A method for regulating the valence of cerium in a cerium-containing neodymium-iron-boron magnet

Abstract

The application belongs to the technical field of magnetic materials, and discloses a method for realizing regulation and control of the valence of cerium elements in a cerium-containing Nd-Fe-B magnet. The method comprises the following steps: doping gadolinium alloy powder into main-phase magnetic powder of the cerium-containing Nd-Fe-B magnet, performing magnetic field orientation forming, and obtaining the cerium-containing Nd-Fe-B magnet through sintering and tempering heat treatment; wherein, during the heat treatment, the gadolinium element diffuses into the main-phase grains, so that the valence of the cerium elements in the main-phase grains moves to a low valence state, thereby realizing regulation and control of the valence of the cerium elements. The application realizes regulation and control of the valence of the cerium elements in the main phase, improves the magnetic crystal anisotropy field and the coercive force, and finally obtains a high-performance cerium-containing Nd-Fe-B magnet.

Description

Technical Field

[0001] This invention belongs to the field of magnetic materials technology, and in particular relates to a method for controlling the valence of cerium in cerium-containing neodymium iron boron magnets. Background Technology

[0002] In recent years, sintered NdFeB permanent magnets have been widely used in various sectors of the national economy, including instrumentation, microwave communication, wind power generation, and electric vehicles, due to their extremely high coercivity and energy product. Ce, a highly abundant rare earth element, has been widely used in NdFeB magnets to replace expensive rare earth elements such as Nd, Pr, Dy, and Tb due to its abundant reserves and low price.

[0003] However, the inventors of this application discovered that: due to Ce2Fe 14 B has low intrinsic properties, and the addition of NdFeB magnets severely dilutes their performance, leading to a significant decrease in magnet performance. Studies have shown that Ce typically has two valence states, +3 and +4. The +3 valence Ce ion has one more 4f free electron in its outer shell than the +4 valence ion. This electron provides the +3 Ce ion with both spin and orbital magnetic moments, macroscopically resulting in increased saturation magnetization and anisotropy of the magnet. However, in NdCe-Fe-B magnets, Ce generally exhibits a mixed valence state of +3 to +4, specifically +3.44. Therefore, it is understood that the saturation magnetization and anisotropy of cerium in cerium-containing NdFeB magnets can be controlled by adjusting the valence of cerium. Summary of the Invention

[0004] This invention is designed to solve the above-mentioned problems in the prior art. The purpose of this invention is to provide a method for controlling the oxidation state of cerium in cerium-containing NdFeB magnets, so that the oxidation state of cerium in the magnets shifts from +4 to +3, thereby improving the magnetocrystalline anisotropy field and coercivity of cerium-containing NdFeB magnets.

[0005] The above objective can be achieved through the following technical solutions:

[0006] According to one aspect of the present invention, a method for controlling the valence of cerium in a cerium-containing NdFeB magnet is provided, comprising: incorporating gadolinium alloy powder into a cerium-containing NdFeB main phase magnetic powder, performing magnetic field orientation molding, and obtaining a cerium-containing NdFeB magnet through sintering and tempering heat treatment, wherein, during the heat treatment process, gadolinium diffuses into the main phase grains, causing the valence of cerium in the main phase grains to shift to a lower valence state, thereby achieving control over the valence of cerium.

[0007] Optionally, the gadolinium alloy is an alloy of gadolinium with one or more selected from copper, iron, aluminum, gallium, cobalt, manganese, vanadium, and titanium.

[0008] Optionally, the gadolinium alloy is one of Gd-Cu, Gd-Al, Gd-Cu-Al, GdGa, GdCuGa, and Gd-Fe alloys.

[0009] Optionally, the gadolinium alloy has the following composition: Gd x M 100-x Where 40≤x<100; M is one or more selected from Cu, Fe, Al, Ga, Co, Mn, V, and Ti.

[0010] Optionally, the chemical composition of the cerium-containing NdFeB main phase is as shown in Formula I:

[0011] (RE 1-x Ce x ) α B β M γ N δ Fe 100-α-β-γ-δ Formula I;

[0012] Where x is a mass percentage, and 0 < x ≤ 1; in terms of mass percentage, 25 ≤ α ≤ 35, 0.9 ≤ β ≤ 1.2, 0 ≤ γ ≤ 10, 0 ≤ δ ≤ 10;

[0013] RE is Nd, or a combination of Nd and one or more selected from La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y and Sc;

[0014] M is selected from one or more of Co, Ni, Mn, Cr, Cu, Zn, Ti, V, Zr and Nb;

[0015] N is selected from one or more of Ga, Al, Sn and Ge.

[0016] Optionally, the amount of gadolinium alloy incorporated is 0.1 wt.% to 20 wt.% of the total amount of gadolinium alloy powder and cerium-containing NdFeB main phase magnetic powder.

[0017] Optionally, the amount of gadolinium alloy incorporated is 2 wt.% to 15 wt.% of the total amount of gadolinium alloy powder and cerium-containing NdFeB main phase magnetic powder.

[0018] In particular, optionally, the amount of gadolinium alloy incorporated is 4 wt.% to 6 wt.% of the total amount of gadolinium alloy powder and cerium-containing NdFeB main phase magnetic powder.

