Ammonia gas sensor

Abstract

Ammonia gas sensor (1), comprising: a solid electrolyte element (310, 940) extending in an axial direction and containing zirconium oxide as the predominant component; a detection section provided on a front surface of the solid electrolyte element (310, 940); a reference electrode section (320, 931) provided on a rear surface of the solid electrolyte element (310, 940); and a detection lead section (350, 960) which is provided directly or via a further element on the front surface of the solid electrolyte element (310, 940) in order to establish an electrical connection between the detection section and an external circuit, wherein an insulating section (340, 380, 950, 970) is provided at least on one surface of the detection lead section (350, 960) or between the detection lead section (350, 960) and the solid electrolyte element (310, 940), wherein the detection section comprises a detection electrode section (335, 980) formed of a noble metal and a selective reaction layer (360, 390) formed of a metal oxide with ammonia gas selectivity, wherein the insulating section (340, 380, 950, 970) is formed on the surface of the detection lead section (350, 960) and comprises a first insulating section (381) extending in the axial direction to the surface of the detection electrode section (335, 980), wherein the detection lead section (350, 960) is insulated from the gas to be measured by means of the insulating section (340, 380, 950, 970).

Description

Technical field

[0001] The invention relates to an ammonia gas sensor for detecting ammonia gas contained in a gas subjected to measurement.

[0002] A generic ammonia gas sensor with the features of claim 1 or 4 is known from US 5 110 442 A. background

[0003] The ammonia gas sensor of the type in question is typically an ammonia gas concentration measuring device as disclosed in patent document 1. This ammonia gas concentration measuring device comprises a solid electrolyte element, a reference electrode section provided on one side of the solid electrolyte element, and a sensing electrode section provided on the opposite side of the solid electrolyte element.

[0004] When this ammonia gas concentration measuring device is used, the reference electrode section is exposed to the atmosphere, while the sensing electrode section is exposed to the gas being measured. The ammonia gas concentration measuring device generates an electromotive force proportional to the difference in oxygen partial pressure between the reference electrode section and the sensing electrode section, depending on the ammonia gas concentration in the gas being measured, in order to detect the ammonia gas concentration.

[0005] US patent 5,110,442 A discloses an electrolyte with two sides on which electrodes are placed. A conduction layer is also provided to conduct the current to the electrodes.

[0006] US 5 032 248 A generally describes an electrode that is connected via a wiring pattern.

[0007] Patent Document 1: Published Japanese patent application JP 2003-83933 A Disclosure of the invention Problems to be solved by the invention

[0008] In the ammonia gas concentration measuring device of patent document 1, a sensing lead section is configured to extend from the sensing electrode section. A portion of this sensing lead section is exposed to the gas being measured, along with the sensing electrode section. Since this sensing lead section is made of an electrically conductive material, such as a precious metal, an electromotive force can arise between the sensing lead section and the reference electrode section due to the ammonia gas within the gas being measured. As a result, the electromotive force attributable to the sensing lead section changes and can reduce the accuracy in measuring the ammonia gas concentration.

[0009] To solve the problem described above, one object of the present invention is to provide an ammonia gas sensor in which an electromotive force is generated only between a reference electrode section and a detection electrode section and not between a detection lead section and the reference electrode section, so that the concentration of ammonia gas in a gas subjected to measurement can be accurately detected. Means to solve the problem

[0010] To solve the problem, an ammonia gas sensor with the features of claim 1 or an ammonia gas sensor with the features of claim 4 is specified. Further advantageous embodiments are defined in the dependent claims.

[0011] An ammonia gas sensor of the present invention comprises a solid electrolyte element extending in an axial direction and containing zirconium oxide as the predominant component; a sensing section provided on a front surface of the solid electrolyte element; a reference electrode section provided on a rear surface of the solid electrolyte element; and a sensing lead section provided directly or via a further element on the front surface of the solid electrolyte element to establish an electrical connection between the sensing section and an external circuit, wherein an insulating section is provided at least on one surface of the sensing lead section or between the sensing lead section and the solid electrolyte element.

[0012] In the case where the insulating section is formed on the surface of the sensing lead section, the sensing lead section is isolated from the gas being measured by the insulating section. Therefore, no electromotive force arises between the sensing lead section and the reference electrode section.

[0013] In cases where an insulating section is provided between the sensing lead section and the solid electrolyte element, the sensing lead section is isolated from the solid electrolyte element by the insulating section. Therefore, even if the sensing lead section is exposed to the gas being measured, no electromotive force arises between the sensing lead section and the reference electrode section.

[0014] Accordingly, in both cases the ammonia gas sensor described above can prevent the generation of an electromotive force between the detection lead section and the reference electrode section and, as a result, accurately measure the concentration of ammonia gas in the gas being measured.

[0015] Preferably, the insulating section is provided on the surface of the sensing lead section and between the sensing lead section and the solid electrolyte element. In this case, the sensing lead section is isolated from the gas being measured by an insulating section and from the solid electrolyte element by a further insulating section. This reliably prevents the generation of an electromotive force between the sensing lead section and the reference electrode section.

[0016] The insulating section can be formed only on the surface of the sensing lead section or only between the sensing lead section and the solid electrolyte element. Furthermore, the insulating section can be formed beyond the surface of the sensing lead section or the interface between the sensing lead section and the solid electrolyte element.

[0017] The detection section includes a detection electrode section made of a noble metal and a selective reaction layer made of a metal oxide with ammonia gas selectivity.

[0018] Due to this design, the selective reaction layer exhibits good gas selectivity for ammonia gas, thus removing interfering gases from the gas being measured alongside the ammonia gas, and allowing the ammonia gas to reach the solid electrolyte element. This enables the sensing electrode section to exhibit good current collection based on the ammonia gas. As a result, the concentration of ammonia gas between the sensing electrode section and the reference electrode section can be accurately measured.

[0019] The insulating section is formed on the surface of the sensing lead section and includes a first insulating section that extends axially onto the surface of the sensing electrode section. Due to this design, even when the ammonia gas sensor is exposed to the gas being measured, the sensing lead section is isolated from the gas being measured by the insulating section. Furthermore, because the first insulating section is located on the surface of the sensing electrode section close to the sensing lead section, the sensing electrode section prevents the sensing lead section from being exposed to the gas being measured. Therefore, the sensing lead section is almost completely isolated from the gas being measured.Accordingly, an electromotive force can hardly arise between the detection lead section and the reference electrode section, which is why, as a result, the concentration of ammonia gas in the gas being measured can be determined more accurately.

