SENSOR ELEMENT AND GASS SENSOR

Abstract

Sensor element (3) comprising: an oxygen ion-conducting solid electrolyte body (3s); a detection electrode (55) arranged on a first surface of the solid electrolyte body (3s) and with which a target gas comes into contact; and a reference electrode (51) arranged on a second surface of the solid electrolyte body (3s) and with which a reference gas comes into contact;wherein the sensor element (3) further comprises a catalyst layer (60) covering the detection electrode (55) and a porous support (63) and at least one catalyst (65) selected from the group consisting of Ru, Rh, Pd, Ir and Pt and carried on the support (63), wherein the support (63) comprises as a main component aggregates of ceramic particles (61) and Ti oxide particles (62) different from the ceramic particles (61), characterized in that the Ti oxide particles (62) have a smaller average circle-equivalent diameter than the ceramic particles (61).

Description

Technical field

[0001] The present invention relates to a sensor element and a gas sensor for detecting the concentration of a target gas. State of the art

[0002] A known gas sensor for detecting the oxygen concentration in exhaust gas, for example from a vehicle, comprises a sensor element with a detection electrode and a reference electrode arranged on the surface of a tubular or plate-shaped solid electrolyte. A porous electrode protection layer is formed on the surface of the detection electrode to protect it from poisoning.

[0003] In recent years, a need has arisen for a gas sensor that allows for more precise combustion control in internal combustion engines, enabling compliance with stricter emissions regulations. This has led to a demand for a gas sensor suitable for this purpose, such as one with a smaller λ-point deviation capable of accurately measuring oxygen concentration. With conventional gas sensors, the accuracy of oxygen concentration measurement can decrease depending on the exhaust gas. For example, hydrogen in the exhaust gas can reach the detection electrode more easily than other exhaust gas components because hydrogen has a high diffusion rate (the rate at which the exhaust gas moves and reaches the detection electrode through a porous protective layer).The hydrogen reaching the detection electrode reacts with it, causing the electrode to make an inaccurate reading. In this case, the measured λ-point may differ from the λ-point being measured, making precise combustion control difficult.

[0004] In light of the above, a technique for reducing the λ-point deviation was developed (Patent Document 1). This technique involves carrying particles, such as Pt particles, on the electrode protective layer to cause hydrogen in the exhaust gas to react within the porous protective layer, thus preventing it from reaching the detection electrode. State of the art document (patent document)

[0005] Patent document 1: Published Japanese patent application (Kokai) No. 2006-58282 Overview of the invention Problem to be solved by the invention

[0006] There is a need for a gas sensor with uncompromised sensitivity. Depending on the shape of the porous layer supporting the catalyst particles, gas permeability and other properties can deteriorate, potentially leading to reduced sensitivity.

[0007] Accordingly, it is an object of the present invention to provide a sensor element which uses a catalyst to improve the accuracy of the detection of a target gas and which prevents a reduction in the sensitivity of the gas sensor, and to provide such a gas sensor. Means to solve the problem

[0008] To solve the problem described above, a sensor element of the present invention comprises an oxygen-ion-conducting solid electrolyte body, a detection electrode arranged on a first surface of the solid electrolyte body and with which a target gas comes into contact, and a reference electrode arranged on a second surface of the solid electrolyte body and with which a reference gas comes into contact. The sensor element is characterized in that it further comprises a catalyst layer covering the detection electrode and a porous support, and at least one catalyst selected from the group consisting of Ru, Rh, Pd, Ir, and Pt, and supported on the support, wherein the support comprises, as a main component, aggregates of ceramic particles and Ti oxide particles, which are different from the ceramic particles and have a smaller diameter than the ceramic particles.

[0009] In this sensor element, the substrate exhibits improved gas permeability, thus preventing a reduction in sensor sensitivity. The reason for this is not entirely clear. However, it could be due to one of the following: Since the majority of the loosely connected Ti oxide particles, forming a network structure, are located in gaps between the large-diameter ceramic particles, these gaps are not sealed, and the gas permeability is not impaired.

[0010] The phrase "Ti oxide particles that are different from the ceramic particles" means that the ceramic particles are not Ti oxide particles. The aggregates are not formed by chemical bonding but by physical bonding (e.g., bonding through sintering).

[0011] In the sensor element of the present invention, the Ti oxide particles can comprise needle-shaped particles.

