Gas sensing member used for gas sensor and method of manufacturing the member

Abstract

A gas sensing member has a unit structure and a porous protective layer disposed on the unit structure. The unit structure has a solid electrolyte body, a gas measurement electrode disposed on a surface of the body and exposed to a measured gas entering at a gas inlet, a reference gas electrode disposed on another surface of the body and exposed to a reference gas, and a heater disposed close to the body. The heater has a heater substrate and heating elements disposed in the heater substrate. The heating elements heat the body. The heater substrate has side corner areas placed on side corners of the unit structure and being adjacent to the heating elements. The protective layer is disposed on the gas inlet such that the side corner areas are not covered with the protective layer and are directly exposed to the measured gas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective side view of a gas sensing member according to the first embodiment of the present invention;

FIG. 2 is a vertical sectional view taken substantially along line A-A of FIG. 1;

FIG. 3 is a rear view, partly in cross section, of the gas sensing member shown in FIG. 1;

FIG. 4 is a plan view of the sensing member shown in FIG. 1;

FIG. 5 is a side view of the sensing member shown in FIG. 1;

FIG. 6 is a flow chart showing a method of manufacturing the sensing member shown in FIG. 1 to FIG. 5;

FIG. 7 is a vertical sectional view of a sensing member wherein a mask layer is formed on a surface of a unit structure to set an uncovered surface area;

FIG. 8 is a vertical sectional view of a sensing member wherein the porous protective layer of a slurry state is attached on a whole surface of the sensing member shown in FIG. 7;

FIG. 9 is a first view explanatorily showing a pad transferring process performed for the sensing member;

FIG. 10 is a second view explanatorily showing the pad transferring process;

FIG. 11 is a third view explanatorily showing the pad transferring process;

FIG. 12 is a fourth view explanatorily showing the pad transferring process;

FIG. 13 is a fifth view explanatorily showing the pad transferring process;

FIG. 14 is a sixth view explanatorily showing the pad transferring process;

FIG. 15 is an explanatory view of a method of attaching a mask material to a unit structure according to the second embodiment;

FIG. 16 shows a coating system used according to the second embodiment;

FIG. 17 is a sectional view of a nozzle tube and a tank of the coating system shown in FIG. 16;

FIG. 18 is a flow chart showing a method of manufacturing the sensing member shown in FIG. 1 to FIG. 5 according to third to fifth embodiments of the present invention;

FIG. 19 is an explanatory view showing a method of attaching a protective layer forming material to a unit structure by using a dispenser according to the third embodiment;

FIG. 20 is an explanatory view showing another method of attaching a protective layer forming material to a unit structure according to a modification of the third embodiment;

FIG. 21 is an explanatory view showing a method of attaching a protective layer forming material to a unit structure according to the fourth embodiment;

FIG. 22 is an explanatory view showing a method of attaching a protective layer forming material to a unit structure according to the fifth embodiment;

FIG. 23 is a vertical sectional view of a gas sensing member according to the sixth embodiment of the present invention;

FIG. 24 is a vertical sectional view of a gas sensing member according to the seventh embodiment of the present invention;

FIG. 25 is a vertical sectional view of a gas sensing member according to the eighth embodiment of the present invention;

FIG. 26 is a perspective side view of a gas sensing member according to the ninth embodiment of the present invention;

FIG. 27 is a vertical sectional view taken substantially along line B-B of FIG. 26;

FIG. 28 is a side view of the sensing member shown in FIG. 26;

FIG. 29 is a flow chart showing a method of manufacturing the sensing member shown in FIG. 26 to FIG. 28 according to the ninth embodiment;

FIG. 30 is a vertical sectional view of a gas sensing member having a porous protective layer formed on the whole surface thereof;

FIG. 31 is an explanatory view showing a step of cutting off portions of the protective layer from the sensing member shown in FIG. 30 by using a waterproof sandpaper;

FIG. 32 is an explanatory view showing a step of cutting off portions of the protective layer from the sensing member shown in FIG. 30 by using an elastic grinding tool;

