A method for preparing NdFeB magnetic powder by chemical method

Abstract

The invention discloses a method for preparing NdFeB magnetic powder by a chemical method, the method comprising the following steps: step 1, mixing iron salt, organic ligand and solvent for coordination reaction to obtain an iron-based metal organic framework material; step 2, impregnating the iron-based metal organic framework material in a rare earth molten salt mixed solution, and obtaining an impregnation precursor after drying; step 3, calcining and reducing the impregnation precursor to obtain a rare earth iron precursor; step 4, mixing the rare earth iron precursor with a reducing agent for reduction diffusion reaction. The method of the present invention obtains a highly uniform and dispersed impregnation precursor by using an iron-based metal organic framework material as an iron source and a template, and obtains a refined, spherical NdFeB magnetic powder by calcination, hydrogen reduction and reduction diffusion reaction. The magnetic powder composition is controllable, and is suitable for preparing a NdFeB magnet with excellent magnetic properties and adjusting the composition and grain boundary distribution of the NdFeB magnet.

Description

Technical Field

[0001] The invention belongs to the technical field of metal magnetic material preparation, and in particular relates to a method for preparing NdFeB magnetic powder by a chemical method. Background Art

[0002] With the rapid development of aerospace, wind power generation, servo motors, new energy vehicles and other fields, rare earth permanent magnets represented by neodymium iron boron magnets with high remanence, high magnetic energy product, high coercive force and other properties have become important supporting materials in the field of contemporary new technologies.

[0003] NdFeB magnetic powder is an intermetallic compound composed of rare earth element Nd and transition metal Fe. It is the technical core and material basis for preparing high-performance NdFeB permanent magnets. Powder metallurgy is a traditional technology for preparing NdFeB magnetic powder. It usually uses high-purity metal neodymium as raw material and adds excessive amounts to compensate for evaporation losses. It has high costs and large rare earth losses. After a series of steps such as high-temperature homogenization, smelting, casting, ball milling, and annealing, it consumes a lot of energy, has a long cycle, and has a complex process. Especially after ball milling, the magnetic powder particles have a complex morphology, different sizes, and many surface defects. Limited by existing processes and technologies, it is difficult to prepare ideal magnetic powder with regular morphology, small size, uniform particle size distribution, and few surface defects, which affects the magnetic properties of permanent magnets. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the above-mentioned prior art and provide a method for preparing NdFeB magnetic powder by chemical method. The method uses an iron-based metal organic framework material as an iron source and a template and immerses it in a rare earth-molten salt mixed solution, so that rare earth elements, boron elements and molten salt are impregnated into the iron-based metal organic framework material in the form of ions, thereby obtaining a highly uniform and dispersed impregnation precursor, and obtaining NdFeB magnetic powder by calcination, reduction reaction under hydrogen atmosphere and reduction diffusion reaction, thereby solving the problem that it is difficult to prepare NdFeB magnetic powder with regular morphology, small size and uniform particle size distribution in the prior art.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing NdFeB magnetic powder by chemical method, characterized in that the method comprises the following steps:

[0006] Step 1: uniformly mixing an iron salt, an organic ligand and a solvent to carry out a coordination reaction to obtain an iron-based metal organic framework material;

[0007] Step 2: Immersing the iron-based metal organic framework material obtained in step 1 in a rare earth-molten salt mixed solution, and obtaining an impregnation precursor after drying;

[0008] Step 3: calcining the impregnation precursor obtained in step 2 in an air environment and reducing it in a hydrogen atmosphere to obtain a rare earth-iron precursor;

[0009] Step 4: Mix the rare earth-iron precursor obtained in step 3 with a reducing agent and perform a reduction diffusion reaction to obtain NdFeB magnetic powder.

[0010] The above-mentioned method for preparing NdFeB magnetic powder by a chemical method is characterized in that the process of the coordination reaction in step one is: the coordination reaction is carried out at 85°C~170°C for 15h~24h, and after the coordination reaction is completed, centrifugation, deionized water washing and drying are carried out in sequence.

