JP5693421B2 - Laminated gas sensor element and laminated gas sensor - Google Patents

Description

  The present invention relates to a laminated gas sensor element for measuring a specific gas component contained in exhaust gas from an internal combustion engine or the like, and a laminated gas sensor using the same, and more particularly to a zirconia solid electrolyte plate and an alumina insulating plate. It is related with the reliability improvement of the laminated | stacked type gas sensor element which joined.

  An exhaust gas sensor for an internal combustion engine is generally composed of a laminated gas sensor element in which a pair of measurement electrodes are formed on both surfaces of an ion conductive solid electrolyte plate and an insulating plate that forms a gas introduction passage and a heater is joined. The In general, zirconia-based materials are used for solid electrolyte plates and alumina-based materials are used for insulating plates. However, since different materials are joined, it is necessary to cope with the stress generated between the layers due to the difference in thermal expansion coefficient. ing.

  As a prior art of such a laminated gas sensor element, Patent Document 1 discloses a zirconia powder having an average particle size of 2.0 μm or less when integrally firing a solid electrolyte plate, an air passage forming plate, an insulating layer, and a heater base. And a raw sheet of a zirconia-based solid electrolyte plate composed of 5-7 mol% yttria and 0-5 wt% alumina with respect to the zirconia powder, an alumina powder having an average particle size of 1.0 μm or less, and 0 with respect to the alumina powder. It is disclosed that a raw sheet of an alumina heater base made of -10 wt% zirconia or yttria partially stabilized zirconia is used, and an air passage forming plate and an insulating layer are sandwiched between them to be fired.

  As a composite material used for a gas sensor element, in Patent Document 2, nano zirconia particles having a particle size of 0.15 μm or less are dispersed in a matrix of alumina particles having an average particle size of 0.7 to 1.8 μm. A composite ceramic body having a content ratio of 80:20 to 95: 5 and a relative density of 93% or more is disclosed. This composite ceramic body constitutes, for example, a gas chamber forming plate, a diffusion layer, a heater sheet, an insulating layer, and an adhesive layer of a gas sensor element.

  Patent Document 3 includes a solid electrolyte body, an insulator, and a pair of electrodes formed so as to sandwich the solid electrolyte body, and the solid electrolyte body or the insulator has 0.1 to 20 wt% of nanoparticles having a size of 100 nm or less. A gas sensor element is disclosed. The insulator includes a sheet constituting a gas chamber, a diffusion layer, a heater, and the like, an insulating layer printed on the sheet, and an adhesive layer.

JP-A-6-300731 JP 2010-24128 A JP 2007-298490 A

  In the gas sensor element of Patent Document 1, alumina is added to a zirconia solid electrolyte plate, and zirconia or yttria partially stabilized zirconia is added to an alumina heater base, thereby reducing the difference in thermal expansion and suppressing the generation of stress. ing. However, when yttria partially stabilized zirconia is added to the alumina-based heater base, yttria partially stabilized zirconia has conductivity, which causes a problem that the withstand voltage of the heater portion is lowered.

  On the other hand, zirconia to which no stabilizer is added has three crystal systems of monoclinic, tetragonal and cubic crystals, and is known to cause a volume change due to phase transformation when the temperature is raised and lowered. For this reason, when zirconia is added to the alumina heater substrate, the volume change accompanying the phase transformation of zirconia causes a crack in the alumina heater substrate.

  Furthermore, although the insulating layer laminated with the heater base is made of alumina from the viewpoint of electrical insulation, it is adjacent to the air passage forming plate made of zirconia, and therefore, due to the difference in thermal expansion coefficient between these layers. Stress is generated. Although the air passage forming plate can be made of alumina, in this case, the same problem occurs with the zirconia solid electrolyte plate.

  In Patent Document 2, nano-zirconia particles are dispersed in a matrix of alumina particles constituting a heater sheet of a gas sensor element, an insulating layer, etc., in order to improve the grain boundary strength, and Patent Document 3 describes a solid electrolyte. Nanoparticles are dispersed in either the body or the insulating ceramic to increase the resistance to stress when exposed to water. However, these obtain the effect of improving the strength of the individual layers, and it is necessary to interpose an adhesive layer between the layers in order to prevent delamination between layers, and the configuration tends to be complicated.

