JP4166404B2 - Gas sensor element and gas sensor including the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a small and inexpensive gas sensor element that can detect oxygen and NOx contained in exhaust gas discharged from an internal combustion engine such as an automobile, and a gas sensor using the same.
[0002]
[Prior art]
Conventionally, gas sensor elements (hereinafter also simply referred to as “elements”) using a cylindrical solid electrolyte body or a plate-type solid electrolyte body are known. Among these, as an element provided with a plate-type solid electrolyte body, an element provided with a plate-type solid electrolyte body laminated in contact with an alumina substrate is disclosed in JP-A-7-55758.
However, since there is a large difference in thermal expansion between the alumina substrate and the solid electrolyte body, a gas sensor element having a solid electrolyte body laminated in contact with the alumina substrate generates stress at these interfaces after firing, causing cracks and the like. It may occur.
In order to solve this problem, Japanese Patent Application Laid-Open No. 9-304321 discloses a technique for suppressing the occurrence of cracks and the like by providing a stress relaxation portion in which the thickness of the outer edge portion of the solid electrolyte body is gradually reduced. However, it has not yet been sufficiently prevented from cracking.
[0003]
[Problems to be solved by the invention]
The present invention solves the above-described problem, and prevents the occurrence of cracks at the interface in a gas sensor element including a solid electrolyte body laminated in contact with a base made of a different material such as an alumina base. For the purpose.
[0004]
[Means for Solving the Problems]
The present invention forms thin peripheral portion of the solid electrolyte body which is disposed on a substrate having an insulating property can be significantly prevent the occurrence of cracks by and on at least a part of the peripheral portion is provided with a suppression layer It was completed based on this knowledge.
[0005]
The element of the first invention has a plate-like substrate extending in the longitudinal direction and having an insulating property, and a layered solid electrolyte body disposed on the substrate and having a reference electrode and a detection electrode formed thereon. In the gas sensor element comprising a detection unit formed on the front side in the longitudinal direction , the detection unit configured to sandwich the solid electrolyte body between the reference electrode unit of the reference electrode and the detection electrode unit of the detection electrode , solid electrolyte body, a main body portion formed by being sandwiched between the reference electrode portion and the detection electrode, than the body portion is disposed longitudinally rearward, rather a thin thickness than the body portion, said body And a peripheral portion divided by a step-like boundary, and a suppression layer that is in contact with at least a part of the peripheral portion of the solid electrolyte body .
The element of the second invention comprises a plate-like substrate extending in the longitudinal direction and having an insulating property, and a layered solid electrolyte body disposed on the substrate and having a reference electrode and a detection electrode formed thereon. A gas sensor element comprising a detection unit formed on the front side in the longitudinal direction , the detection unit being configured to sandwich the solid electrolyte body between the reference electrode unit of the reference electrode and the detection electrode unit of the detection electrode in, solid electrolyte body, a main body portion formed by being sandwiched between the reference electrode portion and the detection electrode, than the body portion is disposed longitudinally rearward, rather a thin thickness than the body portion, It is connected to the main body part, and includes a peripheral part separated from the main body part by a step-like boundary, and further includes an interposed layer that is in contact with at least a part of the peripheral part of the solid electrolyte body. .
[0006]
The “substrate” preferably has an insulation property of 100 times or more compared with the solid electrolyte body at a temperature of 900 ° C. The “solid electrolyte body” only needs to have oxygen ion conductivity. For example, a zirconia-based sintered body or LaGaO ₃ -based sintered body having oxygen ion conductivity can be used. The “peripheral part” included in the solid electrolyte layer is preferably 30 to 70%, more preferably 40 to 60% of the thickness of the “main body part”. The thickness of the main body is preferably 20 to 150 μm (more preferably 30 to 100 μm). In particular, cracks can be sufficiently prevented by setting the thickness of the main body to 150 μm or less. The composition of the main body part and the peripheral part may be the same or different. Furthermore, it may be integral or separate before firing.
[0007]
The peripheral portion is formed to be thin in a stepped manner at the boundary with the main body portion. When forming in a staircase shape, it can be formed by laminating unfired sheets of different thicknesses. Further, the thickness can be changed stepwise by printing the paste in layers. Thus, it is simple to form the solid electrolyte body in a stepped manner, and the efficiency in production is good.
