A low-thermal-conductivity, high-temperature-resistant, structurally ordered nanolayered calcium niobate thermal barrier coating and a preparation method thereof

Abstract

The application provides a low-thermal-conductivity, high-temperature-resistant, structure-ordered nanometer-layered calcium niobate heat-insulating coating, which has the advantages of low thermal conductivity and good thermal stability, and is suitable for being applied to a substrate with a heat-resistant temperature higher than 500 DEG C. Meanwhile, the application also provides a preparation method of the heat-insulating coating, which has the advantages of simple process, easy operation and high efficiency, and is suitable for large-scale application.

Description

Technical Field

[0001] This invention relates to a layered nano-oxide, specifically, to a low thermal conductivity, high temperature resistant, structurally ordered nano-layered calcium niobate heat-insulating coating and its preparation method. Background Technology

[0002] Calcium niobate is a widely used semiconductor material. For example, Chinese patent CN106478090A discloses a bismuth titanate-calcium niobate solid solution used in capacitors, resonators, filters, circuit substrates, integrated circuits, etc.; Chinese patent CN1847471A discloses a neodymium-doped calcium niobate self-frequency doubling laser crystal used in solid-state lasers in spectroscopy, biomedicine, and military fields; and Chinese patent CN105778908A discloses a calcium niobate-based self-activated light-emitting material used in lighting and display fields. However, there are few reports on the thermal insulation properties of calcium niobate. In particular, layered nano-calcium niobate exhibits strong anisotropy, and utilizing its layered structure requires the fabrication of an ordered stacked structure, which is difficult to prepare and limits its application in the thermal insulation field.

[0003] Layer-by-layer self-assembly (LbL) is a simple and inexpensive multilayer formation process that reassembles two-dimensional nanosheets to obtain ordered structures. However, LbL suffers from drawbacks such as low efficiency and difficulty in thick film fabrication. Furthermore, the wet process of assembling two-dimensional nanosheets layer by layer to prepare ordered nanolayered coatings reduces the thermal stability of the coating, posing a challenge to the preparation of high-temperature resistant ordered layered coatings.

[0004] In order to solve the above problems, people have been seeking an ideal technological solution. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a low thermal conductivity, high temperature resistant, structurally ordered nanolayered calcium niobate heat insulation coating and its preparation method.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A low thermal conductivity, high temperature resistant, and structurally ordered nanolayered calcium niobate heat insulation coating is applied to substrates with heat resistance temperatures above 500℃.

[0008] The substrate is Si, glass, 718 nickel alloy or galvanized iron sheet.

[0009] A method for preparing the aforementioned heat-insulating coating includes the following steps:

[0010] The substrate is preheated, and then the precursor solution is sprayed onto the substrate surface. After spraying, the substrate is annealed at 300-500℃ to obtain the product. The annealing holding time is 3-4 hours, and the annealing heating rate is 5-10℃ / min.

[0011] The preparation steps of the precursor solution include: mixing a potassium salt solution with a calcium niobate nanosheet suspension to obtain a mixed solution, and then adding ethanol to the mixed solution to obtain the precursor solution. The preparation method of the calcium niobate nanosheet suspension is as follows: dispersing solid acid (calcium niobate hydrogen HCNO) powder at a ratio of 0.1g:20ml water, then adding 7.5μL of tetrabutylammonium hydroxide (TBAOH) as an organic base to exfoliate the layered solid acid HCNO, and stirring for 4 days to obtain the calcium niobate suspension.

[0012] The potassium salt solution is an aqueous solution of K2CO3, K2SO4, KCl or CH3COOK; the concentration of the potassium salt solution is 0.05-0.1 mol / L; the concentration of the calcium niobate nanosheet suspension is 0.12-0.50 g / L; the volume ratio of the potassium salt solution to the calcium niobate nanosheet suspension is 1:(15-40); the volume ratio of ethanol to the mixture is (1-8):1.

[0013] In the preparation step of the precursor solution, a potassium salt solution is added dropwise to the calcium niobate nanosheet suspension while stirring it.

