A gas sensor element and a method for producing the same

Abstract

The application discloses a gas sensor element, comprising a ceramic sensitive chip, an alumina substrate layer and a TSP coating layer; the upper and lower surfaces of the ceramic sensitive chip are printed with the alumina substrate layer, and the left and right side surfaces of the ceramic sensitive chip are printed with the alumina substrate layer after slitting; and a single-layer TSP coating layer is arranged outside the alumina substrate layer. The application adopts the method of first printing the substrate layer and then immersing the single-layer coating layer, so that the problem of low bonding strength between the coating layer and the substrate which generally exists in the immersion process can be solved; the slurry components of the single-layer structure are the same and the inside and outside sides shrinkage is consistent, the risk of interlayer cracking and outer layer peeling caused by the difference in material thermal expansion rate of two or three layer structures is avoided, the precision of the sensor is reduced, the whole TSP coating structure has good waterproofness and air permeability, the water drop test can reach more than 20 muL, the use requirement is met, and the application is suitable for mass production.

Description

Technical Field

[0001] This application relates to a gas sensor element and its fabrication method, belonging to the field of gas sensor technology. Background Technology

[0002] When a gas sensor is in use, for a period of time immediately after the engine starts, the temperature inside the exhaust pipe is lower than the dew point of water. Water vapor produced by fuel combustion may condense into water droplets in the exhaust pipe. These droplets adhere to the surface of the ceramic sensing chip, causing thermal stress that can lead to cracking. Therefore, a TSP (Thermal Shock Protection Layer) coating can be applied to the entire detection area of ​​the chip to suppress thermal shock caused by localized temperature drops due to water immersion, thus preventing chip cracking. It also prevents poisoning substances such as magnesium from entering the chip. However, if the TSP coating is not applied properly, it can slow down the chip's heating process and prolong the thermal activation time. Furthermore, the difference in thermal expansion rates between the TSP coating and the chip makes it prone to peeling off from the chip during high-temperature use due to vibrations in the environment. The TSP coating must also maintain good adhesion to the chip substrate.

[0003] Currently, the structure of TSP coatings mainly consists of two or more layers, and there are two main manufacturing processes: plasma spraying and immersion.

[0004] For example, patents CN 113597552 A and CN 113614523 A both employ a three-layer structure. The first coating layer has only two main surfaces, while the second and third layers are plasma-sprayed. Patent CN 113597552 A primarily aims to suppress coating peeling by making the length of the two main surfaces of the first layer longer than the lengths of the second and third layers. However, actual experiments revealed that the first layer, as the bonding layer connecting the substrate and the TSP coating, is only placed on two main surfaces, resulting in insufficient bonding strength. Because the contact area between the coating and the two side and front surfaces is much smaller than the contact area with the two main surfaces, the coating on the sides and front is more likely to peel off from the substrate first, ultimately leading to large pieces of the entire coating falling off and product failure.

[0005] Patent CN 113614523A describes a method to suppress water intrusion by changing the ratio of porosity and thickness between the inner and outer layers to ensure rapid heating and maintain the overall strength of the coating. In reality, plasma spraying involves ejecting a flame at high speed from a nozzle at 12,000-16,000°C, melting the material to a semi-molten or molten state and then spraying it onto the substrate surface to form a TSP coating. Experiments revealed that the porosity of molten ceramic materials is generally low, around 3-10%, making it difficult to increase to over 15%. Plasma sputtering severely impacts the chip's heating rate, more than doubling the startup time. It's also difficult to achieve the 50-70% inner layer porosity control mentioned in the patent, and the method of using thermal coatings and pore-forming materials for pore creation is challenging to implement, as the pore-forming agent vaporizes before reaching the substrate at temperatures above 10,000 degrees Celsius. Furthermore, the powder deposition rate on the chip is low during sputtering, with each layer only a few micrometers or tens of micrometers thick, resulting in low powder utilization and significant waste. After each sputtering, cooling is required before re-sputtering, necessitating multiple sputtering cycles to achieve the patented thickness of 800-1000 μm. Experiments also showed that pre-sputtering roughening treatments such as sandblasting and rapid heating / cooling during the sputtering process easily induce hidden microcracks within the zirconia substrate. Plasma sputtering equipment is expensive, the process is complex, and it easily causes secondary damage to the substrate strength. It has been gradually replaced by the simpler and lower-cost immersion method.

