JPH02276956A - Oxygen sensor and production thereof and method for preventing poisoning - Google Patents

Abstract

PURPOSE:To prevent the deterioration in the characteristics of the oxygen sensor by a gaseous or superfine particulate silicon compd. by sticking at least one kind of oxides of Mg, Ca, Sr, and Ba onto the surface or into pores of a protective layer. CONSTITUTION:The oxygen sensor is constituted of a blind cylindrical body 1 forming the partition wall of an oxygen ion conductive solid electrolyte, a reference electrode 2 and measuring electrode 3 provided in contact therewith and the protective layer 4 on the measuring electrode 3. The protective layer 4 is formed by sticking at least one kind among the oxides of the Mg, Ca, Sr, and Ba onto the surface or into the pores thereof. Stabilized or partially stabilized zirconia materials formed by compounding prescribed stabilizers, for example, yttria, calcia, magnesia, etc., with zirconia in particular are used as the solid electrolyte material. A pressure molding method, such as rubber press method, is adopted to form the above-mentioned material to the cylindrical body 1. Platinum catalyst metals, such as platinum, rhodium and palladium are used as the electrode material and plasma thermally sprayed layers, such as alumina and spinel are used as the protective layer 4.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention mainly relates to an oxygen sensor for measuring the amount of oxygen contained in exhaust gas from internal combustion engines, boilers, etc.
The present invention aims to provide a particularly durable oxygen sensor, a method for manufacturing the same, and a method for preventing poisoning.

(Prior art) Exhaust gas, which is discharged from internal combustion engines such as automobiles, boilers, etc., as a gas to be measured has been conventionally used to measure oxygen ion conductive solid electrolytes such as zirconia porcelain, based on the principle of oxygen concentration batteries. It is known to detect the oxygen concentration in internal combustion engines and control the air-fuel ratio or combustion state of such internal combustion engines.

In this type of oxygen sensor, which is an oxygen concentration detector, predetermined electrodes are provided on the inner and outer surfaces of a solid electrolyte body having a bottomed cylindrical shape, plate shape, etc. as a sensor element, and the inner electrode is The structure is such that the reference electrode is exposed to the atmosphere and exposed to a reference gas with a reference oxygen concentration, while the outer electrode is exposed to exhaust gas, which is the gas to be measured, and used as the measurement electrode. The oxygen concentration in the exhaust gas is measured based on the difference in oxygen concentration between the reference electrode and the measurement electrode (by sensing the electromotive force).

By the way, a conventional oxygen sensor of this kind includes an element body having a predetermined shape and made of a solid electrolyte with predetermined oxygen ion conductivity, which is its main element, and a plurality of electrodes provided on the surface of the element body. In the oxygen sensor element, the measurement electrode, which is the outer electrode, is worn out or damaged by the action of the high-temperature exhaust gas that is the gas to be measured, causing problems such as deterioration of the sensor function. In order to protect the measurement electrode, a porous protective coating layer made of spinel or the like is formed on the measurement electrode to a predetermined thickness by plasma spraying, printing and baking, or the like.

(Problem to be Solved by the Invention) However, even in a sensor element provided with such a protective coating layer, when used as an oxygen sensor, for example, by being attached to the exhaust pipe of a car, it is difficult to detect inferior products containing organic silicon, etc. Particulate or gaseous substances of organic and inorganic silicon compounds, which are generated due to incorrect use of fuel or the combustion of silicon compounds contained in engine gaskets, pass through the pores of these protective coating layers and attach to the porcelain surface. Silicon poisoning of oxygen sensors has become a problem because it adsorbs to the surface of the measurement electrode or the interface with porcelain, causing defective sensor output or deterioration of response.