FIG. 33 is an explanatory view showing a step of cutting off portions of the protective layer from the sensing member shown in FIG. 30 by using a belt-like grinding device;

FIG. 34 is a vertical sectional view of a gas sensing member according to the tenth embodiment of the present invention;

FIG. 35 is a vertical sectional view of a gas sensing member according to the eleventh embodiment of the present invention;

FIG. 36 is a vertical sectional view of a gas sensing member according to the twelfth embodiment of the present invention;

FIG. 37 is a vertical sectional view of a gas sensing member according to the thirteenth embodiment of the present invention; and

FIG. 38 is a vertical sectional view of a gas sensing member according to the fourteenth embodiment of the present invention.

Claims

1. A gas sensing member to be exposed to a measured gas, comprising: a unit structure; anda porous protective layer disposed on the unit structure, the unit structure comprising; a solid electrolyte body, through which oxygen ions are transmittable, which has both surfaces opposite to each other along a first direction;a gas measurement electrode which is disposed on one surface of the solid electrolyte body and is exposed to the measured gas entering at a gas inlet of the unit structure;a reference gas electrode which is disposed on the other surface of the solid electrolyte body and is exposed to a reference gas; anda heater which is disposed on or close to the solid electrolyte body so as to face one of the surfaces of the solid electrolyte body and has a heater substrate and a heating element disposed in or on the heater substrate, the heating element heating the solid electrolyte body,wherein the heater substrate of the heater has a side corner area which is placed on a side corner surface of the unit structure in a second direction substantially perpendicular to the first direction and extends along a third direction substantially perpendicular to the first and second directions so as to be adjacent to the heating element along the second direction, and the porous protective layer is disposed at least on the gas inlet so as to indirectly expose the gas measurement electrode to the measured gas transmitted through the porous protective layer such that at least a portion of the side corner area of the heater substrate is directly exposed to the measured gas.

2. The gas sensing member according to claim 1, wherein the unit structure is covered with the porous protective layer such that the whole side corner area of the heater substrate is directly exposed to the measured gas.

3. The gas sensing member according to claim 1, wherein the heater substrate has a second side corner area which is placed on the side corner of the unit structure and extends from the side corner area along the third direction so as to be adjacent to no heating element along the second direction, and the unit structure is covered with the porous protective layer such that 60% or more of a combined area of the side corner area and the second side corner area directly is exposed to the measured gas.

4. The gas sensing member according to claim 1, wherein the heater substrate has a front surface which is placed on a front corner of the unit structure in the third direction and extends along the second direction so as to be adjacent to the heating element along the third direction, and the unit structure is covered with the porous protective layer such that at least a part of the front surface of the heater substrate is directly exposed to the measured gas.

5. The gas sensing member according to claim 2, wherein a first distance D1 along the first direction from the side corner area of the heater substrate to the porous protective layer and a second distance D2 along the first direction from the side corner area of the heater substrate to a surface of the unit structure opposite to the heater with respect to the solid electrolyte body are set to satisfy a relation of D1/D2 equal to or larger than 0.05.

6. The gas sensing member according to claim 1, wherein the heater substrate has a bottom surface which is placed on a bottom side of the unit structure in the first direction, and a part of the bottom surface of the heater substrate is covered with the porous protective layer such that a distance D3 along the second direction from the side corner area of the heater substrate to the porous protective layer disposed on the bottom surface and a width W1 of the bottom surface along the second direction are set to satisfy a relation of D3/W1 equal to or larger than 0.02.

7. The gas sensing member according to claim 1, wherein the porous protective layer is made of γ-alumina, θ-alumina or titania as a major component.

8. The gas sensing member according to claim 1, wherein the porous protective layer has a plurality of layer portions respectively formed of particles such that, as the layer portion becomes far from the surface of the unit structure, a size of the particles of the layer portion becomes large.

