A low-frequency radar absorber with strong weather resistance and preparation method thereof

Abstract

A highly weather-resistant low-frequency radar absorber and its preparation method. The low-frequency radar absorber is composed of nickel-zinc ferrite as a main component, doped with small amounts of sendust and graphene. The nickel-zinc ferrite content is ≥90wt%, the sendust content is 6-8wt%, and the graphene content is 1-2wt%. The sendust is a specially processed flaky sendust, i.e., the sendust is ball-milled with alcohol to a particle size of 20±10μm. The present invention also includes a preparation method for the low-frequency radar absorber. The low-frequency radar absorber of the present invention has strong weather resistance, good radar absorption performance, and is thin in thickness. Its preparation method is simple.

Description

Technical Field

[0001] The present invention relates to a low-frequency radar absorber and a preparation method thereof, and in particular to a low-frequency radar absorber with strong weather resistance and a preparation method thereof. Background Art

[0002] In the field of radar detection, the lower the frequency of electromagnetic waves, the longer their wavelength, the less atmospheric attenuation, and the longer the detection range. Radar absorbing materials, through their unique structure and physical properties, dissipate the energy of incident electromagnetic waves, achieving electromagnetic invisibility. In recent years, research on radar absorbing materials has primarily focused on reducing the thickness and weight of materials suitable for fire control radar frequency ranges (i.e., X and Ku bands), while research on lower-frequency electromagnetic waves has been relatively limited.

[0003] Currently, traditional low-frequency absorbing materials, such as ferrite, only have good absorbing performance in the frequency band below 5GHz when the thickness of the ferrite is very thick. It is usually used as absorbing bricks in darkrooms, so the issues of wavelength and thickness need to be considered. For example, alloy powder has good performance below 2GHz, but the weather resistance of alloy powder is relatively poor and it is easy to rust during actual use. Therefore, the issues of performance and weather resistance need to be considered.

[0004] CN 114101685 A discloses a low-frequency radar wave absorber and a preparation method thereof. The preparation method comprises: (1) adding spherical iron-cobalt alloy powder, a grinding aid, and a coating liquid into a ball mill, ball milling, and drying to obtain silica-coated flaky iron-cobalt alloy powder; wherein the atomic ratio of iron to cobalt in the spherical iron-cobalt alloy powder is 65:35; the grinding aid is calcium stearate; and the coating liquid is ethyl orthosilicate; (2) mixing the flaky iron-cobalt alloy powder and ferrocene to obtain a mixed powder; and (3) placing the mixed powder under an inert atmosphere, sequentially performing a chemical reaction and a heat treatment to obtain the low-frequency radar wave absorber. However, this method is complex to prepare, has strict requirements on the content of the spherical iron-cobalt alloy powder and the coating liquid, and has a high production cost. Moreover, although the method does not record relevant test data on weather resistance, generally speaking, the weather resistance of the alloy powder is poor. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a low-frequency radar absorber with strong weather resistance, good wave absorbing performance and thin thickness.

[0006] A further technical problem to be solved by the present invention is to provide a method for preparing a low-frequency radar absorber with strong weather resistance.

[0007] The technical solution adopted by the present invention to solve the technical problem is to provide a low-frequency radar absorber with strong weather resistance, which is composed of a main component of nickel-zinc ferrite, doped with a small amount of sendust (sendust alloy powder) and graphene, wherein the content of nickel-zinc ferrite is ≥90wt%, the content of sendust is 6-8wt%, and the content of graphene is 1-2wt%.

[0008] Furthermore, the nickel-zinc ferrite is formed by mixing and sintering nickel oxide, zinc oxide, and ferrous oxide as main raw materials and copper oxide as a sintering aid.

[0009] Furthermore, the sendust is a flaky sendust that has been processed by a special process, that is, the sendust is ball-milled with alcohol to a particle size of 20 μm ± 10 μm. The particle size of the flaky sendust is precisely controlled to 20 μm ± 10 μm by controlling the ball-milling time.

[0010] Furthermore, the mass ratio of iron, silicon and aluminum in the Sendust is 80-90:5-10:5-10, preferably 85:9:6.

