The present disclosure relates to an exhaust sensor for detecting a gas, with the exhaust gas from an internal combustion engine as the gas to be detected.
In an exhaust sensor that detects a gas, with the exhaust of an internal combustion engine as the gas to be detected, a sensor element is used in which a detection electrode and a reference electrode are provided on a solid electrolyte body. A porous protective layer that protects the sensor element from water is provided on the surface of the sensor element. The porous protective layer is formed of ceramic particles such as metal oxides.
One aspect of the present disclosure is an exhaust sensor that is provided with a sensor element, and wherein:
the sensor element comprises a solid electrolyte body, a detection electrode, and a reference electrode;
a porous protective layer is provided on at least one of a surface of the detection electrode and a path that guides the gas;
the porous protective layer is composed of a plurality of aggregate particles; and
when a plurality of crystal grains constituting an aggregate particle are observed in cross section, the number of crystal grain boundary intersections where three or more of the crystal grains intersect, per unit area, is in the range of 1 to 10,000/μm2.
It should be noted that that the reference signs in parentheses of the components described for each aspect of the present disclosure indicate correspondence with the reference signs in the drawings of an embodiment, however each component is not limited to the contents of that embodiment.
The above objects and other objects, features and advantages of the present disclosure will be made clearer by the following detailed description, given referring to the appended drawings. In the drawings:
A sensor element of the gas sensor of JP 2010-151575 A has a bottomed tubular solid electrolyte body, a measurement electrode provided on the outer peripheral surface of the solid electrolyte body, and a reference electrode provided on the inner peripheral surface of the solid electrolyte body, and a porous protective layer that covers the measurement electrode, while allowing the gas to be detected to pass through. The film thickness, porosity, etc., of the porous protective layer in the sensor element of JP 2010-151575 A are devised such as to ensure that the sensor element has water resistance.
In the case of a prior art gas sensor such as that of JP 2010-151575 A, the overall properties, characteristics, etc., of the porous protective layer are devised and improved by observing the porous protective layer externally However, no way has been devised for improving the water resistance to a required degree by observing the porous protective layer internally.
Specifically, the porous protective layer is composed of a plurality of aggregate particles such as ceramic. The assignees of the present invention have focused attention on the conditions of the plurality of crystal grains that constitute an aggregate particle, and have found that if the aggregate particles are made difficult to destroy from a microscopic aspect, the water resistance of the porous protective layer can be improved.
It is an objective of the present disclosure to provide an exhaust sensor having a porous protective layer with improved water resistance.
One aspect of the present disclosure is an exhaust sensor that is provided with a sensor element and performs gas detection using the exhaust gas of an internal combustion engine as the gas to be detected, and wherein:
the sensor element comprises a solid electrolyte body, a detection electrode provided on the solid electrolyte body and exposed to the gas to be detected, and a reference electrode provided on the solid electrolyte body;
a porous protective layer is provided on at least one of a surface of the detection electrode and a path that guides the gas to be detected to the surface of the detection electrode;
the porous protective layer is composed of a plurality of aggregate particles that are bonded directly or via an inorganic binder; and
when a plurality of crystal grains constituting an aggregate particle are observed in cross section, the number of crystal grain boundary intersections where three or more of the crystal grains intersect, per unit area, is in the range of 1 to 10,000/μm2.
In the exhaust sensor according to the above aspect, the porous protective layer provided in the sensor element is observed from a microscopic aspect, and measures are taken to increase the strength of the aggregate particles constituting the porous protective layer. Specifically, focusing attention on the state of the plurality of crystal grains constituting an aggregate particle, the number of crystal grain boundary intersections between three or more crystal grains, per unit area, is held within the range of 1 to 10,000/μm2.
The crystal grain boundary intersections are points at which three or more crystal grains are observed to intersect, when the crystal grain boundaries where the crystal grains meet are observed in a cross section of the porous protective layer. It can be considered that when stress energy such as thermal shock is applied to the porous protective layer, the stress energy is transmitted along crystal grain boundaries of the crystal grains constituting the aggregate particles. It can be considered that when the stress energy then passes through the corresponding crystal grain boundary intersections, the energy becomes attenuated by being dispersed among a plurality of crystal grain boundaries.
