A microwave loss dielectric / ferromagnetic composite powder and its preparation method

Abstract

The present invention discloses a microwave loss dielectric / ferromagnetic composite powder and a preparation method thereof. The preparation method comprises the following steps: taking a titanate and a soluble iron salt, and obtaining a titanate solution and an iron salt solution. Under continuous stirring, the iron salt solution is dropped into the titanate solution. After the dropping is completed, the reaction is carried out for 4 to 8 hours to obtain a precursor; taking the precursor, drying it, and then performing heat treatment for 3 to 5 hours to obtain a precursor powder; taking the precursor powder, heating it to 250 to 300 °C under the protection of an inert gas, and then introducing hydrogen and reacting to obtain the product. The present invention adopts an in-situ generation technology, which can effectively control the uniform dispersion of each phase composition, exert the synergistic effect and cross effect between components, and make the performance of the composite powder better; at the same time, by using the method of the present invention, various components are easy to regulate, the electromagnetic parameters can be tailored, and the interface loss effect is improved, making its application range wider.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave loss, and specifically provides a microwave loss dielectric / ferromagnetic composite powder and a preparation method thereof. Background Art

[0002] Electromagnetic waves of different frequencies are entering the fields of human life and production. Electromagnetic wave radiation causes huge environmental pollution and seriously affects human production and life. In the field of electromagnetic wave protection, electromagnetic shielding is usually used for protection. Due to the drawback of high electromagnetic wave reflection caused by electromagnetic shielding, the current requirements for shielding materials have been adjusted from high reflection in the past to high absorption and low reflection; the application of wave-absorbing materials can weaken electromagnetic pollution to a certain extent. There is an urgent need for a dielectric / magnetic composite powder wave-absorbing material to achieve the above purpose.

[0003] The wave-absorbing performance is jointly determined by the complex permittivity and complex permeability of the material at microwave frequencies. Therefore, pure electric loss or magnetic loss wave-absorbing materials are not ideal choices. Only composite materials with both electric loss and magnetic loss are beneficial to broaden the frequency band and improve the absorption rate. The unity of electricity and magnetism is an important research direction for wave-absorbing materials. Modern materials are developing towards composite materials because compounding can maintain the advantages of the two components, tailor the electromagnetic parameters of the materials, broaden the microwave absorption frequency band, improve the absorption efficiency, enhance the comprehensive performance, and meet the requirements of electromagnetic shielding, microwave anechoic chambers, and military stealth, etc.

[0004] Currently, the preparation of such composite materials with relatively high electric and magnetic losses is mainly through mechanical mixing. For example, Zhang Jing et al. prepared nano-graphite-coated BaZn2Fe 16 O 27 composite absorbents by mechanical blending method (Preparation and properties of nano-graphite / ferrite composite absorbents [J]. Non-Metallic Mines, 2023, 46(4): 72-75+80); Li Jun et al. prepared GO / Fe-based metal composite wave-absorbing materials and rGO / Fe-based composite wave-absorbing materials by high-energy ball milling of Fe-based metal magnetic powder with GO and reduced graphene oxide (rGO) respectively (Research on Fe-based magnetic metals and their graphene composite wave-absorbing materials [D]. Master's thesis of Nanjing University of Posts and Telecommunications, April 2019); Zhou Yinmin et al. prepared nano-aluminum-coated carbonyl iron particles by ball milling method. The materials obtained by this method have uneven dispersion of each phase and unsatisfactory microstructure, and do not give full play to the advantage of interfacial loss. Therefore, it is difficult to give full play to the advantages of composite materials, resulting in relatively poor wave-absorbing performance. Summary of the Invention

[0005] In order to solve at least one of the above problems, the present invention provides a microwave loss dielectric / ferromagnetic composite powder.

