A powder for an oxygen sensor protective layer, a method for preparing the same, and an oxygen sensor

Abstract

The application belongs to the technical field of oxygen sensors, and provides a powder for an oxygen sensor protective layer, a preparation method of the powder, and an oxygen sensor, the preparation method of the powder for an oxygen sensor protective layer comprising the following steps: preparing raw materials, including 68-80 parts of aluminum oxide, 5-15 parts of second-phase particles, 8-15 parts of inorganic hydrophobic additives, and 16-20 parts of pore-forming agents in terms of mass fraction; the average particle sizes of the components are matched with each other; and the raw materials are prepared into the powder for an oxygen sensor protective layer through slurry preparation, atomization, drying, collection, and post-processing by a spray granulation process. The powder for an oxygen sensor protective layer prepared by the preparation method has high thermal shock resistance, high adhesion, high porosity, and high water resistance of the oxygen sensor protective layer obtained by plasma spraying, and can meet the working requirements of the oxygen sensor on the protective layer, and the oxygen sensor with the oxygen sensor protective layer can avoid failure, has stable working performance, and has a long service life.

Description

Technical Field

[0001] The present invention belongs to the technical field of oxygen sensors, and in particular relates to a powder for an oxygen sensor protective layer, a preparation method thereof, and an oxygen sensor. Background Art

[0002] As a key component in vehicle emissions control systems, the performance of automotive oxygen sensors directly impacts fuel economy and exhaust emissions control. Currently, widely used heated zirconia oxygen sensors must maintain stable operation within an operating temperature range of 300-900°C. During actual use, during cold engine starts, condensation easily forms because the exhaust system has not yet reached its dew point and the exhaust gas contains high levels of water vapor. When the high-temperature oxygen sensor chip is exposed to more than 2μL of condensed water, the resulting thermal shock causes microcracks in the chip, ultimately causing oxygen sensor failure. Therefore, constructing a dew point protection layer on the surface of the oxygen sensor chip has become a key technological approach to improving the oxygen sensor's waterproof performance and extending its service life. The oxygen sensor's protective layer must simultaneously exhibit excellent water resistance, thermal shock resistance, and low thermal conductivity, requiring high adhesion, high porosity, and an appropriate thickness.

[0003] Existing processes for preparing oxygen sensor dew point protection layers primarily include slurry coating, low-temperature thermal spraying, and screen printing combined with plasma spraying. Plasma spraying, due to its advantages such as strong coating adhesion, simple process, and high production efficiency, is considered the most promising method for preparing oxygen sensor dew point protection layers. However, this process places stringent requirements on the compatibility of the powder used to apply the oxygen sensor protection layer. However, existing powders used in oxygen sensor protection layers have the following drawbacks:

[0004] 1. Insufficient porosity control technology

[0005] Alumina is the most commonly used raw material for preparing the dew point protection layer of oxygen sensors due to its high chemical stability and low cost. In order to improve the coating porosity of the oxygen sensor protective layer, the existing technology mostly adopts the strategy of adding pore-forming agents to the alumina powder, and the pore-forming agents decompose, volatilize or chemically react at high temperatures to form pores, so as to regulate the porosity, morphology and distribution of the coating. In the technical solutions disclosed in patent documents CN113614523A and CN113597552A, a coating with a porosity of 40-60% is prepared by adding a specific proportion of pore-forming materials and combining it with subsequent sintering treatment. However, this method has two major drawbacks: first, the pore-forming agent used is difficult to completely remove during the spraying process, and an additional heat treatment step is required, which increases the complexity of the process; if the residual pore-forming agent undergoes thermal decomposition during the service of the sensor, it will interfere with the normal operation of the sensor. Second, existing methods for preparing powders for oxygen sensor protective layers face technical bottlenecks: The mechanical mixing method, due to the density difference between alumina and the pore-forming agent, causes powder diversion during spraying. The lower-density pore-forming agent aggregates toward the edge of the plasma flame, resulting in uneven pore distribution in the coating. While the solvent evaporation method can achieve agglomeration of micron-sized pore-forming agent and alumina, the resulting irregular secondary particles have poor fluidity and insufficient particle strength, making them prone to disintegration during spraying, severely impacting spraying efficiency and the coating quality of the oxygen sensor protective layer. Furthermore, even when the coating thickness of the oxygen sensor protective layer prepared using existing technology reaches 740μm, its water resistance is still limited to the order of 10μL. Further optimization of the pore-forming agent particle size and an increase in the proportion of closed pores are needed to enhance waterproofing performance.