[0014] The substrate preheating temperature is 120-200℃, and the preheating time is 1-2 minutes.

[0015] The coating is applied using a pneumatic spraying device, which includes an inert gas supply unit, a syringe pump, a syringe, an atomizing nozzle, and a heating platform. The substrate is placed on the heating platform, with the atomizing nozzle facing the substrate.

[0016] The distance between the atomizing nozzle and the substrate is 10-20cm.

[0017] During the spraying process, the gas flow rate of the pneumatic spraying device is 10.0-17.5 L / min, and the injection rate of the precursor solution is 0.3-1.0 mL / min.

[0018] This invention represents a significant advancement and substantial improvement over existing technologies. Specifically, it provides a low thermal conductivity, high temperature resistant, and structurally ordered nanolayered calcium niobate thermal insulation coating. This coating exhibits advantages such as low thermal conductivity and good thermal stability, making it suitable for application on substrates with heat resistance temperatures exceeding 500°C. Furthermore, this invention provides a method for preparing this thermal insulation coating, which is simple, easy to operate, and highly efficient, making it suitable for large-scale applications. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a pneumatic spraying device.

[0020] Figure 2 Images of the coatings prepared under substrate preheating temperatures of 80℃ and 160℃ are shown. Figure 2 (a) is 80℃; Figure 2 (b) is 160℃.

[0021] Figure 3 These are laser confocal microscopy images obtained after deposition on a Si substrate for 5 s at gas flow rates of 7.5 L / min and 15 L / min, respectively. Figure 3 (a) is 7.5 L / min; Figure 3 (b) is 15 L / min.

[0022] Figure 4 XRD patterns of calcium niobate nano-insulating coating after annealing at 200℃ and 400℃; Figure 4 (a) Annealing at 200℃; Figure 4 (b) Annealing at 400℃.

[0023] Figure 5 SEM images of the planar and cross-sectional sections of the calcium niobate nano-insulating coating; Figure 5 (a) is a planar SEM image; Figure 5 (b) is a cross-sectional SEM image.

[0024] Figure 6 XRD patterns of ordered calcium niobate nanocoatings and ordered potassium ion-intercalated calcium niobate nanocoatings after annealing at different temperatures. Figure 6 (a) XRD patterns of the ordered calcium niobate nanocoating after annealing at different temperatures; Figure 6 (b) shows the XRD patterns of the ordered potassium ion-intercalated calcium niobate nanocoating after annealing at different temperatures.

[0025] Figure 7 XRD patterns, planar and cross-sectional SEM images of the coating prepared in Example 3. Figure 7 (a) is the XRD pattern of the coating; Figure 7 (b) is a planar SEM image of the coating; Figure 7 (c) is a cross-sectional SEM image of the coating.

[0026] Figure 8 XRD patterns, planar and cross-sectional SEM images of the coating prepared in Example 4. Figure 8 (a) is the XRD pattern of the coating; Figure 8 (b) is a planar SEM image of the coating; Figure 8 (c) is a cross-sectional SEM image of the coating. Detailed Implementation

[0027] The technical solution of the present invention will be further described in detail below through specific embodiments. It should be noted that in the following embodiments, the pneumatic spraying uses existing pneumatic spraying equipment, as long as it meets the usage requirements of the present invention. Specifically, the pneumatic spraying equipment typically includes a gas path control section and a coating deposition section. The pneumatic spraying device includes an inert gas supply section, a syringe pump, a 5mL-50mL syringe, a plastic conduit, an atomizing nozzle, and a heating platform. The syringe is connected to the hose, the hose is connected to the atomizing nozzle, and the gas conduit is connected to the atomizing nozzle. The deposition section is placed on the heating platform, and the atomizing nozzle is fixed by an iron frame and test tube clamps. Regarding the pneumatic spraying section, the improvement of the present invention focuses on the relevant parameters of the precursor solution spraying. The present invention does not improve the structure of the pneumatic spraying equipment; therefore, the detailed structure of the pneumatic spraying equipment will not be described in detail. Furthermore, the following embodiments and comparative examples provided by the present invention were conducted under laboratory conditions. In actual production, production equipment with the same functions can be replaced as needed.