[0011] The above-mentioned method for preparing NdFeB magnetic powder by a chemical method is characterized in that the iron salt is one of ferric chloride, ferric chloride hydrate, ferric nitrate and ferric nitrate hydrate, the organic ligand is one of terephthalic acid, trimesic acid and fumaric acid, the solvent is one or more of water, N,N-dimethylformamide and ethanol, and the molar ratio of the iron salt, organic ligand and solvent is 1:1~1.5:65~260.

[0012] The above-mentioned method for preparing NdFeB magnetic powder by a chemical method is characterized in that, after immersing in a rare earth-molten salt mixed solution in step 2, stirring and ultrasonic treatment are performed.

[0013] The invention adopts stirring combined with ultrasonic treatment to uniformly mix the rare earth-molten salt mixed solution with the iron-based metal organic framework material.

[0014] The above-mentioned method for preparing NdFeB magnetic powder by a chemical method is characterized in that the rare earth-molten salt mixed solution in step 2 is composed of a water-soluble neodymium salt, a molten salt, boric acid and water, the mass of the water-soluble neodymium salt accounts for 7% to 20% of the total mass of the rare earth-molten salt mixed solution, the water-soluble neodymium salt is one of neodymium chloride, neodymium chloride hydrate, neodymium nitrate, and neodymium nitrate hydrate, and the molten salt is one or more of potassium chloride, sodium chloride and calcium chloride.

[0015] The above-mentioned method for preparing NdFeB magnetic powder by a chemical method is characterized in that the molar ratio of the water-soluble neodymium salt to the reducing agent in step four is 1:2~4, the mass ratio of the molten salt to the reducing agent in step four is 1:5~10, and the molar ratio of the iron element in the iron salt, the neodymium element in the water-soluble neodymium salt, and the boron element in the boric acid is 14:2.1~5.2:1.01~1.05.

[0016] The invention controls the ratio of water-soluble neodymium salt, molten salt and reducing agent, thereby preventing the neodymium element concentration from being too low to reduce the neodymium element immersion efficiency and increase the drying burden, and preventing the neodymium element concentration from being too high to increase the acidity of the mixed solution, which is not conducive to the stable adsorption of iron-based metal organic framework materials; at the same time, it can avoid that the molten salt dosage is too high to dilute the reducing agent concentration, and the molten salt dosage is too low to achieve the effect of providing a liquid dispersion environment; by controlling the molar ratio of iron element, neodymium element and boron element, the composition of the obtained neodymium iron boron magnetic powder is controlled to be Nd 2~5 Fe 14 B. By adjusting the molar ratio of neodymium and boron, the dosage of neodymium and boron is slightly increased to compensate for the evaporation loss of neodymium and boron during the high-temperature reaction.

[0017] The above-mentioned method for preparing NdFeB magnetic powder by a chemical method is characterized in that the calcination system in the air environment in step three is: heating to 500°C~600°C at a rate of 1°C / min~3°C / min and keeping warm for 2h~4h, and the reduction reaction system in the hydrogen atmosphere is: heating to 800°C~900°C at a rate of 2°C / min~5°C / min, keeping warm for 1.5h~3h and then cooling.

[0018] The present invention controls the temperature and the holding time of the calcination process to avoid the collapse of the original structure of the iron-based metal organic framework material and the agglomeration of iron oxide nanoparticles due to the calcination temperature being too high and the holding time being too long, and avoids the residual impurity elements due to the calcination temperature being too low and the holding time being too short, which cannot ensure the complete escape of carbon and the sufficient pyrolysis of the rare earth salt; and controls the temperature and the reaction time during the reduction reaction under the hydrogen atmosphere to avoid the collapse of the original structure of the iron-based metal organic framework material and the growth and sintering of the iron nanoparticles due to the reduction temperature being too high and the holding time being too long, and avoids the insufficient reduction of the iron element due to the reduction temperature being too low and the holding time being too short, and avoids the too low temperature being unfavorable for the molten salt to melt into a liquid form in the rare earth-iron precursor for diffusion and distribution.

