Preparation process of high-temperature composite wave-absorbing stealth coating and coating
By using a composite coating preparation process involving methylphenyl organosilicon-modified polyimide resin and SiC-coated nano-carbonyl iron, the problem of structural instability of existing coatings at extreme temperatures has been solved, achieving a wave-absorbing stealth effect that does not pulverize at high temperatures and does not become brittle at low temperatures.
Patent Information
- Application Number
- CN202610774184.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-06-01
- Publication Date
- 2026-07-24
AI Technical Summary
Existing microwave absorbing coatings have limited high-temperature resistance or high low-temperature brittleness and insufficient toughness under extreme temperature conditions, which leads to the coating powdering and peeling off at high temperatures or cracking at low temperatures, resulting in loss of structural integrity and stealth function.
Using methylphenyl silicone-modified polyimide resin as the matrix, combined with SiC-coated nano-carbonyl iron, hydroxylated multi-walled carbon nanotubes and nano-yttrium oxide, a composite microwave absorbing stealth coating was prepared through a gradient curing process. The dense SiC shell of nano-carbonyl iron and the inorganic ceramic network of aluminum dihydrogen phosphate were used to improve the high-temperature structural strength, while fluororubber provided low-temperature flexibility.
It achieves structural integrity and microwave absorption performance of the coating over a wide temperature range, maintains stability at high temperatures without powdering, and does not become brittle or crack at low temperatures, exhibiting excellent high-temperature resistance and low-temperature flexibility.
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Figure CN122445277A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of microwave absorbing coating technology, specifically to a preparation process and coating of a high-temperature composite microwave absorbing stealth coating. Background Technology
[0002] As an important functional material for modern stealth equipment, radar-absorbing stealth coatings are widely used in aerospace, high-speed aircraft and advanced weaponry. Their service environment is often accompanied by high temperature thermal shock and extremely low temperature alternation, which puts forward stringent requirements on the wide temperature range stability of the coating.
[0003] Existing microwave absorbing coatings are mostly prepared using epoxy resin, ordinary polyimide, etc. as the matrix, combined with microwave absorbing fillers such as carbonyl iron and carbon-based materials. Although they have certain microwave absorption performance at room temperature, they have obvious defects under extreme temperature conditions. Ordinary organic matrices have limited high-temperature resistance and are prone to thermal oxidative aging, softening and decomposition when exposed to environments above 300°C for a long time, leading to coating powdering and peeling. While pure inorganic base coatings have better high-temperature resistance, they suffer from high low-temperature brittleness and insufficient toughness, and are prone to cracking and delamination under extremely cold environments or severe thermal cycling, resulting in loss of structural integrity and stealth function.
[0004] Therefore, it is necessary to propose a high-temperature composite microwave absorbing stealth coating that can withstand extremely cold environments and its preparation process. Summary of the Invention
[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a preparation process and coating of a high-temperature composite microwave absorbing stealth coating.
[0006] This invention provides a process for preparing a high-temperature composite microwave absorbing stealth coating, comprising the following steps: S1: Preparation of modified composite powder SiC-coated carbonyl iron nanoparticles, hydroxylated multi-walled carbon nanotubes, and nano-yttrium oxide were added to a 90% (v / v) ethanol aqueous solution and ultrasonically dispersed for 30-40 min. Then, silane coupling agent KH-570 was added, and the pH was adjusted to 4-5 with 0.1 mol / L dilute acetic acid. The mixture was then heated and stirred at 55-65℃ for 2-3 h. After filtration, washing with anhydrous ethanol 2-3 times, and vacuum drying at 80℃ for 4-5 h, the mixture was ground through a 300-mesh sieve to obtain the modified composite powder. S2: Preparation of prepolymer Methylphenyl silicone-modified polyimide resin was heated and stirred until completely melted, then fluororubber 246 was added and stirred at 800-900 rpm for 30-40 min. When the temperature dropped to 50℃, aluminum dihydrogen phosphate was added and stirring was continued for 20-30 min to obtain the prepolymer. S3: Preparation of composite microwave-absorbing stealth coating While stirring, the modified composite powder was added to the prepolymer, followed by fumed silica. Stirring was continued for 1-2 hours, followed by ultrasonic dispersion for 20-30 minutes. Then, N-methylpyrrolidone was added for dilution to obtain the composite microwave absorbing stealth coating. S4: Preparation of composite microwave absorbing stealth coating After sanding the substrate, it is then degreased with acetone, rinsed with ethanol, and dried with hot air in sequence. Then, the composite microwave absorbing stealth coating is evenly sprayed onto the substrate surface using an air spraying method with the spray gun pressure adjusted to 0.3-0.4 MPa. After gradient curing and cooling, a composite microwave absorbing stealth coating with a thickness of 80-100 μm is obtained.
