Sensitive element, method for manufacturing the same and use thereof

Abstract

This application relates to the field of automotive tubular oxygen sensor technology, and in particular to a sensitive element, its preparation method, and its application. The preparation method of the sensitive element includes: S1. Pre-sintering a zirconia green blank to form a zirconia semi-ceramic substrate; S2. Coating electrode material onto the outer wall, inner wall, and bottom of the zirconia semi-ceramic substrate, and co-sintering to form a first bottom electrode and a second bottom electrode at the bottom of the zirconia ceramic substrate; forming an outer electrode ring layer and an outer electrode lead on the outer wall of the zirconia ceramic substrate; forming an inner electrode ring layer and an inner electrode lead on the inner wall of the zirconia ceramic substrate; S3. Coating a protective coating onto the outer wall of the outer electrode ring layer and the outer wall of the zirconia ceramic substrate; S4. Coating a ring of metal paste along the sealing area during the encapsulation of the zirconia ceramic substrate, and sintering to form a metal thin film ring layer in the sealing area.

Description

Technical Field

[0001] This application relates to the field of automotive tubular oxygen sensor technology, and in particular to a sensitive element, its preparation method and application. Background Technology

[0002] Tubular oxygen sensors are widely used in gasoline vehicles. They are long, tubular in shape and consist of a ceramic sensing element, a heating element, and a protective housing. The heating element, typically a platinum wire, is wound around the ceramic sensing element to heat it to over 300°C and maintain a stable temperature. Air is introduced into the inner side of the ceramic sensing element, while the outer side contacts the exhaust gas from the exhaust pipe. Under high-temperature conditions, the ceramic sensing element becomes a conductor of oxygen ions, causing oxygen ions to move from a high-concentration side to a low-concentration side. The protective housing is covered with tiny pores, allowing exhaust gas to enter and contact the ceramic sensing element while preventing impurities such as oil and carbon deposits from entering the exhaust pipe.

[0003] Currently, after the ceramic sensing element is encapsulated in a protective shell, the sealing ring sandwiched between the outer wall of the ceramic sensing element and the inner wall of the protective shell applies force to the outer wall of the ceramic sensing element. The applied force can damage the external electrode leads on the outer wall of the ceramic sensing element. After prolonged use, the external electrode leads may break, causing the tubular oxygen sensor to fail.

[0004] The existing technical solutions mentioned above have the following drawbacks: the force exerted on the outer wall of the ceramic sensing element by the sealing ring sandwiched between the outer wall of the ceramic sensing element and the inner wall of the protective shell will damage the external electrode lead on the outer wall of the ceramic sensing element. After long-term use, the external electrode lead may break, causing the tubular oxygen sensor to fail. Summary of the Invention

[0005] To avoid damage to the external electrode leads and extend the service life of the tubular oxygen sensor, this application provides a sensitive element, its preparation method, and its application.

[0006] The primary objective of this application is to provide a method for fabricating a sensitive element, employing the following technical solution: A method for preparing a sensitive element, comprising: S1. Pre-sinter the zirconia green body to form a zirconia semi-ceramic matrix; S2. Electrode material is coated on the outer wall, inner wall, and bottom of a zirconia semi-ceramic substrate and co-sintered to form a first bottom electrode and a second bottom electrode separated from each other at the bottom of the zirconia ceramic substrate; an outer electrode ring layer and an outer electrode lead for connecting the outer electrode ring layer and the first bottom electrode are formed on the outer wall of the zirconia ceramic substrate; an inner electrode ring layer and an inner electrode lead for connecting the inner electrode ring layer and the second bottom electrode are formed on the inner wall of the zirconia ceramic substrate. S3. Apply a protective coating to the outer wall of the outer electrode ring layer and the outer wall of the zirconia ceramic substrate; S4. A ring of metal paste is applied along the sealing area of ​​the zirconia ceramic substrate during encapsulation and then sintered to form a metal thin film ring layer in the sealing area.