[0019] The above-mentioned method for preparing NdFeB magnetic powder by a chemical method is characterized in that the reducing agent in step 4 is Ca and / or CaH2, the temperature of the reduction diffusion reaction is 950°C~1050°C, and the time of the reduction diffusion reaction is 3h~6h.

[0020] The present invention controls the reduction diffusion reaction temperature and time to promote the reduction diffusion reaction, avoid excessive temperature and time leading to growth of NdFeB magnetic powder particles, sintering and excessive volatilization of rare earth elements, and avoid insufficient reduction diffusion reaction due to low temperature and short time.

[0021] The above-mentioned method for preparing NdFeB magnetic powder by chemical method is characterized in that the NdFeB magnetic powder in step 4 is a spherical powder with a particle size of 1 μm to 4 μm, and the composition of the NdFeB magnetic powder is Nd 2~5 Fe 14 B.

[0022] The above-mentioned method for preparing NdFeB magnetic powder by a chemical method is characterized in that after the reduction diffusion reaction in step 4 is completed, washing with a dilute acetic acid aqueous solution, magnetic separation, washing with anhydrous ethanol and drying are carried out.

[0023] The invention removes byproducts and molten salt in the NdFeB magnetic powder by washing with a dilute acetic acid aqueous solution, magnetic separation, anhydrous ethanol washing and drying.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] 1. The present invention uses an iron-based metal organic framework material as an iron source and template. During the preparation process, the iron-based metal organic framework template always maintains its original state of uniform size and regular distribution, which is beneficial to controlling the particle size and morphology of the magnetic powder. Through calcination, reduction reaction in a hydrogen atmosphere, and reduction diffusion reaction, NdFeB magnetic powder with regular morphology, small size, and uniform particle size distribution can be obtained. Compared with the sol-gel method and the co-precipitation method, the preparation method is simpler and easier to control.

[0026] 2. The present invention adopts a rare earth-molten salt mixed solution to impregnate the iron-based metal organic framework template, so that the rare earth elements and the molten salt are uniformly adsorbed in the iron-based metal organic framework template, and there is no loss of rare earth elements and molten salt during the impregnation process, thereby improving the utilization rate of rare earth elements and ensuring the uniform dispersion and accurate dosage control of rare earth elements and molten salt; through the high temperature condition during hydrogen reduction, the molten salt is melted and diffused and distributed in the rare earth-iron precursor in liquid form to form a uniform molten salt environment, which can promote the reduction diffusion reaction and reduce the amount of reducing agent, avoiding excessive amount of reducing agent to increase the difficulty of crushing and washing of NdFeB magnetic powder, and effectively improving the purity of the product.

[0027] 3. The present invention prepares NdFeB magnetic powders of different chemical compositions by adjusting the ratio of iron, neodymium and boron elements, which are used to prepare NdFeB magnets and adjust the composition of sintered NdFeB magnets. The iron boron magnetic powders prepared by the present invention are small in size and regular in morphology, and can fill the gaps in the sintered NdFeB magnets and promote the uniform distribution of the grain boundaries of the NdFeB magnets, thereby improving the magnetic properties of the NdFeB magnets.

[0028] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a preparation flow chart of the present invention.

[0030] Figure 2 This is a microstructure diagram of the NdFeB magnetic powder obtained in Example 1 of the present invention.

[0031] Figure 3 This is a microstructure diagram of the NdFeB magnetic powder obtained in Example 2 of the present invention.

[0032] Figure 4 1 is the XRD diagram of the NdFeB magnetic powder obtained in Example 1 and Example 2 of the present invention.

