JP5097238B2 - Method for manufacturing gas sensor element - Google Patents

Description

  The present invention relates to a method for manufacturing a gas sensor element used for measuring the concentration of a specific gas component contained in a gas to be measured.

  As a gas sensor element used for measuring the concentration of a specific gas component contained in a gas to be measured, a solid electrolyte layer, an electrode in contact with the gas to be measured formed on the surface of the solid electrolyte layer, 2. Description of the Related Art A gas sensor element having a porous diffusion rate limiting portion formed so as to cover an electrode is known. In such a gas sensor element, the diffusion rate-determining part protects the electrode contained in the gas under measurement so that a substance that poisons the electrode does not adhere to the electrode, and at the same time a specific gas component (concentration) contained in the gas under measurement. The gas component to be measured is limited to reach the electrode, and a large number of pores are formed for the gas to be measured to pass therethrough so as to obtain a good diffusion rate-determining property.

  Conventionally, as a method for manufacturing such a gas sensor element, an electrode is printed on the surface of a solid electrolyte layer green sheet (unfired body) that becomes a solid electrolyte layer by firing with an electrode paste containing an electrode constituent material. Then, a printing step for producing a printed laminate by printing and forming a diffusion-limited portion so as to cover the electrode with a paste for a diffusion-limited portion including a ceramic aggregate and a pore former, and the printed laminate There is known a manufacturing method including a firing step of firing (see Patent Documents 1 and 2). The pore-forming material contained in the diffusion-controlling part paste is burned off by firing in the firing step, and the burnt-out traces become pores that communicate with each other, whereby a porous diffusion-controlling part is obtained.

  By the way, in the conventional manufacturing methods disclosed in Patent Documents 1 and 2, carbon, graphite, and theobromine powder particles are used as the pore-forming material to be contained in the diffusion-controlling part paste. When the material is used, a large number of fine pores different from the shape and size of the pore former are formed, and the pore diameter distribution is widened. When the gas to be measured is, for example, exhaust gas discharged from an engine, poisoning components contained in the engine or catalyst enter the sensor element as an aqueous solution, but the pore size distribution of the diffusion-controlling portion is wide, and the fine pores are When present, the aqueous solution collects in the fine pores by capillary force. In general, since the gas sensor element is driven in a heated state by a heating means such as a heater, the aqueous solution collected in the fine pores is dried to deposit poisonous components, and the fine pores are blocked by the poisoned components. .

Therefore, in a gas sensor element manufactured by a conventional manufacturing method and having a wide pore size distribution in the diffusion-controlling portion and a large number of fine pores exist in the diffusion-controlling portion, gas sensitivity is caused by blockage (clogging) of these fine pores. There was a problem that would fluctuate greatly. In addition, when carbon, graphite, and theobromine powder particles are used as the pore former, a large number of fine pores having shapes and dimensions different from those of the pore former are formed. It is thought that this is because the arrangement of ceramic aggregates around the pore former collapses by generating a large amount of gas (CO ₂ ) at the time of burning.

  Patent Document 3 discloses a method for manufacturing lightweight ceramics by molding and firing a mixture of a raw material and a thermosetting resin powder as a burnable material (pore forming material). However, since the thermosetting resin powder used in this manufacturing method has a coarse particle size, it is used as a pore-forming material in the production of a gas sensor element and used as a diffusion-controlling part paste. When it was included in the paste, there was a problem that the pore former was settled and separated in the paste.

JP-A-9-15196 JP 2002-286680 A JP 2007-269622 A

  The present invention has been made in view of such conventional circumstances, and the object of the present invention is that the pores are formed in a state where the shape and dimensions of the pore former before burning are substantially maintained. Another object of the present invention is to provide a method for producing a gas sensor element, in which a diffusion rate-determining part having pores having an arbitrary shape and size can be obtained, and blockage of pores due to poisoning components can be suppressed.

  In order to achieve the above object, according to the present invention, the following method for manufacturing a gas sensor element is provided.

[1] A method for manufacturing a gas sensor element, comprising: a solid electrolyte layer; an electrode in contact with a gas to be measured formed on the surface of the solid electrolyte layer; and a porous diffusion rate-limiting part formed so as to cover the electrode. The electrode is printed and formed on the surface of the solid electrolyte layer green sheet that becomes the solid electrolyte layer by firing with the electrode paste containing the constituent material of the electrode, and then the ceramic aggregate and the pore former A diffusion-controlling portion paste containing a printing step of printing and forming a diffusion-controlling portion so as to cover the electrode, and producing a printed laminate, and a firing step of firing the printed laminate. The average particle diameter of the aggregate is 0.1 to 9 μm, the pore former is a thermosetting resin having an average particle diameter of 0.15 to 9 μm, and the inclusion of the pore former in the diffusion-controlling part paste The amount is 1 to 50% by volume of the total volume of the La mix aggregate and the pore-forming material, manufacturing method of the gas sensor element firing temperature is 1200 to 1500 ° C. in the firing step.

[2] The thermosetting resin is at least one selected from the group consisting of melamine resin, benzoguanamine / formaldehyde resin, benzoguanamine resin, urea resin, phenol resin, epoxy resin, nylon resin, urethane resin, and unsaturated polyester resin. The method for producing a gas sensor element according to [1], which is a thermosetting resin.

[3] The ceramic aggregate includes yttria partially stabilized zirconia, calcia partially stabilized zirconia, yttria stabilized zirconia, calcia stabilized zirconia, α-alumina, Al ₂ O ₃ .MgO spinel, mullite, yttria, and magnesia. The method for producing a gas sensor element according to [1] or [2], which is at least one kind of ceramic particles selected from the group.

[4] The method for producing a gas sensor element according to any one of [1] to [3], wherein the porosity of the diffusion rate-determining part after firing is 5 to 50%.

[5] The method for producing a gas sensor element according to any one of [1] to [4], wherein an average pore diameter of the diffusion-controlling portion after firing is 0.05 to 9 μm.

