JPH01213567A - Oxygen detecting element - Google Patents

Abstract

PURPOSE:To obtain a high-accuracy element which is less deteriorated in performance by the synergistic effect of 2 layers; a protective layer of a physical filter for detecting gas particles, etc., a thin catalyst film layer of a chemical filter for a material to be positioned, etc., and a porous catalyst carrying layer which equilibrates gases. CONSTITUTION:The oxygen detecting element 10 is constituted of a bag-shaped solid electrolyte body 20 consisting of ZnO2 partially stabilized by Y2O3, a porous reference gas side electrode 30 provided on the inside surface thereof, and a porous detecting gas side electrode 40 provided on the outside surface of the solid electrolyte body 20. The catalyst carrying layer 50 of a porous heat resistant metal oxide carrying platinum which is a catalyst, the porous thin catalyst film layer 60 consisting of platinum, and the protective layer 70 consisting of a porous spinel layer are successively laminated on the detecting gas side electrode 40 in the front end direction of the solid electrolyte body 20 to be exposed to the detecting gas. The deterioration in performance by the material to be positioned is thus decreased and the correct measurement of an air-fuel ratio is enabled by the synergistic effect of the three layers.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an oxygen detection element for measuring the temperature of oxygen in exhaust gas of, for example, an internal combustion engine or various types of combustion equipment.

[Prior Art] Conventionally, oxygen detection elements have been used to detect the oxygen concentration in detection gas such as exhaust gas in order to control the air-fuel ratio of internal combustion engines, various combustion devices, and the like.

As such an oxygen detection element, a reference gas side porous electrode is provided on one surface of an oxygen ion conductive solid electrolyte body such as zirconia that is exposed to a reference oxygen source such as the atmosphere, and the other surface is provided with a reference gas side porous electrode that is exposed to the ambient atmosphere. Some devices are equipped with a porous electrode on the detection gas side.

This oxygen detection element generates an electromotive force depending on the difference between the oxygen concentration in a detection gas such as exhaust gas and the oxygen concentration in a reference gas. Then, the partial pressure of oxygen gas in the detection gas is detected using this electromotive force.

However, the above-mentioned exhaust gas is generally non-equilibrium, that is, in a state where unburned components and oxygen coexist, and the air-fuel ratio in the wandering gas cannot be accurately measured as it is.

Therefore, a catalyst layer made of a platinum group element that promotes equilibration of exhaust gas is provided in the vicinity of the detection gas side porous buying electrode of the oxygen detection element as follows.

■ The porous electrode on the detection gas side is covered with a porous layer of heat-resistant metal oxide supporting a catalyst such as platinum (Japanese Patent Publication No. 57-181
46. Tokuko Sho 57-34900. Japanese Patent Publication No. 62-2451
48.

JP-A No. 61-153561, etc.).

■ The porous electrode on the detection gas side is covered with a porous layer of heat-resistant metal oxide, and the porous layer is roughly covered with a porous catalyst thin film layer made of a catalyst such as platinum (JP-A-55-13828, etc.).
.

[Problems to be Solved by the Invention] As mentioned in (2) above, when a catalyst is supported on a porous layer, the catalyst can be dispersed over a wide range, improving contact between the catalyst and exhaust gas, and reducing the amount of catalyst used. It becomes less.

However, if a large amount of substances such as lead that poison the catalyst are present in the exhaust gas, the performance of the catalyst will deteriorate significantly, making it impossible to detect the correct air-fuel ratio. Further, in some cases, the porous layer supporting the catalyst may collapse due to a reaction between the poisonous substance and the catalyst to produce a low-melting compound or the like. Further, in order to reduce this performance deterioration, it is good to increase the amount of catalyst used, but this may lower the porosity of the support layer or increase the amount of catalyst used.

Also, like ■ above, touch ILI! :Using a thin film layer reduces performance degradation against poisonous substances.

