JP5097239B2 - 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 porous external electrode (on the outer peripheral surface of a base material formed by laminating a plurality of solid electrolyte layers ( For example, a gas sensor element having a pump electrode constituting a pump cell is known.

  By the way, in the case where the gas to be measured includes water such as exhaust gas discharged from the engine, when water droplets directly adhere to the base material of the gas sensor element, the outer side (surface side) of the base material on which the water droplets have adhered. The temperature decreases, and a steep temperature gradient occurs between the outside of the substrate and the inside (inside), which may cause cracks. In addition, a substance that poisons the electrode contained in the gas to be measured adheres to the external electrode and degrades the electrode.

  For the purpose of solving such problems, Patent Document 1 discloses a gas sensor element in which a porous outer peripheral protective layer is formed so as to cover the outer periphery of a base material. In this gas sensor element, the outer peripheral protective layer prevents water droplets from directly adhering to the base material, so that the temperature gradient generated on the base material becomes gentle, the generation of cracks is suppressed, and the outside of the poisonous substance is prevented. Adhesion to the electrode is also suppressed. The porous outer peripheral protective layer is formed by applying a peripheral protective layer paste containing a ceramic aggregate such as zirconia particles and a pore former (a pore forming agent) to the outer periphery of the base material, and firing it. It is formed by burning out the pore material.

However, in the conventional gas sensor element in which such a peripheral protective layer is formed, theobromine, caffeine, carbon, and graphite powder particles are used as the pore-forming material to be included in the peripheral protective layer paste. When a pore former is used, a large number of fine pores having a shape different from the shape of the pore former are formed in the outer peripheral protective layer after firing, so that the specific surface area (exposed area) of the outer peripheral protective layer is growing. For this reason, when the water droplets adhere to the outer peripheral protective layer, the contact area between the water droplets and the outer peripheral protective layer increases, the temperature decreases rapidly, and the temperature gradient suppression effect of the base material covered with the outer peripheral protective layer is sufficient. There was a problem that it could not be demonstrated. In addition, moisture containing poisonous substances adhering to the outer peripheral protective layer collects in the fine pores of the outer peripheral protective layer and evaporates when the sensor is activated (these gas sensor elements are usually driven at a temperature of 500 ° C. or higher). Since the microporous parts of the protective layer are clogged by poisonous substances, the escape of oxygen discharged from the external electrode to the outside of the element worsens, and the time from when the sensor starts until the signal stabilizes (light-off There was also a problem that the time was long. As the pore former, when theobromine, caffeine, carbon, graphite powder particles are used, a large number of fine pores having a shape different from that of the pore former are formed. It is considered that the arrangement of the ceramic aggregate around the pore former collapses by generating a large amount of gas (CO ₂ ) at the time of burning.

  Further, when the pore diameter of the external electrode is smaller than that of the outer peripheral protective layer covering the external electrode, the moisture containing the poisoning substance attached to the outer peripheral protective layer is caused by the capillary force to cause the external electrode having a smaller pore diameter. By reaching the pores and covering the surface, the discharge of oxygen gas from the internal electrode to the external electrode is hindered, and the time from when the sensor is started until the signal stabilizes (light-off) There was also a problem that the time was long.

Japanese Patent No. 4293579

  The present invention has been made in view of such conventional circumstances, and the object thereof is the use of theobromine, caffeine, carbon, and graphite as a pore former to be included in the outer periphery protective layer paste. Compared to the gas sensor element obtained by the conventional manufacturing method, the specific surface area of the outer peripheral protective layer is small when the porosity of the outer peripheral protective layer is the same, and when the water droplets adhere to the outer peripheral protective layer, The generated temperature gradient is more gradual, cracks are less likely to occur, and water droplets containing poisonous substances adhering to the outer protective layer block the fine pores of the outer protective layer and reach the pores of the external electrode. Thus, an object of the present invention is to provide a method of manufacturing a gas sensor element having high durability that can suppress an increase in signal stabilization time at the time of sensor activation (prolongation of light-off time).

  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 porous outer electrode is provided on the outer peripheral surface of a base material formed by laminating a plurality of solid electrolyte layers, and the outer periphery of the base material covers at least the external electrode. A method of manufacturing a gas sensor element in which a layer is formed, wherein an external electrode is printed and formed on a surface of an unfired body that becomes the solid electrolyte layer by firing with an electrode paste containing the constituent material of the external electrode A printing step in which an outer peripheral protective layer is printed and formed on the green body so as to cover at least the external electrode with a paste for outer peripheral protective layer including a ceramic aggregate and a pore former. And a firing step of firing the printed laminate, and using the thermosetting resin particles as the pore former, the firing temperature in the firing step is 1200 to 1500 ° C., and the outer periphery after the firing The protective layer has a thickness of 10 to 200 μm, a porosity of 15 to 65%, an average pore diameter of 0.05 to 9 μm, and the average pore diameter A of the external electrode after the firing and the outer peripheral protective layer after the firing. The average pore diameter B satisfies the relationship of 0.05 ≦ B / A ≦ 0.9, and the average pore diameter B and the lower limit 20% pore diameter C of the outer peripheral protective layer after firing are 0.5 <C A method of manufacturing a gas sensor element that manufactures a gas sensor element that satisfies the relationship / B <1.

