Nanometer CeO2-PDMS composite anti-corrosion 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 CeO2-PDMS composite anti-corrosion wave-absorbing coating and a preparation method thereof. According to the invention, PDMS is used as a hydrophobic agent, the density of PDMS is smaller than that of epoxy resin, and a small amount of added PDMS can be gathered above the whole coating in a fusion gradual change manner in a curing process, so that first-level anti-corrosion protection is formed; pDMS can also provide better flexibility and elasticity, and the durability and stability of the coating are enhanced. And the green and environment-friendly corrosion inhibitor CeO2 is supplemented, so that not only is the corrosion inhibited, but also the compactness of the coating is improved, the cost is low, and second-level anti-corrosion protection is formed. Through combination of the two, the corrosion current density of the coating is reduced by two orders of magnitude, and good performance can be kept for a long time under severe environmental conditions. The raw materials used in the invention have low requirements on reaction equipment and conditions, and have high adaptability to the wave-absorbing agent; the coating can be prepared by adopting a spraying method, is low in cost and simple and convenient to operate, is not influenced by a base material, and is suitable for large-scale production.

Description

Technical Field

[0001] The present invention relates to the technical field of functional coatings and composite materials thereof, and in particular to a nano CeO 2 -PDMS composite anti-corrosion and microwave-absorbing coating and its preparation method. Background Art

[0002] In the modern defense and military field, the process of reconnaissance and counter-reconnaissance is always accompanied by multi-band and high-intensity electromagnetic confrontation, and radar absorbing coatings have become the main measure to achieve stealth equipment. Carbonyl iron powder is a widely used electromagnetic wave absorber. The radar absorbing coating prepared by it has the characteristics of low density, wide frequency band and excellent performance, which is incomparable to other electromagnetic wave absorbers such as nickel powder, iron silicon aluminum powder, iron silicon chromium powder, etc. However, due to the strong activity of carbonyl iron powder, the radar absorbing coating prepared by it will be exposed to high temperature oxidation and electrochemical corrosion for a long time in a complex application environment, resulting in the inevitable existence of scratches, cracks, and shedding of the absorbing coating. The slightest damage or defect in the coating may cause a significant deterioration in the stealth performance, and even endanger the service safety of the equipment. Therefore, high-performance and excellent corrosion-resistant radar absorbing coatings have a very urgent and important application background demand.

[0003] At present, there are two main technical methods to improve the corrosion resistance of radar absorbing coatings:

[0004] The first technical method: an inert layer is coated on the surface of the carbonyl iron powder, and the contact between the corrosive medium and the magnetic powder is isolated by barrier protection, which hinders the ion migration between the coatings. The coating layer is divided into organic coating, inorganic coating and organic-inorganic composite coating. For example: Patent CN113388231A first modifies the surface of the carbonyl iron powder with a silane coupling agent, and then mixes the treated carbonyl iron powder and epoxy resin, stirs, and solidifies, and finally obtains the epoxy resin-coated carbonyl iron powder absorbing material, which is immersed in water at room temperature for 168 hours without corrosion. Patent CN112563010A uses the "hydrolysis-pyrolysis" method to coat the surface of the iron powder with a dense SiO 2 Thick coating layer, so that no rust spots appeared in the salt spray test for 1500h. Patent CN116355448A uses high weather resistance resin to modify the surface of metal powder, and then adds the treated powder to polyurethane resin and polymer to prepare low surface energy self-sealing gradient radar absorbing coating. The corrosion current density of this invention is 2 orders of magnitude higher than that of the control group. However, coating carbonyl iron powder will reduce the magnetic properties of iron powder, resulting in deterioration of absorbing performance: Professor Wang Jianbo of Lanzhou University (doi:10.1088 / 0957-4484 / 21 / 9 / 095708) uses SiO 2 Coated carbonyl iron powder, the saturation magnetization of the iron powder decreased by 17emu g -1, the reflection loss at 2GHz deteriorates from -10dB to -3dB.

