JPH04166757A - Oxygen sensor element and manufacture thereof - Google Patents

Abstract

PURPOSE:To realize a sensor characterized by excellent low-temperature operability and response by providing a porous cermet electrode structure wherein zirconia particles having the particle diameters of 2mum or less are distributed as a measuring electrode which is exposed to gas to be measured. CONSTITUTION:Of a pair of electrodes, at least the measuring electrode 4 which is exposed to gas to be measured is made to be a specified porous cermet electrode. Namely, the measuring electrode 4 is made to be the porous cermet electrode wherein catalyst metal and ZrO2 are main component. In the porous electrode, the ZrO2 component is present as the zirconia particles which comprise monoclinic ZrO2 or partially stabilized zirconia and have the particle diameters of 2mum or less at the ratio of 5 - 60 weight parts per 100 weight parts of the catalyst metal. The zirconia particle is constituted of the partially stabilized zirconia wherein at least one kind of CaO, Y2O3 and Yb2O3 is added at the ratio of 4mol% or less.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to an oxygen sensor element and a method for manufacturing the same, and in particular to a low-temperature oxygen sensor element for measuring the amount of oxygen contained in exhaust gas from internal combustion engines, boilers, etc. This invention relates to technology that improves operability and responsiveness.

(Background technology) Solid electrolytes made of oxygen ion conductive zirconia porcelain have traditionally been used to measure objects discharged from internal combustion engines such as automobiles, combustion equipment in industrial furnaces, etc., for example, based on the principle of oxygen concentration batteries. It is known to detect the oxygen concentration of exhaust gas as a gas and control the air-fuel ratio or combustion state of such an internal combustion engine.

In this type of oxygen sensor, which is an oxygen concentration detector, the sensor element is made of or contains a catalytic metal such as platinum in a solid electrolyte body having a shape such as a bottomed cylinder or a plate. A structure is adopted in which at least one pair of electrodes is provided and at least one of the electrodes is brought into contact with a gas to be measured such as exhaust gas.

In addition, the electrodes provided in this type of oxygen sensor element are made of catalytic metal powder such as platinum and solid electrolyte to improve durability under severe usage conditions such as long periods of time or extremely high temperatures. A paste is prepared by mixing with a symbiotic zirconia powder, and this paste is screen printed on a sensor body (element body) made of stabilized or partially stabilized zirconia, etc., and is simultaneously integrated with the sensor body. Cermet electrodes formed by firing are known.

However, such cermet electrodes are generally heated to at least 1000°C to improve their durability.
As mentioned above, since the simultaneous integral firing with the sensor body is advantageously carried out at a high temperature of 1300'C or more in the atmosphere, there is a problem that oxidation of the electrode surface is caused, and the electrode by this integral firing However, since the firing temperature of the solid electrolyte raw material is relatively high, sintering of catalyst metals such as platinum tends to proceed easily, and furthermore, a sintering aid is usually added to the solid electrolyte raw material. For this reason, there is a problem in that the sintering aid enters the electrode layer during sintering and becomes an impurity covering the catalyst metal constituting the electrode. For these reasons, the cermet electrode in conventional oxygen sensor elements has low catalytic activity and lacks porosity, which causes problems such as poor low-temperature operation and response of oxygen sensor elements. I was holding it.

In particular, in recent years, exhaust gas regulations have become stricter, and due to constraints such as oxygen sensor elements that operate even when vehicles are idling, and sensor mounting positions, oxygen sensors that operate stably even in the low temperature area behind the exhaust pipe. Although sensor elements are increasingly required, conventional oxygen sensor elements cannot be expected to operate stably under exhaust gas at a low temperature of, for example, 400"C or less.

(Problem to be solved) The present invention has been made against this background, and the problem to be solved is to operate stably and respond even in low-temperature gas to be measured. The object of the present invention is to realize an oxygen sensor element with excellent properties, and to provide a method for advantageously manufacturing an oxygen sensor element having such excellent properties.

(Solution Means) In order to solve the above problems, the present invention has the following features:
In an oxygen sensor element comprising at least one pair of electrodes supported on an oxygen ion conductive zirconia solid electrolyte body, at least the electrode exposed to the gas to be measured out of the at least one pair of electrodes is made of a catalyst metal and ZrO□. In addition to forming a porous cermet electrode, the ZrO□ component in the porous electrode is treated as zirconia particles of monoclinic ZrO□ or partially stabilized zirconia with a particle size of 2 μm or less as a catalyst. 5 per 100 parts by weight of metal
It is characterized in that it is present in a proportion of ~60 parts by weight.

In addition, in the oxygen sensor element according to the present invention, the monoclinic Zr0z constituting the zirconia particles is formed from pure zirconia to which no stabilizer is added, as is well known. Moreover, partially stabilized zirconia is formed by adding at least one of Cab, YzO3, and YbzO3 to zirconia in a proportion of 4 mol% or less.