[0007] Further, the preparation steps of SiC-coated nano-carbonyl iron are as follows: Nano-carbonyl iron and 2,4-pentanedione are added to a mixed solvent at a ratio of (11.8-12.2) g: (0.1-0.2) g: (85-95) mL, and ultrasonically dispersed for 40-50 min. Then, polycarbosilane is added, and the mixture is stirred at 60-70℃ until completely dissolved. Under nitrogen protection, the mixture is kept warm and stirred for 2-3 h, then heated to 120℃ and kept warm and stirred for 1-2 hours. After freezing, the material is filtered, washed, and vacuum dried, then placed in a tube furnace. Under nitrogen protection, the temperature is first increased to 300℃ at 5℃ / min and held for 30-40 min, then increased to 700℃ and held for 1 h, and finally increased to 900℃ and held for 2 h. The material is then cooled to room temperature in the furnace, removed, ground, and passed through a 300-mesh sieve to obtain SiC-coated nano-carbonyl iron. The mixed solvent is composed of ethanol and xylene in a volume ratio of 1:2.
[0008] Furthermore, the amount of polycarbosilane added is 18-22% of the mass of nano-carbonyl iron.
[0009] Further, in step S1, the mass ratio of SiC-coated nano-carbonyl iron, hydroxylated multi-walled carbon nanotubes and nano-yttrium oxide is (8-10):(1.2-1.4):1, and the ratio of the total mass of SiC-coated nano-carbonyl iron, hydroxylated multi-walled carbon nanotubes and nano-yttrium oxide to the ethanol aqueous solution is 1g:(4-6)mL.
[0010] Furthermore, in step S1, the amount of silane coupling agent KH-570 added is 6.6-6.8% of the mass of SiC-coated nano-carbonyl iron.
[0011] Further, in step S2, the preparation steps of the methylphenyl organosilicon modified polyimide resin are as follows: Under nitrogen protection, 4,4'-diaminodiphenyl ether and aminopropyl-terminated polymethylphenylsiloxane are added to N-methylpyrrolidone at a mass ratio of (0.98-1.02):1:(6-8). The mixture is heated and stirred at 40-50℃ until completely dissolved. Then, pyromellitic dianhydride is added in three portions, with an interval of 15 minutes between each addition. The mixture is kept warm and stirred for 2-3 hours. Then, acetic anhydride, pyridine, and toluene are added and stirred until homogeneous. The mixture is then heated to 135-145℃ and refluxed for 3-4 hours. Finally, the mixture is subjected to vacuum distillation, alcohol precipitation, filtration, washing, and vacuum drying to obtain the methylphenyl organosilicon modified polyimide resin.
[0012] Furthermore, the molar ratio of pyromellitic dianhydride to the total molar amounts of 4,4'-diaminodiphenyl ether and aminopropyl-terminated polymethylphenylsiloxane is 1:1, the molar ratio of acetic anhydride to pyromellitic dianhydride is 2:1, the molar ratio of pyridine to pyromellitic dianhydride is 2:1, and the amount of toluene added is 30-35% of the mass of N-methylpyrrolidone.
[0013] Further, in step S3, the raw material composition of the composite microwave absorbing stealth coating, by mass parts, is: 55-65 parts of methylphenyl silicone modified polyimide resin, 10-12 parts of fluororubber 246, 8-10 parts of aluminum dihydrogen phosphate, 16-20 parts of modified composite powder, 0.5-1 parts of fumed silica and 8-10 parts of N-methylpyrrolidone.
[0014] Further, in step S4, the gradient curing process is as follows: First stage: 50-60℃ for 50-60 min; Second stage: 110-120℃ for 1 h; Third stage: 195-205℃ for 40-50 min; Fourth stage: 350℃ for 1 h; Fifth stage: 550℃ for 30 min.
[0015] A high-temperature composite microwave absorbing stealth coating is prepared by the preparation process of a high-temperature composite microwave absorbing stealth coating as described in any one of the above claims.
[0016] The present invention has the following advantages: 1. In this invention, methylphenyl organosilicon modified polyimide resin is used as the matrix. The main chain contains rigid imide rings and high bond energy silicon-oxygen bonds. The imide rings endow the resin with intrinsic thermal stability above 400°C, and the silicon-oxygen bonds are not easily thermally degraded. Furthermore, the synthesis is carried out under nitrogen protection, resulting in a regular molecular structure without easily decomposable side groups. It can maintain structural integrity for a long time under high temperature conditions. Moreover, aminopropyl-terminated polymethylphenylsiloxane is incorporated into the main chain. Its silicon-oxygen bonds have large bond angles and low internal rotation barriers, which enable the resin molecular chains to maintain a certain chain segment movement capability under extremely cold conditions. This solves the defect of low-temperature embrittlement of traditional polyimides and endows the matrix with intrinsic low-temperature flexibility. Among them, polyimide, as the continuous phase, provides structural strength, and fluororubber, as the dispersed phase, plays an elastic toughening role. It can effectively absorb thermal stress under extremely cold conditions, prevent the initiation and propagation of microcracks, and achieve low-temperature non-embrittlement and non-cracking.
