JP2012211928A - Ammonia gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ammonia gas sensor that is superior in gas selectivity and responsiveness with respect to ammonia gas in gas to be measured.SOLUTION: An ammonia gas sensor comprises: a solid electrolyte member 310 extending in an axial direction; a reference electrode 320 provided on the solid electrolyte member 310; and a detection electrode 331, which serves as a counter electrode of the reference electrode 320, and a selective reaction layer 340 provided on the solid electrolyte member 310. The detection electrode 331 contains noble metal as a main component, and the selective reaction layer 340 contains metal oxide as a main component. Thus, the ammonia gas sensor 1, superior in gas selectivity and responsiveness with respect to ammonia gas, can be obtained without being influenced by flammable gas.

Description

  The present invention relates to an ammonia gas sensor suitable for detecting ammonia gas contained in a gas to be measured.

Conventionally, in this type of ammonia gas sensor, an ammonia gas sensor disclosed in Patent Document 1 below has been proposed. The ammonia gas sensor includes a solid electrolyte body, and a reference electrode portion and a detection electrode portion provided on the solid electrolyte body. Then, detection electrode is a metal oxide having ammonia gas selectivity, for example, formed by vanadium oxide (V 2 _{O 5).}

US Patent Publication No. 2006 / 0266659A1

However, the detection electrode portion formed of vanadium oxide (V ₂ O ₅ ) has insufficient gas selectivity and responsiveness to ammonia gas.

  Therefore, an object of the present invention is to provide an ammonia gas sensor excellent in gas selectivity and responsiveness to ammonia gas in a gas to be measured.

  According to the first aspect of the present invention, an ammonia gas sensor extends in the axial direction and has a solid electrolyte body mainly composed of zirconia, a reference electrode section provided on the solid electrolyte body, and a reference electrode section. In an ammonia gas sensor having a detection electrode part and a selective reaction layer provided on a solid electrolyte body as a counter electrode, the detection electrode part is composed mainly of a noble metal, and the selective reaction layer is composed mainly of a metal oxide. It is characterized by.

  By setting it as such a structure, it can suppress that a selective reaction layer combusts and removes combustible gas other than ammonia gas in to-be-measured gas favorably, and combustible gas reaches | attains a solid electrolyte body.

  In addition, the detection electrode unit can exert a current collecting action based on the ammonia gas. For this reason, an electromotive force can be generated satisfactorily between the detection electrode portion and the reference electrode portion according to the concentration of ammonia gas.

  As a result, an ammonia gas sensor excellent in gas selectivity and responsiveness to ammonia gas can be obtained without being affected by the combustible gas.

  In the present invention, the selective reaction layer and the detection electrode portion are provided in two layers. If the selective reaction layer and the detection electrode part are provided in one layer (a layer in which the noble metal contained in the detection electrode part and the metal oxide contained in the selective reaction layer are mixed), the current collecting action of the detection electrode part is reduced. An electromotive force is unlikely to be generated between the reference electrode layer and a combustible gas other than ammonia gas reaches the interface with the solid electrolyte body, thereby obtaining an ammonia gas sensor having excellent gas selectivity and responsiveness. I can't. On the other hand, with the above-described configuration of the present invention, an ammonia gas sensor excellent in gas selectivity and responsiveness can be sufficiently obtained.

  The detection electrode part and the selective reaction layer may be formed on the surface of the solid electrolyte body so as to be a counter electrode with the reference electrode part, and the detection electrode part, the selection reaction layer, and the reference electrode part are the solid electrolyte body. The detection electrode part, the selective reaction layer, and the reference electrode part may be provided on the same surface of the solid electrolyte body. Furthermore, each of the detection electrode part, the selective reaction layer, and the solid electrolyte body may be in direct contact, or may have another member interposed therebetween.

  According to a second aspect of the present invention, the detection electrode portion is provided between the solid electrolyte body and the selective reaction layer. With such a configuration, the gas to be measured is first exposed to the selective reaction layer, so that the combustible gas other than the ammonia gas in the gas to be measured is sufficiently burned, and then the ammonia gas is converted into the solid electrolyte. Can reach the body.

  According to a third aspect of the present invention, the detection electrode portion is provided directly on the solid electrolyte body. By setting it as such a structure, a detection electrode part can exhibit a favorable current collection effect | action more based on ammonia gas. As a result, an electromotive force can be generated more favorably between the detection electrode portion and the reference electrode portion according to the ammonia gas concentration.

  According to a fourth aspect of the present invention, the selective reaction layer covers the detection electrode part so that the detection electrode part is not exposed. In this way, by completely covering the detection electrode portion with the selective reaction layer, the gas to be measured can surely pass through the selective reaction layer in order to reach the solid electrolyte body. Then, after combustible gas other than ammonia gas in the gas to be measured is almost burned in the selective reaction layer, the ammonia gas can reach the solid electrolyte body.

  According to the fifth aspect of the present invention, in order to electrically connect the detection electrode portion and the external circuit, the detection electrode portion has a strip-shaped detection lead portion extending in the axial direction from the detection electrode portion. The detection lead portion overlaps with the detection lead portion. With such a configuration, the detection electrode part and the detection lead part can be electrically connected reliably, and the electromotive force generated in the reference electrode part and the detection electrode part can be reliably transmitted to the external circuit.

  According to a sixth aspect of the present invention, the solid electrolyte body has a bottomed cylindrical shape having a bottom portion on the tip side, the reference electrode portion is formed on the inner surface of the solid electrolyte body, and the detection electrode The portion is provided on the outer surface on the front end side of the solid electrolyte body. Thus, even if the solid electrolyte body is formed in a bottomed cylindrical shape and the reference electrode part and the detection electrode part are provided on the inner surface and the outer surface of the solid electrolyte body, respectively, noble metal is the main component. By providing the detection electrode section and the selective reaction layer mainly composed of a metal oxide, an ammonia gas sensor excellent in gas selectivity and responsiveness to ammonia gas can be obtained.

  As one of the shapes thereof, as described in claim 7, the detection electrode portion extends symmetrically and in a strip shape to the rear end side of the solid electrolyte body through the bottom of the solid electrolyte body. Also good.

  According to claim 8 of the present invention, the detection electrode portion is made of a material containing platinum as a main component and further containing gold, or a material containing gold as a main component. By setting it as such a structure, a detection electrode part can exhibit a favorable current collection effect | action more based on ammonia gas. As a result, an electromotive force can be generated more favorably between the detection electrode portion and the reference electrode portion according to the ammonia gas concentration.

  According to a ninth aspect of the present invention, the detection lead portion is made of a material whose main component is platinum. By adopting such a configuration, an electromotive force generated between the detection electrode unit and the reference electrode unit can be reliably transmitted to the external circuit.

  According to a tenth aspect of the present invention, the detection lead portion contains less gold than the content contained in the detection electrode portion. By containing gold in the detection lead portion, the catalytic property of platinum can be reduced, and the occurrence of a potential difference between the detection lead portion and the reference electrode portion can be suppressed. In addition, by making the gold contained in the detection lead portion smaller than the detection electrode portion, simultaneous firing with the solid electrolyte body becomes possible, and the adhesion strength with the solid electrolyte body can be increased. Furthermore, the adhesion strength with the detection electrode part can also be increased.

  According to the eleventh aspect of the present invention, the reference electrode portion and the detection electrode portion contain zirconia, and the detection electrode portion contains less zirconia than the reference electrode portion. And The reference electrode portion and the detection electrode portion contain zirconia in consideration of adhesion with the solid electrolyte body. And the favorable current collection effect | action based on the ammonia gas of a detection electrode part is also maintained by reducing the zirconia contained in a detection electrode part rather than a reference | standard electrode part.

