METHOD FOR PRODUCING A PERMANENT MAGNET FROM A MAGNETIC STARTING MATERIAL

Abstract

The invention relates to a method of producing a permanent magnet from a powdered magnetic base material. The powdered magnetic base material is shaped, wherein a raw form is prepared. The raw form is sintered, wherein the permanent magnet is produced. In at least one step of the method, between particles of the powdered magnetic base material an electrical resistance layer having a lower electrical conductivity than the powdered magnetic base material is formed.

Claims

1. Method of producing a permanent magnet from a powdered magnetic base material, wherein the powdered magnetic base material is shaped, wherein a raw form is prepared, wherein the raw form is sintered, wherein the permanent magnet is produced, wherein in at least one step of the method, between particles of the powdered magnetic base material an electrical resistance layer having a lower electrical conductivity than the powdered magnetic base material is formed.

2. Method according to claim 1, wherein as magnetic base material a material is used which is made of particles of R.sub.xT.sub.yB alloy and preferably particles of rare-earth-rich phase.

3. Method according to claim 1, wherein the magnetic base material is mixed with an organic binder, wherein a mixture of the magnetic base material) and the organic binder is obtained, wherein the raw form is prepared from the mixture, wherein the organic binder is at least partially removed from the raw form before sintering.

4. Method according to claim 1, wherein the electrical resistance layer is formed from the organic binder.

5. Method according to claim 1, wherein the magnetic base material is mixed with at least one resistance building substance, wherein the electrical resistance layer is formed from the at least one resistance building substance, wherein the at least one resistance building substance is preferably selected from a group consisting of an organic substance, a rare-earth compound, a ceramic, and a reaction gas.

6. Method according to claim 1, wherein the organic substance is selected from a group consisting of a solvent, an oxygen-containing polymer, a halogen-containing polymer, a nitrogen-containing polymer, a carbon-containing polymer, a silicon-containing polymer, a sulfur-containing polymer, and a boron-containing polymer.

7. Method according to claim 1, wherein the rare-earth compound is selected from a group consisting of a carbon-containing rare-earth compound, a sulfur-containing rare-earth compound, an oxygen-containing rare-earth compound, a nitrogen-containing rare-earth compound, a boron-containing rare-earth compound, a silicon-containing rare-earth compound, a fluorine-containing rare-earth compound and a chlorine-containing rare-earth compound.

8. Method according to claim 1, wherein the ceramic is selected from a group consisting of an oxide ceramic, a carbide ceramic, and a nitride ceramic.

9. Method according to claim 1, wherein the reaction gas is selected from a group consisting of an oxygen-containing gas, a nitrogen-containing gas, a carbon-containing gas, a fluorine-containing gas, a chlorine-containing gas, a sulfur-containing gas, and a hydrogen-containing gas.

10. Method according to claim 1, wherein the mixing of the magnetic base material with the at least one resistance building substance is carried out at a temperature of at least 20° C. to at most 1100° C.

11. Method according to claim 1, wherein the magnetic base material is pretreated with a pretreatment gas, wherein the electrical resistance layer is generated by means of the pretreatment gas.

12. Method according to claim 1, wherein the raw form is produced by means of a process selected from a group consisting of injection molding, additive manufacturing, extrusion, cold pressing, and hot pressing.

13. Method according to claim 1, wherein the raw form is produced in an externally applied magnetic field.

14. Method according to claim 1, wherein the raw form is exposed to an atmosphere comprising a process gas selected from a group consisting of an argon-containing gas, an oxygen-containing gas, a nitrogen-containing gas, a carbon-containing gas, a fluorine-containing gas, a chlorine-containing gas, a sulfur-containing gas, and a hydrogen-containing gas.

15. Method according to claim 1, wherein the electrical resistance layer is formed as completely embracing covering of at least one of the particles of the magnetic base material.

16. Method according to claim 1, wherein the electrical resistance layer is formed as a non-closed covering of at least one of the particles of the magnetic base material, wherein the electrical resistance layer is preferably in the form of particles, preferably finely distributed particles, wherein the particles of the electrical resistance layer are arranged between the particles of the magnetic base material.

17. Composite material, in particular for a permanent magnet, wherein the composite material comprises a magnetic material and an electrically insulating material, wherein an electrical resistance layer formed from the electrically insulating material is arranged between particles of the magnetic material and has a lower electrical conductivity than the magnetic material, wherein in particular the electrically insulating material at least partially surrounds the particles of the magnetic material or is present in the form of finely distributed particles between the particles of the magnetic material.

