EP2277180B1 - Method for producing metal-based materials for magnetic cooling or heat pumps - Google Patents

Description

The invention relates to processes for the production of metal-based materials for magnetic cooling or heat pumps, such materials and their use. The materials produced according to the invention are used in magnetic cooling, in heat pumps or air conditioning systems.

Such materials are known in principle and, for example, in WO 2004/068512 described. The magnetic cooling techniques are based on the magnetocaloric effect (MCE) and can be an alternative to the known steam-cycle cooling methods. In a material exhibiting a magnetocaloric effect, the alignment of randomly oriented magnetic moments with an external magnetic field results in heating of the material. This heat can be dissipated from the MCE material into the ambient atmosphere by heat transfer. When the magnetic field is then turned off or removed, the magnetic moments revert to a random arrangement, causing the material to cool to below ambient temperature. This effect can be used for cooling purposes, see also Nature, Vol. 415, 10 January 2002, pages 150 to 152 , Typically, a heat transfer medium such as water is used for heat removal from the magnetocaloric material.

The preparation of conventional materials is carried out by solid phase reaction of the starting materials or starting alloys for the material in a ball mill, subsequent compression, sintering and annealing under an inert gas atmosphere and subsequent slow cooling to room temperature. Such a method is for example in J. Appl. Phys. 99, 2006, 08Q107 described.

Processing by melt spinning is also possible. As a result, a more homogeneous element distribution is possible, which leads to an improved magnetocaloric effect, cf. Rare Metals, Vol. 25, October 2006, pages 544 to 549 , In the process described therein, the output elements are first induction-melted in an argon gas atmosphere and then sprayed in a molten state via a nozzle onto a rotating copper roll. This is followed by sintering at 1000 ° C and slow cooling to room temperature.

DT Cam Thanh, Journal of Applied Physics, Vol. 103, pages 07 B318-1 to 07 B318-3 discloses a production process for MnFeP _1-x Si _x compounds, wherein first a solid phase reaction takes place by high energy input in a ball mill with subsequent pressing and sintering of the moldings. Then it can either be cooled slowly or quenched from different temperatures.

However, these temperatures and the quenching are not explained in detail.

US 2006/0076084 relates to an alloy containing rare earth elements. The alloy can be used for magnetic cooling applications. The preparation is carried out according to Example 1 by melt spinning a lanthanum-containing alloy, after which the melt-spun product is sintered for three hours at 1100 ° C. Subsequently, a pulverization is carried out.

A. Yan et al., Journal of Applied Physics, Vol. 99, pp. 08 K903-1 to 08908-4 refers to the magnetic entropy change in melt-spun MnFePGe. Melt spinning achieves large magnetocaloric effects, which are attributed to a more homogeneous element distribution due to the very high cooling rate. The spun tapes are tempered for one hour at 1000 ° C and then slowly cooled in the oven.

The materials obtained by the known method often show a large thermal hysteresis. For example, in Fe ₂ P-type compounds substituted with germanium or silicon, large values for thermal hysteresis are observed in a wide range of 10 K or more. Thus, these materials are less suitable for magnetocaloric cooling.

The object of the present invention is to provide a method for producing metal-based materials for magnetic cooling, which leads to a reduction of the thermal hysteresis. At the same time, preferably a large magnetocaloric effect (MCE) should be achieved.

1. a) Umsetzung von chemischen Elementen und/oder Legierungen in einer Stöchiometrie, die dem metallbasierten Material entspricht, in der Fest- und/oder Flüssigphase,
2. b) gegebenenfalls Überführen des Umsetzungsproduktes aus Stufe a) in einen Festkörper,
3. c) Sintern und/oder Tempern des Festkörpers aus Stufe a) oder b),
4. d) Abschrecken des gesinterten und/oder getemperten Festkörpers aus Stufe c) mit einer Abkühlgeschwindigkeit von 200 bis 1300 K/s.

The object is achieved according to the invention, according to claim 1, by a method for the production of metal-based materials for magnetic cooling or heat pumps, comprising the following steps

1. a) conversion of chemical elements and / or alloys in a stoichiometry corresponding to the metal-based material, in the solid and / or liquid phase,
2. b) optionally converting the reaction product from stage a) into a solid,
3. c) sintering and / or annealing the solid from step a) or b),
4. d) quenching the sintered and / or tempered solid from step c) at a cooling rate of 200 to 1300 K / s.