  According to the twelfth aspect of the present invention, the detection lead portion contains zirconia, and the detection lead portion has a lower zirconia content than the detection electrode portion. As described above, zirconia is also contained in the detection lead portion in consideration of adhesion to the solid electrolyte body. And the energization effect of a detection lead part can be heightened by reducing the zirconia contained in a detection lead part rather than a detection electrode part.

  According to a thirteenth aspect of the present invention, a porous layer is provided between the detection electrode portion and the selective reaction layer. By setting it as such a structure, the insulation between a selective reaction layer and a detection electrode part is ensured. Therefore, the influence on the detection electrode part due to the temporal change of the selective reaction layer is prevented, and good gas selectivity can be maintained over a long period of time.

  According to a fourteenth aspect of the present invention, the porous layer covers the detection electrode part so that the detection electrode part is not exposed. With such a configuration, the porous layer can reliably ensure insulation between the detection electrode portion and the selective reaction layer.

  According to a fifteenth aspect of the present invention, the selective reaction layer covers the porous layer so that the porous layer is not exposed. By adopting such a configuration, it is possible to prevent the phenomenon that combustible gas other than ammonia gas flows directly into the detection electrode portion through the porous layer without going through the selective reaction layer. An ammonia gas sensor excellent in gas selectivity can be obtained.

According to claim 16 of the present invention, the porous layer contains at least one of Al ₂ O ₃ , MgAl ₂ O ₄ , SiO ₂ , SiO ₂ / Al ₂ O ₃ , zeolite, and SiC. It is characterized by that. Thereby, the insulation by a porous layer can be ensured more specifically.

According to a seventeenth aspect of the present invention, a protective layer covering the selective reaction layer is provided so that the selective reaction layer is not exposed. By adopting such a configuration, the selective reaction layer is not affected by impurities (for example, phosphorus, lead, etc.) in the gas to be measured. Therefore, the selective reaction layer can satisfactorily burn the combustible gas other than the ammonia gas in the gas to be measured, and the combustible gas can be satisfactorily suppressed from reaching the solid electrolyte body. As the protective _{layer, MgAl 2 O 4, Al 2} O 3, SiO 2 / Al 2 O 3, zeolites, and the like.

  According to claim 18 of the present invention, the selective reaction layer has at least one of bismuth vanadium oxide and antimony vanadium oxide as a main component. By setting it as such a structure, the selective reaction layer can burn combustible gas other than ammonia gas in measurement gas favorably.

  According to the nineteenth aspect of the present invention, the selective reaction layer comprises tungsten oxide, molybdenum oxide, niobium oxide, tantalum oxide, magnesium oxide, canoledium oxide, strontium oxide, and barium oxide. It is characterized by further adding at least one of them. When the additive is further added to the selective reaction layer in this way, the selective reaction layer can burn the combustible gas other than the ammonia gas in the gas to be measured more satisfactorily.

  According to claim 20 of the present invention, vanadium is contained in a range of 25 (at%) to 50 (at%). As a result, it is possible to satisfactorily ensure the thermal stability over time and the responsiveness as an ammonia gas sensor and the gas selectivity with respect to the ammonia gas.

  According to a twenty-first aspect of the present invention, the selective reaction layer is thicker than the detection electrode layer. Thereby, the selective reaction layer can favorably suppress the arrival of the combustible gas other than the ammonia gas to the solid electrolyte layer by appropriately selecting the ammonia gas from the combustible gas other than the ammonia gas.

  According to a twenty-second aspect of the present invention, the detection electrode layer has a thickness of less than 30 (μm). As a result, the detection electrode layer can satisfactorily ensure responsiveness to ammonia gas while exhibiting both the thermal shock characteristics and the current collection characteristics.

It is sectional drawing of the ammonia gas sensor 1 of Embodiment 1 which concerns on this invention. FIG. 3 is an enlarged cross-sectional view of the tip side of the sensor element 300 according to the first embodiment. FIG. 3 is an enlarged perspective view of the tip side of the sensor element 300 according to the first embodiment. It is an expanded sectional view of the front end side of the sensor element 400 of Embodiment 2. It is an expansion perspective view of the front end side of the sensor element 400 of Embodiment 2. It is an expanded sectional view of the front end side of the sensor element 500 of Embodiment 3. It is a perspective view of the sensor element 900 of Embodiment 4. It is sectional drawing of the sensor element 900 of Embodiment 4. It is an expansion | deployment perspective view of the sensor element 900 of Embodiment 4. FIG. 3 is an evaluation graph of Test Example 1. 6 is an evaluation graph of Test Example 2. 10 is an evaluation graph of Test Example 3. 10 is an evaluation graph of Test Example 4. 10 is an evaluation graph of Test Example 5. 10 is an evaluation graph of Test Example 6.

  Hereinafter, embodiments of an ammonia gas sensor according to the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a cross-sectional view of an ammonia gas sensor 1 according to the first embodiment. The ammonia gas sensor 1 is used by being attached to an exhaust pipe (not shown) of an internal combustion engine such as an automobile. In the first embodiment, the lower side of FIG. 1 will be described as the front end side, and the upper side will be described as the rear end side.

  The ammonia gas sensor 1 shown in FIG. 1 has a structure in which a cylindrical sensor element 300 whose front end is closed is held in a metal shell 110. Further, from the ammonia gas sensor 1, a lead wire 710 is drawn out for taking out an output signal of the sensor element 300 and energizing the heater 370 provided in the sensor element 300. The lead wire 710 is electrically connected to a sensor control device (not shown) or an electronic control device (ECU) of an automobile.

  The metal shell 110 is a cylindrical member made of stainless steel such as SUS430, and a male screw portion 111 attached to an exhaust pipe (not shown) is provided on the distal end side. Further, a distal end engaging portion 113 to which an outer protector 130 described later is engaged is provided on the distal end side of the male screw portion 111.

  On the other hand, on the rear end side of the male threaded portion 111 of the metal shell 110, a tool engagement portion 114 is provided that engages an attachment tool used when attaching the ammonia gas sensor 1 to the exhaust pipe. Further, a caulking portion 115 for caulking and fixing the sensor element 300 is provided on the rear end side of the metal shell 110. And between the tool engaging part 114 and the crimping part 115, the rear-end engaging part 112 with which the outer cylinder 120 mentioned later is engaged is provided.

  Next, a stepped portion 116 protruding radially inward is provided in the cylinder of the metallic shell 110, and a cylindrical shape made of alumina is provided on the stepped portion 116 through a metal packing (not shown). The support member 210 is supported. Further, the inner periphery of the support member 210 is also formed in a step shape, and a flange portion 301 of the sensor element 300 described later is supported via a metal packing (not shown). Further, a filling member 220 made of talc powder is filled on the rear end side of the support member 210, and a sleeve 230 made of alumina is disposed so as to sandwich the filling member 220 with the support member 210.

  An annular ring 231 is disposed on the rear end side of the sleeve 230, and the sleeve 230 is pressed against the filling member 220 via the ring 231 by crimping the crimping portion 115 of the metal shell 110. .

  Further, an outer protector 130 that covers the distal end side of the sensor element 300 is assembled to the distal end engaging portion 113 of the metal shell 110 by welding. Further, a bottomed cylindrical inner protector 140 is fixed inside the outer protector 130. The outer protector 130 and the inner protector 140 are respectively provided with inlets 131 and 141 for introducing a gas to be measured. In addition, on the bottom surfaces of the outer protector 130 and the inner protector 140, there are provided discharge ports 132 and 142 for discharging water droplets and gas to be measured that have entered the inside, respectively.