  Therefore, the present invention improves the reliability of the joining of the zirconia solid electrolyte plate and the alumina insulating plate, and prevents the deterioration of the insulating property of the alumina insulating plate and the occurrence of cracks, thereby providing a high quality multilayer gas sensor. An object is to realize an element and a stacked gas sensor using the element.

The invention of claim 1 of the present application has a sensor part in which a pair of electrodes is provided on the surface of a zirconia solid electrolyte plate, and an alumina insulating plate is laminated and bonded to at least one surface of the zirconia solid electrolyte plate. In the laminated gas sensor element constituted by
The alumina-based insulating plate includes crystalline zirconia particles having an average particle size of more than 0.15 μm and not more than 0.3 μm in a base material mainly composed of alumina particles having an average particle size of 0.5 to 1 μm. Decentralized,
Among the zirconia particles, at least a part of the zirconia particles present in the vicinity of the interface with the zirconia solid electrolyte plate exceeds the bonding interface layer between the zirconia solid electrolyte plate and the alumina insulating plate, and thus the zirconia solid. It is combined with zirconia particles in the electrolyte plate.

  In the invention of claim 2 of the present application, the amount of zirconia particles added to the alumina insulating plate is 5 to 20% by weight.

In the invention of claim 3, the zirconia-based solid electrolyte plate is made of stabilized zirconia having oxygen ion conductivity, and the crystalline zirconia particles have no conductivity.

  The invention of claim 4 of the present application introduces a reference gas into one of the pair of electrodes provided on one surface of the zirconia solid electrolyte plate, and the pair of electrodes provided on the other surface. On the other hand, it is set as the structure which introduces the to-be-measured gas containing the specific gas component used as detection object.

  The invention of claim 5 of the present application is the invention of claim 4 wherein a reference gas chamber in contact with one surface of the zirconia-based solid electrolyte plate is provided and one of the pair of electrodes is disposed, and the reference gas chamber is The alumina insulating plate joined to the one surface of the zirconia solid electrolyte plate.

  The invention of claim 6 of the present application is the invention of claim 4 or 5, wherein a gas chamber to be measured is provided in contact with the other surface of the zirconia solid electrolyte plate and the other of the pair of electrodes is disposed. The measurement gas chamber is constituted by the alumina insulating plate bonded to the other surface of the zirconia solid electrolyte plate.

  The invention of claim 7 of the present application is configured such that a heater portion is laminated on the sensor portion, and a heater base in contact with the sensor portion is constituted by the alumina insulating plate.

  The invention of claim 8 of the present application is a laminated gas sensor characterized by using the laminated gas sensor element of claims 1 to 7.

  The inventors of the present invention focused on the particle size of zirconia dispersed in the alumina-based insulating plate, and conducted intensive studies to arrive at the invention of claim 1. That is, pure zirconia undergoes a phase transformation from a high temperature stable tetragonal crystal to a low temperature stable monoclinic crystal in the process of cooling from high temperature to room temperature. This phase transformation is accompanied by a volume expansion of 4%, and it is known that cracks are generated. In general, a stabilizer such as yttria is added to keep the tetragonal crystals at room temperature, thereby suppressing the generation of cracks. , Have stabilized.

  This phenomenon is the same for zirconia added to alumina. However, when added to alumina, the zirconia particles are sparsely present in the alumina, so that the zirconia particles can be made smaller. In particular, it has been found that when the zirconia particle size is 0.3 μm or less, tetragonal crystals can be retained up to room temperature, and the occurrence of cracks can be suppressed. Although this mechanism is not necessarily clarified, it is considered that the phase transformation cannot be performed because the stress generated by the phase transformation is smaller than the compressive stress received from the surrounding alumina due to the small zirconia particle diameter.

Furthermore, the zirconia particles added to the alumina are dispersed beyond the bonding interface layer with the adjacent zirconia solid electrolyte plate, and bonded to the zirconia particles in the zirconia solid electrolyte plate. This anchor effect is not observed when the zirconia particle diameter is 0.15 μm or less, and it has been found that sufficient bonding strength can be obtained by using zirconia particles exceeding 0.15 μm. In addition, when the alumina particles of the alumina insulating plate have an average particle size of 0.5 to 1 μm, a sufficient effect of suppressing the phase transformation of the zirconia particles can be obtained without increasing the raw material cost.

