EP2735003A1

EP2735003A1 - Magnetic material and method for producing same

Info

Publication number: EP2735003A1
Application number: EP12729553.3A
Authority: EP
Inventors: Konrad Güth; Oliver Gutfleisch
Original assignee: Robert Bosch GmbH; Aichi Steel Corp
Current assignee: Robert Bosch GmbH; Aichi Steel Corp
Priority date: 2011-07-20
Filing date: 2012-06-20
Publication date: 2014-05-28
Also published as: KR20140053108A; TW201310481A; US20140346388A1; CN103843080A; DE102011108173A1; JP2014523142A; WO2013010741A1

Abstract

The invention relates to a method for producing a magnetic material, said magnetic material consisting of a starting material that comprises a rare earth metal (SE) and at least one transition metal. The method has the following steps: - hydrogenating the starting material, - disproportioning the starting material, - desorption, and - recombination. A magnetic field is applied during at least one step such that a textured magnetic material is obtained and the formation of a texture is promoted in the magnetic material.

Description

Description title

Magnetic material and method for its production. State of the art

The invention relates to a magnetic material, and a method for its production.

Magnetic materials, as well as methods for their preparation are known from the prior art. For example, finely crystalline, so-called nanocrystalline magnetic powders, by ball milling or rapid solidification and subsequent hot-compacting or hot deformation or by "exchange coupling or Remanenzüberhöhung" obtained. A disadvantage of this is the complex processing of the starting alloy, and the often low energy density and remanent magnetization of the resulting

magnetic material. Further, DE 197 52 366 A1 describes a process for producing a hard magnetic samarium-cobalt base material by means of a H DDR process (hydrogenation - disproportionation - desorption - recombination), wherein the disproportionation at a hydrogen pressure of more than 0.5 MPa and a temperature from 500 ° C to 900 ° C is performed. The disadvantage of this is that the obtained in this way magnetic

Materials, since isotropic, thus a relatively low remanent magnetization and crystallite sizes of 300 nm and more after desorption and recombination, have.

Disclosure of the invention

The inventive method with the features of claim 1 is characterized by a simplified feasibility. This is at least one soft magnetic phase having a sufficiently small crystallite size is uniformly and efficiently coupled to a hard magnetic phase, at the same time texturing the hard magnetic phase. Under texturing or texture formation is understood that a

hard magnetic phase is formed with a crystallographic preferred direction. The formation of the magnetic material according to the invention takes place in a continuous process, wherein the desorption and recombination of the magnetic material take place either successively or in parallel. In the following, the abbreviation "desorption / recombination" for both options mentioned above, namely for both a sequential drainage of desorption and recombination, as well as a parallel running of the

Desorption and recombination. Thus, a magnetic material having a high remanent magnetization of preferably about 1.3 to 1.5 tesla is obtained. In addition, the paramagnetic portion of the material, i. the volume of the rare earth metal-rich grain boundary phase, minimized or

ideally eliminates, which increases the remanent magnetization, enhances the magnetic properties of the material through efficient exchange coupling and improves its corrosion resistance. The crystallites of the material according to the invention are characterized by a high degree of texturing, i. they have a crystallographic preferred direction. It has surprisingly been found that the nucleation, the crystal growth and in particular the texturing of the magnetic material can be positively influenced by the application of a magnetic field during at least one of the method steps. This increases the remanent magnetization of the material according to the invention. Furthermore, by appropriate choice of

Magnetic field strength, the remanent magnetization can be set specifically. The final crystallite size of the magnetic material according to the invention can be controlled by the method according to claim 1 so that it is smaller by at least one size unit than in conventional magnetic materials produced by the HDR method. Due to this very small crystallite size of preferably less than 300 nm, and more preferably less than 100 nm or even less than 50 nm, the

Exchange coupling of the material according to the invention particularly high, which has a positive effect on the magnetic properties of the material. The dependent claims show preferred developments of the invention.

Preferably, the magnetic field is applied during the desorption step and the recombination step. By the method according to the invention, the production of the magnetic material is preferably controlled so that between the disproportionation on the one hand and the desorption (for successive desorption and recombination) or the desorption and recombination (for parallel desorption and recombination) on the other side there is an equilibrium that can be shifted in one direction or another by targeted application of the magnetic field.

Particularly when the magnetic field in the equilibrium state between disproportionation and desorption / recombination is applied, the crystallite size and especially the initiation or improvement of the texturing of the magnetic material are particularly strongly influenced by the magnetic field, so that it starts already during nucleation and during germ growth and thus the texturing of the magnetic material can be controlled specifically. This increases the remanent magnetization of the magnetic material.