[0006] The specific solution of the present invention is as follows: A preparation method of a microwave loss dielectric / ferromagnetic composite powder, comprising the following steps:

[0007] Take titanate and soluble iron salt with a molar ratio of 3:1 to 9. Dissolve the titanate in a certain volume of mixed alcohol solution to obtain a titanate solution; dissolve the soluble iron salt in a citric acid aqueous solution and add ethylene glycol to obtain an iron salt solution. Under continuous stirring, drop the iron salt solution into the titanate solution. After the dropping is completed, react at room temperature for 4 to 8 hours to obtain a precursor; wherein, the addition amount of ethylene glycol is 0.4 to 0.6 times the molar amount of the iron salt. In the process of preparing the precursor, it is usually necessary to fully mix the iron salt and the titanate, and ultrasonic or stirring methods can be used. However, from the perspective of efficiency and effect, the ultrasonic method is preferred.

[0008] Take the precursor, dry it, and heat-treat it at 350 to 500 °C for 3 to 5 hours to obtain a precursor powder;

[0009] Take the precursor powder, under the protection of an inert gas, program the temperature to 250 to 300 °C, and then introduce hydrogen and react for 3 to 5 hours to obtain the product.

[0010] One embodiment of the present invention is that the titanate includes n-butyl titanate and isobutyl titanate, and the iron salt is ferric nitrate, ferric sulfate, or ferric chloride.

[0011] One embodiment of the present invention is that the solvent of the titanate is a mixed solution of acetylacetone, n-butanol, and ethanol with a volume ratio of 1:1 to 1.3:1.5 to 2.0, the solvent of the iron salt is water, and the addition amount of the complexing agent is 1 to 2 times the molar amount of the soluble iron salt. In fact, for titanate, there are many alcohol solutions that can dissolve it, such as common absolute ethanol. However, the inventor found through a large number of experiments that using the aforementioned mixed solvent can not only dissolve the titanate well, but also make the performance of the finally prepared composite powder better.

[0012] One embodiment of the present invention is that the complexing agent is one of citric acid and EDTA.

[0013] One embodiment of the present invention is that the mass concentration of the titanate solution is 10 to 20%, and the mass concentration of the iron salt solution is 20 to 25%. Under this concentration condition, the reaction rate of the iron salt and the titanate is faster, more time-saving, and the reaction product is more uniform.

[0014] One embodiment of the present invention is that the programmed heating rate is 5 to 15 °C / min.

[0015] A microwave loss dielectric / ferromagnetic composite powder is prepared by any of the above methods. This powder has high microwave absorption ability.

[0016] Advantages: The in-situ generation technology is adopted in the present invention, which can effectively control the uniform dispersion of each phase composition, give full play to the synergistic and cross effects (composite effect) between components, increase the contact interfaces of different components, and make the performance of the composite powder better; at the same time, by using the method of the present invention, various components are easy to regulate, and the electromagnetic parameters can be tailored, making its application range wider. Brief Description of the Drawings

[0017] Figure 1 is the TEM image of the composite powder;

[0018] Figure 2 is the XRD pattern of the composite powder; Detailed Embodiments

[0019] The present invention will be further described in detail below with reference to the embodiments and the drawings, but the embodiments of the present invention are not limited thereto.

[0020] In the following embodiments, if not otherwise specified, the items mentioned are all conventional commercial products in the art.

[0021] In the following embodiments, if not otherwise specified, the operations mentioned are all conventional operations in the art.

[0022] Embodiment 1

[0023] Step 1: First, measure acetylacetone, n-butanol, and ethanol according to a volume ratio of 1:1.1:1.8. The three are mixed to obtain an alcohol solution of acetylacetone. Weigh 0.1 mol of tetra-n-butyl titanate, and then dissolve it in the above-mentioned 200 mL of mixed alcohol solution to obtain a tetra-n-butyl titanate solution; weigh 0.3 mol of Fe(NO3)3·9H2O, add it to 360 mL of a citric acid aqueous solution with a concentration of 30 wt%, and dropwise add 0.15 mol of ethylene glycol to obtain an iron salt solution. At room temperature and with continuous stirring, the above-mentioned iron salt solution is slowly dropped into the tetra-n-butyl titanate solution. The obtained solution is treated with 60 kHz ultrasonic waves for 10 min, and then left to react for 6 h to obtain a light red complex solid.