[0019] Further, optionally, when the gadolinium alloy is a Gd-Cu, Gd-Al, Gd-Cu-Al, Gd-Ga, or Gd-Cu-Ga alloy, the average valence of cerium in the magnet, as measured by X-ray photoelectron spectroscopy, is reduced to no higher than +3.20.

[0020] Optionally, the cerium-containing NdFeB magnet obtained by sintering and tempering heat treatment has a coercivity that is more than 1.2 times higher than that of the original magnet; wherein, the original magnet refers to a magnet obtained by directly oriented and heat-treated the cerium-containing NdFeB main phase magnetic powder without adding gadolinium alloy powder.

[0021] Optionally, the sintering temperature is 900℃~1200℃, the time is 1h~10h, and the vacuum degree is 1×10 -4 Pa ~ 1×10 -2 Pa.

[0022] Optionally, a two-stage tempering process may be adopted during tempering: the first-stage tempering temperature is 800℃~1000℃ and the time is 1h~6h; the second-stage tempering temperature is 400℃~650℃ and the time is 1h~6h.

[0023] Beneficial Effects: According to one embodiment of the present invention, cerium-containing NdFeB magnets are prepared by incorporating gadolinium alloy powder into cerium-containing NdFeB main phase magnetic powder. The gadolinium element in the alloy powder melts and diffuses into the main phase grains during sintering and tempering heat treatment, occupying the 4f and 4g positions of rare earth elements in the main phase lattice. This causes lattice distortion in the main phase grains, thereby controlling the valence of cerium in the main phase from +4 to +3, improving its magnetocrystalline anisotropy and coercivity, and ultimately obtaining a high-performance cerium-containing NdFeB magnet. This has significant theoretical and practical value. Attached Figure Description

[0024] Figure 1 These are the X-ray photoelectron spectra of Example 2 and Comparative Examples 1-2. Detailed Implementation

[0025] The present invention will be described below with reference to specific embodiments and examples, which will more clearly demonstrate its advantages and various effects. Obviously, the specific embodiments and examples described are only a part of the present invention, and not all of it. The following description of at least one exemplary embodiment or example is merely illustrative and is in no way intended to limit the present invention or its application or use. All other specific embodiments and examples obtained by those skilled in the art based on the embodiments and examples in this invention without inventive effort are within the scope of protection of this invention.

[0026] As described above, the inventors of this application recognized that the +3 valence Ce ion has one more 4f free electron in its outer shell than the +4 valence ion. This electron can provide the +3 valence Ce ion with a spin magnetic moment and an orbital magnetic moment, which macroscopically manifests as an increase in the saturation magnetization and anisotropic field of the magnet. Based on this, the present invention was completed. This application realizes the control of the valence of cerium element in cerium-containing NdFeB magnets to shift to the +3 valence, thereby improving the magnetocrystalline anisotropic field and coercivity, and ultimately obtaining high-performance cerium-containing NdFeB magnets.

[0027] The following is a general description of some implementation methods in this application:

[0028] One embodiment of this application provides a method for preparing cerium-containing NdFeB magnets, which allows for the control of the valence of cerium in the magnet. This method involves incorporating gadolinium alloy powder into cerium-containing NdFeB main phase magnetic powder, followed by magnetic field orientation molding, sintering, and tempering heat treatment to obtain the cerium-containing NdFeB magnet. During the heat treatment process, gadolinium diffuses into the main phase grains, causing the valence of cerium in the main phase grains to shift to a lower valence state, thereby achieving control over the valence of cerium.

[0029] During sintering and tempering, gadolinium alloys can decompose and release freely moving Gd atoms. These Gd atoms diffuse into the main phase grains, replacing rare earth elements in the crystal lattice and occupying the 4f and 4g positions of the rare earth elements in the main phase lattice, causing lattice distortion in the main phase grains (leading to Ce...). 4+ The space around the ion increases, allowing more electrons to be drawn by Ce. 4+ Ion trapping to form Ce 3+ The process involves using ions to shift the valence of cerium in the magnet from +4 to +3, thereby reducing the overall valence state of Ce and thus controlling the valence of cerium. This improves the anisotropic field and coercivity of the magnetocrystalline structure, ultimately resulting in a high-performance cerium-containing NdFeB magnet with controlled cerium valence.

[0030] In one optional embodiment, the incorporated gadolinium alloy is an alloy formed by gadolinium and at least one metallic element selected from copper, iron, aluminum, gallium, cobalt, manganese, vanadium, titanium, etc. For example, it can be a Gd-Cu alloy, Gd-Al alloy, Gd-Fe alloy, Gd-Cu-Al alloy, etc. Preferably, the incorporated gadolinium alloy is a binary alloy formed by gadolinium and one of the metallic elements. During sintering and tempering, the gadolinium alloy decomposes into Gd atoms and metallic elements such as Cu, Al, and Ga. Among them, Gd atoms diffuse into the main phase grains, while the decomposed Cu, Al, Ga, and other metallic elements can optimize the wettability and fluidity of the grain boundary phase at high temperatures, providing channels for the diffusion of Gd atoms, thereby further promoting the migration of Gd atoms into the main phase grains. The diffusion of Gd atoms into the main phase grains causes lattice distortion, realizing the control of the valence of cerium in the magnet, and at the same time enhancing the anisotropic field of the main phase, ultimately improving the coercivity of the magnet.