However, if the flow rate of the detected gas increases or the air-fuel ratio of the detected gas suddenly changes due to pressing the accelerator, etc., sufficient catalytic action may not be achieved, making it difficult to measure the correct air-fuel ratio. I won't be able to do that.

The present invention has little performance deterioration against poisonous substances, and
The objective was to detect the correct air-fuel ratio even if the flow velocity of the detected gas and the air-fuel ratio changed.

[Means for Solving the Problems] The gist of the present invention for solving the above problems is as follows: a solid electrolyte body having oxygen ion conductivity; a reference gas side porous electrode provided on one surface of the solid electrolyte body; , a detection gas side porous electrode provided on the other surface of the solid electrolyte body and exposed to the ambient atmosphere, and a heat-resistant metal oxide layered on the detection gas side porous electrode and supporting a catalyst made of a platinum group element. a porous catalyst support layer made of a porous catalyst support layer, a catalyst thin film layer laminated on the porous catalyst support layer and made of a porous thin film of a platinum group element, and a protection layer laminated on the catalyst thin film layer and made of a heat-resistant metal oxide. An oxygen detection element characterized by comprising a layer.

Here, typical materials for the solid electrolyte body having oxygen ion conductivity include solid solutions of zirconia and yttoria or calcia, and solid solutions of cerium dioxide, thorium dioxide, hafnium dioxide, and velor sky. A solid solution of a trivalent metal oxide, a solid solution of a trivalent metal oxide, etc. can be used.

In addition, platinum, gold, etc. can be used as the material for the porous electrode, and these are made into a paste with the material powder of the porous electrode as the main component, printed using thick film technology, and then sintered to form the porous electrode. The electrodes can be formed into porous electrodes using thin film techniques such as flame spraying or chemical plating or vapor deposition.

As the heat-resistant metal oxide constituting the porous catalyst support layer or the protective layer, spinel (MgO.AQ203), alumina (AQ203), etc. can be used.

A platinum group element is used as the catalyst supported on the porous catalyst support layer or forming the catalyst thin film layer.

These platinum group elements include ruthenium (Ru), rhodium (
Rh), palladium (Pd), osmium (O8) and platinum (Pt).

The porous catalyst supporting layer is formed by forming a porous layer made of the above-mentioned heat-resistant metal oxide on the porous electrode on the detection gas side using plasma [8=1], and then applying a solution containing the above-mentioned catalyst component to the porous electrode at night. For example, a method of dropping a chloroplatinic acid solution onto this porous layer and firing it, or a slurry of a mixture of a heat-resistant metal oxide powder and a catalyst component powder, such as γ-AQ203
It is formed by applying a slurry of a mixture of powder and platinum powder onto a solid electrolyte body and firing it.

Also, touch 11! The thin film layer can be formed as a porous thin film of the catalyst component by plasma spraying on the porous catalyst support layer, or a porous thin film can be formed by applying a paste containing the catalyst component onto the porous catalyst support layer and baking it. It is formed.

The protective layer is laminated on the catalyst thin film layer,
It is formed as a porous layer by plasma spraying or by coating and baking a slurry containing the heat-resistant metal oxide.

[Function/Effect] The oxygen detection element of the present invention includes a protective layer that acts as a physical filter for particles, etc. in the detection gas, a catalyst thin film layer that acts as a chemical filter for poisonous substances, etc. in the detection gas, It has a laminated layer with a porous catalyst support layer that has the function of equilibrating the detected gas.

Therefore, the present invention has the synergistic effect of these three layers,
The oxygen detection element has little performance deterioration with respect to poisonous substances and can measure the correct air-fuel ratio even with detection gas containing a large amount of unburned components.

[Example code] A first embodiment of the present invention will be described with reference to FIG.

In this embodiment, the present invention is applied to a bag-shaped oxygen detection element 10.

The oxygen detection element 10 is made of Z partially stabilized with Y2O3.
A bag-shaped solid electrolyte body 20 made of r02, a porous reference gas side electrode 30 provided on the inner surface of the solid electrolyte body 20
, a porous detection gas side electrode 40 provided on the outer surface of the solid electrolyte body 20.

