Ceramic sensitive element as well as preparation method and application thereof

Abstract

The invention relates to the technical field of tubular oxygen sensors for vehicles, in particular to a ceramic sensitive element and a preparation method and application thereof.The preparation method of the ceramic sensitive element comprises the steps that S2, platinum group metal slurry is coated on the outer wall of a zirconium oxide semi-ceramic substrate, co-sintering is conducted, and the ceramic sensitive element is obtained; the outer wall of the zirconia ceramic matrix is covered with a first platinum group metal layer; s3, coating the outer wall of the first platinum group metal layer with an electrode material, coating the outer wall, the inner wall and the bottom end of the zirconia ceramic matrix with the electrode material, and sintering to form an outer electrode ring layer on the outer wall of the first platinum group metal layer and form an outer electrode lead on the outer wall of the zirconia ceramic matrix, so as to obtain the electrode. An inner electrode ring layer and an inner electrode lead are formed on the inner wall of the zirconia ceramic substrate, and a first bottom electrode and a second bottom electrode are arranged at the bottom end of the zirconia ceramic substrate; and S5, coating the platinum group metal salt solution on the outer wall of the protective coating, and sintering to form a second platinum group metal layer on the outer wall of the protective coating.

Description

Technical Field

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

[0002] Tubular oxygen sensors are widely used in gasoline vehicles. They are elongated tubular in shape and include a ceramic sensing element, a heating element, and a protective housing. The heating element, typically a platinum wire, is wound around the outside of 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 perforations, 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] Existing ceramic sensing elements include a zirconia ceramic substrate, an outer electrode ring layer, an inner electrode ring layer, a first bottom electrode, a second bottom electrode, an outer electrode lead, and an inner electrode lead. The outer electrode ring layer is formed circumferentially on the outer wall of the zirconia ceramic substrate. The inner electrode ring layer is formed circumferentially on the inner wall of the zirconia ceramic 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. The outer electrode lead is formed on the outer wall of the zirconia ceramic substrate and connects the outer electrode ring layer to the first bottom electrode. The inner electrode lead is formed on the inner wall of the zirconia ceramic substrate and connects the inner electrode ring layer to the second bottom electrode. The inner electrode ring layer is in contact with air. The outer electrode ring layer is in contact with exhaust gas. Oxygen molecules in the air gain electrons in the inner electrode ring layer, forming oxygen ions. The oxygen ions move to the outer electrode ring layer through oxygen vacancies in the zirconia ceramic substrate. Oxygen ions lose electrons in the outer electrode ring layer to form oxygen molecules. During this process, an electromotive force is generated between the inner and outer electrode ring layers, and the magnitude of the electromotive force is proportional to the logarithm of the oxygen concentration difference.

[0004] In the fabrication of existing ceramic sensing elements, a rough blank is first prepared using zirconia powder via dry isostatic pressing, followed by a zirconia green blank prepared via continuous flow grinding. The zirconia green blank is then pre-sintered at 1000-1200℃ to form a zirconia semi-ceramic substrate. Electrode material is then coated onto the outer wall, inner wall, and bottom of the zirconia semi-ceramic substrate. After the electrode material dries, it is co-sintered with the zirconia semi-ceramic substrate at 1400-1550℃ to form the existing ceramic sensing element. Finally, a protective coating is sprayed onto the outer electrode ring layer and the outer wall of the zirconia ceramic substrate.

[0005] The existing technical solutions mentioned above have the following drawbacks: due to the co-sintering of the electrode material and the zirconia semi-ceramic substrate at 1400-1550℃, the catalytic performance of the outer electrode ring layer and the inner electrode ring layer decreases, and there is a certain loss at the three-phase interface. Summary of the Invention

[0006] To ensure the catalytic performance of the outer and inner electrode ring layers and reduce losses at the three-phase interface, this application provides a ceramic sensing element, its preparation method, and its application.

