JP2000180402A - Electrochemical measurement sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the risk of the failure of a solid electrolyte due to the high voltage between an electrical heating element and a sensor electrode by providing an electron-conductive ceramic layer between an electrical insulation layer at the upper portion of a resistance electrical heating element and the solid electrolyte. SOLUTION: A resistance electrical heating element 11 is separated by oxygen ion conductive solid electrolytes 9 and 11 and an electrical insulation layer 4. Then, an electrically conductive film connection layer (ceramic layer) 17 is provided between the electrical insulation layer 4 at the upper portion of the resistance electrical heating element 11 and the solid electrolytes 9 and 10 being located on the electrical insulation layer 4. The electrically conductive ceramic layer 17 is formed by modification of a layer that already exists or the introduction of another intermediate layer between the electrical insulation layer 4 and the solid electrolytes 9 and 10, thus avoiding a local electric field strength with high ZrO2 in the electrical insulation layer 4 and balancing potential for increasing critical distance for starting to change into black. Also, the connection of the electrical heating element 11 based on the conductivity of the insulation part is broken.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The invention is based on an electrochemical measuring sensor for measuring gas components in a gas mixture according to the preamble of claim 1.

[0002]

BACKGROUND OF THE INVENTION German Patent No. 31201 has already been published.
In the case of a measuring sensor such as is known from the description of C 59, the sensor element is sensitive against a high voltage between the heating element and the sensor electrode,
During operation, high local electric field strengths in ZrO ₂ in the insulating layer at places where the conductivity is high or the porosity is reduced, this field strength also causes black discoloration. Due to the conductivity of the electrical insulation layer that insulates the resistive heating element, the coupling of the voltage for operating the heating element leads to disturbances of the measuring signal, especially during pulsed operation, and thereby the same disturbance. The distance is reduced.

[0003] At ROBERT BOSCH GmbH,
The means that have attempted to avoid such changes in the sensor element and further reduce the coupling of the failure of the heating element to the sensor electrode are in the insulating material of the sensor element relative to the heating element, Made of ceramic. Printed film tie layer between the electrically insulating ceramic and therewith the solid electrolyte which abut consists of pure ZrO _2.

[0004]

SUMMARY OF THE INVENTION The object of the invention is to determine the gas composition in a gas mixture, in particular with a high sensitivity between the heating element and the sensor electrode, which has a planar sensor element. To improve the electrochemical measurement sensor related to the above. Thereby, the risk of ionic conductivity failure of the solid electrolyte (blackening) is further reduced. Further, the electrochemical measurement sensor according to the present invention should be configured to extend the life of the heating element and to provide a stable measurement signal over the life of the heating sensor. Furthermore, the electrochemical measurement sensor according to the invention should be configured to diffuse the disturbing signal of the heating element into the measurement-active ceramic and thus into the sensor signal.

[0005]

According to the invention, at least the electronically conductive ceramic layer provided according to the invention comprises:-modification of the existing layer or-introduction of another intermediate layer between the electrically insulating layer and the solid electrolyte. Can be achieved by:

[0006] Thereby, a. ) Potential equilibrium to increase the critical distance to the start of and to avoid high localized field strength in ZrO ₂ blackening is performed, and b. ) The connection of the heating element based on the conductivity of the insulating portion is interrupted.

This conductive intermediate layer can be realized, for example, by: a. ) La (eg 10%) and Cu (eg 15
%) Doped with CeO ₂ ; b. ) Zr doped with TiO ₂ (eg 1%)
O ₂ ; c. ) CeO ₂ ; d. ) CeO ₂ doped with 50% ZrO ₂ ; e. ) By joining two electrically conductive properties of the material, and a combination layer ZrO 2 _/ electrically insulating layer to allow a reduction in the difference between the sintering and expansion of ZrO ₂ and Al ₂ O ₃ the potential equilibrium (e.g., 50 pairs 50 mol%). In this case, the insulating layer is made of Al ₂ O ₃ AKP having low sinterability.
53, the porosity of which is controlled by the pore-forming agent.