More preferably, the magnetic field strength of the applied magnetic field is more than 0 to about 100 Tesla, preferably more than 0 to 10 Tesla. These

Field strength is sufficient to cause high texturing in the magnetic material and to promote a crystallite size of the desired size, and preferably of a few 100 nm or even less than 100 nm. The magnetic field strength is not limited to the top. In the preferred range of up to 10 Tesla, the nucleation and growth rate of the crystallites and in particular the texturing of the material is optimally controllable with the lowest possible production costs. The optimum magnetic field strength can be easily found out by a person skilled in the art by simple comparative experiments. The state of equilibrium between disproportionation and

Desorption / recombination is preferably by lowering the

Hydrogen partial pressure achieved. This means that by reducing the hydrogen partial pressure the equilibrium is shifted to the side of the recombined magnetic product, whereas an increase of the hydrogen partial pressure causes the disproportionated state of the promotes magnetic material. The interplay of these two states, the texturing of the magnetic material is promoted particularly well, resulting in a high remanent magnetization of the forming

magnetic material shows.

More preferably, the temperature at the beginning of the desorption

/ Recombination initially kept constant to allow slow reaction rates. This has the advantage that so the promotion of

Equilibrium state between disproportionation and

Desorption / recombination of the magnetic material is more easily targeted adjustable, which in turn is promoted the texturing of the magnetic material.

Furthermore, it is advantageous if the temperature during the

Hydrogenation step about 20 ° C to 350 ° C, preferably about 300 ° C and / or the temperature during the Disproportionierungsschritt.es 500 ° C to 1000 ° C, preferably 750 ° C to 850 ° C and / or the temperature during the

Desorption step 500 ° C to 1000 ° C, preferably 750 ° C to 850 ° C and / or the temperature during the recombination step 500 ° C to 1000 ° C, preferably 750 ° C to 850 ° C. The high temperature of at least

500 ° C and preferably 750 ° C to at most 1000 ° C during the above reaction steps ensures excellent texturing of the magnetic material, the reaction rate in the

Temperature range between 750 ° C and 850 ° C in terms of speed and process costs promotes an optimal course of reaction. In particular, the high temperature during desorption leads to an almost complete recombination to the final magnetic product. The for each

magnetic material optimum temperature, the expert can easily find out by simple comparison experiments.

Furthermore, it is advantageous if the hydrogen partial pressure during the hydrogenation step is 20 kPa to 100 kPa and more, preferably 20 kPa to 40 kPa and especially 30 kPa and / or the hydrogen partial pressure during the disproportionation step 20 kPa to 40 kPa, preferably 30 kPa and / or the hydrogen partial pressure during the desorption step 0.5 kPa to 1, 5 kPa, preferably 1 kPa and / or the hydrogen partial pressure during the recombination step is 0 kPa to 1 kPa, preferably 0 kPa. The high pressures of 100 kPa and more during the hydrogenation step are particularly advantageous for high alloyed starting materials, while for low alloyed starting materials pressures of 20 to about 40 kPa are sufficient. The pressures during the disproportionation step and also during the recombination step may vary depending on the soft magnetic material used. That's how they are

Use of cobalt as a soft magnetic material, or even when using high cobalt-alloyed iron-cobalt alloys, if necessary

preferably higher than when using pure iron. These

Process management promotes the texturing of the magnetic material. Furthermore, it simplifies the reaction procedure and is therefore expedient. The optimum pressure for the respective magnetic material, the expert can easily find out by simple comparison experiments.

During the disproportionation step, it is advantageous if the

Hydrogen partial pressure is at low alloyed starting materials between 20 kPa and 40 kPa to a sufficient amount of hydrogen for the

To ensure absorption by the starting material. One

Hydrogen partial pressure of 30 kPa is particularly preferred from a process engineering and economic point of view.

The hydrogen partial pressure during the desorption step is

Preferably between 0.5 and 1, 5 kPa, to accelerate the desorption of hydrogen, which is particularly simple and complete at one

Hydrogen partial pressure of 1 kPa takes place.

It is particularly advantageous if the crystallite size of the starting material during and if necessary before the hydrogenation step and / or the

Disproportionation step in particular by ball milling, and in particular by reactive ball milling is reduced. If ball milling is already carried out in the hydrogenation step, this is preferably done by reactive ball milling. The ball milling or reactive ball milling promotes the formation of the smallest possible crystallites, which has a positive effect on the crystallite size and the Texturing of the magnetic material according to the invention effects. Another advantage of ball milling is that the particle size of the

Starting material can then be larger, since this is sufficiently crushed by the step of ball milling. By ball milling, the crystallite size of the starting material and / or the during the

Hydrogenation step and / or the Disproportionierungsschrittes resulting material is preferably reduced to less than 50 nm and more preferably to 5 to 20 nm. If the ball milling is carried out before the hydrogenation step, this can also be done at a temperature of about 20 ° C, which significantly reduces the process costs.

