Carbon-coated iron-cobalt-chromium nanoparticles, and preparation method and application thereof

Abstract

The application discloses carbon-coated iron-cobalt-chromium nanoparticles as well as a preparation method and application thereof, and the preparation method comprises the following steps: mixing an iron compound, a cobalt salt, a chromium salt and 2-methyl imidazole with a solvent, stirring and reacting, and then performing spin-drying by using a rotary evaporator to obtain an iron-cobalt-chromium three-metal complex precursor; and pyrolyzing the iron-cobalt-chromium three-metal complex precursor under the protection of an inert gas to obtain the carbon-coated iron-cobalt-chromium nanoparticles. s The graphitized carbon layer of the material can isolate oxygen and corrosive medium, and maintain high M s The electronic coupling effect between the carbon shell and the iron-cobalt-chromium interface can reduce lattice distortion, inhibit magnetic domain wall pinning and reduce coercivity.

Description

Technical Field

[0001] This invention relates to the field of magnetic nanomaterial preparation technology, specifically to a carbon-coated iron-cobalt-chromium nanoparticle, its preparation method, and its application. Background Technology

[0002] Excellent soft magnetic materials, due to their high permeability and low coercivity, are widely used in transformers, motors, generators, electromagnetic relays, inductors, reactors, magnetic shielding, magnetic recording equipment, frequency converters, medical equipment (such as MRI), wireless charging systems, and various sensors to improve efficiency and reduce energy loss. High saturation magnetization means that the material can reach its maximum magnetization state under a relatively low applied magnetic field, which is crucial for improving the magnetic storage density of the material and the sensitivity of the sensor. Low coercivity means that the material can be quickly demagnetized after the applied magnetic field is removed, reducing hysteresis loss and heat accumulation, which is an essential performance characteristic for high-efficiency magnetic materials in practical applications. Both iron and cobalt have high magnetization, so iron-cobalt alloys have attracted much attention due to their excellent magnetic properties. However, the soft magnetic properties of current iron-cobalt alloys are still unsatisfactory. Summary of the Invention

[0003] The technical problem to be solved by this invention is how to improve the soft magnetic properties of iron-cobalt alloys.

[0004] The present invention solves the above-mentioned technical problems through the following technical means:

[0005] A method for preparing carbon-coated iron-cobalt-chromium nanoparticles includes the following steps: S1. Iron compound, cobalt salt, chromium salt, 2-methylimidazole and solvent are mixed, stirred and reacted, and then evaporated to dryness using a rotary evaporator to obtain the iron-cobalt-chromium trimetallic complex precursor; the iron compound is one or a mixture of two of ferric nitrate and ferrous nitrate. S2. The carbon-coated iron-cobalt-chromium nanoparticles are obtained by pyrolyzing the iron-cobalt-chromium trimetallic complex precursor under inert gas protection.

[0006] Preferably, in S1, the molar ratio of the iron compound to the cobalt salt is 1-3 : 1-3.

[0007] Preferably, in S1, the molar ratio of the iron compound to the cobalt salt is 1-3:1-2.

[0008] Preferably, in S1, the molar ratio of the iron compound to the cobalt salt is 1:2-3.

[0009] Preferably, in S1, the molar ratio of the iron compound and the cobalt salt is one of 2:1 and 1:2.

[0010] Preferably, in S1, the molar ratio of the iron compound to the chromium salt is 1:0.07-0.4.

[0011] Preferably, in S1, the molar ratio of the iron compound to the chromium salt is 1:0.1-0.3.

[0012] Preferably, in S1, the molar ratio of the iron compound to the chromium salt is one of 1:0.15, 1:0.3, 1:0.075, 1:0.113, 1:0.187, and 1:0.299.

[0013] Preferably, in S1, the molar ratio of the iron compound and 2-methylimidazole is 1:1-3.

[0014] Preferably, in S1, the molar ratio of the iron compound and 2-methylimidazole is 1:1-2.

[0015] Preferably, in S1, the molar ratio of the iron compound and 2-methylimidazole is one of 1:1.22 and 1:2.44.

[0016] Preferably, in S1, the ratio of the iron compound to the solvent is 0.5-1 mmol: 20 mL.

[0017] Preferably, the ratio of 2-methylimidazole to solvent is 1 g : 200 ml.

