A SmFe12-based alloy of ThMn12 type and a preparation method thereof

Abstract

The application discloses a ThMn 12 type SmFe 12 based alloy and a preparation method thereof, and the composition of the ThMn 12 type SmFe 12 based alloy is Sm a Fe 12‑x‑y‑z‑r Co x Ti y Al z Mo r M, wherein a is 1-1.2, x is 0-0.2, y is 0-0.5, z is 0-0.3, and r is 0-0.2; M is N or C; the diameter of the ThMn 12 type SmFe 12 based alloy is 0.5-5 mu m. The preparation method is to firstly prepare spherical composite oxides from water-soluble metal salts by using an ultrasonic spray pyrolysis method, then to perform reduction treatment at a certain temperature, and finally to perform N\C absorption to generate a uniform and stable ThMn 12 type metal alloy compound. The alloy prepared by the application is controllable in morphology and size, high in performance, simple in preparation process, economical, short in cycle, and convenient for industrialization.

Description

Technical Field

[0001] This invention belongs to the field of metallic magnetic material preparation technology, and relates to a ThMn 12 Type SmFe 12 Basic alloys and their preparation methods. Background Technology

[0002] Heavy rare earth iron-rich ThMn 12 TypeRFe 12 Rare earth permanent magnet materials have high remanence (B) intensity. r ) and magnetic energy product (BH) max Its intrinsic properties are comparable to those of Nd2Fe. 14 Comparable to B permanent magnet materials, it exhibits excellent magnetic properties at high temperatures, making ThMn... 12 Rare earth permanent magnet materials have been widely used in electric vehicles, wind power generation, magnetic resonance imaging and sound equipment.

[0003] However, despite ThMn 12 Samarium-iron alloys possess excellent magnetic properties, but their preparation and processing still present some challenges. Due to the presence of ThMn... 12 The magnetic phase is thermodynamically metastable. To obtain a stable crystal structure, it is necessary to add some non-magnetic elements to stabilize it. Stabilizing elements generally include Ti, V, Nb, Mo, Ta, W, etc. However, the introduction of non-magnetic elements usually leads to a decrease in magnetic properties. Therefore, how to stabilize the crystal structure while ensuring the magnetic properties has always been a problem that researchers need to solve.

[0004] The second problem is that the traditional preparation method mainly involves a combination of melting, spinning, and ball milling. This method involves heating and melting the elemental metal in a vacuum furnace under an inert atmosphere, followed by rapid cooling to obtain an alloy ingot. However, this method has the following drawbacks: First, the melting point of iron is 1538℃, far higher than that of samarium (1072℃), and samarium has a low saturated vapor pressure and is highly volatile. This leads to a large amount of samarium volatilization during the melting process, and the inaccuracy in the samarium content makes it more difficult to obtain a pure phase alloy, making the process difficult to control. Second, due to the high melting temperature, the ingot is prone to problems such as compositional segregation, coarse grains, and uneven grain size distribution during the solidification process, which to some extent affects the ThMn alloy. 12 The magnetic properties of the samarium iron alloy are affected; thirdly, the ball milling process makes it difficult to control the normal distribution of particle size, and the size distribution is extremely discrete. After ball milling, nano-sized and tens of micrometer-sized powders coexist. The highly active nano magnetic powders are oxidized and heated, causing the whole batch to oxidize, which seriously reduces their coercivity.

[0005] Furthermore, processes such as high-energy ball milling and mechanical alloying consume significant amounts of energy, increasing the cost of alloy preparation. During prolonged ball milling of fine powders, oxidation to varying degrees is inevitable, reducing the magnetic properties of the magnet. For example, patent CN112103022A discloses a ThMn... 12 The preparation method of rare earth permanent magnets involves complex processes such as melting, spinning, ball milling, and hot pressing in order to improve the magnetic properties of the powder. However, the coercivity of the powder was not significantly improved, which has certain limitations. Summary of the Invention

[0006] The first objective of this invention is to address the shortcomings of existing technologies by providing a ThMn 12 Type SmFe 12 Base alloy.