[0008]
The “suppression layer” is usually constituted by a part of the insulating layer, and is formed on the peripheral part so as to suppress at least a part of the peripheral part. This suppression layer usually has a higher insulating property than the peripheral part. Further, the peripheral portion can be provided via the insertion layer as in the second invention without directly contacting the base. As a result, the area where the solid electrolyte body and the substrate having a different composition are in contact with each other can be reduced, and the stress can be dispersed to prevent the occurrence of cracks. This intervening layer is usually constituted by a part of the insulating layer. Therefore, the suppression layer and the insertion layer may be integrated. In addition, since the suppression layer and the intervening layer are in direct contact with the peripheral portion of the solid electrolyte body, it is preferably close to the composition of the solid electrolyte body as long as it has sufficient insulation with respect to the solid electrolyte body. Thereby, a thermal expansion difference can be made small. Specifically, the suppression layer and the intervening layer can contain less than 15% by mass (more preferably less than 10% by mass) of components constituting the solid electrolyte body.
[0009]
Further, when no intervening layer is provided, the total thickness of the peripheral portion and the suppression layer is preferably equal to the thickness of the main body portion. Furthermore, when the insertion layer is provided, the total thickness of the peripheral portion, the suppression layer, and the insertion layer is preferably equal to the thickness of the main body portion as in the fourth invention. However, being equal to each other is not only completely the same, but may have a difference of about −60 to 60% (more preferably −40 to 40%). Thus, by making the total thickness of the peripheral portion and the suppression layer and / or the intervening layer equal to the thickness of the main body portion, the stress balance is optimized, and the occurrence of cracks can be effectively prevented. .
[0010]
Furthermore, the substrate Ri plate der and the solid electrolyte body is formed in a layer in contact with at least a portion of one surface of the substrate. As described above, in the production of the solid electrolyte body, it is preferable to perform lamination of unfired sheets or lamination printing of paste. In this case, substrate so that the laminating these Ri integral plate der, thereby becomes particularly easy to handle during manufacture.
[0011]
In the gas sensor elements of the first to sixth inventions, as in the seventh invention, the solid electrolyte body contains 10 to 80% by mass (more preferably 40 to 60% by mass) of components constituting the substrate. preferable. If the content of the component constituting the substrate exceeds 80% by mass, it is not preferable because the characteristics as a solid electrolyte body cannot be sufficiently obtained. On the other hand, if it is less than 10% by mass, it is difficult to sufficiently relax the difference in thermal expansion coefficient. Thereby, the malfunction by a thermal expansion coefficient difference can be improved further. In particular, as in the eighth invention, it is preferable that the solid electrolyte body is mainly composed of zirconia and alumina, and the substrate is mainly composed of alumina. A gas sensor element including such a solid electrolyte body containing a large amount of alumina is inexpensive and has high durability.
[0012]
In the gas sensor element that exhibits the gas detection ability by forming the reference oxygen source as described above and holding it sufficiently, the main body portion needs to be airtight for holding the reference oxygen source. For this reason, the thickness which can ensure this airtightness is required. However, since it is not necessary to ensure airtightness, the thickness of the peripheral part of the solid electrolyte body not subjected to gas detection can be reduced. In this way, the solid electrolyte body is divided into a main body part that mainly exhibits gas detection ability and a peripheral part that does not need to exhibit gas detection ability, and the stress concentration of the solid electrolyte body is reduced by reducing the thickness of the peripheral part. Can be dispersed.
[0013]
Furthermore, by laminating the suppression layer on the peripheral part, deformation due to thermal expansion of the peripheral part can be suppressed. In a gas sensor element that does not have a suppression layer, the force accompanying deformation due to the difference in thermal expansion coefficient between the solid electrolyte body and the substrate acts so that they are peeled off. For this reason, it was necessary to withstand the tensile stress of peeling at the interface. However, the durability of the substrates of different materials with respect to the tensile force is not sufficient, and it is considered that cracks occur. In the gas sensor elements according to the first to sixth inventions, by providing a suppression layer on the side opposite to the peeling direction of the solid electrolyte body, the tensile force acting on the interface between the substrate and the solid electrolyte body is reduced, thereby generating cracks. It can be greatly prevented.
[0014]
A gas sensor according to a seventh aspect of the invention includes the gas sensor according to any one of the first to sixth aspects of the invention.
This gas sensor is inexpensive and has high durability. The form of the gas sensor 2 is not particularly limited. For example, the outer surface of the metal shell 21 is arranged such that the element 1 is disposed in the metal shell 21 and the detection unit disposed on the front side protrudes into the exhaust pipe or the like. Can be used by being exposed to a gas to be measured (exhaust gas). (See Figure 6)
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to examples.