On the other hand, in order to prevent the silicon compound from reaching the measurement electrode, it is possible to make the protective coating thicker or make the pores smaller, but even with this method, it is not possible to prevent the fine particles of the silicon compound component from reaching the measurement electrode. However, it is not possible to completely prevent the arrival of gaseous substances, and if the protective layer is made thicker and the pores are made smaller, the initial response will deteriorate, and the fine pores will easily become clogged. However, there were problems such as a gradual deterioration of responsiveness, and the results were not necessarily satisfactory.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide an oxygen sensor and a method for preventing poisoning, which have particularly good durability against poisoning of silicon components. It should be noted that when an oxygen sensor that has been poisoned by silicon is actually installed in a car and the emission value of exhaust gas is measured, it can be easily seen that NOx exceeds the regulation value compared to an oxygen sensor that has not been poisoned by silicon. Therefore, silicon poisoning is defined as the oxygen sensor being exposed to an atmosphere of silicon compounds and exceeding the exhaust gas regulations for automobiles, particularly the regulation values for NOx.

(Means for Solving the Problems) The oxygen sensor of the present invention includes a partition made of an oxygen ion conductive solid electrolyte, a measurement electrode and a reference electrode provided in contact with the partition, and a protective layer on the measurement electrode. Mg, Ca on the surface of the protective layer or in its pores.
, Sr, and Ba.

In addition, in the oxygen sensor of the present invention, aluminum oxide, silicon oxide, or a compound of both may be present on the surface of the protective layer of the oxygen sensor or in the internal pores together with oxides of Mg, Ca, Sr, and Ba. It is more preferable if an oxide such as mullite is attached. Further, it is preferable that the oxygen sensor element has a means for heating the detection part of the oxygen sensor element.

In addition, such an oxygen sensor includes a reference electrode that is exposed to a gap in which a reference gas is surrounded by winding it into a cylindrical shape or stacking a plurality of layers in a flat plate shape, and a porous protective layer that is provided in contact with the plate-shaped solid electrolyte. and a measurement electrode exposed to a gas to be measured through the oxygen sensor, wherein at least the measurement electrode and the porous protective layer are co-fired, and at least the pores in the porous protective layer are ! Jg,
Ca, Sr.

Preferably, particles containing at least one component of Ba are present.

Moreover, such an oxygen sensor element contains Mg, Ca, Sr,
It can be manufactured by coating or impregnating the protective layer with a solution, suspension, or paste of a Ba compound or oxide, and then heat-treating it to form each oxide. It is preferable that other oxides be applied simultaneously by a similar method or in advance.

Alternatively, the oxygen sensor element may be manufactured by applying Mg, Ca, Sr, or Ba to the surface or inside of the protective layer by a chemical or physical method, and then heating to form the respective oxides.

In the above manufacturing method, the solution and the like can be applied to the protective layer by using an air spray gun, by dipping, etc. as appropriate.

(Function) As the oxygen ion conductive solid electrolyte material forming the oxygen sensor element body (substrate) constituting the oxygen sensor, various known materials can be mentioned, but in the present invention,
In particular, zirconia has certain stabilizers, e.g. IJ
A (Y2O2), Calcia (Cab), Magnesia (Mg
A stabilized or partially stabilized zirconia material containing O), ytterbia (yb2o3), etc. is preferably used. In addition, as is well known, such a solid electrolyte material may contain a predetermined sintering aid, such as clay such as kaolin or 5in.
2. Al2O3 and Fe2O3 can also be blended.

Using a material selected from these solid electrolyte materials, a pressurizing method such as the conventional rubber press method is used to form a molded body that provides the element body of the oxygen sensor element in a predetermined shape. A molding method is employed, whereby a molded body that provides an element body (substrate) having a shape such as a cylinder with a bottom, which is the main body of the oxygen sensor element, is molded.

Another method is to add 5wt% to 2Qwt% of binder and a solvent to these solid electrolyte materials to form a slurry, form it into a tape using a doctor blade, etc., and then layer and bond the tape. The base body of the plate-shaped oxygen sensor element will be molded.

After firing these molded bodies to make dense porcelain,
The oxygen sensor element is formed by a known method such as applying an electrode and a protective coating or applying an electrode material to become an electrode layer by firing on the molded body, and then applying a protective layer on the electrode material and integrally firing it. be done.

