Alumina waterproof heat-insulating coating as well as preparation method and application thereof

Abstract

The invention discloses an aluminum oxide waterproof heat-insulating coating as well as a preparation method and application thereof, relates to the technical field of coating materials, and solves the problem that an existing protective coating material cannot meet the requirements of a high-precision chip on interface bonding strength and thermal mechanical stability of a densified coating. The coating comprises loose and porous aluminum oxide slurry A and relatively dense aluminum oxide slurry B, the aluminum oxide slurry A is printed on the surface of the chip blank through the printing process and dried, and the aluminum oxide slurry A is a first layer sintered at high temperature; printing the aluminum oxide slurry B on the surface of the chip blank with the aluminum oxide coating A, and drying, wherein the aluminum oxide slurry B is a second layer of low-temperature sintering; the method can be applied to protection of the zirconia ceramic chip in the nitrogen-oxygen sensor, and has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of coating materials, and in particular to an aluminum oxide waterproof and heat-insulating coating, a preparation method thereof, and applications thereof. Background Art

[0002] NOx is one of the main components of air pollution, and its source mainly comes from the gas emitted by automobile internal combustion engines. In order to solve the NOx emission problem, nitrogen oxide sensors are usually used to measure the concentration of nitrogen oxides (NOx) in internal combustion engine emissions.

[0003] The core component of the NOx sensor is a zirconia ceramic chip. Pt electrodes are printed on both sides of the solidified ZrO2 green ceramic chip. Under high-temperature operating conditions, when a specific voltage is applied to the chip electrodes, NOx and O2 enter the chamber through the gas channel. The redox reaction generates a current in a closed loop, allowing the NOx and O2 levels to be measured by detecting the current signal.

[0004] However, when operating, the high-velocity gas and water vapor in exhaust gas can impact the chip surface, causing the chip to lose temperature too quickly, leading to cracks and failure. Furthermore, when not operating, condensed water and oil deposited on the chip head can also trigger thermal shock from the sensor, causing cracks and failure of the NOx sensor. Therefore, the key to improving chip sensor reliability lies in developing protective coating technology that combines waterproofing and thermal insulation.

[0005] At present, the common coating preparation processes are mainly plasma spraying and pulling and dipping. However, both have certain defects. The plasma spraying method requires the coating to be melted at a high temperature of more than 2000°C and then sprayed out at high speed. The extreme temperature and spraying pressure can easily lead to thermal stress concentration in the ceramic chip, causing structural fracture. There are problems such as uneven thickness and excessive porosity in the film formation process of the pulling and dipping method. The loose porous structure produces stress concentration under thermal cycle loads, which causes the coating to crack and fail, and the thermal shock resistance is significantly reduced. In summary, it is urgent to develop a new film-forming technology that has both waterproof and heat-insulating functions and meets the interface bonding strength and thermomechanical stability requirements of high-precision chips for densified coatings. Summary of the Invention

[0006] In order to solve the problem that existing protective coating materials cannot meet the interface bonding strength and thermomechanical stability requirements of high-precision chips for densified coatings, the present invention proposes an aluminum oxide waterproof and thermal insulation coating, a preparation method and application thereof.

[0007] The technical solutions of the present invention are as follows: A method for preparing an aluminum oxide waterproof and heat-insulating coating comprises the following steps: S1. Preparation of alumina slurry A: S11. Thoroughly stirring and mixing terpineol, butyl acetate, isophorone, and ethyl cellulose at 80° C. in a sealed condition to form a uniform organic system; S12, fully mixing the activated carbon powder, nano zirconium oxide powder and nano alumina powder using a V mixer to obtain a mixed powder; S13, stirring the organic system and the mixed powder, stirring evenly, grinding and dispersing with a ceramic three-roll mill, vacuum stirring, and then centrifuging for degassing; S2, printing alumina slurry A onto the surface of the chip embryo and drying it, heating it to 1450℃~1500℃ for high temperature sintering, and then keeping it warm; S3. Preparation of alumina slurry B: S31. Thoroughly stir and mix terpineol, butyl acetate, isophorone, and ethyl cellulose under closed conditions at 80° C. to form a uniform organic system; S32, fully mixing the magnesium aluminum spinel powder and the nano-alumina powder using a V mixer to obtain a mixed powder; S33, mixing the organic system with the mixed powder, stirring evenly, grinding and dispersing with a ceramic three-roll mill, vacuum stirring, and then centrifuging for degassing; S4. Printing alumina slurry B onto the surface of the chip embryo with the alumina coating A obtained in step S2 and drying it, heating it to 1100° C. to 1200° C. for low-temperature sintering, and then keeping it warm to obtain an alumina waterproof and heat-insulating coating.

