EP3507039A1

EP3507039A1 - Recycling method for producing magnetic isotropic powders

Info

Publication number: EP3507039A1
Application number: EP17764346.7A
Authority: EP
Inventors: Oliver Diehl; Almut Dirks; Konrad Güth; Eva Brouwer; Hartmut Hibst; Alexandru Lixandru; Alexander Buckow; Roland Gauss; Oliver Gutfleisch
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date: 2016-08-30
Filing date: 2017-08-28
Publication date: 2019-07-10
Also published as: DE102016216353A1; WO2018041776A1

Abstract

The invention relates to a recycling method for producing magnetic isotropic powders, having the following steps: a) providing a magnetic alloy which comprises a1) at least one rare-earth metal, a2) at least one transition metal, and a3) boron; b) hydrogenating the alloy from step a) in a hydrogen-containing atmosphere at temperatures ranging from 0 to 600 °C and at a hydrogen partial pressure ranging from 10,000 to 15,000,000 Pa, thereby forming monocrystalline particles; c) disproportioning the particles from step b) in a hydrogen-containing atmosphere at temperatures ranging from more than 600 to 1,000 °C at a hydrogen partial pressure ranging from 30,000 to 1,000,000 Pa; and d) desorbing and subsequently recombining the hydrogen, thereby forming isotropic powder particles; wherein the alloy provided in step a) is partly or completely scrap magnetic material. The invention additionally relates to the powders which can be produced using said method and to the use thereof.

Description

Recirculation process for the production of isotropic, magnetic powders

The present invention relates to recycling processes for producing isotropic, magnetic powder from old magnetic material. Furthermore, the isotropic, magnetic powders prepared therefrom and their use in

Permanent magnets, in particular in the fields of motors, generators and electrical and electronic applications claimed.

Currently, old magnets are hardly recycled industrially. On a larger scale, recycling usually takes place only from production residues. Here, above all, the energy and material intensive material recycling is operated, i. Old magnets are added to the hydrometallurgical rare earth metal recovery process. The inherent value of the magnetic alloy is lost as a functional value.

For the functional recycling of magnetic alloys, eg neodymium-iron-boron alloys, the process of hydrogen embrittlement

known. This process is also called HD process (Hydrogen Decrepitation).

WO 2012/101398 A1 relates to a method for removing one or more rare earth magnets from an arrangement comprising a plurality of rare earth magnets. At this time, the rare earth magnet (s) are exposed to hydrogen gas to cause hydrogen embrittlement of the magnet, thereby producing a particulate rare earth material which is separated from the remainder of the device.

WO 2012/072989 A1 describes a process for the recovery of particulate rare earth materials from a multi-part construction comprising a rare earth magnet. The method comprises the steps of treating the multi-part structure with hydrogen gas to cause hydrogen embrittlement of the rare earth magnet and to obtain a particulate rare earth material and separating the particulate rare earth material from the remainder of the multi-part structure.

WO 2000/017894 A1 relates to methods for the reuse of permanent magnets comprising the steps of: separating the magnetic material from a composite body under the action of a gaseous material which embrittles the magnetic material by its action, where appropriate before and / or during and / or after the action of the gaseous material Material is a mechanical effect on the composite body, which supports the process of separation and reuse of the recovered magnetic material for the production of brand new permanent magnets.

The embrittlement with hydrogen gives starting powders for the sintering of new magnets, but this procedure can neither change the chemical composition nor the microstructure of the particles. Already in the old magnet contained or taken up during the treatment impurities, especially oxygen and carbon, lead even under ideal conditions to losses in the coercive field strength and the remanence with respect to the original magnet.

Furthermore, a method is known in which the hydrogen embrittlement the subsequent steps of disproportionation, desorption and recombination, this process is also called HDDR process

(Hydrogenation, Disproportionation, Desorption and Recombination) known.

DE 102 55 604 A1 relates to processes for producing an anisotropic magnetic powder, in which a magnet material with anisotropic orientation based on a SE-TM-B alloy with SE as rare earth element including yttrium and TM as transition metal is used as starting material. Hydrogen is generated by a first hydrogenation process under heating under hydrogen pressure. A second hydrogenation process produces a phase transformation which proceeds under hydrogen pressure and an elevated temperature inducing the phase transformation. A mixture with a TM _X B phase, in particular Fe ₂ B phase, is produced and a dehydrogenation process with a reverse phase transformation (HDDR

Procedure) is performed.

