WO2023167632A1

WO2023167632A1 - Compounds for composite rare-earth bonded magnets and methods for producing the same

Info

Publication number: WO2023167632A1
Application number: PCT/SG2022/050113
Authority: WO
Inventors: Zhisan Han; Juo Yan Calvin TAN; Zhongmin Chen
Original assignee: Neo Performance Materials (Singapore) Pte. Ltd.
Priority date: 2022-03-04
Filing date: 2022-03-04
Publication date: 2023-09-07

Abstract

The present disclosure refers to a method of producing a compound for a composite rare-earth bonded magnet, the method comprising preparing a mixture of RE-Fe-M-B and Sm-Fe-N magnetic powders, surfactant and binder, mixing the mixture with stearate and dispersant, and evaporating the dispersant, thereby obtaining the compound for a composite rare-earth bonded magnet, wherein RE is one or more rare earth metals, Fe is iron, M is absent or one or more metals, B is boron, Sm is samarium, and N is nitrogen. The present disclosure also refers to a composite rare- earth bonded magnet comprising RE-Fe-M-B magnetic powder, Sm-Fe-N magnetic powder, stearate and a binder.

Description

Title of Invention: Compounds for Composite Rare-Earth Bonded Magnets and Methods for Producing the Same

Technical Field

The present disclosure generally refers to a method for producing a compound for composite rare-earth bonded magnets. The present disclosure also relates to compounds for composite rare-earth bonded magnets and composite rare-earth bonded magnets.

Background Art

Rare-earth bonded magnets made from rare-earth magnetic powders are used in numerous applications, including computer hardware, automobiles, consumer electronics, motors and household appliances. With the progress of technology, it is becoming increasingly necessary to produce magnets of improved magnetic performance. It is also becoming essential to have an efficient and developed process by which these rare-earth bonded magnets are produced with improved magnetic performance and desirable characteristics.

Common processing methods for bonded magnets include compression molding (CM), injection molding (IM), extrusion and calendaring.

Compression molded magnets are commonly made by mixing raw magnetic powders with a polymer binder and then further compressing the resultant mixed compound in a press mold, where heat and pressure may be required during the process. The rare-earth bonded magnets obtained from compression molding generally exhibit superior magnetic properties when compared with injection molded magnets due to their higher density.

However, there are several problems and challenges when using current compression molding processes to produce bonded magnets. Firstly, there is a powder feeding issue where the compound magnetic powder cannot be loaded efficiently and effectively into a mold cavity due to poor flowability of the compound. This eventually leads to wastage of the compound and more labour and processing time as the compound and polymer binder need to be carefully poured into the mold cavity to fill the cavity precisely. This poor flowability also affects the shape that can be made for the eventual rare-earth bonded magnet as the poor flowability results in poorer suitability for complex mold designs and shapes as there is limited flow of material within the cavity which makes it difficult to eliminate voids, air traps and knit lines when producing more intricate magnet parts. Additionally, this poor flowability results in variations in the weight of the compound which is fed into the cavity which may lead to a final bonded magnet product with poorer dimensional stability. This in turn may cause the final bonded magnet product to not be able to meet the requirements of precision applications.

Secondly, high pressure is typically required to achieve acceptable magnet density. This eventually results in further challenges in the materials and shapes used when creating the mould design as the design and materials required need to be able to withstand high pressure requirements. As a result, material cost may have to increase. In addition, the lifespan of the magnet mold may be shortened due to the use of high pressure, which leads to higher operational (labour) and material cost.

There is therefore a need for better methods for bonded magnets that can overcome, or at least ameliorate, one or more of the disadvantages described above.

Summary of Invention

In one aspect, the present disclosure refers to a method of producing a compound for a composite rare-earth bonded magnet, comprising:

(a) preparing a mixture of RE-Fe-M-B magnetic powder, Sm-Fe-N magnetic powder, surfactant and binder;

(b) mixing the mixture of step (a) with stearate and dispersant;

(c) evaporating the dispersant from the mixture of step (b), thereby obtaining said compound, wherein RE is one or more rare earth metals, Fe is iron, M is absent or one or more metals, B is boron, Sm is samarium, and N is nitrogen.

In another aspect, the present disclosure refers to a composite rare-earth bonded magnet, comprising:

(i) RE-Fe-M-B magnetic powder, wherein RE is one or more rare earth metals,

Fe is iron,

M is absent or one or more metals, and

B is boron;

(ii) Sm-Fe-N magnetic powder, wherein Sm is samarium

Fe is iron, and N is nitrogen;

(iii) stearate; and

(iv) binder.

In a further aspect, the present disclosure refers to a composite rare-earth bonded magnet disclosed herein obtained by the method disclosed herein.

Advantageously, the produced compounds have improved flowability. The produced compounds also advantageously require less pressure to achieve similar magnet density in a bonded magnet. Further advantageously, bonded magnets produced from these compounds display superior aging performance.

Further advantageously, with the above improved chemical, physical, mechanical, and magnetic properties, the material cost of the disclosed composite rare-earth bonded magnets may be lower and have longer lifetime (shelf life).

Also advantageously, the method disclosed herein may be a cost efficient method and may produce a composite rare-earth bonded magnet with high-power and high efficiency.

Definitions

Unless otherwise defined herein, scientific and technical terms used in this application shall have the meanings that are commonly understood by those of ordinary skill in the art. Generally, nomenclature used in connection with, and techniques of, chemistry described herein, are those well-known and commonly used in the art.

Unless the context requires otherwise or specifically stated to the contrary, integers, steps, or elements of the invention recited herein as singular integers, steps or elements clearly encompass both singular and plural forms of the recited integers, steps or elements.

The term “rare earth metal” as used herein refers to a rare earth element and may be cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb) and yttrium (Y).

The terms “flux aging loss” or “aging performance” or “aging loss’ as used herein refers to the loss of magnetic flux of a magnet after being exposed at a specific temperature and for a specific period of time. The word “substantially” does not exclude “completely” e.g. a composition which is “substantially free” from Y may be completely free from Y. Where necessary, the word “substantially” may be omitted from the definition of the invention.

Unless specified otherwise, the terms "comprising" and "comprise", and grammatical variants thereof, are intended to represent "open" or "inclusive" language such that they include recited elements but also permit inclusion of additional, unrecited elements.

As used herein, the term "about", in the context of concentrations of components of the formulations, typically means +/- 5% of the stated value, more typically +/- 4% of the stated value, more typically +/- 3% of the stated value, more typically, +/- 2% of the stated value, even more typically +/- 1% of the stated value, and even more typically +/- 0.5% of the stated value.

Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

Certain embodiments may also be described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the disclosure. This includes the generic description of the embodiments with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.

Brief Description of Drawings

The accompanying drawings illustrate disclosed embodiments and serve to explain the principles of the disclosed embodiments. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

Figure 1

Figure 1 is a schematic depicting the method of producing a compound for a composite rare-earth bonded magnet according to the present invention. Figure 2

Figure 2 is a diagram depicting how fine magnetic powder falls within the spaces or gaps between larger magnetic powders when both are present in a mixture.

Figure 3A

Figure 3A is a series of scanning electron microscope (SEM) images of a compound of Sample 2 of Example 3. Figure 3A is a high magnification SEM of Figure 7(c).

Figure 3B

Figure 3B is a series of SEM images of a compound of Sample 3 of Example3. Figure 3B is a high magnification SEM of Figure 7(d).

Figures 4A, 4B and 4C

Figures 4A, 4B and 4C are a series of graphs showing the density (Figure 4A), alignment (Figure 4B) and remanence (Br) (Figure 4C) against pressure for Samples 1 to 3 using MQA-3.

Figures 5A, 5B, and 5C

Figures 5A, 5B, and 5C are a series of graphs showing the density (Figure 5A), alignment (Figure 5B), and remanence Br (Figure 5C) against mold temperature for Sample 3 using MQA-3.

Figures 6A and 6B

Figures 6A and 6B are graphs showing flux loss at 120°C aging (total flux loss % against time, hour) for Sample 1 (MQA-1, MQA-2, MQA-3, MQA-4) compared with Sample 3 (MQA-1, MQA-2, MQA-3, MQA-4) at 165°C and 1.0 Tesla.

Figure 7

Figure 7 is a series of SEM images of MQA-3 magnetic powder showing the particle shape of the magnetic powder after different treatments (Figures 7(a), 7(b), 7(c), and 7(d)) compared with HDDR magnetic powder after different treatments (Figures 7(e), 7(f), and 7(g)).

Figure 8

Figure 8 is a graph depicting the percentages of the particles (% chan) against the size of the particles (pm) of the Samples in Example 7.

Detailed Disclosure of Selected Drawings

Figure 1 shows a general schematic of a method of producing a compound for a composite rare-earth bonded magnet of the present invention. Surface Treatment Process (W)

Anisotropic magnetic powder ( 1) is added to a surfactant (2) and the resulting mixture is further mixed (A).

Compounding Process (X)

A binder (3) is added to the mixture of (1) and (2), and the mixture undergoes further mixing (B), kneading (C), and sieving (D).

Particle Modification Process (Y)

The mixture is then blended (E) in a V-blender together with stearate and dispersant.

Compression Molding Process (Z)

After blending (E), the resulting compound undergoes 2-step compaction (F) and curing (G) to obtain a compound for a composite rare-earth bonded magnet.

Detailed Disclosure of Embodiments

The present disclosure relates to a method of producing a compound for a composite rare-earth bonded magnet, the method generally comprising preparing a mixture of magnetic powders (e.g., RE-Fe-M-B and Sm-Fe-N magnetic powders), surfactant and binder, followed by mixing the mixture with stearate and dispersant, and then evaporating the dispersant, thereby obtaining the compound for a composite rare-earth bonded magnet. The present disclosure also refers to a compound comprising rare earth magnetic powders, stearate and binder, and composite rare-earth bonded magnets comprising or formed from such compounds. The disclosed compounds may comprise rare earth magnetic powders, stearate, and binder, wherein the dispersant added during the method of producing said compounds was evaporated off. While not present in the final product, the addition of the dispersant during the production of the compounds advantageously dissolves the binder which allows for more even distribution of smaller rare earth powders around larger rare earth powders. The more even distribution of the smaller rare earth powders around the larger rare earth powders advantageously leads to improved flowability of the compound which is useful when pouring the powders into a compression mold for forming a bonded magnet.