The detection gas side electrode 40 in the distal end direction exposed to the detection gas of the solid electrolyte body 20 is provided with a catalyst support layer 50 of a porous heat-resistant metal oxide (spinel) supporting platinum, which is a catalyst. Porous bX thin film layer 6 made of platinum
0. Protective layers 70 made of porous spinel layers are sequentially laminated.

The oxygen detection element 10 as described above is manufactured, for example, as follows.

■ Zirconia powder adjusted to a composition that is partially stabilized with Y2O3 is molded into the bag shape shown in Figure 1, and
The solid electrolyte body 20 is manufactured by firing at a temperature of 1500°C.

■ A porous reference gas side electrode 30 made of platinum is formed on the inner surface of the solid electrolyte body 20 using an electroless plating method, and platinum is formed on the outer surface of the solid electrolyte body 20 using the same electroless plating method. A porous detection gas side electrode 4 made of
form 0.

(2) A porous layer of spinel with a thickness of approximately 50 to 100 μm is formed on the detection gas side electrode 40 by plasma spraying. This porous layer has a platinum concentration of 0.
A catalyst supporting layer 50 is formed by dipping in a chloroplatinic acid solution adjusted to 0.02 g/Q.

(2) Platinum is deposited on the catalyst support layer 50 by sputtering using platinum as a target plate to form a porous catalyst thin IN layer 60.

(2) On the catalyst thin film layer 60, a porous protective layer 70 made of spinel is formed with a thickness of about 50 to 100 um by the plasma spraying method in the same manner as in (1) above.

The porous electrodes 30, 40 can also be formed by a method other than the electroless plating method (2) above, such as electroplating, vapor deposition, paste baking, etc. Further, as the material for the electrodes 30 and 40, it is also possible to use not only platinum but also other metals such as gold and palladium.

Further, in order to strengthen the bond between the porous electrode 30.40 and the solid electrolyte body 20 and to form the electrode 30.40 stably, the surface of the solid electrolyte body 20 may be made uneven.

Further, the catalyst supporting layer 50 and the protective layer 70 on the detection gas side electrode 40 may be formed by a method other than the plasma spraying method using spinel powder, such as coating and baking a mud wall made of alumina, titania, or the like.

Further, the catalyst supporting layer 50. The catalyst of the catalyst thin film layer 60 may be one type or a mixture of two or more platinum group elements depending on the purpose.

Further, the catalyst may be supported on the catalyst support layer 50 by not only simple immersion as in (2) above, but also vacuum evacuation.

Further, the catalyst thin film layer 60 may be formed by coating and baking a solution of an organic compound of a platinum group element adjusted to a high viscosity, in addition to the sputtering method as described in (2) above. Furthermore, if fine particles of organic material that can be burned out by firing are added to this organic compound solution, the N'B layer is more likely to become porous.

Furthermore, when using the oxygen detection element IO of this example,
A heating element such as a ceramic heater may be inserted inside to heat the oxygen detection element 10 to a desired temperature.

A second embodiment of the present invention will be described with reference to FIG.

The oxygen detection element 110 of this embodiment has a hollow cylindrical body 120.
It has a structure in which the solid electrolyte body was circulated for 130 months.

The configuration of the present oxygen detection element 110 will be explained together with the manufacturing method.

(2) Zirconia powder adjusted to a composition partially stabilized with Y2O3 is mixed with an organic resin, and a zirconia green sheet with a thickness of about 0.25 mm, which will become the solid electrolyte body 130, is created by a doctor blade method.

■ Porous reference gas side electrodes 140. The electrode pattern that will become the detection gas side electrode 150 is formed by screen printing a paste containing platinum as a main component.

■ Overlap the electrode pattern of the detection gas side electrode 150,
A pattern of porous catalyst support layer 160 made of alumina paste containing 100% platinum powder is laminated by screen printing to a thickness of about 3 m.