  On the other hand, a cylindrical outer cylinder 120 made of stainless steel such as SUS304 is fixed to the rear end engaging portion 112 of the metal shell 110 by laser welding or the like. Further, the outer cylinder 120 extends toward the rear end side, and surrounds a separator 400 (described later) disposed on the rear end side of the sensor element 300 and on the rear side thereof. A part of the outer peripheral surface of the outer cylinder 120 is crimped to lock the holding metal fitting 610 for holding the separator 400.

  The separator 400 includes four connection terminals 700 (in FIG. 1, three connection terminals 700 are electrically connected to the reference electrode portion 320 and the detection electrode 330 of the sensor element 300 and the heating resistor included in the heater 370, respectively. Is held inside. Core wires of four leads 710 are caulked and joined to each connection terminal 700 (three lead wires 710 are shown in FIG. 1), and each lead wire 710 is a grommet 500 described later. Is drawn out of the ammonia gas sensor 1 via In addition, a flange portion 410 protruding outward in the radial direction is provided on the outer peripheral surface of the separator 400, and the holding fitting 610 supports the flange portion 410.

  Further, a substantially columnar grommet 500 made of fluororubber is disposed so as to close the rear end side opening of the outer cylinder 120. A communication hole 510 for introducing air into the outer cylinder 120 passes through the center of the grommet 500 in the radial direction. Furthermore, four lead wire insertion holes 520 through which the lead wires 710 are inserted are also provided at equal positions in the circumferential direction on the outer peripheral side of the communication hole 510.

  Further, the filter member 840 and the fastener 850 are inserted into the communication hole 510 of the grommet 500. The filter member 840 is a thin-film filter having a network structure formed of a fluororesin such as PTFE (polytetrafluoroethylene), for example, and is configured to allow air to communicate without passing water droplets or the like. The fastener 850 is a member formed in a cylindrical shape, and is fixed to the grommet 500 with a filter member 840 sandwiched between the outer periphery of itself and the inner periphery of the communication hole 510.

  Next, the sensor element 300 will be described. 2 is an enlarged cross-sectional view of the distal end side of the sensor element 300, and FIG. 3 is an enlarged perspective view of the distal end side of the sensor element 300. As shown in FIG. 1, a flange-shaped flange portion 301 that protrudes radially outward is provided at a substantially intermediate position of the sensor element 300. As shown in FIGS. 2 and 3, the sensor element 300 includes a bottomed cylindrical solid electrolyte body 310 mainly composed of zirconia. A rod-shaped heater 350 for heating and activating the solid electrolyte body 310 is inserted into the solid electrolyte body 310.

  In addition, a reference electrode portion 320 containing Pt as a main component is formed on the inner surface of the solid electrolyte body 310 so as to cover the entire surface. On the other hand, the detection electrode portion 331 and the selective reaction layer 340 are directly provided in this order on the outer surface on the front end side of the solid electrolyte body 310. Further, a strip-shaped detection lead portion 332 extending from the detection electrode portion 331 is formed on the outer surface of the solid electrolyte body 310. The detection electrode portion 331 overlaps the outer surface on the distal end side of the detection lead portion 332.

Among these, the detection electrode portion 331 has a thickness of 20 μm, and is formed of a material containing Au as a main component and 10 wt% of ZrO ₂ . The detection lead portion 332 has a thickness of 15 μm and is made of a material containing Pt as a main component, 5 wt% ZrO _2, and 5 wt% Au. ZrO ₂ may be partially stabilized zirconia to which yttria (Y) or the like is added.

The selective reaction layer 340 has a thickness of 30 μm and is made of a metal oxide (for example, bismuth vanadium oxide (BiVO ₄ )) containing vanadium oxide (V ₂ O ₅ ) and bismuth oxide (Bi ₂ O ₃ ) as main components. Is formed. Note that the mixing ratio of vanadium oxide (V ₂ O ₅ ) and bismuth oxide (Bi ₂ O ₃ ) in this metal oxide is 45:55. The selective reaction layer 340 is formed so as to cover the entire outer surface of the detection electrode portion 331 so that the detection electrode portion 331 is not exposed to the outside (see FIGS. 2 and 3). Further, a protective layer 360 made of Al ₂ O ₃ is formed on the surface of the selective reaction layer 340 so as not to expose the selective reaction layer 340.

  Such an ammonia gas sensor 1 can suppress the combustible gas from reaching the solid electrolyte body 310 by allowing the selective reaction layer 340 to burn and remove the combustible gas in the gas to be measured well. And the detection electrode part 331 can exhibit current collection action based on ammonia gas, and can generate | occur | produce the electromotive force favorably between the reference electrode layer 320 and the detection electrode part 331 according to the density | concentration of ammonia gas. . As a result, the ammonia gas sensor 1 having excellent gas selectivity and responsiveness to ammonia gas can be obtained. In particular, since the selective reaction layer 340 and the detection electrode portion 331 are provided in two layers, the gas selectivity and responsiveness are particularly excellent.

  In addition, since the detection electrode unit 331 is provided between the solid electrolyte layer 310 and the selective reaction layer 340, the gas to be measured is first exposed to the selective reaction layer 340, so that the combustible gas other than the ammonia gas in the gas to be measured is combusted. The ammonia gas can reach the solid electrolyte layer 310 after the property gas is sufficiently burned.

  Moreover, since the detection electrode part 331 is directly provided on the solid electrolyte body 310, the detection electrode part 331 can exhibit a more favorable current collecting action based on ammonia gas. As a result, an electromotive force can be generated more favorably between the detection electrode 331 and the reference electrode unit 320 according to the ammonia gas concentration.

  In addition, the selective reaction layer 340 covers the detection electrode unit 331 so that the detection electrode unit 331 is not exposed, so that the gas to be measured passes through the selective reaction layer 340 without fail in order to reach the solid electrolyte body 310. Thus, the combustible gas other than the ammonia gas in the gas to be measured is almost burned in the selective reaction layer 340, and then the ammonia gas can reach the solid electrolyte layer 310.

  In addition, the detection electrode portion 331 overlaps the detection lead portion 332, so that the detection electrode portion 331 and the detection lead portion 332 can be electrically connected reliably, and is generated in the reference electrode portion and the detection electrode portion in an external circuit. The electromotive force can be transmitted reliably.

  Moreover, since the detection electrode part 331 is formed with the material which has gold (Au) as a main component, the detection electrode part 331 can exhibit a favorable current collection capability based on ammonia gas. Furthermore, since the detection lead part 332 is made of a material mainly composed of platinum (Pt), the electromotive force generated between the detection electrode part 331 and the reference electrode part 320 can be reliably transmitted to an external circuit. . Since the detection lead portion 332 contains gold having a smaller content than the detection electrode portion 331, the catalytic property of platinum is reduced, and the detection lead portion 332 and the reference electrode portion 320 are reduced. The adhesion strength with the solid electrolyte body 310 and the detection electrode portion 331 can be increased while suppressing the occurrence of a potential difference.

Further, each of the detection electrode portion 331 and the detection lead portion 332 contains zirconia (ZrO ₂ ), and the detection lead portion 331 has a lower zirconia content than the detection electrode portion 332. Thereby, the detection lead part 331 can improve adhesiveness with the solid electrolyte body 310 and an energization effect.

The selective reaction layer 340 is formed of a metal oxide mainly composed of vanadium oxide (V ₂ O ₅ ) and bismuth oxide (Bi ₂ O ₃ ) mixed at a mixing ratio of 45:55. For this reason, thermal temporal stability and responsiveness as an ammonia gas sensor, and gas selectivity with respect to ammonia gas can be ensured satisfactorily.

