A reduction-diffusion method for preparing Sm2Fe 17 Methods for alloy particles

Abstract

The application discloses a method for preparing Sm2Fe 17 alloy particles by a reduction diffusion method, which comprises the following steps: mixing Sm2O3 powder and Fe powder by using a three-dimensional mixer, then adding Ca powder and CaCl2 to mix again, vacuum packaging the mixed material in a rubber mold, placing the vacuum packaged material in a cavity of a cold isostatic pressing machine, performing cold isostatic pressing treatment, then performing reduction diffusion treatment, wherein the reduction diffusion temperature is 1050-1160 DEG C, the reduction diffusion environment is a vacuum condition or a high-purity Ar atmosphere, and the reduction diffusion time is 6-12 h; crushing the blank after the reduction diffusion treatment, then washing the blank by using water to remove excessive Ca and CaO, then performing acid washing until the pH value is 7+ / -0.2, and finally performing vacuum drying to obtain Sm2Fe 17 alloy particles. By the method, the generation of soft magnetic phase alpha-Fe phase and Sm-rich phase can be effectively avoided after the green body is subjected to the reduction diffusion treatment, and after the excessive Ca and CaO are removed, the Sm2Fe 17 phase obtained is relatively single in phase, which is beneficial to the subsequent preparation of Sm2Fe 17 N x magnetic powder with superior magnetic properties.

Description

Technical Field

[0001] This invention belongs to the field of magnetic materials, specifically relating to a reduction-diffusion method for preparing Sm2Fe. 17 Methods for alloy particles. Background Technology

[0002] Sm-Fe-N compounds possess excellent intrinsic magnetic properties, and their saturation magnetic polarization J s It can reach 1.54T, with a maximum magnetic energy product (BH). max Up to 472kJ / m 3 It is completely comparable to NdFeB magnetic materials, and its anisotropic field H A It is approximately three times that of NdFeB permanent magnet materials. Although the saturation magnetization of NdFeB and Sm-Fe-N is comparable, the Curie temperature of Sm-Fe-N permanent magnet materials is as high as 470℃, which is much higher than that of NdFeB (310℃), and Sm-Fe-N permanent magnet materials have better temperature tolerance.

[0003] Secondly, Sm-Fe-N permanent magnet materials do not contain strategic metal elements, eliminating the need to add expensive heavy rare earth elements Dy and Tb. Rare earth mineral resources often coexist in nature; while Pr and Nd resources are extensively developed, much Sm resource remains idle. Furthermore, due to the non-renewable nature of rare earth resources, significant waste occurs. (Sm2Fe) 17 N x The development of permanent magnet materials can improve the comprehensive utilization rate of rare earth resources. Given Sm2Fe... 17 N x Permanent magnet materials possess both good temperature stability and excellent magnetic properties, and their potential application value has become a new research hotspot and development boom.

[0004] And Sm2Fe 17 N x Permanent magnet material is composed of Sm2Fe 17 It is prepared from alloy as raw material, through the process of Sm2Fe 17 By nitriding the alloy, Sm2Fe with good magnetic properties can be obtained. 17 N3 permanent magnet material. Therefore, Sm2Fe 17 The preparation of alloys and the development of related processes are of particular importance.

[0005] Currently Sm2Fe 17 The main preparation methods for alloys include reduction-diffusion (R / D) and powder metallurgy (PM). Sm₂Fe is prepared using both reduction-diffusion and powder metallurgy methods. 17 The specific processes and characteristics are as follows:

[0006] 1) Reduction-Diffusion (R / D) Method: Sm2O3 (or SmCl3), Fe powder, and reducing agent Ca particles (or CaH2) are mixed in a certain stoichiometric ratio. After mixing, the mixture is molded to obtain a green blank. The green blank is then loaded into a furnace for high-temperature reduction-diffusion. The reduced-diffusion blank is washed with water to remove impurities such as Ca and CaO, yielding Sm2Fe. 17 Alloy particles. Since the green blank is formed by compression molding, whether unidirectional or bidirectional, there will be significant density differences in different locations within the blank. This leads to uneven diffusion of Ca vapor and Sm atoms during the reduction diffusion process, forming localized α-Fe and Sm-rich phases, resulting in Sm₂F particles. 17 The alloy's low purity leads to Sm2F 17 N x Its magnetic properties are poor.