[0011] Furthermore, the content of nickel oxide in the raw material is 10-20 wt %, the content of zinc oxide is 10-20 wt %, the mass content of ferrous oxide is 60-70 wt %, and the mass content of auxiliary agent copper oxide is 1-2 wt %.

[0012] The present invention further solves the technical problem by adopting a technical solution that provides a method for preparing a low-frequency radar absorber with strong weather resistance, comprising the following steps:

[0013] (1) Mixing raw materials of nickel oxide, zinc oxide and ferrous oxide, and then adding an auxiliary agent of copper oxide to obtain a mixture; wet ball milling the mixture to obtain a ball milling slurry;

[0014] (2) spray drying the ball-milled slurry obtained in step (1) to obtain a dry mixture;

[0015] (3) sintering the dry mixed material obtained in step (2) and cooling it to obtain a sintered absorber material;

[0016] (4) finely grinding the absorber sintered material obtained in step (3), crushing it by vibration grinding, and sieving it to obtain a ferrite absorber material;

[0017] (5) The ferrite absorbing material obtained in step (4) is mixed with specially treated sendust and graphene, and stirred evenly to obtain a low-frequency radar absorber with strong weather resistance.

[0018] Furthermore, in step (1), the wet ball milling time is 1-3 hours, and the mass ratio of the mixture: steel balls: water in the ball milling is 1-2:8-15:1-2.

[0019] Furthermore, in step (3), the sintering temperature is 1200-1300° C.; and the sintering holding time is 1-3 hours.

[0020] Furthermore, in step (4), the mesh size of the sieve is 100-200 meshes.

[0021] Furthermore, in step (5), the specially treated sendust is a sheet-like sendust with a particle size of 20 μm±10 μm obtained by alcohol ball milling.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The present invention adopts a composite design of magnetic absorbing materials, with nickel-zinc ferrite as the main component. In the preferred embodiment, the nickel and zinc contents are adjusted to promote lattice structure distortion, so that the material can obtain excellent magnetic properties at low frequencies and achieve good low-frequency absorption effects. The material is doped with iron-silicon-aluminum and graphene to adjust the dielectric properties of the material, increase the dielectric loss, promote the reflection loss peak to shift to low frequencies, and optimize the low-frequency absorption performance.

[0024] (2) The present invention adopts a special process treatment method. First, the sendust is ball-milled with alcohol to perform flaking treatment. The size of the flaked sendust particles is precisely controlled to 20um±10um by controlling the ball-milling time. Then, the sendust powder is evenly mixed with graphene. The alcohol ball-milling is used to prevent the flaked sendust from adhering and agglomerating during the drying process. The most important thing about this process is to control the particle size of sendust, which should be precisely controlled to 20um±10um. This particle size range is consistent with the particle size range of ferrite powder, which can ensure that the magnetic loss and dielectric loss are evenly dispersed in the entire material system. The longer the ball-milling time, the smaller the sendust flake particles, and the larger the maximum reflection loss peak value, but the peak position will gradually move to the high-frequency part, resulting in a decrease in the performance of the low-frequency part.

[0025] (3) The low-frequency radar absorber composite material prepared with ferrite as the main body of the present invention takes into account the characteristics of sendust and graphene, and can have an extremely wide absorption bandwidth at a relatively thin thickness. When the thickness does not exceed 2 mm, the absorption performance is below -5 dB in the range of 0.5 to 5 GHz, and it has excellent weather resistance;

[0026] (4) The processes involved in the present invention are all conventional processes in the powder metallurgy industry, with simple procedures, low costs, and are suitable for industrial mass production. At the same time, they can be further combined with resins, curing agents, etc. to form absorbing coatings, which have a wider range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a state diagram of the low-frequency radar absorbing material of Example 1 of the present invention after undergoing a 1000-h neutral salt spray test.

[0028] Figure 2 This is the state diagram of pure Fe-Si-Al alloy powder after 300h neutral salt spray test. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0030] Example 1

[0031] The low-frequency radar absorber with strong weather resistance in this embodiment is composed of nickel-zinc ferrite as the main component, doped with a small amount of sendust and graphene, wherein the content of nickel-zinc ferrite is 91wt%, the content of sendust is 8wt%, and the content of graphene is 1wt%. The chemical formula of the nickel-zinc ferrite in this embodiment is Ni 0.5 Zn 0.5 The average particle size of Fe2O4, sendust flake powder is 20um.