  In addition, since the thickness of the selective reaction layer 340 is thicker than the thickness of the detection electrode portion 331, the selective reaction layer 340 appropriately selects the ammonia gas from the flammable gas other than the ammonia gas, so that the flammability other than the ammonia gas is obtained. The arrival of the gas at the solid electrolyte layer 310 can be satisfactorily suppressed. In addition, since the thickness of the detection electrode portion 331 is less than 30 (μm), the detection electrode portion 331 exhibits both the thermal shock characteristics and the current collection characteristics well, and has a responsiveness to the gas component of ammonia as an ammonia gas sensor. It can be secured well.

  Furthermore, since the protective layer 360 that covers the selective reaction layer 340 is provided so that the selective reaction layer 340 is not exposed, the selective reaction layer 340 can be measured without being affected by impurities in the measured gas. Combustible gas other than the ammonia gas therein can be combusted satisfactorily, and the arrival of the combustible gas to the solid electrolyte body 310 can be satisfactorily suppressed.

  Next, the manufacturing method of the ammonia gas sensor 1 of Embodiment 1 is demonstrated.

1. Production Step of Solid Electrolyte Layer 310 A partially stabilized zirconia powder is prepared and filled into a bottomed cylindrical rubber mold (not shown). Here, the partially stabilized zirconia is obtained by adding 4.5 (mol%) of yttrium oxide (Y ₂ O ₃ ) as a stabilizer to zirconia (ZrO ₂ ). Then, the partially stabilized zirconia powder is pressure-molded into a bottomed cylindrical shape in a rubber mold and then fired at a firing temperature of 1490 (° C.). Thereby, the bottomed cylindrical solid electrolyte layer 310 is produced.

2. Step of Producing Reference Electrode Layer 320 Next, platinum (Pt) is applied to the inner surface of the solid electrolyte body 310 by electroless plating, and then fired. Thereby, the reference electrode layer 320 is formed on the inner peripheral surface of the solid electrolyte layer 310.

3. Production Step of Detection Lead Portion 332 and Detection Electrode Portion 331 Next, platinum (Pt), zirconia (ZrO ₂ ), an organic solvent, and a dispersant are dispersed and mixed. Next, a predetermined amount of a binder and a viscosity modifier are further added and wet-mixed to produce a detection lead portion paste. Also, gold (Au), zirconia (ZrO2), an organic solvent and a dispersant are dispersed and mixed. Next, a binder and a viscosity adjusting material are further added in predetermined amounts and wet-mixed to produce a detection electrode part paste.

  Then, the detection electrode part paste and the detection lead part paste are printed on the bottom and side surfaces of the solid electrolyte member 310 produced as described above. Specifically, the detection lead portion paste is printed in a strip shape so as to extend in the axial direction of the solid electrolyte body 310, and the detection electrode portion paste is printed so as to overlap the front end side of the printed detection lead portion paste. To do. Thereafter, it is dried and fired at 1000 (° C.) for 1 hour. Thereby, the detection electrode part 331 and the detection lead part 332 are produced on the outer surface of the solid electrolyte layer 310.

4). Next, a composite oxide composed of vanadium oxide (V ₂ O ₅ ) and bismuth oxide (Bi ₂ O ₃ ), an organic solvent, and a dispersant are dispersed and mixed. Note that vanadium and bismuth constituting vanadium oxide and bismuth oxide are 45:55, that is, 45 (at%) in a mixing ratio. Next, a predetermined amount of each of the binder and the viscosity modifier is further added and wet-mixed to prepare a paste for the selective reaction layer.

Then, the paste for the selective reaction layer is printed so as to cover the detection electrode portion 331, dried, fired at 750 (° C.) for 10 minutes, and bismuth vanadium oxide (BiVO ₄ ). A selective reaction layer 340 is produced. Note that the selective reaction layer 340 may be formed mainly from bismuth oxide vanadium and may contain vanadium oxide or bismuth oxide.

5. Step for Producing Protective Layer 360 Next, alumina (Al ₂ O ₃ ), an organic solvent, and a dispersant are dispersed and mixed. Then, a predetermined amount of each of the binder and the viscosity adjusting material is further added and wet-mixed to produce a protective layer paste.

  Then, the protective layer paste is printed so as to cover the selective reaction layer 340, dried, and baked at 750 (° C.) for 10 minutes to prepare the protective layer 360.

7). Other Assembling Process of Ammonia Gas Sensor 1 After the sensor element 300 is manufactured as described above, the sensor element 300 is held in the metal shell 110. Next, the separator 400 is held in the outer cylinder 120 via the holding metal fitting 610, and the grommet 500, each terminal 700, and each covered conductor 710 are assembled in the outer cylinder 120. Thereby, manufacture of ammonia gas sensor 1 is completed.

(Embodiment 2)
4 shows an enlarged cross-sectional view of the tip side of the sensor element 400 attached to the ammonia gas sensor 2 of Embodiment 2, and FIG. 5 shows an enlarged perspective view of the tip side of the sensor element 400. In the second embodiment, in the sensor element 300 described in the first embodiment, a detection electrode portion 371 and a detection lead portion 372 are provided instead of the detection electrode portion 331 and the detection lead portion 332. In addition, about the ammonia gas sensor 2 of Embodiment 2, the description similar to Embodiment 1 is abbreviate | omitted or simplified, and the site | part similar to Embodiment 1 is demonstrated using a same sign.

  In the second embodiment, a detection electrode portion 371 and a detection lead portion 372 are provided on the surface of the solid electrolyte body 310. The detection electrode part 371 passes through the bottom of the solid electrolyte layer 310 and extends symmetrically and in a strip shape toward the rear side of the bottom of the solid electrolyte layer 310. Further, the detection lead part 372 extends in the axial direction of the solid electrolyte body 310 from the rear end side of the detection electrode part 371. The detection electrode portion 371 is provided so as to overlap the tip end side of the detection lead portion 372. Other configurations are the same as those of the first embodiment.

  As described above, even in a configuration in which the detection electrode portion 371 extends symmetrically and in a band shape to the rear end side of the solid electrolyte body 310 through the bottom of the solid electrolyte body 310, ammonia having excellent gas selectivity and responsiveness to ammonia gas. The gas sensor 2 can be obtained.

(Embodiment 3)
FIG. 6 shows an enlarged cross-sectional view of the front end side of the sensor element 500 attached to the ammonia gas sensor 3 according to Embodiment 3 of the present invention. In the third embodiment, the sensor element 300 described in the first embodiment is further provided with a porous layer 380 between the detection electrode portion 331 and the selective reaction layer 340. In addition, about the ammonia gas sensor 3 of Embodiment 3, the description similar to Embodiment 1 is abbreviate | omitted or simplified, and the site | part similar to Embodiment 1 is demonstrated using a same sign.

In the third embodiment, the porous layer 380 is provided so as to cover a part of the detection electrode portion 331 and the detection lead portion 332. The porous layer 380 is formed so as to cover the entire outer surface of the detection electrode portion 331 so that the detection electrode portion 331 of the detection electrode layer 330 is not exposed to the outside. This porous layer 380 is formed of a porous material mainly composed of alumina (Al ₂ O ₃ ).

  Furthermore, as shown in FIG. 6, the selective reaction layer 340 is formed so as to cover the entire outer surface of the porous layer 380 so as not to expose the porous layer 380 to the outside. Other configurations are the same as those of the ammonia gas sensor described in the first embodiment.