[0007] By adopting the above technical solution, the metal thin film ring layer is denser than the external electrode lead, resulting in stronger interfacial bonding with the zirconia ceramic substrate and making it less prone to peeling. After the sensing element is encapsulated in a protective shell, the portion of the metal thin film ring layer in the pressure-bearing area serves as the direct stress-bearing surface, while the portion of the external electrode lead in the pressure-bearing area serves as the indirect stress-bearing surface. The portion of the metal thin film ring layer in the pressure-bearing area bears the force applied by the sealing ring instead of the external electrode lead, thus protecting the external electrode lead. This significantly reduces the stress on the external electrode lead, thereby greatly reducing the strain generated in the pressure-bearing area of ​​the external electrode lead. The microstructure is essentially undamaged, avoiding defects in the transition area of ​​the external electrode lead. Even after prolonged use, the external electrode lead will not break, effectively improving the quality and service life of the tubular oxygen sensor. Simultaneously, the metal thin film ring layer has strong conductivity, reinforcing the conductivity of the portion of the external electrode lead located in the sealed area.

[0008] This application further specifies that the metal paste is a platinum paste, palladium paste, silver paste, or silver-palladium paste.

[0009] By adopting the above technical solutions, when the operating temperature of the tubular oxygen sensor is equal to or greater than 450℃, using platinum or palladium paste results in more stable performance. When the operating temperature of the tubular oxygen sensor is less than 450℃, using silver or silver-palladium paste offers better cost-effectiveness.

[0010] This application further specifies that: in step S2, before sintering, the sample is dried at 100-200℃ for 1-3 hours; in step S4, before sintering, the sample is first dried at room temperature for 1-3 hours, and then dried at 100-200℃ for 1-3 hours.

[0011] This application further specifies that: in step S2, the sintering temperature is 1400-1550℃; and in step S4, the sintering temperature is 800-950℃.

[0012] This application is further configured such that, in step S1, the temperature is sequentially maintained at 1000℃, 1100℃, and 1200℃ for 2 hours, 3 hours, and 1 hour, respectively.

[0013] This application is further configured such that: before step S1, a rough blank is first prepared by dry isostatic pressing of zirconia powder, and then a green zirconia blank is prepared by water-jetting process.

[0014] The second objective of this application is to provide a sensitive element, which adopts the following technical solution: A sensitive element, prepared using the above-described method for preparing a sensitive element, comprising: Zirconia ceramic matrix; An outer electrode ring layer is formed on the outer wall of the zirconia ceramic substrate along the circumferential direction of the substrate; An inner electrode ring layer is formed on the inner wall of the zirconia ceramic substrate along the circumferential direction of the substrate. The first bottom electrode is formed at the bottom end of the zirconia ceramic substrate; The second bottom electrode is formed at the bottom end of the zirconia ceramic substrate and is isolated from the first bottom electrode. External electrode leads are formed on the outer wall of the zirconia ceramic substrate and are used to connect the external electrode ring layer and the first bottom electrode. The inner electrode lead is formed on the inner wall of the zirconia ceramic substrate and is used to connect the inner electrode ring layer and the second bottom electrode. A protective coating is applied to the outer electrode ring layer and the outer wall of the zirconia ceramic substrate. A metal thin film ring layer forms a sealing region of the zirconia ceramic substrate along the circumference of the substrate.

[0015] This application further specifies that the thickness of the metal thin film ring layer is 0.05-0.1 mm.

[0016] This application further specifies that the porosity of the metal thin film ring layer is less than the porosity of the external electrode lead.

[0017] The third objective of this application is to provide a tubular oxygen sensor, employing the following technical solution: A tubular oxygen sensor is fabricated using the aforementioned sensitive element.