The electrode material may be a platinum group catalyst metal such as platinum, rhodium, or palladium, or an alloy of gold or silver, or a mixed layer of ceramic particles (generally an oxygen ion conductive solid electrolyte is used) and the above heat-resistant metal. (cermet) etc. are used.

As the protective layer, there is a ceramic plasma sprayed layer, and alumina, spinel, etc. are generally used.

In addition, in the method of integral firing, the printed layer of alumina,
Alternatively, an adhesive layer of porous tape of solid electrolyte may be used. In this case, the method for forming the porous tape that will become the protective layer may be the same doctor blade method as used for the solid electrolyte material base described above, but the organic matter, carbon, etc. will disappear by heating so that it becomes a porous body after firing. 10 for zirconia, alumina, etc. that make up the protective layer
In order to achieve both durability and responsiveness of the electrode, a mixture containing 40% or more of pores of about 11 to 1 μm (by mercury intrusion method) based on the total pores after firing is used. desirable. The thickness of the protective layer is 10μ
A thickness of ml to 1 mm is sufficient, but as the thickness increases, the gas permeability within the protective layer deteriorates and the responsiveness of the sensor deteriorates, so it is desirable to adjust the porosity ratio appropriately within the range of 5% to 60% as the thickness increases. The protective layer does not need to be a single layer; for example, if a plurality of protective layers are used so that the porosity increases from the electrode side toward the surface, the clogging prevention effect of the protective layer will be enhanced. or,
In particular, the porous protective layer formed by using a ceramic green sheet as the protective layer and firing it at the same time as the measurement electrode installed on the solid electrolytic substrate of the substrate is more efficient than the porous protective layer formed by plasma spraying. Since it can support precipitates such as MgO, the silicon poisoning prevention effect becomes even more excellent. The reason is that the pores in the porous layer formed by plasma spraying are relatively small, so MgO
On the other hand, a porous protective layer using ceramic green sheets is a mixture of organic matter, carbon, etc. that disappears when heated, and can only be supported in small amounts because they tend to clog. This is because the pores in the porous layer can be kept relatively large and a large amount of precipitates such as MgO can be supported.

Whether by plasma spraying or integral firing, these protective layers are exposed to a relatively high temperature such as the melting temperature of the protective layer material or the sintering temperature, and the outer surface of the protective layer and the inside of the layer are The surface of the pores (through which the gas to be measured permeates) has very low activity, that is, it is a stable surface with no gas adsorption ability.

Therefore, gaseous substances can be smoothly transferred to the electrode surface and the interface between the electrode and the oxygen ion conductive porcelain (
(three-phase interface), and the oxygen sensor will show an output according to the 0□ partial pressure of the gas to be measured. On the other hand, foreign substances emitted from automobile engines, combustion residue of engine oil, Pb contained in gasoline, etc., which fly to the surface of the oxygen sensor element as relatively large particles in the form of oxides, are Although it will deposit on the layer surface and some of its pores, by appropriately adjusting the porosity and pore size distribution of the protective layer, there will be no response deterioration due to clogging, etc., and electrode poisoning will also be prevented. It will be done.

However, the organic silicon contained in inferior fuel etc. burns or decomposes in the cylinder of the engine, producing gaseous silicon compounds and granular compounds or silica (S).
102) At the same time that the gas flies to the surface of the oxygen sensor element protective layer as particles and is deposited on the surface, the gas passes through the protective layer and adheres to the electrode surface and three-phase interface, poisoning the electrode. .

According to the inventor's observations and experimental results, especially in the case of silicon compounds, the sensor characteristics are poor even when a relatively small amount of silicon-based particles are deposited on the protective layer (response deterioration due to clogging is unlikely). Therefore, it was assumed that the cause was poisoning of the electrode, and silicon poisoning was a particular problem.

