Neodymium-zirconium co-substituted M-type strontium ferrite wave-absorbing material and preparation method thereof

Abstract

The invention discloses a neodymium-zirconium co-substituted M-type strontium ferrite wave-absorbing material and a preparation method thereof, the chemical formula of the neodymium-zirconium co-substituted M-type strontium ferrite wave-absorbing material is Sr1-xNdxZr0. 2Fe11.8 O19, and x is more than or equal to 0.1 and less than or equal to 0.4. The method comprises the following steps: (1) mixing strontium nitrate, ferric nitrate nonahydrate, neodymium nitrate hexahydrate, zirconium nitrate pentahydrate, citric acid monohydrate and deionized water, stirring and dissolving to obtain sol; (2) adjusting the pH value of the sol to 6.5-7.5, and then heating to carry out sol-gel reaction to obtain wet gel; (3) drying and grinding the wet gel to obtain precursor powder; and (4) performing heat treatment on the precursor powder in a box-type furnace, cooling and grinding to obtain the neodymium-zirconium co-substituted M-type strontium ferrite wave-absorbing material. According to the material, effective wave-absorbing frequency band broadening is achieved, the matching thickness corresponding to the effective wave-absorbing bandwidth is as thin as 0.55-0.7 mm, and meanwhile, the performance requirements of thinness, width and strength in the field of electromagnetic compatibility are met.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic wave absorbing materials, and particularly relates to a neodymium-zirconium co-substituted M-type strontium ferrite absorbing material and a preparation method thereof. Background Art

[0002] With the rapid development of high-tech, electromagnetic wave technology is widely used by humans. However, electromagnetic waves inevitably cause certain problems such as electromagnetic radiation and electromagnetic wave interference, which are harmful to the human body and the environment. Among them, in the military field, stealth aircraft technology has put forward higher requirements for absorbing materials. The original absorbing materials can no longer meet the existing development, and the development and demand for new multifunctional absorbing materials with thin thickness, wide absorption frequency band, and strong absorption ability are becoming more and more urgent. Due to its high uniaxial magnetocrystalline anisotropy, appropriate coercivity, low price, high stability and other advantages, M-type strontium ferrite has become a widely used absorbing material.

[0003] Traditional M-type strontium ferrite (SrFe 12 O 19 ) has high magnetocrystalline anisotropy, but it is difficult to balance its magnetization intensity, dielectric loss and multi-band absorption performance, which limits its application in 5G communication and stealth technology. Existing modification technologies mostly use single-ion substitution, and it is difficult to achieve a comprehensive improvement of magnetic and electrical properties. Substituting strontium ferrite with a single element zirconium has limitations in adjusting the absorption performance, and there are deficiencies such as a relatively thick thickness, a narrow absorption frequency band width, and a need to improve the absorption intensity. Summary of the Invention

[0004] The present invention provides a neodymium-zirconium co-substituted M-type strontium ferrite absorbing material and a preparation method thereof, aiming to solve the technical problems such as insufficient frequency band width, excessive thickness of existing absorbing materials, and limitations of single-element zirconium in performance improvement. On the basis of maintaining low coercivity and high saturation magnetization intensity, this material realizes the broadening of the effective absorption frequency band, the thinning of the matching thickness corresponding to the effective absorption bandwidth, and at the same time meets the performance requirements of "thin, wide, and strong" in the field of electromagnetic compatibility. It is particularly suitable for high-tech fields such as 5G communication equipment, military stealth coatings, and electromagnetic shielding of electronic instruments.

[0005] In one aspect of the present invention, the present invention provides a neodymium-zirconium co-substituted M-type strontium ferrite absorbing material. According to an embodiment of the present invention, the chemical formula of the absorbing material is Sr 1-x Nd x Zr 0.2 Fe 11.8 O 19 , where 0.1 ≤ x ≤ 0.4.

[0006] In another aspect of the present invention, the present invention provides a method for preparing a neodymium-zirconium co-substituted M-type strontium ferrite microwave absorbing material. According to an embodiment of the present invention, the method includes the following steps:

[0007] (1) Mix strontium nitrate, iron(III) nitrate nonahydrate, neodymium(III) nitrate hexahydrate, zirconium(IV) nitrate pentahydrate, citric acid monohydrate and deionized water, and stir to dissolve to obtain a sol;

[0008] (2) Adjust the pH of the sol to 6.5 - 7.5, and then heat it to carry out a sol-gel reaction to obtain a wet gel;

[0009] (3) Dry and grind the wet gel to obtain a precursor powder;

[0010] (4) Place the precursor powder in a box furnace for heat treatment, cool and grind to obtain the neodymium-zirconium co-substituted M-type strontium ferrite microwave absorbing material.