[0033] Figure 5 This is a microstructure diagram of the NdFeB magnetic powder obtained in Example 7 of the present invention. DETAILED DESCRIPTION

[0034] Example 1

[0035] like Figure 1 As shown, the method of this embodiment includes the following steps:

[0036] Step 1, FeCl3·6H2O, terephthalic acid and N,N-dimethylformamide are uniformly mixed in a molar ratio of 1:1:260, and coordination reaction is carried out at 170°C for 15 hours, followed by centrifugation, deionized water washing and drying at 60°C to obtain an iron-based metal organic framework material;

[0037] Step 2: Immerse the iron-based metal organic framework material obtained in step 1 in a rare earth-molten salt mixed solution, stir and ultrasonically treat for 6 hours, and dry at 60°C to obtain an impregnation precursor; the rare earth-molten salt mixed solution is composed of Nd(NO3)3·6H2O, H3BO3, KCl and deionized water, the Nd(NO3)3·6H2O accounts for 7% of the total mass of the rare earth-molten salt mixed solution, and the molar ratio of iron element in FeCl3·6H2O, neodymium element in Nd(NO3)3·6H2O, and boron element in boric acid is 14:2.2:1.03;

[0038] Step 3, heating the impregnation precursor obtained in step 2 to 500°C at a rate of 2°C / min in an air environment and keeping it warm for 3 hours, then heating it to 850°C at a rate of 3°C / min in a hydrogen atmosphere and keeping it warm for 2.5 hours, and then cooling it to obtain a rare earth-iron precursor;

[0039] Step 4: After mixing the rare earth-iron precursor obtained in step 3 with CaH2, argon gas is introduced at a flow rate of 0.1L / min, and then the temperature is raised to 1050°C at a rate of 3°C / min for reduction diffusion reaction for 3h. After cooling, ultrasonic washing and magnetic separation are carried out using a dilute acetic acid aqueous solution with a pH of 5 as a medium until the pH of the washing water reaches 7, and then the mixture is washed 3 times with anhydrous ethanol and dried in a vacuum oven at 50°C to obtain NdFeB magnetic powder; the molar ratio of Nd(NO3)3·6H2O to CaH2 is 1:3.5, and the mass ratio of KCl to CaH2 is 1:10.

[0040] In this embodiment, FeCl3·6H2O can also be replaced by one of ferric chloride, ferric nitrate and ferric nitrate hydrate other than FeCl3·6H2O, Nd(NO3)3·6H2O can also be replaced by one of neodymium chloride, neodymium chloride hydrate and neodymium nitrate other than Nd(NO3)3·6H2O, and KCl can also be replaced by sodium chloride and / or calcium chloride other than KCl.

[0041] The microstructure of the NdFeB magnetic powder obtained in this example was analyzed by scanning electron microscopy. Figure 2 As shown, NdFeB magnetic powder is spherical particles with a particle size of 1μm~4μm and has good dispersibility and uniformity.

[0042] Example 2

[0043] The method of this embodiment includes the following steps:

[0044] Step 1, FeCl3·6H2O, terephthalic acid and N,N-dimethylformamide are uniformly mixed in a molar ratio of 1:1:260, and coordination reaction is carried out at 110°C for 24 hours, followed by centrifugation, deionized water washing and drying at 80°C to obtain an iron-based metal organic framework material;

[0045] Step 2: Immerse the iron-based metal organic framework material obtained in step 1 in a rare earth-molten salt mixed solution, stir and ultrasonically treat for 6 hours, and dry at 60°C to obtain an impregnation precursor; the rare earth-molten salt mixed solution is composed of Nd(NO3)3·6H2O, H3BO3, CaCl2 and deionized water, the Nd(NO3)3·6H2O accounts for 7% of the total mass of the rare earth-molten salt mixed solution, and the molar ratio of iron element in FeCl3·6H2O, neodymium element in Nd(NO3)3·6H2O, and boron element in boric acid is 14:2.1:1.03;

[0046] Step 3, heating the impregnation precursor obtained in step 2 to 500°C at a rate of 2°C / min in an air environment and keeping it warm for 3 hours, then heating it to 850°C at a rate of 3°C / min in a hydrogen atmosphere and keeping it warm for 1.5 hours, and then cooling it to obtain a rare earth-iron precursor;