[6] The lower limit 20% pore diameter ratio (lower limit 20% pore diameter / average pore diameter) to the average pore diameter of the diffusion-controlling portion after firing is 0.5 or more and less than 1 [1] to [5] The manufacturing method of the gas sensor element in any one of.

  According to the present invention, by using a thermosetting resin for the pore former, pores are formed in the diffusion rate controlling portion in a state in which the shape and dimensions of the pore former before burning are substantially maintained. For this reason, by using a pore-forming material having a shape and size equivalent to the shape and size of the target pores, a diffusion rate controlling portion having pores having an arbitrary shape and size can be obtained. Therefore, it is possible to suppress the formation of fine pores that are likely to be clogged by poisoning components, and as a result, it is possible to manufacture a gas sensor element that is less susceptible to fluctuations (sensitivity reduction) in gas sensitivity due to clogging of the fine pores.

It is sectional drawing which shows an example of the gas sensor element which is the manufacture object of this invention.

  Hereinafter, the present invention will be described based on specific embodiments, but the present invention should not be construed as being limited thereto, and based on the knowledge of those skilled in the art without departing from the scope of the present invention. Various changes, modifications, and improvements can be added.

FIG. 1 is a cross-sectional view showing an example of a gas sensor element, which is a manufacturing object of the present invention. This gas sensor element 100 is a NO _x sensor element that detects the concentration of NO _{x in} the gas to be measured, and includes a first substrate layer 1 made of an oxygen ion conductive solid electrolyte layer such as zirconia (ZrO ₂ ). The six layers of the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the spacer layer 5, and the second solid electrolyte layer 6 are laminated in this order from the lower side. The base material 101 is provided. The structure and operating principle of such a gas sensor element 100 are known (see, for example, Japanese Patent Application Laid-Open No. 2008-164411).

  In this gas sensor element 100, a gas introduction port 10, a first diffusion rate limiting unit 11, a buffer space 12, a second space between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4. Diffusion-limiting part 13, first internal space 20, third diffusion-controlling part 30, and second internal space 40 are formed so as to communicate from the tip (left end in FIG. 1) to the back in this order. ing. The gas inlet 10, the buffer space 12, the first internal space 20, and the second internal space 40 are spaces provided by hollowing out the spacer layer 5. In these spaces, the upper part is defined by the lower surface of the second solid electrolyte layer 6, the lower part is defined by the upper surface of the first solid electrolyte layer 4, and the side part is defined by the wall surface of the space in which the spacer layer 5 is hollowed out. Yes. 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 formed as two horizontally long slits (the direction perpendicular to the drawing coincides with the longitudinal direction of the opening). Is provided. In addition, the site | part from the gas inlet 10 to the 2nd internal space 40 is also called a gas distribution part.

Further, a reference gas introduction space 43 is provided at a position farther from the tip than the gas circulation part. The reference gas introduction space 43 is a space provided by hollowing out the first solid electrolyte layer 4. The upper part is defined by the lower surface of the spacer layer 5, and the lower part is defined by the upper surface of the third substrate layer 3. Is partitioned by the wall surface of the hollowed out space of the first solid electrolyte layer 4. For example, the atmosphere is introduced into the reference gas introduction space 43 as a reference gas when measuring the NO _x concentration. An air introduction layer 48 made of porous alumina is provided between the first solid electrolyte layer 4 and the third substrate layer 3. A reference gas is introduced into the atmosphere introduction layer 48 through a 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 between the upper surface of the third substrate layer 3 and the lower surface of the first solid electrolyte layer 4. As described above, the reference electrode 42 is surrounded by the atmosphere connected to the reference gas introduction space 43. An 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.

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. This oxygen partial pressure is adjusted by operating the main pump cell 21. The main pump cell 21 includes an inner pump electrode 22 formed in a tunnel shape in the first inner space 20, and an outer pump electrode provided on the surface of the second solid electrolyte layer 6 opposite to the inner pump electrode 22. The electrochemical pump cell is constituted by the second solid electrolyte layer 6 sandwiched between these electrodes 22 and 23. The inner pump electrode 22 and the outer pump electrode 23 are formed as porous cermet electrodes (for example, a cermet electrode of Pt and ZrO ₂ containing 1% of Au).

  The outer pump electrode 23 is covered with an outer pump electrode protective layer (outer peripheral protective layer) 24. The outer pump electrode protective layer 24 is made of a porous body having a thickness of 10 to 200 μm. The material of the outer pump electrode protective layer 24 is not particularly limited as long as it is a porous body. For example, an alumina porous body or a zirconia porous body (zirconia may be partially stabilized zirconia or fully stabilized zirconia). ), Spinel porous material, cordierite porous material, and the like. These may contain sodium, potassium, calcium, magnesium, barium, aluminum, zirconium, silicon and the like as appropriate.

  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 6, the spacer layer 5, the first solid electrolyte layer 4, The third substrate layer 3 and the reference electrode 42 constitute an electrochemical sensor cell, that is, an oxygen partial pressure detection sensor cell 80 for main pump control. By measuring the electromotive force V0 in the oxygen partial pressure detection sensor cell 80, the oxygen concentration (oxygen partial pressure) in the first internal space 20 can be known. Further, the pump current Ip0 is controlled by feedback control of the variable power supply 25 (voltage Vp0) 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 second internal space 40 is a space for performing processing related to the measurement of the NO _x concentration in the gas to be measured introduced through the third diffusion control unit 30. 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.

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 is further supplied to the gas to be measured introduced through the third diffusion control unit 30. The oxygen partial pressure is adjusted by the above. Thereby, since the oxygen concentration in the second internal space 40 can be kept constant with high accuracy, it is possible to measure the NO _x concentration with high accuracy.

  The auxiliary pump cell 50 is an auxiliary electrochemical cell constituted by an auxiliary pump electrode 51 formed in a tunnel shape in the second internal space 40, an outer pump electrode 23, and the second solid electrolyte layer 6. It is a pump cell.