[0006] 2. Thermal stability defects of hydrophobic materials

[0007] In order to give the coating hydrophobicity, the existing technology often adds hydrophobic organic polymer materials, which are melted in the plasma flame and then sputtered onto the substrate surface to reduce the surface energy of the coating. As described in "Performance and Deposition Mechanism of PFA / Al2O3 Composite Ceramic Hydrophobic Coating Prepared by APS", mechanically mixing Al2O3 with PFA and then spraying it can make the coating contact angle reach 122.6°, significantly improving the hydrophobic performance. However, the continuous use temperature of such hydrophobic organic polymer materials is generally lower than 300°C. In the actual service environment of oxygen sensors at 300~900°C, the material will undergo thermal decomposition, which will not only cause the waterproof performance of the oxygen sensor protective layer to rapidly decay, but its thermal decomposition products will also contaminate the oxygen sensor and affect the detection accuracy.

[0008] 3. Insufficient thermal shock resistance

[0009] The existing powder used for spraying oxygen sensor protective layer, which is mainly composed of aluminum oxide, is easily cracked under the action of thermal shock due to its own brittleness and poor matching with the thermal expansion coefficient of the substrate, resulting in cracking or peeling of the coating, which seriously restricts the thermal shock resistance of the dew point protective layer of the oxygen sensor, and thus affects the performance and service life of the oxygen sensor. It is urgent to optimize the composition of the powder used for the oxygen sensor protective layer to achieve coating toughening and thermal expansion coefficient regulation of the oxygen sensor protective layer.

[0010] In summary, the existing powders for spraying oxygen sensor protective layers and their preparation technologies have obvious shortcomings in porosity control, hydrophobic material stability and thermal shock resistance, making it difficult to meet the demand for preparing high-performance oxygen sensor protective layers through plasma spraying technology and thus obtaining high-performance oxygen sensors. Summary of the Invention

[0011] The object of the present invention is to provide a powder for an oxygen sensor protective layer, a preparation method thereof, and an oxygen sensor. The powder for an oxygen sensor protective layer obtained by the preparation method of the present invention has a more uniform composition and particle size distribution, higher particle strength, and better fluidity, effectively solving problems such as powder diversion and collapse. The oxygen sensor protective layer obtained by plasma spraying the powder for an oxygen sensor protective layer has strong thermal shock resistance, high adhesion, high porosity, and excellent water resistance, thereby obtaining a high-performance oxygen sensor, greatly improving the working performance of the oxygen sensor and extending its service life.

[0012] The specific plan is as follows:

[0013] A method for preparing powder for an oxygen sensor protective layer comprises the following steps:

[0014] S1. Prepare raw materials: in parts by mass, including 68-80 parts of alumina, 5-15 parts of second phase particles, 8-15 parts of inorganic hydrophobic additives, and 16-20 parts of pore-forming agents. The average particle size of the alumina is 0.4-2 μm, the average particle size of the second phase particles is 1 / 4-1 / 2 of the average particle size of the alumina, the average particle size of the inorganic hydrophobic additive is 1 / 4-1 / 2 of the average particle size of the alumina, and the average particle size of the pore-forming agent is 2-4 times the average particle size of the alumina.

[0015] S2. The raw materials are subjected to the slurrying, atomization, drying, collection and post-processing processes of the spray granulation process to prepare a powder for the oxygen sensor protective layer with regular spherical particles.

[0016] Furthermore, the average particle size of the powder for the oxygen sensor protective layer is 28-32 μm, and the flowability index is 75.0-80.0.

[0017] Furthermore, the second phase particles are one or more of zirconium oxide, yttrium oxide and silicon carbide.

[0018] Further, the inorganic hydrophobic aid is one or more of silicon oxide, silicon nitride, and rare earth silicate.

[0019] Further, the pore-forming agent is one or a mixture of both of polyvinyl chloride and polystyrene.