[0017] 2. In this invention, the SiC-coated nano-carbonyl iron is generated by high-temperature pyrolysis of polycarbosilane to form a dense SiC shell. SiC itself possesses excellent high-temperature resistance and oxidation resistance, effectively isolating oxygen from contact with the core carbonyl iron, preventing high-temperature oxidation and deactivation of the microwave absorbing filler, and simultaneously improving the high-temperature structural strength of the coating. During the gradient curing stage, aluminum dihydrogen phosphate undergoes a dehydration reaction and synergistically works with the SiC-coated nano-carbonyl iron. The advantages of this in-situ beneficial effect are best demonstrated through test data in the embodiments. The embodiments only demonstrate thermogravimetric analysis, extreme cold, and thermal cycling performance. An aluminum phosphate-based inorganic ceramic network is generated, which continues to provide structural support during the gradual high-temperature pyrolysis of the organic resin, preventing high-temperature powdering and detachment of the coating, thereby synergistically improving the high-temperature resistance of the microwave absorbing stealth coating. Attached Figure Description
[0018] Figure 1 This is a flowchart illustrating the preparation process of the high-temperature composite microwave absorbing stealth coating used in an embodiment of the present invention. Detailed Implementation
[0019] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this invention.
[0020] Example 1: A preparation process for a high-temperature composite microwave absorbing stealth coating, such as... Figure 1 As shown, it includes the following steps: S1: Preparation of modified composite powder Nano-carbonyl iron and 2,4-pentanedione were added to a mixed solvent at a ratio of 11.8g:0.1g:85mL and ultrasonically dispersed for 40min. Then, polycarbosilane was added and stirred at 60℃ until completely dissolved. The mixture was then kept at this temperature and stirred for 2h under nitrogen protection, then heated to 120℃ and kept at this temperature and stirred for 1h. After freezing, the mixture was filtered, washed, and vacuum dried. It was then placed in a tube furnace and heated to 300℃ at a rate of 5℃ / min under nitrogen protection, kept at this temperature for 30min, then heated to 700℃ and kept at this temperature for 1h, and finally heated to 900℃ and kept at this temperature for 2h. The mixture was then cooled to room temperature with the furnace, removed, ground, and passed through a 300-mesh sieve to obtain SiC-coated nano-carbonyl iron. The mixed solvent was composed of ethanol and xylene in a volume ratio of 1:2, and the amount of polycarbosilane added was 18% of the mass of the nano-carbonyl iron. SiC-coated nano-carbonyl iron, hydroxylated multi-walled carbon nanotubes, and nano-yttrium oxide were added to a 90% (v / v) ethanol aqueous solution and ultrasonically dispersed for 30 min. Then, silane coupling agent KH-570 was added, and the pH was adjusted to 4 with 0.1 mol / L dilute acetic acid. The mixture was then heated and stirred at 55-65℃ for 2 h. After filtration, washing with anhydrous ethanol 2-3 times, and vacuum drying at 80℃ for 4 h, the mixture was ground through a 300-mesh sieve to obtain a modified composite powder. The mass ratio of SiC-coated nano-carbonyl iron, hydroxylated multi-walled carbon nanotubes, and nano-yttrium oxide was 8:1.2:1, the ratio of the total mass of SiC-coated nano-carbonyl iron, hydroxylated multi-walled carbon nanotubes, and nano-yttrium oxide to the ethanol aqueous solution was 1 g:4 mL, and the amount of silane coupling agent KH-570 added was 6.6% of the mass of SiC-coated nano-carbonyl iron. S2: Preparation of prepolymer Under nitrogen protection, 4,4'-diaminodiphenyl ether and aminopropyl-terminated polymethylphenylsiloxane were added to N-methylpyrrolidone at a mass ratio of 0.98:1:6. The mixture was heated and stirred at 40°C until completely dissolved. Then, pyromellitic dianhydride was added in three portions, with 15-minute intervals between each addition. The mixture was kept at this temperature and stirred for 2 hours. Acetic anhydride, pyridine, and toluene were then added and stirred until homogeneous. The mixture was then heated to 135°C and refluxed for 3 hours. Finally, the mixture was subjected to vacuum distillation, alcohol precipitation, filtration, washing, and vacuum drying to obtain methylphenyl organosilicon-modified polyimide resin. The molar ratio of pyromellitic dianhydride to the total molar amount of 4,4'-diaminodiphenyl ether and aminopropyl-terminated polymethylphenylsiloxane was 1:1, the molar ratio of acetic anhydride to pyromellitic dianhydride was 2:1, the molar ratio of pyridine to pyromellitic dianhydride was 2:1, and the amount of toluene added was 30% of the mass of N-methylpyrrolidone. Methylphenyl silicone-modified polyimide resin was heated and