[0024] Step 2: Place the light red complex solid obtained in Step 1 in a drying oven at 100 °C for 72 h. After grinding the product, place it in a muffle furnace, heat it to 350 °C, keep it warm for 5 h, and cool it with the furnace to obtain a precursor powder containing Fe-Ti-O.

[0025] Step 3: Feed the above-mentioned precursor powder into a horizontal quartz reaction tube, introduce high-purity nitrogen gas, and heat it at a rate of 10 °C / min. When the temperature reaches 280 °C, stop introducing nitrogen gas, then introduce hydrogen gas at a rate of 120 mL / min, and carry out a reduction reaction for 5 h. After the reaction is completed, the sample is cooled with the furnace. When the furnace temperature drops to room temperature, stop introducing hydrogen gas to obtain the composite powder.

[0026] Figure 1 Figure 2 is the TEM image of the composite powder prepared in this example. It can be seen from the figure that the powder size is relatively uniform and the mixing is relatively homogeneous. Figure 2 is the XRD pattern of the composite powder prepared in this example. It can be seen from the figure that the final composite powder is mainly a mixture of iron and titanium dioxide.

[0027] Mix the prepared composite powder and epoxy resin according to a mass ratio of 4:1 to make an annular sample with an outer diameter of 7.00 mm, an inner diameter of 3.00 mm, and a thickness of 5.00 mm, and test the microwave electromagnetic parameters in the range of 2 - 12 GHz. The maximum microwave loss is -37 dB, showing good microwave absorption performance.

[0028] Under the same conditions, take titanium dioxide and iron powder in the laboratory and ball-mill and mechanically mix them in a molar ratio of 1:3 for one hour to obtain a mixed powder. Also mix it with epoxy resin according to a mass ratio of 4:1 to make an annular sample with an outer diameter of 7.00 mm, an inner diameter of 3.00 mm, and a thickness of 5.00 mm, and test the microwave electromagnetic parameters in the range of 2 - 12 GHz. The matching thickness is 2 mm, the maximum microwave loss is -48.3 dB, which occurs at 8.3 GHz, and the bandwidth less than -10 dB is 7.3 GHz (3.9 - 11.2 GHz).

[0029] Example 2

[0030] Step 1: First, measure acetylacetone, n-butanol, and ethanol according to a volume ratio of 1:1.1:1.8. Mix the three to obtain an alcohol solution of acetylacetone. Weigh 0.3 mol of tetrabutyl titanate, and then dissolve it in the above-mentioned 600 mL of mixed alcohol solution to obtain a tetrabutyl titanate solution; weigh 0.1 mol of Fe(NO3)3·9H2O, add it to 120 mL of a citric acid aqueous solution with a mass concentration of 30 wt%, and dropwise add 0.05 mol of ethylene glycol to obtain an iron salt solution. At room temperature and with continuous stirring, slowly drop the above-mentioned iron salt solution into the tetrabutyl titanate solution, treat the obtained solution with ultrasonic waves at 60 kHz for 20 min, and then let it stand and react for 4 h to obtain a light red complex coagulum.

[0031] Step 2: Place the light red complex solid obtained in Step 1 in an oven at 120 °C and dry it for 36 h. Then, grind the product and place it in a muffle furnace. Heat it up to 420 °C and keep it at this temperature for 4 h. After cooling down with the furnace, a precursor powder containing Fe-Ti-O is obtained.

[0032] Step 3: Feed the above precursor powder into a horizontal quartz reaction tube, introduce high-purity nitrogen, and heat it up at a rate of 5 °C / min. When the temperature reaches 250 °C, stop introducing nitrogen, then introduce hydrogen at a rate of 150 mL / min and carry out a reduction reaction for 4 h. After the reaction is completed, let the sample cool down with the furnace. When the furnace temperature drops to room temperature, stop introducing hydrogen to obtain a composite powder.

