Gas sensor element

Abstract

The present disclosure provides a gas sensor element which includes a porous protective layer with improved water-repellent properties during continuous water pouring, wherein the gas sensor element comprises: a sensing section with a stack of a solid electrolyte body and a heat-generating body, wherein the solid electrolyte body has at least one pair of electrodes on opposite sides thereof and the heat-generating body includes a heat-generating source; and a porous protective layer formed around the sensing section, wherein the porous protective layer is formed from an aluminum oxide-containing aggregate and a silicon dioxide-containing coating material, and the porous protective layer contains the weight concentration x wt.-% of the coating material, based on the total weight of the aggregate and the coating material, and the porosity y% of the following formula (1) are satisfied: in the porous protective layer the pore volume of the pores with a pore diameter of 100 nm or less is 0.02 mL / g or less.

Description

Technical area

[0001] The present disclosure relates to a gas sensor element mounted on a vehicle, for example, and the concentration of oxygen or NO x recorded in the exhaust gas. State of the art

[0002] A large number of attempts have been made in a large number of industries around the world in order to reduce ecological influences and pollution. In particular, in the automotive industry, the development to promote the spread not only of fuel-efficient gasoline-engine vehicles, but also of so-called environmentally friendly vehicles, such as hybrid vehicles or electric vehicles, as well as to further improve the performance of such vehicles was advanced day by day .

[0003] The purification of exhaust gas and the improvement of the fuel economy performance of vehicles have been accomplished by sensing the concentration of oxygen or NO x carried out in a measurement target gas such as exhaust gas using a gas sensor and accurately controlling fuel oil consumption and the amount of intake air.

[0004] An exemplary basic configuration of a gas sensor element constituting such a gas sensor includes a detection portion which has a stack of a solid electrolyte body with a pair of electrodes on opposite sides thereof and a heat generation body including a heat generation source, and a porous protective layer formed around the detection portion.

[0005] A gas sensor detects the concentration of oxygen or NO x in the exhaust gas at a temperature of approximately 400 ° C to 850 ° C. Therefore, when water drops (i.e., condensed water) in the exhaust gas collide with the gas sensor element constituting the gas sensor, thermal shock due to partial quenching may be generated, and the function of the gas sensor may be reduced.

[0006] In order to overcome such concern, a porous protective layer having a water-repellent property is provided around the detection portion of the gas sensor element.

[0007] As a conventional technique regarding a gas sensor element comprising a porous protective layer having a water-repellent property, here, for example, Patent Literature 1 discloses a gas sensor element comprising a porous protective layer in which the thermal conductivity λ is in a range of 0.2 to 5 W / mK, and the product λCpρ of the thermal conductivity λ (W / mK), the density ρ (g / m 3) and the specific heat Cp (J / gK) in a range of 5.3 × 10 5 up to 2.1 × 10 7 WJ / m 4 K 2 is.

[0008] The water repellent property of the porous protective layer disclosed in Patent Literature 1 is obtained from the Leidenfrost phenomenon. The Leidenfrost phenomenon is a phenomenon by which the surface of a water droplet is instantly vaporized when the water droplet is allowed to come into contact with the surface of a porous protective layer at a high temperature and a barrier layer (vapor film) between the Surface of the porous protective layer and the water droplet is formed due to the evaporated water vapor. According to this Leidenfrost phenomenon, even in a case where water drops adhere to the surface of the porous protective layer, the water drops are immediately separated from the surface of the porous protective layer, and this means that the porous protective layer has a water-repellent property.

