GB2618172A

GB2618172A - Method for enhancing FeSiAl-based microwave absorbing material by plasma-densified polyurethane acrylate (pua)

Info

Publication number: GB2618172A
Application number: GB2217396.7A
Authority: GB
Inventors: jian Xian; Pan Ying; Li Jinyao; Liu Yifan; Ma Xuejuan; Wang Junwei
Original assignee: Yangtze River Delta Research Institute of UESTC Huzhou
Current assignee: Yangtze River Delta Research Institute of UESTC Huzhou
Priority date: 2022-04-25
Filing date: 2022-11-21
Publication date: 2023-11-01
Also published as: GB202217396D0; CN114752113A

Abstract

A method for enhancing a FeSiAl-based microwave absorbing material by plasma-densified polyurethane acrylate (PUA), comprises i) in-situ polymerization of hydroxyl acrylic resin with an isocyanate in the presence of FeSiAl powder, ii) plasma densifying the PUA and iii) reacting with tetraethyl orthosilicate (TEOS) to produce silica coated particles.

Description

METHOD FOR ENHANCING FeSiAl-BASED MICROWAVE ABSORBING MATERIAL BY PLASMA-DENSIFIED POLYURETHANE ACRYLATE (PUA)

TECHNICAL FIELD

100011 The present disclosure belongs to the technical field of new microwave absorption materials, and in particular relates to a method for enhancing the microwave absorption performance and anticorrosion characterization by plasma-densified polyurethane aciylate (PUA), and use in a microwave stealth anti-corrosion coating

BACKGROUND

100021 With the rapid development of the electronics industry, the harm of electromagnetic radiation to electrical equipment and human health has become increasingly prominent. The development of high-efficiency microwave absorbing materials has become a research hotspot. However, most microwave absorbing materials are used in harsh environments such as oceans and acid rain. Corrosive particles with strong penetrating power, such as CP, H', and OH-, tend to react with the microwave absorbing materials, to gradually change their morphology and structure and produce pitting pits, resulting in severe corrosion and aging of the microwave absorbing materials, and deteriorating electromagnetic parameters and performances of the material. Moreover, the corrosion products adhere to the surface of the microwave absorbing material, causing the overall impedance mismatch of the material, leading to reduction or even loss of the microwave absorbing performance, so as to generate huge economic losses and aggravate burden on the environment. Therefore, research and design of composite structures with high-efficiency microwave absorbing performance and excellent corrosion resistance have attracted great attention of researchers.

100031 As a typical soft magnetic material, FeSiAl not only has high saturation magnetization and excellent magnetic loss performance, but also does not contain precious metals, showing a low cost. However, the practical application of FeSiAl is hindered by the shortcomings of easy corrosion, easy magnetic aggregation, and high density. Applying a protective coating is one of the important methods to improve the corrosion resistance of magnetic materials, which can effectively avoid direct contact between magnetic materials and corrosive media. For example, Chinese patent 202110988588.6 disclosed a method for preparing a FeSiAlZrScSr magnetic powder core. On the one hand, adding rare earth elements scandium, zirconium, and strontium to a FeSiAl magnetic powder can reduce hardness and brittleness of the FeSi Al magnetic powder and improve a magnetic performance stability of the FeSiAl magnetic powder core; on the other hand, the corrosion resistance and high-temperature resistance of the magnetic powder core is enhanced by a phosphate-yttrium oxide composite coating process. However, the rare earth elements increase a material cost, and the prepared composite does not effectively improve the microwave absorbing performance.

SUMMARY

[0004] In view of defects in the background, an objective of the present disclosure is to propose a method for enhancing a FeSiAl-based microwave absorbing material by plasma-densified PUA. The FeSiAl composite has a better coating effect. The preparation method is simple and easy. The composite has better corrosion resistance, electromagnetic impedance matching characteristics, and a larger attenuation constant.

[0005] To achieve the above objective, the present disclosure adopts the following technical solutions.