It has been found according to the invention that the thermal hysteresis can be significantly reduced if the metal-based materials are not slowly cooled to ambient temperature after sintering and / or annealing, but are quenched at a high cooling rate. Especially preferred are cooling rates of 300 to 1000 K / s.

The quenching can be achieved by any suitable cooling method, for example by quenching the solid with water or aqueous liquids, such as cooled water or ice / water mixtures. The solids can be dropped, for example, in iced water. It is also possible to quench the solids with undercooled gases such as liquid nitrogen. Other quenching methods are known to those skilled in the art. The advantage here is a controlled and rapid cooling.

Without being bound by theory, the reduced hysteresis can be attributed to smaller grain sizes for the quenched (quenched) compositions.

In the previously known methods, the sintering and tempering were slowly cooled in each case, which leads to the formation of larger particle sizes and thus to the enhancement of the thermal hysteresis.

The rest of the preparation of the metal-based materials is less critical, as long as the quenching of the sintered and / or tempered solid takes place in the last step with the cooling rate according to the invention. The method can be applied to the production of any suitable metal-based materials for magnetic cooling. Typical materials for the magnetic cooling are multimetal materials which often contain at least three metallic elements and optionally also non-metallic elements. The term "metal-based materials" indicates that the majority of these materials are composed of metals or metallic elements. Typically, the proportion of the total material is at least 50 wt .-%, preferably at least 75 wt .-%, in particular at least 80 wt .-%. Suitable metal-based materials are explained in more detail below.

In step (a) of the process according to the invention, the reaction of the elements and / or alloys contained in the later metal-based material takes place in a stoichiometry corresponding to the metal-based material in the solid or liquid phase.

Preferably, the reaction in step a) is carried out by co-heating the elements and / or alloys in a closed container or in an extruder, or by solid-phase reaction in a ball mill. Particularly preferably, a solid phase reaction is carried out, which takes place in particular in a ball mill. Such an implementation is known in principle, compare the introductory listed writings. In this case, powders of the individual elements or powders of alloys of two or more of the individual elements which are present in the later metal-based material are typically mixed in powder form in suitable proportions by weight. If necessary, additional grinding of the mixture can be carried out to obtain a microcrystalline powder mixture. This powder mixture is preferably heated in a ball mill, which leads to a further reduction as well as good mixing and to a solid phase reaction in the powder mixture. Alternatively, the individual elements are mixed in the selected stoichiometry as a powder and then melted.

The common heating in a closed container allows the fixation of volatile elements and the control of the stoichiometry. Especially with the use of phosphorus, this would easily evaporate in an open system.

The reaction is followed by sintering and / or tempering of the solid, wherein one or more intermediate steps may be provided. For example, the solid obtained in step a) can be pressed before it is sintered and / or tempered. As a result, the density of the material is increased, so that there is a high density of the magnetocaloric material in the subsequent application. This is particularly advantageous because the volume in which the magnetic field prevails can be reduced, which can be associated with significant cost savings. The pressing is known per se and can be carried out with or without pressing aids. In this case, any suitable shape can be used for pressing. By pressing, it is already possible to produce shaped bodies in the desired three-dimensional structure. The pressing may be followed by sintering and / or tempering step c) followed by quenching step d).

Alternatively, it is possible to feed the solid obtained from the ball mill to a melt spinning process. Melt spinning processes are known per se and, for example, in Rare Metals, Vol. 25, October 2006, pages 544 to 549 as well as in WO 2004/068512 described.

In this case, the composition obtained in step a) is melted and sprayed onto a rotating cold metal roller. This spraying can be achieved by means of positive pressure in front of the spray nozzle or negative pressure behind the spray nozzle. Typically, a rotating copper drum or roller is used which, if desired, may be cooled. The copper drum preferably rotates at a surface speed of 10 to 40 m / s, in particular 20 to 30 m / s. On the copper drum, the liquid composition is cooled at a rate of preferably 10 ² to 10 ⁷ K / s, more preferably at a rate of at least 10 ⁴ K / s, in particular at a rate of 0.5 to 2 x 10 ⁶ K / s.

