Medium-entropy rare earth silicide carbide electromagnetic wave absorber and preparation method thereof

Abstract

The application discloses a medium-entropy rare earth silicon carbide electromagnetic wave absorber and a preparation method thereof. x RE2 y RE3 z )3Si2C2 / SiCw, wherein RE1, RE2 and RE3 are three mutually different rare earth elements, x, y and z are molar fractions of the respective rare earth elements, and the value range of each is 0.2-0.6, and x+y+z=1 is satisfied. The absorber is contributed by multiple polarization relaxation and moderate conductivity caused by the introduction of medium-entropy design, and the dielectric loss is significantly contributed, and the lowest loss is lower than -30 dB; in combination with the optimized impedance matching of SiCw, the material has strong absorption and wide effective bandwidth at normal temperature, and the maximum effective absorption bandwidth (≤-10 dB) in 2-18 GHz can reach more than 4 GHz.

Description

Technical Field

[0001] This invention relates to the field of medium-entropy rare-earth silicon carbide electromagnetic wave absorbers, specifically to a medium-entropy rare-earth silicon carbide electromagnetic wave absorber and its preparation method. Background Technology

[0002] Currently, silicon carbide-based materials are widely studied as room-temperature microwave absorbers due to their moderate dielectric constant, good chemical stability, and tunable electrical properties. However, intrinsic SiC has weak dielectric loss capability, and its microwave absorption performance heavily relies on the introduction of a second phase, such as carbon materials or magnetic particles, to construct loss cells. These composite materials often face the following problems: 1) Although magnetic fillers are effective at room temperature, their high density, easy oxidation, and narrow bandwidth limit their application. 2) Although carbon materials have high loss, their high conductivity can lead to severe surface reflection and poor impedance matching. Furthermore, the control of their dispersion and structural stability is complex.

[0003] In recent years, rare-earth ternary layered silicon carbide (RE3Si2C2) has attracted attention as a novel dielectric material. Its unique layered crystal structure and the tunable 4f electronic states of rare-earth elements give it superior dielectric polarization properties compared to intrinsic SiC, providing new ideas for designing novel microwave absorbing materials. However, existing research mostly focuses on single rare-earth systems, such as Y3Si2C2 and Gd3Si2C2. The type of a single rare-earth element fixes the intrinsic electronic structure and polarization capability of the material, resulting in a limited range of adjustable dielectric constant and loss factor. This makes it difficult to simultaneously achieve ideal impedance matching and high loss over a wide frequency range, limiting the potential for performance optimization.

[0004] Meanwhile, the high-entropy / medium-entropy design concept has shown great potential in the field of materials science. This concept utilizes the resulting "lattice distortion effect," "slow diffusion effect," and "cocktail effect" to synergistically regulate material properties by dissolving multiple principal elements in the same crystal lattice. In the field of electromagnetic wave absorption, studies have successfully applied high-entropy design to systems such as transition metal chalcogenides and perovskite oxides, demonstrating that multi-principal element solid solutions can significantly enhance dielectric polarization relaxation and broaden the absorption bandwidth. However, this advanced material design strategy has not yet been systematically introduced into rare-earth silicon carbide systems with intrinsic layered structures and rich tunability to address the fundamental problem of insufficient performance regulation of single components.

[0005] Therefore, how to combine the innovative idea of ​​medium entropy design with the intrinsic advantages of rare earth silicon carbide, and cleverly combine it with SiC whiskers in a multi-scale composite process to construct a new type of broadband absorbing material with both good impedance matching and multiple enhanced loss mechanisms, is a technical problem worth exploring and urgently needs to be solved in this field. Summary of the Invention

[0006] This invention provides a medium-entropy rare-earth silicon carbide electromagnetic wave absorber and its preparation method, solving the problems mentioned in the background art.

[0007] This invention provides the following technical solution: a medium-entropy rare-earth silicon carbide electromagnetic wave absorber, with the general molecular formula (RE1). x RE2 y RE3 z The absorber is composed of three rare earth elements (RE1, RE2, and RE3), where RE1, RE2, and RE3 are three distinct rare earth elements. The mole fractions of each rare earth element are x, y, and z, ranging from 0.2 to 0.6, satisfying x + y + z = 1. This absorber utilizes the medium-entropy solid solution formed by multiple rare earth elements within the RE3Si2C2 lattice to induce lattice distortion and enhance polarization loss. The target phase grows in situ on the SiCw surface, forming a petal-like lamellar structure that optimizes impedance matching, significantly improving electromagnetic wave absorption. The minimum loss can reach below -30 dB within the 2-18 GHz range, and the maximum effective absorption bandwidth can exceed 4 GHz. This electromagnetic wave absorber combines strong absorption, wide bandwidth, and thin thickness, making it suitable for large-scale application.