[0028] Example 1

[0029] This embodiment provides a low thermal conductivity, high temperature resistant, and structurally ordered nanolayered calcium niobate heat insulation coating, the preparation method of which includes the following steps:

[0030] (1) Preparation of precursor solution: While stirring, 100 μL of 0.1 M K2CO3 aqueous solution was added dropwise to the calcium niobate nanosheet suspension to obtain a mixed solution. Ethanol was added to the mixed solution in a 1:1 ratio, and the mixture was sonicated for 15 min to obtain a homogeneous precursor solution.

[0031] (2) Substrate treatment: The Si substrate was placed in a beaker containing ethanol, sonicated for 15 min, and then dried in an oven at 60°C for 10 min. After drying, the substrate was cleaned in a plasma cleaner for 15 min.

[0032] (3) Air pressure spraying: Place the substrate on the heating stage and preheat for 1-2 minutes until the substrate temperature reaches 160℃. Turn on the syringe pump and adjust the injection rate to 0.5 mL / min. Draw 20 mL of precursor solution with a syringe, fix it on the syringe pump, and adjust the distance between the atomizing nozzle and the substrate to 15 cm. Then turn on the inert gas switch, adjust the airflow rate to 15 L / min, and start spraying. After spraying for 10 seconds, turn off the gas. This process is to remove the solution that has accumulated on the needle under gravity. Finally, place the substrate directly below the atomizing nozzle, turn on the inert gas and adjust the airflow rate to 15 L / min, run the syringe pump, and start spraying. During the spraying process, keep the substrate at 160℃. After spraying, turn off the gas first, then open the protective chamber door and remove the sample with tweezers. Then remove the syringe and turn off the syringe pump power.

[0033] (4) Coating annealing: After the spraying is completed, the coating is placed in a muffle furnace for annealing. The annealing temperature is 400℃, the holding time is 4h, and the heating rate of annealing is 5K / min.

[0034] Comparative Example 1

[0035] Comparative Example 1 is basically the same as Example 1, except that the substrate temperature in step (3) is 80°C.

[0036] Comparative Example 2

[0037] Comparative Example 2 is basically the same as Example 1, except that the airflow rate in step (3) is 7.5 L / min.

[0038] Comparative Example 3

[0039] Comparative Example 3 is basically the same as Example 1, except that the annealing temperature in step (4) is 200°C.

[0040] Comparative Example 4

[0041] Comparative Example 4 is basically the same as Example 1, except that in step (1), the calcium niobate suspension and ethanol are mixed in a 1:1 ratio and sonicated for 15 minutes to obtain a potassium-free precursor solution for spraying.

[0042] Figure 1 A schematic diagram of the spraying device is shown. The atomizing nozzle is fixed on an iron frame, and the spraying distance can be adjusted as needed. Atomization is powered by gas, and the injection rate is controlled by an injection pump. The solution can be atomized when the airflow rate is greater than 9 L / min. When the nanosheet droplets reach the substrate surface, they undergo self-assembly, and the solvent slowly evaporates under the action of the heating stage.

[0043] Figure 2 These are optical images comparing coatings obtained by spraying at different substrate temperatures. Figure 2 (a) is the coating obtained in Comparative Example 1 with a substrate temperature of 80°C. Figure 2 (b) is the coating obtained in Example 1 with a substrate temperature of 160°C. The lower substrate temperature resulted in more solvent being carried by the droplets when they reached the substrate surface, causing blistering as shown in the figure during the drying process. However, no blistering occurred when the substrate temperature was 160°C.