In the most preferred embodiment, the present invention particularly effectively prevents deterioration of oxygen sensor characteristics caused by gaseous or ultrafine silicon compounds by providing active particles mainly made of magnesia on the surface of the protective layer or in the pores. It is.

The reason why magnesia in the protective layer is effective is that it captures active silicon (in a silicon compound) on its surface, converts silicon into stable silica (S10□) with oxygen in magnesia (MgO), and further binds magnesia and silica. This is thought to be to prevent silicon from reaching the porcelain surface, the electrode surface, or the interface between the electrode and the porcelain.

Therefore, in order to bring the magnesia surface into a highly active adhesion state, there are preferable adhesion methods and forms. The state will be explained below.

■Layered state attached to the outer surface of the protective layer (Figure 6) Magnesia powder is prepared, dispersed with a binder in water or an organic solvent, and solidified by spraying with an air gun, dipping the device, brush painting, printing, etc. After adhering to a predetermined portion of the protective layer 22 that protects the electrode 24 on the surface of the electrolyte 23,
It is dried and fired to form a layer mainly composed of magnesia.

Magnesium carbonate (MgCO) instead of magnesia powder
s) Powders such as magnesium hydroxide may be used. For example, these are slightly soluble in water, so
Adhesion to the protective layer 22 is improved. For magnesia powder, it is preferable to grind coarse particles such as molten magnesia to form fine particles because an active surface can be obtained.

Compared to the protective layer 22, the magnesia layer 21 is preferably deposited with significantly better gas permeability in view of the responsiveness of the oxygen sensor. For this purpose, as an adhesive for magnesia, for example, alumina zonopesilica sol or the like can be mixed.

Further, if the magnesia is fine, it may be formed into a layer by utilizing its agglomeration effect. In addition to significantly improving gas permeability, the layer also peels off from the surface that captures other adhesion-clogging components contained in the exhaust gas, thereby preventing clogging.

The thickness of the Magne 27 layer is preferably 10 μm or more and 300 μm or less. Further, the baking temperature is 1500°C or less, preferably 1000°C or less. When heat is applied above 1500℃, the activity of magnesia tends to decrease,
If the temperature is below ℃, there is almost no change in activity.

In the case of a sensor element in which the element molded body, electrode, and protective layer are integrally fired, good adhesion strength can be obtained if this magnesia layer is also integrally fired.

There is also a method of vapor depositing metallic magnesium on the outer surface of the protective layer, or oxidizing it after sputtering to form magnesia, and by repeating this process, a predetermined thickness can be obtained. Alternatively, the operation of forming the protective layer 22 again on the magnesia layered porcelain layer 21 and then forming another magnesia layer may be repeated to obtain a sandwich-like laminated structure of magnesia protective layers.

■ State of adhesion to the surface of the protective layer and inside the pores (Fig. 7) After impregnating the protective layer 22 with an aqueous solution such as a magnesium chloride solution, an aqueous hydrochloric acid solution of magnesium hydroxide, or an organic solvent solution, each Fine and active MgO particles 25 can be attached by heating above the temperature at which the magnesium salt decomposes. In this case, even a relatively small amount shows sufficient effects. Alternatively, a water-soluble magnesium salt may be precipitated in the protective layer as an insoluble magnesium salt, and then heated to a predetermined decomposition temperature or higher to form MgO particles. In either case, the precipitated M
The larger the specific surface area of the gO particles, the better the effect of preventing silicon poisoning, so it is desirable to have a large number of fine Mgo particles of 0.1 Atm or less.

If the protective layer 22 is impregnated with, for example, an aluminum salt solution and heated in advance to adhere the alumina particles 26, and then magnesia is applied by the above method, an even better effect will be obtained. Instead of the alumina particles 26, particles of silica, spinel, zirconia, etc. can also be used.

The thickness of the protective layer 22 is preferably 50 μm or more.