  Thus, since the porous layer 380 is provided between the detection electrode part 331 and the selective reaction layer 340 so as to cover the entire outer surface of the detection electrode part 331, the detection electrode part 331 and the selective reaction layer 340 Insulation can be secured. Therefore, it is possible to prevent the detection electrode portion 331 from being affected by the change of the selective reaction layer 340 with time.

  Next, only the steps different from those in the first embodiment will be described for the method for manufacturing the ammonia gas sensor in the third embodiment.

First, Al ₂ O ₃ , an organic solvent, and a dispersing agent are dispersed and mixed, and then a binder and a viscosity adjusting material are further added in predetermined amounts, and wet mixing is performed to produce a porous layer paste.

  Then, the porous electrode paste is printed and dried so as to cover the detection electrode portion paste on the solid electrolyte body 310 on which the detection electrode portion paste is printed in step 3 of the first embodiment. .

  Thereafter, the solid electrolyte layer 310 obtained by printing and drying the detection electrode member paste and the porous layer paste is fired at a firing temperature of 1000 (° C.) for 1 hour. Thereby, the detection electrode layer 330 and the porous layer 380 are formed. The porous layer 380 is formed so as to cover the detection electrode layer 330 so that the detection electrode layer 330 is not exposed to the outside.

  Then, the paste for the selective reaction layer described in the first embodiment is printed on the bottom surface and the side surface of the solid electrolyte layer 310 so as to cover the porous layer 380 and dried, and the firing temperature is 750 (° C.). Bake for 10 minutes. Accordingly, the selective reaction layer 340 is formed so as to cover the porous layer 380 so as not to expose the porous layer 380 to the outside. Other manufacturing steps are the same as those in the first embodiment.

(Embodiment 4)
7 to 9 show a sensor element 900 of the ammonia gas sensor 4 according to Embodiment 4 of the present invention. The ammonia gas sensor 4 of the fourth embodiment is configured by assembling a plate-type sensor element 900 instead of the gas sensor element 300 of the first embodiment, and the other parts are the same as those of the first embodiment. In addition, about the ammonia gas sensor 4 of Embodiment 4, the description similar to Embodiment 1 is abbreviate | omitted or simplified, and the site | part similar to Embodiment 1 is demonstrated using a same sign.

  The plate-type sensor element 900 is coaxially held in the metal shell 110. The sensor element 900 includes a solid electrolyte body 940 made of the same material as the solid electrolyte body 310 of the first embodiment.

  Further, a reference electrode portion 931 and a reference lead portion 932 are provided on the back surface of the solid electrolyte body 940 with an insulating film 933 interposed therebetween. Among these, the reference electrode portion 931 is disposed at a position corresponding to the opening 934 formed on the distal end side of the insulating film 933, and is in close contact with the distal end portion of the solid electrolyte body 940. On the other hand, the reference lead portion 932 is formed from the front end side on the back surface of the insulating film 933 toward the rear end side. The reference lead portion 932 is electrically connected to the electrode pad 961 through the through hole 935 of the insulating film 933 and the through hole 941 of the solid electrolyte body 940. The reference electrode portion 931 is made of a material containing 12 wt% of partially stabilized zirconia containing Pt as a main component and containing 5.4 mol% yttria. On the other hand, the reference lead portion 932 is made of a material containing Pt as a main component and 5 wt% alumina.

  Further, a protective layer 925 is formed on the back surface of the reference electrode portion 931. Further, an insulating layer 922 is formed on the back surface of the insulating film 933 so as to sandwich the reference lead portion 932 and the protective layer 925. Further, a heater 920, an insulating layer 915, a temperature sensor 910, and an insulating layer 905 are stacked in this order on the back surface of the insulating layer 922.

  On the other hand, a detection lead portion 960 and an electrode pad 961 made of a material containing platinum (Pt) as a main component and 5 wt% of partially stabilized zirconia containing 4 mol% yttria are formed on the surface of the solid electrolyte body 940. ing. The detection lead portion 960 and the electrode pad 961 extend on the surface of the solid electrolyte body 940 from the front end side toward the rear end side.

A detection electrode portion 980 is formed so as to overlap the distal end portion 962 of the detection lead portion 960. The detection electrode portion 980 is formed of a material containing gold (Au) as a main component and 10 wt% of partially stabilized zirconia containing 4 mol% yttria, and is in close contact with the surface of the solid electrolyte body 940. Further, a selective reaction layer 990 made of the same material as the selective reaction layer 360 described in Embodiment 1 is provided on the surface of the detection electrode unit 980. Further, a protective layer 995 containing Al ₂ O ₃ as a main component is formed on the surface of the selective reaction layer 990 so as not to expose the selective reaction layer 990.

  In the ammonia gas sensor 4 arranged in this way, the selective reaction layer 990 can combust and remove the combustible gas in the gas to be measured well, and the arrival of the combustible gas to the solid electrolyte body 940 can be suppressed. Then, the detection electrode unit 980 exhibits a current collecting action based on the ammonia gas, and generates an electromotive force between the reference electrode unit 932 and the detection electrode unit 980 according to the concentration of the ammonia gas. As a result, gas selectivity and responsiveness to ammonia gas are excellent.

Further, the content of zirconia (ZrO ₂ ) in the detection electrode unit 980 is smaller than the content of zirconia in the reference electrode unit 931. As a result, the detection electrode unit 980 can obtain good responsiveness based on ammonia gas while maintaining adhesion to the solid electrolyte body 940. Further, the content of zirconia (ZrO ₂ ) in the detection lead portion 960 is less than the content of the detection electrode portion 980. Thereby, the electricity supply effect can be enhanced while maintaining the adhesion between the detection lead portion 960 and the solid electrolyte body 940.

(Test Example 1)
As Test Example 1, the sensitivity of the ammonia gas sensor 1 of Embodiment 1 was evaluated. In this evaluation, the ammonia gas sensor 1 of the first embodiment is referred to as Example 1. In addition, a comparative example (hereinafter referred to as comparative example 1) was also prepared as an object to be compared with Example 1.

Specifically, in Comparative Example 1, the detection electrode portion 331 is not provided, and the solid electrolyte layer 310 is manufactured using only bismuth vanadium oxide (BiVO ₄ ).

In the above evaluation, a model gas generator was adopted as an evaluation device. The gas for evaluation generated in this model gas generator is as follows.
10 (%) oxygen (O ₂ ), 5 (%) carbon dioxide (CO ₂ ), 5 (%) water (H ₂ O), and nitrogen (N ₂ ) are used as base gases. For this base gas, ammonia gas (NH ₃ ), propylene gas (C ₃ H ₆ ), carbon monoxide gas (CO) and nitrogen monoxide gas (NO) were added 100 ppm each for evaluation. Gas was used. The temperature of the evaluation gas is 280 (° C.).

  Example 1 and Comparative Example 1 described above were placed in the model gas generator, and an evaluation gas was allowed to flow. In Example 1 and Comparative Example 1, the potential difference generated between the reference electrode layer 320 and the detection electrode unit 331 is measured. In addition, each control temperature of Example 1 and Comparative Example 1 is maintained at 650 (° C.) under heating by the heater 350.

And each gas sensitivity (mV) of Example 1 and Comparative Example 1 was measured in relation to each gas component of the gas for evaluation. The gas sensitivity is obtained by subtracting the electromotive force of the base gas from the electromotive force of the evaluation gas. The results are shown in FIG. In FIG. 10, bar graphs 1 to 1 correspond to the gas components of ammonia (NH ₃ ), propylene (C ₃ H ₆ ), carbon monoxide (CO), and nitrogen monoxide (NO) in Example 1. Indicates gas sensitivity. Moreover, the bar graphs 2 to 2-3 show the gas sensitivities for the ammonia, propylene, carbon monoxide, and nitrogen monoxide gas components of Comparative Example 1.