Further, the present invention provides a method for manufacturing an oxygen sensor element in which at least one pair of electrodes is supported on an oxygen ion-conducting zirconia solid electrolyte body in order to advantageously obtain an oxygen sensor element with excellent low-temperature operability and responsiveness. Of the at least one pair of electrodes, at least the electrode exposed to the gas to be measured is made of zirconia powder or partially stabilized zirconia with a particle size of 0.2 to 2.5 μm consisting of catalyst metal powder and monoclinic ZrO□. The particle size consists of 0.2~2.0a
By applying an electrode forming material prepared from the zirconia powder of m to the solid electrolyte body and firing it,
The gist of the present invention is a method for manufacturing an oxygen sensor element, which includes a step of forming a porous cermet electrode.

Furthermore, in the present invention, the porous cermet electrode formed by firing the oxygen sensor element obtained as described above is subjected to (a) acid treatment and/or (b)
) The gist of the present invention is to perform a post-treatment of heat treatment in at least one of a reducing gas atmosphere and an unsaturated hydrocarbon atmosphere. Characteristics such as low-temperature operability and responsiveness can be further improved.

In addition, even in such a method for manufacturing an oxygen sensor element, as the zirconia powder, at least one of monoclinic ZrO, CaO, YzCh, and Yb2O3 is added in a proportion of 4 mol% or less. Partially stabilized zirconia formed by this process is advantageously used.

(Specific Structure/Operation) First, FIG. 1 shows a typical structure of an oxygen sensor element to which the present invention is applied, in a sensor structure based on the principle of an oxygen concentration battery.

That is, the oxygen sensor element shown in FIG. 1 has a plate-like shape integrally formed by a known lamination method, and has a narrow plate-like solid electrolyte body 2 of a predetermined length. A measuring electrode 4 and a reference electrode 6 are respectively provided on the surface of the measuring electrode 4, and a gas to be measured such as exhaust gas is brought into contact with the measuring electrode 4 through a porous protective layer 8. A spacer 12 for forming an air passage 10 is provided on the side of the body 2 where the reference electrode 6 is provided.
and the plate-like lid member 14 are stacked to form an integral structure. The air passage 1o formed inside the element is opened at the base end side of the element and communicated with the atmosphere, and the air introduced through this air passage 10 is connected to the reference electrode 6. is brought into contact with the gas as a reference gas having a predetermined reference oxygen concentration.

In addition, the oxygen sensor element having such a structure has a lid member 1.
On the outside of 4, there is a heater layer in which the heater element 16 is sandwiched between electrically insulating layers 18 and 20 made of alumina or the like.
The heater element 16 is laminated and integrated with the airtight layer 22 located on the outside thereof, and the electrodes 4 and 6 of the oxygen sensor element are buried by energizing the heater element 16 from the outside and causing the heater element 16 to generate heat. The parts are heated to a predetermined temperature.

And for an oxygen sensor element with such a structure,
As is well known, the oxygen concentration in the atmosphere (measured gas) brought into contact with the measurement electrode 4 through the porous protective layer 8 and the oxygen concentration in the atmosphere (reference gas) brought into contact with the reference electrode 6 are The oxygen concentration in the target gas to be measured is detected according to the electromotive force induced based on the difference in the oxygen sensor element. The electrode 4 that is brought into contact with the gas is a porous cermet electrode.

It should be noted that the present invention is not only applicable to the sensor element having the structure as shown in FIG. It goes without saying that it is also applicable to sensor elements with known structures based on various measurement principles such as the limiting current method and polarography. .

By the way, as the oxygen ion conductive solid electrolyte body (2) constituting the oxygen sensor element, the well-known ZrO2
In addition to the plate-like shape shown above, which is formed using a solid electrolyte material, a known shape such as a cylindrical shape with a bottom may be employed, such as a Cab.

It is formed from an oxygen ion conductive stabilized or partially stabilized zirconia material containing ZrO2 as a main component, to which one or more predetermined stabilizers such as YzO3 and Yb2 (13) are added, according to an appropriate molding method.

As is well known, such solid electrolyte materials also contain certain sintering aids, such as clay such as kaolin and 5iO
z, Affz○3. Fe2O, etc. are appropriately blended.

Note that in the oxygen sensor element shown in FIG. 1, the spacer 12
, the lid member 14, and the airtight layer 22 may all be formed using a known ceramic material, but generally they are formed using the same kind of material as the solid electrolyte body 2, and the porous protection N8
Even if the solid electrolyte body 2 is made of the same material as the solid electrolyte body 2, it will be formed according to a known method. There is no problem.For the formation of the porous protective layer 8, Yb20
It is particularly effective to use a solid electrolyte material such as ZrO stabilized with a stabilizer such as Yb20:+ in the porous protective layer 8. 2, the porous protective layer 8
It is preferable to make the crystal phases of Zr0z different between the solid electrolyte body 2 and the solid electrolyte body 2. More specifically, the crystalline phase of Zroz in the porous protective layer 8 is stable against thermal cycles and thermal shocks, with only or mostly cubic crystals, and a small amount of tetragonal or monoclinic crystals. while forming a crystalline phase containing crystals,
Most of the Z r O2 of the solid electrolyte body 2 is composed of a tetragonal crystal, a mixed phase of a tetragonal crystal, a monoclinic crystal, and a cubic crystal, or a mixed phase of a monoclinic crystal and a cubic crystal. It is desirable that the material has high mechanical strength.