[0044] Figure 3 These are laser confocal microscopy images of droplets deposited on a Si substrate at different gas flow rates. Figure 3 (a) is Comparative Example 2, with an airflow rate of 7.5 L / min; Figure 3 (b) For Example 1, the airflow rate was 15 L / min. At an airflow rate of 7.5 L / min, the droplet size was very large, indicating insufficient atomization of the solution at a lower airflow rate. This leads to excessive solvent content in the coating, resulting in coating blistering and weakened adhesion between the coating and the substrate during subsequent drying. At an airflow rate of 15 L / min, the droplet size was significantly reduced compared to 7.5 L / min.

[0045] Figure 4 The XRD patterns of the coatings after annealing at 200℃ and 400℃ were compared. Figure 4 (a) Comparative Example 3 was annealed at 200℃; Figure 4 (b) Example 1 was annealed at 400℃. After annealing at 200℃, the coating peaks were broad and weak because of the presence of interlayer water and organic matter, resulting in defects in the layered structure. However, after annealing at 400℃, the peak intensity of the coating increased significantly, and the angular spacing between the diffraction peaks was equal, indicating that the coating structure was ordered. Therefore, the coating exhibited better crystallinity and orientation after annealing at 400℃.

[0046] Figure 5 The images shown are SEM images of the planar and cross-sectional surfaces of the coating obtained in Example 1. Figure 5 (a) shows a surface SEM image of the coating, which is flat and uniform. Figure 5 (b) shows a cross-sectional SEM image of the coating, which is obtained by highly ordered stacking of nanosheets.

[0047] Figure 6 The XRD patterns of ordered calcium niobate nanocoatings and ordered potassium ion-intercalated calcium niobate nanocoatings after annealing at different temperatures were compared. Figure 6(a) XRD patterns of the ordered calcium niobate nanocoating (Comparative Example 4) after annealing at different temperatures; after annealing at 600℃, the layered characteristic peaks still exist. After annealing at 800℃, the (00l) series peaks and other peaks disappear, indicating that the layered structure collapses at this point, and the coating transforms into an amorphous or non-crystalline transition state. When the annealing temperature of the calcium niobate coating reaches 1000℃, the coating undergoes a phase transition, transforming into the CaNb2O6 phase. Figure 6 (b) XRD patterns of the ordered potassium ion-intercalated calcium niobate nanocoating (Example 1) after annealing at different temperatures. After annealing at 800℃, the weak XRD peak corresponds to KCa2Nb3O. 10 Even at high temperatures, the presence of equally spaced layered characteristic peaks indicates that the layered structure of the coating still exists. Therefore, potassium ion intercalation can enhance the thermal stability of the calcium niobate nanocoating.

[0048] Example 2

[0049] This embodiment provides a low thermal conductivity, high temperature resistant, and structurally ordered nanolayered calcium niobate heat insulation coating, the preparation method of which includes the following steps:

[0050] (1) Preparation of precursor solution: While stirring, 100 μL of 0.1 M K2CO3 aqueous solution was added dropwise to the calcium niobate nanosheet suspension to obtain a mixed solution. Ethanol was added to the mixed solution in a 1:1 ratio and mixed evenly to obtain the precursor solution.

[0051] (2) Substrate treatment: The 718 nickel alloy substrate was placed in a beaker containing ethanol, sonicated for 15 min, and then dried in an oven at 60°C for 10 min. After drying, the substrate was cleaned in a plasma cleaner for 15 min.

[0052] (3) Air pressure spraying: Place the substrate on the heating stage and preheat for 1-2 minutes until the substrate temperature reaches 160℃. Turn on the syringe pump and adjust the injection rate to 0.5 mL / min. Draw 20 mL of precursor solution with a syringe, fix it on the syringe pump, and adjust the atomizing nozzle to 15 cm. Then turn on the inert gas switch, adjust the airflow rate to 15 L / min, and start spraying. After 10 seconds, turn off the gas. This process is to remove the solution that has accumulated on the needle under gravity. Finally, place the substrate directly below the atomizing nozzle, turn on the inert gas and adjust the airflow rate to 15 L / min, run the syringe pump, and start spraying. During the spraying process, the substrate temperature should be maintained at 160℃. After spraying, turn off the gas first, then open the protective chamber door and remove the sample with tweezers. Then remove the syringe and turn off the syringe pump power.