[0006] For example, patent documents CN 112739665 A and CN 112752738 A propose using an impregnation process to impregnate a two-layer structure, improving water resistance by specifying the porosity and particle size ratio of the inner and outer sides of the coating. The inner side has a higher porosity of 30-85% (preferably 60-70%) than the outer side. The outer side consists of a large number of ceramic coarse particles with a particle size of 5.0μm to 40μm, surrounded by a large number of ceramic microparticles with a particle size of 10nm to 1.0μm and a size of less than 1.0μm. The ceramic coarse particles are connected directly or through the ceramic microparticles to form a coating structure with a porosity of 5% to 50%, and the weight ratio of coarse particles to microparticles is 3 to 35. Through experiments on the embodiments, it was found that the inner side porosity is too high in this patent. The more pores there are, the less contact area with the substrate, the worse the bonding strength, and the easier it is for the coating to peel off in large pieces from the substrate. Furthermore, the outer ceramic particles are large in size and added in large quantities, while the ceramic microparticles are few, making it difficult to achieve dense sintering or requiring a high sintering temperature. The microparticles cannot completely encapsulate and connect the coarse particles. If the 50-nanometer-sized microparticles used in the example are impregnated and dried for curing, cracking is likely to occur, making it difficult to form a highly water-repellent lotus effect. Additionally, the coating has a two-layer structure, with the inner and outer layers made of different materials and having different porosities. The two different slurries shrink asynchronously during drying and firing, easily causing interlayer cracking or outer layer cracking. During long-term heating and cooling of the gas sensor, the outer coating may crack and peel off, leading to a decrease in sensor testing accuracy. Summary of the Invention

[0007] To address the aforementioned issues, this application proposes a gas sensor element and its fabrication method. The method employs a process of first screen-printing a substrate layer and then impregnating it with a single-layer coating. This solves the common problem of low bonding strength between the coating and the substrate in impregnation processes. Furthermore, the single-layer structure uses a slurry with identical composition and exhibits consistent shrinkage on both the inner and outer sides, avoiding the risk of interlayer cracking and outer layer peeling caused by differences in thermal expansion rates in two- or three-layer structures, which could lead to decreased sensor accuracy. Finally, the entire TSP coating structure possesses excellent waterproof and breathable properties, achieving a droplet volume exceeding 20 μL in water tests, meeting usage requirements and suitable for mass production.

[0008] According to one aspect of this application, a gas sensor element is provided, comprising a ceramic sensing chip, an alumina substrate layer, and a TSP coating;

[0009] The alumina substrate layer is printed on the top and bottom surfaces of the ceramic sensitive chip, and the alumina substrate layer is printed on the left and right sides after the ceramic sensitive chip is cut; a single-layer TSP coating is provided on the outside of the alumina substrate layer; the thickness of the alumina substrate layer is 20-40 μm and the porosity is 30-50%.

[0010] Specifically, the alumina paste is made by mixing alumina powder with an organic carrier, ball milling, and three-roll milling, with the solid content controlled at 50-60%, to produce an ink paste suitable for screen printing. The organic carrier is an ethyl cellulose solution.

[0011] Optionally, the roughness of the alumina substrate layer is 10-20 μm.

[0012] Optionally, the TSP coating has a thickness of 800-1000 μm, a porosity of 24-45%, and an average pore size of 0.5-5.0 μm.

[0013] Optionally, the TSP coating is obtained by sintering a composite slurry, the composite slurry comprising coarse ceramic powder and fine ceramic powder.

[0014] Optionally, the particle size of the coarse ceramic powder is 2-10 μm, the particle size of the fine ceramic powder is 0.02-0.8 μm, and the weight ratio of the coarse ceramic powder to the fine ceramic powder is (1-4):1.

[0015] Optionally, the composite slurry further includes a high-temperature binder, an organic binder, a pore-forming agent, a dispersant, and a solvent.