[0047] Step 4: After mixing the rare earth-iron precursor obtained in step 3 with CaH2, argon gas is introduced at a flow rate of 0.1L / min, and then the temperature is raised to 1050°C at a rate of 3°C / min for reduction diffusion reaction for 4h. After cooling, ultrasonic washing and magnetic separation are carried out using a dilute acetic acid aqueous solution with a pH of 6 as a medium until the pH of the washing water reaches 7, and then the mixture is washed 3 times with anhydrous ethanol and dried in a vacuum oven at 60°C to obtain NdFeB magnetic powder; the molar ratio of Nd(NO3)3·6H2O to CaH2 is 1:2, and the mass ratio of KCl to CaH2 is 1:6.67.

[0048] The microstructure of the NdFeB magnetic powder obtained in this example was analyzed by scanning electron microscopy. Figure 3 As shown in FIG. 1 , the NdFeB magnetic powder is a spherical particle with a particle size of 1 μm to 4 μm and good dispersibility and uniformity. XRD analysis was performed on the NdFeB magnetic powders obtained in this embodiment and in Example 1, respectively. Figure 4 As shown, the chemical composition of the NdFeB magnetic powder obtained in this embodiment and in Example 1 is Nd2Fe 14 B.

[0049] Example 3

[0050] The method of this embodiment includes the following steps:

[0051] Step 1, Fe(NO3)3·6H2O, trimesic acid and deionized water are uniformly mixed in a molar ratio of 1:1.5:83, and coordination reaction is carried out at 160°C for 15 hours, followed by centrifugation, deionized water washing and drying at 80°C to obtain an iron-based metal organic framework material;

[0052] Step 2: Immerse the iron-based metal organic framework material obtained in step 1 in a rare earth-molten salt mixed solution, stir and ultrasonically treat for 6 hours, and dry at 100°C to obtain an impregnation precursor; the rare earth-molten salt mixed solution is composed of Nd(NO3)3·6H2O, H3BO3, NaCl and deionized water, the Nd(NO3)3·6H2O accounts for 10% of the total mass of the rare earth-molten salt mixed solution, and the molar ratio of the iron element in Fe(NO3)3·6H2O, the neodymium element in Nd(NO3)3·6H2O, and the boron element in boric acid is 14:2.3:1.01;

[0053] Step 3, heating the impregnation precursor obtained in step 2 to 600° C. at a rate of 1° C. / min in an air environment and keeping it warm for 2 h, then heating it to 800° C. at a rate of 2° C. / min in a hydrogen atmosphere and keeping it warm for 3 h, and then cooling it to obtain a rare earth-iron precursor;

[0054] Step 4: After mixing the rare earth-iron precursor obtained in step 3 with CaH2, argon gas is introduced at a flow rate of 0.1L / min, and then the temperature is raised to 950°C at a rate of 3°C / min for reduction diffusion reaction for 6h. After cooling, ultrasonic washing and magnetic separation are carried out using a dilute acetic acid aqueous solution with a pH of 6 as a medium until the pH of the washing water reaches 7, and then the mixture is washed 3 times with anhydrous ethanol and dried in a vacuum oven at 70°C to obtain NdFeB magnetic powder; the molar ratio of Nd(NO3)3·6H2O to CaH2 is 1:4, and the mass ratio of KCl to CaH2 is 1:6.25.

[0055] In this embodiment, the deionized water may also be replaced by N,N-dimethylformamide and / or ethanol other than deionized water.

[0056] After inspection, the NdFeB magnetic powder obtained in this embodiment is a spherical particle with a particle size of 1 μm to 4 μm, and the chemical composition is Nd2Fe 14 B.

[0057] Example 4

[0058] The difference between this embodiment and embodiment 3 is that the temperature of the reduction diffusion reaction in step 4 is 1000° C., and the reducing agents are Ca and CaH 2 .

