DE102017200142A1 - Segmented permanent magnets - Google Patents

Abstract

A segmented magnet is disclosed comprising first and second layers of permanent magnetic material and an insulating layer therebetween. The insulating layer may include a rare earth element and a ceramic mixture having at least first and second ceramic materials. The ceramic materials may include a halogen and an alkaline earth metal, an alkali metal, or a metal having a +3 or +4 oxidation state. The rare earth element may comprise up to 30% by weight of the insulating layer. The segmented magnet may be formed by depositing the insulating layer on a first sintered permanent magnet layer, stacking a second sintered permanent magnet layer in contact with the insulating layer and spaced from the first sintered permanent magnet layer, and heating the formed magnetic stack. The step of heating may include annealing the magnetic stack at an annealing temperature within 100 ° C of the melting point of the ceramic mixture.

Description

This invention relates to segmented magnets, for example Nd-Fe-B magnets.

Permanent magnet motors are widely used and can be used in electric vehicles. Due to the high conductivity of sintered Nd-Fe-B magnets as well as the Nutharmonischen eddy current losses can occur in the magnet. This can increase the magnet temperature and degrade the performance of the permanent magnets, which can result in a corresponding reduction in the efficiency of the motors. In an attempt to solve these problems and cause the magnets to operate at elevated temperatures, high coercivity magnets can be used in motors. These magnets usually contain expensive heavy rare earth elements (HRE), such as: Tb and Dy. Reducing eddy current losses can improve motor efficiency and reduce material costs.

In at least one embodiment, a segmented magnet is provided. The magnet may comprise a first layer of permanent magnetic material; a second layer of permanent magnetic material; and an insulating layer separating the first and second layers and comprising a rare earth element and a ceramic mixture having at least first and second ceramic materials.

The ceramic mixture may have a melting point lower than a melting point of the first and second ceramic materials. In one embodiment, the first or second ceramic material comprises a compound having a formula AH ₂ wherein A is an alkaline earth metal and H is a halogen. In another embodiment, the first or second ceramic material comprises a compound having a formula MH ₃ , wherein M is a metal having a +3 oxidation state and H is a halogen. In another embodiment, the first or second ceramic material comprises a compound having a formula BH, wherein B is an alkali metal and H is a halogen.

The ceramic mixture may have a melting point that is less than or equal to 1000 ° C. The rare earth element may be part of a rare earth alloy or a rare earth compound. The rare earth alloy may comprise NdCu and / or NdAl and / or DyCu and / or NdGa and / or PrAl and / or PrCu and / or PrAg. In an embodiment, the rare earth element may comprise up to 20% by weight of the insulating layer. The permanent magnetic material in the first and second layers may be an Nd-Fe-B magnet and the rare earth element in the insulating layer may be Nd.

In at least one embodiment, a method of forming a segmented magnet is provided. The method may include applying an insulating layer to a first sintered permanent magnet layer, stacking a second sintered permanent magnet layer in contact with the insulating layer and spaced from the first sintered permanent magnet layer to form a magnetic stack, and heating the magnetic stack. The insulating layer may include a rare earth element and a ceramic mixture having at least first and second ceramic materials.

In an embodiment, the first and second ceramic materials may be selected from the group consisting of: a compound having a formula AH ₂ , wherein A is an alkaline earth metal and H is a halogen; a compound having a formula MH ₃ , wherein M is a metal having a +3 oxidation state and H is a halogen; and a compound having a formula BH, wherein B is an alkali metal and H is a halogen.

The ceramic mixture may have a melting point lower than a melting point of the first and second ceramic materials. The step of heating may include annealing the magnetic stack at an annealing temperature within 100 ° C of the melting point of the ceramic mixture. The method may include applying pressure to the magnetic stack during the step of heating. The method may include segmenting the first and second sintered permanent magnet layers from a sintered block magnet prior to the applying step. In one embodiment, the rare earth element comprises up to 30% by weight of the insulating layer.

In at least one embodiment, a segmented magnet is provided. The magnet may comprise a first layer of permanent magnetic material; a second layer of permanent magnetic material; and an insulating layer separating the first and second layers and comprising: a rare earth element and a ceramic mixture having at least two ceramic materials in a eutectic system. The ceramic mixture may have a melting point that is within 100 ° C of a eutectic point temperature of the eutectic system. The eutectic system can be a binary, ternary or quaternary system.