9. The gas sensing member according to claim 8, wherein the porous protective layer has a first layer portion disposed on the unit structure and a second layer portion disposed on the first layer portion, an average size of the particles of the first layer portion is set within a range from 1 to 40 μm, and an average size of the particles of the second layer portion is set within a range from 2 to 100 μm.

10. The gas sensing member according to claim 1, wherein the porous protective layer includes a catalyst made of a metal or a metallic oxide.

11. The gas sensing member according to claim 10, wherein the catalyst contains at least platinum, rhodium, ruthenium, or palladium as the metal.

12. The gas sensing member according to claim 10, wherein the catalyst is made of a noble metal having an average size of particles set within a range from 0.01 to 5 μm.

13. The gas sensing member according to claim 10, wherein the catalyst is made of a noble metal having an average size of particles set within a range from 0.1 to 2 μm.

14. The gas sensing member according to claim 10, wherein the catalyst contains titania as the metallic oxide.

15. The gas sensing member according to claim 10, wherein a catalyst content is set to be 10 μg/cm2 or more per unit area of a projected area which is defined on a plane perpendicular to a gas passing direction of the measured gas passing through the porous protective layer.

16. The gas sensing member according to claim 10, wherein a catalyst content of the porous protective layer is set within a range from 10 to 500 μg/cm2 per unit area of a projected area which is defined on a plane perpendicular to a gas passing direction of the measured gas passing through the porous protective layer.

17. A gas sensing member to be exposed to a measured gas, comprising: a unit structure; anda porous protective layer disposed on the unit structure, the unit structure comprising; a solid electrolyte body, through which oxygen ions are transmittable, which has both surfaces opposite to each other along a first direction;a gas measurement electrode which is disposed on one surface of the solid electrolyte body and is exposed to the measured gas entering at a gas inlet of the unit structure;a reference gas electrode which is disposed on the other surface of the solid electrolyte body and is exposed to a reference gas; anda heater which is disposed on or close to the solid electrolyte body so as to face one of the surfaces of the solid electrolyte body, the heater heating the solid electrolyte body,wherein the porous protective layer is disposed at least on the gas inlet so as to indirectly expose the gas measurement electrode to the measured gas transmitted through the porous protective layer such that at least a part of a particular surface of the unit structure placed opposite to the heater with respect to the solid electrolyte body is directly exposed to the measured gas.

18. The gas sensing member according to claim 17, wherein the heater has a heater substrate and a heating element disposed in or on the heater substrate, the heater substrate has a side corner area which is placed on a side corner surface of the unit structure in a second direction substantially perpendicular to the first direction and extends along a third direction substantially perpendicular to the first and second directions so as to be adjacent to the heating element along the second direction, and at least a portion of the side corner area of the heater substrate is directly exposed to the measured gas.

19. The gas sensing member according to claim 18, wherein the unit structure is covered with the porous protective layer such that the whole side corner area of the heater substrate is directly exposed to the measured gas.

20. The gas sensing member according to claim 18, wherein the heater substrate has a second side corner area which is placed on the side corner of the unit structure and extends from the side corner area along the third direction so as to be adjacent to no heating element along the second direction, and the unit structure is covered with the porous protective layer such that 60% or more of a combined area of the side corner area and the second side corner area directly is exposed to the measured gas.

21. The gas sensing member according to claim 17, wherein the heater substrate has a front surface which is placed on a front corner of the unit structure in the third direction and extends along the second direction so as to be adjacent to the heating element along the third direction, and the unit structure is covered with the porous protective layer such that at least a part of the front surface of the heater substrate is directly exposed to the measured gas.

22. The gas sensing member according to claim 18, wherein a first distance D1 along the first direction from the side corner area of the heater substrate to the porous protective layer and a second distance D2 along the first direction from the side corner area of the heater substrate to the surface of the unit structure opposite to the heater with respect to the solid electrolyte body are set to satisfy a relation of D1/D2 equal to or larger than 0.05.