[0005] The second technical method is to spray a layer of anti-corrosion topcoat on the surface of the absorbing coating. For example, patent CN110684438B discloses an anti-corrosion and aging-resistant absorbing coating, which is a three-layer structure consisting of an epoxy primer layer, a polyurethane absorbing layer and a polyurethane topcoat layer, and can withstand neutral salt spray for more than 1000 hours. Patent CN107892871B discloses an anti-corrosion absorbing coating and a preparation method thereof. The method also uses a three-layer system of an acrylic polyurethane base layer, an absorbing layer and an anti-corrosion surface layer. However, the three-layer corrosion protection system significantly increases the construction process and costs, and the multi-layer structure has weak interlayer bonding, and the coating is easy to fall off and damage. Summary of the invention

[0006] In view of the above problems and shortcomings, in order to solve the problem that the existing carbonyl iron powder absorbing coating has relatively insufficient anti-corrosion performance, the present invention provides a nano CeO 2 -PDMS composite anti-corrosion and microwave-absorbing coating and its preparation method can achieve the anti-corrosion effect without coating with an inert layer or spraying a multi-layer structure, while the microwave-absorbing performance is not reduced, and the preparation method is simple and low-cost.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A nano CeO 2 -PDMS composite anti-corrosion and wave-absorbing coating, the raw materials of which are calculated by weight percentage, include: 7wt% to 10wt% epoxy resin, 3wt% to 5wt% PDMS (polydimethylsiloxane, polymer organic silicon material), 0.8wt% to 1.5wt% nano CeO 2 , 65wt% to 70wt% of carbonyl iron powder, 15wt% to 20wt% of ethyl acetate, 7wt% to 10wt% of epoxy resin curing agent, 0.3wt% to 0.5wt% of PDMS curing agent, the sum of the masses of each component is 100%; the raw materials of each component are mixed and then sprayed and cured to obtain the product.

[0009] Furthermore, the nano CeO 2 The particle size is ≤30nm, which is conducive to the mixing of components and makes the subsequent coating performance better.

[0010] Furthermore, the epoxy resin: PDMS: nano CeO 2 The mass percentage of carbonyl iron powder:ethyl acetate is 7:3:0.8:70:25.

[0011] The above nano CeO 2 -The preparation method of the PDMS composite anti-corrosion and microwave absorbing coating comprises the following steps:

[0012] Step 1: 7wt% to 10wt% of epoxy resin, 3wt% to 5wt% of PDMS polydimethylsiloxane, 0.8wt% to 1.5wt% of nano CeO 2 , 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 are prepared; the total amount is 1;

[0013] Step 2, mixing the raw materials prepared in step 1 to obtain a slurry;

[0014] 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.

[0015] Furthermore, the surface of the target substrate is cleaned before spraying, so as to improve the adhesion between the coating and the target substrate.

[0016] Furthermore, 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.

[0017] In the present invention, PDMS is mainly used as a hydrophobic agent. PDMS is an organic high molecular polymer, and its molecular structure contains carbon and silicon. This bonding mode makes its surface energy lower, so the surface shows strong hydrophobicity. In addition, the density of PDMS is smaller than that of epoxy resin. During the curing process, a small amount of PDMS added will gather above the inside of the overall coating in a blending and gradual manner, forming a hydrophobic surface, which effectively prevents the corrosive medium from entering the coating. The hydrophobic surface has a self-cleaning property, which can make dirt and corrosive ions easier to clean, and further reduce the corrosive effect of surface residues on the material.

[0018] CeO 2 As a corrosion inhibitor, the surface is easy to react with the hydroxyl, carbonyl and other functional groups in the epoxy resin, and has good dispersion, making the coating surface more dense, less prone to defects inside, and difficult to form corrosion paths. 2 Ce on the surface 3 + and OH - The insoluble cerium-based oxide or hydroxide generated by the reaction is attached to the carbonyl iron powder to play a role in corrosion inhibition.