stirred until completely melted, then fluororubber 246 was added and stirred at 800 rpm for 30 min. When the temperature dropped to 50℃, aluminum dihydrogen phosphate was added and stirring was continued for 20 min to obtain the prepolymer. S3: Preparation of composite microwave-absorbing stealth coating While stirring, the modified composite powder was added to the prepolymer, followed by fumed silica. The mixture was stirred for 1 hour, then ultrasonically dispersed for 20 minutes. Finally, N-methylpyrrolidone was added for dilution to obtain the composite microwave absorbing stealth coating. The raw material composition of the composite microwave absorbing stealth coating, by mass, is as follows: 55 parts methylphenyl silicone modified polyimide resin, 10 parts fluororubber 246, 8 parts aluminum dihydrogen phosphate, 16 parts modified composite powder, 0.5 parts fumed silica, and 8 parts N-methylpyrrolidone. S4: Preparation of composite microwave absorbing stealth coating After sanding the substrate, it was sequentially degreased with acetone, rinsed with ethanol, and dried with hot air. Then, using air spraying with the spray gun pressure adjusted to 0.3 MPa, the composite microwave absorbing stealth coating was evenly sprayed onto the substrate surface. After gradient curing and cooling, a composite microwave absorbing stealth coating with a thickness of 80 μm was obtained. The gradient curing process is as follows: First stage: 50℃ for 50 min; Second stage: 110℃ for 1 h; Third stage: 195℃ for 40 min; Fourth stage: 350℃ for 1 h; Fifth stage: 550℃ for 30 min.
[0021] Example 2: A preparation process for a high-temperature composite microwave absorbing stealth coating, such as... Figure 1 As shown, it includes the following steps: S1: Preparation of modified composite powder Nano-carbonyl iron and 2,4-pentanedione were added to a mixed solvent at a ratio of 12g:0.15g:90mL and ultrasonically dispersed for 45min. Then, polycarbosilane was added and stirred at 65℃ until completely dissolved. The mixture was then kept at this temperature and stirred for 2.5h under nitrogen protection, then heated to 120℃ and kept at this temperature and stirred for 1.5h. After freezing, the mixture was filtered, washed, and vacuum dried. It was then placed in a tube furnace and heated to 300℃ at a rate of 5℃ / min under nitrogen protection, kept at this temperature for 35min, then heated to 700℃ and kept at this temperature for 1h, and finally heated to 900℃ and kept at this temperature for 2h. The mixture was then cooled to room temperature with the furnace, removed, ground, and passed through a 300-mesh sieve to obtain SiC-coated nano-carbonyl iron. The mixed solvent was composed of ethanol and xylene in a volume ratio of 1:2, and the amount of polycarbosilane added was 20% of the mass of the nano-carbonyl iron. SiC-coated nano-carbonyl iron, hydroxylated multi-walled carbon nanotubes, and nano-yttrium oxide were added to a 90% (v / v) ethanol aqueous solution and ultrasonically dispersed for 35 min. Then, silane coupling agent KH-570 was added, and the pH was adjusted to 4.5 with 0.1 mol / L dilute acetic acid. The mixture was then heated and stirred at 60 °C for 2.5 h. After filtration, washing twice with anhydrous ethanol, and vacuum drying at 80 °C for 4 h, the mixture was ground through a 300-mesh sieve to obtain a modified composite powder. The mass ratio of SiC-coated nano-carbonyl iron, hydroxylated multi-walled carbon nanotubes, and nano-yttrium oxide was 9:1.3:1, the ratio of the total mass of SiC-coated nano-carbonyl iron, hydroxylated multi-walled carbon nanotubes, and nano-yttrium oxide to the ethanol aqueous solution was 1 g:5 mL, and the amount of silane coupling agent KH-570 added was 6.7% of the mass of SiC-coated nano-carbonyl iron. S2: Preparation of prepolymer Under nitrogen protection, 4,4'-diaminodiphenyl ether and aminopropyl-terminated polymethylphenylsiloxane were added to N-methylpyrrolidone at a mass ratio of 1:1:7. The mixture was heated and stirred at 45°C until completely dissolved. Then, pyromellitic dianhydride was added in three portions, with an interval of 15 min between each addition. The mixture was kept at this temperature and stirred for 2.5 h. Acetic anhydride, pyridine, and toluene were then added and stirred until homogeneous. The mixture was then heated to 140°C and refluxed for 3.5 h. Finally, the mixture was subjected to vacuum distillation, alcohol precipitation, filtration, washing, and vacuum drying to obtain methylphenyl organosilicon-modified polyimide resin. The molar ratio of pyromellitic dianhydride to the total molar amount of 4,4'-diaminodiphenyl ether and aminopropyl-terminated polymethylphenylsiloxane was 1:1, the molar ratio of acetic anhydride to pyromellitic dianhydride was 2:1, the molar ratio of pyridine to pyromellitic dianhydride was 2:1, and the amount of toluene added was 32.5% of the mass of N-methylpyrrolidone. Methylphenyl