A garnet-type microwave absorbing dielectric ceramic and its preparation method

Abstract

This invention belongs to the field of functional ceramics technology and discloses a garnet-type microwave absorbing dielectric ceramic and its preparation method. The general chemical formula of the garnet-type microwave absorbing dielectric ceramic is Y3Al. 5‑x Fe x O 12 Through a two-step atmosphere sintering method, firstly, high-temperature sintering is carried out in a reducing atmosphere, introducing a specific proportion of Fe. 2+ The introduction of ions, thereby introducing free charge carriers and lattice defects, significantly enhances conductivity loss and interfacial polarization loss; subsequently, medium-temperature annealing in an oxidizing atmosphere stabilizes the crystal structure, allowing Fe to... 2+ with Fe 3+ The molar ratio is controlled within a certain range to prevent over-reduction and optimize magnetic loss. At the same time, it achieves effective synergy between conductivity loss and magnetic loss in the 2-18GHz frequency band, and has the advantages of strong absorption, wide bandwidth, good high temperature stability and high repeatability.

Description

Technical Field

[0001] This application provides a garnet-type microwave absorbing dielectric ceramic and its preparation method, specifically relating to the field of functional ceramics technology. Background Technology

[0002] Yttrium aluminum garnet (Y3Al5O) 12 YAG (yellow alumina) is a high-performance high-temperature structural ceramic, but its intrinsic dielectric constant is low and it is non-magnetic, making it unable to effectively absorb electromagnetic waves. To endow YAG with wave-absorbing properties, an ion substitution strategy is usually adopted, the most classic of which is the introduction of trivalent iron ions (Fe3+). 3+ ) partially replaces aluminum sites (Al) 3+ ), forming Y3Al 5-x Fe x O 12 (YAIG) solid solution. This modification method successfully introduced ferrimagnetism into the YAG lattice. Fe³⁺ occupies octahedral and tetrahedral sites, generating superexchange through oxygen ion mediation, enabling the material to acquire considerable saturation magnetization and magnetic loss capability. The loss mechanism mainly includes natural resonance and domain wall resonance.

[0003] However, in YAIG materials prepared by traditional methods, iron exists almost entirely in the form of Fe³⁺, and its loss mechanism is mainly magnetic loss with weak electrical conduction loss. This makes it difficult to achieve a good match between the dielectric constant and complex permeability of the material, resulting in a narrow absorption bandwidth and insufficient intensity, especially in the wide frequency range of 2-18 GHz, where efficient absorption is difficult to achieve. Summary of the Invention

[0004] The purpose of this application is to provide a garnet-type microwave absorbing dielectric ceramic and its preparation method, overcoming the limitations of existing Y3Al... 5- x Fe x O 12 This paper addresses the shortcomings of absorbing materials, such as a single loss mechanism, poor impedance matching, narrow absorption bandwidth, and insufficient high-temperature performance control, and solves the problems mentioned in the background art.

[0005] According to a first aspect of this application, a garnet-type microwave absorbing dielectric ceramic with the general chemical formula Y3Al is provided. 5- x Fe x O 12 Where x takes values ​​from 2 to 3, Fe 2+ with Fe 3+ The molar ratio is (0.15~0.35):1.

[0006] According to a second aspect of this application, a method for preparing garnet-type microwave absorbing dielectric ceramic is provided, comprising: Step 1: According to the general chemical formula Y3Al 5-x Fe x O 12 Y2O3, Al2O3 and Fe2O3 raw materials were weighed according to stoichiometry, mixed and ground to obtain a precursor mixture; Step 2: The precursor mixture is pre-sintered at high temperature in a reducing atmosphere to obtain Fe-containing... 2+ Intermediate ceramics; Step 3: Anneal the intermediate ceramic in an oxidizing atmosphere, and after cooling, the garnet-type microwave absorbing dielectric ceramic is obtained.

[0007] In some embodiments of this application, based on the aforementioned scheme, the high-temperature pre-sintering temperature in step 2 is 1250℃~1350℃, and the holding time is 2~4h.

[0008] In some embodiments of this application, based on the foregoing scheme, the reducing atmosphere in step 2 is a mixture of 95% N2 and 5% H2 by volume percentage.

[0009] In some embodiments of this application, based on the aforementioned scheme, the annealing temperature in step 3 is 800℃~1000℃, and the holding time is 3~6h.

[0010] In some embodiments of this application, based on the foregoing scheme, the oxidizing atmosphere in step 3 is air or O2.