[0020] Further, the step S2 comprises:

[0021] S201, slurry preparation: the alumina, the second phase particles, and the inorganic hydrophobic aid are premixed with deionized water as the main dispersant, then the deionized water and the binder are added for grinding, and finally the pore-forming agent is added for mixing and grinding to obtain a slurry;

[0022] S202, atomization: the slurry is broken into small droplets by centrifugal atomization;

[0023] S203, drying: the slurry droplets are dried to obtain a powder;

[0024] S204, collection: the powder produced in the drying process is collected;

[0025] S205, post-treatment: further screening to remove abnormal agglomerates or excessively fine powder.

[0026] Further, the binder is one or more of polyvinyl alcohol, carboxymethyl cellulose, and polyacrylic acid.

[0027] A powder for an oxygen sensor protective layer, which is prepared by the method for preparing the powder for an oxygen sensor protective layer.

[0028] An oxygen sensor comprising an oxygen sensor protective layer prepared by plasma spraying the powder for an oxygen sensor protective layer on the surface of an oxygen sensor chip.

[0029] Further, when the average thickness of the coating of the oxygen sensor protective layer is > 250 μm, the average porosity is ≥ 19%, the average adhesion is ≥ 35 N, the average water resistance is ≥ 450 μL, and the oxygen sensor protective layer passes the impact thermal cycle test.

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] The innovative formula of the powder for an oxygen sensor protective layer of the present application is combined with the spray granulation preparation process, so that the composition and particle size distribution of the prepared powder for an oxygen sensor protective layer are more uniform, and the particle strength is higher, solving the problems of powder diversion and collapse;

[0032] The oxygen sensor protective layer prepared by plasma spraying the powder for an oxygen sensor protective layer of the present application has enhanced thermal shock resistance, high adhesion, high porosity, and excellent water resistance.

[0033] The performance of the oxygen sensor provided with the oxygen sensor protective layer of the present invention is greatly improved and the service life is prolonged. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a morphology diagram of the powder used for the oxygen sensor protective layer according to Example 1 of the present invention.

[0035] Figure 2 This is a morphology diagram of the powder used for the oxygen sensor protective layer according to Example 2 of the present invention.

[0036] Figure 3 This is a morphology diagram of the powder used for the oxygen sensor protective layer in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0037] The following is a detailed description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0038] Alumina has become the most commonly used raw material for preparing oxygen sensor protective layers due to its high chemical stability and low cost. The existing preparation processes for oxygen sensor protective layers mainly include slurry coating, low-temperature thermal spraying, and screen printing combined with plasma spraying. Among them, the plasma spraying method is considered to be the preparation method with the most application prospects due to its advantages such as strong coating adhesion, simple process, and high production efficiency. However, this process places strict requirements on the adaptability of the spraying powder, and the existing powders still have the defects of insufficient porosity control technology, poor thermal stability of hydrophobic materials, and insufficient thermal shock resistance. The present invention has made an innovative design to the formula of the oxygen sensor protective layer powder used in the preparation method of the oxygen sensor protective layer powder, so that it overcomes the above-mentioned defects and meets the requirements of the plasma spraying method for powder.

[0039] The method for preparing the powder for the oxygen sensor protective layer provided by the present invention comprises the following steps:

[0040] S1. Prepare raw materials: in parts by mass, including 68-80 parts of alumina, 5-15 parts of second phase particles, 8-15 parts of inorganic hydrophobic additives, and 16-20 parts of pore-forming agents. The average particle size of the alumina is 0.4-2 μm, the average particle size of the second phase particles is 1 / 4-1 / 2 of the average particle size of the alumina, the average particle size of the inorganic hydrophobic additive is 1 / 4-1 / 2 of the average particle size of the alumina, and the average particle size of the pore-forming agent is 2-4 times the average particle size of the alumina.

[0041] S2. The raw materials are subjected to the slurrying, atomization, drying, collection and post-processing processes of the spray granulation process to prepare a powder for the oxygen sensor protective layer with regular spherical particles.