  Therefore, according to the invention of claim 1 of the present application, since the non-conductive zirconia particles are used, the withstand voltage of the alumina insulating plate is not lowered. In addition, by dispersing in a specific particle size range, cracks are not generated in the alumina insulating plate, and the bonding strength between the alumina insulating plate and the zirconia solid electrolyte plate can be improved. Therefore, a high-quality multilayer gas sensor element excellent in reliability can be obtained.

  According to the second aspect of the present invention, the effect of obtaining sufficient bonding strength without generating cracks is enhanced by adding 5 to 20% by weight of the zirconia particles dispersed in the alumina insulating plate.

  Specifically, as in claim 4 of the present application, specifically, a pair of electrodes are arranged on both surfaces of a zirconia-based solid electrolyte plate serving as a sensor portion, a reference gas, for example, the atmosphere is introduced into one of them, and the other is covered. Introduce measurement gas. At this time, the concentration of the specific gas component in the gas to be measured can be known by utilizing the characteristic that oxygen ions move in the zirconia solid electrolyte sandwiched between both electrodes.

  Specifically, as in claim 5 of the present application, specifically, an alumina insulating plate in which zirconia particles having a specific particle diameter are dispersed is disposed in contact with one surface of the zirconia solid electrolyte plate, and the reference gas chamber is formed. By forming, the above-mentioned effect of preventing cracking of the alumina insulating plate and increasing the bonding strength can be obtained.

  As in the invention of claim 6 of the present application, an alumina insulating plate in which zirconia particles having a specific particle diameter are dispersed is disposed in contact with the other surface of the zirconia solid electrolyte plate to form a gas chamber to be measured. By doing so, the same effect can be obtained that prevents cracking of the alumina insulating plate and increases the bonding strength.

  As in the invention of claim 7 of the present application, the heater can be laminated on the sensor unit, and the sensor unit can be activated at an early stage. At this time, if the heater base in contact with the sensor unit is an alumina insulating plate in which zirconia particles having a specific particle size are dispersed, it can be configured integrally with the alumina insulating plate of the sensor unit, and stress generation can be prevented. High suppression effect.

  As in the invention of claim 8 of the present application, such a stacked gas sensor element is suitably used as a stacked gas sensor, for example, an exhaust gas sensor of an internal combustion engine.

It is an expanded sectional view showing the principal part composition of the lamination type gas sensor element in a 1st embodiment of the present invention. It is a figure which shows the whole structure of the exhaust gas sensor to which a laminated | stacked gas sensor element is applied. (A) is a schematic diagram which shows the dispersion | distribution state of the zirconia particle to the alumina type insulation board in the sample produced in the Example of this invention, (b) is a dispersion | distribution of the zirconia particle to the alumina type insulation board in a comparative sample. It is a schematic diagram which shows a state. It is a drawing substitute photograph by the scanning electron microscope (SEM) which shows the particle | grain state of the interface vicinity of the alumina type insulation board and zirconia type solid electrolyte board in the multilayer gas sensor element produced in this invention Example.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a multilayer gas sensor element 1 according to the first embodiment of the present invention, and FIG. 2 is a diagram showing an overall configuration of an exhaust gas sensor S including the multilayer gas sensor element 1. The exhaust gas sensor S as the stacked gas sensor is installed in, for example, an exhaust pipe of an automobile engine as an internal combustion engine, and a specific gas component concentration contained in the exhaust gas that is a measurement gas, for example, oxygen concentration, air-fuel ratio, It can be used as a sensor for detecting NOx concentration and the like.

  In FIG. 2, the exhaust gas sensor S has a cylindrical housing H1 attached to an exhaust pipe wall (not shown) and a laminated gas sensor element 1 insulated and held in the housing H1. The laminated gas sensor element 1 has a long and narrow plate shape, and a central portion is held in a cylindrical insulator H2 disposed in the housing H1. It is accommodated in the element cover H3 fixed to. An atmospheric cover H3 is fixed to the upper end of the housing H1, and a lead wire S1 connected to an external control circuit (not shown) extends into the atmospheric cover H4.