The melt spinning can be carried out as well as the reaction in step a) under reduced pressure or under an inert gas atmosphere.

The Meltspinning a high processing speed is achieved because the subsequent sintering and annealing can be shortened. Especially on an industrial scale so the production of metal-based materials is much more economical. Spray drying also leads to a high processing speed. Particularly preferably, the melt spinning (Melt spinning) is performed.

Alternatively, in step b), a spray cooling may be carried out, in which a melt of the composition from step a) is sprayed into a spray tower. The spray tower can be additionally cooled, for example. In spray towers cooling rates in the range of 10 ³ to 10 ⁵ K / s, in particular about 10 ⁴ K / s are often achieved.

The sintering and / or tempering of the solid takes place in stage c) preferably first at a temperature in the range from 800 to 1400 ° C. for sintering and subsequently at a temperature in the range from 500 to 750 ° C. for tempering. These values apply in particular to shaped bodies, while for powders lower sintering and tempering temperatures can be used. For example, sintering may then take place at a temperature in the range of 500 to 800 ° C. For shaped bodies / solids sintering is particularly preferably carried out at a temperature in the range from 1000 to 1300 ° C., in particular from 1100 to 1300 ° C. The tempering can then take place at 600 to 700 ° C, for example.

The sintering is preferably carried out for a period of 1 to 50 hours, more preferably 2 to 20 hours, especially 5 to 15 hours. The annealing is preferably carried out for a time in the range of 10 to 100 hours, particularly preferably 10 to 60 hours, in particular 30 to 50 hours. Depending on the material, the exact time periods can be adapted to the practical requirements.

When using the melt spinning method, sintering can often be dispensed with, and tempering can be greatly shortened, for example, for periods of 5 minutes to 5 hours, preferably 10 minutes to 1 hour. Compared to the usual values of 10 hours for sintering and 50 hours for annealing, this results in an extreme time advantage.

The sintering / tempering causes the grain boundaries to melt, so that the material continues to densify.

By melting and rapid cooling in stage b), the time duration for stage c) can thus be considerably reduced. This also allows for continuous production of the metal-based materials.

1. a) Festphasenumsetzung von chemischen Elementen und/oder Legierungen in einer Stöchiometrie, die dem metallbasierten Material entspricht, in einer Kugelmühle,
2. b) Schmelzspinnen des in Stufe a) erhaltenen Materials,
3. c) Tempern des Festkörpers aus Stufe b) für einen Zeitraum von 10 Sekunden oder 1 Minute bis 5 Stunden, bevorzugt 30 Minuten bis 2 Stunden bei einer Temperatur im Bereich von 430 bis 1200, bevorzugt 800 bis 1000 °C
4. d) Abschrecken des getemperten Festkörpers aus Stufe c) mit einer Abkühlgeschwindigkeit von 200 bis 1300 K/s.

Particularly preferred according to the invention is the process sequence

1. a) solid phase reaction of chemical elements and / or alloys in a stoichiometry, which corresponds to the metal-based material, in a ball mill,
2. b) melt spinning the material obtained in step a),
3. c) annealing the solid from step b) for a period of 10 seconds or 1 minute to 5 hours, preferably 30 minutes to 2 hours at a temperature in the range of 430 to 1200, preferably 800 to 1000 ° C.
4. d) quenching the tempered solid from step c) with a cooling rate of 200 to 1300 K / s.

The method of the invention can be used for any suitable metal-based materials.