In addition, below, each part before baking and after baking is shown with the same code | symbol for convenience.
[1] Manufacture of an element including a peripheral portion and a suppression layer on the peripheral portion A method of manufacturing an element will be described with reference to FIG.
(1) Production of unsintered alumina sheet 100 parts by mass (hereinafter referred to simply as “parts”) of alumina powder (purity 99.99% or more, average particle size 0.3 μm), 14 parts of butyral resin and 7 parts of dibutyl phthalate After mixing and mixing using a mixed solvent composed of toluene and methyl ethyl ketone to form a slurry, four types of green sheets having different thicknesses and sizes were prepared by a doctor blade method. The first green sheet 11a has a thickness of 0.4 mm and a length of 5 cm, the second green sheet 11b has a thickness of 0.25 mm and a length of 5 cm, and the third green sheet 18a has a thickness of 0.25 mm and a length. The fourth green sheet 18b has a thickness of 0.4 mm and a length of 3.5 cm. After firing, the first green sheet becomes the first base 11a, the second green sheet becomes the second base 11b, the third green sheet becomes the reinforcing layer 18a, and the fourth green sheet becomes the reinforcing layer 18b.
[0016]
(2) Formation of heater pattern Conductive layer paste containing 4 parts of alumina powder (purity 99.99% or more, average particle size 0.3 μm) and 100 parts of platinum powder was used as the first green sheet 11a (after firing) The heating part pattern 121 was printed and dried on one surface of the lower half), and then the heater lead pattern 122 was printed and dried to form the heater pattern 12 (to become the heating resistor 12 after firing). A through hole 111a for conducting the heating resistor is formed near the base end of the first green sheet 11a, and the heater pad pattern 19a is printed and dried at a position corresponding to the through hole 111a on the back surface (terminal after firing). It becomes an electrode pad for connecting. A second green sheet 11b (which becomes the upper half of the base after firing) was laminated on the heater pattern 12 and bonded by pressure bonding.
[0017]
(3) Formation of buffer layer pattern Buffer layer pattern 13 (fired) was formed on the second green sheet 11b of the ceramic laminate produced in (2) using a buffer layer paste containing 80 parts of alumina and 20 parts of zirconia. The post-buffer layer) was printed and dried to a thickness of 40 ± 10 μm.
(4) Formation of reference electrode pattern On the buffer layer pattern formed in (3), using the conductive layer paste used in (2), electrode portion pattern 141a (becomes a reference electrode portion after firing) and electrode lead A reference electrode pattern 14a (being a reference electrode after firing) composed of a portion 142a (being a lead portion of the reference electrode after firing) was printed and dried to a thickness of 20 μm ± 10.
[0018]
(5) Formation of first solid electrolyte layer pattern 50 parts of zirconia powder (purity 99.9% or more, average particle size 0.3 μm) and alumina powder (purity 99.99% or more, average particle size 0.3 mm) Then, 33.3 parts of butyl carbitol, 0.8 part of dibutyl phthalate, 0.5 part of a dispersant and 20 parts of a binder were added with a required amount of acetone, mixed for 4 hours, and then evaporated to obtain a solid electrolyte layer. A paste was prepared.
This solid electrolyte paste is printed and dried to a length of 13 mm and a thickness of 25 ± 10 μm in the length direction of the first green sheet (and the second green sheet) so as to cover the electrode part pattern 141a of the reference electrode pattern 14a. The solid electrolyte layer pattern 15a (becomes part of the main body portion and the peripheral portion of the solid electrolyte body after firing) was formed.
[0019]
(6) Formation of first insulating layer pattern The required amount of acetone is added to 50 parts of butyl carbitol to the green sheet produced in (1) and mixed for 4 hours, and then acetone is evaporated to obtain an insulating layer paste. It was adjusted. This insulating layer paste was printed and dried at a thickness of 25 ± 10 μm on the buffer layer pattern 13 where the first solid electrolyte layer pattern 15a was not printed, thereby forming the first insulating layer pattern 16a. After firing, it becomes part of the insulating layer.
[0020]
(7) Formation of second solid electrolyte layer pattern The same solid electrolyte paste as in (5) is printed and dried to a length of 8 mm and a thickness of 25 ± 10 μm with the tip position aligned from above the first solid electrolyte pattern 15a. The second solid electrolyte layer pattern 15b (becomes a part of the solid electrolyte body after firing) was formed.