23. The gas sensing member according to claim 18, wherein the heater substrate has a bottom surface which is placed on a bottom side of the unit structure in the first direction, and a part of the bottom surface of the heater substrate is covered with the porous protective layer such that a distance D3 along the second direction from the side corner area of the heater substrate to the porous protective layer disposed on the bottom surface and a width W1 of the bottom surface along the second direction are set to satisfy a relation of D3/W1 equal to or larger than 0.02.

24. The gas sensing member according to claim 17, wherein the porous protective layer is made of γ-alumina, θ-alumina or titania as a major component.

25. The gas sensing member according to claim 17, wherein the porous protective layer has a plurality of layer portions respectively formed of particles such that, as the layer portion becomes far from the surface of the unit structure, a size of the particles of the layer portion becomes large.

26. The gas sensing member according to claim 25, wherein the porous protective layer has a first layer portion directly disposed on the unit structure and a second layer portion disposed on the first layer portion, an average size of the particles of the first layer portion is set within a range from 1 to 40 μm, and an average size of the particles of the second layer portion is set within a range from 2 to 100 μm.

27. The gas sensing member according to claim 17, wherein the porous protective layer includes a catalyst made of a metal or a metallic oxide.

28. The gas sensing member according to claim 27, wherein the catalyst contains at least platinum, rhodium, ruthenium, or palladium as the metal.

29. The gas sensing member according to claim 27, wherein the catalyst is made of a noble metal having an average size of particles set within a range from 0.01 to 5 μm.

30. The gas sensing member according to claim 27, wherein the catalyst is made of a noble metal having an average size of particles set within a range from 0.1 to 2 μm.

31. The gas sensing member according to claim 27, wherein the catalyst contains titania as the metallic oxide.

32. The gas sensing member according to claim 27, wherein a catalyst content is set to be 10 μg/cm2 or more per unit area of a projected area which is defined on a plane perpendicular to a gas passing direction of the measured gas passing through the porous protective layer.

33. The gas sensing member according to claim 27, wherein a catalyst content of the porous protective layer is set within a range from 10 to 500 μg/cm2 per unit area of a projected area which is defined on a plane perpendicular to a gas passing direction of the measured gas passing through the porous protective layer.

34. A method of manufacturing a gas sensing member to be exposed to a measured gas, comprising the steps of: assembling, into a unit structure, a solid electrolyte body through which oxygen ions are transmittable and having both surfaces opposite to each other along a first direction, a gas measurement electrode disposed on one surface of the solid electrolyte body and exposed to the measured gas entering at a gas inlet of the unit structure, a reference gas electrode disposed on the other surface of the solid electrolyte body and exposed to a reference gas, and a heater being disposed on or close to the solid electrolyte body so as to face one of the surfaces of the solid electrolyte body and having a heater substrate and a heating element disposed in or on the heater substrate, the heating element heating the solid electrolyte body, the heater substrate having a side corner area which is placed on a side corner surface of the unit structure in a second direction substantially perpendicular to the first direction and extends along a third direction substantially perpendicular to the first and second directions so as to be adjacent to the heating element along the second direction; andforming a porous protective layer on the unit structure,wherein the step of forming the porous protective layer comprises: forming a mask layer made of an organic material on at least a portion of the side corner area of the heater substrate of the heater;attaching a protective layer forming material on a surface of the unit structure such that the gas inlet and the mask layer are covered with the protective layer forming material;performing a thermal treatment for the protective layer forming material to change the protective layer forming material to the porous protective layer such that the gas measurement electrode is allowed to be indirectly exposed to the measured gas transmitted through the porous protective layer; andremoving the mask layer and the porous protective layer attached on the mask layer from the unit structure such that at least the portion of the side corner area is allowed to be directly exposed to the measured gas.

35. The method according to claim 34, wherein the step of forming a mask layer includes attaching the mask layer to a pad material having high flexibility; andtransferring the mask layer of the pad material to at least the portion of the side corner area of the heater substrate.

36. The method according to claim 34, wherein the step of forming a mask layer includes impregnating a felt element with the mask layer; andattaching the mask layer of the felt element to at least the portion of the side corner area of the heater substrate.