[0042] In order to solve the problem of insufficient thermal shock resistance of the coating prepared by the existing powder, the second phase particles are added in the alumina matrix, the average particle size of the alumina is 0.4-2 μm, the average particle size of the second phase particles is 1 / 4-1 of the average particle size of the alumina, and the second phase particles are one or more of zirconium oxide, yttrium oxide and silicon carbide. The second phase particles form a reinforced network structure inside the coating, effectively disperse the thermal stress, and significantly improve the toughness of the oxygen sensor protective layer. At the same time, the introduction of the second phase particles can effectively control the thermal expansion coefficient of the oxygen sensor protective layer, so that it is better matched with the oxygen sensor chip matrix material, and the thermal mismatch phenomenon is reduced. The thermal shock resistance of the oxygen sensor protective layer in the working temperature range of the oxygen sensor is enhanced in two aspects, and the cracking and peeling problems of the oxygen sensor protective layer are effectively avoided.

[0043] In order to overcome the defect of poor thermal stability of the existing hydrophobic material, one or more of the inorganic hydrophobic additives such as silicon oxide, silicon nitride and rare earth silicate replace the traditional organic polymer material, and the average particle size of the inorganic hydrophobic additive is 1 / 4-1 of the average particle size of the alumina. These inorganic hydrophobic additives have excellent high-temperature stability, can maintain stable chemical structure and certain hydrophobic property in the plasma spraying high-temperature environment and sensor service process, avoid the attenuation of waterproof performance caused by thermal decomposition and the pollution problem of the sensor, continuously endow the oxygen sensor protective layer with effective and durable hydrophobic characteristics, thereby improving the water resistance of the oxygen sensor protective layer.

[0044] In order to solve the problems of residual pore-forming agent and poor water resistance of the existing oxygen sensor protective layer, the type, proportion and particle size of the pore-forming agent are optimized and selected. The preferred pore-forming agent can be completely decomposed and / or volatilized in the high temperature of the plasma spraying process, without additional post-treatment process, simplifying the process flow; the porosity of the oxygen sensor protective layer can be stably controlled, and the closed pore ratio can be significantly improved, effectively preventing the condensate from penetrating, and the water resistance of the oxygen sensor protective layer is improved to a new level. The pore-forming agent uses one or a mixture of the other of polyvinyl chloride and polystyrene, and the average particle size is 2-4 times of the average particle size of the alumina.

[0045] The average particle sizes of the alumina, the second phase particles, the inorganic hydrophobic additive and the pore-forming agent must be matched, otherwise the powder for the oxygen sensor protective layer cannot achieve the technical effect.

[0046] The above raw materials were prepared through a spray granulation process involving slurrying, atomization, drying, collection, and post-processing to obtain a powder for the oxygen sensor protective layer. Deionized water was used as the primary dispersant during the slurrying process, with a deionized water to raw material ratio of 2.5:1 to 1:1. Corundum balls were used as the grinding media, with a ball-to-material ratio of 3:1 to 1:1. The milling speed was 30-60 Hz, and the milling time was 2.5-5 hours. Alumina, second-phase particles, and an inorganic hydrophobic additive were premixed. Deionized water and 2-10 parts by weight of a binder were then added for wet milling. Finally, a pore-forming agent was added and stirred to obtain a slurry, which was then atomized. Before atomization, the centrifugal atomizer was set at a speed of 150-220 Hz to break the slurry into fine droplets. During the drying process, the air inlet temperature was set at 210-260°C and the air outlet temperature at 100-130°C. The slurry droplets were then dried and atomized to obtain a powder. The powder produced during the drying process is collected and further sieved using screening equipment to remove any abnormal agglomerates or excessively fine powder. This results in a powder for the oxygen sensor protective layer with an average particle size of 28-32 μm and a flowability index of 75.0-80.0. The binder is one or more of polyvinyl alcohol, carboxymethyl cellulose, and polyacrylic acid.

[0047] In terms of preparation technology, the present invention utilizes a spray granulation method to produce the powder for the oxygen sensor protective layer. This method allows for thorough and uniform mixing of alumina and the modifying component, forming composite particles with a regular spherical shape. Compared to traditional mechanical mixing or solvent evaporation methods, spray granulation produces a powder with more uniform composition and particle size distribution, higher particle strength, and improved flowability. This not only effectively solves problems such as powder diversion and collapse, but also significantly improves plasma spraying efficiency and quality, providing a reliable guarantee for the preparation of oxygen sensor protective layers with excellent water resistance and thermal shock resistance.

[0048] The powder for the protective layer of an oxygen sensor of the present invention is prepared by the method for preparing the powder for the protective layer of an oxygen sensor of the present invention.