■ Layer ζ, which becomes the catalyst support layer 160, is layered with a porous catalyst F' made of a paste containing rhodium powder as a main component.
A pattern that will become the dFA layer 170 is laminated to a thickness of about 3 um by screen printing.

(2) Overlying the layer that will become the catalyst thin film layer 170, a pattern that will become the porous protective layer 180 made of paste containing alumina as a main component is laminated to a thickness of about 15 um by screen printing.

■ Furthermore, on the detection gas side surface of the solid electrolyte body 130,
A heating element 20 made of a paste mainly composed of platinum is inserted through a layer which is formed by screen printing a paste mainly composed of alumina and becomes an insulating layer 190.
An electrode pattern with a value of 0 is printed by screen printing. A layer that will become the protective layer 210 of the heating element 200 is formed by screen printing a paste containing alumina as a main component.

(2) Glue a lid 230 to one end of the zirconia cylinder 120 having the communication hole 220. Then, on this zirconia cylinder 120, an adhesive layer 24 made of zirconia paste is applied.
The laminates produced in steps (1) to (3) above are wound and fixed through a wire.

■ The product manufactured in the above ■ is heated to 1450 to 1500℃.
The oxygen detection element 110 is obtained by performing integral simultaneous firing.

Note that the laminates manufactured in steps (1) to (3) above may be manufactured one by one, but after manufacturing a plurality of laminates at once, the laminates are cut one by one and rolled around the cylinder 120. You can turn it.

A third embodiment of the present invention will be described.

The oxygen detection element of this embodiment has the same structure as the second embodiment except for the structure of the protective layer laminated on the catalyst thin film Nζ, so the explanation will be omitted.

This oxygen detection element is formed and sintered without laminating the protective layer 180 in the second embodiment, but a spinel layer is formed as a protective layer near the tip by thermal spraying.

Next, oxygen detection elements of the following first to fourth comparative examples were created, and experiments 1 to 4 described below were conducted together with the oxygen detection elements of the first to third examples, and the results were are listed in the table.

First Comparative Example Bag-shaped solid electrolyte body 300 and porous reference waste side electrode 3
10, a porous detection gas side electrode 320, and a spinel porous layer 330 laminated on the detection gas side electrode 320 (see FIG. 3).

Second Comparative Example Same structure as the first comparative example, but with porous layer 330
An oxygen sensing element that differs in that platinum is supported on it.

Third Comparative Example Bag-shaped solid electrolyte body 400 and porous reference gas side electrode 4
10, a porous detection gas side electrode 420, a platinum-supported alumina catalyst support layer 430 laminated on the detection gas side electrode 420, and a spinel protective layer 440 further laminated on the catalyst support layer 430. An oxygen detection element consisting of (see Fig. 4).

Fourth Comparative Example Bag-shaped solid electrolyte body 500 and porous reference gas side electrode 5
10, a porous detection gas side electrode 520, a spinel protective layer 530 laminated on the detection gas side electrode 520, a porous catalyst thin film layer 540 made of platinum laminated on the protective layer 530, and a catalyst thin film. An oxygen detection element consisting of N540 and a spinel protective layer 550 (see FIG. 5).

Experiment 1 (Z curve characteristics) The oxygen detection element to be tested was attached to a metal shell used in a normal oxygen sensor, and then attached to a model gas generator.

Then, expose the reference gas side electrode of the oxygen detection element to the atmosphere,
The detection gas side electrode was connected to the test gas (COo, 9%).

H20, 3'1. C0213LC3He 500ppm
, the remainder is N 2 ) and air to form a model force with a desired air-fuel ratio.

Next, the relationship between the air-fuel ratio of this model gas and the electromotive force generated between the reference gas side electrode and the detection gas side electrode of the oxygen detection element, the so-called Z curve characteristic, is investigated.

Then, when the electromotive force changes sharply with respect to the stoichiometric air-fuel ratio, it is judged as good, and when the electromotive force changes gradually, it is judged as bad.