[0018] In summary, the beneficial technical effects of this application are as follows: 1. By adding a metal thin-film ring layer, which is denser than the external electrode leads and has stronger interfacial bonding with the zirconia ceramic substrate, it is less prone to peeling. After the sensing element is encapsulated in a protective shell, the portion of the metal thin-film ring layer in the pressure-bearing area serves as the direct stress-bearing surface, while the portion of the external electrode leads in the pressure-bearing area serves as the indirect stress-bearing surface. The portion of the metal thin-film ring layer in the pressure-bearing area bears the force applied by the sealing ring instead of the external electrode leads, thus protecting them. This significantly reduces the stress on the external electrode leads, thereby greatly reducing the strain generated in the pressure-bearing area of ​​the external electrode leads. The microstructure is essentially undamaged, preventing defects in the transition area of ​​the external electrode leads. Even after prolonged use, the external electrode leads will not break, effectively improving the quality and service life of the tubular oxygen sensor. Simultaneously, the metal thin-film ring layer has strong conductivity, reinforcing the conductivity of the portion of the external electrode leads in the sealed area.

[0019] 2. When the operating temperature of the tubular oxygen sensor is equal to or greater than 450℃, platinum or palladium paste is recommended for more stable performance. When the operating temperature of the tubular oxygen sensor is less than 450℃, silver or silver-palladium paste is recommended for better cost-effectiveness.

[0020] 3. The protective coating effectively prevents oil, carbon deposits, particulate matter, and other debris in the exhaust pipe from directly contaminating the outer electrode ring layer. Simultaneously, the protective coating slows down the diffusion rate of exhaust gas, preventing excessive fluctuations in the sensor output signal due to sudden changes in exhaust gas concentration. Furthermore, the protective coating prevents high-temperature exhaust gas from directly eroding the outer electrode ring layer, extending its service life.

[0021] 4. During the pre-sintering of the zirconia green compact, it is held at 1000℃, 1100℃, and 1200℃ for 2 hours, 3 hours, and 1 hour respectively. Holding at 1000℃ for 2 hours effectively removes the organic binder. Holding at 1100℃ for 3 hours promotes initial grain growth. Holding at 1200℃ for 1 hour ensures the uniform densification of the zirconia semi-ceramic matrix. This effectively improves the dimensional stability of the zirconia semi-ceramic matrix. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of an existing ceramic sensing element; Figure 2 yes Figure 1 The diagram shows a structural schematic of an existing ceramic sensing element from another perspective. Figure 3 yes Figure 1 An exploded view of an existing ceramic sensing element is shown. Figure 4 This is a process flow diagram of the preparation method of the sensitive element in this application; Figure 5 This is a schematic diagram of the structure of the sensitive element in this application; Figure 6 This is a schematic diagram of the internal structure of the zirconia ceramic substrate, external electrode leads, and metal thin film ring layer. Figure 7 This is a schematic diagram showing the condition of the external electrode leads after the pressure-bearing area of ​​an existing ceramic sensing element is subjected to stress. Figure 8 This is a schematic diagram of the metal thin film ring layer after the pressure-bearing area of ​​the sensitive element in this application is subjected to force.

[0023] Reference numerals: 110, Zirconia ceramic substrate; 121, First bottom electrode; 122, Second bottom electrode; 131, Outer electrode ring layer; 132, Inner electrode ring layer; 141, Outer electrode lead; 142, Inner electrode lead; 150, Protective coating; 160, Metal thin film ring layer. Detailed Implementation

[0024] It should be noted that, referring to Figure 1 , Figure 2 and Figure 3The existing ceramic sensing element includes a zirconia ceramic substrate 110, an outer electrode ring layer 131, an inner electrode ring layer 132, a first bottom electrode 121, a second bottom electrode 122, an outer electrode lead 141, an inner electrode lead 142, and a protective coating 150. The outer electrode ring layer 131 is formed circumferentially on the outer wall of the zirconia ceramic substrate 110. The inner electrode ring layer 132 is formed circumferentially on the inner wall of the zirconia ceramic substrate 110. The first bottom electrode 121 is formed at the bottom end of the zirconia ceramic substrate 110. The second bottom electrode 122 is also formed at the bottom end of the zirconia ceramic substrate 110, and is spaced apart from the first bottom electrode 121. The outer electrode lead 141 is formed on the outer wall of the zirconia ceramic substrate 110 and is used for electrically connecting the outer electrode ring layer 131 and the first bottom electrode 121. An inner electrode lead 142 is formed on the inner wall of the zirconia ceramic substrate 110, used for electrically connecting the inner electrode ring layer 132 and the second bottom electrode 122. The inner electrode ring layer 132 is in contact with air. The outer electrode ring layer 131 is in contact with exhaust gas. Oxygen molecules in the air gain electrons in the inner electrode ring layer 132, forming oxygen ions. The oxygen ions move to the outer electrode ring layer 131 through oxygen vacancies in the zirconia ceramic substrate 110. The oxygen ions lose electrons in the outer electrode ring layer 131, forming oxygen molecules. During this process, an electromotive force is generated between the inner electrode ring layer 132 and the outer electrode ring layer 131. A protective coating 150 is applied to the outer electrode ring layer 131 and the outer wall of the zirconia ceramic substrate 110. The protective coating 150 effectively prevents oil, carbon deposits, particulate matter, and other impurities in the exhaust pipe from directly contaminating the outer electrode ring layer 131. At the same time, the protective coating 150 can slow down the diffusion rate of exhaust gas, avoiding excessive fluctuations in the sensor output signal due to sudden changes in exhaust gas concentration. In addition, the protective coating 150 prevents high-temperature exhaust gas from directly scouring the outer electrode ring layer 131, thus extending its service life.