[0009] In the case of a gas sensor element comprising a porous protective layer having a water-repellent property as disclosed in Patent Literature 1, however, the water-repellent property of the porous protective layer is insufficient in some cases when condensed water contained in the exhaust gas is deposited on a location in the high-temperature gas sensor element is continuously dripped or poured. For example, the porous protective layer of the gas sensor element disclosed in Patent Literature 1 exhibits PTC (Positive Temperature Coefficient) characteristics that the thermal conductivity decreases with a decrease in temperature. Accordingly, when the temperature of the porous protective layer is lowered by continuously pouring water, its thermal conductivity lowers, and a vapor film according to the Leidenfrost phenomenon is hardly formed. As a result, the water-repellent property is lowered and a high thermal shock against the gas sensor element is generated. References Patent literature

[0010] Patent literature 1: JP 2016-29360 A Summary of the Invention Technical Problem

[0011] As described above, in the case of a conventional gas sensor element comprising a porous protective layer having a water-repellent property, the water-repellent property is decreased due to a decrease in temperature due to continuous dripping of water, and hence a high thermal shock is applied to the gas sensor element in FIG generated in some cases. Therefore, the present disclosure provides a gas sensor element comprising a porous protective layer having an improved water-repellent property when water is continuously dripped onto the porous protective layer. the solution of the problem

[0012] As a result of intensive studies aimed at achieving the above-mentioned object, the present inventors found that NTC (Negative Temperature Coefficient) properties, by which thermal conductivity increases with decrease in temperature, of the porous protective layer of a gas sensor element Control of the weight concentration of a coating material and the porosity in the porous protective layer of the gas sensor element can be imparted to satisfy a predetermined relational expression, and the water-repellent property with respect to continuous pouring is improved, thereby completing the present disclosure. In particular, the concept of the present disclosure is as follows. (1) A gas sensor element which comprises: a detection portion having a stack of a solid electrolyte body and a heat generating body, the solid electrolyte body having at least a pair of electrodes on opposite sides thereof, and the heat generating body including a heat generating source; and a porous protective layer formed around the sensing portion, wherein the porous protective layer is formed from an aggregate containing alumina and a coating material containing silica, and In the porous protective layer, the weight concentration x% by weight of the coating material, based on the total weight of the aggregate and the coating material, and the porosity y% satisfy the following formula (1): y ≤ 0.0058 x 2 - 1.2666 x + 68 and, in the porous protective layer, the pore volume of the pores with a pore diameter of 100 nm or less is 0.02 mL / g or less. (2) The gas sensor element according to the above item (1), Wherein the weight concentration of the coating material in the porous protective layer is 10 % By weight or more. (3) The gas sensor element according to item (1) or (2) above, wherein the porosity of the porous protective layer is 25% or more. (4) A method for manufacturing the gas sensor element according to any one of (1) to (3) above, comprising: Forming a porous protective layer of an alumina-containing aggregate and a silica-containing coating material around the detection portion; and Baking the formed porous protective layer at 1000 ° C or higher. Advantageous Effects of the Invention

[0013] According to the present disclosure, a gas sensor element including a porous protective layer having an improved water-repellent property with respect to continuous water pouring can be provided. Figure list Fig. 1 is a schematic diagram illustrating an embodiment of a gas sensor element of the present disclosure; Fig. 2 is a graph showing the relationship between temperature and thermal conductivity with respect to the porous protective layers of Example 1 and Comparative Example 1 shows; Fig. 3 is a diagram showing the relationship between the weight concentration of silicon dioxide and the porosity in the porous protective layers of Example 1 and Comparative Examples 1 and 2 shows; Fig. 4 is a graph showing the results of the on the porous protective layers of Example 1 and Comparative Examples 1 and 2 shows performed water repellency tests; Fig. Fig. 5 is a graph showing the relationship between the weight concentration of silica and the bond strength in Example; Fig. Fig. 6 is a graph showing the relationship between the porosity of a porous protective layer and the response value in Example; Fig. 7A is a diagram showing an SEM photo of the porous protective layer of Example 1 shows, and Fig. 7B is a diagram showing an SEM photo of the porous protective layer of Comparative Example 3 shows; Fig. 8 is a diagram showing the relationship between the pore diameter and the pore volume in the porous protective layers of Example 1 and Comparative Example 3 shows; Fig. 9 is a schematic diagram illustrating an embodiment of a gas sensor element of the present disclosure; and Fig. 10 is an enlarged diagram showing an end portion of an embodiment of a gas sensor element of the present disclosure. Description of the Embodiments The present disclosure will be described in detail below.