[0007] The primary objective of this application is to provide a method for preparing a ceramic sensing element, employing the following technical solution: A method for preparing a ceramic sensing element, comprising: S1. Pre-sinter the zirconia green body to form a zirconia semi-ceramic matrix; S2. A platinum group metal paste is coated onto the outer wall of a zirconia semi-ceramic substrate, and the platinum group metal paste and the zirconia semi-ceramic substrate are co-sintered to form a zirconia ceramic substrate with a first platinum group metal layer on the outer wall; S3. Electrode material is coated on the outer wall of the first platinum group metal layer, and electrode material is coated on the outer wall, inner wall and bottom of the zirconia ceramic substrate. After sintering, an outer electrode ring layer is formed on the outer wall of the first platinum group metal layer, an outer electrode lead is formed on the outer wall of the zirconia ceramic substrate, an inner electrode ring layer and an inner electrode lead are formed on the inner wall of the zirconia ceramic substrate, and a first bottom electrode and a second bottom electrode separated from each other are formed at the bottom of the zirconia ceramic substrate. S4. Apply a protective coating to the outer wall of the outer electrode ring layer and the first platinum group metal layer; S5. A platinum group metal salt solution is coated onto the outer wall of the protective coating, and then sintered to form a second platinum group metal layer on the outer wall of the protective coating.

[0008] By adopting the above technical solution and adding a first platinum group metal layer, the length of the three-phase interface can be effectively increased. Adding a second platinum group metal layer can further improve the electrochemical reaction rate, thereby expanding the potential difference.

[0009] The present application further specifies that: in step S1, the sintering temperature is 1000-1200℃; in step S2, the sintering temperature is 1400-1550℃; in step S3, the sintering temperature is 600-1100℃; and in step S5, the sintering temperature is 400-600℃.

[0010] By adopting the above technical solution, the catalytic performance of the outer electrode ring layer and the inner electrode ring layer can be guaranteed and the loss of the three-phase interface can be reduced by lowering the sintering temperature of the outer electrode ring layer and the inner electrode ring layer.

[0011] This application further specifies that, based on the mass percentage of the platinum group metal slurry, the platinum group metal slurry comprises: 30-40 wt% solid oxide powder, 5-15 wt% platinum group metals, 15-25 wt% solvent, 0.5-3 wt% pore-forming agent, 10-15 wt% binder, and 20-40 wt% plasticizer.

[0012] This application further specifies that the platinum group metal salt solution is an aqueous solution composed of platinum group metal ions and acid radical ions.

[0013] This application further specifies that the platinum group metal salt solution is an aqueous solution of chloroplatinic acid, an aqueous solution of platinum nitrate, an aqueous solution of rhodium chloride, an aqueous solution of ammonium chlororhodiumate, an aqueous solution of sodium hexachlororhodiumate, or an aqueous solution of rhodium nitrate.

[0014] This application further specifies that: before sintering, the material is first dried at room temperature for 1-7 hours, and then dried at 100-200℃ for 1-3 hours; in step S3, before sintering, the material is dried at 100-200℃ for 1-3 hours; in step S5, before sintering, the material is first dried at room temperature for 1-7 hours, and then dried at 100-200℃ for 1-3 hours.

[0015] By adopting the above technical solution, drying is carried out before sintering to prevent dripping.

[0016] This application further specifies that: the thickness of the first platinum group metal layer is 40-60 μm and the porosity is 20%-80%; the thickness of the second platinum group metal layer is 40-60 μm.

[0017] 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.

[0018] The second objective of this application is to provide a ceramic sensing element, which adopts the following technical solution: A ceramic sensing element, prepared by the above method, comprises: Zirconia ceramic matrix; The first platinum group metal layer is formed on the outer wall of the zirconia ceramic substrate along the circumferential direction of the substrate; An outer electrode ring layer is formed on the outer wall of the first platinum group metal layer along the circumferential direction of the first platinum group metal layer; 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 wall of the outer electrode ring layer and the first platinum group metal layer; A second platinum group metal layer is formed on the outer wall of the protective coating along the circumference of the protective coating.

[0019] By adopting the above technical solution, the first platinum group metal layer can effectively increase the length of the three-phase interface. The inner electrode ring layer can contact the air. The outer electrode ring layer can contact the exhaust gas. Oxygen molecules in the air gain electrons in the inner electrode ring layer to form oxygen ions. The oxygen ions move to the outer electrode ring layer through oxygen vacancies in the zirconia ceramic matrix. The oxygen ions lose electrons in the outer electrode ring layer to form oxygen molecules. During this process, an electromotive force is generated between the inner and outer electrode ring layers. The protective coating effectively prevents oil, carbon deposits, particulate matter, and other impurities in the exhaust pipe from directly contaminating the outer electrode ring layer and the first platinum group metal layer. At the same time, the protective coating 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 prevents high-temperature exhaust gas from directly scouring the outer electrode ring layer and the first platinum group metal layer, extending their service life. The second platinum group metal layer can further increase the electrochemical reaction rate, thus widening the potential difference.