  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 oxygen partial pressure detection sensor cell 81 for controlling an auxiliary pump. The oxygen partial pressure detection sensor cell 81 detects an electromotive force V <b> 1 between the auxiliary pump electrode 51 and the reference electrode 42. The auxiliary pump cell 50 performs pumping by a variable power source 52 (voltage Vp1) that is voltage-controlled based on the electromotive force V1. Thus, 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 NO _x . At the same time, the pump current Ip1 of the auxiliary pump cell 50 is used to control the electromotive force V0 of the oxygen partial pressure detection sensor cell 80 for main pump control. As a result, the gradient of the oxygen partial pressure in the gas to be measured introduced from the third diffusion control unit 30 into the second internal space 40 is controlled to be always constant.

The measurement pump cell 41 measures the NO _x concentration in the gas to be measured in the second internal space 40. The measurement pump cell 41 is an electrochemical pump cell constituted by the measurement electrode 44, the outer pump electrode 23, the second solid electrolyte layer 6, the spacer layer 5, and the first solid electrolyte layer 4. The measurement electrode 44 is provided on the upper surface of the first solid electrolyte layer 4 facing the second internal space 40 and at a position separated from the third diffusion rate-limiting part 30. The measurement electrode 44 is a porous cermet electrode having a substantially rectangular shape in plan view. The measurement electrode 44 also functions as a NO _x reduction catalyst that reduces NO _x 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 fourth diffusion rate controlling part 45 is a film made of a ceramic porous body. The fourth diffusion control unit 45 plays a role of limiting the amount of NO _x flowing into the measurement electrode 44 and also functions as a protective film for the measurement electrode 44.

The measurement pump cell 41 pumps out oxygen generated by the decomposition of NO _x in the atmosphere around the measurement electrode 44 and detects the generated amount as a pump current Ip 2 flowing between the measurement electrode 44 and the outer pump electrode 23. can do.

  Further, in order to detect the oxygen partial pressure around the measurement electrode 44, the second solid electrolyte layer 6, the spacer layer 5, the first solid electrolyte layer 4, the third substrate layer 3, the measurement electrode 44, The reference electrode 42 constitutes an electrochemical sensor cell, that is, an oxygen partial pressure detection sensor cell 82 for controlling the measurement pump. The variable power supply 46 (voltage Vp2) of the measurement pump cell 41 is controlled based on 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. NO _x in the gas to be measured around the measurement electrode 44 is reduced to generate oxygen (2NO → N ₂ + O ₂ ). The generated oxygen is pumped by the measurement pump cell 41. At this time, the variable power source is set so that the electromotive force V2 detected by the measurement pump control oxygen partial pressure detection sensor cell 82 is constant. 46 voltage Vp2 is controlled. Since the amount of oxygen generated around the measurement electrode 44 is proportional to the concentration of NO _{x in} the gas to be measured, the NO _x concentration in the gas to be measured is determined using the pump current Ip2 in the measurement pump cell 41. Will be calculated. Here, the specific procedure for deriving the NO _x concentration is as follows. That is, the pump current difference ΔIp2 obtained by subtracting the offset current from the pump current Ip2 when the actual measurement gas is supplied is determined by using the pump current Ip2 when the sample gas not containing NO _x is supplied in advance as the offset current. calculating the concentration of NO _x from oxygen amount corresponding to the pump current difference? Ip2.

In the gas sensor element (NO _x sensor element) 100 having such a configuration, by operating the main pump cell 21 and the auxiliary pump cell 50, the oxygen partial pressure always has a constant low value (substantially affects the measurement of NO _x ). The gas to be measured, which is maintained at a value that does not exist, is supplied to the measurement pump cell 41. Therefore, oxygen generated by substantially proportional to the reduction of the NO _x in the concentration of the NO _x in the measurement gas is pumped from the measuring pumping cell 41, based on the pump current Ip2 flowing by it, NO in the measurement gas _{The x} concentration can be known.

  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.

  The heater 70 is formed so as to be sandwiched between the second substrate layer 2 and the third substrate layer 3. The heater 70 plays a role of temperature adjustment for heating and keeping the gas sensor element 100 in order to increase the oxygen ion conductivity of the solid electrolyte of each layer. The heater 70 includes a heater electrode 71, a resistance heating element 72, and a heater insulating layer 74. Further, the heater 70 is communicated with the reference gas introduction space 43 by a pressure diffusion hole 75 penetrating the third substrate layer 3 so that the pressure rise in the heater 70 is alleviated. The heater electrode 71 is formed in contact with the lower surface of the first substrate layer 1. The heater electrode 71 is connected to an external power source (not shown) so as to supply power to the resistance heating element 72 from the outside. The resistance heating element 72 is connected to the heater electrode 71 through a through hole 73 formed in the first substrate 1 and the second substrate 2. The resistance heating element 72 is embedded over the entire area from the first internal space 20 to the second internal space 40, and the entire gas sensor element 100 can be adjusted to a temperature at which the solid electrolyte is activated. It has become. The heater insulating layer 74 is formed of an insulator such as alumina on the upper and lower surfaces of the resistance heating element 72.

  Next, the manufacturing method of the gas sensor element of the present invention will be described by taking as an example the case where such a gas sensor element is a manufacturing object. As described above, the method for manufacturing a gas sensor element of the present invention includes a solid electrolyte layer, an electrode in contact with a gas to be measured formed on the surface of the solid electrolyte layer, and a porous electrode formed so as to cover the electrode. A method of manufacturing a gas sensor element comprising a diffusion rate-determining part, wherein an electrode is printed on the surface of a solid electrolyte layer green sheet that becomes the solid electrolyte layer by firing with an electrode paste containing the constituent material of the electrode After that, a printing step of producing a printed laminate by printing and forming a diffusion-limited layer so as to cover the electrodes with a paste for a diffusion limited portion including a ceramic aggregate and a pore former, and the printed laminate The ceramic aggregate has an average particle size of 0.1 to 9 μm, the pore former is a thermosetting resin having an average particle size of 0.15 to 9 μm, and the diffusion Rate controlling layer The content of the pore former in the paste is 1 to 50% by volume of the total volume of the ceramic aggregate and the pore former, and the firing temperature in the firing step is 1200 to 1500 ° C. To do.