[0049] The present invention also provides an oxygen sensor, which includes an oxygen sensor protective layer obtained by spraying the powder for the oxygen sensor protective layer of the present invention on the surface of an oxygen sensor chip through a plasma spraying process.

[0050] When the average coating thickness of the oxygen sensor protective layer is greater than 250μm, the average porosity is ≥19%, the average adhesion is ≥35N, the average water resistance is ≥450μL, and the oxygen sensor protective layer has passed the shock thermal cycle test.

[0051] In order to further understand the present invention, the following Figure 1 、 Figure 2 、 Figure 3, Examples and Comparative Examples The powder for an oxygen sensor protective layer, its preparation method, and the oxygen sensor of the present invention are described in detail.

[0052] Example 1:

[0053] The specific implementation steps of the technical solution provided by the present invention are as follows:

[0054] Raw material screening and proportioning: 68 parts of alumina with an average particle size of 1 μm; 12 parts of zirconium oxide with an average particle size of 0.5 μm as the second phase particles; 10 parts of silicon nitride with an average particle size of 0.5 μm as the inorganic hydrophobic additive; and 16 parts of polystyrene with an average particle size of 4 μm as the preferred pore-forming agent.

[0055] Spray granulation includes the following steps:

[0056] Slurry Preparation: Premix alumina, zirconia, and silicon nitride, then add deionized water and polyvinyl alcohol (binder) and begin wet milling. Use a 2:1 ratio of deionized water to raw materials and a 2:1 ratio of corundum balls to raw materials at a speed of 40 Hz for 3.5 hours. Finally, add polystyrene and mill for 0.5 hours.

[0057] Atomization: Set the speed of the centrifugal atomization equipment to 190 Hz;

[0058] Drying: Set the air inlet temperature to 225°C and the air outlet temperature to 120°C;

[0059] Collection and post-processing: The powder produced during the drying process is collected and further sieved to obtain the powder for the target oxygen sensor protective layer.

[0060] See Figure 1 As shown, the powder for the oxygen sensor protective layer obtained in Example 1 is in the form of spherical particles, with an average particle size of 29.6 μm and a fluidity index of 76.5.

[0061] The powder from Example 1 was used, sprayed four times at a power of 38.5 kW and a powder feed rate of 20 g / min to prepare an oxygen sensor protective layer on an oxygen sensor chip. The oxygen sensor protective layer had an average thickness of 290 μm, an average porosity of 20.87%, an average adhesion of 40 N, and a water resistance of 520 μL. The coating remained intact after 36 thermal shock cycles, demonstrating excellent thermal shock resistance.

[0062] Test standards: GB / T2423.5 mechanical shock, GB / T4208 waterproof.

[0063] Example 2:

[0064] The specific implementation steps of the technical solution provided by the present invention are as follows:

[0065] Raw material screening and proportioning: 80 parts of alumina with an average particle size of 2 μm; 5 parts of a mixed powder of yttrium oxide and silicon carbide with an average particle size of 0.5 μm as the second phase particles; 8 parts of yttrium silicate with an average particle size of 0.5 μm as the inorganic hydrophobic additive; and 16 parts of polyvinyl chloride with an average particle size of 4 μm as the preferred pore-forming agent.

[0066] Powder preparation: spray granulation:

[0067] Slurry Preparation: Premix alumina, yttrium oxide, silicon carbide powder, and yttrium silicate. Then add deionized water and polyacrylic acid (binder) and begin wet milling. Use a 2:1 ratio of deionized water to raw materials, a 2:1 ratio of corundum balls to raw materials, and mill at 40 Hz for 2.5 hours. Finally, add polyvinyl chloride and mill for 0.5 hours.

[0068] Atomization: Set the speed of the centrifugal atomization equipment to 175Hz;

[0069] Drying: Set the air inlet temperature to 230°C and the air outlet temperature to 120°C;

[0070] Collection and post-processing: The powder produced during the drying process is collected and further sieved to obtain the powder for the target oxygen sensor protective layer.

[0071] See Figure 2 As shown, the powder for the oxygen sensor protective layer obtained in Example 2 is in the form of spherical particles, with an average particle size of 31.0 μm and a fluidity index of 78.00.