[0011] The beneficial effects of this application are: In some embodiments of this application, the garnet-type absorbing dielectric ceramic is permeated with an appropriate amount of Fe 2+ Create an environment with moderate electrical conductivity, with Fe 3+ The provided magnetic loss mechanism allows the dielectric constant and permeability of the material to be adjusted synchronously and in a coordinated manner, thereby achieving good impedance matching over a wider frequency range. This allows electromagnetic waves to penetrate more into the material and be synergistically consumed by the aforementioned multiple mechanisms, ultimately achieving broadband strong absorption. When the frequency is 2~18GHz and the thickness is only 1.5mm~2.0mm, the corresponding minimum reflection loss is -21~-36dB and the maximum effective absorption bandwidth is 5.2~6.6GHz, indicating that the absorbing dielectric ceramic in this application has excellent microwave absorption performance. Attached Figure Description

[0012] Figure 1 This is a microscopic morphology diagram of the ceramic sheet in Example 1.

[0013] Figure 2 The graph shows the real and imaginary parts of the dielectric constant of the ceramic sheet in Example 1.

[0014] Figure 3The graph shows the real and imaginary parts of the magnetic permeability of the ceramic sheet in Example 1.

[0015] Figure 4 This is a graph showing the attenuation coefficient of the ceramic sheet in Example 1.

[0016] Figure 5 The graph shows the eddy current loss coefficient of the ceramic sheet in Example 1.

[0017] Figure 6 The graph shows the reflection loss curve for a ceramic sheet with a thickness of 1.5 mm in Example 1.

[0018] Figure 7 The graph shows the reflection loss curve for a ceramic sheet with a thickness of 1.6 mm in Example 1.

[0019] Figure 8 The graph shows the reflection loss curve for a ceramic sheet with a thickness of 1.7 mm in Example 1.

[0020] Figure 9 The graph shows the reflection loss curve for a ceramic sheet with a thickness of 1.8 mm in Example 1.

[0021] Figure 10 The graph shows the reflection loss curve for a ceramic sheet with a thickness of 1.9 mm in Example 1.

[0022] Figure 11 The graph shows the reflection loss curve for a ceramic sheet with a thickness of 2.0 mm in Example 1. Detailed Implementation

[0023] The exemplary implementation will now be described more fully with reference to the accompanying drawings.

[0024] 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%.

[0025] This application first discloses a garnet-type microwave absorbing dielectric ceramic with the general chemical formula Y3Al. 5- x Fe x O 12 Where x takes values ​​from 2 to 3, Fe 2+ with Fe 3+ The molar ratio is (0.15~0.35):1.

[0026] This application also discloses a method for preparing garnet-type microwave absorbing dielectric ceramics, including: Step 1: According to the general chemical formula Y3Al 5-x Fe x O 12Y2O3, Al2O3 and Fe2O3 raw materials were weighed according to stoichiometry, mixed and ground to obtain a precursor mixture; Step 2: The precursor mixture is pre-sintered at high temperature in a reducing atmosphere to obtain Fe-containing... 2+ Intermediate ceramics; Step 3: Anneal the intermediate ceramic in an oxidizing atmosphere, and after cooling, the garnet-type microwave absorbing dielectric ceramic is obtained.

[0027] In some embodiments of this application, based on the aforementioned scheme, the high-temperature pre-sintering temperature in step 2 is 1250℃~1350℃, and the holding time is 2~4h.

[0028] In some embodiments of this application, based on the foregoing scheme, the reducing atmosphere in step 2 is a mixture of 95% N2 and 5% H2 by volume percentage.

[0029] In some embodiments of this application, based on the aforementioned scheme, the annealing temperature in step 3 is 800℃~1000℃, and the holding time is 3~6h.

[0030] In some embodiments of this application, based on the foregoing scheme, the oxidizing atmosphere in step 3 is air or O2.

[0031] In some embodiments of this application, the core feature of the garnet-type absorbing dielectric ceramic is that it retains Y3Al 5-x Fe x O 12 Without altering the single-phase garnet structure, an innovative preparation process is used to precisely introduce and stabilize a specific ratio of Fe. 2+ Ions, constructing Fe 2+ with Fe 3+ A coexistence system is established, thereby enabling synergistic control of the electrical and magnetic properties and high-temperature stability of materials without introducing foreign elements.