[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 is composed 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, magnesia and cordier. 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 consisting of erite.

  According to the present invention, pores are formed in the outer peripheral protective layer in a state where the shape of the pore former prior to burning is substantially maintained by using a thermosetting resin as the pore former of the outer peripheral protective layer paste. Is done. For this reason, by adjusting the particle size distribution of the pore former, the pore size distribution of the outer peripheral protective layer can be easily controlled, and an outer peripheral protective layer having an arbitrary pore size distribution can be obtained. Therefore, the formation of a large number of micropores that increase the specific surface area of the outer peripheral protective layer is suppressed, and it becomes easy to form an outer peripheral protective layer having a uniform pore diameter and a smaller specific surface area. As compared with the gas sensor element obtained by the conventional manufacturing method using theobromine, caffeine, carbon, graphite as the pore former, the ratio of the outer peripheral protective layer when the porosity of the outer peripheral protective layer is equal A gas sensor element having a small surface area, a gentler temperature gradient generated in the base material when water droplets adhere to the outer peripheral protective layer, and less cracking can be obtained. Furthermore, as described above, by using a thermosetting resin that allows easy control of the pore diameter distribution as the pore former of the outer peripheral protective layer paste, the average pore diameter of the outer peripheral protective layer can be made larger than the average pore diameter of the external electrode. It is also easy to adjust so that the water droplets containing poisonous substances can close the fine pores of the outer peripheral protective layer and reach the pores of the external electrode. This makes it possible to manufacture a highly durable gas sensor element that can prevent the signal stabilization time from becoming longer (longer light-off time).

It is sectional drawing which shows an example of the gas sensor element which is the manufacture object of this invention. It is sectional drawing which shows another example of the gas sensor element which is the manufacture object of this invention. It is a perspective view which shows another 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 described later, it is easy 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 is easily pumped into the external space, or oxygen in the external space is easily 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 easy 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 easy to draw 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 producing a gas sensor element of the present invention has a porous external electrode on the outer peripheral surface of a base material formed by laminating a plurality of solid electrolyte layers, and at least the outer periphery of the base material A method of manufacturing a gas sensor element in which a porous outer peripheral protective layer is formed so as to cover an external electrode, the electrode including a constituent material of the external electrode on a surface of an unfired body that becomes the solid electrolyte layer by firing After the external electrode is printed and formed with paste, the outer peripheral protective layer is printed on the green body so as to cover at least the external electrode with the outer peripheral protective layer paste including the ceramic aggregate and the pore former. And a firing step for firing the printed laminate, and using a thermosetting resin particle as the pore former and a firing temperature in the firing step of 120. ˜1500 ° C., the thickness of the outer peripheral protective layer after firing is 10-200 μm, the porosity is 15-65%, the average pore diameter is 0.05-9 μm, and the average fineness of the external electrode after firing is The pore diameter A and the average pore diameter B of the outer peripheral protective layer after firing satisfy the relationship of 0.05 <B / A <0.9, and the average pore diameter B of the outer peripheral protective layer after firing and the lower limit of 20% A gas sensor element satisfying a relationship of 0.5 <C / B <1 with a pore diameter C is manufactured.

  In the gas sensor element shown in FIG. 1, the outer pump electrode 23 formed on the upper surface of the second solid electrolyte layer 6 corresponds to an “external electrode” in the method of manufacturing a gas sensor element of the present invention. The outer pump electrode protective layer 24 formed so as to cover the pump electrode 23 corresponds to the “outer peripheral protective layer”. Further, as in the embodiment shown in FIGS. 2 and 3, the porous body installed on the entire outer periphery of the gas sensor element also corresponds to the “outer peripheral protective layer” (outer peripheral protective layers 90 to 92).

  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 wiring to each of these electrodes, and further, outer peripheral protective layer (outer pump electrode 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. In addition, the measurement electrode 44 is printed together with the wiring to the electrode by using the measurement electrode paste containing the measurement electrode constituent material, and is printed together with the wiring to each of the electrodes. The fourth diffusion rate-determining part (measurement electrode protective layer) 45 is printed and formed so as to cover the measurement electrode 44 with a paste for the fourth diffusion rate-limiting part (measurement electrode protective layer) containing the constituent material of the layer 45. 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, a part of this green sheet is punched to form a pressure diffusion hole 75 to form a heater wiring.

  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) that becomes the first substrate layer 1 by firing with the heater electrode paste. Further, punching is performed on a part of the green sheet in order to provide a through hole 73.