[0008] As an alternative to the medium-entropy rare-earth silicon carbide electromagnetic wave absorber described in this invention, the RE1 element is preferably one of La, Ce, Pr and Nd; the RE2 element is preferably one of Sm, Gd, Tb and Dy; and the RE3 element is preferably one of Y, Ho, Er and Tm.

[0009] This invention also provides a method for preparing a medium-entropy rare-earth silicon carbide electromagnetic wave absorber, comprising: Step 1: Weigh SiCw rare earth metal powder with a diameter of 50nm-1μm, a length of 5-100μm, and an aspect ratio of not less than 10, and a particle size of 200-300 mesh, according to the general chemical formula of the medium entropy rare earth silicon carbide electromagnetic wave absorber of claim 1 or 2. After weighing, mix them evenly to obtain the reaction raw material. Mix the obtained reaction raw material with molten salt evenly to obtain the mixed raw material. Step 2: Place the mixed raw materials in a conventional inert gas atmosphere furnace for high-temperature reaction. After the reaction is completed, cool, wash and dry to obtain a medium-entropy rare earth silicon carbide electromagnetic wave absorber.

[0010] As an optional embodiment of the method for preparing the medium-entropy rare-earth silicon carbide electromagnetic wave absorber described in this invention, wherein: in step 1, the molten salt is at least one of a fluoride molten salt, a fluorochloride eutectic salt, or a chloride molten salt; the total mass ratio of the molten salt to the reaction raw materials is 1:1 to 5:1. In step 2, the reaction temperature of the high-temperature reaction is 1100℃-1500℃, and the holding time is 3-6 hours.

[0011] This invention has the following beneficial effects: The medium-entropy rare-earth silicon carbide electromagnetic wave absorber employs rare-earth elements with large, medium, and small ionic radii for medium-entropy solid solution in its material composition design. Utilizing the resulting strong lattice distortion and compositional fluctuations, it significantly enhances dielectric polarization capability at the atomic scale, fundamentally broadening the adjustable range of dielectric properties of rare-earth silicon carbide. The innovative introduction of multi-polarization relaxation and moderate conductivity induced by the medium-entropy design synergistically contributes to significant dielectric loss, with a minimum loss below -30dB. Combined with SiCw's optimized impedance matching, the material exhibits both strong absorption and a wide effective bandwidth at room temperature, with a maximum effective absorption bandwidth (≤-10dB) exceeding 4GHz within the 2-18GHz range. Through in-situ synthesis using a one-step molten salt method, the medium-entropy phase is directly grown on the SiCw surface as a layered multi-level structure, achieving a strong interfacial bond and uniform dispersion between the two phases, with a simple and controllable process flow. Attached Figure Description

[0012] Figure 1 The image shows the microstructure of the original SiCw in Comparative Example 1.

[0013] Figure 2 The dielectric constant of the unmodified SiCw in Comparative Example 1 in the range of 2-18 GHz is given when the absorbent loading is 60%.

[0014] Figure 3 The graph shows the reflection loss curves of the unmodified SiCw in Comparative Example 1 at different thicknesses within the range of 2-18 GHz when the absorbent filling amount is 60%.

[0015] Figure 4 In Example 1 (La) 0.34 Sm 0.33 Y 0.33 The microstructure of 3Si2C2 / SiCw shows that the surface has petal-like lamellar layers.

[0016] Figure 5 In Example 1, when the absorbent filling amount is 60%, (La) 0.34 Sm 0.33 Y 0.33 Dielectric constant of 3Si2C2 / SiCw in the range of 2-18 GHz.

[0017] Figure 6 In Example 1, when the absorbent filling amount is 60%, (La) 0.34 Sm 0.33 Y 0.33 Reflection loss curves of 3Si2C2 / SiCw at different thicknesses within the range of 2-18 GHz. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Unless otherwise stated, all raw materials, reagents, instruments and equipment used in this application can be purchased on the market or prepared by existing methods, and the purity of all raw materials used is greater than 99.9%.