37. The method according to claim 34, wherein the mask layer is formed of resin.

38. The method according to claim 34, wherein the step of forming a mask layer includes: attaching a ultraviolet-ray curing resin on at least the portion of the side corner area of the heater substrate; andirradiating the ultraviolet-ray curing resin with a ultraviolet ray to cure the ultraviolet-ray curing resin and to change the ultraviolet-ray curing resin to the mask layer.

39. The method according to claim 34, wherein the step of forming a mask layer includes: coating the mask layer including acrylic resin or α-terpineol as a major material and dye on at least the portion of the side corner area of the heater substrate.

40. The method according to claim 34, wherein the step of attaching a protective layer forming material includes: forming the protective layer forming material in a slurry state;dipping the unit structure into the protective layer forming material to attach the protective layer forming material on the whole surface of the unit structure; anddrying the protective layer forming material attached to the unit structure.

41. The method according to claim 34, wherein the step of performing a thermal treatment includes: baking the protective layer forming material attached on the gas inlet at a temperature ranging from 500 to 1000° C. so as to change the protective layer forming material to the porous protective layer; andburning off the mask layer.

42. The method according to claim 34, wherein the step of removing the mask layer includes removing the mask layer and the porous protective layer by applying an air blow or vibration to the mask layer and the porous protective layer.

43. The method according to claim 34, wherein the step of removing the mask layer includes forming the mask layer on the whole side corner area of the heater substrate, and the step of removing the mask layer includes removing the mask layer such that the whole side corner area is allowed to be directly exposed to the measured gas.

44. A method of manufacturing a gas sensing member to be exposed to a measured gas, comprising the steps of: assembling, into a unit structure, a solid electrolyte body through which oxygen ions are transmittable and having both surfaces opposite to each other along a first direction, a gas measurement electrode disposed on one surface of the solid electrolyte body and exposed to the measured gas entering at a gas inlet of unit structure, a reference gas electrode disposed on the other surface of the solid electrolyte body and exposed to a reference gas, and a heater being disposed on or close to the solid electrolyte body so as to face one of the surfaces of the solid electrolyte body and having a heater substrate and a heating element disposed in the heater substrate, the heating element heating the solid electrolyte body, the heater substrate having a side corner area which is placed on a side corner surface of the unit structure in a second direction substantially perpendicular to the first direction and extends along a third direction substantially perpendicular to the first and second directions so as to be adjacent to the heating element along the second direction; andforming a porous protective layer on the unit structure,wherein the step of forming the porous protective layer comprises: attaching a protective layer forming material on at least the gas inlet of the unit structure such that at least a portion of the side corner area of the heater substrate is not covered with the protective layer forming material; andperforming a thermal treatment for the protective layer forming material to change the protective layer forming material attached at least on the gas inlet to the porous protective layer such that the gas measurement electrode is allowed to be indirectly exposed to the measured gas transmitted through the porous protective layer, and such that at least the portion of the side corner area is allowed to be directly exposed to the measured gas.

45. The method according to claim 44, wherein the step of attaching a protective layer forming material includes coating the protective layer forming material on at least the gas inlet of the unit structure by using a dispenser.

46. The method according to claim 44, wherein the step of attaching a protective layer forming material includes spraying the protective layer forming material discharged from a nozzle on at least the gas inlet of the unit structure.

47. The method according to claim 44, wherein the step of attaching a protective layer forming material includes: attaching the protective layer forming material to a pad material having high flexibility; andtransferring the protective layer forming material of the pad material to at least the gas inlet of the unit structure.

48. The method according to claim 44, wherein the step of attaching a protective layer forming material includes: attaching the protective layer forming material on at least the gas inlet of the unit structure in accordance with a screen printing process.

49. The method according to claim 44, wherein the step of attaching the protective layer forming material includes attaching the protective layer forming material such that the side corner area of the heater substrate is not covered with the protective layer forming material, and the step of performing the thermal treatment includes performing the thermal treatment such that the whole side corner area is allowed to be directly exposed to the measured gas.