WO 2012/002774 A2 A relates to a process for the preparation of

R-Fe-B based rare earth magnetic powders with special magnetic properties. The process comprises the following steps: coarse grinding of sintered rare earth magnets as a raw material, placing the coarse material in a tube furnace, filling the tube furnace with hydrogen and raising the temperature, performing disproportionation in the same hydrogen atmosphere while further raising the temperature, allowing the material to flow out Hydrogen from the interior of the tube furnace and then removing the remaining hydrogen from the tube by vacuum, with recombination taking place

The hitherto known HDDR processes are aimed at the production of anisotropic neodymium-iron-boron powder particles for plastic-bonded magnets. However, it is extremely disadvantageous in these methods that the process conditions for the production of anisotropic particles vary greatly with respect to the proportions of other elements contained in neodymium-iron-boron magnets, such as cobalt and dysprosium. This requires finding suitable process parameters, such as pressure, temperature and time, for each specific alloy composition and dynamic control of these parameters during the process. An anisotropic material having a homogeneous quality can therefore be obtained only from a pure alloy as a starting material. For an industrial recycling of typically not exactly known and mixtures of old magnets of different alloys, the known methods are less suitable, in particular for economic reasons.

On this basis, it was an object of the present invention to provide a method which allows a recycling of old magnets on the alloy level and which allows further processing of the resulting powder particles directly to new magnet. It is a further object of the present invention to provide a process which can be used in an alloy-independent manner, ie. can be operated without elaborate analysis of the starting materials, optionally component separation, and adaptation, and without dynamic control of the process parameters, i. It was a partial task to provide a method in which it is possible to dispense with the use of sensors and regulators for checking the process parameters, ie to provide a method which is both more robust and less expensive than the methods known from the prior art.

This object is achieved by a method having the features of claim 1 and by the powder produced according to this method according to claim 9.

According to the invention, there is provided a recycling process for producing isotropic magnetic powders comprising the steps of: a) providing a magnetic alloy comprising al) at least one rare earth metal, a2) at least one transition metal and a3) boron; b) hydrogenation of the alloy from step a) in a hydrogen-containing atmosphere at temperatures of 0 to 600 ° C and a hydrogen partial pressure of 10,000 to 15,000,000 Pa, with formation of monocrystalline particles; c) disproportionation of the particles from step b) in a hydrogen-containing atmosphere at temperatures in the range from greater than 600 to

1 000 ° C at a hydrogen partial pressure of 30,000 to 1,000,000 Pa; d) desorption of the hydrogen and subsequent recombination to form isotropic powder particles; wherein the alloy provided in step a) is partially or completely recovered magnetic material.

The method according to the invention makes it possible, surprisingly, to prepare isotropic powders which are suitable for the direct production of new permanent magnets, wherein neither a matching of the process conditions to the selected starting material nor a dynamic regulation of the process parameters is necessary.

Preferred embodiments of the method according to the invention are specified in the dependent claims 2 to 8.

In addition, the present invention according to claim 9 powder according to the inventive method, and according to claims 10 and 11 relates to permanent magnets containing this powder.

Furthermore, the present invention relates to uses of a powder prepared by the process according to the invention, these uses are given in claims 12 to 15.

For the purposes of the present invention, an "isotropic" magnetic powder is a powder without a preferred magnetic direction Since the orientation of the dissimilar domains within the magnetic material is randomly distributed, it can be magnetized in any direction , On the other hand, powders with a preferred magnetic direction are understood.

According to the present invention, "monocrystalline" particles are understood to be particles which have a continuous uniform, homogeneous crystal form lattice.

For the purposes of the present invention, "submicrocrystalline" powders have a particle diameter of from 100 to 999 μm, and "nanocrystalline" powders have a diameter of from 1 to 100 nm. These diameters are preferably determined by scanning electron microscopy.

A "precursor" in the sense of the present invention is understood to mean the precursor of a permanent magnet, that is to say a material which already has magnetic properties but has not yet fully unfolded them.