18. Permanent magnet produced by a method according to claim 1.

19. Permanent magnet comprising a composite material according to claim 17.

Description

[0082] FIG. 1 a flow diagram of a method for producing a permanent magnet with an electrical resistance layer,

[0083] FIG. 2 a schematic representation of a first embodiment of a method for producing a first embodiment of a permanent magnet with an electrical resistance layer,

[0084] FIG. 3 a schematic representation of a second embodiment of a method for producing the first embodiment of a permanent magnet with an electrical resistance layer, and

[0085] FIG. 4 a schematic representation of a second embodiment of a permanent magnet with an electrical resistance layer.

[0086] FIG. 1 shows a flow diagram of a method for producing a permanent magnet 1 with an electrical resistance layer 3 shown in FIG. 2. In step a), the magnetic base material 7 is provided, preferably in powdered form. In step b), the magnetic base material 7 is shaped, wherein a raw form 12, also shown in FIG. 2, is created. The raw form 12 is preferably produced by a process selected from a group consisting of injection molding, additive manufacturing, extrusion, cold pressing, and hot pressing. Optionally, the raw form 12 is produced under an externally applied magnetic field, preferably the magnetic field is generated by a switchable electromagnet and/or a permanent magnet. In step c), the raw form 12 is sintered, wherein the permanent magnet 1 is produced. In at least one step of the method, an electrical resistance layer 3 having a lower electrical conductivity than the magnetic base material 7 is formed between particles of the magnetic base material 7.

[0087] Preferably, the raw form 12 comprises the magnetic base material 7 with a volume fraction of 30% to 70%.

[0088] Preferably, the raw form 12 is sintered in the step c) at a temperature of 1000° C. to 1200° C. for a preferred duration of 30 minutes to 300 minutes.

[0089] Between step a) and step b), the following method steps d), e) and f1) to f3)—individually or in combination with each other—can optionally be carried out:

[0090] In step d), the magnetic base material 7 is pretreated with a pretreatment gas, wherein the electrical resistance layer 3 is generated by means of the pretreatment gas. Preferably, the pretreatment gas is selected from a group consisting of an argon-containing gas, an oxygen-containing gas, a nitrogen-containing gas, a carbon-containing gas, a fluorine-containing gas, a chlorine-containing gas, a sulfur-containing gas, and a hydrogen-containing gas. In particular, the pretreatment gas comprises argon and/or nitrogen and/or another inert gas, and at least one substance selected from water, oxygen, and hydrogen. In a preferred embodiment of the method, the pretreatment gas comprises argon and oxygen. In a preferred embodiment of the method, the pretreatment gas consists of argon and oxygen. During treatment with the pretreatment gas, the surfaces of the particles of the magnetic base material 7 oxidize, forming finely distributed rare-earth oxides on the surfaces, which have a lower electrical conductance than the magnetic base material 7. Preferably, the magnetic base material 7 is treated with the pretreatment gas at a temperature of from 20° C. to 250° C., particularly preferably from 100° C. to 250° C.

[0091] In step e), the magnetic base material 7 is mixed with an organic binder 11, wherein a mixture 5 of the magnetic base material 7 and the organic binder 11 is obtained. In this case, the raw form 12 is created from the mixture 5 in step b). Preferably, the electrical resistance layer 3 is formed from the organic binder 11. Preferably, the magnetic base material 7 is mixed with the organic binder 11 at a temperature of from 20° C. to 250° C., more preferably from 60° C. to 200° C. Preferably, when the electrical resistance layer 3 is formed from the organic binder 11, the raw form 12 obtained in step b) has the organic binder 11 in a volume fraction of from 0.01% to 50%, preferably from 1% to 10%.

[0092] In steps f1) to f3)—which can be carried out individually or in combination with one another—the magnetic base material 7 is mixed with at least one resistance building substance 9, wherein the electrical resistance layer 3 is formed from the at least one resistance building substance 9. The at least one resistance building substance 9 is selected from a group consisting of an organic substance, a rare-earth compound, a ceramic and a reaction gas. Preferably, the raw form 12 obtained in the step b) has the at least one resistance building substance 9 with a volume fraction of from 0.01% to 50%, preferably from 1% to 10%. Preferably, the at least one resistance building substance 9 is mixed with the magnetic base material 7 and preferably the organic binder 11 at a temperature of from 20° C. to 250° C., particularly preferably from 60° C. to 200° C.