[0012] With this sensor element, gas permeability is further improved because the majority of the Ti oxide particles are more likely to be loosely bound in the gaps between the ceramic particles.

[0013] A gas sensor according to the present invention comprises a sensor element and a metallic body that holds the sensor element. The gas sensor is characterized in that the sensor element is the sensor element according to claim 1 or 2. Effects of the invention

[0014] According to the present invention, it is possible to improve the accuracy of the detection of a target gas using a catalyst and to prevent a reduction in the sensitivity of the gas sensor. List of characters Fig. Figure 1 is a cross-sectional view of a gas sensor according to an embodiment of the present invention in section along a plane extending in an axial direction. Fig. Figure 2 is a cross-sectional view showing the structures of a sensor element and a catalyst layer. Fig. Figure 3 is an enlarged cross-sectional view showing the structure of the catalyst layer. Fig. Figure 4: is a representation showing a method for measuring the diameters of ceramic particles and Ti oxide particles. Fig. Figure 5 is a graph showing a method for evaluating the sensitivity of the gas sensor. Fig. Figure 6 is a graph showing the sensitivity of the gas sensor at different carrier compositions. Fig. Figure 7 is a SEM image of the outer surface of the catalyst layer. Fig. Figure 8 is a SEM image of a cross-section of the catalyst layer. Ways to implement the invention

[0015] One embodiment of the present invention is described below.

[0016] Fig. Figure 1 shows a cross-sectional structure of a gas sensor. 100 , comprising a sensor element according to an embodiment of the present invention, wherein the cross-section is determined by cutting the gas sensor 100 is obtained along a plane that points in the direction of an axis O (a direction from the front end of the gas sensor). 100 to the rear end of the gas sensor 100 ) extends. In this embodiment, the gas sensor 100 an oxygen sensor that is inserted into the exhaust pipe of a motor vehicle in such a way that the front end of the gas sensor 100 is exposed to the exhaust gas in order to detect the concentration of oxygen in the exhaust gas. The gas sensor 100 Included sensor element 3is a conventional sensor element which is an oxygen concentration cell comprising an oxygen ion conducting electrolyte body and a pair of electrodes stacked on it, and which outputs a detection value corresponding to the amount of oxygen.

[0017] This involves the lower side of the gas sensor. 100 in Fig. 1 as the front end of the gas sensor 100 designated, and the upper side in Fig. 1 is referred to as the rear side of the gas sensor. 100 designated.

[0018] The gas sensor 100 It is essentially constructed in such a way that an almost cylindrical (in the shape of a hollow shaft) sensor element 3 (in this case an oxygen sensor element) with a closed front end in a tubular metal body (metal casing) 20 introduced and maintained by this. As in Fig. The sensor element is shown in section 2. 3a tubular solid electrolyte body 3s , which tapers towards the front end; inner and outer electrodes 51 and 55 , which are formed on the inner and outer circumferential surfaces of the solid electrolyte body; a catalyst layer 60 , which is the outer electrode 55 covered, etc. A heater 15 , which has the shape of a round rod, is located in the cavity of the sensor element. 3 inserted to include the sensor element 3 to heat up to its activation temperature.

[0019] In this context, the outer electrode and the inner electrode correspond to the “detection electrode” and the “reference electrode” respectively in the claims.

[0020] A tubular outer tube 40 is connected to a rear end region of the metallic body 20 connected. The outer pipe 40 holds connecting wires 41 and connections 74 and 94(described below), which are behind the sensor element 3 are arranged, and it covers a rear area of ​​the sensor element. 3 A cylindrical, elongated insulating separator 121 is on the inside of a section of the outer tube 40 attached, with the area on the rear side of the sensor element 3 is arranged. A detection section is located at the front end of the sensor element. 3 is equipped with a protector 7 covered. A male screw area 20d of the metallic body 20 of the gas sensor produced in this way 100 It is attached to a screw hole, for example in an exhaust pipe, in such a way that the detection section is at the front end of the sensor element. 3 The inside of the exhaust pipe is exposed, and the target gas (exhaust gas) is detected thereby. This involves a polygonal flange area. 20cfor intervention using, for example, a hexagonal key near the center of the metallic body 20 provided, and a seal 14 , which prevents gas leakage after being attached to the exhaust pipe, is located in a stepped area between the flange area 20c and the male thread area 20d adjusted.