[0072] The powder from Example 2 was used to prepare an oxygen sensor protective layer on an oxygen sensor chip using the same spraying process as in Example 1. The oxygen sensor protective layer had an average thickness of 301.3 μm, an average porosity of 19.05%, an average adhesion of 40 N, and a water resistance of 600 μL. The coating remained intact after 36 thermal shock cycles, demonstrating excellent thermal shock resistance.

[0073] Example 3:

[0074] The specific implementation steps of the technical solution provided by the present invention are as follows:

[0075] Raw material screening and proportioning: 75 parts of alumina with an average particle size of 2 μm; 15 parts of zirconium oxide powder with an average particle size of 2 μm as the second phase particles; 15 parts of a mixed powder of silicon oxide and silicon nitride with an average particle size of 2 μm as the inorganic hydrophobic additive; 20 parts of polystyrene with an average particle size of 4 μm as the preferred pore-forming agent;

[0076] Powder preparation: spray granulation:

[0077] Slurry preparation: firstly, the mixed powder of alumina, zirconia, silica and silicon nitride is premixed, then deionized water and polyvinyl alcohol (binder) are added to start wet grinding. The ratio of deionized water to raw materials is 2:1, the ratio of corundum ball to raw materials is 2:1, the rotation speed is 60Hz, and the ball milling time is 5h. Finally, polystyrene is added and mixed by ball milling for 0.5h;

[0078] Atomization: the rotation speed of the centrifugal atomization equipment is set to 190Hz;

[0079] Drying: the inlet temperature is set to 225℃, and the outlet temperature is set to 120℃;

[0080] Collection and post-processing: the powder produced in the drying process is collected, and further sieving is performed to obtain the target oxygen sensor protective layer powder.

[0081] The oxygen sensor protective layer powder obtained in Example 3 is in spherical particle shape, the average particle size is 28.2μm, and the flowability index is 77.50.

[0082] An oxygen sensor protective layer is prepared on an oxygen sensor chip using the powder of Example 3 by using the same spraying process as in Example 1. The average thickness of the oxygen sensor protective layer is 295.4μm, the average porosity is 21.33%, the average adhesion is 35N, the water resistance is 500μL, the coating does not fall off after 36 times of impact thermal cycle test, and the impact thermal cycle test is passed, which has good thermal shock resistance.

[0083] Example 4:

[0084] The technical solution provided by the present application is specifically implemented as follows:

[0085] Raw material selection and proportioning: 75 parts of alumina with an average particle size of 0.4μm are taken; 8 parts of mixed powder of yttrium oxide and silicon carbide with an average particle size of 0.3μm are taken as the second phase particles; 8 parts of yttrium silicate with an average particle size of 0.1μm are taken as the inorganic hydrophobic additive; and 20 parts of polyvinyl chloride with an average particle size of 0.6μm are taken as the preferred pore-forming agent;

[0086] Powder preparation: spray granulation:

[0087] Slurry preparation: firstly, the mixed powder of alumina, yttrium oxide and silicon carbide and yttrium silicate is premixed, then deionized water and polyacrylic acid (binder) are added to start wet grinding. The ratio of deionized water to raw materials is 2:1, the ratio of corundum ball to raw materials is 2:1, the rotation speed is 40Hz, and the ball milling time is 3.5h. Finally, polyvinyl chloride is added and mixed by ball milling for 0.5h;

[0088] Atomization: the rotation speed of the centrifugal atomization equipment is set to 175Hz;

[0089] Drying: the inlet temperature is set to 230℃, and the outlet temperature is set to 120℃;

[0090] Collection and post-processing: The powder produced during the drying process is collected and further sieved to obtain the powder for the target oxygen sensor protective layer.

[0091] The powder for the oxygen sensor protective layer obtained in Example 4 was in the form of spherical particles, with an average particle size of 31.3 μm and a fluidity index of 79.50.

[0092] The powder of Example 4 was used, with a spraying power of 38.5 kW and a powder feed rate of 20 g / min, and four spraying cycles were performed to prepare an oxygen sensor protective layer on the oxygen sensor chip. The oxygen sensor protective layer had an average thickness of 315.3 μm, an average porosity of 25.56%, an average adhesion of 35 N, and a water resistance of 510 μL. The coating did not fall off after 36 shock thermal cycling tests, demonstrating excellent thermal shock resistance. After packaging, the chip passed mechanical shock testing, external water mist testing, and output signal detection, meeting application requirements.