  Although the gas sensitivity with respect to ammonia gas of Example 1 and Comparative Example 1 is high, the gas sensitivity with respect to propylene gas, carbon monoxide gas, and nitrogen monoxide gas of Comparative Example 1 is higher than that of Example 1. became. That is, it can be said that Example 1 has higher gas selectivity with respect to ammonia gas than Comparative Example 1.

(Test Example 2)
Next, the responsiveness between Example 1 and Comparative Example 1 was evaluated. Specifically, Example 1 and Comparative Example 1 were arranged using the same model gas generator as in Example 1. The base gas of Example 1 was allowed to flow from the start until 200 (seconds), and from 200 (seconds) to 400 (seconds), the evaluation gas added with 100 (ppm) ammonia gas was added. Washed away. The results are shown in FIG. In addition, FIG. 11 shows the change with respect to time of the electromotive force of Example 1 and Comparative Example 1, that is, responsiveness. In FIG. 11, graph 3 shows the responsiveness of Example 1, and graph 4 shows the responsiveness of Comparative Example 1.

  As shown in FIG. 11, it can be said that Example 1 has better responsiveness at the time of addition of the evaluation gas and at the end of the addition than that of Comparative Example 1.

(Test Example 3)
Next, the gas sensitivity with respect to the mixing ratio of vanadium was evaluated. In Examples 2 to 5, the mixing ratio of vanadium and bismuth constituting vanadium oxide and bismuth oxide is made different from that in Example 1, and the others are made in the same manner as in Example 1. Specifically, vanadium is used in order from Example 2 and Example 3 to Example 8 in the order of 5 (at%), 20 (at%), 25 (at%), 35 (at%), and 50 (at %), 55 (at%), and 95 (at%).

As an evaluation method, the ammonia gas sensor 1 of Examples 2 to 8 is disposed in the same model gas generator as that of Example 1, and ammonia gas (NH ₃ ) is changed to 100 (ppm) as the base gas of Example 1. The added evaluation gas was allowed to flow. The results are shown in FIG. Note that FIG. 12 also shows Example 1.

  In Examples 1-5, it turns out that the gas sensitivity with respect to ammonia gas is high in Example 1 and Examples 4-6 whose mixing ratio of vanadium is 25 (at%)-50 (at%). At%, that is, if the mixing ratio of vanadium in the selective reaction layer is in the range of 25 (at%) to 50 (at%), the gas sensitivity to ammonia gas is better secured.

(Test Example 4)
Next, the gas sensitivity with respect to the additive added to the selective reaction layer 340 was evaluated. In Example 9, the metal oxide forming the selective reaction layer 340 further contains 5 (at%) of tungsten, Example 8 further contains 5 (at%) of niobium, and Example 9 Further, 2.5 (at%) magnesium is contained. In addition, Examples 9-11 are produced similarly to Example 1 except the above-mentioned point.

As an evaluation method, the ammonia gas sensor 1 of Examples 9 to 11 is arranged in the same model gas generator as that of Example 1, and ammonia gas (NH ₃ ) and propylene gas (C ₃ H) are used as the base gas of Example 1. ₆ ) An evaluation gas to which 100 (ppm) of carbon monoxide gas (CO) and nitrogen monoxide gas (NO) was added was allowed to flow. The results are shown in FIG. Note that FIG. 13 also shows Example 1.

  In FIG. 13, bar graphs 6 to 6-3 indicate gas sensitivities for the ammonia, propylene, carbon monoxide, and nitrogen monoxide gases of Example 9. Bar graphs 6-4 to 6-7 show the gas sensitivities for the ammonia, propylene, carbon monoxide, and nitrogen monoxide gases of Example 10. Bar graphs 6-8 to 6-11 show the gas sensitivities for the ammonia, propylene, carbon monoxide, and nitrogen monoxide gases of Example 11.

  In any of the ammonia gas sensors 1 of Examples 1 and 9 to 11, the gas sensitivity to ammonia gas is high, and the gas sensitivity to each gas of propylene, carbon monoxide, and nitrogen monoxide is low as in Example 1. I understand. Therefore, it can be said that the gas selectivity is good as in Example 1 even if the selective reaction layer 340 contains an additive in the metal oxide as in Examples 9-11.

(Test Example 5)
Next, the gas sensitivity with respect to the thickness of the detection electrode part 331 was evaluated. In Example 12, the thickness of the detection electrode portion 331 is 30 μm, and in Example 13, the thickness of the detection electrode is 60 μm. Examples 12 and 13 were produced in the same manner as Example 1 except for the points described above.

As an evaluation method, Examples 12 and 13 are arranged in a model gas generator similar to Example 1, and an evaluation gas in which 10 (ppm) of ammonia gas (NH ₃ ) is added to the base gas of Example 1, Alternatively, an evaluation gas added with 100 (ppm) was allowed to flow. The results are shown in FIG. Note that FIG. 14 also shows Example 1 (thickness: 20 μm). Further, the thickness of the selective reaction layer 340 in each of Examples 12 and 13 is 30 (μm), as in Example 1.

  In FIG. 14, bar graphs 1-4, 7 and 7-2 show gas sensitivities to 10 ppm of ammonia gas in Examples 1, 12 and 13, respectively. Moreover, bar graph 1, 7-1 and 7-3 show the gas sensitivity with respect to 100 (ppm) ammonia gas in Examples 1, 12 and 13, respectively.

  According to FIG. 14, when ammonia gas is 100 (ppm), it turns out that Example 1, 12, 13 has high gas sensitivity with respect to ammonia gas. On the other hand, when the ammonia gas is 10 (ppm), the gas sensitivity to ammonia gas decreases as the thickness of the detection electrode layer 331 increases. And in order to ensure favorable gas sensitivity with respect to ammonia gas as an ammonia gas sensor, it is preferable that the thickness of the selective reaction layer is less than 30 (μm).

(Test Example 6)
Next, the characteristics of the ammonia gas sensor 3 of Embodiment 3 were evaluated with the gas sensitivity before and after the actual machine test. In this evaluation, the ammonia gas sensor 3 of the third embodiment was taken as Example 14. In addition to Example 14, Examples 15 to 19 and Example 1 were prepared. The porous layer forming material of Example 15 is MgAl ₂ O ₄ , the porous layer forming material of Example 16 is SiO _2, and the porous layer forming material of Example 17 is SiO ₂ / Al. ₂ O ₃ was used, the porous layer forming material of Example 18 was zeolite, and the porous layer forming material of Example 16 was SiC. Examples 15 to 19 have the same configuration as that of Example 14 except for the material for forming the porous layer.

As an evaluation method, Examples 14 to 19 are arranged in the same model gas generator as Example 1, and an evaluation gas obtained by adding 100 (ppm) of ammonia gas (NH ₃ ) to the base gas of Example 1 is used. Washed away.

Next, in an actual machine test, an oxidation catalyst device (DOC) or DPF (Diesel) in which a 3.0 L diesel engine was used as an engine bench and each of Examples 1, 11 to 16 was provided in an exhaust pipe of the diesel engine.
It was placed downstream of the Particulate Filter.

  And as an actual machine test method, it was carried out for 500 hours by a cycle test in which engine idling: 10 (minutes) and 3000 (rpm): 30 (minutes) were alternately performed. The results are shown in FIG.