[0020] Please see Figures 1 to 6 The present invention will be further described in detail below through specific embodiments and comparative examples, but the scope of protection of the present invention is not limited thereto. These embodiments demonstrate different element selections, preparation methods, and structural designs to verify the universality and excellent effects of the present invention.

[0021] Example 1

[0022] First, SiCw is uniformly dispersed according to the designed molecular formula (La). 0.34 Sm 0.33 Y 0.33 )3Si2C2 / SiCw, take 100g of SiCw, 7.5g of La metal powder, 7.9g of Sm metal powder and 4.7g of Y metal powder, with a total mixed metal powder of 20.1g, and mix it evenly with molten salt. The total mass ratio of molten salt to reactants is 1:1. NaF and KF are selected as molten salts. The molten salt reaction is carried out in an Ar atmosphere furnace at a reaction temperature of 1300℃ for 4h. After the reaction is completed, it is cooled, washed and dried to obtain (La) 0.34 Sm 0.33 Y 0.33 )3Si2C2 / SiCw absorbent. Its surface microstructure is as follows Figure 4 As shown, after the synthesis reaction, irregular petal-shaped disordered sheets are formed on the surface of SiCw, which is beneficial to improve the impedance matching and dielectric constant of SiCw. At the same time, a large number of heterostructures will significantly increase the interfacial polarization loss. Figure 5 When the absorbent filling amount is 60%, (La) 0.34 Sm 0.33 Y 0.33 The dielectric constant of 3Si2C2 / SiCw in the range of 2-18 GHz has a real part of 7-12.5 and an imaginary part of 2.5-8.5. Both the real and imaginary parts exhibit typical dispersion characteristics. Figure 6 When the absorbent filling amount is 60%, (La) 0.34 Sm 0.33 Y 0.33The absorption performance of 3Si2C2 / SiCw in 1.6-1.9mm thickness is as follows: when the thickness is 1.9mm, the minimum reflection loss can reach -34dB, and when the thickness is 1.7mm, the maximum effective absorption bandwidth (≤-10dB) can reach 4.6GHz.

[0023] Example 2

[0024] SiCw was uniformly dispersed according to the designed molecular formula (Pr 0.60 Dy 0.20 Tm 0.20 )3Si2C2 / SiCw, take 100g of SiCw, 5.6g of Pr metal powder, 2.2g of Dy metal powder and 2.2g of Tm metal powder, and mix the total metal powder 10.0g with molten salt. The total mass ratio of molten salt to reactants is 3:1. The molten salt is selected as NaCl-KF eutectic salt and NaF-KCl eutectic salt. The molten salt reaction is carried out in an Ar atmosphere furnace at a reaction temperature of 1400℃ for 3h. After the reaction is completed, it is cooled, washed and dried to obtain (Pr 0.60 Dy 0.20 Tm 0.20 3Si2C2 / SiCw absorber. When the absorber filling amount is 60% and the thickness is 1.6-2mm, its minimum reflection loss can reach -31dB and the maximum effective absorption bandwidth can reach 4.3GHz.

[0025] Example 3

[0026] SiCw was uniformly dispersed according to the designed molecular formula (Ce). 0.20 Gd 0.20 Er 0.60 )3Si2C2 / SiCw, take 100g of SiCw, 5.2g of Ce metal powder, 6.0g of Gd metal powder and 18.8g of Er metal powder, with a total of 30.0g of mixed metal powder, and mix them evenly with molten salt. The total mass ratio of molten salt to reactants is 5:1. The molten salt is selected from NaCl, NaF and CaF2. The molten salt reaction is carried out in an Ar atmosphere furnace at a reaction temperature of 1100℃ for 6h. After the reaction is completed, it is cooled, washed and dried to obtain (Ce)2C2 / SiCw. 0.20 Gd 0.20 Er 0.60 3Si2C2 / SiCw absorber. When the absorber filling amount is 60% and the thickness is 1.6-2mm, its minimum reflection loss can reach -38dB and the maximum effective absorption bandwidth can reach 4.4GHz.

[0027] Comparative Example 1 SiCw was uniformly dispersed, and according to the designed molecular formula La3Si2C2 / SiCw, 100g of SiCw was mixed with 10g, 20g, and 30g of La metal powder, respectively, and uniformly mixed with molten salt. The total mass ratio of molten salt to reactants was 1:1. NaF and KF were selected as the molten salts. The molten salt reaction was carried out in an Ar atmosphere furnace at a reaction temperature of 1300℃ for 4 hours. After the reaction, the samples were cooled, washed, and dried to obtain three samples (L-1, L-2, and L-3) with different La contents. When the absorbent filling amount was 60%, the dielectric constant of the three contents of La3Si2C2 / SiCw was improved compared with that of unmodified SiCw; however, within the 2-18 GHz range, when the thickness was 1.6-2 mm, the lowest reflection loss was -26dB, and the maximum effective absorption bandwidth was 2.8-3.4 GHz.

