Sensor element and gas sensor

Abstract

To provide a sensor element and a gas sensor that prevents detachment due to the ingress of water into a feeder connected to an electrode and facing a communication hole to communicate with the outside, a gas sensor element (100) comprises: a pair of electrodes (104a, 106a); and a pair of feeders (104b, 106b) each connected to the pair of electrodes, wherein one (104b) of the pair of feeders is an internal feeder arranged within the sensor, and part of one of the pair of feeders faces a communication hole (105a, 106a, 107a, 109a, 111a) provided in the sensor element to communicate with an outside; the internal feed is designed to contain precious metal particles (104M) of one or more types selected from the group Pt, Pd, Rh and Au, ceramic particles (104S) and pores (104V);a porosity of the internal feed is greater than 0% and 11% or less; and a proportion RA of the total area of ​​large diameter pores, each with a cross-sectional area of ​​5 µm; 2 or more, in relation to a total pore area in a cross-section of the internal supply, which is 8% or more.

Description

Field of invention

[0001] The present invention relates to: a sensor element and a gas sensor suitable for use in detecting the concentration of a specific gas contained in combustion gas or exhaust gas from, for example, an internal combustion engine, a combustion engine or the like. State of the art

[0002] Until now, a gas sensor for detecting the concentration of a specific component (e.g., oxygen) in the exhaust gas of an internal combustion engine was known. A gas sensor of this type includes a sensor element with an elongated plate shape. A front end section of the sensor element is equipped with a detection section for detecting the specific component (Publication 1). The detection section consists of a pair of electrodes and a solid electrolyte, with a feed extending from each electrode to the rear end. Within this section, there is a detection section with a structure in which cavities are formed within a reference feed section connected to a reference electrode, such that communication between the gases inside and outside the element is permitted via the reference feed section, thereby adjusting the pressure of a reference gas around the reference electrode. State-of-the-art documents, patent documents

[0003] Publication 1: Japanese patent application JP 2002 - 032 240 A Brief description of the invention; Problem to be solved by the invention

[0004] If water that has entered the gas sensor, or water that has formed due to condensation, comes into contact with a sensor element, a feeder absorbs the water that entered through a communication hole, and if the sensor element is subsequently heated, the water evaporates and expands inside the feeder, which can cause the feeder to break or detach.

[0005] The object of the present invention is to provide a sensor element and a gas sensor that prevent detachment due to water entering a feed connected to an electrode, which is oriented towards a communication hole for communication with the outside. Means of solving the problem

[0006] To solve the above problem, a sensor element comprises: a pair of electrodes; and a pair of feeders, each connected to the pair of electrodes, wherein one of the feeders is an internal feeder arranged within the sensor element, and a portion of the one of the feeders faces a communication hole provided in the sensor element to communicate with an external source; the internal feeder is configured to contain precious metal particles of one or more grades selected from the group consisting of Pt, Pd, Rh, and Au, ceramic particles, and pores; the porosity of the internal feeder is greater than 0% and 11% or less; and a proportion RA of the total area of ​​large-diameter pores, each with a cross-sectional area of ​​5 µm² 2 or more, in relation to a total pore area in a cross-section of the internal supply, which is 8% or more.

[0007] According to this sensor element, because the porosity of the internal feed is greater than 0% and 11% or less, the pressure of a reference gas around the reference electrode can be adjusted at moderate gas permeability. Furthermore, it makes it possible to prevent the occurrence of delamination, which is caused by precious metal particles being separated by pores at high porosity. Because the proportion of RA (radial area) of the total area of ​​the large-diameter pores is 8% or more, water absorbed in the internal feed is easily released from the large-diameter pores to the communication hole. As a result, it is possible to prevent an incident in which, if heating is performed after water has entered the sensor element, the water evaporates and expands within the internal feed, leading to breakage or detachment of the internal feed.

[0008] In the sensor element of the present invention, the proportion RA can be less than 60%.

[0009] According to this sensor element, peeling of the internal feed can be prevented.