[0014] In the gas sensor element of the present disclosure, a solid electrolyte body having at least a pair of electrodes on opposite sides thereof and a heat generating body including a heat generating source are laminated to form a detection portion, and a porous protective layer is formed around this detection portion.

[0015] Fig. 1 is a schematic diagram illustrating an embodiment of a gas sensor element of the present disclosure. One in Fig. 1 gas sensor element 100 shown. generally comprises a detection section 10 which is the concentration of oxygen or NO x detected or recognized in the exhaust gas, and a porous protective layer 20 which is the periphery of the detection section 10 protects against moisture in the exhaust gas, thereby suppressing occurrence of a decrease in output which would otherwise occur due to a temperature drop of the detection portion 10 would occur, which would arise from the moisture entering the detection section 10 achieved, results, and also traps toxic compounds and the like in the exhaust gas passing through it.

[0016] The detection section 10 generally comprises a solid electrolyte layer 3 which have a pair of electrodes on opposite sides of the same 4 including an electrode 41 on the measurement target gas side and an electrode 42 has on the reference gas side, a porous, diffuse resistance layer 2 , which is the electrode 41 on the measurement target gas side above a measurement target gas space 8 surrounds a shielding layer 1 , which is the measurement target gas space 8 together with the porous, diffuse resistance layer 2 defined, a reference gas space protective layer 5 , which is the electrode 42 on the reference gas side above a reference gas space 9 surrounds, and a heat generation source 6 and a heat generating source substrate 7 .

[0017] The heat generation source 6 includes a heater body which is a heat generating body and forms a heat region of the gas sensor element 100 so that it is thermally controlled to achieve the activation energy of the same.

[0018] The detection section 10 has, in the cross-sectional shape shown in the drawing, corner portions which are cut out in cone shapes. With portions cut out in this way, the thickness of the porous protective layer becomes 20 at the corresponding sections of the detection section 10 ensured.

[0019] The solid electrolyte layer 3 is made of zirconium oxide, and the electrode 41 on the measurement target gas side and the electrode 42 on the reference gas side are each made of platinum. In addition, the shielding layer 1 and the reference gas space protective layer 5 each have a gas-impermeable, internal structure, and are formed from aluminum oxide.

[0020] A voltage at which the difference in oxygen concentration and the current have a linear correlation is applied to the pair of electrodes 4 is applied and a measurement target gas is caused to hit the electrode 41 on the measurement target gas side while causing a reference gas such as air to touch the electrode 42 touched on the reference gas side. Then, the value of the current generated between the electrodes is measured in accordance with each difference in oxygen concentration, so that the air-fuel ratio of the vehicle engine can be identified based on the measured current.

[0021] The porous, diffuse resistance layer 2 is provided at a position which the measurement target gas space 8 around the electrode 41 defined on the measurement target gas side to be the amount of the electrode 41 to suppress measurement target gas introduced on the measurement target gas side, and is configured to further introduce hydrogen gas, carbon monoxide gas, oxygen gas, and the like from the exhaust gas passing through the porous protective layer 20 around the detection section 10 into the measurement target gas space 8 over the porous, diffuse resistance layer 2 were introduced. In addition, as in Fig. As shown in FIG. 10, the porous protective layer of the present disclosure which satisfies the following formula (1) can also be applied to the gas sensor element having a structure in which a gas inlet port is arranged at an end portion of the gas sensor element. Fig. 10 is an enlarged diagram showing an end portion of an embodiment of a gas sensor element of the present disclosure. In Fig. 10 is a gas inlet port 103 at an end portion of a gas sensor element 101 arranged. Since a porous protective layer 20A (an upper layer 20Aa and a lower layer 20 Fig) at a lower portion of the end portion of the gas sensor element 101 is formed, it is separated from the heat generating portion, and thus the heat hardly reaches the porous protective layer and the temperature is hardly raised. As a result, due to a decrease in temperature due to continuous dripping of water, the water repellency is easily decreased. By adapting the porous protective layer of the present disclosure, such deficiency is compensated and a preferable water repellent property is obtained.