[0025] For ease of understanding, please refer to Figure 1 After the ceramic sensing element is encapsulated in a protective housing, one end face of the sealing ring sandwiched between the outer wall of the ceramic sensing element and the inner wall of the protective housing contacts the PBA (Pressure-bearing Area) of the SA (Sealing Area). The direction of the force applied to the PBA is as follows: Figure 1As indicated by the middle arrow, the portion of the external electrode lead 141 located in the PBA region bears significant force, causing damage to its microstructure. Conversely, the portion of the external electrode lead 141 located in the NPBA region (Non-pressure-bearing Area) does not bear any force, leading to defects in the TA region (Transition Area) of the SA region. After prolonged use, the external electrode lead 141 may break, resulting in no signal feedback and causing the tubular oxygen sensor to fail, thus limiting the quality and lifespan of the tubular oxygen sensor.

[0026] Reference Figure 4 This application discloses a method for preparing a sensitive element, including... S1. Pre-sinter the zirconia green body to form a zirconia semi-ceramic matrix.

[0027] It should be noted that before step S1, a rough blank is first prepared by dry isostatic pressing of zirconia powder, and then a green zirconia blank is prepared by water grinding process.

[0028] In this embodiment, during pre-sintering, the substrates are sequentially held at 1000℃, 1100℃, and 1200℃ for 2 hours, 3 hours, and 1 hour, respectively. Holding at 1000℃ for 2 hours effectively removes the organic binder. Holding at 1100℃ for 3 hours promotes initial grain growth. Holding at 1200℃ for 1 hour ensures uniform densification of the zirconia semi-ceramic matrix. This effectively improves the dimensional stability of the zirconia semi-ceramic matrix.

[0029] S2. Electrode material is coated onto the outer wall, inner wall, and bottom of the zirconia semi-ceramic substrate and co-sintered to form a first bottom electrode 121 and a second bottom electrode 122 separated from each other at the bottom of the zirconia ceramic substrate 110. An outer electrode ring layer 131 and an outer electrode lead 141 for connecting the outer electrode ring layer 131 and the first bottom electrode 121 are formed on the outer wall of the zirconia ceramic substrate 110. An inner electrode ring layer 132 and an inner electrode lead 142 for connecting the inner electrode ring layer 132 and the second bottom electrode 122 are formed on the inner wall of the zirconia ceramic substrate 110.

[0030] The electrode material in this application embodiment is existing technology and can be platinum or a platinum mixture.

[0031] Before sintering in this embodiment, the electrode material is dried at 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃ or 200℃ for 1h, 1.5h, 2h, 2.5h or 3h to prevent large-scale flow of the electrode material.

[0032] In this embodiment, the sintering temperature is 1400℃, 1410℃, 1420℃, 1430℃, 1440℃, 1450℃, 1460℃, 1470℃, 1480℃, 1490℃, 1500℃, 1510℃, 1520℃, 1530℃, 1540℃, or 1550℃. The first bottom electrode 121, the second bottom electrode 122, the outer electrode ring layer 131, the outer electrode lead 141, the inner electrode ring layer 132, the inner electrode lead 142, and the zirconia ceramic substrate 110 are co-sintered, which effectively saves manufacturing steps and shortens the manufacturing cycle.