[0010] A gas sensor of the present invention is a gas sensor comprising: the sensor element according to claim 1 or 2; and a metal sleeve holding the sensor element. Effects of the invention

[0011] The present invention makes it possible to provide a sensor element and a gas sensor that prevent detachment due to the ingress of water into a feeder connected to an electrode and facing a communication hole for communication with the outside. Brief description of the drawings Fig. 1 Cross-sectional view of a gas sensor, cut along the direction of its axial line. Fig.2 Perspective exploded view, which schematically shows a detection element section and a heating section that form a sensor element. Fig. 3 View showing a cross-sectional SEM image including a first feed section of Example 1. Fig. 4 View showing a cross-sectional SEM image including a first feed section of comparison example 1. Description of the embodiments

[0012] An embodiment of the present invention is described below.

[0013] First, a configuration of a gas sensor (oxygen sensor) 1 including a sensor element 100 according to the present embodiment is described. Fig. Figure 1 is a cross-sectional view of a gas sensor 1, cut along the direction of its axial line L. Fig.Figure 2 is a perspective exploded view schematically showing a detection element section 300 and a heating section 200, which together form the sensor element 100. In the present description, the lower side of the in Fig. The gas sensor shown in section 1 is called the "front end" and the opposite side (top side) is shown. Fig. 1) is referred to as the "back end".

[0014] As shown in the figure, the gas sensor 1 comprises: the sensor element 100, implemented as a stacked body consisting of the detection element section 300 and the heating section 200; a metal sleeve 30 that holds the sensor element 100 and the like, such that they are contained within it; and a protector 24 attached to a front end section of the metal sleeve 30. The sensor element 100 has an overall elongated plate shape and is arranged such that its longitudinal direction extends along the direction of the axial line L. As will be described later, a porous protective layer is formed on the front end of the sensor element 100.

[0015] As in Fig.As shown in Figure 2, the heating section 200 has an overall elongated shape and comprises a first base body 101 and a second base body 103, each containing alumina as its main material; and a heating element 102, sandwiched between the first base body 101 and the second base body 103, which contains platinum as its main material. The heating element 102 comprises: a heat-generating section 102a positioned at the front end; and a pair of heating-supply sections 102b extending from the heat-generating section 102a along the longitudinal direction (the direction of the axial line L) of the first base body 101. The ends of the heating supply sections 102b are each electrically connected to heating-side pads 102 via conductors that are inserted into heating-side through holes 101a provided in the first base body 101.

[0016] Similar to the heating section 200, the detection element section 300 has an overall elongated plate shape and includes an oxygen concentration detection cell 130 and an oxygen pumping cell 140. The oxygen concentration detection cell 130 is composed of: a first solid electrolyte 105; and a first electrode 104 and a second electrode 106, which are formed on both surfaces of the first solid electrolyte 105. The first electrode 104 is composed of: a first electrode section 104a; and a first feed section 104b, which extends along the longitudinal direction (the direction of the axial line L) of the first solid electrolyte 105 from the first electrode section 104a.The second electrode 106 is composed of: a second electrode section 106a; and a second supply section 106b, which extends along the longitudinal direction (the direction of the axial line L) of the first solid electrolyte 105 from the second electrode section 106a.

[0017] One end of the first feed section 104b is electrically connected to a sensor-side pad 121 via a conductor formed in each of a first through-hole 105a provided in the first solid electrolyte 105, a second through-hole 107a provided in an insulating layer 107 described later, a fourth through-hole 109a provided in a second solid electrolyte 109, and a sixth through-hole 111a provided in a protective layer 111. One end of the second feed section 106b is electrically connected to a sensor-side pad 121 via a conductor formed in each of a third through-hole 107b provided in the insulating layer 107 described later, a fifth through-hole 109b provided in the second solid electrolyte 109, and a seventh through-hole 111b provided in the protective layer 111.

[0018] Here, the first electrode section 104a and the second electrode section 106a correspond to the "pair of electrodes" in the claims. The first feed section 104b corresponds to "one of the pair of feeds (internal feed)" in the claims. Furthermore, the first through-hole 105a, the second through-hole 107a, the fourth through-hole 109a, and the sixth through-hole 11a correspond to the "one through-hole" in the claims.