[0028] Figure 1 The image shows the microstructure of unmodified SiCw, revealing that the SiCw lines are straight and the surface is smooth. Figure 2 The dielectric constant of the original SiCw in the range of 2-18 GHz is given when the absorbent filling amount is 60%. The real part of the dielectric constant is 6.9-7.5, and the imaginary part is 1.4-1.9. The overall dielectric constant is relatively low. Figure 3 The graph shows the reflection loss curves of unmodified SiCw at different thicknesses within the 2-18 GHz range. When the thickness is between 1.6-2 mm, the lowest reflection loss is only -10.8 dB, and the maximum effective absorption bandwidth can be only 0.5 GHz.

[0029] Figure 1 The unmodified SiCw in Comparative Example 2 has an effective absorption bandwidth of only 0.5 GHz and a minimum reflection loss of only -10.8 dB; the single rare earth La3Si2C2 / SiCw in Comparative Example 2 has a maximum effective absorption bandwidth of 2.8-3.4 GHz and a minimum reflection loss of -26 dB; while the (RE1) in Examples 1-3 of this application... x RE2 y RE3 z The 3Si2C2 / SiCw electromagnetic wave absorber exhibits a maximum effective absorption bandwidth exceeding 4.3GHz within the 2-18GHz range, with a minimum reflection loss below -31dB. This demonstrates that the medium-entropy solid solution design using rare earth elements with large, medium, and small ionic radii, combined with an in-situ grown petal-like layered structure, significantly enhances the material's wave absorption performance. The performance indicators of the embodiments are all significantly superior to those of the comparative examples, fully showcasing the technical advantages of this invention.

[0030] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0031] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A medium-entropy rare-earth silicon carbide electromagnetic wave absorber, characterized in that, The general molecular formula is (RE1) x RE2 y RE3 z )3Si2C2 / SiCw, where RE1, RE2 and RE3 are three different rare earth elements, and x, y and z are the mole fractions of each rare earth element, with values ​​ranging from 0.2 to 0.6, satisfying x+y+z=1.

2. The medium-entropy rare-earth silicon carbide electromagnetic wave absorber according to claim 1, characterized in that: RE1 elements are selected from La, Ce, Pr, or Nd; RE2 elements are selected from Sm, Gd, Tb, or Dy; RE3 elements are selected from Y, Ho, Er, or Tm.

3. The medium-entropy rare-earth silicon carbide electromagnetic wave absorber according to claim 1, characterized in that: The three rare earth elements have different ionic radii, and the ionic radii vary in a gradient.

4. A method for preparing a medium-entropy rare-earth silicon carbide electromagnetic wave absorber, used to prepare the medium-entropy rare-earth silicon carbide electromagnetic wave absorber of claim 1, 2, or 3, characterized in that: include: Step 1: Weigh SiCw rare earth metal powder with a diameter of 50nm-1μm, a length of 5-100μm, and an aspect ratio of not less than 10, and a particle size of 200-300 mesh, according to the chemical formula of the medium entropy rare earth silicon carbide electromagnetic wave absorber according to claim 1, 2, or 3. After weighing, mix them evenly to obtain the reaction raw material. Mix the obtained reaction raw material with molten salt evenly to obtain the mixed raw material. Step 2: Place the mixed raw materials in a conventional inert gas atmosphere furnace for high-temperature reaction. After the reaction is completed, cool, wash and dry to obtain a medium-entropy rare earth silicon carbide electromagnetic wave absorber.

5. The method for preparing a medium-entropy rare-earth silicon carbide electromagnetic wave absorber according to claim 4, characterized in that: In step 1, the molten salt is at least one of fluoride molten salt, fluorochloride eutectic salt or chloride molten salt; the total mass ratio of molten salt to reactant is 1:1 to 5:

1.

6. The method for preparing a medium-entropy rare-earth silicon carbide electromagnetic wave absorber according to claim 4, characterized in that: In step 2, the reaction temperature of the high-temperature reaction is 1100℃-1500℃, and the holding time is 3-6h.

Images