Gas sensor element with increased durability and related manufacturing method

Abstract

A gas sensor element and a related manufacturing method are disclosed. The gas sensor element comprises a solid electrolyte body 11, having oxygen ion conductivity, which has both surfaces formed with a measuring gas detecting electrode and a reference gas detecting electrode, respectively, and a porous layer, covering the measuring gas detecting electrode and permeating measuring gases, which is formed using a porous layer green sheet containing fibrous organic materials, oriented in a direction substantially perpendicular to a thickness direction thereof, which are caused to burn down to form a coarse layer with large porosity in one area closer to the solid electrolyte and a dense layer with less porosity than that of the coarse layer in the other area remote from the solid electrolyte body to provide capability of permeating measuring gases in a direction perpendicular to a thickness direction of the porous layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view showing a gas sensor element of a first embodiment according to the present invention.

FIG. 2 is a cross sectional view showing a porous layer used in the gas sensor element of the first embodiment sown in FIG. 1.

FIG. 3 is an exploded perspective view showing the gas sensor element of the first embodiment sown in FIG. 1.

FIG. 4 is a view for illustrating a method of forming a porous layer using a doctor blade method.

FIG. 5 is a cross sectional view showing a step of drying a porous layer green sheet to be formed into the porous layer for the gas sensor element of the first embodiment shown in FIG. 1.

FIG. 6 is a view for illustrating a method of forming a porous layer, using an extrusion forming method, of a second embodiment according to the present invention.

FIG. 7 is a cross sectional view for illustrating a porous layer green sheet resulting from the forming method of the second embodiment shown in FIG. 6.

FIG. 8 is an illustrative view showing a lattice structure of a mesh body for use in the forming method of the second embodiment shown in FIG. 6.

FIG. 9 is a cross sectional view of a gas sensor element of a third embodiment according to the present invention.

FIG. 10 is a cross sectional view of a gas sensor element of a fourth embodiment according to the present invention.

FIG. 11 is a cross sectional view of a gas sensor element of a fifth embodiment according to the present invention.

FIG. 12 is a cross sectional view of a gas sensor element of a sixth embodiment according to the present invention.

FIG. 13 is a cross sectional view showing a gas sensor element of the related art.

Claims

1. A gas sensor element comprising: a solid electrolyte body having oxygen ion conductivity;a measuring gas detecting electrode formed on one surface of the solid electrolyte body;a reference gas detecting electrode formed on the other surface of the solid electrolyte body; anda porous layer covering the measuring gas detecting electrode and permeating measuring gas thereto;wherein the porous layer includes a coarse layer with a large porosity formed in close proximity to the solid electrolyte body and a dense layer, having a porosity less than that of the porosity of the coarse layer, which is formed in an area away from the coarse layer with respect to the solid electrolyte body.

2. The gas sensor element according to claim 1, wherein: the dense layer has the porosity less than 5% and the coarse layer has the porosity laying in a value ranging from 5 to 20%.

3. A gas sensor element comprising: a solid electrolyte body having oxygen ion conductivity;a measuring gas detecting electrode formed on one surface of the solid electrolyte body;a reference gas detecting electrode formed on the other surface of the solid electrolyte body; anda porous layer covering the measuring gas detecting electrode and permeating measuring gas thereto;wherein the porous layer has gas permeability mainly in a direction substantially perpendicular to a thickness direction of the porous layer.

4. The gas sensor element according to claim 3, wherein: the porous layer includes a diffusion resistance layer that permeates the measuring gases in a diffused state and adjusts a supply rate of the measuring gases to be fed to the measuring gas detecting electrode.

5. The gas sensor element according to claim 3, wherein: the porous layer acts as a protective layer that captures toxic substances in the measuring gases to protect the measuring gas detecting electrode.

6. A gas sensor element comprising: a solid electrolyte body having oxygen ion conductivity;a measuring gas detecting electrode formed on one surface of the solid electrolyte body;a reference gas detecting electrode formed on the other surface of the solid electrolyte body;a duct forming layer formed on the other surface of the solid electrolyte body and having a reference gas chamber to which the reference gas detecting electrode is exposed; anda porous layer covering the measuring gas detecting electrode and having a coarse layer with a large porosity formed in an area close proximity to the solid electrolyte body and a dense layer, having a porosity less than that of the porosity of the coarse layer, which is formed in another area away from the coarse layer with respect to the solid electrolyte body;wherein the porous layer has at least one sidewall communicating with the coarse layer and the dense layer through which measuring gases are introduced from an outside measuring gas atmosphere to the measuring gas detecting electrode mainly in a direction substantially perpendicular to a thickness direction of the porous layer.