[0018] Preferably, in S1, the iron compound is ferric nitrate; the cobalt salt is cobalt nitrate; the chromium salt is one or a mixture of two of chromium chloride and chromium nitrate; and the solvent is methanol.

[0019] Preferably, in S1, the stirring reaction is carried out at room temperature for 10-30 hours.

[0020] Preferably, in S2, the pyrolysis temperature is 800~1000℃ and the time is 1-3 h.

[0021] Preferably, in S2, the pyrolysis temperature is 850~950℃.

[0022] Preferably, in S2, the pyrolysis temperature is 850°C.

[0023] Preferably, in S2, the heating rate during the pyrolysis process is 5°C / min.

[0024] Preferably, in S2, the inert gas is one or a mixture of two of nitrogen and argon.

[0025] Preferably, in S2, the inert gas flow rate is 30~60 mL / min.

[0026] Preferably, the molar content of iron-cobalt-chromium alloy in the obtained carbon-coated iron-cobalt-chromium nanoparticles is 3% to 30%.

[0027] The present invention also proposes a carbon-coated iron-cobalt-chromium nanoparticle, which is prepared by the method described above.

[0028] Preferably, the carbon-coated iron-cobalt-chromium nanoparticles have a saturation magnetization of 115~182 emu / g and a coercivity of 20~51 Oe.

[0029] Preferably, the carbon-coated iron-cobalt-chromium nanoparticles have a saturation magnetization of 115~182 emu / g and a coercivity of 20~51 Oe, and can be used as a high-efficiency soft magnetic material in various fields.

[0030] Preferably, the carbon-coated iron-cobalt-chromium nanoparticles have a saturation magnetization of 140~182 emu / g and a coercivity of 20~30 Oe.

[0031] Preferably, the carbon-coated iron-cobalt-chromium nanoparticles have a minimum reflection loss RL of -53.5 dB at a frequency of 15.2 GHz and a maximum effective absorption bandwidth EAB of 7.2 GHz (10.4-17.6 GHz) when the matching thickness is 1.7 mm.

[0032] Preferably, the carbon-coated iron-cobalt-chromium nanoparticles have a wide absorption bandwidth and can be used as high-efficiency microwave absorbing materials in various fields.

[0033] The present invention also proposes an application of the aforementioned carbon-coated iron-cobalt-chromium nanoparticles in soft magnetic devices and / or microwave absorbing materials.

[0034] The nanoparticles of this invention can be used to prepare high-performance iron-cobalt-chromium-based composite soft magnetic materials and microwave absorbing materials. They are suitable for various complex, miniaturized, and multifunctional high-power soft magnetic devices, as well as manufacturing industries requiring broadband and strong absorption, and have broad application prospects. This invention features abundant raw material sources, simple process, reliable repeatability, low reaction temperature, corrosion resistance, low energy consumption, and environmental friendliness, making it easy for industrial production.

[0035] This invention uses ferric nitrate and / or ferrous nitrate, cobalt salt, chromium salt, and the organic ligand 2-methylimidazole as raw materials at room temperature. These are mixed evenly in a solvent in a specific ratio and stirred to allow for a complete reaction. The solution is then rotary evaporated to obtain a brown gel-like precursor containing ferric, cobalt, and chromium metal elements uniformly distributed in a preset ratio. The precursor is then pyrolyzed under an inert gas atmosphere. During the pyrolysis process, the ligand releases a reducing atmosphere, causing ferric, cobalt, and chromium ions to be reduced in situ and locally condensed into ferric, cobalt, and chromium alloy nanoparticles in a specific ratio. The resulting organic carbon framework anchors the nanoparticles, preventing them from growing too large, and carbon-coats the alloy particles to prevent them from being oxidized by gases such as oxygen, thus obtaining the desired carbon-coated ferric, cobalt, and chromium nano-alloy particles.

[0036] This invention discovers that nanoscale iron-cobalt-chromium alloy particles can exhibit significant soft magnetic effects. Furthermore, by coating the surface of these alloy particles with a layer of carbon material, the stability problem of nanoalloys can be effectively overcome. The carbon coating not only provides a physical barrier to prevent particle oxidation and agglomeration but also enhances the mechanical strength and chemical stability of the particles. Simultaneously, the conductivity and chemical inertness of the carbon layer itself offer new possibilities for the material's application in fields such as electromagnetic shielding.