[0019] The oxygen pump cell 140 is composed of: the second solid electrolyte 109; and a third electrode 108 and a fourth electrode 110, which are formed on both surfaces of the second solid electrolyte 109. The third electrode 109 is composed of: a third electrode section 108a; and a third feed section 108b, which extends along the longitudinal direction (the direction of the axial line L) of the second solid electrolyte 109 from the third electrode section 108a. The fourth electrode 110 is composed of: a fourth electrode section 110a; and a fourth feed section 110b, which extends along the longitudinal direction (the direction of the axial line L) of the second solid electrolyte 109 from the fourth electrode section 110a.

[0020] One end of the third feed section 108b is electrically connected to a sensing element-side pad 121 via a conductor formed in each of the fifth through-hole 109b provided in the second solid electrolyte 109 and the seventh through-hole 111b provided in the protective layer 111. One end of the fourth feed section 110b is electrically connected to a sensing element-side pad 121 via a conductor formed in an eighth through-hole 111c provided in the protective layer 111. The second feed section 106b and the third feed section 108b have the same electrical potential.

[0021] The first solid electrolyte 105 and the second solid electrolyte (109) are each formed from a partially stabilized zirconia sintered body, which is obtained by adding yttria (Y₂O₃) or calcia (CaO) as a stabilizer to zirconia (ZrO₂). The heating element 102, the first electrode 104, the second electrode 106, the third electrode 108, the fourth electrode 110, the heating-side pads 120, and the sensing-element-side pads 121 can be formed from platinum group elements. Examples of suitable platinum group elements for their formation include Pt, Rh, Pd, and the like. These platinum group elements can be used alone or in a combination of two or more types.

[0022] Preferably, the heating element 102 and the like are mainly composed of platinum, for reasons of heat resistance and oxidation resistance. Furthermore, the heating element 102 and the like preferably include a ceramic component that is different from the platinum group element serving as the main component. From the point of view of fixation, this ceramic component is preferably a component similar to the material that serves as the main component on the side where these components are stacked.

[0023] The insulating layer 107 is formed between the oxygen pump cell 140 and the oxygen concentration detection cell 130, which were described above. The insulating layer 107 consists of an insulating section 114 and a diffusion resistance section 115. In the insulating section 114 of the insulating layer 107, a hollow measuring chamber 107c is formed at a location corresponding to the second electrode section 106a and the third electrode section 108a. The measuring chamber 107c communicates with the outside in the lateral direction of the insulating layer 107. The diffusion resistance section 115 is arranged in each of the communicating sections, which controls gas diffusion between the outside and the measuring chamber 107c according to a predetermined rate. The insulating layer 114 is not restricted as long as it is a ceramic sintered body with insulating properties and is formed from an oxide-based ceramic or the like, such as alumina or mullite. The diffusion resistance section 115 is a porous body formed from alumina, and the velocity of a detection gas flowing into the measuring chamber 107c is controlled by the diffusion resistance section 115, which is formed as a porous body.

[0024] On a surface of the second solid electrolyte 109, the protective layer 111 is formed such that it sandwiches around the fourth electrode 110. The protective layer 111 consists of: a porous electrode protection section 113a to prevent poisoning of the fourth electrode section 110, sandwiched around the fourth electrode section 110; and a reinforcement section 112 to protect the second solid electrolyte 109, sandwiching around the fourth supply section 110b. The sensor element of the present embodiment is an oxygen sensor element in which: the direction and magnitude of the current flowing between the electrodes of the oxygen pump cell 140 is adjusted such that the voltage between the electrodes of the oxygen concentration detection cell 130 has a predetermined value (e.g. 450 mV); and the oxygen concentration in the target gas corresponding to the current flowing in the oxygen pump cell 140 is detected linearly.

[0025] Here, a cross-section of the sensor element 100 perpendicular to the direction of the axial line L is a cross-section with a rectangular shape, the long sides of which are the outer edges formed by the protective layer 111 and the first base body 101, and the short sides of which are two sides along the stacking direction of the protective layer 11 and the first base body 101.