[0059] After inspection, the NdFeB magnetic powder obtained in this embodiment is a spherical particle with a particle size of 1 μm to 4 μm, and the chemical composition is Nd2Fe 14 B.

[0060] Example 5

[0061] The method of this embodiment includes the following steps:

[0062] Step 1, FeCl3·6H2O, fumaric acid and N,N-dimethylformamide are uniformly mixed in a molar ratio of 1:1:65, and coordination reaction is carried out at 85°C for 24 hours, followed by centrifugation, deionized water washing and drying at 80°C to obtain an iron-based metal organic framework material;

[0063] Step 2: Immerse the iron-based metal organic framework material obtained in step 1 in a rare earth-molten salt mixed solution, stir and ultrasonically treat for 6 hours, and dry at 80°C to obtain an impregnation precursor; the rare earth-molten salt mixed solution is composed of Nd(NO3)3·6H2O, H3BO3, KCl and deionized water, the Nd(NO3)3·6H2O accounts for 8% of the total mass of the rare earth-molten salt mixed solution, and the molar ratio of the iron element in the FeCl3·6H2O, the neodymium element in the Nd(NO3)3·6H2O, and the boron element in the boric acid is 14:2.2:1.05;

[0064] Step 3, heating the impregnation precursor obtained in step 2 to 550°C at a rate of 3°C / min in an air environment for 4 hours, and then heating to 900°C at a rate of 5°C / min in a hydrogen atmosphere for 2 hours and then cooling to obtain a rare earth-iron precursor;

[0065] Step 4: After mixing the rare earth-iron precursor obtained in step 3 with Ca, argon gas is introduced at a flow rate of 0.1L / min, and then the temperature is raised to 1050°C at a rate of 3°C / min for reduction diffusion reaction for 3h. After cooling, ultrasonic washing and magnetic separation are performed using a dilute acetic acid aqueous solution with a pH of 6 as a medium until the pH of the washing water reaches 7, and then the mixture is washed 4 times with anhydrous ethanol and dried in a vacuum oven at 50°C to obtain NdFeB magnetic powder; the molar ratio of Nd(NO3)3·6H2O to Ca is 1:3, and the mass ratio of KCl to Ca is 1:5.

[0066] After inspection, the NdFeB magnetic powder obtained in this embodiment is a spherical particle with a particle size of 1 μm to 4 μm, and the chemical composition is Nd2Fe 14 B.

[0067] Example 6

[0068] The method of this embodiment includes the following steps:

[0069] Step 1, FeCl3·6H2O, terephthalic acid and N,N-dimethylformamide are uniformly mixed in a molar ratio of 1:1:260, and coordination reaction is carried out at 170°C for 15 hours, and then centrifuged, washed with deionized water and dried at 60°C to obtain an iron-based metal organic framework material;

[0070] Step 2: Immerse the iron-based metal organic framework material obtained in step 1 in a rare earth-molten salt mixed solution, stir and ultrasonically treat for 6 hours, and dry at 60°C to obtain an impregnation precursor; the rare earth-molten salt mixed solution is composed of Nd(NO3)3·6H2O, H3BO3, KCl and deionized water, the Nd(NO3)3·6H2O accounts for 12% of the total mass of the rare earth-molten salt mixed solution, and the molar ratio of the iron element in the FeCl3·6H2O, the neodymium element in the Nd(NO3)3·6H2O, and the boron element in the boric acid is 14:3.2:1.03;

[0071] Step 3, heating the impregnation precursor obtained in step 2 to 500°C at a rate of 2°C / min in an air environment and keeping it warm for 3 hours, then heating it to 850°C at a rate of 3°C / min in a hydrogen atmosphere and keeping it warm for 2.5 hours, and then cooling it to obtain a rare earth-iron precursor;

[0072] Step 4: After mixing the rare earth-iron precursor obtained in step 3 with CaH2, argon gas is introduced at a flow rate of 0.1L / min, and then the temperature is raised to 1050°C at a rate of 3°C / min for reduction diffusion reaction for 3h. After cooling, ultrasonic washing and magnetic separation are carried out using a dilute acetic acid aqueous solution with a pH of 5 as a medium until the pH of the washing water reaches 7, and then the mixture is washed 4 times with anhydrous ethanol and dried in a vacuum oven at 50°C to obtain NdFeB magnetic powder; the molar ratio of Nd(NO3)3·6H2O to CaH2 is 1:3.5, and the mass ratio of KCl to CaH2 is 1:10.