[0022] The porous protective layer 20 is a porous layer optionally having noble metal catalyst particles (not shown) carried on its surface. The noble metal catalyst particles in the porous protective layer 20 can be used over the entire area of ​​the porous protective layer 20 be distributed, or can just as well only in the lateral area of ​​the same, what the porous, diffuse resistance layer 2 near the electrode 41 on the measurement target gas side, be distributed. Alternatively, the amount of noble metal catalyst particles contained in the porous protective layer can be 20 are supported, be distributed in such a way that a relatively large amount of the noble metal catalyst particles in a region, which is for example the porous, diffuse resistance layer 2 corresponds to be worn. Here, as the noble metal catalyst particles, platinum, palladium, or rhodium particles can be used alone, or an alloy containing two or more of palladium, rhodium, and platinum can be used.

[0023] The porous protective layer 20 can be a one-layer structure, as in Fig. 1 shown have. On the other hand, the porous protective layer can 20 also one, as in Fig. 9, have a laminated two-layer structure in which the porous protective layer 20A from a lower layer 20 Fig which is in contact with the detection section 10 that is inside the gas sensor element 100A and an upper layer 20Aa which is in contact with the exterior of the same. In this case, since the porous protective layer of the present disclosure which satisfies the below-mentioned formula (1) is excellent in water-repellent property, it is preferable to the upper layer 20Aa applied. In addition, the lower layer can be 20 Fig can be used as a poisoning suppression layer. When the porosity of such a poisoning suppressing layer is less than that of the upper layer 20Aa is set, the poisoning suppressing layer becomes a porous layer having a specific surface area larger than the upper layer 20Aa is, and therefore the poison absorption properties of the poisoning suppressing layer can be ensured. In a preferred embodiment, the porous protective layer consists of 20A with a laminated two-layer structure consisting of a lower layer 20 Fig which is used as a poisoning suppressing layer, and an upper layer 20Aa to which the porous protective layer of the present disclosure is applied.

[0024] The gas sensor element of the present disclosure is characterized in that the porous protective layer 20 Has NTC properties. The porous protective layer is described below.

[0025] The porous protective layer is formed from an aggregate containing aluminum oxide (Al 2 O 3) And a coating material containing silicon oxide (SiO 2). A number of alumina-containing aggregates are bonded together by the silica-containing coating material, which serves as a binder, thereby forming a porous protective layer.

[0026] The type of alumina contained in the aggregates is not particularly limited, and any of α-alumina, γ-alumina, and O-alumina can be used. The aggregate may contain components other than alumina as long as it satisfies formula (1) below. Examples of such other components include spinel, silicon carbide, and aluminum nitride. The aggregate preferably consists of aluminum oxide.

[0027] The coating material may contain certain components other than silicon dioxide as long as it satisfies the formula (1) mentioned below. Examples of such other components include titanium dioxide, zirconium dioxide, antimony oxide, and zinc oxide. The coating material preferably consists of silicon dioxide.