  The metal terminal provided at the extending end of the lead wire S1 holds the base end portion (upper end portion in the figure) of the multilayer gas sensor element 1 so as to sandwich it from both sides. Thereby, it conducts with terminal part S2 provided in the base end part of lamination type gas sensor element 1, and enables input and output of a sensor signal. A cylindrical insulator H5 is filled between the air cover H4 and the base end portion of the multilayer gas sensor element 1.

  The element cover H3 projecting into the exhaust pipe has an inner / outer double bottomed cylinder structure, and exhaust ports H61 and H71 are provided on the side wall and the bottom wall of the inner cylinder H6 and the outer cylinder H7, respectively. Thereby, the exhaust gas containing the specific gas flowing through the exhaust pipe can be taken into the element cover H3 where the tip of the stacked gas sensor element 1 is located. On the other hand, an air inlet H8 is formed in the side wall at the upper end of the cylindrical member H4 exposed to the outside of the exhaust pipe, and the air can be introduced into the inside from the base end side of the laminated gas sensor element 1.

  FIG. 1 is an enlarged view of a tip portion of a multilayer gas sensor element 1. The multilayer gas sensor element 1 includes a sensor unit 2 having a zirconia-based solid electrolyte plate 11 and a heater unit for heating the sensor unit 2. 3 and a diffusion resistance layer 4 for controlling the amount of gas to be measured introduced into the sensor unit 2. The sensor unit 2 forms a reference gas side electrode 12 on one surface side (lower side in the figure) surface of the zirconia-based solid electrolyte plate 11, and the gas to be measured on the other side (upper side in the figure) surface. The side electrode 13 is formed as a pair of electrodes. The heater unit 3 is stacked on the lower surface side of the sensor unit 2, and the diffusion resistance layer 4 is stacked on the upper surface side of the sensor unit 2.

The zirconia-based solid electrolyte plate 11 is a sheet of partially stabilized zirconia having oxygen ion conductivity, and a reference gas side electrode 12 and a measured gas side electrode that form a pair of electrodes at opposite positions on both sides thereof. 13 is formed. As the partially stabilized zirconia, for example, yttria partially stabilized zirconia obtained by adding a stabilizer such as yttria (Y ₂ O ₃ ) to zirconia (ZrO ₂ ) is preferably used. A ceramic body 21 that is an alumina insulating plate is laminated on the lower surface of the zirconia solid electrolyte plate 11. The ceramic body 21 has a groove portion that forms a reference gas chamber 22 in the center, and the reference gas side electrode 12 is disposed facing the reference gas chamber 22. On the other hand, a spacer layer 23 which is an alumina insulating plate is laminated on the upper surface of the zirconia solid electrolyte plate 11. In the spacer layer 23, a groove portion provided in the center portion forms a measured gas chamber 24, and the measured gas side electrode 13 is disposed facing the measured gas chamber 24.

  At this time, by providing the reference gas side electrode 12 and the measured gas side electrode 13 as a pair of electrodes on both surfaces of the zirconia-based solid electrolyte plate 11, the difference in oxygen concentration between the reference gas chamber 22 and the measured gas chamber 24 is obtained. Since a corresponding electromotive force is generated, the oxygen concentration in the gas to be measured can be detected. Alternatively, the air-fuel ratio can be detected from the limit current that flows when a predetermined voltage is applied between the reference gas side electrode 12 and the measured gas side electrode 13.

  The heater unit 3 is configured by embedding a heater 32 made of a heating element in a heater base 31 that is an insulator. In the present embodiment, the heater base 31 is integrally provided on the lower surface side of the ceramic body 21 as an alumina insulating plate. The diffusion resistance layer 4 is configured by sequentially laminating a porous diffusion resistance layer 41 and a shielding layer 42 on the upper surface side of the spacer layer 23. The porous diffusion resistance layer 41 is a porous sintered body whose main component is alumina, and is configured so that the gas to be measured can permeate through diffusion. The shielding layer 42 is a dense sintered body mainly composed of alumina. As a result, the amount of gas to be measured that passes through the diffusion resistance layer 4 and is introduced into the gas chamber 24 to be measured can be adjusted appropriately.