[0007] A ThMn 12 Type SmFe 12 The base alloy has the composition Sm a Fe 12-x-y-z-r Co x Ti y Al z Mo r M, where a is 1 to 1.2, x is 0 to 0.2, y is 0 to 0.5, z is 0 to 0.3, and r is 0 to 0.2; M is small molecule substances such as N and C.

[0008] The second objective of this invention is to provide a method for preparing near-spherical ThMn with controllable dimensions without the need for crushing. 12 Type SmFe 12 A method for base alloys. This method optimizes the composition to improve the overall magnetic properties of the powder, has a short experimental cycle, and can effectively control the volatilization of samarium.

[0009] A ThMn 12 Type SmFe 12 The preparation method of the base alloy includes the following steps:

[0010] Step (1): Weigh the Fe, Al, Co, Ti, Mo and Sm elements according to their atomic percentage content in the alloy, mix and dissolve them in water, and stir evenly to form a spray precursor solution;

[0011] Step (2): The spray precursor solution is sprayed out in a mist and transported to a tube furnace under the action of a carrier gas. Spherical oxide precursors are prepared by spray thermal decomposition and then dried.

[0012] Step (3): The dried spherical oxide precursor is first pre-reduced in a hydrogen atmosphere, then reduced with an active metal, and finally nitrided or carburized. After cleaning and drying, the ThMn is obtained. 12 Type SmFe 12 Base alloy; the ThMn 12 Type SmFe 12 The diameter of the base alloy is 0.5-5μm.

[0013] Preferably, the ratio of Fe+Al+Co+Ti+Mo atoms to Sm atoms in step (1) is 10 to 12; within this range, the α-(Fe,Co) soft magnetic phase can be reduced most effectively.

[0014] Preferably, the stirring time in step (1) is 30-60 min.

[0015] Preferably, the carrier gas in step (2) is one or more combinations of air, nitrogen, argon, and helium, and the carrier gas flow rate is 2-20 L / min.

[0016] Preferably, the diameter of the spherical oxide precursor in step (2) is 0.5-8 μm.

[0017] Preferably, the tubular furnace in step (2) adopts a three-stage temperature control. The temperature of the first stage is 300-400℃, during which the atomized droplets undergo evaporation and dehydration. The temperature of the second stage is 800-1000℃, during which salt thermal decomposition occurs. The temperature of the third stage is 800-1000℃, during which oxidation occurs.

[0018] Preferably, the drying temperature in step (2) is 80°C and the drying time is 12-24h.

[0019] Step (3) First, pre-reduction is performed using hydrogen, and then reduction is performed using an active metal at a reduction temperature of 900-1200℃. At this time, the metal elements will generate metal alloy compounds through an adsorption-diffusion process. The Sm obtained from the reduction is adsorbed on the surface of the surrounding Fe powder particles in gaseous form, and then diffuses into the interior of the iron particles, eventually forming a uniform and stable samarium-iron-based alloy.

[0020] As a preferred option, the specific hydrogen reduction process is as follows: The oxide precursor is placed in an atmosphere furnace, and the furnace is repeatedly evacuated three times at room temperature to remove all oxygen. Then, the furnace is heated to 500-700℃, and a fluid H2 atmosphere is introduced at a flow rate of 0.3-2 L / min for reduction reaction. The reduction is carried out for 1-5 hours to obtain the pre-reduced product. The effectiveness of hydrogen reduction is related to the hydrogen flow rate and the reduction temperature. The higher the hydrogen flow rate or the higher the reduction temperature, the more thorough the reduction of the iron-based oxide. If the reduction is incomplete, the amount of metal used in the subsequent active metal reduction treatment will increase.

[0021] As a preferred choice, the active metal is one of calcium, sodium, or potassium.

[0022] As a preferred method, the active metal reduction process is as follows: the product obtained by hydrogen reduction is mixed evenly with the active metal and placed in a crucible. Then, the crucible is placed in an atmosphere furnace, and the furnace is repeatedly evacuated three times at room temperature to remove the oxygen. After that, the temperature is raised to 900-1200℃ and reduced under an argon atmosphere for 0.5-3.5 hours to obtain a samarium-iron-based alloy.