[0028] In the porous protective layer, the pore volume of the pores which have a pore diameter of 100 nm or less is 0.02 mL / g or less. By reducing pores with a pore diameter of 100 nm or less, which is the mean free path or less at which gaseous molecules hardly move, thermal conductivity can be improved. Here, the term “pore diameter” is used to mean a pore diameter (average pore diameter) obtained by measuring according to a gas adsorption method, a mercury intrusion method, or the like. The pore volume (also referred to as “integrated pore volume”) of the pores with a pore diameter of 100 nm or less can be obtained by a gas adsorption method, a mercury intrusion method, and the like. In the production of a porous protective layer, a coating material is melted by baking at a temperature of 1000 ° C or higher, and preferably 1100 ° C or higher, so that the pore volume of the pores with a pore diameter of 100 nm or less becomes 0.02 mL / g or less can be set. Further, by melting the coating material, the strength of the porous protective layer is improved.

[0029] In the porous protective layer, the weight concentration x% by weight of the coating material, based on the total weight of the aggregate and the coating material, and the porosity y% of the porous protective layer of the following formula (1) are sufficient: y ≤ 0.0058 x 2 - 1.2666 x + 68 In addition, the porosity is not 0% (y ≠ 0).

[0030] The porous protective layer which satisfies the above formula (1) has NTC properties. In the present disclosure, “NTC properties” means that the thermal conductivity increases with a decrease in temperature. Since the porous protective layer of the present disclosure has NTC properties, it can preferably have a water-repellent property even if condensed water contained in the exhaust gas is continuously poured thereon.

[0031] The water-repellent mechanism of a porous protective layer which satisfies the above-described formula (1) and has NTC properties when continuously doused with water is described below. In particular, when condensed water in the exhaust gas is continuously dropped on the porous protective layer of a gas sensor element at a high temperature, the temperature of the porous protective layer is lowered. The heat supply capacity (heat flow) of the porous protective layer is increased proportionally to the thermal conductivity of the same. Since the thermal conductivity of the porous protective layer, which has NTC properties, is increased with a decrease in temperature, the heat supply ability is increased. When the heat supply capability of the porous protective layer is increased, a vapor film is easily formed according to the Leidenfrost phenomenon. Therefore, the porous protective layer preferably has a water-repellent property. Therefore, even if water is continuously poured onto the porous protective layer, the water-repellent property of the porous protective layer is not lowered, and thermal shock against the gas sensor element can be reduced. As such, the porous protective layer having NTC properties is excellent in water-repellent property at a low temperature as compared with a protective layer having PTC properties by which thermal conductivity is lowered with a decrease in temperature.

[0032] The weight concentration x of a coating material to the total weight of an aggregate and a coating material in a porous protective layer is preferably 10% by weight or more, and more preferably 10% by weight to 35% by weight. When the weight concentration of the coating material which works to bond aggregates together is 10% by weight or more, the high strength of the porous protective layer is ensured. On the other hand, when it is 35 wt% or less, a state in which the coating material is uniformly dispersed in the porous protective layer can be maintained.

[0033] In addition, the porosity y of the porous protective layer is preferably 25% or more, and more preferably 25% to 55%. When the porosity of the porous protective layer is 25% or more, the exhaust gas permeability becomes sufficiently high and therefore the responsiveness of the sensor output to a change in the exhaust gas atmosphere becomes sufficiently high. On the other hand, when it is 55% or less, a decrease in the strength of the porous protective layer can be suppressed.

[0034] The present disclosure also includes a method of manufacturing a gas sensor element containing the above-described porous protective layer. The method for manufacturing the gas sensor element of the present disclosure includes: forming a porous protective layer of an alumina-containing aggregate and a silica-containing coating material around a detection portion; and baking the formed porous protective layer at 1000 ° C or higher.

[0035] When forming a porous protective layer, the porous protective layer can be formed, for example, by a dipping method, a molding method which enables good film thickness dimensional accuracy, or a thermal spray method which is suitable for producing a compact layer. The immersion method or the thermal spray method is selected depending on the porosity of the porous protective layer.