That, and a thickness 25μm of the portion that becomes the portion after firing peripheral portion of the thickness of 50μm made after firing body portion.
[0021]
(8) Formation of second insulating layer pattern The same insulating layer paste as in (6) is printed and dried to a thickness of 25 ± 10 μm on the first insulating layer pattern 16a where the second solid electrolyte layer pattern is not formed, The second insulating layer pattern 16b (becomes part of the insulating layer after firing, and in particular, the upper part of the first solid electrolyte pattern becomes the suppression layer 162 after firing) was formed.
[0022]
(9) Formation of detection electrode pattern On the second solid electrolyte layer pattern 15b and the second insulating layer pattern 16b formed in (7) to (8), using the conductive layer paste adjusted in (2), print detection electrode pattern 14b made of baking after the detection electrodes become the electrode part pattern 141b (comprising after firing detection electrode) and the electrode lead portion pattern 142b (the firing after the detection electrode lead portion) to a thickness of 20 ± 10 [mu] m -Dried.
(10) Formation of protective layer pattern The same insulating layer paste as in (6) is mixed with resin powder having an average particle size of 50 μm to prepare a protective layer paste, and a length of 10 mm is formed on the second solid electrolyte layer pattern 15b. Then, it was printed and dried to a thickness of 50 ± 20 μm to form a protective layer pattern 17 (which becomes a protective layer after firing).
(11) Lamination of third and fourth green sheets Third green sheet 18a and fourth green sheet 18b (a part of the reinforcing layer after firing and a portion of each of the reinforcing layers so as to cover the portion excluding the protective layer pattern formed in (10)) Layered).
[0023]
(12) Degreasing and firing The laminate obtained in (1) to (11) is heated from room temperature to 420 ° C. at a heating rate of 10 ° C./hour in an air atmosphere and held for 2 hours. Degreasing treatment was performed. Thereafter, the temperature is raised to 1100 ° C. at a temperature rising rate of 100 ° C./hour, and further heated to 1520 ° C. at a temperature rising rate of 60 ° C./hour, held for 1 hour and fired, as shown in FIG. 300 gas sensor elements in which such a solid electrolyte body was provided with a main body portion and a peripheral portion, and the solid electrolyte body and the detection electrode lead portion were separated by the suppression layer were obtained.
[0024]
[2] Manufacture of device including suppression layer and intervening layer According to the steps (7) and (8) of [1], after the first solid electrolyte pattern 15a is formed and dried, the first insulating layer pattern 16a ( Part of the intervening layer 163 is formed and dried. Next, a second solid electrolyte layer pattern 15b (part of which becomes the peripheral portion 152 ) having a larger area than the first solid electrolyte pattern 15a is formed and dried on the first solid electrolyte pattern, and further, the second insulating layer The pattern 16b was formed and dried. Thereafter, a third solid electrolyte pattern having a smaller area than the second solid electrolyte pattern (not shown in FIG. 1) is formed and dried, and further a third insulating layer pattern (part of which becomes the suppression layer 162) is formed. -Dried. Otherwise, 300 elements were obtained in the same manner as [1]. (See Figure 3)
[0025]
[3] Manufacture of an element having only an insertion layer ( element of the second invention shown in FIG. 4 ) According to the steps (7) and (8) of [1], the first solid electrolyte pattern 15a is formed and dried. Thereafter, the first insulating layer pattern 16a (a part of which becomes the insertion layer 163) was formed and dried. Next, a second solid electrolyte layer pattern 15b (part of which becomes the peripheral portion 152 ) having a larger area than the first solid electrolyte pattern 15a is formed and dried on the first solid electrolyte pattern, and further, the second insulating layer The pattern 16b was formed and dried. Otherwise, 300 elements were obtained in the same manner as [1]. (See Figure 4)
[0026]
[4] Manufacture of device having no peripheral portion In the steps (7) and (8) of [1], the size of the second solid electrolyte layer pattern 15b is aligned with the first solid electrolyte pattern 15a, and the second insulating layer 300 elements were obtained in the same manner as in [1] except that the size of the pattern 16b was matched to that of the first insulating layer pattern 16a. (See Figure 5)
[0027]
[5] Evaluation of occurrence rate of cracks and the like due to firing 1200 elements obtained in [1] to [4] are submerged in water so that at least the solid electrolyte body portion is completely immersed, and the reference electrode and water The resistance value between them was measured to evaluate the presence or absence of cracks. As a result, 183 elements having cracks were found between the solid electrolyte body and the insulating layer (position T in FIG. 5) in the element having no peripheral part obtained in [4]. That is, the crack generation rate was 60%. On the other hand, no cracks were generated in the devices obtained in [1] to [3], and the crack generation rate was 0%.