If the number of crystal grain boundary intersections per unit area is appropriate, being in the range of 1 to 10,000/μm2, then the energy can be effectively dispersed when stress such as thermal shock is applied to the aggregate particles. As a result, the strength of the aggregate particles constituting the porous protective layer can be increased, and hence the water resistance of the porous protective layer can be improved.
Thus, the water resistance of the porous protective layer in the exhaust sensor according to the above aspect can be improved.
Preferred embodiments of the above exhaust sensor will be described referring to the drawings.
As shown in
As shown in
The exhaust sensor 1 of this embodiment is described in detail in the following.
As shown in
A catalyst for purifying harmful substances in the exhaust gas is disposed in the exhaust pipe 7, and the exhaust sensor 1 can be located on either the upstream side or the downstream side of the catalyst, with respect to the flow direction of the exhaust gas in the exhaust pipe 7. The exhaust sensor 1 can also be disposed in a pipe at the intake side of a supercharger that uses exhaust gas to increase the density of air drawn in by the internal combustion engine. Furthermore, the exhaust sensor 1 may be disposed in the intake pipe of an exhaust recirculation mechanism which recirculates part of the exhaust gas from the internal combustion engine that is discharged to the exhaust pipe 7, with the recirculated exhaust gas being passed into the intake manifold of the internal combustion engine.
As shown in
As shown in
The solid electrolyte 31A consists of a zirconia-based oxide containing zirconia as the main component (50% by mass or more), formed of stabilized zirconia or partially stabilized zirconia in which part of the zirconia is replaced by a rare earth metal element or by an alkaline earth metal element. Part of the zirconia for constituting the solid electrolyte body 31A can be replaced by yttria, scandia or calcia.
The detection electrode 311 and the reference electrode 312 contain platinum as a noble metal exhibiting catalytic activity for oxygen, and zirconia oxide which functions as a co-material with the solid electrolyte body 31A. The co-material serves to maintain the bonding strength of the detection electrode 311 and the reference electrode 312, when these are printed (coated) as a paste-like electrode material on the solid electrolyte body 31A and fired.
Electrode lead portions are connected to the detection electrode 311 and the reference electrode 312, for electrically connecting these electrodes to the exterior of the exhaust sensor 1. The electrode lead portions extend, in the longitudinal direction L, to the part of the sensor element 2A at the base end L2.
As shown in
Another porous protective layer 38, that uses conventional aggregate particles in which the number of crystal grain boundary intersections X per unit area is less than 1/μm2, may be provided on the surface of the porous protective layer 37, as shown by the other layer 38 in
The porous protective layer 37 can be formed on the outer surface 301 of the solid electrolyte body 31A and the surface of the detection electrode 311 with a thickness in the range of 10 to 1000 μm. If the porous protective layer 37 is formed as a plurality of layers, the total thickness of the plurality of porous protective layers 37 can be set in the range of 10 to 1000 μm. If it is desired to increase the response speed of the exhaust sensor 1, the thickness of the porous protective layer 37 and of the other porous protective layer 38 can be made as small as possible.
The porous protective layer 37 can be provided in various forms. For example, a porous protective layer 37 may be formed on the outer surface 301 of the solid electrolyte body 31A by a thermal spraying method, then a porous protective layer 37 may be formed by the slurry coating method on the surface of the porous protective layer 37 which was formed by the thermal spraying method. Each of these porous protective layers 37 can be formed by using aggregate particles K1 in which the number of crystal grain boundary intersections X per unit area is in the range of 1 to 10,000/μm2. Furthermore, both the porous protective layer 37 that is formed by the thermal spraying method, and the porous protective layer 37 that is formed by the slurry coating method, can be formed by stacking a plurality of layers.
As shown in
As shown in
The parts of the sensor element 2A and the tip end cover 45 that are located at the tip end L1 are disposed within the exhaust pipe 7 of the internal combustion engine. The tip end cover 45 is formed with a gas passage hole 451 for passing the exhaust gas, as the gas G to be detected. The tip end cover 45 may have a double structure or a single structure. The exhaust gas, flowing as the gas G to be detected into the tip end cover 45 from the gas passage hole 451 of the tip end cover, is guided to the detection electrode 311 on the outer peripheral side of the solid electrolyte body 31A by passing through the porous protective layer 37 of the sensor element 2A.