[0016] Specifically, by weight, the composite slurry includes 20-40 parts of coarse ceramic powder, 10-30 parts of fine ceramic powder, 2-8 parts of high-temperature binder, 1-6 parts of organic binder, 6-20 parts of pore-forming agent, 0.5-3 parts of dispersant, and 30-50 parts of solvent.

[0017] Optionally, the ceramic powder is one or more of alumina, magnesium aluminum spinel, and mullite;

[0018] The ceramic powder is one or more of zirconium oxide, aluminum oxide, titanium oxide, silicon oxide, and magnesium oxide.

[0019] Optionally, the high-temperature binder is one or more of silicon dioxide, aluminum oxide, bismuth oxide, and zinc oxide; the organic binder is one of acrylic acid and polyvinyl alcohol; the pore-forming agent is one or more of carbon powder, starch, and organic resin balls; the dispersant is one of ammonium polycarboxylate and ammonium polyacrylate; and the solvent is one or more of water, ethanol, and isopropanol; the viscosity of the composite slurry is 500-3000 mPa·s.

[0020] According to another aspect of this application, a method for fabricating a gas sensor element as described above is provided, characterized by comprising the following steps:

[0021] (1) First, print alumina paste on the top and bottom surfaces of the ceramic sensitive chip. After the ceramic sensitive chip is cut, print alumina paste on the left and right sides. At a temperature of 1350℃~1500℃, the holding time is 2~6h. Then, sinter the ceramic sensitive chip together with the ceramic sensitive chip at high temperature to form a ceramic sensitive chip with an alumina substrate layer attached.

[0022] (2) Use a tooling clamp to hold the tail end of the ceramic sensitive chip while rotating it, and vertically immerse the front detection part of the ceramic sensitive chip into the composite slurry. After reaching the predetermined coating length position (11-13mm), immediately lift it up, shake off the excess composite slurry, and wait for the coating to dry and cure. After the first immersion is completed, repeat the immersion once.

[0023] (3) After the TSP coating is impregnated, it is sintered and cooled at 1000-1200℃ for 1-3 hours.

[0024] Optionally, in step (2), the total thickness of the first impregnation coating is 400-500 μm, and after repeating once, the final total thickness is controlled at 800-1000 μm.

[0025] The beneficial effects that this application may produce include, but are not limited to:

[0026] 1. The gas sensor element provided in this application improves the surface roughness of the substrate to 10-20μm by adjusting the slurry, enabling it to penetrate and interlock with the TSP coating in all directions. The alumina substrate layer has good bonding strength with the ceramic substrate and the TSP coating, and is not easy to crack or peel off, and has good waterproof and breathable properties.

[0027] 2. The gas sensor element provided in this application, by controlling the porosity of the alumina substrate and the TSP coating, can improve the sensing performance of the element and facilitate the adsorption and detection of gas molecules. On the other hand, the pore structure of the TSP coating forms tiny channels in the coating, which ensures air permeability while improving waterproof performance, so that the element can still work normally in a humid environment.

[0028] 3. The gas sensor element provided in this application, by using coarse and fine ceramic powder in a limited ratio, achieves the following: the coarse powder acts as a skeleton in the coating, providing good thermal shock resistance, while the fine powder acts as a binder, ensuring good adhesion. At the same time, this ratio can prevent the coating from peeling off from the ceramic substrate during long-term vibration use. If there is too much coarse powder and too little fine powder, or if the fine powder is too large, the bonding performance of the coarse powder cannot be fully utilized, and the coating structure will be too loose, resulting in poor water resistance. If there is too much fine powder, the film will shrink greatly after impregnation and drying, making it prone to cracking. Other surface defects such as blistering, pinholes, and "volcanic craters" may also occur, making it difficult to control the production process and significantly reducing the product qualification rate.

[0029] 4. The gas sensor element provided in this application, by adding a high-temperature binder and limiting the amount added, generates a liquid phase during melting, which lowers the sintering temperature, causing the ceramic solid particles to bond together to form a whole. This results in higher internal strength of the coating and further improved adhesion to the substrate, ultimately enhancing the bonding strength and waterproof performance of the coating.