  In the gas sensor element, the measurement electrode 44 formed on the upper surface of the first solid electrolyte layer 4 corresponds to the “electrode in contact with the gas to be measured” in the gas sensor element manufacturing method of the present invention. A fourth diffusion-control side portion 45 corresponding to the “diffusion-controlling portion” in the method for manufacturing a gas sensor element of the present invention is formed so as to cover the electrode 44.

  First, a first substrate layer 1, a second substrate layer 2, a third substrate layer 3, and a first solid electrolyte layer 4 are formed by firing in a later firing step using an oxygen ion conductive solid electrolyte material such as zirconia. Then, a green sheet (unfired body) to be the spacer layer 5 and the second solid electrolyte layer 6 is produced.

  Next, the outer pump electrode 23 is placed on the upper surface of the green sheet (second solid electrolyte layer green sheet) that becomes the second solid electrolyte layer 6 by firing, with the electrode paste containing the electrode constituent material, and the inner pump electrode on the lower surface. 22a and auxiliary pump electrode 51a are printed together with the wiring to these electrodes, and an outer pump electrode protective layer (outer peripheral protective layer) 24 is formed to cover outer pump electrode 23 with outer peripheral protective layer paste. To do.

  Similarly, the inner pump electrode 22b and the auxiliary pump electrode 51b are formed on the upper surface of the green sheet (the first solid electrolyte layer green sheet) that becomes the first solid electrolyte layer 4 by firing with an electrode paste containing an electrode constituent material. The measurement electrode 44 is printed with the measurement electrode paste containing the measurement electrode constituent material, together with the wiring to each of the electrodes, and further includes the constituent material of the fourth diffusion regulation side portion (measurement electrode protective layer) 45 A fourth diffusion regulation side portion (measurement electrode protection layer) 45 is printed and formed so as to cover the measurement electrode 44 with a paste for the fourth diffusion regulation side portion (measurement electrode protection layer). A part of the green sheet is punched to provide a reference gas introduction space 43.

  Further, punching for providing the gas introduction port 10, the buffer space 12, the first internal space 20, and the second internal space 40 in a part of the green sheet (spacer layer green sheet) that becomes the spacer layer 5 by firing. In addition, a slit that becomes the first diffusion rate-limiting unit 11, the second diffusion rate-limiting unit 13, and the third diffusion rate-limiting unit 30 is formed on a part of the upper surface and the lower surface of the green sheet. Print the paste. The printed organic paste is burned down by subsequent baking, and the burnout marks become the first diffusion rate-limiting unit 11, the second diffusion rate-limiting unit 13, and the third diffusion rate-limiting unit 30.

  In addition, the reference electrode 42 is printed on the upper surface of the green sheet (third substrate layer green sheet) that becomes the third substrate layer 3 by firing, using electrode paste containing an electrode constituent material, together with wiring to the electrode. Further, the air introduction layer 48 is formed so as to cover the reference electrode 42 with the air introduction layer paste containing the constituent material of the air introduction layer 48. Further, punching is performed on a part of the green sheet in order to provide the pressure diffusion hole 75.

  Further, the heating resistor 72 is sandwiched between the upper surface of the green sheet (second substrate layer green sheet) to be the second substrate layer 2 by firing with the heating resistor paste and the insulating layer paste made of alumina material or the like. In this manner, the heater insulating layer 74 is formed by printing. Further, punching is performed on a part of the green sheet to form a through hole 73 to form a heater wiring.

  In addition, the heater electrode 71 is printed and formed on the lower surface of the green sheet (first substrate layer green sheet) to be the first substrate layer 1 by firing with a heater electrode paste made of platinum or the like. Further, punching is performed on a part of the green sheet to form a through hole 73 to form a heater wiring.

  Subsequently, the green sheet for the first substrate layer, the green sheet for the second substrate layer, the green sheet for the third substrate layer, the green sheet for the first solid electrolyte layer, the green sheet for the spacer layer, and the green for the second solid electrolyte layer. A gas sensor element is obtained by laminating sheets and cutting the end portions as necessary, followed by firing. As a result of the firing, the six green sheets are integrated, and the pore-forming material in the paste for the diffusion rate-determining part that has been printed and burned out, and the burnout marks become pores, resulting in a porous fourth diffusion rate-determining part. (Measurement electrode protective layer) 45 is formed.

  In the present invention, a thermosetting resin is used for the pore former contained in the diffusion-controlling part paste. When a thermosetting resin is used for the pore former, pores are formed in the fourth diffusion rate-determining portion (measurement electrode protective layer) 45 in a state where the shape and dimensions of the pore former before burning are substantially maintained. In this way, pores are formed in a state where the shape and dimensions of the pore former before burning are maintained. In addition to the fact that the thermosetting resin does not deform when heated at a low temperature (room temperature to 300 ° C.), Thus, it is considered that a large amount of gas is not generated at the time of burning, and the amount of gas generated at the time of burning is small, so that the arrangement of the ceramic aggregate around the pore former does not collapse.

  The type of thermosetting resin used as the pore former is not particularly limited, but preferred examples include melamine resin, benzoguanamine / formaldehyde resin, benzoguanamine resin, urea resin, phenol resin, epoxy resin, nylon resin, urethane resin and There may be mentioned at least one thermosetting resin selected from the group consisting of unsaturated polyester resins. In addition, as a melamine resin, a melamine-formaldehyde condensate and a melamine-benzoguanamine condensate are preferable.

The type of ceramic aggregate contained in the diffusion-controlling part paste as well as the pore former is not particularly limited, but preferred examples include yttria partially stabilized zirconia, calcia partially stabilized zirconia, yttria stabilized zirconia, and calcia stabilized zirconia. , Α-alumina, Al ₂ O ₃ .MgO spinel, mullite, yttria, and at least one ceramic particle selected from the group consisting of magnesia.