  In FIG. 15, bar graphs 10-1, 10-3, 10-5, 10-7, 10-9, 10-11, and 10-13 are examples 1 arranged in the model gas generator before the actual machine test, Gas sensitivity of 14-19. Further, in FIG. 15, each graph 10-2, 10-4, 10-6, 10-8, 10-10, 10-12, and 10-14 is shown in each implementation arranged in the model gas generator after the actual machine test. It is the gas sensitivity of Examples 1 and 14-19.

  As shown in FIG. 15, the gas sensitivity of Example 1 is lower after the actual machine test than before the actual machine test. On the other hand, the gas sensitivities of Examples 14 to 19 hardly change. That is, by providing the porous layer 380, it has high gas selectivity with respect to ammonia gas, excellent responsiveness, and excellent long-term stability even after an actual machine test.

In carrying out the present invention, the following various modifications are possible without being limited to the above embodiment.
(1) In Embodiments 1 to 4 of the present invention, the detection electrode portions 331, 371, and 980 are provided on the solid electrolyte bodies 310 and 940, and the selective reaction layers 340 and 990 are further provided. The selective reaction layer is provided on the solid electrolyte layer 310. 340 and 990 may be provided, and detection electrode portions 331, 371, and 980 may be further provided.
(3) The electrode material forming the detection electrode portions 331, 371, and 980 according to the first to fourth embodiments of the present invention may be made of platinum (Pt) as a main component instead of gold.
(4) Antimony oxide (Sb ₂ O ₃ ) may be used in place of the bismuth oxide as the selective reaction material in the first to fourth embodiments of the present invention. In addition, in order to finely adjust the catalytic ability of the selective reaction layer 320 and improve the thermal stability, at least one of WO ₃ , MoO ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ , MgO, CaO, SrO, and BaO. One kind may be added to the selective reaction material up to about 5 (at%).
(5) In Embodiment 4 of the present invention, the reference electrode portion 931 and the detection electrode portion 980 are opposed to each other with the solid electrolyte body 940 interposed therebetween, but the reference electrode portion 931 and the detection electrode portion 980 are made to face each other. It may be arranged side by side on one side of 940.
(6) In the first to fourth embodiments of the present invention, the protective layers 360 and 995 are formed by printing a protective layer paste, but the protective layers 360 and 995 may be provided by thermal spraying.
(7) In carrying out the present invention, the ammonia gas sensor is not limited to an exhaust gas system of an internal combustion engine, and the present invention is applied to any engine or device that generates exhaust gas. Also good.

310 ... Solid electrolyte layer, 331, 371 ... Detection electrode part, 332, 372 ... Detection lead part, 340 ... Selective reaction layer, 360 ... Protective layer, 380 ... Porous layer

According to the first aspect of the present invention, an ammonia gas sensor extends in the axial direction and has a solid electrolyte body mainly composed of zirconia, a reference electrode section provided on the solid electrolyte body, and a reference electrode section. In the ammonia gas sensor having a detection electrode part and a selective reaction layer provided on the solid electrolyte body as a counter electrode, the detection electrode part has a precious metal as a main component, and the selective reaction layer has a metal oxide as a main component , The selective reaction layer has a thickness greater than that of the detection electrode portion .

The detection electrode part and the selective reaction layer may be formed on the surface of the solid electrolyte body so as to be a counter electrode with the reference electrode part, and the detection electrode part, the selection reaction layer, and the reference electrode part are the solid electrolyte body. The detection electrode part, the selective reaction layer, and the reference electrode part may be provided on the same surface of the solid electrolyte body. Furthermore, each of the detection electrode part, the selective reaction layer, and the solid electrolyte body may be in direct contact, or may have another member interposed therebetween.
Moreover, the thickness of the selective reaction layer is thicker than the thickness of the detection electrode layer. Thereby, the selective reaction layer can favorably suppress the arrival of the combustible gas other than the ammonia gas to the solid electrolyte layer by appropriately selecting the ammonia gas from the combustible gas other than the ammonia gas.
According to a second aspect of the present invention, the detection electrode layer has a thickness of less than 30 (μm). As a result, the detection electrode layer can satisfactorily ensure responsiveness to ammonia gas while exhibiting both the thermal shock characteristics and the current collection characteristics.

Further, according to the present invention, the detection electrode unit may be provided between the solid electrolyte body and the selective reaction layer . With such a configuration, the gas to be measured is first exposed to the selective reaction layer, so that the combustible gas other than the ammonia gas in the gas to be measured is sufficiently burned, and then the ammonia gas is converted into the solid electrolyte. Can reach the body.

According to the present invention, the detection electrode part may be provided directly on the solid electrolyte body . By setting it as such a structure, a detection electrode part can exhibit a favorable current collection effect | action more based on ammonia gas. As a result, an electromotive force can be generated more favorably between the detection electrode portion and the reference electrode portion according to the ammonia gas concentration.

Further, according to the present invention, the selective reaction layer, the detection electrode can have I covering the detection electrode so as not to be exposed. In this way, by completely covering the detection electrode portion with the selective reaction layer, the gas to be measured can surely pass through the selective reaction layer in order to reach the solid electrolyte body. Then, after combustible gas other than ammonia gas in the gas to be measured is almost burned in the selective reaction layer, the ammonia gas can reach the solid electrolyte body.

In addition, according to the present invention, in order to electrically connect the detection electrode unit and an external circuit, the detection electrode unit has a strip-shaped detection lead unit extending in the axial direction from the detection electrode unit, and the detection electrode unit is provided on the detection lead unit. can have me heavy Do not. With such a configuration, the detection electrode part and the detection lead part can be electrically connected reliably, and the electromotive force generated in the reference electrode part and the detection electrode part can be reliably transmitted to the external circuit.

According to the present invention, the solid electrolyte body has a bottomed cylindrical shape having a bottom portion on the tip side, the reference electrode portion is formed on the inner surface of the solid electrolyte body, and the detection electrode portion is a solid electrolyte body. It may be provided on the outer surface of the tip side . Thus, even if the solid electrolyte body is formed in a bottomed cylindrical shape and the reference electrode part and the detection electrode part are provided on the inner surface and the outer surface of the solid electrolyte body, respectively, noble metal is the main component. By providing the detection electrode section and the selective reaction layer mainly composed of a metal oxide, an ammonia gas sensor excellent in gas selectivity and responsiveness to ammonia gas can be obtained.

  As one of the shapes, the detection electrode portion may extend symmetrically and in a band shape to the rear end side of the solid electrolyte body through the bottom of the solid electrolyte body.

Further, according to the present invention, the detection electrode is mainly composed of platinum, the material further contains gold, or gold can have I Do a material composed mainly of. By setting it as such a structure, a detection electrode part can exhibit a favorable current collection effect | action more based on ammonia gas. As a result, an electromotive force can be generated more favorably between the detection electrode portion and the reference electrode portion according to the ammonia gas concentration.

Further, according to the present invention, detection lead may have I Do a material composed mainly of platinum. By adopting such a configuration, an electromotive force generated between the detection electrode unit and the reference electrode unit can be reliably transmitted to the external circuit.

According to the present invention, the detection lead portion may contain less gold than the content contained in the detection electrode portion . By containing gold in the detection lead portion, the catalytic property of platinum can be reduced, and the occurrence of a potential difference between the detection lead portion and the reference electrode portion can be suppressed. In addition, by making the gold contained in the detection lead portion smaller than the detection electrode portion, simultaneous firing with the solid electrolyte body becomes possible, and the adhesion strength with the solid electrolyte body can be increased. Furthermore, the adhesion strength with the detection electrode part can also be increased.