[0030] 5. The gas sensor element fabrication method provided in this application, by employing pre-sintering of the alumina substrate layer and multiple impregnation processes with composite slurry, can achieve uniformity in the surface and side thickness of the coating. It eliminates the need for scraping or grinding of each coating layer with tools or sandpaper, and the difference in film thickness can be controlled within 0.05 mm. This prevents micro-cracks from forming due to uneven shrinkage during the drying and firing processes caused by uneven coating thickness. Furthermore, each impregnation, drying, and curing process forms a smooth boundary layer on the coating surface. The boundary layer between layers is slightly denser than the internal porous layer, which can further improve the heat insulation and waterproofing properties of the coating. Attached Figure Description

[0031] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0032] Figure 1 This is a photograph of the appearance of the alumina substrate layer in Example 1 of this application;

[0033] Figure 2 This is a SEM image of the alumina substrate layer in Example 1 of this application;

[0034] Figure 3 This is a SEM image of the TSP coating in Example 1 of this application;

[0035] Figure 4 This is a cross-sectional SEM image of the TSP coating and alumina substrate layer in Example 1 of this application (the part between the ceramic chip and the alumina substrate layer is a platinum electrode);

[0036] Figure 5 This is a schematic diagram of the cross-sectional structure of the gas sensor element along the width direction of this application;

[0037] Figure 6 This is a schematic diagram of the cross-sectional structure of the gas sensor element along its length in this application.

[0038] Figure reference numerals: 1. TSP coating; 2. Alumina substrate; 3. Ceramic sensitive chip. Detailed Implementation

[0039] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. The reagents and raw materials used in this invention are readily available through conventional means, and unless otherwise specified, they shall be used in accordance with conventional methods in the art or as per the product instructions. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described in this patent are for illustrative purposes only.

[0041] In addition, the total thickness of the first impregnation coating in step (2) of this application, which is 400-500 μm, refers to the total thickness of the upper and lower surfaces, that is, it refers to... Figure 5 and Figure 6 The sum of the thicknesses of layers d1 and d2 in the equation is due to... Figure 5 and Figure 6 These are all images of the final product, not showing the condition after the first impregnation. Therefore, the d1+d2 after the first impregnation is 400-500μm. After one repetition, the final total thickness is controlled at 800-1000μm. In other words, the final thickness of this application is... Figure 5 and Figure 6 The d1+d2 in the figure is 800~1000μm.

[0042] Figure 5 and Figure 6 In the figure, d3 and d4 are both 10-20μm. In order to better show the relationship between the layers in the figure, the size scale in the figure of this application is not the actual situation and is only for reference.

[0043] Example 1

[0044] The gas sensor element includes a ceramic sensitive chip 3, an alumina substrate layer 2, and a TSP coating 1; the alumina substrate layer 2 is printed on the top and bottom surfaces of the ceramic sensitive chip 3, and the alumina substrate layer 2 is printed on the left and right sides after the ceramic sensitive chip 3 is cut; the TSP coating 1 is disposed on the outside of the alumina substrate layer 2.

[0045] The alumina substrate 2 has a thickness of 30 μm and a porosity of 40%; the roughness of the alumina substrate 2 is 14 μm. The TSP coating 1 has a thickness of 950 μm, a porosity of 35%, and an average pore size of 2 μm. The TSP coating 1 is obtained by sintering a composite slurry, which, by weight, comprises 30 parts of coarse ceramic powder, 15 parts of fine ceramic powder, 5 parts of high-temperature binder, 4 parts of organic binder, 10 parts of pore-forming agent, 1 part of dispersant, and 35 parts of solvent.

[0046] The coarse ceramic powder has a particle size of 5 μm, and the fine ceramic powder has a particle size of 0.3 μm, with a weight ratio of coarse to fine ceramic powder of 2:1. The coarse ceramic powder is alumina, and the fine ceramic powder is zirconium oxide. The high-temperature binder is silicon dioxide, the organic binder is acrylic acid, the pore-forming agent is organic resin balls, the dispersant is ammonium polycarboxylate, and the solvent is ethanol; the viscosity of the composite slurry is 2000 mPa·s.