  In the present invention, the pore-forming material (thermosetting resin) contained in the diffusion-controlling part paste has an average particle size of 0.15 to 9 μm, preferably 0.5 to 7 μm, more preferably 1 to 5 μm. . If the average particle size of the pore former is less than 0.15 μm, pores communicating after firing are not formed, the gas to be measured cannot reach the measurement electrode, and the concentration of a specific component in the gas to be measured cannot be measured. . On the other hand, if the average particle diameter of the pore former exceeds 9 μm, the pore former particles settle in the diffusion rate-determining part paste, and the fourth diffusion rate-determining part (measuring electrode protective layer having good diffusion rate-determining property) is obtained. ) Can not get. The “average particle size” referred to here is a value measured by a laser diffraction / scattering method in accordance with JIS R1629.

  In the present invention, the ceramic aggregate contained in the diffusion-controlling part paste has an average particle size of 0.1 to 9 μm, preferably 0.1 to 5 μm, and more preferably 0.1 to 3 μm. If the average particle diameter of the ceramic aggregate exceeds 9 μm, the ceramic aggregate particles settle in the diffusion rate-determining part paste, and the fourth diffusion rate-determining part (measuring electrode protective layer) having a good diffusion rate-determining property is formed. Can't get. The “average particle size” referred to here is a value measured by a laser diffraction / scattering method in accordance with JIS R1629.

  In the present invention, the content of the pore former in the diffusion rate controlling part paste is 1 to 50% by volume, preferably 1 to 40% by volume, more preferably the total volume of the ceramic aggregate and the pore former. 1 to 30% by volume. When the content of the pore former in the diffusion rate controlling part paste is less than 1% by volume of the total volume of the ceramic aggregate and the pore former, pores communicating after firing are not formed, and the gas to be measured reaches the measurement electrode. It becomes impossible to measure the concentration of the specific component in the gas to be measured. On the other hand, if the content of the pore-forming material in the diffusion-controlling part paste exceeds 50% by volume of the total volume of the ceramic aggregate and the pore-forming material, the fourth diffusion controlling part (measurement electrode protective layer) after firing The porosity becomes too high, the strength becomes insufficient, and damage such as cracks is likely to occur.

Moreover, in this invention, the calcination temperature in a baking process is 1200-1500 degreeC, Preferably it is 1250-1450 degreeC, More preferably, it is 1300-1400 degreeC. If the firing temperature is less than 1200 ° C., the porosity of the fourth diffusion rate-determining part (measurement electrode protective layer) becomes too high due to insufficient sintering, and the strength becomes insufficient, and damage such as cracks tends to occur. On the other hand, when the firing temperature exceeds 1500 ° C., the porosity of the fourth diffusion rate-determining part (measurement electrode protective layer) becomes too low due to oversintering. Cannot communicate with each other, so that the NO _x gas cannot reach the measurement electrode, and the NO _x concentration cannot be measured.

  In the present invention, as described above, the content of the pore-forming material in the diffusion-controlling part paste is 1 to 50% by volume of the total volume of the ceramic aggregate and the pore-forming material, so that the diffusion-controlled material after firing is controlled. The porosity of the part is about 5 to 50%. When the porosity of the fourth diffusion rate-determining part (measurement electrode protective layer) is in such a range, good diffusion rate-determining property is obtained and damage such as cracks hardly occurs. Note that the “porosity” mentioned here means that the cross section of the fourth diffusion rate-determining part (measuring electrode protective layer) is polished, and the aggregate portion is analyzed by image analysis from a photograph of a scanning electron microscope (SEM) of the polished surface. By binarizing the pore portion into black and white, the area of the pore portion is calculated, and is a value calculated from the ratio of the area of the pore portion to the total area (total of the aggregate portion and the pore portion).

  In the present invention, as described above, the average particle diameter of the pore former (thermosetting resin) contained in the paste for diffusion rate-limiting part is 0.15 to 9 μm, and the shape of the pore former before burnout By forming the pores in a state in which the dimensions are substantially maintained, the average pore diameter of the fourth diffusion rate-determining part (measurement electrode protective layer) after firing becomes about 0.05 to 9 μm. When the average pore diameter of the fourth diffusion-controlling portion (measurement electrode protective layer) is in such a range, a good diffusion-controlling property can be obtained, and the pores are not easily blocked by poisonous substances. It is difficult for the sensitivity of the element to decrease. The “average pore diameter” here means that the average pore diameter of the diffusion limiting part (measuring electrode protective layer) of the sensor element cannot be directly measured. Therefore, the diffusion limiting part formed in the sensor element by the diffusion limiting part paste is used. A diffusion-controlled part molded body sheet having the same thickness as the part is prepared and fired at the same temperature as the sensor element to produce a diffusion-controlled part fired body sheet, and the fired body sheet is used with a mercury porosimeter It is a measured value.

  Furthermore, in the present invention, the ratio of the lower limit 20% pore diameter to the average pore diameter (lower limit 20% pore diameter / average pore diameter) of the diffusion rate controlling portion (measurement electrode protective layer) after firing is 0.5 or more and less than 1. It is preferable that Here, the “lower limit 20% pore diameter” means a pore diameter having a pore volume of 20% from the small pore side in the total pore volume measured by the mercury porosimeter. Moreover, since the "lower limit 20% pore diameter" and the "average pore diameter" referred to here cannot directly measure the average pore diameter of the diffusion rate-limiting part (measurement electrode protective layer) of the sensor element, A molded body sheet of a diffusion rate controlling part having the same thickness as the diffusion rate controlling part formed on the sensor element is produced, and a fired body sheet of the diffusion rate controlling part is produced by firing at the same temperature as the sensor element. It is the value measured about the body sheet using the mercury porosimeter. If the ratio of the lower limit 20% pore diameter to the average pore diameter of the diffusion rate controlling part after firing is 0.5 or more and less than 1, it can be determined that the formation of the fine pores on the lower limit side is suppressed, and the fine pores are blocked. It can be said that a gas sensor element is obtained in which the sensitivity is not easily lowered. If a thermosetting resin having an average particle size of 0.15 to 9 μm is used as the pore former, the value of the ratio is generally within the above range.