[0033] S3. Apply a protective coating 150 to the outer wall of the outer electrode ring layer 131 and the outer wall of the zirconia ceramic substrate 110.

[0034] The protective coating 150 in this embodiment uses existing technology and can be a mixture of alumina and magnesium oxide. The protective coating 150 effectively prevents oil, carbon deposits, particulate matter, and other impurities in the exhaust pipe from directly contaminating the outer electrode ring layer 131. Simultaneously, the protective coating 150 slows down the diffusion rate of exhaust gas, preventing excessive fluctuations in the sensor output signal due to sudden changes in exhaust gas concentration. Furthermore, the protective coating 150 prevents high-temperature exhaust gas from directly eroding the outer electrode ring layer 131, extending its service life.

[0035] In this embodiment, a plasma spraying process is used to attach a protective coating 150 to the outer electrode ring layer 131 and the outer wall of the zirconia ceramic substrate 110.

[0036] S4. A ring of metal paste is applied along the sealing area of ​​the zirconia ceramic substrate 110 during encapsulation and sintered to form a metal thin film ring 160 in the sealing area.

[0037] In the embodiments of this application, the metal paste is platinum paste, palladium paste, silver paste, or silver-palladium paste. When the operating temperature of the tubular oxygen sensor is equal to or greater than 450°C, platinum paste or palladium paste is selected for more stable performance. When the operating temperature of the tubular oxygen sensor is less than 450°C, silver paste or silver-palladium paste is selected for better cost performance. It should be noted that the metal content of the platinum paste, palladium paste, silver paste, or silver-palladium paste is approximately 80 wt%, the diluent content is approximately 15 wt%, and the pore-forming agent content is approximately 5 wt%.

[0038] Before sintering in this embodiment, the metal slurry is first dried at room temperature for 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours, and then dried at 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, or 200°C for 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours to prevent the metal slurry from flowing over a large area.

[0039] In this embodiment, a spraying process is used to attach the metal slurry to the outer wall of the zirconia ceramic substrate 110.

[0040] In this embodiment, the sintering temperature is 800℃, 810℃, 820℃, 830℃, 840℃, 850℃, 860℃, 870℃, 880℃, 890℃, 900℃, 910℃, 920℃, 930℃, 940℃, or 950℃. After sintering, the metal paste transforms into a metal thin film ring layer 160. Compared to the external electrode lead 141, the metal thin film ring layer 160 is more dense, has a stronger interfacial bond with the zirconia ceramic substrate 110, and is less prone to peeling. After the sensitive element is encapsulated in a protective housing, the portion of the metal thin film ring 160 located in the pressure-bearing area serves as the direct stress-bearing surface, while the portion of the external electrode lead 141 located in the pressure-bearing area serves as the indirect stress-bearing surface. The portion of the metal thin film ring 160 in the pressure-bearing area bears the force applied by the sealing ring instead of the external electrode lead 141, thus protecting the external electrode lead 141. This significantly reduces the stress on the external electrode lead 141, thereby greatly reducing the strain generated in the pressure-bearing area of ​​the external electrode lead 141, minimizing damage to the microstructure and preventing defects in the transition area of ​​the external electrode lead 141. Even after prolonged use, the external electrode lead 141 will not break, effectively improving the quality and service life of the tubular oxygen sensor. Simultaneously, the metal thin film ring 160 has strong conductivity, reinforcing the conductivity of the portion of the external electrode lead 141 located in the sealed area.