[0037] The advantages of this invention are: (1) This invention utilizes iron salts, cobalt salts, chromium salts, and suitable organic ligands to synthesize a precursor containing uniformly distributed iron, cobalt, and chromium elements. This precursor is then pyrolyzed under an inert atmosphere to prepare carbon-coated iron-cobalt-chromium nanoparticles (FeCoCr@C). High-performance FeCoCr@C soft magnetic materials and microwave absorbing materials are prepared by adjusting the raw material ratio and pyrolysis temperature. The reaction conditions are mild, energy consumption is low, the synthesis process is simple, and it is easy to mass-produce. Adding chromium can improve the corrosion resistance of the alloy. In terms of microwave absorption, it has advantages such as strong absorption, wide bandwidth, and light weight. The graphitized carbon layer of the material can also isolate oxygen and corrosive media, maintaining the high M of the iron-cobalt-chromium core. s The electronic coupling between the carbon shell and the iron-cobalt-chromium interface can reduce lattice distortion and suppress magnetic domain wall pinning, thereby reducing coercivity.

[0038] (2) The carbon-coated iron-cobalt-chromium nanoalloy particles with high saturation magnetization and low coercivity prepared by this invention utilize a graphite coating layer to regulate the composite structure of the iron-cobalt-chromium nanoalloy. The carbon layer inhibits particle agglomeration through van der Waals forces and reduces interfacial stress through matching thermal expansion coefficients, ensuring the long-term stability of the material. These particles exhibit high saturation magnetization and low coercivity in soft magnetic devices, making them valuable for applications in power electronics, high-frequency devices, magnetic storage, magnetorheological fluids, and electromagnetic shielding.

[0039] (3) The carbon-coated iron-cobalt-chromium nanoparticles with high microwave absorption performance prepared in this invention can be easily constructed into a hierarchical structure of metal particles and carbon materials. The resulting composite material absorbs waves through multiple loss mechanisms. This invention successfully prepared a novel microwave absorber through heat treatment, achieving a synergistic effect of electromagnetic loss and dielectric loss, and obtaining excellent electromagnetic wave absorption performance. It provides an effective strategy for the design and preparation of novel magnetic composite materials. It has important application value in fields such as electronic communication, aerospace, new energy, and medical equipment. Attached Figure Description

[0040] Figure 1 This is a scanning electron microscope (SEM) image of the product obtained in Example 1 of the present invention. Figure 2 This is a high-resolution transmission electron microscope (HRTEM) image of the product obtained in Example 1 of the present invention. Figure 3 The X-ray photoelectron spectrum (XPS) of the product obtained in Example 1 of the present invention. Figure 4 The X-ray diffraction pattern (XRD) of the product obtained in Example 1 of the present invention. Figure 5 Tafel plots of the product (red) obtained in Example 1 of the present invention and the product (black) obtained in Comparative Example 1. Figure 6 This is a reflection loss diagram (RL) of the product with different matching thicknesses obtained in Example 1 of the present invention. Figure 7 This is a reflection loss diagram (RL) of the product with different matching thicknesses obtained in Example 3 of the present invention. Figure 8 This is a reflection loss diagram (RL) of the product with different matching thicknesses obtained in Example 7 of the present invention. Figure 9 The image shows the hysteresis loop (VSM) of the product obtained in Example 1 of this invention. Figure 10 The image shows the hysteresis loop (VSM) of the product obtained in Example 2 of this invention. Figure 11 The image shows the hysteresis loop (VSM) of the product obtained in Example 3 of the present invention. Figure 12 The hysteresis loop (VSM) diagram of the product obtained in Example 4 of the present invention is shown. Figure 13 The image shows the hysteresis loop (VSM) of the product obtained in Example 5 of this invention. Figure 14 The hysteresis loop (VSM) diagram of the product obtained in Example 6 of the present invention is shown. Figure 15The hysteresis loop (VSM) diagram of the product obtained in Example 7 of the present invention is shown. Figure 16 The hysteresis loop (VSM) diagram of the product obtained in Example 8 of the present invention is shown. Figure 17 The hysteresis loop (VSM) diagram of the product obtained in Example 9 of the present invention is shown. Figure 18 The image shows the hysteresis loop (VSM) of the product obtained in Comparative Example 1 of this invention. Figure 19 The image shows the hysteresis loop (VSM) of the product obtained in Comparative Example 2 of this invention. Figure 20 The image shows the hysteresis loop (VSM) of the product obtained in Comparative Example 3 of this invention. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, 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.