silicone-modified polyimide resin was heated and stirred until completely melted, then fluororubber 246 was added and stirred at 850 rpm for 35 min. When the temperature was lowered to 50℃, aluminum dihydrogen phosphate was added and stirring was continued for 25 min to obtain the prepolymer. S3: Preparation of composite microwave-absorbing stealth coating While stirring, the modified composite powder was added to the prepolymer, followed by fumed silica. The mixture was stirred for 1.5 hours, then ultrasonically dispersed for 25 minutes. Finally, N-methylpyrrolidone was added for dilution to obtain the composite microwave absorbing stealth coating. The raw material composition of the composite microwave absorbing stealth coating, by mass, is as follows: 60 parts methylphenyl silicone modified polyimide resin, 11 parts fluororubber 246, 9 parts aluminum dihydrogen phosphate, 18 parts modified composite powder, 0.75 parts fumed silica, and 9 parts N-methylpyrrolidone. S4: Preparation of composite microwave absorbing stealth coating After sanding the substrate, it was sequentially degreased with acetone, rinsed with ethanol, and dried with hot air. Then, using air spraying, the composite microwave absorbing stealth coating was evenly sprayed onto the substrate surface with the spray gun pressure adjusted to 0.35 MPa. After gradient curing and cooling, a composite microwave absorbing stealth coating with a thickness of 90 μm was obtained. The gradient curing process is as follows: First stage: 55℃ for 55 min; Second stage: 115℃ for 1 h; Third stage: 200℃ for 45 min; Fourth stage: 350℃ for 1 h; Fifth stage: 550℃ for 30 min.
[0022] Example 3: A preparation process for a high-temperature composite microwave absorbing stealth coating, such as... Figure 1 As shown, it includes the following steps: S1: Preparation of modified composite powder Nano-carbonyl iron and 2,4-pentanedione were added to a mixed solvent at a ratio of 12.2g:0.2g:95mL and ultrasonically dispersed for 50min. Then, polycarbosilane was added and stirred at 70℃ until completely dissolved. The mixture was then kept at this temperature and stirred for 3h under nitrogen protection, followed by heating to 120℃ and stirring for 2h. After freezing, the mixture was filtered, washed, and vacuum dried. It was then placed in a tube furnace and heated to 300℃ at a rate of 5℃ / min under nitrogen protection, held for 40min, then heated to 700℃ and held for 1h, and finally heated to 900℃ and held for 2h. The mixture was then cooled to room temperature in the furnace, removed, ground, and passed through a 300-mesh sieve to obtain SiC-coated nano-carbonyl iron. The mixed solvent was composed of ethanol and xylene in a volume ratio of 1:2, and the amount of polycarbosilane added was 22% of the mass of the nano-carbonyl iron. SiC-coated nano-carbonyl iron, hydroxylated multi-walled carbon nanotubes, and nano-yttrium oxide were added to a 90% (v / v) ethanol aqueous solution and ultrasonically dispersed for 40 min. Then, silane coupling agent KH-570 was added, and the pH was adjusted to 5 with 0.1 mol / L dilute acetic acid. The mixture was then heated and stirred at 65 °C for 3 h. After filtration, washing three times with anhydrous ethanol, and vacuum drying at 80 °C for 5 h, the mixture was ground through a 300-mesh sieve to obtain a modified composite powder. The mass ratio of SiC-coated nano-carbonyl iron, hydroxylated multi-walled carbon nanotubes, and nano-yttrium oxide was 10:1.4:1, the ratio of the total mass of SiC-coated nano-carbonyl iron, hydroxylated multi-walled carbon nanotubes, and nano-yttrium oxide to the ethanol aqueous solution was 1 g:6 mL, and the amount of silane coupling agent KH-570 added was 6.8% of the mass of SiC-coated nano-carbonyl iron. S2: Preparation of prepolymer Under nitrogen protection, 4,4'-diaminodiphenyl ether and aminopropyl-terminated polymethylphenylsiloxane were added to N-methylpyrrolidone at a mass ratio of 1.02:1:8. The mixture was heated and stirred at 50°C until completely dissolved. Then, pyromellitic dianhydride was added in three portions, with an interval of 15 minutes between each addition. The mixture was kept at this temperature and stirred for 3 hours. Acetic anhydride, pyridine, and toluene were then added and stirred until homogeneous. The mixture was then heated to 145°C and refluxed for 4 hours. Finally, the mixture was subjected to vacuum distillation, alcohol precipitation, filtration, washing, and vacuum drying to obtain methylphenyl organosilicon-modified polyimide resin. The molar ratio of pyromellitic dianhydride to the total molar amount of 4,4'-diaminodiphenyl ether and aminopropyl-terminated polymethylphenylsiloxane was 1:1, the molar ratio of acetic anhydride to pyromellitic dianhydride was 2:1, the molar ratio of pyridine to pyromellitic dianhydride was 2:1, and the amount of toluene added was 35% of the mass of N-methylpyrrolidone. Methylphenyl silicone-modified polyimide