The base end cover 46 is disposed outside the exhaust pipe 7 of the internal combustion engine. The base end cover 46 is formed with a reference gas introduction hole 461 through which atmospheric air A is introduced into the base end cover 46. A filter 462, which does not allow liquid to pass through but allows passage of a gas, is disposed in the reference gas introduction hole 461. Atmospheric air A that is introduced into the base end cover 46 from the reference gas introduction hole 461 passes through a gap in the base end cover 46 and is guided to the reference electrode 312 on the inner peripheral side of the solid electrolyte body 31A.
The plurality of contact terminals 44 are disposed on the insulator 42, connected to the electrode lead portions of the detection electrode 311 and the reference electrode 312, and to the lead portions 342 of the heating element sheet 346 of the heater 340. Lead wires 48 are respectively connected to the contact terminals 44.
As shown in
The sensor control device 6 may be built into the engine control apparatus. Furthermore, depending on the configuration of the exhaust sensor 1, the sensor control device 6 may include a measurement circuit for measuring the current flowing between the detection electrode 311 and the reference electrode 312, a voltage application circuit for applying a voltage between the detection electrode 311 and the reference electrode 312, etc.
The aggregate particles K1 constituting the porous protective layer 37 are composed of metal oxides as illustrated in
The aggregate particles K1 constituting the porous protective layer 37 are preferably composed of a metal oxide having a standard reaction Gibbs energy lower than that of oxides of carbon (higher on the negative side). The metal oxide is thereby less likely to be reduced, in the usage environment of the exhaust sensor 1, and the state of the metal oxide is easily maintained (the metal oxide is likely to exist in a stable condition). Hence the strength of the aggregate particles K1 constituting the porous protective layer 37 can be maintained at a high level.
The standard reaction Gibbs energy of oxides such as those of aluminium (Al) and magnesium (Mg) is lower (higher on the negative side) than that of carbon (C) oxides. Hence it can be said that oxides such as of aluminium and magnesium have the property of not being readily reduced, in the usage environment of the exhaust sensor 1.
Furthermore, other than oxides such as those of aluminium and magnesium, oxides such as those of silicon (Si), titanium (Ti) and calcium (Ca) may be used for the aggregate particles K1. The aggregate particles K1 can be composed of spinel (MgAl2O4), alumina (Al2O3, aluminium oxide), magnesia (MgO, magnesium oxide), silica (SiO2), silicon dioxide), titania (TiO2, titanium oxide), calcia (CaO, calcium oxide), etc,
The crystal grain boundary intersections X, illustrated in
It can be considered that amorphous (non-crystalline) material, which is a state of matter having no crystalline structure, and impurities that are different from the metal oxides constituting the aggregate particles K1, etc., are present at the crystal grain boundary intersections X. Due to the presence of these amorphous substances, impurities, etc., the strength at the crystal grain boundary intersections X is lower than that inside the crystal grains K2.
Furthermore, as observed in cross section, there are parts of the aggregate particles K1 where pores H (including cavities, voids, etc.,) are adjacent to the crystal grains K2. Points where the crystal grain boundaries R of two or more crystal grains K2 intersect, but which are sited adjacent to a pore H, are not included in the crystal grain boundary intersections X. Amorphous substances, impurities, etc., are not present in the vicinity of an intersection where crystal grain boundaries R intersect but which is close to the site of a pore H. Hence when stress such as thermal shock is applied to the aggregate particles K1, the stress energy is not dispersed at those intersections where crystal grain boundaries R intersects and where are at parts adjacent to pores H. For that reason, when an intersection between crystal grain boundaries R is located adjacent to a pore H, it is not included in the number of crystal grain boundary intersections X.
The number of crystal grain boundary intersections X in the aggregate particles K1 can be measured by observing a sliced cross section of the aggregate particles K, using a SEM (scanning electron microscope). The aggregate particles K1 are produced by melting a metal oxide, as the raw material, before forming the porous protective layer 37 with a predetermined particle size. The entire porous protective layer 37 is formed collectively with respect to the sensor element 2A. It can thus be considered that the state of formation of the crystal grains K2 in the aggregate particles K1 is the same at any part of the porous protective layer 37.