[0020] 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 a ceramic sensing element.

[0021] In summary, the beneficial technical effects of this application are as follows: 1. By adding a first platinum group metal layer, the length of the three-phase interface can be effectively increased. By adding a second platinum group metal layer, the electrochemical reaction rate can be further improved, thereby expanding the potential difference.

[0022] 2. By reducing the sintering temperature of the outer electrode ring layer and the inner electrode ring layer, the catalytic performance of the outer electrode ring layer and the inner electrode ring layer can be guaranteed, and the loss of the three-phase interface can be reduced. Attached Figure Description

[0023] 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 This is a schematic diagram of the structure of the ceramic sensing element of this application; Figure 4 yes Figure 3 The diagram shows a structural schematic of the ceramic sensing element from another perspective. Figure 5 yes Figure 3 The exploded view of the ceramic sensing element is shown. Figure 6 These are voltage rise curves of the ceramic sensing elements prepared in Examples 1-3 and Comparative Examples 1-3.

[0024] Reference numerals: 110, Zirconia ceramic substrate; 120, First platinum group metal layer; 131, Outer electrode ring layer; 132, Inner electrode ring layer; 141, First bottom electrode; 142, Second bottom electrode; 151, Outer electrode lead; 152, Inner electrode lead; 160, Protective coating; 170, Second platinum group metal layer. Detailed Implementation

[0025] It should be noted that, referring to Figure 1 and Figure 2 The 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 141, a second bottom electrode 142, an outer electrode lead 151, and an inner electrode lead 152. 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 141 is formed at the bottom end of the zirconia ceramic substrate 110. The second bottom electrode 142 is formed at the bottom end of the zirconia ceramic substrate 110 and is spaced apart from the first bottom electrode 141. The outer electrode lead 151 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 141. An inner electrode lead 152 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 142. 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.

[0026] It should be noted in advance that the three-phase interface refers to the boundary region between the outer electrode ring layer 131 / inner electrode ring layer 132, the zirconia ceramic matrix 110, and the air / exhaust gas. It is the core reaction site for the generation, transport, and transformation of oxygen ions.

[0027] This application discloses a method for preparing a ceramic sensing element, including... S1. Pre-sinter the zirconia green body to form a zirconia semi-ceramic matrix.

[0028] In this embodiment, a rough blank is first prepared by dry isostatic pressing of zirconia powder, and then a green zirconia blank is prepared by water-jet grinding.

[0029] In the embodiments of this application, the sintering temperature is 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, 1050℃, 1060℃, 1070℃, 1080℃, 1090℃, 1100℃, 1110℃, 1120℃, 1130℃, 1140℃, 115℃, 1160℃, 1170℃, 1180℃, 1190℃, or 1200℃.

[0030] S2. A platinum group metal paste is coated onto the outer wall of a zirconia semi-ceramic substrate, and the platinum group metal paste and the zirconia semi-ceramic substrate are co-sintered to form a zirconia ceramic substrate 110 with a first platinum group metal layer 120 covering the outer wall.

[0031] In this embodiment, the platinum group metal slurry comprises, by mass percentage, 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, 35 wt%, 36 wt%, 37 wt%, 38 wt%, 39 wt%, or 40 wt% of solid oxide powder, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, or 15 wt% of platinum group metals, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, or 25 wt% of solvent, and 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, and 1.3 wt%. The following components are included: 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2.0wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt%, or 3.0wt% of pore-forming agent; 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, or 15wt% of binder; and 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, 26wt%, 27wt%, 28wt%, 29wt%, 30wt%, 31wt%, 31wt%, 32wt%, 33wt%, 34wt%, 35wt%, 36wt%, 37wt%, 38wt%, 39wt%, or 40wt% of plasticizer. The solid oxide powder is zirconium oxide powder or powder doped with zirconium oxide. The platinum group metals are ruthenium, rhodium, palladium, osmium, iridium, or platinum. The solvent can be alcohol. The pore-forming agent can be carbon powder. The binder can be polyvinyl butyral. The plasticizer can be dibutyl phthalate. The solid oxide powder has a matching coefficient of thermal expansion with the zirconia ceramic matrix 110, preventing cracking of the first platinum group metal layer 120 due to thermal stress during high-temperature sintering and operation. The solid oxide powder forms a porous framework, supporting the platinum group metal particles and increasing the length of the three-phase interface. The platinum group metals are used as conductive materials and also provide catalytic sites for electrochemical reactions. The solvent ensures uniform mixing of the solid oxide powder, platinum group metals, pore-forming agent, binder, and plasticizer. The pore-forming agent enables the first platinum group metal layer 120 to form a porous structure during sintering. By rationally controlling the proportion of the pore-forming agent, the porosity of the first platinum group metal layer 120 can be rationally controlled. Before sintering, the binder binds the components together, which helps maintain the shape of the first platinum group metal layer 120. Plasticizers are used to improve the flexibility and processing properties of platinum group metal pastes.