Furthermore, if the protective layer 22 is coated with a smaller porosity closer to the measurement electrode and larger closer to the measurement electrode, the effect of magnesia will be even better. The weight ratio of magnesia attached or supported on the protective layer is preferably 0.05% to 60%, more preferably 0.5% to 20%. If it is a known oxygen sensor, it is 0.1 to 200 m per element.
This amount corresponds to the adhesion amount of g.

In order to adjust the amount of support, the concentration of the solution may be varied, or the impregnation and baking may be repeated multiple times using solutions of the same concentration. Furthermore, magnesia does not necessarily need to be uniformly dispersed within the protective layer, and the amount of magnesia supported may have a gradient from the measurement electrode side to the surface. In this case, if the amount of support increases toward the surface, it is effective against poisoning, and conversely, if the amount of support increases toward the surface, it is effective against clogging.

When the protective layer is provided by the green sheet lamination method,
Magnesia can also be provided in the protective layer by mixing magnesia or a magnesium compound that changes to magnesia after firing with the ceramic forming the protective layer during green sheet molding. In this case, since not all of the magnesia is exposed to the porous pores, a larger amount of magnesia is required than in the case where 7 gnesia is supported by a solution or the like after firing as described above.

(2) State where magnesia particles 25 are dispersed and attached to the alumina coat layer (FIG. 8) A ceramic particle layer 27 made of porous alumina may be attached to the surface of the protective layer 22 to support the magnesia particles 25. The alumina layer 27 is made of relatively coarse grained and porous T.
- It is better to use alumina. Further, instead of alumina, other stable ceramic particles such as zirconia, spinel, silica, etc. may be used.

■Protective layer 22 with pt group metal catalyst attached (Fig. 9)
In a state where the catalyst layer 28 is formed inside, the durability of the catalyst layer 28 is improved by attaching the layer 21 mainly made of magnesia to the outer surface thereof.

It is also possible to attach the catalyst metal 28 within the magnesia layer 21, and in this case, the silicon adsorption ability of magnesia can be improved, resulting in an even more effective effect.

■Condition of oxygen sensor with heater In order to enhance the effect of magnesia, it is better to keep the sensor surface temperature a little higher. Therefore, it is preferable to use a sensor with a heater.

In addition, in the case of an oxygen sensor with a heater, temporarily increase the power of the heater during use, or in the case of exhaust gas, take advantage of the high exhaust temperature to raise the element temperature to 850°C or higher, preferably 900°C or higher. By keeping it for 30 minutes to 30 minutes, the deterioration of sensor characteristics caused by silicon can be recovered. This is effective when a large amount of silicon components fly in and the effect of the magnesia layer alone cannot prevent deterioration of sensor characteristics.

It is thought that the sensor characteristics are restored by the silicon compound attached to the electrode surface turning into stable silica (Si20) by heating, or by sintering the silicon compound and reducing its surface activity. It will be done. Although Mg oxide has been described in detail as the most preferred embodiment, Ca
It goes without saying that the provision of oxides of , Sr, and Ba, or the involvement of a plurality of oxides, can be carried out in the same manner as in the case of Mg oxide.

(Example) FIGS. 1 to 3(a) and Q) are diagrams each showing an example of an element main body of an oxygen sensor element of the present invention. First of all,
For example, 94 mol% zirconia and 6 mol% zirconia) I
A small amount of clay was added as a sintering aid to the solid electrolyte raw material consisting of JA, and after thorough mixing, calcining was performed at 1000° C. for 3 hours. The obtained calcined product was milled for 20 hours using a ball mill, and then polyvinyl alcohol was added as a binder at a ratio of 1% by weight (based on solid content) to the resulting slurry, and then a spray dryer was used to mill the calcined product. By granulating, solid electrolyte material powder (granulated powder) having a particle size of about 50 μm was produced.

Next, rubber press molding was performed using the obtained granulated powder of the solid electrolyte material to produce a bottomed cylindrical body and a plate-like sheet. After firing, the bottomed cylindrical body 1 is provided with a reference electrode 2, a measurement electrode 3, and a protective layer 4 at predetermined portions to produce a bottomed cylindrical oxygen sensor element main body 5, and the plate-like sheet is provided with electrodes 2. 3 and a protective layer 6.7 were provided and laminated, and then integrally fired to produce a plate-shaped oxygen sensor element main body 10.

