Waterproof thermal insulation coating as well as preparation method and application thereof

Abstract

The invention discloses a waterproof thermal insulation coating as well as a preparation method and application thereof, relates to the technical field of coating materials, and ensures the bonding strength and thermal shock resistance of the coating and a matrix while simplifying the process. The aluminum oxide waterproof heat preservation coating is of a double-layer structure, wherein the first layer is a pure aluminum oxide coating; the second layer is an aluminum oxide / magnesium aluminate spinel mixed coating, wherein the mass ratio of aluminum oxide to magnesium aluminate spinel is 1: 1; the aluminum oxide waterproof heat preservation coating is coated on the surface of the substrate through a dip coating method, and is formed through a one-step sintering process after being dried. The method is applied to protection of the zirconia ceramic chip of the nitrogen-oxygen gas sensor, balance among coating binding force, thermal stability and waterproofness is achieved through double-layer structure design, dispersion process optimization and a one-step sintering activation method, and an innovative solution is provided for a high-reliability sensor coating.

Description

Technical Field

[0001] The present invention relates to the technical field of coating materials, and in particular to a waterproof and thermal insulation coating, a preparation method thereof, and an application 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 the sensor is operating, high-velocity gas, condensed water, and water vapor in the exhaust gas can impact the chip surface. This can cause uneven heating of the chip, generating stress within the material, leading to cracks and failure. Therefore, preparing a protective coating for the chip that combines waterproofing and thermal insulation is key to improving sensor reliability.

[0005] There are already relevant solutions to this problem in the existing technology. For example, a Chinese patent document (application number 201210042762.9) discloses a multi-level aluminum oxide protective coating that achieves the dual functions of waterproofing and heat insulation through a "porous-dense-porous" layered design. However, this technology requires the chip to be sintered twice to complete the interlayer anchoring. Multiple high-temperature treatment processes are likely to have a significant negative impact on the chip sensitivity, measurement accuracy and electrode catalytic activity. In addition, when preparing aluminum oxide coating powder, the traditional wet mechanical crushing process increases the surface energy of the powder due to mechanical force. As the crushing time increases, the powder agglomeration phenomenon intensifies, and then during the sintering process, stress concentration causes defects such as cracking and shedding of the coating.

[0006] In order to overcome the above technical bottlenecks, it is urgent to develop a new type of coating and its preparation method to simplify the process while ensuring the bonding strength and thermal shock resistance between the coating and the substrate. Summary of the Invention

[0007] In order to prepare a chip protection coating with both waterproof and heat-insulating functions and improve the reliability of the sensor, the present invention proposes a waterproof and heat-insulating coating and its preparation method and application.

[0008] The technical solutions of the present invention are as follows: An aluminum oxide waterproof and thermal insulation coating, the aluminum oxide waterproof and thermal insulation coating has a double-layer structure, the first layer is a pure aluminum oxide coating; the second layer is an aluminum oxide / magnesium aluminum spinel mixed coating, wherein the mass ratio of the aluminum oxide to the magnesium aluminum spinel is 1:1; The aluminum oxide waterproof and thermal insulation coating is coated on the surface of the substrate by a dipping method and is formed by a one-step sintering process after drying.

[0009] Preferably, the thickness of the first layer is 0.1 mm, and the thickness of the second layer is 1.0 mm.

[0010] The present invention also provides a method for preparing the above-mentioned aluminum oxide waterproof and thermal insulation coating, comprising the following steps: S1. Preparation of alumina slurry: PVA, anhydrous ethanol and cod liver oil were sealed and stirred at 90°C to form the first solvent; Adding the first alumina ceramic powder into the first solvent and grinding it thoroughly using a planetary ball mill; The ground slurry is placed in a stainless steel vacuum degassing tank for degassing to obtain alumina slurry; S2. Preparation of alumina / magnesium aluminum spinel mixed slurry: PVA, anhydrous ethanol and cod liver oil were sealed and stirred at 90°C to form the second solvent; Adding the second alumina ceramic powder and the magnesium aluminum spinel powder into the second solvent, and grinding them thoroughly using a planetary ball mill; The ground slurry is placed in a stainless steel vacuum degassing tank for degassing to obtain an alumina / magnesium aluminum spinel mixed slurry; S3. Apply the alumina slurry to the surface of the substrate and dry it, then further apply the alumina / magnesium aluminum spinel mixed slurry on the surface, dry it, heat it to 1300°C for high-temperature sintering, and then keep it warm to obtain an alumina waterproof and thermal insulation coating.