7. The gas sensor element according to claim 6, wherein: the dense layer has the porosity less than 5% and the coarse layer has the porosity laying in a value ranging from 5 to 20%.

8. The gas sensor element according to claim 6, wherein: the dense layer has a central area formed with a measuring gas chamber to which the measuring gases are introduced from the outside measuring gas atmosphere via the coarse layer and the dense layer.

9. The gas sensor element according to claim 6, wherein: the measuring gas detecting electrode is kept in contact with the coarse layer of the porous layer.

10. A gas sensor element comprising: a solid electrolyte body having oxygen ion conductivity;a measuring gas detecting electrode formed on one surface of the solid electrolyte body;a reference gas detecting electrode formed on the other surface of the solid electrolyte body;a duct forming layer formed on the other surface of the solid electrolyte body and having a reference gas chamber to which the reference gas detecting electrode is exposed,a measuring gas chamber forming layer formed on the other surface of the solid electrolyte body and having a measuring gas chamber to which the measuring gas detecting electrode is exposed;a diffusion resistance layer formed on the measuring gas chamber forming layer; anda porous layer covering the diffusion resistance layer and having a coarse layer with a large porosity formed in an area close proximity to the diffusion resistance layer and a dense layer, having a porosity less than that of the porosity of the coarse layer, which is formed in another area away from the coarse layer with respect to the diffusion resistance layer;wherein the porous layer has at least one sidewall communicating with the coarse layer and the dense layer through which measuring gases are introduced from an outside measuring gas atmosphere mainly in a direction substantially perpendicular to a thickness direction of the porous layer; andwherein the diffusion resistance layer has at least one pinhole providing fluid communication between the coarse layer of the porous layer and the measuring gas chamber to introduce the measuring gases to the measuring gas detecting electrode.

11. The gas sensor element according to claim 10, wherein: the dense layer has the porosity less than 5% and the coarse layer has the porosity laying in a value ranging from 5 to 20%.

12. A gas sensor element comprising: a sensor cell including a first solid electrolyte body having oxygen ion conductivity, a measuring gas detecting electrode formed on one surface of the first solid electrolyte body, a reference gas detecting electrode formed on the other surface of the first solid electrolyte body, and a duct forming layer formed on the other surface of the first solid electrolyte body and having a reference gas chamber to which the reference gas detecting electrode is exposed; anda pump cell stacked on the sensor cell and including a second solid electrolyte body, a first pumping electrode formed on one surface of the second solid electrolyte body, a second pumping electrode formed on the other surface of the second solid electrolyte body, and a measuring gas chamber forming layer interposed between the first and second solid electrolyte bodies and having a measuring gas chamber to which the measuring gas detecting electrode and the second pumping electrode are exposed, and a porous layer formed on the one surface of the second solid electrolyte body so as to cover the first pumping electrode and having a coarse layer with a large porosity formed in an area close proximity to the second solid electrolyte body and a dense layer, having a porosity less than that of the porosity of the coarse layer, which is formed in another area away from the coarse layer with respect to the second solid electrolyte body;wherein the porous layer has at least one sidewall communicating with the coarse layer and the dense layer through which measuring gases are introduced from an outside measuring gas atmosphere mainly in a direction substantially perpendicular to a thickness direction of the porous layer; andwherein the second solid electrolyte body has at least one pinhole providing fluid communication between the coarse layer of the porous layer and the measuring gas chamber to introduce the measuring gases to the measuring gas detecting electrode.

13. The gas sensor element according to claim 12, wherein: the dense layer has the porosity less than 5% and the coarse layer has the porosity laying in a value ranging from 5 to 20%.