[0032] In the embodiments of this application, solid oxide powder, platinum group metals, solvent, pore-forming agent, binder and plasticizer are mixed in proportion, and after ball milling for 3h, 4h or 5h, platinum group metal slurry is obtained.

[0033] In this embodiment, a spraying process is used to coat the outer wall of the zirconia semi-ceramic substrate with a platinum group metal paste, so that the platinum group metal paste is adsorbed on the surface of the zirconia semi-ceramic substrate.

[0034] In this embodiment, the sintering temperatures for co-sintering the platinum group metal paste and the zirconia semi-ceramic substrate are 1400℃, 1410℃, 1420℃, 1430℃, 1440℃, 1450℃, 1460℃, 1470℃, 1480℃, 1490℃, 1500℃, 1510℃, 1520℃, 1530℃, 1540℃, or 1550℃. After sintering, the platinum group metal paste transforms into a first platinum group metal layer 120, effectively increasing the length of the three-phase interface. The zirconia semi-ceramic substrate transforms into a zirconia ceramic substrate 110. It should be noted that, since the sintering temperature required for the outer electrode ring layer 131 is lower than that required for the first platinum group metal layer 120, the first platinum group metal layer 120 can only be located in the inner layer of the outer electrode ring layer 131, and not in the outer layer, to avoid forcing the outer electrode ring layer 131 to experience a high-temperature environment above 1400°C. Since the sintering temperature of the first platinum group metal layer 120 is the same as that of the zirconia ceramic substrate 110, the two can be co-sintered, saving manufacturing steps and shortening the production cycle.

[0035] Before sintering in this embodiment, the material is first naturally dried at room temperature for 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or 7 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 platinum group metal slurry from flowing extensively.

[0036] The thickness of the first platinum group metal layer 120 formed in the embodiments of this application is 40μm, 41μm, 42μm, 43μm, 44μm, 45μm, 46μm, 47μm, 48μm, 49μm, 50μm, 51μm, 52μm, 53μm, 54μm, 55μm, 56μm, 57μm, 58μm, 59μm or 60μm, and the porosity is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80%.

[0037] S3. Electrode material is coated on the outer wall of the first platinum group metal layer 120, and electrode material is coated on the outer wall, inner wall and bottom of the zirconia ceramic substrate 110. After sintering, an outer electrode ring layer 131 is formed on the outer wall of the first platinum group metal layer 120, an outer electrode lead 151 is formed on the outer wall of the zirconia ceramic substrate 110, an inner electrode ring layer 132 and an inner electrode lead 152 are formed on the inner wall of the zirconia ceramic substrate 110, and a first bottom electrode 141 and a second bottom electrode 142 that are separated from each other are formed at the bottom of the zirconia ceramic substrate 110.

[0038] The electrode material in this application embodiment is existing technology and can be platinum or a platinum mixture.

[0039] In this embodiment, the sintering temperature is 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, or 1100℃. Compared with existing preparation methods, by reducing the sintering temperature of the outer electrode ring layer 131 and the inner electrode ring layer 132, the catalytic performance of the outer electrode ring layer 131 and the inner electrode ring layer 132 can be guaranteed, and the loss at the three-phase interface can be reduced.

[0040] 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.

[0041] S4. Apply a protective coating 160 to the outer wall of the outer electrode ring layer 131 and the first platinum group metal layer 120.

[0042] The protective coating 160 in this embodiment uses existing technology and can be a mixture of alumina and magnesium oxide. The protective coating 160 effectively prevents oil, carbon deposits, particulate matter, and other impurities in the exhaust pipe from directly contaminating the outer electrode ring layer 131 and the first platinum group metal layer 120. Simultaneously, the protective coating 160 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 160 prevents high-temperature exhaust gas from directly eroding the outer electrode ring layer 131 and the first platinum group metal layer 120, extending their service life.

[0043] In this embodiment, a plasma spraying process is used to attach a protective coating 160 to the outer wall of the outer electrode ring layer 131 and the first platinum group metal layer 120.