The present invention relates to a method of producing a compound for a composite rare-earth bonded magnet, comprising: (a) preparing a mixture of RE-Fe-M-B magnetic powder, Sm-Fe-N magnetic powder, surfactant and binder;

(b) mixing the mixture of step (a) with stearate and dispersant;

The present disclosure also a compound for a composite rare-earth bonded magnet, comprising:

(i) RE-Fe-M-B magnetic powder, wherein RE is one or more rare earth metals,

Fe is iron,

M is absent or one or more metals, and

B is boron;

(ii) Sm-Fe-N magnetic powder, wherein Sm is samarium

Fe is iron, and

N is nitrogen;

(iii) stearate; and

(iv) binder.

The present disclosure further provides a composite rare-earth bonded magnet, wherein the magnet comprises compounds comprising:

(v) RE-Fe-M-B magnetic powder, wherein RE is one or more rare earth metals,

Fe is iron,

M is absent or one or more metals, and

B is boron;

(vi) Sm-Fe-N magnetic powder, wherein Sm is samarium

Fe is iron, and

N is nitrogen;

(vii) stearate; and (viii) binder.

RE may be one or more rare earth metals selected from the group consisting of lanthanum (La), cerium (Ce), neodymium (Nd), praseodymium (Pr), yttrium (Y), gadolinium (Gd), terbium (Tb), dysoprium (Dy), holmium (Ho), and ytterbium (Yb).

M may be absent, or one or more metals selected from the group consisting of zirconium (Zr), niobium (Nb), molybdenum (Mo), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), hafnium (Hf), tantalum (Ta), tungsten (W), cobalt (Co), copper (Cu), gallium (Ga) and aluminum (Al).

Step (a) in the disclosed method may further comprise step (ai) preparing a mixture of RE-Fe-M-B magnetic powder, Sm-Fe-N magnetic powder, surfactant; and step (aii) blending the mixture of step (ai) with binder.

Step (b) may further comprise dissolving the binder with the dispersant. Advantageously, this allows for more even distribution of smaller rare earth powders around larger rare earth powders. The more even distribution of the smaller rare earth powders around the larger rare earth powders advantageously leads to improved flowability of the compound which is useful when pouring the powders into a compression mold for forming a bonded magnet.

The method may further comprise step (d) sieving the compound of step (c); and step (e) subjecting the sieved compound of step (d) to compression molding to obtain a composite rare-earth bonded magnet.

The surfactant in the disclosed method or compound may be a silane or titanate. The surfactant may be either chemically or physically adsorbed to the surface of the magnet powder particles, to aid the rotation of the magnet particles to align with the magnetic field during compression (e.g. warm compaction pressing) in the method of producing the magnet. In addition, the surfactant helps to reduce the interparticle friction of the magnetic particles during warm compaction (e.g. compression) and reduce the friction between the magnet and the compressor wall during compaction and ejection process.

Step (e) may be a warm compaction (second step) step. The mold temperature may be in the range of about 80 °C to about 400°C, about 100 °C to about 400 °C, about 120 °C to about 400 °C, about 140 °C to about 400 °C, about 160 °C to about 400 °C, about 180 °C to about 400 °C, about 200 °C to about 400 °C, about 220 °C to about 400 °C, about 240 °C to about 400 °C, about 260 °C to about 400 °C, about 280 °C to about 400 °C, about 300 °C to about 400 °C, about 320 °C to about 400 °C, about 340 °C to about 400 °C, about 360 °C to about 400 °C, about 380 °C to about 400 °C, about 80 °C to about 380 °C, about 80 °C to about 360 °C, about 80 °C to about 340 °C, about 80 °C to about 320 °C, about 80 °C to about 300 °C, about 80 °C to about 320 °C, about 80 °C to about 300 °C, about 80 °C to about 280 °C, about 80 °C to about 260 °C, about 80 °C to about 240 °C, about 80 °C to about 220 °C, about 80 °C to about 200 °C, about 80 °C to about 180 °C, about 80 °C to about 160 °C, about 80 °C to about 140 °C, about 80 °C to about 120 °C, about 80 °C to about 100 °C, or about 80 °C, about 100 °C, about 120 °C, about 140 °C, about 160 °C, about 180 °C, about 200 °C, about 220 °C, about 240 °C, about 260 °C, about 280 °C, about 300 °C, about 320 °C, about 340 °C, about 360 °C, about 380 °C, about 400 °C, or any value or range therebetween.

The surfactant added in the disclosed method or compound may be in the range of about 0.01 wt % to about 5 wt %, about 0.1 wt % to about 5 wt %, about 0.5 wt % to about 5 wt %, about 1 wt % to about 5 wt %, about 1.5 wt % to about 5 wt %, about 2 wt % to about 5 wt %, about 2.5 wt % to about 5 wt %, about 3 wt % to about 5 wt %, about 3.5 wt % to about 5 wt %, about 4 wt % to about 5 wt %, about 4.5 wt % to about 5 wt %, about 0.01 wt % to about 4.5 wt %, about 0.01 wt % to about 4 wt %, about 0.01 wt % to about 3.5 wt %, about 0.01 wt % to about 3 wt %, about 0.01 wt % to about 2.5 wt %, about 0.01 wt % to about 2 wt %, about 0.01 wt % to about 1.5 wt %, about 0.01 wt % to about 1 wt %, about 0.01 wt % to about 0.5 wt %, about 0.01 wt % to about 0.1 wt %, about 0.01 wt %, about 0.05 wt %, about 0.1 wt %, about 0.15 wt %, about 0.2 wt %, about 0.25 wt %, about 0.3 wt %, about 0.35 wt %, about 0.4 wt %, about 0.45 wt %, about 0.5 wt %, about 0.55 wt %, about 0.6 wt %, about 0.65 wt %, about 0.7 wt %, about 0.75 wt %, about 0.8 wt %, about 0.85 wt %, about 0.9 wt %, about 1 wt %, about 1.05 wt %, about 1.1 wt %, about 1.15 wt %, about 1.2 wt %, about 1.25 wt %, about 1.3 wt %, about 1.35 wt %, about 1.4 wt %, about 1.45 wt %, about 1.5 wt %, about 1.55 wt %, about 1.6 wt %, about 1.65 wt %, about 1.7 wt %, about 1.75 wt %, about 1.8 wt %, about 1.85 wt %, about 1.9 wt %, about 1.95 wt %, about 2 wt %, about 2.05 wt %, about 2.1 wt %, about 2.15 wt %, about 2.2 wt %, about 2.25 wt %, about 2.3 wt %, about 2.35 wt %, about 2.4 wt %, about 2.45 wt %, about 2.5 wt %, about 2.55 wt %, about 2.6 wt %, about 2.65 wt %, about 2.7 wt %, about 2.75 wt %, about 2.8 wt %, about 2.85 wt %, about 2.9 wt %, about 2.95 wt %, about 3 wt %, about 3.05 wt %, about 3.1 wt %, about 3.15 wt %, about 3.2 wt %, about 3.25 wt %, about 3.3 wt %, about 3.35 wt %, about 3.4 wt %, about 3.45 wt %, about 3.5 wt %, about 3.55 wt %, about 3.6 wt %, about 3.65 wt %, about 3.7 wt %, about 3.75 wt %, about 3.8 wt %, about 3.85 wt %, about 3.9 wt %, about 3.95 wt %, about 4 wt %, about 4.05 wt %, about 4. 1 wt %, about 4. 15 wt %, about 4.2 wt %, about 4.25 wt %, about 4.3 wt %, about 4.35 wt %, about 4.4 wt %, about 4.45 wt %, about 4.5 wt %, about 4.55 wt %, about 4.6 wt %, about 4.65 wt %, about 4.7 wt %, about 4.75 wt %, about 4.8 wt %, about 4.85 wt %, about 4.9 wt %, about 4.95 wt %, about 5 wt %, or any value or range therebetween.

The binder in the disclosed method or compound may be a resin or thermoset epoxy, a thermoplastic (such as nylon or polyphenylene sulfide PPS), elastomeric (rubber) polymer, or any mixture thereof.

The stearate in the disclosed method or compound may be selected from the group consisting of metal stearate, calcium stearate, lithium stearate, zinc stearate, stearate acid, ethyl stearate, and mixtures thereof. The metal stearate may be zinc stearate, aluminium stearate, barium stearate, calcium stearate, magnesium stearate, sodium stearate, or any mixture thereof.

The amount of stearate used in the disclosed method or in the disclosed compound may be in the range of about 0.01 wt% to about 1 wt %, about 0.05 wt% to about 1 wt %, about 0. 1 wt% to about 1 wt %, about 0.15 wt% to about 1 wt %, about 0.2 wt% to about 1 wt %, about 0.25 wt% to about 1 wt %, about 0.3 wt% to about 1 wt %, about 0.35 wt% to about 1 wt %, about 0.4 wt% to about 1 wt %, about 0.45 wt% to about 1 wt %, about 0.5 wt% to about 1 wt %, about 0.55 wt% to about 1 wt %, about 0.6 wt% to about 1 wt %, about 0.65 wt% to about 1 wt %, about 0.7 wt% to about 1 wt %, about 0.75 wt% to about 1 wt %, about 0.8 wt% to about 1 wt %, about 0.85 wt% to about 1 wt %, about 0.9 wt% to about 1 wt %, about 0.95 wt% to about 1 wt %, about 0.01 wt% to about 0.95 wt %, about 0.01 wt% to about 0.9 wt %, about 0.01 wt% to about 0.85 wt %, about 0.01 wt% to about 0.8 wt %, about 0.01 wt% to about 0.75 wt %, about 0.01 wt%to about 0.7 wt %, about 0.01 wt%to about 0.65 wt %, about 0.01 wt% to about 0.6 wt %, about 0.01 wt% to about 0.55 wt %, about 0.01 wt% to about 0.5 wt %, about 0.01 wt% to about 0.45 wt %, about 0.01 wt% to about 0.4 wt %, about 0.01 wt% to about 0.35 wt %, about 0.01 wt% to about 0.3 wt %, about 0.01 wt% to about 0.25 wt %, about 0.01 wt% to about 0.2 wt %, about 0.01 wt% to about 0.15 wt %, about 0.01 wt% to about 0.1 wt %, about 0.01 wt% to about 0.05 wt %, about 0.01 wt%, about 0.05 wt%, about 0.1 wt%, about 0.15 wt%, about 0.2 wt%, about 0.25 wt%, about 0.3 wt%, about 0.35 wt%, about 0.4 wt%, about 0.45 wt%, about 0.5 wt%, about 0.55 wt%, about 0.6 wt%, about 0.65 wt%, about 0.7 wt%, about 0.75 wt%, about 0.8 wt%, about 0.85 wt%, about 0.9 wt%, about 0.95 wt%, about 1 wt%, or any value or range therein. The dispersant in the disclosed method may be a ketone, alcohol, water, 2-propanone (acetone), methyl ethyl ketone, methyl isobutyl ketone, 2-butanone, 2-pentanone, 2-hexanone, 2-heptanone, 2-octanone, 2-nonanone, 2- decanone, 3-pentanone, 3-hexanone, 3-heptanone, 3-octanone, 3-nonanone, 3-decanone, methyl phenyl ketone, diphenyl ketone, methyl isopropyl ketone, methyl n-amyl ketone, diacetone alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, n-propyl alcohol, methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, phenol, methylpropanol, methyl-butanol, dimethyl-propanol, cyclohexanol, phenyl methanol, n-butyl acetate, t-butyl acetate, propylene glycol monomethyl ether, propylene glycol mono n-butyl ether, ethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, ethylene glycol, monopropyl ether, xylene, propylene glycol, monomethyl ether acetate, ethyl 3-ethoxy propionate, dimethyl formamide, cyclohexanone, toluene, aromatic 100, or any mixture thereof.