[0021] A flange area 3a is near the center of the sensor element 3 arranged, and a stepped area 20e , whose diameter is reduced towards the inside, is located on the inner circumferential surface of the metallic body 20 provided at a position near its front end. A tubular ceramic holder. 5 is on a rearward-facing surface of the stepped area 20e through a washer 12 held. The sensor element 3 is in the metallic body 20 and the ceramic holder5 introduced, and the flange area 3a of the sensor element 3 It's due to the ceramic holder. 5 from behind.

[0022] A tubular talc powder ring 6 and a tubular ceramic sleeve 10 are on the rear side of the flange area 3a arranged to be positioned in the radial gap between the sensor element 3 and the metallic body 20 to be arranged. A metallic ring 30 is behind the ceramic sleeve 10 arranged. A rear end region of the metallic body 20 is bent inwards to create a crimp area 20a to form the ceramic sleeve 10 to press towards the front end. The Talk-Ring 6 This compresses it, and the ceramic sleeve 10 and the talc powder ring 6 are fixed by crimping. The gap between the sensor element3 and the metallic body 20 This seals it off.

[0023] Insertion holes (four insertion holes in this example) are in the separator. 121 trained, which is behind the sensor element 3 is arranged, and plate-shaped base areas 74 and 94 of internal and external metallic connections 71 and 91 are inserted into two of the insertion holes and attached to them. Connection sections 75 and 95 are located at the rear ends of the plate-shaped base areas 74 and 94 trained, and connecting wires 41 , 41 are connected to the connection areas 75 and 95 by crimping the connection areas 75 and 95 connected. Two heating connection wires. 43 (only one is Fig. 1 shown), which is separated from the heating system. 15The path extends into two not shown insertion holes (heater insertion holes) of the separator. 121 introduced.

[0024] A tubular cable gland 131 is crimped on the inside of a section of the outer tube 40 attached, with the area behind the separator 121 is arranged, with the two connecting wires 41 and the two heating connection wires 43 from four cable entry holes 131 extend outwards.

[0025] At the center of the cable penetration 131 is a through hole 131a formed and is connected to the interior of the sensor element 3 In conjunction. A water-repellent ventilation filter. 141 is in the through hole 131a the cable entry 31 fitted in such a way that a reference gas (atmospheric air) enters the interior of the sensor element. 3is introduced, while preventing water from passing through the ventilation filter. 140 penetrates from the outside.

[0026] The tubular protector 7 is on a front end area of ​​the metallic body 20 Watch from the outside to ensure a front end area of ​​the sensor element 3 , which is attached to the metallic body 20 to cover the protruding part. The protector 7 is formed, for example, by an outer tubular protector 7b and an inner tubular protector 7a , each of which has a plurality of holes (not shown), which has a closed bottom and which is made of a metal, such as stainless steel, and welded together.

[0027] With reference to the Fig. 2 and Fig. 3. The structures of the sensor element will now be described. 3 and the catalyst layer 60described. As in Fig. Shown in 2 is the inner electrode. 51 on the inner circumferential surface of the solid electrolyte body 3s trained, and the outer electrode 55 is located on the outer circumferential surface of the solid electrolyte body 3s formed. The catalyst layer 60 is on the surface of the outer electrode 55 formed. A porous, gas-limiting layer. 57 is between the outer electrode 55 and the catalyst layer 60 arranged. An additional layer (e.g., a porous protective layer) can be applied to the outer surface of the catalyst layer. 60 be trained.

[0028] The gas-limiting layer 57 controls the rate of gas passage and can be formed by plasma spraying of a combustible ceramic, such as aluminum-magnesium spinel.

[0029] The solid electrolyte body 3sIt exhibits conductivity for oxygen ions and can contain, for example, partially stabilized zirconium oxide (YSZ) as a main component, which contains yttrium as a stabilizer. The main component is a component that is part of the solid electrolyte body. 3s is contained at more than 50% by weight.

[0030] The inner electrode 51 is exposed to a reference gas atmosphere that is located inside the sensor element 3 is inserted, and the external electrode 55 is exposed to the target gas. Gas detection is performed between the inner electrode. 51 and the outer electrode 55 through the solid electrolyte body 3s executed.