[0006] The present disclosure provides a method for enhancing a FeSiAl-based microwave absorbing material by plasma-densified PUA, including the following steps: [0007] step 1, dispersing 1 part to 10 parts by weight of a FeSiAl powder in 5 parts to 20 parts by weight of a butyl acetate solution with 10 wt% to 50 wt% of a hydroxyl acrylic resin under stirring, heating in a water bath at 25°C to 60°C for 0.2 h to 0.5 h, adding 0.3 parts to 1 part by weight of a curing agent, stirring for 0.5 h to 8 h, washing with absolute ethanol for 6 to 8 times, conducting magnetic separation, and drying to obtain a spherical FeSi Al composite with in-situ polymerization of PUA, denoted as FeSiAl@PUA; [0008] step 2, placing 0.1 parts to 10 parts by weight of the FeSiAl@PUA in a cavity of a tubular furnace of a plasma-enhanced chemical vapor deposition (PECVD) equipment, and discharging air in the tubular furnace by introducing an induction gas with a total flow rate of 10 mL/min to 100 mL/min; vacuumizing the cavity with a vacuum pump, and adjusting the total flow rate of the induction gas to 10 ml/min to 30 ml/min to maintain a vacuum degree in the cavity at 10 Pa to 50 Pa for 10 min to 30 min; and conducting plasma induction with a plasma excitation source at an excitation power of 100 W to 500 W for 1 min to 120 min to obtain a plasma-densified organic layer PUA, denoted as a PLCVD-FeSiAl@PUA powder; and [0009] step 3, mixing 1 part to 5 parts by weight of the PECVD-FeSiAl@PUA powder, 3 parts to 10 parts by weight of the absolute ethanol, and 1 part to 10 parts by weight of deionized water uniformly, heating in a water bath at 25°C to 60°C for 0.2 h to 0.5 h, and adjusting a resulting mixture to a p1-1 value of 9 to 10 with ammonia water; adding 1 part to 10 parts by weight of tetraethyl orthosilicate (TEOS), and stirring for 0.5 h to 8 h; and washing an obtained mixture with the deionized water and the absolute ethanol 6 to 8 times alternately, conducting magnetic separation, and drying to obtain (PECVD-FeSiA1@PUA)@Si02.

100101 Preferably, in step 1, the curing agent is selected from the group consisting of isocyanate (N3390), pyridine, an amino resin, an epoxy group-containing resin, and titanium tetraisopropanolate. 100111 Preferably, in step 2, the type and the flow rate of the induction gas, the vacuum degree of the cavity, the excitation power, and the induction time each are a process control parameter to affect an organic coverage and a surface roughness of the sample.

100121 Preferably, in steps t and 3, the stirring is mechanical stirring instead of magnetic stirring since the FeSi Al powder is magnetic.

100131 The present disclosure further provides use of the plasma-dens fied PUA-combined FeSiAlbased microwave absorbing material, where the material has desirable microwave absorbing performance and anti-corrosion performance.

100141 In the present disclosure, the method for enhancing a FeSiAl-based microwave absorbing material by plasma-densified PUA has the principle as follows: through a cross-linking reaction between redundant hydroxyl groups on a FeSiAl surface, isocyanate groups in the curing agent N3390, and hydroxyl and carboxyl groups in the hydroxyl acrylic resin, the PUA is polymerized in situ on the spherical FeSiAl surface. PECVD is introduced to improve the density of the PUA coating, The high-energy particles such as a large number of electrons, positive and negative ions, and free radicals in the plasma are reacted with the PUA to increase its coverage on the FeSiAl surface. By a sol-gel method with simple process and low cost, a layer of inorganic Si02 is polymerized in situ on the prepared composite structure, while enhancing corrosion resistance and microwave absorbing performances of the composite structure.