Alternatively, the ball milling can also be carried out under a hydrogen atmosphere, resulting in a shortened grinding time and thus also reduced

Process costs leads. Furthermore, then the hydrogenation takes place within a very short time due to the now small crystallite sizes of the magnetic material, with an almost complete conversion of the starting material is achieved. Another advantage of ball milling is that it allows the temperature to be applied during the recombination step to be reduced by about 200 ° C, which is a preferred

Temperature range during the recombination step of

ball milled magnetic material of about 640 ° C to 750 ° C results. In contrast, such a low temperature range only leads to partial recombination of the magnetic material in the conventional HDDR process. Furthermore, this relatively low temperature during the

Recombination step a particularly small crystallite size of the magnetic

Materials promoted. The ball milling can be carried out by means of conventional devices.

Preferably, the H ₂ pressure applied for grinding is at least 0.1 MPa, preferably at least 1 MPa, more preferably at least 10

MPa, whereby the starting material and / or during the

Hydrogenating step and / or disproportionation step resulting material has a crystallite size of less than 50 nm, and preferably from 5 to 20 nm. The specified H ₂ pressure ensures fast and sufficiently good, homogeneous grinding and thus disproportionation. The Height of the applied H ₂ pressure, the expert can easily find out by appropriate preliminary tests.

It is also advantageous if, after the disproportionation step, a soft magnetic material is added. By adding a

soft magnetic material after disproportionation of the

Starting materials are the nucleation, the crystal growth and

In particular, the texturing and the exchange coupling of the magnetic material positively influenced. This in turn increases the remanent

Magnetization of the material according to the invention.

The time of addition of the soft magnetic material is after disproportionation. This means that said material can be added either directly after disproportionation or at a later stage of the process. The time of addition can be, for example, in

Depending on the output particle size of the magnetic material to be controlled. For example, it has been found that the said soft magnetic material can also be added after recombination, provided that in this particular case the starting particle size of the magnetic material is less than 5 μm.

The soft magnetic material can be added by conventional methods such as physical blending or chemical addition, that is, for example, by vapor deposition or so-called co-milling in a low-intensity agitating mill. The soft magnetic material is preferably mechanically mixed with the disproportionated material, thereby enabling effective exchange coupling. This promotes a homogeneous, nanoscale distribution of soft and hard magnetic phases and a small crystallite size of the magnetic material, which in turn the

Exchange coupling of the magnetic material promotes, so that the magnetic material according to the invention is characterized by a particularly high remanent magnetization. The soft magnetic material is not limited in detail. Preferably, however, the soft magnetic material is formed of Fe and / or Co or of an alloy of these two elements. The elements iron and cobalt, as well as their mixtures or alloys thereof promote the texturing of the magnetic material very well. An alloy of the elements iron and cobalt, which is particularly suitable for the process according to the invention is Fe ₆₅ Co ₃₅ .

Advantageously, the amount of soft magnetic material is in a range of more than 0 to 50 wt .-%, preferably 10 to 30 wt .-%, more preferably about 20 wt .-%, each based on the starting material. In this range, the amount of soft magnetic material is sufficient to allow good exchange coupling associated with high overall magnetization of the magnetic material and thus to create a homogeneous high texture textured magnetic structure therein.

Preferably, the magnetic material is hot-deformed during the desorption step and / or the recombination step and / or

heisskompaktiert. Due to the hot-compacting and / or hot deformation, which can also be a compression, the texturing of the same can also be influenced.

For this, the temperature continues to be during deformation

advantageously 400 to 1200 ° C, preferably 600 to 900 ° C and the pressure during forming at least 100 MPa, preferably at least 150 MPa. In these temperature and pressure ranges, a very good texturing can be achieved. The optimum temperature and the optimum pressure can be easily found out by a person skilled in the art by simple comparative experiments.

Preferably, the rare earth metal is selected from the group consisting of: Nd, Sm, La, Dy, Tb, Gd, more preferably: Nd, Sm, La. These rare earth metals can be due to their physical and chemical properties particularly well with the invention

Implement procedure.

Further preferably, the transition metal is selected from the group consisting of Fe and Co. These two transition metals are readily available and relatively inexpensive and have very good magnetic properties. More preferably, the magnetic material, and preferably the starting material, contains at least one further element, in particular B and / or Ga and / or Nb and / or Si and / or Al. These elements can be the magnetic as well as physical and chemical properties of the material and its resistance, so its chemical or

electrochemical resistance (eg corrosion resistance). Boron is particularly preferred because it promotes the structure formation of the magnetic material, that is to say in particular the hard magnetic phase of the type Nd ₂ Fei ₄ B.

According to a preferred embodiment, the process is carried out so that the intermediate product produced after the disproportionation step and / or after the grinding is a stoichiometric intermediate. This means that the intermediate is single phase, so none

Intergranular Rare earth-rich phases exist. The primary hydrogenated intermediate is thus SEH ₂ , where SE is rare earth metal (s). This can be done by specific choice of the parameters temperature,

Hydrogen partial pressure, reaction time and magnetic field strength can be adjusted. In the case of a Nd ₂ Fe-i ₄ B phase, this means, for example, the stoichiometric (nominal) composition:

Nd ₂ 6.67 Fe ₇ 2.33 Bi.o (% by weight)

Ndii, 77Fe82, 35B ₅ , 88 (atom%).