[0032] The method for preparing the low-frequency radar absorbent with strong weather resistance in this embodiment comprises the following steps:

[0033] (1) Nickel oxide, zinc oxide, ferrous oxide, and copper oxide were mixed in a mass ratio of 15:17:67:1, and wet-milled with deionized water for 2 h to obtain a ball-milled slurry;

[0034] (2) Spray drying the ball mill slurry obtained in step (1) to obtain a dry mixture

[0035] (3) heating the dry mixed material obtained in step (2) to 1250°C and sintering for 2 hours, and then cooling to room temperature to obtain a sintered material;

[0036] (4) crushing the sintered material obtained in step (3) by vibration grinding and passing through a 160 mesh sieve to obtain ferrite powder;

[0037] (5) Alkali was milled in a planetary ball mill with alcohol for 2 h, and dried to obtain flaky powder. The average particle size was 20 μm.

[0038] (6) Mixing the sendust flake powder obtained in step (5) with graphene in a mass ratio of 8:1, stirring evenly, and obtaining a mixture;

[0039] (7) The ferrite powder obtained in step (4) and the mixture obtained in step (6) are mixed in a ratio of 91:9 and stirred evenly to obtain a low-frequency radar wave absorber;

[0040] The performance of the low-frequency radar wave absorber of this embodiment was tested. The test method was to mix the radar wave absorber of this embodiment with resin in a ratio of 80:20, stir for two hours, add a curing agent of 50% of the resin mass, and stir manually for one minute to prepare an absorbing coating. The coating was then sprayed onto an aluminum plate with a thickness of 2mm using a spray gun to prepare a coating test plate for actual measurement of the absorbing performance. The test methods of the following embodiments and comparative examples are the same as those of this embodiment. The test results are shown in Tables 1 and Figures 1 and 2 .

[0041] from Figure 1 and Figure 2 The comparison between them shows that Figure 1 This is a state diagram of the low-frequency radar absorbing material of Example 1 of the present invention after undergoing a 1000-hour neutral salt spray test. The low-frequency radar absorbing material of the present invention is not corroded and has strong weather resistance. Figure 2 It can be seen that pure FeSiAl alloy powder developed rust spots and blisters after only 300 hours of neutral salt spray, and its weather resistance was poor.

[0042] Example 2

[0043] The low-frequency radar absorber with strong weather resistance in this embodiment is composed of nickel-zinc ferrite as the main component, doped with a small amount of sendust and graphene, wherein the content of nickel-zinc ferrite is 91wt%, the content of sendust is 8wt%, and the content of graphene is 1wt%. The chemical formula of the nickel-zinc ferrite in this embodiment is Ni 0.5 Zn 0.5 The average particle size of Fe2O4, sendust flake powder is 13um.

[0044] The method for preparing the low-frequency radar absorbent with strong weather resistance in this embodiment comprises the following steps:

[0045] (1) Nickel oxide, zinc oxide, ferrous oxide, and copper oxide were mixed in a mass ratio of 15:17:67:1, and deionized water was added for wet ball milling for 2 h to obtain a ball mill slurry;

[0046] (2) spray drying the ball-milled slurry obtained in step (1) to obtain a dry mixture;

[0047] (3) heating the dry mixed material obtained in step (2) to 1250°C and sintering for 2 hours, and then cooling to room temperature to obtain a sintered material;

[0048] (4) crushing the sintered material obtained in step (3) by vibration grinding and passing through a 160 mesh sieve to obtain ferrite powder;

[0049] (5) Alkali was milled in a planetary ball mill with alcohol for 2.5 h, and dried to obtain flaky powder. The average particle size was 13 μm.

[0050] (6) Mixing the sendust flake powder obtained in step (5) with graphene in a mass ratio of 8:1, stirring evenly, and obtaining a mixture;

[0051] (7) The ferrite powder obtained in step (4) and the mixture obtained in step (6) are mixed in a ratio of 91:9 and stirred evenly to obtain a low-frequency radar absorber with strong weather resistance.