14. A gas sensor element comprising: a sensor cell including a first solid electrolyte body having oxygen ion conductivity, a measuring gas detecting electrode formed on one surface of the first solid electrolyte body, a reference gas detecting electrode formed on the other surface of the first solid electrolyte body, and a duct forming layer formed on the other surface of the first solid electrolyte body and having a reference gas chamber to which the reference gas detecting electrode is exposed; anda pump cell stacked on the sensor cell and including a second solid electrolyte body, a first pumping electrode formed on one surface of the second solid electrolyte body, a second pumping electrode formed on the other surface of the second solid electrolyte body, and a measuring gas chamber forming layer interposed between the first and second solid electrolyte bodies and having a measuring gas chamber to which the measuring gas detecting electrode and the second pumping electrode are exposed, and a porous layer formed on the one surface of the second solid electrolyte body so as to cover the first pumping electrode and having a coarse layer with a large porosity formed in an area close proximity to the second solid electrolyte body and a dense layer, having a porosity less than that of the porosity of the coarse layer, which is formed in another area away from the coarse layer with respect to the second solid electrolyte body;wherein the measuring gas chamber forming layer comprises a porous layer having a coarse layer with a large porosity and a dense layer having a porosity less than that of the porosity of the coarse layer and having at least one sidewall communicating with the coarse layer and the dense layer through which measuring gases are introduced to the measuring gas chamber from an outside measuring gas atmosphere mainly in a direction substantially perpendicular to a thickness direction of the porous layer of the measuring gas chamber forming layer.

15. The gas sensor element according to claim 14, wherein: the dense layer has the porosity less than 5% and the coarse layer has the porosity laying in a value ranging from 5 to 20%.

16. A method of manufacturing a gas sensor element, the method comprising the steps of: (a) preparing a solid electrolyte body, having oxygen ion conductivity, which has one surface formed with a measuring gas detecting electrode and the other surface formed with a reference gas detecting electrode; and(b) covering the measuring gas detecting electrode with a porous layer;wherein the porous layer is formed by forming a porous layer green sheet using a 10 porous layer forming slurry mixed with fibrous organic materials, orienting the fibrous organic materials in a direction substantially perpendicular to a thickness direction of the porous layer green sheet, and firing the porous layer green sheet while burning down the fibrous organic materials.

17. The method of manufacturing the gas sensor element according to claim 16, wherein: the porous layer green sheet is formed by a doctor blade method.

18. The method of manufacturing the gas sensor element according to claim 16, wherein: the porous layer green sheet forming step includes the steps of passing the porous layer green sheet forming slurry through a mesh body to cause the fibrous organic materials to be oriented in the direction substantially perpendicular to the thickness direction of the porous layer green sheet.

19. The method of manufacturing the gas sensor element according to claim 16, wherein: the porous layer has a coarse layer with a large porosity and a dense layer having a porosity less than that of the porosity of the coarse layer.

20. A method of manufacturing a gas sensor element, the method comprising the steps of: (a) preparing a solid electrolyte body, having oxygen ion conductivity, which has one surface formed with a measuring gas detecting electrode and the other surface formed with a reference gas detecting electrode; and(b) forming a porous layer so as to cover the measuring gas detecting electrode;wherein the porous layer forming step (b) includes the steps of:(c) solidifying binders in a porous layer forming slurry to form solidified organic materials;(d) drying the porous layer forming slurry and kneading the same to form a green clay body and subsequently processing the solidified organic materials into fibrous organic materials;(e) shaping the green clay body into a porous layer green sheet to cause the fibrous organic materials to be oriented in a direction substantially perpendicular to a thickness direction of the porous layer green sheet; and(f) firing the porous layer green sheet while burning down the fibrous organic materials.

21. The method of manufacturing the gas sensor element according to claim 20, wherein: the step (e) of shaping the porous layer green sheet is performed using an extrusion forming method.

22. The method of manufacturing the gas sensor element according to claim 20, wherein: the step of processing the solidified organic materials into the fibrous organic materials comprises the steps of:passing the porous layer forming slurry through a mesh body to form the fibrous organic materials such that the fibrous organic materials are oriented in a direction substantially perpendicular to the thickness direction of the porous layer green sheet.

23. The method of manufacturing the gas sensor element according to claim 20, wherein: the porous layer has a coarse layer with a large porosity and a dense layer having a porosity less than that of the porosity of the coarse layer.