  The laminated gas sensor element 1 of the present invention has a configuration in which an alumina insulating plate in which zirconia particles having a specific particle size are dispersed is laminated and bonded to at least one surface of a zirconia solid electrolyte plate 11 of the sensor unit 2. To do. In this embodiment, the ceramic body 21 and the spacer layer 23 bonded to both surfaces of the zirconia-based solid electrolyte plate 11, and the heater base 31 provided integrally with the ceramic body 21 are made of zirconia particles having such a specific particle size. An alumina insulating plate in which is dispersed.

Specifically, the alumina-based insulating plate is obtained by dispersing zirconia particles having an average particle size of more than 0.15 μm and not more than 0.3 μm in a base material mainly composed of alumina (Al ₂ O ₃ ). . Here, the zirconia particles in the alumina base material are dispersed beyond the interface with the zirconia solid electrolyte plate, and exhibit an anchoring effect that bonds with the zirconia particles in the zirconia solid electrolyte plate of the same material. When the average particle diameter of the zirconia particles is 0.15 μm or less, a sufficient anchor effect cannot be obtained, and peeling is caused by repeating the thermal cycle, which is not preferable. On the other hand, if the average particle size exceeds 0.3 μm, the phase transformation of zirconia particles cannot be suppressed, and cracks may occur.

  The dispersed particles added to the alumina-based insulating plate must have insulating properties. In the present invention, pure zirconia having no electrical conductivity is used. Since zirconia partially or completely stabilized with a stabilizer such as yttria is electrically conductive, it cannot be used for the dispersed particles added in the present invention. However, since pure zirconia changes in volume with monoclinic and tetragonal phase transformation, it causes cracks in the alumina insulating plate. In the present invention, by setting the zirconia particle size to 0.3 μm or less, this volume change is suppressed and the generation of cracks is suppressed.

On the other hand, if the zirconia particle size is too small, the anchor effect due to the bonding between the zirconia particles in the alumina insulating plate and the zirconia solid electrolyte is reduced when the alumina insulating plate and the zirconia solid electrolyte plate are joined. In order to increase the anchor effect, the zirconia particle size needs to exceed 0.15 μm. In the present invention, the occurrence of peeling is suppressed by obtaining sufficient bonding strength . To obtain a sufficient bonding strength, it is necessary particle size of more than 0.15μm zirconia particle size.

  As alumina used as the base material of the alumina-based insulating plate, alumina particles having an average particle diameter in the range of 0.5 μm to 1.0 μm are preferably used. When the average particle size exceeds 1.0 μm, the zirconia particle size present at the grain boundaries of the alumina particles tends to be large, and the effect of suppressing phase transformation may be insufficient. Regarding the effect of suppressing the phase transformation, the average particle diameter of alumina may be smaller than 0.5 μm, but the cost increases rapidly because the raw material used needs to be made fine.

  The zirconia particles added to the substrate of the alumina insulating plate preferably have an addition amount in the range of 5 to 20% by weight. When the addition amount is less than 5% by weight, a sufficient anchor effect cannot be obtained in the interface layer with the zirconia solid electrolyte plate, and there is a possibility of peeling by repeating the thermal cycle. On the other hand, if the amount of zirconia particles added exceeds 20% by weight, the zirconia particle size tends to be large, and the effect of suppressing phase transformation cannot be obtained.

  When manufacturing the laminated gas sensor element 1 of the present invention, for example, a green sheet of an alumina insulating plate that becomes the ceramic body 21, the spacer layer 23, or the heater base 31 is manufactured as follows. First, after adding a solvent to the raw material alumina and pulverizing it for a predetermined time, a mixed slurry is obtained in which a predetermined amount of zirconia, a known dispersant, a binder and the like are added. The mixed slurry is defoamed with a vacuum defoamer, the slurry viscosity is adjusted to a predetermined viscosity, and the mixture is formed into an alumina sheet by a known doctor blade method.