[0031] The inner electrode 51 and the outer electrode 55are mainly composed of Pt, for example. The phrase "mainly composed of Pt" means that the amount of Pt contained in the electrode is more than 50% by weight.

[0032] As in Fig. As shown in section 3, the catalyst layer comprises 60 a porous substrate 63 and at least one catalyst 65 , which is selected from the group consisting of Ru, Rh, Pd, Ir and Pt, and which is attached to the carrier 63 is worn. The catalyst 65 for example, it is present in the form of particles, and a large number of catalyst particles are on the surface of the support. 63 distributed.

[0033] The carrier 63 It comprises aggregates of ceramic particles as a main component. 61 and Ti oxide particles 62 , which have a smaller diameter than the ceramic particles 61The main component is located in the catalyst layer. 60 Component present at more than 50% by weight.

[0034] The ceramic particles 61 preferably comprise at least one type of particle selected from the group consisting, for example, of aluminium oxide particles, aluminium magnesia spinel particles, zirconium oxide particles, and, for example, aluminium magnesia spinel particles.

[0035] The Ti oxide particles 62 Examples include TiO2 particles, but they can also contain non-stoichiometric compositions containing oxygen, such as TiO2,5.

[0036] The thickness of the catalyst layer 60 preferably 10 to 1000 µm.

[0037] If the carrier 63 as a main component the aggregates (sintered aggregates) of the ceramic particles 61 and the Ti oxide particle 62, whose diameters are smaller than those of the ceramic particles 61 , the gas permeability of the carrier 63 It improves performance, and a reduction in sensor sensitivity can be prevented.

[0038] The reason for this is unclear. However, it could be due to the following: Since the majority of Ti oxide particles 62 is loosely connected and forms a network structure that fits into gaps G between the ceramic particles. 61 When large-diameter particles are present, the gaps G are not closed or blocked, and the gas permeability is not affected. However, when other small particles (such as aluminum oxide, zirconium oxide, or YSZ particles) are used, the interaction between the noble metal and the small particles can alter the catalytic ability of the noble metal, and this can affect the sensitivity, although the reasons for this are unclear.

[0039] Since the carrier 63 the Ti oxide particles 62 with a small diameter, it occupies the total surface area of ​​the carrier 63 to, which is why the contact area between the on the carrier 63 trained catalyst 65 and increases with the target gas, thus improving the catalytic capabilities. If only the Ti oxide particles 62 When using ceramic particles, it is difficult to form a porous support, which is why the ceramic particles are used. 61 They can also be used with large diameters.

[0040] The ceramic particles 61 and the Ti oxide particles 62 can be identified by examining a cross-section of a sample of the carrier 63 An elemental analysis is performed using EPMA (electron probe microanalyzer) or EDS (energy dispersive X-ray spectrometer). The diameters of the ceramic particles 61 and the Ti oxide particle 62are determined by calculating the circle-equivalent diameters of the ceramic particles 61 and the Ti oxide particle 62 through elemental analysis of the cross-section of the sample of the support 63 be determined.

[0041] Since a large number of Ti oxide particles 62 on the surfaces of the ceramic particles 61 and in gaps between adjacent ceramic particles 61 are present, as is the case in Fig. As shown in Figure 3, it is difficult to discern the outlines of the individual ceramic particles. 61 to determine.

[0042] To determine the influence of these Ti oxide particles 62 To reduce the effect, ten cross-sectional SEM images of different 20×20 µm viewing surfaces of the substrate are taken. 63 created as in Fig. 4 shown.

[0043] In each of the cross-sectional SEM images, the outline P of a region H containing a ceramic particle is shown. 61xidentified by EPMA or EDS, extracted, and the circle-equivalent diameter of region H is considered the diameter of the ceramic particle. 61x The mean of 50 diameters randomly selected from cross-sectional SEM images is used. 61x used.

[0044] Some ceramic particles 61 They can be connected and aggregated through sintering. In this case, their boundaries are unclear.

[0045] When ceramic particles 61x and their neighboring ceramic particles 61y are joined by sintering, as is done in Fig. As shown in Figure 4, its limit is determined as follows.