  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, if necessary, the outer peripheral protective layer 90-92 is applied and formed on the outer peripheral portion of the laminate with the outer peripheral protective layer paste, and if necessary, the end portion is cut. By firing, a gas sensor element is obtained. As a result of the firing, the six green sheets are integrated, the pore former in the printed outer periphery protective layer paste is burned out, and the burned traces become pores, resulting in a porous outer peripheral protective layer (outside Pump electrode protective layer) 24 and outer peripheral protective layers 90 to 92 are formed.

  In the present invention, thermosetting resin particles are used for the pore former contained in the outer periphery protective layer paste. When the thermosetting resin particles are used for the pore former, pores can be obtained in a state in which the shape of the pore former before burning is substantially maintained in the outer peripheral protective layer (outer pump electrode protective layer) 24 and the outer peripheral protective layers 90 to 92. Is formed. For this reason, by adjusting the particle size distribution of the pore former, the pore size distribution of the outer peripheral protective layer can be easily controlled, and an outer peripheral protective layer having an arbitrary pore size distribution can be obtained. Therefore, the formation of a large number of micropores that increase the specific surface area of the outer peripheral protective layer is suppressed, and it becomes easy to form an outer peripheral protective layer having a uniform pore diameter and a smaller specific surface area. As compared with the gas sensor element obtained by the conventional manufacturing method using theobromine, caffeine, carbon, graphite as the pore former, the ratio of the outer peripheral protective layer when the porosity of the outer peripheral protective layer is equal A gas sensor element having a small surface area, a gentler temperature gradient generated in the base material when water droplets adhere to the outer peripheral protective layer, and less cracking can be obtained. Furthermore, by using a thermosetting resin with easy control of the pore size distribution as the pore forming material for the outer periphery protective layer paste, the average pore size of the outer periphery protective layer is made smaller than the average pore size of the external electrode. This makes it easy to adjust the sensor signal stabilization time by allowing water droplets containing poisonous substances to block the fine pores of the outer peripheral protective layer and reach the pores of the external electrode. It is possible to manufacture a gas sensor element having high durability that can prevent the lengthening (longening of the light-off time).

  When thermosetting resin particles are used as the pore-forming material for the outer peripheral protective layer paste, pores are formed in the outer peripheral protective layer in a state where the shape of the pore-forming material before burning is maintained. The curable resin does not deform when heated at a low temperature (room temperature to 300 ° C.) and, like carbon, does not generate a large amount of gas at the time of burning, and the amount of gas generated at the time of burning is small. This is probably because the arrangement of ceramic aggregates around the material 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 outer peripheral protective layer 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, magnesia, and cordierite.

  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. When the firing temperature is less than 1200 ° C., the porosity of the outer peripheral protective layer becomes too high due to insufficient sintering, and when water droplets adhere to the outer peripheral protective layer, it passes through the pores of the outer peripheral protective layer and is on the inner side. Since it becomes easy to contact a material, generation | occurrence | production of a crack cannot fully be suppressed. On the other hand, if the firing temperature exceeds 1500 ° C., the sintering proceeds too much and the pores of the outer peripheral protective layer do not communicate with each other. As a result, oxygen gas discharged from the internal electrode to the external electrode can be discharged out of the element. It will not function as a sensor.

  In the present invention, as described above, by using the thermosetting resin particles as the pore-forming material of the outer periphery protective layer paste, the shape of the pore former before burning is almost maintained in the outer peripheral protective layer. In this way, pores are formed. Therefore, by adjusting the average particle diameter of the pore former, it is easy to control the average pore diameter of the outer peripheral protective layer after firing to obtain the target average pore diameter.

  In the present invention, the average pore diameter of the outer peripheral protective layer after firing is 0.05 to 9 μm, preferably 0.25 to 7 μm, more preferably 0.8 by utilizing the ease of controlling the average pore diameter. A gas sensor element of 5 to 5 μm is manufactured. If the average pore diameter of the outer peripheral protective layer after firing is less than 0.05 μm, the average pore diameter of the outer peripheral protective layer is too small, and the pores of the outer peripheral protective layer are likely to be clogged with poisonous substances contained in water droplets. As a result, the escape of oxygen gas discharged to the external electrode to the outside of the device becomes worse, and accordingly, the signal stabilization time becomes longer (longer light-off time). On the other hand, when the average pore diameter of the outer peripheral protective layer after firing exceeds 9 μm, the capillary force is reduced, so when water droplets adhere to the outer peripheral protective layer, the function of trapping it with the outer peripheral protective layer is lowered. As a result, water easily passes through the pores of the outer peripheral protective layer and comes into contact with the base material on the inner side, so that generation of cracks cannot be sufficiently suppressed. In addition, since the “average pore diameter” in the present invention cannot directly measure the average pore diameter of the external electrode (external pump electrode) and the outer peripheral protective layer (outer pump electrode protective layer) of the sensor element, The outer electrode (external pump electrode) and outer protective layer (outer pump electrode protective layer) of the same thickness as the outer electrode (external pump electrode) and outer protective layer (outer pump electrode protective layer) formed on the sensor element by the outer peripheral protective layer paste Layer) and a fired body sheet of the outer electrode (external pump electrode) and outer peripheral protective layer (outer pump electrode protective layer) by firing at the same temperature as the sensor element. It is the value measured using the mercury porosimeter about the sintered body sheet of the external electrode (external pump electrode) and the outer peripheral protective layer (outer pump electrode protective layer).