F. ) High Y₂O₃Content (for example, 16
% ZrO)₂Modification of the film tie layer by g. ) Yb₂O₃(Eg 8 mol%)
ZrO₂ZrO ₂Layer modification; and h. ) In₂O₃ZrO₂Denaturation of the layer. This means
When used, an electron conductive intermediate that is also ion conductive
A layer is obtained.

[0009] The conductivity need not be as good as the normal cermet electrodes used in the case of early shielding grids. Significantly better conductivity is achieved than with ZrO ₂ , for example a 10-fold increased conductivity. This effect is
Conductivity can be noted is enhanced by the use of all the ZrO ₂ layer between the reference passageway film and Nernst film heater film when it is slight.

After all, the electrochemical measuring sensor constructed according to the present invention has the following advantages: a. )) Increased safety against blackening during operation and on completion; b. 2.) Reduced heater connection during tact-divided heater operation is achieved.

If the invention is to be understood in connection with the drawings, in which one section of an electrochemical measurement sensor according to the invention, which shows a number of embodiments, is schematically shown in cross-section, Other preferred features of the invention will become more apparent from the description set forth below for the preferred embodiment.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The cross section shown in FIG. 1 consists essentially of a heater film 15, a thermal meander-like portion 11 from an electrically resistive material, and the surrounding electrically insulating layers 4 (upward) and 3 (downward). It can be noted that it represents the layers present around the thermal zone consisting of and the measuring electrode 5 and the reference electrode 6 of the electrochemical measuring sensor. The electrochemical measurement sensor shown in FIG. 1 is a planar oxygen sensor, which is a specialized name of, for example, a “planar λ sensor”, for example, a technology for removing toxic substances from exhaust gas by a catalyst of an internal combustion engine. Used in Thermal meander part 1
1. The heater consisting of the upper electrical insulation layer 4 and the lower electrical insulation layer 3 is provided on the solid electrolyte by means of a heater film 15, the details of which are not further described. Packing frames 2 are present on both sides of the heater. The concepts of "up" and "down" described above refer to "up" and "down" shown in the drawings.

On the heater, ie on the upper electrical insulation layer 4, there is a film bonding layer 17, a reference passage film 9 surrounding the reference gas passage 12 and a reference electrode 6. Above the reference channel film 9 and the reference gas channel 12, there is a Nernst film 10 which forms a solid electrolyte, possibly also provided with a pump cell (not shown) and a measuring electrode 5.

EXAMPLE 1 The upper electrically insulating layer 4 is replaced or modified.
Have been. This can be achieved by:
Can: a. ) At approximately 10 mol% La and approximately 15 mol% Cu
Doped CeO ₂ B. ) TiO₂ZrO doped with 1 mol%
₂C. ) CeO₂A layer; d. ) ZrO₂CeO doped with about 50%₂E. ) Combining the conductive properties of the two materials, and the potential
ZrO with equilibrium₂And Al₂O₃Sintering and expansion
To reduce the difference in tonicity, eg 50 to 50 moles
% Of the combination layer ZrO₂/ Electrical insulation layer. In this case
Means that the insulating layer has low sinterability Al₂O₃Manufacturing from
And the porosity is controlled by the pore-forming agent.

EXAMPLE 2 At least an electronically conductive film bonding layer 17 of ceramic comprises: a. A) a layer 17 modified by ZrO ₂ having a high Y ₂ O ₃ content, for example approximately 16 mol% of Y ₂ O ₃ ; b. ) High Yb ₂ O ₃ , for example approximately 8 mol% of Yb ₂ O ₃
A layer 17 modified by ZrO ₂ doped with c .; c. I) an electron conducting layer and an ion conducting layer are formed;
This can be achieved by a layer 17 that has been modified by n ₂ O ₃ .

Example 3 An electron conductive intermediate layer 19 is additionally formed to form an upper electron insulating layer 4 and ZrO ₂ 17 present thereon. In order to realize the intermediate layer 19, the composition described in Example 1 is suitable.