Further, among the measurement electrode 4 and the reference electrode 6 formed at a predetermined portion on the solid electrolyte body 2, the electrode forming material that provides at least the electrode (4) on the side exposed to the gas to be measured is a catalyst that becomes an electrode conductor. It is composed of metal powder and zirconia powder. Note that a known catalyst metal is used, such as platinum or an alloy of platinum and a metal such as nickel, silver, gold, rhodium, palladium, iridium, or ruthenium. Further, as the zirconia powder, monoclinic Zr○2 powder or CaO, Y
Partially stabilized zirconia powder containing one or more components such as 20z, Ybz (13, etc.) added in a proportion of 4 mol% or less will be used, but especially Zr0z, which causes phase transformation.
, more specifically, Z whose crystal phase is monoclinic at room temperature.
It is preferable to use r0z.

The reason for the improved properties by using monoclinic Zr○2, that is, pure Zr0z without any stabilizer added, is that pure ZrO□ has a higher sintering rate than stabilized zirconia with additives. In addition to being able to suppress the sintering of the catalyst metal constituting the electrode, due to the low Zirconia (Z
It is presumed that this is because cracks occur in the catalyst metal and the catalytic metal, forming a porous electrode with a large surface area.

Therefore, in such an electrode forming material, if the particle size of the zirconia powder constituting the material is too small, it is difficult for the above-mentioned refinement to occur due to phase transition, and in a cermet electrode, the catalytic metal powder The dispersibility (uniform mixing property) of the zirconia powder is poor, and the sintering of the zirconia powder tends to progress, resulting in problems such as the miniaturization effect due to the phase transition described above is reduced. Conversely, if the particle size of the zirconia powder is too large, the adhesion of the electrode obtained by firing to the solid electrolyte body will deteriorate, in addition to the problem of reduced durability of the electrode. Therefore, a problem arises in that the agglomeration of the catalyst metal powder in the electrode increases and sintering of the catalyst metal progresses. Therefore, in the present invention, when using zirconia powder made of single crystal ZrO2, the particle size must be 0.2 to 2.5 μm, more preferably in the range of 0.2 to 1.5 μm. A range of 0.6 to 1.2 μm is particularly preferably selected.

In addition, when using zirconia powder made of partially stabilized zirconia, the particle size is 0.2 to 2.0μ.
m, more preferably 0.2 to 1.5μ
A range of m, particularly preferably a range of 0.6 to 1.2 μm will be adopted. Note that the particle size of the zirconia powder is measured according to a particle size measurement method using a laser scattering method.

In addition, the composition ratio of catalyst metal powder and zirconia powder in such an electrode forming material varies depending on manufacturing conditions such as firing temperature, but if the amount of catalyst metal powder is small, the electrode will not have conductivity, and if it is too large, As sintering of the catalytic metal powder progresses, the electrode becomes denser and the porosity decreases, which is an adverse effect.
The zirconia powder is used in an amount of 0 parts by weight, and more preferably 10 to 20 parts by weight of the zirconia powder.

Then, using the electrode forming material made of such a predetermined catalyst metal powder and zirconia powder, such an electrode forming material is used to form an electrode exposed to at least the gas to be measured at a predetermined portion of the solid electrolyte body. When applying the electrode to a predetermined portion of the solid electrolyte body, a known electrode forming method is appropriately adopted. For example, an electrode forming layer of a predetermined thickness is formed on the solid electrolyte body by a screen printing method or a spray method. After forming, the desired porous cermet electrode can be formed by heating and firing (baking). More specifically, in the screen printing method,
A mixed paste of the catalyst metal powder and zirconia powder described above is prepared, and this is printed on a solid electrolyte body using a screen printing method, and then heated and baked.
In addition, in the spray method, zirconia powder is added to a slurry containing a predetermined catalytic metal powder, and after spraying it onto a predetermined location on the solid electrolyte, the desired porous electrode is formed by heating. You can.

The solid electrolyte body to which such an electrode forming material is applied may be one that has already been fired, but in the present invention, it is preferably in the state of a green sheet or green body before firing. It is desirable that the electrode forming layer (electrode forming material) formed on the solid electrolyte body be heated and baked simultaneously with the firing operation of the solid electrolyte body.