  Further, in the present invention, as described above, since the pores are formed in the outer peripheral protective layer in a state where the shape of the pore former before burning is substantially maintained, the content of the pore former in the outer peripheral protective layer paste By adjusting the ratio, it is easy to control the porosity of the outer peripheral protective layer after firing to obtain the target porosity.

  In the present invention, a gas sensor in which the porosity of the outer peripheral protective layer after firing is 15 to 65%, preferably 18 to 60%, more preferably 20 to 50% by utilizing the ease of controlling the porosity. A device is manufactured. When the porosity of the outer peripheral protective layer after firing is less than 15%, the pores of the outer peripheral protective layer cannot communicate with each other, and as a result, the gas to be measured cannot reach the external electrode, and thus does not function as a sensor. On the other hand, when the porosity of the outer peripheral protective layer after firing exceeds 65%, the voids increase too much, so when water droplets adhere to the outer peripheral protective layer, the function of trapping it with the outer peripheral protective layer is lowered, As a result, water easily passes through the pores of the outer peripheral protective layer and comes into contact with the base material of the gas sensor element on the inner side, so that generation of cracks cannot be sufficiently suppressed. The “porosity” in the present invention is obtained by polishing the cross section of the outer peripheral protective layer and binarizing the aggregate portion and the pore portion into black and white by image analysis based on a scanning electron microscope (SEM) photograph of the polished surface. Thus, 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, since the average pore diameter of the outer peripheral protective layer is easily controlled, the average pore diameter of the external electrode covered by the outer peripheral protective layer and the average pore diameter of the outer peripheral protective layer are small or large. It is easy to adjust the relationship.

  In the present invention, the average pore diameter A of the external electrode after firing and the post-fired external electrode are utilized by utilizing the ease of adjusting the size relationship between the average pore diameter of the external electrode and the average pore diameter of the outer peripheral protective layer. The gas sensor element is manufactured so that the average pore diameter B of the outer peripheral protective layer satisfies the relationship of 0.05 ≦ B / A ≦ 0.9, preferably 0.1 <B / A <0.65. When the relationship of 0.05 ≦ B / A ≦ 0.9 is satisfied, water droplets containing poisonous substances in the outer peripheral protective layer may block fine pores in the outer peripheral protective layer or in the pores of the external electrode. As a result, it is possible to prevent the signal stabilization time of the sensor from increasing (prolonging the light-off time). This is because the average pore diameter of the outer peripheral protective layer covering the external electrode is smaller than the average pore diameter of the external electrode by a certain percentage or more, so that moisture containing poisonous substances attached to the outer peripheral protective layer is caused by capillary force. This is because they gather in the pores of the outer peripheral protective layer having a smaller pore diameter and are less likely to enter the pores of the external electrode.

  In addition, when B / A is less than 0.05, the average pore diameter of the outer peripheral protective layer becomes too small, and the pores of the outer peripheral protective layer are likely to be blocked by poisonous substances contained in the water droplets. Oxygen gas exhausted to the outside of the element deteriorates and the signal stabilization time becomes longer (longer light-off time). On the other hand, if B / A exceeds 0.9, water droplets adhering to the outer peripheral protective layer can easily reach the pores of the external electrode, thereby increasing the signal stabilization time (longening the light-off time). .

  Further, in the present invention, as described above, the pore size distribution of the outer peripheral protective layer can be easily controlled by using the thermosetting resin particles as the pore former contained in the outer peripheral protective layer paste. .

  In the present invention, the average pore diameter B and the lower limit 20% pore diameter C of the outer peripheral protective layer after firing are such that 0.5 <C / A gas sensor element satisfying the relationship B <1 is manufactured. 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. The state in which C / B is 0.5 or less is a state in which a large number of micropores that increase the specific surface area of the outer peripheral protective layer are formed, and in this state, water droplets adhere to the outer peripheral protective layer. The contact area between the water droplet and the outer peripheral protective layer is increased, the temperature is rapidly lowered, and the temperature gradient suppressing effect of the base material covered with the outer peripheral protective layer is not sufficiently exhibited.

