Nano SiO2 composite wave-absorbing coating and preparation method thereof

Abstract

The invention relates to the technical field of functional coatings and composite materials thereof, in particular to a nano SiO2 composite wave-absorbing coating and a preparation method thereof. Aiming at the problem of impedance mismatch caused by high dielectric constant of a traditional carbonyl iron powder wave-absorbing coating, nano SiO2 particles are innovatively introduced to construct a composite system, and the reflection loss of electromagnetic waves on the surface of a material is remarkably reduced by adjusting the effective dielectric constant and magnetic conductivity of the composite coating and optimizing impedance matching, so that the electromagnetic wave-absorbing coating has a good wave-absorbing effect. Incident electromagnetic waves can effectively enter the interior of the material, and efficient attenuation of electromagnetic energy is achieved through multiple scattering and interface polarization effects of the nano SiO2 and the carbonyl iron powder. The process technology disclosed by the invention has universality on a wave-absorbing agent system, can be compatible with various wave-absorbing materials, does not need complex equipment in the preparation process, is wide in base material adaptability, and has remarkable application value in the fields of aerospace stealth, electromagnetic protection and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of functional coatings and their composite materials, and specifically to a nano-SiO₂ composite absorbing coating and a preparation method thereof. Background Art

[0002] Electromagnetic stealth technology has become a key research direction in the global arms race, and the research and development of stealth materials with excellent wave absorption performance is even more urgent.

[0003] When an electromagnetic wave encounters a medium during its propagation in free space, due to the mismatch between the impedance of free space and the impedance of the medium, partial reflection will occur at the interface, and the rest will refract into the interior of the medium. Inside the medium, the electromagnetic wave interacts with the material, and its energy is dissipated in the form of heat energy, electrical energy, or mechanical energy through dielectric loss or magnetic loss mechanisms. Therefore, the design of high-performance absorbing materials needs to focus on two key factors: firstly, achieving high impedance matching to ensure that the electromagnetic wave can enter the material interior to the greatest extent; secondly, having a high attenuation coefficient to enable the electromagnetic wave energy entering the material interior to decay rapidly.

[0004] In the absorbing material system, as a typical magnetic loss type absorber, although carbonyl iron powder has excellent magnetic loss characteristics, its high conductivity easily causes the electromagnetic wave to be reflected on the coating surface, thereby reducing the energy absorption efficiency. Summary of the Invention

[0005] Aiming at the above existing problems or deficiencies, in order to improve the wave absorption performance of the carbonyl iron powder coating, the present invention provides a nano-SiO₂ composite absorbing coating and a preparation method thereof, which can improve the wave absorption performance of the coating without coating, and the preparation method is simple and the cost is low.

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

[0007] A nano-SiO₂ composite absorbing coating, calculated by mass percentage, its raw materials include: 7wt% - 10wt% of epoxy resin, 3wt% - 5wt% of PDMS (polydimethylsiloxane, a high molecular organic silicon material), 0.3wt% - 0.8wt% of nano-SiO₂, 65wt% - 70wt% of carbonyl iron powder, 15wt% - 20wt% of ethyl acetate, 7wt% - 10wt% of epoxy resin curing agent, 0.3wt% - 0.5wt% of PDMS curing agent, and the sum of the masses of each component is 100%; after mixing each component raw material evenly, it is sprayed and cured to obtain.

[0008] Further, the particle size of the nano-SiO₂ ≤ 10nm.

[0009] Furthermore, the mass ratio of the epoxy resin: PDMS: nano-SiO2: carbonyl iron powder: ethyl acetate is 7:3:0.3:70:25.