Among the electrodes provided in the oxygen sensor element, in order to form an electrode other than the electrode exposed to the gas to be measured, for example, the reference electrode 6 in the configuration shown in FIG. 1, the structure of the oxygen sensor element, its manufacturing method, etc. Accordingly, conventionally known plating methods, sputtering methods, methods using thermal decomposition of salts of electrode conductors such as catalytic metals, paste baking methods in which a cermet paste of electrode conductors and ceramic fuchs is baked onto the surface of the solid electrolyte body, and furthermore, An appropriate method is selected and adopted from among various methods such as a cermet paste simultaneous firing method in which such a cermet paste is printed or applied on a solid electrolyte body and then fired together with the solid electrolyte body. However, in the present invention, since the measurement electrode 4 needs to be configured as a cermet electrode, among the above electrode forming methods, either the paste baking method or the cermet paste simultaneous baking method is used. will be advantageously adopted.

In the oxygen sensor element obtained in this way, at least the measurement electrode 4 exposed to the gas to be measured is
Such electrodes are formed as porous cermet electrodes mainly composed of a catalyst metal and ZrO□, while in such porous electrodes, the ZrO□ component is composed of monoclinic ZrO2 or partially stabilized zirconia. Since it is present as zirconia particles of 2 μm or less in an amount of 5 to 60 parts by weight per 100 parts by weight of the catalyst metal,
The microporous structure of such an electrode can be advantageously realized, resulting in an electrode with a large surface area, which can impart effective catalytic activity and can significantly improve the low-temperature operability and responsiveness of the oxygen sensor element. In order to fully exhibit this effect, the particle size of the zirconia powder (particles) in the electrode after firing should be determined regardless of whether the electrode is made of single crystal Zr○2 or partially stabilized zirconia. S of cross section
According to an EM (scanning electron microscope) image, the thickness needs to be 2 μm or less. In addition, when the zirconia powder in such an electrode is made of single crystal ZrO2,
Preferably 1.5 μm or less, more preferably 0.6 μm
It is desirable that the particle size is as follows, and in the case of partially stabilized zirconia, it is preferably 1.7 μm.
Hereinafter, it is more preferable that the particle size is 1.2 μm or less.

Further, in the present invention, the porous cermet electrode obtained by firing the oxygen sensor element thus obtained is subjected to (a) acid treatment and/or (b) reducing gas and/or A heat treatment in a saturated hydrocarbon atmosphere is advantageously employed; by carrying out such a treatment, the catalytic activity of the porous cermet electrode, i.e. the electrode exposed to the gas to be measured, can be significantly increased. Therefore, the low temperature operability and responsiveness of the oxygen sensor element can be further improved.

The purpose of the above acid treatment (a) is to remove impurities covering the surface of the catalyst metal constituting the electrode by the acid that has penetrated into the porous electrode, and the above heat treatment (b) ) is to remove the metal oxide formed on the surface of the porous electrode and increase its catalytic activity, and even if acid treatment (a) and heat treatment (b) are attempted alone, Although some effects can be expected from such treatments, it is particularly recommended in the present invention to perform the two treatments (a) and (b) together. However, if the acid treatment in (a) is not performed, the electrode with impurities attached will be subjected to the heat treatment in (b).
Although the expected catalytic activity effect of the heat treatment in (b) is lowered, the electrode surface is clean after removing impurities by the acid treatment in (a), so the effect of the heat treatment in (b) is lower. This is because a sufficient catalytic activity effect is exhibited by performing the heat treatment.

Further, the acid treatment (a) and heat treatment (b) as described above may be performed on the entire oxygen sensor element at the stage of a single unit, or may be performed on only the porous electrode portion of the element. Furthermore, in the state of the assembled product (finished product) in which the oxygen sensor element is assembled as an oxygen sensor, the electrode part (porous There is no problem even if it is performed only on the quality electrode). In addition, such acid treatment (a) and heat treatment (b) are performed on the electrode (4) of the oxygen sensor element exposed to the gas to be measured, as shown in FIG.
In the case where a porous protective layer (8) is provided,
The acid treatment (a) and heat treatment (b) are performed through the porous protective layer (8).

Incidentally, such acid treatment (a) is generally carried out by immersing the oxygen sensor element in a suitable acid solution, but phosphoric acid is also used as the acid for such acid treatment. , hydrofluoric acid, hydrofluoroboric acid, hydrochloric acid, nitric acid, aqua regia, etc. are appropriately selected and used, among others,
Hydrofluoric acid treatment or borofluoric acid treatment is most desirable. Note that the concentration of the acid used in such acid treatment is appropriately selected so as to remove impurities covering the electrode surface.
For example, in the case of hydrofluoric acid, its concentration is
0.05-40% by weight, preferably 0.1-IO% by weight
It will be used within the scope of. When the concentration of hydrofluoric acid is lower than 0.05% by weight, it is difficult to remove impurities around the electrode, while when it exceeds 40% by weight, hydrogen fluoride is present in the solid electrolyte body itself. This is because the acid starts to react, causing deterioration of the solid electrolyte body.