  Furthermore, in this invention, the thickness of the outer periphery protective layer after baking produces 10-200 micrometers, Preferably it is 15-150 micrometers, More preferably, it is 20-100 micrometers. The thickness of the outer peripheral protective layer after firing can be easily determined by checking the firing shrinkage rate of the outer peripheral protective layer paste in advance and adjusting the thickness when printing the outer protective layer in consideration of the firing shrinkage rate. Can be controlled. When the thickness of the outer peripheral protective layer after firing is less than 10 μm, the outer peripheral protective layer is too thin, and when water droplets adhere to the outer peripheral protective layer, water passes through the outer peripheral protective layer and comes into contact with the substrate. Cracks are likely to occur in the substrate. On the other hand, if the thickness of the outer peripheral protective layer after firing exceeds 200 μm, cracks are likely to occur in the outer peripheral protective layer itself.

Note that the gas sensor element to be manufactured according to the present invention is not limited to the structure shown in FIG. 1, and a porous exterior is provided on the outer peripheral surface of a base material formed by laminating a plurality of solid electrolyte layers. As long as the gas sensor element has an electrode and a porous outer peripheral protective layer is formed on the outer periphery of the substrate so as to cover at least the external electrode, even a gas sensor element having a structure different from that shown in FIG. It becomes a manufacturing object. Further, the gas sensor element to be manufactured according to the present invention is not limited in the range of formation of the outer peripheral protective layer as long as the outer peripheral protective layer is formed so as to cover at least the external electrode. For example, FIG. 2 and FIG. As in the example shown in FIG. 3, the outer peripheral protective layers 24, 90, 91, 92 may be formed so as to cover most of the outer periphery of the base material on the gas inflow side. Further, the gas sensor element to be manufactured of the present invention is not intended gas component to be measured concentration in the measurement gas is limited, NO _x sensor element and the O ₂ concentration for measuring the concentration of NO _x 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.

(Preparation of paste for outer periphery protective layer)
Gas sensor element Nos. Shown in Tables 1 and 2 The paste for outer periphery protective layers used for manufacture of 1-46 was produced in the following procedures. First, various aggregates shown in Tables 1 and 2 and various pores having average particle diameters (average particle diameters measured by a laser diffraction / scattering method) measured according to JIS R1629 shown in the same table An appropriate amount of acetone as a dispersion medium was added to the raw material powder prepared by mixing the materials at the ratio shown in the table, 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 solution and mixing, acetone as the dispersion medium is removed, and butyl carbitol is added as appropriate to adjust the viscosity, whereby the element No. The paste for outer periphery protective layers used for manufacture of each gas sensor element of 1-46 was obtained.

(Preparation of paste for external electrodes)
Preliminary mixing was performed by adding predetermined amounts of platinum, a pore former having a particle size shown in Tables 1 and 2 and acetone as a dispersion medium to yttria partially stabilized zirconia to obtain a premixed solution. 50% by volume of the organic binder liquid obtained by dissolving 20% by mass of polyvinyl butyral in 80% by mass of butyl carbitol with respect to the total volume of yttria partially stabilized zirconia and pore former in the premixed liquid After being added to the premixed solution and mixed, the acetone as the dispersion medium is removed, and the viscosity is adjusted by adding butyl carbitol as appropriate, whereby the external electrode paste used for the production of the gas sensor element Got.

(Production of gas sensor element)
Using the outer periphery protective layer paste and the external electrode paste obtained as described above, a gas sensor element having a structure as shown in FIG. 1 was produced. As a manufacturing procedure, first, zirconia is used as a solid electrolyte material, and the first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, Green sheets (unfired bodies) to be the spacer layer 5 and the second solid electrolyte layer 6 were produced.

  Next, on the upper surface of the green sheet (the second solid electrolyte layer green sheet) that becomes the second solid electrolyte layer 6 by firing, the outer pump electrode 23 is formed on the lower surface with the external electrode paste, and the yttria partially stabilized zirconia is formed on the lower surface. The inner pump electrode 22a and the auxiliary pump electrode 51a are printed and formed together with the wiring to these electrodes using an electrode paste made of platinum or the like. Further, the outer protective layer paste is used in Tables 1 and 2 after firing. An outer peripheral protective layer (outer pump electrode protective layer) 24 was formed on the outer pump electrode 23 so as to have the thickness shown (however, element No. 10 was not formed with an outer peripheral protective layer).

  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 the electrode paste. The measurement electrode 44 is printed and formed together with the wiring to each electrode, using a paste for measurement electrode made of partially stabilized zirconia, platinum, rhodium, etc., and further, a fourth diffusion rate-determining part made of ceramic aggregate and pore former A fourth diffusion rate-determining part (measurement electrode protective layer) 45 was formed by printing so as to cover the measurement electrode 44 with the paste for (measurement electrode protective layer). Further, punching was performed on a part of the green sheet in order to provide the reference gas introduction space 43.

  In addition, punching for providing the gas inlet 10, the first internal space 20, and the second internal space 40 is performed on a part of the green sheet (spacer layer green sheet) that becomes the spacer layer 5 by firing, An organic paste containing a sublimation substance was printed in order to form slits serving as the first diffusion rate-limiting unit 11, the second diffusion rate-limiting unit 13, and the third diffusion rate-limiting unit 30 on a part of the upper surface and the lower surface of the green sheet. . 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.