1. (1) Verbindungen der allgemeinen Formel (I)
   
           (A_yB_1-y)_2+δC_wD_xE_z     (I)
   
   mit der Bedeutung

   A

   Mn oder Co,

   B

   Fe, Cr oder Ni,

   C, D, E

   mindestens zwei von C, D, E sind voneinander verschieden, haben eine nicht-verschwindende Konzentration und sind ausgewählt aus P, B, Se, Ge, Ga, Si, Sn, N, As und Sb, wobei mindestens eines von C, D und E Ge oder Si ist,

   δ

   Zahl im Bereich von - 0,1 bis 0,1

   w, x, y, z

   Zahlen im Bereich von 0 bis 1, wobei w + x + z = 1 ist;

2. (2) auf La und Fe basierenden Verbindungen der allgemeinen Formeln (II) und/oder (III) und/oder (IV)
   
           La(Fe_xAl_1-x)₁₃H_y oder La(Fe_xSi_1-x)₁₃H_y     (II)
   
   mit

   x

   Zahl von 0,7 bis 0,95

   y

   Zahl von 0 bis 3, vorzugsweise 0 bis 2;

   
   
           La(Fe_xAl_yCo_z)₁₃ oder La(Fe_xSi_yCo_z)₁₃     (III)
   
   mit

   x

   Zahl von 0,7 bis 0,95

   y

   Zahl von 0,05 bis 1 - x

   z

   Zahl von 0,005 bis 0,5;

   
   
           LaMn_xFe_2-xGe     (IV)
   
   mit

   x

   Zahl von 1,7 bis 1,95 und

3. (3) Heusler-Legierungen des Typs MnTP mit T Übergangsmetall und P einem p-dotierenden Metall mit einem electron count pro Atom e/a im Bereich von 7 bis 8,5.

Particularly preferably, the metal-based material is selected from

1. (1) Compounds of the general formula (I)
   
   (A _y B _1-y ) _{2 + δ} C _w D _x E _z (I)
   
   with the meaning

   A

   Mn or Co,

   B

   Fe, Cr or Ni,

   C, D, E

   at least two of C, D, E are different from each other, have a non-vanishing concentration, and are selected from P, B, Se, Ge, Ga, Si, Sn, N, As, and Sb, with at least one of C, D, and E is Ge or Si,

   δ

   Number in the range of - 0.1 to 0.1

   w, x, y, z

   Numbers ranging from 0 to 1, where w + x + z = 1;

2. (2) La and Fe based compounds of the general formulas (II) and / or (III) and / or (IV)
   
   La (Fe _x Al _1-x ) ₁₃ H _y or La (Fe _x Si _1-x ) ₁₃ H _y (II)
   
   With

   x

   Number from 0.7 to 0.95

   y

   Number from 0 to 3, preferably 0 to 2;

   
   
   La (Fe _x Al _y Co _z ) ₁₃ or La (Fe _x Si _y Co _z ) ₁₃ (III)
   
   With

   x

   Number from 0.7 to 0.95

   y

   Number from 0.05 to 1 - x

   z

   Number from 0.005 to 0.5;

   
   
   LaMn _x Fe _2-x Ge (IV)
   
   With

   x

   Number from 1.7 to 1.95 and

3. (3) Heusler alloys of the type MnTP with T transition metal and P a p-doping metal with an electron count per atom e / a in the range of 7 to 8.5.

According to the invention particularly suitable materials are, for example, in WO 2004/068512 . Rare Metals, Vol. 25, 2006, pp. 544-549 . J. Appl. Phys. 99.08 Q107 (2006 ) Nature, Vol. 415, 10 January 2002, pages 150 to 152 and Physica B 327 (2003), pages 431 to 437 described.

In the aforementioned compounds of the general formula (I), C, D and E are preferably identical or different and selected from at least one of P, Ge, Si, Sn and Ga.

The metal-based material of the general formula (I) is preferably selected from at least quaternary compounds which in addition to Mn, Fe, P and optionally Sb also Ge or Si or As or Ge and Si or Ge and As or Si and As or Ge, Si and As included.

At least 90% by weight, more preferably at least 95% by weight, of component A are Mn. At least 90% by weight, more preferably at least 95% by weight, of B Fe are preferred. Preferably, at least 90 wt .-%, more preferably at least 95 wt .-% of C P. Preferred are at least 90 wt .-%, more preferably at least 95 wt .-% of D Ge. At least 90% by weight, more preferably at least 95% by weight, of E Si are preferred.

Preferably, the material has the general formula MnFe (P _w Ge _x Si _z ).

Preferably, x is a number in the range of 0.3 to 0.7, w is less than or equal to 1-x and z corresponds to 1-x-w.