The amount of dispersant used in the disclosed method may be in the range of about 0.1 wt% to about 5 wt%, about 0.5 wt% to about 5 wt%, about 1 wt% to about 5 wt%, about 1.5 wt% to about 5 wt%, about 2 wt% to about 5 wt%, about 2.5 wt% to about 5 wt%, about 3 wt% to about 5 wt%, about 3.5 wt% to about 5 wt%, about 4 wt% to about 5 wt%, about 4.5 wt% to about 5 wt%, about 0.1 wt% to about 4.5 wt%, about 0.1 wt% to about 4 wt%, about 0.1 wt% to about 3.5 wt%, about 0.1 wt% to about 3 wt%, about 0.1 wt% to about 2.5 wt%, about 0.1 wt% to about 2 wt%, about 0.1 wt% to about 1.5 wt%, about 0. 1 wt% to about 1 wt%, about 0.1 wt% to about 0.5 wt%, or about 0.1 wt%, about 0.5 wt%, about 1 wt%, about 1.5 wt%, about 2 wt%, about 2.5 wt%, about 3 wt%, about 3.5 wt%, about 4 wt%, about 4.5 wt%, about 5 wt%, or any value or range therebetween.

In step (c) of the disclosed method, evaporation of the dispersant from the mixture of step (b) may be performed to obtain the compound. Evaporation may occur at room temperature (for example about 25 °C, about 26 °C, about 27 °C, about 28 °C, about 29 °C, about 30 °C), or the mixture may be heated.

Step (c) of the disclosed method may further comprise heating the mixture of step (b) at a temperature of about 50 °C to about 100 °C, about 55 °C to about 100 °C, about 60 °C to about 100 °C, about 65 °C to about 100 °C, about 70 °C to about 100 °C, about 75 °C to about 100 °C, about 80 °C to about 100 °C, about 85 °C to about 100 °C, about 90 °C to about 100 °C, about 95 °C to about 100 °C, about 50 °C to about 95 °C, about 50 °C to about 90 °C, about 50 °C to about 85 °C, about 50 °C to about 80 °C, about 50 °C to about 75 °C, about 50 °C to about 70 °C, about 50 °C to about 65 °C, about 50 °C to about 60 °C, about 50 °C to about 55 °C, about 50 °C , about 55 °C , about 60 °C, about 65 °C, about 70 °C, about 75 °C, about 80 °C, about 85 °C, about 90 °C, about 95 °C, about 100 °C , or any value or range therebetween.

In the disclosed method, prior to step (a), RE-Fe-M-B magnetic powder may be produced by: (i) melting an RE-Fe-M-B alloy and ejecting it onto a rotating wheel to quench the melt and obtain an alloy ribbon;

(ii) crushing the alloy ribbon to form an alloy powder;

(iii) subjecting the alloy powder to hot deformation; and

(iv) crushing the product of step (iii) to form the RE-Fe-M-B magnetic powder.

In step (i), a RE-M-Fe-B alloy composition may be in the form of an ingot. The RE-M-Fe-B alloy composition (or ingot) may be prepared by weighing the appropriate amount of raw materials (such as Nd, Fe, Ga, Fe-B) according to the composition formula, placing the raw materials into a melter, melting the respective raw materials under inert atmosphere (such as argon atmosphere) and cooling it to obtain ingots. The ingots may be subsequently broken into pieces and loaded into a melt-spinner. The alloy ingots may be then heated up and re-melted in inert atmosphere (such as argon atmosphere) and ejected onto a rotating metal wheel to form ribbons.

The mass flow rate of the melt flowing onto the rotating wheel may be in the range of about 0.2 kg/min to about 1.90 kg/min. The melt ejecting onto the rotating wheel may be further optimally quenched by adjusting the wheel speed. The wheel may be rotating at a speed in the range of about 20 m/s to about 45 m/s. The melt may be ejected onto the rotating wheel through one or more nozzles. The mass flow rate of the melt flowing onto the rotating wheel may be controlled by controlling the diameter of said nozzle(s). The diameter of the one or more nozzles may be in the range of about 0.5 mm to about 1.4 mm.

Step (i) may comprise a melt spinning process.

In step (ii), the melt-spun ribbons may then be crushed to powder to form a melt- spun powder (or alloy powder).

Step (iii) may comprise the steps of: (iii-a) cold pressing the melt-spun powder of step (ii); (iii-b) hot pressing the cold-pressed powder of step (iii-a) to form the compact body; and (iii-c) hot deforming the compacted body (iii-b) to develop magnetic alignment throughout the entire magnet.

In step (iii-a), the melt-spun body of step (ii) may be pressed into a low density platform to form a low density compact body. Step (iii-a) may be performed at room temperature and normal atmosphere. The lubed melt-spun powder may be pressed into a cold-pressed powder using a hydraulic cold press. In step (iii-b), the cold pressed compact body may be pressed into a hot press die to form a full density compact body. Step (iv-b) may be performed in inert atmosphere comprising argon, helium, or mixtures thereof.

In step (iii-c), the full density compact body of step (iii-b) may be further pressed into a die cavity of larger diameter and hot deformed into a larger die with a height reduction of 60 to 80% at elevated temperature. This process may cause bulk lateral plastic flow, reducing the ribbon thickness and a controlled elongation of the nano-scale Nd2Fel4B grains. The resultant die-upset magnets are fully dense like the hot-pressed compact body but are strongly anisotropic in magnetic performance. The magnetic performance and deformability are dependent on ribbon composition and process parameters such as strain rate, working temperature, and degree of deformation. Step (iii- c) may be performed in inert atmosphere comprising argon, helium, or mixtures thereof.

In step (iv), the die-upset magnet of step (iii-c) is crushed for breaking down the die-upset magnet into smaller pieces for use in subsequent bonded magnets fabrication. The crushing step may be a jaw-crushing step. Jaw crushing may be performed between jaw plates under inert gas protection. The jaw-crushed powder may be subjected to milling and sieving under inert gas protection with oxygen content below 0.5 %. The milling step further reduces the size of the jaw-crushed powder and the sieving step screens the particles to a desired size.

The mass flow rate of the melt flowing onto the rotating wheel may be in the range of about 0.2 kg/min to about 1.90 kg/min. The mass flow rate may be in the range of about 0.30 kg/min to about 1.90 kg/min, about 0.40 kg/min to about 1.90 kg/min, about 0.50 kg/min to about 1.90 kg/min, about 0.60 kg/min to about 1.90 kg/min, about 0.70 kg/min to about 1.90 kg/min, about 0.80 kg/min to about 1.90 kg/min, about 0.90 kg/min to about 1.90 kg/min, about 1.00 kg/min to about 1.90 kg/min, about 1.10 kg/min to about 1.90 kg/min, about 1.20 kg/min to about 1.90 kg/min, about 1.30 kg/min to about 1.90 kg/min, about 1.40 kg/min to about 1.90 kg/min, about 1.50 kg/min to about 1.90 kg/min, about 1.60 kg/min to about 1.90 kg/min, about 1.70 kg/min to about 1.90 kg/min, about 1.80 kg/min to about 1.90 kg/min, about 0.20 kg/min to about 1.80 kg/min, about 0.20 kg/min to about 1.70 kg/min, about 0.20 kg/min to about 1.60 kg/min, about 0.20 kg/min to about 1.50 kg/min, about 0.20 kg/min to about 1.40 kg/min, about 0.20 kg/min to about 1.30 kg/min, about 0.20 kg/min to about 1.20 kg/min, about 0.20 kg/min to about 1.10 kg/min, about 0.20 kg/min to about 1.00 kg/min, about 0.20 kg/min to about 0.90 kg/min, about 0.20 kg/min to about 0.80 kg/min, about 0.20 kg/min to about 0.70 kg/min, about 0.20 kg/min to about 0.60 kg/min, about 0.20 kg/min to about 0.50 kg/min, about 0.20 kg/min to about 0.40 kg/min, about 0.20 kg/min to about 0.30 kg/min, about 0.20 kg/min to about 1.00 kg/min, about 0.30 kg/min to about 1.00 kg/min, about 0.40 kg/min to about 1.00 kg/min, about 0.50 kg/min to about 1.00 kg/min, about 0.60 kg/min to about 1.00 kg/min, about 0.70 kg/min to about 1.00 kg/min, about 0.80 kg/min to about 1.00 kg/min, about 0.90 kg/min to about 1.00 kg/min, about 0.20 kg/min to about 0.90 kg/min, about 0.20 kg/min to about 0.80 kg/min, about 0.20 kg/min to about 0.70 kg/min, about 0.20 kg/min to about 0.60 kg/min, about 0.20 kg/min to about 0.50 kg/min, about 0.20 kg/min to about 0.40 kg/min, about 0.20 kg/min to about 0.30 kg/min, or about 0.20 kg/min, about 0.30 kg/min, about 0.40 kg/min, about 0.50 kg/min, about 0.60 kg/min, about 0.70 kg/min, about 0.80 kg/min, about 0.90 kg/min, about 1.00 kg/min, about 1.10 kg/min, about 1.20 kg/min, about 1.30 kg/min, about 1.40 kg/min, about 1.50 kg/min, about 1.60 kg/min, about 1.70 kg/min, about 1.80 kg/min, about 1.90 kg/min, or any range or value therein.

