WO2014029607A1

WO2014029607A1 - Method for producing magnetic materials

Info

Publication number: WO2014029607A1
Application number: PCT/EP2013/066419
Authority: WO
Inventors: Wolfgang Rossner
Original assignee: Siemens Aktiengesellschaft
Priority date: 2012-08-20
Filing date: 2013-08-05
Publication date: 2014-02-27
Also published as: DE102012214729A1

Abstract

The invention relates to a method for producing magnetic materials, in particular one which is based mainly on nanoscale non-metallic precursors, including for producing polyphase permanent magnets. In this case, at least the metals which react spontaneously with oxygen in air are used in the form of non-metallic metal compounds for production purposes.

Description

description

The invention relates to a method for the production of magnetic materials, in particular one which mainly emanates from nanoscale non-metallic precursors, inter alia for the production of permanent magnets. It is known to produce permanent magnets from crystalline metallic powders which are produced by atomization of metallic melts and are pressed into shape in order to align the crystallographic orientation in the presence of a strong magnetic field

Hochtemperatursinterpozess be compacted into a monolithic material.

Typically, such magnetic powders or polycrystalline bodies consist of metallic compounds in the material system Nd-Fe-B, for example (Nd, Dy) ₂ Fei ₄ B. These and further modified by doping, magnetic materials are respects ^¬ Lich their performance already highly developed. However, there is always the need to develop new material concepts in order to further improve the magnetic properties.

A successful concept is the reduction of

Crystallite sizes of the magnetic microstructure to increase the coercivity. Here, from conventional Nd-Fe-B powders with average particle sizes of typically 100 ym by hydrotreating (hydrogen decomposition-desorption-recombination (HDDR) process) crystallite sizes of typically 200-300 nm are produced by a complicated mechanism, which in one Single particles in tetragonal orientation (texture) are present.

Another promising concept is represented by the Exchange Spring magnets based on the combination of hard and soft soft magnetic magnetic materials based. In this case, the principle of magnetic exchange interaction is used by the soft magnetic parts are magnetized almost permanently by the hard magnetic components. With this principle, the proportion of expensive rare earth-based magnetic materials can be reduced if the soft ^¬ magnetic shares, for example, consist of the known ferrite magnets. The unsolved technical challenge here lies in the fact that the magnetic exchange interaction only a small range of about 100 nm and a nanoscale microstructure in these Di is to generate ^¬ mensionsbereich.

Both concepts, nano-structured and Exchange-Spring-Magnet-Werksoffe, require so far comparatively complex processes for the production of the required nanostructures, since a simple production from metallic nanopowders is not possible because of their pyrophoric character. The object of the present invention is therefore a method for producing nanoscale metallic and / or metallic non-metallic magnetic materials with nanoscale

To create a crystallite structure, in which the disadvantages of the prior art are overcome, in particular a mass production capability is achieved at economically acceptable cost.

General knowledge of the invention is that the spontaneously reacting with sour ^¬ material elements in the preparation of the magnetic material in the form of easily decomposable metal compounds such as oxalate, oxide, nitrate, carbonate, citrate, hydroxide and / or other, also organometallic compound can be used , These as "easy

decomposable ", non-metallic metal compounds - the latter word designates a compound comprising an element which is metallic in elemental form - can be added to the metals in elemental form, for the invention preferably in the form of intermetallic phases, reduce, which are then bound in an alloy, which may just include shares of non-metallic metal compounds, and no longer react with atmospheric oxygen. A solution to the problem and object of the present invention is therefore a method for producing a metallic and / or metallic-nonmetallic magnetic material by processing a mixture of powders of easily decomposable non-metallic metal compounds, characterized by at least the following process steps:

- Preparation of a nanoscale powder mixture of easily decomposable non-metallic metal compounds Manufacture of a powder compact by drying and / or densifying the non-metallic metal compounds

At least partial reduction of the non-metallic metal compounds of the powder compact to at least one intermetallic phase

- Magnetization of at least parts of the intermetallic phases and / or the non-metallic metal compound contained and obtaining a, preferably mehrphasi ^¬ gene, intermetallic and / or an intermetallic oxide magnetic material

- Sintering of the thus obtained powder body under inert gas to the polycrystalline sintered body below the melting temperature of the intermetallic phases

wherein the magnetization is carried out during the reduction and / or during the sintering, and

- Cooling of the magnetic material thus obtained at a rate of 50 to 10 K / min.

As "nanoscale powder mixture" is present in a

Particle mixture, which predominantly has a ^¬ average particle size less than 300 nm, preferably less than 200 nm and more preferably between 10 and 100 nm. According to a preferred embodiment, the powder mixture also comprises crystallites. The size of the crystallites in the nanoscale powder mixture may also be above the average particle size of 300 nm, but may also be lower. Crystallites can also be present in the nanoscale powder mixture up to a size of 500 nm.