[0044] S5. A platinum group metal salt solution is coated onto the outer wall of the protective coating 160, and then sintered to form a second platinum group metal layer 170 on the outer wall of the protective coating 160.

[0045] In this embodiment, the platinum group metal salt solution is an aqueous solution composed of platinum group metal ions and acid radical ions. Specifically, the platinum group metal salt solution is an aqueous solution of chloroplatinic acid, platinum nitrate, rhodium chloride, ammonium rhodium chlororhodate, sodium hexachlororhodate, or rhodium nitrate. Preferably, a saturated aqueous solution of rhodium nitrate can be used.

[0046] In this embodiment, the solution is first naturally dried at room temperature for 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, or 7 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 avoid large-scale flow of the platinum group metal salt solution.

[0047] In this embodiment, a spraying process is used to coat a platinum group metal salt solution onto the outer wall of the protective coating 160, and the platinum group metal salt solution is adsorbed onto the outer wall of the protective coating 160 through capillary action.

[0048] In this embodiment, the sintering temperature is 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 560℃, 570℃, 580℃, 590℃, or 600℃. After sintering, the platinum group metal salt solution transforms into a second platinum group metal layer 170. The second platinum group metal layer 170 can further increase the electrochemical reaction rate, thereby expanding the potential difference.

[0049] The thickness of the second platinum group metal layer 170 formed in the embodiments of this application is 40μm, 41μm, 42μm, 43μm, 44μm, 45μm, 46μm, 47μm, 48μm, 49μm, 50μm, 51μm, 52μm, 53μm, 54μm, 55μm, 56μm, 57μm, 58μm, 59μm or 60μm.

[0050] Overall, by adding a first platinum group metal layer 120, the length of the three-phase interface can be effectively increased. By lowering the sintering temperature of the outer electrode ring layer 131 and the inner electrode ring layer 132, the catalytic performance of the outer electrode ring layer 131 and the inner electrode ring layer 132 can be guaranteed, and the loss of the three-phase interface can be reduced. By adding a second platinum group metal layer 170, the electrochemical reaction rate can be further improved, thereby expanding the potential difference.

[0051] It should be noted that for some vehicle models, the lower engine displacement means lower operating temperatures, which places higher demands on the catalytic performance of the ceramic sensing element. The ceramic sensing element prepared using the above method exhibits catalytic performance that adequately meets the requirements of these vehicle models.

[0052] Reference Figure 3 , Figure 4 and Figure 5 This application also discloses a ceramic sensing element, fabricated using the above-described method, comprising a zirconia ceramic substrate 110, a first platinum group metal layer 120, an outer electrode ring layer 131, an inner electrode ring layer 132, a first bottom electrode 141, a second bottom electrode 142, an outer electrode lead 151, an inner electrode lead 152, a protective coating 160, and a second platinum group metal layer 170. The first platinum group metal layer 120 is formed circumferentially on the outer wall of the zirconia ceramic substrate 110, effectively increasing the length of the three-phase interface. The outer electrode ring layer 131 is formed circumferentially on the outer wall of the first platinum group metal layer 120. The inner electrode ring layer 132 is formed circumferentially on the inner wall of the zirconia ceramic substrate 110. The first bottom electrode 141 is formed at the bottom end of the zirconia ceramic substrate 110. The second bottom electrode 142 is formed at the bottom end of the zirconia ceramic substrate 110, and is isolated from the first bottom electrode 141. An outer electrode lead 151 is formed on the outer wall of the zirconia ceramic substrate 110, used for electrically connecting the outer electrode ring layer 131 and the first bottom electrode 141. An inner electrode lead 152 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 142. The inner electrode ring layer 132 can be in contact with air. The outer electrode ring layer 131 can be 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 160 is applied to the outer wall of the outer electrode ring layer 131 and the first platinum group metal layer 120, effectively preventing oil, carbon deposits, particulate matter, and other impurities in the exhaust pipe from directly contaminating the outer electrode ring layer 131 and the first platinum group metal layer 120. Simultaneously, the protective coating 160 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 160 prevents high-temperature exhaust gas from directly eroding the outer electrode ring layer 131 and the first platinum group metal layer 120, extending their service life. A second platinum group metal layer 170 is formed circumferentially on the outer wall of the protective coating 160, further increasing the electrochemical reaction rate and widening the potential difference.