The number of crystal grain boundary intersections X in the aggregate particles K1 of the porous protective layer 37 can be taken to be the average value of the respective numbers of crystal grain boundary intersections X that are present at a plurality of locations in the porous protective layer 37. A measurement region for measuring the number of crystal grain boundary intersections X at a location can be, for example, an area of 4 μm in the longitudinal direction L by 5 μm in the direction orthogonal to the longitudinal direction L, on the surface of the porous protective layer 37. The number of crystal grain boundary intersections X in this measurement region can be measured, and the number of crystal grain boundary intersections X per 1 μm2, as a unit area, can be calculated from this number.
As shown in
It is also possible to determine the measurement regions used for calculating the average value of the number of crystal grain boundary intersections X based on consideration of differences between numbers of crystal grain boundary intersections X in the thickness direction of the porous protective layer 37. For example, the number of crystal grain boundary intersections X per 1 μm2 can be calculated for a measurement region having an area of 4 μm×5 μm on the outermost surface of the porous protective layer 37 in the thickness direction, for a measurement region having an area of 4 μm×5 μm on the innermost surface of the porous protective layer 37 in the thickness direction, and for a measurement area of 4 μm×5 μm at an intermediate position in the thickness direction of the porous protective layer 37, then the average value of the number of crystal grain boundary intersections per 1 μm2 in these three measurement regions can be calculated.
Furthermore, the average value of the number of crystal grain boundary intersections X per 1 μm2 can be calculated for nine measurement regions that overlap in the thickness direction, consisting of a maximum temperature measurement region Y1 and two adjacent measurement regions Y2 on the outermost surface of the porous protective layer 37, a maximum temperature measurement region Y1 and two adjacent measurement regions Y2 on the innermost surface of the porous protective layer 37, and a maximum temperature measurement region Y1 and two adjacent measurement regions Y2 at an intermediate position in the thickness direction of the porous protective layer 37.
If there are pores H in a measurement region that is used in obtaining the average number of crystal grain boundary intersections X, the average number is calculated using the area obtained by subtracting the area of the pores H from the area of that measurement region.
As shown in
The appropriate number of crystal grain boundary intersections X where three or more crystal grains K2 intersect was determined based on the result of examining the water resistance (water cracking number [times]) of the porous protective layer 37. The water resistance was obtained by a computer simulation in which 1 μL water droplets were dropped vertically on the porous protective layer 37 provided on the sensor element 2A, to find the number of times the water droplets were dropped until cracking of the porous protective layer 37 occurred. The greater the number of times the water droplets dropped before cracking occurs, the higher was the water resistance. The temperature of the sensor element 2A when examining the water resistance was 500° C., and the thickness of the porous protective layer 37 was 100 μm. The position at which the 1 μL water droplets were dropped vertically was that of a maximum temperature measurement region Y1 on the surface of the porous protective layer 37.
It was found that if the number of crystal grain boundary intersections X is 1/μm2, the water resistance is 1,000 times or more, regardless of whether the thermal spraying method or the dip method is used, so that sufficient water resistance can be obtained. On the other hand, it was found that if the number of crystal grain boundary intersections X per unit area is less than 1/μm2, the water resistance is about 10 times, irrespective of whether the thermal spraying method or the dip method is used, so that sufficient water resistance cannot be obtained.
Further it was found that the highest water resistance, of about 100,000 times, is obtained when the number of crystal grain boundary intersections X per unit area is in the range of 10 to 10,000/μm2, irrespective of whether the thermal spraying method or the dip method is used. This result shows that the number of crystal grain boundary intersections X per unit area in the aggregate particles K1 is preferably in the range of 1 to 10,000/μm2, and more preferably in the range of 10 to 10,000/μm2.
It was also found that if the number of crystal grain boundary intersections X exceeds 10,000/μm2, the water resistance decreases. It is thought that in that case, the crystal grains K2 in the aggregate particles K1 become excessively small, and the influence of strain between the aggregate particles K1 increases, so that residual stress in the particles increases and the aggregate particles K1 are thereby weakened.