[0046] If the outline P of the ceramic particle 61x If it tapers in an area between points A and B to form a neck area, a direction parallel to a straight line will be indicated. C1The line connecting points A and B is denoted by L. Then, the greatest length under the outlines of the connected ceramic particles is determined. 61x and 61y in the direction parallel to direction L, it is designated Lx or Ly. If the length of the line C1 If the distance between points A and B is shorter than both Lx and Ly, the two ceramic particles will be 61x and 61y as being connected by sintering in the area between A and B, and the straight line C1 is considered the boundary between the two ceramic particles 61x and 61y defined.

[0047] When an area of ​​a ceramic particle 61x outside an outer edge C2 of the image area is arranged, the outer edge C2 as part of the outline p of the ceramic particle 61x considered.

[0048] If the outermost edge P of the ceramic particle61x a Ti oxide particle 62x when cuts, the edge becomes P1 the boundary between the Ti oxide particle 62x and the ceramic particle 61x as part of the edge P of the ceramic particle 61x Considered. Additionally, Ti oxide particles are considered. 62y , which lie within the outline P of the ceramic particle 61x their existence is ignored.

[0049] Therefore, the straight lines C1 and C2 as part of the outline P of the ceramic particle 61x The area enclosed by the entire outline P is considered, and is taken as the circle-equivalent diameter of the ceramic particle. 61x used.

[0050] Fig. Figure 3 shows areas where Ti oxide particles 62 , which have been identified by EPMA or EDS. If between adjacent Ti oxide particles 62If a clear boundary D exists, the circle-equivalent diameters of the outlines separated by the boundary D are considered to be the diameters of the Ti oxide particles. 62 used. When the boundary E between two Ti oxide particles 62 Since it is unclear and these particles appear as if they are connected, the boundary E is ignored, and the circle-equivalent diameter of the area enclosed by the entire outline is taken as the diameter of the Ti oxide particle. 62 used.

[0051] To determine the diameter of the Ti oxide particle 62 To determine this, one of the cross-sectional SEM images is selected, and the diameters of all Ti oxide particles are determined. 62 The image values ​​are determined. The mean of 50 diameters from all diameters is considered the diameter of the Ti oxide particles. 62 used.

[0052] If the Ti oxide particles 62If needle-shaped particles are included, it is more likely that a majority of Ti oxide particles will be present. 62 in gaps G between the ceramic particles 61 is loosely connected, and this can provide greater gas permeability.

[0053] In particular, the Ti oxide particles can 62 , as in Fig. 3 shown, in addition to the needle-shaped particles 62a spherical particles 62b and irregularly shaped particles 62c include. The "needle-shaped particles" are particles with an aspect ratio of 3 or more. The aspect ratio of a Ti oxide particle 62 is the ratio of the maximum length (major axis) within the outline of the Ti oxide particle. 62 to the maximum width (secondary axis) in a direction perpendicular to the main axis.

[0054] The sensor element 3The present embodiment can be produced, for example, as follows. First, for example, yttrium oxide is added to zirconium oxide, and the mixture is granulated and formed into a predetermined shape (see, for example, Figure 1). Fig. 1) and then fired at a predetermined temperature (e.g. 1400° to 1600°C) to create a solid electrolyte body 3s to produce. The outer electrode 55 is located on the outer circumferential surface of the solid electrolyte body 3s formed using, for example, vapor deposition or chemical plating.

[0055] The inner electrode 51 This does not yet involve the inside of the solid electrolyte body. 3s educated.

[0056] Then, a mixture of ceramic particles is created by mixing them. 61 , the Ti oxide particle 62 and a slurry formed from glass powder onto the surface of the outer electrode 55applied to form a green catalyst layer. If necessary, the gas-limiting layer is 57 or a protective layer is formed using a conventional method before the green catalyst layer is formed.

[0057] Then the entire solid electrolyte body 3s subjected to heat treatment in a reducing atmosphere at a predetermined temperature (e.g. 1000° to 1300°C) to modify the carrier 61 for the catalyst layer 60 to form.

[0058] Then the carrier 61 with a solution of a precious metal, which acts as the catalyst 65 is used (e.g., a precious metal complex solution) to soak and burn in order to achieve small particles of the catalyst. 65 on the surface of the carrier 61 be held.

[0059] Then the inner electrode 51on the inner surface of the heat-treated solid electrolyte body 3s formed, for example by vapor deposition or chemical plating, and the sensor element 3 is thus complete.