[0008] Preferably, in step S12, the particle size of the activated carbon powder is 10-50 nm; the particle size of the nano-alumina powder is 50-500 nm; and the particle size of the nano-zirconia powder is 50-500 nm. The particle size of the magnesium aluminum spinel powder in step S32 is 20-80 nm; the particle size of the nano alumina powder is 20-100 nm.

[0009] Preferably, the mass ratio of the activated carbon powder, nano zirconium oxide powder, nano alumina powder, terpineol, butyl acetate, isophorone, and ethyl cellulose in step S1 is 10:0.3-0.35:40-41:2:6-6.5:1.5:7-8; The mass ratio of the magnesium aluminum spinel powder, nano-alumina powder, terpineol, butyl acetate, isophorone, and ethyl cellulose in step S3 is 1-1.1:38.5-40:2-3:5.6-6.5:1.5:6.5-7.5.

[0010] Preferably, the stirring speed in step S11, step S13, step S31 and step S33 is 40 r / min, and the stirring time is 1 hour.

[0011] Preferably, the stirring rate of the V-type stirrer in step S12 and step S32 is 300 Hz / min, and the stirring time is 3 hours.

[0012] Preferably, the grinding rate of the ceramic three-roller grinder in step S13 and step S33 is 20 Hz / min, the grinding time is 30 min, and the material of the ceramic roller is zirconia.

[0013] Preferably, the vacuum stirring and centrifugal degassing in step S13 and step S33 adopt a non-contact planetary stirring vacuum degassing integrated machine, the vacuum degree is -0.095 MPa, and the degassing time is 1 hour.

[0014] Preferably, the drying temperature in step S2 and step S4 is 70-150° C., the drying time is 30 min, the heating rate is 0.5-1° C. / min, and the holding time is 2-5 h.

[0015] The present invention also provides an aluminum oxide waterproof and heat-insulating coating, which is prepared using the above-mentioned preparation method.

[0016] The present invention also provides an application of the above-mentioned aluminum oxide waterproof and heat-insulating coating, which is specifically applied to the protection of zirconium oxide ceramic chips in nitrogen and oxygen sensors.

[0017] Compared with the prior art, the present invention has the following specific beneficial effects: The present invention employs a differentiated porosity matching strategy to construct a composite protective system consisting of a high-porosity alumina coating A and a low-porosity alumina coating B. Coating A, serving as the base support layer, is sintered and formed simultaneously during the chip embryonic stage. Its porous structure not only achieves mechanical interlocking anchoring with the substrate but also forms a micron-scale ventilation network, which does not affect chip performance and significantly improves interfacial bonding strength while ensuring heat dissipation efficiency. Coating B, with its dense surface layer, uses a low-temperature secondary sintering process to achieve surface densification while avoiding thermal damage, forming a continuous and complete physical barrier layer. The two layers work synergistically to create a gradient protective system that combines stress buffering and dielectric barrier functions.

[0018] Experimental verification shows that the double-layer gradient pore structure designed in the present invention effectively disperses thermal stress, thereby improving the thermal shock resistance of the coating. The synergistic effect of the double-layer interface also greatly increases the bonding strength of the coating, eliminating interlayer cracking caused by hot and cold cycles. The process characteristics of printing and molding ensure that the coating thickness fluctuation is controlled within a reasonable range, allowing the chip to maintain performance stability under special working conditions. DETAILED DESCRIPTION

[0019] First of all, the current mainstream coating preparation processes include plasma spraying and pulling and dipping.

[0020] Plasma spraying is a type of thermal spraying process. Its operating principle is to use a plasma flame to heat and accelerate metal or ceramic powder within a short period of time. The molten or semi-molten powder then impacts the substrate at high speed, forming a layered coating that firmly adheres to the substrate surface. However, this process is affected by factors such as the powder feed rate, the spray gun structure, the operating current and voltage, and the working gas flow rate. Excessive powder flow rates prevent the powder from being fully melted, resulting in increased inclusions in the coating, increased porosity, and a loose structure, which reduces the bonding strength between the coatings. Excessive powder flow rates lead to low powder deposition efficiency, increasing spraying time to achieve a certain coating thickness, causing overheating and deformation of the substrate and reducing spraying efficiency. The substrate material of nitrogen oxide sensors is zirconium oxide. When heated above 2300°C, zirconium oxide transforms from a tetragonal to a cubic phase, indirectly affecting product performance. Therefore, plasma spraying is not suitable for preparing the thermal insulation and waterproofing layer of nitrogen oxide sensors.