The melt ejecting onto the rotating wheel may be further optimally quenched by adjusting the wheel speed. The wheel may be rotating at a speed in the range of about 20 m/s to about 45 m/s, about 25 m/s to about 45 m/s, 30 m/s to about 45 m/s, 35 m/s to about 45 m/s, 40 m/s to about 45 m/s, 20 m/s to about 40 m/s, 20 m/s to about 35 m/s, 20 m/s to about 30 m/s, 20 m/s to about 25 m/s, or about 20 m/s, or about 21 m/s, or about 22 m/s, or about 23 m/s, or about 24 m/s, about 25 m/s, or about 26 m/s, or about 27 m/s, or about 28 m/s, or about 29 m/s, about 30 m/s, about 31 m/s, about 32 m/s, about 33 m/s, about 34 m/s, about 35 m/s, about 36 m/s, about 37 m/s, about 38 m/s, about 39 m/s, about 40 m/s, about 41 m/s, about 42 m/s, about 43 m/s, about 44 m/s, about 45 m/s, or any range or value therein.

When the mass flow rate of the melt ejecting onto the rotating wheel is 0.20 kg/min, the wheel may be rotating at a speed in the range of about 20 m/s to about 25 m/s. When the mass flow rate of the melt ejecting onto the rotating wheel is 0.50 kg/min, the wheel may be rotating at a speed in the range of about 25 m/s to about 30 m/s. When the mass flow rate of the melt ejecting onto the rotating wheel is 0.80 kg/min, the wheel may be rotating at a speed in the range of about 30 m/s to about 35 m/s. When the mass flow rate of the melt ejecting onto the rotating wheel is 1.30 kg/min, the wheel may be rotating at a speed in the range of about 35 m/s to about 40 m/s. When the mass flow rate of the melt ejecting onto the rotating wheel is 1.90 kg/min, the wheel may be rotating at a speed in the range of about 40 m/s to about 45 m/s.

When the mass flow rate of the melt ejecting onto the rotating wheel is 0.20 kg/min, the wheel may be rotating at a speed of about 20 m/s, about 21 m/s, about 22 m/s, about 23 m/s, about 24 m/s, or about 25 m/s. When the mass flow rate of the melt ejecting onto the rotating wheel is 0.50 kg/min, the wheel may be rotating at a speed in the range of about 25 m/s, about 26 m/s, about 27 m/s, about 28 m/s, about 29 m/s, or about 30 m/s. When the mass flow rate of the melt ejecting onto the rotating wheel is 0.80 kg/min, the wheel may be rotating at a speed in the range of about 30 m/s, about 31 m/s, about 32 m/s, about 33 m/s, about 34 m/s, or about 35 m/s. When the mass flow rate of the melt ejecting onto the rotating wheel is 1.30 kg/min, the wheel may be rotating at a speed in the range of about 35 m/s, about 36 m/s, about 37 m/s, about 38 m/s, about 39 m/s, or about 40 m/s. When the mass flow rate of the melt ejecting onto the rotating wheel is 1.90 kg/min, the wheel may be rotating at a speed in the range of about 40 m/s, about 41 m/s, about 42 m/s, about 43 m/s, about 44 m/s, or about 45 m/s.

The melt may be ejected onto the rotating wheel through one or more nozzles. The mass flow rate of the melt flowing onto the rotating wheel may be controlled by controlling the diameter of said nozzle(s).

The diameter of the one or more nozzles may be in the range of about 0.5 mm to about 1.4 mm, or about 0.6 mm to about 1.4 mm, about 0.7 mm to about 1.4 mm, about 0.8 mm to about 1.4 mm, about 0.9 mm to about 1.4 mm, about 1.0 mm to about 1.4 mm, about 1.1 mm to about 1.4 mm, about 1.2 mm to about 1.4 mm, about 1.3 mm to about 1.4 mm, about 0.5 mm to about 1.3 mm, about 0.5 mm to about 1.2 mm, about 0.5 mm to about 1.1 mm, about 0.5 mm to about 1.0 mm, about 0.5 mm to about 0.9 mm, about 0.5 mm to about 0.8 mm, about 0.5 mm to about 0.7 mm, about 0.5 mm to about 0.6 mm, or about 0.5 mm, about 0.6 mm, about 0.7 mm, about 0.8 mm, about 0.9 mm, about 1.0 mm, about 1.1 mm, about 1.2 mm, about 1.3 mm, about 1.4 mm, or any value or range therein.

When the mass flow rate of the melt ejecting onto the rotating wheel is 0.20 kg/min, the nozzle diameter may be 0.5 mm. When the mass flow rate of the melt ejecting onto the rotating wheel is 0.50 kg/min, the nozzle diameter may be 0.7 mm. When the mass flow rate of the melt ejecting onto the rotating wheel is 0.80 kg/min, the nozzle diameter may be 1.0 mm. When the mass flow rate of the melt ejecting onto the rotating wheel is 1.30 kg/min, the nozzle diameter may be 1.2 mm. When the mass flow rate of the melt ejecting onto the rotating wheel is 1.90 kg/min, the nozzle diameter may be 1.4 mm.

In an embodiment, the particles of the Sm-Fe-N magnetic powder in the disclosed method or compound are smaller in size than the particles of the RE-Fe-M-B magnetic powder. The size of the Sm-Fe-N particles may be small enough to fit within the space or gap between the RE-Fe-M-B particles when both are present in a mixture. As the Sm-Fe-N particles are smaller in size, they can fit in between the gaps of adjacent RE-Fe-M-B particles, as depicted in Figure 2. Advantageously, the Sm-Fe-N particles may uniformly coat each RE-Fe-M-B particle (Figure 3b), instead of agglomerating around the surface of the RE-Fe-M-B particle (Figure 3b). The uniform coating of the Sm-Fe-N particles around the RE-Fe-M-B particle advantageously provides for better flowability of the resulting compound for the bonded magnet and allows for a more compact and dense bonded magnet to be produced. The uniform dispersion of the Sm-Fe-N particles around the RE-Fe-M-B particle may be achieved by dissolving the binder with dispersant, which avoids the unwanted agglomeration of the Sm-Fe- N particles around the RE-Fe-M-B particle, such as the agglomeration shown in Figure 3a.

Hence, in an embodiment, the particles of the Sm-Fe-N magnetic powder are substantially uniformly distributed around the surface of each particle of RE-Fe-M-B magnetic powder.

The RE-Fe-M-B magnetic powder in the disclosed method or compound may have an average particle size in the range of about 40 pm to about 200 pm, about 50 pm to about 200 pm, about 60 pm to about 200 pm, about 70 pm to about 200 pm, about 80 pm to about 200 pm, about 90 pm to about 200 pm, about 100 pm to about 200 pm, about 110 pm to about 200 pm, about 120 pm to about 200 pm, about 130 pm to about 200 pm, about 140 pm to about 200 pm, about 150 pm to about 200 pm, about 160 pm to about 200 pm, about 170 pm to about 200 pm, about 180 pm to about 200 pm, about 190 pm to about 200 pm, about 40 pm to about 190 pm, about 40 pm to about 180 pm, about 40 pm to about 170 pm, about 40 pm to about 160 pm, about 40 pm to about 150 pm, about 40 pm to about 140 pm, about 40 pm to about 130 pm, about 40 pm to about 120 pm, about 40 pm to about 110 pm, about 40 pm to about 100 pm, about 40 pm to about 90 pm, about 40 pm to about 80 pm, about 40 pm to about 70 pm, about 40 pm to about 60 pm, about 40 pm to about 50 pm, about 40 pm, about 45 pm, about 50 pm, about 55 pm, about 60 pm, about 65 pm, about 70 pm, about 75 pm, about 80 pm, about 85 pm, about 90 pm, about 95 pm, about 100 pm, about 105 pm, about 110 pm, about 115 pm, about 120 pm, about 125 pm, about 130 pm, about 135 pm, about 140 pm, about 145 un, about 150 pun, about 155 pun, about 160 pun, about 165 pun, about 170 pun, about 175 pun, about 180 pun, about 185 pun, about 190 pun, about 195 pun, about 200 pun, or any value or range therebetween. The average particle size of the Sm-Fe-N magnetic powder may be in the range of about 1 pm to about 10 pm, about 1.5 pm to about 10 pm, about 2 pm to about 10 pm, about 2.5 pm to about 10 pm, about 3 pm to about 10 pm, about 3.5 pm to about 10 pm, about 4 pm to about 10 pm, about 4.5 pm to about 10 pm, about 5 pm to about 10 pm, about 5.5 pm to about 10 pm, about 6 pm to about 10 pm, about 6.5 pm to about 10 pm, about 7 pm to about 10 pm, about 7.5 pm to about 10 pm, about 8 pm to about 10 pm, about 8.5 pm to about 10 pm, about 9 pm to about 10 pm, about 9.5 pm to about 10 pm, about 1 pm to about 9.5 pm, about 1 pm to about 9 pm, about 1 pm to about 8.5 pm, about 1 pm to about 8 pm, about 1 pm to about 7.5 pm, about 1 pm to about 7 pm, about 1 pm to about 6.5 pm, about 1 pm to about 6 pm, about 1 pm to about 5.5 pm, about 1 pm to about 5 pm, about 1 pm to about 4.5 pm, about 1 pm to about 4 pm, about 1 pm to about 3.5 pm, about 1 pm to about 3 pm, about 1 pm to about 2.5 pm, about 1 pm to about 2 pm, about 1 pm to about 1.5 pm, about 1 pm, about 1.1 pm, about 1.2 pm, about 1.3 pm, about 1.4 pm, about 1.5 pm, about 1.6 pm, about 1.7 pm, about 1.8 pm, about 1.9 pm, about 2 pm, about 2.1 pm, about 2.2 pm, about 2.3 pm, about 2.4 pm, about 2.5 pm, about 2.6 pm, about 2.7 pm, about 2.8 pm, about 2.9 pm, about 3 pm, about 3.1 pm, about 3.2 pm, about 3.3 pm, about 3.4 pm, about 3.5 pm, about 3.6 pm, about 3.7 pm, about 3.8 pm, about 3.9 pm, about 4 pm, about 4.1 pm, about 4.2 pm, about 4.3 pm, about 4.4 pm, about 4.5 pm, about 4.6 pm, about 4.7 pm, about 4.8 pm, about 4.9 pm, about 5 pm, about 5.1 pm, about 5.2 pm, about 5.3 pm, about 5.4 pm, about 5.5 pm, about 5.6 pm, about 5.7 pm, about 5.8 pm, about 5.9 pm, about 6 pm, about 6.1 pm, about

6.2 pm, about 6.3 pm, about 6.4 pm, about 6.5 pm, about 6.6 pm, about 6.7 pm, about 6.8 pm, about 6.9 pm, about 7 pm, about 7.1 pm, about 7.2 pm, about 7.3 pm, about 7.4 pm, about 7.5 pm, about 7.6 pm, about 7.7 pm, about 7.8 pm, about 7.9 pm, about 8 pm, about 8.1 pm, about

8.2 pm, about 8.3 pm, about 8.4 pm, about 8.5 pm, about 8.6 pm, about 8.7 pm, about 8.8 pm, about 8.9 pm, about 9 pm, about 9.1 pm, about 9.2 pm, about 9.3 pm, about 9.4 pm, about 9.5 pm, about 9.6 pm, about 9.7 pm, about 9.8 pm, about 9.9 pm, about 10 pm or any value or range therein.