[0011] In addition, according to the method for preparing a neodymium-zirconium co-substituted M-type strontium ferrite microwave absorbing material in the above embodiment of the present invention, the following additional technical features may also be provided:

[0012] In some embodiments of the present invention, in step (1), the molar ratio of strontium nitrate, iron(III) nitrate nonahydrate, neodymium(III) nitrate hexahydrate, zirconium(IV) nitrate pentahydrate and citric acid monohydrate is (1 - x): 11.8: x: 0.2: 15, where 0.1 ≤ x ≤ 0.4.

[0013] In some embodiments of the present invention, in step (1), stir for 30 - 60 min.

[0014] In some embodiments of the present invention, in step (2), ammonia water is used to adjust the pH of the sol.

[0015] In some embodiments of the present invention, in step (2), the heating is carried out in an oil bath at 120 - 140 °C with continuous stirring for 2.5 - 3.5 h.

[0016] In some embodiments of the present invention, in step (3), the drying is carried out in a forced-air drying oven at a drying temperature of 140 - 160 °C for 10 - 12 h.

[0017] In some embodiments of the present invention, in step (4), the heat treatment process is as follows: first heat up to 200 - 300 °C and hold for 1 - 2 h, then heat up to 400 - 500 °C and hold for 2 - 3 h, and finally heat up to 1250 - 1400 °C and hold for 2 - 3 h, and then cool with the furnace.

[0018] In some embodiments of the present invention, in step (4), the grinding time is 10 - 15 min.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) Based on zirconium-substituted M-type strontium ferrite SrZr 0.2 Fe 11.8 O 19 Using the sol-gel method, neodymium is substituted into this strontium ferrite. The rare earth element neodymium replaces strontium in the strontium ferrite. Under the action of natural resonance and exchange resonance, the effective absorption band is broadened and the matching thickness is reduced. The introduction of the rare earth element neodymium can improve the activity of grain boundary magnetic domains, increase domain wall resonance and natural resonance, and the main mechanism of magnetic loss of strontium ferrite absorbing materials at 26.5 - 40 GHz is natural resonance. At the same time, by adjusting the substitution amount of neodymium, a strontium ferrite absorbing material with strong absorption and a wide absorption frequency band is finally obtained.

[0021] (2) By adjusting the amount of neodymium ions substituted into strontium ferrite, the matching thickness of the material can be flexibly adjusted and the effective absorption bandwidth of strontium ferrite can be broadened to a certain extent. Then, by further changing its heat treatment temperature, the influence of temperature on its absorption performance is explored.

[0022] (3) The matching thickness of the neodymium-zirconium co-substituted strontium ferrite absorbing material prepared by the present invention is relatively thin, and the corresponding effective absorption bandwidth is relatively wide. When the heat treatment temperature is 1400 °C, the corresponding material has a lower coercive force and is a soft magnetic material. The more it changes towards the soft magnetic material direction, the greater the magnetic permeability of the material and the lower the magnetocrystalline anisotropy field, which is beneficial to improving the loss ability of the material and adjusting the natural resonance frequency towards the low-frequency direction.

[0023] (4) The preparation process of the present invention is simple, easy to operate, safe, pollution-free, and low in cost, making industrial production possible. At the same time, it provides a new idea and approach for the research of absorbing materials and magnetic materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Absorption performance diagram of the Sr 0.9 Nd 0.1 Zr 0.2 Fe 11.8 O 19 absorbing material prepared in Example 1 of the present invention;

[0025] Figure 2 Absorption performance diagram of the Sr 0.8 Nd 0.2 Zr 0.2 Fe 11.8 O 19 absorbing material prepared in Example 2 of the present invention;

[0026] Figure 3 Absorption performance diagram of the Sr 0.7 Nd0.3 Zr 0.2 Fe 11.8 O 19 Absorbing performance diagram of the wave-absorbing material;

[0027] Figure 4 Sr prepared in Example 4 of the present invention 0.6 Nd 0.4 Zr 0.2 Fe 11.8 O 19 Absorbing performance diagram of the wave-absorbing material;

[0028] Figure 5 Sr prepared in Example 5 of the present invention 0.7 Nd 0.3 Zr 0.2 Fe 11.8 O 19 Absorbing performance diagram of the wave-absorbing material;

[0029] Figure 6 Sr prepared in Example 6 of the present invention 0.7 Nd 0.3 Zr 0.2 Fe 11.8 O 19 Absorbing performance diagram of the wave-absorbing material;

[0030] Figure 7 Sr prepared in Example 7 of the present invention 0.7 Nd 0.3 Zr 0.2 Fe 11.8 O 19 Absorbing performance diagram of the wave-absorbing material. Detailed implementation manners

[0031] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts belong to the scope of protection of the present invention.