[0047] The preparation method includes the following steps:

[0048] (1) First, alumina paste is printed on the top and bottom surfaces of the ceramic sensitive chip 3. After the ceramic sensitive chip 3 is cut, alumina paste is printed on the left and right sides. At a temperature of 1400℃, the holding time is 2.5h. The ceramic sensitive chip 3 is sintered together with the ceramic sensitive chip 3 at high temperature to form a ceramic sensitive chip 3 with an alumina substrate layer 2 attached.

[0049] (2) Using a tooling clamp to hold the tail end of the ceramic sensitive chip 3 while rotating it, the front detection part of the ceramic sensitive chip 3 is vertically immersed into the composite slurry. After reaching the predetermined coating length position (12mm), it is immediately lifted up and the excess composite slurry is thrown off. After the coating dries and cures, the first immersion is repeated once.

[0050] (3) After the TSP coating 1 is impregnated, it is sintered and cooled at 1100℃ for 2 hours.

[0051] In step (2), the total thickness of the first impregnation coating is 450 μm, and after repeating it once, the final total thickness is controlled at 950 μm.

[0052] Example 2

[0053] The gas sensor element includes a ceramic sensitive chip 3, an alumina substrate layer 2, and a TSP coating 1; the alumina substrate layer 2 is printed on the top and bottom surfaces of the ceramic sensitive chip 3, and the alumina substrate layer 2 is printed on the left and right sides after the ceramic sensitive chip 3 is cut; the TSP coating 1 is disposed on the outside of the alumina substrate layer 2.

[0054] The alumina substrate 2 has a thickness of 40 μm and a porosity of 50%; the roughness of the alumina substrate 2 is 20 μm. The TSP coating 1 has a thickness of 800 μm, a porosity of 24%, and an average pore size of 1 μm. The TSP coating 1 is obtained by sintering a composite slurry, which, by weight, comprises 20 parts of coarse ceramic powder, 20 parts of fine ceramic powder, 3 parts of high-temperature binder, 6 parts of organic binder, 8 parts of pore-forming agent, 3 parts of dispersant, and 40 parts of solvent.

[0055] The coarse ceramic powder has a particle size of 3 μm, and the fine ceramic powder has a particle size of 0.1 μm, with a weight ratio of 1:1. Both the coarse and fine ceramic powders are alumina. The high-temperature binder is silicon dioxide, the organic binder is acrylic acid, the pore-forming agent is carbon powder, the dispersant is ammonium polycarboxylate, and the solvent is ethanol; the viscosity of the composite slurry is 1000 mPa·s.

[0056] The preparation method includes the following steps:

[0057] (1) First, alumina paste is printed on the top and bottom surfaces of the ceramic sensitive chip 3. After the ceramic sensitive chip 3 is cut, alumina paste is printed on the left and right sides. At 1350℃, the holding time is 5h. The ceramic sensitive chip 3 is sintered together with the ceramic sensitive chip 3 at high temperature to form a ceramic sensitive chip 3 with an alumina substrate layer 2 attached.

[0058] (2) Using a tooling clamp to hold the tail end of the ceramic sensitive chip 3 while rotating it, the front detection part of the ceramic sensitive chip 3 is vertically immersed into the composite slurry. After reaching the predetermined coating length position (11mm), it is immediately lifted up and the excess composite slurry is thrown off. After the coating dries and cures, the first immersion is repeated once.

[0059] (3) After the TSP coating 1 is impregnated, it is sintered and cooled at 1000℃ for 3 hours.

[0060] In step (2), the total thickness of the first impregnation coating is 400 μm, and after repeating once, the final total thickness is controlled at 800 μm.

[0061] Example 3

[0062] The gas sensor element includes a ceramic sensitive chip 3, an alumina substrate layer 2, and a TSP coating 1; the alumina substrate layer 2 is printed on the top and bottom surfaces of the ceramic sensitive chip 3, and the alumina substrate layer 2 is printed on the left and right sides after the ceramic sensitive chip 3 is cut; the TSP coating 1 is disposed on the outside of the alumina substrate layer 2.