The weight ratio of RE-Fe-M-B magnetic powder to Sm-Fe-N magnetic powder used in the disclosed method or in the disclosed compound may be in the range of about 3:2 (6:4) to about 9: 1, about 65:35 to about 9: 1, about 7:3 to about 9: 1, about 75:25 to about 9: 1, about 8:2 to about 9: 1, about 85: 15 to about 9: 1, about 3:2 to about 85: 15, about 3:2 to about 8:2, about 3:2 to about 75:25, about 3:2 to about 7:3, about 3:2 to about 65:35, or about 3:2, about 65:35, about 7:3, about 75:25, about 8:2, about 85: 15, about 9: 1, or any value or range therein.

The amount of RE-Fe-M-B magnetic powder in the mixture of RE-Fe-M-B magnetic powder and Sm-Fe-N magnetic powder may be about 60 wt% to about 90 wt%, about 65 wt% to about 90 wt%, about 70 wt% to about 90 wt%, about 75 wt% to about 90 wt%, about 80 wt% to about 90 wt%, about 85 wt% to about 90 wt%, about 60 wt% to about 85 wt%, about 60 wt% to about 80 wt%, about 60 wt% to about 75 wt%, about 60 wt% to about 70 wt%, about 60 wt% to about 65 wt%, or about 60 wt%, about 61 wt%, about 62 wt%, about 63 wt%, about 64 wt%, about 65 wt%, about 66 wt%, about 67 wt%, about 68 wt%, about 69 wt%, about 70 wt%, about 71 wt%, about 72 wt%, about 73 wt%, about 74 wt%, about 75 wt%, about 77 wt%, about 77 wt%, about 78 wt%, about 79 wt%, about 80 wt%, about 81 wt%, about 82 wt%, about 83 wt%, about 84 wt%, about 85 wt%, about 86 wt%, about 87 wt%, about 88 wt%, about 89 wt%, about 90 wt%, or any value or range therebetween.

The amount of Sm-Fe-N magnetic powder in the mixture of RE-Fe-M-B magnetic powder and Sm-Fe-N magnetic powder may be about 10 wt% to about 40 wt%, about 15 wt% to about 40 wt%, about 20 wt% to about 40 wt%, about 25 wt% to about 40 wt%, about 30 wt% to about 40 wt%, about 35 wt% to about 40 wt%, about 10 wt% to about 35 wt%, about 10 wt% to about 30 wt%, about 10 wt% to about 25 wt%, about 10 wt% to about 20 wt%, about 10 wt% to about 15 wt%, or about 10 wt%, about 11 wt%, about 12 wt%, about 13 wt%, about 14 wt%, about 15 wt%, about 11 wt%, about 11 wt%, about 18 wt%, about 19 wt%, about 20 wt%, about 21 wt%, about 22 wt%, about 23 wt%, about 24 wt%, about 25 wt%, about 27 wt%, about 22 wt%, about 28 wt%, about 29 wt%, about 30 wt%, about 31 wt%, about 32 wt%, about 33 wt%, about 34 wt%, about 35 wt%, about 33 wt%, about 33 wt%, about 38 wt%, about 39 wt%, about 40 wt%, or any value or range therebetween.

The present invention relates to a method of producing a compound for a composite rare-earth bonded magnet, comprising:

(d) preparing a mixture of RE-Fe-M-B magnetic powder, Sm-Fe-N magnetic powder, surfactant and binder;

(e) mixing the mixture of step (a) with stearate and dispersant;

(f) evaporating the dispersant from the mixture of step (b), thereby obtaining said compound, wherein RE is one or more rare earth metals selected from the group consisting of lanthanum (La), cerium (Ce), neodymium (Nd), praseodymium (Pr), yttrium (Y), gadolinium (Gd), terbium (Tb), dysoprium (Dy), holmium (Ho), and ytterbium (Yb);

M is one or more metals selected from the group consisting of gallium (Ga), zirconium (Zr), niobium (Nb), molybdenum (Mo), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), hafnium (Hf), tantalum (Ta), tungsten (W), copper (Cu), aluminum (Al), and cobalt (Co);

B is boron (B); and

Fe is iron (Fe); wherein:

RE is in the range of 29.0 weight % to 33.0 weight %;

M is in the range of 0.25 weight % to 1.0 weight %;

B is in the range of 0.8 weight % to 1.1 weight %; and

Fe makes up the balance.

(i) RE-Fe-M-B magnetic powder, wherein RE is one or more rare earth metals selected from the group consisting of lanthanum (La), cerium (Ce), neodymium (Nd), praseodymium (Pr), yttrium (Y), gadolinium (Gd), terbium (Tb), dysoprium (Dy), holmium (Ho), and ytterbium (Yb),

Fe is iron,

M is absent or one or more metals selected from the group consisting of gallium (Ga), zirconium (Zr), niobium (Nb), molybdenum (Mo), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), hafnium (Hf), tantalum (Ta), tungsten (W), copper (Cu), aluminum (Al), and cobalt (Co), and

B is boron; wherein:

RE is in the range of 29.0 weight % to 33.0 weight %;

M is in the range of 0.25 weight % to 1.0 weight %;

B is in the range of 0.8 weight % to 1.1 weight %; and

Fe makes up the balance; (ii) Sm-Fe-N magnetic powder, wherein Sm is samarium

Fe is iron, and

N is nitrogen;

(iii) stearate; and

(iv) binder.

Fe is iron,

B is boron; wherein:

RE is in the range of 29.0 weight % to 33.0 weight %;

M is in the range of 0.25 weight % to 1.0 weight %;

B is in the range of 0.8 weight % to 1.1 weight %; and Fe makes up the balance;

(ii) Sm-Fe-N magnetic powder, wherein Sm is samarium

Fe is iron, and

N is nitrogen;

(iii) stearate; and

(iv) binder. RE may be in the range of about 29.0 weight % to about 33.0 weight %, about 29.5 weight % to about 33.0 weight %, about 30.0 weight % to about 33.0 weight %, about 30.5 weight % to about 33.0 weight %, about 31.0 weight % to about 33.0 weight %, about 31.5 weight % to about 33.0 weight %, about 32.0 weight % to about 33.0 weight %, about 32.5 weight % to about 33.0 weight %, about 29.0 weight % to about 32.5 weight %, about 29.0 weight % to about 32.0 weight %, about 29.0 weight % to about 31.5 weight %, about 29.0 weight % to about 31.0 weight %, about 29.0 weight % to about 30.5 weight %, about 29.0 weight % to about 30.0 weight %, about 29.0 weight % to about 29.5 weight %, about 30.0 wt% to about 32.5 wt%, about 30.40 wt% to about 32.45 wt%, about 30.5 wt% to about 32.5 wt%, about 31.0 wt% to about 32.5 wt%, about 31.5 wt% to about 32.5 wt%, about 32.0 wt% to about 32.5 wt%, about 30.0 wt% to about 32.0 wt%, about 30.0 wt% to about 31.5 wt%, about 30.0 wt% to about 31.0 wt%, about 30.6 weight % to about 31.8 weight %, about 30.7 weight % to about 31.8 weight %, about 30.8 weight % to about 31.8 weight %, about 30.9 weight % to about 31.8 weight %, about 31.0 weight % to about 31.8 weight %, about 31.1 weight % to about 31.8 weight %, about 31.2 weight % to about 31.8 weight %, about 31.3 weight % to about 31.8 weight %, about 31.4 weight % to about 31.8 weight %, about 31.5 weight % to about 31.8 weight %, about 31.6 weight % to about 31.8 weight %, about 31.7 weight % to about 31.8 weight %, about 30.6 weight % to about 31.7 weight %, about 30.6 weight % to about 31.6 weight %, about 30.6 weight % to about 31.5 weight %, about 30.6 weight % to about 31.4 weight %, about 30.6 weight % to about 31.3 weight %, about 30.6 weight % to about 31.2 weight %, about 30.6 weight % to about 31.1 weight %, about 30.6 weight % to about 31.0 weight %, about 30.6 weight % to about 30.9 weight %, about 29.0 weight % to about 29.5 weight %, about 29.0 weight %, about 29.5 weight %, about 30.0 weight %, about 30.45 weight %, about 30.5 weight %, about 30.6 weight %, about 30.7 weight %, about 30.8 weight %, about 30.9 weight %, about 31.0 weight %, about 31.1 weight %, about 31.2 weight %, about 31.3 weight %, about 31.4 weight %, about 31.45 weight %, about 31.5 weight %, about 31.6 weight %, about 31.7 weight %, about 31.8 weight %, about 31.9 weight %, about 32.0 weight %, about 32.4 weight %, about 32.5 weight %, or about 33.0 weight %. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range (s).