As shown in
If water droplets come into contact with the porous protective layer 37 when the aggregate particles K1 constituting the porous protective layer 37 have become raised to a high temperature, in the region of 500 to 700° C. for example, then stress due to thermal shock is applied, as illustrated in
At this time, the energy becomes dispersed, and transmitted to a plurality of crystal grain boundaries R at respective crystal grain boundary intersections X.
The aggregate particles K1 that form the porous protective layer 37 of this embodiment are produced as a metal oxide, a spinel (MgAl2O4), which is an oxide of aluminium and magnesium. The aggregate particles K1 can be produced by an electrofusion method or a sintering method. The method of producing the aggregate particles K1 by the electrofusion method is shown in the flowchart of
When the aggregate particles K1 are produced by the electrofusion method, aluminium and magnesium are heated, as materials for the aggregate particles, at 2500° C. for 0.5 hour in an electric furnace (step S01A in
As the proportion of added grain growth inhibitor is increased, the crystal grains K2 in the aggregate particles K1 become smaller, and the number of crystal grain boundary intersections X per unit area in the aggregate particles K1 increases. If the proportion of added grain growth inhibitor is less than 0.01% by mass, then the grain growth inhibitory effect may be insufficient, and the number of crystal grain boundary intersections X per unit area in the aggregate particles K1 may be less than necessary. On the other hand, if the proportion of the added grain growth inhibitor exceeds 5% by mass, the grain growth inhibitory effect may become excessive, and the number of crystal grain boundary intersections X per unit area of the aggregate particles K1 may be greater than necessary.
In order to set the number of crystal grain boundary intersections X per unit area in the range of 1 to 10,000/μm2, the aggregate particles K1 preferably contain grain growth inhibitor: 0.01-5% to metal oxide: 100% by mass. The grain growth inhibitor may be present alone in the aggregate particles K1, separate from the metal oxide, or may be present in a state of being combined with or mixed with the metal oxide. It would be equally possible to use a growth inhibitor other than ZnO.
When a predetermined time has elapsed after the material for the aggregate particles is melted, the material becomes cooled and solidified, forming intermediates of the aggregate particles K1 (step S03 in
Possible methods that can be used to cool the material for the aggregate particles include simply leaving the material to cool, or blowing air, water cooling, etc. Blowing air or water cooling can be performed if it is required to increase the cooling rate.
If the cooling rate is less than 10° C./min, the surface energy of the crystal grain boundary component of the crystal grains K2 in the aggregate particles K1 becomes small, and aggregation causes the crystal grains K2 to increase in size. The number of crystal grain boundary intersections X per unit area of the aggregate particles K1 may thus be smaller than the required number. On the other hand, if the cooling rate exceeds 1000° C./sec, progression of the grain growth of the crystal grains K2 in the aggregate particles K1 becomes excessively slow. The number of crystal grain boundary intersections X per unit area of the aggregate particles K1 may thus be larger than the required number.
It is preferable for the cooling rate of the melted aggregate particle material to be in the range of 10° C./min to 1000° C./sec, in order to set the number of crystal grain boundary intersections X per unit area in the range of 1 to 10,000/μm2,
When aggregate particles K1 are produced by the sintering method, alumina and magnesia, as the materials for the aggregate particles, are mixed, kneaded and dried, and the mixture of alumina and magnesia is then heated to 1000 to 1600° C. and sintered. At this time, the alumina and magnesia become dissolved in a state of a solid solution to form spinel (step S01B in
In the sintering method as well, as in the electrofusion method, the entire amounts of alumina and magnesia as materials for aggregate particles: 100% by mass, and of the grain growth inhibitor such as ZnO (zinc oxide): 0.01 to 5% by mass, can be added (step S02 in
Furthermore, in the sintering method, the heating rate (temperature increase rate) of the mixture of alumina and magnesia when sintering the mixture, and the cooling rate (temperature decrease rate) for cooling the mixture of alumina and magnesia after heating, can be set in the range of 10° C./min to 1000° C./sec. The problems that occur when the heating rate and the cooling rate are less than 10° C./min or exceed 1000° C./sec are the same as in the case of the electrofusion method.