50. A method of manufacturing a gas sensing member to be exposed to a measured gas, comprising the steps of: assembling, into a unit structure, a solid electrolyte body through which oxygen ions are transmittable and having both surfaces opposite to each other along a first direction, a gas measurement electrode disposed on one surface of the solid electrolyte body and exposed to the measured gas entering at a gas inlet of unit structure, a reference gas electrode disposed on the other surface of the solid electrolyte body and exposed to a reference gas, and a heater being disposed on or close to the solid electrolyte body so as to face one of the surfaces of the solid electrolyte body and having a heater substrate and a heating element disposed in the heater substrate, the heating element heating the solid electrolyte body, the heater substrate having a side corner area which is placed on a side corner surface of the unit structure in a second direction substantially perpendicular to the first direction and extends along a third direction substantially perpendicular to the first and second directions so as to be adjacent to the heating element along the second direction; andforming a porous protective layer on the unit structure,wherein the step of forming the porous protective layer comprises: attaching the porous protective layer on both the gas inlet of the unit structure and at least a portion of the side corner area of the heater substrate of the heater;removing a portion of the porous protective layer, which is disposed at least on the portion of the side corner area of the heater substrate, such that at least the portion of the side corner area of the heater substrate is allowed to be directly exposed to the measured gas, and such that the gas measurement electrode is allowed to be indirectly exposed to the measured gas transmitted through the porous protective layer; andperforming a thermal treatment for the porous protective layer.

51. The method according to claim 50, wherein the step of removing the portion of the porous protective layer includes: cutting off the portion of the porous protective layer by using a waterproof sandpaper stuck on a grinding device.

52. The method according to claim 50, wherein the step of removing the portion of the porous protective layer includes: cutting off the portion of the porous protective layer by using an elastic grinding tool formed of elastic foam body including abrasive grains.

53. The method according to claim 50, wherein the step of removing the portion of the porous protective layer includes: cutting off the portion of the porous protective layer by using a belt-like grinding device wherein abrasive grains are attached on a surface of a belt-like element.

54. The method according to claim 50, wherein the step of attaching the porous protective layer includes attaching the porous protective layer on the whole side corner area of the heater substrate, and the step of removing the portion of the porous protective layer includes removing the porous protective layer such that the whole side corner area of the heater substrate is allowed to be directly exposed to the measured gas.

55. A method of manufacturing a gas sensing member to be exposed to a measured gas, comprising the steps of: assembling, into a unit structure, a solid electrolyte body through which oxygen ions are transmittable and having both surfaces opposite to each other along a first direction, a gas measurement electrode disposed on one surface of the solid electrolyte body and exposed to the measured gas entering at a gas inlet of the unit structure, a reference gas electrode disposed on the other surface of the solid electrolyte body and exposed to a reference gas, and a heater being disposed on or close to the solid electrolyte body so as to face one of the surfaces of the solid electrolyte body, the heater heating the solid electrolyte body; andforming a porous protective layer on the unit structure,wherein the step of forming the porous protective layer comprises: forming a mask layer made of an organic material on at least a part of a particular surface of the unit structure placed opposite to the heater with respect to the solid electrolyte body;attaching a protective layer forming material on the unit structure such that the gas inlet and the mask layer are covered with the protective layer forming material;performing a thermal treatment for the protective layer forming material to change the protective layer forming material to the porous protective layer such that the gas measurement electrode is allowed to be indirectly exposed to the measured gas transmitted through the porous protective layer; andremoving the mask layer and the porous protective layer attached on the mask layer from the unit structure such that at least the part of the particular surface of the unit structure placed opposite to the heater with respect to the solid electrolyte body is allowed to be directly exposed to the measured gas.

56. The method according to claim 55, wherein the heater has a heater substrate and a heating element disposed in or on the heater substrate,the heater substrate has a side corner area which is placed on a side corner surface of the unit structure in a second direction substantially perpendicular to the first direction and extends along a third direction substantially perpendicular to the first and second directions so as to be adjacent to the heating element along the second direction,the step of forming the mask layer includes: forming the mask layer on at least a portion of the side corner area of the heater substrate, andthe step of removing the mask layer includes: removing the mask layer such that at least the portion of the side corner area of the heater substrate is allowed to be directly exposed to the measured gas.