[0026] With reference to Fig.The metal sleeve 30 is made of SUS430 and includes: an external threaded section 31 for attaching the gas sensor 1 to an exhaust pipe; and a hexagonal section 32 against which an installation tool engages during installation. The metal sleeve 30 is also equipped with a stepped section 33 on the sleeve side, which projects radially inward. The stepped section 33 on the sleeve side supports a metal holder 34 for holding the sensor element 100. On the inside of the metal holder 34, a ceramic holder 35 and a talc 36 are arranged in that order from the front end. The talc 36 is composed of a first talc 37, arranged in the metal holder 34, and a second talc 38, arranged at the rear end of the metal holder 34. The first talc 37 is filled into the metal holder 34 and compressed, thereby fixing the sensor element 100 to the metal holder 34. The second talc 38 is filled into the metal sleeve 30 and compressed, thus ensuring a seal between the outer surface of the sensor element 100 and the inner surface of the metal sleeve 30.

[0027] An alumina bushing 39 is arranged at the rear end of the second talc 38. The bushing 39 has a multi-stepped design, and an axial hole 39a is provided such that it extends along the axial line L. The sensor element 100 is inserted into the bushing 39 with the axial hole 39a. A crimp section 30a at the rear end of the metal sleeve 30 is bent inwards, and the bushing 39 is pressed through the crimp section 30a towards the front end of the metal sleeve 30 via a stainless steel ring component 40.

[0028] A metal protector 24 is attached to the outer circumference of the front end of the metal sleeve 30 by welding. The protector 24 has a double structure. On the outside of the protector 24, an outer protector 41 with a cylindrical shape, closed at one end and with a uniform diameter, is arranged. On the inside of the protector 24, an inner protector 42 with a cylindrical shape, closed at one end, is arranged such that the outer diameter of a rear end section 42a is larger than the outer diameter of a front end section 42b. The protector 24 covers a front end section of the sensor element 100, projects from the front end of the metal sleeve 30 and has several gas inlet openings 24a.

[0029] The rear end of the metal sleeve 30 is inserted into the front end of an outer housing 25 made of SUS430. The outer housing 25 includes a front end section 25a, the front end of which has an enlarged diameter. The front end section 25a is attached to the metal sleeve 30 by laser welding or a similar process. A separator 50 is arranged inside the rear end of the outer housing 25. A retaining element 51 is positioned in a gap formed between the separator 50 and the outer housing 25. The retaining element 51 engages with a projecting section 50a extending outwards from the circumferential surface of the separator 50 and is secured between the separator and the crimped outer housing 25.

[0030] The separator 50 is equipped with insertion holes 50b for inserting various types of supply wires 11, 12, 13 for the detection element section 300 and the heating section 200, such that the insertion holes 50b extend through the separator 50 from the front end to the rear end. Fig. For the sake of simplicity, only three supply wires 11, 12, 13 are shown in Figure 1, and the other supply wires are not shown. Connection terminals 16, which connect the above supply wires 11 etc. to the sensing element-side pads 121 of the sensing element section 300 and the heater section 200, are housed in the insertion hole 50b. Each supply wire 11 etc. is designed to be connected externally to a connector (not shown), and the input / output of an electrical signal is carried out via the connector between an external device, such as an ECU, and each supply wire 11 etc.

[0031] Furthermore, a rubber cap 52, having a substantially circular column shape, is arranged at the rear end of the outer housing 25 of the separator for closing an opening 25b. The rubber cap 52 is attached to the outer housing 25 by compressing the outer housing 25 radially inward, in such a way that the rubber cap 52 is contained within the rear end of the outer housing 25. The rubber cap 52 also has insertion holes 52a for the respective insertion of the supply wires 11 and the like, such that the insertion holes 52a extend through the rubber cap 52 from the front end to the rear end.

[0032] Next, the first feed section 104b, which constitutes a characterizing part of the present invention, will be described.

[0033] The first feed section 104b is formed from a porous, gas-permeable body and faces the communication holes provided in the sensor element 100 (the first through-hole 105a, the second through-hole 106a, the fourth through-hole 109a, and the sixth through-hole 111a) to communicate with the outside. The sensing element-side pad 121, which is electrically connected to the sixth through-hole 111a, is also formed from a gas-permeable porous body.