Often, a superstoichiometric NdH _{2 + x forms} , which then forms the stable NdH ₂ (stoichiometric composition of this

Phase). In the case of hydrogen milling (ball milling under a hydrogen atmosphere), for example, the Nd ₂ F ₁₄ B is converted into the three disproportionated phases mentioned above, wherein NdH _{2 + x} is formed. When this powder is heated, for example at 650 ° C., this superstoichiometric phase changes to a stable NdH ₂ phase at about 200-300 ° C. and hydrogen is released.

According to an alternative preferred embodiment, the process is carried out such that the intermediate product produced after the disproportionation step and / or after the grinding is a superstoichiometric Intermediate is. This means that in addition to SEH _{2 there is} also SEH ₃ , which is also generally SEH ₂ + x. This can be adjusted by specific selection of the parameters temperature, hydrogen partial pressure and reaction time.

Further according to the invention, a permanent magnet is described, which comprises at least one rare earth metal and at least one transition metal and which has been prepared according to the method described above. This permanent magnet is characterized by a particularly high

Saturation magnetization and high remanent magnetization and high texturing.

Preferred permanent magnet compositions are NdTM ₁₂ and Sm ₂ TM ₁₇ where TM is transition metal. Especially preferred

Compositions are Sm ₂ Fei ₇ , SmCo ₅ , and due to its

excellent magnetic properties are very particularly preferred

Preferably, the permanent magnet of the invention has a remanent magnetization of 1, 3 to 1, 5 Tesla.

In summary, the invention relates to a method for producing a magnetic material from a starting material, wherein the

Starting material comprises at least one rare earth metal (SE) and at least one transition metal, the method comprising the known from the conventional H DDR method steps: hydrogenation of the starting material, disproportionation of the starting material, desorption and recombination, wherein during at least one step, a magnetic field such is present that a textured magnetic material is obtained or the formation of a texture is promoted in the magnetic material.

drawing

Hereinafter, the invention will be described in detail with reference to the drawings 1 to 6. In the drawing is: FIG. 1 shows a schematic overview of the conventional H DDR method,

Figure 2 is a schematic overview of the first invention

Embodiment,

Figure 3 is a schematic overview of a second invention

Embodiment,

Figure 4 is a schematic overview of a third invention

Embodiment,

Figure 5 is a schematic overview of a fourth invention

Embodiment,

Figure 6 is a schematic overview of a fifth invention

Embodiment,

Figure 7 is a schematic overview of a sixth invention

Embodiment.

Figure 8a is a graph showing the dependence of the crystallite size and the

Coercive field strength (μοΗ ₀ ) of a superstoichiometric ball milled magnetic material from the temperature during the recombination step.

Figure 8b is a graph showing the dependence of the crystallite size and the

Coercive field strength (μοΗ ₀ ) of a stoichiometric ball milled magnetic material from the temperature during the recombination step.

9a shows a high resolution SEM (LEO Gemini 1530 FEG) of a Nd28,78Fe _ba iB _1, ₁ Gao, 35Nbo, 26 material, which means

conventional H DDR method was produced. FIG. 9b shows a high-resolution SEM image (LEO FEG 1530 Gemini) of a Nd28.78Fe _ba ₁ , ₁ Gao, 35Nbo, 26 material, which was produced by means of HDDR process and additional ball milling.

Preferred embodiments of the invention

Hereinafter, the conventional HDDR method will be described with reference to FIG.

As can be seen from FIG. 1, the H DDR method 10 comprises the

Reaction steps: hydrogenation 1, disproportionation 2, desorption 3 and

Recombination 4. In the hydrogenation step 1, for example, an Nd ₂ Fe-i ₄ B block piece having an initial particle size of, for example, about 50 to 100 μηη is fed at 840 ° C increasing temperature hydrogen. Of the

Hydrogen partial pressure is thereby raised in the system to 30 kPa, which leads to a disproportionation of the starting material under

Hydrogen absorption and thus the formation of NdH ₂ , Fe and Fe ₂ B comes. The hydrogen partial pressure is maintained until an equilibrium has been established in which several phases, ie NdH ₂ and NdH _{2 + x in} addition to NdH ₃ , are present (superstoichiometric intermediate). The

Composition of the reaction mixture is determined by conventional methods (eg X-ray diffractometry). In the subsequent desorption or recombination steps 3 and 4, the temperature is still maintained at 840 ° C, the hydrogen partial pressure but lowered to 1 kPa to finally 0.1 kPa. In this case, a recombination of the individual phases to Nd ₂ Fe-i ₄ B takes place with liberation of hydrogen. The crystallite size of the resulting magnetic material is typically 200-400 nm

Texturing of the resulting material is low, with a remanent

Magnetization of typically about 0.8 Tesla is achieved.