M may be in the range of about 0.25 weight % to about 1.0 weight %, about 0.3 weight % to about 1.0 weight %, about 0.35 weight % to about 1.0 weight %, about 0.4 weight % to about 1.0 weight %, about 0.45 weight % to about 1.0 weight %, about 0.5 weight % to about 1.0 weight %, about 0.55 weight % to about 1.0 weight %, about 0.6 weight % to about 1.0 weight %, about 0.65 weight % to about 1.0 weight %, about 0.7 weight % to about 1.0 weight %, about 0.75 weight % to about 1.0 weight %, about 0.8 weight % to about 1.0 weight %, about 0.85 weight % to about 1.0 weight %, about 0.9 weight % to about 1.0 weight %, about 0.95 weight % to about 1.0 weight %, about 0.25 weight % to about 0.95 weight %, about 0.25 weight % to about 0.90 weight %, about 0.25 weight % to about 0.85 weight %, about 0.25 weight % to about 0.80 weight %, about 0.25 weight % to about 0.75 weight %, about 0.25 weight % to about 0.70 weight %, about 0.25 weight % to about 0.65 weight %, about 0.25 weight % to about 0.60 weight %, about 0.25 weight % to about 0.55 weight %, about 0.25 weight % to about 0.50 weight %, about 0.25 weight % to about 0.45 weight %, about 0.25 weight % to about 0.40 weight %, about 0.25 weight % to about 0.35 weight %, about 0.25 weight % to about 0.30 weight %, about 0.50 weight % to about 0.75 weight %, about 0.55 weight % to about 0.75 weight %, about 0.60 weight % to about 0.75 weight %, about 0.65 weight % to about 0.75 weight %, about 0.70 weight % to about 0.75 weight %, about 0.50 weight % to about 0.70 weight %, about 0.50 weight % to about 0.65 weight %, about 0.50 weight % to about 0.60 weight %, about 0.50 weight % to about 0.55 weight %, about 0.45 weight % to about 0.55 weight %, about 0.46 weight % to about 0.55 weight %, about 0.47 weight % to about 0.55 weight %, about 0.48 weight % to about 0.55 weight %, about 0.49 weight % to about 0.55 weight %, about 0.50 weight % to about 0.55 weight %, about 0.51 weight % to about 0.55 weight %, about 0.52 weight % to about 0.55 weight %, about 0.53 weight % to about 0.55 weight %, about 0.54 weight % to about 0.55 weight %, about 0.45 weight % to about 0.54 weight %, about 0.45 weight % to about 0.53 weight %, about 0.45 weight % to about 0.52 weight %, about 0.45 weight % to about 0.51 weight %, about 0.45 weight % to about 0.50 weight %, about 0.45 weight % to about 0.49 weight %, about 0.25 weight %, about 0.30 weight %, about 0.35 weight %, about 0.40 weight %, about 0.45 weight %, about 0.46 weight %, about 0.47 weight %, about 0.48 weight %, about 0.49 weight %, about 0.50 weight %, about 0.51 weight %, about 0.52 weight %, about 0.53 weight %, about 0.54 weight %, about 0.55 weight %, about 0.60 weight %, about 0.63 weight %, about 0.65 weight %, about 0.70 weight %, about 0.75 weight %, about 0.78 weight %, about 0.80 weight %, about 0.85 weight %, about 0.90 weight %, about 0.95 weight %, or about 1.0 weight %. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range(s).

The B or Boron element content may be in the range of about 0.8 weight % to about 1.1 weight %, 0.85 weight % to about 1.1 weight %, 0.9 weight % to about 1.1 weight %, 0.95 weight % to about 1.1 weight %, 1.0 weight % to about 1.1 weight %, 1.05 weight % to about 1.1 weight %, about 0.8 weight% to about 1.05 weight%, about 0.8 weight% to about 1.0 weight%, about 0.8 weight%to about 0.95 weight%, about 0.8 weight%to about 0.9 weight%, about 0.8 weight% to about 0.85 weight%, about 0.9 weight % to about 1.0 weight %, about 0.91 weight % to about 1.0 weight %, about 0.92 weight % to about 1.0 weight %, about 0.93 weight % to about 1.0 weight %, about 0.94 weight % to about 1.0 weight %, about 0.95 weight % to about 1.0 weight %, about 0.96 weight % to about 1.0 weight %, about 0.97 weight % to about 1.0 weight %, about 0.98 weight % to about 1.0 weight %, about 0.99 weight % to about 1.0 weight %, about 0.9 weight % to about 0.99 weight %, about 0.9 weight % to about 0.98 weight %, about 0.9 weight % to about 0.97 weight %, about 0.9 weight % to about 0.96 weight %, about 0.9 weight % to about 0.95 weight %, about 0.9 weight % to about 0.94 weight %, about 0.9 weight % to about 0.93 weight %, about 0.9 weight % to about 0.92 weight %, about 0.9 weight % to about 0.91 weight %, about 0.885 weight % to about 0.945 weight %, about 0.890 weight %to about 0.945 weight %, about 0.895 weight %to about 0.945 weight %, about 0.900 weight % to about 0.945 weight %, about 0.905 weight % to about 0.945 weight %, about 0.910 weight %to about 0.945 weight %, about 0.915 weight %to about 0.945 weight %, about 0.920 weight % to about 0.945 weight %, about 0.925 weight % to about 0.945 weight %, about 0.930 weight % to about 0.945 weight %, about 0.935 weight % to about 0.945 weight %, about 0.940 weight % to about 0.945 weight %, about 0.885 weight % to about 0.940 weight %, about 0.885 weight %to about 0.935 weight %, about 0.885 weight %to about 0.930 weight %, about 0.885 weight %to about 0.925 weight %, about 0.885 weight %to about 0.920 weight %, about 0.885 weight %to about 0.915 weight %, about 0.885 weight %to about 0.910 weight %, about 0.885 weight %to about 0.905 weight %, about 0.885 weight %to about 0.900 weight %, about 0.885 weight %to about 0.895 weight %, about 0.885 weight %to about 0.890 weight %, about 0.8 weight %, about 0.85 weight %, about 0.885 weight %, about 0.890 weight %, about 0.895 weight %, about 0.900 weight %, about 0.905 weight %, about 0.910 weight %, about 0.915 weight %, about 0.920 weight %, about 0.925 weight %, about 0.930 weight %, about 0.935 weight %, about 0.940 weight %, or about 0.945 weight %, about 0.95 weight %, about 0.96 weight %, about 0.97 weight %, about 0.98 weight %, about 0.99 weight %, about 1.0 weight %, about 1.05 weight %, or about 1.1 weight %. It is to be appreciated that the above ranges should be interpreted as including and supporting any subranges or discrete values (which may or may not be a whole number) that are within the stated range (s).

The RE-Fe-M-B magnetic powder may be selected from the group consisting of

• NdPr-Ga-B-Fe, wherein NdPr is 30.45 wt%, Ga is 0.53 wt%, B is 0.94 wt%, and Fe is 68.08 wt%;

• NdPr-Ga-B-Fe, wherein NdPr is 31.45 wt%, Ga is 0.53 wt%, B is 0.93 wt%, and Fe is 67.09 wt%;

• NdPr-Ga-B-Fe, wherein NdPr is 31.9 wt%, Ga is 0.63 wt%, B is 0.92 wt%, and Fe is 66.55 wt%; or

• NdPr-Ga-B-Fe, wherein NdPr is 32.4 wt%, Ga is 0.78 wt%, B is 0.91 wt%, and Fe is 65.91 wt%.

The composite rare-earth bonded magnet may be an anisotropic bonded magnet.

The disclosed rare-earth bonded magnets may be obtainable or obtained by a method disclosed herein. The disclosed method may be used to prepare a compound, which is then loaded into a mold and pressed and cured to form a composite rare-earth bonded magnet.

The present disclosure relates to a method with an improved surface treatment process where the magnetic powder particles are first mixed with a surfactant. As mentioned above, the surfactant (e.g. silane or titanate) may improve the flowability of the particles and reduce the interparticle friction between the magnetic particles. The surfactant may further assist in the rotation of the magnetic particles or powder during the compression moulding process (second-step compaction process). Hence, the surfactant may be attributed to the better pressing ability of the magnetic particles.

Further, the improved pressing ability in this present disclosure may be achieved by adding fine SmFeN powder to the coarse RE-Fe-B powder, as well as the treatment of said mixed powder with a surfactant, such as silane. The improved flowability can be achieved by adding dispersant (e.g. acetone) while V-blending the powder mixture with zinc stearate (ZnST) optionally added as a surfactant.

The disclosed method further comprises dissolving the binder with the dispersant. Due to the dispersant (e.g. acetone) dissolving the binder (e.g. epoxy), a magnetic powder with fine SmFeN particles may be more evenly dispersed and distributed around the coarse RE-Fe-B particles. The role of the dispersant (e.g. acetone) ensures a more even distribution of fine SmFeN powder around the coarse RE-Fe-M-B powder.

The disclosed method also comprises an additional particle modification process and this may in turn achieve good flowability of the magnetic particles. This step in the compounding process involves blending of the mixture of RE-Fe-M-B magnetic powder, Sm- Fe-N magnetic powder, surfactant, and a binder. Blending of the mixture may involve any process of combining the mixtures where the resulting mixture is homogenous. This blending process may further allow a more even distribution of fine SmFeN powder around the coarse RE-Fe-M-B powder.

The dispersant may be evaporated with or without the use of heat (temperature) after the compound is blended and before loading to the compaction pressing process. With the improved flowability and good pressing ability of the compound, the compaction process in the disclosed method may result in higher magnet density and alignment, leading to better magnetic properties. The better aging performance (e.g. flux aging loss) of the bonded magnet may be attributed to a combination of SmFeN magnetic powder, surfactant (e.g. silane), and lower pressing pressure required to achieve the same magnet density.

Examples

Non-limiting examples of the invention and comparative examples will be further described in greater detail by reference to specific examples, which should not be construed as in any way limiting the scope of the invention.

Materials

MQA-1 (NdPr 30.45 wt%, Ga 0.53 wt%, B 0.94 wt%, Fe 68.08 wt%) was obtained from Neo Performance Materials.

MQA-2 (NdPr 31.45 wt%, Ga 0.53 wt%, B 0.93 wt%, Fe 67.09 wt%) was obtained from Neo Performance Materials.

MQA-3 (NdPr 31.9 wt%, Ga 0.63wt%, B 0.92wt%, Fe 66.55wt%) was obtained from Neo Performance Materials.

MQA-4 (NdPr 32.4 wt%, Ga 0.78 wt%, B 0.91 wt%, Fe 65.91 wt%) was obtained from Neo Performance Materials.

Hexadecyltrimethoxysilane was obtained from Sigma Aldrich.

SmFeN was obtained from Nichia corporation. Example 1: Method of producing a compound for a composite rare-earth bonded magnet

Step Al: Preparing MQA powder

A rapidly solidified RE-Fe-M-B alloy was prepared by weighing the appropriate amount of raw materials with a total weight of 100 grams, placing all the raw materials into an arc-melter, melting the respective raw materials under argon atmosphere and cooling it to obtain ingots. 1% extra amount of Nd was added prior to melting to compensate for the melting loss. The alloy ingots were flipped and re-melted four times to ensure homogeneity.