[0036] When the porous protective layer is formed by the dipping method, for example, there is an operation to dip a detection portion in a slurry containing an aggregate and a coating material, and remove it from the slurry and then close it dry, repeated several times until a layer of a predetermined thickness can be obtained. The slurry containing an aggregate and a coating material is obtained, for example, by dispersing an aggregate and a coating material in a solvent (water, etc.), optionally using a dispersant (polyvinyl alcohol (PVA), etc.). Alumina serving as an aggregate can be used, for example, in the form of alumina powder. Meanwhile, silicon dioxide serving as a coating material can be used either in a crystalline form or in an amorphous form. Amorphous silicon dioxide is preferably used. When silica sol such as silica is used to adjust the weight concentration of a coating material in the obtained porous protective layer to, for example, 20 wt%, about 38.5 wt% of the silica sol is required as the silica -Sol is an aqueous solution of 40% by weight silicon dioxide.

[0037] When the porous protective layer is formed by the thermal spraying method, for example, mixed powder or an aggregate-containing slurry and a coating material are melted or converted into a state close to such a melted state at a high temperature, and then the obtained is sprayed on a sensing portion to form a porous protective layer.

[0038] When baking the porous protective layer, the porous protective layer thus formed is baked. The baking temperature is 1000 ° C or higher, and preferably 1100 ° C or higher. The baking temperature is, for example, 1000 ° C to 1200 ° C, preferably 1050 ° C to 1150 ° C, and more preferably 1100 ° C. When the baking temperature is 1000 ° C. or higher, the coating material (silicon dioxide) is melted, and the pore volume of the pores with a pore diameter of 100 nm or less can be set to 0.02 mL / g or less. Accordingly, the thermal conductivity and the strength of the porous protective layer are improved as compared with the case of baking a porous protective layer at a temperature lower than 1000 ° C. at which a coating material is not completely melted. The baking time can be chosen appropriately depending on the baking temperature. The baking time is generally 0.5 hours to 2 hours. Examples

[0039] In the following, the present disclosure will be described in more detail in the following example and comparative examples. However, these examples are not intended to limit the scope of the present disclosure. Production of the porous protective layer

[0040] A porous protective layer was formed using aluminum oxide (Al 2 O 3) As an aggregate and also using silicon dioxide (SiO 2) As a coating material, and the prepared porous protective layer was then placed around the detection portion of a gas sensor element to find that in Fig. 1 to produce the gas sensor element shown. The alumina used here as an aggregate had NTC properties. The silicon dioxide used as a coating material exhibited PTC properties and influenced the porosity. Therefore, the porous protective layers of Example 1 and Comparative Examples 1 and 2 , in which the component ratio between alumina and silica and the porosity were changed, was prepared, and a comparative expression required to impart NTC properties to the porous protective layer was obtained. example 1

[0041] Alumina powder (mean particle diameter: 10 µm) and silica powder (mean particle diameter: 15 nm) were dispersed in water using a dispersing agent to make a slurry. The weight concentration of the solid content of silicon dioxide based on the total weight of the solid content of the aluminum oxide and silicon dioxide in the slurry was adjusted to 21% by weight. According to the immersion method, 60 mg of the generated slurry was adhered around the detection portion of a gas sensor element, and was then baked in the atmosphere at 1,100 ° C. for 2 hours to form a porous protective layer. The porosity of the porous protective layer was measured to be 37% according to the mercury intrusion method. Comparative example 1

[0042] Silica powder (mean particle diameter: 10 nm) was dispersed in water using a dispersant to make a slurry. According to the immersion method, 60 mg of the generated slurry was allowed to adhere around the detection area of ​​a gas sensor element, and was then baked in the atmosphere at 1,100 ° C. for 4 hours to form a porous protective layer. The porosity of the porous protective layer was 0.7%. Comparative example 2

[0043] A porous protective layer was prepared in the same manner as that of Example 1, except that the amounts of alumina and silica in the slurry were changed so that the weight concentration of the solid content of silica based on the total weight of the solid contents of the alumina and silica in of the slurry, was adjusted to 22% by weight and that the porosity of the porous protective layer was adjusted to 49%. Evaluation of the thermal conductivity properties