Figures 2 to 7 show an overview of six embodiments of the present invention. In all of these exemplary embodiments, the reaction steps already mentioned above: hydrogenation 1, disproportionation 2, desorption 3 and recombination 4 are carried out in this order. FIG. 2 shows a first exemplary embodiment. Here, a Nd ₂ Fei ₄ B block piece with a starting particle size of 50 to 300 μηη is hydrogenated and

disproportioniert. The starting alloy material is stoichiometric. There are no intergranular rare earth metal-rich phases. The

Composition of the reaction mixture is determined by conventional methods (e.g., X-ray diffractometry). The temperature of the system during the hydrogenation step is 1 200 ° C, during the

Disproportionation step 2 and the desorption step 3 800 ° C, wherein the hydrogen partial pressure is maintained until the desorption step 3 to 30 kPa and during the desorption step 3 is lowered to 1 kPa and then further to 0 kPa. During the desorption step 3 and the

Recombination step 4, and alternatively in the equilibrium state between disproportionation 2 and desorption 3 / recombination 4, is also due to a magnetic field 5 of 8 Tesla on the system. The crystallite size of the

The final magnetic final product is typically about 50 nm. The crystals are characterized by X-ray diffractometry. The texturing of the obtained magnetic material is high. The remanent magnetization of the magnetic material thus obtained is typically about 1.4 Tesla.

FIG. 3 shows a second exemplary embodiment. Here, an Nd ₂ Fei ₄ B block piece with a starting particle size of 100 to 150 μηη is hydrogenated and

Composition of the reaction mixture is determined by conventional methods (eg: X-ray diffractometry). In addition, the starting compound is ground by means of ball milling 6, so that the resulting particle size is 2 to 10 μm. Ball milling is carried out during the hydrogenation and disproportionation steps with an H ₂ pressure of at least 0.1 MPa. The temperature of the system is during the

Hydrogenation step 1 250 ° C, during the disproportionation step 2 and the desorption step 3 800 ° C, wherein the hydrogen partial pressure is maintained until the desorption step 3 to 30 kPa and during the

Desorption step 3 to 1 kPa and then further lowered to 0 kPa. During desorption step 3 and recombination step 4, and alternatively in the equilibrium state between disproportionation 2 and

Desorption 3 / recombination 4, a magnetic field 5 of 8.5 Tesla is also applied to the system. The crystal size of the final magnetic product is typically about 30 nm. The crystals are characterized by X-ray diffractometry. The texturing of the obtained magnetic material is high.

The remanent magnetization is typically about 1.4 Tesla.

FIG. 4 shows a third exemplary embodiment. Here, a Nd ₂ Fei ₄ B block piece with a starting particle size of 50 to 150 μηη is hydrogenated and

disproportioniert. The starting alloy material is superstoichiometric. So there are more rare earth metal-rich phases. The composition of the reaction mixture is determined by conventional methods (e.g.

X-ray diffraction). In addition, the starting compound is ground in step 1 and 2 by means of ball milling 6, so that the resulting crystallite size is 2 to 4 μηη. The temperature of the system is during the

Hydrogenation step 1 300 ° C, during the disproportionation step 2 and the desorption step 3 800 ° C, wherein the hydrogen partial pressure is maintained until the desorption step 3 to 30 kPa and during the

Desorption step 3 to 1 kPa and then further lowered to 0 kPa. During the desorption step 3 and the recombination step 4, and alternatively in the equilibrium state between disproportionation 2 and

Desorption 3 / recombination 4, a magnetic field 5 of 8.5 Tesla is also applied to the system. The crystallite size of the final magnetic product is typically about 40 nm. The crystals are characterized by X-ray diffractometry. The texturing of the obtained magnetic material is high.

The remanent magnetization is typically about 1.4 Tesla.

FIG. 5 shows a fourth exemplary embodiment. Here, an Nd ₂ Fei ₄ B block piece with a starting particle size of 30 to 100 μmη is hydrogenated and

Composition of the reaction mixture is determined by conventional methods (e.g., X-ray diffractometry). The temperature of the system during the hydrogenation step is 1 300 ° C, during the

Recombination step 4, and alternatively in the equilibrium state between disproportionation 2 and desorption 3 / recombination 4, is also present

Magnetic field 5 of 8 Tesla on the system. After this

Disproportionation step 2 are additionally more than 0 wt .-% to 50 wt .-%, preferably 25 wt .-% nanoparticulate iron 7 based on the

Starting compound, add. The particle size of the iron is typically 5 to 50 nm. The crystallite size of the final magnetic product is typically less than 30 nm

X-ray iffractometry characterized. The texturing of the obtained magnetic material is high. The remanent magnetization is typically about 1.4 Tesla.