[0015] The (PECVD-FeSiA1@PUA)@Si02 prepared by the method has a spherical microscopic shape with a particle size of about 10 tm, and has uniformly-distributed fine PUA flakes and nanoSi02 microspheres on the surface. The material has a stable corrosion barrier structure and a multi-interface structure, which effectively improves the microwave absorbing performance and anticorrosion performance of the spherical FeSiAl magnetic powder.

100161 Compared with the prior art, the present disclosure has the following beneficial effects.

100171 1. In the present disclosure, the (PECVD-FeSiAlaPUA)r&Si02 has a larger reflection loss value and effective absorption bandwidth, thereby possessing better microwave absorbing performance and corrosion resistance, which is beneficial to the application in actual engineering. 100181 2. In the present disclosure, the method has mild conditions, low cost, convenient operation, and can realize industrialization, showing a desirable commercial value.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 shows scanning electron microscopy (SEM) images before and after coating of a spherical FeSiAl alloy in the present disclosure; where (a) and (b) are SEM images of a spherical FeSiAl alloy (M) before polymerization; (c) and, (d) are SEM images of FeSiAl@PUA (MP) obtained in Example 1; and (e) and (f) are SEM images of ([email protected])@Si02 ((P-MP)S) obtained in Example 3; 100201 FIG. 2 shows an energy dispersive spectroscopy (EDS) Mapping diagram of the (PECVDFeSiA1@PUA)@Si02 ((P-MP)S) obtained in Example 3 of the present disclosure; where (a) is Fe, (b) is Si, (c) is Al, (d) is C, (e) is N, and (f) is 0; [0021] FIG. 3 shows Raman spectra of the FeSiAlgPUA (MP) obtained in Example 1 and the (PECVD-FeSiAl@PUA)@Si02 ((P-MP)S) composite structure obtained in Example 3; [0022] FIG. 4 shows Fourier transform infrared spectroscopy (FTIR) spectra of the FeSiAl@PUA obtained in Example 1 and the (PECVD-FeSiAl@TUA)@.Si02 composite structure obtained in Example 3 of the present disclosure; [0023] FIG. 5 shows microwave absorbing performances of the spherical FeSiAl (M), the FeSiAlaPUA obtained in Example I, the PECVD-FeSiAl@PUA (P-MP) obtained in Example 2, and the (PECVD-FeSiAl@PUA)aSi02 ((P-MP)S) obtained in Example 3 of the present disclosure; and [0024] FIG. 6 shows a corrosion performance test chart of the spherical FeSiAl (M), the FeSiAlaPUA (MP) obtained in Example 1, and the (PECVD-FeSiAl@PUA)@Si02 ((P-MP)S) obtained in Example 3 of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The technical solutions of the present disclosure will be further described below through specific examples.

[0026] Example 1

[0027] A method for enhancing a FeSi Al -based microwave absorbing material by plasma-densified PUA included the following steps: [0028] 8 g of a FeSiAl powder (denoted as M) was dispersed in 46 g of a butyl acetate solution with 15 wt% of a hydroxyl acrylic resin under stirring, heated in a water bath at 60°C for 0.5 h, 2.4 g of a curing agent N3390 was added, stirred for 0.5 h, washed with absolute ethanol for 6 to 8 times, magnetic separation was conducted, and dried to obtain a spherical FeSiAl composite with in-situ polymerization of PUA, denoted as FeSiAl@PUA and named as MP.

[0029] Example 2

[0030] Compared with Example 1, this example differed in that: the MP sample was treated by PECVD equipment as follows: 5 g of the MP was placed in a cavity of a tubular furnace of the PECVD equipment, and air in the tubular furnace was discharged by introducing an induction gas with a total flow rate of 30 mL/min; the cavity was vacuumized with a vacuum pump, and the total flow rate of the induction gas was adjusted to 10 ml/min to maintain a vacuum degree in the cavity at 30 Pa for 10 min; and plasma induction was conducted with a plasma excitation source at an excitation power of 100 W for 10 min to obtain a plasma-densified organic layer PUA, denoted as a PECVD-FeSiAl@PUA powder and named as P-MR