In one embodiment, at least one of the at least two ceramic materials is made a group selected from: a compound having a formula AH ₂ , wherein A is an alkaline earth metal and H is a halogen; a compound having a formula MH ₃ , wherein M is a metal having a +3 oxidation state and H is a halogen; and a compound having a formula BH, wherein B is an alkali metal and H is a halogen.

• 1 ist ein schematisches Beispiel eines Querschnitts eines gesinterten Magneten;
• 2 ist eine Entmagnetisierungskurve eines gesinterten Nd-Fe-B-Magneten;
• 3 ist eine schematische Darstellung eines Verfahrens zum Ausbilden eines segmentierten Magneten gemäß einer Ausführungsform; und
• 4 ist ein Beispiel eines binären Phasendiagramms umfassend eine eutektische Reaktion für eine Mischung aus CaF₂ und AlF₃.

Further embodiments of the invention are disclosed in the drawings.

• 1 Fig. 10 is a schematic example of a cross section of a sintered magnet;
• 2 is a demagnetization curve of a sintered Nd-Fe-B magnet;
• 3 FIG. 12 is a schematic illustration of a method of forming a segmented magnet according to an embodiment; FIG. and
• 4 is an example of a binary phase diagram comprising a eutectic reaction for a mixture of CaF ₂ and AlF ₃ .

As required, detailed embodiments of the present invention are disclosed herein; however, it should be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. The specific structural and functional details disclosed herein are therefore not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art how to variously employ the present invention.

One approach to reducing eddy current losses is to cut or divide the magnet into smaller and thinner pieces and then bond these segmented magnets to a magnet of the desired size using resin or epoxy. To reduce eddy current losses, the thickness of each segmented magnet piece should be as small as possible. However, this may lead to a new problem of deterioration of properties near the surface of the magnet. In sintered Nd-Fe-B magnets, it is known that the Nd-rich phase is important for the coercive force of the magnet. An exemplary cross section of a magnet 10 is in 1 shown. The magnet 10 includes grains 12 , such as B. Nd ₂ Fe ₁₄ B grains by grain boundaries 14 are separated. The grains near the surface 16 of the magnet tend to lack the Nd-rich phase and therefore tend to have a significantly lower coercive force. Will the magnet 10 cut into smaller pieces and / or ground, defects are introduced into the newly created surfaces. These defects can lattice defects, such. B. unmatched bonds, impurities and / or point defects, as well as larger defects or defects at the macro level, such. B. increased surface roughness and / or residue from the cutting / grinding process include. In general, any mechanical damage to the magnet, and thus to the Nd ₂ Fe ₁₄ B grid, reduces the anisotropy field of the magnet (and thus the coercive field strength).

As a result, kinks in the second quadrant are usually present in the hysteresis curves of sintered Nd-Fe-B magnets. Even with high-quality magnets with heavy rare earth elements (HRE - Heavy Rare Earth) the kink is still visible. An example is in 2 which shows a demagnetization curve of a sintered Nd-Fe-B magnet with high coercive force. The strength of the Knicks 18 may vary based on the surface roughness and the surface to volume ratio of the magnet. In a segmented magnet much more grains are exposed on a surface due to the smaller thickness. These grains generally have a significantly lower coercivity, which can result in a large kink in the second quadrant of the hysteresis curve. Therefore, the performance of the magnet can be significantly worse than with a corresponding block magnet having the same composition and processing history.

The disclosed segmented permanent magnets and methods of forming them can eliminate the surface softness and damage of sintered and segmented Nd-Fe-B magnets while still combining segmented magnets into a block-sized magnet. The disclosed magnets and methods can increase the coercivity of the sintered Nd-Fe-B magnet and also combine the heat treatment and the combination process into one step.

With reference to 3 is a schematic method of forming a segmented magnet 20 shown. A sintered block magnet can be made into smaller sintered magnetic layers 22 cut or segmented, similar to the segmented magnets described above. But instead of the magnetic layers 22 With the help of an epoxy, insulating layers can be used 24 the magnetic layers 22 separate. As described in more detail below, the insulating layers 24 the damaged surfaces 26 the magnetic layers 22 that are generated during segmentation, "heal". Accordingly, the surfaces can 26 the magnetic layers 22 compared to conventionally joined segmented magnets (eg, using epoxy) have an improved anisotropy field, and thus improved coercivity.