[0032] In some embodiments of this application, the main magnetism of the garnet-type absorbing dielectric ceramic originates from Fe. 3+ The Fe doping amount x is 1.5~3.5. If x<1.5, the material has too weak magnetism and insufficient magnetic loss; if x>3.5, the phase structure is not easy to stabilize and may lead to an excessively high dielectric constant, which will destroy the impedance matching.

[0033] In some embodiments of this application, the garnet-type absorbing dielectric ceramic controls Fe 2+ with Fe 3+ The molar ratio was in the range of (0.15~0.35):1, ensuring Fe 3+The main framework of the network remains intact, thus preserving strong and stable intrinsic magnetic losses; Fe 2+ The introduction of Fe slightly alters the local crystal field, potentially fine-tuning magnetic anisotropy and helping to broaden the magnetic loss peak; due to Fe 2+ (3d) 6 (relative to Fe) 3+ (3d) 5 It has additional electrons, which, in the garnet lattice, can be found in adjacent Fe atoms. 2+ with Fe 3+ Ions conduct electricity by jumping between each other, forming a microscopic current loop. Under the action of an alternating electromagnetic field, this jumping conductivity is directly converted into conductivity loss; Fe 2+ / Fe 3+ Ion pairs can also form defect dipoles in the crystal lattice, generating strong ionic relaxation polarization losses at microwave frequencies, further improving the electromagnetic wave loss capability of the material.

[0034] The method for preparing the garnet-type microwave absorbing dielectric ceramic in this application employs a two-step atmosphere sintering method, which has the following advantages: The first step is high-temperature sintering in a reducing atmosphere. A homogeneous mixture of Y₂O₃, Al₂O₃, and Fe₂O₃ precursors is placed in a reducing atmosphere such as 95% N₂ + 5% H₂ and pre-sintered at 1250–1350 °C. This step promotes the formation of Fe₂O₃ within the Fe₂O₃. 3+ Reduced to Fe 2+ This drives the formation of the garnet main phase.

[0035] The second step is medium-temperature annealing in an oxidizing atmosphere. The intermediate obtained in the first step is placed in air or oxygen and annealed at 800~1000℃. This process serves two purposes: firstly, it removes excess Fe from the surface layer... 2+ The two-step method achieves bulk Fe by first slightly re-oxidizing to prevent electromagnetic wave reflection due to excessive surface conductivity; secondly, it eliminates excessive defects such as oxygen vacancies that may be introduced by reduction sintering, stabilizes the crystal structure, and ensures the long-term stability and mechanical strength of the material as a whole. 2+ Separation and control of proportional controllability and surface state optimization.

[0036] The present invention will be further described in detail below through three specific embodiments, but the scope of protection of the present invention is not limited thereto. These embodiments respectively demonstrate different element selections, preparation methods and structural designs to verify the universality and excellent effects of the present invention.

[0037] Example 1: Based on the chemical formula Y3Al 5-x Fe x O 12 The value of x is 2.5, Fe 2+ with Fe 3+The molar ratio was 0.25:1. 340g of Y₂O₃, 130g of Al₂O₃, and 200g of Fe₂O₃ were weighed, mixed, and ground to obtain a precursor mixture. The precursor mixture was then subjected to high-temperature pre-sintering at 1300°C for 3 hours in a reducing atmosphere of a mixture of 95% N₂ and 5% H₂ (by volume percentage) to obtain a Fe₂O₃-containing precursor mixture. 2+ The intermediate ceramic was annealed in air at 900°C for 4 hours, and then cooled to obtain the Y3Al. 5-x Fe x O 12 Wave-absorbing dielectric ceramics. Figure 1 Y3Al was prepared for Example 1 5-x Fe x O 12 The microstructure of the absorbing dielectric ceramic shows that its surface has a porous structure, which is beneficial for impedance matching and electromagnetic wave loss; according to Figure 2 It can be seen that the real part of the dielectric constant of this absorbing dielectric ceramic is between 6 and 10, and the imaginary part is between 1 and 3, and a suitable dielectric constant range can ensure its good absorption capability; according to Figure 3 It can be seen that its real permeability is between 1 and 2.2, and its imaginary permeability is between 0 and 1, which ensures the magnetic loss capability of the material; Figure 4 The display shows that the attenuation coefficient of the absorbing dielectric ceramic is continuously increasing, proving that its electromagnetic wave loss capability is continuously enhanced. Figure 5 The eddy current loss coefficient of the absorbing dielectric ceramic changes with frequency and is not constant, proving that its magnetic loss comes from eddy current loss and natural ferromagnetic resonance, with eddy current loss playing a dominant role. Figures 6-11 To reduce the reflection loss of absorbing dielectric ceramics with a thickness of 1.5mm to 2.0mm, [the following is a description of the process]. Figures 6-11 The minimum reflection loss is -26 to -35 dB, and the maximum effective absorption bandwidth is 5.6 to 6.5 GHz, proving that it has excellent wave absorption performance.