[0053] (4) Coating annealing: After spraying, the coating is placed in a muffle furnace for annealing at temperatures of 200℃, 400℃, 600℃, 800℃ and 1000℃, with a holding time of 4h and a heating rate of 5K / min, to obtain structurally ordered nano-layered calcium niobate heat insulation coatings annealed at different temperatures.

[0054] Testing revealed that the thermal conductivity of the ordered nanolayered calcium niobate thermal insulation coating after annealing at 200℃, 400℃, 600℃, 800℃, and 1000℃ was 0.09 W·m. -1 ·k -1 0.29 W·m -1 ·k -1 0.15 W·m -1 ·k -1 0.03 W·m -1 ·k -1 0.19 W·m -1 ·k -1 .

[0055] Example 3

[0056] This embodiment provides a low thermal conductivity, high temperature resistant, and structurally ordered nanolayered calcium niobate heat insulation coating, the preparation method of which includes the following steps:

[0057] (1) Preparation of precursor solution: While stirring, 100 μL of 0.1 M K2SO4 aqueous solution was added dropwise to the calcium niobate nanosheet suspension to obtain a mixed solution. Ethanol was added to the mixed solution at a ratio of 8:1 and mixed evenly to obtain the precursor solution.

[0058] (2) Substrate treatment: The 718 nickel alloy substrate was placed in a beaker containing ethanol, sonicated for 15 min, and then dried in an oven at 60°C for 10 min. After drying, the substrate was cleaned in a plasma cleaner for 15 min.

[0059] (3) Air pressure spraying: Place the substrate on the heating stage and preheat for 1-2 minutes until the substrate temperature reaches 200℃. Turn on the syringe pump and adjust the injection rate to 0.5 mL / min. Draw 20 mL of precursor solution with a syringe, fix it on the syringe pump, and adjust the atomizing nozzle to 15 cm. Then turn on the inert gas switch, adjust the airflow rate to 10 L / min, and start spraying. After 10 seconds, turn off the gas. This process is to remove the solution that has accumulated on the needle under gravity. Finally, place the substrate directly below the atomizing nozzle, turn on the inert gas and adjust the airflow rate to 10 L / min, run the syringe pump, and start spraying. During the spraying process, the substrate should be kept at 200℃. After spraying, turn off the gas first, then open the protective chamber door and remove the sample with tweezers. Then remove the syringe and turn off the syringe pump power.

[0060] (4) Coating annealing: After the spraying is completed, the coating is placed in a muffle furnace for annealing. The annealing temperature is 300℃, the holding time is 4h, and the heating rate of annealing is 8K / min.

[0061] Figure 7 The XRD patterns, planar and cross-sectional SEM images of the coating prepared under the conditions shown in Example 3 are presented. Figure 7 As shown in (a), the coating prepared under these conditions has layered characteristic peaks with equal spacing, indicating that the coating has a layered structure. Figure 7 (b) The coating surface is smooth and uniform. Figure 7 (c) A cross-sectional morphology diagram showing the highly oriented stacked layers of nanosheets. Therefore, a flat, uniform, and highly oriented stacked calcium niobate nanosheet coating can be prepared under the conditions shown in the example.

[0062] Example 4

[0063] This embodiment provides a low thermal conductivity, high temperature resistant, and structurally ordered nanolayered calcium niobate heat insulation coating, the preparation method of which includes the following steps:

[0064] (1) Preparation of precursor solution: 100 μL of 0.1 M K2SO4 aqueous solution was added dropwise to the calcium niobate nanosheet suspension to obtain a mixed solution. Ethanol was added to the mixed solution in a ratio of 4:1 and mixed evenly to obtain the precursor solution.

[0065] (2) Substrate treatment: The 718 nickel alloy substrate was placed in a beaker containing ethanol, sonicated for 15 min, and then dried in an oven at 60°C for 10 min. After drying, the substrate was cleaned in a plasma cleaner for 15 min.