[0023] The collected samarium-iron-based alloy products were subjected to nitriding or carburizing treatment at 400-600℃ for 0.5-2 hours, with a gas flow rate controlled at 0.2-0.8 L / min. The products were then repeatedly magnetically separated and washed with deionized water and dilute acetic acid until the pH of the final supernatant reached 7. Next, they were magnetically separated and washed 3-4 times with organic alcohol to remove the washing water, and finally vacuum dried at 20-80℃ to obtain the final product. Nitriding or carburizing was performed using a gas diffusion method. Nitriding primarily used ammonia or a mixture of ammonia and argon; carburizing primarily used methane or ethane.

[0024] The ThMn described in this invention 12 Type SmFe 12 The advantages of basic alloys and their preparation methods are mainly reflected in:

[0025] (1) The present invention effectively improves the microstructure of grain boundaries by co-doping with Al and Mo, and effectively improves the magnetic properties of magnets by doping with small molecules such as N and C.

[0026] (2) This invention combines spray pyrolysis with reduction diffusion, effectively avoiding the process of rapid quenching and ball milling. It eliminates the need for ball milling and crushing processes, and can directly prepare ThMn particles with a size of 0.5-5μm and near-spherical shape. 12 Type SmFe 12 The alloy powder ensures that the samarium iron alloy grains are intact and has good flowability when combined with polymers, overcoming the problem of decreased magnetic powder coercivity caused by ball milling.

[0027] (3) In this invention, the addition of elements Ti and Mo and Co replaces the position of Fe atoms, thereby stabilizing ThMn. 12 The alloy has a typical crystal structure. The addition of Ti can refine the grains and improve the anisotropy of the alloy, but it will reduce the remanence of the alloy. Co doping can improve the saturation magnetization to some extent, but it will impair the coercivity to some extent. Therefore, a small amount of Al is added to the alloy. As a low-melting-point alloy, Al can be co-doped with other elements. At high temperatures, it has a certain solubility in the main phase and will exist in the grain boundary region, improving the microstructure of the grain boundary and thus improving the intrinsic coercivity of the magnet. To further improve the alloy performance, nitriding or carburizing is performed to further enhance its anisotropy. Attached Figure Description

[0028] Figure 1 A schematic diagram of a spray thermal decomposition device for preparing oxide precursors; in the diagram: ultrasonic atomizer 1, spray precursor solution 2, spray droplets 3, powder collector 4, and waste gas collection device 5.

[0029] Figure 2 (a) is a SEM image of the spherical oxide precursor prepared by spray pyrolysis, and (b) is the final ThMn obtained. 12 Morphology diagram of the alloy.

[0030] Figure 3 (a) The prepared ThMn 12 Type SmFe 12 XRD patterns of the base alloy, (b) is the XRD pattern of the product with only Al added, and (c) is the XRD pattern of the bio-based alloy with Al and Mo added.

[0031] Figure 4 This is a schematic diagram illustrating the experimental process and effects of the present invention. Detailed Implementation

[0032] As mentioned above, in view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention, the main basis of which includes at least the following:

[0033] (1) In this invention, in order to stabilize ThMn 12 Type SmFe 12 The base alloy contains elements such as Ti, Mo, and Co. To avoid affecting the intrinsic magnetic properties of the alloy, Al is added in this invention. As a low-melting-point alloy, Al, along with other elements such as Mo, serves as a co-doping agent. At high temperatures, Al has a certain solubility in the main phase and will be distributed in the grain boundary region, improving the microstructure of the grain boundaries and thus enhancing the intrinsic coercivity of the magnet. Furthermore, to further improve the alloy performance, nitrogen and carbon absorption treatments are performed to enhance the anisotropy of the powder alloy.

[0034] (2) This invention combines spray pyrolysis with reduction diffusion, effectively avoiding the volatilization of Sm elements during the smelting process. It eliminates the need for subsequent ball milling and crushing processes, allowing for precise control of the amount of Sm added. This enables the direct preparation of ThMn particles with a size of 0.5-5 micrometers and near-spherical shape. 12 Type SmFe 12 Alloy powder is used to ensure the integrity of samarium-iron alloy grains.