The ingots were then broken into pieces and loaded into a crucible tube with a small nozzle underneath and placed into a melt-spinner. The alloy ingots were heated up and remelted in argon atmosphere and ejected onto a rotating metal wheel to form ribbons. The ejection temperature was about 1400 °C to 1600 °C, the ejection pressure was about 200 torr to 500 torr, the nozzle size was about 0.5 mm to 1.4 mm, and the wheel speed was about 20 m/s to 45m/s. The ribbons were crushed to -40mesh powder by a twin-roller crusher.

The crushed melt-spun powders were then pressed at room temperature and in air into a low density preform to form a cylinder-shape compact body with densities in the range of 4.5-5.5 g/cm³. A 0.01-0.1% Zinc stearic powder was used as internal lubricant. The cold pressed compact body was then placed in a hot press die and was hot pressed at 600-800°C to form a full density compact body under inert atmosphere argon protection. The full density cylinder-shape compact body was then further placed into a die cavity of larger diameter and hot deformed with a height reduction of 60 to 80% at 700-900°C under argon protection to form a disc-shape magnet. The resultant die-upset magnets are fully dense like the hot-pressed compact body but are strongly anisotropic in magnetic performance.

The die-upset magnet was then further crushed for breaking down the die-upset magnet into smaller pieces with desired particle size distribution for use in subsequent bonded magnets fabrication. The crushing step was performed with a jaw-crusher under inert argon or nitrogen gas protection. The jaw-crushed powder was then subjected to further milling and sieving under inert argon or nitrogen gas protection with oxygen content below 0.5 %. The milling step further reduces the size of the jaw-crushed powder and the sieving step screens the particles to a desired size.

Step A: Pre-Treatment Step

Based on a 600 g/batch, 80% (480 g) of MQA powder (MQA-1, MQA-2, MQA-3 or MQA-4), 20% (120 g) of SmFeN, and 0.1 wt% (0.6 g) hexadecyltrimethoxysilane were placed into a beaker and mixed by a mechanical stirrer at 300 r/min for 5 minutes at room temperature and normal atmosphere. The resulting mixture is referred to as “pre-treated powders”.

Step B: Kneading Step

15.4 g of epoxy was added to the pre-treated powders and mixed with a V-blender for 30 minutes at 34 r/min. The mixture was loaded to a Banbury mixer and a warm kneading process was performed for 15 minutes at 90°C with the Banbury mixer. The compound was discharged and sieved by a -60 mesh and further blended for 30 minutes to obtain a kneaded compound.

Step C: Particle/Morphology Modification Step

The morphology of the kneaded compound particles was modified by a mixing process. 1 wt% of dispersant (e.g. acetone) and 0.2 wt% of zinc stearate were added to 100 g of the kneaded compound and mixed with a V-blender for 30 minutes at 34 r/min.

After V-blending, the dispersant (e.g. acetone) was evaporated by placing the compound in a ventilation cabinet. The product was sieved at -60 mesh to obtain a compound ready for pressing into a composite rare-earth bonded magnet.

Example 2: Method of producing a composite rare-earth bonded magnet

Steps A to C were performed according to Example 1.

Step D: Two-Step Compaction

Bonded magnets were fabricated by a two-step compaction process. The compound from Step (C) was fed into a cavity of a mold at room temperature, compressed into a preform magnet with a density of 4-5 g/cm³, then the preform magnet was transferred and loaded into a mold for warm compaction (second step). The warm compaction was performed at elevated molding temperatures while applying 1.0 T alignment field and a molding pressure (in the range of 1.5, 3, 5, 7 t/cm²). 10x10x10 mm cube-shaped green compact was obtained after the molded body was ejected from the mold.

Step E: Curing Step

The green compacts were cured by applying a heat treatment at 180 °C with a Blue M oven, and the bonded magnets were obtained.

Example 3: Sample Preparation

Compounds for a composite rare-earth bonded magnet were prepared as described below. “MQA” used below refers to MQA-1, MQA-2, MQA-3, or MQA-4.

Example 3a: Preparation of Sample 1

Sample 1: 100% MQA, 0.2 wt% ZnST (no silane)

Step B of Example 1 with 97.5 part of MQA and 2.5 part of epoxy were performed to form a kneaded compound.

0.2 part of zinc stearate were added to 100 part of kneaded compound and mixed with a V-blender for 30 minutes at 34 r/min. The product was sieved at -60 mesh to obtain a compound ready for pressing.

Example 3b: Preparation of Sample 2

Sample 2: 80% MQA, 20% SmFeN, 0.1 wt% silane, 0.2 H4% ZnST

Step A of Example 1 with 80 part of MQA, 20 part of SmFeN and 0. 1 part of silane were performed to form a pre-treated powder, then Step B of Example 1 with 97.5 part of pretreated powder and 2.5 part of epoxy to form a kneaded compound.

Thereafter, 0.2 part of zinc stearate was added to 100 part of kneaded compound and mixed with a V-blender for 30 minutes at 34 r/min. The product was sieved at -60 mesh to obtain a compound ready for pressing. Example 3c: Preparation of Sample 3

Sample 3: 80% MQA, 20% SmFeN, 0.1 wt% silane, 0.2 wt% ZnST, 1 wt% acetone

Step C of Example 1 with 100 part of Sample 2, 0.2 part of ZnST, and 1 part of acetone to form Sample 3.

Example 4: Pressing ability and magnetic properties

An anisotropic compression molded magnet is typically fabricated by Step D of Example 2. The pressing ability and magnetic properties lie on the warm compaction (second step) step, which is performed at an elevated temperature and under the presence of a magnetic alignment field.

When investigating the pressing ability of the compounds produced by the methods, parameters such as magnet density, alignment and remanence (Br) are measured and compared against the pressing pressure. Generally, magnet Br is proportional to magnet density and alignment.

The pressing ability of Samples 1 to 3 (prepared using MQA-3) were investigated.

Figures 4A, 4B, 4C and show the results of pressing Samples 1 to 3. It was observed that Samples 2 and 3 (containing both SmFeN and silane) require less pressure to achieve a higher density when compared to Sample 1 (Figure 2). This means that higher alignment can be achieved at the same density due to a lower pressing pressure required. As a result, a higher the remanence (Br) is advantageously achieved at a low pressure range.

Table 1A shows the results of Figures 4A, 4B and 4C.

[Table 1A] Samples prepared with MQA-3 powder

The pressing ability of Samples 1 and 3 (prepared using MQA-1, MQA-2, MQA-3, MQA-4) were also investigated. It was observed that Sample 3 (containing silane and acetone) required less pressure to achieve a higher density when compared to Sample 1 (Table IB). This means that higher alignment can be achieved at the same density due to a lower pressing pressure required. As a result, a higher the remanence (Br) is advantageously achieved at a low pressure range.

[Table IB]

Example 5: Effect of mold temperature

The effect of mold temperature during warm compaction (second step) was investigated using Sample 3 (MQA-3) as the test subject.

As shown in Table 2 and Figures 5A to 5C, higher mold temperature leads to higher magnet density, better alignment, and higher remanence value. These values were measured at a fixed pressing pressure of 7t/cm². These results demonstrate that warm compaction (second step) at a temperature range of more than 80 °C is beneficial for obtaining good magnetic properties. [Table 2]

Example 6: Ageing Performance

Flux aging loss measures the long-term thermal stability of the magnet and is important to magnet circuit designs. The rare-earth bonded magnet end users desire materials of low flux aging loss, so that the magnet will deliver a stable performance when exposed to high operational temperatures over a sustained period of time.

Figures 6A and 6B and Table 3 illustrate the total flux loss (%) against time (hour) after 1000 hr 120°C dry aging for compression molded magnets of Sample 1 (MQA-1, MQA-2, MQA-3, MQA-4) and Sample 3 (MQA-1, MQA-2, MQA-3, MQA-4).

It is observed that compression molded magnets of Sample 3 (MQA-1, MQA-2, MQA-3, MQA-4) have a much lower dry aging flux loss than that compression molded magnets of Sample 1 (MQA-1, MQA-2, MQA-3, MQA-4). Possible reasons for these observations are due to the presence of SmFeN magnet particles and silane which result in a lower pressing pressure required for the same magnet density. [Table 3]

Example 7: Flowability and Particle Size Distribution (PSD) Comparison

RE-Fe-M-B anisotropic magnetic powders (MQA) used in compounds of the present invention are prepared via rapid solidification, hot deformation and crushing. In this method, the RE-Fe-M-B alloy ingots are melted and rapidly solidified to form thin ribbons with very fine RE2Fel4B grains The ribbons are then crushed and subjected to hot deformation to develop c-axis alignment and form anisotropic bulk magnet. The magnet is further crushed to form the final anisotropic RE-Fe-M-B powders (MQA).

Another processing route for producing anisotropic RE-Fe-M-B powder is the Hydrogenation-Disproportionation-Desorption-Recombination (HDDR) method. In the HDDR method, the RE-Fe-M-B alloy ingot pieces are subjected to hydrogen atmosphere and are heated to elevated temperature so the Re2Fe 14B absorbs the hydrogen (hydrogenation) and reacts with it (disproportionation) to become a powder mixture of RE hydride (REHx), ferro boride (FeB2) and pure iron (Fe). A vacuum is then applied to the mixture to remove the hydrogen out of the mixture (desorption) and make the mixture return to RE2Fel4B phase (recombination). The final product is a RE-Fe-M-B powder mixture with each powder particle consisting of RE2Fel4B fine grains and their c-axis parallel to each other (so the powder is magnetically anisotropic).

MQA powders and HDDR powders have similar room-temperature magnetic properties, however MQA powders have better thermal stability at high-temperatures (e.g., lower flux aging loss at high-temperature) due to their smaller grain size in each powder particle. Therefore, MQA powders are more desirable than HDDR powders for high- temperature applications such as in the automotive industry. However, MQA powders generally exhibit poorer flowability compared to HDDR powders. The poor flowability of MQA powders may cause MQA bonded magnets produced via mass production to have undesirable large fluctuations of magnet mass, density, and dimension In some cases, because of the poor flowability, the powders cannot be used to fill a mold cavity via feeding mechanism and thus cannot be used to make bonded magnets.