The magnetic layers 22 may be formed of any suitable hard or permanent magnetic material. In an embodiment, the magnetic material may be a rare earth element, such as a rare earth element. Neodymium or samarium. For example, the magnetic material may be a neodymium-iron-boron (Nd-Fe-B) magnet or a samarium-cobalt (Sm-Co) magnet. The specific magnetic material compositions may include Nd ₂ Fe ₁₄ B or SmCo ₅ , however, it should be understood that variations of these compositions or other permanent magnet compositions may also be used. Other materials and / or elements may also be included in the magnetic material to enhance the properties of the magnet (eg, magnetic properties such as coercive force), for example, heavy rare earth elements such as e.g. Y, Tb, Dy, Ho, Er, Tm, Yb and Lu.

The insulation layers 24 may be formed of any suitable material having an electrical resistance greater than that of the magnetic layers 22 is. In an embodiment, the insulating layers 24 a ceramic material. An example of a material that has been tested is calcium fluoride (CaF ₂ ). It has been found, however, that insulating layers of CaF ₂ must be relatively thick to provide suitable resistance. However, thick layers of CaF ₂ cause a magnet to have poor mechanical properties, which may be due to the relatively high melting point of CaF ₂ , which is higher than the sintering and annealing temperatures typically used for Nd-Fe-B magnets ,

It has been found that mixtures of ceramic materials in the insulation layers 24 can be used, which may have lower melting points than the underlying ceramics. These mixtures can utilize eutectic reactions. Although the ceramics tend to have high melting points, the eutectic reaction between ceramics can significantly reduce the melting point of a ceramic mixture. Even if the total composition of the mixture of a system is not at or near the eutectic point, the melting point on the surface of the particles of the mixture may be significantly reduced. In the densification process of ceramics, the formation of a liquid phase can improve the compaction rate and thus increase the cohesive force of the insulation layers. In liquid phase sintering, material transport through a continuous liquid grain boundary film is much faster and is assisted by capillary forces created by voids in the liquid present in the interstices between the particles. Further, increasing the liquid phase volume during sintering may improve the interaction between the magnet and the insulating layers.

In an embodiment, the insulating layers 24 a mixture of (eg, two or more) compounds comprising an alkaline earth metal and a halogen. These compounds may have a formula AH ₂ , such as. B. difluorides include, wherein A is an alkaline earth metal and H is a halogen. The alkaline earth metals may include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). The halogens may include fluorine (F), chlorine (Cl), bromine (Br), iodine (I) and astatine (At). In at least one embodiment, the alkaline earth metal may be calcium and / or magnesium. In at least one embodiment, the halogen may be fluorine (F) or chloro (Cl). Mixtures may be formed of two or more of any combination of the above. For example, the mixture may include MgF ₂ and CaF ₂ .

The insulation layers 24 also compounds with a formula MH ₃ , such as. Trifluorides, where M is a metal having a +3 oxidation state and H is a halogen. Compounds having a formula MH ₄ may also be included, wherein the metal has a +4 oxidation state. Examples of metals M may include aluminum, iron, zirconium, rare earth elements or other metals in the aluminum and scandium columns of the periodic table. These compounds may be mixed with AH ₂ compounds as described above.

In addition to the above compounds, the mixture may include one or more compounds comprising an alkali metal and a halogen. The alkali metals may include lithium (Li), sodium (Na), potassium (K), rubidium (Rb) or cesium (Cs). Accordingly, the mixture compounds such. LiF, NaF, KF, LiCl, NaCl, KCl or any other combination. These compounds may have a formula BH, wherein B is an alkali metal and H is a halogen.

The above compounds may be mixed in any combination to form binary, ternary or quaternary systems or higher (eg, systems having 2, 3, 4 or more components). All systems may include one type of compound (e.g., binary or ternary systems, all being alkaline earth metal halide or all alkali metal halide compounds), such as. B. a binary System MgF ₂ and CaF ₂ or a ternary system LiF-NaF-KF. Or the systems can be mixed, such. A binary system comprising an alkaline earth metal halide and an alkali metal halide compound or a ternary system having two of one type and one of the other type. Similarly, metal halo compounds may be included in any of the above.