[0063] The alumina substrate 2 has a thickness of 20 μm and a porosity of 30%; the roughness of the alumina substrate 2 is 10 μm. The TSP coating 1 has a thickness of 1000 μm, a porosity of 45%, and an average pore size of 5.0 μm. The TSP coating 1 is obtained by sintering a composite slurry, which, by weight, comprises 40 parts of coarse ceramic powder, 8 parts of fine ceramic powder, 7 parts of high-temperature binder, 2 parts of organic binder, 12 parts of pore-forming agent, 1 part of dispersant, and 30 parts of solvent.

[0064] The coarse ceramic powder has a particle size of 10 μm, and the fine ceramic powder has a particle size of 0.7 μm, with a weight ratio of 5:1. The coarse ceramic powder is magnesium aluminum spinel, and the fine ceramic powder is titanium dioxide. The high-temperature binder is alumina, the organic binder is polyvinyl alcohol, the pore-forming agent is organic resin balls, the dispersant is ammonium polycarboxylate, and the solvent is water; the viscosity of the composite slurry is 3000 mPa·s.

[0065] The preparation method includes the following steps:

[0066] (1) First, alumina paste is printed on the top and bottom surfaces of the ceramic sensitive chip 3. After the ceramic sensitive chip 3 is cut, alumina paste is printed on the left and right sides. At a temperature of 1500℃, the holding time is 1.5h. The ceramic sensitive chip 3 is sintered together with the ceramic sensitive chip 3 at high temperature to form a ceramic sensitive chip 3 with an alumina substrate layer 2 attached.

[0067] (2) Use a tooling clamp to hold the tail end of the ceramic sensitive chip 3 while rotating it, and vertically immerse the front detection part of the ceramic sensitive chip 3 into the composite slurry. After reaching the predetermined coating length position (13mm), immediately lift it up, shake off the excess composite slurry, and wait for the coating to dry and cure. After the first immersion is completed, repeat the immersion once.

[0068] (3) After the TSP coating 1 is impregnated, it is sintered and cooled at 1200℃ for 1 hour.

[0069] In step (2), the total thickness of the first impregnation coating is 500 μm, and after repeating once, the final total thickness is controlled at 1000 μm.

[0070] Example 4

[0071] The difference between Example 4 and Example 1 is that the weight ratio of coarse ceramic powder to fine ceramic powder in Example 4 is 3:1.

[0072] Example 5

[0073] The difference between Example 5 and Example 1 is that the weight ratio of coarse ceramic powder to fine ceramic powder in Example 5 is 1:2.

[0074] Comparative Example 1

[0075] The difference between Comparative Example 1 and Example 1 is that the alumina substrate layer in Comparative Example 1 is only set on the upper and lower main surfaces.

[0076] Comparative Example 2

[0077] The difference between Comparative Example 2 and Example 1 is that the alumina substrate layer of Comparative Example 2 is only set on the upper and lower main surfaces and adopts a two-layer structure, with the inner layer having a high porosity of 60% and the outer layer having a low porosity of 20%.

[0078] Comparative Example 3

[0079] The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 simulates the example in the published document CN112739665A. The ratio of coarse to fine powder was adjusted so that the ratio of coarse particles (average particle size of alumina is 6 μm) to fine particles (average particle size of titanium dioxide is 0.25 μm) in the inner slurry was 1:1; and the ratio of coarse particles (average particle size of spinel is 20 μm) to fine particles (average particle size of magnesium oxide is 0.05 μm) in the outer slurry was 20:1.

[0080] Comparative Example 4

[0081] The difference between Comparative Example 4 and Example 1 is that the alumina substrate layer is only set on the upper and lower main surfaces, and Comparative Example 4 uses plasma spraying process instead of immersion process, only ceramic coarse powder, porosity of 15%, and coating thickness of 700μm.

[0082] Comparative Example 5

[0083] The difference between Comparative Example 5 and Example 1 is that the amount of high-temperature adhesive added in Comparative Example 5 is 10 parts.