The "multi-phase" is classically called a "of several Kris ^¬ tallphasen existing network.

The magnetic material is preferably a permanent magnet.

As a "non-metallic metal compound" is one one Me ^¬ tallatom in the chemical molecular formula comprehensive, dung connects to any typical metallic properties as

Gloss, conductivity etc .. indicates designated. In the nichtme ^¬-metallic metal compound the metal atom is formally present in oxidized form.

Intermetallic phase is referred to herein as an intermetallic compound (more precisely, intermetallic phase), which is a homogeneous chemical compound of two or more ^metals . In contrast to alloys, they show lattice structures that differ from those of the constituent metals. In their lattice, there is a mixed bond consisting of a metallic bond portion and lower Atombin- dungs- and / or ion-binding proportions.

According to an advantageous embodiment of the invention, the metallic powders are selected from the group of the following metals: iron (Fe), cobalt (Co), silicon (Si), nickel (Ni), aluminum (Al), chromium (Cr), titanium (Ti ), Manganese (Mn), zinc (Zn), neodymium (Nd), samarium (Sm), dysprosium (Dy) and / or boron (B). Others, especially rare earth metals, Übergangsme ^¬ metals and / or other soft and / or hard magnetic metals can be used according to the invention also. The chemical elements with atomic numbers of 21 to 30, 39 to 48, 57 to 80 and 89 to 112 are commonly referred to as transition elements. In addition to the use of commercially available metal compounds in the form of powder metal compounds can be prepared fresh in the first step for preparing the powder mixture by dissolving, for example, metal oxide powders or salts in acid and corresponding precipitation of the metal compounds. In particular, metal ^¬ hydroxides, metal nitrates and / or metal oxalates fresh Herge ^¬ represents may be, which are then dried and compacted to form powder compacts alone or with other metal compounds, such as boron oxide mixed.

When mixing the metal compounds to form the powder mixture and before compacting the powder compact, it may be provided to carry out the mixing by grinding, wherein it is preferred that a powder mixture of light weight

decomposable metal compounds with nanoscale

Crystallite structure is produced. It is particularly preferred that the average crystallite size is in the range of less than 500 nm, more preferably less than 300 nm and most preferably 100 nm, and these crystallites may be in the form of agglomerated particles.

Present crystallite size of particle size is so far discriminated as a plurality of crystallites in the form of Agglomera ^¬ th, which are then called particles and per se

polycrystalline, may be present in the powder mixture. Under certain circumstances, the particles differ in size many times from the crystallites, which are monocrystalline. In the preparation of the powder mixture can still more

Aggregates, which are common for the production of magnetic materials, mixed. In the present case, all types of metallic compounds are referred to as "metal compound" which in their empirical formula contain elements which are metallic in elemental form but are not present in elemental form but in oxidized form. such as oxalate, oxide, nitrate, carbo ^¬ carbonate, citrate, hydroxide, and / or any other, also metallor ^¬ ganic, compound. These metal compounds are known, commercially available and / or by the occurring in a preferred embodiment of the method of precipitating the metal compounds from acid produced within the process of the invention. the readily decomposable metal compounds may be in the subsequent process step as a compact powder, for example, in what ^¬ serstoffström reduced.

According to an advantageous embodiment of the method, the reduction is carried out under elevated temperature, for example at temperatures above 600 ° C, in particular above 1000 ° C and most preferably at temperatures up to 1500 ° C.

The reduction preferably takes place in a reducing Gasatmosphä ^¬ acid, for example hydrogen and / or forming gas instead. In this case, an increased pressure, a flow, an aerosol and / or a gas mixture can be used.

For example, reduction of the nonmetallic metal compound in the powder compact takes place in the range of 0.1 to 5 hours, especially 1/2 to 2 hours.

According to a further advantageous embodiment of the invention, the reduction with the sintering is carried out as a single-stage process step, ie in a homogeneous process management. For example, the transition from reduction to sintering can be carried out by increasing the temperature and / or pressure, wherein the product of the reduction without prior Cooling and / or contact with oxidizing atmosphere is sintered.

The sintering, like the previous and subsequent process steps, can be carried out under a protective gas atmosphere and in particular under a reducing gas atmosphere.

According to an advantageous embodiment of the method is cooled under a protective gas atmosphere, in particular under argon or an argon-containing inert gas atmosphere. It is preferred that is additionally cooled in a reducing acting Gasat ^¬ atmosphere.