A phase diagram showing a mixture of AlF ₃ and CaF _{2 is} shown in FIG 4 shown. The eutectic temperature for this system is about 836 ° C, which is much lower than any of the individual melting points of 1,410 ° C (CaF ₂ ) and 1,291 ° C (AlF ₃ ). The eutectic composition is about 37.5 mol% AlF ₃ .

These binary, ternary, quaternary or higher systems can be eutectic systems. The overall composition used for the insulation material mixture may be at or near the eutectic point such that the melting point of the mixture is reduced compared to the underlying components. For example, the composition may be within a certain molar ratio of the eutectic point, such as. 5%, 10%, 15%, 20%, 25% or 30%. This is very easy for a binary system, such as B. AlF ₃ and CaF ₂ described. The eutectic point of this system is about 37.5 mol% AlF ₃ and 62.5% CaF ₂ , therefore, for a composition that is within 10% of the eutectic point, the composition may have 27.5% to 47, 5% AlF ₃ and 52.5% to 72.5% CaF ₂ . The same can apply to other binary systems or to ternary and quaternary systems. In one embodiment, the composition of the mixture for the binary system AlF ₃ and CaF _{2 may be} 30% to 60% AlF ₃ in molar ratio and 40% to 70% CaF ₂ in molar ratio.

As described above, even if the composition of the mixture is not a eutectic composition, melting on the surface of the particles or powders may still occur at temperatures below the melting point. Accordingly, even relatively small amounts of second or additional compound can enhance sintering. Thus, the composition may comprise at least 5 mole% of a second or additional compound, for example at least 10 mole%, 15 mole%, 20 mole% or 25 mole%. The second or additional connection can be any of the connections in a binary system. For example, if the second 10 mol% compound is present in the AlF ₃ and CaF ₂ system, the composition may be either 10 mol% AlF ₃ or 20 mol% CaF ₂ . The same can apply to other binary systems or to ternary and quaternary systems.

In other words, the overall composition used for the insulating material mixture may be at or near the eutectic point such that the melting point of the mixture is at or near the temperature of the eutectic point. For example, the composition may be designed such that the melting point is within a certain temperature of the temperature of the eutectic point, such. Within 5 ° C, 10 ° C, 25 ° C, 50 ° C, 75 ° C or 100 ° C. Accordingly, if the composition is designed to have a melting point within 50 ° C of the temperature of the eutectic point for a mixture of AlF ₃ and CaF ₂ (eutectic point of 836 ° C), then the composition may have a melting point of 786 ° C to 886 ° C have. However, since the eutectic point is typically a minimum melting point (or at least a local minimum), the composition may have a melting point from the temperature of the eutectic point (836 ° C) to 886 ° C.

Depending on the composition of the mixtures used for the insulating layers, the melting point may vary. The composition of the insulating material mixture may be designed such that the melting point is less than or equal to 1100 ° C, 1050 ° C or 1000 ° C, for example 800 ° C to 1100 ° C, 850 ° C to 1000 ° C, 800 ° C to 950 ° C, 850 ° C to 950 ° C, 800 ° C to 900 ° C, 900 ° C to 1000 ° C, 950 ° C to 1000 ° C, 800 ° C to 875 ° C or 800 ° C to 850 ° C , The melting point of the mixture may be lower than a sintering temperature of the magnetic material. In one embodiment, the sintering temperature of the magnetic material may be 1000 ° C to 1100 ° C, for example, 1025 ° C to 1075 ° C or about 1060 ° C. The melting point of the insulating layers may be at or near the annealing temperature of the magnetic layers 22 lie. For example, the melting point may be within (eg ±) 10 ° C, 25 ° C, 50 ° C, 75 ° C or 100 ° C of the annealing temperature. Therefore, when the annealing temperature is 900 ° C and the melting point is within 25 ° C, the melting point may be 875 ° C to 925 ° C. Likewise, the annealing temperature may be within (eg ±) 10 ° C, 25 ° C or 50 ° C of the melting temperature. As described above, even if the composition of the mixture is not a eutectic composition (e.g., molar ratio of about 1: 1 for MgF ₂ and CaF ₂ and 37.5 mol% AlF ₃ for AlF ₃ and CaF ₂ ), still melting occurs on the surface of the particles or powders, thereby improving material transport and densification during sintering.