[0032] The raw materials used in the embodiments are all of analytical purity.

[0033] Example 1

[0034] Preparation method of a neodymium-zirconium co-substituted M-type strontium ferrite wave-absorbing material, comprising the following steps:

[0035] (1) adding ferric nitrate nonahydrate, zirconium nitrate pentahydrate, strontium nitrate, neodymium nitrate hexahydrate and citric acid monohydrate to deionized water in a molar ratio of 11.8:0.2:0.9:0.1:15, stirring for 40 minutes to dissolve and obtain a sol;

[0036] (2) adding an appropriate amount of ammonia water to the sol obtained in step (1) to adjust the pH value to 7, and then placing the sol in an oil bath at 130° C. and continuously stirring and heating for 3 h to obtain a brown wet gel;

[0037] (3) placing the brown wet gel obtained in step (2) in a 150° C. forced air drying oven and drying for 12 h to form a dry gel;

[0038] (4) grinding the dry gel obtained in step (3) in an agate mortar to obtain a brown precursor powder;

[0039] (5) The precursor powder obtained in step (4) is placed in a box furnace, first heated to 250°C and kept warm for 1.5 hours, then heated to 450°C and kept warm for 2 hours, and finally heated to 1400°C and kept warm for 3 hours. After cooling to room temperature with the furnace, it is placed in a mortar and ground for 10 minutes to finally obtain the neodymium-zirconium co-substituted strontium ferrite absorber material Sr 0.9 Nd 0.1 Zr 0.2 Fe 11.8 O 19 .

[0040] The prepared Nd:Zr co-substituted Sr:Fe ferrite absorbing material was tested for performance as follows:

[0041] (1) Wave absorption performance test method: A ZNA43 vector network analyzer from Rohde & Schwarz of Germany was used to measure the electromagnetic parameters of the material. The powder sample was prepared into a special test block using the waveguide method. The test ring was made by evenly mixing the sample and paraffin in different proportions and then pressing them into tablets. Steps for preparing the test ring: Weigh 80 mg of sample and 20 mg of paraffin, put them together in a clean quartz evaporating dish, place the quartz evaporating dish containing paraffin and powder on the heater, set the temperature to 90°C, wait for the paraffin to melt, stir it with the powder, and then transfer it to the fixture, place the fixture in the tablet press and press it into a sample. The paraffin sample in the 26.5-40GHz test range is in block shape, 7.112 mm long and 3.556 mm wide.

[0042] (2) Magnetic property test method: A vibrating sample magnetometer (VSM) model 7404 was used to test the hysteresis loop of the sample.

[0043] like Figure 1As shown, the selected matching thickness of the sample in the 26.5 - 40 GHz band is 0.7 mm, and the corresponding effective absorption bandwidth is 10.675 GHz, which is in the 26.5 - 37.175 GHz frequency band.

[0044] Example 2

[0045] The preparation method of the neodymium - zirconium co - substituted M - type strontium ferrite absorbing material. Compared with Example 1, the difference is only that: in step (1), the molar ratio of ferric nitrate nonahydrate, zirconium nitrate pentahydrate, strontium nitrate, neodymium nitrate hexahydrate and citric acid monohydrate is 11.8:0.2:0.8:0.2:15. Finally, the neodymium - zirconium co - substituted strontium ferrite absorbing material Sr 0.8 Nd 0.2 Zr 0.2 Fe 11.8 O 19 .

[0046] As Figure 2 shown, when the selected matching thickness of the sample in the 26.5 - 40 GHz band is 0.65 mm, the corresponding effective absorption bandwidth is 8.995 GHz, which is in the 26.938 - 35.933 GHz frequency band.

[0047] Example 3

[0048] The preparation method of the neodymium - zirconium co - substituted M - type strontium ferrite absorbing material. Compared with Example 1, the difference is only that: in step (1), the molar ratio of ferric nitrate nonahydrate, zirconium nitrate pentahydrate, strontium nitrate, neodymium nitrate hexahydrate and citric acid monohydrate is 11.8:0.2:0.7:0.3:15. Finally, the neodymium - zirconium co - substituted strontium ferrite absorbing material Sr 0.7 Nd 0.3 Zr 0.2 Fe 11.8 O 19 .