That is, as shown in FIG. 2 as an enlarged view of the detection part of the bottomed cylindrical oxygen sensor element 5 shown in FIG. A porous platinum layer is provided as a reference electrode 2 on the gas side, and a porous platinum layer is provided as a measurement electrode 3 on the gas side to be measured. The measurement electrode 3 is covered with a porous protective layer 4 for protection. The porous protective layer 4 was formed by plasma spraying spinel powder using Ar/N2 thermal spray gas. The thickness, porosity, and pore diameter were adjusted by adjusting the spinel powder particle size, thermal spraying power, etc.

Further, as shown in FIG. 3(a) showing the external appearance of the plate-shaped oxygen sensor element 10, and FIG. 3(b) showing the AA' cross section of the detection part, the measuring electrode 3 is made of a porous ceramic printed layer. It is doubly covered and protected by a lower porous protective layer 6 consisting of a porous ceramic tape molded body and an upper porous protective layer 7 formed by bonding and integrally firing the porous ceramic tape molded body. In this embodiment, the lower protective layer 6 is denser than the upper protective layer 7, and has lower permeability to the gas to be measured.

Furthermore, a heater heat generating section 8 is integrated into the plate-shaped sensor element main body 10 via an insulating layer 9.

Next, an assembly structure of an oxygen sensor using a bottomed cylindrical oxygen sensor element will be described with reference to FIG. For examples of plate-shaped oxygen sensor elements, see, for example, Japanese Patent Application Laid-Open No. 60-15
Since the one disclosed in Publication No. 0450 can be used, its explanation will be omitted.

In FIG. 4, the oxygen sensor element main body 5, which has a cylindrical shape with a bottom, is connected to an exhaust gas (not shown) passing through an exhaust gas pipe (not shown).
The oxygen sensor element is housed in a housing 11 using a sealant 12 made of talc, a metal washer 13, and a metal ring 14 so that the inside of the cylinder is airtightly separated from the oxygen sensor element. A heating heater 15 is housed within the cylinder of the main body 50. A bottomed cylindrical metal cover 16 is provided on the outer periphery of the closed end side of the oxygen sensor element main body 5 to prevent the exhaust gas from directly hitting the oxygen sensor element detection section, and the upper end thereof is attached to the housing. 1
It is fixed to the bottom of 1. In addition, this metal cover 16
, a looper 17 is cut out toward the inside of the metal cover 16 on the side wall surface thereof, and an exhaust gas inlet 18 is formed.
is formed.

The heating heater 15 inserted and arranged in the cylinder of the oxygen sensor element main body 5 in FIG. A ceramic heater constructed by embedding a heating wire 20b can be used.

Example 1 Oxygen sensor elements (1) to (4) shown below were manufactured, assembled into an oxygen sensor, and the durability of the oxygen sensor performance was investigated.

■ Magnesia powder with an average particle size of 0.7 μm was made into a paste by adding a binder dispersant and an organic solvent, and after printing on the porous protective layer of the plate-shaped sensor element shown in Fig. 3,
It was dried at ℃ for 30 minutes and baked at 600℃ for 1 hour in the air. The thickness of the magnesia layer is 30 μm on average.

■This replica was made by dispersing magnesia powder with an average particle size of 0.3 μm in water with a binder added while stirring slowly, and placing the sensor element shown in Figure 1 in the solution until the measurement electrode was submerged, then pulling it out and drying it. was carried out three times. 800
Baked in air at ℃ for 30 minutes. The average thickness is 50 μm.

(2) Magnesium hydroxide was dissolved in a dilute aqueous hydrochloric acid solution to create a saturated solution at room temperature. The sensing portion of the plate-shaped sensor element shown in FIG. 3 was immersed in this solution, and then treated in air at 600° C. for 1 hour to deposit magnesia in the pores in the protective layer and on the surface.