  In order to produce a green sheet of the zirconia-based solid electrolyte plate 11, first, yttria is added to the raw material zirconia, followed by dry mixing and pulverization. Next, a solvent is added to the zirconia powder, mixed and pulverized, and a mixed slurry in which a dispersant, a binder, and the like are further added is obtained. The mixed slurry is defoamed with a vacuum defoamer, the slurry viscosity is adjusted to a predetermined viscosity, and the mixture slurry is formed into a zirconia-based sheet by a known doctor blade method.

  The green sheet of the zirconia-based solid electrolyte plate 11 thus obtained is printed and formed with an electrode paste such as platinum (Pt) to be the reference gas side electrode 12 and the gas side electrode 13 to be measured, and then the alumina constituting each layer. An unsintered laminate is produced by laminating a system insulating plate and other green sheets. After degreasing the unfired laminate, the laminated gas sensor element 1 can be obtained by heating to a predetermined temperature and firing for a predetermined time.

  In the laminated gas sensor element 1 of the present invention, the ceramic body 21 joined to the zirconia solid electrolyte plate 11 and the spacer layer 23 are made of an alumina insulating plate in which zirconia particles having a specific particle size are dispersed. The bonding strength with the zirconia solid electrolyte plate 11 can be ensured while suppressing cracks. Moreover, since the non-conductive zirconia particles are dispersed, the withstand voltage is not lowered.

  Furthermore, the ceramic body 21 and the heater base 31 of the heater part 3 are integrally provided, and the sensor part 2 reaches the activation temperature by using alumina, which is cheaper than zirconia and has high thermal conductivity, as the heater base material. The effect of shortening the period of time and activating early is obtained. Therefore, the stacked gas sensor element 1 having a simple configuration, low cost, and high reliability can be obtained.

(Examples 1-4, Comparative Examples 1-5)
In order to confirm the effect of the present invention, various test pieces in which a zirconia-based solid electrolyte plate and an alumina-based insulating plate are bonded are prepared by the following method, and the separation of the bonded interface by dispersed zirconia particles and the alumina-based insulating plate are performed. The effect on the cracks was investigated.

1) Manufacture of zirconia-based solid electrolyte plate green sheet About 6 mol% of yttria was added to the raw material zirconia powder, and it was mixed and pulverized by a dry method. Next, a solvent such as ethanol was added to the yttria-added zirconia powder, and the coarse particles were pulverized at the same time with a ball mill for 24 hours. Furthermore, a dispersant (ED216; manufactured by Enomoto Kasei Co., Ltd.) is 2% by weight based on zirconia, a binder (PVB: polyvinyl butyral) 7.5% by weight, and a plasticizer (benzylbutyl phthalate) 4.5% by weight. The slurry was added and mixed with a high-pressure homogenizer for 1 hour to obtain a slurry.

  The obtained mixed slurry was defoamed with a vacuum defoamer, and the slurry viscosity was adjusted to a predetermined viscosity. Using this mixed slurry, it was formed into a sheet by a doctor blade method to obtain a zirconia green sheet to be a yttria-added zirconia solid electrolyte plate.

2) Manufacture of Alumina-based Insulating Plate Green Sheet Submicron zirconia (average particle size 0.2 μm) is added to the raw material alumina powder (LS-412; manufactured by Nippon Light Metal Co., Ltd.) and a solvent such as ethanol. The zirconia addition amount was added so as to be a predetermined amount. The raw material powder was mixed with a ball mill for 24 hours, and at the same time, coarse particles were pulverized. Further, a dispersant (ED216; manufactured by Enomoto Kasei Co., Ltd.) capable of dispersing alumina and zirconia at the primary particle level is 2% by weight based on the total weight of alumina and zirconia, and binder (PVB; polyvinyl butyral) 12.5%. % And a plasticizer (benzylbutyl phthalate) 7.5% by weight were added and mixed with a high-pressure homogenizer for 1 hour to obtain a slurry.

  The obtained mixed slurry was defoamed with a vacuum defoamer, and the slurry viscosity was adjusted to a predetermined viscosity. Using this mixed slurry, it was molded into a sheet by a doctor blade method to obtain an alumina green sheet in which zirconia particles were dispersed in an alumina base material.