[0038] Example 2: Based on the chemical formula Y3Al 5-x Fe x O 12 The value of x is 2, Fe 2+ with Fe 3+ The molar ratio was 0.35:1. 340g of Y₂O₃, 150g of Al₂O₃, and 160g of Fe₂O₃ were weighed, mixed, and ground to obtain a precursor mixture. The precursor mixture was then subjected to high-temperature pre-sintering at 1250°C for 4 hours in a reducing atmosphere of a mixture of 95% N₂ and 5% H₂ (by volume percentage) to obtain a Fe₂O₃-containing precursor mixture. 2+The intermediate ceramic was annealed in air at 1000°C for 3 hours, and then cooled to obtain the Y3Al. 5-x Fe x O 12 Microwave-absorbing dielectric ceramic. After performance testing, the microwave-absorbing dielectric ceramic sample prepared in Example 2 had a minimum reflection loss of -21 to -32 dB and a maximum effective absorption bandwidth of 5.2 to 6.6 GHz at a thickness of 1.5 mm to 2.0 mm in the range of 2 to 18 GHz.

[0039] Example 3: Based on the chemical formula Y3Al 5-x Fe x O 12 The value of x is 3, Fe 2+ with Fe 3+ The molar ratio was 0.25:1. 340g of Y₂O₃, 100g of Al₂O₃, and 240g of Fe₂O₃ were weighed, mixed, and ground to obtain a precursor mixture. The precursor mixture was then subjected to high-temperature pre-sintering at 1350°C for 2 hours in a reducing atmosphere of a mixture of 95% N₂ and 5% H₂ (by volume percentage) to obtain a Fe₂O₃-containing precursor mixture. 2+ The intermediate ceramic was annealed in air at 800°C for 6 hours, and then cooled to obtain the Y3Al. 5-x Fe x O 12 Microwave-absorbing dielectric ceramic. After performance testing, the microwave-absorbing dielectric ceramic sample prepared in Example 3 had a minimum reflection loss of -24 to -36 dB and a maximum effective absorption bandwidth of 5.4 to 6.2 GHz at a thickness of 1.5 mm to 2.0 mm in the range of 2 to 18 GHz.

[0040] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the patent protection scope of this application.

Claims

1. A garnet-type microwave absorbing dielectric ceramic, characterized in that, Its general chemical formula is Y3Al 5-x Fe x O 12 .

2. The garnet-type absorbing dielectric ceramic according to claim 1, characterized in that, The value of x in the general chemical formula is in the range of 2 to 3.

3. The garnet-type absorbing dielectric ceramic according to claim 1, characterized in that, In the general chemical formula, Fe 2+ with Fe 3+ The molar ratio is (0.15~0.35):

1.

4. The method for preparing garnet-type microwave absorbing dielectric ceramics according to any one of claims 1 to 3, characterized in that, include: Step 1: According to the general chemical formula Y3Al 5-x Fe x O 12 Y2O3, Al2O3 and Fe2O3 raw materials were weighed according to stoichiometry, mixed and ground to obtain a precursor mixture; Step 2: The precursor mixture is pre-sintered at high temperature in a reducing atmosphere to obtain Fe-containing... 2+ Intermediate ceramics; Step 3: Anneal the intermediate ceramic in an oxidizing atmosphere, and after cooling, the garnet-type microwave absorbing dielectric ceramic is obtained.

5. The preparation method according to claim 4, characterized in that, The high-temperature pre-sintering temperature in step 2 is 1250℃~1350℃, and the holding time is 2~4h.

6. The preparation method according to claim 4, characterized in that, The reducing atmosphere described in step 2 is a mixture of 95% N2 and 5% H2 by volume percentage.

7. The preparation method according to claim 4, characterized in that, The annealing temperature in step 3 is 800℃~1000℃, and the holding time is 3~6h.

8. The preparation method according to claim 4, characterized in that, The oxidizing atmosphere mentioned in step 3 is air or O2.

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