The sintering takes place at elevated temperature, for example above 1000 ° C and below 1500 ° C instead. In particular, the sintering z as simple sintering. B. under atmospheric pressure (1 bar), reduced pressure or vacuum or by simultaneous application of mechanical pressure as Gasdrucksintern, as hot pressing and / or hot isostatic pressing are performed. The sintering with application of mechanical pressure can be carried out, for example, at a maximum pressure of 100 MPa. Preferably, the residence time at the maximum temperature and / or the maximum compacting pressure is only very short, 0 to 30 minutes, preferably 10 minutes.

The cooling after sintering is carried out in particular at a rate of about 50 to 10 K / min. It can be provided that the rate of 50 to 20 K / min when cooling to 800 ° C, 700 ° C or 600 ° C is used and then a slower cooling of the magnetic material is provided to room temperature.

In the present case, magnetization means that in the individual process steps, such as reduction and / or sintering, mechanical, thermal and / or magnetic fields act on the magnetic material and its precursors, resulting in a preferential orientation (texturing) of the magnetic phases, which are metallic, metal oxide or not -metallic and / or nanoscale or non-nanoscale, lead. Follow-up steps for magnetization follow, for example, the conventional techniques. With suitable powder syntheses anisotropic particle morphologies can be generated, which also allow the formation of texturing of the magnetic phases of the magnetic material. In addition, more complex magnetic composite materials can be produced, such as the combination of two metallic alloys, by employing not only the rare, expensive and / or pyrophoric metals in the form of their non-metal compounds, but also in that iron, cobalt, Nickel and other metals can be used, for example, as hydroxides for the production of magnetic materials. In the following, exemplary embodiments are described which describe the basic application of the method according to the invention for different magnetic materials:

1) Production of a Magnetic Nd-Fe-B Magnetic Material:

According to one embodiment of the invention, the desired composition corresponding metal oxides, preferably Nd203, Fe203, in acid, for example nitric acid are completely dissolved and then precipitated so that a pre ^¬ zipitat with crystalline and / or amorphous non-metallic phases, preferably as metal hydroxides or metal oxalates, arises. For example, the precipitate has a

Primary particle size below 300 nm, preferably below 100 nm. This precipitate is then separated and dried. An ^¬ closing the desired amount of boron, for example in the form of boron oxide or metal borates, and other additives will be distributed in finely dispersed form, that is in a fine powder form and homogeneously, was added and by grinding a homogeneous micro research of the powder offset, so the powder mixture , generated.

It may be provided that, by grinding, further comminution of the mean crystallite size of the powder or parts of the powder mixture. This powder mixture is then compacted, for example by dry pressing, to give the powder compact. The powder compact obtained is then reduced and alloyed in a reducing atmosphere, preferably hydrogen, under predetermined pressure of 30 KPa to 1 kPa, at 600 ° C to 1000 ° C via Kom ^¬ plex reduction mechanisms to metallic magnetic phases. By increasing the temperature is DIE ses product then by sintering, preferably completely through Heißpres ^¬ sen, heißistostatisches pressing, or gas pressure sintering compacted to a residual porosity, for example, un ^¬ ter 5 vol% results. In order to enable texturing of the magnetic material, a magnetic field can be applied during the reduction step and / or the sintering.

With suitable process control, a magnetic material is thus obtained, which consists of finely dispersed intermetallic

hard magnetic phases, for example, have an average crystallite size below 300 nm.

2) Production of a Metallic Magnetic Material in the Form of a Metallkomposits of Soft Magnetic and hartmagneti ^¬ shear phase:

For this purpose, the powder mixture mentioned under 1) is added to a non-metallic nanopowders or a mixture of nanopowders in the composition of the intended metallic soft magnetic phase, which are prepared either by precipitation analogous to 1) and / or by grinding coarser powders. In turn, a homogeneous powder mixture is produced by means of a milling process, which is then further processed analogously to 1). With suitable process control, a magnetic material is thus obtained which comprises a uniform distribution of finely dispersed hard magnetic portions which preferably have dimensions below 300 nm and a total proportion of up to approximately 50 Vol%, preferably up to 60% by volume and particularly preferably up to 70% by volume, and consists of finely dispersed metallic soft magnetic portions, which preferably have dimensions below 300 nm and a total content of, for example, 30% by volume or more.

3) Preparation of a magnetic material in the form of a metal oxide metal composite, wherein the metallic component Kom ^¬ hard-magnetic and the non-metallic component is preferably magnetically soft, for example a ferrite, is:

For this purpose, the non-metallic nanopowder of a soft magnetic phase, preferably a ferrite, which are produced either by precipitation analogous to 1) or by grinding of coarser powders, is added to the powder mixture mentioned under 1). In turn, a homogeneous powder mixture is produced by means of a milling process, which is then further processed analogously to 1). Here, the soft magnetic An ^¬ part is sized and adapted to guide the reduction process that only a part of the non-metallic weichmag ^¬ netic phase is reduced.