[0007] 2) Powder metallurgy (PM): Raw materials Sm and Fe blocks are smelted according to a certain ratio, and the ingot is homogenized and annealed to obtain Sm2Fe. 17 The alloy was subjected to staged crushing to obtain Sm2Fe. 17 Particles. To ensure that the ingot composition does not segregate, multiple smelting processes are required, due to Sm2Fe. 17 The solid solution region is very narrow, and the cooling rate of the alloy liquid in the water-cooled copper mold is insufficient. The microstructure of the Sm-Fe alloy is extremely heterogeneous, containing a large amount of α-Fe phase and Sm-rich phase. To obtain a relatively homogeneous Sm2Fe alloy... 17 The alloy requires a long period of homogenization heat treatment, which also results in a huge energy consumption. Summary of the Invention

[0008] To address the limitations of existing technologies, such as the conventional reduction-diffusion (R / D) method for preparing Sm2Fe 17 In the alloying process, the raw materials are mixed and then pressed into green blanks using a die. The resulting green blanks have poor density uniformity, leading to the appearance of impurities such as α-Fe phase and Sm-rich phase after reduction and diffusion. The purpose of this invention is to provide a reduction-diffusion method for preparing high-purity Sm₂Fe. 17 The method for preparing alloy particles involves obtaining green blanks through cold isostatic pressing, rather than traditional pressing and forming. This method yields samarium-iron alloy green blanks for reduction diffusion with good density uniformity. Furthermore, through reduction diffusion heat treatment, high-purity Sm2Fe free of α-Fe can be prepared. 17 alloy.

[0009] The technical solution adopted in this invention is as follows:

[0010] A reduction-diffusion method for preparing high-purity Sm2Fe 17 The method for alloy particles includes the following steps:

[0011] 1) Mixing Method 1: Mix Sm2O3 powder and Fe powder using a three-dimensional mixer. The mixing atmosphere is at least one of air, nitrogen, and argon.

[0012] 2) Mixing 2: Add reducing agent Ca powder and auxiliary agent CaCl2 to the mixture in step 1) for secondary mixing. The mixing atmosphere is at least one of air, nitrogen, and argon.

[0013] 3) Molding: Fill the rubber mold with the mixed material from step 2);

[0014] 4) Sealing: Vacuum seal the mold containing the material to remove air;

[0015] 5) Isostatic pressing: Place the vacuum-sealed workpiece inside the cavity of the cold isostatic press, set the pressure and holding time of the cold isostatic press, and perform cold isostatic pressing on the above-mentioned sealed semi-finished product.

[0016] 6) Reduction diffusion: The green billet that has been isostatically pressed is placed in a reduction diffusion furnace for reduction diffusion. The reduction diffusion temperature is 1050-1160℃, the reduction diffusion environment is a vacuum or a high-purity Ar atmosphere, and the reduction diffusion time is 6-12h.

[0017] 7) Purification: The reduced-diffusion blank was crushed in stages, and the crushed particles were washed several times with water to remove excess Ca and CaO. Then, it was acid-washed until the pH was 7±0.2, and finally vacuum dried to obtain Sm2Fe. 17 Alloy particles.

[0018] Furthermore, the reaction equation for reduction diffusion is: 17Fe + Sm₂O₃ + 3Ca → Sm₂Fe 17 +3CaO. The theoretical molar ratio of Fe:Sm2O3:Ca is 17:1:3. Considering the burn-off during the reduction diffusion process, the molar ratio of Sm2O3 powder, Fe powder, and reducing agent Ca powder is limited to 17:(1.05~1.45):(3.3~5.4). The mass of the auxiliary agent CaCl2 is 1~8% of the total mass of Sm2O3 powder, Fe powder, and reducing agent Ca powder.