[0019] In summary, the present invention uses PDMS as a hydrophobic agent. The density of PDMS is smaller than that of epoxy resin. During the curing process, a small amount of PDMS added will be accumulated on the top of the overall coating in a blending gradient manner to form a hydrophobic surface, which effectively prevents the corrosive medium from entering the coating to form the first level of corrosion protection. PDMS can also provide good flexibility and elasticity, can adapt to the deformation of different surfaces, is not easy to crack or fall off, and enhances the durability and stability of the coating. With the help of CeO 2 As a corrosion inhibitor, green and environmentally friendly corrosion inhibitor CeO 2 It can not only inhibit corrosion, but also increase the density of the coating, and is cheap, forming a second level of corrosion protection. 2 , PDMS, ethyl acetate, etc. are all commonly used raw materials, with low requirements for reaction equipment and mild reaction conditions; they have high adaptability to the particle size and shape of the absorber; the coating can be prepared by spraying, which is low in cost, easy to operate, and is not affected by the substrate, and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is the infrared spectrum of the coating surface and bottom surface of Example 1.

[0021] Figure 2 are the contact angles of the control group and Examples 1 to 3.

[0022] Figure 3 These are digital photos of the control group and Examples 1 to 3 after 60 days of salt spray.

[0023] Figure 4 These are SEM images of the coating surfaces of the control group and Examples 1 to 3 before and after 60 days of salt spray.

[0024] Figure 5 It is the XRD diagram of the control group and Examples 1 to 3 before and after 60 days of salt spray.

[0025] Figure 6 The EDS graphs of the control group and Examples 1 to 3 after 60 days of salt spray

[0026] Figure 7 The polarization curves of the control group and Examples 1 to 3 tested in 3.5% NaCl solution.

[0027] Figure 8 It is the reflection loss of the control group and Examples 1 to 3.

[0028] Fig. 9 It is a simple preparation flow chart of the present invention.

[0029] Fig.10 It is the anti-corrosion principle diagram of the present invention. DETAILED DESCRIPTION

[0030] The present invention is further described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Example

[0032] A nano CeO 2 -The preparation method of the PDMS composite anti-corrosion and microwave absorbing coating comprises the following steps:

[0033] Step 1: 7wt% to 10wt% of epoxy resin, 3wt% to 5wt% of PDMS polydimethylsiloxane, 0.8wt% to 1.5wt% of nano CeO 2 (particle size 20 ~ 40nm), 65wt% ~ 70wt% carbonyl iron powder, 15wt% ~ 20wt% ethyl acetate, 7wt% ~ 10wt% epoxy resin curing agent, 0.3wt% ~ 0.5wt% PDMS curing agent, prepare the materials; the total amount is 1.

[0034] Step 2, mixing the raw materials prepared in step 1 to obtain a slurry;

[0035] Add PDMS and ethyl acetate to the epoxy resin and disperse them ultrasonically for 10 minutes; then add nano-CeO 2 and carbonyl iron powder, and dispersed them with a pneumatic disperser for 10 minutes at a speed of 200-300 r / min; finally, epoxy resin and PDMS curing agent were added respectively. The specific formula is shown in the table below.

[0036]

[0037] Step 3: Spray the slurry mixed in step 2 onto the cleaned target substrate surface:

[0038] Target substrate cleaning: Use 400-mesh SiC sandpaper to polish the steel plate (Q235, 80×120×1mm) to create a metallic luster, then use ethanol and acetone to remove water and oil from the steel surface, and then place it in a 60°C oven for later use.

[0039] Use a spray gun to evenly spray the slurry mixed in step 2 on the surface of the target steel plate, and cure it at room temperature for 1 hour; then place it in a 60℃ electric heating blast drying oven for 6 hours. After the coating is completely cured, perform electrochemical and salt spray tests.

[0040] from Figure 1 From the infrared spectrum, we can see that at 788cm -1The stretching vibration absorption peak of PDMS silicon-carbon bond is 1080-1009cm -1 The wide and strong absorption peak in the range is the stretching vibration peak of the silicon-oxygen bond (Si-O-Si) on the PDMS main chain. -1 The peak at can be attributed to the bending vibration absorption peak of silicon-carbon bond (Si-C). Figure 1 It shows that the PDMS characteristic peak on the coating surface is stronger than that on the bottom surface, indicating that the coating forms a low surface energy surface composed of PDMS.