[0021] The pull-and-dip method involves vertically immersing the substrate in an alumina composite solution / sol. Pulling begins by exploiting the interaction between the viscosity, surface tension, and gravity of the alumina composite solution. The pulling process must ensure the liquid surface remains vibration-free, and the substrate rises vertically, uniformly, and steadily, continuously, to ensure the formation of a continuous, uniform oxide film on the substrate surface. However, this method requires repeated pull-and-dip cycles, a long process cycle, and uncontrollable thickness, making it unsuitable for preparing the thermal insulation and waterproofing layer of nitrogen oxide sensors.

[0022] To this end, the present invention provides a new aluminum oxide waterproof and heat-insulating coating, which can realize the preparation of a heat-insulating and waterproof layer for nitrogen oxide sensors and has excellent performance.

[0023] In order to make the technical solution of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below. It should be noted that the following embodiments are only used to better understand the technical solution of the present invention and should not be understood as limiting the present invention.

[0024] The alumina waterproof coating for the nitrogen oxide sensor was prepared strictly according to the different formula ratios in Table 1 (ingredients of alumina slurry A) and Table 2 (ingredients of alumina slurry B). The coating included alumina slurry A and alumina slurry B. Alumina slurry A was used as the first layer sintered at high temperature, and alumina slurry B was used as the second layer sintered at low temperature. 1. Preparation of alumina slurry A: The first step is to prepare an organic system: terpineol, butyl acetate, isophorone, and ethyl cellulose are fully stirred and mixed at a temperature of 80° C. under closed conditions to form a uniform organic system; Step 2: Dispersion of porous alumina slurry: fully mix the activated carbon powder, nano zirconium oxide powder and nano alumina powder using a V mixer; The third step is to mix the organic system with the mixed powder of activated carbon powder, nano zirconium oxide powder and nano alumina powder in strict accordance with the formula ratio. After stirring evenly, grind and disperse it with a ceramic three-roll grinder, vacuum stir and centrifuge to degas. The ceramic roller is made of zirconium oxide.

[0025] A. The particle size of the high-activity carbon powder used is 10-50nm; B. The nano-alumina powder used is 50-500nm; C. The nano zirconium oxide powder used is 50-500nm.

[0026] Alumina slurry A is printed onto the surface of the chip embryo through a printing process and dried at 120°C for 30 minutes. It is then sintered at a high temperature of 1450°C~1500°C at a heating rate of <1°C / min and then kept warm for 3 hours to obtain a loose and porous alumina coating A.

[0027] Wherein, in step 1 and step 3, the stirrer speed is 40 r / min and the mixing time is 1 h; In step 2, the stirring rate of the V-type stirrer is 300 Hz / min, and the mixing time is 3 h; The three-roll mill speed in step 3 was 20 Hz / min and the mixing time was 30 min; The vacuum degree of the non-contact planetary stirring vacuum degassing machine is -0.095MPa, and the degassing time is 1h.

[0028] 2. Preparation of Alumina Slurry B: The first step is to prepare the organic system: terpineol, butyl acetate, isophorone, and ethyl cellulose are first stirred and mixed under closed conditions at a temperature of 80° C. to form a uniform organic system; Step 2: Dispersion of porous alumina slurry: Magnesium aluminum spinel powder and nano alumina powder are fully mixed using a V mixer; The third step is to mix the organic system with the mixed powder of magnesium aluminum spinel powder and nano alumina powder in strict accordance with the formula ratio, stir evenly and then grind and disperse with a ceramic three-roll grinder, and use non-contact planetary vacuum stirring centrifugal degassing. The ceramic roller is made of zirconia. A. The particle size of the magnesium aluminum spinel glass system powder used is 20-80nm; B. The nano-alumina powder used is 20-100nm; Alumina slurry B is printed onto the surface of the chip embryo with alumina coating A through a printing process, and is dried at 120°C for 30 minutes. Then, the temperature is raised to 1100°C~1200°C at a heating rate of <1°C / min and sintered at low temperature. The temperature is then kept at this temperature for 3 hours to obtain a chip with an alumina waterproof and thermal insulation coating.

[0029] Table 1

[0030] Table 2

[0031] Effect example. The coated chip components prepared in Examples 1 to 5 were subjected to performance tests, including thermal vibration resistance test, hot and cold start-stop test, and service life test. The test results are shown in Table 3.

[0032] Table 3

[0033] According to the above test results, the nitrogen oxide sensor chip worked at 840°C and under vibration for 20,000 hours. The coatings and sensor elements in Examples 1 to 5 showed no obvious damage or cracks and were able to work normally.

[0034] The nitrogen oxide sensor chip was operated at 840° C. and subjected to 10,000 hot and cold starts and stops. The coatings and sensor elements in Examples 1 to 5 showed no obvious damage or cracks and were able to operate normally.