By reducing the melting temperature of the insulating layer material, the insulating layer may be at least partially exposed during annealing. Heat treatment after joining the magnetic layers 22 and the insulation layers 24 melt. This melting can increase the adhesion force between the magnetic and insulating layers, while also improving inter-layer diffusion. This may cause "sticking" (eg, joining) of the magnetic layers 22 and the annealing of the magnetic layer 22 be carried out in a single step. This step may include the application of pressure, for example perpendicular to the stacked layers. The pressure can be increased when the melting temperature of the insulation layers 24 is higher than the annealing temperature. In contrast, the pressure may be reduced or, in some embodiments, omitted when the melting temperature of the insulating layers 24 lower than the annealing temperature.

In at least one embodiment, the insulating layers 24 one or more rare earth elements (REE), rare earth alloys (REA) or rare earth compounds (REC). Rare earth elements may include 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), which include light and heavy rare earth elements. Rare earth alloys may include any alloy comprising at least one rare earth element and may include non-rare earth elements. Similarly, rare earth compounds may include any compound comprising at least one rare earth element and may include non-rare earth elements. Examples of possible rare earth alloys may include NdCu, NdAl, DyCu, NdGa, PrAl, PrCu and / or PrAg. The rare earth alloys may include one or more rare earth elements as well as copper and / or aluminum and / or gallium and / or silver. The rare earth elements, rare earth alloys and / or rare earth compounds may be used with others above with respect to the insulating layers 24 disclosed materials may be mixed. For example, the insulation layers 24 MgF ₂ and CaF ₂ and NdCu or AlF ₃ and CaF ₂ and NdAl include.

The rare earth elements, rare earth alloys or rare earth compounds may serve as a type of adhesive or binder when mixed with the insulation materials. The total melting point of the insulation layers 24 The rare earth elements may also be within the ranges disclosed above. When melting or partial melting of the insulating layers occurs, the rare earth elements in the insulating layers 24 into the magnetic layers 22 diffuse. As described above, the surfaces of the segmented magnetic layers can have significant damage from the segmentation process. The diffusion of the rare earth elements from the insulation layers 24 , such as B. Nd, the magnetic layers 22 "cure" by increasing the concentration of Nd on the surface of the magnet. Nd-rich phases are very important for the coercivity of Nd-Fe-B magnets; therefore, increasing Nd at the surface can increase the coercive force at the surface of the magnetic layers 22 increase. The rare earth alloys having a low melting point can improve diffusion of the rare earth elements into the surface of the magnetic layers 22 enable.

While addition of rare earth elements / alloys / compounds may improve the magnetic properties and bonding between the magnetic and insulating layers, they typically have very low electrical resistance, and placing them in an insulating layer may serve the purpose of the insulating layer conflict. However, it has been found that the conductivity of a mixture of metallic and dielectric materials is subject to percolation theory. Therefore, the conductivity of the insulating layers can be modulated by controlling the amount of metal or alloy powders in the mixture. If the volume ratio of the metallic component is less than a threshold, the conductivity of the mixture may be close to zero. If the volume ratio of the metallic component is above the threshold, the conductivity of the mixture of a dielectric and a metallic component may be approximately expressed as: $$\sigma ~{\left(p-p_c\right)}^{\mu }$$

Where μ is the critical exponent that describes the behavior of conductivity with varying volume ratio of metal and insulating materials, p can be considered as the volume ratio of the metallic component and p _{c is} the threshold indicating the formation of long-range metal phase compounds. Therefore, rare earth elements / alloys / compounds can be mixed with insulation powders to a certain amount to improve the mechanical and / or magnetic properties of segmented magnetic layers, but without increasing the conductivity to an unacceptable level. If the ratio of the metallic powders is below the threshold, the insulating layer would still be dielectric. When a certain level of electrical conductivity is acceptable, the proportion of rare earth elements can be increased until this level is reached. It has been found, for example, that at a weight ratio of 20% by weight, the specific resistance of the insulating layer can still be up to 1.5 × 10 ⁵ Ω · cm. In one embodiment, the rare earth elements, rare earth alloys, and / or rare earth compounds 1 to 30 % By weight of the insulation layers 24 or any portion thereof. For example, the rare earth elements, rare earth alloys or rare earth compounds 5 to 30 Wt%, 5 to 25 wt%, 10 to 25 wt%, 15 to 25 wt% or about 20 wt% (eg ± 5 wt%).