[0028]
[6] Using the element obtained in the thermal cycle durability test [1] to [4], which was evaluated as not cracked in the test [5], a voltage of 16 V was applied to the resistance heating element. The thermal cycle test was repeated for 10 cycles by applying and heating the solid electrolyte body until the temperature of the solid electrolyte body reached about 1000 ° C., then stopping the application of voltage, and allowing the solid electrolyte body to stand at room temperature. Thereafter, the occurrence of cracks was evaluated by the same test as in [5]. As a result, in the device obtained in [4], cracks occurred in 29% of the devices, whereas in the devices obtained in [1] to [3], the crack occurrence rate was 0%.
From this result, it can be seen that the element of the present invention does not generate cracks during firing, and has high durability that does not generate cracks even in a thermal cycle test after firing.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram for explaining a manufacturing process of a gas sensor element of the present invention.
FIG. 2 is a cross-sectional view of an example of a gas sensor element of the present invention.
FIG. 3 is a cross-sectional view of another example of the gas sensor element of the present invention.
FIG. 4 is a cross-sectional view of another example of the gas sensor element of the present invention.
FIG. 5 is a cross-sectional view of an example of a gas sensor element outside the scope of the present invention.
FIG. 6 is a cross-sectional view of the gas sensor of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1; Gas sensor element, 11a; 1st base | substrate, 11b; 2nd base | substrate, 111; Through-hole, 12; Heat generating resistor, 121; Heat generating part, 122: Heater lead part, 13: Buffer layer, 14a; Reference electrode, 14b Detection electrode, 15; solid electrolyte layer, 151; body portion, 152; peripheral portion, 16a; first insulating layer, 16b; second insulating layer, 162; suppression layer, 163; 18; 1st reinforcement layer, 18b 2nd reinforcement layer, 2; Gas sensor, 21: Main metal fitting, 211; Main metal fitting screw part.

Claims (7)

A plate-like substrate extending in the longitudinal direction and having an insulating property, and a layered solid electrolyte body disposed on the substrate and having a reference electrode and a detection electrode formed thereon, are formed on the front side in the longitudinal direction. In the gas sensor element comprising a detection unit configured to sandwich the solid electrolyte body between the reference electrode unit of the reference electrode and the detection electrode unit of the detection electrode ,
Solid electrolyte body, a main body portion formed by being sandwiched between the reference electrode portion and the detection electrode, than the body portion is disposed longitudinally rearward, rather a thin thickness than the body portion, said body And a peripheral part separated by a step-like boundary with the main body part ,
A gas sensor element comprising a suppression layer that is in contact with at least a part of the peripheral portion of the solid electrolyte body . A plate-like substrate extending in the longitudinal direction and having an insulating property, and a layered solid electrolyte body disposed on the substrate and having a reference electrode and a detection electrode formed thereon, are formed on the front side in the longitudinal direction. In the gas sensor element comprising a detection unit configured to sandwich the solid electrolyte body between the reference electrode unit of the reference electrode and the detection electrode unit of the detection electrode ,
Solid electrolyte body, a main body portion formed by being sandwiched between the reference electrode portion and the detection electrode, than the body portion is disposed longitudinally rearward, rather a thin thickness than the body portion, said body And a peripheral part separated by a step-like boundary with the main body part ,
A gas sensor element comprising an intervening layer that is in contact with at least a part of the peripheral portion of the solid electrolyte body .   The gas sensor element according to claim 1, further comprising an insertion layer that is in contact with the peripheral portion.   The gas sensor element according to claim 3, wherein a total thickness of the peripheral portion, the suppression layer, and the insertion layer is equal to a thickness of the main body portion. The gas sensor element according to any one of claims 1 to 4 , wherein the solid electrolyte body contains 10 to 80 mass% of a component constituting the substrate. 6. The gas sensor element according to claim 5, wherein the solid electrolyte body has zirconia and alumina as main components, and the base body has alumina as main components. The gas sensor characterized in that it comprises a gas sensor element according to any one of claims 1 to 6.

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