[0053] This application also discloses a tubular oxygen sensor, which is made using the above-mentioned ceramic sensing element. Preparation Example

[0054] Preparation Example 1 A platinum group metal slurry was prepared by mixing 35 wt% solid oxide powder, 10 wt% platinum group metals, 20 wt% solvent, 1.5 wt% pore-forming agent, 13 wt% binder, and 20.5 wt% plasticizer, and then ball-milling for 4 hours. The solid oxide powder was zirconium oxide powder. The platinum group metal was platinum. The solvent was alcohol. The pore-forming agent was carbon powder. The binder was polyvinyl butyral. The plasticizer was dibutyl phthalate.

[0055] Preparation Example 2 A platinum group metal slurry was prepared by mixing 30 wt% solid oxide powder, 15 wt% platinum group metals, 20 wt% solvent, 1.5 wt% pore-forming agent, 10 wt% binder, and 23.5 wt% plasticizer, and then ball-milling for 4 hours. The solid oxide powder was zirconium oxide powder. The platinum group metal was platinum. The solvent was alcohol. The pore-forming agent was carbon powder. The binder was polyvinyl butyral. The plasticizer was dibutyl phthalate.

[0056] Preparation Example 3 A platinum group metal slurry was prepared by mixing 40 wt% solid oxide powder, 5 wt% platinum group metals, 18 wt% solvent, 1.5 wt% pore-forming agent, 15 wt% binder, and 20.5 wt% plasticizer, and then ball-milling for 4 hours. The solid oxide powder was zirconium oxide powder. The platinum group metal was platinum. The solvent was alcohol. The pore-forming agent was carbon powder. The binder was polyvinyl butyral. The plasticizer was dibutyl phthalate. Example Example 1

[0057] S1. The zirconia green body is pre-sintered at a temperature of 1100℃ to form a zirconia semi-ceramic matrix.

[0058] S2. First, a platinum group metal slurry is coated onto the outer wall of a zirconia semi-ceramic substrate. It is then allowed to dry naturally at room temperature for 4 hours, followed by drying at 120°C for 2 hours. Afterward, the platinum group metal slurry and the zirconia semi-ceramic substrate are co-sintered at 1480°C to form a zirconia ceramic substrate 110 with a first platinum group metal layer 120 covering its outer wall. The first platinum group metal layer 120 has a thickness of 50 μm and a porosity of 55%.

[0059] S3. Electrode material is coated onto the outer wall of the first platinum group metal layer 120, and onto the outer wall, inner wall, and bottom of the zirconia ceramic substrate 110. The coating is dried at 120°C for 2 hours and then sintered at 850°C. An outer electrode ring layer 131 is formed on the outer wall of the first platinum group metal layer 120, an outer electrode lead 151 is formed on the outer wall of the zirconia ceramic substrate 110, an inner electrode ring layer 132 and an inner electrode lead 152 are formed on the inner wall of the zirconia ceramic substrate 110, and a first bottom electrode 141 and a second bottom electrode 142, separated from each other, are formed at the bottom of the zirconia ceramic substrate 110. The amount of electrode material used is 23 mg.

[0060] S4. A protective coating 160 is applied to the outer wall of the outer electrode ring layer 131 and the first platinum group metal layer 120 using a plasma spraying process.

[0061] S5. A platinum group metal salt solution is coated onto the outer wall of the protective coating 160. It is then allowed to dry naturally at room temperature for 4 hours, followed by drying at 120°C for 2 hours. Afterward, it is sintered at 510°C to form a second platinum group metal layer 170 on the outer wall of the protective coating 160. The platinum group metal salt solution is a saturated aqueous solution of rhodium nitrate. The thickness of the formed second platinum group metal layer 170 is 50 μm. Example 2

[0062] The difference from Example 1 is that the amount of electrode material used is 22 mg. Example 3

[0063] The difference from Example 1 is that the amount of electrode material used is 21 mg. Example 4

[0064] The difference from Example 1 is that the thickness of the first platinum group metal layer 120 is 40 μm and the porosity is 70%. Example 5

[0065] The difference from Example 1 is that the thickness of the first platinum group metal layer 120 is 60 μm and the porosity is 35%. Example 6

[0066] The difference from Example 1 is that the sintering temperature in step S3 is 650°C. Example 7

[0067] The difference from Example 1 is that the sintering temperature in step S3 is 1100°C. Example 8

[0068] The difference from Example 1 is that the sintering temperature in step S5 is 420°C. Example 9

[0069] The difference from Example 1 is that in step S5, the sintering temperature is 580°C. Example 10

[0070] The difference from Example 1 is that the thickness of the second platinum group metal layer 170 is 40 μm. Example 11

[0071] The difference from Example 1 is that the thickness of the second platinum group metal layer 170 is 60 μm. Example 12

[0072] The difference from Example 1 is that the platinum group metal paste used is the platinum group metal paste prepared in Preparation Example 1. Example 13

[0073] The difference from Example 1 is that the platinum group metal paste used is the platinum group metal paste prepared in Preparation Example 2. Example 14

[0074] The difference from Example 1 is that the platinum group metal paste used is the platinum group metal paste prepared in Preparation Example 3. Comparative Example

[0075] 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 ceramic sensing element. The electrode material dosage was 23 mg.