[0044] The porous protective layers of Example 1 and Comparative Examples 1 and 2 were measured for the relationship between temperature and thermal conductivity. Fig. 2 shows the relationship between the temperature and the thermal conductivity with regard to the porous protective layers of Example 1 and Comparative Example 1. As in Fig. As shown in Fig. 2, the porous protective layer of Example 1 had NTC properties by which the thermal conductivity was increased with a decrease in temperature. In contrast, the porous protective layer of Comparative Example 1 exhibited PTC properties that lowered thermal conductivity with a decrease in temperature. Further, the porous protective layer of Comparative Example 2 had PTC properties, although it is not shown in the figures.

[0045] A comparison expression was then obtained, which is required in order to impart NTC properties to the porous protective layer. As described above, it is considered that the component ratio between the alumina used as an aggregate and the silica used as a coating material in the porous protective layer and the porosity of the porous protective layer have an influence on the imparting of NTC properties to the porous protective layer. Thereby, from the results obtained by confirming the thermal conductivity properties of the porous protective layer of Example 1 and Comparative Examples 1 and 2, a comparative expression (formula (1)) between the weight concentration of silica used as a coating material in the porous protective layer and the porosity of the porous protective layer obtained, which is necessary for imparting the NTC properties to the porous protective layer. Fig. 3 shows the relationship between the weight concentration of silicon dioxide and the porosity in the porous protective layers of Example 1 and Comparative Examples 1 and 2. As in Fig. 3, the material exhibited NTC properties when the weight concentration x% by weight of the coating material based on the total weight of the aggregate and the coating material in the porous protective layer, and the porosity y% of the porous protective layer represented by the following formula ( 1) sufficed: y ≤ 0.0058 x 2 - 1.2666 x + 68 Evaluation of the water-repellent effect

[0046] Regarding the porous protective layers of Example 1 and Comparative Examples 1 and 2, water drops (dropped amount: 2 µL) were continuously added dropwise to the surface of a porous protective layer at a high temperature (700 ° C), and the number of water repellency was then measured . Fig. 4 shows the results of water repellency tests carried out on the porous protective layers of Example 1 and Comparative Examples 1 and 2. As in Fig. As shown in Fig. 4, the number of continuous water repellency of the porous protective layer of Example 1, which has NTC properties, was markedly increased compared with the protective layers of Comparative Examples 1 and 2, which had PTC properties. Accordingly, it was revealed that when the weight concentration x% by weight of a coating material and the porosity y% of a porous protective layer were controlled so as to satisfy the above-described formula (1) so that the porous protective layer is allowed to exhibit NTC properties , the water-repellent property of the porous protective layer is significantly improved when continuously doused with water, compared to a porous protective layer which has PTC properties. Relationship between weight concentration of silicon oxide and bond strength

[0047] Gas sensor elements in which the weight concentration of silica based on the total weight of the solid contents of alumina and silica in the slurry was changed so that the weight concentration of silica in a porous protective layer was changed were manufactured in the same manner as that of Example 1 described above . The bonding strength between the porous protective layer and an element base material mainly composed of alumina was measured. The weight concentration of silica was adjusted to 2.8% by weight, 5.8% by weight, 12.1% by weight, or 19.1% by weight. Fig. 5 shows the relationship between the weight concentration of silicon dioxide and the bond strength. As in Fig. As shown in FIG. 5, it was revealed that the stable bonding strength of the porous protective layer is ensured in a range in which the weight concentration of silicon dioxide in the porous protective layer is 10% by weight or more. Correlation between the porosity and the response value

[0048] Gas sensor elements in which the porosity of a porous protective layer was changed were manufactured in the same manner as that of Example 1. The porosity of the porous protective layer was set to 10%, 35%, or 69%. When the porosity was 30% or less, the thermal spray method was used instead of the immersion method.