[0042] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0043] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0044] All chemical reagents used in the following examples are chemically pure and readily available on the market.

[0045] The ferric nitrate is ferric nitrate nonahydrate (Fe(NO3)3·9H2O), the cobalt nitrate is cobalt nitrate hexahydrate (Co(NO3)2·6H2O), and the chromium chloride is chromium chloride hexahydrate (CrCl3·6H2O).

[0046] Example 1 A method for preparing carbon-coated iron-cobalt-chromium nanoparticles with high saturation magnetization and low coercivity includes the following steps: (1) Add 4 g (10 mmol) of ferric nitrate, 1.45 g (5 mmol) of cobalt nitrate, 1 g (12.2 mmol) of 2-methylimidazole and 0.4 g (1.5 mmol) of chromium chloride to 200 mL of methanol and dissolve by sonication at room temperature.

[0047] (2) Stir the solution obtained in step (1) at room temperature for 24 h.

[0048] (3) The solution in step (2) was dried by rotary evaporation and vacuum dried to collect the iron-cobalt-chromium precursor.

[0049] (4) The iron-cobalt-chromium precursor obtained in step (3) is heated to 850 °C for 2 h in a tube furnace under argon protection at a flow rate of 30 mL / min to obtain the carbon-coated iron-cobalt-chromium nanoparticles with high saturation magnetization and low coercivity.

[0050] The SEM image of the carbon-coated iron-cobalt-chromium nanoparticles obtained in this embodiment is shown below. Figure 1 As shown, the product is a graphite-coated iron-cobalt-chromium nanoalloy structure.

[0051] The high-resolution transmission electron microscope image of the carbon-coated iron-cobalt-chromium nanoparticles obtained in this embodiment is shown below. Figure 2 As shown, the lattice spacing of the graphite-coated iron-cobalt-chromium nanoalloy is 0.1430 nm, 0.2022 nm and 0.2524 nm, which corresponds to its XRD pattern.

[0052] The XPS image of the carbon-coated iron-cobalt-chromium nanoparticles obtained in this embodiment is as follows: Figure 3 As shown, the product contains iron, cobalt, chromium, and carbon elements.

[0053] The XRD pattern of the carbon-coated iron-cobalt-chromium nanoparticles obtained in this embodiment is as follows: Figure 4 As shown in the figure, it can be seen that the peaks at 2θ of 35.5, 44.8 and 65.2 are the 100, 110 and 200 crystal planes of the iron-cobalt-chromium nanoalloy, respectively.

[0054] The absorption performance of the carbon-coated iron-cobalt-chromium nanoparticles with high saturation magnetization and low coercivity obtained in this embodiment was tested using an Agilent E5071C vector network analyzer via the coaxial method. One end of two cables was connected to the electromagnetic wave emission port and electromagnetic wave input port of the vector network analyzer, respectively, and the other end was connected to the coaxial mold to be tested. The magnetic mode was selected, along with the number of test points and frequency. Two-port calibration was then performed. The testing software was opened for calibration. If the calibration result was within ±0.005, the next test could proceed; otherwise, calibration continued until the range condition was met. Finally, the test button was clicked to perform the test. The RL diagram of the carbon-coated iron-cobalt-chromium nanoparticles obtained in this embodiment is shown below. Figure 6As shown, the product exhibits strong reflection loss and a large absorption bandwidth. The minimum reflection loss (RL) is -53.5 dB at a frequency of 15.2 GHz, and the maximum effective absorption bandwidth (EAB) reaches 7.2 GHz (10.4-17.6 GHz) when the matching thickness is 1.7 mm.

[0055] Hysteresis loop tests were performed on the carbon-coated iron-cobalt-chromium nanoparticles with high saturation magnetization and low coercivity obtained in this embodiment. The equipment used for this test was a LakeShore 8604 vibrating sample magnetometer (VSM) from the United States. The specific steps were as follows: After the instrument was powered on and warmed up for half an hour, the VSM was calibrated using a Ni standard sample. Then, the sample tube containing the sample was fixed to the sample rod, the sample rod was installed on the VSM vibrating head, and the saddle point was aligned. A suitable test program was selected to start the test. The hysteresis loop diagram of the carbon-coated iron-cobalt-chromium nanoparticles with high saturation magnetization and low coercivity obtained in this embodiment is shown below. Figure 9 As shown, the carbon-coated iron-cobalt-chromium nanoparticles exhibit a saturation magnetization of 182 emu / g and a coercivity of only 20 Oe. This demonstrates that the carbon-coated iron-cobalt-chromium nanoparticles obtained in this embodiment possess both high saturation magnetization and low coercivity.