[0041] Reference Figure 5This application also discloses a sensitive element, fabricated using the aforementioned method, comprising a zirconia ceramic substrate 110, an outer electrode ring layer 131, an inner electrode ring layer 132, a first bottom electrode 121, a second bottom electrode 122, an outer electrode lead 141, an inner electrode lead 142, a protective coating 150, and a metal thin film ring layer 160. The outer electrode ring layer 131 is formed circumferentially on the outer wall of the zirconia ceramic substrate 110. The inner electrode ring layer 132 is formed circumferentially on the inner wall of the zirconia ceramic substrate 110. The first bottom electrode 121 is formed at the bottom end of the zirconia ceramic substrate 110. The second bottom electrode 122 is formed at the bottom end of the zirconia ceramic substrate 110 and is spaced apart from the first bottom electrode 121. An external electrode lead 141 is formed on the outer wall of the zirconia ceramic substrate 110 for electrically connecting the external electrode ring layer 131 and the first bottom electrode 121. An internal electrode lead 142 is formed on the inner wall of the zirconia ceramic substrate 110 for electrically connecting the internal electrode ring layer 132 and the second bottom electrode 122. The internal electrode ring layer 132 is in contact with air. The external electrode ring layer 131 is in contact with exhaust gas. Oxygen molecules in the air gain electrons in the internal electrode ring layer 132, forming oxygen ions. The oxygen ions move to the external electrode ring layer 131 through oxygen vacancies in the zirconia ceramic substrate 110. The oxygen ions lose electrons in the external electrode ring layer 131, forming oxygen molecules. During this process, an electromotive force is generated between the internal electrode ring layer 132 and the external electrode ring layer 131. A protective coating 150 is applied to the external electrode ring layer 131 and the outer wall of the zirconia ceramic substrate 110. The protective coating 150 effectively prevents oil, carbon deposits, particulate matter, and other impurities in the exhaust pipe from directly contaminating the outer electrode ring layer 131. Simultaneously, the protective coating 150 slows down the diffusion rate of exhaust gas, preventing excessive fluctuations in the sensor output signal due to sudden changes in exhaust gas concentration. Furthermore, the protective coating 150 prevents high-temperature exhaust gas from directly eroding the outer electrode ring layer 131, extending its service life. The metal thin film ring layer 160 forms a sealing area of ​​the zirconia ceramic substrate 110 along its circumference. Compared to the outer electrode lead 141, the metal thin film ring layer 160 is denser, has stronger interfacial adhesion to the zirconia ceramic substrate 110, and is less prone to peeling. After the sensitive element is encapsulated in the protective shell, the portion of the metal thin film ring 160 located in the pressure-bearing area serves as the direct stress-bearing surface, while the portion of the external electrode lead 141 located in the pressure-bearing area serves as the indirect stress-bearing surface. The portion of the metal thin film ring 160 located in the pressure-bearing area replaces the external electrode lead 141 in bearing the force applied by the sealing ring, thus protecting the external electrode lead 141. This significantly reduces the stress on the external electrode lead 141, thereby significantly reducing the strain generated in the portion of the external electrode lead 141 located in the pressure-bearing area. The microstructure is basically not damaged, thus avoiding defects in the portion of the external electrode lead 141 located in the transition area.Even after prolonged use, the external electrode lead 141 will not break, effectively improving the quality and service life of the tubular oxygen sensor. Simultaneously, the metal thin film ring layer 160 has strong conductivity, reinforcing the conductivity of the external electrode lead 141 located in the sealed area.

[0042] Preferably, the thickness of the metal thin film ring layer 160 is 0.05mm, 0.055mm, 0.06mm, 0.065mm, 0.07mm, 0.075mm, 0.08mm, 0.085mm, 0.09mm, 0.095mm or 0.1mm.

[0043] Preferably, such as Figure 6 As shown, the porosity of the metal thin film ring layer 160 is less than that of the external electrode lead 141, resulting in stronger interfacial bonding with the zirconia ceramic substrate 110 and making it less prone to peeling.

[0044] This application also discloses a tubular oxygen sensor, which is made using the above-mentioned sensitive element. Example Example 1

[0045] S1. The zirconia green body is pre-sintered. During the pre-sintering process, it is held at 1000℃, 1100℃, and 1200℃ for 2h, 3h, and 1h respectively to form a zirconia semi-ceramic matrix.

