or absence of peeling of the porous protective layer 91a was examined in the same manner as in Experimental Example 1, peeling did not occur.

[Experimental Example 7]
With the shape of the gap forming portion 114a in Experimental Example 1 changed and the mask placed in step (a), the gap 116a is not formed in the same cross section as in FIG. 6 (height T = 0 mm, length M = 0 mm). , Area S = 0 mm ² ) The same process as in Experimental Example 1 was performed except that the gas sensor of Experimental Example 7 was obtained. In Experimental Example 7, when the mask was removed in step (c), the portion of the porous protective layer 91a that was in contact with the front end of the mask was peeled off.

  Table 1 summarizes the film thickness t, height T, length M, area S, and presence / absence of peeling of the porous protective layer 91a in Experimental Examples 1 to 7. In Table 1, the figure numbers corresponding to the shapes of the gaps in Experimental Examples 1 to 6 are also shown.

  From the results of Experimental Examples 1 to 7, a mask is arranged so as to form a gap opened to the formation region 102a side at the end of the non-formation region 103a on the formation region 102a side, and the height T of the opening of the gap T> It was confirmed that the peeling of the porous protective layer 91a when removing the mask can be further suppressed by the film thickness t.

  Even when the gas sensor was produced in the same manner as in each of Experimental Examples 1 to 6 except that the mask material was Teflon, the porous protective layer 91a was not peeled off as in Experimental Examples 1 to 6. In addition, when the gas sensor was produced in the same manner as in each of Experimental Examples 1 to 6 except that the mask material was stainless steel coated with Teflon, the porous protective layer 91a was peeled off in the same manner as in Experimental Examples 1 to 6. It did not occur.

  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, 7a-7e contact bonding layer, 10 gas inlet, 11 1st Diffusion limiting part, 12 Buffer space, 13 Second diffusion 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 Third diffusion rate limiting unit, 40 Second internal space, 41 Measurement pump cell, 42 Reference electrode, 43 Reference gas introduction space, 44 Measurement electrode, 45 Fourth diffusion rate limiting unit, 46 Variable Power supply, 48 Air introduction layer, 50 Auxiliary pump cell, 51 Auxiliary pump electrode, 51a Ceiling electrode part, 51b Bottom electrode part, 52 Variable power supply, 70 Heater part, 71 Heater Connector electrode, 72 heater, 73 through hole, 74 heater insulation layer, 75 pressure dissipation hole, 76, 76a to 76c heater lead wire, 80 oxygen partial pressure detection sensor cell for main pump control, 81 oxygen partial pressure detection for auxiliary pump control Sensor cell, 82 Oxygen partial pressure detection sensor cell for controlling pump for measurement, 83 Sensor cell, 90 Porous protective part, 91, 91a to 91e Porous protective layer, 100 Gas sensor, 101 Sensor element, 102, 102a to 102d Formation region, 103, 103a-103d non-formation region, 110 mask, 112 body part, 112a body part end face, 112b body part opening, 112c internal space, 113 bottom part, 114, 114a-114d gap formation part, 115 gap formation part opening, 116, 116a- 116d clearance, 117, 117a- 17d Clearance opening, 120 Plasma gun, 122 Outer peripheral part, 123 Insulating part, 124 Water cooling jacket, 126 Anode, 126a Nozzle, 128 Cathode, 130 Plasma generating gas, 132 Powder supply part, 134 Powder sprayed material, 210, 310, 410 Mask, 214, 314, 414, 214a, 314a, 414a Gap forming part, 216a, 316a, 416a Gap, 217a, 317a, 417a Gap opening, 901 Object, 910 Mask, 991 Coating.

Claims (8)

A method for producing a coating by plasma spraying on a long rectangular parallelepiped sensor element ,
(A) Of the surface of the sensor element, a part of each of the four surfaces along the longitudinal direction of the sensor element is defined as the film formation region, and four non-formation regions adjacent to the four formation regions, respectively. Arranging a mask to cover at the same time ;
(B) forming the coating film on the four formation regions by plasma spraying;
(C) removing the mask;
Including
When the mask is disposed in the step (a), a gap that forms a gap opened to the formation region side at an end portion of the non-formation region on the formation region side for each of the four surfaces. Has a forming part,
For each of the four surfaces, the opening height T of the gap is larger than the film thickness t of the coating formed in the step (b).
A method for producing a coating. For one or more of the four surfaces, the height T is twice or more the film thickness t.
The manufacturing method of the film of Claim 1. With respect to one or more of the four surfaces, the gap forming portion is a film formed perpendicularly to the opening surface of the gap and formed in the step (b) with the mask disposed in the step (a). When viewed in a cross section parallel to the thickness direction, the area S of the gap is 0.2 mm ² or more,
The manufacturing method of the film of Claim 1 or 2. With respect to one or more of the four surfaces, the gap forming portion is a film formed perpendicularly to the opening surface of the gap and formed in the step (b) with the mask disposed in the step (a). When viewed in a cross-section parallel to the thickness direction, the length M of the portion exposed to the gap in the non-formed region is 1 mm or more,
The manufacturing method of the film of any one of Claims 1-3. For each of the four surfaces, the gap forming portion has a shape that is spaced apart from the non-forming region and protrudes toward the forming region with the mask disposed in the step (a). ,
The manufacturing method of the film of any one of Claims 1-4. The mask is made of metal or resin.
The manufacturing method of the film of any one of Claims 1-5. The mask is made of water repellent resin or is coated with water repellent,
The manufacturing method of the film of any one of Claims 1-6. A gas sensor manufacturing method comprising a long rectangular parallelepiped sensor element and a film formed on the surface of the sensor element,
A first step of preparing the sensor element;
By the method for manufacturing a coating film according to any one of claims 1 to 7, a part of each of four surfaces along the longitudinal direction of the sensor element among the surface of the sensor element is used as the formation region. A second step of forming the film in four formation regions;
The manufacturing method of the gas sensor containing this.