[0011] Preferably, the purity of the first alumina ceramic powder is 3N and the median particle size is 500 nm; The purity of the second alumina ceramic powder is 3N, and the median particle size is 1 μm; the purity of the magnesia alumina spinel powder is 3N, and the median particle size is 10 μm; the mass ratio of the second alumina ceramic powder to the magnesia alumina spinel powder is 1:1.

[0012] Preferably, the mass ratio of PVA, anhydrous ethanol, cod liver oil and the first alumina ceramic powder in step S1 is 1:8:0.4:10; the mass ratio of PVA, anhydrous ethanol, cod liver oil, the second alumina ceramic powder and magnesia alumina spinel powder in step S2 is 2:16:0.4:10:10.

[0013] Preferably, the stirring speed in step S1 and step S2 is both 600 r / min, and the stirring time is both 1 h.

[0014] Preferably, the parameters of the planetary ball mill in step S1 are 800 r / min, and the grinding time is 8 hours; the parameters of the planetary ball mill in step S2 are 600 r / min, and the stirring time is 5 hours.

[0015] Preferably, the vacuum degree of the degassing treatment in step S1 is -0.095 MPa, and the degassing treatment time is 1 hour; the vacuum degree of the degassing treatment in step S2 is -0.095 MPa, and the degassing treatment time is 2 hours.

[0016] Preferably, the heating rate in step S3 is 5-10° C. / min, and the holding time is 2-5 h.

[0017] The present invention also provides an application of the above-mentioned aluminum oxide waterproof and thermal insulation coating, specifically, application in protecting zirconium oxide ceramic chips of nitrogen and oxygen gas sensors.

[0018] Compared with the prior art, the present invention has the following specific beneficial effects: 1. This invention utilizes a dual-layer gradient composite coating, utilizing the synergistic effect of nano- and micron-sized particles to achieve dual waterproofing and thermal insulation. The inner layer, composed of dense alumina dispersed in an alcohol-solvent system, forms a low-porosity barrier, blocking water penetration. The outer mixed layer creates a gradient pore structure, leveraging the low thermal conductivity of spinel to reduce heat loss. Thermal expansion coefficient matching also buffers thermal stress, ensuring the coating remains crack-free after 10,000 cycles of thermal cycling at 840°C.

[0019] 2. This invention incorporates steric hindrance and a one-step sintering process, addressing the shortcomings of traditional processes. The alcohol-solvent dispersion system, through the dual effects of electrostatic repulsion and steric hindrance, inhibits nano-alumina agglomeration, resulting in a uniform slurry particle size distribution and avoiding the stress concentration caused by traditional wet mechanical crushing. The one-step sintering activation method simultaneously achieves coating densification and interfacial chemical bonding in a single high-temperature process, enhancing bonding strength and withstanding 500 50 m / s gas shocks without damage. The risk of cracking is significantly reduced compared to the traditional two-step sintering process.

[0020] 3. This invention achieves efficient production through slurry formulation optimization and process integration. Simultaneous sintering of the two coating layers eliminates the intermediate layer anchoring step, compressing traditional multiple sintering processes into a single pass and significantly reducing energy consumption. The alcohol solvent system improves powder utilization, significantly enhancing production line compatibility and scalable production feasibility while maintaining coating performance. DETAILED DESCRIPTION

[0021] In order to make the technical solution of the present invention clearer, the technical solution in the embodiments of the present invention is 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.

[0022] Example 1. In this embodiment, the coating material is prepared according to the following steps: (1) Preparation process of alumina slurry: Step 1: Prepare the organic solvent: first, seal and stir 1g PVA, 8g anhydrous ethanol, and 0.4g cod liver oil at 90°C for 1h at a stirring speed of 600r / min.

[0023] Step 2: Prepare ceramic slurry: Add 10 g of alumina ceramic powder to the solvent system of the above "step 1" and grind it thoroughly for 8 hours using a planetary ball mill at 800 r / min.

[0024] Step 3: Degassing of the slurry: Place the ground slurry in a stainless steel vacuum degassing tank with a vacuum degree of -0.095 MPa for degassing for 1 hour.

[0025] The parameters of the alumina ceramic raw material powder used are as follows: The purity is 3N and the median particle size (D50) is 500nm.