100311 Example 3

100321 Compared with Example 1, this example differed in that: a Si02 layer was coated on a surface of the P-MP sample by a sol-gel method as follows: 3 g of the PECVD-FeSiAl@PUA powder, 30 mL of the absolute ethanol, and 8 mL of deionized water were mixed uniformly, heated in a water bath at 30°C for 0.5 h, and a resulting mixture was adjusted to a pH value of 9 with ammonia water; 5 mL of TEOS was added, and stirred for 0.5 h to 8 h; and an obtained mixture was washed with the deionized water and the absolute ethanol 6 to 8 times alternately, magnetic separation was conducted, and dried to obtain (PECVD-FeSiAl@PHA)@Si02, named as (P-MP)S. 100331 FIG. 1 shows scanning electron microscopy (SEM) images before and after coating of a spherical FeSiAl alloy in the present disclosure; where (a) and (b) are SEM images of a spherical FeSiAl alloy (WI) before polymerization; (c) and, (d) are SEM images of FeSiAl@PUA (MP) obtained in Example 1; and (e) and (0 are SEM images of ([email protected])a Sift ((P-MP)S) obtained in Example 3; [0034] As shown in FIG. 1, there were Si02 spherical particles on the surface of MS with an average particle size of 0.2 pm, and there was an obvious flaky coating on the surface of the MSP sample.

[0035] FIG. 2 shows an energy dispersive spectroscopy (EDS) Mapping diagram of the (PECVDFeSiAk&PUA)@Si02 ((P-MP)S) obtained in Example 3 of the present disclosure; where (a) is Fe, (b) is Si, (c) is Al, (d) is C, (e) is N, and (f) is 0; [0036] FIG. 2(a) showed that all three samples contained elements such as C, Si, Al, and 0, and the peak intensifies of Fe and Al elements in the three samples of M, MS, and MSP decreased in sequence. In the three samples of M, MS, and MSP, the peak intensity of Si element increased and then decreased, indicating that the outer layer of MS was coated with Si02 layer. Only MSP contained N element, indicating that the surface of the MSP sample had a layer of material containing N but not Si. (b), (c), and (d) showed that only the surface of the M sample contained simple Si; the surfaces of M, MS, and MSP samples were all Si-0 bonds, at 102.4 eV, 103.3 eV, and 103.6 eV, respectively. The increasing binding energy indicated that Si lost electrons and the electron cloud density decreased. (0 showed that there were C-C, C-N, C-0 and other bonds on the surface of MSP samples, which were inherent groups of PUA, thus being consistent with the conclusion obtained by infrared spectroscopy analysis. It is proved that the Si02/PUA bilayer structure was formed on the surface of FeSiAl, improving the microwave absorbing and corrosion resistance of the composite.

100371 FIG. 3 showed Raman spectra of the FeSiAl@PUA (MP) obtained in Example 1 and the (PECVD-FeSiAl@PUA)@Si02 ((P-MP)S) composite structure obtained in Example 3; the characteristic peak of MP composite structure at 620 cm-I was the stretching vibration of methyl -CH3 in the polymer chain. In addition, the characteristic peaks at 1,000 cm-I, 1,032 cm-1, and 1,192 cm -I were stretching vibrations of -C-O-C-in PUA. The characteristic peak at 1,450 cm -I was the asymmetric stretching vibration of C=0 in an amide unit -C(0)-NIA-of the PUA. The characteristic peak at 1,602 cm-1 indicated the existence of unsaturated bond C=C in the polymer chain. For (PMP)S, the characteristic peak at 480 cm-1 was the strong stretching vibration of Si-O-Si, indicating that the Si02 inorganic layer was successfully synthesized on the surface of P-MP. In addition, (PMP)S had a characteristic peak at 1,463 cm -I that was asymmetric stretching vibration of C=0 in the polymer chain, and a characteristic peak at 1,528 cm -I that was strong stretching vibration of C-0 in a carboxylate unit -0-C(0)-of the PUA. In summary, the characterization and analysis of Raman spectra could strongly prove the existence of PUA in the composite structures of MP and (P-MP)S, and the existence of Si02 in the composite structure of (P-MP)S.