[0031] In a preferred embodiment, the gadolinium alloy has the following composition: Gd x M 100-x Where 40 ≤ x < 100; M is at least one of the metallic elements Cu, Fe, Al, Ga, Co, Mn, V, Ti, etc. x refers to the proportion of Gd in the total alloy, in atomic percentage. For example, a gadolinium-doped alloy can have Gd... 40 Cu 60 Gd 40 Al 60 Gd 40 (Cu 0.5 Al 0.5 ) 60 Gd 40 Ga 60 Gd 40 (Cu 0.5 Ga 0.5 ) 60 The gadolinium alloy composed of the above-mentioned components allows gadolinium to diffuse more effectively into the main phase grains, causing lattice distortion. This maximizes the shift of the valence of cerium in the magnet from +4 to +3, reducing the overall valence state of Ce, and significantly improving the magnetocrystalline anisotropy field and coercivity, resulting in a high-performance cerium-containing NdFeB magnet. This invention uses a gadolinium alloy that does not contain a NdFeB main phase grain structure. The inventors have also discovered that if the auxiliary alloy contains a main phase grain structure, most of the Gd element will be distributed within these main phase grains. During high-temperature heat treatment, only a small portion of the Gd element in these main phase grains participates in the diffusion process; most of the Gd element is "confined" within the lattice of the main phase grains. This significantly weakens the mobility of Gd atoms in the lattice, preventing the formation of freely moving Gd atoms. The gadolinium alloy used in this application decomposes into freely moving Gd atoms during high-temperature heat treatment. These atoms have high activity and strong migration and diffusion capabilities, enabling them to enter the crystal lattice of the main phase grains to the greatest extent.

[0032] In an optional embodiment, the chemical composition of the cerium-neodymium-iron-boron main phase is as follows:

[0033] (RE 1-x Ce x ) α B β M γ N δ Fe 100-α-β-γ-δ Formula I;

[0034] Where x is a mass percentage and 0 < x ≤ 1; by mass percentage, 25 ≤ α ≤ 35, 0.9 ≤ β ≤ 1.2, 0 ≤ γ ≤ 10, 0 ≤ δ ≤ 10. RE represents rare earth elements; specifically, RE can be Nd, or RE can be Nd and one or more selected from La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc. When γ ≠ 0, M is one or more selected from Co, Ni, Mn, Cr, Cu, Zn, Ti, V, Zr, and Nb. When δ ≠ 0, N is one or more selected from Ga, Al, Sn, and Ge. By using the above formula I as the main phase chemical composition of cerium-containing NdFeB magnets and incorporating gadolinium alloy powder, the valence of cerium can be controlled while obtaining high-magnetic-performance cerium-containing NdFeB magnets.

[0035] In an optional embodiment, the amount of gadolinium alloy incorporated can be from 0.1 wt.% to 20 wt.% of the total amount, for example, 0.1%, 0.5%, 1%, 4%, 5%, 6%, 7%, 8%, 9%, 11%, 13%, 15%, 17%, 19%, 20%, etc. By controlling the proportion of gadolinium alloy incorporated, it is possible to ensure that the freely moving Gd atoms decomposed during high-temperature heat treatment can cause lattice distortion in the main phase grains, thereby enabling the regulation of the valence of cerium in the main phase and improving the coercivity of the magnet.

[0036] Furthermore, the amount of gadolinium alloy incorporated can be 2 wt.% to 15 wt.% of the total amount. Within this range, the average valence of cerium in the magnet, as measured by X-ray photoelectron spectroscopy, can be reduced to below +3.25, and the coercivity of the magnet can be increased by more than 1.2 times. In particular, when the amount of gadolinium alloy incorporated can be 4 wt.% to 6 wt.% of the total amount, the average valence of cerium can be reduced to no higher than +3.20, and the coercivity of the magnet can be increased by more than 2 times.

[0037] In one optional embodiment, after thorough mixing, a magnet green blank is obtained by magnetic field orientation. The magnet green blank is then subjected to sintering and tempering heat treatment to obtain a cerium-containing NdFeB magnet. The sintering temperature is 900℃~1200℃, for example, 900℃, 1000℃, 1100℃, 1200℃, etc.; the sintering time is 1h~10h, for example, 1h, 5h, 7h, 9h, etc.; and the vacuum degree is 1×10⁻⁶. -4 Pa ~ 1×10 - 2Pa. A two-stage tempering process is employed. The first-stage tempering temperature is 800℃~1000℃, for example, 800℃, 900℃, 1000℃, etc., for 1h~6h, for example, 1h, 3h, 5h, 6h, etc. The second-stage tempering temperature is 400℃~650℃, for example, 400℃, 500℃, 600℃, etc., for 1h~6h, for example, 1h, 3h, 5h, 6h, etc. During the above-mentioned sintering and tempering high-temperature heat treatment, the temperature environment is fully utilized, enabling the gadolinium alloy to effectively decompose and release freely moving Gd atoms. These atoms then effectively diffuse into the main phase lattice within the above-mentioned treatment time, occupying the positions of rare earth elements in the main phase lattice and causing lattice distortion in the main phase grains. This reduces the overall valence state of Ce, thereby improving the magnetocrystalline anisotropy and coercivity of the cerium-containing NdFeB magnet.