Referring again to 3 is a segmented sintered magnet 20 shown in cross section. The magnet 20 can have multiple magnetic layers 22 and one or more insulating layers (IL) 24. The insulation layers 24 can be between the magnetic layers 22 be arranged to the electrical resistance of the magnet 20 increase and reduce eddy current losses. The insulation layers 24 can be in direct contact with two spaced and opposite magnetic layers 22 be. The magnetic and / or insulating layers 24 may have a uniform or substantially uniform thickness (eg, within 5% of the average thickness). There can be several layers of insulation 24 be present, for example, an insulation layer 24 between each pair of adjacent magnetic layers 22 , In one embodiment, "x-1" isolation layers 24 be present when "x" magnetic layers 22 available. In the in 3 Example shown are three magnetic layers 22 and two insulation layers 24 but any suitable number of each layer may be present. The magnet can have at least two magnetic layers 22 such that they pass through an insulating layer 24 are separated. However, there may be 3, 4, 5, 10 or more magnetic layers 22 be present, corresponding to 2, 3, 4, 9 or more insulation layers 24 may include, between each pair of magnetic layers 22 are arranged.

In at least one embodiment, the insulating layer (s) may / may 24 be relatively thin. For example, the insulation layer (s) may / may 24 have a thickness (eg, average thickness) of 1 to 1,000 μm or each portion therein. In an embodiment, the insulating layers 24 a thickness of 5 to 500 μm, 5 to 300 μm, 5 to 200 μm, 5 to 150 μm, 5 to 100 μm, 5 to 50 μm, 5 to 25 μm, 10 to 500 μm, 10 to 250 μm, 10 to 150 μm, 25 to 250 μm, 25 to 150 μm, 50 to 150 μm, 50 to 100 μm or 25 to 100 μm. However, thicknesses outside these ranges may also be possible. In one embodiment, the thickness may be thick enough to be in spite of the surface roughness of the magnetic layers 22 to provide a continuous layer of resistive material.

To the magnet 20 For example, a block magnet that has been previously sintered may be thinned into pieces or layers 22 cut, segmented or otherwise shared. Depending on the roughness of the layers, a polishing or grinding step may follow after segmentation. The block magnet may be a rare earth magnet, such as. A Nd-Fe-B or Sm-Co magnet. After the layers 22 are formed, an insulating layer 24 on the magnetic layer 22 applied, applied or arranged. The insulation layer 24 may comprise a mixture of materials which may include insulation materials and "adhesive" materials as described above. For example, the insulation materials AH ₂ - and / or MH ₃ materials, such as. As Ca / MgF ₂ and / or AlF ₃ include. As described above, these mixtures may have reduced melting points as compared to their individual components.

The insulation layers 24 may be applied as a powder, a suspension, a spray, a liquid, a plate, a green body or in any other suitable form. For example, when the layer is applied as a powder, the magnetic layers may 22 placed in a mold and the insulating powder can be applied to or over a magnetic layer. The powder can be leveled, pressed or otherwise made uniform before another magnetic layer 22 is placed on or over the insulating powder layer. These steps can be repeated until a desired number of insulation layers 24 a desired number of magnetic layers 22 separates.

Once the stack of magnetic layers 22 and insulation layers 24 is formed, a coalescing process can be performed. This process may include heating the magnetic stack and optionally applying pressure (eg, perpendicular to the stacked layers as shown). This process can be performed at the same temperature and / or for the same duration as the conventional annealing process, and therefore can replace the annealing process. In the disclosed magnetic stack, the heat treatment may also cause the sintered magnetic layers 22 and the unsintered insulating layers 24 bind together. The bond may be due to diffusion due to the heat treatment occurring at or near the melting point of the insulating material. In at least one embodiment, the bond is formed without any adhesive or resin, such as e.g. As polymers or epoxides. The insulating layer may in one embodiment only consist of inorganic materials (eg ceramics) and metal (s).