The material preferably has the crystalline hexagonal Fe ₂ P structure. Examples of suitable structures are MnFeP _{0.45 to 0.7} , Ge _{0.55 to 0.30} and MnFeP _{0.5 to 0.70} , (Si / Ge) _{0.5 to 0.30} .

Other suitable compounds are Mn _{1 + x} Fe _{1 -x} P _{1 -y} Ge _y where x is in the range of -0.3 to 0.5, y is in the range of 0.1 to 0.6. Also suitable are compounds of the general formula Mn _{1 + x} Fe _{1 -x} P _1-y Ge _yz Sb _z with x in the range of -0.3 to 0.5, y in the range of 0.1 to 0.6 and z less than y and less than 0.2. Furthermore, compounds of the formula Mn _{1 +} x Fe ₁ -x P _1-y Ge _yz Si _{z are} suitable with x number in the range of 0.3 to 0.5, y in the range of 0.1 to 0.66, z smaller or equal to y and less than 0.6.

Preferred La and Fe based compounds of the general formulas (II) and / or (III) and / or (IV) are La (Fe _0.90 Si _0.10 ) ₁₃ , La (Fe _0.89 Si _0.11 ) ₁₃ , La (Fe _0.880 Si _0.120 ) ₁₃ , La (Fe _0.877 Si _0.123 ) ₁₃ , L a F e _11.8 Si _1.2 , La (Fe _0.88 Si _0.12 ) ₁₃ H _0.5 , La (Fe _0.88 Si _0.12 ) ₁₃ H _1.0 , LaFe _11.7 Si _1.3 H _1.1 , LaFe _11.57 Si _1.43 H _1.3 , La (Fe _0.88 Si _{0 , 12} ) H _1.5 , LaFe _11.2 Co _0.7 Si _1.1 , LaFe _11.5 Al _1.5 C _0.1 , LaFe _11.5 Al _1.5 C _0.2 , LaFe _{11, 5} Al _1.5 C _0.4 , LaFe _11.5 Al _1.5 Co _0.5 , La (Fe _0.94 Co _0.06 ) _11.83 Al _1.17 , La (Fe _0.92 Co _{0 , 08} ) _11.83 Al _1.17 .

Suitable manganese-containing compounds are MnFeGe, MnFe _0.9 Co _0.1 Ge, MnFe _0.8 Co _0.2 Ge, MnFe _0.7 Co _0.3 Ge, MnFe _0.6 Co _0.4 Ge, MnFe _{0, 5} Co _0.5 Ge, MnFe _0.4 Co _0.6 Ge, MnFe _0.3 Co _0.7 Ge, MnFe _0.2 Co _0.8 Ge, MnFe _0.15 Co _0.85 Ge, MnFe _{0, 1} Co _0.9 Ge, MnCoGe, Mn ₅ Ge _2.5 Si _0.5 , Mn ₅ Ge ₂ Si, Mn ₅ Ge _1.5 Si _1.5 , Mn ₅ GeSi ₂ , Mn ₅ Ge ₃ , Mn ₅ Ge _2.9 Sb _0.1 , Mn ₅ Ge _2.5 Si _0.5 , Mn ₅ Ge ₂ Si, Mn ₅ Ge _1.5 Si _1.5 , Mn ₅ GeSi ₂ , Mn ₅ Ge ₃ , Mn ₅ Ge _2.9 Sb _0.1 , Mn ₅ Ge _2.8 Sb _0.2 , Mn ₅ Ge _2.7 Sb _0.3 , LaMn _1.9 Fe _0.1 Ge, LaMn _1.85 Fe _0.15 Ge, LaMn _1.8 Fe _0.2 Ge , (Fe _0.9 Mn _0.1 ) ₃ C, (Fe _0.8 Mn _0.2 ) C, (Fe _0.7 Mn _0.3 ) ₃ C, Mn ₃ GaC, MnAs, (Mn, Fe) As, Mn _{1 + δ} As _0.8 Sb _0.2 , MnAs _0.75 Sb _0.25 , Mn _1.1 As _0.75 Sb _0.25 , Mn _1.5 As _0.75 Sb _0.25 .