[0010] The preparation method of the above nano-SiO2-PDMS composite anti-corrosion and wave-absorbing coating includes the following steps:

[0011] Step 1: Prepare the raw materials according to the mass percentages: 7wt% - 10wt% of epoxy resin, 3wt% - 5wt% of PDMS (polydimethylsiloxane), 0.3wt% - 0.8wt% of nano-SiO2, 65wt% - 70wt% of carbonyl iron powder, 15wt% - 20wt% of ethyl acetate, 7wt% - 10wt% of epoxy resin curing agent, 0.3wt% - 0.5wt% of PDMS curing agent, with the total amount being 1;

[0012] Step 2: Mix the raw materials prepared in Step 1 to obtain a slurry.

[0013] Step 3: Spray the slurry after mixing in Step 2 on the surface of the target substrate, first cure at room temperature for at least 1 hour, and then dry in an environment below 100°C until it is completely cured to obtain the coating.

[0014] Furthermore, the surface of the target substrate is cleaned before spraying to improve the adhesion between the coating and the target substrate.

[0015] Furthermore, the surface of the target substrate is polished with sandpaper before spraying to improve the adhesion between the coating and the target substrate.

[0016] In the present invention, the typical wave-transparent material SiO2 is added to the material system of the composite wave-absorbing coating: First, the dielectric constant of SiO2 is much lower than that of carbonyl iron powder, and its uniform dispersion will reduce the overall dielectric constant of the composite material, making the equivalent impedance of the material closer to the free space impedance, thereby reducing the reflection of electromagnetic waves on the material surface and promoting more electromagnetic waves to enter the interior of the coating; Second, a large number of defects and dipoles will be formed at the interface between SiO2 and carbonyl iron powder. Under the action of an alternating electromagnetic field, significant interfacial polarization effects will be induced in these interfacial regions, enhancing the dielectric loss ability; At the same time, as an insulating phase, SiO2 can effectively isolate carbonyl iron powder particles, inhibit their agglomeration and form a more uniform microstructure, which not only prolongs the propagation path of electromagnetic waves inside the material, but also repeatedly consumes the electromagnetic wave energy through the multiple scattering effect. Finally, the nano-SiO2 composite wave-absorbing coating provided by the present invention can significantly regulate its wave-absorbing performance. Description of the Drawings

[0017] Figure 1 are the reflection losses of the control group and Examples 1 - 3.

[0018] Figure 2are the electromagnetic parameters of the control group and Examples 1-3. Detailed implementation manners

[0019] The present invention will be further described below in conjunction with embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work belong to the scope of protection of the present invention.

[0020] Embodiment

[0021] A preparation method of a nano-SiO2 composite wave-absorbing coating includes the following steps:

[0022] Step 1: Weigh the raw materials of each component by mass percentage: 7wt% - 10wt% of epoxy resin, 3wt% - 5wt% of PDMS polydimethylsiloxane, 0.3wt% - 0.8wt% of nano-SiO2, 65wt% - 70wt% of carbonyl iron powder, 15wt% - 20wt% of ethyl acetate, 7wt% - 10wt% of epoxy resin curing agent, 0.3wt% - 0.5wt% of PDMS curing agent, and the total amount is 1.

[0023] Step 2: Mix the raw materials prepared in Step 1 to obtain a slurry;

[0024] Add PDMS and ethyl acetate to the epoxy resin and ultrasonically disperse for 10 min; then add nano-SiO2 and carbonyl iron powder, and perform dispersion treatment for 10 min with a pneumatic disperser, and the rotation speed of the disperser is 200 - 300 r / min; finally, add the curing agents of epoxy resin and PDMS respectively. The specific formula is shown in the following table.

[0025]

[0026] Step 3: Spray the slurry mixed in Step 2 on the surface of the cleaned target substrate:

[0027] Cleaning of the target substrate: Polish the surface of the steel plate (Q235, 80×120×1 mm) with 400-mesh SiC sandpaper until metallic luster appears, then remove the water and oil stains on the steel surface with ethanol and acetone, and then place it in an oven at 60°C for standby.

[0028] Use a spray gun to evenly spray the slurry mixed in Step 2 on the surface of the target steel plate, cure at room temperature for 1 h; then place it in an electrothermal blast drying oven at 60°C and dry for 6 h. After the coating is completely cured, perform wave-absorbing performance testing.