Furthermore, the treatment temperature during such acid treatment is also selected appropriately depending on the type of acid in order to fully exhibit the treatment effect. For example, in the case of hydrofluoric acid treatment, the temperature It is particularly preferable to maintain the temperature at 30 to 50°C in order to stabilize the impurity removal effect of hydrofluoric acid. In addition, oxygen sensor elements that have been treated with acids such as hydrofluoric acid may be subjected to known cleaning processes such as thoroughly washing the acid-treated elements with running water or ultrasonic cleaning. It is preferable that M g (N (13 ) 2 or Ca (NO 3 )
If the oxygen sensor element is treated with a solution of an alkaline earth metal salt such as No. 2, fluoride ions are fixed and the impurity removal effect of hydrofluoric acid can be completely blocked. It is possible to avoid the harmful effects of residual acid.

Further, the above-described heat treatment (b) performed on the porous cerment electrode according to the present invention may be performed in an atmosphere of at least one of a reducing gas and an unsaturated hydrocarbon. Become. The temperature of this heat treatment is preferably in the range of 300 to 1100°C, more preferably in the range of 500 to 950°C. Also, the temperature during treatment does not need to be constant, and is between 300 and 1100.
There is no problem even if a thermal cycle is applied between .degree. If the heat treatment temperature is lower than 300°C, the above-mentioned activation effect of the oxygen sensor element will be weak, and the resulting products may vary widely; if the heat treatment temperature exceeds 1100°C, There is also the problem of rapid sintering and wear and tear of the metal used in the electrodes. Further, the heat treatment time is preferably about 1 to 48 hours, more preferably 5 to 16 hours. If the heat treatment time is less than 1 hour, the activation effect will be weak and the resulting products will vary widely, and if the heat treatment time exceeds 48 hours, the metal used for the electrode may be sintered or worn out. It becomes noticeable.

The reducing gas used in such heat treatment (b) includes N2. Co or a mixture of these gases with N
2. Gas diluted with CO2 or a mixture thereof, or gas obtained by incomplete combustion of natural gas, LPG, etc., will be used, but in particular, N2 of 10 to 40% by volume and N2 of 10 to 40% by volume are used. It is desirable to use a mixed gas having a composition in the range of 0.1 to 5 volume % of CO□ and 5 to 40 volume % of C◯.

In addition, as unsaturated hydrocarbons, acetylene, ethylene, propylene, butylene, etc., which are in a gaseous state at room temperature, are used, and a neutral gas such as H2 or He is used as a balance gas.
The target oxygen sensor element is heat-treated in an atmosphere containing such unsaturated hydrocarbons at a concentration in the range of 1100 ppm to 10% by volume, preferably 500 ppm to 5% by volume. When the concentration of this unsaturated hydrocarbon is less than 1100 pp, the above-mentioned activation effect of the oxygen sensor element becomes weak, and the variation in the obtained products increases, and when it exceeds 10% by volume,
This is because carbon may precipitate during heat treatment and deteriorate the electrode.

Note that the reducing gas atmosphere and unsaturated hydrocarbon atmosphere employed during the heat treatment described above do not need to be constant; for example, in a reducing gas atmosphere, 0□ or air may be periodically introduced. It is equally possible to perform an atmosphere cycle in which a rich atmosphere and a dark atmosphere are alternately achieved by, for example,

In addition, although heat treatment in a reducing gas atmosphere and heat treatment in an unsaturated hydrocarbon atmosphere as described above can be performed individually, the desired effect can be obtained, but it is particularly important to perform these two treatments in combination. is more effective. These two treatments can be performed separately in manufacturing the oxygen sensor element, but by using a mixed gas containing a predetermined amount of unsaturated hydrocarbon in a reducing gas as the heat treatment atmosphere, It is efficient to do both at the same time. In addition, the amount of unsaturated hydrocarbon present in the reducing gas at that time is 1100 pp to 10% by volume, preferably 500 pp, as in the case of unsaturated hydrocarbon alone.
The concentration will be within the range of m to 5% by volume.

(Examples) In order to clarify the present invention more specifically, typical examples according to the present invention will be shown below, but the present invention should be construed in a limited manner by the description of such examples. It goes without saying that it is nothing.

In addition, the present invention can be implemented in various embodiments other than the detailed description of the present invention described above and the following examples, and as long as it does not depart from the spirit of the present invention, it is possible to implement the present invention in various embodiments as well as within the knowledge of those skilled in the art. It should be understood that any of the various embodiments implemented based on the above belong to the scope of the present invention.

Example 1 3 parts of clay as a sintering aid was added to 100 parts by weight of a mixture of 4 mol% Y2O3 and 96 mol% ZrO□.
ZrO□ raw material powder containing parts by weight is dry-pulverized, and then 10 parts by weight of polyvinyl butyral as a binder and D as a plasticizer are added to 100 parts by weight of this powder.
A slurry was prepared by adding 5 parts by weight of OP and further 100 parts by weight of toluene solvent, and its viscosity was adjusted. Thereafter, a zirconia green sheet for a solid electrolyte body having a thickness of 0.4 mm was formed from the obtained slurry using a doctor blade.