[0046] S2. First, electrode material is coated onto the outer wall, inner wall, and bottom of the zirconia semi-ceramic substrate. Then, it is dried at 120°C for 2 hours. Afterward, the electrode material and the zirconia semi-ceramic substrate are co-sintered at 1480°C, forming a first bottom electrode 121 and a second bottom electrode 122 separated from each other at the bottom of the zirconia ceramic substrate 110. An outer electrode ring layer 131 and an outer electrode lead 141 for connecting the outer electrode ring layer 131 and the first bottom electrode 121 are formed on the outer wall of the zirconia ceramic substrate 110. An inner electrode ring layer 132 and an inner electrode lead 142 for connecting the inner electrode ring layer 132 and the second bottom electrode 122 are formed on the inner wall of the zirconia ceramic substrate 110. The amount of electrode material used is 23 mg.

[0047] S3. A protective coating 150 is applied to the outer wall of the outer electrode ring layer 131 and the outer wall of the zirconia ceramic substrate 110 using a plasma spraying process.

[0048] S4. First, a ring of platinum paste is applied along the sealing area of ​​the zirconia ceramic substrate 110 during encapsulation. Then, it is dried at room temperature for 1 hour. Next, it is dried at 120°C for 1 hour. Afterward, it is sintered at 850°C to form a metal thin film ring layer 160 in the sealing area. The thickness of the formed metal thin film ring layer 160 is 0.075 mm. Example 2

[0049] The difference from Example 1 is that in step S4, the thickness of the metal thin film ring layer 160 formed is 0.05 mm. Example 3

[0050] The difference from Example 1 is that in step S4, the thickness of the metal thin film ring layer 160 formed is 0.1 mm. Example 4

[0051] The difference from Example 1 is that in step S4, the metal paste used is palladium paste. Example 5

[0052] The difference from Example 1 is that in step S4, the metal paste used is silver paste. Example 6

[0053] The difference from Example 1 is that in step S4, the metal paste used is a silver-palladium paste. Example 7

[0054] The difference from Example 1 is that the sintering temperature in step S4 is 950°C. Comparative Example

[0055] Comparative Example 1 First, a rough blank was prepared using zirconia powder via dry isostatic pressing, followed by a zirconia green blank produced by continuous flow grinding. The green blank was pre-sintered at 1100℃ to form a zirconia semi-ceramic substrate. Then, electrode material was coated onto the outer wall, inner wall, and bottom of the zirconia semi-ceramic substrate. After the electrode material dried, it was co-sintered with the zirconia semi-ceramic substrate at 1480℃ to form the existing sensing element. The electrode material dosage was 23 mg. Performance testing

[0056] Test 1: A pressure of 6 MPa was applied to the pressure-bearing areas of the sensitive elements prepared in Examples 1-7 and Comparative Example 1 for a period of time. During this period, the integrity rate of the external electrode lead 141 located in the sealed area was tested. The test results are shown in Table 1. Figure 7 The diagram shows the situation where the external electrode lead 141 of the sensitive element made in Comparative Example 1 is located in the sealed area after the test is completed. Figure 8 The diagram shows the situation where the metal thin film ring layer 160 is located in the sealed area after the sensitive element prepared in Example 1 has been tested.

[0057] Table 1 sample Integrity rate after 1 hour of testing Integrity rate after 24 hours of testing Integrity rate at 30 days Example 1 100% 100% 100% Example 2 100% 100% 99% Example 3 100% 100% 100% Example 4 100% 100% 100% Example 5 100% 100% 99% Example 6 100% 100% 100% Example 7 100% 100% 100% Comparative Example 1 100% 100% 75% Refer to Table 1. Figure 7 and Figure 8As can be seen from Examples 1-7 and Comparative Example 1, after a certain period of pressure testing, the integrity rate of the outer electrode lead 141 in the sealed area of ​​the sensitive element prepared in Examples 1-7 is higher than 99%, while the integrity rate of the outer electrode lead 141 in the sealed area of ​​the sensitive element prepared in Comparative Example 1 is significantly reduced after a certain period of pressure testing. This indicates that the metal thin film ring layer 160 can provide good protection for the outer electrode lead 141. As can be seen from Examples 1 and 2, when the metal thin film ring layer 160 is thinner, the protective performance is slightly reduced. At the same time, a higher sintering temperature can further improve the density of the metal thin film ring layer 160 and further improve the interfacial bonding force between the metal thin film ring layer 160 and the zirconia ceramic substrate 110.