[0019] Furthermore, in step 3), the rubber mold can be any regular or irregular shape, such as a cuboid, cube, cylinder, sphere, or prism. The rubber mold can be a single mold with a single cavity, such as... Figure 1 As shown; rubber molds can also be multi-cavity molds, such as... Figure 2 As shown.

[0020] Furthermore, in step 4), the vacuum level during encapsulation is 1.0 × 10⁻⁶. -3 ~1.0×10 2Pa.

[0021] Furthermore, in step 5), the isostatic pressure is 5-100 MPa, and the pressure holding time is 0.5-10 minutes.

[0022] Furthermore, in step 7), the particle size range of the crushed particles is 8 to 300 mesh.

[0023] Further, in step 7), the pickling solution is an aqueous solution of formic acid or acetic acid with a volume fraction of 0.5-5%.

[0024] The beneficial effects achieved by this invention are:

[0025] 1) The process method of this invention can effectively solve the problem of poor density uniformity leading to a large number of impurity phases in the reduction-diffusion blank, such as Sm2Fe, during traditional green die pressing. 17 Technical problems such as low phase purity.

[0026] 2) Compared to traditional unidirectional or bidirectional mold pressing, the green body forming process described in this invention offers advantages such as simple switching between green body size and shape, low production cost, high safety and efficiency, and excellent density consistency. After reduction and diffusion, the formation of the soft magnetic α-Fe phase and Sm-rich phase can be effectively avoided. After removing excess Ca and CaO, a relatively uniform Sm2Fe phase can be obtained. 17 This phase is beneficial for the subsequent preparation of Sm2Fe with superior magnetic properties. 17 N x Magnetic powder. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of a single-cavity rubber mold;

[0028] Figure 2 This is a schematic diagram of a multi-cavity rubber mold;

[0029] Figure 3 SEM image of green compact after reduction and diffusion;

[0030] Figure 4 XRD pattern of green body after reduction and diffusion. Detailed Implementation

[0031] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0032] Example 1:

[0033] A reduction-diffusion method for preparing high-purity Sm2Fe 17 The method for alloy particles includes the following steps:

[0034] (1) Mixing 1: Load Fe powder with an average mesh size of 500 mesh and Sm2O3 powder with an average mesh size of 500 mesh into a three-dimensional mixer and mix for 2 hours under a nitrogen atmosphere.

[0035] (2) Mixing 2: Add metal Ca particles with a particle size of 1-3 mm and auxiliary CaCl2 powder with an average mesh size of 300 to the mixture in step (1) and continue mixing for 2 hours.

[0036] The molar ratio of Fe:Sm2O3:Ca is 17:1.25:4.3, and the mass of the auxiliary agent CaCl2 is 1% of the total mass of Sm2O3 powder, Fe powder, and reducing agent Ca powder.

[0037] (3) Molding: Add the mixed materials into the rectangular rubber mold, and try to make the materials pile up evenly and the surface flat.

[0038] (4) Sealing: Vacuum seal the packaged materials and mold together, with a vacuum degree of 5×10⁻⁶. 1 Pa;

[0039] (5) Isostatic pressing: The vacuum-sealed workpiece is placed inside the cavity of the cold isostatic press. The pressure of the cold isostatic press is set to 70MPa and the holding time is 5 minutes. The above-sealed semi-finished product is subjected to cold isostatic pressing. The vacuum packaging bag is removed to obtain the cold isostatic pressed green blank.

[0040] (6) Reduction Diffusion: The isostatically pressed green billets were charged into the furnace for reduction diffusion at a temperature of 1050℃, in a high-purity Ar atmosphere, for 8 hours. After reduction diffusion, the main phase distribution of the green billet was uniform, and no impurities such as α-Fe or Sm-rich phases were observed. The microstructure and crystal phase analysis of the green billet after reduction diffusion were as follows: Figure 3 and Figure 4 As shown. (Through) Figure 3 SEM analysis shows that after reduction and diffusion, the raw material reaction was complete, and the desired Sm2Fe was generated in the preform. 17 The alloy phase (gray area) is accompanied by the formation of CaO, a reduction byproduct (black area).