The gas sensor element to be manufactured according to the present invention is not limited to the structure as shown in FIG. 1, and includes a solid electrolyte layer and an electrode that is in contact with a gas to be measured formed on the surface of the solid electrolyte layer. If the gas sensor element includes a porous diffusion rate-determining portion formed so as to cover the electrode, even a gas sensor element having a structure different from that shown in FIG. Further, the gas sensor element to be manufactured according to the present invention is not limited to the gas component whose concentration in the gas to be measured is to be measured. The NO _x sensor element or the O ₂ concentration for measuring the NO _x concentration is not limited. Various gas sensor elements such as an O ₂ sensor element for measuring the above can be manufactured.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to these Examples.

(Examples 1-37 and Comparative Examples 1-12)
The various ceramic aggregates having the average particle diameters shown in Tables 1 and 2 and the various pore formers having the average particle diameters and the D20 particle diameters shown in the same table, respectively, at the ratios shown in the same table. An appropriate amount of acetone as a dispersion medium was added to the prepared raw material powder and premixed to obtain a premixed solution. An organic binder liquid obtained by dissolving 20% by mass of polyvinyl butyral in 80% by mass of butyl carbitol is 50% by volume with respect to the total volume of the ceramic aggregate and the pore former in the premixed liquid. Thus, after adding to the premixed liquid and mixing, acetone as the dispersion medium is removed, and butyl carbitol is added as appropriate to adjust the viscosity. 1 to 35 diffusion-controlling part pastes were obtained. In addition, the average particle diameter of the aggregate shown in Tables 1 and 2, the average particle diameter of the pore former, and the D20 particle diameter were measured by a laser diffraction / scattering method according to JIS R1629. Here, “D20 particle size” is a particle size measured by a laser diffraction / scattering method, and particles in a volume in which the accumulated volume of the granular material is 20% from the fine particle side with respect to the total volume of the granular material. Means diameter.

  No. obtained as described above. A gas sensor element having a structure as shown in FIG. 1 was produced using 1 to 35 diffusion-controlling part pastes. As a production procedure, first, yttria partially stabilized zirconia is used as a solid electrolyte material, and the first substrate layer 1, the second substrate layer 2, the third substrate layer 3, and the first solid are respectively fired by firing in a later firing step. A green sheet (unfired body) to be the electrolyte layer 4, the spacer layer 5, and the second solid electrolyte layer 6 was produced.

  Next, on the upper surface of the solid electrolyte layer green sheet (second solid electrolyte green sheet) that becomes the second solid electrolyte layer 6 by firing, an outer pump is formed with an electrode paste made of partially stabilized zirconia, platinum, and a binder solution. The electrode 23 is formed by printing the inner pump electrode 22a and the auxiliary pump electrode 51a on the lower surface together with the wiring to these electrodes, and the outer pump electrode 23 is covered with an electrode protective layer paste made of an alumina material or the like. The outer pump electrode protective layer 24 was formed by printing.

  Similarly, the inner pump electrode 22b and the auxiliary pump electrode 51b are formed on the upper surface of the solid electrolyte layer green sheet (first solid electrolyte green sheet) that becomes the first solid electrolyte layer 4 by firing, using the electrode paste. A printed electrode is formed with wiring to each of these electrodes, a measurement electrode 44 is printed with a wiring to each of these electrodes, using a partially stabilized zirconia and platinum, rhodium, binder solution for measurement electrode paste, No. A fourth diffusion rate-determining part (measuring electrode protective layer) 45 was printed and formed so as to cover the measuring electrode 44 with a paste for diffusion rate-determining part 1 to 35.

  Further, punching for providing the gas introduction port 10, the buffer space 12, the first internal space 20, and the second internal space 40 in a part of the green sheet (spacer layer green sheet) that becomes the spacer layer 5 by firing. In addition, a slit that becomes the first diffusion rate-limiting unit 11, the second diffusion rate-limiting unit 13, and the third diffusion rate-limiting unit 30 is formed on a part of the upper surface and the lower surface of the green sheet. The paste was printed. The printed organic paste is burned down by subsequent baking, and the burnout marks become the first diffusion rate-limiting unit 11, the second diffusion rate-limiting unit 13, and the third diffusion rate-limiting unit 30.

  In addition, a reference electrode 42 is printed on the upper surface of the green sheet (third substrate layer green sheet) to be the third substrate layer 3 by firing, using electrode paste together with the wiring to the electrode, and the atmosphere. The atmosphere introduction layer 48 was formed so as to cover the reference electrode 42 with an atmosphere introduction layer paste made of an alumina material or the like that is a constituent material of the introduction layer 48. Further, punching was performed on a part of the green sheet in order to provide the pressure diffusion hole 75.

  In addition, a heating resistor is formed on the upper surface of the green sheet (second substrate layer green sheet) that is to be the second substrate layer 2 by firing with a heating resistor paste made of platinum or the like and an insulating layer paste made of an alumina material or the like. The heating resistor 72 and the heater insulating layer 74 were printed and formed so as to sandwich the body 72. Further, a part of this green sheet was punched to provide a through hole 73 to form a heater wiring.

  Moreover, the heater electrode 71 was printed and formed with the paste for heater electrodes on the lower surface of the green sheet (green sheet for 1st board | substrate layers) used as the 1st board | substrate layer 1 by baking. Further, a part of this green sheet was punched to form a through hole 73 to form a heater wiring.

Subsequently, the green sheet for the first substrate layer, the green sheet for the second substrate layer, the green sheet for the third substrate layer, the green sheet for the first solid electrolyte layer, the green sheet for the spacer layer, and the green for the second solid electrolyte layer. After laminating the sheets and cutting the end portions, as a firing step, firing is performed for 5 hours at the firing temperatures shown in Tables 3 to 8 to burn away the pore former in the diffusion rate limiting portion paste. A porous fourth diffusion rate-determining part (measurement electrode protective layer) 45 having a thickness of 80 μm was formed, and gas sensor elements (NO _x sensor elements) of Examples 1 to 37 and Comparative Examples 1 to 12 were obtained.