[0034] A reference gas generated at the first electrode is discharged to the outside via the first feed section 104b and the communication holes.

[0035] If water has entered the sensor element 100 in this case, the first feed section 104b absorbs the water that entered through the communication holes, and if the sensor element 100 is subsequently heated, the water evaporates and expands within the first feed section 104b, which may cause the first feed section 104b to break or detach.

[0036] Therefore, in the present invention, the first feed section 104b is configured to include: precious metal particles of one or more grades selected from the group consisting of Pt, Pd, Rh, and Au; ceramic particles; and pores, wherein the porosity is greater than 0% and 11% or less, and a proportion RA of the total area of ​​large-diameter pores, each having a cross-sectional area of ​​5 µm² 2 or more, representing 8% or more of the total pore area in a cross-section.

[0037] The reason why the porosity of the first feed section 104b is greater than 0% is that if the first feed section 104b has no pores, the first feed section 104b becomes gas-impermeable and thus unable to adjust the pressure of the reference gas from the first electrode section 104a. However, if the porosity of the first feed section 104b is greater, the gas passes through easily, but if the porosity exceeds 11%, precious metal particles that are a conductor in the first electrode section 104b are separated by pores, causing detachment to occur easily. The porosity is preferably 5% or more and more preferably 8% or more.

[0038] Furthermore, if in the first feed section 104b the proportion RA of the total area of ​​large diameter pores, each with a cross-sectional area of ​​5 µm 2or more, in relation to the total area of ​​pores in a cross-section, is 8% or more, water absorbed in the first feed section 104b is easily released towards the communication holes. As a result, it is possible to avoid an incident in which, if heating is performed after water has entered the sensor element 100, the water evaporates and expands within the first feed section 104b, causing it to break or detach. It is preferred that the proportion RA is less than 60%. If the proportion RA is 60% or more, detachment of the first feed section 104b may occur.

[0039] The RA is preferably 40% or less, more preferably 30% or less, and most preferably 21.6% or less.

[0040] The RA is preferably 10% or more, more preferably 15% or more, and most preferably 20% or more.

[0041] The range of RA is preferably 10 to 40%, more preferably 15 to 30%, and most preferably, for example, 20 to 21.6%.

[0042] A measurement method for the porosity of the first feed section 104b is performed on the basis of a cross-sectional SEM image of the first feed section 104b, as described in Fig. 3 shown. Fig. Figure 3 is a cross-sectional SEM image of the example described later. First, the cross-sectional SEM image is binarized (binarization software: ImageJ) to extract pores 104V as empty parts, and the area of ​​each individual pore and the number of pores per unit area are calculated based on an "Analyze Particle" command. The pores 104V are the darkest section in the cross-sectional SEM image, and the precious metal particles 104M forming the first feed section 104b are the brightest section. The ceramic particles 104S forming the first feed section 104b exhibit medium brightness.

[0043] Next, a terminal section of a pore 104V is taken from the pores 104V, which is connected to the precious metal particles 104M and is located on the outermost side (in the top-bottom direction). Fig. 3) in the thickness direction of the first feed section 104b, a parallel line BL in the plane direction (the left-right direction in Fig. 3) of the first feed section 104b. The parallel line BL is drawn on the upper and lower sides of the first feed section 104b. Then the region of the cross-sectional SEM image between the two parallel lines BL is considered to be the cross-sectional area of ​​the first feed section 104b, and the porosity is calculated from the total area of ​​the pores 104V.

[0044] Those pores 104V that are not connected to the precious metal particles 104M (i.e., located far from the precious metal particles 104M with respect to the parallel lines BL) can be considered as cavities within the remaining layers adjacent to the first feed section 104b and are therefore excluded. In a case where, with reference to those pores 104V that are associated with the precious metal particles 104M, another precious metal particle 104M is located on the outermost side in the thickness direction, the position of the precious metal particle 104M is used as the position of the parallel line BL.