  Further, the reference electrode 42 is printed and formed with the electrode paste on the upper surface of the green sheet (third substrate layer green sheet) to be the third substrate layer 3 by firing, The air introduction layer 48 was formed so as to cover the reference electrode 42 with an air introduction layer paste made of an alumina material or the like which is a constituent material of the air 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 heater insulating layer 74 was printed and formed so as to sandwich the body 72. Further, punching was performed on a part of the green sheet in order to provide a through hole 73.

  In addition, the heater electrode 71 was 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 the heater electrode paste. Further, punching was performed on a part of the green sheet in order to provide a through hole 73.

  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 edges, the outer periphery protective layer and the external electrodes are shown in Table 3 by firing for 5 hours at the firing temperature shown in Tables 1 and 2 as a firing step. Gas sensor element no. 1-46 were obtained.

(Examples 1-9 and Comparative Examples 1-4)
The gas sensor element No. obtained as described above was used. 1 to 46, element Nos. For the gas sensor element, the crack generation temperature and the rate of increase in signal stabilization time before and after the durability test were determined by the following procedure, and the paste for the outer protective layer used for forming the outer peripheral protective layer of the gas sensor element was stabilized. The results are shown in the same table.

[Paste stability]
24 hours after the preparation of the outer periphery protective layer paste, the presence or absence of sedimentation separation between the pore former particles and the liquid in the paste was examined. When the occurrence was confirmed, it was set as “x”.

[Crack generation temperature]
After each gas sensor element is heated to 200 ° C. with a built-in heater and the temperature is stabilized, 3 μL of water droplets are formed on the outer peripheral protective layer of the gas sensor element (on the base material for gas sensor element No. 10 having no outer peripheral protective layer). Was dripped. When cracks occurred in the base material of the gas sensor element, the temperature was regarded as the crack occurrence temperature. When cracks did not occur, the temperature was raised to 50 ° C., and the same test was performed on the elements produced under the same materials and conditions. The test was conducted by increasing the temperature by 50 ° C. until cracks occurred. The presence or absence of cracks was confirmed by immersing the gas sensor element after dropping water droplets in the ink liquid, wiping off the ink liquid on the surface, and visually observing whether the ink soaked. When the outer peripheral protective layer was formed, after removing the outer peripheral protective layer by polishing, the outer peripheral protective layer was immersed in an ink liquid to check for cracks.

[Increase rate of signal stabilization time before and after durability test]
Using each gas sensor element produced, the temperature is raised in a constant heater temperature rise pattern (here, a pattern for reaching the set temperature in about 40 seconds), and then each pump electrode is driven to output. The time until the signal was stabilized (signal stabilization time) was measured. Next, 10 μL of an aqueous solution containing Mg ions (Mg ion concentration 5 mmol / L) was dropped on the outer peripheral protective layer of each gas sensor element (on the base material for gas sensor element No. 10 in which the outer peripheral protective layer was not formed). After standing still for 50 minutes, a cycle of driving the gas sensor element at 800 ° C. for 10 minutes was repeated 50 times, and a total of 500 μL of Mg ion solution was dropped. After that, the same signal stabilization time is measured at each gas sensor element after the durability test, and the increase rate of the signal stabilization time before and after the durability test ((signal stabilization time after the durability test−signal stabilization before the durability test). Conversion time) / signal stabilization time before the durability test).

  As shown in Table 4, the gas sensor element No. manufactured using the outer periphery protective layer paste containing the thermosetting resin as the pore former. In 1 to 9 (Examples 1 to 9), the average pore diameter B and the lower limit 20% pore diameter C of the outer peripheral protective layer after firing satisfy the relationship of 0.5 <C / B <1. In both cases, the crack generation temperature was high and the temperature gradient suppression effect of the base material by the outer peripheral protective layer was excellent. On the other hand, the sensor element No. having no outer peripheral protective layer formed thereon. No. 10 (Comparative Example 1) had a very low cracking temperature. In addition, as a pore former, gas sensor element No. 1 produced using a paste for outer periphery protective layer containing carbon, graphite, and theobromine, which have been conventionally used, respectively. Nos. 11 to 13 (Comparative Examples 2 to 4) have C / B of 0.5 or less. Compared with 1-9 (Examples 1-9), the crack generation temperature was low, and the temperature gradient suppression effect of the base material by the outer periphery protective layer was inadequate.

(Examples 10 to 19)
The gas sensor element No. obtained as described above was used. 1 to 46, element Nos. Shown in Table 5 were used. For the gas sensor element, the crack generation temperature and the rate of increase in signal stabilization time before and after the durability test were determined according to the above procedure, and the paste for the outer protective layer paste used for forming the outer peripheral protective layer of the gas sensor element was stabilized. The results are shown in the same table.