[0056] Example 2 In this embodiment, carbon-coated iron-cobalt-chromium nanoparticles with high saturation magnetization and low coercivity were prepared using the same method as in Example 1. The difference was that in step (1), the raw material iron nitrate was changed to 2 g (5 mmol) and cobalt nitrate was changed to 2.9 g (10 mmol).

[0057] The carbon-coated iron-cobalt-chromium nanoparticles obtained in this example were subjected to hysteresis loop testing using the same method as in Example 1. Figure 10 As shown, at room temperature, the saturation magnetization of the carbon-coated iron-cobalt-chromium nanoparticles in this embodiment is 162 emu / g, and its coercivity is 27 Oe.

[0058] Example 3 In this embodiment, carbon-coated iron-cobalt-chromium nanoparticles with high saturation magnetization and low coercivity were prepared using the same method as in Example 1. The only difference was that the amount of chromium chloride used in step (1) was changed to 0.2 g (0.75 mmol).

[0059] The carbon-coated iron-cobalt-chromium nanoparticles with high saturation magnetization and low coercivity obtained in this example were subjected to hysteresis loop testing and microwave absorption performance testing, using the same method as in Example 1. Figure 11 As shown, at room temperature, the saturation magnetization of the carbon-coated iron-cobalt-chromium nanoparticles in this embodiment is 167 emu / g, and its coercivity is 26 Oe. The RL diagram of the carbon-coated iron-cobalt-chromium nanoparticles obtained in this embodiment is shown below. Figure 7As shown, it can be seen that due to the large dielectric constant leading to impedance mismatch, the product has almost no reflection loss.

[0060] Example 4 In this embodiment, carbon-coated iron-cobalt-chromium nanoparticles with high saturation magnetization and low coercivity were prepared using the same method as in Example 1. The only difference was that the amount of chromium chloride used in step (1) was changed to 0.3 g (1.13 mmol).

[0061] The carbon-coated iron-cobalt-chromium nanoparticles with high saturation magnetization and low coercivity obtained in this example were subjected to hysteresis loop testing using the same method as in Example 1. Figure 12 As shown, at room temperature, the saturation magnetization of the carbon-coated iron-cobalt-chromium nanoparticles in this embodiment is 174 emu / g, and its coercivity is 21 Oe.

[0062] Example 5 In this embodiment, carbon-coated iron-cobalt-chromium nanoparticles with high saturation magnetization and low coercivity were prepared using the same method as in Example 1. The only difference was that the amount of chromium chloride used in step (1) was changed to 0.5 g (1.87 mmol).

[0063] The carbon-coated iron-cobalt-chromium nanoparticles with high saturation magnetization and low coercivity obtained in this example were subjected to hysteresis loop testing and microwave absorption performance testing, using the same method as in Example 1. Figure 13 As shown, at room temperature, the saturation magnetization of the carbon-coated iron-cobalt-chromium nanoparticles in this embodiment is 144 emu / g, and its coercivity is 29 Oe.

[0064] The carbon-coated iron-cobalt-chromium nanoparticles obtained in this embodiment have almost no reflection loss.

[0065] Example 6 In this embodiment, carbon-coated iron-cobalt-chromium nanoparticles with high saturation magnetization and low coercivity are prepared using the same method as in Example 1, except that the pyrolysis temperature in step (4) is changed to 950 °C.

[0066] The carbon-coated iron-cobalt-chromium nanoparticles with high saturation magnetization and low coercivity obtained in this example were subjected to hysteresis loop testing using the same method as in Example 1. Figure 14 As shown, at room temperature, the saturation magnetization of the carbon-coated iron-cobalt-chromium nanoparticles in this embodiment is 154 emu / g, and its coercivity is 23 Oe.

[0067] Example 7 In this embodiment, carbon-coated iron-cobalt-chromium nanoparticles with high saturation magnetization and low coercivity were prepared using the same method as in Example 1. The only difference was that the amount of chromium chloride used in step (1) was changed to 0.8 g (2.99 mmol).