[0026] (2) Preparation process of alumina / magnesium aluminum spinel mixed slurry: Step 1: Prepare the organic solvent: First, seal and stir 2g PVA, 16g anhydrous ethanol, and 0.4g cod liver oil at 90°C for 1h at a stirring speed of 600r / min.

[0027] Step 2: Prepare ceramic slurry: add 10g of alumina and 10g of magnesium aluminum spinel powder into the solvent system of the above "step 1", and grind them thoroughly for 5h using a planetary ball mill at 600r / min.

[0028] Step 3: Degassing of the slurry: Place the ground slurry in a stainless steel vacuum degassing tank with a vacuum degree of -0.095 MPa for degassing for 2 hours.

[0029] The parameters of the alumina / magnesium aluminum spinel ceramic raw material powder used are as follows: The purity of the alumina raw material powder used was 3N, and the median particle size (D50) was 1 μm; The purity of the magnesium aluminum spinel raw material powder used is 3N, and the median particle size (D50) is 10 μm.

[0030] (3) Apply alumina slurry to the surface of the chip head and dry it. Then apply alumina / magnesium aluminum spinel mixed slurry to the surface of the chip head with alumina slurry. After drying, increase the temperature to 1300℃ at a rate of 5~10℃ / min, perform high-temperature sintering at 1300℃, and then keep it warm for 2~5h.

[0031] Comparative Example 1. (1) In this embodiment, the coating material is prepared according to the following steps: Alumina slurry preparation process: Step 1: Prepare the organic solvent: first, seal and stir 1g PVA, 8g anhydrous ethanol, and 0.4g cod liver oil at 90°C for 1h at a stirring speed of 600r / min.

[0032] Step 2: Prepare ceramic slurry: Add 10 g of alumina ceramic powder to the solvent system of the above "step 1" and grind it thoroughly for 8 hours using a planetary ball mill at 800 r / min.

[0033] Step 3: Degassing of the slurry: Place the ground slurry in a stainless steel vacuum degassing tank with a vacuum degree of -0.095 MPa for degassing for 1 hour.

[0034] The parameters of the alumina ceramic raw material powder used are as follows: The purity is 3N and the median particle size (D50) is 500nm.

[0035] (2) Apply alumina slurry to the surface of the chip head and dry it, then heat it to 1300℃ at a rate of 5~10℃ / min, sinter it at 1300℃, and keep it warm for 2~5h.

[0036] Comparative Example 2. In this embodiment, the coating material is prepared according to the following steps: (1) Preparation process of alumina / magnesium aluminum spinel mixed slurry: Step 1: Prepare the organic solvent: First, seal and stir 2g PVA, 16g anhydrous ethanol, and 0.4g cod liver oil at 90°C for 1h at a stirring speed of 600r / min.

[0037] Step 2: Prepare ceramic slurry: add 10g of alumina and 10g of magnesium aluminum spinel powder into the solvent system of the above "step 1", and grind them thoroughly for 5h using a planetary ball mill at 600r / min.

[0038] Step 3: Degassing of the slurry: Place the ground slurry in a stainless steel vacuum degassing tank with a vacuum degree of -0.095 MPa for degassing for 2 hours.

[0039] The parameters of the alumina / magnesium aluminum spinel ceramic raw material powder used are as follows: The purity of the alumina raw material powder used was 3N, and the median particle size (D50) was 1 μm; The purity of the magnesium aluminum spinel raw material powder used is 3N, and the median particle size (D50) is 10 μm.

[0040] (2) Apply the alumina / magnesium aluminum spinel mixed slurry on the surface of the chip head, dry it, and then heat it to 1300℃ at a rate of 5~10℃ / min, sinter it at 1300℃, and keep it warm for 2~5h.

[0041] Comparative Example 3. Coating materials are prepared using conventional wet mechanical crushing processes: (1) Preparation process of alumina slurry: Step 1: Prepare slurry: Use 6g of deionized water as solvent, add 10g of alumina powder and 0.3g of dispersant, and use a planetary ball mill at a speed of 400r / min for 30min for pre-dispersion.

[0042] Step 2: Add 2 g of PVA to the slurry system of "Step 1" and use a planetary ball mill for ball milling at a speed of 800 r / min for 12 h, and record the change in powder particle size over time.

[0043] Step 3: Slurry degassing treatment: Place the ground slurry in a stainless steel vacuum degassing tank with a vacuum degree of -0.095MPa for degassing treatment for 2h.