  As shown in Table 5, the gas sensor element No. Although 1 and 14-22 (Examples 10-19) were produced using the paste for outer periphery protective layers each containing a different kind of aggregate, all gas sensor elements had high crack generation temperature. . Therefore, if a thermosetting resin is used as the pore forming material for the outer periphery protective layer paste, a gas sensor element excellent in the effect of suppressing the temperature gradient of the substrate by the outer periphery protective layer can be obtained regardless of the type of aggregate. I understand.

(Examples 20 to 24 and Comparative Examples 5 and 6)
The gas sensor element No. obtained as described above was used. 1 to 46, the element numbers shown in Table 6 were used. For the gas sensor element, the crack generation temperature and the rate of increase in signal stabilization time before and after the durability test were determined according to the above procedure, and the paste for the outer protective layer paste used for forming the outer peripheral protective layer of the gas sensor element was stabilized. The results are shown in the same table.

  As shown in Table 6, the gas sensor element in which the average pore diameter A of the external electrode after firing and the average pore diameter B of the outer peripheral protective layer after firing satisfy the relationship of 0.05 ≦ B / A ≦ 0.9 No. In 24, 25, 1, 26 and 27 (Examples 20 to 24), the rate of increase in signal stabilization time (light-off time) before and after the durability test was as low as 10% or less, particularly 0.1 <B / A. <Gas sensor element No. In Example 1 (Example 22), the rate of decrease in sensitivity after the durability test was only 1%. On the other hand, the gas sensor element No. B / A is less than 0.05. 23 (Comparative Example 5) and gas sensor element No. B / A exceeding 0.9. In 28 (Comparative Example 6), the rate of increase in signal stabilization time (light-off time) before and after the durability test reached approximately 30%.

(Examples 25 to 28 and Comparative Examples 7 and 8)
The gas sensor element No. obtained as described above was used. 1 to 46, element Nos. For the gas sensor element, the crack generation temperature and the rate of increase in signal stabilization time before and after the durability test were determined according to the above procedure, and the paste for the outer protective layer paste used for forming the outer peripheral protective layer of the gas sensor element was stabilized. The results are shown in the same table.

  As shown in Table 7, the average pore diameter of the outer peripheral protective layer after firing was in the range of 0.05 to 9 μm. 30, 1, 31, and 32 (Examples 25-28) had high crack generation temperature and were excellent in the temperature gradient suppression effect of the base material by an outer periphery protective layer. On the other hand, gas sensor element No. whose average pore diameter of the outer peripheral protective layer after firing is less than 0.05 μm. No. 29 (Comparative Example 7) has a fine pore diameter of the outer peripheral protective layer, so that the outer peripheral protective layer is clogged with poisonous substances, and oxygen gas discharged to the external electrode is discharged from the outer peripheral protective layer to the outside of the device. The rate of increase in signal stabilization time (light-off time) before and after the endurance test was increased due to poor omission. Moreover, the gas sensor element No. whose average pore diameter of the outer periphery protective layer after baking exceeds 9 μm. 33 (Comparative Example 8) has a pore size that is too large and the capillary force is small, so the function of trapping water droplets adhering to the outer peripheral protective layer with the outer peripheral protective layer is reduced. It became easy to contact the base material inside through the pores, and the crack generation temperature was lowered.

(Examples 29 to 31 and Comparative Examples 9 and 10)
The gas sensor element No. obtained as described above was used. 1 to 46, the element numbers shown in Table 8 are shown. For the gas sensor element, the crack generation temperature and the rate of increase in signal stabilization time before and after the durability test were determined according to the above procedure, and the paste for the outer protective layer paste used for forming the outer peripheral protective layer of the gas sensor element was stabilized. The results are shown in the same table.

  As shown in Table 8, the gas sensor element No. in which the porosity of the outer peripheral protective layer after firing is in the range of 15 to 65%. 35, 1 and 36 (Examples 29 to 31) had high crack generation temperatures and were excellent in the temperature gradient suppressing effect of the base material by the outer peripheral protective layer. On the other hand, gas sensor element No. whose porosity of the outer periphery protective layer after baking is less than 15%. No. 34 (Comparative Example 9) did not function as a sensor because the pores of the outer peripheral protective layer did not communicate with each other, and as a result, the gas to be measured could not reach the external electrode. Moreover, the gas sensor element No. whose porosity of the outer periphery protective layer after baking exceeds 65%. 37 (Comparative Example 10) has too many voids, so when water droplets adhere to the outer peripheral protective layer, the function of trapping it with the outer peripheral protective layer is lowered, and as a result, the water blocks the pores of the outer peripheral protective layer. It became easier to pass through and contact the inner substrate, and the crack generation temperature was lowered.

(Examples 32-35 and Comparative Examples 11 and 12)
The gas sensor element No. obtained as described above was used. 1 to 46, the element numbers shown in Table 9 are shown. For the gas sensor element, the crack generation temperature and the rate of increase in signal stabilization time before and after the durability test were determined according to the above procedure, and the paste for the outer protective layer paste used for forming the outer peripheral protective layer of the gas sensor element was stabilized. The results are shown in the same table.