[0033] Mix the prepared composite powder and epoxy resin according to the mass ratio of powder:resin = 4:1 to make an annular sample with an outer diameter of 7.00 mm, an inner diameter of 3.00 mm, and a thickness of 5.00 mm. Test the microwave electromagnetic parameters at 2 - 12 GHz. The microwave loss is -23 dB, indicating good microwave absorption performance.

[0034] Take titanium dioxide and iron powder and ball-mill and mechanically mix them in a molar ratio of 3:1 for one hour to obtain a mixed powder in the same way. Also mix them according to the mass ratio of powder:resin = 4:1 to make an annular sample with an outer diameter of 7.00 mm, an inner diameter of 3.00 mm, and a thickness of 4 - 5.00 mm. Test the microwave electromagnetic parameters at 2 - 12 GHz. The matching thickness is 2.5 mm, the maximum microwave loss is -23.5 dB, which occurs at 6.8 GHz, and the bandwidth less than -10 dB is 4.6 GHz (4.5 - 9.1 GHz).

[0035] Example 3

[0036] Step 1: First, measure acetylacetone, n-butanol, and ethanol in a volume ratio of 1:1.1:1. Mix the three to obtain an alcohol solution of acetylacetone. Weigh 0.2 mol of tetrabutyl titanate and dissolve it in the above 400 mL of mixed alcohol solution to obtain a tetrabutyl titanate solution. Weigh 0.2 mol of Fe(NO3)3·9H2O, add it to 240 mL of a citric acid aqueous solution with a mass concentration of 30 wt%, and dropwise add 0.10 mol of ethylene glycol to obtain an iron salt solution. At room temperature and with continuous stirring, slowly drop the above iron salt solution into the tetrabutyl titanate solution. Treat the obtained solution with ultrasonic waves at 60 kHz for 20 min, and then let it stand and react for 8 h to obtain a light red complex solid.

[0037] Step 2: Place the light red complex solid obtained in Step 1 in an oven at 100 °C and dry it for 48 h. Then, grind the product and place it in a muffle furnace. Heat it up to 500 °C and keep it at this temperature for 3 h. After cooling down with the furnace, a precursor powder containing Fe-Ti-O is obtained.

[0038] Step 3: Feed the above precursor powder into a horizontal quartz reaction tube, introduce high-purity nitrogen gas, and heat it at a rate of 15 °C / min. When the temperature reaches 300 °C, stop introducing nitrogen gas, then introduce hydrogen gas at a rate of 80 mL / min, and carry out a reduction reaction for 3 h. After the reaction is completed, the sample is cooled with the furnace. When the furnace temperature drops to room temperature, stop introducing hydrogen gas to obtain the composite powder.

[0039] Mix the prepared composite powder and epoxy resin according to the mass ratio of powder:resin = 4:1 to make an annular sample with an outer diameter of 7.00 mm, an inner diameter of 3.00 mm, and a thickness of 5.00 mm, and test the microwave electromagnetic parameters at 2 - 12 GHz. The microwave loss is -30 dB, indicating good microwave absorption performance.

[0040] Under the same conditions, take titanium dioxide and iron powder in the laboratory and ball-mill and mechanically mix them in a molar ratio of 1:1 for one hour to obtain a mixed powder in the same way. Also mix them according to the mass ratio of powder:resin = 4:1 to make an annular sample with an outer diameter of 7.00 mm, an inner diameter of 3.00 mm, and a thickness of 4 - 5.00 mm, and test the microwave electromagnetic parameters at 2 - 12 GHz. The microwave loss is -8 dB. The matching thickness is 2.2 mm, the maximum microwave loss is -34.1 dB, which occurs at 5.3 GHz, and the bandwidth less than -10 dB is 4.5 GHz (3.5 - 8.0 GHz).

[0041] Comparative Example 1

[0042] The difference from Example 1 is that hydrogen gas is not introduced in Step 3, and the rest are the same.