FIG. 6 shows a fifth exemplary embodiment. Here, a Nd ₂ Fei ₄ B block piece with a starting particle size of 50 to 150 μηη is hydrogenated and

Composition of the reaction mixture is determined by conventional methods (e.g., X-ray diffractometry). In addition, the starting compound is ground in step 1 and 2 by means of ball milling 6, so that the resulting primary crystallite size is 2 to 5 μηη. The temperature of the system during the hydrogenation step is 1 300 ° C, during the

Disproportionation step 2 and the desorption step 3 800 ° C, wherein the

Hydrogen partial pressure is maintained until the desorption step 3 to 30 kPa and during the desorption step 3 is lowered to 1 kPa and then further to 0 kPa. During the desorption step 3 and the

Magnetic field 5 of 8.0 Tesla on the system. After this

Disproportionation step 2 are additionally more than 0 wt .-% to 50 wt .-%, preferably 30 wt .-% nanoparticulate iron 7 based on the

Starting compound, add. The particle size of the iron is typically 5 to 50 nm. The crystallite size of the final magnetic product is typically less than 30 nm. The crystals are formed by means of

FIG. 7 shows a sixth exemplary embodiment. Here, a Nd ₂ Fe-i ₄ B block piece having a starting particle size of 120 to 200 μm is hydrogenated and disproportionated. The starting alloy material is stoichiometric. There are no intergranular rare earth metal-rich phases. The

Composition of the reaction mixture is determined by conventional methods (e.g., X-ray diffractometry). In addition, the starting compound is ground in step 1 and 2 by means of ball milling 6, so that the resulting crystallite size is 2 to 5 μηη. The temperature of the system during the hydrogenation step 1 is 250 ° C, during the disproportionation step 2 and the desorption step 3 800 ° C, the hydrogen partial pressure is maintained until the desorption step 3 to 30 kPa and during the

Desorption step 3 to 1 kPa and then further lowered to 0 kPa. After the disproportionation step 2, in addition more than 0 wt .-% to 50 wt .-%, preferably 25 wt .-% nanoparticulate iron 7 based on the starting compound, add. The particle size of the iron is typically 5 to 50 nm. During the desorption step 3 and the recombination step 4, and alternatively in the equilibrium state between disproportionation 2 and desorption 3 / recombination 4, there is also a magnetic field 5 of 8.0 Tesla on the system and Reaction mixture is hot-deformed in step 3 and 4 by a hot deformation 8 at a temperature of 850 ° C and a pressure of 150 MPa by means of a press. The crystallite size of the final magnetic product is typically less than 30 nm. The crystals are characterized by X-ray diffractometry. The texturing of the obtained magnetic material is high. The remanent magnetization is typically 1.4 Tesla.

Further, comparative experiments for producing a magnetic material were carried out. The following starting materials were used:

a) Nd28.78Fe _ba ₁ , ₁ Gao, 35Nbo, 26 (more than stoichiometric, rich in Nd) b) Nd27, o7FebaiB ₁ , oGa ₀ , 32Nbo, 28 (near-stoichiometric, negligible Nd excess).

The starting materials were homogenized for about 40 hours in an oven at a temperature of 1140 ° C under argon atmosphere, i. through the

Heat treatment, the Nd ₂ Fei ₄ B phase was set in the material. Then, the obtained material was coarsely ground and sieved to obtain a particle size of about 250 μm. The coarse powders were then ground mechanically by ball milling in a grinding jar for five hours under 5-10 MPa hydrogen partial pressure. Das_Material hydrogenated and disproportioniert here. The desorption and recombination step was then carried out in a temperature range of 600 ° C to 840 ° C within about 15 minutes, during the desorption step 3 and the

Recombination step 4, and alternatively in the equilibrium state between disproportionation 2 and desorption 3 / recombination 4, a magnetic field 5 of about 8 Tesla was.

The composition of each phase of the magnetic material, as well as the crystallite size thereof, was determined by X-ray diffraction (Rietveld refinement as described in JI Langford, Proc. Int Conf: Accuracy in Powder Diffraction II, Washington, DC: NIST Special Publication No. 846 US Government Printing Office, 10 (1992) ") .The morphology of the obtained magnetic powder material was determined by means of high-resolution SEM (LEO FEG 1530 Gemini)

Determination of the magnetic properties in a transverse magnetic field of 2 Tesla pressed onto a cylindrical shape (diameter: 3.73 mm, height: about 2.1 mm) and fixed by a commercially available epoxy resin. The

Magnetic measurements were carried out in a vibrating sample magnetometer (VSM) in a magnetic field of up to 9 Tesla at room temperature. The X-ray density was 7.5 g / cm ³ and the demagnetization factor N was 1/3.