resin was heated and stirred until completely melted, then fluororubber 246 was added and stirred at 900 rpm for 40 min. When the temperature dropped to 50℃, aluminum dihydrogen phosphate was added and stirring was continued for 30 min to obtain the prepolymer. S3: Preparation of composite microwave-absorbing stealth coating While stirring, the modified composite powder was added to the prepolymer, followed by fumed silica. The mixture was stirred for 2 hours, then ultrasonically dispersed for 30 minutes. Finally, N-methylpyrrolidone was added for dilution to obtain the composite microwave absorbing stealth coating. The raw material composition of the composite microwave absorbing stealth coating, by mass, is as follows: 65 parts methylphenyl silicone modified polyimide resin, 12 parts fluororubber 246, 10 parts aluminum dihydrogen phosphate, 20 parts modified composite powder, 1 part fumed silica, and 10 parts N-methylpyrrolidone. S4: Preparation of composite microwave absorbing stealth coating After sanding the substrate, it was sequentially degreased with acetone, rinsed with ethanol, and dried with hot air. Then, using air spraying with the spray gun pressure adjusted to 0.4 MPa, the composite microwave absorbing stealth coating was evenly sprayed onto the substrate surface. After gradient curing and cooling, a composite microwave absorbing stealth coating with a thickness of 100 μm was obtained. The gradient curing process is as follows: First stage: 60℃ for 60 min; Second stage: 120℃ for 1 h; Third stage: 205℃ for 50 min; Fourth stage: 350℃ for 1 h; Fifth stage: 550℃ for 30 min.
[0023] Comparative Example 1 differs from Example 1 in that the aminopropyl-terminated polymethylphenylsiloxane in step S2 is replaced with an equimolar amount of 4,4'-diaminodiphenyl ether.
[0024] Comparative Example 2 differs from Example 1 in that the fluororubber 246 in step S2 is removed.
[0025] Comparative Example 3 differs from Example 1 in that the SiC-coated nano-carbonyl iron in step S1 is removed, and aluminum dihydrogen phosphate of the same mass as the removed SiC-coated nano-carbonyl iron is added in step S2.
[0026] Comparative Example 4 differs from Example 1 in that aluminum dihydrogen phosphate in step S2 is replaced with SiC-coated nano-carbonyl iron, which is added in step S1 with the same mass as the aluminum dihydrogen phosphate removed.
[0027] Test example: Test 1: The composite microwave absorbing coatings prepared in Examples 1-3 and Comparative Examples 1, 3 and 4 were placed in an oven at 550℃ and heated at a constant temperature for 1 hour. The thermal weight loss rate was tested. Each group was tested three times and the average value was taken. The results are shown in Table 1.
[0028] Table 1: Results of thermogravimetric analysis at 550℃ for 1 hour Example 1 1.8 Example 2 1.5 Example 3 1.3 Comparative Example 1 4.3 Comparative Example 3 2.5 Comparative Example 4 3.6 As shown in Table 1, the thermal weight loss rate of the composite microwave absorbing stealth coating prepared in Comparative Example 1 without modification of polyimide was significantly higher than that in Example 1. This indicates that by using methylphenyl organosilicon modified polyimide resin as the matrix, the main chain contains rigid imide rings and high bond energy silicon-oxygen bonds. The imide rings endow the resin with intrinsic thermal stability of over 400°C, and the silicon-oxygen bonds are not easily thermally degraded. Furthermore, the synthesis is carried out under nitrogen protection, resulting in a regular molecular structure without easily decomposable side groups, which can maintain structural integrity for a long time in a high-temperature environment. Furthermore, in Comparative Examples 3 and 4, when only one of aluminum dihydrogen phosphate or SiC-coated nano-carbonyl iron was added, the thermal weight loss rate of the resulting composite microwave absorbing stealth coating was higher than that in Example 1. This indicates that SiC-coated nano-carbonyl iron is produced by high-temperature pyrolysis of polycarbosilane to generate a dense SiC shell. SiC itself has excellent high-temperature resistance and oxidation resistance, which can effectively isolate oxygen from contact with the core carbonyl iron, prevent the microwave absorbing filler from high-temperature oxidation and deactivation, and improve the high-temperature structural strength of the coating. In the gradient curing stage, aluminum dihydrogen phosphate undergoes a dehydration reaction and works synergistically with SiC-coated nano-carbonyl iron to generate an aluminum phosphate-based inorganic ceramic network in situ. During the gradual high-temperature pyrolysis of the organic resin, it continues to play a structural support role, preventing the coating from high-temperature pulverization and peeling, thereby synergistically improving the high-temperature resistance of the microwave absorbing stealth coating.