[0041] from Figure 2 From the contact angle photos of the coating, it can be seen that the synergistic effect of PDMS and nano-CeO2 reduces the surface energy of the coating, and the contact angle increases from 88.32 to 106.08, 107.85 and 108.8. Figure 3 The photos of the coating before and after salt spray show that the carbonyl iron powder in the control group coating does not have PDMS and CeO 2 The protection of the coating was poor, and a large number of rust spots, blistering, and shedding appeared on the coating surface. Examples 1 to 3 had less surface pitting.

[0042] from Figure 4 From the SEM images of the coating before and after salt spray, it can be seen that a large number of defects appeared in the iron powder of the control group, the surface of the iron powder was covered with needle-shaped corrosion products, and the structure of the iron powder became loose; the carbonyl iron powder in Examples 1 to 3 did not undergo obvious corrosion, and the overall structure was a regular and smooth spherical shape with a dense structure.

[0043] from Figure 5 The XRD patterns of the coating before and after salt spray show that the coating of the control group has very obvious Fe 2 O 3 , Fe 3 O 4 The peak intensity of the iron oxide in Examples 1 to 3 is relatively weak, and the degree of corrosion of the coating is relatively light.

[0044] from Figure 6 The EDS graph of the coating after salt spraying combined with the table below shows that the contents of O, Cl and Na in Examples 1 to 3 are lower than those in the control group.

[0045]

[0046] from Figure 7 It can be seen from the polarization curves that Examples 1 to 3 have lower corrosion current density and higher corrosion potential than the control group. The coating impedance increases and the Tafel slope increases. The changes in corrosion parameters are shown in the table below.

[0047]

[0048] from Figure 8It can be seen from the reflection loss diagram that CeO 2 Optimize impedance matching and reduce reflection loss.

[0049] from Fig.10 As can be seen from the schematic diagram, in Examples 1 to 3, PDMS provides a low surface energy surface, which prevents the corrosive medium from entering the coating and also provides the coating with self-cleaning properties. 2 Ce on the surface 3+ and OH - The reaction generates insoluble cerium-based oxides or hydroxides, which attach to the carbonyl iron powder and inhibit corrosion. The electrochemical reaction is as follows:

[0050] The cathode reaction is:

[0051] Ce 3+ +3OH - →Ce(OH) 3 (1)

[0052] 2Ce(OH) 3 +2OH - →2CeO 2 +4H 2 O+2e - (2)

[0053] The anode reaction is:

[0054] Fe→Fe 2+ +2e - (3)

[0055] It can be seen from the above examples that the present invention uses PDMS and CeO 2 Constructing an anti-corrosion structure, it is more resistant to salt spray corrosion than the traditional pure carbonyl iron powder absorbing coating. 2 The addition of CeO makes the coating dense and reduces surface defects; 2 It is a green slow-release agent that improves the corrosion resistance of the coating and its non-toxic and harmless environmental protection requirements, achieving long-term function; CeO 2 It also has good high temperature resistance and can resist the negative impact of aerodynamic heating generated by the target object under high-speed movement. PDMS also makes it have better antioxidant and weather resistance. This enables the coating to maintain good performance under harsh environmental conditions, reduce the corrosion current density by two orders of magnitude, and extend its service life. The invention is simple to make, does not require coating, can be sprayed once, has low cost, is applicable to a variety of substrates, and has great industrial value.

Claims

1. A nano CeO2-PDMS composite anti-corrosion and microwave absorbing coating, characterized in that: The raw materials include, by mass percentage, 7wt% to 10wt% of epoxy resin, 3wt% to 5wt% of PDMS polydimethylsiloxane, 0.8wt% to 1.5wt% of nano CeO2, 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 CeO2-PDMS composite anti-corrosion and microwave absorbing coating as claimed in claim 1, characterized in that: The particle size of the nano CeO2 is ≤30nm.

3. The nano CeO2-PDMS composite anti-corrosion and wave-absorbing coating as claimed in claim 1, characterized in that: The mass percentage of the epoxy resin: PDMS: nano-CeO2: carbonyl iron powder: ethyl acetate is 7:3:0.8:70:

25.

4. The method for preparing the nano CeO2-PDMS composite anti-corrosion and wave-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, 0.8wt% to 1.5wt% nano CeO2, 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 CeO2-PDMS composite anti-corrosion and wave-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 CeO2-PDMS composite anti-corrosion and wave-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.

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