[0049] With respect to the prepared porous protective layers, the value of the responsiveness of the sensor output when the exhaust atmosphere was largely changed was measured in an exhaust environment in a real engine machine. Fig. 6 shows the relationship between the porosity of a porous protective layer and the response value. It should be noted that the responsiveness becomes better as the value of the responsiveness is increased. As in Fig. 6, it was revealed that the exhaust gas permeability becomes sufficiently high and preferable responsiveness of the sensor output to a change in exhaust gas is ensured in a range in which the porosity of the porous protective layer is 25% or more. Influence of the baking temperature

[0050] The influence of the baking temperature in the production of a porous protective layer was investigated. A porous protective layer formed according to the dipping method and then baked at 1100 ° C. (Example 1) was compared with a porous protective layer formed according to the dipping method and then baked at 900 ° C. (Comparative Example 3). The porous protective layer of Comparative Example 3 was produced in the same manner as that of Example 1 except that the baking temperature was changed to 900 ° C. Scanning electron microscopy (SEM) images of the porous protective layers of Example 1 and Comparative Example 3 are in Fig. 7 shown. Fig. 7A shows an SEM photo of the porous protective layer of Example 1, and Fig. 7B shows an SEM photo of the porous protective layer of Comparative Example 3. Further, Fig. shows. 8 shows the relationship between the pore diameter and the pore volume measured in the porous protective layers of Example 1 and Comparative Example 3 according to a gas adsorption method. From Fig. 7A, Fig. 7B and Fig. 8, it was found that the silica particles used as a coating material in the porous protective layer of Example 1, which was baked at 1100 ° C, were melted, and the pore volume of pores with a pore diameter of 100 nm or less was 0.02 mL / g or less. On the other hand, in the porous protective layer of Comparative Example 3 which was baked at 900 ° C, the silica particles used as a coating material were not sufficiently melted, and the pore volume of pores with a pore diameter of 100 nm or less was significantly larger than that in FIG porous protective layer of example 1. List of reference symbols 1 shielding layer 2 Porous, diffuse resistance layer 3 solid electrolyte layer 4 pairs of electrodes 41 Electrode on the measurement target gas side 42 Electrode on the reference gas side 5 Reference gas space protective layer 6 heat generation source (heating) 7 Heat generating source substrate 8 Target gas space 9 reference gas space 10 acquisition section 20, 20A Porous protective layer 20Aa upper layer 20 From lower layer 100, 100A, 101 gas sensor element 103 gas inlet port QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Patent literature cited

[0000] JP 2016029360 A

[0010]

Claims

[1] Gas sensor element comprising: a capture section comprising a stack of a solid electrolyte body and a heat generating body, wherein the solid electrolyte body has at least one pair of electrodes on opposite sides of the same and the heat generating body comprises a heat generating source; and a porous protective layer formed around the detection section, wherein the porous protective layer is formed from an aluminum oxide-containing aggregate and a silicon dioxide-containing coating material, and in the porous protective layer the weight concentration x wt.% of the coating material, based on the total weight of the aggregate and the coating material, and the porosity y% of the following formula (1) are satisfied: y ≤ 0,0058 x 2 − 1,2666 x + 68 and, in the porous protective layer, the pore volume of the pores with a pore diameter of 100 nm or less is 0.02 mL / g or less. [2] Gas sensor element according to claim 1, wherein the weight concentration of the coating material in the porous protective layer is 10 wt.% or more. [3] Gas sensor element according to claim 1 or 2, wherein the porosity of the porous protective layer is 25% or more. [4] Method for manufacturing the gas sensor element according to any one of claims 1 to 3, comprising: Forming a porous protective layer of an aluminum oxide-containing aggregate and a silicon dioxide-containing coating material around the detection section; and Baking of the formed porous protective layer at 1000 °C or higher.