The particle size of the intermediate of the aggregate particles K1 produced is larger than that of the aggregate particles K1. The intermediate of the aggregate particles K1 are then pulverized, to produce aggregate particles K1 having a maximum particle size in the range of 1 to 500 μm (step S04 of
The aggregate particles K1 can also be produced by a spray drying method or the like, in which a liquid or a mixture of a liquid and a solid is sprayed into a gas and rapidly dried to produce a dry powder.
The aggregate particles K1 can be produced by the above-mentioned electrofusion method or sintering method irrespective of whether the metal oxide constituting the material for the aggregate particles is alumina, silica, titania, calcia, etc. The aggregate particles K1 that are produced are used to form the porous protective layer 37 by a thermal spraying method, a slurry coating method, or the like.
The aggregate particles K1 constituting the porous protective layer 37 of this embodiment are bonded to each other without the intervention of an inorganic binder B, as illustrated in
In the aggregate particles K1 constituting the porous protective layer 37 formed by the thermal spraying method, the strength of the joint portions between the aggregate particles K1 is equal to the internal strength of the aggregate particles K1. In the porous protective layer 37 formed by the thermal spraying method, the crystal grain boundaries R between the crystal grains K2 constituting the aggregate particles K1 are portions that have low strength against stress such as thermal shock. Thus, when stress such as thermal shock is applied to a porous protective layer 37 formed by the thermal spraying method, cracks or the like are liable to occur at the crystal grain boundaries R between the aggregate particles K1.
In addition to the plasma spraying method of spraying the aggregate particles K1 on the solid electrolyte 31A, thermal spraying methods of spraying the aggregate particles K1 on the solid electrolyte body 31A also include frame spraying, cold spraying, etc.
The aggregate particles K1 constituting the porous protective layer 37 may be bonded to each other via an inorganic binder B, as illustrated in
When sintering the slurry, it is necessary to prevent the characteristics of the sensor element 2A from being changed by heat. The slurry is therefore preferably sintered at a relatively low temperature, in the range of 500 to 1000° C. Furthermore, a material that becomes sintered at a relatively low temperature is often selected as the inorganic binder B. As a result, when stress such as thermal shock is applied to a porous protective layer 37 formed by the slurry coating method, a situation arises in which cracks or the like are liable to occur not in the aggregate particles K1, but in the inorganic binder B.
However, as various techniques for improving the strength of the inorganic binder B have been developed, it can be assumed that cracks or the like may arise in the aggregate particles K1 if the strength of the inorganic binder B is high. One technique for improving the strength of the inorganic binder B, for example, is disclosed in JP 2014-178179 A. The higher the strength of the bonding that is provided by the inorganic binder B between aggregate particles K1, the greater becomes the possibility of cracking in the crystal grains K2 constituting the aggregate particles K1.
In addition to the thermal spraying method and the slurry coating method, the porous protective layer 37 can also be formed by CVD (chemical vapor deposition), an aerosol deposition method, etc. However, from the aspects of material yield, takt time (work time), etc., it is preferable to use the thermal spraying method or the slurry coating method.
When manufacturing the sensor element 2A, a bottomed cylindrical solid electrolyte body 31A is prepared and plated to form a reference electrode 312 on the inner surface 302 of the solid electrolyte body 31A, while also forming a detection electrode 311 on the outer surface 301 of the solid electrolyte body 31A. The solid electrolyte body 31A, with the detection electrode 311 and the reference electrode 312 thereon, is then fired, to form the sensor element 2A. Next, the aggregate particles K1 are sprayed by a thermal spraying method onto the outer surface 301 of the formed sensor element 2A, including the detection electrode 311, to form the porous protective layer 37.
Alternatively, the slurry coating method may be used instead of the thermal spraying method. In that case, the aggregate particles K1 and the inorganic binder B are made to adhere to the outer surface 301 of the sensor element 2A including the detection electrode 311 to form the porous protective layer 37, and the porous protective layer 37 is fired.