[0020] According to claim 2, the detection electrode section is provided directly or via a further element on the solid electrolyte element; and the selective reaction layer is provided directly or via a further element on the detection electrode section. By virtue of this design, the gas being measured is initially exposed to the selective reaction layer, so that, after interfering gases in the gas being measured have been sufficiently combusted at the selective reaction layer alongside the ammonia gas, the ammonia gas reaches the solid electrolyte element. As a result, the concentration of the ammonia gas can be determined more accurately.

[0021] According to claim 3, the length of the first insulating section, as measured in the axial direction, is greater than the thickness of the sensing electrode section. Due to this design, the phenomenon whereby the gas being measured reaches the sensing lead-in section while bypassing the first insulating section, whose length is greater than the thickness of the sensing electrode section, is virtually eliminated, and the sensing lead-in section can be almost completely isolated from the gas being measured.

[0022] According to claim 4, the insulating section is provided between the sensing lead section and the solid electrolyte element and includes a second insulating section extending axially between the sensing electrode section and the solid electrolyte element. By virtue of this design, the sensing lead section is isolated from the solid electrolyte element by the insulating section. Therefore, even when the sensing lead section is exposed to the gas being measured, no electromotive force arises between the sensing lead section and the sensing electrode section. Additionally, the second insulating section is provided between the solid electrolyte element and a section of the sensing electrode section, with this section being located near the sensing lead section.This design suppresses the generation of an electromotive force between the detection lead section and the reference electrode section near the detection lead section. As a result, the concentration of ammonia gas in the measured gas can be determined more accurately.

[0023] According to claim 5, the length of the second insulating section, as measured in the axial direction, is greater than the thickness of the sensing electrode section. This configuration can suppress the generation of an electromotive force between the sensing lead section and the reference electrode layer near the sensing lead layer via a path that bypasses the second insulating section, the length of which is greater than the thickness of the sensing electrode section.

[0024] As described in claim 6, the length of the first insulating section, as measured in the axial direction, is greater than that of the second insulating section. The first insulating section being longer than the second prevents the gas being measured from reaching the sensing lead section. This design reliably prevents the generation of an electromotive force between the sensing lead section and the reference electrode section. As a result, the concentration of ammonia gas in the measured gas can be accurately determined.

[0025] According to claim 7, the solid electrolyte takes the form of a tube with a bottom at a front end section thereof; the reference electrode section is formed on an inner surface of the solid electrolyte member; the sensing section is formed on an outer surface of the front end section of the solid electrolyte member; and the sensing lead section takes the form of a strip and extends axially behind the sensing section.Even in an ammonia gas sensor comprising a tubular solid electrolyte element with a sensing section formed on an outer surface of a front end section and a strip-shaped sensing lead section extending axially behind the sensing section, it is possible, by providing an insulating layer at least on the surface of the sensing lead section or between the sensing lead section and the solid electrolyte element, to prevent the generation of an electromotive force between the sensing lead section and the reference electrode section, in order to accurately detect the concentration of ammonia gas in the gas being measured.

[0026] As described in claim 8, the reference electrode section and the sensing lead section are oriented towards each other via the solid electrolyte element. In this configuration, the generation of an electromotive force between the sensing lead section and the reference electrode section is likely. However, by providing an insulating layer at least on the surface of the sensing lead section or between the sensing lead section and the solid electrolyte element, it becomes possible to prevent the generation of an electromotive force between the sensing lead section and the reference electrode section, thus enabling the accurate measurement of the ammonia gas concentration in the gas being measured.

[0027] According to claim 9, a heating device is provided in the tubular solid electrolyte element such that the heating device is in contact with the reference electrode section and the contact position between the heating device and the reference electrode section is located upstream of the insulating section. The ammonia gas sensor can be configured such that the heating device is brought into contact with the solid electrolyte element (in particular, the heating device is brought into contact with the reference electrode section formed on the inner surface of the solid electrolyte element) in order to rapidly activate the solid electrolyte layer.In such a case, by adjusting the contact position between the heating device and the reference electrode section upstream of the insulating section, a section of the solid electrolyte element, where the reference electrode section and the sensing electrode section for detecting the concentration of ammonia gas are located, can be rapidly activated.

[0028] According to claim 10, the heating device comprises a heating resistor arranged in a front end section thereof and a heating device supply line section extending behind the heating resistor, the heating resistor being located in front of the insulating layer. This configuration enables concentrated heating of the section of the solid electrolyte element where the reference electrode section and the sensing electrode section for sensing the concentration of ammonia gas are arranged.

[0029] According to claim 11, the solid electrolyte element has a sensing section on a front end section thereof and takes the form of a plate extending in the axial direction; the sensing section is provided on a front surface of a front end section of the solid electrolyte element; and the sensing lead section takes the form of a strip extending behind the sensing section in the axial direction.Even in an ammonia gas sensor comprising a plate-shaped solid electrolyte element with a sensing section on the front surface of the front end section and a strip-shaped sensing lead section extending behind the sensing section, it is possible to prevent the generation of an electromotive force between the sensing lead section and the reference electrode section by providing a strip-shaped insulating layer at least on the surface of the sensing lead section or between the sensing lead section and the further surface of the solid electrolyte element, and thus to accurately detect the concentration of ammonia gas in the gas being measured.

[0030] As described in claim 12, the selective reaction layer covers the detection electrode section in such a way that the detection electrode section is not exposed. Since the detection electrode section is covered by the selective reaction layer in such a way that it is not exposed, the gas being measured passes through the selective reaction layer without problems before reaching the solid electrolyte element. Thus, the ammonia gas reaches the solid electrolyte element after interfering gases in the gas being measured have been almost completely combusted at the selective reaction layer alongside the ammonia gas. As a result, the concentration of ammonia gas can be accurately determined.

[0031] As described in claim 13, the sensing electrode section and the sensing lead section each contain gold or platinum, or both, as the predominant component. If gold, platinum, their alloys, or the like are used for the sensing electrode section and the sensing lead section, the ammonia gas sensor can effectively exhibit a current-collecting effect based on ammonia gas and transmit an electromotive force to an external circuit.

[0032] As described in claim 14, the sensing electrode section comprises zirconium oxide, while the sensing lead section comprises aluminum oxide. By virtue of this design, the sensing electrode section exhibits improved adhesion to the solid electrolyte element, while the sensing lead section exhibits improved adhesion to the insulating section.