[0060] It is evident that the present invention is not limited to the embodiment described above and includes various modifications and equivalents within the idea and scope of protection of the present invention. Examples

[0061] YSZ, which was prepared by adding 5 mol% of yttrium oxide to zirconium oxide, was granulated and then fired to form the solid electrolyte body. 3s , who in Fig. As shown in Figure 1, to produce. Then the outer electrode was 55 on the outer circumferential surface of the solid electrolyte body 3s formed by Pt deposition.

[0062] Then the spinel was applied to the surface of the outer electrode by plasma spraying. 55 applied to the porous gas-limiting layer 57 to form. The inner electrode 51 was on the inner surface of the solid electrolyte body 3s Formed by platinum plating. A slurry for the catalytic green layer. 60 was applied to the surface of the gas-limiting layer 67 applied. The slurry contained 63 wt% spinel particles with an average diameter of 30 to 40 µm, 8 wt% glass powder and 29 wt% of the following small particles with a mean diameter of 0.3 µm.

[0063] The small particles were TiO2 particles, aluminum oxide particles, ZrO 2- Particles or YSZ particles.

[0064] Then the entire solid electrolyte body was 3s subjected to heat treatment in a reducing atmosphere, and the carrier63 The catalyst layer was impregnated with a platinum solution and subjected to heat treatment. 60 with the small Pt particles that are on the surface of the support 61 The system, which is worn, was thereby completed. A plurality of sensor elements. 3 Sensors, differing from each other in terms of the type of small particles they contained, were produced. Each sensor element 3 was in the Fig. Mounted as shown in section 1. Gas sensors 100 , as in Fig. 1 shown, were thereby obtained.

[0065] Each gas sensor was attached to an exhaust pipe of an engine, and the time between the change in engine gas (exhaust) from lean to rich, until the sensor output reached 450 mV or more, was measured as TLS, as shown in Fig. 5 shown. Then the time between the change of the engine gas from rich to lean, until the time when the sensor output became 450 mV or less, was measured as TRS.

[0066] The results obtained are in Fig. 6 is shown. It is made of Fig. 6. It is evident that the response time given by (TRS + TLS) is shortest and the sensitivity of the gas sensor is greatest when the carrier contains TiO2 particles and the ceramic particles.

[0067] If the support contains aluminium oxide, ZrO2 or YSZ particles and ceramic particles, the response time given by (TRS + TLS) is longer than if TiO2 particles are present.

[0068] Fig. Figure 7 shows a SEM image of the outer surface of the catalyst layer 60 , and Fig. Figure 8 shows a SEM image of a cross-section of the catalyst layer 60 . The Fig. 7 and Fig. Figure 8 are secondary electron images, and the areas contained in circles in the Fig. 7 and Fig. 8 correspond to ceramic particles 61 To enable the Ti oxide particles 62 easily visible, the Fig. 7 and Fig. 8 catalyst layers each 60 , which were burned without a catalyst (Pt) being applied to them.

[0069] In Fig. The dark areas are ceramic particles. 61 , and the light particle areas (needle-shaped areas) are Ti oxide particles. 62 . Reference symbol list 3 Sensor element 3s solid electrolyte body 20 metallic bodies 51 Reference electrode 55 Detection electrode (outer electrode) 60 catalyst layer 61 ceramic particles 62 Ti oxide particles 63 carriers 65 Catalyst 100 gas sensor QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 200658282

[0005]

Claims

[1] Sensor element, comprising: a solid electrolyte body that conducts oxygen ions; a detection electrode which is arranged on a first surface of the solid electrolyte body and with which a target gas comes into contact; and a reference electrode which is arranged on a second surface of the solid electrolyte body and with which a reference gas comes into contact; where the sensor element characterized by is that it further comprises a catalyst layer covering the detection electrode and a porous support and at least one catalyst selected from the group consisting of Ru, Rh, Pd, Ir and Pt and carried on the support, wherein the support comprises as a main component aggregates of ceramic particles and Ti oxide particles, which are different from the ceramic particles and have a smaller diameter than the ceramic particles. [2] Sensor element according to claim 1, wherein the Ti oxide particles comprise needle-shaped particles. [3] Gas sensor comprising a sensor element and a metallic body which holds the sensor element, wherein the gas sensor characterized by is that the sensor element is the sensor element according to claim 1 or 2.

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