[0029] From Figure 1 the reflection loss diagram, it can be seen that after adding nano-SiO2, the reflection loss decreases and the wave-absorbing performance improves.

[0030] From Figure 2 It can be seen from the electromagnetic parameters of that SiO2 is a non-magnetic material. After adding it, the magnetic phase will be diluted, resulting in a slight decrease in the real and imaginary parts of the overall magnetic permeability. The dielectric constant of SiO2 is relatively low. After adding it, the overall dielectric constant of the composite material is reduced.

[0031] Through the above experimental data and analysis, it can be known that the present invention innovatively uses nano-SiO2 to compound and modify the carbonyl iron powder coating, and successfully realizes a significant improvement in the wave absorption performance. Specifically, by adjusting the addition ratio of nano-SiO2, the dielectric constant of the composite material can be effectively reduced, making its equivalent impedance closer to the free space impedance, thereby greatly improving the impedance matching characteristics and reducing the reflection loss of electromagnetic waves on the material surface. At the same time, the uniform dispersion of nano-SiO2 not only inhibits the particle agglomeration of carbonyl iron powder, forms a multi-scale heterogeneous interface, but also enhances the energy dissipation of electromagnetic waves through the interface polarization effect and the multiple scattering mechanism. This modification strategy based on nano-SiO2 breaks through the technical bottleneck of the traditional carbonyl iron powder coating with too high dielectric constant and serious impedance mismatch, provides a new idea for the development of broadband, high-efficiency and lightweight wave absorption materials, and has important application potential in the fields of stealth technology, electromagnetic shielding, etc.

Claims

1. A nano-SiO2 composite radar absorbing coating, characterized in that: The raw materials include, by mass percentage, 7wt% to 10wt% of epoxy resin, 3wt% to 5wt% of PDMS polydimethylsiloxane, 0.3wt% to 0.8wt% of nano-SiO2, 65wt% to 70wt% of carbonyl iron powder, 15wt% to 20wt% of ethyl acetate, 7wt% to 10wt% of epoxy resin curing agent, and 0.3wt% to 0.5wt% of PDMS curing agent, and the sum of the masses of the components is 100%. The raw materials of the components are mixed evenly, sprayed and cured to obtain the product.

2. The nano-SiO2 composite microwave absorbing coating according to claim 1, characterized in that: The particle size of the nano-SiO2 is ≤10nm.

3. The nano-SiO2 composite microwave absorbing coating according to claim 1, characterized in that: The mass percentage of the epoxy resin: PDMS: nano-SiO2: carbonyl iron powder: ethyl acetate is 7:3:0.3:70:

25.

4. The method for preparing the nano-SiO2 composite microwave absorbing coating according to claim 1, characterized in that: The following steps are involved: Step 1, prepare the raw materials of each component by mass percentage: 7wt% to 10wt% epoxy resin, 3wt% to 5wt% PDMS polydimethylsiloxane, 0.3wt% to 0.8wt% nano-SiO2, 65wt% to 70wt% carbonyl iron powder, 15wt% to 20wt% ethyl acetate, 7wt% to 10wt% epoxy resin curing agent, and 0.3wt% to 0.5wt% PDMS curing agent; the total amount is 1; Step 2, mixing the raw materials prepared in step 1 to obtain a slurry; Step 3: spray the slurry mixed in step 2 onto the surface of the target substrate, first cure it at room temperature for at least 1 hour, and then dry it in an environment below 100° C. until it is completely cured.

5. The method for preparing the nano-SiO2 composite microwave absorbing coating according to claim 4, characterized in that: The surface of the target substrate is cleaned before spraying to improve the adhesion between the coating and the target substrate.

6. The method for preparing the nano-SiO2 composite microwave absorbing coating according to claim 4, characterized in that: The surface of the target substrate is polished with sandpaper before spraying, so as to improve the adhesion between the coating and the target substrate.

Images