In general, the importance of electron conductivity applies first to the above-described embodiments for realizing the ceramic layers 4, 17, 19; In the case of the described ceramic layer, ionic conductivity is present, but ionic conductivity does not contribute to the effect according to the invention.

[Brief description of the drawings]

FIG. 1 is a professional name of “planar λ sensor”, for example.
FIG. 1 is a cross-sectional view of an electrochemical measurement sensor according to the present invention, which is a planar oxygen sensor used for example in a technique for removing toxic substances from exhaust gas by a catalyst of an internal combustion engine.

[Explanation of symbols]

2 packing frame, 3 lower electrical insulation layer,
4 Upper insulating layer, 5 Measurement electrode, 6 Reference electrode, 9 Oxygen ion conductive solid electrolyte, 10 Oxygen ion conductive solid electrolyte, 11 Thermal meander part,
12 Reference gas passage, 15 Heater film, 1
7 film bonding layer, 19 electron conductive intermediate layer

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Olaf Jach Germany Böblingen Mel Zedesdestraße 16 (72) Inventor Ulrich Eiselle Germany Schuttgart Becklerstraße 6 Baes (72) Inventor Elisabeth Buehler Germany Republic Korntal-Mün-Hingen Martin-Luter-Strasse 15 (72) Inventor Karl-Heinz Heusner Germany Leonberg Marc Groeninger Weg 1 (72) Inventor Roter Deal Germany Federal Republic Schuttgart Grubenecker 141

Claims (15)

[Claims] 1. An oxygen-ion-conductive solid electrolyte (9, 10) comprising an electrolyte layer and at least one resistance heating element (11) arranged at a distance from each other by means of an electrically insulating layer (4). 9, 10), and a film bonding layer (17) is provided between the electrical insulating layer (4) above the resistance heating element (11) and the solid electrolyte (9, 10) thereover. At least one ceramic layer (4, 17, 1) in an electrochemical measurement sensor for measuring gas components in a gas mixture.
9) is oriented in the direction of the electrically insulating layer (4) and the electrodes (5, 6) above the resistance heating element (11).
0), characterized in that these ceramic layers are at least electronically conductive. 2. The measuring sensor according to claim 1, wherein a ceramic layer is present as an additional layer (19) between the electrically insulating layer (4) on the electrode side and the film bonding layer (17) thereover. . 3. The measuring sensor according to claim 1, wherein the upper electrically insulating layer is replaced by an electronically conductive ceramic layer. 4. The measuring sensor according to claim 1, wherein the upper electrically insulating layer is modified with a ceramic material so that it is at least electronically conductive. 5. The measuring sensor according to claim 1, wherein the film tie layer (17) is modified to be at least electronically conductive. 6. The ceramic layer (4, 17, 19) is made of La
6. The measuring sensor according to claim 1, comprising CeO ₂ doped with Cu and Cu. 7. CeO₂La content is about 10
% And CeO ₂Almost 15 mol of Cu
% According to any one of claims 1 to 6, wherein
Measurement sensor. 8. The ceramic layer (4, 17, 19) is made of Zr.
The measurement sensor according to claim 1, comprising CeO ₂ having a content of 50 mol% of O ₂ . 9. The ceramic layer (4, 17, 19) is made of Ti.
The measuring sensor according to claim 1, comprising ZrO ₂ doped with O ₂ . 10. The TiO ₂ content is 1 mol%.
The measurement sensor according to claim 9. 11. A ceramic layer comprising: an electrically insulating layer (4);
It contains a combination of a and rO _2, measurement sensor according to claim 4, wherein. 12. The film tie layer (17) comprises ZrO ₂ with a high content of Y ₂ O _3.
The measurement sensor described. 13. The measuring sensor according to claim 12, wherein the content of Y ₂ O ₃ is approximately 16 mol%. 14. The film tie layer (17) comprising Yb ₂ O ₃
Measurement sensor THAT is doped contains a ZrO _2, claim 5. 15. The measuring sensor according to claim 14, wherein the doping content of Yb ₂ O ₃ is approximately 8 mol%.