(2) Alumina sol and water were added to porous γ-alumina powder with an average particle size of 3.7 μm, and the sensor element shown in FIG. 1 was immersed in the solution and baked at 500°C.

This sensor element was immersed in the solution used in (1) above, and then baked in the air at 600°C for 1 hour.

■ Platinum and rhodium are added to alumina on the detection part coating of the plate-shaped sensor element shown in Figure 3 in a ratio of 10:1:0.1.
A catalyzed alumina porous layer with a thickness of 10 μm was formed at a weight ratio of 10 μm.

Further, a suspension was prepared by adding alumina sol to magnesia powder having an average particle size of 3 μm so that the amount was 5 wt % of the total. The plate-shaped sensor element was immersed in this suspension to form a magnesia layer with a thickness of 25 μm.

A magnesia layer with a thickness of 150 μm was formed under the conditions of ■■.

Silica powder with a particle size of 1.3 μm was added at 12 wt % to magnesia under the conditions of ■■.

Oxygen sensor elements (1) to (2) were prepared as described above, and a durability test was conducted using an engine bench.

For the durability test, a four-cylinder gasoline engine with 1.51 EGI was used, and operating conditions were selected in which the exhaust gas temperature varied between 400°C and 700°C in a 30-minute cycle.

Organic silicones (B, P, about 80°C) were added to the gasoline so that the content was 0.03 g per 1β at 81 minutes. The λ characteristics and response time (TRL) were measured before durability and after 10 hours of durability.

The λ characteristic was determined by changing the λ value of the engine exhaust gas from 0.95 to 1.05 using an external signal, and measuring the λ value when the sensor output reached 0.4V.

The λ value of exhaust gas is determined using a gas analyzer.

Additionally, the exhaust gas temperature is controlled at 350°C ± 10°C.

The response time (TRL) was determined as the time required for the output to reach 0.4V when λ was changed from 0.95 to 1.05 using the same engine. And the result is ΔTRL(-T
Displayed as (after RL durability - before TRL durability).

The number of samples was 3 for each condition, test N.

1, 4. 6. 8. On 9.11.13.15, the heater heating voltage was set to constant C113V, and
For No. 2.5°12, the heater heating voltage was adjusted so that each element temperature was as shown in Table 1. Also, the λ value, AT
For all R5 measurements that involve heater heating, input C.

Measured at 13V. Further, the element temperature was the maximum temperature of the sensor element during durability, and the outer surface of the element was measured using an R thermocouple with a wire having a diameter of 0.2 mm. The results are shown in Table 1.

From the results in Table 1, all the oxygen sensors of the present invention exhibit better durability than the comparative examples.

Example 2 After immersing the detection part of the plate-shaped sensor element shown in Fig. 3 in a saturated aqueous solution of each nitrate of Mg, Ca, Sr, and Ba and a mixed solution of Mg and Ca, it was exposed to air at 900°C for 1 hour. Each i,! gO, Cab, SrO, BaO and! Five types of devices were prepared in which AgO, CaO composites were adhered to the protective layer and the voids in the measuring electrodes or on the surface thereof, and assembled as oxygen sensors as shown in FIG. 4.

A total of six types of oxygen sensors, including these five types and a comparative sensor without any special treatment, were subjected to durability tests using an engine bench. For the durability test, a 4-cylinder gasoline engine with 1.51 EGI was used, the exhaust gas temperature was kept constant at approximately 500°C, and organic silicon was added to the gasoline so that the silicon content was approximately 0.02 g per 1 β.
I did a time durability test.

The results are shown in Table 2.

The λ characteristics and response time (TR) were measured in the same manner as in the previous example.

As is clear from Table 2, even the oxides of Ca, Sr, and Ba and their composites have a higher
Similar to the oxide of g, it also showed good results against silicon poisoning. However, the change in λ value was the smallest in the case where Mg oxide was added, and showed the best results against silicon poisoning.