[0076] Comparative Example 2 The difference from Comparative Example 1 is that the amount of electrode material used is 22 mg.

[0077] Comparative Example 3 The difference from Comparative Example 1 is that the amount of electrode material used is 21 mg. Performance testing

[0078] The ceramic sensing elements prepared in Examples 1-14 and Comparative Examples 1-3 were respectively encapsulated in test fixtures, and the sensing signals were tested by passing the exhaust gas in the test equipment.

[0079] Test 1: The ceramic sensing elements prepared in Examples 1-14 and Comparative Examples 1-3 were heated to 400±10℃, and the time taken for the voltage value to reach 700mV under the same conditions was recorded. The test results are shown in Table 1. Simultaneously, the voltage rise of the ceramic sensing elements prepared in Examples 1-3 and Comparative Examples 1-3 was recorded, and the test results are shown in Table 1. Figure 6 As shown.

[0080] Test 2: The Lambda (λ) value of the simulated exhaust gas was switched between 0.97 and 1.03. When Lambda = 0.97, the output voltage of the ceramic sensing element was called high voltage. When Lambda = 1.03, the output voltage of the ceramic sensing element was called low voltage. The time taken for the voltage value to jump from 600mV to 300mV was called T2, and the time taken for the voltage value to jump from 300mV to 600mV was called T4. The high voltage value, low voltage value, T2 value, and T4 value of the ceramic sensing elements prepared in Examples 1-14 and Comparative Examples 1-3 were tested, and the test results are shown in Table 2.

[0081] Table 1 sample Time (s) required for the voltage to reach 700mV Example 1 32.3 Example 2 33.5 Example 3 34.1 Example 4 33.6 Example 5 31.7 Example 6 31.7 Example 7 36.2 Example 8 32.5 Example 9 32.1 Example 10 33.8 Example 11 31.2 Example 12 32.4 Example 13 32.1 Example 14 32.5 Comparative Example 1 40.4 Comparative Example 2 43.2 Comparative Example 3 44.6 Table 2 sample High voltage (mV) Low voltage (mV) [T2 (ms)] [T4 (ms)] Example 1 863 128 62 54 Example 2 853 119 54 45 Example 3 848 132 71 56 Example 4 838 124 59 39 Example 5 819 108 45 33 Example 6 832 119 49 31 Example 7 824 106 47 38 Example 8 843 112 52 42 Example 9 857 121 72 46 Example 10 861 117 61 53 Example 11 837 125 58 51 Example 12 843 129 56 37 Example 13 835 109 50 42 Example 14 852 131 64 32 Comparative Example 1 880 226 126 75 Comparative Example 2 857 202 105 81 Comparative Example 3 942 199 102 75 Refer to Table 1 and Figure 6 As shown in Examples 1-3 and Comparative Examples 1-3, under the same electrode material dosage, the ceramic sensing element prepared in Examples 1-3 reaches a voltage value of 700mV in a shorter time and with a faster voltage rise rate, exhibiting superior low-temperature catalytic performance. With increasing electrode material dosage, the time required to reach 700mV decreases, and the catalytic performance improves. As shown in Examples 1, 4, and 5, increasing the thickness of the first platinum group metal layer decreases the time required to reach 700mV, and the catalytic performance improves. As shown in Examples 1, 6, 7, and Comparative Example 1, increasing the sintering temperature of the inner and outer electrode ring layers increases the time required to reach 700mV, and the catalytic performance deteriorates. As shown in Examples 1, 8, and 9, the sintering temperature of the second platinum group metal layer has no effect on the catalytic performance. As can be seen from Examples 1, 10 and 11, as the thickness of the second platinum group metal layer increases, the time required to reach 700mV becomes shorter and the catalytic performance becomes better.