[0049] As Figure 3 shown, the selected matching thickness of the sample in the 26.5 - 40 GHz band is 0.55 mm, and at the same time the corresponding effective absorption bandwidth is 9.158 GHz, which is in the range of 28.062 - 37.220 GHz.

[0050] Example 4

[0051] Preparation method of neodymium-zirconium co-substituted M-type strontium ferrite microwave absorption material. Compared with Example 1, the difference in this example is only that in step (1), the molar ratio of ferric nitrate nonahydrate, zirconium nitrate pentahydrate, strontium nitrate, neodymium nitrate hexahydrate and citric acid monohydrate is 11.8:0.2:0.6:0.4:15. Finally, the neodymium-zirconium co-substituted strontium ferrite microwave absorption material Sr 0.6 Nd 0.4 Zr 0.2 Fe 11.8 O 19 is obtained.

[0052] As Figure 4 shown, when the selected matching thickness of the sample is 0.6 mm in the 26.5 - 40 GHz band, the effective microwave absorption bandwidth is 9.341 GHz, which is in the frequency band of 27.597 - 36.938 GHz.

[0053] Example 5

[0054] Preparation method of neodymium-zirconium co-substituted M-type strontium ferrite microwave absorption material. Compared with Example 3, the difference in this example is only that in step (5), the temperature is finally raised to 1250 °C and held for 3 h, and finally the neodymium-zirconium co-substituted strontium ferrite microwave absorption material Sr 0.7 Nd 0.3 Zr 0.2 Fe 11.8 O 19 is obtained.

[0055] As Figure 5 shown, when the selected matching thickness of the sample is 2 mm in the 26.5 - 40 GHz band, the effective microwave absorption bandwidth is 2.446 GHz, which is in the frequency band of 37.554 - 40 GHz.

[0056] Example 6

[0057] Preparation method of neodymium-zirconium co-substituted M-type strontium ferrite microwave absorption material. Compared with Example 3, the difference in this example is only that in step (5), the temperature is finally raised to 1300 °C and held for 3 h, and finally the neodymium-zirconium co-substituted strontium ferrite microwave absorption material Sr 0.7 Nd 0.3 Zr 0.2 Fe 11.8 O 19 is obtained.

[0058] As Figure 6 shown, when the selected matching thickness of the sample is 0.7 mm in the 26.5 - 40 GHz band, the effective microwave absorption bandwidth is 8.934 GHz, which is in the frequency band of 31.066 - 40 GHz.

[0059] Example 7

[0060] Preparation method of neodymium-zirconium co-substituted M-type strontium ferrite microwave absorbing material. Compared with Example 3, the difference in this example is only that: in step (5), the temperature is finally raised to 1350 °C and held for 3 h, and finally the neodymium-zirconium co-substituted strontium ferrite microwave absorbing material Sr 0.7 Nd 0.3 Zr 0.2 Fe 11.8 O 19 is obtained.

[0061] As Figure 7 shown, when the matching thickness selected for the sample in the 26.5 - 40 GHz band is 0.65 mm, the corresponding effective microwave absorption bandwidth is 11.138 GHz, which is in the 28.862 - 40 GHz frequency band.

[0062] The performance test results of the microwave absorbing materials prepared in Examples 1 - 7 are specifically shown in the following table:

[0063] Table 1 Microwave absorbing materials prepared in Examples 1 - 7 and their performance test results

[0064] Chemical formula Matched thickness Corresponding frequency band (GHz) / Frequency bandwidth Example 1 <![CDATA[Sr 0.9 Nd 0.1 Zr 0.2 Fe 11.8 O 19 > 0.7 26.5-37.175 / 10.675 Example 2 <![CDATA[Sr 0.8 Nd 0.2 Zr 0.2 Fe 11.8 O 19 > 0.65 26.938-35.933 / 8.995 Example 3 <![CDATA[Sr 0.7 Nd 0.3 Zr 0.2 Fe 11.8 O 19 > 0.55 28.062-37.220 / 9.158 Example 4 <![CDATA[Sr 0.6 Nd 0.4 Zr 0.2 Fe 11.8 O 19 > 0.6 27.597-36.938 / 9.341 Example 5 <![CDATA[Sr 0.7 Nd 0.3 Zr 0.2 Fe 11.8 O 19 > 2 37.554-40 / 2.446 Example 6 <![CDATA[Sr 0.7 Nd 0.3 Zr 0.2 Fe 11.8 O 19 > 0.7 31.066-40 / 8.934 Example 7 <![CDATA[Sr 0.7 Nd 0.3 Zr 0.2 Fe 11.8 O 19 > 0.65 28.862-40 / 11.138