[0029] Test 2: The composite microwave absorbing stealth coatings prepared in Examples 1-3 and Comparative Examples 1-2 were placed in a -60℃ low temperature chamber for 24 hours. After being taken out, the cracks were observed. Then, each group of composite microwave absorbing stealth coatings was treated at -60℃ for 30 minutes and then at 550℃ for 10 minutes. This cycle was repeated 50 times. The coating state was observed. The results are shown in Table 2.
[0030] Table 2: Test Results of Extreme Cold Performance and Thermal Cycling Performance Example 1 No cracks, no brittleness No cracks, no peeling Example 2 No cracks, no brittleness No cracks, no peeling Example 3 No cracks, no brittleness No cracks, no peeling Comparative Example 1 Significant embrittlement and multiple cracks Large-area cracks Comparative Example 2 Localized microcracks Interface debonding, dense cracks As shown in Table 2, in Comparative Example 1, without modification of polyimide, the resulting composite microwave absorbing stealth coating exhibited significant embrittlement and cracking in extremely cold environments. After 50 cycles of thermal cycling, large-area cracking and peeling occurred. In contrast, in Comparative Example 2, without the addition of fluororubber 246, the resulting composite microwave absorbing stealth coating showed localized microcracks in extremely cold environments. After 50 cycles of thermal cycling, the coating interface debonded and was riddled with cracks. This demonstrates that the aminopropyl-terminated polymethylphenylsiloxane in the methylphenyl silicone-modified polyimide resin, with its large silicon-oxygen bond angle and low internal rotation barrier, enables the resin molecular chains to maintain a certain degree of chain segment movement in extremely cold environments. This solves the defect of low-temperature embrittlement in traditional polyimides and endows the matrix with intrinsic low-temperature flexibility. Polyimide, as the continuous phase, provides structural strength, while fluororubber, as the dispersed phase, plays an elastic toughening role. It can effectively absorb thermal stress in extremely cold environments, prevent the initiation and propagation of microcracks, and achieve low-temperature non-embrittlement and non-cracking.
[0031] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.
Claims
1. A preparation process for a high-temperature composite microwave absorbing stealth coating, characterized in that, Includes the following steps: S1: Preparation of modified composite powder SiC-coated carbonyl iron nanoparticles, hydroxylated multi-walled carbon nanotubes, and nano-yttrium oxide were added to a 90% (v / v) ethanol aqueous solution and ultrasonically dispersed for 30-40 min. Then, silane coupling agent KH-570 was added, and the pH was adjusted to 4-5 with 0.1 mol / L dilute acetic acid. The mixture was then heated and stirred at 55-65℃ for 2-3 h. After filtration, washing with anhydrous ethanol 2-3 times, and vacuum drying at 80℃ for 4-5 h, the mixture was ground through a 300-mesh sieve to obtain the modified composite powder. S2: Preparation of prepolymer Methylphenyl silicone-modified polyimide resin was heated and stirred until completely melted, then fluororubber 246 was added and stirred at 800-900 rpm for 30-40 min. When the temperature dropped to 50℃, aluminum dihydrogen phosphate was added and stirring was continued for 20-30 min to obtain the prepolymer. S3: Preparation of composite microwave-absorbing stealth coating While stirring, the modified composite powder was added to the prepolymer, followed by fumed silica. Stirring was continued for 1-2 hours, followed by ultrasonic dispersion for 20-30 minutes. Then, N-methylpyrrolidone was added for dilution to obtain the composite microwave absorbing stealth coating. S4: Preparation of composite microwave absorbing stealth coating After sanding the substrate, it is then degreased with acetone, rinsed with ethanol, and dried with hot air in sequence. Then, the composite microwave absorbing stealth coating is evenly sprayed onto the substrate surface using an air spraying method with the spray gun pressure adjusted to 0.3-0.4 MPa. After gradient curing and cooling, a composite microwave absorbing stealth coating with a thickness of 80-100 μm is obtained.