  As shown in Table 9, the thickness of the outer peripheral protective layer after firing is in the range of 10 to 200 μm. Nos. 39, 1, 40 and 41 (Examples 32-35) had high crack generation temperatures, were excellent in the temperature gradient suppression effect of the base material by the outer peripheral protective layer, and the sensitivity reduction rate after the durability test was also low. . On the other hand, gas sensor element No. whose thickness of the outer periphery protective layer after baking is less than 10 μm. In 38 (Comparative Example 11), the outer peripheral protective layer was too thin, and water droplets adhering to the outer peripheral protective layer passed through the outer peripheral protective layer and contacted the base material. The effect of suppressing the temperature gradient of the substrate due to was insufficient. In addition, the thickness of the outer peripheral protective layer after firing exceeds 200 μm. In 42 (Comparative Example 12), cracks occurred in the outer peripheral protective layer during firing during the production of the sensor element.

(Examples 36 to 38 and Comparative Examples 13 and 14)
The gas sensor element No. obtained as described above was used. 1 to 46, the element Nos. Shown in Table 10 were used. For the gas sensor element, the crack generation temperature and the rate of increase in signal stabilization time before and after the durability test were determined according to the above procedure, and the paste for the outer protective layer paste used for forming the outer peripheral protective layer of the gas sensor element was stabilized. The results are shown in the same table.

  As shown in Table 10, the gas sensor element No. produced by setting the firing temperature in the firing step to the range of 1200 to 1500 ° C. Nos. 44, 1 and 45 (Examples 36 to 38) had high crack generation temperatures and were excellent in the effect of suppressing the temperature gradient of the base material by the outer peripheral protective layer. On the other hand, the gas sensor element No. produced by setting the firing temperature in the firing step to less than 1200 ° C. In 43 (Comparative Example 13), the porosity was too high due to insufficient sintering, and water droplets adhering to the outer peripheral protective layer passed through the outer peripheral protective layer and contacted the base material. The effect of suppressing the temperature gradient of the substrate by the outer peripheral protective layer was insufficient. In addition, the gas sensor element No. produced by setting the firing temperature in the firing step to over 1500 ° C. 46 (Comparative Example 14) is a sensor in which sintering proceeds too much and the pores of the outer peripheral protective layer do not communicate with each other. As a result, oxygen gas pumped from the internal electrode to the external electrode cannot be discharged outside the device. Did not work as.

  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: external electrode (outer pump electrode), 24: outer peripheral protective layer (outer pump electrode protective layer), 25: variable power source, 30: third diffusion rate limiting part, 40: second inner space, 41: measurement pump cell, 42: reference electrode, 43: reference gas introduction space, 44: measurement electrode, 45: fourth diffusion rate limiting part (measurement electrode protective layer), 46: variable power supply, 48: atmospheric 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 : Oxygen partial pressure detection sensor cell for main pump control, 81: oxygen partial pressure detection sensor cell for auxiliary pump control, 82: oxygen partial pressure detection sensor cell for measurement pump control, 83: sensor external oxygen partial pressure detection sensor cell, 90: outer periphery protection Layer, 91: outer peripheral protective layer, 92: outer peripheral protective layer, 100: gas sensor element, 101: base material.

Claims (3)

A porous outer electrode is formed on the outer peripheral surface of a base material formed by laminating a plurality of solid electrolyte layers, and a porous outer protective layer is formed on the outer periphery of the base material so as to cover at least the outer electrode. A gas sensor element manufacturing method comprising:
An outer peripheral protective layer containing a ceramic aggregate and a pore former after an external electrode is printed on the surface of an unfired body that becomes the solid electrolyte layer by firing with an electrode paste containing the constituent material of the external electrode In the paste for printing, a printing step of printing a peripheral protective layer on the green body so as to cover at least the external electrode, and producing a printed laminate,
A firing step of firing the printed laminate,
As the pore former, using thermosetting resin particles,
The firing temperature in the firing step is 1200-1500 ° C.
The thickness of the outer peripheral protective layer after the firing is 10 to 200 μm, the porosity is 15 to 65%, the average pore diameter is 0.05 to 9 μm,
The average pore diameter A of the external electrode after firing and the average pore diameter B of the outer peripheral protective layer after firing satisfy the relationship of 0.05 ≦ B / A ≦ 0.9,
A method for producing a gas sensor element, comprising producing a gas sensor element in which an average pore diameter B and a lower limit 20% pore diameter C of the outer peripheral protective layer after firing satisfy a relationship of 0.5 <C / B <1.   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 from yttria partially stabilized zirconia, calcia partially stabilized zirconia, yttria stabilized zirconia, calcia stabilized zirconia, α-alumina, Al ₂ O ₃ .MgO spinel, mullite, yttria, magnesia and cordierite. The method for producing a gas sensor element according to claim 1, wherein the method is at least one kind of ceramic particles selected from the group consisting of:

Images