Heusler alloys suitable according to the invention are, for example, Fe ₂ MnSi _0.5 Ge _0.5 , Ni _52.9 Mn _22.4 Ga _24.7 , Ni _50.9 Mn _24.7 Ga _24.4 , Ni _55.2 Mn _{18 , 6} Ga _26.2 , Ni _51.6 Mn _24.7 Ga _23.8 , Ni _52.7 Mn _23.9 Ga _23.4 , CoMnSb, CoNb _0.2 Mn _0.8 Sb, CoNb _0.4 Mn _0.6 SB, CoNb _0.6 Mn _0.4 Sb, Ni ₅₀ Mn ₃₅ Sn ₁₅ , Ni ₅₀ Mn ₃₇ Sn ₁₃ , MnFeP _0.45 As _0.55 , MnFeP _0.47 AS _0.53 , Mn _{1, 1} Fe _0.9 P _0.47 As _0.53 , MnFeP _0.89-χ Si _χ Ge _0.11 , χ = 0.22, χ = 0.26, χ = 0.30, χ = 0.33 ,

The disclosure also relates to a metal-based magnetic cooling material obtainable by a method as defined above, as defined above by the composition, except for As-containing materials, having an average crystallite size in the range of 10 to 400 nm, more preferably 20 to 200 nm, in particular 30 to 80 nm. The average crystallite size can be determined by X-ray diffraction. If the crystallite size becomes too small, the maximum magnetocaloric effect is reduced. if the crystallite size is too large, however, the hysteresis of the system increases.

The metal-based materials are preferably used in the magnetic cooling as described above. A corresponding refrigerator has in addition to a magnet, preferably permanent magnets, metal-based materials, as described above. The cooling of computer chips and solar power generators is also considered. Further applications are heat pumps and air conditioning systems.

The metal-based materials produced by the process according to the invention may have any solid form. They may be present, for example, in the form of flakes, ribbons, wires, powders, as well as in the form of shaped bodies. Shaped bodies such as monoliths or honeycomb bodies can be produced, for example, by a hot extrusion process. For example, cell densities of 400 to 1600 CPI or more may be present. Also obtainable by rolling thin sheets are inventively preferred. Advantageous are non-porous molded body made of molded thin material, eg. As tubes, plates, nets, grids or rods. Shaping by metal injection molding (MIM) is possible according to the invention.

The invention is further illustrated by the following examples.

Examples example 1

Evacuated quartz ampoules containing pressed samples of MnFePGe were kept at 1100 ° C for 10 hours to sinter the powder. This sintering was followed by annealing at 650 ° C for 60 hours to homogenize. However, instead of slowly cooling to room temperature in the oven, the samples were immediately quenched in water at room temperature. Quenching in water caused a degree of oxidation on the sample surfaces. The outer oxidized shell was removed by dilute acid etching. The XRD patterns show that all samples crystallize in a Fe ₂ P-type structure.

• Mn_1,1Fe_0,9P_0,81Ge_0,19; Mn_1.1Fe_0.9P_0.78Ge_0.22, Mn_1,1Fe_0,9P_0,75Ge_0,25 und Mn_1,2Fe_0,8P_0,81Ge_0,19. Die beobachteten Werte für die thermische Hysterese sind für diese Proben in der angegebenen Reihenfolge 7 K, 5 K, 2 K und 3 K. Gegenüber einer langsam abgekühlten Probe war die eine thermische Hysterese von mehr als 10 K aufweist, konnte die thermische Hysterese stark vermindert werden.

The following compositions were obtained:

• Mn _1.1 Fe _0.9 P _0.81 Ge _0.19 ; Mn _1.1 Fe _0.9 P _0.78 Ge _0.22 , Mn _1.1 Fe _0.9 P _0.75 Ge _0.25 and Mn _1.2 Fe _0.8 P _0.81 Ge _0.19 . The observed values for the thermal hysteresis are 7 K, 5 K, 2 K and 3 K for these samples in the order given. Compared to a slowly cooled sample which had a thermal hysteresis of more than 10 K, the thermal hysteresis could be greatly reduced become.