[0033] According to claim 15, the insulating section contains at least one of the following as its predominant components: aluminum oxide, silicon oxide, silicon oxide-aluminum oxide, mullite, silicate glass, borate glass, borosilicate glass, and phosphate glass. This configuration can prevent the gas being measured from reaching the detection inlet section and isolate the detection inlet section from the solid electrolyte element.

[0034] As described in claim 16, the metal oxide is vanadium oxide, bismuth oxide, or a mixed oxide of vanadium oxide and bismuth oxide. This ensures better gas selectivity for ammonia gas.

[0035] As described in claim 17, the selective reaction layer includes palladium instead of the metal oxide. Even when palladium is used instead of the metal oxide, gas selectivity for ammonia gas can be ensured. Brief description of the drawing Fig. Figure 1 is a cross-sectional view of an ammonia gas sensor 1 of embodiment 1. Fig. Figure 2 is an enlarged cross-sectional view of a front end section of a sensor element 300. Fig. 1. Fig. Figure 3 is an enlarged cross-sectional view of a front end section of a sensor element 400 of an ammonia gas sensor 2 of embodiment 2. Fig. Figure 4 is an enlarged cross-sectional view of a front end section of a sensor element 500 of an ammonia gas sensor 3 of embodiment 3. Fig. Figure 5 is a perspective view showing a sensor element 900 of an ammonia gas sensor 4 of embodiment 4. Fig. Figure 6 is a cross-sectional view of sensor element 900 along line 14-14 of Fig. 5. Fig. Figure 7 is a perspective exploded view of sensor element 900. Fig. 5. Fig. Figure 8 shows data that demonstrate the relationship between gas sensitivities of embodiments 1 to 3 and a comparison example, as well as the concentrations of ammonia and propylene gases. Optimal implementation of the invention

[0036] Exemplary embodiments of an ammonia gas sensor according to the present invention are described below with reference to the drawing. Example 1

[0037] Fig. Figure 1 is a sectional view of an ammonia gas sensor 1 from embodiment 1. In use, the ammonia gas sensor 1 is, for example, attached to an exhaust pipe (not shown) of an (internal) combustion engine of a motor vehicle or the like. In particular, the underside and the top side of the sensor are shown in the following description of embodiment 1. Fig. 1 referred to as the front end or back end.

[0038] The in Fig. The ammonia gas sensor 1 shown is designed such that a tubular sensor element 300, which is closed at the front end, is held in a metallic housing 110. Furthermore, connecting wires 710 extend from the ammonia gas sensor 1 to carry out an output signal from the sensor element 300 and to supply electricity to a heating element 370, which is located adjacent to the sensor element 300. The connecting wires 710 are electrically connected to a sensor control device (not shown) or to an electronic control unit (ECU) of the motor vehicle.

[0039] The metallic sheath 110 is a tubular member made of stainless steel, for example SUS430, and includes at its front end an externally threaded section 111, which is mounted on an exhaust pipe (not shown). Furthermore, a front-end engagement section 113, with which an external guard 130, described below, engages, is provided at the front end of the externally threaded section 111.

[0040] Furthermore, a tool engagement section 114 is provided at the rear end of the externally threaded section 111 of the metallic casing 110. This section engages an installation tool used to attach the ammonia gas sensor 1 to the exhaust pipe. Additionally, a clamping or crimping section 115 is attached to the rear end of the metallic casing 110 such that it clamps or crimps the sensor element 300. A rear-end engagement section 112, with which an outer tube 120 (described below) engages, is provided between the tool engagement section 114 and the clamping or crimping section 115.

[0041] A stepped section 116, projecting radially inwards, is provided within the metallic shell 110. A tubular support member 210, made of aluminum oxide, is supported on the stepped section 116 by a metal packing (not shown). The inner circumference of the support member 210 is also shaped to include a step that supports a flanged section 301 of the sensor element 300, which will be described below, by a metal packing (not shown). Furthermore, the rear end of the support member 210 is fitted with a component material 220, consisting of talc powder, while a sleeve 230, made of aluminum oxide, is arranged such that the component material 220 is held between the sleeve 230 and the support member 210.

[0042] An annular ring 231 is arranged at the rear end of the sleeve 230. By clamping or crimping the clamping or crimping section 115 of the metallic shell 110, the sleeve 230 is pressed against the mounting material 220 over the ring 231.

[0043] The outer guard 130, which covers a front end section of the sensor element 300, is attached to the front end engagement section 113 of the metallic casing 110 by welding. An inner guard 140 in the form of a tube with a base is fixed inside the outer guard 130. Inlet openings 131 and 141 are formed in the outer guard 130 and the inner guard 140, respectively, such that they introduce a gas to be measured into the interior of the inner guard 140. Furthermore, outlet openings 132 and 142 are formed in the base walls of the outer guard 130 and the inner guard 140, respectively, such that they discharge a droplet of water and the gas to be measured that have entered the interior of the inner guard 140.

[0044] Furthermore, the tubular outer tube 120, which is made of stainless steel, for example SUS304, is attached to the rear engagement section 112 of the metallic casing 110 by laser welding or the like. The outer tube 120 extends behind and surrounds a rear engagement section of the sensor element 300 and a separator 400, which will be described below and is located on the rear side of the sensor element 300. In particular, a section of the outer tube 120 is clamped or crimped to engage and secure a retaining metal piece 610, which holds the separator 400.

[0045] The separator 400 has four connection ports 700 (in Fig. Figure 1 shows three connection terminals 700), which are electrically connected to a reference electrode section 320 and a detection electrode section 335 of the sensor element 300 and to a heating resistor of the heating device 370. The conductors of the four supply wires 710 are connected to the corresponding connection terminals 700 by clamps or crimps ( Fig. Figure 1 shows three supply wires 710. The supply wires 710 extend into the exterior of the ammonia gas sensor 1 via a feedthrough seal 500, which will be described below. The separator 400 has a flange section 410 that extends radially outward from the outer circumferential surface of the separator 400. The retaining metal piece 610 supports the flange section 410.

[0046] Furthermore, the feedthrough seal 500, which generally has a cylindrical column shape and is made of fluororubber, is arranged close to the rear opening of the outer tube 120. A communication hole 510 runs through a radially central section of the feedthrough seal 500 to introduce the atmosphere into the interior of the outer tube 120. In addition, four supply wire insertion holes 520 are provided at equal intervals circumferentially on the radially outer side of the communication hole 510. The supply wires 710 are inserted into and pass through the supply wire insertion holes 520.