With the exhaust sensor 1 of this embodiment, the porous protective layer 37 provided on the sensor element 2A is observed from a microscopic viewpoint, and measures are taken to increase the strength of the aggregate particles K1 constituting the porous protective layer 37. Specifically, focusing attention on the states of the plurality of crystal grains K2 constituting the aggregate particles K1, the number of crystal grain boundary intersections X where three or more crystal grains K2 intersect in an aggregate particle K1, per unit area, is made to be within the range of 1 to 10,000/μm2.
As a result, the number of crystal grain boundary intersections X in the aggregate particles K1 is appropriate, so that when stress such as thermal shock is applied to the aggregate particles K1, the energy of the stress can be effectively dispersed. The strength of the aggregate particles K1 constituting the porous protective layer 37 can thereby be increased, and as a result, the water resistance of the porous protective layer 37 can be improved.
Hence, the exhaust sensor 1 of this embodiment enables the water resistance of the porous protective layer 37 to be improved.
In the aggregate particles K1, crystal grain boundary intersections X are formed in three dimensions. Hence it could be considered that the crystal grain boundary intersections X should be obtained as a number per unit volume. However, the crystal grain boundary intersections X are observed in cross section, and so are obtained as a number per unit area.
In the exhaust sensor 1 of this embodiment, the solid electrolyte body 31B is plate-shaped and the sensor element 2B is of laminated type.
As shown in
As shown in
As shown in
As shown in
As shown in
The porous protective layer 37 of this embodiment is provided over the entire part of the sensor element 2B at the tip end L1, in the longitudinal direction L. The surface of the diffusion resistance portion 32 is covered with the porous protective layer 37. However as shown in
The porosity of the porous protective layer 37 is greater than the porosity of the diffusion resistance portion 32. The flow rate at which the gas G to be detected can permeate the porous protective layer 37 is higher than the flow rate at which the gas G to be detected can permeate the diffusion resistance portion 32.
As shown in
As shown in
The insulator 33 is formed using an insulating metal oxide such as alumina. The insulator 33 is laminated on the solid electrolyte body 31B to constitute the gas chamber 35, the reference gas duct 36, the diffusion resistance portion 32, etc.
In the exhaust sensor 1 of this embodiment, as shown in
When manufacturing the sensor element 2B, a sheet constituting the solid electrolyte body 31B, a sheet constituting the insulator 33, etc., are successively laminated and made to adhere to each other via layers of an adhesive material. In addition, a paste material constituting the pair of electrodes 311, 312 is printed (coated) on the sheet constituting the solid electrolyte body 31B, and a paste material constituting the heating element 34 is printed (coated) on the sheet constituting the insulator 33. The intermediate bodies of the sensor element 2B, constituted by the respective sheets and paste material, are then fired at a predetermined firing temperature, to form the sensor element 2B. The aggregate particles K1 are then sprayed on the surface of the formed sensor element 2B by a thermal spraying method, to form the porous protective layer 37. Alternatively, a slurry coating method may be used instead of the thermal spraying method.
In the exhaust sensor 1 using the sensor element 2B of the present embodiment also, the water resistance of the porous protective layer 37 is improved by forming the protective layer using aggregate particles K1 in which the number of crystal grain boundary intersections X per unit area is in the range of 1 to 10,000/μm2.
Other configurations, actions and effects etc., of the exhaust sensor 1 of this embodiment are the same as those of the first embodiment. Furthermore, in this embodiment also, components indicated by the same reference signs as those shown for the first embodiment are the same as those in the first embodiment.
The present disclosure is not limited to the respective embodiments, and it would be possible to configure different embodiments without departing from the gist of the disclosure. In addition, the scope of the present disclosure includes various modifications, modifications within a range of equivalents, and the like. Furthermore, the technical concepts of the present disclosure also include combinations, forms, etc., of various components that can be assumed from the present disclosure.
Number | Date | Country | Kind |
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2019-012059 | Jan 2019 | JP | national |
The present application is a continuation application of International Application No. PCT/JP2020/000554 filed on Jan. 10, 2020, which is based on and claims the benefit of priority from Japanese Patent Application No. 2019-012059 filed on Jan. 28, 2019. The contents of these applications are incorporated herein by reference in their entirety.
Number | Date | Country | |
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Parent | PCT/JP2020/000554 | Jan 2020 | US |
Child | 17386357 | US |