For the purposes of the present invention, a "static control" is understood to mean that the process parameters are set at the beginning of a process step and remain constant within the usual fluctuations, but no regulation is made depending on the degree of conversion or the composition of the material to be reacted. which would be the case with a "dynamic regulation". In the "hydrogenation" according to step b) of the process according to the present invention, the alloy provided in step a) absorbs hydrogen and at least partially hydrides are formed under the "disproportionation" after step c) of the process according to the invention further treatment with hydrogen induces a phase transformation. By the "desorption" according to step d) according to the method of the invention is meant the removal of the hydrogen, followed by the "recombination", i. the recovery of the alloy to form an isotropic magnetic powder follows. The starting material for the process according to the invention is in principle any magnetic alloy which is at least partially derived from used magnetic material and which contains at least one rare earth element (component al), at least one transition metal (component a2) and boron (component a3).

According to a preferred embodiment, the reaction mixture provided in step a) contains presented alloy as components al), a2) and a3) neodymium, iron and boron.

According to another preferred embodiment, the alloy provided in step a) contains the following components:

A rare earth metal selected from the group consisting of

Scandium, lanthanum, cerium, praseodymium, neodymium, promethium, europium, yttrium, gadolinium, terbium, dysprosium, holmium, erbium, and mixtures thereof, wherein the proportion of rare earth metals in total from 28 to 34 wt .-%, preferably 29 to 32 wt .-%, based on the total weight of the alloy is; and or

A transition metal selected from the group consisting of iron, copper, titanium, cobalt and nickel and mixtures thereof, wherein the proportion of the transition metals in total from 62.8 to 71.2 wt .-%, preferably 65.4 to 69, 8 wt .-%, based on the total weight of the alloy and wherein the proportion of the transition metal cobalt in the total weight of the alloy is below 3 wt.%, Preferably below 2 wt.%, Particularly preferably below 1.5 wt .-%; and / or boron, the boron content being from 0.8 to 1.2% by weight, preferably from 0.9 to 1.1% by weight, based on the total weight of the alloy; and or

• further elements selected from the group consisting of aluminum, silicon, zirconium, gallium, niobium, hafnium, tungsten, vanadium, molybdenum, carbon, oxygen, nitrogen and sulfur and mixtures thereof; wherein the proportion of the further elements in total from 0 to 2 wt .-%, preferably 0.3 to 1.5 wt .-%, based on the total weight of the alloy is; with the proviso that the proportions by weight of the rare earth metal, of the transition metal, of boron and the optionally further elements add up to 100% by weight. A further preferred embodiment of the method according to the invention provides that the used magnetic material is selected from the group consisting of production committees, magnets from waste products, waste material from the processing of magnets and mixtures thereof.

According to another preferred embodiment of the process, the hydrogenation according to step b) at temperatures of 20 to 400 ° C and preferably from 20 to 200 ° C and a hydrogen partial pressure of 100,000 to 5,000,000 Pa and preferably 100,000 to 1,000,000 Pa carried out.

According to a further preferred embodiment of the process, the disproportionation according to step c) is carried out at temperatures in the range of greater than 600 to 1000 ° C. and a hydrogen partial pressure of 30 000 to 500 000 Pa.

A further preferred embodiment of the method according to the invention provides for static regulation of the temperature and of the hydrogen partial pressure in step c).

According to another embodiment of the process according to the invention, the desorption of the hydrogen in step d) is carried out by applying a vacuum and / or displacing the hydrogen with an inert gas, the temperature being adjusted to the range from 600 to 1000 ° C. and simultaneously the desorption is carried out for 1 to 3,000 minutes and preferably for 2 to 300 minutes. Suitable inert gases are the noble gases, in particular argon.

The powders which can be prepared by the process according to the invention are preferably submicrocrystalline.

The powders according to the invention can be used directly for the production of permanent magnets, in particular polymer-bonded permanent magnets. A preferred method of making such permanent magnets involves the following steps: i. Providing at least one powder prepared by a process according to the present invention; ii. Heating the at least one powder from step i) to a temperature of 600 to 750 ° C and compressing the powder at pressures of 90 to 500 MPa to form a precursor; iii. Forming the precursor from step ii. at a temperature of 700 to 850 ° C to a permanent magnet.

According to a preferred embodiment of the method for producing a permanent magnet, step ii. at a temperature of 700 to 750 ° C and pressures of 90 to 200 MPa performed. Preferably, step iii. carried out at a temperature of 725 to 800 ° C.