[0045] The total area of ​​the large-diameter pores, each with a cross-sectional area of ​​5 µm² 2 The number of pores in the cross-section of the first feed section 104b, or more, is calculated by generating a histogram based on the number of individual pores 104V per unit area that were subjected to image analysis as described above. Then, the proportion of large-diameter pores is calculated from the total area of ​​the pores that were subjected to image analysis as described above.

[0046] It is unnecessary to emphasize that the present invention is not limited to the embodiment described above, but is applicable to various modifications and equivalents encompassed by the concept and scope of the present invention.

[0047] The gas sensor is not limited to an oxygen sensor, but can also be a NOx sensor. Example

[0048] Several in Fig. 1 and Fig.Two sensor elements 100 shown were fabricated using Pt as the precious metal particles of the first feed section 104, using alumina as the ceramic particles, and varying the porosity of the first feed section 104 in different ways. Each resulting sensor element 100 was immersed in water to induce water penetration into the first feed section 104, and then the resulting first feed section 104 was dried. Next, the heating section 200 of the sensor element 100 was energized to raise the temperature to a predetermined temperature, and the puncture rate of the first feed section 104 was measured by a characteristic inspection. The puncture rate represents the proportion at which breakage or detachment of the feed section occurred.

[0049] Regarding sensor elements 100 of the same batch (for which the detachment rate was not measured) as those of sensor element 100 for which the detachment rate was measured, a cross-sectional SEM image of the first feed section 104 was acquired. Based on this cross-sectional SEM image, the porosity of the first feed section 104 and the fraction RA of the total area of ​​the large-diameter pores were calculated using the image analysis described above. The results obtained are shown in Table 1. Fig. 3 and Fig. 4 shown. Table 1 Porosity (%) Percentage of RA of the total pores of large Ds (%) Transfer rate (%) Example 1 10,1 21,6 0 See example 1 8,4 0 100 See example 2 9,2 0 100 See example 3 11,2 8,3 83

[0050] As shown in Table 1, in the case of Example 1, where the porosity was 11% or less and the proportion RA of the total area of ​​the large diameter pores was 8% or more, the breakage or detachment of the feed was prevented. On the other hand, in the cases of comparative examples 1 and 2, where the porosity was 11% or less, but the proportion RA of the total area of ​​the large diameter pores was less than 8%, the detachment rate was 100%, and breakage or detachment of the feed occurred. In the case of comparative example 3, where the proportion RA of the total area of ​​the large diameter pores was more than 8%, but the porosity exceeded 11%, the detachment rate was high and breakage or detachment of the feed occurred.

[0051] Fig. 3 and Fig. Figure 4 shows cross-sectional SEM images including the first feed section 104 of Example 1 or Comparison Example 1. It can be seen that the cross-sectional area of ​​individual pores 104V in Comparison Example 1 is smaller, and absorbed water is released less easily. Description of the reference symbols 1 gas sensor 30 metal sleeve 100 sensor elements 104a first electrode section (one pair of electrodes) 104b first feed section (one of the pair of feeds) (internal feed) 104M precious metal particles 104S ceramic particles 104V Pore 105a First through hole (communication hole) 106a second electrode section (one pair of electrodes) 106b second feed section (a pair of feeders) 107a second through hole (communication hole) 109a fourth through hole (communication hole) 111a sixth through hole (communication hole) 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 2002 - 032 240 A

[0003]

Claims

[1] Sensor element, comprising: a pair of electrodes; and a pair of leads each connected to the pair of electrodes, wherein one of the pair of feeders is an internal feeder arranged within the sensor element, and part of one of the pair of feeders faces a communication hole provided in the sensor element in order to be in communication with an external device; the internal feed is designed to contain precious metal particles of one or more types selected from the group Pt, Pd, Rh and Au, ceramic particles and pores; a porosity of the internal feed is greater than 0% and 11% or less; and a proportion RA of the total area of ​​large diameter pores, each with a cross-sectional area of ​​5 µm 2or more, in relation to a total pore area in a cross-section of the internal supply, which is 8% or more. [2] Sensor element according to claim 1, wherein the proportion RA is less than 60%. [3] Gas sensor, comprising: the sensor element according to claim 1 or 2; and a metal sleeve holding the sensor element.

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