Experiment 2 (Transient response characteristics) The oxygen detection element to be tested was attached to a main metal fitting used in a normal oxygen sensor, and then attached to the exhaust pipe of an engine.

Then, the amount of fuel injected into the engine is self-feedback controlled to the stoichiometric air-fuel ratio based on the output of this oxygen detection element.

The output voltage of the oxygen detection element in rich and lean conditions during this control is measured (transient response characteristics).

Then, the difference in output voltage in lean mode is 50
A value of 0 mV or more was determined to be good, and a value less than 0 mV was determined to be poor.

Experiment 3 (Durability) In the same manner as Experiment 2, the oxygen detection element to be tested
00 hours, perform self-feedback control of the engine and observe changes over time in the controlled air-fuel ratio and the state of the protective layer (durability)
.

The control air-fuel ratio is 4/1 compared to the initial air-fuel ratio (A/F)
Those with a change of 00 or more or those with peeling of the protective layer were determined to be defective.

Experiment 4 (Lead Resistance) In Experiment 3, one gallon of gasoline (3,7
850) with 50 mg of lead added,
After operating for 100 hours, observe changes in the controlled air-fuel ratio and the state of the protective layer (lead resistance) as in Experiment 3.

The control air-fuel ratio is 4/1 compared to the initial air-fuel ratio (A/F)
Those with a change of 00 or more or those with peeling of the protective layer were determined to be defective.

In Experiment 3 (durability), the controlled air-fuel ratio of the first comparative example became larger than the predetermined value after 500 hours.

Further, in the second example, the protective layer peeled off after 750 hours.

** In Experiment 4 (lead resistance), the controlled air-fuel ratio was large on the rich side for 15 hours in the first example, 30 hours in the second example, 45 hours in the third example, and 40 hours in the fourth example. It changed to In addition, the protective layer peeled off in some cases.

As is clear from the table, the oxygen detection element of the above example is
It was confirmed that all had excellent performance in Experiments 1 to 4.

The oxygen detection element of the above embodiment balances the detection gas with a protective layer that acts as a physical filter for particles, etc. in the detection gas, and a catalyst thin film layer that acts as a chemical filter for poisonous substances, etc. in the detection gas. It has a porous catalyst support layer which has a layered structure.

Therefore, due to the synergistic effect of these three layers, the oxygen detection element of the above example has little performance deterioration against poisonous substances.
It is also estimated that the oxygen detection element can accurately measure the air-fuel ratio even with detection gas containing a large amount of unburned components.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the first embodiment of the present invention, FIG. 2 is an exploded perspective view of the second embodiment of the present invention, and FIGS. 3 to 5 are partially enlarged diagrams illustrating oxygen detection elements of comparative examples. It is a diagram. 10.110... Oxygen detection element 20.130, 300, 400, 500... Solid electrolyte body 30.140, 310, 410, 510... Reference gas side electrode 40.150, 320, 420, 520.・
・Detection gas side electrode 50.160.430...Catalyst supporting layer 60.170.540...Catalyst thin film layer 70.180
, 330, 440, 530, 550...Protective layer agent Patent attorney Tsutomu Sadatsu (and 2 others) Figure 1 Figure 2 Hoei 7&) Kumimi 22 (, 1 Figure 3 Figure 4'): Figure 25

Claims (1)

[Scope of Claims] A solid electrolyte body having oxygen ion conductivity, a reference gas side porous electrode provided on one surface of the solid electrolyte body, and a reference gas side porous electrode provided on the other surface of the solid electrolyte body, and a reference gas side porous electrode provided on the other surface of the solid electrolyte body, a porous electrode on the detection gas side that is exposed to the atmosphere; a porous catalyst support layer of a heat-resistant metal oxide that is laminated on the porous electrode on the detection gas side and supports a catalyst made of a platinum group element; and the porous catalyst support layer. 1. An oxygen detection element comprising: a catalyst thin film layer made of a porous thin film of a platinum group element and laminated in layers; and a protective layer made of a heat-resistant metal oxide and laminated on the catalyst thin film layer.