The thermal hysteresis was determined in a magnetic field of 0.5 Tesla.

The Curie temperature can be adjusted by varying the Mn / Fe ratio and Ge concentration, as well as the thermal hysteresis value.

The change in magnetic entropy calculated from the DC magnetization using the Maxwell relationship for a maximum field change of 0 to 2 Tesla for the first three samples is 14 J / kgK, 20 J / kgK and 12.7 J / kgK, respectively.

The Curie temperature and the thermal hysteresis decrease with increasing Mn / Fe ratio. As a result, the MnFePGe compounds show relatively high MCE values in the low field. The thermal hysteresis of these materials is very small.

Example 2 Melt spinning of MnFeP (GeSb)

The polycrystalline MnFeP (Ge, Sb) alloys were first prepared in a high energy ball mill and by solid phase reaction techniques as described in U.S. Pat WO 2004/068512 and J. Appl. Phys. 99.08 Q107 (2006 ) are described. The pieces of material were then placed in a quartz tube with a nozzle. The chamber was evacuated to a vacuum of 10 ^-2 mbar and then filled with argon gas of high purity. The samples were melted by high frequency and sprayed through the nozzle due to a pressure difference to a chamber with a rotating copper drum. The surface speed of the copper wheel could be adjusted and cooling rates of about 10 ⁵ K / s were achieved. Subsequently, the spun ribbons were annealed at 900 ° C for one hour.

X-ray diffractometry shows that all samples crystallize in the hexagonal Fe ₂ P structural pattern. Unlike samples prepared by the melt spinning method, no minor impurity phase of MnO was observed.

The values obtained for the Curie temperature, hysteresis and entropy were determined for different melt spinning peripheral speeds. The results are shown in Tables 1 and 2 below. In each case low hysteresis temperatures were determined. Table 1: bands V (m / s) T _c (K) ΔT _hys (K) -ΔS (J / kgK) Mn _1.2 Fe _0.8 P _0.73 Ge _0.25 Sb _0.02 30 269 4 12.1 Mn _1.2 Fe _0.8 P _0.70 Ge _0.20 Sb _0.10 30 304 4.5 19.0 45 314 3 11.0 MnFeP _0.70 Ge _0.20 Sb _0.10 20 306 8th 17.2 30 340 3 9.5 MnFeP _0.75 Ge _0.25 20 316 9 13.5 40 302 8th - Mn _1.1 Fe _0.9 P _0.78 Ge _0.22 20 302 5 - 40 299 7 - Mn _1.1 Fe _0.9 P _0.75 Ge _0.25 30 283 9 11.2 Mn _1.2 Fe _0.8 P _0.75 Ge _0.25 30 240 8th 14.2 Mn _1.1 Fe _0.9 P _0.73 Ge _0.27 30 262 5 10.1 Bulk T _c (K) ΔT _hys (K) -ΔS (J / kgK) MnFeP _0.75 Ge _0.25 327 3 11.0 Mn _1.1 Fe _0.9 P _0.81 Ge _0.19 260 7 14.0 Mn _1.1 Fe _0.9 P _0.78 Ge _0.22 296 5 20.0 Mn _1.1 Fe _0.9 P _0.75 Ge _0.25 330 2 13.0 Mn _1.2 Fe _0.8 P _0.81 Ge _0.19 220 3 7.7 Mn _1.2 Fe _0.8 P _0.75 Ge _0.25 305 3 - Mn _1.2 Fe _0.8 P _0.73 Ge _0.27 313 5 - Mn _1.3 Fe _0.7 P _0.78 Ge _0.22 203 3 5.1 Mn _1.3 Fe _0.7 P _0.75 Ge _0.25 264 1 - Bulk T _c (K) ΔT _hys (K) -ΔS (J / kgK) MnFeP _0.75 Ge _0.25 327 3 11.0 Mn _1.16 Fe _0.84 P _0.75 Ge _0.25 330 5 22.5 Mn _1.18 Fe _0.82 P _0.75 Ge _0.25 310 3 16.1 Mn _1.20 Fe _0.80 P _0.75 Ge _0.25 302 1 12.0 Mn _1.22 Fe _0.78 P _0.75 Ge _0.25 276 4 11.7 Mn _1.26 Fe _0.74 P _0.75 Ge _0.25 270 1 8.5 Mn _1.1 Fe _0.9 P _0.81 Ge _0.19 260 6 13.8 Mn _1.1 Fe _0.9 P _0.78 Ge _0.22 296 4 20.0 Mn _1.1 Fe _0.9 P _0.77 Ge _0.23 312 2 14.6 Mn _1.1 Fe _0.9 P _0.75 Ge _0.25 329 2 13.0 bands Mn _1.20 Fe _0.80 P _0.75 Ge _0.25 288 1 20.3 Mn _1.22 Fe _0.78 P _0.75 Ge _0.25 274 2 15.3 Mn _1.24 Fe _0.76 P _0.75 Ge _0.25 254 2 16.4 Mn _1.26 Fe _0.74 P _0.75 Ge _0.25 250 4 14.4 Mn _1.30 Fe _0.70 P _0.75 Ge _0.25 230 0 9.8