[0058] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a sensitive element, characterized in that, include: S1. Pre-sinter the zirconia green body to form a zirconia semi-ceramic matrix; S2. Electrode material is coated on the outer wall, inner wall, and bottom of the zirconia semi-ceramic substrate and co-sintered to form a first bottom electrode (121) and a second bottom electrode (122) separated from each other at the bottom of the zirconia ceramic substrate (110); an outer electrode ring layer (131) and an outer electrode lead (141) for connecting the outer electrode ring layer (131) and the first bottom electrode (121) are formed on the outer wall of the zirconia ceramic substrate (110); an inner electrode ring layer (132) and an inner electrode lead (142) for connecting the inner electrode ring layer (132) and the second bottom electrode (122) are formed on the inner wall of the zirconia ceramic substrate (110); S3. A protective coating (150) is applied to the outer wall of the outer electrode ring layer (131) and the outer wall of the zirconia ceramic substrate (110); S4. A ring of metal paste is applied along the sealing area of ​​the zirconia ceramic substrate (110) during encapsulation and sintered to form a metal thin film ring layer (160) in the sealing area.

2. The method for preparing the sensitive element according to claim 1, characterized in that, The metal paste is a platinum paste, palladium paste, silver paste, or silver-palladium paste.

3. The method for preparing the sensitive element according to claim 1, characterized in that, In step S2, before sintering, the sample is dried at 100-200℃ for 1-3 hours; in step S4, before sintering, the sample is dried at room temperature for 1-3 hours, and then dried at 100-200℃ for 1-3 hours.

4. The method for preparing the sensitive element according to claim 1, characterized in that, In step S2, the sintering temperature is 1400-1550℃; in step S4, the sintering temperature is 800-950℃.

5. The method for preparing the sensitive element according to claim 1, characterized in that, In step S1, the temperature is kept at 1000℃, 1100℃, and 1200℃ for 2 hours, 3 hours, and 1 hour respectively.

6. The method for preparing the sensitive element according to claim 1, characterized in that, Before step S1, a rough blank is first prepared by dry isostatic pressing of zirconium powder, and then the zirconium green blank is prepared by water-jetting process.

7. A sensitive element, characterized in that, The sensitive element is prepared by the method described in any one of claims 1 to 6, comprising: The zirconia ceramic matrix (110); The outer electrode ring layer (131) is formed on the outer wall of the zirconia ceramic substrate (110) along the circumferential direction of the zirconia ceramic substrate (110); The inner electrode ring layer (132) is formed on the inner wall of the zirconia ceramic substrate (110) along the circumferential direction of the zirconia ceramic substrate (110); The first bottom electrode (121) is formed at the bottom end of the zirconium oxide ceramic substrate (110); The second bottom electrode (122) is formed at the bottom end of the zirconia ceramic substrate (110) and is separated from the first bottom electrode (121); The external electrode lead (141) is formed on the outer wall of the zirconia ceramic substrate (110) and is used to connect the external electrode ring layer (131) and the first bottom electrode (121). The inner electrode lead (142) is formed on the inner wall of the zirconia ceramic substrate (110) and is used to connect the inner electrode ring layer (132) and the second bottom electrode (122). The protective coating (150) is applied to the outer electrode ring layer (131) and the outer wall of the zirconia ceramic substrate (110); The metal thin film ring layer (160) forms a sealing region of the zirconia ceramic substrate (110) along the circumference of the zirconia ceramic substrate (110).

8. The sensitive element according to claim 7, characterized in that, The thickness of the metal thin film ring layer (160) is 0.05-0.1 mm.

9. The sensitive element according to claim 7, characterized in that, The porosity of the metal thin film ring layer (160) is less than that of the external electrode lead (141).

10. A tubular oxygen sensor, characterized in that, It is prepared using the sensitive element described in claim 7.

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