[0047] A filter element 840 and a retaining metal piece 850 are inserted into the communication hole 510 of the feedthrough seal 500. The filter element 840 is a membrane filter made of a fluorocarbon resin, such as PTFE (polytetrafluoroethylene), and has a mesh structure. The filter element 840 prevents water droplets or the like from passing through it, while allowing atmospheric air to pass through. The retaining metal piece 850 is a tubular element that holds the filter 840 between its outer circumference and the inner circumference of the communication hole 510 and is attached to the feedthrough seal 500.

[0048] The sensor element 300 is described below. As in Fig. As shown in Figure 1, the sensor element 300 includes the flange section 301, which extends radially outwards from a generally central section of the sensor element 300. As shown in Fig. As shown in Figure 2, the sensor element 300 includes a solid electrolyte element 310, which contains zirconium oxide as its predominant component and has the form of a tube with a base. In particular, Fig. Figure 2 shows an enlarged cross-sectional view of a front-end section of the sensor element 300. A rod-shaped heating device 370 is inserted into the solid electrolyte element 310 to heat and activate it. The heating device 370 includes a heating resistor 371 located at the front end and a heating device lead section 372 extending behind the heating resistor 371.

[0049] The reference electrode section 320, whose predominant component is platinum or a platinum alloy, is formed over the entire inner surface of the solid electrolyte element 310. In addition, a detection electrode section 335 (thickness: 20 µm) and a selective reaction layer 360 (thickness: 30 µm) are provided on the outer surface of a front-end section of the solid electrolyte element 310. The selective reaction layer 360 is formed from a metal oxide containing vanadium oxide (V₂O₅) and bismuth oxide (Bi₂O₃) as predominant components; for example, bismuth vanadium oxide (BiVO₄). Furthermore, a strip-shaped detection lead section 350 is formed on the outer surface of the solid electrolyte element 310 such that it extends from the detection electrode section 335. The detection electrode section 335 and the detection lead section 305 are made of a material containing gold (Au) as the predominant component.

[0050] In the ammonia gas sensor 1, which is arranged as described above, the selective reaction layer 360 removes interfering gases from the gas being measured and allows the ammonia gas to reach the solid electrolyte element 310. This enables the sensing electrode section 335 to exhibit a current collection effect based on the ammonia gas. As a result, the concentration of the ammonia gas can be accurately measured.

[0051] An insulating layer 340, containing aluminum oxide (Al2O3) as its predominant component, is provided between the detection lead section 350 and the solid electrolyte element 310. In particular, in embodiment 1, the insulating layer 340 is provided not only between the detection lead section 350 and the solid electrolyte element 310, but over the entire outer surface of the solid electrolyte element 310.

[0052] Since the insulating layer 340 is provided between the detection lead section 350 and the solid electrolyte element 310, the detection lead section 350 is isolated from the solid electrolyte element 310 by the insulating layer 340. Therefore, even if the detection lead section 350 is exposed to the gas being measured, no electromotive force arises between the detection lead section 350 and the reference electrode section 320.

[0053] Furthermore, an insulating layer 380, containing aluminum oxide (Al2O3) as its predominant component, is provided on the surface of the detection lead section 350. In particular, in embodiment 1, the insulating layer 380 is provided not only on the surface of the detection lead section 350, but over the entire surface of the insulating layer 340.

[0054] Since the insulating layer 380 is formed on the surface of the detection lead section 350, the detection lead section 350 is isolated from the gas being measured by the insulating layer 380. Therefore, no electromotive force arises between the detection lead section 350 and the detection electrode section 320.

[0055] Accordingly, the ammonia gas sensor 1 can prevent the generation of an electromotive force between the detection lead section 350 and the reference electrode section 320. As a result, the concentration of ammonia gas in the gas being measured can be accurately determined.

[0056] The insulating layer 380 includes a first insulating section 381 that extends axially onto the surface of the sensing electrode section 335. The first insulating section 381 is located on the surface of the sensing electrode section 335 near the sensing lead section 350. This configuration prevents the sensing lead section 350 from being exposed to the gas being measured by the sensing electrode section 335. Therefore, the sensing lead section 350 is essentially isolated from the gas being measured. Consequently, a small electromotive force is generated between the sensing lead section 350 and the reference electrode section 320. As a result, the concentration of ammonia gas in the gas being measured can be determined more accurately.

[0057] The axial length t2 of the first insulating section 381 is 100 µm, which is greater than the thickness t1 of the sensing electrode section 335. Therefore, the phenomenon in which the gas being measured bypasses the first insulating section 381 and reaches the sensing lead section 350 hardly occurs, which is why the sensing lead section 350 can be almost completely isolated from the gas being measured.

[0058] Furthermore, the insulating section 340 includes a second insulating section 341, which extends axially between the sensing electrode section 335 and the solid electrolyte element 310. The second insulating section 341 is located between the solid electrolyte element 310 and a section of the sensing electrode section 335, with the section being situated near the sensing lead section 350. This configuration suppresses the generation of an electromotive force between the sensing lead section 350 and the reference electrode section 320 near the sensing lead section 350. As a result, the concentration of ammonia gas in the gas being measured can be determined more accurately.

[0059] The axial length t3 of the second insulating section 341 is 50 µm, which is greater than the thickness t2 of the sensing electrode section 335. Therefore, it is possible to prevent the generation of an electromotive force between the sensing lead section 350 and the reference electrode section 320 near the sensing lead section 350 by means of a path that bypasses the second insulating section 341. As a result, the concentration of ammonia gas in the gas being measured can be accurately determined.

[0060] Additionally, the axial length t2 of the first insulating section 381 is greater than the axial length t3 of the second insulating section 341. This prevents the gas being measured from reaching the detection lead section 350, thus even more reliably preventing the generation of an electromotive force between the detection lead section 350 and the reference electrode section 320. As a result, the concentration of ammonia gas in the gas being measured can be accurately determined.

[0061] In embodiment 1, where the reference electrode section 320 and the sensing lead section 350 face each other via the solid electrolyte element 310, the generation of an electromotive force is likely, particularly between the sensing lead section 350 and the reference electrode section 320. However, by providing the insulating layers 340 and 380, the generation of an electromotive force between the sensing lead section 350 and the reference electrode section 320 can be prevented, and the concentration of ammonia gas in the gas being measured can be accurately determined.

[0062] Furthermore, contact position A between the heating device 370 and the reference electrode section 320 is located upstream of the insulating sections 340 and 380. Therefore, the front end section of the solid electrolyte element 310, where the sensing electrode section 335 and the reference electrode section 320 are provided, can be activated quickly.