(Effects of the Invention) As is clear from the above detailed explanation, according to the oxygen sensor and the manufacturing method thereof of the present invention, oxides of Mg, Ca, Sr, and Ba are present on the surface of the protective layer or in the pores. By attaching at least one type of silicon compound, deterioration of the characteristics of the oxygen sensor due to gaseous or ultrafine silicon compounds can be prevented. Also, Mg, Ca.

Since it is a simple method of adding oxides of Sr and Ba onto or into the protective layer, it is inexpensive and easy to produce.

[Brief explanation of drawings]

FIG. 1 is a partial sectional view showing an example of the oxygen sensor element main body used in the oxygen sensor of the present invention, FIG. 2 is a sectional view showing details of the embodiment shown in FIG. 1, and FIG. 3(a) , (b) are respectively a perspective view and a sectional view showing another example of the oxygen sensor element main body used in the oxygen sensor of the present invention, and FIG. 4 is an example of the oxygen sensor element used in the oxygen sensor of the present invention. FIG. 5 is a partial cross-sectional view showing an example of the heating heater used in the present invention, and FIGS. 6 to 9 are cross-sectional views showing the adhesion state of magnesia in the present invention. 1... Bottomed cylindrical body 2... Reference electrode 3... Measuring electrode 4... Protective layer 5... Oxygen sensor element body 6... Lower porous protective layer 7... Upper porous Quality protective layer...Heater heating part 9...Insulating layer 10...Plate sensor element body 11...Housing 12...Sealant 13...
...Metal washer 14...Metal ring 15...Heating heater 1
6...1 cover 17...louver 18...
・Exhaust gas inlet 19...Ceramic 20a...Lead wire 20
b...Heating wire 21...Layer mainly composed of magnesia

Claims (1)

[Scope of Claims] 1. Consisting of at least a partition wall of an oxygen ion conductive solid electrolyte, a measuring electrode and a reference electrode provided in contact with the partition wall, and a protective layer on the measuring electrode, and the protective layer An oxygen sensor using an oxygen sensor element characterized in that at least one of Mg, Ca, Sr, and Ba oxides is attached to the surface or in the pores thereof. 2. Any of the three oxides of aluminum oxide, silicon oxide, and a compound of aluminum oxide and silicon oxide, Mg,
2. The oxygen sensor according to claim 1, wherein a mixture with at least one of Ca, Sr, and Ba oxides is attached. 3. The oxygen sensor according to claim 1, further comprising a heating heater. 4. After coating or impregnating the protective layer with a solution, suspension or paste of Mg, Ca, Sr, Ba compounds or oxides, Mg, Ca, Sr.
3. The method for manufacturing an oxygen sensor according to claim 1, wherein the oxygen sensor is an oxide of r, Ba. 5. The method for manufacturing an oxygen sensor according to claim 1 or 2, wherein Mg, Ca, Sr, and Ba are applied to the surface or inside of the protective layer by a chemical or physical method, and then heated to form each oxide. . 6. A method for preventing poisoning of an oxygen sensor comprising at least an oxygen ion conductive solid electrolyte, a measuring electrode and a reference electrode provided in contact with the solid electrolyte, and a protective layer on the measuring electrode, the method comprising: In order to prevent the measurement electrode from being poisoned by silicon compounds present in the measurement gas, the method includes a step of depositing at least one of Mg, Ca, Sr, and Ba oxides on the surface of the protective layer or in its pores. A method for preventing poisoning of an oxygen sensor, characterized by: 7. An oxygen sensor composed of a solid electrolyte, a reference electrode in contact with the solid electrolyte, and a measurement electrode provided in contact with the solid electrolyte and exposed to a gas to be measured through a porous protective layer, the oxygen sensor comprising at least the measurement The electrode and the porous protective layer are fired at the same time, and particles containing at least one of Mg, Ca, Sr, and Ba are present in the pores of the porous protective layer. sensor.