[0038] Furthermore, during orientation forming, an orientation magnetic field of ≥1.6T is sufficient to obtain a dense magnet green blank. To increase the density of the magnet green blank, isostatic pressing can be performed after magnetic field orientation forming, with an isostatic pressing pressure of ≥150MPa.

[0039] Furthermore, the method for obtaining cerium-containing NdFeB main phase magnetic powder can be as follows: prepare each component raw material according to the raw material ratio of cerium-containing NdFeB main phase, mix the component raw materials, and then sequentially pass them through rapid solidification melting, hydrogen crushing, and air jet milling to obtain the main phase magnetic powder. The method for obtaining gadolinium alloy powder can be as follows: prepare each component raw material according to the raw material ratio of gadolinium alloy, mix the component raw materials, and then sequentially pass them through rapid solidification melting, hydrogen crushing, and air jet milling to obtain gadolinium alloy powder. Alternatively, the method for obtaining gadolinium alloy powder can be as follows: prepare each component raw material according to the raw material ratio of gadolinium alloy, mix the component raw materials, first pass them through induction melting, and then through mechanical crushing and / or ball milling to obtain gadolinium alloy powder.

[0040] In a preferred embodiment, the particle size of the cerium-containing NdFeB main phase magnetic powder is 1.5 μm to 4.5 μm. The particle size of the gadolinium alloy powder is 1.0 μm to 3.5 μm. By using cerium-containing NdFeB main phase magnetic powder and gadolinium alloy powder within the above particle size range, it is more conducive to subsequent orientation forming, obtaining a denser magnet green blank, and more conducive to promoting the migration of Gd atoms into the main phase grains during heat treatment.

[0041] According to the method provided in this application for controlling the oxidation state of cerium in cerium-containing NdFeB magnets, the average oxidation state of cerium in the magnets can be reduced to achieve oxidation state control. For example, in some embodiments, the average oxidation state can be reduced to no higher than +3.20. The coercivity of the cerium-containing NdFeB magnets obtained by the method is improved, and can be increased by more than 1.27 times, and even in some embodiments, the coercivity of the cerium-containing NdFeB magnets can be increased by more than 2 times.

[0042] The present application will now be described in more detail with reference to specific embodiments:

[0043] Example 1

[0044] Preparation of main phase magnetic powder: Mix the various metal raw materials according to the ratio, and the mixture is rapidly solidified and smelted to obtain alloy castings. The alloy castings are hydrogen-crushed to obtain coarse powder, and the coarse powder is milled by air jet milling to obtain main phase magnetic powder.

[0045] Chemical formula of the main phase: [(PrNd)] 0.5 Ce 0.5 ] 29.5 B 0.98 Co 0.5 Zr 0.2 Al 0.1 Ga 0.1 Fe bal (mass ratio, defined as Ce50).

[0046] Preparation of gadolinium alloy powder: Mix the various metal raw materials according to the formula, and the mixture is rapidly solidified and smelted to obtain alloy castings. The alloy castings are hydrogen-crushed to obtain coarse powder, and the coarse powder is milled by air jet milling to obtain gadolinium alloy powder.

[0047] The chemical formula for gadolinium alloys is: Gd 40 Cu 60 (Atomic ratio).

[0048] The prepared gadolinium alloy powder was added to the main phase magnetic powder at a mass ratio of 2 wt.% of the total amount of gadolinium alloy powder and main phase magnetic powder. The mixture was mixed evenly and shaped into a green blank by magnetic field orientation. Then it was placed in a high vacuum sintering furnace for high-temperature sintering and tempering treatment to finally obtain cerium-containing neodymium iron boron magnets.

[0049] The specific sintering and tempering process is as follows: vacuum degree is 1×10 -4 Pa, sintering temperature is 990℃, sintering holding time is 4h; first tempering temperature is 900℃, holding time is 2h; second tempering temperature is 600℃, holding time is 2h.

[0050] The prepared magnet was placed in an open-circuit PFM permanent magnet material measurement system, and the magnetic properties were measured as follows: B r =12.01kGs, H cj = 5.31 kOe, (BH) max =27.11MGOe.

[0051] Example 2

[0052] Preparation of main phase magnetic powder: Mix the various metal raw materials according to the ratio, and the mixture is rapidly solidified and smelted to obtain alloy castings. The alloy castings are hydrogen-crushed to obtain coarse powder, and the coarse powder is milled by air jet milling to obtain main phase magnetic powder.

[0053] Chemical formula of the main phase: [(PrNd)] 0.5 Ce0.5 ] 29.5 B 0.98 Co 0.5 Zr 0.2 Al 0.1 Ga 0.1 Fe bal (mass ratio, defined as Ce50).

[0054] Preparation of gadolinium alloy powder: Mix the various metal raw materials according to the formula, and the mixture is rapidly solidified and smelted to obtain alloy castings. The alloy castings are hydrogen-crushed to obtain coarse powder, and the coarse powder is milled by air jet milling to obtain gadolinium alloy powder.

[0055] The chemical formula for gadolinium alloys is: Gd 40 Cu 60 (Atomic ratio).