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0036] In a first aspect, the present invention provides a ThMn 12 Type SmFe 12 The base alloy, the ThMn 12 Type SmFe 12 The composition of the base alloy, expressed as an atomic percentage, is: Sm a Fe 12-x-y-z-r Co x Ti y Al z Mo r M, where a is between 1 and 1.2, x is between 0 and 0.2, y is between 0 and 0.5, z is between 0 and 0.3, and r is between 0 and 0.2; M is small molecule substances such as N and C.

[0037] Secondly, the present invention provides a ThMn 12 Type SmFe 12 The preparation method of the base alloy includes the following steps:

[0038] Step (1): Weigh the Fe, Al, Co, Ti, Mo and Sm elements according to their atomic percentage content in the alloy, mix and dissolve them in water, and stir thoroughly for 30-60 minutes to form a spray precursor solution;

[0039] Step (2): Using the principle of ultrasonic spraying, the spray precursor solution is placed in a container with an ultrasonic atomizer. The prepared metal salt solution is sprayed out in the form of mist by the action of ultrasonic waves. Then, under the action of the carrier gas, it is transported to the heated tube furnace at a certain flow rate. The collected composite oxide powder is placed in a collection bottle and dried in an oven at 80°C for 12-24 hours. Then, a reduction treatment is performed.

[0040] In this embodiment of the invention, the frequency of the ultrasonic atomizer is 0.5-10MHz, the carrier gas is one or more of the following combinations: air, nitrogen, argon, and helium, the flow rate is set to 2-20L / min, and the size of the composite oxide is about 0.5-8μm.

[0041] In this embodiment of the invention, the tubular furnace adopts a three-stage temperature control, with the first stage temperature at 300-400℃, the center temperature at 800-1000℃, and the rear stage temperature at 800-1000℃. Under the high temperature of the tubular furnace, the atomized mixed solution successively undergoes evaporation and dehydration, salt thermal decomposition, and oxidation reactions to form composite oxides, which are collected on the collector at the end of the tubular furnace.

[0042] Step (3): The dried oxide precursor powder is pre-reduced and then reduced with an active metal at a reduction temperature of 900-1200℃. At this time, the metal elements will generate metal alloy compounds through adsorption-diffusion process. The Sm obtained from the reduction is adsorbed on the surface of the surrounding Fe powder particles in gas form and then diffuses into the interior of the iron particles, eventually forming a uniform and stable samarium-iron-based alloy.

[0043] In this embodiment of the invention, the pre-reduction temperature is 500-700℃, and a fluid H2 atmosphere is introduced at a flow rate of 0.3-2L / min to carry out the reduction reaction for 1-5 hours.

[0044] In this embodiment of the invention, the active metal is selected from calcium, sodium, and potassium.

[0045] Step (4): The reduced product is infiltrated with small molecules (carbon or nitrogen) using a gas infiltration method. The main temperature for gas infiltration is 400-600℃, the time is 0.5h-2h, and the gas flow rate is 0.2-0.8L / min. Nitriding mainly uses ammonia or a mixture of ammonia and argon. Carburizing mainly uses methane or ethane.

[0046] Step (5): The reduction product is repeatedly magnetically separated and washed with deionized water and dilute acetic acid until the pH of the final supernatant reaches 7. Then, it is magnetically separated and washed 3-4 times with organic alcohol to remove the washing water. Finally, it is vacuum dried at 20-80℃ to collect the ThMn. 12 Type SmFe 12 Base alloy.

[0047] The mechanism of the above experimental procedure is as follows: Figure 4 As shown.

[0048] The technical solution of the present invention will be further explained and described below with reference to several preferred embodiments, but the experimental conditions and setting parameters therein should not be regarded as limitations on the basic technical solution of the present invention. Furthermore, the scope of protection of the present invention is not limited to the following embodiments.