100381 FIG. 4 showed FTlit spectra of the FeSiAl@PUA obtained in Example 1 and the (PECVDFeSiA1@PUA)@Si02 composite structure obtained in Example 3 of the present disclosure. It was seen from the figure that in the MP composite structure: the peaks at 3,506 cm -I and 3,390 cm -I were the Nil stretching vibrations of the amide group in PUA; the peak at 1,631 cm" was due to the strong stretching vibration of C=0; the peak at 1,680 cm-1 was due to the stretching vibration of the amide group C(0)-NH-; the peak at 754 cm-1 was due to the stretching vibration of C-N in the amide group; the peak at 695 cm-1 indicated the bending vibration of C=0; the peak at 1,450 cm-1 was due to the stretching vibration of methylene -C112-in PUA; the peak at 3,431 cm-1 indicated the 0-H stretching vibration of the MP surface. In addition, due to the densification and thinning of PUA by PECVD, and the coating of Si02 inorganic layer blocking the Raman detection signal, the Raman peaks of (P-MP)S were less than those of MP samples. The peak at 1,684 cm-1 indicated the strong stretching vibration of C=0, the peak at 1,200 cm-1 indicated the stretching vibration of C-C in the polymer chain, and the peak at 1,089 cm -I indicated the stretching vibration of Si-O-Si. In summary, the Raman and infrared spectroscopic characterizations could strongly prove the existence of PUA in the composite structures of MP and (P-IVIP)S, and the existence of Si02 in the composite structure of (P-MP)S.

100391 FIG. 5 showed (a) microwave absorbing performances of the spherical FeSiAl (M), (b) the FeSiAl@PUA obtained in Example 1, (c) the PECVD-FeSiAl@PUA (P-MP) obtained in Example 2, and (d) the (PECVD-FeSiAl@PUA)@Si02 ((P-MP)S) obtained in Example 3 of the present disclosure. As shown in (a), the pure sample M had an RE,,in of -36 dB at a thicker thickness (5 mm), with an effective absorption frequency band of 2.8-5.2 GHz, and an EAB of only 2.4 GHz. Therefore, the polymer in-situ polymerization, PECVD, and Sol-Gel method were used to modify the surface of pure FeSi Al to improve a microwave absorption performance. As shown in (b) to (d), the MP, P-MP, and (P-MP)S composite structures each had a significantly improved electromagnetic wave absorbing performance. The MP composite structure obtained by in sing polymerization of PUA on M could achieve!Thin', of -42 dB and EAB of 4.5 Gbh (12.0 Gbh to 16.5 GHz) at a matching thickness of 2.0 mm. It was found that the NIP composite structure achieved a higher ItLmin value and a greater EAB at a matching thickness of 3 mm lower than that of the M, and had a microwave absorbing performance significantly optimized compared with that of the M. 100401 FIG. 6 showed a corrosion performance test chart of the spherical FeSi Al (M), the FeSiAlaPUA (MP) obtained in Example 1, and the (PECVD-FeSiAl@PUA)@Si02 ((P-MP)S) obtained in Example 3 of the present disclosure; where (a) was an OCP curve; (b) was a Tafel curve; (c) was a Nyquist diagram; (d) was a Bode diagram. It was seen from (a) that the OCP values of M, MP and (P-MP)S after testing for 1,600 s were -0.154 V, -0.209 V and -0.065 V, respectively; compared with M and MP, the OCP value of (P-MP)S was closest to zero. It was seen from (b) that compared with pure M and MP coated with a single layer of organic PUA on the surface of M, the (P-MP)S composite structure protected by organic PUA/inorganic Si02 double-layer structure had a corrosion potential closer to zero. It was seen from (c) that the (P-MP)S composite structure had a larger capacitive reactance loop radius than that of M and NIP, and a larger capacitive reactance loop radius meant greater charge transfer resistance. This could indicate that the corrosion reaction of (PMP)S was more difficult to occur in a salt solution. It was seen from (d) that at a same frequency, compared with M and MP, (P-MP)S had larger impedance modulus and phase angle values. This was consistent with the conclusions obtained from the OCP curve, EIS curve, and Tafel curve analysis, proving that the composite structure (P-MP)S obtained after the organic PUA/inorganic Si02 double-layer structure coated M had a greater improvement in anti-corrosion performance than that of M and MP. This indicated that the (P-MP)S composite structure was more stable, more inert and less prone to corrosion reactions than the M and MP structures in a neutral salt solution.