  For the gas sensor elements of Examples 1 to 37 and Comparative Examples 1 to 12, the porosity, average pore diameter, lower limit 20% pore diameter, and lower limit 20% pore diameter / average of the fourth diffusion rate-limiting part (measurement electrode protective layer) The values of the pore diameters were determined and are shown in Tables 3-8. Moreover, paste stability was evaluated about the paste for diffusion control parts used for formation of the 4th diffusion control part (measurement electrode protective layer) of the gas sensor element of Examples 1-37 and Comparative Examples 1-12, and a result was represented. It was shown in 3-8. Furthermore, about the gas sensor element of Examples 1-37 and Comparative Examples 1-12, an endurance test was implemented, the sensitivity fall rate after an endurance test, the presence or absence of the obstruction | occlusion of the pore of a 4th diffusion control part (measurement electrode protective layer), and The presence or absence of cracks was examined, and the results are shown in the same table. The porosity, average pore diameter, lower limit 20% pore diameter measurement method, paste stability evaluation method, and gas sensor element durability test method of the fourth diffusion rate-limiting part (measurement electrode protective layer) are as follows. is there.

[Measurement Method of Porosity of Fourth Diffusion Controlling Part (Measurement Electrode Protective Layer)]
By polishing the cross section of the fourth diffusion rate-determining part and binarizing the aggregate part and the pore part into black and white by image analysis from the scanning electron microscope (SEM) photograph of the polished surface, the area of the pore part can be reduced. Calculated from the ratio of the area of the pore portion to the total area (total of the aggregate portion and the pore portion).

[Measuring Method of Average Pore Diameter, Lower Limit 20% Pore Diameter of Fourth Diffusion Controlling Part (Measurement Electrode Protective Layer)]
Since the average pore diameter and the lower limit 20% pore diameter of the fourth diffusion rate-determining part (measurement electrode protective layer) of the sensor element cannot be directly measured, the same as the diffusion rate-limiting part formed in the sensor element with each diffusion rate-determining part paste A molded body sheet of a fourth diffusion rate-limiting part having a thickness is prepared, and fired at the same temperature as the sensor element, a sintered body sheet of the fourth diffusion rate-limiting part is prepared, and the fired body sheet is measured using a mercury porosimeter. did. The average pore diameter is a pore diameter that is 50% of the total pore volume from the small pore side, and the lower limit 20% pore diameter is 20% of the total pore volume from the small pore side. It is the pore diameter that becomes the volume.

[Paste stability evaluation method]
24 hours after the preparation of the diffusion-controlling part paste, the presence or absence of sedimentation separation between the pore former particles and the liquid in the paste was examined. If no sedimentation separation was confirmed, “○” When the occurrence was confirmed, it was set as “x”.

[Durability test method of gas sensor element]
Using each gas sensor element manufactured performs NO _x sensitivity measured in 500 ppm NO _x model gas, it was the sensitivity and initial NO _x sensitivity. Next, a cycle of dropping 1 μL of an aqueous solution containing Mg ions (Mg ion concentration: 5 mmol / L) at the gas inlet of each gas sensor element, letting it stand for 1 minute, and then driving the gas sensor at 800 ° C. for 10 minutes is repeated 100 times. A total of 100 μL of Mg ion solution was dropped. Then, using the gas sensor element, was measured of the NO _x sensitivity NO _x model gas again, the measured NO _x sensitivity compared to the initial NO _x sensitivity was calculated sensitivity decrease rate. Further, after these measurements, the gas sensor element is disassembled, the presence or absence of cracks in the fourth diffusion rate-limiting part (measurement electrode protective layer) is confirmed, and the fourth diffusion rate-limiting part (measurement electrode protective layer) cross section (polished surface) ) Was measured, and it was confirmed whether or not the pores of the fourth diffusion rate-limiting part (measurement electrode protective layer) were blocked by the Mg compound.

  As shown in Table 3, Examples 1 to 9 using a thermosetting resin as the pore-forming material of the diffusion rate-determining part paste were, in the fourth diffusion rate-determining part (measurement electrode protective layer), on the lower limit side that was easily clogged. The formation of fine pores was suppressed, and the sensitivity reduction rate after the durability test of the gas sensor element was suppressed to a low level. On the other hand, Comparative Examples 1 to 3 using carbon, graphite, and theobromine, which have been conventionally used as a pore-forming material for the diffusion-controlling part paste, have a ratio of the lower limit 20% pore diameter to the average pore diameter (lower limit 20% pore diameter). / Average pore diameter) was less than 0.5, and the rate of decrease in sensitivity after the durability test was increased. In addition, the pores were blocked by Mg compounds in the fourth diffusion rate-determining part (measurement electrode protective layer) after the durability test.

As shown in Table 4, Examples 10 to 13 using a thermosetting resin having an average particle size in the range of 0.15 to 9 μm as the pore-forming material of the diffusion-controlling part paste are durability tests of gas sensor elements. The subsequent sensitivity reduction rate was kept low. On the other hand, in Comparative Example 4 using a thermosetting resin having an average particle diameter of less than 0.15 μm as the pore-forming material for the diffusion-controlling part paste, no continuous pores were formed, and NO _x gas reached the measurement electrode. it can not be, could not be measured concentration of NO _x. Further, as Comparative Example 5 using a thermosetting resin having an average particle diameter of more than 9 μm as the pore-forming material of the diffusion-controlling part paste, the pore-forming material particles settled in the diffusion-controlling part paste. 4 Diffusion rate limiting part (measurement electrode protective layer) could not be produced.

  As shown in Table 5, although Examples 14-22 differed in the kind of aggregate of the diffusion rate-determining part paste, the fourth diffusion rate-determining part (measuring electrode protective layer) was measured when any aggregate was used. ), The fine pores that were easily closed were hardly formed, the rate of decrease in sensitivity after the durability test of the gas sensor element was 3% or less, and the pores in the diffusion-controlling portion were not blocked and cracks after the durability test were not observed.