FIG. 8a shows the dependence of the crystallite size and the

Coercive field strength H _c (μ ₀ Η _ο ) of the superstoichiometric magnetic material of the temperature during the recombination step, during which Desorption step 3 and the recombination step 4, and alternatively in the equilibrium state between disproportionation 2 and desorption

3 / recombination 4, a magnetic field 5 of about 8 Tesla was applied. The shaded area in FIG. 8a shows the temperature range in which the

Recombination is incomplete. FIG. 8a thus illustrates that the

Recombination at temperatures of less than 650 ° C is incomplete, while recombination at temperatures of 840 ° C or above leads to a significantly larger crystallite size of the Nd2Fe-14B product of about 15 nm, presumably due to melting of the Nd-rich phase at temperatures above 670 ° C is due. This leads to an increased diffusion and thus increased crystallite growth. An increase in the temperature during the recombination step above 700 ° C in this case leads to no appreciable increase in the crystallite size of the α-Fe. The crystallite size of the a-Fe was largely around 30 nm.

As already stated, the same tests were used for the

superstoichiometric material were carried out, even for the o.g.

stoichiometric material (material b)) executed. After grinding, the stoichiometric product was also composed of α-Fe and NdH ₂ (Fe ₂ B was not detected for the same reasons as mentioned above). After recombination too

Nd ₂ Fei ₄ B were also detected as by-products α-Fe (about 6-7 wt .-%) and NdO (0.6 to 0.8 wt .-%). FIG. 8b shows the dependence of the crystallite size of the magnetic material on the temperature and the coercive force H _c (μ ₀ Η _ο ) during the recombination step of the stoichiometric material mentioned above under b), The shaded area in Figure 8b again shows the temperature range in which the recombination is incomplete. The crystallite size at temperatures up to about 700 ° C was almost identical to that obtained for the superstoichiometric product in the same temperature range. However, an increase in the temperature during the recombination step to over 700 ° C led here to a

Increasing the crystallite size of the α-Fe to about 70 nm. At a temperature of 840 ° C, however, the crystallite size of the Nd ₂ Fei ₄ B, obtained from the stoichiometric material b), with 80 nm lower than in the superstoichiometric case (1 15 nm , so). This is presumably due to the absence of Nd-rich phases in the stoichiometric material. For the respective magnetic materials obtained from the stoichiometric and superstoichiometric starting material, the above-mentioned measurements were carried out. The materials showed magnetic behavior indicative of a single magnetic phase. The at about 650 ° C

recombined materials from the superstoichiometric starting alloy exhibited a coercive field strength of 1.35 Tesla, while the materials from the superstoichiometric starting alloy recombined at about 840 ° C had a coercive force of only 0.9 Tesla, presumably due to the sharp increase in the crystallite size of the α-Fe is due. The remanent

Magnetization was 0.85 Tesla, regardless of the temperature during the recombination step and can be increased if necessary by adding iron. The recombined material from the stoichiometric starting alloy showed a coercive field strength of 1.05 Tesla.

In a further comparative experiment, magnetic materials were produced according to the conventional H DDR process shown in FIG. When

Starting materials for this were again the above-stoichiometric material, Nd28.78Feb _a iB ₁ , ₁ Ga ₀ , 35Nbo, 26 _! as well as the abovementioned stoichiometric material, Nd27, o7FebaiB ₁ , oGa ₀ , 32Nbo, 28 _! used. After disproportionation was the

Composition of the materials as follows: 70 wt .-% a-Fe, 25.4 wt .-% NdH ₂ and 4.6 wt .-% Fe ₂ B. However, the crystallite size of the individual phases was 30 nm, 15 nm and 20 nm and was thus significantly larger than that obtained in the above method by additional ball milling. The micro-deformation of α-Fe was 0.20%, that of NdH ₂ 0.77% and that of Fe ₂ B 0.08%, and was thus significantly lower than in the above-mentioned method. Complete recombination was obtained only at a temperature of at least 840 ° C (about 99.5 wt% recombination to Nd ₂ Fei ₄ B) with the balance decreasing to NdO (about 0.5 wt%). The average crystallite size of the magnetic material was about each

300 nm and was thus more than an order of magnitude greater than that by o.g. Procedure was obtained. The remanent magnetization of the superstoichiometric material was 1.25 Tesla. The coercive field strength of the superstoichiometric material was 1.55 Tesla. The remanent

Magnetization of the stoichiometric material was 0.94 Tesla and was therewith significantly lower than in the superstoichiometric case. The coercive field strength of the stoichiometric material was about 0.22 Tesla due to lack of Nd-rich phases. FIGS. 9a and 9b show high-resolution SEM images (LEO FEG 1530

Gemini), by means of which the morphology of a superstoichiometric Nd28,78FebaiB _{1 1} Ga ₀ , 35Nbo, 26 material prepared by conventional HDDR method (Figure 9a) compared to a

superstoichiometric Nd28,78FebaiB _{1 1} Ga _0, 35Nbo, 26 material, which means HDDR- method and additional grinding by ball mill (figure 9b), as stated above, was prepared, was determined. The images of both materials were taken before the respective desorption and recombination step at 800 ° C. It can be seen very clearly that the crystallite size of the additional ball-milled material (FIG. 9b) is significantly lower than that of a material produced by the conventional H DDR process.