[0065] Table 2 Magnetic properties of the microwave absorbing materials prepared in Examples 1 - 7

[0066] Coercivity (Oe) Saturation magnetization (emu / g) Example 1 164.2 71.236 Example 2 123.2 69.967 Example 3 143.2 64.813 Example 4 133.1 59.690 Example 5 2781.1 56.675 Example 6 2591.1 54.567 Example 7 1490.5 59.899

[0067] As can be seen from Tables 1 - 2, by adjusting the neodymium substitution amount and optimizing the heat treatment temperature, the microwave absorption performance of the material is improved. When the substitution amount is 0.3 and the heat treatment temperature is 1400 °C, the effective microwave absorption bandwidth of the material in the 26.5 - 40 GHz frequency band reaches 9.158 GHz, the corresponding matching thickness is 0.55 mm, the corresponding effective microwave absorption band is 28.062 - 37.220 GHz, the coercivity is 143.2 Oe, and the saturation magnetization intensity is 64.813 emu / g.

[0068] The above detailed description of various exemplary embodiments of the present invention should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics and implementation schemes of the present invention.

[0069] It should be understood that the terms described in the present invention are only for describing specific implementation modes and are not used to limit the present invention. In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0070] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0071] Without departing from the scope or spirit of the present invention, various modifications and variations can be made to the specific embodiments of the present invention specification, which will be apparent to those skilled in the art. Other embodiments obtained from the specification of the present invention will be apparent to those skilled in the art. The specification and examples of the present invention are merely exemplary.

[0072] The embodiments described above are only for describing the preferred mode of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solution of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A neodymium-zirconium co-substituted M-type strontium ferrite absorbing material, characterized in that: The chemical formula of the absorbing material is Sr 1- x Nd x Zr 0.2 Fe 11.8 O 19 , where 0.1≤x≤0.

4.

2. A method for preparing the Nd:Zr co-substituted M-type strontium ferrite wave absorbing material according to claim 1, characterized in that: The following steps are involved: (1) mixing strontium nitrate, ferric nitrate nonahydrate, neodymium nitrate hexahydrate, zirconium nitrate pentahydrate, citric acid monohydrate and deionized water, stirring and dissolving to obtain a sol; (2) adjusting the pH of the sol to 6.5-7.5, and then heating to perform a sol-gel reaction to obtain a wet gel; (3) drying and grinding the wet gel to obtain a precursor powder; (4) placing the precursor powder in a box furnace for heat treatment, cooling, and grinding to obtain the neodymium-zirconium co-substituted M-type strontium ferrite wave absorbing material.

3. The method for preparing the Nd:Zr co-substituted M-type strontium ferrite absorbing material according to claim 2, characterized in that: In step (1), the molar ratio of strontium nitrate, ferric nitrate nonahydrate, neodymium nitrate hexahydrate, zirconium nitrate pentahydrate and citric acid monohydrate is (1-x): 11.8:x:0.2:15, wherein 0.1≤x≤0.

4.

4. The method for preparing the Nd:Zr co-substituted M-type strontium ferrite absorbing material according to claim 2, characterized in that: In step (1), stirring is performed for 30 to 60 minutes.

5. The method for preparing the Nd:Zr co-substituted M-type strontium ferrite absorbing material according to claim 2, characterized in that: In step (2), the pH of the sol is adjusted using aqueous ammonia.

6. The method for preparing the Nd:Zr co-substituted M-type strontium ferrite absorbing material according to claim 2, characterized in that: In step (2), the heating is carried out in an oil bath at 120-140° C. with continuous stirring for 2.5-3.5 h.

7. The method for preparing the Nd:Zr co-substituted M-type strontium ferrite wave absorbing material according to claim 2, characterized in that: In step (3), the drying is carried out in a blast drying oven at a drying temperature of 140-160° C. for a time of 10-12 h.

8. The method for preparing the Nd:Zr co-substituted M-type strontium ferrite absorbing material according to claim 2, characterized in that: In step (4), the heat treatment process is as follows: first, the temperature is raised to 200-300°C and kept for 1-2 hours, then the temperature is raised to 400-500°C and kept for 2-3 hours, and finally the temperature is raised to 1250-1400°C and kept for 2-3 hours, and then cooled in the furnace.

9. The method for preparing the Nd:Zr co-substituted M-type strontium ferrite wave absorbing material according to claim 2, characterized in that: In step (4), the grinding time is 10-15 min.

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