[0056] The prepared gadolinium alloy powder was added to the main phase magnetic powder at a mass ratio of 4 wt.% of the total amount of gadolinium alloy powder and main phase magnetic powder. The mixture was mixed evenly and shaped into a green blank by magnetic field orientation. Then it was placed in a high vacuum sintering furnace for high-temperature sintering and tempering treatment to finally obtain cerium-containing neodymium iron boron magnets.

[0057] The specific sintering and tempering process is as follows: vacuum degree is 1×10 -4 Pa, sintering temperature is 985℃, sintering holding time is 4h; first tempering temperature is 900℃, holding time is 2h; second tempering temperature is 600℃, holding time is 2h.

[0058] The prepared magnet was placed in an open-circuit PFM permanent magnet material measurement system, and the magnetic properties were measured as follows: B r =11.78kGs, H cj = 9.38 kOe, (BH) max =29.72MGOe.

[0059] Example 3

[0060] Preparation of main phase magnetic powder: Mix the various metal raw materials according to the ratio, and the mixture is rapidly solidified and smelted to obtain alloy castings. The alloy castings are hydrogen-crushed to obtain coarse powder, and the coarse powder is milled by air jet milling to obtain main phase magnetic powder.

[0061] Chemical formula of the main phase: [(PrNd)] 0.5 Ce 0.5 ] 29.5 B 0.98 Co 0.5 Zr 0.2 Al 0.1 Ga 0.1 Fe bal (mass ratio, defined as Ce50).

[0062] Gadolinium alloy composition: Mix the various metal raw materials according to the formula, and the mixture is rapidly solidified and smelted to obtain alloy castings. The alloy castings are hydrogen-crushed to obtain coarse powder, and the coarse powder is milled by air jet milling to obtain gadolinium alloy powder.

[0063] The chemical formula for gadolinium alloys is: Gd 40 Cu 60 (Atomic ratio).

[0064] The prepared gadolinium alloy powder was added to the main phase magnetic powder at a mass ratio of 6 wt.% of the total amount of gadolinium alloy powder and main phase magnetic powder. The mixture was mixed evenly and shaped into a green blank by magnetic field orientation. Then it was placed in a high vacuum sintering furnace for high-temperature sintering and tempering treatment to finally obtain cerium-containing neodymium iron boron magnets.

[0065] The specific sintering and tempering process is as follows: vacuum degree is 1×10 -4 Pa, sintering temperature is 985℃, sintering holding time is 4h; first tempering temperature is 900℃, holding time is 2h; second tempering temperature is 600℃, holding time is 2h.

[0066] The prepared magnet was placed in an open-circuit PFM permanent magnet material measurement system, and the magnetic properties were measured as follows: B r =10.69kGs, H cj = 6.53 kOe, (BH) max =26.19MGOe.

[0067] Example 4

[0068] Preparation of main phase magnetic powder: Mix the various metal raw materials according to the ratio, and the mixture is rapidly solidified and smelted to obtain alloy castings. The alloy castings are hydrogen-crushed to obtain coarse powder, and the coarse powder is milled by air jet milling to obtain main phase magnetic powder.

[0069] Chemical formula of the main phase: [(PrNd)] 0.5 Ce 0.5 ] 29.5 B 0.98 Co 0.5 Zr 0.2 Al 0.1 Ga 0.1 Fe bal (mass ratio, defined as Ce50).

[0070] Preparation of gadolinium alloy powder: Mix the various metal raw materials according to the formula, and the mixture is rapidly solidified and smelted to obtain alloy castings. The alloy castings are hydrogen-crushed to obtain coarse powder, and the coarse powder is milled by air jet milling to obtain gadolinium alloy powder.

[0071] The chemical formula for gadolinium alloys is: Gd 40 Al 60 (Atomic ratio).

[0072] The prepared gadolinium alloy powder was added to the main phase magnetic powder at a mass ratio of 4 wt.% of the total amount of gadolinium alloy powder and main phase magnetic powder. The mixture was mixed evenly and shaped into a green blank by magnetic field orientation. Then it was placed in a high vacuum sintering furnace for high-temperature sintering and tempering treatment to finally obtain cerium-containing neodymium iron boron magnets.

[0073] The specific sintering and tempering process is as follows: vacuum degree is 1×10 -4 Pa, sintering temperature is 970℃, sintering holding time is 4h; first tempering temperature is 900℃, holding time is 2h; second tempering temperature is 580℃, holding time is 2h.

[0074] The prepared magnet was placed in an open-circuit PFM permanent magnet material measurement system, and the magnetic properties were measured as follows: B r =11.54kGs, H cj = 9.674 kOe, (BH) max =30.82MGOe.

[0075] Example 5

[0076] Preparation of main phase magnetic powder: Mix the various metal raw materials according to the ratio, and the mixture is rapidly solidified and smelted to obtain alloy castings. The alloy castings are hydrogen-crushed to obtain coarse powder, and the coarse powder is milled by air jet milling to obtain main phase magnetic powder.

[0077] Chemical formula of the main phase: [(PrNd)] 0.5 Ce 0.5 ] 29.5 B 0.98 Co 0.5 Zr 0.2 Al 0.1 Ga 0.1 Fe bal (mass ratio, defined as Ce50).