[0049] Example 1:

[0050] (1) Accurately measure 41.985 ml of 0.2 mol / L Sm(NO3)3 solution, 362.595 ml of Fe(NO3)3 solution, 76.336 ml of Co(NO3)2 solution, and 19.084 ml of TiCl3 solution into a beaker, mix well, and then pour into the atomizing device. Figure 1 In the spray pyrolysis apparatus shown, a tubular furnace heating program is set with a heating rate of 10℃ / min, a front-end temperature of 300℃, a middle section temperature of 1000℃, and a rear-end temperature of 1000℃. After the heating program is completed, the atomizing device is turned on. The ultrasonic atomizer has a frequency of 1.5MHz. To ensure continuous atomization, the atomizing device is equipped with automatic liquid replenishment, adding 50mL of liquid every 30min. Air is selected as the carrier gas, and the gas flow rate is set to 10L / min through a gas flow meter. The air will transport the atomized water mist to the tubular furnace for reaction. After the solution is atomized, the ultrasonic atomizer is turned off, the heating program of the tubular furnace is stopped, and the furnace is closed after the temperature inside the furnace drops to room temperature. The sprayed product, i.e., the spherical oxide precursor, is collected in the filter funnel at the rear end.

[0051] The SEM image of the spherical oxide precursor is as follows: Figure 2 As shown in (a).

[0052] (2) The collected powder was placed in a collection bottle and dried in an oven at 80°C for 12 hours. 1.5 g of the collected oxide powder was weighed and spread evenly in a small porcelain boat, then placed in a tube furnace. The furnace was repeatedly evacuated three times to ensure no oxygen residue remained. The reaction was carried out at 600°C under a flowing H2 atmosphere for 3 hours to obtain the pre-reduction product. 1 g of the pre-reduction product was weighed and 0.3 g of metallic calcium granules were added. The two were thoroughly mixed and placed in a crucible, then placed in a tube furnace. The furnace was repeatedly evacuated three times to ensure no oxygen residue remained. The reaction was carried out at 900°C under a flowing Ar atmosphere for 2 hours. Then, the mixture was nitrided at 600°C for 2 hours. The atmosphere in the tube furnace was a mixture of ammonia and argon, with a gas flow rate of 0.4 L / min. After the reaction, samples were taken using a glove box. The obtained powder was allowed to cool to room temperature before being placed in a mortar and mixed with deionized water. The mixture was then ground and washed until no obvious calcium particles remained. Next, it was washed three times with an acetic acid solution (pH approximately 5.5), followed by three more washes with deionized water, ensuring the washing solution pH was approximately 7. Finally, it was washed three times with anhydrous ethanol to remove water from the powder surface. The cleaned product was then placed in a vacuum drying oven, evacuated to 0.05 MPa, and heated to 60°C for 12 hours. Clean alloy powder was then collected.

[0053] (3) The composition of the alloy powder was analyzed using X-ray diffraction (XRD), and the results are as follows: Figure 3 As shown in (a), it can be determined that it is ThMn. 12 Type SmFe 12 The diffraction peaks of the base alloy crystal were observed, but no diffraction peaks were found for α-Fe or other alloys. The microstructure of the alloy powder was observed using scanning electron microscopy (SEM), and the results are as follows: Figure 2 As shown in (b), the magnetic properties were tested using a vibrating sample magnetometer (VSM), and the results are shown in Table 1.

[0054] Example 2:

[0055] The procedure was carried out according to the steps listed in Example 1, wherein small molecule infiltration selective carburizing was performed at 800°C for 2 hours, the atmosphere of the tube furnace was a mixture of methane and argon, the gas flow rate was 0.4 L / min, and other conditions were the same as in Example 1.

[0056] Examples 3-6:

[0057] The steps listed in Example 1 were followed, except that the atomic ratio of Al element in the precursor solution was adjusted to 0.1, 0.2, 0.3, and 0.4, respectively; the corresponding element addition amounts were: 358.779 ml of Fe(NO3)3 solution and 3.817 ml of Al(NO3)3 solution; 354.962 ml of Fe(NO3)3 solution and 7.634 ml of Al(NO3)3 solution; 351.145 ml of Fe(NO3)3 solution and 11.450 ml of Al(NO3)3 solution; and 347.328 ml of Fe(NO3)3 solution and 15.267 ml of Al(NO3)3 solution. Other conditions were the same as in Example 1. Example 3 prepared Al-containing ThMn. 12 Type SmFe 12 The XRD pattern of the base alloy is as follows Figure 3 As shown in (b).