[0093] In step f1), the magnetic base material 7 is mixed with an organic substance selected from a group consisting of a solvent, an oxygen-containing polymer, a halogen-containing polymer, a nitrogen-containing polymer, a carbon-containing polymer, a silicon-containing polymer, a sulfur-containing polymer and a boron-containing polymer. In particular, the organic substance is liquid or solid at room temperature. In an embodiment of the method, the organic substance is selected from a group consisting of waxes, thermoplastic resin, alcohols, silicones, and fluorochlorohydrocarbons.

[0094] In step f2), the magnetic base material 7 is treated with a rare-earth compound selected from a group consisting of a carbon-containing rare-earth compound, a sulfur-containing rare-earth compound, an oxygen-containing rare-earth compound, a nitrogen-containing rare-earth compound, a boron-containing rare-earth compound, a silicon-containing rare-earth compound, a fluorine-containing rare-earth compound and a chlorine-containing rare-earth compound.

[0095] Alternatively or additionally, in step f2), the magnetic base material 7 is mixed with a ceramic, preferably ceramic particles selected from a group consisting of an oxide ceramic—in particular aluminium oxide, zirconium oxide or titanium oxide —, a carbide ceramic and a nitride ceramic.

[0096] In step f3), the magnetic base material 7 is mixed with a reaction gas selected from a group consisting of an oxygen-containing gas, a nitrogen-containing gas, a carbon-containing gas, a fluorine-containing gas, a chlorine-containing gas, a sulfur-containing gas, and a hydrogen-containing gas. Preferably, the magnetic base material 7 is treated with the reaction gas at a temperature of from 20° C. to 250° C., particularly preferably from 100° C. to 250° C.

[0097] In an embodiment, the at least one resistance building substance 9 forms the electrical resistance layer 3. Alternatively or additionally, at least two resistance building substances 9 react with each other, or the resistance building substance 9 decomposes, or the resistance building substance 9 reacts with another substance, and at least one resulting reaction product forms the electrical resistance layer 3. Alternatively or additionally, the at least one resistance building substance 9 acts as a catalyst in forming the electrical resistance layer 3. Alternatively or additionally, the magnetic base material 7 acts as a catalyst in a reaction of at least two resistance building substances 9, the decay of the resistance building substance 9, or the reaction of the resistance building substance 9 with another substance to form the electrical resistance layer 3.

[0098] Optionally, the mixing of the magnetic base material 7 with the at least one resistance building substance 9 is carried out at a temperature of from at least 20° C. to at most 1100° C., preferably from 150° C. to 1100° C. Preferably, the effect of temperature causes activation of the at least one resistance building substance 9. Alternatively or additionally, the at least one resistance building substance 9 decomposes under the effect of temperature to form the electrical resistance layer 3.

[0099] Between step b) and step c), the following method steps—individually or in combination with one another—can optionally be carried out:

[0100] In step g), an organic binder 11, which was added to the magnetic base material 7 in step e), is at least partially removed. The parts of the organic binder 11 remaining in the raw form 12 remain in the raw form 12 during sintering and are accumulated around the particles of the magnetic base material 7 and/or at the grain boundaries and form the electrical resistance layer 3. It is also possible that the parts of the binder 11 remaining in the raw form 12 are chemically changed during sintering and in this way form the electrical resistance layer 3.

[0101] Alternatively, in step g), a liquid component which has been added to the magnetic base material 7, in particular during wet cold pressing, is removed. Preferably, in step g) a thermal debinding is carried out, in particular to thermally decompose the organic binder 11 which is present in the raw form 12. Particularly preferably, the raw form 12 is thermally debinded, in particular thermally decomposed, at a temperature of 150° C. to 900° C. In particular, the thermal debinding, in particular thermal decomposition, is carried out for a duration of 3 hours to 16 hours. Particularly preferably, at least one temperature selected from a group consisting of 150° C., 200° C., 250° C., 300° C., 350° C., 400° C., 450° C., 500° C., 550° C., 600° C., 650° C., 700° C., 750° C., 800° C., 850° C., and 900° C. is kept constant for a duration of 30 minutes to 180 minutes during the thermal debinding.