[0078] Gadolinium alloy powder is prepared by mixing various metal raw materials according to the formula, and the mixture is rapidly solidified and smelted to obtain alloy castings. The alloy castings are hydrogen-crushed to obtain coarse powder, and the coarse powder is milled by air jet milling to obtain gadolinium alloy powder.

[0079] The chemical formula for gadolinium alloys is: Gd 40 (Cu 0.5 Al 0.5 ) 60 (Atomic ratio).

[0080] The prepared gadolinium alloy powder was added to the main phase magnetic powder at a mass ratio of 4 wt.% of the total amount of gadolinium alloy powder and main phase magnetic powder. The mixture was mixed evenly and shaped into a green blank by magnetic field orientation. Then it was placed in a high vacuum sintering furnace for high-temperature sintering and tempering treatment to finally obtain cerium-containing neodymium iron boron magnets.

[0081] The specific sintering and tempering process is as follows: vacuum degree is 1×10-4 Pa, sintering temperature is 975℃, sintering holding time is 4h; first tempering temperature is 900℃, holding time is 2h; second tempering temperature is 590℃, holding time is 2h.

[0082] The prepared magnet was placed in an open-circuit PFM permanent magnet material measurement system, and the magnetic properties were measured as follows: B r =11.45kGs, H cj = 9.103 kOe, (BH) max =28.67MGOe.

[0083] Example 6

[0084] Preparation of main phase magnetic powder: Mix the various metal raw materials according to the ratio, and the mixture is rapidly solidified and smelted to obtain alloy castings. The alloy castings are hydrogen-crushed to obtain coarse powder, and the coarse powder is milled by air jet milling to obtain main phase magnetic powder.

[0085] Chemical formula of the main phase: [(PrNd)] 0.5 Ce 0.5 ] 29.5 B 0.98 Co 0.5 Zr 0.2 Al 0.1 Ga 0.1 Fe bal (mass ratio, defined as Ce50).

[0086] Gadolinium alloy composition: Mix the various metal raw materials according to the formula, and the mixture is rapidly solidified and smelted to obtain alloy castings. The alloy castings are hydrogen-crushed to obtain coarse powder, and the coarse powder is milled by air jet milling to obtain gadolinium alloy powder.

[0087] The chemical formula for gadolinium alloys is: Gd 40 Ga 60 (Atomic ratio).

[0088] The prepared gadolinium alloy powder was added to the main phase magnetic powder at a mass ratio of 4 wt.% of the total amount of gadolinium alloy powder and main phase magnetic powder. The mixture was mixed evenly and shaped into a green blank by magnetic field orientation. Then it was placed in a high vacuum sintering furnace for high-temperature sintering and tempering treatment to finally obtain cerium-containing neodymium iron boron magnets.

[0089] The specific sintering and tempering process is as follows: vacuum degree is 1×10 -4 Pa, sintering temperature is 965℃, sintering holding time is 4h; first tempering temperature is 900℃, holding time is 2h; second tempering temperature is 580℃, holding time is 2h.

[0090] The prepared magnet was placed in an open-circuit PFM permanent magnet material measurement system, and the magnetic properties were measured as follows: B r =11.58kGs, H cj= 10.648 kOe, (BH) max =31.23MGOe.

[0091] Example 7

[0092] Preparation of main phase magnetic powder: Mix the various metal raw materials according to the ratio, and the mixture is rapidly solidified and smelted to obtain alloy castings. The alloy castings are hydrogen-crushed to obtain coarse powder, and the coarse powder is milled by air jet milling to obtain main phase magnetic powder.

[0093] Chemical formula of the main phase: [(PrNd)] 0.5 Ce 0.5 ] 29.5 B 0.98 Co 0.5 Zr 0.2 Al 0.1 Ga 0.1 Fe bal (mass ratio, defined as Ce50).

[0094] Preparation of gadolinium alloy powder: Mix the various metal raw materials according to the formula, and the mixture is rapidly solidified and smelted to obtain alloy castings. The alloy castings are hydrogen-crushed to obtain coarse powder, and the coarse powder is milled by air jet milling to obtain gadolinium alloy powder.

[0095] The chemical formula for gadolinium alloys is: Gd 40 (Cu 0.5 Ga 0.5 ) 60 (Atomic ratio).

[0096] The prepared gadolinium alloy powder was added to the main phase magnetic powder at a mass ratio of 4 wt.% of the total amount of gadolinium alloy powder and main phase magnetic powder. The mixture was mixed evenly and shaped into a green blank by magnetic field orientation. Then it was placed in a high vacuum sintering furnace for high-temperature sintering and tempering treatment to finally obtain cerium-containing neodymium iron boron magnets.

[0097] The specific sintering and tempering process is as follows: vacuum degree is 1×10 -4 Pa, sintering temperature is 975℃, sintering holding time is 4h; first tempering temperature is 900℃, holding time is 2h; second tempering temperature is 590℃, holding time is 2h.

[0098] The prepared magnet was placed in an open-circuit PFM permanent magnet material measurement system, and the magnetic properties were measured as follows: B r =11.56kGs, H cj = 9.732 kOe, (BH) max =30.69MGOe.