Claims

WHAT IS CLAIMED IS: 1. A method for enhancing a FeSi Al-based microwave absorbing material by plasma-densified polyurethane acrylate (PUA), comprising the following steps: step 1, dispersing 1 part to 10 parts by weight of a FeSiAl powder in 5 parts to 20 parts by weight of a butyl acetate solution with 10 wt% to 50 wt% of a hydroxyl acrylic resin under stirring, heating in a water bath at 25°C to 60°C for 0.2 h to 0.5 h, adding 0.3 parts to 1 part by weight of a curing agent, stirring for 0.5 h to 8 h, washing with absolute ethanol for 6 to 8 times, conducting magnetic separation, and drying to obtain a spherical FeSiAl composite with in-situ polymerization of PUA, denoted as FeSiAl@PUA; step 2, placing 0.1 parts to 10 parts by weight of the FeSiAl@PUA in a cavity of a tubular furnace of a plasma-enhanced chemical vapor deposition (PECVD) equipment, and discharging air in the tubular furnace by introducing an induction gas with a total flow rate of 10 mL/min to 100 mL/min; vacuumizing the cavity with a vacuum pump, and adjusting the total flow rate of the induction gas to 10 ml/min to 30 ml/min to maintain a vacuum degree in the cavity at 10 Pa to 50 Pa for 10 min to 30 min; and conducting plasma induction with a plasma excitation source at an excitation power of 100 W to 500 W for 1 min to 120 mm to obtain a plasma-densified organic layer PUA, denoted as a PECVD-FeSiAl@PUA powder; and step 3, mixing 1 part to 5 parts by weight of the PECVD-FeSiAlr&PUA powder, 3 parts to 10 parts by weight of the absolute ethanol, and 1 part to 10 parts by weight of deionized water uniformly, heating in a water bath at 25°C to 60°C for 0.2 h to 0.5 h, and adjusting a resulting mixture to a pH value of 9 to 10 with ammonia water; adding 1 part to 10 parts by weight of tetraethyl orthosilicate (TEOS), and stirring for 0.5 h to 8 h; and washing an obtained mixture with the deionized water and the absolute ethanol 6 to 8 times alternately, conducting magnetic separation, and drying to obtain (PECVD-FeSiAl@PUA)@Si02.
2. The method for enhancing a FeSiAl-based microwave absorbing material by plasma-densified PUA according to claim 1, wherein in step 1, the curing agent is selected from the group consisting of isocyanate (N3390), pyridine, an amino resin, an epoxy group-containing resin, and titanium tetrai sopropanolate.
3. The method for enhancing a FeSi Al-based microwave absorbing material by plasma-dens fied PUA according to claim 1, wherein in step 2, the type and the flow rate of the induction gas, the vacuum degree of the cavity, the excitation power, and the induction time each are a process control parameter to affect an organic coverage and a surface roughness of the sample.
4. The method for enhancing a FeSiAl-based microwave absorbing material by plasma-densified PUA according to claim 1, wherein in steps 1 and 3, the stirring is mechanical stirring instead of magnetic stirring since the FeSiAl powder is magnetic.