[0073] After inspection, the NdFeB magnetic powder obtained in this embodiment is a spherical particle with a particle size of 1 μm to 4 μm, and the chemical composition is Nd3Fe 14 B.

[0074] Example 7

[0075] The method of this embodiment includes the following steps:

[0076] Step 1, FeCl3·6H2O, terephthalic acid and N,N-dimethylformamide are uniformly mixed in a molar ratio of 1:1:260, and coordination reaction is carried out at 170°C for 15 hours, and then centrifuged, washed with deionized water and dried at 60°C to obtain an iron-based metal organic framework material;

[0077] Step 2: Immerse the iron-based metal organic framework material obtained in step 1 in a rare earth-molten salt mixed solution, stir and ultrasonically treat for 6 hours, and dry at 60°C to obtain an impregnation precursor; the rare earth-molten salt mixed solution is composed of Nd(NO3)3·6H2O, H3BO3, KCl and deionized water, the Nd(NO3)3·6H2O accounts for 20% of the total mass of the rare earth-molten salt mixed solution, and the molar ratio of the iron element in the FeCl3·6H2O, the neodymium element in the Nd(NO3)3·6H2O, and the boron element in the boric acid is 14:5.2:1.03;

[0078] Step 3, heating the impregnation precursor obtained in step 2 to 500°C at a rate of 2°C / min in an air environment and keeping it warm for 3 hours, then heating it to 850°C at a rate of 3°C / min in a hydrogen atmosphere and keeping it warm for 2.5 hours, and then cooling it to obtain a rare earth-iron precursor;

[0079] Step 4: After mixing the rare earth-iron precursor obtained in step 3 with CaH2, argon gas is introduced at a flow rate of 0.1L / min, and then the temperature is raised to 1050°C at a rate of 3°C / min for reduction diffusion reaction for 3h. After cooling, ultrasonic washing and magnetic separation are carried out using a dilute acetic acid aqueous solution with a pH of 5 as a medium until the pH of the washing water reaches 7, and then the mixture is washed 3 times with anhydrous ethanol and dried in a vacuum oven at 50°C to obtain NdFeB magnetic powder; the molar ratio of Nd(NO3)3·6H2O to CaH2 is 1:3.5, and the mass ratio of KCl to CaH2 is 1:10.

[0080] The microstructure of the NdFeB magnetic powder obtained in this example was analyzed by scanning electron microscopy. Figure 5 As shown in Figure 2, NdFeB magnetic powder is a spherical particle with a particle size of 1μm~4μm, and has good dispersion and uniformity. Figure 2 and Figure 3 In comparison, since the chemical composition of the NdFeB magnetic powder obtained in this embodiment is Nd5Fe 14 B, the neodymium phase content is higher, and the surface roughness is greater than the magnetic powder obtained in Example 1 and Example 2.

[0081] The NdFeB magnetic powders obtained in Example 1, Example 6 and Example 7 were subjected to inductively coupled plasma spectroscopy analysis. The results are shown in Table 1.

[0082] Table 1 Composition of NdFeB magnetic powders of Example 1, Example 6 and Example 7

[0083]

[0084] As shown in Table 1, the chemical composition of the NdFeB magnetic powder obtained in Example 1 is Nd2Fe 14B. The chemical composition of the NdFeB magnetic powder obtained in Example 6 is Nd3Fe 14 B. The chemical composition of the NdFeB magnetic powder obtained in Example 7 is Nd5Fe 14 B, indicating that the preparation method of the present invention can achieve controlled preparation of NdFeB magnetic powders with different element contents by adjusting the molar ratio of iron, neodymium and boron during the preparation process.