[0044] The parameters of the alumina raw material powder and PVA used are as follows: The purity of the alumina raw material powder used was 3N and the median particle size (D50) was 1 μm.

[0045] The PVA used is water-soluble.

[0046] (2) Preparation process of alumina / magnesium aluminum spinel mixed slurry: Step 1: Prepare ceramic slurry: Use 13g deionized water as solvent, add 10g alumina powder, 10g magnesia spinel powder and 0.6g dispersant, and use a planetary ball mill at 400r / min speed for 30min for pre-dispersion.

[0047] Step 2: Add 4 g of PVA to the slurry system of "Step 1" and use a planetary ball mill for ball milling at a speed of 800 r / min for 12 h.

[0048] Step 3: Slurry degassing treatment: Place the ground slurry in a stainless steel vacuum degassing tank with a vacuum degree of -0.095MPa for degassing treatment for 2h.

[0049] The parameters of the alumina / magnesium aluminum spinel ceramic raw material powder used are as follows: The purity of the alumina raw material powder used was 3N, and the median particle size (D50) was 1 μm; The purity of the magnesium aluminum spinel raw material powder used is 3N, and the median particle size (D50) is 10 μm.

[0050] The PVA used is water-soluble.

[0051] (3) Apply alumina slurry to the surface of the chip head and dry it. Then apply alumina / magnesium aluminum spinel mixed slurry to the surface of the chip head with alumina slurry. After drying, increase the temperature to 1300℃ at a rate of 5~10℃ / min, perform high-temperature sintering at 1300℃, and then keep it warm for 2~5h.

[0052] Due to low grinding efficiency and poor slurry dispersion, cracks, peeling and local agglomeration of the waterproof and thermal insulation coating surface can be observed after coating and sintering, making it impossible to assemble the finished product for subsequent testing.

[0053] Effect example. The coated chip components and uncoated chip components prepared in the above embodiments and comparative examples were subjected to performance tests, including high-flow gas shock, hot and cold cycle startup, thermal shock resistance and water dripping tests, with 16 samples in each test.

[0054] The nitrogen and oxygen sensor chip was operated at 840°C and subjected to 500 repeated impacts of 50 m / s high-velocity gas. The coating and sensor element in Example 1 showed no damage or cracks and were able to operate normally. However, the coatings or elements in the comparative examples were damaged to varying degrees.

[0055] When the nitrogen oxide sensor chip was operated at 840°C and started and stopped hot and cold 10,000 times, the coating and sensor element in Example 1 showed no damage or cracks and could work normally; while the coatings or elements in Comparative Examples 1 and 3 were damaged to varying degrees.

[0056] When the nitrogen and oxygen sensor chip was operated at 840° C. and under vibration for 20,000 hours, the coating and sensor element in Example 1 showed no damage or cracks and could operate normally; whereas the coatings or elements in the comparative examples were damaged to varying degrees.

[0057] The nitrogen oxygen sensor chip was subjected to a water dripping test at a rate of 1 mL / min under an operating temperature of 840°C. The coating and sensor element in Example 1 showed no damage or cracks and were able to operate normally; however, the coatings or elements in the comparative examples were damaged to varying degrees.

[0058] The above specific experimental results are shown in Table 1.

[0059] Table 1

[0060] The above experimental results can prove that the present invention first achieves synergistic effect through a double-layer structure. The first layer of pure alumina effectively blocks water penetration, and the dense structure slows down heat loss, but does not completely isolate heat conduction to avoid local overheating. The thermal expansion coefficient of the second layer of magnesium aluminum spinel is close to that of the zirconium oxide substrate of the sensor chip, which reduces the interfacial thermal stress; the micron-sized spinel is mixed with submicron-sized alumina to form a pore gradient structure, which enhances the thermal insulation performance and absorbs thermal stress. Secondly, the present invention optimizes the one-step sintering process so that the two layers of material diffuse with each other in the melting stage to form chemical bonds, thereby improving the bonding strength; and the heating rate and the holding time match the sintering dynamics of the material to reduce residual stress and avoid cracking. In addition, the dispersion process of the present invention has also been innovated. The cod liver oil and PVA work synergistically to inhibit the agglomeration of nano-alumina through electrostatic repulsion and steric hindrance, thereby improving the uniformity of the slurry. Combined with vacuum degassing, compared with traditional wet crushing, it has the advantages of a waterproof and heat-insulating slurry with uniform particle size distribution, eliminating pore defects.