[0063] Furthermore, the heating resistor 371 is located in front of the insulating layers 340 and 380. Therefore, the front end section of the solid electrolyte element 310, where the sensing electrode section 335 and the reference electrode section 320 are provided, can be heated in a concentrated manner.

[0064] Furthermore, the selective reaction layer 360 covers the detection electrode section 335 in such a way that the detection electrode section 335 is not exposed. This design ensures that the gas being measured passes through the selective reaction layer 360 without problems before reaching the solid electrolyte element 310, so that the ammonia gas reaches the solid electrolyte element 310 after interfering gases in the gas being measured have been almost completely combusted at the selective reaction layer 360 alongside the ammonia gas.

[0065] The following describes a method for manufacturing the ammonia gas sensor 1 of embodiment 1. Step 1 of forming the solid electrolyte element 310

[0066] A powder of partially stabilized zirconia is prepared and filled into a tubular rubber mold (not shown) with a bottom. The partially stabilized zirconia is produced by adding 4.5 mol% yttrium oxide (Y₂O₃) (stabilizer) to the zirconia (ZrO₂). The partially stabilized zirconia powder is press-molded within the rubber mold into a tubular shape with a bottom, followed by firing at 1490 °C. This produces the solid electrolyte element 310 in a tubular shape with a bottom. Step 2 of forming the reference electrode section 320

[0067] Platinum (Pt) is then applied to the inner surface of the solid electrolyte element 310 by electroless plating and subsequently fired. This creates the reference electrode section 320 on the inner surface of the solid electrolyte element 310. Step 3 of forming the insulating layer 340

[0068] Next, aluminum oxide (Al₂O₃), an organic solvent, and a dispersant are mixed to create a dispersion mixture. Following this, a binder and a viscosity modifier are added to the mixture in predetermined amounts, and the mixture is subjected to wet blending. This produces the paste for the insulating layer, which, after firing, will become insulating layer 340.

[0069] This insulating paste is applied to the outer surface of the solid electrolyte element 310 and then dried, followed by firing at 1400 °C for one hour. This forms the insulating layer 340 over the entire outer surface of the solid electrolyte element 310. Step 4 of forming the detection electrode section 335 and the detection lead section 350

[0070] Gold (Au), zirconium oxide (ZrO2), an organic solvent, and a dispersant are then mixed to create a dispersion mixture. A binder and a viscosity modifier are subsequently added to the mixture in predetermined amounts, and the mixture is wet blended. This completes the paste for the sensing electrode section.

[0071] Furthermore, gold (Au), aluminum oxide (Al2O3), an organic solvent, and a dispersant are mixed to provide a dispersion mixture. Subsequently, a binder and a viscosity modifier are added to the mixture in predetermined amounts, and the mixture is subjected to wet blending. This completes the paste for the detection inlet section.

[0072] The paste for the lead electrode section and the paste for the detection lead section are printed onto the outer surface of the solid electrolyte element 310 and the outer surface of the insulating layer 340, which have been formed as described above. After drying, the components are baked at 1000 °C for one hour. This forms the detection electrode section 335 on the outer surface of a front-end section of the solid electrolyte element 310 and on the outer surface of a front-end section of the insulating layer 340. Furthermore, the detection lead section 350 is formed on the outer surface of the insulating layer 340 such that it assumes a strip-like shape and extends from the detection electrode section 335.

[0073] The sensing electrode section 335 is formed such that it contains zirconium oxide, while the sensing lead section is formed such that it contains aluminum oxide. Therefore, the sensing electrode section 335 exhibits improved adhesion to the solid electrolyte element 310, while the sensing lead section 350 exhibits improved adhesion to the insulating sections 340 and 380. Step 5 of forming the insulating layer 380

[0074] The paste described above for the insulating layer is then applied to the outer surfaces of the sensing electrode section 335, the sensing lead section 350, and the insulating layer 340 and dried, followed by firing at 1000 °C for one hour. This forms the insulating layer 380 over the entire outer surface of the solid electrolyte element 310. Step 6 of forming the selective reaction layer 360

[0075] A mixed oxide composed of vanadium oxide (V₂O₅) and bismuth oxide (Bi₂O₃), an organic solvent, and a dispersant are then mixed to produce a dispersion mixture. Subsequently, a binder and a viscosity modifier are added to the mixture in predetermined amounts, and the mixture is wet blended. This completes the paste for the selective reaction layer.

[0076] The paste for the selective reaction layer is applied to the outer surfaces of the detection electrode section 335 and the insulating layer 380 and dried, followed by firing at 750 °C for 10 minutes. This forms the selective reaction layer 360, which consists of bismuth vanadium oxide (BiVO4). Step 7 of assembling the ammonia gas sensor 1

[0077] After the sensor element 300 has been manufactured as described above, it is held within the metallic casing 110. Subsequently, the separator 400 is held within the outer tube 120 above the retaining metal piece 610, and the feedthrough seal 500, the terminals 700, and the covered wires 710 are inserted into the outer tube 120. This completes the manufacture of the ammonia gas sensor 1. Example 2

[0078] Fig. Figure 3 is an enlarged cross-sectional view of a front-end section of a sensor element 400 attached to an ammonia gas sensor 2 of embodiment 2. The sensor element 400 of embodiment 2 differs from the sensor element 300 of embodiment 1 in that the insulating layer 380 is not provided and the selective reaction layer 360 is provided directly on the surfaces of the sensing electrode section 335 and the sensing lead section 350. In the ammonia gas sensor 2 of embodiment 2, the same descriptions as in embodiment 1 have been omitted or simplified, with sections identical to those of embodiment 1 being designated with the same reference numerals.

[0079] In embodiment 2, the selective reaction layer 360 is provided on the surface of the detection electrode section 335 and on the surface of a front-end section of the detection supply line section 350. The selective reaction layer 360 covers the detection electrode section 335 in such a way that the detection electrode section 335 is not exposed. Thus, the ammonia gas reaches the detection electrode section 335 after interfering gases in the gas being measured have been almost completely combusted at the selective reaction layer 360, in addition to the ammonia gas. The remaining structure is identical to that of embodiment 1.