3) Manufacture and evaluation of test piece Cold isostatic pressing (CIP) with one green sheet of zirconia solid electrolyte plate prepared in 1) and one green sheet of alumina insulating plate prepared in 2) Was bonded at 85 ° C. and 50 MPa. What cut | disconnected this to 20 mm x 10 mm was baked at 1450 degreeC, and the various test pieces shown in Table 1 were produced (Examples 1-4, Comparative Examples 1-5). In Table 1, the zirconia particle size and the added amount of zirconia are the average particle size and added amount of zirconia particles dispersed in the alumina-based insulating plate, and the alumina particle size is the alumina particles serving as the base material of the alumina-based insulating plate. The average particle size.

  Using these test pieces, the anchor effect and phase transformation effect of the dispersed zirconia particles were evaluated as follows. The heat cycle which raises temperature from Example 1-4 to Comparative Example 1-5 from room temperature to 1000 degreeC in a furnace (temperature increase rate of 150 degreeC / h), and cools to room temperature by furnace cooling after that is 50. Repeated times. In order to confirm the anchor effect after the thermal cycle, an ultrasonic flaw meter (50 MHz) was used to examine the presence or absence of peeling at the joint interface between the zirconia solid electrolyte plate and the alumina insulating plate. The results are also shown in Table 1 with ◯ when no peeling was observed and x when peeling was observed.

  In addition, the effect on the phase transformation was examined by observing with an electron microscope whether or not each test piece after thermal cycling was immersed in a dyeing solution, vacuum degassed, washed with water and dried. The results are also shown in Table 1, with ◯ indicating no cracks and x indicating cracks.

  As is apparent from Table 1, in Comparative Example 1 having a zirconia particle size of 0.15 μm, peeling was observed after the thermal cycle, and a sufficient anchor effect was not obtained. In contrast, in Examples 1 to 4 having a zirconia particle size of 0.16 to 0.30 μm, neither peeling nor cracking was observed after the thermal cycle. In Comparative Example 2 having a zirconia particle size of 0.41 μm, no peeling was observed, but cracks were confirmed, and the effect of suppressing phase transformation was not obtained.

  Further, in Table 1, in Comparative Example 3 where the amount of zirconia added was as small as 2% by weight, peeling was observed after the thermal cycle, indicating that the anchor effect was insufficient. On the other hand, in Comparative Example 4 where the amount of zirconia added was as large as 25% by weight, cracks were observed after the thermal cycle. This is presumed that the effect of suppressing the phase transformation cannot be obtained because the zirconia particle size becomes large when the addition amount is large. Further, in Comparative Example 5 where the alumina particle size is as large as 1.3 μm, the zirconia particle size is large, so that the effect of suppressing the phase transformation cannot be obtained.

  From the above results, it can be seen that if the zirconia particle size added to the alumina insulating plate is greater than 0.15 μm and less than or equal to 0.30 μm, both the anchor effect and the effect of suppressing phase transformation can be achieved. FIGS. 3A and 3B are schematic views showing the state of the zirconia particles dispersed in the alumina base material by observation with an electron microscope for the alumina insulating plate of Example 1 and the alumina insulating plate of Comparative Example 2, respectively. It is a representation. As is clear from FIG. 3A, in the configuration of Example 1 of the present invention, the zirconia particles are dispersed in the grain boundaries of the alumina particles, and no cracks are observed. On the other hand, in the structure of the comparative example 2 of FIG.3 (b), the zirconia particle size which exists in a grain boundary is large, and the crack has generate | occur | produced in the alumina particle | grains which are base materials.

  Pure zirconia causes a volume expansion of about 4% during phase transformation from a high temperature stable tetragonal crystal to a low temperature stable monoclinic crystal in the process of cooling from high temperature to room temperature. This phenomenon is the same for zirconia added to alumina. In Comparative Example 2 in FIG. 3B, it is considered that cracks occurred in the surrounding alumina due to the stress generated by the phase transformation. On the other hand, in Example 1 of FIG. 3A, since the zirconia particle diameter is as small as 0.16 μm, the stress generated by the phase transformation is smaller than the compressive stress received from the surrounding alumina, and consequently the phase transformation is suppressed. It is considered to be done.