Preferred permanent magnets according to the present invention additionally contain at least one polymer and the permanent magnet is in polymer bound form.

These polymer-bonded permanent magnets can be produced by a process with the following steps:

I. providing at least one powder prepared by a process according to the present invention;

II. Providing at least one polymer;

III. Pressing the components provided in steps I. and II into a polymer-bound permanent magnet. In one embodiment of the present invention, the polymer for the polymer-bonded permanent magnet is selected from the group consisting of thermosets, preferably epoxy resins or thermoplastics, preferably polyamides such as e.g. PA 6 or PA 12 or polyphenylene sulfides and mixtures thereof, with epoxy resins being preferred.

r

According to a further embodiment, the proportion of the magnetic powder is 75 to 95 wt .-%, preferably 80 to 90 wt .-% of the permanent magnet and the proportion of the polymer 5 to 25 wt.%, Preferably 10 to 20 wt .-% of Permanent magnets, provided that the weight proportions of the powder and of the polymer supplement to 100 wt .-%. The permanent magnets containing a powder producible by a method according to the present invention are preferably used for motors, generators, electrical and electronic applications.

The subject according to the invention is intended to be explained in more detail with reference to the following examples, without wishing to restrict it to the specific embodiments shown here.

An alloy having the composition shown in Table 1 was recycled according to the process of the invention.

Table 1: Composition of the starting material. From the old magnetic material of the composition mentioned in Table 1, 50 g were hydrogenated. For this purpose, the material was exposed for one hour at 50 bar pressure and room temperature to a hydrogen atmosphere. The previously compact and still slightly magnetized metal cuboid was then disintegrated to a no longer magnetized, brittle powder. The hydrogen content of the powder and thus the increase in comparison to the starting material could be measured by comparative hot-extraction techniques on comparable samples.

Of this hydrogenated powder, 7 g was subjected to the HDDR process. For this purpose, the powder stored after the hydrogenation under argon was again brought into a hydrogen atmosphere, in this case a hydrogen pressure of 1500 mbar was used. The material was heated under this hydrogen atmosphere to a temperature of 780 ° C and this temperature for 30 min. held, then the temperature was increased to 900 ° C and held there for 1 hour. Subsequently, the hydrogen was pumped off to 10 mbar and the temperature was kept at 900 ° C. for a further 90 minutes before the hydrogen was completely pumped off and kept at 900 ° C. for a further 30 minutes. Finally, the material was cooled under vacuum and returned to an argon atmosphere. In order to determine the magnetic properties of the obtained powder, 50 mg thereof were embedded in a capsule with wax, aligned in liquid wax in an external magnetic field and magnetically measured this capsule on a PPMS (Physical Properties Measurement System). Figure 1 shows the in two directions (in the direction of the previously applied external Magnetic field and perpendicular thereto) measured hysteresis loop (polarization μ ₀ Μ in dependence on the applied magnetic field μ ₀ Η). Since the measurement in the two directions shows no difference in contrast to anisotropic magnets, this is an isotropic material.

1.8 g of this powder were then mixed with 0.2 g of a PTFE powder (polytetrafluoroethylene), that is to say in a ratio of 90% by weight to 10% by weight, and this material in a compression mold to form a cuboid body. which is then heated in a tube furnace under vacuum to 360 ° C in order to obtain a dimensionally stable magnet from the two compressed powders. By means of Permagraph were the magnetic properties

(Hysteresis loop, remanence B _R , coercive field strength H _c ) this

determined polymer-bound magnet. They are shown in Table 2

Table 2: Properties of the polymer-bound magnet.

H _C [kA / m] BR [T] Dy fraction

1200 0.47 3% by weight

Claims

claims

A recycling process for producing isotropic magnetic powders, comprising the steps of: a) providing a magnetic alloy comprising a) at least one rare earth metal, a2) at least one transition metal and a3) boron; b) hydrogenation of the alloy from step a) in a hydrogen-containing atmosphere at temperatures of 0 to 600 ° C and a hydrogen partial pressure of 10,000 to 15,000,000 Pa, with formation of monocrystalline particles; c) disproportionation of the particles from step b) in a hydrogen-containing atmosphere at temperatures in the range of greater than 600 to 1,000 ° C at a hydrogen partial pressure of 30,000 to

1 000 000 Pa; d) desorption of the hydrogen and subsequent recombination to form isotropic powder particles; wherein the alloy provided in step a) is partially or completely recovered magnetic material.