[0093] Comparative Example 1:

[0094] An oxygen sensor protective layer was prepared on an oxygen sensor chip using 100 parts pure alumina powder with an average particle size of 30 μm as raw material, following the spray coating process described in Example 1. The powder particles were irregular in shape and had a flowability index of 72.00. The resulting alumina coating had an average thickness of 290 μm, an average porosity of 9.75%, an average adhesion of 40 N, and a maximum water resistance of 50 μL. These average porosity and water resistance were too low to require further testing.

[0095] Comparative Example 2:

[0096] Mix 68 parts of irregular alumina powder with an average particle size of 20 μm, 12 parts of zirconium oxide, 10 parts of silicon nitride and 16 parts of polystyrene with an average particle size of 4 μm. Figure 3 As shown, the powder for the oxygen sensor protective layer formed by briquetting and granulation is irregular in shape. The flowability index of the powder is 60.5. The continuity of the spray powder feeding is poor and the coating cannot be obtained. Therefore, other tests cannot be performed.

[0097] Comparative Example 3:

[0098] Raw material screening and proportioning: 86 parts of alumina with an average particle size of 0.6 μm; 2 parts of zirconium oxide with an average particle size of 0.5 μm as the second phase particles; 5 parts of silicon nitride with an average particle size of 0.5 μm as the inorganic hydrophobic additive; 10 parts of polystyrene with an average particle size of 4 μm as the pore-forming agent;

[0099] Powder preparation: spray granulation:

[0100] Slurry Preparation: Premix alumina, zirconia, and silicon nitride. Then add deionized water and polyvinyl alcohol (binder) and begin wet milling. Use a 2:1 ratio of deionized water to raw materials and a 2:1 ratio of corundum balls to raw materials. Mill at 40 Hz for 3.5 hours. Finally, add polystyrene and mill for 0.5 hours.

[0101] Atomization: Set the speed of the centrifugal atomization equipment to 120Hz;

[0102] Drying: Set the air inlet temperature to 225°C and the air outlet temperature to 120°C;

[0103] Collection and post-processing: The powder produced during the drying process is collected and further sieved to obtain the powder for the target oxygen sensor protective layer.

[0104] The powder for the oxygen sensor protective layer obtained in Comparative Example 3 was in the form of spherical particles, with an average particle size of 42.3 μm and a fluidity index of 85.0.

[0105] An oxygen sensor protective layer was prepared on the oxygen sensor chip according to the spraying process in Example 1. The average thickness of the oxygen sensor protective layer was 334.5 μm, and the average porosity was 14.33%, which would weaken the electrical signal. Therefore, the powder could be eliminated. The average adhesion was 45 N, and the coating fell off after 36 shock thermal cycle tests. The product failed the shock thermal cycle test and had poor thermal shock resistance.

[0106] Examples 1-4 and Comparative Examples 1-3 were tested to obtain Table 1:

[0107]

[0108] Comparative Example 1 was made of pure alumina powder. Compared with Examples 1-4, the powder prepared in Comparative Example 1 had an irregular shape. When the average coating thickness was 290 μm, the average porosity was 9.75, the flow index was 72, the average adhesion was 40 N, and the average water resistance was ≤50 μL. The average porosity and water resistance were too low, and no further testing was required.

[0109] The average particle size of the alumina powder in Comparative Example 2 was outside the range of the present invention, and the average particle sizes of the other components were not proportionally matched to the average particle size of the alumina. The resulting powder was irregular in shape, with the particles of the components bonded together. The strength was too low to effectively measure the average particle size. The flowability index was 60.5, indicating that normal powder feeding, i.e., a coating, could not be obtained. Therefore, no other tests could be performed.

[0110] The mass fractions of the raw material components in Comparative Example 3 were all outside the range, and the average porosity of 14.33 was too low, which would weaken the electrical signal. Therefore, the powder could be eliminated and there was no need to conduct water resistance testing. After 36 shock thermal cycle tests, the coating fell off, and the shock thermal cycle test failed.