[0035] The nitrogen oxide sensor chip was tested at 840°C and continuously operated for 20,000 hours in an automobile exhaust environment. After the test, the chip's appearance, size, resistance value and electrical performance still met the product specification requirements.

[0036] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing an aluminum oxide waterproof and heat-insulating coating, characterized in that: The alumina waterproof and heat-insulating coating comprises alumina slurry A and alumina slurry B, wherein the alumina slurry A is obtained by sintering the first layer and the alumina slurry B is obtained by sintering the second layer; The preparation method comprises the following steps: S1. Preparation of alumina slurry A: S11. Thoroughly stirring and mixing terpineol, butyl acetate, isophorone, and ethyl cellulose at 80° C. in a sealed condition to form a uniform organic system; S12, fully mixing the activated carbon powder, nano zirconium oxide powder and nano alumina powder using a V mixer to obtain a mixed powder; S13, stirring the organic system and the mixed powder, stirring evenly, grinding and dispersing with a ceramic three-roll mill, vacuum stirring, and then centrifuging for degassing; S2, printing alumina slurry A onto the surface of the chip embryo and drying it, heating it to 1450℃~1500℃ for sintering, and then keeping it warm; S3. Preparation of alumina slurry B: S31. Thoroughly stirring and mixing terpineol, butyl acetate, isophorone, and ethyl cellulose at 80° C. in a sealed environment to form a uniform organic system; S32, fully mixing the magnesium aluminum spinel powder and the nano-alumina powder using a V mixer to obtain a mixed powder; S33, mixing the organic system with the mixed powder, stirring evenly, grinding and dispersing with a ceramic three-roll mill, vacuum stirring, and then centrifuging for degassing; S4. Printing alumina slurry B onto the surface of the chip embryo with the alumina coating A obtained in step S2 and drying it, heating it to 1100° C. to 1200° C. for sintering, and then keeping it warm to obtain an alumina waterproof and heat-insulating coating.

2. The method for preparing the aluminum oxide waterproof and heat-insulating coating according to claim 1, characterized in that: In step S12, the particle size of the activated carbon powder is 10-50 nm; the particle size of the nano-alumina powder is 50-500 nm; and the particle size of the nano-zirconia powder is 50-500 nm. The particle size of the magnesium aluminum spinel powder in step S32 is 20-80 nm; the particle size of the nano alumina powder is 20-100 nm.

3. The method for preparing the aluminum oxide waterproof and heat-insulating coating according to claim 1, characterized in that: The mass ratio of the activated carbon powder, nano zirconium oxide powder, nano alumina powder, terpineol, butyl acetate, isophorone, and ethyl cellulose in step S1 is 10:0.3-0.35:40-41:2:6-6.5:1.5:7-8; The mass ratio of the magnesium aluminum spinel powder, nano-alumina powder, terpineol, butyl acetate, isophorone, and ethyl cellulose in step S3 is 1-1.1:38.5-40:2-3:5.6-6.5:1.5:6.5-7.

5.

4. The method for preparing the aluminum oxide waterproof and heat-insulating coating according to claim 1, characterized in that: The stirring speed in step S11, step S13, step S31 and step S33 is 40 r / min, and the stirring time is 1 hour.

5. The method for preparing the aluminum oxide waterproof and heat-insulating coating according to claim 1, characterized in that: The stirring rate of the V-type stirrer in step S12 and step S32 is 300 Hz / min, and the stirring time is 3 h.

6. The method for preparing the aluminum oxide waterproof and heat-insulating coating according to claim 1, characterized in that: The grinding rate of the ceramic three-roller grinder in step S13 and step S33 is 20 Hz / min, the grinding time is 30 min, and the material of the ceramic roller is zirconia.

7. The method for preparing the aluminum oxide waterproof and heat-insulating coating according to claim 1, characterized in that: The vacuum stirring and centrifugal degassing in step S13 and step S33 adopt a non-contact planetary stirring vacuum degassing integrated machine with a vacuum degree of -0.095 MPa and a degassing time of 1 hour.

8. The method for preparing the aluminum oxide waterproof and heat-insulating coating according to claim 1, characterized in that: The drying temperature in step S2 and step S4 is 70-150° C., the drying time is 30 min, the heating rate is 0.5-1° C. / min, and the holding time is 2-5 h.

9. An aluminum oxide waterproof and heat-insulating coating, characterized in that: The method is prepared according to any one of claims 1 to 8.

10. An application of the aluminum oxide waterproof and heat-insulating coating according to claim 9, characterized in that: Used to protect zirconium oxide ceramic chips in nitrogen and oxygen sensors.

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