[0084] Experimental Example

[0085] 1. Testing Method

[0086] (1) Water Resistance Test Method: The water resistance of the TSP coating was evaluated using a water drop test device. Test conditions: The ceramic sensing chip was heated to 780℃. Using a dPette electronic pipette (0.5-10μL), 0.5μL of water was dropped onto the front (pump electrode surface) and 4.5mm from the side of the chip, with a 10s interval between drops. The pump current Ip0 was used as the criterion for judging whether the ceramic chip had cracked when the water droplets hit the TSP protective coating. The total amount of water dropped during the rapid increase in Ip0 was recorded. (Because when the water droplets cause thermal shock to the ceramic sensing chip, leading to cracking, oxygen flows into the internal first main chamber through the crack, which increases the value of the pump current Ip0.)

[0087] Water droplet volume = 0.5 μL, droplet method: probe pipetting, time interval > 10 s, ceramic core temperature = 780℃, and finally read the total water resistance (μL) that occurred when IP0 increased sharply.

[0088] (2) High-Temperature Vibration Test Method: To evaluate the bonding strength of the TSP coating, a sensor with the TSP coating was placed on a high-temperature vibration device, which consisted of a vibrator connected to a propane gas burner. The sensor was exposed to temperature and vibration curves at the following frequencies: 50...100...150...250Hz, acceleration: 30G...40G...50G, vibration scan cycle: 30 minutes / scan cycle; gas temperature: 850℃ (combustion gas λ set to 1.05); test time: 150h; vibration direction: up and down vibration (sensor direction not fixed). After vibration, an industrial CT scanner was used to scan various parts of the TSP coating for peeling or cracking.

[0089] (3) Air permeability evaluation method: The air permeability of the coating is evaluated by testing whether the IPO current decreases and the start-up time increases before and after the ceramic sensing chip is immersed in the TSP coating. The ceramic sensing chip is heated from room temperature to the operating temperature of 780℃, and the IPO pump current between the first oxygen pumping electrode and the external electrode in the air is measured to see if the addition of the TSP coating affects the air intake and oxygen pumping capacity of the ceramic sensing chip. Start-up time: The time from power-on start-up (when the dew point is reached) to the normal operation and stable signal output of the sensor is tested to see if the addition of the TSP coating affects the rapid heating capacity of the ceramic sensing chip.

[0090] (4) Thermal shock resistance test method: The ceramic sensitive chip with TSP coating is placed in a box furnace and heated from room temperature to 200℃, held at that temperature for 0.5h, then removed and quickly immersed in cold water (25±5℃). If the coating does not peel off, the sample is dried and the experiment is repeated, with each temperature increase being 50℃ higher than the previous one, until the TSP coating on the sample peels off. At the end of the experiment, the highest temperature at which the coating peels off is recorded to evaluate the thermal shock resistance of the coating.

[0091] 2. Evaluation Criteria

[0092] Regarding water resistance, the test results show that a maximum dripping volume of 20μL or more indicates excellent waterproofing of the coating; a maximum dripping volume between 10-20μL indicates good waterproofing; and a maximum dripping volume below 10μL indicates poor waterproofing.

[0093] Regarding air permeability, the test results show that if the IP current drop is within 200μA and the start-up time is within 45 seconds, it indicates that the coating has good air permeability and has no impact on the heating performance and oxygen pumping capacity of the ceramic sensitive chip; if the IP current drop is between 200-500μA and the start-up time is within 45-55 seconds, it indicates that the coating has good air permeability; if the IP current drop is above 500μA and the start-up time is above 55 seconds, it indicates that the coating has poor air permeability.

[0094] Regarding bonding strength, the absence of cracking or peeling in any part of the coating after the high-temperature vibration test indicates good bonding. If the main surface, sides, front surface, or outer layer of the coating shows varying degrees of peeling or cracking, it indicates poor bonding strength.

[0095] Regarding thermal shock resistance, coatings with a maximum temperature above 550℃ during rapid cooling and heating are considered to have good thermal shock resistance; coatings with a maximum temperature between 400-550℃ during peeling are considered to have relatively good thermal shock resistance; and coatings with a maximum temperature below 400℃ during peeling are considered to have poor thermal shock resistance.