As shown, a textured magnetic material having a very high remanent magnetization of preferably 1.3 to 1.5 tesla can be obtained by the methods according to the invention. Accordingly, improved permanent magnets can be produced from this magnetic material. The magnetic material according to the invention can be produced in a particularly cost-effective manner. By applying the external magnetic field 5, in particular during the desorption step 3 and the

Recombination step 4, and alternatively in the equilibrium state between disproportionation 2 and desorption 3 / recombination 4, the texturing, as well as the nucleation and the growth process can be positively influenced with respect to the remanent magnetization. This is further promoted by adjusting the hydrogen partial pressure according to the invention. For all described embodiments, it should also be noted that the

Magnetic field also only during a step, in particular the step 3 or 4, may be applied. Alternatively, the magnetic field in all described embodiments may also be applied during step 1 and / or 2.

Claims

claims

1 . Process for producing a magnetic material from a

Starting material, wherein the starting material comprises at least one rare earth metal (SE) and at least one transition metal, comprising the steps:

Hydrogenation of the starting material,

Disproportionation of the starting material and formation of a disproportionated phase,

Desorption, and

recombination

wherein during at least one step, a magnetic field is applied such that a textured magnetic material is obtained and the formation of a texture in the magnetic material is promoted.

2. The method according to claim 1, characterized in that the magnetic field during the desorption step and recombination step is applied.

3. The method according to claim 1, characterized in that the magnetic field is applied during a state of equilibrium between disproportionation on the one hand and desorption / recombination on the other hand.

4. The method according to any one of the preceding claims, characterized

characterized in that the magnetic field strength of the applied magnetic field is greater than 0 to 100 Tesla, preferably greater than 0 to 10 Tesla.

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

characterized in that the equilibrium state is achieved by lowering the hydrogen partial pressure.

6. The method according to claim 5, characterized in that the temperature is initially kept constant at the onset of desorption / recombination.

7. The method according to any one of the preceding claims, characterized

characterized in that the temperature during the hydrogenation step is about 20 ° C to 350 ° C, preferably about 300 ° C and / or the temperature during the disproportionation step. 500 ° C to 1000 ° C,

preferably 750 ° C to 850 ° C and / or the temperature during the desorption step 500 ° C to 1000 ° C, preferably 750 ° C to 850 ° C and / or the temperature during the recombination step 500 ° C to 1000 ° C, preferably 750 ° C to 850 ° C, is.

8. The method according to any one of the preceding claims, characterized

characterized in that the hydrogen partial pressure during the

Hydrogenation step 20 kPa to 100 kPa and more, preferably 20 kPa to 40 kPa and in particular 30 kPa and / or the hydrogen partial pressure during the disproportionation step.es 20 kPa to 40 kPa,

preferably 30 kPa and / or the hydrogen partial pressure during the desorption step 0.5 kPa to 1, 5 kPa, preferably 1 kPa and / or the hydrogen partial pressure during the recombination step is 0 kPa to 1 kPa, preferably 0 kPa.

9. The method according to any one of the preceding claims, characterized

in that the crystallite size of the starting material during and / or before the hydrogenation step and / or the

Disproportionation step is reduced in particular by ball milling.

10. The method according to claim 9, characterized in that the

The applied hydrogen pressure is at least 0.1 MPa, preferably at least 1 MPa and more preferably at least 10 MPa, whereby the starting material and / or the product formed during the hydrogenation step and / or disproportionation step Material has a crystallite size of less than 50 nm, preferably from 5 to 20 nm experiences.

1 1. Method according to one of the preceding claims, characterized

characterized in that after the disproportionation step, a soft magnetic material is added, in particular Fe and / or Co and / or an alloy of Fe and Co.

12. The method according to claim 1 1, characterized in that the amount of soft magnetic material more than 0 wt .-% to 50 wt .-%, preferably 10 wt .-% to 30 wt .-%, based on the

Starting material amounts.

13. The method according to any one of the preceding claims, characterized

in that during or after the desorption / recombination the magnetic material is hot-compacted and / or hot-deformed.

14. The method according to claim 13, characterized in that the

Temperature during hot-forming and / or hot-compacting 400 to 1200 ° C, preferably 600 to 900 ° C and the pressure at least

100 MPa, preferably at least 150 MPa.

15. The method according to any one of the preceding claims, characterized

marked that

- The rare earth metal (SE) is selected from the group consisting of: Nd, Sm, La, Dy, Tb, Gd, preferably from: Nd, Sm, La, and / or

the transition metal is selected from the group consisting of Fe and Co

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

in that the magnetic material contains at least one further element, in particular B and / or Ga and / or Nb and / or Si and / or Al.

17. The method according to any one of the preceding claims, characterized in that the starting material is superstoichiometric or stoichiometric.

18. Permanent magnet produced by a method according to one of the preceding claims, wherein in particular the the

Magnetic material forming permanent magnet Nd ₂ Fei ₄ B is.