[0111] The oxygen sensor protective powders prepared in Examples 1-4 were spherical particles. When the average coating thickness was greater than 250 μm, the average porosity was greater than 19%, the average adhesion was greater than 35 N, the average water resistance was greater than 450 μL, and all passed the shock thermal cycle test. This indicates that as long as the values ​​of the components in the raw materials are within the value ranges of the present invention, the performance parameters of the powders for the prepared oxygen sensor protective layer can achieve the technical effects of the present invention. The oxygen sensor protective layers prepared using the powders can meet the operating requirements of the oxygen sensor, resulting in high-performance oxygen sensors that can avoid failure problems, improve operating stability, and extend service life.

[0112] After the sample of the preferred embodiment 4 was packaged, the oxygen sensor obtained after packaging was subjected to a mechanical impact test, a post-packaging external water mist test, and a post-packaging output signal detection. The oxygen sensor passed all the tests, demonstrating that the oxygen sensor protective layer prepared using the powder for the oxygen sensor protective layer of the present invention can meet the working requirements of the oxygen sensor, thereby obtaining a high-performance oxygen sensor. The oxygen sensor of the present invention avoids the risk of failure, improves working stability, and extends service life. During the testing process, the post-packaging mechanical impact test test standard is: GB / T2423.5-1995; the post-packaging external water mist test test standard is: GB / T2423.5-1995; the post-packaging output signal detection test standard is: QC / T803-2017.

[0113] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing powder for an oxygen sensor protective layer, characterized in that: The steps are as follows: S1. Prepare raw materials: in parts by mass, including 68-80 parts of alumina, 5-15 parts of second-phase particles, 8-15 parts of an inorganic hydrophobic additive, and 16-20 parts of a pore-forming agent. The average particle size of the alumina is 0.4-2 μm, the average particle size of the second-phase particles is 1 / 4-1 / 2 of the average particle size of alumina, the average particle size of the inorganic hydrophobic additive is 1 / 4-1 / 2 of the average particle size of alumina, and the average particle size of the pore-forming agent is 2-4 times the average particle size of alumina. S2. The raw materials are subjected to slurrying, atomization, drying, collection and post-processing through a spray granulation process to prepare the powder for the oxygen sensor protective layer having regular spherical particles and uniform distribution; The second phase particles are one or more of zirconium oxide, yttrium oxide and silicon carbide; The inorganic hydrophobic additive is one or more of silicon oxide, silicon nitride, and rare earth silicate.

2. The method for preparing the powder for the oxygen sensor protective layer according to claim 1, wherein: The powder for the oxygen sensor protective layer has an average particle size of 28 to 32 μm and a fluidity index of 75.0 to 80.

0.

3. The method for preparing the powder for the oxygen sensor protective layer according to claim 1, wherein: The pore-forming agent is one of polyvinyl chloride and polystyrene or a mixture of the two.

4. The method for preparing the powder for the oxygen sensor protective layer according to claim 1, wherein: Step S2 includes: S201, slurry preparation: using deionized water as a main dispersant, premixing alumina, second phase particles and an inorganic hydrophobic additive, then adding deionized water and a binder and grinding, and finally adding a pore-forming agent and mixing and grinding to obtain a slurry; S202, atomization: breaking the slurry into tiny droplets by centrifugal atomization; S203, drying: drying the slurry droplets to obtain powder; S204, collecting: collecting powder generated during the drying process; S205, post-processing: further screening to remove abnormal agglomerates or overly fine powder.

5. The method for preparing the powder for the oxygen sensor protective layer according to claim 4, characterized in that: The binder is one or more of polyvinyl alcohol, carboxymethyl cellulose, and polyacrylic acid.

6. A powder for an oxygen sensor protective layer, characterized in that: The oxygen sensor protective layer powder is prepared by the method for preparing the oxygen sensor protective layer powder according to any one of claims 1 to 5.

7. An oxygen sensor, characterized in that: The oxygen sensor protective layer is obtained by spraying the powder for the oxygen sensor protective layer as claimed in claim 6 on the surface of the oxygen sensor chip through a plasma spraying process.

8. The oxygen sensor according to claim 7, characterized in that When the average coating thickness of the oxygen sensor protective layer is greater than 250 μm, the average porosity is greater than or equal to 19%, the average adhesion is greater than or equal to 35 N, the average water resistance is greater than or equal to 450 μL, and the oxygen sensor protective layer passes the shock thermal cycle test.

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