The rare earth elements, rare earth alloys or rare earth compounds at or near the segmented surfaces of the magnet may be those in the surfaces of the magnetic layers 22 "heal" damage resulting from the segmentation process. Rare earth elements such. B. Nd, can be made of the insulating material in the surface of the magnetic layers 22 which increases the amount of Nd-rich phase at the surface and increases the coercivity of the layers. Pressure can also be applied to improve the bond between the insulating layers and the magnetic layers. Higher pressures can be applied if the insulating materials have a melting point higher than the heat treatment temperature. Lower pressures (or no pressure) can be applied if the insulating materials have a melting point as high or lower than the heat treatment temperature.

The disclosed magnets can be used for any magnetic application in which hard / permanent magnets are used. The magnets can be advantageous when eddy currents arise. In one embodiment, the magnets may be used in electric motors or generators, as described, for. B. used in hybrid or electric vehicles. The disclosed magnets and methods of forming the same may reduce the temperature of the magnet, thus requiring a lower coercive force of the magnet. Therefore, less heavy rare earth materials are required, which reduces the cost of electric motors. In addition, energy is saved, which can improve the fuel consumption / range (MPG - Miles Per Gallon) of electric vehicles.

Although exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Moreover, the features of various implementation embodiments may be combined to form further embodiments of the invention.

Claims (17)

Segmented magnet, comprising: a first layer of permanent magnetic material; a second layer of permanent magnetic material; and an insulating layer separating the first and second layers and comprising a rare earth element and a ceramic mixture having at least first and second ceramic materials. Magnet after Claim 1 wherein the ceramic mixture has a melting point lower than a melting point of the first and second ceramic materials. Magnet after Claim 1 or 2 wherein the first or second ceramic material comprises a compound having a formula AH ₂ wherein A is an alkaline earth metal and H is a halogen. A magnet according to any one of the preceding claims, wherein the first or second ceramic material comprises a compound having a formula MH ₃ , wherein M is a metal having a +3 oxidation state and H is a halogen. A magnet according to any one of the preceding claims, wherein the first or second ceramic material comprises a compound having a formula BH, wherein B is an alkali metal and H is a halogen. A magnet according to any one of the preceding claims, wherein the ceramic mixture has a melting point of less than or equal to 1000 ° C. A magnet according to any one of the preceding claims, wherein the rare earth element is part of a rare earth alloy or a rare earth compound. Magnet after Claim 7 wherein the rare earth alloy comprises NdCu and / or NdAl and / or DyCu and / or NdGa and / or PrAl and / or PrCu and / or PrAg. A magnet according to any one of the preceding claims, wherein the rare earth element comprises up to 20% by weight of the insulating layer. A magnet according to any one of the preceding claims, wherein the permanent magnetic material in the first and second layers is an Nd-Fe-B magnet and the rare earth element is in the insulating layer Nd. A method for forming a segmented magnet, in particular a magnet according to one of the preceding claims, comprising: applying an insulating layer to a first sintered permanent magnet layer, wherein the insulating layer is a rare earth element and a Ceramic mixture comprising at least first and second ceramic materials; Stacking a second sintered permanent magnet layer in contact with the insulating layer and spaced from the first sintered permanent magnet layer to form a magnetic stack; and heating the magnetic stack. Method according to Claim 11 wherein the first and second ceramic materials are selected from a group consisting of: a compound having a formula AH ₂ , wherein A is an alkaline earth metal and H is a halogen; a compound having a formula MH ₃ , wherein M is a metal having a +3 oxidation state and H is a halogen; and a compound having a formula BH, wherein B is an alkali metal and H is a halogen. Method according to Claim 11 or 12 wherein the ceramic mixture has a melting point lower than a melting point of the first and second ceramic materials. Method according to Claim 13 wherein the step of heating comprises annealing the magnetic stack at an annealing temperature within 100 ° C of the melting point of the ceramic mixture. Method according to one of Claims 11 to 14 further comprising applying pressure to the magnetic stack during the step of heating. Method according to one of Claims 11 to 15 further comprising segmenting the first and second sintered permanent magnet layers from a sintered block magnet prior to the applying step. Method according to one of Claims 11 to 16 wherein the rare earth element comprises up to 30% by weight of the insulating layer.

Images