[0052] Example 3

[0053] The low-frequency radar absorber with strong weather resistance in this embodiment is composed of nickel-zinc ferrite as the main component, doped with a small amount of sendust and graphene, wherein the content of nickel-zinc ferrite is 91wt%, the content of sendust is 8wt%, and the content of graphene is 1wt%. 0.4 Zn 0.6 The average particle size of Fe2O4, sendust flake powder is 20um.

[0054] The method for preparing the low-frequency radar absorbent with strong weather resistance in this embodiment comprises the following steps:

[0055] (1) Nickel oxide, zinc oxide, ferrous oxide, and copper oxide were mixed in a mass ratio of 12:20:67:1, and wet-milled with deionized water for 2 h to obtain a ball-milled slurry;

[0056] (2) spray drying the ball-milled slurry obtained in step (1) to obtain a dry mixture;

[0057] (3) heating the dry mixed material obtained in step (2) to 1230°C and sintering for 2 h, and then cooling to room temperature to obtain a sintered material;

[0058] (4) crushing the sintered material obtained in step (3) by vibration grinding and passing through a 160 mesh sieve to obtain ferrite powder;

[0059] (5) Alkali was milled in a planetary ball mill with alcohol for 2 h, and dried to obtain flaky powder. The average particle size was 20 μm.

[0060] (6) Mixing the sendust flake powder obtained in step (5) with graphene in a mass ratio of 8:1, stirring evenly, and obtaining a mixture;

[0061] (7) The ferrite powder obtained in step (4) and the mixture obtained in step (6) are mixed in a ratio of 91:9, and stirred evenly to obtain a low-frequency radar absorber with strong weather resistance.

[0062] Comparative Example 1

[0063] Compared with Example 1, the difference is that the flaky Sendust particles doped in Comparative Example 1 are less than 10 μm, and the maximum reflection loss peak of the obtained radar absorber is relatively larger, but the performance at low frequencies is insufficient.

[0064] The preparation method of the radar absorbent of this comparative example comprises the following steps:

[0065] (1) Nickel oxide, zinc oxide, ferrous oxide, and copper oxide were mixed in a mass ratio of 15:17:67:1, and wet-milled with deionized water for 5 h to obtain a ball-milled slurry;

[0066] (2) spray drying the ball-milled slurry obtained in step (1) to obtain a dry mixture;

[0067] (3) heating the dry mixed material obtained in step (2) to 1250°C and sintering for 2 hours, and then cooling to room temperature to obtain a sintered material;

[0068] (4) crushing the sintered material obtained in step (3) by vibration grinding and passing through a 160 mesh sieve to obtain ferrite powder;

[0069] (5) Alkali was milled in a planetary ball mill with alcohol for 2 h, and dried to obtain flaky powder. The average particle size was 3 μm.

[0070] (6) Mixing the sendust flake powder obtained in step (5) with graphene in a mass ratio of 8:1, stirring evenly, and obtaining a mixture;

[0071] (7) The ferrite powder obtained in step (4) and the mixture obtained in step (6) are mixed at a ratio of 91:9 and stirred evenly to obtain a radar absorbent.

[0072] Comparative Example 2

[0073] Compared with Example 2, the difference is that the flaky Sendust particles doped in Comparative Example 2 are larger than 20 μm, resulting in poor overall performance of the obtained radar absorber.

[0074] The preparation method of the radar wave absorber of this comparative example comprises the following steps:

[0075] (1) Nickel oxide, zinc oxide, ferrous oxide, and copper oxide were mixed in a mass ratio of 15:17:67:1, and wet-milled with deionized water for 5 h to obtain a ball-milled slurry;

[0076] (2) spray drying the ball-milled slurry obtained in step (1) to obtain a dry mixture;

[0077] (3) heating the dry mixed material obtained in step (2) to 1250°C and sintering for 2 hours, and then cooling to room temperature to obtain a sintered material;

[0078] (4) crushing the sintered material obtained in step (3) by vibration grinding and passing through a 160 mesh sieve to obtain ferrite powder;

[0079] (5) Alkali was milled in a planetary ball mill with alcohol for 1 h, and dried to obtain flaky powder. The average particle size of the powder was 36 μm.