2. The preparation process of a high-temperature composite microwave absorbing stealth coating according to claim 1, characterized in that, The preparation steps of SiC-coated nano-carbonyl iron are as follows: Nano-carbonyl iron and 2,4-pentanedione are added to a mixed solvent at a ratio of (11.8-12.2) g: (0.1-0.2) g: (85-95) mL. The mixture is ultrasonically dispersed for 40-50 min, then polycarbosilane is added and stirred at 60-70℃ until completely dissolved. The mixture is then kept warm and stirred for 2-3 h under nitrogen protection, then heated to 120℃ and kept warm and stirred for 1-2 h. After freezing, the mixture is filtered, washed, and vacuum dried. It is then placed in a tube furnace and heated to 300℃ at 5℃ / min under nitrogen protection, kept warm for 30-40 min, then heated to 700℃ and kept warm for 1 h, and finally heated to 900℃ and kept warm for 2 h. The mixture is cooled to room temperature with the furnace, taken out, ground, and passed through a 300-mesh sieve to obtain SiC-coated nano-carbonyl iron. The mixed solvent is composed of ethanol and xylene in a volume ratio of 1:
2.
3. The preparation process of a high-temperature composite microwave absorbing stealth coating according to claim 2, characterized in that, The amount of polycarbosilane added is 18-22% of the mass of nano-carbonyl iron.
4. The preparation process of a high-temperature composite microwave absorbing stealth coating according to claim 1, characterized in that, In step S1, the mass ratio of SiC-coated nano-carbonyl iron, hydroxylated multi-walled carbon nanotubes and nano-yttrium oxide is (8-10):(1.2-1.4):1, and the ratio of the total mass of SiC-coated nano-carbonyl iron, hydroxylated multi-walled carbon nanotubes and nano-yttrium oxide to the ethanol aqueous solution is 1g:(4-6)mL.
5. The preparation process of a high-temperature composite microwave absorbing stealth coating according to claim 1, characterized in that, In step S1, the amount of silane coupling agent KH-570 added is 6.6-6.8% of the mass of SiC-coated nano-carbonyl iron.
6. The preparation process of a high-temperature composite microwave absorbing stealth coating according to claim 1, characterized in that, In step S2, the preparation steps of methylphenyl organosilicon modified polyimide resin are as follows: Under nitrogen protection, 4,4'-diaminodiphenyl ether and aminopropyl-terminated polymethylphenylsiloxane are added to N-methylpyrrolidone at a mass ratio of (0.98-1.02):1:(6-8). The mixture is heated and stirred at 40-50℃ until completely dissolved. Then, pyromellitic dianhydride is added in three portions, with an interval of 15 min between each addition. The mixture is kept warm and stirred for 2-3 hours. Then, acetic anhydride, pyridine, and toluene are added and stirred until homogeneous. The mixture is then heated to 135-145℃ and refluxed for 3-4 hours. Finally, the mixture is distilled under reduced pressure, precipitated with alcohol, filtered, washed, and dried under vacuum to obtain methylphenyl organosilicon modified polyimide resin.
7. The preparation process of a high-temperature composite microwave absorbing stealth coating according to claim 6, characterized in that, The molar ratio of pyromellitic dianhydride to 4,4'-diaminodiphenyl ether and aminopropyl-terminated polymethylphenylsiloxane is 1:1, the molar ratio of acetic anhydride to pyromellitic dianhydride is 2:1, the molar ratio of pyridine to pyromellitic dianhydride is 2:1, and the amount of toluene added is 30-35% of the mass of N-methylpyrrolidone.
8. The preparation process of a high-temperature composite microwave absorbing stealth coating according to claim 1, characterized in that, In step S3, the raw material composition of the composite microwave absorbing stealth coating, by mass parts, is: 55-65 parts of methylphenyl silicone modified polyimide resin, 10-12 parts of fluororubber 246, 8-10 parts of aluminum dihydrogen phosphate, 16-20 parts of modified composite powder, 0.5-1 parts of fumed silica and 8-10 parts of N-methylpyrrolidone.
9. The preparation process of a high-temperature composite microwave absorbing stealth coating according to claim 1, characterized in that, In step S4, the gradient curing process is as follows: First stage: 50-60℃ for 50-60 min; Second stage: 110-120℃ for 1 h; Third stage: 195-205℃ for 40-50 min; Fourth stage: 350℃ for 1 h; Fifth stage: 550℃ for 30 min.
10. A high-temperature composite microwave absorbing stealth coating, characterized in that, It is prepared by the process described in any one of claims 1-9.