[0068] The carbon-coated iron-cobalt-chromium nanoparticles with high saturation magnetization and low coercivity obtained in this example were subjected to hysteresis loop testing and microwave absorption performance testing, using the same method as in Example 1. Figure 15 As shown, at room temperature, the saturation magnetization of the carbon-coated iron-cobalt-chromium nanoparticles in this embodiment is 119 emu / g, and its coercivity is 27 Oe.

[0069] The RL diagram of the carbon-coated iron-cobalt-chromium nanoparticles obtained in this embodiment is shown below. Figure 8 As shown, the product has a relatively low reflection loss intensity and almost no wave absorption performance.

[0070] Example 8 In this embodiment, carbon-coated iron-cobalt-chromium nanoparticles with high saturation magnetization and low coercivity are prepared using the same method as in Example 1, except that the pyrolysis temperature in step (4) is changed to 800 °C.

[0071] The carbon-coated iron-cobalt-chromium nanoparticles with high saturation magnetization and low coercivity obtained in this example were subjected to hysteresis loop testing using the same method as in Example 1. Figure 16 As shown, at room temperature, the saturation magnetization of the carbon-coated iron-cobalt-chromium nanoparticles in this embodiment is 145 emu / g, and its coercivity is 36 Oe.

[0072] Example 9 In this embodiment, carbon-coated iron-cobalt-chromium nanoparticles with high saturation magnetization and low coercivity are prepared using the same method as in Example 1, except that the pyrolysis temperature in step (4) is changed to 1000 ℃.

[0073] The carbon-coated iron-cobalt-chromium nanoparticles with high saturation magnetization and low coercivity obtained in this example were subjected to hysteresis loop testing using the same method as in Example 1. Figure 17 As shown, at room temperature, the saturation magnetization of the carbon-coated iron-cobalt-chromium nanoparticles in this embodiment is 115 emu / g, and its coercivity is 51 Oe.

[0074] Comparative Example 1 This comparative example prepared carbon-coated iron-cobalt nanoparticles using the same method as in Example 1, except that the amount of chromium chloride in the raw materials in step (1) was changed to 0 g (0 mmol).

[0075] The carbon-coated iron-cobalt nanoparticles obtained in this comparative example were subjected to hysteresis loop and microwave absorption performance tests using the same method as in Example 1. Figure 18 As shown, at room temperature, the saturation magnetization of the carbon-coated iron-cobalt nanoparticles in this comparative example is 171 emu / g, and its coercivity is 127 Oe.

[0076] The carbon-coated iron-cobalt nanoparticles obtained in this comparative example have almost no reflection loss.

[0077] Tafel graphs of the products obtained in Example 1 and Comparative Example 1 in 5% wt NaCl solution are shown below. Figure 5 As shown, the self-corrosion current density of Example 1 (0.7 × 10⁻⁶) is... -5 A / cm 2 Both the self-corrosion potential (-0.31 V) and the self-corrosion current density (4.1 × 10⁻⁶ V) of the product in Comparative Example 1 are lower than those of the product in Comparative Example 1. -5 A / cm 2 The self-corrosion potential (-0.56 V) is low. In contrast, the self-corrosion current density in Example 3 is 15.2 × 10⁻⁶ V. -5 A / cm 2 The self-corrosion potential is -0.4 V; the self-corrosion current density in Example 5 is 18.2 × 10⁻⁶ V. -5 A / cm 2 The self-corrosion potential is -0.46 V, and the self-corrosion current density in Example 4 is 7.1 × 10⁻⁶ V. -5 A / cm 2 The self-corrosion potential was -0.35 V, which was higher than that of Example 1, indicating that adding an appropriate amount of chromium can effectively enhance the corrosion resistance of the material.

[0078] Comparative Example 2 This comparative example prepared carbon-coated iron-cobalt-vanadium nanoparticles using the same method as in Example 1, except that the raw material chromium chloride in step (1) was replaced with an equimolar amount of vanadium chloride.

[0079] The carbon-coated iron-cobalt-vanadium nanoparticles obtained in this comparative example were subjected to hysteresis loop testing using the same method as in Example 1. Figure 19 As shown, at room temperature, the saturation magnetization of the carbon-coated iron-cobalt-vanadium nanoparticles in this comparative example is 130 emu / g, and its coercivity is 71 Oe.