As shown in Table 6, in Examples 23 to 28 in which the firing temperature was set in the range of 1200 to 1500 ° C., the cracks of the fourth diffusion rate controlling part (measurement electrode protective layer) were observed after the durability test of the gas sensor element. It was not seen and the sensitivity reduction rate was also low. On the other hand, in Comparative Examples 6 and 8, which were fired at a firing temperature of less than 1200 ° C., the porosity was too high due to insufficient sintering, and the strength of the fourth diffusion rate-determining part (measuring electrode protective layer) was lowered, and durability Cracks occurred during the test. In Comparative Examples 7 and 9, which were fired at a firing temperature exceeding 1500 ° C., pores communicating with the fourth diffusion rate-limiting part (measurement electrode protective layer) were not formed by oversintering, and NO _x gas was measured. The electrode could not be reached and the NO _x concentration could not be measured.

As shown in Table 7, Examples 29 to 32 in which the content of the pore former in the diffusion rate limiting portion paste is in the range of 1 to 50% by volume of the total volume of the aggregate and the pore former are gas sensor elements. The sensitivity decrease rate after the durability test was kept low. On the other hand, in Comparative Example 10 in which the content of the pore-forming material in the diffusion-controlling portion paste is less than 1 volume% of the total volume of the aggregate and the pore-forming material, no continuous pores are formed, and NO _x gas is generated. The measurement electrode could not be reached, and the NO _x concentration could not be measured. Further, in Comparative Example 11 in which the content of the pore former in the diffusion rate limiting part paste exceeds 50% by volume of the total volume of the aggregate and the pore former, the porosity becomes too high, and the fourth diffusion rate limiting part. The strength of the (measurement electrode protective layer) decreased, and cracks occurred during the durability test.

  As shown in Table 8, in Examples 33 to 37, in which the average particle diameter of the aggregate in the diffusion rate limiting portion paste is in the range of 0.1 to 9 μm, the sensitivity decrease rate after the durability test of the gas sensor element is kept low. It was. On the other hand, in Comparative Example 12 in which the average particle diameter of the aggregate in the diffusion rate-limiting part paste exceeds 9 μm, the aggregate particles settle in the diffusion rate-limiting part paste, and the fourth diffusion rate-limiting part (measurement electrode protective layer) Could not be produced.

  The present invention can be suitably used as a method for producing a gas sensor element used for measuring the concentration of a specific gas component contained in a gas to be measured.

1: first substrate layer, 2: second substrate layer, 3: third substrate layer, 4: first solid electrolyte layer, 5: spacer layer, 6: second solid electrolyte layer, 10: gas inlet, 11: First diffusion limiting part, 12: buffer space, 13: second diffusion limiting part, 20: first internal space, 21: main pump cell, 22: inner pump electrode (22a: upper inner pump electrode, 22b: lower side Inner pump electrode), 23: outer pump electrode, 24: outer pump electrode protective layer (peripheral protective layer), 25: variable power source, 30: third diffusion rate limiting part, 40: second inner space, 41: for measurement Pump cell, 42: reference electrode, 43: reference gas introduction space, 44: measurement electrode, 45: fourth diffusion control part (measurement electrode protective layer), 46: variable power supply, 48: air introduction layer, 50: auxiliary pump cell, 51 : Auxiliary pump electrode (51a: Upper auxiliary pump electrode, 51b Lower auxiliary pump electrode), 52: variable power supply, 70: heater, 71: heater electrode, 72: resistance heating element, 73: through hole, 74: heater insulating layer, 75: pressure dissipation hole, 80: main pump control 81: oxygen partial pressure detection sensor cell for auxiliary pump control, 82: oxygen partial pressure detection sensor cell for measurement pump control, 83: sensor external oxygen partial pressure detection sensor cell, 100: gas sensor element, 101: base Wood.

Claims (6)

A method for producing a gas sensor element, comprising: a solid electrolyte layer; an electrode in contact with a gas to be measured formed on the surface of the solid electrolyte layer; and a porous diffusion rate-limiting part formed so as to cover the electrode. ,
After the electrode is printed and formed on the surface of the solid electrolyte layer green sheet that becomes the solid electrolyte layer by firing with the electrode paste containing the constituent material of the electrode, the diffusion rate-limiting including the ceramic aggregate and the pore former A printing process for producing a printed laminate by printing and forming a diffusion-limiting part so as to cover the electrode with a part paste,
A firing step of firing the printed laminate,
The ceramic aggregate has an average particle size of 0.1 to 9 μm,
The pore former is a thermosetting resin having an average particle size of 0.15 to 9 μm,
The content of the pore former in the diffusion-controlling part paste is 1 to 50% by volume of the total volume of the ceramic aggregate and the pore former,
The manufacturing method of the gas sensor element whose baking temperature in the said baking process is 1200-1500 degreeC.   The thermosetting resin is at least one thermosetting selected from the group consisting of melamine resin, benzoguanamine / formaldehyde resin, benzoguanamine resin, urea resin, phenol resin, epoxy resin, nylon resin, urethane resin and unsaturated polyester resin. The method for producing a gas sensor element according to claim 1, wherein the gas sensor element is a resin. The ceramic aggregate is selected from the group consisting of yttria partially stabilized zirconia, calcia partially stabilized zirconia, yttria stabilized zirconia, calcia stabilized zirconia, α-alumina, Al ₂ O ₃ .MgO spinel, mullite, yttria and magnesia. The method for producing a gas sensor element according to claim 1, wherein the at least one kind of ceramic particles is used.   The method for producing a gas sensor element according to any one of claims 1 to 3, wherein a porosity of the diffusion rate-determining part after firing is 5 to 50%.   The method for producing a gas sensor element according to any one of claims 1 to 4, wherein an average pore diameter of the diffusion-controlling portion after firing is 0.05 to 9 µm.   The ratio of the lower limit 20% pore diameter to the average pore diameter of the diffusion-controlling portion after firing (lower limit 20% pore diameter / average pore diameter) is 0.5 or more and less than 1, 6. The manufacturing method of the gas sensor element of description.

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