Figure 7 is a series of SEM images of MQA-3 magnetic powder showing the particle shape of the magnetic powder after different treatments compared with HDDR magnetic powder after different treatments. Table 4 below summarises the treatments performed on the powders and their corresponding SEM image. [Table 4]

As shown in Figure 7, one of the differences between MQA powders versus HDDR powders lies in the particle shape and surface morphology of the resulting powders. As shown in Figure 7(a), MQA powders have a particle shape and surface morphology that are generally flake-like and have irregular surfaces, whereas as shown in Figure 7(e), powders produced via HDDR have a particle shape and morphology that are generally spherical.

The flake-like shape of MQA is not ideal for forming dense bonded magnets due to the spaces that form between the MQA powder particles. Instead, it is beneficial to have particles with a round-shape that can lay on top of and next to each other in a more compact manner. Additionally, when the particles undergo the alignment step, round-shape particles face less resistance when rotating to align with the alignment field. Hence, HDDR compounds, with their generally round particle shape, inherently have advantages in achieving higher magnet density and better magnet alignment when compared to compounds containing flake-like particles.

Additionally, the flowability of a compound is inherently affected by the shape of ‘naked’ powder. Generally, MQA compound inherently has poorer flowability due to their flake-like shape as compared to HDDR compound. There is therefore a need to find a way to improve MQA compound’s flowability. Otherwise, there are difficulties properly feeding MQA compound into a mold cavity which results in the difficulty in making bonded magnets from MQA compounds.

The present inventors have found a surprising way to do so. By subjecting MQA powders to the processing steps of the present invention, the particle shape of the MQA compound can be changed to a round-shape which leads to improved flowability. Table 5 below shows the flowability and PSD comparison of the compounds of Figure 7. PSD is shown in Figure 8.

[Table 5]

As shown in Table 5, compounds with 100% MQA-3 powder have poorer flowability when compared with pure HDDR powder (Sample 1: 35 seconds; Sample A: 30 seconds).

The flowability further decreases when SmFeN powder is added when comparing MQA-3 powder with HDDR powder (Sample 2: no flow; Sample B: 55 seconds). This poorer flowability is attributed to MQA-3 having a flake-like powder morphology, while HDDR’s particles are spherical shape (Figure 7(a) versus Figure 7(e)). Additionally, MQA powder has a broader Particle Size Distribution (PSD), as shown in figure 8, MQA has more fine and coarse powders than HDDR powder. Additionally, MQA compound is made up of irregular shape particles with a rough particle surface (Figure 7 (c) and 3A).

Surprisingly, it is found in this invention that the flowability of Sample 2 can be dramatically improved by a novel particle/morphology modification step (Step C of Example 1). The flowability surprisingly improves with the addition of a dispersant (acetone) (Sample 3) which the addition of is able to achieve an even more spherical particle shape and a having a smoother particle surface (Figure 7(d) and 3B). Additionally, a sharper PSD is achieved (Figure 8) which can be attributed to almost all fine SmFeN particles being attached to the larger MQA-3 particles. As such, there are almost no loose SmFeN fine particles. In summary, an improvement in the flowability of MQA powders is achieved through the method of the present invention. As mentioned above, MQA powders are more desirable than HDDR powders as they have better thermal stability at high temperatures. Therefore, being able to achieve better flowability for the MQA powders to effectively form bonded magnets is advantageous as it advantageously results in the production of bonded magnets which perform better in high temperature environments.

Example 8: Magnetic Properties The magnetic properties of Sample 2 (MQA-3) and Sample 3 (MQA-3) were investigated and compared. The results are found in Table 6.

The magnetic properties of Sample 1 (MQA-1, MQA-2, MQA-3, MQA-4) and Sample 3 (MQA-1, MQA-2, MQA-3, MQA-4) were also investigated and compared. The results are found in Table 6.

[Table 6]

Industrial Applicability

The present disclosure generally refers to a method for producing a compound for composite rare-earth bonded magnets. The present disclosure also relates to compounds for composite rare-earth bonded magnets, and composite rare-earth bonded magnets.

The rare-earth bonded magnets can be used and applied in numerous applications, including computer hardware, automobiles, motors, consumer electronics and household appliances. It is beneficial for such magnets to possess superior magnetic properties and exhibit high Br and Hci values.

Advantageously, the disclosed composite rare-earth bonded magnet may exhibit improved properties of good flowability, good pressing ability and superior aging performance (magnetic properties). This allows the compound to be loaded into the mould freely without any powder feeding problem. It also possesses high magnet density which can be obtained at low pressing pressure. Furthermore, there is minimal flux loss at 120°C for 1000 hours.

Further advantageously, with the above improved chemical, physical, mechanical, and magnetic properties, the material cost of the disclosed composite rare-earth bonded magnet with these properties may be lower and these magnets have longer lifetime (shelf life). These rare-earth bonded magnets with better flowability, lower pressing pressure can also be more easily molded to various shapes, designs and sizes and can be applied to various applications in the industry.

The methods disclosed herein may advantageously result in a composite rare-earth bonded magnet with improved properties of good flowability, good pressing ability and superior aging performance (magnetic properties). Also advantageously, the method disclosed herein may also result cost efficient method and may produce a composite rare-earth bonded magnet with high-power and high efficiency.

It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.

Claims

1. A method of producing a compound for a composite rare-earth bonded magnet, comprising:

(b) mixing the mixture of step (a) with stearate and dispersant;

2. The method of claim 1, wherein step (a) comprises:

(ai) preparing a mixture of RE-Fe-M-B magnetic powder, Sm-Fe-N magnetic powder, surfactant; and

(aii) blending the mixture of step (ai) with binder.

3. The method of claim 1 or 2, wherein step (b) comprises dissolving the binder with dispersant.

4. The method of any one of claims 1-3, further comprising:

(d) sieving the compound of step (c); and

(e) subjecting the sieved compound of step (d) to compression molding to obtain a composite rare-earth bonded magnet.

5. The method of any one of claims 1-4, wherein the dispersant is selected from the group consisting of ketones, alcohols, and water.

6. The method of any one of claims 1-5, wherein step (b) comprises adding about 0.01 wt % to about 5 wt % surfactant.

7. The method of any one of claims 1-6, wherein the stearate is selected from the group consisting of metal stearate, zinc stearate, stearate acid, ethyl stearate, and mixtures thereof.

8. The method of any one of claims 1-7, wherein the surfactant is silane or titanate.

9. The method of any one of claims 1-8, wherein step (c) comprises heating the dispersant at a temperature of about 50 °C to about 100 °C.

10. The method of anyone of claims 1 to 9, wherein prior to step (a):

(i) a RE-Fe-M-B alloy is melted and ejected onto a rotating wheel to quench the melt and obtain an alloy ribbon;

(ii) the alloy ribbon is crushed to form an alloy powder;

(iii) the alloy powder is subjected to hot deformation; and

(iv) the product of step (iii) is crushed to form the RE-Fe-M-B magnetic powder.

11. A composite rare-earth bonded magnet, comprising:

(i) RE-Fe-M-B magnetic powder, wherein RE is one or more rare earth metals,

Fe is iron,

M is absent or one or more metals, and

B is boron;

(ii) Sm-Fe-N magnetic powder, wherein Sm is samarium

Fe is iron, and

N is nitrogen;

(iii) stearate; and

(iv) binder.

12. The composite rare-earth bonded magnet of claim 11, wherein particles of the Sm-Fe- N magnetic powder are substantially uniformly distributed around the surface of each particle of RE-Fe-M-B magnetic powder.

13. The composite rare-earth bonded magnet of claim 11 or 12, wherein weight ratio of RE-Fe-M-B magnetic powder to Sm-Fe-N magnetic powder is in the range of about 3:2 to about 9: 1.

14. The composite rare-earth bonded magnet of any one of claims 11-13, wherein the RE- Fe-M-B magnetic powder has an average particle size of about 40 pm to about 200 pm.

15. The composite rare-earth bonded magnet of any one of claims 11-14, wherein RE is one or more rare earth metals selected from the group consisting of lanthanum (La), cerium (Ce), neodymium (Nd), praseodymium (Pr), yttrium (Y), gadolinium (Gd), terbium (Tb), dysoprium (Dy), holmium (Ho), and ytterbium (Yb).

16. The composite rare-earth bonded magnet of any one of claims 11-15, wherein M is absent or one or more metals selected from the group consisting of zirconium (Zr), niobium (Nb), molybdenum (Mo), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), hafnium (Hf), tantalum (Ta), tungsten (W), cobalt (Co), copper (Cu), gallium (Ga) and aluminum (Al).

17. The composite rare-earth bonded magnet of any one of claims 11-16, wherein:

RE is one or more rare earth metals selected from the group consisting of lanthanum (La), cerium (Ce), neodymium (Nd), praseodymium (Pr), yttrium (Y), gadolinium (Gd), terbium (Tb), dysoprium (Dy), holmium (Ho), and ytterbium (Yb);

B is boron (B); and Fe is iron (Fe); wherein:

RE is in the range of 29.0 weight % to 33.0 weight %;

M is in the range of 0.25 weight % to 1.0 weight %; B is in the range of 0.8 weight % to 1.1 weight %; and Fe makes up the balance.

18. The composite rare-earth bonded magnet of any one of claims 11-17, wherein RE-Fe- M-B is:

19. The composite rare-earth bonded magnet of any one of claims 11-18, wherein the Sm- Fe-N magnetic powder has an average particle size of about 1 pm to about 10 pm.

20. The composite rare-earth bonded magnet of any one of claims 11-19, wherein the stearate is selected from the group consisting of metal stearate, calcium stearate, lithium stearate, zinc stearate, stearate acid, ethyl stearate, and mixtures thereof.

21. The composite rare-earth bonded magnet of any one of claims 11-20, comprising about 0.01 wt% to about 1 wt % stearate.

22. The composite rare-earth bonded magnet of any one of claims 11-21, wherein the binder is resin or thermoset epoxy.

23. The composite rare-earth bonded magnet of any one of claims 11-22, further comprising a surfactant selected from the group consisting of silane and titanate.

24. The composite rare-earth bonded magnet of any one of claims 11-23, comprising about 0.01 wt % to about 0.5 wt % of surfactant.

25. A composite rare-earth bonded magnet of any one of claims 1 l-24obtained by the method of any one of claims 1-9.

26. The composite rare-earth bonded magnet of any one of claims 11-25, wherein the composite rare-earth bonded magnet is an anisotropic bonded magnet.