[0061] In summary, the present invention achieves a balance between coating adhesion, thermal stability, and water resistance through a double-layer structure design, dispersion process optimization, and a one-step sintering activation method, providing an innovative solution for high-reliability sensor coatings.

[0062] 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. An aluminum oxide waterproof and thermal insulation coating, characterized in that: The alumina waterproof and thermal insulation coating has a double-layer structure, with the first layer being a pure alumina coating; The second layer is an aluminum oxide / magnesium aluminum spinel mixed coating, wherein the mass ratio of the aluminum oxide to the magnesium aluminum spinel is 1:1; The aluminum oxide waterproof and thermal insulation coating is coated on the surface of the substrate by a dipping method and is formed by a one-step sintering process after drying.

2. The alumina waterproof and thermal insulation coating according to claim 1, characterized in that: The thickness of the first layer is 0.1 mm, and the thickness of the second layer is 1.0 mm.

3. A method for preparing the aluminum oxide waterproof and thermal insulation coating according to claim 1 or 2, characterized in that: The steps include: S1. Preparation of alumina slurry: PVA, anhydrous ethanol and cod liver oil were sealed and stirred at 90°C to form the first solvent; Adding the first alumina ceramic powder into the first solvent and grinding it thoroughly using a planetary ball mill; The ground slurry is placed in a stainless steel vacuum degassing tank for degassing to obtain alumina slurry; S2. Preparation of alumina / magnesium aluminum spinel mixed slurry: PVA, anhydrous ethanol and cod liver oil were sealed and stirred at 90°C to form the second solvent; Adding the second alumina ceramic powder and the magnesium aluminum spinel powder into the second solvent, and grinding them thoroughly using a planetary ball mill; The ground slurry is placed in a stainless steel vacuum degassing tank for degassing to obtain an alumina / magnesium aluminum spinel mixed slurry; S3. Apply the alumina slurry to the surface of the substrate and dry it, then further apply the alumina / magnesium aluminum spinel mixed slurry on the surface, dry it, heat it to 1300°C for high-temperature sintering, and then keep it warm to obtain an alumina waterproof and thermal insulation coating.

4. The method for preparing the aluminum oxide waterproof and thermal insulation coating according to claim 3, characterized in that: The purity of the first alumina ceramic powder is 3N, and the median particle size is 500 nm; The purity of the second alumina ceramic powder is 3N, and the median particle size is 1 μm; the purity of the magnesia alumina spinel powder is 3N, and the median particle size is 10 μm; the mass ratio of the second alumina ceramic powder to the magnesia alumina spinel powder is 1:

1.

5. The method for preparing the aluminum oxide waterproof and thermal insulation coating according to claim 3, characterized in that: The mass ratio of PVA, anhydrous ethanol, cod liver oil and the first alumina ceramic powder in step S1 is 1:8:0.4:10; the mass ratio of PVA, anhydrous ethanol, cod liver oil, the second alumina ceramic powder and magnesium aluminum spinel powder in step S2 is 2:16:0.4:10:

10.

6. The method for preparing the aluminum oxide waterproof and thermal insulation coating according to claim 3, characterized in that: The stirring speed in step S1 and step S2 is both 600 r / min, and the stirring time is both 1 h.

7. The method for preparing the aluminum oxide waterproof and thermal insulation coating according to claim 3, characterized in that: The parameters of the planetary ball mill in step S1 are 800 r / min, and the grinding time is 8 hours; the parameters of the planetary ball mill in step S2 are 600 r / min, and the grinding time is 5 hours.

8. The method for preparing the aluminum oxide waterproof and thermal insulation coating according to claim 3, characterized in that: The vacuum degree of the degassing treatment in step S1 is -0.095 MPa, and the degassing treatment time is 1 hour; the vacuum degree of the degassing treatment in step S2 is -0.095 MPa, and the degassing treatment time is 2 hours.

9. The method for preparing the aluminum oxide waterproof and thermal insulation coating according to claim 3, characterized in that: The heating rate in step S3 is 5-10°C / min, and the holding time is 2-5h.

10. An application of the aluminum oxide waterproof and thermal insulation coating as claimed in claim 1 or 2, characterized in that: Zirconia ceramic chip protection for nitrogen and oxygen gas sensors.

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