On the other hand, a porous sheet with a thickness of 0.2 rnm made of a ZrO2 raw material of 8 mol% Y2O3-92 mol% Zr0z containing 15% by weight of sublimable powder (theobromine) was prepared using a method similar to the method for producing the green sheet described above. A green sheet for a protective layer was formed.

Next, in order to obtain an oxygen sensor element having the structure shown in FIG. 1, the above-mentioned zirconia green sheet for a solid electrolyte body was used, and the following method consisting only of ZrO2 with no stabilizer added was applied to predetermined portions on the upper and lower surfaces of the zirconia green sheet. ZrO with various average particle sizes shown in Table 1, 15% by weight of powder and pt as catalyst metal
Using a cermet paste consisting of 85% by weight of powder of
4) and a reference electrode (6) were formed to obtain green sheets for various electrode-forming solid electrolyte bodies.

Furthermore, a spacer (12) for forming an air passageway (10) and a plate-like lid member (14) were prepared using the zirconia green sheet for solid electrolyte body.

Table 1 Furthermore, a zirconia green sheet for a solid electrolyte body similar to the above is used as a green sheet for a heater to provide an airtight layer (22), and on top of that a zirconia green sheet of A Rz O3 of 10
A obtained by adding 2 parts by weight of MgO to 0 parts by weight
An electrical insulating layer (20) is formed using an alumina paste prepared by blending 35 parts by weight of polyvinyl butyral, 710 parts by weight of DOP, and 20 parts by weight of butyl calpitol with respect to 100 parts by weight of powder raw material 12 (13). Screen print and onto this electrically insulating layer (20) Pt:
90% by weight - Affi20. : Heater element (1
6) Prepare a fourth sheet in which an electrically insulating layer (1B) is formed using the same Sarno-7 paste as the electrically insulating layer (20) so that the heater element (16) is embedded therein. did.

Thereafter, the four sheets prepared as described above (green sheet for electrode forming solid electrolyte body, green sheet for spacer, green sheet for plate-like lid member, and fourth sheet) and the green sheet for porous protective layer ( 8) were laminated and integrated, and then fired simultaneously at a temperature of 1400''C for 3 hours to produce various oxygen sensor elements having structures as shown in FIG.

Example 2 Using various firing elements obtained in the same manner as Example 1,
This was immersed for 10 minutes in a 0.5% hydrofluoric acid aqueous solution heated to 30°C, and then thoroughly washed with running water. Next, the device subjected to such treatment is immersed in a 10% Ca (NO:l)Z aqueous solution while remaining undried, the pressure is reduced, and the Ca (No.2 aqueous solution is applied to the porous protective layer of the device). After sufficiently penetrating the inside, the oxygen sensor element was subjected to ultrasonic cleaning, and then dried, thereby producing an acid-treated oxygen sensor element.

Example 3 Using various firing elements obtained in the same manner as Example 1,
Such an element (measuring electrode) was heat-treated in a reducing gas and an unsaturated hydrocarbon.

That is, NZ, H2 and CO2 gases are fed into a catalytic conversion reactor where CO/CO□/H2/N.

After converting the volume ratio to lo/2150/38 to prepare a base gas, propylene as an unsaturated hydrocarbon was added at a ratio of 0.5 part by volume to 100 volumes of this base gas. , into a reduction processing furnace, and in this reduction processing furnace, the firing element is heated at 800°C.
By performing heat treatment at a temperature of 5 hours, an oxygen sensor element subjected to the desired heat treatment was produced.

Example 4 Using various acid-treated elements obtained in the same manner as in Example 2, the elements were subjected to the same heat treatment in a reducing gas as in Example 3, thereby performing acid treatment and heat treatment. An oxygen sensor element was fabricated using the following method.

Examples 5 to 8 ZrCh raw material powder (4 mol% Y2O39) constituting the zirconia green sheet for solid electrolyte body in Example 1
6 mol% Zr0z), 15% by weight of various particles whose average particle diameter is shown in Table 2 below, and PL (catalytic metal)
An oxygen sensor element was produced by a simultaneous firing operation in the same manner as in Example 1, except that the electrodes (4, 6) were formed by screen printing using a cerment paste consisting of 85% by weight of powder. did.

Table 2 Next, Examples 2 to 4 were prepared for the obtained fired elements.
Hydrofluoric acid treatment and/or heat treatment in a reducing atmosphere were performed according to the same method as above to produce an oxygen sensor element subjected to the desired acid treatment and/or heat treatment.

Among the oxygen sensor elements thus obtained, those that were not subjected to any post-treatment were used as the elements of Example 5, while those that were subjected to only acid treatment, only heat treatment, or both were treated as the elements of Example 5. Examples 6 and 7 are elements of 8°.