[0080] In the ammonia gas sensor 2 of embodiment 2, the insulating section 340 is also provided between the detection lead section 350 and the solid electrolyte element 310, so that the detection lead section 350 is isolated from the solid electrolyte element 310 by the insulating section 350. Therefore, even if the detection lead section 350 is exposed to the gas being measured, no electromotive force arises between the detection lead section 350 and the reference electrode section 320. As a result, the concentration of ammonia gas in the gas being measured can be accurately determined. Example 3

[0081] Fig. Figure 4 is an enlarged cross-sectional view of a front-end section of a sensor element 500 attached to an ammonia gas sensor 3 of embodiment 3. The sensor element 500 of embodiment 3 differs from the sensor element 300 of embodiment 1 in that the insulating layer 340 is not provided and the sensing electrode section 335 and the sensing lead section 350 are provided directly on the surface of the solid electrolyte element 310. In the ammonia gas sensor 3 of embodiment 3, the same descriptions as in embodiment 1 are omitted or simplified, and sections identical to those of embodiment 1 are designated with the same reference numerals.

[0082] In embodiment 3, the detection electrode section 335 and the detection lead section 350 are provided on the surface of the solid electrolyte element 310. Furthermore, the insulating layer 380 is provided such that it covers the detection lead section 350. The remaining structure is identical to that of embodiment 1.

[0083] In the ammonia gas sensor 3 of embodiment 3, the insulating layer 380 is also formed on the sensing lead section 350, so that the sensing lead section 350 is isolated from the gas being measured by the insulating section 380. Therefore, no electromotive force arises between the sensing lead section 350 and the reference electrode section 320. As a result, the concentration of ammonia gas in the gas being measured can be accurately determined. Example 4

[0084] Fig. Figures 5 to 7 show a sensor element 900 of an ammonia gas sensor 4 of embodiment 4. The ammonia gas sensor 4 of embodiment 4 differs from that of embodiment 1 in that a plate-type sensor element 900 is installed in the ammonia gas sensor 4 instead of the gas sensor element 300. The remaining sections are structurally identical to those of embodiment 1. In particular, the same descriptions as in embodiment 1 are omitted or simplified in the ammonia gas sensor 4 of embodiment 4, and sections that are identical to those of embodiment 1 are designated with the same reference numerals.

[0085] The plate-type sensor element 900 is held coaxially within the metallic casing 110. The sensor element 900 includes a solid electrolyte element 940, which is made of the same material as the solid electrolyte element 310 of embodiment 1.

[0086] A reference electrode section 931 and a reference lead section 932, formed from the same material as the reference electrode section 320 of embodiment 1, are provided on the rear surface of the solid electrolyte element 940 via an insulating film 933. The reference electrode section 931 is positioned corresponding to an opening section 934 formed in a front end section of the insulating film 933 and is in close contact with a front end section of the solid electrolyte element 940. Furthermore, the reference lead section 932 is configured to extend from a front end section to a rear end section of the rear surface of the insulating film 933.The reference lead section 932 is electrically connected to an electrode field 961 via a through-hole 935 of the insulating film 933, a through-hole 941 of the solid electrolyte element 940 and a through-hole 952 of an insulating film 950, which will be described below.

[0087] Furthermore, an insulating film 922, a sealing layer 920, an insulating film 912, a support layer 910, and an insulating film 911 are applied in this sequence to the rear surface of the insulating film 933 in such a stacked manner that the reference electrode section 931 and the reference lead section 932 are enclosed layer by layer between them. Of these films and layers, the sealing layer 920 has a communication groove section 921 that extends from one front end to the other. The communication groove section 921 establishes a path between the atmosphere and the reference electrode section 931.

[0088] Furthermore, a detection lead section 960 and an electrode array 961, formed from a material containing platinum (Pt) (predominant component) and aluminum oxide, are provided on the front surface of the solid electrolyte element 940 via an insulating film 950. The detection lead section 960 and the electrode array 961 extend along the surface of the insulating film 950 from the front end to the rear end. A front end section 962 of the detection lead section 960 is extended into an opening section 951 of the insulating film 950 for connection with a detection electrode section 980, which will be described below.

[0089] Furthermore, an insulating film 970 is stacked on the surface of the insulating film 950 in such a way that the detection lead section 960 is enclosed layer by layer between them. The insulating film 970 has an opening section 971 at its front end. The opening section 971 is formed such that it coincides with the opening section 951 of the insulating section 950.

[0090] Furthermore, the sensing electrode section 980, which is formed from the same material as the sensing electrode section 335 as described in embodiment 1, is provided in the opening section 971 of the insulating film 970 and the opening section 951 of the insulating film 950. The sensing electrode section 980 is in close contact with the front surface of the solid electrolyte element 940. In addition, a selective reaction layer 990, which is formed from the same material as the selective reaction layer 360 as described in embodiment 1, is provided on the surface of the sensing electrode section 980.

[0091] Since the insulating layer 950 is provided between the detection lead section 960 and the solid electrolyte element 940 as described above, the detection lead section 960 is isolated from the solid electrolyte element 940 by the insulating section 950. Therefore, even if the detection lead section 960 is exposed to the gas being measured, no electromotive force arises between the detection lead section 960 and the reference lead section 932.

[0092] Furthermore, since the insulating layer 970 is formed on the surface of the sensing lead section 960, the sensing lead section 960 is isolated from the gas being measured by the insulating layer 970. Therefore, no electromotive force arises between the sensing lead section 960 and the reference lead section 932.

[0093] Accordingly, the ammonia gas sensor 4 can prevent the generation of an electromotive force between the detection supply line section 960 and the reference supply line section 932, so that as a result the concentration of ammonia gas in the gas being measured can be accurately detected.

[0094] A method for manufacturing the ammonia gas sensor 4 is described below. The paste for the insulating layer of embodiment 1 is printed onto the back surface of a pre-fabricated blank, which is to become the solid electrolyte element 940. Therefore, the paste is applied in an area corresponding to the insulating film 933 and then dried. The blank is formed from partially stabilized zirconia, which is produced by adding 5.4 mol% yttrium oxide (Y₂O₃) (stabilizer) to zirconia (ZrO₂).

[0095] Platinum (Pt) (predominant component) and partially stabilized zirconia at 14% (by weight relative to the platinum) are then mixed to create a dispersion, along with an organic solvent and a dispersant. A binder and a viscosity modifier are then added to the mixture in predetermined amounts, and the mixture is wet blended. This completes the electrode paste. Specifically, a few percent of gold (Au) is added to the platinum to suppress its catalytic activity.

[0096] The electrode paste is then applied by screen printing to the previously described paste film for the insulating film 933 such that the electrode paste is applied to areas corresponding to the reference electrode section 931 and the reference lead section 932, after which drying takes place. Subsequently, the insulating layer paste from embodiment 1 is printed onto the insulating film 933 over the electrode layer paste such that the insulating layer paste is applied to an area corresponding to the insulating film 922, after which drying takes place.