[0099] Comparative Example 1

[0100] Preparation of main phase magnetic powder: Mix the various metal raw materials according to the ratio, and the mixture is rapidly solidified and smelted to obtain alloy castings. The alloy castings are hydrogen-crushed to obtain coarse powder, and the coarse powder is milled by air jet milling to obtain main phase magnetic powder.

[0101] Chemical formula of the main phase: [(PrNd)] 0.5 Ce 0.5 ] 29.5 B 0.98 Co 0.5 Zr 0.2 Al 0.1 Ga 0.1 Fe bal (mass ratio, defined as Ce50).

[0102] The main phase Ce50 magnetic powder is oriented and formed into a green blank through a magnetic field, and then placed in a high-vacuum sintering furnace for high-temperature sintering and tempering treatment to finally obtain cerium-containing neodymium iron boron magnets.

[0103] The specific sintering and tempering process is as follows: vacuum degree is 1×10 -4 Pa, sintering temperature is 1010℃, sintering holding time is 4h; first-stage tempering temperature is 900℃, holding time is 2h; second-stage tempering temperature is 500℃, holding time is 2h.

[0104] The prepared magnet was placed in an open-circuit PFM permanent magnet material measurement system, and the magnetic properties were measured as follows: B r =12.12kGs, H cj = 4.15 kOe, (BH) max =27.51MGOe.

[0105] Comparative Example 2

[0106] Preparation of main phase magnetic powder: Mix the various metal raw materials according to the ratio, and the mixture is rapidly solidified and smelted to obtain alloy castings. The alloy castings are hydrogen-crushed to obtain coarse powder, and the coarse powder is milled by air jet milling to obtain main phase magnetic powder.

[0107] Chemical formula of the main phase: [(PrNd)] 0.5 Ce 0.5 ] 29.5 B 0.98 Co 0.5 Zr 0.2 Al 0.1 Ga 0.1 Fe bal (mass ratio, defined as Ce50).

[0108] Preparation of Nd: copper alloy powder: Mix the various metal raw materials according to the formula, the mixture is rapidly solidified and smelted to obtain alloy castings, the alloy castings are hydrogen-crushed to obtain coarse powder, and the coarse powder is air-jet milled to obtain Nd: copper alloy powder.

[0109] The chemical formula of neodymium copper alloy: Nd 40 Cu 60 (Atomic ratio).

[0110] The prepared gadolinium alloy powder was added to the main phase magnetic powder at a mass ratio of 4 wt.% of the total amount of neodymium copper alloy powder and main phase magnetic powder. The mixture was mixed evenly and shaped into a green blank by magnetic field orientation. Then it was placed in a high vacuum sintering furnace for high-temperature sintering and tempering treatment to finally obtain cerium-containing neodymium iron boron magnets.

[0111] The specific sintering and tempering process is as follows: vacuum degree is 1×10 -4 Pa, sintering temperature is 985℃, sintering holding time is 4h; first tempering temperature is 900℃, holding time is 2h; second tempering temperature is 600℃, holding time is 2h.

[0112] The prepared magnet was placed in an open-circuit PFM permanent magnet material measurement system, and the magnetic properties were measured as follows: B r =11.31kGs, H cj = 5.83 kOe, (BH) max =27.52MGOe.

[0113] Table 1 shows the room temperature magnetic properties of the samples obtained in Examples 1-7 and Comparative Examples 1-2.

[0114] Table 1. Room temperature magnetic properties of the samples

[0115]

[0116] Comparative Example 1 shows the performance of the original Ce50 magnet without Gd-Cu, and it can be found that its coercivity is less than that of magnets with GdCu, GdAl, GdGa, GdCuAl and GdCuGa.

[0117] Comparative Example 2 is a magnet with 4 wt.% Nd-Cu added. Although its coercivity is improved to some extent, the improvement effect is far less than that of 4 wt.% GdCu, GdAl, GdGa, GdCuAl and GdCuGa on the coercivity of the magnet.

[0118] As can be seen from Examples 1-3 with added Gd-Cu, the coercivity of the NdCe-Fe-B magnet continuously increases with the increase of Gd-Cu alloy content, but its remanent magnetization decreases, resulting in slight fluctuations in the maximum energy product of the magnet. Adding 4 wt.% gadolinium alloy yields the best magnetic properties. In Examples 2, 4, and 6, after adding 4 wt.% GdCu, GdAl, and GdGa, the GdGa alloy has the greatest effect on improving coercivity. When the Al and Ga portions in GdAl and GdGa are replaced by Cu to form GdCuAl and GdCuGa alloys (i.e., Examples 5 and 7), the effect on enhancing coercivity decreases, indicating that the binary alloy of Gd has a relatively good effect on improving magnet performance.

[0119] As shown in the table above, the coercivity of the original Ce50 magnet in Comparative Example 1 was only 4.151 kOe. The coercivity of Examples 1-7 was greater than that of Comparative Example 1, and the coercivity was increased by more than 1.2 times. In particular, in Examples 2 and Examples 4-7, Gd-Cu, Gd-Al, Gd-Cu-Al, Gd-Ga and Gd-Cu-Ga were added at 4 wt.%, and the coercivity of the magnets could reach 9 kOe to 10 kOe or more, which was more than twice that of Comparative Example 1.