[0102] Prior to and/or during the sintering in step c), the raw form 12 is exposed to a process gas in step h), in particular during the removal of the organic binder 11 or the liquid component in step g).

[0103] The process gas is preferably selected from a group consisting of an argon-containing gas, an oxygen-containing gas, a nitrogen-containing gas, a carbon-containing gas, a fluorine-containing gas, a chlorine-containing gas, a sulfur-containing gas and a hydrogen-containing gas. Preferably, the process gas serves as a reactant and/or a catalyst of the at least one resistance building substance 9.

[0104] FIG. 2 shows a schematic representation of a first embodiment of a method for producing a first embodiment of a permanent magnet 1 having an electrical resistance layer 3.

[0105] FIG. 2a) shows a mixture 5 of a magnetic base material 7, preferably an R.sub.xT.sub.yB alloy, in particular an Nd.sub.xFe.sub.yB alloy, a resistance building substance 9 and an organic binder 11. A raw form 12 is produced from the mixture 5 by a process, preferably selected from a group consisting of injection molding, additive manufacturing, extrusion, cold pressing, and hot pressing.

[0106] Preferably, the mixture 5 is prepared by mixing the magnetic base material 7, the resistance building substance 9, and the organic binder 11 in one step. Alternatively, preferably the magnetic base material 7 is first mixed with the organic binder 11 and then the resistance building substance 9 is added. Alternatively, a dry mixture is preferably prepared from the magnetic base material 7 and the resistance building substance 9, and then the dry mixture is mixed with the organic binder 11.

[0107] FIG. 2b) shows the raw form 12 after at least partial removal of the organic binder 11. The at least partial removal of the organic binder 11 was carried out under the effect of temperature, preferably from at least 20° C. to at most 1100° C. Alternatively, the organic binder is partially removed from the raw form by solvent extraction. Thereafter, the organic binder is removed from the raw form by means of thermal decomposition. Alternatively, the organic binder is chemically cleaved by means of a chemical reaction. Thereafter, the organic binder is removed from the raw form by means of thermal decomposition.

[0108] During the at least partial removal of the organic binder 11 under the effect of temperature, the electrical resistance layer 3 is formed around the particles of the magnetic base material 7—in particular from the binder 11 itself, or by decomposition of the binder 11, or by reaction of the binder 11 with the resistance building substance 9. Alternatively or additionally, the resistance building substance 9 reacts with the particles of the magnetic base material 7 to form the electrical resistance layer 3.

[0109] FIG. 2c) shows the permanent magnet 1 after sintering. The particles of the magnetic base material 7 form grains 13, in particular R.sub.xT.sub.yB grains. The grains 13 are each enclosed by the electrical resistance layer 3. An additional phase 15, in particular a rare-earth-rich phase, is formed between the grains 13 with the electrical resistance layer 3.

[0110] FIG. 3 shows a schematic representation of a second embodiment of a method for producing the first embodiment of a permanent magnet 1 with an electrical resistance layer 3.

[0111] In FIG. 3a) a mixture 5 of a magnetic base material 7, preferably of an R.sub.xT.sub.yB alloy, in particular of an Nd.sub.xFe.sub.yB alloy, and a resistance building substance 9 is shown.

[0112] In FIG. 3b) the mixture 5 is shown after a reaction of the resistance building substance 9 with the particles of the magnetic base material 7. The resistance building substance 9 accumulates around the particles of the magnetic base material 7 to form the electrical resistance layer 3. Alternatively or additionally, the resistance building substance 9 reacts with the particles of the magnetic base material 7 to form the electrical resistance layer 3.

[0113] FIG. 3c) shows the permanent magnet 1 after the raw form 12 has been produced and sintered. The particles of the magnetic base material 7 form grains 13, in particular R.sub.xT.sub.yB grains. The grains 13 are each enclosed by the electrical resistance layer 3. The additional phase 15, in particular a rare-earth-rich phase, is formed between the grains 13 with the electrical resistance layer 3.

[0114] FIG. 4 shows a schematic diagram of a second embodiment of a permanent magnet 1 with an electrical resistance layer 3. A resistance building substance 9 is deposited between the grains 13 of the magnetic base material 7 as the electrical resistance layer 3. In this case, the resistance building substance 9 is embedded in the additional phase 15, in particular a rare-earth-rich phase. The additional phase 15 is preferably a thin layer at the grain boundaries of the microstructure of the permanent magnet 1.