[0096] The results of the above tests are shown in Table 1.

[0097] Table 1 Performance test results of each sample

[0098]

[0099] The above experimental results show that, except for Examples 1, 2, and 4, which were prepared using the methods and materials specified in this application and exhibited excellent performance in all tests, Examples 5 and Comparative Examples 2, 4, and 5 had poor air permeability; Examples 3 and Comparative Examples 1-3 had poor bonding strength. Examples 3 and Comparative Examples 1 and 3 had moderate water resistance and high dispersibility.

[0100] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

[0101] The above description is merely an embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of this application should be included within the scope of the claims of this application.

Claims

1. A gas sensor element, characterized in that, The system comprises a ceramic sensing chip, an alumina substrate layer, and a TSP coating. During fabrication, alumina paste is printed on the top and bottom surfaces of a ceramic chip laminate preform. After the preform is slit, the ceramic sensing chip is obtained, and alumina paste is then printed on both sides of the chip. The alumina-coated ceramic sensing chip is then sintered, forming the alumina substrate layer around the chip. A single-layer TSP coating is applied to the outside of the alumina substrate layer. The alumina substrate layer has a thickness of 20–40 μm and a porosity of 30–50%.

2. The gas sensor element according to claim 1, characterized in that, The roughness of the alumina substrate layer is 10-20 μm.

3. The gas sensor element according to claim 1, characterized in that, The TSP coating has a thickness of 800-1000 μm, a porosity of 24-45%, and an average pore size of 0.5-5.0 μm.

4. The gas sensor element according to claim 3, characterized in that, The TSP coating is obtained by sintering a composite slurry, which includes coarse ceramic powder and fine ceramic powder.

5. The gas sensor element according to claim 4, characterized in that, The coarse ceramic powder has a particle size of 2-10 μm, and the fine ceramic powder has a particle size of 0.02-0.8 μm. The weight ratio of the coarse ceramic powder to the fine ceramic powder is (1-4):

1.

6. The gas sensor element according to claim 4, characterized in that, The coarse ceramic powder is one or more of alumina, magnesium aluminum spinel, and mullite; the fine ceramic powder is one or more of zirconium oxide, alumina, titanium oxide, and magnesium oxide.

7. The gas sensor element according to claim 4, characterized in that, The composite slurry also includes a high-temperature binder, an organic binder, a pore-forming agent, a dispersant, and a solvent.

8. The gas sensor element according to claim 7, characterized in that, The high-temperature binder is one or more of silicon oxide, aluminum oxide, bismuth oxide, and zinc oxide; the organic binder is one of acrylic binder and polyvinyl alcohol; the pore-forming agent is one or more of toner, starch, and organic resin balls; the dispersant is ammonium polycarboxylate; and the solvent is one or more of water, ethanol, and isopropanol.

9. A method for preparing a gas sensor element as described in any one of claims 1-8, characterized in that, Includes the following steps: (1) First, print alumina paste on the top and bottom sides of the ceramic chip stack blank. After cutting the ceramic chip stack blank, obtain the ceramic sensitive chip. Then print alumina paste on the left and right sides of the ceramic sensitive chip. At a temperature of 1350℃~1500℃, sinter the ceramic sensitive chip after printing alumina paste at high temperature to form a ceramic sensitive chip with an alumina substrate layer attached. (2) Use a tooling to hold the tail end of the ceramic sensitive chip with the alumina substrate layer attached, rotate it while vertically immersing the front detection part of the ceramic sensitive chip with the alumina substrate layer attached into the composite slurry. After reaching the predetermined coating length position, immediately lift it up, throw off the excess composite slurry, wait for the coating to dry and cure, and repeat the immersion once after the first immersion is completed. (3) After the TSP coating is impregnated, it is sintered and cooled at 1000-1200℃ for 1-3 hours.

10. The method for preparing a gas sensor element according to claim 9, characterized in that, In step (2), the total thickness of the first impregnation coating is 400~500μm, and after repeating it once, the final total thickness is controlled at 800~1000μm.

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