[0082] Referring to Table 2, and in conjunction with Examples 1-14 and Comparative Examples 1-3, it can be seen that the ceramic sensing elements prepared in Examples 1-14 have lower low-voltage values ​​and shorter times to jump from 600mV to 300mV or from 300mV to 600mV. Therefore, their low-temperature catalytic performance is superior.

[0083] 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 ceramic sensing element, characterized in that, include: S1. Pre-sinter the zirconia green body to form a zirconia semi-ceramic matrix; S2. A platinum group metal paste is coated on the outer wall of the zirconia semi-ceramic substrate, and the platinum group metal paste is co-sintered with the zirconia semi-ceramic substrate to form a zirconia ceramic substrate (110) with a first platinum group metal layer (120) covering the outer wall. S3. Electrode material is coated on the outer wall of the first platinum group metal layer (120), and the electrode material is coated on the outer wall, inner wall and bottom of the zirconia ceramic substrate (110). After sintering, an outer electrode ring layer (131) is formed on the outer wall of the first platinum group metal layer (120), an outer electrode lead (151) is formed on the outer wall of the zirconia ceramic substrate (110), an inner electrode ring layer (132) and an inner electrode lead (152) are formed on the inner wall of the zirconia ceramic substrate (110), and a first bottom electrode (141) and a second bottom electrode (142) are formed at the bottom of the zirconia ceramic substrate (110). S4. A protective coating (160) is applied to the outer wall of the outer electrode ring layer (131) and the first platinum group metal layer (120); S5. A platinum group metal salt solution is coated onto the outer wall of the protective coating (160), and sintered to form a second platinum group metal layer (170) on the outer wall of the protective coating (160).

2. The method for preparing the ceramic sensing element according to claim 1, characterized in that, In step S1, the sintering temperature is 1000-1200℃; in step S2, the sintering temperature is 1400-1550℃; in step S3, the sintering temperature is 600-1100℃; and in step S5, the sintering temperature is 400-600℃.

3. The method for preparing the ceramic sensing element according to claim 1, characterized in that, The platinum group metal slurry comprises, by weight percentage: 30-40 wt% solid oxide powder, 5-15 wt% platinum group metals, 15-25 wt% solvent, 0.5-3 wt% pore-forming agent, 10-15 wt% binder, and 20-40 wt% plasticizer.

4. The method for preparing the ceramic sensing element according to claim 1, characterized in that, The platinum group metal salt solution is an aqueous solution composed of platinum group metal ions and acid radical ions.

5. The method for preparing the ceramic sensing element according to claim 4, characterized in that, The platinum group metal salt solution is an aqueous solution of chloroplatinic acid, platinum nitrate, rhodium chloride, ammonium chlororhodiumate, sodium hexachlororhodiumate, or rhodium nitrate.

6. The method for preparing a ceramic sensing element according to claim 1, characterized in that, In step S2, before sintering, the sample is dried at room temperature for 1-7 hours and then dried at 100-200℃ for 1-3 hours; in step S3, before sintering, the sample is dried at 100-200℃ for 1-3 hours; in step S5, before sintering, the sample is dried at room temperature for 1-7 hours and then dried at 100-200℃ for 1-3 hours.

7. The method for preparing a ceramic sensing element according to claim 1, characterized in that, The first platinum group metal layer (120) has a thickness of 40-60 μm and a porosity of 20%-80%; the second platinum group metal layer (170) has a thickness of 40-60 μm.

8. The method for preparing a ceramic sensing 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.

9. A ceramic sensing element, characterized in that, The ceramic sensing element is prepared by the method described in any one of claims 1 to 8, comprising: The zirconia ceramic matrix (110); The first platinum group metal layer (120) is formed on the outer wall of the zirconia ceramic substrate (110) along the circumferential direction of the substrate. The outer electrode ring layer (131) is formed on the outer wall of the first platinum group metal layer (120) along the circumferential direction of the first platinum group metal layer (120); 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 (141) is formed at the bottom end of the zirconium oxide ceramic substrate (110); The second bottom electrode (142) is formed at the bottom end of the zirconia ceramic substrate (110) and is separated from the first bottom electrode (141); The external electrode lead (151) 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 (141). The inner electrode lead (152) 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 (142). The protective coating (160) is applied to the outer wall of the outer electrode ring layer (131) and the first platinum group metal layer (120); A second platinum group metal layer (170) is formed on the outer wall of the protective coating (160) along the circumference of the protective coating (160).

10. A tubular oxygen sensor, characterized in that, It is prepared using the ceramic sensing element described in claim 9.

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