2. The method according to claim 1, characterized in that in

Step a) provided alloy is a neodymium, iron and boron-containing alloy. A method according to claim 1 or 2, characterized in that the alloy provided in step a) contains the following components: a rare earth metal selected from the group consisting of scandium, lanthanum, cerium, praseodymium, neodymium, promethium, europium, yttrium, gadolinium, terbium, Dysprosium, holmium, erbium, and mixtures thereof, wherein the proportion of the rare earth metals in total from 28 to 34 wt .-%, preferably 29 to 32 wt .-%, based on the total weight of the alloy is; and / or · a transition metal selected from the group consisting of iron, copper, titanium, cobalt and nickel and mixtures thereof, wherein the proportion of the transition metals in total from 62.8 to 71.2 wt .-%, preferably 65.4 to 69.8 wt .-%, based on the total weight of the alloy and wherein the proportion of the transition metal cobalt in the total weight of the alloy is less than 3 wt.%, Preferably less than 2 wt.%, Particularly preferably less than 1.5 wt .-%; and or

Boron, wherein the boron content of 0.8 to 1.2 wt .-%, preferably 0.9 to 1.1 wt .-%, particularly preferably 0.95 to 1.05 wt .-%, based on the total weight of the alloy is;

and or

• further elements selected from the group consisting of aluminum, silicon, zirconium, gallium, niobium, hafnium, tungsten, vanadium, molybdenum, carbon, oxygen, nitrogen and sulfur, and mixtures thereof; wherein the proportion of the further elements in total from 0 to 2 wt .-%, preferably 0.3 to 1.5 wt .-%, based on the total weight of the alloy is; with the proviso that the proportions by weight of the rare earth metal, of the transition metal, of boron and the optionally further elements add up to 100% by weight. Method according to one of the preceding claims, characterized in that the old magnetic material is selected from the group consisting of production committees, magnets from waste products, waste material from the processing of magnets and mixtures thereof.

Method according to one of the preceding claims, characterized in that the regulation of the temperature and the hydrogen partial pressure in step c) takes place statically.

Method according to one of the preceding claims, characterized in that the hydrogenation according to step b) at temperatures of 20 to 400 ° C and preferably from 20 to 200 ° C and at a hydrogen partial pressure of 100,000 to 5,000,000 Pa and preferably 100 000 to 1 000 000 Pa is performed.

Method according to one of the preceding claims, characterized in that the disproportionation according to step c) at temperatures ranging from greater 600 to 1000 ° C and a hydrogen partial pressure of 30 000 to 1 000 000 Pa, preferably 30 000 to 500 000 Pa performed becomes.

Method according to one of the preceding claims, characterized in that the desorption of the hydrogen in step d) by applying vacuum and / or displacement with an inert gas and adjusting the temperature in the range of 600 to 1000 ° C, for 1 to 3 000 and preferably for 2 to 300 minutes, wherein the resulting isotropic powders are preferably submicrocrystalline, in particular nanocrystalline.

9. Powder producible by a process according to one of claims 1 to 8.

10. Permanent magnet containing a powder preparable by a method according to any one of claims 1 to 8. 11. Permanent magnet according to claim 10, characterized in that additionally at least one polymer is contained and the permanent magnet is present in polymer bound form.

Use of at least one powder preparable by a process according to one of claims 1 to 8 for the production of a permanent magnet.

Use according to claim 12, characterized in that it is a polymer-bonded permanent magnet.

Use according to claim 13, characterized in that the polymer is selected from the group consisting of thermosets, preferably epoxy resins or thermoplastics, preferably polyamides or polyphenylene sulfides and mixtures thereof, wherein epoxy resins are preferred; and / or the proportion of the powder is 75 to 95 wt .-%, preferably 80 to 90 wt .-% of the permanent magnet and the proportion of the polymer 5 to 25 wt .-%, preferably 10-20 wt .-% of the polymer-bonded permanent magnet with the proviso that the weight proportions of the powder and the polymer add up to 100% by weight.

Use according to any one of claims 12 to 14 for motors, generators, electrical and electronic applications.