[0120] Figure 1 These are the X-ray photoelectron spectra of Examples 2 and Comparative Examples 1-2. Figure a shows the total XPS spectrum of Examples 2 and Comparative Examples 1-2 in the energy range of 870 eV to 920 eV; Figure b shows the XPS fitted spectrum of Comparative Example 1; Figure c shows the XPS fitted spectrum of Comparative Example 1; and Figure d shows the XPS fitted spectrum of Example 2. In the figures, Ce 3d 3 / 2 and Ce 3d 5 / 2 This represents two different energy levels in the 3d orbital of Ce, indicating that Ce has two valence states: +3 and +4, within the magnet.

[0121] Table 2 shows the average valence of cerium in the samples obtained in Examples 1-7 and Comparative Examples 1-2. The average valence was determined by... Figure 1 Ce in (b), (c) and (d) 3+ and Ce 4+ It is calculated from the area ratio enclosed by the ion spectrum.

[0122] Table 2 shows the average valence of cerium in the samples.

[0123] sample sample Average valence Example 1 Ce50+2%GdCu +3.24 Example 2 Ce50+4%GdCu +3.18 Example 3 Ce50+6%GdCu +3.20 Example 4 Ce50+4%GdAl +3.16 Example 5 Ce50+4%GdCuAl +3.19 Example 6 Ce50+4%GdGa +3.10 Example 7 Ce50+4%GdCuGa +3.13 Comparative Example 1 Ce50 +3.25 Comparative Example 2 Ce50+4%NdCu +3.21

[0124] The table above shows that the valence of cerium in Comparative Examples 1 and 2 is basically the same, indicating that Nd-Cu has little effect on regulating the valence of cerium in cerium-containing NdFeB magnets.

[0125] However, compared to Comparative Example 1 (+3.25 valence), the valence of cerium in Examples 1-7 was lower; especially in Examples 2-7, the valence of cerium decreased to +3.20 and below, clearly biased towards +3, indicating that the addition of gadolinium alloy promoted the shift of cerium from +4 to +3 valence, ultimately improving the coercivity of the magnet. Compared to Examples 1 and 3, Example 2 is superior, with its average valence reduced to +3.18, more biased towards +3.

[0126] The description of this invention is given for illustrative and descriptive purposes only and is not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described in order to better illustrate the principles and practical application of the invention and to enable those skilled in the art to understand the invention and to design various embodiments with various modifications suitable for a particular purpose.

Claims

1. A method for controlling the valence of cerium in a cerium-containing neodymium iron boron magnet, characterized in that, include: Cerium-containing NdFeB magnets are obtained by incorporating gadolinium alloy powder into cerium-containing NdFeB main phase magnetic powder, followed by magnetic field orientation molding, sintering, and tempering heat treatment. During the heat treatment process, gadolinium diffuses into the main phase grains, causing the valence of cerium in the main phase grains to shift to a lower valence state. According to X-ray photoelectron spectroscopy, the average valence of cerium in the magnet is reduced to below +3.25, thus achieving the control of the valence of cerium. The amount of gadolinium alloy incorporated is 2 wt.% to 15 wt.% of the total amount of gadolinium alloy powder and cerium-containing NdFeB main phase magnetic powder. The gadolinium alloy has a composition formula of Gd x M 100-x ; wherein 40≤x<100; M is one or more selected from Cu, Fe, Al, Ga, Co, Mn, V, Ti. The chemical composition of the cerium-containing NdFeB main phase is as shown in Formula I: (RE 1-x Ce x ) α B β M γ N δ Fe 100-α-β-γ-δ Formula I; Where x is a mass percentage, and 0 < x ≤ 1; in terms of mass percentage, 25 ≤ α ≤ 35, 0.9 ≤ β ≤ 1.2, 0 ≤ γ ≤ 10, 0 ≤ δ ≤ 10; RE is Nd, or a combination of Nd and one or more selected from La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y and Sc; M is selected from one or more of Co, Ni, Mn, Cr, Cu, Zn, Ti, V, Zr and Nb; N is selected from one or more of Ga, Al, Sn and Ge.

2. The method according to claim 1, characterized in that, The amount of gadolinium alloy incorporated is 4 wt.% to 6 wt.% of the total amount of gadolinium alloy powder and cerium-containing neodymium iron boron main phase magnetic powder; when the gadolinium alloy is Gd-Cu, Gd-Al, Gd-Cu-Al, Gd-Ga, or Gd-Cu-Ga alloy, the average oxidation state of cerium in the magnet is reduced to no higher than +3.20, as measured by X-ray photoelectron spectroscopy.

3. The method according to claim 1, characterized in that, The cerium-containing NdFeB magnet obtained by sintering and tempering heat treatment has a coercivity that is more than 1.2 times higher than that of the original magnet. The original magnet refers to the magnet obtained by directly oriented and heat-treated the cerium-containing NdFeB main phase magnetic powder without adding gadolinium alloy powder.

4. The method according to claim 1, characterized in that, The sintering temperature is 900℃~1200℃, the time is 1h~10h, and the vacuum degree is 1×10 -4 Pa ~ 1×10 -2 Pa; The tempering process employs a two-stage tempering process: the first-stage tempering temperature is 800℃~1000℃, and the time is 1 h~6 h; the second-stage tempering temperature is 400℃~650℃, and the time is 1 h~6 h.

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