The various oxygen sensor elements manufactured in each of the above examples were assembled into an oxygen sensor in the same manner as in the past, and their low-temperature operability and response were determined. We conducted a sex evaluation.

Note that low-temperature operability is evaluated by maintaining each sensor element at a predetermined temperature by applying t pressure to a heater element built into the sensor element to generate heat.
2. The excess air ratio in the gas to be measured consisting of N2 and air was varied, the sensor electromotive force was measured, and the excess air ratio when the sensor electromotive force reached 0.45■ was: λ0
It was used as a measure of low temperature operability.

In addition, the responsiveness was evaluated by driving an actual engine at a rotation speed of 1150 rprrl while each oxygen sensor element was maintained at a predetermined temperature by heat generated by supplying voltage to the built-in heater element. ,
When performing feedback control using such a sensor element, the feed hack frequency (FLC) at which the sensor electromotive force reaches between 0.30 and 0.60 V within a certain period of time was determined and used as a measure of responsiveness.

The evaluation results of the low-temperature operability and responsiveness of the oxygen sensor elements obtained in Examples 1 to 8 are shown in Tables 3 to 4 below and FIGS. 2 to 7, respectively. In addition, FIG. 2 and FIG. 3 respectively show N in each example.
o. The evaluation results for the sensor elements of No. 3 are shown, and the evaluation results of low-temperature operability shown in FIG. The particle size dependence of monoclinic ZrO2 powder and the particle size dependence of zirconia particles in the fired electrode are shown. Furthermore, the operability evaluation results shown in FIG. 6 and FIG. As is clear from the results shown in Tables 3 and 4 and FIGS. 2 to 7, the relationship between the particle size of the zirconia particles in the electrode and the particle size of the zirconia particles in the electrode exposed to the gas to be measured is clear from the results shown in Tables 3 and 4 and FIGS. The low-temperature operability of the oxygen sensor element can be improved by using a porous cermet electrode made of particles distributed with a particle size of 2 μm or less, and by applying prescribed acid treatment or heat treatment to such a porous electrode. It is understood that both the response and responsiveness can be greatly improved.

(Effects of the Invention) As is clear from the above description, in the oxygen sensor element according to the present invention, the electrode exposed to the gas to be measured has a porous cermet electrode structure with a large surface area, and the catalytic activity is increased. Therefore, the oxygen sensor element has excellent low-temperature operability and responsiveness, and according to the method of the present invention, it is possible to advantageously manufacture an oxygen sensor element with such excellent low-temperature operability and responsiveness. Moreover, the characteristics such as low-temperature operability and responsiveness of such an oxygen sensor element are further improved, and low-temperature measurement gases can be detected advantageously.

[Brief explanation of the drawing]

FIG. 1 is an exploded perspective view showing an example of a typical structure of an oxygen sensor element to which the present invention is applied, and FIG. 2 and FIGS. 3 is a graph showing the relationship between sensor element temperature and excess air ratio for oxygen sensor elements, and FIG. 3 is a graph showing the relationship between sensor element temperature and feedback frequency for various oxygen sensor elements obtained in Examples 1 to 8. It is a graph showing the relationship between. 2: Solid electrolyte body 4: Measuring electrode 6: Reference electrode 8: Porous protective layer 10: Air passage 12 Varnish spacer 14: Plate lid member 16: Heater elements 1B, 2
0: Electrical insulation layer 22: Airtight layer

Claims (14)