[0066] (3) Air pressure spraying: Place the substrate on the heating stage and preheat for 1-2 minutes until the substrate temperature reaches 120℃. Turn on the syringe pump and adjust the injection rate to 0.5 mL / min. Draw 20 mL of precursor solution with a syringe, fix it on the syringe pump, and adjust the atomizing nozzle to 15 cm. Then turn on the inert gas switch, adjust the airflow rate to 17.5 L / min, and start spraying. After 10 seconds, turn off the gas. This process is to remove the solution that has accumulated on the needle under gravity. Finally, place the substrate directly below the atomizing nozzle, turn on the inert gas and adjust the airflow rate to 17.5 L / min, run the syringe pump, and start spraying. During the spraying process, the substrate temperature is maintained at 120℃. After spraying, turn off the gas first, then open the protective chamber door and remove the sample with tweezers. Then remove the syringe and turn off the syringe pump power.

[0067] (4) Coating annealing: After the spraying is completed, the coating is placed in a muffle furnace for annealing. The annealing temperature is 500℃, the holding time is 4h, and the heating rate of annealing is 10K / min.

[0068] Figure 8 The XRD patterns, planar and cross-sectional SEM images of the coating prepared under the conditions shown in Example 4 are presented. Figure 8 As shown in (a), the coating prepared under these conditions has layered characteristic peaks with equal spacing. The sharpness of this series of layered characteristic peaks indicates that the coating has a layered structure and good crystallinity and high orientation. Figure 8 (b) The coating exhibits a smooth and uniform surface morphology. Figure 8 (c) A cross-sectional morphology diagram showing the highly oriented stacked layers of nanosheets. Therefore, a flat, uniform, and highly oriented stacked calcium niobate nanosheet coating can be prepared under the conditions shown in the example.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A low thermal conductivity, high temperature resistant, structurally ordered nanolayered calcium niobate heat-insulating coating, characterized in that: Applicable to applications with heat resistance temperatures above 500℃; The method for preparing the heat-insulating coating includes the following steps: A precursor solution for preparing a low thermal conductivity, high temperature resistant, and structurally ordered nanolayered calcium niobate heat insulation coating is prepared by the following steps: mixing a potassium salt solution with a calcium niobate nanosheet suspension to obtain a mixture, and then adding ethanol to the mixture to obtain the precursor solution. The preparation of a low thermal conductivity, high temperature resistant, and structurally ordered nanolayered calcium niobate thermal insulation coating includes the following steps: preheating the substrate to the target temperature and then spraying the precursor solution onto the substrate surface; after spraying, annealing the substrate at 300-500 ℃.

2. The heat-insulating coating according to claim 1, characterized in that: The potassium salt solution is an aqueous solution of K2CO3, K2SO4, KCl or CH3COOK; the concentration of the potassium salt solution is 0.05-0.1 mol / L; the concentration of the calcium niobate nanosheet suspension is 0.12-0.50 g / L; the volume ratio of the potassium salt solution to the calcium niobate nanosheet suspension is 1:(15-40); the volume ratio of ethanol to the mixture is (1-8):

1.

3. The heat-insulating coating according to claim 1, characterized in that: In the preparation step of the precursor solution, a potassium salt solution is added dropwise to the calcium niobate nanosheet suspension while stirring it.

4. The heat-insulating coating according to claim 1, characterized in that: The substrate preheating temperature is 120-200 ℃, and the preheating time is 1-2 min.

5. The heat-insulating coating according to claim 1, characterized in that: The coating is applied using a pneumatic spraying device, which includes an inert gas supply unit, a syringe pump, a syringe, an atomizing nozzle, and a heating platform. The substrate is placed on the heating platform, with the atomizing nozzle facing the substrate.

6. The heat-insulating coating according to claim 5, characterized in that: The distance between the atomizing nozzle and the substrate is 10-20 cm. During the spraying process, the airflow rate of the air pressure spraying device is 10.0-17.5 L / min, and the injection rate of the precursor solution is 0.3-1.0 mL / min.

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