With suitable process control, a magnetic material is thus obtained which comprises a uniform distribution of fine-hard hard magnetic fractions which preferably have dimensions below 300 nm and a total proportion of up to about 50% by volume, preferably up to 60% by volume and particularly preferably up to 70% by volume. and of finely dispersed metallic soft magnetic portions which preferably have dimensions below 300 nm and have a total content of, for example, 30% by volume or more and can consist of both metallic and non-metallic soft magnetic portions, but preferably soft magnetic ferritic portions.

The invention relates to a method for the production of magnetic materials, in particular for the production of permanent magnets. At least the metals that are in the air abreact spontaneously with oxygen, used for the production in the form of non-metallic metal compounds.

Claims

claims

1. A process for producing a metallic and / or metallic-nonmetallic magnetic material by processing a mixture of powders of easily decomposable non-metallic metal compounds, characterized by at least the following process steps:

- Producing a nanoscale powder mixture of easily decomposable non-metallic metal compounds, manufacturing a powder compact by drying and / or compacting the non-metallic metal compounds

- Cooling of the magnetic material thus obtained at a rate of 50 to 10 K / min.

2. The method according to claim 1,

characterized in that there are crystallites in the Pu 1 ve rmi sung.

3. The method according to any one of claims 1 or 2,

wherein in the Pu 1 ve rmi cheung nonmetallic Me ta 11 ib tions such as oxalates, oxides, Hydro ^¬ xide, carbonates, citrates, nitrates, and / or organometallic compounds are present.

4. The method according to any one of the preceding claims, characterized in that the powder mixture comprises non-metallic metal compounds of neodymium, samarium, dysprosium and / or other side earths, transition metals, such as iron, ferrites, and / or boron.

5. The method according to any one of the preceding claims, characterized in that

the step of at least partially reducing the non-metallic metal compounds in the powder compact at a temperature in the range above 600 ° C ° C, in particular in the range of 800 ° C to 1000 ° C is performed.

6. The method according to any one of the preceding claims, characterized in that

the step of at least partially reducing the non-metallic metal compound in the powder compact is carried out under a hydrogen and / or forming gas atmosphere.

7. The method according to any one of the preceding claims, characterized in that the at least partially Redukti ^¬ on is carried out at hydrogen partial pressures between 50 kPa to 1 kPa.

8. The method according to any one of the preceding claims, wherein the sintering is carried out at a maximum temperature of 1500 ° C.

9. The method according to any one of the preceding claims, wherein the sintering is carried out under reduced gas pressure and / or under vacuum.

10. The method according to any one of the preceding claims, wherein the sintering is carried out using mechanical pressure.

11. The method of claim 10, wherein the sintering under

Application of mechanical pressure to lOOMPa is performed.

12. The method of claim 8 or 9, wherein the residence time of the reduced powder body at the maximum temperature and / or the maximum pressure of the sintering 30 minutes or less.

13. The method according to any one of the preceding claims, characterized in that the transition from reduction to sintering is carried out in homogeneous process control.

14. The method according to any one of the preceding claims, characterized in that the powder mixture comprises at least ei ^¬ ne fraction having an average particle size less than or equal to 300nm, in particular less than or equal to 100 nm.

15. The method according to any one of the preceding claims, d a - characterized in that

the at least partial reduction of the non-metallic metal compound in the powder compact is carried out in the range from 0.1 to 5 hours, in particular from 1/2 to 2 hours.

16. The method according to any one of the preceding claims, characterized in that

the hard magnetic phases in the magnetic material

Particle sizes and / or phase sizes are under 300 nm dimensioned.

17. The method according to any one of the preceding claims, characterized in that

the finely dispersed hard magnetic components are evenly distributed in the magnetic material.

18. The method according to any one of the preceding claims, characterized in that the powder mixture and process is set so that a magnetic material with ei ^¬ nem proportion of finely dispersed hard magnetic phases of up to 70% by volume results.

19. The method according to any one of the preceding claims, characterized in that the powder mixture and process ^¬ leadership is adjusted so that a magnetic material with ei ^¬ nem proportion of finely dispersed soft magnetic metallic or non-metallic phase of at least 30Vol% results.

20. The method according to any one of the preceding claims, characterized in that

the soft-magnetic metallic or non-metallic phases in the magnetic material are dimensioned to particle sizes below 300 nm.

21. The method according to any one of the preceding claims, characterized in that the soft magnetic me ^¬ metallic or non-metallic phases in the magnetic material preferably comprise soft magnetic ferritic phases.

22. The method according to any one of the preceding claims, characterized in that

In the individual process steps additional mechanical, thermal and / or magnetic fields act on the magnetic material and its precursors, which lead to a preferential orientation (texturing) of the magnetic phases.