[0085] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural transformation made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing NdFeB magnetic powder by chemical method, characterized in that: The method comprises the following steps: Step 1, uniformly mixing an iron salt, an organic ligand and a solvent and carrying out coordination reaction at 85°C to 170°C for 15h to 24h to obtain an iron-based metal organic framework material; the organic ligand is one of terephthalic acid, trimesic acid and fumaric acid, and the solvent is one or more of water, N,N-dimethylformamide and ethanol; Step 2: Immersing the iron-based metal organic framework material obtained in step 1 in a rare earth-molten salt mixed solution, and obtaining an impregnation precursor after drying; the rare earth-molten salt mixed solution is composed of a water-soluble neodymium salt, a molten salt, boric acid and water, and the molten salt is one or more of potassium chloride, sodium chloride and calcium chloride; Step 3, the impregnation precursor obtained in step 2 is calcined in air and reduced in hydrogen atmosphere to obtain a rare earth-iron precursor; the calcination in air is as follows: heating to 500°C~600°C at a rate of 1°C / min~3°C / min and keeping warm for 2h~4h, and the reduction reaction in hydrogen atmosphere is as follows: heating to 800°C~900°C at a rate of 2°C / min~5°C / min and keeping warm for 1.5h~3h and then cooling; Step 4: Mix the rare earth-iron precursor obtained in step 3 with a reducing agent and perform a reduction diffusion reaction to obtain NdFeB magnetic powder; the reducing agent is Ca and / or CaH2, and the temperature of the reduction diffusion reaction is 950°C~1050°C.

2. The method for preparing NdFeB magnetic powder by chemical method according to claim 1, characterized in that: After the coordination reaction in step 1 is completed, centrifugation, deionized water washing and drying are performed in sequence.

3. The method for preparing NdFeB magnetic powder by chemical method according to claim 1, characterized in that: The iron salt in step 1 is one of ferric chloride, ferric chloride hydrate, ferric nitrate and ferric nitrate hydrate, and the molar ratio of the iron salt, the organic ligand and the solvent is 1:1~1.5:65~260.

4. The method for preparing NdFeB magnetic powder by chemical method according to claim 1, characterized in that: In step 2, the mixture is immersed in the rare earth-molten salt mixed solution and then stirred and ultrasonically treated.

5. The method for preparing NdFeB magnetic powder by chemical method according to claim 1, characterized in that: The mass of the water-soluble neodymium salt in step 2 accounts for 7% to 20% of the total mass of the rare earth-molten salt mixed solution, and the water-soluble neodymium salt is one of neodymium chloride, neodymium chloride hydrate, neodymium nitrate, and neodymium nitrate hydrate.

6. The method for preparing NdFeB magnetic powder by chemical method according to claim 5, characterized in that: The molar ratio of the water-soluble neodymium salt to the reducing agent in step four is 1:2~4, the mass ratio of the molten salt to the reducing agent in step four is 1:5~10, and the molar ratio of the iron element in the iron salt, the neodymium element in the water-soluble neodymium salt, and the boron element in the boric acid is 14:2.1~5.2:1.01~1.

05.

7. The method for preparing NdFeB magnetic powder by chemical method according to claim 1, characterized in that: The time of the reduction diffusion reaction in step 4 is 3h~6h.

8. The method for preparing NdFeB magnetic powder by chemical method according to claim 1, characterized in that: The NdFeB magnetic powder in step 4 is a spherical powder with a particle size of 1 μm to 4 μm, and the composition of the NdFeB magnetic powder is Nd 2~5 Fe 14 B.

9. The method for preparing NdFeB magnetic powder by chemical method according to claim 1, characterized in that: After the reduction diffusion reaction in step 4 is completed, washing with dilute acetic acid aqueous solution, magnetic separation, anhydrous ethanol washing and drying are performed.

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