[Claims] (1) In an oxygen sensor element formed by supporting at least one pair of electrodes on an oxygen ion conductive zirconia solid electrolyte body, at least the electrode exposed to the gas to be measured out of the at least one pair of electrodes is made of a catalytic metal and ZrO_2. The ZrO_2 component is contained in the porous electrode as zirconia particles having a particle size of 2 μm or less and made of monoclinic ZrO_2 or partially stabilized zirconia. An oxygen sensor element characterized in that the oxygen sensor element is present in an amount of 5 to 60 parts by weight per 100 parts by weight of metal. (2) The zirconia particles are CaO, Y_2O_3
and 4 mol% of at least one of Yb_2O_3
The oxygen sensor element according to claim 1, wherein the oxygen sensor element is made of partially stabilized zirconia added in the following proportions. (3) When manufacturing an oxygen sensor element in which at least one pair of electrodes is supported on an oxygen ion conductive zirconia solid electrolyte body, among the at least one pair of electrodes,
At least, the electrode exposed to the gas to be measured is made of catalyst metal powder and monoclinic ZrO_2 with a particle size of 0.2 to 2.5μ.
By applying an electrode forming material prepared from the zirconia powder of m to the solid electrolyte body and firing it,
A method for manufacturing an oxygen sensor element, comprising the step of forming a porous cermet electrode. (4) When manufacturing an oxygen sensor element in which at least one pair of electrodes is supported on an oxygen ion conductive zirconia solid electrolyte body, at least one of the at least one pair of electrodes, which is exposed to the gas to be measured, is Metal powder and monoclinic ZrO_2
A step of applying an electrode forming material prepared from a zirconia powder having a particle size of 0.2 to 2.5 μm to the solid electrolyte body and then firing it to form a porous cermet electrode; A method for manufacturing an oxygen sensor element, comprising the step of treating the porous electrode formed by such firing with an acid. (5) When manufacturing an oxygen sensor element in which at least one pair of electrodes is supported on an oxygen ion conductive zirconia solid electrolyte body, at least one of the at least one pair of electrodes, which is exposed to the gas to be measured, is Metal powder and monoclinic ZrO_2
A step of applying an electrode forming material prepared from a zirconia powder having a particle size of 0.2 to 2.5 μm to the solid electrolyte body and then firing it to form a porous cermet electrode; A method for manufacturing an oxygen sensor element, comprising the step of heat-treating the porous electrode formed by such firing in a reducing gas and/or unsaturated hydrocarbon atmosphere. (6) When manufacturing an oxygen sensor element in which at least one pair of electrodes is supported on an oxygen ion conductive zirconia solid electrolyte body, at least one of the at least one pair of electrodes, which is exposed to the gas to be measured, is Metal powder and monoclinic ZrO_2
A step of applying an electrode forming material prepared from a zirconia powder having a particle size of 0.2 to 2.5 μm to the solid electrolyte body and then firing it to form a porous cermet electrode; It is characterized by comprising the steps of: treating the porous electrode formed by such firing with an acid; and heat-treating the porous electrode formed by such firing in a reducing gas and/or unsaturated hydrocarbon atmosphere. A method for manufacturing an oxygen sensor element. (7) The zirconia powder is CaO, Y_2O_3
and 4 mol% of at least one of Yb_2O_3
The manufacturing method according to any one of claims (3) to (6), comprising partially stabilized zirconia added in the following proportions. (8) The manufacturing method according to claim (5) or (6), wherein the heat treatment under the reducing gas atmosphere and the heat treatment under the unsaturated hydrocarbon atmosphere are performed simultaneously. (9) When manufacturing an oxygen sensor element in which at least one pair of electrodes is supported by an oxygen ion conductive zirconia solid electrolyte body, among the at least one pair of electrodes,
At least the electrode exposed to the gas to be measured is made of catalyst metal powder and partially stabilized zirconia with a particle size of 0.2 to 2.
A method for manufacturing an oxygen sensor element, comprising the step of applying an electrode forming material prepared from a 0 μm zirconia powder to the solid electrolyte body and then firing it to form a porous cermet electrode. . (10) When manufacturing an oxygen sensor element in which at least one pair of electrodes is supported on an oxygen ion conductive zirconia solid electrolyte body, at least one of the at least one pair of electrodes is exposed to a gas to be measured using a catalyst. An electrode forming material prepared from a metal powder and a zirconia powder made of partially stabilized zirconia and having a particle size of 0.2 to 2.0 μm is applied to the solid electrolyte body and then fired to form a porous cermet. A method for manufacturing an oxygen sensor element, comprising the steps of: forming an electrode; and treating the porous electrode formed by such firing with an acid. (11) When manufacturing an oxygen sensor element in which at least one pair of electrodes is supported on an oxygen ion conductive zirconia solid electrolyte body, at least one of the at least one pair of electrodes, which is exposed to the gas to be measured, is An electrode forming material prepared from a metal powder and a zirconia powder made of partially stabilized zirconia and having a particle size of 0.2 to 2.0 μm is applied to the solid electrolyte body and then fired to form a porous cermet. A method for manufacturing an oxygen sensor element, comprising the steps of: forming an electrode; and heat-treating the porous electrode formed by such firing in a reducing gas and/or unsaturated hydrocarbon atmosphere. (12) When manufacturing an oxygen sensor element in which at least one pair of electrodes is supported on an oxygen ion conductive zirconia solid electrolyte body, at least one of the at least one pair of electrodes, which is exposed to the gas to be measured, is An electrode forming material prepared from a metal powder and a zirconia powder made of partially stabilized zirconia and having a particle size of 0.2 to 2.0 μm is applied to the solid electrolyte body and then fired to form a porous cermet. a step of forming an electrode, a step of acid-treating the porous electrode formed by such firing, and a step of heat-treating the porous electrode formed by such firing in a reducing gas and/or unsaturated hydrocarbon atmosphere. A method for manufacturing an oxygen sensor element, comprising: (13) The zirconia powder is CaO, Y_2O_
3 and Yb_2O_3 in a proportion of 4 mol% or less. Method. (14) The manufacturing method according to claim (11) or (12), wherein the heat treatment under the reducing gas atmosphere and the heat treatment under the unsaturated hydrocarbon atmosphere are performed simultaneously.