[0097] Furthermore, the paste for the insulating layer of embodiment 1 is printed onto the front surface of the raw sheet such that the paste is applied to an area corresponding to the insulating film 950, after which drying takes place. Subsequently, the paste for the electrode layer is applied to the paste for the insulating film 950 such that the paste for the electrode layer is applied to areas corresponding to the detection lead sections 960 and 961, after which drying takes place.

[0098] The paste for the insulating layer of embodiment 1 is then printed onto the paste for the insulating film 950 over the paste for the electrode such that the paste for the insulating layer is applied to an area corresponding to the insulating film 970, after which drying takes place. Subsequently, predetermined pastes, which are to become the support layer 910 and the sealing layer 920, are printed on, dried, and made bondable by compression, followed by debindering at 400 °C and firing at 1470 °C. In particular, a heating element and a temperature-sensing resistor (not shown) are connected to the insulating film 911 of the sensor element assembly described above. However, the heating element and the temperature-sensing resistor can also be integrated into the sensor element assembly.

[0099] The paste for the detection electrode section is then applied by screen printing, as described in embodiment 1, into an opening area of ​​the paste for the insulating film 970 (corresponding to the opening section 971 of the insulating film 970) such that the paste for the detection electrode section is applied to an area corresponding to the detection electrode section 980 and comes into close contact with the front surface of the raw sheet. The paste for the detection electrode section is then dried and baked at 1000 °C for one hour.

[0100] Finally, the paste for the selective reaction layer, as described in embodiment 1, is applied to the sensing electrode section 980 and then baked at 750 °C for 10 minutes. This completes the production of the sensor element 900. Test example

[0101] The characteristic values ​​of ammonia gas sensors 1 to 3 from embodiments 1 to 3 were evaluated. For this evaluation, ammonia gas sensor 1 from embodiment 1 was designated "Example 1", ammonia gas sensor 2 from embodiment 2 was designated "Example 2", and ammonia gas sensor 3 from embodiment 3 was designated "Example 3". Furthermore, an ammonia gas sensor, serving as a comparison example, was manufactured for comparison purposes. The ammonia gas sensor of the comparison example is designed such that the insulating layers 340 and 380 are not provided and the detection lead section 350 is arranged directly on the outer surface of the solid electrolyte element 310.

[0102] To perform the aforementioned evaluation, a model gas generation device was used as the evaluation device. The model gas generation device produces a gas for evaluation according to the following description.

[0103] A base gas containing 10% oxygen (O2), 5% carbon dioxide (CO2), 5% water (H2O), and nitrogen (N2) was first produced. Then, 10 ppm or 100 ppm ammonia (NH3) and 100 ppm propylene (C3H6) were selectively added to the base gas to obtain the gas for evaluation. The temperature of the gas for evaluation was set at 280 °C.

[0104] Examples 1 to 3 and the comparison example were introduced into the gas for evaluation within the model gas generation device. Subsequently, the resulting potential difference between the reference electrode layer 320 and the detection electrode section 335 was measured for each of Examples 1 to 3 and the comparison example. Furthermore, the temperatures of Examples 1 to 3 and the comparison example were controlled and maintained at 650 °C by heating via the heating device 370.

[0105] For each of examples 1 to 3 and the comparison example, the relationship between the gas sensitivity (mV) and the ammonia or propylene gas of the gas for evaluation was measured. In particular, the gas sensitivity was determined by subtracting an electromotive force generated in the presence of the base gas from an electromotive force generated when the ammonia or propylene gas is added to the base gas. Fig. Figure 8 shows the results.

[0106] As in Fig.As shown in Figure 8, bars 1 to 1-2 show the gas sensitivities of Example 1; bars 2 to 2-2 show the gas sensitivities of Example 2; bars 3 to 3-2 show the gas sensitivities of Example 3; and bars 4 to 4-2 show the gas sensitivities of the comparison example. Furthermore, bars 1 to 4 show the respective gas sensitivities of Examples 1 to 3 and the comparison example when the gas for evaluation is produced by adding 10 ppm of ammonia gas to the base gas. Bars 1-1 to 4-1 show the respective gas sensitivities of Examples 1 to 3 and the comparison example when the gas for evaluation is produced by adding 100 ppm of ammonia gas to the base gas.Bars 1-2 to 4-2 show the respective gas sensitivities of examples 1 to 3 and the comparison example for the case where the gas for evaluation is produced by adding 100 ppm propylene gas to the base gas.

[0107] The ammonia sensors in examples 1 to 3 each show higher gas sensitivity compared to the ammonia sensor in the comparison example for the case where 10 ppm of ammonia gas has been added (bars 1 to 3), and for the case where 100 ppm of ammonia gas has been added (bars 1-1 to 3-1). The ammonia sensors in examples 1 to 3 each show lower gas sensitivity compared to the ammonia sensor in the comparison example for the case where propylene gas has been added (bars 1-2 to 3-2).

[0108] The present invention is not limited to the described embodiments and can be modified as follows in practical implementation. (1) Instead of gold, the detection electrode material used to form the detection electrode sections 335 and 980 may contain platinum (Pt) or platinum and gold as the predominant component. The predominant component is not limited to gold and platinum, but may also be in the form of other precious metals. (2) The material of the detection lead sections 350 and 960 is not limited to detection electrode material containing gold (Au) as the predominant component. The material of the detection lead sections 350 and 960 may contain platinum (Pt) or platinum and gold as the predominant component. (3) The material of the insulating layers 340, 380 and the insulating films 950, 970 is not limited to aluminium oxide. These layers and films may be formed from an electrically insulating material which contains at least one of the following as its predominant components: silicon dioxide, silicon dioxide-aluminium oxide, mullite, silicate glass, borate glass, borosilicate glass and phosphate glass. (4) The metal oxide is not limited to oxides of bismuth-vanadium, such as bismuth-vanadium oxide, but may be vanadium oxide, bismuth oxide or a mixed oxide of vanadium oxide and bismuth oxide. (5) In order to fine-tune the catalytic performance of the selective reaction electrode layers 360 and 990 and / or to improve their thermal stability, at least one of WO3, MoO3, Nb2O5, Ta2O5, MgO, CaO, SrO and BaO may be added to the metal oxide in an amount of up to about 5 at%. (6) Instead of the metal oxide, the selective reaction layers 360 and 990 can be formed from a material containing palladium. In this case, too, the gas selectivity of the ammonia gas sensor for ammonia gas can be ensured. (7) The shape of the insulating layers 340 and 380, as described in Examples 1 to 3, is not limited to the strip shape, and the insulating layers 340 and 380 can be formed over the entire circumference of the solid electrolyte element 310. In addition, the insulating films 950 and 970, as described in embodiment 4, can assume the shape of a strip with a width corresponding to that of the supply line 960. (8) The detection electrode section 335 and the detection lead section 350 as described in embodiments 1 to 3 do not overlap. However, the detection electrode section 335 can be arranged to overlap with the detection lead section 350 in order to improve the reliability of the electrical connection. (9) The application of the ammonia gas sensor of the present invention is not limited to the exhaust system of an (internal) internal combustion engine. Rather, the present invention can be used in any other engine as well as in any other device or the like in which exhaust gases are produced. Reference symbol list 310, 940 solid electrolyte element 320, 931 Reference electrode section 335, 980 Detection electrode section 340, 380 insulating section 950, 970 insulating layer 350, 960 Acquisition feeder section 360, 990 Selective reaction layer