Claims (7)

1. A process for preparing metal-based materials for magnetic cooling or heat pumps, comprising the following steps:

   a) reacting chemical elements and/or alloys in a stoichiometry which corresponds to the metal-based material in the solid phase and/or liquid phase,

   b) optionally converting the reaction product from stage a) to a solid,

   c) sintering and/or heat treating the solid from stage a) or b),

   d) quenching the sintered and/or heat treated solid from stage c) at a cooling rate in the range from 200 to 1300 K/s.
2. The process according to claim 1, wherein the reaction in stage a) is effected by heating the elements and/or alloys together in a closed vessel or in an extruder, or by solid phase reaction in a ball mill.
3. The process according to either of claims 1 and 2, wherein the conversion to a solid in stage b) is effected by melt spinning or spray cooling.
4. The process according to any one of claims 1 to 3, wherein, in stage c), first sintering is effected at a temperature in the range from 800 to 1400°C and then heat treatment at a temperature in the range from 500 to 750°C.
5. The process according to any one of claims 1 to 4, wherein the metal-based material is selected from

   (1) compounds of the general formula (I)
   
           (A_yB_y-1)_2+δC_wD_xE_z     (I)
   
   where

   A is Mn or Co,

   B is Fe, Cr or Ni,

   C, D, E at least two of C, D, E are different, have a non-vanishing concentration and are selected from P, B, Se, Ge, Ga, Si, Sn, N, As and Sb, where at least one of C, D and E is Ge or Si,

   δ is a number in the range from -0.1 to 0.1,

   w, x, y, z are numbers in the range from 0 to 1, where w + x + z = 1;

   (2) La- and Fe-based compounds of the general formulae (II) and/or (III) and/or (IV)
   
           La(Fe_xSi_1-x)₁₃H_y     (II)
   
   where

   x is a number from 0.7 to 0.95;

   y is a number from 0 to 3;

   
   
           La(Fe_xAl_yCo_z)₁₃ or La(Fe_xSi_yCo_z)₁₃     (III)
   
   where

   x is a number from 0.7 to 0.95;

   y is a number from 0.05 to 1-x;

   z is a number from 0.005 to 0.5;

   
   
           LaMn_xFe_2-xGe     (IV)
   
   where

   x is a number from 1.7 to 1.95 and

   (3) Heusler alloys of the MnTP type where T is a transition metal and P is a p-doping metal with an electron count per atom e/a in the range from 7 to 8.5.
6. The process according to claim 5, wherein the metal-based material is selected from at least quaternary compounds of the general formula (I) which, as well as Mn, Fe, P and optionally Sb, additionally comprise Ge or Si or As or Ge and As or Si and As, or Ge, Si and As.
7. The process according to claim 1, having the process sequence of:

   a) reacting chemical elements and/or alloys in the solid phase in a stoichiometry which corresponds to the metal-based material in a ball mill,

   b) melt spinning the material obtained from stage a),

   c) heat treating the solid material from stage b) at a temperature in the range from 430 to 1200°C for a period of 10 seconds to 5 hours,

   d) quenching the heat treated solid material from stage c) at a cooling rate of 200 to 1300 K/s.