57. The method according to claim 56, wherein the step of forming the mask layer on at least the portion of the side corner area includes forming the mask layer on the whole side corner area, and the step of removing the mask layer includes removing the mask layer such that the whole side corner area of the heater substrate is allowed to be directly exposed to the measured gas.

58. The method according to claim 55, wherein the step of forming a mask layer includes: attaching the mask layer to a pad material having high flexibility; andtransferring the mask layer of the pad material to at least the part of the particular surface of the unit structure placed opposite to the heater.

59. The method according to claim 55, wherein the step of forming a mask layer includes: impregnating a felt element with the mask layer; andattaching the mask layer of the felt element to at least the part of the particular surface of the unit structure placed opposite to the heater.

60. The method according to claim 55, wherein the mask layer is formed of resin.

61. The method according to claim 55, wherein the step of forming a mask layer includes: attaching a ultraviolet-ray curing resin on at least the part of the particular surface of the unit structure placed opposite to the heater; andirradiating the ultraviolet-ray curing resin with a ultraviolet ray to cure the ultraviolet-ray curing resin and to change the ultraviolet-ray curing resin to the mask layer.

62. The method according to claim 55, wherein the step of forming a mask layer includes: coating the mask layer including acrylic resin or α-terpineol as a major material and dye on at least the part of the particular surface of the unit structure placed opposite to the heater.

63. The method according to claim 55, wherein the step of attaching a protective layer forming material includes: forming the protective layer forming material in a slurry state;dipping the unit structure into the protective layer forming material to attach the protective layer forming material on the whole surface of the unit structure; anddrying the protective layer forming material attached to the unit structure.

64. The method according to claim 55, wherein the step of performing a thermal treatment includes: baking the protective layer forming material attached on the gas inlet at a temperature ranging from 500 to 1000° C. so as to change the protective layer forming material to the porous protective layer; andburning off the mask layer.

65. The method according to claim 55, wherein the step of removing the mask layer includes removing the mask layer and the porous protective layer by applying an air blow or vibration to the mask layer and the porous protective layer.

66. A method of manufacturing a gas sensing member to be exposed to a measured gas, comprising the steps of: assembling, into a unit structure, a solid electrolyte body through which oxygen ions are transmittable and having both surfaces opposite to each other along a first direction, a gas measurement electrode disposed on one surface of the solid electrolyte body and exposed to the measured gas entering at a gas inlet of unit structure, a reference gas electrode disposed on the other surface of the solid electrolyte body and exposed to a reference gas, and a heater being disposed on or close to the solid electrolyte body so as to face one of the surfaces of the solid electrolyte body, the heater heating the solid electrolyte body; andforming a porous protective layer on the unit structure,wherein the step of forming the porous protective layer comprises: attaching a protective layer forming material on at least the gas inlet of the unit structure such that at least a part of a particular surface of the unit structure placed opposite to the heater with respect to the solid electrolyte body is not covered with the protective layer forming material; andperforming a thermal treatment for the protective layer forming material to change the protective layer forming material attached at least on the gas inlet to the porous protective layer such that the gas measurement electrode is allowed to be indirectly exposed to the measured gas transmitted through the porous protective layer, and such that at least the part of the particular surface of the unit structure placed opposite to the heater with respect to the solid electrolyte body is allowed to be directly exposed to the measured gas.

67. The method according to claim 66, wherein the heater has a heater substrate and a heating element disposed in or on the heater substrate,the heater substrate has a side corner area which is placed on a side corner surface of the unit structure in a second direction substantially perpendicular to the first direction and extends along a third direction substantially perpendicular to the first and second directions so as to be adjacent to the heating element along the second direction,the step of attaching the protective layer forming material includes: attaching the protective layer forming material such that at least a portion of the side corner area of the heater substrate is not covered with the protective layer forming material; andthe step of performing a thermal treatment includes: performing the thermal treatment such that at least the portion of the side corner area of the heater substrate is allowed to be directly exposed to the measured gas.