[0080] Comparative Example 3 This comparative example prepared carbon-coated iron-cobalt-manganese nanoparticles using the same method as in Example 1, except that the raw material chromium chloride in step (1) was replaced with an equimolar amount of manganese chloride.

[0081] The carbon-coated iron-cobalt-manganese nanoparticles obtained in this comparative example were subjected to hysteresis loop testing using the same method as in Example 1. Figure 20 As shown, at room temperature, the saturation magnetization of the carbon-coated iron-cobalt-manganese nanoparticles in this comparative example is 77 emu / g, and its coercivity is 98 Oe.

[0082] The preparation method of this invention includes mixing ferric nitrate and / or ferrous nitrate, cobalt salt, chromium salt, 2-methylimidazole with a solvent, stirring, and then evaporating to obtain an iron-cobalt-chromium trimetallic complex precursor; the molar ratio of ferric nitrate and / or ferrous nitrate to cobalt salt is 1-3:1-3; the molar ratio of ferric nitrate and / or ferrous nitrate to chromium salt is 1:0.07-0.4; the molar ratio of ferric nitrate and / or ferrous nitrate to 2-methylimidazole is 1:1-3; and the iron-cobalt-chromium trimetallic complex precursor is pyrolyzed under an inert gas at 800-1000℃ to obtain carbon-coated iron-cobalt-chromium nanoparticles with high saturation magnetization and low coercivity. This invention features mild conditions, a simple process, and is easy to mass-produce. The graphitized carbon layer of the material can isolate oxygen and corrosive media, maintaining the high M of the iron-cobalt-chromium core. s The electronic coupling between the carbon shell and the iron-cobalt-chromium interface can reduce lattice distortion, suppress magnetic domain wall pinning, and reduce coercivity.

[0083] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing carbon-coated iron-cobalt-chromium nanoparticles, characterized in that: Includes the following steps: S1. Iron compound, cobalt salt, chromium salt, 2-methylimidazole and solvent are mixed, stirred and reacted, and then evaporated to dryness using a rotary evaporator to obtain the iron-cobalt-chromium trimetallic complex precursor; the iron compound is one or a mixture of two of ferric nitrate and ferrous nitrate. S2. The carbon-coated iron-cobalt-chromium nanoparticles are obtained by pyrolyzing the iron-cobalt-chromium trimetallic complex precursor under inert gas protection.

2. The method for preparing carbon-coated iron-cobalt-chromium nanoparticles according to claim 1, characterized in that: In S1, the molar ratio of the iron compound to the cobalt salt is 1-3 : 1-3.

3. The method for preparing carbon-coated iron-cobalt-chromium nanoparticles according to claim 1, characterized in that: In S1, the molar ratio of the iron compound to the chromium salt is 1:0.07-0.

4.

4. The method for preparing carbon-coated iron-cobalt-chromium nanoparticles according to claim 1, characterized in that: In S1, the molar ratio of the iron compound and 2-methylimidazole is 1:1-3.

5. The method for preparing carbon-coated iron-cobalt-chromium nanoparticles according to claim 1, characterized in that: In S1, the ratio of the iron compound to the solvent is 0.5-1 mmol: 20 mL.

6. The method for preparing carbon-coated iron-cobalt-chromium nanoparticles according to claim 1, characterized in that: In S1, the iron compound is ferric nitrate; the cobalt salt is cobalt nitrate; the chromium salt is one or a mixture of two of chromium chloride and chromium nitrate; and the solvent is methanol.

7. The method for preparing carbon-coated iron-cobalt-chromium nanoparticles according to any one of claims 1-6, characterized in that: In S2, the pyrolysis temperature is 800~1000℃ and the time is 1-3 h.

8. A carbon-coated iron-cobalt-chromium nanoparticle, characterized in that: It is prepared by the method for preparing carbon-coated iron-cobalt-chromium nanoparticles as described in any one of claims 1-7.

9. The carbon-coated iron-cobalt-chromium nanoparticles according to claim 8, characterized in that: Its saturation magnetization is 115~182 emu / g, and its coercivity is 20~51 Oe.

10. The application of carbon-coated iron-cobalt-chromium nanoparticles as described in claim 8 or 9 in soft magnetic devices and / or microwave absorbing materials.

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