  FIG. 4 is an electron micrograph showing the state of the bonding interface between the zirconia solid electrolyte plate and the alumina insulating plate for the test piece of Example 1. As is clear from FIG. 4, in the vicinity of the bonding interface, the zirconia particles added to the alumina insulating plate are bonded to the base material of the zirconia solid electrolyte plate beyond the bonding interface. Thereby, it is considered that the bonding strength can be improved and peeling can be suppressed even if the heat cycle is repeated.

  The laminated gas sensor element 1 of the present invention is not limited to the configuration of the embodiment of FIG. 1 but can be applied to a gas sensor element configured by joining a zirconia solid electrolyte plate and an alumina insulating plate. Moreover, the structure of the sensor part 2, the heater part 3, and the diffused resistance layer 4 can be changed, and another structure can also be added.

  The laminated gas sensor element of the present invention can be used as an exhaust gas sensor for an internal combustion engine, for example, to detect oxygen concentration, air-fuel ratio, NOx concentration, etc. in exhaust gas. At this time, even if it is placed in an environment where the temperature changes drastically, such as an exhaust pipe, it exhibits high reliability over a long period of time, and thus has high utility value. Of course, the present invention can be applied to a stacked gas sensor for detecting a specific gas component in various fields as well as the internal combustion engine.

S Exhaust gas sensor (stacked gas sensor)
H Housing 1 Multilayer Gas Sensor Element 11 Zirconia Solid Electrolyte Plate 12 Reference Gas Side Electrode 13. Measured gas side electrode 2 Sensor part 21 Ceramic body (alumina insulating plate)
22 Reference gas chamber 23 Spacer layer (alumina insulating plate)
24 Gas chamber to be measured 3 Heater section 31 Heater base (alumina insulating plate)
32 Heater 4 Diffusion resistance layer 41 Porous diffusion resistance layer 42 Shielding layer

Claims (8)

A laminated gas sensor having a sensor portion having a pair of electrodes provided on the surface of a zirconia solid electrolyte plate and laminating and bonding an alumina insulating plate on at least one surface of the zirconia solid electrolyte plate. In the element
The alumina-based insulating plate includes crystalline zirconia particles having an average particle size of more than 0.15 μm and not more than 0.3 μm in a base material mainly composed of alumina particles having an average particle size of 0.5 to 1 μm. Decentralized,
Among the zirconia particles, at least a part of the zirconia particles present in the vicinity of the interface with the zirconia solid electrolyte plate exceeds the bonding interface layer between the zirconia solid electrolyte plate and the alumina insulating plate, and thus the zirconia solid. A laminated gas sensor element characterized by being bonded to zirconia particles in an electrolyte plate.   2. The laminated gas sensor element according to claim 1, wherein the amount of zirconia particles dispersed in the alumina insulating plate is 5 to 20% by weight. The stacked gas sensor element according to claim 1 or 2 , wherein the zirconia-based solid electrolyte plate is made of stabilized zirconia having oxygen ion conductivity, and the crystalline zirconia particles have no conductivity .   A reference gas is introduced into one of the pair of electrodes provided on one surface of the zirconia-based solid electrolyte plate, and the sensor unit is identified as a detection target on the other of the pair of electrodes provided on the other surface. The stacked gas sensor element according to any one of claims 1 to 3, wherein a measurement gas containing a gas component is introduced.   The reference gas chamber is provided in contact with one surface of the zirconia solid electrolyte plate, and one of the pair of electrodes is disposed, and the reference gas chamber is joined to the one surface of the zirconia solid electrolyte plate. The multi-layer gas sensor element according to claim 4, wherein the multi-layer gas sensor element is composed of an alumina insulating plate.   A gas chamber to be measured is provided in contact with the other surface of the zirconia solid electrolyte plate, the other of the pair of electrodes is disposed, and the gas chamber to be measured is joined to the other surface of the zirconia solid electrolyte plate. 6. The laminated gas sensor element according to claim 4, wherein the laminated gas sensor element is constituted by the alumina-based insulating plate.   The multilayer gas sensor element according to any one of claims 1 to 5, wherein a heater part is laminated on the sensor part, and a heater base in contact with the sensor part is constituted by the alumina insulating plate.   The stacked gas sensor according to claim 1, wherein the stacked gas sensor element is used.