[0080] (6) Mixing the sendust flake powder obtained in step (5) with graphene in a mass ratio of 8:1, stirring evenly, and obtaining a mixture;

[0081] (7) The ferrite powder obtained in step (4) and the mixture obtained in step (6) are mixed at a ratio of 91:9 and stirred evenly to obtain a radar absorbent.

[0082] Comparative Example 3

[0083] Compared with Example 3, the difference is that the chemical formula of the nickel-zinc ferrite in Comparative Example 3 is Ni 0.8 Zn 0.2 Fe2O4, high nickel content and low zinc content result in poor overall performance of the obtained radar absorber.

[0084] The preparation method of the radar wave absorber of this comparative example comprises the following steps:

[0085] (1) Nickel oxide, zinc oxide, ferrous oxide, and copper oxide were mixed in a mass ratio of 25:7:67:1, and wet-milled with deionized water for 5 h to obtain a ball-milled slurry;

[0086] (2) spray drying the ball-milled slurry obtained in step (1) to obtain a dry mixture;

[0087] (3) heating the dry mixed material obtained in step (2) to 1270°C and sintering for 2 h, and then cooling to room temperature to obtain a sintered material;

[0088] (4) crushing the sintered material obtained in step (3) by vibration grinding and passing through a 160 mesh sieve to obtain ferrite powder;

[0089] (5) Alkali was milled in a planetary ball mill with alcohol for 2 h, and dried to obtain flaky powder. The average particle size was 20 μm.

[0090] (6) Mixing the sendust flake powder obtained in step (5) with graphene in a mass ratio of 8:1, stirring evenly, and obtaining a mixture;

[0091] (7) The ferrite powder obtained in step (4) and the mixture obtained in step (6) are mixed at a ratio of 91:9 and stirred evenly to obtain a radar absorbent.

[0092] Table 1 Test results of the radar wave absorbers of Examples 1 to 3 and Comparative Examples 1 to 3

[0093]

Claims

1. A low-frequency radar absorber with strong weather resistance, characterized in that: The invention comprises nickel-zinc ferrite as the main component, doped with a small amount of sendust and graphene, wherein the content of nickel-zinc ferrite is ≥90wt%, the content of sendust is 6-8wt%, and the content of graphene is 1-2wt%. The sendust is prepared by ball-milling sendust alloy powder with alcohol to a particle size of 20um±10um in the form of flaky sendust powder. The mass ratio of iron, silicon and aluminum in the sendust is 80-90:5-10:5-10. The nickel-zinc ferrite is prepared by mixing and sintering nickel oxide, zinc oxide and ferrous oxide as the main raw materials and copper oxide as the sintering aid. The content of nickel oxide in the raw materials is 10-20wt%, the content of zinc oxide is 10-20wt%, the mass content of ferrous oxide is 60-70wt%, and the mass content of the copper oxide additive is 1-2wt%.

2. A method for preparing the weather-resistant low-frequency radar absorbent according to claim 1, characterized in that: The following steps are involved: (1) Mixing raw materials of nickel oxide, zinc oxide and ferrous oxide, and then adding an auxiliary agent of copper oxide to obtain a mixture; wet ball milling the mixture to obtain a ball milling slurry; (2) spray drying the ball-milled slurry obtained in step (1) to obtain a dry mixture; (3) sintering the dry mixed material obtained in step (2) and cooling it to obtain a sintered absorber material; (4) finely grinding the absorber sintered material obtained in step (3), crushing it by vibration grinding, and sieving it to obtain a ferrite absorber material; (5) The ferrite absorbing material obtained in step (4) is mixed with specially treated sendust and graphene, and stirred evenly to obtain a low-frequency radar absorber with strong weather resistance.

3. The method for preparing a low-frequency radar absorbent with strong weather resistance according to claim 2, characterized in that: In step (1), the wet ball milling time is 1-3 hours, and the mass ratio of the mixture: steel balls: water in the ball milling is 1-2:8-15:1-2.

4. The method for preparing a low-frequency radar absorbent with strong weather resistance according to claim 2 or 3, characterized in that: In step (3), the sintering temperature is 1200-1300° C.; the sintering holding time is 1-3 hours.

5. The method for preparing a low-frequency radar absorbent with strong weather resistance according to claim 4, characterized in that: In step (4), the mesh size of the sieve is 100-200 meshes.

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