[0058] Examples 7-9:

[0059] The steps listed in Example 1 were followed, wherein the optimal amount of Al added was determined by measuring 41.985 ml of Sm(NO3)3 solution, 76.336 ml of Co(NO3)2 solution, 19.084 ml of TiCl3 solution, and 11.450 ml of Al(NO3)3 solution; the atomic ratio of Mo was adjusted to 0.1, 0.2, and 0.3 when preparing the precursor solution; the corresponding amounts of added elements were 347.328 ml of Fe(NO3)3 solution and 3.817 ml of Mo(NO3)6 solution; 343.511 ml of Fe(NO3)3 solution and 7.634 ml of Mo(NO3)6 solution; and 339.695 ml of Fe(NO3)3 solution and 11.450 ml of Mo(NO3)6 solution, with other conditions being the same as in Example 1; Example 7 prepared ThMn containing Al and Mo. 12 Type SmFe 12 The XRD pattern of the base alloy is as follows Figure 3 As shown in (c).

[0060] Compare with Example 1

[0061] In Examples 1 and 2, without the small molecule infiltration treatment, all other procedures and experimental parameters were the same, and ThMn was finally obtained. 12 Type SmFe 12 Base alloy.

[0062] The products obtained above were subjected to performance tests, and the following data were obtained (Table 1):

[0063] Table 1. Performance comparison of the final product powders from Examples 1-9 and Comparative Example 1

[0064]

[0065]

[0066] This shows that the infiltration of small molecules effectively supplements ThMn. 12 The interstitial position helps improve performance. The addition of Al increases both coercivity and remanence, with the best effect observed at an addition ratio of 0.3. When Mo is added, the two are co-doped, and as the amount added increases, coercivity and remanence continue to improve, with an addition ratio of 0.2 being the optimal choice.

Claims

1. A ThMn 12 Type SmFe 12 The base alloy is characterized by, The ThMn 12 Type SmFe 12 The composition of the base alloy is Sm a Fe 12-x-y-z-r Co x Ti y Al z Mo r M, where a is 1~1.2, x is greater than 0 and not greater than 0.2, y is greater than 0 and not greater than 0.5, z is 0.1~0.3, r is 0.1~0.2, and the ratio of the sum of the number of Fe, Al, Co, Ti, and Mo atoms to the number of Sm atoms is 10~12; M is N or C; the ThMn 12 Type SmFe 12 The diameter of the base alloy is 0.5-5μm.

2. A ThMn as described in claim 1 12 Type SmFe 12 The method for preparing the base alloy is characterized by, The preparation method includes the following steps: Step (1): Weigh the Fe, Al, Co, Ti, Mo and Sm elements according to their atomic percentage content in the alloy, mix and dissolve them in water, and stir evenly to form a spray precursor solution; Step (2): The spray precursor solution is sprayed out in a mist and transported to a tube furnace under the action of a carrier gas. Spherical oxide precursors are prepared by spray thermal decomposition and then dried. Step (3): The dried spherical oxide precursor is first pre-reduced in a hydrogen atmosphere, then reduced with an active metal, and finally nitrided or carburized. After cleaning and drying, the ThMn is obtained. 12 Type SmFe 12 Base alloy.

3. The preparation method according to claim 2, characterized in that, The carrier gas mentioned in step (2) is one or more combinations of air, nitrogen, argon and helium.

4. The preparation method according to claim 3, characterized in that, The carrier gas flow rate is 2-20 L / min.

5. The preparation method according to claim 2, characterized in that, The tubular furnace described in step (2) adopts a three-stage temperature control system, with the first stage temperature being 300-400℃, the second stage temperature being 800-1000℃, and the third stage temperature being 800-1000℃.

6. The preparation method according to claim 2, characterized in that, The active metal mentioned in step (3) is one of calcium, sodium, and potassium.

7. The preparation method according to claim 2, characterized in that, The temperature for reducing the active metal in step (3) is 900-1200℃, and the reduction time is 0.5-3.5h.

8. The preparation method according to claim 2, characterized in that, The nitriding or carburizing in step (3) is carried out by gas diffusion method; nitriding uses ammonia or a mixture of ammonia and argon; carburizing mainly uses methane or ethane gas.

9. The preparation method according to claim 8, characterized in that, The main temperature for gas infiltration is 400-600℃, the time is 0.5h-2h, and the gas flow rate is 0.2-0.8 L / min.

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