Claims

[1] Ammonia gas sensor (1), comprising: a solid electrolyte element (310, 940) extending in an axial direction and containing zirconium oxide as the predominant component; a detection section provided on a front surface of the solid electrolyte element (310, 940); a reference electrode section (320, 931) provided on a rear surface of the solid electrolyte element (310, 940); and a detection lead section (350, 960) which is provided directly or via a further element on the front surface of the solid electrolyte element (310, 940) in order to establish an electrical connection between the detection section and an external circuit, wherein an insulating section (340, 380, 950, 970) is provided at least on one surface of the detection lead section (350, 960) or between the detection lead section (350, 960) and the solid electrolyte element (310, 940), wherein the detection section comprises a detection electrode section (335, 980) formed of a noble metal and a selective reaction layer (360, 390) formed of a metal oxide with ammonia gas selectivity, wherein the insulating section (340, 380, 950, 970) is formed on the surface of the detection lead section (350, 960) and comprises a first insulating section (381) extending in the axial direction to the surface of the detection electrode section (335, 980), wherein the detection lead section (350, 960) is insulated from the gas to be measured by means of the insulating section (340, 380, 950, 970). [2] Ammonia gas sensor (1) according to claim 1, wherein the detection electrode section (335, 980) is provided directly or via a further link on the solid electrolyte link (310, 940); and wherein the selective reaction layer (360, 390) is provided directly or via a further link on the detection electrode section (335, 980). [3] Ammonia gas sensor (1) according to claim 1 or 2, wherein the length of the first insulating section (381) as measured in the axial direction is greater than the thickness of the sensing electrode section (335). [4] Ammonia gas sensor (1), comprising: a solid electrolyte element (310, 940) extending in an axial direction and contains zirconium oxide as the predominant component; a detection section provided on a front surface of the solid electrolyte element (310, 940); a reference electrode section (320, 931) provided on a rear surface of the solid electrolyte element (310, 940); and a detection lead section (350, 960) which is provided directly or via a further element on the front surface of the solid electrolyte element (310, 940) in order to establish an electrical connection between the detection section and an external circuit, wherein an insulating section (340, 380, 950, 970) is provided at least on one surface of the detection lead section (350, 960) or between the detection lead section (350, 960) and the solid electrolyte element (310, 940), wherein the detection section comprises a detection electrode section (335, 980) formed of a noble metal and a selective reaction layer (360, 390) formed of a metal oxide with ammonia gas selectivity, wherein the insulating section (340, 380, 950, 970) is provided between the detection lead section (350, 960) and the solid electrolyte element (310, 940) and includes a second insulating section extending in the axial direction between the detection electrode section (350, 960) and the solid electrolyte element (310, 940). [5] Ammonia gas sensor (1) according to claim 4, wherein the length of the second insulating section as measured in the axial direction is greater than the thickness of the sensing electrode section (335, 580). [6] Ammonia gas sensor (1) according to claim 5, wherein the insulating section further comprises a first insulating section (381) whose length, as measured in the axial direction, is greater than that of the second insulating section. [7] Ammonia gas sensor (1) according to any one of claims 1 to 6, wherein the solid electrolyte element (310) takes the form of a tube with a bottom at a front end section thereof; the reference electrode section (320) is formed on an inner surface of the solid electrolyte element (310); the detection section is provided on an outer surface of the front end section of the solid electrolyte element (310); and the detection feeder section (350) takes the form of a strip and extends behind the detection section in the axial direction. [8] Ammonia gas sensor (1) according to claim 7, wherein the reference electrode section (320) and the detection lead section (350) point towards each other via the solid electrolyte element (310). [9] Ammonia gas sensor according to claim 7 or 8, wherein a heating device (370) is provided in the tubular solid electrolyte element (310) such that the heating device (370) is in contact with the reference electrode section (320) and the contact position between the heating device (370) and the reference electrode section (320) is located upstream of the insulating section (340, 380). [10] Ammonia gas sensor (1) according to claim 9, wherein the heating device (370) includes a heating resistor arranged in a front end section thereof and a heating device supply line section extending behind the heating resistor, and the heating resistor is located in front of the insulating section (340, 380). [11] Ammonia gas sensor (1) according to any one of claims 1 to 6, wherein the solid electrolyte element (940) takes the form of a plate extending in the axial direction; the detection section (980) is provided on a front surface of a front end section of the solid electrolyte element (940); and the detection feeder section (960) takes the form of a strip extending behind the detection section (980) in the axial direction. [12] Ammonia gas sensor (1) according to one of claims 1 to 11, wherein the selective reaction layer (350, 950) covers the detection electrode section in such a way that the detection electrode section is not exposed. [13] Ammonia gas sensor (1) according to any one of claims 1 to 12, wherein the sensing electrode section (335, 950) and the sensing lead section (350, 960) each contain gold or platinum or both as the predominant component. [14] Ammonia gas sensor (1) according to claim 13, wherein the sensing electrode section (335, 980) comprises zirconium oxide and the sensing lead section (350, 960) comprises aluminium oxide. [15] Ammonia gas sensor (1) according to any one of claims 1 to 14, wherein the insulating section (340, 380, 950, 870) contains at least one of the predominant components of aluminium oxide, silicon oxide, silicon oxide-aluminium oxide, mullite, silicate glass, borate glass, borosilicate glass and phosphate glass. [16] Ammonia gas sensor (1) according to any one of claims 1 to 15, wherein the metal oxide is vanadium oxide, bismuth oxide or a mixed oxide of vanadium oxide and bismuth oxide. [17] Ammonia gas sensor (1) according to any one of claims 1 to 17, wherein the selective reaction layer (360, 980) contains palladium instead of the metal oxide.

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