68. The method according to claim 67, wherein the step of attaching the protective layer forming material includes attaching the protective layer forming material such that the side corner area of the heater substrate is not covered with the protective layer forming material, and the step of performing the thermal treatment includes performing the thermal treatment such that the whole side corner area of the heater substrate is allowed to be directly exposed to the measured gas.

69. The method according to claim 66, wherein the step of attaching the protective layer forming material includes coating the protective layer forming material on at least the gas inlet of the unit structure by using a dispenser.

70. The method according to claim 66, wherein the step of attaching the protective layer forming material includes spraying the protective layer forming material discharged from a nozzle on at least the gas inlet of the unit structure.

71. The method according to claim 66, wherein the step of attaching a protective layer forming material includes: attaching the protective layer forming material to a pad material having high flexibility; andtransferring the protective layer forming material of the pad material to at least the gas inlet of the unit structure.

72. The method according to claim 66, wherein the step of attaching the protective layer forming material includes attaching the protective layer forming material on at least the gas inlet of the unit structure in accordance with a screen printing process.

73. A method of manufacturing a gas sensing member to be exposed to a measured gas, comprising the steps of: assembling, into a unit structure, a solid electrolyte body through which oxygen ions are transmittable and having both surfaces opposite to each other along a first direction, a gas measurement electrode disposed on one surface of the solid electrolyte body and exposed to the measured gas entering at a gas inlet of unit structure, a reference gas electrode disposed on the other surface of the solid electrolyte body and exposed to a reference gas, and a heater being disposed on or close to the solid electrolyte body so as to face one of the surfaces of the solid electrolyte body, the heater heating the solid electrolyte body; andforming a porous protective layer on the unit structure,wherein the step of forming the porous protective layer comprises: attaching the porous protective layer on both the gas inlet of the unit structure and at least a part of a particular surface of the unit structure placed opposite to the heater with respect to the solid electrolyte body;removing a portion of the porous protective layer, which is disposed at least on the part of the particular surface of the unit structure, such that at least the part of the particular surface of the unit structure is allowed to be directly exposed to the measured gas, and such that the gas measurement electrode is allowed to be indirectly exposed to the measured gas transmitted through the porous protective layer; andperforming a thermal treatment for the porous protective layer.

74. The method according to claim 73, wherein the heater has a heater substrate and a heating element disposed in or on the heater substrate,the heater substrate has a side corner area which is placed on a side corner surface of the unit structure in a second direction substantially perpendicular to the first direction and extends along a third direction substantially perpendicular to the first and second directions so as to be adjacent to the heating element along the second direction,the step of attaching the porous protective layer includes attaching the porous protective layer on at least a portion of the side corner area of the heater substrate, andthe step of removing the portion of the porous protective layer includes removing the porous protective layer such that at least the portion of the side corner area of the heater substrate is allowed to be directly exposed to the measured gas.

75. The method according to claim 74, wherein the step of attaching the porous protective layer includes attaching the porous protective layer on the whole side corner area of the heater substrate, and the step of removing the porous protective layer includes removing the porous protective layer such that the whole side corner area of the heater substrate is allowed to be directly exposed to the measured gas.

76. The method according to claim 73, wherein the step of removing the portion of the porous protective layer includes: cutting off the portion of the porous protective layer by using a waterproof sandpaper stuck on a grinding device.

77. The method according to claim 73, wherein the step of removing the portion of the porous protective layer includes: cutting off the portion of the porous protective layer by using an elastic grinding tool formed of elastic foam body including abrasive grains.

78. The method according to claim 73, wherein the step of removing the portion of the porous protective layer includes: cutting off the portion of the porous protective layer by using a belt-like grinding device wherein abrasive grains are attached on a surface of a belt-like element.