Further, according to the present invention, the reference electrode and the detection electrode, the zirconia has been contained, the detection electrode may be rather low content of zirconia than the reference electrode. The reference electrode portion and the detection electrode portion contain zirconia in consideration of adhesion with the solid electrolyte body. And the favorable current collection effect | action based on the ammonia gas of a detection electrode part is also maintained by reducing the zirconia contained in a detection electrode part rather than a reference | standard electrode part.

Further, according to the present invention, the detection lead zirconia has been contained, detection lead may be rather low content of zirconia than the detection electrode unit. As described above, zirconia is also contained in the detection lead portion in consideration of adhesion to the solid electrolyte body. And the energization effect of a detection lead part can be heightened by reducing the zirconia contained in a detection lead part rather than a detection electrode part.

According to the present invention, a porous layer may be provided between the detection electrode portion and the selective reaction layer . By setting it as such a structure, the insulation between a selective reaction layer and a detection electrode part is ensured. Therefore, the influence on the detection electrode part due to the temporal change of the selective reaction layer is prevented, and good gas selectivity can be maintained over a long period of time.

Further, according to the present invention, the porous layer, the detection electrode portion can have I covering the detection electrode so as not to be exposed. With such a configuration, the porous layer can reliably ensure insulation between the detection electrode portion and the selective reaction layer.

Further, according to the present invention, the selective reaction layer, the porous layer may have I covering the porous layer so as not to be exposed. By adopting such a configuration, it is possible to prevent the phenomenon that combustible gas other than ammonia gas flows directly into the detection electrode portion through the porous layer without going through the selective reaction layer. An ammonia gas sensor excellent in gas selectivity can be obtained.

According to the present invention, the porous layer may contain at least one of Al ₂ O ₃ , MgAl ₂ O ₄ , SiO ₂ , SiO ₂ / Al ₂ O ₃ , zeolite, and SiC . Thereby, the insulation by a porous layer can be ensured more specifically.

Moreover, according to this invention, the protective layer which covers a selective reaction layer so that a selective reaction layer may not be exposed may be provided. By adopting such a configuration, the selective reaction layer is not affected by impurities (for example, phosphorus, lead, etc.) in the gas to be measured. Therefore, the selective reaction layer can satisfactorily burn the combustible gas other than the ammonia gas in the gas to be measured, and the combustible gas can be satisfactorily suppressed from reaching the solid electrolyte body. As the protective _{layer, MgAl 2 O 4, Al 2} O 3, SiO 2 / Al 2 O 3, zeolites, and the like.

Further, according to the present invention, the selective reaction layer, at least one of bismuth vanadium oxide and antimony vanadium oxide may be a main component. By setting it as such a structure, the selective reaction layer can burn combustible gas other than ammonia gas in measurement gas favorably.

According to the present invention, the selective reaction layer is at least one of tungsten oxide, molybdenum oxide, niobium oxide, tantalum oxide, magnesium oxide, canoledium oxide, strontium oxide, and barium oxide. May be further added . When the additive is further added to the selective reaction layer in this way, the selective reaction layer can burn the combustible gas other than the ammonia gas in the gas to be measured more satisfactorily.

Moreover, according to this invention, vanadium may be contained in the range of 25 (at%) to 50 (at%) . As a result, it is possible to satisfactorily ensure the thermal stability over time and the responsiveness as an ammonia gas sensor and the gas selectivity with respect to the ammonia gas.

Then, a pair one strike for this selective reaction layer, and dried by printing so as to cover the detection electrode 331, and calcined between 750 (° C.) for 10 (minutes), bismuth oxide, vanadium (BiVO ₄₎ A selective reaction layer 340 is produced. Note that the selective reaction layer 340 may be formed mainly from bismuth oxide vanadium and may contain vanadium oxide or bismuth oxide.

Then, a pair one strike protective layer, and dried by printing so as to cover the selective reaction layer 340, and fired between 750 (° C.) for 10 minutes to produce a protective layer 360.

Claims (22)

A solid electrolyte body extending in the axial direction and mainly composed of zirconia;
A reference electrode provided on the solid electrolyte body;
In the ammonia gas sensor provided with a detection electrode part and a selective reaction layer provided on the solid electrolyte body as a counter electrode with the reference electrode part,
The detection electrode part is mainly composed of a noble metal,
The selective reaction layer is an ammonia gas sensor whose main component is a metal oxide.   The ammonia gas sensor according to claim 1, wherein the detection electrode unit is provided between the solid electrolyte body and the selective reaction layer.   The ammonia gas sensor according to claim 2, wherein the detection electrode unit is directly provided on the solid electrolyte body.   The ammonia gas sensor according to any one of claims 1 to 3, wherein the selective reaction layer covers the detection electrode part so that the detection electrode part is not exposed. In order to electrically connect the detection electrode part and an external circuit, it further has a strip-shaped detection lead part extending in the axial direction from the detection electrode part,
The ammonia gas sensor according to claim 4, wherein the detection electrode portion overlaps the detection lead portion. The solid electrolyte body has a bottomed cylindrical shape having a bottom on the tip side,
The reference electrode portion is formed on the inner surface of the solid electrolyte body,
The ammonia gas sensor according to claim 1, wherein the detection electrode unit is provided on an outer surface on a front end side of the solid electrolyte body.   The ammonia gas sensor according to claim 6, wherein the detection electrode portion extends symmetrically and in a band shape to the rear end side of the solid electrolyte body through the bottom portion of the solid electrolyte body.   The ammonia gas sensor according to any one of claims 4 to 7, wherein the detection electrode portion is made of a material containing platinum as a main component and further containing gold, or a material containing gold as a main component.   The ammonia gas sensor according to any one of claims 4 to 8, wherein the detection lead portion is made of a material whose main component is platinum.   The ammonia gas sensor according to claim 9, wherein the detection lead portion contains less gold than the content contained in the detection electrode portion.   The reference electrode part and the detection electrode part contain zirconia, and the detection electrode part contains less zirconia than the reference electrode part. The ammonia gas sensor according to one item.   The zirconia is contained in the detection lead part, and the content of the zirconia in the detection lead part is smaller than that of the detection electrode part. Ammonia gas sensor.   The ammonia gas sensor according to any one of claims 2 to 12, wherein a porous layer is provided between the detection electrode portion and the selective reaction layer.   The ammonia gas sensor according to claim 13, wherein the porous layer covers the detection electrode portion so that the detection electrode portion is not exposed.   The ammonia gas sensor according to claim 13 or 14, wherein the selective reaction layer covers the porous layer so that the porous layer is not exposed. The porous layer contains at least one of Al ₂ O ₃ , MgAl ₂ O ₄ , SiO ₂ , SiO ₂ / Al ₂ O ₃ , zeolite, and SiC. The ammonia gas sensor according to one item.   The ammonia gas sensor according to any one of claims 2 to 16, further comprising a protective layer that covers the selective reaction layer so that the selective reaction layer is not exposed.   The ammonia gas sensor according to any one of claims 1 to 17, wherein the selective reaction layer contains at least one of bismuth vanadium oxide and antimony vanadium oxide as a main component.   The selective reaction layer is formed by further adding at least one of tungsten oxide, molybdenum oxide, niobium oxide, tantalum oxide, magnesium oxide, calcium oxide, strontium oxide, and barium oxide. The ammonia gas sensor according to claim 18.   The ammonia gas sensor according to claim 18 or 19, wherein the selective reaction layer contains 25 (at%) to 50 (at%) of vanadium.   21. The ammonia gas sensor according to claim 1, wherein a thickness of the selective reaction layer is thicker than a thickness of the detection electrode portion.   The thickness of the said detection electrode part is less than 30 (micrometer), The ammonia gas sensor as described in any one of Claims 1-21 characterized by the above-mentioned.