[0041] from Figure 4 XRD analysis showed that the green body contained three components after reduction and diffusion, namely a large amount of Sm2Fe. 17 It contained a relatively large amount of CaO and trace amounts of Ca, but no impurities such as α-Fe phase or Sm-rich phase were observed.

[0042] (7) Purification: The reduced and diffused blank was crushed into particles with an average mesh size of 20 mesh. Excess Ca, CaO and CaCl2 were removed by washing with water. Then, it was acid-washed with a 2% formic acid aqueous solution until the pH was about 7. Finally, it was vacuum dried to obtain Sm2Fe 17 Alloy particles. For purified Sm2Fe 17 SEM and XRD analyses of the alloy particles revealed that the final product is primarily composed of Sm2Fe. 17 It has a pure phase composition and does not contain impurities such as CaO, Ca, and CaCl2.

[0043] Sm2Fe was prepared according to the method in Example 1. 17 The only difference with alloy particles is that when the isostatic pressing operation in step (5) is replaced with the conventional pressing operation (press pressure is 50KN, holding time is 2s), the problem is that the pressing pressure is uneven and the pressing pressure is too small compared with the isostatic pressing pressure. During the pressing process, the pressure head on the mold is deformed and damaged due to pressure. In addition, the blank also has a serious corner chipping phenomenon.

[0044] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A reduction-diffusion method for preparing Sm2Fe 17 The method for alloy particles is characterized by Includes the following steps: 1) Mixing Method 1: Mix Sm2O3 powder and Fe powder using a three-dimensional mixer. The mixing atmosphere is at least one of air and nitrogen. 2) Mixing 2: Add reducing agent Ca powder and auxiliary agent CaCl2 to the mixture in step 1) for secondary mixing. The mixing atmosphere is at least one of air and nitrogen. 3) Molding: Fill the rubber mold with the mixed material from step 2); 4) Sealing: Vacuum seal the mold containing the material to remove air; 5) Isostatic pressing: Place the vacuum-sealed workpiece inside the cavity of the cold isostatic press, set the pressure and holding time of the cold isostatic press, and perform cold isostatic pressing on the above-mentioned sealed semi-finished product. 6) Reduction diffusion: The green billet that has been isostatically pressed is placed in a reduction diffusion furnace for reduction diffusion. The reduction diffusion temperature is 1050-1160℃, the reduction diffusion environment is a vacuum or a high-purity Ar atmosphere, and the reduction diffusion time is 6-12h. 7) Purification: The reduced-diffusion blank was crushed in stages, and the crushed particles were washed several times with water to remove excess Ca and CaO. Then, it was acid washed until the pH was 7±0.2, and finally vacuum dried to obtain Sm2Fe. 17 Alloy particles; The molar ratio of Sm2O3 powder, Fe powder, and reducing agent Ca powder is 17:(1.05~1.45):(3.3~5.4), and the mass of the auxiliary agent CaCl2 is 1~8% of the total mass of Sm2O3 powder, Fe powder, and reducing agent Ca powder. In step 5), the isostatic pressure is 5-100 MPa, and the holding time is 0.5-10 minutes.

2. The reduction-diffusion method for preparing Sm2Fe as described in claim 1 17 The method for alloy particles is characterized by In step 3), the shape of the rubber mold is any regular or irregular shape such as cuboid, cube, cylinder, sphere, or prism, and the rubber mold is one mold with one cavity or one mold with multiple cavities.

3. The reduction-diffusion method for preparing Sm2Fe as described in claim 1 17 The method for alloy particles is characterized by In step 4), the vacuum level during encapsulation is 1.0 × 10⁻⁶. -3 ~1.0×10 2 Pa.

4. The reduction-diffusion method for preparing Sm2Fe as described in claim 1 17 The method for alloy particles is characterized by In step 7), the particle size range of the crushed particles is 8 to 300 mesh.

5. The reduction-diffusion method for preparing Sm2Fe as described in claim 1 17 The method for alloy particles is characterized by In step 7), the pickling solution is an aqueous solution of formic acid or acetic acid with a volume fraction of 0.5-5%.

Images