[0043] Mix the prepared composite powder and epoxy resin according to the mass ratio of powder:resin = 4:1 to make an annular sample with an outer diameter of 7.00 mm, an inner diameter of 3.00 mm, and a thickness of 5.00 mm, and test the microwave electromagnetic parameters at 2 - 12 GHz. The maximum microwave loss is -19.8 dB.

[0044] Comparative Example 2

[0045] The difference from Example 3 is that in Step 2, the temperature of the muffle furnace is 550 °C, and the rest are the same.

[0046] Mix the prepared composite powder and epoxy resin according to the mass ratio of powder:resin = 4:1 to make an annular sample with an outer diameter of 7.00 mm, an inner diameter of 3.00 mm, and a thickness of 5.00 mm, and test the microwave electromagnetic parameters at 2 - 12 GHz. The maximum microwave loss is -9.2 dB.

[0047] Comparative Example 3:

[0048] The difference from Example 1 is that in Step 2, the temperature of the muffle furnace is 300 °C, and the rest are the same.

[0049] The prepared composite powder and epoxy resin were mixed at a mass ratio of powder:resin = 4:1 to form an annular sample with an outer diameter of 7.00 mm, an inner diameter of 3.00 mm, and a thickness of 5.00 mm. The microwave electromagnetic parameters in the range of 2 - 12 GHz were measured, and the maximum microwave loss was -17.6 dB.

[0050] Comparative Example 4

[0051] The difference from Example 2 is that in Step 3, the temperature was 330 °C, and the rest were the same.

[0052] The prepared composite powder and epoxy resin were mixed at a mass ratio of powder:resin = 4:1 to form an annular sample with an outer diameter of 7.00 mm, an inner diameter of 3.00 mm, and a thickness of 5.00 mm. The microwave electromagnetic parameters in the range of 2 - 12 GHz were measured, and the maximum microwave loss was -14.5 dB.

[0053] Comparative Example 5

[0054] The difference from Example 3 is that in Step 3, the temperature was 220 °C, and the rest were the same.

[0055] Step 9: The prepared composite powder and epoxy resin were mixed at a mass ratio of powder:resin = 4:1 to form an annular sample with an outer diameter of 7.00 mm, an inner diameter of 3.00 mm, and a thickness of 5.00 mm. The microwave electromagnetic parameters in the range of 2 - 12 GHz were measured, and the maximum microwave loss was -10.3 dB.

[0056] As described above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed in the embodiments of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a microwave lossy dielectric / ferromagnetic composite powder, characterized in that: The following steps are involved: Take titanate and soluble iron salt in a molar ratio of 3:1-9, dissolve the titanate in a certain volume of mixed alcohol solution to obtain a titanate solution; dissolve the soluble iron salt in a citric acid aqueous solution, and add ethylene glycol to obtain an iron salt solution, and drop the iron salt solution into the titanate solution under continuous stirring. After the dropwise addition is completed, react at room temperature for 4-8 hours to obtain a precursor; wherein the amount of ethylene glycol added is 0.4-0.6 times the molar amount of the iron salt, and the solvent of the titanate is a mixed solution of acetylacetone, n-butanol and ethanol in a volume ratio of 1:1-1.3:1.5-2.0; Taking the precursor, drying it, and heat treating it at 350-500° C. for 3-5 hours to obtain a precursor powder; Take the precursor powder, and under the protection of inert gas, raise the temperature to 250-300°C, then introduce hydrogen and react for 3-5 hours to obtain the product.

2. The method according to claim 1, characterized in that The titanate includes n-butyl titanate and isobutyl titanate, and the iron salt includes iron nitrate, iron sulfate and iron chloride.

3. The method according to claim 1, characterized in that: The amount of citric acid added is 1 to 2 times the molar amount of the soluble iron salt.

4. The method according to claim 1, characterized in that: The mass concentration of the titanate solution is 10-20%, and the mass concentration of the iron salt solution is 20-25%.

5. The method according to claim 1, characterized in that The programmed heating rate is 5 to 15° C. / min.

6. A microwave lossy dielectric / ferromagnetic composite powder, characterized in that: The method is prepared by any one of claims 1 to 5.

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